[www-releases] r331981 - Add 5.0.2 docs and update download.html
Tom Stellard via llvm-commits
llvm-commits at lists.llvm.org
Thu May 10 06:54:19 PDT 2018
Added: www-releases/trunk/5.0.2/docs/_sources/Coroutines.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.2/docs/_sources/Coroutines.txt?rev=331981&view=auto
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--- www-releases/trunk/5.0.2/docs/_sources/Coroutines.txt (added)
+++ www-releases/trunk/5.0.2/docs/_sources/Coroutines.txt Thu May 10 06:54:16 2018
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+=====================================
+Coroutines in LLVM
+=====================================
+
+.. contents::
+ :local:
+ :depth: 3
+
+.. warning::
+ This is a work in progress. Compatibility across LLVM releases is not
+ guaranteed.
+
+Introduction
+============
+
+.. _coroutine handle:
+
+LLVM coroutines are functions that have one or more `suspend points`_.
+When a suspend point is reached, the execution of a coroutine is suspended and
+control is returned back to its caller. A suspended coroutine can be resumed
+to continue execution from the last suspend point or it can be destroyed.
+
+In the following example, we call function `f` (which may or may not be a
+coroutine itself) that returns a handle to a suspended coroutine
+(**coroutine handle**) that is used by `main` to resume the coroutine twice and
+then destroy it:
+
+.. code-block:: llvm
+
+ define i32 @main() {
+ entry:
+ %hdl = call i8* @f(i32 4)
+ call void @llvm.coro.resume(i8* %hdl)
+ call void @llvm.coro.resume(i8* %hdl)
+ call void @llvm.coro.destroy(i8* %hdl)
+ ret i32 0
+ }
+
+.. _coroutine frame:
+
+In addition to the function stack frame which exists when a coroutine is
+executing, there is an additional region of storage that contains objects that
+keep the coroutine state when a coroutine is suspended. This region of storage
+is called **coroutine frame**. It is created when a coroutine is called and
+destroyed when a coroutine runs to completion or destroyed by a call to
+the `coro.destroy`_ intrinsic.
+
+An LLVM coroutine is represented as an LLVM function that has calls to
+`coroutine intrinsics`_ defining the structure of the coroutine.
+After lowering, a coroutine is split into several
+functions that represent three different ways of how control can enter the
+coroutine:
+
+1. a ramp function, which represents an initial invocation of the coroutine that
+ creates the coroutine frame and executes the coroutine code until it
+ encounters a suspend point or reaches the end of the function;
+
+2. a coroutine resume function that is invoked when the coroutine is resumed;
+
+3. a coroutine destroy function that is invoked when the coroutine is destroyed.
+
+.. note:: Splitting out resume and destroy functions are just one of the
+ possible ways of lowering the coroutine. We chose it for initial
+ implementation as it matches closely the mental model and results in
+ reasonably nice code.
+
+Coroutines by Example
+=====================
+
+Coroutine Representation
+------------------------
+
+Let's look at an example of an LLVM coroutine with the behavior sketched
+by the following pseudo-code.
+
+.. code-block:: c++
+
+ void *f(int n) {
+ for(;;) {
+ print(n++);
+ <suspend> // returns a coroutine handle on first suspend
+ }
+ }
+
+This coroutine calls some function `print` with value `n` as an argument and
+suspends execution. Every time this coroutine resumes, it calls `print` again with an argument one bigger than the last time. This coroutine never completes by itself and must be destroyed explicitly. If we use this coroutine with
+a `main` shown in the previous section. It will call `print` with values 4, 5
+and 6 after which the coroutine will be destroyed.
+
+The LLVM IR for this coroutine looks like this:
+
+.. code-block:: llvm
+
+ define i8* @f(i32 %n) {
+ entry:
+ %id = call token @llvm.coro.id(i32 0, i8* null, i8* null, i8* null)
+ %size = call i32 @llvm.coro.size.i32()
+ %alloc = call i8* @malloc(i32 %size)
+ %hdl = call noalias i8* @llvm.coro.begin(token %id, i8* %alloc)
+ br label %loop
+ loop:
+ %n.val = phi i32 [ %n, %entry ], [ %inc, %loop ]
+ %inc = add nsw i32 %n.val, 1
+ call void @print(i32 %n.val)
+ %0 = call i8 @llvm.coro.suspend(token none, i1 false)
+ switch i8 %0, label %suspend [i8 0, label %loop
+ i8 1, label %cleanup]
+ cleanup:
+ %mem = call i8* @llvm.coro.free(token %id, i8* %hdl)
+ call void @free(i8* %mem)
+ br label %suspend
+ suspend:
+ %unused = call i1 @llvm.coro.end(i8* %hdl, i1 false)
+ ret i8* %hdl
+ }
+
+The `entry` block establishes the coroutine frame. The `coro.size`_ intrinsic is
+lowered to a constant representing the size required for the coroutine frame.
+The `coro.begin`_ intrinsic initializes the coroutine frame and returns the
+coroutine handle. The second parameter of `coro.begin` is given a block of memory
+to be used if the coroutine frame needs to be allocated dynamically.
+The `coro.id`_ intrinsic serves as coroutine identity useful in cases when the
+`coro.begin`_ intrinsic get duplicated by optimization passes such as
+jump-threading.
+
+The `cleanup` block destroys the coroutine frame. The `coro.free`_ intrinsic,
+given the coroutine handle, returns a pointer of the memory block to be freed or
+`null` if the coroutine frame was not allocated dynamically. The `cleanup`
+block is entered when coroutine runs to completion by itself or destroyed via
+call to the `coro.destroy`_ intrinsic.
+
+The `suspend` block contains code to be executed when coroutine runs to
+completion or suspended. The `coro.end`_ intrinsic marks the point where
+a coroutine needs to return control back to the caller if it is not an initial
+invocation of the coroutine.
+
+The `loop` blocks represents the body of the coroutine. The `coro.suspend`_
+intrinsic in combination with the following switch indicates what happens to
+control flow when a coroutine is suspended (default case), resumed (case 0) or
+destroyed (case 1).
+
+Coroutine Transformation
+------------------------
+
+One of the steps of coroutine lowering is building the coroutine frame. The
+def-use chains are analyzed to determine which objects need be kept alive across
+suspend points. In the coroutine shown in the previous section, use of virtual register
+`%n.val` is separated from the definition by a suspend point, therefore, it
+cannot reside on the stack frame since the latter goes away once the coroutine
+is suspended and control is returned back to the caller. An i32 slot is
+allocated in the coroutine frame and `%n.val` is spilled and reloaded from that
+slot as needed.
+
+We also store addresses of the resume and destroy functions so that the
+`coro.resume` and `coro.destroy` intrinsics can resume and destroy the coroutine
+when its identity cannot be determined statically at compile time. For our
+example, the coroutine frame will be:
+
+.. code-block:: llvm
+
+ %f.frame = type { void (%f.frame*)*, void (%f.frame*)*, i32 }
+
+After resume and destroy parts are outlined, function `f` will contain only the
+code responsible for creation and initialization of the coroutine frame and
+execution of the coroutine until a suspend point is reached:
+
+.. code-block:: llvm
+
+ define i8* @f(i32 %n) {
+ entry:
+ %id = call token @llvm.coro.id(i32 0, i8* null, i8* null, i8* null)
+ %alloc = call noalias i8* @malloc(i32 24)
+ %0 = call noalias i8* @llvm.coro.begin(token %id, i8* %alloc)
+ %frame = bitcast i8* %0 to %f.frame*
+ %1 = getelementptr %f.frame, %f.frame* %frame, i32 0, i32 0
+ store void (%f.frame*)* @f.resume, void (%f.frame*)** %1
+ %2 = getelementptr %f.frame, %f.frame* %frame, i32 0, i32 1
+ store void (%f.frame*)* @f.destroy, void (%f.frame*)** %2
+
+ %inc = add nsw i32 %n, 1
+ %inc.spill.addr = getelementptr inbounds %f.Frame, %f.Frame* %FramePtr, i32 0, i32 2
+ store i32 %inc, i32* %inc.spill.addr
+ call void @print(i32 %n)
+
+ ret i8* %frame
+ }
+
+Outlined resume part of the coroutine will reside in function `f.resume`:
+
+.. code-block:: llvm
+
+ define internal fastcc void @f.resume(%f.frame* %frame.ptr.resume) {
+ entry:
+ %inc.spill.addr = getelementptr %f.frame, %f.frame* %frame.ptr.resume, i64 0, i32 2
+ %inc.spill = load i32, i32* %inc.spill.addr, align 4
+ %inc = add i32 %n.val, 1
+ store i32 %inc, i32* %inc.spill.addr, align 4
+ tail call void @print(i32 %inc)
+ ret void
+ }
+
+Whereas function `f.destroy` will contain the cleanup code for the coroutine:
+
+.. code-block:: llvm
+
+ define internal fastcc void @f.destroy(%f.frame* %frame.ptr.destroy) {
+ entry:
+ %0 = bitcast %f.frame* %frame.ptr.destroy to i8*
+ tail call void @free(i8* %0)
+ ret void
+ }
+
+Avoiding Heap Allocations
+-------------------------
+
+A particular coroutine usage pattern, which is illustrated by the `main`
+function in the overview section, where a coroutine is created, manipulated and
+destroyed by the same calling function, is common for coroutines implementing
+RAII idiom and is suitable for allocation elision optimization which avoid
+dynamic allocation by storing the coroutine frame as a static `alloca` in its
+caller.
+
+In the entry block, we will call `coro.alloc`_ intrinsic that will return `true`
+when dynamic allocation is required, and `false` if dynamic allocation is
+elided.
+
+.. code-block:: llvm
+
+ entry:
+ %id = call token @llvm.coro.id(i32 0, i8* null, i8* null, i8* null)
+ %need.dyn.alloc = call i1 @llvm.coro.alloc(token %id)
+ br i1 %need.dyn.alloc, label %dyn.alloc, label %coro.begin
+ dyn.alloc:
+ %size = call i32 @llvm.coro.size.i32()
+ %alloc = call i8* @CustomAlloc(i32 %size)
+ br label %coro.begin
+ coro.begin:
+ %phi = phi i8* [ null, %entry ], [ %alloc, %dyn.alloc ]
+ %hdl = call noalias i8* @llvm.coro.begin(token %id, i8* %phi)
+
+In the cleanup block, we will make freeing the coroutine frame conditional on
+`coro.free`_ intrinsic. If allocation is elided, `coro.free`_ returns `null`
+thus skipping the deallocation code:
+
+.. code-block:: llvm
+
+ cleanup:
+ %mem = call i8* @llvm.coro.free(token %id, i8* %hdl)
+ %need.dyn.free = icmp ne i8* %mem, null
+ br i1 %need.dyn.free, label %dyn.free, label %if.end
+ dyn.free:
+ call void @CustomFree(i8* %mem)
+ br label %if.end
+ if.end:
+ ...
+
+With allocations and deallocations represented as described as above, after
+coroutine heap allocation elision optimization, the resulting main will be:
+
+.. code-block:: llvm
+
+ define i32 @main() {
+ entry:
+ call void @print(i32 4)
+ call void @print(i32 5)
+ call void @print(i32 6)
+ ret i32 0
+ }
+
+Multiple Suspend Points
+-----------------------
+
+Let's consider the coroutine that has more than one suspend point:
+
+.. code-block:: c++
+
+ void *f(int n) {
+ for(;;) {
+ print(n++);
+ <suspend>
+ print(-n);
+ <suspend>
+ }
+ }
+
+Matching LLVM code would look like (with the rest of the code remaining the same
+as the code in the previous section):
+
+.. code-block:: llvm
+
+ loop:
+ %n.addr = phi i32 [ %n, %entry ], [ %inc, %loop.resume ]
+ call void @print(i32 %n.addr) #4
+ %2 = call i8 @llvm.coro.suspend(token none, i1 false)
+ switch i8 %2, label %suspend [i8 0, label %loop.resume
+ i8 1, label %cleanup]
+ loop.resume:
+ %inc = add nsw i32 %n.addr, 1
+ %sub = xor i32 %n.addr, -1
+ call void @print(i32 %sub)
+ %3 = call i8 @llvm.coro.suspend(token none, i1 false)
+ switch i8 %3, label %suspend [i8 0, label %loop
+ i8 1, label %cleanup]
+
+In this case, the coroutine frame would include a suspend index that will
+indicate at which suspend point the coroutine needs to resume. The resume
+function will use an index to jump to an appropriate basic block and will look
+as follows:
+
+.. code-block:: llvm
+
+ define internal fastcc void @f.Resume(%f.Frame* %FramePtr) {
+ entry.Resume:
+ %index.addr = getelementptr inbounds %f.Frame, %f.Frame* %FramePtr, i64 0, i32 2
+ %index = load i8, i8* %index.addr, align 1
+ %switch = icmp eq i8 %index, 0
+ %n.addr = getelementptr inbounds %f.Frame, %f.Frame* %FramePtr, i64 0, i32 3
+ %n = load i32, i32* %n.addr, align 4
+ br i1 %switch, label %loop.resume, label %loop
+
+ loop.resume:
+ %sub = xor i32 %n, -1
+ call void @print(i32 %sub)
+ br label %suspend
+ loop:
+ %inc = add nsw i32 %n, 1
+ store i32 %inc, i32* %n.addr, align 4
+ tail call void @print(i32 %inc)
+ br label %suspend
+
+ suspend:
+ %storemerge = phi i8 [ 0, %loop ], [ 1, %loop.resume ]
+ store i8 %storemerge, i8* %index.addr, align 1
+ ret void
+ }
+
+If different cleanup code needs to get executed for different suspend points,
+a similar switch will be in the `f.destroy` function.
+
+.. note ::
+
+ Using suspend index in a coroutine state and having a switch in `f.resume` and
+ `f.destroy` is one of the possible implementation strategies. We explored
+ another option where a distinct `f.resume1`, `f.resume2`, etc. are created for
+ every suspend point, and instead of storing an index, the resume and destroy
+ function pointers are updated at every suspend. Early testing showed that the
+ current approach is easier on the optimizer than the latter so it is a
+ lowering strategy implemented at the moment.
+
+Distinct Save and Suspend
+-------------------------
+
+In the previous example, setting a resume index (or some other state change that
+needs to happen to prepare a coroutine for resumption) happens at the same time as
+a suspension of a coroutine. However, in certain cases, it is necessary to control
+when coroutine is prepared for resumption and when it is suspended.
+
+In the following example, a coroutine represents some activity that is driven
+by completions of asynchronous operations `async_op1` and `async_op2` which get
+a coroutine handle as a parameter and resume the coroutine once async
+operation is finished.
+
+.. code-block:: text
+
+ void g() {
+ for (;;)
+ if (cond()) {
+ async_op1(<coroutine-handle>); // will resume once async_op1 completes
+ <suspend>
+ do_one();
+ }
+ else {
+ async_op2(<coroutine-handle>); // will resume once async_op2 completes
+ <suspend>
+ do_two();
+ }
+ }
+ }
+
+In this case, coroutine should be ready for resumption prior to a call to
+`async_op1` and `async_op2`. The `coro.save`_ intrinsic is used to indicate a
+point when coroutine should be ready for resumption (namely, when a resume index
+should be stored in the coroutine frame, so that it can be resumed at the
+correct resume point):
+
+.. code-block:: llvm
+
+ if.true:
+ %save1 = call token @llvm.coro.save(i8* %hdl)
+ call void @async_op1(i8* %hdl)
+ %suspend1 = call i1 @llvm.coro.suspend(token %save1, i1 false)
+ switch i8 %suspend1, label %suspend [i8 0, label %resume1
+ i8 1, label %cleanup]
+ if.false:
+ %save2 = call token @llvm.coro.save(i8* %hdl)
+ call void @async_op2(i8* %hdl)
+ %suspend2 = call i1 @llvm.coro.suspend(token %save2, i1 false)
+ switch i8 %suspend1, label %suspend [i8 0, label %resume2
+ i8 1, label %cleanup]
+
+.. _coroutine promise:
+
+Coroutine Promise
+-----------------
+
+A coroutine author or a frontend may designate a distinguished `alloca` that can
+be used to communicate with the coroutine. This distinguished alloca is called
+**coroutine promise** and is provided as the second parameter to the
+`coro.id`_ intrinsic.
+
+The following coroutine designates a 32 bit integer `promise` and uses it to
+store the current value produced by a coroutine.
+
+.. code-block:: llvm
+
+ define i8* @f(i32 %n) {
+ entry:
+ %promise = alloca i32
+ %pv = bitcast i32* %promise to i8*
+ %id = call token @llvm.coro.id(i32 0, i8* %pv, i8* null, i8* null)
+ %need.dyn.alloc = call i1 @llvm.coro.alloc(token %id)
+ br i1 %need.dyn.alloc, label %dyn.alloc, label %coro.begin
+ dyn.alloc:
+ %size = call i32 @llvm.coro.size.i32()
+ %alloc = call i8* @malloc(i32 %size)
+ br label %coro.begin
+ coro.begin:
+ %phi = phi i8* [ null, %entry ], [ %alloc, %dyn.alloc ]
+ %hdl = call noalias i8* @llvm.coro.begin(token %id, i8* %phi)
+ br label %loop
+ loop:
+ %n.val = phi i32 [ %n, %coro.begin ], [ %inc, %loop ]
+ %inc = add nsw i32 %n.val, 1
+ store i32 %n.val, i32* %promise
+ %0 = call i8 @llvm.coro.suspend(token none, i1 false)
+ switch i8 %0, label %suspend [i8 0, label %loop
+ i8 1, label %cleanup]
+ cleanup:
+ %mem = call i8* @llvm.coro.free(token %id, i8* %hdl)
+ call void @free(i8* %mem)
+ br label %suspend
+ suspend:
+ %unused = call i1 @llvm.coro.end(i8* %hdl, i1 false)
+ ret i8* %hdl
+ }
+
+A coroutine consumer can rely on the `coro.promise`_ intrinsic to access the
+coroutine promise.
+
+.. code-block:: llvm
+
+ define i32 @main() {
+ entry:
+ %hdl = call i8* @f(i32 4)
+ %promise.addr.raw = call i8* @llvm.coro.promise(i8* %hdl, i32 4, i1 false)
+ %promise.addr = bitcast i8* %promise.addr.raw to i32*
+ %val0 = load i32, i32* %promise.addr
+ call void @print(i32 %val0)
+ call void @llvm.coro.resume(i8* %hdl)
+ %val1 = load i32, i32* %promise.addr
+ call void @print(i32 %val1)
+ call void @llvm.coro.resume(i8* %hdl)
+ %val2 = load i32, i32* %promise.addr
+ call void @print(i32 %val2)
+ call void @llvm.coro.destroy(i8* %hdl)
+ ret i32 0
+ }
+
+After example in this section is compiled, result of the compilation will be:
+
+.. code-block:: llvm
+
+ define i32 @main() {
+ entry:
+ tail call void @print(i32 4)
+ tail call void @print(i32 5)
+ tail call void @print(i32 6)
+ ret i32 0
+ }
+
+.. _final:
+.. _final suspend:
+
+Final Suspend
+-------------
+
+A coroutine author or a frontend may designate a particular suspend to be final,
+by setting the second argument of the `coro.suspend`_ intrinsic to `true`.
+Such a suspend point has two properties:
+
+* it is possible to check whether a suspended coroutine is at the final suspend
+ point via `coro.done`_ intrinsic;
+
+* a resumption of a coroutine stopped at the final suspend point leads to
+ undefined behavior. The only possible action for a coroutine at a final
+ suspend point is destroying it via `coro.destroy`_ intrinsic.
+
+From the user perspective, the final suspend point represents an idea of a
+coroutine reaching the end. From the compiler perspective, it is an optimization
+opportunity for reducing number of resume points (and therefore switch cases) in
+the resume function.
+
+The following is an example of a function that keeps resuming the coroutine
+until the final suspend point is reached after which point the coroutine is
+destroyed:
+
+.. code-block:: llvm
+
+ define i32 @main() {
+ entry:
+ %hdl = call i8* @f(i32 4)
+ br label %while
+ while:
+ call void @llvm.coro.resume(i8* %hdl)
+ %done = call i1 @llvm.coro.done(i8* %hdl)
+ br i1 %done, label %end, label %while
+ end:
+ call void @llvm.coro.destroy(i8* %hdl)
+ ret i32 0
+ }
+
+Usually, final suspend point is a frontend injected suspend point that does not
+correspond to any explicitly authored suspend point of the high level language.
+For example, for a Python generator that has only one suspend point:
+
+.. code-block:: python
+
+ def coroutine(n):
+ for i in range(n):
+ yield i
+
+Python frontend would inject two more suspend points, so that the actual code
+looks like this:
+
+.. code-block:: c
+
+ void* coroutine(int n) {
+ int current_value;
+ <designate current_value to be coroutine promise>
+ <SUSPEND> // injected suspend point, so that the coroutine starts suspended
+ for (int i = 0; i < n; ++i) {
+ current_value = i; <SUSPEND>; // corresponds to "yield i"
+ }
+ <SUSPEND final=true> // injected final suspend point
+ }
+
+and python iterator `__next__` would look like:
+
+.. code-block:: c++
+
+ int __next__(void* hdl) {
+ coro.resume(hdl);
+ if (coro.done(hdl)) throw StopIteration();
+ return *(int*)coro.promise(hdl, 4, false);
+ }
+
+Intrinsics
+==========
+
+Coroutine Manipulation Intrinsics
+---------------------------------
+
+Intrinsics described in this section are used to manipulate an existing
+coroutine. They can be used in any function which happen to have a pointer
+to a `coroutine frame`_ or a pointer to a `coroutine promise`_.
+
+.. _coro.destroy:
+
+'llvm.coro.destroy' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.coro.destroy(i8* <handle>)
+
+Overview:
+"""""""""
+
+The '``llvm.coro.destroy``' intrinsic destroys a suspended
+coroutine.
+
+Arguments:
+""""""""""
+
+The argument is a coroutine handle to a suspended coroutine.
+
+Semantics:
+""""""""""
+
+When possible, the `coro.destroy` intrinsic is replaced with a direct call to
+the coroutine destroy function. Otherwise it is replaced with an indirect call
+based on the function pointer for the destroy function stored in the coroutine
+frame. Destroying a coroutine that is not suspended leads to undefined behavior.
+
+.. _coro.resume:
+
+'llvm.coro.resume' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+::
+
+ declare void @llvm.coro.resume(i8* <handle>)
+
+Overview:
+"""""""""
+
+The '``llvm.coro.resume``' intrinsic resumes a suspended coroutine.
+
+Arguments:
+""""""""""
+
+The argument is a handle to a suspended coroutine.
+
+Semantics:
+""""""""""
+
+When possible, the `coro.resume` intrinsic is replaced with a direct call to the
+coroutine resume function. Otherwise it is replaced with an indirect call based
+on the function pointer for the resume function stored in the coroutine frame.
+Resuming a coroutine that is not suspended leads to undefined behavior.
+
+.. _coro.done:
+
+'llvm.coro.done' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+::
+
+ declare i1 @llvm.coro.done(i8* <handle>)
+
+Overview:
+"""""""""
+
+The '``llvm.coro.done``' intrinsic checks whether a suspended coroutine is at
+the final suspend point or not.
+
+Arguments:
+""""""""""
+
+The argument is a handle to a suspended coroutine.
+
+Semantics:
+""""""""""
+
+Using this intrinsic on a coroutine that does not have a `final suspend`_ point
+or on a coroutine that is not suspended leads to undefined behavior.
+
+.. _coro.promise:
+
+'llvm.coro.promise' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+::
+
+ declare i8* @llvm.coro.promise(i8* <ptr>, i32 <alignment>, i1 <from>)
+
+Overview:
+"""""""""
+
+The '``llvm.coro.promise``' intrinsic obtains a pointer to a
+`coroutine promise`_ given a coroutine handle and vice versa.
+
+Arguments:
+""""""""""
+
+The first argument is a handle to a coroutine if `from` is false. Otherwise,
+it is a pointer to a coroutine promise.
+
+The second argument is an alignment requirements of the promise.
+If a frontend designated `%promise = alloca i32` as a promise, the alignment
+argument to `coro.promise` should be the alignment of `i32` on the target
+platform. If a frontend designated `%promise = alloca i32, align 16` as a
+promise, the alignment argument should be 16.
+This argument only accepts constants.
+
+The third argument is a boolean indicating a direction of the transformation.
+If `from` is true, the intrinsic returns a coroutine handle given a pointer
+to a promise. If `from` is false, the intrinsics return a pointer to a promise
+from a coroutine handle. This argument only accepts constants.
+
+Semantics:
+""""""""""
+
+Using this intrinsic on a coroutine that does not have a coroutine promise
+leads to undefined behavior. It is possible to read and modify coroutine
+promise of the coroutine which is currently executing. The coroutine author and
+a coroutine user are responsible to makes sure there is no data races.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ define i8* @f(i32 %n) {
+ entry:
+ %promise = alloca i32
+ %pv = bitcast i32* %promise to i8*
+ ; the second argument to coro.id points to the coroutine promise.
+ %id = call token @llvm.coro.id(i32 0, i8* %pv, i8* null, i8* null)
+ ...
+ %hdl = call noalias i8* @llvm.coro.begin(token %id, i8* %alloc)
+ ...
+ store i32 42, i32* %promise ; store something into the promise
+ ...
+ ret i8* %hdl
+ }
+
+ define i32 @main() {
+ entry:
+ %hdl = call i8* @f(i32 4) ; starts the coroutine and returns its handle
+ %promise.addr.raw = call i8* @llvm.coro.promise(i8* %hdl, i32 4, i1 false)
+ %promise.addr = bitcast i8* %promise.addr.raw to i32*
+ %val = load i32, i32* %promise.addr ; load a value from the promise
+ call void @print(i32 %val)
+ call void @llvm.coro.destroy(i8* %hdl)
+ ret i32 0
+ }
+
+.. _coroutine intrinsics:
+
+Coroutine Structure Intrinsics
+------------------------------
+Intrinsics described in this section are used within a coroutine to describe
+the coroutine structure. They should not be used outside of a coroutine.
+
+.. _coro.size:
+
+'llvm.coro.size' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+::
+
+ declare i32 @llvm.coro.size.i32()
+ declare i64 @llvm.coro.size.i64()
+
+Overview:
+"""""""""
+
+The '``llvm.coro.size``' intrinsic returns the number of bytes
+required to store a `coroutine frame`_.
+
+Arguments:
+""""""""""
+
+None
+
+Semantics:
+""""""""""
+
+The `coro.size` intrinsic is lowered to a constant representing the size of
+the coroutine frame.
+
+.. _coro.begin:
+
+'llvm.coro.begin' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+::
+
+ declare i8* @llvm.coro.begin(token <id>, i8* <mem>)
+
+Overview:
+"""""""""
+
+The '``llvm.coro.begin``' intrinsic returns an address of the coroutine frame.
+
+Arguments:
+""""""""""
+
+The first argument is a token returned by a call to '``llvm.coro.id``'
+identifying the coroutine.
+
+The second argument is a pointer to a block of memory where coroutine frame
+will be stored if it is allocated dynamically.
+
+Semantics:
+""""""""""
+
+Depending on the alignment requirements of the objects in the coroutine frame
+and/or on the codegen compactness reasons the pointer returned from `coro.begin`
+may be at offset to the `%mem` argument. (This could be beneficial if
+instructions that express relative access to data can be more compactly encoded
+with small positive and negative offsets).
+
+A frontend should emit exactly one `coro.begin` intrinsic per coroutine.
+
+.. _coro.free:
+
+'llvm.coro.free' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+::
+
+ declare i8* @llvm.coro.free(token %id, i8* <frame>)
+
+Overview:
+"""""""""
+
+The '``llvm.coro.free``' intrinsic returns a pointer to a block of memory where
+coroutine frame is stored or `null` if this instance of a coroutine did not use
+dynamically allocated memory for its coroutine frame.
+
+Arguments:
+""""""""""
+
+The first argument is a token returned by a call to '``llvm.coro.id``'
+identifying the coroutine.
+
+The second argument is a pointer to the coroutine frame. This should be the same
+pointer that was returned by prior `coro.begin` call.
+
+Example (custom deallocation function):
+"""""""""""""""""""""""""""""""""""""""
+
+.. code-block:: llvm
+
+ cleanup:
+ %mem = call i8* @llvm.coro.free(token %id, i8* %frame)
+ %mem_not_null = icmp ne i8* %mem, null
+ br i1 %mem_not_null, label %if.then, label %if.end
+ if.then:
+ call void @CustomFree(i8* %mem)
+ br label %if.end
+ if.end:
+ ret void
+
+Example (standard deallocation functions):
+""""""""""""""""""""""""""""""""""""""""""
+
+.. code-block:: llvm
+
+ cleanup:
+ %mem = call i8* @llvm.coro.free(token %id, i8* %frame)
+ call void @free(i8* %mem)
+ ret void
+
+.. _coro.alloc:
+
+'llvm.coro.alloc' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+::
+
+ declare i1 @llvm.coro.alloc(token <id>)
+
+Overview:
+"""""""""
+
+The '``llvm.coro.alloc``' intrinsic returns `true` if dynamic allocation is
+required to obtain a memory for the coroutine frame and `false` otherwise.
+
+Arguments:
+""""""""""
+
+The first argument is a token returned by a call to '``llvm.coro.id``'
+identifying the coroutine.
+
+Semantics:
+""""""""""
+
+A frontend should emit at most one `coro.alloc` intrinsic per coroutine.
+The intrinsic is used to suppress dynamic allocation of the coroutine frame
+when possible.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ entry:
+ %id = call token @llvm.coro.id(i32 0, i8* null, i8* null, i8* null)
+ %dyn.alloc.required = call i1 @llvm.coro.alloc(token %id)
+ br i1 %dyn.alloc.required, label %coro.alloc, label %coro.begin
+
+ coro.alloc:
+ %frame.size = call i32 @llvm.coro.size()
+ %alloc = call i8* @MyAlloc(i32 %frame.size)
+ br label %coro.begin
+
+ coro.begin:
+ %phi = phi i8* [ null, %entry ], [ %alloc, %coro.alloc ]
+ %frame = call i8* @llvm.coro.begin(token %id, i8* %phi)
+
+.. _coro.frame:
+
+'llvm.coro.frame' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+::
+
+ declare i8* @llvm.coro.frame()
+
+Overview:
+"""""""""
+
+The '``llvm.coro.frame``' intrinsic returns an address of the coroutine frame of
+the enclosing coroutine.
+
+Arguments:
+""""""""""
+
+None
+
+Semantics:
+""""""""""
+
+This intrinsic is lowered to refer to the `coro.begin`_ instruction. This is
+a frontend convenience intrinsic that makes it easier to refer to the
+coroutine frame.
+
+.. _coro.id:
+
+'llvm.coro.id' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+::
+
+ declare token @llvm.coro.id(i32 <align>, i8* <promise>, i8* <coroaddr>,
+ i8* <fnaddrs>)
+
+Overview:
+"""""""""
+
+The '``llvm.coro.id``' intrinsic returns a token identifying a coroutine.
+
+Arguments:
+""""""""""
+
+The first argument provides information on the alignment of the memory returned
+by the allocation function and given to `coro.begin` by the first argument. If
+this argument is 0, the memory is assumed to be aligned to 2 * sizeof(i8*).
+This argument only accepts constants.
+
+The second argument, if not `null`, designates a particular alloca instruction
+to be a `coroutine promise`_.
+
+The third argument is `null` coming out of the frontend. The CoroEarly pass sets
+this argument to point to the function this coro.id belongs to.
+
+The fourth argument is `null` before coroutine is split, and later is replaced
+to point to a private global constant array containing function pointers to
+outlined resume and destroy parts of the coroutine.
+
+
+Semantics:
+""""""""""
+
+The purpose of this intrinsic is to tie together `coro.id`, `coro.alloc` and
+`coro.begin` belonging to the same coroutine to prevent optimization passes from
+duplicating any of these instructions unless entire body of the coroutine is
+duplicated.
+
+A frontend should emit exactly one `coro.id` intrinsic per coroutine.
+
+.. _coro.end:
+
+'llvm.coro.end' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+::
+
+ declare i1 @llvm.coro.end(i8* <handle>, i1 <unwind>)
+
+Overview:
+"""""""""
+
+The '``llvm.coro.end``' marks the point where execution of the resume part of
+the coroutine should end and control should return to the caller.
+
+
+Arguments:
+""""""""""
+
+The first argument should refer to the coroutine handle of the enclosing
+coroutine. A frontend is allowed to supply null as the first parameter, in this
+case `coro-early` pass will replace the null with an appropriate coroutine
+handle value.
+
+The second argument should be `true` if this coro.end is in the block that is
+part of the unwind sequence leaving the coroutine body due to an exception and
+`false` otherwise.
+
+Semantics:
+""""""""""
+The purpose of this intrinsic is to allow frontends to mark the cleanup and
+other code that is only relevant during the initial invocation of the coroutine
+and should not be present in resume and destroy parts.
+
+This intrinsic is lowered when a coroutine is split into
+the start, resume and destroy parts. In the start part, it is a no-op,
+in resume and destroy parts, it is replaced with `ret void` instruction and
+the rest of the block containing `coro.end` instruction is discarded.
+In landing pads it is replaced with an appropriate instruction to unwind to
+caller. The handling of coro.end differs depending on whether the target is
+using landingpad or WinEH exception model.
+
+For landingpad based exception model, it is expected that frontend uses the
+`coro.end`_ intrinsic as follows:
+
+.. code-block:: llvm
+
+ ehcleanup:
+ %InResumePart = call i1 @llvm.coro.end(i8* null, i1 true)
+ br i1 %InResumePart, label %eh.resume, label %cleanup.cont
+
+ cleanup.cont:
+ ; rest of the cleanup
+
+ eh.resume:
+ %exn = load i8*, i8** %exn.slot, align 8
+ %sel = load i32, i32* %ehselector.slot, align 4
+ %lpad.val = insertvalue { i8*, i32 } undef, i8* %exn, 0
+ %lpad.val29 = insertvalue { i8*, i32 } %lpad.val, i32 %sel, 1
+ resume { i8*, i32 } %lpad.val29
+
+The `CoroSpit` pass replaces `coro.end` with ``True`` in the resume functions,
+thus leading to immediate unwind to the caller, whereas in start function it
+is replaced with ``False``, thus allowing to proceed to the rest of the cleanup
+code that is only needed during initial invocation of the coroutine.
+
+For Windows Exception handling model, a frontend should attach a funclet bundle
+referring to an enclosing cleanuppad as follows:
+
+.. code-block:: llvm
+
+ ehcleanup:
+ %tok = cleanuppad within none []
+ %unused = call i1 @llvm.coro.end(i8* null, i1 true) [ "funclet"(token %tok) ]
+ cleanupret from %tok unwind label %RestOfTheCleanup
+
+The `CoroSplit` pass, if the funclet bundle is present, will insert
+``cleanupret from %tok unwind to caller`` before
+the `coro.end`_ intrinsic and will remove the rest of the block.
+
+The following table summarizes the handling of `coro.end`_ intrinsic.
+
++--------------------------+-------------------+-------------------------------+
+| | In Start Function | In Resume/Destroy Functions |
++--------------------------+-------------------+-------------------------------+
+|unwind=false | nothing |``ret void`` |
++------------+-------------+-------------------+-------------------------------+
+| | WinEH | nothing |``cleanupret unwind to caller``|
+|unwind=true +-------------+-------------------+-------------------------------+
+| | Landingpad | nothing | nothing |
++------------+-------------+-------------------+-------------------------------+
+
+.. _coro.suspend:
+.. _suspend points:
+
+'llvm.coro.suspend' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+::
+
+ declare i8 @llvm.coro.suspend(token <save>, i1 <final>)
+
+Overview:
+"""""""""
+
+The '``llvm.coro.suspend``' marks the point where execution of the coroutine
+need to get suspended and control returned back to the caller.
+Conditional branches consuming the result of this intrinsic lead to basic blocks
+where coroutine should proceed when suspended (-1), resumed (0) or destroyed
+(1).
+
+Arguments:
+""""""""""
+
+The first argument refers to a token of `coro.save` intrinsic that marks the
+point when coroutine state is prepared for suspension. If `none` token is passed,
+the intrinsic behaves as if there were a `coro.save` immediately preceding
+the `coro.suspend` intrinsic.
+
+The second argument indicates whether this suspension point is `final`_.
+The second argument only accepts constants. If more than one suspend point is
+designated as final, the resume and destroy branches should lead to the same
+basic blocks.
+
+Example (normal suspend point):
+"""""""""""""""""""""""""""""""
+
+.. code-block:: llvm
+
+ %0 = call i8 @llvm.coro.suspend(token none, i1 false)
+ switch i8 %0, label %suspend [i8 0, label %resume
+ i8 1, label %cleanup]
+
+Example (final suspend point):
+""""""""""""""""""""""""""""""
+
+.. code-block:: llvm
+
+ while.end:
+ %s.final = call i8 @llvm.coro.suspend(token none, i1 true)
+ switch i8 %s.final, label %suspend [i8 0, label %trap
+ i8 1, label %cleanup]
+ trap:
+ call void @llvm.trap()
+ unreachable
+
+Semantics:
+""""""""""
+
+If a coroutine that was suspended at the suspend point marked by this intrinsic
+is resumed via `coro.resume`_ the control will transfer to the basic block
+of the 0-case. If it is resumed via `coro.destroy`_, it will proceed to the
+basic block indicated by the 1-case. To suspend, coroutine proceed to the
+default label.
+
+If suspend intrinsic is marked as final, it can consider the `true` branch
+unreachable and can perform optimizations that can take advantage of that fact.
+
+.. _coro.save:
+
+'llvm.coro.save' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+::
+
+ declare token @llvm.coro.save(i8* <handle>)
+
+Overview:
+"""""""""
+
+The '``llvm.coro.save``' marks the point where a coroutine need to update its
+state to prepare for resumption to be considered suspended (and thus eligible
+for resumption).
+
+Arguments:
+""""""""""
+
+The first argument points to a coroutine handle of the enclosing coroutine.
+
+Semantics:
+""""""""""
+
+Whatever coroutine state changes are required to enable resumption of
+the coroutine from the corresponding suspend point should be done at the point
+of `coro.save` intrinsic.
+
+Example:
+""""""""
+
+Separate save and suspend points are necessary when a coroutine is used to
+represent an asynchronous control flow driven by callbacks representing
+completions of asynchronous operations.
+
+In such a case, a coroutine should be ready for resumption prior to a call to
+`async_op` function that may trigger resumption of a coroutine from the same or
+a different thread possibly prior to `async_op` call returning control back
+to the coroutine:
+
+.. code-block:: llvm
+
+ %save1 = call token @llvm.coro.save(i8* %hdl)
+ call void @async_op1(i8* %hdl)
+ %suspend1 = call i1 @llvm.coro.suspend(token %save1, i1 false)
+ switch i8 %suspend1, label %suspend [i8 0, label %resume1
+ i8 1, label %cleanup]
+
+.. _coro.param:
+
+'llvm.coro.param' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+::
+
+ declare i1 @llvm.coro.param(i8* <original>, i8* <copy>)
+
+Overview:
+"""""""""
+
+The '``llvm.coro.param``' is used by a frontend to mark up the code used to
+construct and destruct copies of the parameters. If the optimizer discovers that
+a particular parameter copy is not used after any suspends, it can remove the
+construction and destruction of the copy by replacing corresponding coro.param
+with `i1 false` and replacing any use of the `copy` with the `original`.
+
+Arguments:
+""""""""""
+
+The first argument points to an `alloca` storing the value of a parameter to a
+coroutine.
+
+The second argument points to an `alloca` storing the value of the copy of that
+parameter.
+
+Semantics:
+""""""""""
+
+The optimizer is free to always replace this intrinsic with `i1 true`.
+
+The optimizer is also allowed to replace it with `i1 false` provided that the
+parameter copy is only used prior to control flow reaching any of the suspend
+points. The code that would be DCE'd if the `coro.param` is replaced with
+`i1 false` is not considered to be a use of the parameter copy.
+
+The frontend can emit this intrinsic if its language rules allow for this
+optimization.
+
+Example:
+""""""""
+Consider the following example. A coroutine takes two parameters `a` and `b`
+that has a destructor and a move constructor.
+
+.. code-block:: c++
+
+ struct A { ~A(); A(A&&); bool foo(); void bar(); };
+
+ task<int> f(A a, A b) {
+ if (a.foo())
+ return 42;
+
+ a.bar();
+ co_await read_async(); // introduces suspend point
+ b.bar();
+ }
+
+Note that, uses of `b` is used after a suspend point and thus must be copied
+into a coroutine frame, whereas `a` does not have to, since it never used
+after suspend.
+
+A frontend can create parameter copies for `a` and `b` as follows:
+
+.. code-block:: text
+
+ task<int> f(A a', A b') {
+ a = alloca A;
+ b = alloca A;
+ // move parameters to its copies
+ if (coro.param(a', a)) A::A(a, A&& a');
+ if (coro.param(b', b)) A::A(b, A&& b');
+ ...
+ // destroy parameters copies
+ if (coro.param(a', a)) A::~A(a);
+ if (coro.param(b', b)) A::~A(b);
+ }
+
+The optimizer can replace coro.param(a',a) with `i1 false` and replace all uses
+of `a` with `a'`, since it is not used after suspend.
+
+The optimizer must replace coro.param(b', b) with `i1 true`, since `b` is used
+after suspend and therefore, it has to reside in the coroutine frame.
+
+Coroutine Transformation Passes
+===============================
+CoroEarly
+---------
+The pass CoroEarly lowers coroutine intrinsics that hide the details of the
+structure of the coroutine frame, but, otherwise not needed to be preserved to
+help later coroutine passes. This pass lowers `coro.frame`_, `coro.done`_,
+and `coro.promise`_ intrinsics.
+
+.. _CoroSplit:
+
+CoroSplit
+---------
+The pass CoroSplit buides coroutine frame and outlines resume and destroy parts
+into separate functions.
+
+CoroElide
+---------
+The pass CoroElide examines if the inlined coroutine is eligible for heap
+allocation elision optimization. If so, it replaces
+`coro.begin` intrinsic with an address of a coroutine frame placed on its caller
+and replaces `coro.alloc` and `coro.free` intrinsics with `false` and `null`
+respectively to remove the deallocation code.
+This pass also replaces `coro.resume` and `coro.destroy` intrinsics with direct
+calls to resume and destroy functions for a particular coroutine where possible.
+
+CoroCleanup
+-----------
+This pass runs late to lower all coroutine related intrinsics not replaced by
+earlier passes.
+
+Areas Requiring Attention
+=========================
+#. A coroutine frame is bigger than it could be. Adding stack packing and stack
+ coloring like optimization on the coroutine frame will result in tighter
+ coroutine frames.
+
+#. Take advantage of the lifetime intrinsics for the data that goes into the
+ coroutine frame. Leave lifetime intrinsics as is for the data that stays in
+ allocas.
+
+#. The CoroElide optimization pass relies on coroutine ramp function to be
+ inlined. It would be beneficial to split the ramp function further to
+ increase the chance that it will get inlined into its caller.
+
+#. Design a convention that would make it possible to apply coroutine heap
+ elision optimization across ABI boundaries.
+
+#. Cannot handle coroutines with `inalloca` parameters (used in x86 on Windows).
+
+#. Alignment is ignored by coro.begin and coro.free intrinsics.
+
+#. Make required changes to make sure that coroutine optimizations work with
+ LTO.
+
+#. More tests, more tests, more tests
Added: www-releases/trunk/5.0.2/docs/_sources/CoverageMappingFormat.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.2/docs/_sources/CoverageMappingFormat.txt?rev=331981&view=auto
==============================================================================
--- www-releases/trunk/5.0.2/docs/_sources/CoverageMappingFormat.txt (added)
+++ www-releases/trunk/5.0.2/docs/_sources/CoverageMappingFormat.txt Thu May 10 06:54:16 2018
@@ -0,0 +1,605 @@
+.. role:: raw-html(raw)
+ :format: html
+
+=================================
+LLVM Code Coverage Mapping Format
+=================================
+
+.. contents::
+ :local:
+
+Introduction
+============
+
+LLVM's code coverage mapping format is used to provide code coverage
+analysis using LLVM's and Clang's instrumenation based profiling
+(Clang's ``-fprofile-instr-generate`` option).
+
+This document is aimed at those who use LLVM's code coverage mapping to provide
+code coverage analysis for their own programs, and for those who would like
+to know how it works under the hood. A prior knowledge of how Clang's profile
+guided optimization works is useful, but not required.
+
+We start by showing how to use LLVM and Clang for code coverage analysis,
+then we briefly describe LLVM's code coverage mapping format and the
+way that Clang and LLVM's code coverage tool work with this format. After
+the basics are down, more advanced features of the coverage mapping format
+are discussed - such as the data structures, LLVM IR representation and
+the binary encoding.
+
+Quick Start
+===========
+
+Here's a short story that describes how to generate code coverage overview
+for a sample source file called *test.c*.
+
+* First, compile an instrumented version of your program using Clang's
+ ``-fprofile-instr-generate`` option with the additional ``-fcoverage-mapping``
+ option:
+
+ ``clang -o test -fprofile-instr-generate -fcoverage-mapping test.c``
+* Then, run the instrumented binary. The runtime will produce a file called
+ *default.profraw* containing the raw profile instrumentation data:
+
+ ``./test``
+* After that, merge the profile data using the *llvm-profdata* tool:
+
+ ``llvm-profdata merge -o test.profdata default.profraw``
+* Finally, run LLVM's code coverage tool (*llvm-cov*) to produce the code
+ coverage overview for the sample source file:
+
+ ``llvm-cov show ./test -instr-profile=test.profdata test.c``
+
+High Level Overview
+===================
+
+LLVM's code coverage mapping format is designed to be a self contained
+data format, that can be embedded into the LLVM IR and object files.
+It's described in this document as a **mapping** format because its goal is
+to store the data that is required for a code coverage tool to map between
+the specific source ranges in a file and the execution counts obtained
+after running the instrumented version of the program.
+
+The mapping data is used in two places in the code coverage process:
+
+1. When clang compiles a source file with ``-fcoverage-mapping``, it
+ generates the mapping information that describes the mapping between the
+ source ranges and the profiling instrumentation counters.
+ This information gets embedded into the LLVM IR and conveniently
+ ends up in the final executable file when the program is linked.
+
+2. It is also used by *llvm-cov* - the mapping information is extracted from an
+ object file and is used to associate the execution counts (the values of the
+ profile instrumentation counters), and the source ranges in a file.
+ After that, the tool is able to generate various code coverage reports
+ for the program.
+
+The coverage mapping format aims to be a "universal format" that would be
+suitable for usage by any frontend, and not just by Clang. It also aims to
+provide the frontend the possibility of generating the minimal coverage mapping
+data in order to reduce the size of the IR and object files - for example,
+instead of emitting mapping information for each statement in a function, the
+frontend is allowed to group the statements with the same execution count into
+regions of code, and emit the mapping information only for those regions.
+
+Advanced Concepts
+=================
+
+The remainder of this guide is meant to give you insight into the way the
+coverage mapping format works.
+
+The coverage mapping format operates on a per-function level as the
+profile instrumentation counters are associated with a specific function.
+For each function that requires code coverage, the frontend has to create
+coverage mapping data that can map between the source code ranges and
+the profile instrumentation counters for that function.
+
+Mapping Region
+--------------
+
+The function's coverage mapping data contains an array of mapping regions.
+A mapping region stores the `source code range`_ that is covered by this region,
+the `file id <coverage file id_>`_, the `coverage mapping counter`_ and
+the region's kind.
+There are several kinds of mapping regions:
+
+* Code regions associate portions of source code and `coverage mapping
+ counters`_. They make up the majority of the mapping regions. They are used
+ by the code coverage tool to compute the execution counts for lines,
+ highlight the regions of code that were never executed, and to obtain
+ the various code coverage statistics for a function.
+ For example:
+
+ :raw-html:`<pre class='highlight' style='line-height:initial;'><span>int main(int argc, const char *argv[]) </span><span style='background-color:#4A789C'>{ </span> <span class='c1'>// Code Region from 1:40 to 9:2</span>
+ <span style='background-color:#4A789C'> </span>
+ <span style='background-color:#4A789C'> if (argc > 1) </span><span style='background-color:#85C1F5'>{ </span> <span class='c1'>// Code Region from 3:17 to 5:4</span>
+ <span style='background-color:#85C1F5'> printf("%s\n", argv[1]); </span>
+ <span style='background-color:#85C1F5'> }</span><span style='background-color:#4A789C'> else </span><span style='background-color:#F6D55D'>{ </span> <span class='c1'>// Code Region from 5:10 to 7:4</span>
+ <span style='background-color:#F6D55D'> printf("\n"); </span>
+ <span style='background-color:#F6D55D'> }</span><span style='background-color:#4A789C'> </span>
+ <span style='background-color:#4A789C'> return 0; </span>
+ <span style='background-color:#4A789C'>}</span>
+ </pre>`
+* Skipped regions are used to represent source ranges that were skipped
+ by Clang's preprocessor. They don't associate with
+ `coverage mapping counters`_, as the frontend knows that they are never
+ executed. They are used by the code coverage tool to mark the skipped lines
+ inside a function as non-code lines that don't have execution counts.
+ For example:
+
+ :raw-html:`<pre class='highlight' style='line-height:initial;'><span>int main() </span><span style='background-color:#4A789C'>{ </span> <span class='c1'>// Code Region from 1:12 to 6:2</span>
+ <span style='background-color:#85C1F5'>#ifdef DEBUG </span> <span class='c1'>// Skipped Region from 2:1 to 4:2</span>
+ <span style='background-color:#85C1F5'> printf("Hello world"); </span>
+ <span style='background-color:#85C1F5'>#</span><span style='background-color:#4A789C'>endif </span>
+ <span style='background-color:#4A789C'> return 0; </span>
+ <span style='background-color:#4A789C'>}</span>
+ </pre>`
+* Expansion regions are used to represent Clang's macro expansions. They
+ have an additional property - *expanded file id*. This property can be
+ used by the code coverage tool to find the mapping regions that are created
+ as a result of this macro expansion, by checking if their file id matches the
+ expanded file id. They don't associate with `coverage mapping counters`_,
+ as the code coverage tool can determine the execution count for this region
+ by looking up the execution count of the first region with a corresponding
+ file id.
+ For example:
+
+ :raw-html:`<pre class='highlight' style='line-height:initial;'><span>int func(int x) </span><span style='background-color:#4A789C'>{ </span>
+ <span style='background-color:#4A789C'> #define MAX(x,y) </span><span style='background-color:#85C1F5'>((x) > (y)? </span><span style='background-color:#F6D55D'>(x)</span><span style='background-color:#85C1F5'> : </span><span style='background-color:#F4BA70'>(y)</span><span style='background-color:#85C1F5'>)</span><span style='background-color:#4A789C'> </span>
+ <span style='background-color:#4A789C'> return </span><span style='background-color:#7FCA9F'>MAX</span><span style='background-color:#4A789C'>(x, 42); </span> <span class='c1'>// Expansion Region from 3:10 to 3:13</span>
+ <span style='background-color:#4A789C'>}</span>
+ </pre>`
+
+.. _source code range:
+
+Source Range:
+^^^^^^^^^^^^^
+
+The source range record contains the starting and ending location of a certain
+mapping region. Both locations include the line and the column numbers.
+
+.. _coverage file id:
+
+File ID:
+^^^^^^^^
+
+The file id an integer value that tells us
+in which source file or macro expansion is this region located.
+It enables Clang to produce mapping information for the code
+defined inside macros, like this example demonstrates:
+
+:raw-html:`<pre class='highlight' style='line-height:initial;'><span>void func(const char *str) </span><span style='background-color:#4A789C'>{ </span> <span class='c1'>// Code Region from 1:28 to 6:2 with file id 0</span>
+<span style='background-color:#4A789C'> #define PUT </span><span style='background-color:#85C1F5'>printf("%s\n", str)</span><span style='background-color:#4A789C'> </span> <span class='c1'>// 2 Code Regions from 2:15 to 2:34 with file ids 1 and 2</span>
+<span style='background-color:#4A789C'> if(*str) </span>
+<span style='background-color:#4A789C'> </span><span style='background-color:#F6D55D'>PUT</span><span style='background-color:#4A789C'>; </span> <span class='c1'>// Expansion Region from 4:5 to 4:8 with file id 0 that expands a macro with file id 1</span>
+<span style='background-color:#4A789C'> </span><span style='background-color:#F6D55D'>PUT</span><span style='background-color:#4A789C'>; </span> <span class='c1'>// Expansion Region from 5:3 to 5:6 with file id 0 that expands a macro with file id 2</span>
+<span style='background-color:#4A789C'>}</span>
+</pre>`
+
+.. _coverage mapping counter:
+.. _coverage mapping counters:
+
+Counter:
+^^^^^^^^
+
+A coverage mapping counter can represents a reference to the profile
+instrumentation counter. The execution count for a region with such counter
+is determined by looking up the value of the corresponding profile
+instrumentation counter.
+
+It can also represent a binary arithmetical expression that operates on
+coverage mapping counters or other expressions.
+The execution count for a region with an expression counter is determined by
+evaluating the expression's arguments and then adding them together or
+subtracting them from one another.
+In the example below, a subtraction expression is used to compute the execution
+count for the compound statement that follows the *else* keyword:
+
+:raw-html:`<pre class='highlight' style='line-height:initial;'><span>int main(int argc, const char *argv[]) </span><span style='background-color:#4A789C'>{ </span> <span class='c1'>// Region's counter is a reference to the profile counter #0</span>
+<span style='background-color:#4A789C'> </span>
+<span style='background-color:#4A789C'> if (argc > 1) </span><span style='background-color:#85C1F5'>{ </span> <span class='c1'>// Region's counter is a reference to the profile counter #1</span>
+<span style='background-color:#85C1F5'> printf("%s\n", argv[1]); </span><span> </span>
+<span style='background-color:#85C1F5'> }</span><span style='background-color:#4A789C'> else </span><span style='background-color:#F6D55D'>{ </span> <span class='c1'>// Region's counter is an expression (reference to the profile counter #0 - reference to the profile counter #1)</span>
+<span style='background-color:#F6D55D'> printf("\n"); </span>
+<span style='background-color:#F6D55D'> }</span><span style='background-color:#4A789C'> </span>
+<span style='background-color:#4A789C'> return 0; </span>
+<span style='background-color:#4A789C'>}</span>
+</pre>`
+
+Finally, a coverage mapping counter can also represent an execution count of
+of zero. The zero counter is used to provide coverage mapping for
+unreachable statements and expressions, like in the example below:
+
+:raw-html:`<pre class='highlight' style='line-height:initial;'><span>int main() </span><span style='background-color:#4A789C'>{ </span>
+<span style='background-color:#4A789C'> return 0; </span>
+<span style='background-color:#4A789C'> </span><span style='background-color:#85C1F5'>printf("Hello world!\n")</span><span style='background-color:#4A789C'>; </span> <span class='c1'>// Unreachable region's counter is zero</span>
+<span style='background-color:#4A789C'>}</span>
+</pre>`
+
+The zero counters allow the code coverage tool to display proper line execution
+counts for the unreachable lines and highlight the unreachable code.
+Without them, the tool would think that those lines and regions were still
+executed, as it doesn't possess the frontend's knowledge.
+
+LLVM IR Representation
+======================
+
+The coverage mapping data is stored in the LLVM IR using a single global
+constant structure variable called *__llvm_coverage_mapping*
+with the *__llvm_covmap* section specifier.
+
+For example, letâs consider a C file and how it gets compiled to LLVM:
+
+.. _coverage mapping sample:
+
+.. code-block:: c
+
+ int foo() {
+ return 42;
+ }
+ int bar() {
+ return 13;
+ }
+
+The coverage mapping variable generated by Clang has 3 fields:
+
+* Coverage mapping header.
+
+* An array of function records.
+
+* Coverage mapping data which is an array of bytes. Zero paddings are added at the end to force 8 byte alignment.
+
+.. code-block:: llvm
+
+ @__llvm_coverage_mapping = internal constant { { i32, i32, i32, i32 }, [2 x { i64, i32, i64 }], [40 x i8] }
+ {
+ { i32, i32, i32, i32 } ; Coverage map header
+ {
+ i32 2, ; The number of function records
+ i32 20, ; The length of the string that contains the encoded translation unit filenames
+ i32 20, ; The length of the string that contains the encoded coverage mapping data
+ i32 1, ; Coverage mapping format version
+ },
+ [2 x { i64, i32, i64 }] [ ; Function records
+ { i64, i32, i64 } {
+ i64 0x5cf8c24cdb18bdac, ; Function's name MD5
+ i32 9, ; Function's encoded coverage mapping data string length
+ i64 0 ; Function's structural hash
+ },
+ { i64, i32, i64 } {
+ i64 0xe413754a191db537, ; Function's name MD5
+ i32 9, ; Function's encoded coverage mapping data string length
+ i64 0 ; Function's structural hash
+ }],
+ [40 x i8] c"..." ; Encoded data (dissected later)
+ }, section "__llvm_covmap", align 8
+
+The function record layout has evolved since version 1. In version 1, the function record for *foo* is defined as follows:
+
+.. code-block:: llvm
+
+ { i8*, i32, i32, i64 } { i8* getelementptr inbounds ([3 x i8]* @__profn_foo, i32 0, i32 0), ; Function's name
+ i32 3, ; Function's name length
+ i32 9, ; Function's encoded coverage mapping data string length
+ i64 0 ; Function's structural hash
+ }
+
+
+Coverage Mapping Header:
+------------------------
+
+The coverage mapping header has the following fields:
+
+* The number of function records.
+
+* The length of the string in the third field of *__llvm_coverage_mapping* that contains the encoded translation unit filenames.
+
+* The length of the string in the third field of *__llvm_coverage_mapping* that contains the encoded coverage mapping data.
+
+* The format version. The current version is 2 (encoded as a 1).
+
+.. _function records:
+
+Function record:
+----------------
+
+A function record is a structure of the following type:
+
+.. code-block:: llvm
+
+ { i64, i32, i64 }
+
+It contains function name's MD5, the length of the encoded mapping data for that function, and function's
+structural hash value.
+
+Encoded data:
+-------------
+
+The encoded data is stored in a single string that contains
+the encoded filenames used by this translation unit and the encoded coverage
+mapping data for each function in this translation unit.
+
+The encoded data has the following structure:
+
+``[filenames, coverageMappingDataForFunctionRecord0, coverageMappingDataForFunctionRecord1, ..., padding]``
+
+If necessary, the encoded data is padded with zeroes so that the size
+of the data string is rounded up to the nearest multiple of 8 bytes.
+
+Dissecting the sample:
+^^^^^^^^^^^^^^^^^^^^^^
+
+Here's an overview of the encoded data that was stored in the
+IR for the `coverage mapping sample`_ that was shown earlier:
+
+* The IR contains the following string constant that represents the encoded
+ coverage mapping data for the sample translation unit:
+
+ .. code-block:: llvm
+
+ c"\01\12/Users/alex/test.c\01\00\00\01\01\01\0C\02\02\01\00\00\01\01\04\0C\02\02\00\00"
+
+* The string contains values that are encoded in the LEB128 format, which is
+ used throughout for storing integers. It also contains a string value.
+
+* The length of the substring that contains the encoded translation unit
+ filenames is the value of the second field in the *__llvm_coverage_mapping*
+ structure, which is 20, thus the filenames are encoded in this string:
+
+ .. code-block:: llvm
+
+ c"\01\12/Users/alex/test.c"
+
+ This string contains the following data:
+
+ * Its first byte has a value of ``0x01``. It stores the number of filenames
+ contained in this string.
+ * Its second byte stores the length of the first filename in this string.
+ * The remaining 18 bytes are used to store the first filename.
+
+* The length of the substring that contains the encoded coverage mapping data
+ for the first function is the value of the third field in the first
+ structure in an array of `function records`_ stored in the
+ third field of the *__llvm_coverage_mapping* structure, which is the 9.
+ Therefore, the coverage mapping for the first function record is encoded
+ in this string:
+
+ .. code-block:: llvm
+
+ c"\01\00\00\01\01\01\0C\02\02"
+
+ This string consists of the following bytes:
+
+ +----------+-------------------------------------------------------------------------------------------------------------------------+
+ | ``0x01`` | The number of file ids used by this function. There is only one file id used by the mapping data in this function. |
+ +----------+-------------------------------------------------------------------------------------------------------------------------+
+ | ``0x00`` | An index into the filenames array which corresponds to the file "/Users/alex/test.c". |
+ +----------+-------------------------------------------------------------------------------------------------------------------------+
+ | ``0x00`` | The number of counter expressions used by this function. This function doesn't use any expressions. |
+ +----------+-------------------------------------------------------------------------------------------------------------------------+
+ | ``0x01`` | The number of mapping regions that are stored in an array for the function's file id #0. |
+ +----------+-------------------------------------------------------------------------------------------------------------------------+
+ | ``0x01`` | The coverage mapping counter for the first region in this function. The value of 1 tells us that it's a coverage |
+ | | mapping counter that is a reference to the profile instrumentation counter with an index of 0. |
+ +----------+-------------------------------------------------------------------------------------------------------------------------+
+ | ``0x01`` | The starting line of the first mapping region in this function. |
+ +----------+-------------------------------------------------------------------------------------------------------------------------+
+ | ``0x0C`` | The starting column of the first mapping region in this function. |
+ +----------+-------------------------------------------------------------------------------------------------------------------------+
+ | ``0x02`` | The ending line of the first mapping region in this function. |
+ +----------+-------------------------------------------------------------------------------------------------------------------------+
+ | ``0x02`` | The ending column of the first mapping region in this function. |
+ +----------+-------------------------------------------------------------------------------------------------------------------------+
+
+* The length of the substring that contains the encoded coverage mapping data
+ for the second function record is also 9. It's structured like the mapping data
+ for the first function record.
+
+* The two trailing bytes are zeroes and are used to pad the coverage mapping
+ data to give it the 8 byte alignment.
+
+Encoding
+========
+
+The per-function coverage mapping data is encoded as a stream of bytes,
+with a simple structure. The structure consists of the encoding
+`types <cvmtypes_>`_ like variable-length unsigned integers, that
+are used to encode `File ID Mapping`_, `Counter Expressions`_ and
+the `Mapping Regions`_.
+
+The format of the structure follows:
+
+ ``[file id mapping, counter expressions, mapping regions]``
+
+The translation unit filenames are encoded using the same encoding
+`types <cvmtypes_>`_ as the per-function coverage mapping data, with the
+following structure:
+
+ ``[numFilenames : LEB128, filename0 : string, filename1 : string, ...]``
+
+.. _cvmtypes:
+
+Types
+-----
+
+This section describes the basic types that are used by the encoding format
+and can appear after ``:`` in the ``[foo : type]`` description.
+
+.. _LEB128:
+
+LEB128
+^^^^^^
+
+LEB128 is an unsigned integer value that is encoded using DWARF's LEB128
+encoding, optimizing for the case where values are small
+(1 byte for values less than 128).
+
+.. _CoverageStrings:
+
+Strings
+^^^^^^^
+
+``[length : LEB128, characters...]``
+
+String values are encoded with a `LEB value <LEB128_>`_ for the length
+of the string and a sequence of bytes for its characters.
+
+.. _file id mapping:
+
+File ID Mapping
+---------------
+
+``[numIndices : LEB128, filenameIndex0 : LEB128, filenameIndex1 : LEB128, ...]``
+
+File id mapping in a function's coverage mapping stream
+contains the indices into the translation unit's filenames array.
+
+Counter
+-------
+
+``[value : LEB128]``
+
+A `coverage mapping counter`_ is stored in a single `LEB value <LEB128_>`_.
+It is composed of two things --- the `tag <counter-tag_>`_
+which is stored in the lowest 2 bits, and the `counter data`_ which is stored
+in the remaining bits.
+
+.. _counter-tag:
+
+Tag:
+^^^^
+
+The counter's tag encodes the counter's kind
+and, if the counter is an expression, the expression's kind.
+The possible tag values are:
+
+* 0 - The counter is zero.
+
+* 1 - The counter is a reference to the profile instrumentation counter.
+
+* 2 - The counter is a subtraction expression.
+
+* 3 - The counter is an addition expression.
+
+.. _counter data:
+
+Data:
+^^^^^
+
+The counter's data is interpreted in the following manner:
+
+* When the counter is a reference to the profile instrumentation counter,
+ then the counter's data is the id of the profile counter.
+* When the counter is an expression, then the counter's data
+ is the index into the array of counter expressions.
+
+.. _Counter Expressions:
+
+Counter Expressions
+-------------------
+
+``[numExpressions : LEB128, expr0LHS : LEB128, expr0RHS : LEB128, expr1LHS : LEB128, expr1RHS : LEB128, ...]``
+
+Counter expressions consist of two counters as they
+represent binary arithmetic operations.
+The expression's kind is determined from the `tag <counter-tag_>`_ of the
+counter that references this expression.
+
+.. _Mapping Regions:
+
+Mapping Regions
+---------------
+
+``[numRegionArrays : LEB128, regionsForFile0, regionsForFile1, ...]``
+
+The mapping regions are stored in an array of sub-arrays where every
+region in a particular sub-array has the same file id.
+
+The file id for a sub-array of regions is the index of that
+sub-array in the main array e.g. The first sub-array will have the file id
+of 0.
+
+Sub-Array of Regions
+^^^^^^^^^^^^^^^^^^^^
+
+``[numRegions : LEB128, region0, region1, ...]``
+
+The mapping regions for a specific file id are stored in an array that is
+sorted in an ascending order by the region's starting location.
+
+Mapping Region
+^^^^^^^^^^^^^^
+
+``[header, source range]``
+
+The mapping region record contains two sub-records ---
+the `header`_, which stores the counter and/or the region's kind,
+and the `source range`_ that contains the starting and ending
+location of this region.
+
+.. _header:
+
+Header
+^^^^^^
+
+``[counter]``
+
+or
+
+``[pseudo-counter]``
+
+The header encodes the region's counter and the region's kind.
+
+The value of the counter's tag distinguishes between the counters and
+pseudo-counters --- if the tag is zero, than this header contains a
+pseudo-counter, otherwise this header contains an ordinary counter.
+
+Counter:
+""""""""
+
+A mapping region whose header has a counter with a non-zero tag is
+a code region.
+
+Pseudo-Counter:
+"""""""""""""""
+
+``[value : LEB128]``
+
+A pseudo-counter is stored in a single `LEB value <LEB128_>`_, just like
+the ordinary counter. It has the following interpretation:
+
+* bits 0-1: tag, which is always 0.
+
+* bit 2: expansionRegionTag. If this bit is set, then this mapping region
+ is an expansion region.
+
+* remaining bits: data. If this region is an expansion region, then the data
+ contains the expanded file id of that region.
+
+ Otherwise, the data contains the region's kind. The possible region
+ kind values are:
+
+ * 0 - This mapping region is a code region with a counter of zero.
+ * 2 - This mapping region is a skipped region.
+
+.. _source range:
+
+Source Range
+^^^^^^^^^^^^
+
+``[deltaLineStart : LEB128, columnStart : LEB128, numLines : LEB128, columnEnd : LEB128]``
+
+The source range record contains the following fields:
+
+* *deltaLineStart*: The difference between the starting line of the
+ current mapping region and the starting line of the previous mapping region.
+
+ If the current mapping region is the first region in the current
+ sub-array, then it stores the starting line of that region.
+
+* *columnStart*: The starting column of the mapping region.
+
+* *numLines*: The difference between the ending line and the starting line
+ of the current mapping region.
+
+* *columnEnd*: The ending column of the mapping region.
Added: www-releases/trunk/5.0.2/docs/_sources/DebuggingJITedCode.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.2/docs/_sources/DebuggingJITedCode.txt?rev=331981&view=auto
==============================================================================
--- www-releases/trunk/5.0.2/docs/_sources/DebuggingJITedCode.txt (added)
+++ www-releases/trunk/5.0.2/docs/_sources/DebuggingJITedCode.txt Thu May 10 06:54:16 2018
@@ -0,0 +1,143 @@
+==============================
+Debugging JIT-ed Code With GDB
+==============================
+
+Background
+==========
+
+Without special runtime support, debugging dynamically generated code with
+GDB (as well as most debuggers) can be quite painful. Debuggers generally
+read debug information from the object file of the code, but for JITed
+code, there is no such file to look for.
+
+In order to communicate the necessary debug info to GDB, an interface for
+registering JITed code with debuggers has been designed and implemented for
+GDB and LLVM MCJIT. At a high level, whenever MCJIT generates new machine code,
+it does so in an in-memory object file that contains the debug information in
+DWARF format. MCJIT then adds this in-memory object file to a global list of
+dynamically generated object files and calls a special function
+(``__jit_debug_register_code``) marked noinline that GDB knows about. When
+GDB attaches to a process, it puts a breakpoint in this function and loads all
+of the object files in the global list. When MCJIT calls the registration
+function, GDB catches the breakpoint signal, loads the new object file from
+the inferior's memory, and resumes the execution. In this way, GDB can get the
+necessary debug information.
+
+GDB Version
+===========
+
+In order to debug code JIT-ed by LLVM, you need GDB 7.0 or newer, which is
+available on most modern distributions of Linux. The version of GDB that
+Apple ships with Xcode has been frozen at 6.3 for a while. LLDB may be a
+better option for debugging JIT-ed code on Mac OS X.
+
+
+Debugging MCJIT-ed code
+=======================
+
+The emerging MCJIT component of LLVM allows full debugging of JIT-ed code with
+GDB. This is due to MCJIT's ability to use the MC emitter to provide full
+DWARF debugging information to GDB.
+
+Note that lli has to be passed the ``-use-mcjit`` flag to JIT the code with
+MCJIT instead of the old JIT.
+
+Example
+-------
+
+Consider the following C code (with line numbers added to make the example
+easier to follow):
+
+..
+ FIXME:
+ Sphinx has the ability to automatically number these lines by adding
+ :linenos: on the line immediately following the `.. code-block:: c`, but
+ it looks like garbage; the line numbers don't even line up with the
+ lines. Is this a Sphinx bug, or is it a CSS problem?
+
+.. code-block:: c
+
+ 1 int compute_factorial(int n)
+ 2 {
+ 3 if (n <= 1)
+ 4 return 1;
+ 5
+ 6 int f = n;
+ 7 while (--n > 1)
+ 8 f *= n;
+ 9 return f;
+ 10 }
+ 11
+ 12
+ 13 int main(int argc, char** argv)
+ 14 {
+ 15 if (argc < 2)
+ 16 return -1;
+ 17 char firstletter = argv[1][0];
+ 18 int result = compute_factorial(firstletter - '0');
+ 19
+ 20 // Returned result is clipped at 255...
+ 21 return result;
+ 22 }
+
+Here is a sample command line session that shows how to build and run this
+code via ``lli`` inside GDB:
+
+.. code-block:: bash
+
+ $ $BINPATH/clang -cc1 -O0 -g -emit-llvm showdebug.c
+ $ gdb --quiet --args $BINPATH/lli -use-mcjit showdebug.ll 5
+ Reading symbols from $BINPATH/lli...done.
+ (gdb) b showdebug.c:6
+ No source file named showdebug.c.
+ Make breakpoint pending on future shared library load? (y or [n]) y
+ Breakpoint 1 (showdebug.c:6) pending.
+ (gdb) r
+ Starting program: $BINPATH/lli -use-mcjit showdebug.ll 5
+ [Thread debugging using libthread_db enabled]
+
+ Breakpoint 1, compute_factorial (n=5) at showdebug.c:6
+ 6 int f = n;
+ (gdb) p n
+ $1 = 5
+ (gdb) p f
+ $2 = 0
+ (gdb) n
+ 7 while (--n > 1)
+ (gdb) p f
+ $3 = 5
+ (gdb) b showdebug.c:9
+ Breakpoint 2 at 0x7ffff7ed404c: file showdebug.c, line 9.
+ (gdb) c
+ Continuing.
+
+ Breakpoint 2, compute_factorial (n=1) at showdebug.c:9
+ 9 return f;
+ (gdb) p f
+ $4 = 120
+ (gdb) bt
+ #0 compute_factorial (n=1) at showdebug.c:9
+ #1 0x00007ffff7ed40a9 in main (argc=2, argv=0x16677e0) at showdebug.c:18
+ #2 0x3500000001652748 in ?? ()
+ #3 0x00000000016677e0 in ?? ()
+ #4 0x0000000000000002 in ?? ()
+ #5 0x0000000000d953b3 in llvm::MCJIT::runFunction (this=0x16151f0, F=0x1603020, ArgValues=...) at /home/ebenders_test/llvm_svn_rw/lib/ExecutionEngine/MCJIT/MCJIT.cpp:161
+ #6 0x0000000000dc8872 in llvm::ExecutionEngine::runFunctionAsMain (this=0x16151f0, Fn=0x1603020, argv=..., envp=0x7fffffffe040)
+ at /home/ebenders_test/llvm_svn_rw/lib/ExecutionEngine/ExecutionEngine.cpp:397
+ #7 0x000000000059c583 in main (argc=4, argv=0x7fffffffe018, envp=0x7fffffffe040) at /home/ebenders_test/llvm_svn_rw/tools/lli/lli.cpp:324
+ (gdb) finish
+ Run till exit from #0 compute_factorial (n=1) at showdebug.c:9
+ 0x00007ffff7ed40a9 in main (argc=2, argv=0x16677e0) at showdebug.c:18
+ 18 int result = compute_factorial(firstletter - '0');
+ Value returned is $5 = 120
+ (gdb) p result
+ $6 = 23406408
+ (gdb) n
+ 21 return result;
+ (gdb) p result
+ $7 = 120
+ (gdb) c
+ Continuing.
+
+ Program exited with code 0170.
+ (gdb)
Added: www-releases/trunk/5.0.2/docs/_sources/DeveloperPolicy.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.2/docs/_sources/DeveloperPolicy.txt?rev=331981&view=auto
==============================================================================
--- www-releases/trunk/5.0.2/docs/_sources/DeveloperPolicy.txt (added)
+++ www-releases/trunk/5.0.2/docs/_sources/DeveloperPolicy.txt Thu May 10 06:54:16 2018
@@ -0,0 +1,746 @@
+=====================
+LLVM Developer Policy
+=====================
+
+.. contents::
+ :local:
+
+Introduction
+============
+
+This document contains the LLVM Developer Policy which defines the project's
+policy towards developers and their contributions. The intent of this policy is
+to eliminate miscommunication, rework, and confusion that might arise from the
+distributed nature of LLVM's development. By stating the policy in clear terms,
+we hope each developer can know ahead of time what to expect when making LLVM
+contributions. This policy covers all llvm.org subprojects, including Clang,
+LLDB, libc++, etc.
+
+This policy is also designed to accomplish the following objectives:
+
+#. Attract both users and developers to the LLVM project.
+
+#. Make life as simple and easy for contributors as possible.
+
+#. Keep the top of Subversion trees as stable as possible.
+
+#. Establish awareness of the project's :ref:`copyright, license, and patent
+ policies <copyright-license-patents>` with contributors to the project.
+
+This policy is aimed at frequent contributors to LLVM. People interested in
+contributing one-off patches can do so in an informal way by sending them to the
+`llvm-commits mailing list
+<http://lists.llvm.org/mailman/listinfo/llvm-commits>`_ and engaging another
+developer to see it through the process.
+
+Developer Policies
+==================
+
+This section contains policies that pertain to frequent LLVM developers. We
+always welcome `one-off patches`_ from people who do not routinely contribute to
+LLVM, but we expect more from frequent contributors to keep the system as
+efficient as possible for everyone. Frequent LLVM contributors are expected to
+meet the following requirements in order for LLVM to maintain a high standard of
+quality.
+
+Stay Informed
+-------------
+
+Developers should stay informed by reading at least the "dev" mailing list for
+the projects you are interested in, such as `llvm-dev
+<http://lists.llvm.org/mailman/listinfo/llvm-dev>`_ for LLVM, `cfe-dev
+<http://lists.llvm.org/mailman/listinfo/cfe-dev>`_ for Clang, or `lldb-dev
+<http://lists.llvm.org/mailman/listinfo/lldb-dev>`_ for LLDB. If you are
+doing anything more than just casual work on LLVM, it is suggested that you also
+subscribe to the "commits" mailing list for the subproject you're interested in,
+such as `llvm-commits
+<http://lists.llvm.org/mailman/listinfo/llvm-commits>`_, `cfe-commits
+<http://lists.llvm.org/mailman/listinfo/cfe-commits>`_, or `lldb-commits
+<http://lists.llvm.org/mailman/listinfo/lldb-commits>`_. Reading the
+"commits" list and paying attention to changes being made by others is a good
+way to see what other people are interested in and watching the flow of the
+project as a whole.
+
+We recommend that active developers register an email account with `LLVM
+Bugzilla <https://bugs.llvm.org/>`_ and preferably subscribe to the `llvm-bugs
+<http://lists.llvm.org/mailman/listinfo/llvm-bugs>`_ email list to keep track
+of bugs and enhancements occurring in LLVM. We really appreciate people who are
+proactive at catching incoming bugs in their components and dealing with them
+promptly.
+
+Please be aware that all public LLVM mailing lists are public and archived, and
+that notices of confidentiality or non-disclosure cannot be respected.
+
+.. _patch:
+.. _one-off patches:
+
+Making and Submitting a Patch
+-----------------------------
+
+When making a patch for review, the goal is to make it as easy for the reviewer
+to read it as possible. As such, we recommend that you:
+
+#. Make your patch against the Subversion trunk, not a branch, and not an old
+ version of LLVM. This makes it easy to apply the patch. For information on
+ how to check out SVN trunk, please see the `Getting Started
+ Guide <GettingStarted.html#checkout>`_.
+
+#. Similarly, patches should be submitted soon after they are generated. Old
+ patches may not apply correctly if the underlying code changes between the
+ time the patch was created and the time it is applied.
+
+#. Patches should be made with ``svn diff``, or similar. If you use a
+ different tool, make sure it uses the ``diff -u`` format and that it
+ doesn't contain clutter which makes it hard to read.
+
+#. If you are modifying generated files, such as the top-level ``configure``
+ script, please separate out those changes into a separate patch from the rest
+ of your changes.
+
+Once your patch is ready, submit it by emailing it to the appropriate project's
+commit mailing list (or commit it directly if applicable). Alternatively, some
+patches get sent to the project's development list or component of the LLVM bug
+tracker, but the commit list is the primary place for reviews and should
+generally be preferred.
+
+When sending a patch to a mailing list, it is a good idea to send it as an
+*attachment* to the message, not embedded into the text of the message. This
+ensures that your mailer will not mangle the patch when it sends it (e.g. by
+making whitespace changes or by wrapping lines).
+
+*For Thunderbird users:* Before submitting a patch, please open *Preferences >
+Advanced > General > Config Editor*, find the key
+``mail.content_disposition_type``, and set its value to ``1``. Without this
+setting, Thunderbird sends your attachment using ``Content-Disposition: inline``
+rather than ``Content-Disposition: attachment``. Apple Mail gamely displays such
+a file inline, making it difficult to work with for reviewers using that
+program.
+
+When submitting patches, please do not add confidentiality or non-disclosure
+notices to the patches themselves. These notices conflict with the `LLVM
+License`_ and may result in your contribution being excluded.
+
+.. _code review:
+
+Code Reviews
+------------
+
+LLVM has a code review policy. Code review is one way to increase the quality of
+software. We generally follow these policies:
+
+#. All developers are required to have significant changes reviewed before they
+ are committed to the repository.
+
+#. Code reviews are conducted by email on the relevant project's commit mailing
+ list, or alternatively on the project's development list or bug tracker.
+
+#. Code can be reviewed either before it is committed or after. We expect major
+ changes to be reviewed before being committed, but smaller changes (or
+ changes where the developer owns the component) can be reviewed after commit.
+
+#. The developer responsible for a code change is also responsible for making
+ all necessary review-related changes.
+
+#. Code review can be an iterative process, which continues until the patch is
+ ready to be committed. Specifically, once a patch is sent out for review, it
+ needs an explicit "looks good" before it is submitted. Do not assume silent
+ approval, or request active objections to the patch with a deadline.
+
+Sometimes code reviews will take longer than you would hope for, especially for
+larger features. Accepted ways to speed up review times for your patches are:
+
+* Review other people's patches. If you help out, everybody will be more
+ willing to do the same for you; goodwill is our currency.
+* Ping the patch. If it is urgent, provide reasons why it is important to you to
+ get this patch landed and ping it every couple of days. If it is
+ not urgent, the common courtesy ping rate is one week. Remember that you're
+ asking for valuable time from other professional developers.
+* Ask for help on IRC. Developers on IRC will be able to either help you
+ directly, or tell you who might be a good reviewer.
+* Split your patch into multiple smaller patches that build on each other. The
+ smaller your patch, the higher the probability that somebody will take a quick
+ look at it.
+
+Developers should participate in code reviews as both reviewers and
+reviewees. If someone is kind enough to review your code, you should return the
+favor for someone else. Note that anyone is welcome to review and give feedback
+on a patch, but only people with Subversion write access can approve it.
+
+There is a web based code review tool that can optionally be used
+for code reviews. See :doc:`Phabricator`.
+
+.. _code owners:
+
+Code Owners
+-----------
+
+The LLVM Project relies on two features of its process to maintain rapid
+development in addition to the high quality of its source base: the combination
+of code review plus post-commit review for trusted maintainers. Having both is
+a great way for the project to take advantage of the fact that most people do
+the right thing most of the time, and only commit patches without pre-commit
+review when they are confident they are right.
+
+The trick to this is that the project has to guarantee that all patches that are
+committed are reviewed after they go in: you don't want everyone to assume
+someone else will review it, allowing the patch to go unreviewed. To solve this
+problem, we have a notion of an 'owner' for a piece of the code. The sole
+responsibility of a code owner is to ensure that a commit to their area of the
+code is appropriately reviewed, either by themself or by someone else. The list
+of current code owners can be found in the file
+`CODE_OWNERS.TXT <http://llvm.org/klaus/llvm/blob/master/CODE_OWNERS.TXT>`_
+in the root of the LLVM source tree.
+
+Note that code ownership is completely different than reviewers: anyone can
+review a piece of code, and we welcome code review from anyone who is
+interested. Code owners are the "last line of defense" to guarantee that all
+patches that are committed are actually reviewed.
+
+Being a code owner is a somewhat unglamorous position, but it is incredibly
+important for the ongoing success of the project. Because people get busy,
+interests change, and unexpected things happen, code ownership is purely opt-in,
+and anyone can choose to resign their "title" at any time. For now, we do not
+have an official policy on how one gets elected to be a code owner.
+
+.. _include a testcase:
+
+Test Cases
+----------
+
+Developers are required to create test cases for any bugs fixed and any new
+features added. Some tips for getting your testcase approved:
+
+* All feature and regression test cases are added to the ``llvm/test``
+ directory. The appropriate sub-directory should be selected (see the
+ :doc:`Testing Guide <TestingGuide>` for details).
+
+* Test cases should be written in :doc:`LLVM assembly language <LangRef>`.
+
+* Test cases, especially for regressions, should be reduced as much as possible,
+ by :doc:`bugpoint <Bugpoint>` or manually. It is unacceptable to place an
+ entire failing program into ``llvm/test`` as this creates a *time-to-test*
+ burden on all developers. Please keep them short.
+
+Note that llvm/test and clang/test are designed for regression and small feature
+tests only. More extensive test cases (e.g., entire applications, benchmarks,
+etc) should be added to the ``llvm-test`` test suite. The llvm-test suite is
+for coverage (correctness, performance, etc) testing, not feature or regression
+testing.
+
+Quality
+-------
+
+The minimum quality standards that any change must satisfy before being
+committed to the main development branch are:
+
+#. Code must adhere to the `LLVM Coding Standards <CodingStandards.html>`_.
+
+#. Code must compile cleanly (no errors, no warnings) on at least one platform.
+
+#. Bug fixes and new features should `include a testcase`_ so we know if the
+ fix/feature ever regresses in the future.
+
+#. Code must pass the ``llvm/test`` test suite.
+
+#. The code must not cause regressions on a reasonable subset of llvm-test,
+ where "reasonable" depends on the contributor's judgement and the scope of
+ the change (more invasive changes require more testing). A reasonable subset
+ might be something like "``llvm-test/MultiSource/Benchmarks``".
+
+Additionally, the committer is responsible for addressing any problems found in
+the future that the change is responsible for. For example:
+
+* The code should compile cleanly on all supported platforms.
+
+* The changes should not cause any correctness regressions in the ``llvm-test``
+ suite and must not cause any major performance regressions.
+
+* The change set should not cause performance or correctness regressions for the
+ LLVM tools.
+
+* The changes should not cause performance or correctness regressions in code
+ compiled by LLVM on all applicable targets.
+
+* You are expected to address any `Bugzilla bugs <https://bugs.llvm.org/>`_ that
+ result from your change.
+
+We prefer for this to be handled before submission but understand that it isn't
+possible to test all of this for every submission. Our build bots and nightly
+testing infrastructure normally finds these problems. A good rule of thumb is
+to check the nightly testers for regressions the day after your change. Build
+bots will directly email you if a group of commits that included yours caused a
+failure. You are expected to check the build bot messages to see if they are
+your fault and, if so, fix the breakage.
+
+Commits that violate these quality standards (e.g. are very broken) may be
+reverted. This is necessary when the change blocks other developers from making
+progress. The developer is welcome to re-commit the change after the problem has
+been fixed.
+
+.. _commit messages:
+
+Commit messages
+---------------
+
+Although we don't enforce the format of commit messages, we prefer that
+you follow these guidelines to help review, search in logs, email formatting
+and so on. These guidelines are very similar to rules used by other open source
+projects.
+
+Most importantly, the contents of the message should be carefully written to
+convey the rationale of the change (without delving too much in detail). It
+also should avoid being vague or overly specific. For example, "bits were not
+set right" will leave the reviewer wondering about which bits, and why they
+weren't right, while "Correctly set overflow bits in TargetInfo" conveys almost
+all there is to the change.
+
+Below are some guidelines about the format of the message itself:
+
+* Separate the commit message into title, body and, if you're not the original
+ author, a "Patch by" attribution line (see below).
+
+* The title should be concise. Because all commits are emailed to the list with
+ the first line as the subject, long titles are frowned upon. Short titles
+ also look better in `git log`.
+
+* When the changes are restricted to a specific part of the code (e.g. a
+ back-end or optimization pass), it is customary to add a tag to the
+ beginning of the line in square brackets. For example, "[SCEV] ..."
+ or "[OpenMP] ...". This helps email filters and searches for post-commit
+ reviews.
+
+* The body, if it exists, should be separated from the title by an empty line.
+
+* The body should be concise, but explanatory, including a complete
+ reasoning. Unless it is required to understand the change, examples,
+ code snippets and gory details should be left to bug comments, web
+ review or the mailing list.
+
+* If the patch fixes a bug in bugzilla, please include the PR# in the message.
+
+* `Attribution of Changes`_ should be in a separate line, after the end of
+ the body, as simple as "Patch by John Doe.". This is how we officially
+ handle attribution, and there are automated processes that rely on this
+ format.
+
+* Text formatting and spelling should follow the same rules as documentation
+ and in-code comments, ex. capitalization, full stop, etc.
+
+* If the commit is a bug fix on top of another recently committed patch, or a
+ revert or reapply of a patch, include the svn revision number of the prior
+ related commit. This could be as simple as "Revert rNNNN because it caused
+ PR#".
+
+For minor violations of these recommendations, the community normally favors
+reminding the contributor of this policy over reverting. Minor corrections and
+omissions can be handled by sending a reply to the commits mailing list.
+
+Obtaining Commit Access
+-----------------------
+
+We grant commit access to contributors with a track record of submitting high
+quality patches. If you would like commit access, please send an email to
+`Chris <mailto:clattner at llvm.org>`_ with the following information:
+
+#. The user name you want to commit with, e.g. "hacker".
+
+#. The full name and email address you want message to llvm-commits to come
+ from, e.g. "J. Random Hacker <hacker at yoyodyne.com>".
+
+#. A "password hash" of the password you want to use, e.g. "``2ACR96qjUqsyM``".
+ Note that you don't ever tell us what your password is; you just give it to
+ us in an encrypted form. To get this, run "``htpasswd``" (a utility that
+ comes with apache) in *crypt* mode (often enabled with "``-d``"), or find a web
+ page that will do it for you. Note that our system does not work with MD5
+ hashes. These are significantly longer than a crypt hash - e.g.
+ "``$apr1$vea6bBV2$Z8IFx.AfeD8LhqlZFqJer0``", we only accept the shorter crypt hash.
+
+Once you've been granted commit access, you should be able to check out an LLVM
+tree with an SVN URL of "https://username@llvm.org/..." instead of the normal
+anonymous URL of "http://llvm.org/...". The first time you commit you'll have
+to type in your password. Note that you may get a warning from SVN about an
+untrusted key; you can ignore this. To verify that your commit access works,
+please do a test commit (e.g. change a comment or add a blank line). Your first
+commit to a repository may require the autogenerated email to be approved by a
+mailing list. This is normal and will be done when the mailing list owner has
+time.
+
+If you have recently been granted commit access, these policies apply:
+
+#. You are granted *commit-after-approval* to all parts of LLVM. To get
+ approval, submit a `patch`_ to `llvm-commits
+ <http://lists.llvm.org/mailman/listinfo/llvm-commits>`_. When approved,
+ you may commit it yourself.
+
+#. You are allowed to commit patches without approval which you think are
+ obvious. This is clearly a subjective decision --- we simply expect you to
+ use good judgement. Examples include: fixing build breakage, reverting
+ obviously broken patches, documentation/comment changes, any other minor
+ changes.
+
+#. You are allowed to commit patches without approval to those portions of LLVM
+ that you have contributed or maintain (i.e., have been assigned
+ responsibility for), with the proviso that such commits must not break the
+ build. This is a "trust but verify" policy, and commits of this nature are
+ reviewed after they are committed.
+
+#. Multiple violations of these policies or a single egregious violation may
+ cause commit access to be revoked.
+
+In any case, your changes are still subject to `code review`_ (either before or
+after they are committed, depending on the nature of the change). You are
+encouraged to review other peoples' patches as well, but you aren't required
+to do so.
+
+.. _discuss the change/gather consensus:
+
+Making a Major Change
+---------------------
+
+When a developer begins a major new project with the aim of contributing it back
+to LLVM, they should inform the community with an email to the `llvm-dev
+<http://lists.llvm.org/mailman/listinfo/llvm-dev>`_ email list, to the extent
+possible. The reason for this is to:
+
+#. keep the community informed about future changes to LLVM,
+
+#. avoid duplication of effort by preventing multiple parties working on the
+ same thing and not knowing about it, and
+
+#. ensure that any technical issues around the proposed work are discussed and
+ resolved before any significant work is done.
+
+The design of LLVM is carefully controlled to ensure that all the pieces fit
+together well and are as consistent as possible. If you plan to make a major
+change to the way LLVM works or want to add a major new extension, it is a good
+idea to get consensus with the development community before you start working on
+it.
+
+Once the design of the new feature is finalized, the work itself should be done
+as a series of `incremental changes`_, not as a long-term development branch.
+
+.. _incremental changes:
+
+Incremental Development
+-----------------------
+
+In the LLVM project, we do all significant changes as a series of incremental
+patches. We have a strong dislike for huge changes or long-term development
+branches. Long-term development branches have a number of drawbacks:
+
+#. Branches must have mainline merged into them periodically. If the branch
+ development and mainline development occur in the same pieces of code,
+ resolving merge conflicts can take a lot of time.
+
+#. Other people in the community tend to ignore work on branches.
+
+#. Huge changes (produced when a branch is merged back onto mainline) are
+ extremely difficult to `code review`_.
+
+#. Branches are not routinely tested by our nightly tester infrastructure.
+
+#. Changes developed as monolithic large changes often don't work until the
+ entire set of changes is done. Breaking it down into a set of smaller
+ changes increases the odds that any of the work will be committed to the main
+ repository.
+
+To address these problems, LLVM uses an incremental development style and we
+require contributors to follow this practice when making a large/invasive
+change. Some tips:
+
+* Large/invasive changes usually have a number of secondary changes that are
+ required before the big change can be made (e.g. API cleanup, etc). These
+ sorts of changes can often be done before the major change is done,
+ independently of that work.
+
+* The remaining inter-related work should be decomposed into unrelated sets of
+ changes if possible. Once this is done, define the first increment and get
+ consensus on what the end goal of the change is.
+
+* Each change in the set can be stand alone (e.g. to fix a bug), or part of a
+ planned series of changes that works towards the development goal.
+
+* Each change should be kept as small as possible. This simplifies your work
+ (into a logical progression), simplifies code review and reduces the chance
+ that you will get negative feedback on the change. Small increments also
+ facilitate the maintenance of a high quality code base.
+
+* Often, an independent precursor to a big change is to add a new API and slowly
+ migrate clients to use the new API. Each change to use the new API is often
+ "obvious" and can be committed without review. Once the new API is in place
+ and used, it is much easier to replace the underlying implementation of the
+ API. This implementation change is logically separate from the API
+ change.
+
+If you are interested in making a large change, and this scares you, please make
+sure to first `discuss the change/gather consensus`_ then ask about the best way
+to go about making the change.
+
+Attribution of Changes
+----------------------
+
+When contributors submit a patch to an LLVM project, other developers with
+commit access may commit it for the author once appropriate (based on the
+progression of code review, etc.). When doing so, it is important to retain
+correct attribution of contributions to their contributors. However, we do not
+want the source code to be littered with random attributions "this code written
+by J. Random Hacker" (this is noisy and distracting). In practice, the revision
+control system keeps a perfect history of who changed what, and the CREDITS.txt
+file describes higher-level contributions. If you commit a patch for someone
+else, please follow the attribution of changes in the simple manner as outlined
+by the `commit messages`_ section. Overall, please do not add contributor names
+to the source code.
+
+Also, don't commit patches authored by others unless they have submitted the
+patch to the project or you have been authorized to submit them on their behalf
+(you work together and your company authorized you to contribute the patches,
+etc.). The author should first submit them to the relevant project's commit
+list, development list, or LLVM bug tracker component. If someone sends you
+a patch privately, encourage them to submit it to the appropriate list first.
+
+
+.. _IR backwards compatibility:
+
+IR Backwards Compatibility
+--------------------------
+
+When the IR format has to be changed, keep in mind that we try to maintain some
+backwards compatibility. The rules are intended as a balance between convenience
+for llvm users and not imposing a big burden on llvm developers:
+
+* The textual format is not backwards compatible. We don't change it too often,
+ but there are no specific promises.
+
+* Additions and changes to the IR should be reflected in
+ ``test/Bitcode/compatibility.ll``.
+
+* The current LLVM version supports loading any bitcode since version 3.0.
+
+* After each X.Y release, ``compatibility.ll`` must be copied to
+ ``compatibility-X.Y.ll``. The corresponding bitcode file should be assembled
+ using the X.Y build and committed as ``compatibility-X.Y.ll.bc``.
+
+* Newer releases can ignore features from older releases, but they cannot
+ miscompile them. For example, if nsw is ever replaced with something else,
+ dropping it would be a valid way to upgrade the IR.
+
+* Debug metadata is special in that it is currently dropped during upgrades.
+
+* Non-debug metadata is defined to be safe to drop, so a valid way to upgrade
+ it is to drop it. That is not very user friendly and a bit more effort is
+ expected, but no promises are made.
+
+C API Changes
+----------------
+
+* Stability Guarantees: The C API is, in general, a "best effort" for stability.
+ This means that we make every attempt to keep the C API stable, but that
+ stability will be limited by the abstractness of the interface and the
+ stability of the C++ API that it wraps. In practice, this means that things
+ like "create debug info" or "create this type of instruction" are likely to be
+ less stable than "take this IR file and JIT it for my current machine".
+
+* Release stability: We won't break the C API on the release branch with patches
+ that go on that branch, with the exception that we will fix an unintentional
+ C API break that will keep the release consistent with both the previous and
+ next release.
+
+* Testing: Patches to the C API are expected to come with tests just like any
+ other patch.
+
+* Including new things into the API: If an LLVM subcomponent has a C API already
+ included, then expanding that C API is acceptable. Adding C API for
+ subcomponents that don't currently have one needs to be discussed on the
+ mailing list for design and maintainability feedback prior to implementation.
+
+* Documentation: Any changes to the C API are required to be documented in the
+ release notes so that it's clear to external users who do not follow the
+ project how the C API is changing and evolving.
+
+New Targets
+-----------
+
+LLVM is very receptive to new targets, even experimental ones, but a number of
+problems can appear when adding new large portions of code, and back-ends are
+normally added in bulk. We have found that landing large pieces of new code
+and then trying to fix emergent problems in-tree is problematic for a variety
+of reasons.
+
+For these reasons, new targets are *always* added as *experimental* until
+they can be proven stable, and later moved to non-experimental. The difference
+between both classes is that experimental targets are not built by default
+(need to be added to -DLLVM_TARGETS_TO_BUILD at CMake time).
+
+The basic rules for a back-end to be upstreamed in **experimental** mode are:
+
+* Every target must have a :ref:`code owner<code owners>`. The `CODE_OWNERS.TXT`
+ file has to be updated as part of the first merge. The code owner makes sure
+ that changes to the target get reviewed and steers the overall effort.
+
+* There must be an active community behind the target. This community
+ will help maintain the target by providing buildbots, fixing
+ bugs, answering the LLVM community's questions and making sure the new
+ target doesn't break any of the other targets, or generic code. This
+ behavior is expected to continue throughout the lifetime of the
+ target's code.
+
+* The code must be free of contentious issues, for example, large
+ changes in how the IR behaves or should be formed by the front-ends,
+ unless agreed by the majority of the community via refactoring of the
+ (:doc:`IR standard<LangRef>`) **before** the merge of the new target changes,
+ following the :ref:`IR backwards compatibility`.
+
+* The code conforms to all of the policies laid out in this developer policy
+ document, including license, patent, and coding standards.
+
+* The target should have either reasonable documentation on how it
+ works (ISA, ABI, etc.) or a publicly available simulator/hardware
+ (either free or cheap enough) - preferably both. This allows
+ developers to validate assumptions, understand constraints and review code
+ that can affect the target.
+
+In addition, the rules for a back-end to be promoted to **official** are:
+
+* The target must have addressed every other minimum requirement and
+ have been stable in tree for at least 3 months. This cool down
+ period is to make sure that the back-end and the target community can
+ endure continuous upstream development for the foreseeable future.
+
+* The target's code must have been completely adapted to this policy
+ as well as the :doc:`coding standards<CodingStandards>`. Any exceptions that
+ were made to move into experimental mode must have been fixed **before**
+ becoming official.
+
+* The test coverage needs to be broad and well written (small tests,
+ well documented). The build target ``check-all`` must pass with the
+ new target built, and where applicable, the ``test-suite`` must also
+ pass without errors, in at least one configuration (publicly
+ demonstrated, for example, via buildbots).
+
+* Public buildbots need to be created and actively maintained, unless
+ the target requires no additional buildbots (ex. ``check-all`` covers
+ all tests). The more relevant and public the new target's CI infrastructure
+ is, the more the LLVM community will embrace it.
+
+To **continue** as a supported and official target:
+
+* The maintainer(s) must continue following these rules throughout the lifetime
+ of the target. Continuous violations of aforementioned rules and policies
+ could lead to complete removal of the target from the code base.
+
+* Degradation in support, documentation or test coverage will make the target as
+ nuisance to other targets and be considered a candidate for deprecation and
+ ultimately removed.
+
+In essences, these rules are necessary for targets to gain and retain their
+status, but also markers to define bit-rot, and will be used to clean up the
+tree from unmaintained targets.
+
+.. _copyright-license-patents:
+
+Copyright, License, and Patents
+===============================
+
+.. note::
+
+ This section deals with legal matters but does not provide legal advice. We
+ are not lawyers --- please seek legal counsel from an attorney.
+
+This section addresses the issues of copyright, license and patents for the LLVM
+project. The copyright for the code is held by the individual contributors of
+the code and the terms of its license to LLVM users and developers is the
+`University of Illinois/NCSA Open Source License
+<http://www.opensource.org/licenses/UoI-NCSA.php>`_ (with portions dual licensed
+under the `MIT License <http://www.opensource.org/licenses/mit-license.php>`_,
+see below). As contributor to the LLVM project, you agree to allow any
+contributions to the project to licensed under these terms.
+
+Copyright
+---------
+
+The LLVM project does not require copyright assignments, which means that the
+copyright for the code in the project is held by its respective contributors who
+have each agreed to release their contributed code under the terms of the `LLVM
+License`_.
+
+An implication of this is that the LLVM license is unlikely to ever change:
+changing it would require tracking down all the contributors to LLVM and getting
+them to agree that a license change is acceptable for their contribution. Since
+there are no plans to change the license, this is not a cause for concern.
+
+As a contributor to the project, this means that you (or your company) retain
+ownership of the code you contribute, that it cannot be used in a way that
+contradicts the license (which is a liberal BSD-style license), and that the
+license for your contributions won't change without your approval in the
+future.
+
+.. _LLVM License:
+
+License
+-------
+
+We intend to keep LLVM perpetually open source and to use a liberal open source
+license. **As a contributor to the project, you agree that any contributions be
+licensed under the terms of the corresponding subproject.** All of the code in
+LLVM is available under the `University of Illinois/NCSA Open Source License
+<http://www.opensource.org/licenses/UoI-NCSA.php>`_, which boils down to
+this:
+
+* You can freely distribute LLVM.
+* You must retain the copyright notice if you redistribute LLVM.
+* Binaries derived from LLVM must reproduce the copyright notice (e.g. in an
+ included readme file).
+* You can't use our names to promote your LLVM derived products.
+* There's no warranty on LLVM at all.
+
+We believe this fosters the widest adoption of LLVM because it **allows
+commercial products to be derived from LLVM** with few restrictions and without
+a requirement for making any derived works also open source (i.e. LLVM's
+license is not a "copyleft" license like the GPL). We suggest that you read the
+`License <http://www.opensource.org/licenses/UoI-NCSA.php>`_ if further
+clarification is needed.
+
+In addition to the UIUC license, the runtime library components of LLVM
+(**compiler_rt, libc++, and libclc**) are also licensed under the `MIT License
+<http://www.opensource.org/licenses/mit-license.php>`_, which does not contain
+the binary redistribution clause. As a user of these runtime libraries, it
+means that you can choose to use the code under either license (and thus don't
+need the binary redistribution clause), and as a contributor to the code that
+you agree that any contributions to these libraries be licensed under both
+licenses. We feel that this is important for runtime libraries, because they
+are implicitly linked into applications and therefore should not subject those
+applications to the binary redistribution clause. This also means that it is ok
+to move code from (e.g.) libc++ to the LLVM core without concern, but that code
+cannot be moved from the LLVM core to libc++ without the copyright owner's
+permission.
+
+Note that the LLVM Project does distribute dragonegg, **which is
+GPL.** This means that anything "linked" into dragonegg must itself be compatible
+with the GPL, and must be releasable under the terms of the GPL. This implies
+that **any code linked into dragonegg and distributed to others may be subject to
+the viral aspects of the GPL** (for example, a proprietary code generator linked
+into dragonegg must be made available under the GPL). This is not a problem for
+code already distributed under a more liberal license (like the UIUC license),
+and GPL-containing subprojects are kept in separate SVN repositories whose
+LICENSE.txt files specifically indicate that they contain GPL code.
+
+We have no plans to change the license of LLVM. If you have questions or
+comments about the license, please contact the `LLVM Developer's Mailing
+List <mailto:llvm-dev at lists.llvm.org>`_.
+
+Patents
+-------
+
+To the best of our knowledge, LLVM does not infringe on any patents (we have
+actually removed code from LLVM in the past that was found to infringe). Having
+code in LLVM that infringes on patents would violate an important goal of the
+project by making it hard or impossible to reuse the code for arbitrary purposes
+(including commercial use).
+
+When contributing code, we expect contributors to notify us of any potential for
+patent-related trouble with their changes (including from third parties). If
+you or your employer own the rights to a patent and would like to contribute
+code to LLVM that relies on it, we require that the copyright owner sign an
+agreement that allows any other user of LLVM to freely use your patent. Please
+contact the `LLVM Foundation Board of Directors <mailto:board at llvm.org>`_ for more
+details.
Added: www-releases/trunk/5.0.2/docs/_sources/Docker.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.2/docs/_sources/Docker.txt?rev=331981&view=auto
==============================================================================
--- www-releases/trunk/5.0.2/docs/_sources/Docker.txt (added)
+++ www-releases/trunk/5.0.2/docs/_sources/Docker.txt Thu May 10 06:54:16 2018
@@ -0,0 +1,199 @@
+=========================================
+A guide to Dockerfiles for building LLVM
+=========================================
+
+Introduction
+============
+You can find a number of sources to build docker images with LLVM components in
+``llvm/utils/docker``. They can be used by anyone who wants to build the docker
+images for their own use, or as a starting point for someone who wants to write
+their own Dockerfiles.
+
+We currently provide Dockerfiles with ``debian8`` and ``nvidia-cuda`` base images.
+We also provide an ``example`` image, which contains placeholders that one would need
+to fill out in order to produce Dockerfiles for a new docker image.
+
+Why?
+----
+Docker images provide a way to produce binary distributions of
+software inside a controlled environment. Having Dockerfiles to builds docker images
+inside LLVM repo makes them much more discoverable than putting them into any other
+place.
+
+Docker basics
+-------------
+If you've never heard about Docker before, you might find this section helpful
+to get a very basic explanation of it.
+`Docker <https://www.docker.com/>`_ is a popular solution for running programs in
+an isolated and reproducible environment, especially to maintain releases for
+software deployed to large distributed fleets.
+It uses linux kernel namespaces and cgroups to provide a lightweight isolation
+inside currently running linux kernel.
+A single active instance of dockerized environment is called a *docker
+container*.
+A snapshot of a docker container filesystem is called a *docker image*.
+One can start a container from a prebuilt docker image.
+
+Docker images are built from a so-called *Dockerfile*, a source file written in
+a specialized language that defines instructions to be used when build
+the docker image (see `official
+documentation <https://docs.docker.com/engine/reference/builder/>`_ for more
+details). A minimal Dockerfile typically contains a base image and a number
+of RUN commands that have to be executed to build the image. When building a new
+image, docker will first download your base image, mount its filesystem as
+read-only and then add a writable overlay on top of it to keep track of all
+filesystem modifications, performed while building your image. When the build
+process is finished, a diff between your image's final filesystem state and the
+base image's filesystem is stored in the resulting image.
+
+Overview
+========
+The ``llvm/utils/docker`` folder contains Dockerfiles and simple bash scripts to
+serve as a basis for anyone who wants to create their own Docker image with
+LLVM components, compiled from sources. The sources are checked out from the
+upstream svn repository when building the image.
+
+Inside each subfolder we host Dockerfiles for two images:
+
+- ``build/`` image is used to compile LLVM, it installs a system compiler and all
+ build dependencies of LLVM. After the build process is finished, the build
+ image will have an archive with compiled components at ``/tmp/clang.tar.gz``.
+- ``release/`` image usually only contains LLVM components, compiled by the
+ ``build/`` image, and also libstdc++ and binutils to make image minimally
+ useful for C++ development. The assumption is that you usually want clang to
+ be one of the provided components.
+
+To build both of those images, use ``build_docker_image.sh`` script.
+It will checkout LLVM sources and build clang in the ``build`` container, copy results
+of the build to the local filesystem and then build the ``release`` container using
+those. The ``build_docker_image.sh`` accepts a list of LLVM repositories to
+checkout, and arguments for CMake invocation.
+
+If you want to write your own docker image, start with an ``example/`` subfolder.
+It provides incomplete Dockerfiles with (very few) FIXMEs explaining the steps
+you need to take in order to make your Dockerfiles functional.
+
+Usage
+=====
+The ``llvm/utils/build_docker_image.sh`` script provides a rather high degree of
+control on how to run the build. It allows you to specify the projects to
+checkout from svn and provide a list of CMake arguments to use during when
+building LLVM inside docker container.
+
+Here's a very simple example of getting a docker image with clang binary,
+compiled by the system compiler in the debian8 image:
+
+.. code-block:: bash
+
+ ./llvm/utils/docker/build_docker_image.sh \
+ --source debian8 \
+ --docker-repository clang-debian8 --docker-tag "staging" \
+ -p clang -i install-clang -i install-clang-headers \
+ -- \
+ -DCMAKE_BUILD_TYPE=Release
+
+Note that a build like that doesn't use a 2-stage build process that
+you probably want for clang. Running a 2-stage build is a little more intricate,
+this command will do that:
+
+.. code-block:: bash
+
+ # Run a 2-stage build.
+ # LLVM_TARGETS_TO_BUILD=Native is to reduce stage1 compile time.
+ # Options, starting with BOOTSTRAP_* are passed to stage2 cmake invocation.
+ ./build_docker_image.sh \
+ --source debian8 \
+ --docker-repository clang-debian8 --docker-tag "staging" \
+ -p clang -i stage2-install-clang -i stage2-install-clang-headers \
+ -- \
+ -DLLVM_TARGETS_TO_BUILD=Native -DCMAKE_BUILD_TYPE=Release \
+ -DBOOTSTRAP_CMAKE_BUILD_TYPE=Release \
+ -DCLANG_ENABLE_BOOTSTRAP=ON -DCLANG_BOOTSTRAP_TARGETS="install-clang;install-clang-headers"
+
+This will produce two images, a release image ``clang-debian8:staging`` and a
+build image ``clang-debian8-build:staging`` from the latest upstream revision.
+After the image is built you can run bash inside a container based on your
+image like this:
+
+.. code-block:: bash
+
+ docker run -ti clang-debian8:staging bash
+
+Now you can run bash commands as you normally would:
+
+.. code-block:: bash
+
+ root at 80f351b51825:/# clang -v
+ clang version 5.0.0 (trunk 305064)
+ Target: x86_64-unknown-linux-gnu
+ Thread model: posix
+ InstalledDir: /bin
+ Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8
+ Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8.4
+ Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
+ Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9.2
+ Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
+ Candidate multilib: .;@m64
+ Selected multilib: .;@m64
+
+
+Which image should I choose?
+============================
+We currently provide two images: debian8-based and nvidia-cuda-based. They
+differ in the base image that they use, i.e. they have a different set of
+preinstalled binaries. Debian8 is very minimal, nvidia-cuda is larger, but has
+preinstalled CUDA libraries and allows to access a GPU, installed on your
+machine.
+
+If you need a minimal linux distribution with only clang and libstdc++ included,
+you should try debian8-based image.
