[www-releases] r290368 - Add 3.9.1 docs.
Tom Stellard via llvm-commits
llvm-commits at lists.llvm.org
Thu Dec 22 12:04:06 PST 2016
Added: www-releases/trunk/3.9.1/docs/_sources/Statepoints.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.9.1/docs/_sources/Statepoints.txt?rev=290368&view=auto
==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/Statepoints.txt (added)
+++ www-releases/trunk/3.9.1/docs/_sources/Statepoints.txt Thu Dec 22 14:04:03 2016
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+=====================================
+Garbage Collection Safepoints in LLVM
+=====================================
+
+.. contents::
+ :local:
+ :depth: 2
+
+Status
+=======
+
+This document describes a set of experimental extensions to LLVM. Use
+with caution. Because the intrinsics have experimental status,
+compatibility across LLVM releases is not guaranteed.
+
+LLVM currently supports an alternate mechanism for conservative
+garbage collection support using the ``gcroot`` intrinsic. The mechanism
+described here shares little in common with the alternate ``gcroot``
+implementation and it is hoped that this mechanism will eventually
+replace the gc_root mechanism.
+
+Overview
+========
+
+To collect dead objects, garbage collectors must be able to identify
+any references to objects contained within executing code, and,
+depending on the collector, potentially update them. The collector
+does not need this information at all points in code - that would make
+the problem much harder - but only at well-defined points in the
+execution known as 'safepoints' For most collectors, it is sufficient
+to track at least one copy of each unique pointer value. However, for
+a collector which wishes to relocate objects directly reachable from
+running code, a higher standard is required.
+
+One additional challenge is that the compiler may compute intermediate
+results ("derived pointers") which point outside of the allocation or
+even into the middle of another allocation. The eventual use of this
+intermediate value must yield an address within the bounds of the
+allocation, but such "exterior derived pointers" may be visible to the
+collector. Given this, a garbage collector can not safely rely on the
+runtime value of an address to indicate the object it is associated
+with. If the garbage collector wishes to move any object, the
+compiler must provide a mapping, for each pointer, to an indication of
+its allocation.
+
+To simplify the interaction between a collector and the compiled code,
+most garbage collectors are organized in terms of three abstractions:
+load barriers, store barriers, and safepoints.
+
+#. A load barrier is a bit of code executed immediately after the
+ machine load instruction, but before any use of the value loaded.
+ Depending on the collector, such a barrier may be needed for all
+ loads, merely loads of a particular type (in the original source
+ language), or none at all.
+
+#. Analogously, a store barrier is a code fragment that runs
+ immediately before the machine store instruction, but after the
+ computation of the value stored. The most common use of a store
+ barrier is to update a 'card table' in a generational garbage
+ collector.
+
+#. A safepoint is a location at which pointers visible to the compiled
+ code (i.e. currently in registers or on the stack) are allowed to
+ change. After the safepoint completes, the actual pointer value
+ may differ, but the 'object' (as seen by the source language)
+ pointed to will not.
+
+ Note that the term 'safepoint' is somewhat overloaded. It refers to
+ both the location at which the machine state is parsable and the
+ coordination protocol involved in bring application threads to a
+ point at which the collector can safely use that information. The
+ term "statepoint" as used in this document refers exclusively to the
+ former.
+
+This document focuses on the last item - compiler support for
+safepoints in generated code. We will assume that an outside
+mechanism has decided where to place safepoints. From our
+perspective, all safepoints will be function calls. To support
+relocation of objects directly reachable from values in compiled code,
+the collector must be able to:
+
+#. identify every copy of a pointer (including copies introduced by
+ the compiler itself) at the safepoint,
+#. identify which object each pointer relates to, and
+#. potentially update each of those copies.
+
+This document describes the mechanism by which an LLVM based compiler
+can provide this information to a language runtime/collector, and
+ensure that all pointers can be read and updated if desired. The
+heart of the approach is to construct (or rewrite) the IR in a manner
+where the possible updates performed by the garbage collector are
+explicitly visible in the IR. Doing so requires that we:
+
+#. create a new SSA value for each potentially relocated pointer, and
+ ensure that no uses of the original (non relocated) value is
+ reachable after the safepoint,
+#. specify the relocation in a way which is opaque to the compiler to
+ ensure that the optimizer can not introduce new uses of an
+ unrelocated value after a statepoint. This prevents the optimizer
+ from performing unsound optimizations.
+#. recording a mapping of live pointers (and the allocation they're
+ associated with) for each statepoint.
+
+At the most abstract level, inserting a safepoint can be thought of as
+replacing a call instruction with a call to a multiple return value
+function which both calls the original target of the call, returns
+it's result, and returns updated values for any live pointers to
+garbage collected objects.
+
+ Note that the task of identifying all live pointers to garbage
+ collected values, transforming the IR to expose a pointer giving the
+ base object for every such live pointer, and inserting all the
+ intrinsics correctly is explicitly out of scope for this document.
+ The recommended approach is to use the :ref:`utility passes
+ <statepoint-utilities>` described below.
+
+This abstract function call is concretely represented by a sequence of
+intrinsic calls known collectively as a "statepoint relocation sequence".
+
+Let's consider a simple call in LLVM IR:
+
+.. code-block:: llvm
+
+ define i8 addrspace(1)* @test1(i8 addrspace(1)* %obj)
+ gc "statepoint-example" {
+ call void ()* @foo()
+ ret i8 addrspace(1)* %obj
+ }
+
+Depending on our language we may need to allow a safepoint during the execution
+of ``foo``. If so, we need to let the collector update local values in the
+current frame. If we don't, we'll be accessing a potential invalid reference
+once we eventually return from the call.
+
+In this example, we need to relocate the SSA value ``%obj``. Since we can't
+actually change the value in the SSA value ``%obj``, we need to introduce a new
+SSA value ``%obj.relocated`` which represents the potentially changed value of
+``%obj`` after the safepoint and update any following uses appropriately. The
+resulting relocation sequence is:
+
+.. code-block:: text
+
+ define i8 addrspace(1)* @test1(i8 addrspace(1)* %obj)
+ gc "statepoint-example" {
+ %0 = call token (i64, i32, void ()*, i32, i32, ...)* @llvm.experimental.gc.statepoint.p0f_isVoidf(i64 0, i32 0, void ()* @foo, i32 0, i32 0, i32 0, i32 0, i8 addrspace(1)* %obj)
+ %obj.relocated = call coldcc i8 addrspace(1)* @llvm.experimental.gc.relocate.p1i8(token %0, i32 7, i32 7)
+ ret i8 addrspace(1)* %obj.relocated
+ }
+
+Ideally, this sequence would have been represented as a M argument, N
+return value function (where M is the number of values being
+relocated + the original call arguments and N is the original return
+value + each relocated value), but LLVM does not easily support such a
+representation.
+
+Instead, the statepoint intrinsic marks the actual site of the
+safepoint or statepoint. The statepoint returns a token value (which
+exists only at compile time). To get back the original return value
+of the call, we use the ``gc.result`` intrinsic. To get the relocation
+of each pointer in turn, we use the ``gc.relocate`` intrinsic with the
+appropriate index. Note that both the ``gc.relocate`` and ``gc.result`` are
+tied to the statepoint. The combination forms a "statepoint relocation
+sequence" and represents the entirety of a parseable call or 'statepoint'.
+
+When lowered, this example would generate the following x86 assembly:
+
+.. code-block:: gas
+
+ .globl test1
+ .align 16, 0x90
+ pushq %rax
+ callq foo
+ .Ltmp1:
+ movq (%rsp), %rax # This load is redundant (oops!)
+ popq %rdx
+ retq
+
+Each of the potentially relocated values has been spilled to the
+stack, and a record of that location has been recorded to the
+:ref:`Stack Map section <stackmap-section>`. If the garbage collector
+needs to update any of these pointers during the call, it knows
+exactly what to change.
+
+The relevant parts of the StackMap section for our example are:
+
+.. code-block:: gas
+
+ # This describes the call site
+ # Stack Maps: callsite 2882400000
+ .quad 2882400000
+ .long .Ltmp1-test1
+ .short 0
+ # .. 8 entries skipped ..
+ # This entry describes the spill slot which is directly addressable
+ # off RSP with offset 0. Given the value was spilled with a pushq,
+ # that makes sense.
+ # Stack Maps: Loc 8: Direct RSP [encoding: .byte 2, .byte 8, .short 7, .int 0]
+ .byte 2
+ .byte 8
+ .short 7
+ .long 0
+
+This example was taken from the tests for the :ref:`RewriteStatepointsForGC` utility pass. As such, it's full StackMap can be easily examined with the following command.
+
+.. code-block:: bash
+
+ opt -rewrite-statepoints-for-gc test/Transforms/RewriteStatepointsForGC/basics.ll -S | llc -debug-only=stackmaps
+
+Base & Derived Pointers
+^^^^^^^^^^^^^^^^^^^^^^^
+
+A "base pointer" is one which points to the starting address of an allocation
+(object). A "derived pointer" is one which is offset from a base pointer by
+some amount. When relocating objects, a garbage collector needs to be able
+to relocate each derived pointer associated with an allocation to the same
+offset from the new address.
+
+"Interior derived pointers" remain within the bounds of the allocation
+they're associated with. As a result, the base object can be found at
+runtime provided the bounds of allocations are known to the runtime system.
+
+"Exterior derived pointers" are outside the bounds of the associated object;
+they may even fall within *another* allocations address range. As a result,
+there is no way for a garbage collector to determine which allocation they
+are associated with at runtime and compiler support is needed.
+
+The ``gc.relocate`` intrinsic supports an explicit operand for describing the
+allocation associated with a derived pointer. This operand is frequently
+referred to as the base operand, but does not strictly speaking have to be
+a base pointer, but it does need to lie within the bounds of the associated
+allocation. Some collectors may require that the operand be an actual base
+pointer rather than merely an internal derived pointer. Note that during
+lowering both the base and derived pointer operands are required to be live
+over the associated call safepoint even if the base is otherwise unused
+afterwards.
+
+If we extend our previous example to include a pointless derived pointer,
+we get:
+
+.. code-block:: text
+
+ define i8 addrspace(1)* @test1(i8 addrspace(1)* %obj)
+ gc "statepoint-example" {
+ %gep = getelementptr i8, i8 addrspace(1)* %obj, i64 20000
+ %token = call token (i64, i32, void ()*, i32, i32, ...)* @llvm.experimental.gc.statepoint.p0f_isVoidf(i64 0, i32 0, void ()* @foo, i32 0, i32 0, i32 0, i32 0, i8 addrspace(1)* %obj, i8 addrspace(1)* %gep)
+ %obj.relocated = call i8 addrspace(1)* @llvm.experimental.gc.relocate.p1i8(token %token, i32 7, i32 7)
+ %gep.relocated = call i8 addrspace(1)* @llvm.experimental.gc.relocate.p1i8(token %token, i32 7, i32 8)
+ %p = getelementptr i8, i8 addrspace(1)* %gep, i64 -20000
+ ret i8 addrspace(1)* %p
+ }
+
+Note that in this example %p and %obj.relocate are the same address and we
+could replace one with the other, potentially removing the derived pointer
+from the live set at the safepoint entirely.
+
+.. _gc_transition_args:
+
+GC Transitions
+^^^^^^^^^^^^^^^^^^
+
+As a practical consideration, many garbage-collected systems allow code that is
+collector-aware ("managed code") to call code that is not collector-aware
+("unmanaged code"). It is common that such calls must also be safepoints, since
+it is desirable to allow the collector to run during the execution of
+unmanaged code. Furthermore, it is common that coordinating the transition from
+managed to unmanaged code requires extra code generation at the call site to
+inform the collector of the transition. In order to support these needs, a
+statepoint may be marked as a GC transition, and data that is necessary to
+perform the transition (if any) may be provided as additional arguments to the
+statepoint.
+
+ Note that although in many cases statepoints may be inferred to be GC
+ transitions based on the function symbols involved (e.g. a call from a
+ function with GC strategy "foo" to a function with GC strategy "bar"),
+ indirect calls that are also GC transitions must also be supported. This
+ requirement is the driving force behind the decision to require that GC
+ transitions are explicitly marked.
+
+Let's revisit the sample given above, this time treating the call to ``@foo``
+as a GC transition. Depending on our target, the transition code may need to
+access some extra state in order to inform the collector of the transition.
+Let's assume a hypothetical GC--somewhat unimaginatively named "hypothetical-gc"
+--that requires that a TLS variable must be written to before and after a call
+to unmanaged code. The resulting relocation sequence is:
+
+.. code-block:: text
+
+ @flag = thread_local global i32 0, align 4
+
+ define i8 addrspace(1)* @test1(i8 addrspace(1) *%obj)
+ gc "hypothetical-gc" {
+
+ %0 = call token (i64, i32, void ()*, i32, i32, ...)* @llvm.experimental.gc.statepoint.p0f_isVoidf(i64 0, i32 0, void ()* @foo, i32 0, i32 1, i32* @Flag, i32 0, i8 addrspace(1)* %obj)
+ %obj.relocated = call coldcc i8 addrspace(1)* @llvm.experimental.gc.relocate.p1i8(token %0, i32 7, i32 7)
+ ret i8 addrspace(1)* %obj.relocated
+ }
+
+During lowering, this will result in a instruction selection DAG that looks
+something like:
+
+::
+
+ CALLSEQ_START
+ ...
+ GC_TRANSITION_START (lowered i32 *@Flag), SRCVALUE i32* Flag
+ STATEPOINT
+ GC_TRANSITION_END (lowered i32 *@Flag), SRCVALUE i32 *Flag
+ ...
+ CALLSEQ_END
+
+In order to generate the necessary transition code, the backend for each target
+supported by "hypothetical-gc" must be modified to lower ``GC_TRANSITION_START``
+and ``GC_TRANSITION_END`` nodes appropriately when the "hypothetical-gc"
+strategy is in use for a particular function. Assuming that such lowering has
+been added for X86, the generated assembly would be:
+
+.. code-block:: gas
+
+ .globl test1
+ .align 16, 0x90
+ pushq %rax
+ movl $1, %fs:Flag at TPOFF
+ callq foo
+ movl $0, %fs:Flag at TPOFF
+ .Ltmp1:
+ movq (%rsp), %rax # This load is redundant (oops!)
+ popq %rdx
+ retq
+
+Note that the design as presented above is not fully implemented: in particular,
+strategy-specific lowering is not present, and all GC transitions are emitted as
+as single no-op before and after the call instruction. These no-ops are often
+removed by the backend during dead machine instruction elimination.
+
+
+Intrinsics
+===========
+
+'llvm.experimental.gc.statepoint' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare token
+ @llvm.experimental.gc.statepoint(i64 <id>, i32 <num patch bytes>,
+ func_type <target>,
+ i64 <#call args>, i64 <flags>,
+ ... (call parameters),
+ i64 <# transition args>, ... (transition parameters),
+ i64 <# deopt args>, ... (deopt parameters),
+ ... (gc parameters))
+
+Overview:
+"""""""""
+
+The statepoint intrinsic represents a call which is parse-able by the
+runtime.
+
+Operands:
+"""""""""
+
+The 'id' operand is a constant integer that is reported as the ID
+field in the generated stackmap. LLVM does not interpret this
+parameter in any way and its meaning is up to the statepoint user to
+decide. Note that LLVM is free to duplicate code containing
+statepoint calls, and this may transform IR that had a unique 'id' per
+lexical call to statepoint to IR that does not.
+
+If 'num patch bytes' is non-zero then the call instruction
+corresponding to the statepoint is not emitted and LLVM emits 'num
+patch bytes' bytes of nops in its place. LLVM will emit code to
+prepare the function arguments and retrieve the function return value
+in accordance to the calling convention; the former before the nop
+sequence and the latter after the nop sequence. It is expected that
+the user will patch over the 'num patch bytes' bytes of nops with a
+calling sequence specific to their runtime before executing the
+generated machine code. There are no guarantees with respect to the
+alignment of the nop sequence. Unlike :doc:`StackMaps` statepoints do
+not have a concept of shadow bytes. Note that semantically the
+statepoint still represents a call or invoke to 'target', and the nop
+sequence after patching is expected to represent an operation
+equivalent to a call or invoke to 'target'.
+
+The 'target' operand is the function actually being called. The
+target can be specified as either a symbolic LLVM function, or as an
+arbitrary Value of appropriate function type. Note that the function
+type must match the signature of the callee and the types of the 'call
+parameters' arguments.
+
+The '#call args' operand is the number of arguments to the actual
+call. It must exactly match the number of arguments passed in the
+'call parameters' variable length section.
+
+The 'flags' operand is used to specify extra information about the
+statepoint. This is currently only used to mark certain statepoints
+as GC transitions. This operand is a 64-bit integer with the following
+layout, where bit 0 is the least significant bit:
+
+ +-------+---------------------------------------------------+
+ | Bit # | Usage |
+ +=======+===================================================+
+ | 0 | Set if the statepoint is a GC transition, cleared |
+ | | otherwise. |
+ +-------+---------------------------------------------------+
+ | 1-63 | Reserved for future use; must be cleared. |
+ +-------+---------------------------------------------------+
+
+The 'call parameters' arguments are simply the arguments which need to
+be passed to the call target. They will be lowered according to the
+specified calling convention and otherwise handled like a normal call
+instruction. The number of arguments must exactly match what is
+specified in '# call args'. The types must match the signature of
+'target'.
+
+The 'transition parameters' arguments contain an arbitrary list of
+Values which need to be passed to GC transition code. They will be
+lowered and passed as operands to the appropriate GC_TRANSITION nodes
+in the selection DAG. It is assumed that these arguments must be
+available before and after (but not necessarily during) the execution
+of the callee. The '# transition args' field indicates how many operands
+are to be interpreted as 'transition parameters'.
+
+The 'deopt parameters' arguments contain an arbitrary list of Values
+which is meaningful to the runtime. The runtime may read any of these
+values, but is assumed not to modify them. If the garbage collector
+might need to modify one of these values, it must also be listed in
+the 'gc pointer' argument list. The '# deopt args' field indicates
+how many operands are to be interpreted as 'deopt parameters'.
+
+The 'gc parameters' arguments contain every pointer to a garbage
+collector object which potentially needs to be updated by the garbage
+collector. Note that the argument list must explicitly contain a base
+pointer for every derived pointer listed. The order of arguments is
+unimportant. Unlike the other variable length parameter sets, this
+list is not length prefixed.
+
+Semantics:
+""""""""""
+
+A statepoint is assumed to read and write all memory. As a result,
+memory operations can not be reordered past a statepoint. It is
+illegal to mark a statepoint as being either 'readonly' or 'readnone'.
+
+Note that legal IR can not perform any memory operation on a 'gc
+pointer' argument of the statepoint in a location statically reachable
+from the statepoint. Instead, the explicitly relocated value (from a
+``gc.relocate``) must be used.
+
+'llvm.experimental.gc.result' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare type*
+ @llvm.experimental.gc.result(token %statepoint_token)
+
+Overview:
+"""""""""
+
+``gc.result`` extracts the result of the original call instruction
+which was replaced by the ``gc.statepoint``. The ``gc.result``
+intrinsic is actually a family of three intrinsics due to an
+implementation limitation. Other than the type of the return value,
+the semantics are the same.
+
+Operands:
+"""""""""
+
+The first and only argument is the ``gc.statepoint`` which starts
+the safepoint sequence of which this ``gc.result`` is a part.
+Despite the typing of this as a generic token, *only* the value defined
+by a ``gc.statepoint`` is legal here.
+
+Semantics:
+""""""""""
+
+The ``gc.result`` represents the return value of the call target of
+the ``statepoint``. The type of the ``gc.result`` must exactly match
+the type of the target. If the call target returns void, there will
+be no ``gc.result``.
+
+A ``gc.result`` is modeled as a 'readnone' pure function. It has no
+side effects since it is just a projection of the return value of the
+previous call represented by the ``gc.statepoint``.
+
+'llvm.experimental.gc.relocate' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <pointer type>
+ @llvm.experimental.gc.relocate(token %statepoint_token,
+ i32 %base_offset,
+ i32 %pointer_offset)
+
+Overview:
+"""""""""
+
+A ``gc.relocate`` returns the potentially relocated value of a pointer
+at the safepoint.
+
+Operands:
+"""""""""
+
+The first argument is the ``gc.statepoint`` which starts the
+safepoint sequence of which this ``gc.relocation`` is a part.
+Despite the typing of this as a generic token, *only* the value defined
+by a ``gc.statepoint`` is legal here.
+
+The second argument is an index into the statepoints list of arguments
+which specifies the allocation for the pointer being relocated.
+This index must land within the 'gc parameter' section of the
+statepoint's argument list. The associated value must be within the
+object with which the pointer being relocated is associated. The optimizer
+is free to change *which* interior derived pointer is reported, provided that
+it does not replace an actual base pointer with another interior derived
+pointer. Collectors are allowed to rely on the base pointer operand
+remaining an actual base pointer if so constructed.
+
+The third argument is an index into the statepoint's list of arguments
+which specify the (potentially) derived pointer being relocated. It
+is legal for this index to be the same as the second argument
+if-and-only-if a base pointer is being relocated. This index must land
+within the 'gc parameter' section of the statepoint's argument list.
+
+Semantics:
+""""""""""
+
+The return value of ``gc.relocate`` is the potentially relocated value
+of the pointer specified by it's arguments. It is unspecified how the
+value of the returned pointer relates to the argument to the
+``gc.statepoint`` other than that a) it points to the same source
+language object with the same offset, and b) the 'based-on'
+relationship of the newly relocated pointers is a projection of the
+unrelocated pointers. In particular, the integer value of the pointer
+returned is unspecified.
+
+A ``gc.relocate`` is modeled as a ``readnone`` pure function. It has no
+side effects since it is just a way to extract information about work
+done during the actual call modeled by the ``gc.statepoint``.
+
+.. _statepoint-stackmap-format:
+
+Stack Map Format
+================
+
+Locations for each pointer value which may need read and/or updated by
+the runtime or collector are provided via the :ref:`Stack Map format
+<stackmap-format>` specified in the PatchPoint documentation.
+
+Each statepoint generates the following Locations:
+
+* Constant which describes the calling convention of the call target. This
+ constant is a valid :ref:`calling convention identifier <callingconv>` for
+ the version of LLVM used to generate the stackmap. No additional compatibility
+ guarantees are made for this constant over what LLVM provides elsewhere w.r.t.
+ these identifiers.
+* Constant which describes the flags passed to the statepoint intrinsic
+* Constant which describes number of following deopt *Locations* (not
+ operands)
+* Variable number of Locations, one for each deopt parameter listed in
+ the IR statepoint (same number as described by previous Constant). At
+ the moment, only deopt parameters with a bitwidth of 64 bits or less
+ are supported. Values of a type larger than 64 bits can be specified
+ and reported only if a) the value is constant at the call site, and b)
+ the constant can be represented with less than 64 bits (assuming zero
+ extension to the original bitwidth).
+* Variable number of relocation records, each of which consists of
+ exactly two Locations. Relocation records are described in detail
+ below.
+
+Each relocation record provides sufficient information for a collector to
+relocate one or more derived pointers. Each record consists of a pair of
+Locations. The second element in the record represents the pointer (or
+pointers) which need updated. The first element in the record provides a
+pointer to the base of the object with which the pointer(s) being relocated is
+associated. This information is required for handling generalized derived
+pointers since a pointer may be outside the bounds of the original allocation,
+but still needs to be relocated with the allocation. Additionally:
+
+* It is guaranteed that the base pointer must also appear explicitly as a
+ relocation pair if used after the statepoint.
+* There may be fewer relocation records then gc parameters in the IR
+ statepoint. Each *unique* pair will occur at least once; duplicates
+ are possible.
+* The Locations within each record may either be of pointer size or a
+ multiple of pointer size. In the later case, the record must be
+ interpreted as describing a sequence of pointers and their corresponding
+ base pointers. If the Location is of size N x sizeof(pointer), then
+ there will be N records of one pointer each contained within the Location.
+ Both Locations in a pair can be assumed to be of the same size.
+
+Note that the Locations used in each section may describe the same
+physical location. e.g. A stack slot may appear as a deopt location,
+a gc base pointer, and a gc derived pointer.
+
+The LiveOut section of the StkMapRecord will be empty for a statepoint
+record.
+
+Safepoint Semantics & Verification
+==================================
+
+The fundamental correctness property for the compiled code's
+correctness w.r.t. the garbage collector is a dynamic one. It must be
+the case that there is no dynamic trace such that a operation
+involving a potentially relocated pointer is observably-after a
+safepoint which could relocate it. 'observably-after' is this usage
+means that an outside observer could observe this sequence of events
+in a way which precludes the operation being performed before the
+safepoint.
+
+To understand why this 'observable-after' property is required,
+consider a null comparison performed on the original copy of a
+relocated pointer. Assuming that control flow follows the safepoint,
+there is no way to observe externally whether the null comparison is
+performed before or after the safepoint. (Remember, the original
+Value is unmodified by the safepoint.) The compiler is free to make
+either scheduling choice.
+
+The actual correctness property implemented is slightly stronger than
+this. We require that there be no *static path* on which a
+potentially relocated pointer is 'observably-after' it may have been
+relocated. This is slightly stronger than is strictly necessary (and
+thus may disallow some otherwise valid programs), but greatly
+simplifies reasoning about correctness of the compiled code.
+
+By construction, this property will be upheld by the optimizer if
+correctly established in the source IR. This is a key invariant of
+the design.
+
+The existing IR Verifier pass has been extended to check most of the
+local restrictions on the intrinsics mentioned in their respective
+documentation. The current implementation in LLVM does not check the
+key relocation invariant, but this is ongoing work on developing such
+a verifier. Please ask on llvm-dev if you're interested in
+experimenting with the current version.
+
+.. _statepoint-utilities:
+
+Utility Passes for Safepoint Insertion
+======================================
+
+.. _RewriteStatepointsForGC:
+
+RewriteStatepointsForGC
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+The pass RewriteStatepointsForGC transforms a functions IR by replacing a
+``gc.statepoint`` (with an optional ``gc.result``) with a full relocation
+sequence, including all required ``gc.relocates``. To function, the pass
+requires that the GC strategy specified for the function be able to reliably
+distinguish between GC references and non-GC references in IR it is given.
+
+As an example, given this code:
+
+.. code-block:: text
+
+ define i8 addrspace(1)* @test1(i8 addrspace(1)* %obj)
+ gc "statepoint-example" {
+ call token (i64, i32, void ()*, i32, i32, ...)* @llvm.experimental.gc.statepoint.p0f_isVoidf(i64 2882400000, i32 0, void ()* @foo, i32 0, i32 0, i32 0, i32 5, i32 0, i32 -1, i32 0, i32 0, i32 0)
+ ret i8 addrspace(1)* %obj
+ }
+
+The pass would produce this IR:
+
+.. code-block:: text
+
+ define i8 addrspace(1)* @test1(i8 addrspace(1)* %obj)
+ gc "statepoint-example" {
+ %0 = call token (i64, i32, void ()*, i32, i32, ...)* @llvm.experimental.gc.statepoint.p0f_isVoidf(i64 2882400000, i32 0, void ()* @foo, i32 0, i32 0, i32 0, i32 5, i32 0, i32 -1, i32 0, i32 0, i32 0, i8 addrspace(1)* %obj)
+ %obj.relocated = call coldcc i8 addrspace(1)* @llvm.experimental.gc.relocate.p1i8(token %0, i32 12, i32 12)
+ ret i8 addrspace(1)* %obj.relocated
+ }
+
+In the above examples, the addrspace(1) marker on the pointers is the mechanism
+that the ``statepoint-example`` GC strategy uses to distinguish references from
+non references. Address space 1 is not globally reserved for this purpose.
+
+This pass can be used an utility function by a language frontend that doesn't
+want to manually reason about liveness, base pointers, or relocation when
+constructing IR. As currently implemented, RewriteStatepointsForGC must be
+run after SSA construction (i.e. mem2ref).
+
+RewriteStatepointsForGC will ensure that appropriate base pointers are listed
+for every relocation created. It will do so by duplicating code as needed to
+propagate the base pointer associated with each pointer being relocated to
+the appropriate safepoints. The implementation assumes that the following
+IR constructs produce base pointers: loads from the heap, addresses of global
+variables, function arguments, function return values. Constant pointers (such
+as null) are also assumed to be base pointers. In practice, this constraint
+can be relaxed to producing interior derived pointers provided the target
+collector can find the associated allocation from an arbitrary interior
+derived pointer.
+
+In practice, RewriteStatepointsForGC can be run much later in the pass
+pipeline, after most optimization is already done. This helps to improve
+the quality of the generated code when compiled with garbage collection support.
+In the long run, this is the intended usage model. At this time, a few details
+have yet to be worked out about the semantic model required to guarantee this
+is always correct. As such, please use with caution and report bugs.
+
+.. _PlaceSafepoints:
+
+PlaceSafepoints
+^^^^^^^^^^^^^^^^
+
+The pass PlaceSafepoints transforms a function's IR by replacing any call or
+invoke instructions with appropriate ``gc.statepoint`` and ``gc.result`` pairs,
+and inserting safepoint polls sufficient to ensure running code checks for a
+safepoint request on a timely manner. This pass is expected to be run before
+RewriteStatepointsForGC and thus does not produce full relocation sequences.
+
+As an example, given input IR of the following:
+
+.. code-block:: llvm
+
+ define void @test() gc "statepoint-example" {
+ call void @foo()
+ ret void
+ }
+
+ declare void @do_safepoint()
+ define void @gc.safepoint_poll() {
+ call void @do_safepoint()
+ ret void
+ }
+
+
+This pass would produce the following IR:
+
+.. code-block:: text
+
+ define void @test() gc "statepoint-example" {
+ %safepoint_token = call token (i64, i32, void ()*, i32, i32, ...)* @llvm.experimental.gc.statepoint.p0f_isVoidf(i64 2882400000, i32 0, void ()* @do_safepoint, i32 0, i32 0, i32 0, i32 0)
+ %safepoint_token1 = call token (i64, i32, void ()*, i32, i32, ...)* @llvm.experimental.gc.statepoint.p0f_isVoidf(i64 2882400000, i32 0, void ()* @foo, i32 0, i32 0, i32 0, i32 0)
+ ret void
+ }
+
+In this case, we've added an (unconditional) entry safepoint poll and converted the call into a ``gc.statepoint``. Note that despite appearances, the entry poll is not necessarily redundant. We'd have to know that ``foo`` and ``test`` were not mutually recursive for the poll to be redundant. In practice, you'd probably want to your poll definition to contain a conditional branch of some form.
+
+
+At the moment, PlaceSafepoints can insert safepoint polls at method entry and
+loop backedges locations. Extending this to work with return polls would be
+straight forward if desired.
+
+PlaceSafepoints includes a number of optimizations to avoid placing safepoint
+polls at particular sites unless needed to ensure timely execution of a poll
+under normal conditions. PlaceSafepoints does not attempt to ensure timely
+execution of a poll under worst case conditions such as heavy system paging.
+
+The implementation of a safepoint poll action is specified by looking up a
+function of the name ``gc.safepoint_poll`` in the containing Module. The body
+of this function is inserted at each poll site desired. While calls or invokes
+inside this method are transformed to a ``gc.statepoints``, recursive poll
+insertion is not performed.
+
+By default PlaceSafepoints passes in ``0xABCDEF00`` as the statepoint
+ID and ``0`` as the number of patchable bytes to the newly constructed
+``gc.statepoint``. These values can be configured on a per-callsite
+basis using the attributes ``"statepoint-id"`` and
+``"statepoint-num-patch-bytes"``. If a call site is marked with a
+``"statepoint-id"`` function attribute and its value is a positive
+integer (represented as a string), then that value is used as the ID
+of the newly constructed ``gc.statepoint``. If a call site is marked
+with a ``"statepoint-num-patch-bytes"`` function attribute and its
+value is a positive integer, then that value is used as the 'num patch
+bytes' parameter of the newly constructed ``gc.statepoint``. The
+``"statepoint-id"`` and ``"statepoint-num-patch-bytes"`` attributes
+are not propagated to the ``gc.statepoint`` call or invoke if they
+could be successfully parsed.
+
+If you are scheduling the RewriteStatepointsForGC pass late in the pass order,
+you should probably schedule this pass immediately before it. The exception
+would be if you need to preserve abstract frame information (e.g. for
+deoptimization or introspection) at safepoints. In that case, ask on the
+llvm-dev mailing list for suggestions.
+
+
+Supported Architectures
+=======================
+
+Support for statepoint generation requires some code for each backend.
+Today, only X86_64 is supported.
+
+Problem Areas and Active Work
+=============================
+
+#. As the existing users of the late rewriting model have matured, we've found
+ cases where the optimizer breaks the assumption that an SSA value of
+ gc-pointer type actually contains a gc-pointer and vice-versa. We need to
+ clarify our expectations and propose at least one small IR change. (Today,
+ the gc-pointer distinction is managed via address spaces. This turns out
+ not to be quite strong enough.)
+
+#. Support for languages which allow unmanaged pointers to garbage collected
+ objects (i.e. pass a pointer to an object to a C routine) via pinning.
+
+#. Support for garbage collected objects allocated on the stack. Specifically,
+ allocas are always assumed to be in address space 0 and we need a
+ cast/promotion operator to let rewriting identify them.
+
+#. The current statepoint lowering is known to be somewhat poor. In the very
+ long term, we'd like to integrate statepoints with the register allocator;
+ in the near term this is unlikely to happen. We've found the quality of
+ lowering to be relatively unimportant as hot-statepoints are almost always
+ inliner bugs.
+
+#. Concerns have been raised that the statepoint representation results in a
+ large amount of IR being produced for some examples and that this
+ contributes to higher than expected memory usage and compile times. There's
+ no immediate plans to make changes due to this, but alternate models may be
+ explored in the future.
+
+#. Relocations along exceptional paths are currently broken in ToT. In
+ particular, there is current no way to represent a rethrow on a path which
+ also has relocations. See `this llvm-dev discussion
+ <https://groups.google.com/forum/#!topic/llvm-dev/AE417XjgxvI>`_ for more
+ detail.
+
+Bugs and Enhancements
+=====================
+
+Currently known bugs and enhancements under consideration can be
+tracked by performing a `bugzilla search
+<http://llvm.org/bugs/buglist.cgi?cmdtype=runnamed&namedcmd=Statepoint%20Bugs&list_id=64342>`_
+for [Statepoint] in the summary field. When filing new bugs, please
+use this tag so that interested parties see the newly filed bug. As
+with most LLVM features, design discussions take place on `llvm-dev
+<http://lists.llvm.org/mailman/listinfo/llvm-dev>`_, and patches
+should be sent to `llvm-commits
+<http://lists.llvm.org/mailman/listinfo/llvm-commits>`_ for review.
+
Added: www-releases/trunk/3.9.1/docs/_sources/SystemLibrary.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.9.1/docs/_sources/SystemLibrary.txt?rev=290368&view=auto
==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/SystemLibrary.txt (added)
+++ www-releases/trunk/3.9.1/docs/_sources/SystemLibrary.txt Thu Dec 22 14:04:03 2016
@@ -0,0 +1,247 @@
+==============
+System Library
+==============
+
+Abstract
+========
+
+This document provides some details on LLVM's System Library, located in the
+source at ``lib/System`` and ``include/llvm/System``. The library's purpose is
+to shield LLVM from the differences between operating systems for the few
+services LLVM needs from the operating system. Much of LLVM is written using
+portability features of standard C++. However, in a few areas, system dependent
+facilities are needed and the System Library is the wrapper around those system
+calls.
+
+By centralizing LLVM's use of operating system interfaces, we make it possible
+for the LLVM tool chain and runtime libraries to be more easily ported to new
+platforms since (theoretically) only ``lib/System`` needs to be ported. This
+library also unclutters the rest of LLVM from #ifdef use and special cases for
+specific operating systems. Such uses are replaced with simple calls to the
+interfaces provided in ``include/llvm/System``.
+
+Note that the System Library is not intended to be a complete operating system
+wrapper (such as the Adaptive Communications Environment (ACE) or Apache
+Portable Runtime (APR)), but only provides the functionality necessary to
+support LLVM.
+
+The System Library was written by Reid Spencer who formulated the design based
+on similar work originating from the eXtensible Programming System (XPS).
+Several people helped with the effort; especially, Jeff Cohen and Henrik Bach
+on the Win32 port.
+
+Keeping LLVM Portable
+=====================
+
+In order to keep LLVM portable, LLVM developers should adhere to a set of
+portability rules associated with the System Library. Adherence to these rules
+should help the System Library achieve its goal of shielding LLVM from the
+variations in operating system interfaces and doing so efficiently. The
+following sections define the rules needed to fulfill this objective.
+
+Don't Include System Headers
+----------------------------
+
+Except in ``lib/System``, no LLVM source code should directly ``#include`` a
+system header. Care has been taken to remove all such ``#includes`` from LLVM
+while ``lib/System`` was being developed. Specifically this means that header
+files like "``unistd.h``", "``windows.h``", "``stdio.h``", and "``string.h``"
+are forbidden to be included by LLVM source code outside the implementation of
+``lib/System``.
+
+To obtain system-dependent functionality, existing interfaces to the system
+found in ``include/llvm/System`` should be used. If an appropriate interface is
+not available, it should be added to ``include/llvm/System`` and implemented in
+``lib/System`` for all supported platforms.
+
+Don't Expose System Headers
+---------------------------
+
+The System Library must shield LLVM from **all** system headers. To obtain
+system level functionality, LLVM source must ``#include "llvm/System/Thing.h"``
+and nothing else. This means that ``Thing.h`` cannot expose any system header
+files. This protects LLVM from accidentally using system specific functionality
+and only allows it via the ``lib/System`` interface.
+
+Use Standard C Headers
+----------------------
+
+The **standard** C headers (the ones beginning with "c") are allowed to be
+exposed through the ``lib/System`` interface. These headers and the things they
+declare are considered to be platform agnostic. LLVM source files may include
+them directly or obtain their inclusion through ``lib/System`` interfaces.
+
+Use Standard C++ Headers
+------------------------
+
+The **standard** C++ headers from the standard C++ library and standard
+template library may be exposed through the ``lib/System`` interface. These
+headers and the things they declare are considered to be platform agnostic.
+LLVM source files may include them or obtain their inclusion through
+``lib/System`` interfaces.
+
+High Level Interface
+--------------------
+
+The entry points specified in the interface of ``lib/System`` must be aimed at
+completing some reasonably high level task needed by LLVM. We do not want to
+simply wrap each operating system call. It would be preferable to wrap several
+operating system calls that are always used in conjunction with one another by
+LLVM.
+
+For example, consider what is needed to execute a program, wait for it to
+complete, and return its result code. On Unix, this involves the following
+operating system calls: ``getenv``, ``fork``, ``execve``, and ``wait``. The
+correct thing for ``lib/System`` to provide is a function, say
+``ExecuteProgramAndWait``, that implements the functionality completely. what
+we don't want is wrappers for the operating system calls involved.
+
+There must **not** be a one-to-one relationship between operating system
+calls and the System library's interface. Any such interface function will be
+suspicious.
+
+No Unused Functionality
+-----------------------
+
+There must be no functionality specified in the interface of ``lib/System``
+that isn't actually used by LLVM. We're not writing a general purpose operating
+system wrapper here, just enough to satisfy LLVM's needs. And, LLVM doesn't
+need much. This design goal aims to keep the ``lib/System`` interface small and
+understandable which should foster its actual use and adoption.
+
+No Duplicate Implementations
+----------------------------
+
+The implementation of a function for a given platform must be written exactly
+once. This implies that it must be possible to apply a function's
+implementation to multiple operating systems if those operating systems can
+share the same implementation. This rule applies to the set of operating
+systems supported for a given class of operating system (e.g. Unix, Win32).
+
+No Virtual Methods
+------------------
+
+The System Library interfaces can be called quite frequently by LLVM. In order
+to make those calls as efficient as possible, we discourage the use of virtual
+methods. There is no need to use inheritance for implementation differences, it
+just adds complexity. The ``#include`` mechanism works just fine.
+
+No Exposed Functions
+--------------------
+
+Any functions defined by system libraries (i.e. not defined by ``lib/System``)
+must not be exposed through the ``lib/System`` interface, even if the header
+file for that function is not exposed. This prevents inadvertent use of system
+specific functionality.
+
+For example, the ``stat`` system call is notorious for having variations in the
+data it provides. ``lib/System`` must not declare ``stat`` nor allow it to be
+declared. Instead it should provide its own interface to discovering
+information about files and directories. Those interfaces may be implemented in
+terms of ``stat`` but that is strictly an implementation detail. The interface
+provided by the System Library must be implemented on all platforms (even those
+without ``stat``).
+
+No Exposed Data
+---------------
+
+Any data defined by system libraries (i.e. not defined by ``lib/System``) must
+not be exposed through the ``lib/System`` interface, even if the header file
+for that function is not exposed. As with functions, this prevents inadvertent
+use of data that might not exist on all platforms.
+
+Minimize Soft Errors
+--------------------
+
+Operating system interfaces will generally provide error results for every
+little thing that could go wrong. In almost all cases, you can divide these
+error results into two groups: normal/good/soft and abnormal/bad/hard. That is,
+some of the errors are simply information like "file not found", "insufficient
+privileges", etc. while other errors are much harder like "out of space", "bad
+disk sector", or "system call interrupted". We'll call the first group "*soft*"
+errors and the second group "*hard*" errors.
+
+``lib/System`` must always attempt to minimize soft errors. This is a design
+requirement because the minimization of soft errors can affect the granularity
+and the nature of the interface. In general, if you find that you're wanting to
+throw soft errors, you must review the granularity of the interface because it
+is likely you're trying to implement something that is too low level. The rule
+of thumb is to provide interface functions that **can't** fail, except when
+faced with hard errors.
+
+For a trivial example, suppose we wanted to add an "``OpenFileForWriting``"
+function. For many operating systems, if the file doesn't exist, attempting to
+open the file will produce an error. However, ``lib/System`` should not simply
+throw that error if it occurs because its a soft error. The problem is that the
+interface function, ``OpenFileForWriting`` is too low level. It should be
+``OpenOrCreateFileForWriting``. In the case of the soft "doesn't exist" error,
+this function would just create it and then open it for writing.
+
+This design principle needs to be maintained in ``lib/System`` because it
+avoids the propagation of soft error handling throughout the rest of LLVM.
+Hard errors will generally just cause a termination for an LLVM tool so don't
+be bashful about throwing them.
+
+Rules of thumb:
+
+#. Don't throw soft errors, only hard errors.
+
+#. If you're tempted to throw a soft error, re-think the interface.
+
+#. Handle internally the most common normal/good/soft error conditions
+ so the rest of LLVM doesn't have to.
+
+No throw Specifications
+-----------------------
+
+None of the ``lib/System`` interface functions may be declared with C++
+``throw()`` specifications on them. This requirement makes sure that the
+compiler does not insert additional exception handling code into the interface
+functions. This is a performance consideration: ``lib/System`` functions are at
+the bottom of many call chains and as such can be frequently called. We need
+them to be as efficient as possible. However, no routines in the system
+library should actually throw exceptions.
+
+Code Organization
+-----------------
+
+Implementations of the System Library interface are separated by their general
+class of operating system. Currently only Unix and Win32 classes are defined
+but more could be added for other operating system classifications. To
+distinguish which implementation to compile, the code in ``lib/System`` uses
+the ``LLVM_ON_UNIX`` and ``LLVM_ON_WIN32`` ``#defines`` provided via configure
+through the ``llvm/Config/config.h`` file. Each source file in ``lib/System``,
+after implementing the generic (operating system independent) functionality
+needs to include the correct implementation using a set of
+``#if defined(LLVM_ON_XYZ)`` directives. For example, if we had
+``lib/System/File.cpp``, we'd expect to see in that file:
+
+.. code-block:: c++
+
+ #if defined(LLVM_ON_UNIX)
+ #include "Unix/File.cpp"
+ #endif
+ #if defined(LLVM_ON_WIN32)
+ #include "Win32/File.cpp"
+ #endif
+
+The implementation in ``lib/System/Unix/File.cpp`` should handle all Unix
+variants. The implementation in ``lib/System/Win32/File.cpp`` should handle all
+Win32 variants. What this does is quickly differentiate the basic class of
+operating system that will provide the implementation. The specific details for
+a given platform must still be determined through the use of ``#ifdef``.
+
+Consistent Semantics
+--------------------
+
+The implementation of a ``lib/System`` interface can vary drastically between
+platforms. That's okay as long as the end result of the interface function is
+the same. For example, a function to create a directory is pretty straight
+forward on all operating system. System V IPC on the other hand isn't even
+supported on all platforms. Instead of "supporting" System V IPC,
+``lib/System`` should provide an interface to the basic concept of
+inter-process communications. The implementations might use System V IPC if
+that was available or named pipes, or whatever gets the job done effectively
+for a given operating system. In all cases, the interface and the
+implementation must be semantically consistent.
+
Added: www-releases/trunk/3.9.1/docs/_sources/TableGen/BackEnds.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.9.1/docs/_sources/TableGen/BackEnds.txt?rev=290368&view=auto
==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/TableGen/BackEnds.txt (added)
+++ www-releases/trunk/3.9.1/docs/_sources/TableGen/BackEnds.txt Thu Dec 22 14:04:03 2016
@@ -0,0 +1,427 @@
+=================
+TableGen BackEnds
+=================
+
+.. contents::
+ :local:
+
+Introduction
+============
+
+TableGen backends are at the core of TableGen's functionality. The source files
+provide the semantics to a generated (in memory) structure, but it's up to the
+backend to print this out in a way that is meaningful to the user (normally a
+C program including a file or a textual list of warnings, options and error
+messages).
+
+TableGen is used by both LLVM and Clang with very different goals. LLVM uses it
+as a way to automate the generation of massive amounts of information regarding
+instructions, schedules, cores and architecture features. Some backends generate
+output that is consumed by more than one source file, so they need to be created
+in a way that is easy to use pre-processor tricks. Some backends can also print
+C code structures, so that they can be directly included as-is.
+
+Clang, on the other hand, uses it mainly for diagnostic messages (errors,
+warnings, tips) and attributes, so more on the textual end of the scale.
+
+LLVM BackEnds
+=============
+
+.. warning::
+ This document is raw. Each section below needs three sub-sections: description
+ of its purpose with a list of users, output generated from generic input, and
+ finally why it needed a new backend (in case there's something similar).
+
+Overall, each backend will take the same TableGen file type and transform into
+similar output for different targets/uses. There is an implicit contract between
+the TableGen files, the back-ends and their users.
+
+For instance, a global contract is that each back-end produces macro-guarded
+sections. Based on whether the file is included by a header or a source file,
+or even in which context of each file the include is being used, you have
+todefine a macro just before including it, to get the right output:
+
+.. code-block:: c++
+
+ #define GET_REGINFO_TARGET_DESC
+ #include "ARMGenRegisterInfo.inc"
+
+And just part of the generated file would be included. This is useful if
+you need the same information in multiple formats (instantiation, initialization,
+getter/setter functions, etc) from the same source TableGen file without having
+to re-compile the TableGen file multiple times.
+
+Sometimes, multiple macros might be defined before the same include file to
+output multiple blocks:
+
+.. code-block:: c++
+
+ #define GET_REGISTER_MATCHER
+ #define GET_SUBTARGET_FEATURE_NAME
+ #define GET_MATCHER_IMPLEMENTATION
+ #include "ARMGenAsmMatcher.inc"
+
+The macros will be undef'd automatically as they're used, in the include file.
+
+On all LLVM back-ends, the ``llvm-tblgen`` binary will be executed on the root
+TableGen file ``<Target>.td``, which should include all others. This guarantees
+that all information needed is accessible, and that no duplication is needed
+in the TbleGen files.
+
+CodeEmitter
+-----------
+
+**Purpose**: CodeEmitterGen uses the descriptions of instructions and their fields to
+construct an automated code emitter: a function that, given a MachineInstr,
+returns the (currently, 32-bit unsigned) value of the instruction.
+
+**Output**: C++ code, implementing the target's CodeEmitter
+class by overriding the virtual functions as ``<Target>CodeEmitter::function()``.
+
+**Usage**: Used to include directly at the end of ``<Target>MCCodeEmitter.cpp``.
+
+RegisterInfo
+------------
+
+**Purpose**: This tablegen backend is responsible for emitting a description of a target
+register file for a code generator. It uses instances of the Register,
+RegisterAliases, and RegisterClass classes to gather this information.
+
+**Output**: C++ code with enums and structures representing the register mappings,
+properties, masks, etc.
+
+**Usage**: Both on ``<Target>BaseRegisterInfo`` and ``<Target>MCTargetDesc`` (headers
+and source files) with macros defining in which they are for declaration vs.
+initialization issues.
+
+InstrInfo
+---------
+
+**Purpose**: This tablegen backend is responsible for emitting a description of the target
+instruction set for the code generator. (what are the differences from CodeEmitter?)
+
+**Output**: C++ code with enums and structures representing the register mappings,
+properties, masks, etc.
+
+**Usage**: Both on ``<Target>BaseInstrInfo`` and ``<Target>MCTargetDesc`` (headers
+and source files) with macros defining in which they are for declaration vs.
+
+AsmWriter
+---------
+
+**Purpose**: Emits an assembly printer for the current target.
+
+**Output**: Implementation of ``<Target>InstPrinter::printInstruction()``, among
+other things.
+
+**Usage**: Included directly into ``InstPrinter/<Target>InstPrinter.cpp``.
+
+AsmMatcher
+----------
+
+**Purpose**: Emits a target specifier matcher for
+converting parsed assembly operands in the MCInst structures. It also
+emits a matcher for custom operand parsing. Extensive documentation is
+written on the ``AsmMatcherEmitter.cpp`` file.
+
+**Output**: Assembler parsers' matcher functions, declarations, etc.
+
+**Usage**: Used in back-ends' ``AsmParser/<Target>AsmParser.cpp`` for
+building the AsmParser class.
+
+Disassembler
+------------
+
+**Purpose**: Contains disassembler table emitters for various
+architectures. Extensive documentation is written on the
+``DisassemblerEmitter.cpp`` file.
+
+**Output**: Decoding tables, static decoding functions, etc.
+
+**Usage**: Directly included in ``Disassembler/<Target>Disassembler.cpp``
+to cater for all default decodings, after all hand-made ones.
+
+PseudoLowering
+--------------
+
+**Purpose**: Generate pseudo instruction lowering.
+
+**Output**: Implements ``ARMAsmPrinter::emitPseudoExpansionLowering()``.
+
+**Usage**: Included directly into ``<Target>AsmPrinter.cpp``.
+
+CallingConv
+-----------
+
+**Purpose**: Responsible for emitting descriptions of the calling
+conventions supported by this target.
+
+**Output**: Implement static functions to deal with calling conventions
+chained by matching styles, returning false on no match.
+
+**Usage**: Used in ISelLowering and FastIsel as function pointers to
+implementation returned by a CC sellection function.
+
+DAGISel
+-------
+
+**Purpose**: Generate a DAG instruction selector.
+
+**Output**: Creates huge functions for automating DAG selection.
+
+**Usage**: Included in ``<Target>ISelDAGToDAG.cpp`` inside the target's
+implementation of ``SelectionDAGISel``.
+
+DFAPacketizer
+-------------
+
+**Purpose**: This class parses the Schedule.td file and produces an API that
+can be used to reason about whether an instruction can be added to a packet
+on a VLIW architecture. The class internally generates a deterministic finite
+automaton (DFA) that models all possible mappings of machine instructions
+to functional units as instructions are added to a packet.
+
+**Output**: Scheduling tables for GPU back-ends (Hexagon, AMD).
+
+**Usage**: Included directly on ``<Target>InstrInfo.cpp``.
+
+FastISel
+--------
+
+**Purpose**: This tablegen backend emits code for use by the "fast"
+instruction selection algorithm. See the comments at the top of
+lib/CodeGen/SelectionDAG/FastISel.cpp for background. This file
+scans through the target's tablegen instruction-info files
+and extracts instructions with obvious-looking patterns, and it emits
+code to look up these instructions by type and operator.
+
+**Output**: Generates ``Predicate`` and ``FastEmit`` methods.
+
+**Usage**: Implements private methods of the targets' implementation
+of ``FastISel`` class.
+
+Subtarget
+---------
+
+**Purpose**: Generate subtarget enumerations.
+
+**Output**: Enums, globals, local tables for sub-target information.
+
+**Usage**: Populates ``<Target>Subtarget`` and
+``MCTargetDesc/<Target>MCTargetDesc`` files (both headers and source).
+
+Intrinsic
+---------
+
+**Purpose**: Generate (target) intrinsic information.
+
+OptParserDefs
+-------------
+
+**Purpose**: Print enum values for a class.
+
+CTags
+-----
+
+**Purpose**: This tablegen backend emits an index of definitions in ctags(1)
+format. A helper script, utils/TableGen/tdtags, provides an easier-to-use
+interface; run 'tdtags -H' for documentation.
+
+Clang BackEnds
+==============
+
+ClangAttrClasses
+----------------
+
+**Purpose**: Creates Attrs.inc, which contains semantic attribute class
+declarations for any attribute in ``Attr.td`` that has not set ``ASTNode = 0``.
+This file is included as part of ``Attr.h``.
+
+ClangAttrParserStringSwitches
+-----------------------------
+
+**Purpose**: Creates AttrParserStringSwitches.inc, which contains
+StringSwitch::Case statements for parser-related string switches. Each switch
+is given its own macro (such as ``CLANG_ATTR_ARG_CONTEXT_LIST``, or
+``CLANG_ATTR_IDENTIFIER_ARG_LIST``), which is expected to be defined before
+including AttrParserStringSwitches.inc, and undefined after.
+
+ClangAttrImpl
+-------------
+
+**Purpose**: Creates AttrImpl.inc, which contains semantic attribute class
+definitions for any attribute in ``Attr.td`` that has not set ``ASTNode = 0``.
+This file is included as part of ``AttrImpl.cpp``.
+
+ClangAttrList
+-------------
+
+**Purpose**: Creates AttrList.inc, which is used when a list of semantic
+attribute identifiers is required. For instance, ``AttrKinds.h`` includes this
+file to generate the list of ``attr::Kind`` enumeration values. This list is
+separated out into multiple categories: attributes, inheritable attributes, and
+inheritable parameter attributes. This categorization happens automatically
+based on information in ``Attr.td`` and is used to implement the ``classof``
+functionality required for ``dyn_cast`` and similar APIs.
+
+ClangAttrPCHRead
+----------------
+
+**Purpose**: Creates AttrPCHRead.inc, which is used to deserialize attributes
+in the ``ASTReader::ReadAttributes`` function.
+
+ClangAttrPCHWrite
+-----------------
+
+**Purpose**: Creates AttrPCHWrite.inc, which is used to serialize attributes in
+the ``ASTWriter::WriteAttributes`` function.
+
+ClangAttrSpellings
+---------------------
+
+**Purpose**: Creates AttrSpellings.inc, which is used to implement the
+``__has_attribute`` feature test macro.
+
+ClangAttrSpellingListIndex
+--------------------------
+
+**Purpose**: Creates AttrSpellingListIndex.inc, which is used to map parsed
+attribute spellings (including which syntax or scope was used) to an attribute
+spelling list index. These spelling list index values are internal
+implementation details exposed via
+``AttributeList::getAttributeSpellingListIndex``.
+
+ClangAttrVisitor
+-------------------
+
+**Purpose**: Creates AttrVisitor.inc, which is used when implementing
+recursive AST visitors.
+
+ClangAttrTemplateInstantiate
+----------------------------
+
+**Purpose**: Creates AttrTemplateInstantiate.inc, which implements the
+``instantiateTemplateAttribute`` function, used when instantiating a template
+that requires an attribute to be cloned.
+
+ClangAttrParsedAttrList
+-----------------------
+
+**Purpose**: Creates AttrParsedAttrList.inc, which is used to generate the
+``AttributeList::Kind`` parsed attribute enumeration.
+
+ClangAttrParsedAttrImpl
+-----------------------
+
+**Purpose**: Creates AttrParsedAttrImpl.inc, which is used by
+``AttributeList.cpp`` to implement several functions on the ``AttributeList``
+class. This functionality is implemented via the ``AttrInfoMap ParsedAttrInfo``
+array, which contains one element per parsed attribute object.
+
+ClangAttrParsedAttrKinds
+------------------------
+
+**Purpose**: Creates AttrParsedAttrKinds.inc, which is used to implement the
+``AttributeList::getKind`` function, mapping a string (and syntax) to a parsed
+attribute ``AttributeList::Kind`` enumeration.
+
+ClangAttrDump
+-------------
+
+**Purpose**: Creates AttrDump.inc, which dumps information about an attribute.
+It is used to implement ``ASTDumper::dumpAttr``.
+
+ClangDiagsDefs
+--------------
+
+Generate Clang diagnostics definitions.
+
+ClangDiagGroups
+---------------
+
+Generate Clang diagnostic groups.
+
+ClangDiagsIndexName
+-------------------
+
+Generate Clang diagnostic name index.
+
+ClangCommentNodes
+-----------------
+
+Generate Clang AST comment nodes.
+
+ClangDeclNodes
+--------------
+
+Generate Clang AST declaration nodes.
+
+ClangStmtNodes
+--------------
+
+Generate Clang AST statement nodes.
+
+ClangSACheckers
+---------------
+
+Generate Clang Static Analyzer checkers.
+
+ClangCommentHTMLTags
+--------------------
+
+Generate efficient matchers for HTML tag names that are used in documentation comments.
+
+ClangCommentHTMLTagsProperties
+------------------------------
+
+Generate efficient matchers for HTML tag properties.
+
+ClangCommentHTMLNamedCharacterReferences
+----------------------------------------
+
+Generate function to translate named character references to UTF-8 sequences.
+
+ClangCommentCommandInfo
+-----------------------
+
+Generate command properties for commands that are used in documentation comments.
+
+ClangCommentCommandList
+-----------------------
+
+Generate list of commands that are used in documentation comments.
+
+ArmNeon
+-------
+
+Generate arm_neon.h for clang.
+
+ArmNeonSema
+-----------
+
+Generate ARM NEON sema support for clang.
+
+ArmNeonTest
+-----------
+
+Generate ARM NEON tests for clang.
+
+AttrDocs
+--------
+
+**Purpose**: Creates ``AttributeReference.rst`` from ``AttrDocs.td``, and is
+used for documenting user-facing attributes.
+
+How to write a back-end
+=======================
+
+TODO.
+
+Until we get a step-by-step HowTo for writing TableGen backends, you can at
+least grab the boilerplate (build system, new files, etc.) from Clang's
+r173931.
+
+TODO: How they work, how to write one. This section should not contain details
+about any particular backend, except maybe ``-print-enums`` as an example. This
+should highlight the APIs in ``TableGen/Record.h``.
+
Added: www-releases/trunk/3.9.1/docs/_sources/TableGen/Deficiencies.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.9.1/docs/_sources/TableGen/Deficiencies.txt?rev=290368&view=auto
==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/TableGen/Deficiencies.txt (added)
+++ www-releases/trunk/3.9.1/docs/_sources/TableGen/Deficiencies.txt Thu Dec 22 14:04:03 2016
@@ -0,0 +1,31 @@
+=====================
+TableGen Deficiencies
+=====================
+
+.. contents::
+ :local:
+
+Introduction
+============
+
+Despite being very generic, TableGen has some deficiencies that have been
+pointed out numerous times. The common theme is that, while TableGen allows
+you to build Domain-Specific-Languages, the final languages that you create
+lack the power of other DSLs, which in turn increase considerably the size
+and complexity of TableGen files.
+
+At the same time, TableGen allows you to create virtually any meaning of
+the basic concepts via custom-made back-ends, which can pervert the original
+design and make it very hard for newcomers to understand it.
+
+There are some in favour of extending the semantics even more, but making sure
+back-ends adhere to strict rules. Others suggesting we should move to more
+powerful DSLs designed with specific purposes, or even re-using existing
+DSLs.
+
+Known Problems
+==============
+
+TODO: Add here frequently asked questions about why TableGen doesn't do
+what you want, how it might, and how we could extend/restrict it to
+be more use friendly.
Added: www-releases/trunk/3.9.1/docs/_sources/TableGen/LangIntro.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.9.1/docs/_sources/TableGen/LangIntro.txt?rev=290368&view=auto
==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/TableGen/LangIntro.txt (added)
+++ www-releases/trunk/3.9.1/docs/_sources/TableGen/LangIntro.txt Thu Dec 22 14:04:03 2016
@@ -0,0 +1,615 @@
+==============================
+TableGen Language Introduction
+==============================
+
+.. contents::
+ :local:
+
+.. warning::
+ This document is extremely rough. If you find something lacking, please
+ fix it, file a documentation bug, or ask about it on llvm-dev.
+
+Introduction
+============
+
+This document is not meant to be a normative spec about the TableGen language
+in and of itself (i.e. how to understand a given construct in terms of how
+it affects the final set of records represented by the TableGen file). For
+the formal language specification, see :doc:`LangRef`.
+
+TableGen syntax
+===============
+
+TableGen doesn't care about the meaning of data (that is up to the backend to
+define), but it does care about syntax, and it enforces a simple type system.
+This section describes the syntax and the constructs allowed in a TableGen file.
+
+TableGen primitives
+-------------------
+
+TableGen comments
+^^^^^^^^^^^^^^^^^
+
+TableGen supports C++ style "``//``" comments, which run to the end of the
+line, and it also supports **nestable** "``/* */``" comments.
+
+.. _TableGen type:
+
+The TableGen type system
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+TableGen files are strongly typed, in a simple (but complete) type-system.
+These types are used to perform automatic conversions, check for errors, and to
+help interface designers constrain the input that they allow. Every `value
+definition`_ is required to have an associated type.
+
+TableGen supports a mixture of very low-level types (such as ``bit``) and very
+high-level types (such as ``dag``). This flexibility is what allows it to
+describe a wide range of information conveniently and compactly. The TableGen
+types are:
+
+``bit``
+ A 'bit' is a boolean value that can hold either 0 or 1.
+
+``int``
+ The 'int' type represents a simple 32-bit integer value, such as 5.
+
+``string``
+ The 'string' type represents an ordered sequence of characters of arbitrary
+ length.
+
+``bits<n>``
+ A 'bits' type is an arbitrary, but fixed, size integer that is broken up
+ into individual bits. This type is useful because it can handle some bits
+ being defined while others are undefined.
+
+``list<ty>``
+ This type represents a list whose elements are some other type. The
+ contained type is arbitrary: it can even be another list type.
+
+Class type
+ Specifying a class name in a type context means that the defined value must
+ be a subclass of the specified class. This is useful in conjunction with
+ the ``list`` type, for example, to constrain the elements of the list to a
+ common base class (e.g., a ``list<Register>`` can only contain definitions
+ derived from the "``Register``" class).
+
+``dag``
+ This type represents a nestable directed graph of elements.
+
+To date, these types have been sufficient for describing things that TableGen
+has been used for, but it is straight-forward to extend this list if needed.
+
+.. _TableGen expressions:
+
+TableGen values and expressions
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+TableGen allows for a pretty reasonable number of different expression forms
+when building up values. These forms allow the TableGen file to be written in a
+natural syntax and flavor for the application. The current expression forms
+supported include:
+
+``?``
+ uninitialized field
+
+``0b1001011``
+ binary integer value.
+ Note that this is sized by the number of bits given and will not be
+ silently extended/truncated.
+
+``07654321``
+ octal integer value (indicated by a leading 0)
+
+``7``
+ decimal integer value
+
+``0x7F``
+ hexadecimal integer value
+
+``"foo"``
+ string value
+
+``[{ ... }]``
+ usually called a "code fragment", but is just a multiline string literal
+
+``[ X, Y, Z ]<type>``
+ list value. <type> is the type of the list element and is usually optional.
+ In rare cases, TableGen is unable to deduce the element type in which case
+ the user must specify it explicitly.
+
+``{ a, b, 0b10 }``
+ initializer for a "bits<4>" value.
+ 1-bit from "a", 1-bit from "b", 2-bits from 0b10.
+
+``value``
+ value reference
+
+``value{17}``
+ access to one bit of a value
+
+``value{15-17}``
+ access to multiple bits of a value
+
+``DEF``
+ reference to a record definition
+
+``CLASS<val list>``
+ reference to a new anonymous definition of CLASS with the specified template
+ arguments.
+
+``X.Y``
+ reference to the subfield of a value
+
+``list[4-7,17,2-3]``
+ A slice of the 'list' list, including elements 4,5,6,7,17,2, and 3 from it.
+ Elements may be included multiple times.
+
+``foreach <var> = [ <list> ] in { <body> }``
+
+``foreach <var> = [ <list> ] in <def>``
+ Replicate <body> or <def>, replacing instances of <var> with each value
+ in <list>. <var> is scoped at the level of the ``foreach`` loop and must
+ not conflict with any other object introduced in <body> or <def>. Currently
+ only ``def``\s are expanded within <body>.
+
+``foreach <var> = 0-15 in ...``
+
+``foreach <var> = {0-15,32-47} in ...``
+ Loop over ranges of integers. The braces are required for multiple ranges.
+
+``(DEF a, b)``
+ a dag value. The first element is required to be a record definition, the
+ remaining elements in the list may be arbitrary other values, including
+ nested ```dag``' values.
+
+``!listconcat(a, b, ...)``
+ A list value that is the result of concatenating the 'a' and 'b' lists.
+ The lists must have the same element type.
+ More than two arguments are accepted with the result being the concatenation
+ of all the lists given.
+
+``!strconcat(a, b, ...)``
+ A string value that is the result of concatenating the 'a' and 'b' strings.
+ More than two arguments are accepted with the result being the concatenation
+ of all the strings given.
+
+``str1#str2``
+ "#" (paste) is a shorthand for !strconcat. It may concatenate things that
+ are not quoted strings, in which case an implicit !cast<string> is done on
+ the operand of the paste.
+
+``!cast<type>(a)``
+ A symbol of type *type* obtained by looking up the string 'a' in the symbol
+ table. If the type of 'a' does not match *type*, TableGen aborts with an
+ error. !cast<string> is a special case in that the argument must be an
+ object defined by a 'def' construct.
+
+``!subst(a, b, c)``
+ If 'a' and 'b' are of string type or are symbol references, substitute 'b'
+ for 'a' in 'c.' This operation is analogous to $(subst) in GNU make.
+
+``!foreach(a, b, c)``
+ For each member of dag or list 'b' apply operator 'c.' 'a' is a dummy
+ variable that should be declared as a member variable of an instantiated
+ class. This operation is analogous to $(foreach) in GNU make.
+
+``!head(a)``
+ The first element of list 'a.'
+
+``!tail(a)``
+ The 2nd-N elements of list 'a.'
+
+``!empty(a)``
+ An integer {0,1} indicating whether list 'a' is empty.
+
+``!if(a,b,c)``
+ 'b' if the result of 'int' or 'bit' operator 'a' is nonzero, 'c' otherwise.
+
+``!eq(a,b)``
+ 'bit 1' if string a is equal to string b, 0 otherwise. This only operates
+ on string, int and bit objects. Use !cast<string> to compare other types of
+ objects.
+
+``!shl(a,b)`` ``!srl(a,b)`` ``!sra(a,b)`` ``!add(a,b)`` ``!and(a,b)``
+ The usual binary and arithmetic operators.
+
+Note that all of the values have rules specifying how they convert to values
+for different types. These rules allow you to assign a value like "``7``"
+to a "``bits<4>``" value, for example.
+
+Classes and definitions
+-----------------------
+
+As mentioned in the :doc:`introduction <index>`, classes and definitions (collectively known as
+'records') in TableGen are the main high-level unit of information that TableGen
+collects. Records are defined with a ``def`` or ``class`` keyword, the record
+name, and an optional list of "`template arguments`_". If the record has
+superclasses, they are specified as a comma separated list that starts with a
+colon character ("``:``"). If `value definitions`_ or `let expressions`_ are
+needed for the class, they are enclosed in curly braces ("``{}``"); otherwise,
+the record ends with a semicolon.
+
+Here is a simple TableGen file:
+
+.. code-block:: text
+
+ class C { bit V = 1; }
+ def X : C;
+ def Y : C {
+ string Greeting = "hello";
+ }
+
+This example defines two definitions, ``X`` and ``Y``, both of which derive from
+the ``C`` class. Because of this, they both get the ``V`` bit value. The ``Y``
+definition also gets the Greeting member as well.
+
+In general, classes are useful for collecting together the commonality between a
+group of records and isolating it in a single place. Also, classes permit the
+specification of default values for their subclasses, allowing the subclasses to
+override them as they wish.
+
+.. _value definition:
+.. _value definitions:
+
+Value definitions
+^^^^^^^^^^^^^^^^^
+
+Value definitions define named entries in records. A value must be defined
+before it can be referred to as the operand for another value definition or
+before the value is reset with a `let expression`_. A value is defined by
+specifying a `TableGen type`_ and a name. If an initial value is available, it
+may be specified after the type with an equal sign. Value definitions require
+terminating semicolons.
+
+.. _let expression:
+.. _let expressions:
+.. _"let" expressions within a record:
+
+'let' expressions
+^^^^^^^^^^^^^^^^^
+
+A record-level let expression is used to change the value of a value definition
+in a record. This is primarily useful when a superclass defines a value that a
+derived class or definition wants to override. Let expressions consist of the
+'``let``' keyword followed by a value name, an equal sign ("``=``"), and a new
+value. For example, a new class could be added to the example above, redefining
+the ``V`` field for all of its subclasses:
+
+.. code-block:: text
+
+ class D : C { let V = 0; }
+ def Z : D;
+
+In this case, the ``Z`` definition will have a zero value for its ``V`` value,
+despite the fact that it derives (indirectly) from the ``C`` class, because the
+``D`` class overrode its value.
+
+.. _template arguments:
+
+Class template arguments
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+TableGen permits the definition of parameterized classes as well as normal
+concrete classes. Parameterized TableGen classes specify a list of variable
+bindings (which may optionally have defaults) that are bound when used. Here is
+a simple example:
+
+.. code-block:: text
+
+ class FPFormat<bits<3> val> {
+ bits<3> Value = val;
+ }
+ def NotFP : FPFormat<0>;
+ def ZeroArgFP : FPFormat<1>;
+ def OneArgFP : FPFormat<2>;
+ def OneArgFPRW : FPFormat<3>;
+ def TwoArgFP : FPFormat<4>;
+ def CompareFP : FPFormat<5>;
+ def CondMovFP : FPFormat<6>;
+ def SpecialFP : FPFormat<7>;
+
+In this case, template arguments are used as a space efficient way to specify a
+list of "enumeration values", each with a "``Value``" field set to the specified
+integer.
+
+The more esoteric forms of `TableGen expressions`_ are useful in conjunction
+with template arguments. As an example:
+
+.. code-block:: text
+
+ class ModRefVal<bits<2> val> {
+ bits<2> Value = val;
+ }
+
+ def None : ModRefVal<0>;
+ def Mod : ModRefVal<1>;
+ def Ref : ModRefVal<2>;
+ def ModRef : ModRefVal<3>;
+
+ class Value<ModRefVal MR> {
+ // Decode some information into a more convenient format, while providing
+ // a nice interface to the user of the "Value" class.
+ bit isMod = MR.Value{0};
+ bit isRef = MR.Value{1};
+
+ // other stuff...
+ }
+
+ // Example uses
+ def bork : Value<Mod>;
+ def zork : Value<Ref>;
+ def hork : Value<ModRef>;
+
+This is obviously a contrived example, but it shows how template arguments can
+be used to decouple the interface provided to the user of the class from the
+actual internal data representation expected by the class. In this case,
+running ``llvm-tblgen`` on the example prints the following definitions:
+
+.. code-block:: text
+
+ def bork { // Value
+ bit isMod = 1;
+ bit isRef = 0;
+ }
+ def hork { // Value
+ bit isMod = 1;
+ bit isRef = 1;
+ }
+ def zork { // Value
+ bit isMod = 0;
+ bit isRef = 1;
+ }
+
+This shows that TableGen was able to dig into the argument and extract a piece
+of information that was requested by the designer of the "Value" class. For
+more realistic examples, please see existing users of TableGen, such as the X86
+backend.
+
+Multiclass definitions and instances
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+While classes with template arguments are a good way to factor commonality
+between two instances of a definition, multiclasses allow a convenient notation
+for defining multiple definitions at once (instances of implicitly constructed
+classes). For example, consider an 3-address instruction set whose instructions
+come in two forms: "``reg = reg op reg``" and "``reg = reg op imm``"
+(e.g. SPARC). In this case, you'd like to specify in one place that this
+commonality exists, then in a separate place indicate what all the ops are.
+
+Here is an example TableGen fragment that shows this idea:
+
+.. code-block:: text
+
+ def ops;
+ def GPR;
+ def Imm;
+ class inst<int opc, string asmstr, dag operandlist>;
+
+ multiclass ri_inst<int opc, string asmstr> {
+ def _rr : inst<opc, !strconcat(asmstr, " $dst, $src1, $src2"),
+ (ops GPR:$dst, GPR:$src1, GPR:$src2)>;
+ def _ri : inst<opc, !strconcat(asmstr, " $dst, $src1, $src2"),
+ (ops GPR:$dst, GPR:$src1, Imm:$src2)>;
+ }
+
+ // Instantiations of the ri_inst multiclass.
+ defm ADD : ri_inst<0b111, "add">;
+ defm SUB : ri_inst<0b101, "sub">;
+ defm MUL : ri_inst<0b100, "mul">;
+ ...
+
+The name of the resultant definitions has the multidef fragment names appended
+to them, so this defines ``ADD_rr``, ``ADD_ri``, ``SUB_rr``, etc. A defm may
+inherit from multiple multiclasses, instantiating definitions from each
+multiclass. Using a multiclass this way is exactly equivalent to instantiating
+the classes multiple times yourself, e.g. by writing:
+
+.. code-block:: text
+
+ def ops;
+ def GPR;
+ def Imm;
+ class inst<int opc, string asmstr, dag operandlist>;
+
+ class rrinst<int opc, string asmstr>
+ : inst<opc, !strconcat(asmstr, " $dst, $src1, $src2"),
+ (ops GPR:$dst, GPR:$src1, GPR:$src2)>;
+
+ class riinst<int opc, string asmstr>
+ : inst<opc, !strconcat(asmstr, " $dst, $src1, $src2"),
+ (ops GPR:$dst, GPR:$src1, Imm:$src2)>;
+
+ // Instantiations of the ri_inst multiclass.
+ def ADD_rr : rrinst<0b111, "add">;
+ def ADD_ri : riinst<0b111, "add">;
+ def SUB_rr : rrinst<0b101, "sub">;
+ def SUB_ri : riinst<0b101, "sub">;
+ def MUL_rr : rrinst<0b100, "mul">;
+ def MUL_ri : riinst<0b100, "mul">;
+ ...
+
+A ``defm`` can also be used inside a multiclass providing several levels of
+multiclass instantiations.
+
+.. code-block:: text
+
+ class Instruction<bits<4> opc, string Name> {
+ bits<4> opcode = opc;
+ string name = Name;
+ }
+
+ multiclass basic_r<bits<4> opc> {
+ def rr : Instruction<opc, "rr">;
+ def rm : Instruction<opc, "rm">;
+ }
+
+ multiclass basic_s<bits<4> opc> {
+ defm SS : basic_r<opc>;
+ defm SD : basic_r<opc>;
+ def X : Instruction<opc, "x">;
+ }
+
+ multiclass basic_p<bits<4> opc> {
+ defm PS : basic_r<opc>;
+ defm PD : basic_r<opc>;
+ def Y : Instruction<opc, "y">;
+ }
+
+ defm ADD : basic_s<0xf>, basic_p<0xf>;
+ ...
+
+ // Results
+ def ADDPDrm { ...
+ def ADDPDrr { ...
+ def ADDPSrm { ...
+ def ADDPSrr { ...
+ def ADDSDrm { ...
+ def ADDSDrr { ...
+ def ADDY { ...
+ def ADDX { ...
+
+``defm`` declarations can inherit from classes too, the rule to follow is that
+the class list must start after the last multiclass, and there must be at least
+one multiclass before them.
+
+.. code-block:: text
+
+ class XD { bits<4> Prefix = 11; }
+ class XS { bits<4> Prefix = 12; }
+
+ class I<bits<4> op> {
+ bits<4> opcode = op;
+ }
+
+ multiclass R {
+ def rr : I<4>;
+ def rm : I<2>;
+ }
+
+ multiclass Y {
+ defm SS : R, XD;
+ defm SD : R, XS;
+ }
+
+ defm Instr : Y;
+
+ // Results
+ def InstrSDrm {
+ bits<4> opcode = { 0, 0, 1, 0 };
+ bits<4> Prefix = { 1, 1, 0, 0 };
+ }
+ ...
+ def InstrSSrr {
+ bits<4> opcode = { 0, 1, 0, 0 };
+ bits<4> Prefix = { 1, 0, 1, 1 };
+ }
+
+File scope entities
+-------------------
+
+File inclusion
+^^^^^^^^^^^^^^
+
+TableGen supports the '``include``' token, which textually substitutes the
+specified file in place of the include directive. The filename should be
+specified as a double quoted string immediately after the '``include``' keyword.
+Example:
+
+.. code-block:: text
+
+ include "foo.td"
+
+'let' expressions
+^^^^^^^^^^^^^^^^^
+
+"Let" expressions at file scope are similar to `"let" expressions within a
+record`_, except they can specify a value binding for multiple records at a
+time, and may be useful in certain other cases. File-scope let expressions are
+really just another way that TableGen allows the end-user to factor out
+commonality from the records.
+
+File-scope "let" expressions take a comma-separated list of bindings to apply,
+and one or more records to bind the values in. Here are some examples:
+
+.. code-block:: text
+
+ let isTerminator = 1, isReturn = 1, isBarrier = 1, hasCtrlDep = 1 in
+ def RET : I<0xC3, RawFrm, (outs), (ins), "ret", [(X86retflag 0)]>;
+
+ let isCall = 1 in
+ // All calls clobber the non-callee saved registers...
+ let Defs = [EAX, ECX, EDX, FP0, FP1, FP2, FP3, FP4, FP5, FP6, ST0,
+ MM0, MM1, MM2, MM3, MM4, MM5, MM6, MM7,
+ XMM0, XMM1, XMM2, XMM3, XMM4, XMM5, XMM6, XMM7, EFLAGS] in {
+ def CALLpcrel32 : Ii32<0xE8, RawFrm, (outs), (ins i32imm:$dst,variable_ops),
+ "call\t${dst:call}", []>;
+ def CALL32r : I<0xFF, MRM2r, (outs), (ins GR32:$dst, variable_ops),
+ "call\t{*}$dst", [(X86call GR32:$dst)]>;
+ def CALL32m : I<0xFF, MRM2m, (outs), (ins i32mem:$dst, variable_ops),
+ "call\t{*}$dst", []>;
+ }
+
+File-scope "let" expressions are often useful when a couple of definitions need
+to be added to several records, and the records do not otherwise need to be
+opened, as in the case with the ``CALL*`` instructions above.
+
+It's also possible to use "let" expressions inside multiclasses, providing more
+ways to factor out commonality from the records, specially if using several
+levels of multiclass instantiations. This also avoids the need of using "let"
+expressions within subsequent records inside a multiclass.
+
+.. code-block:: text
+
+ multiclass basic_r<bits<4> opc> {
+ let Predicates = [HasSSE2] in {
+ def rr : Instruction<opc, "rr">;
+ def rm : Instruction<opc, "rm">;
+ }
+ let Predicates = [HasSSE3] in
+ def rx : Instruction<opc, "rx">;
+ }
+
+ multiclass basic_ss<bits<4> opc> {
+ let IsDouble = 0 in
+ defm SS : basic_r<opc>;
+
+ let IsDouble = 1 in
+ defm SD : basic_r<opc>;
+ }
+
+ defm ADD : basic_ss<0xf>;
+
+Looping
+^^^^^^^
+
+TableGen supports the '``foreach``' block, which textually replicates the loop
+body, substituting iterator values for iterator references in the body.
+Example:
+
+.. code-block:: text
+
+ foreach i = [0, 1, 2, 3] in {
+ def R#i : Register<...>;
+ def F#i : Register<...>;
+ }
+
+This will create objects ``R0``, ``R1``, ``R2`` and ``R3``. ``foreach`` blocks
+may be nested. If there is only one item in the body the braces may be
+elided:
+
+.. code-block:: text
+
+ foreach i = [0, 1, 2, 3] in
+ def R#i : Register<...>;
+
+Code Generator backend info
+===========================
+
+Expressions used by code generator to describe instructions and isel patterns:
+
+``(implicit a)``
+ an implicitly defined physical register. This tells the dag instruction
+ selection emitter the input pattern's extra definitions matches implicit
+ physical register definitions.
+
Added: www-releases/trunk/3.9.1/docs/_sources/TableGen/LangRef.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.9.1/docs/_sources/TableGen/LangRef.txt?rev=290368&view=auto
==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/TableGen/LangRef.txt (added)
+++ www-releases/trunk/3.9.1/docs/_sources/TableGen/LangRef.txt Thu Dec 22 14:04:03 2016
@@ -0,0 +1,388 @@
+===========================
+TableGen Language Reference
+===========================
+
+.. contents::
+ :local:
+
+.. warning::
+ This document is extremely rough. If you find something lacking, please
+ fix it, file a documentation bug, or ask about it on llvm-dev.
+
+Introduction
+============
+
+This document is meant to be a normative spec about the TableGen language
+in and of itself (i.e. how to understand a given construct in terms of how
+it affects the final set of records represented by the TableGen file). If
+you are unsure if this document is really what you are looking for, please
+read the :doc:`introduction to TableGen <index>` first.
+
+Notation
+========
+
+The lexical and syntax notation used here is intended to imitate
+`Python's`_. In particular, for lexical definitions, the productions
+operate at the character level and there is no implied whitespace between
+elements. The syntax definitions operate at the token level, so there is
+implied whitespace between tokens.
+
+.. _`Python's`: http://docs.python.org/py3k/reference/introduction.html#notation
+
+Lexical Analysis
+================
+
+TableGen supports BCPL (``// ...``) and nestable C-style (``/* ... */``)
+comments.
+
+The following is a listing of the basic punctuation tokens::
+
+ - + [ ] { } ( ) < > : ; . = ? #
+
+Numeric literals take one of the following forms:
+
+.. TableGen actually will lex some pretty strange sequences an interpret
+ them as numbers. What is shown here is an attempt to approximate what it
+ "should" accept.
+
+.. productionlist::
+ TokInteger: `DecimalInteger` | `HexInteger` | `BinInteger`
+ DecimalInteger: ["+" | "-"] ("0"..."9")+
+ HexInteger: "0x" ("0"..."9" | "a"..."f" | "A"..."F")+
+ BinInteger: "0b" ("0" | "1")+
+
+One aspect to note is that the :token:`DecimalInteger` token *includes* the
+``+`` or ``-``, as opposed to having ``+`` and ``-`` be unary operators as
+most languages do.
+
+Also note that :token:`BinInteger` creates a value of type ``bits<n>``
+(where ``n`` is the number of bits). This will implicitly convert to
+integers when needed.
+
+TableGen has identifier-like tokens:
+
+.. productionlist::
+ ualpha: "a"..."z" | "A"..."Z" | "_"
+ TokIdentifier: ("0"..."9")* `ualpha` (`ualpha` | "0"..."9")*
+ TokVarName: "$" `ualpha` (`ualpha` | "0"..."9")*
+
+Note that unlike most languages, TableGen allows :token:`TokIdentifier` to
+begin with a number. In case of ambiguity, a token will be interpreted as a
+numeric literal rather than an identifier.
+
+TableGen also has two string-like literals:
+
+.. productionlist::
+ TokString: '"' <non-'"' characters and C-like escapes> '"'
+ TokCodeFragment: "[{" <shortest text not containing "}]"> "}]"
+
+:token:`TokCodeFragment` is essentially a multiline string literal
+delimited by ``[{`` and ``}]``.
+
+.. note::
+ The current implementation accepts the following C-like escapes::
+
+ \\ \' \" \t \n
+
+TableGen also has the following keywords::
+
+ bit bits class code dag
+ def foreach defm field in
+ int let list multiclass string
+
+TableGen also has "bang operators" which have a
+wide variety of meanings:
+
+.. productionlist::
+ BangOperator: one of
+ :!eq !if !head !tail !con
+ :!add !shl !sra !srl !and
+ :!cast !empty !subst !foreach !listconcat !strconcat
+
+Syntax
+======
+
+TableGen has an ``include`` mechanism. It does not play a role in the
+syntax per se, since it is lexically replaced with the contents of the
+included file.
+
+.. productionlist::
+ IncludeDirective: "include" `TokString`
+
+TableGen's top-level production consists of "objects".
+
+.. productionlist::
+ TableGenFile: `Object`*
+ Object: `Class` | `Def` | `Defm` | `Let` | `MultiClass` | `Foreach`
+
+``class``\es
+------------
+
+.. productionlist::
+ Class: "class" `TokIdentifier` [`TemplateArgList`] `ObjectBody`
+
+A ``class`` declaration creates a record which other records can inherit
+from. A class can be parametrized by a list of "template arguments", whose
+values can be used in the class body.
+
+A given class can only be defined once. A ``class`` declaration is
+considered to define the class if any of the following is true:
+
+.. break ObjectBody into its consituents so that they are present here?
+
+#. The :token:`TemplateArgList` is present.
+#. The :token:`Body` in the :token:`ObjectBody` is present and is not empty.
+#. The :token:`BaseClassList` in the :token:`ObjectBody` is present.
+
+You can declare an empty class by giving and empty :token:`TemplateArgList`
+and an empty :token:`ObjectBody`. This can serve as a restricted form of
+forward declaration: note that records deriving from the forward-declared
+class will inherit no fields from it since the record expansion is done
+when the record is parsed.
+
+.. productionlist::
+ TemplateArgList: "<" `Declaration` ("," `Declaration`)* ">"
+
+Declarations
+------------
+
+.. Omitting mention of arcane "field" prefix to discourage its use.
+
+The declaration syntax is pretty much what you would expect as a C++
+programmer.
+
+.. productionlist::
+ Declaration: `Type` `TokIdentifier` ["=" `Value`]
+
+It assigns the value to the identifier.
+
+Types
+-----
+
+.. productionlist::
+ Type: "string" | "code" | "bit" | "int" | "dag"
+ :| "bits" "<" `TokInteger` ">"
+ :| "list" "<" `Type` ">"
+ :| `ClassID`
+ ClassID: `TokIdentifier`
+
+Both ``string`` and ``code`` correspond to the string type; the difference
+is purely to indicate programmer intention.
+
+The :token:`ClassID` must identify a class that has been previously
+declared or defined.
+
+Values
+------
+
+.. productionlist::
+ Value: `SimpleValue` `ValueSuffix`*
+ ValueSuffix: "{" `RangeList` "}"
+ :| "[" `RangeList` "]"
+ :| "." `TokIdentifier`
+ RangeList: `RangePiece` ("," `RangePiece`)*
+ RangePiece: `TokInteger`
+ :| `TokInteger` "-" `TokInteger`
+ :| `TokInteger` `TokInteger`
+
+The peculiar last form of :token:`RangePiece` is due to the fact that the
+"``-``" is included in the :token:`TokInteger`, hence ``1-5`` gets lexed as
+two consecutive :token:`TokInteger`'s, with values ``1`` and ``-5``,
+instead of "1", "-", and "5".
+The :token:`RangeList` can be thought of as specifying "list slice" in some
+contexts.
+
+
+:token:`SimpleValue` has a number of forms:
+
+
+.. productionlist::
+ SimpleValue: `TokIdentifier`
+
+The value will be the variable referenced by the identifier. It can be one
+of:
+
+.. The code for this is exceptionally abstruse. These examples are a
+ best-effort attempt.
+
+* name of a ``def``, such as the use of ``Bar`` in::
+
+ def Bar : SomeClass {
+ int X = 5;
+ }
+
+ def Foo {
+ SomeClass Baz = Bar;
+ }
+
+* value local to a ``def``, such as the use of ``Bar`` in::
+
+ def Foo {
+ int Bar = 5;
+ int Baz = Bar;
+ }
+
+* a template arg of a ``class``, such as the use of ``Bar`` in::
+
+ class Foo<int Bar> {
+ int Baz = Bar;
+ }
+
+* value local to a ``multiclass``, such as the use of ``Bar`` in::
+
+ multiclass Foo {
+ int Bar = 5;
+ int Baz = Bar;
+ }
+
+* a template arg to a ``multiclass``, such as the use of ``Bar`` in::
+
+ multiclass Foo<int Bar> {
+ int Baz = Bar;
+ }
+
+.. productionlist::
+ SimpleValue: `TokInteger`
+
+This represents the numeric value of the integer.
+
+.. productionlist::
+ SimpleValue: `TokString`+
+
+Multiple adjacent string literals are concatenated like in C/C++. The value
+is the concatenation of the strings.
+
+.. productionlist::
+ SimpleValue: `TokCodeFragment`
+
+The value is the string value of the code fragment.
+
+.. productionlist::
+ SimpleValue: "?"
+
+``?`` represents an "unset" initializer.
+
+.. productionlist::
+ SimpleValue: "{" `ValueList` "}"
+ ValueList: [`ValueListNE`]
+ ValueListNE: `Value` ("," `Value`)*
+
+This represents a sequence of bits, as would be used to initialize a
+``bits<n>`` field (where ``n`` is the number of bits).
+
+.. productionlist::
+ SimpleValue: `ClassID` "<" `ValueListNE` ">"
+
+This generates a new anonymous record definition (as would be created by an
+unnamed ``def`` inheriting from the given class with the given template
+arguments) and the value is the value of that record definition.
+
+.. productionlist::
+ SimpleValue: "[" `ValueList` "]" ["<" `Type` ">"]
+
+A list initializer. The optional :token:`Type` can be used to indicate a
+specific element type, otherwise the element type will be deduced from the
+given values.
+
+.. The initial `DagArg` of the dag must start with an identifier or
+ !cast, but this is more of an implementation detail and so for now just
+ leave it out.
+
+.. productionlist::
+ SimpleValue: "(" `DagArg` `DagArgList` ")"
+ DagArgList: `DagArg` ("," `DagArg`)*
+ DagArg: `Value` [":" `TokVarName`] | `TokVarName`
+
+The initial :token:`DagArg` is called the "operator" of the dag.
+
+.. productionlist::
+ SimpleValue: `BangOperator` ["<" `Type` ">"] "(" `ValueListNE` ")"
+
+Bodies
+------
+
+.. productionlist::
+ ObjectBody: `BaseClassList` `Body`
+ BaseClassList: [":" `BaseClassListNE`]
+ BaseClassListNE: `SubClassRef` ("," `SubClassRef`)*
+ SubClassRef: (`ClassID` | `MultiClassID`) ["<" `ValueList` ">"]
+ DefmID: `TokIdentifier`
+
+The version with the :token:`MultiClassID` is only valid in the
+:token:`BaseClassList` of a ``defm``.
+The :token:`MultiClassID` should be the name of a ``multiclass``.
+
+.. put this somewhere else
+
+It is after parsing the base class list that the "let stack" is applied.
+
+.. productionlist::
+ Body: ";" | "{" BodyList "}"
+ BodyList: BodyItem*
+ BodyItem: `Declaration` ";"
+ :| "let" `TokIdentifier` [`RangeList`] "=" `Value` ";"
+
+The ``let`` form allows overriding the value of an inherited field.
+
+``def``
+-------
+
+.. TODO::
+ There can be pastes in the names here, like ``#NAME#``. Look into that
+ and document it (it boils down to ParseIDValue with IDParseMode ==
+ ParseNameMode). ParseObjectName calls into the general ParseValue, with
+ the only different from "arbitrary expression parsing" being IDParseMode
+ == Mode.
+
+.. productionlist::
+ Def: "def" `TokIdentifier` `ObjectBody`
+
+Defines a record whose name is given by the :token:`TokIdentifier`. The
+fields of the record are inherited from the base classes and defined in the
+body.
+
+Special handling occurs if this ``def`` appears inside a ``multiclass`` or
+a ``foreach``.
+
+``defm``
+--------
+
+.. productionlist::
+ Defm: "defm" `TokIdentifier` ":" `BaseClassListNE` ";"
+
+Note that in the :token:`BaseClassList`, all of the ``multiclass``'s must
+precede any ``class``'s that appear.
+
+``foreach``
+-----------
+
+.. productionlist::
+ Foreach: "foreach" `Declaration` "in" "{" `Object`* "}"
+ :| "foreach" `Declaration` "in" `Object`
+
+The value assigned to the variable in the declaration is iterated over and
+the object or object list is reevaluated with the variable set at each
+iterated value.
+
+Top-Level ``let``
+-----------------
+
+.. productionlist::
+ Let: "let" `LetList` "in" "{" `Object`* "}"
+ :| "let" `LetList` "in" `Object`
+ LetList: `LetItem` ("," `LetItem`)*
+ LetItem: `TokIdentifier` [`RangeList`] "=" `Value`
+
+This is effectively equivalent to ``let`` inside the body of a record
+except that it applies to multiple records at a time. The bindings are
+applied at the end of parsing the base classes of a record.
+
+``multiclass``
+--------------
+
+.. productionlist::
+ MultiClass: "multiclass" `TokIdentifier` [`TemplateArgList`]
+ : [":" `BaseMultiClassList`] "{" `MultiClassObject`+ "}"
+ BaseMultiClassList: `MultiClassID` ("," `MultiClassID`)*
+ MultiClassID: `TokIdentifier`
+ MultiClassObject: `Def` | `Defm` | `Let` | `Foreach`
Added: www-releases/trunk/3.9.1/docs/_sources/TableGen/index.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.9.1/docs/_sources/TableGen/index.txt?rev=290368&view=auto
==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/TableGen/index.txt (added)
+++ www-releases/trunk/3.9.1/docs/_sources/TableGen/index.txt Thu Dec 22 14:04:03 2016
@@ -0,0 +1,308 @@
+========
+TableGen
+========
+
+.. contents::
+ :local:
+
+.. toctree::
+ :hidden:
+
+ BackEnds
+ LangRef
+ LangIntro
+ Deficiencies
+
+Introduction
+============
+
+TableGen's purpose is to help a human develop and maintain records of
+domain-specific information. Because there may be a large number of these
+records, it is specifically designed to allow writing flexible descriptions and
+for common features of these records to be factored out. This reduces the
+amount of duplication in the description, reduces the chance of error, and makes
+it easier to structure domain specific information.
+
+The core part of TableGen parses a file, instantiates the declarations, and
+hands the result off to a domain-specific `backend`_ for processing.
+
+The current major users of TableGen are :doc:`../CodeGenerator`
+and the
+`Clang diagnostics and attributes <http://clang.llvm.org/docs/UsersManual.html#controlling-errors-and-warnings>`_.
+
+Note that if you work on TableGen much, and use emacs or vim, that you can find
+an emacs "TableGen mode" and a vim language file in the ``llvm/utils/emacs`` and
+``llvm/utils/vim`` directories of your LLVM distribution, respectively.
+
+.. _intro:
+
+
+The TableGen program
+====================
+
+TableGen files are interpreted by the TableGen program: `llvm-tblgen` available
+on your build directory under `bin`. It is not installed in the system (or where
+your sysroot is set to), since it has no use beyond LLVM's build process.
+
+Running TableGen
+----------------
+
+TableGen runs just like any other LLVM tool. The first (optional) argument
+specifies the file to read. If a filename is not specified, ``llvm-tblgen``
+reads from standard input.
+
+To be useful, one of the `backends`_ must be used. These backends are
+selectable on the command line (type '``llvm-tblgen -help``' for a list). For
+example, to get a list of all of the definitions that subclass a particular type
+(which can be useful for building up an enum list of these records), use the
+``-print-enums`` option:
+
+.. code-block:: bash
+
+ $ llvm-tblgen X86.td -print-enums -class=Register
+ AH, AL, AX, BH, BL, BP, BPL, BX, CH, CL, CX, DH, DI, DIL, DL, DX, EAX, EBP, EBX,
+ ECX, EDI, EDX, EFLAGS, EIP, ESI, ESP, FP0, FP1, FP2, FP3, FP4, FP5, FP6, IP,
+ MM0, MM1, MM2, MM3, MM4, MM5, MM6, MM7, R10, R10B, R10D, R10W, R11, R11B, R11D,
+ R11W, R12, R12B, R12D, R12W, R13, R13B, R13D, R13W, R14, R14B, R14D, R14W, R15,
+ R15B, R15D, R15W, R8, R8B, R8D, R8W, R9, R9B, R9D, R9W, RAX, RBP, RBX, RCX, RDI,
+ RDX, RIP, RSI, RSP, SI, SIL, SP, SPL, ST0, ST1, ST2, ST3, ST4, ST5, ST6, ST7,
+ XMM0, XMM1, XMM10, XMM11, XMM12, XMM13, XMM14, XMM15, XMM2, XMM3, XMM4, XMM5,
+ XMM6, XMM7, XMM8, XMM9,
+
+ $ llvm-tblgen X86.td -print-enums -class=Instruction
+ ABS_F, ABS_Fp32, ABS_Fp64, ABS_Fp80, ADC32mi, ADC32mi8, ADC32mr, ADC32ri,
+ ADC32ri8, ADC32rm, ADC32rr, ADC64mi32, ADC64mi8, ADC64mr, ADC64ri32, ADC64ri8,
+ ADC64rm, ADC64rr, ADD16mi, ADD16mi8, ADD16mr, ADD16ri, ADD16ri8, ADD16rm,
+ ADD16rr, ADD32mi, ADD32mi8, ADD32mr, ADD32ri, ADD32ri8, ADD32rm, ADD32rr,
+ ADD64mi32, ADD64mi8, ADD64mr, ADD64ri32, ...
+
+The default backend prints out all of the records.
+
+If you plan to use TableGen, you will most likely have to write a `backend`_
+that extracts the information specific to what you need and formats it in the
+appropriate way.
+
+Example
+-------
+
+With no other arguments, `llvm-tblgen` parses the specified file and prints out all
+of the classes, then all of the definitions. This is a good way to see what the
+various definitions expand to fully. Running this on the ``X86.td`` file prints
+this (at the time of this writing):
+
+.. code-block:: text
+
+ ...
+ def ADD32rr { // Instruction X86Inst I
+ string Namespace = "X86";
+ dag OutOperandList = (outs GR32:$dst);
+ dag InOperandList = (ins GR32:$src1, GR32:$src2);
+ string AsmString = "add{l}\t{$src2, $dst|$dst, $src2}";
+ list<dag> Pattern = [(set GR32:$dst, (add GR32:$src1, GR32:$src2))];
+ list<Register> Uses = [];
+ list<Register> Defs = [EFLAGS];
+ list<Predicate> Predicates = [];
+ int CodeSize = 3;
+ int AddedComplexity = 0;
+ bit isReturn = 0;
+ bit isBranch = 0;
+ bit isIndirectBranch = 0;
+ bit isBarrier = 0;
+ bit isCall = 0;
+ bit canFoldAsLoad = 0;
+ bit mayLoad = 0;
+ bit mayStore = 0;
+ bit isImplicitDef = 0;
+ bit isConvertibleToThreeAddress = 1;
+ bit isCommutable = 1;
+ bit isTerminator = 0;
+ bit isReMaterializable = 0;
+ bit isPredicable = 0;
+ bit hasDelaySlot = 0;
+ bit usesCustomInserter = 0;
+ bit hasCtrlDep = 0;
+ bit isNotDuplicable = 0;
+ bit hasSideEffects = 0;
+ InstrItinClass Itinerary = NoItinerary;
+ string Constraints = "";
+ string DisableEncoding = "";
+ bits<8> Opcode = { 0, 0, 0, 0, 0, 0, 0, 1 };
+ Format Form = MRMDestReg;
+ bits<6> FormBits = { 0, 0, 0, 0, 1, 1 };
+ ImmType ImmT = NoImm;
+ bits<3> ImmTypeBits = { 0, 0, 0 };
+ bit hasOpSizePrefix = 0;
+ bit hasAdSizePrefix = 0;
+ bits<4> Prefix = { 0, 0, 0, 0 };
+ bit hasREX_WPrefix = 0;
+ FPFormat FPForm = ?;
+ bits<3> FPFormBits = { 0, 0, 0 };
+ }
+ ...
+
+This definition corresponds to the 32-bit register-register ``add`` instruction
+of the x86 architecture. ``def ADD32rr`` defines a record named
+``ADD32rr``, and the comment at the end of the line indicates the superclasses
+of the definition. The body of the record contains all of the data that
+TableGen assembled for the record, indicating that the instruction is part of
+the "X86" namespace, the pattern indicating how the instruction is selected by
+the code generator, that it is a two-address instruction, has a particular
+encoding, etc. The contents and semantics of the information in the record are
+specific to the needs of the X86 backend, and are only shown as an example.
+
+As you can see, a lot of information is needed for every instruction supported
+by the code generator, and specifying it all manually would be unmaintainable,
+prone to bugs, and tiring to do in the first place. Because we are using
+TableGen, all of the information was derived from the following definition:
+
+.. code-block:: text
+
+ let Defs = [EFLAGS],
+ isCommutable = 1, // X = ADD Y,Z --> X = ADD Z,Y
+ isConvertibleToThreeAddress = 1 in // Can transform into LEA.
+ def ADD32rr : I<0x01, MRMDestReg, (outs GR32:$dst),
+ (ins GR32:$src1, GR32:$src2),
+ "add{l}\t{$src2, $dst|$dst, $src2}",
+ [(set GR32:$dst, (add GR32:$src1, GR32:$src2))]>;
+
+This definition makes use of the custom class ``I`` (extended from the custom
+class ``X86Inst``), which is defined in the X86-specific TableGen file, to
+factor out the common features that instructions of its class share. A key
+feature of TableGen is that it allows the end-user to define the abstractions
+they prefer to use when describing their information.
+
+Each ``def`` record has a special entry called "NAME". This is the name of the
+record ("``ADD32rr``" above). In the general case ``def`` names can be formed
+from various kinds of string processing expressions and ``NAME`` resolves to the
+final value obtained after resolving all of those expressions. The user may
+refer to ``NAME`` anywhere she desires to use the ultimate name of the ``def``.
+``NAME`` should not be defined anywhere else in user code to avoid conflicts.
+
+Syntax
+======
+
+TableGen has a syntax that is loosely based on C++ templates, with built-in
+types and specification. In addition, TableGen's syntax introduces some
+automation concepts like multiclass, foreach, let, etc.
+
+Basic concepts
+--------------
+
+TableGen files consist of two key parts: 'classes' and 'definitions', both of
+which are considered 'records'.
+
+**TableGen records** have a unique name, a list of values, and a list of
+superclasses. The list of values is the main data that TableGen builds for each
+record; it is this that holds the domain specific information for the
+application. The interpretation of this data is left to a specific `backend`_,
+but the structure and format rules are taken care of and are fixed by
+TableGen.
+
+**TableGen definitions** are the concrete form of 'records'. These generally do
+not have any undefined values, and are marked with the '``def``' keyword.
+
+.. code-block:: text
+
+ def FeatureFPARMv8 : SubtargetFeature<"fp-armv8", "HasFPARMv8", "true",
+ "Enable ARMv8 FP">;
+
+In this example, FeatureFPARMv8 is ``SubtargetFeature`` record initialised
+with some values. The names of the classes are defined via the
+keyword `class` either on the same file or some other included. Most target
+TableGen files include the generic ones in ``include/llvm/Target``.
+
+**TableGen classes** are abstract records that are used to build and describe
+other records. These classes allow the end-user to build abstractions for
+either the domain they are targeting (such as "Register", "RegisterClass", and
+"Instruction" in the LLVM code generator) or for the implementor to help factor
+out common properties of records (such as "FPInst", which is used to represent
+floating point instructions in the X86 backend). TableGen keeps track of all of
+the classes that are used to build up a definition, so the backend can find all
+definitions of a particular class, such as "Instruction".
+
+.. code-block:: text
+
+ class ProcNoItin<string Name, list<SubtargetFeature> Features>
+ : Processor<Name, NoItineraries, Features>;
+
+Here, the class ProcNoItin, receiving parameters `Name` of type `string` and
+a list of target features is specializing the class Processor by passing the
+arguments down as well as hard-coding NoItineraries.
+
+**TableGen multiclasses** are groups of abstract records that are instantiated
+all at once. Each instantiation can result in multiple TableGen definitions.
+If a multiclass inherits from another multiclass, the definitions in the
+sub-multiclass become part of the current multiclass, as if they were declared
+in the current multiclass.
+
+.. code-block:: text
+
+ multiclass ro_signed_pats<string T, string Rm, dag Base, dag Offset, dag Extend,
+ dag address, ValueType sty> {
+ def : Pat<(i32 (!cast<SDNode>("sextload" # sty) address)),
+ (!cast<Instruction>("LDRS" # T # "w_" # Rm # "_RegOffset")
+ Base, Offset, Extend)>;
+
+ def : Pat<(i64 (!cast<SDNode>("sextload" # sty) address)),
+ (!cast<Instruction>("LDRS" # T # "x_" # Rm # "_RegOffset")
+ Base, Offset, Extend)>;
+ }
+
+ defm : ro_signed_pats<"B", Rm, Base, Offset, Extend,
+ !foreach(decls.pattern, address,
+ !subst(SHIFT, imm_eq0, decls.pattern)),
+ i8>;
+
+
+
+See the :doc:`TableGen Language Introduction <LangIntro>` for more generic
+information on the usage of the language, and the
+:doc:`TableGen Language Reference <LangRef>` for more in-depth description
+of the formal language specification.
+
+.. _backend:
+.. _backends:
+
+TableGen backends
+=================
+
+TableGen files have no real meaning without a back-end. The default operation
+of running ``llvm-tblgen`` is to print the information in a textual format, but
+that's only useful for debugging of the TableGen files themselves. The power
+in TableGen is, however, to interpret the source files into an internal
+representation that can be generated into anything you want.
+
+Current usage of TableGen is to create huge include files with tables that you
+can either include directly (if the output is in the language you're coding),
+or be used in pre-processing via macros surrounding the include of the file.
+
+Direct output can be used if the back-end already prints a table in C format
+or if the output is just a list of strings (for error and warning messages).
+Pre-processed output should be used if the same information needs to be used
+in different contexts (like Instruction names), so your back-end should print
+a meta-information list that can be shaped into different compile-time formats.
+
+See the `TableGen BackEnds <BackEnds.html>`_ for more information.
+
+TableGen Deficiencies
+=====================
+
+Despite being very generic, TableGen has some deficiencies that have been
+pointed out numerous times. The common theme is that, while TableGen allows
+you to build Domain-Specific-Languages, the final languages that you create
+lack the power of other DSLs, which in turn increase considerably the size
+and complexity of TableGen files.
+
+At the same time, TableGen allows you to create virtually any meaning of
+the basic concepts via custom-made back-ends, which can pervert the original
+design and make it very hard for newcomers to understand the evil TableGen
+file.
+
+There are some in favour of extending the semantics even more, but making sure
+back-ends adhere to strict rules. Others are suggesting we should move to less,
+more powerful DSLs designed with specific purposes, or even re-using existing
+DSLs.
+
+Either way, this is a discussion that will likely span across several years,
+if not decades. You can read more in the `TableGen Deficiencies <Deficiencies.html>`_
+document.
Added: www-releases/trunk/3.9.1/docs/_sources/TableGenFundamentals.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.9.1/docs/_sources/TableGenFundamentals.txt?rev=290368&view=auto
==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/TableGenFundamentals.txt (added)
+++ www-releases/trunk/3.9.1/docs/_sources/TableGenFundamentals.txt Thu Dec 22 14:04:03 2016
@@ -0,0 +1,10 @@
+=====================
+TableGen Fundamentals
+=====================
+
+Moved
+=====
+
+The TableGen fundamentals documentation has moved to a directory on its own
+and is now available at :doc:`TableGen/index`. Please, change your links to
+that page.
Added: www-releases/trunk/3.9.1/docs/_sources/TestSuiteMakefileGuide.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.9.1/docs/_sources/TestSuiteMakefileGuide.txt?rev=290368&view=auto
==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/TestSuiteMakefileGuide.txt (added)
+++ www-releases/trunk/3.9.1/docs/_sources/TestSuiteMakefileGuide.txt Thu Dec 22 14:04:03 2016
@@ -0,0 +1,346 @@
+=====================
+LLVM test-suite Guide
+=====================
+
+.. contents::
+ :local:
+
+Overview
+========
+
+This document describes the features of the Makefile-based LLVM
+test-suite as well as the cmake based replacement. This way of interacting
+with the test-suite is deprecated in favor of running the test-suite using LNT,
+but may continue to prove useful for some users. See the Testing
+Guide's :ref:`test-suite Quickstart <test-suite-quickstart>` section for more
+information.
+
+Test suite Structure
+====================
+
+The ``test-suite`` module contains a number of programs that can be
+compiled with LLVM and executed. These programs are compiled using the
+native compiler and various LLVM backends. The output from the program
+compiled with the native compiler is assumed correct; the results from
+the other programs are compared to the native program output and pass if
+they match.
+
+When executing tests, it is usually a good idea to start out with a
+subset of the available tests or programs. This makes test run times
+smaller at first and later on this is useful to investigate individual
+test failures. To run some test only on a subset of programs, simply
+change directory to the programs you want tested and run ``gmake``
+there. Alternatively, you can run a different test using the ``TEST``
+variable to change what tests or run on the selected programs (see below
+for more info).
+
+In addition for testing correctness, the ``test-suite`` directory also
+performs timing tests of various LLVM optimizations. It also records
+compilation times for the compilers and the JIT. This information can be
+used to compare the effectiveness of LLVM's optimizations and code
+generation.
+
+``test-suite`` tests are divided into three types of tests: MultiSource,
+SingleSource, and External.
+
+- ``test-suite/SingleSource``
+
+ The SingleSource directory contains test programs that are only a
+ single source file in size. These are usually small benchmark
+ programs or small programs that calculate a particular value. Several
+ such programs are grouped together in each directory.
+
+- ``test-suite/MultiSource``
+
+ The MultiSource directory contains subdirectories which contain
+ entire programs with multiple source files. Large benchmarks and
+ whole applications go here.