+
+If you want to use CUDA libraries and have access to a GPU on your machine,
+you should choose nvidia-cuda-based image and use `nvidia-docker
+<https://github.com/NVIDIA/nvidia-docker>`_ to run your docker containers. Note
+that you don't need nvidia-docker to build the images, but you need it in order
+to have an access to GPU from a docker container that is running the built
+image.
+
+If you have a different use-case, you could create your own image based on
+``example/`` folder.
+
+Any docker image can be built and run using only the docker binary, i.e. you can
+run debian8 build on Fedora or any other Linux distribution. You don't need to
+install CMake, compilers or any other clang dependencies. It is all handled
+during the build process inside Docker's isolated environment.
+
+Stable build
+============
+If you want a somewhat recent and somewhat stable build, use the
+``branches/google/stable`` branch, i.e. the following command will produce a
+debian8-based image using the latest ``google/stable`` sources for you:
+
+.. code-block:: bash
+
+ ./llvm/utils/docker/build_docker_image.sh \
+ -s debian8 --d clang-debian8 -t "staging" \
+ --branch branches/google/stable \
+ -p clang -i install-clang -i install-clang-headers \
+ -- \
+ -DCMAKE_BUILD_TYPE=Release
+
+
+Minimizing docker image size
+============================
+Due to Docker restrictions we use two images (i.e., build and release folders)
+for the release image to be as small as possible. It's much easier to achieve
+that using two images, because Docker would store a filesystem layer for each
+command in the Dockerfile, i.e. if you install some packages in one command,
+then remove those in a separate command, the size of the resulting image will
+still be proportinal to the size of an image with installed packages.
+Therefore, we strive to provide a very simple release image which only copies
+compiled clang and does not do anything else.
+
+Docker 1.13 added a ``--squash`` flag that allows to flatten the layers of the
+image, i.e. remove the parts that were actually deleted. That is an easier way
+to produce the smallest images possible by using just a single image. We do not
+use it because as of today the flag is in experimental stage and not everyone
+may have the latest docker version available. When the flag is out of
+experimental stage, we should investigate replacing two images approach with
+just a single image, built using ``--squash`` flag.
Added: www-releases/trunk/5.0.2/docs/_sources/ExceptionHandling.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.2/docs/_sources/ExceptionHandling.txt?rev=331981&view=auto
==============================================================================
--- www-releases/trunk/5.0.2/docs/_sources/ExceptionHandling.txt (added)
+++ www-releases/trunk/5.0.2/docs/_sources/ExceptionHandling.txt Thu May 10 06:54:16 2018
@@ -0,0 +1,841 @@
+==========================
+Exception Handling in LLVM
+==========================
+
+.. contents::
+ :local:
+
+Introduction
+============
+
+This document is the central repository for all information pertaining to
+exception handling in LLVM. It describes the format that LLVM exception
+handling information takes, which is useful for those interested in creating
+front-ends or dealing directly with the information. Further, this document
+provides specific examples of what exception handling information is used for in
+C and C++.
+
+Itanium ABI Zero-cost Exception Handling
+----------------------------------------
+
+Exception handling for most programming languages is designed to recover from
+conditions that rarely occur during general use of an application. To that end,
+exception handling should not interfere with the main flow of an application's
+algorithm by performing checkpointing tasks, such as saving the current pc or
+register state.
+
+The Itanium ABI Exception Handling Specification defines a methodology for
+providing outlying data in the form of exception tables without inlining
+speculative exception handling code in the flow of an application's main
+algorithm. Thus, the specification is said to add "zero-cost" to the normal
+execution of an application.
+
+A more complete description of the Itanium ABI exception handling runtime
+support of can be found at `Itanium C++ ABI: Exception Handling
+<http://mentorembedded.github.com/cxx-abi/abi-eh.html>`_. A description of the
+exception frame format can be found at `Exception Frames
+<http://refspecs.linuxfoundation.org/LSB_3.0.0/LSB-Core-generic/LSB-Core-generic/ehframechpt.html>`_,
+with details of the DWARF 4 specification at `DWARF 4 Standard
+<http://dwarfstd.org/Dwarf4Std.php>`_. A description for the C++ exception
+table formats can be found at `Exception Handling Tables
+<http://mentorembedded.github.com/cxx-abi/exceptions.pdf>`_.
+
+Setjmp/Longjmp Exception Handling
+---------------------------------
+
+Setjmp/Longjmp (SJLJ) based exception handling uses LLVM intrinsics
+`llvm.eh.sjlj.setjmp`_ and `llvm.eh.sjlj.longjmp`_ to handle control flow for
+exception handling.
+
+For each function which does exception processing --- be it ``try``/``catch``
+blocks or cleanups --- that function registers itself on a global frame
+list. When exceptions are unwinding, the runtime uses this list to identify
+which functions need processing.
+
+Landing pad selection is encoded in the call site entry of the function
+context. The runtime returns to the function via `llvm.eh.sjlj.longjmp`_, where
+a switch table transfers control to the appropriate landing pad based on the
+index stored in the function context.
+
+In contrast to DWARF exception handling, which encodes exception regions and
+frame information in out-of-line tables, SJLJ exception handling builds and
+removes the unwind frame context at runtime. This results in faster exception
+handling at the expense of slower execution when no exceptions are thrown. As
+exceptions are, by their nature, intended for uncommon code paths, DWARF
+exception handling is generally preferred to SJLJ.
+
+Windows Runtime Exception Handling
+-----------------------------------
+
+LLVM supports handling exceptions produced by the Windows runtime, but it
+requires a very different intermediate representation. It is not based on the
+":ref:`landingpad <i_landingpad>`" instruction like the other two models, and is
+described later in this document under :ref:`wineh`.
+
+Overview
+--------
+
+When an exception is thrown in LLVM code, the runtime does its best to find a
+handler suited to processing the circumstance.
+
+The runtime first attempts to find an *exception frame* corresponding to the
+function where the exception was thrown. If the programming language supports
+exception handling (e.g. C++), the exception frame contains a reference to an
+exception table describing how to process the exception. If the language does
+not support exception handling (e.g. C), or if the exception needs to be
+forwarded to a prior activation, the exception frame contains information about
+how to unwind the current activation and restore the state of the prior
+activation. This process is repeated until the exception is handled. If the
+exception is not handled and no activations remain, then the application is
+terminated with an appropriate error message.
+
+Because different programming languages have different behaviors when handling
+exceptions, the exception handling ABI provides a mechanism for
+supplying *personalities*. An exception handling personality is defined by
+way of a *personality function* (e.g. ``__gxx_personality_v0`` in C++),
+which receives the context of the exception, an *exception structure*
+containing the exception object type and value, and a reference to the exception
+table for the current function. The personality function for the current
+compile unit is specified in a *common exception frame*.
+
+The organization of an exception table is language dependent. For C++, an
+exception table is organized as a series of code ranges defining what to do if
+an exception occurs in that range. Typically, the information associated with a
+range defines which types of exception objects (using C++ *type info*) that are
+handled in that range, and an associated action that should take place. Actions
+typically pass control to a *landing pad*.
+
+A landing pad corresponds roughly to the code found in the ``catch`` portion of
+a ``try``/``catch`` sequence. When execution resumes at a landing pad, it
+receives an *exception structure* and a *selector value* corresponding to the
+*type* of exception thrown. The selector is then used to determine which *catch*
+should actually process the exception.
+
+LLVM Code Generation
+====================
+
+From a C++ developer's perspective, exceptions are defined in terms of the
+``throw`` and ``try``/``catch`` statements. In this section we will describe the
+implementation of LLVM exception handling in terms of C++ examples.
+
+Throw
+-----
+
+Languages that support exception handling typically provide a ``throw``
+operation to initiate the exception process. Internally, a ``throw`` operation
+breaks down into two steps.
+
+#. A request is made to allocate exception space for an exception structure.
+ This structure needs to survive beyond the current activation. This structure
+ will contain the type and value of the object being thrown.
+
+#. A call is made to the runtime to raise the exception, passing the exception
+ structure as an argument.
+
+In C++, the allocation of the exception structure is done by the
+``__cxa_allocate_exception`` runtime function. The exception raising is handled
+by ``__cxa_throw``. The type of the exception is represented using a C++ RTTI
+structure.
+
+Try/Catch
+---------
+
+A call within the scope of a *try* statement can potentially raise an
+exception. In those circumstances, the LLVM C++ front-end replaces the call with
+an ``invoke`` instruction. Unlike a call, the ``invoke`` has two potential
+continuation points:
+
+#. where to continue when the call succeeds as per normal, and
+
+#. where to continue if the call raises an exception, either by a throw or the
+ unwinding of a throw
+
+The term used to define the place where an ``invoke`` continues after an
+exception is called a *landing pad*. LLVM landing pads are conceptually
+alternative function entry points where an exception structure reference and a
+type info index are passed in as arguments. The landing pad saves the exception
+structure reference and then proceeds to select the catch block that corresponds
+to the type info of the exception object.
+
+The LLVM :ref:`i_landingpad` is used to convey information about the landing
+pad to the back end. For C++, the ``landingpad`` instruction returns a pointer
+and integer pair corresponding to the pointer to the *exception structure* and
+the *selector value* respectively.
+
+The ``landingpad`` instruction looks for a reference to the personality
+function to be used for this ``try``/``catch`` sequence in the parent
+function's attribute list. The instruction contains a list of *cleanup*,
+*catch*, and *filter* clauses. The exception is tested against the clauses
+sequentially from first to last. The clauses have the following meanings:
+
+- ``catch <type> @ExcType``
+
+ - This clause means that the landingpad block should be entered if the
+ exception being thrown is of type ``@ExcType`` or a subtype of
+ ``@ExcType``. For C++, ``@ExcType`` is a pointer to the ``std::type_info``
+ object (an RTTI object) representing the C++ exception type.
+
+ - If ``@ExcType`` is ``null``, any exception matches, so the landingpad
+ should always be entered. This is used for C++ catch-all blocks ("``catch
+ (...)``").
+
+ - When this clause is matched, the selector value will be equal to the value
+ returned by "``@llvm.eh.typeid.for(i8* @ExcType)``". This will always be a
+ positive value.
+
+- ``filter <type> [<type> @ExcType1, ..., <type> @ExcTypeN]``
+
+ - This clause means that the landingpad should be entered if the exception
+ being thrown does *not* match any of the types in the list (which, for C++,
+ are again specified as ``std::type_info`` pointers).
+
+ - C++ front-ends use this to implement C++ exception specifications, such as
+ "``void foo() throw (ExcType1, ..., ExcTypeN) { ... }``".
+
+ - When this clause is matched, the selector value will be negative.
+
+ - The array argument to ``filter`` may be empty; for example, "``[0 x i8**]
+ undef``". This means that the landingpad should always be entered. (Note
+ that such a ``filter`` would not be equivalent to "``catch i8* null``",
+ because ``filter`` and ``catch`` produce negative and positive selector
+ values respectively.)
+
+- ``cleanup``
+
+ - This clause means that the landingpad should always be entered.
+
+ - C++ front-ends use this for calling objects' destructors.
+
+ - When this clause is matched, the selector value will be zero.
+
+ - The runtime may treat "``cleanup``" differently from "``catch <type>
+ null``".
+
+ In C++, if an unhandled exception occurs, the language runtime will call
+ ``std::terminate()``, but it is implementation-defined whether the runtime
+ unwinds the stack and calls object destructors first. For example, the GNU
+ C++ unwinder does not call object destructors when an unhandled exception
+ occurs. The reason for this is to improve debuggability: it ensures that
+ ``std::terminate()`` is called from the context of the ``throw``, so that
+ this context is not lost by unwinding the stack. A runtime will typically
+ implement this by searching for a matching non-``cleanup`` clause, and
+ aborting if it does not find one, before entering any landingpad blocks.
+
+Once the landing pad has the type info selector, the code branches to the code
+for the first catch. The catch then checks the value of the type info selector
+against the index of type info for that catch. Since the type info index is not
+known until all the type infos have been gathered in the backend, the catch code
+must call the `llvm.eh.typeid.for`_ intrinsic to determine the index for a given
+type info. If the catch fails to match the selector then control is passed on to
+the next catch.
+
+Finally, the entry and exit of catch code is bracketed with calls to
+``__cxa_begin_catch`` and ``__cxa_end_catch``.
+
+* ``__cxa_begin_catch`` takes an exception structure reference as an argument
+ and returns the value of the exception object.
+
+* ``__cxa_end_catch`` takes no arguments. This function:
+
+ #. Locates the most recently caught exception and decrements its handler
+ count,
+
+ #. Removes the exception from the *caught* stack if the handler count goes to
+ zero, and
+
+ #. Destroys the exception if the handler count goes to zero and the exception
+ was not re-thrown by throw.
+
+ .. note::
+
+ a rethrow from within the catch may replace this call with a
+ ``__cxa_rethrow``.
+
+Cleanups
+--------
+
+A cleanup is extra code which needs to be run as part of unwinding a scope. C++
+destructors are a typical example, but other languages and language extensions
+provide a variety of different kinds of cleanups. In general, a landing pad may
+need to run arbitrary amounts of cleanup code before actually entering a catch
+block. To indicate the presence of cleanups, a :ref:`i_landingpad` should have
+a *cleanup* clause. Otherwise, the unwinder will not stop at the landing pad if
+there are no catches or filters that require it to.
+
+.. note::
+
+ Do not allow a new exception to propagate out of the execution of a
+ cleanup. This can corrupt the internal state of the unwinder. Different
+ languages describe different high-level semantics for these situations: for
+ example, C++ requires that the process be terminated, whereas Ada cancels both
+ exceptions and throws a third.
+
+When all cleanups are finished, if the exception is not handled by the current
+function, resume unwinding by calling the :ref:`resume instruction <i_resume>`,
+passing in the result of the ``landingpad`` instruction for the original
+landing pad.
+
+Throw Filters
+-------------
+
+C++ allows the specification of which exception types may be thrown from a
+function. To represent this, a top level landing pad may exist to filter out
+invalid types. To express this in LLVM code the :ref:`i_landingpad` will have a
+filter clause. The clause consists of an array of type infos.
+``landingpad`` will return a negative value
+if the exception does not match any of the type infos. If no match is found then
+a call to ``__cxa_call_unexpected`` should be made, otherwise
+``_Unwind_Resume``. Each of these functions requires a reference to the
+exception structure. Note that the most general form of a ``landingpad``
+instruction can have any number of catch, cleanup, and filter clauses (though
+having more than one cleanup is pointless). The LLVM C++ front-end can generate
+such ``landingpad`` instructions due to inlining creating nested exception
+handling scopes.
+
+.. _undefined:
+
+Restrictions
+------------
+
+The unwinder delegates the decision of whether to stop in a call frame to that
+call frame's language-specific personality function. Not all unwinders guarantee
+that they will stop to perform cleanups. For example, the GNU C++ unwinder
+doesn't do so unless the exception is actually caught somewhere further up the
+stack.
+
+In order for inlining to behave correctly, landing pads must be prepared to
+handle selector results that they did not originally advertise. Suppose that a
+function catches exceptions of type ``A``, and it's inlined into a function that
+catches exceptions of type ``B``. The inliner will update the ``landingpad``
+instruction for the inlined landing pad to include the fact that ``B`` is also
+caught. If that landing pad assumes that it will only be entered to catch an
+``A``, it's in for a rude awakening. Consequently, landing pads must test for
+the selector results they understand and then resume exception propagation with
+the `resume instruction <LangRef.html#i_resume>`_ if none of the conditions
+match.
+
+Exception Handling Intrinsics
+=============================
+
+In addition to the ``landingpad`` and ``resume`` instructions, LLVM uses several
+intrinsic functions (name prefixed with ``llvm.eh``) to provide exception
+handling information at various points in generated code.
+
+.. _llvm.eh.typeid.for:
+
+``llvm.eh.typeid.for``
+----------------------
+
+.. code-block:: llvm
+
+ i32 @llvm.eh.typeid.for(i8* %type_info)
+
+
+This intrinsic returns the type info index in the exception table of the current
+function. This value can be used to compare against the result of
+``landingpad`` instruction. The single argument is a reference to a type info.
+
+Uses of this intrinsic are generated by the C++ front-end.
+
+.. _llvm.eh.begincatch:
+
+``llvm.eh.begincatch``
+----------------------
+
+.. code-block:: llvm
+
+ void @llvm.eh.begincatch(i8* %ehptr, i8* %ehobj)
+
+
+This intrinsic marks the beginning of catch handling code within the blocks
+following a ``landingpad`` instruction. The exact behavior of this function
+depends on the compilation target and the personality function associated
+with the ``landingpad`` instruction.
+
+The first argument to this intrinsic is a pointer that was previously extracted
+from the aggregate return value of the ``landingpad`` instruction. The second
+argument to the intrinsic is a pointer to stack space where the exception object
+should be stored. The runtime handles the details of copying the exception
+object into the slot. If the second parameter is null, no copy occurs.
+
+Uses of this intrinsic are generated by the C++ front-end. Many targets will
+use implementation-specific functions (such as ``__cxa_begin_catch``) instead
+of this intrinsic. The intrinsic is provided for targets that require a more
+abstract interface.
+
+When used in the native Windows C++ exception handling implementation, this
+intrinsic serves as a placeholder to delimit code before a catch handler is
+outlined. When the handler is is outlined, this intrinsic will be replaced
+by instructions that retrieve the exception object pointer from the frame
+allocation block.
+
+
+.. _llvm.eh.endcatch:
+
+``llvm.eh.endcatch``
+----------------------
+
+.. code-block:: llvm
+
+ void @llvm.eh.endcatch()
+
+
+This intrinsic marks the end of catch handling code within the current block,
+which will be a successor of a block which called ``llvm.eh.begincatch''.
+The exact behavior of this function depends on the compilation target and the
+personality function associated with the corresponding ``landingpad``
+instruction.
+
+There may be more than one call to ``llvm.eh.endcatch`` for any given call to
+``llvm.eh.begincatch`` with each ``llvm.eh.endcatch`` call corresponding to the
+end of a different control path. All control paths following a call to
+``llvm.eh.begincatch`` must reach a call to ``llvm.eh.endcatch``.
+
+Uses of this intrinsic are generated by the C++ front-end. Many targets will
+use implementation-specific functions (such as ``__cxa_begin_catch``) instead
+of this intrinsic. The intrinsic is provided for targets that require a more
+abstract interface.
+
+When used in the native Windows C++ exception handling implementation, this
+intrinsic serves as a placeholder to delimit code before a catch handler is
+outlined. After the handler is outlined, this intrinsic is simply removed.
+
+
+.. _llvm.eh.exceptionpointer:
+
+``llvm.eh.exceptionpointer``
+----------------------------
+
+.. code-block:: text
+
+ i8 addrspace(N)* @llvm.eh.padparam.pNi8(token %catchpad)
+
+
+This intrinsic retrieves a pointer to the exception caught by the given
+``catchpad``.
+
+
+SJLJ Intrinsics
+---------------
+
+The ``llvm.eh.sjlj`` intrinsics are used internally within LLVM's
+backend. Uses of them are generated by the backend's
+``SjLjEHPrepare`` pass.
+
+.. _llvm.eh.sjlj.setjmp:
+
+``llvm.eh.sjlj.setjmp``
+~~~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: text
+
+ i32 @llvm.eh.sjlj.setjmp(i8* %setjmp_buf)
+
+For SJLJ based exception handling, this intrinsic forces register saving for the
+current function and stores the address of the following instruction for use as
+a destination address by `llvm.eh.sjlj.longjmp`_. The buffer format and the
+overall functioning of this intrinsic is compatible with the GCC
+``__builtin_setjmp`` implementation allowing code built with the clang and GCC
+to interoperate.
+
+The single parameter is a pointer to a five word buffer in which the calling
+context is saved. The front end places the frame pointer in the first word, and
+the target implementation of this intrinsic should place the destination address
+for a `llvm.eh.sjlj.longjmp`_ in the second word. The following three words are
+available for use in a target-specific manner.
+
+.. _llvm.eh.sjlj.longjmp:
+
+``llvm.eh.sjlj.longjmp``
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: llvm
+
+ void @llvm.eh.sjlj.longjmp(i8* %setjmp_buf)
+
+For SJLJ based exception handling, the ``llvm.eh.sjlj.longjmp`` intrinsic is
+used to implement ``__builtin_longjmp()``. The single parameter is a pointer to
+a buffer populated by `llvm.eh.sjlj.setjmp`_. The frame pointer and stack
+pointer are restored from the buffer, then control is transferred to the
+destination address.
+
+``llvm.eh.sjlj.lsda``
+~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: llvm
+
+ i8* @llvm.eh.sjlj.lsda()
+
+For SJLJ based exception handling, the ``llvm.eh.sjlj.lsda`` intrinsic returns
+the address of the Language Specific Data Area (LSDA) for the current
+function. The SJLJ front-end code stores this address in the exception handling
+function context for use by the runtime.
+
+``llvm.eh.sjlj.callsite``
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: llvm
+
+ void @llvm.eh.sjlj.callsite(i32 %call_site_num)
+
+For SJLJ based exception handling, the ``llvm.eh.sjlj.callsite`` intrinsic
+identifies the callsite value associated with the following ``invoke``
+instruction. This is used to ensure that landing pad entries in the LSDA are
+generated in matching order.
+
+Asm Table Formats
+=================
+
+There are two tables that are used by the exception handling runtime to
+determine which actions should be taken when an exception is thrown.
+
+Exception Handling Frame
+------------------------
+
+An exception handling frame ``eh_frame`` is very similar to the unwind frame
+used by DWARF debug info. The frame contains all the information necessary to
+tear down the current frame and restore the state of the prior frame. There is
+an exception handling frame for each function in a compile unit, plus a common
+exception handling frame that defines information common to all functions in the
+unit.
+
+The format of this call frame information (CFI) is often platform-dependent,
+however. ARM, for example, defines their own format. Apple has their own compact
+unwind info format. On Windows, another format is used for all architectures
+since 32-bit x86. LLVM will emit whatever information is required by the
+target.
+
+Exception Tables
+----------------
+
+An exception table contains information about what actions to take when an
+exception is thrown in a particular part of a function's code. This is typically
+referred to as the language-specific data area (LSDA). The format of the LSDA
+table is specific to the personality function, but the majority of personalities
+out there use a variation of the tables consumed by ``__gxx_personality_v0``.
+There is one exception table per function, except leaf functions and functions
+that have calls only to non-throwing functions. They do not need an exception
+table.
+
+.. _wineh:
+
+Exception Handling using the Windows Runtime
+=================================================
+
+Background on Windows exceptions
+---------------------------------
+
+Interacting with exceptions on Windows is significantly more complicated than
+on Itanium C++ ABI platforms. The fundamental difference between the two models
+is that Itanium EH is designed around the idea of "successive unwinding," while
+Windows EH is not.
+
+Under Itanium, throwing an exception typically involes allocating thread local
+memory to hold the exception, and calling into the EH runtime. The runtime
+identifies frames with appropriate exception handling actions, and successively
+resets the register context of the current thread to the most recently active
+frame with actions to run. In LLVM, execution resumes at a ``landingpad``
+instruction, which produces register values provided by the runtime. If a
+function is only cleaning up allocated resources, the function is responsible
+for calling ``_Unwind_Resume`` to transition to the next most recently active
+frame after it is finished cleaning up. Eventually, the frame responsible for
+handling the exception calls ``__cxa_end_catch`` to destroy the exception,
+release its memory, and resume normal control flow.
+
+The Windows EH model does not use these successive register context resets.
+Instead, the active exception is typically described by a frame on the stack.
+In the case of C++ exceptions, the exception object is allocated in stack memory
+and its address is passed to ``__CxxThrowException``. General purpose structured
+exceptions (SEH) are more analogous to Linux signals, and they are dispatched by
+userspace DLLs provided with Windows. Each frame on the stack has an assigned EH
+personality routine, which decides what actions to take to handle the exception.
+There are a few major personalities for C and C++ code: the C++ personality
+(``__CxxFrameHandler3``) and the SEH personalities (``_except_handler3``,
+``_except_handler4``, and ``__C_specific_handler``). All of them implement
+cleanups by calling back into a "funclet" contained in the parent function.
+
+Funclets, in this context, are regions of the parent function that can be called
+as though they were a function pointer with a very special calling convention.
+The frame pointer of the parent frame is passed into the funclet either using
+the standard EBP register or as the first parameter register, depending on the
+architecture. The funclet implements the EH action by accessing local variables
+in memory through the frame pointer, and returning some appropriate value,
+continuing the EH process. No variables live in to or out of the funclet can be
+allocated in registers.
+
+The C++ personality also uses funclets to contain the code for catch blocks
+(i.e. all user code between the braces in ``catch (Type obj) { ... }``). The
+runtime must use funclets for catch bodies because the C++ exception object is
+allocated in a child stack frame of the function handling the exception. If the
+runtime rewound the stack back to frame of the catch, the memory holding the
+exception would be overwritten quickly by subsequent function calls. The use of
+funclets also allows ``__CxxFrameHandler3`` to implement rethrow without
+resorting to TLS. Instead, the runtime throws a special exception, and then uses
+SEH (``__try / __except``) to resume execution with new information in the child
+frame.
+
+In other words, the successive unwinding approach is incompatible with Visual
+C++ exceptions and general purpose Windows exception handling. Because the C++
+exception object lives in stack memory, LLVM cannot provide a custom personality
+function that uses landingpads. Similarly, SEH does not provide any mechanism
+to rethrow an exception or continue unwinding. Therefore, LLVM must use the IR
+constructs described later in this document to implement compatible exception
+handling.
+
+SEH filter expressions
+-----------------------
+
+The SEH personality functions also use funclets to implement filter expressions,
+which allow executing arbitrary user code to decide which exceptions to catch.
+Filter expressions should not be confused with the ``filter`` clause of the LLVM
+``landingpad`` instruction. Typically filter expressions are used to determine
+if the exception came from a particular DLL or code region, or if code faulted
+while accessing a particular memory address range. LLVM does not currently have
+IR to represent filter expressions because it is difficult to represent their
+control dependencies. Filter expressions run during the first phase of EH,
+before cleanups run, making it very difficult to build a faithful control flow
+graph. For now, the new EH instructions cannot represent SEH filter
+expressions, and frontends must outline them ahead of time. Local variables of
+the parent function can be escaped and accessed using the ``llvm.localescape``
+and ``llvm.localrecover`` intrinsics.
+
+New exception handling instructions
+------------------------------------
+
+The primary design goal of the new EH instructions is to support funclet
+generation while preserving information about the CFG so that SSA formation
+still works. As a secondary goal, they are designed to be generic across MSVC
+and Itanium C++ exceptions. They make very few assumptions about the data
+required by the personality, so long as it uses the familiar core EH actions:
+catch, cleanup, and terminate. However, the new instructions are hard to modify
+without knowing details of the EH personality. While they can be used to
+represent Itanium EH, the landingpad model is strictly better for optimization
+purposes.
+
+The following new instructions are considered "exception handling pads", in that
+they must be the first non-phi instruction of a basic block that may be the
+unwind destination of an EH flow edge:
+``catchswitch``, ``catchpad``, and ``cleanuppad``.
+As with landingpads, when entering a try scope, if the
+frontend encounters a call site that may throw an exception, it should emit an
+invoke that unwinds to a ``catchswitch`` block. Similarly, inside the scope of a
+C++ object with a destructor, invokes should unwind to a ``cleanuppad``.
+
+New instructions are also used to mark the points where control is transferred
+out of a catch/cleanup handler (which will correspond to exits from the
+generated funclet). A catch handler which reaches its end by normal execution
+executes a ``catchret`` instruction, which is a terminator indicating where in
+the function control is returned to. A cleanup handler which reaches its end
+by normal execution executes a ``cleanupret`` instruction, which is a terminator
+indicating where the active exception will unwind to next.
+
+Each of these new EH pad instructions has a way to identify which action should
+be considered after this action. The ``catchswitch`` instruction is a terminator
+and has an unwind destination operand analogous to the unwind destination of an
+invoke. The ``cleanuppad`` instruction is not
+a terminator, so the unwind destination is stored on the ``cleanupret``
+instruction instead. Successfully executing a catch handler should resume
+normal control flow, so neither ``catchpad`` nor ``catchret`` instructions can
+unwind. All of these "unwind edges" may refer to a basic block that contains an
+EH pad instruction, or they may unwind to the caller. Unwinding to the caller
+has roughly the same semantics as the ``resume`` instruction in the landingpad
+model. When inlining through an invoke, instructions that unwind to the caller
+are hooked up to unwind to the unwind destination of the call site.
+
+Putting things together, here is a hypothetical lowering of some C++ that uses
+all of the new IR instructions:
+
+.. code-block:: c
+
+ struct Cleanup {
+ Cleanup();
+ ~Cleanup();
+ int m;
+ };
+ void may_throw();
+ int f() noexcept {
+ try {
+ Cleanup obj;
+ may_throw();
+ } catch (int e) {
+ may_throw();
+ return e;
+ }
+ return 0;
+ }
+
+.. code-block:: text
+
+ define i32 @f() nounwind personality i32 (...)* @__CxxFrameHandler3 {
+ entry:
+ %obj = alloca %struct.Cleanup, align 4
+ %e = alloca i32, align 4
+ %call = invoke %struct.Cleanup* @"\01??0Cleanup@@QEAA at XZ"(%struct.Cleanup* nonnull %obj)
+ to label %invoke.cont unwind label %lpad.catch
+
+ invoke.cont: ; preds = %entry
+ invoke void @"\01?may_throw@@YAXXZ"()
+ to label %invoke.cont.2 unwind label %lpad.cleanup
+
+ invoke.cont.2: ; preds = %invoke.cont
+ call void @"\01??_DCleanup@@QEAA at XZ"(%struct.Cleanup* nonnull %obj) nounwind
+ br label %return
+
+ return: ; preds = %invoke.cont.3, %invoke.cont.2
+ %retval.0 = phi i32 [ 0, %invoke.cont.2 ], [ %3, %invoke.cont.3 ]
+ ret i32 %retval.0
+
+ lpad.cleanup: ; preds = %invoke.cont.2
+ %0 = cleanuppad within none []
+ call void @"\01??1Cleanup@@QEAA at XZ"(%struct.Cleanup* nonnull %obj) nounwind
+ cleanupret %0 unwind label %lpad.catch
+
+ lpad.catch: ; preds = %lpad.cleanup, %entry
+ %1 = catchswitch within none [label %catch.body] unwind label %lpad.terminate
+
+ catch.body: ; preds = %lpad.catch
+ %catch = catchpad within %1 [%rtti.TypeDescriptor2* @"\01??_R0H at 8", i32 0, i32* %e]
+ invoke void @"\01?may_throw@@YAXXZ"()
+ to label %invoke.cont.3 unwind label %lpad.terminate
+
+ invoke.cont.3: ; preds = %catch.body
+ %3 = load i32, i32* %e, align 4
+ catchret from %catch to label %return
+
+ lpad.terminate: ; preds = %catch.body, %lpad.catch
+ cleanuppad within none []
+ call void @"\01?terminate@@YAXXZ"
+ unreachable
+ }
+
+Funclet parent tokens
+-----------------------
+
+In order to produce tables for EH personalities that use funclets, it is
+necessary to recover the nesting that was present in the source. This funclet
+parent relationship is encoded in the IR using tokens produced by the new "pad"
+instructions. The token operand of a "pad" or "ret" instruction indicates which
+funclet it is in, or "none" if it is not nested within another funclet.
+
+The ``catchpad`` and ``cleanuppad`` instructions establish new funclets, and
+their tokens are consumed by other "pad" instructions to establish membership.
+The ``catchswitch`` instruction does not create a funclet, but it produces a
+token that is always consumed by its immediate successor ``catchpad``
+instructions. This ensures that every catch handler modelled by a ``catchpad``
+belongs to exactly one ``catchswitch``, which models the dispatch point after a
+C++ try.
+
+Here is an example of what this nesting looks like using some hypothetical
+C++ code:
+
+.. code-block:: c
+
+ void f() {
+ try {
+ throw;
+ } catch (...) {
+ try {
+ throw;
+ } catch (...) {
+ }
+ }
+ }
+
+.. code-block:: text
+
+ define void @f() #0 personality i8* bitcast (i32 (...)* @__CxxFrameHandler3 to i8*) {
+ entry:
+ invoke void @_CxxThrowException(i8* null, %eh.ThrowInfo* null) #1
+ to label %unreachable unwind label %catch.dispatch
+
+ catch.dispatch: ; preds = %entry
+ %0 = catchswitch within none [label %catch] unwind to caller
+
+ catch: ; preds = %catch.dispatch
+ %1 = catchpad within %0 [i8* null, i32 64, i8* null]
+ invoke void @_CxxThrowException(i8* null, %eh.ThrowInfo* null) #1
+ to label %unreachable unwind label %catch.dispatch2
+
+ catch.dispatch2: ; preds = %catch
+ %2 = catchswitch within %1 [label %catch3] unwind to caller
+
+ catch3: ; preds = %catch.dispatch2
+ %3 = catchpad within %2 [i8* null, i32 64, i8* null]
+ catchret from %3 to label %try.cont
+
+ try.cont: ; preds = %catch3
+ catchret from %1 to label %try.cont6
+
+ try.cont6: ; preds = %try.cont
+ ret void
+
+ unreachable: ; preds = %catch, %entry
+ unreachable
+ }
+
+The "inner" ``catchswitch`` consumes ``%1`` which is produced by the outer
+catchswitch.
+
+.. _wineh-constraints:
+
+Funclet transitions
+-----------------------
+
+The EH tables for personalities that use funclets make implicit use of the
+funclet nesting relationship to encode unwind destinations, and so are
+constrained in the set of funclet transitions they can represent. The related
+LLVM IR instructions accordingly have constraints that ensure encodability of
+the EH edges in the flow graph.
+
+A ``catchswitch``, ``catchpad``, or ``cleanuppad`` is said to be "entered"
+when it executes. It may subsequently be "exited" by any of the following
+means:
+
+* A ``catchswitch`` is immediately exited when none of its constituent
+ ``catchpad``\ s are appropriate for the in-flight exception and it unwinds
+ to its unwind destination or the caller.
+* A ``catchpad`` and its parent ``catchswitch`` are both exited when a
+ ``catchret`` from the ``catchpad`` is executed.
+* A ``cleanuppad`` is exited when a ``cleanupret`` from it is executed.
+* Any of these pads is exited when control unwinds to the function's caller,
+ either by a ``call`` which unwinds all the way to the function's caller,
+ a nested ``catchswitch`` marked "``unwinds to caller``", or a nested
+ ``cleanuppad``\ 's ``cleanupret`` marked "``unwinds to caller"``.
+* Any of these pads is exited when an unwind edge (from an ``invoke``,
+ nested ``catchswitch``, or nested ``cleanuppad``\ 's ``cleanupret``)
+ unwinds to a destination pad that is not a descendant of the given pad.
+
+Note that the ``ret`` instruction is *not* a valid way to exit a funclet pad;
+it is undefined behavior to execute a ``ret`` when a pad has been entered but
+not exited.
+
+A single unwind edge may exit any number of pads (with the restrictions that
+the edge from a ``catchswitch`` must exit at least itself, and the edge from
+a ``cleanupret`` must exit at least its ``cleanuppad``), and then must enter
+exactly one pad, which must be distinct from all the exited pads. The parent
+of the pad that an unwind edge enters must be the most-recently-entered
+not-yet-exited pad (after exiting from any pads that the unwind edge exits),
+or "none" if there is no such pad. This ensures that the stack of executing
+funclets at run-time always corresponds to some path in the funclet pad tree
+that the parent tokens encode.
+
+All unwind edges which exit any given funclet pad (including ``cleanupret``
+edges exiting their ``cleanuppad`` and ``catchswitch`` edges exiting their
+``catchswitch``) must share the same unwind destination. Similarly, any
+funclet pad which may be exited by unwind to caller must not be exited by
+any exception edges which unwind anywhere other than the caller. This
+ensures that each funclet as a whole has only one unwind destination, which
+EH tables for funclet personalities may require. Note that any unwind edge
+which exits a ``catchpad`` also exits its parent ``catchswitch``, so this
+implies that for any given ``catchswitch``, its unwind destination must also
+be the unwind destination of any unwind edge that exits any of its constituent
+``catchpad``\s. Because ``catchswitch`` has no ``nounwind`` variant, and
+because IR producers are not *required* to annotate calls which will not
+unwind as ``nounwind``, it is legal to nest a ``call`` or an "``unwind to
+caller``\ " ``catchswitch`` within a funclet pad that has an unwind
+destination other than caller; it is undefined behavior for such a ``call``
+or ``catchswitch`` to unwind.
+
+Finally, the funclet pads' unwind destinations cannot form a cycle. This
+ensures that EH lowering can construct "try regions" with a tree-like
+structure, which funclet-based personalities may require.
Added: www-releases/trunk/5.0.2/docs/_sources/ExtendingLLVM.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.2/docs/_sources/ExtendingLLVM.txt?rev=331981&view=auto
==============================================================================
--- www-releases/trunk/5.0.2/docs/_sources/ExtendingLLVM.txt (added)
+++ www-releases/trunk/5.0.2/docs/_sources/ExtendingLLVM.txt Thu May 10 06:54:16 2018
@@ -0,0 +1,327 @@
+============================================================
+Extending LLVM: Adding instructions, intrinsics, types, etc.
+============================================================
+
+Introduction and Warning
+========================
+
+
+During the course of using LLVM, you may wish to customize it for your research
+project or for experimentation. At this point, you may realize that you need to
+add something to LLVM, whether it be a new fundamental type, a new intrinsic
+function, or a whole new instruction.
+
+When you come to this realization, stop and think. Do you really need to extend
+LLVM? Is it a new fundamental capability that LLVM does not support at its
+current incarnation or can it be synthesized from already pre-existing LLVM
+elements? If you are not sure, ask on the `LLVM-dev
+<http://lists.llvm.org/mailman/listinfo/llvm-dev>`_ list. The reason is that
+extending LLVM will get involved as you need to update all the different passes
+that you intend to use with your extension, and there are ``many`` LLVM analyses
+and transformations, so it may be quite a bit of work.
+
+Adding an `intrinsic function`_ is far easier than adding an
+instruction, and is transparent to optimization passes. If your added
+functionality can be expressed as a function call, an intrinsic function is the
+method of choice for LLVM extension.
+
+Before you invest a significant amount of effort into a non-trivial extension,
+**ask on the list** if what you are looking to do can be done with
+already-existing infrastructure, or if maybe someone else is already working on
+it. You will save yourself a lot of time and effort by doing so.
+
+.. _intrinsic function:
+
+Adding a new intrinsic function
+===============================
+
+Adding a new intrinsic function to LLVM is much easier than adding a new
+instruction. Almost all extensions to LLVM should start as an intrinsic
+function and then be turned into an instruction if warranted.
+
+#. ``llvm/docs/LangRef.html``:
+
+ Document the intrinsic. Decide whether it is code generator specific and
+ what the restrictions are. Talk to other people about it so that you are
+ sure it's a good idea.
+
+#. ``llvm/include/llvm/IR/Intrinsics*.td``:
+
+ Add an entry for your intrinsic. Describe its memory access characteristics
+ for optimization (this controls whether it will be DCE'd, CSE'd, etc). Note
+ that any intrinsic using one of the ``llvm_any*_ty`` types for an argument or
+ return type will be deemed by ``tblgen`` as overloaded and the corresponding
+ suffix will be required on the intrinsic's name.
+
+#. ``llvm/lib/Analysis/ConstantFolding.cpp``:
+
+ If it is possible to constant fold your intrinsic, add support to it in the
+ ``canConstantFoldCallTo`` and ``ConstantFoldCall`` functions.
+
+#. ``llvm/test/*``:
+
+ Add test cases for your test cases to the test suite
+
+Once the intrinsic has been added to the system, you must add code generator
+support for it. Generally you must do the following steps:
+
+Add support to the .td file for the target(s) of your choice in
+``lib/Target/*/*.td``.
+
+ This is usually a matter of adding a pattern to the .td file that matches the
+ intrinsic, though it may obviously require adding the instructions you want to
+ generate as well. There are lots of examples in the PowerPC and X86 backend
+ to follow.
+
+Adding a new SelectionDAG node
+==============================
+
+As with intrinsics, adding a new SelectionDAG node to LLVM is much easier than
+adding a new instruction. New nodes are often added to help represent
+instructions common to many targets. These nodes often map to an LLVM
+instruction (add, sub) or intrinsic (byteswap, population count). In other
+cases, new nodes have been added to allow many targets to perform a common task
+(converting between floating point and integer representation) or capture more
+complicated behavior in a single node (rotate).
+
+#. ``include/llvm/CodeGen/ISDOpcodes.h``:
+
+ Add an enum value for the new SelectionDAG node.
+
+#. ``lib/CodeGen/SelectionDAG/SelectionDAG.cpp``:
+
+ Add code to print the node to ``getOperationName``. If your new node can be
+ evaluated at compile time when given constant arguments (such as an add of a
+ constant with another constant), find the ``getNode`` method that takes the
+ appropriate number of arguments, and add a case for your node to the switch
+ statement that performs constant folding for nodes that take the same number
+ of arguments as your new node.
+
+#. ``lib/CodeGen/SelectionDAG/LegalizeDAG.cpp``:
+
+ Add code to `legalize, promote, and expand
+ <CodeGenerator.html#selectiondag_legalize>`_ the node as necessary. At a
+ minimum, you will need to add a case statement for your node in
+ ``LegalizeOp`` which calls LegalizeOp on the node's operands, and returns a
+ new node if any of the operands changed as a result of being legalized. It
+ is likely that not all targets supported by the SelectionDAG framework will
+ natively support the new node. In this case, you must also add code in your
+ node's case statement in ``LegalizeOp`` to Expand your node into simpler,
+ legal operations. The case for ``ISD::UREM`` for expanding a remainder into
+ a divide, multiply, and a subtract is a good example.
+
+#. ``lib/CodeGen/SelectionDAG/LegalizeDAG.cpp``:
+
+ If targets may support the new node being added only at certain sizes, you
+ will also need to add code to your node's case statement in ``LegalizeOp``
+ to Promote your node's operands to a larger size, and perform the correct
+ operation. You will also need to add code to ``PromoteOp`` to do this as
+ well. For a good example, see ``ISD::BSWAP``, which promotes its operand to
+ a wider size, performs the byteswap, and then shifts the correct bytes right
+ to emulate the narrower byteswap in the wider type.
+
+#. ``lib/CodeGen/SelectionDAG/LegalizeDAG.cpp``:
+
+ Add a case for your node in ``ExpandOp`` to teach the legalizer how to
+ perform the action represented by the new node on a value that has been split
+ into high and low halves. This case will be used to support your node with a
+ 64 bit operand on a 32 bit target.
+
+#. ``lib/CodeGen/SelectionDAG/DAGCombiner.cpp``:
+
+ If your node can be combined with itself, or other existing nodes in a
+ peephole-like fashion, add a visit function for it, and call that function
+ from. There are several good examples for simple combines you can do;
+ ``visitFABS`` and ``visitSRL`` are good starting places.
+
+#. ``lib/Target/PowerPC/PPCISelLowering.cpp``:
+
+ Each target has an implementation of the ``TargetLowering`` class, usually in
+ its own file (although some targets include it in the same file as the
+ DAGToDAGISel). The default behavior for a target is to assume that your new
+ node is legal for all types that are legal for that target. If this target
+ does not natively support your node, then tell the target to either Promote
+ it (if it is supported at a larger type) or Expand it. This will cause the
+ code you wrote in ``LegalizeOp`` above to decompose your new node into other
+ legal nodes for this target.
+
+#. ``lib/Target/TargetSelectionDAG.td``:
+
+ Most current targets supported by LLVM generate code using the DAGToDAG
+ method, where SelectionDAG nodes are pattern matched to target-specific
+ nodes, which represent individual instructions. In order for the targets to
+ match an instruction to your new node, you must add a def for that node to
+ the list in this file, with the appropriate type constraints. Look at
+ ``add``, ``bswap``, and ``fadd`` for examples.
+
+#. ``lib/Target/PowerPC/PPCInstrInfo.td``:
+
+ Each target has a tablegen file that describes the target's instruction set.
+ For targets that use the DAGToDAG instruction selection framework, add a
+ pattern for your new node that uses one or more target nodes. Documentation
+ for this is a bit sparse right now, but there are several decent examples.
+ See the patterns for ``rotl`` in ``PPCInstrInfo.td``.
+
+#. TODO: document complex patterns.
+
+#. ``llvm/test/CodeGen/*``:
+
+ Add test cases for your new node to the test suite.
+ ``llvm/test/CodeGen/X86/bswap.ll`` is a good example.
+
+Adding a new instruction
+========================
+
+.. warning::
+
+ Adding instructions changes the bitcode format, and it will take some effort
+ to maintain compatibility with the previous version. Only add an instruction
+ if it is absolutely necessary.
+
+#. ``llvm/include/llvm/IR/Instruction.def``:
+
+ add a number for your instruction and an enum name
+
+#. ``llvm/include/llvm/IR/Instructions.h``:
+
+ add a definition for the class that will represent your instruction
+
+#. ``llvm/include/llvm/IR/InstVisitor.h``:
+
+ add a prototype for a visitor to your new instruction type
+
+#. ``llvm/lib/AsmParser/LLLexer.cpp``:
+
+ add a new token to parse your instruction from assembly text file
+
+#. ``llvm/lib/AsmParser/LLParser.cpp``:
+
+ add the grammar on how your instruction can be read and what it will
+ construct as a result
+
+#. ``llvm/lib/Bitcode/Reader/BitcodeReader.cpp``:
+
+ add a case for your instruction and how it will be parsed from bitcode
+
+#. ``llvm/lib/Bitcode/Writer/BitcodeWriter.cpp``:
+
+ add a case for your instruction and how it will be parsed from bitcode
+
+#. ``llvm/lib/IR/Instruction.cpp``:
+
+ add a case for how your instruction will be printed out to assembly
+
+#. ``llvm/lib/IR/Instructions.cpp``:
+
+ implement the class you defined in ``llvm/include/llvm/Instructions.h``
+
+#. Test your instruction
+
+#. ``llvm/lib/Target/*``:
+
+ add support for your instruction to code generators, or add a lowering pass.
+
+#. ``llvm/test/*``:
+
+ add your test cases to the test suite.
+
+Also, you need to implement (or modify) any analyses or passes that you want to
+understand this new instruction.
+
+Adding a new type
+=================
+
+.. warning::
+
+ Adding new types changes the bitcode format, and will break compatibility with
+ currently-existing LLVM installations. Only add new types if it is absolutely
+ necessary.
+
+Adding a fundamental type
+-------------------------
+
+#. ``llvm/include/llvm/IR/Type.h``:
+
+ add enum for the new type; add static ``Type*`` for this type
+
+#. ``llvm/lib/IR/Type.cpp`` and ``llvm/lib/IR/ValueTypes.cpp``:
+
+ add mapping from ``TypeID`` => ``Type*``; initialize the static ``Type*``
+
+#. ``llvm/llvm/llvm-c/Core.cpp``:
+
+ add enum ``LLVMTypeKind`` and modify
+ ``LLVMTypeKind LLVMGetTypeKind(LLVMTypeRef Ty)`` for the new type
+
+#. ``llvm/include/llvm/IR/TypeBuilder.h``:
+
+ add new class to represent new type in the hierarchy
+
+#. ``llvm/lib/AsmParser/LLLexer.cpp``:
+
+ add ability to parse in the type from text assembly
+
+#. ``llvm/lib/AsmParser/LLParser.cpp``:
+
+ add a token for that type
+
+#. ``llvm/lib/Bitcode/Writer/BitcodeWriter.cpp``:
+
+ modify ``static void WriteTypeTable(const ValueEnumerator &VE,
+ BitstreamWriter &Stream)`` to serialize your type
+
+#. ``llvm/lib/Bitcode/Reader/BitcodeReader.cpp``:
+
+ modify ``bool BitcodeReader::ParseTypeType()`` to read your data type
+
+#. ``include/llvm/Bitcode/LLVMBitCodes.h``:
+
+ add enum ``TypeCodes`` for the new type
+
+Adding a derived type
+---------------------
+
+#. ``llvm/include/llvm/IR/Type.h``:
+
+ add enum for the new type; add a forward declaration of the type also
+
+#. ``llvm/include/llvm/IR/DerivedTypes.h``:
+
+ add new class to represent new class in the hierarchy; add forward
+ declaration to the TypeMap value type
+
+#. ``llvm/lib/IR/Type.cpp`` and ``llvm/lib/IR/ValueTypes.cpp``:
+
+ add support for derived type, notably `enum TypeID` and `is`, `get` methods.
+
+#. ``llvm/llvm/llvm-c/Core.cpp``:
+
+ add enum ``LLVMTypeKind`` and modify
+ `LLVMTypeKind LLVMGetTypeKind(LLVMTypeRef Ty)` for the new type
+
+#. ``llvm/include/llvm/IR/TypeBuilder.h``:
+
+ add new class to represent new class in the hierarchy
+
+#. ``llvm/lib/AsmParser/LLLexer.cpp``:
+
+ modify ``lltok::Kind LLLexer::LexIdentifier()`` to add ability to
+ parse in the type from text assembly
+
+#. ``llvm/lib/Bitcode/Writer/BitcodeWriter.cpp``:
+
+ modify ``static void WriteTypeTable(const ValueEnumerator &VE,
+ BitstreamWriter &Stream)`` to serialize your type
+
+#. ``llvm/lib/Bitcode/Reader/BitcodeReader.cpp``:
+
+ modify ``bool BitcodeReader::ParseTypeType()`` to read your data type
+
+#. ``include/llvm/Bitcode/LLVMBitCodes.h``:
+
+ add enum ``TypeCodes`` for the new type
+
+#. ``llvm/lib/IR/AsmWriter.cpp``:
+
+ modify ``void TypePrinting::print(Type *Ty, raw_ostream &OS)``
+ to output the new derived type
Added: www-releases/trunk/5.0.2/docs/_sources/Extensions.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.2/docs/_sources/Extensions.txt?rev=331981&view=auto
==============================================================================
--- www-releases/trunk/5.0.2/docs/_sources/Extensions.txt (added)
+++ www-releases/trunk/5.0.2/docs/_sources/Extensions.txt Thu May 10 06:54:16 2018
@@ -0,0 +1,290 @@
+===============
+LLVM Extensions
+===============
+
+.. contents::
+ :local:
+
+.. toctree::
+ :hidden:
+
+Introduction
+============
+
+This document describes extensions to tools and formats LLVM seeks compatibility
+with.
+
+General Assembly Syntax
+===========================
+
+C99-style Hexadecimal Floating-point Constants
+----------------------------------------------
+
+LLVM's assemblers allow floating-point constants to be written in C99's
+hexadecimal format instead of decimal if desired.
+
+.. code-block:: gas
+
+ .section .data
+ .float 0x1c2.2ap3
+
+Machine-specific Assembly Syntax
+================================
+
+X86/COFF-Dependent
+------------------
+
+Relocations
+^^^^^^^^^^^
+
+The following additional relocation types are supported:
+
+**@IMGREL** (AT&T syntax only) generates an image-relative relocation that
+corresponds to the COFF relocation types ``IMAGE_REL_I386_DIR32NB`` (32-bit) or
+``IMAGE_REL_AMD64_ADDR32NB`` (64-bit).
+
+.. code-block:: text
+
+ .text
+ fun:
+ mov foo at IMGREL(%ebx, %ecx, 4), %eax
+
+ .section .pdata
+ .long fun at IMGREL
+ .long (fun at imgrel + 0x3F)
+ .long $unwind$fun at imgrel
+
+**.secrel32** generates a relocation that corresponds to the COFF relocation
+types ``IMAGE_REL_I386_SECREL`` (32-bit) or ``IMAGE_REL_AMD64_SECREL`` (64-bit).
+
+**.secidx** relocation generates an index of the section that contains
+the target. It corresponds to the COFF relocation types
+``IMAGE_REL_I386_SECTION`` (32-bit) or ``IMAGE_REL_AMD64_SECTION`` (64-bit).
+
+.. code-block:: none
+
+ .section .debug$S,"rn"
+ .long 4
+ .long 242
+ .long 40
+ .secrel32 _function_name + 0
+ .secidx _function_name
+ ...
+
+``.linkonce`` Directive
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+
+ ``.linkonce [ comdat type ]``
+
+Supported COMDAT types:
+
+``discard``
+ Discards duplicate sections with the same COMDAT symbol. This is the default
+ if no type is specified.
+
+``one_only``
+ If the symbol is defined multiple times, the linker issues an error.
+
+``same_size``
+ Duplicates are discarded, but the linker issues an error if any have
+ different sizes.
+
+``same_contents``
+ Duplicates are discarded, but the linker issues an error if any duplicates
+ do not have exactly the same content.
+
+``largest``
+ Links the largest section from among the duplicates.
+
+``newest``
+ Links the newest section from among the duplicates.
+
+
+.. code-block:: gas
+
+ .section .text$foo
+ .linkonce
+ ...
+
+``.section`` Directive
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+MC supports passing the information in ``.linkonce`` at the end of
+``.section``. For example, these two codes are equivalent
+
+.. code-block:: gas
+
+ .section secName, "dr", discard, "Symbol1"
+ .globl Symbol1
+ Symbol1:
+ .long 1
+
+.. code-block:: gas
+
+ .section secName, "dr"
+ .linkonce discard
+ .globl Symbol1
+ Symbol1:
+ .long 1
+
+Note that in the combined form the COMDAT symbol is explicit. This
+extension exists to support multiple sections with the same name in
+different COMDATs:
+
+
+.. code-block:: gas
+
+ .section secName, "dr", discard, "Symbol1"
+ .globl Symbol1
+ Symbol1:
+ .long 1
+
+ .section secName, "dr", discard, "Symbol2"
+ .globl Symbol2
+ Symbol2:
+ .long 1
+
+In addition to the types allowed with ``.linkonce``, ``.section`` also accepts
+``associative``. The meaning is that the section is linked if a certain other
+COMDAT section is linked. This other section is indicated by the comdat symbol
+in this directive. It can be any symbol defined in the associated section, but
+is usually the associated section's comdat.
+
+ The following restrictions apply to the associated section:
+
+ 1. It must be a COMDAT section.
+ 2. It cannot be another associative COMDAT section.
+
+In the following example the symobl ``sym`` is the comdat symbol of ``.foo``
+and ``.bar`` is associated to ``.foo``.
+
+.. code-block:: gas
+
+ .section .foo,"bw",discard, "sym"
+ .section .bar,"rd",associative, "sym"
+
+MC supports these flags in the COFF ``.section`` directive:
+
+ - ``b``: BSS section (``IMAGE_SCN_CNT_INITIALIZED_DATA``)
+ - ``d``: Data section (``IMAGE_SCN_CNT_UNINITIALIZED_DATA``)
+ - ``n``: Section is not loaded (``IMAGE_SCN_LNK_REMOVE``)
+ - ``r``: Read-only
+ - ``s``: Shared section
+ - ``w``: Writable
+ - ``x``: Executable section
+ - ``y``: Not readable
+ - ``D``: Discardable (``IMAGE_SCN_MEM_DISCARDABLE``)
+
+These flags are all compatible with gas, with the exception of the ``D`` flag,
+which gnu as does not support. For gas compatibility, sections with a name
+starting with ".debug" are implicitly discardable.
+
+
+ELF-Dependent
+-------------
+
+``.section`` Directive
+^^^^^^^^^^^^^^^^^^^^^^
+
+In order to support creating multiple sections with the same name and comdat,
+it is possible to add an unique number at the end of the ``.seciton`` directive.
+For example, the following code creates two sections named ``.text``.
+
+.. code-block:: gas
+
+ .section .text,"ax", at progbits,unique,1
+ nop
+
+ .section .text,"ax", at progbits,unique,2
+ nop
+
+
+The unique number is not present in the resulting object at all. It is just used
+in the assembler to differentiate the sections.
+
+The 'o' flag is mapped to SHF_LINK_ORDER. If it is present, a symbol
+must be given that identifies the section to be placed is the
+.sh_link.
+
+.. code-block:: gas
+
+ .section .foo,"a", at progbits
+ .Ltmp:
+ .section .bar,"ao", at progbits,.Ltmp
+
+which is equivalent to just
+
+.. code-block:: gas
+
+ .section .foo,"a", at progbits
+ .section .bar,"ao", at progbits,.foo
+
+
+Target Specific Behaviour
+=========================
+
+X86
+---
+
+Relocations
+^^^^^^^^^^^
+
+``@ABS8`` can be applied to symbols which appear as immediate operands to
+instructions that have an 8-bit immediate form for that operand. It causes
+the assembler to use the 8-bit form and an 8-bit relocation (e.g. ``R_386_8``
+or ``R_X86_64_8``) for the symbol.
+
+For example:
+
+.. code-block:: gas
+
+ cmpq $foo at ABS8, %rdi
+
+This causes the assembler to select the form of the 64-bit ``cmpq`` instruction
+that takes an 8-bit immediate operand that is sign extended to 64 bits, as
+opposed to ``cmpq $foo, %rdi`` which takes a 32-bit immediate operand. This
+is also not the same as ``cmpb $foo, %dil``, which is an 8-bit comparison.
+
+Windows on ARM
+--------------
+
+Stack Probe Emission
+^^^^^^^^^^^^^^^^^^^^
+
+The reference implementation (Microsoft Visual Studio 2012) emits stack probes
+in the following fashion:
+
+.. code-block:: gas
+
+ movw r4, #constant
+ bl __chkstk
+ sub.w sp, sp, r4
+
+However, this has the limitation of 32 MiB (±16MiB). In order to accommodate
+larger binaries, LLVM supports the use of ``-mcode-model=large`` to allow a 4GiB
+range via a slight deviation. It will generate an indirect jump as follows:
+
+.. code-block:: gas
+
+ movw r4, #constant
+ movw r12, :lower16:__chkstk
+ movt r12, :upper16:__chkstk
+ blx r12
+ sub.w sp, sp, r4
+
+Variable Length Arrays
+^^^^^^^^^^^^^^^^^^^^^^
+
+The reference implementation (Microsoft Visual Studio 2012) does not permit the
+emission of Variable Length Arrays (VLAs).
+
+The Windows ARM Itanium ABI extends the base ABI by adding support for emitting
+a dynamic stack allocation. When emitting a variable stack allocation, a call
+to ``__chkstk`` is emitted unconditionally to ensure that guard pages are setup
+properly. The emission of this stack probe emission is handled similar to the
+standard stack probe emission.
+
+The MSVC environment does not emit code for VLAs currently.
+
Added: www-releases/trunk/5.0.2/docs/_sources/FAQ.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.2/docs/_sources/FAQ.txt?rev=331981&view=auto
==============================================================================
--- www-releases/trunk/5.0.2/docs/_sources/FAQ.txt (added)
+++ www-releases/trunk/5.0.2/docs/_sources/FAQ.txt Thu May 10 06:54:16 2018
@@ -0,0 +1,345 @@
+================================
+Frequently Asked Questions (FAQ)
+================================
+
+.. contents::
+ :local:
+
+
+License
+=======
+
+Does the University of Illinois Open Source License really qualify as an "open source" license?
+-----------------------------------------------------------------------------------------------
+Yes, the license is `certified
+<http://www.opensource.org/licenses/UoI-NCSA.php>`_ by the Open Source
+Initiative (OSI).
+
+
+Can I modify LLVM source code and redistribute the modified source?
+-------------------------------------------------------------------
+Yes. The modified source distribution must retain the copyright notice and
+follow the three bulleted conditions listed in the `LLVM license
+<http://llvm.org/svn/llvm-project/llvm/trunk/LICENSE.TXT>`_.
+
+
+Can I modify the LLVM source code and redistribute binaries or other tools based on it, without redistributing the source?
+--------------------------------------------------------------------------------------------------------------------------
+Yes. This is why we distribute LLVM under a less restrictive license than GPL,
+as explained in the first question above.
+
+
+Source Code
+===========
+
+In what language is LLVM written?
+---------------------------------
+All of the LLVM tools and libraries are written in C++ with extensive use of
+the STL.
+
+
+How portable is the LLVM source code?
+-------------------------------------
+The LLVM source code should be portable to most modern Unix-like operating
+systems. Most of the code is written in standard C++ with operating system
+services abstracted to a support library. The tools required to build and
+test LLVM have been ported to a plethora of platforms.
+
+Some porting problems may exist in the following areas:
+
+* The autoconf/makefile build system relies heavily on UNIX shell tools,
+ like the Bourne Shell and sed. Porting to systems without these tools
+ (MacOS 9, Plan 9) will require more effort.
+
+What API do I use to store a value to one of the virtual registers in LLVM IR's SSA representation?
+---------------------------------------------------------------------------------------------------
+
+In short: you can't. It's actually kind of a silly question once you grok
+what's going on. Basically, in code like:
+
+.. code-block:: llvm
+
+ %result = add i32 %foo, %bar
+
+, ``%result`` is just a name given to the ``Value`` of the ``add``
+instruction. In other words, ``%result`` *is* the add instruction. The
+"assignment" doesn't explicitly "store" anything to any "virtual register";
+the "``=``" is more like the mathematical sense of equality.
+
+Longer explanation: In order to generate a textual representation of the
+IR, some kind of name has to be given to each instruction so that other
+instructions can textually reference it. However, the isomorphic in-memory
+representation that you manipulate from C++ has no such restriction since
+instructions can simply keep pointers to any other ``Value``'s that they
+reference. In fact, the names of dummy numbered temporaries like ``%1`` are
+not explicitly represented in the in-memory representation at all (see
+``Value::getName()``).
+
+
+Source Languages
+================
+
+What source languages are supported?
+------------------------------------
+
+LLVM currently has full support for C and C++ source languages through
+`Clang <http://clang.llvm.org/>`_. Many other language frontends have
+been written using LLVM, and an incomplete list is available at
+`projects with LLVM <http://llvm.org/ProjectsWithLLVM/>`_.
+
+
+I'd like to write a self-hosting LLVM compiler. How should I interface with the LLVM middle-end optimizers and back-end code generators?
+----------------------------------------------------------------------------------------------------------------------------------------
+Your compiler front-end will communicate with LLVM by creating a module in the
+LLVM intermediate representation (IR) format. Assuming you want to write your
+language's compiler in the language itself (rather than C++), there are 3
+major ways to tackle generating LLVM IR from a front-end:
+
+1. **Call into the LLVM libraries code using your language's FFI (foreign
+ function interface).**
+
+ * *for:* best tracks changes to the LLVM IR, .ll syntax, and .bc format
+
+ * *for:* enables running LLVM optimization passes without a emit/parse
+ overhead
+
+ * *for:* adapts well to a JIT context
+
+ * *against:* lots of ugly glue code to write
+
+2. **Emit LLVM assembly from your compiler's native language.**
+
+ * *for:* very straightforward to get started
+
+ * *against:* the .ll parser is slower than the bitcode reader when
+ interfacing to the middle end
+
+ * *against:* it may be harder to track changes to the IR
+
+3. **Emit LLVM bitcode from your compiler's native language.**
+
+ * *for:* can use the more-efficient bitcode reader when interfacing to the
+ middle end
+
+ * *against:* you'll have to re-engineer the LLVM IR object model and bitcode
+ writer in your language
+
+ * *against:* it may be harder to track changes to the IR
+
+If you go with the first option, the C bindings in include/llvm-c should help
+a lot, since most languages have strong support for interfacing with C. The
+most common hurdle with calling C from managed code is interfacing with the
+garbage collector. The C interface was designed to require very little memory
+management, and so is straightforward in this regard.
+
+What support is there for a higher level source language constructs for building a compiler?
+--------------------------------------------------------------------------------------------
+Currently, there isn't much. LLVM supports an intermediate representation
+which is useful for code representation but will not support the high level
+(abstract syntax tree) representation needed by most compilers. There are no
+facilities for lexical nor semantic analysis.
+
+
+I don't understand the ``GetElementPtr`` instruction. Help!
+-----------------------------------------------------------
+See `The Often Misunderstood GEP Instruction <GetElementPtr.html>`_.
+
+
+Using the C and C++ Front Ends
+==============================
+
+Can I compile C or C++ code to platform-independent LLVM bitcode?
+-----------------------------------------------------------------
+No. C and C++ are inherently platform-dependent languages. The most obvious
+example of this is the preprocessor. A very common way that C code is made
+portable is by using the preprocessor to include platform-specific code. In
+practice, information about other platforms is lost after preprocessing, so
+the result is inherently dependent on the platform that the preprocessing was
+targeting.
+
+Another example is ``sizeof``. It's common for ``sizeof(long)`` to vary
+between platforms. In most C front-ends, ``sizeof`` is expanded to a
+constant immediately, thus hard-wiring a platform-specific detail.
+
+Also, since many platforms define their ABIs in terms of C, and since LLVM is
+lower-level than C, front-ends currently must emit platform-specific IR in
+order to have the result conform to the platform ABI.
+
+
+Questions about code generated by the demo page
+===============================================
+
+What is this ``llvm.global_ctors`` and ``_GLOBAL__I_a...`` stuff that happens when I ``#include <iostream>``?
+-------------------------------------------------------------------------------------------------------------
+If you ``#include`` the ``<iostream>`` header into a C++ translation unit,
+the file will probably use the ``std::cin``/``std::cout``/... global objects.
+However, C++ does not guarantee an order of initialization between static
+objects in different translation units, so if a static ctor/dtor in your .cpp
+file used ``std::cout``, for example, the object would not necessarily be
+automatically initialized before your use.
+
+To make ``std::cout`` and friends work correctly in these scenarios, the STL
+that we use declares a static object that gets created in every translation
+unit that includes ``<iostream>``. This object has a static constructor
+and destructor that initializes and destroys the global iostream objects
+before they could possibly be used in the file. The code that you see in the
+``.ll`` file corresponds to the constructor and destructor registration code.
+
+If you would like to make it easier to *understand* the LLVM code generated
+by the compiler in the demo page, consider using ``printf()`` instead of
+``iostream``\s to print values.
+
+
+Where did all of my code go??
+-----------------------------
+If you are using the LLVM demo page, you may often wonder what happened to
+all of the code that you typed in. Remember that the demo script is running
+the code through the LLVM optimizers, so if your code doesn't actually do
+anything useful, it might all be deleted.
+
+To prevent this, make sure that the code is actually needed. For example, if
+you are computing some expression, return the value from the function instead
+of leaving it in a local variable. If you really want to constrain the
+optimizer, you can read from and assign to ``volatile`` global variables.
+
+
+What is this "``undef``" thing that shows up in my code?
+--------------------------------------------------------
+``undef`` is the LLVM way of representing a value that is not defined. You
+can get these if you do not initialize a variable before you use it. For
+example, the C function:
+
+.. code-block:: c
+
+ int X() { int i; return i; }
+
+Is compiled to "``ret i32 undef``" because "``i``" never has a value specified
+for it.
+
+
+Why does instcombine + simplifycfg turn a call to a function with a mismatched calling convention into "unreachable"? Why not make the verifier reject it?
+----------------------------------------------------------------------------------------------------------------------------------------------------------
+This is a common problem run into by authors of front-ends that are using
+custom calling conventions: you need to make sure to set the right calling
+convention on both the function and on each call to the function. For
+example, this code:
+
+.. code-block:: llvm
+
+ define fastcc void @foo() {
+ ret void
+ }
+ define void @bar() {
+ call void @foo()
+ ret void
+ }
+
+Is optimized to:
+
+.. code-block:: llvm
+
+ define fastcc void @foo() {
+ ret void
+ }
+ define void @bar() {
+ unreachable
+ }
+
+... with "``opt -instcombine -simplifycfg``". This often bites people because
+"all their code disappears". Setting the calling convention on the caller and
+callee is required for indirect calls to work, so people often ask why not
+make the verifier reject this sort of thing.
+
+The answer is that this code has undefined behavior, but it is not illegal.
+If we made it illegal, then every transformation that could potentially create
+this would have to ensure that it doesn't, and there is valid code that can
+create this sort of construct (in dead code). The sorts of things that can
+cause this to happen are fairly contrived, but we still need to accept them.
+Here's an example:
+
+.. code-block:: llvm
+
+ define fastcc void @foo() {
+ ret void
+ }
+ define internal void @bar(void()* %FP, i1 %cond) {
+ br i1 %cond, label %T, label %F
+ T:
+ call void %FP()
+ ret void
+ F:
+ call fastcc void %FP()
+ ret void
+ }
+ define void @test() {
+ %X = or i1 false, false
+ call void @bar(void()* @foo, i1 %X)
+ ret void
+ }
+
+In this example, "test" always passes ``@foo``/``false`` into ``bar``, which
+ensures that it is dynamically called with the right calling conv (thus, the
+code is perfectly well defined). If you run this through the inliner, you
+get this (the explicit "or" is there so that the inliner doesn't dead code
+eliminate a bunch of stuff):
+
+.. code-block:: llvm
+
+ define fastcc void @foo() {
+ ret void
+ }
+ define void @test() {
+ %X = or i1 false, false
+ br i1 %X, label %T.i, label %F.i
+ T.i:
+ call void @foo()
+ br label %bar.exit
+ F.i:
+ call fastcc void @foo()
+ br label %bar.exit
+ bar.exit:
+ ret void
+ }
+
+Here you can see that the inlining pass made an undefined call to ``@foo``
+with the wrong calling convention. We really don't want to make the inliner
+have to know about this sort of thing, so it needs to be valid code. In this
+case, dead code elimination can trivially remove the undefined code. However,
+if ``%X`` was an input argument to ``@test``, the inliner would produce this:
+
+.. code-block:: llvm
+
+ define fastcc void @foo() {
+ ret void
+ }
+
+ define void @test(i1 %X) {
+ br i1 %X, label %T.i, label %F.i
+ T.i:
+ call void @foo()
+ br label %bar.exit
+ F.i:
+ call fastcc void @foo()
+ br label %bar.exit
+ bar.exit:
+ ret void
+ }
+
+The interesting thing about this is that ``%X`` *must* be false for the
+code to be well-defined, but no amount of dead code elimination will be able
+to delete the broken call as unreachable. However, since
+``instcombine``/``simplifycfg`` turns the undefined call into unreachable, we
+end up with a branch on a condition that goes to unreachable: a branch to
+unreachable can never happen, so "``-inline -instcombine -simplifycfg``" is
+able to produce:
+
+.. code-block:: llvm
+
+ define fastcc void @foo() {
+ ret void
+ }
+ define void @test(i1 %X) {
+ F.i:
+ call fastcc void @foo()
+ ret void
+ }
Added: www-releases/trunk/5.0.2/docs/_sources/FaultMaps.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.2/docs/_sources/FaultMaps.txt?rev=331981&view=auto
==============================================================================
--- www-releases/trunk/5.0.2/docs/_sources/FaultMaps.txt (added)
+++ www-releases/trunk/5.0.2/docs/_sources/FaultMaps.txt Thu May 10 06:54:16 2018
@@ -0,0 +1,133 @@
+==============================
+FaultMaps and implicit checks
+==============================
+
+.. contents::
+ :local:
+ :depth: 2
+
+Motivation
+==========
+
+Code generated by managed language runtimes tend to have checks that
+are required for safety but never fail in practice. In such cases, it
+is profitable to make the non-failing case cheaper even if it makes
+the failing case significantly more expensive. This asymmetry can be
+exploited by folding such safety checks into operations that can be
+made to fault reliably if the check would have failed, and recovering
+from such a fault by using a signal handler.
+
+For example, Java requires null checks on objects before they are read
+from or written to. If the object is ``null`` then a
+``NullPointerException`` has to be thrown, interrupting normal
+execution. In practice, however, dereferencing a ``null`` pointer is
+extremely rare in well-behaved Java programs, and typically the null
+check can be folded into a nearby memory operation that operates on
+the same memory location.
+
+The Fault Map Section
+=====================
+
+Information about implicit checks generated by LLVM are put in a
+special "fault map" section. On Darwin this section is named
+``__llvm_faultmaps``.
+
+The format of this section is
+
+.. code-block:: none
+
+ Header {
+ uint8 : Fault Map Version (current version is 1)
+ uint8 : Reserved (expected to be 0)
+ uint16 : Reserved (expected to be 0)
+ }
+ uint32 : NumFunctions
+ FunctionInfo[NumFunctions] {
+ uint64 : FunctionAddress
+ uint32 : NumFaultingPCs
+ uint32 : Reserved (expected to be 0)
+ FunctionFaultInfo[NumFaultingPCs] {
+ uint32 : FaultKind
+ uint32 : FaultingPCOffset
+ uint32 : HandlerPCOffset
+ }
+ }
+
+FailtKind describes the reason of expected fault. Currently three kind
+of faults are supported:
+
+ 1. ``FaultMaps::FaultingLoad`` - fault due to load from memory.
+ 2. ``FaultMaps::FaultingLoadStore`` - fault due to instruction load and store.
+ 3. ``FaultMaps::FaultingStore`` - fault due to store to memory.
+
+The ``ImplicitNullChecks`` pass
+===============================
+
+The ``ImplicitNullChecks`` pass transforms explicit control flow for
+checking if a pointer is ``null``, like:
+
+.. code-block:: llvm
+
+ %ptr = call i32* @get_ptr()
+ %ptr_is_null = icmp i32* %ptr, null
+ br i1 %ptr_is_null, label %is_null, label %not_null, !make.implicit !0
+
+ not_null:
+ %t = load i32, i32* %ptr
+ br label %do_something_with_t
+
+ is_null:
+ call void @HFC()
+ unreachable
+
+ !0 = !{}
+
+to control flow implicit in the instruction loading or storing through
+the pointer being null checked:
+
+.. code-block:: llvm
+
+ %ptr = call i32* @get_ptr()
+ %t = load i32, i32* %ptr ;; handler-pc = label %is_null
+ br label %do_something_with_t
+
+ is_null:
+ call void @HFC()
+ unreachable
+
+This transform happens at the ``MachineInstr`` level, not the LLVM IR
+level (so the above example is only representative, not literal). The
+``ImplicitNullChecks`` pass runs during codegen, if
+``-enable-implicit-null-checks`` is passed to ``llc``.
+
+The ``ImplicitNullChecks`` pass adds entries to the
+``__llvm_faultmaps`` section described above as needed.
+
+``make.implicit`` metadata
+--------------------------
+
+Making null checks implicit is an aggressive optimization, and it can
+be a net performance pessimization if too many memory operations end
+up faulting because of it. A language runtime typically needs to
+ensure that only a negligible number of implicit null checks actually
+fault once the application has reached a steady state. A standard way
+of doing this is by healing failed implicit null checks into explicit
+null checks via code patching or recompilation. It follows that there
+are two requirements an explicit null check needs to satisfy for it to
+be profitable to convert it to an implicit null check:
+
+ 1. The case where the pointer is actually null (i.e. the "failing"
+ case) is extremely rare.
+
+ 2. The failing path heals the implicit null check into an explicit
+ null check so that the application does not repeatedly page
+ fault.
+
+The frontend is expected to mark branches that satisfy (1) and (2)
+using a ``!make.implicit`` metadata node (the actual content of the
+metadata node is ignored). Only branches that are marked with
+``!make.implicit`` metadata are considered as candidates for
+conversion into implicit null checks.
+
+(Note that while we could deal with (1) using profiling data, dealing
+with (2) requires some information not present in branch profiles.)
Added: www-releases/trunk/5.0.2/docs/_sources/Frontend/PerformanceTips.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.2/docs/_sources/Frontend/PerformanceTips.txt?rev=331981&view=auto
==============================================================================
--- www-releases/trunk/5.0.2/docs/_sources/Frontend/PerformanceTips.txt (added)
+++ www-releases/trunk/5.0.2/docs/_sources/Frontend/PerformanceTips.txt Thu May 10 06:54:16 2018
@@ -0,0 +1,296 @@
+=====================================
+Performance Tips for Frontend Authors
+=====================================
+
+.. contents::
+ :local:
+ :depth: 2
+
+Abstract
+========
+
+The intended audience of this document is developers of language frontends
+targeting LLVM IR. This document is home to a collection of tips on how to
+generate IR that optimizes well.
+
+IR Best Practices
+=================
+
+As with any optimizer, LLVM has its strengths and weaknesses. In some cases,
+surprisingly small changes in the source IR can have a large effect on the
+generated code.
+
+Beyond the specific items on the list below, it's worth noting that the most
+mature frontend for LLVM is Clang. As a result, the further your IR gets from what Clang might emit, the less likely it is to be effectively optimized. It
+can often be useful to write a quick C program with the semantics you're trying
+to model and see what decisions Clang's IRGen makes about what IR to emit.
+Studying Clang's CodeGen directory can also be a good source of ideas. Note
+that Clang and LLVM are explicitly version locked so you'll need to make sure
+you're using a Clang built from the same svn revision or release as the LLVM
+library you're using. As always, it's *strongly* recommended that you track
+tip of tree development, particularly during bring up of a new project.
+
+The Basics
+^^^^^^^^^^^
+
+#. Make sure that your Modules contain both a data layout specification and
+ target triple. Without these pieces, non of the target specific optimization
+ will be enabled. This can have a major effect on the generated code quality.
+
+#. For each function or global emitted, use the most private linkage type
+ possible (private, internal or linkonce_odr preferably). Doing so will
+ make LLVM's inter-procedural optimizations much more effective.
+
+#. Avoid high in-degree basic blocks (e.g. basic blocks with dozens or hundreds
+ of predecessors). Among other issues, the register allocator is known to
+ perform badly with confronted with such structures. The only exception to
+ this guidance is that a unified return block with high in-degree is fine.
+
+Use of allocas
+^^^^^^^^^^^^^^
+
+An alloca instruction can be used to represent a function scoped stack slot,
+but can also represent dynamic frame expansion. When representing function
+scoped variables or locations, placing alloca instructions at the beginning of
+the entry block should be preferred. In particular, place them before any
+call instructions. Call instructions might get inlined and replaced with
+multiple basic blocks. The end result is that a following alloca instruction
+would no longer be in the entry basic block afterward.
+
+The SROA (Scalar Replacement Of Aggregates) and Mem2Reg passes only attempt
+to eliminate alloca instructions that are in the entry basic block. Given
+SSA is the canonical form expected by much of the optimizer; if allocas can
+not be eliminated by Mem2Reg or SROA, the optimizer is likely to be less
+effective than it could be.
+
+Avoid loads and stores of large aggregate type
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+LLVM currently does not optimize well loads and stores of large :ref:`aggregate
+types <t_aggregate>` (i.e. structs and arrays). As an alternative, consider
+loading individual fields from memory.
+
+Aggregates that are smaller than the largest (performant) load or store
+instruction supported by the targeted hardware are well supported. These can
+be an effective way to represent collections of small packed fields.
+
+Prefer zext over sext when legal
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+On some architectures (X86_64 is one), sign extension can involve an extra
+instruction whereas zero extension can be folded into a load. LLVM will try to
+replace a sext with a zext when it can be proven safe, but if you have
+information in your source language about the range of a integer value, it can
+be profitable to use a zext rather than a sext.
+
+Alternatively, you can :ref:`specify the range of the value using metadata
+<range-metadata>` and LLVM can do the sext to zext conversion for you.
+
+Zext GEP indices to machine register width
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Internally, LLVM often promotes the width of GEP indices to machine register
+width. When it does so, it will default to using sign extension (sext)
+operations for safety. If your source language provides information about
+the range of the index, you may wish to manually extend indices to machine
+register width using a zext instruction.
+
+When to specify alignment
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+LLVM will always generate correct code if you donât specify alignment, but may
+generate inefficient code. For example, if you are targeting MIPS (or older
+ARM ISAs) then the hardware does not handle unaligned loads and stores, and
+so you will enter a trap-and-emulate path if you do a load or store with
+lower-than-natural alignment. To avoid this, LLVM will emit a slower
+sequence of loads, shifts and masks (or load-right + load-left on MIPS) for
+all cases where the load / store does not have a sufficiently high alignment
+in the IR.
+
+The alignment is used to guarantee the alignment on allocas and globals,
+though in most cases this is unnecessary (most targets have a sufficiently
+high default alignment that theyâll be fine). It is also used to provide a
+contract to the back end saying âeither this load/store has this alignment, or
+it is undefined behaviorâ. This means that the back end is free to emit
+instructions that rely on that alignment (and mid-level optimizers are free to
+perform transforms that require that alignment). For x86, it doesnât make
+much difference, as almost all instructions are alignment-independent. For
+MIPS, it can make a big difference.
+
+Note that if your loads and stores are atomic, the backend will be unable to
+lower an under aligned access into a sequence of natively aligned accesses.
+As a result, alignment is mandatory for atomic loads and stores.
+
+Other Things to Consider
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+#. Use ptrtoint/inttoptr sparingly (they interfere with pointer aliasing
+ analysis), prefer GEPs
+
+#. Prefer globals over inttoptr of a constant address - this gives you
+ dereferencability information. In MCJIT, use getSymbolAddress to provide
+ actual address.
+
+#. Be wary of ordered and atomic memory operations. They are hard to optimize
+ and may not be well optimized by the current optimizer. Depending on your
+ source language, you may consider using fences instead.
+
+#. If calling a function which is known to throw an exception (unwind), use
+ an invoke with a normal destination which contains an unreachable
+ instruction. This form conveys to the optimizer that the call returns
+ abnormally. For an invoke which neither returns normally or requires unwind
+ code in the current function, you can use a noreturn call instruction if
+ desired. This is generally not required because the optimizer will convert
+ an invoke with an unreachable unwind destination to a call instruction.
+
+#. Use profile metadata to indicate statically known cold paths, even if
+ dynamic profiling information is not available. This can make a large
+ difference in code placement and thus the performance of tight loops.
+
+#. When generating code for loops, try to avoid terminating the header block of
+ the loop earlier than necessary. If the terminator of the loop header
+ block is a loop exiting conditional branch, the effectiveness of LICM will
+ be limited for loads not in the header. (This is due to the fact that LLVM
+ may not know such a load is safe to speculatively execute and thus can't
+ lift an otherwise loop invariant load unless it can prove the exiting
+ condition is not taken.) It can be profitable, in some cases, to emit such
+ instructions into the header even if they are not used along a rarely
+ executed path that exits the loop. This guidance specifically does not
+ apply if the condition which terminates the loop header is itself invariant,
+ or can be easily discharged by inspecting the loop index variables.
+
+#. In hot loops, consider duplicating instructions from small basic blocks
+ which end in highly predictable terminators into their successor blocks.
+ If a hot successor block contains instructions which can be vectorized
+ with the duplicated ones, this can provide a noticeable throughput
+ improvement. Note that this is not always profitable and does involve a
+ potentially large increase in code size.
+
+#. When checking a value against a constant, emit the check using a consistent
+ comparison type. The GVN pass *will* optimize redundant equalities even if
+ the type of comparison is inverted, but GVN only runs late in the pipeline.
+ As a result, you may miss the opportunity to run other important
+ optimizations. Improvements to EarlyCSE to remove this issue are tracked in
+ Bug 23333.
+
+#. Avoid using arithmetic intrinsics unless you are *required* by your source
+ language specification to emit a particular code sequence. The optimizer
+ is quite good at reasoning about general control flow and arithmetic, it is
+ not anywhere near as strong at reasoning about the various intrinsics. If
+ profitable for code generation purposes, the optimizer will likely form the
+ intrinsics itself late in the optimization pipeline. It is *very* rarely
+ profitable to emit these directly in the language frontend. This item
+ explicitly includes the use of the :ref:`overflow intrinsics <int_overflow>`.
+
+#. Avoid using the :ref:`assume intrinsic <int_assume>` until you've
+ established that a) there's no other way to express the given fact and b)
+ that fact is critical for optimization purposes. Assumes are a great
+ prototyping mechanism, but they can have negative effects on both compile
+ time and optimization effectiveness. The former is fixable with enough
+ effort, but the later is fairly fundamental to their designed purpose.
+
+
+Describing Language Specific Properties
+=======================================
+
+When translating a source language to LLVM, finding ways to express concepts
+and guarantees available in your source language which are not natively
+provided by LLVM IR will greatly improve LLVM's ability to optimize your code.
+As an example, C/C++'s ability to mark every add as "no signed wrap (nsw)" goes
+a long way to assisting the optimizer in reasoning about loop induction
+variables and thus generating more optimal code for loops.
+
+The LLVM LangRef includes a number of mechanisms for annotating the IR with
+additional semantic information. It is *strongly* recommended that you become
+highly familiar with this document. The list below is intended to highlight a
+couple of items of particular interest, but is by no means exhaustive.
+
+Restricted Operation Semantics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+#. Add nsw/nuw flags as appropriate. Reasoning about overflow is
+ generally hard for an optimizer so providing these facts from the frontend
+ can be very impactful.
+
+#. Use fast-math flags on floating point operations if legal. If you don't
+ need strict IEEE floating point semantics, there are a number of additional
+ optimizations that can be performed. This can be highly impactful for
+ floating point intensive computations.
+
+Describing Aliasing Properties
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+#. Add noalias/align/dereferenceable/nonnull to function arguments and return
+ values as appropriate
+
+#. Use pointer aliasing metadata, especially tbaa metadata, to communicate
+ otherwise-non-deducible pointer aliasing facts
+
+#. Use inbounds on geps. This can help to disambiguate some aliasing queries.
+
+
+Modeling Memory Effects
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+#. Mark functions as readnone/readonly/argmemonly or noreturn/nounwind when
+ known. The optimizer will try to infer these flags, but may not always be
+ able to. Manual annotations are particularly important for external
+ functions that the optimizer can not analyze.
+
+#. Use the lifetime.start/lifetime.end and invariant.start/invariant.end
+ intrinsics where possible. Common profitable uses are for stack like data
+ structures (thus allowing dead store elimination) and for describing
+ life times of allocas (thus allowing smaller stack sizes).
+
+#. Mark invariant locations using !invariant.load and TBAA's constant flags
+
+Pass Ordering
+^^^^^^^^^^^^^
+
+One of the most common mistakes made by new language frontend projects is to
+use the existing -O2 or -O3 pass pipelines as is. These pass pipelines make a
+good starting point for an optimizing compiler for any language, but they have
+been carefully tuned for C and C++, not your target language. You will almost
+certainly need to use a custom pass order to achieve optimal performance. A
+couple specific suggestions:
+
+#. For languages with numerous rarely executed guard conditions (e.g. null
+ checks, type checks, range checks) consider adding an extra execution or
+ two of LoopUnswith and LICM to your pass order. The standard pass order,
+ which is tuned for C and C++ applications, may not be sufficient to remove
+ all dischargeable checks from loops.
+
+#. If you language uses range checks, consider using the IRCE pass. It is not
+ currently part of the standard pass order.
+
+#. A useful sanity check to run is to run your optimized IR back through the
+ -O2 pipeline again. If you see noticeable improvement in the resulting IR,
+ you likely need to adjust your pass order.
+
+
+I Still Can't Find What I'm Looking For
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+If you didn't find what you were looking for above, consider proposing an piece
+of metadata which provides the optimization hint you need. Such extensions are
+relatively common and are generally well received by the community. You will
+need to ensure that your proposal is sufficiently general so that it benefits
+others if you wish to contribute it upstream.
+
+You should also consider describing the problem you're facing on `llvm-dev
+<http://lists.llvm.org/mailman/listinfo/llvm-dev>`_ and asking for advice.
+It's entirely possible someone has encountered your problem before and can
+give good advice. If there are multiple interested parties, that also
+increases the chances that a metadata extension would be well received by the
+community as a whole.
+
+Adding to this document
+=======================
+
+If you run across a case that you feel deserves to be covered here, please send
+a patch to `llvm-commits
+<http://lists.llvm.org/mailman/listinfo/llvm-commits>`_ for review.
+
+If you have questions on these items, please direct them to `llvm-dev
+<http://lists.llvm.org/mailman/listinfo/llvm-dev>`_. The more relevant
+context you are able to give to your question, the more likely it is to be
+answered.
+
Added: www-releases/trunk/5.0.2/docs/_sources/GarbageCollection.txt
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==============================================================================
--- www-releases/trunk/5.0.2/docs/_sources/GarbageCollection.txt (added)
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@@ -0,0 +1,1098 @@
+=====================================
+Garbage Collection with LLVM
+=====================================
+
+.. contents::
+ :local:
+
+Abstract
+========
+
+This document covers how to integrate LLVM into a compiler for a language which
+supports garbage collection. **Note that LLVM itself does not provide a
+garbage collector.** You must provide your own.
+
+Quick Start
+============
+
+First, you should pick a collector strategy. LLVM includes a number of built
+in ones, but you can also implement a loadable plugin with a custom definition.
+Note that the collector strategy is a description of how LLVM should generate
+code such that it interacts with your collector and runtime, not a description
+of the collector itself.
+
+Next, mark your generated functions as using your chosen collector strategy.
+From c++, you can call:
+
+.. code-block:: c++
+
+ F.setGC(<collector description name>);
+
+
+This will produce IR like the following fragment:
+
+.. code-block:: llvm
+
+ define void @foo() gc "<collector description name>" { ... }
+
+
+When generating LLVM IR for your functions, you will need to:
+
+* Use ``@llvm.gcread`` and/or ``@llvm.gcwrite`` in place of standard load and
+ store instructions. These intrinsics are used to represent load and store
+ barriers. If you collector does not require such barriers, you can skip
+ this step.
+
+* Use the memory allocation routines provided by your garbage collector's
+ runtime library.
+
+* If your collector requires them, generate type maps according to your
+ runtime's binary interface. LLVM is not involved in the process. In
+ particular, the LLVM type system is not suitable for conveying such
+ information though the compiler.
+
+* Insert any coordination code required for interacting with your collector.
+ Many collectors require running application code to periodically check a
+ flag and conditionally call a runtime function. This is often referred to
+ as a safepoint poll.
+
+You will need to identify roots (i.e. references to heap objects your collector
+needs to know about) in your generated IR, so that LLVM can encode them into
+your final stack maps. Depending on the collector strategy chosen, this is
+accomplished by using either the ``@llvm.gcroot`` intrinsics or an
+``gc.statepoint`` relocation sequence.
+
+Don't forget to create a root for each intermediate value that is generated when
+evaluating an expression. In ``h(f(), g())``, the result of ``f()`` could
+easily be collected if evaluating ``g()`` triggers a collection.
+
+Finally, you need to link your runtime library with the generated program
+executable (for a static compiler) or ensure the appropriate symbols are
+available for the runtime linker (for a JIT compiler).
+
+
+Introduction
+============
+
+What is Garbage Collection?
+---------------------------
+
+Garbage collection is a widely used technique that frees the programmer from
+having to know the lifetimes of heap objects, making software easier to produce
+and maintain. Many programming languages rely on garbage collection for
+automatic memory management. There are two primary forms of garbage collection:
+conservative and accurate.
+
+Conservative garbage collection often does not require any special support from
+either the language or the compiler: it can handle non-type-safe programming
+languages (such as C/C++) and does not require any special information from the
+compiler. The `Boehm collector
+<http://www.hpl.hp.com/personal/Hans_Boehm/gc/>`__ is an example of a
+state-of-the-art conservative collector.
+
+Accurate garbage collection requires the ability to identify all pointers in the
+program at run-time (which requires that the source-language be type-safe in
+most cases). Identifying pointers at run-time requires compiler support to
+locate all places that hold live pointer variables at run-time, including the
+:ref:`processor stack and registers <gcroot>`.
+
+Conservative garbage collection is attractive because it does not require any
+special compiler support, but it does have problems. In particular, because the
+conservative garbage collector cannot *know* that a particular word in the
+machine is a pointer, it cannot move live objects in the heap (preventing the
+use of compacting and generational GC algorithms) and it can occasionally suffer
+from memory leaks due to integer values that happen to point to objects in the
+program. In addition, some aggressive compiler transformations can break
+conservative garbage collectors (though these seem rare in practice).
+
+Accurate garbage collectors do not suffer from any of these problems, but they
+can suffer from degraded scalar optimization of the program. In particular,
+because the runtime must be able to identify and update all pointers active in
+the program, some optimizations are less effective. In practice, however, the
+locality and performance benefits of using aggressive garbage collection
+techniques dominates any low-level losses.
+
+This document describes the mechanisms and interfaces provided by LLVM to
+support accurate garbage collection.
+
+Goals and non-goals
+-------------------
+
+LLVM's intermediate representation provides :ref:`garbage collection intrinsics
+<gc_intrinsics>` that offer support for a broad class of collector models. For
+instance, the intrinsics permit:
+
+* semi-space collectors
+
+* mark-sweep collectors
+
+* generational collectors
+
+* incremental collectors
+
+* concurrent collectors
+
+* cooperative collectors
+
+* reference counting
+
+We hope that the support built into the LLVM IR is sufficient to support a
+broad class of garbage collected languages including Scheme, ML, Java, C#,
+Perl, Python, Lua, Ruby, other scripting languages, and more.
+
+Note that LLVM **does not itself provide a garbage collector** --- this should
+be part of your language's runtime library. LLVM provides a framework for
+describing the garbage collectors requirements to the compiler. In particular,
+LLVM provides support for generating stack maps at call sites, polling for a
+safepoint, and emitting load and store barriers. You can also extend LLVM -
+possibly through a loadable :ref:`code generation plugins <plugin>` - to
+generate code and data structures which conforms to the *binary interface*
+specified by the *runtime library*. This is similar to the relationship between
+LLVM and DWARF debugging info, for example. The difference primarily lies in
+the lack of an established standard in the domain of garbage collection --- thus
+the need for a flexible extension mechanism.
+
+The aspects of the binary interface with which LLVM's GC support is
+concerned are:
+
+* Creation of GC safepoints within code where collection is allowed to execute
+ safely.
+
+* Computation of the stack map. For each safe point in the code, object
+ references within the stack frame must be identified so that the collector may
+ traverse and perhaps update them.
+
+* Write barriers when storing object references to the heap. These are commonly
+ used to optimize incremental scans in generational collectors.
+
+* Emission of read barriers when loading object references. These are useful
+ for interoperating with concurrent collectors.
+
+There are additional areas that LLVM does not directly address:
+
+* Registration of global roots with the runtime.
+
+* Registration of stack map entries with the runtime.
+
+* The functions used by the program to allocate memory, trigger a collection,
+ etc.
+
+* Computation or compilation of type maps, or registration of them with the
+ runtime. These are used to crawl the heap for object references.
+
+In general, LLVM's support for GC does not include features which can be
+adequately addressed with other features of the IR and does not specify a
+particular binary interface. On the plus side, this means that you should be
+able to integrate LLVM with an existing runtime. On the other hand, it can
+have the effect of leaving a lot of work for the developer of a novel
+language. We try to mitigate this by providing built in collector strategy
+descriptions that can work with many common collector designs and easy
+extension points. If you don't already have a specific binary interface
+you need to support, we recommend trying to use one of these built in collector
+strategies.
+
+.. _gc_intrinsics:
+
+LLVM IR Features
+================
+
+This section describes the garbage collection facilities provided by the
+:doc:`LLVM intermediate representation <LangRef>`. The exact behavior of these
+IR features is specified by the selected :ref:`GC strategy description
+<plugin>`.
+
+Specifying GC code generation: ``gc "..."``
+-------------------------------------------
+
+.. code-block:: text
+
+ define <returntype> @name(...) gc "name" { ... }
+
+The ``gc`` function attribute is used to specify the desired GC strategy to the
+compiler. Its programmatic equivalent is the ``setGC`` method of ``Function``.
+
+Setting ``gc "name"`` on a function triggers a search for a matching subclass
+of GCStrategy. Some collector strategies are built in. You can add others
+using either the loadable plugin mechanism, or by patching your copy of LLVM.
+It is the selected GC strategy which defines the exact nature of the code
+generated to support GC. If none is found, the compiler will raise an error.
+
+Specifying the GC style on a per-function basis allows LLVM to link together
+programs that use different garbage collection algorithms (or none at all).
+
+.. _gcroot:
+
+Identifying GC roots on the stack
+----------------------------------
+
+LLVM currently supports two different mechanisms for describing references in
+compiled code at safepoints. ``llvm.gcroot`` is the older mechanism;
+``gc.statepoint`` has been added more recently. At the moment, you can choose
+either implementation (on a per :ref:`GC strategy <plugin>` basis). Longer
+term, we will probably either migrate away from ``llvm.gcroot`` entirely, or
+substantially merge their implementations. Note that most new development
+work is focused on ``gc.statepoint``.
+
+Using ``gc.statepoint``
+^^^^^^^^^^^^^^^^^^^^^^^^
+:doc:`This page <Statepoints>` contains detailed documentation for
+``gc.statepoint``.
+
+Using ``llvm.gcwrite``
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: llvm
+
+ void @llvm.gcroot(i8** %ptrloc, i8* %metadata)
+
+The ``llvm.gcroot`` intrinsic is used to inform LLVM that a stack variable
+references an object on the heap and is to be tracked for garbage collection.
+The exact impact on generated code is specified by the Function's selected
+:ref:`GC strategy <plugin>`. All calls to ``llvm.gcroot`` **must** reside
+inside the first basic block.
+
+The first argument **must** be a value referring to an alloca instruction or a
+bitcast of an alloca. The second contains a pointer to metadata that should be
+associated with the pointer, and **must** be a constant or global value
+address. If your target collector uses tags, use a null pointer for metadata.
+
+A compiler which performs manual SSA construction **must** ensure that SSA
+values representing GC references are stored in to the alloca passed to the
+respective ``gcroot`` before every call site and reloaded after every call.
+A compiler which uses mem2reg to raise imperative code using ``alloca`` into
+SSA form need only add a call to ``@llvm.gcroot`` for those variables which
+are pointers into the GC heap.
+
+It is also important to mark intermediate values with ``llvm.gcroot``. For
+example, consider ``h(f(), g())``. Beware leaking the result of ``f()`` in the
+case that ``g()`` triggers a collection. Note, that stack variables must be
+initialized and marked with ``llvm.gcroot`` in function's prologue.
+
+The ``%metadata`` argument can be used to avoid requiring heap objects to have
+'isa' pointers or tag bits. [Appel89_, Goldberg91_, Tolmach94_] If specified,
+its value will be tracked along with the location of the pointer in the stack
+frame.
+
+Consider the following fragment of Java code:
+
+.. code-block:: java
+
+ {
+ Object X; // A null-initialized reference to an object
+ ...
+ }
+
+This block (which may be located in the middle of a function or in a loop nest),
+could be compiled to this LLVM code:
+
+.. code-block:: llvm
+
+ Entry:
+ ;; In the entry block for the function, allocate the
+ ;; stack space for X, which is an LLVM pointer.
+ %X = alloca %Object*
+
+ ;; Tell LLVM that the stack space is a stack root.
+ ;; Java has type-tags on objects, so we pass null as metadata.
+ %tmp = bitcast %Object** %X to i8**
+ call void @llvm.gcroot(i8** %tmp, i8* null)
+ ...
+
+ ;; "CodeBlock" is the block corresponding to the start
+ ;; of the scope above.
+ CodeBlock:
+ ;; Java null-initializes pointers.
+ store %Object* null, %Object** %X
+
+ ...
+
+ ;; As the pointer goes out of scope, store a null value into
+ ;; it, to indicate that the value is no longer live.
+ store %Object* null, %Object** %X
+ ...
+
+Reading and writing references in the heap
+------------------------------------------
+
+Some collectors need to be informed when the mutator (the program that needs
+garbage collection) either reads a pointer from or writes a pointer to a field
+of a heap object. The code fragments inserted at these points are called *read
+barriers* and *write barriers*, respectively. The amount of code that needs to
+be executed is usually quite small and not on the critical path of any
+computation, so the overall performance impact of the barrier is tolerable.
+
+Barriers often require access to the *object pointer* rather than the *derived
+pointer* (which is a pointer to the field within the object). Accordingly,
+these intrinsics take both pointers as separate arguments for completeness. In
+this snippet, ``%object`` is the object pointer, and ``%derived`` is the derived
+pointer:
+
+.. code-block:: llvm
+
+ ;; An array type.
+ %class.Array = type { %class.Object, i32, [0 x %class.Object*] }
+ ...
+
+ ;; Load the object pointer from a gcroot.
+ %object = load %class.Array** %object_addr
+
+ ;; Compute the derived pointer.
+ %derived = getelementptr %object, i32 0, i32 2, i32 %n
+
+LLVM does not enforce this relationship between the object and derived pointer
+(although a particular :ref:`collector strategy <plugin>` might). However, it
+would be an unusual collector that violated it.
+
+The use of these intrinsics is naturally optional if the target GC does not
+require the corresponding barrier. The GC strategy used with such a collector
+should replace the intrinsic calls with the corresponding ``load`` or
+``store`` instruction if they are used.
+
+One known deficiency with the current design is that the barrier intrinsics do
+not include the size or alignment of the underlying operation performed. It is
+currently assumed that the operation is of pointer size and the alignment is
+assumed to be the target machine's default alignment.
+
+Write barrier: ``llvm.gcwrite``
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: llvm
+
+ void @llvm.gcwrite(i8* %value, i8* %object, i8** %derived)
+
+For write barriers, LLVM provides the ``llvm.gcwrite`` intrinsic function. It
+has exactly the same semantics as a non-volatile ``store`` to the derived
+pointer (the third argument). The exact code generated is specified by the
+Function's selected :ref:`GC strategy <plugin>`.
+
+Many important algorithms require write barriers, including generational and
+concurrent collectors. Additionally, write barriers could be used to implement
+reference counting.
+
+Read barrier: ``llvm.gcread``
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: llvm
+
+ i8* @llvm.gcread(i8* %object, i8** %derived)
+
+For read barriers, LLVM provides the ``llvm.gcread`` intrinsic function. It has
+exactly the same semantics as a non-volatile ``load`` from the derived pointer
+(the second argument). The exact code generated is specified by the Function's
+selected :ref:`GC strategy <plugin>`.
+
+Read barriers are needed by fewer algorithms than write barriers, and may have a
+greater performance impact since pointer reads are more frequent than writes.
+
+.. _plugin:
+
+.. _builtin-gc-strategies:
+
+Built In GC Strategies
+======================
+
+LLVM includes built in support for several varieties of garbage collectors.
+
+The Shadow Stack GC
+----------------------
+
+To use this collector strategy, mark your functions with:
+
+.. code-block:: c++
+
+ F.setGC("shadow-stack");
+
+Unlike many GC algorithms which rely on a cooperative code generator to compile
+stack maps, this algorithm carefully maintains a linked list of stack roots
+[:ref:`Henderson2002 <henderson02>`]. This so-called "shadow stack" mirrors the
+machine stack. Maintaining this data structure is slower than using a stack map
+compiled into the executable as constant data, but has a significant portability
+advantage because it requires no special support from the target code generator,
+and does not require tricky platform-specific code to crawl the machine stack.
+
+The tradeoff for this simplicity and portability is:
+
+* High overhead per function call.
+
+* Not thread-safe.
+
+Still, it's an easy way to get started. After your compiler and runtime are up
+and running, writing a :ref:`plugin <plugin>` will allow you to take advantage
+of :ref:`more advanced GC features <collector-algos>` of LLVM in order to
+improve performance.
+
+
+The shadow stack doesn't imply a memory allocation algorithm. A semispace
+collector or building atop ``malloc`` are great places to start, and can be
+implemented with very little code.
+
+When it comes time to collect, however, your runtime needs to traverse the stack
+roots, and for this it needs to integrate with the shadow stack. Luckily, doing
+so is very simple. (This code is heavily commented to help you understand the
+data structure, but there are only 20 lines of meaningful code.)
+
+.. code-block:: c++
+
+ /// @brief The map for a single function's stack frame. One of these is
+ /// compiled as constant data into the executable for each function.
+ ///
+ /// Storage of metadata values is elided if the %metadata parameter to
+ /// @llvm.gcroot is null.
+ struct FrameMap {
+ int32_t NumRoots; //< Number of roots in stack frame.
+ int32_t NumMeta; //< Number of metadata entries. May be < NumRoots.
+ const void *Meta[0]; //< Metadata for each root.
+ };
+
+ /// @brief A link in the dynamic shadow stack. One of these is embedded in
+ /// the stack frame of each function on the call stack.
+ struct StackEntry {
+ StackEntry *Next; //< Link to next stack entry (the caller's).
+ const FrameMap *Map; //< Pointer to constant FrameMap.
+ void *Roots[0]; //< Stack roots (in-place array).
+ };
+
+ /// @brief The head of the singly-linked list of StackEntries. Functions push
+ /// and pop onto this in their prologue and epilogue.
+ ///
+ /// Since there is only a global list, this technique is not threadsafe.
+ StackEntry *llvm_gc_root_chain;
+
+ /// @brief Calls Visitor(root, meta) for each GC root on the stack.
+ /// root and meta are exactly the values passed to
+ /// @llvm.gcroot.
+ ///
+ /// Visitor could be a function to recursively mark live objects. Or it
+ /// might copy them to another heap or generation.
+ ///
+ /// @param Visitor A function to invoke for every GC root on the stack.
+ void visitGCRoots(void (*Visitor)(void **Root, const void *Meta)) {
+ for (StackEntry *R = llvm_gc_root_chain; R; R = R->Next) {
+ unsigned i = 0;
+
+ // For roots [0, NumMeta), the metadata pointer is in the FrameMap.
+ for (unsigned e = R->Map->NumMeta; i != e; ++i)
+ Visitor(&R->Roots[i], R->Map->Meta[i]);
+
+ // For roots [NumMeta, NumRoots), the metadata pointer is null.
+ for (unsigned e = R->Map->NumRoots; i != e; ++i)
+ Visitor(&R->Roots[i], NULL);
+ }
+ }
+
+
+The 'Erlang' and 'Ocaml' GCs
+-----------------------------
+
+LLVM ships with two example collectors which leverage the ``gcroot``
+mechanisms. To our knowledge, these are not actually used by any language
+runtime, but they do provide a reasonable starting point for someone interested
+in writing an ``gcroot`` compatible GC plugin. In particular, these are the
+only in tree examples of how to produce a custom binary stack map format using
+a ``gcroot`` strategy.
+
+As there names imply, the binary format produced is intended to model that
+used by the Erlang and OCaml compilers respectively.
+
+.. _statepoint_example_gc:
+
+The Statepoint Example GC
+-------------------------
+
+.. code-block:: c++
+
+ F.setGC("statepoint-example");
+
+This GC provides an example of how one might use the infrastructure provided
+by ``gc.statepoint``. This example GC is compatible with the
+:ref:`PlaceSafepoints` and :ref:`RewriteStatepointsForGC` utility passes
+which simplify ``gc.statepoint`` sequence insertion. If you need to build a
+custom GC strategy around the ``gc.statepoints`` mechanisms, it is recommended
+that you use this one as a starting point.
+
+This GC strategy does not support read or write barriers. As a result, these
+intrinsics are lowered to normal loads and stores.
+
+The stack map format generated by this GC strategy can be found in the
+:ref:`stackmap-section` using a format documented :ref:`here
+<statepoint-stackmap-format>`. This format is intended to be the standard
+format supported by LLVM going forward.
+
+The CoreCLR GC
+-------------------------
+
+.. code-block:: c++
+
+ F.setGC("coreclr");
+
+This GC leverages the ``gc.statepoint`` mechanism to support the
+`CoreCLR <https://github.com/dotnet/coreclr>`__ runtime.
+
+Support for this GC strategy is a work in progress. This strategy will
+differ from
+:ref:`statepoint-example GC<statepoint_example_gc>` strategy in
+certain aspects like:
+
+* Base-pointers of interior pointers are not explicitly
+ tracked and reported.
+
+* A different format is used for encoding stack maps.
+
+* Safe-point polls are only needed before loop-back edges
+ and before tail-calls (not needed at function-entry).
+
+Custom GC Strategies
+====================
+
+If none of the built in GC strategy descriptions met your needs above, you will
+need to define a custom GCStrategy and possibly, a custom LLVM pass to perform
+lowering. Your best example of where to start defining a custom GCStrategy
+would be to look at one of the built in strategies.
+
+You may be able to structure this additional code as a loadable plugin library.
+Loadable plugins are sufficient if all you need is to enable a different
+combination of built in functionality, but if you need to provide a custom
+lowering pass, you will need to build a patched version of LLVM. If you think
+you need a patched build, please ask for advice on llvm-dev. There may be an
+easy way we can extend the support to make it work for your use case without
+requiring a custom build.
+
+Collector Requirements
+----------------------
+
+You should be able to leverage any existing collector library that includes the following elements:
+
+#. A memory allocator which exposes an allocation function your compiled
+ code can call.
+
+#. A binary format for the stack map. A stack map describes the location
+ of references at a safepoint and is used by precise collectors to identify
+ references within a stack frame on the machine stack. Note that collectors
+ which conservatively scan the stack don't require such a structure.
+
+#. A stack crawler to discover functions on the call stack, and enumerate the
+ references listed in the stack map for each call site.
+
+#. A mechanism for identifying references in global locations (e.g. global
+ variables).
+
+#. If you collector requires them, an LLVM IR implementation of your collectors
+ load and store barriers. Note that since many collectors don't require
+ barriers at all, LLVM defaults to lowering such barriers to normal loads
+ and stores unless you arrange otherwise.
+
+
+Implementing a collector plugin
+-------------------------------
+
+User code specifies which GC code generation to use with the ``gc`` function
+attribute or, equivalently, with the ``setGC`` method of ``Function``.
+
+To implement a GC plugin, it is necessary to subclass ``llvm::GCStrategy``,
+which can be accomplished in a few lines of boilerplate code. LLVM's
+infrastructure provides access to several important algorithms. For an
+uncontroversial collector, all that remains may be to compile LLVM's computed
+stack map to assembly code (using the binary representation expected by the
+runtime library). This can be accomplished in about 100 lines of code.
+
+This is not the appropriate place to implement a garbage collected heap or a
+garbage collector itself. That code should exist in the language's runtime
+library. The compiler plugin is responsible for generating code which conforms
+to the binary interface defined by library, most essentially the :ref:`stack map
+<stack-map>`.
+
+To subclass ``llvm::GCStrategy`` and register it with the compiler:
+
+.. code-block:: c++
+
+ // lib/MyGC/MyGC.cpp - Example LLVM GC plugin
+
+ #include "llvm/CodeGen/GCStrategy.h"
+ #include "llvm/CodeGen/GCMetadata.h"
+ #include "llvm/Support/Compiler.h"
+
+ using namespace llvm;
+
+ namespace {
+ class LLVM_LIBRARY_VISIBILITY MyGC : public GCStrategy {
+ public:
+ MyGC() {}
+ };
+
+ GCRegistry::Add<MyGC>
+ X("mygc", "My bespoke garbage collector.");
+ }
+
+This boilerplate collector does nothing. More specifically:
+
+* ``llvm.gcread`` calls are replaced with the corresponding ``load``
+ instruction.
+
+* ``llvm.gcwrite`` calls are replaced with the corresponding ``store``
+ instruction.
+
+* No safe points are added to the code.
+
+* The stack map is not compiled into the executable.
+
+Using the LLVM makefiles, this code
+can be compiled as a plugin using a simple makefile:
+
+.. code-block:: make
+
+ # lib/MyGC/Makefile
+
+ LEVEL := ../..
+ LIBRARYNAME = MyGC
+ LOADABLE_MODULE = 1
+
+ include $(LEVEL)/Makefile.common
+
+Once the plugin is compiled, code using it may be compiled using ``llc
+-load=MyGC.so`` (though MyGC.so may have some other platform-specific
+extension):
+
+::
+
+ $ cat sample.ll
+ define void @f() gc "mygc" {
+ entry:
+ ret void
+ }
+ $ llvm-as < sample.ll | llc -load=MyGC.so
+
+It is also possible to statically link the collector plugin into tools, such as
+a language-specific compiler front-end.
+
+.. _collector-algos:
+
+Overview of available features
+------------------------------
+
+``GCStrategy`` provides a range of features through which a plugin may do useful
+work. Some of these are callbacks, some are algorithms that can be enabled,
+disabled, or customized. This matrix summarizes the supported (and planned)
+features and correlates them with the collection techniques which typically
+require them.
+
+.. |v| unicode:: 0x2714
+ :trim:
+
+.. |x| unicode:: 0x2718
+ :trim:
+
++------------+------+--------+----------+-------+---------+-------------+----------+------------+
+| Algorithm | Done | Shadow | refcount | mark- | copying | incremental | threaded | concurrent |
+| | | stack | | sweep | | | | |
++============+======+========+==========+=======+=========+=============+==========+============+
+| stack map | |v| | | | |x| | |x| | |x| | |x| | |x| |
++------------+------+--------+----------+-------+---------+-------------+----------+------------+
+| initialize | |v| | |x| | |x| | |x| | |x| | |x| | |x| | |x| |
+| roots | | | | | | | | |
++------------+------+--------+----------+-------+---------+-------------+----------+------------+
+| derived | NO | | | | | | **N**\* | **N**\* |
+| pointers | | | | | | | | |
++------------+------+--------+----------+-------+---------+-------------+----------+------------+
+| **custom | |v| | | | | | | | |
+| lowering** | | | | | | | | |
++------------+------+--------+----------+-------+---------+-------------+----------+------------+
+| *gcroot* | |v| | |x| | |x| | | | | | |
++------------+------+--------+----------+-------+---------+-------------+----------+------------+
+| *gcwrite* | |v| | | |x| | | | |x| | | |x| |
++------------+------+--------+----------+-------+---------+-------------+----------+------------+
+| *gcread* | |v| | | | | | | | |x| |
++------------+------+--------+----------+-------+---------+-------------+----------+------------+
+| **safe | | | | | | | | |
+| points** | | | | | | | | |
++------------+------+--------+----------+-------+---------+-------------+----------+------------+
+| *in | |v| | | | |x| | |x| | |x| | |x| | |x| |
+| calls* | | | | | | | | |
++------------+------+--------+----------+-------+---------+-------------+----------+------------+
+| *before | |v| | | | | | | |x| | |x| |
+| calls* | | | | | | | | |
++------------+------+--------+----------+-------+---------+-------------+----------+------------+
+| *for | NO | | | | | | **N** | **N** |
+| loops* | | | | | | | | |
++------------+------+--------+----------+-------+---------+-------------+----------+------------+
+| *before | |v| | | | | | | |x| | |x| |
+| escape* | | | | | | | | |
++------------+------+--------+----------+-------+---------+-------------+----------+------------+
+| emit code | NO | | | | | | **N** | **N** |
+| at safe | | | | | | | | |
+| points | | | | | | | | |
++------------+------+--------+----------+-------+---------+-------------+----------+------------+
+| **output** | | | | | | | | |
++------------+------+--------+----------+-------+---------+-------------+----------+------------+
+| *assembly* | |v| | | | |x| | |x| | |x| | |x| | |x| |
++------------+------+--------+----------+-------+---------+-------------+----------+------------+
+| *JIT* | NO | | | **?** | **?** | **?** | **?** | **?** |
++------------+------+--------+----------+-------+---------+-------------+----------+------------+
+| *obj* | NO | | | **?** | **?** | **?** | **?** | **?** |
++------------+------+--------+----------+-------+---------+-------------+----------+------------+
+| live | NO | | | **?** | **?** | **?** | **?** | **?** |
+| analysis | | | | | | | | |
++------------+------+--------+----------+-------+---------+-------------+----------+------------+
+| register | NO | | | **?** | **?** | **?** | **?** | **?** |
+| map | | | | | | | | |
++------------+------+--------+----------+-------+---------+-------------+----------+------------+
+| \* Derived pointers only pose a hasard to copying collections. |
++------------+------+--------+----------+-------+---------+-------------+----------+------------+
+| **?** denotes a feature which could be utilized if available. |
++------------+------+--------+----------+-------+---------+-------------+----------+------------+
+
+To be clear, the collection techniques above are defined as:
+
+Shadow Stack
+ The mutator carefully maintains a linked list of stack roots.
+
+Reference Counting
+ The mutator maintains a reference count for each object and frees an object
+ when its count falls to zero.
+
+Mark-Sweep
+ When the heap is exhausted, the collector marks reachable objects starting
+ from the roots, then deallocates unreachable objects in a sweep phase.
+
+Copying
+ As reachability analysis proceeds, the collector copies objects from one heap
+ area to another, compacting them in the process. Copying collectors enable
+ highly efficient "bump pointer" allocation and can improve locality of
+ reference.
+
+Incremental
+ (Including generational collectors.) Incremental collectors generally have all
+ the properties of a copying collector (regardless of whether the mature heap
+ is compacting), but bring the added complexity of requiring write barriers.
+
+Threaded
+ Denotes a multithreaded mutator; the collector must still stop the mutator
+ ("stop the world") before beginning reachability analysis. Stopping a
+ multithreaded mutator is a complicated problem. It generally requires highly
+ platform-specific code in the runtime, and the production of carefully
+ designed machine code at safe points.
+
+Concurrent
+ In this technique, the mutator and the collector run concurrently, with the
+ goal of eliminating pause times. In a *cooperative* collector, the mutator
+ further aids with collection should a pause occur, allowing collection to take
+ advantage of multiprocessor hosts. The "stop the world" problem of threaded
+ collectors is generally still present to a limited extent. Sophisticated
+ marking algorithms are necessary. Read barriers may be necessary.
+
+As the matrix indicates, LLVM's garbage collection infrastructure is already
+suitable for a wide variety of collectors, but does not currently extend to
+multithreaded programs. This will be added in the future as there is
+interest.
+
+.. _stack-map:
+
+Computing stack maps
+--------------------
+
+LLVM automatically computes a stack map. One of the most important features
+of a ``GCStrategy`` is to compile this information into the executable in
+the binary representation expected by the runtime library.
+
+The stack map consists of the location and identity of each GC root in the
+each function in the module. For each root:
+
+* ``RootNum``: The index of the root.
+
+* ``StackOffset``: The offset of the object relative to the frame pointer.
+
+* ``RootMetadata``: The value passed as the ``%metadata`` parameter to the
+ ``@llvm.gcroot`` intrinsic.
+
+Also, for the function as a whole:
+
+* ``getFrameSize()``: The overall size of the function's initial stack frame,
+ not accounting for any dynamic allocation.
+
+* ``roots_size()``: The count of roots in the function.
+
+To access the stack map, use ``GCFunctionMetadata::roots_begin()`` and
+-``end()`` from the :ref:`GCMetadataPrinter <assembly>`:
+
+.. code-block:: c++
+
+ for (iterator I = begin(), E = end(); I != E; ++I) {
+ GCFunctionInfo *FI = *I;
+ unsigned FrameSize = FI->getFrameSize();
+ size_t RootCount = FI->roots_size();
+
+ for (GCFunctionInfo::roots_iterator RI = FI->roots_begin(),
+ RE = FI->roots_end();
+ RI != RE; ++RI) {
+ int RootNum = RI->Num;
+ int RootStackOffset = RI->StackOffset;
+ Constant *RootMetadata = RI->Metadata;
+ }
+ }
+
+If the ``llvm.gcroot`` intrinsic is eliminated before code generation by a
+custom lowering pass, LLVM will compute an empty stack map. This may be useful
+for collector plugins which implement reference counting or a shadow stack.
+
+.. _init-roots:
+
+Initializing roots to null: ``InitRoots``
+-----------------------------------------
+
+.. code-block:: c++
+
+ MyGC::MyGC() {
+ InitRoots = true;
+ }
+
+When set, LLVM will automatically initialize each root to ``null`` upon entry to
+the function. This prevents the GC's sweep phase from visiting uninitialized
+pointers, which will almost certainly cause it to crash. This initialization
+occurs before custom lowering, so the two may be used together.
+
+Since LLVM does not yet compute liveness information, there is no means of
+distinguishing an uninitialized stack root from an initialized one. Therefore,
+this feature should be used by all GC plugins. It is enabled by default.
+
+Custom lowering of intrinsics: ``CustomRoots``, ``CustomReadBarriers``, and ``CustomWriteBarriers``
+---------------------------------------------------------------------------------------------------
+
+For GCs which use barriers or unusual treatment of stack roots, these
+flags allow the collector to perform arbitrary transformations of the
+LLVM IR:
+
+.. code-block:: c++
+
+ class MyGC : public GCStrategy {
+ public:
+ MyGC() {
+ CustomRoots = true;
+ CustomReadBarriers = true;
+ CustomWriteBarriers = true;
+ }
+ };
+
+If any of these flags are set, LLVM suppresses its default lowering for
+the corresponding intrinsics. Instead, you must provide a custom Pass
+which lowers the intrinsics as desired. If you have opted in to custom
+lowering of a particular intrinsic your pass **must** eliminate all
+instances of the corresponding intrinsic in functions which opt in to
+your GC. The best example of such a pass is the ShadowStackGC and it's
+ShadowStackGCLowering pass.
+
+There is currently no way to register such a custom lowering pass
+without building a custom copy of LLVM.
+
+.. _safe-points:
+
+Generating safe points: ``NeededSafePoints``
+--------------------------------------------
+
+LLVM can compute four kinds of safe points:
+
+.. code-block:: c++
+
+ namespace GC {
+ /// PointKind - The type of a collector-safe point.
+ ///
+ enum PointKind {
+ Loop, //< Instr is a loop (backwards branch).
+ Return, //< Instr is a return instruction.
+ PreCall, //< Instr is a call instruction.
+ PostCall //< Instr is the return address of a call.
+ };
+ }
+
+A collector can request any combination of the four by setting the
+``NeededSafePoints`` mask:
+
+.. code-block:: c++
+
+ MyGC::MyGC() {
+ NeededSafePoints = 1 << GC::Loop
+ | 1 << GC::Return
+ | 1 << GC::PreCall
+ | 1 << GC::PostCall;
+ }
+
+It can then use the following routines to access safe points.
+
+.. code-block:: c++
+
+ for (iterator I = begin(), E = end(); I != E; ++I) {
+ GCFunctionInfo *MD = *I;
+ size_t PointCount = MD->size();
+
+ for (GCFunctionInfo::iterator PI = MD->begin(),
+ PE = MD->end(); PI != PE; ++PI) {
+ GC::PointKind PointKind = PI->Kind;
+ unsigned PointNum = PI->Num;
+ }
+ }
+
+Almost every collector requires ``PostCall`` safe points, since these correspond
+to the moments when the function is suspended during a call to a subroutine.
+
+Threaded programs generally require ``Loop`` safe points to guarantee that the
+application will reach a safe point within a bounded amount of time, even if it
+is executing a long-running loop which contains no function calls.
+
+Threaded collectors may also require ``Return`` and ``PreCall`` safe points to
+implement "stop the world" techniques using self-modifying code, where it is
+important that the program not exit the function without reaching a safe point
+(because only the topmost function has been patched).
+
+.. _assembly:
+
+Emitting assembly code: ``GCMetadataPrinter``
+---------------------------------------------
+
+LLVM allows a plugin to print arbitrary assembly code before and after the rest
+of a module's assembly code. At the end of the module, the GC can compile the
+LLVM stack map into assembly code. (At the beginning, this information is not
+yet computed.)
+
+Since AsmWriter and CodeGen are separate components of LLVM, a separate abstract
+base class and registry is provided for printing assembly code, the
+``GCMetadaPrinter`` and ``GCMetadataPrinterRegistry``. The AsmWriter will look
+for such a subclass if the ``GCStrategy`` sets ``UsesMetadata``:
+
+.. code-block:: c++
+
+ MyGC::MyGC() {
+ UsesMetadata = true;
+ }
+
+This separation allows JIT-only clients to be smaller.
+
+Note that LLVM does not currently have analogous APIs to support code generation
+in the JIT, nor using the object writers.
+
+.. code-block:: c++
+
+ // lib/MyGC/MyGCPrinter.cpp - Example LLVM GC printer
+
+ #include "llvm/CodeGen/GCMetadataPrinter.h"
+ #include "llvm/Support/Compiler.h"
+
+ using namespace llvm;
+
+ namespace {
+ class LLVM_LIBRARY_VISIBILITY MyGCPrinter : public GCMetadataPrinter {
+ public:
+ virtual void beginAssembly(AsmPrinter &AP);
+
+ virtual void finishAssembly(AsmPrinter &AP);
+ };
+
+ GCMetadataPrinterRegistry::Add<MyGCPrinter>
+ X("mygc", "My bespoke garbage collector.");
+ }
+
+The collector should use ``AsmPrinter`` to print portable assembly code. The
+collector itself contains the stack map for the entire module, and may access
+the ``GCFunctionInfo`` using its own ``begin()`` and ``end()`` methods. Here's
+a realistic example:
+
+.. code-block:: c++
+
+ #include "llvm/CodeGen/AsmPrinter.h"
+ #include "llvm/IR/Function.h"
+ #include "llvm/IR/DataLayout.h"
+ #include "llvm/Target/TargetAsmInfo.h"
+ #include "llvm/Target/TargetMachine.h"
+
+ void MyGCPrinter::beginAssembly(AsmPrinter &AP) {
+ // Nothing to do.
+ }
+
+ void MyGCPrinter::finishAssembly(AsmPrinter &AP) {
+ MCStreamer &OS = AP.OutStreamer;
+ unsigned IntPtrSize = AP.getPointerSize();
+
+ // Put this in the data section.
+ OS.SwitchSection(AP.getObjFileLowering().getDataSection());
+
+ // For each function...
+ for (iterator FI = begin(), FE = end(); FI != FE; ++FI) {
+ GCFunctionInfo &MD = **FI;
+
+ // A compact GC layout. Emit this data structure:
+ //
+ // struct {
+ // int32_t PointCount;
+ // void *SafePointAddress[PointCount];
+ // int32_t StackFrameSize; // in words
+ // int32_t StackArity;
+ // int32_t LiveCount;
+ // int32_t LiveOffsets[LiveCount];
+ // } __gcmap_<FUNCTIONNAME>;
+
+ // Align to address width.
+ AP.EmitAlignment(IntPtrSize == 4 ? 2 : 3);
+
+ // Emit PointCount.
+ OS.AddComment("safe point count");
+ AP.EmitInt32(MD.size());
+
+ // And each safe point...
+ for (GCFunctionInfo::iterator PI = MD.begin(),
+ PE = MD.end(); PI != PE; ++PI) {
+ // Emit the address of the safe point.
+ OS.AddComment("safe point address");
+ MCSymbol *Label = PI->Label;
+ AP.EmitLabelPlusOffset(Label/*Hi*/, 0/*Offset*/, 4/*Size*/);
+ }
+
+ // Stack information never change in safe points! Only print info from the
+ // first call-site.
+ GCFunctionInfo::iterator PI = MD.begin();
+
+ // Emit the stack frame size.
+ OS.AddComment("stack frame size (in words)");
+ AP.EmitInt32(MD.getFrameSize() / IntPtrSize);
+
+ // Emit stack arity, i.e. the number of stacked arguments.
+ unsigned RegisteredArgs = IntPtrSize == 4 ? 5 : 6;
+ unsigned StackArity = MD.getFunction().arg_size() > RegisteredArgs ?
+ MD.getFunction().arg_size() - RegisteredArgs : 0;
+ OS.AddComment("stack arity");
+ AP.EmitInt32(StackArity);
+
+ // Emit the number of live roots in the function.
+ OS.AddComment("live root count");
+ AP.EmitInt32(MD.live_size(PI));
+
+ // And for each live root...
+ for (GCFunctionInfo::live_iterator LI = MD.live_begin(PI),
+ LE = MD.live_end(PI);
+ LI != LE; ++LI) {
+ // Emit live root's offset within the stack frame.
+ OS.AddComment("stack index (offset / wordsize)");
+ AP.EmitInt32(LI->StackOffset);
+ }
+ }
+ }
+
+References
+==========
+
+.. _appel89:
+
+[Appel89] Runtime Tags Aren't Necessary. Andrew W. Appel. Lisp and Symbolic
+Computation 19(7):703-705, July 1989.
+
+.. _goldberg91:
+
+[Goldberg91] Tag-free garbage collection for strongly typed programming
+languages. Benjamin Goldberg. ACM SIGPLAN PLDI'91.
+
+.. _tolmach94:
+
+[Tolmach94] Tag-free garbage collection using explicit type parameters. Andrew
+Tolmach. Proceedings of the 1994 ACM conference on LISP and functional
+programming.
+
+.. _henderson02:
+
+[Henderson2002] `Accurate Garbage Collection in an Uncooperative Environment
+<http://citeseer.ist.psu.edu/henderson02accurate.html>`__
Added: www-releases/trunk/5.0.2/docs/_sources/GetElementPtr.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.2/docs/_sources/GetElementPtr.txt?rev=331981&view=auto
==============================================================================
--- www-releases/trunk/5.0.2/docs/_sources/GetElementPtr.txt (added)
+++ www-releases/trunk/5.0.2/docs/_sources/GetElementPtr.txt Thu May 10 06:54:16 2018
@@ -0,0 +1,538 @@
+=======================================
+The Often Misunderstood GEP Instruction
+=======================================
+
+.. contents::
+ :local:
+
+Introduction
+============
+
+This document seeks to dispel the mystery and confusion surrounding LLVM's
+`GetElementPtr <LangRef.html#getelementptr-instruction>`_ (GEP) instruction.
+Questions about the wily GEP instruction are probably the most frequently
+occurring questions once a developer gets down to coding with LLVM. Here we lay
+out the sources of confusion and show that the GEP instruction is really quite
+simple.
+
+Address Computation
+===================
+
+When people are first confronted with the GEP instruction, they tend to relate
+it to known concepts from other programming paradigms, most notably C array
+indexing and field selection. GEP closely resembles C array indexing and field
+selection, however it is a little different and this leads to the following
+questions.
+
+What is the first index of the GEP instruction?
+-----------------------------------------------
+
+Quick answer: The index stepping through the second operand.
+
+The confusion with the first index usually arises from thinking about the
+GetElementPtr instruction as if it was a C index operator. They aren't the
+same. For example, when we write, in "C":
+
+.. code-block:: c++
+
+ AType *Foo;
+ ...
+ X = &Foo->F;
+
+it is natural to think that there is only one index, the selection of the field
+``F``. However, in this example, ``Foo`` is a pointer. That pointer
+must be indexed explicitly in LLVM. C, on the other hand, indices through it
+transparently. To arrive at the same address location as the C code, you would
+provide the GEP instruction with two index operands. The first operand indexes
+through the pointer; the second operand indexes the field ``F`` of the
+structure, just as if you wrote:
+
+.. code-block:: c++
+
+ X = &Foo[0].F;
+
+Sometimes this question gets rephrased as:
+
+.. _GEP index through first pointer:
+
+ *Why is it okay to index through the first pointer, but subsequent pointers
+ won't be dereferenced?*
+
+The answer is simply because memory does not have to be accessed to perform the
+computation. The second operand to the GEP instruction must be a value of a
+pointer type. The value of the pointer is provided directly to the GEP
+instruction as an operand without any need for accessing memory. It must,
+therefore be indexed and requires an index operand. Consider this example:
+
+.. code-block:: c++
+
+ struct munger_struct {
+ int f1;
+ int f2;
+ };
+ void munge(struct munger_struct *P) {
+ P[0].f1 = P[1].f1 + P[2].f2;
+ }
+ ...
+ munger_struct Array[3];
+ ...
+ munge(Array);
+
+In this "C" example, the front end compiler (Clang) will generate three GEP
+instructions for the three indices through "P" in the assignment statement. The
+function argument ``P`` will be the second operand of each of these GEP
+instructions. The third operand indexes through that pointer. The fourth
+operand will be the field offset into the ``struct munger_struct`` type, for
+either the ``f1`` or ``f2`` field. So, in LLVM assembly the ``munge`` function
+looks like:
+
+.. code-block:: llvm
+
+ void %munge(%struct.munger_struct* %P) {
+ entry:
+ %tmp = getelementptr %struct.munger_struct, %struct.munger_struct* %P, i32 1, i32 0
+ %tmp = load i32* %tmp
+ %tmp6 = getelementptr %struct.munger_struct, %struct.munger_struct* %P, i32 2, i32 1
+ %tmp7 = load i32* %tmp6
+ %tmp8 = add i32 %tmp7, %tmp
+ %tmp9 = getelementptr %struct.munger_struct, %struct.munger_struct* %P, i32 0, i32 0
+ store i32 %tmp8, i32* %tmp9
+ ret void
+ }
+
+In each case the second operand is the pointer through which the GEP instruction
+starts. The same is true whether the second operand is an argument, allocated
+memory, or a global variable.
+
+To make this clear, let's consider a more obtuse example:
+
+.. code-block:: text
+
+ %MyVar = uninitialized global i32
+ ...
+ %idx1 = getelementptr i32, i32* %MyVar, i64 0
+ %idx2 = getelementptr i32, i32* %MyVar, i64 1
+ %idx3 = getelementptr i32, i32* %MyVar, i64 2
+
+These GEP instructions are simply making address computations from the base
+address of ``MyVar``. They compute, as follows (using C syntax):
+
+.. code-block:: c++
+
+ idx1 = (char*) &MyVar + 0
+ idx2 = (char*) &MyVar + 4
+ idx3 = (char*) &MyVar + 8
+
+Since the type ``i32`` is known to be four bytes long, the indices 0, 1 and 2
+translate into memory offsets of 0, 4, and 8, respectively. No memory is
+accessed to make these computations because the address of ``%MyVar`` is passed
+directly to the GEP instructions.
+
+The obtuse part of this example is in the cases of ``%idx2`` and ``%idx3``. They
+result in the computation of addresses that point to memory past the end of the
+``%MyVar`` global, which is only one ``i32`` long, not three ``i32``\s long.
+While this is legal in LLVM, it is inadvisable because any load or store with
+the pointer that results from these GEP instructions would produce undefined
+results.
+
+Why is the extra 0 index required?
+----------------------------------
+
+Quick answer: there are no superfluous indices.
+
+This question arises most often when the GEP instruction is applied to a global
+variable which is always a pointer type. For example, consider this:
+
+.. code-block:: text
+
+ %MyStruct = uninitialized global { float*, i32 }
+ ...
+ %idx = getelementptr { float*, i32 }, { float*, i32 }* %MyStruct, i64 0, i32 1
+
+The GEP above yields an ``i32*`` by indexing the ``i32`` typed field of the
+structure ``%MyStruct``. When people first look at it, they wonder why the ``i64
+0`` index is needed. However, a closer inspection of how globals and GEPs work
+reveals the need. Becoming aware of the following facts will dispel the
+confusion:
+
+#. The type of ``%MyStruct`` is *not* ``{ float*, i32 }`` but rather ``{ float*,
+ i32 }*``. That is, ``%MyStruct`` is a pointer to a structure containing a
+ pointer to a ``float`` and an ``i32``.
+
+#. Point #1 is evidenced by noticing the type of the second operand of the GEP
+ instruction (``%MyStruct``) which is ``{ float*, i32 }*``.
+
+#. The first index, ``i64 0`` is required to step over the global variable
+ ``%MyStruct``. Since the second argument to the GEP instruction must always
+ be a value of pointer type, the first index steps through that pointer. A
+ value of 0 means 0 elements offset from that pointer.
+
+#. The second index, ``i32 1`` selects the second field of the structure (the
+ ``i32``).
+
+What is dereferenced by GEP?
+----------------------------
+
+Quick answer: nothing.
+
+The GetElementPtr instruction dereferences nothing. That is, it doesn't access
+memory in any way. That's what the Load and Store instructions are for. GEP is
+only involved in the computation of addresses. For example, consider this:
+
+.. code-block:: text
+
+ %MyVar = uninitialized global { [40 x i32 ]* }
+ ...
+ %idx = getelementptr { [40 x i32]* }, { [40 x i32]* }* %MyVar, i64 0, i32 0, i64 0, i64 17
+
+In this example, we have a global variable, ``%MyVar`` that is a pointer to a
+structure containing a pointer to an array of 40 ints. The GEP instruction seems
+to be accessing the 18th integer of the structure's array of ints. However, this
+is actually an illegal GEP instruction. It won't compile. The reason is that the
+pointer in the structure *must* be dereferenced in order to index into the
+array of 40 ints. Since the GEP instruction never accesses memory, it is
+illegal.
+
+In order to access the 18th integer in the array, you would need to do the
+following:
+
+.. code-block:: text
+
+ %idx = getelementptr { [40 x i32]* }, { [40 x i32]* }* %, i64 0, i32 0
+ %arr = load [40 x i32]** %idx
+ %idx = getelementptr [40 x i32], [40 x i32]* %arr, i64 0, i64 17
+
+In this case, we have to load the pointer in the structure with a load
+instruction before we can index into the array. If the example was changed to:
+
+.. code-block:: text
+
+ %MyVar = uninitialized global { [40 x i32 ] }
+ ...
+ %idx = getelementptr { [40 x i32] }, { [40 x i32] }*, i64 0, i32 0, i64 17
+
+then everything works fine. In this case, the structure does not contain a
+pointer and the GEP instruction can index through the global variable, into the
+first field of the structure and access the 18th ``i32`` in the array there.
+
+Why don't GEP x,0,0,1 and GEP x,1 alias?
+----------------------------------------
+
+Quick Answer: They compute different address locations.
+
+If you look at the first indices in these GEP instructions you find that they
+are different (0 and 1), therefore the address computation diverges with that
+index. Consider this example:
+
+.. code-block:: llvm
+
+ %MyVar = global { [10 x i32] }
+ %idx1 = getelementptr { [10 x i32] }, { [10 x i32] }* %MyVar, i64 0, i32 0, i64 1
+ %idx2 = getelementptr { [10 x i32] }, { [10 x i32] }* %MyVar, i64 1
+
+In this example, ``idx1`` computes the address of the second integer in the
+array that is in the structure in ``%MyVar``, that is ``MyVar+4``. The type of
+``idx1`` is ``i32*``. However, ``idx2`` computes the address of *the next*
+structure after ``%MyVar``. The type of ``idx2`` is ``{ [10 x i32] }*`` and its
+value is equivalent to ``MyVar + 40`` because it indexes past the ten 4-byte
+integers in ``MyVar``. Obviously, in such a situation, the pointers don't
+alias.
+
+Why do GEP x,1,0,0 and GEP x,1 alias?
+-------------------------------------
+
+Quick Answer: They compute the same address location.
+
+These two GEP instructions will compute the same address because indexing
+through the 0th element does not change the address. However, it does change the
+type. Consider this example:
+
+.. code-block:: llvm
+
+ %MyVar = global { [10 x i32] }
+ %idx1 = getelementptr { [10 x i32] }, { [10 x i32] }* %MyVar, i64 1, i32 0, i64 0
+ %idx2 = getelementptr { [10 x i32] }, { [10 x i32] }* %MyVar, i64 1
+
+In this example, the value of ``%idx1`` is ``%MyVar+40`` and its type is
+``i32*``. The value of ``%idx2`` is also ``MyVar+40`` but its type is ``{ [10 x
+i32] }*``.
+
+Can GEP index into vector elements?
+-----------------------------------
+
+This hasn't always been forcefully disallowed, though it's not recommended. It
+leads to awkward special cases in the optimizers, and fundamental inconsistency
+in the IR. In the future, it will probably be outright disallowed.
+
+What effect do address spaces have on GEPs?
+-------------------------------------------
+
+None, except that the address space qualifier on the second operand pointer type
+always matches the address space qualifier on the result type.
+
+How is GEP different from ``ptrtoint``, arithmetic, and ``inttoptr``?
+---------------------------------------------------------------------
+
+It's very similar; there are only subtle differences.
+
+With ptrtoint, you have to pick an integer type. One approach is to pick i64;
+this is safe on everything LLVM supports (LLVM internally assumes pointers are
+never wider than 64 bits in many places), and the optimizer will actually narrow
+the i64 arithmetic down to the actual pointer size on targets which don't
+support 64-bit arithmetic in most cases. However, there are some cases where it
+doesn't do this. With GEP you can avoid this problem.
+
+Also, GEP carries additional pointer aliasing rules. It's invalid to take a GEP
+from one object, address into a different separately allocated object, and
+dereference it. IR producers (front-ends) must follow this rule, and consumers
+(optimizers, specifically alias analysis) benefit from being able to rely on
+it. See the `Rules`_ section for more information.
+
+And, GEP is more concise in common cases.
+
+However, for the underlying integer computation implied, there is no
+difference.
+
+
+I'm writing a backend for a target which needs custom lowering for GEP. How do I do this?
+-----------------------------------------------------------------------------------------
+
+You don't. The integer computation implied by a GEP is target-independent.
+Typically what you'll need to do is make your backend pattern-match expressions
+trees involving ADD, MUL, etc., which are what GEP is lowered into. This has the
+advantage of letting your code work correctly in more cases.
+
+GEP does use target-dependent parameters for the size and layout of data types,
+which targets can customize.
+
+If you require support for addressing units which are not 8 bits, you'll need to
+fix a lot of code in the backend, with GEP lowering being only a small piece of
+the overall picture.
+
+How does VLA addressing work with GEPs?
+---------------------------------------
+
+GEPs don't natively support VLAs. LLVM's type system is entirely static, and GEP
+address computations are guided by an LLVM type.
+
+VLA indices can be implemented as linearized indices. For example, an expression
+like ``X[a][b][c]``, must be effectively lowered into a form like
+``X[a*m+b*n+c]``, so that it appears to the GEP as a single-dimensional array
+reference.
+
+This means if you want to write an analysis which understands array indices and
+you want to support VLAs, your code will have to be prepared to reverse-engineer
+the linearization. One way to solve this problem is to use the ScalarEvolution
+library, which always presents VLA and non-VLA indexing in the same manner.
+
+.. _Rules:
+
+Rules
+=====
+
+What happens if an array index is out of bounds?
+------------------------------------------------
+
+There are two senses in which an array index can be out of bounds.
+
+First, there's the array type which comes from the (static) type of the first
+operand to the GEP. Indices greater than the number of elements in the
+corresponding static array type are valid. There is no problem with out of
+bounds indices in this sense. Indexing into an array only depends on the size of
+the array element, not the number of elements.
+
+A common example of how this is used is arrays where the size is not known.
+It's common to use array types with zero length to represent these. The fact
+that the static type says there are zero elements is irrelevant; it's perfectly
+valid to compute arbitrary element indices, as the computation only depends on
+the size of the array element, not the number of elements. Note that zero-sized
+arrays are not a special case here.
+
+This sense is unconnected with ``inbounds`` keyword. The ``inbounds`` keyword is
+designed to describe low-level pointer arithmetic overflow conditions, rather
+than high-level array indexing rules.
+
+Analysis passes which wish to understand array indexing should not assume that
+the static array type bounds are respected.
+
+The second sense of being out of bounds is computing an address that's beyond
+the actual underlying allocated object.
+
+With the ``inbounds`` keyword, the result value of the GEP is undefined if the
+address is outside the actual underlying allocated object and not the address
+one-past-the-end.
+
+Without the ``inbounds`` keyword, there are no restrictions on computing
+out-of-bounds addresses. Obviously, performing a load or a store requires an
+address of allocated and sufficiently aligned memory. But the GEP itself is only
+concerned with computing addresses.
+
+Can array indices be negative?
+------------------------------
+
+Yes. This is basically a special case of array indices being out of bounds.
+
+Can I compare two values computed with GEPs?
+--------------------------------------------
+
+Yes. If both addresses are within the same allocated object, or
+one-past-the-end, you'll get the comparison result you expect. If either is
+outside of it, integer arithmetic wrapping may occur, so the comparison may not
+be meaningful.
+
+Can I do GEP with a different pointer type than the type of the underlying object?
+----------------------------------------------------------------------------------
+
+Yes. There are no restrictions on bitcasting a pointer value to an arbitrary
+pointer type. The types in a GEP serve only to define the parameters for the
+underlying integer computation. They need not correspond with the actual type of
+the underlying object.
+
+Furthermore, loads and stores don't have to use the same types as the type of
+the underlying object. Types in this context serve only to specify memory size
+and alignment. Beyond that there are merely a hint to the optimizer indicating
+how the value will likely be used.
+
+Can I cast an object's address to integer and add it to null?
+-------------------------------------------------------------
+
+You can compute an address that way, but if you use GEP to do the add, you can't
+use that pointer to actually access the object, unless the object is managed
+outside of LLVM.
+
+The underlying integer computation is sufficiently defined; null has a defined
+value --- zero --- and you can add whatever value you want to it.
+
+However, it's invalid to access (load from or store to) an LLVM-aware object
+with such a pointer. This includes ``GlobalVariables``, ``Allocas``, and objects
+pointed to by noalias pointers.
+
+If you really need this functionality, you can do the arithmetic with explicit
+integer instructions, and use inttoptr to convert the result to an address. Most
+of GEP's special aliasing rules do not apply to pointers computed from ptrtoint,
+arithmetic, and inttoptr sequences.
+
+Can I compute the distance between two objects, and add that value to one address to compute the other address?
+---------------------------------------------------------------------------------------------------------------
+
+As with arithmetic on null, you can use GEP to compute an address that way, but
+you can't use that pointer to actually access the object if you do, unless the
+object is managed outside of LLVM.
+
+Also as above, ptrtoint and inttoptr provide an alternative way to do this which
+do not have this restriction.
+
+Can I do type-based alias analysis on LLVM IR?
+----------------------------------------------
+
+You can't do type-based alias analysis using LLVM's built-in type system,
+because LLVM has no restrictions on mixing types in addressing, loads or stores.
+
+LLVM's type-based alias analysis pass uses metadata to describe a different type
+system (such as the C type system), and performs type-based aliasing on top of
+that. Further details are in the
+`language reference <LangRef.html#tbaa-metadata>`_.
+
+What happens if a GEP computation overflows?
+--------------------------------------------
+
+If the GEP lacks the ``inbounds`` keyword, the value is the result from
+evaluating the implied two's complement integer computation. However, since
+there's no guarantee of where an object will be allocated in the address space,
+such values have limited meaning.
+
+If the GEP has the ``inbounds`` keyword, the result value is undefined (a "trap
+value") if the GEP overflows (i.e. wraps around the end of the address space).
+
+As such, there are some ramifications of this for inbounds GEPs: scales implied
+by array/vector/pointer indices are always known to be "nsw" since they are
+signed values that are scaled by the element size. These values are also
+allowed to be negative (e.g. "``gep i32 *%P, i32 -1``") but the pointer itself
+is logically treated as an unsigned value. This means that GEPs have an
+asymmetric relation between the pointer base (which is treated as unsigned) and
+the offset applied to it (which is treated as signed). The result of the
+additions within the offset calculation cannot have signed overflow, but when
+applied to the base pointer, there can be signed overflow.
+
+How can I tell if my front-end is following the rules?
+------------------------------------------------------
+
+There is currently no checker for the getelementptr rules. Currently, the only
+way to do this is to manually check each place in your front-end where
+GetElementPtr operators are created.
+
+It's not possible to write a checker which could find all rule violations
+statically. It would be possible to write a checker which works by instrumenting
+the code with dynamic checks though. Alternatively, it would be possible to
+write a static checker which catches a subset of possible problems. However, no
+such checker exists today.
+
+Rationale
+=========
+
+Why is GEP designed this way?
+-----------------------------
+
+The design of GEP has the following goals, in rough unofficial order of
+priority:
+
+* Support C, C-like languages, and languages which can be conceptually lowered
+ into C (this covers a lot).
+
+* Support optimizations such as those that are common in C compilers. In
+ particular, GEP is a cornerstone of LLVM's `pointer aliasing
+ model <LangRef.html#pointeraliasing>`_.
+
+* Provide a consistent method for computing addresses so that address
+ computations don't need to be a part of load and store instructions in the IR.
+
+* Support non-C-like languages, to the extent that it doesn't interfere with
+ other goals.
+
+* Minimize target-specific information in the IR.
+
+Why do struct member indices always use ``i32``?
+------------------------------------------------
+
+The specific type i32 is probably just a historical artifact, however it's wide
+enough for all practical purposes, so there's been no need to change it. It
+doesn't necessarily imply i32 address arithmetic; it's just an identifier which
+identifies a field in a struct. Requiring that all struct indices be the same
+reduces the range of possibilities for cases where two GEPs are effectively the
+same but have distinct operand types.
+
+What's an uglygep?
+------------------
+
+Some LLVM optimizers operate on GEPs by internally lowering them into more
+primitive integer expressions, which allows them to be combined with other
+integer expressions and/or split into multiple separate integer expressions. If
+they've made non-trivial changes, translating back into LLVM IR can involve
+reverse-engineering the structure of the addressing in order to fit it into the
+static type of the original first operand. It isn't always possibly to fully
+reconstruct this structure; sometimes the underlying addressing doesn't
+correspond with the static type at all. In such cases the optimizer instead will
+emit a GEP with the base pointer casted to a simple address-unit pointer, using
+the name "uglygep". This isn't pretty, but it's just as valid, and it's
+sufficient to preserve the pointer aliasing guarantees that GEP provides.
+
+Summary
+=======
+
+In summary, here's some things to always remember about the GetElementPtr
+instruction:
+
+
+#. The GEP instruction never accesses memory, it only provides pointer
+ computations.
+
+#. The second operand to the GEP instruction is always a pointer and it must be
+ indexed.
+
+#. There are no superfluous indices for the GEP instruction.
+
+#. Trailing zero indices are superfluous for pointer aliasing, but not for the
+ types of the pointers.
+
+#. Leading zero indices are not superfluous for pointer aliasing nor the types
+ of the pointers.
Added: www-releases/trunk/5.0.2/docs/_sources/GettingStarted.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.2/docs/_sources/GettingStarted.txt?rev=331981&view=auto
==============================================================================
--- www-releases/trunk/5.0.2/docs/_sources/GettingStarted.txt (added)
+++ www-releases/trunk/5.0.2/docs/_sources/GettingStarted.txt Thu May 10 06:54:16 2018
@@ -0,0 +1,1340 @@
+====================================
+Getting Started with the LLVM System
+====================================
+
+.. contents::
+ :local:
+
+Overview
+========
+
+Welcome to LLVM! In order to get started, you first need to know some basic
+information.
+
+First, LLVM comes in three pieces. The first piece is the LLVM suite. This
+contains all of the tools, libraries, and header files needed to use LLVM. It
+contains an assembler, disassembler, bitcode analyzer and bitcode optimizer. It
+also contains basic regression tests that can be used to test the LLVM tools and
+the Clang front end.
+
+The second piece is the `Clang <http://clang.llvm.org/>`_ front end. This
+component compiles C, C++, Objective C, and Objective C++ code into LLVM
+bitcode. Once compiled into LLVM bitcode, a program can be manipulated with the
+LLVM tools from the LLVM suite.
+
+There is a third, optional piece called Test Suite. It is a suite of programs
+with a testing harness that can be used to further test LLVM's functionality
+and performance.
+
+Getting Started Quickly (A Summary)
+===================================
+
+The LLVM Getting Started documentation may be out of date. So, the `Clang
+Getting Started <http://clang.llvm.org/get_started.html>`_ page might also be a
+good place to start.
+
+Here's the short story for getting up and running quickly with LLVM:
+
+#. Read the documentation.
+#. Read the documentation.
+#. Remember that you were warned twice about reading the documentation.
+
+ * In particular, the *relative paths specified are important*.
+
+#. Checkout LLVM:
+
+ * ``cd where-you-want-llvm-to-live``
+ * ``svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm``
+
+#. Checkout Clang:
+
+ * ``cd where-you-want-llvm-to-live``
+ * ``cd llvm/tools``
+ * ``svn co http://llvm.org/svn/llvm-project/cfe/trunk clang``
+
+#. Checkout LLD linker **[Optional]**:
+
+ * ``cd where-you-want-llvm-to-live``
+ * ``cd llvm/tools``
+ * ``svn co http://llvm.org/svn/llvm-project/lld/trunk lld``
+
+#. Checkout Polly Loop Optimizer **[Optional]**:
+
+ * ``cd where-you-want-llvm-to-live``
+ * ``cd llvm/tools``
+ * ``svn co http://llvm.org/svn/llvm-project/polly/trunk polly``
+
+#. Checkout Compiler-RT (required to build the sanitizers) **[Optional]**:
+
+ * ``cd where-you-want-llvm-to-live``
+ * ``cd llvm/projects``
+ * ``svn co http://llvm.org/svn/llvm-project/compiler-rt/trunk compiler-rt``
+
+#. Checkout Libomp (required for OpenMP support) **[Optional]**:
+
+ * ``cd where-you-want-llvm-to-live``
+ * ``cd llvm/projects``
+ * ``svn co http://llvm.org/svn/llvm-project/openmp/trunk openmp``
+
+#. Checkout libcxx and libcxxabi **[Optional]**:
+
+ * ``cd where-you-want-llvm-to-live``
+ * ``cd llvm/projects``
+ * ``svn co http://llvm.org/svn/llvm-project/libcxx/trunk libcxx``
+ * ``svn co http://llvm.org/svn/llvm-project/libcxxabi/trunk libcxxabi``
+
+#. Get the Test Suite Source Code **[Optional]**
+
+ * ``cd where-you-want-llvm-to-live``
+ * ``cd llvm/projects``
+ * ``svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite``
+
+#. Configure and build LLVM and Clang:
+
+ *Warning:* Make sure you've checked out *all of* the source code
+ before trying to configure with cmake. cmake does not pickup newly
+ added source directories in incremental builds.
+
+ The build uses `CMake <CMake.html>`_. LLVM requires CMake 3.4.3 to build. It
+ is generally recommended to use a recent CMake, especially if you're
+ generating Ninja build files. This is because the CMake project is constantly
+ improving the quality of the generators, and the Ninja generator gets a lot
+ of attention.
+
+ * ``cd where you want to build llvm``
+ * ``mkdir build``
+ * ``cd build``
+ * ``cmake -G <generator> [options] <path to llvm sources>``
+
+ Some common generators are:
+
+ * ``Unix Makefiles`` --- for generating make-compatible parallel makefiles.
+ * ``Ninja`` --- for generating `Ninja <https://ninja-build.org>`_
+ build files. Most llvm developers use Ninja.
+ * ``Visual Studio`` --- for generating Visual Studio projects and
+ solutions.
+ * ``Xcode`` --- for generating Xcode projects.
+
+ Some Common options:
+
+ * ``-DCMAKE_INSTALL_PREFIX=directory`` --- Specify for *directory* the full
+ pathname of where you want the LLVM tools and libraries to be installed
+ (default ``/usr/local``).
+
+ * ``-DCMAKE_BUILD_TYPE=type`` --- Valid options for *type* are Debug,
+ Release, RelWithDebInfo, and MinSizeRel. Default is Debug.
+
+ * ``-DLLVM_ENABLE_ASSERTIONS=On`` --- Compile with assertion checks enabled
+ (default is Yes for Debug builds, No for all other build types).
+
+ * Run your build tool of choice!
+
+ * The default target (i.e. ``make``) will build all of LLVM
+
+ * The ``check-all`` target (i.e. ``make check-all``) will run the
+ regression tests to ensure everything is in working order.
+
+ * CMake will generate build targets for each tool and library, and most
+ LLVM sub-projects generate their own ``check-<project>`` target.
+
+ * Running a serial build will be *slow*. Make sure you run a
+ parallel build; for ``make``, use ``make -j``.
+
+ * For more information see `CMake <CMake.html>`_
+
+ * If you get an "internal compiler error (ICE)" or test failures, see
+ `below`_.
+
+Consult the `Getting Started with LLVM`_ section for detailed information on
+configuring and compiling LLVM. Go to `Directory Layout`_ to learn about the
+layout of the source code tree.
+
+Requirements
+============
+
+Before you begin to use the LLVM system, review the requirements given below.
+This may save you some trouble by knowing ahead of time what hardware and
+software you will need.
+
+Hardware
+--------
+
+LLVM is known to work on the following host platforms:
+
+================== ===================== =============
+OS Arch Compilers
+================== ===================== =============
+Linux x86\ :sup:`1` GCC, Clang
+Linux amd64 GCC, Clang
+Linux ARM\ :sup:`4` GCC, Clang
+Linux PowerPC GCC, Clang
+Solaris V9 (Ultrasparc) GCC
+FreeBSD x86\ :sup:`1` GCC, Clang
+FreeBSD amd64 GCC, Clang
+NetBSD x86\ :sup:`1` GCC, Clang
+NetBSD amd64 GCC, Clang
+MacOS X\ :sup:`2` PowerPC GCC
+MacOS X x86 GCC, Clang
+Cygwin/Win32 x86\ :sup:`1, 3` GCC
+Windows x86\ :sup:`1` Visual Studio
+Windows x64 x86-64 Visual Studio
+================== ===================== =============
+
+.. note::
+
+ #. Code generation supported for Pentium processors and up
+ #. Code generation supported for 32-bit ABI only
+ #. To use LLVM modules on Win32-based system, you may configure LLVM
+ with ``-DBUILD_SHARED_LIBS=On``.
+ #. MCJIT not working well pre-v7, old JIT engine not supported any more.
+
+Note that Debug builds require a lot of time and disk space. An LLVM-only build
+will need about 1-3 GB of space. A full build of LLVM and Clang will need around
+15-20 GB of disk space. The exact space requirements will vary by system. (It
+is so large because of all the debugging information and the fact that the
+libraries are statically linked into multiple tools).
+
+If you you are space-constrained, you can build only selected tools or only
+selected targets. The Release build requires considerably less space.
+
+The LLVM suite *may* compile on other platforms, but it is not guaranteed to do
+so. If compilation is successful, the LLVM utilities should be able to
+assemble, disassemble, analyze, and optimize LLVM bitcode. Code generation
+should work as well, although the generated native code may not work on your
+platform.
+
+Software
+--------
+
+Compiling LLVM requires that you have several software packages installed. The
+table below lists those required packages. The Package column is the usual name
+for the software package that LLVM depends on. The Version column provides
+"known to work" versions of the package. The Notes column describes how LLVM
+uses the package and provides other details.
+
+=========================================================== ============ ==========================================
+Package Version Notes
+=========================================================== ============ ==========================================
+`GNU Make <http://savannah.gnu.org/projects/make>`_ 3.79, 3.79.1 Makefile/build processor
+`GCC <http://gcc.gnu.org/>`_ >=4.8.0 C/C++ compiler\ :sup:`1`
+`python <http://www.python.org/>`_ >=2.7 Automated test suite\ :sup:`2`
+`zlib <http://zlib.net>`_ >=1.2.3.4 Compression library\ :sup:`3`
+=========================================================== ============ ==========================================
+
+.. note::
+
+ #. Only the C and C++ languages are needed so there's no need to build the
+ other languages for LLVM's purposes. See `below` for specific version
+ info.
+ #. Only needed if you want to run the automated test suite in the
+ ``llvm/test`` directory.
+ #. Optional, adds compression / uncompression capabilities to selected LLVM
+ tools.
+
+Additionally, your compilation host is expected to have the usual plethora of
+Unix utilities. Specifically:
+
+* **ar** --- archive library builder
+* **bzip2** --- bzip2 command for distribution generation
+* **bunzip2** --- bunzip2 command for distribution checking
+* **chmod** --- change permissions on a file
+* **cat** --- output concatenation utility
+* **cp** --- copy files
+* **date** --- print the current date/time
+* **echo** --- print to standard output
+* **egrep** --- extended regular expression search utility
+* **find** --- find files/dirs in a file system
+* **grep** --- regular expression search utility
+* **gzip** --- gzip command for distribution generation
+* **gunzip** --- gunzip command for distribution checking
+* **install** --- install directories/files
+* **mkdir** --- create a directory
+* **mv** --- move (rename) files
+* **ranlib** --- symbol table builder for archive libraries
+* **rm** --- remove (delete) files and directories
+* **sed** --- stream editor for transforming output
+* **sh** --- Bourne shell for make build scripts
+* **tar** --- tape archive for distribution generation
+* **test** --- test things in file system
+* **unzip** --- unzip command for distribution checking
+* **zip** --- zip command for distribution generation
+
+.. _below:
+.. _check here:
+
+Host C++ Toolchain, both Compiler and Standard Library
+------------------------------------------------------
+
+LLVM is very demanding of the host C++ compiler, and as such tends to expose
+bugs in the compiler. We are also planning to follow improvements and
+developments in the C++ language and library reasonably closely. As such, we
+require a modern host C++ toolchain, both compiler and standard library, in
+order to build LLVM.
+
+For the most popular host toolchains we check for specific minimum versions in
+our build systems:
+
+* Clang 3.1
+* GCC 4.8
+* Visual Studio 2015 (Update 3)
+
+Anything older than these toolchains *may* work, but will require forcing the
+build system with a special option and is not really a supported host platform.
+Also note that older versions of these compilers have often crashed or
+miscompiled LLVM.
+
+For less widely used host toolchains such as ICC or xlC, be aware that a very
+recent version may be required to support all of the C++ features used in LLVM.
+
+We track certain versions of software that are *known* to fail when used as
+part of the host toolchain. These even include linkers at times.
+
+**GNU ld 2.16.X**. Some 2.16.X versions of the ld linker will produce very long
+warning messages complaining that some "``.gnu.linkonce.t.*``" symbol was
+defined in a discarded section. You can safely ignore these messages as they are
+erroneous and the linkage is correct. These messages disappear using ld 2.17.
+
+**GNU binutils 2.17**: Binutils 2.17 contains `a bug
+<http://sourceware.org/bugzilla/show_bug.cgi?id=3111>`__ which causes huge link
+times (minutes instead of seconds) when building LLVM. We recommend upgrading
+to a newer version (2.17.50.0.4 or later).
+
+**GNU Binutils 2.19.1 Gold**: This version of Gold contained `a bug
+<http://sourceware.org/bugzilla/show_bug.cgi?id=9836>`__ which causes
+intermittent failures when building LLVM with position independent code. The
+symptom is an error about cyclic dependencies. We recommend upgrading to a
+newer version of Gold.
+
+Getting a Modern Host C++ Toolchain
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This section mostly applies to Linux and older BSDs. On Mac OS X, you should
+have a sufficiently modern Xcode, or you will likely need to upgrade until you
+do. Windows does not have a "system compiler", so you must install either Visual
+Studio 2015 or a recent version of mingw64. FreeBSD 10.0 and newer have a modern
+Clang as the system compiler.
+
+However, some Linux distributions and some other or older BSDs sometimes have
+extremely old versions of GCC. These steps attempt to help you upgrade you
+compiler even on such a system. However, if at all possible, we encourage you
+to use a recent version of a distribution with a modern system compiler that
+meets these requirements. Note that it is tempting to to install a prior
+version of Clang and libc++ to be the host compiler, however libc++ was not
+well tested or set up to build on Linux until relatively recently. As
+a consequence, this guide suggests just using libstdc++ and a modern GCC as the
+initial host in a bootstrap, and then using Clang (and potentially libc++).
+
+The first step is to get a recent GCC toolchain installed. The most common
+distribution on which users have struggled with the version requirements is
+Ubuntu Precise, 12.04 LTS. For this distribution, one easy option is to install
+the `toolchain testing PPA`_ and use it to install a modern GCC. There is
+a really nice discussions of this on the `ask ubuntu stack exchange`_. However,
+not all users can use PPAs and there are many other distributions, so it may be
+necessary (or just useful, if you're here you *are* doing compiler development
+after all) to build and install GCC from source. It is also quite easy to do
+these days.
+
+.. _toolchain testing PPA:
+ https://launchpad.net/~ubuntu-toolchain-r/+archive/test
+.. _ask ubuntu stack exchange:
+ http://askubuntu.com/questions/271388/how-to-install-gcc-4-8-in-ubuntu-12-04-from-the-terminal
+
+Easy steps for installing GCC 4.8.2:
+
+.. code-block:: console
+
+ % wget https://ftp.gnu.org/gnu/gcc/gcc-4.8.2/gcc-4.8.2.tar.bz2
+ % wget https://ftp.gnu.org/gnu/gcc/gcc-4.8.2/gcc-4.8.2.tar.bz2.sig
+ % wget https://ftp.gnu.org/gnu/gnu-keyring.gpg
+ % signature_invalid=`gpg --verify --no-default-keyring --keyring ./gnu-keyring.gpg gcc-4.8.2.tar.bz2.sig`
+ % if [ $signature_invalid ]; then echo "Invalid signature" ; exit 1 ; fi
+ % tar -xvjf gcc-4.8.2.tar.bz2
+ % cd gcc-4.8.2
+ % ./contrib/download_prerequisites
+ % cd ..
+ % mkdir gcc-4.8.2-build
+ % cd gcc-4.8.2-build
+ % $PWD/../gcc-4.8.2/configure --prefix=$HOME/toolchains --enable-languages=c,c++
+ % make -j$(nproc)
+ % make install
+
+For more details, check out the excellent `GCC wiki entry`_, where I got most
+of this information from.
+
+.. _GCC wiki entry:
+ http://gcc.gnu.org/wiki/InstallingGCC
+
+Once you have a GCC toolchain, configure your build of LLVM to use the new
+toolchain for your host compiler and C++ standard library. Because the new
+version of libstdc++ is not on the system library search path, you need to pass
+extra linker flags so that it can be found at link time (``-L``) and at runtime
+(``-rpath``). If you are using CMake, this invocation should produce working
+binaries:
+
+.. code-block:: console
+
+ % mkdir build
+ % cd build
+ % CC=$HOME/toolchains/bin/gcc CXX=$HOME/toolchains/bin/g++ \
+ cmake .. -DCMAKE_CXX_LINK_FLAGS="-Wl,-rpath,$HOME/toolchains/lib64 -L$HOME/toolchains/lib64"
+
+If you fail to set rpath, most LLVM binaries will fail on startup with a message
+from the loader similar to ``libstdc++.so.6: version `GLIBCXX_3.4.20' not
+found``. This means you need to tweak the -rpath linker flag.
+
+When you build Clang, you will need to give *it* access to modern C++11
+standard library in order to use it as your new host in part of a bootstrap.
+There are two easy ways to do this, either build (and install) libc++ along
+with Clang and then use it with the ``-stdlib=libc++`` compile and link flag,
+or install Clang into the same prefix (``$HOME/toolchains`` above) as GCC.
+Clang will look within its own prefix for libstdc++ and use it if found. You
+can also add an explicit prefix for Clang to look in for a GCC toolchain with
+the ``--gcc-toolchain=/opt/my/gcc/prefix`` flag, passing it to both compile and
+link commands when using your just-built-Clang to bootstrap.
+
+.. _Getting Started with LLVM:
+
+Getting Started with LLVM
+=========================
+
+The remainder of this guide is meant to get you up and running with LLVM and to
+give you some basic information about the LLVM environment.
+
+The later sections of this guide describe the `general layout`_ of the LLVM
+source tree, a `simple example`_ using the LLVM tool chain, and `links`_ to find
+more information about LLVM or to get help via e-mail.
+
+Terminology and Notation
+------------------------
+
+Throughout this manual, the following names are used to denote paths specific to
+the local system and working environment. *These are not environment variables
+you need to set but just strings used in the rest of this document below*. In
+any of the examples below, simply replace each of these names with the
+appropriate pathname on your local system. All these paths are absolute:
+
+``SRC_ROOT``
+
+ This is the top level directory of the LLVM source tree.
+
+``OBJ_ROOT``
+
+ This is the top level directory of the LLVM object tree (i.e. the tree where
+ object files and compiled programs will be placed. It can be the same as
+ SRC_ROOT).
+
+Unpacking the LLVM Archives
+---------------------------
+
+If you have the LLVM distribution, you will need to unpack it before you can
+begin to compile it. LLVM is distributed as a set of two files: the LLVM suite
+and the LLVM GCC front end compiled for your platform. There is an additional
+test suite that is optional. Each file is a TAR archive that is compressed with
+the gzip program.
+
+The files are as follows, with *x.y* marking the version number:
+
+``llvm-x.y.tar.gz``
+
+ Source release for the LLVM libraries and tools.
+
+``llvm-test-x.y.tar.gz``
+
+ Source release for the LLVM test-suite.
+
+.. _checkout:
+
+Checkout LLVM from Subversion
+-----------------------------
+
+If you have access to our Subversion repository, you can get a fresh copy of the
+entire source code. All you need to do is check it out from Subversion as
+follows:
+
+* ``cd where-you-want-llvm-to-live``
+* Read-Only: ``svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm``
+* Read-Write: ``svn co https://user@llvm.org/svn/llvm-project/llvm/trunk llvm``
+
+This will create an '``llvm``' directory in the current directory and fully
+populate it with the LLVM source code, Makefiles, test directories, and local
+copies of documentation files.
+
+If you want to get a specific release (as opposed to the most recent revision),
+you can checkout it from the '``tags``' directory (instead of '``trunk``'). The
+following releases are located in the following subdirectories of the '``tags``'
+directory:
+
+* Release 3.4: **RELEASE_34/final**
+* Release 3.3: **RELEASE_33/final**
+* Release 3.2: **RELEASE_32/final**
+* Release 3.1: **RELEASE_31/final**
+* Release 3.0: **RELEASE_30/final**
+* Release 2.9: **RELEASE_29/final**
+* Release 2.8: **RELEASE_28**
+* Release 2.7: **RELEASE_27**
+* Release 2.6: **RELEASE_26**
+* Release 2.5: **RELEASE_25**
+* Release 2.4: **RELEASE_24**
+* Release 2.3: **RELEASE_23**
+* Release 2.2: **RELEASE_22**
+* Release 2.1: **RELEASE_21**
+* Release 2.0: **RELEASE_20**
+* Release 1.9: **RELEASE_19**
+* Release 1.8: **RELEASE_18**
+* Release 1.7: **RELEASE_17**
+* Release 1.6: **RELEASE_16**
+* Release 1.5: **RELEASE_15**
+* Release 1.4: **RELEASE_14**
+* Release 1.3: **RELEASE_13**
+* Release 1.2: **RELEASE_12**
+* Release 1.1: **RELEASE_11**
+* Release 1.0: **RELEASE_1**
+
+If you would like to get the LLVM test suite (a separate package as of 1.4), you
+get it from the Subversion repository:
+
+.. code-block:: console
+
+ % cd llvm/projects
+ % svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite
+
+By placing it in the ``llvm/projects``, it will be automatically configured by
+the LLVM cmake configuration.
+
+Git Mirror
+----------
+
+Git mirrors are available for a number of LLVM subprojects. These mirrors sync
+automatically with each Subversion commit and contain all necessary git-svn
+marks (so, you can recreate git-svn metadata locally). Note that right now
+mirrors reflect only ``trunk`` for each project. You can do the read-only Git
+clone of LLVM via:
+
+.. code-block:: console
+
+ % git clone http://llvm.org/git/llvm.git
+
+If you want to check out clang too, run:
+
+.. code-block:: console
+
+ % cd llvm/tools
+ % git clone http://llvm.org/git/clang.git
+
+If you want to check out compiler-rt (required to build the sanitizers), run:
+
+.. code-block:: console
+
+ % cd llvm/projects
+ % git clone http://llvm.org/git/compiler-rt.git
+
+If you want to check out libomp (required for OpenMP support), run:
+
+.. code-block:: console
+
+ % cd llvm/projects
+ % git clone http://llvm.org/git/openmp.git
+
+If you want to check out libcxx and libcxxabi (optional), run:
+
+.. code-block:: console
+
+ % cd llvm/projects
+ % git clone http://llvm.org/git/libcxx.git
+ % git clone http://llvm.org/git/libcxxabi.git
+
+If you want to check out the Test Suite Source Code (optional), run:
+
+.. code-block:: console
+
+ % cd llvm/projects
+ % git clone http://llvm.org/git/test-suite.git
+
+Since the upstream repository is in Subversion, you should use ``git
+pull --rebase`` instead of ``git pull`` to avoid generating a non-linear history
+in your clone. To configure ``git pull`` to pass ``--rebase`` by default on the
+master branch, run the following command:
+
+.. code-block:: console
+
+ % git config branch.master.rebase true
+
+Sending patches with Git
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+Please read `Developer Policy <DeveloperPolicy.html#one-off-patches>`_, too.
+
+Assume ``master`` points the upstream and ``mybranch`` points your working
+branch, and ``mybranch`` is rebased onto ``master``. At first you may check
+sanity of whitespaces:
+
+.. code-block:: console
+
+ % git diff --check master..mybranch
+
+The easiest way to generate a patch is as below:
+
+.. code-block:: console
+
+ % git diff master..mybranch > /path/to/mybranch.diff
+
+It is a little different from svn-generated diff. git-diff-generated diff has
+prefixes like ``a/`` and ``b/``. Don't worry, most developers might know it
+could be accepted with ``patch -p1 -N``.
+
+But you may generate patchset with git-format-patch. It generates by-each-commit
+patchset. To generate patch files to attach to your article:
+
+.. code-block:: console
+
+ % git format-patch --no-attach master..mybranch -o /path/to/your/patchset
+
+If you would like to send patches directly, you may use git-send-email or
+git-imap-send. Here is an example to generate the patchset in Gmail's [Drafts].
+
+.. code-block:: console
+
+ % git format-patch --attach master..mybranch --stdout | git imap-send
+
+Then, your .git/config should have [imap] sections.
+
+.. code-block:: ini
+
+ [imap]
+ host = imaps://imap.gmail.com
+ user = your.gmail.account at gmail.com
+ pass = himitsu!
+ port = 993
+ sslverify = false
+ ; in English
+ folder = "[Gmail]/Drafts"
+ ; example for Japanese, "Modified UTF-7" encoded.
+ folder = "[Gmail]/&Tgtm+DBN-"
+ ; example for Traditional Chinese
+ folder = "[Gmail]/&g0l6Pw-"
+
+.. _developers-work-with-git-svn:
+
+For developers to work with git-svn
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+To set up clone from which you can submit code using ``git-svn``, run:
+
+.. code-block:: console
+
+ % git clone http://llvm.org/git/llvm.git
+ % cd llvm
+ % git svn init https://llvm.org/svn/llvm-project/llvm/trunk --username=<username>
+ % git config svn-remote.svn.fetch :refs/remotes/origin/master
+ % git svn rebase -l # -l avoids fetching ahead of the git mirror.
+
+ # If you have clang too:
+ % cd tools
+ % git clone http://llvm.org/git/clang.git
+ % cd clang
+ % git svn init https://llvm.org/svn/llvm-project/cfe/trunk --username=<username>
+ % git config svn-remote.svn.fetch :refs/remotes/origin/master
+ % git svn rebase -l
+
+Likewise for compiler-rt, libomp and test-suite.
+
+To update this clone without generating git-svn tags that conflict with the
+upstream Git repo, run:
+
+.. code-block:: console
+
+ % git fetch && (cd tools/clang && git fetch) # Get matching revisions of both trees.
+ % git checkout master
+ % git svn rebase -l
+ % (cd tools/clang &&
+ git checkout master &&
+ git svn rebase -l)
+
+Likewise for compiler-rt, libomp and test-suite.
+
+This leaves your working directories on their master branches, so you'll need to
+``checkout`` each working branch individually and ``rebase`` it on top of its
+parent branch.
+
+For those who wish to be able to update an llvm repo/revert patches easily using
+git-svn, please look in the directory for the scripts ``git-svnup`` and
+``git-svnrevert``.
+
+To perform the aforementioned update steps go into your source directory and
+just type ``git-svnup`` or ``git svnup`` and everything will just work.
+
+If one wishes to revert a commit with git-svn, but do not want the git hash to
+escape into the commit message, one can use the script ``git-svnrevert`` or
+``git svnrevert`` which will take in the git hash for the commit you want to
+revert, look up the appropriate svn revision, and output a message where all
+references to the git hash have been replaced with the svn revision.
+
+To commit back changes via git-svn, use ``git svn dcommit``:
+
+.. code-block:: console
+
+ % git svn dcommit
+
+Note that git-svn will create one SVN commit for each Git commit you have pending,
+so squash and edit each commit before executing ``dcommit`` to make sure they all
+conform to the coding standards and the developers' policy.
+
+On success, ``dcommit`` will rebase against the HEAD of SVN, so to avoid conflict,
+please make sure your current branch is up-to-date (via fetch/rebase) before
+proceeding.
+
+The git-svn metadata can get out of sync after you mess around with branches and
+``dcommit``. When that happens, ``git svn dcommit`` stops working, complaining
+about files with uncommitted changes. The fix is to rebuild the metadata:
+
+.. code-block:: console
+
+ % rm -rf .git/svn
+ % git svn rebase -l
+
+Please, refer to the Git-SVN manual (``man git-svn``) for more information.
+
+For developers to work with a git monorepo
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. note::
+
+ This set-up is using an unofficial mirror hosted on GitHub, use with caution.
+
+To set up a clone of all the llvm projects using a unified repository:
+
+.. code-block:: console
+
+ % export TOP_LEVEL_DIR=`pwd`
+ % git clone https://github.com/llvm-project/llvm-project-20170507/ llvm-project
+ % cd llvm-project
+ % git config branch.master.rebase true
+
+You can configure various build directory from this clone, starting with a build
+of LLVM alone:
+
+.. code-block:: console
+
+ % cd $TOP_LEVEL_DIR
+ % mkdir llvm-build && cd llvm-build
+ % cmake -GNinja ../llvm-project/llvm
+
+Or lldb:
+
+.. code-block:: console
+
+ % cd $TOP_LEVEL_DIR
+ % mkdir lldb-build && cd lldb-build
+ % cmake -GNinja ../llvm-project/llvm -DLLVM_ENABLE_PROJECTS=lldb
+
+Or a combination of multiple projects:
+
+.. code-block:: console
+
+ % cd $TOP_LEVEL_DIR
+ % mkdir clang-build && cd clang-build
+ % cmake -GNinja ../llvm-project/llvm -DLLVM_ENABLE_PROJECTS="clang;libcxx;libcxxabi"
+
+A helper script is provided in ``llvm/utils/git-svn/git-llvm``. After you add it
+to your path, you can push committed changes upstream with ``git llvm push``.
+
+.. code-block:: console
+
+ % export PATH=$PATH:$TOP_LEVEL_DIR/llvm-project/llvm/utils/git-svn/
+ % git llvm push
+
+While this is using SVN under the hood, it does not require any interaction from
+you with git-svn.
+After a few minutes, ``git pull`` should get back the changes as they were
+committed. Note that a current limitation is that ``git`` does not directly
+record file rename, and thus it is propagated to SVN as a combination of
+delete-add instead of a file rename.
+
+The SVN revision of each monorepo commit can be found in the commit notes. git
+does not fetch notes by default. The following commands will fetch the notes and
+configure git to fetch future notes. Use ``git notes show $commit`` to look up
+the SVN revision of a git commit. The notes show up ``git log``, and searching
+the log is currently the recommended way to look up the git commit for a given
+SVN revision.
+
+.. code-block:: console
+
+ % git config --add remote.origin.fetch +refs/notes/commits:refs/notes/commits
+ % git fetch
+
+If you are using `arc` to interact with Phabricator, you need to manually put it
+at the root of the checkout:
+
+.. code-block:: console
+
+ % cd $TOP_LEVEL_DIR
+ % cp llvm/.arcconfig ./
+ % mkdir -p .git/info/
+ % echo .arcconfig >> .git/info/exclude
+
+
+Local LLVM Configuration
+------------------------
+
+Once checked out from the Subversion repository, the LLVM suite source code must
+be configured before being built. This process uses CMake.
+Unlinke the normal ``configure`` script, CMake
+generates the build files in whatever format you request as well as various
+``*.inc`` files, and ``llvm/include/Config/config.h``.
+
+Variables are passed to ``cmake`` on the command line using the format
+``-D<variable name>=<value>``. The following variables are some common options
+used by people developing LLVM.
+
++-------------------------+----------------------------------------------------+
+| Variable | Purpose |
++=========================+====================================================+
+| CMAKE_C_COMPILER | Tells ``cmake`` which C compiler to use. By |
+| | default, this will be /usr/bin/cc. |
++-------------------------+----------------------------------------------------+
+| CMAKE_CXX_COMPILER | Tells ``cmake`` which C++ compiler to use. By |
+| | default, this will be /usr/bin/c++. |
++-------------------------+----------------------------------------------------+
+| CMAKE_BUILD_TYPE | Tells ``cmake`` what type of build you are trying |
+| | to generate files for. Valid options are Debug, |
+| | Release, RelWithDebInfo, and MinSizeRel. Default |
+| | is Debug. |
++-------------------------+----------------------------------------------------+
+| CMAKE_INSTALL_PREFIX | Specifies the install directory to target when |
+| | running the install action of the build files. |
++-------------------------+----------------------------------------------------+
+| LLVM_TARGETS_TO_BUILD | A semicolon delimited list controlling which |
+| | targets will be built and linked into llc. This is |
+| | equivalent to the ``--enable-targets`` option in |
+| | the configure script. The default list is defined |
+| | as ``LLVM_ALL_TARGETS``, and can be set to include |
+| | out-of-tree targets. The default value includes: |
+| | ``AArch64, AMDGPU, ARM, BPF, Hexagon, Mips, |
+| | MSP430, NVPTX, PowerPC, Sparc, SystemZ, X86, |
+| | XCore``. |
++-------------------------+----------------------------------------------------+
+| LLVM_ENABLE_DOXYGEN | Build doxygen-based documentation from the source |
+| | code This is disabled by default because it is |
+| | slow and generates a lot of output. |
++-------------------------+----------------------------------------------------+
+| LLVM_ENABLE_SPHINX | Build sphinx-based documentation from the source |
+| | code. This is disabled by default because it is |
+| | slow and generates a lot of output. Sphinx version |
+| | 1.5 or later recommended. |
++-------------------------+----------------------------------------------------+
+| LLVM_BUILD_LLVM_DYLIB | Generate libLLVM.so. This library contains a |
+| | default set of LLVM components that can be |
+| | overridden with ``LLVM_DYLIB_COMPONENTS``. The |
+| | default contains most of LLVM and is defined in |
+| | ``tools/llvm-shlib/CMakelists.txt``. |
++-------------------------+----------------------------------------------------+
+| LLVM_OPTIMIZED_TABLEGEN | Builds a release tablegen that gets used during |
+| | the LLVM build. This can dramatically speed up |
+| | debug builds. |
++-------------------------+----------------------------------------------------+
+
+To configure LLVM, follow these steps:
+
+#. Change directory into the object root directory:
+
+ .. code-block:: console
+
+ % cd OBJ_ROOT
+
+#. Run the ``cmake``:
+
+ .. code-block:: console
+
+ % cmake -G "Unix Makefiles" -DCMAKE_INSTALL_PREFIX=prefix=/install/path
+ [other options] SRC_ROOT
+
+Compiling the LLVM Suite Source Code
+------------------------------------
+
+Unlike with autotools, with CMake your build type is defined at configuration.
+If you want to change your build type, you can re-run cmake with the following
+invocation:
+
+ .. code-block:: console
+
+ % cmake -G "Unix Makefiles" -DCMAKE_BUILD_TYPE=type SRC_ROOT
+
+Between runs, CMake preserves the values set for all options. CMake has the
+following build types defined:
+
+Debug
+
+ These builds are the default. The build system will compile the tools and
+ libraries unoptimized, with debugging information, and asserts enabled.
+
+Release
+
+ For these builds, the build system will compile the tools and libraries
+ with optimizations enabled and not generate debug info. CMakes default
+ optimization level is -O3. This can be configured by setting the
+ ``CMAKE_CXX_FLAGS_RELEASE`` variable on the CMake command line.
+
+RelWithDebInfo
+
+ These builds are useful when debugging. They generate optimized binaries with
+ debug information. CMakes default optimization level is -O2. This can be
+ configured by setting the ``CMAKE_CXX_FLAGS_RELWITHDEBINFO`` variable on the
+ CMake command line.
+
+Once you have LLVM configured, you can build it by entering the *OBJ_ROOT*
+directory and issuing the following command:
+
+.. code-block:: console
+
+ % make
+
+If the build fails, please `check here`_ to see if you are using a version of
+GCC that is known not to compile LLVM.
+
+If you have multiple processors in your machine, you may wish to use some of the
+parallel build options provided by GNU Make. For example, you could use the
+command:
+
+.. code-block:: console
+
+ % make -j2
+
+There are several special targets which are useful when working with the LLVM
+source code:
+
+``make clean``
+
+ Removes all files generated by the build. This includes object files,
+ generated C/C++ files, libraries, and executables.
+
+``make install``
+
+ Installs LLVM header files, libraries, tools, and documentation in a hierarchy
+ under ``$PREFIX``, specified with ``CMAKE_INSTALL_PREFIX``, which
+ defaults to ``/usr/local``.
+
+``make docs-llvm-html``
+
+ If configured with ``-DLLVM_ENABLE_SPHINX=On``, this will generate a directory
+ at ``OBJ_ROOT/docs/html`` which contains the HTML formatted documentation.
+
+Cross-Compiling LLVM
+--------------------
+
+It is possible to cross-compile LLVM itself. That is, you can create LLVM
+executables and libraries to be hosted on a platform different from the platform
+where they are built (a Canadian Cross build). To generate build files for
+cross-compiling CMake provides a variable ``CMAKE_TOOLCHAIN_FILE`` which can
+define compiler flags and variables used during the CMake test operations.
+
+The result of such a build is executables that are not runnable on on the build
+host but can be executed on the target. As an example the following CMake
+invocation can generate build files targeting iOS. This will work on Mac OS X
+with the latest Xcode:
+
+.. code-block:: console
+
+ % cmake -G "Ninja" -DCMAKE_OSX_ARCHITECTURES="armv7;armv7s;arm64"
+ -DCMAKE_TOOLCHAIN_FILE=<PATH_TO_LLVM>/cmake/platforms/iOS.cmake
+ -DCMAKE_BUILD_TYPE=Release -DLLVM_BUILD_RUNTIME=Off -DLLVM_INCLUDE_TESTS=Off
+ -DLLVM_INCLUDE_EXAMPLES=Off -DLLVM_ENABLE_BACKTRACES=Off [options]
+ <PATH_TO_LLVM>
+
+Note: There are some additional flags that need to be passed when building for
+iOS due to limitations in the iOS SDK.
+
+Check :doc:`HowToCrossCompileLLVM` and `Clang docs on how to cross-compile in general
+<http://clang.llvm.org/docs/CrossCompilation.html>`_ for more information
+about cross-compiling.
+
+The Location of LLVM Object Files
+---------------------------------
+
+The LLVM build system is capable of sharing a single LLVM source tree among
+several LLVM builds. Hence, it is possible to build LLVM for several different
+platforms or configurations using the same source tree.
+
+* Change directory to where the LLVM object files should live:
+
+ .. code-block:: console
+
+ % cd OBJ_ROOT
+
+* Run ``cmake``:
+
+ .. code-block:: console
+
+ % cmake -G "Unix Makefiles" SRC_ROOT
+
+The LLVM build will create a structure underneath *OBJ_ROOT* that matches the
+LLVM source tree. At each level where source files are present in the source
+tree there will be a corresponding ``CMakeFiles`` directory in the *OBJ_ROOT*.
+Underneath that directory there is another directory with a name ending in
+``.dir`` under which you'll find object files for each source.
+
+For example:
+
+ .. code-block:: console
+
+ % cd llvm_build_dir
+ % find lib/Support/ -name APFloat*
+ lib/Support/CMakeFiles/LLVMSupport.dir/APFloat.cpp.o
+
+Optional Configuration Items
+----------------------------
+
+If you're running on a Linux system that supports the `binfmt_misc
+<http://en.wikipedia.org/wiki/binfmt_misc>`_
+module, and you have root access on the system, you can set your system up to
+execute LLVM bitcode files directly. To do this, use commands like this (the
+first command may not be required if you are already using the module):
+
+.. code-block:: console
+
+ % mount -t binfmt_misc none /proc/sys/fs/binfmt_misc
+ % echo ':llvm:M::BC::/path/to/lli:' > /proc/sys/fs/binfmt_misc/register
+ % chmod u+x hello.bc (if needed)
+ % ./hello.bc
+
+This allows you to execute LLVM bitcode files directly. On Debian, you can also
+use this command instead of the 'echo' command above:
+
+.. code-block:: console
+
+ % sudo update-binfmts --install llvm /path/to/lli --magic 'BC'
+
+.. _Program Layout:
+.. _general layout:
+
+Directory Layout
+================
+
+One useful source of information about the LLVM source base is the LLVM `doxygen
+<http://www.doxygen.org/>`_ documentation available at
+`<http://llvm.org/doxygen/>`_. The following is a brief introduction to code
+layout:
+
+``llvm/examples``
+-----------------
+
+Simple examples using the LLVM IR and JIT.
+
+``llvm/include``
+----------------
+
+Public header files exported from the LLVM library. The three main subdirectories:
+
+``llvm/include/llvm``
+
+ All LLVM-specific header files, and subdirectories for different portions of
+ LLVM: ``Analysis``, ``CodeGen``, ``Target``, ``Transforms``, etc...
+
+``llvm/include/llvm/Support``
+
+ Generic support libraries provided with LLVM but not necessarily specific to
+ LLVM. For example, some C++ STL utilities and a Command Line option processing
+ library store header files here.
+
+``llvm/include/llvm/Config``
+
+ Header files configured by the ``configure`` script.
+ They wrap "standard" UNIX and C header files. Source code can include these
+ header files which automatically take care of the conditional #includes that
+ the ``configure`` script generates.
+
+``llvm/lib``
+------------
+
+Most source files are here. By putting code in libraries, LLVM makes it easy to
+share code among the `tools`_.
+
+``llvm/lib/IR/``
+
+ Core LLVM source files that implement core classes like Instruction and
+ BasicBlock.
+
+``llvm/lib/AsmParser/``
+
+ Source code for the LLVM assembly language parser library.
+
+``llvm/lib/Bitcode/``
+
+ Code for reading and writing bitcode.
+
+``llvm/lib/Analysis/``
+
+ A variety of program analyses, such as Call Graphs, Induction Variables,
+ Natural Loop Identification, etc.
+
+``llvm/lib/Transforms/``
+
+ IR-to-IR program transformations, such as Aggressive Dead Code Elimination,
+ Sparse Conditional Constant Propagation, Inlining, Loop Invariant Code Motion,
+ Dead Global Elimination, and many others.
+
+``llvm/lib/Target/``
+
+ Files describing target architectures for code generation. For example,
+ ``llvm/lib/Target/X86`` holds the X86 machine description.
+
+``llvm/lib/CodeGen/``
+
+ The major parts of the code generator: Instruction Selector, Instruction
+ Scheduling, and Register Allocation.
+
+``llvm/lib/MC/``
+
+ (FIXME: T.B.D.) ....?
+
+``llvm/lib/ExecutionEngine/``
+
+ Libraries for directly executing bitcode at runtime in interpreted and
+ JIT-compiled scenarios.
+
+``llvm/lib/Support/``
+
+ Source code that corresponding to the header files in ``llvm/include/ADT/``
+ and ``llvm/include/Support/``.
+
+``llvm/projects``
+-----------------
+
+Projects not strictly part of LLVM but shipped with LLVM. This is also the
+directory for creating your own LLVM-based projects which leverage the LLVM
+build system.
+
+``llvm/test``
+-------------
+
+Feature and regression tests and other sanity checks on LLVM infrastructure. These
+are intended to run quickly and cover a lot of territory without being exhaustive.
+
+``test-suite``
+--------------
+
+A comprehensive correctness, performance, and benchmarking test suite for LLVM.
+Comes in a separate Subversion module because not every LLVM user is interested
+in such a comprehensive suite. For details see the :doc:`Testing Guide
+<TestingGuide>` document.
+
+.. _tools:
+
+``llvm/tools``
+--------------
+
+Executables built out of the libraries
+above, which form the main part of the user interface. You can always get help
+for a tool by typing ``tool_name -help``. The following is a brief introduction
+to the most important tools. More detailed information is in
+the `Command Guide <CommandGuide/index.html>`_.
+
+``bugpoint``
+
+ ``bugpoint`` is used to debug optimization passes or code generation backends
+ by narrowing down the given test case to the minimum number of passes and/or
+ instructions that still cause a problem, whether it is a crash or
+ miscompilation. See `<HowToSubmitABug.html>`_ for more information on using
+ ``bugpoint``.
+
+``llvm-ar``
+
+ The archiver produces an archive containing the given LLVM bitcode files,
+ optionally with an index for faster lookup.
+
+``llvm-as``
+
+ The assembler transforms the human readable LLVM assembly to LLVM bitcode.
+
+``llvm-dis``
+
+ The disassembler transforms the LLVM bitcode to human readable LLVM assembly.
+
+``llvm-link``
+
+ ``llvm-link``, not surprisingly, links multiple LLVM modules into a single
+ program.
+
+``lli``
+
+ ``lli`` is the LLVM interpreter, which can directly execute LLVM bitcode
+ (although very slowly...). For architectures that support it (currently x86,
+ Sparc, and PowerPC), by default, ``lli`` will function as a Just-In-Time
+ compiler (if the functionality was compiled in), and will execute the code
+ *much* faster than the interpreter.
+
+``llc``
+
+ ``llc`` is the LLVM backend compiler, which translates LLVM bitcode to a
+ native code assembly file.
+
+``opt``
+
+ ``opt`` reads LLVM bitcode, applies a series of LLVM to LLVM transformations
+ (which are specified on the command line), and outputs the resultant
+ bitcode. '``opt -help``' is a good way to get a list of the
+ program transformations available in LLVM.
+
+ ``opt`` can also run a specific analysis on an input LLVM bitcode
+ file and print the results. Primarily useful for debugging
+ analyses, or familiarizing yourself with what an analysis does.
+
+``llvm/utils``
+--------------
+
+Utilities for working with LLVM source code; some are part of the build process
+because they are code generators for parts of the infrastructure.
+
+
+``codegen-diff``
+
+ ``codegen-diff`` finds differences between code that LLC
+ generates and code that LLI generates. This is useful if you are
+ debugging one of them, assuming that the other generates correct output. For
+ the full user manual, run ```perldoc codegen-diff'``.
+
+``emacs/``
+
+ Emacs and XEmacs syntax highlighting for LLVM assembly files and TableGen
+ description files. See the ``README`` for information on using them.
+
+``getsrcs.sh``
+
+ Finds and outputs all non-generated source files,
+ useful if one wishes to do a lot of development across directories
+ and does not want to find each file. One way to use it is to run,
+ for example: ``xemacs `utils/getsources.sh``` from the top of the LLVM source
+ tree.
+
+``llvmgrep``
+
+ Performs an ``egrep -H -n`` on each source file in LLVM and
+ passes to it a regular expression provided on ``llvmgrep``'s command
+ line. This is an efficient way of searching the source base for a
+ particular regular expression.
+
+``makellvm``
+
+ Compiles all files in the current directory, then
+ compiles and links the tool that is the first argument. For example, assuming
+ you are in ``llvm/lib/Target/Sparc``, if ``makellvm`` is in your
+ path, running ``makellvm llc`` will make a build of the current
+ directory, switch to directory ``llvm/tools/llc`` and build it, causing a
+ re-linking of LLC.
+
+``TableGen/``
+
+ Contains the tool used to generate register
+ descriptions, instruction set descriptions, and even assemblers from common
+ TableGen description files.
+
+``vim/``
+
+ vim syntax-highlighting for LLVM assembly files
+ and TableGen description files. See the ``README`` for how to use them.
+
+.. _simple example:
+
+An Example Using the LLVM Tool Chain
+====================================
+
+This section gives an example of using LLVM with the Clang front end.
+
+Example with clang
+------------------
+
+#. First, create a simple C file, name it 'hello.c':
+
+ .. code-block:: c
+
+ #include <stdio.h>
+
+ int main() {
+ printf("hello world\n");
+ return 0;
+ }
+
+#. Next, compile the C file into a native executable:
+
+ .. code-block:: console
+
+ % clang hello.c -o hello
+
+ .. note::
+
+ Clang works just like GCC by default. The standard -S and -c arguments
+ work as usual (producing a native .s or .o file, respectively).
+
+#. Next, compile the C file into an LLVM bitcode file:
+
+ .. code-block:: console
+
+ % clang -O3 -emit-llvm hello.c -c -o hello.bc
+
+ The -emit-llvm option can be used with the -S or -c options to emit an LLVM
+ ``.ll`` or ``.bc`` file (respectively) for the code. This allows you to use
+ the `standard LLVM tools <CommandGuide/index.html>`_ on the bitcode file.
+
+#. Run the program in both forms. To run the program, use:
+
+ .. code-block:: console
+
+ % ./hello
+
+ and
+
+ .. code-block:: console
+
+ % lli hello.bc
+
+ The second examples shows how to invoke the LLVM JIT, :doc:`lli
+ <CommandGuide/lli>`.
+
+#. Use the ``llvm-dis`` utility to take a look at the LLVM assembly code:
+
+ .. code-block:: console
+
+ % llvm-dis < hello.bc | less
+
+#. Compile the program to native assembly using the LLC code generator:
+
+ .. code-block:: console
+
+ % llc hello.bc -o hello.s
+
+#. Assemble the native assembly language file into a program:
+
+ .. code-block:: console
+
+ % /opt/SUNWspro/bin/cc -xarch=v9 hello.s -o hello.native # On Solaris
+
+ % gcc hello.s -o hello.native # On others
+
+#. Execute the native code program:
+
+ .. code-block:: console
+
+ % ./hello.native
+
+ Note that using clang to compile directly to native code (i.e. when the
+ ``-emit-llvm`` option is not present) does steps 6/7/8 for you.
+
+Common Problems
+===============
+
+If you are having problems building or using LLVM, or if you have any other
+general questions about LLVM, please consult the `Frequently Asked
+Questions <FAQ.html>`_ page.
+
+.. _links:
+
+Links
+=====
+
+This document is just an **introduction** on how to use LLVM to do some simple
+things... there are many more interesting and complicated things that you can do
+that aren't documented here (but we'll gladly accept a patch if you want to
+write something up!). For more information about LLVM, check out:
+
+* `LLVM Homepage <http://llvm.org/>`_
+* `LLVM Doxygen Tree <http://llvm.org/doxygen/>`_
+* `Starting a Project that Uses LLVM <http://llvm.org/docs/Projects.html>`_
Added: www-releases/trunk/5.0.2/docs/_sources/GettingStartedVS.txt
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@@ -0,0 +1,236 @@
+==================================================================
+Getting Started with the LLVM System using Microsoft Visual Studio
+==================================================================
+
+.. contents::
+ :local:
+
+
+Overview
+========
+Welcome to LLVM on Windows! This document only covers LLVM on Windows using
+Visual Studio, not mingw or cygwin. In order to get started, you first need to
+know some basic information.
+
+There are many different projects that compose LLVM. The first piece is the
+LLVM suite. This contains all of the tools, libraries, and header files needed
+to use LLVM. It contains an assembler, disassembler, bitcode analyzer and
+bitcode optimizer. It also contains basic regression tests that can be used to
+test the LLVM tools and the Clang front end.
+
+The second piece is the `Clang <http://clang.llvm.org/>`_ front end. This
+component compiles C, C++, Objective C, and Objective C++ code into LLVM
+bitcode. Clang typically uses LLVM libraries to optimize the bitcode and emit
+machine code. LLVM fully supports the COFF object file format, which is
+compatible with all other existing Windows toolchains.
+
+The last major part of LLVM, the execution Test Suite, does not run on Windows,
+and this document does not discuss it.
+
+Additional information about the LLVM directory structure and tool chain
+can be found on the main :doc:`GettingStarted` page.
+
+
+Requirements
+============
+Before you begin to use the LLVM system, review the requirements given
+below. This may save you some trouble by knowing ahead of time what hardware
+and software you will need.
+
+Hardware
+--------
+Any system that can adequately run Visual Studio 2015 is fine. The LLVM
+source tree and object files, libraries and executables will consume
+approximately 3GB.
+
+Software
+--------
+You will need Visual Studio 2015 or higher, with the latest Update installed.
+
+You will also need the `CMake <http://www.cmake.org/>`_ build system since it
+generates the project files you will use to build with.
+
+If you would like to run the LLVM tests you will need `Python
+<http://www.python.org/>`_. Version 2.7 and newer are known to work. You will
+need `GnuWin32 <http://gnuwin32.sourceforge.net/>`_ tools, too.
+
+Do not install the LLVM directory tree into a path containing spaces (e.g.
+``C:\Documents and Settings\...``) as the configure step will fail.
+
+
+Getting Started
+===============
+Here's the short story for getting up and running quickly with LLVM:
+
+1. Read the documentation.
+2. Seriously, read the documentation.
+3. Remember that you were warned twice about reading the documentation.
+4. Get the Source Code
+
+ * With the distributed files:
+
+ 1. ``cd <where-you-want-llvm-to-live>``
+ 2. ``gunzip --stdout llvm-VERSION.tar.gz | tar -xvf -``
+ (*or use WinZip*)
+ 3. ``cd llvm``
+
+ * With anonymous Subversion access:
+
+ 1. ``cd <where-you-want-llvm-to-live>``
+ 2. ``svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm``
+ 3. ``cd llvm``
+
+5. Use `CMake <http://www.cmake.org/>`_ to generate up-to-date project files:
+
+ * Once CMake is installed then the simplest way is to just start the
+ CMake GUI, select the directory where you have LLVM extracted to, and
+ the default options should all be fine. One option you may really
+ want to change, regardless of anything else, might be the
+ ``CMAKE_INSTALL_PREFIX`` setting to select a directory to INSTALL to
+ once compiling is complete, although installation is not mandatory for
+ using LLVM. Another important option is ``LLVM_TARGETS_TO_BUILD``,
+ which controls the LLVM target architectures that are included on the
+ build.
+ * If CMake complains that it cannot find the compiler, make sure that
+ you have the Visual Studio C++ Tools installed, not just Visual Studio
+ itself (trying to create a C++ project in Visual Studio will generally
+ download the C++ tools if they haven't already been).
+ * See the :doc:`LLVM CMake guide <CMake>` for detailed information about
+ how to configure the LLVM build.
+ * CMake generates project files for all build types. To select a specific
+ build type, use the Configuration manager from the VS IDE or the
+ ``/property:Configuration`` command line option when using MSBuild.
+ * By default, the Visual Studio project files generated by CMake use the
+ 32-bit toolset. If you are developing on a 64-bit version of Windows and
+ want to use the 64-bit toolset, pass the ``-Thost=x64`` flag when
+ generating the Visual Studio solution. This requires CMake 3.8.0 or later.
+
+6. Start Visual Studio
+
+ * In the directory you created the project files will have an ``llvm.sln``
+ file, just double-click on that to open Visual Studio.
+
+7. Build the LLVM Suite:
+
+ * The projects may still be built individually, but to build them all do
+ not just select all of them in batch build (as some are meant as
+ configuration projects), but rather select and build just the
+ ``ALL_BUILD`` project to build everything, or the ``INSTALL`` project,
+ which first builds the ``ALL_BUILD`` project, then installs the LLVM
+ headers, libs, and other useful things to the directory set by the
+ ``CMAKE_INSTALL_PREFIX`` setting when you first configured CMake.
+ * The Fibonacci project is a sample program that uses the JIT. Modify the
+ project's debugging properties to provide a numeric command line argument
+ or run it from the command line. The program will print the
+ corresponding fibonacci value.
+
+8. Test LLVM in Visual Studio:
+
+ * If ``%PATH%`` does not contain GnuWin32, you may specify
+ ``LLVM_LIT_TOOLS_DIR`` on CMake for the path to GnuWin32.
+ * You can run LLVM tests by merely building the project "check". The test
+ results will be shown in the VS output window.
+
+9. Test LLVM on the command line:
+
+ * The LLVM tests can be run by changing directory to the llvm source
+ directory and running:
+
+ .. code-block:: bat
+
+ C:\..\llvm> python ..\build\bin\llvm-lit --param build_config=Win32 --param build_mode=Debug --param llvm_site_config=../build/test/lit.site.cfg test
+
+ This example assumes that Python is in your PATH variable, you
+ have built a Win32 Debug version of llvm with a standard out of
+ line build. You should not see any unexpected failures, but will
+ see many unsupported tests and expected failures.
+
+ A specific test or test directory can be run with:
+
+ .. code-block:: bat
+
+ C:\..\llvm> python ..\build\bin\llvm-lit --param build_config=Win32 --param build_mode=Debug --param llvm_site_config=../build/test/lit.site.cfg test/path/to/test
+
+
+An Example Using the LLVM Tool Chain
+====================================
+
+1. First, create a simple C file, name it '``hello.c``':
+
+ .. code-block:: c
+
+ #include <stdio.h>
+ int main() {
+ printf("hello world\n");
+ return 0;
+ }
+
+2. Next, compile the C file into an LLVM bitcode file:
+
+ .. code-block:: bat
+
+ C:\..> clang -c hello.c -emit-llvm -o hello.bc
+
+ This will create the result file ``hello.bc`` which is the LLVM bitcode
+ that corresponds the compiled program and the library facilities that
+ it required. You can execute this file directly using ``lli`` tool,
+ compile it to native assembly with the ``llc``, optimize or analyze it
+ further with the ``opt`` tool, etc.
+
+ Alternatively you can directly output an executable with clang with:
+
+ .. code-block:: bat
+
+ C:\..> clang hello.c -o hello.exe
+
+ The ``-o hello.exe`` is required because clang currently outputs ``a.out``
+ when neither ``-o`` nor ``-c`` are given.
+
+3. Run the program using the just-in-time compiler:
+
+ .. code-block:: bat
+
+ C:\..> lli hello.bc
+
+4. Use the ``llvm-dis`` utility to take a look at the LLVM assembly code:
+
+ .. code-block:: bat
+
+ C:\..> llvm-dis < hello.bc | more
+
+5. Compile the program to object code using the LLC code generator:
+
+ .. code-block:: bat
+
+ C:\..> llc -filetype=obj hello.bc
+
+6. Link to binary using Microsoft link:
+
+ .. code-block:: bat
+
+ C:\..> link hello.obj -defaultlib:libcmt
+
+7. Execute the native code program:
+
+ .. code-block:: bat
+
+ C:\..> hello.exe
+
+
+Common Problems
+===============
+If you are having problems building or using LLVM, or if you have any other
+general questions about LLVM, please consult the :doc:`Frequently Asked Questions
+<FAQ>` page.
+
+
+Links
+=====
+This document is just an **introduction** to how to use LLVM to do some simple
+things... there are many more interesting and complicated things that you can
+do that aren't documented here (but we'll gladly accept a patch if you want to
+write something up!). For more information about LLVM, check out:
+
+* `LLVM homepage <http://llvm.org/>`_
+* `LLVM doxygen tree <http://llvm.org/doxygen/>`_
+
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--- www-releases/trunk/5.0.2/docs/_sources/GlobalISel.txt (added)
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@@ -0,0 +1,637 @@
+============================
+Global Instruction Selection
+============================
+
+.. contents::
+ :local:
+ :depth: 1
+
+.. warning::
+ This document is a work in progress. It reflects the current state of the
+ implementation, as well as open design and implementation issues.
+
+Introduction
+============
+
+GlobalISel is a framework that provides a set of reusable passes and utilities
+for instruction selection --- translation from LLVM IR to target-specific
+Machine IR (MIR).
+
+GlobalISel is intended to be a replacement for SelectionDAG and FastISel, to
+solve three major problems:
+
+* **Performance** --- SelectionDAG introduces a dedicated intermediate
+ representation, which has a compile-time cost.
+
+ GlobalISel directly operates on the post-isel representation used by the
+ rest of the code generator, MIR.
+ It does require extensions to that representation to support arbitrary
+ incoming IR: :ref:`gmir`.
+
+* **Granularity** --- SelectionDAG and FastISel operate on individual basic
+ blocks, losing some global optimization opportunities.
+
+ GlobalISel operates on the whole function.
+
+* **Modularity** --- SelectionDAG and FastISel are radically different and share
+ very little code.
+
+ GlobalISel is built in a way that enables code reuse. For instance, both the
+ optimized and fast selectors share the :ref:`pipeline`, and targets can
+ configure that pipeline to better suit their needs.
+
+
+.. _gmir:
+
+Generic Machine IR
+==================
+
+Machine IR operates on physical registers, register classes, and (mostly)
+target-specific instructions.
+
+To bridge the gap with LLVM IR, GlobalISel introduces "generic" extensions to
+Machine IR:
+
+.. contents::
+ :local:
+
+``NOTE``:
+The generic MIR (GMIR) representation still contains references to IR
+constructs (such as ``GlobalValue``). Removing those should let us write more
+accurate tests, or delete IR after building the initial MIR. However, it is
+not part of the GlobalISel effort.
+
+.. _gmir-instructions:
+
+Generic Instructions
+--------------------
+
+The main addition is support for pre-isel generic machine instructions (e.g.,
+``G_ADD``). Like other target-independent instructions (e.g., ``COPY`` or
+``PHI``), these are available on all targets.
+
+``TODO``:
+While we're progressively adding instructions, one kind in particular exposes
+interesting problems: compares and how to represent condition codes.
+Some targets (x86, ARM) have generic comparisons setting multiple flags,
+which are then used by predicated variants.
+Others (IR) specify the predicate in the comparison and users just get a single
+bit. SelectionDAG uses SETCC/CONDBR vs BR_CC (and similar for select) to
+represent this.
+
+The ``MachineIRBuilder`` class wraps the ``MachineInstrBuilder`` and provides
+a convenient way to create these generic instructions.
+
+.. _gmir-gvregs:
+
+Generic Virtual Registers
+-------------------------
+
+Generic instructions operate on a new kind of register: "generic" virtual
+registers. As opposed to non-generic vregs, they are not assigned a Register
+Class. Instead, generic vregs have a :ref:`gmir-llt`, and can be assigned
+a :ref:`gmir-regbank`.
+
+``MachineRegisterInfo`` tracks the same information that it does for
+non-generic vregs (e.g., use-def chains). Additionally, it also tracks the
+:ref:`gmir-llt` of the register, and, instead of the ``TargetRegisterClass``,
+its :ref:`gmir-regbank`, if any.
+
+For simplicity, most generic instructions only accept generic vregs:
+
+* instead of immediates, they use a gvreg defined by an instruction
+ materializing the immediate value (see :ref:`irtranslator-constants`).
+* instead of physical register, they use a gvreg defined by a ``COPY``.
+
+``NOTE``:
+We started with an alternative representation, where MRI tracks a size for
+each gvreg, and instructions have lists of types.
+That had two flaws: the type and size are redundant, and there was no generic
+way of getting a given operand's type (as there was no 1:1 mapping between
+instruction types and operands).
+We considered putting the type in some variant of MCInstrDesc instead:
+See `PR26576 <http://llvm.org/PR26576>`_: [GlobalISel] Generic MachineInstrs
+need a type but this increases the memory footprint of the related objects
+
+.. _gmir-regbank:
+
+Register Bank
+-------------
+
+A Register Bank is a set of register classes defined by the target.
+A bank has a size, which is the maximum store size of all covered classes.
+
+In general, cross-class copies inside a bank are expected to be cheaper than
+copies across banks. They are also coalesceable by the register coalescer,
+whereas cross-bank copies are not.
+
+Also, equivalent operations can be performed on different banks using different
+instructions.
+
+For example, X86 can be seen as having 3 main banks: general-purpose, x87, and
+vector (which could be further split into a bank per domain for single vs
+double precision instructions).
+
+Register banks are described by a target-provided API,
+:ref:`RegisterBankInfo <api-registerbankinfo>`.
+
+.. _gmir-llt:
+
+Low Level Type
+--------------
+
+Additionally, every generic virtual register has a type, represented by an
+instance of the ``LLT`` class.
+
+Like ``EVT``/``MVT``/``Type``, it has no distinction between unsigned and signed
+integer types. Furthermore, it also has no distinction between integer and
+floating-point types: it mainly conveys absolutely necessary information, such
+as size and number of vector lanes:
+
+* ``sN`` for scalars
+* ``pN`` for pointers
+* ``<N x sM>`` for vectors
+* ``unsized`` for labels, etc..
+
+``LLT`` is intended to replace the usage of ``EVT`` in SelectionDAG.
+
+Here are some LLT examples and their ``EVT`` and ``Type`` equivalents:
+
+ ============= ========= ======================================
+ LLT EVT IR Type
+ ============= ========= ======================================
+ ``s1`` ``i1`` ``i1``
+ ``s8`` ``i8`` ``i8``
+ ``s32`` ``i32`` ``i32``
+ ``s32`` ``f32`` ``float``
+ ``s17`` ``i17`` ``i17``
+ ``s16`` N/A ``{i8, i8}``
+ ``s32`` N/A ``[4 x i8]``
+ ``p0`` ``iPTR`` ``i8*``, ``i32*``, ``%opaque*``
+ ``p2`` ``iPTR`` ``i8 addrspace(2)*``
+ ``<4 x s32>`` ``v4f32`` ``<4 x float>``
+ ``s64`` ``v1f64`` ``<1 x double>``
+ ``<3 x s32>`` ``v3i32`` ``<3 x i32>``
+ ``unsized`` ``Other`` ``label``
+ ============= ========= ======================================
+
+
+Rationale: instructions already encode a specific interpretation of types
+(e.g., ``add`` vs. ``fadd``, or ``sdiv`` vs. ``udiv``). Also encoding that
+information in the type system requires introducing bitcast with no real
+advantage for the selector.
+
+Pointer types are distinguished by address space. This matches IR, as opposed
+to SelectionDAG where address space is an attribute on operations.
+This representation better supports pointers having different sizes depending
+on their addressspace.
+
+``NOTE``:
+Currently, LLT requires at least 2 elements in vectors, but some targets have
+the concept of a '1-element vector'. Representing them as their underlying
+scalar type is a nice simplification.
+
+``TODO``:
+Currently, non-generic virtual registers, defined by non-pre-isel-generic
+instructions, cannot have a type, and thus cannot be used by a pre-isel generic
+instruction. Instead, they are given a type using a COPY. We could relax that
+and allow types on all vregs: this would reduce the number of MI required when
+emitting target-specific MIR early in the pipeline. This should purely be
+a compile-time optimization.
+
+.. _pipeline:
+
+Core Pipeline
+=============
+
+There are four required passes, regardless of the optimization mode:
+
+.. contents::
+ :local:
+
+Additional passes can then be inserted at higher optimization levels or for
+specific targets. For example, to match the current SelectionDAG set of
+transformations: MachineCSE and a better MachineCombiner between every pass.
+
+``NOTE``:
+In theory, not all passes are always necessary.
+As an additional compile-time optimization, we could skip some of the passes by
+setting the relevant MachineFunction properties. For instance, if the
+IRTranslator did not encounter any illegal instruction, it would set the
+``legalized`` property to avoid running the :ref:`milegalizer`.
+Similarly, we considered specializing the IRTranslator per-target to directly
+emit target-specific MI.
+However, we instead decided to keep the core pipeline simple, and focus on
+minimizing the overhead of the passes in the no-op cases.
+
+
+.. _irtranslator:
+
+IRTranslator
+------------
+
+This pass translates the input LLVM IR ``Function`` to a GMIR
+``MachineFunction``.
+
+``TODO``:
+This currently doesn't support the more complex instructions, in particular
+those involving control flow (``switch``, ``invoke``, ...).
+For ``switch`` in particular, we can initially use the ``LowerSwitch`` pass.
+
+.. _api-calllowering:
+
+API: CallLowering
+^^^^^^^^^^^^^^^^^
+
+The ``IRTranslator`` (using the ``CallLowering`` target-provided utility) also
+implements the ABI's calling convention by lowering calls, returns, and
+arguments to the appropriate physical register usage and instruction sequences.
+
+.. _irtranslator-aggregates:
+
+Aggregates
+^^^^^^^^^^
+
+Aggregates are lowered to a single scalar vreg.
+This differs from SelectionDAG's multiple vregs via ``GetValueVTs``.
+
+``TODO``:
+As some of the bits are undef (padding), we should consider augmenting the
+representation with additional metadata (in effect, caching computeKnownBits
+information on vregs).
+See `PR26161 <http://llvm.org/PR26161>`_: [GlobalISel] Value to vreg during
+IR to MachineInstr translation for aggregate type
+
+.. _irtranslator-constants:
+
+Constant Lowering
+^^^^^^^^^^^^^^^^^
+
+The ``IRTranslator`` lowers ``Constant`` operands into uses of gvregs defined
+by ``G_CONSTANT`` or ``G_FCONSTANT`` instructions.
+Currently, these instructions are always emitted in the entry basic block.
+In a ``MachineFunction``, each ``Constant`` is materialized by a single gvreg.
+
+This is beneficial as it allows us to fold constants into immediate operands
+during :ref:`instructionselect`, while still avoiding redundant materializations
+for expensive non-foldable constants.
+However, this can lead to unnecessary spills and reloads in an -O0 pipeline, as
+these vregs can have long live ranges.
+
+``TODO``:
+We're investigating better placement of these instructions, in fast and
+optimized modes.
+
+
+.. _milegalizer:
+
+Legalizer
+---------
+
+This pass transforms the generic machine instructions such that they are legal.
+
+A legal instruction is defined as:
+
+* **selectable** --- the target will later be able to select it to a
+ target-specific (non-generic) instruction.
+
+* operating on **vregs that can be loaded and stored** -- if necessary, the
+ target can select a ``G_LOAD``/``G_STORE`` of each gvreg operand.
+
+As opposed to SelectionDAG, there are no legalization phases. In particular,
+'type' and 'operation' legalization are not separate.
+
+Legalization is iterative, and all state is contained in GMIR. To maintain the
+validity of the intermediate code, instructions are introduced:
+
+* ``G_SEQUENCE`` --- concatenate multiple registers into a single wider
+ register.
+
+* ``G_EXTRACT`` --- extract multiple registers (as contiguous sequences of bits)
+ from a single wider register.
+
+As they are expected to be temporary byproducts of the legalization process,
+they are combined at the end of the :ref:`milegalizer` pass.
+If any remain, they are expected to always be selectable, using loads and stores
+if necessary.
+
+.. _api-legalizerinfo:
+
+API: LegalizerInfo
+^^^^^^^^^^^^^^^^^^
+
+Currently the API is broadly similar to SelectionDAG/TargetLowering, but
+extended in two ways:
+
+* The set of available actions is wider, avoiding the currently very
+ overloaded ``Expand`` (which can cover everything from libcalls to
+ scalarization depending on the node's opcode).
+
+* Since there's no separate type legalization, independently varying
+ types on an instruction can have independent actions. For example a
+ ``G_ICMP`` has 2 independent types: the result and the inputs; we need
+ to be able to say that comparing 2 s32s is OK, but the s1 result
+ must be dealt with in another way.
+
+As such, the primary key when deciding what to do is the ``InstrAspect``,
+essentially a tuple consisting of ``(Opcode, TypeIdx, Type)`` and mapping to a
+suggested course of action.
+
+An example use might be:
+
+ .. code-block:: c++
+
+ // The CPU can't deal with an s1 result, do something about it.
+ setAction({G_ICMP, 0, s1}, WidenScalar);
+ // An s32 input (the second type) is fine though.
+ setAction({G_ICMP, 1, s32}, Legal);
+
+
+``TODO``:
+An alternative worth investigating is to generalize the API to represent
+actions using ``std::function`` that implements the action, instead of explicit
+enum tokens (``Legal``, ``WidenScalar``, ...).
+
+``TODO``:
+Moreover, we could use TableGen to initially infer legality of operation from
+existing patterns (as any pattern we can select is by definition legal).
+Expanding that to describe legalization actions is a much larger but
+potentially useful project.
+
+.. _milegalizer-non-power-of-2:
+
+Non-power of 2 types
+^^^^^^^^^^^^^^^^^^^^
+
+``TODO``:
+Types which have a size that isn't a power of 2 aren't currently supported.
+The setAction API will probably require changes to support them.
+Even notionally explicitly specified operations only make suggestions
+like "Widen" or "Narrow". The eventual type is still unspecified and a
+search is performed by repeated doubling/halving of the type's
+size.
+This is incorrect for types that aren't a power of 2. It's reasonable to
+expect we could construct an efficient set of side-tables for more general
+lookups though, encoding a map from the integers (i.e. the size of the current
+type) to types (the legal size).
+
+.. _milegalizer-vector:
+
+Vector types
+^^^^^^^^^^^^
+
+Vectors first get their element type legalized: ``<A x sB>`` becomes
+``<A x sC>`` such that at least one operation is legal with ``sC``.
+
+This is currently specified by the function ``setScalarInVectorAction``, called
+for example as:
+
+ setScalarInVectorAction(G_ICMP, s1, WidenScalar);
+
+Next the number of elements is chosen so that the entire operation is
+legal. This aspect is not controllable at the moment, but probably
+should be (you could imagine disagreements on whether a ``<2 x s8>``
+operation should be scalarized or extended to ``<8 x s8>``).
+
+
+.. _regbankselect:
+
+RegBankSelect
+-------------
+
+This pass constrains the :ref:`gmir-gvregs` operands of generic
+instructions to some :ref:`gmir-regbank`.
+
+It iteratively maps instructions to a set of per-operand bank assignment.
+The possible mappings are determined by the target-provided
+:ref:`RegisterBankInfo <api-registerbankinfo>`.
+The mapping is then applied, possibly introducing ``COPY`` instructions if
+necessary.
+
+It traverses the ``MachineFunction`` top down so that all operands are already
+mapped when analyzing an instruction.
+
+This pass could also remap target-specific instructions when beneficial.
+In the future, this could replace the ExeDepsFix pass, as we can directly
+select the best variant for an instruction that's available on multiple banks.
+
+.. _api-registerbankinfo:
+
+API: RegisterBankInfo
+^^^^^^^^^^^^^^^^^^^^^
+
+The ``RegisterBankInfo`` class describes multiple aspects of register banks.
+
+* **Banks**: ``addRegBankCoverage`` --- which register bank covers each
+ register class.
+
+* **Cross-Bank Copies**: ``copyCost`` --- the cost of a ``COPY`` from one bank
+ to another.
+
+* **Default Mapping**: ``getInstrMapping`` --- the default bank assignments for
+ a given instruction.