+
+- ``test-suite/External``
+
+ The External directory contains Makefiles for building code that is
+ external to (i.e., not distributed with) LLVM. The most prominent
+ members of this directory are the SPEC 95 and SPEC 2000 benchmark
+ suites. The ``External`` directory does not contain these actual
+ tests, but only the Makefiles that know how to properly compile these
+ programs from somewhere else. The presence and location of these
+ external programs is configured by the test-suite ``configure``
+ script.
+
+Each tree is then subdivided into several categories, including
+applications, benchmarks, regression tests, code that is strange
+grammatically, etc. These organizations should be relatively self
+explanatory.
+
+Some tests are known to fail. Some are bugs that we have not fixed yet;
+others are features that we haven't added yet (or may never add). In the
+regression tests, the result for such tests will be XFAIL (eXpected
+FAILure). In this way, you can tell the difference between an expected
+and unexpected failure.
+
+The tests in the test suite have no such feature at this time. If the
+test passes, only warnings and other miscellaneous output will be
+generated. If a test fails, a large <program> FAILED message will be
+displayed. This will help you separate benign warnings from actual test
+failures.
+
+Running the test suite via CMake
+================================
+
+To run the test suite, you need to use the following steps:
+
+#. The test suite uses the lit test runner to run the test-suite,
+ you need to have lit installed first. Check out LLVM and install lit:
+
+ .. code-block:: bash
+
+ % svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm
+ % cd llvm/utils/lit
+ % sudo python setup.py install # Or without sudo, install in virtual-env.
+ running install
+ running bdist_egg
+ running egg_info
+ writing lit.egg-info/PKG-INFO
+ ...
+ % lit --version
+ lit 0.5.0dev
+
+#. Check out the ``test-suite`` module with:
+
+ .. code-block:: bash
+
+ % svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite
+
+#. Use CMake to configure the test suite in a new directory. You cannot build
+ the test suite in the source tree.
+
+ .. code-block:: bash
+
+ % mkdir test-suite-build
+ % cd test-suite-build
+ % cmake ../test-suite
+
+#. Build the benchmarks, using the makefiles CMake generated.
+
+.. code-block:: bash
+
+ % make
+ Scanning dependencies of target timeit-target
+ [ 0%] Building C object tools/CMakeFiles/timeit-target.dir/timeit.c.o
+ [ 0%] Linking C executable timeit-target
+ [ 0%] Built target timeit-target
+ Scanning dependencies of target fpcmp-host
+ [ 0%] [TEST_SUITE_HOST_CC] Building host executable fpcmp
+ [ 0%] Built target fpcmp-host
+ Scanning dependencies of target timeit-host
+ [ 0%] [TEST_SUITE_HOST_CC] Building host executable timeit
+ [ 0%] Built target timeit-host
+
+
+#. Run the tests with lit:
+
+.. code-block:: bash
+
+ % lit -v -j 1 . -o results.json
+ -- Testing: 474 tests, 1 threads --
+ PASS: test-suite :: MultiSource/Applications/ALAC/decode/alacconvert-decode.test (1 of 474)
+ ********** TEST 'test-suite :: MultiSource/Applications/ALAC/decode/alacconvert-decode.test' RESULTS **********
+ compile_time: 0.2192
+ exec_time: 0.0462
+ hash: "59620e187c6ac38b36382685ccd2b63b"
+ size: 83348
+ **********
+ PASS: test-suite :: MultiSource/Applications/ALAC/encode/alacconvert-encode.test (2 of 474)
+
+
+Running the test suite via Makefiles (deprecated)
+=================================================
+
+First, all tests are executed within the LLVM object directory tree.
+They *are not* executed inside of the LLVM source tree. This is because
+the test suite creates temporary files during execution.
+
+To run the test suite, you need to use the following steps:
+
+#. ``cd`` into the ``llvm/projects`` directory in your source tree.
+#. Check out the ``test-suite`` module with:
+
+ .. code-block:: bash
+
+ % svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite
+
+ This will get the test suite into ``llvm/projects/test-suite``.
+
+#. Configure and build ``llvm``.
+
+#. Configure and build ``llvm-gcc``.
+
+#. Install ``llvm-gcc`` somewhere.
+
+#. *Re-configure* ``llvm`` from the top level of each build tree (LLVM
+ object directory tree) in which you want to run the test suite, just
+ as you do before building LLVM.
+
+ During the *re-configuration*, you must either: (1) have ``llvm-gcc``
+ you just built in your path, or (2) specify the directory where your
+ just-built ``llvm-gcc`` is installed using
+ ``--with-llvmgccdir=$LLVM_GCC_DIR``.
+
+ You must also tell the configure machinery that the test suite is
+ available so it can be configured for your build tree:
+
+ .. code-block:: bash
+
+ % cd $LLVM_OBJ_ROOT ; $LLVM_SRC_ROOT/configure [--with-llvmgccdir=$LLVM_GCC_DIR]
+
+ [Remember that ``$LLVM_GCC_DIR`` is the directory where you
+ *installed* llvm-gcc, not its src or obj directory.]
+
+#. You can now run the test suite from your build tree as follows:
+
+ .. code-block:: bash
+
+ % cd $LLVM_OBJ_ROOT/projects/test-suite
+ % make
+
+Note that the second and third steps only need to be done once. After
+you have the suite checked out and configured, you don't need to do it
+again (unless the test code or configure script changes).
+
+Configuring External Tests
+--------------------------
+
+In order to run the External tests in the ``test-suite`` module, you
+must specify *--with-externals*. This must be done during the
+*re-configuration* step (see above), and the ``llvm`` re-configuration
+must recognize the previously-built ``llvm-gcc``. If any of these is
+missing or neglected, the External tests won't work.
+
+* *--with-externals*
+
+* *--with-externals=<directory>*
+
+This tells LLVM where to find any external tests. They are expected to
+be in specifically named subdirectories of <``directory``>. If
+``directory`` is left unspecified, ``configure`` uses the default value
+``/home/vadve/shared/benchmarks/speccpu2000/benchspec``. Subdirectory
+names known to LLVM include:
+
+* spec95
+
+* speccpu2000
+
+* speccpu2006
+
+* povray31
+
+Others are added from time to time, and can be determined from
+``configure``.
+
+Running different tests
+-----------------------
+
+In addition to the regular "whole program" tests, the ``test-suite``
+module also provides a mechanism for compiling the programs in different
+ways. If the variable TEST is defined on the ``gmake`` command line, the
+test system will include a Makefile named
+``TEST.<value of TEST variable>.Makefile``. This Makefile can modify
+build rules to yield different results.
+
+For example, the LLVM nightly tester uses ``TEST.nightly.Makefile`` to
+create the nightly test reports. To run the nightly tests, run
+``gmake TEST=nightly``.
+
+There are several TEST Makefiles available in the tree. Some of them are
+designed for internal LLVM research and will not work outside of the
+LLVM research group. They may still be valuable, however, as a guide to
+writing your own TEST Makefile for any optimization or analysis passes
+that you develop with LLVM.
+
+Generating test output
+----------------------
+
+There are a number of ways to run the tests and generate output. The
+most simple one is simply running ``gmake`` with no arguments. This will
+compile and run all programs in the tree using a number of different
+methods and compare results. Any failures are reported in the output,
+but are likely drowned in the other output. Passes are not reported
+explicitly.
+
+Somewhat better is running ``gmake TEST=sometest test``, which runs the
+specified test and usually adds per-program summaries to the output
+(depending on which sometest you use). For example, the ``nightly`` test
+explicitly outputs TEST-PASS or TEST-FAIL for every test after each
+program. Though these lines are still drowned in the output, it's easy
+to grep the output logs in the Output directories.
+
+Even better are the ``report`` and ``report.format`` targets (where
+``format`` is one of ``html``, ``csv``, ``text`` or ``graphs``). The
+exact contents of the report are dependent on which ``TEST`` you are
+running, but the text results are always shown at the end of the run and
+the results are always stored in the ``report.<type>.format`` file (when
+running with ``TEST=<type>``). The ``report`` also generate a file
+called ``report.<type>.raw.out`` containing the output of the entire
+test run.
+
+Writing custom tests for the test suite
+---------------------------------------
+
+Assuming you can run the test suite, (e.g.
+"``gmake TEST=nightly report``" should work), it is really easy to run
+optimizations or code generator components against every program in the
+tree, collecting statistics or running custom checks for correctness. At
+base, this is how the nightly tester works, it's just one example of a
+general framework.
+
+Lets say that you have an LLVM optimization pass, and you want to see
+how many times it triggers. First thing you should do is add an LLVM
+`statistic <ProgrammersManual.html#Statistic>`_ to your pass, which will
+tally counts of things you care about.
+
+Following this, you can set up a test and a report that collects these
+and formats them for easy viewing. This consists of two files, a
+"``test-suite/TEST.XXX.Makefile``" fragment (where XXX is the name of
+your test) and a "``test-suite/TEST.XXX.report``" file that indicates
+how to format the output into a table. There are many example reports of
+various levels of sophistication included with the test suite, and the
+framework is very general.
+
+If you are interested in testing an optimization pass, check out the
+"libcalls" test as an example. It can be run like this:
+
+.. code-block:: bash
+
+ % cd llvm/projects/test-suite/MultiSource/Benchmarks # or some other level
+ % make TEST=libcalls report
+
+This will do a bunch of stuff, then eventually print a table like this:
+
+::
+
+ Name | total | #exit |
+ ...
+ FreeBench/analyzer/analyzer | 51 | 6 |
+ FreeBench/fourinarow/fourinarow | 1 | 1 |
+ FreeBench/neural/neural | 19 | 9 |
+ FreeBench/pifft/pifft | 5 | 3 |
+ MallocBench/cfrac/cfrac | 1 | * |
+ MallocBench/espresso/espresso | 52 | 12 |
+ MallocBench/gs/gs | 4 | * |
+ Prolangs-C/TimberWolfMC/timberwolfmc | 302 | * |
+ Prolangs-C/agrep/agrep | 33 | 12 |
+ Prolangs-C/allroots/allroots | * | * |
+ Prolangs-C/assembler/assembler | 47 | * |
+ Prolangs-C/bison/mybison | 74 | * |
+ ...
+
+This basically is grepping the -stats output and displaying it in a
+table. You can also use the "TEST=libcalls report.html" target to get
+the table in HTML form, similarly for report.csv and report.tex.
+
+The source for this is in ``test-suite/TEST.libcalls.*``. The format is
+pretty simple: the Makefile indicates how to run the test (in this case,
+"``opt -simplify-libcalls -stats``"), and the report contains one line
+for each column of the output. The first value is the header for the
+column and the second is the regex to grep the output of the command
+for. There are lots of example reports that can do fancy stuff.
Added: www-releases/trunk/3.9.1/docs/_sources/TestingGuide.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.9.1/docs/_sources/TestingGuide.txt?rev=290368&view=auto
==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/TestingGuide.txt (added)
+++ www-releases/trunk/3.9.1/docs/_sources/TestingGuide.txt Thu Dec 22 14:04:03 2016
@@ -0,0 +1,619 @@
+=================================
+LLVM Testing Infrastructure Guide
+=================================
+
+.. contents::
+ :local:
+
+.. toctree::
+ :hidden:
+
+ TestSuiteMakefileGuide
+
+Overview
+========
+
+This document is the reference manual for the LLVM testing
+infrastructure. It documents the structure of the LLVM testing
+infrastructure, the tools needed to use it, and how to add and run
+tests.
+
+Requirements
+============
+
+In order to use the LLVM testing infrastructure, you will need all of the
+software required to build LLVM, as well as `Python <http://python.org>`_ 2.7 or
+later.
+
+If you intend to run the :ref:`test-suite <test-suite-overview>`, you will also
+need a development version of zlib (zlib1g-dev is known to work on several Linux
+distributions).
+
+LLVM testing infrastructure organization
+========================================
+
+The LLVM testing infrastructure contains two major categories of tests:
+regression tests and whole programs. The regression tests are contained
+inside the LLVM repository itself under ``llvm/test`` and are expected
+to always pass -- they should be run before every commit.
+
+The whole programs tests are referred to as the "LLVM test suite" (or
+"test-suite") and are in the ``test-suite`` module in subversion. For
+historical reasons, these tests are also referred to as the "nightly
+tests" in places, which is less ambiguous than "test-suite" and remains
+in use although we run them much more often than nightly.
+
+Regression tests
+----------------
+
+The regression tests are small pieces of code that test a specific
+feature of LLVM or trigger a specific bug in LLVM. The language they are
+written in depends on the part of LLVM being tested. These tests are driven by
+the :doc:`Lit <CommandGuide/lit>` testing tool (which is part of LLVM), and
+are located in the ``llvm/test`` directory.
+
+Typically when a bug is found in LLVM, a regression test containing just
+enough code to reproduce the problem should be written and placed
+somewhere underneath this directory. For example, it can be a small
+piece of LLVM IR distilled from an actual application or benchmark.
+
+``test-suite``
+--------------
+
+The test suite contains whole programs, which are pieces of code which
+can be compiled and linked into a stand-alone program that can be
+executed. These programs are generally written in high level languages
+such as C or C++.
+
+These programs are compiled using a user specified compiler and set of
+flags, and then executed to capture the program output and timing
+information. The output of these programs is compared to a reference
+output to ensure that the program is being compiled correctly.
+
+In addition to compiling and executing programs, whole program tests
+serve as a way of benchmarking LLVM performance, both in terms of the
+efficiency of the programs generated as well as the speed with which
+LLVM compiles, optimizes, and generates code.
+
+The test-suite is located in the ``test-suite`` Subversion module.
+
+Debugging Information tests
+---------------------------
+
+The test suite contains tests to check quality of debugging information.
+The test are written in C based languages or in LLVM assembly language.
+
+These tests are compiled and run under a debugger. The debugger output
+is checked to validate of debugging information. See README.txt in the
+test suite for more information . This test suite is located in the
+``debuginfo-tests`` Subversion module.
+
+Quick start
+===========
+
+The tests are located in two separate Subversion modules. The
+regressions tests are in the main "llvm" module under the directory
+``llvm/test`` (so you get these tests for free with the main LLVM tree).
+Use ``make check-all`` to run the regression tests after building LLVM.
+
+The more comprehensive test suite that includes whole programs in C and C++
+is in the ``test-suite`` module. See :ref:`test-suite Quickstart
+<test-suite-quickstart>` for more information on running these tests.
+
+Regression tests
+----------------
+
+To run all of the LLVM regression tests use the check-llvm target:
+
+.. code-block:: bash
+
+ % make check-llvm
+
+If you have `Clang <http://clang.llvm.org/>`_ checked out and built, you
+can run the LLVM and Clang tests simultaneously using:
+
+.. code-block:: bash
+
+ % make check-all
+
+To run the tests with Valgrind (Memcheck by default), use the ``LIT_ARGS`` make
+variable to pass the required options to lit. For example, you can use:
+
+.. code-block:: bash
+
+ % make check LIT_ARGS="-v --vg --vg-leak"
+
+to enable testing with valgrind and with leak checking enabled.
+
+To run individual tests or subsets of tests, you can use the ``llvm-lit``
+script which is built as part of LLVM. For example, to run the
+``Integer/BitPacked.ll`` test by itself you can run:
+
+.. code-block:: bash
+
+ % llvm-lit ~/llvm/test/Integer/BitPacked.ll
+
+or to run all of the ARM CodeGen tests:
+
+.. code-block:: bash
+
+ % llvm-lit ~/llvm/test/CodeGen/ARM
+
+For more information on using the :program:`lit` tool, see ``llvm-lit --help``
+or the :doc:`lit man page <CommandGuide/lit>`.
+
+Debugging Information tests
+---------------------------
+
+To run debugging information tests simply checkout the tests inside
+clang/test directory.
+
+.. code-block:: bash
+
+ % cd clang/test
+ % svn co http://llvm.org/svn/llvm-project/debuginfo-tests/trunk debuginfo-tests
+
+These tests are already set up to run as part of clang regression tests.
+
+Regression test structure
+=========================
+
+The LLVM regression tests are driven by :program:`lit` and are located in the
+``llvm/test`` directory.
+
+This directory contains a large array of small tests that exercise
+various features of LLVM and to ensure that regressions do not occur.
+The directory is broken into several sub-directories, each focused on a
+particular area of LLVM.
+
+Writing new regression tests
+----------------------------
+
+The regression test structure is very simple, but does require some
+information to be set. This information is gathered via ``configure``
+and is written to a file, ``test/lit.site.cfg`` in the build directory.
+The ``llvm/test`` Makefile does this work for you.
+
+In order for the regression tests to work, each directory of tests must
+have a ``lit.local.cfg`` file. :program:`lit` looks for this file to determine
+how to run the tests. This file is just Python code and thus is very
+flexible, but we've standardized it for the LLVM regression tests. If
+you're adding a directory of tests, just copy ``lit.local.cfg`` from
+another directory to get running. The standard ``lit.local.cfg`` simply
+specifies which files to look in for tests. Any directory that contains
+only directories does not need the ``lit.local.cfg`` file. Read the :doc:`Lit
+documentation <CommandGuide/lit>` for more information.
+
+Each test file must contain lines starting with "RUN:" that tell :program:`lit`
+how to run it. If there are no RUN lines, :program:`lit` will issue an error
+while running a test.
+
+RUN lines are specified in the comments of the test program using the
+keyword ``RUN`` followed by a colon, and lastly the command (pipeline)
+to execute. Together, these lines form the "script" that :program:`lit`
+executes to run the test case. The syntax of the RUN lines is similar to a
+shell's syntax for pipelines including I/O redirection and variable
+substitution. However, even though these lines may *look* like a shell
+script, they are not. RUN lines are interpreted by :program:`lit`.
+Consequently, the syntax differs from shell in a few ways. You can specify
+as many RUN lines as needed.
+
+:program:`lit` performs substitution on each RUN line to replace LLVM tool names
+with the full paths to the executable built for each tool (in
+``$(LLVM_OBJ_ROOT)/$(BuildMode)/bin)``. This ensures that :program:`lit` does
+not invoke any stray LLVM tools in the user's path during testing.
+
+Each RUN line is executed on its own, distinct from other lines unless
+its last character is ``\``. This continuation character causes the RUN
+line to be concatenated with the next one. In this way you can build up
+long pipelines of commands without making huge line lengths. The lines
+ending in ``\`` are concatenated until a RUN line that doesn't end in
+``\`` is found. This concatenated set of RUN lines then constitutes one
+execution. :program:`lit` will substitute variables and arrange for the pipeline
+to be executed. If any process in the pipeline fails, the entire line (and
+test case) fails too.
+
+Below is an example of legal RUN lines in a ``.ll`` file:
+
+.. code-block:: llvm
+
+ ; RUN: llvm-as < %s | llvm-dis > %t1
+ ; RUN: llvm-dis < %s.bc-13 > %t2
+ ; RUN: diff %t1 %t2
+
+As with a Unix shell, the RUN lines permit pipelines and I/O
+redirection to be used.
+
+There are some quoting rules that you must pay attention to when writing
+your RUN lines. In general nothing needs to be quoted. :program:`lit` won't
+strip off any quote characters so they will get passed to the invoked program.
+To avoid this use curly braces to tell :program:`lit` that it should treat
+everything enclosed as one value.
+
+In general, you should strive to keep your RUN lines as simple as possible,
+using them only to run tools that generate textual output you can then examine.
+The recommended way to examine output to figure out if the test passes is using
+the :doc:`FileCheck tool <CommandGuide/FileCheck>`. *[The usage of grep in RUN
+lines is deprecated - please do not send or commit patches that use it.]*
+
+Put related tests into a single file rather than having a separate file per
+test. Check if there are files already covering your feature and consider
+adding your code there instead of creating a new file.
+
+Extra files
+-----------
+
+If your test requires extra files besides the file containing the ``RUN:``
+lines, the idiomatic place to put them is in a subdirectory ``Inputs``.
+You can then refer to the extra files as ``%S/Inputs/foo.bar``.
+
+For example, consider ``test/Linker/ident.ll``. The directory structure is
+as follows::
+
+ test/
+ Linker/
+ ident.ll
+ Inputs/
+ ident.a.ll
+ ident.b.ll
+
+For convenience, these are the contents:
+
+.. code-block:: llvm
+
+ ;;;;; ident.ll:
+
+ ; RUN: llvm-link %S/Inputs/ident.a.ll %S/Inputs/ident.b.ll -S | FileCheck %s
+
+ ; Verify that multiple input llvm.ident metadata are linked together.
+
+ ; CHECK-DAG: !llvm.ident = !{!0, !1, !2}
+ ; CHECK-DAG: "Compiler V1"
+ ; CHECK-DAG: "Compiler V2"
+ ; CHECK-DAG: "Compiler V3"
+
+ ;;;;; Inputs/ident.a.ll:
+
+ !llvm.ident = !{!0, !1}
+ !0 = metadata !{metadata !"Compiler V1"}
+ !1 = metadata !{metadata !"Compiler V2"}
+
+ ;;;;; Inputs/ident.b.ll:
+
+ !llvm.ident = !{!0}
+ !0 = metadata !{metadata !"Compiler V3"}
+
+For symmetry reasons, ``ident.ll`` is just a dummy file that doesn't
+actually participate in the test besides holding the ``RUN:`` lines.
+
+.. note::
+
+ Some existing tests use ``RUN: true`` in extra files instead of just
+ putting the extra files in an ``Inputs/`` directory. This pattern is
+ deprecated.
+
+Fragile tests
+-------------
+
+It is easy to write a fragile test that would fail spuriously if the tool being
+tested outputs a full path to the input file. For example, :program:`opt` by
+default outputs a ``ModuleID``:
+
+.. code-block:: console
+
+ $ cat example.ll
+ define i32 @main() nounwind {
+ ret i32 0
+ }
+
+ $ opt -S /path/to/example.ll
+ ; ModuleID = '/path/to/example.ll'
+
+ define i32 @main() nounwind {
+ ret i32 0
+ }
+
+``ModuleID`` can unexpetedly match against ``CHECK`` lines. For example:
+
+.. code-block:: llvm
+
+ ; RUN: opt -S %s | FileCheck
+
+ define i32 @main() nounwind {
+ ; CHECK-NOT: load
+ ret i32 0
+ }
+
+This test will fail if placed into a ``download`` directory.
+
+To make your tests robust, always use ``opt ... < %s`` in the RUN line.
+:program:`opt` does not output a ``ModuleID`` when input comes from stdin.
+
+Platform-Specific Tests
+-----------------------
+
+Whenever adding tests that require the knowledge of a specific platform,
+either related to code generated, specific output or back-end features,
+you must make sure to isolate the features, so that buildbots that
+run on different architectures (and don't even compile all back-ends),
+don't fail.
+
+The first problem is to check for target-specific output, for example sizes
+of structures, paths and architecture names, for example:
+
+* Tests containing Windows paths will fail on Linux and vice-versa.
+* Tests that check for ``x86_64`` somewhere in the text will fail anywhere else.
+* Tests where the debug information calculates the size of types and structures.
+
+Also, if the test rely on any behaviour that is coded in any back-end, it must
+go in its own directory. So, for instance, code generator tests for ARM go
+into ``test/CodeGen/ARM`` and so on. Those directories contain a special
+``lit`` configuration file that ensure all tests in that directory will
+only run if a specific back-end is compiled and available.
+
+For instance, on ``test/CodeGen/ARM``, the ``lit.local.cfg`` is:
+
+.. code-block:: python
+
+ config.suffixes = ['.ll', '.c', '.cpp', '.test']
+ if not 'ARM' in config.root.targets:
+ config.unsupported = True
+
+Other platform-specific tests are those that depend on a specific feature
+of a specific sub-architecture, for example only to Intel chips that support ``AVX2``.
+
+For instance, ``test/CodeGen/X86/psubus.ll`` tests three sub-architecture
+variants:
+
+.. code-block:: llvm
+
+ ; RUN: llc -mcpu=core2 < %s | FileCheck %s -check-prefix=SSE2
+ ; RUN: llc -mcpu=corei7-avx < %s | FileCheck %s -check-prefix=AVX1
+ ; RUN: llc -mcpu=core-avx2 < %s | FileCheck %s -check-prefix=AVX2
+
+And the checks are different:
+
+.. code-block:: llvm
+
+ ; SSE2: @test1
+ ; SSE2: psubusw LCPI0_0(%rip), %xmm0
+ ; AVX1: @test1
+ ; AVX1: vpsubusw LCPI0_0(%rip), %xmm0, %xmm0
+ ; AVX2: @test1
+ ; AVX2: vpsubusw LCPI0_0(%rip), %xmm0, %xmm0
+
+So, if you're testing for a behaviour that you know is platform-specific or
+depends on special features of sub-architectures, you must add the specific
+triple, test with the specific FileCheck and put it into the specific
+directory that will filter out all other architectures.
+
+REQUIRES and REQUIRES-ANY directive
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Some tests can be enabled only in specific situation - like having
+debug build. Use ``REQUIRES`` directive to specify those requirements.
+
+.. code-block:: llvm
+
+ ; This test will be only enabled in the build with asserts
+ ; REQUIRES: asserts
+
+You can separate requirements by a comma.
+``REQUIRES`` means all listed requirements must be satisfied.
+``REQUIRES-ANY`` means at least one must be satisfied.
+
+List of features that can be used in ``REQUIRES`` and ``REQUIRES-ANY`` can be
+found in lit.cfg files.
+
+Substitutions
+-------------
+
+Besides replacing LLVM tool names the following substitutions are performed in
+RUN lines:
+
+``%%``
+ Replaced by a single ``%``. This allows escaping other substitutions.
+
+``%s``
+ File path to the test case's source. This is suitable for passing on the
+ command line as the input to an LLVM tool.
+
+ Example: ``/home/user/llvm/test/MC/ELF/foo_test.s``
+
+``%S``
+ Directory path to the test case's source.
+
+ Example: ``/home/user/llvm/test/MC/ELF``
+
+``%t``
+ File path to a temporary file name that could be used for this test case.
+ The file name won't conflict with other test cases. You can append to it
+ if you need multiple temporaries. This is useful as the destination of
+ some redirected output.
+
+ Example: ``/home/user/llvm.build/test/MC/ELF/Output/foo_test.s.tmp``
+
+``%T``
+ Directory of ``%t``.
+
+ Example: ``/home/user/llvm.build/test/MC/ELF/Output``
+
+``%{pathsep}``
+
+ Expands to the path separator, i.e. ``:`` (or ``;`` on Windows).
+
+
+**LLVM-specific substitutions:**
+
+``%shlibext``
+ The suffix for the host platforms shared library files. This includes the
+ period as the first character.
+
+ Example: ``.so`` (Linux), ``.dylib`` (OS X), ``.dll`` (Windows)
+
+``%exeext``
+ The suffix for the host platforms executable files. This includes the
+ period as the first character.
+
+ Example: ``.exe`` (Windows), empty on Linux.
+
+``%(line)``, ``%(line+<number>)``, ``%(line-<number>)``
+ The number of the line where this substitution is used, with an optional
+ integer offset. This can be used in tests with multiple RUN lines, which
+ reference test file's line numbers.
+
+
+**Clang-specific substitutions:**
+
+``%clang``
+ Invokes the Clang driver.
+
+``%clang_cpp``
+ Invokes the Clang driver for C++.
+
+``%clang_cl``
+ Invokes the CL-compatible Clang driver.
+
+``%clangxx``
+ Invokes the G++-compatible Clang driver.
+
+``%clang_cc1``
+ Invokes the Clang frontend.
+
+``%itanium_abi_triple``, ``%ms_abi_triple``
+ These substitutions can be used to get the current target triple adjusted to
+ the desired ABI. For example, if the test suite is running with the
+ ``i686-pc-win32`` target, ``%itanium_abi_triple`` will expand to
+ ``i686-pc-mingw32``. This allows a test to run with a specific ABI without
+ constraining it to a specific triple.
+
+To add more substituations, look at ``test/lit.cfg`` or ``lit.local.cfg``.
+
+
+Options
+-------
+
+The llvm lit configuration allows to customize some things with user options:
+
+``llc``, ``opt``, ...
+ Substitute the respective llvm tool name with a custom command line. This
+ allows to specify custom paths and default arguments for these tools.
+ Example:
+
+ % llvm-lit "-Dllc=llc -verify-machineinstrs"
+
+``run_long_tests``
+ Enable the execution of long running tests.
+
+``llvm_site_config``
+ Load the specified lit configuration instead of the default one.
+
+
+Other Features
+--------------
+
+To make RUN line writing easier, there are several helper programs. These
+helpers are in the PATH when running tests, so you can just call them using
+their name. For example:
+
+``not``
+ This program runs its arguments and then inverts the result code from it.
+ Zero result codes become 1. Non-zero result codes become 0.
+
+Sometimes it is necessary to mark a test case as "expected fail" or
+XFAIL. You can easily mark a test as XFAIL just by including ``XFAIL:``
+on a line near the top of the file. This signals that the test case
+should succeed if the test fails. Such test cases are counted separately
+by the testing tool. To specify an expected fail, use the XFAIL keyword
+in the comments of the test program followed by a colon and one or more
+failure patterns. Each failure pattern can be either ``*`` (to specify
+fail everywhere), or a part of a target triple (indicating the test
+should fail on that platform), or the name of a configurable feature
+(for example, ``loadable_module``). If there is a match, the test is
+expected to fail. If not, the test is expected to succeed. To XFAIL
+everywhere just specify ``XFAIL: *``. Here is an example of an ``XFAIL``
+line:
+
+.. code-block:: llvm
+
+ ; XFAIL: darwin,sun
+
+To make the output more useful, :program:`lit` will scan
+the lines of the test case for ones that contain a pattern that matches
+``PR[0-9]+``. This is the syntax for specifying a PR (Problem Report) number
+that is related to the test case. The number after "PR" specifies the
+LLVM bugzilla number. When a PR number is specified, it will be used in
+the pass/fail reporting. This is useful to quickly get some context when
+a test fails.
+
+Finally, any line that contains "END." will cause the special
+interpretation of lines to terminate. This is generally done right after
+the last RUN: line. This has two side effects:
+
+(a) it prevents special interpretation of lines that are part of the test
+ program, not the instructions to the test case, and
+
+(b) it speeds things up for really big test cases by avoiding
+ interpretation of the remainder of the file.
+
+.. _test-suite-overview:
+
+``test-suite`` Overview
+=======================
+
+The ``test-suite`` module contains a number of programs that can be
+compiled and executed. The ``test-suite`` includes reference outputs for
+all of the programs, so that the output of the executed program can be
+checked for correctness.
+
+``test-suite`` tests are divided into three types of tests: MultiSource,
+SingleSource, and External.
+
+- ``test-suite/SingleSource``
+
+ The SingleSource directory contains test programs that are only a
+ single source file in size. These are usually small benchmark
+ programs or small programs that calculate a particular value. Several
+ such programs are grouped together in each directory.
+
+- ``test-suite/MultiSource``
+
+ The MultiSource directory contains subdirectories which contain
+ entire programs with multiple source files. Large benchmarks and
+ whole applications go here.
+
+- ``test-suite/External``
+
+ The External directory contains Makefiles for building code that is
+ external to (i.e., not distributed with) LLVM. The most prominent
+ members of this directory are the SPEC 95 and SPEC 2000 benchmark
+ suites. The ``External`` directory does not contain these actual
+ tests, but only the Makefiles that know how to properly compile these
+ programs from somewhere else. When using ``LNT``, use the
+ ``--test-externals`` option to include these tests in the results.
+
+.. _test-suite-quickstart:
+
+``test-suite`` Quickstart
+-------------------------
+
+The modern way of running the ``test-suite`` is focused on testing and
+benchmarking complete compilers using the
+`LNT <http://llvm.org/docs/lnt>`_ testing infrastructure.
+
+For more information on using LNT to execute the ``test-suite``, please
+see the `LNT Quickstart <http://llvm.org/docs/lnt/quickstart.html>`_
+documentation.
+
+``test-suite`` Makefiles
+------------------------
+
+Historically, the ``test-suite`` was executed using a complicated setup
+of Makefiles. The LNT based approach above is recommended for most
+users, but there are some testing scenarios which are not supported by
+the LNT approach. In addition, LNT currently uses the Makefile setup
+under the covers and so developers who are interested in how LNT works
+under the hood may want to understand the Makefile based setup.
+
+For more information on the ``test-suite`` Makefile setup, please see
+the :doc:`Test Suite Makefile Guide <TestSuiteMakefileGuide>`.
Added: www-releases/trunk/3.9.1/docs/_sources/TypeMetadata.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.9.1/docs/_sources/TypeMetadata.txt?rev=290368&view=auto
==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/TypeMetadata.txt (added)
+++ www-releases/trunk/3.9.1/docs/_sources/TypeMetadata.txt Thu Dec 22 14:04:03 2016
@@ -0,0 +1,226 @@
+=============
+Type Metadata
+=============
+
+Type metadata is a mechanism that allows IR modules to co-operatively build
+pointer sets corresponding to addresses within a given set of globals. LLVM's
+`control flow integrity`_ implementation uses this metadata to efficiently
+check (at each call site) that a given address corresponds to either a
+valid vtable or function pointer for a given class or function type, and its
+whole-program devirtualization pass uses the metadata to identify potential
+callees for a given virtual call.
+
+To use the mechanism, a client creates metadata nodes with two elements:
+
+1. a byte offset into the global (generally zero for functions)
+2. a metadata object representing an identifier for the type
+
+These metadata nodes are associated with globals by using global object
+metadata attachments with the ``!type`` metadata kind.
+
+Each type identifier must exclusively identify either global variables
+or functions.
+
+.. admonition:: Limitation
+
+ The current implementation only supports attaching metadata to functions on
+ the x86-32 and x86-64 architectures.
+
+An intrinsic, :ref:`llvm.type.test <type.test>`, is used to test whether a
+given pointer is associated with a type identifier.
+
+.. _control flow integrity: http://clang.llvm.org/docs/ControlFlowIntegrity.html
+
+Representing Type Information using Type Metadata
+=================================================
+
+This section describes how Clang represents C++ type information associated with
+virtual tables using type metadata.
+
+Consider the following inheritance hierarchy:
+
+.. code-block:: c++
+
+ struct A {
+ virtual void f();
+ };
+
+ struct B : A {
+ virtual void f();
+ virtual void g();
+ };
+
+ struct C {
+ virtual void h();
+ };
+
+ struct D : A, C {
+ virtual void f();
+ virtual void h();
+ };
+
+The virtual table objects for A, B, C and D look like this (under the Itanium ABI):
+
+.. csv-table:: Virtual Table Layout for A, B, C, D
+ :header: Class, 0, 1, 2, 3, 4, 5, 6
+
+ A, A::offset-to-top, &A::rtti, &A::f
+ B, B::offset-to-top, &B::rtti, &B::f, &B::g
+ C, C::offset-to-top, &C::rtti, &C::h
+ D, D::offset-to-top, &D::rtti, &D::f, &D::h, D::offset-to-top, &D::rtti, thunk for &D::h
+
+When an object of type A is constructed, the address of ``&A::f`` in A's
+virtual table object is stored in the object's vtable pointer. In ABI parlance
+this address is known as an `address point`_. Similarly, when an object of type
+B is constructed, the address of ``&B::f`` is stored in the vtable pointer. In
+this way, the vtable in B's virtual table object is compatible with A's vtable.
+
+D is a little more complicated, due to the use of multiple inheritance. Its
+virtual table object contains two vtables, one compatible with A's vtable and
+the other compatible with C's vtable. Objects of type D contain two virtual
+pointers, one belonging to the A subobject and containing the address of
+the vtable compatible with A's vtable, and the other belonging to the C
+subobject and containing the address of the vtable compatible with C's vtable.
+
+The full set of compatibility information for the above class hierarchy is
+shown below. The following table shows the name of a class, the offset of an
+address point within that class's vtable and the name of one of the classes
+with which that address point is compatible.
+
+.. csv-table:: Type Offsets for A, B, C, D
+ :header: VTable for, Offset, Compatible Class
+
+ A, 16, A
+ B, 16, A
+ , , B
+ C, 16, C
+ D, 16, A
+ , , D
+ , 48, C
+
+The next step is to encode this compatibility information into the IR. The way
+this is done is to create type metadata named after each of the compatible
+classes, with which we associate each of the compatible address points in
+each vtable. For example, these type metadata entries encode the compatibility
+information for the above hierarchy:
+
+::
+
+ @_ZTV1A = constant [...], !type !0
+ @_ZTV1B = constant [...], !type !0, !type !1
+ @_ZTV1C = constant [...], !type !2
+ @_ZTV1D = constant [...], !type !0, !type !3, !type !4
+
+ !0 = !{i64 16, !"_ZTS1A"}
+ !1 = !{i64 16, !"_ZTS1B"}
+ !2 = !{i64 16, !"_ZTS1C"}
+ !3 = !{i64 16, !"_ZTS1D"}
+ !4 = !{i64 48, !"_ZTS1C"}
+
+With this type metadata, we can now use the ``llvm.type.test`` intrinsic to
+test whether a given pointer is compatible with a type identifier. Working
+backwards, if ``llvm.type.test`` returns true for a particular pointer,
+we can also statically determine the identities of the virtual functions
+that a particular virtual call may call. For example, if a program assumes
+a pointer to be a member of ``!"_ZST1A"``, we know that the address can
+be only be one of ``_ZTV1A+16``, ``_ZTV1B+16`` or ``_ZTV1D+16`` (i.e. the
+address points of the vtables of A, B and D respectively). If we then load
+an address from that pointer, we know that the address can only be one of
+``&A::f``, ``&B::f`` or ``&D::f``.
+
+.. _address point: https://mentorembedded.github.io/cxx-abi/abi.html#vtable-general
+
+Testing Addresses For Type Membership
+=====================================
+
+If a program tests an address using ``llvm.type.test``, this will cause
+a link-time optimization pass, ``LowerTypeTests``, to replace calls to this
+intrinsic with efficient code to perform type member tests. At a high level,
+the pass will lay out referenced globals in a consecutive memory region in
+the object file, construct bit vectors that map onto that memory region,
+and generate code at each of the ``llvm.type.test`` call sites to test
+pointers against those bit vectors. Because of the layout manipulation, the
+globals' definitions must be available at LTO time. For more information,
+see the `control flow integrity design document`_.
+
+A type identifier that identifies functions is transformed into a jump table,
+which is a block of code consisting of one branch instruction for each
+of the functions associated with the type identifier that branches to the
+target function. The pass will redirect any taken function addresses to the
+corresponding jump table entry. In the object file's symbol table, the jump
+table entries take the identities of the original functions, so that addresses
+taken outside the module will pass any verification done inside the module.
+
+Jump tables may call external functions, so their definitions need not
+be available at LTO time. Note that if an externally defined function is
+associated with a type identifier, there is no guarantee that its identity
+within the module will be the same as its identity outside of the module,
+as the former will be the jump table entry if a jump table is necessary.
+
+The `GlobalLayoutBuilder`_ class is responsible for laying out the globals
+efficiently to minimize the sizes of the underlying bitsets.
+
+.. _control flow integrity design document: http://clang.llvm.org/docs/ControlFlowIntegrityDesign.html
+
+:Example:
+
+::
+
+ target datalayout = "e-p:32:32"
+
+ @a = internal global i32 0, !type !0
+ @b = internal global i32 0, !type !0, !type !1
+ @c = internal global i32 0, !type !1
+ @d = internal global [2 x i32] [i32 0, i32 0], !type !2
+
+ define void @e() !type !3 {
+ ret void
+ }
+
+ define void @f() {
+ ret void
+ }
+
+ declare void @g() !type !3
+
+ !0 = !{i32 0, !"typeid1"}
+ !1 = !{i32 0, !"typeid2"}
+ !2 = !{i32 4, !"typeid2"}
+ !3 = !{i32 0, !"typeid3"}
+
+ declare i1 @llvm.type.test(i8* %ptr, metadata %typeid) nounwind readnone
+
+ define i1 @foo(i32* %p) {
+ %pi8 = bitcast i32* %p to i8*
+ %x = call i1 @llvm.type.test(i8* %pi8, metadata !"typeid1")
+ ret i1 %x
+ }
+
+ define i1 @bar(i32* %p) {
+ %pi8 = bitcast i32* %p to i8*
+ %x = call i1 @llvm.type.test(i8* %pi8, metadata !"typeid2")
+ ret i1 %x
+ }
+
+ define i1 @baz(void ()* %p) {
+ %pi8 = bitcast void ()* %p to i8*
+ %x = call i1 @llvm.type.test(i8* %pi8, metadata !"typeid3")
+ ret i1 %x
+ }
+
+ define void @main() {
+ %a1 = call i1 @foo(i32* @a) ; returns 1
+ %b1 = call i1 @foo(i32* @b) ; returns 1
+ %c1 = call i1 @foo(i32* @c) ; returns 0
+ %a2 = call i1 @bar(i32* @a) ; returns 0
+ %b2 = call i1 @bar(i32* @b) ; returns 1
+ %c2 = call i1 @bar(i32* @c) ; returns 1
+ %d02 = call i1 @bar(i32* getelementptr ([2 x i32]* @d, i32 0, i32 0)) ; returns 0
+ %d12 = call i1 @bar(i32* getelementptr ([2 x i32]* @d, i32 0, i32 1)) ; returns 1
+ %e = call i1 @baz(void ()* @e) ; returns 1
+ %f = call i1 @baz(void ()* @f) ; returns 0
+ %g = call i1 @baz(void ()* @g) ; returns 1
+ ret void
+ }
+
+.. _GlobalLayoutBuilder: http://llvm.org/klaus/llvm/blob/master/include/llvm/Transforms/IPO/LowerTypeTests.h
Added: www-releases/trunk/3.9.1/docs/_sources/Vectorizers.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.9.1/docs/_sources/Vectorizers.txt?rev=290368&view=auto
==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/Vectorizers.txt (added)
+++ www-releases/trunk/3.9.1/docs/_sources/Vectorizers.txt Thu Dec 22 14:04:03 2016
@@ -0,0 +1,426 @@
+==========================
+Auto-Vectorization in LLVM
+==========================
+
+.. contents::
+ :local:
+
+LLVM has two vectorizers: The :ref:`Loop Vectorizer <loop-vectorizer>`,
+which operates on Loops, and the :ref:`SLP Vectorizer
+<slp-vectorizer>`. These vectorizers
+focus on different optimization opportunities and use different techniques.
+The SLP vectorizer merges multiple scalars that are found in the code into
+vectors while the Loop Vectorizer widens instructions in loops
+to operate on multiple consecutive iterations.
+
+Both the Loop Vectorizer and the SLP Vectorizer are enabled by default.
+
+.. _loop-vectorizer:
+
+The Loop Vectorizer
+===================
+
+Usage
+-----
+
+The Loop Vectorizer is enabled by default, but it can be disabled
+through clang using the command line flag:
+
+.. code-block:: console
+
+ $ clang ... -fno-vectorize file.c
+
+Command line flags
+^^^^^^^^^^^^^^^^^^
+
+The loop vectorizer uses a cost model to decide on the optimal vectorization factor
+and unroll factor. However, users of the vectorizer can force the vectorizer to use
+specific values. Both 'clang' and 'opt' support the flags below.
+
+Users can control the vectorization SIMD width using the command line flag "-force-vector-width".
+
+.. code-block:: console
+
+ $ clang -mllvm -force-vector-width=8 ...
+ $ opt -loop-vectorize -force-vector-width=8 ...
+
+Users can control the unroll factor using the command line flag "-force-vector-unroll"
+
+.. code-block:: console
+
+ $ clang -mllvm -force-vector-unroll=2 ...
+ $ opt -loop-vectorize -force-vector-unroll=2 ...
+
+Pragma loop hint directives
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The ``#pragma clang loop`` directive allows loop vectorization hints to be
+specified for the subsequent for, while, do-while, or c++11 range-based for
+loop. The directive allows vectorization and interleaving to be enabled or
+disabled. Vector width as well as interleave count can also be manually
+specified. The following example explicitly enables vectorization and
+interleaving:
+
+.. code-block:: c++
+
+ #pragma clang loop vectorize(enable) interleave(enable)
+ while(...) {
+ ...
+ }
+
+The following example implicitly enables vectorization and interleaving by
+specifying a vector width and interleaving count:
+
+.. code-block:: c++
+
+ #pragma clang loop vectorize_width(2) interleave_count(2)
+ for(...) {
+ ...
+ }
+
+See the Clang
+`language extensions
+<http://clang.llvm.org/docs/LanguageExtensions.html#extensions-for-loop-hint-optimizations>`_
+for details.
+
+Diagnostics
+-----------
+
+Many loops cannot be vectorized including loops with complicated control flow,
+unvectorizable types, and unvectorizable calls. The loop vectorizer generates
+optimization remarks which can be queried using command line options to identify
+and diagnose loops that are skipped by the loop-vectorizer.
+
+Optimization remarks are enabled using:
+
+``-Rpass=loop-vectorize`` identifies loops that were successfully vectorized.
+
+``-Rpass-missed=loop-vectorize`` identifies loops that failed vectorization and
+indicates if vectorization was specified.
+
+``-Rpass-analysis=loop-vectorize`` identifies the statements that caused
+vectorization to fail.
+
+Consider the following loop:
+
+.. code-block:: c++
+
+ #pragma clang loop vectorize(enable)
+ for (int i = 0; i < Length; i++) {
+ switch(A[i]) {
+ case 0: A[i] = i*2; break;
+ case 1: A[i] = i; break;
+ default: A[i] = 0;
+ }
+ }
+
+The command line ``-Rpass-missed=loop-vectorized`` prints the remark:
+
+.. code-block:: console
+
+ no_switch.cpp:4:5: remark: loop not vectorized: vectorization is explicitly enabled [-Rpass-missed=loop-vectorize]
+
+And the command line ``-Rpass-analysis=loop-vectorize`` indicates that the
+switch statement cannot be vectorized.
+
+.. code-block:: console
+
+ no_switch.cpp:4:5: remark: loop not vectorized: loop contains a switch statement [-Rpass-analysis=loop-vectorize]
+ switch(A[i]) {
+ ^
+
+To ensure line and column numbers are produced include the command line options
+``-gline-tables-only`` and ``-gcolumn-info``. See the Clang `user manual
+<http://clang.llvm.org/docs/UsersManual.html#options-to-emit-optimization-reports>`_
+for details
+
+Features
+--------
+
+The LLVM Loop Vectorizer has a number of features that allow it to vectorize
+complex loops.
+
+Loops with unknown trip count
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The Loop Vectorizer supports loops with an unknown trip count.
+In the loop below, the iteration ``start`` and ``finish`` points are unknown,
+and the Loop Vectorizer has a mechanism to vectorize loops that do not start
+at zero. In this example, 'n' may not be a multiple of the vector width, and
+the vectorizer has to execute the last few iterations as scalar code. Keeping
+a scalar copy of the loop increases the code size.
+
+.. code-block:: c++
+
+ void bar(float *A, float* B, float K, int start, int end) {
+ for (int i = start; i < end; ++i)
+ A[i] *= B[i] + K;
+ }
+
+Runtime Checks of Pointers
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+In the example below, if the pointers A and B point to consecutive addresses,
+then it is illegal to vectorize the code because some elements of A will be
+written before they are read from array B.
+
+Some programmers use the 'restrict' keyword to notify the compiler that the
+pointers are disjointed, but in our example, the Loop Vectorizer has no way of
+knowing that the pointers A and B are unique. The Loop Vectorizer handles this
+loop by placing code that checks, at runtime, if the arrays A and B point to
+disjointed memory locations. If arrays A and B overlap, then the scalar version
+of the loop is executed.
+
+.. code-block:: c++
+
+ void bar(float *A, float* B, float K, int n) {
+ for (int i = 0; i < n; ++i)
+ A[i] *= B[i] + K;
+ }
+
+
+Reductions
+^^^^^^^^^^
+
+In this example the ``sum`` variable is used by consecutive iterations of
+the loop. Normally, this would prevent vectorization, but the vectorizer can
+detect that 'sum' is a reduction variable. The variable 'sum' becomes a vector
+of integers, and at the end of the loop the elements of the array are added
+together to create the correct result. We support a number of different
+reduction operations, such as addition, multiplication, XOR, AND and OR.
+
+.. code-block:: c++
+
+ int foo(int *A, int *B, int n) {
+ unsigned sum = 0;
+ for (int i = 0; i < n; ++i)
+ sum += A[i] + 5;
+ return sum;
+ }
+
+We support floating point reduction operations when `-ffast-math` is used.
+
+Inductions
+^^^^^^^^^^
+
+In this example the value of the induction variable ``i`` is saved into an
+array. The Loop Vectorizer knows to vectorize induction variables.
+
+.. code-block:: c++
+
+ void bar(float *A, float* B, float K, int n) {
+ for (int i = 0; i < n; ++i)
+ A[i] = i;
+ }
+
+If Conversion
+^^^^^^^^^^^^^
+
+The Loop Vectorizer is able to "flatten" the IF statement in the code and
+generate a single stream of instructions. The Loop Vectorizer supports any
+control flow in the innermost loop. The innermost loop may contain complex
+nesting of IFs, ELSEs and even GOTOs.
+
+.. code-block:: c++
+
+ int foo(int *A, int *B, int n) {
+ unsigned sum = 0;
+ for (int i = 0; i < n; ++i)
+ if (A[i] > B[i])
+ sum += A[i] + 5;
+ return sum;
+ }
+
+Pointer Induction Variables
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This example uses the "accumulate" function of the standard c++ library. This
+loop uses C++ iterators, which are pointers, and not integer indices.
+The Loop Vectorizer detects pointer induction variables and can vectorize
+this loop. This feature is important because many C++ programs use iterators.
+
+.. code-block:: c++
+
+ int baz(int *A, int n) {
+ return std::accumulate(A, A + n, 0);
+ }
+
+Reverse Iterators
+^^^^^^^^^^^^^^^^^
+
+The Loop Vectorizer can vectorize loops that count backwards.
+
+.. code-block:: c++
+
+ int foo(int *A, int *B, int n) {
+ for (int i = n; i > 0; --i)
+ A[i] +=1;
+ }
+
+Scatter / Gather
+^^^^^^^^^^^^^^^^
+
+The Loop Vectorizer can vectorize code that becomes a sequence of scalar instructions
+that scatter/gathers memory.
+
+.. code-block:: c++
+
+ int foo(int * A, int * B, int n) {
+ for (intptr_t i = 0; i < n; ++i)
+ A[i] += B[i * 4];
+ }
+
+In many situations the cost model will inform LLVM that this is not beneficial
+and LLVM will only vectorize such code if forced with "-mllvm -force-vector-width=#".
+
+Vectorization of Mixed Types
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The Loop Vectorizer can vectorize programs with mixed types. The Vectorizer
+cost model can estimate the cost of the type conversion and decide if
+vectorization is profitable.
+
+.. code-block:: c++
+
+ int foo(int *A, char *B, int n, int k) {
+ for (int i = 0; i < n; ++i)
+ A[i] += 4 * B[i];
+ }
+
+Global Structures Alias Analysis
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Access to global structures can also be vectorized, with alias analysis being
+used to make sure accesses don't alias. Run-time checks can also be added on
+pointer access to structure members.
+
+Many variations are supported, but some that rely on undefined behaviour being
+ignored (as other compilers do) are still being left un-vectorized.
+
+.. code-block:: c++
+
+ struct { int A[100], K, B[100]; } Foo;
+
+ int foo() {
+ for (int i = 0; i < 100; ++i)
+ Foo.A[i] = Foo.B[i] + 100;
+ }
+
+Vectorization of function calls
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The Loop Vectorize can vectorize intrinsic math functions.
+See the table below for a list of these functions.
+
++-----+-----+---------+
+| pow | exp | exp2 |
++-----+-----+---------+
+| sin | cos | sqrt |
++-----+-----+---------+
+| log |log2 | log10 |
++-----+-----+---------+
+|fabs |floor| ceil |
++-----+-----+---------+
+|fma |trunc|nearbyint|
++-----+-----+---------+
+| | | fmuladd |
++-----+-----+---------+
+
+The loop vectorizer knows about special instructions on the target and will
+vectorize a loop containing a function call that maps to the instructions. For
+example, the loop below will be vectorized on Intel x86 if the SSE4.1 roundps
+instruction is available.
+
+.. code-block:: c++
+
+ void foo(float *f) {
+ for (int i = 0; i != 1024; ++i)
+ f[i] = floorf(f[i]);
+ }
+
+Partial unrolling during vectorization
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Modern processors feature multiple execution units, and only programs that contain a
+high degree of parallelism can fully utilize the entire width of the machine.
+The Loop Vectorizer increases the instruction level parallelism (ILP) by
+performing partial-unrolling of loops.
+
+In the example below the entire array is accumulated into the variable 'sum'.
+This is inefficient because only a single execution port can be used by the processor.
+By unrolling the code the Loop Vectorizer allows two or more execution ports
+to be used simultaneously.
+
+.. code-block:: c++
+
+ int foo(int *A, int *B, int n) {
+ unsigned sum = 0;
+ for (int i = 0; i < n; ++i)
+ sum += A[i];
+ return sum;
+ }
+
+The Loop Vectorizer uses a cost model to decide when it is profitable to unroll loops.
+The decision to unroll the loop depends on the register pressure and the generated code size.
+
+Performance
+-----------
+
+This section shows the execution time of Clang on a simple benchmark:
+`gcc-loops <http://llvm.org/viewvc/llvm-project/test-suite/trunk/SingleSource/UnitTests/Vectorizer/>`_.
+This benchmarks is a collection of loops from the GCC autovectorization
+`page <http://gcc.gnu.org/projects/tree-ssa/vectorization.html>`_ by Dorit Nuzman.
+
+The chart below compares GCC-4.7, ICC-13, and Clang-SVN with and without loop vectorization at -O3, tuned for "corei7-avx", running on a Sandybridge iMac.
+The Y-axis shows the time in msec. Lower is better. The last column shows the geomean of all the kernels.
+
+.. image:: gcc-loops.png
+
+And Linpack-pc with the same configuration. Result is Mflops, higher is better.
+
+.. image:: linpack-pc.png
+
+.. _slp-vectorizer:
+
+The SLP Vectorizer
+==================
+
+Details
+-------
+
+The goal of SLP vectorization (a.k.a. superword-level parallelism) is
+to combine similar independent instructions
+into vector instructions. Memory accesses, arithmetic operations, comparison
+operations, PHI-nodes, can all be vectorized using this technique.
+
+For example, the following function performs very similar operations on its
+inputs (a1, b1) and (a2, b2). The basic-block vectorizer may combine these
+into vector operations.
+
+.. code-block:: c++
+
+ void foo(int a1, int a2, int b1, int b2, int *A) {
+ A[0] = a1*(a1 + b1)/b1 + 50*b1/a1;
+ A[1] = a2*(a2 + b2)/b2 + 50*b2/a2;
+ }
+
+The SLP-vectorizer processes the code bottom-up, across basic blocks, in search of scalars to combine.
+
+Usage
+------
+
+The SLP Vectorizer is enabled by default, but it can be disabled
+through clang using the command line flag:
+
+.. code-block:: console
+
+ $ clang -fno-slp-vectorize file.c
+
+LLVM has a second basic block vectorization phase
+which is more compile-time intensive (The BB vectorizer). This optimization
+can be enabled through clang using the command line flag:
+
+.. code-block:: console
+
+ $ clang -fslp-vectorize-aggressive file.c
+
Added: www-releases/trunk/3.9.1/docs/_sources/WritingAnLLVMBackend.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.9.1/docs/_sources/WritingAnLLVMBackend.txt?rev=290368&view=auto
==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/WritingAnLLVMBackend.txt (added)
+++ www-releases/trunk/3.9.1/docs/_sources/WritingAnLLVMBackend.txt Thu Dec 22 14:04:03 2016
@@ -0,0 +1,1939 @@
+=======================
+Writing an LLVM Backend
+=======================
+
+.. toctree::
+ :hidden:
+
+ HowToUseInstrMappings
+
+.. contents::
+ :local:
+
+Introduction
+============
+
+This document describes techniques for writing compiler backends that convert
+the LLVM Intermediate Representation (IR) to code for a specified machine or
+other languages. Code intended for a specific machine can take the form of
+either assembly code or binary code (usable for a JIT compiler).
+
+The backend of LLVM features a target-independent code generator that may
+create output for several types of target CPUs --- including X86, PowerPC,
+ARM, and SPARC. The backend may also be used to generate code targeted at SPUs
+of the Cell processor or GPUs to support the execution of compute kernels.
+
+The document focuses on existing examples found in subdirectories of
+``llvm/lib/Target`` in a downloaded LLVM release. In particular, this document
+focuses on the example of creating a static compiler (one that emits text
+assembly) for a SPARC target, because SPARC has fairly standard
+characteristics, such as a RISC instruction set and straightforward calling
+conventions.
+
+Audience
+--------
+
+The audience for this document is anyone who needs to write an LLVM backend to
+generate code for a specific hardware or software target.
+
+Prerequisite Reading
+--------------------
+
+These essential documents must be read before reading this document:
+
+* `LLVM Language Reference Manual <LangRef.html>`_ --- a reference manual for
+ the LLVM assembly language.
+
+* :doc:`CodeGenerator` --- a guide to the components (classes and code
+ generation algorithms) for translating the LLVM internal representation into
+ machine code for a specified target. Pay particular attention to the
+ descriptions of code generation stages: Instruction Selection, Scheduling and
+ Formation, SSA-based Optimization, Register Allocation, Prolog/Epilog Code
+ Insertion, Late Machine Code Optimizations, and Code Emission.
+
+* :doc:`TableGen/index` --- a document that describes the TableGen
+ (``tblgen``) application that manages domain-specific information to support
+ LLVM code generation. TableGen processes input from a target description
+ file (``.td`` suffix) and generates C++ code that can be used for code
+ generation.
+
+* :doc:`WritingAnLLVMPass` --- The assembly printer is a ``FunctionPass``, as
+ are several ``SelectionDAG`` processing steps.
+
+To follow the SPARC examples in this document, have a copy of `The SPARC
+Architecture Manual, Version 8 <http://www.sparc.org/standards/V8.pdf>`_ for
+reference. For details about the ARM instruction set, refer to the `ARM
+Architecture Reference Manual <http://infocenter.arm.com/>`_. For more about
+the GNU Assembler format (``GAS``), see `Using As
+<http://sourceware.org/binutils/docs/as/index.html>`_, especially for the
+assembly printer. "Using As" contains a list of target machine dependent
+features.
+
+Basic Steps
+-----------
+
+To write a compiler backend for LLVM that converts the LLVM IR to code for a
+specified target (machine or other language), follow these steps:
+
+* Create a subclass of the ``TargetMachine`` class that describes
+ characteristics of your target machine. Copy existing examples of specific
+ ``TargetMachine`` class and header files; for example, start with
+ ``SparcTargetMachine.cpp`` and ``SparcTargetMachine.h``, but change the file
+ names for your target. Similarly, change code that references "``Sparc``" to
+ reference your target.
+
+* Describe the register set of the target. Use TableGen to generate code for
+ register definition, register aliases, and register classes from a
+ target-specific ``RegisterInfo.td`` input file. You should also write
+ additional code for a subclass of the ``TargetRegisterInfo`` class that
+ represents the class register file data used for register allocation and also
+ describes the interactions between registers.
+
+* Describe the instruction set of the target. Use TableGen to generate code
+ for target-specific instructions from target-specific versions of
+ ``TargetInstrFormats.td`` and ``TargetInstrInfo.td``. You should write
+ additional code for a subclass of the ``TargetInstrInfo`` class to represent
+ machine instructions supported by the target machine.
+
+* Describe the selection and conversion of the LLVM IR from a Directed Acyclic
+ Graph (DAG) representation of instructions to native target-specific
+ instructions. Use TableGen to generate code that matches patterns and
+ selects instructions based on additional information in a target-specific
+ version of ``TargetInstrInfo.td``. Write code for ``XXXISelDAGToDAG.cpp``,
+ where ``XXX`` identifies the specific target, to perform pattern matching and
+ DAG-to-DAG instruction selection. Also write code in ``XXXISelLowering.cpp``
+ to replace or remove operations and data types that are not supported
+ natively in a SelectionDAG.
+
+* Write code for an assembly printer that converts LLVM IR to a GAS format for
+ your target machine. You should add assembly strings to the instructions
+ defined in your target-specific version of ``TargetInstrInfo.td``. You
+ should also write code for a subclass of ``AsmPrinter`` that performs the
+ LLVM-to-assembly conversion and a trivial subclass of ``TargetAsmInfo``.
+
+* Optionally, add support for subtargets (i.e., variants with different
+ capabilities). You should also write code for a subclass of the
+ ``TargetSubtarget`` class, which allows you to use the ``-mcpu=`` and
+ ``-mattr=`` command-line options.
+
+* Optionally, add JIT support and create a machine code emitter (subclass of
+ ``TargetJITInfo``) that is used to emit binary code directly into memory.
+
+In the ``.cpp`` and ``.h``. files, initially stub up these methods and then
+implement them later. Initially, you may not know which private members that
+the class will need and which components will need to be subclassed.
+
+Preliminaries
+-------------
+
+To actually create your compiler backend, you need to create and modify a few
+files. The absolute minimum is discussed here. But to actually use the LLVM
+target-independent code generator, you must perform the steps described in the
+:doc:`LLVM Target-Independent Code Generator <CodeGenerator>` document.
+
+First, you should create a subdirectory under ``lib/Target`` to hold all the
+files related to your target. If your target is called "Dummy", create the
+directory ``lib/Target/Dummy``.
+
+In this new directory, create a ``CMakeLists.txt``. It is easiest to copy a
+``CMakeLists.txt`` of another target and modify it. It should at least contain
+the ``LLVM_TARGET_DEFINITIONS`` variable. The library can be named ``LLVMDummy``
+(for example, see the MIPS target). Alternatively, you can split the library
+into ``LLVMDummyCodeGen`` and ``LLVMDummyAsmPrinter``, the latter of which
+should be implemented in a subdirectory below ``lib/Target/Dummy`` (for example,
+see the PowerPC target).
+
+Note that these two naming schemes are hardcoded into ``llvm-config``. Using
+any other naming scheme will confuse ``llvm-config`` and produce a lot of
+(seemingly unrelated) linker errors when linking ``llc``.
+
+To make your target actually do something, you need to implement a subclass of
+``TargetMachine``. This implementation should typically be in the file
+``lib/Target/DummyTargetMachine.cpp``, but any file in the ``lib/Target``
+directory will be built and should work. To use LLVM's target independent code
+generator, you should do what all current machine backends do: create a
+subclass of ``LLVMTargetMachine``. (To create a target from scratch, create a
+subclass of ``TargetMachine``.)
+
+To get LLVM to actually build and link your target, you need to run ``cmake``
+with ``-DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD=Dummy``. This will build your
+target without needing to add it to the list of all the targets.
+
+Once your target is stable, you can add it to the ``LLVM_ALL_TARGETS`` variable
+located in the main ``CMakeLists.txt``.
+
+Target Machine
+==============
+
+``LLVMTargetMachine`` is designed as a base class for targets implemented with
+the LLVM target-independent code generator. The ``LLVMTargetMachine`` class
+should be specialized by a concrete target class that implements the various
+virtual methods. ``LLVMTargetMachine`` is defined as a subclass of
+``TargetMachine`` in ``include/llvm/Target/TargetMachine.h``. The
+``TargetMachine`` class implementation (``TargetMachine.cpp``) also processes
+numerous command-line options.
+
+To create a concrete target-specific subclass of ``LLVMTargetMachine``, start
+by copying an existing ``TargetMachine`` class and header. You should name the
+files that you create to reflect your specific target. For instance, for the
+SPARC target, name the files ``SparcTargetMachine.h`` and
+``SparcTargetMachine.cpp``.
+
+For a target machine ``XXX``, the implementation of ``XXXTargetMachine`` must
+have access methods to obtain objects that represent target components. These
+methods are named ``get*Info``, and are intended to obtain the instruction set
+(``getInstrInfo``), register set (``getRegisterInfo``), stack frame layout
+(``getFrameInfo``), and similar information. ``XXXTargetMachine`` must also
+implement the ``getDataLayout`` method to access an object with target-specific
+data characteristics, such as data type size and alignment requirements.
+
+For instance, for the SPARC target, the header file ``SparcTargetMachine.h``
+declares prototypes for several ``get*Info`` and ``getDataLayout`` methods that
+simply return a class member.
+
+.. code-block:: c++
+
+ namespace llvm {
+
+ class Module;
+
+ class SparcTargetMachine : public LLVMTargetMachine {
+ const DataLayout DataLayout; // Calculates type size & alignment
+ SparcSubtarget Subtarget;
+ SparcInstrInfo InstrInfo;
+ TargetFrameInfo FrameInfo;
+
+ protected:
+ virtual const TargetAsmInfo *createTargetAsmInfo() const;
+
+ public:
+ SparcTargetMachine(const Module &M, const std::string &FS);
+
+ virtual const SparcInstrInfo *getInstrInfo() const {return &InstrInfo; }
+ virtual const TargetFrameInfo *getFrameInfo() const {return &FrameInfo; }
+ virtual const TargetSubtarget *getSubtargetImpl() const{return &Subtarget; }
+ virtual const TargetRegisterInfo *getRegisterInfo() const {
+ return &InstrInfo.getRegisterInfo();
+ }
+ virtual const DataLayout *getDataLayout() const { return &DataLayout; }
+ static unsigned getModuleMatchQuality(const Module &M);
+
+ // Pass Pipeline Configuration
+ virtual bool addInstSelector(PassManagerBase &PM, bool Fast);
+ virtual bool addPreEmitPass(PassManagerBase &PM, bool Fast);
+ };
+
+ } // end namespace llvm
+
+* ``getInstrInfo()``
+* ``getRegisterInfo()``
+* ``getFrameInfo()``
+* ``getDataLayout()``
+* ``getSubtargetImpl()``
+
+For some targets, you also need to support the following methods:
+
+* ``getTargetLowering()``
+* ``getJITInfo()``
+
+Some architectures, such as GPUs, do not support jumping to an arbitrary
+program location and implement branching using masked execution and loop using
+special instructions around the loop body. In order to avoid CFG modifications
+that introduce irreducible control flow not handled by such hardware, a target
+must call `setRequiresStructuredCFG(true)` when being initialized.
+
+In addition, the ``XXXTargetMachine`` constructor should specify a
+``TargetDescription`` string that determines the data layout for the target
+machine, including characteristics such as pointer size, alignment, and
+endianness. For example, the constructor for ``SparcTargetMachine`` contains
+the following:
+
+.. code-block:: c++
+
+ SparcTargetMachine::SparcTargetMachine(const Module &M, const std::string &FS)
+ : DataLayout("E-p:32:32-f128:128:128"),
+ Subtarget(M, FS), InstrInfo(Subtarget),
+ FrameInfo(TargetFrameInfo::StackGrowsDown, 8, 0) {
+ }
+
+Hyphens separate portions of the ``TargetDescription`` string.
+
+* An upper-case "``E``" in the string indicates a big-endian target data model.
+ A lower-case "``e``" indicates little-endian.
+
+* "``p:``" is followed by pointer information: size, ABI alignment, and
+ preferred alignment. If only two figures follow "``p:``", then the first
+ value is pointer size, and the second value is both ABI and preferred
+ alignment.
+
+* Then a letter for numeric type alignment: "``i``", "``f``", "``v``", or
+ "``a``" (corresponding to integer, floating point, vector, or aggregate).
+ "``i``", "``v``", or "``a``" are followed by ABI alignment and preferred
+ alignment. "``f``" is followed by three values: the first indicates the size
+ of a long double, then ABI alignment, and then ABI preferred alignment.
+
+Target Registration
+===================
+
+You must also register your target with the ``TargetRegistry``, which is what
+other LLVM tools use to be able to lookup and use your target at runtime. The
+``TargetRegistry`` can be used directly, but for most targets there are helper
+templates which should take care of the work for you.
+
+All targets should declare a global ``Target`` object which is used to
+represent the target during registration. Then, in the target's ``TargetInfo``
+library, the target should define that object and use the ``RegisterTarget``
+template to register the target. For example, the Sparc registration code
+looks like this:
+
+.. code-block:: c++
+
+ Target llvm::TheSparcTarget;
+
+ extern "C" void LLVMInitializeSparcTargetInfo() {
+ RegisterTarget<Triple::sparc, /*HasJIT=*/false>
+ X(TheSparcTarget, "sparc", "Sparc");
+ }
+
+This allows the ``TargetRegistry`` to look up the target by name or by target
+triple. In addition, most targets will also register additional features which
+are available in separate libraries. These registration steps are separate,
+because some clients may wish to only link in some parts of the target --- the
+JIT code generator does not require the use of the assembler printer, for
+example. Here is an example of registering the Sparc assembly printer:
+
+.. code-block:: c++
+
+ extern "C" void LLVMInitializeSparcAsmPrinter() {
+ RegisterAsmPrinter<SparcAsmPrinter> X(TheSparcTarget);
+ }
+
+For more information, see "`llvm/Target/TargetRegistry.h
+</doxygen/TargetRegistry_8h-source.html>`_".
+
+Register Set and Register Classes
+=================================
+
+You should describe a concrete target-specific class that represents the
+register file of a target machine. This class is called ``XXXRegisterInfo``
+(where ``XXX`` identifies the target) and represents the class register file
+data that is used for register allocation. It also describes the interactions
+between registers.
+
+You also need to define register classes to categorize related registers. A
+register class should be added for groups of registers that are all treated the
+same way for some instruction. Typical examples are register classes for
+integer, floating-point, or vector registers. A register allocator allows an
+instruction to use any register in a specified register class to perform the
+instruction in a similar manner. Register classes allocate virtual registers
+to instructions from these sets, and register classes let the
+target-independent register allocator automatically choose the actual
+registers.
+
+Much of the code for registers, including register definition, register
+aliases, and register classes, is generated by TableGen from
+``XXXRegisterInfo.td`` input files and placed in ``XXXGenRegisterInfo.h.inc``
+and ``XXXGenRegisterInfo.inc`` output files. Some of the code in the
+implementation of ``XXXRegisterInfo`` requires hand-coding.
+
+Defining a Register
+-------------------
+
+The ``XXXRegisterInfo.td`` file typically starts with register definitions for
+a target machine. The ``Register`` class (specified in ``Target.td``) is used
+to define an object for each register. The specified string ``n`` becomes the
+``Name`` of the register. The basic ``Register`` object does not have any
+subregisters and does not specify any aliases.
+
+.. code-block:: text
+
+ class Register<string n> {
+ string Namespace = "";
+ string AsmName = n;
+ string Name = n;
+ int SpillSize = 0;
+ int SpillAlignment = 0;
+ list<Register> Aliases = [];
+ list<Register> SubRegs = [];
+ list<int> DwarfNumbers = [];
+ }
+
+For example, in the ``X86RegisterInfo.td`` file, there are register definitions
+that utilize the ``Register`` class, such as:
+
+.. code-block:: text
+
+ def AL : Register<"AL">, DwarfRegNum<[0, 0, 0]>;
+
+This defines the register ``AL`` and assigns it values (with ``DwarfRegNum``)
+that are used by ``gcc``, ``gdb``, or a debug information writer to identify a
+register. For register ``AL``, ``DwarfRegNum`` takes an array of 3 values
+representing 3 different modes: the first element is for X86-64, the second for
+exception handling (EH) on X86-32, and the third is generic. -1 is a special
+Dwarf number that indicates the gcc number is undefined, and -2 indicates the
+register number is invalid for this mode.
+
+From the previously described line in the ``X86RegisterInfo.td`` file, TableGen
+generates this code in the ``X86GenRegisterInfo.inc`` file:
+
+.. code-block:: c++
+
+ static const unsigned GR8[] = { X86::AL, ... };
+
+ const unsigned AL_AliasSet[] = { X86::AX, X86::EAX, X86::RAX, 0 };
+
+ const TargetRegisterDesc RegisterDescriptors[] = {
+ ...
+ { "AL", "AL", AL_AliasSet, Empty_SubRegsSet, Empty_SubRegsSet, AL_SuperRegsSet }, ...
+
+From the register info file, TableGen generates a ``TargetRegisterDesc`` object
+for each register. ``TargetRegisterDesc`` is defined in
+``include/llvm/Target/TargetRegisterInfo.h`` with the following fields:
+
+.. code-block:: c++
+
+ struct TargetRegisterDesc {
+ const char *AsmName; // Assembly language name for the register
+ const char *Name; // Printable name for the reg (for debugging)
+ const unsigned *AliasSet; // Register Alias Set
+ const unsigned *SubRegs; // Sub-register set
+ const unsigned *ImmSubRegs; // Immediate sub-register set
+ const unsigned *SuperRegs; // Super-register set
+ };
+
+TableGen uses the entire target description file (``.td``) to determine text
+names for the register (in the ``AsmName`` and ``Name`` fields of
+``TargetRegisterDesc``) and the relationships of other registers to the defined
+register (in the other ``TargetRegisterDesc`` fields). In this example, other
+definitions establish the registers "``AX``", "``EAX``", and "``RAX``" as
+aliases for one another, so TableGen generates a null-terminated array
+(``AL_AliasSet``) for this register alias set.
+
+The ``Register`` class is commonly used as a base class for more complex
+classes. In ``Target.td``, the ``Register`` class is the base for the
+``RegisterWithSubRegs`` class that is used to define registers that need to
+specify subregisters in the ``SubRegs`` list, as shown here:
+
+.. code-block:: text
+
+ class RegisterWithSubRegs<string n, list<Register> subregs> : Register<n> {
+ let SubRegs = subregs;
+ }
+
+In ``SparcRegisterInfo.td``, additional register classes are defined for SPARC:
+a ``Register`` subclass, ``SparcReg``, and further subclasses: ``Ri``, ``Rf``,
+and ``Rd``. SPARC registers are identified by 5-bit ID numbers, which is a
+feature common to these subclasses. Note the use of "``let``" expressions to
+override values that are initially defined in a superclass (such as ``SubRegs``
+field in the ``Rd`` class).
+
+.. code-block:: text
+
+ class SparcReg<string n> : Register<n> {
+ field bits<5> Num;
+ let Namespace = "SP";
+ }
+ // Ri - 32-bit integer registers
+ class Ri<bits<5> num, string n> :
+ SparcReg<n> {
+ let Num = num;
+ }
+ // Rf - 32-bit floating-point registers
+ class Rf<bits<5> num, string n> :
+ SparcReg<n> {
+ let Num = num;
+ }
+ // Rd - Slots in the FP register file for 64-bit floating-point values.
+ class Rd<bits<5> num, string n, list<Register> subregs> : SparcReg<n> {
+ let Num = num;
+ let SubRegs = subregs;
+ }
+
+In the ``SparcRegisterInfo.td`` file, there are register definitions that
+utilize these subclasses of ``Register``, such as:
+
+.. code-block:: text
+
+ def G0 : Ri< 0, "G0">, DwarfRegNum<[0]>;
+ def G1 : Ri< 1, "G1">, DwarfRegNum<[1]>;
+ ...
+ def F0 : Rf< 0, "F0">, DwarfRegNum<[32]>;
+ def F1 : Rf< 1, "F1">, DwarfRegNum<[33]>;
+ ...
+ def D0 : Rd< 0, "F0", [F0, F1]>, DwarfRegNum<[32]>;
+ def D1 : Rd< 2, "F2", [F2, F3]>, DwarfRegNum<[34]>;
+
+The last two registers shown above (``D0`` and ``D1``) are double-precision
+floating-point registers that are aliases for pairs of single-precision
+floating-point sub-registers. In addition to aliases, the sub-register and
+super-register relationships of the defined register are in fields of a
+register's ``TargetRegisterDesc``.
+
+Defining a Register Class
+-------------------------
+
+The ``RegisterClass`` class (specified in ``Target.td``) is used to define an
+object that represents a group of related registers and also defines the
+default allocation order of the registers. A target description file
+``XXXRegisterInfo.td`` that uses ``Target.td`` can construct register classes
+using the following class:
+
+.. code-block:: text
+
+ class RegisterClass<string namespace,
+ list<ValueType> regTypes, int alignment, dag regList> {
+ string Namespace = namespace;
+ list<ValueType> RegTypes = regTypes;
+ int Size = 0; // spill size, in bits; zero lets tblgen pick the size
+ int Alignment = alignment;
+
+ // CopyCost is the cost of copying a value between two registers
+ // default value 1 means a single instruction
+ // A negative value means copying is extremely expensive or impossible
+ int CopyCost = 1;
+ dag MemberList = regList;
+
+ // for register classes that are subregisters of this class
+ list<RegisterClass> SubRegClassList = [];
+
+ code MethodProtos = [{}]; // to insert arbitrary code
+ code MethodBodies = [{}];
+ }
+
+To define a ``RegisterClass``, use the following 4 arguments:
+
+* The first argument of the definition is the name of the namespace.
+
+* The second argument is a list of ``ValueType`` register type values that are
+ defined in ``include/llvm/CodeGen/ValueTypes.td``. Defined values include
+ integer types (such as ``i16``, ``i32``, and ``i1`` for Boolean),
+ floating-point types (``f32``, ``f64``), and vector types (for example,
+ ``v8i16`` for an ``8 x i16`` vector). All registers in a ``RegisterClass``
+ must have the same ``ValueType``, but some registers may store vector data in
+ different configurations. For example a register that can process a 128-bit
+ vector may be able to handle 16 8-bit integer elements, 8 16-bit integers, 4
+ 32-bit integers, and so on.
+
+* The third argument of the ``RegisterClass`` definition specifies the
+ alignment required of the registers when they are stored or loaded to
+ memory.
+
+* The final argument, ``regList``, specifies which registers are in this class.
+ If an alternative allocation order method is not specified, then ``regList``
+ also defines the order of allocation used by the register allocator. Besides
+ simply listing registers with ``(add R0, R1, ...)``, more advanced set
+ operators are available. See ``include/llvm/Target/Target.td`` for more
+ information.
+
+In ``SparcRegisterInfo.td``, three ``RegisterClass`` objects are defined:
+``FPRegs``, ``DFPRegs``, and ``IntRegs``. For all three register classes, the
+first argument defines the namespace with the string "``SP``". ``FPRegs``
+defines a group of 32 single-precision floating-point registers (``F0`` to
+``F31``); ``DFPRegs`` defines a group of 16 double-precision registers
+(``D0-D15``).
+
+.. code-block:: text
+
+ // F0, F1, F2, ..., F31
+ def FPRegs : RegisterClass<"SP", [f32], 32, (sequence "F%u", 0, 31)>;
+
+ def DFPRegs : RegisterClass<"SP", [f64], 64,
+ (add D0, D1, D2, D3, D4, D5, D6, D7, D8,
+ D9, D10, D11, D12, D13, D14, D15)>;
+
+ def IntRegs : RegisterClass<"SP", [i32], 32,
+ (add L0, L1, L2, L3, L4, L5, L6, L7,
+ I0, I1, I2, I3, I4, I5,
+ O0, O1, O2, O3, O4, O5, O7,
+ G1,
+ // Non-allocatable regs:
+ G2, G3, G4,
+ O6, // stack ptr
+ I6, // frame ptr
+ I7, // return address
+ G0, // constant zero
+ G5, G6, G7 // reserved for kernel
+ )>;
+
+Using ``SparcRegisterInfo.td`` with TableGen generates several output files
+that are intended for inclusion in other source code that you write.
+``SparcRegisterInfo.td`` generates ``SparcGenRegisterInfo.h.inc``, which should
+be included in the header file for the implementation of the SPARC register
+implementation that you write (``SparcRegisterInfo.h``). In
+``SparcGenRegisterInfo.h.inc`` a new structure is defined called
+``SparcGenRegisterInfo`` that uses ``TargetRegisterInfo`` as its base. It also
+specifies types, based upon the defined register classes: ``DFPRegsClass``,
+``FPRegsClass``, and ``IntRegsClass``.
+
+``SparcRegisterInfo.td`` also generates ``SparcGenRegisterInfo.inc``, which is
+included at the bottom of ``SparcRegisterInfo.cpp``, the SPARC register
+implementation. The code below shows only the generated integer registers and
+associated register classes. The order of registers in ``IntRegs`` reflects
+the order in the definition of ``IntRegs`` in the target description file.
+
+.. code-block:: c++
+
+ // IntRegs Register Class...
+ static const unsigned IntRegs[] = {
+ SP::L0, SP::L1, SP::L2, SP::L3, SP::L4, SP::L5,
+ SP::L6, SP::L7, SP::I0, SP::I1, SP::I2, SP::I3,
+ SP::I4, SP::I5, SP::O0, SP::O1, SP::O2, SP::O3,
+ SP::O4, SP::O5, SP::O7, SP::G1, SP::G2, SP::G3,
+ SP::G4, SP::O6, SP::I6, SP::I7, SP::G0, SP::G5,
+ SP::G6, SP::G7,
+ };
+
+ // IntRegsVTs Register Class Value Types...
+ static const MVT::ValueType IntRegsVTs[] = {
+ MVT::i32, MVT::Other
+ };
+
+ namespace SP { // Register class instances
+ DFPRegsClass DFPRegsRegClass;
+ FPRegsClass FPRegsRegClass;
+ IntRegsClass IntRegsRegClass;
+ ...
+ // IntRegs Sub-register Classess...
+ static const TargetRegisterClass* const IntRegsSubRegClasses [] = {
+ NULL
+ };
+ ...
+ // IntRegs Super-register Classess...
+ static const TargetRegisterClass* const IntRegsSuperRegClasses [] = {
+ NULL
+ };
+ ...
+ // IntRegs Register Class sub-classes...
+ static const TargetRegisterClass* const IntRegsSubclasses [] = {
+ NULL
+ };
+ ...
+ // IntRegs Register Class super-classes...
+ static const TargetRegisterClass* const IntRegsSuperclasses [] = {
+ NULL
+ };
+
+ IntRegsClass::IntRegsClass() : TargetRegisterClass(IntRegsRegClassID,
+ IntRegsVTs, IntRegsSubclasses, IntRegsSuperclasses, IntRegsSubRegClasses,
+ IntRegsSuperRegClasses, 4, 4, 1, IntRegs, IntRegs + 32) {}
+ }
+
+The register allocators will avoid using reserved registers, and callee saved
+registers are not used until all the volatile registers have been used. That
+is usually good enough, but in some cases it may be necessary to provide custom
+allocation orders.
+
+Implement a subclass of ``TargetRegisterInfo``
+----------------------------------------------
+
+The final step is to hand code portions of ``XXXRegisterInfo``, which
+implements the interface described in ``TargetRegisterInfo.h`` (see
+:ref:`TargetRegisterInfo`). These functions return ``0``, ``NULL``, or
+``false``, unless overridden. Here is a list of functions that are overridden
+for the SPARC implementation in ``SparcRegisterInfo.cpp``:
+
+* ``getCalleeSavedRegs`` --- Returns a list of callee-saved registers in the
+ order of the desired callee-save stack frame offset.
+
+* ``getReservedRegs`` --- Returns a bitset indexed by physical register
+ numbers, indicating if a particular register is unavailable.
+
+* ``hasFP`` --- Return a Boolean indicating if a function should have a
+ dedicated frame pointer register.
+
+* ``eliminateCallFramePseudoInstr`` --- If call frame setup or destroy pseudo
+ instructions are used, this can be called to eliminate them.
+
+* ``eliminateFrameIndex`` --- Eliminate abstract frame indices from
+ instructions that may use them.
+
+* ``emitPrologue`` --- Insert prologue code into the function.
+
+* ``emitEpilogue`` --- Insert epilogue code into the function.
+
+.. _instruction-set:
+
+Instruction Set
+===============
+
+During the early stages of code generation, the LLVM IR code is converted to a
+``SelectionDAG`` with nodes that are instances of the ``SDNode`` class
+containing target instructions. An ``SDNode`` has an opcode, operands, type
+requirements, and operation properties. For example, is an operation
+commutative, does an operation load from memory. The various operation node
+types are described in the ``include/llvm/CodeGen/SelectionDAGNodes.h`` file
+(values of the ``NodeType`` enum in the ``ISD`` namespace).
+
+TableGen uses the following target description (``.td``) input files to
+generate much of the code for instruction definition:
+
+* ``Target.td`` --- Where the ``Instruction``, ``Operand``, ``InstrInfo``, and
+ other fundamental classes are defined.
+
+* ``TargetSelectionDAG.td`` --- Used by ``SelectionDAG`` instruction selection
+ generators, contains ``SDTC*`` classes (selection DAG type constraint),
+ definitions of ``SelectionDAG`` nodes (such as ``imm``, ``cond``, ``bb``,
+ ``add``, ``fadd``, ``sub``), and pattern support (``Pattern``, ``Pat``,
+ ``PatFrag``, ``PatLeaf``, ``ComplexPattern``.
+
+* ``XXXInstrFormats.td`` --- Patterns for definitions of target-specific
+ instructions.
+
+* ``XXXInstrInfo.td`` --- Target-specific definitions of instruction templates,
+ condition codes, and instructions of an instruction set. For architecture
+ modifications, a different file name may be used. For example, for Pentium
+ with SSE instruction, this file is ``X86InstrSSE.td``, and for Pentium with
+ MMX, this file is ``X86InstrMMX.td``.
+
+There is also a target-specific ``XXX.td`` file, where ``XXX`` is the name of
+the target. The ``XXX.td`` file includes the other ``.td`` input files, but
+its contents are only directly important for subtargets.
+
+You should describe a concrete target-specific class ``XXXInstrInfo`` that
+represents machine instructions supported by a target machine.
+``XXXInstrInfo`` contains an array of ``XXXInstrDescriptor`` objects, each of
+which describes one instruction. An instruction descriptor defines:
+
+* Opcode mnemonic
+* Number of operands
+* List of implicit register definitions and uses
+* Target-independent properties (such as memory access, is commutable)
+* Target-specific flags
+
+The Instruction class (defined in ``Target.td``) is mostly used as a base for
+more complex instruction classes.
+
+.. code-block:: text
+
+ class Instruction {
+ string Namespace = "";
+ dag OutOperandList; // A dag containing the MI def operand list.
+ dag InOperandList; // A dag containing the MI use operand list.
+ string AsmString = ""; // The .s format to print the instruction with.
+ list<dag> Pattern; // Set to the DAG pattern for this instruction.
+ list<Register> Uses = [];
+ list<Register> Defs = [];
+ list<Predicate> Predicates = []; // predicates turned into isel match code
+ ... remainder not shown for space ...
+ }
+
+A ``SelectionDAG`` node (``SDNode``) should contain an object representing a
+target-specific instruction that is defined in ``XXXInstrInfo.td``. The
+instruction objects should represent instructions from the architecture manual
+of the target machine (such as the SPARC Architecture Manual for the SPARC
+target).
+
+A single instruction from the architecture manual is often modeled as multiple
+target instructions, depending upon its operands. For example, a manual might
+describe an add instruction that takes a register or an immediate operand. An
+LLVM target could model this with two instructions named ``ADDri`` and
+``ADDrr``.
+
+You should define a class for each instruction category and define each opcode
+as a subclass of the category with appropriate parameters such as the fixed
+binary encoding of opcodes and extended opcodes. You should map the register
+bits to the bits of the instruction in which they are encoded (for the JIT).
+Also you should specify how the instruction should be printed when the
+automatic assembly printer is used.
+
+As is described in the SPARC Architecture Manual, Version 8, there are three
+major 32-bit formats for instructions. Format 1 is only for the ``CALL``
+instruction. Format 2 is for branch on condition codes and ``SETHI`` (set high
+bits of a register) instructions. Format 3 is for other instructions.
+
+Each of these formats has corresponding classes in ``SparcInstrFormat.td``.
+``InstSP`` is a base class for other instruction classes. Additional base
+classes are specified for more precise formats: for example in
+``SparcInstrFormat.td``, ``F2_1`` is for ``SETHI``, and ``F2_2`` is for
+branches. There are three other base classes: ``F3_1`` for register/register
+operations, ``F3_2`` for register/immediate operations, and ``F3_3`` for
+floating-point operations. ``SparcInstrInfo.td`` also adds the base class
+``Pseudo`` for synthetic SPARC instructions.
+
+``SparcInstrInfo.td`` largely consists of operand and instruction definitions
+for the SPARC target. In ``SparcInstrInfo.td``, the following target
+description file entry, ``LDrr``, defines the Load Integer instruction for a
+Word (the ``LD`` SPARC opcode) from a memory address to a register. The first
+parameter, the value 3 (``11``\ :sub:`2`), is the operation value for this
+category of operation. The second parameter (``000000``\ :sub:`2`) is the
+specific operation value for ``LD``/Load Word. The third parameter is the
+output destination, which is a register operand and defined in the ``Register``
+target description file (``IntRegs``).
+
+.. code-block:: text
+
+ def LDrr : F3_1 <3, 0b000000, (outs IntRegs:$dst), (ins MEMrr:$addr),
+ "ld [$addr], $dst",
+ [(set i32:$dst, (load ADDRrr:$addr))]>;
+
+The fourth parameter is the input source, which uses the address operand
+``MEMrr`` that is defined earlier in ``SparcInstrInfo.td``:
+
+.. code-block:: text
+
+ def MEMrr : Operand<i32> {
+ let PrintMethod = "printMemOperand";
+ let MIOperandInfo = (ops IntRegs, IntRegs);
+ }
+
+The fifth parameter is a string that is used by the assembly printer and can be
+left as an empty string until the assembly printer interface is implemented.
+The sixth and final parameter is the pattern used to match the instruction
+during the SelectionDAG Select Phase described in :doc:`CodeGenerator`.
+This parameter is detailed in the next section, :ref:`instruction-selector`.
+
+Instruction class definitions are not overloaded for different operand types,
+so separate versions of instructions are needed for register, memory, or
+immediate value operands. For example, to perform a Load Integer instruction
+for a Word from an immediate operand to a register, the following instruction
+class is defined:
+
+.. code-block:: text
+
+ def LDri : F3_2 <3, 0b000000, (outs IntRegs:$dst), (ins MEMri:$addr),
+ "ld [$addr], $dst",
+ [(set i32:$dst, (load ADDRri:$addr))]>;
+
+Writing these definitions for so many similar instructions can involve a lot of
+cut and paste. In ``.td`` files, the ``multiclass`` directive enables the
+creation of templates to define several instruction classes at once (using the
+``defm`` directive). For example in ``SparcInstrInfo.td``, the ``multiclass``
+pattern ``F3_12`` is defined to create 2 instruction classes each time
+``F3_12`` is invoked:
+
+.. code-block:: text
+
+ multiclass F3_12 <string OpcStr, bits<6> Op3Val, SDNode OpNode> {
+ def rr : F3_1 <2, Op3Val,
+ (outs IntRegs:$dst), (ins IntRegs:$b, IntRegs:$c),
+ !strconcat(OpcStr, " $b, $c, $dst"),
+ [(set i32:$dst, (OpNode i32:$b, i32:$c))]>;
+ def ri : F3_2 <2, Op3Val,
+ (outs IntRegs:$dst), (ins IntRegs:$b, i32imm:$c),
+ !strconcat(OpcStr, " $b, $c, $dst"),
+ [(set i32:$dst, (OpNode i32:$b, simm13:$c))]>;
+ }
+
+So when the ``defm`` directive is used for the ``XOR`` and ``ADD``
+instructions, as seen below, it creates four instruction objects: ``XORrr``,
+``XORri``, ``ADDrr``, and ``ADDri``.
+
+.. code-block:: text
+
+ defm XOR : F3_12<"xor", 0b000011, xor>;
+ defm ADD : F3_12<"add", 0b000000, add>;
+
+``SparcInstrInfo.td`` also includes definitions for condition codes that are
+referenced by branch instructions. The following definitions in
+``SparcInstrInfo.td`` indicate the bit location of the SPARC condition code.
+For example, the 10\ :sup:`th` bit represents the "greater than" condition for
+integers, and the 22\ :sup:`nd` bit represents the "greater than" condition for
+floats.
+
+.. code-block:: text
+
+ def ICC_NE : ICC_VAL< 9>; // Not Equal
+ def ICC_E : ICC_VAL< 1>; // Equal
+ def ICC_G : ICC_VAL<10>; // Greater
+ ...
+ def FCC_U : FCC_VAL<23>; // Unordered
+ def FCC_G : FCC_VAL<22>; // Greater
+ def FCC_UG : FCC_VAL<21>; // Unordered or Greater
+ ...
+
+(Note that ``Sparc.h`` also defines enums that correspond to the same SPARC
+condition codes. Care must be taken to ensure the values in ``Sparc.h``
+correspond to the values in ``SparcInstrInfo.td``. I.e., ``SPCC::ICC_NE = 9``,
+``SPCC::FCC_U = 23`` and so on.)
+
+Instruction Operand Mapping
+---------------------------
+
+The code generator backend maps instruction operands to fields in the
+instruction. Operands are assigned to unbound fields in the instruction in the
+order they are defined. Fields are bound when they are assigned a value. For
+example, the Sparc target defines the ``XNORrr`` instruction as a ``F3_1``
+format instruction having three operands.
+
+.. code-block:: text
+
+ def XNORrr : F3_1<2, 0b000111,
+ (outs IntRegs:$dst), (ins IntRegs:$b, IntRegs:$c),
+ "xnor $b, $c, $dst",
+ [(set i32:$dst, (not (xor i32:$b, i32:$c)))]>;
+
+The instruction templates in ``SparcInstrFormats.td`` show the base class for
+``F3_1`` is ``InstSP``.
+
+.. code-block:: text
+
+ class InstSP<dag outs, dag ins, string asmstr, list<dag> pattern> : Instruction {
+ field bits<32> Inst;
+ let Namespace = "SP";
+ bits<2> op;
+ let Inst{31-30} = op;
+ dag OutOperandList = outs;
+ dag InOperandList = ins;
+ let AsmString = asmstr;
+ let Pattern = pattern;
+ }
+
+``InstSP`` leaves the ``op`` field unbound.
+
+.. code-block:: text
+
+ class F3<dag outs, dag ins, string asmstr, list<dag> pattern>
+ : InstSP<outs, ins, asmstr, pattern> {
+ bits<5> rd;
+ bits<6> op3;
+ bits<5> rs1;
+ let op{1} = 1; // Op = 2 or 3
+ let Inst{29-25} = rd;
+ let Inst{24-19} = op3;
+ let Inst{18-14} = rs1;
+ }
+
+``F3`` binds the ``op`` field and defines the ``rd``, ``op3``, and ``rs1``
+fields. ``F3`` format instructions will bind the operands ``rd``, ``op3``, and
+``rs1`` fields.
+
+.. code-block:: text
+
+ class F3_1<bits<2> opVal, bits<6> op3val, dag outs, dag ins,
+ string asmstr, list<dag> pattern> : F3<outs, ins, asmstr, pattern> {
+ bits<8> asi = 0; // asi not currently used
+ bits<5> rs2;
+ let op = opVal;
+ let op3 = op3val;
+ let Inst{13} = 0; // i field = 0
+ let Inst{12-5} = asi; // address space identifier
+ let Inst{4-0} = rs2;
+ }
+
+``F3_1`` binds the ``op3`` field and defines the ``rs2`` fields. ``F3_1``
+format instructions will bind the operands to the ``rd``, ``rs1``, and ``rs2``
+fields. This results in the ``XNORrr`` instruction binding ``$dst``, ``$b``,
+and ``$c`` operands to the ``rd``, ``rs1``, and ``rs2`` fields respectively.
+
+Instruction Operand Name Mapping
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+TableGen will also generate a function called getNamedOperandIdx() which
+can be used to look up an operand's index in a MachineInstr based on its
+TableGen name. Setting the UseNamedOperandTable bit in an instruction's
+TableGen definition will add all of its operands to an enumeration in the
+llvm::XXX:OpName namespace and also add an entry for it into the OperandMap
+table, which can be queried using getNamedOperandIdx()
+
+.. code-block:: text
+
+ int DstIndex = SP::getNamedOperandIdx(SP::XNORrr, SP::OpName::dst); // => 0
+ int BIndex = SP::getNamedOperandIdx(SP::XNORrr, SP::OpName::b); // => 1
+ int CIndex = SP::getNamedOperandIdx(SP::XNORrr, SP::OpName::c); // => 2
+ int DIndex = SP::getNamedOperandIdx(SP::XNORrr, SP::OpName::d); // => -1
+
+ ...
+
+The entries in the OpName enum are taken verbatim from the TableGen definitions,
+so operands with lowercase names will have lower case entries in the enum.
+
+To include the getNamedOperandIdx() function in your backend, you will need
+to define a few preprocessor macros in XXXInstrInfo.cpp and XXXInstrInfo.h.
+For example:
+
+XXXInstrInfo.cpp:
+
+.. code-block:: c++
+
+ #define GET_INSTRINFO_NAMED_OPS // For getNamedOperandIdx() function
+ #include "XXXGenInstrInfo.inc"
+
+XXXInstrInfo.h:
+
+.. code-block:: c++
+
+ #define GET_INSTRINFO_OPERAND_ENUM // For OpName enum
+ #include "XXXGenInstrInfo.inc"
+
+ namespace XXX {
+ int16_t getNamedOperandIdx(uint16_t Opcode, uint16_t NamedIndex);
+ } // End namespace XXX
+
+Instruction Operand Types
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+TableGen will also generate an enumeration consisting of all named Operand
+types defined in the backend, in the llvm::XXX::OpTypes namespace.
+Some common immediate Operand types (for instance i8, i32, i64, f32, f64)
+are defined for all targets in ``include/llvm/Target/Target.td``, and are
+available in each Target's OpTypes enum. Also, only named Operand types appear
+in the enumeration: anonymous types are ignored.
+For example, the X86 backend defines ``brtarget`` and ``brtarget8``, both
+instances of the TableGen ``Operand`` class, which represent branch target
+operands:
+
+.. code-block:: text
+
+ def brtarget : Operand<OtherVT>;
+ def brtarget8 : Operand<OtherVT>;
+
+This results in:
+
+.. code-block:: c++
+
+ namespace X86 {
+ namespace OpTypes {
+ enum OperandType {
+ ...
+ brtarget,
+ brtarget8,
+ ...
+ i32imm,
+ i64imm,
+ ...
+ OPERAND_TYPE_LIST_END
+ } // End namespace OpTypes
+ } // End namespace X86
+
+In typical TableGen fashion, to use the enum, you will need to define a
+preprocessor macro:
+
+.. code-block:: c++
+
+ #define GET_INSTRINFO_OPERAND_TYPES_ENUM // For OpTypes enum
+ #include "XXXGenInstrInfo.inc"
+
+
+Instruction Scheduling
+----------------------
+
+Instruction itineraries can be queried using MCDesc::getSchedClass(). The
+value can be named by an enumemation in llvm::XXX::Sched namespace generated
+by TableGen in XXXGenInstrInfo.inc. The name of the schedule classes are
+the same as provided in XXXSchedule.td plus a default NoItinerary class.
+
+Instruction Relation Mapping
+----------------------------
+
+This TableGen feature is used to relate instructions with each other. It is
+particularly useful when you have multiple instruction formats and need to
+switch between them after instruction selection. This entire feature is driven
+by relation models which can be defined in ``XXXInstrInfo.td`` files
+according to the target-specific instruction set. Relation models are defined
+using ``InstrMapping`` class as a base. TableGen parses all the models
+and generates instruction relation maps using the specified information.
+Relation maps are emitted as tables in the ``XXXGenInstrInfo.inc`` file
+along with the functions to query them. For the detailed information on how to
+use this feature, please refer to :doc:`HowToUseInstrMappings`.
+
+Implement a subclass of ``TargetInstrInfo``
+-------------------------------------------
+
+The final step is to hand code portions of ``XXXInstrInfo``, which implements
+the interface described in ``TargetInstrInfo.h`` (see :ref:`TargetInstrInfo`).
+These functions return ``0`` or a Boolean or they assert, unless overridden.
+Here's a list of functions that are overridden for the SPARC implementation in
+``SparcInstrInfo.cpp``:
+
+* ``isLoadFromStackSlot`` --- If the specified machine instruction is a direct
+ load from a stack slot, return the register number of the destination and the
+ ``FrameIndex`` of the stack slot.
+
+* ``isStoreToStackSlot`` --- If the specified machine instruction is a direct
+ store to a stack slot, return the register number of the destination and the
+ ``FrameIndex`` of the stack slot.
+
+* ``copyPhysReg`` --- Copy values between a pair of physical registers.
+
+* ``storeRegToStackSlot`` --- Store a register value to a stack slot.
+
+* ``loadRegFromStackSlot`` --- Load a register value from a stack slot.
+
+* ``storeRegToAddr`` --- Store a register value to memory.
+
+* ``loadRegFromAddr`` --- Load a register value from memory.
+
+* ``foldMemoryOperand`` --- Attempt to combine instructions of any load or
+ store instruction for the specified operand(s).
+
+Branch Folding and If Conversion
+--------------------------------
+
+Performance can be improved by combining instructions or by eliminating
+instructions that are never reached. The ``AnalyzeBranch`` method in
+``XXXInstrInfo`` may be implemented to examine conditional instructions and
+remove unnecessary instructions. ``AnalyzeBranch`` looks at the end of a
+machine basic block (MBB) for opportunities for improvement, such as branch
+folding and if conversion. The ``BranchFolder`` and ``IfConverter`` machine
+function passes (see the source files ``BranchFolding.cpp`` and
+``IfConversion.cpp`` in the ``lib/CodeGen`` directory) call ``AnalyzeBranch``
+to improve the control flow graph that represents the instructions.
+
+Several implementations of ``AnalyzeBranch`` (for ARM, Alpha, and X86) can be
+examined as models for your own ``AnalyzeBranch`` implementation. Since SPARC
+does not implement a useful ``AnalyzeBranch``, the ARM target implementation is
+shown below.
+
+``AnalyzeBranch`` returns a Boolean value and takes four parameters:
+
+* ``MachineBasicBlock &MBB`` --- The incoming block to be examined.
+
+* ``MachineBasicBlock *&TBB`` --- A destination block that is returned. For a
+ conditional branch that evaluates to true, ``TBB`` is the destination.
+
+* ``MachineBasicBlock *&FBB`` --- For a conditional branch that evaluates to
+ false, ``FBB`` is returned as the destination.
+
+* ``std::vector<MachineOperand> &Cond`` --- List of operands to evaluate a
+ condition for a conditional branch.
+
+In the simplest case, if a block ends without a branch, then it falls through
+to the successor block. No destination blocks are specified for either ``TBB``
+or ``FBB``, so both parameters return ``NULL``. The start of the
+``AnalyzeBranch`` (see code below for the ARM target) shows the function
+parameters and the code for the simplest case.
+
+.. code-block:: c++
+
+ bool ARMInstrInfo::AnalyzeBranch(MachineBasicBlock &MBB,
+ MachineBasicBlock *&TBB,
+ MachineBasicBlock *&FBB,
+ std::vector<MachineOperand> &Cond) const
+ {
+ MachineBasicBlock::iterator I = MBB.end();
+ if (I == MBB.begin() || !isUnpredicatedTerminator(--I))
+ return false;
+
+If a block ends with a single unconditional branch instruction, then
+``AnalyzeBranch`` (shown below) should return the destination of that branch in
+the ``TBB`` parameter.
+
+.. code-block:: c++
+
+ if (LastOpc == ARM::B || LastOpc == ARM::tB) {
+ TBB = LastInst->getOperand(0).getMBB();
+ return false;
+ }
+
+If a block ends with two unconditional branches, then the second branch is
+never reached. In that situation, as shown below, remove the last branch
+instruction and return the penultimate branch in the ``TBB`` parameter.
+
+.. code-block:: c++
+
+ if ((SecondLastOpc == ARM::B || SecondLastOpc == ARM::tB) &&
+ (LastOpc == ARM::B || LastOpc == ARM::tB)) {
+ TBB = SecondLastInst->getOperand(0).getMBB();
+ I = LastInst;
+ I->eraseFromParent();
+ return false;
+ }
+
+A block may end with a single conditional branch instruction that falls through
+to successor block if the condition evaluates to false. In that case,
+``AnalyzeBranch`` (shown below) should return the destination of that
+conditional branch in the ``TBB`` parameter and a list of operands in the
+``Cond`` parameter to evaluate the condition.
+
+.. code-block:: c++
+
+ if (LastOpc == ARM::Bcc || LastOpc == ARM::tBcc) {
+ // Block ends with fall-through condbranch.
+ TBB = LastInst->getOperand(0).getMBB();
+ Cond.push_back(LastInst->getOperand(1));
+ Cond.push_back(LastInst->getOperand(2));
+ return false;
+ }
+
+If a block ends with both a conditional branch and an ensuing unconditional
+branch, then ``AnalyzeBranch`` (shown below) should return the conditional
+branch destination (assuming it corresponds to a conditional evaluation of
+"``true``") in the ``TBB`` parameter and the unconditional branch destination
+in the ``FBB`` (corresponding to a conditional evaluation of "``false``"). A
+list of operands to evaluate the condition should be returned in the ``Cond``
+parameter.
+
+.. code-block:: c++
+
+ unsigned SecondLastOpc = SecondLastInst->getOpcode();
+
+ if ((SecondLastOpc == ARM::Bcc && LastOpc == ARM::B) ||
+ (SecondLastOpc == ARM::tBcc && LastOpc == ARM::tB)) {
+ TBB = SecondLastInst->getOperand(0).getMBB();
+ Cond.push_back(SecondLastInst->getOperand(1));
+ Cond.push_back(SecondLastInst->getOperand(2));
+ FBB = LastInst->getOperand(0).getMBB();
+ return false;
+ }
+
+For the last two cases (ending with a single conditional branch or ending with
+one conditional and one unconditional branch), the operands returned in the
+``Cond`` parameter can be passed to methods of other instructions to create new
+branches or perform other operations. An implementation of ``AnalyzeBranch``
+requires the helper methods ``RemoveBranch`` and ``InsertBranch`` to manage
+subsequent operations.
+
+``AnalyzeBranch`` should return false indicating success in most circumstances.
+``AnalyzeBranch`` should only return true when the method is stumped about what
+to do, for example, if a block has three terminating branches.
+``AnalyzeBranch`` may return true if it encounters a terminator it cannot
+handle, such as an indirect branch.
+
+.. _instruction-selector:
+
+Instruction Selector
+====================
+
+LLVM uses a ``SelectionDAG`` to represent LLVM IR instructions, and nodes of
+the ``SelectionDAG`` ideally represent native target instructions. During code
+generation, instruction selection passes are performed to convert non-native
+DAG instructions into native target-specific instructions. The pass described
+in ``XXXISelDAGToDAG.cpp`` is used to match patterns and perform DAG-to-DAG
+instruction selection. Optionally, a pass may be defined (in
+``XXXBranchSelector.cpp``) to perform similar DAG-to-DAG operations for branch
+instructions. Later, the code in ``XXXISelLowering.cpp`` replaces or removes
+operations and data types not supported natively (legalizes) in a
+``SelectionDAG``.
+
+TableGen generates code for instruction selection using the following target
+description input files:
+
+* ``XXXInstrInfo.td`` --- Contains definitions of instructions in a
+ target-specific instruction set, generates ``XXXGenDAGISel.inc``, which is
+ included in ``XXXISelDAGToDAG.cpp``.
+
+* ``XXXCallingConv.td`` --- Contains the calling and return value conventions
+ for the target architecture, and it generates ``XXXGenCallingConv.inc``,
+ which is included in ``XXXISelLowering.cpp``.
+
+The implementation of an instruction selection pass must include a header that
+declares the ``FunctionPass`` class or a subclass of ``FunctionPass``. In
+``XXXTargetMachine.cpp``, a Pass Manager (PM) should add each instruction
+selection pass into the queue of passes to run.
+
+The LLVM static compiler (``llc``) is an excellent tool for visualizing the
+contents of DAGs. To display the ``SelectionDAG`` before or after specific
+processing phases, use the command line options for ``llc``, described at
+:ref:`SelectionDAG-Process`.
+
+To describe instruction selector behavior, you should add patterns for lowering
+LLVM code into a ``SelectionDAG`` as the last parameter of the instruction
+definitions in ``XXXInstrInfo.td``. For example, in ``SparcInstrInfo.td``,
+this entry defines a register store operation, and the last parameter describes
+a pattern with the store DAG operator.
+
+.. code-block:: text
+
+ def STrr : F3_1< 3, 0b000100, (outs), (ins MEMrr:$addr, IntRegs:$src),
+ "st $src, [$addr]", [(store i32:$src, ADDRrr:$addr)]>;
+
+``ADDRrr`` is a memory mode that is also defined in ``SparcInstrInfo.td``:
+
+.. code-block:: text
+
+ def ADDRrr : ComplexPattern<i32, 2, "SelectADDRrr", [], []>;
+
+The definition of ``ADDRrr`` refers to ``SelectADDRrr``, which is a function
+defined in an implementation of the Instructor Selector (such as
+``SparcISelDAGToDAG.cpp``).
+
+In ``lib/Target/TargetSelectionDAG.td``, the DAG operator for store is defined
+below:
+
+.. code-block:: text
+
+ def store : PatFrag<(ops node:$val, node:$ptr),
+ (st node:$val, node:$ptr), [{
+ if (StoreSDNode *ST = dyn_cast<StoreSDNode>(N))
+ return !ST->isTruncatingStore() &&
+ ST->getAddressingMode() == ISD::UNINDEXED;
+ return false;
+ }]>;
+
+``XXXInstrInfo.td`` also generates (in ``XXXGenDAGISel.inc``) the
+``SelectCode`` method that is used to call the appropriate processing method
+for an instruction. In this example, ``SelectCode`` calls ``Select_ISD_STORE``
+for the ``ISD::STORE`` opcode.
+
+.. code-block:: c++
+
+ SDNode *SelectCode(SDValue N) {
+ ...
+ MVT::ValueType NVT = N.getNode()->getValueType(0);
+ switch (N.getOpcode()) {
+ case ISD::STORE: {
+ switch (NVT) {
+ default:
+ return Select_ISD_STORE(N);
+ break;
+ }
+ break;
+ }
+ ...
+
+The pattern for ``STrr`` is matched, so elsewhere in ``XXXGenDAGISel.inc``,
+code for ``STrr`` is created for ``Select_ISD_STORE``. The ``Emit_22`` method
+is also generated in ``XXXGenDAGISel.inc`` to complete the processing of this
+instruction.