+
+* **Alternative Mapping**: ``getInstrAlternativeMapping`` --- the other
+ possible bank assignments for a given instruction.
+
+``TODO``:
+All this information should eventually be static and generated by TableGen,
+mostly using existing information augmented by bank descriptions.
+
+``TODO``:
+``getInstrMapping`` is currently separate from ``getInstrAlternativeMapping``
+because the latter is more expensive: as we move to static mapping info,
+both methods should be free, and we should merge them.
+
+.. _regbankselect-modes:
+
+RegBankSelect Modes
+^^^^^^^^^^^^^^^^^^^
+
+``RegBankSelect`` currently has two modes:
+
+* **Fast** --- For each instruction, pick a target-provided "default" bank
+ assignment. This is the default at -O0.
+
+* **Greedy** --- For each instruction, pick the cheapest of several
+ target-provided bank assignment alternatives.
+
+We intend to eventually introduce an additional optimizing mode:
+
+* **Global** --- Across multiple instructions, pick the cheapest combination of
+ bank assignments.
+
+``NOTE``:
+On AArch64, we are considering using the Greedy mode even at -O0 (or perhaps at
+backend -O1): because :ref:`gmir-llt` doesn't distinguish floating point from
+integer scalars, the default assignment for loads and stores is the integer
+bank, introducing cross-bank copies on most floating point operations.
+
+
+.. _instructionselect:
+
+InstructionSelect
+-----------------
+
+This pass transforms generic machine instructions into equivalent
+target-specific instructions. It traverses the ``MachineFunction`` bottom-up,
+selecting uses before definitions, enabling trivial dead code elimination.
+
+.. _api-instructionselector:
+
+API: InstructionSelector
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+The target implements the ``InstructionSelector`` class, containing the
+target-specific selection logic proper.
+
+The instance is provided by the subtarget, so that it can specialize the
+selector by subtarget feature (with, e.g., a vector selector overriding parts
+of a general-purpose common selector).
+We might also want to parameterize it by MachineFunction, to enable selector
+variants based on function attributes like optsize.
+
+The simple API consists of:
+
+ .. code-block:: c++
+
+ virtual bool select(MachineInstr &MI)
+
+This target-provided method is responsible for mutating (or replacing) a
+possibly-generic MI into a fully target-specific equivalent.
+It is also responsible for doing the necessary constraining of gvregs into the
+appropriate register classes.
+
+The ``InstructionSelector`` can fold other instructions into the selected MI,
+by walking the use-def chain of the vreg operands.
+As GlobalISel is Global, this folding can occur across basic blocks.
+
+``TODO``:
+Currently, the Select pass is implemented with hand-written c++, similar to
+FastISel, rather than backed by tblgen'erated pattern-matching.
+We intend to eventually reuse SelectionDAG patterns.
+
+
+.. _maintainability:
+
+Maintainability
+===============
+
+.. _maintainability-iterative:
+
+Iterative Transformations
+-------------------------
+
+Passes are split into small, iterative transformations, with all state
+represented in the MIR.
+
+This differs from SelectionDAG (in particular, the legalizer) using various
+in-memory side-tables.
+
+
+.. _maintainability-mir:
+
+MIR Serialization
+-----------------
+
+.. FIXME: Update the MIRLangRef to include GMI additions.
+
+:ref:`gmir` is serializable (see :doc:`MIRLangRef`).
+Combined with :ref:`maintainability-iterative`, this enables much finer-grained
+testing, rather than requiring large and fragile IR-to-assembly tests.
+
+The current "stage" in the :ref:`pipeline` is represented by a set of
+``MachineFunctionProperties``:
+
+* ``legalized``
+* ``regBankSelected``
+* ``selected``
+
+
+.. _maintainability-verifier:
+
+MachineVerifier
+---------------
+
+The pass approach lets us use the ``MachineVerifier`` to enforce invariants.
+For instance, a ``regBankSelected`` function may not have gvregs without
+a bank.
+
+``TODO``:
+The ``MachineVerifier`` being monolithic, some of the checks we want to do
+can't be integrated to it: GlobalISel is a separate library, so we can't
+directly reference it from CodeGen. For instance, legality checks are
+currently done in RegBankSelect/InstructionSelect proper. We could #ifdef out
+the checks, or we could add some sort of verifier API.
+
+
+.. _progress:
+
+Progress and Future Work
+========================
+
+The initial goal is to replace FastISel on AArch64. The next step will be to
+replace SelectionDAG as the optimized ISel.
+
+``NOTE``:
+While we iterate on GlobalISel, we strive to avoid affecting the performance of
+SelectionDAG, FastISel, or the other MIR passes. For instance, the types of
+:ref:`gmir-gvregs` are stored in a separate table in ``MachineRegisterInfo``,
+that is destroyed after :ref:`instructionselect`.
+
+.. _progress-fastisel:
+
+FastISel Replacement
+--------------------
+
+For the initial FastISel replacement, we intend to fallback to SelectionDAG on
+selection failures.
+
+Currently, compile-time of the fast pipeline is within 1.5x of FastISel.
+We're optimistic we can get to within 1.1/1.2x, but beating FastISel will be
+challenging given the multi-pass approach.
+Still, supporting all IR (via a complete legalizer) and avoiding the fallback
+to SelectionDAG in the worst case should enable better amortized performance
+than SelectionDAG+FastISel.
+
+``NOTE``:
+We considered never having a fallback to SelectionDAG, instead deciding early
+whether a given function is supported by GlobalISel or not. The decision would
+be based on :ref:`milegalizer` queries.
+We abandoned that for two reasons:
+a) on IR inputs, we'd need to basically simulate the :ref:`irtranslator`;
+b) to be robust against unforeseen failures and to enable iterative
+improvements.
+
+.. _progress-targets:
+
+Support For Other Targets
+-------------------------
+
+In parallel, we're investigating adding support for other - ideally quite
+different - targets. For instance, there is some initial AMDGPU support.
+
+
+.. _porting:
+
+Porting GlobalISel to A New Target
+==================================
+
+There are four major classes to implement by the target:
+
+* :ref:`CallLowering <api-calllowering>` --- lower calls, returns, and arguments
+ according to the ABI.
+* :ref:`RegisterBankInfo <api-registerbankinfo>` --- describe
+ :ref:`gmir-regbank` coverage, cross-bank copy cost, and the mapping of
+ operands onto banks for each instruction.
+* :ref:`LegalizerInfo <api-legalizerinfo>` --- describe what is legal, and how
+ to legalize what isn't.
+* :ref:`InstructionSelector <api-instructionselector>` --- select generic MIR
+ to target-specific MIR.
+
+Additionally:
+
+* ``TargetPassConfig`` --- create the passes constituting the pipeline,
+ including additional passes not included in the :ref:`pipeline`.
+* ``GISelAccessor`` --- setup the various subtarget-provided classes, with a
+ graceful fallback to no-op when GlobalISel isn't enabled.
Added: www-releases/trunk/5.0.2/docs/_sources/GoldPlugin.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.2/docs/_sources/GoldPlugin.txt?rev=331981&view=auto
==============================================================================
--- www-releases/trunk/5.0.2/docs/_sources/GoldPlugin.txt (added)
+++ www-releases/trunk/5.0.2/docs/_sources/GoldPlugin.txt Thu May 10 06:54:16 2018
@@ -0,0 +1,170 @@
+====================
+The LLVM gold plugin
+====================
+
+Introduction
+============
+
+Building with link time optimization requires cooperation from
+the system linker. LTO support on Linux systems requires that you use the
+`gold linker`_ or ld.bfd from binutils >= 2.21.51.0.2, as they support LTO via plugins. This is the same mechanism
+used by the `GCC LTO`_ project.
+
+The LLVM gold plugin implements the gold plugin interface on top of
+:ref:`libLTO`. The same plugin can also be used by other tools such as
+``ar`` and ``nm``.
+
+.. _`gold linker`: http://sourceware.org/binutils
+.. _`GCC LTO`: http://gcc.gnu.org/wiki/LinkTimeOptimization
+.. _`gold plugin interface`: http://gcc.gnu.org/wiki/whopr/driver
+
+.. _lto-how-to-build:
+
+How to build it
+===============
+
+Check for plugin support by running ``/usr/bin/ld -plugin``. If it complains
+"missing argument" then you have plugin support. If not, such as an "unknown option"
+error then you will either need to build gold or install a recent version
+of ld.bfd with plugin support and then build gold plugin.
+
+* Download, configure and build ld.bfd with plugin support:
+
+ .. code-block:: bash
+
+ $ git clone --depth 1 git://sourceware.org/git/binutils-gdb.git binutils
+ $ mkdir build
+ $ cd build
+ $ ../binutils/configure --disable-werror # ld.bfd includes plugin support by default
+ $ make all-ld
+
+ That should leave you with ``build/ld/ld-new`` which supports
+ the ``-plugin`` option. Running ``make`` will additionally build
+ ``build/binutils/ar`` and ``nm-new`` binaries supporting plugins.
+
+* Build the LLVMgold plugin. Run CMake with
+ ``-DLLVM_BINUTILS_INCDIR=/path/to/binutils/include``. The correct include
+ path will contain the file ``plugin-api.h``.
+
+Usage
+=====
+
+The linker takes a ``-plugin`` option that points to the path of
+the plugin ``.so`` file. To find out what link command ``gcc``
+would run in a given situation, run ``gcc -v [...]`` and
+look for the line where it runs ``collect2``. Replace that with
+``ld-new -plugin /path/to/LLVMgold.so`` to test it out. Once you're
+ready to switch to using gold, backup your existing ``/usr/bin/ld``
+then replace it with ``ld-new``.
+
+You should produce bitcode files from ``clang`` with the option
+``-flto``. This flag will also cause ``clang`` to look for the gold plugin in
+the ``lib`` directory under its prefix and pass the ``-plugin`` option to
+``ld``. It will not look for an alternate linker, which is why you need
+gold to be the installed system linker in your path.
+
+``ar`` and ``nm`` also accept the ``-plugin`` option and it's possible to
+to install ``LLVMgold.so`` to ``/usr/lib/bfd-plugins`` for a seamless setup.
+If you built your own gold, be sure to install the ``ar`` and ``nm-new`` you
+built to ``/usr/bin``.
+
+
+Example of link time optimization
+---------------------------------
+
+The following example shows a worked example of the gold plugin mixing LLVM
+bitcode and native code.
+
+.. code-block:: c
+
+ --- a.c ---
+ #include <stdio.h>
+
+ extern void foo1(void);
+ extern void foo4(void);
+
+ void foo2(void) {
+ printf("Foo2\n");
+ }
+
+ void foo3(void) {
+ foo4();
+ }
+
+ int main(void) {
+ foo1();
+ }
+
+ --- b.c ---
+ #include <stdio.h>
+
+ extern void foo2(void);
+
+ void foo1(void) {
+ foo2();
+ }
+
+ void foo4(void) {
+ printf("Foo4");
+ }
+
+.. code-block:: bash
+
+ --- command lines ---
+ $ clang -flto a.c -c -o a.o # <-- a.o is LLVM bitcode file
+ $ ar q a.a a.o # <-- a.a is an archive with LLVM bitcode
+ $ clang b.c -c -o b.o # <-- b.o is native object file
+ $ clang -flto a.a b.o -o main # <-- link with LLVMgold plugin
+
+Gold informs the plugin that foo3 is never referenced outside the IR,
+leading LLVM to delete that function. However, unlike in the :ref:`libLTO
+example <libLTO-example>` gold does not currently eliminate foo4.
+
+Quickstart for using LTO with autotooled projects
+=================================================
+
+Once your system ``ld``, ``ar``, and ``nm`` all support LLVM bitcode,
+everything is in place for an easy to use LTO build of autotooled projects:
+
+* Follow the instructions :ref:`on how to build LLVMgold.so
+ <lto-how-to-build>`.
+
+* Install the newly built binutils to ``$PREFIX``
+
+* Copy ``Release/lib/LLVMgold.so`` to ``$PREFIX/lib/bfd-plugins/``
+
+* Set environment variables (``$PREFIX`` is where you installed clang and
+ binutils):
+
+ .. code-block:: bash
+
+ export CC="$PREFIX/bin/clang -flto"
+ export CXX="$PREFIX/bin/clang++ -flto"
+ export AR="$PREFIX/bin/ar"
+ export NM="$PREFIX/bin/nm"
+ export RANLIB=/bin/true #ranlib is not needed, and doesn't support .bc files in .a
+
+* Or you can just set your path:
+
+ .. code-block:: bash
+
+ export PATH="$PREFIX/bin:$PATH"
+ export CC="clang -flto"
+ export CXX="clang++ -flto"
+ export RANLIB=/bin/true
+* Configure and build the project as usual:
+
+ .. code-block:: bash
+
+ % ./configure && make && make check
+
+The environment variable settings may work for non-autotooled projects too,
+but you may need to set the ``LD`` environment variable as well.
+
+Licensing
+=========
+
+Gold is licensed under the GPLv3. LLVMgold uses the interface file
+``plugin-api.h`` from gold which means that the resulting ``LLVMgold.so``
+binary is also GPLv3. This can still be used to link non-GPLv3 programs
+just as much as gold could without the plugin.
Added: www-releases/trunk/5.0.2/docs/_sources/HowToAddABuilder.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.2/docs/_sources/HowToAddABuilder.txt?rev=331981&view=auto
==============================================================================
--- www-releases/trunk/5.0.2/docs/_sources/HowToAddABuilder.txt (added)
+++ www-releases/trunk/5.0.2/docs/_sources/HowToAddABuilder.txt Thu May 10 06:54:16 2018
@@ -0,0 +1,106 @@
+===================================================================
+How To Add Your Build Configuration To LLVM Buildbot Infrastructure
+===================================================================
+
+Introduction
+============
+
+This document contains information about adding a build configuration and
+buildslave to private slave builder to LLVM Buildbot Infrastructure.
+
+Buildmasters
+============
+
+There are two buildmasters running.
+
+* The main buildmaster at `<http://lab.llvm.org:8011>`_. All builders attached
+ to this machine will notify commit authors every time they break the build.
+* The staging buildbot at `<http://lab.llvm.org:8014>`_. All builders attached
+ to this machine will be completely silent by default when the build is broken.
+ Builders for experimental backends should generally be attached to this
+ buildmaster.
+
+Steps To Add Builder To LLVM Buildbot
+=====================================
+Volunteers can provide their build machines to work as build slaves to
+public LLVM Buildbot.
+
+Here are the steps you can follow to do so:
+
+#. Check the existing build configurations to make sure the one you are
+ interested in is not covered yet or gets built on your computer much
+ faster than on the existing one. We prefer faster builds so developers
+ will get feedback sooner after changes get committed.
+
+#. The computer you will be registering with the LLVM buildbot
+ infrastructure should have all dependencies installed and you can
+ actually build your configuration successfully. Please check what degree
+ of parallelism (-j param) would give the fastest build. You can build
+ multiple configurations on one computer.
+
+#. Install buildslave (currently we are using buildbot version 0.8.5).
+ Depending on the platform, buildslave could be available to download and
+ install with your package manager, or you can download it directly from
+ `<http://trac.buildbot.net>`_ and install it manually.
+
+#. Create a designated user account, your buildslave will be running under,
+ and set appropriate permissions.
+
+#. Choose the buildslave root directory (all builds will be placed under
+ it), buildslave access name and password the build master will be using
+ to authenticate your buildslave.
+
+#. Create a buildslave in context of that buildslave account. Point it to
+ the **lab.llvm.org** port **9990** (see `Buildbot documentation,
+ Creating a slave
+ <http://docs.buildbot.net/current/tutorial/firstrun.html#creating-a-slave>`_
+ for more details) by running the following command:
+
+ .. code-block:: bash
+
+ $ buildslave create-slave <buildslave-root-directory> \
+ lab.llvm.org:9990 \
+ <buildslave-access-name> <buildslave-access-password>
+
+ To point a slave to silent master please use lab.llvm.org:9994 instead
+ of lab.llvm.org:9990.
+
+#. Fill the buildslave description and admin name/e-mail. Here is an
+ example of the buildslave description::
+
+ Windows 7 x64
+ Core i7 (2.66GHz), 16GB of RAM
+
+ g++.exe (TDM-1 mingw32) 4.4.0
+ GNU Binutils 2.19.1
+ cmake version 2.8.4
+ Microsoft(R) 32-bit C/C++ Optimizing Compiler Version 16.00.40219.01 for 80x86
+
+#. Make sure you can actually start the buildslave successfully. Then set
+ up your buildslave to start automatically at the start up time. See the
+ buildbot documentation for help. You may want to restart your computer
+ to see if it works.
+
+#. Send a patch which adds your build slave and your builder to zorg.
+
+ * slaves are added to ``buildbot/osuosl/master/config/slaves.py``
+ * builders are added to ``buildbot/osuosl/master/config/builders.py``
+
+ Please make sure your builder name and its builddir are unique through the file.
+
+ It is possible to whitelist email addresses to unconditionally receive notifications
+ on build failure; for this you'll need to add an ``InformativeMailNotifier`` to
+ ``buildbot/osuosl/master/config/status.py``. This is particularly useful for the
+ staging buildmaster which is silent otherwise.
+
+#. Send the buildslave access name and the access password directly to
+ `Galina Kistanova <mailto:gkistanova at gmail.com>`_, and wait till she
+ will let you know that your changes are applied and buildmaster is
+ reconfigured.
+
+#. Check the status of your buildslave on the `Waterfall Display
+ <http://lab.llvm.org:8011/waterfall>`_ to make sure it is connected, and
+ ``http://lab.llvm.org:8011/buildslaves/<your-buildslave-name>`` to see
+ if administrator contact and slave information are correct.
+
+#. Wait for the first build to succeed and enjoy.
Added: www-releases/trunk/5.0.2/docs/_sources/HowToBuildOnARM.txt
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==============================================================================
--- www-releases/trunk/5.0.2/docs/_sources/HowToBuildOnARM.txt (added)
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@@ -0,0 +1,85 @@
+===================================================================
+How To Build On ARM
+===================================================================
+
+Introduction
+============
+
+This document contains information about building/testing LLVM and
+Clang on an ARM machine.
+
+This document is *NOT* tailored to help you cross-compile LLVM/Clang
+to ARM on another architecture, for example an x86_64 machine. To find
+out more about cross-compiling, please check :doc:`HowToCrossCompileLLVM`.
+
+Notes On Building LLVM/Clang on ARM
+=====================================
+Here are some notes on building/testing LLVM/Clang on ARM. Note that
+ARM encompasses a wide variety of CPUs; this advice is primarily based
+on the ARMv6 and ARMv7 architectures and may be inapplicable to older chips.
+
+#. The most popular Linaro/Ubuntu OS's for ARM boards, e.g., the
+ Pandaboard, have become hard-float platforms. There are a number of
+ choices when using CMake. Autoconf usage is deprecated as of 3.8.
+
+ Building LLVM/Clang in ``Relese`` mode is preferred since it consumes
+ a lot less memory. Otherwise, the building process will very likely
+ fail due to insufficient memory. It's also a lot quicker to only build
+ the relevant back-ends (ARM and AArch64), since it's very unlikely that
+ you'll use an ARM board to cross-compile to other arches. If you're
+ running Compiler-RT tests, also include the x86 back-end, or some tests
+ will fail.
+
+ .. code-block:: bash
+
+ cmake $LLVM_SRC_DIR -DCMAKE_BUILD_TYPE=Release \
+ -DLLVM_TARGETS_TO_BUILD="ARM;X86;AArch64"
+
+ Other options you can use are:
+
+ .. code-block:: bash
+
+ Use Ninja instead of Make: "-G Ninja"
+ Build with assertions on: "-DLLVM_ENABLE_ASSERTIONS=True"
+ Force Python2: "-DPYTHON_EXECUTABLE=/usr/bin/python2"
+ Local (non-sudo) install path: "-DCMAKE_INSTALL_PREFIX=$HOME/llvm/instal"
+ CPU flags: "DCMAKE_C_FLAGS=-mcpu=cortex-a15" (same for CXX_FLAGS)
+
+ After that, just typing ``make -jN`` or ``ninja`` will build everything.
+ ``make -jN check-all`` or ``ninja check-all`` will run all compiler tests. For
+ running the test suite, please refer to :doc:`TestingGuide`.
+
+#. If you are building LLVM/Clang on an ARM board with 1G of memory or less,
+ please use ``gold`` rather then GNU ``ld``. In any case it is probably a good
+ idea to set up a swap partition, too.
+
+ .. code-block:: bash
+
+ $ sudo ln -sf /usr/bin/ld /usr/bin/ld.gold
+
+#. ARM development boards can be unstable and you may experience that cores
+ are disappearing, caches being flushed on every big.LITTLE switch, and
+ other similar issues. To help ease the effect of this, set the Linux
+ scheduler to "performance" on **all** cores using this little script:
+
+ .. code-block:: bash
+
+ # The code below requires the package 'cpufrequtils' to be installed.
+ for ((cpu=0; cpu<`grep -c proc /proc/cpuinfo`; cpu++)); do
+ sudo cpufreq-set -c $cpu -g performance
+ done
+
+ Remember to turn that off after the build, or you may risk burning your
+ CPU. Most modern kernels don't need that, so only use it if you have
+ problems.
+
+#. Running the build on SD cards is ok, but they are more prone to failures
+ than good quality USB sticks, and those are more prone to failures than
+ external hard-drives (those are also a lot faster). So, at least, you
+ should consider to buy a fast USB stick. On systems with a fast eMMC,
+ that's a good option too.
+
+#. Make sure you have a decent power supply (dozens of dollars worth) that can
+ provide *at least* 4 amperes, this is especially important if you use USB
+ devices with your board. Externally powered USB/SATA harddrives are even
+ better than having a good power supply.
Added: www-releases/trunk/5.0.2/docs/_sources/HowToCrossCompileLLVM.txt
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==============================================================================
--- www-releases/trunk/5.0.2/docs/_sources/HowToCrossCompileLLVM.txt (added)
+++ www-releases/trunk/5.0.2/docs/_sources/HowToCrossCompileLLVM.txt Thu May 10 06:54:16 2018
@@ -0,0 +1,205 @@
+===================================================================
+How To Cross-Compile Clang/LLVM using Clang/LLVM
+===================================================================
+
+Introduction
+============
+
+This document contains information about building LLVM and
+Clang on host machine, targeting another platform.
+
+For more information on how to use Clang as a cross-compiler,
+please check http://clang.llvm.org/docs/CrossCompilation.html.
+
+TODO: Add MIPS and other platforms to this document.
+
+Cross-Compiling from x86_64 to ARM
+==================================
+
+In this use case, we'll be using CMake and Ninja, on a Debian-based Linux
+system, cross-compiling from an x86_64 host (most Intel and AMD chips
+nowadays) to a hard-float ARM target (most ARM targets nowadays).
+
+The packages you'll need are:
+
+ * ``cmake``
+ * ``ninja-build`` (from backports in Ubuntu)
+ * ``gcc-4.7-arm-linux-gnueabihf``
+ * ``gcc-4.7-multilib-arm-linux-gnueabihf``
+ * ``binutils-arm-linux-gnueabihf``
+ * ``libgcc1-armhf-cross``
+ * ``libsfgcc1-armhf-cross``
+ * ``libstdc++6-armhf-cross``
+ * ``libstdc++6-4.7-dev-armhf-cross``
+
+Configuring CMake
+-----------------
+
+For more information on how to configure CMake for LLVM/Clang,
+see :doc:`CMake`.
+
+The CMake options you need to add are:
+
+ * ``-DCMAKE_CROSSCOMPILING=True``
+ * ``-DCMAKE_INSTALL_PREFIX=<install-dir>``
+ * ``-DLLVM_TABLEGEN=<path-to-host-bin>/llvm-tblgen``
+ * ``-DCLANG_TABLEGEN=<path-to-host-bin>/clang-tblgen``
+ * ``-DLLVM_DEFAULT_TARGET_TRIPLE=arm-linux-gnueabihf``
+ * ``-DLLVM_TARGET_ARCH=ARM``
+ * ``-DLLVM_TARGETS_TO_BUILD=ARM``
+
+If you're compiling with GCC, you can use architecture options for your target,
+and the compiler driver will detect everything that it needs:
+
+ * ``-DCMAKE_CXX_FLAGS='-march=armv7-a -mcpu=cortex-a9 -mfloat-abi=hard'``
+
+However, if you're using Clang, the driver might not be up-to-date with your
+specific Linux distribution, version or GCC layout, so you'll need to fudge.
+
+In addition to the ones above, you'll also need:
+
+ * ``'-target arm-linux-gnueabihf'`` or whatever is the triple of your cross GCC.
+ * ``'--sysroot=/usr/arm-linux-gnueabihf'``, ``'--sysroot=/opt/gcc/arm-linux-gnueabihf'``
+ or whatever is the location of your GCC's sysroot (where /lib, /bin etc are).
+ * Appropriate use of ``-I`` and ``-L``, depending on how the cross GCC is installed,
+ and where are the libraries and headers.
+
+The TableGen options are required to compile it with the host compiler,
+so you'll need to compile LLVM (or at least ``llvm-tblgen``) to your host
+platform before you start. The CXX flags define the target, cpu (which in this case
+defaults to ``fpu=VFP3`` with NEON), and forcing the hard-float ABI. If you're
+using Clang as a cross-compiler, you will *also* have to set ``--sysroot``
+to make sure it picks the correct linker.
+
+When using Clang, it's important that you choose the triple to be *identical*
+to the GCC triple and the sysroot. This will make it easier for Clang to
+find the correct tools and include headers. But that won't mean all headers and
+libraries will be found. You'll still need to use ``-I`` and ``-L`` to locate
+those extra ones, depending on your distribution.
+
+Most of the time, what you want is to have a native compiler to the
+platform itself, but not others. So there's rarely a point in compiling
+all back-ends. For that reason, you should also set the
+``TARGETS_TO_BUILD`` to only build the back-end you're targeting to.
+
+You must set the ``CMAKE_INSTALL_PREFIX``, otherwise a ``ninja install``
+will copy ARM binaries to your root filesystem, which is not what you
+want.
+
+Hacks
+-----
+
+There are some bugs in current LLVM, which require some fiddling before
+running CMake:
+
+#. If you're using Clang as the cross-compiler, there is a problem in
+ the LLVM ARM back-end that is producing absolute relocations on
+ position-independent code (``R_ARM_THM_MOVW_ABS_NC``), so for now, you
+ should disable PIC:
+
+ .. code-block:: bash
+
+ -DLLVM_ENABLE_PIC=False
+
+ This is not a problem, since Clang/LLVM libraries are statically
+ linked anyway, it shouldn't affect much.
+
+#. The ARM libraries won't be installed in your system.
+ But the CMake prepare step, which checks for
+ dependencies, will check the *host* libraries, not the *target*
+ ones. Below there's a list of some dependencies, but your project could
+ have more, or this document could be outdated. You'll see the errors
+ while linking as an indication of that.
+
+ Debian based distros have a way to add ``multiarch``, which adds
+ a new architecture and allows you to install packages for those
+ systems. See https://wiki.debian.org/Multiarch/HOWTO for more info.
+
+ But not all distros will have that, and possibly not an easy way to
+ install them in any anyway, so you'll have to build/download
+ them separately.
+
+ A quick way of getting the libraries is to download them from
+ a distribution repository, like Debian (http://packages.debian.org/jessie/),
+ and download the missing libraries. Note that the ``libXXX``
+ will have the shared objects (``.so``) and the ``libXXX-dev`` will
+ give you the headers and the static (``.a``) library. Just in
+ case, download both.
+
+ The ones you need for ARM are: ``libtinfo``, ``zlib1g``,
+ ``libxml2`` and ``liblzma``. In the Debian repository you'll
+ find downloads for all architectures.
+
+ After you download and unpack all ``.deb`` packages, copy all
+ ``.so`` and ``.a`` to a directory, make the appropriate
+ symbolic links (if necessary), and add the relevant ``-L``
+ and ``-I`` paths to ``-DCMAKE_CXX_FLAGS`` above.
+
+
+Running CMake and Building
+--------------------------
+
+Finally, if you're using your platform compiler, run:
+
+ .. code-block:: bash
+
+ $ cmake -G Ninja <source-dir> <options above>
+
+If you're using Clang as the cross-compiler, run:
+
+ .. code-block:: bash
+
+ $ CC='clang' CXX='clang++' cmake -G Ninja <source-dir> <options above>
+
+If you have ``clang``/``clang++`` on the path, it should just work, and special
+Ninja files will be created in the build directory. I strongly suggest
+you to run ``cmake`` on a separate build directory, *not* inside the
+source tree.
+
+To build, simply type:
+
+ .. code-block:: bash
+
+ $ ninja
+
+It should automatically find out how many cores you have, what are
+the rules that needs building and will build the whole thing.
+
+You can't run ``ninja check-all`` on this tree because the created
+binaries are targeted to ARM, not x86_64.
+
+Installing and Using
+--------------------
+
+After the LLVM/Clang has built successfully, you should install it
+via:
+
+ .. code-block:: bash
+
+ $ ninja install
+
+which will create a sysroot on the install-dir. You can then tar
+that directory into a binary with the full triple name (for easy
+identification), like:
+
+ .. code-block:: bash
+
+ $ ln -sf <install-dir> arm-linux-gnueabihf-clang
+ $ tar zchf arm-linux-gnueabihf-clang.tar.gz arm-linux-gnueabihf-clang
+
+If you copy that tarball to your target board, you'll be able to use
+it for running the test-suite, for example. Follow the guidelines at
+http://llvm.org/docs/lnt/quickstart.html, unpack the tarball in the
+test directory, and use options:
+
+ .. code-block:: bash
+
+ $ ./sandbox/bin/python sandbox/bin/lnt runtest nt \
+ --sandbox sandbox \
+ --test-suite `pwd`/test-suite \
+ --cc `pwd`/arm-linux-gnueabihf-clang/bin/clang \
+ --cxx `pwd`/arm-linux-gnueabihf-clang/bin/clang++
+
+Remember to add the ``-jN`` options to ``lnt`` to the number of CPUs
+on your board. Also, the path to your clang has to be absolute, so
+you'll need the `pwd` trick above.
Added: www-releases/trunk/5.0.2/docs/_sources/HowToReleaseLLVM.txt
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==============================================================================
--- www-releases/trunk/5.0.2/docs/_sources/HowToReleaseLLVM.txt (added)
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@@ -0,0 +1,364 @@
+=================================
+How To Release LLVM To The Public
+=================================
+
+Introduction
+============
+
+This document contains information about successfully releasing LLVM ---
+including sub-projects: e.g., ``clang`` and ``compiler-rt`` --- to the public.
+It is the Release Manager's responsibility to ensure that a high quality build
+of LLVM is released.
+
+If you're looking for the document on how to test the release candidates and
+create the binary packages, please refer to the :doc:`ReleaseProcess` instead.
+
+.. _timeline:
+
+Release Timeline
+================
+
+LLVM is released on a time based schedule --- with major releases roughly
+every 6 months. In between major releases there may be dot releases.
+The release manager will determine if and when to make a dot release based
+on feedback from the community. Typically, dot releases should be made if
+there are large number of bug-fixes in the stable branch or a critical bug
+has been discovered that affects a large number of users.
+
+Unless otherwise stated, dot releases will follow the same procedure as
+major releases.
+
+The release process is roughly as follows:
+
+* Set code freeze and branch creation date for 6 months after last code freeze
+ date. Announce release schedule to the LLVM community and update the website.
+
+* Create release branch and begin release process.
+
+* Send out release candidate sources for first round of testing. Testing lasts
+ 7-10 days. During the first round of testing, any regressions found should be
+ fixed. Patches are merged from mainline into the release branch. Also, all
+ features need to be completed during this time. Any features not completed at
+ the end of the first round of testing will be removed or disabled for the
+ release.
+
+* Generate and send out the second release candidate sources. Only *critical*
+ bugs found during this testing phase will be fixed. Any bugs introduced by
+ merged patches will be fixed. If so a third round of testing is needed.
+
+* The release notes are updated.
+
+* Finally, release!
+
+The release process will be accelerated for dot releases. If the first round
+of testing finds no critical bugs and no regressions since the last major release,
+then additional rounds of testing will not be required.
+
+Release Process
+===============
+
+.. contents::
+ :local:
+
+Release Administrative Tasks
+----------------------------
+
+This section describes a few administrative tasks that need to be done for the
+release process to begin. Specifically, it involves:
+
+* Creating the release branch,
+
+* Setting version numbers, and
+
+* Tagging release candidates for the release team to begin testing.
+
+Create Release Branch
+^^^^^^^^^^^^^^^^^^^^^
+
+Branch the Subversion trunk using the following procedure:
+
+#. Remind developers that the release branching is imminent and to refrain from
+ committing patches that might break the build. E.g., new features, large
+ patches for works in progress, an overhaul of the type system, an exciting
+ new TableGen feature, etc.
+
+#. Verify that the current Subversion trunk is in decent shape by
+ examining nightly tester and buildbot results.
+
+#. Create the release branch for ``llvm``, ``clang``, and other sub-projects,
+ from the last known good revision. The branch's name is
+ ``release_XY``, where ``X`` is the major and ``Y`` the minor release
+ numbers. Use ``utils/release/tag.sh`` to tag the release.
+
+#. Advise developers that they may now check their patches into the Subversion
+ tree again.
+
+#. The Release Manager should switch to the release branch, because all changes
+ to the release will now be done in the branch. The easiest way to do this is
+ to grab a working copy using the following commands:
+
+ ::
+
+ $ svn co https://llvm.org/svn/llvm-project/llvm/branches/release_XY llvm-X.Y
+
+ $ svn co https://llvm.org/svn/llvm-project/cfe/branches/release_XY clang-X.Y
+
+ $ svn co https://llvm.org/svn/llvm-project/test-suite/branches/release_XY test-suite-X.Y
+
+Update LLVM Version
+^^^^^^^^^^^^^^^^^^^
+
+After creating the LLVM release branch, update the release branches'
+``autoconf`` and ``configure.ac`` versions from '``X.Ysvn``' to '``X.Y``'.
+Update it on mainline as well to be the next version ('``X.Y+1svn``').
+Regenerate the configure scripts for both ``llvm`` and the ``test-suite``.
+
+In addition, the version numbers of all the Bugzilla components must be updated
+for the next release.
+
+Tagging the LLVM Release Candidates
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Tag release candidates using the tag.sh script in utils/release.
+
+::
+
+ $ ./tag.sh -release X.Y.Z -rc $RC
+
+The Release Manager may supply pre-packaged source tarballs for users. This can
+be done with the export.sh script in utils/release.
+
+::
+
+ $ ./export.sh -release X.Y.Z -rc $RC
+
+This will generate source tarballs for each LLVM project being validated, which
+can be uploaded to the website for further testing.
+
+Build Clang Binary Distribution
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Creating the ``clang`` binary distribution requires following the instructions
+:doc:`here <ReleaseProcess>`.
+
+That process will perform both Release+Asserts and Release builds but only
+pack the Release build for upload. You should use the Release+Asserts sysroot,
+normally under ``final/Phase3/Release+Asserts/llvmCore-3.8.1-RCn.install/``,
+for test-suite and run-time benchmarks, to make sure nothing serious has
+passed through the net. For compile-time benchmarks, use the Release version.
+
+The minimum required version of the tools you'll need are :doc:`here <GettingStarted>`
+
+Release Qualification Criteria
+------------------------------
+
+A release is qualified when it has no regressions from the previous release (or
+baseline). Regressions are related to correctness first and performance second.
+(We may tolerate some minor performance regressions if they are deemed
+necessary for the general quality of the compiler.)
+
+More specifically, Clang/LLVM is qualified when it has a clean test with all
+supported sub-projects included (``make check-all``), per target, and it has no
+regressions with the ``test-suite`` in relation to the previous release.
+
+Regressions are new failures in the set of tests that are used to qualify
+each product and only include things on the list. Every release will have
+some bugs in it. It is the reality of developing a complex piece of
+software. We need a very concrete and definitive release criteria that
+ensures we have monotonically improving quality on some metric. The metric we
+use is described below. This doesn't mean that we don't care about other
+criteria, but these are the criteria which we found to be most important and
+which must be satisfied before a release can go out.
+
+Official Testing
+----------------
+
+A few developers in the community have dedicated time to validate the release
+candidates and volunteered to be the official release testers for each
+architecture.
+
+These will be the ones testing, generating and uploading the official binaries
+to the server, and will be the minimum tests *necessary* for the release to
+proceed.
+
+This will obviously not cover all OSs and distributions, so additional community
+validation is important. However, if community input is not reached before the
+release is out, all bugs reported will have to go on the next stable release.
+
+The official release managers are:
+
+* Major releases (X.0): Hans Wennborg
+* Stable releases (X.n): Tom Stellard
+
+The official release testers are volunteered from the community and have
+consistently validated and released binaries for their targets/OSs. To contact
+them, you should email the ``release-testers at lists.llvm.org`` mailing list.
+
+The official testers list is in the file ``RELEASE_TESTERS.TXT``, in the ``LLVM``
+repository.
+
+Community Testing
+-----------------
+
+Once all testing has been completed and appropriate bugs filed, the release
+candidate tarballs are put on the website and the LLVM community is notified.
+
+We ask that all LLVM developers test the release in any the following ways:
+
+#. Download ``llvm-X.Y``, ``llvm-test-X.Y``, and the appropriate ``clang``
+ binary. Build LLVM. Run ``make check`` and the full LLVM test suite (``make
+ TEST=nightly report``).
+
+#. Download ``llvm-X.Y``, ``llvm-test-X.Y``, and the ``clang`` sources. Compile
+ everything. Run ``make check`` and the full LLVM test suite (``make
+ TEST=nightly report``).
+
+#. Download ``llvm-X.Y``, ``llvm-test-X.Y``, and the appropriate ``clang``
+ binary. Build whole programs with it (ex. Chromium, Firefox, Apache) for
+ your platform.
+
+#. Download ``llvm-X.Y``, ``llvm-test-X.Y``, and the appropriate ``clang``
+ binary. Build *your* programs with it and check for conformance and
+ performance regressions.
+
+#. Run the :doc:`release process <ReleaseProcess>`, if your platform is
+ *different* than that which is officially supported, and report back errors
+ only if they were not reported by the official release tester for that
+ architecture.
+
+We also ask that the OS distribution release managers test their packages with
+the first candidate of every release, and report any *new* errors in Bugzilla.
+If the bug can be reproduced with an unpatched upstream version of the release
+candidate (as opposed to the distribution's own build), the priority should be
+release blocker.
+
+During the first round of testing, all regressions must be fixed before the
+second release candidate is tagged.
+
+In the subsequent stages, the testing is only to ensure that bug
+fixes previously merged in have not created new major problems. *This is not
+the time to solve additional and unrelated bugs!* If no patches are merged in,
+the release is determined to be ready and the release manager may move onto the
+next stage.
+
+Reporting Regressions
+---------------------
+
+Every regression that is found during the tests (as per the criteria above),
+should be filled in a bug in Bugzilla with the priority *release blocker* and
+blocking a specific release.
+
+To help manage all the bugs reported and which ones are blockers or not, a new
+"[meta]" bug should be created and all regressions *blocking* that Meta. Once
+all blockers are done, the Meta can be closed.
+
+If a bug can't be reproduced, or stops being a blocker, it should be removed
+from the Meta and its priority decreased to *normal*. Debugging can continue,
+but on trunk.
+
+Release Patch Rules
+-------------------
+
+Below are the rules regarding patching the release branch:
+
+#. Patches applied to the release branch may only be applied by the release
+ manager, the official release testers or the code owners with approval from
+ the release manager.
+
+#. During the first round of testing, patches that fix regressions or that are
+ small and relatively risk free (verified by the appropriate code owner) are
+ applied to the branch. Code owners are asked to be very conservative in
+ approving patches for the branch. We reserve the right to reject any patch
+ that does not fix a regression as previously defined.
+
+#. During the remaining rounds of testing, only patches that fix critical
+ regressions may be applied.
+
+#. For dot releases all patches must maintain both API and ABI compatibility with
+ the previous major release. Only bug-fixes will be accepted.
+
+Merging Patches
+^^^^^^^^^^^^^^^
+
+The ``utils/release/merge.sh`` script can be used to merge individual revisions
+into any one of the llvm projects. To merge revision ``$N`` into project
+``$PROJ``, do:
+
+#. ``svn co https://llvm.org/svn/llvm-project/$PROJ/branches/release_XX
+ $PROJ.src``
+
+#. ``$PROJ.src/utils/release/merge.sh --proj $PROJ --rev $N``
+
+#. Run regression tests.
+
+#. ``cd $PROJ.src``. Run the ``svn commit`` command printed out by ``merge.sh``
+ in step 2.
+
+Release Final Tasks
+-------------------
+
+The final stages of the release process involves tagging the "final" release
+branch, updating documentation that refers to the release, and updating the
+demo page.
+
+Update Documentation
+^^^^^^^^^^^^^^^^^^^^
+
+Review the documentation and ensure that it is up to date. The "Release Notes"
+must be updated to reflect new features, bug fixes, new known issues, and
+changes in the list of supported platforms. The "Getting Started Guide" should
+be updated to reflect the new release version number tag available from
+Subversion and changes in basic system requirements. Merge both changes from
+mainline into the release branch.
+
+.. _tag:
+
+Tag the LLVM Final Release
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Tag the final release sources using the tag.sh script in utils/release.
+
+::
+
+ $ ./tag.sh -release X.Y.Z -final
+
+Update the LLVM Demo Page
+-------------------------
+
+The LLVM demo page must be updated to use the new release. This consists of
+using the new ``clang`` binary and building LLVM.
+
+Update the LLVM Website
+^^^^^^^^^^^^^^^^^^^^^^^
+
+The website must be updated before the release announcement is sent out. Here
+is what to do:
+
+#. Check out the ``www`` module from Subversion.
+
+#. Create a new sub-directory ``X.Y`` in the releases directory.
+
+#. Commit the ``llvm``, ``test-suite``, ``clang`` source and binaries in this
+ new directory.
+
+#. Copy and commit the ``llvm/docs`` and ``LICENSE.txt`` files into this new
+ directory. The docs should be built with ``BUILD_FOR_WEBSITE=1``.
+
+#. Commit the ``index.html`` to the ``release/X.Y`` directory to redirect (use
+ from previous release).
+
+#. Update the ``releases/download.html`` file with the new release.
+
+#. Update the ``releases/index.html`` with the new release and link to release
+ documentation.
+
+#. Finally, update the main page (``index.html`` and sidebar) to point to the
+ new release and release announcement. Make sure this all gets committed back
+ into Subversion.
+
+Announce the Release
+^^^^^^^^^^^^^^^^^^^^
+
+Send an email to the list announcing the release, pointing people to all the
+relevant documentation, download pages and bugs fixed.
+
Added: www-releases/trunk/5.0.2/docs/_sources/HowToSetUpLLVMStyleRTTI.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.2/docs/_sources/HowToSetUpLLVMStyleRTTI.txt?rev=331981&view=auto
==============================================================================
--- www-releases/trunk/5.0.2/docs/_sources/HowToSetUpLLVMStyleRTTI.txt (added)
+++ www-releases/trunk/5.0.2/docs/_sources/HowToSetUpLLVMStyleRTTI.txt Thu May 10 06:54:16 2018
@@ -0,0 +1,414 @@
+======================================================
+How to set up LLVM-style RTTI for your class hierarchy
+======================================================
+
+.. contents::
+
+Background
+==========
+
+LLVM avoids using C++'s built in RTTI. Instead, it pervasively uses its
+own hand-rolled form of RTTI which is much more efficient and flexible,
+although it requires a bit more work from you as a class author.
+
+A description of how to use LLVM-style RTTI from a client's perspective is
+given in the `Programmer's Manual <ProgrammersManual.html#isa>`_. This
+document, in contrast, discusses the steps you need to take as a class
+hierarchy author to make LLVM-style RTTI available to your clients.
+
+Before diving in, make sure that you are familiar with the Object Oriented
+Programming concept of "`is-a`_".
+
+.. _is-a: http://en.wikipedia.org/wiki/Is-a
+
+Basic Setup
+===========
+
+This section describes how to set up the most basic form of LLVM-style RTTI
+(which is sufficient for 99.9% of the cases). We will set up LLVM-style
+RTTI for this class hierarchy:
+
+.. code-block:: c++
+
+ class Shape {
+ public:
+ Shape() {}
+ virtual double computeArea() = 0;
+ };
+
+ class Square : public Shape {
+ double SideLength;
+ public:
+ Square(double S) : SideLength(S) {}
+ double computeArea() override;
+ };
+
+ class Circle : public Shape {
+ double Radius;
+ public:
+ Circle(double R) : Radius(R) {}
+ double computeArea() override;
+ };
+
+The most basic working setup for LLVM-style RTTI requires the following
+steps:
+
+#. In the header where you declare ``Shape``, you will want to ``#include
+ "llvm/Support/Casting.h"``, which declares LLVM's RTTI templates. That
+ way your clients don't even have to think about it.
+
+ .. code-block:: c++
+
+ #include "llvm/Support/Casting.h"
+
+#. In the base class, introduce an enum which discriminates all of the
+ different concrete classes in the hierarchy, and stash the enum value
+ somewhere in the base class.
+
+ Here is the code after introducing this change:
+
+ .. code-block:: c++
+
+ class Shape {
+ public:
+ + /// Discriminator for LLVM-style RTTI (dyn_cast<> et al.)
+ + enum ShapeKind {
+ + SK_Square,
+ + SK_Circle
+ + };
+ +private:
+ + const ShapeKind Kind;
+ +public:
+ + ShapeKind getKind() const { return Kind; }
+ +
+ Shape() {}
+ virtual double computeArea() = 0;
+ };
+
+ You will usually want to keep the ``Kind`` member encapsulated and
+ private, but let the enum ``ShapeKind`` be public along with providing a
+ ``getKind()`` method. This is convenient for clients so that they can do
+ a ``switch`` over the enum.
+
+ A common naming convention is that these enums are "kind"s, to avoid
+ ambiguity with the words "type" or "class" which have overloaded meanings
+ in many contexts within LLVM. Sometimes there will be a natural name for
+ it, like "opcode". Don't bikeshed over this; when in doubt use ``Kind``.
+
+ You might wonder why the ``Kind`` enum doesn't have an entry for
+ ``Shape``. The reason for this is that since ``Shape`` is abstract
+ (``computeArea() = 0;``), you will never actually have non-derived
+ instances of exactly that class (only subclasses). See `Concrete Bases
+ and Deeper Hierarchies`_ for information on how to deal with
+ non-abstract bases. It's worth mentioning here that unlike
+ ``dynamic_cast<>``, LLVM-style RTTI can be used (and is often used) for
+ classes that don't have v-tables.
+
+#. Next, you need to make sure that the ``Kind`` gets initialized to the
+ value corresponding to the dynamic type of the class. Typically, you will
+ want to have it be an argument to the constructor of the base class, and
+ then pass in the respective ``XXXKind`` from subclass constructors.
+
+ Here is the code after that change:
+
+ .. code-block:: c++
+
+ class Shape {
+ public:
+ /// Discriminator for LLVM-style RTTI (dyn_cast<> et al.)
+ enum ShapeKind {
+ SK_Square,
+ SK_Circle
+ };
+ private:
+ const ShapeKind Kind;
+ public:
+ ShapeKind getKind() const { return Kind; }
+
+ - Shape() {}
+ + Shape(ShapeKind K) : Kind(K) {}
+ virtual double computeArea() = 0;
+ };
+
+ class Square : public Shape {
+ double SideLength;
+ public:
+ - Square(double S) : SideLength(S) {}
+ + Square(double S) : Shape(SK_Square), SideLength(S) {}
+ double computeArea() override;
+ };
+
+ class Circle : public Shape {
+ double Radius;
+ public:
+ - Circle(double R) : Radius(R) {}
+ + Circle(double R) : Shape(SK_Circle), Radius(R) {}
+ double computeArea() override;
+ };
+
+#. Finally, you need to inform LLVM's RTTI templates how to dynamically
+ determine the type of a class (i.e. whether the ``isa<>``/``dyn_cast<>``
+ should succeed). The default "99.9% of use cases" way to accomplish this
+ is through a small static member function ``classof``. In order to have
+ proper context for an explanation, we will display this code first, and
+ then below describe each part:
+
+ .. code-block:: c++
+
+ class Shape {
+ public:
+ /// Discriminator for LLVM-style RTTI (dyn_cast<> et al.)
+ enum ShapeKind {
+ SK_Square,
+ SK_Circle
+ };
+ private:
+ const ShapeKind Kind;
+ public:
+ ShapeKind getKind() const { return Kind; }
+
+ Shape(ShapeKind K) : Kind(K) {}
+ virtual double computeArea() = 0;
+ };
+
+ class Square : public Shape {
+ double SideLength;
+ public:
+ Square(double S) : Shape(SK_Square), SideLength(S) {}
+ double computeArea() override;
+ +
+ + static bool classof(const Shape *S) {
+ + return S->getKind() == SK_Square;
+ + }
+ };
+
+ class Circle : public Shape {
+ double Radius;
+ public:
+ Circle(double R) : Shape(SK_Circle), Radius(R) {}
+ double computeArea() override;
+ +
+ + static bool classof(const Shape *S) {
+ + return S->getKind() == SK_Circle;
+ + }
+ };
+
+ The job of ``classof`` is to dynamically determine whether an object of
+ a base class is in fact of a particular derived class. In order to
+ downcast a type ``Base`` to a type ``Derived``, there needs to be a
+ ``classof`` in ``Derived`` which will accept an object of type ``Base``.
+
+ To be concrete, consider the following code:
+
+ .. code-block:: c++
+
+ Shape *S = ...;
+ if (isa<Circle>(S)) {
+ /* do something ... */
+ }
+
+ The code of the ``isa<>`` test in this code will eventually boil
+ down---after template instantiation and some other machinery---to a
+ check roughly like ``Circle::classof(S)``. For more information, see
+ :ref:`classof-contract`.
+
+ The argument to ``classof`` should always be an *ancestor* class because
+ the implementation has logic to allow and optimize away
+ upcasts/up-``isa<>``'s automatically. It is as though every class
+ ``Foo`` automatically has a ``classof`` like:
+
+ .. code-block:: c++
+
+ class Foo {
+ [...]
+ template <class T>
+ static bool classof(const T *,
+ ::std::enable_if<
+ ::std::is_base_of<Foo, T>::value
+ >::type* = 0) { return true; }
+ [...]
+ };
+
+ Note that this is the reason that we did not need to introduce a
+ ``classof`` into ``Shape``: all relevant classes derive from ``Shape``,
+ and ``Shape`` itself is abstract (has no entry in the ``Kind`` enum),
+ so this notional inferred ``classof`` is all we need. See `Concrete
+ Bases and Deeper Hierarchies`_ for more information about how to extend
+ this example to more general hierarchies.
+
+Although for this small example setting up LLVM-style RTTI seems like a lot
+of "boilerplate", if your classes are doing anything interesting then this
+will end up being a tiny fraction of the code.
+
+Concrete Bases and Deeper Hierarchies
+=====================================
+
+For concrete bases (i.e. non-abstract interior nodes of the inheritance
+tree), the ``Kind`` check inside ``classof`` needs to be a bit more
+complicated. The situation differs from the example above in that
+
+* Since the class is concrete, it must itself have an entry in the ``Kind``
+ enum because it is possible to have objects with this class as a dynamic
+ type.
+
+* Since the class has children, the check inside ``classof`` must take them
+ into account.
+
+Say that ``SpecialSquare`` and ``OtherSpecialSquare`` derive
+from ``Square``, and so ``ShapeKind`` becomes:
+
+.. code-block:: c++
+
+ enum ShapeKind {
+ SK_Square,
+ + SK_SpecialSquare,
+ + SK_OtherSpecialSquare,
+ SK_Circle
+ }
+
+Then in ``Square``, we would need to modify the ``classof`` like so:
+
+.. code-block:: c++
+
+ - static bool classof(const Shape *S) {
+ - return S->getKind() == SK_Square;
+ - }
+ + static bool classof(const Shape *S) {
+ + return S->getKind() >= SK_Square &&
+ + S->getKind() <= SK_OtherSpecialSquare;
+ + }
+
+The reason that we need to test a range like this instead of just equality
+is that both ``SpecialSquare`` and ``OtherSpecialSquare`` "is-a"
+``Square``, and so ``classof`` needs to return ``true`` for them.
+
+This approach can be made to scale to arbitrarily deep hierarchies. The
+trick is that you arrange the enum values so that they correspond to a
+preorder traversal of the class hierarchy tree. With that arrangement, all
+subclass tests can be done with two comparisons as shown above. If you just
+list the class hierarchy like a list of bullet points, you'll get the
+ordering right::
+
+ | Shape
+ | Square
+ | SpecialSquare
+ | OtherSpecialSquare
+ | Circle
+
+A Bug to be Aware Of
+--------------------
+
+The example just given opens the door to bugs where the ``classof``\s are
+not updated to match the ``Kind`` enum when adding (or removing) classes to
+(from) the hierarchy.
+
+Continuing the example above, suppose we add a ``SomewhatSpecialSquare`` as
+a subclass of ``Square``, and update the ``ShapeKind`` enum like so:
+
+.. code-block:: c++
+
+ enum ShapeKind {
+ SK_Square,
+ SK_SpecialSquare,
+ SK_OtherSpecialSquare,
+ + SK_SomewhatSpecialSquare,
+ SK_Circle
+ }
+
+Now, suppose that we forget to update ``Square::classof()``, so it still
+looks like:
+
+.. code-block:: c++
+
+ static bool classof(const Shape *S) {
+ // BUG: Returns false when S->getKind() == SK_SomewhatSpecialSquare,
+ // even though SomewhatSpecialSquare "is a" Square.
+ return S->getKind() >= SK_Square &&
+ S->getKind() <= SK_OtherSpecialSquare;
+ }
+
+As the comment indicates, this code contains a bug. A straightforward and
+non-clever way to avoid this is to introduce an explicit ``SK_LastSquare``
+entry in the enum when adding the first subclass(es). For example, we could
+rewrite the example at the beginning of `Concrete Bases and Deeper
+Hierarchies`_ as:
+
+.. code-block:: c++
+
+ enum ShapeKind {
+ SK_Square,
+ + SK_SpecialSquare,
+ + SK_OtherSpecialSquare,
+ + SK_LastSquare,
+ SK_Circle
+ }
+ ...
+ // Square::classof()
+ - static bool classof(const Shape *S) {
+ - return S->getKind() == SK_Square;
+ - }
+ + static bool classof(const Shape *S) {
+ + return S->getKind() >= SK_Square &&
+ + S->getKind() <= SK_LastSquare;
+ + }
+
+Then, adding new subclasses is easy:
+
+.. code-block:: c++
+
+ enum ShapeKind {
+ SK_Square,
+ SK_SpecialSquare,
+ SK_OtherSpecialSquare,
+ + SK_SomewhatSpecialSquare,
+ SK_LastSquare,
+ SK_Circle
+ }
+
+Notice that ``Square::classof`` does not need to be changed.
+
+.. _classof-contract:
+
+The Contract of ``classof``
+---------------------------
+
+To be more precise, let ``classof`` be inside a class ``C``. Then the
+contract for ``classof`` is "return ``true`` if the dynamic type of the
+argument is-a ``C``". As long as your implementation fulfills this
+contract, you can tweak and optimize it as much as you want.
+
+For example, LLVM-style RTTI can work fine in the presence of
+multiple-inheritance by defining an appropriate ``classof``.
+An example of this in practice is
+`Decl <http://clang.llvm.org/doxygen/classclang_1_1Decl.html>`_ vs.
+`DeclContext <http://clang.llvm.org/doxygen/classclang_1_1DeclContext.html>`_
+inside Clang.
+The ``Decl`` hierarchy is done very similarly to the example setup
+demonstrated in this tutorial.
+The key part is how to then incorporate ``DeclContext``: all that is needed
+is in ``bool DeclContext::classof(const Decl *)``, which asks the question
+"Given a ``Decl``, how can I determine if it is-a ``DeclContext``?".
+It answers this with a simple switch over the set of ``Decl`` "kinds", and
+returning true for ones that are known to be ``DeclContext``'s.
+
+.. TODO::
+
+ Touch on some of the more advanced features, like ``isa_impl`` and
+ ``simplify_type``. However, those two need reference documentation in
+ the form of doxygen comments as well. We need the doxygen so that we can
+ say "for full details, see http://llvm.org/doxygen/..."
+
+Rules of Thumb
+==============
+
+#. The ``Kind`` enum should have one entry per concrete class, ordered
+ according to a preorder traversal of the inheritance tree.
+#. The argument to ``classof`` should be a ``const Base *``, where ``Base``
+ is some ancestor in the inheritance hierarchy. The argument should
+ *never* be a derived class or the class itself: the template machinery
+ for ``isa<>`` already handles this case and optimizes it.
+#. For each class in the hierarchy that has no children, implement a
+ ``classof`` that checks only against its ``Kind``.
+#. For each class in the hierarchy that has children, implement a
+ ``classof`` that checks a range of the first child's ``Kind`` and the
+ last child's ``Kind``.
Added: www-releases/trunk/5.0.2/docs/_sources/HowToSubmitABug.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.2/docs/_sources/HowToSubmitABug.txt?rev=331981&view=auto
==============================================================================
--- www-releases/trunk/5.0.2/docs/_sources/HowToSubmitABug.txt (added)
+++ www-releases/trunk/5.0.2/docs/_sources/HowToSubmitABug.txt Thu May 10 06:54:16 2018
@@ -0,0 +1,229 @@
+================================
+How to submit an LLVM bug report
+================================
+
+Introduction - Got bugs?
+========================
+
+
+If you're working with LLVM and run into a bug, we definitely want to know
+about it. This document describes what you can do to increase the odds of
+getting it fixed quickly.
+
+Basically you have to do two things at a minimum. First, decide whether
+the bug `crashes the compiler`_ (or an LLVM pass), or if the
+compiler is `miscompiling`_ the program (i.e., the
+compiler successfully produces an executable, but it doesn't run right).
+Based on what type of bug it is, follow the instructions in the linked
+section to narrow down the bug so that the person who fixes it will be able
+to find the problem more easily.
+
+Once you have a reduced test-case, go to `the LLVM Bug Tracking System
+<https://bugs.llvm.org/enter_bug.cgi>`_ and fill out the form with the
+necessary details (note that you don't need to pick a category, just use
+the "new-bugs" category if you're not sure). The bug description should
+contain the following information:
+
+* All information necessary to reproduce the problem.
+* The reduced test-case that triggers the bug.
+* The location where you obtained LLVM (if not from our Subversion
+ repository).
+
+Thanks for helping us make LLVM better!
+
+.. _crashes the compiler:
+
+Crashing Bugs
+=============
+
+More often than not, bugs in the compiler cause it to crash---often due to
+an assertion failure of some sort. The most important piece of the puzzle
+is to figure out if it is crashing in the GCC front-end or if it is one of
+the LLVM libraries (e.g. the optimizer or code generator) that has
+problems.
+
+To figure out which component is crashing (the front-end, optimizer or code
+generator), run the ``clang`` command line as you were when the crash
+occurred, but with the following extra command line options:
+
+* ``-O0 -emit-llvm``: If ``clang`` still crashes when passed these
+ options (which disable the optimizer and code generator), then the crash
+ is in the front-end. Jump ahead to the section on :ref:`front-end bugs
+ <front-end>`.
+
+* ``-emit-llvm``: If ``clang`` crashes with this option (which disables
+ the code generator), you found an optimizer bug. Jump ahead to
+ `compile-time optimization bugs`_.
+
+* Otherwise, you have a code generator crash. Jump ahead to `code
+ generator bugs`_.
+
+.. _front-end bug:
+.. _front-end:
+
+Front-end bugs
+--------------
+
+If the problem is in the front-end, you should re-run the same ``clang``
+command that resulted in the crash, but add the ``-save-temps`` option.
+The compiler will crash again, but it will leave behind a ``foo.i`` file
+(containing preprocessed C source code) and possibly ``foo.s`` for each
+compiled ``foo.c`` file. Send us the ``foo.i`` file, along with the options
+you passed to ``clang``, and a brief description of the error it caused.
+
+The `delta <http://delta.tigris.org/>`_ tool helps to reduce the
+preprocessed file down to the smallest amount of code that still replicates
+the problem. You're encouraged to use delta to reduce the code to make the
+developers' lives easier. `This website
+<http://gcc.gnu.org/wiki/A_guide_to_testcase_reduction>`_ has instructions
+on the best way to use delta.
+
+.. _compile-time optimization bugs:
+
+Compile-time optimization bugs
+------------------------------
+
+If you find that a bug crashes in the optimizer, compile your test-case to a
+``.bc`` file by passing "``-emit-llvm -O0 -c -o foo.bc``".
+Then run:
+
+.. code-block:: bash
+
+ opt -O3 -debug-pass=Arguments foo.bc -disable-output
+
+This command should do two things: it should print out a list of passes, and
+then it should crash in the same way as clang. If it doesn't crash, please
+follow the instructions for a `front-end bug`_.
+
+If this does crash, then you should be able to debug this with the following
+bugpoint command:
+
+.. code-block:: bash
+
+ bugpoint foo.bc <list of passes printed by opt>
+
+Please run this, then file a bug with the instructions and reduced .bc
+files that bugpoint emits. If something goes wrong with bugpoint, please
+submit the "foo.bc" file and the list of passes printed by ``opt``.
+
+.. _code generator bugs:
+
+Code generator bugs
+-------------------
+
+If you find a bug that crashes clang in the code generator, compile your
+source file to a .bc file by passing "``-emit-llvm -c -o foo.bc``" to
+clang (in addition to the options you already pass). Once your have
+foo.bc, one of the following commands should fail:
+
+#. ``llc foo.bc``
+#. ``llc foo.bc -relocation-model=pic``
+#. ``llc foo.bc -relocation-model=static``
+
+If none of these crash, please follow the instructions for a `front-end
+bug`_. If one of these do crash, you should be able to reduce this with
+one of the following bugpoint command lines (use the one corresponding to
+the command above that failed):
+
+#. ``bugpoint -run-llc foo.bc``
+#. ``bugpoint -run-llc foo.bc --tool-args -relocation-model=pic``
+#. ``bugpoint -run-llc foo.bc --tool-args -relocation-model=static``
+
+Please run this, then file a bug with the instructions and reduced .bc file
+that bugpoint emits. If something goes wrong with bugpoint, please submit
+the "foo.bc" file and the option that llc crashes with.
+
+.. _miscompiling:
+
+Miscompilations
+===============
+
+If clang successfully produces an executable, but that executable
+doesn't run right, this is either a bug in the code or a bug in the
+compiler. The first thing to check is to make sure it is not using
+undefined behavior (e.g. reading a variable before it is defined). In
+particular, check to see if the program `valgrind
+<http://valgrind.org/>`_'s clean, passes purify, or some other memory
+checker tool. Many of the "LLVM bugs" that we have chased down ended up
+being bugs in the program being compiled, not LLVM.
+
+Once you determine that the program itself is not buggy, you should choose
+which code generator you wish to compile the program with (e.g. LLC or the JIT)
+and optionally a series of LLVM passes to run. For example:
+
+.. code-block:: bash
+
+ bugpoint -run-llc [... optzn passes ...] file-to-test.bc --args -- [program arguments]
+
+bugpoint will try to narrow down your list of passes to the one pass that
+causes an error, and simplify the bitcode file as much as it can to assist
+you. It will print a message letting you know how to reproduce the
+resulting error.
+
+Incorrect code generation
+=========================
+
+Similarly to debugging incorrect compilation by mis-behaving passes, you
+can debug incorrect code generation by either LLC or the JIT, using
+``bugpoint``. The process ``bugpoint`` follows in this case is to try to
+narrow the code down to a function that is miscompiled by one or the other
+method, but since for correctness, the entire program must be run,
+``bugpoint`` will compile the code it deems to not be affected with the C
+Backend, and then link in the shared object it generates.
+
+To debug the JIT:
+
+.. code-block:: bash
+
+ bugpoint -run-jit -output=[correct output file] [bitcode file] \
+ --tool-args -- [arguments to pass to lli] \
+ --args -- [program arguments]
+
+Similarly, to debug the LLC, one would run:
+
+.. code-block:: bash
+
+ bugpoint -run-llc -output=[correct output file] [bitcode file] \
+ --tool-args -- [arguments to pass to llc] \
+ --args -- [program arguments]
+
+**Special note:** if you are debugging MultiSource or SPEC tests that
+already exist in the ``llvm/test`` hierarchy, there is an easier way to
+debug the JIT, LLC, and CBE, using the pre-written Makefile targets, which
+will pass the program options specified in the Makefiles:
+
+.. code-block:: bash
+
+ cd llvm/test/../../program
+ make bugpoint-jit
+
+At the end of a successful ``bugpoint`` run, you will be presented
+with two bitcode files: a *safe* file which can be compiled with the C
+backend and the *test* file which either LLC or the JIT
+mis-codegenerates, and thus causes the error.
+
+To reproduce the error that ``bugpoint`` found, it is sufficient to do
+the following:
+
+#. Regenerate the shared object from the safe bitcode file:
+
+ .. code-block:: bash
+
+ llc -march=c safe.bc -o safe.c
+ gcc -shared safe.c -o safe.so
+
+#. If debugging LLC, compile test bitcode native and link with the shared
+ object:
+
+ .. code-block:: bash
+
+ llc test.bc -o test.s
+ gcc test.s safe.so -o test.llc
+ ./test.llc [program options]
+
+#. If debugging the JIT, load the shared object and supply the test
+ bitcode:
+
+ .. code-block:: bash
+
+ lli -load=safe.so test.bc [program options]
Added: www-releases/trunk/5.0.2/docs/_sources/HowToUseAttributes.txt
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==============================================================================
--- www-releases/trunk/5.0.2/docs/_sources/HowToUseAttributes.txt (added)
+++ www-releases/trunk/5.0.2/docs/_sources/HowToUseAttributes.txt Thu May 10 06:54:16 2018
@@ -0,0 +1,80 @@
+=====================
+How To Use Attributes
+=====================
+
+.. contents::
+ :local:
+
+Introduction
+============
+
+Attributes in LLVM have changed in some fundamental ways. It was necessary to
+do this to support expanding the attributes to encompass more than a handful of
+attributes --- e.g. command line options. The old way of handling attributes
+consisted of representing them as a bit mask of values. This bit mask was
+stored in a "list" structure that was reference counted. The advantage of this
+was that attributes could be manipulated with 'or's and 'and's. The
+disadvantage of this was that there was limited room for expansion, and
+virtually no support for attribute-value pairs other than alignment.
+
+In the new scheme, an ``Attribute`` object represents a single attribute that's
+uniqued. You use the ``Attribute::get`` methods to create a new ``Attribute``
+object. An attribute can be a single "enum" value (the enum being the
+``Attribute::AttrKind`` enum), a string representing a target-dependent
+attribute, or an attribute-value pair. Some examples:
+
+* Target-independent: ``noinline``, ``zext``
+* Target-dependent: ``"no-sse"``, ``"thumb2"``
+* Attribute-value pair: ``"cpu" = "cortex-a8"``, ``align = 4``
+
+Note: for an attribute value pair, we expect a target-dependent attribute to
+have a string for the value.
+
+``Attribute``
+=============
+An ``Attribute`` object is designed to be passed around by value.
+
+Because attributes are no longer represented as a bit mask, you will need to
+convert any code which does treat them as a bit mask to use the new query
+methods on the Attribute class.
+
+``AttributeList``
+=================
+
+The ``AttributeList`` stores a collection of Attribute objects for each kind of
+object that may have an attribute associated with it: the function as a whole,
+the return type, or the function's parameters. A function's attributes are at
+index ``AttributeList::FunctionIndex``; the return type's attributes are at
+index ``AttributeList::ReturnIndex``; and the function's parameters' attributes
+are at indices 1, ..., n (where 'n' is the number of parameters). Most methods
+on the ``AttributeList`` class take an index parameter.
+
+An ``AttributeList`` is also a uniqued and immutable object. You create an
+``AttributeList`` through the ``AttributeList::get`` methods. You can add and
+remove attributes, which result in the creation of a new ``AttributeList``.
+
+An ``AttributeList`` object is designed to be passed around by value.
+
+Note: It is advised that you do *not* use the ``AttributeList`` "introspection"
+methods (e.g. ``Raw``, ``getRawPointer``, etc.). These methods break
+encapsulation, and may be removed in a future release (i.e. LLVM 4.0).
+
+``AttrBuilder``
+===============
+
+Lastly, we have a "builder" class to help create the ``AttributeList`` object
+without having to create several different intermediate uniqued
+``AttributeList`` objects. The ``AttrBuilder`` class allows you to add and
+remove attributes at will. The attributes won't be uniqued until you call the
+appropriate ``AttributeList::get`` method.
+
+An ``AttrBuilder`` object is *not* designed to be passed around by value. It
+should be passed by reference.
+
+Note: It is advised that you do *not* use the ``AttrBuilder::addRawValue()``
+method or the ``AttrBuilder(uint64_t Val)`` constructor. These are for
+backwards compatibility and may be removed in a future release (i.e. LLVM 4.0).
+
+And that's basically it! A lot of functionality is hidden behind these classes,
+but the interfaces are pretty straight forward.
+
Added: www-releases/trunk/5.0.2/docs/_sources/HowToUseInstrMappings.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.2/docs/_sources/HowToUseInstrMappings.txt?rev=331981&view=auto
==============================================================================
--- www-releases/trunk/5.0.2/docs/_sources/HowToUseInstrMappings.txt (added)
+++ www-releases/trunk/5.0.2/docs/_sources/HowToUseInstrMappings.txt Thu May 10 06:54:16 2018
@@ -0,0 +1,175 @@
+===============================
+How To Use Instruction Mappings
+===============================
+
+.. contents::
+ :local:
+
+Introduction
+============
+
+This document contains information about adding instruction mapping support
+for a target. The motivation behind this feature comes from the need to switch
+between different instruction formats during various optimizations. One approach
+could be to use switch cases which list all the instructions along with formats
+they can transition to. However, it has large maintenance overhead
+because of the hardcoded instruction names. Also, whenever a new instruction is
+added in the .td files, all the relevant switch cases should be modified
+accordingly. Instead, the same functionality could be achieved with TableGen and
+some support from the .td files for a fraction of maintenance cost.
+
+``InstrMapping`` Class Overview
+===============================
+
+TableGen uses relationship models to map instructions with each other. These
+models are described using ``InstrMapping`` class as a base. Each model sets
+various fields of the ``InstrMapping`` class such that they can uniquely
+describe all the instructions using that model. TableGen parses all the relation
+models and uses the information to construct relation tables which relate
+instructions with each other. These tables are emitted in the
+``XXXInstrInfo.inc`` file along with the functions to query them. Following
+is the definition of ``InstrMapping`` class definied in Target.td file:
+
+.. code-block:: text
+
+ class InstrMapping {
+ // Used to reduce search space only to the instructions using this
+ // relation model.
+ string FilterClass;
+
+ // List of fields/attributes that should be same for all the instructions in
+ // a row of the relation table. Think of this as a set of properties shared
+ // by all the instructions related by this relationship.
+ list<string> RowFields = [];
+
+ // List of fields/attributes that are same for all the instructions
+ // in a column of the relation table.
+ list<string> ColFields = [];
+
+ // Values for the fields/attributes listed in 'ColFields' corresponding to
+ // the key instruction. This is the instruction that will be transformed
+ // using this relation model.
+ list<string> KeyCol = [];
+
+ // List of values for the fields/attributes listed in 'ColFields', one for
+ // each column in the relation table. These are the instructions a key
+ // instruction will be transformed into.
+ list<list<string> > ValueCols = [];
+ }
+
+Sample Example
+--------------
+
+Let's say that we want to have a function
+``int getPredOpcode(uint16_t Opcode, enum PredSense inPredSense)`` which
+takes a non-predicated instruction and returns its predicated true or false form
+depending on some input flag, ``inPredSense``. The first step in the process is
+to define a relationship model that relates predicated instructions to their
+non-predicated form by assigning appropriate values to the ``InstrMapping``
+fields. For this relationship, non-predicated instructions are treated as key
+instruction since they are the one used to query the interface function.
+
+.. code-block:: text
+
+ def getPredOpcode : InstrMapping {
+ // Choose a FilterClass that is used as a base class for all the
+ // instructions modeling this relationship. This is done to reduce the
+ // search space only to these set of instructions.
+ let FilterClass = "PredRel";
+
+ // Instructions with same values for all the fields in RowFields form a
+ // row in the resulting relation table.
+ // For example, if we want to relate 'ADD' (non-predicated) with 'Add_pt'
+ // (predicated true) and 'Add_pf' (predicated false), then all 3
+ // instructions need to have same value for BaseOpcode field. It can be any
+ // unique value (Ex: XYZ) and should not be shared with any other
+ // instruction not related to 'add'.
+ let RowFields = ["BaseOpcode"];
+
+ // List of attributes that can be used to define key and column instructions
+ // for a relation. Key instruction is passed as an argument
+ // to the function used for querying relation tables. Column instructions
+ // are the instructions they (key) can transform into.
+ //
+ // Here, we choose 'PredSense' as ColFields since this is the unique
+ // attribute of the key (non-predicated) and column (true/false)
+ // instructions involved in this relationship model.
+ let ColFields = ["PredSense"];
+
+ // The key column contains non-predicated instructions.
+ let KeyCol = ["none"];
+
+ // Two value columns - first column contains instructions with
+ // PredSense=true while second column has instructions with PredSense=false.
+ let ValueCols = [["true"], ["false"]];
+ }
+
+TableGen uses the above relationship model to emit relation table that maps
+non-predicated instructions with their predicated forms. It also outputs the
+interface function
+``int getPredOpcode(uint16_t Opcode, enum PredSense inPredSense)`` to query
+the table. Here, Function ``getPredOpcode`` takes two arguments, opcode of the
+current instruction and PredSense of the desired instruction, and returns
+predicated form of the instruction, if found in the relation table.
+In order for an instruction to be added into the relation table, it needs
+to include relevant information in its definition. For example, consider
+following to be the current definitions of ADD, ADD_pt (true) and ADD_pf (false)
+instructions:
+
+.. code-block:: text
+
+ def ADD : ALU32_rr<(outs IntRegs:$dst), (ins IntRegs:$a, IntRegs:$b),
+ "$dst = add($a, $b)",
+ [(set (i32 IntRegs:$dst), (add (i32 IntRegs:$a),
+ (i32 IntRegs:$b)))]>;
+
+ def ADD_Pt : ALU32_rr<(outs IntRegs:$dst),
+ (ins PredRegs:$p, IntRegs:$a, IntRegs:$b),
+ "if ($p) $dst = add($a, $b)",
+ []>;
+
+ def ADD_Pf : ALU32_rr<(outs IntRegs:$dst),
+ (ins PredRegs:$p, IntRegs:$a, IntRegs:$b),
+ "if (!$p) $dst = add($a, $b)",
+ []>;
+
+In this step, we modify these instructions to include the information
+required by the relationship model, <tt>getPredOpcode</tt>, so that they can
+be related.
+
+.. code-block:: text
+
+ def ADD : PredRel, ALU32_rr<(outs IntRegs:$dst), (ins IntRegs:$a, IntRegs:$b),
+ "$dst = add($a, $b)",
+ [(set (i32 IntRegs:$dst), (add (i32 IntRegs:$a),
+ (i32 IntRegs:$b)))]> {
+ let BaseOpcode = "ADD";
+ let PredSense = "none";
+ }
+
+ def ADD_Pt : PredRel, ALU32_rr<(outs IntRegs:$dst),
+ (ins PredRegs:$p, IntRegs:$a, IntRegs:$b),
+ "if ($p) $dst = add($a, $b)",
+ []> {
+ let BaseOpcode = "ADD";
+ let PredSense = "true";
+ }
+
+ def ADD_Pf : PredRel, ALU32_rr<(outs IntRegs:$dst),
+ (ins PredRegs:$p, IntRegs:$a, IntRegs:$b),
+ "if (!$p) $dst = add($a, $b)",
+ []> {
+ let BaseOpcode = "ADD";
+ let PredSense = "false";
+ }
+
+Please note that all the above instructions use ``PredRel`` as a base class.
+This is extremely important since TableGen uses it as a filter for selecting
+instructions for ``getPredOpcode`` model. Any instruction not derived from
+``PredRel`` is excluded from the analysis. ``BaseOpcode`` is another important
+field. Since it's selected as a ``RowFields`` of the model, it is required
+to have the same value for all 3 instructions in order to be related. Next,
+``PredSense`` is used to determine their column positions by comparing its value
+with ``KeyCol`` and ``ValueCols``. If an instruction sets its ``PredSense``
+value to something not used in the relation model, it will not be assigned
+a column in the relation table.
Added: www-releases/trunk/5.0.2/docs/_sources/InAlloca.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.2/docs/_sources/InAlloca.txt?rev=331981&view=auto
==============================================================================
--- www-releases/trunk/5.0.2/docs/_sources/InAlloca.txt (added)
+++ www-releases/trunk/5.0.2/docs/_sources/InAlloca.txt Thu May 10 06:54:16 2018
@@ -0,0 +1,160 @@
+==========================================
+Design and Usage of the InAlloca Attribute
+==========================================
+
+Introduction
+============
+
+The :ref:`inalloca <attr_inalloca>` attribute is designed to allow
+taking the address of an aggregate argument that is being passed by
+value through memory. Primarily, this feature is required for
+compatibility with the Microsoft C++ ABI. Under that ABI, class
+instances that are passed by value are constructed directly into
+argument stack memory. Prior to the addition of inalloca, calls in LLVM
+were indivisible instructions. There was no way to perform intermediate
+work, such as object construction, between the first stack adjustment
+and the final control transfer. With inalloca, all arguments passed in
+memory are modelled as a single alloca, which can be stored to prior to
+the call. Unfortunately, this complicated feature comes with a large
+set of restrictions designed to bound the lifetime of the argument
+memory around the call.
+
+For now, it is recommended that frontends and optimizers avoid producing
+this construct, primarily because it forces the use of a base pointer.
+This feature may grow in the future to allow general mid-level
+optimization, but for now, it should be regarded as less efficient than
+passing by value with a copy.
+
+Intended Usage
+==============
+
+The example below is the intended LLVM IR lowering for some C++ code
+that passes two default-constructed ``Foo`` objects to ``g`` in the
+32-bit Microsoft C++ ABI.
+
+.. code-block:: c++
+
+ // Foo is non-trivial.
+ struct Foo { int a, b; Foo(); ~Foo(); Foo(const Foo &); };
+ void g(Foo a, Foo b);
+ void f() {
+ g(Foo(), Foo());
+ }
+
+.. code-block:: text
+
+ %struct.Foo = type { i32, i32 }
+ declare void @Foo_ctor(%struct.Foo* %this)
+ declare void @Foo_dtor(%struct.Foo* %this)
+ declare void @g(<{ %struct.Foo, %struct.Foo }>* inalloca %memargs)
+
+ define void @f() {
+ entry:
+ %base = call i8* @llvm.stacksave()
+ %memargs = alloca <{ %struct.Foo, %struct.Foo }>
+ %b = getelementptr <{ %struct.Foo, %struct.Foo }>* %memargs, i32 1
+ call void @Foo_ctor(%struct.Foo* %b)
+
+ ; If a's ctor throws, we must destruct b.
+ %a = getelementptr <{ %struct.Foo, %struct.Foo }>* %memargs, i32 0
+ invoke void @Foo_ctor(%struct.Foo* %a)
+ to label %invoke.cont unwind %invoke.unwind
+
+ invoke.cont:
+ call void @g(<{ %struct.Foo, %struct.Foo }>* inalloca %memargs)
+ call void @llvm.stackrestore(i8* %base)
+ ...
+
+ invoke.unwind:
+ call void @Foo_dtor(%struct.Foo* %b)
+ call void @llvm.stackrestore(i8* %base)
+ ...
+ }
+
+To avoid stack leaks, the frontend saves the current stack pointer with
+a call to :ref:`llvm.stacksave <int_stacksave>`. Then, it allocates the
+argument stack space with alloca and calls the default constructor. The
+default constructor could throw an exception, so the frontend has to
+create a landing pad. The frontend has to destroy the already
+constructed argument ``b`` before restoring the stack pointer. If the
+constructor does not unwind, ``g`` is called. In the Microsoft C++ ABI,
+``g`` will destroy its arguments, and then the stack is restored in
+``f``.
+
+Design Considerations
+=====================
+
+Lifetime
+--------
+
+The biggest design consideration for this feature is object lifetime.
+We cannot model the arguments as static allocas in the entry block,
+because all calls need to use the memory at the top of the stack to pass
+arguments. We cannot vend pointers to that memory at function entry
+because after code generation they will alias.
+
+The rule against allocas between argument allocations and the call site
+avoids this problem, but it creates a cleanup problem. Cleanup and
+lifetime is handled explicitly with stack save and restore calls. In
+the future, we may want to introduce a new construct such as ``freea``
+or ``afree`` to make it clear that this stack adjusting cleanup is less
+powerful than a full stack save and restore.
+
+Nested Calls and Copy Elision
+-----------------------------
+
+We also want to be able to support copy elision into these argument
+slots. This means we have to support multiple live argument
+allocations.
+
+Consider the evaluation of:
+
+.. code-block:: c++
+
+ // Foo is non-trivial.
+ struct Foo { int a; Foo(); Foo(const &Foo); ~Foo(); };
+ Foo bar(Foo b);
+ int main() {
+ bar(bar(Foo()));
+ }
+
+In this case, we want to be able to elide copies into ``bar``'s argument
+slots. That means we need to have more than one set of argument frames
+active at the same time. First, we need to allocate the frame for the
+outer call so we can pass it in as the hidden struct return pointer to
+the middle call. Then we do the same for the middle call, allocating a
+frame and passing its address to ``Foo``'s default constructor. By
+wrapping the evaluation of the inner ``bar`` with stack save and
+restore, we can have multiple overlapping active call frames.
+
+Callee-cleanup Calling Conventions
+----------------------------------
+
+Another wrinkle is the existence of callee-cleanup conventions. On
+Windows, all methods and many other functions adjust the stack to clear
+the memory used to pass their arguments. In some sense, this means that
+the allocas are automatically cleared by the call. However, LLVM
+instead models this as a write of undef to all of the inalloca values
+passed to the call instead of a stack adjustment. Frontends should
+still restore the stack pointer to avoid a stack leak.
+
+Exceptions
+----------
+
+There is also the possibility of an exception. If argument evaluation
+or copy construction throws an exception, the landing pad must do
+cleanup, which includes adjusting the stack pointer to avoid a stack
+leak. This means the cleanup of the stack memory cannot be tied to the
+call itself. There needs to be a separate IR-level instruction that can
+perform independent cleanup of arguments.
+
+Efficiency
+----------
+
+Eventually, it should be possible to generate efficient code for this
+construct. In particular, using inalloca should not require a base
+pointer. If the backend can prove that all points in the CFG only have
+one possible stack level, then it can address the stack directly from
+the stack pointer. While this is not yet implemented, the plan is that
+the inalloca attribute should not change much, but the frontend IR
+generation recommendations may change.
Added: www-releases/trunk/5.0.2/docs/_sources/LLVMBuild.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.2/docs/_sources/LLVMBuild.txt?rev=331981&view=auto
==============================================================================
--- www-releases/trunk/5.0.2/docs/_sources/LLVMBuild.txt (added)
+++ www-releases/trunk/5.0.2/docs/_sources/LLVMBuild.txt Thu May 10 06:54:16 2018
@@ -0,0 +1,323 @@
+===============
+LLVMBuild Guide
+===============
+
+.. contents::
+ :local:
+
+Introduction
+============
+
+This document describes the ``LLVMBuild`` organization and files which
+we use to describe parts of the LLVM ecosystem. For description of
+specific LLVMBuild related tools, please see the command guide.
+
+LLVM is designed to be a modular set of libraries which can be flexibly
+mixed together in order to build a variety of tools, like compilers,
+JITs, custom code generators, optimization passes, interpreters, and so
+on. Related projects in the LLVM system like Clang and LLDB also tend to
+follow this philosophy.
+
+In order to support this usage style, LLVM has a fairly strict structure
+as to how the source code and various components are organized. The
+``LLVMBuild.txt`` files are the explicit specification of that
+structure, and are used by the build systems and other tools in order to
+develop the LLVM project.
+
+Project Organization
+====================
+
+The source code for LLVM projects using the LLVMBuild system (LLVM,
+Clang, and LLDB) is organized into *components*, which define the
+separate pieces of functionality that make up the project. These
+projects may consist of many libraries, associated tools, build tools,
+or other utility tools (for example, testing tools).
+
+For the most part, the project contents are organized around defining
+one main component per each subdirectory. Each such directory contains
+an ``LLVMBuild.txt`` which contains the component definitions.
+
+The component descriptions for the project as a whole are automatically
+gathered by the LLVMBuild tools. The tools automatically traverse the
+source directory structure to find all of the component description
+files. NOTE: For performance/sanity reasons, we only traverse into
+subdirectories when the parent itself contains an ``LLVMBuild.txt``
+description file.
+
+Build Integration
+=================
+
+The LLVMBuild files themselves are just a declarative way to describe
+the project structure. The actual building of the LLVM project is
+handled by another build system (See: :doc:`CMake <CMake>`).
+
+The build system implementation will load the relevant contents of the
+LLVMBuild files and use that to drive the actual project build.
+Typically, the build system will only need to load this information at
+"configure" time, and use it to generate native information. Build
+systems will also handle automatically reconfiguring their information
+when the contents of the ``LLVMBuild.txt`` files change.
+
+Developers generally are not expected to need to be aware of the details
+of how the LLVMBuild system is integrated into their build. Ideally,
+LLVM developers who are not working on the build system would only ever
+need to modify the contents of the ``LLVMBuild.txt`` description files
+(although we have not reached this goal yet).
+
+For more information on the utility tool we provide to help interfacing
+with the build system, please see the :doc:`llvm-build
+<CommandGuide/llvm-build>` documentation.
+
+Component Overview
+==================
+
+As mentioned earlier, LLVM projects are organized into logical
+*components*. Every component is typically grouped into its own
+subdirectory. Generally, a component is organized around a coherent
+group of sources which have some kind of clear API separation from other
+parts of the code.
+
+LLVM primarily uses the following types of components:
+
+- *Libraries* - Library components define a distinct API which can be
+ independently linked into LLVM client applications. Libraries typically
+ have private and public header files, and may specify a link of required
+ libraries that they build on top of.
+- *Build Tools* - Build tools are applications which are designed to be run
+ as part of the build process (typically to generate other source files).
+ Currently, LLVM uses one main build tool called :doc:`TableGen/index`
+ to generate a variety of source files.
+- *Tools* - Command line applications which are built using the LLVM
+ component libraries. Most LLVM tools are small and are primarily
+ frontends to the library interfaces.
+
+Components are described using ``LLVMBuild.txt`` files in the directories
+that define the component. See the `LLVMBuild Format Reference`_ section
+for information on the exact format of these files.
+
+LLVMBuild Format Reference
+==========================
+
+LLVMBuild files are written in a simple variant of the INI or configuration
+file format (`Wikipedia entry`_). The format defines a list of sections
+each of which may contain some number of properties. A simple example of
+the file format is below:
+
+.. _Wikipedia entry: http://en.wikipedia.org/wiki/INI_file
+
+.. code-block:: ini
+
+ ; Comments start with a semi-colon.
+
+ ; Sections are declared using square brackets.
+ [component_0]
+
+ ; Properties are declared using '=' and are contained in the previous section.
+ ;
+ ; We support simple string and boolean scalar values and list values, where
+ ; items are separated by spaces. There is no support for quoting, and so
+ ; property values may not contain spaces.
+ property_name = property_value
+ list_property_name = value_1 value_2 ... value_n
+ boolean_property_name = 1 (or 0)
+
+LLVMBuild files are expected to define a strict set of sections and
+properties. A typical component description file for a library
+component would look like the following example:
+
+.. code-block:: ini
+
+ [component_0]
+ type = Library
+ name = Linker
+ parent = Libraries
+ required_libraries = Archive BitReader Core Support TransformUtils
+
+A full description of the exact sections and properties which are
+allowed follows.
+
+Each file may define exactly one common component, named ``common``. The
+common component may define the following properties:
+
+- ``subdirectories`` **[optional]**
+
+ If given, a list of the names of the subdirectories from the current
+ subpath to search for additional LLVMBuild files.
+
+Each file may define multiple components. Each component is described by a
+section who name starts with ``component``. The remainder of the section
+name is ignored, but each section name must be unique. Typically components
+are just number in order for files with multiple components
+(``component_0``, ``component_1``, and so on).
+
+.. warning::
+
+ Section names not matching this format (or the ``common`` section) are
+ currently unused and are disallowed.
+
+Every component is defined by the properties in the section. The exact
+list of properties that are allowed depends on the component type.
+Components **may not** define any properties other than those expected
+by the component type.
+
+Every component must define the following properties:
+
+- ``type`` **[required]**
+
+ The type of the component. Supported component types are detailed
+ below. Most components will define additional properties which may be
+ required or optional.
+
+- ``name`` **[required]**
+
+ The name of the component. Names are required to be unique across the
+ entire project.
+
+- ``parent`` **[required]**
+
+ The name of the logical parent of the component. Components are
+ organized into a logical tree to make it easier to navigate and
+ organize groups of components. The parents have no semantics as far
+ as the project build is concerned, however. Typically, the parent
+ will be the main component of the parent directory.
+
+ Components may reference the root pseudo component using ``$ROOT`` to
+ indicate they should logically be grouped at the top-level.
+
+Components may define the following properties:
+
+- ``dependencies`` **[optional]**
+
+ If specified, a list of names of components which *must* be built
+ prior to this one. This should only be exactly those components which
+ produce some tool or source code required for building the component.
+
+ .. note::
+
+ ``Group`` and ``LibraryGroup`` components have no semantics for the
+ actual build, and are not allowed to specify dependencies.
+
+The following section lists the available component types, as well as
+the properties which are associated with that component.
+
+- ``type = Group``
+
+ Group components exist purely to allow additional arbitrary structuring
+ of the logical components tree. For example, one might define a
+ ``Libraries`` group to hold all of the root library components.
+
+ ``Group`` components have no additionally properties.
+
+- ``type = Library``
+
+ Library components define an individual library which should be built
+ from the source code in the component directory.
+
+ Components with this type use the following properties:
+
+ - ``library_name`` **[optional]**
+
+ If given, the name to use for the actual library file on disk. If
+ not given, the name is derived from the component name itself.
+
+ - ``required_libraries`` **[optional]**
+
+ If given, a list of the names of ``Library`` or ``LibraryGroup``
+ components which must also be linked in whenever this library is
+ used. That is, the link time dependencies for this component. When
+ tools are built, the build system will include the transitive closure
+ of all ``required_libraries`` for the components the tool needs.
+
+ - ``add_to_library_groups`` **[optional]**
+
+ If given, a list of the names of ``LibraryGroup`` components which
+ this component is also part of. This allows nesting groups of
+ components. For example, the ``X86`` target might define a library
+ group for all of the ``X86`` components. That library group might
+ then be included in the ``all-targets`` library group.
+
+ - ``installed`` **[optional]** **[boolean]**
+
+ Whether this library is installed. Libraries that are not installed
+ are only reported by ``llvm-config`` when it is run as part of a
+ development directory.
+
+- ``type = LibraryGroup``
+
+ ``LibraryGroup`` components are a mechanism to allow easy definition of
+ useful sets of related components. In particular, we use them to easily
+ specify things like "all targets", or "all assembly printers".
+
+ Components with this type use the following properties:
+
+ - ``required_libraries`` **[optional]**
+
+ See the ``Library`` type for a description of this property.
+
+ - ``add_to_library_groups`` **[optional]**
+
+ See the ``Library`` type for a description of this property.
+
+- ``type = TargetGroup``
+
+ ``TargetGroup`` components are an extension of ``LibraryGroup``\s,
+ specifically for defining LLVM targets (which are handled specially in a
+ few places).
+
+ The name of the component should always be the name of the target.
+
+ Components with this type use the ``LibraryGroup`` properties in
+ addition to:
+
+ - ``has_asmparser`` **[optional]** **[boolean]**
+
+ Whether this target defines an assembly parser.
+
+ - ``has_asmprinter`` **[optional]** **[boolean]**
+
+ Whether this target defines an assembly printer.
+
+ - ``has_disassembler`` **[optional]** **[boolean]**
+
+ Whether this target defines a disassembler.
+
+ - ``has_jit`` **[optional]** **[boolean]**
+
+ Whether this target supports JIT compilation.
+
+- ``type = Tool``
+
+ ``Tool`` components define standalone command line tools which should be
+ built from the source code in the component directory and linked.
+
+ Components with this type use the following properties:
+
+ - ``required_libraries`` **[optional]**
+
+ If given, a list of the names of ``Library`` or ``LibraryGroup``
+ components which this tool is required to be linked with.
+
+ .. note::
+
+ The values should be the component names, which may not always
+ match up with the actual library names on disk.
+
+ Build systems are expected to properly include all of the libraries
+ required by the linked components (i.e., the transitive closure of
+ ``required_libraries``).
+
+ Build systems are also expected to understand that those library
+ components must be built prior to linking -- they do not also need
+ to be listed under ``dependencies``.
+
+- ``type = BuildTool``
+
+ ``BuildTool`` components are like ``Tool`` components, except that the
+ tool is supposed to be built for the platform where the build is running
+ (instead of that platform being targeted). Build systems are expected
+ to handle the fact that required libraries may need to be built for
+ multiple platforms in order to be able to link this tool.
+
+ ``BuildTool`` components currently use the exact same properties as
+ ``Tool`` components, the type distinction is only used to differentiate
+ what the tool is built for.
Added: www-releases/trunk/5.0.2/docs/_sources/LangRef.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.2/docs/_sources/LangRef.txt?rev=331981&view=auto
==============================================================================
--- www-releases/trunk/5.0.2/docs/_sources/LangRef.txt (added)
+++ www-releases/trunk/5.0.2/docs/_sources/LangRef.txt Thu May 10 06:54:16 2018
@@ -0,0 +1,14339 @@
+==============================
+LLVM Language Reference Manual
+==============================
+
+.. contents::
+ :local:
+ :depth: 4
+
+Abstract
+========
+
+This document is a reference manual for the LLVM assembly language. LLVM
+is a Static Single Assignment (SSA) based representation that provides
+type safety, low-level operations, flexibility, and the capability of
+representing 'all' high-level languages cleanly. It is the common code
+representation used throughout all phases of the LLVM compilation
+strategy.
+
+Introduction
+============
+
+The LLVM code representation is designed to be used in three different
+forms: as an in-memory compiler IR, as an on-disk bitcode representation
+(suitable for fast loading by a Just-In-Time compiler), and as a human
+readable assembly language representation. This allows LLVM to provide a
+powerful intermediate representation for efficient compiler
+transformations and analysis, while providing a natural means to debug
+and visualize the transformations. The three different forms of LLVM are
+all equivalent. This document describes the human readable
+representation and notation.
+
+The LLVM representation aims to be light-weight and low-level while
+being expressive, typed, and extensible at the same time. It aims to be
+a "universal IR" of sorts, by being at a low enough level that
+high-level ideas may be cleanly mapped to it (similar to how
+microprocessors are "universal IR's", allowing many source languages to
+be mapped to them). By providing type information, LLVM can be used as
+the target of optimizations: for example, through pointer analysis, it
+can be proven that a C automatic variable is never accessed outside of
+the current function, allowing it to be promoted to a simple SSA value
+instead of a memory location.
+
+.. _wellformed:
+
+Well-Formedness
+---------------
+
+It is important to note that this document describes 'well formed' LLVM
+assembly language. There is a difference between what the parser accepts
+and what is considered 'well formed'. For example, the following
+instruction is syntactically okay, but not well formed:
+
+.. code-block:: llvm
+
+ %x = add i32 1, %x
+
+because the definition of ``%x`` does not dominate all of its uses. The
+LLVM infrastructure provides a verification pass that may be used to
+verify that an LLVM module is well formed. This pass is automatically
+run by the parser after parsing input assembly and by the optimizer
+before it outputs bitcode. The violations pointed out by the verifier
+pass indicate bugs in transformation passes or input to the parser.
+
+.. _identifiers:
+
+Identifiers
+===========
+
+LLVM identifiers come in two basic types: global and local. Global
+identifiers (functions, global variables) begin with the ``'@'``
+character. Local identifiers (register names, types) begin with the
+``'%'`` character. Additionally, there are three different formats for
+identifiers, for different purposes:
+
+#. Named values are represented as a string of characters with their
+ prefix. For example, ``%foo``, ``@DivisionByZero``,
+ ``%a.really.long.identifier``. The actual regular expression used is
+ '``[%@][-a-zA-Z$._][-a-zA-Z$._0-9]*``'. Identifiers that require other
+ characters in their names can be surrounded with quotes. Special
+ characters may be escaped using ``"\xx"`` where ``xx`` is the ASCII
+ code for the character in hexadecimal. In this way, any character can
+ be used in a name value, even quotes themselves. The ``"\01"`` prefix
+ can be used on global variables to suppress mangling.
+#. Unnamed values are represented as an unsigned numeric value with
+ their prefix. For example, ``%12``, ``@2``, ``%44``.
+#. Constants, which are described in the section Constants_ below.
+
+LLVM requires that values start with a prefix for two reasons: Compilers
+don't need to worry about name clashes with reserved words, and the set
+of reserved words may be expanded in the future without penalty.
+Additionally, unnamed identifiers allow a compiler to quickly come up
+with a temporary variable without having to avoid symbol table
+conflicts.
+
+Reserved words in LLVM are very similar to reserved words in other
+languages. There are keywords for different opcodes ('``add``',
+'``bitcast``', '``ret``', etc...), for primitive type names ('``void``',
+'``i32``', etc...), and others. These reserved words cannot conflict
+with variable names, because none of them start with a prefix character
+(``'%'`` or ``'@'``).
+
+Here is an example of LLVM code to multiply the integer variable
+'``%X``' by 8:
+
+The easy way:
+
+.. code-block:: llvm
+
+ %result = mul i32 %X, 8
+
+After strength reduction:
+
+.. code-block:: llvm
+
+ %result = shl i32 %X, 3
+
+And the hard way:
+
+.. code-block:: llvm
+
+ %0 = add i32 %X, %X ; yields i32:%0
+ %1 = add i32 %0, %0 ; yields i32:%1
+ %result = add i32 %1, %1
+
+This last way of multiplying ``%X`` by 8 illustrates several important
+lexical features of LLVM:
+
+#. Comments are delimited with a '``;``' and go until the end of line.
+#. Unnamed temporaries are created when the result of a computation is
+ not assigned to a named value.
+#. Unnamed temporaries are numbered sequentially (using a per-function
+ incrementing counter, starting with 0). Note that basic blocks and unnamed
+ function parameters are included in this numbering. For example, if the
+ entry basic block is not given a label name and all function parameters are
+ named, then it will get number 0.
+
+It also shows a convention that we follow in this document. When
+demonstrating instructions, we will follow an instruction with a comment
+that defines the type and name of value produced.
+
+High Level Structure
+====================
+
+Module Structure
+----------------
+
+LLVM programs are composed of ``Module``'s, each of which is a
+translation unit of the input programs. Each module consists of
+functions, global variables, and symbol table entries. Modules may be
+combined together with the LLVM linker, which merges function (and
+global variable) definitions, resolves forward declarations, and merges
+symbol table entries. Here is an example of the "hello world" module:
+
+.. code-block:: llvm
+
+ ; Declare the string constant as a global constant.
+ @.str = private unnamed_addr constant [13 x i8] c"hello world\0A\00"
+
+ ; External declaration of the puts function
+ declare i32 @puts(i8* nocapture) nounwind
+
+ ; Definition of main function
+ define i32 @main() { ; i32()*
+ ; Convert [13 x i8]* to i8*...
+ %cast210 = getelementptr [13 x i8], [13 x i8]* @.str, i64 0, i64 0
+
+ ; Call puts function to write out the string to stdout.
+ call i32 @puts(i8* %cast210)
+ ret i32 0
+ }
+
+ ; Named metadata
+ !0 = !{i32 42, null, !"string"}
+ !foo = !{!0}
+
+This example is made up of a :ref:`global variable <globalvars>` named
+"``.str``", an external declaration of the "``puts``" function, a
+:ref:`function definition <functionstructure>` for "``main``" and
+:ref:`named metadata <namedmetadatastructure>` "``foo``".
+
+In general, a module is made up of a list of global values (where both
+functions and global variables are global values). Global values are
+represented by a pointer to a memory location (in this case, a pointer
+to an array of char, and a pointer to a function), and have one of the
+following :ref:`linkage types <linkage>`.
+
+.. _linkage:
+
+Linkage Types
+-------------
+
+All Global Variables and Functions have one of the following types of
+linkage:
+
+``private``
+ Global values with "``private``" linkage are only directly
+ accessible by objects in the current module. In particular, linking
+ code into a module with a private global value may cause the
+ private to be renamed as necessary to avoid collisions. Because the
+ symbol is private to the module, all references can be updated. This
+ doesn't show up in any symbol table in the object file.
+``internal``
+ Similar to private, but the value shows as a local symbol
+ (``STB_LOCAL`` in the case of ELF) in the object file. This
+ corresponds to the notion of the '``static``' keyword in C.
+``available_externally``
+ Globals with "``available_externally``" linkage are never emitted into
+ the object file corresponding to the LLVM module. From the linker's
+ perspective, an ``available_externally`` global is equivalent to
+ an external declaration. They exist to allow inlining and other
+ optimizations to take place given knowledge of the definition of the
+ global, which is known to be somewhere outside the module. Globals
+ with ``available_externally`` linkage are allowed to be discarded at
+ will, and allow inlining and other optimizations. This linkage type is
+ only allowed on definitions, not declarations.
+``linkonce``
+ Globals with "``linkonce``" linkage are merged with other globals of
+ the same name when linkage occurs. This can be used to implement
+ some forms of inline functions, templates, or other code which must
+ be generated in each translation unit that uses it, but where the
+ body may be overridden with a more definitive definition later.
+ Unreferenced ``linkonce`` globals are allowed to be discarded. Note
+ that ``linkonce`` linkage does not actually allow the optimizer to
+ inline the body of this function into callers because it doesn't
+ know if this definition of the function is the definitive definition
+ within the program or whether it will be overridden by a stronger
+ definition. To enable inlining and other optimizations, use
+ "``linkonce_odr``" linkage.
+``weak``
+ "``weak``" linkage has the same merging semantics as ``linkonce``
+ linkage, except that unreferenced globals with ``weak`` linkage may
+ not be discarded. This is used for globals that are declared "weak"
+ in C source code.
+``common``
+ "``common``" linkage is most similar to "``weak``" linkage, but they
+ are used for tentative definitions in C, such as "``int X;``" at
+ global scope. Symbols with "``common``" linkage are merged in the
+ same way as ``weak symbols``, and they may not be deleted if
+ unreferenced. ``common`` symbols may not have an explicit section,
+ must have a zero initializer, and may not be marked
+ ':ref:`constant <globalvars>`'. Functions and aliases may not have
+ common linkage.
+
+.. _linkage_appending:
+
+``appending``
+ "``appending``" linkage may only be applied to global variables of
+ pointer to array type. When two global variables with appending
+ linkage are linked together, the two global arrays are appended
+ together. This is the LLVM, typesafe, equivalent of having the
+ system linker append together "sections" with identical names when
+ .o files are linked.
+
+ Unfortunately this doesn't correspond to any feature in .o files, so it
+ can only be used for variables like ``llvm.global_ctors`` which llvm
+ interprets specially.
+
+``extern_weak``
+ The semantics of this linkage follow the ELF object file model: the
+ symbol is weak until linked, if not linked, the symbol becomes null
+ instead of being an undefined reference.
+``linkonce_odr``, ``weak_odr``
+ Some languages allow differing globals to be merged, such as two
+ functions with different semantics. Other languages, such as
+ ``C++``, ensure that only equivalent globals are ever merged (the
+ "one definition rule" --- "ODR"). Such languages can use the
+ ``linkonce_odr`` and ``weak_odr`` linkage types to indicate that the
+ global will only be merged with equivalent globals. These linkage
+ types are otherwise the same as their non-``odr`` versions.
+``external``
+ If none of the above identifiers are used, the global is externally
+ visible, meaning that it participates in linkage and can be used to
+ resolve external symbol references.
+
+It is illegal for a function *declaration* to have any linkage type
+other than ``external`` or ``extern_weak``.
+
+.. _callingconv:
+
+Calling Conventions
+-------------------
+
+LLVM :ref:`functions <functionstructure>`, :ref:`calls <i_call>` and
+:ref:`invokes <i_invoke>` can all have an optional calling convention
+specified for the call. The calling convention of any pair of dynamic
+caller/callee must match, or the behavior of the program is undefined.
+The following calling conventions are supported by LLVM, and more may be
+added in the future:
+
+"``ccc``" - The C calling convention
+ This calling convention (the default if no other calling convention
+ is specified) matches the target C calling conventions. This calling
+ convention supports varargs function calls and tolerates some
+ mismatch in the declared prototype and implemented declaration of
+ the function (as does normal C).
+"``fastcc``" - The fast calling convention
+ This calling convention attempts to make calls as fast as possible
+ (e.g. by passing things in registers). This calling convention
+ allows the target to use whatever tricks it wants to produce fast
+ code for the target, without having to conform to an externally
+ specified ABI (Application Binary Interface). `Tail calls can only
+ be optimized when this, the GHC or the HiPE convention is
+ used. <CodeGenerator.html#id80>`_ This calling convention does not
+ support varargs and requires the prototype of all callees to exactly
+ match the prototype of the function definition.
+"``coldcc``" - The cold calling convention
+ This calling convention attempts to make code in the caller as
+ efficient as possible under the assumption that the call is not
+ commonly executed. As such, these calls often preserve all registers
+ so that the call does not break any live ranges in the caller side.
+ This calling convention does not support varargs and requires the
+ prototype of all callees to exactly match the prototype of the
+ function definition. Furthermore the inliner doesn't consider such function
+ calls for inlining.
+"``cc 10``" - GHC convention
+ This calling convention has been implemented specifically for use by
+ the `Glasgow Haskell Compiler (GHC) <http://www.haskell.org/ghc>`_.
+ It passes everything in registers, going to extremes to achieve this
+ by disabling callee save registers. This calling convention should
+ not be used lightly but only for specific situations such as an
+ alternative to the *register pinning* performance technique often
+ used when implementing functional programming languages. At the
+ moment only X86 supports this convention and it has the following
+ limitations:
+
+ - On *X86-32* only supports up to 4 bit type parameters. No
+ floating point types are supported.
+ - On *X86-64* only supports up to 10 bit type parameters and 6
+ floating point parameters.
+
+ This calling convention supports `tail call
+ optimization <CodeGenerator.html#id80>`_ but requires both the
+ caller and callee are using it.
+"``cc 11``" - The HiPE calling convention
+ This calling convention has been implemented specifically for use by
+ the `High-Performance Erlang
+ (HiPE) <http://www.it.uu.se/research/group/hipe/>`_ compiler, *the*
+ native code compiler of the `Ericsson's Open Source Erlang/OTP
+ system <http://www.erlang.org/download.shtml>`_. It uses more
+ registers for argument passing than the ordinary C calling
+ convention and defines no callee-saved registers. The calling
+ convention properly supports `tail call
+ optimization <CodeGenerator.html#id80>`_ but requires that both the
+ caller and the callee use it. It uses a *register pinning*
+ mechanism, similar to GHC's convention, for keeping frequently
+ accessed runtime components pinned to specific hardware registers.
+ At the moment only X86 supports this convention (both 32 and 64
+ bit).
+"``webkit_jscc``" - WebKit's JavaScript calling convention
+ This calling convention has been implemented for `WebKit FTL JIT
+ <https://trac.webkit.org/wiki/FTLJIT>`_. It passes arguments on the
+ stack right to left (as cdecl does), and returns a value in the
+ platform's customary return register.
+"``anyregcc``" - Dynamic calling convention for code patching
+ This is a special convention that supports patching an arbitrary code
+ sequence in place of a call site. This convention forces the call
+ arguments into registers but allows them to be dynamically
+ allocated. This can currently only be used with calls to
+ llvm.experimental.patchpoint because only this intrinsic records
+ the location of its arguments in a side table. See :doc:`StackMaps`.
+"``preserve_mostcc``" - The `PreserveMost` calling convention
+ This calling convention attempts to make the code in the caller as
+ unintrusive as possible. This convention behaves identically to the `C`
+ calling convention on how arguments and return values are passed, but it
+ uses a different set of caller/callee-saved registers. This alleviates the
+ burden of saving and recovering a large register set before and after the
+ call in the caller. If the arguments are passed in callee-saved registers,
+ then they will be preserved by the callee across the call. This doesn't
+ apply for values returned in callee-saved registers.
+
+ - On X86-64 the callee preserves all general purpose registers, except for
+ R11. R11 can be used as a scratch register. Floating-point registers
+ (XMMs/YMMs) are not preserved and need to be saved by the caller.
+
+ The idea behind this convention is to support calls to runtime functions
+ that have a hot path and a cold path. The hot path is usually a small piece
+ of code that doesn't use many registers. The cold path might need to call out to
+ another function and therefore only needs to preserve the caller-saved
+ registers, which haven't already been saved by the caller. The
+ `PreserveMost` calling convention is very similar to the `cold` calling
+ convention in terms of caller/callee-saved registers, but they are used for
+ different types of function calls. `coldcc` is for function calls that are
+ rarely executed, whereas `preserve_mostcc` function calls are intended to be
+ on the hot path and definitely executed a lot. Furthermore `preserve_mostcc`
+ doesn't prevent the inliner from inlining the function call.
+
+ This calling convention will be used by a future version of the ObjectiveC
+ runtime and should therefore still be considered experimental at this time.
+ Although this convention was created to optimize certain runtime calls to
+ the ObjectiveC runtime, it is not limited to this runtime and might be used
+ by other runtimes in the future too. The current implementation only
+ supports X86-64, but the intention is to support more architectures in the
+ future.
+"``preserve_allcc``" - The `PreserveAll` calling convention
+ This calling convention attempts to make the code in the caller even less
+ intrusive than the `PreserveMost` calling convention. This calling
+ convention also behaves identical to the `C` calling convention on how
+ arguments and return values are passed, but it uses a different set of
+ caller/callee-saved registers. This removes the burden of saving and
+ recovering a large register set before and after the call in the caller. If
+ the arguments are passed in callee-saved registers, then they will be
+ preserved by the callee across the call. This doesn't apply for values
+ returned in callee-saved registers.
+
+ - On X86-64 the callee preserves all general purpose registers, except for
+ R11. R11 can be used as a scratch register. Furthermore it also preserves
+ all floating-point registers (XMMs/YMMs).
+
+ The idea behind this convention is to support calls to runtime functions
+ that don't need to call out to any other functions.
+
+ This calling convention, like the `PreserveMost` calling convention, will be
+ used by a future version of the ObjectiveC runtime and should be considered
+ experimental at this time.
+"``cxx_fast_tlscc``" - The `CXX_FAST_TLS` calling convention for access functions
+ Clang generates an access function to access C++-style TLS. The access
+ function generally has an entry block, an exit block and an initialization
+ block that is run at the first time. The entry and exit blocks can access
+ a few TLS IR variables, each access will be lowered to a platform-specific
+ sequence.
+
+ This calling convention aims to minimize overhead in the caller by
+ preserving as many registers as possible (all the registers that are
+ perserved on the fast path, composed of the entry and exit blocks).
+
+ This calling convention behaves identical to the `C` calling convention on
+ how arguments and return values are passed, but it uses a different set of
+ caller/callee-saved registers.
+
+ Given that each platform has its own lowering sequence, hence its own set
+ of preserved registers, we can't use the existing `PreserveMost`.
+
+ - On X86-64 the callee preserves all general purpose registers, except for
+ RDI and RAX.
+"``swiftcc``" - This calling convention is used for Swift language.
+ - On X86-64 RCX and R8 are available for additional integer returns, and
+ XMM2 and XMM3 are available for additional FP/vector returns.
+ - On iOS platforms, we use AAPCS-VFP calling convention.
+"``cc <n>``" - Numbered convention
+ Any calling convention may be specified by number, allowing
+ target-specific calling conventions to be used. Target specific
+ calling conventions start at 64.
+
+More calling conventions can be added/defined on an as-needed basis, to
+support Pascal conventions or any other well-known target-independent
+convention.
+
+.. _visibilitystyles:
+
+Visibility Styles
+-----------------
+
+All Global Variables and Functions have one of the following visibility
+styles:
+
+"``default``" - Default style
+ On targets that use the ELF object file format, default visibility
+ means that the declaration is visible to other modules and, in
+ shared libraries, means that the declared entity may be overridden.
+ On Darwin, default visibility means that the declaration is visible
+ to other modules. Default visibility corresponds to "external
+ linkage" in the language.
+"``hidden``" - Hidden style
+ Two declarations of an object with hidden visibility refer to the
+ same object if they are in the same shared object. Usually, hidden
+ visibility indicates that the symbol will not be placed into the
+ dynamic symbol table, so no other module (executable or shared
+ library) can reference it directly.
+"``protected``" - Protected style
+ On ELF, protected visibility indicates that the symbol will be
+ placed in the dynamic symbol table, but that references within the
+ defining module will bind to the local symbol. That is, the symbol
+ cannot be overridden by another module.
+
+A symbol with ``internal`` or ``private`` linkage must have ``default``
+visibility.
+
+.. _dllstorageclass:
+
+DLL Storage Classes
+-------------------
+
+All Global Variables, Functions and Aliases can have one of the following
+DLL storage class:
+
+``dllimport``
+ "``dllimport``" causes the compiler to reference a function or variable via
+ a global pointer to a pointer that is set up by the DLL exporting the
+ symbol. On Microsoft Windows targets, the pointer name is formed by
+ combining ``__imp_`` and the function or variable name.
+``dllexport``
+ "``dllexport``" causes the compiler to provide a global pointer to a pointer
+ in a DLL, so that it can be referenced with the ``dllimport`` attribute. On
+ Microsoft Windows targets, the pointer name is formed by combining
+ ``__imp_`` and the function or variable name. Since this storage class
+ exists for defining a dll interface, the compiler, assembler and linker know
+ it is externally referenced and must refrain from deleting the symbol.
+
+.. _tls_model:
+
+Thread Local Storage Models
+---------------------------
+
+A variable may be defined as ``thread_local``, which means that it will
+not be shared by threads (each thread will have a separated copy of the
+variable). Not all targets support thread-local variables. Optionally, a
+TLS model may be specified:
+
+``localdynamic``
+ For variables that are only used within the current shared library.
+``initialexec``
+ For variables in modules that will not be loaded dynamically.
+``localexec``
+ For variables defined in the executable and only used within it.
+
+If no explicit model is given, the "general dynamic" model is used.
+
+The models correspond to the ELF TLS models; see `ELF Handling For
+Thread-Local Storage <http://people.redhat.com/drepper/tls.pdf>`_ for
+more information on under which circumstances the different models may
+be used. The target may choose a different TLS model if the specified
+model is not supported, or if a better choice of model can be made.
+
+A model can also be specified in an alias, but then it only governs how
+the alias is accessed. It will not have any effect in the aliasee.
+
+For platforms without linker support of ELF TLS model, the -femulated-tls
+flag can be used to generate GCC compatible emulated TLS code.
+
+.. _namedtypes:
+
+Structure Types
+---------------
+
+LLVM IR allows you to specify both "identified" and "literal" :ref:`structure
+types <t_struct>`. Literal types are uniqued structurally, but identified types
+are never uniqued. An :ref:`opaque structural type <t_opaque>` can also be used
+to forward declare a type that is not yet available.
+
+An example of an identified structure specification is:
+
+.. code-block:: llvm
+
+ %mytype = type { %mytype*, i32 }
+
+Prior to the LLVM 3.0 release, identified types were structurally uniqued. Only
+literal types are uniqued in recent versions of LLVM.
+
+.. _nointptrtype:
+
+Non-Integral Pointer Type
+-------------------------
+
+Note: non-integral pointer types are a work in progress, and they should be
+considered experimental at this time.
+
+LLVM IR optionally allows the frontend to denote pointers in certain address
+spaces as "non-integral" via the :ref:`datalayout string<langref_datalayout>`.
+Non-integral pointer types represent pointers that have an *unspecified* bitwise
+representation; that is, the integral representation may be target dependent or
+unstable (not backed by a fixed integer).
+
+``inttoptr`` instructions converting integers to non-integral pointer types are
+ill-typed, and so are ``ptrtoint`` instructions converting values of
+non-integral pointer types to integers. Vector versions of said instructions
+are ill-typed as well.
+
+.. _globalvars:
+
+Global Variables
+----------------
+
+Global variables define regions of memory allocated at compilation time
+instead of run-time.
+
+Global variable definitions must be initialized.
+
+Global variables in other translation units can also be declared, in which
+case they don't have an initializer.
+
+Either global variable definitions or declarations may have an explicit section
+to be placed in and may have an optional explicit alignment specified.
+
+A variable may be defined as a global ``constant``, which indicates that
+the contents of the variable will **never** be modified (enabling better
+optimization, allowing the global data to be placed in the read-only
+section of an executable, etc). Note that variables that need runtime
+initialization cannot be marked ``constant`` as there is a store to the
+variable.
+
+LLVM explicitly allows *declarations* of global variables to be marked
+constant, even if the final definition of the global is not. This
+capability can be used to enable slightly better optimization of the
+program, but requires the language definition to guarantee that
+optimizations based on the 'constantness' are valid for the translation
+units that do not include the definition.
+
+As SSA values, global variables define pointer values that are in scope
+(i.e. they dominate) all basic blocks in the program. Global variables
+always define a pointer to their "content" type because they describe a
+region of memory, and all memory objects in LLVM are accessed through
+pointers.
+
+Global variables can be marked with ``unnamed_addr`` which indicates
+that the address is not significant, only the content. Constants marked
+like this can be merged with other constants if they have the same
+initializer. Note that a constant with significant address *can* be
+merged with a ``unnamed_addr`` constant, the result being a constant
+whose address is significant.
+
+If the ``local_unnamed_addr`` attribute is given, the address is known to
+not be significant within the module.
+
+A global variable may be declared to reside in a target-specific
+numbered address space. For targets that support them, address spaces
+may affect how optimizations are performed and/or what target
+instructions are used to access the variable. The default address space
+is zero. The address space qualifier must precede any other attributes.
+
+LLVM allows an explicit section to be specified for globals. If the
+target supports it, it will emit globals to the section specified.
+Additionally, the global can placed in a comdat if the target has the necessary
+support.
+
+By default, global initializers are optimized by assuming that global
+variables defined within the module are not modified from their
+initial values before the start of the global initializer. This is
+true even for variables potentially accessible from outside the
+module, including those with external linkage or appearing in
+``@llvm.used`` or dllexported variables. This assumption may be suppressed
+by marking the variable with ``externally_initialized``.
+
+An explicit alignment may be specified for a global, which must be a
+power of 2. If not present, or if the alignment is set to zero, the
+alignment of the global is set by the target to whatever it feels
+convenient. If an explicit alignment is specified, the global is forced
+to have exactly that alignment. Targets and optimizers are not allowed
+to over-align the global if the global has an assigned section. In this
+case, the extra alignment could be observable: for example, code could
+assume that the globals are densely packed in their section and try to
+iterate over them as an array, alignment padding would break this
+iteration. The maximum alignment is ``1 << 29``.
+
+Globals can also have a :ref:`DLL storage class <dllstorageclass>`,
+an optional :ref:`global attributes <glattrs>` and
+an optional list of attached :ref:`metadata <metadata>`.
+
+Variables and aliases can have a
+:ref:`Thread Local Storage Model <tls_model>`.
+
+Syntax::
+
+ @<GlobalVarName> = [Linkage] [Visibility] [DLLStorageClass] [ThreadLocal]
+ [(unnamed_addr|local_unnamed_addr)] [AddrSpace]
+ [ExternallyInitialized]
+ <global | constant> <Type> [<InitializerConstant>]
+ [, section "name"] [, comdat [($name)]]
+ [, align <Alignment>] (, !name !N)*
+
+For example, the following defines a global in a numbered address space
+with an initializer, section, and alignment:
+
+.. code-block:: llvm
+
+ @G = addrspace(5) constant float 1.0, section "foo", align 4
+
+The following example just declares a global variable
+
+.. code-block:: llvm
+
+ @G = external global i32
+
+The following example defines a thread-local global with the
+``initialexec`` TLS model:
+
+.. code-block:: llvm
+
+ @G = thread_local(initialexec) global i32 0, align 4
+
+.. _functionstructure:
+
+Functions
+---------
+
+LLVM function definitions consist of the "``define``" keyword, an
+optional :ref:`linkage type <linkage>`, an optional :ref:`visibility
+style <visibility>`, an optional :ref:`DLL storage class <dllstorageclass>`,
+an optional :ref:`calling convention <callingconv>`,
+an optional ``unnamed_addr`` attribute, a return type, an optional
+:ref:`parameter attribute <paramattrs>` for the return type, a function
+name, a (possibly empty) argument list (each with optional :ref:`parameter
+attributes <paramattrs>`), optional :ref:`function attributes <fnattrs>`,
+an optional section, an optional alignment,
+an optional :ref:`comdat <langref_comdats>`,
+an optional :ref:`garbage collector name <gc>`, an optional :ref:`prefix <prefixdata>`,
+an optional :ref:`prologue <prologuedata>`,
+an optional :ref:`personality <personalityfn>`,
+an optional list of attached :ref:`metadata <metadata>`,
+an opening curly brace, a list of basic blocks, and a closing curly brace.
+
+LLVM function declarations consist of the "``declare``" keyword, an
+optional :ref:`linkage type <linkage>`, an optional :ref:`visibility style
+<visibility>`, an optional :ref:`DLL storage class <dllstorageclass>`, an
+optional :ref:`calling convention <callingconv>`, an optional ``unnamed_addr``
+or ``local_unnamed_addr`` attribute, a return type, an optional :ref:`parameter
+attribute <paramattrs>` for the return type, a function name, a possibly
+empty list of arguments, an optional alignment, an optional :ref:`garbage
+collector name <gc>`, an optional :ref:`prefix <prefixdata>`, and an optional
+:ref:`prologue <prologuedata>`.
+
+A function definition contains a list of basic blocks, forming the CFG (Control
+Flow Graph) for the function. Each basic block may optionally start with a label
+(giving the basic block a symbol table entry), contains a list of instructions,
+and ends with a :ref:`terminator <terminators>` instruction (such as a branch or
+function return). If an explicit label is not provided, a block is assigned an
+implicit numbered label, using the next value from the same counter as used for
+unnamed temporaries (:ref:`see above<identifiers>`). For example, if a function
+entry block does not have an explicit label, it will be assigned label "%0",
+then the first unnamed temporary in that block will be "%1", etc.
+
+The first basic block in a function is special in two ways: it is
+immediately executed on entrance to the function, and it is not allowed
+to have predecessor basic blocks (i.e. there can not be any branches to
+the entry block of a function). Because the block can have no
+predecessors, it also cannot have any :ref:`PHI nodes <i_phi>`.
+
+LLVM allows an explicit section to be specified for functions. If the
+target supports it, it will emit functions to the section specified.
+Additionally, the function can be placed in a COMDAT.
+
+An explicit alignment may be specified for a function. If not present,
+or if the alignment is set to zero, the alignment of the function is set
+by the target to whatever it feels convenient. If an explicit alignment
+is specified, the function is forced to have at least that much
+alignment. All alignments must be a power of 2.
+
+If the ``unnamed_addr`` attribute is given, the address is known to not
+be significant and two identical functions can be merged.
+
+If the ``local_unnamed_addr`` attribute is given, the address is known to
+not be significant within the module.
+
+Syntax::
+
+ define [linkage] [visibility] [DLLStorageClass]
+ [cconv] [ret attrs]
+ <ResultType> @<FunctionName> ([argument list])
+ [(unnamed_addr|local_unnamed_addr)] [fn Attrs] [section "name"]
+ [comdat [($name)]] [align N] [gc] [prefix Constant]
+ [prologue Constant] [personality Constant] (!name !N)* { ... }
+
+The argument list is a comma separated sequence of arguments where each
+argument is of the following form:
+
+Syntax::
+
+ <type> [parameter Attrs] [name]
+
+
+.. _langref_aliases:
+
+Aliases
+-------
+
+Aliases, unlike function or variables, don't create any new data. They
+are just a new symbol and metadata for an existing position.
+
+Aliases have a name and an aliasee that is either a global value or a
+constant expression.
+
+Aliases may have an optional :ref:`linkage type <linkage>`, an optional
+:ref:`visibility style <visibility>`, an optional :ref:`DLL storage class
+<dllstorageclass>` and an optional :ref:`tls model <tls_model>`.
+
+Syntax::
+
+ @<Name> = [Linkage] [Visibility] [DLLStorageClass] [ThreadLocal] [(unnamed_addr|local_unnamed_addr)] alias <AliaseeTy>, <AliaseeTy>* @<Aliasee>
+
+The linkage must be one of ``private``, ``internal``, ``linkonce``, ``weak``,
+``linkonce_odr``, ``weak_odr``, ``external``. Note that some system linkers
+might not correctly handle dropping a weak symbol that is aliased.
+
+Aliases that are not ``unnamed_addr`` are guaranteed to have the same address as
+the aliasee expression. ``unnamed_addr`` ones are only guaranteed to point
+to the same content.
+
+If the ``local_unnamed_addr`` attribute is given, the address is known to
+not be significant within the module.
+
+Since aliases are only a second name, some restrictions apply, of which
+some can only be checked when producing an object file:
+
+* The expression defining the aliasee must be computable at assembly
+ time. Since it is just a name, no relocations can be used.
+
+* No alias in the expression can be weak as the possibility of the
+ intermediate alias being overridden cannot be represented in an
+ object file.
+
+* No global value in the expression can be a declaration, since that
+ would require a relocation, which is not possible.
+
+.. _langref_ifunc:
+
+IFuncs
+-------
+
+IFuncs, like as aliases, don't create any new data or func. They are just a new
+symbol that dynamic linker resolves at runtime by calling a resolver function.
+
+IFuncs have a name and a resolver that is a function called by dynamic linker
+that returns address of another function associated with the name.
+
+IFunc may have an optional :ref:`linkage type <linkage>` and an optional
+:ref:`visibility style <visibility>`.
+
+Syntax::
+
+ @<Name> = [Linkage] [Visibility] ifunc <IFuncTy>, <ResolverTy>* @<Resolver>
+
+
+.. _langref_comdats:
+
+Comdats
+-------
+
+Comdat IR provides access to COFF and ELF object file COMDAT functionality.
+
+Comdats have a name which represents the COMDAT key. All global objects that
+specify this key will only end up in the final object file if the linker chooses
+that key over some other key. Aliases are placed in the same COMDAT that their
+aliasee computes to, if any.
+
+Comdats have a selection kind to provide input on how the linker should
+choose between keys in two different object files.
+
+Syntax::
+
+ $<Name> = comdat SelectionKind
+
+The selection kind must be one of the following:
+
+``any``
+ The linker may choose any COMDAT key, the choice is arbitrary.
+``exactmatch``
+ The linker may choose any COMDAT key but the sections must contain the
+ same data.
+``largest``
+ The linker will choose the section containing the largest COMDAT key.
+``noduplicates``
+ The linker requires that only section with this COMDAT key exist.
+``samesize``
+ The linker may choose any COMDAT key but the sections must contain the
+ same amount of data.
+
+Note that the Mach-O platform doesn't support COMDATs and ELF only supports
+``any`` as a selection kind.
+
+Here is an example of a COMDAT group where a function will only be selected if
+the COMDAT key's section is the largest:
+
+.. code-block:: text
+
+ $foo = comdat largest
+ @foo = global i32 2, comdat($foo)
+
+ define void @bar() comdat($foo) {
+ ret void
+ }
+
+As a syntactic sugar the ``$name`` can be omitted if the name is the same as
+the global name:
+
+.. code-block:: text
+
+ $foo = comdat any
+ @foo = global i32 2, comdat
+
+
+In a COFF object file, this will create a COMDAT section with selection kind
+``IMAGE_COMDAT_SELECT_LARGEST`` containing the contents of the ``@foo`` symbol
+and another COMDAT section with selection kind
+``IMAGE_COMDAT_SELECT_ASSOCIATIVE`` which is associated with the first COMDAT
+section and contains the contents of the ``@bar`` symbol.
+
+There are some restrictions on the properties of the global object.
+It, or an alias to it, must have the same name as the COMDAT group when
+targeting COFF.
+The contents and size of this object may be used during link-time to determine
+which COMDAT groups get selected depending on the selection kind.
+Because the name of the object must match the name of the COMDAT group, the
+linkage of the global object must not be local; local symbols can get renamed
+if a collision occurs in the symbol table.
+
+The combined use of COMDATS and section attributes may yield surprising results.
+For example:
+
+.. code-block:: text
+
+ $foo = comdat any
+ $bar = comdat any
+ @g1 = global i32 42, section "sec", comdat($foo)
+ @g2 = global i32 42, section "sec", comdat($bar)
+
+From the object file perspective, this requires the creation of two sections
+with the same name. This is necessary because both globals belong to different
+COMDAT groups and COMDATs, at the object file level, are represented by
+sections.
+
+Note that certain IR constructs like global variables and functions may
+create COMDATs in the object file in addition to any which are specified using
+COMDAT IR. This arises when the code generator is configured to emit globals
+in individual sections (e.g. when `-data-sections` or `-function-sections`
+is supplied to `llc`).
+
+.. _namedmetadatastructure:
+
+Named Metadata
+--------------
+
+Named metadata is a collection of metadata. :ref:`Metadata
+nodes <metadata>` (but not metadata strings) are the only valid
+operands for a named metadata.
+
+#. Named metadata are represented as a string of characters with the
+ metadata prefix. The rules for metadata names are the same as for
+ identifiers, but quoted names are not allowed. ``"\xx"`` type escapes
+ are still valid, which allows any character to be part of a name.
+
+Syntax::
+
+ ; Some unnamed metadata nodes, which are referenced by the named metadata.
+ !0 = !{!"zero"}
+ !1 = !{!"one"}
+ !2 = !{!"two"}
+ ; A named metadata.
+ !name = !{!0, !1, !2}
+
+.. _paramattrs:
+
+Parameter Attributes
+--------------------
+
+The return type and each parameter of a function type may have a set of
+*parameter attributes* associated with them. Parameter attributes are
+used to communicate additional information about the result or
+parameters of a function. Parameter attributes are considered to be part
+of the function, not of the function type, so functions with different
+parameter attributes can have the same function type.
+
+Parameter attributes are simple keywords that follow the type specified.
+If multiple parameter attributes are needed, they are space separated.
+For example:
+
+.. code-block:: llvm
+
+ declare i32 @printf(i8* noalias nocapture, ...)
+ declare i32 @atoi(i8 zeroext)
+ declare signext i8 @returns_signed_char()
+
+Note that any attributes for the function result (``nounwind``,
+``readonly``) come immediately after the argument list.
+
+Currently, only the following parameter attributes are defined:
+
+``zeroext``
+ This indicates to the code generator that the parameter or return
+ value should be zero-extended to the extent required by the target's
+ ABI by the caller (for a parameter) or the callee (for a return value).
+``signext``
+ This indicates to the code generator that the parameter or return
+ value should be sign-extended to the extent required by the target's
+ ABI (which is usually 32-bits) by the caller (for a parameter) or
+ the callee (for a return value).
+``inreg``
+ This indicates that this parameter or return value should be treated
+ in a special target-dependent fashion while emitting code for
+ a function call or return (usually, by putting it in a register as
+ opposed to memory, though some targets use it to distinguish between
+ two different kinds of registers). Use of this attribute is
+ target-specific.
+``byval``
+ This indicates that the pointer parameter should really be passed by
+ value to the function. The attribute implies that a hidden copy of
+ the pointee is made between the caller and the callee, so the callee
+ is unable to modify the value in the caller. This attribute is only
+ valid on LLVM pointer arguments. It is generally used to pass
+ structs and arrays by value, but is also valid on pointers to
+ scalars. The copy is considered to belong to the caller not the
+ callee (for example, ``readonly`` functions should not write to
+ ``byval`` parameters). This is not a valid attribute for return
+ values.
+
+ The byval attribute also supports specifying an alignment with the
+ align attribute. It indicates the alignment of the stack slot to
+ form and the known alignment of the pointer specified to the call
+ site. If the alignment is not specified, then the code generator
+ makes a target-specific assumption.
+
+.. _attr_inalloca:
+
+``inalloca``
+
+ The ``inalloca`` argument attribute allows the caller to take the
+ address of outgoing stack arguments. An ``inalloca`` argument must
+ be a pointer to stack memory produced by an ``alloca`` instruction.
+ The alloca, or argument allocation, must also be tagged with the
+ inalloca keyword. Only the last argument may have the ``inalloca``
+ attribute, and that argument is guaranteed to be passed in memory.
+
+ An argument allocation may be used by a call at most once because
+ the call may deallocate it. The ``inalloca`` attribute cannot be
+ used in conjunction with other attributes that affect argument
+ storage, like ``inreg``, ``nest``, ``sret``, or ``byval``. The
+ ``inalloca`` attribute also disables LLVM's implicit lowering of
+ large aggregate return values, which means that frontend authors
+ must lower them with ``sret`` pointers.
+
+ When the call site is reached, the argument allocation must have
+ been the most recent stack allocation that is still live, or the
+ results are undefined. It is possible to allocate additional stack
+ space after an argument allocation and before its call site, but it
+ must be cleared off with :ref:`llvm.stackrestore
+ <int_stackrestore>`.
+
+ See :doc:`InAlloca` for more information on how to use this
+ attribute.
+
+``sret``
+ This indicates that the pointer parameter specifies the address of a
+ structure that is the return value of the function in the source
+ program. This pointer must be guaranteed by the caller to be valid:
+ loads and stores to the structure may be assumed by the callee not
+ to trap and to be properly aligned. This is not a valid attribute
+ for return values.
+
+``align <n>``
+ This indicates that the pointer value may be assumed by the optimizer to
+ have the specified alignment.
+
+ Note that this attribute has additional semantics when combined with the
+ ``byval`` attribute.
+
+.. _noalias:
+
+``noalias``
+ This indicates that objects accessed via pointer values
+ :ref:`based <pointeraliasing>` on the argument or return value are not also
+ accessed, during the execution of the function, via pointer values not
+ *based* on the argument or return value. The attribute on a return value
+ also has additional semantics described below. The caller shares the
+ responsibility with the callee for ensuring that these requirements are met.
+ For further details, please see the discussion of the NoAlias response in
+ :ref:`alias analysis <Must, May, or No>`.
+
+ Note that this definition of ``noalias`` is intentionally similar
+ to the definition of ``restrict`` in C99 for function arguments.
+
+ For function return values, C99's ``restrict`` is not meaningful,
+ while LLVM's ``noalias`` is. Furthermore, the semantics of the ``noalias``
+ attribute on return values are stronger than the semantics of the attribute
+ when used on function arguments. On function return values, the ``noalias``
+ attribute indicates that the function acts like a system memory allocation
+ function, returning a pointer to allocated storage disjoint from the
+ storage for any other object accessible to the caller.
+
+``nocapture``
+ This indicates that the callee does not make any copies of the
+ pointer that outlive the callee itself. This is not a valid
+ attribute for return values. Addresses used in volatile operations
+ are considered to be captured.
+
+.. _nest:
+
+``nest``
+ This indicates that the pointer parameter can be excised using the
+ :ref:`trampoline intrinsics <int_trampoline>`. This is not a valid
+ attribute for return values and can only be applied to one parameter.
+
+``returned``
+ This indicates that the function always returns the argument as its return
+ value. This is a hint to the optimizer and code generator used when
+ generating the caller, allowing value propagation, tail call optimization,
+ and omission of register saves and restores in some cases; it is not
+ checked or enforced when generating the callee. The parameter and the
+ function return type must be valid operands for the
+ :ref:`bitcast instruction <i_bitcast>`. This is not a valid attribute for
+ return values and can only be applied to one parameter.
+
+``nonnull``
+ This indicates that the parameter or return pointer is not null. This
+ attribute may only be applied to pointer typed parameters. This is not
+ checked or enforced by LLVM, the caller must ensure that the pointer
+ passed in is non-null, or the callee must ensure that the returned pointer
+ is non-null.
+
+``dereferenceable(<n>)``
+ This indicates that the parameter or return pointer is dereferenceable. This
+ attribute may only be applied to pointer typed parameters. A pointer that
+ is dereferenceable can be loaded from speculatively without a risk of
+ trapping. The number of bytes known to be dereferenceable must be provided
+ in parentheses. It is legal for the number of bytes to be less than the
+ size of the pointee type. The ``nonnull`` attribute does not imply
+ dereferenceability (consider a pointer to one element past the end of an
+ array), however ``dereferenceable(<n>)`` does imply ``nonnull`` in
+ ``addrspace(0)`` (which is the default address space).
+
+``dereferenceable_or_null(<n>)``
+ This indicates that the parameter or return value isn't both
+ non-null and non-dereferenceable (up to ``<n>`` bytes) at the same
+ time. All non-null pointers tagged with
+ ``dereferenceable_or_null(<n>)`` are ``dereferenceable(<n>)``.
+ For address space 0 ``dereferenceable_or_null(<n>)`` implies that
+ a pointer is exactly one of ``dereferenceable(<n>)`` or ``null``,
+ and in other address spaces ``dereferenceable_or_null(<n>)``
+ implies that a pointer is at least one of ``dereferenceable(<n>)``
+ or ``null`` (i.e. it may be both ``null`` and
+ ``dereferenceable(<n>)``). This attribute may only be applied to
+ pointer typed parameters.
+
+``swiftself``
+ This indicates that the parameter is the self/context parameter. This is not
+ a valid attribute for return values and can only be applied to one
+ parameter.
+
+``swifterror``
+ This attribute is motivated to model and optimize Swift error handling. It
+ can be applied to a parameter with pointer to pointer type or a
+ pointer-sized alloca. At the call site, the actual argument that corresponds
+ to a ``swifterror`` parameter has to come from a ``swifterror`` alloca or
+ the ``swifterror`` parameter of the caller. A ``swifterror`` value (either
+ the parameter or the alloca) can only be loaded and stored from, or used as
+ a ``swifterror`` argument. This is not a valid attribute for return values
+ and can only be applied to one parameter.
+
+ These constraints allow the calling convention to optimize access to
+ ``swifterror`` variables by associating them with a specific register at
+ call boundaries rather than placing them in memory. Since this does change
+ the calling convention, a function which uses the ``swifterror`` attribute
+ on a parameter is not ABI-compatible with one which does not.
+
+ These constraints also allow LLVM to assume that a ``swifterror`` argument
+ does not alias any other memory visible within a function and that a
+ ``swifterror`` alloca passed as an argument does not escape.
+
+.. _gc:
+
+Garbage Collector Strategy Names
+--------------------------------
+
+Each function may specify a garbage collector strategy name, which is simply a
+string:
+
+.. code-block:: llvm
+
+ define void @f() gc "name" { ... }
+
+The supported values of *name* includes those :ref:`built in to LLVM
+<builtin-gc-strategies>` and any provided by loaded plugins. Specifying a GC
+strategy will cause the compiler to alter its output in order to support the
+named garbage collection algorithm. Note that LLVM itself does not contain a
+garbage collector, this functionality is restricted to generating machine code
+which can interoperate with a collector provided externally.
+
+.. _prefixdata:
+
+Prefix Data
+-----------
+
+Prefix data is data associated with a function which the code
+generator will emit immediately before the function's entrypoint.
+The purpose of this feature is to allow frontends to associate
+language-specific runtime metadata with specific functions and make it
+available through the function pointer while still allowing the
+function pointer to be called.
+
+To access the data for a given function, a program may bitcast the
+function pointer to a pointer to the constant's type and dereference
+index -1. This implies that the IR symbol points just past the end of
+the prefix data. For instance, take the example of a function annotated
+with a single ``i32``,
+
+.. code-block:: llvm
+
+ define void @f() prefix i32 123 { ... }
+
+The prefix data can be referenced as,
+
+.. code-block:: llvm
+
+ %0 = bitcast void* () @f to i32*
+ %a = getelementptr inbounds i32, i32* %0, i32 -1
+ %b = load i32, i32* %a
+
+Prefix data is laid out as if it were an initializer for a global variable
+of the prefix data's type. The function will be placed such that the
+beginning of the prefix data is aligned. This means that if the size
+of the prefix data is not a multiple of the alignment size, the
+function's entrypoint will not be aligned. If alignment of the
+function's entrypoint is desired, padding must be added to the prefix
+data.
+
+A function may have prefix data but no body. This has similar semantics
+to the ``available_externally`` linkage in that the data may be used by the
+optimizers but will not be emitted in the object file.
+
+.. _prologuedata:
+
+Prologue Data
+-------------
+
+The ``prologue`` attribute allows arbitrary code (encoded as bytes) to
+be inserted prior to the function body. This can be used for enabling
+function hot-patching and instrumentation.
+
+To maintain the semantics of ordinary function calls, the prologue data must
+have a particular format. Specifically, it must begin with a sequence of
+bytes which decode to a sequence of machine instructions, valid for the
+module's target, which transfer control to the point immediately succeeding
+the prologue data, without performing any other visible action. This allows
+the inliner and other passes to reason about the semantics of the function
+definition without needing to reason about the prologue data. Obviously this
+makes the format of the prologue data highly target dependent.
+
+A trivial example of valid prologue data for the x86 architecture is ``i8 144``,
+which encodes the ``nop`` instruction:
+
+.. code-block:: text
+
+ define void @f() prologue i8 144 { ... }
+
+Generally prologue data can be formed by encoding a relative branch instruction
+which skips the metadata, as in this example of valid prologue data for the
+x86_64 architecture, where the first two bytes encode ``jmp .+10``:
+
+.. code-block:: text
+
+ %0 = type <{ i8, i8, i8* }>
+
+ define void @f() prologue %0 <{ i8 235, i8 8, i8* @md}> { ... }
+
+A function may have prologue data but no body. This has similar semantics
+to the ``available_externally`` linkage in that the data may be used by the
+optimizers but will not be emitted in the object file.
+
+.. _personalityfn:
+
+Personality Function
+--------------------
+
+The ``personality`` attribute permits functions to specify what function
+to use for exception handling.
+
+.. _attrgrp:
+
+Attribute Groups
+----------------
+
+Attribute groups are groups of attributes that are referenced by objects within
+the IR. They are important for keeping ``.ll`` files readable, because a lot of
+functions will use the same set of attributes. In the degenerative case of a
+``.ll`` file that corresponds to a single ``.c`` file, the single attribute
+group will capture the important command line flags used to build that file.
+
+An attribute group is a module-level object. To use an attribute group, an
+object references the attribute group's ID (e.g. ``#37``). An object may refer
+to more than one attribute group. In that situation, the attributes from the
+different groups are merged.
+
+Here is an example of attribute groups for a function that should always be
+inlined, has a stack alignment of 4, and which shouldn't use SSE instructions:
+
+.. code-block:: llvm
+
+ ; Target-independent attributes:
+ attributes #0 = { alwaysinline alignstack=4 }
+
+ ; Target-dependent attributes:
+ attributes #1 = { "no-sse" }
+
+ ; Function @f has attributes: alwaysinline, alignstack=4, and "no-sse".
+ define void @f() #0 #1 { ... }
+
+.. _fnattrs:
+
+Function Attributes
+-------------------
+
+Function attributes are set to communicate additional information about
+a function. Function attributes are considered to be part of the
+function, not of the function type, so functions with different function
+attributes can have the same function type.
+
+Function attributes are simple keywords that follow the type specified.
+If multiple attributes are needed, they are space separated. For
+example:
+
+.. code-block:: llvm
+
+ define void @f() noinline { ... }
+ define void @f() alwaysinline { ... }
+ define void @f() alwaysinline optsize { ... }
+ define void @f() optsize { ... }
+
+``alignstack(<n>)``
+ This attribute indicates that, when emitting the prologue and
+ epilogue, the backend should forcibly align the stack pointer.
+ Specify the desired alignment, which must be a power of two, in
+ parentheses.
+``allocsize(<EltSizeParam>[, <NumEltsParam>])``
+ This attribute indicates that the annotated function will always return at
+ least a given number of bytes (or null). Its arguments are zero-indexed
+ parameter numbers; if one argument is provided, then it's assumed that at
+ least ``CallSite.Args[EltSizeParam]`` bytes will be available at the
+ returned pointer. If two are provided, then it's assumed that
+ ``CallSite.Args[EltSizeParam] * CallSite.Args[NumEltsParam]`` bytes are
+ available. The referenced parameters must be integer types. No assumptions
+ are made about the contents of the returned block of memory.
+``alwaysinline``
+ This attribute indicates that the inliner should attempt to inline
+ this function into callers whenever possible, ignoring any active
+ inlining size threshold for this caller.
+``builtin``
+ This indicates that the callee function at a call site should be
+ recognized as a built-in function, even though the function's declaration
+ uses the ``nobuiltin`` attribute. This is only valid at call sites for
+ direct calls to functions that are declared with the ``nobuiltin``
+ attribute.
+``cold``
+ This attribute indicates that this function is rarely called. When
+ computing edge weights, basic blocks post-dominated by a cold
+ function call are also considered to be cold; and, thus, given low
+ weight.
+``convergent``
+ In some parallel execution models, there exist operations that cannot be
+ made control-dependent on any additional values. We call such operations
+ ``convergent``, and mark them with this attribute.
+
+ The ``convergent`` attribute may appear on functions or call/invoke
+ instructions. When it appears on a function, it indicates that calls to
+ this function should not be made control-dependent on additional values.
+ For example, the intrinsic ``llvm.nvvm.barrier0`` is ``convergent``, so
+ calls to this intrinsic cannot be made control-dependent on additional
+ values.
+
+ When it appears on a call/invoke, the ``convergent`` attribute indicates
+ that we should treat the call as though we're calling a convergent
+ function. This is particularly useful on indirect calls; without this we
+ may treat such calls as though the target is non-convergent.
+
+ The optimizer may remove the ``convergent`` attribute on functions when it
+ can prove that the function does not execute any convergent operations.
+ Similarly, the optimizer may remove ``convergent`` on calls/invokes when it
+ can prove that the call/invoke cannot call a convergent function.
+``inaccessiblememonly``
+ This attribute indicates that the function may only access memory that
+ is not accessible by the module being compiled. This is a weaker form
+ of ``readnone``.
+``inaccessiblemem_or_argmemonly``
+ This attribute indicates that the function may only access memory that is
+ either not accessible by the module being compiled, or is pointed to
+ by its pointer arguments. This is a weaker form of ``argmemonly``
+``inlinehint``
+ This attribute indicates that the source code contained a hint that
+ inlining this function is desirable (such as the "inline" keyword in
+ C/C++). It is just a hint; it imposes no requirements on the
+ inliner.
+``jumptable``
+ This attribute indicates that the function should be added to a
+ jump-instruction table at code-generation time, and that all address-taken
+ references to this function should be replaced with a reference to the
+ appropriate jump-instruction-table function pointer. Note that this creates
+ a new pointer for the original function, which means that code that depends
+ on function-pointer identity can break. So, any function annotated with
+ ``jumptable`` must also be ``unnamed_addr``.
+``minsize``
+ This attribute suggests that optimization passes and code generator
+ passes make choices that keep the code size of this function as small
+ as possible and perform optimizations that may sacrifice runtime
+ performance in order to minimize the size of the generated code.
+``naked``
+ This attribute disables prologue / epilogue emission for the
+ function. This can have very system-specific consequences.
+``nobuiltin``
+ This indicates that the callee function at a call site is not recognized as
+ a built-in function. LLVM will retain the original call and not replace it
+ with equivalent code based on the semantics of the built-in function, unless
+ the call site uses the ``builtin`` attribute. This is valid at call sites
+ and on function declarations and definitions.
+``noduplicate``
+ This attribute indicates that calls to the function cannot be
+ duplicated. A call to a ``noduplicate`` function may be moved
+ within its parent function, but may not be duplicated within
+ its parent function.
+
+ A function containing a ``noduplicate`` call may still
+ be an inlining candidate, provided that the call is not
+ duplicated by inlining. That implies that the function has
+ internal linkage and only has one call site, so the original
+ call is dead after inlining.
+``noimplicitfloat``
+ This attributes disables implicit floating point instructions.
+``noinline``
+ This attribute indicates that the inliner should never inline this
+ function in any situation. This attribute may not be used together
+ with the ``alwaysinline`` attribute.
+``nonlazybind``
+ This attribute suppresses lazy symbol binding for the function. This
+ may make calls to the function faster, at the cost of extra program
+ startup time if the function is not called during program startup.
+``noredzone``
+ This attribute indicates that the code generator should not use a
+ red zone, even if the target-specific ABI normally permits it.
+``noreturn``
+ This function attribute indicates that the function never returns
+ normally. This produces undefined behavior at runtime if the
+ function ever does dynamically return.
+``norecurse``
+ This function attribute indicates that the function does not call itself
+ either directly or indirectly down any possible call path. This produces
+ undefined behavior at runtime if the function ever does recurse.
+``nounwind``
+ This function attribute indicates that the function never raises an
+ exception. If the function does raise an exception, its runtime
+ behavior is undefined. However, functions marked nounwind may still
+ trap or generate asynchronous exceptions. Exception handling schemes
+ that are recognized by LLVM to handle asynchronous exceptions, such
+ as SEH, will still provide their implementation defined semantics.
+``optnone``
+ This function attribute indicates that most optimization passes will skip
+ this function, with the exception of interprocedural optimization passes.
+ Code generation defaults to the "fast" instruction selector.
+ This attribute cannot be used together with the ``alwaysinline``
+ attribute; this attribute is also incompatible
+ with the ``minsize`` attribute and the ``optsize`` attribute.
+
+ This attribute requires the ``noinline`` attribute to be specified on
+ the function as well, so the function is never inlined into any caller.
+ Only functions with the ``alwaysinline`` attribute are valid
+ candidates for inlining into the body of this function.
+``optsize``
+ This attribute suggests that optimization passes and code generator
+ passes make choices that keep the code size of this function low,
+ and otherwise do optimizations specifically to reduce code size as
+ long as they do not significantly impact runtime performance.
+``"patchable-function"``
+ This attribute tells the code generator that the code
+ generated for this function needs to follow certain conventions that
+ make it possible for a runtime function to patch over it later.
+ The exact effect of this attribute depends on its string value,
+ for which there currently is one legal possibility:
+
+ * ``"prologue-short-redirect"`` - This style of patchable
+ function is intended to support patching a function prologue to
+ redirect control away from the function in a thread safe
+ manner. It guarantees that the first instruction of the
+ function will be large enough to accommodate a short jump
+ instruction, and will be sufficiently aligned to allow being
+ fully changed via an atomic compare-and-swap instruction.
+ While the first requirement can be satisfied by inserting large
+ enough NOP, LLVM can and will try to re-purpose an existing
+ instruction (i.e. one that would have to be emitted anyway) as
+ the patchable instruction larger than a short jump.
+
+ ``"prologue-short-redirect"`` is currently only supported on
+ x86-64.
+
+ This attribute by itself does not imply restrictions on
+ inter-procedural optimizations. All of the semantic effects the
+ patching may have to be separately conveyed via the linkage type.
+``"probe-stack"``
+ This attribute indicates that the function will trigger a guard region
+ in the end of the stack. It ensures that accesses to the stack must be
+ no further apart than the size of the guard region to a previous
+ access of the stack. It takes one required string value, the name of
+ the stack probing function that will be called.
+
+ If a function that has a ``"probe-stack"`` attribute is inlined into
+ a function with another ``"probe-stack"`` attribute, the resulting
+ function has the ``"probe-stack"`` attribute of the caller. If a
+ function that has a ``"probe-stack"`` attribute is inlined into a
+ function that has no ``"probe-stack"`` attribute at all, the resulting
+ function has the ``"probe-stack"`` attribute of the callee.
+``readnone``
+ On a function, this attribute indicates that the function computes its
+ result (or decides to unwind an exception) based strictly on its arguments,
+ without dereferencing any pointer arguments or otherwise accessing
+ any mutable state (e.g. memory, control registers, etc) visible to
+ caller functions. It does not write through any pointer arguments
+ (including ``byval`` arguments) and never changes any state visible
+ to callers. This means while it cannot unwind exceptions by calling
+ the ``C++`` exception throwing methods (since they write to memory), there may
+ be non-``C++`` mechanisms that throw exceptions without writing to LLVM
+ visible memory.
+
+ On an argument, this attribute indicates that the function does not
+ dereference that pointer argument, even though it may read or write the
+ memory that the pointer points to if accessed through other pointers.
+``readonly``
+ On a function, this attribute indicates that the function does not write
+ through any pointer arguments (including ``byval`` arguments) or otherwise
+ modify any state (e.g. memory, control registers, etc) visible to
+ caller functions. It may dereference pointer arguments and read
+ state that may be set in the caller. A readonly function always
+ returns the same value (or unwinds an exception identically) when
+ called with the same set of arguments and global state. This means while it
+ cannot unwind exceptions by calling the ``C++`` exception throwing methods
+ (since they write to memory), there may be non-``C++`` mechanisms that throw
+ exceptions without writing to LLVM visible memory.
+
+ On an argument, this attribute indicates that the function does not write
+ through this pointer argument, even though it may write to the memory that
+ the pointer points to.
+``"stack-probe-size"``
+ This attribute controls the behavior of stack probes: either
+ the ``"probe-stack"`` attribute, or ABI-required stack probes, if any.
+ It defines the size of the guard region. It ensures that if the function
+ may use more stack space than the size of the guard region, stack probing
+ sequence will be emitted. It takes one required integer value, which
+ is 4096 by default.
+
+ If a function that has a ``"stack-probe-size"`` attribute is inlined into
+ a function with another ``"stack-probe-size"`` attribute, the resulting
+ function has the ``"stack-probe-size"`` attribute that has the lower
+ numeric value. If a function that has a ``"stack-probe-size"`` attribute is
+ inlined into a function that has no ``"stack-probe-size"`` attribute
+ at all, the resulting function has the ``"stack-probe-size"`` attribute
+ of the callee.
+``writeonly``
+ On a function, this attribute indicates that the function may write to but
+ does not read from memory.
+
+ On an argument, this attribute indicates that the function may write to but
+ does not read through this pointer argument (even though it may read from
+ the memory that the pointer points to).
+``argmemonly``
+ This attribute indicates that the only memory accesses inside function are
+ loads and stores from objects pointed to by its pointer-typed arguments,
+ with arbitrary offsets. Or in other words, all memory operations in the
+ function can refer to memory only using pointers based on its function
+ arguments.
+ Note that ``argmemonly`` can be used together with ``readonly`` attribute
+ in order to specify that function reads only from its arguments.
+``returns_twice``
+ This attribute indicates that this function can return twice. The C
+ ``setjmp`` is an example of such a function. The compiler disables
+ some optimizations (like tail calls) in the caller of these
+ functions.
+``safestack``
+ This attribute indicates that
+ `SafeStack <http://clang.llvm.org/docs/SafeStack.html>`_
+ protection is enabled for this function.
+
+ If a function that has a ``safestack`` attribute is inlined into a
+ function that doesn't have a ``safestack`` attribute or which has an
+ ``ssp``, ``sspstrong`` or ``sspreq`` attribute, then the resulting
+ function will have a ``safestack`` attribute.
+``sanitize_address``
+ This attribute indicates that AddressSanitizer checks
+ (dynamic address safety analysis) are enabled for this function.
+``sanitize_memory``
+ This attribute indicates that MemorySanitizer checks (dynamic detection
+ of accesses to uninitialized memory) are enabled for this function.
+``sanitize_thread``
+ This attribute indicates that ThreadSanitizer checks
+ (dynamic thread safety analysis) are enabled for this function.
+``speculatable``
+ This function attribute indicates that the function does not have any
+ effects besides calculating its result and does not have undefined behavior.
+ Note that ``speculatable`` is not enough to conclude that along any
+ particular execution path the number of calls to this function will not be
+ externally observable. This attribute is only valid on functions
+ and declarations, not on individual call sites. If a function is
+ incorrectly marked as speculatable and really does exhibit
+ undefined behavior, the undefined behavior may be observed even
+ if the call site is dead code.
+
+``ssp``
+ This attribute indicates that the function should emit a stack
+ smashing protector. It is in the form of a "canary" --- a random value
+ placed on the stack before the local variables that's checked upon
+ return from the function to see if it has been overwritten. A
+ heuristic is used to determine if a function needs stack protectors
+ or not. The heuristic used will enable protectors for functions with:
+
+ - Character arrays larger than ``ssp-buffer-size`` (default 8).
+ - Aggregates containing character arrays larger than ``ssp-buffer-size``.
+ - Calls to alloca() with variable sizes or constant sizes greater than
+ ``ssp-buffer-size``.
+
+ Variables that are identified as requiring a protector will be arranged
+ on the stack such that they are adjacent to the stack protector guard.
+
+ If a function that has an ``ssp`` attribute is inlined into a
+ function that doesn't have an ``ssp`` attribute, then the resulting
+ function will have an ``ssp`` attribute.
+``sspreq``
+ This attribute indicates that the function should *always* emit a
+ stack smashing protector. This overrides the ``ssp`` function
+ attribute.
+
+ Variables that are identified as requiring a protector will be arranged
+ on the stack such that they are adjacent to the stack protector guard.
+ The specific layout rules are:
+
+ #. Large arrays and structures containing large arrays
+ (``>= ssp-buffer-size``) are closest to the stack protector.
+ #. Small arrays and structures containing small arrays
+ (``< ssp-buffer-size``) are 2nd closest to the protector.
+ #. Variables that have had their address taken are 3rd closest to the
+ protector.
+
+ If a function that has an ``sspreq`` attribute is inlined into a
+ function that doesn't have an ``sspreq`` attribute or which has an
+ ``ssp`` or ``sspstrong`` attribute, then the resulting function will have
+ an ``sspreq`` attribute.
+``sspstrong``
+ This attribute indicates that the function should emit a stack smashing
+ protector. This attribute causes a strong heuristic to be used when
+ determining if a function needs stack protectors. The strong heuristic
+ will enable protectors for functions with:
+
+ - Arrays of any size and type
+ - Aggregates containing an array of any size and type.
+ - Calls to alloca().
+ - Local variables that have had their address taken.
+
+ Variables that are identified as requiring a protector will be arranged
+ on the stack such that they are adjacent to the stack protector guard.
+ The specific layout rules are:
+
+ #. Large arrays and structures containing large arrays
+ (``>= ssp-buffer-size``) are closest to the stack protector.
+ #. Small arrays and structures containing small arrays
+ (``< ssp-buffer-size``) are 2nd closest to the protector.
+ #. Variables that have had their address taken are 3rd closest to the
+ protector.
+
+ This overrides the ``ssp`` function attribute.
+
+ If a function that has an ``sspstrong`` attribute is inlined into a
+ function that doesn't have an ``sspstrong`` attribute, then the
+ resulting function will have an ``sspstrong`` attribute.
+``"thunk"``
+ This attribute indicates that the function will delegate to some other
+ function with a tail call. The prototype of a thunk should not be used for
+ optimization purposes. The caller is expected to cast the thunk prototype to
+ match the thunk target prototype.
+``uwtable``
+ This attribute indicates that the ABI being targeted requires that
+ an unwind table entry be produced for this function even if we can
+ show that no exceptions passes by it. This is normally the case for
+ the ELF x86-64 abi, but it can be disabled for some compilation
+ units.
+
+.. _glattrs:
+
+Global Attributes
+-----------------
+
+Attributes may be set to communicate additional information about a global variable.
+Unlike :ref:`function attributes <fnattrs>`, attributes on a global variable
+are grouped into a single :ref:`attribute group <attrgrp>`.
+
+.. _opbundles:
+
+Operand Bundles
+---------------
+
+Operand bundles are tagged sets of SSA values that can be associated
+with certain LLVM instructions (currently only ``call`` s and
+``invoke`` s). In a way they are like metadata, but dropping them is
+incorrect and will change program semantics.
+
+Syntax::
+
+ operand bundle set ::= '[' operand bundle (, operand bundle )* ']'
+ operand bundle ::= tag '(' [ bundle operand ] (, bundle operand )* ')'
+ bundle operand ::= SSA value
+ tag ::= string constant
+
+Operand bundles are **not** part of a function's signature, and a
+given function may be called from multiple places with different kinds
+of operand bundles. This reflects the fact that the operand bundles
+are conceptually a part of the ``call`` (or ``invoke``), not the
+callee being dispatched to.
+
+Operand bundles are a generic mechanism intended to support
+runtime-introspection-like functionality for managed languages. While
+the exact semantics of an operand bundle depend on the bundle tag,
+there are certain limitations to how much the presence of an operand
+bundle can influence the semantics of a program. These restrictions
+are described as the semantics of an "unknown" operand bundle. As
+long as the behavior of an operand bundle is describable within these
+restrictions, LLVM does not need to have special knowledge of the
+operand bundle to not miscompile programs containing it.
+
+- The bundle operands for an unknown operand bundle escape in unknown
+ ways before control is transferred to the callee or invokee.
+- Calls and invokes with operand bundles have unknown read / write
+ effect on the heap on entry and exit (even if the call target is
+ ``readnone`` or ``readonly``), unless they're overridden with
+ callsite specific attributes.
+- An operand bundle at a call site cannot change the implementation
+ of the called function. Inter-procedural optimizations work as
+ usual as long as they take into account the first two properties.
+
+More specific types of operand bundles are described below.
+
+.. _deopt_opbundles:
+
+Deoptimization Operand Bundles
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Deoptimization operand bundles are characterized by the ``"deopt"``
+operand bundle tag. These operand bundles represent an alternate
+"safe" continuation for the call site they're attached to, and can be
+used by a suitable runtime to deoptimize the compiled frame at the
+specified call site. There can be at most one ``"deopt"`` operand
+bundle attached to a call site. Exact details of deoptimization is
+out of scope for the language reference, but it usually involves
+rewriting a compiled frame into a set of interpreted frames.
+
+From the compiler's perspective, deoptimization operand bundles make
+the call sites they're attached to at least ``readonly``. They read
+through all of their pointer typed operands (even if they're not
+otherwise escaped) and the entire visible heap. Deoptimization
+operand bundles do not capture their operands except during
+deoptimization, in which case control will not be returned to the
+compiled frame.
+
+The inliner knows how to inline through calls that have deoptimization
+operand bundles. Just like inlining through a normal call site
+involves composing the normal and exceptional continuations, inlining
+through a call site with a deoptimization operand bundle needs to
+appropriately compose the "safe" deoptimization continuation. The
+inliner does this by prepending the parent's deoptimization
+continuation to every deoptimization continuation in the inlined body.
+E.g. inlining ``@f`` into ``@g`` in the following example
+
+.. code-block:: llvm
+
+ define void @f() {
+ call void @x() ;; no deopt state
+ call void @y() [ "deopt"(i32 10) ]
+ call void @y() [ "deopt"(i32 10), "unknown"(i8* null) ]
+ ret void
+ }
+
+ define void @g() {
+ call void @f() [ "deopt"(i32 20) ]
+ ret void
+ }
+
+will result in
+
+.. code-block:: llvm
+
+ define void @g() {
+ call void @x() ;; still no deopt state
+ call void @y() [ "deopt"(i32 20, i32 10) ]
+ call void @y() [ "deopt"(i32 20, i32 10), "unknown"(i8* null) ]
+ ret void
+ }
+
+It is the frontend's responsibility to structure or encode the
+deoptimization state in a way that syntactically prepending the
+caller's deoptimization state to the callee's deoptimization state is
+semantically equivalent to composing the caller's deoptimization
+continuation after the callee's deoptimization continuation.
+
+.. _ob_funclet:
+
+Funclet Operand Bundles
+^^^^^^^^^^^^^^^^^^^^^^^
+
+Funclet operand bundles are characterized by the ``"funclet"``
+operand bundle tag. These operand bundles indicate that a call site
+is within a particular funclet. There can be at most one
+``"funclet"`` operand bundle attached to a call site and it must have
+exactly one bundle operand.
+
+If any funclet EH pads have been "entered" but not "exited" (per the
+`description in the EH doc\ <ExceptionHandling.html#wineh-constraints>`_),
+it is undefined behavior to execute a ``call`` or ``invoke`` which:
+
+* does not have a ``"funclet"`` bundle and is not a ``call`` to a nounwind
+ intrinsic, or
+* has a ``"funclet"`` bundle whose operand is not the most-recently-entered
+ not-yet-exited funclet EH pad.
+
+Similarly, if no funclet EH pads have been entered-but-not-yet-exited,
+executing a ``call`` or ``invoke`` with a ``"funclet"`` bundle is undefined behavior.
+
+GC Transition Operand Bundles
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+GC transition operand bundles are characterized by the
+``"gc-transition"`` operand bundle tag. These operand bundles mark a
+call as a transition between a function with one GC strategy to a
+function with a different GC strategy. If coordinating the transition
+between GC strategies requires additional code generation at the call
+site, these bundles may contain any values that are needed by the
+generated code. For more details, see :ref:`GC Transitions
+<gc_transition_args>`.
+
+.. _moduleasm:
+
+Module-Level Inline Assembly
+----------------------------
+
+Modules may contain "module-level inline asm" blocks, which corresponds
+to the GCC "file scope inline asm" blocks. These blocks are internally
+concatenated by LLVM and treated as a single unit, but may be separated
+in the ``.ll`` file if desired. The syntax is very simple:
+
+.. code-block:: llvm
+
+ module asm "inline asm code goes here"
+ module asm "more can go here"
+
+The strings can contain any character by escaping non-printable
+characters. The escape sequence used is simply "\\xx" where "xx" is the
+two digit hex code for the number.
+
+Note that the assembly string *must* be parseable by LLVM's integrated assembler
+(unless it is disabled), even when emitting a ``.s`` file.
+
+.. _langref_datalayout:
+
+Data Layout
+-----------
+
+A module may specify a target specific data layout string that specifies
+how data is to be laid out in memory. The syntax for the data layout is
+simply:
+
+.. code-block:: llvm
+
+ target datalayout = "layout specification"
+
+The *layout specification* consists of a list of specifications
+separated by the minus sign character ('-'). Each specification starts
+with a letter and may include other information after the letter to
+define some aspect of the data layout. The specifications accepted are
+as follows:
+
+``E``
+ Specifies that the target lays out data in big-endian form. That is,
+ the bits with the most significance have the lowest address
+ location.
+``e``
+ Specifies that the target lays out data in little-endian form. That
+ is, the bits with the least significance have the lowest address
+ location.
+``S<size>``
+ Specifies the natural alignment of the stack in bits. Alignment
+ promotion of stack variables is limited to the natural stack
+ alignment to avoid dynamic stack realignment. The stack alignment
+ must be a multiple of 8-bits. If omitted, the natural stack
+ alignment defaults to "unspecified", which does not prevent any
+ alignment promotions.
+``A<address space>``
+ Specifies the address space of objects created by '``alloca``'.
+ Defaults to the default address space of 0.
+``p[n]:<size>:<abi>:<pref>``
+ This specifies the *size* of a pointer and its ``<abi>`` and
+ ``<pref>``\erred alignments for address space ``n``. All sizes are in
+ bits. The address space, ``n``, is optional, and if not specified,
+ denotes the default address space 0. The value of ``n`` must be
+ in the range [1,2^23).
+``i<size>:<abi>:<pref>``
+ This specifies the alignment for an integer type of a given bit
+ ``<size>``. The value of ``<size>`` must be in the range [1,2^23).
+``v<size>:<abi>:<pref>``
+ This specifies the alignment for a vector type of a given bit
+ ``<size>``.
+``f<size>:<abi>:<pref>``
+ This specifies the alignment for a floating point type of a given bit
+ ``<size>``. Only values of ``<size>`` that are supported by the target
+ will work. 32 (float) and 64 (double) are supported on all targets; 80
+ or 128 (different flavors of long double) are also supported on some
+ targets.
+``a:<abi>:<pref>``
+ This specifies the alignment for an object of aggregate type.
+``m:<mangling>``
+ If present, specifies that llvm names are mangled in the output. The
+ options are
+
+ * ``e``: ELF mangling: Private symbols get a ``.L`` prefix.
+ * ``m``: Mips mangling: Private symbols get a ``$`` prefix.
+ * ``o``: Mach-O mangling: Private symbols get ``L`` prefix. Other
+ symbols get a ``_`` prefix.
+ * ``w``: Windows COFF prefix: Similar to Mach-O, but stdcall and fastcall
+ functions also get a suffix based on the frame size.
+ * ``x``: Windows x86 COFF prefix: Similar to Windows COFF, but use a ``_``
+ prefix for ``__cdecl`` functions.
+``n<size1>:<size2>:<size3>...``
+ This specifies a set of native integer widths for the target CPU in
+ bits. For example, it might contain ``n32`` for 32-bit PowerPC,
+ ``n32:64`` for PowerPC 64, or ``n8:16:32:64`` for X86-64. Elements of
+ this set are considered to support most general arithmetic operations
+ efficiently.
+``ni:<address space0>:<address space1>:<address space2>...``
+ This specifies pointer types with the specified address spaces
+ as :ref:`Non-Integral Pointer Type <nointptrtype>` s. The ``0``
+ address space cannot be specified as non-integral.
+
+On every specification that takes a ``<abi>:<pref>``, specifying the
+``<pref>`` alignment is optional. If omitted, the preceding ``:``
+should be omitted too and ``<pref>`` will be equal to ``<abi>``.
+
+When constructing the data layout for a given target, LLVM starts with a
+default set of specifications which are then (possibly) overridden by
+the specifications in the ``datalayout`` keyword. The default
+specifications are given in this list:
+
+- ``E`` - big endian
+- ``p:64:64:64`` - 64-bit pointers with 64-bit alignment.
+- ``p[n]:64:64:64`` - Other address spaces are assumed to be the
+ same as the default address space.
+- ``S0`` - natural stack alignment is unspecified
+- ``i1:8:8`` - i1 is 8-bit (byte) aligned
+- ``i8:8:8`` - i8 is 8-bit (byte) aligned
+- ``i16:16:16`` - i16 is 16-bit aligned
+- ``i32:32:32`` - i32 is 32-bit aligned
+- ``i64:32:64`` - i64 has ABI alignment of 32-bits but preferred
+ alignment of 64-bits
+- ``f16:16:16`` - half is 16-bit aligned
+- ``f32:32:32`` - float is 32-bit aligned
+- ``f64:64:64`` - double is 64-bit aligned
+- ``f128:128:128`` - quad is 128-bit aligned
+- ``v64:64:64`` - 64-bit vector is 64-bit aligned
+- ``v128:128:128`` - 128-bit vector is 128-bit aligned
+- ``a:0:64`` - aggregates are 64-bit aligned
+
+When LLVM is determining the alignment for a given type, it uses the
+following rules:
+
+#. If the type sought is an exact match for one of the specifications,
+ that specification is used.
+#. If no match is found, and the type sought is an integer type, then
+ the smallest integer type that is larger than the bitwidth of the
+ sought type is used. If none of the specifications are larger than
+ the bitwidth then the largest integer type is used. For example,
+ given the default specifications above, the i7 type will use the
+ alignment of i8 (next largest) while both i65 and i256 will use the
+ alignment of i64 (largest specified).
+#. If no match is found, and the type sought is a vector type, then the
+ largest vector type that is smaller than the sought vector type will
+ be used as a fall back. This happens because <128 x double> can be
+ implemented in terms of 64 <2 x double>, for example.
+
+The function of the data layout string may not be what you expect.
+Notably, this is not a specification from the frontend of what alignment
+the code generator should use.
+
+Instead, if specified, the target data layout is required to match what
+the ultimate *code generator* expects. This string is used by the
+mid-level optimizers to improve code, and this only works if it matches
+what the ultimate code generator uses. There is no way to generate IR
+that does not embed this target-specific detail into the IR. If you
+don't specify the string, the default specifications will be used to
+generate a Data Layout and the optimization phases will operate
+accordingly and introduce target specificity into the IR with respect to
+these default specifications.
+
+.. _langref_triple:
+
+Target Triple
+-------------
+
+A module may specify a target triple string that describes the target
+host. The syntax for the target triple is simply:
+
+.. code-block:: llvm
+
+ target triple = "x86_64-apple-macosx10.7.0"
+
+The *target triple* string consists of a series of identifiers delimited
+by the minus sign character ('-'). The canonical forms are:
+
+::
+
+ ARCHITECTURE-VENDOR-OPERATING_SYSTEM
+ ARCHITECTURE-VENDOR-OPERATING_SYSTEM-ENVIRONMENT
+
+This information is passed along to the backend so that it generates
+code for the proper architecture. It's possible to override this on the
+command line with the ``-mtriple`` command line option.
+
+.. _pointeraliasing:
+
+Pointer Aliasing Rules
+----------------------
+
+Any memory access must be done through a pointer value associated with
+an address range of the memory access, otherwise the behavior is
+undefined. Pointer values are associated with address ranges according
+to the following rules:
+
+- A pointer value is associated with the addresses associated with any
+ value it is *based* on.
+- An address of a global variable is associated with the address range
+ of the variable's storage.
+- The result value of an allocation instruction is associated with the
+ address range of the allocated storage.
+- A null pointer in the default address-space is associated with no
+ address.
+- An integer constant other than zero or a pointer value returned from
+ a function not defined within LLVM may be associated with address
+ ranges allocated through mechanisms other than those provided by
+ LLVM. Such ranges shall not overlap with any ranges of addresses
+ allocated by mechanisms provided by LLVM.
+
+A pointer value is *based* on another pointer value according to the
+following rules:
+
+- A pointer value formed from a ``getelementptr`` operation is *based*
+ on the second value operand of the ``getelementptr``.
+- The result value of a ``bitcast`` is *based* on the operand of the
+ ``bitcast``.
+- A pointer value formed by an ``inttoptr`` is *based* on all pointer
+ values that contribute (directly or indirectly) to the computation of
+ the pointer's value.
+- The "*based* on" relationship is transitive.
+
+Note that this definition of *"based"* is intentionally similar to the
+definition of *"based"* in C99, though it is slightly weaker.
+
+LLVM IR does not associate types with memory. The result type of a
+``load`` merely indicates the size and alignment of the memory from
+which to load, as well as the interpretation of the value. The first
+operand type of a ``store`` similarly only indicates the size and
+alignment of the store.
+
+Consequently, type-based alias analysis, aka TBAA, aka
+``-fstrict-aliasing``, is not applicable to general unadorned LLVM IR.
+:ref:`Metadata <metadata>` may be used to encode additional information
+which specialized optimization passes may use to implement type-based
+alias analysis.
+
+.. _volatile:
+
+Volatile Memory Accesses
+------------------------
+
+Certain memory accesses, such as :ref:`load <i_load>`'s,
+:ref:`store <i_store>`'s, and :ref:`llvm.memcpy <int_memcpy>`'s may be
+marked ``volatile``. The optimizers must not change the number of
+volatile operations or change their order of execution relative to other
+volatile operations. The optimizers *may* change the order of volatile
+operations relative to non-volatile operations. This is not Java's
+"volatile" and has no cross-thread synchronization behavior.
+
+IR-level volatile loads and stores cannot safely be optimized into
+llvm.memcpy or llvm.memmove intrinsics even when those intrinsics are
+flagged volatile. Likewise, the backend should never split or merge
+target-legal volatile load/store instructions.
+
+.. admonition:: Rationale
+
+ Platforms may rely on volatile loads and stores of natively supported
+ data width to be executed as single instruction. For example, in C
+ this holds for an l-value of volatile primitive type with native
+ hardware support, but not necessarily for aggregate types. The
+ frontend upholds these expectations, which are intentionally
+ unspecified in the IR. The rules above ensure that IR transformations
+ do not violate the frontend's contract with the language.
+
+.. _memmodel:
+
+Memory Model for Concurrent Operations
+--------------------------------------
+
+The LLVM IR does not define any way to start parallel threads of
+execution or to register signal handlers. Nonetheless, there are
+platform-specific ways to create them, and we define LLVM IR's behavior
+in their presence. This model is inspired by the C++0x memory model.
+
+For a more informal introduction to this model, see the :doc:`Atomics`.
+
+We define a *happens-before* partial order as the least partial order
+that
+
+- Is a superset of single-thread program order, and
+- When a *synchronizes-with* ``b``, includes an edge from ``a`` to
+ ``b``. *Synchronizes-with* pairs are introduced by platform-specific
+ techniques, like pthread locks, thread creation, thread joining,
+ etc., and by atomic instructions. (See also :ref:`Atomic Memory Ordering
+ Constraints <ordering>`).
+
+Note that program order does not introduce *happens-before* edges
+between a thread and signals executing inside that thread.
+
+Every (defined) read operation (load instructions, memcpy, atomic
+loads/read-modify-writes, etc.) R reads a series of bytes written by
+(defined) write operations (store instructions, atomic
+stores/read-modify-writes, memcpy, etc.). For the purposes of this
+section, initialized globals are considered to have a write of the
+initializer which is atomic and happens before any other read or write
+of the memory in question. For each byte of a read R, R\ :sub:`byte`
+may see any write to the same byte, except:
+
+- If write\ :sub:`1` happens before write\ :sub:`2`, and
+ write\ :sub:`2` happens before R\ :sub:`byte`, then
+ R\ :sub:`byte` does not see write\ :sub:`1`.
+- If R\ :sub:`byte` happens before write\ :sub:`3`, then
+ R\ :sub:`byte` does not see write\ :sub:`3`.
+
+Given that definition, R\ :sub:`byte` is defined as follows:
+
+- If R is volatile, the result is target-dependent. (Volatile is
+ supposed to give guarantees which can support ``sig_atomic_t`` in
+ C/C++, and may be used for accesses to addresses that do not behave
+ like normal memory. It does not generally provide cross-thread
+ synchronization.)
+- Otherwise, if there is no write to the same byte that happens before
+ R\ :sub:`byte`, R\ :sub:`byte` returns ``undef`` for that byte.
+- Otherwise, if R\ :sub:`byte` may see exactly one write,
+ R\ :sub:`byte` returns the value written by that write.
+- Otherwise, if R is atomic, and all the writes R\ :sub:`byte` may
+ see are atomic, it chooses one of the values written. See the :ref:`Atomic
+ Memory Ordering Constraints <ordering>` section for additional
+ constraints on how the choice is made.
+- Otherwise R\ :sub:`byte` returns ``undef``.
+
+R returns the value composed of the series of bytes it read. This
+implies that some bytes within the value may be ``undef`` **without**
+the entire value being ``undef``. Note that this only defines the
+semantics of the operation; it doesn't mean that targets will emit more
+than one instruction to read the series of bytes.
+
+Note that in cases where none of the atomic intrinsics are used, this
+model places only one restriction on IR transformations on top of what
+is required for single-threaded execution: introducing a store to a byte
+which might not otherwise be stored is not allowed in general.
+(Specifically, in the case where another thread might write to and read
+from an address, introducing a store can change a load that may see
+exactly one write into a load that may see multiple writes.)
+
+.. _ordering:
+
+Atomic Memory Ordering Constraints
+----------------------------------
+
+Atomic instructions (:ref:`cmpxchg <i_cmpxchg>`,
+:ref:`atomicrmw <i_atomicrmw>`, :ref:`fence <i_fence>`,
+:ref:`atomic load <i_load>`, and :ref:`atomic store <i_store>`) take
+ordering parameters that determine which other atomic instructions on
+the same address they *synchronize with*. These semantics are borrowed
+from Java and C++0x, but are somewhat more colloquial. If these
+descriptions aren't precise enough, check those specs (see spec
+references in the :doc:`atomics guide <Atomics>`).
+:ref:`fence <i_fence>` instructions treat these orderings somewhat
+differently since they don't take an address. See that instruction's
+documentation for details.
+
+For a simpler introduction to the ordering constraints, see the
+:doc:`Atomics`.
+
+``unordered``
+ The set of values that can be read is governed by the happens-before
+ partial order. A value cannot be read unless some operation wrote
+ it. This is intended to provide a guarantee strong enough to model
+ Java's non-volatile shared variables. This ordering cannot be
+ specified for read-modify-write operations; it is not strong enough
+ to make them atomic in any interesting way.
+``monotonic``
+ In addition to the guarantees of ``unordered``, there is a single
+ total order for modifications by ``monotonic`` operations on each
+ address. All modification orders must be compatible with the
+ happens-before order. There is no guarantee that the modification
+ orders can be combined to a global total order for the whole program
+ (and this often will not be possible). The read in an atomic
+ read-modify-write operation (:ref:`cmpxchg <i_cmpxchg>` and
+ :ref:`atomicrmw <i_atomicrmw>`) reads the value in the modification
+ order immediately before the value it writes. If one atomic read
+ happens before another atomic read of the same address, the later
+ read must see the same value or a later value in the address's
+ modification order. This disallows reordering of ``monotonic`` (or
+ stronger) operations on the same address. If an address is written
+ ``monotonic``-ally by one thread, and other threads ``monotonic``-ally
+ read that address repeatedly, the other threads must eventually see
+ the write. This corresponds to the C++0x/C1x
+ ``memory_order_relaxed``.
+``acquire``
+ In addition to the guarantees of ``monotonic``, a
+ *synchronizes-with* edge may be formed with a ``release`` operation.
+ This is intended to model C++'s ``memory_order_acquire``.
+``release``
+ In addition to the guarantees of ``monotonic``, if this operation
+ writes a value which is subsequently read by an ``acquire``
+ operation, it *synchronizes-with* that operation. (This isn't a
+ complete description; see the C++0x definition of a release
+ sequence.) This corresponds to the C++0x/C1x
+ ``memory_order_release``.
+``acq_rel`` (acquire+release)
+ Acts as both an ``acquire`` and ``release`` operation on its
+ address. This corresponds to the C++0x/C1x ``memory_order_acq_rel``.
+``seq_cst`` (sequentially consistent)
+ In addition to the guarantees of ``acq_rel`` (``acquire`` for an
+ operation that only reads, ``release`` for an operation that only
+ writes), there is a global total order on all
+ sequentially-consistent operations on all addresses, which is
+ consistent with the *happens-before* partial order and with the
+ modification orders of all the affected addresses. Each
+ sequentially-consistent read sees the last preceding write to the
+ same address in this global order. This corresponds to the C++0x/C1x
+ ``memory_order_seq_cst`` and Java volatile.
+
+.. _syncscope:
+
+If an atomic operation is marked ``syncscope("singlethread")``, it only
+*synchronizes with* and only participates in the seq\_cst total orderings of
+other operations running in the same thread (for example, in signal handlers).
+
+If an atomic operation is marked ``syncscope("<target-scope>")``, where
+``<target-scope>`` is a target specific synchronization scope, then it is target
+dependent if it *synchronizes with* and participates in the seq\_cst total
+orderings of other operations.
+
+Otherwise, an atomic operation that is not marked ``syncscope("singlethread")``
+or ``syncscope("<target-scope>")`` *synchronizes with* and participates in the
+seq\_cst total orderings of other operations that are not marked
+``syncscope("singlethread")`` or ``syncscope("<target-scope>")``.
+
+.. _fastmath:
+
+Fast-Math Flags
+---------------
+
+LLVM IR floating-point binary ops (:ref:`fadd <i_fadd>`,
+:ref:`fsub <i_fsub>`, :ref:`fmul <i_fmul>`, :ref:`fdiv <i_fdiv>`,
+:ref:`frem <i_frem>`, :ref:`fcmp <i_fcmp>`) and :ref:`call <i_call>`
+instructions have the following flags that can be set to enable
+otherwise unsafe floating point transformations.
+
+``nnan``
+ No NaNs - Allow optimizations to assume the arguments and result are not
+ NaN. Such optimizations are required to retain defined behavior over
+ NaNs, but the value of the result is undefined.
+
+``ninf``
+ No Infs - Allow optimizations to assume the arguments and result are not
+ +/-Inf. Such optimizations are required to retain defined behavior over
+ +/-Inf, but the value of the result is undefined.
+
+``nsz``
+ No Signed Zeros - Allow optimizations to treat the sign of a zero
+ argument or result as insignificant.
+
+``arcp``
+ Allow Reciprocal - Allow optimizations to use the reciprocal of an
+ argument rather than perform division.
+
+``contract``
+ Allow floating-point contraction (e.g. fusing a multiply followed by an
+ addition into a fused multiply-and-add).
+
+``fast``
+ Fast - Allow algebraically equivalent transformations that may
+ dramatically change results in floating point (e.g. reassociate). This
+ flag implies all the others.
+
+.. _uselistorder:
+
+Use-list Order Directives
+-------------------------
+
+Use-list directives encode the in-memory order of each use-list, allowing the
+order to be recreated. ``<order-indexes>`` is a comma-separated list of
+indexes that are assigned to the referenced value's uses. The referenced
+value's use-list is immediately sorted by these indexes.
+
+Use-list directives may appear at function scope or global scope. They are not
+instructions, and have no effect on the semantics of the IR. When they're at
+function scope, they must appear after the terminator of the final basic block.
+
+If basic blocks have their address taken via ``blockaddress()`` expressions,
+``uselistorder_bb`` can be used to reorder their use-lists from outside their
+function's scope.
+
+:Syntax:
+
+::
+
+ uselistorder <ty> <value>, { <order-indexes> }
+ uselistorder_bb @function, %block { <order-indexes> }
+
+:Examples:
+
+::
+
+ define void @foo(i32 %arg1, i32 %arg2) {
+ entry:
+ ; ... instructions ...
+ bb:
+ ; ... instructions ...
+
+ ; At function scope.
+ uselistorder i32 %arg1, { 1, 0, 2 }
+ uselistorder label %bb, { 1, 0 }
+ }
+
+ ; At global scope.
+ uselistorder i32* @global, { 1, 2, 0 }
+ uselistorder i32 7, { 1, 0 }
+ uselistorder i32 (i32) @bar, { 1, 0 }
+ uselistorder_bb @foo, %bb, { 5, 1, 3, 2, 0, 4 }
+
+.. _source_filename:
+
+Source Filename
+---------------
+
+The *source filename* string is set to the original module identifier,
+which will be the name of the compiled source file when compiling from
+source through the clang front end, for example. It is then preserved through
+the IR and bitcode.
+
+This is currently necessary to generate a consistent unique global
+identifier for local functions used in profile data, which prepends the
+source file name to the local function name.
+
+The syntax for the source file name is simply:
+
+.. code-block:: text
+
+ source_filename = "/path/to/source.c"
+
+.. _typesystem:
+
+Type System
+===========
+
+The LLVM type system is one of the most important features of the
+intermediate representation. Being typed enables a number of
+optimizations to be performed on the intermediate representation
+directly, without having to do extra analyses on the side before the
+transformation. A strong type system makes it easier to read the
+generated code and enables novel analyses and transformations that are
+not feasible to perform on normal three address code representations.
+
+.. _t_void:
+
+Void Type
+---------
+
+:Overview:
+
+
+The void type does not represent any value and has no size.
+
+:Syntax:
+
+
+::
+
+ void
+
+
+.. _t_function:
+
+Function Type
+-------------
+
+:Overview:
+
+
+The function type can be thought of as a function signature. It consists of a
+return type and a list of formal parameter types. The return type of a function
+type is a void type or first class type --- except for :ref:`label <t_label>`
+and :ref:`metadata <t_metadata>` types.
+
+:Syntax:
+
+::
+
+ <returntype> (<parameter list>)
+
+...where '``<parameter list>``' is a comma-separated list of type
+specifiers. Optionally, the parameter list may include a type ``...``, which
+indicates that the function takes a variable number of arguments. Variable
+argument functions can access their arguments with the :ref:`variable argument
+handling intrinsic <int_varargs>` functions. '``<returntype>``' is any type
+except :ref:`label <t_label>` and :ref:`metadata <t_metadata>`.
+
+:Examples:
+
++---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
+| ``i32 (i32)`` | function taking an ``i32``, returning an ``i32`` |
++---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
+| ``float (i16, i32 *) *`` | :ref:`Pointer <t_pointer>` to a function that takes an ``i16`` and a :ref:`pointer <t_pointer>` to ``i32``, returning ``float``. |
++---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
+| ``i32 (i8*, ...)`` | A vararg function that takes at least one :ref:`pointer <t_pointer>` to ``i8`` (char in C), which returns an integer. This is the signature for ``printf`` in LLVM. |
++---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
+| ``{i32, i32} (i32)`` | A function taking an ``i32``, returning a :ref:`structure <t_struct>` containing two ``i32`` values |
++---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
+
+.. _t_firstclass:
+
+First Class Types
+-----------------
+
+The :ref:`first class <t_firstclass>` types are perhaps the most important.
+Values of these types are the only ones which can be produced by
+instructions.
+
+.. _t_single_value:
+
+Single Value Types
+^^^^^^^^^^^^^^^^^^
+
+These are the types that are valid in registers from CodeGen's perspective.
+
+.. _t_integer:
+
+Integer Type
+""""""""""""
+
+:Overview:
+
+The integer type is a very simple type that simply specifies an
+arbitrary bit width for the integer type desired. Any bit width from 1
+bit to 2\ :sup:`23`\ -1 (about 8 million) can be specified.
+
+:Syntax:
+
+::
+
+ iN
+
+The number of bits the integer will occupy is specified by the ``N``
+value.
+
+Examples:
+*********
+
++----------------+------------------------------------------------+
+| ``i1`` | a single-bit integer. |
++----------------+------------------------------------------------+
+| ``i32`` | a 32-bit integer. |
++----------------+------------------------------------------------+
+| ``i1942652`` | a really big integer of over 1 million bits. |
++----------------+------------------------------------------------+
+
+.. _t_floating:
+
+Floating Point Types
+""""""""""""""""""""
+
+.. list-table::
+ :header-rows: 1
+
+ * - Type
+ - Description
+
+ * - ``half``
+ - 16-bit floating point value
+
+ * - ``float``
+ - 32-bit floating point value
+
+ * - ``double``
+ - 64-bit floating point value
+
+ * - ``fp128``
+ - 128-bit floating point value (112-bit mantissa)
+
+ * - ``x86_fp80``
+ - 80-bit floating point value (X87)
+
+ * - ``ppc_fp128``
+ - 128-bit floating point value (two 64-bits)
+
+X86_mmx Type
+""""""""""""
+
+:Overview:
+
+The x86_mmx type represents a value held in an MMX register on an x86
+machine. The operations allowed on it are quite limited: parameters and
+return values, load and store, and bitcast. User-specified MMX
+instructions are represented as intrinsic or asm calls with arguments
+and/or results of this type. There are no arrays, vectors or constants
+of this type.
+
+:Syntax:
+
+::
+
+ x86_mmx
+
+
+.. _t_pointer:
+
+Pointer Type
+""""""""""""
+
+:Overview:
+
+The pointer type is used to specify memory locations. Pointers are
+commonly used to reference objects in memory.
+
+Pointer types may have an optional address space attribute defining the
+numbered address space where the pointed-to object resides. The default
+address space is number zero. The semantics of non-zero address spaces
+are target-specific.
+
+Note that LLVM does not permit pointers to void (``void*``) nor does it
+permit pointers to labels (``label*``). Use ``i8*`` instead.
+
+:Syntax:
+
+::
+
+ <type> *
+
+:Examples:
+
++-------------------------+--------------------------------------------------------------------------------------------------------------+
+| ``[4 x i32]*`` | A :ref:`pointer <t_pointer>` to :ref:`array <t_array>` of four ``i32`` values. |
++-------------------------+--------------------------------------------------------------------------------------------------------------+
+| ``i32 (i32*) *`` | A :ref:`pointer <t_pointer>` to a :ref:`function <t_function>` that takes an ``i32*``, returning an ``i32``. |
++-------------------------+--------------------------------------------------------------------------------------------------------------+
+| ``i32 addrspace(5)*`` | A :ref:`pointer <t_pointer>` to an ``i32`` value that resides in address space #5. |
++-------------------------+--------------------------------------------------------------------------------------------------------------+
+
+.. _t_vector:
+
+Vector Type
+"""""""""""
+
+:Overview:
+
+A vector type is a simple derived type that represents a vector of
+elements. Vector types are used when multiple primitive data are
+operated in parallel using a single instruction (SIMD). A vector type
+requires a size (number of elements) and an underlying primitive data
+type. Vector types are considered :ref:`first class <t_firstclass>`.
+
+:Syntax:
+
+::
+
+ < <# elements> x <elementtype> >
+
+The number of elements is a constant integer value larger than 0;
+elementtype may be any integer, floating point or pointer type. Vectors
+of size zero are not allowed.
+
+:Examples:
+
++-------------------+--------------------------------------------------+
+| ``<4 x i32>`` | Vector of 4 32-bit integer values. |
++-------------------+--------------------------------------------------+
+| ``<8 x float>`` | Vector of 8 32-bit floating-point values. |
++-------------------+--------------------------------------------------+
+| ``<2 x i64>`` | Vector of 2 64-bit integer values. |
++-------------------+--------------------------------------------------+
+| ``<4 x i64*>`` | Vector of 4 pointers to 64-bit integer values. |
++-------------------+--------------------------------------------------+
+
+.. _t_label:
+
+Label Type
+^^^^^^^^^^
+
+:Overview:
+
+The label type represents code labels.
+
+:Syntax:
+
+::
+
+ label
+
+.. _t_token:
+
+Token Type
+^^^^^^^^^^
+
+:Overview:
+
+The token type is used when a value is associated with an instruction
+but all uses of the value must not attempt to introspect or obscure it.
+As such, it is not appropriate to have a :ref:`phi <i_phi>` or
+:ref:`select <i_select>` of type token.
+
+:Syntax:
+
+::
+
+ token
+
+
+
+.. _t_metadata:
+
+Metadata Type
+^^^^^^^^^^^^^
+
+:Overview:
+
+The metadata type represents embedded metadata. No derived types may be
+created from metadata except for :ref:`function <t_function>` arguments.
+
+:Syntax:
+
+::
+
+ metadata
+
+.. _t_aggregate:
+
+Aggregate Types
+^^^^^^^^^^^^^^^
+
+Aggregate Types are a subset of derived types that can contain multiple
+member types. :ref:`Arrays <t_array>` and :ref:`structs <t_struct>` are
+aggregate types. :ref:`Vectors <t_vector>` are not considered to be
+aggregate types.
+
+.. _t_array:
+
+Array Type
+""""""""""
+
+:Overview:
+
+The array type is a very simple derived type that arranges elements
+sequentially in memory. The array type requires a size (number of
+elements) and an underlying data type.
+
+:Syntax:
+
+::
+
+ [<# elements> x <elementtype>]
+
+The number of elements is a constant integer value; ``elementtype`` may
+be any type with a size.
+
+:Examples:
+
++------------------+--------------------------------------+
+| ``[40 x i32]`` | Array of 40 32-bit integer values. |
++------------------+--------------------------------------+
+| ``[41 x i32]`` | Array of 41 32-bit integer values. |
++------------------+--------------------------------------+
+| ``[4 x i8]`` | Array of 4 8-bit integer values. |
++------------------+--------------------------------------+
+
+Here are some examples of multidimensional arrays:
+
++-----------------------------+----------------------------------------------------------+
+| ``[3 x [4 x i32]]`` | 3x4 array of 32-bit integer values. |
++-----------------------------+----------------------------------------------------------+
+| ``[12 x [10 x float]]`` | 12x10 array of single precision floating point values. |
++-----------------------------+----------------------------------------------------------+
+| ``[2 x [3 x [4 x i16]]]`` | 2x3x4 array of 16-bit integer values. |
++-----------------------------+----------------------------------------------------------+
+
+There is no restriction on indexing beyond the end of the array implied
+by a static type (though there are restrictions on indexing beyond the
+bounds of an allocated object in some cases). This means that
+single-dimension 'variable sized array' addressing can be implemented in
+LLVM with a zero length array type. An implementation of 'pascal style
+arrays' in LLVM could use the type "``{ i32, [0 x float]}``", for
+example.
+
+.. _t_struct:
+
+Structure Type
+""""""""""""""
+
+:Overview:
+
+The structure type is used to represent a collection of data members
+together in memory. The elements of a structure may be any type that has
+a size.
+
+Structures in memory are accessed using '``load``' and '``store``' by
+getting a pointer to a field with the '``getelementptr``' instruction.
+Structures in registers are accessed using the '``extractvalue``' and
+'``insertvalue``' instructions.
+
+Structures may optionally be "packed" structures, which indicate that
+the alignment of the struct is one byte, and that there is no padding
+between the elements. In non-packed structs, padding between field types
+is inserted as defined by the DataLayout string in the module, which is
+required to match what the underlying code generator expects.
+
+Structures can either be "literal" or "identified". A literal structure
+is defined inline with other types (e.g. ``{i32, i32}*``) whereas
+identified types are always defined at the top level with a name.
+Literal types are uniqued by their contents and can never be recursive
+or opaque since there is no way to write one. Identified types can be
+recursive, can be opaqued, and are never uniqued.
+
+:Syntax:
+
+::
+
+ %T1 = type { <type list> } ; Identified normal struct type
+ %T2 = type <{ <type list> }> ; Identified packed struct type
+
+:Examples:
+
++------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
+| ``{ i32, i32, i32 }`` | A triple of three ``i32`` values |
++------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
+| ``{ float, i32 (i32) * }`` | A pair, where the first element is a ``float`` and the second element is a :ref:`pointer <t_pointer>` to a :ref:`function <t_function>` that takes an ``i32``, returning an ``i32``. |
++------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
+| ``<{ i8, i32 }>`` | A packed struct known to be 5 bytes in size. |
++------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
+
+.. _t_opaque:
+
+Opaque Structure Types
+""""""""""""""""""""""
+
+:Overview:
+
+Opaque structure types are used to represent named structure types that
+do not have a body specified. This corresponds (for example) to the C
+notion of a forward declared structure.
+
+:Syntax:
+
+::
+
+ %X = type opaque
+ %52 = type opaque
+
+:Examples:
+
++--------------+-------------------+
+| ``opaque`` | An opaque type. |
++--------------+-------------------+
+
+.. _constants:
+
+Constants
+=========
+
+LLVM has several different basic types of constants. This section
+describes them all and their syntax.
+
+Simple Constants
+----------------
+
+**Boolean constants**
+ The two strings '``true``' and '``false``' are both valid constants
+ of the ``i1`` type.
+**Integer constants**
+ Standard integers (such as '4') are constants of the
+ :ref:`integer <t_integer>` type. Negative numbers may be used with
+ integer types.
+**Floating point constants**
+ Floating point constants use standard decimal notation (e.g.
+ 123.421), exponential notation (e.g. 1.23421e+2), or a more precise
+ hexadecimal notation (see below). The assembler requires the exact
+ decimal value of a floating-point constant. For example, the
+ assembler accepts 1.25 but rejects 1.3 because 1.3 is a repeating
+ decimal in binary. Floating point constants must have a :ref:`floating
+ point <t_floating>` type.
+**Null pointer constants**
+ The identifier '``null``' is recognized as a null pointer constant
+ and must be of :ref:`pointer type <t_pointer>`.
+**Token constants**
+ The identifier '``none``' is recognized as an empty token constant
+ and must be of :ref:`token type <t_token>`.
+
+The one non-intuitive notation for constants is the hexadecimal form of
+floating point constants. For example, the form
+'``double 0x432ff973cafa8000``' is equivalent to (but harder to read
+than) '``double 4.5e+15``'. The only time hexadecimal floating point
+constants are required (and the only time that they are generated by the
+disassembler) is when a floating point constant must be emitted but it
+cannot be represented as a decimal floating point number in a reasonable
+number of digits. For example, NaN's, infinities, and other special
+values are represented in their IEEE hexadecimal format so that assembly
+and disassembly do not cause any bits to change in the constants.
+
+When using the hexadecimal form, constants of types half, float, and
+double are represented using the 16-digit form shown above (which
+matches the IEEE754 representation for double); half and float values
+must, however, be exactly representable as IEEE 754 half and single
+precision, respectively. Hexadecimal format is always used for long
+double, and there are three forms of long double. The 80-bit format used
+by x86 is represented as ``0xK`` followed by 20 hexadecimal digits. The
+128-bit format used by PowerPC (two adjacent doubles) is represented by
+``0xM`` followed by 32 hexadecimal digits. The IEEE 128-bit format is
+represented by ``0xL`` followed by 32 hexadecimal digits. Long doubles
+will only work if they match the long double format on your target.
+The IEEE 16-bit format (half precision) is represented by ``0xH``
+followed by 4 hexadecimal digits. All hexadecimal formats are big-endian
+(sign bit at the left).
+
+There are no constants of type x86_mmx.
+
+.. _complexconstants:
+
+Complex Constants
+-----------------
+
+Complex constants are a (potentially recursive) combination of simple
+constants and smaller complex constants.
+
+**Structure constants**
+ Structure constants are represented with notation similar to
+ structure type definitions (a comma separated list of elements,
+ surrounded by braces (``{}``)). For example:
+ "``{ i32 4, float 17.0, i32* @G }``", where "``@G``" is declared as
+ "``@G = external global i32``". Structure constants must have
+ :ref:`structure type <t_struct>`, and the number and types of elements
+ must match those specified by the type.
+**Array constants**
+ Array constants are represented with notation similar to array type
+ definitions (a comma separated list of elements, surrounded by
+ square brackets (``[]``)). For example:
+ "``[ i32 42, i32 11, i32 74 ]``". Array constants must have
+ :ref:`array type <t_array>`, and the number and types of elements must
+ match those specified by the type. As a special case, character array
+ constants may also be represented as a double-quoted string using the ``c``
+ prefix. For example: "``c"Hello World\0A\00"``".
+**Vector constants**
+ Vector constants are represented with notation similar to vector
+ type definitions (a comma separated list of elements, surrounded by
+ less-than/greater-than's (``<>``)). For example:
+ "``< i32 42, i32 11, i32 74, i32 100 >``". Vector constants
+ must have :ref:`vector type <t_vector>`, and the number and types of
+ elements must match those specified by the type.
+**Zero initialization**
+ The string '``zeroinitializer``' can be used to zero initialize a
+ value to zero of *any* type, including scalar and
+ :ref:`aggregate <t_aggregate>` types. This is often used to avoid
+ having to print large zero initializers (e.g. for large arrays) and
+ is always exactly equivalent to using explicit zero initializers.
+**Metadata node**
+ A metadata node is a constant tuple without types. For example:
+ "``!{!0, !{!2, !0}, !"test"}``". Metadata can reference constant values,
+ for example: "``!{!0, i32 0, i8* @global, i64 (i64)* @function, !"str"}``".
+ Unlike other typed constants that are meant to be interpreted as part of
+ the instruction stream, metadata is a place to attach additional
+ information such as debug info.
+
+Global Variable and Function Addresses
+--------------------------------------
+
+The addresses of :ref:`global variables <globalvars>` and
+:ref:`functions <functionstructure>` are always implicitly valid
+(link-time) constants. These constants are explicitly referenced when
+the :ref:`identifier for the global <identifiers>` is used and always have
+:ref:`pointer <t_pointer>` type. For example, the following is a legal LLVM
+file:
+
+.. code-block:: llvm
+
+ @X = global i32 17
+ @Y = global i32 42
+ @Z = global [2 x i32*] [ i32* @X, i32* @Y ]
+
+.. _undefvalues:
+
+Undefined Values
+----------------
+
+The string '``undef``' can be used anywhere a constant is expected, and
+indicates that the user of the value may receive an unspecified
+bit-pattern. Undefined values may be of any type (other than '``label``'
+or '``void``') and be used anywhere a constant is permitted.
+
+Undefined values are useful because they indicate to the compiler that
+the program is well defined no matter what value is used. This gives the
+compiler more freedom to optimize. Here are some examples of
+(potentially surprising) transformations that are valid (in pseudo IR):
+
+.. code-block:: llvm
+
+ %A = add %X, undef
+ %B = sub %X, undef
+ %C = xor %X, undef
+ Safe:
+ %A = undef
+ %B = undef
+ %C = undef
+
+This is safe because all of the output bits are affected by the undef
+bits. Any output bit can have a zero or one depending on the input bits.
+
+.. code-block:: llvm
+
+ %A = or %X, undef
+ %B = and %X, undef
+ Safe:
+ %A = -1
+ %B = 0
+ Safe:
+ %A = %X ;; By choosing undef as 0
+ %B = %X ;; By choosing undef as -1
+ Unsafe:
+ %A = undef
+ %B = undef
+
+These logical operations have bits that are not always affected by the
+input. For example, if ``%X`` has a zero bit, then the output of the
+'``and``' operation will always be a zero for that bit, no matter what
+the corresponding bit from the '``undef``' is. As such, it is unsafe to
+optimize or assume that the result of the '``and``' is '``undef``'.
+However, it is safe to assume that all bits of the '``undef``' could be
+0, and optimize the '``and``' to 0. Likewise, it is safe to assume that
+all the bits of the '``undef``' operand to the '``or``' could be set,
+allowing the '``or``' to be folded to -1.
+
+.. code-block:: llvm
+
+ %A = select undef, %X, %Y
+ %B = select undef, 42, %Y
+ %C = select %X, %Y, undef
+ Safe:
+ %A = %X (or %Y)
+ %B = 42 (or %Y)
+ %C = %Y
+ Unsafe:
+ %A = undef
+ %B = undef
+ %C = undef
+
+This set of examples shows that undefined '``select``' (and conditional
+branch) conditions can go *either way*, but they have to come from one
+of the two operands. In the ``%A`` example, if ``%X`` and ``%Y`` were
+both known to have a clear low bit, then ``%A`` would have to have a
+cleared low bit. However, in the ``%C`` example, the optimizer is
+allowed to assume that the '``undef``' operand could be the same as
+``%Y``, allowing the whole '``select``' to be eliminated.
+
+.. code-block:: text
+
+ %A = xor undef, undef
+
+ %B = undef
+ %C = xor %B, %B
+
+ %D = undef
+ %E = icmp slt %D, 4
+ %F = icmp gte %D, 4
+
+ Safe:
+ %A = undef
+ %B = undef
+ %C = undef
+ %D = undef
+ %E = undef
+ %F = undef
+
+This example points out that two '``undef``' operands are not
+necessarily the same. This can be surprising to people (and also matches
+C semantics) where they assume that "``X^X``" is always zero, even if
+``X`` is undefined. This isn't true for a number of reasons, but the
+short answer is that an '``undef``' "variable" can arbitrarily change
+its value over its "live range". This is true because the variable
+doesn't actually *have a live range*. Instead, the value is logically
+read from arbitrary registers that happen to be around when needed, so
+the value is not necessarily consistent over time. In fact, ``%A`` and
+``%C`` need to have the same semantics or the core LLVM "replace all
+uses with" concept would not hold.
+
+.. code-block:: llvm
+
+ %A = fdiv undef, %X
+ %B = fdiv %X, undef
+ Safe:
+ %A = undef
+ b: unreachable
+
+These examples show the crucial difference between an *undefined value*
+and *undefined behavior*. An undefined value (like '``undef``') is
+allowed to have an arbitrary bit-pattern. This means that the ``%A``
+operation can be constant folded to '``undef``', because the '``undef``'
+could be an SNaN, and ``fdiv`` is not (currently) defined on SNaN's.
+However, in the second example, we can make a more aggressive
+assumption: because the ``undef`` is allowed to be an arbitrary value,
+we are allowed to assume that it could be zero. Since a divide by zero
+has *undefined behavior*, we are allowed to assume that the operation
+does not execute at all. This allows us to delete the divide and all
+code after it. Because the undefined operation "can't happen", the
+optimizer can assume that it occurs in dead code.
+
+.. code-block:: text
+
+ a: store undef -> %X
+ b: store %X -> undef
+ Safe:
+ a: <deleted>
+ b: unreachable
+
+These examples reiterate the ``fdiv`` example: a store *of* an undefined
+value can be assumed to not have any effect; we can assume that the
+value is overwritten with bits that happen to match what was already
+there. However, a store *to* an undefined location could clobber
+arbitrary memory, therefore, it has undefined behavior.
+
+.. _poisonvalues:
+
+Poison Values
+-------------
+
+Poison values are similar to :ref:`undef values <undefvalues>`, however
+they also represent the fact that an instruction or constant expression
+that cannot evoke side effects has nevertheless detected a condition
+that results in undefined behavior.
+
+There is currently no way of representing a poison value in the IR; they
+only exist when produced by operations such as :ref:`add <i_add>` with
+the ``nsw`` flag.
+
+Poison value behavior is defined in terms of value *dependence*:
+
+- Values other than :ref:`phi <i_phi>` nodes depend on their operands.
+- :ref:`Phi <i_phi>` nodes depend on the operand corresponding to
+ their dynamic predecessor basic block.
+- Function arguments depend on the corresponding actual argument values
+ in the dynamic callers of their functions.
+- :ref:`Call <i_call>` instructions depend on the :ref:`ret <i_ret>`
+ instructions that dynamically transfer control back to them.
+- :ref:`Invoke <i_invoke>` instructions depend on the
+ :ref:`ret <i_ret>`, :ref:`resume <i_resume>`, or exception-throwing
+ call instructions that dynamically transfer control back to them.
+- Non-volatile loads and stores depend on the most recent stores to all
+ of the referenced memory addresses, following the order in the IR
+ (including loads and stores implied by intrinsics such as
+ :ref:`@llvm.memcpy <int_memcpy>`.)
+- An instruction with externally visible side effects depends on the
+ most recent preceding instruction with externally visible side
+ effects, following the order in the IR. (This includes :ref:`volatile
+ operations <volatile>`.)
+- An instruction *control-depends* on a :ref:`terminator
+ instruction <terminators>` if the terminator instruction has
+ multiple successors and the instruction is always executed when
+ control transfers to one of the successors, and may not be executed
+ when control is transferred to another.
+- Additionally, an instruction also *control-depends* on a terminator
+ instruction if the set of instructions it otherwise depends on would
+ be different if the terminator had transferred control to a different
+ successor.
+- Dependence is transitive.
+
+Poison values have the same behavior as :ref:`undef values <undefvalues>`,
+with the additional effect that any instruction that has a *dependence*
+on a poison value has undefined behavior.
+
+Here are some examples:
+
+.. code-block:: llvm
+
+ entry:
+ %poison = sub nuw i32 0, 1 ; Results in a poison value.
+ %still_poison = and i32 %poison, 0 ; 0, but also poison.
+ %poison_yet_again = getelementptr i32, i32* @h, i32 %still_poison
+ store i32 0, i32* %poison_yet_again ; memory at @h[0] is poisoned
+
+ store i32 %poison, i32* @g ; Poison value stored to memory.
+ %poison2 = load i32, i32* @g ; Poison value loaded back from memory.
+
+ store volatile i32 %poison, i32* @g ; External observation; undefined behavior.
+
+ %narrowaddr = bitcast i32* @g to i16*
+ %wideaddr = bitcast i32* @g to i64*
+ %poison3 = load i16, i16* %narrowaddr ; Returns a poison value.
+ %poison4 = load i64, i64* %wideaddr ; Returns a poison value.
+
+ %cmp = icmp slt i32 %poison, 0 ; Returns a poison value.
+ br i1 %cmp, label %true, label %end ; Branch to either destination.
+
+ true:
+ store volatile i32 0, i32* @g ; This is control-dependent on %cmp, so
+ ; it has undefined behavior.
+ br label %end
+
+ end:
+ %p = phi i32 [ 0, %entry ], [ 1, %true ]
+ ; Both edges into this PHI are
+ ; control-dependent on %cmp, so this
+ ; always results in a poison value.
+
+ store volatile i32 0, i32* @g ; This would depend on the store in %true
+ ; if %cmp is true, or the store in %entry
+ ; otherwise, so this is undefined behavior.
+
+ br i1 %cmp, label %second_true, label %second_end
+ ; The same branch again, but this time the
+ ; true block doesn't have side effects.
+
+ second_true:
+ ; No side effects!
+ ret void
+
+ second_end:
+ store volatile i32 0, i32* @g ; This time, the instruction always depends
+ ; on the store in %end. Also, it is
+ ; control-equivalent to %end, so this is
+ ; well-defined (ignoring earlier undefined
+ ; behavior in this example).
+
+.. _blockaddress:
+
+Addresses of Basic Blocks
+-------------------------
+
+``blockaddress(@function, %block)``
+
+The '``blockaddress``' constant computes the address of the specified
+basic block in the specified function, and always has an ``i8*`` type.
+Taking the address of the entry block is illegal.
+
+This value only has defined behavior when used as an operand to the
+':ref:`indirectbr <i_indirectbr>`' instruction, or for comparisons
+against null. Pointer equality tests between labels addresses results in
+undefined behavior --- though, again, comparison against null is ok, and
+no label is equal to the null pointer. This may be passed around as an
+opaque pointer sized value as long as the bits are not inspected. This
+allows ``ptrtoint`` and arithmetic to be performed on these values so
+long as the original value is reconstituted before the ``indirectbr``
+instruction.
+
+Finally, some targets may provide defined semantics when using the value
+as the operand to an inline assembly, but that is target specific.
+
+.. _constantexprs:
+
+Constant Expressions
+--------------------
+
+Constant expressions are used to allow expressions involving other
+constants to be used as constants. Constant expressions may be of any
+:ref:`first class <t_firstclass>` type and may involve any LLVM operation
+that does not have side effects (e.g. load and call are not supported).
+The following is the syntax for constant expressions:
+
+``trunc (CST to TYPE)``
+ Truncate a constant to another type. The bit size of CST must be
+ larger than the bit size of TYPE. Both types must be integers.
+``zext (CST to TYPE)``
+ Zero extend a constant to another type. The bit size of CST must be
+ smaller than the bit size of TYPE. Both types must be integers.
+``sext (CST to TYPE)``
+ Sign extend a constant to another type. The bit size of CST must be
+ smaller than the bit size of TYPE. Both types must be integers.
+``fptrunc (CST to TYPE)``
+ Truncate a floating point constant to another floating point type.
+ The size of CST must be larger than the size of TYPE. Both types
+ must be floating point.
+``fpext (CST to TYPE)``
+ Floating point extend a constant to another type. The size of CST
+ must be smaller or equal to the size of TYPE. Both types must be
+ floating point.
+``fptoui (CST to TYPE)``
+ Convert a floating point constant to the corresponding unsigned
+ integer constant. TYPE must be a scalar or vector integer type. CST
+ must be of scalar or vector floating point type. Both CST and TYPE
+ must be scalars, or vectors of the same number of elements. If the
+ value won't fit in the integer type, the results are undefined.
+``fptosi (CST to TYPE)``
+ Convert a floating point constant to the corresponding signed
+ integer constant. TYPE must be a scalar or vector integer type. CST
+ must be of scalar or vector floating point type. Both CST and TYPE
+ must be scalars, or vectors of the same number of elements. If the
+ value won't fit in the integer type, the results are undefined.
+``uitofp (CST to TYPE)``
+ Convert an unsigned integer constant to the corresponding floating
+ point constant. TYPE must be a scalar or vector floating point type.
+ CST must be of scalar or vector integer type. Both CST and TYPE must
+ be scalars, or vectors of the same number of elements. If the value
+ won't fit in the floating point type, the results are undefined.
+``sitofp (CST to TYPE)``
+ Convert a signed integer constant to the corresponding floating
+ point constant. TYPE must be a scalar or vector floating point type.
+ CST must be of scalar or vector integer type. Both CST and TYPE must
+ be scalars, or vectors of the same number of elements. If the value
+ won't fit in the floating point type, the results are undefined.
+``ptrtoint (CST to TYPE)``
+ Convert a pointer typed constant to the corresponding integer
+ constant. ``TYPE`` must be an integer type. ``CST`` must be of
+ pointer type. The ``CST`` value is zero extended, truncated, or
+ unchanged to make it fit in ``TYPE``.
+``inttoptr (CST to TYPE)``
+ Convert an integer constant to a pointer constant. TYPE must be a
+ pointer type. CST must be of integer type. The CST value is zero
+ extended, truncated, or unchanged to make it fit in a pointer size.
+ This one is *really* dangerous!
+``bitcast (CST to TYPE)``
+ Convert a constant, CST, to another TYPE. The constraints of the
+ operands are the same as those for the :ref:`bitcast
+ instruction <i_bitcast>`.
+``addrspacecast (CST to TYPE)``
+ Convert a constant pointer or constant vector of pointer, CST, to another
+ TYPE in a different address space. The constraints of the operands are the
+ same as those for the :ref:`addrspacecast instruction <i_addrspacecast>`.
+``getelementptr (TY, CSTPTR, IDX0, IDX1, ...)``, ``getelementptr inbounds (TY, CSTPTR, IDX0, IDX1, ...)``
+ Perform the :ref:`getelementptr operation <i_getelementptr>` on
+ constants. As with the :ref:`getelementptr <i_getelementptr>`
+ instruction, the index list may have one or more indexes, which are
+ required to make sense for the type of "pointer to TY".
+``select (COND, VAL1, VAL2)``
+ Perform the :ref:`select operation <i_select>` on constants.
+``icmp COND (VAL1, VAL2)``
+ Performs the :ref:`icmp operation <i_icmp>` on constants.
+``fcmp COND (VAL1, VAL2)``
+ Performs the :ref:`fcmp operation <i_fcmp>` on constants.
+``extractelement (VAL, IDX)``
+ Perform the :ref:`extractelement operation <i_extractelement>` on
+ constants.
+``insertelement (VAL, ELT, IDX)``
+ Perform the :ref:`insertelement operation <i_insertelement>` on
+ constants.
+``shufflevector (VEC1, VEC2, IDXMASK)``
+ Perform the :ref:`shufflevector operation <i_shufflevector>` on
+ constants.
+``extractvalue (VAL, IDX0, IDX1, ...)``
+ Perform the :ref:`extractvalue operation <i_extractvalue>` on
+ constants. The index list is interpreted in a similar manner as
+ indices in a ':ref:`getelementptr <i_getelementptr>`' operation. At
+ least one index value must be specified.
+``insertvalue (VAL, ELT, IDX0, IDX1, ...)``
+ Perform the :ref:`insertvalue operation <i_insertvalue>` on constants.
+ The index list is interpreted in a similar manner as indices in a
+ ':ref:`getelementptr <i_getelementptr>`' operation. At least one index
+ value must be specified.
+``OPCODE (LHS, RHS)``
+ Perform the specified operation of the LHS and RHS constants. OPCODE
+ may be any of the :ref:`binary <binaryops>` or :ref:`bitwise
+ binary <bitwiseops>` operations. The constraints on operands are
+ the same as those for the corresponding instruction (e.g. no bitwise
+ operations on floating point values are allowed).
+
+Other Values
+============
+
+.. _inlineasmexprs:
+
+Inline Assembler Expressions
+----------------------------
+
+LLVM supports inline assembler expressions (as opposed to :ref:`Module-Level
+Inline Assembly <moduleasm>`) through the use of a special value. This value
+represents the inline assembler as a template string (containing the
+instructions to emit), a list of operand constraints (stored as a string), a
+flag that indicates whether or not the inline asm expression has side effects,
+and a flag indicating whether the function containing the asm needs to align its
+stack conservatively.
+
+The template string supports argument substitution of the operands using "``$``"
+followed by a number, to indicate substitution of the given register/memory
+location, as specified by the constraint string. "``${NUM:MODIFIER}``" may also
+be used, where ``MODIFIER`` is a target-specific annotation for how to print the
+operand (See :ref:`inline-asm-modifiers`).
+
+A literal "``$``" may be included by using "``$$``" in the template. To include
+other special characters into the output, the usual "``\XX``" escapes may be
+used, just as in other strings. Note that after template substitution, the
+resulting assembly string is parsed by LLVM's integrated assembler unless it is
+disabled -- even when emitting a ``.s`` file -- and thus must contain assembly
+syntax known to LLVM.
+
+LLVM also supports a few more substitions useful for writing inline assembly:
+
+- ``${:uid}``: Expands to a decimal integer unique to this inline assembly blob.
+ This substitution is useful when declaring a local label. Many standard
+ compiler optimizations, such as inlining, may duplicate an inline asm blob.
+ Adding a blob-unique identifier ensures that the two labels will not conflict
+ during assembly. This is used to implement `GCC's %= special format
+ string <https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html>`_.
+- ``${:comment}``: Expands to the comment character of the current target's
+ assembly dialect. This is usually ``#``, but many targets use other strings,
+ such as ``;``, ``//``, or ``!``.
+- ``${:private}``: Expands to the assembler private label prefix. Labels with
+ this prefix will not appear in the symbol table of the assembled object.
+ Typically the prefix is ``L``, but targets may use other strings. ``.L`` is
+ relatively popular.
+
+LLVM's support for inline asm is modeled closely on the requirements of Clang's
+GCC-compatible inline-asm support. Thus, the feature-set and the constraint and
+modifier codes listed here are similar or identical to those in GCC's inline asm
+support. However, to be clear, the syntax of the template and constraint strings
+described here is *not* the same as the syntax accepted by GCC and Clang, and,
+while most constraint letters are passed through as-is by Clang, some get
+translated to other codes when converting from the C source to the LLVM
+assembly.