+
+.. code-block:: c++
+
+ SDNode *Select_ISD_STORE(const SDValue &N) {
+ SDValue Chain = N.getOperand(0);
+ if (Predicate_store(N.getNode())) {
+ SDValue N1 = N.getOperand(1);
+ SDValue N2 = N.getOperand(2);
+ SDValue CPTmp0;
+ SDValue CPTmp1;
+
+ // Pattern: (st:void i32:i32:$src,
+ // ADDRrr:i32:$addr)<<P:Predicate_store>>
+ // Emits: (STrr:void ADDRrr:i32:$addr, IntRegs:i32:$src)
+ // Pattern complexity = 13 cost = 1 size = 0
+ if (SelectADDRrr(N, N2, CPTmp0, CPTmp1) &&
+ N1.getNode()->getValueType(0) == MVT::i32 &&
+ N2.getNode()->getValueType(0) == MVT::i32) {
+ return Emit_22(N, SP::STrr, CPTmp0, CPTmp1);
+ }
+ ...
+
+The SelectionDAG Legalize Phase
+-------------------------------
+
+The Legalize phase converts a DAG to use types and operations that are natively
+supported by the target. For natively unsupported types and operations, you
+need to add code to the target-specific ``XXXTargetLowering`` implementation to
+convert unsupported types and operations to supported ones.
+
+In the constructor for the ``XXXTargetLowering`` class, first use the
+``addRegisterClass`` method to specify which types are supported and which
+register classes are associated with them. The code for the register classes
+are generated by TableGen from ``XXXRegisterInfo.td`` and placed in
+``XXXGenRegisterInfo.h.inc``. For example, the implementation of the
+constructor for the SparcTargetLowering class (in ``SparcISelLowering.cpp``)
+starts with the following code:
+
+.. code-block:: c++
+
+ addRegisterClass(MVT::i32, SP::IntRegsRegisterClass);
+ addRegisterClass(MVT::f32, SP::FPRegsRegisterClass);
+ addRegisterClass(MVT::f64, SP::DFPRegsRegisterClass);
+
+You should examine the node types in the ``ISD`` namespace
+(``include/llvm/CodeGen/SelectionDAGNodes.h``) and determine which operations
+the target natively supports. For operations that do **not** have native
+support, add a callback to the constructor for the ``XXXTargetLowering`` class,
+so the instruction selection process knows what to do. The ``TargetLowering``
+class callback methods (declared in ``llvm/Target/TargetLowering.h``) are:
+
+* ``setOperationAction`` --- General operation.
+* ``setLoadExtAction`` --- Load with extension.
+* ``setTruncStoreAction`` --- Truncating store.
+* ``setIndexedLoadAction`` --- Indexed load.
+* ``setIndexedStoreAction`` --- Indexed store.
+* ``setConvertAction`` --- Type conversion.
+* ``setCondCodeAction`` --- Support for a given condition code.
+
+Note: on older releases, ``setLoadXAction`` is used instead of
+``setLoadExtAction``. Also, on older releases, ``setCondCodeAction`` may not
+be supported. Examine your release to see what methods are specifically
+supported.
+
+These callbacks are used to determine that an operation does or does not work
+with a specified type (or types). And in all cases, the third parameter is a
+``LegalAction`` type enum value: ``Promote``, ``Expand``, ``Custom``, or
+``Legal``. ``SparcISelLowering.cpp`` contains examples of all four
+``LegalAction`` values.
+
+Promote
+^^^^^^^
+
+For an operation without native support for a given type, the specified type
+may be promoted to a larger type that is supported. For example, SPARC does
+not support a sign-extending load for Boolean values (``i1`` type), so in
+``SparcISelLowering.cpp`` the third parameter below, ``Promote``, changes
+``i1`` type values to a large type before loading.
+
+.. code-block:: c++
+
+ setLoadExtAction(ISD::SEXTLOAD, MVT::i1, Promote);
+
+Expand
+^^^^^^
+
+For a type without native support, a value may need to be broken down further,
+rather than promoted. For an operation without native support, a combination
+of other operations may be used to similar effect. In SPARC, the
+floating-point sine and cosine trig operations are supported by expansion to
+other operations, as indicated by the third parameter, ``Expand``, to
+``setOperationAction``:
+
+.. code-block:: c++
+
+ setOperationAction(ISD::FSIN, MVT::f32, Expand);
+ setOperationAction(ISD::FCOS, MVT::f32, Expand);
+
+Custom
+^^^^^^
+
+For some operations, simple type promotion or operation expansion may be
+insufficient. In some cases, a special intrinsic function must be implemented.
+
+For example, a constant value may require special treatment, or an operation
+may require spilling and restoring registers in the stack and working with
+register allocators.
+
+As seen in ``SparcISelLowering.cpp`` code below, to perform a type conversion
+from a floating point value to a signed integer, first the
+``setOperationAction`` should be called with ``Custom`` as the third parameter:
+
+.. code-block:: c++
+
+ setOperationAction(ISD::FP_TO_SINT, MVT::i32, Custom);
+
+In the ``LowerOperation`` method, for each ``Custom`` operation, a case
+statement should be added to indicate what function to call. In the following
+code, an ``FP_TO_SINT`` opcode will call the ``LowerFP_TO_SINT`` method:
+
+.. code-block:: c++
+
+ SDValue SparcTargetLowering::LowerOperation(SDValue Op, SelectionDAG &DAG) {
+ switch (Op.getOpcode()) {
+ case ISD::FP_TO_SINT: return LowerFP_TO_SINT(Op, DAG);
+ ...
+ }
+ }
+
+Finally, the ``LowerFP_TO_SINT`` method is implemented, using an FP register to
+convert the floating-point value to an integer.
+
+.. code-block:: c++
+
+ static SDValue LowerFP_TO_SINT(SDValue Op, SelectionDAG &DAG) {
+ assert(Op.getValueType() == MVT::i32);
+ Op = DAG.getNode(SPISD::FTOI, MVT::f32, Op.getOperand(0));
+ return DAG.getNode(ISD::BITCAST, MVT::i32, Op);
+ }
+
+Legal
+^^^^^
+
+The ``Legal`` ``LegalizeAction`` enum value simply indicates that an operation
+**is** natively supported. ``Legal`` represents the default condition, so it
+is rarely used. In ``SparcISelLowering.cpp``, the action for ``CTPOP`` (an
+operation to count the bits set in an integer) is natively supported only for
+SPARC v9. The following code enables the ``Expand`` conversion technique for
+non-v9 SPARC implementations.
+
+.. code-block:: c++
+
+ setOperationAction(ISD::CTPOP, MVT::i32, Expand);
+ ...
+ if (TM.getSubtarget<SparcSubtarget>().isV9())
+ setOperationAction(ISD::CTPOP, MVT::i32, Legal);
+
+Calling Conventions
+-------------------
+
+To support target-specific calling conventions, ``XXXGenCallingConv.td`` uses
+interfaces (such as ``CCIfType`` and ``CCAssignToReg``) that are defined in
+``lib/Target/TargetCallingConv.td``. TableGen can take the target descriptor
+file ``XXXGenCallingConv.td`` and generate the header file
+``XXXGenCallingConv.inc``, which is typically included in
+``XXXISelLowering.cpp``. You can use the interfaces in
+``TargetCallingConv.td`` to specify:
+
+* The order of parameter allocation.
+
+* Where parameters and return values are placed (that is, on the stack or in
+ registers).
+
+* Which registers may be used.
+
+* Whether the caller or callee unwinds the stack.
+
+The following example demonstrates the use of the ``CCIfType`` and
+``CCAssignToReg`` interfaces. If the ``CCIfType`` predicate is true (that is,
+if the current argument is of type ``f32`` or ``f64``), then the action is
+performed. In this case, the ``CCAssignToReg`` action assigns the argument
+value to the first available register: either ``R0`` or ``R1``.
+
+.. code-block:: text
+
+ CCIfType<[f32,f64], CCAssignToReg<[R0, R1]>>
+
+``SparcCallingConv.td`` contains definitions for a target-specific return-value
+calling convention (``RetCC_Sparc32``) and a basic 32-bit C calling convention
+(``CC_Sparc32``). The definition of ``RetCC_Sparc32`` (shown below) indicates
+which registers are used for specified scalar return types. A single-precision
+float is returned to register ``F0``, and a double-precision float goes to
+register ``D0``. A 32-bit integer is returned in register ``I0`` or ``I1``.
+
+.. code-block:: text
+
+ def RetCC_Sparc32 : CallingConv<[
+ CCIfType<[i32], CCAssignToReg<[I0, I1]>>,
+ CCIfType<[f32], CCAssignToReg<[F0]>>,
+ CCIfType<[f64], CCAssignToReg<[D0]>>
+ ]>;
+
+The definition of ``CC_Sparc32`` in ``SparcCallingConv.td`` introduces
+``CCAssignToStack``, which assigns the value to a stack slot with the specified
+size and alignment. In the example below, the first parameter, 4, indicates
+the size of the slot, and the second parameter, also 4, indicates the stack
+alignment along 4-byte units. (Special cases: if size is zero, then the ABI
+size is used; if alignment is zero, then the ABI alignment is used.)
+
+.. code-block:: text
+
+ def CC_Sparc32 : CallingConv<[
+ // All arguments get passed in integer registers if there is space.
+ CCIfType<[i32, f32, f64], CCAssignToReg<[I0, I1, I2, I3, I4, I5]>>,
+ CCAssignToStack<4, 4>
+ ]>;
+
+``CCDelegateTo`` is another commonly used interface, which tries to find a
+specified sub-calling convention, and, if a match is found, it is invoked. In
+the following example (in ``X86CallingConv.td``), the definition of
+``RetCC_X86_32_C`` ends with ``CCDelegateTo``. After the current value is
+assigned to the register ``ST0`` or ``ST1``, the ``RetCC_X86Common`` is
+invoked.
+
+.. code-block:: text
+
+ def RetCC_X86_32_C : CallingConv<[
+ CCIfType<[f32], CCAssignToReg<[ST0, ST1]>>,
+ CCIfType<[f64], CCAssignToReg<[ST0, ST1]>>,
+ CCDelegateTo<RetCC_X86Common>
+ ]>;
+
+``CCIfCC`` is an interface that attempts to match the given name to the current
+calling convention. If the name identifies the current calling convention,
+then a specified action is invoked. In the following example (in
+``X86CallingConv.td``), if the ``Fast`` calling convention is in use, then
+``RetCC_X86_32_Fast`` is invoked. If the ``SSECall`` calling convention is in
+use, then ``RetCC_X86_32_SSE`` is invoked.
+
+.. code-block:: text
+
+ def RetCC_X86_32 : CallingConv<[
+ CCIfCC<"CallingConv::Fast", CCDelegateTo<RetCC_X86_32_Fast>>,
+ CCIfCC<"CallingConv::X86_SSECall", CCDelegateTo<RetCC_X86_32_SSE>>,
+ CCDelegateTo<RetCC_X86_32_C>
+ ]>;
+
+Other calling convention interfaces include:
+
+* ``CCIf <predicate, action>`` --- If the predicate matches, apply the action.
+
+* ``CCIfInReg <action>`` --- If the argument is marked with the "``inreg``"
+ attribute, then apply the action.
+
+* ``CCIfNest <action>`` --- If the argument is marked with the "``nest``"
+ attribute, then apply the action.
+
+* ``CCIfNotVarArg <action>`` --- If the current function does not take a
+ variable number of arguments, apply the action.
+
+* ``CCAssignToRegWithShadow <registerList, shadowList>`` --- similar to
+ ``CCAssignToReg``, but with a shadow list of registers.
+
+* ``CCPassByVal <size, align>`` --- Assign value to a stack slot with the
+ minimum specified size and alignment.
+
+* ``CCPromoteToType <type>`` --- Promote the current value to the specified
+ type.
+
+* ``CallingConv <[actions]>`` --- Define each calling convention that is
+ supported.
+
+Assembly Printer
+================
+
+During the code emission stage, the code generator may utilize an LLVM pass to
+produce assembly output. To do this, you want to implement the code for a
+printer that converts LLVM IR to a GAS-format assembly language for your target
+machine, using the following steps:
+
+* Define all the assembly strings for your target, adding them to the
+ instructions defined in the ``XXXInstrInfo.td`` file. (See
+ :ref:`instruction-set`.) TableGen will produce an output file
+ (``XXXGenAsmWriter.inc``) with an implementation of the ``printInstruction``
+ method for the ``XXXAsmPrinter`` class.
+
+* Write ``XXXTargetAsmInfo.h``, which contains the bare-bones declaration of
+ the ``XXXTargetAsmInfo`` class (a subclass of ``TargetAsmInfo``).
+
+* Write ``XXXTargetAsmInfo.cpp``, which contains target-specific values for
+ ``TargetAsmInfo`` properties and sometimes new implementations for methods.
+
+* Write ``XXXAsmPrinter.cpp``, which implements the ``AsmPrinter`` class that
+ performs the LLVM-to-assembly conversion.
+
+The code in ``XXXTargetAsmInfo.h`` is usually a trivial declaration of the
+``XXXTargetAsmInfo`` class for use in ``XXXTargetAsmInfo.cpp``. Similarly,
+``XXXTargetAsmInfo.cpp`` usually has a few declarations of ``XXXTargetAsmInfo``
+replacement values that override the default values in ``TargetAsmInfo.cpp``.
+For example in ``SparcTargetAsmInfo.cpp``:
+
+.. code-block:: c++
+
+ SparcTargetAsmInfo::SparcTargetAsmInfo(const SparcTargetMachine &TM) {
+ Data16bitsDirective = "\t.half\t";
+ Data32bitsDirective = "\t.word\t";
+ Data64bitsDirective = 0; // .xword is only supported by V9.
+ ZeroDirective = "\t.skip\t";
+ CommentString = "!";
+ ConstantPoolSection = "\t.section \".rodata\",#alloc\n";
+ }
+
+The X86 assembly printer implementation (``X86TargetAsmInfo``) is an example
+where the target specific ``TargetAsmInfo`` class uses an overridden methods:
+``ExpandInlineAsm``.
+
+A target-specific implementation of ``AsmPrinter`` is written in
+``XXXAsmPrinter.cpp``, which implements the ``AsmPrinter`` class that converts
+the LLVM to printable assembly. The implementation must include the following
+headers that have declarations for the ``AsmPrinter`` and
+``MachineFunctionPass`` classes. The ``MachineFunctionPass`` is a subclass of
+``FunctionPass``.
+
+.. code-block:: c++
+
+ #include "llvm/CodeGen/AsmPrinter.h"
+ #include "llvm/CodeGen/MachineFunctionPass.h"
+
+As a ``FunctionPass``, ``AsmPrinter`` first calls ``doInitialization`` to set
+up the ``AsmPrinter``. In ``SparcAsmPrinter``, a ``Mangler`` object is
+instantiated to process variable names.
+
+In ``XXXAsmPrinter.cpp``, the ``runOnMachineFunction`` method (declared in
+``MachineFunctionPass``) must be implemented for ``XXXAsmPrinter``. In
+``MachineFunctionPass``, the ``runOnFunction`` method invokes
+``runOnMachineFunction``. Target-specific implementations of
+``runOnMachineFunction`` differ, but generally do the following to process each
+machine function:
+
+* Call ``SetupMachineFunction`` to perform initialization.
+
+* Call ``EmitConstantPool`` to print out (to the output stream) constants which
+ have been spilled to memory.
+
+* Call ``EmitJumpTableInfo`` to print out jump tables used by the current
+ function.
+
+* Print out the label for the current function.
+
+* Print out the code for the function, including basic block labels and the
+ assembly for the instruction (using ``printInstruction``)
+
+The ``XXXAsmPrinter`` implementation must also include the code generated by
+TableGen that is output in the ``XXXGenAsmWriter.inc`` file. The code in
+``XXXGenAsmWriter.inc`` contains an implementation of the ``printInstruction``
+method that may call these methods:
+
+* ``printOperand``
+* ``printMemOperand``
+* ``printCCOperand`` (for conditional statements)
+* ``printDataDirective``
+* ``printDeclare``
+* ``printImplicitDef``
+* ``printInlineAsm``
+
+The implementations of ``printDeclare``, ``printImplicitDef``,
+``printInlineAsm``, and ``printLabel`` in ``AsmPrinter.cpp`` are generally
+adequate for printing assembly and do not need to be overridden.
+
+The ``printOperand`` method is implemented with a long ``switch``/``case``
+statement for the type of operand: register, immediate, basic block, external
+symbol, global address, constant pool index, or jump table index. For an
+instruction with a memory address operand, the ``printMemOperand`` method
+should be implemented to generate the proper output. Similarly,
+``printCCOperand`` should be used to print a conditional operand.
+
+``doFinalization`` should be overridden in ``XXXAsmPrinter``, and it should be
+called to shut down the assembly printer. During ``doFinalization``, global
+variables and constants are printed to output.
+
+Subtarget Support
+=================
+
+Subtarget support is used to inform the code generation process of instruction
+set variations for a given chip set. For example, the LLVM SPARC
+implementation provided covers three major versions of the SPARC microprocessor
+architecture: Version 8 (V8, which is a 32-bit architecture), Version 9 (V9, a
+64-bit architecture), and the UltraSPARC architecture. V8 has 16
+double-precision floating-point registers that are also usable as either 32
+single-precision or 8 quad-precision registers. V8 is also purely big-endian.
+V9 has 32 double-precision floating-point registers that are also usable as 16
+quad-precision registers, but cannot be used as single-precision registers.
+The UltraSPARC architecture combines V9 with UltraSPARC Visual Instruction Set
+extensions.
+
+If subtarget support is needed, you should implement a target-specific
+``XXXSubtarget`` class for your architecture. This class should process the
+command-line options ``-mcpu=`` and ``-mattr=``.
+
+TableGen uses definitions in the ``Target.td`` and ``Sparc.td`` files to
+generate code in ``SparcGenSubtarget.inc``. In ``Target.td``, shown below, the
+``SubtargetFeature`` interface is defined. The first 4 string parameters of
+the ``SubtargetFeature`` interface are a feature name, an attribute set by the
+feature, the value of the attribute, and a description of the feature. (The
+fifth parameter is a list of features whose presence is implied, and its
+default value is an empty array.)
+
+.. code-block:: text
+
+ class SubtargetFeature<string n, string a, string v, string d,
+ list<SubtargetFeature> i = []> {
+ string Name = n;
+ string Attribute = a;
+ string Value = v;
+ string Desc = d;
+ list<SubtargetFeature> Implies = i;
+ }
+
+In the ``Sparc.td`` file, the ``SubtargetFeature`` is used to define the
+following features.
+
+.. code-block:: text
+
+ def FeatureV9 : SubtargetFeature<"v9", "IsV9", "true",
+ "Enable SPARC-V9 instructions">;
+ def FeatureV8Deprecated : SubtargetFeature<"deprecated-v8",
+ "V8DeprecatedInsts", "true",
+ "Enable deprecated V8 instructions in V9 mode">;
+ def FeatureVIS : SubtargetFeature<"vis", "IsVIS", "true",
+ "Enable UltraSPARC Visual Instruction Set extensions">;
+
+Elsewhere in ``Sparc.td``, the ``Proc`` class is defined and then is used to
+define particular SPARC processor subtypes that may have the previously
+described features.
+
+.. code-block:: text
+
+ class Proc<string Name, list<SubtargetFeature> Features>
+ : Processor<Name, NoItineraries, Features>;
+
+ def : Proc<"generic", []>;
+ def : Proc<"v8", []>;
+ def : Proc<"supersparc", []>;
+ def : Proc<"sparclite", []>;
+ def : Proc<"f934", []>;
+ def : Proc<"hypersparc", []>;
+ def : Proc<"sparclite86x", []>;
+ def : Proc<"sparclet", []>;
+ def : Proc<"tsc701", []>;
+ def : Proc<"v9", [FeatureV9]>;
+ def : Proc<"ultrasparc", [FeatureV9, FeatureV8Deprecated]>;
+ def : Proc<"ultrasparc3", [FeatureV9, FeatureV8Deprecated]>;
+ def : Proc<"ultrasparc3-vis", [FeatureV9, FeatureV8Deprecated, FeatureVIS]>;
+
+From ``Target.td`` and ``Sparc.td`` files, the resulting
+``SparcGenSubtarget.inc`` specifies enum values to identify the features,
+arrays of constants to represent the CPU features and CPU subtypes, and the
+``ParseSubtargetFeatures`` method that parses the features string that sets
+specified subtarget options. The generated ``SparcGenSubtarget.inc`` file
+should be included in the ``SparcSubtarget.cpp``. The target-specific
+implementation of the ``XXXSubtarget`` method should follow this pseudocode:
+
+.. code-block:: c++
+
+ XXXSubtarget::XXXSubtarget(const Module &M, const std::string &FS) {
+ // Set the default features
+ // Determine default and user specified characteristics of the CPU
+ // Call ParseSubtargetFeatures(FS, CPU) to parse the features string
+ // Perform any additional operations
+ }
+
+JIT Support
+===========
+
+The implementation of a target machine optionally includes a Just-In-Time (JIT)
+code generator that emits machine code and auxiliary structures as binary
+output that can be written directly to memory. To do this, implement JIT code
+generation by performing the following steps:
+
+* Write an ``XXXCodeEmitter.cpp`` file that contains a machine function pass
+ that transforms target-machine instructions into relocatable machine
+ code.
+
+* Write an ``XXXJITInfo.cpp`` file that implements the JIT interfaces for
+ target-specific code-generation activities, such as emitting machine code and
+ stubs.
+
+* Modify ``XXXTargetMachine`` so that it provides a ``TargetJITInfo`` object
+ through its ``getJITInfo`` method.
+
+There are several different approaches to writing the JIT support code. For
+instance, TableGen and target descriptor files may be used for creating a JIT
+code generator, but are not mandatory. For the Alpha and PowerPC target
+machines, TableGen is used to generate ``XXXGenCodeEmitter.inc``, which
+contains the binary coding of machine instructions and the
+``getBinaryCodeForInstr`` method to access those codes. Other JIT
+implementations do not.
+
+Both ``XXXJITInfo.cpp`` and ``XXXCodeEmitter.cpp`` must include the
+``llvm/CodeGen/MachineCodeEmitter.h`` header file that defines the
+``MachineCodeEmitter`` class containing code for several callback functions
+that write data (in bytes, words, strings, etc.) to the output stream.
+
+Machine Code Emitter
+--------------------
+
+In ``XXXCodeEmitter.cpp``, a target-specific of the ``Emitter`` class is
+implemented as a function pass (subclass of ``MachineFunctionPass``). The
+target-specific implementation of ``runOnMachineFunction`` (invoked by
+``runOnFunction`` in ``MachineFunctionPass``) iterates through the
+``MachineBasicBlock`` calls ``emitInstruction`` to process each instruction and
+emit binary code. ``emitInstruction`` is largely implemented with case
+statements on the instruction types defined in ``XXXInstrInfo.h``. For
+example, in ``X86CodeEmitter.cpp``, the ``emitInstruction`` method is built
+around the following ``switch``/``case`` statements:
+
+.. code-block:: c++
+
+ switch (Desc->TSFlags & X86::FormMask) {
+ case X86II::Pseudo: // for not yet implemented instructions
+ ... // or pseudo-instructions
+ break;
+ case X86II::RawFrm: // for instructions with a fixed opcode value
+ ...
+ break;
+ case X86II::AddRegFrm: // for instructions that have one register operand
+ ... // added to their opcode
+ break;
+ case X86II::MRMDestReg:// for instructions that use the Mod/RM byte
+ ... // to specify a destination (register)
+ break;
+ case X86II::MRMDestMem:// for instructions that use the Mod/RM byte
+ ... // to specify a destination (memory)
+ break;
+ case X86II::MRMSrcReg: // for instructions that use the Mod/RM byte
+ ... // to specify a source (register)
+ break;
+ case X86II::MRMSrcMem: // for instructions that use the Mod/RM byte
+ ... // to specify a source (memory)
+ break;
+ case X86II::MRM0r: case X86II::MRM1r: // for instructions that operate on
+ case X86II::MRM2r: case X86II::MRM3r: // a REGISTER r/m operand and
+ case X86II::MRM4r: case X86II::MRM5r: // use the Mod/RM byte and a field
+ case X86II::MRM6r: case X86II::MRM7r: // to hold extended opcode data
+ ...
+ break;
+ case X86II::MRM0m: case X86II::MRM1m: // for instructions that operate on
+ case X86II::MRM2m: case X86II::MRM3m: // a MEMORY r/m operand and
+ case X86II::MRM4m: case X86II::MRM5m: // use the Mod/RM byte and a field
+ case X86II::MRM6m: case X86II::MRM7m: // to hold extended opcode data
+ ...
+ break;
+ case X86II::MRMInitReg: // for instructions whose source and
+ ... // destination are the same register
+ break;
+ }
+
+The implementations of these case statements often first emit the opcode and
+then get the operand(s). Then depending upon the operand, helper methods may
+be called to process the operand(s). For example, in ``X86CodeEmitter.cpp``,
+for the ``X86II::AddRegFrm`` case, the first data emitted (by ``emitByte``) is
+the opcode added to the register operand. Then an object representing the
+machine operand, ``MO1``, is extracted. The helper methods such as
+``isImmediate``, ``isGlobalAddress``, ``isExternalSymbol``,
+``isConstantPoolIndex``, and ``isJumpTableIndex`` determine the operand type.
+(``X86CodeEmitter.cpp`` also has private methods such as ``emitConstant``,
+``emitGlobalAddress``, ``emitExternalSymbolAddress``, ``emitConstPoolAddress``,
+and ``emitJumpTableAddress`` that emit the data into the output stream.)
+
+.. code-block:: c++
+
+ case X86II::AddRegFrm:
+ MCE.emitByte(BaseOpcode + getX86RegNum(MI.getOperand(CurOp++).getReg()));
+
+ if (CurOp != NumOps) {
+ const MachineOperand &MO1 = MI.getOperand(CurOp++);
+ unsigned Size = X86InstrInfo::sizeOfImm(Desc);
+ if (MO1.isImmediate())
+ emitConstant(MO1.getImm(), Size);
+ else {
+ unsigned rt = Is64BitMode ? X86::reloc_pcrel_word
+ : (IsPIC ? X86::reloc_picrel_word : X86::reloc_absolute_word);
+ if (Opcode == X86::MOV64ri)
+ rt = X86::reloc_absolute_dword; // FIXME: add X86II flag?
+ if (MO1.isGlobalAddress()) {
+ bool NeedStub = isa<Function>(MO1.getGlobal());
+ bool isLazy = gvNeedsLazyPtr(MO1.getGlobal());
+ emitGlobalAddress(MO1.getGlobal(), rt, MO1.getOffset(), 0,
+ NeedStub, isLazy);
+ } else if (MO1.isExternalSymbol())
+ emitExternalSymbolAddress(MO1.getSymbolName(), rt);
+ else if (MO1.isConstantPoolIndex())
+ emitConstPoolAddress(MO1.getIndex(), rt);
+ else if (MO1.isJumpTableIndex())
+ emitJumpTableAddress(MO1.getIndex(), rt);
+ }
+ }
+ break;
+
+In the previous example, ``XXXCodeEmitter.cpp`` uses the variable ``rt``, which
+is a ``RelocationType`` enum that may be used to relocate addresses (for
+example, a global address with a PIC base offset). The ``RelocationType`` enum
+for that target is defined in the short target-specific ``XXXRelocations.h``
+file. The ``RelocationType`` is used by the ``relocate`` method defined in
+``XXXJITInfo.cpp`` to rewrite addresses for referenced global symbols.
+
+For example, ``X86Relocations.h`` specifies the following relocation types for
+the X86 addresses. In all four cases, the relocated value is added to the
+value already in memory. For ``reloc_pcrel_word`` and ``reloc_picrel_word``,
+there is an additional initial adjustment.
+
+.. code-block:: c++
+
+ enum RelocationType {
+ reloc_pcrel_word = 0, // add reloc value after adjusting for the PC loc
+ reloc_picrel_word = 1, // add reloc value after adjusting for the PIC base
+ reloc_absolute_word = 2, // absolute relocation; no additional adjustment
+ reloc_absolute_dword = 3 // absolute relocation; no additional adjustment
+ };
+
+Target JIT Info
+---------------
+
+``XXXJITInfo.cpp`` implements the JIT interfaces for target-specific
+code-generation activities, such as emitting machine code and stubs. At
+minimum, a target-specific version of ``XXXJITInfo`` implements the following:
+
+* ``getLazyResolverFunction`` --- Initializes the JIT, gives the target a
+ function that is used for compilation.
+
+* ``emitFunctionStub`` --- Returns a native function with a specified address
+ for a callback function.
+
+* ``relocate`` --- Changes the addresses of referenced globals, based on
+ relocation types.
+
+* Callback function that are wrappers to a function stub that is used when the
+ real target is not initially known.
+
+``getLazyResolverFunction`` is generally trivial to implement. It makes the
+incoming parameter as the global ``JITCompilerFunction`` and returns the
+callback function that will be used a function wrapper. For the Alpha target
+(in ``AlphaJITInfo.cpp``), the ``getLazyResolverFunction`` implementation is
+simply:
+
+.. code-block:: c++
+
+ TargetJITInfo::LazyResolverFn AlphaJITInfo::getLazyResolverFunction(
+ JITCompilerFn F) {
+ JITCompilerFunction = F;
+ return AlphaCompilationCallback;
+ }
+
+For the X86 target, the ``getLazyResolverFunction`` implementation is a little
+more complicated, because it returns a different callback function for
+processors with SSE instructions and XMM registers.
+
+The callback function initially saves and later restores the callee register
+values, incoming arguments, and frame and return address. The callback
+function needs low-level access to the registers or stack, so it is typically
+implemented with assembler.
+
Added: www-releases/trunk/3.9.1/docs/_sources/WritingAnLLVMPass.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.9.1/docs/_sources/WritingAnLLVMPass.txt?rev=290368&view=auto
==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/WritingAnLLVMPass.txt (added)
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@@ -0,0 +1,1438 @@
+====================
+Writing an LLVM Pass
+====================
+
+.. contents::
+ :local:
+
+Introduction --- What is a pass?
+================================
+
+The LLVM Pass Framework is an important part of the LLVM system, because LLVM
+passes are where most of the interesting parts of the compiler exist. Passes
+perform the transformations and optimizations that make up the compiler, they
+build the analysis results that are used by these transformations, and they
+are, above all, a structuring technique for compiler code.
+
+All LLVM passes are subclasses of the `Pass
+<http://llvm.org/doxygen/classllvm_1_1Pass.html>`_ class, which implement
+functionality by overriding virtual methods inherited from ``Pass``. Depending
+on how your pass works, you should inherit from the :ref:`ModulePass
+<writing-an-llvm-pass-ModulePass>` , :ref:`CallGraphSCCPass
+<writing-an-llvm-pass-CallGraphSCCPass>`, :ref:`FunctionPass
+<writing-an-llvm-pass-FunctionPass>` , or :ref:`LoopPass
+<writing-an-llvm-pass-LoopPass>`, or :ref:`RegionPass
+<writing-an-llvm-pass-RegionPass>`, or :ref:`BasicBlockPass
+<writing-an-llvm-pass-BasicBlockPass>` classes, which gives the system more
+information about what your pass does, and how it can be combined with other
+passes. One of the main features of the LLVM Pass Framework is that it
+schedules passes to run in an efficient way based on the constraints that your
+pass meets (which are indicated by which class they derive from).
+
+We start by showing you how to construct a pass, everything from setting up the
+code, to compiling, loading, and executing it. After the basics are down, more
+advanced features are discussed.
+
+Quick Start --- Writing hello world
+===================================
+
+Here we describe how to write the "hello world" of passes. The "Hello" pass is
+designed to simply print out the name of non-external functions that exist in
+the program being compiled. It does not modify the program at all, it just
+inspects it. The source code and files for this pass are available in the LLVM
+source tree in the ``lib/Transforms/Hello`` directory.
+
+.. _writing-an-llvm-pass-makefile:
+
+Setting up the build environment
+--------------------------------
+
+First, configure and build LLVM. Next, you need to create a new directory
+somewhere in the LLVM source base. For this example, we'll assume that you
+made ``lib/Transforms/Hello``. Finally, you must set up a build script
+(``Makefile``) that will compile the source code for the new pass. To do this,
+copy the following into ``Makefile``:
+
+.. code-block:: make
+
+ # Makefile for hello pass
+
+ # Path to top level of LLVM hierarchy
+ LEVEL = ../../..
+
+ # Name of the library to build
+ LIBRARYNAME = Hello
+
+ # Make the shared library become a loadable module so the tools can
+ # dlopen/dlsym on the resulting library.
+ LOADABLE_MODULE = 1
+
+ # Include the makefile implementation stuff
+ include $(LEVEL)/Makefile.common
+
+This makefile specifies that all of the ``.cpp`` files in the current directory
+are to be compiled and linked together into a shared object
+``$(LEVEL)/Debug+Asserts/lib/Hello.so`` that can be dynamically loaded by the
+:program:`opt` or :program:`bugpoint` tools via their :option:`-load` options.
+If your operating system uses a suffix other than ``.so`` (such as Windows or Mac
+OS X), the appropriate extension will be used.
+
+If you are used CMake to build LLVM, see :ref:`cmake-out-of-source-pass`.
+
+Now that we have the build scripts set up, we just need to write the code for
+the pass itself.
+
+.. _writing-an-llvm-pass-basiccode:
+
+Basic code required
+-------------------
+
+Now that we have a way to compile our new pass, we just have to write it.
+Start out with:
+
+.. code-block:: c++
+
+ #include "llvm/Pass.h"
+ #include "llvm/IR/Function.h"
+ #include "llvm/Support/raw_ostream.h"
+
+Which are needed because we are writing a `Pass
+<http://llvm.org/doxygen/classllvm_1_1Pass.html>`_, we are operating on
+`Function <http://llvm.org/doxygen/classllvm_1_1Function.html>`_\ s, and we will
+be doing some printing.
+
+Next we have:
+
+.. code-block:: c++
+
+ using namespace llvm;
+
+... which is required because the functions from the include files live in the
+llvm namespace.
+
+Next we have:
+
+.. code-block:: c++
+
+ namespace {
+
+... which starts out an anonymous namespace. Anonymous namespaces are to C++
+what the "``static``" keyword is to C (at global scope). It makes the things
+declared inside of the anonymous namespace visible only to the current file.
+If you're not familiar with them, consult a decent C++ book for more
+information.
+
+Next, we declare our pass itself:
+
+.. code-block:: c++
+
+ struct Hello : public FunctionPass {
+
+This declares a "``Hello``" class that is a subclass of :ref:`FunctionPass
+<writing-an-llvm-pass-FunctionPass>`. The different builtin pass subclasses
+are described in detail :ref:`later <writing-an-llvm-pass-pass-classes>`, but
+for now, know that ``FunctionPass`` operates on a function at a time.
+
+.. code-block:: c++
+
+ static char ID;
+ Hello() : FunctionPass(ID) {}
+
+This declares pass identifier used by LLVM to identify pass. This allows LLVM
+to avoid using expensive C++ runtime information.
+
+.. code-block:: c++
+
+ bool runOnFunction(Function &F) override {
+ errs() << "Hello: ";
+ errs().write_escaped(F.getName()) << "\n";
+ return false;
+ }
+ }; // end of struct Hello
+ } // end of anonymous namespace
+
+We declare a :ref:`runOnFunction <writing-an-llvm-pass-runOnFunction>` method,
+which overrides an abstract virtual method inherited from :ref:`FunctionPass
+<writing-an-llvm-pass-FunctionPass>`. This is where we are supposed to do our
+thing, so we just print out our message with the name of each function.
+
+.. code-block:: c++
+
+ char Hello::ID = 0;
+
+We initialize pass ID here. LLVM uses ID's address to identify a pass, so
+initialization value is not important.
+
+.. code-block:: c++
+
+ static RegisterPass<Hello> X("hello", "Hello World Pass",
+ false /* Only looks at CFG */,
+ false /* Analysis Pass */);
+
+Lastly, we :ref:`register our class <writing-an-llvm-pass-registration>`
+``Hello``, giving it a command line argument "``hello``", and a name "Hello
+World Pass". The last two arguments describe its behavior: if a pass walks CFG
+without modifying it then the third argument is set to ``true``; if a pass is
+an analysis pass, for example dominator tree pass, then ``true`` is supplied as
+the fourth argument.
+
+As a whole, the ``.cpp`` file looks like:
+
+.. code-block:: c++
+
+ #include "llvm/Pass.h"
+ #include "llvm/IR/Function.h"
+ #include "llvm/Support/raw_ostream.h"
+
+ using namespace llvm;
+
+ namespace {
+ struct Hello : public FunctionPass {
+ static char ID;
+ Hello() : FunctionPass(ID) {}
+
+ bool runOnFunction(Function &F) override {
+ errs() << "Hello: ";
+ errs().write_escaped(F.getName()) << '\n';
+ return false;
+ }
+ };
+ }
+
+ char Hello::ID = 0;
+ static RegisterPass<Hello> X("hello", "Hello World Pass", false, false);
+
+Now that it's all together, compile the file with a simple "``gmake``" command
+from the top level of your build directory and you should get a new file
+"``Debug+Asserts/lib/Hello.so``". Note that everything in this file is
+contained in an anonymous namespace --- this reflects the fact that passes
+are self contained units that do not need external interfaces (although they
+can have them) to be useful.
+
+Running a pass with ``opt``
+---------------------------
+
+Now that you have a brand new shiny shared object file, we can use the
+:program:`opt` command to run an LLVM program through your pass. Because you
+registered your pass with ``RegisterPass``, you will be able to use the
+:program:`opt` tool to access it, once loaded.
+
+To test it, follow the example at the end of the :doc:`GettingStarted` to
+compile "Hello World" to LLVM. We can now run the bitcode file (hello.bc) for
+the program through our transformation like this (or course, any bitcode file
+will work):
+
+.. code-block:: console
+
+ $ opt -load ../../Debug+Asserts/lib/Hello.so -hello < hello.bc > /dev/null
+ Hello: __main
+ Hello: puts
+ Hello: main
+
+The :option:`-load` option specifies that :program:`opt` should load your pass
+as a shared object, which makes "``-hello``" a valid command line argument
+(which is one reason you need to :ref:`register your pass
+<writing-an-llvm-pass-registration>`). Because the Hello pass does not modify
+the program in any interesting way, we just throw away the result of
+:program:`opt` (sending it to ``/dev/null``).
+
+To see what happened to the other string you registered, try running
+:program:`opt` with the :option:`-help` option:
+
+.. code-block:: console
+
+ $ opt -load ../../Debug+Asserts/lib/Hello.so -help
+ OVERVIEW: llvm .bc -> .bc modular optimizer
+
+ USAGE: opt [options] <input bitcode>
+
+ OPTIONS:
+ Optimizations available:
+ ...
+ -globalopt - Global Variable Optimizer
+ -globalsmodref-aa - Simple mod/ref analysis for globals
+ -gvn - Global Value Numbering
+ -hello - Hello World Pass
+ -indvars - Induction Variable Simplification
+ -inline - Function Integration/Inlining
+ ...
+
+The pass name gets added as the information string for your pass, giving some
+documentation to users of :program:`opt`. Now that you have a working pass,
+you would go ahead and make it do the cool transformations you want. Once you
+get it all working and tested, it may become useful to find out how fast your
+pass is. The :ref:`PassManager <writing-an-llvm-pass-passmanager>` provides a
+nice command line option (:option:`--time-passes`) that allows you to get
+information about the execution time of your pass along with the other passes
+you queue up. For example:
+
+.. code-block:: console
+
+ $ opt -load ../../Debug+Asserts/lib/Hello.so -hello -time-passes < hello.bc > /dev/null
+ Hello: __main
+ Hello: puts
+ Hello: main
+ ===============================================================================
+ ... Pass execution timing report ...
+ ===============================================================================
+ Total Execution Time: 0.02 seconds (0.0479059 wall clock)
+
+ ---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Pass Name ---
+ 0.0100 (100.0%) 0.0000 ( 0.0%) 0.0100 ( 50.0%) 0.0402 ( 84.0%) Bitcode Writer
+ 0.0000 ( 0.0%) 0.0100 (100.0%) 0.0100 ( 50.0%) 0.0031 ( 6.4%) Dominator Set Construction
+ 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0013 ( 2.7%) Module Verifier
+ 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0033 ( 6.9%) Hello World Pass
+ 0.0100 (100.0%) 0.0100 (100.0%) 0.0200 (100.0%) 0.0479 (100.0%) TOTAL
+
+As you can see, our implementation above is pretty fast. The additional
+passes listed are automatically inserted by the :program:`opt` tool to verify
+that the LLVM emitted by your pass is still valid and well formed LLVM, which
+hasn't been broken somehow.
+
+Now that you have seen the basics of the mechanics behind passes, we can talk
+about some more details of how they work and how to use them.
+
+.. _writing-an-llvm-pass-pass-classes:
+
+Pass classes and requirements
+=============================
+
+One of the first things that you should do when designing a new pass is to
+decide what class you should subclass for your pass. The :ref:`Hello World
+<writing-an-llvm-pass-basiccode>` example uses the :ref:`FunctionPass
+<writing-an-llvm-pass-FunctionPass>` class for its implementation, but we did
+not discuss why or when this should occur. Here we talk about the classes
+available, from the most general to the most specific.
+
+When choosing a superclass for your ``Pass``, you should choose the **most
+specific** class possible, while still being able to meet the requirements
+listed. This gives the LLVM Pass Infrastructure information necessary to
+optimize how passes are run, so that the resultant compiler isn't unnecessarily
+slow.
+
+The ``ImmutablePass`` class
+---------------------------
+
+The most plain and boring type of pass is the "`ImmutablePass
+<http://llvm.org/doxygen/classllvm_1_1ImmutablePass.html>`_" class. This pass
+type is used for passes that do not have to be run, do not change state, and
+never need to be updated. This is not a normal type of transformation or
+analysis, but can provide information about the current compiler configuration.
+
+Although this pass class is very infrequently used, it is important for
+providing information about the current target machine being compiled for, and
+other static information that can affect the various transformations.
+
+``ImmutablePass``\ es never invalidate other transformations, are never
+invalidated, and are never "run".
+
+.. _writing-an-llvm-pass-ModulePass:
+
+The ``ModulePass`` class
+------------------------
+
+The `ModulePass <http://llvm.org/doxygen/classllvm_1_1ModulePass.html>`_ class
+is the most general of all superclasses that you can use. Deriving from
+``ModulePass`` indicates that your pass uses the entire program as a unit,
+referring to function bodies in no predictable order, or adding and removing
+functions. Because nothing is known about the behavior of ``ModulePass``
+subclasses, no optimization can be done for their execution.
+
+A module pass can use function level passes (e.g. dominators) using the
+``getAnalysis`` interface ``getAnalysis<DominatorTree>(llvm::Function *)`` to
+provide the function to retrieve analysis result for, if the function pass does
+not require any module or immutable passes. Note that this can only be done
+for functions for which the analysis ran, e.g. in the case of dominators you
+should only ask for the ``DominatorTree`` for function definitions, not
+declarations.
+
+To write a correct ``ModulePass`` subclass, derive from ``ModulePass`` and
+overload the ``runOnModule`` method with the following signature:
+
+The ``runOnModule`` method
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: c++
+
+ virtual bool runOnModule(Module &M) = 0;
+
+The ``runOnModule`` method performs the interesting work of the pass. It
+should return ``true`` if the module was modified by the transformation and
+``false`` otherwise.
+
+.. _writing-an-llvm-pass-CallGraphSCCPass:
+
+The ``CallGraphSCCPass`` class
+------------------------------
+
+The `CallGraphSCCPass
+<http://llvm.org/doxygen/classllvm_1_1CallGraphSCCPass.html>`_ is used by
+passes that need to traverse the program bottom-up on the call graph (callees
+before callers). Deriving from ``CallGraphSCCPass`` provides some mechanics
+for building and traversing the ``CallGraph``, but also allows the system to
+optimize execution of ``CallGraphSCCPass``\ es. If your pass meets the
+requirements outlined below, and doesn't meet the requirements of a
+:ref:`FunctionPass <writing-an-llvm-pass-FunctionPass>` or :ref:`BasicBlockPass
+<writing-an-llvm-pass-BasicBlockPass>`, you should derive from
+``CallGraphSCCPass``.
+
+``TODO``: explain briefly what SCC, Tarjan's algo, and B-U mean.
+
+To be explicit, CallGraphSCCPass subclasses are:
+
+#. ... *not allowed* to inspect or modify any ``Function``\ s other than those
+ in the current SCC and the direct callers and direct callees of the SCC.
+#. ... *required* to preserve the current ``CallGraph`` object, updating it to
+ reflect any changes made to the program.
+#. ... *not allowed* to add or remove SCC's from the current Module, though
+ they may change the contents of an SCC.
+#. ... *allowed* to add or remove global variables from the current Module.
+#. ... *allowed* to maintain state across invocations of :ref:`runOnSCC
+ <writing-an-llvm-pass-runOnSCC>` (including global data).
+
+Implementing a ``CallGraphSCCPass`` is slightly tricky in some cases because it
+has to handle SCCs with more than one node in it. All of the virtual methods
+described below should return ``true`` if they modified the program, or
+``false`` if they didn't.
+
+The ``doInitialization(CallGraph &)`` method
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: c++
+
+ virtual bool doInitialization(CallGraph &CG);
+
+The ``doInitialization`` method is allowed to do most of the things that
+``CallGraphSCCPass``\ es are not allowed to do. They can add and remove
+functions, get pointers to functions, etc. The ``doInitialization`` method is
+designed to do simple initialization type of stuff that does not depend on the
+SCCs being processed. The ``doInitialization`` method call is not scheduled to
+overlap with any other pass executions (thus it should be very fast).
+
+.. _writing-an-llvm-pass-runOnSCC:
+
+The ``runOnSCC`` method
+^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: c++
+
+ virtual bool runOnSCC(CallGraphSCC &SCC) = 0;
+
+The ``runOnSCC`` method performs the interesting work of the pass, and should
+return ``true`` if the module was modified by the transformation, ``false``
+otherwise.
+
+The ``doFinalization(CallGraph &)`` method
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: c++
+
+ virtual bool doFinalization(CallGraph &CG);
+
+The ``doFinalization`` method is an infrequently used method that is called
+when the pass framework has finished calling :ref:`runOnSCC
+<writing-an-llvm-pass-runOnSCC>` for every SCC in the program being compiled.
+
+.. _writing-an-llvm-pass-FunctionPass:
+
+The ``FunctionPass`` class
+--------------------------
+
+In contrast to ``ModulePass`` subclasses, `FunctionPass
+<http://llvm.org/doxygen/classllvm_1_1Pass.html>`_ subclasses do have a
+predictable, local behavior that can be expected by the system. All
+``FunctionPass`` execute on each function in the program independent of all of
+the other functions in the program. ``FunctionPass``\ es do not require that
+they are executed in a particular order, and ``FunctionPass``\ es do not modify
+external functions.
+
+To be explicit, ``FunctionPass`` subclasses are not allowed to:
+
+#. Inspect or modify a ``Function`` other than the one currently being processed.
+#. Add or remove ``Function``\ s from the current ``Module``.
+#. Add or remove global variables from the current ``Module``.
+#. Maintain state across invocations of :ref:`runOnFunction
+ <writing-an-llvm-pass-runOnFunction>` (including global data).
+
+Implementing a ``FunctionPass`` is usually straightforward (See the :ref:`Hello
+World <writing-an-llvm-pass-basiccode>` pass for example).
+``FunctionPass``\ es may overload three virtual methods to do their work. All
+of these methods should return ``true`` if they modified the program, or
+``false`` if they didn't.
+
+.. _writing-an-llvm-pass-doInitialization-mod:
+
+The ``doInitialization(Module &)`` method
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: c++
+
+ virtual bool doInitialization(Module &M);
+
+The ``doInitialization`` method is allowed to do most of the things that
+``FunctionPass``\ es are not allowed to do. They can add and remove functions,
+get pointers to functions, etc. The ``doInitialization`` method is designed to
+do simple initialization type of stuff that does not depend on the functions
+being processed. The ``doInitialization`` method call is not scheduled to
+overlap with any other pass executions (thus it should be very fast).
+
+A good example of how this method should be used is the `LowerAllocations
+<http://llvm.org/doxygen/LowerAllocations_8cpp-source.html>`_ pass. This pass
+converts ``malloc`` and ``free`` instructions into platform dependent
+``malloc()`` and ``free()`` function calls. It uses the ``doInitialization``
+method to get a reference to the ``malloc`` and ``free`` functions that it
+needs, adding prototypes to the module if necessary.
+
+.. _writing-an-llvm-pass-runOnFunction:
+
+The ``runOnFunction`` method
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: c++
+
+ virtual bool runOnFunction(Function &F) = 0;
+
+The ``runOnFunction`` method must be implemented by your subclass to do the
+transformation or analysis work of your pass. As usual, a ``true`` value
+should be returned if the function is modified.
+
+.. _writing-an-llvm-pass-doFinalization-mod:
+
+The ``doFinalization(Module &)`` method
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: c++
+
+ virtual bool doFinalization(Module &M);
+
+The ``doFinalization`` method is an infrequently used method that is called
+when the pass framework has finished calling :ref:`runOnFunction
+<writing-an-llvm-pass-runOnFunction>` for every function in the program being
+compiled.
+
+.. _writing-an-llvm-pass-LoopPass:
+
+The ``LoopPass`` class
+----------------------
+
+All ``LoopPass`` execute on each loop in the function independent of all of the
+other loops in the function. ``LoopPass`` processes loops in loop nest order
+such that outer most loop is processed last.
+
+``LoopPass`` subclasses are allowed to update loop nest using ``LPPassManager``
+interface. Implementing a loop pass is usually straightforward.
+``LoopPass``\ es may overload three virtual methods to do their work. All
+these methods should return ``true`` if they modified the program, or ``false``
+if they didn't.
+
+A ``LoopPass`` subclass which is intended to run as part of the main loop pass
+pipeline needs to preserve all of the same *function* analyses that the other
+loop passes in its pipeline require. To make that easier,
+a ``getLoopAnalysisUsage`` function is provided by ``LoopUtils.h``. It can be
+called within the subclass's ``getAnalysisUsage`` override to get consistent
+and correct behavior. Analogously, ``INITIALIZE_PASS_DEPENDENCY(LoopPass)``
+will initialize this set of function analyses.
+
+The ``doInitialization(Loop *, LPPassManager &)`` method
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: c++
+
+ virtual bool doInitialization(Loop *, LPPassManager &LPM);
+
+The ``doInitialization`` method is designed to do simple initialization type of
+stuff that does not depend on the functions being processed. The
+``doInitialization`` method call is not scheduled to overlap with any other
+pass executions (thus it should be very fast). ``LPPassManager`` interface
+should be used to access ``Function`` or ``Module`` level analysis information.
+
+.. _writing-an-llvm-pass-runOnLoop:
+
+The ``runOnLoop`` method
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: c++
+
+ virtual bool runOnLoop(Loop *, LPPassManager &LPM) = 0;
+
+The ``runOnLoop`` method must be implemented by your subclass to do the
+transformation or analysis work of your pass. As usual, a ``true`` value
+should be returned if the function is modified. ``LPPassManager`` interface
+should be used to update loop nest.
+
+The ``doFinalization()`` method
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: c++
+
+ virtual bool doFinalization();
+
+The ``doFinalization`` method is an infrequently used method that is called
+when the pass framework has finished calling :ref:`runOnLoop
+<writing-an-llvm-pass-runOnLoop>` for every loop in the program being compiled.
+
+.. _writing-an-llvm-pass-RegionPass:
+
+The ``RegionPass`` class
+------------------------
+
+``RegionPass`` is similar to :ref:`LoopPass <writing-an-llvm-pass-LoopPass>`,
+but executes on each single entry single exit region in the function.
+``RegionPass`` processes regions in nested order such that the outer most
+region is processed last.
+
+``RegionPass`` subclasses are allowed to update the region tree by using the
+``RGPassManager`` interface. You may overload three virtual methods of
+``RegionPass`` to implement your own region pass. All these methods should
+return ``true`` if they modified the program, or ``false`` if they did not.
+
+The ``doInitialization(Region *, RGPassManager &)`` method
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: c++
+
+ virtual bool doInitialization(Region *, RGPassManager &RGM);
+
+The ``doInitialization`` method is designed to do simple initialization type of
+stuff that does not depend on the functions being processed. The
+``doInitialization`` method call is not scheduled to overlap with any other
+pass executions (thus it should be very fast). ``RPPassManager`` interface
+should be used to access ``Function`` or ``Module`` level analysis information.
+
+.. _writing-an-llvm-pass-runOnRegion:
+
+The ``runOnRegion`` method
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: c++
+
+ virtual bool runOnRegion(Region *, RGPassManager &RGM) = 0;
+
+The ``runOnRegion`` method must be implemented by your subclass to do the
+transformation or analysis work of your pass. As usual, a true value should be
+returned if the region is modified. ``RGPassManager`` interface should be used to
+update region tree.
+
+The ``doFinalization()`` method
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: c++
+
+ virtual bool doFinalization();
+
+The ``doFinalization`` method is an infrequently used method that is called
+when the pass framework has finished calling :ref:`runOnRegion
+<writing-an-llvm-pass-runOnRegion>` for every region in the program being
+compiled.
+
+.. _writing-an-llvm-pass-BasicBlockPass:
+
+The ``BasicBlockPass`` class
+----------------------------
+
+``BasicBlockPass``\ es are just like :ref:`FunctionPass's
+<writing-an-llvm-pass-FunctionPass>` , except that they must limit their scope
+of inspection and modification to a single basic block at a time. As such,
+they are **not** allowed to do any of the following:
+
+#. Modify or inspect any basic blocks outside of the current one.
+#. Maintain state across invocations of :ref:`runOnBasicBlock
+ <writing-an-llvm-pass-runOnBasicBlock>`.
+#. Modify the control flow graph (by altering terminator instructions)
+#. Any of the things forbidden for :ref:`FunctionPasses
+ <writing-an-llvm-pass-FunctionPass>`.
+
+``BasicBlockPass``\ es are useful for traditional local and "peephole"
+optimizations. They may override the same :ref:`doInitialization(Module &)
+<writing-an-llvm-pass-doInitialization-mod>` and :ref:`doFinalization(Module &)
+<writing-an-llvm-pass-doFinalization-mod>` methods that :ref:`FunctionPass's
+<writing-an-llvm-pass-FunctionPass>` have, but also have the following virtual
+methods that may also be implemented:
+
+The ``doInitialization(Function &)`` method
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: c++
+
+ virtual bool doInitialization(Function &F);
+
+The ``doInitialization`` method is allowed to do most of the things that
+``BasicBlockPass``\ es are not allowed to do, but that ``FunctionPass``\ es
+can. The ``doInitialization`` method is designed to do simple initialization
+that does not depend on the ``BasicBlock``\ s being processed. The
+``doInitialization`` method call is not scheduled to overlap with any other
+pass executions (thus it should be very fast).
+
+.. _writing-an-llvm-pass-runOnBasicBlock:
+
+The ``runOnBasicBlock`` method
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: c++
+
+ virtual bool runOnBasicBlock(BasicBlock &BB) = 0;
+
+Override this function to do the work of the ``BasicBlockPass``. This function
+is not allowed to inspect or modify basic blocks other than the parameter, and
+are not allowed to modify the CFG. A ``true`` value must be returned if the
+basic block is modified.
+
+The ``doFinalization(Function &)`` method
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: c++
+
+ virtual bool doFinalization(Function &F);
+
+The ``doFinalization`` method is an infrequently used method that is called
+when the pass framework has finished calling :ref:`runOnBasicBlock
+<writing-an-llvm-pass-runOnBasicBlock>` for every ``BasicBlock`` in the program
+being compiled. This can be used to perform per-function finalization.
+
+The ``MachineFunctionPass`` class
+---------------------------------
+
+A ``MachineFunctionPass`` is a part of the LLVM code generator that executes on
+the machine-dependent representation of each LLVM function in the program.
+
+Code generator passes are registered and initialized specially by
+``TargetMachine::addPassesToEmitFile`` and similar routines, so they cannot
+generally be run from the :program:`opt` or :program:`bugpoint` commands.
+
+A ``MachineFunctionPass`` is also a ``FunctionPass``, so all the restrictions
+that apply to a ``FunctionPass`` also apply to it. ``MachineFunctionPass``\ es
+also have additional restrictions. In particular, ``MachineFunctionPass``\ es
+are not allowed to do any of the following:
+
+#. Modify or create any LLVM IR ``Instruction``\ s, ``BasicBlock``\ s,
+ ``Argument``\ s, ``Function``\ s, ``GlobalVariable``\ s,
+ ``GlobalAlias``\ es, or ``Module``\ s.
+#. Modify a ``MachineFunction`` other than the one currently being processed.
+#. Maintain state across invocations of :ref:`runOnMachineFunction
+ <writing-an-llvm-pass-runOnMachineFunction>` (including global data).
+
+.. _writing-an-llvm-pass-runOnMachineFunction:
+
+The ``runOnMachineFunction(MachineFunction &MF)`` method
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: c++
+
+ virtual bool runOnMachineFunction(MachineFunction &MF) = 0;
+
+``runOnMachineFunction`` can be considered the main entry point of a
+``MachineFunctionPass``; that is, you should override this method to do the
+work of your ``MachineFunctionPass``.
+
+The ``runOnMachineFunction`` method is called on every ``MachineFunction`` in a
+``Module``, so that the ``MachineFunctionPass`` may perform optimizations on
+the machine-dependent representation of the function. If you want to get at
+the LLVM ``Function`` for the ``MachineFunction`` you're working on, use
+``MachineFunction``'s ``getFunction()`` accessor method --- but remember, you
+may not modify the LLVM ``Function`` or its contents from a
+``MachineFunctionPass``.
+
+.. _writing-an-llvm-pass-registration:
+
+Pass registration
+-----------------
+
+In the :ref:`Hello World <writing-an-llvm-pass-basiccode>` example pass we
+illustrated how pass registration works, and discussed some of the reasons that
+it is used and what it does. Here we discuss how and why passes are
+registered.
+
+As we saw above, passes are registered with the ``RegisterPass`` template. The
+template parameter is the name of the pass that is to be used on the command
+line to specify that the pass should be added to a program (for example, with
+:program:`opt` or :program:`bugpoint`). The first argument is the name of the
+pass, which is to be used for the :option:`-help` output of programs, as well
+as for debug output generated by the `--debug-pass` option.
+
+If you want your pass to be easily dumpable, you should implement the virtual
+print method:
+
+The ``print`` method
+^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: c++
+
+ virtual void print(llvm::raw_ostream &O, const Module *M) const;
+
+The ``print`` method must be implemented by "analyses" in order to print a
+human readable version of the analysis results. This is useful for debugging
+an analysis itself, as well as for other people to figure out how an analysis
+works. Use the opt ``-analyze`` argument to invoke this method.
+
+The ``llvm::raw_ostream`` parameter specifies the stream to write the results
+on, and the ``Module`` parameter gives a pointer to the top level module of the
+program that has been analyzed. Note however that this pointer may be ``NULL``
+in certain circumstances (such as calling the ``Pass::dump()`` from a
+debugger), so it should only be used to enhance debug output, it should not be
+depended on.
+
+.. _writing-an-llvm-pass-interaction:
+
+Specifying interactions between passes
+--------------------------------------
+
+One of the main responsibilities of the ``PassManager`` is to make sure that
+passes interact with each other correctly. Because ``PassManager`` tries to
+:ref:`optimize the execution of passes <writing-an-llvm-pass-passmanager>` it
+must know how the passes interact with each other and what dependencies exist
+between the various passes. To track this, each pass can declare the set of
+passes that are required to be executed before the current pass, and the passes
+which are invalidated by the current pass.
+
+Typically this functionality is used to require that analysis results are
+computed before your pass is run. Running arbitrary transformation passes can
+invalidate the computed analysis results, which is what the invalidation set
+specifies. If a pass does not implement the :ref:`getAnalysisUsage
+<writing-an-llvm-pass-getAnalysisUsage>` method, it defaults to not having any
+prerequisite passes, and invalidating **all** other passes.
+
+.. _writing-an-llvm-pass-getAnalysisUsage:
+
+The ``getAnalysisUsage`` method
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: c++
+
+ virtual void getAnalysisUsage(AnalysisUsage &Info) const;
+
+By implementing the ``getAnalysisUsage`` method, the required and invalidated
+sets may be specified for your transformation. The implementation should fill
+in the `AnalysisUsage
+<http://llvm.org/doxygen/classllvm_1_1AnalysisUsage.html>`_ object with
+information about which passes are required and not invalidated. To do this, a
+pass may call any of the following methods on the ``AnalysisUsage`` object:
+
+The ``AnalysisUsage::addRequired<>`` and ``AnalysisUsage::addRequiredTransitive<>`` methods
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+If your pass requires a previous pass to be executed (an analysis for example),
+it can use one of these methods to arrange for it to be run before your pass.
+LLVM has many different types of analyses and passes that can be required,
+spanning the range from ``DominatorSet`` to ``BreakCriticalEdges``. Requiring
+``BreakCriticalEdges``, for example, guarantees that there will be no critical
+edges in the CFG when your pass has been run.
+
+Some analyses chain to other analyses to do their job. For example, an
+`AliasAnalysis <AliasAnalysis>` implementation is required to :ref:`chain
+<aliasanalysis-chaining>` to other alias analysis passes. In cases where
+analyses chain, the ``addRequiredTransitive`` method should be used instead of
+the ``addRequired`` method. This informs the ``PassManager`` that the
+transitively required pass should be alive as long as the requiring pass is.
+
+The ``AnalysisUsage::addPreserved<>`` method
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+One of the jobs of the ``PassManager`` is to optimize how and when analyses are
+run. In particular, it attempts to avoid recomputing data unless it needs to.
+For this reason, passes are allowed to declare that they preserve (i.e., they
+don't invalidate) an existing analysis if it's available. For example, a
+simple constant folding pass would not modify the CFG, so it can't possibly
+affect the results of dominator analysis. By default, all passes are assumed
+to invalidate all others.
+
+The ``AnalysisUsage`` class provides several methods which are useful in
+certain circumstances that are related to ``addPreserved``. In particular, the
+``setPreservesAll`` method can be called to indicate that the pass does not
+modify the LLVM program at all (which is true for analyses), and the
+``setPreservesCFG`` method can be used by transformations that change
+instructions in the program but do not modify the CFG or terminator
+instructions (note that this property is implicitly set for
+:ref:`BasicBlockPass <writing-an-llvm-pass-BasicBlockPass>`\ es).
+
+``addPreserved`` is particularly useful for transformations like
+``BreakCriticalEdges``. This pass knows how to update a small set of loop and
+dominator related analyses if they exist, so it can preserve them, despite the
+fact that it hacks on the CFG.
+
+Example implementations of ``getAnalysisUsage``
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: c++
+
+ // This example modifies the program, but does not modify the CFG
+ void LICM::getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.setPreservesCFG();
+ AU.addRequired<LoopInfoWrapperPass>();
+ }
+
+.. _writing-an-llvm-pass-getAnalysis:
+
+The ``getAnalysis<>`` and ``getAnalysisIfAvailable<>`` methods
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The ``Pass::getAnalysis<>`` method is automatically inherited by your class,
+providing you with access to the passes that you declared that you required
+with the :ref:`getAnalysisUsage <writing-an-llvm-pass-getAnalysisUsage>`
+method. It takes a single template argument that specifies which pass class
+you want, and returns a reference to that pass. For example:
+
+.. code-block:: c++
+
+ bool LICM::runOnFunction(Function &F) {
+ LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
+ //...
+ }
+
+This method call returns a reference to the pass desired. You may get a
+runtime assertion failure if you attempt to get an analysis that you did not
+declare as required in your :ref:`getAnalysisUsage
+<writing-an-llvm-pass-getAnalysisUsage>` implementation. This method can be
+called by your ``run*`` method implementation, or by any other local method
+invoked by your ``run*`` method.
+
+A module level pass can use function level analysis info using this interface.
+For example:
+
+.. code-block:: c++
+
+ bool ModuleLevelPass::runOnModule(Module &M) {
+ //...
+ DominatorTree &DT = getAnalysis<DominatorTree>(Func);
+ //...
+ }
+
+In above example, ``runOnFunction`` for ``DominatorTree`` is called by pass
+manager before returning a reference to the desired pass.
+
+If your pass is capable of updating analyses if they exist (e.g.,
+``BreakCriticalEdges``, as described above), you can use the
+``getAnalysisIfAvailable`` method, which returns a pointer to the analysis if
+it is active. For example:
+
+.. code-block:: c++
+
+ if (DominatorSet *DS = getAnalysisIfAvailable<DominatorSet>()) {
+ // A DominatorSet is active. This code will update it.
+ }
+
+Implementing Analysis Groups
+----------------------------
+
+Now that we understand the basics of how passes are defined, how they are used,
+and how they are required from other passes, it's time to get a little bit
+fancier. All of the pass relationships that we have seen so far are very
+simple: one pass depends on one other specific pass to be run before it can
+run. For many applications, this is great, for others, more flexibility is
+required.
+
+In particular, some analyses are defined such that there is a single simple
+interface to the analysis results, but multiple ways of calculating them.
+Consider alias analysis for example. The most trivial alias analysis returns
+"may alias" for any alias query. The most sophisticated analysis a
+flow-sensitive, context-sensitive interprocedural analysis that can take a
+significant amount of time to execute (and obviously, there is a lot of room
+between these two extremes for other implementations). To cleanly support
+situations like this, the LLVM Pass Infrastructure supports the notion of
+Analysis Groups.
+
+Analysis Group Concepts
+^^^^^^^^^^^^^^^^^^^^^^^
+
+An Analysis Group is a single simple interface that may be implemented by
+multiple different passes. Analysis Groups can be given human readable names
+just like passes, but unlike passes, they need not derive from the ``Pass``
+class. An analysis group may have one or more implementations, one of which is
+the "default" implementation.
+
+Analysis groups are used by client passes just like other passes are: the
+``AnalysisUsage::addRequired()`` and ``Pass::getAnalysis()`` methods. In order
+to resolve this requirement, the :ref:`PassManager
+<writing-an-llvm-pass-passmanager>` scans the available passes to see if any
+implementations of the analysis group are available. If none is available, the
+default implementation is created for the pass to use. All standard rules for
+:ref:`interaction between passes <writing-an-llvm-pass-interaction>` still
+apply.
+
+Although :ref:`Pass Registration <writing-an-llvm-pass-registration>` is
+optional for normal passes, all analysis group implementations must be
+registered, and must use the :ref:`INITIALIZE_AG_PASS
+<writing-an-llvm-pass-RegisterAnalysisGroup>` template to join the
+implementation pool. Also, a default implementation of the interface **must**
+be registered with :ref:`RegisterAnalysisGroup
+<writing-an-llvm-pass-RegisterAnalysisGroup>`.
+
+As a concrete example of an Analysis Group in action, consider the
+`AliasAnalysis <http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html>`_
+analysis group. The default implementation of the alias analysis interface
+(the `basicaa <http://llvm.org/doxygen/structBasicAliasAnalysis.html>`_ pass)
+just does a few simple checks that don't require significant analysis to
+compute (such as: two different globals can never alias each other, etc).
+Passes that use the `AliasAnalysis
+<http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html>`_ interface (for
+example the `gcse <http://llvm.org/doxygen/structGCSE.html>`_ pass), do not
+care which implementation of alias analysis is actually provided, they just use
+the designated interface.
+
+From the user's perspective, commands work just like normal. Issuing the
+command ``opt -gcse ...`` will cause the ``basicaa`` class to be instantiated
+and added to the pass sequence. Issuing the command ``opt -somefancyaa -gcse
+...`` will cause the ``gcse`` pass to use the ``somefancyaa`` alias analysis
+(which doesn't actually exist, it's just a hypothetical example) instead.
+
+.. _writing-an-llvm-pass-RegisterAnalysisGroup:
+
+Using ``RegisterAnalysisGroup``
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The ``RegisterAnalysisGroup`` template is used to register the analysis group
+itself, while the ``INITIALIZE_AG_PASS`` is used to add pass implementations to
+the analysis group. First, an analysis group should be registered, with a
+human readable name provided for it. Unlike registration of passes, there is
+no command line argument to be specified for the Analysis Group Interface
+itself, because it is "abstract":
+
+.. code-block:: c++
+
+ static RegisterAnalysisGroup<AliasAnalysis> A("Alias Analysis");
+
+Once the analysis is registered, passes can declare that they are valid
+implementations of the interface by using the following code:
+
+.. code-block:: c++
+
+ namespace {
+ // Declare that we implement the AliasAnalysis interface
+ INITIALIZE_AG_PASS(FancyAA, AliasAnalysis , "somefancyaa",
+ "A more complex alias analysis implementation",
+ false, // Is CFG Only?
+ true, // Is Analysis?
+ false); // Is default Analysis Group implementation?
+ }
+
+This just shows a class ``FancyAA`` that uses the ``INITIALIZE_AG_PASS`` macro
+both to register and to "join" the `AliasAnalysis
+<http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html>`_ analysis group.
+Every implementation of an analysis group should join using this macro.
+
+.. code-block:: c++
+
+ namespace {
+ // Declare that we implement the AliasAnalysis interface
+ INITIALIZE_AG_PASS(BasicAA, AliasAnalysis, "basicaa",
+ "Basic Alias Analysis (default AA impl)",
+ false, // Is CFG Only?
+ true, // Is Analysis?
+ true); // Is default Analysis Group implementation?
+ }
+
+Here we show how the default implementation is specified (using the final
+argument to the ``INITIALIZE_AG_PASS`` template). There must be exactly one
+default implementation available at all times for an Analysis Group to be used.
+Only default implementation can derive from ``ImmutablePass``. Here we declare
+that the `BasicAliasAnalysis
+<http://llvm.org/doxygen/structBasicAliasAnalysis.html>`_ pass is the default
+implementation for the interface.
+
+Pass Statistics
+===============
+
+The `Statistic <http://llvm.org/doxygen/Statistic_8h-source.html>`_ class is
+designed to be an easy way to expose various success metrics from passes.
+These statistics are printed at the end of a run, when the :option:`-stats`
+command line option is enabled on the command line. See the :ref:`Statistics
+section <Statistic>` in the Programmer's Manual for details.
+
+.. _writing-an-llvm-pass-passmanager:
+
+What PassManager does
+---------------------
+
+The `PassManager <http://llvm.org/doxygen/PassManager_8h-source.html>`_ `class
+<http://llvm.org/doxygen/classllvm_1_1PassManager.html>`_ takes a list of
+passes, ensures their :ref:`prerequisites <writing-an-llvm-pass-interaction>`
+are set up correctly, and then schedules passes to run efficiently. All of the
+LLVM tools that run passes use the PassManager for execution of these passes.
+
+The PassManager does two main things to try to reduce the execution time of a
+series of passes:
+
+#. **Share analysis results.** The ``PassManager`` attempts to avoid
+ recomputing analysis results as much as possible. This means keeping track
+ of which analyses are available already, which analyses get invalidated, and
+ which analyses are needed to be run for a pass. An important part of work
+ is that the ``PassManager`` tracks the exact lifetime of all analysis
+ results, allowing it to :ref:`free memory
+ <writing-an-llvm-pass-releaseMemory>` allocated to holding analysis results
+ as soon as they are no longer needed.
+
+#. **Pipeline the execution of passes on the program.** The ``PassManager``
+ attempts to get better cache and memory usage behavior out of a series of
+ passes by pipelining the passes together. This means that, given a series
+ of consecutive :ref:`FunctionPass <writing-an-llvm-pass-FunctionPass>`, it
+ will execute all of the :ref:`FunctionPass
+ <writing-an-llvm-pass-FunctionPass>` on the first function, then all of the
+ :ref:`FunctionPasses <writing-an-llvm-pass-FunctionPass>` on the second
+ function, etc... until the entire program has been run through the passes.
+
+ This improves the cache behavior of the compiler, because it is only
+ touching the LLVM program representation for a single function at a time,
+ instead of traversing the entire program. It reduces the memory consumption
+ of compiler, because, for example, only one `DominatorSet
+ <http://llvm.org/doxygen/classllvm_1_1DominatorSet.html>`_ needs to be
+ calculated at a time. This also makes it possible to implement some
+ :ref:`interesting enhancements <writing-an-llvm-pass-SMP>` in the future.
+
+The effectiveness of the ``PassManager`` is influenced directly by how much
+information it has about the behaviors of the passes it is scheduling. For
+example, the "preserved" set is intentionally conservative in the face of an
+unimplemented :ref:`getAnalysisUsage <writing-an-llvm-pass-getAnalysisUsage>`
+method. Not implementing when it should be implemented will have the effect of
+not allowing any analysis results to live across the execution of your pass.
+
+The ``PassManager`` class exposes a ``--debug-pass`` command line options that
+is useful for debugging pass execution, seeing how things work, and diagnosing
+when you should be preserving more analyses than you currently are. (To get
+information about all of the variants of the ``--debug-pass`` option, just type
+"``opt -help-hidden``").
+
+By using the --debug-pass=Structure option, for example, we can see how our
+:ref:`Hello World <writing-an-llvm-pass-basiccode>` pass interacts with other
+passes. Lets try it out with the gcse and licm passes:
+
+.. code-block:: console
+
+ $ opt -load ../../Debug+Asserts/lib/Hello.so -gcse -licm --debug-pass=Structure < hello.bc > /dev/null
+ Module Pass Manager
+ Function Pass Manager
+ Dominator Set Construction
+ Immediate Dominators Construction
+ Global Common Subexpression Elimination
+ -- Immediate Dominators Construction
+ -- Global Common Subexpression Elimination
+ Natural Loop Construction
+ Loop Invariant Code Motion
+ -- Natural Loop Construction
+ -- Loop Invariant Code Motion
+ Module Verifier
+ -- Dominator Set Construction
+ -- Module Verifier
+ Bitcode Writer
+ --Bitcode Writer
+
+This output shows us when passes are constructed and when the analysis results
+are known to be dead (prefixed with "``--``"). Here we see that GCSE uses
+dominator and immediate dominator information to do its job. The LICM pass
+uses natural loop information, which uses dominator sets, but not immediate
+dominators. Because immediate dominators are no longer useful after the GCSE
+pass, it is immediately destroyed. The dominator sets are then reused to
+compute natural loop information, which is then used by the LICM pass.
+
+After the LICM pass, the module verifier runs (which is automatically added by
+the :program:`opt` tool), which uses the dominator set to check that the
+resultant LLVM code is well formed. After it finishes, the dominator set
+information is destroyed, after being computed once, and shared by three
+passes.
+
+Lets see how this changes when we run the :ref:`Hello World
+<writing-an-llvm-pass-basiccode>` pass in between the two passes:
+
+.. code-block:: console
+
+ $ opt -load ../../Debug+Asserts/lib/Hello.so -gcse -hello -licm --debug-pass=Structure < hello.bc > /dev/null
+ Module Pass Manager
+ Function Pass Manager
+ Dominator Set Construction
+ Immediate Dominators Construction
+ Global Common Subexpression Elimination
+ -- Dominator Set Construction
+ -- Immediate Dominators Construction
+ -- Global Common Subexpression Elimination
+ Hello World Pass
+ -- Hello World Pass
+ Dominator Set Construction
+ Natural Loop Construction
+ Loop Invariant Code Motion
+ -- Natural Loop Construction
+ -- Loop Invariant Code Motion
+ Module Verifier
+ -- Dominator Set Construction
+ -- Module Verifier
+ Bitcode Writer
+ --Bitcode Writer
+ Hello: __main
+ Hello: puts
+ Hello: main
+
+Here we see that the :ref:`Hello World <writing-an-llvm-pass-basiccode>` pass
+has killed the Dominator Set pass, even though it doesn't modify the code at
+all! To fix this, we need to add the following :ref:`getAnalysisUsage
+<writing-an-llvm-pass-getAnalysisUsage>` method to our pass:
+
+.. code-block:: c++
+
+ // We don't modify the program, so we preserve all analyses
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ AU.setPreservesAll();
+ }
+
+Now when we run our pass, we get this output:
+
+.. code-block:: console
+
+ $ opt -load ../../Debug+Asserts/lib/Hello.so -gcse -hello -licm --debug-pass=Structure < hello.bc > /dev/null
+ Pass Arguments: -gcse -hello -licm
+ Module Pass Manager
+ Function Pass Manager
+ Dominator Set Construction
+ Immediate Dominators Construction
+ Global Common Subexpression Elimination
+ -- Immediate Dominators Construction
+ -- Global Common Subexpression Elimination
+ Hello World Pass
+ -- Hello World Pass
+ Natural Loop Construction
+ Loop Invariant Code Motion
+ -- Loop Invariant Code Motion
+ -- Natural Loop Construction
+ Module Verifier
+ -- Dominator Set Construction
+ -- Module Verifier
+ Bitcode Writer
+ --Bitcode Writer
+ Hello: __main
+ Hello: puts
+ Hello: main
+
+Which shows that we don't accidentally invalidate dominator information
+anymore, and therefore do not have to compute it twice.
+
+.. _writing-an-llvm-pass-releaseMemory:
+
+The ``releaseMemory`` method
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: c++
+
+ virtual void releaseMemory();
+
+The ``PassManager`` automatically determines when to compute analysis results,
+and how long to keep them around for. Because the lifetime of the pass object
+itself is effectively the entire duration of the compilation process, we need
+some way to free analysis results when they are no longer useful. The
+``releaseMemory`` virtual method is the way to do this.
+
+If you are writing an analysis or any other pass that retains a significant
+amount of state (for use by another pass which "requires" your pass and uses
+the :ref:`getAnalysis <writing-an-llvm-pass-getAnalysis>` method) you should
+implement ``releaseMemory`` to, well, release the memory allocated to maintain
+this internal state. This method is called after the ``run*`` method for the
+class, before the next call of ``run*`` in your pass.
+
+Registering dynamically loaded passes
+=====================================
+
+*Size matters* when constructing production quality tools using LLVM, both for
+the purposes of distribution, and for regulating the resident code size when
+running on the target system. Therefore, it becomes desirable to selectively
+use some passes, while omitting others and maintain the flexibility to change
+configurations later on. You want to be able to do all this, and, provide
+feedback to the user. This is where pass registration comes into play.
+
+The fundamental mechanisms for pass registration are the
+``MachinePassRegistry`` class and subclasses of ``MachinePassRegistryNode``.
+
+An instance of ``MachinePassRegistry`` is used to maintain a list of
+``MachinePassRegistryNode`` objects. This instance maintains the list and
+communicates additions and deletions to the command line interface.
+
+An instance of ``MachinePassRegistryNode`` subclass is used to maintain
+information provided about a particular pass. This information includes the
+command line name, the command help string and the address of the function used
+to create an instance of the pass. A global static constructor of one of these
+instances *registers* with a corresponding ``MachinePassRegistry``, the static
+destructor *unregisters*. Thus a pass that is statically linked in the tool
+will be registered at start up. A dynamically loaded pass will register on
+load and unregister at unload.
+
+Using existing registries
+-------------------------
+
+There are predefined registries to track instruction scheduling
+(``RegisterScheduler``) and register allocation (``RegisterRegAlloc``) machine
+passes. Here we will describe how to *register* a register allocator machine
+pass.
+
+Implement your register allocator machine pass. In your register allocator
+``.cpp`` file add the following include:
+
+.. code-block:: c++
+
+ #include "llvm/CodeGen/RegAllocRegistry.h"
+
+Also in your register allocator ``.cpp`` file, define a creator function in the
+form:
+
+.. code-block:: c++
+
+ FunctionPass *createMyRegisterAllocator() {
+ return new MyRegisterAllocator();
+ }
+
+Note that the signature of this function should match the type of
+``RegisterRegAlloc::FunctionPassCtor``. In the same file add the "installing"
+declaration, in the form:
+
+.. code-block:: c++
+
+ static RegisterRegAlloc myRegAlloc("myregalloc",
+ "my register allocator help string",
+ createMyRegisterAllocator);
+
+Note the two spaces prior to the help string produces a tidy result on the
+:option:`-help` query.
+
+.. code-block:: console
+
+ $ llc -help
+ ...
+ -regalloc - Register allocator to use (default=linearscan)
+ =linearscan - linear scan register allocator
+ =local - local register allocator
+ =simple - simple register allocator
+ =myregalloc - my register allocator help string
+ ...
+
+And that's it. The user is now free to use ``-regalloc=myregalloc`` as an
+option. Registering instruction schedulers is similar except use the
+``RegisterScheduler`` class. Note that the
+``RegisterScheduler::FunctionPassCtor`` is significantly different from
+``RegisterRegAlloc::FunctionPassCtor``.
+
+To force the load/linking of your register allocator into the
+:program:`llc`/:program:`lli` tools, add your creator function's global
+declaration to ``Passes.h`` and add a "pseudo" call line to
+``llvm/Codegen/LinkAllCodegenComponents.h``.
+
+Creating new registries
+-----------------------
+
+The easiest way to get started is to clone one of the existing registries; we
+recommend ``llvm/CodeGen/RegAllocRegistry.h``. The key things to modify are
+the class name and the ``FunctionPassCtor`` type.
+
+Then you need to declare the registry. Example: if your pass registry is
+``RegisterMyPasses`` then define:
+
+.. code-block:: c++
+
+ MachinePassRegistry RegisterMyPasses::Registry;
+
+And finally, declare the command line option for your passes. Example:
+
+.. code-block:: c++
+
+ cl::opt<RegisterMyPasses::FunctionPassCtor, false,
+ RegisterPassParser<RegisterMyPasses> >
+ MyPassOpt("mypass",
+ cl::init(&createDefaultMyPass),
+ cl::desc("my pass option help"));
+
+Here the command option is "``mypass``", with ``createDefaultMyPass`` as the
+default creator.
+
+Using GDB with dynamically loaded passes
+----------------------------------------
+
+Unfortunately, using GDB with dynamically loaded passes is not as easy as it
+should be. First of all, you can't set a breakpoint in a shared object that
+has not been loaded yet, and second of all there are problems with inlined
+functions in shared objects. Here are some suggestions to debugging your pass
+with GDB.
+
+For sake of discussion, I'm going to assume that you are debugging a
+transformation invoked by :program:`opt`, although nothing described here
+depends on that.
+
+Setting a breakpoint in your pass
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+First thing you do is start gdb on the opt process:
+
+.. code-block:: console
+
+ $ gdb opt
+ GNU gdb 5.0
+ Copyright 2000 Free Software Foundation, Inc.
+ GDB is free software, covered by the GNU General Public License, and you are
+ welcome to change it and/or distribute copies of it under certain conditions.
+ Type "show copying" to see the conditions.
+ There is absolutely no warranty for GDB. Type "show warranty" for details.
+ This GDB was configured as "sparc-sun-solaris2.6"...
+ (gdb)
+
+Note that :program:`opt` has a lot of debugging information in it, so it takes
+time to load. Be patient. Since we cannot set a breakpoint in our pass yet
+(the shared object isn't loaded until runtime), we must execute the process,
+and have it stop before it invokes our pass, but after it has loaded the shared
+object. The most foolproof way of doing this is to set a breakpoint in
+``PassManager::run`` and then run the process with the arguments you want:
+
+.. code-block:: console
+
+ $ (gdb) break llvm::PassManager::run
+ Breakpoint 1 at 0x2413bc: file Pass.cpp, line 70.
+ (gdb) run test.bc -load $(LLVMTOP)/llvm/Debug+Asserts/lib/[libname].so -[passoption]
+ Starting program: opt test.bc -load $(LLVMTOP)/llvm/Debug+Asserts/lib/[libname].so -[passoption]
+ Breakpoint 1, PassManager::run (this=0xffbef174, M=@0x70b298) at Pass.cpp:70
+ 70 bool PassManager::run(Module &M) { return PM->run(M); }
+ (gdb)
+
+Once the :program:`opt` stops in the ``PassManager::run`` method you are now
+free to set breakpoints in your pass so that you can trace through execution or
+do other standard debugging stuff.
+
+Miscellaneous Problems
+^^^^^^^^^^^^^^^^^^^^^^
+
+Once you have the basics down, there are a couple of problems that GDB has,
+some with solutions, some without.
+
+* Inline functions have bogus stack information. In general, GDB does a pretty
+ good job getting stack traces and stepping through inline functions. When a
+ pass is dynamically loaded however, it somehow completely loses this
+ capability. The only solution I know of is to de-inline a function (move it
+ from the body of a class to a ``.cpp`` file).
+
+* Restarting the program breaks breakpoints. After following the information
+ above, you have succeeded in getting some breakpoints planted in your pass.
+ Next thing you know, you restart the program (i.e., you type "``run``" again),
+ and you start getting errors about breakpoints being unsettable. The only
+ way I have found to "fix" this problem is to delete the breakpoints that are
+ already set in your pass, run the program, and re-set the breakpoints once
+ execution stops in ``PassManager::run``.
+
+Hopefully these tips will help with common case debugging situations. If you'd
+like to contribute some tips of your own, just contact `Chris
+<mailto:sabre at nondot.org>`_.
+
+Future extensions planned
+-------------------------
+
+Although the LLVM Pass Infrastructure is very capable as it stands, and does
+some nifty stuff, there are things we'd like to add in the future. Here is
+where we are going:
+
+.. _writing-an-llvm-pass-SMP:
+
+Multithreaded LLVM
+^^^^^^^^^^^^^^^^^^
+
+Multiple CPU machines are becoming more common and compilation can never be
+fast enough: obviously we should allow for a multithreaded compiler. Because
+of the semantics defined for passes above (specifically they cannot maintain
+state across invocations of their ``run*`` methods), a nice clean way to
+implement a multithreaded compiler would be for the ``PassManager`` class to
+create multiple instances of each pass object, and allow the separate instances
+to be hacking on different parts of the program at the same time.
+
+This implementation would prevent each of the passes from having to implement
+multithreaded constructs, requiring only the LLVM core to have locking in a few
+places (for global resources). Although this is a simple extension, we simply
+haven't had time (or multiprocessor machines, thus a reason) to implement this.
+Despite that, we have kept the LLVM passes SMP ready, and you should too.
+
Added: www-releases/trunk/3.9.1/docs/_sources/YamlIO.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.9.1/docs/_sources/YamlIO.txt?rev=290368&view=auto
==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/YamlIO.txt (added)
+++ www-releases/trunk/3.9.1/docs/_sources/YamlIO.txt Thu Dec 22 14:04:03 2016
@@ -0,0 +1,1035 @@
+=====================
+YAML I/O
+=====================
+
+.. contents::
+ :local:
+
+Introduction to YAML
+====================
+
+YAML is a human readable data serialization language. The full YAML language
+spec can be read at `yaml.org
+<http://www.yaml.org/spec/1.2/spec.html#Introduction>`_. The simplest form of
+yaml is just "scalars", "mappings", and "sequences". A scalar is any number
+or string. The pound/hash symbol (#) begins a comment line. A mapping is
+a set of key-value pairs where the key ends with a colon. For example:
+
+.. code-block:: yaml
+
+ # a mapping
+ name: Tom
+ hat-size: 7
+
+A sequence is a list of items where each item starts with a leading dash ('-').
+For example:
+
+.. code-block:: yaml
+
+ # a sequence
+ - x86
+ - x86_64
+ - PowerPC
+
+You can combine mappings and sequences by indenting. For example a sequence
+of mappings in which one of the mapping values is itself a sequence:
+
+.. code-block:: yaml
+
+ # a sequence of mappings with one key's value being a sequence
+ - name: Tom
+ cpus:
+ - x86
+ - x86_64
+ - name: Bob
+ cpus:
+ - x86
+ - name: Dan
+ cpus:
+ - PowerPC
+ - x86
+
+Sometime sequences are known to be short and the one entry per line is too
+verbose, so YAML offers an alternate syntax for sequences called a "Flow
+Sequence" in which you put comma separated sequence elements into square
+brackets. The above example could then be simplified to :
+
+
+.. code-block:: yaml
+
+ # a sequence of mappings with one key's value being a flow sequence
+ - name: Tom
+ cpus: [ x86, x86_64 ]
+ - name: Bob
+ cpus: [ x86 ]
+ - name: Dan
+ cpus: [ PowerPC, x86 ]
+
+
+Introduction to YAML I/O
+========================
+
+The use of indenting makes the YAML easy for a human to read and understand,
+but having a program read and write YAML involves a lot of tedious details.
+The YAML I/O library structures and simplifies reading and writing YAML
+documents.
+
+YAML I/O assumes you have some "native" data structures which you want to be
+able to dump as YAML and recreate from YAML. The first step is to try
+writing example YAML for your data structures. You may find after looking at
+possible YAML representations that a direct mapping of your data structures
+to YAML is not very readable. Often the fields are not in the order that
+a human would find readable. Or the same information is replicated in multiple
+locations, making it hard for a human to write such YAML correctly.
+
+In relational database theory there is a design step called normalization in
+which you reorganize fields and tables. The same considerations need to
+go into the design of your YAML encoding. But, you may not want to change
+your existing native data structures. Therefore, when writing out YAML
+there may be a normalization step, and when reading YAML there would be a
+corresponding denormalization step.
+
+YAML I/O uses a non-invasive, traits based design. YAML I/O defines some
+abstract base templates. You specialize those templates on your data types.
+For instance, if you have an enumerated type FooBar you could specialize
+ScalarEnumerationTraits on that type and define the enumeration() method:
+
+.. code-block:: c++
+
+ using llvm::yaml::ScalarEnumerationTraits;
+ using llvm::yaml::IO;
+
+ template <>
+ struct ScalarEnumerationTraits<FooBar> {
+ static void enumeration(IO &io, FooBar &value) {
+ ...
+ }
+ };
+
+
+As with all YAML I/O template specializations, the ScalarEnumerationTraits is used for
+both reading and writing YAML. That is, the mapping between in-memory enum
+values and the YAML string representation is only in one place.
+This assures that the code for writing and parsing of YAML stays in sync.
+
+To specify a YAML mappings, you define a specialization on
+llvm::yaml::MappingTraits.
+If your native data structure happens to be a struct that is already normalized,
+then the specialization is simple. For example:
+
+.. code-block:: c++
+
+ using llvm::yaml::MappingTraits;
+ using llvm::yaml::IO;
+
+ template <>
+ struct MappingTraits<Person> {
+ static void mapping(IO &io, Person &info) {
+ io.mapRequired("name", info.name);
+ io.mapOptional("hat-size", info.hatSize);
+ }
+ };
+
+
+A YAML sequence is automatically inferred if you data type has begin()/end()
+iterators and a push_back() method. Therefore any of the STL containers
+(such as std::vector<>) will automatically translate to YAML sequences.
+
+Once you have defined specializations for your data types, you can
+programmatically use YAML I/O to write a YAML document:
+
+.. code-block:: c++
+
+ using llvm::yaml::Output;
+
+ Person tom;
+ tom.name = "Tom";
+ tom.hatSize = 8;
+ Person dan;
+ dan.name = "Dan";
+ dan.hatSize = 7;
+ std::vector<Person> persons;
+ persons.push_back(tom);
+ persons.push_back(dan);
+
+ Output yout(llvm::outs());
+ yout << persons;
+
+This would write the following:
+
+.. code-block:: yaml
+
+ - name: Tom
+ hat-size: 8
+ - name: Dan
+ hat-size: 7
+
+And you can also read such YAML documents with the following code:
+
+.. code-block:: c++
+
+ using llvm::yaml::Input;
+
+ typedef std::vector<Person> PersonList;
+ std::vector<PersonList> docs;
+
+ Input yin(document.getBuffer());
+ yin >> docs;
+
+ if ( yin.error() )
+ return;
+
+ // Process read document
+ for ( PersonList &pl : docs ) {
+ for ( Person &person : pl ) {
+ cout << "name=" << person.name;
+ }
+ }
+
+One other feature of YAML is the ability to define multiple documents in a
+single file. That is why reading YAML produces a vector of your document type.
+
+
+
+Error Handling
+==============
+
+When parsing a YAML document, if the input does not match your schema (as
+expressed in your XxxTraits<> specializations). YAML I/O
+will print out an error message and your Input object's error() method will
+return true. For instance the following document:
+
+.. code-block:: yaml
+
+ - name: Tom
+ shoe-size: 12
+ - name: Dan
+ hat-size: 7
+
+Has a key (shoe-size) that is not defined in the schema. YAML I/O will
+automatically generate this error:
+
+.. code-block:: yaml
+
+ YAML:2:2: error: unknown key 'shoe-size'
+ shoe-size: 12
+ ^~~~~~~~~
+
+Similar errors are produced for other input not conforming to the schema.
+
+
+Scalars
+=======
+
+YAML scalars are just strings (i.e. not a sequence or mapping). The YAML I/O
+library provides support for translating between YAML scalars and specific
+C++ types.
+
+
+Built-in types
+--------------
+The following types have built-in support in YAML I/O:
+
+* bool
+* float
+* double
+* StringRef
+* std::string
+* int64_t
+* int32_t
+* int16_t
+* int8_t
+* uint64_t
+* uint32_t
+* uint16_t
+* uint8_t
+
+That is, you can use those types in fields of MappingTraits or as element type
+in sequence. When reading, YAML I/O will validate that the string found
+is convertible to that type and error out if not.
+
+
+Unique types
+------------
+Given that YAML I/O is trait based, the selection of how to convert your data
+to YAML is based on the type of your data. But in C++ type matching, typedefs
+do not generate unique type names. That means if you have two typedefs of
+unsigned int, to YAML I/O both types look exactly like unsigned int. To
+facilitate make unique type names, YAML I/O provides a macro which is used
+like a typedef on built-in types, but expands to create a class with conversion
+operators to and from the base type. For example:
+
+.. code-block:: c++
+
+ LLVM_YAML_STRONG_TYPEDEF(uint32_t, MyFooFlags)
+ LLVM_YAML_STRONG_TYPEDEF(uint32_t, MyBarFlags)
+
+This generates two classes MyFooFlags and MyBarFlags which you can use in your
+native data structures instead of uint32_t. They are implicitly
+converted to and from uint32_t. The point of creating these unique types
+is that you can now specify traits on them to get different YAML conversions.
+
+Hex types
+---------
+An example use of a unique type is that YAML I/O provides fixed sized unsigned
+integers that are written with YAML I/O as hexadecimal instead of the decimal
+format used by the built-in integer types:
+
+* Hex64
+* Hex32
+* Hex16
+* Hex8
+
+You can use llvm::yaml::Hex32 instead of uint32_t and the only different will
+be that when YAML I/O writes out that type it will be formatted in hexadecimal.
+
+
+ScalarEnumerationTraits
+-----------------------
+YAML I/O supports translating between in-memory enumerations and a set of string
+values in YAML documents. This is done by specializing ScalarEnumerationTraits<>
+on your enumeration type and define a enumeration() method.
+For instance, suppose you had an enumeration of CPUs and a struct with it as
+a field:
+
+.. code-block:: c++
+
+ enum CPUs {
+ cpu_x86_64 = 5,
+ cpu_x86 = 7,
+ cpu_PowerPC = 8
+ };
+
+ struct Info {
+ CPUs cpu;
+ uint32_t flags;
+ };
+
+To support reading and writing of this enumeration, you can define a
+ScalarEnumerationTraits specialization on CPUs, which can then be used
+as a field type:
+
+.. code-block:: c++
+
+ using llvm::yaml::ScalarEnumerationTraits;
+ using llvm::yaml::MappingTraits;
+ using llvm::yaml::IO;
+
+ template <>
+ struct ScalarEnumerationTraits<CPUs> {
+ static void enumeration(IO &io, CPUs &value) {
+ io.enumCase(value, "x86_64", cpu_x86_64);
+ io.enumCase(value, "x86", cpu_x86);
+ io.enumCase(value, "PowerPC", cpu_PowerPC);
+ }
+ };
+
+ template <>
+ struct MappingTraits<Info> {
+ static void mapping(IO &io, Info &info) {
+ io.mapRequired("cpu", info.cpu);
+ io.mapOptional("flags", info.flags, 0);
+ }
+ };
+
+When reading YAML, if the string found does not match any of the strings
+specified by enumCase() methods, an error is automatically generated.
+When writing YAML, if the value being written does not match any of the values
+specified by the enumCase() methods, a runtime assertion is triggered.
+
+
+BitValue
+--------
+Another common data structure in C++ is a field where each bit has a unique
+meaning. This is often used in a "flags" field. YAML I/O has support for
+converting such fields to a flow sequence. For instance suppose you
+had the following bit flags defined:
+
+.. code-block:: c++
+
+ enum {
+ flagsPointy = 1
+ flagsHollow = 2
+ flagsFlat = 4
+ flagsRound = 8
+ };
+
+ LLVM_YAML_STRONG_TYPEDEF(uint32_t, MyFlags)
+
+To support reading and writing of MyFlags, you specialize ScalarBitSetTraits<>
+on MyFlags and provide the bit values and their names.
+
+.. code-block:: c++
+
+ using llvm::yaml::ScalarBitSetTraits;
+ using llvm::yaml::MappingTraits;
+ using llvm::yaml::IO;
+
+ template <>
+ struct ScalarBitSetTraits<MyFlags> {
+ static void bitset(IO &io, MyFlags &value) {
+ io.bitSetCase(value, "hollow", flagHollow);
+ io.bitSetCase(value, "flat", flagFlat);
+ io.bitSetCase(value, "round", flagRound);
+ io.bitSetCase(value, "pointy", flagPointy);
+ }
+ };
+
+ struct Info {
+ StringRef name;
+ MyFlags flags;
+ };
+
+ template <>
+ struct MappingTraits<Info> {
+ static void mapping(IO &io, Info& info) {
+ io.mapRequired("name", info.name);
+ io.mapRequired("flags", info.flags);
+ }
+ };
+
+With the above, YAML I/O (when writing) will test mask each value in the
+bitset trait against the flags field, and each that matches will
+cause the corresponding string to be added to the flow sequence. The opposite
+is done when reading and any unknown string values will result in a error. With
+the above schema, a same valid YAML document is:
+
+.. code-block:: yaml
+
+ name: Tom
+ flags: [ pointy, flat ]
+
+Sometimes a "flags" field might contains an enumeration part
+defined by a bit-mask.
+
+.. code-block:: c++
+
+ enum {
+ flagsFeatureA = 1,
+ flagsFeatureB = 2,
+ flagsFeatureC = 4,
+
+ flagsCPUMask = 24,
+
+ flagsCPU1 = 8,
+ flagsCPU2 = 16
+ };
+
+To support reading and writing such fields, you need to use the maskedBitSet()
+method and provide the bit values, their names and the enumeration mask.
+
+.. code-block:: c++
+
+ template <>
+ struct ScalarBitSetTraits<MyFlags> {
+ static void bitset(IO &io, MyFlags &value) {
+ io.bitSetCase(value, "featureA", flagsFeatureA);
+ io.bitSetCase(value, "featureB", flagsFeatureB);
+ io.bitSetCase(value, "featureC", flagsFeatureC);
+ io.maskedBitSetCase(value, "CPU1", flagsCPU1, flagsCPUMask);
+ io.maskedBitSetCase(value, "CPU2", flagsCPU2, flagsCPUMask);
+ }
+ };
+
+YAML I/O (when writing) will apply the enumeration mask to the flags field,
+and compare the result and values from the bitset. As in case of a regular
+bitset, each that matches will cause the corresponding string to be added
+to the flow sequence.
+
+Custom Scalar
+-------------
+Sometimes for readability a scalar needs to be formatted in a custom way. For
+instance your internal data structure may use a integer for time (seconds since
+some epoch), but in YAML it would be much nicer to express that integer in
+some time format (e.g. 4-May-2012 10:30pm). YAML I/O has a way to support
+custom formatting and parsing of scalar types by specializing ScalarTraits<> on
+your data type. When writing, YAML I/O will provide the native type and
+your specialization must create a temporary llvm::StringRef. When reading,
+YAML I/O will provide an llvm::StringRef of scalar and your specialization
+must convert that to your native data type. An outline of a custom scalar type
+looks like:
+
+.. code-block:: c++
+
+ using llvm::yaml::ScalarTraits;
+ using llvm::yaml::IO;
+
+ template <>
+ struct ScalarTraits<MyCustomType> {
+ static void output(const MyCustomType &value, void*,
+ llvm::raw_ostream &out) {
+ out << value; // do custom formatting here
+ }
+ static StringRef input(StringRef scalar, void*, MyCustomType &value) {
+ // do custom parsing here. Return the empty string on success,
+ // or an error message on failure.
+ return StringRef();
+ }
+ // Determine if this scalar needs quotes.
+ static bool mustQuote(StringRef) { return true; }
+ };
+
+Block Scalars
+-------------
+
+YAML block scalars are string literals that are represented in YAML using the
+literal block notation, just like the example shown below:
+
+.. code-block:: yaml
+
+ text: |
+ First line
+ Second line
+
+The YAML I/O library provides support for translating between YAML block scalars
+and specific C++ types by allowing you to specialize BlockScalarTraits<> on
+your data type. The library doesn't provide any built-in support for block
+scalar I/O for types like std::string and llvm::StringRef as they are already
+supported by YAML I/O and use the ordinary scalar notation by default.
+
+BlockScalarTraits specializations are very similar to the
+ScalarTraits specialization - YAML I/O will provide the native type and your
+specialization must create a temporary llvm::StringRef when writing, and
+it will also provide an llvm::StringRef that has the value of that block scalar
+and your specialization must convert that to your native data type when reading.
+An example of a custom type with an appropriate specialization of
+BlockScalarTraits is shown below:
+
+.. code-block:: c++
+
+ using llvm::yaml::BlockScalarTraits;
+ using llvm::yaml::IO;
+
+ struct MyStringType {
+ std::string Str;
+ };
+
+ template <>
+ struct BlockScalarTraits<MyStringType> {
+ static void output(const MyStringType &Value, void *Ctxt,
+ llvm::raw_ostream &OS) {
+ OS << Value.Str;
+ }
+
+ static StringRef input(StringRef Scalar, void *Ctxt,
+ MyStringType &Value) {
+ Value.Str = Scalar.str();
+ return StringRef();
+ }
+ };
+
+
+
+Mappings
+========
+
+To be translated to or from a YAML mapping for your type T you must specialize
+llvm::yaml::MappingTraits on T and implement the "void mapping(IO &io, T&)"
+method. If your native data structures use pointers to a class everywhere,
+you can specialize on the class pointer. Examples:
+
+.. code-block:: c++
+
+ using llvm::yaml::MappingTraits;
+ using llvm::yaml::IO;
+
+ // Example of struct Foo which is used by value
+ template <>
+ struct MappingTraits<Foo> {
+ static void mapping(IO &io, Foo &foo) {
+ io.mapOptional("size", foo.size);
+ ...
+ }
+ };
+
+ // Example of struct Bar which is natively always a pointer
+ template <>
+ struct MappingTraits<Bar*> {
+ static void mapping(IO &io, Bar *&bar) {
+ io.mapOptional("size", bar->size);
+ ...
+ }
+ };
+
+
+No Normalization
+----------------
+
+The mapping() method is responsible, if needed, for normalizing and
+denormalizing. In a simple case where the native data structure requires no
+normalization, the mapping method just uses mapOptional() or mapRequired() to
+bind the struct's fields to YAML key names. For example:
+
+.. code-block:: c++
+
+ using llvm::yaml::MappingTraits;
+ using llvm::yaml::IO;
+
+ template <>
+ struct MappingTraits<Person> {
+ static void mapping(IO &io, Person &info) {
+ io.mapRequired("name", info.name);
+ io.mapOptional("hat-size", info.hatSize);
+ }
+ };
+
+
+Normalization
+----------------
+
+When [de]normalization is required, the mapping() method needs a way to access
+normalized values as fields. To help with this, there is
+a template MappingNormalization<> which you can then use to automatically
+do the normalization and denormalization. The template is used to create
+a local variable in your mapping() method which contains the normalized keys.
+
+Suppose you have native data type
+Polar which specifies a position in polar coordinates (distance, angle):
+
+.. code-block:: c++
+
+ struct Polar {
+ float distance;
+ float angle;
+ };
+
+but you've decided the normalized YAML for should be in x,y coordinates. That
+is, you want the yaml to look like:
+
+.. code-block:: yaml
+
+ x: 10.3
+ y: -4.7
+
+You can support this by defining a MappingTraits that normalizes the polar
+coordinates to x,y coordinates when writing YAML and denormalizes x,y
+coordinates into polar when reading YAML.
+
+.. code-block:: c++
+
+ using llvm::yaml::MappingTraits;
+ using llvm::yaml::IO;
+
+ template <>
+ struct MappingTraits<Polar> {
+
+ class NormalizedPolar {
+ public:
+ NormalizedPolar(IO &io)
+ : x(0.0), y(0.0) {
+ }
+ NormalizedPolar(IO &, Polar &polar)
+ : x(polar.distance * cos(polar.angle)),
+ y(polar.distance * sin(polar.angle)) {
+ }
+ Polar denormalize(IO &) {
+ return Polar(sqrt(x*x+y*y), arctan(x,y));
+ }
+
+ float x;
+ float y;
+ };
+
+ static void mapping(IO &io, Polar &polar) {
+ MappingNormalization<NormalizedPolar, Polar> keys(io, polar);
+
+ io.mapRequired("x", keys->x);
+ io.mapRequired("y", keys->y);
+ }
+ };
+
+When writing YAML, the local variable "keys" will be a stack allocated
+instance of NormalizedPolar, constructed from the supplied polar object which
+initializes it x and y fields. The mapRequired() methods then write out the x
+and y values as key/value pairs.
+
+When reading YAML, the local variable "keys" will be a stack allocated instance
+of NormalizedPolar, constructed by the empty constructor. The mapRequired
+methods will find the matching key in the YAML document and fill in the x and y
+fields of the NormalizedPolar object keys. At the end of the mapping() method
+when the local keys variable goes out of scope, the denormalize() method will
+automatically be called to convert the read values back to polar coordinates,
+and then assigned back to the second parameter to mapping().
+
+In some cases, the normalized class may be a subclass of the native type and
+could be returned by the denormalize() method, except that the temporary
+normalized instance is stack allocated. In these cases, the utility template
+MappingNormalizationHeap<> can be used instead. It just like
+MappingNormalization<> except that it heap allocates the normalized object
+when reading YAML. It never destroys the normalized object. The denormalize()
+method can this return "this".
+
+
+Default values
+--------------
+Within a mapping() method, calls to io.mapRequired() mean that that key is
+required to exist when parsing YAML documents, otherwise YAML I/O will issue an
+error.
+
+On the other hand, keys registered with io.mapOptional() are allowed to not
+exist in the YAML document being read. So what value is put in the field
+for those optional keys?
+There are two steps to how those optional fields are filled in. First, the
+second parameter to the mapping() method is a reference to a native class. That
+native class must have a default constructor. Whatever value the default
+constructor initially sets for an optional field will be that field's value.
+Second, the mapOptional() method has an optional third parameter. If provided
+it is the value that mapOptional() should set that field to if the YAML document
+does not have that key.
+
+There is one important difference between those two ways (default constructor
+and third parameter to mapOptional). When YAML I/O generates a YAML document,
+if the mapOptional() third parameter is used, if the actual value being written
+is the same as (using ==) the default value, then that key/value is not written.
+
+
+Order of Keys
+--------------
+
+When writing out a YAML document, the keys are written in the order that the
+calls to mapRequired()/mapOptional() are made in the mapping() method. This
+gives you a chance to write the fields in an order that a human reader of
+the YAML document would find natural. This may be different that the order
+of the fields in the native class.
+
+When reading in a YAML document, the keys in the document can be in any order,
+but they are processed in the order that the calls to mapRequired()/mapOptional()
+are made in the mapping() method. That enables some interesting
+functionality. For instance, if the first field bound is the cpu and the second
+field bound is flags, and the flags are cpu specific, you can programmatically
+switch how the flags are converted to and from YAML based on the cpu.
+This works for both reading and writing. For example:
+
+.. code-block:: c++
+
+ using llvm::yaml::MappingTraits;
+ using llvm::yaml::IO;
+
+ struct Info {
+ CPUs cpu;
+ uint32_t flags;
+ };
+
+ template <>
+ struct MappingTraits<Info> {
+ static void mapping(IO &io, Info &info) {
+ io.mapRequired("cpu", info.cpu);
+ // flags must come after cpu for this to work when reading yaml
+ if ( info.cpu == cpu_x86_64 )
+ io.mapRequired("flags", *(My86_64Flags*)info.flags);
+ else
+ io.mapRequired("flags", *(My86Flags*)info.flags);
+ }
+ };
+
+
+Tags
+----
+
+The YAML syntax supports tags as a way to specify the type of a node before
+it is parsed. This allows dynamic types of nodes. But the YAML I/O model uses
+static typing, so there are limits to how you can use tags with the YAML I/O
+model. Recently, we added support to YAML I/O for checking/setting the optional
+tag on a map. Using this functionality it is even possbile to support different
+mappings, as long as they are convertable.
+
+To check a tag, inside your mapping() method you can use io.mapTag() to specify
+what the tag should be. This will also add that tag when writing yaml.
+
+Validation
+----------
+
+Sometimes in a yaml map, each key/value pair is valid, but the combination is
+not. This is similar to something having no syntax errors, but still having
+semantic errors. To support semantic level checking, YAML I/O allows
+an optional ``validate()`` method in a MappingTraits template specialization.
+
+When parsing yaml, the ``validate()`` method is call *after* all key/values in
+the map have been processed. Any error message returned by the ``validate()``
+method during input will be printed just a like a syntax error would be printed.
+When writing yaml, the ``validate()`` method is called *before* the yaml
+key/values are written. Any error during output will trigger an ``assert()``
+because it is a programming error to have invalid struct values.
+
+
+.. code-block:: c++
+
+ using llvm::yaml::MappingTraits;
+ using llvm::yaml::IO;
+
+ struct Stuff {
+ ...
+ };
+
+ template <>
+ struct MappingTraits<Stuff> {
+ static void mapping(IO &io, Stuff &stuff) {
+ ...
+ }
+ static StringRef validate(IO &io, Stuff &stuff) {
+ // Look at all fields in 'stuff' and if there
+ // are any bad values return a string describing
+ // the error. Otherwise return an empty string.
+ return StringRef();
+ }
+ };
+
+Flow Mapping
+------------
+A YAML "flow mapping" is a mapping that uses the inline notation
+(e.g { x: 1, y: 0 } ) when written to YAML. To specify that a type should be
+written in YAML using flow mapping, your MappingTraits specialization should
+add "static const bool flow = true;". For instance:
+
+.. code-block:: c++
+
+ using llvm::yaml::MappingTraits;
+ using llvm::yaml::IO;
+
+ struct Stuff {
+ ...