+
+An example inline assembler expression is:
+
+.. code-block:: llvm
+
+ i32 (i32) asm "bswap $0", "=r,r"
+
+Inline assembler expressions may **only** be used as the callee operand
+of a :ref:`call <i_call>` or an :ref:`invoke <i_invoke>` instruction.
+Thus, typically we have:
+
+.. code-block:: llvm
+
+ %X = call i32 asm "bswap $0", "=r,r"(i32 %Y)
+
+Inline asms with side effects not visible in the constraint list must be
+marked as having side effects. This is done through the use of the
+'``sideeffect``' keyword, like so:
+
+.. code-block:: llvm
+
+ call void asm sideeffect "eieio", ""()
+
+In some cases inline asms will contain code that will not work unless
+the stack is aligned in some way, such as calls or SSE instructions on
+x86, yet will not contain code that does that alignment within the asm.
+The compiler should make conservative assumptions about what the asm
+might contain and should generate its usual stack alignment code in the
+prologue if the '``alignstack``' keyword is present:
+
+.. code-block:: llvm
+
+ call void asm alignstack "eieio", ""()
+
+Inline asms also support using non-standard assembly dialects. The
+assumed dialect is ATT. When the '``inteldialect``' keyword is present,
+the inline asm is using the Intel dialect. Currently, ATT and Intel are
+the only supported dialects. An example is:
+
+.. code-block:: llvm
+
+ call void asm inteldialect "eieio", ""()
+
+If multiple keywords appear the '``sideeffect``' keyword must come
+first, the '``alignstack``' keyword second and the '``inteldialect``'
+keyword last.
+
+Inline Asm Constraint String
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The constraint list is a comma-separated string, each element containing one or
+more constraint codes.
+
+For each element in the constraint list an appropriate register or memory
+operand will be chosen, and it will be made available to assembly template
+string expansion as ``$0`` for the first constraint in the list, ``$1`` for the
+second, etc.
+
+There are three different types of constraints, which are distinguished by a
+prefix symbol in front of the constraint code: Output, Input, and Clobber. The
+constraints must always be given in that order: outputs first, then inputs, then
+clobbers. They cannot be intermingled.
+
+There are also three different categories of constraint codes:
+
+- Register constraint. This is either a register class, or a fixed physical
+ register. This kind of constraint will allocate a register, and if necessary,
+ bitcast the argument or result to the appropriate type.
+- Memory constraint. This kind of constraint is for use with an instruction
+ taking a memory operand. Different constraints allow for different addressing
+ modes used by the target.
+- Immediate value constraint. This kind of constraint is for an integer or other
+ immediate value which can be rendered directly into an instruction. The
+ various target-specific constraints allow the selection of a value in the
+ proper range for the instruction you wish to use it with.
+
+Output constraints
+""""""""""""""""""
+
+Output constraints are specified by an "``=``" prefix (e.g. "``=r``"). This
+indicates that the assembly will write to this operand, and the operand will
+then be made available as a return value of the ``asm`` expression. Output
+constraints do not consume an argument from the call instruction. (Except, see
+below about indirect outputs).
+
+Normally, it is expected that no output locations are written to by the assembly
+expression until *all* of the inputs have been read. As such, LLVM may assign
+the same register to an output and an input. If this is not safe (e.g. if the
+assembly contains two instructions, where the first writes to one output, and
+the second reads an input and writes to a second output), then the "``&``"
+modifier must be used (e.g. "``=&r``") to specify that the output is an
+"early-clobber" output. Marking an output as "early-clobber" ensures that LLVM
+will not use the same register for any inputs (other than an input tied to this
+output).
+
+Input constraints
+"""""""""""""""""
+
+Input constraints do not have a prefix -- just the constraint codes. Each input
+constraint will consume one argument from the call instruction. It is not
+permitted for the asm to write to any input register or memory location (unless
+that input is tied to an output). Note also that multiple inputs may all be
+assigned to the same register, if LLVM can determine that they necessarily all
+contain the same value.
+
+Instead of providing a Constraint Code, input constraints may also "tie"
+themselves to an output constraint, by providing an integer as the constraint
+string. Tied inputs still consume an argument from the call instruction, and
+take up a position in the asm template numbering as is usual -- they will simply
+be constrained to always use the same register as the output they've been tied
+to. For example, a constraint string of "``=r,0``" says to assign a register for
+output, and use that register as an input as well (it being the 0'th
+constraint).
+
+It is permitted to tie an input to an "early-clobber" output. In that case, no
+*other* input may share the same register as the input tied to the early-clobber
+(even when the other input has the same value).
+
+You may only tie an input to an output which has a register constraint, not a
+memory constraint. Only a single input may be tied to an output.
+
+There is also an "interesting" feature which deserves a bit of explanation: if a
+register class constraint allocates a register which is too small for the value
+type operand provided as input, the input value will be split into multiple
+registers, and all of them passed to the inline asm.
+
+However, this feature is often not as useful as you might think.
+
+Firstly, the registers are *not* guaranteed to be consecutive. So, on those
+architectures that have instructions which operate on multiple consecutive
+instructions, this is not an appropriate way to support them. (e.g. the 32-bit
+SparcV8 has a 64-bit load, which instruction takes a single 32-bit register. The
+hardware then loads into both the named register, and the next register. This
+feature of inline asm would not be useful to support that.)
+
+A few of the targets provide a template string modifier allowing explicit access
+to the second register of a two-register operand (e.g. MIPS ``L``, ``M``, and
+``D``). On such an architecture, you can actually access the second allocated
+register (yet, still, not any subsequent ones). But, in that case, you're still
+probably better off simply splitting the value into two separate operands, for
+clarity. (e.g. see the description of the ``A`` constraint on X86, which,
+despite existing only for use with this feature, is not really a good idea to
+use)
+
+Indirect inputs and outputs
+"""""""""""""""""""""""""""
+
+Indirect output or input constraints can be specified by the "``*``" modifier
+(which goes after the "``=``" in case of an output). This indicates that the asm
+will write to or read from the contents of an *address* provided as an input
+argument. (Note that in this way, indirect outputs act more like an *input* than
+an output: just like an input, they consume an argument of the call expression,
+rather than producing a return value. An indirect output constraint is an
+"output" only in that the asm is expected to write to the contents of the input
+memory location, instead of just read from it).
+
+This is most typically used for memory constraint, e.g. "``=*m``", to pass the
+address of a variable as a value.
+
+It is also possible to use an indirect *register* constraint, but only on output
+(e.g. "``=*r``"). This will cause LLVM to allocate a register for an output
+value normally, and then, separately emit a store to the address provided as
+input, after the provided inline asm. (It's not clear what value this
+functionality provides, compared to writing the store explicitly after the asm
+statement, and it can only produce worse code, since it bypasses many
+optimization passes. I would recommend not using it.)
+
+
+Clobber constraints
+"""""""""""""""""""
+
+A clobber constraint is indicated by a "``~``" prefix. A clobber does not
+consume an input operand, nor generate an output. Clobbers cannot use any of the
+general constraint code letters -- they may use only explicit register
+constraints, e.g. "``~{eax}``". The one exception is that a clobber string of
+"``~{memory}``" indicates that the assembly writes to arbitrary undeclared
+memory locations -- not only the memory pointed to by a declared indirect
+output.
+
+Note that clobbering named registers that are also present in output
+constraints is not legal.
+
+
+Constraint Codes
+""""""""""""""""
+After a potential prefix comes constraint code, or codes.
+
+A Constraint Code is either a single letter (e.g. "``r``"), a "``^``" character
+followed by two letters (e.g. "``^wc``"), or "``{``" register-name "``}``"
+(e.g. "``{eax}``").
+
+The one and two letter constraint codes are typically chosen to be the same as
+GCC's constraint codes.
+
+A single constraint may include one or more than constraint code in it, leaving
+it up to LLVM to choose which one to use. This is included mainly for
+compatibility with the translation of GCC inline asm coming from clang.
+
+There are two ways to specify alternatives, and either or both may be used in an
+inline asm constraint list:
+
+1) Append the codes to each other, making a constraint code set. E.g. "``im``"
+ or "``{eax}m``". This means "choose any of the options in the set". The
+ choice of constraint is made independently for each constraint in the
+ constraint list.
+
+2) Use "``|``" between constraint code sets, creating alternatives. Every
+ constraint in the constraint list must have the same number of alternative
+ sets. With this syntax, the same alternative in *all* of the items in the
+ constraint list will be chosen together.
+
+Putting those together, you might have a two operand constraint string like
+``"rm|r,ri|rm"``. This indicates that if operand 0 is ``r`` or ``m``, then
+operand 1 may be one of ``r`` or ``i``. If operand 0 is ``r``, then operand 1
+may be one of ``r`` or ``m``. But, operand 0 and 1 cannot both be of type m.
+
+However, the use of either of the alternatives features is *NOT* recommended, as
+LLVM is not able to make an intelligent choice about which one to use. (At the
+point it currently needs to choose, not enough information is available to do so
+in a smart way.) Thus, it simply tries to make a choice that's most likely to
+compile, not one that will be optimal performance. (e.g., given "``rm``", it'll
+always choose to use memory, not registers). And, if given multiple registers,
+or multiple register classes, it will simply choose the first one. (In fact, it
+doesn't currently even ensure explicitly specified physical registers are
+unique, so specifying multiple physical registers as alternatives, like
+``{r11}{r12},{r11}{r12}``, will assign r11 to both operands, not at all what was
+intended.)
+
+Supported Constraint Code List
+""""""""""""""""""""""""""""""
+
+The constraint codes are, in general, expected to behave the same way they do in
+GCC. LLVM's support is often implemented on an 'as-needed' basis, to support C
+inline asm code which was supported by GCC. A mismatch in behavior between LLVM
+and GCC likely indicates a bug in LLVM.
+
+Some constraint codes are typically supported by all targets:
+
+- ``r``: A register in the target's general purpose register class.
+- ``m``: A memory address operand. It is target-specific what addressing modes
+ are supported, typical examples are register, or register + register offset,
+ or register + immediate offset (of some target-specific size).
+- ``i``: An integer constant (of target-specific width). Allows either a simple
+ immediate, or a relocatable value.
+- ``n``: An integer constant -- *not* including relocatable values.
+- ``s``: An integer constant, but allowing *only* relocatable values.
+- ``X``: Allows an operand of any kind, no constraint whatsoever. Typically
+ useful to pass a label for an asm branch or call.
+
+ .. FIXME: but that surely isn't actually okay to jump out of an asm
+ block without telling llvm about the control transfer???)
+
+- ``{register-name}``: Requires exactly the named physical register.
+
+Other constraints are target-specific:
+
+AArch64:
+
+- ``z``: An immediate integer 0. Outputs ``WZR`` or ``XZR``, as appropriate.
+- ``I``: An immediate integer valid for an ``ADD`` or ``SUB`` instruction,
+ i.e. 0 to 4095 with optional shift by 12.
+- ``J``: An immediate integer that, when negated, is valid for an ``ADD`` or
+ ``SUB`` instruction, i.e. -1 to -4095 with optional left shift by 12.
+- ``K``: An immediate integer that is valid for the 'bitmask immediate 32' of a
+ logical instruction like ``AND``, ``EOR``, or ``ORR`` with a 32-bit register.
+- ``L``: An immediate integer that is valid for the 'bitmask immediate 64' of a
+ logical instruction like ``AND``, ``EOR``, or ``ORR`` with a 64-bit register.
+- ``M``: An immediate integer for use with the ``MOV`` assembly alias on a
+ 32-bit register. This is a superset of ``K``: in addition to the bitmask
+ immediate, also allows immediate integers which can be loaded with a single
+ ``MOVZ`` or ``MOVL`` instruction.
+- ``N``: An immediate integer for use with the ``MOV`` assembly alias on a
+ 64-bit register. This is a superset of ``L``.
+- ``Q``: Memory address operand must be in a single register (no
+ offsets). (However, LLVM currently does this for the ``m`` constraint as
+ well.)
+- ``r``: A 32 or 64-bit integer register (W* or X*).
+- ``w``: A 32, 64, or 128-bit floating-point/SIMD register.
+- ``x``: A lower 128-bit floating-point/SIMD register (``V0`` to ``V15``).
+
+AMDGPU:
+
+- ``r``: A 32 or 64-bit integer register.
+- ``[0-9]v``: The 32-bit VGPR register, number 0-9.
+- ``[0-9]s``: The 32-bit SGPR register, number 0-9.
+
+
+All ARM modes:
+
+- ``Q``, ``Um``, ``Un``, ``Uq``, ``Us``, ``Ut``, ``Uv``, ``Uy``: Memory address
+ operand. Treated the same as operand ``m``, at the moment.
+
+ARM and ARM's Thumb2 mode:
+
+- ``j``: An immediate integer between 0 and 65535 (valid for ``MOVW``)
+- ``I``: An immediate integer valid for a data-processing instruction.
+- ``J``: An immediate integer between -4095 and 4095.
+- ``K``: An immediate integer whose bitwise inverse is valid for a
+ data-processing instruction. (Can be used with template modifier "``B``" to
+ print the inverted value).
+- ``L``: An immediate integer whose negation is valid for a data-processing
+ instruction. (Can be used with template modifier "``n``" to print the negated
+ value).
+- ``M``: A power of two or a integer between 0 and 32.
+- ``N``: Invalid immediate constraint.
+- ``O``: Invalid immediate constraint.
+- ``r``: A general-purpose 32-bit integer register (``r0-r15``).
+- ``l``: In Thumb2 mode, low 32-bit GPR registers (``r0-r7``). In ARM mode, same
+ as ``r``.
+- ``h``: In Thumb2 mode, a high 32-bit GPR register (``r8-r15``). In ARM mode,
+ invalid.
+- ``w``: A 32, 64, or 128-bit floating-point/SIMD register: ``s0-s31``,
+ ``d0-d31``, or ``q0-q15``.
+- ``x``: A 32, 64, or 128-bit floating-point/SIMD register: ``s0-s15``,
+ ``d0-d7``, or ``q0-q3``.
+- ``t``: A floating-point/SIMD register, only supports 32-bit values:
+ ``s0-s31``.
+
+ARM's Thumb1 mode:
+
+- ``I``: An immediate integer between 0 and 255.
+- ``J``: An immediate integer between -255 and -1.
+- ``K``: An immediate integer between 0 and 255, with optional left-shift by
+ some amount.
+- ``L``: An immediate integer between -7 and 7.
+- ``M``: An immediate integer which is a multiple of 4 between 0 and 1020.
+- ``N``: An immediate integer between 0 and 31.
+- ``O``: An immediate integer which is a multiple of 4 between -508 and 508.
+- ``r``: A low 32-bit GPR register (``r0-r7``).
+- ``l``: A low 32-bit GPR register (``r0-r7``).
+- ``h``: A high GPR register (``r0-r7``).
+- ``w``: A 32, 64, or 128-bit floating-point/SIMD register: ``s0-s31``,
+ ``d0-d31``, or ``q0-q15``.
+- ``x``: A 32, 64, or 128-bit floating-point/SIMD register: ``s0-s15``,
+ ``d0-d7``, or ``q0-q3``.
+- ``t``: A floating-point/SIMD register, only supports 32-bit values:
+ ``s0-s31``.
+
+
+Hexagon:
+
+- ``o``, ``v``: A memory address operand, treated the same as constraint ``m``,
+ at the moment.
+- ``r``: A 32 or 64-bit register.
+
+MSP430:
+
+- ``r``: An 8 or 16-bit register.
+
+MIPS:
+
+- ``I``: An immediate signed 16-bit integer.
+- ``J``: An immediate integer zero.
+- ``K``: An immediate unsigned 16-bit integer.
+- ``L``: An immediate 32-bit integer, where the lower 16 bits are 0.
+- ``N``: An immediate integer between -65535 and -1.
+- ``O``: An immediate signed 15-bit integer.
+- ``P``: An immediate integer between 1 and 65535.
+- ``m``: A memory address operand. In MIPS-SE mode, allows a base address
+ register plus 16-bit immediate offset. In MIPS mode, just a base register.
+- ``R``: A memory address operand. In MIPS-SE mode, allows a base address
+ register plus a 9-bit signed offset. In MIPS mode, the same as constraint
+ ``m``.
+- ``ZC``: A memory address operand, suitable for use in a ``pref``, ``ll``, or
+ ``sc`` instruction on the given subtarget (details vary).
+- ``r``, ``d``, ``y``: A 32 or 64-bit GPR register.
+- ``f``: A 32 or 64-bit FPU register (``F0-F31``), or a 128-bit MSA register
+ (``W0-W31``). In the case of MSA registers, it is recommended to use the ``w``
+ argument modifier for compatibility with GCC.
+- ``c``: A 32-bit or 64-bit GPR register suitable for indirect jump (always
+ ``25``).
+- ``l``: The ``lo`` register, 32 or 64-bit.
+- ``x``: Invalid.
+
+NVPTX:
+
+- ``b``: A 1-bit integer register.
+- ``c`` or ``h``: A 16-bit integer register.
+- ``r``: A 32-bit integer register.
+- ``l`` or ``N``: A 64-bit integer register.
+- ``f``: A 32-bit float register.
+- ``d``: A 64-bit float register.
+
+
+PowerPC:
+
+- ``I``: An immediate signed 16-bit integer.
+- ``J``: An immediate unsigned 16-bit integer, shifted left 16 bits.
+- ``K``: An immediate unsigned 16-bit integer.
+- ``L``: An immediate signed 16-bit integer, shifted left 16 bits.
+- ``M``: An immediate integer greater than 31.
+- ``N``: An immediate integer that is an exact power of 2.
+- ``O``: The immediate integer constant 0.
+- ``P``: An immediate integer constant whose negation is a signed 16-bit
+ constant.
+- ``es``, ``o``, ``Q``, ``Z``, ``Zy``: A memory address operand, currently
+ treated the same as ``m``.
+- ``r``: A 32 or 64-bit integer register.
+- ``b``: A 32 or 64-bit integer register, excluding ``R0`` (that is:
+ ``R1-R31``).
+- ``f``: A 32 or 64-bit float register (``F0-F31``), or when QPX is enabled, a
+ 128 or 256-bit QPX register (``Q0-Q31``; aliases the ``F`` registers).
+- ``v``: For ``4 x f32`` or ``4 x f64`` types, when QPX is enabled, a
+ 128 or 256-bit QPX register (``Q0-Q31``), otherwise a 128-bit
+ altivec vector register (``V0-V31``).
+
+ .. FIXME: is this a bug that v accepts QPX registers? I think this
+ is supposed to only use the altivec vector registers?
+
+- ``y``: Condition register (``CR0-CR7``).
+- ``wc``: An individual CR bit in a CR register.
+- ``wa``, ``wd``, ``wf``: Any 128-bit VSX vector register, from the full VSX
+ register set (overlapping both the floating-point and vector register files).
+- ``ws``: A 32 or 64-bit floating point register, from the full VSX register
+ set.
+
+Sparc:
+
+- ``I``: An immediate 13-bit signed integer.
+- ``r``: A 32-bit integer register.
+- ``f``: Any floating-point register on SparcV8, or a floating point
+ register in the "low" half of the registers on SparcV9.
+- ``e``: Any floating point register. (Same as ``f`` on SparcV8.)
+
+SystemZ:
+
+- ``I``: An immediate unsigned 8-bit integer.
+- ``J``: An immediate unsigned 12-bit integer.
+- ``K``: An immediate signed 16-bit integer.
+- ``L``: An immediate signed 20-bit integer.
+- ``M``: An immediate integer 0x7fffffff.
+- ``Q``: A memory address operand with a base address and a 12-bit immediate
+ unsigned displacement.
+- ``R``: A memory address operand with a base address, a 12-bit immediate
+ unsigned displacement, and an index register.
+- ``S``: A memory address operand with a base address and a 20-bit immediate
+ signed displacement.
+- ``T``: A memory address operand with a base address, a 20-bit immediate
+ signed displacement, and an index register.
+- ``r`` or ``d``: A 32, 64, or 128-bit integer register.
+- ``a``: A 32, 64, or 128-bit integer address register (excludes R0, which in an
+ address context evaluates as zero).
+- ``h``: A 32-bit value in the high part of a 64bit data register
+ (LLVM-specific)
+- ``f``: A 32, 64, or 128-bit floating point register.
+
+X86:
+
+- ``I``: An immediate integer between 0 and 31.
+- ``J``: An immediate integer between 0 and 64.
+- ``K``: An immediate signed 8-bit integer.
+- ``L``: An immediate integer, 0xff or 0xffff or (in 64-bit mode only)
+ 0xffffffff.
+- ``M``: An immediate integer between 0 and 3.
+- ``N``: An immediate unsigned 8-bit integer.
+- ``O``: An immediate integer between 0 and 127.
+- ``e``: An immediate 32-bit signed integer.
+- ``Z``: An immediate 32-bit unsigned integer.
+- ``o``, ``v``: Treated the same as ``m``, at the moment.
+- ``q``: An 8, 16, 32, or 64-bit register which can be accessed as an 8-bit
+ ``l`` integer register. On X86-32, this is the ``a``, ``b``, ``c``, and ``d``
+ registers, and on X86-64, it is all of the integer registers.
+- ``Q``: An 8, 16, 32, or 64-bit register which can be accessed as an 8-bit
+ ``h`` integer register. This is the ``a``, ``b``, ``c``, and ``d`` registers.
+- ``r`` or ``l``: An 8, 16, 32, or 64-bit integer register.
+- ``R``: An 8, 16, 32, or 64-bit "legacy" integer register -- one which has
+ existed since i386, and can be accessed without the REX prefix.
+- ``f``: A 32, 64, or 80-bit '387 FPU stack pseudo-register.
+- ``y``: A 64-bit MMX register, if MMX is enabled.
+- ``x``: If SSE is enabled: a 32 or 64-bit scalar operand, or 128-bit vector
+ operand in a SSE register. If AVX is also enabled, can also be a 256-bit
+ vector operand in an AVX register. If AVX-512 is also enabled, can also be a
+ 512-bit vector operand in an AVX512 register, Otherwise, an error.
+- ``Y``: The same as ``x``, if *SSE2* is enabled, otherwise an error.
+- ``A``: Special case: allocates EAX first, then EDX, for a single operand (in
+ 32-bit mode, a 64-bit integer operand will get split into two registers). It
+ is not recommended to use this constraint, as in 64-bit mode, the 64-bit
+ operand will get allocated only to RAX -- if two 32-bit operands are needed,
+ you're better off splitting it yourself, before passing it to the asm
+ statement.
+
+XCore:
+
+- ``r``: A 32-bit integer register.
+
+
+.. _inline-asm-modifiers:
+
+Asm template argument modifiers
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+In the asm template string, modifiers can be used on the operand reference, like
+"``${0:n}``".
+
+The modifiers are, in general, expected to behave the same way they do in
+GCC. LLVM's support is often implemented on an 'as-needed' basis, to support C
+inline asm code which was supported by GCC. A mismatch in behavior between LLVM
+and GCC likely indicates a bug in LLVM.
+
+Target-independent:
+
+- ``c``: Print an immediate integer constant unadorned, without
+ the target-specific immediate punctuation (e.g. no ``$`` prefix).
+- ``n``: Negate and print immediate integer constant unadorned, without the
+ target-specific immediate punctuation (e.g. no ``$`` prefix).
+- ``l``: Print as an unadorned label, without the target-specific label
+ punctuation (e.g. no ``$`` prefix).
+
+AArch64:
+
+- ``w``: Print a GPR register with a ``w*`` name instead of ``x*`` name. E.g.,
+ instead of ``x30``, print ``w30``.
+- ``x``: Print a GPR register with a ``x*`` name. (this is the default, anyhow).
+- ``b``, ``h``, ``s``, ``d``, ``q``: Print a floating-point/SIMD register with a
+ ``b*``, ``h*``, ``s*``, ``d*``, or ``q*`` name, rather than the default of
+ ``v*``.
+
+AMDGPU:
+
+- ``r``: No effect.
+
+ARM:
+
+- ``a``: Print an operand as an address (with ``[`` and ``]`` surrounding a
+ register).
+- ``P``: No effect.
+- ``q``: No effect.
+- ``y``: Print a VFP single-precision register as an indexed double (e.g. print
+ as ``d4[1]`` instead of ``s9``)
+- ``B``: Bitwise invert and print an immediate integer constant without ``#``
+ prefix.
+- ``L``: Print the low 16-bits of an immediate integer constant.
+- ``M``: Print as a register set suitable for ldm/stm. Also prints *all*
+ register operands subsequent to the specified one (!), so use carefully.
+- ``Q``: Print the low-order register of a register-pair, or the low-order
+ register of a two-register operand.
+- ``R``: Print the high-order register of a register-pair, or the high-order
+ register of a two-register operand.
+- ``H``: Print the second register of a register-pair. (On a big-endian system,
+ ``H`` is equivalent to ``Q``, and on little-endian system, ``H`` is equivalent
+ to ``R``.)
+
+ .. FIXME: H doesn't currently support printing the second register
+ of a two-register operand.
+
+- ``e``: Print the low doubleword register of a NEON quad register.
+- ``f``: Print the high doubleword register of a NEON quad register.
+- ``m``: Print the base register of a memory operand without the ``[`` and ``]``
+ adornment.
+
+Hexagon:
+
+- ``L``: Print the second register of a two-register operand. Requires that it
+ has been allocated consecutively to the first.
+
+ .. FIXME: why is it restricted to consecutive ones? And there's
+ nothing that ensures that happens, is there?
+
+- ``I``: Print the letter 'i' if the operand is an integer constant, otherwise
+ nothing. Used to print 'addi' vs 'add' instructions.
+
+MSP430:
+
+No additional modifiers.
+
+MIPS:
+
+- ``X``: Print an immediate integer as hexadecimal
+- ``x``: Print the low 16 bits of an immediate integer as hexadecimal.
+- ``d``: Print an immediate integer as decimal.
+- ``m``: Subtract one and print an immediate integer as decimal.
+- ``z``: Print $0 if an immediate zero, otherwise print normally.
+- ``L``: Print the low-order register of a two-register operand, or prints the
+ address of the low-order word of a double-word memory operand.
+
+ .. FIXME: L seems to be missing memory operand support.
+
+- ``M``: Print the high-order register of a two-register operand, or prints the
+ address of the high-order word of a double-word memory operand.
+
+ .. FIXME: M seems to be missing memory operand support.
+
+- ``D``: Print the second register of a two-register operand, or prints the
+ second word of a double-word memory operand. (On a big-endian system, ``D`` is
+ equivalent to ``L``, and on little-endian system, ``D`` is equivalent to
+ ``M``.)
+- ``w``: No effect. Provided for compatibility with GCC which requires this
+ modifier in order to print MSA registers (``W0-W31``) with the ``f``
+ constraint.
+
+NVPTX:
+
+- ``r``: No effect.
+
+PowerPC:
+
+- ``L``: Print the second register of a two-register operand. Requires that it
+ has been allocated consecutively to the first.
+
+ .. FIXME: why is it restricted to consecutive ones? And there's
+ nothing that ensures that happens, is there?
+
+- ``I``: Print the letter 'i' if the operand is an integer constant, otherwise
+ nothing. Used to print 'addi' vs 'add' instructions.
+- ``y``: For a memory operand, prints formatter for a two-register X-form
+ instruction. (Currently always prints ``r0,OPERAND``).
+- ``U``: Prints 'u' if the memory operand is an update form, and nothing
+ otherwise. (NOTE: LLVM does not support update form, so this will currently
+ always print nothing)
+- ``X``: Prints 'x' if the memory operand is an indexed form. (NOTE: LLVM does
+ not support indexed form, so this will currently always print nothing)
+
+Sparc:
+
+- ``r``: No effect.
+
+SystemZ:
+
+SystemZ implements only ``n``, and does *not* support any of the other
+target-independent modifiers.
+
+X86:
+
+- ``c``: Print an unadorned integer or symbol name. (The latter is
+ target-specific behavior for this typically target-independent modifier).
+- ``A``: Print a register name with a '``*``' before it.
+- ``b``: Print an 8-bit register name (e.g. ``al``); do nothing on a memory
+ operand.
+- ``h``: Print the upper 8-bit register name (e.g. ``ah``); do nothing on a
+ memory operand.
+- ``w``: Print the 16-bit register name (e.g. ``ax``); do nothing on a memory
+ operand.
+- ``k``: Print the 32-bit register name (e.g. ``eax``); do nothing on a memory
+ operand.
+- ``q``: Print the 64-bit register name (e.g. ``rax``), if 64-bit registers are
+ available, otherwise the 32-bit register name; do nothing on a memory operand.
+- ``n``: Negate and print an unadorned integer, or, for operands other than an
+ immediate integer (e.g. a relocatable symbol expression), print a '-' before
+ the operand. (The behavior for relocatable symbol expressions is a
+ target-specific behavior for this typically target-independent modifier)
+- ``H``: Print a memory reference with additional offset +8.
+- ``P``: Print a memory reference or operand for use as the argument of a call
+ instruction. (E.g. omit ``(rip)``, even though it's PC-relative.)
+
+XCore:
+
+No additional modifiers.
+
+
+Inline Asm Metadata
+^^^^^^^^^^^^^^^^^^^
+
+The call instructions that wrap inline asm nodes may have a
+"``!srcloc``" MDNode attached to it that contains a list of constant
+integers. If present, the code generator will use the integer as the
+location cookie value when report errors through the ``LLVMContext``
+error reporting mechanisms. This allows a front-end to correlate backend
+errors that occur with inline asm back to the source code that produced
+it. For example:
+
+.. code-block:: llvm
+
+ call void asm sideeffect "something bad", ""(), !srcloc !42
+ ...
+ !42 = !{ i32 1234567 }
+
+It is up to the front-end to make sense of the magic numbers it places
+in the IR. If the MDNode contains multiple constants, the code generator
+will use the one that corresponds to the line of the asm that the error
+occurs on.
+
+.. _metadata:
+
+Metadata
+========
+
+LLVM IR allows metadata to be attached to instructions in the program
+that can convey extra information about the code to the optimizers and
+code generator. One example application of metadata is source-level
+debug information. There are two metadata primitives: strings and nodes.
+
+Metadata does not have a type, and is not a value. If referenced from a
+``call`` instruction, it uses the ``metadata`` type.
+
+All metadata are identified in syntax by a exclamation point ('``!``').
+
+.. _metadata-string:
+
+Metadata Nodes and Metadata Strings
+-----------------------------------
+
+A metadata string is a string surrounded by double quotes. It can
+contain any character by escaping non-printable characters with
+"``\xx``" where "``xx``" is the two digit hex code. For example:
+"``!"test\00"``".
+
+Metadata nodes are represented with notation similar to structure
+constants (a comma separated list of elements, surrounded by braces and
+preceded by an exclamation point). Metadata nodes can have any values as
+their operand. For example:
+
+.. code-block:: llvm
+
+ !{ !"test\00", i32 10}
+
+Metadata nodes that aren't uniqued use the ``distinct`` keyword. For example:
+
+.. code-block:: text
+
+ !0 = distinct !{!"test\00", i32 10}
+
+``distinct`` nodes are useful when nodes shouldn't be merged based on their
+content. They can also occur when transformations cause uniquing collisions
+when metadata operands change.
+
+A :ref:`named metadata <namedmetadatastructure>` is a collection of
+metadata nodes, which can be looked up in the module symbol table. For
+example:
+
+.. code-block:: llvm
+
+ !foo = !{!4, !3}
+
+Metadata can be used as function arguments. Here ``llvm.dbg.value``
+function is using two metadata arguments:
+
+.. code-block:: llvm
+
+ call void @llvm.dbg.value(metadata !24, i64 0, metadata !25)
+
+Metadata can be attached to an instruction. Here metadata ``!21`` is attached
+to the ``add`` instruction using the ``!dbg`` identifier:
+
+.. code-block:: llvm
+
+ %indvar.next = add i64 %indvar, 1, !dbg !21
+
+Metadata can also be attached to a function or a global variable. Here metadata
+``!22`` is attached to the ``f1`` and ``f2 functions, and the globals ``g1``
+and ``g2`` using the ``!dbg`` identifier:
+
+.. code-block:: llvm
+
+ declare !dbg !22 void @f1()
+ define void @f2() !dbg !22 {
+ ret void
+ }
+
+ @g1 = global i32 0, !dbg !22
+ @g2 = external global i32, !dbg !22
+
+A transformation is required to drop any metadata attachment that it does not
+know or know it can't preserve. Currently there is an exception for metadata
+attachment to globals for ``!type`` and ``!absolute_symbol`` which can't be
+unconditionally dropped unless the global is itself deleted.
+
+Metadata attached to a module using named metadata may not be dropped, with
+the exception of debug metadata (named metadata with the name ``!llvm.dbg.*``).
+
+More information about specific metadata nodes recognized by the
+optimizers and code generator is found below.
+
+.. _specialized-metadata:
+
+Specialized Metadata Nodes
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Specialized metadata nodes are custom data structures in metadata (as opposed
+to generic tuples). Their fields are labelled, and can be specified in any
+order.
+
+These aren't inherently debug info centric, but currently all the specialized
+metadata nodes are related to debug info.
+
+.. _DICompileUnit:
+
+DICompileUnit
+"""""""""""""
+
+``DICompileUnit`` nodes represent a compile unit. The ``enums:``,
+``retainedTypes:``, ``globals:``, ``imports:`` and ``macros:`` fields are tuples
+containing the debug info to be emitted along with the compile unit, regardless
+of code optimizations (some nodes are only emitted if there are references to
+them from instructions). The ``debugInfoForProfiling:`` field is a boolean
+indicating whether or not line-table discriminators are updated to provide
+more-accurate debug info for profiling results.
+
+.. code-block:: text
+
+ !0 = !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang",
+ isOptimized: true, flags: "-O2", runtimeVersion: 2,
+ splitDebugFilename: "abc.debug", emissionKind: FullDebug,
+ enums: !2, retainedTypes: !3, globals: !4, imports: !5,
+ macros: !6, dwoId: 0x0abcd)
+
+Compile unit descriptors provide the root scope for objects declared in a
+specific compilation unit. File descriptors are defined using this scope. These
+descriptors are collected by a named metadata node ``!llvm.dbg.cu``. They keep
+track of global variables, type information, and imported entities (declarations
+and namespaces).
+
+.. _DIFile:
+
+DIFile
+""""""
+
+``DIFile`` nodes represent files. The ``filename:`` can include slashes.
+
+.. code-block:: none
+
+ !0 = !DIFile(filename: "path/to/file", directory: "/path/to/dir",
+ checksumkind: CSK_MD5,
+ checksum: "000102030405060708090a0b0c0d0e0f")
+
+Files are sometimes used in ``scope:`` fields, and are the only valid target
+for ``file:`` fields.
+Valid values for ``checksumkind:`` field are: {CSK_None, CSK_MD5, CSK_SHA1}
+
+.. _DIBasicType:
+
+DIBasicType
+"""""""""""
+
+``DIBasicType`` nodes represent primitive types, such as ``int``, ``bool`` and
+``float``. ``tag:`` defaults to ``DW_TAG_base_type``.
+
+.. code-block:: text
+
+ !0 = !DIBasicType(name: "unsigned char", size: 8, align: 8,
+ encoding: DW_ATE_unsigned_char)
+ !1 = !DIBasicType(tag: DW_TAG_unspecified_type, name: "decltype(nullptr)")
+
+The ``encoding:`` describes the details of the type. Usually it's one of the
+following:
+
+.. code-block:: text
+
+ DW_ATE_address = 1
+ DW_ATE_boolean = 2
+ DW_ATE_float = 4
+ DW_ATE_signed = 5
+ DW_ATE_signed_char = 6
+ DW_ATE_unsigned = 7
+ DW_ATE_unsigned_char = 8
+
+.. _DISubroutineType:
+
+DISubroutineType
+""""""""""""""""
+
+``DISubroutineType`` nodes represent subroutine types. Their ``types:`` field
+refers to a tuple; the first operand is the return type, while the rest are the
+types of the formal arguments in order. If the first operand is ``null``, that
+represents a function with no return value (such as ``void foo() {}`` in C++).
+
+.. code-block:: text
+
+ !0 = !BasicType(name: "int", size: 32, align: 32, DW_ATE_signed)
+ !1 = !BasicType(name: "char", size: 8, align: 8, DW_ATE_signed_char)
+ !2 = !DISubroutineType(types: !{null, !0, !1}) ; void (int, char)
+
+.. _DIDerivedType:
+
+DIDerivedType
+"""""""""""""
+
+``DIDerivedType`` nodes represent types derived from other types, such as
+qualified types.
+
+.. code-block:: text
+
+ !0 = !DIBasicType(name: "unsigned char", size: 8, align: 8,
+ encoding: DW_ATE_unsigned_char)
+ !1 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !0, size: 32,
+ align: 32)
+
+The following ``tag:`` values are valid:
+
+.. code-block:: text
+
+ DW_TAG_member = 13
+ DW_TAG_pointer_type = 15
+ DW_TAG_reference_type = 16
+ DW_TAG_typedef = 22
+ DW_TAG_inheritance = 28
+ DW_TAG_ptr_to_member_type = 31
+ DW_TAG_const_type = 38
+ DW_TAG_friend = 42
+ DW_TAG_volatile_type = 53
+ DW_TAG_restrict_type = 55
+ DW_TAG_atomic_type = 71
+
+.. _DIDerivedTypeMember:
+
+``DW_TAG_member`` is used to define a member of a :ref:`composite type
+<DICompositeType>`. The type of the member is the ``baseType:``. The
+``offset:`` is the member's bit offset. If the composite type has an ODR
+``identifier:`` and does not set ``flags: DIFwdDecl``, then the member is
+uniqued based only on its ``name:`` and ``scope:``.
+
+``DW_TAG_inheritance`` and ``DW_TAG_friend`` are used in the ``elements:``
+field of :ref:`composite types <DICompositeType>` to describe parents and
+friends.
+
+``DW_TAG_typedef`` is used to provide a name for the ``baseType:``.
+
+``DW_TAG_pointer_type``, ``DW_TAG_reference_type``, ``DW_TAG_const_type``,
+``DW_TAG_volatile_type``, ``DW_TAG_restrict_type`` and ``DW_TAG_atomic_type``
+are used to qualify the ``baseType:``.
+
+Note that the ``void *`` type is expressed as a type derived from NULL.
+
+.. _DICompositeType:
+
+DICompositeType
+"""""""""""""""
+
+``DICompositeType`` nodes represent types composed of other types, like
+structures and unions. ``elements:`` points to a tuple of the composed types.
+
+If the source language supports ODR, the ``identifier:`` field gives the unique
+identifier used for type merging between modules. When specified,
+:ref:`subprogram declarations <DISubprogramDeclaration>` and :ref:`member
+derived types <DIDerivedTypeMember>` that reference the ODR-type in their
+``scope:`` change uniquing rules.
+
+For a given ``identifier:``, there should only be a single composite type that
+does not have ``flags: DIFlagFwdDecl`` set. LLVM tools that link modules
+together will unique such definitions at parse time via the ``identifier:``
+field, even if the nodes are ``distinct``.
+
+.. code-block:: text
+
+ !0 = !DIEnumerator(name: "SixKind", value: 7)
+ !1 = !DIEnumerator(name: "SevenKind", value: 7)
+ !2 = !DIEnumerator(name: "NegEightKind", value: -8)
+ !3 = !DICompositeType(tag: DW_TAG_enumeration_type, name: "Enum", file: !12,
+ line: 2, size: 32, align: 32, identifier: "_M4Enum",
+ elements: !{!0, !1, !2})
+
+The following ``tag:`` values are valid:
+
+.. code-block:: text
+
+ DW_TAG_array_type = 1
+ DW_TAG_class_type = 2
+ DW_TAG_enumeration_type = 4
+ DW_TAG_structure_type = 19
+ DW_TAG_union_type = 23
+
+For ``DW_TAG_array_type``, the ``elements:`` should be :ref:`subrange
+descriptors <DISubrange>`, each representing the range of subscripts at that
+level of indexing. The ``DIFlagVector`` flag to ``flags:`` indicates that an
+array type is a native packed vector.
+
+For ``DW_TAG_enumeration_type``, the ``elements:`` should be :ref:`enumerator
+descriptors <DIEnumerator>`, each representing the definition of an enumeration
+value for the set. All enumeration type descriptors are collected in the
+``enums:`` field of the :ref:`compile unit <DICompileUnit>`.
+
+For ``DW_TAG_structure_type``, ``DW_TAG_class_type``, and
+``DW_TAG_union_type``, the ``elements:`` should be :ref:`derived types
+<DIDerivedType>` with ``tag: DW_TAG_member``, ``tag: DW_TAG_inheritance``, or
+``tag: DW_TAG_friend``; or :ref:`subprograms <DISubprogram>` with
+``isDefinition: false``.
+
+.. _DISubrange:
+
+DISubrange
+""""""""""
+
+``DISubrange`` nodes are the elements for ``DW_TAG_array_type`` variants of
+:ref:`DICompositeType`. ``count: -1`` indicates an empty array.
+
+.. code-block:: llvm
+
+ !0 = !DISubrange(count: 5, lowerBound: 0) ; array counting from 0
+ !1 = !DISubrange(count: 5, lowerBound: 1) ; array counting from 1
+ !2 = !DISubrange(count: -1) ; empty array.
+
+.. _DIEnumerator:
+
+DIEnumerator
+""""""""""""
+
+``DIEnumerator`` nodes are the elements for ``DW_TAG_enumeration_type``
+variants of :ref:`DICompositeType`.
+
+.. code-block:: llvm
+
+ !0 = !DIEnumerator(name: "SixKind", value: 7)
+ !1 = !DIEnumerator(name: "SevenKind", value: 7)
+ !2 = !DIEnumerator(name: "NegEightKind", value: -8)
+
+DITemplateTypeParameter
+"""""""""""""""""""""""
+
+``DITemplateTypeParameter`` nodes represent type parameters to generic source
+language constructs. They are used (optionally) in :ref:`DICompositeType` and
+:ref:`DISubprogram` ``templateParams:`` fields.
+
+.. code-block:: llvm
+
+ !0 = !DITemplateTypeParameter(name: "Ty", type: !1)
+
+DITemplateValueParameter
+""""""""""""""""""""""""
+
+``DITemplateValueParameter`` nodes represent value parameters to generic source
+language constructs. ``tag:`` defaults to ``DW_TAG_template_value_parameter``,
+but if specified can also be set to ``DW_TAG_GNU_template_template_param`` or
+``DW_TAG_GNU_template_param_pack``. They are used (optionally) in
+:ref:`DICompositeType` and :ref:`DISubprogram` ``templateParams:`` fields.
+
+.. code-block:: llvm
+
+ !0 = !DITemplateValueParameter(name: "Ty", type: !1, value: i32 7)
+
+DINamespace
+"""""""""""
+
+``DINamespace`` nodes represent namespaces in the source language.
+
+.. code-block:: llvm
+
+ !0 = !DINamespace(name: "myawesomeproject", scope: !1, file: !2, line: 7)
+
+DIGlobalVariable
+""""""""""""""""
+
+``DIGlobalVariable`` nodes represent global variables in the source language.
+
+.. code-block:: llvm
+
+ !0 = !DIGlobalVariable(name: "foo", linkageName: "foo", scope: !1,
+ file: !2, line: 7, type: !3, isLocal: true,
+ isDefinition: false, variable: i32* @foo,
+ declaration: !4)
+
+All global variables should be referenced by the `globals:` field of a
+:ref:`compile unit <DICompileUnit>`.
+
+.. _DISubprogram:
+
+DISubprogram
+""""""""""""
+
+``DISubprogram`` nodes represent functions from the source language. A
+``DISubprogram`` may be attached to a function definition using ``!dbg``
+metadata. The ``variables:`` field points at :ref:`variables <DILocalVariable>`
+that must be retained, even if their IR counterparts are optimized out of
+the IR. The ``type:`` field must point at an :ref:`DISubroutineType`.
+
+.. _DISubprogramDeclaration:
+
+When ``isDefinition: false``, subprograms describe a declaration in the type
+tree as opposed to a definition of a function. If the scope is a composite
+type with an ODR ``identifier:`` and that does not set ``flags: DIFwdDecl``,
+then the subprogram declaration is uniqued based only on its ``linkageName:``
+and ``scope:``.
+
+.. code-block:: text
+
+ define void @_Z3foov() !dbg !0 {
+ ...
+ }
+
+ !0 = distinct !DISubprogram(name: "foo", linkageName: "_Zfoov", scope: !1,
+ file: !2, line: 7, type: !3, isLocal: true,
+ isDefinition: true, scopeLine: 8,
+ containingType: !4,
+ virtuality: DW_VIRTUALITY_pure_virtual,
+ virtualIndex: 10, flags: DIFlagPrototyped,
+ isOptimized: true, unit: !5, templateParams: !6,
+ declaration: !7, variables: !8, thrownTypes: !9)
+
+.. _DILexicalBlock:
+
+DILexicalBlock
+""""""""""""""
+
+``DILexicalBlock`` nodes describe nested blocks within a :ref:`subprogram
+<DISubprogram>`. The line number and column numbers are used to distinguish
+two lexical blocks at same depth. They are valid targets for ``scope:``
+fields.
+
+.. code-block:: text
+
+ !0 = distinct !DILexicalBlock(scope: !1, file: !2, line: 7, column: 35)
+
+Usually lexical blocks are ``distinct`` to prevent node merging based on
+operands.
+
+.. _DILexicalBlockFile:
+
+DILexicalBlockFile
+""""""""""""""""""
+
+``DILexicalBlockFile`` nodes are used to discriminate between sections of a
+:ref:`lexical block <DILexicalBlock>`. The ``file:`` field can be changed to
+indicate textual inclusion, or the ``discriminator:`` field can be used to
+discriminate between control flow within a single block in the source language.
+
+.. code-block:: llvm
+
+ !0 = !DILexicalBlock(scope: !3, file: !4, line: 7, column: 35)
+ !1 = !DILexicalBlockFile(scope: !0, file: !4, discriminator: 0)
+ !2 = !DILexicalBlockFile(scope: !0, file: !4, discriminator: 1)
+
+.. _DILocation:
+
+DILocation
+""""""""""
+
+``DILocation`` nodes represent source debug locations. The ``scope:`` field is
+mandatory, and points at an :ref:`DILexicalBlockFile`, an
+:ref:`DILexicalBlock`, or an :ref:`DISubprogram`.
+
+.. code-block:: llvm
+
+ !0 = !DILocation(line: 2900, column: 42, scope: !1, inlinedAt: !2)
+
+.. _DILocalVariable:
+
+DILocalVariable
+"""""""""""""""
+
+``DILocalVariable`` nodes represent local variables in the source language. If
+the ``arg:`` field is set to non-zero, then this variable is a subprogram
+parameter, and it will be included in the ``variables:`` field of its
+:ref:`DISubprogram`.
+
+.. code-block:: text
+
+ !0 = !DILocalVariable(name: "this", arg: 1, scope: !3, file: !2, line: 7,
+ type: !3, flags: DIFlagArtificial)
+ !1 = !DILocalVariable(name: "x", arg: 2, scope: !4, file: !2, line: 7,
+ type: !3)
+ !2 = !DILocalVariable(name: "y", scope: !5, file: !2, line: 7, type: !3)
+
+DIExpression
+""""""""""""
+
+``DIExpression`` nodes represent expressions that are inspired by the DWARF
+expression language. They are used in :ref:`debug intrinsics<dbg_intrinsics>`
+(such as ``llvm.dbg.declare`` and ``llvm.dbg.value``) to describe how the
+referenced LLVM variable relates to the source language variable.
+
+The current supported vocabulary is limited:
+
+- ``DW_OP_deref`` dereferences the top of the expression stack.
+- ``DW_OP_plus`` pops the last two entries from the expression stack, adds
+ them together and appends the result to the expression stack.
+- ``DW_OP_minus`` pops the last two entries from the expression stack, subtracts
+ the last entry from the second last entry and appends the result to the
+ expression stack.
+- ``DW_OP_plus_uconst, 93`` adds ``93`` to the working expression.
+- ``DW_OP_LLVM_fragment, 16, 8`` specifies the offset and size (``16`` and ``8``
+ here, respectively) of the variable fragment from the working expression. Note
+ that contrary to DW_OP_bit_piece, the offset is describing the the location
+ within the described source variable.
+- ``DW_OP_swap`` swaps top two stack entries.
+- ``DW_OP_xderef`` provides extended dereference mechanism. The entry at the top
+ of the stack is treated as an address. The second stack entry is treated as an
+ address space identifier.
+- ``DW_OP_stack_value`` marks a constant value.
+
+DWARF specifies three kinds of simple location descriptions: Register, memory,
+and implicit location descriptions. Register and memory location descriptions
+describe the *location* of a source variable (in the sense that a debugger might
+modify its value), whereas implicit locations describe merely the *value* of a
+source variable. DIExpressions also follow this model: A DIExpression that
+doesn't have a trailing ``DW_OP_stack_value`` will describe an *address* when
+combined with a concrete location.
+
+.. code-block:: llvm
+
+ !0 = !DIExpression(DW_OP_deref)
+ !1 = !DIExpression(DW_OP_plus_uconst, 3)
+ !1 = !DIExpression(DW_OP_constu, 3, DW_OP_plus)
+ !2 = !DIExpression(DW_OP_bit_piece, 3, 7)
+ !3 = !DIExpression(DW_OP_deref, DW_OP_constu, 3, DW_OP_plus, DW_OP_LLVM_fragment, 3, 7)
+ !4 = !DIExpression(DW_OP_constu, 2, DW_OP_swap, DW_OP_xderef)
+ !5 = !DIExpression(DW_OP_constu, 42, DW_OP_stack_value)
+
+DIObjCProperty
+""""""""""""""
+
+``DIObjCProperty`` nodes represent Objective-C property nodes.
+
+.. code-block:: llvm
+
+ !3 = !DIObjCProperty(name: "foo", file: !1, line: 7, setter: "setFoo",
+ getter: "getFoo", attributes: 7, type: !2)
+
+DIImportedEntity
+""""""""""""""""
+
+``DIImportedEntity`` nodes represent entities (such as modules) imported into a
+compile unit.
+
+.. code-block:: text
+
+ !2 = !DIImportedEntity(tag: DW_TAG_imported_module, name: "foo", scope: !0,
+ entity: !1, line: 7)
+
+DIMacro
+"""""""
+
+``DIMacro`` nodes represent definition or undefinition of a macro identifiers.
+The ``name:`` field is the macro identifier, followed by macro parameters when
+defining a function-like macro, and the ``value`` field is the token-string
+used to expand the macro identifier.
+
+.. code-block:: text
+
+ !2 = !DIMacro(macinfo: DW_MACINFO_define, line: 7, name: "foo(x)",
+ value: "((x) + 1)")
+ !3 = !DIMacro(macinfo: DW_MACINFO_undef, line: 30, name: "foo")
+
+DIMacroFile
+"""""""""""
+
+``DIMacroFile`` nodes represent inclusion of source files.
+The ``nodes:`` field is a list of ``DIMacro`` and ``DIMacroFile`` nodes that
+appear in the included source file.
+
+.. code-block:: text
+
+ !2 = !DIMacroFile(macinfo: DW_MACINFO_start_file, line: 7, file: !2,
+ nodes: !3)
+
+'``tbaa``' Metadata
+^^^^^^^^^^^^^^^^^^^
+
+In LLVM IR, memory does not have types, so LLVM's own type system is not
+suitable for doing type based alias analysis (TBAA). Instead, metadata is
+added to the IR to describe a type system of a higher level language. This
+can be used to implement C/C++ strict type aliasing rules, but it can also
+be used to implement custom alias analysis behavior for other languages.
+
+This description of LLVM's TBAA system is broken into two parts:
+:ref:`Semantics<tbaa_node_semantics>` talks about high level issues, and
+:ref:`Representation<tbaa_node_representation>` talks about the metadata
+encoding of various entities.
+
+It is always possible to trace any TBAA node to a "root" TBAA node (details
+in the :ref:`Representation<tbaa_node_representation>` section). TBAA
+nodes with different roots have an unknown aliasing relationship, and LLVM
+conservatively infers ``MayAlias`` between them. The rules mentioned in
+this section only pertain to TBAA nodes living under the same root.
+
+.. _tbaa_node_semantics:
+
+Semantics
+"""""""""
+
+The TBAA metadata system, referred to as "struct path TBAA" (not to be
+confused with ``tbaa.struct``), consists of the following high level
+concepts: *Type Descriptors*, further subdivided into scalar type
+descriptors and struct type descriptors; and *Access Tags*.
+
+**Type descriptors** describe the type system of the higher level language
+being compiled. **Scalar type descriptors** describe types that do not
+contain other types. Each scalar type has a parent type, which must also
+be a scalar type or the TBAA root. Via this parent relation, scalar types
+within a TBAA root form a tree. **Struct type descriptors** denote types
+that contain a sequence of other type descriptors, at known offsets. These
+contained type descriptors can either be struct type descriptors themselves
+or scalar type descriptors.
+
+**Access tags** are metadata nodes attached to load and store instructions.
+Access tags use type descriptors to describe the *location* being accessed
+in terms of the type system of the higher level language. Access tags are
+tuples consisting of a base type, an access type and an offset. The base
+type is a scalar type descriptor or a struct type descriptor, the access
+type is a scalar type descriptor, and the offset is a constant integer.
+
+The access tag ``(BaseTy, AccessTy, Offset)`` can describe one of two
+things:
+
+ * If ``BaseTy`` is a struct type, the tag describes a memory access (load
+ or store) of a value of type ``AccessTy`` contained in the struct type
+ ``BaseTy`` at offset ``Offset``.
+
+ * If ``BaseTy`` is a scalar type, ``Offset`` must be 0 and ``BaseTy`` and
+ ``AccessTy`` must be the same; and the access tag describes a scalar
+ access with scalar type ``AccessTy``.
+
+We first define an ``ImmediateParent`` relation on ``(BaseTy, Offset)``
+tuples this way:
+
+ * If ``BaseTy`` is a scalar type then ``ImmediateParent(BaseTy, 0)`` is
+ ``(ParentTy, 0)`` where ``ParentTy`` is the parent of the scalar type as
+ described in the TBAA metadata. ``ImmediateParent(BaseTy, Offset)`` is
+ undefined if ``Offset`` is non-zero.
+
+ * If ``BaseTy`` is a struct type then ``ImmediateParent(BaseTy, Offset)``
+ is ``(NewTy, NewOffset)`` where ``NewTy`` is the type contained in
+ ``BaseTy`` at offset ``Offset`` and ``NewOffset`` is ``Offset`` adjusted
+ to be relative within that inner type.
+
+A memory access with an access tag ``(BaseTy1, AccessTy1, Offset1)``
+aliases a memory access with an access tag ``(BaseTy2, AccessTy2,
+Offset2)`` if either ``(BaseTy1, Offset1)`` is reachable from ``(Base2,
+Offset2)`` via the ``Parent`` relation or vice versa.
+
+As a concrete example, the type descriptor graph for the following program
+
+.. code-block:: c
+
+ struct Inner {
+ int i; // offset 0
+ float f; // offset 4
+ };
+
+ struct Outer {
+ float f; // offset 0
+ double d; // offset 4
+ struct Inner inner_a; // offset 12
+ };
+
+ void f(struct Outer* outer, struct Inner* inner, float* f, int* i, char* c) {
+ outer->f = 0; // tag0: (OuterStructTy, FloatScalarTy, 0)
+ outer->inner_a.i = 0; // tag1: (OuterStructTy, IntScalarTy, 12)
+ outer->inner_a.f = 0.0; // tag2: (OuterStructTy, IntScalarTy, 16)
+ *f = 0.0; // tag3: (FloatScalarTy, FloatScalarTy, 0)
+ }
+
+is (note that in C and C++, ``char`` can be used to access any arbitrary
+type):
+
+.. code-block:: text
+
+ Root = "TBAA Root"
+ CharScalarTy = ("char", Root, 0)
+ FloatScalarTy = ("float", CharScalarTy, 0)
+ DoubleScalarTy = ("double", CharScalarTy, 0)
+ IntScalarTy = ("int", CharScalarTy, 0)
+ InnerStructTy = {"Inner" (IntScalarTy, 0), (FloatScalarTy, 4)}
+ OuterStructTy = {"Outer", (FloatScalarTy, 0), (DoubleScalarTy, 4),
+ (InnerStructTy, 12)}
+
+
+with (e.g.) ``ImmediateParent(OuterStructTy, 12)`` = ``(InnerStructTy,
+0)``, ``ImmediateParent(InnerStructTy, 0)`` = ``(IntScalarTy, 0)``, and
+``ImmediateParent(IntScalarTy, 0)`` = ``(CharScalarTy, 0)``.
+
+.. _tbaa_node_representation:
+
+Representation
+""""""""""""""
+
+The root node of a TBAA type hierarchy is an ``MDNode`` with 0 operands or
+with exactly one ``MDString`` operand.
+
+Scalar type descriptors are represented as an ``MDNode`` s with two
+operands. The first operand is an ``MDString`` denoting the name of the
+struct type. LLVM does not assign meaning to the value of this operand, it
+only cares about it being an ``MDString``. The second operand is an
+``MDNode`` which points to the parent for said scalar type descriptor,
+which is either another scalar type descriptor or the TBAA root. Scalar
+type descriptors can have an optional third argument, but that must be the
+constant integer zero.
+
+Struct type descriptors are represented as ``MDNode`` s with an odd number
+of operands greater than 1. The first operand is an ``MDString`` denoting
+the name of the struct type. Like in scalar type descriptors the actual
+value of this name operand is irrelevant to LLVM. After the name operand,
+the struct type descriptors have a sequence of alternating ``MDNode`` and
+``ConstantInt`` operands. With N starting from 1, the 2N - 1 th operand,
+an ``MDNode``, denotes a contained field, and the 2N th operand, a
+``ConstantInt``, is the offset of the said contained field. The offsets
+must be in non-decreasing order.
+
+Access tags are represented as ``MDNode`` s with either 3 or 4 operands.
+The first operand is an ``MDNode`` pointing to the node representing the
+base type. The second operand is an ``MDNode`` pointing to the node
+representing the access type. The third operand is a ``ConstantInt`` that
+states the offset of the access. If a fourth field is present, it must be
+a ``ConstantInt`` valued at 0 or 1. If it is 1 then the access tag states
+that the location being accessed is "constant" (meaning
+``pointsToConstantMemory`` should return true; see `other useful
+AliasAnalysis methods <AliasAnalysis.html#OtherItfs>`_). The TBAA root of
+the access type and the base type of an access tag must be the same, and
+that is the TBAA root of the access tag.
+
+'``tbaa.struct``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The :ref:`llvm.memcpy <int_memcpy>` is often used to implement
+aggregate assignment operations in C and similar languages, however it
+is defined to copy a contiguous region of memory, which is more than
+strictly necessary for aggregate types which contain holes due to
+padding. Also, it doesn't contain any TBAA information about the fields
+of the aggregate.
+
+``!tbaa.struct`` metadata can describe which memory subregions in a
+memcpy are padding and what the TBAA tags of the struct are.
+
+The current metadata format is very simple. ``!tbaa.struct`` metadata
+nodes are a list of operands which are in conceptual groups of three.
+For each group of three, the first operand gives the byte offset of a
+field in bytes, the second gives its size in bytes, and the third gives
+its tbaa tag. e.g.:
+
+.. code-block:: llvm
+
+ !4 = !{ i64 0, i64 4, !1, i64 8, i64 4, !2 }
+
+This describes a struct with two fields. The first is at offset 0 bytes
+with size 4 bytes, and has tbaa tag !1. The second is at offset 8 bytes
+and has size 4 bytes and has tbaa tag !2.
+
+Note that the fields need not be contiguous. In this example, there is a
+4 byte gap between the two fields. This gap represents padding which
+does not carry useful data and need not be preserved.
+
+'``noalias``' and '``alias.scope``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+``noalias`` and ``alias.scope`` metadata provide the ability to specify generic
+noalias memory-access sets. This means that some collection of memory access
+instructions (loads, stores, memory-accessing calls, etc.) that carry
+``noalias`` metadata can specifically be specified not to alias with some other
+collection of memory access instructions that carry ``alias.scope`` metadata.
+Each type of metadata specifies a list of scopes where each scope has an id and
+a domain.
+
+When evaluating an aliasing query, if for some domain, the set
+of scopes with that domain in one instruction's ``alias.scope`` list is a
+subset of (or equal to) the set of scopes for that domain in another
+instruction's ``noalias`` list, then the two memory accesses are assumed not to
+alias.
+
+Because scopes in one domain don't affect scopes in other domains, separate
+domains can be used to compose multiple independent noalias sets. This is
+used for example during inlining. As the noalias function parameters are
+turned into noalias scope metadata, a new domain is used every time the
+function is inlined.
+
+The metadata identifying each domain is itself a list containing one or two
+entries. The first entry is the name of the domain. Note that if the name is a
+string then it can be combined across functions and translation units. A
+self-reference can be used to create globally unique domain names. A
+descriptive string may optionally be provided as a second list entry.
+
+The metadata identifying each scope is also itself a list containing two or
+three entries. The first entry is the name of the scope. Note that if the name
+is a string then it can be combined across functions and translation units. A
+self-reference can be used to create globally unique scope names. A metadata
+reference to the scope's domain is the second entry. A descriptive string may
+optionally be provided as a third list entry.
+
+For example,
+
+.. code-block:: llvm
+
+ ; Two scope domains:
+ !0 = !{!0}
+ !1 = !{!1}
+
+ ; Some scopes in these domains:
+ !2 = !{!2, !0}
+ !3 = !{!3, !0}
+ !4 = !{!4, !1}
+
+ ; Some scope lists:
+ !5 = !{!4} ; A list containing only scope !4
+ !6 = !{!4, !3, !2}
+ !7 = !{!3}
+
+ ; These two instructions don't alias:
+ %0 = load float, float* %c, align 4, !alias.scope !5
+ store float %0, float* %arrayidx.i, align 4, !noalias !5
+
+ ; These two instructions also don't alias (for domain !1, the set of scopes
+ ; in the !alias.scope equals that in the !noalias list):
+ %2 = load float, float* %c, align 4, !alias.scope !5
+ store float %2, float* %arrayidx.i2, align 4, !noalias !6
+
+ ; These two instructions may alias (for domain !0, the set of scopes in
+ ; the !noalias list is not a superset of, or equal to, the scopes in the
+ ; !alias.scope list):
+ %2 = load float, float* %c, align 4, !alias.scope !6
+ store float %0, float* %arrayidx.i, align 4, !noalias !7
+
+'``fpmath``' Metadata
+^^^^^^^^^^^^^^^^^^^^^
+
+``fpmath`` metadata may be attached to any instruction of floating point
+type. It can be used to express the maximum acceptable error in the
+result of that instruction, in ULPs, thus potentially allowing the
+compiler to use a more efficient but less accurate method of computing
+it. ULP is defined as follows:
+
+ If ``x`` is a real number that lies between two finite consecutive
+ floating-point numbers ``a`` and ``b``, without being equal to one
+ of them, then ``ulp(x) = |b - a|``, otherwise ``ulp(x)`` is the
+ distance between the two non-equal finite floating-point numbers
+ nearest ``x``. Moreover, ``ulp(NaN)`` is ``NaN``.
+
+The metadata node shall consist of a single positive float type number
+representing the maximum relative error, for example:
+
+.. code-block:: llvm
+
+ !0 = !{ float 2.5 } ; maximum acceptable inaccuracy is 2.5 ULPs
+
+.. _range-metadata:
+
+'``range``' Metadata
+^^^^^^^^^^^^^^^^^^^^
+
+``range`` metadata may be attached only to ``load``, ``call`` and ``invoke`` of
+integer types. It expresses the possible ranges the loaded value or the value
+returned by the called function at this call site is in. The ranges are
+represented with a flattened list of integers. The loaded value or the value
+returned is known to be in the union of the ranges defined by each consecutive
+pair. Each pair has the following properties:
+
+- The type must match the type loaded by the instruction.
+- The pair ``a,b`` represents the range ``[a,b)``.
+- Both ``a`` and ``b`` are constants.
+- The range is allowed to wrap.
+- The range should not represent the full or empty set. That is,
+ ``a!=b``.
+
+In addition, the pairs must be in signed order of the lower bound and
+they must be non-contiguous.
+
+Examples:
+
+.. code-block:: llvm
+
+ %a = load i8, i8* %x, align 1, !range !0 ; Can only be 0 or 1
+ %b = load i8, i8* %y, align 1, !range !1 ; Can only be 255 (-1), 0 or 1
+ %c = call i8 @foo(), !range !2 ; Can only be 0, 1, 3, 4 or 5
+ %d = invoke i8 @bar() to label %cont
+ unwind label %lpad, !range !3 ; Can only be -2, -1, 3, 4 or 5
+ ...
+ !0 = !{ i8 0, i8 2 }
+ !1 = !{ i8 255, i8 2 }
+ !2 = !{ i8 0, i8 2, i8 3, i8 6 }
+ !3 = !{ i8 -2, i8 0, i8 3, i8 6 }
+
+'``absolute_symbol``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+``absolute_symbol`` metadata may be attached to a global variable
+declaration. It marks the declaration as a reference to an absolute symbol,
+which causes the backend to use absolute relocations for the symbol even
+in position independent code, and expresses the possible ranges that the
+global variable's *address* (not its value) is in, in the same format as
+``range`` metadata, with the extension that the pair ``all-ones,all-ones``
+may be used to represent the full set.
+
+Example (assuming 64-bit pointers):
+
+.. code-block:: llvm
+
+ @a = external global i8, !absolute_symbol !0 ; Absolute symbol in range [0,256)
+ @b = external global i8, !absolute_symbol !1 ; Absolute symbol in range [0,2^64)
+
+ ...
+ !0 = !{ i64 0, i64 256 }
+ !1 = !{ i64 -1, i64 -1 }
+
+'``unpredictable``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+``unpredictable`` metadata may be attached to any branch or switch
+instruction. It can be used to express the unpredictability of control
+flow. Similar to the llvm.expect intrinsic, it may be used to alter
+optimizations related to compare and branch instructions. The metadata
+is treated as a boolean value; if it exists, it signals that the branch
+or switch that it is attached to is completely unpredictable.
+
+'``llvm.loop``'
+^^^^^^^^^^^^^^^
+
+It is sometimes useful to attach information to loop constructs. Currently,
+loop metadata is implemented as metadata attached to the branch instruction
+in the loop latch block. This type of metadata refer to a metadata node that is
+guaranteed to be separate for each loop. The loop identifier metadata is
+specified with the name ``llvm.loop``.
+
+The loop identifier metadata is implemented using a metadata that refers to
+itself to avoid merging it with any other identifier metadata, e.g.,
+during module linkage or function inlining. That is, each loop should refer
+to their own identification metadata even if they reside in separate functions.
+The following example contains loop identifier metadata for two separate loop
+constructs:
+
+.. code-block:: llvm
+
+ !0 = !{!0}
+ !1 = !{!1}
+
+The loop identifier metadata can be used to specify additional
+per-loop metadata. Any operands after the first operand can be treated
+as user-defined metadata. For example the ``llvm.loop.unroll.count``
+suggests an unroll factor to the loop unroller:
+
+.. code-block:: llvm
+
+ br i1 %exitcond, label %._crit_edge, label %.lr.ph, !llvm.loop !0
+ ...
+ !0 = !{!0, !1}
+ !1 = !{!"llvm.loop.unroll.count", i32 4}
+
+'``llvm.loop.vectorize``' and '``llvm.loop.interleave``'
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Metadata prefixed with ``llvm.loop.vectorize`` or ``llvm.loop.interleave`` are
+used to control per-loop vectorization and interleaving parameters such as
+vectorization width and interleave count. These metadata should be used in
+conjunction with ``llvm.loop`` loop identification metadata. The
+``llvm.loop.vectorize`` and ``llvm.loop.interleave`` metadata are only
+optimization hints and the optimizer will only interleave and vectorize loops if
+it believes it is safe to do so. The ``llvm.mem.parallel_loop_access`` metadata
+which contains information about loop-carried memory dependencies can be helpful
+in determining the safety of these transformations.
+
+'``llvm.loop.interleave.count``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This metadata suggests an interleave count to the loop interleaver.
+The first operand is the string ``llvm.loop.interleave.count`` and the
+second operand is an integer specifying the interleave count. For
+example:
+
+.. code-block:: llvm
+
+ !0 = !{!"llvm.loop.interleave.count", i32 4}
+
+Note that setting ``llvm.loop.interleave.count`` to 1 disables interleaving
+multiple iterations of the loop. If ``llvm.loop.interleave.count`` is set to 0
+then the interleave count will be determined automatically.
+
+'``llvm.loop.vectorize.enable``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This metadata selectively enables or disables vectorization for the loop. The
+first operand is the string ``llvm.loop.vectorize.enable`` and the second operand
+is a bit. If the bit operand value is 1 vectorization is enabled. A value of
+0 disables vectorization:
+
+.. code-block:: llvm
+
+ !0 = !{!"llvm.loop.vectorize.enable", i1 0}
+ !1 = !{!"llvm.loop.vectorize.enable", i1 1}
+
+'``llvm.loop.vectorize.width``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This metadata sets the target width of the vectorizer. The first
+operand is the string ``llvm.loop.vectorize.width`` and the second
+operand is an integer specifying the width. For example:
+
+.. code-block:: llvm
+
+ !0 = !{!"llvm.loop.vectorize.width", i32 4}
+
+Note that setting ``llvm.loop.vectorize.width`` to 1 disables
+vectorization of the loop. If ``llvm.loop.vectorize.width`` is set to
+0 or if the loop does not have this metadata the width will be
+determined automatically.
+
+'``llvm.loop.unroll``'
+^^^^^^^^^^^^^^^^^^^^^^
+
+Metadata prefixed with ``llvm.loop.unroll`` are loop unrolling
+optimization hints such as the unroll factor. ``llvm.loop.unroll``
+metadata should be used in conjunction with ``llvm.loop`` loop
+identification metadata. The ``llvm.loop.unroll`` metadata are only
+optimization hints and the unrolling will only be performed if the
+optimizer believes it is safe to do so.
+
+'``llvm.loop.unroll.count``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This metadata suggests an unroll factor to the loop unroller. The
+first operand is the string ``llvm.loop.unroll.count`` and the second
+operand is a positive integer specifying the unroll factor. For
+example:
+
+.. code-block:: llvm
+
+ !0 = !{!"llvm.loop.unroll.count", i32 4}
+
+If the trip count of the loop is less than the unroll count the loop
+will be partially unrolled.
+
+'``llvm.loop.unroll.disable``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This metadata disables loop unrolling. The metadata has a single operand
+which is the string ``llvm.loop.unroll.disable``. For example:
+
+.. code-block:: llvm
+
+ !0 = !{!"llvm.loop.unroll.disable"}
+
+'``llvm.loop.unroll.runtime.disable``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This metadata disables runtime loop unrolling. The metadata has a single
+operand which is the string ``llvm.loop.unroll.runtime.disable``. For example:
+
+.. code-block:: llvm
+
+ !0 = !{!"llvm.loop.unroll.runtime.disable"}
+
+'``llvm.loop.unroll.enable``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This metadata suggests that the loop should be fully unrolled if the trip count
+is known at compile time and partially unrolled if the trip count is not known
+at compile time. The metadata has a single operand which is the string
+``llvm.loop.unroll.enable``. For example:
+
+.. code-block:: llvm
+
+ !0 = !{!"llvm.loop.unroll.enable"}
+
+'``llvm.loop.unroll.full``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This metadata suggests that the loop should be unrolled fully. The
+metadata has a single operand which is the string ``llvm.loop.unroll.full``.
+For example:
+
+.. code-block:: llvm
+
+ !0 = !{!"llvm.loop.unroll.full"}
+
+'``llvm.loop.licm_versioning.disable``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This metadata indicates that the loop should not be versioned for the purpose
+of enabling loop-invariant code motion (LICM). The metadata has a single operand
+which is the string ``llvm.loop.licm_versioning.disable``. For example:
+
+.. code-block:: llvm
+
+ !0 = !{!"llvm.loop.licm_versioning.disable"}
+
+'``llvm.loop.distribute.enable``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Loop distribution allows splitting a loop into multiple loops. Currently,
+this is only performed if the entire loop cannot be vectorized due to unsafe
+memory dependencies. The transformation will attempt to isolate the unsafe
+dependencies into their own loop.
+
+This metadata can be used to selectively enable or disable distribution of the
+loop. The first operand is the string ``llvm.loop.distribute.enable`` and the
+second operand is a bit. If the bit operand value is 1 distribution is
+enabled. A value of 0 disables distribution:
+
+.. code-block:: llvm
+
+ !0 = !{!"llvm.loop.distribute.enable", i1 0}
+ !1 = !{!"llvm.loop.distribute.enable", i1 1}
+
+This metadata should be used in conjunction with ``llvm.loop`` loop
+identification metadata.
+
+'``llvm.mem``'
+^^^^^^^^^^^^^^^
+
+Metadata types used to annotate memory accesses with information helpful
+for optimizations are prefixed with ``llvm.mem``.
+
+'``llvm.mem.parallel_loop_access``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The ``llvm.mem.parallel_loop_access`` metadata refers to a loop identifier,
+or metadata containing a list of loop identifiers for nested loops.
+The metadata is attached to memory accessing instructions and denotes that
+no loop carried memory dependence exist between it and other instructions denoted
+with the same loop identifier. The metadata on memory reads also implies that
+if conversion (i.e. speculative execution within a loop iteration) is safe.
+
+Precisely, given two instructions ``m1`` and ``m2`` that both have the
+``llvm.mem.parallel_loop_access`` metadata, with ``L1`` and ``L2`` being the
+set of loops associated with that metadata, respectively, then there is no loop
+carried dependence between ``m1`` and ``m2`` for loops in both ``L1`` and
+``L2``.
+
+As a special case, if all memory accessing instructions in a loop have
+``llvm.mem.parallel_loop_access`` metadata that refers to that loop, then the
+loop has no loop carried memory dependences and is considered to be a parallel
+loop.
+
+Note that if not all memory access instructions have such metadata referring to
+the loop, then the loop is considered not being trivially parallel. Additional
+memory dependence analysis is required to make that determination. As a fail
+safe mechanism, this causes loops that were originally parallel to be considered
+sequential (if optimization passes that are unaware of the parallel semantics
+insert new memory instructions into the loop body).
+
+Example of a loop that is considered parallel due to its correct use of
+both ``llvm.loop`` and ``llvm.mem.parallel_loop_access``
+metadata types that refer to the same loop identifier metadata.
+
+.. code-block:: llvm
+
+ for.body:
+ ...
+ %val0 = load i32, i32* %arrayidx, !llvm.mem.parallel_loop_access !0
+ ...
+ store i32 %val0, i32* %arrayidx1, !llvm.mem.parallel_loop_access !0
+ ...
+ br i1 %exitcond, label %for.end, label %for.body, !llvm.loop !0
+
+ for.end:
+ ...
+ !0 = !{!0}
+
+It is also possible to have nested parallel loops. In that case the
+memory accesses refer to a list of loop identifier metadata nodes instead of
+the loop identifier metadata node directly:
+
+.. code-block:: llvm
+
+ outer.for.body:
+ ...
+ %val1 = load i32, i32* %arrayidx3, !llvm.mem.parallel_loop_access !2
+ ...
+ br label %inner.for.body
+
+ inner.for.body:
+ ...
+ %val0 = load i32, i32* %arrayidx1, !llvm.mem.parallel_loop_access !0
+ ...
+ store i32 %val0, i32* %arrayidx2, !llvm.mem.parallel_loop_access !0
+ ...
+ br i1 %exitcond, label %inner.for.end, label %inner.for.body, !llvm.loop !1
+
+ inner.for.end:
+ ...
+ store i32 %val1, i32* %arrayidx4, !llvm.mem.parallel_loop_access !2
+ ...
+ br i1 %exitcond, label %outer.for.end, label %outer.for.body, !llvm.loop !2
+
+ outer.for.end: ; preds = %for.body
+ ...
+ !0 = !{!1, !2} ; a list of loop identifiers
+ !1 = !{!1} ; an identifier for the inner loop
+ !2 = !{!2} ; an identifier for the outer loop
+
+'``invariant.group``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The ``invariant.group`` metadata may be attached to ``load``/``store`` instructions.
+The existence of the ``invariant.group`` metadata on the instruction tells
+the optimizer that every ``load`` and ``store`` to the same pointer operand
+within the same invariant group can be assumed to load or store the same
+value (but see the ``llvm.invariant.group.barrier`` intrinsic which affects
+when two pointers are considered the same). Pointers returned by bitcast or
+getelementptr with only zero indices are considered the same.
+
+Examples:
+
+.. code-block:: llvm
+
+ @unknownPtr = external global i8
+ ...
+ %ptr = alloca i8
+ store i8 42, i8* %ptr, !invariant.group !0
+ call void @foo(i8* %ptr)
+
+ %a = load i8, i8* %ptr, !invariant.group !0 ; Can assume that value under %ptr didn't change
+ call void @foo(i8* %ptr)
+ %b = load i8, i8* %ptr, !invariant.group !1 ; Can't assume anything, because group changed
+
+ %newPtr = call i8* @getPointer(i8* %ptr)
+ %c = load i8, i8* %newPtr, !invariant.group !0 ; Can't assume anything, because we only have information about %ptr
+
+ %unknownValue = load i8, i8* @unknownPtr
+ store i8 %unknownValue, i8* %ptr, !invariant.group !0 ; Can assume that %unknownValue == 42
+
+ call void @foo(i8* %ptr)
+ %newPtr2 = call i8* @llvm.invariant.group.barrier(i8* %ptr)
+ %d = load i8, i8* %newPtr2, !invariant.group !0 ; Can't step through invariant.group.barrier to get value of %ptr
+
+ ...
+ declare void @foo(i8*)
+ declare i8* @getPointer(i8*)
+ declare i8* @llvm.invariant.group.barrier(i8*)
+
+ !0 = !{!"magic ptr"}
+ !1 = !{!"other ptr"}
+
+The invariant.group metadata must be dropped when replacing one pointer by
+another based on aliasing information. This is because invariant.group is tied
+to the SSA value of the pointer operand.
+
+.. code-block:: llvm
+
+ %v = load i8, i8* %x, !invariant.group !0
+ ; if %x mustalias %y then we can replace the above instruction with
+ %v = load i8, i8* %y
+
+
+'``type``' Metadata
+^^^^^^^^^^^^^^^^^^^
+
+See :doc:`TypeMetadata`.
+
+'``associated``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The ``associated`` metadata may be attached to a global object
+declaration with a single argument that references another global object.
+
+This metadata prevents discarding of the global object in linker GC
+unless the referenced object is also discarded. The linker support for
+this feature is spotty. For best compatibility, globals carrying this
+metadata may also:
+
+- Be in a comdat with the referenced global.
+- Be in @llvm.compiler.used.
+- Have an explicit section with a name which is a valid C identifier.
+
+It does not have any effect on non-ELF targets.
+
+Example:
+
+.. code-block:: llvm
+
+ $a = comdat any
+ @a = global i32 1, comdat $a
+ @b = internal global i32 2, comdat $a, section "abc", !associated !0
+ !0 = !{i32* @a}
+
+
+'``prof``' Metadata
+^^^^^^^^^^^^^^^^^^^
+
+The ``prof`` metadata is used to record profile data in the IR.
+The first operand of the metadata node indicates the profile metadata
+type. There are currently 3 types:
+:ref:`branch_weights<prof_node_branch_weights>`,
+:ref:`function_entry_count<prof_node_function_entry_count>`, and
+:ref:`VP<prof_node_VP>`.
+
+.. _prof_node_branch_weights:
+
+branch_weights
+""""""""""""""
+
+Branch weight metadata attached to a branch, select, switch or call instruction
+represents the likeliness of the associated branch being taken.
+For more information, see :doc:`BranchWeightMetadata`.
+
+.. _prof_node_function_entry_count:
+
+function_entry_count
+""""""""""""""""""""
+
+Function entry count metadata can be attached to function definitions
+to record the number of times the function is called. Used with BFI
+information, it is also used to derive the basic block profile count.
+For more information, see :doc:`BranchWeightMetadata`.
+
+.. _prof_node_VP:
+
+VP
+""
+
+VP (value profile) metadata can be attached to instructions that have
+value profile information. Currently this is indirect calls (where it
+records the hottest callees) and calls to memory intrinsics such as memcpy,
+memmove, and memset (where it records the hottest byte lengths).
+
+Each VP metadata node contains "VP" string, then a uint32_t value for the value
+profiling kind, a uint64_t value for the total number of times the instruction
+is executed, followed by uint64_t value and execution count pairs.
+The value profiling kind is 0 for indirect call targets and 1 for memory
+operations. For indirect call targets, each profile value is a hash
+of the callee function name, and for memory operations each value is the
+byte length.
+
+Note that the value counts do not need to add up to the total count
+listed in the third operand (in practice only the top hottest values
+are tracked and reported).
+
+Indirect call example:
+
+.. code-block:: llvm
+
+ call void %f(), !prof !1
+ !1 = !{!"VP", i32 0, i64 1600, i64 7651369219802541373, i64 1030, i64 -4377547752858689819, i64 410}
+
+Note that the VP type is 0 (the second operand), which indicates this is
+an indirect call value profile data. The third operand indicates that the
+indirect call executed 1600 times. The 4th and 6th operands give the
+hashes of the 2 hottest target functions' names (this is the same hash used
+to represent function names in the profile database), and the 5th and 7th
+operands give the execution count that each of the respective prior target
+functions was called.
+
+Module Flags Metadata
+=====================
+
+Information about the module as a whole is difficult to convey to LLVM's
+subsystems. The LLVM IR isn't sufficient to transmit this information.
+The ``llvm.module.flags`` named metadata exists in order to facilitate
+this. These flags are in the form of key / value pairs --- much like a
+dictionary --- making it easy for any subsystem who cares about a flag to
+look it up.
+
+The ``llvm.module.flags`` metadata contains a list of metadata triplets.
+Each triplet has the following form:
+
+- The first element is a *behavior* flag, which specifies the behavior
+ when two (or more) modules are merged together, and it encounters two
+ (or more) metadata with the same ID. The supported behaviors are
+ described below.
+- The second element is a metadata string that is a unique ID for the
+ metadata. Each module may only have one flag entry for each unique ID (not
+ including entries with the **Require** behavior).
+- The third element is the value of the flag.
+
+When two (or more) modules are merged together, the resulting
+``llvm.module.flags`` metadata is the union of the modules' flags. That is, for
+each unique metadata ID string, there will be exactly one entry in the merged
+modules ``llvm.module.flags`` metadata table, and the value for that entry will
+be determined by the merge behavior flag, as described below. The only exception
+is that entries with the *Require* behavior are always preserved.
+
+The following behaviors are supported:
+
+.. list-table::
+ :header-rows: 1
+ :widths: 10 90
+
+ * - Value
+ - Behavior
+
+ * - 1
+ - **Error**
+ Emits an error if two values disagree, otherwise the resulting value
+ is that of the operands.
+
+ * - 2
+ - **Warning**
+ Emits a warning if two values disagree. The result value will be the
+ operand for the flag from the first module being linked.
+
+ * - 3
+ - **Require**
+ Adds a requirement that another module flag be present and have a
+ specified value after linking is performed. The value must be a
+ metadata pair, where the first element of the pair is the ID of the
+ module flag to be restricted, and the second element of the pair is
+ the value the module flag should be restricted to. This behavior can
+ be used to restrict the allowable results (via triggering of an
+ error) of linking IDs with the **Override** behavior.
+
+ * - 4
+ - **Override**
+ Uses the specified value, regardless of the behavior or value of the
+ other module. If both modules specify **Override**, but the values
+ differ, an error will be emitted.
+
+ * - 5
+ - **Append**
+ Appends the two values, which are required to be metadata nodes.
+
+ * - 6
+ - **AppendUnique**
+ Appends the two values, which are required to be metadata
+ nodes. However, duplicate entries in the second list are dropped
+ during the append operation.
+
+ * - 7
+ - **Max**
+ Takes the max of the two values, which are required to be integers.
+
+It is an error for a particular unique flag ID to have multiple behaviors,
+except in the case of **Require** (which adds restrictions on another metadata
+value) or **Override**.
+
+An example of module flags:
+
+.. code-block:: llvm
+
+ !0 = !{ i32 1, !"foo", i32 1 }
+ !1 = !{ i32 4, !"bar", i32 37 }
+ !2 = !{ i32 2, !"qux", i32 42 }
+ !3 = !{ i32 3, !"qux",
+ !{
+ !"foo", i32 1
+ }
+ }
+ !llvm.module.flags = !{ !0, !1, !2, !3 }
+
+- Metadata ``!0`` has the ID ``!"foo"`` and the value '1'. The behavior
+ if two or more ``!"foo"`` flags are seen is to emit an error if their
+ values are not equal.
+
+- Metadata ``!1`` has the ID ``!"bar"`` and the value '37'. The
+ behavior if two or more ``!"bar"`` flags are seen is to use the value
+ '37'.
+
+- Metadata ``!2`` has the ID ``!"qux"`` and the value '42'. The
+ behavior if two or more ``!"qux"`` flags are seen is to emit a
+ warning if their values are not equal.
+
+- Metadata ``!3`` has the ID ``!"qux"`` and the value:
+
+ ::
+
+ !{ !"foo", i32 1 }
+
+ The behavior is to emit an error if the ``llvm.module.flags`` does not
+ contain a flag with the ID ``!"foo"`` that has the value '1' after linking is
+ performed.
+
+Objective-C Garbage Collection Module Flags Metadata
+----------------------------------------------------
+
+On the Mach-O platform, Objective-C stores metadata about garbage
+collection in a special section called "image info". The metadata
+consists of a version number and a bitmask specifying what types of
+garbage collection are supported (if any) by the file. If two or more
+modules are linked together their garbage collection metadata needs to
+be merged rather than appended together.
+
+The Objective-C garbage collection module flags metadata consists of the
+following key-value pairs:
+
+.. list-table::
+ :header-rows: 1
+ :widths: 30 70
+
+ * - Key
+ - Value
+
+ * - ``Objective-C Version``
+ - **[Required]** --- The Objective-C ABI version. Valid values are 1 and 2.
+
+ * - ``Objective-C Image Info Version``
+ - **[Required]** --- The version of the image info section. Currently
+ always 0.
+
+ * - ``Objective-C Image Info Section``
+ - **[Required]** --- The section to place the metadata. Valid values are
+ ``"__OBJC, __image_info, regular"`` for Objective-C ABI version 1, and
+ ``"__DATA,__objc_imageinfo, regular, no_dead_strip"`` for
+ Objective-C ABI version 2.
+
+ * - ``Objective-C Garbage Collection``
+ - **[Required]** --- Specifies whether garbage collection is supported or
+ not. Valid values are 0, for no garbage collection, and 2, for garbage
+ collection supported.
+
+ * - ``Objective-C GC Only``
+ - **[Optional]** --- Specifies that only garbage collection is supported.
+ If present, its value must be 6. This flag requires that the
+ ``Objective-C Garbage Collection`` flag have the value 2.
+
+Some important flag interactions:
+
+- If a module with ``Objective-C Garbage Collection`` set to 0 is
+ merged with a module with ``Objective-C Garbage Collection`` set to
+ 2, then the resulting module has the
+ ``Objective-C Garbage Collection`` flag set to 0.
+- A module with ``Objective-C Garbage Collection`` set to 0 cannot be
+ merged with a module with ``Objective-C GC Only`` set to 6.
+
+C type width Module Flags Metadata
+----------------------------------
+
+The ARM backend emits a section into each generated object file describing the
+options that it was compiled with (in a compiler-independent way) to prevent
+linking incompatible objects, and to allow automatic library selection. Some
+of these options are not visible at the IR level, namely wchar_t width and enum
+width.
+
+To pass this information to the backend, these options are encoded in module
+flags metadata, using the following key-value pairs:
+
+.. list-table::
+ :header-rows: 1
+ :widths: 30 70
+
+ * - Key
+ - Value
+
+ * - short_wchar
+ - * 0 --- sizeof(wchar_t) == 4
+ * 1 --- sizeof(wchar_t) == 2
+
+ * - short_enum
+ - * 0 --- Enums are at least as large as an ``int``.
+ * 1 --- Enums are stored in the smallest integer type which can
+ represent all of its values.
+
+For example, the following metadata section specifies that the module was
+compiled with a ``wchar_t`` width of 4 bytes, and the underlying type of an
+enum is the smallest type which can represent all of its values::
+
+ !llvm.module.flags = !{!0, !1}
+ !0 = !{i32 1, !"short_wchar", i32 1}
+ !1 = !{i32 1, !"short_enum", i32 0}
+
+Automatic Linker Flags Named Metadata
+=====================================
+
+Some targets support embedding flags to the linker inside individual object
+files. Typically this is used in conjunction with language extensions which
+allow source files to explicitly declare the libraries they depend on, and have
+these automatically be transmitted to the linker via object files.
+
+These flags are encoded in the IR using named metadata with the name
+``!llvm.linker.options``. Each operand is expected to be a metadata node
+which should be a list of other metadata nodes, each of which should be a
+list of metadata strings defining linker options.
+
+For example, the following metadata section specifies two separate sets of
+linker options, presumably to link against ``libz`` and the ``Cocoa``
+framework::
+
+ !0 = !{ !"-lz" },
+ !1 = !{ !"-framework", !"Cocoa" } } }
+ !llvm.linker.options = !{ !0, !1 }
+
+The metadata encoding as lists of lists of options, as opposed to a collapsed
+list of options, is chosen so that the IR encoding can use multiple option
+strings to specify e.g., a single library, while still having that specifier be
+preserved as an atomic element that can be recognized by a target specific
+assembly writer or object file emitter.
+
+Each individual option is required to be either a valid option for the target's
+linker, or an option that is reserved by the target specific assembly writer or
+object file emitter. No other aspect of these options is defined by the IR.
+
+.. _intrinsicglobalvariables:
+
+Intrinsic Global Variables
+==========================
+
+LLVM has a number of "magic" global variables that contain data that
+affect code generation or other IR semantics. These are documented here.
+All globals of this sort should have a section specified as
+"``llvm.metadata``". This section and all globals that start with
+"``llvm.``" are reserved for use by LLVM.
+
+.. _gv_llvmused:
+
+The '``llvm.used``' Global Variable
+-----------------------------------
+
+The ``@llvm.used`` global is an array which has
+:ref:`appending linkage <linkage_appending>`. This array contains a list of
+pointers to named global variables, functions and aliases which may optionally
+have a pointer cast formed of bitcast or getelementptr. For example, a legal
+use of it is:
+
+.. code-block:: llvm
+
+ @X = global i8 4
+ @Y = global i32 123
+
+ @llvm.used = appending global [2 x i8*] [
+ i8* @X,
+ i8* bitcast (i32* @Y to i8*)
+ ], section "llvm.metadata"
+
+If a symbol appears in the ``@llvm.used`` list, then the compiler, assembler,
+and linker are required to treat the symbol as if there is a reference to the
+symbol that it cannot see (which is why they have to be named). For example, if
+a variable has internal linkage and no references other than that from the
+``@llvm.used`` list, it cannot be deleted. This is commonly used to represent
+references from inline asms and other things the compiler cannot "see", and
+corresponds to "``attribute((used))``" in GNU C.
+
+On some targets, the code generator must emit a directive to the
+assembler or object file to prevent the assembler and linker from
+molesting the symbol.
+
+.. _gv_llvmcompilerused:
+
+The '``llvm.compiler.used``' Global Variable
+--------------------------------------------
+
+The ``@llvm.compiler.used`` directive is the same as the ``@llvm.used``
+directive, except that it only prevents the compiler from touching the
+symbol. On targets that support it, this allows an intelligent linker to
+optimize references to the symbol without being impeded as it would be
+by ``@llvm.used``.
+
+This is a rare construct that should only be used in rare circumstances,
+and should not be exposed to source languages.
+
+.. _gv_llvmglobalctors:
+
+The '``llvm.global_ctors``' Global Variable
+-------------------------------------------
+
+.. code-block:: llvm
+
+ %0 = type { i32, void ()*, i8* }
+ @llvm.global_ctors = appending global [1 x %0] [%0 { i32 65535, void ()* @ctor, i8* @data }]
+
+The ``@llvm.global_ctors`` array contains a list of constructor
+functions, priorities, and an optional associated global or function.
+The functions referenced by this array will be called in ascending order
+of priority (i.e. lowest first) when the module is loaded. The order of
+functions with the same priority is not defined.
+
+If the third field is present, non-null, and points to a global variable
+or function, the initializer function will only run if the associated
+data from the current module is not discarded.
+
+.. _llvmglobaldtors:
+
+The '``llvm.global_dtors``' Global Variable
+-------------------------------------------
+
+.. code-block:: llvm
+
+ %0 = type { i32, void ()*, i8* }
+ @llvm.global_dtors = appending global [1 x %0] [%0 { i32 65535, void ()* @dtor, i8* @data }]
+
+The ``@llvm.global_dtors`` array contains a list of destructor
+functions, priorities, and an optional associated global or function.
+The functions referenced by this array will be called in descending
+order of priority (i.e. highest first) when the module is unloaded. The
+order of functions with the same priority is not defined.
+
+If the third field is present, non-null, and points to a global variable
+or function, the destructor function will only run if the associated
+data from the current module is not discarded.
+
+Instruction Reference
+=====================
+
+The LLVM instruction set consists of several different classifications
+of instructions: :ref:`terminator instructions <terminators>`, :ref:`binary
+instructions <binaryops>`, :ref:`bitwise binary
+instructions <bitwiseops>`, :ref:`memory instructions <memoryops>`, and
+:ref:`other instructions <otherops>`.
+
+.. _terminators:
+
+Terminator Instructions
+-----------------------
+
+As mentioned :ref:`previously <functionstructure>`, every basic block in a
+program ends with a "Terminator" instruction, which indicates which
+block should be executed after the current block is finished. These
+terminator instructions typically yield a '``void``' value: they produce
+control flow, not values (the one exception being the
+':ref:`invoke <i_invoke>`' instruction).
+
+The terminator instructions are: ':ref:`ret <i_ret>`',
+':ref:`br <i_br>`', ':ref:`switch <i_switch>`',
+':ref:`indirectbr <i_indirectbr>`', ':ref:`invoke <i_invoke>`',
+':ref:`resume <i_resume>`', ':ref:`catchswitch <i_catchswitch>`',
+':ref:`catchret <i_catchret>`',
+':ref:`cleanupret <i_cleanupret>`',
+and ':ref:`unreachable <i_unreachable>`'.
+
+.. _i_ret:
+
+'``ret``' Instruction
+^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ ret <type> <value> ; Return a value from a non-void function
+ ret void ; Return from void function
+
+Overview:
+"""""""""
+
+The '``ret``' instruction is used to return control flow (and optionally
+a value) from a function back to the caller.
+
+There are two forms of the '``ret``' instruction: one that returns a
+value and then causes control flow, and one that just causes control
+flow to occur.
+
+Arguments:
+""""""""""
+
+The '``ret``' instruction optionally accepts a single argument, the
+return value. The type of the return value must be a ':ref:`first
+class <t_firstclass>`' type.
+
+A function is not :ref:`well formed <wellformed>` if it it has a non-void
+return type and contains a '``ret``' instruction with no return value or
+a return value with a type that does not match its type, or if it has a
+void return type and contains a '``ret``' instruction with a return
+value.
+
+Semantics:
+""""""""""
+
+When the '``ret``' instruction is executed, control flow returns back to
+the calling function's context. If the caller is a
+":ref:`call <i_call>`" instruction, execution continues at the
+instruction after the call. If the caller was an
+":ref:`invoke <i_invoke>`" instruction, execution continues at the
+beginning of the "normal" destination block. If the instruction returns
+a value, that value shall set the call or invoke instruction's return
+value.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ ret i32 5 ; Return an integer value of 5
+ ret void ; Return from a void function
+ ret { i32, i8 } { i32 4, i8 2 } ; Return a struct of values 4 and 2
+
+.. _i_br:
+
+'``br``' Instruction
+^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ br i1 <cond>, label <iftrue>, label <iffalse>
+ br label <dest> ; Unconditional branch
+
+Overview:
+"""""""""
+
+The '``br``' instruction is used to cause control flow to transfer to a
+different basic block in the current function. There are two forms of
+this instruction, corresponding to a conditional branch and an
+unconditional branch.
+
+Arguments:
+""""""""""
+
+The conditional branch form of the '``br``' instruction takes a single
+'``i1``' value and two '``label``' values. The unconditional form of the
+'``br``' instruction takes a single '``label``' value as a target.
+
+Semantics:
+""""""""""
+
+Upon execution of a conditional '``br``' instruction, the '``i1``'
+argument is evaluated. If the value is ``true``, control flows to the
+'``iftrue``' ``label`` argument. If "cond" is ``false``, control flows
+to the '``iffalse``' ``label`` argument.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ Test:
+ %cond = icmp eq i32 %a, %b
+ br i1 %cond, label %IfEqual, label %IfUnequal
+ IfEqual:
+ ret i32 1
+ IfUnequal:
+ ret i32 0
+
+.. _i_switch:
+
+'``switch``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ switch <intty> <value>, label <defaultdest> [ <intty> <val>, label <dest> ... ]
+
+Overview:
+"""""""""
+
+The '``switch``' instruction is used to transfer control flow to one of
+several different places. It is a generalization of the '``br``'
+instruction, allowing a branch to occur to one of many possible
+destinations.
+
+Arguments:
+""""""""""
+
+The '``switch``' instruction uses three parameters: an integer
+comparison value '``value``', a default '``label``' destination, and an
+array of pairs of comparison value constants and '``label``'s. The table
+is not allowed to contain duplicate constant entries.
+
+Semantics:
+""""""""""
+
+The ``switch`` instruction specifies a table of values and destinations.
+When the '``switch``' instruction is executed, this table is searched
+for the given value. If the value is found, control flow is transferred
+to the corresponding destination; otherwise, control flow is transferred
+to the default destination.
+
+Implementation:
+"""""""""""""""
+
+Depending on properties of the target machine and the particular
+``switch`` instruction, this instruction may be code generated in
+different ways. For example, it could be generated as a series of
+chained conditional branches or with a lookup table.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ ; Emulate a conditional br instruction
+ %Val = zext i1 %value to i32
+ switch i32 %Val, label %truedest [ i32 0, label %falsedest ]
+
+ ; Emulate an unconditional br instruction
+ switch i32 0, label %dest [ ]
+
+ ; Implement a jump table:
+ switch i32 %val, label %otherwise [ i32 0, label %onzero
+ i32 1, label %onone
+ i32 2, label %ontwo ]
+
+.. _i_indirectbr:
+
+'``indirectbr``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ indirectbr <somety>* <address>, [ label <dest1>, label <dest2>, ... ]
+
+Overview:
+"""""""""
+
+The '``indirectbr``' instruction implements an indirect branch to a
+label within the current function, whose address is specified by
+"``address``". Address must be derived from a
+:ref:`blockaddress <blockaddress>` constant.
+
+Arguments:
+""""""""""
+
+The '``address``' argument is the address of the label to jump to. The
+rest of the arguments indicate the full set of possible destinations
+that the address may point to. Blocks are allowed to occur multiple
+times in the destination list, though this isn't particularly useful.
+
+This destination list is required so that dataflow analysis has an
+accurate understanding of the CFG.
+
+Semantics:
+""""""""""
+
+Control transfers to the block specified in the address argument. All
+possible destination blocks must be listed in the label list, otherwise
+this instruction has undefined behavior. This implies that jumps to
+labels defined in other functions have undefined behavior as well.
+
+Implementation:
+"""""""""""""""
+
+This is typically implemented with a jump through a register.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ indirectbr i8* %Addr, [ label %bb1, label %bb2, label %bb3 ]
+
+.. _i_invoke:
+
+'``invoke``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = invoke [cconv] [ret attrs] <ty>|<fnty> <fnptrval>(<function args>) [fn attrs]
+ [operand bundles] to label <normal label> unwind label <exception label>
+
+Overview:
+"""""""""
+
+The '``invoke``' instruction causes control to transfer to a specified
+function, with the possibility of control flow transfer to either the
+'``normal``' label or the '``exception``' label. If the callee function
+returns with the "``ret``" instruction, control flow will return to the
+"normal" label. If the callee (or any indirect callees) returns via the
+":ref:`resume <i_resume>`" instruction or other exception handling
+mechanism, control is interrupted and continued at the dynamically
+nearest "exception" label.
+
+The '``exception``' label is a `landing
+pad <ExceptionHandling.html#overview>`_ for the exception. As such,
+'``exception``' label is required to have the
+":ref:`landingpad <i_landingpad>`" instruction, which contains the
+information about the behavior of the program after unwinding happens,
+as its first non-PHI instruction. The restrictions on the
+"``landingpad``" instruction's tightly couples it to the "``invoke``"
+instruction, so that the important information contained within the
+"``landingpad``" instruction can't be lost through normal code motion.
+
+Arguments:
+""""""""""
+
+This instruction requires several arguments:
+
+#. The optional "cconv" marker indicates which :ref:`calling
+ convention <callingconv>` the call should use. If none is
+ specified, the call defaults to using C calling conventions.
+#. The optional :ref:`Parameter Attributes <paramattrs>` list for return
+ values. Only '``zeroext``', '``signext``', and '``inreg``' attributes
+ are valid here.
+#. '``ty``': the type of the call instruction itself which is also the
+ type of the return value. Functions that return no value are marked
+ ``void``.
+#. '``fnty``': shall be the signature of the function being invoked. The
+ argument types must match the types implied by this signature. This
+ type can be omitted if the function is not varargs.
+#. '``fnptrval``': An LLVM value containing a pointer to a function to
+ be invoked. In most cases, this is a direct function invocation, but
+ indirect ``invoke``'s are just as possible, calling an arbitrary pointer
+ to function value.
+#. '``function args``': argument list whose types match the function
+ signature argument types and parameter attributes. All arguments must
+ be of :ref:`first class <t_firstclass>` type. If the function signature
+ indicates the function accepts a variable number of arguments, the
+ extra arguments can be specified.
+#. '``normal label``': the label reached when the called function
+ executes a '``ret``' instruction.
+#. '``exception label``': the label reached when a callee returns via
+ the :ref:`resume <i_resume>` instruction or other exception handling
+ mechanism.
+#. The optional :ref:`function attributes <fnattrs>` list.
+#. The optional :ref:`operand bundles <opbundles>` list.
+
+Semantics:
+""""""""""
+
+This instruction is designed to operate as a standard '``call``'
+instruction in most regards. The primary difference is that it
+establishes an association with a label, which is used by the runtime
+library to unwind the stack.
+
+This instruction is used in languages with destructors to ensure that
+proper cleanup is performed in the case of either a ``longjmp`` or a
+thrown exception. Additionally, this is important for implementation of
+'``catch``' clauses in high-level languages that support them.
+
+For the purposes of the SSA form, the definition of the value returned
+by the '``invoke``' instruction is deemed to occur on the edge from the
+current block to the "normal" label. If the callee unwinds then no
+return value is available.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %retval = invoke i32 @Test(i32 15) to label %Continue
+ unwind label %TestCleanup ; i32:retval set
+ %retval = invoke coldcc i32 %Testfnptr(i32 15) to label %Continue
+ unwind label %TestCleanup ; i32:retval set
+
+.. _i_resume:
+
+'``resume``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ resume <type> <value>
+
+Overview:
+"""""""""
+
+The '``resume``' instruction is a terminator instruction that has no
+successors.
+
+Arguments:
+""""""""""
+
+The '``resume``' instruction requires one argument, which must have the
+same type as the result of any '``landingpad``' instruction in the same
+function.
+
+Semantics:
+""""""""""
+
+The '``resume``' instruction resumes propagation of an existing
+(in-flight) exception whose unwinding was interrupted with a
+:ref:`landingpad <i_landingpad>` instruction.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ resume { i8*, i32 } %exn
+
+.. _i_catchswitch:
+
+'``catchswitch``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <resultval> = catchswitch within <parent> [ label <handler1>, label <handler2>, ... ] unwind to caller
+ <resultval> = catchswitch within <parent> [ label <handler1>, label <handler2>, ... ] unwind label <default>
+
+Overview:
+"""""""""
+
+The '``catchswitch``' instruction is used by `LLVM's exception handling system
+<ExceptionHandling.html#overview>`_ to describe the set of possible catch handlers
+that may be executed by the :ref:`EH personality routine <personalityfn>`.
+
+Arguments:
+""""""""""
+
+The ``parent`` argument is the token of the funclet that contains the
+``catchswitch`` instruction. If the ``catchswitch`` is not inside a funclet,
+this operand may be the token ``none``.
+
+The ``default`` argument is the label of another basic block beginning with
+either a ``cleanuppad`` or ``catchswitch`` instruction. This unwind destination
+must be a legal target with respect to the ``parent`` links, as described in
+the `exception handling documentation\ <ExceptionHandling.html#wineh-constraints>`_.
+
+The ``handlers`` are a nonempty list of successor blocks that each begin with a
+:ref:`catchpad <i_catchpad>` instruction.
+
+Semantics:
+""""""""""
+
+Executing this instruction transfers control to one of the successors in
+``handlers``, if appropriate, or continues to unwind via the unwind label if
+present.
+
+The ``catchswitch`` is both a terminator and a "pad" instruction, meaning that
+it must be both the first non-phi instruction and last instruction in the basic
+block. Therefore, it must be the only non-phi instruction in the block.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ dispatch1:
+ %cs1 = catchswitch within none [label %handler0, label %handler1] unwind to caller
+ dispatch2:
+ %cs2 = catchswitch within %parenthandler [label %handler0] unwind label %cleanup
+
+.. _i_catchret:
+
+'``catchret``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ catchret from <token> to label <normal>
+
+Overview:
+"""""""""
+
+The '``catchret``' instruction is a terminator instruction that has a
+single successor.
+
+
+Arguments:
+""""""""""
+
+The first argument to a '``catchret``' indicates which ``catchpad`` it
+exits. It must be a :ref:`catchpad <i_catchpad>`.
+The second argument to a '``catchret``' specifies where control will
+transfer to next.
+
+Semantics:
+""""""""""
+
+The '``catchret``' instruction ends an existing (in-flight) exception whose
+unwinding was interrupted with a :ref:`catchpad <i_catchpad>` instruction. The
+:ref:`personality function <personalityfn>` gets a chance to execute arbitrary
+code to, for example, destroy the active exception. Control then transfers to
+``normal``.
+
+The ``token`` argument must be a token produced by a ``catchpad`` instruction.
+If the specified ``catchpad`` is not the most-recently-entered not-yet-exited
+funclet pad (as described in the `EH documentation\ <ExceptionHandling.html#wineh-constraints>`_),
+the ``catchret``'s behavior is undefined.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ catchret from %catch label %continue
+
+.. _i_cleanupret:
+
+'``cleanupret``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ cleanupret from <value> unwind label <continue>
+ cleanupret from <value> unwind to caller
+
+Overview:
+"""""""""
+
+The '``cleanupret``' instruction is a terminator instruction that has
+an optional successor.
+
+
+Arguments:
+""""""""""
+
+The '``cleanupret``' instruction requires one argument, which indicates
+which ``cleanuppad`` it exits, and must be a :ref:`cleanuppad <i_cleanuppad>`.
+If the specified ``cleanuppad`` is not the most-recently-entered not-yet-exited
+funclet pad (as described in the `EH documentation\ <ExceptionHandling.html#wineh-constraints>`_),
+the ``cleanupret``'s behavior is undefined.
+
+The '``cleanupret``' instruction also has an optional successor, ``continue``,
+which must be the label of another basic block beginning with either a
+``cleanuppad`` or ``catchswitch`` instruction. This unwind destination must
+be a legal target with respect to the ``parent`` links, as described in the
+`exception handling documentation\ <ExceptionHandling.html#wineh-constraints>`_.
+
+Semantics:
+""""""""""
+
+The '``cleanupret``' instruction indicates to the
+:ref:`personality function <personalityfn>` that one
+:ref:`cleanuppad <i_cleanuppad>` it transferred control to has ended.
+It transfers control to ``continue`` or unwinds out of the function.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ cleanupret from %cleanup unwind to caller
+ cleanupret from %cleanup unwind label %continue
+
+.. _i_unreachable:
+
+'``unreachable``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ unreachable
+
+Overview:
+"""""""""
+
+The '``unreachable``' instruction has no defined semantics. This
+instruction is used to inform the optimizer that a particular portion of
+the code is not reachable. This can be used to indicate that the code
+after a no-return function cannot be reached, and other facts.
+
+Semantics:
+""""""""""
+
+The '``unreachable``' instruction has no defined semantics.
+
+.. _binaryops:
+
+Binary Operations
+-----------------
+
+Binary operators are used to do most of the computation in a program.
+They require two operands of the same type, execute an operation on
+them, and produce a single value. The operands might represent multiple
+data, as is the case with the :ref:`vector <t_vector>` data type. The
+result value has the same type as its operands.
+
+There are several different binary operators:
+
+.. _i_add:
+
+'``add``' Instruction
+^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = add <ty> <op1>, <op2> ; yields ty:result
+ <result> = add nuw <ty> <op1>, <op2> ; yields ty:result
+ <result> = add nsw <ty> <op1>, <op2> ; yields ty:result
+ <result> = add nuw nsw <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``add``' instruction returns the sum of its two operands.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``add``' instruction must be
+:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
+arguments must have identical types.
+
+Semantics:
+""""""""""
+
+The value produced is the integer sum of the two operands.
+
+If the sum has unsigned overflow, the result returned is the
+mathematical result modulo 2\ :sup:`n`\ , where n is the bit width of
+the result.
+
+Because LLVM integers use a two's complement representation, this
+instruction is appropriate for both signed and unsigned integers.
+
+``nuw`` and ``nsw`` stand for "No Unsigned Wrap" and "No Signed Wrap",
+respectively. If the ``nuw`` and/or ``nsw`` keywords are present, the
+result value of the ``add`` is a :ref:`poison value <poisonvalues>` if
+unsigned and/or signed overflow, respectively, occurs.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = add i32 4, %var ; yields i32:result = 4 + %var
+
+.. _i_fadd:
+
+'``fadd``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = fadd [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``fadd``' instruction returns the sum of its two operands.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``fadd``' instruction must be :ref:`floating
+point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
+Both arguments must have identical types.
+
+Semantics:
+""""""""""
+
+The value produced is the floating point sum of the two operands. This
+instruction can also take any number of :ref:`fast-math flags <fastmath>`,
+which are optimization hints to enable otherwise unsafe floating point
+optimizations:
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = fadd float 4.0, %var ; yields float:result = 4.0 + %var
+
+'``sub``' Instruction
+^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = sub <ty> <op1>, <op2> ; yields ty:result
+ <result> = sub nuw <ty> <op1>, <op2> ; yields ty:result
+ <result> = sub nsw <ty> <op1>, <op2> ; yields ty:result
+ <result> = sub nuw nsw <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``sub``' instruction returns the difference of its two operands.