+ };
+
+ template <>
+ struct MappingTraits<Stuff> {
+ static void mapping(IO &io, Stuff &stuff) {
+ ...
+ }
+
+ static const bool flow = true;
+ }
+
+Flow mappings are subject to line wrapping according to the Output object
+configuration.
+
+Sequence
+========
+
+To be translated to or from a YAML sequence for your type T you must specialize
+llvm::yaml::SequenceTraits on T and implement two methods:
+``size_t size(IO &io, T&)`` and
+``T::value_type& element(IO &io, T&, size_t indx)``. For example:
+
+.. code-block:: c++
+
+ template <>
+ struct SequenceTraits<MySeq> {
+ static size_t size(IO &io, MySeq &list) { ... }
+ static MySeqEl &element(IO &io, MySeq &list, size_t index) { ... }
+ };
+
+The size() method returns how many elements are currently in your sequence.
+The element() method returns a reference to the i'th element in the sequence.
+When parsing YAML, the element() method may be called with an index one bigger
+than the current size. Your element() method should allocate space for one
+more element (using default constructor if element is a C++ object) and returns
+a reference to that new allocated space.
+
+
+Flow Sequence
+-------------
+A YAML "flow sequence" is a sequence that when written to YAML it uses the
+inline notation (e.g [ foo, bar ] ). To specify that a sequence type should
+be written in YAML as a flow sequence, your SequenceTraits specialization should
+add "static const bool flow = true;". For instance:
+
+.. code-block:: c++
+
+ template <>
+ struct SequenceTraits<MyList> {
+ static size_t size(IO &io, MyList &list) { ... }
+ static MyListEl &element(IO &io, MyList &list, size_t index) { ... }
+
+ // The existence of this member causes YAML I/O to use a flow sequence
+ static const bool flow = true;
+ };
+
+With the above, if you used MyList as the data type in your native data
+structures, then when converted to YAML, a flow sequence of integers
+will be used (e.g. [ 10, -3, 4 ]).
+
+Flow sequences are subject to line wrapping according to the Output object
+configuration.
+
+Utility Macros
+--------------
+Since a common source of sequences is std::vector<>, YAML I/O provides macros:
+LLVM_YAML_IS_SEQUENCE_VECTOR() and LLVM_YAML_IS_FLOW_SEQUENCE_VECTOR() which
+can be used to easily specify SequenceTraits<> on a std::vector type. YAML
+I/O does not partial specialize SequenceTraits on std::vector<> because that
+would force all vectors to be sequences. An example use of the macros:
+
+.. code-block:: c++
+
+ std::vector<MyType1>;
+ std::vector<MyType2>;
+ LLVM_YAML_IS_SEQUENCE_VECTOR(MyType1)
+ LLVM_YAML_IS_FLOW_SEQUENCE_VECTOR(MyType2)
+
+
+
+Document List
+=============
+
+YAML allows you to define multiple "documents" in a single YAML file. Each
+new document starts with a left aligned "---" token. The end of all documents
+is denoted with a left aligned "..." token. Many users of YAML will never
+have need for multiple documents. The top level node in their YAML schema
+will be a mapping or sequence. For those cases, the following is not needed.
+But for cases where you do want multiple documents, you can specify a
+trait for you document list type. The trait has the same methods as
+SequenceTraits but is named DocumentListTraits. For example:
+
+.. code-block:: c++
+
+ template <>
+ struct DocumentListTraits<MyDocList> {
+ static size_t size(IO &io, MyDocList &list) { ... }
+ static MyDocType element(IO &io, MyDocList &list, size_t index) { ... }
+ };
+
+
+User Context Data
+=================
+When an llvm::yaml::Input or llvm::yaml::Output object is created their
+constructors take an optional "context" parameter. This is a pointer to
+whatever state information you might need.
+
+For instance, in a previous example we showed how the conversion type for a
+flags field could be determined at runtime based on the value of another field
+in the mapping. But what if an inner mapping needs to know some field value
+of an outer mapping? That is where the "context" parameter comes in. You
+can set values in the context in the outer map's mapping() method and
+retrieve those values in the inner map's mapping() method.
+
+The context value is just a void*. All your traits which use the context
+and operate on your native data types, need to agree what the context value
+actually is. It could be a pointer to an object or struct which your various
+traits use to shared context sensitive information.
+
+
+Output
+======
+
+The llvm::yaml::Output class is used to generate a YAML document from your
+in-memory data structures, using traits defined on your data types.
+To instantiate an Output object you need an llvm::raw_ostream, an optional
+context pointer and an optional wrapping column:
+
+.. code-block:: c++
+
+ class Output : public IO {
+ public:
+ Output(llvm::raw_ostream &, void *context = NULL, int WrapColumn = 70);
+
+Once you have an Output object, you can use the C++ stream operator on it
+to write your native data as YAML. One thing to recall is that a YAML file
+can contain multiple "documents". If the top level data structure you are
+streaming as YAML is a mapping, scalar, or sequence, then Output assumes you
+are generating one document and wraps the mapping output
+with "``---``" and trailing "``...``".
+
+The WrapColumn parameter will cause the flow mappings and sequences to
+line-wrap when they go over the supplied column. Pass 0 to completely
+suppress the wrapping.
+
+.. code-block:: c++
+
+ using llvm::yaml::Output;
+
+ void dumpMyMapDoc(const MyMapType &info) {
+ Output yout(llvm::outs());
+ yout << info;
+ }
+
+The above could produce output like:
+
+.. code-block:: yaml
+
+ ---
+ name: Tom
+ hat-size: 7
+ ...
+
+On the other hand, if the top level data structure you are streaming as YAML
+has a DocumentListTraits specialization, then Output walks through each element
+of your DocumentList and generates a "---" before the start of each element
+and ends with a "...".
+
+.. code-block:: c++
+
+ using llvm::yaml::Output;
+
+ void dumpMyMapDoc(const MyDocListType &docList) {
+ Output yout(llvm::outs());
+ yout << docList;
+ }
+
+The above could produce output like:
+
+.. code-block:: yaml
+
+ ---
+ name: Tom
+ hat-size: 7
+ ---
+ name: Tom
+ shoe-size: 11
+ ...
+
+Input
+=====
+
+The llvm::yaml::Input class is used to parse YAML document(s) into your native
+data structures. To instantiate an Input
+object you need a StringRef to the entire YAML file, and optionally a context
+pointer:
+
+.. code-block:: c++
+
+ class Input : public IO {
+ public:
+ Input(StringRef inputContent, void *context=NULL);
+
+Once you have an Input object, you can use the C++ stream operator to read
+the document(s). If you expect there might be multiple YAML documents in
+one file, you'll need to specialize DocumentListTraits on a list of your
+document type and stream in that document list type. Otherwise you can
+just stream in the document type. Also, you can check if there was
+any syntax errors in the YAML be calling the error() method on the Input
+object. For example:
+
+.. code-block:: c++
+
+ // Reading a single document
+ using llvm::yaml::Input;
+
+ Input yin(mb.getBuffer());
+
+ // Parse the YAML file
+ MyDocType theDoc;
+ yin >> theDoc;
+
+ // Check for error
+ if ( yin.error() )
+ return;
+
+
+.. code-block:: c++
+
+ // Reading multiple documents in one file
+ using llvm::yaml::Input;
+
+ LLVM_YAML_IS_DOCUMENT_LIST_VECTOR(std::vector<MyDocType>)
+
+ Input yin(mb.getBuffer());
+
+ // Parse the YAML file
+ std::vector<MyDocType> theDocList;
+ yin >> theDocList;
+
+ // Check for error
+ if ( yin.error() )
+ return;
+
+
Added: www-releases/trunk/3.9.1/docs/_sources/index.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.9.1/docs/_sources/index.txt?rev=290368&view=auto
==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/index.txt (added)
+++ www-releases/trunk/3.9.1/docs/_sources/index.txt Thu Dec 22 14:04:03 2016
@@ -0,0 +1,491 @@
+Overview
+========
+
+The LLVM compiler infrastructure supports a wide range of projects, from
+industrial strength compilers to specialized JIT applications to small
+research projects.
+
+Similarly, documentation is broken down into several high-level groupings
+targeted at different audiences:
+
+LLVM Design & Overview
+======================
+
+Several introductory papers and presentations.
+
+.. toctree::
+ :hidden:
+
+ LangRef
+
+:doc:`LangRef`
+ Defines the LLVM intermediate representation.
+
+`Introduction to the LLVM Compiler`__
+ Presentation providing a users introduction to LLVM.
+
+ .. __: http://llvm.org/pubs/2008-10-04-ACAT-LLVM-Intro.html
+
+`Intro to LLVM`__
+ Book chapter providing a compiler hacker's introduction to LLVM.
+
+ .. __: http://www.aosabook.org/en/llvm.html
+
+
+`LLVM: A Compilation Framework for Lifelong Program Analysis & Transformation`__
+ Design overview.
+
+ .. __: http://llvm.org/pubs/2004-01-30-CGO-LLVM.html
+
+`LLVM: An Infrastructure for Multi-Stage Optimization`__
+ More details (quite old now).
+
+ .. __: http://llvm.org/pubs/2002-12-LattnerMSThesis.html
+
+`Publications mentioning LLVM <http://llvm.org/pubs>`_
+ ..
+
+User Guides
+===========
+
+For those new to the LLVM system.
+
+NOTE: If you are a user who is only interested in using LLVM-based
+compilers, you should look into `Clang <http://clang.llvm.org>`_ or
+`DragonEgg <http://dragonegg.llvm.org>`_ instead. The documentation here is
+intended for users who have a need to work with the intermediate LLVM
+representation.
+
+.. toctree::
+ :hidden:
+
+ CMake
+ CMakePrimer
+ AdvancedBuilds
+ HowToBuildOnARM
+ HowToCrossCompileLLVM
+ CommandGuide/index
+ GettingStarted
+ GettingStartedVS
+ FAQ
+ Lexicon
+ HowToAddABuilder
+ yaml2obj
+ HowToSubmitABug
+ SphinxQuickstartTemplate
+ Phabricator
+ TestingGuide
+ tutorial/index
+ ReleaseNotes
+ Passes
+ YamlIO
+ GetElementPtr
+ Frontend/PerformanceTips
+ MCJITDesignAndImplementation
+ CodeOfConduct
+ CompileCudaWithLLVM
+ ReportingGuide
+
+:doc:`GettingStarted`
+ Discusses how to get up and running quickly with the LLVM infrastructure.
+ Everything from unpacking and compilation of the distribution to execution
+ of some tools.
+
+:doc:`CMake`
+ An addendum to the main Getting Started guide for those using the `CMake
+ build system <http://www.cmake.org>`_.
+
+:doc:`HowToBuildOnARM`
+ Notes on building and testing LLVM/Clang on ARM.
+
+:doc:`HowToCrossCompileLLVM`
+ Notes on cross-building and testing LLVM/Clang.
+
+:doc:`GettingStartedVS`
+ An addendum to the main Getting Started guide for those using Visual Studio
+ on Windows.
+
+:doc:`tutorial/index`
+ Tutorials about using LLVM. Includes a tutorial about making a custom
+ language with LLVM.
+
+:doc:`LLVM Command Guide <CommandGuide/index>`
+ A reference manual for the LLVM command line utilities ("man" pages for LLVM
+ tools).
+
+:doc:`Passes`
+ A list of optimizations and analyses implemented in LLVM.
+
+:doc:`FAQ`
+ A list of common questions and problems and their solutions.
+
+:doc:`Release notes for the current release <ReleaseNotes>`
+ This describes new features, known bugs, and other limitations.
+
+:doc:`HowToSubmitABug`
+ Instructions for properly submitting information about any bugs you run into
+ in the LLVM system.
+
+:doc:`SphinxQuickstartTemplate`
+ A template + tutorial for writing new Sphinx documentation. It is meant
+ to be read in source form.
+
+:doc:`LLVM Testing Infrastructure Guide <TestingGuide>`
+ A reference manual for using the LLVM testing infrastructure.
+
+`How to build the C, C++, ObjC, and ObjC++ front end`__
+ Instructions for building the clang front-end from source.
+
+ .. __: http://clang.llvm.org/get_started.html
+
+:doc:`Lexicon`
+ Definition of acronyms, terms and concepts used in LLVM.
+
+:doc:`HowToAddABuilder`
+ Instructions for adding new builder to LLVM buildbot master.
+
+:doc:`YamlIO`
+ A reference guide for using LLVM's YAML I/O library.
+
+:doc:`GetElementPtr`
+ Answers to some very frequent questions about LLVM's most frequently
+ misunderstood instruction.
+
+:doc:`Frontend/PerformanceTips`
+ A collection of tips for frontend authors on how to generate IR
+ which LLVM is able to effectively optimize.
+
+
+Programming Documentation
+=========================
+
+For developers of applications which use LLVM as a library.
+
+.. toctree::
+ :hidden:
+
+ Atomics
+ CodingStandards
+ CommandLine
+ CompilerWriterInfo
+ ExtendingLLVM
+ HowToSetUpLLVMStyleRTTI
+ ProgrammersManual
+ Extensions
+ LibFuzzer
+ ScudoHardenedAllocator
+
+:doc:`LLVM Language Reference Manual <LangRef>`
+ Defines the LLVM intermediate representation and the assembly form of the
+ different nodes.
+
+:doc:`Atomics`
+ Information about LLVM's concurrency model.
+
+:doc:`ProgrammersManual`
+ Introduction to the general layout of the LLVM sourcebase, important classes
+ and APIs, and some tips & tricks.
+
+:doc:`Extensions`
+ LLVM-specific extensions to tools and formats LLVM seeks compatibility with.
+
+:doc:`CommandLine`
+ Provides information on using the command line parsing library.
+
+:doc:`CodingStandards`
+ Details the LLVM coding standards and provides useful information on writing
+ efficient C++ code.
+
+:doc:`HowToSetUpLLVMStyleRTTI`
+ How to make ``isa<>``, ``dyn_cast<>``, etc. available for clients of your
+ class hierarchy.
+
+:doc:`ExtendingLLVM`
+ Look here to see how to add instructions and intrinsics to LLVM.
+
+`Doxygen generated documentation <http://llvm.org/doxygen/>`_
+ (`classes <http://llvm.org/doxygen/inherits.html>`_)
+ (`tarball <http://llvm.org/doxygen/doxygen.tar.gz>`_)
+
+`Documentation for Go bindings <http://godoc.org/llvm.org/llvm/bindings/go/llvm>`_
+
+`ViewVC Repository Browser <http://llvm.org/viewvc/>`_
+ ..
+
+:doc:`CompilerWriterInfo`
+ A list of helpful links for compiler writers.
+
+:doc:`LibFuzzer`
+ A library for writing in-process guided fuzzers.
+
+:doc:`ScudoHardenedAllocator`
+ A library that implements a security-hardened `malloc()`.
+
+Subsystem Documentation
+=======================
+
+For API clients and LLVM developers.
+
+.. toctree::
+ :hidden:
+
+ AliasAnalysis
+ BitCodeFormat
+ BlockFrequencyTerminology
+ BranchWeightMetadata
+ Bugpoint
+ CodeGenerator
+ ExceptionHandling
+ LinkTimeOptimization
+ SegmentedStacks
+ TableGenFundamentals
+ TableGen/index
+ DebuggingJITedCode
+ GoldPlugin
+ MarkedUpDisassembly
+ SystemLibrary
+ SourceLevelDebugging
+ Vectorizers
+ WritingAnLLVMBackend
+ GarbageCollection
+ WritingAnLLVMPass
+ HowToUseAttributes
+ NVPTXUsage
+ AMDGPUUsage
+ StackMaps
+ InAlloca
+ BigEndianNEON
+ CoverageMappingFormat
+ Statepoints
+ MergeFunctions
+ TypeMetadata
+ FaultMaps
+ MIRLangRef
+
+:doc:`WritingAnLLVMPass`
+ Information on how to write LLVM transformations and analyses.
+
+:doc:`WritingAnLLVMBackend`
+ Information on how to write LLVM backends for machine targets.
+
+:doc:`CodeGenerator`
+ The design and implementation of the LLVM code generator. Useful if you are
+ working on retargetting LLVM to a new architecture, designing a new codegen
+ pass, or enhancing existing components.
+
+:doc:`Machine IR (MIR) Format Reference Manual <MIRLangRef>`
+ A reference manual for the MIR serialization format, which is used to test
+ LLVM's code generation passes.
+
+:doc:`TableGen <TableGen/index>`
+ Describes the TableGen tool, which is used heavily by the LLVM code
+ generator.
+
+:doc:`AliasAnalysis`
+ Information on how to write a new alias analysis implementation or how to
+ use existing analyses.
+
+:doc:`GarbageCollection`
+ The interfaces source-language compilers should use for compiling GC'd
+ programs.
+
+:doc:`Source Level Debugging with LLVM <SourceLevelDebugging>`
+ This document describes the design and philosophy behind the LLVM
+ source-level debugger.
+
+:doc:`Vectorizers`
+ This document describes the current status of vectorization in LLVM.
+
+:doc:`ExceptionHandling`
+ This document describes the design and implementation of exception handling
+ in LLVM.
+
+:doc:`Bugpoint`
+ Automatic bug finder and test-case reducer description and usage
+ information.
+
+:doc:`BitCodeFormat`
+ This describes the file format and encoding used for LLVM "bc" files.
+
+:doc:`System Library <SystemLibrary>`
+ This document describes the LLVM System Library (``lib/System``) and
+ how to keep LLVM source code portable
+
+:doc:`LinkTimeOptimization`
+ This document describes the interface between LLVM intermodular optimizer
+ and the linker and its design
+
+:doc:`GoldPlugin`
+ How to build your programs with link-time optimization on Linux.
+
+:doc:`DebuggingJITedCode`
+ How to debug JITed code with GDB.
+
+:doc:`MCJITDesignAndImplementation`
+ Describes the inner workings of MCJIT execution engine.
+
+:doc:`BranchWeightMetadata`
+ Provides information about Branch Prediction Information.
+
+:doc:`BlockFrequencyTerminology`
+ Provides information about terminology used in the ``BlockFrequencyInfo``
+ analysis pass.
+
+:doc:`SegmentedStacks`
+ This document describes segmented stacks and how they are used in LLVM.
+
+:doc:`MarkedUpDisassembly`
+ This document describes the optional rich disassembly output syntax.
+
+:doc:`HowToUseAttributes`
+ Answers some questions about the new Attributes infrastructure.
+
+:doc:`NVPTXUsage`
+ This document describes using the NVPTX back-end to compile GPU kernels.
+
+:doc:`AMDGPUUsage`
+ This document describes how to use the AMDGPU back-end.
+
+:doc:`StackMaps`
+ LLVM support for mapping instruction addresses to the location of
+ values and allowing code to be patched.
+
+:doc:`BigEndianNEON`
+ LLVM's support for generating NEON instructions on big endian ARM targets is
+ somewhat nonintuitive. This document explains the implementation and rationale.
+
+:doc:`CoverageMappingFormat`
+ This describes the format and encoding used for LLVM’s code coverage mapping.
+
+:doc:`Statepoints`
+ This describes a set of experimental extensions for garbage
+ collection support.
+
+:doc:`MergeFunctions`
+ Describes functions merging optimization.
+
+:doc:`InAlloca`
+ Description of the ``inalloca`` argument attribute.
+
+:doc:`FaultMaps`
+ LLVM support for folding control flow into faulting machine instructions.
+
+:doc:`CompileCudaWithLLVM`
+ LLVM support for CUDA.
+
+Development Process Documentation
+=================================
+
+Information about LLVM's development process.
+
+.. toctree::
+ :hidden:
+
+ DeveloperPolicy
+ Projects
+ LLVMBuild
+ HowToReleaseLLVM
+ Packaging
+ ReleaseProcess
+ Phabricator
+
+:doc:`DeveloperPolicy`
+ The LLVM project's policy towards developers and their contributions.
+
+:doc:`Projects`
+ How-to guide and templates for new projects that *use* the LLVM
+ infrastructure. The templates (directory organization, Makefiles, and test
+ tree) allow the project code to be located outside (or inside) the ``llvm/``
+ tree, while using LLVM header files and libraries.
+
+:doc:`LLVMBuild`
+ Describes the LLVMBuild organization and files used by LLVM to specify
+ component descriptions.
+
+:doc:`HowToReleaseLLVM`
+ This is a guide to preparing LLVM releases. Most developers can ignore it.
+
+:doc:`ReleaseProcess`
+ This is a guide to validate a new release, during the release process. Most developers can ignore it.
+
+:doc:`Packaging`
+ Advice on packaging LLVM into a distribution.
+
+:doc:`Phabricator`
+ Describes how to use the Phabricator code review tool hosted on
+ http://reviews.llvm.org/ and its command line interface, Arcanist.
+
+Community
+=========
+
+LLVM has a thriving community of friendly and helpful developers.
+The two primary communication mechanisms in the LLVM community are mailing
+lists and IRC.
+
+Mailing Lists
+-------------
+
+If you can't find what you need in these docs, try consulting the mailing
+lists.
+
+`Developer's List (llvm-dev)`__
+ This list is for people who want to be included in technical discussions of
+ LLVM. People post to this list when they have questions about writing code
+ for or using the LLVM tools. It is relatively low volume.
+
+ .. __: http://lists.llvm.org/mailman/listinfo/llvm-dev
+
+`Commits Archive (llvm-commits)`__
+ This list contains all commit messages that are made when LLVM developers
+ commit code changes to the repository. It also serves as a forum for
+ patch review (i.e. send patches here). It is useful for those who want to
+ stay on the bleeding edge of LLVM development. This list is very high
+ volume.
+
+ .. __: http://lists.llvm.org/pipermail/llvm-commits/
+
+`Bugs & Patches Archive (llvm-bugs)`__
+ This list gets emailed every time a bug is opened and closed. It is
+ higher volume than the LLVM-dev list.
+
+ .. __: http://lists.llvm.org/pipermail/llvm-bugs/
+
+`Test Results Archive (llvm-testresults)`__
+ A message is automatically sent to this list by every active nightly tester
+ when it completes. As such, this list gets email several times each day,
+ making it a high volume list.
+
+ .. __: http://lists.llvm.org/pipermail/llvm-testresults/
+
+`LLVM Announcements List (llvm-announce)`__
+ This is a low volume list that provides important announcements regarding
+ LLVM. It gets email about once a month.
+
+ .. __: http://lists.llvm.org/mailman/listinfo/llvm-announce
+
+IRC
+---
+
+Users and developers of the LLVM project (including subprojects such as Clang)
+can be found in #llvm on `irc.oftc.net <irc://irc.oftc.net/llvm>`_.
+
+This channel has several bots.
+
+* Buildbot reporters
+
+ * llvmbb - Bot for the main LLVM buildbot master.
+ http://lab.llvm.org:8011/console
+ * bb-chapuni - An individually run buildbot master. http://bb.pgr.jp/console
+ * smooshlab - Apple's internal buildbot master.
+
+* robot - Bugzilla linker. %bug <number>
+
+* clang-bot - A `geordi <http://www.eelis.net/geordi/>`_ instance running
+ near-trunk clang instead of gcc.
+
+
+Indices and tables
+==================
+
+* :ref:`genindex`
+* :ref:`search`
Added: www-releases/trunk/3.9.1/docs/_sources/tutorial/BuildingAJIT1.txt
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==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/tutorial/BuildingAJIT1.txt (added)
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@@ -0,0 +1,375 @@
+=======================================================
+Building a JIT: Starting out with KaleidoscopeJIT
+=======================================================
+
+.. contents::
+ :local:
+
+Chapter 1 Introduction
+======================
+
+Welcome to Chapter 1 of the "Building an ORC-based JIT in LLVM" tutorial. This
+tutorial runs through the implementation of a JIT compiler using LLVM's
+On-Request-Compilation (ORC) APIs. It begins with a simplified version of the
+KaleidoscopeJIT class used in the
+`Implementing a language with LLVM <LangImpl1.html>`_ tutorials and then
+introduces new features like optimization, lazy compilation and remote
+execution.
+
+The goal of this tutorial is to introduce you to LLVM's ORC JIT APIs, show how
+these APIs interact with other parts of LLVM, and to teach you how to recombine
+them to build a custom JIT that is suited to your use-case.
+
+The structure of the tutorial is:
+
+- Chapter #1: Investigate the simple KaleidoscopeJIT class. This will
+ introduce some of the basic concepts of the ORC JIT APIs, including the
+ idea of an ORC *Layer*.
+
+- `Chapter #2 <BuildingAJIT2.html>`_: Extend the basic KaleidoscopeJIT by adding
+ a new layer that will optimize IR and generated code.
+
+- `Chapter #3 <BuildingAJIT3.html>`_: Further extend the JIT by adding a
+ Compile-On-Demand layer to lazily compile IR.
+
+- `Chapter #4 <BuildingAJIT4.html>`_: Improve the laziness of our JIT by
+ replacing the Compile-On-Demand layer with a custom layer that uses the ORC
+ Compile Callbacks API directly to defer IR-generation until functions are
+ called.
+
+- `Chapter #5 <BuildingAJIT5.html>`_: Add process isolation by JITing code into
+ a remote process with reduced privileges using the JIT Remote APIs.
+
+To provide input for our JIT we will use the Kaleidoscope REPL from
+`Chapter 7 <LangImpl7.html>`_ of the "Implementing a language in LLVM tutorial",
+with one minor modification: We will remove the FunctionPassManager from the
+code for that chapter and replace it with optimization support in our JIT class
+in Chapter #2.
+
+Finally, a word on API generations: ORC is the 3rd generation of LLVM JIT API.
+It was preceded by MCJIT, and before that by the (now deleted) legacy JIT.
+These tutorials don't assume any experience with these earlier APIs, but
+readers acquainted with them will see many familiar elements. Where appropriate
+we will make this connection with the earlier APIs explicit to help people who
+are transitioning from them to ORC.
+
+JIT API Basics
+==============
+
+The purpose of a JIT compiler is to compile code "on-the-fly" as it is needed,
+rather than compiling whole programs to disk ahead of time as a traditional
+compiler does. To support that aim our initial, bare-bones JIT API will be:
+
+1. Handle addModule(Module &M) -- Make the given IR module available for
+ execution.
+2. JITSymbol findSymbol(const std::string &Name) -- Search for pointers to
+ symbols (functions or variables) that have been added to the JIT.
+3. void removeModule(Handle H) -- Remove a module from the JIT, releasing any
+ memory that had been used for the compiled code.
+
+A basic use-case for this API, executing the 'main' function from a module,
+will look like:
+
+.. code-block:: c++
+
+ std::unique_ptr<Module> M = buildModule();
+ JIT J;
+ Handle H = J.addModule(*M);
+ int (*Main)(int, char*[]) =
+ (int(*)(int, char*[])J.findSymbol("main").getAddress();
+ int Result = Main();
+ J.removeModule(H);
+
+The APIs that we build in these tutorials will all be variations on this simple
+theme. Behind the API we will refine the implementation of the JIT to add
+support for optimization and lazy compilation. Eventually we will extend the
+API itself to allow higher-level program representations (e.g. ASTs) to be
+added to the JIT.
+
+KaleidoscopeJIT
+===============
+
+In the previous section we described our API, now we examine a simple
+implementation of it: The KaleidoscopeJIT class [1]_ that was used in the
+`Implementing a language with LLVM <LangImpl1.html>`_ tutorials. We will use
+the REPL code from `Chapter 7 <LangImpl7.html>`_ of that tutorial to supply the
+input for our JIT: Each time the user enters an expression the REPL will add a
+new IR module containing the code for that expression to the JIT. If the
+expression is a top-level expression like '1+1' or 'sin(x)', the REPL will also
+use the findSymbol method of our JIT class find and execute the code for the
+expression, and then use the removeModule method to remove the code again
+(since there's no way to re-invoke an anonymous expression). In later chapters
+of this tutorial we'll modify the REPL to enable new interactions with our JIT
+class, but for now we will take this setup for granted and focus our attention on
+the implementation of our JIT itself.
+
+Our KaleidoscopeJIT class is defined in the KaleidoscopeJIT.h header. After the
+usual include guards and #includes [2]_, we get to the definition of our class:
+
+.. code-block:: c++
+
+ #ifndef LLVM_EXECUTIONENGINE_ORC_KALEIDOSCOPEJIT_H
+ #define LLVM_EXECUTIONENGINE_ORC_KALEIDOSCOPEJIT_H
+
+ #include "llvm/ExecutionEngine/ExecutionEngine.h"
+ #include "llvm/ExecutionEngine/RTDyldMemoryManager.h"
+ #include "llvm/ExecutionEngine/Orc/CompileUtils.h"
+ #include "llvm/ExecutionEngine/Orc/IRCompileLayer.h"
+ #include "llvm/ExecutionEngine/Orc/LambdaResolver.h"
+ #include "llvm/ExecutionEngine/Orc/ObjectLinkingLayer.h"
+ #include "llvm/IR/Mangler.h"
+ #include "llvm/Support/DynamicLibrary.h"
+
+ namespace llvm {
+ namespace orc {
+
+ class KaleidoscopeJIT {
+ private:
+
+ std::unique_ptr<TargetMachine> TM;
+ const DataLayout DL;
+ ObjectLinkingLayer<> ObjectLayer;
+ IRCompileLayer<decltype(ObjectLayer)> CompileLayer;
+
+ public:
+
+ typedef decltype(CompileLayer)::ModuleSetHandleT ModuleHandleT;
+
+Our class begins with four members: A TargetMachine, TM, which will be used
+to build our LLVM compiler instance; A DataLayout, DL, which will be used for
+symbol mangling (more on that later), and two ORC *layers*: an
+ObjectLinkingLayer and a IRCompileLayer. We'll be talking more about layers in
+the next chapter, but for now you can think of them as analogous to LLVM
+Passes: they wrap up useful JIT utilities behind an easy to compose interface.
+The first layer, ObjectLinkingLayer, is the foundation of our JIT: it takes
+in-memory object files produced by a compiler and links them on the fly to make
+them executable. This JIT-on-top-of-a-linker design was introduced in MCJIT,
+however the linker was hidden inside the MCJIT class. In ORC we expose the
+linker so that clients can access and configure it directly if they need to. In
+this tutorial our ObjectLinkingLayer will just be used to support the next layer
+in our stack: the IRCompileLayer, which will be responsible for taking LLVM IR,
+compiling it, and passing the resulting in-memory object files down to the
+object linking layer below.
+
+That's it for member variables, after that we have a single typedef:
+ModuleHandle. This is the handle type that will be returned from our JIT's
+addModule method, and can be passed to the removeModule method to remove a
+module. The IRCompileLayer class already provides a convenient handle type
+(IRCompileLayer::ModuleSetHandleT), so we just alias our ModuleHandle to this.
+
+.. code-block:: c++
+
+ KaleidoscopeJIT()
+ : TM(EngineBuilder().selectTarget()), DL(TM->createDataLayout()),
+ CompileLayer(ObjectLayer, SimpleCompiler(*TM)) {
+ llvm::sys::DynamicLibrary::LoadLibraryPermanently(nullptr);
+ }
+
+ TargetMachine &getTargetMachine() { return *TM; }
+
+Next up we have our class constructor. We begin by initializing TM using the
+EngineBuilder::selectTarget helper method, which constructs a TargetMachine for
+the current process. Next we use our newly created TargetMachine to initialize
+DL, our DataLayout. Then we initialize our IRCompileLayer. Our IRCompile layer
+needs two things: (1) A reference to our object linking layer, and (2) a
+compiler instance to use to perform the actual compilation from IR to object
+files. We use the off-the-shelf SimpleCompiler instance for now. Finally, in
+the body of the constructor, we call the DynamicLibrary::LoadLibraryPermanently
+method with a nullptr argument. Normally the LoadLibraryPermanently method is
+called with the path of a dynamic library to load, but when passed a null
+pointer it will 'load' the host process itself, making its exported symbols
+available for execution.
+
+.. code-block:: c++
+
+ ModuleHandle addModule(std::unique_ptr<Module> M) {
+ // Build our symbol resolver:
+ // Lambda 1: Look back into the JIT itself to find symbols that are part of
+ // the same "logical dylib".
+ // Lambda 2: Search for external symbols in the host process.
+ auto Resolver = createLambdaResolver(
+ [&](const std::string &Name) {
+ if (auto Sym = CompileLayer.findSymbol(Name, false))
+ return Sym.toRuntimeDyldSymbol();
+ return RuntimeDyld::SymbolInfo(nullptr);
+ },
+ [](const std::string &S) {
+ if (auto SymAddr =
+ RTDyldMemoryManager::getSymbolAddressInProcess(Name))
+ return RuntimeDyld::SymbolInfo(SymAddr, JITSymbolFlags::Exported);
+ return RuntimeDyld::SymbolInfo(nullptr);
+ });
+
+ // Build a singlton module set to hold our module.
+ std::vector<std::unique_ptr<Module>> Ms;
+ Ms.push_back(std::move(M));
+
+ // Add the set to the JIT with the resolver we created above and a newly
+ // created SectionMemoryManager.
+ return CompileLayer.addModuleSet(std::move(Ms),
+ make_unique<SectionMemoryManager>(),
+ std::move(Resolver));
+ }
+
+Now we come to the first of our JIT API methods: addModule. This method is
+responsible for adding IR to the JIT and making it available for execution. In
+this initial implementation of our JIT we will make our modules "available for
+execution" by adding them straight to the IRCompileLayer, which will
+immediately compile them. In later chapters we will teach our JIT to be lazier
+and instead add the Modules to a "pending" list to be compiled if and when they
+are first executed.
+
+To add our module to the IRCompileLayer we need to supply two auxiliary objects
+(as well as the module itself): a memory manager and a symbol resolver. The
+memory manager will be responsible for managing the memory allocated to JIT'd
+machine code, setting memory permissions, and registering exception handling
+tables (if the JIT'd code uses exceptions). For our memory manager we will use
+the SectionMemoryManager class: another off-the-shelf utility that provides all
+the basic functionality we need. The second auxiliary class, the symbol
+resolver, is more interesting for us. It exists to tell the JIT where to look
+when it encounters an *external symbol* in the module we are adding. External
+symbols are any symbol not defined within the module itself, including calls to
+functions outside the JIT and calls to functions defined in other modules that
+have already been added to the JIT. It may seem as though modules added to the
+JIT should "know about one another" by default, but since we would still have to
+supply a symbol resolver for references to code outside the JIT it turns out to
+be easier to just re-use this one mechanism for all symbol resolution. This has
+the added benefit that the user has full control over the symbol resolution
+process. Should we search for definitions within the JIT first, then fall back
+on external definitions? Or should we prefer external definitions where
+available and only JIT code if we don't already have an available
+implementation? By using a single symbol resolution scheme we are free to choose
+whatever makes the most sense for any given use case.
+
+Building a symbol resolver is made especially easy by the *createLambdaResolver*
+function. This function takes two lambdas [3]_ and returns a
+RuntimeDyld::SymbolResolver instance. The first lambda is used as the
+implementation of the resolver's findSymbolInLogicalDylib method, which searches
+for symbol definitions that should be thought of as being part of the same
+"logical" dynamic library as this Module. If you are familiar with static
+linking: this means that findSymbolInLogicalDylib should expose symbols with
+common linkage and hidden visibility. If all this sounds foreign you can ignore
+the details and just remember that this is the first method that the linker will
+use to try to find a symbol definition. If the findSymbolInLogicalDylib method
+returns a null result then the linker will call the second symbol resolver
+method, called findSymbol, which searches for symbols that should be thought of
+as external to (but visibile from) the module and its logical dylib. In this
+tutorial we will adopt the following simple scheme: All modules added to the JIT
+will behave as if they were linked into a single, ever-growing logical dylib. To
+implement this our first lambda (the one defining findSymbolInLogicalDylib) will
+just search for JIT'd code by calling the CompileLayer's findSymbol method. If
+we don't find a symbol in the JIT itself we'll fall back to our second lambda,
+which implements findSymbol. This will use the
+RTDyldMemoyrManager::getSymbolAddressInProcess method to search for the symbol
+within the program itself. If we can't find a symbol definition via either of
+these paths the JIT will refuse to accept our module, returning a "symbol not
+found" error.
+
+Now that we've built our symbol resolver we're ready to add our module to the
+JIT. We do this by calling the CompileLayer's addModuleSet method [4]_. Since
+we only have a single Module and addModuleSet expects a collection, we will
+create a vector of modules and add our module as the only member. Since we
+have already typedef'd our ModuleHandle type to be the same as the
+CompileLayer's handle type, we can return the handle from addModuleSet
+directly from our addModule method.
+
+.. code-block:: c++
+
+ JITSymbol findSymbol(const std::string Name) {
+ std::string MangledName;
+ raw_string_ostream MangledNameStream(MangledName);
+ Mangler::getNameWithPrefix(MangledNameStream, Name, DL);
+ return CompileLayer.findSymbol(MangledNameStream.str(), true);
+ }
+
+ void removeModule(ModuleHandle H) {
+ CompileLayer.removeModuleSet(H);
+ }
+
+Now that we can add code to our JIT, we need a way to find the symbols we've
+added to it. To do that we call the findSymbol method on our IRCompileLayer,
+but with a twist: We have to *mangle* the name of the symbol we're searching
+for first. The reason for this is that the ORC JIT components use mangled
+symbols internally the same way a static compiler and linker would, rather
+than using plain IR symbol names. The kind of mangling will depend on the
+DataLayout, which in turn depends on the target platform. To allow us to
+remain portable and search based on the un-mangled name, we just re-produce
+this mangling ourselves.
+
+We now come to the last method in our JIT API: removeModule. This method is
+responsible for destructing the MemoryManager and SymbolResolver that were
+added with a given module, freeing any resources they were using in the
+process. In our Kaleidoscope demo we rely on this method to remove the module
+representing the most recent top-level expression, preventing it from being
+treated as a duplicate definition when the next top-level expression is
+entered. It is generally good to free any module that you know you won't need
+to call further, just to free up the resources dedicated to it. However, you
+don't strictly need to do this: All resources will be cleaned up when your
+JIT class is destructed, if the haven't been freed before then.
+
+This brings us to the end of Chapter 1 of Building a JIT. You now have a basic
+but fully functioning JIT stack that you can use to take LLVM IR and make it
+executable within the context of your JIT process. In the next chapter we'll
+look at how to extend this JIT to produce better quality code, and in the
+process take a deeper look at the ORC layer concept.
+
+`Next: Extending the KaleidoscopeJIT <BuildingAJIT2.html>`_
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example. To build this
+example, use:
+
+.. code-block:: bash
+
+ # Compile
+ clang++ -g toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core orc native` -O3 -o toy
+ # Run
+ ./toy
+
+Here is the code:
+
+.. literalinclude:: ../../examples/Kaleidoscope/BuildingAJIT/Chapter1/KaleidoscopeJIT.h
+ :language: c++
+
+.. [1] Actually we use a cut-down version of KaleidoscopeJIT that makes a
+ simplifying assumption: symbols cannot be re-defined. This will make it
+ impossible to re-define symbols in the REPL, but will make our symbol
+ lookup logic simpler. Re-introducing support for symbol redefinition is
+ left as an exercise for the reader. (The KaleidoscopeJIT.h used in the
+ original tutorials will be a helpful reference).
+
+.. [2] +-----------------------+-----------------------------------------------+
+ | File | Reason for inclusion |
+ +=======================+===============================================+
+ | ExecutionEngine.h | Access to the EngineBuilder::selectTarget |
+ | | method. |
+ +-----------------------+-----------------------------------------------+
+ | | Access to the |
+ | RTDyldMemoryManager.h | RTDyldMemoryManager::getSymbolAddressInProcess|
+ | | method. |
+ +-----------------------+-----------------------------------------------+
+ | CompileUtils.h | Provides the SimpleCompiler class. |
+ +-----------------------+-----------------------------------------------+
+ | IRCompileLayer.h | Provides the IRCompileLayer class. |
+ +-----------------------+-----------------------------------------------+
+ | | Access the createLambdaResolver function, |
+ | LambdaResolver.h | which provides easy construction of symbol |
+ | | resolvers. |
+ +-----------------------+-----------------------------------------------+
+ | ObjectLinkingLayer.h | Provides the ObjectLinkingLayer class. |
+ +-----------------------+-----------------------------------------------+
+ | Mangler.h | Provides the Mangler class for platform |
+ | | specific name-mangling. |
+ +-----------------------+-----------------------------------------------+
+ | DynamicLibrary.h | Provides the DynamicLibrary class, which |
+ | | makes symbols in the host process searchable. |
+ +-----------------------+-----------------------------------------------+
+
+.. [3] Actually they don't have to be lambdas, any object with a call operator
+ will do, including plain old functions or std::functions.
+
+.. [4] ORC layers accept sets of Modules, rather than individual ones, so that
+ all Modules in the set could be co-located by the memory manager, though
+ this feature is not yet implemented.
Added: www-releases/trunk/3.9.1/docs/_sources/tutorial/BuildingAJIT2.txt
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==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/tutorial/BuildingAJIT2.txt (added)
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@@ -0,0 +1,336 @@
+=====================================================================
+Building a JIT: Adding Optimizations -- An introduction to ORC Layers
+=====================================================================
+
+.. contents::
+ :local:
+
+**This tutorial is under active development. It is incomplete and details may
+change frequently.** Nonetheless we invite you to try it out as it stands, and
+we welcome any feedback.
+
+Chapter 2 Introduction
+======================
+
+Welcome to Chapter 2 of the "Building an ORC-based JIT in LLVM" tutorial. In
+`Chapter 1 <BuildingAJIT1.html>`_ of this series we examined a basic JIT
+class, KaleidoscopeJIT, that could take LLVM IR modules as input and produce
+executable code in memory. KaleidoscopeJIT was able to do this with relatively
+little code by composing two off-the-shelf *ORC layers*: IRCompileLayer and
+ObjectLinkingLayer, to do much of the heavy lifting.
+
+In this layer we'll learn more about the ORC layer concept by using a new layer,
+IRTransformLayer, to add IR optimization support to KaleidoscopeJIT.
+
+Optimizing Modules using the IRTransformLayer
+=============================================
+
+In `Chapter 4 <LangImpl4.html>`_ of the "Implementing a language with LLVM"
+tutorial series the llvm *FunctionPassManager* is introduced as a means for
+optimizing LLVM IR. Interested readers may read that chapter for details, but
+in short: to optimize a Module we create an llvm::FunctionPassManager
+instance, configure it with a set of optimizations, then run the PassManager on
+a Module to mutate it into a (hopefully) more optimized but semantically
+equivalent form. In the original tutorial series the FunctionPassManager was
+created outside the KaleidoscopeJIT and modules were optimized before being
+added to it. In this Chapter we will make optimization a phase of our JIT
+instead. For now this will provide us a motivation to learn more about ORC
+layers, but in the long term making optimization part of our JIT will yield an
+important benefit: When we begin lazily compiling code (i.e. deferring
+compilation of each function until the first time it's run), having
+optimization managed by our JIT will allow us to optimize lazily too, rather
+than having to do all our optimization up-front.
+
+To add optimization support to our JIT we will take the KaleidoscopeJIT from
+Chapter 1 and compose an ORC *IRTransformLayer* on top. We will look at how the
+IRTransformLayer works in more detail below, but the interface is simple: the
+constructor for this layer takes a reference to the layer below (as all layers
+do) plus an *IR optimization function* that it will apply to each Module that
+is added via addModuleSet:
+
+.. code-block:: c++
+
+ class KaleidoscopeJIT {
+ private:
+ std::unique_ptr<TargetMachine> TM;
+ const DataLayout DL;
+ ObjectLinkingLayer<> ObjectLayer;
+ IRCompileLayer<decltype(ObjectLayer)> CompileLayer;
+
+ typedef std::function<std::unique_ptr<Module>(std::unique_ptr<Module>)>
+ OptimizeFunction;
+
+ IRTransformLayer<decltype(CompileLayer), OptimizeFunction> OptimizeLayer;
+
+ public:
+ typedef decltype(OptimizeLayer)::ModuleSetHandleT ModuleHandle;
+
+ KaleidoscopeJIT()
+ : TM(EngineBuilder().selectTarget()), DL(TM->createDataLayout()),
+ CompileLayer(ObjectLayer, SimpleCompiler(*TM)),
+ OptimizeLayer(CompileLayer,
+ [this](std::unique_ptr<Module> M) {
+ return optimizeModule(std::move(M));
+ }) {
+ llvm::sys::DynamicLibrary::LoadLibraryPermanently(nullptr);
+ }
+
+Our extended KaleidoscopeJIT class starts out the same as it did in Chapter 1,
+but after the CompileLayer we introduce a typedef for our optimization function.
+In this case we use a std::function (a handy wrapper for "function-like" things)
+from a single unique_ptr<Module> input to a std::unique_ptr<Module> output. With
+our optimization function typedef in place we can declare our OptimizeLayer,
+which sits on top of our CompileLayer.
+
+To initialize our OptimizeLayer we pass it a reference to the CompileLayer
+below (standard practice for layers), and we initialize the OptimizeFunction
+using a lambda that calls out to an "optimizeModule" function that we will
+define below.
+
+.. code-block:: c++
+
+ // ...
+ auto Resolver = createLambdaResolver(
+ [&](const std::string &Name) {
+ if (auto Sym = OptimizeLayer.findSymbol(Name, false))
+ return Sym.toRuntimeDyldSymbol();
+ return RuntimeDyld::SymbolInfo(nullptr);
+ },
+ // ...
+
+.. code-block:: c++
+
+ // ...
+ return OptimizeLayer.addModuleSet(std::move(Ms),
+ make_unique<SectionMemoryManager>(),
+ std::move(Resolver));
+ // ...
+
+.. code-block:: c++
+
+ // ...
+ return OptimizeLayer.findSymbol(MangledNameStream.str(), true);
+ // ...
+
+.. code-block:: c++
+
+ // ...
+ OptimizeLayer.removeModuleSet(H);
+ // ...
+
+Next we need to replace references to 'CompileLayer' with references to
+OptimizeLayer in our key methods: addModule, findSymbol, and removeModule. In
+addModule we need to be careful to replace both references: the findSymbol call
+inside our resolver, and the call through to addModuleSet.
+
+.. code-block:: c++
+
+ std::unique_ptr<Module> optimizeModule(std::unique_ptr<Module> M) {
+ // Create a function pass manager.
+ auto FPM = llvm::make_unique<legacy::FunctionPassManager>(M.get());
+
+ // Add some optimizations.
+ FPM->add(createInstructionCombiningPass());
+ FPM->add(createReassociatePass());
+ FPM->add(createGVNPass());
+ FPM->add(createCFGSimplificationPass());
+ FPM->doInitialization();
+
+ // Run the optimizations over all functions in the module being added to
+ // the JIT.
+ for (auto &F : *M)
+ FPM->run(F);
+
+ return M;
+ }
+
+At the bottom of our JIT we add a private method to do the actual optimization:
+*optimizeModule*. This function sets up a FunctionPassManager, adds some passes
+to it, runs it over every function in the module, and then returns the mutated
+module. The specific optimizations are the same ones used in
+`Chapter 4 <LangImpl4.html>`_ of the "Implementing a language with LLVM"
+tutorial series. Readers may visit that chapter for a more in-depth
+discussion of these, and of IR optimization in general.
+
+And that's it in terms of changes to KaleidoscopeJIT: When a module is added via
+addModule the OptimizeLayer will call our optimizeModule function before passing
+the transformed module on to the CompileLayer below. Of course, we could have
+called optimizeModule directly in our addModule function and not gone to the
+bother of using the IRTransformLayer, but doing so gives us another opportunity
+to see how layers compose. It also provides a neat entry point to the *layer*
+concept itself, because IRTransformLayer turns out to be one of the simplest
+implementations of the layer concept that can be devised:
+
+.. code-block:: c++
+
+ template <typename BaseLayerT, typename TransformFtor>
+ class IRTransformLayer {
+ public:
+ typedef typename BaseLayerT::ModuleSetHandleT ModuleSetHandleT;
+
+ IRTransformLayer(BaseLayerT &BaseLayer,
+ TransformFtor Transform = TransformFtor())
+ : BaseLayer(BaseLayer), Transform(std::move(Transform)) {}
+
+ template <typename ModuleSetT, typename MemoryManagerPtrT,
+ typename SymbolResolverPtrT>
+ ModuleSetHandleT addModuleSet(ModuleSetT Ms,
+ MemoryManagerPtrT MemMgr,
+ SymbolResolverPtrT Resolver) {
+
+ for (auto I = Ms.begin(), E = Ms.end(); I != E; ++I)
+ *I = Transform(std::move(*I));
+
+ return BaseLayer.addModuleSet(std::move(Ms), std::move(MemMgr),
+ std::move(Resolver));
+ }
+
+ void removeModuleSet(ModuleSetHandleT H) { BaseLayer.removeModuleSet(H); }
+
+ JITSymbol findSymbol(const std::string &Name, bool ExportedSymbolsOnly) {
+ return BaseLayer.findSymbol(Name, ExportedSymbolsOnly);
+ }
+
+ JITSymbol findSymbolIn(ModuleSetHandleT H, const std::string &Name,
+ bool ExportedSymbolsOnly) {
+ return BaseLayer.findSymbolIn(H, Name, ExportedSymbolsOnly);
+ }
+
+ void emitAndFinalize(ModuleSetHandleT H) {
+ BaseLayer.emitAndFinalize(H);
+ }
+
+ TransformFtor& getTransform() { return Transform; }
+
+ const TransformFtor& getTransform() const { return Transform; }
+
+ private:
+ BaseLayerT &BaseLayer;
+ TransformFtor Transform;
+ };
+
+This is the whole definition of IRTransformLayer, from
+``llvm/include/llvm/ExecutionEngine/Orc/IRTransformLayer.h``, stripped of its
+comments. It is a template class with two template arguments: ``BaesLayerT`` and
+``TransformFtor`` that provide the type of the base layer and the type of the
+"transform functor" (in our case a std::function) respectively. This class is
+concerned with two very simple jobs: (1) Running every IR Module that is added
+with addModuleSet through the transform functor, and (2) conforming to the ORC
+layer interface. The interface consists of one typedef and five methods:
+
++------------------+-----------------------------------------------------------+
+| Interface | Description |
++==================+===========================================================+
+| | Provides a handle that can be used to identify a module |
+| ModuleSetHandleT | set when calling findSymbolIn, removeModuleSet, or |
+| | emitAndFinalize. |
++------------------+-----------------------------------------------------------+
+| | Takes a given set of Modules and makes them "available |
+| | for execution. This means that symbols in those modules |
+| | should be searchable via findSymbol and findSymbolIn, and |
+| | the address of the symbols should be read/writable (for |
+| | data symbols), or executable (for function symbols) after |
+| | JITSymbol::getAddress() is called. Note: This means that |
+| addModuleSet | addModuleSet doesn't have to compile (or do any other |
+| | work) up-front. It *can*, like IRCompileLayer, act |
+| | eagerly, but it can also simply record the module and |
+| | take no further action until somebody calls |
+| | JITSymbol::getAddress(). In IRTransformLayer's case |
+| | addModuleSet eagerly applies the transform functor to |
+| | each module in the set, then passes the resulting set |
+| | of mutated modules down to the layer below. |
++------------------+-----------------------------------------------------------+
+| | Removes a set of modules from the JIT. Code or data |
+| removeModuleSet | defined in these modules will no longer be available, and |
+| | the memory holding the JIT'd definitions will be freed. |
++------------------+-----------------------------------------------------------+
+| | Searches for the named symbol in all modules that have |
+| | previously been added via addModuleSet (and not yet |
+| findSymbol | removed by a call to removeModuleSet). In |
+| | IRTransformLayer we just pass the query on to the layer |
+| | below. In our REPL this is our default way to search for |
+| | function definitions. |
++------------------+-----------------------------------------------------------+
+| | Searches for the named symbol in the module set indicated |
+| | by the given ModuleSetHandleT. This is just an optimized |
+| | search, better for lookup-speed when you know exactly |
+| | a symbol definition should be found. In IRTransformLayer |
+| findSymbolIn | we just pass this query on to the layer below. In our |
+| | REPL we use this method to search for functions |
+| | representing top-level expressions, since we know exactly |
+| | where we'll find them: in the top-level expression module |
+| | we just added. |
++------------------+-----------------------------------------------------------+
+| | Forces all of the actions required to make the code and |
+| | data in a module set (represented by a ModuleSetHandleT) |
+| | accessible. Behaves as if some symbol in the set had been |
+| | searched for and JITSymbol::getSymbolAddress called. This |
+| emitAndFinalize | is rarely needed, but can be useful when dealing with |
+| | layers that usually behave lazily if the user wants to |
+| | trigger early compilation (for example, to use idle CPU |
+| | time to eagerly compile code in the background). |
++------------------+-----------------------------------------------------------+
+
+This interface attempts to capture the natural operations of a JIT (with some
+wrinkles like emitAndFinalize for performance), similar to the basic JIT API
+operations we identified in Chapter 1. Conforming to the layer concept allows
+classes to compose neatly by implementing their behaviors in terms of the these
+same operations, carried out on the layer below. For example, an eager layer
+(like IRTransformLayer) can implement addModuleSet by running each module in the
+set through its transform up-front and immediately passing the result to the
+layer below. A lazy layer, by contrast, could implement addModuleSet by
+squirreling away the modules doing no other up-front work, but applying the
+transform (and calling addModuleSet on the layer below) when the client calls
+findSymbol instead. The JIT'd program behavior will be the same either way, but
+these choices will have different performance characteristics: Doing work
+eagerly means the JIT takes longer up-front, but proceeds smoothly once this is
+done. Deferring work allows the JIT to get up-and-running quickly, but will
+force the JIT to pause and wait whenever some code or data is needed that hasn't
+already been processed.
+
+Our current REPL is eager: Each function definition is optimized and compiled as
+soon as it's typed in. If we were to make the transform layer lazy (but not
+change things otherwise) we could defer optimization until the first time we
+reference a function in a top-level expression (see if you can figure out why,
+then check out the answer below [1]_). In the next chapter, however we'll
+introduce fully lazy compilation, in which function's aren't compiled until
+they're first called at run-time. At this point the trade-offs get much more
+interesting: the lazier we are, the quicker we can start executing the first
+function, but the more often we'll have to pause to compile newly encountered
+functions. If we only code-gen lazily, but optimize eagerly, we'll have a slow
+startup (which everything is optimized) but relatively short pauses as each
+function just passes through code-gen. If we both optimize and code-gen lazily
+we can start executing the first function more quickly, but we'll have longer
+pauses as each function has to be both optimized and code-gen'd when it's first
+executed. Things become even more interesting if we consider interproceedural
+optimizations like inlining, which must be performed eagerly. These are
+complex trade-offs, and there is no one-size-fits all solution to them, but by
+providing composable layers we leave the decisions to the person implementing
+the JIT, and make it easy for them to experiment with different configurations.
+
+`Next: Adding Per-function Lazy Compilation <BuildingAJIT3.html>`_
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example with an
+IRTransformLayer added to enable optimization. To build this example, use:
+
+.. code-block:: bash
+
+ # Compile
+ clang++ -g toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core orc native` -O3 -o toy
+ # Run
+ ./toy
+
+Here is the code:
+
+.. literalinclude:: ../../examples/Kaleidoscope/BuildingAJIT/Chapter2/KaleidoscopeJIT.h
+ :language: c++
+
+.. [1] When we add our top-level expression to the JIT, any calls to functions
+ that we defined earlier will appear to the ObjectLinkingLayer as
+ external symbols. The ObjectLinkingLayer will call the SymbolResolver
+ that we defined in addModuleSet, which in turn calls findSymbol on the
+ OptimizeLayer, at which point even a lazy transform layer will have to
+ do its work.
Added: www-releases/trunk/3.9.1/docs/_sources/tutorial/BuildingAJIT3.txt
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@@ -0,0 +1,171 @@
+=============================================
+Building a JIT: Per-function Lazy Compilation
+=============================================
+
+.. contents::
+ :local:
+
+**This tutorial is under active development. It is incomplete and details may
+change frequently.** Nonetheless we invite you to try it out as it stands, and
+we welcome any feedback.
+
+Chapter 3 Introduction
+======================
+
+Welcome to Chapter 3 of the "Building an ORC-based JIT in LLVM" tutorial. This
+chapter discusses lazy JITing and shows you how to enable it by adding an ORC
+CompileOnDemand layer the JIT from `Chapter 2 <BuildingAJIT2.html>`_.
+
+Lazy Compilation
+================
+
+When we add a module to the KaleidoscopeJIT class described in Chapter 2 it is
+immediately optimized, compiled and linked for us by the IRTransformLayer,
+IRCompileLayer and ObjectLinkingLayer respectively. This scheme, where all the
+work to make a Module executable is done up front, is relatively simple to
+understand its performance characteristics are easy to reason about. However,
+it will lead to very high startup times if the amount of code to be compiled is
+large, and may also do a lot of unnecessary compilation if only a few compiled
+functions are ever called at runtime. A truly "just-in-time" compiler should
+allow us to defer the compilation of any given function until the moment that
+function is first called, improving launch times and eliminating redundant work.
+In fact, the ORC APIs provide us with a layer to lazily compile LLVM IR:
+*CompileOnDemandLayer*.
+
+The CompileOnDemandLayer conforms to the layer interface described in Chapter 2,
+but the addModuleSet method behaves quite differently from the layers we have
+seen so far: rather than doing any work up front, it just constructs a *stub*
+for each function in the module and arranges for the stub to trigger compilation
+of the actual function the first time it is called. Because stub functions are
+very cheap to produce CompileOnDemand's addModuleSet method runs very quickly,
+reducing the time required to launch the first function to be executed, and
+saving us from doing any redundant compilation. By conforming to the layer
+interface, CompileOnDemand can be easily added on top of our existing JIT class.
+We just need a few changes:
+
+.. code-block:: c++
+
+ ...
+ #include "llvm/ExecutionEngine/SectionMemoryManager.h"
+ #include "llvm/ExecutionEngine/Orc/CompileOnDemandLayer.h"
+ #include "llvm/ExecutionEngine/Orc/CompileUtils.h"
+ ...
+
+ ...
+ class KaleidoscopeJIT {
+ private:
+ std::unique_ptr<TargetMachine> TM;
+ const DataLayout DL;
+ std::unique_ptr<JITCompileCallbackManager> CompileCallbackManager;
+ ObjectLinkingLayer<> ObjectLayer;
+ IRCompileLayer<decltype(ObjectLayer)> CompileLayer;
+
+ typedef std::function<std::unique_ptr<Module>(std::unique_ptr<Module>)>
+ OptimizeFunction;
+
+ IRTransformLayer<decltype(CompileLayer), OptimizeFunction> OptimizeLayer;
+ CompileOnDemandLayer<decltype(OptimizeLayer)> CODLayer;
+
+ public:
+ typedef decltype(CODLayer)::ModuleSetHandleT ModuleHandle;
+
+First we need to include the CompileOnDemandLayer.h header, then add two new
+members: a std::unique_ptr<CompileCallbackManager> and a CompileOnDemandLayer,
+to our class. The CompileCallbackManager is a utility that enables us to
+create re-entry points into the compiler for functions that we want to lazily
+compile. In the next chapter we'll be looking at this class in detail, but for
+now we'll be treating it as an opaque utility: We just need to pass a reference
+to it into our new CompileOnDemandLayer, and the layer will do all the work of
+setting up the callbacks using the callback manager we gave it.
+
+.. code-block:: c++
+
+ KaleidoscopeJIT()
+ : TM(EngineBuilder().selectTarget()), DL(TM->createDataLayout()),
+ CompileLayer(ObjectLayer, SimpleCompiler(*TM)),
+ OptimizeLayer(CompileLayer,
+ [this](std::unique_ptr<Module> M) {
+ return optimizeModule(std::move(M));
+ }),
+ CompileCallbackManager(
+ orc::createLocalCompileCallbackManager(TM->getTargetTriple(), 0)),
+ CODLayer(OptimizeLayer,
+ [this](Function &F) { return std::set<Function*>({&F}); },
+ *CompileCallbackManager,
+ orc::createLocalIndirectStubsManagerBuilder(
+ TM->getTargetTriple())) {
+ llvm::sys::DynamicLibrary::LoadLibraryPermanently(nullptr);
+ }
+
+Next we have to update our constructor to initialize the new members. To create
+an appropriate compile callback manager we use the
+createLocalCompileCallbackManager function, which takes a TargetMachine and a
+TargetAddress to call if it receives a request to compile an unknown function.
+In our simple JIT this situation is unlikely to come up, so we'll cheat and
+just pass '0' here. In a production quality JIT you could give the address of a
+function that throws an exception in order to unwind the JIT'd code stack.
+
+Now we can construct our CompileOnDemandLayer. Following the pattern from
+previous layers we start by passing a reference to the next layer down in our
+stack -- the OptimizeLayer. Next we need to supply a 'partitioning function':
+when a not-yet-compiled function is called, the CompileOnDemandLayer will call
+this function to ask us what we would like to compile. At a minimum we need to
+compile the function being called (given by the argument to the partitioning
+function), but we could also request that the CompileOnDemandLayer compile other
+functions that are unconditionally called (or highly likely to be called) from
+the function being called. For KaleidoscopeJIT we'll keep it simple and just
+request compilation of the function that was called. Next we pass a reference to
+our CompileCallbackManager. Finally, we need to supply an "indirect stubs
+manager builder". This is a function that constructs IndirectStubManagers, which
+are in turn used to build the stubs for each module. The CompileOnDemandLayer
+will call the indirect stub manager builder once for each call to addModuleSet,
+and use the resulting indirect stubs manager to create stubs for all functions
+in all modules added. If/when the module set is removed from the JIT the
+indirect stubs manager will be deleted, freeing any memory allocated to the
+stubs. We supply this function by using the
+createLocalIndirectStubsManagerBuilder utility.
+
+.. code-block:: c++
+
+ // ...
+ if (auto Sym = CODLayer.findSymbol(Name, false))
+ // ...
+ return CODLayer.addModuleSet(std::move(Ms),
+ make_unique<SectionMemoryManager>(),
+ std::move(Resolver));
+ // ...
+
+ // ...
+ return CODLayer.findSymbol(MangledNameStream.str(), true);
+ // ...
+
+ // ...
+ CODLayer.removeModuleSet(H);
+ // ...
+
+Finally, we need to replace the references to OptimizeLayer in our addModule,
+findSymbol, and removeModule methods. With that, we're up and running.
+
+**To be done:**
+
+** Discuss CompileCallbackManagers and IndirectStubManagers in more detail.**
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example with a CompileOnDemand
+layer added to enable lazy function-at-a-time compilation. To build this example, use:
+
+.. code-block:: bash
+
+ # Compile
+ clang++ -g toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core orc native` -O3 -o toy
+ # Run
+ ./toy
+
+Here is the code:
+
+.. literalinclude:: ../../examples/Kaleidoscope/BuildingAJIT/Chapter3/KaleidoscopeJIT.h
+ :language: c++
+
+`Next: Extreme Laziness -- Using Compile Callbacks to JIT directly from ASTs <BuildingAJIT4.html>`_
Added: www-releases/trunk/3.9.1/docs/_sources/tutorial/BuildingAJIT4.txt
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@@ -0,0 +1,48 @@
+===========================================================================
+Building a JIT: Extreme Laziness - Using Compile Callbacks to JIT from ASTs
+===========================================================================
+
+.. contents::
+ :local:
+
+**This tutorial is under active development. It is incomplete and details may
+change frequently.** Nonetheless we invite you to try it out as it stands, and
+we welcome any feedback.
+
+Chapter 4 Introduction
+======================
+
+Welcome to Chapter 4 of the "Building an ORC-based JIT in LLVM" tutorial. This
+chapter introduces the Compile Callbacks and Indirect Stubs APIs and shows how
+they can be used to replace the CompileOnDemand layer from
+`Chapter 3 <BuildingAJIT3.html>`_ with a custom lazy-JITing scheme that JITs
+directly from Kaleidoscope ASTs.
+
+**To be done:**
+
+**(1) Describe the drawbacks of JITing from IR (have to compile to IR first,
+which reduces the benefits of laziness).**
+
+**(2) Describe CompileCallbackManagers and IndirectStubManagers in detail.**
+
+**(3) Run through the implementation of addFunctionAST.**
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example that JITs lazily from
+Kaleidoscope ASTS. To build this example, use:
+
+.. code-block:: bash
+
+ # Compile
+ clang++ -g toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core orc native` -O3 -o toy
+ # Run
+ ./toy
+
+Here is the code:
+
+.. literalinclude:: ../../examples/Kaleidoscope/BuildingAJIT/Chapter4/KaleidoscopeJIT.h
+ :language: c++
+
+`Next: Remote-JITing -- Process-isolation and laziness-at-a-distance <BuildingAJIT5.html>`_
Added: www-releases/trunk/3.9.1/docs/_sources/tutorial/BuildingAJIT5.txt
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@@ -0,0 +1,55 @@
+=============================================================================
+Building a JIT: Remote-JITing -- Process Isolation and Laziness at a Distance
+=============================================================================
+
+.. contents::
+ :local:
+
+**This tutorial is under active development. It is incomplete and details may
+change frequently.** Nonetheless we invite you to try it out as it stands, and
+we welcome any feedback.
+
+Chapter 5 Introduction
+======================
+
+Welcome to Chapter 5 of the "Building an ORC-based JIT in LLVM" tutorial. This
+chapter introduces the ORC RemoteJIT Client/Server APIs and shows how to use
+them to build a JIT stack that will execute its code via a communications
+channel with a different process. This can be a separate process on the same
+machine, a process on a different machine, or even a process on a different
+platform/architecture. The code builds on top of the lazy-AST-compiling JIT
+stack from `Chapter 4 <BuildingAJIT3.html>`_.
+
+**To be done -- this is going to be a long one:**
+
+**(1) Introduce channels, RPC, RemoteJIT Client and Server APIs**
+
+**(2) Describe the client code in greater detail. Discuss modifications of the
+KaleidoscopeJIT class, and the REPL itself.**
+
+**(3) Describe the server code.**
+
+**(4) Describe how to run the demo.**
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example that JITs lazily from
+Kaleidoscope ASTS. To build this example, use:
+
+.. code-block:: bash
+
+ # Compile
+ clang++ -g toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core orc native` -O3 -o toy
+ # Run
+ ./toy
+
+Here is the code for the modified KaleidoscopeJIT:
+
+.. literalinclude:: ../../examples/Kaleidoscope/BuildingAJIT/Chapter5/KaleidoscopeJIT.h
+ :language: c++
+
+And the code for the JIT server:
+
+.. literalinclude:: ../../examples/Kaleidoscope/BuildingAJIT/Chapter5/Server/server.cpp
+ :language: c++
Added: www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl01.txt
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@@ -0,0 +1,293 @@
+=================================================
+Kaleidoscope: Tutorial Introduction and the Lexer
+=================================================
+
+.. contents::
+ :local:
+
+Tutorial Introduction
+=====================
+
+Welcome to the "Implementing a language with LLVM" tutorial. This
+tutorial runs through the implementation of a simple language, showing
+how fun and easy it can be. This tutorial will get you up and started as
+well as help to build a framework you can extend to other languages. The
+code in this tutorial can also be used as a playground to hack on other
+LLVM specific things.
+
+The goal of this tutorial is to progressively unveil our language,
+describing how it is built up over time. This will let us cover a fairly
+broad range of language design and LLVM-specific usage issues, showing
+and explaining the code for it all along the way, without overwhelming
+you with tons of details up front.
+
+It is useful to point out ahead of time that this tutorial is really
+about teaching compiler techniques and LLVM specifically, *not* about
+teaching modern and sane software engineering principles. In practice,
+this means that we'll take a number of shortcuts to simplify the
+exposition. For example, the code uses global variables
+all over the place, doesn't use nice design patterns like
+`visitors <http://en.wikipedia.org/wiki/Visitor_pattern>`_, etc... but
+it is very simple. If you dig in and use the code as a basis for future
+projects, fixing these deficiencies shouldn't be hard.
+
+I've tried to put this tutorial together in a way that makes chapters
+easy to skip over if you are already familiar with or are uninterested
+in the various pieces. The structure of the tutorial is:
+
+- `Chapter #1 <#language>`_: Introduction to the Kaleidoscope
+ language, and the definition of its Lexer - This shows where we are
+ going and the basic functionality that we want it to do. In order to
+ make this tutorial maximally understandable and hackable, we choose
+ to implement everything in C++ instead of using lexer and parser
+ generators. LLVM obviously works just fine with such tools, feel free
+ to use one if you prefer.
+- `Chapter #2 <LangImpl02.html>`_: Implementing a Parser and AST -
+ With the lexer in place, we can talk about parsing techniques and
+ basic AST construction. This tutorial describes recursive descent
+ parsing and operator precedence parsing. Nothing in Chapters 1 or 2
+ is LLVM-specific, the code doesn't even link in LLVM at this point.
+ :)
+- `Chapter #3 <LangImpl03.html>`_: Code generation to LLVM IR - With
+ the AST ready, we can show off how easy generation of LLVM IR really
+ is.
+- `Chapter #4 <LangImpl04.html>`_: Adding JIT and Optimizer Support
+ - Because a lot of people are interested in using LLVM as a JIT,
+ we'll dive right into it and show you the 3 lines it takes to add JIT
+ support. LLVM is also useful in many other ways, but this is one
+ simple and "sexy" way to show off its power. :)
+- `Chapter #5 <LangImpl05.html>`_: Extending the Language: Control
+ Flow - With the language up and running, we show how to extend it
+ with control flow operations (if/then/else and a 'for' loop). This
+ gives us a chance to talk about simple SSA construction and control
+ flow.
+- `Chapter #6 <LangImpl06.html>`_: Extending the Language:
+ User-defined Operators - This is a silly but fun chapter that talks
+ about extending the language to let the user program define their own
+ arbitrary unary and binary operators (with assignable precedence!).
+ This lets us build a significant piece of the "language" as library
+ routines.
+- `Chapter #7 <LangImpl07.html>`_: Extending the Language: Mutable
+ Variables - This chapter talks about adding user-defined local
+ variables along with an assignment operator. The interesting part
+ about this is how easy and trivial it is to construct SSA form in
+ LLVM: no, LLVM does *not* require your front-end to construct SSA
+ form!
+- `Chapter #8 <LangImpl08.html>`_: Compiling to Object Files - This
+ chapter explains how to take LLVM IR and compile it down to object
+ files.
+- `Chapter #9 <LangImpl09.html>`_: Extending the Language: Debug
+ Information - Having built a decent little programming language with
+ control flow, functions and mutable variables, we consider what it
+ takes to add debug information to standalone executables. This debug
+ information will allow you to set breakpoints in Kaleidoscope
+ functions, print out argument variables, and call functions - all
+ from within the debugger!
+- `Chapter #10 <LangImpl10.html>`_: Conclusion and other useful LLVM
+ tidbits - This chapter wraps up the series by talking about
+ potential ways to extend the language, but also includes a bunch of
+ pointers to info about "special topics" like adding garbage
+ collection support, exceptions, debugging, support for "spaghetti
+ stacks", and a bunch of other tips and tricks.
+
+By the end of the tutorial, we'll have written a bit less than 1000 lines
+of non-comment, non-blank, lines of code. With this small amount of
+code, we'll have built up a very reasonable compiler for a non-trivial
+language including a hand-written lexer, parser, AST, as well as code
+generation support with a JIT compiler. While other systems may have
+interesting "hello world" tutorials, I think the breadth of this
+tutorial is a great testament to the strengths of LLVM and why you
+should consider it if you're interested in language or compiler design.
+
+A note about this tutorial: we expect you to extend the language and
+play with it on your own. Take the code and go crazy hacking away at it,
+compilers don't need to be scary creatures - it can be a lot of fun to
+play with languages!
+
+The Basic Language
+==================
+
+This tutorial will be illustrated with a toy language that we'll call
+"`Kaleidoscope <http://en.wikipedia.org/wiki/Kaleidoscope>`_" (derived
+from "meaning beautiful, form, and view"). Kaleidoscope is a procedural
+language that allows you to define functions, use conditionals, math,
+etc. Over the course of the tutorial, we'll extend Kaleidoscope to
+support the if/then/else construct, a for loop, user defined operators,
+JIT compilation with a simple command line interface, etc.
+
+Because we want to keep things simple, the only datatype in Kaleidoscope
+is a 64-bit floating point type (aka 'double' in C parlance). As such,
+all values are implicitly double precision and the language doesn't
+require type declarations. This gives the language a very nice and
+simple syntax. For example, the following simple example computes
+`Fibonacci numbers: <http://en.wikipedia.org/wiki/Fibonacci_number>`_
+
+::
+
+ # Compute the x'th fibonacci number.
+ def fib(x)
+ if x < 3 then
+ 1
+ else
+ fib(x-1)+fib(x-2)
+
+ # This expression will compute the 40th number.
+ fib(40)
+
+We also allow Kaleidoscope to call into standard library functions (the
+LLVM JIT makes this completely trivial). This means that you can use the
+'extern' keyword to define a function before you use it (this is also
+useful for mutually recursive functions). For example:
+
+::
+
+ extern sin(arg);
+ extern cos(arg);
+ extern atan2(arg1 arg2);
+
+ atan2(sin(.4), cos(42))
+
+A more interesting example is included in Chapter 6 where we write a
+little Kaleidoscope application that `displays a Mandelbrot
+Set <LangImpl06.html#kicking-the-tires>`_ at various levels of magnification.
+
+Lets dive into the implementation of this language!
+
+The Lexer
+=========
+
+When it comes to implementing a language, the first thing needed is the
+ability to process a text file and recognize what it says. The
+traditional way to do this is to use a
+"`lexer <http://en.wikipedia.org/wiki/Lexical_analysis>`_" (aka
+'scanner') to break the input up into "tokens". Each token returned by
+the lexer includes a token code and potentially some metadata (e.g. the
+numeric value of a number). First, we define the possibilities:
+
+.. code-block:: c++
+
+ // The lexer returns tokens [0-255] if it is an unknown character, otherwise one
+ // of these for known things.
+ enum Token {
+ tok_eof = -1,
+
+ // commands
+ tok_def = -2,
+ tok_extern = -3,
+
+ // primary
+ tok_identifier = -4,
+ tok_number = -5,
+ };
+
+ static std::string IdentifierStr; // Filled in if tok_identifier
+ static double NumVal; // Filled in if tok_number
+
+Each token returned by our lexer will either be one of the Token enum
+values or it will be an 'unknown' character like '+', which is returned
+as its ASCII value. If the current token is an identifier, the
+``IdentifierStr`` global variable holds the name of the identifier. If
+the current token is a numeric literal (like 1.0), ``NumVal`` holds its
+value. Note that we use global variables for simplicity, this is not the
+best choice for a real language implementation :).
+
+The actual implementation of the lexer is a single function named
+``gettok``. The ``gettok`` function is called to return the next token
+from standard input. Its definition starts as:
+
+.. code-block:: c++
+
+ /// gettok - Return the next token from standard input.
+ static int gettok() {
+ static int LastChar = ' ';
+
+ // Skip any whitespace.
+ while (isspace(LastChar))
+ LastChar = getchar();
+
+``gettok`` works by calling the C ``getchar()`` function to read
+characters one at a time from standard input. It eats them as it
+recognizes them and stores the last character read, but not processed,
+in LastChar. The first thing that it has to do is ignore whitespace
+between tokens. This is accomplished with the loop above.
+
+The next thing ``gettok`` needs to do is recognize identifiers and
+specific keywords like "def". Kaleidoscope does this with this simple
+loop:
+
+.. code-block:: c++
+
+ if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
+ IdentifierStr = LastChar;
+ while (isalnum((LastChar = getchar())))
+ IdentifierStr += LastChar;
+
+ if (IdentifierStr == "def")
+ return tok_def;
+ if (IdentifierStr == "extern")
+ return tok_extern;
+ return tok_identifier;
+ }
+
+Note that this code sets the '``IdentifierStr``' global whenever it
+lexes an identifier. Also, since language keywords are matched by the
+same loop, we handle them here inline. Numeric values are similar:
+
+.. code-block:: c++
+
+ if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+
+ std::string NumStr;
+ do {
+ NumStr += LastChar;
+ LastChar = getchar();
+ } while (isdigit(LastChar) || LastChar == '.');
+
+ NumVal = strtod(NumStr.c_str(), 0);
+ return tok_number;
+ }
+
+This is all pretty straight-forward code for processing input. When
+reading a numeric value from input, we use the C ``strtod`` function to
+convert it to a numeric value that we store in ``NumVal``. Note that
+this isn't doing sufficient error checking: it will incorrectly read
+"1.23.45.67" and handle it as if you typed in "1.23". Feel free to
+extend it :). Next we handle comments:
+
+.. code-block:: c++
+
+ if (LastChar == '#') {
+ // Comment until end of line.
+ do
+ LastChar = getchar();
+ while (LastChar != EOF && LastChar != '\n' && LastChar != '\r');
+
+ if (LastChar != EOF)
+ return gettok();
+ }
+
+We handle comments by skipping to the end of the line and then return
+the next token. Finally, if the input doesn't match one of the above
+cases, it is either an operator character like '+' or the end of the
+file. These are handled with this code:
+
+.. code-block:: c++
+
+ // Check for end of file. Don't eat the EOF.
+ if (LastChar == EOF)
+ return tok_eof;
+
+ // Otherwise, just return the character as its ascii value.
+ int ThisChar = LastChar;
+ LastChar = getchar();
+ return ThisChar;
+ }
+
+With this, we have the complete lexer for the basic Kaleidoscope
+language (the `full code listing <LangImpl02.html#full-code-listing>`_ for the Lexer
+is available in the `next chapter <LangImpl02.html>`_ of the tutorial).
+Next we'll `build a simple parser that uses this to build an Abstract
+Syntax Tree <LangImpl02.html>`_. When we have that, we'll include a
+driver so that you can use the lexer and parser together.
+
+`Next: Implementing a Parser and AST <LangImpl02.html>`_
+
Added: www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl02.txt
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==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl02.txt (added)
+++ www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl02.txt Thu Dec 22 14:04:03 2016
@@ -0,0 +1,735 @@
+===========================================
+Kaleidoscope: Implementing a Parser and AST
+===========================================
+
+.. contents::
+ :local:
+
+Chapter 2 Introduction
+======================
+
+Welcome to Chapter 2 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. This chapter shows you how to use the
+lexer, built in `Chapter 1 <LangImpl1.html>`_, to build a full
+`parser <http://en.wikipedia.org/wiki/Parsing>`_ for our Kaleidoscope
+language. Once we have a parser, we'll define and build an `Abstract
+Syntax Tree <http://en.wikipedia.org/wiki/Abstract_syntax_tree>`_ (AST).
+
+The parser we will build uses a combination of `Recursive Descent
+Parsing <http://en.wikipedia.org/wiki/Recursive_descent_parser>`_ and
+`Operator-Precedence
+Parsing <http://en.wikipedia.org/wiki/Operator-precedence_parser>`_ to
+parse the Kaleidoscope language (the latter for binary expressions and
+the former for everything else). Before we get to parsing though, lets
+talk about the output of the parser: the Abstract Syntax Tree.
+
+The Abstract Syntax Tree (AST)
+==============================
+
+The AST for a program captures its behavior in such a way that it is
+easy for later stages of the compiler (e.g. code generation) to
+interpret. We basically want one object for each construct in the
+language, and the AST should closely model the language. In
+Kaleidoscope, we have expressions, a prototype, and a function object.
+We'll start with expressions first:
+
+.. code-block:: c++
+
+ /// ExprAST - Base class for all expression nodes.
+ class ExprAST {
+ public:
+ virtual ~ExprAST() {}
+ };
+
+ /// NumberExprAST - Expression class for numeric literals like "1.0".
+ class NumberExprAST : public ExprAST {
+ double Val;
+
+ public:
+ NumberExprAST(double Val) : Val(Val) {}
+ };
+
+The code above shows the definition of the base ExprAST class and one
+subclass which we use for numeric literals. The important thing to note
+about this code is that the NumberExprAST class captures the numeric
+value of the literal as an instance variable. This allows later phases
+of the compiler to know what the stored numeric value is.
+
+Right now we only create the AST, so there are no useful accessor
+methods on them. It would be very easy to add a virtual method to pretty
+print the code, for example. Here are the other expression AST node
+definitions that we'll use in the basic form of the Kaleidoscope
+language:
+
+.. code-block:: c++
+
+ /// VariableExprAST - Expression class for referencing a variable, like "a".
+ class VariableExprAST : public ExprAST {
+ std::string Name;
+
+ public:
+ VariableExprAST(const std::string &Name) : Name(Name) {}
+ };
+
+ /// BinaryExprAST - Expression class for a binary operator.
+ class BinaryExprAST : public ExprAST {
+ char Op;
+ std::unique_ptr<ExprAST> LHS, RHS;
+
+ public:
+ BinaryExprAST(char op, std::unique_ptr<ExprAST> LHS,
+ std::unique_ptr<ExprAST> RHS)
+ : Op(op), LHS(std::move(LHS)), RHS(std::move(RHS)) {}
+ };
+
+ /// CallExprAST - Expression class for function calls.
+ class CallExprAST : public ExprAST {
+ std::string Callee;
+ std::vector<std::unique_ptr<ExprAST>> Args;
+
+ public:
+ CallExprAST(const std::string &Callee,
+ std::vector<std::unique_ptr<ExprAST>> Args)
+ : Callee(Callee), Args(std::move(Args)) {}
+ };
+
+This is all (intentionally) rather straight-forward: variables capture
+the variable name, binary operators capture their opcode (e.g. '+'), and
+calls capture a function name as well as a list of any argument
+expressions. One thing that is nice about our AST is that it captures
+the language features without talking about the syntax of the language.
+Note that there is no discussion about precedence of binary operators,
+lexical structure, etc.
+
+For our basic language, these are all of the expression nodes we'll
+define. Because it doesn't have conditional control flow, it isn't
+Turing-complete; we'll fix that in a later installment. The two things
+we need next are a way to talk about the interface to a function, and a
+way to talk about functions themselves:
+
+.. code-block:: c++
+
+ /// PrototypeAST - This class represents the "prototype" for a function,
+ /// which captures its name, and its argument names (thus implicitly the number
+ /// of arguments the function takes).
+ class PrototypeAST {
+ std::string Name;
+ std::vector<std::string> Args;
+
+ public:
+ PrototypeAST(const std::string &name, std::vector<std::string> Args)
+ : Name(name), Args(std::move(Args)) {}
+ };
+
+ /// FunctionAST - This class represents a function definition itself.
+ class FunctionAST {
+ std::unique_ptr<PrototypeAST> Proto;
+ std::unique_ptr<ExprAST> Body;
+
+ public:
+ FunctionAST(std::unique_ptr<PrototypeAST> Proto,
+ std::unique_ptr<ExprAST> Body)
+ : Proto(std::move(Proto)), Body(std::move(Body)) {}
+ };
+
+In Kaleidoscope, functions are typed with just a count of their
+arguments. Since all values are double precision floating point, the
+type of each argument doesn't need to be stored anywhere. In a more
+aggressive and realistic language, the "ExprAST" class would probably
+have a type field.
+
+With this scaffolding, we can now talk about parsing expressions and
+function bodies in Kaleidoscope.
+
+Parser Basics
+=============
+
+Now that we have an AST to build, we need to define the parser code to
+build it. The idea here is that we want to parse something like "x+y"
+(which is returned as three tokens by the lexer) into an AST that could
+be generated with calls like this:
+
+.. code-block:: c++
+
+ auto LHS = llvm::make_unique<VariableExprAST>("x");
+ auto RHS = llvm::make_unique<VariableExprAST>("y");
+ auto Result = std::make_unique<BinaryExprAST>('+', std::move(LHS),
+ std::move(RHS));
+
+In order to do this, we'll start by defining some basic helper routines:
+
+.. code-block:: c++
+
+ /// CurTok/getNextToken - Provide a simple token buffer. CurTok is the current
+ /// token the parser is looking at. getNextToken reads another token from the
+ /// lexer and updates CurTok with its results.
+ static int CurTok;
+ static int getNextToken() {
+ return CurTok = gettok();
+ }
+
+This implements a simple token buffer around the lexer. This allows us
+to look one token ahead at what the lexer is returning. Every function
+in our parser will assume that CurTok is the current token that needs to
+be parsed.
+
+.. code-block:: c++
+
+
+ /// LogError* - These are little helper functions for error handling.
+ std::unique_ptr<ExprAST> LogError(const char *Str) {
+ fprintf(stderr, "LogError: %s\n", Str);
+ return nullptr;
+ }
+ std::unique_ptr<PrototypeAST> LogErrorP(const char *Str) {
+ LogError(Str);
+ return nullptr;
+ }
+
+The ``LogError`` routines are simple helper routines that our parser will
+use to handle errors. The error recovery in our parser will not be the
+best and is not particular user-friendly, but it will be enough for our
+tutorial. These routines make it easier to handle errors in routines
+that have various return types: they always return null.
+
+With these basic helper functions, we can implement the first piece of
+our grammar: numeric literals.
+
+Basic Expression Parsing
+========================
+
+We start with numeric literals, because they are the simplest to
+process. For each production in our grammar, we'll define a function
+which parses that production. For numeric literals, we have:
+
+.. code-block:: c++
+
+ /// numberexpr ::= number
+ static std::unique_ptr<ExprAST> ParseNumberExpr() {
+ auto Result = llvm::make_unique<NumberExprAST>(NumVal);
+ getNextToken(); // consume the number
+ return std::move(Result);
+ }
+
+This routine is very simple: it expects to be called when the current
+token is a ``tok_number`` token. It takes the current number value,
+creates a ``NumberExprAST`` node, advances the lexer to the next token,
+and finally returns.
+
+There are some interesting aspects to this. The most important one is
+that this routine eats all of the tokens that correspond to the
+production and returns the lexer buffer with the next token (which is
+not part of the grammar production) ready to go. This is a fairly
+standard way to go for recursive descent parsers. For a better example,
+the parenthesis operator is defined like this:
+
+.. code-block:: c++
+
+ /// parenexpr ::= '(' expression ')'
+ static std::unique_ptr<ExprAST> ParseParenExpr() {
+ getNextToken(); // eat (.
+ auto V = ParseExpression();
+ if (!V)
+ return nullptr;
+
+ if (CurTok != ')')
+ return LogError("expected ')'");
+ getNextToken(); // eat ).
+ return V;
+ }
+
+This function illustrates a number of interesting things about the
+parser:
+
+1) It shows how we use the LogError routines. When called, this function
+expects that the current token is a '(' token, but after parsing the
+subexpression, it is possible that there is no ')' waiting. For example,
+if the user types in "(4 x" instead of "(4)", the parser should emit an
+error. Because errors can occur, the parser needs a way to indicate that
+they happened: in our parser, we return null on an error.
+
+2) Another interesting aspect of this function is that it uses recursion
+by calling ``ParseExpression`` (we will soon see that
+``ParseExpression`` can call ``ParseParenExpr``). This is powerful
+because it allows us to handle recursive grammars, and keeps each
+production very simple. Note that parentheses do not cause construction
+of AST nodes themselves. While we could do it this way, the most
+important role of parentheses are to guide the parser and provide
+grouping. Once the parser constructs the AST, parentheses are not
+needed.
+
+The next simple production is for handling variable references and
+function calls:
+
+.. code-block:: c++
+
+ /// identifierexpr
+ /// ::= identifier
+ /// ::= identifier '(' expression* ')'
+ static std::unique_ptr<ExprAST> ParseIdentifierExpr() {
+ std::string IdName = IdentifierStr;
+
+ getNextToken(); // eat identifier.
+
+ if (CurTok != '(') // Simple variable ref.
+ return llvm::make_unique<VariableExprAST>(IdName);
+
+ // Call.
+ getNextToken(); // eat (
+ std::vector<std::unique_ptr<ExprAST>> Args;
+ if (CurTok != ')') {
+ while (1) {
+ if (auto Arg = ParseExpression())
+ Args.push_back(std::move(Arg));
+ else
+ return nullptr;
+
+ if (CurTok == ')')
+ break;
+
+ if (CurTok != ',')
+ return LogError("Expected ')' or ',' in argument list");
+ getNextToken();
+ }
+ }
+
+ // Eat the ')'.
+ getNextToken();
+
+ return llvm::make_unique<CallExprAST>(IdName, std::move(Args));
+ }
+
+This routine follows the same style as the other routines. (It expects
+to be called if the current token is a ``tok_identifier`` token). It
+also has recursion and error handling. One interesting aspect of this is
+that it uses *look-ahead* to determine if the current identifier is a
+stand alone variable reference or if it is a function call expression.
+It handles this by checking to see if the token after the identifier is
+a '(' token, constructing either a ``VariableExprAST`` or
+``CallExprAST`` node as appropriate.
+
+Now that we have all of our simple expression-parsing logic in place, we
+can define a helper function to wrap it together into one entry point.
+We call this class of expressions "primary" expressions, for reasons
+that will become more clear `later in the
+tutorial <LangImpl6.html#user-defined-unary-operators>`_. In order to parse an arbitrary
+primary expression, we need to determine what sort of expression it is:
+
+.. code-block:: c++
+
+ /// primary
+ /// ::= identifierexpr
+ /// ::= numberexpr
+ /// ::= parenexpr
+ static std::unique_ptr<ExprAST> ParsePrimary() {
+ switch (CurTok) {
+ default:
+ return LogError("unknown token when expecting an expression");
+ case tok_identifier:
+ return ParseIdentifierExpr();
+ case tok_number:
+ return ParseNumberExpr();
+ case '(':
+ return ParseParenExpr();
+ }
+ }
+
+Now that you see the definition of this function, it is more obvious why
+we can assume the state of CurTok in the various functions. This uses
+look-ahead to determine which sort of expression is being inspected, and
+then parses it with a function call.
+
+Now that basic expressions are handled, we need to handle binary
+expressions. They are a bit more complex.
+
+Binary Expression Parsing
+=========================
+
+Binary expressions are significantly harder to parse because they are
+often ambiguous. For example, when given the string "x+y\*z", the parser
+can choose to parse it as either "(x+y)\*z" or "x+(y\*z)". With common
+definitions from mathematics, we expect the later parse, because "\*"
+(multiplication) has higher *precedence* than "+" (addition).
+
+There are many ways to handle this, but an elegant and efficient way is
+to use `Operator-Precedence
+Parsing <http://en.wikipedia.org/wiki/Operator-precedence_parser>`_.
+This parsing technique uses the precedence of binary operators to guide
+recursion. To start with, we need a table of precedences:
+
+.. code-block:: c++
+
+ /// BinopPrecedence - This holds the precedence for each binary operator that is
+ /// defined.
+ static std::map<char, int> BinopPrecedence;
+
+ /// GetTokPrecedence - Get the precedence of the pending binary operator token.
+ static int GetTokPrecedence() {
+ if (!isascii(CurTok))
+ return -1;
+
+ // Make sure it's a declared binop.
+ int TokPrec = BinopPrecedence[CurTok];
+ if (TokPrec <= 0) return -1;
+ return TokPrec;
+ }
+
+ int main() {
+ // Install standard binary operators.
+ // 1 is lowest precedence.
+ BinopPrecedence['<'] = 10;
+ BinopPrecedence['+'] = 20;
+ BinopPrecedence['-'] = 20;
+ BinopPrecedence['*'] = 40; // highest.
+ ...
+ }
+
+For the basic form of Kaleidoscope, we will only support 4 binary
+operators (this can obviously be extended by you, our brave and intrepid
+reader). The ``GetTokPrecedence`` function returns the precedence for
+the current token, or -1 if the token is not a binary operator. Having a
+map makes it easy to add new operators and makes it clear that the
+algorithm doesn't depend on the specific operators involved, but it
+would be easy enough to eliminate the map and do the comparisons in the
+``GetTokPrecedence`` function. (Or just use a fixed-size array).
+
+With the helper above defined, we can now start parsing binary
+expressions. The basic idea of operator precedence parsing is to break
+down an expression with potentially ambiguous binary operators into
+pieces. Consider, for example, the expression "a+b+(c+d)\*e\*f+g".
+Operator precedence parsing considers this as a stream of primary
+expressions separated by binary operators. As such, it will first parse
+the leading primary expression "a", then it will see the pairs [+, b]
+[+, (c+d)] [\*, e] [\*, f] and [+, g]. Note that because parentheses are
+primary expressions, the binary expression parser doesn't need to worry
+about nested subexpressions like (c+d) at all.
+
+To start, an expression is a primary expression potentially followed by
+a sequence of [binop,primaryexpr] pairs:
+
+.. code-block:: c++
+
+ /// expression
+ /// ::= primary binoprhs
+ ///
+ static std::unique_ptr<ExprAST> ParseExpression() {
+ auto LHS = ParsePrimary();
+ if (!LHS)
+ return nullptr;
+
+ return ParseBinOpRHS(0, std::move(LHS));
+ }
+
+``ParseBinOpRHS`` is the function that parses the sequence of pairs for
+us. It takes a precedence and a pointer to an expression for the part
+that has been parsed so far. Note that "x" is a perfectly valid
+expression: As such, "binoprhs" is allowed to be empty, in which case it
+returns the expression that is passed into it. In our example above, the
+code passes the expression for "a" into ``ParseBinOpRHS`` and the
+current token is "+".
+
+The precedence value passed into ``ParseBinOpRHS`` indicates the
+*minimal operator precedence* that the function is allowed to eat. For
+example, if the current pair stream is [+, x] and ``ParseBinOpRHS`` is
+passed in a precedence of 40, it will not consume any tokens (because
+the precedence of '+' is only 20). With this in mind, ``ParseBinOpRHS``
+starts with:
+
+.. code-block:: c++
+
+ /// binoprhs
+ /// ::= ('+' primary)*
+ static std::unique_ptr<ExprAST> ParseBinOpRHS(int ExprPrec,
+ std::unique_ptr<ExprAST> LHS) {
+ // If this is a binop, find its precedence.
+ while (1) {
+ int TokPrec = GetTokPrecedence();
+
+ // If this is a binop that binds at least as tightly as the current binop,
+ // consume it, otherwise we are done.
+ if (TokPrec < ExprPrec)
+ return LHS;
+
+This code gets the precedence of the current token and checks to see if
+if is too low. Because we defined invalid tokens to have a precedence of
+-1, this check implicitly knows that the pair-stream ends when the token
+stream runs out of binary operators. If this check succeeds, we know
+that the token is a binary operator and that it will be included in this
+expression:
+
+.. code-block:: c++
+
+ // Okay, we know this is a binop.
+ int BinOp = CurTok;
+ getNextToken(); // eat binop
+
+ // Parse the primary expression after the binary operator.
+ auto RHS = ParsePrimary();
+ if (!RHS)
+ return nullptr;
+
+As such, this code eats (and remembers) the binary operator and then
+parses the primary expression that follows. This builds up the whole
+pair, the first of which is [+, b] for the running example.
+
+Now that we parsed the left-hand side of an expression and one pair of
+the RHS sequence, we have to decide which way the expression associates.
+In particular, we could have "(a+b) binop unparsed" or "a + (b binop
+unparsed)". To determine this, we look ahead at "binop" to determine its
+precedence and compare it to BinOp's precedence (which is '+' in this
+case):
+
+.. code-block:: c++
+
+ // If BinOp binds less tightly with RHS than the operator after RHS, let
+ // the pending operator take RHS as its LHS.
+ int NextPrec = GetTokPrecedence();
+ if (TokPrec < NextPrec) {
+
+If the precedence of the binop to the right of "RHS" is lower or equal
+to the precedence of our current operator, then we know that the
+parentheses associate as "(a+b) binop ...". In our example, the current
+operator is "+" and the next operator is "+", we know that they have the
+same precedence. In this case we'll create the AST node for "a+b", and
+then continue parsing:
+
+.. code-block:: c++
+
+ ... if body omitted ...
+ }
+
+ // Merge LHS/RHS.
+ LHS = llvm::make_unique<BinaryExprAST>(BinOp, std::move(LHS),
+ std::move(RHS));
+ } // loop around to the top of the while loop.
+ }
+
+In our example above, this will turn "a+b+" into "(a+b)" and execute the
+next iteration of the loop, with "+" as the current token. The code
+above will eat, remember, and parse "(c+d)" as the primary expression,
+which makes the current pair equal to [+, (c+d)]. It will then evaluate
+the 'if' conditional above with "\*" as the binop to the right of the
+primary. In this case, the precedence of "\*" is higher than the
+precedence of "+" so the if condition will be entered.
+
+The critical question left here is "how can the if condition parse the
+right hand side in full"? In particular, to build the AST correctly for
+our example, it needs to get all of "(c+d)\*e\*f" as the RHS expression
+variable. The code to do this is surprisingly simple (code from the
+above two blocks duplicated for context):
+
+.. code-block:: c++
+
+ // If BinOp binds less tightly with RHS than the operator after RHS, let
+ // the pending operator take RHS as its LHS.
+ int NextPrec = GetTokPrecedence();
+ if (TokPrec < NextPrec) {
+ RHS = ParseBinOpRHS(TokPrec+1, std::move(RHS));
+ if (!RHS)
+ return nullptr;
+ }
+ // Merge LHS/RHS.
+ LHS = llvm::make_unique<BinaryExprAST>(BinOp, std::move(LHS),
+ std::move(RHS));
+ } // loop around to the top of the while loop.
+ }
+
+At this point, we know that the binary operator to the RHS of our
+primary has higher precedence than the binop we are currently parsing.
+As such, we know that any sequence of pairs whose operators are all
+higher precedence than "+" should be parsed together and returned as
+"RHS". To do this, we recursively invoke the ``ParseBinOpRHS`` function
+specifying "TokPrec+1" as the minimum precedence required for it to
+continue. In our example above, this will cause it to return the AST
+node for "(c+d)\*e\*f" as RHS, which is then set as the RHS of the '+'
+expression.
+
+Finally, on the next iteration of the while loop, the "+g" piece is
+parsed and added to the AST. With this little bit of code (14
+non-trivial lines), we correctly handle fully general binary expression
+parsing in a very elegant way. This was a whirlwind tour of this code,
+and it is somewhat subtle. I recommend running through it with a few
+tough examples to see how it works.
+
+This wraps up handling of expressions. At this point, we can point the
+parser at an arbitrary token stream and build an expression from it,
+stopping at the first token that is not part of the expression. Next up
+we need to handle function definitions, etc.
+
+Parsing the Rest
+================
+
+The next thing missing is handling of function prototypes. In
+Kaleidoscope, these are used both for 'extern' function declarations as
+well as function body definitions. The code to do this is
+straight-forward and not very interesting (once you've survived
+expressions):
+
+.. code-block:: c++
+
+ /// prototype
+ /// ::= id '(' id* ')'
+ static std::unique_ptr<PrototypeAST> ParsePrototype() {
+ if (CurTok != tok_identifier)
+ return LogErrorP("Expected function name in prototype");
+
+ std::string FnName = IdentifierStr;
+ getNextToken();
+
+ if (CurTok != '(')
+ return LogErrorP("Expected '(' in prototype");
+
+ // Read the list of argument names.
+ std::vector<std::string> ArgNames;
+ while (getNextToken() == tok_identifier)
+ ArgNames.push_back(IdentifierStr);
+ if (CurTok != ')')
+ return LogErrorP("Expected ')' in prototype");
+
+ // success.
+ getNextToken(); // eat ')'.
+
+ return llvm::make_unique<PrototypeAST>(FnName, std::move(ArgNames));
+ }
+
+Given this, a function definition is very simple, just a prototype plus
+an expression to implement the body:
+
+.. code-block:: c++
+
+ /// definition ::= 'def' prototype expression
+ static std::unique_ptr<FunctionAST> ParseDefinition() {
+ getNextToken(); // eat def.
+ auto Proto = ParsePrototype();
+ if (!Proto) return nullptr;
+
+ if (auto E = ParseExpression())
+ return llvm::make_unique<FunctionAST>(std::move(Proto), std::move(E));
+ return nullptr;
+ }
+
+In addition, we support 'extern' to declare functions like 'sin' and
+'cos' as well as to support forward declaration of user functions. These
+'extern's are just prototypes with no body:
+
+.. code-block:: c++
+
+ /// external ::= 'extern' prototype
+ static std::unique_ptr<PrototypeAST> ParseExtern() {
+ getNextToken(); // eat extern.
+ return ParsePrototype();
+ }
+
+Finally, we'll also let the user type in arbitrary top-level expressions
+and evaluate them on the fly. We will handle this by defining anonymous
+nullary (zero argument) functions for them:
+
+.. code-block:: c++
+
+ /// toplevelexpr ::= expression
+ static std::unique_ptr<FunctionAST> ParseTopLevelExpr() {
+ if (auto E = ParseExpression()) {
+ // Make an anonymous proto.
+ auto Proto = llvm::make_unique<PrototypeAST>("", std::vector<std::string>());
+ return llvm::make_unique<FunctionAST>(std::move(Proto), std::move(E));
+ }
+ return nullptr;
+ }
+
+Now that we have all the pieces, let's build a little driver that will
+let us actually *execute* this code we've built!
+
+The Driver
+==========
+
+The driver for this simply invokes all of the parsing pieces with a
+top-level dispatch loop. There isn't much interesting here, so I'll just
+include the top-level loop. See `below <#full-code-listing>`_ for full code in the
+"Top-Level Parsing" section.
+
+.. code-block:: c++
+
+ /// top ::= definition | external | expression | ';'
+ static void MainLoop() {
+ while (1) {
+ fprintf(stderr, "ready> ");
+ switch (CurTok) {
+ case tok_eof:
+ return;
+ case ';': // ignore top-level semicolons.
+ getNextToken();
+ break;
+ case tok_def:
+ HandleDefinition();
+ break;
+ case tok_extern:
+ HandleExtern();
+ break;
+ default:
+ HandleTopLevelExpression();
+ break;
+ }
+ }
+ }
+
+The most interesting part of this is that we ignore top-level
+semicolons. Why is this, you ask? The basic reason is that if you type
+"4 + 5" at the command line, the parser doesn't know whether that is the
+end of what you will type or not. For example, on the next line you
+could type "def foo..." in which case 4+5 is the end of a top-level
+expression. Alternatively you could type "\* 6", which would continue
+the expression. Having top-level semicolons allows you to type "4+5;",
+and the parser will know you are done.
+
+Conclusions
+===========
+
+With just under 400 lines of commented code (240 lines of non-comment,
+non-blank code), we fully defined our minimal language, including a
+lexer, parser, and AST builder. With this done, the executable will
+validate Kaleidoscope code and tell us if it is grammatically invalid.
+For example, here is a sample interaction:
+
+.. code-block:: bash
+
+ $ ./a.out
+ ready> def foo(x y) x+foo(y, 4.0);
+ Parsed a function definition.
+ ready> def foo(x y) x+y y;
+ Parsed a function definition.
+ Parsed a top-level expr
+ ready> def foo(x y) x+y );
+ Parsed a function definition.
+ Error: unknown token when expecting an expression
+ ready> extern sin(a);
+ ready> Parsed an extern
+ ready> ^D
+ $
+
+There is a lot of room for extension here. You can define new AST nodes,
+extend the language in many ways, etc. In the `next
+installment <LangImpl3.html>`_, we will describe how to generate LLVM
+Intermediate Representation (IR) from the AST.
+
+Full Code Listing
+=================
+
+Here is the complete code listing for this and the previous chapter.
+Note that it is fully self-contained: you don't need LLVM or any
+external libraries at all for this. (Besides the C and C++ standard
+libraries, of course.) To build this, just compile with:
+
+.. code-block:: bash
+
+ # Compile
+ clang++ -g -O3 toy.cpp
+ # Run
+ ./a.out
+
+Here is the code:
+
+.. literalinclude:: ../../examples/Kaleidoscope/Chapter2/toy.cpp
+ :language: c++
+
+`Next: Implementing Code Generation to LLVM IR <LangImpl03.html>`_
+
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--- www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl03.txt (added)
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@@ -0,0 +1,567 @@
+========================================
+Kaleidoscope: Code generation to LLVM IR
+========================================
+
+.. contents::
+ :local:
+
+Chapter 3 Introduction
+======================
+
+Welcome to Chapter 3 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. This chapter shows you how to transform
+the `Abstract Syntax Tree <LangImpl2.html>`_, built in Chapter 2, into
+LLVM IR. This will teach you a little bit about how LLVM does things, as
+well as demonstrate how easy it is to use. It's much more work to build
+a lexer and parser than it is to generate LLVM IR code. :)
+
+**Please note**: the code in this chapter and later require LLVM 3.7 or
+later. LLVM 3.6 and before will not work with it. Also note that you
+need to use a version of this tutorial that matches your LLVM release:
+If you are using an official LLVM release, use the version of the
+documentation included with your release or on the `llvm.org releases
+page <http://llvm.org/releases/>`_.
+
+Code Generation Setup
+=====================
+
+In order to generate LLVM IR, we want some simple setup to get started.
+First we define virtual code generation (codegen) methods in each AST
+class:
+
+.. code-block:: c++
+
+ /// ExprAST - Base class for all expression nodes.
+ class ExprAST {
+ public:
+ virtual ~ExprAST() {}
+ virtual Value *codegen() = 0;
+ };
+
+ /// NumberExprAST - Expression class for numeric literals like "1.0".
+ class NumberExprAST : public ExprAST {
+ double Val;
+
+ public:
+ NumberExprAST(double Val) : Val(Val) {}
+ virtual Value *codegen();
+ };
+ ...
+
+The codegen() method says to emit IR for that AST node along with all
+the things it depends on, and they all return an LLVM Value object.
+"Value" is the class used to represent a "`Static Single Assignment
+(SSA) <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_
+register" or "SSA value" in LLVM. The most distinct aspect of SSA values
+is that their value is computed as the related instruction executes, and
+it does not get a new value until (and if) the instruction re-executes.
+In other words, there is no way to "change" an SSA value. For more
+information, please read up on `Static Single
+Assignment <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_
+- the concepts are really quite natural once you grok them.
+
+Note that instead of adding virtual methods to the ExprAST class
+hierarchy, it could also make sense to use a `visitor
+pattern <http://en.wikipedia.org/wiki/Visitor_pattern>`_ or some other
+way to model this. Again, this tutorial won't dwell on good software
+engineering practices: for our purposes, adding a virtual method is
+simplest.
+
+The second thing we want is an "LogError" method like we used for the
+parser, which will be used to report errors found during code generation
+(for example, use of an undeclared parameter):
+
+.. code-block:: c++
+
+ static LLVMContext TheContext;
+ static IRBuilder<> Builder(TheContext);
+ static std::unique_ptr<Module> TheModule;
+ static std::map<std::string, Value *> NamedValues;
+
+ Value *LogErrorV(const char *Str) {
+ LogError(Str);
+ return nullptr;
+ }
+
+The static variables will be used during code generation. ``TheContext``
+is an opaque object that owns a lot of core LLVM data structures, such as
+the type and constant value tables. We don't need to understand it in
+detail, we just need a single instance to pass into APIs that require it.
+
+The ``Builder`` object is a helper object that makes it easy to generate
+LLVM instructions. Instances of the
+`IRBuilder <http://llvm.org/doxygen/IRBuilder_8h-source.html>`_
+class template keep track of the current place to insert instructions
+and has methods to create new instructions.
+
+``TheModule`` is an LLVM construct that contains functions and global
+variables. In many ways, it is the top-level structure that the LLVM IR
+uses to contain code. It will own the memory for all of the IR that we
+generate, which is why the codegen() method returns a raw Value\*,
+rather than a unique_ptr<Value>.
+
+The ``NamedValues`` map keeps track of which values are defined in the
+current scope and what their LLVM representation is. (In other words, it
+is a symbol table for the code). In this form of Kaleidoscope, the only
+things that can be referenced are function parameters. As such, function
+parameters will be in this map when generating code for their function
+body.
+
+With these basics in place, we can start talking about how to generate
+code for each expression. Note that this assumes that the ``Builder``
+has been set up to generate code *into* something. For now, we'll assume
+that this has already been done, and we'll just use it to emit code.
+
+Expression Code Generation
+==========================
+
+Generating LLVM code for expression nodes is very straightforward: less
+than 45 lines of commented code for all four of our expression nodes.
+First we'll do numeric literals:
+
+.. code-block:: c++
+
+ Value *NumberExprAST::codegen() {
+ return ConstantFP::get(LLVMContext, APFloat(Val));
+ }
+
+In the LLVM IR, numeric constants are represented with the
+``ConstantFP`` class, which holds the numeric value in an ``APFloat``
+internally (``APFloat`` has the capability of holding floating point
+constants of Arbitrary Precision). This code basically just creates
+and returns a ``ConstantFP``. Note that in the LLVM IR that constants
+are all uniqued together and shared. For this reason, the API uses the
+"foo::get(...)" idiom instead of "new foo(..)" or "foo::Create(..)".
+
+.. code-block:: c++
+
+ Value *VariableExprAST::codegen() {
+ // Look this variable up in the function.
+ Value *V = NamedValues[Name];
+ if (!V)
+ LogErrorV("Unknown variable name");
+ return V;
+ }
+
+References to variables are also quite simple using LLVM. In the simple
+version of Kaleidoscope, we assume that the variable has already been
+emitted somewhere and its value is available. In practice, the only
+values that can be in the ``NamedValues`` map are function arguments.
+This code simply checks to see that the specified name is in the map (if
+not, an unknown variable is being referenced) and returns the value for
+it. In future chapters, we'll add support for `loop induction
+variables <LangImpl5.html#for-loop-expression>`_ in the symbol table, and for `local
+variables <LangImpl7.html#user-defined-local-variables>`_.
+
+.. code-block:: c++
+
+ Value *BinaryExprAST::codegen() {
+ Value *L = LHS->codegen();
+ Value *R = RHS->codegen();
+ if (!L || !R)
+ return nullptr;
+
+ switch (Op) {
+ case '+':
+ return Builder.CreateFAdd(L, R, "addtmp");
+ case '-':
+ return Builder.CreateFSub(L, R, "subtmp");
+ case '*':
+ return Builder.CreateFMul(L, R, "multmp");
+ case '<':
+ L = Builder.CreateFCmpULT(L, R, "cmptmp");
+ // Convert bool 0/1 to double 0.0 or 1.0
+ return Builder.CreateUIToFP(L, Type::getDoubleTy(LLVMContext),
+ "booltmp");
+ default:
+ return LogErrorV("invalid binary operator");
+ }
+ }
+
+Binary operators start to get more interesting. The basic idea here is
+that we recursively emit code for the left-hand side of the expression,
+then the right-hand side, then we compute the result of the binary
+expression. In this code, we do a simple switch on the opcode to create
+the right LLVM instruction.
+
+In the example above, the LLVM builder class is starting to show its
+value. IRBuilder knows where to insert the newly created instruction,
+all you have to do is specify what instruction to create (e.g. with
+``CreateFAdd``), which operands to use (``L`` and ``R`` here) and
+optionally provide a name for the generated instruction.
+
+One nice thing about LLVM is that the name is just a hint. For instance,
+if the code above emits multiple "addtmp" variables, LLVM will
+automatically provide each one with an increasing, unique numeric
+suffix. Local value names for instructions are purely optional, but it
+makes it much easier to read the IR dumps.
+
+`LLVM instructions <../LangRef.html#instruction-reference>`_ are constrained by strict
+rules: for example, the Left and Right operators of an `add
+instruction <../LangRef.html#add-instruction>`_ must have the same type, and the
+result type of the add must match the operand types. Because all values
+in Kaleidoscope are doubles, this makes for very simple code for add,
+sub and mul.
+
+On the other hand, LLVM specifies that the `fcmp
+instruction <../LangRef.html#fcmp-instruction>`_ always returns an 'i1' value (a
+one bit integer). The problem with this is that Kaleidoscope wants the
+value to be a 0.0 or 1.0 value. In order to get these semantics, we
+combine the fcmp instruction with a `uitofp
+instruction <../LangRef.html#uitofp-to-instruction>`_. This instruction converts its
+input integer into a floating point value by treating the input as an
+unsigned value. In contrast, if we used the `sitofp
+instruction <../LangRef.html#sitofp-to-instruction>`_, the Kaleidoscope '<' operator
+would return 0.0 and -1.0, depending on the input value.
+
+.. code-block:: c++
+
+ Value *CallExprAST::codegen() {
+ // Look up the name in the global module table.
+ Function *CalleeF = TheModule->getFunction(Callee);
+ if (!CalleeF)
+ return LogErrorV("Unknown function referenced");
+
+ // If argument mismatch error.
+ if (CalleeF->arg_size() != Args.size())
+ return LogErrorV("Incorrect # arguments passed");
+
+ std::vector<Value *> ArgsV;
+ for (unsigned i = 0, e = Args.size(); i != e; ++i) {
+ ArgsV.push_back(Args[i]->codegen());
+ if (!ArgsV.back())
+ return nullptr;
+ }
+
+ return Builder.CreateCall(CalleeF, ArgsV, "calltmp");
+ }
+
+Code generation for function calls is quite straightforward with LLVM. The code
+above initially does a function name lookup in the LLVM Module's symbol table.
+Recall that the LLVM Module is the container that holds the functions we are
+JIT'ing. By giving each function the same name as what the user specifies, we
+can use the LLVM symbol table to resolve function names for us.
+
+Once we have the function to call, we recursively codegen each argument
+that is to be passed in, and create an LLVM `call
+instruction <../LangRef.html#call-instruction>`_. Note that LLVM uses the native C
+calling conventions by default, allowing these calls to also call into
+standard library functions like "sin" and "cos", with no additional
+effort.
+
+This wraps up our handling of the four basic expressions that we have so
+far in Kaleidoscope. Feel free to go in and add some more. For example,
+by browsing the `LLVM language reference <../LangRef.html>`_ you'll find
+several other interesting instructions that are really easy to plug into
+our basic framework.
+
+Function Code Generation
+========================
+
+Code generation for prototypes and functions must handle a number of
+details, which make their code less beautiful than expression code
+generation, but allows us to illustrate some important points. First,
+lets talk about code generation for prototypes: they are used both for
+function bodies and external function declarations. The code starts
+with:
+
+.. code-block:: c++
+
+ Function *PrototypeAST::codegen() {
+ // Make the function type: double(double,double) etc.
+ std::vector<Type*> Doubles(Args.size(),
+ Type::getDoubleTy(LLVMContext));
+ FunctionType *FT =
+ FunctionType::get(Type::getDoubleTy(LLVMContext), Doubles, false);
+
+ Function *F =
+ Function::Create(FT, Function::ExternalLinkage, Name, TheModule);
+
+This code packs a lot of power into a few lines. Note first that this
+function returns a "Function\*" instead of a "Value\*". Because a
+"prototype" really talks about the external interface for a function
+(not the value computed by an expression), it makes sense for it to
+return the LLVM Function it corresponds to when codegen'd.
+
+The call to ``FunctionType::get`` creates the ``FunctionType`` that
+should be used for a given Prototype. Since all function arguments in
+Kaleidoscope are of type double, the first line creates a vector of "N"
+LLVM double types. It then uses the ``Functiontype::get`` method to
+create a function type that takes "N" doubles as arguments, returns one
+double as a result, and that is not vararg (the false parameter
+indicates this). Note that Types in LLVM are uniqued just like Constants
+are, so you don't "new" a type, you "get" it.
+
+The final line above actually creates the IR Function corresponding to
+the Prototype. This indicates the type, linkage and name to use, as
+well as which module to insert into. "`external
+linkage <../LangRef.html#linkage>`_" means that the function may be
+defined outside the current module and/or that it is callable by
+functions outside the module. The Name passed in is the name the user
+specified: since "``TheModule``" is specified, this name is registered
+in "``TheModule``"s symbol table.
+
+.. code-block:: c++
+
+ // Set names for all arguments.
+ unsigned Idx = 0;
+ for (auto &Arg : F->args())
+ Arg.setName(Args[Idx++]);
+
+ return F;
+
+Finally, we set the name of each of the function's arguments according to the
+names given in the Prototype. This step isn't strictly necessary, but keeping
+the names consistent makes the IR more readable, and allows subsequent code to
+refer directly to the arguments for their names, rather than having to look up
+them up in the Prototype AST.
+
+At this point we have a function prototype with no body. This is how LLVM IR
+represents function declarations. For extern statements in Kaleidoscope, this
+is as far as we need to go. For function definitions however, we need to
+codegen and attach a function body.
+
+.. code-block:: c++
+
+ Function *FunctionAST::codegen() {
+ // First, check for an existing function from a previous 'extern' declaration.
+ Function *TheFunction = TheModule->getFunction(Proto->getName());
+
+ if (!TheFunction)
+ TheFunction = Proto->codegen();
+
+ if (!TheFunction)
+ return nullptr;
+
+ if (!TheFunction->empty())
+ return (Function*)LogErrorV("Function cannot be redefined.");
+
+
+For function definitions, we start by searching TheModule's symbol table for an
+existing version of this function, in case one has already been created using an
+'extern' statement. If Module::getFunction returns null then no previous version
+exists, so we'll codegen one from the Prototype. In either case, we want to
+assert that the function is empty (i.e. has no body yet) before we start.
+
+.. code-block:: c++
+
+ // Create a new basic block to start insertion into.
+ BasicBlock *BB = BasicBlock::Create(LLVMContext, "entry", TheFunction);
+ Builder.SetInsertPoint(BB);
+
+ // Record the function arguments in the NamedValues map.
+ NamedValues.clear();
+ for (auto &Arg : TheFunction->args())
+ NamedValues[Arg.getName()] = &Arg;
+
+Now we get to the point where the ``Builder`` is set up. The first line
+creates a new `basic block <http://en.wikipedia.org/wiki/Basic_block>`_
+(named "entry"), which is inserted into ``TheFunction``. The second line
+then tells the builder that new instructions should be inserted into the
+end of the new basic block. Basic blocks in LLVM are an important part
+of functions that define the `Control Flow
+Graph <http://en.wikipedia.org/wiki/Control_flow_graph>`_. Since we
+don't have any control flow, our functions will only contain one block
+at this point. We'll fix this in `Chapter 5 <LangImpl5.html>`_ :).
+
+Next we add the function arguments to the NamedValues map (after first clearing
+it out) so that they're accessible to ``VariableExprAST`` nodes.
+
+.. code-block:: c++
+
+ if (Value *RetVal = Body->codegen()) {
+ // Finish off the function.
+ Builder.CreateRet(RetVal);
+
+ // Validate the generated code, checking for consistency.
+ verifyFunction(*TheFunction);
+
+ return TheFunction;
+ }
+
+Once the insertion point has been set up and the NamedValues map populated,
+we call the ``codegen()`` method for the root expression of the function. If no
+error happens, this emits code to compute the expression into the entry block
+and returns the value that was computed. Assuming no error, we then create an
+LLVM `ret instruction <../LangRef.html#ret-instruction>`_, which completes the function.
+Once the function is built, we call ``verifyFunction``, which is
+provided by LLVM. This function does a variety of consistency checks on
+the generated code, to determine if our compiler is doing everything
+right. Using this is important: it can catch a lot of bugs. Once the
+function is finished and validated, we return it.
+
+.. code-block:: c++
+
+ // Error reading body, remove function.
+ TheFunction->eraseFromParent();
+ return nullptr;
+ }
+
+The only piece left here is handling of the error case. For simplicity,
+we handle this by merely deleting the function we produced with the
+``eraseFromParent`` method. This allows the user to redefine a function
+that they incorrectly typed in before: if we didn't delete it, it would
+live in the symbol table, with a body, preventing future redefinition.
+
+This code does have a bug, though: If the ``FunctionAST::codegen()`` method
+finds an existing IR Function, it does not validate its signature against the
+definition's own prototype. This means that an earlier 'extern' declaration will
+take precedence over the function definition's signature, which can cause
+codegen to fail, for instance if the function arguments are named differently.
+There are a number of ways to fix this bug, see what you can come up with! Here
+is a testcase:
+
+::
+
+ extern foo(a); # ok, defines foo.
+ def foo(b) b; # Error: Unknown variable name. (decl using 'a' takes precedence).
+
+Driver Changes and Closing Thoughts
+===================================
+
+For now, code generation to LLVM doesn't really get us much, except that
+we can look at the pretty IR calls. The sample code inserts calls to
+codegen into the "``HandleDefinition``", "``HandleExtern``" etc
+functions, and then dumps out the LLVM IR. This gives a nice way to look
+at the LLVM IR for simple functions. For example:
+
+::
+
+ ready> 4+5;
+ Read top-level expression:
+ define double @0() {
+ entry:
+ ret double 9.000000e+00
+ }
+
+Note how the parser turns the top-level expression into anonymous
+functions for us. This will be handy when we add `JIT
+support <LangImpl4.html#adding-a-jit-compiler>`_ in the next chapter. Also note that the
+code is very literally transcribed, no optimizations are being performed
+except simple constant folding done by IRBuilder. We will `add
+optimizations <LangImpl4.html#trivial-constant-folding>`_ explicitly in the next
+chapter.
+
+::
+
+ ready> def foo(a b) a*a + 2*a*b + b*b;
+ Read function definition:
+ define double @foo(double %a, double %b) {
+ entry:
+ %multmp = fmul double %a, %a
+ %multmp1 = fmul double 2.000000e+00, %a
+ %multmp2 = fmul double %multmp1, %b
+ %addtmp = fadd double %multmp, %multmp2
+ %multmp3 = fmul double %b, %b
+ %addtmp4 = fadd double %addtmp, %multmp3
+ ret double %addtmp4
+ }
+
+This shows some simple arithmetic. Notice the striking similarity to the
+LLVM builder calls that we use to create the instructions.
+
+::
+
+ ready> def bar(a) foo(a, 4.0) + bar(31337);
+ Read function definition:
+ define double @bar(double %a) {
+ entry:
+ %calltmp = call double @foo(double %a, double 4.000000e+00)
+ %calltmp1 = call double @bar(double 3.133700e+04)
+ %addtmp = fadd double %calltmp, %calltmp1
+ ret double %addtmp
+ }
+
+This shows some function calls. Note that this function will take a long
+time to execute if you call it. In the future we'll add conditional
+control flow to actually make recursion useful :).
+
+::
+
+ ready> extern cos(x);
+ Read extern:
+ declare double @cos(double)
+
+ ready> cos(1.234);
+ Read top-level expression:
+ define double @1() {
+ entry:
+ %calltmp = call double @cos(double 1.234000e+00)
+ ret double %calltmp
+ }
+
+This shows an extern for the libm "cos" function, and a call to it.
+
+.. TODO:: Abandon Pygments' horrible `llvm` lexer. It just totally gives up
+ on highlighting this due to the first line.
+
+::
+
+ ready> ^D
+ ; ModuleID = 'my cool jit'
+
+ define double @0() {
+ entry:
+ %addtmp = fadd double 4.000000e+00, 5.000000e+00
+ ret double %addtmp
+ }
+
+ define double @foo(double %a, double %b) {
+ entry:
+ %multmp = fmul double %a, %a
+ %multmp1 = fmul double 2.000000e+00, %a
+ %multmp2 = fmul double %multmp1, %b
+ %addtmp = fadd double %multmp, %multmp2
+ %multmp3 = fmul double %b, %b
+ %addtmp4 = fadd double %addtmp, %multmp3
+ ret double %addtmp4
+ }
+
+ define double @bar(double %a) {
+ entry:
+ %calltmp = call double @foo(double %a, double 4.000000e+00)
+ %calltmp1 = call double @bar(double 3.133700e+04)
+ %addtmp = fadd double %calltmp, %calltmp1
+ ret double %addtmp
+ }
+
+ declare double @cos(double)
+
+ define double @1() {
+ entry:
+ %calltmp = call double @cos(double 1.234000e+00)
+ ret double %calltmp
+ }
+
+When you quit the current demo, it dumps out the IR for the entire
+module generated. Here you can see the big picture with all the
+functions referencing each other.
+
+This wraps up the third chapter of the Kaleidoscope tutorial. Up next,
+we'll describe how to `add JIT codegen and optimizer
+support <LangImpl4.html>`_ to this so we can actually start running
+code!
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example, enhanced with
+the LLVM code generator. Because this uses the LLVM libraries, we need
+to link them in. To do this, we use the
+`llvm-config <http://llvm.org/cmds/llvm-config.html>`_ tool to inform
+our makefile/command line about which options to use:
+
+.. code-block:: bash
+
+ # Compile
+ clang++ -g -O3 toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core` -o toy
+ # Run
+ ./toy
+
+Here is the code:
+
+.. literalinclude:: ../../examples/Kaleidoscope/Chapter3/toy.cpp
+ :language: c++
+
+`Next: Adding JIT and Optimizer Support <LangImpl04.html>`_
+
Added: www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl04.txt
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==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl04.txt (added)
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@@ -0,0 +1,610 @@
+==============================================
+Kaleidoscope: Adding JIT and Optimizer Support
+==============================================
+
+.. contents::
+ :local:
+
+Chapter 4 Introduction
+======================
+
+Welcome to Chapter 4 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. Chapters 1-3 described the implementation
+of a simple language and added support for generating LLVM IR. This
+chapter describes two new techniques: adding optimizer support to your
+language, and adding JIT compiler support. These additions will
+demonstrate how to get nice, efficient code for the Kaleidoscope
+language.
+
+Trivial Constant Folding
+========================
+
+Our demonstration for Chapter 3 is elegant and easy to extend.
+Unfortunately, it does not produce wonderful code. The IRBuilder,
+however, does give us obvious optimizations when compiling simple code:
+
+::
+
+ ready> def test(x) 1+2+x;
+ Read function definition:
+ define double @test(double %x) {
+ entry:
+ %addtmp = fadd double 3.000000e+00, %x
+ ret double %addtmp
+ }
+
+This code is not a literal transcription of the AST built by parsing the
+input. That would be:
+
+::
+
+ ready> def test(x) 1+2+x;
+ Read function definition:
+ define double @test(double %x) {
+ entry:
+ %addtmp = fadd double 2.000000e+00, 1.000000e+00
+ %addtmp1 = fadd double %addtmp, %x
+ ret double %addtmp1
+ }
+
+Constant folding, as seen above, in particular, is a very common and
+very important optimization: so much so that many language implementors
+implement constant folding support in their AST representation.
+
+With LLVM, you don't need this support in the AST. Since all calls to
+build LLVM IR go through the LLVM IR builder, the builder itself checked
+to see if there was a constant folding opportunity when you call it. If
+so, it just does the constant fold and return the constant instead of
+creating an instruction.
+
+Well, that was easy :). In practice, we recommend always using
+``IRBuilder`` when generating code like this. It has no "syntactic
+overhead" for its use (you don't have to uglify your compiler with
+constant checks everywhere) and it can dramatically reduce the amount of
+LLVM IR that is generated in some cases (particular for languages with a
+macro preprocessor or that use a lot of constants).
+
+On the other hand, the ``IRBuilder`` is limited by the fact that it does
+all of its analysis inline with the code as it is built. If you take a
+slightly more complex example:
+
+::
+
+ ready> def test(x) (1+2+x)*(x+(1+2));
+ ready> Read function definition:
+ define double @test(double %x) {
+ entry:
+ %addtmp = fadd double 3.000000e+00, %x
+ %addtmp1 = fadd double %x, 3.000000e+00
+ %multmp = fmul double %addtmp, %addtmp1
+ ret double %multmp
+ }
+
+In this case, the LHS and RHS of the multiplication are the same value.
+We'd really like to see this generate "``tmp = x+3; result = tmp*tmp;``"
+instead of computing "``x+3``" twice.
+
+Unfortunately, no amount of local analysis will be able to detect and
+correct this. This requires two transformations: reassociation of
+expressions (to make the add's lexically identical) and Common
+Subexpression Elimination (CSE) to delete the redundant add instruction.
+Fortunately, LLVM provides a broad range of optimizations that you can
+use, in the form of "passes".
+
+LLVM Optimization Passes
+========================
+
+LLVM provides many optimization passes, which do many different sorts of
+things and have different tradeoffs. Unlike other systems, LLVM doesn't
+hold to the mistaken notion that one set of optimizations is right for
+all languages and for all situations. LLVM allows a compiler implementor
+to make complete decisions about what optimizations to use, in which
+order, and in what situation.
+
+As a concrete example, LLVM supports both "whole module" passes, which
+look across as large of body of code as they can (often a whole file,
+but if run at link time, this can be a substantial portion of the whole
+program). It also supports and includes "per-function" passes which just
+operate on a single function at a time, without looking at other
+functions. For more information on passes and how they are run, see the
+`How to Write a Pass <../WritingAnLLVMPass.html>`_ document and the
+`List of LLVM Passes <../Passes.html>`_.
+
+For Kaleidoscope, we are currently generating functions on the fly, one
+at a time, as the user types them in. We aren't shooting for the
+ultimate optimization experience in this setting, but we also want to
+catch the easy and quick stuff where possible. As such, we will choose
+to run a few per-function optimizations as the user types the function
+in. If we wanted to make a "static Kaleidoscope compiler", we would use
+exactly the code we have now, except that we would defer running the
+optimizer until the entire file has been parsed.
+
+In order to get per-function optimizations going, we need to set up a
+`FunctionPassManager <../WritingAnLLVMPass.html#what-passmanager-doesr>`_ to hold
+and organize the LLVM optimizations that we want to run. Once we have
+that, we can add a set of optimizations to run. We'll need a new
+FunctionPassManager for each module that we want to optimize, so we'll
+write a function to create and initialize both the module and pass manager
+for us:
+
+.. code-block:: c++
+
+ void InitializeModuleAndPassManager(void) {
+ // Open a new module.
+ Context LLVMContext;
+ TheModule = llvm::make_unique<Module>("my cool jit", LLVMContext);
+ TheModule->setDataLayout(TheJIT->getTargetMachine().createDataLayout());
+
+ // Create a new pass manager attached to it.
+ TheFPM = llvm::make_unique<FunctionPassManager>(TheModule.get());
+
+ // Provide basic AliasAnalysis support for GVN.
+ TheFPM.add(createBasicAliasAnalysisPass());
+ // Do simple "peephole" optimizations and bit-twiddling optzns.
+ TheFPM.add(createInstructionCombiningPass());
+ // Reassociate expressions.
+ TheFPM.add(createReassociatePass());
+ // Eliminate Common SubExpressions.
+ TheFPM.add(createGVNPass());
+ // Simplify the control flow graph (deleting unreachable blocks, etc).
+ TheFPM.add(createCFGSimplificationPass());
+
+ TheFPM.doInitialization();
+ }
+
+This code initializes the global module ``TheModule``, and the function pass
+manager ``TheFPM``, which is attached to ``TheModule``. Once the pass manager is
+set up, we use a series of "add" calls to add a bunch of LLVM passes.
+
+In this case, we choose to add five passes: one analysis pass (alias analysis),
+and four optimization passes. The passes we choose here are a pretty standard set
+of "cleanup" optimizations that are useful for a wide variety of code. I won't
+delve into what they do but, believe me, they are a good starting place :).
+
+Once the PassManager is set up, we need to make use of it. We do this by
+running it after our newly created function is constructed (in
+``FunctionAST::codegen()``), but before it is returned to the client:
+
+.. code-block:: c++
+
+ if (Value *RetVal = Body->codegen()) {
+ // Finish off the function.
+ Builder.CreateRet(RetVal);
+
+ // Validate the generated code, checking for consistency.
+ verifyFunction(*TheFunction);
+
+ // Optimize the function.
+ TheFPM->run(*TheFunction);
+
+ return TheFunction;
+ }
+
+As you can see, this is pretty straightforward. The
+``FunctionPassManager`` optimizes and updates the LLVM Function\* in
+place, improving (hopefully) its body. With this in place, we can try
+our test above again:
+
+::
+
+ ready> def test(x) (1+2+x)*(x+(1+2));
+ ready> Read function definition:
+ define double @test(double %x) {
+ entry:
+ %addtmp = fadd double %x, 3.000000e+00
+ %multmp = fmul double %addtmp, %addtmp
+ ret double %multmp
+ }
+
+As expected, we now get our nicely optimized code, saving a floating
+point add instruction from every execution of this function.
+
+LLVM provides a wide variety of optimizations that can be used in
+certain circumstances. Some `documentation about the various
+passes <../Passes.html>`_ is available, but it isn't very complete.
+Another good source of ideas can come from looking at the passes that
+``Clang`` runs to get started. The "``opt``" tool allows you to
+experiment with passes from the command line, so you can see if they do
+anything.
+
+Now that we have reasonable code coming out of our front-end, lets talk
+about executing it!
+
+Adding a JIT Compiler
+=====================
+
+Code that is available in LLVM IR can have a wide variety of tools
+applied to it. For example, you can run optimizations on it (as we did
+above), you can dump it out in textual or binary forms, you can compile
+the code to an assembly file (.s) for some target, or you can JIT
+compile it. The nice thing about the LLVM IR representation is that it
+is the "common currency" between many different parts of the compiler.
+
+In this section, we'll add JIT compiler support to our interpreter. The
+basic idea that we want for Kaleidoscope is to have the user enter
+function bodies as they do now, but immediately evaluate the top-level
+expressions they type in. For example, if they type in "1 + 2;", we
+should evaluate and print out 3. If they define a function, they should
+be able to call it from the command line.
+
+In order to do this, we first declare and initialize the JIT. This is
+done by adding a global variable ``TheJIT``, and initializing it in
+``main``:
+
+.. code-block:: c++
+
+ static std::unique_ptr<KaleidoscopeJIT> TheJIT;
+ ...
+ int main() {
+ ..
+ TheJIT = llvm::make_unique<KaleidoscopeJIT>();
+
+ // Run the main "interpreter loop" now.
+ MainLoop();
+
+ return 0;
+ }
+
+The KaleidoscopeJIT class is a simple JIT built specifically for these
+tutorials. In later chapters we will look at how it works and extend it with
+new features, but for now we will take it as given. Its API is very simple::
+``addModule`` adds an LLVM IR module to the JIT, making its functions
+available for execution; ``removeModule`` removes a module, freeing any
+memory associated with the code in that module; and ``findSymbol`` allows us
+to look up pointers to the compiled code.
+
+We can take this simple API and change our code that parses top-level expressions to
+look like this:
+
+.. code-block:: c++
+
+ static void HandleTopLevelExpression() {
+ // Evaluate a top-level expression into an anonymous function.
+ if (auto FnAST = ParseTopLevelExpr()) {
+ if (FnAST->codegen()) {
+
+ // JIT the module containing the anonymous expression, keeping a handle so
+ // we can free it later.
+ auto H = TheJIT->addModule(std::move(TheModule));
+ InitializeModuleAndPassManager();
+
+ // Search the JIT for the __anon_expr symbol.
+ auto ExprSymbol = TheJIT->findSymbol("__anon_expr");
+ assert(ExprSymbol && "Function not found");
+
+ // Get the symbol's address and cast it to the right type (takes no
+ // arguments, returns a double) so we can call it as a native function.
+ double (*FP)() = (double (*)())(intptr_t)ExprSymbol.getAddress();
+ fprintf(stderr, "Evaluated to %f\n", FP());
+
+ // Delete the anonymous expression module from the JIT.
+ TheJIT->removeModule(H);
+ }
+
+If parsing and codegen succeeed, the next step is to add the module containing
+the top-level expression to the JIT. We do this by calling addModule, which
+triggers code generation for all the functions in the module, and returns a
+handle that can be used to remove the module from the JIT later. Once the module
+has been added to the JIT it can no longer be modified, so we also open a new
+module to hold subsequent code by calling ``InitializeModuleAndPassManager()``.
+
+Once we've added the module to the JIT we need to get a pointer to the final
+generated code. We do this by calling the JIT's findSymbol method, and passing
+the name of the top-level expression function: ``__anon_expr``. Since we just
+added this function, we assert that findSymbol returned a result.
+
+Next, we get the in-memory address of the ``__anon_expr`` function by calling
+``getAddress()`` on the symbol. Recall that we compile top-level expressions
+into a self-contained LLVM function that takes no arguments and returns the
+computed double. Because the LLVM JIT compiler matches the native platform ABI,
+this means that you can just cast the result pointer to a function pointer of
+that type and call it directly. This means, there is no difference between JIT
+compiled code and native machine code that is statically linked into your
+application.
+
+Finally, since we don't support re-evaluation of top-level expressions, we
+remove the module from the JIT when we're done to free the associated memory.
+Recall, however, that the module we created a few lines earlier (via
+``InitializeModuleAndPassManager``) is still open and waiting for new code to be
+added.
+
+With just these two changes, lets see how Kaleidoscope works now!
+
+::
+
+ ready> 4+5;
+ Read top-level expression:
+ define double @0() {
+ entry:
+ ret double 9.000000e+00
+ }
+
+ Evaluated to 9.000000
+
+Well this looks like it is basically working. The dump of the function
+shows the "no argument function that always returns double" that we
+synthesize for each top-level expression that is typed in. This
+demonstrates very basic functionality, but can we do more?
+
+::
+
+ ready> def testfunc(x y) x + y*2;
+ Read function definition:
+ define double @testfunc(double %x, double %y) {
+ entry:
+ %multmp = fmul double %y, 2.000000e+00
+ %addtmp = fadd double %multmp, %x
+ ret double %addtmp
+ }
+
+ ready> testfunc(4, 10);
+ Read top-level expression:
+ define double @1() {
+ entry:
+ %calltmp = call double @testfunc(double 4.000000e+00, double 1.000000e+01)
+ ret double %calltmp
+ }
+
+ Evaluated to 24.000000
+
+ ready> testfunc(5, 10);
+ ready> LLVM ERROR: Program used external function 'testfunc' which could not be resolved!
+
+
+Function definitions and calls also work, but something went very wrong on that
+last line. The call looks valid, so what happened? As you may have guessed from
+the the API a Module is a unit of allocation for the JIT, and testfunc was part
+of the same module that contained anonymous expression. When we removed that
+module from the JIT to free the memory for the anonymous expression, we deleted
+the definition of ``testfunc`` along with it. Then, when we tried to call
+testfunc a second time, the JIT could no longer find it.
+
+The easiest way to fix this is to put the anonymous expression in a separate
+module from the rest of the function definitions. The JIT will happily resolve
+function calls across module boundaries, as long as each of the functions called
+has a prototype, and is added to the JIT before it is called. By putting the
+anonymous expression in a different module we can delete it without affecting
+the rest of the functions.
+
+In fact, we're going to go a step further and put every function in its own
+module. Doing so allows us to exploit a useful property of the KaleidoscopeJIT
+that will make our environment more REPL-like: Functions can be added to the
+JIT more than once (unlike a module where every function must have a unique
+definition). When you look up a symbol in KaleidoscopeJIT it will always return
+the most recent definition:
+
+::
+
+ ready> def foo(x) x + 1;
+ Read function definition:
+ define double @foo(double %x) {
+ entry:
+ %addtmp = fadd double %x, 1.000000e+00
+ ret double %addtmp
+ }
+
+ ready> foo(2);
+ Evaluated to 3.000000
+
+ ready> def foo(x) x + 2;
+ define double @foo(double %x) {
+ entry:
+ %addtmp = fadd double %x, 2.000000e+00
+ ret double %addtmp
+ }
+
+ ready> foo(2);
+ Evaluated to 4.000000
+
+
+To allow each function to live in its own module we'll need a way to
+re-generate previous function declarations into each new module we open:
+
+.. code-block:: c++
+
+ static std::unique_ptr<KaleidoscopeJIT> TheJIT;
+
+ ...
+
+ Function *getFunction(std::string Name) {
+ // First, see if the function has already been added to the current module.
+ if (auto *F = TheModule->getFunction(Name))
+ return F;
+
+ // If not, check whether we can codegen the declaration from some existing
+ // prototype.
+ auto FI = FunctionProtos.find(Name);
+ if (FI != FunctionProtos.end())
+ return FI->second->codegen();
+
+ // If no existing prototype exists, return null.
+ return nullptr;
+ }
+
+ ...
+
+ Value *CallExprAST::codegen() {
+ // Look up the name in the global module table.
+ Function *CalleeF = getFunction(Callee);
+
+ ...
+
+ Function *FunctionAST::codegen() {
+ // Transfer ownership of the prototype to the FunctionProtos map, but keep a
+ // reference to it for use below.
+ auto &P = *Proto;
+ FunctionProtos[Proto->getName()] = std::move(Proto);
+ Function *TheFunction = getFunction(P.getName());
+ if (!TheFunction)
+ return nullptr;
+
+
+To enable this, we'll start by adding a new global, ``FunctionProtos``, that
+holds the most recent prototype for each function. We'll also add a convenience
+method, ``getFunction()``, to replace calls to ``TheModule->getFunction()``.
+Our convenience method searches ``TheModule`` for an existing function
+declaration, falling back to generating a new declaration from FunctionProtos if
+it doesn't find one. In ``CallExprAST::codegen()`` we just need to replace the
+call to ``TheModule->getFunction()``. In ``FunctionAST::codegen()`` we need to
+update the FunctionProtos map first, then call ``getFunction()``. With this
+done, we can always obtain a function declaration in the current module for any
+previously declared function.
+
+We also need to update HandleDefinition and HandleExtern:
+
+.. code-block:: c++
+
+ static void HandleDefinition() {
+ if (auto FnAST = ParseDefinition()) {
+ if (auto *FnIR = FnAST->codegen()) {
+ fprintf(stderr, "Read function definition:");
+ FnIR->dump();
+ TheJIT->addModule(std::move(TheModule));
+ InitializeModuleAndPassManager();
+ }
+ } else {
+ // Skip token for error recovery.
+ getNextToken();
+ }
+ }
+
+ static void HandleExtern() {
+ if (auto ProtoAST = ParseExtern()) {
+ if (auto *FnIR = ProtoAST->codegen()) {
+ fprintf(stderr, "Read extern: ");
+ FnIR->dump();
+ FunctionProtos[ProtoAST->getName()] = std::move(ProtoAST);
+ }
+ } else {
+ // Skip token for error recovery.
+ getNextToken();
+ }
+ }
+
+In HandleDefinition, we add two lines to transfer the newly defined function to
+the JIT and open a new module. In HandleExtern, we just need to add one line to
+add the prototype to FunctionProtos.
+
+With these changes made, lets try our REPL again (I removed the dump of the
+anonymous functions this time, you should get the idea by now :) :
+
+::
+
+ ready> def foo(x) x + 1;
+ ready> foo(2);
+ Evaluated to 3.000000
+
+ ready> def foo(x) x + 2;
+ ready> foo(2);
+ Evaluated to 4.000000
+
+It works!
+
+Even with this simple code, we get some surprisingly powerful capabilities -
+check this out:
+
+::
+
+ ready> extern sin(x);
+ Read extern:
+ declare double @sin(double)
+
+ ready> extern cos(x);
+ Read extern:
+ declare double @cos(double)
+
+ ready> sin(1.0);
+ Read top-level expression:
+ define double @2() {
+ entry:
+ ret double 0x3FEAED548F090CEE
+ }
+
+ Evaluated to 0.841471
+
+ ready> def foo(x) sin(x)*sin(x) + cos(x)*cos(x);
+ Read function definition:
+ define double @foo(double %x) {
+ entry:
+ %calltmp = call double @sin(double %x)
+ %multmp = fmul double %calltmp, %calltmp
+ %calltmp2 = call double @cos(double %x)
+ %multmp4 = fmul double %calltmp2, %calltmp2
+ %addtmp = fadd double %multmp, %multmp4
+ ret double %addtmp
+ }
+
+ ready> foo(4.0);
+ Read top-level expression:
+ define double @3() {
+ entry:
+ %calltmp = call double @foo(double 4.000000e+00)
+ ret double %calltmp
+ }
+
+ Evaluated to 1.000000
+
+Whoa, how does the JIT know about sin and cos? The answer is surprisingly
+simple: The KaleidoscopeJIT has a straightforward symbol resolution rule that
+it uses to find symbols that aren't available in any given module: First
+it searches all the modules that have already been added to the JIT, from the
+most recent to the oldest, to find the newest definition. If no definition is
+found inside the JIT, it falls back to calling "``dlsym("sin")``" on the
+Kaleidoscope process itself. Since "``sin``" is defined within the JIT's
+address space, it simply patches up calls in the module to call the libm
+version of ``sin`` directly.
+
+In the future we'll see how tweaking this symbol resolution rule can be used to
+enable all sorts of useful features, from security (restricting the set of
+symbols available to JIT'd code), to dynamic code generation based on symbol
+names, and even lazy compilation.
+
+One immediate benefit of the symbol resolution rule is that we can now extend
+the language by writing arbitrary C++ code to implement operations. For example,
+if we add:
+
+.. code-block:: c++
+
+ /// putchard - putchar that takes a double and returns 0.
+ extern "C" double putchard(double X) {
+ fputc((char)X, stderr);
+ return 0;
+ }
+
+Now we can produce simple output to the console by using things like:
+"``extern putchard(x); putchard(120);``", which prints a lowercase 'x'
+on the console (120 is the ASCII code for 'x'). Similar code could be
+used to implement file I/O, console input, and many other capabilities
+in Kaleidoscope.
+
+This completes the JIT and optimizer chapter of the Kaleidoscope
+tutorial. At this point, we can compile a non-Turing-complete
+programming language, optimize and JIT compile it in a user-driven way.
+Next up we'll look into `extending the language with control flow
+constructs <LangImpl5.html>`_, tackling some interesting LLVM IR issues
+along the way.
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example, enhanced with
+the LLVM JIT and optimizer. To build this example, use:
+
+.. code-block:: bash
+
+ # Compile
+ clang++ -g toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core mcjit native` -O3 -o toy
+ # Run
+ ./toy
+
+If you are compiling this on Linux, make sure to add the "-rdynamic"
+option as well. This makes sure that the external functions are resolved
+properly at runtime.
+
+Here is the code:
+
+.. literalinclude:: ../../examples/Kaleidoscope/Chapter4/toy.cpp
+ :language: c++
+
+`Next: Extending the language: control flow <LangImpl05.html>`_
+
Added: www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl05.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl05.txt?rev=290368&view=auto
==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl05.txt (added)
+++ www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl05.txt Thu Dec 22 14:04:03 2016
@@ -0,0 +1,790 @@
+==================================================
+Kaleidoscope: Extending the Language: Control Flow
+==================================================
+
+.. contents::
+ :local:
+
+Chapter 5 Introduction
+======================
+
+Welcome to Chapter 5 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. Parts 1-4 described the implementation of
+the simple Kaleidoscope language and included support for generating
+LLVM IR, followed by optimizations and a JIT compiler. Unfortunately, as
+presented, Kaleidoscope is mostly useless: it has no control flow other
+than call and return. This means that you can't have conditional
+branches in the code, significantly limiting its power. In this episode
+of "build that compiler", we'll extend Kaleidoscope to have an
+if/then/else expression plus a simple 'for' loop.
+
+If/Then/Else
+============
+
+Extending Kaleidoscope to support if/then/else is quite straightforward.
+It basically requires adding support for this "new" concept to the
+lexer, parser, AST, and LLVM code emitter. This example is nice, because
+it shows how easy it is to "grow" a language over time, incrementally
+extending it as new ideas are discovered.
+
+Before we get going on "how" we add this extension, lets talk about
+"what" we want. The basic idea is that we want to be able to write this
+sort of thing:
+
+::
+
+ def fib(x)
+ if x < 3 then
+ 1
+ else
+ fib(x-1)+fib(x-2);
+
+In Kaleidoscope, every construct is an expression: there are no
+statements. As such, the if/then/else expression needs to return a value
+like any other. Since we're using a mostly functional form, we'll have
+it evaluate its conditional, then return the 'then' or 'else' value
+based on how the condition was resolved. This is very similar to the C
+"?:" expression.
+
+The semantics of the if/then/else expression is that it evaluates the
+condition to a boolean equality value: 0.0 is considered to be false and
+everything else is considered to be true. If the condition is true, the
+first subexpression is evaluated and returned, if the condition is
+false, the second subexpression is evaluated and returned. Since
+Kaleidoscope allows side-effects, this behavior is important to nail
+down.
+
+Now that we know what we "want", lets break this down into its
+constituent pieces.
+
+Lexer Extensions for If/Then/Else
+---------------------------------
+
+The lexer extensions are straightforward. First we add new enum values
+for the relevant tokens:
+
+.. code-block:: c++
+
+ // control
+ tok_if = -6,
+ tok_then = -7,
+ tok_else = -8,
+
+Once we have that, we recognize the new keywords in the lexer. This is
+pretty simple stuff:
+
+.. code-block:: c++
+
+ ...
+ if (IdentifierStr == "def")
+ return tok_def;
+ if (IdentifierStr == "extern")
+ return tok_extern;
+ if (IdentifierStr == "if")
+ return tok_if;
+ if (IdentifierStr == "then")
+ return tok_then;
+ if (IdentifierStr == "else")
+ return tok_else;
+ return tok_identifier;
+
+AST Extensions for If/Then/Else
+-------------------------------
+
+To represent the new expression we add a new AST node for it:
+
+.. code-block:: c++
+
+ /// IfExprAST - Expression class for if/then/else.
+ class IfExprAST : public ExprAST {
+ std::unique_ptr<ExprAST> Cond, Then, Else;
+
+ public:
+ IfExprAST(std::unique_ptr<ExprAST> Cond, std::unique_ptr<ExprAST> Then,
+ std::unique_ptr<ExprAST> Else)
+ : Cond(std::move(Cond)), Then(std::move(Then)), Else(std::move(Else)) {}
+ virtual Value *codegen();
+ };
+
+The AST node just has pointers to the various subexpressions.
+
+Parser Extensions for If/Then/Else
+----------------------------------
+
+Now that we have the relevant tokens coming from the lexer and we have
+the AST node to build, our parsing logic is relatively straightforward.
+First we define a new parsing function:
+
+.. code-block:: c++
+
+ /// ifexpr ::= 'if' expression 'then' expression 'else' expression
+ static std::unique_ptr<ExprAST> ParseIfExpr() {
+ getNextToken(); // eat the if.
+
+ // condition.
+ auto Cond = ParseExpression();
+ if (!Cond)
+ return nullptr;
+
+ if (CurTok != tok_then)
+ return LogError("expected then");
+ getNextToken(); // eat the then
+
+ auto Then = ParseExpression();
+ if (!Then)
+ return nullptr;
+
+ if (CurTok != tok_else)
+ return LogError("expected else");
+
+ getNextToken();
+
+ auto Else = ParseExpression();
+ if (!Else)
+ return nullptr;
+
+ return llvm::make_unique<IfExprAST>(std::move(Cond), std::move(Then),
+ std::move(Else));
+ }
+
+Next we hook it up as a primary expression:
+
+.. code-block:: c++
+
+ static std::unique_ptr<ExprAST> ParsePrimary() {
+ switch (CurTok) {
+ default:
+ return LogError("unknown token when expecting an expression");
+ case tok_identifier:
+ return ParseIdentifierExpr();
+ case tok_number:
+ return ParseNumberExpr();
+ case '(':
+ return ParseParenExpr();
+ case tok_if:
+ return ParseIfExpr();
+ }
+ }
+
+LLVM IR for If/Then/Else
+------------------------
+
+Now that we have it parsing and building the AST, the final piece is
+adding LLVM code generation support. This is the most interesting part
+of the if/then/else example, because this is where it starts to
+introduce new concepts. All of the code above has been thoroughly
+described in previous chapters.
+
+To motivate the code we want to produce, lets take a look at a simple
+example. Consider:
+
+::
+
+ extern foo();
+ extern bar();
+ def baz(x) if x then foo() else bar();
+
+If you disable optimizations, the code you'll (soon) get from
+Kaleidoscope looks like this:
+
+.. code-block:: llvm
+
+ declare double @foo()
+
+ declare double @bar()
+
+ define double @baz(double %x) {
+ entry:
+ %ifcond = fcmp one double %x, 0.000000e+00
+ br i1 %ifcond, label %then, label %else
+
+ then: ; preds = %entry
+ %calltmp = call double @foo()
+ br label %ifcont
+
+ else: ; preds = %entry
+ %calltmp1 = call double @bar()
+ br label %ifcont
+
+ ifcont: ; preds = %else, %then
+ %iftmp = phi double [ %calltmp, %then ], [ %calltmp1, %else ]
+ ret double %iftmp
+ }
+
+To visualize the control flow graph, you can use a nifty feature of the
+LLVM '`opt <http://llvm.org/cmds/opt.html>`_' tool. If you put this LLVM
+IR into "t.ll" and run "``llvm-as < t.ll | opt -analyze -view-cfg``", `a
+window will pop up <../ProgrammersManual.html#viewing-graphs-while-debugging-code>`_ and you'll
+see this graph:
+
+.. figure:: LangImpl05-cfg.png
+ :align: center
+ :alt: Example CFG
+
+ Example CFG
+
+Another way to get this is to call "``F->viewCFG()``" or
+"``F->viewCFGOnly()``" (where F is a "``Function*``") either by
+inserting actual calls into the code and recompiling or by calling these
+in the debugger. LLVM has many nice features for visualizing various
+graphs.
+
+Getting back to the generated code, it is fairly simple: the entry block
+evaluates the conditional expression ("x" in our case here) and compares
+the result to 0.0 with the "``fcmp one``" instruction ('one' is "Ordered
+and Not Equal"). Based on the result of this expression, the code jumps
+to either the "then" or "else" blocks, which contain the expressions for
+the true/false cases.
+
+Once the then/else blocks are finished executing, they both branch back
+to the 'ifcont' block to execute the code that happens after the
+if/then/else. In this case the only thing left to do is to return to the
+caller of the function. The question then becomes: how does the code
+know which expression to return?
+
+The answer to this question involves an important SSA operation: the
+`Phi
+operation <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_.
+If you're not familiar with SSA, `the wikipedia
+article <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_
+is a good introduction and there are various other introductions to it
+available on your favorite search engine. The short version is that
+"execution" of the Phi operation requires "remembering" which block
+control came from. The Phi operation takes on the value corresponding to
+the input control block. In this case, if control comes in from the
+"then" block, it gets the value of "calltmp". If control comes from the
+"else" block, it gets the value of "calltmp1".
+
+At this point, you are probably starting to think "Oh no! This means my
+simple and elegant front-end will have to start generating SSA form in
+order to use LLVM!". Fortunately, this is not the case, and we strongly
+advise *not* implementing an SSA construction algorithm in your
+front-end unless there is an amazingly good reason to do so. In
+practice, there are two sorts of values that float around in code
+written for your average imperative programming language that might need
+Phi nodes:
+
+#. Code that involves user variables: ``x = 1; x = x + 1;``
+#. Values that are implicit in the structure of your AST, such as the
+ Phi node in this case.
+
+In `Chapter 7 <LangImpl7.html>`_ of this tutorial ("mutable variables"),
+we'll talk about #1 in depth. For now, just believe me that you don't
+need SSA construction to handle this case. For #2, you have the choice
+of using the techniques that we will describe for #1, or you can insert
+Phi nodes directly, if convenient. In this case, it is really
+easy to generate the Phi node, so we choose to do it directly.
+
+Okay, enough of the motivation and overview, lets generate code!
+
+Code Generation for If/Then/Else
+--------------------------------
+
+In order to generate code for this, we implement the ``codegen`` method
+for ``IfExprAST``:
+
+.. code-block:: c++
+
+ Value *IfExprAST::codegen() {
+ Value *CondV = Cond->codegen();
+ if (!CondV)
+ return nullptr;
+
+ // Convert condition to a bool by comparing equal to 0.0.
+ CondV = Builder.CreateFCmpONE(
+ CondV, ConstantFP::get(LLVMContext, APFloat(0.0)), "ifcond");
+
+This code is straightforward and similar to what we saw before. We emit
+the expression for the condition, then compare that value to zero to get
+a truth value as a 1-bit (bool) value.
+
+.. code-block:: c++
+
+ Function *TheFunction = Builder.GetInsertBlock()->getParent();
+
+ // Create blocks for the then and else cases. Insert the 'then' block at the
+ // end of the function.
+ BasicBlock *ThenBB =
+ BasicBlock::Create(LLVMContext, "then", TheFunction);
+ BasicBlock *ElseBB = BasicBlock::Create(LLVMContext, "else");
+ BasicBlock *MergeBB = BasicBlock::Create(LLVMContext, "ifcont");
+
+ Builder.CreateCondBr(CondV, ThenBB, ElseBB);
+
+This code creates the basic blocks that are related to the if/then/else
+statement, and correspond directly to the blocks in the example above.
+The first line gets the current Function object that is being built. It
+gets this by asking the builder for the current BasicBlock, and asking
+that block for its "parent" (the function it is currently embedded
+into).
+
+Once it has that, it creates three blocks. Note that it passes
+"TheFunction" into the constructor for the "then" block. This causes the
+constructor to automatically insert the new block into the end of the
+specified function. The other two blocks are created, but aren't yet
+inserted into the function.
+
+Once the blocks are created, we can emit the conditional branch that
+chooses between them. Note that creating new blocks does not implicitly
+affect the IRBuilder, so it is still inserting into the block that the
+condition went into. Also note that it is creating a branch to the
+"then" block and the "else" block, even though the "else" block isn't
+inserted into the function yet. This is all ok: it is the standard way
+that LLVM supports forward references.
+
+.. code-block:: c++
+
+ // Emit then value.
+ Builder.SetInsertPoint(ThenBB);
+
+ Value *ThenV = Then->codegen();
+ if (!ThenV)
+ return nullptr;
+
+ Builder.CreateBr(MergeBB);
+ // Codegen of 'Then' can change the current block, update ThenBB for the PHI.
+ ThenBB = Builder.GetInsertBlock();
+
+After the conditional branch is inserted, we move the builder to start
+inserting into the "then" block. Strictly speaking, this call moves the
+insertion point to be at the end of the specified block. However, since
+the "then" block is empty, it also starts out by inserting at the
+beginning of the block. :)
+
+Once the insertion point is set, we recursively codegen the "then"
+expression from the AST. To finish off the "then" block, we create an
+unconditional branch to the merge block. One interesting (and very
+important) aspect of the LLVM IR is that it `requires all basic blocks
+to be "terminated" <../LangRef.html#functionstructure>`_ with a `control
+flow instruction <../LangRef.html#terminators>`_ such as return or
+branch. This means that all control flow, *including fall throughs* must
+be made explicit in the LLVM IR. If you violate this rule, the verifier
+will emit an error.
+
+The final line here is quite subtle, but is very important. The basic
+issue is that when we create the Phi node in the merge block, we need to
+set up the block/value pairs that indicate how the Phi will work.
+Importantly, the Phi node expects to have an entry for each predecessor
+of the block in the CFG. Why then, are we getting the current block when
+we just set it to ThenBB 5 lines above? The problem is that the "Then"
+expression may actually itself change the block that the Builder is
+emitting into if, for example, it contains a nested "if/then/else"
+expression. Because calling ``codegen()`` recursively could arbitrarily change
+the notion of the current block, we are required to get an up-to-date
+value for code that will set up the Phi node.
+
+.. code-block:: c++
+
+ // Emit else block.
+ TheFunction->getBasicBlockList().push_back(ElseBB);
+ Builder.SetInsertPoint(ElseBB);
+
+ Value *ElseV = Else->codegen();
+ if (!ElseV)
+ return nullptr;
+
+ Builder.CreateBr(MergeBB);
+ // codegen of 'Else' can change the current block, update ElseBB for the PHI.
+ ElseBB = Builder.GetInsertBlock();
+
+Code generation for the 'else' block is basically identical to codegen
+for the 'then' block. The only significant difference is the first line,
+which adds the 'else' block to the function. Recall previously that the
+'else' block was created, but not added to the function. Now that the
+'then' and 'else' blocks are emitted, we can finish up with the merge
+code:
+
+.. code-block:: c++
+
+ // Emit merge block.
+ TheFunction->getBasicBlockList().push_back(MergeBB);
+ Builder.SetInsertPoint(MergeBB);
+ PHINode *PN =
+ Builder.CreatePHI(Type::getDoubleTy(LLVMContext), 2, "iftmp");
+
+ PN->addIncoming(ThenV, ThenBB);
+ PN->addIncoming(ElseV, ElseBB);
+ return PN;
+ }
+
+The first two lines here are now familiar: the first adds the "merge"
+block to the Function object (it was previously floating, like the else
+block above). The second changes the insertion point so that newly
+created code will go into the "merge" block. Once that is done, we need
+to create the PHI node and set up the block/value pairs for the PHI.
+
+Finally, the CodeGen function returns the phi node as the value computed
+by the if/then/else expression. In our example above, this returned
+value will feed into the code for the top-level function, which will
+create the return instruction.
+
+Overall, we now have the ability to execute conditional code in
+Kaleidoscope. With this extension, Kaleidoscope is a fairly complete
+language that can calculate a wide variety of numeric functions. Next up
+we'll add another useful expression that is familiar from non-functional
+languages...
+
+'for' Loop Expression
+=====================
+
+Now that we know how to add basic control flow constructs to the
+language, we have the tools to add more powerful things. Lets add
+something more aggressive, a 'for' expression:
+
+::
+
+ extern putchard(char)
+ def printstar(n)
+ for i = 1, i < n, 1.0 in
+ putchard(42); # ascii 42 = '*'
+
+ # print 100 '*' characters
+ printstar(100);
+
+This expression defines a new variable ("i" in this case) which iterates
+from a starting value, while the condition ("i < n" in this case) is
+true, incrementing by an optional step value ("1.0" in this case). If
+the step value is omitted, it defaults to 1.0. While the loop is true,
+it executes its body expression. Because we don't have anything better
+to return, we'll just define the loop as always returning 0.0. In the
+future when we have mutable variables, it will get more useful.
+
+As before, lets talk about the changes that we need to Kaleidoscope to
+support this.
+
+Lexer Extensions for the 'for' Loop
+-----------------------------------
+
+The lexer extensions are the same sort of thing as for if/then/else:
+
+.. code-block:: c++
+
+ ... in enum Token ...
+ // control
+ tok_if = -6, tok_then = -7, tok_else = -8,
+ tok_for = -9, tok_in = -10
+
+ ... in gettok ...
+ if (IdentifierStr == "def")
+ return tok_def;
+ if (IdentifierStr == "extern")
+ return tok_extern;
+ if (IdentifierStr == "if")
+ return tok_if;
+ if (IdentifierStr == "then")
+ return tok_then;
+ if (IdentifierStr == "else")
+ return tok_else;
+ if (IdentifierStr == "for")
+ return tok_for;
+ if (IdentifierStr == "in")
+ return tok_in;
+ return tok_identifier;
+
+AST Extensions for the 'for' Loop
+---------------------------------
+
+The AST node is just as simple. It basically boils down to capturing the
+variable name and the constituent expressions in the node.
+
+.. code-block:: c++
+
+ /// ForExprAST - Expression class for for/in.
+ class ForExprAST : public ExprAST {
+ std::string VarName;
+ std::unique_ptr<ExprAST> Start, End, Step, Body;
+
+ public:
+ ForExprAST(const std::string &VarName, std::unique_ptr<ExprAST> Start,
+ std::unique_ptr<ExprAST> End, std::unique_ptr<ExprAST> Step,
+ std::unique_ptr<ExprAST> Body)
+ : VarName(VarName), Start(std::move(Start)), End(std::move(End)),
+ Step(std::move(Step)), Body(std::move(Body)) {}
+ virtual Value *codegen();
+ };
+
+Parser Extensions for the 'for' Loop
+------------------------------------
+
+The parser code is also fairly standard. The only interesting thing here
+is handling of the optional step value. The parser code handles it by
+checking to see if the second comma is present. If not, it sets the step
+value to null in the AST node:
+
+.. code-block:: c++
+
+ /// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression
+ static std::unique_ptr<ExprAST> ParseForExpr() {
+ getNextToken(); // eat the for.
+
+ if (CurTok != tok_identifier)
+ return LogError("expected identifier after for");
+
+ std::string IdName = IdentifierStr;
+ getNextToken(); // eat identifier.
+
+ if (CurTok != '=')
+ return LogError("expected '=' after for");
+ getNextToken(); // eat '='.
+
+
+ auto Start = ParseExpression();
+ if (!Start)
+ return nullptr;
+ if (CurTok != ',')
+ return LogError("expected ',' after for start value");
+ getNextToken();
+
+ auto End = ParseExpression();
+ if (!End)
+ return nullptr;
+
+ // The step value is optional.
+ std::unique_ptr<ExprAST> Step;
+ if (CurTok == ',') {
+ getNextToken();
+ Step = ParseExpression();
+ if (!Step)
+ return nullptr;
+ }
+
+ if (CurTok != tok_in)
+ return LogError("expected 'in' after for");
+ getNextToken(); // eat 'in'.
+
+ auto Body = ParseExpression();
+ if (!Body)
+ return nullptr;
+
+ return llvm::make_unique<ForExprAST>(IdName, std::move(Start),
+ std::move(End), std::move(Step),
+ std::move(Body));
+ }
+
+LLVM IR for the 'for' Loop
+--------------------------
+
+Now we get to the good part: the LLVM IR we want to generate for this
+thing. With the simple example above, we get this LLVM IR (note that
+this dump is generated with optimizations disabled for clarity):
+
+.. code-block:: llvm
+
+ declare double @putchard(double)
+
+ define double @printstar(double %n) {
+ entry:
+ ; initial value = 1.0 (inlined into phi)
+ br label %loop
+
+ loop: ; preds = %loop, %entry
+ %i = phi double [ 1.000000e+00, %entry ], [ %nextvar, %loop ]
+ ; body
+ %calltmp = call double @putchard(double 4.200000e+01)
+ ; increment
+ %nextvar = fadd double %i, 1.000000e+00
+
+ ; termination test
+ %cmptmp = fcmp ult double %i, %n
+ %booltmp = uitofp i1 %cmptmp to double
+ %loopcond = fcmp one double %booltmp, 0.000000e+00
+ br i1 %loopcond, label %loop, label %afterloop
+
+ afterloop: ; preds = %loop
+ ; loop always returns 0.0
+ ret double 0.000000e+00
+ }
+
+This loop contains all the same constructs we saw before: a phi node,
+several expressions, and some basic blocks. Lets see how this fits
+together.
+
+Code Generation for the 'for' Loop
+----------------------------------
+
+The first part of codegen is very simple: we just output the start
+expression for the loop value:
+
+.. code-block:: c++
+
+ Value *ForExprAST::codegen() {
+ // Emit the start code first, without 'variable' in scope.
+ Value *StartVal = Start->codegen();
+ if (StartVal == 0) return 0;
+
+With this out of the way, the next step is to set up the LLVM basic
+block for the start of the loop body. In the case above, the whole loop
+body is one block, but remember that the body code itself could consist
+of multiple blocks (e.g. if it contains an if/then/else or a for/in
+expression).
+
+.. code-block:: c++
+
+ // Make the new basic block for the loop header, inserting after current
+ // block.
+ Function *TheFunction = Builder.GetInsertBlock()->getParent();
+ BasicBlock *PreheaderBB = Builder.GetInsertBlock();
+ BasicBlock *LoopBB =
+ BasicBlock::Create(LLVMContext, "loop", TheFunction);
+
+ // Insert an explicit fall through from the current block to the LoopBB.
+ Builder.CreateBr(LoopBB);
+
+This code is similar to what we saw for if/then/else. Because we will
+need it to create the Phi node, we remember the block that falls through
+into the loop. Once we have that, we create the actual block that starts
+the loop and create an unconditional branch for the fall-through between
+the two blocks.
+
+.. code-block:: c++
+
+ // Start insertion in LoopBB.
+ Builder.SetInsertPoint(LoopBB);
+
+ // Start the PHI node with an entry for Start.
+ PHINode *Variable = Builder.CreatePHI(Type::getDoubleTy(LLVMContext),
+ 2, VarName.c_str());
+ Variable->addIncoming(StartVal, PreheaderBB);
+
+Now that the "preheader" for the loop is set up, we switch to emitting
+code for the loop body. To begin with, we move the insertion point and
+create the PHI node for the loop induction variable. Since we already
+know the incoming value for the starting value, we add it to the Phi
+node. Note that the Phi will eventually get a second value for the
+backedge, but we can't set it up yet (because it doesn't exist!).
+
+.. code-block:: c++
+
+ // Within the loop, the variable is defined equal to the PHI node. If it
+ // shadows an existing variable, we have to restore it, so save it now.
+ Value *OldVal = NamedValues[VarName];
+ NamedValues[VarName] = Variable;
+
+ // Emit the body of the loop. This, like any other expr, can change the
+ // current BB. Note that we ignore the value computed by the body, but don't
+ // allow an error.
+ if (!Body->codegen())
+ return nullptr;
+
+Now the code starts to get more interesting. Our 'for' loop introduces a
+new variable to the symbol table. This means that our symbol table can
+now contain either function arguments or loop variables. To handle this,
+before we codegen the body of the loop, we add the loop variable as the
+current value for its name. Note that it is possible that there is a
+variable of the same name in the outer scope. It would be easy to make
+this an error (emit an error and return null if there is already an
+entry for VarName) but we choose to allow shadowing of variables. In
+order to handle this correctly, we remember the Value that we are
+potentially shadowing in ``OldVal`` (which will be null if there is no
+shadowed variable).
+
+Once the loop variable is set into the symbol table, the code
+recursively codegen's the body. This allows the body to use the loop
+variable: any references to it will naturally find it in the symbol
+table.
+
+.. code-block:: c++
+
+ // Emit the step value.
+ Value *StepVal = nullptr;
+ if (Step) {
+ StepVal = Step->codegen();
+ if (!StepVal)
+ return nullptr;
+ } else {
+ // If not specified, use 1.0.
+ StepVal = ConstantFP::get(LLVMContext, APFloat(1.0));
+ }
+
+ Value *NextVar = Builder.CreateFAdd(Variable, StepVal, "nextvar");
+
+Now that the body is emitted, we compute the next value of the iteration
+variable by adding the step value, or 1.0 if it isn't present.
+'``NextVar``' will be the value of the loop variable on the next
+iteration of the loop.
+
+.. code-block:: c++
+
+ // Compute the end condition.
+ Value *EndCond = End->codegen();
+ if (!EndCond)
+ return nullptr;
+
+ // Convert condition to a bool by comparing equal to 0.0.
+ EndCond = Builder.CreateFCmpONE(
+ EndCond, ConstantFP::get(LLVMContext, APFloat(0.0)), "loopcond");
+
+Finally, we evaluate the exit value of the loop, to determine whether
+the loop should exit. This mirrors the condition evaluation for the
+if/then/else statement.
+
+.. code-block:: c++
+
+ // Create the "after loop" block and insert it.
+ BasicBlock *LoopEndBB = Builder.GetInsertBlock();
+ BasicBlock *AfterBB =
+ BasicBlock::Create(LLVMContext, "afterloop", TheFunction);
+
+ // Insert the conditional branch into the end of LoopEndBB.
+ Builder.CreateCondBr(EndCond, LoopBB, AfterBB);
+
+ // Any new code will be inserted in AfterBB.
+ Builder.SetInsertPoint(AfterBB);
+
+With the code for the body of the loop complete, we just need to finish
+up the control flow for it. This code remembers the end block (for the
+phi node), then creates the block for the loop exit ("afterloop"). Based
+on the value of the exit condition, it creates a conditional branch that
+chooses between executing the loop again and exiting the loop. Any
+future code is emitted in the "afterloop" block, so it sets the
+insertion position to it.
+
+.. code-block:: c++
+
+ // Add a new entry to the PHI node for the backedge.
+ Variable->addIncoming(NextVar, LoopEndBB);
+
+ // Restore the unshadowed variable.
+ if (OldVal)
+ NamedValues[VarName] = OldVal;
+ else
+ NamedValues.erase(VarName);
+
+ // for expr always returns 0.0.
+ return Constant::getNullValue(Type::getDoubleTy(LLVMContext));
+ }
+
+The final code handles various cleanups: now that we have the "NextVar"
+value, we can add the incoming value to the loop PHI node. After that,
+we remove the loop variable from the symbol table, so that it isn't in
+scope after the for loop. Finally, code generation of the for loop
+always returns 0.0, so that is what we return from
+``ForExprAST::codegen()``.
+
+With this, we conclude the "adding control flow to Kaleidoscope" chapter
+of the tutorial. In this chapter we added two control flow constructs,
+and used them to motivate a couple of aspects of the LLVM IR that are
+important for front-end implementors to know. In the next chapter of our
+saga, we will get a bit crazier and add `user-defined
+operators <LangImpl6.html>`_ to our poor innocent language.
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example, enhanced with
+the if/then/else and for expressions.. To build this example, use:
+
+.. code-block:: bash
+
+ # Compile
+ clang++ -g toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core mcjit native` -O3 -o toy
+ # Run
+ ./toy
+
+Here is the code:
+
+.. literalinclude:: ../../examples/Kaleidoscope/Chapter5/toy.cpp
+ :language: c++
+
+`Next: Extending the language: user-defined operators <LangImpl06.html>`_
+
Added: www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl06.txt
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==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl06.txt (added)
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+============================================================
+Kaleidoscope: Extending the Language: User-defined Operators
+============================================================
+
+.. contents::
+ :local:
+
+Chapter 6 Introduction
+======================
+
+Welcome to Chapter 6 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. At this point in our tutorial, we now
+have a fully functional language that is fairly minimal, but also
+useful. There is still one big problem with it, however. Our language
+doesn't have many useful operators (like division, logical negation, or
+even any comparisons besides less-than).
+
+This chapter of the tutorial takes a wild digression into adding
+user-defined operators to the simple and beautiful Kaleidoscope
+language. This digression now gives us a simple and ugly language in
+some ways, but also a powerful one at the same time. One of the great
+things about creating your own language is that you get to decide what
+is good or bad. In this tutorial we'll assume that it is okay to use
+this as a way to show some interesting parsing techniques.
+
+At the end of this tutorial, we'll run through an example Kaleidoscope
+application that `renders the Mandelbrot set <#kicking-the-tires>`_. This gives an
+example of what you can build with Kaleidoscope and its feature set.
+
+User-defined Operators: the Idea
+================================
+
+The "operator overloading" that we will add to Kaleidoscope is more
+general than languages like C++. In C++, you are only allowed to
+redefine existing operators: you can't programatically change the
+grammar, introduce new operators, change precedence levels, etc. In this
+chapter, we will add this capability to Kaleidoscope, which will let the
+user round out the set of operators that are supported.
+
+The point of going into user-defined operators in a tutorial like this
+is to show the power and flexibility of using a hand-written parser.
+Thus far, the parser we have been implementing uses recursive descent
+for most parts of the grammar and operator precedence parsing for the
+expressions. See `Chapter 2 <LangImpl2.html>`_ for details. Without
+using operator precedence parsing, it would be very difficult to allow
+the programmer to introduce new operators into the grammar: the grammar
+is dynamically extensible as the JIT runs.
+
+The two specific features we'll add are programmable unary operators
+(right now, Kaleidoscope has no unary operators at all) as well as
+binary operators. An example of this is:
+
+::
+
+ # Logical unary not.
+ def unary!(v)
+ if v then
+ 0
+ else
+ 1;
+
+ # Define > with the same precedence as <.
+ def binary> 10 (LHS RHS)
+ RHS < LHS;
+
+ # Binary "logical or", (note that it does not "short circuit")
+ def binary| 5 (LHS RHS)
+ if LHS then
+ 1
+ else if RHS then
+ 1
+ else
+ 0;
+
+ # Define = with slightly lower precedence than relationals.
+ def binary= 9 (LHS RHS)
+ !(LHS < RHS | LHS > RHS);
+
+Many languages aspire to being able to implement their standard runtime
+library in the language itself. In Kaleidoscope, we can implement
+significant parts of the language in the library!
+
+We will break down implementation of these features into two parts:
+implementing support for user-defined binary operators and adding unary
+operators.
+
+User-defined Binary Operators
+=============================
+
+Adding support for user-defined binary operators is pretty simple with
+our current framework. We'll first add support for the unary/binary
+keywords:
+
+.. code-block:: c++
+
+ enum Token {
+ ...
+ // operators
+ tok_binary = -11,
+ tok_unary = -12
+ };
+ ...
+ static int gettok() {
+ ...
+ if (IdentifierStr == "for")
+ return tok_for;
+ if (IdentifierStr == "in")
+ return tok_in;
+ if (IdentifierStr == "binary")
+ return tok_binary;
+ if (IdentifierStr == "unary")
+ return tok_unary;
+ return tok_identifier;
+
+This just adds lexer support for the unary and binary keywords, like we
+did in `previous chapters <LangImpl5.html#lexer-extensions-for-if-then-else>`_. One nice thing
+about our current AST, is that we represent binary operators with full
+generalisation by using their ASCII code as the opcode. For our extended
+operators, we'll use this same representation, so we don't need any new
+AST or parser support.
+
+On the other hand, we have to be able to represent the definitions of
+these new operators, in the "def binary\| 5" part of the function
+definition. In our grammar so far, the "name" for the function
+definition is parsed as the "prototype" production and into the
+``PrototypeAST`` AST node. To represent our new user-defined operators
+as prototypes, we have to extend the ``PrototypeAST`` AST node like
+this:
+
+.. code-block:: c++
+
+ /// PrototypeAST - This class represents the "prototype" for a function,
+ /// which captures its argument names as well as if it is an operator.
+ class PrototypeAST {
+ std::string Name;
+ std::vector<std::string> Args;
+ bool IsOperator;
+ unsigned Precedence; // Precedence if a binary op.
+
+ public:
+ PrototypeAST(const std::string &name, std::vector<std::string> Args,
+ bool IsOperator = false, unsigned Prec = 0)
+ : Name(name), Args(std::move(Args)), IsOperator(IsOperator),
+ Precedence(Prec) {}
+
+ bool isUnaryOp() const { return IsOperator && Args.size() == 1; }
+ bool isBinaryOp() const { return IsOperator && Args.size() == 2; }
+
+ char getOperatorName() const {
+ assert(isUnaryOp() || isBinaryOp());
+ return Name[Name.size()-1];
+ }
+
+ unsigned getBinaryPrecedence() const { return Precedence; }
+
+ Function *codegen();
+ };
+
+Basically, in addition to knowing a name for the prototype, we now keep
+track of whether it was an operator, and if it was, what precedence
+level the operator is at. The precedence is only used for binary
+operators (as you'll see below, it just doesn't apply for unary
+operators). Now that we have a way to represent the prototype for a
+user-defined operator, we need to parse it:
+
+.. code-block:: c++
+
+ /// prototype
+ /// ::= id '(' id* ')'
+ /// ::= binary LETTER number? (id, id)
+ static std::unique_ptr<PrototypeAST> ParsePrototype() {
+ std::string FnName;
+
+ unsigned Kind = 0; // 0 = identifier, 1 = unary, 2 = binary.
+ unsigned BinaryPrecedence = 30;
+
+ switch (CurTok) {
+ default:
+ return LogErrorP("Expected function name in prototype");
+ case tok_identifier:
+ FnName = IdentifierStr;
+ Kind = 0;
+ getNextToken();
+ break;
+ case tok_binary:
+ getNextToken();
+ if (!isascii(CurTok))
+ return LogErrorP("Expected binary operator");
+ FnName = "binary";
+ FnName += (char)CurTok;
+ Kind = 2;
+ getNextToken();
+
+ // Read the precedence if present.
+ if (CurTok == tok_number) {
+ if (NumVal < 1 || NumVal > 100)
+ return LogErrorP("Invalid precedecnce: must be 1..100");
+ BinaryPrecedence = (unsigned)NumVal;
+ getNextToken();
+ }
+ break;
+ }
+
+ if (CurTok != '(')
+ return LogErrorP("Expected '(' in prototype");
+
+ std::vector<std::string> ArgNames;
+ while (getNextToken() == tok_identifier)
+ ArgNames.push_back(IdentifierStr);
+ if (CurTok != ')')
+ return LogErrorP("Expected ')' in prototype");
+
+ // success.
+ getNextToken(); // eat ')'.
+
+ // Verify right number of names for operator.
+ if (Kind && ArgNames.size() != Kind)
+ return LogErrorP("Invalid number of operands for operator");
+
+ return llvm::make_unique<PrototypeAST>(FnName, std::move(ArgNames), Kind != 0,
+ BinaryPrecedence);
+ }
+
+This is all fairly straightforward parsing code, and we have already
+seen a lot of similar code in the past. One interesting part about the
+code above is the couple lines that set up ``FnName`` for binary
+operators. This builds names like "binary@" for a newly defined "@"
+operator. This then takes advantage of the fact that symbol names in the
+LLVM symbol table are allowed to have any character in them, including
+embedded nul characters.
+
+The next interesting thing to add, is codegen support for these binary
+operators. Given our current structure, this is a simple addition of a
+default case for our existing binary operator node:
+
+.. code-block:: c++
+
+ Value *BinaryExprAST::codegen() {
+ Value *L = LHS->codegen();
+ Value *R = RHS->codegen();
+ if (!L || !R)
+ return nullptr;
+
+ switch (Op) {
+ case '+':
+ return Builder.CreateFAdd(L, R, "addtmp");
+ case '-':
+ return Builder.CreateFSub(L, R, "subtmp");
+ case '*':
+ return Builder.CreateFMul(L, R, "multmp");
+ case '<':
+ L = Builder.CreateFCmpULT(L, R, "cmptmp");
+ // Convert bool 0/1 to double 0.0 or 1.0
+ return Builder.CreateUIToFP(L, Type::getDoubleTy(LLVMContext),
+ "booltmp");
+ default:
+ break;
+ }
+
+ // If it wasn't a builtin binary operator, it must be a user defined one. Emit
+ // a call to it.
+ Function *F = TheModule->getFunction(std::string("binary") + Op);
+ assert(F && "binary operator not found!");
+
+ Value *Ops[2] = { L, R };
+ return Builder.CreateCall(F, Ops, "binop");
+ }
+
+As you can see above, the new code is actually really simple. It just
+does a lookup for the appropriate operator in the symbol table and
+generates a function call to it. Since user-defined operators are just
+built as normal functions (because the "prototype" boils down to a
+function with the right name) everything falls into place.
+
+The final piece of code we are missing, is a bit of top-level magic:
+
+.. code-block:: c++
+
+ Function *FunctionAST::codegen() {
+ NamedValues.clear();
+
+ Function *TheFunction = Proto->codegen();
+ if (!TheFunction)
+ return nullptr;
+
+ // If this is an operator, install it.
+ if (Proto->isBinaryOp())
+ BinopPrecedence[Proto->getOperatorName()] = Proto->getBinaryPrecedence();
+
+ // Create a new basic block to start insertion into.
+ BasicBlock *BB = BasicBlock::Create(LLVMContext, "entry", TheFunction);
+ Builder.SetInsertPoint(BB);
+
+ if (Value *RetVal = Body->codegen()) {
+ ...
+
+Basically, before codegening a function, if it is a user-defined
+operator, we register it in the precedence table. This allows the binary
+operator parsing logic we already have in place to handle it. Since we
+are working on a fully-general operator precedence parser, this is all
+we need to do to "extend the grammar".
+
+Now we have useful user-defined binary operators. This builds a lot on
+the previous framework we built for other operators. Adding unary
+operators is a bit more challenging, because we don't have any framework
+for it yet - lets see what it takes.
+
+User-defined Unary Operators
+============================
+
+Since we don't currently support unary operators in the Kaleidoscope
+language, we'll need to add everything to support them. Above, we added
+simple support for the 'unary' keyword to the lexer. In addition to
+that, we need an AST node:
+
+.. code-block:: c++
+
+ /// UnaryExprAST - Expression class for a unary operator.
+ class UnaryExprAST : public ExprAST {
+ char Opcode;
+ std::unique_ptr<ExprAST> Operand;
+
+ public:
+ UnaryExprAST(char Opcode, std::unique_ptr<ExprAST> Operand)
+ : Opcode(Opcode), Operand(std::move(Operand)) {}
+ virtual Value *codegen();
+ };
+
+This AST node is very simple and obvious by now. It directly mirrors the
+binary operator AST node, except that it only has one child. With this,
+we need to add the parsing logic. Parsing a unary operator is pretty
+simple: we'll add a new function to do it:
+
+.. code-block:: c++
+
+ /// unary
+ /// ::= primary
+ /// ::= '!' unary
+ static std::unique_ptr<ExprAST> ParseUnary() {
+ // If the current token is not an operator, it must be a primary expr.
+ if (!isascii(CurTok) || CurTok == '(' || CurTok == ',')
+ return ParsePrimary();
+
+ // If this is a unary operator, read it.
+ int Opc = CurTok;
+ getNextToken();
+ if (auto Operand = ParseUnary())
+ return llvm::unique_ptr<UnaryExprAST>(Opc, std::move(Operand));
+ return nullptr;
+ }
+
+The grammar we add is pretty straightforward here. If we see a unary
+operator when parsing a primary operator, we eat the operator as a
+prefix and parse the remaining piece as another unary operator. This
+allows us to handle multiple unary operators (e.g. "!!x"). Note that
+unary operators can't have ambiguous parses like binary operators can,
+so there is no need for precedence information.
+
+The problem with this function, is that we need to call ParseUnary from
+somewhere. To do this, we change previous callers of ParsePrimary to
+call ParseUnary instead:
+
+.. code-block:: c++
+
+ /// binoprhs
+ /// ::= ('+' unary)*
+ static std::unique_ptr<ExprAST> ParseBinOpRHS(int ExprPrec,
+ std::unique_ptr<ExprAST> LHS) {
+ ...
+ // Parse the unary expression after the binary operator.
+ auto RHS = ParseUnary();
+ if (!RHS)
+ return nullptr;
+ ...
+ }
+ /// expression
+ /// ::= unary binoprhs
+ ///
+ static std::unique_ptr<ExprAST> ParseExpression() {
+ auto LHS = ParseUnary();
+ if (!LHS)
+ return nullptr;
+
+ return ParseBinOpRHS(0, std::move(LHS));
+ }
+
+With these two simple changes, we are now able to parse unary operators
+and build the AST for them. Next up, we need to add parser support for
+prototypes, to parse the unary operator prototype. We extend the binary
+operator code above with:
+
+.. code-block:: c++
+
+ /// prototype
+ /// ::= id '(' id* ')'
+ /// ::= binary LETTER number? (id, id)
+ /// ::= unary LETTER (id)
+ static std::unique_ptr<PrototypeAST> ParsePrototype() {
+ std::string FnName;
+
+ unsigned Kind = 0; // 0 = identifier, 1 = unary, 2 = binary.
+ unsigned BinaryPrecedence = 30;
+
+ switch (CurTok) {
+ default:
+ return LogErrorP("Expected function name in prototype");
+ case tok_identifier:
+ FnName = IdentifierStr;
+ Kind = 0;
+ getNextToken();
+ break;
+ case tok_unary:
+ getNextToken();
+ if (!isascii(CurTok))
+ return LogErrorP("Expected unary operator");
+ FnName = "unary";
+ FnName += (char)CurTok;
+ Kind = 1;
+ getNextToken();
+ break;
+ case tok_binary:
+ ...
+
+As with binary operators, we name unary operators with a name that
+includes the operator character. This assists us at code generation
+time. Speaking of, the final piece we need to add is codegen support for
+unary operators. It looks like this:
+
+.. code-block:: c++
+
+ Value *UnaryExprAST::codegen() {
+ Value *OperandV = Operand->codegen();
+ if (!OperandV)
+ return nullptr;
+
+ Function *F = TheModule->getFunction(std::string("unary")+Opcode);
+ if (!F)
+ return LogErrorV("Unknown unary operator");
+
+ return Builder.CreateCall(F, OperandV, "unop");
+ }
+
+This code is similar to, but simpler than, the code for binary
+operators. It is simpler primarily because it doesn't need to handle any
+predefined operators.
+
+Kicking the Tires
+=================
+
+It is somewhat hard to believe, but with a few simple extensions we've
+covered in the last chapters, we have grown a real-ish language. With
+this, we can do a lot of interesting things, including I/O, math, and a
+bunch of other things. For example, we can now add a nice sequencing
+operator (printd is defined to print out the specified value and a
+newline):
+
+::
+
+ ready> extern printd(x);
+ Read extern:
+ declare double @printd(double)
+
+ ready> def binary : 1 (x y) 0; # Low-precedence operator that ignores operands.
+ ..
+ ready> printd(123) : printd(456) : printd(789);
+ 123.000000
+ 456.000000
+ 789.000000
+ Evaluated to 0.000000
+
+We can also define a bunch of other "primitive" operations, such as:
+
+::
+
+ # Logical unary not.
+ def unary!(v)
+ if v then
+ 0
+ else
+ 1;
+
+ # Unary negate.
+ def unary-(v)
+ 0-v;
+
+ # Define > with the same precedence as <.
+ def binary> 10 (LHS RHS)
+ RHS < LHS;
+
+ # Binary logical or, which does not short circuit.
+ def binary| 5 (LHS RHS)
+ if LHS then
+ 1
+ else if RHS then
+ 1
+ else
+ 0;
+
+ # Binary logical and, which does not short circuit.
+ def binary& 6 (LHS RHS)
+ if !LHS then
+ 0
+ else
+ !!RHS;
+
+ # Define = with slightly lower precedence than relationals.
+ def binary = 9 (LHS RHS)
+ !(LHS < RHS | LHS > RHS);
+
+ # Define ':' for sequencing: as a low-precedence operator that ignores operands
+ # and just returns the RHS.
+ def binary : 1 (x y) y;
+
+Given the previous if/then/else support, we can also define interesting
+functions for I/O. For example, the following prints out a character
+whose "density" reflects the value passed in: the lower the value, the
+denser the character:
+
+::
+
+ ready>
+
+ extern putchard(char)
+ def printdensity(d)
+ if d > 8 then
+ putchard(32) # ' '
+ else if d > 4 then
+ putchard(46) # '.'
+ else if d > 2 then
+ putchard(43) # '+'
+ else
+ putchard(42); # '*'
+ ...
+ ready> printdensity(1): printdensity(2): printdensity(3):
+ printdensity(4): printdensity(5): printdensity(9):
+ putchard(10);
+ **++.
+ Evaluated to 0.000000
+
+Based on these simple primitive operations, we can start to define more
+interesting things. For example, here's a little function that solves
+for the number of iterations it takes a function in the complex plane to
+converge:
+
+::
+
+ # Determine whether the specific location diverges.
+ # Solve for z = z^2 + c in the complex plane.
+ def mandelconverger(real imag iters creal cimag)
+ if iters > 255 | (real*real + imag*imag > 4) then
+ iters
+ else
+ mandelconverger(real*real - imag*imag + creal,
+ 2*real*imag + cimag,
+ iters+1, creal, cimag);
+
+ # Return the number of iterations required for the iteration to escape
+ def mandelconverge(real imag)
+ mandelconverger(real, imag, 0, real, imag);
+
+This "``z = z2 + c``" function is a beautiful little creature that is
+the basis for computation of the `Mandelbrot
+Set <http://en.wikipedia.org/wiki/Mandelbrot_set>`_. Our
+``mandelconverge`` function returns the number of iterations that it
+takes for a complex orbit to escape, saturating to 255. This is not a
+very useful function by itself, but if you plot its value over a
+two-dimensional plane, you can see the Mandelbrot set. Given that we are
+limited to using putchard here, our amazing graphical output is limited,
+but we can whip together something using the density plotter above:
+
+::
+
+ # Compute and plot the mandelbrot set with the specified 2 dimensional range
+ # info.
+ def mandelhelp(xmin xmax xstep ymin ymax ystep)
+ for y = ymin, y < ymax, ystep in (
+ (for x = xmin, x < xmax, xstep in
+ printdensity(mandelconverge(x,y)))
+ : putchard(10)
+ )
+
+ # mandel - This is a convenient helper function for plotting the mandelbrot set
+ # from the specified position with the specified Magnification.
+ def mandel(realstart imagstart realmag imagmag)
+ mandelhelp(realstart, realstart+realmag*78, realmag,
+ imagstart, imagstart+imagmag*40, imagmag);
+
+Given this, we can try plotting out the mandelbrot set! Lets try it out:
+
+::
+
+ ready> mandel(-2.3, -1.3, 0.05, 0.07);
+ *******************************+++++++++++*************************************
+ *************************+++++++++++++++++++++++*******************************
+ **********************+++++++++++++++++++++++++++++****************************
+ *******************+++++++++++++++++++++.. ...++++++++*************************
+ *****************++++++++++++++++++++++.... ...+++++++++***********************
+ ***************+++++++++++++++++++++++..... ...+++++++++*********************
+ **************+++++++++++++++++++++++.... ....+++++++++********************
+ *************++++++++++++++++++++++...... .....++++++++*******************
+ ************+++++++++++++++++++++....... .......+++++++******************
+ ***********+++++++++++++++++++.... ... .+++++++*****************
+ **********+++++++++++++++++....... .+++++++****************
+ *********++++++++++++++........... ...+++++++***************
+ ********++++++++++++............ ...++++++++**************
+ ********++++++++++... .......... .++++++++**************
+ *******+++++++++..... .+++++++++*************
+ *******++++++++...... ..+++++++++*************
+ *******++++++....... ..+++++++++*************
+ *******+++++...... ..+++++++++*************
+ *******.... .... ...+++++++++*************
+ *******.... . ...+++++++++*************
+ *******+++++...... ...+++++++++*************
+ *******++++++....... ..+++++++++*************
+ *******++++++++...... .+++++++++*************
+ *******+++++++++..... ..+++++++++*************
+ ********++++++++++... .......... .++++++++**************
+ ********++++++++++++............ ...++++++++**************
+ *********++++++++++++++.......... ...+++++++***************
+ **********++++++++++++++++........ .+++++++****************
+ **********++++++++++++++++++++.... ... ..+++++++****************
+ ***********++++++++++++++++++++++....... .......++++++++*****************
+ ************+++++++++++++++++++++++...... ......++++++++******************
+ **************+++++++++++++++++++++++.... ....++++++++********************
+ ***************+++++++++++++++++++++++..... ...+++++++++*********************
+ *****************++++++++++++++++++++++.... ...++++++++***********************
+ *******************+++++++++++++++++++++......++++++++*************************
+ *********************++++++++++++++++++++++.++++++++***************************
+ *************************+++++++++++++++++++++++*******************************
+ ******************************+++++++++++++************************************
+ *******************************************************************************
+ *******************************************************************************
+ *******************************************************************************
+ Evaluated to 0.000000
+ ready> mandel(-2, -1, 0.02, 0.04);
+ **************************+++++++++++++++++++++++++++++++++++++++++++++++++++++
+ ***********************++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+ *********************+++++++++++++++++++++++++++++++++++++++++++++++++++++++++.
+ *******************+++++++++++++++++++++++++++++++++++++++++++++++++++++++++...
+ *****************+++++++++++++++++++++++++++++++++++++++++++++++++++++++++.....
+ ***************++++++++++++++++++++++++++++++++++++++++++++++++++++++++........
+ **************++++++++++++++++++++++++++++++++++++++++++++++++++++++...........
+ ************+++++++++++++++++++++++++++++++++++++++++++++++++++++..............
+ ***********++++++++++++++++++++++++++++++++++++++++++++++++++........ .
+ **********++++++++++++++++++++++++++++++++++++++++++++++.............
+ ********+++++++++++++++++++++++++++++++++++++++++++..................
+ *******+++++++++++++++++++++++++++++++++++++++.......................
+ ******+++++++++++++++++++++++++++++++++++...........................
+ *****++++++++++++++++++++++++++++++++............................
+ *****++++++++++++++++++++++++++++...............................
+ ****++++++++++++++++++++++++++...... .........................
+ ***++++++++++++++++++++++++......... ...... ...........
+ ***++++++++++++++++++++++............
+ **+++++++++++++++++++++..............
+ **+++++++++++++++++++................
+ *++++++++++++++++++.................
+ *++++++++++++++++............ ...
+ *++++++++++++++..............
+ *+++....++++................
+ *.......... ...........
+ *
+ *.......... ...........
+ *+++....++++................
+ *++++++++++++++..............
+ *++++++++++++++++............ ...
+ *++++++++++++++++++.................
+ **+++++++++++++++++++................
+ **+++++++++++++++++++++..............
+ ***++++++++++++++++++++++............
+ ***++++++++++++++++++++++++......... ...... ...........
+ ****++++++++++++++++++++++++++...... .........................
+ *****++++++++++++++++++++++++++++...............................
+ *****++++++++++++++++++++++++++++++++............................
+ ******+++++++++++++++++++++++++++++++++++...........................
+ *******+++++++++++++++++++++++++++++++++++++++.......................
+ ********+++++++++++++++++++++++++++++++++++++++++++..................
+ Evaluated to 0.000000
+ ready> mandel(-0.9, -1.4, 0.02, 0.03);
+ *******************************************************************************
+ *******************************************************************************
+ *******************************************************************************
+ **********+++++++++++++++++++++************************************************
+ *+++++++++++++++++++++++++++++++++++++++***************************************
+ +++++++++++++++++++++++++++++++++++++++++++++**********************************
+ ++++++++++++++++++++++++++++++++++++++++++++++++++*****************************
+ ++++++++++++++++++++++++++++++++++++++++++++++++++++++*************************
+ +++++++++++++++++++++++++++++++++++++++++++++++++++++++++**********************
+ +++++++++++++++++++++++++++++++++.........++++++++++++++++++*******************
+ +++++++++++++++++++++++++++++++.... ......+++++++++++++++++++****************
+ +++++++++++++++++++++++++++++....... ........+++++++++++++++++++**************
+ ++++++++++++++++++++++++++++........ ........++++++++++++++++++++************
+ +++++++++++++++++++++++++++......... .. ...+++++++++++++++++++++**********
+ ++++++++++++++++++++++++++........... ....++++++++++++++++++++++********
+ ++++++++++++++++++++++++............. .......++++++++++++++++++++++******
+ +++++++++++++++++++++++............. ........+++++++++++++++++++++++****
+ ++++++++++++++++++++++........... ..........++++++++++++++++++++++***
+ ++++++++++++++++++++........... .........++++++++++++++++++++++*
+ ++++++++++++++++++............ ...........++++++++++++++++++++
+ ++++++++++++++++............... .............++++++++++++++++++
+ ++++++++++++++................. ...............++++++++++++++++
+ ++++++++++++.................. .................++++++++++++++
+ +++++++++.................. .................+++++++++++++
+ ++++++........ . ......... ..++++++++++++
+ ++............ ...... ....++++++++++
+ .............. ...++++++++++
+ .............. ....+++++++++
+ .............. .....++++++++
+ ............. ......++++++++
+ ........... .......++++++++
+ ......... ........+++++++
+ ......... ........+++++++
+ ......... ....+++++++
+ ........ ...+++++++
+ ....... ...+++++++
+ ....+++++++
+ .....+++++++
+ ....+++++++
+ ....+++++++
+ ....+++++++
+ Evaluated to 0.000000
+ ready> ^D
+
+At this point, you may be starting to realize that Kaleidoscope is a
+real and powerful language. It may not be self-similar :), but it can be
+used to plot things that are!
+
+With this, we conclude the "adding user-defined operators" chapter of
+the tutorial. We have successfully augmented our language, adding the
+ability to extend the language in the library, and we have shown how
+this can be used to build a simple but interesting end-user application
+in Kaleidoscope. At this point, Kaleidoscope can build a variety of
+applications that are functional and can call functions with
+side-effects, but it can't actually define and mutate a variable itself.
+
+Strikingly, variable mutation is an important feature of some languages,
+and it is not at all obvious how to `add support for mutable
+variables <LangImpl7.html>`_ without having to add an "SSA construction"
+phase to your front-end. In the next chapter, we will describe how you
+can add variable mutation without building SSA in your front-end.
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example, enhanced with
+the if/then/else and for expressions.. To build this example, use:
+
+.. code-block:: bash
+
+ # Compile
+ clang++ -g toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core mcjit native` -O3 -o toy
+ # Run
+ ./toy
+
+On some platforms, you will need to specify -rdynamic or
+-Wl,--export-dynamic when linking. This ensures that symbols defined in
+the main executable are exported to the dynamic linker and so are
+available for symbol resolution at run time. This is not needed if you
+compile your support code into a shared library, although doing that
+will cause problems on Windows.
+
+Here is the code:
+
+.. literalinclude:: ../../examples/Kaleidoscope/Chapter6/toy.cpp
+ :language: c++
+
+`Next: Extending the language: mutable variables / SSA
+construction <LangImpl07.html>`_
+
Added: www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl07.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl07.txt?rev=290368&view=auto
==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl07.txt (added)
+++ www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl07.txt Thu Dec 22 14:04:03 2016
@@ -0,0 +1,881 @@
+=======================================================
+Kaleidoscope: Extending the Language: Mutable Variables
+=======================================================
+
+.. contents::
+ :local:
+
+Chapter 7 Introduction
+======================
+
+Welcome to Chapter 7 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. In chapters 1 through 6, we've built a
+very respectable, albeit simple, `functional programming
+language <http://en.wikipedia.org/wiki/Functional_programming>`_. In our
+journey, we learned some parsing techniques, how to build and represent
+an AST, how to build LLVM IR, and how to optimize the resultant code as
+well as JIT compile it.
+
+While Kaleidoscope is interesting as a functional language, the fact
+that it is functional makes it "too easy" to generate LLVM IR for it. In
+particular, a functional language makes it very easy to build LLVM IR
+directly in `SSA
+form <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_.
+Since LLVM requires that the input code be in SSA form, this is a very
+nice property and it is often unclear to newcomers how to generate code
+for an imperative language with mutable variables.
+
+The short (and happy) summary of this chapter is that there is no need
+for your front-end to build SSA form: LLVM provides highly tuned and
+well tested support for this, though the way it works is a bit
+unexpected for some.
+
+Why is this a hard problem?
+===========================
+
+To understand why mutable variables cause complexities in SSA
+construction, consider this extremely simple C example:
+
+.. code-block:: c
+
+ int G, H;
+ int test(_Bool Condition) {
+ int X;
+ if (Condition)
+ X = G;
+ else
+ X = H;
+ return X;
+ }
+
+In this case, we have the variable "X", whose value depends on the path
+executed in the program. Because there are two different possible values
+for X before the return instruction, a PHI node is inserted to merge the
+two values. The LLVM IR that we want for this example looks like this:
+
+.. code-block:: llvm
+
+ @G = weak global i32 0 ; type of @G is i32*
+ @H = weak global i32 0 ; type of @H is i32*
+
+ define i32 @test(i1 %Condition) {
+ entry:
+ br i1 %Condition, label %cond_true, label %cond_false
+
+ cond_true:
+ %X.0 = load i32* @G
+ br label %cond_next
+
+ cond_false:
+ %X.1 = load i32* @H
+ br label %cond_next
+
+ cond_next:
+ %X.2 = phi i32 [ %X.1, %cond_false ], [ %X.0, %cond_true ]
+ ret i32 %X.2
+ }
+
+In this example, the loads from the G and H global variables are
+explicit in the LLVM IR, and they live in the then/else branches of the
+if statement (cond\_true/cond\_false). In order to merge the incoming
+values, the X.2 phi node in the cond\_next block selects the right value
+to use based on where control flow is coming from: if control flow comes
+from the cond\_false block, X.2 gets the value of X.1. Alternatively, if
+control flow comes from cond\_true, it gets the value of X.0. The intent
+of this chapter is not to explain the details of SSA form. For more
+information, see one of the many `online
+references <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_.
+
+The question for this article is "who places the phi nodes when lowering
+assignments to mutable variables?". The issue here is that LLVM
+*requires* that its IR be in SSA form: there is no "non-ssa" mode for
+it. However, SSA construction requires non-trivial algorithms and data
+structures, so it is inconvenient and wasteful for every front-end to
+have to reproduce this logic.
+
+Memory in LLVM
+==============
+
+The 'trick' here is that while LLVM does require all register values to
+be in SSA form, it does not require (or permit) memory objects to be in
+SSA form. In the example above, note that the loads from G and H are
+direct accesses to G and H: they are not renamed or versioned. This
+differs from some other compiler systems, which do try to version memory
+objects. In LLVM, instead of encoding dataflow analysis of memory into
+the LLVM IR, it is handled with `Analysis
+Passes <../WritingAnLLVMPass.html>`_ which are computed on demand.
+
+With this in mind, the high-level idea is that we want to make a stack
+variable (which lives in memory, because it is on the stack) for each
+mutable object in a function. To take advantage of this trick, we need
+to talk about how LLVM represents stack variables.
+
+In LLVM, all memory accesses are explicit with load/store instructions,
+and it is carefully designed not to have (or need) an "address-of"
+operator. Notice how the type of the @G/@H global variables is actually
+"i32\*" even though the variable is defined as "i32". What this means is
+that @G defines *space* for an i32 in the global data area, but its
+*name* actually refers to the address for that space. Stack variables
+work the same way, except that instead of being declared with global
+variable definitions, they are declared with the `LLVM alloca
+instruction <../LangRef.html#alloca-instruction>`_:
+
+.. code-block:: llvm
+
+ define i32 @example() {
+ entry:
+ %X = alloca i32 ; type of %X is i32*.
+ ...
+ %tmp = load i32* %X ; load the stack value %X from the stack.
+ %tmp2 = add i32 %tmp, 1 ; increment it
+ store i32 %tmp2, i32* %X ; store it back
+ ...
+
+This code shows an example of how you can declare and manipulate a stack
+variable in the LLVM IR. Stack memory allocated with the alloca
+instruction is fully general: you can pass the address of the stack slot
+to functions, you can store it in other variables, etc. In our example
+above, we could rewrite the example to use the alloca technique to avoid
+using a PHI node:
+
+.. code-block:: llvm
+
+ @G = weak global i32 0 ; type of @G is i32*
+ @H = weak global i32 0 ; type of @H is i32*
+
+ define i32 @test(i1 %Condition) {
+ entry:
+ %X = alloca i32 ; type of %X is i32*.
+ br i1 %Condition, label %cond_true, label %cond_false
+
+ cond_true:
+ %X.0 = load i32* @G
+ store i32 %X.0, i32* %X ; Update X
+ br label %cond_next
+
+ cond_false:
+ %X.1 = load i32* @H
+ store i32 %X.1, i32* %X ; Update X
+ br label %cond_next
+
+ cond_next:
+ %X.2 = load i32* %X ; Read X
+ ret i32 %X.2
+ }
+
+With this, we have discovered a way to handle arbitrary mutable
+variables without the need to create Phi nodes at all:
+
+#. Each mutable variable becomes a stack allocation.
+#. Each read of the variable becomes a load from the stack.
+#. Each update of the variable becomes a store to the stack.
+#. Taking the address of a variable just uses the stack address
+ directly.
+
+While this solution has solved our immediate problem, it introduced
+another one: we have now apparently introduced a lot of stack traffic
+for very simple and common operations, a major performance problem.
+Fortunately for us, the LLVM optimizer has a highly-tuned optimization
+pass named "mem2reg" that handles this case, promoting allocas like this
+into SSA registers, inserting Phi nodes as appropriate. If you run this
+example through the pass, for example, you'll get:
+
+.. code-block:: bash
+
+ $ llvm-as < example.ll | opt -mem2reg | llvm-dis
+ @G = weak global i32 0
+ @H = weak global i32 0
+
+ define i32 @test(i1 %Condition) {
+ entry:
+ br i1 %Condition, label %cond_true, label %cond_false
+
+ cond_true:
+ %X.0 = load i32* @G
+ br label %cond_next
+
+ cond_false:
+ %X.1 = load i32* @H
+ br label %cond_next
+
+ cond_next:
+ %X.01 = phi i32 [ %X.1, %cond_false ], [ %X.0, %cond_true ]
+ ret i32 %X.01
+ }
+
+The mem2reg pass implements the standard "iterated dominance frontier"
+algorithm for constructing SSA form and has a number of optimizations
+that speed up (very common) degenerate cases. The mem2reg optimization
+pass is the answer to dealing with mutable variables, and we highly
+recommend that you depend on it. Note that mem2reg only works on
+variables in certain circumstances:
+
+#. mem2reg is alloca-driven: it looks for allocas and if it can handle
+ them, it promotes them. It does not apply to global variables or heap
+ allocations.
+#. mem2reg only looks for alloca instructions in the entry block of the
+ function. Being in the entry block guarantees that the alloca is only
+ executed once, which makes analysis simpler.
+#. mem2reg only promotes allocas whose uses are direct loads and stores.
+ If the address of the stack object is passed to a function, or if any
+ funny pointer arithmetic is involved, the alloca will not be
+ promoted.
+#. mem2reg only works on allocas of `first
+ class <../LangRef.html#first-class-types>`_ values (such as pointers,
+ scalars and vectors), and only if the array size of the allocation is
+ 1 (or missing in the .ll file). mem2reg is not capable of promoting
+ structs or arrays to registers. Note that the "sroa" pass is
+ more powerful and can promote structs, "unions", and arrays in many
+ cases.
+
+All of these properties are easy to satisfy for most imperative
+languages, and we'll illustrate it below with Kaleidoscope. The final
+question you may be asking is: should I bother with this nonsense for my
+front-end? Wouldn't it be better if I just did SSA construction
+directly, avoiding use of the mem2reg optimization pass? In short, we
+strongly recommend that you use this technique for building SSA form,
+unless there is an extremely good reason not to. Using this technique
+is:
+
+- Proven and well tested: clang uses this technique
+ for local mutable variables. As such, the most common clients of LLVM
+ are using this to handle a bulk of their variables. You can be sure
+ that bugs are found fast and fixed early.
+- Extremely Fast: mem2reg has a number of special cases that make it
+ fast in common cases as well as fully general. For example, it has
+ fast-paths for variables that are only used in a single block,
+ variables that only have one assignment point, good heuristics to
+ avoid insertion of unneeded phi nodes, etc.
+- Needed for debug info generation: `Debug information in
+ LLVM <../SourceLevelDebugging.html>`_ relies on having the address of
+ the variable exposed so that debug info can be attached to it. This
+ technique dovetails very naturally with this style of debug info.
+
+If nothing else, this makes it much easier to get your front-end up and
+running, and is very simple to implement. Let's extend Kaleidoscope with
+mutable variables now!
+
+Mutable Variables in Kaleidoscope
+=================================
+
+Now that we know the sort of problem we want to tackle, let's see what
+this looks like in the context of our little Kaleidoscope language.
+We're going to add two features:
+
+#. The ability to mutate variables with the '=' operator.
+#. The ability to define new variables.
+
+While the first item is really what this is about, we only have
+variables for incoming arguments as well as for induction variables, and
+redefining those only goes so far :). Also, the ability to define new
+variables is a useful thing regardless of whether you will be mutating
+them. Here's a motivating example that shows how we could use these:
+
+::
+
+ # Define ':' for sequencing: as a low-precedence operator that ignores operands
+ # and just returns the RHS.
+ def binary : 1 (x y) y;
+
+ # Recursive fib, we could do this before.
+ def fib(x)
+ if (x < 3) then
+ 1
+ else
+ fib(x-1)+fib(x-2);
+
+ # Iterative fib.
+ def fibi(x)
+ var a = 1, b = 1, c in
+ (for i = 3, i < x in
+ c = a + b :
+ a = b :
+ b = c) :
+ b;
+
+ # Call it.
+ fibi(10);
+
+In order to mutate variables, we have to change our existing variables
+to use the "alloca trick". Once we have that, we'll add our new
+operator, then extend Kaleidoscope to support new variable definitions.
+
+Adjusting Existing Variables for Mutation
+=========================================
+
+The symbol table in Kaleidoscope is managed at code generation time by
+the '``NamedValues``' map. This map currently keeps track of the LLVM
+"Value\*" that holds the double value for the named variable. In order
+to support mutation, we need to change this slightly, so that
+``NamedValues`` holds the *memory location* of the variable in question.
+Note that this change is a refactoring: it changes the structure of the
+code, but does not (by itself) change the behavior of the compiler. All
+of these changes are isolated in the Kaleidoscope code generator.
+
+At this point in Kaleidoscope's development, it only supports variables
+for two things: incoming arguments to functions and the induction
+variable of 'for' loops. For consistency, we'll allow mutation of these
+variables in addition to other user-defined variables. This means that
+these will both need memory locations.
+
+To start our transformation of Kaleidoscope, we'll change the
+NamedValues map so that it maps to AllocaInst\* instead of Value\*. Once
+we do this, the C++ compiler will tell us what parts of the code we need
+to update:
+
+.. code-block:: c++
+
+ static std::map<std::string, AllocaInst*> NamedValues;
+
+Also, since we will need to create these alloca's, we'll use a helper
+function that ensures that the allocas are created in the entry block of
+the function:
+
+.. code-block:: c++
+
+ /// CreateEntryBlockAlloca - Create an alloca instruction in the entry block of
+ /// the function. This is used for mutable variables etc.
+ static AllocaInst *CreateEntryBlockAlloca(Function *TheFunction,
+ const std::string &VarName) {
+ IRBuilder<> TmpB(&TheFunction->getEntryBlock(),
+ TheFunction->getEntryBlock().begin());
+ return TmpB.CreateAlloca(Type::getDoubleTy(LLVMContext), 0,
+ VarName.c_str());
+ }
+
+This funny looking code creates an IRBuilder object that is pointing at
+the first instruction (.begin()) of the entry block. It then creates an
+alloca with the expected name and returns it. Because all values in
+Kaleidoscope are doubles, there is no need to pass in a type to use.
+
+With this in place, the first functionality change we want to make is to
+variable references. In our new scheme, variables live on the stack, so
+code generating a reference to them actually needs to produce a load
+from the stack slot:
+
+.. code-block:: c++
+
+ Value *VariableExprAST::codegen() {
+ // Look this variable up in the function.
+ Value *V = NamedValues[Name];
+ if (!V)
+ return LogErrorV("Unknown variable name");
+
+ // Load the value.
+ return Builder.CreateLoad(V, Name.c_str());
+ }
+
+As you can see, this is pretty straightforward. Now we need to update
+the things that define the variables to set up the alloca. We'll start
+with ``ForExprAST::codegen()`` (see the `full code listing <#id1>`_ for
+the unabridged code):
+
+.. code-block:: c++
+
+ Function *TheFunction = Builder.GetInsertBlock()->getParent();
+
+ // Create an alloca for the variable in the entry block.
+ AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, VarName);
+
+ // Emit the start code first, without 'variable' in scope.
+ Value *StartVal = Start->codegen();
+ if (!StartVal)
+ return nullptr;
+
+ // Store the value into the alloca.
+ Builder.CreateStore(StartVal, Alloca);
+ ...
+
+ // Compute the end condition.
+ Value *EndCond = End->codegen();
+ if (!EndCond)
+ return nullptr;
+
+ // Reload, increment, and restore the alloca. This handles the case where
+ // the body of the loop mutates the variable.
+ Value *CurVar = Builder.CreateLoad(Alloca);
+ Value *NextVar = Builder.CreateFAdd(CurVar, StepVal, "nextvar");
+ Builder.CreateStore(NextVar, Alloca);
+ ...
+
+This code is virtually identical to the code `before we allowed mutable
+variables <LangImpl5.html#code-generation-for-the-for-loop>`_. The big difference is that we
+no longer have to construct a PHI node, and we use load/store to access
+the variable as needed.
+
+To support mutable argument variables, we need to also make allocas for
+them. The code for this is also pretty simple:
+
+.. code-block:: c++
+
+ /// CreateArgumentAllocas - Create an alloca for each argument and register the
+ /// argument in the symbol table so that references to it will succeed.
+ void PrototypeAST::CreateArgumentAllocas(Function *F) {
+ Function::arg_iterator AI = F->arg_begin();
+ for (unsigned Idx = 0, e = Args.size(); Idx != e; ++Idx, ++AI) {
+ // Create an alloca for this variable.
+ AllocaInst *Alloca = CreateEntryBlockAlloca(F, Args[Idx]);
+
+ // Store the initial value into the alloca.
+ Builder.CreateStore(AI, Alloca);
+
+ // Add arguments to variable symbol table.
+ NamedValues[Args[Idx]] = Alloca;
+ }
+ }
+
+For each argument, we make an alloca, store the input value to the
+function into the alloca, and register the alloca as the memory location
+for the argument. This method gets invoked by ``FunctionAST::codegen()``
+right after it sets up the entry block for the function.
+
+The final missing piece is adding the mem2reg pass, which allows us to
+get good codegen once again:
+
+.. code-block:: c++
+
+ // Set up the optimizer pipeline. Start with registering info about how the
+ // target lays out data structures.
+ OurFPM.add(new DataLayout(*TheExecutionEngine->getDataLayout()));
+ // Promote allocas to registers.
+ OurFPM.add(createPromoteMemoryToRegisterPass());
+ // Do simple "peephole" optimizations and bit-twiddling optzns.
+ OurFPM.add(createInstructionCombiningPass());
+ // Reassociate expressions.
+ OurFPM.add(createReassociatePass());
+
+It is interesting to see what the code looks like before and after the
+mem2reg optimization runs. For example, this is the before/after code
+for our recursive fib function. Before the optimization:
+
+.. code-block:: llvm
+
+ define double @fib(double %x) {
+ entry:
+ %x1 = alloca double
+ store double %x, double* %x1
+ %x2 = load double* %x1
+ %cmptmp = fcmp ult double %x2, 3.000000e+00
+ %booltmp = uitofp i1 %cmptmp to double
+ %ifcond = fcmp one double %booltmp, 0.000000e+00
+ br i1 %ifcond, label %then, label %else
+
+ then: ; preds = %entry
+ br label %ifcont
+
+ else: ; preds = %entry
+ %x3 = load double* %x1
+ %subtmp = fsub double %x3, 1.000000e+00
+ %calltmp = call double @fib(double %subtmp)
+ %x4 = load double* %x1
+ %subtmp5 = fsub double %x4, 2.000000e+00
+ %calltmp6 = call double @fib(double %subtmp5)
+ %addtmp = fadd double %calltmp, %calltmp6
+ br label %ifcont
+
+ ifcont: ; preds = %else, %then
+ %iftmp = phi double [ 1.000000e+00, %then ], [ %addtmp, %else ]
+ ret double %iftmp
+ }
+
+Here there is only one variable (x, the input argument) but you can
+still see the extremely simple-minded code generation strategy we are
+using. In the entry block, an alloca is created, and the initial input
+value is stored into it. Each reference to the variable does a reload
+from the stack. Also, note that we didn't modify the if/then/else
+expression, so it still inserts a PHI node. While we could make an
+alloca for it, it is actually easier to create a PHI node for it, so we
+still just make the PHI.
+
+Here is the code after the mem2reg pass runs:
+
+.. code-block:: llvm
+
+ define double @fib(double %x) {
+ entry:
+ %cmptmp = fcmp ult double %x, 3.000000e+00
+ %booltmp = uitofp i1 %cmptmp to double
+ %ifcond = fcmp one double %booltmp, 0.000000e+00
+ br i1 %ifcond, label %then, label %else
+
+ then:
+ br label %ifcont
+
+ else:
+ %subtmp = fsub double %x, 1.000000e+00
+ %calltmp = call double @fib(double %subtmp)
+ %subtmp5 = fsub double %x, 2.000000e+00
+ %calltmp6 = call double @fib(double %subtmp5)
+ %addtmp = fadd double %calltmp, %calltmp6
+ br label %ifcont
+
+ ifcont: ; preds = %else, %then
+ %iftmp = phi double [ 1.000000e+00, %then ], [ %addtmp, %else ]
+ ret double %iftmp
+ }
+
+This is a trivial case for mem2reg, since there are no redefinitions of
+the variable. The point of showing this is to calm your tension about
+inserting such blatent inefficiencies :).
+
+After the rest of the optimizers run, we get:
+
+.. code-block:: llvm
+
+ define double @fib(double %x) {
+ entry:
+ %cmptmp = fcmp ult double %x, 3.000000e+00
+ %booltmp = uitofp i1 %cmptmp to double
+ %ifcond = fcmp ueq double %booltmp, 0.000000e+00
+ br i1 %ifcond, label %else, label %ifcont
+
+ else:
+ %subtmp = fsub double %x, 1.000000e+00
+ %calltmp = call double @fib(double %subtmp)
+ %subtmp5 = fsub double %x, 2.000000e+00
+ %calltmp6 = call double @fib(double %subtmp5)
+ %addtmp = fadd double %calltmp, %calltmp6
+ ret double %addtmp
+
+ ifcont:
+ ret double 1.000000e+00
+ }
+
+Here we see that the simplifycfg pass decided to clone the return
+instruction into the end of the 'else' block. This allowed it to
+eliminate some branches and the PHI node.
+
+Now that all symbol table references are updated to use stack variables,
+we'll add the assignment operator.
+
+New Assignment Operator
+=======================
+
+With our current framework, adding a new assignment operator is really
+simple. We will parse it just like any other binary operator, but handle
+it internally (instead of allowing the user to define it). The first
+step is to set a precedence:
+
+.. code-block:: c++
+
+ int main() {
+ // Install standard binary operators.
+ // 1 is lowest precedence.