+
+Note that the '``sub``' instruction is used to represent the '``neg``'
+instruction present in most other intermediate representations.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``sub``' instruction must be
+:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
+arguments must have identical types.
+
+Semantics:
+""""""""""
+
+The value produced is the integer difference of the two operands.
+
+If the difference has unsigned overflow, the result returned is the
+mathematical result modulo 2\ :sup:`n`\ , where n is the bit width of
+the result.
+
+Because LLVM integers use a two's complement representation, this
+instruction is appropriate for both signed and unsigned integers.
+
+``nuw`` and ``nsw`` stand for "No Unsigned Wrap" and "No Signed Wrap",
+respectively. If the ``nuw`` and/or ``nsw`` keywords are present, the
+result value of the ``sub`` is a :ref:`poison value <poisonvalues>` if
+unsigned and/or signed overflow, respectively, occurs.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = sub i32 4, %var ; yields i32:result = 4 - %var
+ <result> = sub i32 0, %val ; yields i32:result = -%var
+
+.. _i_fsub:
+
+'``fsub``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = fsub [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``fsub``' instruction returns the difference of its two operands.
+
+Note that the '``fsub``' instruction is used to represent the '``fneg``'
+instruction present in most other intermediate representations.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``fsub``' instruction must be :ref:`floating
+point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
+Both arguments must have identical types.
+
+Semantics:
+""""""""""
+
+The value produced is the floating point difference of the two operands.
+This instruction can also take any number of :ref:`fast-math
+flags <fastmath>`, which are optimization hints to enable otherwise
+unsafe floating point optimizations:
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = fsub float 4.0, %var ; yields float:result = 4.0 - %var
+ <result> = fsub float -0.0, %val ; yields float:result = -%var
+
+'``mul``' Instruction
+^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = mul <ty> <op1>, <op2> ; yields ty:result
+ <result> = mul nuw <ty> <op1>, <op2> ; yields ty:result
+ <result> = mul nsw <ty> <op1>, <op2> ; yields ty:result
+ <result> = mul nuw nsw <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``mul``' instruction returns the product of its two operands.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``mul``' instruction must be
+:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
+arguments must have identical types.
+
+Semantics:
+""""""""""
+
+The value produced is the integer product of the two operands.
+
+If the result of the multiplication has unsigned overflow, the result
+returned is the mathematical result modulo 2\ :sup:`n`\ , where n is the
+bit width of the result.
+
+Because LLVM integers use a two's complement representation, and the
+result is the same width as the operands, this instruction returns the
+correct result for both signed and unsigned integers. If a full product
+(e.g. ``i32`` * ``i32`` -> ``i64``) is needed, the operands should be
+sign-extended or zero-extended as appropriate to the width of the full
+product.
+
+``nuw`` and ``nsw`` stand for "No Unsigned Wrap" and "No Signed Wrap",
+respectively. If the ``nuw`` and/or ``nsw`` keywords are present, the
+result value of the ``mul`` is a :ref:`poison value <poisonvalues>` if
+unsigned and/or signed overflow, respectively, occurs.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = mul i32 4, %var ; yields i32:result = 4 * %var
+
+.. _i_fmul:
+
+'``fmul``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = fmul [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``fmul``' instruction returns the product of its two operands.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``fmul``' instruction must be :ref:`floating
+point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
+Both arguments must have identical types.
+
+Semantics:
+""""""""""
+
+The value produced is the floating point product of the two operands.
+This instruction can also take any number of :ref:`fast-math
+flags <fastmath>`, which are optimization hints to enable otherwise
+unsafe floating point optimizations:
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = fmul float 4.0, %var ; yields float:result = 4.0 * %var
+
+'``udiv``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = udiv <ty> <op1>, <op2> ; yields ty:result
+ <result> = udiv exact <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``udiv``' instruction returns the quotient of its two operands.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``udiv``' instruction must be
+:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
+arguments must have identical types.
+
+Semantics:
+""""""""""
+
+The value produced is the unsigned integer quotient of the two operands.
+
+Note that unsigned integer division and signed integer division are
+distinct operations; for signed integer division, use '``sdiv``'.
+
+Division by zero is undefined behavior. For vectors, if any element
+of the divisor is zero, the operation has undefined behavior.
+
+
+If the ``exact`` keyword is present, the result value of the ``udiv`` is
+a :ref:`poison value <poisonvalues>` if %op1 is not a multiple of %op2 (as
+such, "((a udiv exact b) mul b) == a").
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = udiv i32 4, %var ; yields i32:result = 4 / %var
+
+'``sdiv``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = sdiv <ty> <op1>, <op2> ; yields ty:result
+ <result> = sdiv exact <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``sdiv``' instruction returns the quotient of its two operands.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``sdiv``' instruction must be
+:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
+arguments must have identical types.
+
+Semantics:
+""""""""""
+
+The value produced is the signed integer quotient of the two operands
+rounded towards zero.
+
+Note that signed integer division and unsigned integer division are
+distinct operations; for unsigned integer division, use '``udiv``'.
+
+Division by zero is undefined behavior. For vectors, if any element
+of the divisor is zero, the operation has undefined behavior.
+Overflow also leads to undefined behavior; this is a rare case, but can
+occur, for example, by doing a 32-bit division of -2147483648 by -1.
+
+If the ``exact`` keyword is present, the result value of the ``sdiv`` is
+a :ref:`poison value <poisonvalues>` if the result would be rounded.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = sdiv i32 4, %var ; yields i32:result = 4 / %var
+
+.. _i_fdiv:
+
+'``fdiv``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = fdiv [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``fdiv``' instruction returns the quotient of its two operands.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``fdiv``' instruction must be :ref:`floating
+point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
+Both arguments must have identical types.
+
+Semantics:
+""""""""""
+
+The value produced is the floating point quotient of the two operands.
+This instruction can also take any number of :ref:`fast-math
+flags <fastmath>`, which are optimization hints to enable otherwise
+unsafe floating point optimizations:
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = fdiv float 4.0, %var ; yields float:result = 4.0 / %var
+
+'``urem``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = urem <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``urem``' instruction returns the remainder from the unsigned
+division of its two arguments.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``urem``' instruction must be
+:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
+arguments must have identical types.
+
+Semantics:
+""""""""""
+
+This instruction returns the unsigned integer *remainder* of a division.
+This instruction always performs an unsigned division to get the
+remainder.
+
+Note that unsigned integer remainder and signed integer remainder are
+distinct operations; for signed integer remainder, use '``srem``'.
+
+Taking the remainder of a division by zero is undefined behavior.
+For vectors, if any element of the divisor is zero, the operation has
+undefined behavior.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = urem i32 4, %var ; yields i32:result = 4 % %var
+
+'``srem``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = srem <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``srem``' instruction returns the remainder from the signed
+division of its two operands. This instruction can also take
+:ref:`vector <t_vector>` versions of the values in which case the elements
+must be integers.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``srem``' instruction must be
+:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
+arguments must have identical types.
+
+Semantics:
+""""""""""
+
+This instruction returns the *remainder* of a division (where the result
+is either zero or has the same sign as the dividend, ``op1``), not the
+*modulo* operator (where the result is either zero or has the same sign
+as the divisor, ``op2``) of a value. For more information about the
+difference, see `The Math
+Forum <http://mathforum.org/dr.math/problems/anne.4.28.99.html>`_. For a
+table of how this is implemented in various languages, please see
+`Wikipedia: modulo
+operation <http://en.wikipedia.org/wiki/Modulo_operation>`_.
+
+Note that signed integer remainder and unsigned integer remainder are
+distinct operations; for unsigned integer remainder, use '``urem``'.
+
+Taking the remainder of a division by zero is undefined behavior.
+For vectors, if any element of the divisor is zero, the operation has
+undefined behavior.
+Overflow also leads to undefined behavior; this is a rare case, but can
+occur, for example, by taking the remainder of a 32-bit division of
+-2147483648 by -1. (The remainder doesn't actually overflow, but this
+rule lets srem be implemented using instructions that return both the
+result of the division and the remainder.)
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = srem i32 4, %var ; yields i32:result = 4 % %var
+
+.. _i_frem:
+
+'``frem``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = frem [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``frem``' instruction returns the remainder from the division of
+its two operands.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``frem``' instruction must be :ref:`floating
+point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
+Both arguments must have identical types.
+
+Semantics:
+""""""""""
+
+This instruction returns the *remainder* of a division. The remainder
+has the same sign as the dividend. This instruction can also take any
+number of :ref:`fast-math flags <fastmath>`, which are optimization hints
+to enable otherwise unsafe floating point optimizations:
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = frem float 4.0, %var ; yields float:result = 4.0 % %var
+
+.. _bitwiseops:
+
+Bitwise Binary Operations
+-------------------------
+
+Bitwise binary operators are used to do various forms of bit-twiddling
+in a program. They are generally very efficient instructions and can
+commonly be strength reduced from other instructions. They require two
+operands of the same type, execute an operation on them, and produce a
+single value. The resulting value is the same type as its operands.
+
+'``shl``' Instruction
+^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = shl <ty> <op1>, <op2> ; yields ty:result
+ <result> = shl nuw <ty> <op1>, <op2> ; yields ty:result
+ <result> = shl nsw <ty> <op1>, <op2> ; yields ty:result
+ <result> = shl nuw nsw <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``shl``' instruction returns the first operand shifted to the left
+a specified number of bits.
+
+Arguments:
+""""""""""
+
+Both arguments to the '``shl``' instruction must be the same
+:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer type.
+'``op2``' is treated as an unsigned value.
+
+Semantics:
+""""""""""
+
+The value produced is ``op1`` \* 2\ :sup:`op2` mod 2\ :sup:`n`,
+where ``n`` is the width of the result. If ``op2`` is (statically or
+dynamically) equal to or larger than the number of bits in
+``op1``, this instruction returns a :ref:`poison value <poisonvalues>`.
+If the arguments are vectors, each vector element of ``op1`` is shifted
+by the corresponding shift amount in ``op2``.
+
+If the ``nuw`` keyword is present, then the shift produces a poison
+value if it shifts out any non-zero bits.
+If the ``nsw`` keyword is present, then the shift produces a poison
+value it shifts out any bits that disagree with the resultant sign bit.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = shl i32 4, %var ; yields i32: 4 << %var
+ <result> = shl i32 4, 2 ; yields i32: 16
+ <result> = shl i32 1, 10 ; yields i32: 1024
+ <result> = shl i32 1, 32 ; undefined
+ <result> = shl <2 x i32> < i32 1, i32 1>, < i32 1, i32 2> ; yields: result=<2 x i32> < i32 2, i32 4>
+
+'``lshr``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = lshr <ty> <op1>, <op2> ; yields ty:result
+ <result> = lshr exact <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``lshr``' instruction (logical shift right) returns the first
+operand shifted to the right a specified number of bits with zero fill.
+
+Arguments:
+""""""""""
+
+Both arguments to the '``lshr``' instruction must be the same
+:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer type.
+'``op2``' is treated as an unsigned value.
+
+Semantics:
+""""""""""
+
+This instruction always performs a logical shift right operation. The
+most significant bits of the result will be filled with zero bits after
+the shift. If ``op2`` is (statically or dynamically) equal to or larger
+than the number of bits in ``op1``, this instruction returns a :ref:`poison
+value <poisonvalues>`. If the arguments are vectors, each vector element
+of ``op1`` is shifted by the corresponding shift amount in ``op2``.
+
+If the ``exact`` keyword is present, the result value of the ``lshr`` is
+a poison value if any of the bits shifted out are non-zero.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = lshr i32 4, 1 ; yields i32:result = 2
+ <result> = lshr i32 4, 2 ; yields i32:result = 1
+ <result> = lshr i8 4, 3 ; yields i8:result = 0
+ <result> = lshr i8 -2, 1 ; yields i8:result = 0x7F
+ <result> = lshr i32 1, 32 ; undefined
+ <result> = lshr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 2> ; yields: result=<2 x i32> < i32 0x7FFFFFFF, i32 1>
+
+'``ashr``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = ashr <ty> <op1>, <op2> ; yields ty:result
+ <result> = ashr exact <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``ashr``' instruction (arithmetic shift right) returns the first
+operand shifted to the right a specified number of bits with sign
+extension.
+
+Arguments:
+""""""""""
+
+Both arguments to the '``ashr``' instruction must be the same
+:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer type.
+'``op2``' is treated as an unsigned value.
+
+Semantics:
+""""""""""
+
+This instruction always performs an arithmetic shift right operation,
+The most significant bits of the result will be filled with the sign bit
+of ``op1``. If ``op2`` is (statically or dynamically) equal to or larger
+than the number of bits in ``op1``, this instruction returns a :ref:`poison
+value <poisonvalues>`. If the arguments are vectors, each vector element
+of ``op1`` is shifted by the corresponding shift amount in ``op2``.
+
+If the ``exact`` keyword is present, the result value of the ``ashr`` is
+a poison value if any of the bits shifted out are non-zero.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = ashr i32 4, 1 ; yields i32:result = 2
+ <result> = ashr i32 4, 2 ; yields i32:result = 1
+ <result> = ashr i8 4, 3 ; yields i8:result = 0
+ <result> = ashr i8 -2, 1 ; yields i8:result = -1
+ <result> = ashr i32 1, 32 ; undefined
+ <result> = ashr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 3> ; yields: result=<2 x i32> < i32 -1, i32 0>
+
+'``and``' Instruction
+^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = and <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``and``' instruction returns the bitwise logical and of its two
+operands.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``and``' instruction must be
+:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
+arguments must have identical types.
+
+Semantics:
+""""""""""
+
+The truth table used for the '``and``' instruction is:
+
++-----+-----+-----+
+| In0 | In1 | Out |
++-----+-----+-----+
+| 0 | 0 | 0 |
++-----+-----+-----+
+| 0 | 1 | 0 |
++-----+-----+-----+
+| 1 | 0 | 0 |
++-----+-----+-----+
+| 1 | 1 | 1 |
++-----+-----+-----+
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = and i32 4, %var ; yields i32:result = 4 & %var
+ <result> = and i32 15, 40 ; yields i32:result = 8
+ <result> = and i32 4, 8 ; yields i32:result = 0
+
+'``or``' Instruction
+^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = or <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``or``' instruction returns the bitwise logical inclusive or of its
+two operands.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``or``' instruction must be
+:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
+arguments must have identical types.
+
+Semantics:
+""""""""""
+
+The truth table used for the '``or``' instruction is:
+
++-----+-----+-----+
+| In0 | In1 | Out |
++-----+-----+-----+
+| 0 | 0 | 0 |
++-----+-----+-----+
+| 0 | 1 | 1 |
++-----+-----+-----+
+| 1 | 0 | 1 |
++-----+-----+-----+
+| 1 | 1 | 1 |
++-----+-----+-----+
+
+Example:
+""""""""
+
+::
+
+ <result> = or i32 4, %var ; yields i32:result = 4 | %var
+ <result> = or i32 15, 40 ; yields i32:result = 47
+ <result> = or i32 4, 8 ; yields i32:result = 12
+
+'``xor``' Instruction
+^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = xor <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``xor``' instruction returns the bitwise logical exclusive or of
+its two operands. The ``xor`` is used to implement the "one's
+complement" operation, which is the "~" operator in C.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``xor``' instruction must be
+:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
+arguments must have identical types.
+
+Semantics:
+""""""""""
+
+The truth table used for the '``xor``' instruction is:
+
++-----+-----+-----+
+| In0 | In1 | Out |
++-----+-----+-----+
+| 0 | 0 | 0 |
++-----+-----+-----+
+| 0 | 1 | 1 |
++-----+-----+-----+
+| 1 | 0 | 1 |
++-----+-----+-----+
+| 1 | 1 | 0 |
++-----+-----+-----+
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = xor i32 4, %var ; yields i32:result = 4 ^ %var
+ <result> = xor i32 15, 40 ; yields i32:result = 39
+ <result> = xor i32 4, 8 ; yields i32:result = 12
+ <result> = xor i32 %V, -1 ; yields i32:result = ~%V
+
+Vector Operations
+-----------------
+
+LLVM supports several instructions to represent vector operations in a
+target-independent manner. These instructions cover the element-access
+and vector-specific operations needed to process vectors effectively.
+While LLVM does directly support these vector operations, many
+sophisticated algorithms will want to use target-specific intrinsics to
+take full advantage of a specific target.
+
+.. _i_extractelement:
+
+'``extractelement``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = extractelement <n x <ty>> <val>, <ty2> <idx> ; yields <ty>
+
+Overview:
+"""""""""
+
+The '``extractelement``' instruction extracts a single scalar element
+from a vector at a specified index.
+
+Arguments:
+""""""""""
+
+The first operand of an '``extractelement``' instruction is a value of
+:ref:`vector <t_vector>` type. The second operand is an index indicating
+the position from which to extract the element. The index may be a
+variable of any integer type.
+
+Semantics:
+""""""""""
+
+The result is a scalar of the same type as the element type of ``val``.
+Its value is the value at position ``idx`` of ``val``. If ``idx``
+exceeds the length of ``val``, the results are undefined.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = extractelement <4 x i32> %vec, i32 0 ; yields i32
+
+.. _i_insertelement:
+
+'``insertelement``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = insertelement <n x <ty>> <val>, <ty> <elt>, <ty2> <idx> ; yields <n x <ty>>
+
+Overview:
+"""""""""
+
+The '``insertelement``' instruction inserts a scalar element into a
+vector at a specified index.
+
+Arguments:
+""""""""""
+
+The first operand of an '``insertelement``' instruction is a value of
+:ref:`vector <t_vector>` type. The second operand is a scalar value whose
+type must equal the element type of the first operand. The third operand
+is an index indicating the position at which to insert the value. The
+index may be a variable of any integer type.
+
+Semantics:
+""""""""""
+
+The result is a vector of the same type as ``val``. Its element values
+are those of ``val`` except at position ``idx``, where it gets the value
+``elt``. If ``idx`` exceeds the length of ``val``, the results are
+undefined.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = insertelement <4 x i32> %vec, i32 1, i32 0 ; yields <4 x i32>
+
+.. _i_shufflevector:
+
+'``shufflevector``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = shufflevector <n x <ty>> <v1>, <n x <ty>> <v2>, <m x i32> <mask> ; yields <m x <ty>>
+
+Overview:
+"""""""""
+
+The '``shufflevector``' instruction constructs a permutation of elements
+from two input vectors, returning a vector with the same element type as
+the input and length that is the same as the shuffle mask.
+
+Arguments:
+""""""""""
+
+The first two operands of a '``shufflevector``' instruction are vectors
+with the same type. The third argument is a shuffle mask whose element
+type is always 'i32'. The result of the instruction is a vector whose
+length is the same as the shuffle mask and whose element type is the
+same as the element type of the first two operands.
+
+The shuffle mask operand is required to be a constant vector with either
+constant integer or undef values.
+
+Semantics:
+""""""""""
+
+The elements of the two input vectors are numbered from left to right
+across both of the vectors. The shuffle mask operand specifies, for each
+element of the result vector, which element of the two input vectors the
+result element gets. If the shuffle mask is undef, the result vector is
+undef. If any element of the mask operand is undef, that element of the
+result is undef. If the shuffle mask selects an undef element from one
+of the input vectors, the resulting element is undef.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = shufflevector <4 x i32> %v1, <4 x i32> %v2,
+ <4 x i32> <i32 0, i32 4, i32 1, i32 5> ; yields <4 x i32>
+ <result> = shufflevector <4 x i32> %v1, <4 x i32> undef,
+ <4 x i32> <i32 0, i32 1, i32 2, i32 3> ; yields <4 x i32> - Identity shuffle.
+ <result> = shufflevector <8 x i32> %v1, <8 x i32> undef,
+ <4 x i32> <i32 0, i32 1, i32 2, i32 3> ; yields <4 x i32>
+ <result> = shufflevector <4 x i32> %v1, <4 x i32> %v2,
+ <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7 > ; yields <8 x i32>
+
+Aggregate Operations
+--------------------
+
+LLVM supports several instructions for working with
+:ref:`aggregate <t_aggregate>` values.
+
+.. _i_extractvalue:
+
+'``extractvalue``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = extractvalue <aggregate type> <val>, <idx>{, <idx>}*
+
+Overview:
+"""""""""
+
+The '``extractvalue``' instruction extracts the value of a member field
+from an :ref:`aggregate <t_aggregate>` value.
+
+Arguments:
+""""""""""
+
+The first operand of an '``extractvalue``' instruction is a value of
+:ref:`struct <t_struct>` or :ref:`array <t_array>` type. The other operands are
+constant indices to specify which value to extract in a similar manner
+as indices in a '``getelementptr``' instruction.
+
+The major differences to ``getelementptr`` indexing are:
+
+- Since the value being indexed is not a pointer, the first index is
+ omitted and assumed to be zero.
+- At least one index must be specified.
+- Not only struct indices but also array indices must be in bounds.
+
+Semantics:
+""""""""""
+
+The result is the value at the position in the aggregate specified by
+the index operands.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = extractvalue {i32, float} %agg, 0 ; yields i32
+
+.. _i_insertvalue:
+
+'``insertvalue``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = insertvalue <aggregate type> <val>, <ty> <elt>, <idx>{, <idx>}* ; yields <aggregate type>
+
+Overview:
+"""""""""
+
+The '``insertvalue``' instruction inserts a value into a member field in
+an :ref:`aggregate <t_aggregate>` value.
+
+Arguments:
+""""""""""
+
+The first operand of an '``insertvalue``' instruction is a value of
+:ref:`struct <t_struct>` or :ref:`array <t_array>` type. The second operand is
+a first-class value to insert. The following operands are constant
+indices indicating the position at which to insert the value in a
+similar manner as indices in a '``extractvalue``' instruction. The value
+to insert must have the same type as the value identified by the
+indices.
+
+Semantics:
+""""""""""
+
+The result is an aggregate of the same type as ``val``. Its value is
+that of ``val`` except that the value at the position specified by the
+indices is that of ``elt``.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %agg1 = insertvalue {i32, float} undef, i32 1, 0 ; yields {i32 1, float undef}
+ %agg2 = insertvalue {i32, float} %agg1, float %val, 1 ; yields {i32 1, float %val}
+ %agg3 = insertvalue {i32, {float}} undef, float %val, 1, 0 ; yields {i32 undef, {float %val}}
+
+.. _memoryops:
+
+Memory Access and Addressing Operations
+---------------------------------------
+
+A key design point of an SSA-based representation is how it represents
+memory. In LLVM, no memory locations are in SSA form, which makes things
+very simple. This section describes how to read, write, and allocate
+memory in LLVM.
+
+.. _i_alloca:
+
+'``alloca``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = alloca [inalloca] <type> [, <ty> <NumElements>] [, align <alignment>] [, addrspace(<num>)] ; yields type addrspace(num)*:result
+
+Overview:
+"""""""""
+
+The '``alloca``' instruction allocates memory on the stack frame of the
+currently executing function, to be automatically released when this
+function returns to its caller. The object is always allocated in the
+address space for allocas indicated in the datalayout.
+
+Arguments:
+""""""""""
+
+The '``alloca``' instruction allocates ``sizeof(<type>)*NumElements``
+bytes of memory on the runtime stack, returning a pointer of the
+appropriate type to the program. If "NumElements" is specified, it is
+the number of elements allocated, otherwise "NumElements" is defaulted
+to be one. If a constant alignment is specified, the value result of the
+allocation is guaranteed to be aligned to at least that boundary. The
+alignment may not be greater than ``1 << 29``. If not specified, or if
+zero, the target can choose to align the allocation on any convenient
+boundary compatible with the type.
+
+'``type``' may be any sized type.
+
+Semantics:
+""""""""""
+
+Memory is allocated; a pointer is returned. The operation is undefined
+if there is insufficient stack space for the allocation. '``alloca``'d
+memory is automatically released when the function returns. The
+'``alloca``' instruction is commonly used to represent automatic
+variables that must have an address available. When the function returns
+(either with the ``ret`` or ``resume`` instructions), the memory is
+reclaimed. Allocating zero bytes is legal, but the result is undefined.
+The order in which memory is allocated (ie., which way the stack grows)
+is not specified.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %ptr = alloca i32 ; yields i32*:ptr
+ %ptr = alloca i32, i32 4 ; yields i32*:ptr
+ %ptr = alloca i32, i32 4, align 1024 ; yields i32*:ptr
+ %ptr = alloca i32, align 1024 ; yields i32*:ptr
+
+.. _i_load:
+
+'``load``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = load [volatile] <ty>, <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>][, !invariant.load !<index>][, !invariant.group !<index>][, !nonnull !<index>][, !dereferenceable !<deref_bytes_node>][, !dereferenceable_or_null !<deref_bytes_node>][, !align !<align_node>]
+ <result> = load atomic [volatile] <ty>, <ty>* <pointer> [syncscope("<target-scope>")] <ordering>, align <alignment> [, !invariant.group !<index>]
+ !<index> = !{ i32 1 }
+ !<deref_bytes_node> = !{i64 <dereferenceable_bytes>}
+ !<align_node> = !{ i64 <value_alignment> }
+
+Overview:
+"""""""""
+
+The '``load``' instruction is used to read from memory.
+
+Arguments:
+""""""""""
+
+The argument to the ``load`` instruction specifies the memory address from which
+to load. The type specified must be a :ref:`first class <t_firstclass>` type of
+known size (i.e. not containing an :ref:`opaque structural type <t_opaque>`). If
+the ``load`` is marked as ``volatile``, then the optimizer is not allowed to
+modify the number or order of execution of this ``load`` with other
+:ref:`volatile operations <volatile>`.
+
+If the ``load`` is marked as ``atomic``, it takes an extra :ref:`ordering
+<ordering>` and optional ``syncscope("<target-scope>")`` argument. The
+``release`` and ``acq_rel`` orderings are not valid on ``load`` instructions.
+Atomic loads produce :ref:`defined <memmodel>` results when they may see
+multiple atomic stores. The type of the pointee must be an integer, pointer, or
+floating-point type whose bit width is a power of two greater than or equal to
+eight and less than or equal to a target-specific size limit. ``align`` must be
+explicitly specified on atomic loads, and the load has undefined behavior if the
+alignment is not set to a value which is at least the size in bytes of the
+pointee. ``!nontemporal`` does not have any defined semantics for atomic loads.
+
+The optional constant ``align`` argument specifies the alignment of the
+operation (that is, the alignment of the memory address). A value of 0
+or an omitted ``align`` argument means that the operation has the ABI
+alignment for the target. It is the responsibility of the code emitter
+to ensure that the alignment information is correct. Overestimating the
+alignment results in undefined behavior. Underestimating the alignment
+may produce less efficient code. An alignment of 1 is always safe. The
+maximum possible alignment is ``1 << 29``. An alignment value higher
+than the size of the loaded type implies memory up to the alignment
+value bytes can be safely loaded without trapping in the default
+address space. Access of the high bytes can interfere with debugging
+tools, so should not be accessed if the function has the
+``sanitize_thread`` or ``sanitize_address`` attributes.
+
+The optional ``!nontemporal`` metadata must reference a single
+metadata name ``<index>`` corresponding to a metadata node with one
+``i32`` entry of value 1. The existence of the ``!nontemporal``
+metadata on the instruction tells the optimizer and code generator
+that this load is not expected to be reused in the cache. The code
+generator may select special instructions to save cache bandwidth, such
+as the ``MOVNT`` instruction on x86.
+
+The optional ``!invariant.load`` metadata must reference a single
+metadata name ``<index>`` corresponding to a metadata node with no
+entries. If a load instruction tagged with the ``!invariant.load``
+metadata is executed, the optimizer may assume the memory location
+referenced by the load contains the same value at all points in the
+program where the memory location is known to be dereferenceable.
+
+The optional ``!invariant.group`` metadata must reference a single metadata name
+ ``<index>`` corresponding to a metadata node. See ``invariant.group`` metadata.
+
+The optional ``!nonnull`` metadata must reference a single
+metadata name ``<index>`` corresponding to a metadata node with no
+entries. The existence of the ``!nonnull`` metadata on the
+instruction tells the optimizer that the value loaded is known to
+never be null. This is analogous to the ``nonnull`` attribute
+on parameters and return values. This metadata can only be applied
+to loads of a pointer type.
+
+The optional ``!dereferenceable`` metadata must reference a single metadata
+name ``<deref_bytes_node>`` corresponding to a metadata node with one ``i64``
+entry. The existence of the ``!dereferenceable`` metadata on the instruction
+tells the optimizer that the value loaded is known to be dereferenceable.
+The number of bytes known to be dereferenceable is specified by the integer
+value in the metadata node. This is analogous to the ''dereferenceable''
+attribute on parameters and return values. This metadata can only be applied
+to loads of a pointer type.
+
+The optional ``!dereferenceable_or_null`` metadata must reference a single
+metadata name ``<deref_bytes_node>`` corresponding to a metadata node with one
+``i64`` entry. The existence of the ``!dereferenceable_or_null`` metadata on the
+instruction tells the optimizer that the value loaded is known to be either
+dereferenceable or null.
+The number of bytes known to be dereferenceable is specified by the integer
+value in the metadata node. This is analogous to the ''dereferenceable_or_null''
+attribute on parameters and return values. This metadata can only be applied
+to loads of a pointer type.
+
+The optional ``!align`` metadata must reference a single metadata name
+``<align_node>`` corresponding to a metadata node with one ``i64`` entry.
+The existence of the ``!align`` metadata on the instruction tells the
+optimizer that the value loaded is known to be aligned to a boundary specified
+by the integer value in the metadata node. The alignment must be a power of 2.
+This is analogous to the ''align'' attribute on parameters and return values.
+This metadata can only be applied to loads of a pointer type.
+
+Semantics:
+""""""""""
+
+The location of memory pointed to is loaded. If the value being loaded
+is of scalar type then the number of bytes read does not exceed the
+minimum number of bytes needed to hold all bits of the type. For
+example, loading an ``i24`` reads at most three bytes. When loading a
+value of a type like ``i20`` with a size that is not an integral number
+of bytes, the result is undefined if the value was not originally
+written using a store of the same type.
+
+Examples:
+"""""""""
+
+.. code-block:: llvm
+
+ %ptr = alloca i32 ; yields i32*:ptr
+ store i32 3, i32* %ptr ; yields void
+ %val = load i32, i32* %ptr ; yields i32:val = i32 3
+
+.. _i_store:
+
+'``store``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ store [volatile] <ty> <value>, <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>][, !invariant.group !<index>] ; yields void
+ store atomic [volatile] <ty> <value>, <ty>* <pointer> [syncscope("<target-scope>")] <ordering>, align <alignment> [, !invariant.group !<index>] ; yields void
+
+Overview:
+"""""""""
+
+The '``store``' instruction is used to write to memory.
+
+Arguments:
+""""""""""
+
+There are two arguments to the ``store`` instruction: a value to store and an
+address at which to store it. The type of the ``<pointer>`` operand must be a
+pointer to the :ref:`first class <t_firstclass>` type of the ``<value>``
+operand. If the ``store`` is marked as ``volatile``, then the optimizer is not
+allowed to modify the number or order of execution of this ``store`` with other
+:ref:`volatile operations <volatile>`. Only values of :ref:`first class
+<t_firstclass>` types of known size (i.e. not containing an :ref:`opaque
+structural type <t_opaque>`) can be stored.
+
+If the ``store`` is marked as ``atomic``, it takes an extra :ref:`ordering
+<ordering>` and optional ``syncscope("<target-scope>")`` argument. The
+``acquire`` and ``acq_rel`` orderings aren't valid on ``store`` instructions.
+Atomic loads produce :ref:`defined <memmodel>` results when they may see
+multiple atomic stores. The type of the pointee must be an integer, pointer, or
+floating-point type whose bit width is a power of two greater than or equal to
+eight and less than or equal to a target-specific size limit. ``align`` must be
+explicitly specified on atomic stores, and the store has undefined behavior if
+the alignment is not set to a value which is at least the size in bytes of the
+pointee. ``!nontemporal`` does not have any defined semantics for atomic stores.
+
+The optional constant ``align`` argument specifies the alignment of the
+operation (that is, the alignment of the memory address). A value of 0
+or an omitted ``align`` argument means that the operation has the ABI
+alignment for the target. It is the responsibility of the code emitter
+to ensure that the alignment information is correct. Overestimating the
+alignment results in undefined behavior. Underestimating the
+alignment may produce less efficient code. An alignment of 1 is always
+safe. The maximum possible alignment is ``1 << 29``. An alignment
+value higher than the size of the stored type implies memory up to the
+alignment value bytes can be stored to without trapping in the default
+address space. Storing to the higher bytes however may result in data
+races if another thread can access the same address. Introducing a
+data race is not allowed. Storing to the extra bytes is not allowed
+even in situations where a data race is known to not exist if the
+function has the ``sanitize_address`` attribute.
+
+The optional ``!nontemporal`` metadata must reference a single metadata
+name ``<index>`` corresponding to a metadata node with one ``i32`` entry of
+value 1. The existence of the ``!nontemporal`` metadata on the instruction
+tells the optimizer and code generator that this load is not expected to
+be reused in the cache. The code generator may select special
+instructions to save cache bandwidth, such as the ``MOVNT`` instruction on
+x86.
+
+The optional ``!invariant.group`` metadata must reference a
+single metadata name ``<index>``. See ``invariant.group`` metadata.
+
+Semantics:
+""""""""""
+
+The contents of memory are updated to contain ``<value>`` at the
+location specified by the ``<pointer>`` operand. If ``<value>`` is
+of scalar type then the number of bytes written does not exceed the
+minimum number of bytes needed to hold all bits of the type. For
+example, storing an ``i24`` writes at most three bytes. When writing a
+value of a type like ``i20`` with a size that is not an integral number
+of bytes, it is unspecified what happens to the extra bits that do not
+belong to the type, but they will typically be overwritten.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %ptr = alloca i32 ; yields i32*:ptr
+ store i32 3, i32* %ptr ; yields void
+ %val = load i32, i32* %ptr ; yields i32:val = i32 3
+
+.. _i_fence:
+
+'``fence``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ fence [syncscope("<target-scope>")] <ordering> ; yields void
+
+Overview:
+"""""""""
+
+The '``fence``' instruction is used to introduce happens-before edges
+between operations.
+
+Arguments:
+""""""""""
+
+'``fence``' instructions take an :ref:`ordering <ordering>` argument which
+defines what *synchronizes-with* edges they add. They can only be given
+``acquire``, ``release``, ``acq_rel``, and ``seq_cst`` orderings.
+
+Semantics:
+""""""""""
+
+A fence A which has (at least) ``release`` ordering semantics
+*synchronizes with* a fence B with (at least) ``acquire`` ordering
+semantics if and only if there exist atomic operations X and Y, both
+operating on some atomic object M, such that A is sequenced before X, X
+modifies M (either directly or through some side effect of a sequence
+headed by X), Y is sequenced before B, and Y observes M. This provides a
+*happens-before* dependency between A and B. Rather than an explicit
+``fence``, one (but not both) of the atomic operations X or Y might
+provide a ``release`` or ``acquire`` (resp.) ordering constraint and
+still *synchronize-with* the explicit ``fence`` and establish the
+*happens-before* edge.
+
+A ``fence`` which has ``seq_cst`` ordering, in addition to having both
+``acquire`` and ``release`` semantics specified above, participates in
+the global program order of other ``seq_cst`` operations and/or fences.
+
+A ``fence`` instruction can also take an optional
+":ref:`syncscope <syncscope>`" argument.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ fence acquire ; yields void
+ fence syncscope("singlethread") seq_cst ; yields void
+ fence syncscope("agent") seq_cst ; yields void
+
+.. _i_cmpxchg:
+
+'``cmpxchg``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ cmpxchg [weak] [volatile] <ty>* <pointer>, <ty> <cmp>, <ty> <new> [syncscope("<target-scope>")] <success ordering> <failure ordering> ; yields { ty, i1 }
+
+Overview:
+"""""""""
+
+The '``cmpxchg``' instruction is used to atomically modify memory. It
+loads a value in memory and compares it to a given value. If they are
+equal, it tries to store a new value into the memory.
+
+Arguments:
+""""""""""
+
+There are three arguments to the '``cmpxchg``' instruction: an address
+to operate on, a value to compare to the value currently be at that
+address, and a new value to place at that address if the compared values
+are equal. The type of '<cmp>' must be an integer or pointer type whose
+bit width is a power of two greater than or equal to eight and less
+than or equal to a target-specific size limit. '<cmp>' and '<new>' must
+have the same type, and the type of '<pointer>' must be a pointer to
+that type. If the ``cmpxchg`` is marked as ``volatile``, then the
+optimizer is not allowed to modify the number or order of execution of
+this ``cmpxchg`` with other :ref:`volatile operations <volatile>`.
+
+The success and failure :ref:`ordering <ordering>` arguments specify how this
+``cmpxchg`` synchronizes with other atomic operations. Both ordering parameters
+must be at least ``monotonic``, the ordering constraint on failure must be no
+stronger than that on success, and the failure ordering cannot be either
+``release`` or ``acq_rel``.
+
+A ``cmpxchg`` instruction can also take an optional
+":ref:`syncscope <syncscope>`" argument.
+
+The pointer passed into cmpxchg must have alignment greater than or
+equal to the size in memory of the operand.
+
+Semantics:
+""""""""""
+
+The contents of memory at the location specified by the '``<pointer>``' operand
+is read and compared to '``<cmp>``'; if the read value is the equal, the
+'``<new>``' is written. The original value at the location is returned, together
+with a flag indicating success (true) or failure (false).
+
+If the cmpxchg operation is marked as ``weak`` then a spurious failure is
+permitted: the operation may not write ``<new>`` even if the comparison
+matched.
+
+If the cmpxchg operation is strong (the default), the i1 value is 1 if and only
+if the value loaded equals ``cmp``.
+
+A successful ``cmpxchg`` is a read-modify-write instruction for the purpose of
+identifying release sequences. A failed ``cmpxchg`` is equivalent to an atomic
+load with an ordering parameter determined the second ordering parameter.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ entry:
+ %orig = load atomic i32, i32* %ptr unordered, align 4 ; yields i32
+ br label %loop
+
+ loop:
+ %cmp = phi i32 [ %orig, %entry ], [%value_loaded, %loop]
+ %squared = mul i32 %cmp, %cmp
+ %val_success = cmpxchg i32* %ptr, i32 %cmp, i32 %squared acq_rel monotonic ; yields { i32, i1 }
+ %value_loaded = extractvalue { i32, i1 } %val_success, 0
+ %success = extractvalue { i32, i1 } %val_success, 1
+ br i1 %success, label %done, label %loop
+
+ done:
+ ...
+
+.. _i_atomicrmw:
+
+'``atomicrmw``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ atomicrmw [volatile] <operation> <ty>* <pointer>, <ty> <value> [syncscope("<target-scope>")] <ordering> ; yields ty
+
+Overview:
+"""""""""
+
+The '``atomicrmw``' instruction is used to atomically modify memory.
+
+Arguments:
+""""""""""
+
+There are three arguments to the '``atomicrmw``' instruction: an
+operation to apply, an address whose value to modify, an argument to the
+operation. The operation must be one of the following keywords:
+
+- xchg
+- add
+- sub
+- and
+- nand
+- or
+- xor
+- max
+- min
+- umax
+- umin
+
+The type of '<value>' must be an integer type whose bit width is a power
+of two greater than or equal to eight and less than or equal to a
+target-specific size limit. The type of the '``<pointer>``' operand must
+be a pointer to that type. If the ``atomicrmw`` is marked as
+``volatile``, then the optimizer is not allowed to modify the number or
+order of execution of this ``atomicrmw`` with other :ref:`volatile
+operations <volatile>`.
+
+A ``atomicrmw`` instruction can also take an optional
+":ref:`syncscope <syncscope>`" argument.
+
+Semantics:
+""""""""""
+
+The contents of memory at the location specified by the '``<pointer>``'
+operand are atomically read, modified, and written back. The original
+value at the location is returned. The modification is specified by the
+operation argument:
+
+- xchg: ``*ptr = val``
+- add: ``*ptr = *ptr + val``
+- sub: ``*ptr = *ptr - val``
+- and: ``*ptr = *ptr & val``
+- nand: ``*ptr = ~(*ptr & val)``
+- or: ``*ptr = *ptr | val``
+- xor: ``*ptr = *ptr ^ val``
+- max: ``*ptr = *ptr > val ? *ptr : val`` (using a signed comparison)
+- min: ``*ptr = *ptr < val ? *ptr : val`` (using a signed comparison)
+- umax: ``*ptr = *ptr > val ? *ptr : val`` (using an unsigned
+ comparison)
+- umin: ``*ptr = *ptr < val ? *ptr : val`` (using an unsigned
+ comparison)
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %old = atomicrmw add i32* %ptr, i32 1 acquire ; yields i32
+
+.. _i_getelementptr:
+
+'``getelementptr``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = getelementptr <ty>, <ty>* <ptrval>{, [inrange] <ty> <idx>}*
+ <result> = getelementptr inbounds <ty>, <ty>* <ptrval>{, [inrange] <ty> <idx>}*
+ <result> = getelementptr <ty>, <ptr vector> <ptrval>, [inrange] <vector index type> <idx>
+
+Overview:
+"""""""""
+
+The '``getelementptr``' instruction is used to get the address of a
+subelement of an :ref:`aggregate <t_aggregate>` data structure. It performs
+address calculation only and does not access memory. The instruction can also
+be used to calculate a vector of such addresses.
+
+Arguments:
+""""""""""
+
+The first argument is always a type used as the basis for the calculations.
+The second argument is always a pointer or a vector of pointers, and is the
+base address to start from. The remaining arguments are indices
+that indicate which of the elements of the aggregate object are indexed.
+The interpretation of each index is dependent on the type being indexed
+into. The first index always indexes the pointer value given as the
+second argument, the second index indexes a value of the type pointed to
+(not necessarily the value directly pointed to, since the first index
+can be non-zero), etc. The first type indexed into must be a pointer
+value, subsequent types can be arrays, vectors, and structs. Note that
+subsequent types being indexed into can never be pointers, since that
+would require loading the pointer before continuing calculation.
+
+The type of each index argument depends on the type it is indexing into.
+When indexing into a (optionally packed) structure, only ``i32`` integer
+**constants** are allowed (when using a vector of indices they must all
+be the **same** ``i32`` integer constant). When indexing into an array,
+pointer or vector, integers of any width are allowed, and they are not
+required to be constant. These integers are treated as signed values
+where relevant.
+
+For example, let's consider a C code fragment and how it gets compiled
+to LLVM:
+
+.. code-block:: c
+
+ struct RT {
+ char A;
+ int B[10][20];
+ char C;
+ };
+ struct ST {
+ int X;
+ double Y;
+ struct RT Z;
+ };
+
+ int *foo(struct ST *s) {
+ return &s[1].Z.B[5][13];
+ }
+
+The LLVM code generated by Clang is:
+
+.. code-block:: llvm
+
+ %struct.RT = type { i8, [10 x [20 x i32]], i8 }
+ %struct.ST = type { i32, double, %struct.RT }
+
+ define i32* @foo(%struct.ST* %s) nounwind uwtable readnone optsize ssp {
+ entry:
+ %arrayidx = getelementptr inbounds %struct.ST, %struct.ST* %s, i64 1, i32 2, i32 1, i64 5, i64 13
+ ret i32* %arrayidx
+ }
+
+Semantics:
+""""""""""
+
+In the example above, the first index is indexing into the
+'``%struct.ST*``' type, which is a pointer, yielding a '``%struct.ST``'
+= '``{ i32, double, %struct.RT }``' type, a structure. The second index
+indexes into the third element of the structure, yielding a
+'``%struct.RT``' = '``{ i8 , [10 x [20 x i32]], i8 }``' type, another
+structure. The third index indexes into the second element of the
+structure, yielding a '``[10 x [20 x i32]]``' type, an array. The two
+dimensions of the array are subscripted into, yielding an '``i32``'
+type. The '``getelementptr``' instruction returns a pointer to this
+element, thus computing a value of '``i32*``' type.
+
+Note that it is perfectly legal to index partially through a structure,
+returning a pointer to an inner element. Because of this, the LLVM code
+for the given testcase is equivalent to:
+
+.. code-block:: llvm
+
+ define i32* @foo(%struct.ST* %s) {
+ %t1 = getelementptr %struct.ST, %struct.ST* %s, i32 1 ; yields %struct.ST*:%t1
+ %t2 = getelementptr %struct.ST, %struct.ST* %t1, i32 0, i32 2 ; yields %struct.RT*:%t2
+ %t3 = getelementptr %struct.RT, %struct.RT* %t2, i32 0, i32 1 ; yields [10 x [20 x i32]]*:%t3
+ %t4 = getelementptr [10 x [20 x i32]], [10 x [20 x i32]]* %t3, i32 0, i32 5 ; yields [20 x i32]*:%t4
+ %t5 = getelementptr [20 x i32], [20 x i32]* %t4, i32 0, i32 13 ; yields i32*:%t5
+ ret i32* %t5
+ }
+
+If the ``inbounds`` keyword is present, the result value of the
+``getelementptr`` is a :ref:`poison value <poisonvalues>` if the base
+pointer is not an *in bounds* address of an allocated object, or if any
+of the addresses that would be formed by successive addition of the
+offsets implied by the indices to the base address with infinitely
+precise signed arithmetic are not an *in bounds* address of that
+allocated object. The *in bounds* addresses for an allocated object are
+all the addresses that point into the object, plus the address one byte
+past the end. The only *in bounds* address for a null pointer in the
+default address-space is the null pointer itself. In cases where the
+base is a vector of pointers the ``inbounds`` keyword applies to each
+of the computations element-wise.
+
+If the ``inbounds`` keyword is not present, the offsets are added to the
+base address with silently-wrapping two's complement arithmetic. If the
+offsets have a different width from the pointer, they are sign-extended
+or truncated to the width of the pointer. The result value of the
+``getelementptr`` may be outside the object pointed to by the base
+pointer. The result value may not necessarily be used to access memory
+though, even if it happens to point into allocated storage. See the
+:ref:`Pointer Aliasing Rules <pointeraliasing>` section for more
+information.
+
+If the ``inrange`` keyword is present before any index, loading from or
+storing to any pointer derived from the ``getelementptr`` has undefined
+behavior if the load or store would access memory outside of the bounds of
+the element selected by the index marked as ``inrange``. The result of a
+pointer comparison or ``ptrtoint`` (including ``ptrtoint``-like operations
+involving memory) involving a pointer derived from a ``getelementptr`` with
+the ``inrange`` keyword is undefined, with the exception of comparisons
+in the case where both operands are in the range of the element selected
+by the ``inrange`` keyword, inclusive of the address one past the end of
+that element. Note that the ``inrange`` keyword is currently only allowed
+in constant ``getelementptr`` expressions.
+
+The getelementptr instruction is often confusing. For some more insight
+into how it works, see :doc:`the getelementptr FAQ <GetElementPtr>`.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ ; yields [12 x i8]*:aptr
+ %aptr = getelementptr {i32, [12 x i8]}, {i32, [12 x i8]}* %saptr, i64 0, i32 1
+ ; yields i8*:vptr
+ %vptr = getelementptr {i32, <2 x i8>}, {i32, <2 x i8>}* %svptr, i64 0, i32 1, i32 1
+ ; yields i8*:eptr
+ %eptr = getelementptr [12 x i8], [12 x i8]* %aptr, i64 0, i32 1
+ ; yields i32*:iptr
+ %iptr = getelementptr [10 x i32], [10 x i32]* @arr, i16 0, i16 0
+
+Vector of pointers:
+"""""""""""""""""""
+
+The ``getelementptr`` returns a vector of pointers, instead of a single address,
+when one or more of its arguments is a vector. In such cases, all vector
+arguments should have the same number of elements, and every scalar argument
+will be effectively broadcast into a vector during address calculation.
+
+.. code-block:: llvm
+
+ ; All arguments are vectors:
+ ; A[i] = ptrs[i] + offsets[i]*sizeof(i8)
+ %A = getelementptr i8, <4 x i8*> %ptrs, <4 x i64> %offsets
+
+ ; Add the same scalar offset to each pointer of a vector:
+ ; A[i] = ptrs[i] + offset*sizeof(i8)
+ %A = getelementptr i8, <4 x i8*> %ptrs, i64 %offset
+
+ ; Add distinct offsets to the same pointer:
+ ; A[i] = ptr + offsets[i]*sizeof(i8)
+ %A = getelementptr i8, i8* %ptr, <4 x i64> %offsets
+
+ ; In all cases described above the type of the result is <4 x i8*>
+
+The two following instructions are equivalent:
+
+.. code-block:: llvm
+
+ getelementptr %struct.ST, <4 x %struct.ST*> %s, <4 x i64> %ind1,
+ <4 x i32> <i32 2, i32 2, i32 2, i32 2>,
+ <4 x i32> <i32 1, i32 1, i32 1, i32 1>,
+ <4 x i32> %ind4,
+ <4 x i64> <i64 13, i64 13, i64 13, i64 13>
+
+ getelementptr %struct.ST, <4 x %struct.ST*> %s, <4 x i64> %ind1,
+ i32 2, i32 1, <4 x i32> %ind4, i64 13
+
+Let's look at the C code, where the vector version of ``getelementptr``
+makes sense:
+
+.. code-block:: c
+
+ // Let's assume that we vectorize the following loop:
+ double *A, *B; int *C;
+ for (int i = 0; i < size; ++i) {
+ A[i] = B[C[i]];
+ }
+
+.. code-block:: llvm
+
+ ; get pointers for 8 elements from array B
+ %ptrs = getelementptr double, double* %B, <8 x i32> %C
+ ; load 8 elements from array B into A
+ %A = call <8 x double> @llvm.masked.gather.v8f64.v8p0f64(<8 x double*> %ptrs,
+ i32 8, <8 x i1> %mask, <8 x double> %passthru)
+
+Conversion Operations
+---------------------
+
+The instructions in this category are the conversion instructions
+(casting) which all take a single operand and a type. They perform
+various bit conversions on the operand.
+
+'``trunc .. to``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = trunc <ty> <value> to <ty2> ; yields ty2
+
+Overview:
+"""""""""
+
+The '``trunc``' instruction truncates its operand to the type ``ty2``.
+
+Arguments:
+""""""""""
+
+The '``trunc``' instruction takes a value to trunc, and a type to trunc
+it to. Both types must be of :ref:`integer <t_integer>` types, or vectors
+of the same number of integers. The bit size of the ``value`` must be
+larger than the bit size of the destination type, ``ty2``. Equal sized
+types are not allowed.
+
+Semantics:
+""""""""""
+
+The '``trunc``' instruction truncates the high order bits in ``value``
+and converts the remaining bits to ``ty2``. Since the source size must
+be larger than the destination size, ``trunc`` cannot be a *no-op cast*.
+It will always truncate bits.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %X = trunc i32 257 to i8 ; yields i8:1
+ %Y = trunc i32 123 to i1 ; yields i1:true
+ %Z = trunc i32 122 to i1 ; yields i1:false
+ %W = trunc <2 x i16> <i16 8, i16 7> to <2 x i8> ; yields <i8 8, i8 7>
+
+'``zext .. to``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = zext <ty> <value> to <ty2> ; yields ty2
+
+Overview:
+"""""""""
+
+The '``zext``' instruction zero extends its operand to type ``ty2``.
+
+Arguments:
+""""""""""
+
+The '``zext``' instruction takes a value to cast, and a type to cast it
+to. Both types must be of :ref:`integer <t_integer>` types, or vectors of
+the same number of integers. The bit size of the ``value`` must be
+smaller than the bit size of the destination type, ``ty2``.
+
+Semantics:
+""""""""""
+
+The ``zext`` fills the high order bits of the ``value`` with zero bits
+until it reaches the size of the destination type, ``ty2``.
+
+When zero extending from i1, the result will always be either 0 or 1.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %X = zext i32 257 to i64 ; yields i64:257
+ %Y = zext i1 true to i32 ; yields i32:1
+ %Z = zext <2 x i16> <i16 8, i16 7> to <2 x i32> ; yields <i32 8, i32 7>
+
+'``sext .. to``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = sext <ty> <value> to <ty2> ; yields ty2
+
+Overview:
+"""""""""
+
+The '``sext``' sign extends ``value`` to the type ``ty2``.
+
+Arguments:
+""""""""""
+
+The '``sext``' instruction takes a value to cast, and a type to cast it
+to. Both types must be of :ref:`integer <t_integer>` types, or vectors of
+the same number of integers. The bit size of the ``value`` must be
+smaller than the bit size of the destination type, ``ty2``.
+
+Semantics:
+""""""""""
+
+The '``sext``' instruction performs a sign extension by copying the sign
+bit (highest order bit) of the ``value`` until it reaches the bit size
+of the type ``ty2``.
+
+When sign extending from i1, the extension always results in -1 or 0.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %X = sext i8 -1 to i16 ; yields i16 :65535
+ %Y = sext i1 true to i32 ; yields i32:-1
+ %Z = sext <2 x i16> <i16 8, i16 7> to <2 x i32> ; yields <i32 8, i32 7>
+
+'``fptrunc .. to``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = fptrunc <ty> <value> to <ty2> ; yields ty2
+
+Overview:
+"""""""""
+
+The '``fptrunc``' instruction truncates ``value`` to type ``ty2``.
+
+Arguments:
+""""""""""
+
+The '``fptrunc``' instruction takes a :ref:`floating point <t_floating>`
+value to cast and a :ref:`floating point <t_floating>` type to cast it to.
+The size of ``value`` must be larger than the size of ``ty2``. This
+implies that ``fptrunc`` cannot be used to make a *no-op cast*.
+
+Semantics:
+""""""""""
+
+The '``fptrunc``' instruction casts a ``value`` from a larger
+:ref:`floating point <t_floating>` type to a smaller :ref:`floating
+point <t_floating>` type. If the value cannot fit (i.e. overflows) within the
+destination type, ``ty2``, then the results are undefined. If the cast produces
+an inexact result, how rounding is performed (e.g. truncation, also known as
+round to zero) is undefined.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %X = fptrunc double 123.0 to float ; yields float:123.0
+ %Y = fptrunc double 1.0E+300 to float ; yields undefined
+
+'``fpext .. to``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = fpext <ty> <value> to <ty2> ; yields ty2
+
+Overview:
+"""""""""
+
+The '``fpext``' extends a floating point ``value`` to a larger floating
+point value.
+
+Arguments:
+""""""""""
+
+The '``fpext``' instruction takes a :ref:`floating point <t_floating>`
+``value`` to cast, and a :ref:`floating point <t_floating>` type to cast it
+to. The source type must be smaller than the destination type.
+
+Semantics:
+""""""""""
+
+The '``fpext``' instruction extends the ``value`` from a smaller
+:ref:`floating point <t_floating>` type to a larger :ref:`floating
+point <t_floating>` type. The ``fpext`` cannot be used to make a
+*no-op cast* because it always changes bits. Use ``bitcast`` to make a
+*no-op cast* for a floating point cast.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %X = fpext float 3.125 to double ; yields double:3.125000e+00
+ %Y = fpext double %X to fp128 ; yields fp128:0xL00000000000000004000900000000000
+
+'``fptoui .. to``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = fptoui <ty> <value> to <ty2> ; yields ty2
+
+Overview:
+"""""""""
+
+The '``fptoui``' converts a floating point ``value`` to its unsigned
+integer equivalent of type ``ty2``.
+
+Arguments:
+""""""""""
+
+The '``fptoui``' instruction takes a value to cast, which must be a
+scalar or vector :ref:`floating point <t_floating>` value, and a type to
+cast it to ``ty2``, which must be an :ref:`integer <t_integer>` type. If
+``ty`` is a vector floating point type, ``ty2`` must be a vector integer
+type with the same number of elements as ``ty``
+
+Semantics:
+""""""""""
+
+The '``fptoui``' instruction converts its :ref:`floating
+point <t_floating>` operand into the nearest (rounding towards zero)
+unsigned integer value. If the value cannot fit in ``ty2``, the results
+are undefined.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %X = fptoui double 123.0 to i32 ; yields i32:123
+ %Y = fptoui float 1.0E+300 to i1 ; yields undefined:1
+ %Z = fptoui float 1.04E+17 to i8 ; yields undefined:1
+
+'``fptosi .. to``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = fptosi <ty> <value> to <ty2> ; yields ty2
+
+Overview:
+"""""""""
+
+The '``fptosi``' instruction converts :ref:`floating point <t_floating>`
+``value`` to type ``ty2``.
+
+Arguments:
+""""""""""
+
+The '``fptosi``' instruction takes a value to cast, which must be a
+scalar or vector :ref:`floating point <t_floating>` value, and a type to
+cast it to ``ty2``, which must be an :ref:`integer <t_integer>` type. If
+``ty`` is a vector floating point type, ``ty2`` must be a vector integer
+type with the same number of elements as ``ty``
+
+Semantics:
+""""""""""
+
+The '``fptosi``' instruction converts its :ref:`floating
+point <t_floating>` operand into the nearest (rounding towards zero)
+signed integer value. If the value cannot fit in ``ty2``, the results
+are undefined.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %X = fptosi double -123.0 to i32 ; yields i32:-123
+ %Y = fptosi float 1.0E-247 to i1 ; yields undefined:1
+ %Z = fptosi float 1.04E+17 to i8 ; yields undefined:1
+
+'``uitofp .. to``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = uitofp <ty> <value> to <ty2> ; yields ty2
+
+Overview:
+"""""""""
+
+The '``uitofp``' instruction regards ``value`` as an unsigned integer
+and converts that value to the ``ty2`` type.
+
+Arguments:
+""""""""""
+
+The '``uitofp``' instruction takes a value to cast, which must be a
+scalar or vector :ref:`integer <t_integer>` value, and a type to cast it to
+``ty2``, which must be an :ref:`floating point <t_floating>` type. If
+``ty`` is a vector integer type, ``ty2`` must be a vector floating point
+type with the same number of elements as ``ty``
+
+Semantics:
+""""""""""
+
+The '``uitofp``' instruction interprets its operand as an unsigned
+integer quantity and converts it to the corresponding floating point
+value. If the value cannot fit in the floating point value, the results
+are undefined.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %X = uitofp i32 257 to float ; yields float:257.0
+ %Y = uitofp i8 -1 to double ; yields double:255.0
+
+'``sitofp .. to``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = sitofp <ty> <value> to <ty2> ; yields ty2
+
+Overview:
+"""""""""
+
+The '``sitofp``' instruction regards ``value`` as a signed integer and
+converts that value to the ``ty2`` type.
+
+Arguments:
+""""""""""
+
+The '``sitofp``' instruction takes a value to cast, which must be a
+scalar or vector :ref:`integer <t_integer>` value, and a type to cast it to
+``ty2``, which must be an :ref:`floating point <t_floating>` type. If
+``ty`` is a vector integer type, ``ty2`` must be a vector floating point
+type with the same number of elements as ``ty``
+
+Semantics:
+""""""""""
+
+The '``sitofp``' instruction interprets its operand as a signed integer
+quantity and converts it to the corresponding floating point value. If
+the value cannot fit in the floating point value, the results are
+undefined.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %X = sitofp i32 257 to float ; yields float:257.0
+ %Y = sitofp i8 -1 to double ; yields double:-1.0
+
+.. _i_ptrtoint:
+
+'``ptrtoint .. to``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = ptrtoint <ty> <value> to <ty2> ; yields ty2
+
+Overview:
+"""""""""
+
+The '``ptrtoint``' instruction converts the pointer or a vector of
+pointers ``value`` to the integer (or vector of integers) type ``ty2``.
+
+Arguments:
+""""""""""
+
+The '``ptrtoint``' instruction takes a ``value`` to cast, which must be
+a value of type :ref:`pointer <t_pointer>` or a vector of pointers, and a
+type to cast it to ``ty2``, which must be an :ref:`integer <t_integer>` or
+a vector of integers type.
+
+Semantics:
+""""""""""
+
+The '``ptrtoint``' instruction converts ``value`` to integer type
+``ty2`` by interpreting the pointer value as an integer and either
+truncating or zero extending that value to the size of the integer type.
+If ``value`` is smaller than ``ty2`` then a zero extension is done. If
+``value`` is larger than ``ty2`` then a truncation is done. If they are
+the same size, then nothing is done (*no-op cast*) other than a type
+change.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %X = ptrtoint i32* %P to i8 ; yields truncation on 32-bit architecture
+ %Y = ptrtoint i32* %P to i64 ; yields zero extension on 32-bit architecture
+ %Z = ptrtoint <4 x i32*> %P to <4 x i64>; yields vector zero extension for a vector of addresses on 32-bit architecture
+
+.. _i_inttoptr:
+
+'``inttoptr .. to``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = inttoptr <ty> <value> to <ty2> ; yields ty2
+
+Overview:
+"""""""""
+
+The '``inttoptr``' instruction converts an integer ``value`` to a
+pointer type, ``ty2``.
+
+Arguments:
+""""""""""
+
+The '``inttoptr``' instruction takes an :ref:`integer <t_integer>` value to
+cast, and a type to cast it to, which must be a :ref:`pointer <t_pointer>`
+type.
+
+Semantics:
+""""""""""
+
+The '``inttoptr``' instruction converts ``value`` to type ``ty2`` by
+applying either a zero extension or a truncation depending on the size
+of the integer ``value``. If ``value`` is larger than the size of a
+pointer then a truncation is done. If ``value`` is smaller than the size
+of a pointer then a zero extension is done. If they are the same size,
+nothing is done (*no-op cast*).
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %X = inttoptr i32 255 to i32* ; yields zero extension on 64-bit architecture
+ %Y = inttoptr i32 255 to i32* ; yields no-op on 32-bit architecture
+ %Z = inttoptr i64 0 to i32* ; yields truncation on 32-bit architecture
+ %Z = inttoptr <4 x i32> %G to <4 x i8*>; yields truncation of vector G to four pointers
+
+.. _i_bitcast:
+
+'``bitcast .. to``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = bitcast <ty> <value> to <ty2> ; yields ty2
+
+Overview:
+"""""""""
+
+The '``bitcast``' instruction converts ``value`` to type ``ty2`` without
+changing any bits.
+
+Arguments:
+""""""""""
+
+The '``bitcast``' instruction takes a value to cast, which must be a
+non-aggregate first class value, and a type to cast it to, which must
+also be a non-aggregate :ref:`first class <t_firstclass>` type. The
+bit sizes of ``value`` and the destination type, ``ty2``, must be
+identical. If the source type is a pointer, the destination type must
+also be a pointer of the same size. This instruction supports bitwise
+conversion of vectors to integers and to vectors of other types (as
+long as they have the same size).
+
+Semantics:
+""""""""""
+
+The '``bitcast``' instruction converts ``value`` to type ``ty2``. It
+is always a *no-op cast* because no bits change with this
+conversion. The conversion is done as if the ``value`` had been stored
+to memory and read back as type ``ty2``. Pointer (or vector of
+pointers) types may only be converted to other pointer (or vector of
+pointers) types with the same address space through this instruction.
+To convert pointers to other types, use the :ref:`inttoptr <i_inttoptr>`
+or :ref:`ptrtoint <i_ptrtoint>` instructions first.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ %X = bitcast i8 255 to i8 ; yields i8 :-1
+ %Y = bitcast i32* %x to sint* ; yields sint*:%x
+ %Z = bitcast <2 x int> %V to i64; ; yields i64: %V
+ %Z = bitcast <2 x i32*> %V to <2 x i64*> ; yields <2 x i64*>
+
+.. _i_addrspacecast:
+
+'``addrspacecast .. to``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = addrspacecast <pty> <ptrval> to <pty2> ; yields pty2
+
+Overview:
+"""""""""
+
+The '``addrspacecast``' instruction converts ``ptrval`` from ``pty`` in
+address space ``n`` to type ``pty2`` in address space ``m``.
+
+Arguments:
+""""""""""
+
+The '``addrspacecast``' instruction takes a pointer or vector of pointer value
+to cast and a pointer type to cast it to, which must have a different
+address space.
+
+Semantics:
+""""""""""
+
+The '``addrspacecast``' instruction converts the pointer value
+``ptrval`` to type ``pty2``. It can be a *no-op cast* or a complex
+value modification, depending on the target and the address space
+pair. Pointer conversions within the same address space must be
+performed with the ``bitcast`` instruction. Note that if the address space
+conversion is legal then both result and operand refer to the same memory
+location.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %X = addrspacecast i32* %x to i32 addrspace(1)* ; yields i32 addrspace(1)*:%x
+ %Y = addrspacecast i32 addrspace(1)* %y to i64 addrspace(2)* ; yields i64 addrspace(2)*:%y
+ %Z = addrspacecast <4 x i32*> %z to <4 x float addrspace(3)*> ; yields <4 x float addrspace(3)*>:%z
+
+.. _otherops:
+
+Other Operations
+----------------
+
+The instructions in this category are the "miscellaneous" instructions,
+which defy better classification.
+
+.. _i_icmp:
+
+'``icmp``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = icmp <cond> <ty> <op1>, <op2> ; yields i1 or <N x i1>:result
+
+Overview:
+"""""""""
+
+The '``icmp``' instruction returns a boolean value or a vector of
+boolean values based on comparison of its two integer, integer vector,
+pointer, or pointer vector operands.
+
+Arguments:
+""""""""""
+
+The '``icmp``' instruction takes three operands. The first operand is
+the condition code indicating the kind of comparison to perform. It is
+not a value, just a keyword. The possible condition codes are:
+
+#. ``eq``: equal
+#. ``ne``: not equal
+#. ``ugt``: unsigned greater than
+#. ``uge``: unsigned greater or equal
+#. ``ult``: unsigned less than
+#. ``ule``: unsigned less or equal
+#. ``sgt``: signed greater than
+#. ``sge``: signed greater or equal
+#. ``slt``: signed less than
+#. ``sle``: signed less or equal
+
+The remaining two arguments must be :ref:`integer <t_integer>` or
+:ref:`pointer <t_pointer>` or integer :ref:`vector <t_vector>` typed. They
+must also be identical types.
+
+Semantics:
+""""""""""
+
+The '``icmp``' compares ``op1`` and ``op2`` according to the condition
+code given as ``cond``. The comparison performed always yields either an
+:ref:`i1 <t_integer>` or vector of ``i1`` result, as follows:
+
+#. ``eq``: yields ``true`` if the operands are equal, ``false``
+ otherwise. No sign interpretation is necessary or performed.
+#. ``ne``: yields ``true`` if the operands are unequal, ``false``
+ otherwise. No sign interpretation is necessary or performed.
+#. ``ugt``: interprets the operands as unsigned values and yields
+ ``true`` if ``op1`` is greater than ``op2``.
+#. ``uge``: interprets the operands as unsigned values and yields
+ ``true`` if ``op1`` is greater than or equal to ``op2``.
+#. ``ult``: interprets the operands as unsigned values and yields
+ ``true`` if ``op1`` is less than ``op2``.
+#. ``ule``: interprets the operands as unsigned values and yields
+ ``true`` if ``op1`` is less than or equal to ``op2``.
+#. ``sgt``: interprets the operands as signed values and yields ``true``
+ if ``op1`` is greater than ``op2``.
+#. ``sge``: interprets the operands as signed values and yields ``true``
+ if ``op1`` is greater than or equal to ``op2``.
+#. ``slt``: interprets the operands as signed values and yields ``true``
+ if ``op1`` is less than ``op2``.
+#. ``sle``: interprets the operands as signed values and yields ``true``
+ if ``op1`` is less than or equal to ``op2``.
+
+If the operands are :ref:`pointer <t_pointer>` typed, the pointer values
+are compared as if they were integers.
+
+If the operands are integer vectors, then they are compared element by
+element. The result is an ``i1`` vector with the same number of elements
+as the values being compared. Otherwise, the result is an ``i1``.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = icmp eq i32 4, 5 ; yields: result=false
+ <result> = icmp ne float* %X, %X ; yields: result=false
+ <result> = icmp ult i16 4, 5 ; yields: result=true
+ <result> = icmp sgt i16 4, 5 ; yields: result=false
+ <result> = icmp ule i16 -4, 5 ; yields: result=false
+ <result> = icmp sge i16 4, 5 ; yields: result=false
+
+.. _i_fcmp:
+
+'``fcmp``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = fcmp [fast-math flags]* <cond> <ty> <op1>, <op2> ; yields i1 or <N x i1>:result
+
+Overview:
+"""""""""
+
+The '``fcmp``' instruction returns a boolean value or vector of boolean
+values based on comparison of its operands.
+
+If the operands are floating point scalars, then the result type is a
+boolean (:ref:`i1 <t_integer>`).
+
+If the operands are floating point vectors, then the result type is a
+vector of boolean with the same number of elements as the operands being
+compared.
+
+Arguments:
+""""""""""
+
+The '``fcmp``' instruction takes three operands. The first operand is
+the condition code indicating the kind of comparison to perform. It is
+not a value, just a keyword. The possible condition codes are:
+
+#. ``false``: no comparison, always returns false
+#. ``oeq``: ordered and equal
+#. ``ogt``: ordered and greater than
+#. ``oge``: ordered and greater than or equal
+#. ``olt``: ordered and less than
+#. ``ole``: ordered and less than or equal
+#. ``one``: ordered and not equal
+#. ``ord``: ordered (no nans)
+#. ``ueq``: unordered or equal
+#. ``ugt``: unordered or greater than
+#. ``uge``: unordered or greater than or equal
+#. ``ult``: unordered or less than
+#. ``ule``: unordered or less than or equal
+#. ``une``: unordered or not equal
+#. ``uno``: unordered (either nans)
+#. ``true``: no comparison, always returns true
+
+*Ordered* means that neither operand is a QNAN while *unordered* means
+that either operand may be a QNAN.
+
+Each of ``val1`` and ``val2`` arguments must be either a :ref:`floating
+point <t_floating>` type or a :ref:`vector <t_vector>` of floating point
+type. They must have identical types.
+
+Semantics:
+""""""""""
+
+The '``fcmp``' instruction compares ``op1`` and ``op2`` according to the
+condition code given as ``cond``. If the operands are vectors, then the
+vectors are compared element by element. Each comparison performed
+always yields an :ref:`i1 <t_integer>` result, as follows:
+
+#. ``false``: always yields ``false``, regardless of operands.
+#. ``oeq``: yields ``true`` if both operands are not a QNAN and ``op1``
+ is equal to ``op2``.
+#. ``ogt``: yields ``true`` if both operands are not a QNAN and ``op1``
+ is greater than ``op2``.
+#. ``oge``: yields ``true`` if both operands are not a QNAN and ``op1``
+ is greater than or equal to ``op2``.
+#. ``olt``: yields ``true`` if both operands are not a QNAN and ``op1``
+ is less than ``op2``.
+#. ``ole``: yields ``true`` if both operands are not a QNAN and ``op1``
+ is less than or equal to ``op2``.
+#. ``one``: yields ``true`` if both operands are not a QNAN and ``op1``
+ is not equal to ``op2``.
+#. ``ord``: yields ``true`` if both operands are not a QNAN.
+#. ``ueq``: yields ``true`` if either operand is a QNAN or ``op1`` is
+ equal to ``op2``.
+#. ``ugt``: yields ``true`` if either operand is a QNAN or ``op1`` is
+ greater than ``op2``.
+#. ``uge``: yields ``true`` if either operand is a QNAN or ``op1`` is
+ greater than or equal to ``op2``.
+#. ``ult``: yields ``true`` if either operand is a QNAN or ``op1`` is
+ less than ``op2``.
+#. ``ule``: yields ``true`` if either operand is a QNAN or ``op1`` is
+ less than or equal to ``op2``.
+#. ``une``: yields ``true`` if either operand is a QNAN or ``op1`` is
+ not equal to ``op2``.
+#. ``uno``: yields ``true`` if either operand is a QNAN.
+#. ``true``: always yields ``true``, regardless of operands.
+
+The ``fcmp`` instruction can also optionally take any number of
+:ref:`fast-math flags <fastmath>`, which are optimization hints to enable
+otherwise unsafe floating point optimizations.
+
+Any set of fast-math flags are legal on an ``fcmp`` instruction, but the
+only flags that have any effect on its semantics are those that allow
+assumptions to be made about the values of input arguments; namely
+``nnan``, ``ninf``, and ``nsz``. See :ref:`fastmath` for more information.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = fcmp oeq float 4.0, 5.0 ; yields: result=false
+ <result> = fcmp one float 4.0, 5.0 ; yields: result=true
+ <result> = fcmp olt float 4.0, 5.0 ; yields: result=true
+ <result> = fcmp ueq double 1.0, 2.0 ; yields: result=false
+
+.. _i_phi:
+
+'``phi``' Instruction
+^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = phi <ty> [ <val0>, <label0>], ...
+
+Overview:
+"""""""""
+
+The '``phi``' instruction is used to implement the Ï node in the SSA
+graph representing the function.
+
+Arguments:
+""""""""""
+
+The type of the incoming values is specified with the first type field.
+After this, the '``phi``' instruction takes a list of pairs as
+arguments, with one pair for each predecessor basic block of the current
+block. Only values of :ref:`first class <t_firstclass>` type may be used as
+the value arguments to the PHI node. Only labels may be used as the
+label arguments.
+
+There must be no non-phi instructions between the start of a basic block
+and the PHI instructions: i.e. PHI instructions must be first in a basic
+block.
+
+For the purposes of the SSA form, the use of each incoming value is
+deemed to occur on the edge from the corresponding predecessor block to
+the current block (but after any definition of an '``invoke``'
+instruction's return value on the same edge).
+
+Semantics:
+""""""""""
+
+At runtime, the '``phi``' instruction logically takes on the value
+specified by the pair corresponding to the predecessor basic block that
+executed just prior to the current block.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ Loop: ; Infinite loop that counts from 0 on up...
+ %indvar = phi i32 [ 0, %LoopHeader ], [ %nextindvar, %Loop ]
+ %nextindvar = add i32 %indvar, 1
+ br label %Loop
+
+.. _i_select:
+
+'``select``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = select selty <cond>, <ty> <val1>, <ty> <val2> ; yields ty
+
+ selty is either i1 or {<N x i1>}
+
+Overview:
+"""""""""
+
+The '``select``' instruction is used to choose one value based on a
+condition, without IR-level branching.
+
+Arguments:
+""""""""""
+
+The '``select``' instruction requires an 'i1' value or a vector of 'i1'
+values indicating the condition, and two values of the same :ref:`first
+class <t_firstclass>` type.
+
+Semantics:
+""""""""""
+
+If the condition is an i1 and it evaluates to 1, the instruction returns
+the first value argument; otherwise, it returns the second value
+argument.
+
+If the condition is a vector of i1, then the value arguments must be
+vectors of the same size, and the selection is done element by element.
+
+If the condition is an i1 and the value arguments are vectors of the
+same size, then an entire vector is selected.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %X = select i1 true, i8 17, i8 42 ; yields i8:17
+
+.. _i_call:
+
+'``call``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = [tail | musttail | notail ] call [fast-math flags] [cconv] [ret attrs] <ty>|<fnty> <fnptrval>(<function args>) [fn attrs]
+ [ operand bundles ]
+
+Overview:
+"""""""""
+
+The '``call``' instruction represents a simple function call.
+
+Arguments:
+""""""""""
+
+This instruction requires several arguments:
+
+#. The optional ``tail`` and ``musttail`` markers indicate that the optimizers
+ should perform tail call optimization. The ``tail`` marker is a hint that
+ `can be ignored <CodeGenerator.html#sibcallopt>`_. The ``musttail`` marker
+ means that the call must be tail call optimized in order for the program to
+ be correct. The ``musttail`` marker provides these guarantees:
+
+ #. The call will not cause unbounded stack growth if it is part of a
+ recursive cycle in the call graph.
+ #. Arguments with the :ref:`inalloca <attr_inalloca>` attribute are
+ forwarded in place.
+
+ Both markers imply that the callee does not access allocas or varargs from
+ the caller. Calls marked ``musttail`` must obey the following additional
+ rules:
+
+ - The call must immediately precede a :ref:`ret <i_ret>` instruction,
+ or a pointer bitcast followed by a ret instruction.
+ - The ret instruction must return the (possibly bitcasted) value
+ produced by the call or void.
+ - The caller and callee prototypes must match. Pointer types of
+ parameters or return types may differ in pointee type, but not
+ in address space.
+ - The calling conventions of the caller and callee must match.
+ - All ABI-impacting function attributes, such as sret, byval, inreg,
+ returned, and inalloca, must match.
+ - The callee must be varargs iff the caller is varargs. Bitcasting a
+ non-varargs function to the appropriate varargs type is legal so
+ long as the non-varargs prefixes obey the other rules.
+
+ Tail call optimization for calls marked ``tail`` is guaranteed to occur if
+ the following conditions are met:
+
+ - Caller and callee both have the calling convention ``fastcc``.
+ - The call is in tail position (ret immediately follows call and ret
+ uses value of call or is void).
+ - Option ``-tailcallopt`` is enabled, or
+ ``llvm::GuaranteedTailCallOpt`` is ``true``.
+ - `Platform-specific constraints are
+ met. <CodeGenerator.html#tailcallopt>`_
+
+#. The optional ``notail`` marker indicates that the optimizers should not add
+ ``tail`` or ``musttail`` markers to the call. It is used to prevent tail
+ call optimization from being performed on the call.
+
+#. The optional ``fast-math flags`` marker indicates that the call has one or more
+ :ref:`fast-math flags <fastmath>`, which are optimization hints to enable
+ otherwise unsafe floating-point optimizations. Fast-math flags are only valid
+ for calls that return a floating-point scalar or vector type.
+
+#. The optional "cconv" marker indicates which :ref:`calling
+ convention <callingconv>` the call should use. If none is
+ specified, the call defaults to using C calling conventions. The
+ calling convention of the call must match the calling convention of
+ the target function, or else the behavior is undefined.
+#. The optional :ref:`Parameter Attributes <paramattrs>` list for return
+ values. Only '``zeroext``', '``signext``', and '``inreg``' attributes
+ are valid here.
+#. '``ty``': the type of the call instruction itself which is also the
+ type of the return value. Functions that return no value are marked
+ ``void``.
+#. '``fnty``': shall be the signature of the function being called. The
+ argument types must match the types implied by this signature. This
+ type can be omitted if the function is not varargs.
+#. '``fnptrval``': An LLVM value containing a pointer to a function to
+ be called. In most cases, this is a direct function call, but
+ indirect ``call``'s are just as possible, calling an arbitrary pointer
+ to function value.
+#. '``function args``': argument list whose types match the function
+ signature argument types and parameter attributes. All arguments must
+ be of :ref:`first class <t_firstclass>` type. If the function signature
+ indicates the function accepts a variable number of arguments, the
+ extra arguments can be specified.
+#. The optional :ref:`function attributes <fnattrs>` list.
+#. The optional :ref:`operand bundles <opbundles>` list.
+
+Semantics:
+""""""""""
+
+The '``call``' instruction is used to cause control flow to transfer to
+a specified function, with its incoming arguments bound to the specified
+values. Upon a '``ret``' instruction in the called function, control
+flow continues with the instruction after the function call, and the
+return value of the function is bound to the result argument.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %retval = call i32 @test(i32 %argc)
+ call i32 (i8*, ...)* @printf(i8* %msg, i32 12, i8 42) ; yields i32
+ %X = tail call i32 @foo() ; yields i32
+ %Y = tail call fastcc i32 @foo() ; yields i32
+ call void %foo(i8 97 signext)
+
+ %struct.A = type { i32, i8 }
+ %r = call %struct.A @foo() ; yields { i32, i8 }
+ %gr = extractvalue %struct.A %r, 0 ; yields i32
+ %gr1 = extractvalue %struct.A %r, 1 ; yields i8
+ %Z = call void @foo() noreturn ; indicates that %foo never returns normally
+ %ZZ = call zeroext i32 @bar() ; Return value is %zero extended
+
+llvm treats calls to some functions with names and arguments that match
+the standard C99 library as being the C99 library functions, and may
+perform optimizations or generate code for them under that assumption.
+This is something we'd like to change in the future to provide better
+support for freestanding environments and non-C-based languages.
+
+.. _i_va_arg:
+
+'``va_arg``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <resultval> = va_arg <va_list*> <arglist>, <argty>
+
+Overview:
+"""""""""
+
+The '``va_arg``' instruction is used to access arguments passed through
+the "variable argument" area of a function call. It is used to implement
+the ``va_arg`` macro in C.
+
+Arguments:
+""""""""""
+
+This instruction takes a ``va_list*`` value and the type of the
+argument. It returns a value of the specified argument type and
+increments the ``va_list`` to point to the next argument. The actual
+type of ``va_list`` is target specific.
+
+Semantics:
+""""""""""
+
+The '``va_arg``' instruction loads an argument of the specified type
+from the specified ``va_list`` and causes the ``va_list`` to point to
+the next argument. For more information, see the variable argument
+handling :ref:`Intrinsic Functions <int_varargs>`.
+
+It is legal for this instruction to be called in a function which does
+not take a variable number of arguments, for example, the ``vfprintf``
+function.
+
+``va_arg`` is an LLVM instruction instead of an :ref:`intrinsic
+function <intrinsics>` because it takes a type as an argument.
+
+Example:
+""""""""
+
+See the :ref:`variable argument processing <int_varargs>` section.
+
+Note that the code generator does not yet fully support va\_arg on many
+targets. Also, it does not currently support va\_arg with aggregate
+types on any target.
+
+.. _i_landingpad:
+
+'``landingpad``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <resultval> = landingpad <resultty> <clause>+
+ <resultval> = landingpad <resultty> cleanup <clause>*
+
+ <clause> := catch <type> <value>
+ <clause> := filter <array constant type> <array constant>
+
+Overview:
+"""""""""
+
+The '``landingpad``' instruction is used by `LLVM's exception handling
+system <ExceptionHandling.html#overview>`_ to specify that a basic block
+is a landing pad --- one where the exception lands, and corresponds to the
+code found in the ``catch`` portion of a ``try``/``catch`` sequence. It
+defines values supplied by the :ref:`personality function <personalityfn>` upon
+re-entry to the function. The ``resultval`` has the type ``resultty``.
+
+Arguments:
+""""""""""
+
+The optional
+``cleanup`` flag indicates that the landing pad block is a cleanup.
+
+A ``clause`` begins with the clause type --- ``catch`` or ``filter`` --- and
+contains the global variable representing the "type" that may be caught
+or filtered respectively. Unlike the ``catch`` clause, the ``filter``
+clause takes an array constant as its argument. Use
+"``[0 x i8**] undef``" for a filter which cannot throw. The
+'``landingpad``' instruction must contain *at least* one ``clause`` or
+the ``cleanup`` flag.
+
+Semantics:
+""""""""""
+
+The '``landingpad``' instruction defines the values which are set by the
+:ref:`personality function <personalityfn>` upon re-entry to the function, and
+therefore the "result type" of the ``landingpad`` instruction. As with
+calling conventions, how the personality function results are
+represented in LLVM IR is target specific.
+
+The clauses are applied in order from top to bottom. If two
+``landingpad`` instructions are merged together through inlining, the
+clauses from the calling function are appended to the list of clauses.
+When the call stack is being unwound due to an exception being thrown,
+the exception is compared against each ``clause`` in turn. If it doesn't
+match any of the clauses, and the ``cleanup`` flag is not set, then
+unwinding continues further up the call stack.
+
+The ``landingpad`` instruction has several restrictions:
+
+- A landing pad block is a basic block which is the unwind destination
+ of an '``invoke``' instruction.
+- A landing pad block must have a '``landingpad``' instruction as its
+ first non-PHI instruction.
+- There can be only one '``landingpad``' instruction within the landing
+ pad block.
+- A basic block that is not a landing pad block may not include a
+ '``landingpad``' instruction.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ ;; A landing pad which can catch an integer.
+ %res = landingpad { i8*, i32 }
+ catch i8** @_ZTIi
+ ;; A landing pad that is a cleanup.
+ %res = landingpad { i8*, i32 }
+ cleanup
+ ;; A landing pad which can catch an integer and can only throw a double.
+ %res = landingpad { i8*, i32 }
+ catch i8** @_ZTIi
+ filter [1 x i8**] [@_ZTId]
+
+.. _i_catchpad:
+
+'``catchpad``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <resultval> = catchpad within <catchswitch> [<args>*]
+
+Overview:
+"""""""""
+
+The '``catchpad``' instruction is used by `LLVM's exception handling
+system <ExceptionHandling.html#overview>`_ to specify that a basic block
+begins a catch handler --- one where a personality routine attempts to transfer
+control to catch an exception.
+
+Arguments:
+""""""""""
+
+The ``catchswitch`` operand must always be a token produced by a
+:ref:`catchswitch <i_catchswitch>` instruction in a predecessor block. This
+ensures that each ``catchpad`` has exactly one predecessor block, and it always
+terminates in a ``catchswitch``.
+
+The ``args`` correspond to whatever information the personality routine
+requires to know if this is an appropriate handler for the exception. Control
+will transfer to the ``catchpad`` if this is the first appropriate handler for
+the exception.
+
+The ``resultval`` has the type :ref:`token <t_token>` and is used to match the
+``catchpad`` to corresponding :ref:`catchrets <i_catchret>` and other nested EH
+pads.
+
+Semantics:
+""""""""""
+
+When the call stack is being unwound due to an exception being thrown, the
+exception is compared against the ``args``. If it doesn't match, control will
+not reach the ``catchpad`` instruction. The representation of ``args`` is
+entirely target and personality function-specific.
+
+Like the :ref:`landingpad <i_landingpad>` instruction, the ``catchpad``
+instruction must be the first non-phi of its parent basic block.
+
+The meaning of the tokens produced and consumed by ``catchpad`` and other "pad"
+instructions is described in the
+`Windows exception handling documentation\ <ExceptionHandling.html#wineh>`_.
+
+When a ``catchpad`` has been "entered" but not yet "exited" (as
+described in the `EH documentation\ <ExceptionHandling.html#wineh-constraints>`_),
+it is undefined behavior to execute a :ref:`call <i_call>` or :ref:`invoke <i_invoke>`
+that does not carry an appropriate :ref:`"funclet" bundle <ob_funclet>`.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ dispatch:
+ %cs = catchswitch within none [label %handler0] unwind to caller
+ ;; A catch block which can catch an integer.
+ handler0:
+ %tok = catchpad within %cs [i8** @_ZTIi]
+
+.. _i_cleanuppad:
+
+'``cleanuppad``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <resultval> = cleanuppad within <parent> [<args>*]
+
+Overview:
+"""""""""
+
+The '``cleanuppad``' instruction is used by `LLVM's exception handling
+system <ExceptionHandling.html#overview>`_ to specify that a basic block
+is a cleanup block --- one where a personality routine attempts to
+transfer control to run cleanup actions.
+The ``args`` correspond to whatever additional
+information the :ref:`personality function <personalityfn>` requires to
+execute the cleanup.
+The ``resultval`` has the type :ref:`token <t_token>` and is used to
+match the ``cleanuppad`` to corresponding :ref:`cleanuprets <i_cleanupret>`.
+The ``parent`` argument is the token of the funclet that contains the
+``cleanuppad`` instruction. If the ``cleanuppad`` is not inside a funclet,
+this operand may be the token ``none``.
+
+Arguments:
+""""""""""
+
+The instruction takes a list of arbitrary values which are interpreted
+by the :ref:`personality function <personalityfn>`.
+
+Semantics:
+""""""""""
+
+When the call stack is being unwound due to an exception being thrown,
+the :ref:`personality function <personalityfn>` transfers control to the
+``cleanuppad`` with the aid of the personality-specific arguments.
+As with calling conventions, how the personality function results are
+represented in LLVM IR is target specific.
+
+The ``cleanuppad`` instruction has several restrictions:
+
+- A cleanup block is a basic block which is the unwind destination of
+ an exceptional instruction.
+- A cleanup block must have a '``cleanuppad``' instruction as its
+ first non-PHI instruction.
+- There can be only one '``cleanuppad``' instruction within the
+ cleanup block.
+- A basic block that is not a cleanup block may not include a
+ '``cleanuppad``' instruction.
+
+When a ``cleanuppad`` has been "entered" but not yet "exited" (as
+described in the `EH documentation\ <ExceptionHandling.html#wineh-constraints>`_),
+it is undefined behavior to execute a :ref:`call <i_call>` or :ref:`invoke <i_invoke>`
+that does not carry an appropriate :ref:`"funclet" bundle <ob_funclet>`.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ %tok = cleanuppad within %cs []
+
+.. _intrinsics:
+
+Intrinsic Functions
+===================
+
+LLVM supports the notion of an "intrinsic function". These functions
+have well known names and semantics and are required to follow certain
+restrictions. Overall, these intrinsics represent an extension mechanism
+for the LLVM language that does not require changing all of the
+transformations in LLVM when adding to the language (or the bitcode
+reader/writer, the parser, etc...).
+
+Intrinsic function names must all start with an "``llvm.``" prefix. This
+prefix is reserved in LLVM for intrinsic names; thus, function names may
+not begin with this prefix. Intrinsic functions must always be external
+functions: you cannot define the body of intrinsic functions. Intrinsic
+functions may only be used in call or invoke instructions: it is illegal
+to take the address of an intrinsic function. Additionally, because
+intrinsic functions are part of the LLVM language, it is required if any
+are added that they be documented here.
+
+Some intrinsic functions can be overloaded, i.e., the intrinsic
+represents a family of functions that perform the same operation but on
+different data types. Because LLVM can represent over 8 million
+different integer types, overloading is used commonly to allow an
+intrinsic function to operate on any integer type. One or more of the
+argument types or the result type can be overloaded to accept any
+integer type. Argument types may also be defined as exactly matching a
+previous argument's type or the result type. This allows an intrinsic
+function which accepts multiple arguments, but needs all of them to be
+of the same type, to only be overloaded with respect to a single
+argument or the result.
+
+Overloaded intrinsics will have the names of its overloaded argument
+types encoded into its function name, each preceded by a period. Only
+those types which are overloaded result in a name suffix. Arguments
+whose type is matched against another type do not. For example, the
+``llvm.ctpop`` function can take an integer of any width and returns an
+integer of exactly the same integer width. This leads to a family of
+functions such as ``i8 @llvm.ctpop.i8(i8 %val)`` and
+``i29 @llvm.ctpop.i29(i29 %val)``. Only one type, the return type, is
+overloaded, and only one type suffix is required. Because the argument's
+type is matched against the return type, it does not require its own
+name suffix.
+
+To learn how to add an intrinsic function, please see the `Extending
+LLVM Guide <ExtendingLLVM.html>`_.
+
+.. _int_varargs:
+
+Variable Argument Handling Intrinsics
+-------------------------------------
+
+Variable argument support is defined in LLVM with the
+:ref:`va_arg <i_va_arg>` instruction and these three intrinsic
+functions. These functions are related to the similarly named macros
+defined in the ``<stdarg.h>`` header file.
+
+All of these functions operate on arguments that use a target-specific
+value type "``va_list``". The LLVM assembly language reference manual
+does not define what this type is, so all transformations should be
+prepared to handle these functions regardless of the type used.
+
+This example shows how the :ref:`va_arg <i_va_arg>` instruction and the
+variable argument handling intrinsic functions are used.
+
+.. code-block:: llvm
+
+ ; This struct is different for every platform. For most platforms,
+ ; it is merely an i8*.
+ %struct.va_list = type { i8* }
+
+ ; For Unix x86_64 platforms, va_list is the following struct:
+ ; %struct.va_list = type { i32, i32, i8*, i8* }
+
+ define i32 @test(i32 %X, ...) {
+ ; Initialize variable argument processing
+ %ap = alloca %struct.va_list
+ %ap2 = bitcast %struct.va_list* %ap to i8*
+ call void @llvm.va_start(i8* %ap2)
+
+ ; Read a single integer argument
+ %tmp = va_arg i8* %ap2, i32
+
+ ; Demonstrate usage of llvm.va_copy and llvm.va_end
+ %aq = alloca i8*
+ %aq2 = bitcast i8** %aq to i8*
+ call void @llvm.va_copy(i8* %aq2, i8* %ap2)
+ call void @llvm.va_end(i8* %aq2)
+
+ ; Stop processing of arguments.
+ call void @llvm.va_end(i8* %ap2)
+ ret i32 %tmp
+ }
+
+ declare void @llvm.va_start(i8*)
+ declare void @llvm.va_copy(i8*, i8*)
+ declare void @llvm.va_end(i8*)
+
+.. _int_va_start:
+
+'``llvm.va_start``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.va_start(i8* <arglist>)
+
+Overview:
+"""""""""
+
+The '``llvm.va_start``' intrinsic initializes ``*<arglist>`` for
+subsequent use by ``va_arg``.
+
+Arguments:
+""""""""""
+
+The argument is a pointer to a ``va_list`` element to initialize.
+
+Semantics:
+""""""""""
+
+The '``llvm.va_start``' intrinsic works just like the ``va_start`` macro
+available in C. In a target-dependent way, it initializes the
+``va_list`` element to which the argument points, so that the next call
+to ``va_arg`` will produce the first variable argument passed to the
+function. Unlike the C ``va_start`` macro, this intrinsic does not need
+to know the last argument of the function as the compiler can figure
+that out.
+
+'``llvm.va_end``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.va_end(i8* <arglist>)
+
+Overview:
+"""""""""
+
+The '``llvm.va_end``' intrinsic destroys ``*<arglist>``, which has been
+initialized previously with ``llvm.va_start`` or ``llvm.va_copy``.
+
+Arguments:
+""""""""""
+
+The argument is a pointer to a ``va_list`` to destroy.
+
+Semantics:
+""""""""""
+
+The '``llvm.va_end``' intrinsic works just like the ``va_end`` macro
+available in C. In a target-dependent way, it destroys the ``va_list``
+element to which the argument points. Calls to
+:ref:`llvm.va_start <int_va_start>` and
+:ref:`llvm.va_copy <int_va_copy>` must be matched exactly with calls to
+``llvm.va_end``.
+
+.. _int_va_copy:
+
+'``llvm.va_copy``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.va_copy(i8* <destarglist>, i8* <srcarglist>)
+
+Overview:
+"""""""""
+
+The '``llvm.va_copy``' intrinsic copies the current argument position
+from the source argument list to the destination argument list.
+
+Arguments:
+""""""""""
+
+The first argument is a pointer to a ``va_list`` element to initialize.
+The second argument is a pointer to a ``va_list`` element to copy from.
+
+Semantics:
+""""""""""
+
+The '``llvm.va_copy``' intrinsic works just like the ``va_copy`` macro
+available in C. In a target-dependent way, it copies the source
+``va_list`` element into the destination ``va_list`` element. This
+intrinsic is necessary because the `` llvm.va_start`` intrinsic may be
+arbitrarily complex and require, for example, memory allocation.
+
+Accurate Garbage Collection Intrinsics
+--------------------------------------
+
+LLVM's support for `Accurate Garbage Collection <GarbageCollection.html>`_
+(GC) requires the frontend to generate code containing appropriate intrinsic
+calls and select an appropriate GC strategy which knows how to lower these
+intrinsics in a manner which is appropriate for the target collector.
+
+These intrinsics allow identification of :ref:`GC roots on the
+stack <int_gcroot>`, as well as garbage collector implementations that
+require :ref:`read <int_gcread>` and :ref:`write <int_gcwrite>` barriers.
+Frontends for type-safe garbage collected languages should generate
+these intrinsics to make use of the LLVM garbage collectors. For more
+details, see `Garbage Collection with LLVM <GarbageCollection.html>`_.
+
+Experimental Statepoint Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+LLVM provides an second experimental set of intrinsics for describing garbage
+collection safepoints in compiled code. These intrinsics are an alternative
+to the ``llvm.gcroot`` intrinsics, but are compatible with the ones for
+:ref:`read <int_gcread>` and :ref:`write <int_gcwrite>` barriers. The
+differences in approach are covered in the `Garbage Collection with LLVM
+<GarbageCollection.html>`_ documentation. The intrinsics themselves are
+described in :doc:`Statepoints`.
+
+.. _int_gcroot:
+
+'``llvm.gcroot``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.gcroot(i8** %ptrloc, i8* %metadata)
+
+Overview:
+"""""""""
+
+The '``llvm.gcroot``' intrinsic declares the existence of a GC root to
+the code generator, and allows some metadata to be associated with it.
+
+Arguments:
+""""""""""
+
+The first argument specifies the address of a stack object that contains
+the root pointer. The second pointer (which must be either a constant or
+a global value address) contains the meta-data to be associated with the
+root.
+
+Semantics:
+""""""""""
+
+At runtime, a call to this intrinsic stores a null pointer into the
+"ptrloc" location. At compile-time, the code generator generates
+information to allow the runtime to find the pointer at GC safe points.
+The '``llvm.gcroot``' intrinsic may only be used in a function which
+:ref:`specifies a GC algorithm <gc>`.
+
+.. _int_gcread:
+
+'``llvm.gcread``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i8* @llvm.gcread(i8* %ObjPtr, i8** %Ptr)
+
+Overview:
+"""""""""
+
+The '``llvm.gcread``' intrinsic identifies reads of references from heap
+locations, allowing garbage collector implementations that require read
+barriers.
+
+Arguments:
+""""""""""
+
+The second argument is the address to read from, which should be an
+address allocated from the garbage collector. The first object is a
+pointer to the start of the referenced object, if needed by the language
+runtime (otherwise null).
+
+Semantics:
+""""""""""
+
+The '``llvm.gcread``' intrinsic has the same semantics as a load
+instruction, but may be replaced with substantially more complex code by
+the garbage collector runtime, as needed. The '``llvm.gcread``'
+intrinsic may only be used in a function which :ref:`specifies a GC
+algorithm <gc>`.
+
+.. _int_gcwrite:
+
+'``llvm.gcwrite``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.gcwrite(i8* %P1, i8* %Obj, i8** %P2)
+
+Overview:
+"""""""""
+
+The '``llvm.gcwrite``' intrinsic identifies writes of references to heap
+locations, allowing garbage collector implementations that require write
+barriers (such as generational or reference counting collectors).
+
+Arguments:
+""""""""""
+
+The first argument is the reference to store, the second is the start of
+the object to store it to, and the third is the address of the field of
+Obj to store to. If the runtime does not require a pointer to the
+object, Obj may be null.
+
+Semantics:
+""""""""""
+
+The '``llvm.gcwrite``' intrinsic has the same semantics as a store
+instruction, but may be replaced with substantially more complex code by
+the garbage collector runtime, as needed. The '``llvm.gcwrite``'
+intrinsic may only be used in a function which :ref:`specifies a GC
+algorithm <gc>`.
+
+Code Generator Intrinsics
+-------------------------
+
+These intrinsics are provided by LLVM to expose special features that
+may only be implemented with code generator support.
+
+'``llvm.returnaddress``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i8* @llvm.returnaddress(i32 <level>)
+
+Overview:
+"""""""""
+
+The '``llvm.returnaddress``' intrinsic attempts to compute a
+target-specific value indicating the return address of the current
+function or one of its callers.
+
+Arguments:
+""""""""""
+
+The argument to this intrinsic indicates which function to return the
+address for. Zero indicates the calling function, one indicates its
+caller, etc. The argument is **required** to be a constant integer
+value.
+
+Semantics:
+""""""""""
+
+The '``llvm.returnaddress``' intrinsic either returns a pointer
+indicating the return address of the specified call frame, or zero if it
+cannot be identified. The value returned by this intrinsic is likely to
+be incorrect or 0 for arguments other than zero, so it should only be
+used for debugging purposes.
+
+Note that calling this intrinsic does not prevent function inlining or
+other aggressive transformations, so the value returned may not be that
+of the obvious source-language caller.
+
+'``llvm.addressofreturnaddress``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i8* @llvm.addressofreturnaddress()
+
+Overview:
+"""""""""
+
+The '``llvm.addressofreturnaddress``' intrinsic returns a target-specific
+pointer to the place in the stack frame where the return address of the
+current function is stored.
+
+Semantics:
+""""""""""
+
+Note that calling this intrinsic does not prevent function inlining or
+other aggressive transformations, so the value returned may not be that
+of the obvious source-language caller.
+
+This intrinsic is only implemented for x86.
+
+'``llvm.frameaddress``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i8* @llvm.frameaddress(i32 <level>)
+
+Overview:
+"""""""""
+
+The '``llvm.frameaddress``' intrinsic attempts to return the
+target-specific frame pointer value for the specified stack frame.
+
+Arguments:
+""""""""""
+
+The argument to this intrinsic indicates which function to return the
+frame pointer for. Zero indicates the calling function, one indicates
+its caller, etc. The argument is **required** to be a constant integer
+value.
+
+Semantics:
+""""""""""
+
+The '``llvm.frameaddress``' intrinsic either returns a pointer
+indicating the frame address of the specified call frame, or zero if it
+cannot be identified. The value returned by this intrinsic is likely to
+be incorrect or 0 for arguments other than zero, so it should only be
+used for debugging purposes.
+
+Note that calling this intrinsic does not prevent function inlining or
+other aggressive transformations, so the value returned may not be that
+of the obvious source-language caller.
+
+'``llvm.localescape``' and '``llvm.localrecover``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.localescape(...)
+ declare i8* @llvm.localrecover(i8* %func, i8* %fp, i32 %idx)
+
+Overview:
+"""""""""
+
+The '``llvm.localescape``' intrinsic escapes offsets of a collection of static
+allocas, and the '``llvm.localrecover``' intrinsic applies those offsets to a
+live frame pointer to recover the address of the allocation. The offset is
+computed during frame layout of the caller of ``llvm.localescape``.
+
+Arguments:
+""""""""""
+
+All arguments to '``llvm.localescape``' must be pointers to static allocas or
+casts of static allocas. Each function can only call '``llvm.localescape``'
+once, and it can only do so from the entry block.
+
+The ``func`` argument to '``llvm.localrecover``' must be a constant
+bitcasted pointer to a function defined in the current module. The code
+generator cannot determine the frame allocation offset of functions defined in
+other modules.
+
+The ``fp`` argument to '``llvm.localrecover``' must be a frame pointer of a
+call frame that is currently live. The return value of '``llvm.localaddress``'
+is one way to produce such a value, but various runtimes also expose a suitable
+pointer in platform-specific ways.
+
+The ``idx`` argument to '``llvm.localrecover``' indicates which alloca passed to
+'``llvm.localescape``' to recover. It is zero-indexed.
+
+Semantics:
+""""""""""
+
+These intrinsics allow a group of functions to share access to a set of local
+stack allocations of a one parent function. The parent function may call the
+'``llvm.localescape``' intrinsic once from the function entry block, and the
+child functions can use '``llvm.localrecover``' to access the escaped allocas.
+The '``llvm.localescape``' intrinsic blocks inlining, as inlining changes where
+the escaped allocas are allocated, which would break attempts to use
+'``llvm.localrecover``'.
+
+.. _int_read_register:
+.. _int_write_register:
+
+'``llvm.read_register``' and '``llvm.write_register``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i32 @llvm.read_register.i32(metadata)
+ declare i64 @llvm.read_register.i64(metadata)
+ declare void @llvm.write_register.i32(metadata, i32 @value)
+ declare void @llvm.write_register.i64(metadata, i64 @value)
+ !0 = !{!"sp\00"}
+
+Overview:
+"""""""""
+
+The '``llvm.read_register``' and '``llvm.write_register``' intrinsics
+provides access to the named register. The register must be valid on
+the architecture being compiled to. The type needs to be compatible
+with the register being read.
+
+Semantics:
+""""""""""
+
+The '``llvm.read_register``' intrinsic returns the current value of the
+register, where possible. The '``llvm.write_register``' intrinsic sets
+the current value of the register, where possible.
+
+This is useful to implement named register global variables that need
+to always be mapped to a specific register, as is common practice on
+bare-metal programs including OS kernels.
+
+The compiler doesn't check for register availability or use of the used
+register in surrounding code, including inline assembly. Because of that,
+allocatable registers are not supported.
+
+Warning: So far it only works with the stack pointer on selected
+architectures (ARM, AArch64, PowerPC and x86_64). Significant amount of
+work is needed to support other registers and even more so, allocatable
+registers.
+
+.. _int_stacksave:
+
+'``llvm.stacksave``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i8* @llvm.stacksave()
+
+Overview:
+"""""""""
+
+The '``llvm.stacksave``' intrinsic is used to remember the current state
+of the function stack, for use with
+:ref:`llvm.stackrestore <int_stackrestore>`. This is useful for
+implementing language features like scoped automatic variable sized
+arrays in C99.
+
+Semantics:
+""""""""""
+
+This intrinsic returns a opaque pointer value that can be passed to
+:ref:`llvm.stackrestore <int_stackrestore>`. When an
+``llvm.stackrestore`` intrinsic is executed with a value saved from
+``llvm.stacksave``, it effectively restores the state of the stack to
+the state it was in when the ``llvm.stacksave`` intrinsic executed. In
+practice, this pops any :ref:`alloca <i_alloca>` blocks from the stack that
+were allocated after the ``llvm.stacksave`` was executed.
+
+.. _int_stackrestore:
+
+'``llvm.stackrestore``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.stackrestore(i8* %ptr)
+
+Overview:
+"""""""""
+
+The '``llvm.stackrestore``' intrinsic is used to restore the state of
+the function stack to the state it was in when the corresponding
+:ref:`llvm.stacksave <int_stacksave>` intrinsic executed. This is
+useful for implementing language features like scoped automatic variable
+sized arrays in C99.
+
+Semantics:
+""""""""""
+
+See the description for :ref:`llvm.stacksave <int_stacksave>`.
+
+.. _int_get_dynamic_area_offset:
+
+'``llvm.get.dynamic.area.offset``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i32 @llvm.get.dynamic.area.offset.i32()
+ declare i64 @llvm.get.dynamic.area.offset.i64()
+
+Overview:
+"""""""""
+
+ The '``llvm.get.dynamic.area.offset.*``' intrinsic family is used to
+ get the offset from native stack pointer to the address of the most
+ recent dynamic alloca on the caller's stack. These intrinsics are
+ intendend for use in combination with
+ :ref:`llvm.stacksave <int_stacksave>` to get a
+ pointer to the most recent dynamic alloca. This is useful, for example,
+ for AddressSanitizer's stack unpoisoning routines.
+
+Semantics:
+""""""""""
+
+ These intrinsics return a non-negative integer value that can be used to
+ get the address of the most recent dynamic alloca, allocated by :ref:`alloca <i_alloca>`
+ on the caller's stack. In particular, for targets where stack grows downwards,
+ adding this offset to the native stack pointer would get the address of the most
+ recent dynamic alloca. For targets where stack grows upwards, the situation is a bit more
+ complicated, because subtracting this value from stack pointer would get the address
+ one past the end of the most recent dynamic alloca.
+
+ Although for most targets `llvm.get.dynamic.area.offset <int_get_dynamic_area_offset>`
+ returns just a zero, for others, such as PowerPC and PowerPC64, it returns a
+ compile-time-known constant value.
+
+ The return value type of :ref:`llvm.get.dynamic.area.offset <int_get_dynamic_area_offset>`
+ must match the target's default address space's (address space 0) pointer type.
+
+'``llvm.prefetch``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.prefetch(i8* <address>, i32 <rw>, i32 <locality>, i32 <cache type>)
+
+Overview:
+"""""""""
+
+The '``llvm.prefetch``' intrinsic is a hint to the code generator to
+insert a prefetch instruction if supported; otherwise, it is a noop.
+Prefetches have no effect on the behavior of the program but can change
+its performance characteristics.
+
+Arguments:
+""""""""""
+
+``address`` is the address to be prefetched, ``rw`` is the specifier
+determining if the fetch should be for a read (0) or write (1), and
+``locality`` is a temporal locality specifier ranging from (0) - no
+locality, to (3) - extremely local keep in cache. The ``cache type``
+specifies whether the prefetch is performed on the data (1) or
+instruction (0) cache. The ``rw``, ``locality`` and ``cache type``
+arguments must be constant integers.
+
+Semantics:
+""""""""""
+
+This intrinsic does not modify the behavior of the program. In
+particular, prefetches cannot trap and do not produce a value. On
+targets that support this intrinsic, the prefetch can provide hints to
+the processor cache for better performance.
+
+'``llvm.pcmarker``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.pcmarker(i32 <id>)
+
+Overview:
+"""""""""
+
+The '``llvm.pcmarker``' intrinsic is a method to export a Program
+Counter (PC) in a region of code to simulators and other tools. The
+method is target specific, but it is expected that the marker will use
+exported symbols to transmit the PC of the marker. The marker makes no
+guarantees that it will remain with any specific instruction after
+optimizations. It is possible that the presence of a marker will inhibit
+optimizations. The intended use is to be inserted after optimizations to
+allow correlations of simulation runs.
+
+Arguments:
+""""""""""
+
+``id`` is a numerical id identifying the marker.
+
+Semantics:
+""""""""""
+
+This intrinsic does not modify the behavior of the program. Backends
+that do not support this intrinsic may ignore it.
+
+'``llvm.readcyclecounter``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i64 @llvm.readcyclecounter()
+
+Overview:
+"""""""""
+
+The '``llvm.readcyclecounter``' intrinsic provides access to the cycle
+counter register (or similar low latency, high accuracy clocks) on those
+targets that support it. On X86, it should map to RDTSC. On Alpha, it
+should map to RPCC. As the backing counters overflow quickly (on the
+order of 9 seconds on alpha), this should only be used for small
+timings.
+
+Semantics:
+""""""""""
+
+When directly supported, reading the cycle counter should not modify any
+memory. Implementations are allowed to either return a application
+specific value or a system wide value. On backends without support, this
+is lowered to a constant 0.
+
+Note that runtime support may be conditional on the privilege-level code is
+running at and the host platform.
+
+'``llvm.clear_cache``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.clear_cache(i8*, i8*)
+
+Overview:
+"""""""""
+
+The '``llvm.clear_cache``' intrinsic ensures visibility of modifications
+in the specified range to the execution unit of the processor. On
+targets with non-unified instruction and data cache, the implementation
+flushes the instruction cache.
+
+Semantics:
+""""""""""
+
+On platforms with coherent instruction and data caches (e.g. x86), this
+intrinsic is a nop. On platforms with non-coherent instruction and data
+cache (e.g. ARM, MIPS), the intrinsic is lowered either to appropriate
+instructions or a system call, if cache flushing requires special
+privileges.
+
+The default behavior is to emit a call to ``__clear_cache`` from the run
+time library.
+
+This instrinsic does *not* empty the instruction pipeline. Modifications
+of the current function are outside the scope of the intrinsic.
+
+'``llvm.instrprof_increment``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.instrprof_increment(i8* <name>, i64 <hash>,
+ i32 <num-counters>, i32 <index>)
+
+Overview:
+"""""""""
+
+The '``llvm.instrprof_increment``' intrinsic can be emitted by a
+frontend for use with instrumentation based profiling. These will be
+lowered by the ``-instrprof`` pass to generate execution counts of a
+program at runtime.