+ BinopPrecedence['='] = 2;
+ BinopPrecedence['<'] = 10;
+ BinopPrecedence['+'] = 20;
+ BinopPrecedence['-'] = 20;
+
+Now that the parser knows the precedence of the binary operator, it
+takes care of all the parsing and AST generation. We just need to
+implement codegen for the assignment operator. This looks like:
+
+.. code-block:: c++
+
+ Value *BinaryExprAST::codegen() {
+ // Special case '=' because we don't want to emit the LHS as an expression.
+ if (Op == '=') {
+ // Assignment requires the LHS to be an identifier.
+ VariableExprAST *LHSE = dynamic_cast<VariableExprAST*>(LHS.get());
+ if (!LHSE)
+ return LogErrorV("destination of '=' must be a variable");
+
+Unlike the rest of the binary operators, our assignment operator doesn't
+follow the "emit LHS, emit RHS, do computation" model. As such, it is
+handled as a special case before the other binary operators are handled.
+The other strange thing is that it requires the LHS to be a variable. It
+is invalid to have "(x+1) = expr" - only things like "x = expr" are
+allowed.
+
+.. code-block:: c++
+
+ // Codegen the RHS.
+ Value *Val = RHS->codegen();
+ if (!Val)
+ return nullptr;
+
+ // Look up the name.
+ Value *Variable = NamedValues[LHSE->getName()];
+ if (!Variable)
+ return LogErrorV("Unknown variable name");
+
+ Builder.CreateStore(Val, Variable);
+ return Val;
+ }
+ ...
+
+Once we have the variable, codegen'ing the assignment is
+straightforward: we emit the RHS of the assignment, create a store, and
+return the computed value. Returning a value allows for chained
+assignments like "X = (Y = Z)".
+
+Now that we have an assignment operator, we can mutate loop variables
+and arguments. For example, we can now run code like this:
+
+::
+
+ # Function to print a double.
+ extern printd(x);
+
+ # Define ':' for sequencing: as a low-precedence operator that ignores operands
+ # and just returns the RHS.
+ def binary : 1 (x y) y;
+
+ def test(x)
+ printd(x) :
+ x = 4 :
+ printd(x);
+
+ test(123);
+
+When run, this example prints "123" and then "4", showing that we did
+actually mutate the value! Okay, we have now officially implemented our
+goal: getting this to work requires SSA construction in the general
+case. However, to be really useful, we want the ability to define our
+own local variables, let's add this next!
+
+User-defined Local Variables
+============================
+
+Adding var/in is just like any other extension we made to
+Kaleidoscope: we extend the lexer, the parser, the AST and the code
+generator. The first step for adding our new 'var/in' construct is to
+extend the lexer. As before, this is pretty trivial, the code looks like
+this:
+
+.. code-block:: c++
+
+ enum Token {
+ ...
+ // var definition
+ tok_var = -13
+ ...
+ }
+ ...
+ static int gettok() {
+ ...
+ if (IdentifierStr == "in")
+ return tok_in;
+ if (IdentifierStr == "binary")
+ return tok_binary;
+ if (IdentifierStr == "unary")
+ return tok_unary;
+ if (IdentifierStr == "var")
+ return tok_var;
+ return tok_identifier;
+ ...
+
+The next step is to define the AST node that we will construct. For
+var/in, it looks like this:
+
+.. code-block:: c++
+
+ /// VarExprAST - Expression class for var/in
+ class VarExprAST : public ExprAST {
+ std::vector<std::pair<std::string, std::unique_ptr<ExprAST>>> VarNames;
+ std::unique_ptr<ExprAST> Body;
+
+ public:
+ VarExprAST(std::vector<std::pair<std::string, std::unique_ptr<ExprAST>>> VarNames,
+ std::unique_ptr<ExprAST> body)
+ : VarNames(std::move(VarNames)), Body(std::move(Body)) {}
+
+ virtual Value *codegen();
+ };
+
+var/in allows a list of names to be defined all at once, and each name
+can optionally have an initializer value. As such, we capture this
+information in the VarNames vector. Also, var/in has a body, this body
+is allowed to access the variables defined by the var/in.
+
+With this in place, we can define the parser pieces. The first thing we
+do is add it as a primary expression:
+
+.. code-block:: c++
+
+ /// primary
+ /// ::= identifierexpr
+ /// ::= numberexpr
+ /// ::= parenexpr
+ /// ::= ifexpr
+ /// ::= forexpr
+ /// ::= varexpr
+ static std::unique_ptr<ExprAST> ParsePrimary() {
+ switch (CurTok) {
+ default:
+ return LogError("unknown token when expecting an expression");
+ case tok_identifier:
+ return ParseIdentifierExpr();
+ case tok_number:
+ return ParseNumberExpr();
+ case '(':
+ return ParseParenExpr();
+ case tok_if:
+ return ParseIfExpr();
+ case tok_for:
+ return ParseForExpr();
+ case tok_var:
+ return ParseVarExpr();
+ }
+ }
+
+Next we define ParseVarExpr:
+
+.. code-block:: c++
+
+ /// varexpr ::= 'var' identifier ('=' expression)?
+ // (',' identifier ('=' expression)?)* 'in' expression
+ static std::unique_ptr<ExprAST> ParseVarExpr() {
+ getNextToken(); // eat the var.
+
+ std::vector<std::pair<std::string, std::unique_ptr<ExprAST>>> VarNames;
+
+ // At least one variable name is required.
+ if (CurTok != tok_identifier)
+ return LogError("expected identifier after var");
+
+The first part of this code parses the list of identifier/expr pairs
+into the local ``VarNames`` vector.
+
+.. code-block:: c++
+
+ while (1) {
+ std::string Name = IdentifierStr;
+ getNextToken(); // eat identifier.
+
+ // Read the optional initializer.
+ std::unique_ptr<ExprAST> Init;
+ if (CurTok == '=') {
+ getNextToken(); // eat the '='.
+
+ Init = ParseExpression();
+ if (!Init) return nullptr;
+ }
+
+ VarNames.push_back(std::make_pair(Name, std::move(Init)));
+
+ // End of var list, exit loop.
+ if (CurTok != ',') break;
+ getNextToken(); // eat the ','.
+
+ if (CurTok != tok_identifier)
+ return LogError("expected identifier list after var");
+ }
+
+Once all the variables are parsed, we then parse the body and create the
+AST node:
+
+.. code-block:: c++
+
+ // At this point, we have to have 'in'.
+ if (CurTok != tok_in)
+ return LogError("expected 'in' keyword after 'var'");
+ getNextToken(); // eat 'in'.
+
+ auto Body = ParseExpression();
+ if (!Body)
+ return nullptr;
+
+ return llvm::make_unique<VarExprAST>(std::move(VarNames),
+ std::move(Body));
+ }
+
+Now that we can parse and represent the code, we need to support
+emission of LLVM IR for it. This code starts out with:
+
+.. code-block:: c++
+
+ Value *VarExprAST::codegen() {
+ std::vector<AllocaInst *> OldBindings;
+
+ Function *TheFunction = Builder.GetInsertBlock()->getParent();
+
+ // Register all variables and emit their initializer.
+ for (unsigned i = 0, e = VarNames.size(); i != e; ++i) {
+ const std::string &VarName = VarNames[i].first;
+ ExprAST *Init = VarNames[i].second.get();
+
+Basically it loops over all the variables, installing them one at a
+time. For each variable we put into the symbol table, we remember the
+previous value that we replace in OldBindings.
+
+.. code-block:: c++
+
+ // Emit the initializer before adding the variable to scope, this prevents
+ // the initializer from referencing the variable itself, and permits stuff
+ // like this:
+ // var a = 1 in
+ // var a = a in ... # refers to outer 'a'.
+ Value *InitVal;
+ if (Init) {
+ InitVal = Init->codegen();
+ if (!InitVal)
+ return nullptr;
+ } else { // If not specified, use 0.0.
+ InitVal = ConstantFP::get(LLVMContext, APFloat(0.0));
+ }
+
+ AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, VarName);
+ Builder.CreateStore(InitVal, Alloca);
+
+ // Remember the old variable binding so that we can restore the binding when
+ // we unrecurse.
+ OldBindings.push_back(NamedValues[VarName]);
+
+ // Remember this binding.
+ NamedValues[VarName] = Alloca;
+ }
+
+There are more comments here than code. The basic idea is that we emit
+the initializer, create the alloca, then update the symbol table to
+point to it. Once all the variables are installed in the symbol table,
+we evaluate the body of the var/in expression:
+
+.. code-block:: c++
+
+ // Codegen the body, now that all vars are in scope.
+ Value *BodyVal = Body->codegen();
+ if (!BodyVal)
+ return nullptr;
+
+Finally, before returning, we restore the previous variable bindings:
+
+.. code-block:: c++
+
+ // Pop all our variables from scope.
+ for (unsigned i = 0, e = VarNames.size(); i != e; ++i)
+ NamedValues[VarNames[i].first] = OldBindings[i];
+
+ // Return the body computation.
+ return BodyVal;
+ }
+
+The end result of all of this is that we get properly scoped variable
+definitions, and we even (trivially) allow mutation of them :).
+
+With this, we completed what we set out to do. Our nice iterative fib
+example from the intro compiles and runs just fine. The mem2reg pass
+optimizes all of our stack variables into SSA registers, inserting PHI
+nodes where needed, and our front-end remains simple: no "iterated
+dominance frontier" computation anywhere in sight.
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example, enhanced with
+mutable variables and var/in support. To build this example, use:
+
+.. code-block:: bash
+
+ # Compile
+ clang++ -g toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core mcjit native` -O3 -o toy
+ # Run
+ ./toy
+
+Here is the code:
+
+.. literalinclude:: ../../examples/Kaleidoscope/Chapter7/toy.cpp
+ :language: c++
+
+`Next: Compiling to Object Code <LangImpl08.html>`_
+
Added: www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl08.txt
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--- www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl08.txt (added)
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@@ -0,0 +1,218 @@
+========================================
+ Kaleidoscope: Compiling to Object Code
+========================================
+
+.. contents::
+ :local:
+
+Chapter 8 Introduction
+======================
+
+Welcome to Chapter 8 of the "`Implementing a language with LLVM
+<index.html>`_" tutorial. This chapter describes how to compile our
+language down to object files.
+
+Choosing a target
+=================
+
+LLVM has native support for cross-compilation. You can compile to the
+architecture of your current machine, or just as easily compile for
+other architectures. In this tutorial, we'll target the current
+machine.
+
+To specify the architecture that you want to target, we use a string
+called a "target triple". This takes the form
+``<arch><sub>-<vendor>-<sys>-<abi>`` (see the `cross compilation docs
+<http://clang.llvm.org/docs/CrossCompilation.html#target-triple>`_).
+
+As an example, we can see what clang thinks is our current target
+triple:
+
+::
+
+ $ clang --version | grep Target
+ Target: x86_64-unknown-linux-gnu
+
+Running this command may show something different on your machine as
+you might be using a different architecture or operating system to me.
+
+Fortunately, we don't need to hard-code a target triple to target the
+current machine. LLVM provides ``sys::getDefaultTargetTriple``, which
+returns the target triple of the current machine.
+
+.. code-block:: c++
+
+ auto TargetTriple = sys::getDefaultTargetTriple();
+
+LLVM doesn't require us to to link in all the target
+functionality. For example, if we're just using the JIT, we don't need
+the assembly printers. Similarly, if we're only targeting certain
+architectures, we can only link in the functionality for those
+architectures.
+
+For this example, we'll initialize all the targets for emitting object
+code.
+
+.. code-block:: c++
+
+ InitializeAllTargetInfos();
+ InitializeAllTargets();
+ InitializeAllTargetMCs();
+ InitializeAllAsmParsers();
+ InitializeAllAsmPrinters();
+
+We can now use our target triple to get a ``Target``:
+
+.. code-block:: c++
+
+ std::string Error;
+ auto Target = TargetRegistry::lookupTarget(TargetTriple, Error);
+
+ // Print an error and exit if we couldn't find the requested target.
+ // This generally occurs if we've forgotten to initialise the
+ // TargetRegistry or we have a bogus target triple.
+ if (!Target) {
+ errs() << Error;
+ return 1;
+ }
+
+Target Machine
+==============
+
+We will also need a ``TargetMachine``. This class provides a complete
+machine description of the machine we're targeting. If we want to
+target a specific feature (such as SSE) or a specific CPU (such as
+Intel's Sandylake), we do so now.
+
+To see which features and CPUs that LLVM knows about, we can use
+``llc``. For example, let's look at x86:
+
+::
+
+ $ llvm-as < /dev/null | llc -march=x86 -mattr=help
+ Available CPUs for this target:
+
+ amdfam10 - Select the amdfam10 processor.
+ athlon - Select the athlon processor.
+ athlon-4 - Select the athlon-4 processor.
+ ...
+
+ Available features for this target:
+
+ 16bit-mode - 16-bit mode (i8086).
+ 32bit-mode - 32-bit mode (80386).
+ 3dnow - Enable 3DNow! instructions.
+ 3dnowa - Enable 3DNow! Athlon instructions.
+ ...
+
+For our example, we'll use the generic CPU without any additional
+features, options or relocation model.
+
+.. code-block:: c++
+
+ auto CPU = "generic";
+ auto Features = "";
+
+ TargetOptions opt;
+ auto RM = Optional<Reloc::Model>();
+ auto TargetMachine = Target->createTargetMachine(TargetTriple, CPU, Features, opt, RM);
+
+
+Configuring the Module
+======================
+
+We're now ready to configure our module, to specify the target and
+data layout. This isn't strictly necessary, but the `frontend
+performance guide <../Frontend/PerformanceTips.html>`_ recommends
+this. Optimizations benefit from knowing about the target and data
+layout.
+
+.. code-block:: c++
+
+ TheModule->setDataLayout(TargetMachine->createDataLayout());
+ TheModule->setTargetTriple(TargetTriple);
+
+Emit Object Code
+================
+
+We're ready to emit object code! Let's define where we want to write
+our file to:
+
+.. code-block:: c++
+
+ auto Filename = "output.o";
+ std::error_code EC;
+ raw_fd_ostream dest(Filename, EC, sys::fs::F_None);
+
+ if (EC) {
+ errs() << "Could not open file: " << EC.message();
+ return 1;
+ }
+
+Finally, we define a pass that emits object code, then we run that
+pass:
+
+.. code-block:: c++
+
+ legacy::PassManager pass;
+ auto FileType = TargetMachine::CGFT_ObjectFile;
+
+ if (TargetMachine->addPassesToEmitFile(pass, dest, FileType)) {
+ errs() << "TargetMachine can't emit a file of this type";
+ return 1;
+ }
+
+ pass.run(*TheModule);
+ dest.flush();
+
+Putting It All Together
+=======================
+
+Does it work? Let's give it a try. We need to compile our code, but
+note that the arguments to ``llvm-config`` are different to the previous chapters.
+
+::
+
+ $ clang++ -g -O3 toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs all` -o toy
+
+Let's run it, and define a simple ``average`` function. Press Ctrl-D
+when you're done.
+
+::
+
+ $ ./toy
+ ready> def average(x y) (x + y) * 0.5;
+ ^D
+ Wrote output.o
+
+We have an object file! To test it, let's write a simple program and
+link it with our output. Here's the source code:
+
+.. code-block:: c++
+
+ #include <iostream>
+
+ extern "C" {
+ double average(double, double);
+ }
+
+ int main() {
+ std::cout << "average of 3.0 and 4.0: " << average(3.0, 4.0) << std::endl;
+ }
+
+We link our program to output.o and check the result is what we
+expected:
+
+::
+
+ $ clang++ main.cpp output.o -o main
+ $ ./main
+ average of 3.0 and 4.0: 3.5
+
+Full Code Listing
+=================
+
+.. literalinclude:: ../../examples/Kaleidoscope/Chapter8/toy.cpp
+ :language: c++
+
+`Next: Adding Debug Information <LangImpl09.html>`_
Added: www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl09.txt
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--- www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl09.txt (added)
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@@ -0,0 +1,462 @@
+======================================
+Kaleidoscope: Adding Debug Information
+======================================
+
+.. contents::
+ :local:
+
+Chapter 9 Introduction
+======================
+
+Welcome to Chapter 9 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. In chapters 1 through 8, we've built a
+decent little programming language with functions and variables.
+What happens if something goes wrong though, how do you debug your
+program?
+
+Source level debugging uses formatted data that helps a debugger
+translate from binary and the state of the machine back to the
+source that the programmer wrote. In LLVM we generally use a format
+called `DWARF <http://dwarfstd.org>`_. DWARF is a compact encoding
+that represents types, source locations, and variable locations.
+
+The short summary of this chapter is that we'll go through the
+various things you have to add to a programming language to
+support debug info, and how you translate that into DWARF.
+
+Caveat: For now we can't debug via the JIT, so we'll need to compile
+our program down to something small and standalone. As part of this
+we'll make a few modifications to the running of the language and
+how programs are compiled. This means that we'll have a source file
+with a simple program written in Kaleidoscope rather than the
+interactive JIT. It does involve a limitation that we can only
+have one "top level" command at a time to reduce the number of
+changes necessary.
+
+Here's the sample program we'll be compiling:
+
+.. code-block:: python
+
+ def fib(x)
+ if x < 3 then
+ 1
+ else
+ fib(x-1)+fib(x-2);
+
+ fib(10)
+
+
+Why is this a hard problem?
+===========================
+
+Debug information is a hard problem for a few different reasons - mostly
+centered around optimized code. First, optimization makes keeping source
+locations more difficult. In LLVM IR we keep the original source location
+for each IR level instruction on the instruction. Optimization passes
+should keep the source locations for newly created instructions, but merged
+instructions only get to keep a single location - this can cause jumping
+around when stepping through optimized programs. Secondly, optimization
+can move variables in ways that are either optimized out, shared in memory
+with other variables, or difficult to track. For the purposes of this
+tutorial we're going to avoid optimization (as you'll see with one of the
+next sets of patches).
+
+Ahead-of-Time Compilation Mode
+==============================
+
+To highlight only the aspects of adding debug information to a source
+language without needing to worry about the complexities of JIT debugging
+we're going to make a few changes to Kaleidoscope to support compiling
+the IR emitted by the front end into a simple standalone program that
+you can execute, debug, and see results.
+
+First we make our anonymous function that contains our top level
+statement be our "main":
+
+.. code-block:: udiff
+
+ - auto Proto = llvm::make_unique<PrototypeAST>("", std::vector<std::string>());
+ + auto Proto = llvm::make_unique<PrototypeAST>("main", std::vector<std::string>());
+
+just with the simple change of giving it a name.
+
+Then we're going to remove the command line code wherever it exists:
+
+.. code-block:: udiff
+
+ @@ -1129,7 +1129,6 @@ static void HandleTopLevelExpression() {
+ /// top ::= definition | external | expression | ';'
+ static void MainLoop() {
+ while (1) {
+ - fprintf(stderr, "ready> ");
+ switch (CurTok) {
+ case tok_eof:
+ return;
+ @@ -1184,7 +1183,6 @@ int main() {
+ BinopPrecedence['*'] = 40; // highest.
+
+ // Prime the first token.
+ - fprintf(stderr, "ready> ");
+ getNextToken();
+
+Lastly we're going to disable all of the optimization passes and the JIT so
+that the only thing that happens after we're done parsing and generating
+code is that the llvm IR goes to standard error:
+
+.. code-block:: udiff
+
+ @@ -1108,17 +1108,8 @@ static void HandleExtern() {
+ static void HandleTopLevelExpression() {
+ // Evaluate a top-level expression into an anonymous function.
+ if (auto FnAST = ParseTopLevelExpr()) {
+ - if (auto *FnIR = FnAST->codegen()) {
+ - // We're just doing this to make sure it executes.
+ - TheExecutionEngine->finalizeObject();
+ - // JIT the function, returning a function pointer.
+ - void *FPtr = TheExecutionEngine->getPointerToFunction(FnIR);
+ -
+ - // Cast it to the right type (takes no arguments, returns a double) so we
+ - // can call it as a native function.
+ - double (*FP)() = (double (*)())(intptr_t)FPtr;
+ - // Ignore the return value for this.
+ - (void)FP;
+ + if (!F->codegen()) {
+ + fprintf(stderr, "Error generating code for top level expr");
+ }
+ } else {
+ // Skip token for error recovery.
+ @@ -1439,11 +1459,11 @@ int main() {
+ // target lays out data structures.
+ TheModule->setDataLayout(TheExecutionEngine->getDataLayout());
+ OurFPM.add(new DataLayoutPass());
+ +#if 0
+ OurFPM.add(createBasicAliasAnalysisPass());
+ // Promote allocas to registers.
+ OurFPM.add(createPromoteMemoryToRegisterPass());
+ @@ -1218,7 +1210,7 @@ int main() {
+ OurFPM.add(createGVNPass());
+ // Simplify the control flow graph (deleting unreachable blocks, etc).
+ OurFPM.add(createCFGSimplificationPass());
+ -
+ + #endif
+ OurFPM.doInitialization();
+
+ // Set the global so the code gen can use this.
+
+This relatively small set of changes get us to the point that we can compile
+our piece of Kaleidoscope language down to an executable program via this
+command line:
+
+.. code-block:: bash
+
+ Kaleidoscope-Ch9 < fib.ks | & clang -x ir -
+
+which gives an a.out/a.exe in the current working directory.
+
+Compile Unit
+============
+
+The top level container for a section of code in DWARF is a compile unit.
+This contains the type and function data for an individual translation unit
+(read: one file of source code). So the first thing we need to do is
+construct one for our fib.ks file.
+
+DWARF Emission Setup
+====================
+
+Similar to the ``IRBuilder`` class we have a
+`DIBuilder <http://llvm.org/doxygen/classllvm_1_1DIBuilder.html>`_ class
+that helps in constructing debug metadata for an llvm IR file. It
+corresponds 1:1 similarly to ``IRBuilder`` and llvm IR, but with nicer names.
+Using it does require that you be more familiar with DWARF terminology than
+you needed to be with ``IRBuilder`` and ``Instruction`` names, but if you
+read through the general documentation on the
+`Metadata Format <http://llvm.org/docs/SourceLevelDebugging.html>`_ it
+should be a little more clear. We'll be using this class to construct all
+of our IR level descriptions. Construction for it takes a module so we
+need to construct it shortly after we construct our module. We've left it
+as a global static variable to make it a bit easier to use.
+
+Next we're going to create a small container to cache some of our frequent
+data. The first will be our compile unit, but we'll also write a bit of
+code for our one type since we won't have to worry about multiple typed
+expressions:
+
+.. code-block:: c++
+
+ static DIBuilder *DBuilder;
+
+ struct DebugInfo {
+ DICompileUnit *TheCU;
+ DIType *DblTy;
+
+ DIType *getDoubleTy();
+ } KSDbgInfo;
+
+ DIType *DebugInfo::getDoubleTy() {
+ if (DblTy.isValid())
+ return DblTy;
+
+ DblTy = DBuilder->createBasicType("double", 64, 64, dwarf::DW_ATE_float);
+ return DblTy;
+ }
+
+And then later on in ``main`` when we're constructing our module:
+
+.. code-block:: c++
+
+ DBuilder = new DIBuilder(*TheModule);
+
+ KSDbgInfo.TheCU = DBuilder->createCompileUnit(
+ dwarf::DW_LANG_C, "fib.ks", ".", "Kaleidoscope Compiler", 0, "", 0);
+
+There are a couple of things to note here. First, while we're producing a
+compile unit for a language called Kaleidoscope we used the language
+constant for C. This is because a debugger wouldn't necessarily understand
+the calling conventions or default ABI for a language it doesn't recognize
+and we follow the C ABI in our llvm code generation so it's the closest
+thing to accurate. This ensures we can actually call functions from the
+debugger and have them execute. Secondly, you'll see the "fib.ks" in the
+call to ``createCompileUnit``. This is a default hard coded value since
+we're using shell redirection to put our source into the Kaleidoscope
+compiler. In a usual front end you'd have an input file name and it would
+go there.
+
+One last thing as part of emitting debug information via DIBuilder is that
+we need to "finalize" the debug information. The reasons are part of the
+underlying API for DIBuilder, but make sure you do this near the end of
+main:
+
+.. code-block:: c++
+
+ DBuilder->finalize();
+
+before you dump out the module.
+
+Functions
+=========
+
+Now that we have our ``Compile Unit`` and our source locations, we can add
+function definitions to the debug info. So in ``PrototypeAST::codegen()`` we
+add a few lines of code to describe a context for our subprogram, in this
+case the "File", and the actual definition of the function itself.
+
+So the context:
+
+.. code-block:: c++
+
+ DIFile *Unit = DBuilder->createFile(KSDbgInfo.TheCU.getFilename(),
+ KSDbgInfo.TheCU.getDirectory());
+
+giving us an DIFile and asking the ``Compile Unit`` we created above for the
+directory and filename where we are currently. Then, for now, we use some
+source locations of 0 (since our AST doesn't currently have source location
+information) and construct our function definition:
+
+.. code-block:: c++
+
+ DIScope *FContext = Unit;
+ unsigned LineNo = 0;
+ unsigned ScopeLine = 0;
+ DISubprogram *SP = DBuilder->createFunction(
+ FContext, Name, StringRef(), Unit, LineNo,
+ CreateFunctionType(Args.size(), Unit), false /* internal linkage */,
+ true /* definition */, ScopeLine, DINode::FlagPrototyped, false);
+ F->setSubprogram(SP);
+
+and we now have an DISubprogram that contains a reference to all of our
+metadata for the function.
+
+Source Locations
+================
+
+The most important thing for debug information is accurate source location -
+this makes it possible to map your source code back. We have a problem though,
+Kaleidoscope really doesn't have any source location information in the lexer
+or parser so we'll need to add it.
+
+.. code-block:: c++
+
+ struct SourceLocation {
+ int Line;
+ int Col;
+ };
+ static SourceLocation CurLoc;
+ static SourceLocation LexLoc = {1, 0};
+
+ static int advance() {
+ int LastChar = getchar();
+
+ if (LastChar == '\n' || LastChar == '\r') {
+ LexLoc.Line++;
+ LexLoc.Col = 0;
+ } else
+ LexLoc.Col++;
+ return LastChar;
+ }
+
+In this set of code we've added some functionality on how to keep track of the
+line and column of the "source file". As we lex every token we set our current
+current "lexical location" to the assorted line and column for the beginning
+of the token. We do this by overriding all of the previous calls to
+``getchar()`` with our new ``advance()`` that keeps track of the information
+and then we have added to all of our AST classes a source location:
+
+.. code-block:: c++
+
+ class ExprAST {
+ SourceLocation Loc;
+
+ public:
+ ExprAST(SourceLocation Loc = CurLoc) : Loc(Loc) {}
+ virtual ~ExprAST() {}
+ virtual Value* codegen() = 0;
+ int getLine() const { return Loc.Line; }
+ int getCol() const { return Loc.Col; }
+ virtual raw_ostream &dump(raw_ostream &out, int ind) {
+ return out << ':' << getLine() << ':' << getCol() << '\n';
+ }
+
+that we pass down through when we create a new expression:
+
+.. code-block:: c++
+
+ LHS = llvm::make_unique<BinaryExprAST>(BinLoc, BinOp, std::move(LHS),
+ std::move(RHS));
+
+giving us locations for each of our expressions and variables.
+
+From this we can make sure to tell ``DIBuilder`` when we're at a new source
+location so it can use that when we generate the rest of our code and make
+sure that each instruction has source location information. We do this
+by constructing another small function:
+
+.. code-block:: c++
+
+ void DebugInfo::emitLocation(ExprAST *AST) {
+ DIScope *Scope;
+ if (LexicalBlocks.empty())
+ Scope = TheCU;
+ else
+ Scope = LexicalBlocks.back();
+ Builder.SetCurrentDebugLocation(
+ DebugLoc::get(AST->getLine(), AST->getCol(), Scope));
+ }
+
+that both tells the main ``IRBuilder`` where we are, but also what scope
+we're in. Since we've just created a function above we can either be in
+the main file scope (like when we created our function), or now we can be
+in the function scope we just created. To represent this we create a stack
+of scopes:
+
+.. code-block:: c++
+
+ std::vector<DIScope *> LexicalBlocks;
+ std::map<const PrototypeAST *, DIScope *> FnScopeMap;
+
+and keep a map of each function to the scope that it represents (an
+DISubprogram is also an DIScope).
+
+Then we make sure to:
+
+.. code-block:: c++
+
+ KSDbgInfo.emitLocation(this);
+
+emit the location every time we start to generate code for a new AST, and
+also:
+
+.. code-block:: c++
+
+ KSDbgInfo.FnScopeMap[this] = SP;
+
+store the scope (function) when we create it and use it:
+
+ KSDbgInfo.LexicalBlocks.push_back(&KSDbgInfo.FnScopeMap[Proto]);
+
+when we start generating the code for each function.
+
+also, don't forget to pop the scope back off of your scope stack at the
+end of the code generation for the function:
+
+.. code-block:: c++
+
+ // Pop off the lexical block for the function since we added it
+ // unconditionally.
+ KSDbgInfo.LexicalBlocks.pop_back();
+
+Variables
+=========
+
+Now that we have functions, we need to be able to print out the variables
+we have in scope. Let's get our function arguments set up so we can get
+decent backtraces and see how our functions are being called. It isn't
+a lot of code, and we generally handle it when we're creating the
+argument allocas in ``PrototypeAST::CreateArgumentAllocas``.
+
+.. code-block:: c++
+
+ DIScope *Scope = KSDbgInfo.LexicalBlocks.back();
+ DIFile *Unit = DBuilder->createFile(KSDbgInfo.TheCU.getFilename(),
+ KSDbgInfo.TheCU.getDirectory());
+ DILocalVariable D = DBuilder->createParameterVariable(
+ Scope, Args[Idx], Idx + 1, Unit, Line, KSDbgInfo.getDoubleTy(), true);
+
+ DBuilder->insertDeclare(Alloca, D, DBuilder->createExpression(),
+ DebugLoc::get(Line, 0, Scope),
+ Builder.GetInsertBlock());
+
+Here we're doing a few things. First, we're grabbing our current scope
+for the variable so we can say what range of code our variable is valid
+through. Second, we're creating the variable, giving it the scope,
+the name, source location, type, and since it's an argument, the argument
+index. Third, we create an ``lvm.dbg.declare`` call to indicate at the IR
+level that we've got a variable in an alloca (and it gives a starting
+location for the variable), and setting a source location for the
+beginning of the scope on the declare.
+
+One interesting thing to note at this point is that various debuggers have
+assumptions based on how code and debug information was generated for them
+in the past. In this case we need to do a little bit of a hack to avoid
+generating line information for the function prologue so that the debugger
+knows to skip over those instructions when setting a breakpoint. So in
+``FunctionAST::CodeGen`` we add a couple of lines:
+
+.. code-block:: c++
+
+ // Unset the location for the prologue emission (leading instructions with no
+ // location in a function are considered part of the prologue and the debugger
+ // will run past them when breaking on a function)
+ KSDbgInfo.emitLocation(nullptr);
+
+and then emit a new location when we actually start generating code for the
+body of the function:
+
+.. code-block:: c++
+
+ KSDbgInfo.emitLocation(Body);
+
+With this we have enough debug information to set breakpoints in functions,
+print out argument variables, and call functions. Not too bad for just a
+few simple lines of code!
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example, enhanced with
+debug information. To build this example, use:
+
+.. code-block:: bash
+
+ # Compile
+ clang++ -g toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core mcjit native` -O3 -o toy
+ # Run
+ ./toy
+
+Here is the code:
+
+.. literalinclude:: ../../examples/Kaleidoscope/Chapter9/toy.cpp
+ :language: c++
+
+`Next: Conclusion and other useful LLVM tidbits <LangImpl10.html>`_
+
Added: www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl1.txt
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--- www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl1.txt (added)
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@@ -0,0 +1,290 @@
+=================================================
+Kaleidoscope: Tutorial Introduction and the Lexer
+=================================================
+
+.. contents::
+ :local:
+
+Tutorial Introduction
+=====================
+
+Welcome to the "Implementing a language with LLVM" tutorial. This
+tutorial runs through the implementation of a simple language, showing
+how fun and easy it can be. This tutorial will get you up and started as
+well as help to build a framework you can extend to other languages. The
+code in this tutorial can also be used as a playground to hack on other
+LLVM specific things.
+
+The goal of this tutorial is to progressively unveil our language,
+describing how it is built up over time. This will let us cover a fairly
+broad range of language design and LLVM-specific usage issues, showing
+and explaining the code for it all along the way, without overwhelming
+you with tons of details up front.
+
+It is useful to point out ahead of time that this tutorial is really
+about teaching compiler techniques and LLVM specifically, *not* about
+teaching modern and sane software engineering principles. In practice,
+this means that we'll take a number of shortcuts to simplify the
+exposition. For example, the code uses global variables
+all over the place, doesn't use nice design patterns like
+`visitors <http://en.wikipedia.org/wiki/Visitor_pattern>`_, etc... but
+it is very simple. If you dig in and use the code as a basis for future
+projects, fixing these deficiencies shouldn't be hard.
+
+I've tried to put this tutorial together in a way that makes chapters
+easy to skip over if you are already familiar with or are uninterested
+in the various pieces. The structure of the tutorial is:
+
+- `Chapter #1 <#language>`_: Introduction to the Kaleidoscope
+ language, and the definition of its Lexer - This shows where we are
+ going and the basic functionality that we want it to do. In order to
+ make this tutorial maximally understandable and hackable, we choose
+ to implement everything in C++ instead of using lexer and parser
+ generators. LLVM obviously works just fine with such tools, feel free
+ to use one if you prefer.
+- `Chapter #2 <LangImpl2.html>`_: Implementing a Parser and AST -
+ With the lexer in place, we can talk about parsing techniques and
+ basic AST construction. This tutorial describes recursive descent
+ parsing and operator precedence parsing. Nothing in Chapters 1 or 2
+ is LLVM-specific, the code doesn't even link in LLVM at this point.
+ :)
+- `Chapter #3 <LangImpl3.html>`_: Code generation to LLVM IR - With
+ the AST ready, we can show off how easy generation of LLVM IR really
+ is.
+- `Chapter #4 <LangImpl4.html>`_: Adding JIT and Optimizer Support
+ - Because a lot of people are interested in using LLVM as a JIT,
+ we'll dive right into it and show you the 3 lines it takes to add JIT
+ support. LLVM is also useful in many other ways, but this is one
+ simple and "sexy" way to show off its power. :)
+- `Chapter #5 <LangImpl5.html>`_: Extending the Language: Control
+ Flow - With the language up and running, we show how to extend it
+ with control flow operations (if/then/else and a 'for' loop). This
+ gives us a chance to talk about simple SSA construction and control
+ flow.
+- `Chapter #6 <LangImpl6.html>`_: Extending the Language:
+ User-defined Operators - This is a silly but fun chapter that talks
+ about extending the language to let the user program define their own
+ arbitrary unary and binary operators (with assignable precedence!).
+ This lets us build a significant piece of the "language" as library
+ routines.
+- `Chapter #7 <LangImpl7.html>`_: Extending the Language: Mutable
+ Variables - This chapter talks about adding user-defined local
+ variables along with an assignment operator. The interesting part
+ about this is how easy and trivial it is to construct SSA form in
+ LLVM: no, LLVM does *not* require your front-end to construct SSA
+ form!
+- `Chapter #8 <LangImpl8.html>`_: Extending the Language: Debug
+ Information - Having built a decent little programming language with
+ control flow, functions and mutable variables, we consider what it
+ takes to add debug information to standalone executables. This debug
+ information will allow you to set breakpoints in Kaleidoscope
+ functions, print out argument variables, and call functions - all
+ from within the debugger!
+- `Chapter #9 <LangImpl8.html>`_: Conclusion and other useful LLVM
+ tidbits - This chapter wraps up the series by talking about
+ potential ways to extend the language, but also includes a bunch of
+ pointers to info about "special topics" like adding garbage
+ collection support, exceptions, debugging, support for "spaghetti
+ stacks", and a bunch of other tips and tricks.
+
+By the end of the tutorial, we'll have written a bit less than 1000 lines
+of non-comment, non-blank, lines of code. With this small amount of
+code, we'll have built up a very reasonable compiler for a non-trivial
+language including a hand-written lexer, parser, AST, as well as code
+generation support with a JIT compiler. While other systems may have
+interesting "hello world" tutorials, I think the breadth of this
+tutorial is a great testament to the strengths of LLVM and why you
+should consider it if you're interested in language or compiler design.
+
+A note about this tutorial: we expect you to extend the language and
+play with it on your own. Take the code and go crazy hacking away at it,
+compilers don't need to be scary creatures - it can be a lot of fun to
+play with languages!
+
+The Basic Language
+==================
+
+This tutorial will be illustrated with a toy language that we'll call
+"`Kaleidoscope <http://en.wikipedia.org/wiki/Kaleidoscope>`_" (derived
+from "meaning beautiful, form, and view"). Kaleidoscope is a procedural
+language that allows you to define functions, use conditionals, math,
+etc. Over the course of the tutorial, we'll extend Kaleidoscope to
+support the if/then/else construct, a for loop, user defined operators,
+JIT compilation with a simple command line interface, etc.
+
+Because we want to keep things simple, the only datatype in Kaleidoscope
+is a 64-bit floating point type (aka 'double' in C parlance). As such,
+all values are implicitly double precision and the language doesn't
+require type declarations. This gives the language a very nice and
+simple syntax. For example, the following simple example computes
+`Fibonacci numbers: <http://en.wikipedia.org/wiki/Fibonacci_number>`_
+
+::
+
+ # Compute the x'th fibonacci number.
+ def fib(x)
+ if x < 3 then
+ 1
+ else
+ fib(x-1)+fib(x-2)
+
+ # This expression will compute the 40th number.
+ fib(40)
+
+We also allow Kaleidoscope to call into standard library functions (the
+LLVM JIT makes this completely trivial). This means that you can use the
+'extern' keyword to define a function before you use it (this is also
+useful for mutually recursive functions). For example:
+
+::
+
+ extern sin(arg);
+ extern cos(arg);
+ extern atan2(arg1 arg2);
+
+ atan2(sin(.4), cos(42))
+
+A more interesting example is included in Chapter 6 where we write a
+little Kaleidoscope application that `displays a Mandelbrot
+Set <LangImpl6.html#kicking-the-tires>`_ at various levels of magnification.
+
+Lets dive into the implementation of this language!
+
+The Lexer
+=========
+
+When it comes to implementing a language, the first thing needed is the
+ability to process a text file and recognize what it says. The
+traditional way to do this is to use a
+"`lexer <http://en.wikipedia.org/wiki/Lexical_analysis>`_" (aka
+'scanner') to break the input up into "tokens". Each token returned by
+the lexer includes a token code and potentially some metadata (e.g. the
+numeric value of a number). First, we define the possibilities:
+
+.. code-block:: c++
+
+ // The lexer returns tokens [0-255] if it is an unknown character, otherwise one
+ // of these for known things.
+ enum Token {
+ tok_eof = -1,
+
+ // commands
+ tok_def = -2,
+ tok_extern = -3,
+
+ // primary
+ tok_identifier = -4,
+ tok_number = -5,
+ };
+
+ static std::string IdentifierStr; // Filled in if tok_identifier
+ static double NumVal; // Filled in if tok_number
+
+Each token returned by our lexer will either be one of the Token enum
+values or it will be an 'unknown' character like '+', which is returned
+as its ASCII value. If the current token is an identifier, the
+``IdentifierStr`` global variable holds the name of the identifier. If
+the current token is a numeric literal (like 1.0), ``NumVal`` holds its
+value. Note that we use global variables for simplicity, this is not the
+best choice for a real language implementation :).
+
+The actual implementation of the lexer is a single function named
+``gettok``. The ``gettok`` function is called to return the next token
+from standard input. Its definition starts as:
+
+.. code-block:: c++
+
+ /// gettok - Return the next token from standard input.
+ static int gettok() {
+ static int LastChar = ' ';
+
+ // Skip any whitespace.
+ while (isspace(LastChar))
+ LastChar = getchar();
+
+``gettok`` works by calling the C ``getchar()`` function to read
+characters one at a time from standard input. It eats them as it
+recognizes them and stores the last character read, but not processed,
+in LastChar. The first thing that it has to do is ignore whitespace
+between tokens. This is accomplished with the loop above.
+
+The next thing ``gettok`` needs to do is recognize identifiers and
+specific keywords like "def". Kaleidoscope does this with this simple
+loop:
+
+.. code-block:: c++
+
+ if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
+ IdentifierStr = LastChar;
+ while (isalnum((LastChar = getchar())))
+ IdentifierStr += LastChar;
+
+ if (IdentifierStr == "def")
+ return tok_def;
+ if (IdentifierStr == "extern")
+ return tok_extern;
+ return tok_identifier;
+ }
+
+Note that this code sets the '``IdentifierStr``' global whenever it
+lexes an identifier. Also, since language keywords are matched by the
+same loop, we handle them here inline. Numeric values are similar:
+
+.. code-block:: c++
+
+ if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+
+ std::string NumStr;
+ do {
+ NumStr += LastChar;
+ LastChar = getchar();
+ } while (isdigit(LastChar) || LastChar == '.');
+
+ NumVal = strtod(NumStr.c_str(), 0);
+ return tok_number;
+ }
+
+This is all pretty straight-forward code for processing input. When
+reading a numeric value from input, we use the C ``strtod`` function to
+convert it to a numeric value that we store in ``NumVal``. Note that
+this isn't doing sufficient error checking: it will incorrectly read
+"1.23.45.67" and handle it as if you typed in "1.23". Feel free to
+extend it :). Next we handle comments:
+
+.. code-block:: c++
+
+ if (LastChar == '#') {
+ // Comment until end of line.
+ do
+ LastChar = getchar();
+ while (LastChar != EOF && LastChar != '\n' && LastChar != '\r');
+
+ if (LastChar != EOF)
+ return gettok();
+ }
+
+We handle comments by skipping to the end of the line and then return
+the next token. Finally, if the input doesn't match one of the above
+cases, it is either an operator character like '+' or the end of the
+file. These are handled with this code:
+
+.. code-block:: c++
+
+ // Check for end of file. Don't eat the EOF.
+ if (LastChar == EOF)
+ return tok_eof;
+
+ // Otherwise, just return the character as its ascii value.
+ int ThisChar = LastChar;
+ LastChar = getchar();
+ return ThisChar;
+ }
+
+With this, we have the complete lexer for the basic Kaleidoscope
+language (the `full code listing <LangImpl2.html#full-code-listing>`_ for the Lexer
+is available in the `next chapter <LangImpl2.html>`_ of the tutorial).
+Next we'll `build a simple parser that uses this to build an Abstract
+Syntax Tree <LangImpl2.html>`_. When we have that, we'll include a
+driver so that you can use the lexer and parser together.
+
+`Next: Implementing a Parser and AST <LangImpl2.html>`_
+
Added: www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl10.txt
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@@ -0,0 +1,259 @@
+======================================================
+Kaleidoscope: Conclusion and other useful LLVM tidbits
+======================================================
+
+.. contents::
+ :local:
+
+Tutorial Conclusion
+===================
+
+Welcome to the final chapter of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. In the course of this tutorial, we have
+grown our little Kaleidoscope language from being a useless toy, to
+being a semi-interesting (but probably still useless) toy. :)
+
+It is interesting to see how far we've come, and how little code it has
+taken. We built the entire lexer, parser, AST, code generator, an
+interactive run-loop (with a JIT!), and emitted debug information in
+standalone executables - all in under 1000 lines of (non-comment/non-blank)
+code.
+
+Our little language supports a couple of interesting features: it
+supports user defined binary and unary operators, it uses JIT
+compilation for immediate evaluation, and it supports a few control flow
+constructs with SSA construction.
+
+Part of the idea of this tutorial was to show you how easy and fun it
+can be to define, build, and play with languages. Building a compiler
+need not be a scary or mystical process! Now that you've seen some of
+the basics, I strongly encourage you to take the code and hack on it.
+For example, try adding:
+
+- **global variables** - While global variables have questional value
+ in modern software engineering, they are often useful when putting
+ together quick little hacks like the Kaleidoscope compiler itself.
+ Fortunately, our current setup makes it very easy to add global
+ variables: just have value lookup check to see if an unresolved
+ variable is in the global variable symbol table before rejecting it.
+ To create a new global variable, make an instance of the LLVM
+ ``GlobalVariable`` class.
+- **typed variables** - Kaleidoscope currently only supports variables
+ of type double. This gives the language a very nice elegance, because
+ only supporting one type means that you never have to specify types.
+ Different languages have different ways of handling this. The easiest
+ way is to require the user to specify types for every variable
+ definition, and record the type of the variable in the symbol table
+ along with its Value\*.
+- **arrays, structs, vectors, etc** - Once you add types, you can start
+ extending the type system in all sorts of interesting ways. Simple
+ arrays are very easy and are quite useful for many different
+ applications. Adding them is mostly an exercise in learning how the
+ LLVM `getelementptr <../LangRef.html#getelementptr-instruction>`_ instruction
+ works: it is so nifty/unconventional, it `has its own
+ FAQ <../GetElementPtr.html>`_!
+- **standard runtime** - Our current language allows the user to access
+ arbitrary external functions, and we use it for things like "printd"
+ and "putchard". As you extend the language to add higher-level
+ constructs, often these constructs make the most sense if they are
+ lowered to calls into a language-supplied runtime. For example, if
+ you add hash tables to the language, it would probably make sense to
+ add the routines to a runtime, instead of inlining them all the way.
+- **memory management** - Currently we can only access the stack in
+ Kaleidoscope. It would also be useful to be able to allocate heap
+ memory, either with calls to the standard libc malloc/free interface
+ or with a garbage collector. If you would like to use garbage
+ collection, note that LLVM fully supports `Accurate Garbage
+ Collection <../GarbageCollection.html>`_ including algorithms that
+ move objects and need to scan/update the stack.
+- **exception handling support** - LLVM supports generation of `zero
+ cost exceptions <../ExceptionHandling.html>`_ which interoperate with
+ code compiled in other languages. You could also generate code by
+ implicitly making every function return an error value and checking
+ it. You could also make explicit use of setjmp/longjmp. There are
+ many different ways to go here.
+- **object orientation, generics, database access, complex numbers,
+ geometric programming, ...** - Really, there is no end of crazy
+ features that you can add to the language.
+- **unusual domains** - We've been talking about applying LLVM to a
+ domain that many people are interested in: building a compiler for a
+ specific language. However, there are many other domains that can use
+ compiler technology that are not typically considered. For example,
+ LLVM has been used to implement OpenGL graphics acceleration,
+ translate C++ code to ActionScript, and many other cute and clever
+ things. Maybe you will be the first to JIT compile a regular
+ expression interpreter into native code with LLVM?
+
+Have fun - try doing something crazy and unusual. Building a language
+like everyone else always has, is much less fun than trying something a
+little crazy or off the wall and seeing how it turns out. If you get
+stuck or want to talk about it, feel free to email the `llvm-dev mailing
+list <http://lists.llvm.org/mailman/listinfo/llvm-dev>`_: it has lots
+of people who are interested in languages and are often willing to help
+out.
+
+Before we end this tutorial, I want to talk about some "tips and tricks"
+for generating LLVM IR. These are some of the more subtle things that
+may not be obvious, but are very useful if you want to take advantage of
+LLVM's capabilities.
+
+Properties of the LLVM IR
+=========================
+
+We have a couple of common questions about code in the LLVM IR form -
+let's just get these out of the way right now, shall we?
+
+Target Independence
+-------------------
+
+Kaleidoscope is an example of a "portable language": any program written
+in Kaleidoscope will work the same way on any target that it runs on.
+Many other languages have this property, e.g. lisp, java, haskell,
+javascript, python, etc (note that while these languages are portable,
+not all their libraries are).
+
+One nice aspect of LLVM is that it is often capable of preserving target
+independence in the IR: you can take the LLVM IR for a
+Kaleidoscope-compiled program and run it on any target that LLVM
+supports, even emitting C code and compiling that on targets that LLVM
+doesn't support natively. You can trivially tell that the Kaleidoscope
+compiler generates target-independent code because it never queries for
+any target-specific information when generating code.
+
+The fact that LLVM provides a compact, target-independent,
+representation for code gets a lot of people excited. Unfortunately,
+these people are usually thinking about C or a language from the C
+family when they are asking questions about language portability. I say
+"unfortunately", because there is really no way to make (fully general)
+C code portable, other than shipping the source code around (and of
+course, C source code is not actually portable in general either - ever
+port a really old application from 32- to 64-bits?).
+
+The problem with C (again, in its full generality) is that it is heavily
+laden with target specific assumptions. As one simple example, the
+preprocessor often destructively removes target-independence from the
+code when it processes the input text:
+
+.. code-block:: c
+
+ #ifdef __i386__
+ int X = 1;
+ #else
+ int X = 42;
+ #endif
+
+While it is possible to engineer more and more complex solutions to
+problems like this, it cannot be solved in full generality in a way that
+is better than shipping the actual source code.
+
+That said, there are interesting subsets of C that can be made portable.
+If you are willing to fix primitive types to a fixed size (say int =
+32-bits, and long = 64-bits), don't care about ABI compatibility with
+existing binaries, and are willing to give up some other minor features,
+you can have portable code. This can make sense for specialized domains
+such as an in-kernel language.
+
+Safety Guarantees
+-----------------
+
+Many of the languages above are also "safe" languages: it is impossible
+for a program written in Java to corrupt its address space and crash the
+process (assuming the JVM has no bugs). Safety is an interesting
+property that requires a combination of language design, runtime
+support, and often operating system support.
+
+It is certainly possible to implement a safe language in LLVM, but LLVM
+IR does not itself guarantee safety. The LLVM IR allows unsafe pointer
+casts, use after free bugs, buffer over-runs, and a variety of other
+problems. Safety needs to be implemented as a layer on top of LLVM and,
+conveniently, several groups have investigated this. Ask on the `llvm-dev
+mailing list <http://lists.llvm.org/mailman/listinfo/llvm-dev>`_ if
+you are interested in more details.
+
+Language-Specific Optimizations
+-------------------------------
+
+One thing about LLVM that turns off many people is that it does not
+solve all the world's problems in one system (sorry 'world hunger',
+someone else will have to solve you some other day). One specific
+complaint is that people perceive LLVM as being incapable of performing
+high-level language-specific optimization: LLVM "loses too much
+information".
+
+Unfortunately, this is really not the place to give you a full and
+unified version of "Chris Lattner's theory of compiler design". Instead,
+I'll make a few observations:
+
+First, you're right that LLVM does lose information. For example, as of
+this writing, there is no way to distinguish in the LLVM IR whether an
+SSA-value came from a C "int" or a C "long" on an ILP32 machine (other
+than debug info). Both get compiled down to an 'i32' value and the
+information about what it came from is lost. The more general issue
+here, is that the LLVM type system uses "structural equivalence" instead
+of "name equivalence". Another place this surprises people is if you
+have two types in a high-level language that have the same structure
+(e.g. two different structs that have a single int field): these types
+will compile down into a single LLVM type and it will be impossible to
+tell what it came from.
+
+Second, while LLVM does lose information, LLVM is not a fixed target: we
+continue to enhance and improve it in many different ways. In addition
+to adding new features (LLVM did not always support exceptions or debug
+info), we also extend the IR to capture important information for
+optimization (e.g. whether an argument is sign or zero extended,
+information about pointers aliasing, etc). Many of the enhancements are
+user-driven: people want LLVM to include some specific feature, so they
+go ahead and extend it.
+
+Third, it is *possible and easy* to add language-specific optimizations,
+and you have a number of choices in how to do it. As one trivial
+example, it is easy to add language-specific optimization passes that
+"know" things about code compiled for a language. In the case of the C
+family, there is an optimization pass that "knows" about the standard C
+library functions. If you call "exit(0)" in main(), it knows that it is
+safe to optimize that into "return 0;" because C specifies what the
+'exit' function does.
+
+In addition to simple library knowledge, it is possible to embed a
+variety of other language-specific information into the LLVM IR. If you
+have a specific need and run into a wall, please bring the topic up on
+the llvm-dev list. At the very worst, you can always treat LLVM as if it
+were a "dumb code generator" and implement the high-level optimizations
+you desire in your front-end, on the language-specific AST.
+
+Tips and Tricks
+===============
+
+There is a variety of useful tips and tricks that you come to know after
+working on/with LLVM that aren't obvious at first glance. Instead of
+letting everyone rediscover them, this section talks about some of these
+issues.
+
+Implementing portable offsetof/sizeof
+-------------------------------------
+
+One interesting thing that comes up, if you are trying to keep the code
+generated by your compiler "target independent", is that you often need
+to know the size of some LLVM type or the offset of some field in an
+llvm structure. For example, you might need to pass the size of a type
+into a function that allocates memory.
+
+Unfortunately, this can vary widely across targets: for example the
+width of a pointer is trivially target-specific. However, there is a
+`clever way to use the getelementptr
+instruction <http://nondot.org/sabre/LLVMNotes/SizeOf-OffsetOf-VariableSizedStructs.txt>`_
+that allows you to compute this in a portable way.
+
+Garbage Collected Stack Frames
+------------------------------
+
+Some languages want to explicitly manage their stack frames, often so
+that they are garbage collected or to allow easy implementation of
+closures. There are often better ways to implement these features than
+explicit stack frames, but `LLVM does support
+them, <http://nondot.org/sabre/LLVMNotes/ExplicitlyManagedStackFrames.txt>`_
+if you want. It requires your front-end to convert the code into
+`Continuation Passing
+Style <http://en.wikipedia.org/wiki/Continuation-passing_style>`_ and
+the use of tail calls (which LLVM also supports).
+
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--- www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl2.txt (added)
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+===========================================
+Kaleidoscope: Implementing a Parser and AST
+===========================================
+
+.. contents::
+ :local:
+
+Chapter 2 Introduction
+======================
+
+Welcome to Chapter 2 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. This chapter shows you how to use the
+lexer, built in `Chapter 1 <LangImpl1.html>`_, to build a full
+`parser <http://en.wikipedia.org/wiki/Parsing>`_ for our Kaleidoscope
+language. Once we have a parser, we'll define and build an `Abstract
+Syntax Tree <http://en.wikipedia.org/wiki/Abstract_syntax_tree>`_ (AST).
+
+The parser we will build uses a combination of `Recursive Descent
+Parsing <http://en.wikipedia.org/wiki/Recursive_descent_parser>`_ and
+`Operator-Precedence
+Parsing <http://en.wikipedia.org/wiki/Operator-precedence_parser>`_ to
+parse the Kaleidoscope language (the latter for binary expressions and
+the former for everything else). Before we get to parsing though, lets
+talk about the output of the parser: the Abstract Syntax Tree.
+
+The Abstract Syntax Tree (AST)
+==============================
+
+The AST for a program captures its behavior in such a way that it is
+easy for later stages of the compiler (e.g. code generation) to
+interpret. We basically want one object for each construct in the
+language, and the AST should closely model the language. In
+Kaleidoscope, we have expressions, a prototype, and a function object.
+We'll start with expressions first:
+
+.. code-block:: c++
+
+ /// ExprAST - Base class for all expression nodes.
+ class ExprAST {
+ public:
+ virtual ~ExprAST() {}
+ };
+
+ /// NumberExprAST - Expression class for numeric literals like "1.0".
+ class NumberExprAST : public ExprAST {
+ double Val;
+
+ public:
+ NumberExprAST(double Val) : Val(Val) {}
+ };
+
+The code above shows the definition of the base ExprAST class and one
+subclass which we use for numeric literals. The important thing to note
+about this code is that the NumberExprAST class captures the numeric
+value of the literal as an instance variable. This allows later phases
+of the compiler to know what the stored numeric value is.
+
+Right now we only create the AST, so there are no useful accessor
+methods on them. It would be very easy to add a virtual method to pretty
+print the code, for example. Here are the other expression AST node
+definitions that we'll use in the basic form of the Kaleidoscope
+language:
+
+.. code-block:: c++
+
+ /// VariableExprAST - Expression class for referencing a variable, like "a".
+ class VariableExprAST : public ExprAST {
+ std::string Name;
+
+ public:
+ VariableExprAST(const std::string &Name) : Name(Name) {}
+ };
+
+ /// BinaryExprAST - Expression class for a binary operator.
+ class BinaryExprAST : public ExprAST {
+ char Op;
+ std::unique_ptr<ExprAST> LHS, RHS;
+
+ public:
+ BinaryExprAST(char op, std::unique_ptr<ExprAST> LHS,
+ std::unique_ptr<ExprAST> RHS)
+ : Op(op), LHS(std::move(LHS)), RHS(std::move(RHS)) {}
+ };
+
+ /// CallExprAST - Expression class for function calls.
+ class CallExprAST : public ExprAST {
+ std::string Callee;
+ std::vector<std::unique_ptr<ExprAST>> Args;
+
+ public:
+ CallExprAST(const std::string &Callee,
+ std::vector<std::unique_ptr<ExprAST>> Args)
+ : Callee(Callee), Args(std::move(Args)) {}
+ };
+
+This is all (intentionally) rather straight-forward: variables capture
+the variable name, binary operators capture their opcode (e.g. '+'), and
+calls capture a function name as well as a list of any argument
+expressions. One thing that is nice about our AST is that it captures
+the language features without talking about the syntax of the language.
+Note that there is no discussion about precedence of binary operators,
+lexical structure, etc.
+
+For our basic language, these are all of the expression nodes we'll
+define. Because it doesn't have conditional control flow, it isn't
+Turing-complete; we'll fix that in a later installment. The two things
+we need next are a way to talk about the interface to a function, and a
+way to talk about functions themselves:
+
+.. code-block:: c++
+
+ /// PrototypeAST - This class represents the "prototype" for a function,
+ /// which captures its name, and its argument names (thus implicitly the number
+ /// of arguments the function takes).
+ class PrototypeAST {
+ std::string Name;
+ std::vector<std::string> Args;
+
+ public:
+ PrototypeAST(const std::string &name, std::vector<std::string> Args)
+ : Name(name), Args(std::move(Args)) {}
+ };
+
+ /// FunctionAST - This class represents a function definition itself.
+ class FunctionAST {
+ std::unique_ptr<PrototypeAST> Proto;
+ std::unique_ptr<ExprAST> Body;
+
+ public:
+ FunctionAST(std::unique_ptr<PrototypeAST> Proto,
+ std::unique_ptr<ExprAST> Body)
+ : Proto(std::move(Proto)), Body(std::move(Body)) {}
+ };
+
+In Kaleidoscope, functions are typed with just a count of their
+arguments. Since all values are double precision floating point, the
+type of each argument doesn't need to be stored anywhere. In a more
+aggressive and realistic language, the "ExprAST" class would probably
+have a type field.
+
+With this scaffolding, we can now talk about parsing expressions and
+function bodies in Kaleidoscope.
+
+Parser Basics
+=============
+
+Now that we have an AST to build, we need to define the parser code to
+build it. The idea here is that we want to parse something like "x+y"
+(which is returned as three tokens by the lexer) into an AST that could
+be generated with calls like this:
+
+.. code-block:: c++
+
+ auto LHS = llvm::make_unique<VariableExprAST>("x");
+ auto RHS = llvm::make_unique<VariableExprAST>("y");
+ auto Result = std::make_unique<BinaryExprAST>('+', std::move(LHS),
+ std::move(RHS));
+
+In order to do this, we'll start by defining some basic helper routines:
+
+.. code-block:: c++
+
+ /// CurTok/getNextToken - Provide a simple token buffer. CurTok is the current
+ /// token the parser is looking at. getNextToken reads another token from the
+ /// lexer and updates CurTok with its results.
+ static int CurTok;
+ static int getNextToken() {
+ return CurTok = gettok();
+ }
+
+This implements a simple token buffer around the lexer. This allows us
+to look one token ahead at what the lexer is returning. Every function
+in our parser will assume that CurTok is the current token that needs to
+be parsed.
+
+.. code-block:: c++
+
+
+ /// Error* - These are little helper functions for error handling.
+ std::unique_ptr<ExprAST> Error(const char *Str) {
+ fprintf(stderr, "Error: %s\n", Str);
+ return nullptr;
+ }
+ std::unique_ptr<PrototypeAST> ErrorP(const char *Str) {
+ Error(Str);
+ return nullptr;
+ }
+
+The ``Error`` routines are simple helper routines that our parser will
+use to handle errors. The error recovery in our parser will not be the
+best and is not particular user-friendly, but it will be enough for our
+tutorial. These routines make it easier to handle errors in routines
+that have various return types: they always return null.
+
+With these basic helper functions, we can implement the first piece of
+our grammar: numeric literals.
+
+Basic Expression Parsing
+========================
+
+We start with numeric literals, because they are the simplest to
+process. For each production in our grammar, we'll define a function
+which parses that production. For numeric literals, we have:
+
+.. code-block:: c++
+
+ /// numberexpr ::= number
+ static std::unique_ptr<ExprAST> ParseNumberExpr() {
+ auto Result = llvm::make_unique<NumberExprAST>(NumVal);
+ getNextToken(); // consume the number
+ return std::move(Result);
+ }
+
+This routine is very simple: it expects to be called when the current
+token is a ``tok_number`` token. It takes the current number value,
+creates a ``NumberExprAST`` node, advances the lexer to the next token,
+and finally returns.
+
+There are some interesting aspects to this. The most important one is
+that this routine eats all of the tokens that correspond to the
+production and returns the lexer buffer with the next token (which is
+not part of the grammar production) ready to go. This is a fairly
+standard way to go for recursive descent parsers. For a better example,
+the parenthesis operator is defined like this:
+
+.. code-block:: c++
+
+ /// parenexpr ::= '(' expression ')'
+ static std::unique_ptr<ExprAST> ParseParenExpr() {
+ getNextToken(); // eat (.
+ auto V = ParseExpression();
+ if (!V)
+ return nullptr;
+
+ if (CurTok != ')')
+ return Error("expected ')'");
+ getNextToken(); // eat ).
+ return V;
+ }
+
+This function illustrates a number of interesting things about the
+parser:
+
+1) It shows how we use the Error routines. When called, this function
+expects that the current token is a '(' token, but after parsing the
+subexpression, it is possible that there is no ')' waiting. For example,
+if the user types in "(4 x" instead of "(4)", the parser should emit an
+error. Because errors can occur, the parser needs a way to indicate that
+they happened: in our parser, we return null on an error.
+
+2) Another interesting aspect of this function is that it uses recursion
+by calling ``ParseExpression`` (we will soon see that
+``ParseExpression`` can call ``ParseParenExpr``). This is powerful
+because it allows us to handle recursive grammars, and keeps each
+production very simple. Note that parentheses do not cause construction
+of AST nodes themselves. While we could do it this way, the most
+important role of parentheses are to guide the parser and provide
+grouping. Once the parser constructs the AST, parentheses are not
+needed.
+
+The next simple production is for handling variable references and
+function calls:
+
+.. code-block:: c++
+
+ /// identifierexpr
+ /// ::= identifier
+ /// ::= identifier '(' expression* ')'
+ static std::unique_ptr<ExprAST> ParseIdentifierExpr() {
+ std::string IdName = IdentifierStr;
+
+ getNextToken(); // eat identifier.
+
+ if (CurTok != '(') // Simple variable ref.
+ return llvm::make_unique<VariableExprAST>(IdName);
+
+ // Call.
+ getNextToken(); // eat (
+ std::vector<std::unique_ptr<ExprAST>> Args;
+ if (CurTok != ')') {
+ while (1) {
+ if (auto Arg = ParseExpression())
+ Args.push_back(std::move(Arg));
+ else
+ return nullptr;
+
+ if (CurTok == ')')
+ break;
+
+ if (CurTok != ',')
+ return Error("Expected ')' or ',' in argument list");
+ getNextToken();
+ }
+ }
+
+ // Eat the ')'.
+ getNextToken();
+
+ return llvm::make_unique<CallExprAST>(IdName, std::move(Args));
+ }
+
+This routine follows the same style as the other routines. (It expects
+to be called if the current token is a ``tok_identifier`` token). It
+also has recursion and error handling. One interesting aspect of this is
+that it uses *look-ahead* to determine if the current identifier is a
+stand alone variable reference or if it is a function call expression.
+It handles this by checking to see if the token after the identifier is
+a '(' token, constructing either a ``VariableExprAST`` or
+``CallExprAST`` node as appropriate.
+
+Now that we have all of our simple expression-parsing logic in place, we
+can define a helper function to wrap it together into one entry point.
+We call this class of expressions "primary" expressions, for reasons
+that will become more clear `later in the
+tutorial <LangImpl6.html#user-defined-unary-operators>`_. In order to parse an arbitrary
+primary expression, we need to determine what sort of expression it is:
+
+.. code-block:: c++
+
+ /// primary
+ /// ::= identifierexpr
+ /// ::= numberexpr
+ /// ::= parenexpr
+ static std::unique_ptr<ExprAST> ParsePrimary() {
+ switch (CurTok) {
+ default:
+ return Error("unknown token when expecting an expression");
+ case tok_identifier:
+ return ParseIdentifierExpr();
+ case tok_number:
+ return ParseNumberExpr();
+ case '(':
+ return ParseParenExpr();
+ }
+ }
+
+Now that you see the definition of this function, it is more obvious why
+we can assume the state of CurTok in the various functions. This uses
+look-ahead to determine which sort of expression is being inspected, and
+then parses it with a function call.
+
+Now that basic expressions are handled, we need to handle binary
+expressions. They are a bit more complex.
+
+Binary Expression Parsing
+=========================
+
+Binary expressions are significantly harder to parse because they are
+often ambiguous. For example, when given the string "x+y\*z", the parser
+can choose to parse it as either "(x+y)\*z" or "x+(y\*z)". With common
+definitions from mathematics, we expect the later parse, because "\*"
+(multiplication) has higher *precedence* than "+" (addition).
+
+There are many ways to handle this, but an elegant and efficient way is
+to use `Operator-Precedence
+Parsing <http://en.wikipedia.org/wiki/Operator-precedence_parser>`_.
+This parsing technique uses the precedence of binary operators to guide
+recursion. To start with, we need a table of precedences:
+
+.. code-block:: c++
+
+ /// BinopPrecedence - This holds the precedence for each binary operator that is
+ /// defined.
+ static std::map<char, int> BinopPrecedence;
+
+ /// GetTokPrecedence - Get the precedence of the pending binary operator token.
+ static int GetTokPrecedence() {
+ if (!isascii(CurTok))
+ return -1;
+
+ // Make sure it's a declared binop.
+ int TokPrec = BinopPrecedence[CurTok];
+ if (TokPrec <= 0) return -1;
+ return TokPrec;
+ }
+
+ int main() {
+ // Install standard binary operators.
+ // 1 is lowest precedence.
+ BinopPrecedence['<'] = 10;
+ BinopPrecedence['+'] = 20;
+ BinopPrecedence['-'] = 20;
+ BinopPrecedence['*'] = 40; // highest.
+ ...
+ }
+
+For the basic form of Kaleidoscope, we will only support 4 binary
+operators (this can obviously be extended by you, our brave and intrepid
+reader). The ``GetTokPrecedence`` function returns the precedence for
+the current token, or -1 if the token is not a binary operator. Having a
+map makes it easy to add new operators and makes it clear that the
+algorithm doesn't depend on the specific operators involved, but it
+would be easy enough to eliminate the map and do the comparisons in the
+``GetTokPrecedence`` function. (Or just use a fixed-size array).
+
+With the helper above defined, we can now start parsing binary
+expressions. The basic idea of operator precedence parsing is to break
+down an expression with potentially ambiguous binary operators into
+pieces. Consider, for example, the expression "a+b+(c+d)\*e\*f+g".
+Operator precedence parsing considers this as a stream of primary
+expressions separated by binary operators. As such, it will first parse
+the leading primary expression "a", then it will see the pairs [+, b]
+[+, (c+d)] [\*, e] [\*, f] and [+, g]. Note that because parentheses are
+primary expressions, the binary expression parser doesn't need to worry
+about nested subexpressions like (c+d) at all.
+
+To start, an expression is a primary expression potentially followed by
+a sequence of [binop,primaryexpr] pairs:
+
+.. code-block:: c++
+
+ /// expression
+ /// ::= primary binoprhs
+ ///
+ static std::unique_ptr<ExprAST> ParseExpression() {
+ auto LHS = ParsePrimary();
+ if (!LHS)
+ return nullptr;
+
+ return ParseBinOpRHS(0, std::move(LHS));
+ }
+
+``ParseBinOpRHS`` is the function that parses the sequence of pairs for
+us. It takes a precedence and a pointer to an expression for the part
+that has been parsed so far. Note that "x" is a perfectly valid
+expression: As such, "binoprhs" is allowed to be empty, in which case it
+returns the expression that is passed into it. In our example above, the
+code passes the expression for "a" into ``ParseBinOpRHS`` and the
+current token is "+".
+
+The precedence value passed into ``ParseBinOpRHS`` indicates the
+*minimal operator precedence* that the function is allowed to eat. For
+example, if the current pair stream is [+, x] and ``ParseBinOpRHS`` is
+passed in a precedence of 40, it will not consume any tokens (because
+the precedence of '+' is only 20). With this in mind, ``ParseBinOpRHS``
+starts with:
+
+.. code-block:: c++
+
+ /// binoprhs
+ /// ::= ('+' primary)*
+ static std::unique_ptr<ExprAST> ParseBinOpRHS(int ExprPrec,
+ std::unique_ptr<ExprAST> LHS) {
+ // If this is a binop, find its precedence.
+ while (1) {
+ int TokPrec = GetTokPrecedence();
+
+ // If this is a binop that binds at least as tightly as the current binop,
+ // consume it, otherwise we are done.
+ if (TokPrec < ExprPrec)
+ return LHS;
+
+This code gets the precedence of the current token and checks to see if
+if is too low. Because we defined invalid tokens to have a precedence of
+-1, this check implicitly knows that the pair-stream ends when the token
+stream runs out of binary operators. If this check succeeds, we know
+that the token is a binary operator and that it will be included in this
+expression:
+
+.. code-block:: c++
+
+ // Okay, we know this is a binop.
+ int BinOp = CurTok;
+ getNextToken(); // eat binop
+
+ // Parse the primary expression after the binary operator.
+ auto RHS = ParsePrimary();
+ if (!RHS)
+ return nullptr;
+
+As such, this code eats (and remembers) the binary operator and then
+parses the primary expression that follows. This builds up the whole
+pair, the first of which is [+, b] for the running example.
+
+Now that we parsed the left-hand side of an expression and one pair of
+the RHS sequence, we have to decide which way the expression associates.
+In particular, we could have "(a+b) binop unparsed" or "a + (b binop
+unparsed)". To determine this, we look ahead at "binop" to determine its
+precedence and compare it to BinOp's precedence (which is '+' in this
+case):
+
+.. code-block:: c++
+
+ // If BinOp binds less tightly with RHS than the operator after RHS, let
+ // the pending operator take RHS as its LHS.
+ int NextPrec = GetTokPrecedence();
+ if (TokPrec < NextPrec) {
+
+If the precedence of the binop to the right of "RHS" is lower or equal
+to the precedence of our current operator, then we know that the
+parentheses associate as "(a+b) binop ...". In our example, the current
+operator is "+" and the next operator is "+", we know that they have the
+same precedence. In this case we'll create the AST node for "a+b", and
+then continue parsing:
+
+.. code-block:: c++
+
+ ... if body omitted ...
+ }
+
+ // Merge LHS/RHS.
+ LHS = llvm::make_unique<BinaryExprAST>(BinOp, std::move(LHS),
+ std::move(RHS));
+ } // loop around to the top of the while loop.
+ }
+
+In our example above, this will turn "a+b+" into "(a+b)" and execute the
+next iteration of the loop, with "+" as the current token. The code
+above will eat, remember, and parse "(c+d)" as the primary expression,
+which makes the current pair equal to [+, (c+d)]. It will then evaluate
+the 'if' conditional above with "\*" as the binop to the right of the
+primary. In this case, the precedence of "\*" is higher than the
+precedence of "+" so the if condition will be entered.
+
+The critical question left here is "how can the if condition parse the
+right hand side in full"? In particular, to build the AST correctly for
+our example, it needs to get all of "(c+d)\*e\*f" as the RHS expression
+variable. The code to do this is surprisingly simple (code from the
+above two blocks duplicated for context):
+
+.. code-block:: c++
+
+ // If BinOp binds less tightly with RHS than the operator after RHS, let
+ // the pending operator take RHS as its LHS.
+ int NextPrec = GetTokPrecedence();
+ if (TokPrec < NextPrec) {
+ RHS = ParseBinOpRHS(TokPrec+1, std::move(RHS));
+ if (!RHS)
+ return nullptr;
+ }
+ // Merge LHS/RHS.
+ LHS = llvm::make_unique<BinaryExprAST>(BinOp, std::move(LHS),
+ std::move(RHS));
+ } // loop around to the top of the while loop.
+ }
+
+At this point, we know that the binary operator to the RHS of our
+primary has higher precedence than the binop we are currently parsing.
+As such, we know that any sequence of pairs whose operators are all
+higher precedence than "+" should be parsed together and returned as
+"RHS". To do this, we recursively invoke the ``ParseBinOpRHS`` function
+specifying "TokPrec+1" as the minimum precedence required for it to
+continue. In our example above, this will cause it to return the AST
+node for "(c+d)\*e\*f" as RHS, which is then set as the RHS of the '+'
+expression.
+
+Finally, on the next iteration of the while loop, the "+g" piece is
+parsed and added to the AST. With this little bit of code (14
+non-trivial lines), we correctly handle fully general binary expression
+parsing in a very elegant way. This was a whirlwind tour of this code,
+and it is somewhat subtle. I recommend running through it with a few
+tough examples to see how it works.
+
+This wraps up handling of expressions. At this point, we can point the
+parser at an arbitrary token stream and build an expression from it,
+stopping at the first token that is not part of the expression. Next up
+we need to handle function definitions, etc.
+
+Parsing the Rest
+================
+
+The next thing missing is handling of function prototypes. In
+Kaleidoscope, these are used both for 'extern' function declarations as
+well as function body definitions. The code to do this is
+straight-forward and not very interesting (once you've survived
+expressions):
+
+.. code-block:: c++
+
+ /// prototype
+ /// ::= id '(' id* ')'
+ static std::unique_ptr<PrototypeAST> ParsePrototype() {
+ if (CurTok != tok_identifier)
+ return ErrorP("Expected function name in prototype");
+
+ std::string FnName = IdentifierStr;
+ getNextToken();
+
+ if (CurTok != '(')
+ return ErrorP("Expected '(' in prototype");
+
+ // Read the list of argument names.
+ std::vector<std::string> ArgNames;
+ while (getNextToken() == tok_identifier)
+ ArgNames.push_back(IdentifierStr);
+ if (CurTok != ')')
+ return ErrorP("Expected ')' in prototype");
+
+ // success.
+ getNextToken(); // eat ')'.
+
+ return llvm::make_unique<PrototypeAST>(FnName, std::move(ArgNames));
+ }
+
+Given this, a function definition is very simple, just a prototype plus
+an expression to implement the body:
+
+.. code-block:: c++
+
+ /// definition ::= 'def' prototype expression
+ static std::unique_ptr<FunctionAST> ParseDefinition() {
+ getNextToken(); // eat def.
+ auto Proto = ParsePrototype();
+ if (!Proto) return nullptr;
+
+ if (auto E = ParseExpression())
+ return llvm::make_unique<FunctionAST>(std::move(Proto), std::move(E));
+ return nullptr;
+ }
+
+In addition, we support 'extern' to declare functions like 'sin' and
+'cos' as well as to support forward declaration of user functions. These
+'extern's are just prototypes with no body:
+
+.. code-block:: c++
+
+ /// external ::= 'extern' prototype
+ static std::unique_ptr<PrototypeAST> ParseExtern() {
+ getNextToken(); // eat extern.
+ return ParsePrototype();
+ }
+
+Finally, we'll also let the user type in arbitrary top-level expressions
+and evaluate them on the fly. We will handle this by defining anonymous
+nullary (zero argument) functions for them:
+
+.. code-block:: c++
+
+ /// toplevelexpr ::= expression
+ static std::unique_ptr<FunctionAST> ParseTopLevelExpr() {
+ if (auto E = ParseExpression()) {
+ // Make an anonymous proto.
+ auto Proto = llvm::make_unique<PrototypeAST>("", std::vector<std::string>());
+ return llvm::make_unique<FunctionAST>(std::move(Proto), std::move(E));
+ }
+ return nullptr;
+ }
+
+Now that we have all the pieces, let's build a little driver that will
+let us actually *execute* this code we've built!
+
+The Driver
+==========
+
+The driver for this simply invokes all of the parsing pieces with a
+top-level dispatch loop. There isn't much interesting here, so I'll just
+include the top-level loop. See `below <#full-code-listing>`_ for full code in the
+"Top-Level Parsing" section.
+
+.. code-block:: c++
+
+ /// top ::= definition | external | expression | ';'
+ static void MainLoop() {
+ while (1) {
+ fprintf(stderr, "ready> ");
+ switch (CurTok) {
+ case tok_eof:
+ return;
+ case ';': // ignore top-level semicolons.
+ getNextToken();
+ break;
+ case tok_def:
+ HandleDefinition();
+ break;
+ case tok_extern:
+ HandleExtern();
+ break;
+ default:
+ HandleTopLevelExpression();
+ break;
+ }
+ }
+ }
+
+The most interesting part of this is that we ignore top-level
+semicolons. Why is this, you ask? The basic reason is that if you type
+"4 + 5" at the command line, the parser doesn't know whether that is the
+end of what you will type or not. For example, on the next line you
+could type "def foo..." in which case 4+5 is the end of a top-level
+expression. Alternatively you could type "\* 6", which would continue
+the expression. Having top-level semicolons allows you to type "4+5;",
+and the parser will know you are done.
+
+Conclusions
+===========
+
+With just under 400 lines of commented code (240 lines of non-comment,
+non-blank code), we fully defined our minimal language, including a
+lexer, parser, and AST builder. With this done, the executable will
+validate Kaleidoscope code and tell us if it is grammatically invalid.
+For example, here is a sample interaction:
+
+.. code-block:: bash
+
+ $ ./a.out
+ ready> def foo(x y) x+foo(y, 4.0);
+ Parsed a function definition.
+ ready> def foo(x y) x+y y;
+ Parsed a function definition.
+ Parsed a top-level expr
+ ready> def foo(x y) x+y );
+ Parsed a function definition.
+ Error: unknown token when expecting an expression
+ ready> extern sin(a);
+ ready> Parsed an extern
+ ready> ^D
+ $
+
+There is a lot of room for extension here. You can define new AST nodes,
+extend the language in many ways, etc. In the `next
+installment <LangImpl3.html>`_, we will describe how to generate LLVM
+Intermediate Representation (IR) from the AST.
+
+Full Code Listing
+=================
+
+Here is the complete code listing for this and the previous chapter.
+Note that it is fully self-contained: you don't need LLVM or any
+external libraries at all for this. (Besides the C and C++ standard
+libraries, of course.) To build this, just compile with:
+
+.. code-block:: bash
+
+ # Compile
+ clang++ -g -O3 toy.cpp
+ # Run
+ ./a.out
+
+Here is the code:
+
+.. literalinclude:: ../../examples/Kaleidoscope/Chapter2/toy.cpp
+ :language: c++
+
+`Next: Implementing Code Generation to LLVM IR <LangImpl3.html>`_
+
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+========================================
+Kaleidoscope: Code generation to LLVM IR
+========================================
+
+.. contents::
+ :local:
+
+Chapter 3 Introduction
+======================
+
+Welcome to Chapter 3 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. This chapter shows you how to transform
+the `Abstract Syntax Tree <LangImpl2.html>`_, built in Chapter 2, into
+LLVM IR. This will teach you a little bit about how LLVM does things, as
+well as demonstrate how easy it is to use. It's much more work to build
+a lexer and parser than it is to generate LLVM IR code. :)
+
+**Please note**: the code in this chapter and later require LLVM 3.7 or
+later. LLVM 3.6 and before will not work with it. Also note that you
+need to use a version of this tutorial that matches your LLVM release:
+If you are using an official LLVM release, use the version of the
+documentation included with your release or on the `llvm.org releases
+page <http://llvm.org/releases/>`_.
+
+Code Generation Setup
+=====================
+
+In order to generate LLVM IR, we want some simple setup to get started.
+First we define virtual code generation (codegen) methods in each AST
+class:
+
+.. code-block:: c++
+
+ /// ExprAST - Base class for all expression nodes.
+ class ExprAST {
+ public:
+ virtual ~ExprAST() {}
+ virtual Value *codegen() = 0;
+ };
+
+ /// NumberExprAST - Expression class for numeric literals like "1.0".
+ class NumberExprAST : public ExprAST {
+ double Val;
+
+ public:
+ NumberExprAST(double Val) : Val(Val) {}
+ virtual Value *codegen();
+ };
+ ...
+
+The codegen() method says to emit IR for that AST node along with all
+the things it depends on, and they all return an LLVM Value object.
+"Value" is the class used to represent a "`Static Single Assignment
+(SSA) <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_
+register" or "SSA value" in LLVM. The most distinct aspect of SSA values
+is that their value is computed as the related instruction executes, and
+it does not get a new value until (and if) the instruction re-executes.
+In other words, there is no way to "change" an SSA value. For more
+information, please read up on `Static Single
+Assignment <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_
+- the concepts are really quite natural once you grok them.
+
+Note that instead of adding virtual methods to the ExprAST class
+hierarchy, it could also make sense to use a `visitor
+pattern <http://en.wikipedia.org/wiki/Visitor_pattern>`_ or some other
+way to model this. Again, this tutorial won't dwell on good software
+engineering practices: for our purposes, adding a virtual method is
+simplest.
+
+The second thing we want is an "Error" method like we used for the
+parser, which will be used to report errors found during code generation
+(for example, use of an undeclared parameter):
+
+.. code-block:: c++
+
+ static std::unique_ptr<Module> *TheModule;
+ static IRBuilder<> Builder(getGlobalContext());
+ static std::map<std::string, Value*> NamedValues;
+
+ Value *ErrorV(const char *Str) {
+ Error(Str);
+ return nullptr;
+ }
+
+The static variables will be used during code generation. ``TheModule``
+is an LLVM construct that contains functions and global variables. In many
+ways, it is the top-level structure that the LLVM IR uses to contain code.
+It will own the memory for all of the IR that we generate, which is why
+the codegen() method returns a raw Value\*, rather than a unique_ptr<Value>.
+
+The ``Builder`` object is a helper object that makes it easy to generate
+LLVM instructions. Instances of the
+`IRBuilder <http://llvm.org/doxygen/IRBuilder_8h-source.html>`_
+class template keep track of the current place to insert instructions
+and has methods to create new instructions.
+
+The ``NamedValues`` map keeps track of which values are defined in the
+current scope and what their LLVM representation is. (In other words, it
+is a symbol table for the code). In this form of Kaleidoscope, the only
+things that can be referenced are function parameters. As such, function
+parameters will be in this map when generating code for their function
+body.
+
+With these basics in place, we can start talking about how to generate
+code for each expression. Note that this assumes that the ``Builder``
+has been set up to generate code *into* something. For now, we'll assume
+that this has already been done, and we'll just use it to emit code.
+
+Expression Code Generation
+==========================
+
+Generating LLVM code for expression nodes is very straightforward: less
+than 45 lines of commented code for all four of our expression nodes.
+First we'll do numeric literals:
+
+.. code-block:: c++
+
+ Value *NumberExprAST::codegen() {
+ return ConstantFP::get(getGlobalContext(), APFloat(Val));
+ }
+
+In the LLVM IR, numeric constants are represented with the
+``ConstantFP`` class, which holds the numeric value in an ``APFloat``
+internally (``APFloat`` has the capability of holding floating point
+constants of Arbitrary Precision). This code basically just creates
+and returns a ``ConstantFP``. Note that in the LLVM IR that constants
+are all uniqued together and shared. For this reason, the API uses the
+"foo::get(...)" idiom instead of "new foo(..)" or "foo::Create(..)".
+
+.. code-block:: c++
+
+ Value *VariableExprAST::codegen() {
+ // Look this variable up in the function.
+ Value *V = NamedValues[Name];
+ if (!V)
+ ErrorV("Unknown variable name");
+ return V;
+ }
+
+References to variables are also quite simple using LLVM. In the simple
+version of Kaleidoscope, we assume that the variable has already been
+emitted somewhere and its value is available. In practice, the only
+values that can be in the ``NamedValues`` map are function arguments.
+This code simply checks to see that the specified name is in the map (if
+not, an unknown variable is being referenced) and returns the value for
+it. In future chapters, we'll add support for `loop induction
+variables <LangImpl5.html#for-loop-expression>`_ in the symbol table, and for `local
+variables <LangImpl7.html#user-defined-local-variables>`_.
+
+.. code-block:: c++
+
+ Value *BinaryExprAST::codegen() {
+ Value *L = LHS->codegen();
+ Value *R = RHS->codegen();
+ if (!L || !R)
+ return nullptr;
+
+ switch (Op) {
+ case '+':
+ return Builder.CreateFAdd(L, R, "addtmp");
+ case '-':
+ return Builder.CreateFSub(L, R, "subtmp");
+ case '*':
+ return Builder.CreateFMul(L, R, "multmp");
+ case '<':
+ L = Builder.CreateFCmpULT(L, R, "cmptmp");
+ // Convert bool 0/1 to double 0.0 or 1.0
+ return Builder.CreateUIToFP(L, Type::getDoubleTy(getGlobalContext()),
+ "booltmp");
+ default:
+ return ErrorV("invalid binary operator");
+ }
+ }
+
+Binary operators start to get more interesting. The basic idea here is
+that we recursively emit code for the left-hand side of the expression,
+then the right-hand side, then we compute the result of the binary
+expression. In this code, we do a simple switch on the opcode to create
+the right LLVM instruction.
+
+In the example above, the LLVM builder class is starting to show its
+value. IRBuilder knows where to insert the newly created instruction,
+all you have to do is specify what instruction to create (e.g. with
+``CreateFAdd``), which operands to use (``L`` and ``R`` here) and
+optionally provide a name for the generated instruction.
+
+One nice thing about LLVM is that the name is just a hint. For instance,
+if the code above emits multiple "addtmp" variables, LLVM will
+automatically provide each one with an increasing, unique numeric
+suffix. Local value names for instructions are purely optional, but it
+makes it much easier to read the IR dumps.
+
+`LLVM instructions <../LangRef.html#instruction-reference>`_ are constrained by strict
+rules: for example, the Left and Right operators of an `add
+instruction <../LangRef.html#add-instruction>`_ must have the same type, and the
+result type of the add must match the operand types. Because all values
+in Kaleidoscope are doubles, this makes for very simple code for add,
+sub and mul.
+
+On the other hand, LLVM specifies that the `fcmp
+instruction <../LangRef.html#fcmp-instruction>`_ always returns an 'i1' value (a
+one bit integer). The problem with this is that Kaleidoscope wants the
+value to be a 0.0 or 1.0 value. In order to get these semantics, we
+combine the fcmp instruction with a `uitofp
+instruction <../LangRef.html#uitofp-to-instruction>`_. This instruction converts its
+input integer into a floating point value by treating the input as an
+unsigned value. In contrast, if we used the `sitofp
+instruction <../LangRef.html#sitofp-to-instruction>`_, the Kaleidoscope '<' operator
+would return 0.0 and -1.0, depending on the input value.
+
+.. code-block:: c++
+
+ Value *CallExprAST::codegen() {
+ // Look up the name in the global module table.
+ Function *CalleeF = TheModule->getFunction(Callee);
+ if (!CalleeF)
+ return ErrorV("Unknown function referenced");
+
+ // If argument mismatch error.
+ if (CalleeF->arg_size() != Args.size())
+ return ErrorV("Incorrect # arguments passed");
+
+ std::vector<Value *> ArgsV;
+ for (unsigned i = 0, e = Args.size(); i != e; ++i) {
+ ArgsV.push_back(Args[i]->codegen());
+ if (!ArgsV.back())
+ return nullptr;
+ }
+
+ return Builder.CreateCall(CalleeF, ArgsV, "calltmp");
+ }
+
+Code generation for function calls is quite straightforward with LLVM. The code
+above initially does a function name lookup in the LLVM Module's symbol table.
+Recall that the LLVM Module is the container that holds the functions we are
+JIT'ing. By giving each function the same name as what the user specifies, we
+can use the LLVM symbol table to resolve function names for us.
+
+Once we have the function to call, we recursively codegen each argument
+that is to be passed in, and create an LLVM `call
+instruction <../LangRef.html#call-instruction>`_. Note that LLVM uses the native C
+calling conventions by default, allowing these calls to also call into
+standard library functions like "sin" and "cos", with no additional
+effort.
+
+This wraps up our handling of the four basic expressions that we have so
+far in Kaleidoscope. Feel free to go in and add some more. For example,
+by browsing the `LLVM language reference <../LangRef.html>`_ you'll find
+several other interesting instructions that are really easy to plug into
+our basic framework.
+
+Function Code Generation
+========================
+
+Code generation for prototypes and functions must handle a number of
+details, which make their code less beautiful than expression code
+generation, but allows us to illustrate some important points. First,
+lets talk about code generation for prototypes: they are used both for
+function bodies and external function declarations. The code starts
+with:
+
+.. code-block:: c++
+
+ Function *PrototypeAST::codegen() {
+ // Make the function type: double(double,double) etc.
+ std::vector<Type*> Doubles(Args.size(),
+ Type::getDoubleTy(getGlobalContext()));
+ FunctionType *FT =
+ FunctionType::get(Type::getDoubleTy(getGlobalContext()), Doubles, false);
+
+ Function *F =
+ Function::Create(FT, Function::ExternalLinkage, Name, TheModule);
+
+This code packs a lot of power into a few lines. Note first that this
+function returns a "Function\*" instead of a "Value\*". Because a
+"prototype" really talks about the external interface for a function
+(not the value computed by an expression), it makes sense for it to
+return the LLVM Function it corresponds to when codegen'd.
+
+The call to ``FunctionType::get`` creates the ``FunctionType`` that
+should be used for a given Prototype. Since all function arguments in
+Kaleidoscope are of type double, the first line creates a vector of "N"
+LLVM double types. It then uses the ``Functiontype::get`` method to
+create a function type that takes "N" doubles as arguments, returns one
+double as a result, and that is not vararg (the false parameter
+indicates this). Note that Types in LLVM are uniqued just like Constants
+are, so you don't "new" a type, you "get" it.
+
+The final line above actually creates the IR Function corresponding to
+the Prototype. This indicates the type, linkage and name to use, as
+well as which module to insert into. "`external
+linkage <../LangRef.html#linkage>`_" means that the function may be
+defined outside the current module and/or that it is callable by
+functions outside the module. The Name passed in is the name the user
+specified: since "``TheModule``" is specified, this name is registered
+in "``TheModule``"s symbol table.
+
+.. code-block:: c++
+
+ // Set names for all arguments.
+ unsigned Idx = 0;
+ for (auto &Arg : F->args())
+ Arg.setName(Args[Idx++]);
+
+ return F;
+
+Finally, we set the name of each of the function's arguments according to the
+names given in the Prototype. This step isn't strictly necessary, but keeping
+the names consistent makes the IR more readable, and allows subsequent code to
+refer directly to the arguments for their names, rather than having to look up
+them up in the Prototype AST.
+
+At this point we have a function prototype with no body. This is how LLVM IR
+represents function declarations. For extern statements in Kaleidoscope, this
+is as far as we need to go. For function definitions however, we need to
+codegen and attach a function body.
+
+.. code-block:: c++
+
+ Function *FunctionAST::codegen() {
+ // First, check for an existing function from a previous 'extern' declaration.
+ Function *TheFunction = TheModule->getFunction(Proto->getName());
+
+ if (!TheFunction)
+ TheFunction = Proto->codegen();
+
+ if (!TheFunction)
+ return nullptr;
+
+ if (!TheFunction->empty())
+ return (Function*)ErrorV("Function cannot be redefined.");
+
+
+For function definitions, we start by searching TheModule's symbol table for an
+existing version of this function, in case one has already been created using an
+'extern' statement. If Module::getFunction returns null then no previous version
+exists, so we'll codegen one from the Prototype. In either case, we want to
+assert that the function is empty (i.e. has no body yet) before we start.
+
+.. code-block:: c++
+
+ // Create a new basic block to start insertion into.
+ BasicBlock *BB = BasicBlock::Create(getGlobalContext(), "entry", TheFunction);
+ Builder.SetInsertPoint(BB);
+
+ // Record the function arguments in the NamedValues map.
+ NamedValues.clear();
+ for (auto &Arg : TheFunction->args())
+ NamedValues[Arg.getName()] = &Arg;
+
+Now we get to the point where the ``Builder`` is set up. The first line
+creates a new `basic block <http://en.wikipedia.org/wiki/Basic_block>`_
+(named "entry"), which is inserted into ``TheFunction``. The second line
+then tells the builder that new instructions should be inserted into the
+end of the new basic block. Basic blocks in LLVM are an important part
+of functions that define the `Control Flow
+Graph <http://en.wikipedia.org/wiki/Control_flow_graph>`_. Since we
+don't have any control flow, our functions will only contain one block
+at this point. We'll fix this in `Chapter 5 <LangImpl5.html>`_ :).
+
+Next we add the function arguments to the NamedValues map (after first clearing
+it out) so that they're accessible to ``VariableExprAST`` nodes.
+
+.. code-block:: c++
+
+ if (Value *RetVal = Body->codegen()) {
+ // Finish off the function.
+ Builder.CreateRet(RetVal);
+
+ // Validate the generated code, checking for consistency.
+ verifyFunction(*TheFunction);
+
+ return TheFunction;
+ }
+
+Once the insertion point has been set up and the NamedValues map populated,
+we call the ``codegen()`` method for the root expression of the function. If no
+error happens, this emits code to compute the expression into the entry block
+and returns the value that was computed. Assuming no error, we then create an
+LLVM `ret instruction <../LangRef.html#ret-instruction>`_, which completes the function.
+Once the function is built, we call ``verifyFunction``, which is
+provided by LLVM. This function does a variety of consistency checks on
+the generated code, to determine if our compiler is doing everything
+right. Using this is important: it can catch a lot of bugs. Once the
+function is finished and validated, we return it.
+
+.. code-block:: c++
+
+ // Error reading body, remove function.
+ TheFunction->eraseFromParent();
+ return nullptr;
+ }
+
+The only piece left here is handling of the error case. For simplicity,
+we handle this by merely deleting the function we produced with the
+``eraseFromParent`` method. This allows the user to redefine a function
+that they incorrectly typed in before: if we didn't delete it, it would
+live in the symbol table, with a body, preventing future redefinition.
+
+This code does have a bug, though: If the ``FunctionAST::codegen()`` method
+finds an existing IR Function, it does not validate its signature against the
+definition's own prototype. This means that an earlier 'extern' declaration will
+take precedence over the function definition's signature, which can cause
+codegen to fail, for instance if the function arguments are named differently.
+There are a number of ways to fix this bug, see what you can come up with! Here
+is a testcase:
+
+::
+
+ extern foo(a); # ok, defines foo.
+ def foo(b) b; # Error: Unknown variable name. (decl using 'a' takes precedence).
+
+Driver Changes and Closing Thoughts
+===================================
+
+For now, code generation to LLVM doesn't really get us much, except that
+we can look at the pretty IR calls. The sample code inserts calls to
+codegen into the "``HandleDefinition``", "``HandleExtern``" etc
+functions, and then dumps out the LLVM IR. This gives a nice way to look
+at the LLVM IR for simple functions. For example:
+
+::
+
+ ready> 4+5;
+ Read top-level expression:
+ define double @0() {
+ entry:
+ ret double 9.000000e+00
+ }
+
+Note how the parser turns the top-level expression into anonymous
+functions for us. This will be handy when we add `JIT
+support <LangImpl4.html#adding-a-jit-compiler>`_ in the next chapter. Also note that the
+code is very literally transcribed, no optimizations are being performed
+except simple constant folding done by IRBuilder. We will `add
+optimizations <LangImpl4.html#trivial-constant-folding>`_ explicitly in the next
+chapter.
+
+::
+
+ ready> def foo(a b) a*a + 2*a*b + b*b;
+ Read function definition:
+ define double @foo(double %a, double %b) {
+ entry:
+ %multmp = fmul double %a, %a
+ %multmp1 = fmul double 2.000000e+00, %a
+ %multmp2 = fmul double %multmp1, %b
+ %addtmp = fadd double %multmp, %multmp2
+ %multmp3 = fmul double %b, %b
+ %addtmp4 = fadd double %addtmp, %multmp3
+ ret double %addtmp4
+ }
+
+This shows some simple arithmetic. Notice the striking similarity to the
+LLVM builder calls that we use to create the instructions.
+
+::
+
+ ready> def bar(a) foo(a, 4.0) + bar(31337);
+ Read function definition:
+ define double @bar(double %a) {
+ entry:
+ %calltmp = call double @foo(double %a, double 4.000000e+00)
+ %calltmp1 = call double @bar(double 3.133700e+04)
+ %addtmp = fadd double %calltmp, %calltmp1
+ ret double %addtmp
+ }
+
+This shows some function calls. Note that this function will take a long
+time to execute if you call it. In the future we'll add conditional
+control flow to actually make recursion useful :).
+
+::
+
+ ready> extern cos(x);
+ Read extern:
+ declare double @cos(double)
+
+ ready> cos(1.234);
+ Read top-level expression:
+ define double @1() {
+ entry:
+ %calltmp = call double @cos(double 1.234000e+00)
+ ret double %calltmp
+ }
+
+This shows an extern for the libm "cos" function, and a call to it.
+
+.. TODO:: Abandon Pygments' horrible `llvm` lexer. It just totally gives up
+ on highlighting this due to the first line.
+
+::
+
+ ready> ^D
+ ; ModuleID = 'my cool jit'
+
+ define double @0() {
+ entry:
+ %addtmp = fadd double 4.000000e+00, 5.000000e+00
+ ret double %addtmp
+ }
+
+ define double @foo(double %a, double %b) {
+ entry:
+ %multmp = fmul double %a, %a
+ %multmp1 = fmul double 2.000000e+00, %a
+ %multmp2 = fmul double %multmp1, %b
+ %addtmp = fadd double %multmp, %multmp2
+ %multmp3 = fmul double %b, %b
+ %addtmp4 = fadd double %addtmp, %multmp3
+ ret double %addtmp4
+ }
+
+ define double @bar(double %a) {
+ entry:
+ %calltmp = call double @foo(double %a, double 4.000000e+00)
+ %calltmp1 = call double @bar(double 3.133700e+04)
+ %addtmp = fadd double %calltmp, %calltmp1
+ ret double %addtmp
+ }
+
+ declare double @cos(double)
+
+ define double @1() {
+ entry:
+ %calltmp = call double @cos(double 1.234000e+00)
+ ret double %calltmp
+ }
+
+When you quit the current demo, it dumps out the IR for the entire
+module generated. Here you can see the big picture with all the
+functions referencing each other.
+
+This wraps up the third chapter of the Kaleidoscope tutorial. Up next,
+we'll describe how to `add JIT codegen and optimizer
+support <LangImpl4.html>`_ to this so we can actually start running
+code!
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example, enhanced with
+the LLVM code generator. Because this uses the LLVM libraries, we need
+to link them in. To do this, we use the
+`llvm-config <http://llvm.org/cmds/llvm-config.html>`_ tool to inform
+our makefile/command line about which options to use:
+
+.. code-block:: bash
+
+ # Compile
+ clang++ -g -O3 toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core` -o toy
+ # Run
+ ./toy
+
+Here is the code:
+
+.. literalinclude:: ../../examples/Kaleidoscope/Chapter3/toy.cpp
+ :language: c++
+
+`Next: Adding JIT and Optimizer Support <LangImpl4.html>`_
+
Added: www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl4.txt
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==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl4.txt (added)
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@@ -0,0 +1,609 @@
+==============================================
+Kaleidoscope: Adding JIT and Optimizer Support
+==============================================
+
+.. contents::
+ :local:
+
+Chapter 4 Introduction
+======================
+
+Welcome to Chapter 4 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. Chapters 1-3 described the implementation
+of a simple language and added support for generating LLVM IR. This
+chapter describes two new techniques: adding optimizer support to your
+language, and adding JIT compiler support. These additions will
+demonstrate how to get nice, efficient code for the Kaleidoscope
+language.
+
+Trivial Constant Folding
+========================
+
+Our demonstration for Chapter 3 is elegant and easy to extend.
+Unfortunately, it does not produce wonderful code. The IRBuilder,
+however, does give us obvious optimizations when compiling simple code:
+
+::
+
+ ready> def test(x) 1+2+x;
+ Read function definition:
+ define double @test(double %x) {
+ entry:
+ %addtmp = fadd double 3.000000e+00, %x
+ ret double %addtmp
+ }
+
+This code is not a literal transcription of the AST built by parsing the
+input. That would be:
+
+::
+
+ ready> def test(x) 1+2+x;
+ Read function definition:
+ define double @test(double %x) {
+ entry:
+ %addtmp = fadd double 2.000000e+00, 1.000000e+00
+ %addtmp1 = fadd double %addtmp, %x
+ ret double %addtmp1
+ }
+
+Constant folding, as seen above, in particular, is a very common and
+very important optimization: so much so that many language implementors
+implement constant folding support in their AST representation.
+
+With LLVM, you don't need this support in the AST. Since all calls to
+build LLVM IR go through the LLVM IR builder, the builder itself checked
+to see if there was a constant folding opportunity when you call it. If
+so, it just does the constant fold and return the constant instead of
+creating an instruction.
+
+Well, that was easy :). In practice, we recommend always using
+``IRBuilder`` when generating code like this. It has no "syntactic
+overhead" for its use (you don't have to uglify your compiler with
+constant checks everywhere) and it can dramatically reduce the amount of
+LLVM IR that is generated in some cases (particular for languages with a
+macro preprocessor or that use a lot of constants).
+
+On the other hand, the ``IRBuilder`` is limited by the fact that it does
+all of its analysis inline with the code as it is built. If you take a
+slightly more complex example:
+
+::
+
+ ready> def test(x) (1+2+x)*(x+(1+2));
+ ready> Read function definition:
+ define double @test(double %x) {
+ entry:
+ %addtmp = fadd double 3.000000e+00, %x
+ %addtmp1 = fadd double %x, 3.000000e+00
+ %multmp = fmul double %addtmp, %addtmp1
+ ret double %multmp
+ }
+
+In this case, the LHS and RHS of the multiplication are the same value.
+We'd really like to see this generate "``tmp = x+3; result = tmp*tmp;``"
+instead of computing "``x+3``" twice.
+
+Unfortunately, no amount of local analysis will be able to detect and
+correct this. This requires two transformations: reassociation of
+expressions (to make the add's lexically identical) and Common
+Subexpression Elimination (CSE) to delete the redundant add instruction.
+Fortunately, LLVM provides a broad range of optimizations that you can
+use, in the form of "passes".
+
+LLVM Optimization Passes
+========================
+
+LLVM provides many optimization passes, which do many different sorts of
+things and have different tradeoffs. Unlike other systems, LLVM doesn't
+hold to the mistaken notion that one set of optimizations is right for
+all languages and for all situations. LLVM allows a compiler implementor
+to make complete decisions about what optimizations to use, in which
+order, and in what situation.
+
+As a concrete example, LLVM supports both "whole module" passes, which
+look across as large of body of code as they can (often a whole file,
+but if run at link time, this can be a substantial portion of the whole
+program). It also supports and includes "per-function" passes which just
+operate on a single function at a time, without looking at other
+functions. For more information on passes and how they are run, see the
+`How to Write a Pass <../WritingAnLLVMPass.html>`_ document and the
+`List of LLVM Passes <../Passes.html>`_.
+
+For Kaleidoscope, we are currently generating functions on the fly, one
+at a time, as the user types them in. We aren't shooting for the
+ultimate optimization experience in this setting, but we also want to
+catch the easy and quick stuff where possible. As such, we will choose
+to run a few per-function optimizations as the user types the function
+in. If we wanted to make a "static Kaleidoscope compiler", we would use
+exactly the code we have now, except that we would defer running the
+optimizer until the entire file has been parsed.
+
+In order to get per-function optimizations going, we need to set up a
+`FunctionPassManager <../WritingAnLLVMPass.html#what-passmanager-doesr>`_ to hold
+and organize the LLVM optimizations that we want to run. Once we have
+that, we can add a set of optimizations to run. We'll need a new
+FunctionPassManager for each module that we want to optimize, so we'll
+write a function to create and initialize both the module and pass manager
+for us:
+
+.. code-block:: c++
+
+ void InitializeModuleAndPassManager(void) {
+ // Open a new module.
+ TheModule = llvm::make_unique<Module>("my cool jit", getGlobalContext());
+ TheModule->setDataLayout(TheJIT->getTargetMachine().createDataLayout());
+
+ // Create a new pass manager attached to it.
+ TheFPM = llvm::make_unique<FunctionPassManager>(TheModule.get());
+
+ // Provide basic AliasAnalysis support for GVN.
+ TheFPM.add(createBasicAliasAnalysisPass());
+ // Do simple "peephole" optimizations and bit-twiddling optzns.
+ TheFPM.add(createInstructionCombiningPass());
+ // Reassociate expressions.
+ TheFPM.add(createReassociatePass());
+ // Eliminate Common SubExpressions.
+ TheFPM.add(createGVNPass());
+ // Simplify the control flow graph (deleting unreachable blocks, etc).
+ TheFPM.add(createCFGSimplificationPass());
+
+ TheFPM.doInitialization();
+ }
+
+This code initializes the global module ``TheModule``, and the function pass
+manager ``TheFPM``, which is attached to ``TheModule``. Once the pass manager is
+set up, we use a series of "add" calls to add a bunch of LLVM passes.
+
+In this case, we choose to add five passes: one analysis pass (alias analysis),
+and four optimization passes. The passes we choose here are a pretty standard set
+of "cleanup" optimizations that are useful for a wide variety of code. I won't
+delve into what they do but, believe me, they are a good starting place :).
+
+Once the PassManager is set up, we need to make use of it. We do this by
+running it after our newly created function is constructed (in
+``FunctionAST::codegen()``), but before it is returned to the client:
+
+.. code-block:: c++
+
+ if (Value *RetVal = Body->codegen()) {
+ // Finish off the function.
+ Builder.CreateRet(RetVal);
+
+ // Validate the generated code, checking for consistency.
+ verifyFunction(*TheFunction);
+
+ // Optimize the function.
+ TheFPM->run(*TheFunction);
+
+ return TheFunction;
+ }
+
+As you can see, this is pretty straightforward. The
+``FunctionPassManager`` optimizes and updates the LLVM Function\* in
+place, improving (hopefully) its body. With this in place, we can try
+our test above again:
+
+::
+
+ ready> def test(x) (1+2+x)*(x+(1+2));
+ ready> Read function definition:
+ define double @test(double %x) {
+ entry:
+ %addtmp = fadd double %x, 3.000000e+00
+ %multmp = fmul double %addtmp, %addtmp
+ ret double %multmp
+ }
+
+As expected, we now get our nicely optimized code, saving a floating
+point add instruction from every execution of this function.
+
+LLVM provides a wide variety of optimizations that can be used in
+certain circumstances. Some `documentation about the various
+passes <../Passes.html>`_ is available, but it isn't very complete.
+Another good source of ideas can come from looking at the passes that
+``Clang`` runs to get started. The "``opt``" tool allows you to
+experiment with passes from the command line, so you can see if they do
+anything.
+
+Now that we have reasonable code coming out of our front-end, lets talk
+about executing it!
+
+Adding a JIT Compiler
+=====================
+
+Code that is available in LLVM IR can have a wide variety of tools
+applied to it. For example, you can run optimizations on it (as we did
+above), you can dump it out in textual or binary forms, you can compile
+the code to an assembly file (.s) for some target, or you can JIT
+compile it. The nice thing about the LLVM IR representation is that it
+is the "common currency" between many different parts of the compiler.
+
+In this section, we'll add JIT compiler support to our interpreter. The
+basic idea that we want for Kaleidoscope is to have the user enter
+function bodies as they do now, but immediately evaluate the top-level
+expressions they type in. For example, if they type in "1 + 2;", we
+should evaluate and print out 3. If they define a function, they should
+be able to call it from the command line.
+
+In order to do this, we first declare and initialize the JIT. This is
+done by adding a global variable ``TheJIT``, and initializing it in
+``main``:
+
+.. code-block:: c++
+
+ static std::unique_ptr<KaleidoscopeJIT> TheJIT;
+ ...
+ int main() {
+ ..
+ TheJIT = llvm::make_unique<KaleidoscopeJIT>();
+
+ // Run the main "interpreter loop" now.
+ MainLoop();
+
+ return 0;
+ }
+
+The KaleidoscopeJIT class is a simple JIT built specifically for these
+tutorials. In later chapters we will look at how it works and extend it with
+new features, but for now we will take it as given. Its API is very simple::
+``addModule`` adds an LLVM IR module to the JIT, making its functions
+available for execution; ``removeModule`` removes a module, freeing any
+memory associated with the code in that module; and ``findSymbol`` allows us
+to look up pointers to the compiled code.
+
+We can take this simple API and change our code that parses top-level expressions to
+look like this:
+
+.. code-block:: c++
+
+ static void HandleTopLevelExpression() {
+ // Evaluate a top-level expression into an anonymous function.
+ if (auto FnAST = ParseTopLevelExpr()) {
+ if (FnAST->codegen()) {
+
+ // JIT the module containing the anonymous expression, keeping a handle so
+ // we can free it later.
+ auto H = TheJIT->addModule(std::move(TheModule));
+ InitializeModuleAndPassManager();
+
+ // Search the JIT for the __anon_expr symbol.
+ auto ExprSymbol = TheJIT->findSymbol("__anon_expr");
+ assert(ExprSymbol && "Function not found");
+
+ // Get the symbol's address and cast it to the right type (takes no
+ // arguments, returns a double) so we can call it as a native function.
+ double (*FP)() = (double (*)())(intptr_t)ExprSymbol.getAddress();
+ fprintf(stderr, "Evaluated to %f\n", FP());
+
+ // Delete the anonymous expression module from the JIT.
+ TheJIT->removeModule(H);
+ }
+
+If parsing and codegen succeeed, the next step is to add the module containing
+the top-level expression to the JIT. We do this by calling addModule, which
+triggers code generation for all the functions in the module, and returns a
+handle that can be used to remove the module from the JIT later. Once the module
+has been added to the JIT it can no longer be modified, so we also open a new
+module to hold subsequent code by calling ``InitializeModuleAndPassManager()``.
+
+Once we've added the module to the JIT we need to get a pointer to the final
+generated code. We do this by calling the JIT's findSymbol method, and passing
+the name of the top-level expression function: ``__anon_expr``. Since we just
+added this function, we assert that findSymbol returned a result.
+
+Next, we get the in-memory address of the ``__anon_expr`` function by calling
+``getAddress()`` on the symbol. Recall that we compile top-level expressions
+into a self-contained LLVM function that takes no arguments and returns the
+computed double. Because the LLVM JIT compiler matches the native platform ABI,
+this means that you can just cast the result pointer to a function pointer of
+that type and call it directly. This means, there is no difference between JIT
+compiled code and native machine code that is statically linked into your
+application.
+
+Finally, since we don't support re-evaluation of top-level expressions, we
+remove the module from the JIT when we're done to free the associated memory.
+Recall, however, that the module we created a few lines earlier (via
+``InitializeModuleAndPassManager``) is still open and waiting for new code to be
+added.
+
+With just these two changes, lets see how Kaleidoscope works now!
+
+::
+
+ ready> 4+5;
+ Read top-level expression:
+ define double @0() {
+ entry:
+ ret double 9.000000e+00
+ }
+
+ Evaluated to 9.000000
+
+Well this looks like it is basically working. The dump of the function
+shows the "no argument function that always returns double" that we
+synthesize for each top-level expression that is typed in. This
+demonstrates very basic functionality, but can we do more?
+
+::
+
+ ready> def testfunc(x y) x + y*2;
+ Read function definition:
+ define double @testfunc(double %x, double %y) {
+ entry:
+ %multmp = fmul double %y, 2.000000e+00
+ %addtmp = fadd double %multmp, %x
+ ret double %addtmp
+ }
+
+ ready> testfunc(4, 10);
+ Read top-level expression:
+ define double @1() {
+ entry:
+ %calltmp = call double @testfunc(double 4.000000e+00, double 1.000000e+01)
+ ret double %calltmp
+ }
+
+ Evaluated to 24.000000
+
+ ready> testfunc(5, 10);
+ ready> LLVM ERROR: Program used external function 'testfunc' which could not be resolved!
+
+
+Function definitions and calls also work, but something went very wrong on that
+last line. The call looks valid, so what happened? As you may have guessed from
+the the API a Module is a unit of allocation for the JIT, and testfunc was part
+of the same module that contained anonymous expression. When we removed that
+module from the JIT to free the memory for the anonymous expression, we deleted
+the definition of ``testfunc`` along with it. Then, when we tried to call
+testfunc a second time, the JIT could no longer find it.
+
+The easiest way to fix this is to put the anonymous expression in a separate
+module from the rest of the function definitions. The JIT will happily resolve
+function calls across module boundaries, as long as each of the functions called
+has a prototype, and is added to the JIT before it is called. By putting the
+anonymous expression in a different module we can delete it without affecting
+the rest of the functions.
+
+In fact, we're going to go a step further and put every function in its own
+module. Doing so allows us to exploit a useful property of the KaleidoscopeJIT
+that will make our environment more REPL-like: Functions can be added to the
+JIT more than once (unlike a module where every function must have a unique
+definition). When you look up a symbol in KaleidoscopeJIT it will always return
+the most recent definition:
+
+::
+
+ ready> def foo(x) x + 1;
+ Read function definition:
+ define double @foo(double %x) {
+ entry:
+ %addtmp = fadd double %x, 1.000000e+00
+ ret double %addtmp
+ }
+
+ ready> foo(2);
+ Evaluated to 3.000000
+
+ ready> def foo(x) x + 2;
+ define double @foo(double %x) {
+ entry:
+ %addtmp = fadd double %x, 2.000000e+00
+ ret double %addtmp
+ }
+
+ ready> foo(2);
+ Evaluated to 4.000000
+
+
+To allow each function to live in its own module we'll need a way to
+re-generate previous function declarations into each new module we open:
+
+.. code-block:: c++
+
+ static std::unique_ptr<KaleidoscopeJIT> TheJIT;
+
+ ...
+
+ Function *getFunction(std::string Name) {
+ // First, see if the function has already been added to the current module.
+ if (auto *F = TheModule->getFunction(Name))
+ return F;
+
+ // If not, check whether we can codegen the declaration from some existing
+ // prototype.
+ auto FI = FunctionProtos.find(Name);
+ if (FI != FunctionProtos.end())
+ return FI->second->codegen();
+
+ // If no existing prototype exists, return null.
+ return nullptr;
+ }
+
+ ...
+
+ Value *CallExprAST::codegen() {
+ // Look up the name in the global module table.
+ Function *CalleeF = getFunction(Callee);
+
+ ...
+
+ Function *FunctionAST::codegen() {
+ // Transfer ownership of the prototype to the FunctionProtos map, but keep a
+ // reference to it for use below.
+ auto &P = *Proto;
+ FunctionProtos[Proto->getName()] = std::move(Proto);
+ Function *TheFunction = getFunction(P.getName());
+ if (!TheFunction)
+ return nullptr;
+
+
+To enable this, we'll start by adding a new global, ``FunctionProtos``, that
+holds the most recent prototype for each function. We'll also add a convenience
+method, ``getFunction()``, to replace calls to ``TheModule->getFunction()``.
+Our convenience method searches ``TheModule`` for an existing function
+declaration, falling back to generating a new declaration from FunctionProtos if
+it doesn't find one. In ``CallExprAST::codegen()`` we just need to replace the
+call to ``TheModule->getFunction()``. In ``FunctionAST::codegen()`` we need to
+update the FunctionProtos map first, then call ``getFunction()``. With this
+done, we can always obtain a function declaration in the current module for any
+previously declared function.
+
+We also need to update HandleDefinition and HandleExtern:
+
+.. code-block:: c++
+
+ static void HandleDefinition() {
+ if (auto FnAST = ParseDefinition()) {
+ if (auto *FnIR = FnAST->codegen()) {
+ fprintf(stderr, "Read function definition:");
+ FnIR->dump();
+ TheJIT->addModule(std::move(TheModule));
+ InitializeModuleAndPassManager();
+ }
+ } else {
+ // Skip token for error recovery.
+ getNextToken();
+ }
+ }
+
+ static void HandleExtern() {
+ if (auto ProtoAST = ParseExtern()) {
+ if (auto *FnIR = ProtoAST->codegen()) {
+ fprintf(stderr, "Read extern: ");
+ FnIR->dump();
+ FunctionProtos[ProtoAST->getName()] = std::move(ProtoAST);
+ }
+ } else {
+ // Skip token for error recovery.
+ getNextToken();
+ }
+ }
+
+In HandleDefinition, we add two lines to transfer the newly defined function to
+the JIT and open a new module. In HandleExtern, we just need to add one line to
+add the prototype to FunctionProtos.
+
+With these changes made, lets try our REPL again (I removed the dump of the
+anonymous functions this time, you should get the idea by now :) :
+
+::
+
+ ready> def foo(x) x + 1;
+ ready> foo(2);
+ Evaluated to 3.000000
+
+ ready> def foo(x) x + 2;
+ ready> foo(2);
+ Evaluated to 4.000000
+
+It works!
+
+Even with this simple code, we get some surprisingly powerful capabilities -
+check this out:
+
+::
+
+ ready> extern sin(x);
+ Read extern:
+ declare double @sin(double)
+
+ ready> extern cos(x);
+ Read extern:
+ declare double @cos(double)
+
+ ready> sin(1.0);
+ Read top-level expression:
+ define double @2() {
+ entry:
+ ret double 0x3FEAED548F090CEE
+ }
+
+ Evaluated to 0.841471
+
+ ready> def foo(x) sin(x)*sin(x) + cos(x)*cos(x);
+ Read function definition:
+ define double @foo(double %x) {
+ entry:
+ %calltmp = call double @sin(double %x)
+ %multmp = fmul double %calltmp, %calltmp
+ %calltmp2 = call double @cos(double %x)
+ %multmp4 = fmul double %calltmp2, %calltmp2
+ %addtmp = fadd double %multmp, %multmp4
+ ret double %addtmp
+ }
+
+ ready> foo(4.0);
+ Read top-level expression:
+ define double @3() {
+ entry:
+ %calltmp = call double @foo(double 4.000000e+00)
+ ret double %calltmp
+ }
+
+ Evaluated to 1.000000
+
+Whoa, how does the JIT know about sin and cos? The answer is surprisingly
+simple: The KaleidoscopeJIT has a straightforward symbol resolution rule that
+it uses to find symbols that aren't available in any given module: First
+it searches all the modules that have already been added to the JIT, from the
+most recent to the oldest, to find the newest definition. If no definition is
+found inside the JIT, it falls back to calling "``dlsym("sin")``" on the
+Kaleidoscope process itself. Since "``sin``" is defined within the JIT's
+address space, it simply patches up calls in the module to call the libm
+version of ``sin`` directly.
+
+In the future we'll see how tweaking this symbol resolution rule can be used to
+enable all sorts of useful features, from security (restricting the set of
+symbols available to JIT'd code), to dynamic code generation based on symbol
+names, and even lazy compilation.
+
+One immediate benefit of the symbol resolution rule is that we can now extend
+the language by writing arbitrary C++ code to implement operations. For example,
+if we add:
+
+.. code-block:: c++
+
+ /// putchard - putchar that takes a double and returns 0.
+ extern "C" double putchard(double X) {
+ fputc((char)X, stderr);
+ return 0;
+ }
+
+Now we can produce simple output to the console by using things like:
+"``extern putchard(x); putchard(120);``", which prints a lowercase 'x'
+on the console (120 is the ASCII code for 'x'). Similar code could be
+used to implement file I/O, console input, and many other capabilities
+in Kaleidoscope.
+
+This completes the JIT and optimizer chapter of the Kaleidoscope
+tutorial. At this point, we can compile a non-Turing-complete
+programming language, optimize and JIT compile it in a user-driven way.
+Next up we'll look into `extending the language with control flow
+constructs <LangImpl5.html>`_, tackling some interesting LLVM IR issues
+along the way.
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example, enhanced with
+the LLVM JIT and optimizer. To build this example, use:
+
+.. code-block:: bash
+
+ # Compile
+ clang++ -g toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core mcjit native` -O3 -o toy
+ # Run
+ ./toy
+
+If you are compiling this on Linux, make sure to add the "-rdynamic"
+option as well. This makes sure that the external functions are resolved
+properly at runtime.
+
+Here is the code:
+
+.. literalinclude:: ../../examples/Kaleidoscope/Chapter4/toy.cpp
+ :language: c++
+
+`Next: Extending the language: control flow <LangImpl5.html>`_
+
Added: www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl5.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl5.txt?rev=290368&view=auto
==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl5.txt (added)
+++ www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl5.txt Thu Dec 22 14:04:03 2016
@@ -0,0 +1,790 @@
+==================================================
+Kaleidoscope: Extending the Language: Control Flow
+==================================================
+
+.. contents::
+ :local:
+
+Chapter 5 Introduction
+======================
+
+Welcome to Chapter 5 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. Parts 1-4 described the implementation of
+the simple Kaleidoscope language and included support for generating
+LLVM IR, followed by optimizations and a JIT compiler. Unfortunately, as
+presented, Kaleidoscope is mostly useless: it has no control flow other
+than call and return. This means that you can't have conditional
+branches in the code, significantly limiting its power. In this episode
+of "build that compiler", we'll extend Kaleidoscope to have an
+if/then/else expression plus a simple 'for' loop.
+
+If/Then/Else
+============
+
+Extending Kaleidoscope to support if/then/else is quite straightforward.
+It basically requires adding support for this "new" concept to the
+lexer, parser, AST, and LLVM code emitter. This example is nice, because
+it shows how easy it is to "grow" a language over time, incrementally
+extending it as new ideas are discovered.
+
+Before we get going on "how" we add this extension, lets talk about
+"what" we want. The basic idea is that we want to be able to write this
+sort of thing:
+
+::
+
+ def fib(x)
+ if x < 3 then
+ 1
+ else
+ fib(x-1)+fib(x-2);
+
+In Kaleidoscope, every construct is an expression: there are no
+statements. As such, the if/then/else expression needs to return a value
+like any other. Since we're using a mostly functional form, we'll have
+it evaluate its conditional, then return the 'then' or 'else' value
+based on how the condition was resolved. This is very similar to the C
+"?:" expression.
+
+The semantics of the if/then/else expression is that it evaluates the
+condition to a boolean equality value: 0.0 is considered to be false and
+everything else is considered to be true. If the condition is true, the
+first subexpression is evaluated and returned, if the condition is
+false, the second subexpression is evaluated and returned. Since
+Kaleidoscope allows side-effects, this behavior is important to nail
+down.
+
+Now that we know what we "want", lets break this down into its
+constituent pieces.
+
+Lexer Extensions for If/Then/Else
+---------------------------------
+
+The lexer extensions are straightforward. First we add new enum values
+for the relevant tokens:
+
+.. code-block:: c++
+
+ // control
+ tok_if = -6,
+ tok_then = -7,
+ tok_else = -8,
+
+Once we have that, we recognize the new keywords in the lexer. This is
+pretty simple stuff:
+
+.. code-block:: c++
+
+ ...
+ if (IdentifierStr == "def")
+ return tok_def;
+ if (IdentifierStr == "extern")
+ return tok_extern;
+ if (IdentifierStr == "if")
+ return tok_if;
+ if (IdentifierStr == "then")
+ return tok_then;
+ if (IdentifierStr == "else")
+ return tok_else;
+ return tok_identifier;
+
+AST Extensions for If/Then/Else
+-------------------------------
+
+To represent the new expression we add a new AST node for it:
+
+.. code-block:: c++
+
+ /// IfExprAST - Expression class for if/then/else.
+ class IfExprAST : public ExprAST {
+ std::unique_ptr<ExprAST> Cond, Then, Else;
+
+ public:
+ IfExprAST(std::unique_ptr<ExprAST> Cond, std::unique_ptr<ExprAST> Then,
+ std::unique_ptr<ExprAST> Else)
+ : Cond(std::move(Cond)), Then(std::move(Then)), Else(std::move(Else)) {}
+ virtual Value *codegen();
+ };
+
+The AST node just has pointers to the various subexpressions.
+
+Parser Extensions for If/Then/Else
+----------------------------------
+
+Now that we have the relevant tokens coming from the lexer and we have
+the AST node to build, our parsing logic is relatively straightforward.
+First we define a new parsing function:
+
+.. code-block:: c++
+
+ /// ifexpr ::= 'if' expression 'then' expression 'else' expression
+ static std::unique_ptr<ExprAST> ParseIfExpr() {
+ getNextToken(); // eat the if.
+
+ // condition.
+ auto Cond = ParseExpression();
+ if (!Cond)
+ return nullptr;
+
+ if (CurTok != tok_then)
+ return Error("expected then");
+ getNextToken(); // eat the then
+
+ auto Then = ParseExpression();
+ if (!Then)
+ return nullptr;
+
+ if (CurTok != tok_else)
+ return Error("expected else");
+
+ getNextToken();
+
+ auto Else = ParseExpression();
+ if (!Else)
+ return nullptr;
+
+ return llvm::make_unique<IfExprAST>(std::move(Cond), std::move(Then),
+ std::move(Else));
+ }
+
+Next we hook it up as a primary expression:
+
+.. code-block:: c++
+
+ static std::unique_ptr<ExprAST> ParsePrimary() {
+ switch (CurTok) {
+ default:
+ return Error("unknown token when expecting an expression");
+ case tok_identifier:
+ return ParseIdentifierExpr();
+ case tok_number:
+ return ParseNumberExpr();
+ case '(':
+ return ParseParenExpr();
+ case tok_if:
+ return ParseIfExpr();
+ }
+ }
+
+LLVM IR for If/Then/Else
+------------------------
+
+Now that we have it parsing and building the AST, the final piece is
+adding LLVM code generation support. This is the most interesting part
+of the if/then/else example, because this is where it starts to
+introduce new concepts. All of the code above has been thoroughly
+described in previous chapters.
+
+To motivate the code we want to produce, lets take a look at a simple
+example. Consider:
+
+::
+
+ extern foo();
+ extern bar();
+ def baz(x) if x then foo() else bar();
+
+If you disable optimizations, the code you'll (soon) get from
+Kaleidoscope looks like this:
+
+.. code-block:: llvm
+
+ declare double @foo()
+
+ declare double @bar()
+
+ define double @baz(double %x) {
+ entry:
+ %ifcond = fcmp one double %x, 0.000000e+00
+ br i1 %ifcond, label %then, label %else
+
+ then: ; preds = %entry
+ %calltmp = call double @foo()
+ br label %ifcont
+
+ else: ; preds = %entry
+ %calltmp1 = call double @bar()
+ br label %ifcont
+
+ ifcont: ; preds = %else, %then
+ %iftmp = phi double [ %calltmp, %then ], [ %calltmp1, %else ]
+ ret double %iftmp
+ }
+
+To visualize the control flow graph, you can use a nifty feature of the
+LLVM '`opt <http://llvm.org/cmds/opt.html>`_' tool. If you put this LLVM
+IR into "t.ll" and run "``llvm-as < t.ll | opt -analyze -view-cfg``", `a
+window will pop up <../ProgrammersManual.html#viewing-graphs-while-debugging-code>`_ and you'll
+see this graph:
+
+.. figure:: LangImpl5-cfg.png
+ :align: center
+ :alt: Example CFG
+
+ Example CFG
+
+Another way to get this is to call "``F->viewCFG()``" or
+"``F->viewCFGOnly()``" (where F is a "``Function*``") either by
+inserting actual calls into the code and recompiling or by calling these
+in the debugger. LLVM has many nice features for visualizing various
+graphs.
+
+Getting back to the generated code, it is fairly simple: the entry block
+evaluates the conditional expression ("x" in our case here) and compares
+the result to 0.0 with the "``fcmp one``" instruction ('one' is "Ordered
+and Not Equal"). Based on the result of this expression, the code jumps
+to either the "then" or "else" blocks, which contain the expressions for
+the true/false cases.
+
+Once the then/else blocks are finished executing, they both branch back
+to the 'ifcont' block to execute the code that happens after the
+if/then/else. In this case the only thing left to do is to return to the
+caller of the function. The question then becomes: how does the code
+know which expression to return?
+
+The answer to this question involves an important SSA operation: the
+`Phi
+operation <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_.
+If you're not familiar with SSA, `the wikipedia
+article <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_
+is a good introduction and there are various other introductions to it
+available on your favorite search engine. The short version is that
+"execution" of the Phi operation requires "remembering" which block
+control came from. The Phi operation takes on the value corresponding to
+the input control block. In this case, if control comes in from the
+"then" block, it gets the value of "calltmp". If control comes from the
+"else" block, it gets the value of "calltmp1".
+
+At this point, you are probably starting to think "Oh no! This means my
+simple and elegant front-end will have to start generating SSA form in
+order to use LLVM!". Fortunately, this is not the case, and we strongly
+advise *not* implementing an SSA construction algorithm in your
+front-end unless there is an amazingly good reason to do so. In
+practice, there are two sorts of values that float around in code
+written for your average imperative programming language that might need
+Phi nodes:
+
+#. Code that involves user variables: ``x = 1; x = x + 1;``
+#. Values that are implicit in the structure of your AST, such as the
+ Phi node in this case.
+
+In `Chapter 7 <LangImpl7.html>`_ of this tutorial ("mutable variables"),
+we'll talk about #1 in depth. For now, just believe me that you don't
+need SSA construction to handle this case. For #2, you have the choice
+of using the techniques that we will describe for #1, or you can insert
+Phi nodes directly, if convenient. In this case, it is really
+easy to generate the Phi node, so we choose to do it directly.
+
+Okay, enough of the motivation and overview, lets generate code!
+
+Code Generation for If/Then/Else
+--------------------------------
+
+In order to generate code for this, we implement the ``codegen`` method
+for ``IfExprAST``:
+
+.. code-block:: c++
+
+ Value *IfExprAST::codegen() {
+ Value *CondV = Cond->codegen();
+ if (!CondV)
+ return nullptr;
+
+ // Convert condition to a bool by comparing equal to 0.0.
+ CondV = Builder.CreateFCmpONE(
+ CondV, ConstantFP::get(getGlobalContext(), APFloat(0.0)), "ifcond");
+
+This code is straightforward and similar to what we saw before. We emit
+the expression for the condition, then compare that value to zero to get
+a truth value as a 1-bit (bool) value.
+
+.. code-block:: c++
+
+ Function *TheFunction = Builder.GetInsertBlock()->getParent();
+
+ // Create blocks for the then and else cases. Insert the 'then' block at the
+ // end of the function.
+ BasicBlock *ThenBB =
+ BasicBlock::Create(getGlobalContext(), "then", TheFunction);
+ BasicBlock *ElseBB = BasicBlock::Create(getGlobalContext(), "else");
+ BasicBlock *MergeBB = BasicBlock::Create(getGlobalContext(), "ifcont");
+
+ Builder.CreateCondBr(CondV, ThenBB, ElseBB);
+
+This code creates the basic blocks that are related to the if/then/else
+statement, and correspond directly to the blocks in the example above.
+The first line gets the current Function object that is being built. It
+gets this by asking the builder for the current BasicBlock, and asking
+that block for its "parent" (the function it is currently embedded
+into).
+
+Once it has that, it creates three blocks. Note that it passes
+"TheFunction" into the constructor for the "then" block. This causes the
+constructor to automatically insert the new block into the end of the
+specified function. The other two blocks are created, but aren't yet
+inserted into the function.
+
+Once the blocks are created, we can emit the conditional branch that
+chooses between them. Note that creating new blocks does not implicitly
+affect the IRBuilder, so it is still inserting into the block that the
+condition went into. Also note that it is creating a branch to the
+"then" block and the "else" block, even though the "else" block isn't
+inserted into the function yet. This is all ok: it is the standard way
+that LLVM supports forward references.
+
+.. code-block:: c++
+
+ // Emit then value.
+ Builder.SetInsertPoint(ThenBB);
+
+ Value *ThenV = Then->codegen();
+ if (!ThenV)
+ return nullptr;
+
+ Builder.CreateBr(MergeBB);
+ // Codegen of 'Then' can change the current block, update ThenBB for the PHI.
+ ThenBB = Builder.GetInsertBlock();
+
+After the conditional branch is inserted, we move the builder to start
+inserting into the "then" block. Strictly speaking, this call moves the
+insertion point to be at the end of the specified block. However, since
+the "then" block is empty, it also starts out by inserting at the
+beginning of the block. :)
+
+Once the insertion point is set, we recursively codegen the "then"
+expression from the AST. To finish off the "then" block, we create an
+unconditional branch to the merge block. One interesting (and very
+important) aspect of the LLVM IR is that it `requires all basic blocks
+to be "terminated" <../LangRef.html#functionstructure>`_ with a `control
+flow instruction <../LangRef.html#terminators>`_ such as return or
+branch. This means that all control flow, *including fall throughs* must
+be made explicit in the LLVM IR. If you violate this rule, the verifier
+will emit an error.
+
+The final line here is quite subtle, but is very important. The basic
+issue is that when we create the Phi node in the merge block, we need to
+set up the block/value pairs that indicate how the Phi will work.
+Importantly, the Phi node expects to have an entry for each predecessor
+of the block in the CFG. Why then, are we getting the current block when
+we just set it to ThenBB 5 lines above? The problem is that the "Then"
+expression may actually itself change the block that the Builder is
+emitting into if, for example, it contains a nested "if/then/else"
+expression. Because calling ``codegen()`` recursively could arbitrarily change
+the notion of the current block, we are required to get an up-to-date
+value for code that will set up the Phi node.
+
+.. code-block:: c++
+
+ // Emit else block.
+ TheFunction->getBasicBlockList().push_back(ElseBB);
+ Builder.SetInsertPoint(ElseBB);
+
+ Value *ElseV = Else->codegen();
+ if (!ElseV)
+ return nullptr;
+
+ Builder.CreateBr(MergeBB);
+ // codegen of 'Else' can change the current block, update ElseBB for the PHI.
+ ElseBB = Builder.GetInsertBlock();
+
+Code generation for the 'else' block is basically identical to codegen
+for the 'then' block. The only significant difference is the first line,
+which adds the 'else' block to the function. Recall previously that the
+'else' block was created, but not added to the function. Now that the
+'then' and 'else' blocks are emitted, we can finish up with the merge
+code:
+
+.. code-block:: c++
+
+ // Emit merge block.
+ TheFunction->getBasicBlockList().push_back(MergeBB);
+ Builder.SetInsertPoint(MergeBB);
+ PHINode *PN =
+ Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()), 2, "iftmp");
+
+ PN->addIncoming(ThenV, ThenBB);
+ PN->addIncoming(ElseV, ElseBB);
+ return PN;
+ }
+
+The first two lines here are now familiar: the first adds the "merge"
+block to the Function object (it was previously floating, like the else
+block above). The second changes the insertion point so that newly
+created code will go into the "merge" block. Once that is done, we need
+to create the PHI node and set up the block/value pairs for the PHI.
+
+Finally, the CodeGen function returns the phi node as the value computed
+by the if/then/else expression. In our example above, this returned
+value will feed into the code for the top-level function, which will
+create the return instruction.
+
+Overall, we now have the ability to execute conditional code in
+Kaleidoscope. With this extension, Kaleidoscope is a fairly complete
+language that can calculate a wide variety of numeric functions. Next up
+we'll add another useful expression that is familiar from non-functional
+languages...
+
+'for' Loop Expression
+=====================
+
+Now that we know how to add basic control flow constructs to the
+language, we have the tools to add more powerful things. Lets add
+something more aggressive, a 'for' expression:
+
+::
+
+ extern putchard(char)
+ def printstar(n)
+ for i = 1, i < n, 1.0 in
+ putchard(42); # ascii 42 = '*'
+
+ # print 100 '*' characters
+ printstar(100);
+
+This expression defines a new variable ("i" in this case) which iterates
+from a starting value, while the condition ("i < n" in this case) is
+true, incrementing by an optional step value ("1.0" in this case). If
+the step value is omitted, it defaults to 1.0. While the loop is true,
+it executes its body expression. Because we don't have anything better
+to return, we'll just define the loop as always returning 0.0. In the
+future when we have mutable variables, it will get more useful.
+
+As before, lets talk about the changes that we need to Kaleidoscope to
+support this.
+
+Lexer Extensions for the 'for' Loop
+-----------------------------------
+
+The lexer extensions are the same sort of thing as for if/then/else:
+
+.. code-block:: c++
+
+ ... in enum Token ...
+ // control
+ tok_if = -6, tok_then = -7, tok_else = -8,
+ tok_for = -9, tok_in = -10
+
+ ... in gettok ...
+ if (IdentifierStr == "def")
+ return tok_def;
+ if (IdentifierStr == "extern")
+ return tok_extern;
+ if (IdentifierStr == "if")
+ return tok_if;
+ if (IdentifierStr == "then")
+ return tok_then;
+ if (IdentifierStr == "else")
+ return tok_else;
+ if (IdentifierStr == "for")
+ return tok_for;
+ if (IdentifierStr == "in")
+ return tok_in;
+ return tok_identifier;
+
+AST Extensions for the 'for' Loop
+---------------------------------
+
+The AST node is just as simple. It basically boils down to capturing the
+variable name and the constituent expressions in the node.
+
+.. code-block:: c++
+
+ /// ForExprAST - Expression class for for/in.
+ class ForExprAST : public ExprAST {
+ std::string VarName;
+ std::unique_ptr<ExprAST> Start, End, Step, Body;
+
+ public:
+ ForExprAST(const std::string &VarName, std::unique_ptr<ExprAST> Start,
+ std::unique_ptr<ExprAST> End, std::unique_ptr<ExprAST> Step,
+ std::unique_ptr<ExprAST> Body)
+ : VarName(VarName), Start(std::move(Start)), End(std::move(End)),
+ Step(std::move(Step)), Body(std::move(Body)) {}
+ virtual Value *codegen();
+ };
+
+Parser Extensions for the 'for' Loop
+------------------------------------
+
+The parser code is also fairly standard. The only interesting thing here
+is handling of the optional step value. The parser code handles it by
+checking to see if the second comma is present. If not, it sets the step
+value to null in the AST node:
+
+.. code-block:: c++
+
+ /// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression
+ static std::unique_ptr<ExprAST> ParseForExpr() {
+ getNextToken(); // eat the for.
+
+ if (CurTok != tok_identifier)
+ return Error("expected identifier after for");
+
+ std::string IdName = IdentifierStr;
+ getNextToken(); // eat identifier.
+
+ if (CurTok != '=')
+ return Error("expected '=' after for");
+ getNextToken(); // eat '='.
+
+
+ auto Start = ParseExpression();
+ if (!Start)
+ return nullptr;
+ if (CurTok != ',')
+ return Error("expected ',' after for start value");
+ getNextToken();
+
+ auto End = ParseExpression();
+ if (!End)
+ return nullptr;
+
+ // The step value is optional.
+ std::unique_ptr<ExprAST> Step;
+ if (CurTok == ',') {
+ getNextToken();
+ Step = ParseExpression();
+ if (!Step)
+ return nullptr;
+ }
+
+ if (CurTok != tok_in)
+ return Error("expected 'in' after for");
+ getNextToken(); // eat 'in'.
+
+ auto Body = ParseExpression();
+ if (!Body)
+ return nullptr;
+
+ return llvm::make_unique<ForExprAST>(IdName, std::move(Start),
+ std::move(End), std::move(Step),
+ std::move(Body));
+ }
+
+LLVM IR for the 'for' Loop
+--------------------------
+
+Now we get to the good part: the LLVM IR we want to generate for this
+thing. With the simple example above, we get this LLVM IR (note that
+this dump is generated with optimizations disabled for clarity):
+
+.. code-block:: llvm
+
+ declare double @putchard(double)
+
+ define double @printstar(double %n) {
+ entry:
+ ; initial value = 1.0 (inlined into phi)
+ br label %loop
+
+ loop: ; preds = %loop, %entry
+ %i = phi double [ 1.000000e+00, %entry ], [ %nextvar, %loop ]
+ ; body
+ %calltmp = call double @putchard(double 4.200000e+01)
+ ; increment
+ %nextvar = fadd double %i, 1.000000e+00
+
+ ; termination test
+ %cmptmp = fcmp ult double %i, %n
+ %booltmp = uitofp i1 %cmptmp to double
+ %loopcond = fcmp one double %booltmp, 0.000000e+00
+ br i1 %loopcond, label %loop, label %afterloop
+
+ afterloop: ; preds = %loop
+ ; loop always returns 0.0
+ ret double 0.000000e+00
+ }
+
+This loop contains all the same constructs we saw before: a phi node,
+several expressions, and some basic blocks. Lets see how this fits
+together.
+
+Code Generation for the 'for' Loop
+----------------------------------
+
+The first part of codegen is very simple: we just output the start
+expression for the loop value:
+
+.. code-block:: c++
+
+ Value *ForExprAST::codegen() {
+ // Emit the start code first, without 'variable' in scope.
+ Value *StartVal = Start->codegen();
+ if (StartVal == 0) return 0;
+
+With this out of the way, the next step is to set up the LLVM basic
+block for the start of the loop body. In the case above, the whole loop
+body is one block, but remember that the body code itself could consist
+of multiple blocks (e.g. if it contains an if/then/else or a for/in
+expression).
+
+.. code-block:: c++
+
+ // Make the new basic block for the loop header, inserting after current
+ // block.
+ Function *TheFunction = Builder.GetInsertBlock()->getParent();
+ BasicBlock *PreheaderBB = Builder.GetInsertBlock();
+ BasicBlock *LoopBB =
+ BasicBlock::Create(getGlobalContext(), "loop", TheFunction);
+
+ // Insert an explicit fall through from the current block to the LoopBB.
+ Builder.CreateBr(LoopBB);
+
+This code is similar to what we saw for if/then/else. Because we will
+need it to create the Phi node, we remember the block that falls through
+into the loop. Once we have that, we create the actual block that starts
+the loop and create an unconditional branch for the fall-through between
+the two blocks.
+
+.. code-block:: c++
+
+ // Start insertion in LoopBB.
+ Builder.SetInsertPoint(LoopBB);
+
+ // Start the PHI node with an entry for Start.
+ PHINode *Variable = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()),
+ 2, VarName.c_str());
+ Variable->addIncoming(StartVal, PreheaderBB);
+
+Now that the "preheader" for the loop is set up, we switch to emitting
+code for the loop body. To begin with, we move the insertion point and
+create the PHI node for the loop induction variable. Since we already
+know the incoming value for the starting value, we add it to the Phi
+node. Note that the Phi will eventually get a second value for the
+backedge, but we can't set it up yet (because it doesn't exist!).
+
+.. code-block:: c++
+
+ // Within the loop, the variable is defined equal to the PHI node. If it
+ // shadows an existing variable, we have to restore it, so save it now.
+ Value *OldVal = NamedValues[VarName];
+ NamedValues[VarName] = Variable;
+
+ // Emit the body of the loop. This, like any other expr, can change the
+ // current BB. Note that we ignore the value computed by the body, but don't
+ // allow an error.
+ if (!Body->codegen())
+ return nullptr;
+
+Now the code starts to get more interesting. Our 'for' loop introduces a
+new variable to the symbol table. This means that our symbol table can
+now contain either function arguments or loop variables. To handle this,
+before we codegen the body of the loop, we add the loop variable as the
+current value for its name. Note that it is possible that there is a
+variable of the same name in the outer scope. It would be easy to make
+this an error (emit an error and return null if there is already an
+entry for VarName) but we choose to allow shadowing of variables. In
+order to handle this correctly, we remember the Value that we are
+potentially shadowing in ``OldVal`` (which will be null if there is no
+shadowed variable).
+
+Once the loop variable is set into the symbol table, the code
+recursively codegen's the body. This allows the body to use the loop
+variable: any references to it will naturally find it in the symbol
+table.
+
+.. code-block:: c++
+
+ // Emit the step value.
+ Value *StepVal = nullptr;
+ if (Step) {
+ StepVal = Step->codegen();
+ if (!StepVal)
+ return nullptr;
+ } else {
+ // If not specified, use 1.0.
+ StepVal = ConstantFP::get(getGlobalContext(), APFloat(1.0));
+ }
+
+ Value *NextVar = Builder.CreateFAdd(Variable, StepVal, "nextvar");
+
+Now that the body is emitted, we compute the next value of the iteration
+variable by adding the step value, or 1.0 if it isn't present.
+'``NextVar``' will be the value of the loop variable on the next
+iteration of the loop.
+
+.. code-block:: c++
+
+ // Compute the end condition.
+ Value *EndCond = End->codegen();
+ if (!EndCond)
+ return nullptr;
+
+ // Convert condition to a bool by comparing equal to 0.0.
+ EndCond = Builder.CreateFCmpONE(
+ EndCond, ConstantFP::get(getGlobalContext(), APFloat(0.0)), "loopcond");
+
+Finally, we evaluate the exit value of the loop, to determine whether
+the loop should exit. This mirrors the condition evaluation for the
+if/then/else statement.
+
+.. code-block:: c++
+
+ // Create the "after loop" block and insert it.
+ BasicBlock *LoopEndBB = Builder.GetInsertBlock();
+ BasicBlock *AfterBB =
+ BasicBlock::Create(getGlobalContext(), "afterloop", TheFunction);
+
+ // Insert the conditional branch into the end of LoopEndBB.
+ Builder.CreateCondBr(EndCond, LoopBB, AfterBB);
+
+ // Any new code will be inserted in AfterBB.
+ Builder.SetInsertPoint(AfterBB);
+
+With the code for the body of the loop complete, we just need to finish
+up the control flow for it. This code remembers the end block (for the
+phi node), then creates the block for the loop exit ("afterloop"). Based
+on the value of the exit condition, it creates a conditional branch that
+chooses between executing the loop again and exiting the loop. Any
+future code is emitted in the "afterloop" block, so it sets the
+insertion position to it.
+
+.. code-block:: c++
+
+ // Add a new entry to the PHI node for the backedge.
+ Variable->addIncoming(NextVar, LoopEndBB);
+
+ // Restore the unshadowed variable.
+ if (OldVal)
+ NamedValues[VarName] = OldVal;
+ else
+ NamedValues.erase(VarName);
+
+ // for expr always returns 0.0.
+ return Constant::getNullValue(Type::getDoubleTy(getGlobalContext()));
+ }
+
+The final code handles various cleanups: now that we have the "NextVar"
+value, we can add the incoming value to the loop PHI node. After that,
+we remove the loop variable from the symbol table, so that it isn't in
+scope after the for loop. Finally, code generation of the for loop
+always returns 0.0, so that is what we return from
+``ForExprAST::codegen()``.
+
+With this, we conclude the "adding control flow to Kaleidoscope" chapter
+of the tutorial. In this chapter we added two control flow constructs,
+and used them to motivate a couple of aspects of the LLVM IR that are
+important for front-end implementors to know. In the next chapter of our
+saga, we will get a bit crazier and add `user-defined
+operators <LangImpl6.html>`_ to our poor innocent language.
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example, enhanced with
+the if/then/else and for expressions.. To build this example, use:
+
+.. code-block:: bash
+
+ # Compile
+ clang++ -g toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core mcjit native` -O3 -o toy
+ # Run
+ ./toy
+
+Here is the code:
+
+.. literalinclude:: ../../examples/Kaleidoscope/Chapter5/toy.cpp
+ :language: c++
+
+`Next: Extending the language: user-defined operators <LangImpl6.html>`_
+
Added: www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl6.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl6.txt?rev=290368&view=auto
==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl6.txt (added)
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@@ -0,0 +1,768 @@
+============================================================
+Kaleidoscope: Extending the Language: User-defined Operators
+============================================================
+
+.. contents::
+ :local:
+
+Chapter 6 Introduction
+======================
+
+Welcome to Chapter 6 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. At this point in our tutorial, we now
+have a fully functional language that is fairly minimal, but also
+useful. There is still one big problem with it, however. Our language
+doesn't have many useful operators (like division, logical negation, or
+even any comparisons besides less-than).
+
+This chapter of the tutorial takes a wild digression into adding
+user-defined operators to the simple and beautiful Kaleidoscope
+language. This digression now gives us a simple and ugly language in
+some ways, but also a powerful one at the same time. One of the great
+things about creating your own language is that you get to decide what
+is good or bad. In this tutorial we'll assume that it is okay to use
+this as a way to show some interesting parsing techniques.
+
+At the end of this tutorial, we'll run through an example Kaleidoscope
+application that `renders the Mandelbrot set <#kicking-the-tires>`_. This gives an
+example of what you can build with Kaleidoscope and its feature set.
+
+User-defined Operators: the Idea
+================================
+
+The "operator overloading" that we will add to Kaleidoscope is more
+general than languages like C++. In C++, you are only allowed to
+redefine existing operators: you can't programatically change the
+grammar, introduce new operators, change precedence levels, etc. In this
+chapter, we will add this capability to Kaleidoscope, which will let the
+user round out the set of operators that are supported.
+
+The point of going into user-defined operators in a tutorial like this
+is to show the power and flexibility of using a hand-written parser.
+Thus far, the parser we have been implementing uses recursive descent
+for most parts of the grammar and operator precedence parsing for the
+expressions. See `Chapter 2 <LangImpl2.html>`_ for details. Without
+using operator precedence parsing, it would be very difficult to allow
+the programmer to introduce new operators into the grammar: the grammar
+is dynamically extensible as the JIT runs.
+
+The two specific features we'll add are programmable unary operators
+(right now, Kaleidoscope has no unary operators at all) as well as
+binary operators. An example of this is:
+
+::
+
+ # Logical unary not.
+ def unary!(v)
+ if v then
+ 0
+ else
+ 1;
+
+ # Define > with the same precedence as <.
+ def binary> 10 (LHS RHS)
+ RHS < LHS;
+
+ # Binary "logical or", (note that it does not "short circuit")
+ def binary| 5 (LHS RHS)
+ if LHS then
+ 1
+ else if RHS then
+ 1
+ else
+ 0;
+
+ # Define = with slightly lower precedence than relationals.
+ def binary= 9 (LHS RHS)
+ !(LHS < RHS | LHS > RHS);
+
+Many languages aspire to being able to implement their standard runtime
+library in the language itself. In Kaleidoscope, we can implement
+significant parts of the language in the library!
+
+We will break down implementation of these features into two parts:
+implementing support for user-defined binary operators and adding unary
+operators.
+
+User-defined Binary Operators
+=============================
+
+Adding support for user-defined binary operators is pretty simple with
+our current framework. We'll first add support for the unary/binary
+keywords:
+
+.. code-block:: c++
+
+ enum Token {
+ ...
+ // operators
+ tok_binary = -11,
+ tok_unary = -12
+ };
+ ...
+ static int gettok() {
+ ...
+ if (IdentifierStr == "for")
+ return tok_for;
+ if (IdentifierStr == "in")
+ return tok_in;
+ if (IdentifierStr == "binary")
+ return tok_binary;
+ if (IdentifierStr == "unary")
+ return tok_unary;
+ return tok_identifier;
+
+This just adds lexer support for the unary and binary keywords, like we
+did in `previous chapters <LangImpl5.html#lexer-extensions-for-if-then-else>`_. One nice thing
+about our current AST, is that we represent binary operators with full
+generalisation by using their ASCII code as the opcode. For our extended
+operators, we'll use this same representation, so we don't need any new
+AST or parser support.
+
+On the other hand, we have to be able to represent the definitions of
+these new operators, in the "def binary\| 5" part of the function
+definition. In our grammar so far, the "name" for the function
+definition is parsed as the "prototype" production and into the
+``PrototypeAST`` AST node. To represent our new user-defined operators
+as prototypes, we have to extend the ``PrototypeAST`` AST node like
+this:
+
+.. code-block:: c++
+
+ /// PrototypeAST - This class represents the "prototype" for a function,
+ /// which captures its argument names as well as if it is an operator.
+ class PrototypeAST {
+ std::string Name;
+ std::vector<std::string> Args;
+ bool IsOperator;
+ unsigned Precedence; // Precedence if a binary op.
+
+ public:
+ PrototypeAST(const std::string &name, std::vector<std::string> Args,
+ bool IsOperator = false, unsigned Prec = 0)
+ : Name(name), Args(std::move(Args)), IsOperator(IsOperator),
+ Precedence(Prec) {}
+
+ bool isUnaryOp() const { return IsOperator && Args.size() == 1; }
+ bool isBinaryOp() const { return IsOperator && Args.size() == 2; }
+
+ char getOperatorName() const {
+ assert(isUnaryOp() || isBinaryOp());
+ return Name[Name.size()-1];
+ }
+
+ unsigned getBinaryPrecedence() const { return Precedence; }
+
+ Function *codegen();
+ };
+
+Basically, in addition to knowing a name for the prototype, we now keep
+track of whether it was an operator, and if it was, what precedence
+level the operator is at. The precedence is only used for binary
+operators (as you'll see below, it just doesn't apply for unary
+operators). Now that we have a way to represent the prototype for a
+user-defined operator, we need to parse it:
+
+.. code-block:: c++
+
+ /// prototype
+ /// ::= id '(' id* ')'
+ /// ::= binary LETTER number? (id, id)
+ static std::unique_ptr<PrototypeAST> ParsePrototype() {
+ std::string FnName;
+
+ unsigned Kind = 0; // 0 = identifier, 1 = unary, 2 = binary.
+ unsigned BinaryPrecedence = 30;
+
+ switch (CurTok) {
+ default:
+ return ErrorP("Expected function name in prototype");
+ case tok_identifier:
+ FnName = IdentifierStr;
+ Kind = 0;
+ getNextToken();
+ break;
+ case tok_binary:
+ getNextToken();
+ if (!isascii(CurTok))
+ return ErrorP("Expected binary operator");
+ FnName = "binary";
+ FnName += (char)CurTok;
+ Kind = 2;
+ getNextToken();
+
+ // Read the precedence if present.
+ if (CurTok == tok_number) {
+ if (NumVal < 1 || NumVal > 100)
+ return ErrorP("Invalid precedecnce: must be 1..100");
+ BinaryPrecedence = (unsigned)NumVal;
+ getNextToken();
+ }
+ break;
+ }
+
+ if (CurTok != '(')
+ return ErrorP("Expected '(' in prototype");
+
+ std::vector<std::string> ArgNames;
+ while (getNextToken() == tok_identifier)
+ ArgNames.push_back(IdentifierStr);
+ if (CurTok != ')')
+ return ErrorP("Expected ')' in prototype");
+
+ // success.
+ getNextToken(); // eat ')'.
+
+ // Verify right number of names for operator.
+ if (Kind && ArgNames.size() != Kind)
+ return ErrorP("Invalid number of operands for operator");
+
+ return llvm::make_unique<PrototypeAST>(FnName, std::move(ArgNames), Kind != 0,
+ BinaryPrecedence);
+ }
+
+This is all fairly straightforward parsing code, and we have already
+seen a lot of similar code in the past. One interesting part about the
+code above is the couple lines that set up ``FnName`` for binary
+operators. This builds names like "binary@" for a newly defined "@"
+operator. This then takes advantage of the fact that symbol names in the
+LLVM symbol table are allowed to have any character in them, including
+embedded nul characters.
+
+The next interesting thing to add, is codegen support for these binary
+operators. Given our current structure, this is a simple addition of a
+default case for our existing binary operator node:
+
+.. code-block:: c++
+
+ Value *BinaryExprAST::codegen() {
+ Value *L = LHS->codegen();
+ Value *R = RHS->codegen();
+ if (!L || !R)
+ return nullptr;
+
+ switch (Op) {
+ case '+':
+ return Builder.CreateFAdd(L, R, "addtmp");
+ case '-':
+ return Builder.CreateFSub(L, R, "subtmp");
+ case '*':
+ return Builder.CreateFMul(L, R, "multmp");
+ case '<':
+ L = Builder.CreateFCmpULT(L, R, "cmptmp");
+ // Convert bool 0/1 to double 0.0 or 1.0
+ return Builder.CreateUIToFP(L, Type::getDoubleTy(getGlobalContext()),
+ "booltmp");
+ default:
+ break;
+ }
+
+ // If it wasn't a builtin binary operator, it must be a user defined one. Emit
+ // a call to it.
+ Function *F = TheModule->getFunction(std::string("binary") + Op);
+ assert(F && "binary operator not found!");
+
+ Value *Ops[2] = { L, R };
+ return Builder.CreateCall(F, Ops, "binop");
+ }
+
+As you can see above, the new code is actually really simple. It just
+does a lookup for the appropriate operator in the symbol table and
+generates a function call to it. Since user-defined operators are just
+built as normal functions (because the "prototype" boils down to a
+function with the right name) everything falls into place.
+
+The final piece of code we are missing, is a bit of top-level magic:
+
+.. code-block:: c++
+
+ Function *FunctionAST::codegen() {
+ NamedValues.clear();
+
+ Function *TheFunction = Proto->codegen();
+ if (!TheFunction)
+ return nullptr;
+
+ // If this is an operator, install it.
+ if (Proto->isBinaryOp())
+ BinopPrecedence[Proto->getOperatorName()] = Proto->getBinaryPrecedence();
+
+ // Create a new basic block to start insertion into.
+ BasicBlock *BB = BasicBlock::Create(getGlobalContext(), "entry", TheFunction);
+ Builder.SetInsertPoint(BB);
+
+ if (Value *RetVal = Body->codegen()) {
+ ...
+
+Basically, before codegening a function, if it is a user-defined
+operator, we register it in the precedence table. This allows the binary
+operator parsing logic we already have in place to handle it. Since we
+are working on a fully-general operator precedence parser, this is all
+we need to do to "extend the grammar".
+
+Now we have useful user-defined binary operators. This builds a lot on
+the previous framework we built for other operators. Adding unary
+operators is a bit more challenging, because we don't have any framework
+for it yet - lets see what it takes.
+
+User-defined Unary Operators
+============================
+
+Since we don't currently support unary operators in the Kaleidoscope
+language, we'll need to add everything to support them. Above, we added
+simple support for the 'unary' keyword to the lexer. In addition to
+that, we need an AST node:
+
+.. code-block:: c++
+
+ /// UnaryExprAST - Expression class for a unary operator.
+ class UnaryExprAST : public ExprAST {
+ char Opcode;
+ std::unique_ptr<ExprAST> Operand;
+
+ public:
+ UnaryExprAST(char Opcode, std::unique_ptr<ExprAST> Operand)
+ : Opcode(Opcode), Operand(std::move(Operand)) {}
+ virtual Value *codegen();
+ };
+
+This AST node is very simple and obvious by now. It directly mirrors the
+binary operator AST node, except that it only has one child. With this,
+we need to add the parsing logic. Parsing a unary operator is pretty
+simple: we'll add a new function to do it:
+
+.. code-block:: c++
+
+ /// unary
+ /// ::= primary
+ /// ::= '!' unary
+ static std::unique_ptr<ExprAST> ParseUnary() {
+ // If the current token is not an operator, it must be a primary expr.
+ if (!isascii(CurTok) || CurTok == '(' || CurTok == ',')
+ return ParsePrimary();
+
+ // If this is a unary operator, read it.
+ int Opc = CurTok;
+ getNextToken();
+ if (auto Operand = ParseUnary())
+ return llvm::unique_ptr<UnaryExprAST>(Opc, std::move(Operand));
+ return nullptr;
+ }
+
+The grammar we add is pretty straightforward here. If we see a unary
+operator when parsing a primary operator, we eat the operator as a
+prefix and parse the remaining piece as another unary operator. This
+allows us to handle multiple unary operators (e.g. "!!x"). Note that
+unary operators can't have ambiguous parses like binary operators can,
+so there is no need for precedence information.
+
+The problem with this function, is that we need to call ParseUnary from
+somewhere. To do this, we change previous callers of ParsePrimary to
+call ParseUnary instead:
+
+.. code-block:: c++
+
+ /// binoprhs
+ /// ::= ('+' unary)*
+ static std::unique_ptr<ExprAST> ParseBinOpRHS(int ExprPrec,
+ std::unique_ptr<ExprAST> LHS) {
+ ...
+ // Parse the unary expression after the binary operator.
+ auto RHS = ParseUnary();
+ if (!RHS)
+ return nullptr;
+ ...
+ }
+ /// expression
+ /// ::= unary binoprhs
+ ///
+ static std::unique_ptr<ExprAST> ParseExpression() {
+ auto LHS = ParseUnary();
+ if (!LHS)
+ return nullptr;
+
+ return ParseBinOpRHS(0, std::move(LHS));
+ }
+
+With these two simple changes, we are now able to parse unary operators
+and build the AST for them. Next up, we need to add parser support for
+prototypes, to parse the unary operator prototype. We extend the binary
+operator code above with:
+
+.. code-block:: c++
+
+ /// prototype
+ /// ::= id '(' id* ')'
+ /// ::= binary LETTER number? (id, id)
+ /// ::= unary LETTER (id)
+ static std::unique_ptr<PrototypeAST> ParsePrototype() {
+ std::string FnName;
+
+ unsigned Kind = 0; // 0 = identifier, 1 = unary, 2 = binary.
+ unsigned BinaryPrecedence = 30;
+
+ switch (CurTok) {
+ default:
+ return ErrorP("Expected function name in prototype");
+ case tok_identifier:
+ FnName = IdentifierStr;
+ Kind = 0;
+ getNextToken();
+ break;
+ case tok_unary:
+ getNextToken();
+ if (!isascii(CurTok))
+ return ErrorP("Expected unary operator");
+ FnName = "unary";
+ FnName += (char)CurTok;
+ Kind = 1;
+ getNextToken();
+ break;
+ case tok_binary:
+ ...
+
+As with binary operators, we name unary operators with a name that
+includes the operator character. This assists us at code generation
+time. Speaking of, the final piece we need to add is codegen support for
+unary operators. It looks like this:
+
+.. code-block:: c++
+
+ Value *UnaryExprAST::codegen() {
+ Value *OperandV = Operand->codegen();
+ if (!OperandV)
+ return nullptr;
+
+ Function *F = TheModule->getFunction(std::string("unary")+Opcode);
+ if (!F)
+ return ErrorV("Unknown unary operator");
+
+ return Builder.CreateCall(F, OperandV, "unop");
+ }
+
+This code is similar to, but simpler than, the code for binary
+operators. It is simpler primarily because it doesn't need to handle any
+predefined operators.
+
+Kicking the Tires
+=================
+
+It is somewhat hard to believe, but with a few simple extensions we've
+covered in the last chapters, we have grown a real-ish language. With
+this, we can do a lot of interesting things, including I/O, math, and a
+bunch of other things. For example, we can now add a nice sequencing
+operator (printd is defined to print out the specified value and a
+newline):
+
+::
+
+ ready> extern printd(x);
+ Read extern:
+ declare double @printd(double)
+
+ ready> def binary : 1 (x y) 0; # Low-precedence operator that ignores operands.
+ ..
+ ready> printd(123) : printd(456) : printd(789);
+ 123.000000
+ 456.000000
+ 789.000000
+ Evaluated to 0.000000
+
+We can also define a bunch of other "primitive" operations, such as:
+
+::
+
+ # Logical unary not.
+ def unary!(v)
+ if v then
+ 0
+ else
+ 1;
+
+ # Unary negate.
+ def unary-(v)
+ 0-v;
+
+ # Define > with the same precedence as <.
+ def binary> 10 (LHS RHS)
+ RHS < LHS;
+
+ # Binary logical or, which does not short circuit.
+ def binary| 5 (LHS RHS)
+ if LHS then
+ 1
+ else if RHS then
+ 1
+ else
+ 0;
+
+ # Binary logical and, which does not short circuit.
+ def binary& 6 (LHS RHS)
+ if !LHS then
+ 0
+ else
+ !!RHS;
+
+ # Define = with slightly lower precedence than relationals.
+ def binary = 9 (LHS RHS)
+ !(LHS < RHS | LHS > RHS);
+
+ # Define ':' for sequencing: as a low-precedence operator that ignores operands
+ # and just returns the RHS.
+ def binary : 1 (x y) y;
+
+Given the previous if/then/else support, we can also define interesting
+functions for I/O. For example, the following prints out a character
+whose "density" reflects the value passed in: the lower the value, the
+denser the character:
+
+::
+
+ ready>
+
+ extern putchard(char)
+ def printdensity(d)
+ if d > 8 then
+ putchard(32) # ' '
+ else if d > 4 then
+ putchard(46) # '.'
+ else if d > 2 then
+ putchard(43) # '+'
+ else
+ putchard(42); # '*'
+ ...
+ ready> printdensity(1): printdensity(2): printdensity(3):
+ printdensity(4): printdensity(5): printdensity(9):
+ putchard(10);
+ **++.
+ Evaluated to 0.000000
+
+Based on these simple primitive operations, we can start to define more
+interesting things. For example, here's a little function that solves
+for the number of iterations it takes a function in the complex plane to
+converge:
+
+::
+
+ # Determine whether the specific location diverges.
+ # Solve for z = z^2 + c in the complex plane.
+ def mandleconverger(real imag iters creal cimag)
+ if iters > 255 | (real*real + imag*imag > 4) then
+ iters
+ else
+ mandleconverger(real*real - imag*imag + creal,
+ 2*real*imag + cimag,
+ iters+1, creal, cimag);
+
+ # Return the number of iterations required for the iteration to escape
+ def mandleconverge(real imag)
+ mandleconverger(real, imag, 0, real, imag);
+
+This "``z = z2 + c``" function is a beautiful little creature that is
+the basis for computation of the `Mandelbrot
+Set <http://en.wikipedia.org/wiki/Mandelbrot_set>`_. Our
+``mandelconverge`` function returns the number of iterations that it
+takes for a complex orbit to escape, saturating to 255. This is not a
+very useful function by itself, but if you plot its value over a
+two-dimensional plane, you can see the Mandelbrot set. Given that we are
+limited to using putchard here, our amazing graphical output is limited,
+but we can whip together something using the density plotter above:
+
+::
+
+ # Compute and plot the mandlebrot set with the specified 2 dimensional range
+ # info.
+ def mandelhelp(xmin xmax xstep ymin ymax ystep)
+ for y = ymin, y < ymax, ystep in (
+ (for x = xmin, x < xmax, xstep in
+ printdensity(mandleconverge(x,y)))
+ : putchard(10)
+ )
+
+ # mandel - This is a convenient helper function for plotting the mandelbrot set
+ # from the specified position with the specified Magnification.
+ def mandel(realstart imagstart realmag imagmag)
+ mandelhelp(realstart, realstart+realmag*78, realmag,
+ imagstart, imagstart+imagmag*40, imagmag);
+
+Given this, we can try plotting out the mandlebrot set! Lets try it out:
+
+::
+
+ ready> mandel(-2.3, -1.3, 0.05, 0.07);
+ *******************************+++++++++++*************************************
+ *************************+++++++++++++++++++++++*******************************
+ **********************+++++++++++++++++++++++++++++****************************
+ *******************+++++++++++++++++++++.. ...++++++++*************************
+ *****************++++++++++++++++++++++.... ...+++++++++***********************
+ ***************+++++++++++++++++++++++..... ...+++++++++*********************
+ **************+++++++++++++++++++++++.... ....+++++++++********************
+ *************++++++++++++++++++++++...... .....++++++++*******************
+ ************+++++++++++++++++++++....... .......+++++++******************
+ ***********+++++++++++++++++++.... ... .+++++++*****************
+ **********+++++++++++++++++....... .+++++++****************
+ *********++++++++++++++........... ...+++++++***************
+ ********++++++++++++............ ...++++++++**************
+ ********++++++++++... .......... .++++++++**************
+ *******+++++++++..... .+++++++++*************
+ *******++++++++...... ..+++++++++*************
+ *******++++++....... ..+++++++++*************
+ *******+++++...... ..+++++++++*************
+ *******.... .... ...+++++++++*************
+ *******.... . ...+++++++++*************
+ *******+++++...... ...+++++++++*************
+ *******++++++....... ..+++++++++*************
+ *******++++++++...... .+++++++++*************
+ *******+++++++++..... ..+++++++++*************
+ ********++++++++++... .......... .++++++++**************
+ ********++++++++++++............ ...++++++++**************
+ *********++++++++++++++.......... ...+++++++***************
+ **********++++++++++++++++........ .+++++++****************
+ **********++++++++++++++++++++.... ... ..+++++++****************
+ ***********++++++++++++++++++++++....... .......++++++++*****************
+ ************+++++++++++++++++++++++...... ......++++++++******************
+ **************+++++++++++++++++++++++.... ....++++++++********************
+ ***************+++++++++++++++++++++++..... ...+++++++++*********************
+ *****************++++++++++++++++++++++.... ...++++++++***********************
+ *******************+++++++++++++++++++++......++++++++*************************
+ *********************++++++++++++++++++++++.++++++++***************************
+ *************************+++++++++++++++++++++++*******************************
+ ******************************+++++++++++++************************************
+ *******************************************************************************
+ *******************************************************************************
+ *******************************************************************************
+ Evaluated to 0.000000
+ ready> mandel(-2, -1, 0.02, 0.04);
+ **************************+++++++++++++++++++++++++++++++++++++++++++++++++++++
+ ***********************++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+ *********************+++++++++++++++++++++++++++++++++++++++++++++++++++++++++.
+ *******************+++++++++++++++++++++++++++++++++++++++++++++++++++++++++...
+ *****************+++++++++++++++++++++++++++++++++++++++++++++++++++++++++.....
+ ***************++++++++++++++++++++++++++++++++++++++++++++++++++++++++........
+ **************++++++++++++++++++++++++++++++++++++++++++++++++++++++...........
+ ************+++++++++++++++++++++++++++++++++++++++++++++++++++++..............
+ ***********++++++++++++++++++++++++++++++++++++++++++++++++++........ .
+ **********++++++++++++++++++++++++++++++++++++++++++++++.............
+ ********+++++++++++++++++++++++++++++++++++++++++++..................
+ *******+++++++++++++++++++++++++++++++++++++++.......................
+ ******+++++++++++++++++++++++++++++++++++...........................
+ *****++++++++++++++++++++++++++++++++............................
+ *****++++++++++++++++++++++++++++...............................
+ ****++++++++++++++++++++++++++...... .........................
+ ***++++++++++++++++++++++++......... ...... ...........
+ ***++++++++++++++++++++++............
+ **+++++++++++++++++++++..............
+ **+++++++++++++++++++................
+ *++++++++++++++++++.................
+ *++++++++++++++++............ ...
+ *++++++++++++++..............
+ *+++....++++................
+ *.......... ...........
+ *
+ *.......... ...........
+ *+++....++++................
+ *++++++++++++++..............
+ *++++++++++++++++............ ...
+ *++++++++++++++++++.................
+ **+++++++++++++++++++................
+ **+++++++++++++++++++++..............
+ ***++++++++++++++++++++++............
+ ***++++++++++++++++++++++++......... ...... ...........
+ ****++++++++++++++++++++++++++...... .........................
+ *****++++++++++++++++++++++++++++...............................
+ *****++++++++++++++++++++++++++++++++............................
+ ******+++++++++++++++++++++++++++++++++++...........................
+ *******+++++++++++++++++++++++++++++++++++++++.......................
+ ********+++++++++++++++++++++++++++++++++++++++++++..................
+ Evaluated to 0.000000
+ ready> mandel(-0.9, -1.4, 0.02, 0.03);
+ *******************************************************************************
+ *******************************************************************************
+ *******************************************************************************
+ **********+++++++++++++++++++++************************************************
+ *+++++++++++++++++++++++++++++++++++++++***************************************
+ +++++++++++++++++++++++++++++++++++++++++++++**********************************
+ ++++++++++++++++++++++++++++++++++++++++++++++++++*****************************
+ ++++++++++++++++++++++++++++++++++++++++++++++++++++++*************************
+ +++++++++++++++++++++++++++++++++++++++++++++++++++++++++**********************
+ +++++++++++++++++++++++++++++++++.........++++++++++++++++++*******************
+ +++++++++++++++++++++++++++++++.... ......+++++++++++++++++++****************
+ +++++++++++++++++++++++++++++....... ........+++++++++++++++++++**************
+ ++++++++++++++++++++++++++++........ ........++++++++++++++++++++************
+ +++++++++++++++++++++++++++......... .. ...+++++++++++++++++++++**********
+ ++++++++++++++++++++++++++........... ....++++++++++++++++++++++********
+ ++++++++++++++++++++++++............. .......++++++++++++++++++++++******
+ +++++++++++++++++++++++............. ........+++++++++++++++++++++++****
+ ++++++++++++++++++++++........... ..........++++++++++++++++++++++***
+ ++++++++++++++++++++........... .........++++++++++++++++++++++*
+ ++++++++++++++++++............ ...........++++++++++++++++++++
+ ++++++++++++++++............... .............++++++++++++++++++
+ ++++++++++++++................. ...............++++++++++++++++
+ ++++++++++++.................. .................++++++++++++++
+ +++++++++.................. .................+++++++++++++
+ ++++++........ . ......... ..++++++++++++
+ ++............ ...... ....++++++++++
+ .............. ...++++++++++
+ .............. ....+++++++++
+ .............. .....++++++++
+ ............. ......++++++++
+ ........... .......++++++++
+ ......... ........+++++++
+ ......... ........+++++++
+ ......... ....+++++++
+ ........ ...+++++++
+ ....... ...+++++++
+ ....+++++++
+ .....+++++++
+ ....+++++++
+ ....+++++++
+ ....+++++++
+ Evaluated to 0.000000
+ ready> ^D
+
+At this point, you may be starting to realize that Kaleidoscope is a
+real and powerful language. It may not be self-similar :), but it can be
+used to plot things that are!
+
+With this, we conclude the "adding user-defined operators" chapter of
+the tutorial. We have successfully augmented our language, adding the
+ability to extend the language in the library, and we have shown how
+this can be used to build a simple but interesting end-user application
+in Kaleidoscope. At this point, Kaleidoscope can build a variety of
+applications that are functional and can call functions with
+side-effects, but it can't actually define and mutate a variable itself.
+
+Strikingly, variable mutation is an important feature of some languages,
+and it is not at all obvious how to `add support for mutable
+variables <LangImpl7.html>`_ without having to add an "SSA construction"
+phase to your front-end. In the next chapter, we will describe how you
+can add variable mutation without building SSA in your front-end.
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example, enhanced with
+the if/then/else and for expressions.. To build this example, use:
+
+.. code-block:: bash
+
+ # Compile
+ clang++ -g toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core mcjit native` -O3 -o toy
+ # Run
+ ./toy
+
+On some platforms, you will need to specify -rdynamic or
+-Wl,--export-dynamic when linking. This ensures that symbols defined in
+the main executable are exported to the dynamic linker and so are
+available for symbol resolution at run time. This is not needed if you
+compile your support code into a shared library, although doing that
+will cause problems on Windows.
+
+Here is the code:
+
+.. literalinclude:: ../../examples/Kaleidoscope/Chapter6/toy.cpp
+ :language: c++
+
+`Next: Extending the language: mutable variables / SSA
+construction <LangImpl7.html>`_
+
Added: www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl7.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl7.txt?rev=290368&view=auto
==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl7.txt (added)
+++ www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl7.txt Thu Dec 22 14:04:03 2016
@@ -0,0 +1,881 @@
+=======================================================
+Kaleidoscope: Extending the Language: Mutable Variables
+=======================================================
+
+.. contents::
+ :local:
+
+Chapter 7 Introduction
+======================
+
+Welcome to Chapter 7 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. In chapters 1 through 6, we've built a
+very respectable, albeit simple, `functional programming
+language <http://en.wikipedia.org/wiki/Functional_programming>`_. In our
+journey, we learned some parsing techniques, how to build and represent
+an AST, how to build LLVM IR, and how to optimize the resultant code as
+well as JIT compile it.
+
+While Kaleidoscope is interesting as a functional language, the fact
+that it is functional makes it "too easy" to generate LLVM IR for it. In
+particular, a functional language makes it very easy to build LLVM IR
+directly in `SSA
+form <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_.
+Since LLVM requires that the input code be in SSA form, this is a very
+nice property and it is often unclear to newcomers how to generate code
+for an imperative language with mutable variables.
+
+The short (and happy) summary of this chapter is that there is no need
+for your front-end to build SSA form: LLVM provides highly tuned and
+well tested support for this, though the way it works is a bit
+unexpected for some.
+
+Why is this a hard problem?
+===========================
+
+To understand why mutable variables cause complexities in SSA
+construction, consider this extremely simple C example:
+
+.. code-block:: c
+
+ int G, H;
+ int test(_Bool Condition) {
+ int X;
+ if (Condition)
+ X = G;
+ else
+ X = H;
+ return X;
+ }
+
+In this case, we have the variable "X", whose value depends on the path
+executed in the program. Because there are two different possible values
+for X before the return instruction, a PHI node is inserted to merge the
+two values. The LLVM IR that we want for this example looks like this:
+
+.. code-block:: llvm
+
+ @G = weak global i32 0 ; type of @G is i32*
+ @H = weak global i32 0 ; type of @H is i32*
+
+ define i32 @test(i1 %Condition) {
+ entry:
+ br i1 %Condition, label %cond_true, label %cond_false
+
+ cond_true:
+ %X.0 = load i32* @G
+ br label %cond_next
+
+ cond_false:
+ %X.1 = load i32* @H
+ br label %cond_next
+
+ cond_next:
+ %X.2 = phi i32 [ %X.1, %cond_false ], [ %X.0, %cond_true ]
+ ret i32 %X.2
+ }
+
+In this example, the loads from the G and H global variables are
+explicit in the LLVM IR, and they live in the then/else branches of the
+if statement (cond\_true/cond\_false). In order to merge the incoming
+values, the X.2 phi node in the cond\_next block selects the right value
+to use based on where control flow is coming from: if control flow comes
+from the cond\_false block, X.2 gets the value of X.1. Alternatively, if
+control flow comes from cond\_true, it gets the value of X.0. The intent
+of this chapter is not to explain the details of SSA form. For more
+information, see one of the many `online
+references <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_.
+
+The question for this article is "who places the phi nodes when lowering
+assignments to mutable variables?". The issue here is that LLVM
+*requires* that its IR be in SSA form: there is no "non-ssa" mode for
+it. However, SSA construction requires non-trivial algorithms and data
+structures, so it is inconvenient and wasteful for every front-end to
+have to reproduce this logic.
+
+Memory in LLVM
+==============
+
+The 'trick' here is that while LLVM does require all register values to
+be in SSA form, it does not require (or permit) memory objects to be in
+SSA form. In the example above, note that the loads from G and H are
+direct accesses to G and H: they are not renamed or versioned. This
+differs from some other compiler systems, which do try to version memory
+objects. In LLVM, instead of encoding dataflow analysis of memory into
+the LLVM IR, it is handled with `Analysis
+Passes <../WritingAnLLVMPass.html>`_ which are computed on demand.
+
+With this in mind, the high-level idea is that we want to make a stack
+variable (which lives in memory, because it is on the stack) for each
+mutable object in a function. To take advantage of this trick, we need
+to talk about how LLVM represents stack variables.
+
+In LLVM, all memory accesses are explicit with load/store instructions,
+and it is carefully designed not to have (or need) an "address-of"
+operator. Notice how the type of the @G/@H global variables is actually
+"i32\*" even though the variable is defined as "i32". What this means is
+that @G defines *space* for an i32 in the global data area, but its
+*name* actually refers to the address for that space. Stack variables
+work the same way, except that instead of being declared with global
+variable definitions, they are declared with the `LLVM alloca
+instruction <../LangRef.html#alloca-instruction>`_:
+
+.. code-block:: llvm
+
+ define i32 @example() {
+ entry:
+ %X = alloca i32 ; type of %X is i32*.
+ ...
+ %tmp = load i32* %X ; load the stack value %X from the stack.
+ %tmp2 = add i32 %tmp, 1 ; increment it
+ store i32 %tmp2, i32* %X ; store it back
+ ...
+
+This code shows an example of how you can declare and manipulate a stack
+variable in the LLVM IR. Stack memory allocated with the alloca
+instruction is fully general: you can pass the address of the stack slot
+to functions, you can store it in other variables, etc. In our example
+above, we could rewrite the example to use the alloca technique to avoid
+using a PHI node:
+
+.. code-block:: llvm
+
+ @G = weak global i32 0 ; type of @G is i32*
+ @H = weak global i32 0 ; type of @H is i32*
+
+ define i32 @test(i1 %Condition) {
+ entry:
+ %X = alloca i32 ; type of %X is i32*.
+ br i1 %Condition, label %cond_true, label %cond_false
+
+ cond_true:
+ %X.0 = load i32* @G
+ store i32 %X.0, i32* %X ; Update X
+ br label %cond_next
+
+ cond_false:
+ %X.1 = load i32* @H
+ store i32 %X.1, i32* %X ; Update X
+ br label %cond_next
+
+ cond_next:
+ %X.2 = load i32* %X ; Read X
+ ret i32 %X.2
+ }
+
+With this, we have discovered a way to handle arbitrary mutable
+variables without the need to create Phi nodes at all:
+
+#. Each mutable variable becomes a stack allocation.
+#. Each read of the variable becomes a load from the stack.
+#. Each update of the variable becomes a store to the stack.
+#. Taking the address of a variable just uses the stack address
+ directly.
+
+While this solution has solved our immediate problem, it introduced
+another one: we have now apparently introduced a lot of stack traffic
+for very simple and common operations, a major performance problem.
+Fortunately for us, the LLVM optimizer has a highly-tuned optimization
+pass named "mem2reg" that handles this case, promoting allocas like this
+into SSA registers, inserting Phi nodes as appropriate. If you run this
+example through the pass, for example, you'll get:
+
+.. code-block:: bash
+
+ $ llvm-as < example.ll | opt -mem2reg | llvm-dis
+ @G = weak global i32 0
+ @H = weak global i32 0
+
+ define i32 @test(i1 %Condition) {
+ entry:
+ br i1 %Condition, label %cond_true, label %cond_false
+
+ cond_true:
+ %X.0 = load i32* @G
+ br label %cond_next
+
+ cond_false:
+ %X.1 = load i32* @H
+ br label %cond_next
+
+ cond_next:
+ %X.01 = phi i32 [ %X.1, %cond_false ], [ %X.0, %cond_true ]
+ ret i32 %X.01
+ }
+
+The mem2reg pass implements the standard "iterated dominance frontier"
+algorithm for constructing SSA form and has a number of optimizations
+that speed up (very common) degenerate cases. The mem2reg optimization
+pass is the answer to dealing with mutable variables, and we highly
+recommend that you depend on it. Note that mem2reg only works on
+variables in certain circumstances:
+
+#. mem2reg is alloca-driven: it looks for allocas and if it can handle
+ them, it promotes them. It does not apply to global variables or heap
+ allocations.
+#. mem2reg only looks for alloca instructions in the entry block of the
+ function. Being in the entry block guarantees that the alloca is only
+ executed once, which makes analysis simpler.
+#. mem2reg only promotes allocas whose uses are direct loads and stores.
+ If the address of the stack object is passed to a function, or if any
+ funny pointer arithmetic is involved, the alloca will not be
+ promoted.
+#. mem2reg only works on allocas of `first
+ class <../LangRef.html#first-class-types>`_ values (such as pointers,
+ scalars and vectors), and only if the array size of the allocation is
+ 1 (or missing in the .ll file). mem2reg is not capable of promoting
+ structs or arrays to registers. Note that the "scalarrepl" pass is
+ more powerful and can promote structs, "unions", and arrays in many
+ cases.
+
+All of these properties are easy to satisfy for most imperative
+languages, and we'll illustrate it below with Kaleidoscope. The final
+question you may be asking is: should I bother with this nonsense for my
+front-end? Wouldn't it be better if I just did SSA construction
+directly, avoiding use of the mem2reg optimization pass? In short, we
+strongly recommend that you use this technique for building SSA form,
+unless there is an extremely good reason not to. Using this technique
+is:
+
+- Proven and well tested: clang uses this technique
+ for local mutable variables. As such, the most common clients of LLVM
+ are using this to handle a bulk of their variables. You can be sure
+ that bugs are found fast and fixed early.
+- Extremely Fast: mem2reg has a number of special cases that make it
+ fast in common cases as well as fully general. For example, it has
+ fast-paths for variables that are only used in a single block,
+ variables that only have one assignment point, good heuristics to
+ avoid insertion of unneeded phi nodes, etc.
+- Needed for debug info generation: `Debug information in
+ LLVM <../SourceLevelDebugging.html>`_ relies on having the address of
+ the variable exposed so that debug info can be attached to it. This
+ technique dovetails very naturally with this style of debug info.
+
+If nothing else, this makes it much easier to get your front-end up and
+running, and is very simple to implement. Lets extend Kaleidoscope with
+mutable variables now!
+
+Mutable Variables in Kaleidoscope
+=================================
+
+Now that we know the sort of problem we want to tackle, lets see what
+this looks like in the context of our little Kaleidoscope language.
+We're going to add two features:
+
+#. The ability to mutate variables with the '=' operator.
+#. The ability to define new variables.
+
+While the first item is really what this is about, we only have
+variables for incoming arguments as well as for induction variables, and
+redefining those only goes so far :). Also, the ability to define new
+variables is a useful thing regardless of whether you will be mutating
+them. Here's a motivating example that shows how we could use these:
+
+::
+
+ # Define ':' for sequencing: as a low-precedence operator that ignores operands
+ # and just returns the RHS.
+ def binary : 1 (x y) y;
+
+ # Recursive fib, we could do this before.
+ def fib(x)
+ if (x < 3) then
+ 1
+ else
+ fib(x-1)+fib(x-2);
+
+ # Iterative fib.
+ def fibi(x)
+ var a = 1, b = 1, c in
+ (for i = 3, i < x in
+ c = a + b :
+ a = b :
+ b = c) :
+ b;
+
+ # Call it.
+ fibi(10);
+
+In order to mutate variables, we have to change our existing variables
+to use the "alloca trick". Once we have that, we'll add our new
+operator, then extend Kaleidoscope to support new variable definitions.
+
+Adjusting Existing Variables for Mutation
+=========================================
+
+The symbol table in Kaleidoscope is managed at code generation time by
+the '``NamedValues``' map. This map currently keeps track of the LLVM
+"Value\*" that holds the double value for the named variable. In order
+to support mutation, we need to change this slightly, so that it
+``NamedValues`` holds the *memory location* of the variable in question.
+Note that this change is a refactoring: it changes the structure of the
+code, but does not (by itself) change the behavior of the compiler. All
+of these changes are isolated in the Kaleidoscope code generator.
+
+At this point in Kaleidoscope's development, it only supports variables
+for two things: incoming arguments to functions and the induction
+variable of 'for' loops. For consistency, we'll allow mutation of these
+variables in addition to other user-defined variables. This means that
+these will both need memory locations.
+
+To start our transformation of Kaleidoscope, we'll change the
+NamedValues map so that it maps to AllocaInst\* instead of Value\*. Once
+we do this, the C++ compiler will tell us what parts of the code we need
+to update:
+
+.. code-block:: c++
+
+ static std::map<std::string, AllocaInst*> NamedValues;
+
+Also, since we will need to create these alloca's, we'll use a helper
+function that ensures that the allocas are created in the entry block of
+the function:
+
+.. code-block:: c++
+
+ /// CreateEntryBlockAlloca - Create an alloca instruction in the entry block of
+ /// the function. This is used for mutable variables etc.
+ static AllocaInst *CreateEntryBlockAlloca(Function *TheFunction,
+ const std::string &VarName) {
+ IRBuilder<> TmpB(&TheFunction->getEntryBlock(),
+ TheFunction->getEntryBlock().begin());
+ return TmpB.CreateAlloca(Type::getDoubleTy(getGlobalContext()), 0,
+ VarName.c_str());
+ }
+
+This funny looking code creates an IRBuilder object that is pointing at
+the first instruction (.begin()) of the entry block. It then creates an
+alloca with the expected name and returns it. Because all values in
+Kaleidoscope are doubles, there is no need to pass in a type to use.
+
+With this in place, the first functionality change we want to make is to
+variable references. In our new scheme, variables live on the stack, so
+code generating a reference to them actually needs to produce a load
+from the stack slot:
+
+.. code-block:: c++
+
+ Value *VariableExprAST::codegen() {
+ // Look this variable up in the function.
+ Value *V = NamedValues[Name];
+ if (!V)
+ return ErrorV("Unknown variable name");
+
+ // Load the value.
+ return Builder.CreateLoad(V, Name.c_str());
+ }
+
+As you can see, this is pretty straightforward. Now we need to update
+the things that define the variables to set up the alloca. We'll start
+with ``ForExprAST::codegen()`` (see the `full code listing <#id1>`_ for
+the unabridged code):
+
+.. code-block:: c++
+
+ Function *TheFunction = Builder.GetInsertBlock()->getParent();
+
+ // Create an alloca for the variable in the entry block.
+ AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, VarName);
+
+ // Emit the start code first, without 'variable' in scope.
+ Value *StartVal = Start->codegen();
+ if (!StartVal)
+ return nullptr;
+
+ // Store the value into the alloca.
+ Builder.CreateStore(StartVal, Alloca);
+ ...
+
+ // Compute the end condition.
+ Value *EndCond = End->codegen();
+ if (!EndCond)
+ return nullptr;
+
+ // Reload, increment, and restore the alloca. This handles the case where
+ // the body of the loop mutates the variable.
+ Value *CurVar = Builder.CreateLoad(Alloca);
+ Value *NextVar = Builder.CreateFAdd(CurVar, StepVal, "nextvar");
+ Builder.CreateStore(NextVar, Alloca);
+ ...
+
+This code is virtually identical to the code `before we allowed mutable
+variables <LangImpl5.html#code-generation-for-the-for-loop>`_. The big difference is that we
+no longer have to construct a PHI node, and we use load/store to access
+the variable as needed.
+
+To support mutable argument variables, we need to also make allocas for
+them. The code for this is also pretty simple:
+
+.. code-block:: c++
+
+ /// CreateArgumentAllocas - Create an alloca for each argument and register the
+ /// argument in the symbol table so that references to it will succeed.
+ void PrototypeAST::CreateArgumentAllocas(Function *F) {
+ Function::arg_iterator AI = F->arg_begin();
+ for (unsigned Idx = 0, e = Args.size(); Idx != e; ++Idx, ++AI) {
+ // Create an alloca for this variable.
+ AllocaInst *Alloca = CreateEntryBlockAlloca(F, Args[Idx]);
+
+ // Store the initial value into the alloca.
+ Builder.CreateStore(AI, Alloca);
+
+ // Add arguments to variable symbol table.
+ NamedValues[Args[Idx]] = Alloca;
+ }
+ }
+
+For each argument, we make an alloca, store the input value to the
+function into the alloca, and register the alloca as the memory location
+for the argument. This method gets invoked by ``FunctionAST::codegen()``
+right after it sets up the entry block for the function.
+
+The final missing piece is adding the mem2reg pass, which allows us to
+get good codegen once again:
+
+.. code-block:: c++
+
+ // Set up the optimizer pipeline. Start with registering info about how the
+ // target lays out data structures.
+ OurFPM.add(new DataLayout(*TheExecutionEngine->getDataLayout()));
+ // Promote allocas to registers.
+ OurFPM.add(createPromoteMemoryToRegisterPass());
+ // Do simple "peephole" optimizations and bit-twiddling optzns.
+ OurFPM.add(createInstructionCombiningPass());
+ // Reassociate expressions.
+ OurFPM.add(createReassociatePass());
+
+It is interesting to see what the code looks like before and after the
+mem2reg optimization runs. For example, this is the before/after code
+for our recursive fib function. Before the optimization:
+
+.. code-block:: llvm
+
+ define double @fib(double %x) {
+ entry:
+ %x1 = alloca double
+ store double %x, double* %x1
+ %x2 = load double* %x1
+ %cmptmp = fcmp ult double %x2, 3.000000e+00
+ %booltmp = uitofp i1 %cmptmp to double
+ %ifcond = fcmp one double %booltmp, 0.000000e+00
+ br i1 %ifcond, label %then, label %else
+
+ then: ; preds = %entry
+ br label %ifcont
+
+ else: ; preds = %entry
+ %x3 = load double* %x1
+ %subtmp = fsub double %x3, 1.000000e+00
+ %calltmp = call double @fib(double %subtmp)
+ %x4 = load double* %x1
+ %subtmp5 = fsub double %x4, 2.000000e+00
+ %calltmp6 = call double @fib(double %subtmp5)
+ %addtmp = fadd double %calltmp, %calltmp6
+ br label %ifcont
+
+ ifcont: ; preds = %else, %then
+ %iftmp = phi double [ 1.000000e+00, %then ], [ %addtmp, %else ]
+ ret double %iftmp
+ }
+
+Here there is only one variable (x, the input argument) but you can
+still see the extremely simple-minded code generation strategy we are
+using. In the entry block, an alloca is created, and the initial input
+value is stored into it. Each reference to the variable does a reload
+from the stack. Also, note that we didn't modify the if/then/else
+expression, so it still inserts a PHI node. While we could make an
+alloca for it, it is actually easier to create a PHI node for it, so we
+still just make the PHI.
+
+Here is the code after the mem2reg pass runs:
+
+.. code-block:: llvm
+
+ define double @fib(double %x) {
+ entry:
+ %cmptmp = fcmp ult double %x, 3.000000e+00
+ %booltmp = uitofp i1 %cmptmp to double
+ %ifcond = fcmp one double %booltmp, 0.000000e+00
+ br i1 %ifcond, label %then, label %else
+
+ then:
+ br label %ifcont
+
+ else:
+ %subtmp = fsub double %x, 1.000000e+00
+ %calltmp = call double @fib(double %subtmp)
+ %subtmp5 = fsub double %x, 2.000000e+00
+ %calltmp6 = call double @fib(double %subtmp5)
+ %addtmp = fadd double %calltmp, %calltmp6
+ br label %ifcont
+
+ ifcont: ; preds = %else, %then
+ %iftmp = phi double [ 1.000000e+00, %then ], [ %addtmp, %else ]
+ ret double %iftmp
+ }
+
+This is a trivial case for mem2reg, since there are no redefinitions of
+the variable. The point of showing this is to calm your tension about
+inserting such blatent inefficiencies :).
+
+After the rest of the optimizers run, we get:
+
+.. code-block:: llvm
+
+ define double @fib(double %x) {
+ entry:
+ %cmptmp = fcmp ult double %x, 3.000000e+00
+ %booltmp = uitofp i1 %cmptmp to double
+ %ifcond = fcmp ueq double %booltmp, 0.000000e+00
+ br i1 %ifcond, label %else, label %ifcont
+
+ else:
+ %subtmp = fsub double %x, 1.000000e+00
+ %calltmp = call double @fib(double %subtmp)
+ %subtmp5 = fsub double %x, 2.000000e+00
+ %calltmp6 = call double @fib(double %subtmp5)
+ %addtmp = fadd double %calltmp, %calltmp6
+ ret double %addtmp
+
+ ifcont:
+ ret double 1.000000e+00
+ }
+
+Here we see that the simplifycfg pass decided to clone the return
+instruction into the end of the 'else' block. This allowed it to
+eliminate some branches and the PHI node.
+
+Now that all symbol table references are updated to use stack variables,
+we'll add the assignment operator.
+
+New Assignment Operator
+=======================
+
+With our current framework, adding a new assignment operator is really
+simple. We will parse it just like any other binary operator, but handle
+it internally (instead of allowing the user to define it). The first
+step is to set a precedence:
+
+.. code-block:: c++
+
+ int main() {
+ // Install standard binary operators.
+ // 1 is lowest precedence.
+ BinopPrecedence['='] = 2;
+ BinopPrecedence['<'] = 10;
+ BinopPrecedence['+'] = 20;
+ BinopPrecedence['-'] = 20;
+
+Now that the parser knows the precedence of the binary operator, it
+takes care of all the parsing and AST generation. We just need to
+implement codegen for the assignment operator. This looks like:
+
+.. code-block:: c++
+
+ Value *BinaryExprAST::codegen() {
+ // Special case '=' because we don't want to emit the LHS as an expression.
+ if (Op == '=') {
+ // Assignment requires the LHS to be an identifier.
+ VariableExprAST *LHSE = dynamic_cast<VariableExprAST*>(LHS.get());
+ if (!LHSE)
+ return ErrorV("destination of '=' must be a variable");
+
+Unlike the rest of the binary operators, our assignment operator doesn't
+follow the "emit LHS, emit RHS, do computation" model. As such, it is
+handled as a special case before the other binary operators are handled.
+The other strange thing is that it requires the LHS to be a variable. It
+is invalid to have "(x+1) = expr" - only things like "x = expr" are
+allowed.
+
+.. code-block:: c++
+
+ // Codegen the RHS.
+ Value *Val = RHS->codegen();
+ if (!Val)
+ return nullptr;
+
+ // Look up the name.
+ Value *Variable = NamedValues[LHSE->getName()];
+ if (!Variable)
+ return ErrorV("Unknown variable name");
+
+ Builder.CreateStore(Val, Variable);
+ return Val;
+ }
+ ...
+
+Once we have the variable, codegen'ing the assignment is
+straightforward: we emit the RHS of the assignment, create a store, and
+return the computed value. Returning a value allows for chained
+assignments like "X = (Y = Z)".
+
+Now that we have an assignment operator, we can mutate loop variables
+and arguments. For example, we can now run code like this:
+
+::
+
+ # Function to print a double.
+ extern printd(x);
+
+ # Define ':' for sequencing: as a low-precedence operator that ignores operands
+ # and just returns the RHS.
+ def binary : 1 (x y) y;
+
+ def test(x)
+ printd(x) :
+ x = 4 :
+ printd(x);
+
+ test(123);
+
+When run, this example prints "123" and then "4", showing that we did
+actually mutate the value! Okay, we have now officially implemented our
+goal: getting this to work requires SSA construction in the general
+case. However, to be really useful, we want the ability to define our
+own local variables, lets add this next!
+
+User-defined Local Variables
+============================
+
+Adding var/in is just like any other extension we made to
+Kaleidoscope: we extend the lexer, the parser, the AST and the code
+generator. The first step for adding our new 'var/in' construct is to
+extend the lexer. As before, this is pretty trivial, the code looks like
+this:
+
+.. code-block:: c++
+
+ enum Token {
+ ...
+ // var definition
+ tok_var = -13
+ ...
+ }
+ ...
+ static int gettok() {
+ ...
+ if (IdentifierStr == "in")
+ return tok_in;
+ if (IdentifierStr == "binary")
+ return tok_binary;
+ if (IdentifierStr == "unary")
+ return tok_unary;
+ if (IdentifierStr == "var")
+ return tok_var;
+ return tok_identifier;
+ ...
+
+The next step is to define the AST node that we will construct. For
+var/in, it looks like this:
+
+.. code-block:: c++
+
+ /// VarExprAST - Expression class for var/in
+ class VarExprAST : public ExprAST {
+ std::vector<std::pair<std::string, std::unique_ptr<ExprAST>>> VarNames;
+ std::unique_ptr<ExprAST> Body;
+
+ public:
+ VarExprAST(std::vector<std::pair<std::string, std::unique_ptr<ExprAST>>> VarNames,
+ std::unique_ptr<ExprAST> body)
+ : VarNames(std::move(VarNames)), Body(std::move(Body)) {}
+
+ virtual Value *codegen();
+ };
+
+var/in allows a list of names to be defined all at once, and each name
+can optionally have an initializer value. As such, we capture this
+information in the VarNames vector. Also, var/in has a body, this body
+is allowed to access the variables defined by the var/in.
+
+With this in place, we can define the parser pieces. The first thing we
+do is add it as a primary expression:
+
+.. code-block:: c++
+
+ /// primary
+ /// ::= identifierexpr
+ /// ::= numberexpr
+ /// ::= parenexpr
+ /// ::= ifexpr
+ /// ::= forexpr
+ /// ::= varexpr
+ static std::unique_ptr<ExprAST> ParsePrimary() {
+ switch (CurTok) {
+ default:
+ return Error("unknown token when expecting an expression");
+ case tok_identifier:
+ return ParseIdentifierExpr();
+ case tok_number:
+ return ParseNumberExpr();
+ case '(':
+ return ParseParenExpr();
+ case tok_if:
+ return ParseIfExpr();
+ case tok_for:
+ return ParseForExpr();
+ case tok_var:
+ return ParseVarExpr();
+ }
+ }
+
+Next we define ParseVarExpr:
+
+.. code-block:: c++
+
+ /// varexpr ::= 'var' identifier ('=' expression)?
+ // (',' identifier ('=' expression)?)* 'in' expression
+ static std::unique_ptr<ExprAST> ParseVarExpr() {
+ getNextToken(); // eat the var.
+
+ std::vector<std::pair<std::string, std::unique_ptr<ExprAST>>> VarNames;
+
+ // At least one variable name is required.
+ if (CurTok != tok_identifier)
+ return Error("expected identifier after var");
+
+The first part of this code parses the list of identifier/expr pairs
+into the local ``VarNames`` vector.
+
+.. code-block:: c++
+
+ while (1) {
+ std::string Name = IdentifierStr;
+ getNextToken(); // eat identifier.
+
+ // Read the optional initializer.
+ std::unique_ptr<ExprAST> Init;
+ if (CurTok == '=') {
+ getNextToken(); // eat the '='.
+
+ Init = ParseExpression();
+ if (!Init) return nullptr;
+ }
+
+ VarNames.push_back(std::make_pair(Name, std::move(Init)));
+
+ // End of var list, exit loop.
+ if (CurTok != ',') break;
+ getNextToken(); // eat the ','.
+
+ if (CurTok != tok_identifier)
+ return Error("expected identifier list after var");
+ }
+
+Once all the variables are parsed, we then parse the body and create the
+AST node:
+
+.. code-block:: c++
+
+ // At this point, we have to have 'in'.
+ if (CurTok != tok_in)
+ return Error("expected 'in' keyword after 'var'");
+ getNextToken(); // eat 'in'.
+
+ auto Body = ParseExpression();
+ if (!Body)
+ return nullptr;
+
+ return llvm::make_unique<VarExprAST>(std::move(VarNames),
+ std::move(Body));
+ }
+
+Now that we can parse and represent the code, we need to support
+emission of LLVM IR for it. This code starts out with:
+
+.. code-block:: c++
+
+ Value *VarExprAST::codegen() {
+ std::vector<AllocaInst *> OldBindings;
+
+ Function *TheFunction = Builder.GetInsertBlock()->getParent();
+
+ // Register all variables and emit their initializer.
+ for (unsigned i = 0, e = VarNames.size(); i != e; ++i) {
+ const std::string &VarName = VarNames[i].first;
+ ExprAST *Init = VarNames[i].second.get();
+
+Basically it loops over all the variables, installing them one at a
+time. For each variable we put into the symbol table, we remember the
+previous value that we replace in OldBindings.
+
+.. code-block:: c++
+
+ // Emit the initializer before adding the variable to scope, this prevents
+ // the initializer from referencing the variable itself, and permits stuff
+ // like this:
+ // var a = 1 in
+ // var a = a in ... # refers to outer 'a'.
+ Value *InitVal;
+ if (Init) {
+ InitVal = Init->codegen();
+ if (!InitVal)
+ return nullptr;
+ } else { // If not specified, use 0.0.
+ InitVal = ConstantFP::get(getGlobalContext(), APFloat(0.0));
+ }
+
+ AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, VarName);
+ Builder.CreateStore(InitVal, Alloca);
+
+ // Remember the old variable binding so that we can restore the binding when
+ // we unrecurse.
+ OldBindings.push_back(NamedValues[VarName]);
+
+ // Remember this binding.
+ NamedValues[VarName] = Alloca;
+ }
+
+There are more comments here than code. The basic idea is that we emit
+the initializer, create the alloca, then update the symbol table to
+point to it. Once all the variables are installed in the symbol table,
+we evaluate the body of the var/in expression:
+
+.. code-block:: c++
+
+ // Codegen the body, now that all vars are in scope.
+ Value *BodyVal = Body->codegen();
+ if (!BodyVal)
+ return nullptr;
+
+Finally, before returning, we restore the previous variable bindings:
+
+.. code-block:: c++
+
+ // Pop all our variables from scope.
+ for (unsigned i = 0, e = VarNames.size(); i != e; ++i)
+ NamedValues[VarNames[i].first] = OldBindings[i];
+
+ // Return the body computation.
+ return BodyVal;
+ }
+
+The end result of all of this is that we get properly scoped variable
+definitions, and we even (trivially) allow mutation of them :).
+
+With this, we completed what we set out to do. Our nice iterative fib
+example from the intro compiles and runs just fine. The mem2reg pass
+optimizes all of our stack variables into SSA registers, inserting PHI
+nodes where needed, and our front-end remains simple: no "iterated
+dominance frontier" computation anywhere in sight.
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example, enhanced with
+mutable variables and var/in support. To build this example, use:
+
+.. code-block:: bash
+
+ # Compile
+ clang++ -g toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core mcjit native` -O3 -o toy
+ # Run
+ ./toy
+
+Here is the code:
+
+.. literalinclude:: ../../examples/Kaleidoscope/Chapter7/toy.cpp
+ :language: c++
+
+`Next: Adding Debug Information <LangImpl8.html>`_
+
Added: www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl8.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl8.txt?rev=290368&view=auto
==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl8.txt (added)
+++ www-releases/trunk/3.9.1/docs/_sources/tutorial/LangImpl8.txt Thu Dec 22 14:04:03 2016
@@ -0,0 +1,462 @@
+======================================
+Kaleidoscope: Adding Debug Information
+======================================
+
+.. contents::
+ :local:
+
+Chapter 8 Introduction
+======================
+
+Welcome to Chapter 8 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. In chapters 1 through 7, we've built a
+decent little programming language with functions and variables.
+What happens if something goes wrong though, how do you debug your
+program?
+
+Source level debugging uses formatted data that helps a debugger
+translate from binary and the state of the machine back to the
+source that the programmer wrote. In LLVM we generally use a format
+called `DWARF <http://dwarfstd.org>`_. DWARF is a compact encoding
+that represents types, source locations, and variable locations.
+
+The short summary of this chapter is that we'll go through the
+various things you have to add to a programming language to
+support debug info, and how you translate that into DWARF.
+
+Caveat: For now we can't debug via the JIT, so we'll need to compile
+our program down to something small and standalone. As part of this
+we'll make a few modifications to the running of the language and
+how programs are compiled. This means that we'll have a source file
+with a simple program written in Kaleidoscope rather than the
+interactive JIT. It does involve a limitation that we can only
+have one "top level" command at a time to reduce the number of
+changes necessary.
+
+Here's the sample program we'll be compiling:
+
+.. code-block:: python
+
+ def fib(x)
+ if x < 3 then
+ 1
+ else
+ fib(x-1)+fib(x-2);
+
+ fib(10)
+
+
+Why is this a hard problem?
+===========================
+
+Debug information is a hard problem for a few different reasons - mostly
+centered around optimized code. First, optimization makes keeping source
+locations more difficult. In LLVM IR we keep the original source location
+for each IR level instruction on the instruction. Optimization passes
+should keep the source locations for newly created instructions, but merged
+instructions only get to keep a single location - this can cause jumping
+around when stepping through optimized programs. Secondly, optimization
+can move variables in ways that are either optimized out, shared in memory
+with other variables, or difficult to track. For the purposes of this
+tutorial we're going to avoid optimization (as you'll see with one of the
+next sets of patches).
+
+Ahead-of-Time Compilation Mode
+==============================
+
+To highlight only the aspects of adding debug information to a source
+language without needing to worry about the complexities of JIT debugging
+we're going to make a few changes to Kaleidoscope to support compiling
+the IR emitted by the front end into a simple standalone program that
+you can execute, debug, and see results.
+
+First we make our anonymous function that contains our top level
+statement be our "main":
+
+.. code-block:: udiff
+
+ - auto Proto = llvm::make_unique<PrototypeAST>("", std::vector<std::string>());
+ + auto Proto = llvm::make_unique<PrototypeAST>("main", std::vector<std::string>());
+
+just with the simple change of giving it a name.
+
+Then we're going to remove the command line code wherever it exists:
+
+.. code-block:: udiff
+
+ @@ -1129,7 +1129,6 @@ static void HandleTopLevelExpression() {
+ /// top ::= definition | external | expression | ';'
+ static void MainLoop() {
+ while (1) {
+ - fprintf(stderr, "ready> ");
+ switch (CurTok) {
+ case tok_eof:
+ return;
+ @@ -1184,7 +1183,6 @@ int main() {
+ BinopPrecedence['*'] = 40; // highest.
+
+ // Prime the first token.
+ - fprintf(stderr, "ready> ");
+ getNextToken();
+
+Lastly we're going to disable all of the optimization passes and the JIT so
+that the only thing that happens after we're done parsing and generating
+code is that the llvm IR goes to standard error:
+
+.. code-block:: udiff
+
+ @@ -1108,17 +1108,8 @@ static void HandleExtern() {
+ static void HandleTopLevelExpression() {
+ // Evaluate a top-level expression into an anonymous function.
+ if (auto FnAST = ParseTopLevelExpr()) {
+ - if (auto *FnIR = FnAST->codegen()) {
+ - // We're just doing this to make sure it executes.
+ - TheExecutionEngine->finalizeObject();
+ - // JIT the function, returning a function pointer.
+ - void *FPtr = TheExecutionEngine->getPointerToFunction(FnIR);
+ -
+ - // Cast it to the right type (takes no arguments, returns a double) so we
+ - // can call it as a native function.
+ - double (*FP)() = (double (*)())(intptr_t)FPtr;
+ - // Ignore the return value for this.
+ - (void)FP;
+ + if (!F->codegen()) {
+ + fprintf(stderr, "Error generating code for top level expr");
+ }
+ } else {
+ // Skip token for error recovery.
+ @@ -1439,11 +1459,11 @@ int main() {
+ // target lays out data structures.
+ TheModule->setDataLayout(TheExecutionEngine->getDataLayout());
+ OurFPM.add(new DataLayoutPass());
+ +#if 0
+ OurFPM.add(createBasicAliasAnalysisPass());
+ // Promote allocas to registers.
+ OurFPM.add(createPromoteMemoryToRegisterPass());
+ @@ -1218,7 +1210,7 @@ int main() {
+ OurFPM.add(createGVNPass());
+ // Simplify the control flow graph (deleting unreachable blocks, etc).
+ OurFPM.add(createCFGSimplificationPass());
+ -
+ + #endif
+ OurFPM.doInitialization();
+
+ // Set the global so the code gen can use this.
+
+This relatively small set of changes get us to the point that we can compile
+our piece of Kaleidoscope language down to an executable program via this
+command line:
+
+.. code-block:: bash
+
+ Kaleidoscope-Ch8 < fib.ks | & clang -x ir -
+
+which gives an a.out/a.exe in the current working directory.
+
+Compile Unit
+============
+
+The top level container for a section of code in DWARF is a compile unit.
+This contains the type and function data for an individual translation unit
+(read: one file of source code). So the first thing we need to do is
+construct one for our fib.ks file.
+
+DWARF Emission Setup
+====================
+
+Similar to the ``IRBuilder`` class we have a
+`DIBuilder <http://llvm.org/doxygen/classllvm_1_1DIBuilder.html>`_ class
+that helps in constructing debug metadata for an llvm IR file. It
+corresponds 1:1 similarly to ``IRBuilder`` and llvm IR, but with nicer names.
+Using it does require that you be more familiar with DWARF terminology than
+you needed to be with ``IRBuilder`` and ``Instruction`` names, but if you
+read through the general documentation on the
+`Metadata Format <http://llvm.org/docs/SourceLevelDebugging.html>`_ it
+should be a little more clear. We'll be using this class to construct all
+of our IR level descriptions. Construction for it takes a module so we
+need to construct it shortly after we construct our module. We've left it
+as a global static variable to make it a bit easier to use.
+
+Next we're going to create a small container to cache some of our frequent
+data. The first will be our compile unit, but we'll also write a bit of
+code for our one type since we won't have to worry about multiple typed
+expressions:
+
+.. code-block:: c++
+
+ static DIBuilder *DBuilder;
+
+ struct DebugInfo {
+ DICompileUnit *TheCU;
+ DIType *DblTy;
+
+ DIType *getDoubleTy();
+ } KSDbgInfo;
+
+ DIType *DebugInfo::getDoubleTy() {
+ if (DblTy.isValid())
+ return DblTy;
+
+ DblTy = DBuilder->createBasicType("double", 64, 64, dwarf::DW_ATE_float);
+ return DblTy;
+ }
+
+And then later on in ``main`` when we're constructing our module:
+
+.. code-block:: c++
+
+ DBuilder = new DIBuilder(*TheModule);
+
+ KSDbgInfo.TheCU = DBuilder->createCompileUnit(
+ dwarf::DW_LANG_C, "fib.ks", ".", "Kaleidoscope Compiler", 0, "", 0);
+
+There are a couple of things to note here. First, while we're producing a
+compile unit for a language called Kaleidoscope we used the language
+constant for C. This is because a debugger wouldn't necessarily understand
+the calling conventions or default ABI for a language it doesn't recognize
+and we follow the C ABI in our llvm code generation so it's the closest
+thing to accurate. This ensures we can actually call functions from the
+debugger and have them execute. Secondly, you'll see the "fib.ks" in the
+call to ``createCompileUnit``. This is a default hard coded value since
+we're using shell redirection to put our source into the Kaleidoscope
+compiler. In a usual front end you'd have an input file name and it would
+go there.
+
+One last thing as part of emitting debug information via DIBuilder is that
+we need to "finalize" the debug information. The reasons are part of the
+underlying API for DIBuilder, but make sure you do this near the end of
+main:
+
+.. code-block:: c++
+
+ DBuilder->finalize();
+
+before you dump out the module.
+
+Functions
+=========
+
+Now that we have our ``Compile Unit`` and our source locations, we can add
+function definitions to the debug info. So in ``PrototypeAST::codegen()`` we
+add a few lines of code to describe a context for our subprogram, in this
+case the "File", and the actual definition of the function itself.
+
+So the context:
+
+.. code-block:: c++
+
+ DIFile *Unit = DBuilder->createFile(KSDbgInfo.TheCU.getFilename(),
+ KSDbgInfo.TheCU.getDirectory());
+
+giving us an DIFile and asking the ``Compile Unit`` we created above for the
+directory and filename where we are currently. Then, for now, we use some
+source locations of 0 (since our AST doesn't currently have source location
+information) and construct our function definition:
+
+.. code-block:: c++
+
+ DIScope *FContext = Unit;
+ unsigned LineNo = 0;
+ unsigned ScopeLine = 0;
+ DISubprogram *SP = DBuilder->createFunction(
+ FContext, Name, StringRef(), Unit, LineNo,
+ CreateFunctionType(Args.size(), Unit), false /* internal linkage */,
+ true /* definition */, ScopeLine, DINode::FlagPrototyped, false);
+ F->setSubprogram(SP);
+
+and we now have an DISubprogram that contains a reference to all of our
+metadata for the function.
+
+Source Locations
+================
+
+The most important thing for debug information is accurate source location -
+this makes it possible to map your source code back. We have a problem though,
+Kaleidoscope really doesn't have any source location information in the lexer
+or parser so we'll need to add it.
+
+.. code-block:: c++
+
+ struct SourceLocation {
+ int Line;
+ int Col;
+ };
+ static SourceLocation CurLoc;
+ static SourceLocation LexLoc = {1, 0};
+
+ static int advance() {
+ int LastChar = getchar();
+
+ if (LastChar == '\n' || LastChar == '\r') {
+ LexLoc.Line++;
+ LexLoc.Col = 0;
+ } else
+ LexLoc.Col++;
+ return LastChar;
+ }
+
+In this set of code we've added some functionality on how to keep track of the
+line and column of the "source file". As we lex every token we set our current
+current "lexical location" to the assorted line and column for the beginning
+of the token. We do this by overriding all of the previous calls to
+``getchar()`` with our new ``advance()`` that keeps track of the information
+and then we have added to all of our AST classes a source location:
+
+.. code-block:: c++
+
+ class ExprAST {
+ SourceLocation Loc;
+
+ public:
+ ExprAST(SourceLocation Loc = CurLoc) : Loc(Loc) {}
+ virtual ~ExprAST() {}
+ virtual Value* codegen() = 0;
+ int getLine() const { return Loc.Line; }
+ int getCol() const { return Loc.Col; }
+ virtual raw_ostream &dump(raw_ostream &out, int ind) {
+ return out << ':' << getLine() << ':' << getCol() << '\n';
+ }
+
+that we pass down through when we create a new expression:
+
+.. code-block:: c++
+
+ LHS = llvm::make_unique<BinaryExprAST>(BinLoc, BinOp, std::move(LHS),
+ std::move(RHS));
+
+giving us locations for each of our expressions and variables.
+
+From this we can make sure to tell ``DIBuilder`` when we're at a new source
+location so it can use that when we generate the rest of our code and make
+sure that each instruction has source location information. We do this
+by constructing another small function:
+
+.. code-block:: c++
+
+ void DebugInfo::emitLocation(ExprAST *AST) {
+ DIScope *Scope;
+ if (LexicalBlocks.empty())
+ Scope = TheCU;
+ else
+ Scope = LexicalBlocks.back();
+ Builder.SetCurrentDebugLocation(
+ DebugLoc::get(AST->getLine(), AST->getCol(), Scope));
+ }
+
+that both tells the main ``IRBuilder`` where we are, but also what scope
+we're in. Since we've just created a function above we can either be in
+the main file scope (like when we created our function), or now we can be
+in the function scope we just created. To represent this we create a stack
+of scopes:
+
+.. code-block:: c++
+
+ std::vector<DIScope *> LexicalBlocks;
+ std::map<const PrototypeAST *, DIScope *> FnScopeMap;
+
+and keep a map of each function to the scope that it represents (an
+DISubprogram is also an DIScope).
+
+Then we make sure to:
+
+.. code-block:: c++
+
+ KSDbgInfo.emitLocation(this);
+
+emit the location every time we start to generate code for a new AST, and
+also:
+
+.. code-block:: c++
+
+ KSDbgInfo.FnScopeMap[this] = SP;
+
+store the scope (function) when we create it and use it:
+
+ KSDbgInfo.LexicalBlocks.push_back(&KSDbgInfo.FnScopeMap[Proto]);
+
+when we start generating the code for each function.
+
+also, don't forget to pop the scope back off of your scope stack at the
+end of the code generation for the function:
+
+.. code-block:: c++
+
+ // Pop off the lexical block for the function since we added it
+ // unconditionally.
+ KSDbgInfo.LexicalBlocks.pop_back();
+
+Variables
+=========
+
+Now that we have functions, we need to be able to print out the variables
+we have in scope. Let's get our function arguments set up so we can get
+decent backtraces and see how our functions are being called. It isn't
+a lot of code, and we generally handle it when we're creating the
+argument allocas in ``PrototypeAST::CreateArgumentAllocas``.
+
+.. code-block:: c++
+
+ DIScope *Scope = KSDbgInfo.LexicalBlocks.back();
+ DIFile *Unit = DBuilder->createFile(KSDbgInfo.TheCU.getFilename(),
+ KSDbgInfo.TheCU.getDirectory());
+ DILocalVariable D = DBuilder->createParameterVariable(
+ Scope, Args[Idx], Idx + 1, Unit, Line, KSDbgInfo.getDoubleTy(), true);
+
+ DBuilder->insertDeclare(Alloca, D, DBuilder->createExpression(),
+ DebugLoc::get(Line, 0, Scope),
+ Builder.GetInsertBlock());
+
+Here we're doing a few things. First, we're grabbing our current scope
+for the variable so we can say what range of code our variable is valid
+through. Second, we're creating the variable, giving it the scope,
+the name, source location, type, and since it's an argument, the argument
+index. Third, we create an ``lvm.dbg.declare`` call to indicate at the IR
+level that we've got a variable in an alloca (and it gives a starting
+location for the variable), and setting a source location for the
+beginning of the scope on the declare.
+
+One interesting thing to note at this point is that various debuggers have
+assumptions based on how code and debug information was generated for them
+in the past. In this case we need to do a little bit of a hack to avoid
+generating line information for the function prologue so that the debugger
+knows to skip over those instructions when setting a breakpoint. So in
+``FunctionAST::CodeGen`` we add a couple of lines:
+
+.. code-block:: c++
+
+ // Unset the location for the prologue emission (leading instructions with no
+ // location in a function are considered part of the prologue and the debugger
+ // will run past them when breaking on a function)
+ KSDbgInfo.emitLocation(nullptr);
+
+and then emit a new location when we actually start generating code for the
+body of the function:
+
+.. code-block:: c++
+
+ KSDbgInfo.emitLocation(Body);
+
+With this we have enough debug information to set breakpoints in functions,
+print out argument variables, and call functions. Not too bad for just a
+few simple lines of code!