+
+Arguments:
+""""""""""
+
+The first argument is a pointer to a global variable containing the
+name of the entity being instrumented. This should generally be the
+(mangled) function name for a set of counters.
+
+The second argument is a hash value that can be used by the consumer
+of the profile data to detect changes to the instrumented source, and
+the third is the number of counters associated with ``name``. It is an
+error if ``hash`` or ``num-counters`` differ between two instances of
+``instrprof_increment`` that refer to the same name.
+
+The last argument refers to which of the counters for ``name`` should
+be incremented. It should be a value between 0 and ``num-counters``.
+
+Semantics:
+""""""""""
+
+This intrinsic represents an increment of a profiling counter. It will
+cause the ``-instrprof`` pass to generate the appropriate data
+structures and the code to increment the appropriate value, in a
+format that can be written out by a compiler runtime and consumed via
+the ``llvm-profdata`` tool.
+
+'``llvm.instrprof_increment_step``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.instrprof_increment_step(i8* <name>, i64 <hash>,
+ i32 <num-counters>,
+ i32 <index>, i64 <step>)
+
+Overview:
+"""""""""
+
+The '``llvm.instrprof_increment_step``' intrinsic is an extension to
+the '``llvm.instrprof_increment``' intrinsic with an additional fifth
+argument to specify the step of the increment.
+
+Arguments:
+""""""""""
+The first four arguments are the same as '``llvm.instrprof_increment``'
+instrinsic.
+
+The last argument specifies the value of the increment of the counter variable.
+
+Semantics:
+""""""""""
+See description of '``llvm.instrprof_increment``' instrinsic.
+
+
+'``llvm.instrprof_value_profile``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.instrprof_value_profile(i8* <name>, i64 <hash>,
+ i64 <value>, i32 <value_kind>,
+ i32 <index>)
+
+Overview:
+"""""""""
+
+The '``llvm.instrprof_value_profile``' intrinsic can be emitted by a
+frontend for use with instrumentation based profiling. This will be
+lowered by the ``-instrprof`` pass to find out the target values,
+instrumented expressions take in a program at runtime.
+
+Arguments:
+""""""""""
+
+The first argument is a pointer to a global variable containing the
+name of the entity being instrumented. ``name`` should generally be the
+(mangled) function name for a set of counters.
+
+The second argument is a hash value that can be used by the consumer
+of the profile data to detect changes to the instrumented source. It
+is an error if ``hash`` differs between two instances of
+``llvm.instrprof_*`` that refer to the same name.
+
+The third argument is the value of the expression being profiled. The profiled
+expression's value should be representable as an unsigned 64-bit value. The
+fourth argument represents the kind of value profiling that is being done. The
+supported value profiling kinds are enumerated through the
+``InstrProfValueKind`` type declared in the
+``<include/llvm/ProfileData/InstrProf.h>`` header file. The last argument is the
+index of the instrumented expression within ``name``. It should be >= 0.
+
+Semantics:
+""""""""""
+
+This intrinsic represents the point where a call to a runtime routine
+should be inserted for value profiling of target expressions. ``-instrprof``
+pass will generate the appropriate data structures and replace the
+``llvm.instrprof_value_profile`` intrinsic with the call to the profile
+runtime library with proper arguments.
+
+'``llvm.thread.pointer``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i8* @llvm.thread.pointer()
+
+Overview:
+"""""""""
+
+The '``llvm.thread.pointer``' intrinsic returns the value of the thread
+pointer.
+
+Semantics:
+""""""""""
+
+The '``llvm.thread.pointer``' intrinsic returns a pointer to the TLS area
+for the current thread. The exact semantics of this value are target
+specific: it may point to the start of TLS area, to the end, or somewhere
+in the middle. Depending on the target, this intrinsic may read a register,
+call a helper function, read from an alternate memory space, or perform
+other operations necessary to locate the TLS area. Not all targets support
+this intrinsic.
+
+Standard C Library Intrinsics
+-----------------------------
+
+LLVM provides intrinsics for a few important standard C library
+functions. These intrinsics allow source-language front-ends to pass
+information about the alignment of the pointer arguments to the code
+generator, providing opportunity for more efficient code generation.
+
+.. _int_memcpy:
+
+'``llvm.memcpy``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.memcpy`` on any
+integer bit width and for different address spaces. Not all targets
+support all bit widths however.
+
+::
+
+ declare void @llvm.memcpy.p0i8.p0i8.i32(i8* <dest>, i8* <src>,
+ i32 <len>, i32 <align>, i1 <isvolatile>)
+ declare void @llvm.memcpy.p0i8.p0i8.i64(i8* <dest>, i8* <src>,
+ i64 <len>, i32 <align>, i1 <isvolatile>)
+
+Overview:
+"""""""""
+
+The '``llvm.memcpy.*``' intrinsics copy a block of memory from the
+source location to the destination location.
+
+Note that, unlike the standard libc function, the ``llvm.memcpy.*``
+intrinsics do not return a value, takes extra alignment/isvolatile
+arguments and the pointers can be in specified address spaces.
+
+Arguments:
+""""""""""
+
+The first argument is a pointer to the destination, the second is a
+pointer to the source. The third argument is an integer argument
+specifying the number of bytes to copy, the fourth argument is the
+alignment of the source and destination locations, and the fifth is a
+boolean indicating a volatile access.
+
+If the call to this intrinsic has an alignment value that is not 0 or 1,
+then the caller guarantees that both the source and destination pointers
+are aligned to that boundary.
+
+If the ``isvolatile`` parameter is ``true``, the ``llvm.memcpy`` call is
+a :ref:`volatile operation <volatile>`. The detailed access behavior is not
+very cleanly specified and it is unwise to depend on it.
+
+Semantics:
+""""""""""
+
+The '``llvm.memcpy.*``' intrinsics copy a block of memory from the
+source location to the destination location, which are not allowed to
+overlap. It copies "len" bytes of memory over. If the argument is known
+to be aligned to some boundary, this can be specified as the fourth
+argument, otherwise it should be set to 0 or 1 (both meaning no alignment).
+
+.. _int_memmove:
+
+'``llvm.memmove``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use llvm.memmove on any integer
+bit width and for different address space. Not all targets support all
+bit widths however.
+
+::
+
+ declare void @llvm.memmove.p0i8.p0i8.i32(i8* <dest>, i8* <src>,
+ i32 <len>, i32 <align>, i1 <isvolatile>)
+ declare void @llvm.memmove.p0i8.p0i8.i64(i8* <dest>, i8* <src>,
+ i64 <len>, i32 <align>, i1 <isvolatile>)
+
+Overview:
+"""""""""
+
+The '``llvm.memmove.*``' intrinsics move a block of memory from the
+source location to the destination location. It is similar to the
+'``llvm.memcpy``' intrinsic but allows the two memory locations to
+overlap.
+
+Note that, unlike the standard libc function, the ``llvm.memmove.*``
+intrinsics do not return a value, takes extra alignment/isvolatile
+arguments and the pointers can be in specified address spaces.
+
+Arguments:
+""""""""""
+
+The first argument is a pointer to the destination, the second is a
+pointer to the source. The third argument is an integer argument
+specifying the number of bytes to copy, the fourth argument is the
+alignment of the source and destination locations, and the fifth is a
+boolean indicating a volatile access.
+
+If the call to this intrinsic has an alignment value that is not 0 or 1,
+then the caller guarantees that the source and destination pointers are
+aligned to that boundary.
+
+If the ``isvolatile`` parameter is ``true``, the ``llvm.memmove`` call
+is a :ref:`volatile operation <volatile>`. The detailed access behavior is
+not very cleanly specified and it is unwise to depend on it.
+
+Semantics:
+""""""""""
+
+The '``llvm.memmove.*``' intrinsics copy a block of memory from the
+source location to the destination location, which may overlap. It
+copies "len" bytes of memory over. If the argument is known to be
+aligned to some boundary, this can be specified as the fourth argument,
+otherwise it should be set to 0 or 1 (both meaning no alignment).
+
+.. _int_memset:
+
+'``llvm.memset.*``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use llvm.memset on any integer
+bit width and for different address spaces. However, not all targets
+support all bit widths.
+
+::
+
+ declare void @llvm.memset.p0i8.i32(i8* <dest>, i8 <val>,
+ i32 <len>, i32 <align>, i1 <isvolatile>)
+ declare void @llvm.memset.p0i8.i64(i8* <dest>, i8 <val>,
+ i64 <len>, i32 <align>, i1 <isvolatile>)
+
+Overview:
+"""""""""
+
+The '``llvm.memset.*``' intrinsics fill a block of memory with a
+particular byte value.
+
+Note that, unlike the standard libc function, the ``llvm.memset``
+intrinsic does not return a value and takes extra alignment/volatile
+arguments. Also, the destination can be in an arbitrary address space.
+
+Arguments:
+""""""""""
+
+The first argument is a pointer to the destination to fill, the second
+is the byte value with which to fill it, the third argument is an
+integer argument specifying the number of bytes to fill, and the fourth
+argument is the known alignment of the destination location.
+
+If the call to this intrinsic has an alignment value that is not 0 or 1,
+then the caller guarantees that the destination pointer is aligned to
+that boundary.
+
+If the ``isvolatile`` parameter is ``true``, the ``llvm.memset`` call is
+a :ref:`volatile operation <volatile>`. The detailed access behavior is not
+very cleanly specified and it is unwise to depend on it.
+
+Semantics:
+""""""""""
+
+The '``llvm.memset.*``' intrinsics fill "len" bytes of memory starting
+at the destination location. If the argument is known to be aligned to
+some boundary, this can be specified as the fourth argument, otherwise
+it should be set to 0 or 1 (both meaning no alignment).
+
+'``llvm.sqrt.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.sqrt`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.sqrt.f32(float %Val)
+ declare double @llvm.sqrt.f64(double %Val)
+ declare x86_fp80 @llvm.sqrt.f80(x86_fp80 %Val)
+ declare fp128 @llvm.sqrt.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.sqrt.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.sqrt``' intrinsics return the square root of the specified value,
+returning the same value as the libm '``sqrt``' functions would, but without
+trapping or setting ``errno``.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same type.
+
+Semantics:
+""""""""""
+
+This function returns the square root of the operand if it is a nonnegative
+floating point number.
+
+'``llvm.powi.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.powi`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.powi.f32(float %Val, i32 %power)
+ declare double @llvm.powi.f64(double %Val, i32 %power)
+ declare x86_fp80 @llvm.powi.f80(x86_fp80 %Val, i32 %power)
+ declare fp128 @llvm.powi.f128(fp128 %Val, i32 %power)
+ declare ppc_fp128 @llvm.powi.ppcf128(ppc_fp128 %Val, i32 %power)
+
+Overview:
+"""""""""
+
+The '``llvm.powi.*``' intrinsics return the first operand raised to the
+specified (positive or negative) power. The order of evaluation of
+multiplications is not defined. When a vector of floating point type is
+used, the second argument remains a scalar integer value.
+
+Arguments:
+""""""""""
+
+The second argument is an integer power, and the first is a value to
+raise to that power.
+
+Semantics:
+""""""""""
+
+This function returns the first value raised to the second power with an
+unspecified sequence of rounding operations.
+
+'``llvm.sin.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.sin`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.sin.f32(float %Val)
+ declare double @llvm.sin.f64(double %Val)
+ declare x86_fp80 @llvm.sin.f80(x86_fp80 %Val)
+ declare fp128 @llvm.sin.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.sin.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.sin.*``' intrinsics return the sine of the operand.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same type.
+
+Semantics:
+""""""""""
+
+This function returns the sine of the specified operand, returning the
+same values as the libm ``sin`` functions would, and handles error
+conditions in the same way.
+
+'``llvm.cos.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.cos`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.cos.f32(float %Val)
+ declare double @llvm.cos.f64(double %Val)
+ declare x86_fp80 @llvm.cos.f80(x86_fp80 %Val)
+ declare fp128 @llvm.cos.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.cos.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.cos.*``' intrinsics return the cosine of the operand.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same type.
+
+Semantics:
+""""""""""
+
+This function returns the cosine of the specified operand, returning the
+same values as the libm ``cos`` functions would, and handles error
+conditions in the same way.
+
+'``llvm.pow.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.pow`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.pow.f32(float %Val, float %Power)
+ declare double @llvm.pow.f64(double %Val, double %Power)
+ declare x86_fp80 @llvm.pow.f80(x86_fp80 %Val, x86_fp80 %Power)
+ declare fp128 @llvm.pow.f128(fp128 %Val, fp128 %Power)
+ declare ppc_fp128 @llvm.pow.ppcf128(ppc_fp128 %Val, ppc_fp128 Power)
+
+Overview:
+"""""""""
+
+The '``llvm.pow.*``' intrinsics return the first operand raised to the
+specified (positive or negative) power.
+
+Arguments:
+""""""""""
+
+The second argument is a floating point power, and the first is a value
+to raise to that power.
+
+Semantics:
+""""""""""
+
+This function returns the first value raised to the second power,
+returning the same values as the libm ``pow`` functions would, and
+handles error conditions in the same way.
+
+'``llvm.exp.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.exp`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.exp.f32(float %Val)
+ declare double @llvm.exp.f64(double %Val)
+ declare x86_fp80 @llvm.exp.f80(x86_fp80 %Val)
+ declare fp128 @llvm.exp.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.exp.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.exp.*``' intrinsics compute the base-e exponential of the specified
+value.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same type.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``exp`` functions
+would, and handles error conditions in the same way.
+
+'``llvm.exp2.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.exp2`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.exp2.f32(float %Val)
+ declare double @llvm.exp2.f64(double %Val)
+ declare x86_fp80 @llvm.exp2.f80(x86_fp80 %Val)
+ declare fp128 @llvm.exp2.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.exp2.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.exp2.*``' intrinsics compute the base-2 exponential of the
+specified value.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same type.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``exp2`` functions
+would, and handles error conditions in the same way.
+
+'``llvm.log.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.log`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.log.f32(float %Val)
+ declare double @llvm.log.f64(double %Val)
+ declare x86_fp80 @llvm.log.f80(x86_fp80 %Val)
+ declare fp128 @llvm.log.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.log.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.log.*``' intrinsics compute the base-e logarithm of the specified
+value.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same type.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``log`` functions
+would, and handles error conditions in the same way.
+
+'``llvm.log10.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.log10`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.log10.f32(float %Val)
+ declare double @llvm.log10.f64(double %Val)
+ declare x86_fp80 @llvm.log10.f80(x86_fp80 %Val)
+ declare fp128 @llvm.log10.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.log10.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.log10.*``' intrinsics compute the base-10 logarithm of the
+specified value.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same type.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``log10`` functions
+would, and handles error conditions in the same way.
+
+'``llvm.log2.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.log2`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.log2.f32(float %Val)
+ declare double @llvm.log2.f64(double %Val)
+ declare x86_fp80 @llvm.log2.f80(x86_fp80 %Val)
+ declare fp128 @llvm.log2.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.log2.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.log2.*``' intrinsics compute the base-2 logarithm of the specified
+value.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same type.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``log2`` functions
+would, and handles error conditions in the same way.
+
+'``llvm.fma.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.fma`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.fma.f32(float %a, float %b, float %c)
+ declare double @llvm.fma.f64(double %a, double %b, double %c)
+ declare x86_fp80 @llvm.fma.f80(x86_fp80 %a, x86_fp80 %b, x86_fp80 %c)
+ declare fp128 @llvm.fma.f128(fp128 %a, fp128 %b, fp128 %c)
+ declare ppc_fp128 @llvm.fma.ppcf128(ppc_fp128 %a, ppc_fp128 %b, ppc_fp128 %c)
+
+Overview:
+"""""""""
+
+The '``llvm.fma.*``' intrinsics perform the fused multiply-add
+operation.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same
+type.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``fma`` functions
+would, and does not set errno.
+
+'``llvm.fabs.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.fabs`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.fabs.f32(float %Val)
+ declare double @llvm.fabs.f64(double %Val)
+ declare x86_fp80 @llvm.fabs.f80(x86_fp80 %Val)
+ declare fp128 @llvm.fabs.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.fabs.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.fabs.*``' intrinsics return the absolute value of the
+operand.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same
+type.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``fabs`` functions
+would, and handles error conditions in the same way.
+
+'``llvm.minnum.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.minnum`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.minnum.f32(float %Val0, float %Val1)
+ declare double @llvm.minnum.f64(double %Val0, double %Val1)
+ declare x86_fp80 @llvm.minnum.f80(x86_fp80 %Val0, x86_fp80 %Val1)
+ declare fp128 @llvm.minnum.f128(fp128 %Val0, fp128 %Val1)
+ declare ppc_fp128 @llvm.minnum.ppcf128(ppc_fp128 %Val0, ppc_fp128 %Val1)
+
+Overview:
+"""""""""
+
+The '``llvm.minnum.*``' intrinsics return the minimum of the two
+arguments.
+
+
+Arguments:
+""""""""""
+
+The arguments and return value are floating point numbers of the same
+type.
+
+Semantics:
+""""""""""
+
+Follows the IEEE-754 semantics for minNum, which also match for libm's
+fmin.
+
+If either operand is a NaN, returns the other non-NaN operand. Returns
+NaN only if both operands are NaN. If the operands compare equal,
+returns a value that compares equal to both operands. This means that
+fmin(+/-0.0, +/-0.0) could return either -0.0 or 0.0.
+
+'``llvm.maxnum.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.maxnum`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.maxnum.f32(float %Val0, float %Val1l)
+ declare double @llvm.maxnum.f64(double %Val0, double %Val1)
+ declare x86_fp80 @llvm.maxnum.f80(x86_fp80 %Val0, x86_fp80 %Val1)
+ declare fp128 @llvm.maxnum.f128(fp128 %Val0, fp128 %Val1)
+ declare ppc_fp128 @llvm.maxnum.ppcf128(ppc_fp128 %Val0, ppc_fp128 %Val1)
+
+Overview:
+"""""""""
+
+The '``llvm.maxnum.*``' intrinsics return the maximum of the two
+arguments.
+
+
+Arguments:
+""""""""""
+
+The arguments and return value are floating point numbers of the same
+type.
+
+Semantics:
+""""""""""
+Follows the IEEE-754 semantics for maxNum, which also match for libm's
+fmax.
+
+If either operand is a NaN, returns the other non-NaN operand. Returns
+NaN only if both operands are NaN. If the operands compare equal,
+returns a value that compares equal to both operands. This means that
+fmax(+/-0.0, +/-0.0) could return either -0.0 or 0.0.
+
+'``llvm.copysign.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.copysign`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.copysign.f32(float %Mag, float %Sgn)
+ declare double @llvm.copysign.f64(double %Mag, double %Sgn)
+ declare x86_fp80 @llvm.copysign.f80(x86_fp80 %Mag, x86_fp80 %Sgn)
+ declare fp128 @llvm.copysign.f128(fp128 %Mag, fp128 %Sgn)
+ declare ppc_fp128 @llvm.copysign.ppcf128(ppc_fp128 %Mag, ppc_fp128 %Sgn)
+
+Overview:
+"""""""""
+
+The '``llvm.copysign.*``' intrinsics return a value with the magnitude of the
+first operand and the sign of the second operand.
+
+Arguments:
+""""""""""
+
+The arguments and return value are floating point numbers of the same
+type.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``copysign``
+functions would, and handles error conditions in the same way.
+
+'``llvm.floor.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.floor`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.floor.f32(float %Val)
+ declare double @llvm.floor.f64(double %Val)
+ declare x86_fp80 @llvm.floor.f80(x86_fp80 %Val)
+ declare fp128 @llvm.floor.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.floor.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.floor.*``' intrinsics return the floor of the operand.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same
+type.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``floor`` functions
+would, and handles error conditions in the same way.
+
+'``llvm.ceil.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.ceil`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.ceil.f32(float %Val)
+ declare double @llvm.ceil.f64(double %Val)
+ declare x86_fp80 @llvm.ceil.f80(x86_fp80 %Val)
+ declare fp128 @llvm.ceil.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.ceil.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.ceil.*``' intrinsics return the ceiling of the operand.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same
+type.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``ceil`` functions
+would, and handles error conditions in the same way.
+
+'``llvm.trunc.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.trunc`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.trunc.f32(float %Val)
+ declare double @llvm.trunc.f64(double %Val)
+ declare x86_fp80 @llvm.trunc.f80(x86_fp80 %Val)
+ declare fp128 @llvm.trunc.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.trunc.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.trunc.*``' intrinsics returns the operand rounded to the
+nearest integer not larger in magnitude than the operand.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same
+type.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``trunc`` functions
+would, and handles error conditions in the same way.
+
+'``llvm.rint.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.rint`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.rint.f32(float %Val)
+ declare double @llvm.rint.f64(double %Val)
+ declare x86_fp80 @llvm.rint.f80(x86_fp80 %Val)
+ declare fp128 @llvm.rint.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.rint.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.rint.*``' intrinsics returns the operand rounded to the
+nearest integer. It may raise an inexact floating-point exception if the
+operand isn't an integer.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same
+type.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``rint`` functions
+would, and handles error conditions in the same way.
+
+'``llvm.nearbyint.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.nearbyint`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.nearbyint.f32(float %Val)
+ declare double @llvm.nearbyint.f64(double %Val)
+ declare x86_fp80 @llvm.nearbyint.f80(x86_fp80 %Val)
+ declare fp128 @llvm.nearbyint.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.nearbyint.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.nearbyint.*``' intrinsics returns the operand rounded to the
+nearest integer.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same
+type.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``nearbyint``
+functions would, and handles error conditions in the same way.
+
+'``llvm.round.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.round`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.round.f32(float %Val)
+ declare double @llvm.round.f64(double %Val)
+ declare x86_fp80 @llvm.round.f80(x86_fp80 %Val)
+ declare fp128 @llvm.round.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.round.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.round.*``' intrinsics returns the operand rounded to the
+nearest integer.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same
+type.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``round``
+functions would, and handles error conditions in the same way.
+
+Bit Manipulation Intrinsics
+---------------------------
+
+LLVM provides intrinsics for a few important bit manipulation
+operations. These allow efficient code generation for some algorithms.
+
+'``llvm.bitreverse.*``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic function. You can use bitreverse on any
+integer type.
+
+::
+
+ declare i16 @llvm.bitreverse.i16(i16 <id>)
+ declare i32 @llvm.bitreverse.i32(i32 <id>)
+ declare i64 @llvm.bitreverse.i64(i64 <id>)
+
+Overview:
+"""""""""
+
+The '``llvm.bitreverse``' family of intrinsics is used to reverse the
+bitpattern of an integer value; for example ``0b10110110`` becomes
+``0b01101101``.
+
+Semantics:
+""""""""""
+
+The ``llvm.bitreverse.iN`` intrinsic returns an iN value that has bit
+``M`` in the input moved to bit ``N-M`` in the output.
+
+'``llvm.bswap.*``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic function. You can use bswap on any
+integer type that is an even number of bytes (i.e. BitWidth % 16 == 0).
+
+::
+
+ declare i16 @llvm.bswap.i16(i16 <id>)
+ declare i32 @llvm.bswap.i32(i32 <id>)
+ declare i64 @llvm.bswap.i64(i64 <id>)
+
+Overview:
+"""""""""
+
+The '``llvm.bswap``' family of intrinsics is used to byte swap integer
+values with an even number of bytes (positive multiple of 16 bits).
+These are useful for performing operations on data that is not in the
+target's native byte order.
+
+Semantics:
+""""""""""
+
+The ``llvm.bswap.i16`` intrinsic returns an i16 value that has the high
+and low byte of the input i16 swapped. Similarly, the ``llvm.bswap.i32``
+intrinsic returns an i32 value that has the four bytes of the input i32
+swapped, so that if the input bytes are numbered 0, 1, 2, 3 then the
+returned i32 will have its bytes in 3, 2, 1, 0 order. The
+``llvm.bswap.i48``, ``llvm.bswap.i64`` and other intrinsics extend this
+concept to additional even-byte lengths (6 bytes, 8 bytes and more,
+respectively).
+
+'``llvm.ctpop.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use llvm.ctpop on any integer
+bit width, or on any vector with integer elements. Not all targets
+support all bit widths or vector types, however.
+
+::
+
+ declare i8 @llvm.ctpop.i8(i8 <src>)
+ declare i16 @llvm.ctpop.i16(i16 <src>)
+ declare i32 @llvm.ctpop.i32(i32 <src>)
+ declare i64 @llvm.ctpop.i64(i64 <src>)
+ declare i256 @llvm.ctpop.i256(i256 <src>)
+ declare <2 x i32> @llvm.ctpop.v2i32(<2 x i32> <src>)
+
+Overview:
+"""""""""
+
+The '``llvm.ctpop``' family of intrinsics counts the number of bits set
+in a value.
+
+Arguments:
+""""""""""
+
+The only argument is the value to be counted. The argument may be of any
+integer type, or a vector with integer elements. The return type must
+match the argument type.
+
+Semantics:
+""""""""""
+
+The '``llvm.ctpop``' intrinsic counts the 1's in a variable, or within
+each element of a vector.
+
+'``llvm.ctlz.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.ctlz`` on any
+integer bit width, or any vector whose elements are integers. Not all
+targets support all bit widths or vector types, however.
+
+::
+
+ declare i8 @llvm.ctlz.i8 (i8 <src>, i1 <is_zero_undef>)
+ declare i16 @llvm.ctlz.i16 (i16 <src>, i1 <is_zero_undef>)
+ declare i32 @llvm.ctlz.i32 (i32 <src>, i1 <is_zero_undef>)
+ declare i64 @llvm.ctlz.i64 (i64 <src>, i1 <is_zero_undef>)
+ declare i256 @llvm.ctlz.i256(i256 <src>, i1 <is_zero_undef>)
+ declare <2 x i32> @llvm.ctlz.v2i32(<2 x i32> <src>, i1 <is_zero_undef>)
+
+Overview:
+"""""""""
+
+The '``llvm.ctlz``' family of intrinsic functions counts the number of
+leading zeros in a variable.
+
+Arguments:
+""""""""""
+
+The first argument is the value to be counted. This argument may be of
+any integer type, or a vector with integer element type. The return
+type must match the first argument type.
+
+The second argument must be a constant and is a flag to indicate whether
+the intrinsic should ensure that a zero as the first argument produces a
+defined result. Historically some architectures did not provide a
+defined result for zero values as efficiently, and many algorithms are
+now predicated on avoiding zero-value inputs.
+
+Semantics:
+""""""""""
+
+The '``llvm.ctlz``' intrinsic counts the leading (most significant)
+zeros in a variable, or within each element of the vector. If
+``src == 0`` then the result is the size in bits of the type of ``src``
+if ``is_zero_undef == 0`` and ``undef`` otherwise. For example,
+``llvm.ctlz(i32 2) = 30``.
+
+'``llvm.cttz.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.cttz`` on any
+integer bit width, or any vector of integer elements. Not all targets
+support all bit widths or vector types, however.
+
+::
+
+ declare i8 @llvm.cttz.i8 (i8 <src>, i1 <is_zero_undef>)
+ declare i16 @llvm.cttz.i16 (i16 <src>, i1 <is_zero_undef>)
+ declare i32 @llvm.cttz.i32 (i32 <src>, i1 <is_zero_undef>)
+ declare i64 @llvm.cttz.i64 (i64 <src>, i1 <is_zero_undef>)
+ declare i256 @llvm.cttz.i256(i256 <src>, i1 <is_zero_undef>)
+ declare <2 x i32> @llvm.cttz.v2i32(<2 x i32> <src>, i1 <is_zero_undef>)
+
+Overview:
+"""""""""
+
+The '``llvm.cttz``' family of intrinsic functions counts the number of
+trailing zeros.
+
+Arguments:
+""""""""""
+
+The first argument is the value to be counted. This argument may be of
+any integer type, or a vector with integer element type. The return
+type must match the first argument type.
+
+The second argument must be a constant and is a flag to indicate whether
+the intrinsic should ensure that a zero as the first argument produces a
+defined result. Historically some architectures did not provide a
+defined result for zero values as efficiently, and many algorithms are
+now predicated on avoiding zero-value inputs.
+
+Semantics:
+""""""""""
+
+The '``llvm.cttz``' intrinsic counts the trailing (least significant)
+zeros in a variable, or within each element of a vector. If ``src == 0``
+then the result is the size in bits of the type of ``src`` if
+``is_zero_undef == 0`` and ``undef`` otherwise. For example,
+``llvm.cttz(2) = 1``.
+
+.. _int_overflow:
+
+Arithmetic with Overflow Intrinsics
+-----------------------------------
+
+LLVM provides intrinsics for fast arithmetic overflow checking.
+
+Each of these intrinsics returns a two-element struct. The first
+element of this struct contains the result of the corresponding
+arithmetic operation modulo 2\ :sup:`n`\ , where n is the bit width of
+the result. Therefore, for example, the first element of the struct
+returned by ``llvm.sadd.with.overflow.i32`` is always the same as the
+result of a 32-bit ``add`` instruction with the same operands, where
+the ``add`` is *not* modified by an ``nsw`` or ``nuw`` flag.
+
+The second element of the result is an ``i1`` that is 1 if the
+arithmetic operation overflowed and 0 otherwise. An operation
+overflows if, for any values of its operands ``A`` and ``B`` and for
+any ``N`` larger than the operands' width, ``ext(A op B) to iN`` is
+not equal to ``(ext(A) to iN) op (ext(B) to iN)`` where ``ext`` is
+``sext`` for signed overflow and ``zext`` for unsigned overflow, and
+``op`` is the underlying arithmetic operation.
+
+The behavior of these intrinsics is well-defined for all argument
+values.
+
+'``llvm.sadd.with.overflow.*``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.sadd.with.overflow``
+on any integer bit width.
+
+::
+
+ declare {i16, i1} @llvm.sadd.with.overflow.i16(i16 %a, i16 %b)
+ declare {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b)
+ declare {i64, i1} @llvm.sadd.with.overflow.i64(i64 %a, i64 %b)
+
+Overview:
+"""""""""
+
+The '``llvm.sadd.with.overflow``' family of intrinsic functions perform
+a signed addition of the two arguments, and indicate whether an overflow
+occurred during the signed summation.
+
+Arguments:
+""""""""""
+
+The arguments (%a and %b) and the first element of the result structure
+may be of integer types of any bit width, but they must have the same
+bit width. The second element of the result structure must be of type
+``i1``. ``%a`` and ``%b`` are the two values that will undergo signed
+addition.
+
+Semantics:
+""""""""""
+
+The '``llvm.sadd.with.overflow``' family of intrinsic functions perform
+a signed addition of the two variables. They return a structure --- the
+first element of which is the signed summation, and the second element
+of which is a bit specifying if the signed summation resulted in an
+overflow.
+
+Examples:
+"""""""""
+
+.. code-block:: llvm
+
+ %res = call {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b)
+ %sum = extractvalue {i32, i1} %res, 0
+ %obit = extractvalue {i32, i1} %res, 1
+ br i1 %obit, label %overflow, label %normal
+
+'``llvm.uadd.with.overflow.*``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.uadd.with.overflow``
+on any integer bit width.
+
+::
+
+ declare {i16, i1} @llvm.uadd.with.overflow.i16(i16 %a, i16 %b)
+ declare {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)
+ declare {i64, i1} @llvm.uadd.with.overflow.i64(i64 %a, i64 %b)
+
+Overview:
+"""""""""
+
+The '``llvm.uadd.with.overflow``' family of intrinsic functions perform
+an unsigned addition of the two arguments, and indicate whether a carry
+occurred during the unsigned summation.
+
+Arguments:
+""""""""""
+
+The arguments (%a and %b) and the first element of the result structure
+may be of integer types of any bit width, but they must have the same
+bit width. The second element of the result structure must be of type
+``i1``. ``%a`` and ``%b`` are the two values that will undergo unsigned
+addition.
+
+Semantics:
+""""""""""
+
+The '``llvm.uadd.with.overflow``' family of intrinsic functions perform
+an unsigned addition of the two arguments. They return a structure --- the
+first element of which is the sum, and the second element of which is a
+bit specifying if the unsigned summation resulted in a carry.
+
+Examples:
+"""""""""
+
+.. code-block:: llvm
+
+ %res = call {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)
+ %sum = extractvalue {i32, i1} %res, 0
+ %obit = extractvalue {i32, i1} %res, 1
+ br i1 %obit, label %carry, label %normal
+
+'``llvm.ssub.with.overflow.*``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.ssub.with.overflow``
+on any integer bit width.
+
+::
+
+ declare {i16, i1} @llvm.ssub.with.overflow.i16(i16 %a, i16 %b)
+ declare {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b)
+ declare {i64, i1} @llvm.ssub.with.overflow.i64(i64 %a, i64 %b)
+
+Overview:
+"""""""""
+
+The '``llvm.ssub.with.overflow``' family of intrinsic functions perform
+a signed subtraction of the two arguments, and indicate whether an
+overflow occurred during the signed subtraction.
+
+Arguments:
+""""""""""
+
+The arguments (%a and %b) and the first element of the result structure
+may be of integer types of any bit width, but they must have the same
+bit width. The second element of the result structure must be of type
+``i1``. ``%a`` and ``%b`` are the two values that will undergo signed
+subtraction.
+
+Semantics:
+""""""""""
+
+The '``llvm.ssub.with.overflow``' family of intrinsic functions perform
+a signed subtraction of the two arguments. They return a structure --- the
+first element of which is the subtraction, and the second element of
+which is a bit specifying if the signed subtraction resulted in an
+overflow.
+
+Examples:
+"""""""""
+
+.. code-block:: llvm
+
+ %res = call {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b)
+ %sum = extractvalue {i32, i1} %res, 0
+ %obit = extractvalue {i32, i1} %res, 1
+ br i1 %obit, label %overflow, label %normal
+
+'``llvm.usub.with.overflow.*``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.usub.with.overflow``
+on any integer bit width.
+
+::
+
+ declare {i16, i1} @llvm.usub.with.overflow.i16(i16 %a, i16 %b)
+ declare {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b)
+ declare {i64, i1} @llvm.usub.with.overflow.i64(i64 %a, i64 %b)
+
+Overview:
+"""""""""
+
+The '``llvm.usub.with.overflow``' family of intrinsic functions perform
+an unsigned subtraction of the two arguments, and indicate whether an
+overflow occurred during the unsigned subtraction.
+
+Arguments:
+""""""""""
+
+The arguments (%a and %b) and the first element of the result structure
+may be of integer types of any bit width, but they must have the same
+bit width. The second element of the result structure must be of type
+``i1``. ``%a`` and ``%b`` are the two values that will undergo unsigned
+subtraction.
+
+Semantics:
+""""""""""
+
+The '``llvm.usub.with.overflow``' family of intrinsic functions perform
+an unsigned subtraction of the two arguments. They return a structure ---
+the first element of which is the subtraction, and the second element of
+which is a bit specifying if the unsigned subtraction resulted in an
+overflow.
+
+Examples:
+"""""""""
+
+.. code-block:: llvm
+
+ %res = call {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b)
+ %sum = extractvalue {i32, i1} %res, 0
+ %obit = extractvalue {i32, i1} %res, 1
+ br i1 %obit, label %overflow, label %normal
+
+'``llvm.smul.with.overflow.*``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.smul.with.overflow``
+on any integer bit width.
+
+::
+
+ declare {i16, i1} @llvm.smul.with.overflow.i16(i16 %a, i16 %b)
+ declare {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b)
+ declare {i64, i1} @llvm.smul.with.overflow.i64(i64 %a, i64 %b)
+
+Overview:
+"""""""""
+
+The '``llvm.smul.with.overflow``' family of intrinsic functions perform
+a signed multiplication of the two arguments, and indicate whether an
+overflow occurred during the signed multiplication.
+
+Arguments:
+""""""""""
+
+The arguments (%a and %b) and the first element of the result structure
+may be of integer types of any bit width, but they must have the same
+bit width. The second element of the result structure must be of type
+``i1``. ``%a`` and ``%b`` are the two values that will undergo signed
+multiplication.
+
+Semantics:
+""""""""""
+
+The '``llvm.smul.with.overflow``' family of intrinsic functions perform
+a signed multiplication of the two arguments. They return a structure ---
+the first element of which is the multiplication, and the second element
+of which is a bit specifying if the signed multiplication resulted in an
+overflow.
+
+Examples:
+"""""""""
+
+.. code-block:: llvm
+
+ %res = call {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b)
+ %sum = extractvalue {i32, i1} %res, 0
+ %obit = extractvalue {i32, i1} %res, 1
+ br i1 %obit, label %overflow, label %normal
+
+'``llvm.umul.with.overflow.*``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.umul.with.overflow``
+on any integer bit width.
+
+::
+
+ declare {i16, i1} @llvm.umul.with.overflow.i16(i16 %a, i16 %b)
+ declare {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b)
+ declare {i64, i1} @llvm.umul.with.overflow.i64(i64 %a, i64 %b)
+
+Overview:
+"""""""""
+
+The '``llvm.umul.with.overflow``' family of intrinsic functions perform
+a unsigned multiplication of the two arguments, and indicate whether an
+overflow occurred during the unsigned multiplication.
+
+Arguments:
+""""""""""
+
+The arguments (%a and %b) and the first element of the result structure
+may be of integer types of any bit width, but they must have the same
+bit width. The second element of the result structure must be of type
+``i1``. ``%a`` and ``%b`` are the two values that will undergo unsigned
+multiplication.
+
+Semantics:
+""""""""""
+
+The '``llvm.umul.with.overflow``' family of intrinsic functions perform
+an unsigned multiplication of the two arguments. They return a structure ---
+the first element of which is the multiplication, and the second
+element of which is a bit specifying if the unsigned multiplication
+resulted in an overflow.
+
+Examples:
+"""""""""
+
+.. code-block:: llvm
+
+ %res = call {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b)
+ %sum = extractvalue {i32, i1} %res, 0
+ %obit = extractvalue {i32, i1} %res, 1
+ br i1 %obit, label %overflow, label %normal
+
+Specialised Arithmetic Intrinsics
+---------------------------------
+
+'``llvm.canonicalize.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare float @llvm.canonicalize.f32(float %a)
+ declare double @llvm.canonicalize.f64(double %b)
+
+Overview:
+"""""""""
+
+The '``llvm.canonicalize.*``' intrinsic returns the platform specific canonical
+encoding of a floating point number. This canonicalization is useful for
+implementing certain numeric primitives such as frexp. The canonical encoding is
+defined by IEEE-754-2008 to be:
+
+::
+
+ 2.1.8 canonical encoding: The preferred encoding of a floating-point
+ representation in a format. Applied to declets, significands of finite
+ numbers, infinities, and NaNs, especially in decimal formats.
+
+This operation can also be considered equivalent to the IEEE-754-2008
+conversion of a floating-point value to the same format. NaNs are handled
+according to section 6.2.
+
+Examples of non-canonical encodings:
+
+- x87 pseudo denormals, pseudo NaNs, pseudo Infinity, Unnormals. These are
+ converted to a canonical representation per hardware-specific protocol.
+- Many normal decimal floating point numbers have non-canonical alternative
+ encodings.
+- Some machines, like GPUs or ARMv7 NEON, do not support subnormal values.
+ These are treated as non-canonical encodings of zero and will be flushed to
+ a zero of the same sign by this operation.
+
+Note that per IEEE-754-2008 6.2, systems that support signaling NaNs with
+default exception handling must signal an invalid exception, and produce a
+quiet NaN result.
+
+This function should always be implementable as multiplication by 1.0, provided
+that the compiler does not constant fold the operation. Likewise, division by
+1.0 and ``llvm.minnum(x, x)`` are possible implementations. Addition with
+-0.0 is also sufficient provided that the rounding mode is not -Infinity.
+
+``@llvm.canonicalize`` must preserve the equality relation. That is:
+
+- ``(@llvm.canonicalize(x) == x)`` is equivalent to ``(x == x)``
+- ``(@llvm.canonicalize(x) == @llvm.canonicalize(y))`` is equivalent to
+ to ``(x == y)``
+
+Additionally, the sign of zero must be conserved:
+``@llvm.canonicalize(-0.0) = -0.0`` and ``@llvm.canonicalize(+0.0) = +0.0``
+
+The payload bits of a NaN must be conserved, with two exceptions.
+First, environments which use only a single canonical representation of NaN
+must perform said canonicalization. Second, SNaNs must be quieted per the
+usual methods.
+
+The canonicalization operation may be optimized away if:
+
+- The input is known to be canonical. For example, it was produced by a
+ floating-point operation that is required by the standard to be canonical.
+- The result is consumed only by (or fused with) other floating-point
+ operations. That is, the bits of the floating point value are not examined.
+
+'``llvm.fmuladd.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare float @llvm.fmuladd.f32(float %a, float %b, float %c)
+ declare double @llvm.fmuladd.f64(double %a, double %b, double %c)
+
+Overview:
+"""""""""
+
+The '``llvm.fmuladd.*``' intrinsic functions represent multiply-add
+expressions that can be fused if the code generator determines that (a) the
+target instruction set has support for a fused operation, and (b) that the
+fused operation is more efficient than the equivalent, separate pair of mul
+and add instructions.
+
+Arguments:
+""""""""""
+
+The '``llvm.fmuladd.*``' intrinsics each take three arguments: two
+multiplicands, a and b, and an addend c.
+
+Semantics:
+""""""""""
+
+The expression:
+
+::
+
+ %0 = call float @llvm.fmuladd.f32(%a, %b, %c)
+
+is equivalent to the expression a \* b + c, except that rounding will
+not be performed between the multiplication and addition steps if the
+code generator fuses the operations. Fusion is not guaranteed, even if
+the target platform supports it. If a fused multiply-add is required the
+corresponding llvm.fma.\* intrinsic function should be used
+instead. This never sets errno, just as '``llvm.fma.*``'.
+
+Examples:
+"""""""""
+
+.. code-block:: llvm
+
+ %r2 = call float @llvm.fmuladd.f32(float %a, float %b, float %c) ; yields float:r2 = (a * b) + c
+
+
+Experimental Vector Reduction Intrinsics
+----------------------------------------
+
+Horizontal reductions of vectors can be expressed using the following
+intrinsics. Each one takes a vector operand as an input and applies its
+respective operation across all elements of the vector, returning a single
+scalar result of the same element type.
+
+
+'``llvm.experimental.vector.reduce.add.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i32 @llvm.experimental.vector.reduce.add.i32.v4i32(<4 x i32> %a)
+ declare i64 @llvm.experimental.vector.reduce.add.i64.v2i64(<2 x i64> %a)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.vector.reduce.add.*``' intrinsics do an integer ``ADD``
+reduction of a vector, returning the result as a scalar. The return type matches
+the element-type of the vector input.
+
+Arguments:
+""""""""""
+The argument to this intrinsic must be a vector of integer values.
+
+'``llvm.experimental.vector.reduce.fadd.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare float @llvm.experimental.vector.reduce.fadd.f32.v4f32(float %acc, <4 x float> %a)
+ declare double @llvm.experimental.vector.reduce.fadd.f64.v2f64(double %acc, <2 x double> %a)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.vector.reduce.fadd.*``' intrinsics do a floating point
+``ADD`` reduction of a vector, returning the result as a scalar. The return type
+matches the element-type of the vector input.
+
+If the intrinsic call has fast-math flags, then the reduction will not preserve
+the associativity of an equivalent scalarized counterpart. If it does not have
+fast-math flags, then the reduction will be *ordered*, implying that the
+operation respects the associativity of a scalarized reduction.
+
+
+Arguments:
+""""""""""
+The first argument to this intrinsic is a scalar accumulator value, which is
+only used when there are no fast-math flags attached. This argument may be undef
+when fast-math flags are used.
+
+The second argument must be a vector of floating point values.
+
+Examples:
+"""""""""
+
+.. code-block:: llvm
+
+ %fast = call fast float @llvm.experimental.vector.reduce.fadd.f32.v4f32(float undef, <4 x float> %input) ; fast reduction
+ %ord = call float @llvm.experimental.vector.reduce.fadd.f32.v4f32(float %acc, <4 x float> %input) ; ordered reduction
+
+
+'``llvm.experimental.vector.reduce.mul.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i32 @llvm.experimental.vector.reduce.mul.i32.v4i32(<4 x i32> %a)
+ declare i64 @llvm.experimental.vector.reduce.mul.i64.v2i64(<2 x i64> %a)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.vector.reduce.mul.*``' intrinsics do an integer ``MUL``
+reduction of a vector, returning the result as a scalar. The return type matches
+the element-type of the vector input.
+
+Arguments:
+""""""""""
+The argument to this intrinsic must be a vector of integer values.
+
+'``llvm.experimental.vector.reduce.fmul.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare float @llvm.experimental.vector.reduce.fmul.f32.v4f32(float %acc, <4 x float> %a)
+ declare double @llvm.experimental.vector.reduce.fmul.f64.v2f64(double %acc, <2 x double> %a)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.vector.reduce.fmul.*``' intrinsics do a floating point
+``MUL`` reduction of a vector, returning the result as a scalar. The return type
+matches the element-type of the vector input.
+
+If the intrinsic call has fast-math flags, then the reduction will not preserve
+the associativity of an equivalent scalarized counterpart. If it does not have
+fast-math flags, then the reduction will be *ordered*, implying that the
+operation respects the associativity of a scalarized reduction.
+
+
+Arguments:
+""""""""""
+The first argument to this intrinsic is a scalar accumulator value, which is
+only used when there are no fast-math flags attached. This argument may be undef
+when fast-math flags are used.
+
+The second argument must be a vector of floating point values.
+
+Examples:
+"""""""""
+
+.. code-block:: llvm
+
+ %fast = call fast float @llvm.experimental.vector.reduce.fmul.f32.v4f32(float undef, <4 x float> %input) ; fast reduction
+ %ord = call float @llvm.experimental.vector.reduce.fmul.f32.v4f32(float %acc, <4 x float> %input) ; ordered reduction
+
+'``llvm.experimental.vector.reduce.and.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i32 @llvm.experimental.vector.reduce.and.i32.v4i32(<4 x i32> %a)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.vector.reduce.and.*``' intrinsics do a bitwise ``AND``
+reduction of a vector, returning the result as a scalar. The return type matches
+the element-type of the vector input.
+
+Arguments:
+""""""""""
+The argument to this intrinsic must be a vector of integer values.
+
+'``llvm.experimental.vector.reduce.or.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i32 @llvm.experimental.vector.reduce.or.i32.v4i32(<4 x i32> %a)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.vector.reduce.or.*``' intrinsics do a bitwise ``OR`` reduction
+of a vector, returning the result as a scalar. The return type matches the
+element-type of the vector input.
+
+Arguments:
+""""""""""
+The argument to this intrinsic must be a vector of integer values.
+
+'``llvm.experimental.vector.reduce.xor.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i32 @llvm.experimental.vector.reduce.xor.i32.v4i32(<4 x i32> %a)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.vector.reduce.xor.*``' intrinsics do a bitwise ``XOR``
+reduction of a vector, returning the result as a scalar. The return type matches
+the element-type of the vector input.
+
+Arguments:
+""""""""""
+The argument to this intrinsic must be a vector of integer values.
+
+'``llvm.experimental.vector.reduce.smax.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i32 @llvm.experimental.vector.reduce.smax.i32.v4i32(<4 x i32> %a)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.vector.reduce.smax.*``' intrinsics do a signed integer
+``MAX`` reduction of a vector, returning the result as a scalar. The return type
+matches the element-type of the vector input.
+
+Arguments:
+""""""""""
+The argument to this intrinsic must be a vector of integer values.
+
+'``llvm.experimental.vector.reduce.smin.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i32 @llvm.experimental.vector.reduce.smin.i32.v4i32(<4 x i32> %a)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.vector.reduce.smin.*``' intrinsics do a signed integer
+``MIN`` reduction of a vector, returning the result as a scalar. The return type
+matches the element-type of the vector input.
+
+Arguments:
+""""""""""
+The argument to this intrinsic must be a vector of integer values.
+
+'``llvm.experimental.vector.reduce.umax.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i32 @llvm.experimental.vector.reduce.umax.i32.v4i32(<4 x i32> %a)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.vector.reduce.umax.*``' intrinsics do an unsigned
+integer ``MAX`` reduction of a vector, returning the result as a scalar. The
+return type matches the element-type of the vector input.
+
+Arguments:
+""""""""""
+The argument to this intrinsic must be a vector of integer values.
+
+'``llvm.experimental.vector.reduce.umin.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i32 @llvm.experimental.vector.reduce.umin.i32.v4i32(<4 x i32> %a)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.vector.reduce.umin.*``' intrinsics do an unsigned
+integer ``MIN`` reduction of a vector, returning the result as a scalar. The
+return type matches the element-type of the vector input.
+
+Arguments:
+""""""""""
+The argument to this intrinsic must be a vector of integer values.
+
+'``llvm.experimental.vector.reduce.fmax.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare float @llvm.experimental.vector.reduce.fmax.f32.v4f32(<4 x float> %a)
+ declare double @llvm.experimental.vector.reduce.fmax.f64.v2f64(<2 x double> %a)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.vector.reduce.fmax.*``' intrinsics do a floating point
+``MAX`` reduction of a vector, returning the result as a scalar. The return type
+matches the element-type of the vector input.
+
+If the intrinsic call has the ``nnan`` fast-math flag then the operation can
+assume that NaNs are not present in the input vector.
+
+Arguments:
+""""""""""
+The argument to this intrinsic must be a vector of floating point values.
+
+'``llvm.experimental.vector.reduce.fmin.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare float @llvm.experimental.vector.reduce.fmin.f32.v4f32(<4 x float> %a)
+ declare double @llvm.experimental.vector.reduce.fmin.f64.v2f64(<2 x double> %a)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.vector.reduce.fmin.*``' intrinsics do a floating point
+``MIN`` reduction of a vector, returning the result as a scalar. The return type
+matches the element-type of the vector input.
+
+If the intrinsic call has the ``nnan`` fast-math flag then the operation can
+assume that NaNs are not present in the input vector.
+
+Arguments:
+""""""""""
+The argument to this intrinsic must be a vector of floating point values.
+
+Half Precision Floating Point Intrinsics
+----------------------------------------
+
+For most target platforms, half precision floating point is a
+storage-only format. This means that it is a dense encoding (in memory)
+but does not support computation in the format.
+
+This means that code must first load the half-precision floating point
+value as an i16, then convert it to float with
+:ref:`llvm.convert.from.fp16 <int_convert_from_fp16>`. Computation can
+then be performed on the float value (including extending to double
+etc). To store the value back to memory, it is first converted to float
+if needed, then converted to i16 with
+:ref:`llvm.convert.to.fp16 <int_convert_to_fp16>`, then storing as an
+i16 value.
+
+.. _int_convert_to_fp16:
+
+'``llvm.convert.to.fp16``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i16 @llvm.convert.to.fp16.f32(float %a)
+ declare i16 @llvm.convert.to.fp16.f64(double %a)
+
+Overview:
+"""""""""
+
+The '``llvm.convert.to.fp16``' intrinsic function performs a conversion from a
+conventional floating point type to half precision floating point format.
+
+Arguments:
+""""""""""
+
+The intrinsic function contains single argument - the value to be
+converted.
+
+Semantics:
+""""""""""
+
+The '``llvm.convert.to.fp16``' intrinsic function performs a conversion from a
+conventional floating point format to half precision floating point format. The
+return value is an ``i16`` which contains the converted number.
+
+Examples:
+"""""""""
+
+.. code-block:: llvm
+
+ %res = call i16 @llvm.convert.to.fp16.f32(float %a)
+ store i16 %res, i16* @x, align 2
+
+.. _int_convert_from_fp16:
+
+'``llvm.convert.from.fp16``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare float @llvm.convert.from.fp16.f32(i16 %a)
+ declare double @llvm.convert.from.fp16.f64(i16 %a)
+
+Overview:
+"""""""""
+
+The '``llvm.convert.from.fp16``' intrinsic function performs a
+conversion from half precision floating point format to single precision
+floating point format.
+
+Arguments:
+""""""""""
+
+The intrinsic function contains single argument - the value to be
+converted.
+
+Semantics:
+""""""""""
+
+The '``llvm.convert.from.fp16``' intrinsic function performs a
+conversion from half single precision floating point format to single
+precision floating point format. The input half-float value is
+represented by an ``i16`` value.
+
+Examples:
+"""""""""
+
+.. code-block:: llvm
+
+ %a = load i16, i16* @x, align 2
+ %res = call float @llvm.convert.from.fp16(i16 %a)
+
+.. _dbg_intrinsics:
+
+Debugger Intrinsics
+-------------------
+
+The LLVM debugger intrinsics (which all start with ``llvm.dbg.``
+prefix), are described in the `LLVM Source Level
+Debugging <SourceLevelDebugging.html#format_common_intrinsics>`_
+document.
+
+Exception Handling Intrinsics
+-----------------------------
+
+The LLVM exception handling intrinsics (which all start with
+``llvm.eh.`` prefix), are described in the `LLVM Exception
+Handling <ExceptionHandling.html#format_common_intrinsics>`_ document.
+
+.. _int_trampoline:
+
+Trampoline Intrinsics
+---------------------
+
+These intrinsics make it possible to excise one parameter, marked with
+the :ref:`nest <nest>` attribute, from a function. The result is a
+callable function pointer lacking the nest parameter - the caller does
+not need to provide a value for it. Instead, the value to use is stored
+in advance in a "trampoline", a block of memory usually allocated on the
+stack, which also contains code to splice the nest value into the
+argument list. This is used to implement the GCC nested function address
+extension.
+
+For example, if the function is ``i32 f(i8* nest %c, i32 %x, i32 %y)``
+then the resulting function pointer has signature ``i32 (i32, i32)*``.
+It can be created as follows:
+
+.. code-block:: llvm
+
+ %tramp = alloca [10 x i8], align 4 ; size and alignment only correct for X86
+ %tramp1 = getelementptr [10 x i8], [10 x i8]* %tramp, i32 0, i32 0
+ call i8* @llvm.init.trampoline(i8* %tramp1, i8* bitcast (i32 (i8*, i32, i32)* @f to i8*), i8* %nval)
+ %p = call i8* @llvm.adjust.trampoline(i8* %tramp1)
+ %fp = bitcast i8* %p to i32 (i32, i32)*
+
+The call ``%val = call i32 %fp(i32 %x, i32 %y)`` is then equivalent to
+``%val = call i32 %f(i8* %nval, i32 %x, i32 %y)``.
+
+.. _int_it:
+
+'``llvm.init.trampoline``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.init.trampoline(i8* <tramp>, i8* <func>, i8* <nval>)
+
+Overview:
+"""""""""
+
+This fills the memory pointed to by ``tramp`` with executable code,
+turning it into a trampoline.
+
+Arguments:
+""""""""""
+
+The ``llvm.init.trampoline`` intrinsic takes three arguments, all
+pointers. The ``tramp`` argument must point to a sufficiently large and
+sufficiently aligned block of memory; this memory is written to by the
+intrinsic. Note that the size and the alignment are target-specific -
+LLVM currently provides no portable way of determining them, so a
+front-end that generates this intrinsic needs to have some
+target-specific knowledge. The ``func`` argument must hold a function
+bitcast to an ``i8*``.
+
+Semantics:
+""""""""""
+
+The block of memory pointed to by ``tramp`` is filled with target
+dependent code, turning it into a function. Then ``tramp`` needs to be
+passed to :ref:`llvm.adjust.trampoline <int_at>` to get a pointer which can
+be :ref:`bitcast (to a new function) and called <int_trampoline>`. The new
+function's signature is the same as that of ``func`` with any arguments
+marked with the ``nest`` attribute removed. At most one such ``nest``
+argument is allowed, and it must be of pointer type. Calling the new
+function is equivalent to calling ``func`` with the same argument list,
+but with ``nval`` used for the missing ``nest`` argument. If, after
+calling ``llvm.init.trampoline``, the memory pointed to by ``tramp`` is
+modified, then the effect of any later call to the returned function
+pointer is undefined.
+
+.. _int_at:
+
+'``llvm.adjust.trampoline``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i8* @llvm.adjust.trampoline(i8* <tramp>)
+
+Overview:
+"""""""""
+
+This performs any required machine-specific adjustment to the address of
+a trampoline (passed as ``tramp``).
+
+Arguments:
+""""""""""
+
+``tramp`` must point to a block of memory which already has trampoline
+code filled in by a previous call to
+:ref:`llvm.init.trampoline <int_it>`.
+
+Semantics:
+""""""""""
+
+On some architectures the address of the code to be executed needs to be
+different than the address where the trampoline is actually stored. This
+intrinsic returns the executable address corresponding to ``tramp``
+after performing the required machine specific adjustments. The pointer
+returned can then be :ref:`bitcast and executed <int_trampoline>`.
+
+.. _int_mload_mstore:
+
+Masked Vector Load and Store Intrinsics
+---------------------------------------
+
+LLVM provides intrinsics for predicated vector load and store operations. The predicate is specified by a mask operand, which holds one bit per vector element, switching the associated vector lane on or off. The memory addresses corresponding to the "off" lanes are not accessed. When all bits of the mask are on, the intrinsic is identical to a regular vector load or store. When all bits are off, no memory is accessed.
+
+.. _int_mload:
+
+'``llvm.masked.load.*``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+This is an overloaded intrinsic. The loaded data is a vector of any integer, floating point or pointer data type.
+
+::
+
+ declare <16 x float> @llvm.masked.load.v16f32.p0v16f32 (<16 x float>* <ptr>, i32 <alignment>, <16 x i1> <mask>, <16 x float> <passthru>)
+ declare <2 x double> @llvm.masked.load.v2f64.p0v2f64 (<2 x double>* <ptr>, i32 <alignment>, <2 x i1> <mask>, <2 x double> <passthru>)
+ ;; The data is a vector of pointers to double
+ declare <8 x double*> @llvm.masked.load.v8p0f64.p0v8p0f64 (<8 x double*>* <ptr>, i32 <alignment>, <8 x i1> <mask>, <8 x double*> <passthru>)
+ ;; The data is a vector of function pointers
+ declare <8 x i32 ()*> @llvm.masked.load.v8p0f_i32f.p0v8p0f_i32f (<8 x i32 ()*>* <ptr>, i32 <alignment>, <8 x i1> <mask>, <8 x i32 ()*> <passthru>)
+
+Overview:
+"""""""""
+
+Reads a vector from memory according to the provided mask. The mask holds a bit for each vector lane, and is used to prevent memory accesses to the masked-off lanes. The masked-off lanes in the result vector are taken from the corresponding lanes of the '``passthru``' operand.
+
+
+Arguments:
+""""""""""
+
+The first operand is the base pointer for the load. The second operand is the alignment of the source location. It must be a constant integer value. The third operand, mask, is a vector of boolean values with the same number of elements as the return type. The fourth is a pass-through value that is used to fill the masked-off lanes of the result. The return type, underlying type of the base pointer and the type of the '``passthru``' operand are the same vector types.
+
+
+Semantics:
+""""""""""
+
+The '``llvm.masked.load``' intrinsic is designed for conditional reading of selected vector elements in a single IR operation. It is useful for targets that support vector masked loads and allows vectorizing predicated basic blocks on these targets. Other targets may support this intrinsic differently, for example by lowering it into a sequence of branches that guard scalar load operations.
+The result of this operation is equivalent to a regular vector load instruction followed by a 'select' between the loaded and the passthru values, predicated on the same mask. However, using this intrinsic prevents exceptions on memory access to masked-off lanes.
+
+
+::
+
+ %res = call <16 x float> @llvm.masked.load.v16f32.p0v16f32 (<16 x float>* %ptr, i32 4, <16 x i1>%mask, <16 x float> %passthru)
+
+ ;; The result of the two following instructions is identical aside from potential memory access exception
+ %loadlal = load <16 x float>, <16 x float>* %ptr, align 4
+ %res = select <16 x i1> %mask, <16 x float> %loadlal, <16 x float> %passthru
+
+.. _int_mstore:
+
+'``llvm.masked.store.*``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+This is an overloaded intrinsic. The data stored in memory is a vector of any integer, floating point or pointer data type.
+
+::
+
+ declare void @llvm.masked.store.v8i32.p0v8i32 (<8 x i32> <value>, <8 x i32>* <ptr>, i32 <alignment>, <8 x i1> <mask>)
+ declare void @llvm.masked.store.v16f32.p0v16f32 (<16 x float> <value>, <16 x float>* <ptr>, i32 <alignment>, <16 x i1> <mask>)
+ ;; The data is a vector of pointers to double
+ declare void @llvm.masked.store.v8p0f64.p0v8p0f64 (<8 x double*> <value>, <8 x double*>* <ptr>, i32 <alignment>, <8 x i1> <mask>)
+ ;; The data is a vector of function pointers
+ declare void @llvm.masked.store.v4p0f_i32f.p0v4p0f_i32f (<4 x i32 ()*> <value>, <4 x i32 ()*>* <ptr>, i32 <alignment>, <4 x i1> <mask>)
+
+Overview:
+"""""""""
+
+Writes a vector to memory according to the provided mask. The mask holds a bit for each vector lane, and is used to prevent memory accesses to the masked-off lanes.
+
+Arguments:
+""""""""""
+
+The first operand is the vector value to be written to memory. The second operand is the base pointer for the store, it has the same underlying type as the value operand. The third operand is the alignment of the destination location. The fourth operand, mask, is a vector of boolean values. The types of the mask and the value operand must have the same number of vector elements.
+
+
+Semantics:
+""""""""""
+
+The '``llvm.masked.store``' intrinsics is designed for conditional writing of selected vector elements in a single IR operation. It is useful for targets that support vector masked store and allows vectorizing predicated basic blocks on these targets. Other targets may support this intrinsic differently, for example by lowering it into a sequence of branches that guard scalar store operations.
+The result of this operation is equivalent to a load-modify-store sequence. However, using this intrinsic prevents exceptions and data races on memory access to masked-off lanes.
+
+::
+
+ call void @llvm.masked.store.v16f32.p0v16f32(<16 x float> %value, <16 x float>* %ptr, i32 4, <16 x i1> %mask)
+
+ ;; The result of the following instructions is identical aside from potential data races and memory access exceptions
+ %oldval = load <16 x float>, <16 x float>* %ptr, align 4
+ %res = select <16 x i1> %mask, <16 x float> %value, <16 x float> %oldval
+ store <16 x float> %res, <16 x float>* %ptr, align 4
+
+
+Masked Vector Gather and Scatter Intrinsics
+-------------------------------------------
+
+LLVM provides intrinsics for vector gather and scatter operations. They are similar to :ref:`Masked Vector Load and Store <int_mload_mstore>`, except they are designed for arbitrary memory accesses, rather than sequential memory accesses. Gather and scatter also employ a mask operand, which holds one bit per vector element, switching the associated vector lane on or off. The memory addresses corresponding to the "off" lanes are not accessed. When all bits are off, no memory is accessed.
+
+.. _int_mgather:
+
+'``llvm.masked.gather.*``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+This is an overloaded intrinsic. The loaded data are multiple scalar values of any integer, floating point or pointer data type gathered together into one vector.
+
+::
+
+ declare <16 x float> @llvm.masked.gather.v16f32.v16p0f32 (<16 x float*> <ptrs>, i32 <alignment>, <16 x i1> <mask>, <16 x float> <passthru>)
+ declare <2 x double> @llvm.masked.gather.v2f64.v2p1f64 (<2 x double addrspace(1)*> <ptrs>, i32 <alignment>, <2 x i1> <mask>, <2 x double> <passthru>)
+ declare <8 x float*> @llvm.masked.gather.v8p0f32.v8p0p0f32 (<8 x float**> <ptrs>, i32 <alignment>, <8 x i1> <mask>, <8 x float*> <passthru>)
+
+Overview:
+"""""""""
+
+Reads scalar values from arbitrary memory locations and gathers them into one vector. The memory locations are provided in the vector of pointers '``ptrs``'. The memory is accessed according to the provided mask. The mask holds a bit for each vector lane, and is used to prevent memory accesses to the masked-off lanes. The masked-off lanes in the result vector are taken from the corresponding lanes of the '``passthru``' operand.
+
+
+Arguments:
+""""""""""
+
+The first operand is a vector of pointers which holds all memory addresses to read. The second operand is an alignment of the source addresses. It must be a constant integer value. The third operand, mask, is a vector of boolean values with the same number of elements as the return type. The fourth is a pass-through value that is used to fill the masked-off lanes of the result. The return type, underlying type of the vector of pointers and the type of the '``passthru``' operand are the same vector types.
+
+
+Semantics:
+""""""""""
+
+The '``llvm.masked.gather``' intrinsic is designed for conditional reading of multiple scalar values from arbitrary memory locations in a single IR operation. It is useful for targets that support vector masked gathers and allows vectorizing basic blocks with data and control divergence. Other targets may support this intrinsic differently, for example by lowering it into a sequence of scalar load operations.
+The semantics of this operation are equivalent to a sequence of conditional scalar loads with subsequent gathering all loaded values into a single vector. The mask restricts memory access to certain lanes and facilitates vectorization of predicated basic blocks.
+
+
+::
+
+ %res = call <4 x double> @llvm.masked.gather.v4f64.v4p0f64 (<4 x double*> %ptrs, i32 8, <4 x i1> <i1 true, i1 true, i1 true, i1 true>, <4 x double> undef)
+
+ ;; The gather with all-true mask is equivalent to the following instruction sequence
+ %ptr0 = extractelement <4 x double*> %ptrs, i32 0
+ %ptr1 = extractelement <4 x double*> %ptrs, i32 1
+ %ptr2 = extractelement <4 x double*> %ptrs, i32 2
+ %ptr3 = extractelement <4 x double*> %ptrs, i32 3
+
+ %val0 = load double, double* %ptr0, align 8
+ %val1 = load double, double* %ptr1, align 8
+ %val2 = load double, double* %ptr2, align 8
+ %val3 = load double, double* %ptr3, align 8
+
+ %vec0 = insertelement <4 x double>undef, %val0, 0
+ %vec01 = insertelement <4 x double>%vec0, %val1, 1
+ %vec012 = insertelement <4 x double>%vec01, %val2, 2
+ %vec0123 = insertelement <4 x double>%vec012, %val3, 3
+
+.. _int_mscatter:
+
+'``llvm.masked.scatter.*``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+This is an overloaded intrinsic. The data stored in memory is a vector of any integer, floating point or pointer data type. Each vector element is stored in an arbitrary memory address. Scatter with overlapping addresses is guaranteed to be ordered from least-significant to most-significant element.
+
+::
+
+ declare void @llvm.masked.scatter.v8i32.v8p0i32 (<8 x i32> <value>, <8 x i32*> <ptrs>, i32 <alignment>, <8 x i1> <mask>)
+ declare void @llvm.masked.scatter.v16f32.v16p1f32 (<16 x float> <value>, <16 x float addrspace(1)*> <ptrs>, i32 <alignment>, <16 x i1> <mask>)
+ declare void @llvm.masked.scatter.v4p0f64.v4p0p0f64 (<4 x double*> <value>, <4 x double**> <ptrs>, i32 <alignment>, <4 x i1> <mask>)
+
+Overview:
+"""""""""
+
+Writes each element from the value vector to the corresponding memory address. The memory addresses are represented as a vector of pointers. Writing is done according to the provided mask. The mask holds a bit for each vector lane, and is used to prevent memory accesses to the masked-off lanes.
+
+Arguments:
+""""""""""
+
+The first operand is a vector value to be written to memory. The second operand is a vector of pointers, pointing to where the value elements should be stored. It has the same underlying type as the value operand. The third operand is an alignment of the destination addresses. The fourth operand, mask, is a vector of boolean values. The types of the mask and the value operand must have the same number of vector elements.
+
+
+Semantics:
+""""""""""
+
+The '``llvm.masked.scatter``' intrinsics is designed for writing selected vector elements to arbitrary memory addresses in a single IR operation. The operation may be conditional, when not all bits in the mask are switched on. It is useful for targets that support vector masked scatter and allows vectorizing basic blocks with data and control divergence. Other targets may support this intrinsic differently, for example by lowering it into a sequence of branches that guard scalar store operations.
+
+::
+
+ ;; This instruction unconditionally stores data vector in multiple addresses
+ call @llvm.masked.scatter.v8i32.v8p0i32 (<8 x i32> %value, <8 x i32*> %ptrs, i32 4, <8 x i1> <true, true, .. true>)
+
+ ;; It is equivalent to a list of scalar stores
+ %val0 = extractelement <8 x i32> %value, i32 0
+ %val1 = extractelement <8 x i32> %value, i32 1
+ ..
+ %val7 = extractelement <8 x i32> %value, i32 7
+ %ptr0 = extractelement <8 x i32*> %ptrs, i32 0
+ %ptr1 = extractelement <8 x i32*> %ptrs, i32 1
+ ..
+ %ptr7 = extractelement <8 x i32*> %ptrs, i32 7
+ ;; Note: the order of the following stores is important when they overlap:
+ store i32 %val0, i32* %ptr0, align 4
+ store i32 %val1, i32* %ptr1, align 4
+ ..
+ store i32 %val7, i32* %ptr7, align 4
+
+
+Memory Use Markers
+------------------
+
+This class of intrinsics provides information about the lifetime of
+memory objects and ranges where variables are immutable.
+
+.. _int_lifestart:
+
+'``llvm.lifetime.start``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.lifetime.start(i64 <size>, i8* nocapture <ptr>)
+
+Overview:
+"""""""""
+
+The '``llvm.lifetime.start``' intrinsic specifies the start of a memory
+object's lifetime.
+
+Arguments:
+""""""""""
+
+The first argument is a constant integer representing the size of the
+object, or -1 if it is variable sized. The second argument is a pointer
+to the object.
+
+Semantics:
+""""""""""
+
+This intrinsic indicates that before this point in the code, the value
+of the memory pointed to by ``ptr`` is dead. This means that it is known
+to never be used and has an undefined value. A load from the pointer
+that precedes this intrinsic can be replaced with ``'undef'``.
+
+.. _int_lifeend:
+
+'``llvm.lifetime.end``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.lifetime.end(i64 <size>, i8* nocapture <ptr>)
+
+Overview:
+"""""""""
+
+The '``llvm.lifetime.end``' intrinsic specifies the end of a memory
+object's lifetime.
+
+Arguments:
+""""""""""
+
+The first argument is a constant integer representing the size of the
+object, or -1 if it is variable sized. The second argument is a pointer
+to the object.
+
+Semantics:
+""""""""""
+
+This intrinsic indicates that after this point in the code, the value of
+the memory pointed to by ``ptr`` is dead. This means that it is known to
+never be used and has an undefined value. Any stores into the memory
+object following this intrinsic may be removed as dead.
+
+'``llvm.invariant.start``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+This is an overloaded intrinsic. The memory object can belong to any address space.
+
+::
+
+ declare {}* @llvm.invariant.start.p0i8(i64 <size>, i8* nocapture <ptr>)
+
+Overview:
+"""""""""
+
+The '``llvm.invariant.start``' intrinsic specifies that the contents of
+a memory object will not change.
+
+Arguments:
+""""""""""
+
+The first argument is a constant integer representing the size of the
+object, or -1 if it is variable sized. The second argument is a pointer
+to the object.
+
+Semantics:
+""""""""""
+
+This intrinsic indicates that until an ``llvm.invariant.end`` that uses
+the return value, the referenced memory location is constant and
+unchanging.
+
+'``llvm.invariant.end``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+This is an overloaded intrinsic. The memory object can belong to any address space.
+
+::
+
+ declare void @llvm.invariant.end.p0i8({}* <start>, i64 <size>, i8* nocapture <ptr>)
+
+Overview:
+"""""""""
+
+The '``llvm.invariant.end``' intrinsic specifies that the contents of a
+memory object are mutable.
+
+Arguments:
+""""""""""
+
+The first argument is the matching ``llvm.invariant.start`` intrinsic.
+The second argument is a constant integer representing the size of the
+object, or -1 if it is variable sized and the third argument is a
+pointer to the object.
+
+Semantics:
+""""""""""
+
+This intrinsic indicates that the memory is mutable again.
+
+'``llvm.invariant.group.barrier``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i8* @llvm.invariant.group.barrier(i8* <ptr>)
+
+Overview:
+"""""""""
+
+The '``llvm.invariant.group.barrier``' intrinsic can be used when an invariant
+established by invariant.group metadata no longer holds, to obtain a new pointer
+value that does not carry the invariant information.
+
+
+Arguments:
+""""""""""
+
+The ``llvm.invariant.group.barrier`` takes only one argument, which is
+the pointer to the memory for which the ``invariant.group`` no longer holds.
+
+Semantics:
+""""""""""
+
+Returns another pointer that aliases its argument but which is considered different
+for the purposes of ``load``/``store`` ``invariant.group`` metadata.
+
+Constrained Floating Point Intrinsics
+-------------------------------------
+
+These intrinsics are used to provide special handling of floating point
+operations when specific rounding mode or floating point exception behavior is
+required. By default, LLVM optimization passes assume that the rounding mode is
+round-to-nearest and that floating point exceptions will not be monitored.
+Constrained FP intrinsics are used to support non-default rounding modes and
+accurately preserve exception behavior without compromising LLVM's ability to
+optimize FP code when the default behavior is used.
+
+Each of these intrinsics corresponds to a normal floating point operation. The
+first two arguments and the return value are the same as the corresponding FP
+operation.
+
+The third argument is a metadata argument specifying the rounding mode to be
+assumed. This argument must be one of the following strings:
+
+::
+
+ "round.dynamic"
+ "round.tonearest"
+ "round.downward"
+ "round.upward"
+ "round.towardzero"
+
+If this argument is "round.dynamic" optimization passes must assume that the
+rounding mode is unknown and may change at runtime. No transformations that
+depend on rounding mode may be performed in this case.
+
+The other possible values for the rounding mode argument correspond to the
+similarly named IEEE rounding modes. If the argument is any of these values
+optimization passes may perform transformations as long as they are consistent
+with the specified rounding mode.
+
+For example, 'x-0'->'x' is not a valid transformation if the rounding mode is
+"round.downward" or "round.dynamic" because if the value of 'x' is +0 then
+'x-0' should evaluate to '-0' when rounding downward. However, this
+transformation is legal for all other rounding modes.
+
+For values other than "round.dynamic" optimization passes may assume that the
+actual runtime rounding mode (as defined in a target-specific manner) matches
+the specified rounding mode, but this is not guaranteed. Using a specific
+non-dynamic rounding mode which does not match the actual rounding mode at
+runtime results in undefined behavior.
+
+The fourth argument to the constrained floating point intrinsics specifies the
+required exception behavior. This argument must be one of the following
+strings:
+
+::
+
+ "fpexcept.ignore"
+ "fpexcept.maytrap"
+ "fpexcept.strict"
+
+If this argument is "fpexcept.ignore" optimization passes may assume that the
+exception status flags will not be read and that floating point exceptions will
+be masked. This allows transformations to be performed that may change the
+exception semantics of the original code. For example, FP operations may be
+speculatively executed in this case whereas they must not be for either of the
+other possible values of this argument.
+
+If the exception behavior argument is "fpexcept.maytrap" optimization passes
+must avoid transformations that may raise exceptions that would not have been
+raised by the original code (such as speculatively executing FP operations), but
+passes are not required to preserve all exceptions that are implied by the
+original code. For example, exceptions may be potentially hidden by constant
+folding.
+
+If the exception behavior argument is "fpexcept.strict" all transformations must
+strictly preserve the floating point exception semantics of the original code.
+Any FP exception that would have been raised by the original code must be raised
+by the transformed code, and the transformed code must not raise any FP
+exceptions that would not have been raised by the original code. This is the
+exception behavior argument that will be used if the code being compiled reads
+the FP exception status flags, but this mode can also be used with code that
+unmasks FP exceptions.
+
+The number and order of floating point exceptions is NOT guaranteed. For
+example, a series of FP operations that each may raise exceptions may be
+vectorized into a single instruction that raises each unique exception a single
+time.
+
+
+'``llvm.experimental.constrained.fadd``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.fadd(<type> <op1>, <type> <op2>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.fadd``' intrinsic returns the sum of its
+two operands.
+
+
+Arguments:
+""""""""""
+
+The first two arguments to the '``llvm.experimental.constrained.fadd``'
+intrinsic must be :ref:`floating point <t_floating>` or :ref:`vector <t_vector>`
+of floating point values. Both arguments must have identical types.
+
+The third and fourth arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+The value produced is the floating point sum of the two value operands and has
+the same type as the operands.
+
+
+'``llvm.experimental.constrained.fsub``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.fsub(<type> <op1>, <type> <op2>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.fsub``' intrinsic returns the difference
+of its two operands.
+
+
+Arguments:
+""""""""""
+
+The first two arguments to the '``llvm.experimental.constrained.fsub``'
+intrinsic must be :ref:`floating point <t_floating>` or :ref:`vector <t_vector>`
+of floating point values. Both arguments must have identical types.
+
+The third and fourth arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+The value produced is the floating point difference of the two value operands
+and has the same type as the operands.
+
+
+'``llvm.experimental.constrained.fmul``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.fmul(<type> <op1>, <type> <op2>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.fmul``' intrinsic returns the product of
+its two operands.
+
+
+Arguments:
+""""""""""
+
+The first two arguments to the '``llvm.experimental.constrained.fmul``'
+intrinsic must be :ref:`floating point <t_floating>` or :ref:`vector <t_vector>`
+of floating point values. Both arguments must have identical types.
+
+The third and fourth arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+The value produced is the floating point product of the two value operands and
+has the same type as the operands.
+
+
+'``llvm.experimental.constrained.fdiv``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.fdiv(<type> <op1>, <type> <op2>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.fdiv``' intrinsic returns the quotient of
+its two operands.
+
+
+Arguments:
+""""""""""
+
+The first two arguments to the '``llvm.experimental.constrained.fdiv``'
+intrinsic must be :ref:`floating point <t_floating>` or :ref:`vector <t_vector>`
+of floating point values. Both arguments must have identical types.
+
+The third and fourth arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+The value produced is the floating point quotient of the two value operands and
+has the same type as the operands.
+
+
+'``llvm.experimental.constrained.frem``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.frem(<type> <op1>, <type> <op2>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.frem``' intrinsic returns the remainder
+from the division of its two operands.
+
+
+Arguments:
+""""""""""
+
+The first two arguments to the '``llvm.experimental.constrained.frem``'
+intrinsic must be :ref:`floating point <t_floating>` or :ref:`vector <t_vector>`
+of floating point values. Both arguments must have identical types.
+
+The third and fourth arguments specify the rounding mode and exception
+behavior as described above. The rounding mode argument has no effect, since
+the result of frem is never rounded, but the argument is included for
+consistency with the other constrained floating point intrinsics.
+
+Semantics:
+""""""""""
+
+The value produced is the floating point remainder from the division of the two
+value operands and has the same type as the operands. The remainder has the
+same sign as the dividend.
+
+
+Constrained libm-equivalent Intrinsics
+--------------------------------------
+
+In addition to the basic floating point operations for which constrained
+intrinsics are described above, there are constrained versions of various
+operations which provide equivalent behavior to a corresponding libm function.
+These intrinsics allow the precise behavior of these operations with respect to
+rounding mode and exception behavior to be controlled.
+
+As with the basic constrained floating point intrinsics, the rounding mode
+and exception behavior arguments only control the behavior of the optimizer.
+They do not change the runtime floating point environment.
+
+
+'``llvm.experimental.constrained.sqrt``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.sqrt(<type> <op1>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.sqrt``' intrinsic returns the square root
+of the specified value, returning the same value as the libm '``sqrt``'
+functions would, but without setting ``errno``.
+
+Arguments:
+""""""""""
+
+The first argument and the return type are floating point numbers of the same
+type.
+
+The second and third arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+This function returns the nonnegative square root of the specified value.
+If the value is less than negative zero, a floating point exception occurs
+and the the return value is architecture specific.
+
+
+'``llvm.experimental.constrained.pow``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.pow(<type> <op1>, <type> <op2>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.pow``' intrinsic returns the first operand
+raised to the (positive or negative) power specified by the second operand.
+
+Arguments:
+""""""""""
+
+The first two arguments and the return value are floating point numbers of the
+same type. The second argument specifies the power to which the first argument
+should be raised.
+
+The third and fourth arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+This function returns the first value raised to the second power,
+returning the same values as the libm ``pow`` functions would, and
+handles error conditions in the same way.
+
+
+'``llvm.experimental.constrained.powi``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.powi(<type> <op1>, i32 <op2>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.powi``' intrinsic returns the first operand
+raised to the (positive or negative) power specified by the second operand. The
+order of evaluation of multiplications is not defined. When a vector of floating
+point type is used, the second argument remains a scalar integer value.
+
+
+Arguments:
+""""""""""
+
+The first argument and the return value are floating point numbers of the same
+type. The second argument is a 32-bit signed integer specifying the power to
+which the first argument should be raised.
+
+The third and fourth arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+This function returns the first value raised to the second power with an
+unspecified sequence of rounding operations.
+
+
+'``llvm.experimental.constrained.sin``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.sin(<type> <op1>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.sin``' intrinsic returns the sine of the
+first operand.
+
+Arguments:
+""""""""""
+
+The first argument and the return type are floating point numbers of the same
+type.
+
+The second and third arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+This function returns the sine of the specified operand, returning the
+same values as the libm ``sin`` functions would, and handles error
+conditions in the same way.
+
+
+'``llvm.experimental.constrained.cos``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.cos(<type> <op1>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.cos``' intrinsic returns the cosine of the
+first operand.
+
+Arguments:
+""""""""""
+
+The first argument and the return type are floating point numbers of the same
+type.
+
+The second and third arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+This function returns the cosine of the specified operand, returning the
+same values as the libm ``cos`` functions would, and handles error
+conditions in the same way.
+
+
+'``llvm.experimental.constrained.exp``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.exp(<type> <op1>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.exp``' intrinsic computes the base-e
+exponential of the specified value.
+
+Arguments:
+""""""""""
+
+The first argument and the return value are floating point numbers of the same
+type.
+
+The second and third arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``exp`` functions
+would, and handles error conditions in the same way.
+
+
+'``llvm.experimental.constrained.exp2``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.exp2(<type> <op1>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.exp2``' intrinsic computes the base-2
+exponential of the specified value.
+
+
+Arguments:
+""""""""""
+
+The first argument and the return value are floating point numbers of the same
+type.
+
+The second and third arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``exp2`` functions
+would, and handles error conditions in the same way.
+
+
+'``llvm.experimental.constrained.log``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.log(<type> <op1>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.log``' intrinsic computes the base-e
+logarithm of the specified value.
+
+Arguments:
+""""""""""
+
+The first argument and the return value are floating point numbers of the same
+type.
+
+The second and third arguments specify the rounding mode and exception
+behavior as described above.
+
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``log`` functions
+would, and handles error conditions in the same way.
+
+
+'``llvm.experimental.constrained.log10``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.log10(<type> <op1>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.log10``' intrinsic computes the base-10
+logarithm of the specified value.
+
+Arguments:
+""""""""""
+
+The first argument and the return value are floating point numbers of the same
+type.
+
+The second and third arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``log10`` functions
+would, and handles error conditions in the same way.
+
+
+'``llvm.experimental.constrained.log2``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.log2(<type> <op1>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.log2``' intrinsic computes the base-2
+logarithm of the specified value.
+
+Arguments:
+""""""""""
+
+The first argument and the return value are floating point numbers of the same
+type.
+
+The second and third arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``log2`` functions
+would, and handles error conditions in the same way.
+
+
+'``llvm.experimental.constrained.rint``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.rint(<type> <op1>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.rint``' intrinsic returns the first
+operand rounded to the nearest integer. It may raise an inexact floating point
+exception if the operand is not an integer.
+
+Arguments:
+""""""""""
+
+The first argument and the return value are floating point numbers of the same
+type.
+
+The second and third arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``rint`` functions
+would, and handles error conditions in the same way. The rounding mode is
+described, not determined, by the rounding mode argument. The actual rounding
+mode is determined by the runtime floating point environment. The rounding
+mode argument is only intended as information to the compiler.
+
+
+'``llvm.experimental.constrained.nearbyint``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.nearbyint(<type> <op1>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.nearbyint``' intrinsic returns the first
+operand rounded to the nearest integer. It will not raise an inexact floating
+point exception if the operand is not an integer.
+
+
+Arguments:
+""""""""""
+
+The first argument and the return value are floating point numbers of the same
+type.
+
+The second and third arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``nearbyint`` functions
+would, and handles error conditions in the same way. The rounding mode is
+described, not determined, by the rounding mode argument. The actual rounding
+mode is determined by the runtime floating point environment. The rounding
+mode argument is only intended as information to the compiler.
+
+
+General Intrinsics
+------------------
+
+This class of intrinsics is designed to be generic and has no specific
+purpose.
+
+'``llvm.var.annotation``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.var.annotation(i8* <val>, i8* <str>, i8* <str>, i32 <int>)
+
+Overview:
+"""""""""
+
+The '``llvm.var.annotation``' intrinsic.
+
+Arguments:
+""""""""""
+
+The first argument is a pointer to a value, the second is a pointer to a
+global string, the third is a pointer to a global string which is the
+source file name, and the last argument is the line number.
+
+Semantics:
+""""""""""
+
+This intrinsic allows annotation of local variables with arbitrary
+strings. This can be useful for special purpose optimizations that want
+to look for these annotations. These have no other defined use; they are
+ignored by code generation and optimization.
+
+'``llvm.ptr.annotation.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use '``llvm.ptr.annotation``' on a
+pointer to an integer of any width. *NOTE* you must specify an address space for
+the pointer. The identifier for the default address space is the integer
+'``0``'.
+
+::
+
+ declare i8* @llvm.ptr.annotation.p<address space>i8(i8* <val>, i8* <str>, i8* <str>, i32 <int>)
+ declare i16* @llvm.ptr.annotation.p<address space>i16(i16* <val>, i8* <str>, i8* <str>, i32 <int>)
+ declare i32* @llvm.ptr.annotation.p<address space>i32(i32* <val>, i8* <str>, i8* <str>, i32 <int>)
+ declare i64* @llvm.ptr.annotation.p<address space>i64(i64* <val>, i8* <str>, i8* <str>, i32 <int>)
+ declare i256* @llvm.ptr.annotation.p<address space>i256(i256* <val>, i8* <str>, i8* <str>, i32 <int>)
+
+Overview:
+"""""""""
+
+The '``llvm.ptr.annotation``' intrinsic.
+
+Arguments:
+""""""""""
+
+The first argument is a pointer to an integer value of arbitrary bitwidth
+(result of some expression), the second is a pointer to a global string, the
+third is a pointer to a global string which is the source file name, and the
+last argument is the line number. It returns the value of the first argument.
+
+Semantics:
+""""""""""
+
+This intrinsic allows annotation of a pointer to an integer with arbitrary
+strings. This can be useful for special purpose optimizations that want to look
+for these annotations. These have no other defined use; they are ignored by code
+generation and optimization.
+
+'``llvm.annotation.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use '``llvm.annotation``' on
+any integer bit width.
+
+::
+
+ declare i8 @llvm.annotation.i8(i8 <val>, i8* <str>, i8* <str>, i32 <int>)
+ declare i16 @llvm.annotation.i16(i16 <val>, i8* <str>, i8* <str>, i32 <int>)
+ declare i32 @llvm.annotation.i32(i32 <val>, i8* <str>, i8* <str>, i32 <int>)
+ declare i64 @llvm.annotation.i64(i64 <val>, i8* <str>, i8* <str>, i32 <int>)
+ declare i256 @llvm.annotation.i256(i256 <val>, i8* <str>, i8* <str>, i32 <int>)
+
+Overview:
+"""""""""
+
+The '``llvm.annotation``' intrinsic.
+
+Arguments:
+""""""""""
+
+The first argument is an integer value (result of some expression), the
+second is a pointer to a global string, the third is a pointer to a
+global string which is the source file name, and the last argument is
+the line number. It returns the value of the first argument.
+
+Semantics:
+""""""""""
+
+This intrinsic allows annotations to be put on arbitrary expressions
+with arbitrary strings. This can be useful for special purpose
+optimizations that want to look for these annotations. These have no
+other defined use; they are ignored by code generation and optimization.
+
+'``llvm.trap``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.trap() noreturn nounwind
+
+Overview:
+"""""""""
+
+The '``llvm.trap``' intrinsic.
+
+Arguments:
+""""""""""
+
+None.
+
+Semantics:
+""""""""""
+
+This intrinsic is lowered to the target dependent trap instruction. If
+the target does not have a trap instruction, this intrinsic will be
+lowered to a call of the ``abort()`` function.
+
+'``llvm.debugtrap``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.debugtrap() nounwind
+
+Overview:
+"""""""""
+
+The '``llvm.debugtrap``' intrinsic.
+
+Arguments:
+""""""""""
+
+None.
+
+Semantics:
+""""""""""
+
+This intrinsic is lowered to code which is intended to cause an
+execution trap with the intention of requesting the attention of a
+debugger.
+
+'``llvm.stackprotector``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.stackprotector(i8* <guard>, i8** <slot>)
+
+Overview:
+"""""""""
+
+The ``llvm.stackprotector`` intrinsic takes the ``guard`` and stores it
+onto the stack at ``slot``. The stack slot is adjusted to ensure that it
+is placed on the stack before local variables.
+
+Arguments:
+""""""""""
+
+The ``llvm.stackprotector`` intrinsic requires two pointer arguments.
+The first argument is the value loaded from the stack guard
+``@__stack_chk_guard``. The second variable is an ``alloca`` that has
+enough space to hold the value of the guard.
+
+Semantics:
+""""""""""
+
+This intrinsic causes the prologue/epilogue inserter to force the position of
+the ``AllocaInst`` stack slot to be before local variables on the stack. This is
+to ensure that if a local variable on the stack is overwritten, it will destroy
+the value of the guard. When the function exits, the guard on the stack is
+checked against the original guard by ``llvm.stackprotectorcheck``. If they are
+different, then ``llvm.stackprotectorcheck`` causes the program to abort by
+calling the ``__stack_chk_fail()`` function.
+
+'``llvm.stackguard``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i8* @llvm.stackguard()
+
+Overview:
+"""""""""
+
+The ``llvm.stackguard`` intrinsic returns the system stack guard value.
+
+It should not be generated by frontends, since it is only for internal usage.
+The reason why we create this intrinsic is that we still support IR form Stack
+Protector in FastISel.
+
+Arguments:
+""""""""""
+
+None.
+
+Semantics:
+""""""""""
+
+On some platforms, the value returned by this intrinsic remains unchanged
+between loads in the same thread. On other platforms, it returns the same
+global variable value, if any, e.g. ``@__stack_chk_guard``.
+
+Currently some platforms have IR-level customized stack guard loading (e.g.
+X86 Linux) that is not handled by ``llvm.stackguard()``, while they should be
+in the future.
+
+'``llvm.objectsize``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i32 @llvm.objectsize.i32(i8* <object>, i1 <min>, i1 <nullunknown>)
+ declare i64 @llvm.objectsize.i64(i8* <object>, i1 <min>, i1 <nullunknown>)
+
+Overview:
+"""""""""
+
+The ``llvm.objectsize`` intrinsic is designed to provide information to
+the optimizers to determine at compile time whether a) an operation
+(like memcpy) will overflow a buffer that corresponds to an object, or
+b) that a runtime check for overflow isn't necessary. An object in this
+context means an allocation of a specific class, structure, array, or
+other object.
+
+Arguments:
+""""""""""
+
+The ``llvm.objectsize`` intrinsic takes three arguments. The first argument is
+a pointer to or into the ``object``. The second argument determines whether
+``llvm.objectsize`` returns 0 (if true) or -1 (if false) when the object size
+is unknown. The third argument controls how ``llvm.objectsize`` acts when
+``null`` is used as its pointer argument. If it's true and the pointer is in
+address space 0, ``null`` is treated as an opaque value with an unknown number
+of bytes. Otherwise, ``llvm.objectsize`` reports 0 bytes available when given
+``null``.
+
+The second and third arguments only accept constants.
+
+Semantics:
+""""""""""
+
+The ``llvm.objectsize`` intrinsic is lowered to a constant representing
+the size of the object concerned. If the size cannot be determined at
+compile time, ``llvm.objectsize`` returns ``i32/i64 -1 or 0`` (depending
+on the ``min`` argument).
+
+'``llvm.expect``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.expect`` on any
+integer bit width.
+
+::
+
+ declare i1 @llvm.expect.i1(i1 <val>, i1 <expected_val>)
+ declare i32 @llvm.expect.i32(i32 <val>, i32 <expected_val>)
+ declare i64 @llvm.expect.i64(i64 <val>, i64 <expected_val>)
+
+Overview:
+"""""""""
+
+The ``llvm.expect`` intrinsic provides information about expected (the
+most probable) value of ``val``, which can be used by optimizers.
+
+Arguments:
+""""""""""
+
+The ``llvm.expect`` intrinsic takes two arguments. The first argument is
+a value. The second argument is an expected value, this needs to be a
+constant value, variables are not allowed.
+
+Semantics:
+""""""""""
+
+This intrinsic is lowered to the ``val``.
+
+.. _int_assume:
+
+'``llvm.assume``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.assume(i1 %cond)
+
+Overview:
+"""""""""
+
+The ``llvm.assume`` allows the optimizer to assume that the provided
+condition is true. This information can then be used in simplifying other parts
+of the code.
+
+Arguments:
+""""""""""
+
+The condition which the optimizer may assume is always true.
+
+Semantics:
+""""""""""
+
+The intrinsic allows the optimizer to assume that the provided condition is
+always true whenever the control flow reaches the intrinsic call. No code is
+generated for this intrinsic, and instructions that contribute only to the
+provided condition are not used for code generation. If the condition is
+violated during execution, the behavior is undefined.
+
+Note that the optimizer might limit the transformations performed on values
+used by the ``llvm.assume`` intrinsic in order to preserve the instructions
+only used to form the intrinsic's input argument. This might prove undesirable
+if the extra information provided by the ``llvm.assume`` intrinsic does not cause
+sufficient overall improvement in code quality. For this reason,
+``llvm.assume`` should not be used to document basic mathematical invariants
+that the optimizer can otherwise deduce or facts that are of little use to the
+optimizer.
+
+.. _int_ssa_copy:
+
+'``llvm.ssa_copy``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare type @llvm.ssa_copy(type %operand) returned(1) readnone
+
+Arguments:
+""""""""""
+
+The first argument is an operand which is used as the returned value.
+
+Overview:
+""""""""""
+
+The ``llvm.ssa_copy`` intrinsic can be used to attach information to
+operations by copying them and giving them new names. For example,
+the PredicateInfo utility uses it to build Extended SSA form, and
+attach various forms of information to operands that dominate specific
+uses. It is not meant for general use, only for building temporary
+renaming forms that require value splits at certain points.
+
+.. _type.test:
+
+'``llvm.type.test``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i1 @llvm.type.test(i8* %ptr, metadata %type) nounwind readnone
+
+
+Arguments:
+""""""""""
+
+The first argument is a pointer to be tested. The second argument is a
+metadata object representing a :doc:`type identifier <TypeMetadata>`.
+
+Overview:
+"""""""""
+
+The ``llvm.type.test`` intrinsic tests whether the given pointer is associated
+with the given type identifier.
+
+'``llvm.type.checked.load``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare {i8*, i1} @llvm.type.checked.load(i8* %ptr, i32 %offset, metadata %type) argmemonly nounwind readonly
+
+
+Arguments:
+""""""""""
+
+The first argument is a pointer from which to load a function pointer. The
+second argument is the byte offset from which to load the function pointer. The
+third argument is a metadata object representing a :doc:`type identifier
+<TypeMetadata>`.
+
+Overview:
+"""""""""
+
+The ``llvm.type.checked.load`` intrinsic safely loads a function pointer from a
+virtual table pointer using type metadata. This intrinsic is used to implement
+control flow integrity in conjunction with virtual call optimization. The
+virtual call optimization pass will optimize away ``llvm.type.checked.load``
+intrinsics associated with devirtualized calls, thereby removing the type
+check in cases where it is not needed to enforce the control flow integrity
+constraint.
+
+If the given pointer is associated with a type metadata identifier, this
+function returns true as the second element of its return value. (Note that
+the function may also return true if the given pointer is not associated
+with a type metadata identifier.) If the function's return value's second
+element is true, the following rules apply to the first element:
+
+- If the given pointer is associated with the given type metadata identifier,
+ it is the function pointer loaded from the given byte offset from the given
+ pointer.
+
+- If the given pointer is not associated with the given type metadata
+ identifier, it is one of the following (the choice of which is unspecified):
+
+ 1. The function pointer that would have been loaded from an arbitrarily chosen
+ (through an unspecified mechanism) pointer associated with the type
+ metadata.
+
+ 2. If the function has a non-void return type, a pointer to a function that
+ returns an unspecified value without causing side effects.
+
+If the function's return value's second element is false, the value of the
+first element is undefined.
+
+
+'``llvm.donothing``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.donothing() nounwind readnone
+
+Overview:
+"""""""""
+
+The ``llvm.donothing`` intrinsic doesn't perform any operation. It's one of only
+three intrinsics (besides ``llvm.experimental.patchpoint`` and
+``llvm.experimental.gc.statepoint``) that can be called with an invoke
+instruction.
+
+Arguments:
+""""""""""
+
+None.
+
+Semantics:
+""""""""""
+
+This intrinsic does nothing, and it's removed by optimizers and ignored
+by codegen.
+
+'``llvm.experimental.deoptimize``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare type @llvm.experimental.deoptimize(...) [ "deopt"(...) ]
+
+Overview:
+"""""""""
+
+This intrinsic, together with :ref:`deoptimization operand bundles
+<deopt_opbundles>`, allow frontends to express transfer of control and
+frame-local state from the currently executing (typically more specialized,
+hence faster) version of a function into another (typically more generic, hence
+slower) version.
+
+In languages with a fully integrated managed runtime like Java and JavaScript
+this intrinsic can be used to implement "uncommon trap" or "side exit" like
+functionality. In unmanaged languages like C and C++, this intrinsic can be
+used to represent the slow paths of specialized functions.
+
+
+Arguments:
+""""""""""
+
+The intrinsic takes an arbitrary number of arguments, whose meaning is
+decided by the :ref:`lowering strategy<deoptimize_lowering>`.
+
+Semantics:
+""""""""""
+
+The ``@llvm.experimental.deoptimize`` intrinsic executes an attached
+deoptimization continuation (denoted using a :ref:`deoptimization
+operand bundle <deopt_opbundles>`) and returns the value returned by
+the deoptimization continuation. Defining the semantic properties of
+the continuation itself is out of scope of the language reference --
+as far as LLVM is concerned, the deoptimization continuation can
+invoke arbitrary side effects, including reading from and writing to
+the entire heap.
+
+Deoptimization continuations expressed using ``"deopt"`` operand bundles always
+continue execution to the end of the physical frame containing them, so all
+calls to ``@llvm.experimental.deoptimize`` must be in "tail position":
+
+ - ``@llvm.experimental.deoptimize`` cannot be invoked.
+ - The call must immediately precede a :ref:`ret <i_ret>` instruction.
+ - The ``ret`` instruction must return the value produced by the
+ ``@llvm.experimental.deoptimize`` call if there is one, or void.
+
+Note that the above restrictions imply that the return type for a call to
+``@llvm.experimental.deoptimize`` will match the return type of its immediate
+caller.
+
+The inliner composes the ``"deopt"`` continuations of the caller into the
+``"deopt"`` continuations present in the inlinee, and also updates calls to this
+intrinsic to return directly from the frame of the function it inlined into.
+
+All declarations of ``@llvm.experimental.deoptimize`` must share the
+same calling convention.
+
+.. _deoptimize_lowering:
+
+Lowering:
+"""""""""
+
+Calls to ``@llvm.experimental.deoptimize`` are lowered to calls to the
+symbol ``__llvm_deoptimize`` (it is the frontend's responsibility to
+ensure that this symbol is defined). The call arguments to
+``@llvm.experimental.deoptimize`` are lowered as if they were formal
+arguments of the specified types, and not as varargs.
+
+
+'``llvm.experimental.guard``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.experimental.guard(i1, ...) [ "deopt"(...) ]
+
+Overview:
+"""""""""
+
+This intrinsic, together with :ref:`deoptimization operand bundles
+<deopt_opbundles>`, allows frontends to express guards or checks on
+optimistic assumptions made during compilation. The semantics of
+``@llvm.experimental.guard`` is defined in terms of
+``@llvm.experimental.deoptimize`` -- its body is defined to be
+equivalent to:
+
+.. code-block:: text
+
+ define void @llvm.experimental.guard(i1 %pred, <args...>) {
+ %realPred = and i1 %pred, undef
+ br i1 %realPred, label %continue, label %leave [, !make.implicit !{}]
+
+ leave:
+ call void @llvm.experimental.deoptimize(<args...>) [ "deopt"() ]
+ ret void
+
+ continue:
+ ret void
+ }
+
+
+with the optional ``[, !make.implicit !{}]`` present if and only if it
+is present on the call site. For more details on ``!make.implicit``,
+see :doc:`FaultMaps`.
+
+In words, ``@llvm.experimental.guard`` executes the attached
+``"deopt"`` continuation if (but **not** only if) its first argument
+is ``false``. Since the optimizer is allowed to replace the ``undef``
+with an arbitrary value, it can optimize guard to fail "spuriously",
+i.e. without the original condition being false (hence the "not only
+if"); and this allows for "check widening" type optimizations.
+
+``@llvm.experimental.guard`` cannot be invoked.
+
+
+'``llvm.load.relative``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i8* @llvm.load.relative.iN(i8* %ptr, iN %offset) argmemonly nounwind readonly
+
+Overview:
+"""""""""
+
+This intrinsic loads a 32-bit value from the address ``%ptr + %offset``,
+adds ``%ptr`` to that value and returns it. The constant folder specifically
+recognizes the form of this intrinsic and the constant initializers it may
+load from; if a loaded constant initializer is known to have the form
+``i32 trunc(x - %ptr)``, the intrinsic call is folded to ``x``.
+
+LLVM provides that the calculation of such a constant initializer will
+not overflow at link time under the medium code model if ``x`` is an
+``unnamed_addr`` function. However, it does not provide this guarantee for
+a constant initializer folded into a function body. This intrinsic can be
+used to avoid the possibility of overflows when loading from such a constant.
+
+Stack Map Intrinsics
+--------------------
+
+LLVM provides experimental intrinsics to support runtime patching
+mechanisms commonly desired in dynamic language JITs. These intrinsics
+are described in :doc:`StackMaps`.
+
+Element Wise Atomic Memory Intrinsics
+-------------------------------------
+
+These intrinsics are similar to the standard library memory intrinsics except
+that they perform memory transfer as a sequence of atomic memory accesses.
+
+.. _int_memcpy_element_unordered_atomic:
+
+'``llvm.memcpy.element.unordered.atomic``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.memcpy.element.unordered.atomic`` on
+any integer bit width and for different address spaces. Not all targets
+support all bit widths however.
+
+::
+
+ declare void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i32(i8* <dest>,
+ i8* <src>,
+ i32 <len>,
+ i32 <element_size>)
+ declare void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* <dest>,
+ i8* <src>,
+ i64 <len>,
+ i32 <element_size>)
+
+Overview:
+"""""""""
+
+The '``llvm.memcpy.element.unordered.atomic.*``' intrinsic is a specialization of the
+'``llvm.memcpy.*``' intrinsic. It differs in that the ``dest`` and ``src`` are treated
+as arrays with elements that are exactly ``element_size`` bytes, and the copy between
+buffers uses a sequence of :ref:`unordered atomic <ordering>` load/store operations
+that are a positive integer multiple of the ``element_size`` in size.
+
+Arguments:
+""""""""""
+
+The first three arguments are the same as they are in the :ref:`@llvm.memcpy <int_memcpy>`
+intrinsic, with the added constraint that ``len`` is required to be a positive integer
+multiple of the ``element_size``. If ``len`` is not a positive integer multiple of
+``element_size``, then the behaviour of the intrinsic is undefined.
+
+``element_size`` must be a compile-time constant positive power of two no greater than
+target-specific atomic access size limit.
+
+For each of the input pointers ``align`` parameter attribute must be specified. It
+must be a power of two no less than the ``element_size``. Caller guarantees that
+both the source and destination pointers are aligned to that boundary.
+
+Semantics:
+""""""""""
+
+The '``llvm.memcpy.element.unordered.atomic.*``' intrinsic copies ``len`` bytes of
+memory from the source location to the destination location. These locations are not
+allowed to overlap. The memory copy is performed as a sequence of load/store operations
+where each access is guaranteed to be a multiple of ``element_size`` bytes wide and
+aligned at an ``element_size`` boundary.
+
+The order of the copy is unspecified. The same value may be read from the source
+buffer many times, but only one write is issued to the destination buffer per
+element. It is well defined to have concurrent reads and writes to both source and
+destination provided those reads and writes are unordered atomic when specified.
+
+This intrinsic does not provide any additional ordering guarantees over those
+provided by a set of unordered loads from the source location and stores to the
+destination.
+
+Lowering:
+"""""""""
+
+In the most general case call to the '``llvm.memcpy.element.unordered.atomic.*``' is
+lowered to a call to the symbol ``__llvm_memcpy_element_unordered_atomic_*``. Where '*'
+is replaced with an actual element size.
+
+Optimizer is allowed to inline memory copy when it's profitable to do so.
+
+'``llvm.memmove.element.unordered.atomic``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use
+``llvm.memmove.element.unordered.atomic`` on any integer bit width and for
+different address spaces. Not all targets support all bit widths however.
+
+::
+
+ declare void @llvm.memmove.element.unordered.atomic.p0i8.p0i8.i32(i8* <dest>,
+ i8* <src>,
+ i32 <len>,
+ i32 <element_size>)
+ declare void @llvm.memmove.element.unordered.atomic.p0i8.p0i8.i64(i8* <dest>,
+ i8* <src>,
+ i64 <len>,
+ i32 <element_size>)
+
+Overview:
+"""""""""
+
+The '``llvm.memmove.element.unordered.atomic.*``' intrinsic is a specialization
+of the '``llvm.memmove.*``' intrinsic. It differs in that the ``dest`` and
+``src`` are treated as arrays with elements that are exactly ``element_size``
+bytes, and the copy between buffers uses a sequence of
+:ref:`unordered atomic <ordering>` load/store operations that are a positive
+integer multiple of the ``element_size`` in size.
+
+Arguments:
+""""""""""
+
+The first three arguments are the same as they are in the
+:ref:`@llvm.memmove <int_memmove>` intrinsic, with the added constraint that
+``len`` is required to be a positive integer multiple of the ``element_size``.
+If ``len`` is not a positive integer multiple of ``element_size``, then the
+behaviour of the intrinsic is undefined.
+
+``element_size`` must be a compile-time constant positive power of two no
+greater than a target-specific atomic access size limit.
+
+For each of the input pointers the ``align`` parameter attribute must be
+specified. It must be a power of two no less than the ``element_size``. Caller
+guarantees that both the source and destination pointers are aligned to that
+boundary.
+
+Semantics:
+""""""""""
+
+The '``llvm.memmove.element.unordered.atomic.*``' intrinsic copies ``len`` bytes
+of memory from the source location to the destination location. These locations
+are allowed to overlap. The memory copy is performed as a sequence of load/store
+operations where each access is guaranteed to be a multiple of ``element_size``
+bytes wide and aligned at an ``element_size`` boundary.
+
+The order of the copy is unspecified. The same value may be read from the source
+buffer many times, but only one write is issued to the destination buffer per
+element. It is well defined to have concurrent reads and writes to both source
+and destination provided those reads and writes are unordered atomic when
+specified.
+
+This intrinsic does not provide any additional ordering guarantees over those
+provided by a set of unordered loads from the source location and stores to the
+destination.
+
+Lowering:
+"""""""""
+
+In the most general case call to the
+'``llvm.memmove.element.unordered.atomic.*``' is lowered to a call to the symbol
+``__llvm_memmove_element_unordered_atomic_*``. Where '*' is replaced with an
+actual element size.
+
+The optimizer is allowed to inline the memory copy when it's profitable to do so.
+
+.. _int_memset_element_unordered_atomic:
+
+'``llvm.memset.element.unordered.atomic``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.memset.element.unordered.atomic`` on
+any integer bit width and for different address spaces. Not all targets
+support all bit widths however.
+
+::
+
+ declare void @llvm.memset.element.unordered.atomic.p0i8.i32(i8* <dest>,
+ i8 <value>,
+ i32 <len>,
+ i32 <element_size>)
+ declare void @llvm.memset.element.unordered.atomic.p0i8.i64(i8* <dest>,
+ i8 <value>,
+ i64 <len>,
+ i32 <element_size>)
+
+Overview:
+"""""""""
+
+The '``llvm.memset.element.unordered.atomic.*``' intrinsic is a specialization of the
+'``llvm.memset.*``' intrinsic. It differs in that the ``dest`` is treated as an array
+with elements that are exactly ``element_size`` bytes, and the assignment to that array
+uses uses a sequence of :ref:`unordered atomic <ordering>` store operations
+that are a positive integer multiple of the ``element_size`` in size.
+
+Arguments:
+""""""""""
+
+The first three arguments are the same as they are in the :ref:`@llvm.memset <int_memset>`
+intrinsic, with the added constraint that ``len`` is required to be a positive integer
+multiple of the ``element_size``. If ``len`` is not a positive integer multiple of
+``element_size``, then the behaviour of the intrinsic is undefined.
+
+``element_size`` must be a compile-time constant positive power of two no greater than
+target-specific atomic access size limit.
+
+The ``dest`` input pointer must have the ``align`` parameter attribute specified. It
+must be a power of two no less than the ``element_size``. Caller guarantees that
+the destination pointer is aligned to that boundary.
+
+Semantics:
+""""""""""
+
+The '``llvm.memset.element.unordered.atomic.*``' intrinsic sets the ``len`` bytes of
+memory starting at the destination location to the given ``value``. The memory is
+set with a sequence of store operations where each access is guaranteed to be a
+multiple of ``element_size`` bytes wide and aligned at an ``element_size`` boundary.
+
+The order of the assignment is unspecified. Only one write is issued to the
+destination buffer per element. It is well defined to have concurrent reads and
+writes to the destination provided those reads and writes are unordered atomic
+when specified.
+
+This intrinsic does not provide any additional ordering guarantees over those
+provided by a set of unordered stores to the destination.
+
+Lowering:
+"""""""""
+
+In the most general case call to the '``llvm.memset.element.unordered.atomic.*``' is
+lowered to a call to the symbol ``__llvm_memset_element_unordered_atomic_*``. Where '*'
+is replaced with an actual element size.
+
+The optimizer is allowed to inline the memory assignment when it's profitable to do so.
+
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