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example, enhanced with
+debug information. To build this example, use:
+
+.. code-block:: bash
+
+ # Compile
+ clang++ -g toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core mcjit native` -O3 -o toy
+ # Run
+ ./toy
+
+Here is the code:
+
+.. literalinclude:: ../../examples/Kaleidoscope/Chapter8/toy.cpp
+ :language: c++
+
+`Next: Conclusion and other useful LLVM tidbits <LangImpl9.html>`_
+
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+======================================================
+Kaleidoscope: Conclusion and other useful LLVM tidbits
+======================================================
+
+.. contents::
+ :local:
+
+Tutorial Conclusion
+===================
+
+Welcome to the final chapter of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. In the course of this tutorial, we have
+grown our little Kaleidoscope language from being a useless toy, to
+being a semi-interesting (but probably still useless) toy. :)
+
+It is interesting to see how far we've come, and how little code it has
+taken. We built the entire lexer, parser, AST, code generator, an
+interactive run-loop (with a JIT!), and emitted debug information in
+standalone executables - all in under 1000 lines of (non-comment/non-blank)
+code.
+
+Our little language supports a couple of interesting features: it
+supports user defined binary and unary operators, it uses JIT
+compilation for immediate evaluation, and it supports a few control flow
+constructs with SSA construction.
+
+Part of the idea of this tutorial was to show you how easy and fun it
+can be to define, build, and play with languages. Building a compiler
+need not be a scary or mystical process! Now that you've seen some of
+the basics, I strongly encourage you to take the code and hack on it.
+For example, try adding:
+
+- **global variables** - While global variables have questional value
+ in modern software engineering, they are often useful when putting
+ together quick little hacks like the Kaleidoscope compiler itself.
+ Fortunately, our current setup makes it very easy to add global
+ variables: just have value lookup check to see if an unresolved
+ variable is in the global variable symbol table before rejecting it.
+ To create a new global variable, make an instance of the LLVM
+ ``GlobalVariable`` class.
+- **typed variables** - Kaleidoscope currently only supports variables
+ of type double. This gives the language a very nice elegance, because
+ only supporting one type means that you never have to specify types.
+ Different languages have different ways of handling this. The easiest
+ way is to require the user to specify types for every variable
+ definition, and record the type of the variable in the symbol table
+ along with its Value\*.
+- **arrays, structs, vectors, etc** - Once you add types, you can start
+ extending the type system in all sorts of interesting ways. Simple
+ arrays are very easy and are quite useful for many different
+ applications. Adding them is mostly an exercise in learning how the
+ LLVM `getelementptr <../LangRef.html#getelementptr-instruction>`_ instruction
+ works: it is so nifty/unconventional, it `has its own
+ FAQ <../GetElementPtr.html>`_! If you add support for recursive types
+ (e.g. linked lists), make sure to read the `section in the LLVM
+ Programmer's Manual <../ProgrammersManual.html#TypeResolve>`_ that
+ describes how to construct them.
+- **standard runtime** - Our current language allows the user to access
+ arbitrary external functions, and we use it for things like "printd"
+ and "putchard". As you extend the language to add higher-level
+ constructs, often these constructs make the most sense if they are
+ lowered to calls into a language-supplied runtime. For example, if
+ you add hash tables to the language, it would probably make sense to
+ add the routines to a runtime, instead of inlining them all the way.
+- **memory management** - Currently we can only access the stack in
+ Kaleidoscope. It would also be useful to be able to allocate heap
+ memory, either with calls to the standard libc malloc/free interface
+ or with a garbage collector. If you would like to use garbage
+ collection, note that LLVM fully supports `Accurate Garbage
+ Collection <../GarbageCollection.html>`_ including algorithms that
+ move objects and need to scan/update the stack.
+- **exception handling support** - LLVM supports generation of `zero
+ cost exceptions <../ExceptionHandling.html>`_ which interoperate with
+ code compiled in other languages. You could also generate code by
+ implicitly making every function return an error value and checking
+ it. You could also make explicit use of setjmp/longjmp. There are
+ many different ways to go here.
+- **object orientation, generics, database access, complex numbers,
+ geometric programming, ...** - Really, there is no end of crazy
+ features that you can add to the language.
+- **unusual domains** - We've been talking about applying LLVM to a
+ domain that many people are interested in: building a compiler for a
+ specific language. However, there are many other domains that can use
+ compiler technology that are not typically considered. For example,
+ LLVM has been used to implement OpenGL graphics acceleration,
+ translate C++ code to ActionScript, and many other cute and clever
+ things. Maybe you will be the first to JIT compile a regular
+ expression interpreter into native code with LLVM?
+
+Have fun - try doing something crazy and unusual. Building a language
+like everyone else always has, is much less fun than trying something a
+little crazy or off the wall and seeing how it turns out. If you get
+stuck or want to talk about it, feel free to email the `llvm-dev mailing
+list <http://lists.llvm.org/mailman/listinfo/llvm-dev>`_: it has lots
+of people who are interested in languages and are often willing to help
+out.
+
+Before we end this tutorial, I want to talk about some "tips and tricks"
+for generating LLVM IR. These are some of the more subtle things that
+may not be obvious, but are very useful if you want to take advantage of
+LLVM's capabilities.
+
+Properties of the LLVM IR
+=========================
+
+We have a couple common questions about code in the LLVM IR form - lets
+just get these out of the way right now, shall we?
+
+Target Independence
+-------------------
+
+Kaleidoscope is an example of a "portable language": any program written
+in Kaleidoscope will work the same way on any target that it runs on.
+Many other languages have this property, e.g. lisp, java, haskell,
+javascript, python, etc (note that while these languages are portable,
+not all their libraries are).
+
+One nice aspect of LLVM is that it is often capable of preserving target
+independence in the IR: you can take the LLVM IR for a
+Kaleidoscope-compiled program and run it on any target that LLVM
+supports, even emitting C code and compiling that on targets that LLVM
+doesn't support natively. You can trivially tell that the Kaleidoscope
+compiler generates target-independent code because it never queries for
+any target-specific information when generating code.
+
+The fact that LLVM provides a compact, target-independent,
+representation for code gets a lot of people excited. Unfortunately,
+these people are usually thinking about C or a language from the C
+family when they are asking questions about language portability. I say
+"unfortunately", because there is really no way to make (fully general)
+C code portable, other than shipping the source code around (and of
+course, C source code is not actually portable in general either - ever
+port a really old application from 32- to 64-bits?).
+
+The problem with C (again, in its full generality) is that it is heavily
+laden with target specific assumptions. As one simple example, the
+preprocessor often destructively removes target-independence from the
+code when it processes the input text:
+
+.. code-block:: c
+
+ #ifdef __i386__
+ int X = 1;
+ #else
+ int X = 42;
+ #endif
+
+While it is possible to engineer more and more complex solutions to
+problems like this, it cannot be solved in full generality in a way that
+is better than shipping the actual source code.
+
+That said, there are interesting subsets of C that can be made portable.
+If you are willing to fix primitive types to a fixed size (say int =
+32-bits, and long = 64-bits), don't care about ABI compatibility with
+existing binaries, and are willing to give up some other minor features,
+you can have portable code. This can make sense for specialized domains
+such as an in-kernel language.
+
+Safety Guarantees
+-----------------
+
+Many of the languages above are also "safe" languages: it is impossible
+for a program written in Java to corrupt its address space and crash the
+process (assuming the JVM has no bugs). Safety is an interesting
+property that requires a combination of language design, runtime
+support, and often operating system support.
+
+It is certainly possible to implement a safe language in LLVM, but LLVM
+IR does not itself guarantee safety. The LLVM IR allows unsafe pointer
+casts, use after free bugs, buffer over-runs, and a variety of other
+problems. Safety needs to be implemented as a layer on top of LLVM and,
+conveniently, several groups have investigated this. Ask on the `llvm-dev
+mailing list <http://lists.llvm.org/mailman/listinfo/llvm-dev>`_ if
+you are interested in more details.
+
+Language-Specific Optimizations
+-------------------------------
+
+One thing about LLVM that turns off many people is that it does not
+solve all the world's problems in one system (sorry 'world hunger',
+someone else will have to solve you some other day). One specific
+complaint is that people perceive LLVM as being incapable of performing
+high-level language-specific optimization: LLVM "loses too much
+information".
+
+Unfortunately, this is really not the place to give you a full and
+unified version of "Chris Lattner's theory of compiler design". Instead,
+I'll make a few observations:
+
+First, you're right that LLVM does lose information. For example, as of
+this writing, there is no way to distinguish in the LLVM IR whether an
+SSA-value came from a C "int" or a C "long" on an ILP32 machine (other
+than debug info). Both get compiled down to an 'i32' value and the
+information about what it came from is lost. The more general issue
+here, is that the LLVM type system uses "structural equivalence" instead
+of "name equivalence". Another place this surprises people is if you
+have two types in a high-level language that have the same structure
+(e.g. two different structs that have a single int field): these types
+will compile down into a single LLVM type and it will be impossible to
+tell what it came from.
+
+Second, while LLVM does lose information, LLVM is not a fixed target: we
+continue to enhance and improve it in many different ways. In addition
+to adding new features (LLVM did not always support exceptions or debug
+info), we also extend the IR to capture important information for
+optimization (e.g. whether an argument is sign or zero extended,
+information about pointers aliasing, etc). Many of the enhancements are
+user-driven: people want LLVM to include some specific feature, so they
+go ahead and extend it.
+
+Third, it is *possible and easy* to add language-specific optimizations,
+and you have a number of choices in how to do it. As one trivial
+example, it is easy to add language-specific optimization passes that
+"know" things about code compiled for a language. In the case of the C
+family, there is an optimization pass that "knows" about the standard C
+library functions. If you call "exit(0)" in main(), it knows that it is
+safe to optimize that into "return 0;" because C specifies what the
+'exit' function does.
+
+In addition to simple library knowledge, it is possible to embed a
+variety of other language-specific information into the LLVM IR. If you
+have a specific need and run into a wall, please bring the topic up on
+the llvm-dev list. At the very worst, you can always treat LLVM as if it
+were a "dumb code generator" and implement the high-level optimizations
+you desire in your front-end, on the language-specific AST.
+
+Tips and Tricks
+===============
+
+There is a variety of useful tips and tricks that you come to know after
+working on/with LLVM that aren't obvious at first glance. Instead of
+letting everyone rediscover them, this section talks about some of these
+issues.
+
+Implementing portable offsetof/sizeof
+-------------------------------------
+
+One interesting thing that comes up, if you are trying to keep the code
+generated by your compiler "target independent", is that you often need
+to know the size of some LLVM type or the offset of some field in an
+llvm structure. For example, you might need to pass the size of a type
+into a function that allocates memory.
+
+Unfortunately, this can vary widely across targets: for example the
+width of a pointer is trivially target-specific. However, there is a
+`clever way to use the getelementptr
+instruction <http://nondot.org/sabre/LLVMNotes/SizeOf-OffsetOf-VariableSizedStructs.txt>`_
+that allows you to compute this in a portable way.
+
+Garbage Collected Stack Frames
+------------------------------
+
+Some languages want to explicitly manage their stack frames, often so
+that they are garbage collected or to allow easy implementation of
+closures. There are often better ways to implement these features than
+explicit stack frames, but `LLVM does support
+them, <http://nondot.org/sabre/LLVMNotes/ExplicitlyManagedStackFrames.txt>`_
+if you want. It requires your front-end to convert the code into
+`Continuation Passing
+Style <http://en.wikipedia.org/wiki/Continuation-passing_style>`_ and
+the use of tail calls (which LLVM also supports).
+
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+=================================================
+Kaleidoscope: Tutorial Introduction and the Lexer
+=================================================
+
+.. contents::
+ :local:
+
+Tutorial Introduction
+=====================
+
+Welcome to the "Implementing a language with LLVM" tutorial. This
+tutorial runs through the implementation of a simple language, showing
+how fun and easy it can be. This tutorial will get you up and started as
+well as help to build a framework you can extend to other languages. The
+code in this tutorial can also be used as a playground to hack on other
+LLVM specific things.
+
+The goal of this tutorial is to progressively unveil our language,
+describing how it is built up over time. This will let us cover a fairly
+broad range of language design and LLVM-specific usage issues, showing
+and explaining the code for it all along the way, without overwhelming
+you with tons of details up front.
+
+It is useful to point out ahead of time that this tutorial is really
+about teaching compiler techniques and LLVM specifically, *not* about
+teaching modern and sane software engineering principles. In practice,
+this means that we'll take a number of shortcuts to simplify the
+exposition. For example, the code leaks memory, uses global variables
+all over the place, doesn't use nice design patterns like
+`visitors <http://en.wikipedia.org/wiki/Visitor_pattern>`_, etc... but
+it is very simple. If you dig in and use the code as a basis for future
+projects, fixing these deficiencies shouldn't be hard.
+
+I've tried to put this tutorial together in a way that makes chapters
+easy to skip over if you are already familiar with or are uninterested
+in the various pieces. The structure of the tutorial is:
+
+- `Chapter #1 <#language>`_: Introduction to the Kaleidoscope
+ language, and the definition of its Lexer - This shows where we are
+ going and the basic functionality that we want it to do. In order to
+ make this tutorial maximally understandable and hackable, we choose
+ to implement everything in Objective Caml instead of using lexer and
+ parser generators. LLVM obviously works just fine with such tools,
+ feel free to use one if you prefer.
+- `Chapter #2 <OCamlLangImpl2.html>`_: Implementing a Parser and
+ AST - With the lexer in place, we can talk about parsing techniques
+ and basic AST construction. This tutorial describes recursive descent
+ parsing and operator precedence parsing. Nothing in Chapters 1 or 2
+ is LLVM-specific, the code doesn't even link in LLVM at this point.
+ :)
+- `Chapter #3 <OCamlLangImpl3.html>`_: Code generation to LLVM IR -
+ With the AST ready, we can show off how easy generation of LLVM IR
+ really is.
+- `Chapter #4 <OCamlLangImpl4.html>`_: Adding JIT and Optimizer
+ Support - Because a lot of people are interested in using LLVM as a
+ JIT, we'll dive right into it and show you the 3 lines it takes to
+ add JIT support. LLVM is also useful in many other ways, but this is
+ one simple and "sexy" way to shows off its power. :)
+- `Chapter #5 <OCamlLangImpl5.html>`_: Extending the Language:
+ Control Flow - With the language up and running, we show how to
+ extend it with control flow operations (if/then/else and a 'for'
+ loop). This gives us a chance to talk about simple SSA construction
+ and control flow.
+- `Chapter #6 <OCamlLangImpl6.html>`_: Extending the Language:
+ User-defined Operators - This is a silly but fun chapter that talks
+ about extending the language to let the user program define their own
+ arbitrary unary and binary operators (with assignable precedence!).
+ This lets us build a significant piece of the "language" as library
+ routines.
+- `Chapter #7 <OCamlLangImpl7.html>`_: Extending the Language:
+ Mutable Variables - This chapter talks about adding user-defined
+ local variables along with an assignment operator. The interesting
+ part about this is how easy and trivial it is to construct SSA form
+ in LLVM: no, LLVM does *not* require your front-end to construct SSA
+ form!
+- `Chapter #8 <OCamlLangImpl8.html>`_: Conclusion and other useful
+ LLVM tidbits - This chapter wraps up the series by talking about
+ potential ways to extend the language, but also includes a bunch of
+ pointers to info about "special topics" like adding garbage
+ collection support, exceptions, debugging, support for "spaghetti
+ stacks", and a bunch of other tips and tricks.
+
+By the end of the tutorial, we'll have written a bit less than 700 lines
+of non-comment, non-blank, lines of code. With this small amount of
+code, we'll have built up a very reasonable compiler for a non-trivial
+language including a hand-written lexer, parser, AST, as well as code
+generation support with a JIT compiler. While other systems may have
+interesting "hello world" tutorials, I think the breadth of this
+tutorial is a great testament to the strengths of LLVM and why you
+should consider it if you're interested in language or compiler design.
+
+A note about this tutorial: we expect you to extend the language and
+play with it on your own. Take the code and go crazy hacking away at it,
+compilers don't need to be scary creatures - it can be a lot of fun to
+play with languages!
+
+The Basic Language
+==================
+
+This tutorial will be illustrated with a toy language that we'll call
+"`Kaleidoscope <http://en.wikipedia.org/wiki/Kaleidoscope>`_" (derived
+from "meaning beautiful, form, and view"). Kaleidoscope is a procedural
+language that allows you to define functions, use conditionals, math,
+etc. Over the course of the tutorial, we'll extend Kaleidoscope to
+support the if/then/else construct, a for loop, user defined operators,
+JIT compilation with a simple command line interface, etc.
+
+Because we want to keep things simple, the only datatype in Kaleidoscope
+is a 64-bit floating point type (aka 'float' in OCaml parlance). As
+such, all values are implicitly double precision and the language
+doesn't require type declarations. This gives the language a very nice
+and simple syntax. For example, the following simple example computes
+`Fibonacci numbers: <http://en.wikipedia.org/wiki/Fibonacci_number>`_
+
+::
+
+ # Compute the x'th fibonacci number.
+ def fib(x)
+ if x < 3 then
+ 1
+ else
+ fib(x-1)+fib(x-2)
+
+ # This expression will compute the 40th number.
+ fib(40)
+
+We also allow Kaleidoscope to call into standard library functions (the
+LLVM JIT makes this completely trivial). This means that you can use the
+'extern' keyword to define a function before you use it (this is also
+useful for mutually recursive functions). For example:
+
+::
+
+ extern sin(arg);
+ extern cos(arg);
+ extern atan2(arg1 arg2);
+
+ atan2(sin(.4), cos(42))
+
+A more interesting example is included in Chapter 6 where we write a
+little Kaleidoscope application that `displays a Mandelbrot
+Set <OCamlLangImpl6.html#kicking-the-tires>`_ at various levels of magnification.
+
+Lets dive into the implementation of this language!
+
+The Lexer
+=========
+
+When it comes to implementing a language, the first thing needed is the
+ability to process a text file and recognize what it says. The
+traditional way to do this is to use a
+"`lexer <http://en.wikipedia.org/wiki/Lexical_analysis>`_" (aka
+'scanner') to break the input up into "tokens". Each token returned by
+the lexer includes a token code and potentially some metadata (e.g. the
+numeric value of a number). First, we define the possibilities:
+
+.. code-block:: ocaml
+
+ (* The lexer returns these 'Kwd' if it is an unknown character, otherwise one of
+ * these others for known things. *)
+ type token =
+ (* commands *)
+ | Def | Extern
+
+ (* primary *)
+ | Ident of string | Number of float
+
+ (* unknown *)
+ | Kwd of char
+
+Each token returned by our lexer will be one of the token variant
+values. An unknown character like '+' will be returned as
+``Token.Kwd '+'``. If the curr token is an identifier, the value will be
+``Token.Ident s``. If the current token is a numeric literal (like 1.0),
+the value will be ``Token.Number 1.0``.
+
+The actual implementation of the lexer is a collection of functions
+driven by a function named ``Lexer.lex``. The ``Lexer.lex`` function is
+called to return the next token from standard input. We will use
+`Camlp4 <http://caml.inria.fr/pub/docs/manual-camlp4/index.html>`_ to
+simplify the tokenization of the standard input. Its definition starts
+as:
+
+.. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Lexer
+ *===----------------------------------------------------------------------===*)
+
+ let rec lex = parser
+ (* Skip any whitespace. *)
+ | [< ' (' ' | '\n' | '\r' | '\t'); stream >] -> lex stream
+
+``Lexer.lex`` works by recursing over a ``char Stream.t`` to read
+characters one at a time from the standard input. It eats them as it
+recognizes them and stores them in in a ``Token.token`` variant. The
+first thing that it has to do is ignore whitespace between tokens. This
+is accomplished with the recursive call above.
+
+The next thing ``Lexer.lex`` needs to do is recognize identifiers and
+specific keywords like "def". Kaleidoscope does this with a pattern
+match and a helper function.
+
+.. code-block:: ocaml
+
+ (* identifier: [a-zA-Z][a-zA-Z0-9] *)
+ | [< ' ('A' .. 'Z' | 'a' .. 'z' as c); stream >] ->
+ let buffer = Buffer.create 1 in
+ Buffer.add_char buffer c;
+ lex_ident buffer stream
+
+ ...
+
+ and lex_ident buffer = parser
+ | [< ' ('A' .. 'Z' | 'a' .. 'z' | '0' .. '9' as c); stream >] ->
+ Buffer.add_char buffer c;
+ lex_ident buffer stream
+ | [< stream=lex >] ->
+ match Buffer.contents buffer with
+ | "def" -> [< 'Token.Def; stream >]
+ | "extern" -> [< 'Token.Extern; stream >]
+ | id -> [< 'Token.Ident id; stream >]
+
+Numeric values are similar:
+
+.. code-block:: ocaml
+
+ (* number: [0-9.]+ *)
+ | [< ' ('0' .. '9' as c); stream >] ->
+ let buffer = Buffer.create 1 in
+ Buffer.add_char buffer c;
+ lex_number buffer stream
+
+ ...
+
+ and lex_number buffer = parser
+ | [< ' ('0' .. '9' | '.' as c); stream >] ->
+ Buffer.add_char buffer c;
+ lex_number buffer stream
+ | [< stream=lex >] ->
+ [< 'Token.Number (float_of_string (Buffer.contents buffer)); stream >]
+
+This is all pretty straight-forward code for processing input. When
+reading a numeric value from input, we use the ocaml ``float_of_string``
+function to convert it to a numeric value that we store in
+``Token.Number``. Note that this isn't doing sufficient error checking:
+it will raise ``Failure`` if the string "1.23.45.67". Feel free to
+extend it :). Next we handle comments:
+
+.. code-block:: ocaml
+
+ (* Comment until end of line. *)
+ | [< ' ('#'); stream >] ->
+ lex_comment stream
+
+ ...
+
+ and lex_comment = parser
+ | [< ' ('\n'); stream=lex >] -> stream
+ | [< 'c; e=lex_comment >] -> e
+ | [< >] -> [< >]
+
+We handle comments by skipping to the end of the line and then return
+the next token. Finally, if the input doesn't match one of the above
+cases, it is either an operator character like '+' or the end of the
+file. These are handled with this code:
+
+.. code-block:: ocaml
+
+ (* Otherwise, just return the character as its ascii value. *)
+ | [< 'c; stream >] ->
+ [< 'Token.Kwd c; lex stream >]
+
+ (* end of stream. *)
+ | [< >] -> [< >]
+
+With this, we have the complete lexer for the basic Kaleidoscope
+language (the `full code listing <OCamlLangImpl2.html#full-code-listing>`_ for the
+Lexer is available in the `next chapter <OCamlLangImpl2.html>`_ of the
+tutorial). Next we'll `build a simple parser that uses this to build an
+Abstract Syntax Tree <OCamlLangImpl2.html>`_. When we have that, we'll
+include a driver so that you can use the lexer and parser together.
+
+`Next: Implementing a Parser and AST <OCamlLangImpl2.html>`_
+
Added: www-releases/trunk/3.9.1/docs/_sources/tutorial/OCamlLangImpl2.txt
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==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/tutorial/OCamlLangImpl2.txt (added)
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+===========================================
+Kaleidoscope: Implementing a Parser and AST
+===========================================
+
+.. contents::
+ :local:
+
+Chapter 2 Introduction
+======================
+
+Welcome to Chapter 2 of the "`Implementing a language with LLVM in
+Objective Caml <index.html>`_" tutorial. This chapter shows you how to
+use the lexer, built in `Chapter 1 <OCamlLangImpl1.html>`_, to build a
+full `parser <http://en.wikipedia.org/wiki/Parsing>`_ for our
+Kaleidoscope language. Once we have a parser, we'll define and build an
+`Abstract Syntax
+Tree <http://en.wikipedia.org/wiki/Abstract_syntax_tree>`_ (AST).
+
+The parser we will build uses a combination of `Recursive Descent
+Parsing <http://en.wikipedia.org/wiki/Recursive_descent_parser>`_ and
+`Operator-Precedence
+Parsing <http://en.wikipedia.org/wiki/Operator-precedence_parser>`_ to
+parse the Kaleidoscope language (the latter for binary expressions and
+the former for everything else). Before we get to parsing though, lets
+talk about the output of the parser: the Abstract Syntax Tree.
+
+The Abstract Syntax Tree (AST)
+==============================
+
+The AST for a program captures its behavior in such a way that it is
+easy for later stages of the compiler (e.g. code generation) to
+interpret. We basically want one object for each construct in the
+language, and the AST should closely model the language. In
+Kaleidoscope, we have expressions, a prototype, and a function object.
+We'll start with expressions first:
+
+.. code-block:: ocaml
+
+ (* expr - Base type for all expression nodes. *)
+ type expr =
+ (* variant for numeric literals like "1.0". *)
+ | Number of float
+
+The code above shows the definition of the base ExprAST class and one
+subclass which we use for numeric literals. The important thing to note
+about this code is that the Number variant captures the numeric value of
+the literal as an instance variable. This allows later phases of the
+compiler to know what the stored numeric value is.
+
+Right now we only create the AST, so there are no useful functions on
+them. It would be very easy to add a function to pretty print the code,
+for example. Here are the other expression AST node definitions that
+we'll use in the basic form of the Kaleidoscope language:
+
+.. code-block:: ocaml
+
+ (* variant for referencing a variable, like "a". *)
+ | Variable of string
+
+ (* variant for a binary operator. *)
+ | Binary of char * expr * expr
+
+ (* variant for function calls. *)
+ | Call of string * expr array
+
+This is all (intentionally) rather straight-forward: variables capture
+the variable name, binary operators capture their opcode (e.g. '+'), and
+calls capture a function name as well as a list of any argument
+expressions. One thing that is nice about our AST is that it captures
+the language features without talking about the syntax of the language.
+Note that there is no discussion about precedence of binary operators,
+lexical structure, etc.
+
+For our basic language, these are all of the expression nodes we'll
+define. Because it doesn't have conditional control flow, it isn't
+Turing-complete; we'll fix that in a later installment. The two things
+we need next are a way to talk about the interface to a function, and a
+way to talk about functions themselves:
+
+.. code-block:: ocaml
+
+ (* proto - This type represents the "prototype" for a function, which captures
+ * its name, and its argument names (thus implicitly the number of arguments the
+ * function takes). *)
+ type proto = Prototype of string * string array
+
+ (* func - This type represents a function definition itself. *)
+ type func = Function of proto * expr
+
+In Kaleidoscope, functions are typed with just a count of their
+arguments. Since all values are double precision floating point, the
+type of each argument doesn't need to be stored anywhere. In a more
+aggressive and realistic language, the "expr" variants would probably
+have a type field.
+
+With this scaffolding, we can now talk about parsing expressions and
+function bodies in Kaleidoscope.
+
+Parser Basics
+=============
+
+Now that we have an AST to build, we need to define the parser code to
+build it. The idea here is that we want to parse something like "x+y"
+(which is returned as three tokens by the lexer) into an AST that could
+be generated with calls like this:
+
+.. code-block:: ocaml
+
+ let x = Variable "x" in
+ let y = Variable "y" in
+ let result = Binary ('+', x, y) in
+ ...
+
+The error handling routines make use of the builtin ``Stream.Failure``
+and ``Stream.Error``s. ``Stream.Failure`` is raised when the parser is
+unable to find any matching token in the first position of a pattern.
+``Stream.Error`` is raised when the first token matches, but the rest do
+not. The error recovery in our parser will not be the best and is not
+particular user-friendly, but it will be enough for our tutorial. These
+exceptions make it easier to handle errors in routines that have various
+return types.
+
+With these basic types and exceptions, we can implement the first piece
+of our grammar: numeric literals.
+
+Basic Expression Parsing
+========================
+
+We start with numeric literals, because they are the simplest to
+process. For each production in our grammar, we'll define a function
+which parses that production. We call this class of expressions
+"primary" expressions, for reasons that will become more clear `later in
+the tutorial <OCamlLangImpl6.html#user-defined-unary-operators>`_. In order to parse an
+arbitrary primary expression, we need to determine what sort of
+expression it is. For numeric literals, we have:
+
+.. code-block:: ocaml
+
+ (* primary
+ * ::= identifier
+ * ::= numberexpr
+ * ::= parenexpr *)
+ parse_primary = parser
+ (* numberexpr ::= number *)
+ | [< 'Token.Number n >] -> Ast.Number n
+
+This routine is very simple: it expects to be called when the current
+token is a ``Token.Number`` token. It takes the current number value,
+creates a ``Ast.Number`` node, advances the lexer to the next token, and
+finally returns.
+
+There are some interesting aspects to this. The most important one is
+that this routine eats all of the tokens that correspond to the
+production and returns the lexer buffer with the next token (which is
+not part of the grammar production) ready to go. This is a fairly
+standard way to go for recursive descent parsers. For a better example,
+the parenthesis operator is defined like this:
+
+.. code-block:: ocaml
+
+ (* parenexpr ::= '(' expression ')' *)
+ | [< 'Token.Kwd '('; e=parse_expr; 'Token.Kwd ')' ?? "expected ')'" >] -> e
+
+This function illustrates a number of interesting things about the
+parser:
+
+1) It shows how we use the ``Stream.Error`` exception. When called, this
+function expects that the current token is a '(' token, but after
+parsing the subexpression, it is possible that there is no ')' waiting.
+For example, if the user types in "(4 x" instead of "(4)", the parser
+should emit an error. Because errors can occur, the parser needs a way
+to indicate that they happened. In our parser, we use the camlp4
+shortcut syntax ``token ?? "parse error"``, where if the token before
+the ``??`` does not match, then ``Stream.Error "parse error"`` will be
+raised.
+
+2) Another interesting aspect of this function is that it uses recursion
+by calling ``Parser.parse_primary`` (we will soon see that
+``Parser.parse_primary`` can call ``Parser.parse_primary``). This is
+powerful because it allows us to handle recursive grammars, and keeps
+each production very simple. Note that parentheses do not cause
+construction of AST nodes themselves. While we could do it this way, the
+most important role of parentheses are to guide the parser and provide
+grouping. Once the parser constructs the AST, parentheses are not
+needed.
+
+The next simple production is for handling variable references and
+function calls:
+
+.. code-block:: ocaml
+
+ (* identifierexpr
+ * ::= identifier
+ * ::= identifier '(' argumentexpr ')' *)
+ | [< 'Token.Ident id; stream >] ->
+ let rec parse_args accumulator = parser
+ | [< e=parse_expr; stream >] ->
+ begin parser
+ | [< 'Token.Kwd ','; e=parse_args (e :: accumulator) >] -> e
+ | [< >] -> e :: accumulator
+ end stream
+ | [< >] -> accumulator
+ in
+ let rec parse_ident id = parser
+ (* Call. *)
+ | [< 'Token.Kwd '(';
+ args=parse_args [];
+ 'Token.Kwd ')' ?? "expected ')'">] ->
+ Ast.Call (id, Array.of_list (List.rev args))
+
+ (* Simple variable ref. *)
+ | [< >] -> Ast.Variable id
+ in
+ parse_ident id stream
+
+This routine follows the same style as the other routines. (It expects
+to be called if the current token is a ``Token.Ident`` token). It also
+has recursion and error handling. One interesting aspect of this is that
+it uses *look-ahead* to determine if the current identifier is a stand
+alone variable reference or if it is a function call expression. It
+handles this by checking to see if the token after the identifier is a
+'(' token, constructing either a ``Ast.Variable`` or ``Ast.Call`` node
+as appropriate.
+
+We finish up by raising an exception if we received a token we didn't
+expect:
+
+.. code-block:: ocaml
+
+ | [< >] -> raise (Stream.Error "unknown token when expecting an expression.")
+
+Now that basic expressions are handled, we need to handle binary
+expressions. They are a bit more complex.
+
+Binary Expression Parsing
+=========================
+
+Binary expressions are significantly harder to parse because they are
+often ambiguous. For example, when given the string "x+y\*z", the parser
+can choose to parse it as either "(x+y)\*z" or "x+(y\*z)". With common
+definitions from mathematics, we expect the later parse, because "\*"
+(multiplication) has higher *precedence* than "+" (addition).
+
+There are many ways to handle this, but an elegant and efficient way is
+to use `Operator-Precedence
+Parsing <http://en.wikipedia.org/wiki/Operator-precedence_parser>`_.
+This parsing technique uses the precedence of binary operators to guide
+recursion. To start with, we need a table of precedences:
+
+.. code-block:: ocaml
+
+ (* binop_precedence - This holds the precedence for each binary operator that is
+ * defined *)
+ let binop_precedence:(char, int) Hashtbl.t = Hashtbl.create 10
+
+ (* precedence - Get the precedence of the pending binary operator token. *)
+ let precedence c = try Hashtbl.find binop_precedence c with Not_found -> -1
+
+ ...
+
+ let main () =
+ (* Install standard binary operators.
+ * 1 is the lowest precedence. *)
+ Hashtbl.add Parser.binop_precedence '<' 10;
+ Hashtbl.add Parser.binop_precedence '+' 20;
+ Hashtbl.add Parser.binop_precedence '-' 20;
+ Hashtbl.add Parser.binop_precedence '*' 40; (* highest. *)
+ ...
+
+For the basic form of Kaleidoscope, we will only support 4 binary
+operators (this can obviously be extended by you, our brave and intrepid
+reader). The ``Parser.precedence`` function returns the precedence for
+the current token, or -1 if the token is not a binary operator. Having a
+``Hashtbl.t`` makes it easy to add new operators and makes it clear that
+the algorithm doesn't depend on the specific operators involved, but it
+would be easy enough to eliminate the ``Hashtbl.t`` and do the
+comparisons in the ``Parser.precedence`` function. (Or just use a
+fixed-size array).
+
+With the helper above defined, we can now start parsing binary
+expressions. The basic idea of operator precedence parsing is to break
+down an expression with potentially ambiguous binary operators into
+pieces. Consider, for example, the expression "a+b+(c+d)\*e\*f+g".
+Operator precedence parsing considers this as a stream of primary
+expressions separated by binary operators. As such, it will first parse
+the leading primary expression "a", then it will see the pairs [+, b]
+[+, (c+d)] [\*, e] [\*, f] and [+, g]. Note that because parentheses are
+primary expressions, the binary expression parser doesn't need to worry
+about nested subexpressions like (c+d) at all.
+
+To start, an expression is a primary expression potentially followed by
+a sequence of [binop,primaryexpr] pairs:
+
+.. code-block:: ocaml
+
+ (* expression
+ * ::= primary binoprhs *)
+ and parse_expr = parser
+ | [< lhs=parse_primary; stream >] -> parse_bin_rhs 0 lhs stream
+
+``Parser.parse_bin_rhs`` is the function that parses the sequence of
+pairs for us. It takes a precedence and a pointer to an expression for
+the part that has been parsed so far. Note that "x" is a perfectly valid
+expression: As such, "binoprhs" is allowed to be empty, in which case it
+returns the expression that is passed into it. In our example above, the
+code passes the expression for "a" into ``Parser.parse_bin_rhs`` and the
+current token is "+".
+
+The precedence value passed into ``Parser.parse_bin_rhs`` indicates the
+*minimal operator precedence* that the function is allowed to eat. For
+example, if the current pair stream is [+, x] and
+``Parser.parse_bin_rhs`` is passed in a precedence of 40, it will not
+consume any tokens (because the precedence of '+' is only 20). With this
+in mind, ``Parser.parse_bin_rhs`` starts with:
+
+.. code-block:: ocaml
+
+ (* binoprhs
+ * ::= ('+' primary)* *)
+ and parse_bin_rhs expr_prec lhs stream =
+ match Stream.peek stream with
+ (* If this is a binop, find its precedence. *)
+ | Some (Token.Kwd c) when Hashtbl.mem binop_precedence c ->
+ let token_prec = precedence c in
+
+ (* If this is a binop that binds at least as tightly as the current binop,
+ * consume it, otherwise we are done. *)
+ if token_prec < expr_prec then lhs else begin
+
+This code gets the precedence of the current token and checks to see if
+if is too low. Because we defined invalid tokens to have a precedence of
+-1, this check implicitly knows that the pair-stream ends when the token
+stream runs out of binary operators. If this check succeeds, we know
+that the token is a binary operator and that it will be included in this
+expression:
+
+.. code-block:: ocaml
+
+ (* Eat the binop. *)
+ Stream.junk stream;
+
+ (* Parse the primary expression after the binary operator *)
+ let rhs = parse_primary stream in
+
+ (* Okay, we know this is a binop. *)
+ let rhs =
+ match Stream.peek stream with
+ | Some (Token.Kwd c2) ->
+
+As such, this code eats (and remembers) the binary operator and then
+parses the primary expression that follows. This builds up the whole
+pair, the first of which is [+, b] for the running example.
+
+Now that we parsed the left-hand side of an expression and one pair of
+the RHS sequence, we have to decide which way the expression associates.
+In particular, we could have "(a+b) binop unparsed" or "a + (b binop
+unparsed)". To determine this, we look ahead at "binop" to determine its
+precedence and compare it to BinOp's precedence (which is '+' in this
+case):
+
+.. code-block:: ocaml
+
+ (* If BinOp binds less tightly with rhs than the operator after
+ * rhs, let the pending operator take rhs as its lhs. *)
+ let next_prec = precedence c2 in
+ if token_prec < next_prec
+
+If the precedence of the binop to the right of "RHS" is lower or equal
+to the precedence of our current operator, then we know that the
+parentheses associate as "(a+b) binop ...". In our example, the current
+operator is "+" and the next operator is "+", we know that they have the
+same precedence. In this case we'll create the AST node for "a+b", and
+then continue parsing:
+
+.. code-block:: ocaml
+
+ ... if body omitted ...
+ in
+
+ (* Merge lhs/rhs. *)
+ let lhs = Ast.Binary (c, lhs, rhs) in
+ parse_bin_rhs expr_prec lhs stream
+ end
+
+In our example above, this will turn "a+b+" into "(a+b)" and execute the
+next iteration of the loop, with "+" as the current token. The code
+above will eat, remember, and parse "(c+d)" as the primary expression,
+which makes the current pair equal to [+, (c+d)]. It will then evaluate
+the 'if' conditional above with "\*" as the binop to the right of the
+primary. In this case, the precedence of "\*" is higher than the
+precedence of "+" so the if condition will be entered.
+
+The critical question left here is "how can the if condition parse the
+right hand side in full"? In particular, to build the AST correctly for
+our example, it needs to get all of "(c+d)\*e\*f" as the RHS expression
+variable. The code to do this is surprisingly simple (code from the
+above two blocks duplicated for context):
+
+.. code-block:: ocaml
+
+ match Stream.peek stream with
+ | Some (Token.Kwd c2) ->
+ (* If BinOp binds less tightly with rhs than the operator after
+ * rhs, let the pending operator take rhs as its lhs. *)
+ if token_prec < precedence c2
+ then parse_bin_rhs (token_prec + 1) rhs stream
+ else rhs
+ | _ -> rhs
+ in
+
+ (* Merge lhs/rhs. *)
+ let lhs = Ast.Binary (c, lhs, rhs) in
+ parse_bin_rhs expr_prec lhs stream
+ end
+
+At this point, we know that the binary operator to the RHS of our
+primary has higher precedence than the binop we are currently parsing.
+As such, we know that any sequence of pairs whose operators are all
+higher precedence than "+" should be parsed together and returned as
+"RHS". To do this, we recursively invoke the ``Parser.parse_bin_rhs``
+function specifying "token\_prec+1" as the minimum precedence required
+for it to continue. In our example above, this will cause it to return
+the AST node for "(c+d)\*e\*f" as RHS, which is then set as the RHS of
+the '+' expression.
+
+Finally, on the next iteration of the while loop, the "+g" piece is
+parsed and added to the AST. With this little bit of code (14
+non-trivial lines), we correctly handle fully general binary expression
+parsing in a very elegant way. This was a whirlwind tour of this code,
+and it is somewhat subtle. I recommend running through it with a few
+tough examples to see how it works.
+
+This wraps up handling of expressions. At this point, we can point the
+parser at an arbitrary token stream and build an expression from it,
+stopping at the first token that is not part of the expression. Next up
+we need to handle function definitions, etc.
+
+Parsing the Rest
+================
+
+The next thing missing is handling of function prototypes. In
+Kaleidoscope, these are used both for 'extern' function declarations as
+well as function body definitions. The code to do this is
+straight-forward and not very interesting (once you've survived
+expressions):
+
+.. code-block:: ocaml
+
+ (* prototype
+ * ::= id '(' id* ')' *)
+ let parse_prototype =
+ let rec parse_args accumulator = parser
+ | [< 'Token.Ident id; e=parse_args (id::accumulator) >] -> e
+ | [< >] -> accumulator
+ in
+
+ parser
+ | [< 'Token.Ident id;
+ 'Token.Kwd '(' ?? "expected '(' in prototype";
+ args=parse_args [];
+ 'Token.Kwd ')' ?? "expected ')' in prototype" >] ->
+ (* success. *)
+ Ast.Prototype (id, Array.of_list (List.rev args))
+
+ | [< >] ->
+ raise (Stream.Error "expected function name in prototype")
+
+Given this, a function definition is very simple, just a prototype plus
+an expression to implement the body:
+
+.. code-block:: ocaml
+
+ (* definition ::= 'def' prototype expression *)
+ let parse_definition = parser
+ | [< 'Token.Def; p=parse_prototype; e=parse_expr >] ->
+ Ast.Function (p, e)
+
+In addition, we support 'extern' to declare functions like 'sin' and
+'cos' as well as to support forward declaration of user functions. These
+'extern's are just prototypes with no body:
+
+.. code-block:: ocaml
+
+ (* external ::= 'extern' prototype *)
+ let parse_extern = parser
+ | [< 'Token.Extern; e=parse_prototype >] -> e
+
+Finally, we'll also let the user type in arbitrary top-level expressions
+and evaluate them on the fly. We will handle this by defining anonymous
+nullary (zero argument) functions for them:
+
+.. code-block:: ocaml
+
+ (* toplevelexpr ::= expression *)
+ let parse_toplevel = parser
+ | [< e=parse_expr >] ->
+ (* Make an anonymous proto. *)
+ Ast.Function (Ast.Prototype ("", [||]), e)
+
+Now that we have all the pieces, let's build a little driver that will
+let us actually *execute* this code we've built!
+
+The Driver
+==========
+
+The driver for this simply invokes all of the parsing pieces with a
+top-level dispatch loop. There isn't much interesting here, so I'll just
+include the top-level loop. See `below <#full-code-listing>`_ for full code in the
+"Top-Level Parsing" section.
+
+.. code-block:: ocaml
+
+ (* top ::= definition | external | expression | ';' *)
+ let rec main_loop stream =
+ match Stream.peek stream with
+ | None -> ()
+
+ (* ignore top-level semicolons. *)
+ | Some (Token.Kwd ';') ->
+ Stream.junk stream;
+ main_loop stream
+
+ | Some token ->
+ begin
+ try match token with
+ | Token.Def ->
+ ignore(Parser.parse_definition stream);
+ print_endline "parsed a function definition.";
+ | Token.Extern ->
+ ignore(Parser.parse_extern stream);
+ print_endline "parsed an extern.";
+ | _ ->
+ (* Evaluate a top-level expression into an anonymous function. *)
+ ignore(Parser.parse_toplevel stream);
+ print_endline "parsed a top-level expr";
+ with Stream.Error s ->
+ (* Skip token for error recovery. *)
+ Stream.junk stream;
+ print_endline s;
+ end;
+ print_string "ready> "; flush stdout;
+ main_loop stream
+
+The most interesting part of this is that we ignore top-level
+semicolons. Why is this, you ask? The basic reason is that if you type
+"4 + 5" at the command line, the parser doesn't know whether that is the
+end of what you will type or not. For example, on the next line you
+could type "def foo..." in which case 4+5 is the end of a top-level
+expression. Alternatively you could type "\* 6", which would continue
+the expression. Having top-level semicolons allows you to type "4+5;",
+and the parser will know you are done.
+
+Conclusions
+===========
+
+With just under 300 lines of commented code (240 lines of non-comment,
+non-blank code), we fully defined our minimal language, including a
+lexer, parser, and AST builder. With this done, the executable will
+validate Kaleidoscope code and tell us if it is grammatically invalid.
+For example, here is a sample interaction:
+
+.. code-block:: bash
+
+ $ ./toy.byte
+ ready> def foo(x y) x+foo(y, 4.0);
+ Parsed a function definition.
+ ready> def foo(x y) x+y y;
+ Parsed a function definition.
+ Parsed a top-level expr
+ ready> def foo(x y) x+y );
+ Parsed a function definition.
+ Error: unknown token when expecting an expression
+ ready> extern sin(a);
+ ready> Parsed an extern
+ ready> ^D
+ $
+
+There is a lot of room for extension here. You can define new AST nodes,
+extend the language in many ways, etc. In the `next
+installment <OCamlLangImpl3.html>`_, we will describe how to generate
+LLVM Intermediate Representation (IR) from the AST.
+
+Full Code Listing
+=================
+
+Here is the complete code listing for this and the previous chapter.
+Note that it is fully self-contained: you don't need LLVM or any
+external libraries at all for this. (Besides the ocaml standard
+libraries, of course.) To build this, just compile with:
+
+.. code-block:: bash
+
+ # Compile
+ ocamlbuild toy.byte
+ # Run
+ ./toy.byte
+
+Here is the code:
+
+\_tags:
+ ::
+
+ <{lexer,parser}.ml>: use_camlp4, pp(camlp4of)
+
+token.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Lexer Tokens
+ *===----------------------------------------------------------------------===*)
+
+ (* The lexer returns these 'Kwd' if it is an unknown character, otherwise one of
+ * these others for known things. *)
+ type token =
+ (* commands *)
+ | Def | Extern
+
+ (* primary *)
+ | Ident of string | Number of float
+
+ (* unknown *)
+ | Kwd of char
+
+lexer.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Lexer
+ *===----------------------------------------------------------------------===*)
+
+ let rec lex = parser
+ (* Skip any whitespace. *)
+ | [< ' (' ' | '\n' | '\r' | '\t'); stream >] -> lex stream
+
+ (* identifier: [a-zA-Z][a-zA-Z0-9] *)
+ | [< ' ('A' .. 'Z' | 'a' .. 'z' as c); stream >] ->
+ let buffer = Buffer.create 1 in
+ Buffer.add_char buffer c;
+ lex_ident buffer stream
+
+ (* number: [0-9.]+ *)
+ | [< ' ('0' .. '9' as c); stream >] ->
+ let buffer = Buffer.create 1 in
+ Buffer.add_char buffer c;
+ lex_number buffer stream
+
+ (* Comment until end of line. *)
+ | [< ' ('#'); stream >] ->
+ lex_comment stream
+
+ (* Otherwise, just return the character as its ascii value. *)
+ | [< 'c; stream >] ->
+ [< 'Token.Kwd c; lex stream >]
+
+ (* end of stream. *)
+ | [< >] -> [< >]
+
+ and lex_number buffer = parser
+ | [< ' ('0' .. '9' | '.' as c); stream >] ->
+ Buffer.add_char buffer c;
+ lex_number buffer stream
+ | [< stream=lex >] ->
+ [< 'Token.Number (float_of_string (Buffer.contents buffer)); stream >]
+
+ and lex_ident buffer = parser
+ | [< ' ('A' .. 'Z' | 'a' .. 'z' | '0' .. '9' as c); stream >] ->
+ Buffer.add_char buffer c;
+ lex_ident buffer stream
+ | [< stream=lex >] ->
+ match Buffer.contents buffer with
+ | "def" -> [< 'Token.Def; stream >]
+ | "extern" -> [< 'Token.Extern; stream >]
+ | id -> [< 'Token.Ident id; stream >]
+
+ and lex_comment = parser
+ | [< ' ('\n'); stream=lex >] -> stream
+ | [< 'c; e=lex_comment >] -> e
+ | [< >] -> [< >]
+
+ast.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Abstract Syntax Tree (aka Parse Tree)
+ *===----------------------------------------------------------------------===*)
+
+ (* expr - Base type for all expression nodes. *)
+ type expr =
+ (* variant for numeric literals like "1.0". *)
+ | Number of float
+
+ (* variant for referencing a variable, like "a". *)
+ | Variable of string
+
+ (* variant for a binary operator. *)
+ | Binary of char * expr * expr
+
+ (* variant for function calls. *)
+ | Call of string * expr array
+
+ (* proto - This type represents the "prototype" for a function, which captures
+ * its name, and its argument names (thus implicitly the number of arguments the
+ * function takes). *)
+ type proto = Prototype of string * string array
+
+ (* func - This type represents a function definition itself. *)
+ type func = Function of proto * expr
+
+parser.ml:
+ .. code-block:: ocaml
+
+ (*===---------------------------------------------------------------------===
+ * Parser
+ *===---------------------------------------------------------------------===*)
+
+ (* binop_precedence - This holds the precedence for each binary operator that is
+ * defined *)
+ let binop_precedence:(char, int) Hashtbl.t = Hashtbl.create 10
+
+ (* precedence - Get the precedence of the pending binary operator token. *)
+ let precedence c = try Hashtbl.find binop_precedence c with Not_found -> -1
+
+ (* primary
+ * ::= identifier
+ * ::= numberexpr
+ * ::= parenexpr *)
+ let rec parse_primary = parser
+ (* numberexpr ::= number *)
+ | [< 'Token.Number n >] -> Ast.Number n
+
+ (* parenexpr ::= '(' expression ')' *)
+ | [< 'Token.Kwd '('; e=parse_expr; 'Token.Kwd ')' ?? "expected ')'" >] -> e
+
+ (* identifierexpr
+ * ::= identifier
+ * ::= identifier '(' argumentexpr ')' *)
+ | [< 'Token.Ident id; stream >] ->
+ let rec parse_args accumulator = parser
+ | [< e=parse_expr; stream >] ->
+ begin parser
+ | [< 'Token.Kwd ','; e=parse_args (e :: accumulator) >] -> e
+ | [< >] -> e :: accumulator
+ end stream
+ | [< >] -> accumulator
+ in
+ let rec parse_ident id = parser
+ (* Call. *)
+ | [< 'Token.Kwd '(';
+ args=parse_args [];
+ 'Token.Kwd ')' ?? "expected ')'">] ->
+ Ast.Call (id, Array.of_list (List.rev args))
+
+ (* Simple variable ref. *)
+ | [< >] -> Ast.Variable id
+ in
+ parse_ident id stream
+
+ | [< >] -> raise (Stream.Error "unknown token when expecting an expression.")
+
+ (* binoprhs
+ * ::= ('+' primary)* *)
+ and parse_bin_rhs expr_prec lhs stream =
+ match Stream.peek stream with
+ (* If this is a binop, find its precedence. *)
+ | Some (Token.Kwd c) when Hashtbl.mem binop_precedence c ->
+ let token_prec = precedence c in
+
+ (* If this is a binop that binds at least as tightly as the current binop,
+ * consume it, otherwise we are done. *)
+ if token_prec < expr_prec then lhs else begin
+ (* Eat the binop. *)
+ Stream.junk stream;
+
+ (* Parse the primary expression after the binary operator. *)
+ let rhs = parse_primary stream in
+
+ (* Okay, we know this is a binop. *)
+ let rhs =
+ match Stream.peek stream with
+ | Some (Token.Kwd c2) ->
+ (* If BinOp binds less tightly with rhs than the operator after
+ * rhs, let the pending operator take rhs as its lhs. *)
+ let next_prec = precedence c2 in
+ if token_prec < next_prec
+ then parse_bin_rhs (token_prec + 1) rhs stream
+ else rhs
+ | _ -> rhs
+ in
+
+ (* Merge lhs/rhs. *)
+ let lhs = Ast.Binary (c, lhs, rhs) in
+ parse_bin_rhs expr_prec lhs stream
+ end
+ | _ -> lhs
+
+ (* expression
+ * ::= primary binoprhs *)
+ and parse_expr = parser
+ | [< lhs=parse_primary; stream >] -> parse_bin_rhs 0 lhs stream
+
+ (* prototype
+ * ::= id '(' id* ')' *)
+ let parse_prototype =
+ let rec parse_args accumulator = parser
+ | [< 'Token.Ident id; e=parse_args (id::accumulator) >] -> e
+ | [< >] -> accumulator
+ in
+
+ parser
+ | [< 'Token.Ident id;
+ 'Token.Kwd '(' ?? "expected '(' in prototype";
+ args=parse_args [];
+ 'Token.Kwd ')' ?? "expected ')' in prototype" >] ->
+ (* success. *)
+ Ast.Prototype (id, Array.of_list (List.rev args))
+
+ | [< >] ->
+ raise (Stream.Error "expected function name in prototype")
+
+ (* definition ::= 'def' prototype expression *)
+ let parse_definition = parser
+ | [< 'Token.Def; p=parse_prototype; e=parse_expr >] ->
+ Ast.Function (p, e)
+
+ (* toplevelexpr ::= expression *)
+ let parse_toplevel = parser
+ | [< e=parse_expr >] ->
+ (* Make an anonymous proto. *)
+ Ast.Function (Ast.Prototype ("", [||]), e)
+
+ (* external ::= 'extern' prototype *)
+ let parse_extern = parser
+ | [< 'Token.Extern; e=parse_prototype >] -> e
+
+toplevel.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Top-Level parsing and JIT Driver
+ *===----------------------------------------------------------------------===*)
+
+ (* top ::= definition | external | expression | ';' *)
+ let rec main_loop stream =
+ match Stream.peek stream with
+ | None -> ()
+
+ (* ignore top-level semicolons. *)
+ | Some (Token.Kwd ';') ->
+ Stream.junk stream;
+ main_loop stream
+
+ | Some token ->
+ begin
+ try match token with
+ | Token.Def ->
+ ignore(Parser.parse_definition stream);
+ print_endline "parsed a function definition.";
+ | Token.Extern ->
+ ignore(Parser.parse_extern stream);
+ print_endline "parsed an extern.";
+ | _ ->
+ (* Evaluate a top-level expression into an anonymous function. *)
+ ignore(Parser.parse_toplevel stream);
+ print_endline "parsed a top-level expr";
+ with Stream.Error s ->
+ (* Skip token for error recovery. *)
+ Stream.junk stream;
+ print_endline s;
+ end;
+ print_string "ready> "; flush stdout;
+ main_loop stream
+
+toy.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Main driver code.
+ *===----------------------------------------------------------------------===*)
+
+ let main () =
+ (* Install standard binary operators.
+ * 1 is the lowest precedence. *)
+ Hashtbl.add Parser.binop_precedence '<' 10;
+ Hashtbl.add Parser.binop_precedence '+' 20;
+ Hashtbl.add Parser.binop_precedence '-' 20;
+ Hashtbl.add Parser.binop_precedence '*' 40; (* highest. *)
+
+ (* Prime the first token. *)
+ print_string "ready> "; flush stdout;
+ let stream = Lexer.lex (Stream.of_channel stdin) in
+
+ (* Run the main "interpreter loop" now. *)
+ Toplevel.main_loop stream;
+ ;;
+
+ main ()
+
+`Next: Implementing Code Generation to LLVM IR <OCamlLangImpl3.html>`_
+
Added: www-releases/trunk/3.9.1/docs/_sources/tutorial/OCamlLangImpl3.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.9.1/docs/_sources/tutorial/OCamlLangImpl3.txt?rev=290368&view=auto
==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/tutorial/OCamlLangImpl3.txt (added)
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@@ -0,0 +1,961 @@
+========================================
+Kaleidoscope: Code generation to LLVM IR
+========================================
+
+.. contents::
+ :local:
+
+Chapter 3 Introduction
+======================
+
+Welcome to Chapter 3 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. This chapter shows you how to transform
+the `Abstract Syntax Tree <OCamlLangImpl2.html>`_, built in Chapter 2,
+into LLVM IR. This will teach you a little bit about how LLVM does
+things, as well as demonstrate how easy it is to use. It's much more
+work to build a lexer and parser than it is to generate LLVM IR code. :)
+
+**Please note**: the code in this chapter and later require LLVM 2.3 or
+LLVM SVN to work. LLVM 2.2 and before will not work with it.
+
+Code Generation Setup
+=====================
+
+In order to generate LLVM IR, we want some simple setup to get started.
+First we define virtual code generation (codegen) methods in each AST
+class:
+
+.. code-block:: ocaml
+
+ let rec codegen_expr = function
+ | Ast.Number n -> ...
+ | Ast.Variable name -> ...
+
+The ``Codegen.codegen_expr`` function says to emit IR for that AST node
+along with all the things it depends on, and they all return an LLVM
+Value object. "Value" is the class used to represent a "`Static Single
+Assignment
+(SSA) <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_
+register" or "SSA value" in LLVM. The most distinct aspect of SSA values
+is that their value is computed as the related instruction executes, and
+it does not get a new value until (and if) the instruction re-executes.
+In other words, there is no way to "change" an SSA value. For more
+information, please read up on `Static Single
+Assignment <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_
+- the concepts are really quite natural once you grok them.
+
+The second thing we want is an "Error" exception like we used for the
+parser, which will be used to report errors found during code generation
+(for example, use of an undeclared parameter):
+
+.. code-block:: ocaml
+
+ exception Error of string
+
+ let context = global_context ()
+ let the_module = create_module context "my cool jit"
+ let builder = builder context
+ let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10
+ let double_type = double_type context
+
+The static variables will be used during code generation.
+``Codgen.the_module`` is the LLVM construct that contains all of the
+functions and global variables in a chunk of code. In many ways, it is
+the top-level structure that the LLVM IR uses to contain code.
+
+The ``Codegen.builder`` object is a helper object that makes it easy to
+generate LLVM instructions. Instances of the
+`IRBuilder <http://llvm.org/doxygen/IRBuilder_8h-source.html>`_
+class keep track of the current place to insert instructions and has
+methods to create new instructions.
+
+The ``Codegen.named_values`` map keeps track of which values are defined
+in the current scope and what their LLVM representation is. (In other
+words, it is a symbol table for the code). In this form of Kaleidoscope,
+the only things that can be referenced are function parameters. As such,
+function parameters will be in this map when generating code for their
+function body.
+
+With these basics in place, we can start talking about how to generate
+code for each expression. Note that this assumes that the
+``Codgen.builder`` has been set up to generate code *into* something.
+For now, we'll assume that this has already been done, and we'll just
+use it to emit code.
+
+Expression Code Generation
+==========================
+
+Generating LLVM code for expression nodes is very straightforward: less
+than 30 lines of commented code for all four of our expression nodes.
+First we'll do numeric literals:
+
+.. code-block:: ocaml
+
+ | Ast.Number n -> const_float double_type n
+
+In the LLVM IR, numeric constants are represented with the
+``ConstantFP`` class, which holds the numeric value in an ``APFloat``
+internally (``APFloat`` has the capability of holding floating point
+constants of Arbitrary Precision). This code basically just creates
+and returns a ``ConstantFP``. Note that in the LLVM IR that constants
+are all uniqued together and shared. For this reason, the API uses "the
+foo::get(..)" idiom instead of "new foo(..)" or "foo::Create(..)".
+
+.. code-block:: ocaml
+
+ | Ast.Variable name ->
+ (try Hashtbl.find named_values name with
+ | Not_found -> raise (Error "unknown variable name"))
+
+References to variables are also quite simple using LLVM. In the simple
+version of Kaleidoscope, we assume that the variable has already been
+emitted somewhere and its value is available. In practice, the only
+values that can be in the ``Codegen.named_values`` map are function
+arguments. This code simply checks to see that the specified name is in
+the map (if not, an unknown variable is being referenced) and returns
+the value for it. In future chapters, we'll add support for `loop
+induction variables <LangImpl5.html#for-loop-expression>`_ in the symbol table, and for
+`local variables <LangImpl7.html#user-defined-local-variables>`_.
+
+.. code-block:: ocaml
+
+ | Ast.Binary (op, lhs, rhs) ->
+ let lhs_val = codegen_expr lhs in
+ let rhs_val = codegen_expr rhs in
+ begin
+ match op with
+ | '+' -> build_fadd lhs_val rhs_val "addtmp" builder
+ | '-' -> build_fsub lhs_val rhs_val "subtmp" builder
+ | '*' -> build_fmul lhs_val rhs_val "multmp" builder
+ | '<' ->
+ (* Convert bool 0/1 to double 0.0 or 1.0 *)
+ let i = build_fcmp Fcmp.Ult lhs_val rhs_val "cmptmp" builder in
+ build_uitofp i double_type "booltmp" builder
+ | _ -> raise (Error "invalid binary operator")
+ end
+
+Binary operators start to get more interesting. The basic idea here is
+that we recursively emit code for the left-hand side of the expression,
+then the right-hand side, then we compute the result of the binary
+expression. In this code, we do a simple switch on the opcode to create
+the right LLVM instruction.
+
+In the example above, the LLVM builder class is starting to show its
+value. IRBuilder knows where to insert the newly created instruction,
+all you have to do is specify what instruction to create (e.g. with
+``Llvm.create_add``), which operands to use (``lhs`` and ``rhs`` here)
+and optionally provide a name for the generated instruction.
+
+One nice thing about LLVM is that the name is just a hint. For instance,
+if the code above emits multiple "addtmp" variables, LLVM will
+automatically provide each one with an increasing, unique numeric
+suffix. Local value names for instructions are purely optional, but it
+makes it much easier to read the IR dumps.
+
+`LLVM instructions <../LangRef.html#instruction-reference>`_ are constrained by strict
+rules: for example, the Left and Right operators of an `add
+instruction <../LangRef.html#add-instruction>`_ must have the same type, and the
+result type of the add must match the operand types. Because all values
+in Kaleidoscope are doubles, this makes for very simple code for add,
+sub and mul.
+
+On the other hand, LLVM specifies that the `fcmp
+instruction <../LangRef.html#fcmp-instruction>`_ always returns an 'i1' value (a
+one bit integer). The problem with this is that Kaleidoscope wants the
+value to be a 0.0 or 1.0 value. In order to get these semantics, we
+combine the fcmp instruction with a `uitofp
+instruction <../LangRef.html#uitofp-to-instruction>`_. This instruction converts its
+input integer into a floating point value by treating the input as an
+unsigned value. In contrast, if we used the `sitofp
+instruction <../LangRef.html#sitofp-to-instruction>`_, the Kaleidoscope '<' operator
+would return 0.0 and -1.0, depending on the input value.
+
+.. code-block:: ocaml
+
+ | Ast.Call (callee, args) ->
+ (* Look up the name in the module table. *)
+ let callee =
+ match lookup_function callee the_module with
+ | Some callee -> callee
+ | None -> raise (Error "unknown function referenced")
+ in
+ let params = params callee in
+
+ (* If argument mismatch error. *)
+ if Array.length params == Array.length args then () else
+ raise (Error "incorrect # arguments passed");
+ let args = Array.map codegen_expr args in
+ build_call callee args "calltmp" builder
+
+Code generation for function calls is quite straightforward with LLVM.
+The code above initially does a function name lookup in the LLVM
+Module's symbol table. Recall that the LLVM Module is the container that
+holds all of the functions we are JIT'ing. By giving each function the
+same name as what the user specifies, we can use the LLVM symbol table
+to resolve function names for us.
+
+Once we have the function to call, we recursively codegen each argument
+that is to be passed in, and create an LLVM `call
+instruction <../LangRef.html#call-instruction>`_. Note that LLVM uses the native C
+calling conventions by default, allowing these calls to also call into
+standard library functions like "sin" and "cos", with no additional
+effort.
+
+This wraps up our handling of the four basic expressions that we have so
+far in Kaleidoscope. Feel free to go in and add some more. For example,
+by browsing the `LLVM language reference <../LangRef.html>`_ you'll find
+several other interesting instructions that are really easy to plug into
+our basic framework.
+
+Function Code Generation
+========================
+
+Code generation for prototypes and functions must handle a number of
+details, which make their code less beautiful than expression code
+generation, but allows us to illustrate some important points. First,
+lets talk about code generation for prototypes: they are used both for
+function bodies and external function declarations. The code starts
+with:
+
+.. code-block:: ocaml
+
+ let codegen_proto = function
+ | Ast.Prototype (name, args) ->
+ (* Make the function type: double(double,double) etc. *)
+ let doubles = Array.make (Array.length args) double_type in
+ let ft = function_type double_type doubles in
+ let f =
+ match lookup_function name the_module with
+
+This code packs a lot of power into a few lines. Note first that this
+function returns a "Function\*" instead of a "Value\*" (although at the
+moment they both are modeled by ``llvalue`` in ocaml). Because a
+"prototype" really talks about the external interface for a function
+(not the value computed by an expression), it makes sense for it to
+return the LLVM Function it corresponds to when codegen'd.
+
+The call to ``Llvm.function_type`` creates the ``Llvm.llvalue`` that
+should be used for a given Prototype. Since all function arguments in
+Kaleidoscope are of type double, the first line creates a vector of "N"
+LLVM double types. It then uses the ``Llvm.function_type`` method to
+create a function type that takes "N" doubles as arguments, returns one
+double as a result, and that is not vararg (that uses the function
+``Llvm.var_arg_function_type``). Note that Types in LLVM are uniqued
+just like ``Constant``'s are, so you don't "new" a type, you "get" it.
+
+The final line above checks if the function has already been defined in
+``Codegen.the_module``. If not, we will create it.
+
+.. code-block:: ocaml
+
+ | None -> declare_function name ft the_module
+
+This indicates the type and name to use, as well as which module to
+insert into. By default we assume a function has
+``Llvm.Linkage.ExternalLinkage``. "`external
+linkage <../LangRef.html#linkage>`_" means that the function may be defined
+outside the current module and/or that it is callable by functions
+outside the module. The "``name``" passed in is the name the user
+specified: this name is registered in "``Codegen.the_module``"s symbol
+table, which is used by the function call code above.
+
+In Kaleidoscope, I choose to allow redefinitions of functions in two
+cases: first, we want to allow 'extern'ing a function more than once, as
+long as the prototypes for the externs match (since all arguments have
+the same type, we just have to check that the number of arguments
+match). Second, we want to allow 'extern'ing a function and then
+defining a body for it. This is useful when defining mutually recursive
+functions.
+
+.. code-block:: ocaml
+
+ (* If 'f' conflicted, there was already something named 'name'. If it
+ * has a body, don't allow redefinition or reextern. *)
+ | Some f ->
+ (* If 'f' already has a body, reject this. *)
+ if Array.length (basic_blocks f) == 0 then () else
+ raise (Error "redefinition of function");
+
+ (* If 'f' took a different number of arguments, reject. *)
+ if Array.length (params f) == Array.length args then () else
+ raise (Error "redefinition of function with different # args");
+ f
+ in
+
+In order to verify the logic above, we first check to see if the
+pre-existing function is "empty". In this case, empty means that it has
+no basic blocks in it, which means it has no body. If it has no body, it
+is a forward declaration. Since we don't allow anything after a full
+definition of the function, the code rejects this case. If the previous
+reference to a function was an 'extern', we simply verify that the
+number of arguments for that definition and this one match up. If not,
+we emit an error.
+
+.. code-block:: ocaml
+
+ (* Set names for all arguments. *)
+ Array.iteri (fun i a ->
+ let n = args.(i) in
+ set_value_name n a;
+ Hashtbl.add named_values n a;
+ ) (params f);
+ f
+
+The last bit of code for prototypes loops over all of the arguments in
+the function, setting the name of the LLVM Argument objects to match,
+and registering the arguments in the ``Codegen.named_values`` map for
+future use by the ``Ast.Variable`` variant. Once this is set up, it
+returns the Function object to the caller. Note that we don't check for
+conflicting argument names here (e.g. "extern foo(a b a)"). Doing so
+would be very straight-forward with the mechanics we have already used
+above.
+
+.. code-block:: ocaml
+
+ let codegen_func = function
+ | Ast.Function (proto, body) ->
+ Hashtbl.clear named_values;
+ let the_function = codegen_proto proto in
+
+Code generation for function definitions starts out simply enough: we
+just codegen the prototype (Proto) and verify that it is ok. We then
+clear out the ``Codegen.named_values`` map to make sure that there isn't
+anything in it from the last function we compiled. Code generation of
+the prototype ensures that there is an LLVM Function object that is
+ready to go for us.
+
+.. code-block:: ocaml
+
+ (* Create a new basic block to start insertion into. *)
+ let bb = append_block context "entry" the_function in
+ position_at_end bb builder;
+
+ try
+ let ret_val = codegen_expr body in
+
+Now we get to the point where the ``Codegen.builder`` is set up. The
+first line creates a new `basic
+block <http://en.wikipedia.org/wiki/Basic_block>`_ (named "entry"),
+which is inserted into ``the_function``. The second line then tells the
+builder that new instructions should be inserted into the end of the new
+basic block. Basic blocks in LLVM are an important part of functions
+that define the `Control Flow
+Graph <http://en.wikipedia.org/wiki/Control_flow_graph>`_. Since we
+don't have any control flow, our functions will only contain one block
+at this point. We'll fix this in `Chapter 5 <OCamlLangImpl5.html>`_ :).
+
+.. code-block:: ocaml
+
+ let ret_val = codegen_expr body in
+
+ (* Finish off the function. *)
+ let _ = build_ret ret_val builder in
+
+ (* Validate the generated code, checking for consistency. *)
+ Llvm_analysis.assert_valid_function the_function;
+
+ the_function
+
+Once the insertion point is set up, we call the ``Codegen.codegen_func``
+method for the root expression of the function. If no error happens,
+this emits code to compute the expression into the entry block and
+returns the value that was computed. Assuming no error, we then create
+an LLVM `ret instruction <../LangRef.html#ret-instruction>`_, which completes the
+function. Once the function is built, we call
+``Llvm_analysis.assert_valid_function``, which is provided by LLVM. This
+function does a variety of consistency checks on the generated code, to
+determine if our compiler is doing everything right. Using this is
+important: it can catch a lot of bugs. Once the function is finished and
+validated, we return it.
+
+.. code-block:: ocaml
+
+ with e ->
+ delete_function the_function;
+ raise e
+
+The only piece left here is handling of the error case. For simplicity,
+we handle this by merely deleting the function we produced with the
+``Llvm.delete_function`` method. This allows the user to redefine a
+function that they incorrectly typed in before: if we didn't delete it,
+it would live in the symbol table, with a body, preventing future
+redefinition.
+
+This code does have a bug, though. Since the ``Codegen.codegen_proto``
+can return a previously defined forward declaration, our code can
+actually delete a forward declaration. There are a number of ways to fix
+this bug, see what you can come up with! Here is a testcase:
+
+::
+
+ extern foo(a b); # ok, defines foo.
+ def foo(a b) c; # error, 'c' is invalid.
+ def bar() foo(1, 2); # error, unknown function "foo"
+
+Driver Changes and Closing Thoughts
+===================================
+
+For now, code generation to LLVM doesn't really get us much, except that
+we can look at the pretty IR calls. The sample code inserts calls to
+Codegen into the "``Toplevel.main_loop``", and then dumps out the LLVM
+IR. This gives a nice way to look at the LLVM IR for simple functions.
+For example:
+
+::
+
+ ready> 4+5;
+ Read top-level expression:
+ define double @""() {
+ entry:
+ %addtmp = fadd double 4.000000e+00, 5.000000e+00
+ ret double %addtmp
+ }
+
+Note how the parser turns the top-level expression into anonymous
+functions for us. This will be handy when we add `JIT
+support <OCamlLangImpl4.html#adding-a-jit-compiler>`_ in the next chapter. Also note that
+the code is very literally transcribed, no optimizations are being
+performed. We will `add
+optimizations <OCamlLangImpl4.html#trivial-constant-folding>`_ explicitly in the
+next chapter.
+
+::
+
+ ready> def foo(a b) a*a + 2*a*b + b*b;
+ Read function definition:
+ define double @foo(double %a, double %b) {
+ entry:
+ %multmp = fmul double %a, %a
+ %multmp1 = fmul double 2.000000e+00, %a
+ %multmp2 = fmul double %multmp1, %b
+ %addtmp = fadd double %multmp, %multmp2
+ %multmp3 = fmul double %b, %b
+ %addtmp4 = fadd double %addtmp, %multmp3
+ ret double %addtmp4
+ }
+
+This shows some simple arithmetic. Notice the striking similarity to the
+LLVM builder calls that we use to create the instructions.
+
+::
+
+ ready> def bar(a) foo(a, 4.0) + bar(31337);
+ Read function definition:
+ define double @bar(double %a) {
+ entry:
+ %calltmp = call double @foo(double %a, double 4.000000e+00)
+ %calltmp1 = call double @bar(double 3.133700e+04)
+ %addtmp = fadd double %calltmp, %calltmp1
+ ret double %addtmp
+ }
+
+This shows some function calls. Note that this function will take a long
+time to execute if you call it. In the future we'll add conditional
+control flow to actually make recursion useful :).
+
+::
+
+ ready> extern cos(x);
+ Read extern:
+ declare double @cos(double)
+
+ ready> cos(1.234);
+ Read top-level expression:
+ define double @""() {
+ entry:
+ %calltmp = call double @cos(double 1.234000e+00)
+ ret double %calltmp
+ }
+
+This shows an extern for the libm "cos" function, and a call to it.
+
+::
+
+ ready> ^D
+ ; ModuleID = 'my cool jit'
+
+ define double @""() {
+ entry:
+ %addtmp = fadd double 4.000000e+00, 5.000000e+00
+ ret double %addtmp
+ }
+
+ define double @foo(double %a, double %b) {
+ entry:
+ %multmp = fmul double %a, %a
+ %multmp1 = fmul double 2.000000e+00, %a
+ %multmp2 = fmul double %multmp1, %b
+ %addtmp = fadd double %multmp, %multmp2
+ %multmp3 = fmul double %b, %b
+ %addtmp4 = fadd double %addtmp, %multmp3
+ ret double %addtmp4
+ }
+
+ define double @bar(double %a) {
+ entry:
+ %calltmp = call double @foo(double %a, double 4.000000e+00)
+ %calltmp1 = call double @bar(double 3.133700e+04)
+ %addtmp = fadd double %calltmp, %calltmp1
+ ret double %addtmp
+ }
+
+ declare double @cos(double)
+
+ define double @""() {
+ entry:
+ %calltmp = call double @cos(double 1.234000e+00)
+ ret double %calltmp
+ }
+
+When you quit the current demo, it dumps out the IR for the entire
+module generated. Here you can see the big picture with all the
+functions referencing each other.
+
+This wraps up the third chapter of the Kaleidoscope tutorial. Up next,
+we'll describe how to `add JIT codegen and optimizer
+support <OCamlLangImpl4.html>`_ to this so we can actually start running
+code!
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example, enhanced with
+the LLVM code generator. Because this uses the LLVM libraries, we need
+to link them in. To do this, we use the
+`llvm-config <http://llvm.org/cmds/llvm-config.html>`_ tool to inform
+our makefile/command line about which options to use:
+
+.. code-block:: bash
+
+ # Compile
+ ocamlbuild toy.byte
+ # Run
+ ./toy.byte
+
+Here is the code:
+
+\_tags:
+ ::
+
+ <{lexer,parser}.ml>: use_camlp4, pp(camlp4of)
+ <*.{byte,native}>: g++, use_llvm, use_llvm_analysis
+
+myocamlbuild.ml:
+ .. code-block:: ocaml
+
+ open Ocamlbuild_plugin;;
+
+ ocaml_lib ~extern:true "llvm";;
+ ocaml_lib ~extern:true "llvm_analysis";;
+
+ flag ["link"; "ocaml"; "g++"] (S[A"-cc"; A"g++"]);;
+
+token.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Lexer Tokens
+ *===----------------------------------------------------------------------===*)
+
+ (* The lexer returns these 'Kwd' if it is an unknown character, otherwise one of
+ * these others for known things. *)
+ type token =
+ (* commands *)
+ | Def | Extern
+
+ (* primary *)
+ | Ident of string | Number of float
+
+ (* unknown *)
+ | Kwd of char
+
+lexer.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Lexer
+ *===----------------------------------------------------------------------===*)
+
+ let rec lex = parser
+ (* Skip any whitespace. *)
+ | [< ' (' ' | '\n' | '\r' | '\t'); stream >] -> lex stream
+
+ (* identifier: [a-zA-Z][a-zA-Z0-9] *)
+ | [< ' ('A' .. 'Z' | 'a' .. 'z' as c); stream >] ->
+ let buffer = Buffer.create 1 in
+ Buffer.add_char buffer c;
+ lex_ident buffer stream
+
+ (* number: [0-9.]+ *)
+ | [< ' ('0' .. '9' as c); stream >] ->
+ let buffer = Buffer.create 1 in
+ Buffer.add_char buffer c;
+ lex_number buffer stream
+
+ (* Comment until end of line. *)
+ | [< ' ('#'); stream >] ->
+ lex_comment stream
+
+ (* Otherwise, just return the character as its ascii value. *)
+ | [< 'c; stream >] ->
+ [< 'Token.Kwd c; lex stream >]
+
+ (* end of stream. *)
+ | [< >] -> [< >]
+
+ and lex_number buffer = parser
+ | [< ' ('0' .. '9' | '.' as c); stream >] ->
+ Buffer.add_char buffer c;
+ lex_number buffer stream
+ | [< stream=lex >] ->
+ [< 'Token.Number (float_of_string (Buffer.contents buffer)); stream >]
+
+ and lex_ident buffer = parser
+ | [< ' ('A' .. 'Z' | 'a' .. 'z' | '0' .. '9' as c); stream >] ->
+ Buffer.add_char buffer c;
+ lex_ident buffer stream
+ | [< stream=lex >] ->
+ match Buffer.contents buffer with
+ | "def" -> [< 'Token.Def; stream >]
+ | "extern" -> [< 'Token.Extern; stream >]
+ | id -> [< 'Token.Ident id; stream >]
+
+ and lex_comment = parser
+ | [< ' ('\n'); stream=lex >] -> stream
+ | [< 'c; e=lex_comment >] -> e
+ | [< >] -> [< >]
+
+ast.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Abstract Syntax Tree (aka Parse Tree)
+ *===----------------------------------------------------------------------===*)
+
+ (* expr - Base type for all expression nodes. *)
+ type expr =
+ (* variant for numeric literals like "1.0". *)
+ | Number of float
+
+ (* variant for referencing a variable, like "a". *)
+ | Variable of string
+
+ (* variant for a binary operator. *)
+ | Binary of char * expr * expr
+
+ (* variant for function calls. *)
+ | Call of string * expr array
+
+ (* proto - This type represents the "prototype" for a function, which captures
+ * its name, and its argument names (thus implicitly the number of arguments the
+ * function takes). *)
+ type proto = Prototype of string * string array
+
+ (* func - This type represents a function definition itself. *)
+ type func = Function of proto * expr
+
+parser.ml:
+ .. code-block:: ocaml
+
+ (*===---------------------------------------------------------------------===
+ * Parser
+ *===---------------------------------------------------------------------===*)
+
+ (* binop_precedence - This holds the precedence for each binary operator that is
+ * defined *)
+ let binop_precedence:(char, int) Hashtbl.t = Hashtbl.create 10
+
+ (* precedence - Get the precedence of the pending binary operator token. *)
+ let precedence c = try Hashtbl.find binop_precedence c with Not_found -> -1
+
+ (* primary
+ * ::= identifier
+ * ::= numberexpr
+ * ::= parenexpr *)
+ let rec parse_primary = parser
+ (* numberexpr ::= number *)
+ | [< 'Token.Number n >] -> Ast.Number n
+
+ (* parenexpr ::= '(' expression ')' *)
+ | [< 'Token.Kwd '('; e=parse_expr; 'Token.Kwd ')' ?? "expected ')'" >] -> e
+
+ (* identifierexpr
+ * ::= identifier
+ * ::= identifier '(' argumentexpr ')' *)
+ | [< 'Token.Ident id; stream >] ->
+ let rec parse_args accumulator = parser
+ | [< e=parse_expr; stream >] ->
+ begin parser
+ | [< 'Token.Kwd ','; e=parse_args (e :: accumulator) >] -> e
+ | [< >] -> e :: accumulator
+ end stream
+ | [< >] -> accumulator
+ in
+ let rec parse_ident id = parser
+ (* Call. *)
+ | [< 'Token.Kwd '(';
+ args=parse_args [];
+ 'Token.Kwd ')' ?? "expected ')'">] ->
+ Ast.Call (id, Array.of_list (List.rev args))
+
+ (* Simple variable ref. *)
+ | [< >] -> Ast.Variable id
+ in
+ parse_ident id stream
+
+ | [< >] -> raise (Stream.Error "unknown token when expecting an expression.")
+
+ (* binoprhs
+ * ::= ('+' primary)* *)
+ and parse_bin_rhs expr_prec lhs stream =
+ match Stream.peek stream with
+ (* If this is a binop, find its precedence. *)
+ | Some (Token.Kwd c) when Hashtbl.mem binop_precedence c ->
+ let token_prec = precedence c in
+
+ (* If this is a binop that binds at least as tightly as the current binop,
+ * consume it, otherwise we are done. *)
+ if token_prec < expr_prec then lhs else begin
+ (* Eat the binop. *)
+ Stream.junk stream;
+
+ (* Parse the primary expression after the binary operator. *)
+ let rhs = parse_primary stream in
+
+ (* Okay, we know this is a binop. *)
+ let rhs =
+ match Stream.peek stream with
+ | Some (Token.Kwd c2) ->
+ (* If BinOp binds less tightly with rhs than the operator after
+ * rhs, let the pending operator take rhs as its lhs. *)
+ let next_prec = precedence c2 in
+ if token_prec < next_prec
+ then parse_bin_rhs (token_prec + 1) rhs stream
+ else rhs
+ | _ -> rhs
+ in
+
+ (* Merge lhs/rhs. *)
+ let lhs = Ast.Binary (c, lhs, rhs) in
+ parse_bin_rhs expr_prec lhs stream
+ end
+ | _ -> lhs
+
+ (* expression
+ * ::= primary binoprhs *)
+ and parse_expr = parser
+ | [< lhs=parse_primary; stream >] -> parse_bin_rhs 0 lhs stream
+
+ (* prototype
+ * ::= id '(' id* ')' *)
+ let parse_prototype =
+ let rec parse_args accumulator = parser
+ | [< 'Token.Ident id; e=parse_args (id::accumulator) >] -> e
+ | [< >] -> accumulator
+ in
+
+ parser
+ | [< 'Token.Ident id;
+ 'Token.Kwd '(' ?? "expected '(' in prototype";
+ args=parse_args [];
+ 'Token.Kwd ')' ?? "expected ')' in prototype" >] ->
+ (* success. *)
+ Ast.Prototype (id, Array.of_list (List.rev args))
+
+ | [< >] ->
+ raise (Stream.Error "expected function name in prototype")
+
+ (* definition ::= 'def' prototype expression *)
+ let parse_definition = parser
+ | [< 'Token.Def; p=parse_prototype; e=parse_expr >] ->
+ Ast.Function (p, e)
+
+ (* toplevelexpr ::= expression *)
+ let parse_toplevel = parser
+ | [< e=parse_expr >] ->
+ (* Make an anonymous proto. *)
+ Ast.Function (Ast.Prototype ("", [||]), e)
+
+ (* external ::= 'extern' prototype *)
+ let parse_extern = parser
+ | [< 'Token.Extern; e=parse_prototype >] -> e
+
+codegen.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Code Generation
+ *===----------------------------------------------------------------------===*)
+
+ open Llvm
+
+ exception Error of string
+
+ let context = global_context ()
+ let the_module = create_module context "my cool jit"
+ let builder = builder context
+ let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10
+ let double_type = double_type context
+
+ let rec codegen_expr = function
+ | Ast.Number n -> const_float double_type n
+ | Ast.Variable name ->
+ (try Hashtbl.find named_values name with
+ | Not_found -> raise (Error "unknown variable name"))
+ | Ast.Binary (op, lhs, rhs) ->
+ let lhs_val = codegen_expr lhs in
+ let rhs_val = codegen_expr rhs in
+ begin
+ match op with
+ | '+' -> build_add lhs_val rhs_val "addtmp" builder
+ | '-' -> build_sub lhs_val rhs_val "subtmp" builder
+ | '*' -> build_mul lhs_val rhs_val "multmp" builder
+ | '<' ->
+ (* Convert bool 0/1 to double 0.0 or 1.0 *)
+ let i = build_fcmp Fcmp.Ult lhs_val rhs_val "cmptmp" builder in
+ build_uitofp i double_type "booltmp" builder
+ | _ -> raise (Error "invalid binary operator")
+ end
+ | Ast.Call (callee, args) ->
+ (* Look up the name in the module table. *)
+ let callee =
+ match lookup_function callee the_module with
+ | Some callee -> callee
+ | None -> raise (Error "unknown function referenced")
+ in
+ let params = params callee in
+
+ (* If argument mismatch error. *)
+ if Array.length params == Array.length args then () else
+ raise (Error "incorrect # arguments passed");
+ let args = Array.map codegen_expr args in
+ build_call callee args "calltmp" builder
+
+ let codegen_proto = function
+ | Ast.Prototype (name, args) ->
+ (* Make the function type: double(double,double) etc. *)
+ let doubles = Array.make (Array.length args) double_type in
+ let ft = function_type double_type doubles in
+ let f =
+ match lookup_function name the_module with
+ | None -> declare_function name ft the_module
+
+ (* If 'f' conflicted, there was already something named 'name'. If it
+ * has a body, don't allow redefinition or reextern. *)
+ | Some f ->
+ (* If 'f' already has a body, reject this. *)
+ if block_begin f <> At_end f then
+ raise (Error "redefinition of function");
+
+ (* If 'f' took a different number of arguments, reject. *)
+ if element_type (type_of f) <> ft then
+ raise (Error "redefinition of function with different # args");
+ f
+ in
+
+ (* Set names for all arguments. *)
+ Array.iteri (fun i a ->
+ let n = args.(i) in
+ set_value_name n a;
+ Hashtbl.add named_values n a;
+ ) (params f);
+ f
+
+ let codegen_func = function
+ | Ast.Function (proto, body) ->
+ Hashtbl.clear named_values;
+ let the_function = codegen_proto proto in
+
+ (* Create a new basic block to start insertion into. *)
+ let bb = append_block context "entry" the_function in
+ position_at_end bb builder;
+
+ try
+ let ret_val = codegen_expr body in
+
+ (* Finish off the function. *)
+ let _ = build_ret ret_val builder in
+
+ (* Validate the generated code, checking for consistency. *)
+ Llvm_analysis.assert_valid_function the_function;
+
+ the_function
+ with e ->
+ delete_function the_function;
+ raise e
+
+toplevel.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Top-Level parsing and JIT Driver
+ *===----------------------------------------------------------------------===*)
+
+ open Llvm
+
+ (* top ::= definition | external | expression | ';' *)
+ let rec main_loop stream =
+ match Stream.peek stream with
+ | None -> ()
+
+ (* ignore top-level semicolons. *)
+ | Some (Token.Kwd ';') ->
+ Stream.junk stream;
+ main_loop stream
+
+ | Some token ->
+ begin
+ try match token with
+ | Token.Def ->
+ let e = Parser.parse_definition stream in
+ print_endline "parsed a function definition.";
+ dump_value (Codegen.codegen_func e);
+ | Token.Extern ->
+ let e = Parser.parse_extern stream in
+ print_endline "parsed an extern.";
+ dump_value (Codegen.codegen_proto e);
+ | _ ->
+ (* Evaluate a top-level expression into an anonymous function. *)
+ let e = Parser.parse_toplevel stream in
+ print_endline "parsed a top-level expr";
+ dump_value (Codegen.codegen_func e);
+ with Stream.Error s | Codegen.Error s ->
+ (* Skip token for error recovery. *)
+ Stream.junk stream;
+ print_endline s;
+ end;
+ print_string "ready> "; flush stdout;
+ main_loop stream
+
+toy.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Main driver code.
+ *===----------------------------------------------------------------------===*)
+
+ open Llvm
+
+ let main () =
+ (* Install standard binary operators.
+ * 1 is the lowest precedence. *)
+ Hashtbl.add Parser.binop_precedence '<' 10;
+ Hashtbl.add Parser.binop_precedence '+' 20;
+ Hashtbl.add Parser.binop_precedence '-' 20;
+ Hashtbl.add Parser.binop_precedence '*' 40; (* highest. *)
+
+ (* Prime the first token. *)
+ print_string "ready> "; flush stdout;
+ let stream = Lexer.lex (Stream.of_channel stdin) in
+
+ (* Run the main "interpreter loop" now. *)
+ Toplevel.main_loop stream;
+
+ (* Print out all the generated code. *)
+ dump_module Codegen.the_module
+ ;;
+
+ main ()
+
+`Next: Adding JIT and Optimizer Support <OCamlLangImpl4.html>`_
+
Added: www-releases/trunk/3.9.1/docs/_sources/tutorial/OCamlLangImpl4.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.9.1/docs/_sources/tutorial/OCamlLangImpl4.txt?rev=290368&view=auto
==============================================================================
--- www-releases/trunk/3.9.1/docs/_sources/tutorial/OCamlLangImpl4.txt (added)
+++ www-releases/trunk/3.9.1/docs/_sources/tutorial/OCamlLangImpl4.txt Thu Dec 22 14:04:03 2016
@@ -0,0 +1,915 @@
+==============================================
+Kaleidoscope: Adding JIT and Optimizer Support
+==============================================
+
+.. contents::
+ :local:
+
+Chapter 4 Introduction
+======================
+
+Welcome to Chapter 4 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. Chapters 1-3 described the implementation
+of a simple language and added support for generating LLVM IR. This
+chapter describes two new techniques: adding optimizer support to your
+language, and adding JIT compiler support. These additions will
+demonstrate how to get nice, efficient code for the Kaleidoscope
+language.
+
+Trivial Constant Folding
+========================
+
+**Note:** the default ``IRBuilder`` now always includes the constant
+folding optimisations below.
+
+Our demonstration for Chapter 3 is elegant and easy to extend.
+Unfortunately, it does not produce wonderful code. For example, when
+compiling simple code, we don't get obvious optimizations:
+
+::
+
+ ready> def test(x) 1+2+x;
+ Read function definition:
+ define double @test(double %x) {
+ entry:
+ %addtmp = fadd double 1.000000e+00, 2.000000e+00
+ %addtmp1 = fadd double %addtmp, %x
+ ret double %addtmp1
+ }
+
+This code is a very, very literal transcription of the AST built by
+parsing the input. As such, this transcription lacks optimizations like
+constant folding (we'd like to get "``add x, 3.0``" in the example
+above) as well as other more important optimizations. Constant folding,
+in particular, is a very common and very important optimization: so much
+so that many language implementors implement constant folding support in
+their AST representation.
+
+With LLVM, you don't need this support in the AST. Since all calls to
+build LLVM IR go through the LLVM builder, it would be nice if the
+builder itself checked to see if there was a constant folding
+opportunity when you call it. If so, it could just do the constant fold
+and return the constant instead of creating an instruction. This is
+exactly what the ``LLVMFoldingBuilder`` class does.
+
+All we did was switch from ``LLVMBuilder`` to ``LLVMFoldingBuilder``.
+Though we change no other code, we now have all of our instructions
+implicitly constant folded without us having to do anything about it.
+For example, the input above now compiles to:
+
+::
+
+ ready> def test(x) 1+2+x;
+ Read function definition:
+ define double @test(double %x) {
+ entry:
+ %addtmp = fadd double 3.000000e+00, %x
+ ret double %addtmp
+ }
+
+Well, that was easy :). In practice, we recommend always using
+``LLVMFoldingBuilder`` when generating code like this. It has no
+"syntactic overhead" for its use (you don't have to uglify your compiler
+with constant checks everywhere) and it can dramatically reduce the
+amount of LLVM IR that is generated in some cases (particular for
+languages with a macro preprocessor or that use a lot of constants).
+
+On the other hand, the ``LLVMFoldingBuilder`` is limited by the fact
+that it does all of its analysis inline with the code as it is built. If
+you take a slightly more complex example:
+
+::
+
+ ready> def test(x) (1+2+x)*(x+(1+2));
+ ready> Read function definition:
+ define double @test(double %x) {
+ entry:
+ %addtmp = fadd double 3.000000e+00, %x
+ %addtmp1 = fadd double %x, 3.000000e+00
+ %multmp = fmul double %addtmp, %addtmp1
+ ret double %multmp
+ }
+
+In this case, the LHS and RHS of the multiplication are the same value.
+We'd really like to see this generate "``tmp = x+3; result = tmp*tmp;``"
+instead of computing "``x*3``" twice.
+
+Unfortunately, no amount of local analysis will be able to detect and
+correct this. This requires two transformations: reassociation of
+expressions (to make the add's lexically identical) and Common
+Subexpression Elimination (CSE) to delete the redundant add instruction.
+Fortunately, LLVM provides a broad range of optimizations that you can
+use, in the form of "passes".
+
+LLVM Optimization Passes
+========================
+
+LLVM provides many optimization passes, which do many different sorts of
+things and have different tradeoffs. Unlike other systems, LLVM doesn't
+hold to the mistaken notion that one set of optimizations is right for
+all languages and for all situations. LLVM allows a compiler implementor
+to make complete decisions about what optimizations to use, in which
+order, and in what situation.
+
+As a concrete example, LLVM supports both "whole module" passes, which
+look across as large of body of code as they can (often a whole file,
+but if run at link time, this can be a substantial portion of the whole
+program). It also supports and includes "per-function" passes which just
+operate on a single function at a time, without looking at other
+functions. For more information on passes and how they are run, see the
+`How to Write a Pass <../WritingAnLLVMPass.html>`_ document and the
+`List of LLVM Passes <../Passes.html>`_.
+
+For Kaleidoscope, we are currently generating functions on the fly, one
+at a time, as the user types them in. We aren't shooting for the
+ultimate optimization experience in this setting, but we also want to
+catch the easy and quick stuff where possible. As such, we will choose
+to run a few per-function optimizations as the user types the function
+in. If we wanted to make a "static Kaleidoscope compiler", we would use
+exactly the code we have now, except that we would defer running the
+optimizer until the entire file has been parsed.
+
+In order to get per-function optimizations going, we need to set up a
+`Llvm.PassManager <../WritingAnLLVMPass.html#what-passmanager-does>`_ to hold and
+organize the LLVM optimizations that we want to run. Once we have that,
+we can add a set of optimizations to run. The code looks like this:
+
+.. code-block:: ocaml
+
+ (* Create the JIT. *)
+ let the_execution_engine = ExecutionEngine.create Codegen.the_module in
+ let the_fpm = PassManager.create_function Codegen.the_module in
+
+ (* Set up the optimizer pipeline. Start with registering info about how the
+ * target lays out data structures. *)
+ DataLayout.add (ExecutionEngine.target_data the_execution_engine) the_fpm;
+
+ (* Do simple "peephole" optimizations and bit-twiddling optzn. *)
+ add_instruction_combining the_fpm;
+
+ (* reassociate expressions. *)
+ add_reassociation the_fpm;
+
+ (* Eliminate Common SubExpressions. *)
+ add_gvn the_fpm;
+
+ (* Simplify the control flow graph (deleting unreachable blocks, etc). *)
+ add_cfg_simplification the_fpm;
+
+ ignore (PassManager.initialize the_fpm);
+
+ (* Run the main "interpreter loop" now. *)
+ Toplevel.main_loop the_fpm the_execution_engine stream;
+
+The meat of the matter here, is the definition of "``the_fpm``". It
+requires a pointer to the ``the_module`` to construct itself. Once it is
+set up, we use a series of "add" calls to add a bunch of LLVM passes.
+The first pass is basically boilerplate, it adds a pass so that later
+optimizations know how the data structures in the program are laid out.
+The "``the_execution_engine``" variable is related to the JIT, which we
+will get to in the next section.
+
+In this case, we choose to add 4 optimization passes. The passes we
+chose here are a pretty standard set of "cleanup" optimizations that are
+useful for a wide variety of code. I won't delve into what they do but,
+believe me, they are a good starting place :).
+
+Once the ``Llvm.PassManager.`` is set up, we need to make use of it. We
+do this by running it after our newly created function is constructed
+(in ``Codegen.codegen_func``), but before it is returned to the client:
+
+.. code-block:: ocaml
+
+ let codegen_func the_fpm = function
+ ...
+ try
+ let ret_val = codegen_expr body in
+
+ (* Finish off the function. *)
+ let _ = build_ret ret_val builder in
+
+ (* Validate the generated code, checking for consistency. *)
+ Llvm_analysis.assert_valid_function the_function;
+
+ (* Optimize the function. *)
+ let _ = PassManager.run_function the_function the_fpm in
+
+ the_function
+
+As you can see, this is pretty straightforward. The ``the_fpm``
+optimizes and updates the LLVM Function\* in place, improving
+(hopefully) its body. With this in place, we can try our test above
+again:
+
+::
+
+ ready> def test(x) (1+2+x)*(x+(1+2));
+ ready> Read function definition:
+ define double @test(double %x) {
+ entry:
+ %addtmp = fadd double %x, 3.000000e+00
+ %multmp = fmul double %addtmp, %addtmp
+ ret double %multmp
+ }
+
+As expected, we now get our nicely optimized code, saving a floating
+point add instruction from every execution of this function.
+
+LLVM provides a wide variety of optimizations that can be used in
+certain circumstances. Some `documentation about the various
+passes <../Passes.html>`_ is available, but it isn't very complete.
+Another good source of ideas can come from looking at the passes that
+``Clang`` runs to get started. The "``opt``" tool allows you to
+experiment with passes from the command line, so you can see if they do
+anything.
+
+Now that we have reasonable code coming out of our front-end, lets talk
+about executing it!
+
+Adding a JIT Compiler
+=====================
+
+Code that is available in LLVM IR can have a wide variety of tools
+applied to it. For example, you can run optimizations on it (as we did
+above), you can dump it out in textual or binary forms, you can compile
+the code to an assembly file (.s) for some target, or you can JIT
+compile it. The nice thing about the LLVM IR representation is that it
+is the "common currency" between many different parts of the compiler.
+
+In this section, we'll add JIT compiler support to our interpreter. The
+basic idea that we want for Kaleidoscope is to have the user enter
+function bodies as they do now, but immediately evaluate the top-level
+expressions they type in. For example, if they type in "1 + 2;", we
+should evaluate and print out 3. If they define a function, they should
+be able to call it from the command line.
+
+In order to do this, we first declare and initialize the JIT. This is
+done by adding a global variable and a call in ``main``:
+
+.. code-block:: ocaml
+
+ ...
+ let main () =
+ ...
+ (* Create the JIT. *)
+ let the_execution_engine = ExecutionEngine.create Codegen.the_module in
+ ...
+
+This creates an abstract "Execution Engine" which can be either a JIT
+compiler or the LLVM interpreter. LLVM will automatically pick a JIT
+compiler for you if one is available for your platform, otherwise it
+will fall back to the interpreter.
+
+Once the ``Llvm_executionengine.ExecutionEngine.t`` is created, the JIT
+is ready to be used. There are a variety of APIs that are useful, but
+the simplest one is the
+"``Llvm_executionengine.ExecutionEngine.run_function``" function. This
+method JIT compiles the specified LLVM Function and returns a function
+pointer to the generated machine code. In our case, this means that we
+can change the code that parses a top-level expression to look like
+this:
+
+.. code-block:: ocaml
+
+ (* Evaluate a top-level expression into an anonymous function. *)
+ let e = Parser.parse_toplevel stream in
+ print_endline "parsed a top-level expr";
+ let the_function = Codegen.codegen_func the_fpm e in
+ dump_value the_function;
+
+ (* JIT the function, returning a function pointer. *)
+ let result = ExecutionEngine.run_function the_function [||]
+ the_execution_engine in
+
+ print_string "Evaluated to ";
+ print_float (GenericValue.as_float Codegen.double_type result);
+ print_newline ();
+
+Recall that we compile top-level expressions into a self-contained LLVM
+function that takes no arguments and returns the computed double.
+Because the LLVM JIT compiler matches the native platform ABI, this
+means that you can just cast the result pointer to a function pointer of
+that type and call it directly. This means, there is no difference
+between JIT compiled code and native machine code that is statically
+linked into your application.
+
+With just these two changes, lets see how Kaleidoscope works now!
+
+::
+
+ ready> 4+5;
+ define double @""() {
+ entry:
+ ret double 9.000000e+00
+ }
+
+ Evaluated to 9.000000
+
+Well this looks like it is basically working. The dump of the function
+shows the "no argument function that always returns double" that we
+synthesize for each top level expression that is typed in. This
+demonstrates very basic functionality, but can we do more?
+
+::
+
+ ready> def testfunc(x y) x + y*2;
+ Read function definition:
+ define double @testfunc(double %x, double %y) {
+ entry:
+ %multmp = fmul double %y, 2.000000e+00
+ %addtmp = fadd double %multmp, %x
+ ret double %addtmp
+ }
+
+ ready> testfunc(4, 10);
+ define double @""() {
+ entry:
+ %calltmp = call double @testfunc(double 4.000000e+00, double 1.000000e+01)
+ ret double %calltmp
+ }
+
+ Evaluated to 24.000000
+
+This illustrates that we can now call user code, but there is something
+a bit subtle going on here. Note that we only invoke the JIT on the
+anonymous functions that *call testfunc*, but we never invoked it on
+*testfunc* itself. What actually happened here is that the JIT scanned
+for all non-JIT'd functions transitively called from the anonymous
+function and compiled all of them before returning from
+``run_function``.
+
+The JIT provides a number of other more advanced interfaces for things
+like freeing allocated machine code, rejit'ing functions to update them,
+etc. However, even with this simple code, we get some surprisingly
+powerful capabilities - check this out (I removed the dump of the
+anonymous functions, you should get the idea by now :) :
+
+::
+
+ ready> extern sin(x);
+ Read extern:
+ declare double @sin(double)
+
+ ready> extern cos(x);
+ Read extern:
+ declare double @cos(double)
+
+ ready> sin(1.0);
+ Evaluated to 0.841471
+
+ ready> def foo(x) sin(x)*sin(x) + cos(x)*cos(x);
+ Read function definition:
+ define double @foo(double %x) {
+ entry:
+ %calltmp = call double @sin(double %x)
+ %multmp = fmul double %calltmp, %calltmp
+ %calltmp2 = call double @cos(double %x)
+ %multmp4 = fmul double %calltmp2, %calltmp2
+ %addtmp = fadd double %multmp, %multmp4
+ ret double %addtmp
+ }
+
+ ready> foo(4.0);
+ Evaluated to 1.000000
+
+Whoa, how does the JIT know about sin and cos? The answer is
+surprisingly simple: in this example, the JIT started execution of a
+function and got to a function call. It realized that the function was
+not yet JIT compiled and invoked the standard set of routines to resolve
+the function. In this case, there is no body defined for the function,
+so the JIT ended up calling "``dlsym("sin")``" on the Kaleidoscope
+process itself. Since "``sin``" is defined within the JIT's address
+space, it simply patches up calls in the module to call the libm version
+of ``sin`` directly.
+
+The LLVM JIT provides a number of interfaces (look in the
+``llvm_executionengine.mli`` file) for controlling how unknown functions
+get resolved. It allows you to establish explicit mappings between IR
+objects and addresses (useful for LLVM global variables that you want to
+map to static tables, for example), allows you to dynamically decide on
+the fly based on the function name, and even allows you to have the JIT
+compile functions lazily the first time they're called.
+
+One interesting application of this is that we can now extend the
+language by writing arbitrary C code to implement operations. For
+example, if we add:
+
+.. code-block:: c++
+
+ /* putchard - putchar that takes a double and returns 0. */
+ extern "C"
+ double putchard(double X) {
+ putchar((char)X);
+ return 0;
+ }
+
+Now we can produce simple output to the console by using things like:
+"``extern putchard(x); putchard(120);``", which prints a lowercase 'x'
+on the console (120 is the ASCII code for 'x'). Similar code could be
+used to implement file I/O, console input, and many other capabilities
+in Kaleidoscope.
+
+This completes the JIT and optimizer chapter of the Kaleidoscope
+tutorial. At this point, we can compile a non-Turing-complete
+programming language, optimize and JIT compile it in a user-driven way.
+Next up we'll look into `extending the language with control flow
+constructs <OCamlLangImpl5.html>`_, tackling some interesting LLVM IR
+issues along the way.
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example, enhanced with
+the LLVM JIT and optimizer. To build this example, use:
+
+.. code-block:: bash
+
+ # Compile
+ ocamlbuild toy.byte
+ # Run
+ ./toy.byte
+
+Here is the code:
+
+\_tags:
+ ::
+
+ <{lexer,parser}.ml>: use_camlp4, pp(camlp4of)
+ <*.{byte,native}>: g++, use_llvm, use_llvm_analysis
+ <*.{byte,native}>: use_llvm_executionengine, use_llvm_target
+ <*.{byte,native}>: use_llvm_scalar_opts, use_bindings
+
+myocamlbuild.ml:
+ .. code-block:: ocaml
+
+ open Ocamlbuild_plugin;;
+
+ ocaml_lib ~extern:true "llvm";;
+ ocaml_lib ~extern:true "llvm_analysis";;
+ ocaml_lib ~extern:true "llvm_executionengine";;
+ ocaml_lib ~extern:true "llvm_target";;
+ ocaml_lib ~extern:true "llvm_scalar_opts";;
+
+ flag ["link"; "ocaml"; "g++"] (S[A"-cc"; A"g++"]);;
+ dep ["link"; "ocaml"; "use_bindings"] ["bindings.o"];;
+
+token.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Lexer Tokens
+ *===----------------------------------------------------------------------===*)
+
+ (* The lexer returns these 'Kwd' if it is an unknown character, otherwise one of
+ * these others for known things. *)
+ type token =
+ (* commands *)
+ | Def | Extern
+
+ (* primary *)
+ | Ident of string | Number of float
+
+ (* unknown *)
+ | Kwd of char
+
+lexer.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Lexer
+ *===----------------------------------------------------------------------===*)
+
+ let rec lex = parser
+ (* Skip any whitespace. *)
+ | [< ' (' ' | '\n' | '\r' | '\t'); stream >] -> lex stream
+
+ (* identifier: [a-zA-Z][a-zA-Z0-9] *)
+ | [< ' ('A' .. 'Z' | 'a' .. 'z' as c); stream >] ->
+ let buffer = Buffer.create 1 in
+ Buffer.add_char buffer c;
+ lex_ident buffer stream
+
+ (* number: [0-9.]+ *)
+ | [< ' ('0' .. '9' as c); stream >] ->
+ let buffer = Buffer.create 1 in
+ Buffer.add_char buffer c;
+ lex_number buffer stream
+
+ (* Comment until end of line. *)
+ | [< ' ('#'); stream >] ->
+ lex_comment stream
+
+ (* Otherwise, just return the character as its ascii value. *)
+ | [< 'c; stream >] ->
+ [< 'Token.Kwd c; lex stream >]
+
+ (* end of stream. *)
+ | [< >] -> [< >]
+
+ and lex_number buffer = parser
+ | [< ' ('0' .. '9' | '.' as c); stream >] ->
+ Buffer.add_char buffer c;
+ lex_number buffer stream
+ | [< stream=lex >] ->
+ [< 'Token.Number (float_of_string (Buffer.contents buffer)); stream >]
+
+ and lex_ident buffer = parser
+ | [< ' ('A' .. 'Z' | 'a' .. 'z' | '0' .. '9' as c); stream >] ->
+ Buffer.add_char buffer c;
+ lex_ident buffer stream
+ | [< stream=lex >] ->
+ match Buffer.contents buffer with
+ | "def" -> [< 'Token.Def; stream >]
+ | "extern" -> [< 'Token.Extern; stream >]
+ | id -> [< 'Token.Ident id; stream >]
+
+ and lex_comment = parser
+ | [< ' ('\n'); stream=lex >] -> stream
+ | [< 'c; e=lex_comment >] -> e
+ | [< >] -> [< >]
+
+ast.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Abstract Syntax Tree (aka Parse Tree)
+ *===----------------------------------------------------------------------===*)
+
+ (* expr - Base type for all expression nodes. *)
+ type expr =
+ (* variant for numeric literals like "1.0". *)
+ | Number of float
+
+ (* variant for referencing a variable, like "a". *)
+ | Variable of string
+
+ (* variant for a binary operator. *)
+ | Binary of char * expr * expr
+
+ (* variant for function calls. *)
+ | Call of string * expr array
+
+ (* proto - This type represents the "prototype" for a function, which captures
+ * its name, and its argument names (thus implicitly the number of arguments the
+ * function takes). *)
+ type proto = Prototype of string * string array
+
+ (* func - This type represents a function definition itself. *)
+ type func = Function of proto * expr
+
+parser.ml:
+ .. code-block:: ocaml
+
+ (*===---------------------------------------------------------------------===
+ * Parser
+ *===---------------------------------------------------------------------===*)
+
+ (* binop_precedence - This holds the precedence for each binary operator that is
+ * defined *)
+ let binop_precedence:(char, int) Hashtbl.t = Hashtbl.create 10
+
+ (* precedence - Get the precedence of the pending binary operator token. *)
+ let precedence c = try Hashtbl.find binop_precedence c with Not_found -> -1
+
+ (* primary
+ * ::= identifier
+ * ::= numberexpr
+ * ::= parenexpr *)
+ let rec parse_primary = parser
+ (* numberexpr ::= number *)
+ | [< 'Token.Number n >] -> Ast.Number n
+
+ (* parenexpr ::= '(' expression ')' *)
+ | [< 'Token.Kwd '('; e=parse_expr; 'Token.Kwd ')' ?? "expected ')'" >] -> e
+
+ (* identifierexpr
+ * ::= identifier
+ * ::= identifier '(' argumentexpr ')' *)
+ | [< 'Token.Ident id; stream >] ->
+ let rec parse_args accumulator = parser
+ | [< e=parse_expr; stream >] ->
+ begin parser
+ | [< 'Token.Kwd ','; e=parse_args (e :: accumulator) >] -> e
+ | [< >] -> e :: accumulator
+ end stream
+ | [< >] -> accumulator
+ in
+ let rec parse_ident id = parser
+ (* Call. *)
+ | [< 'Token.Kwd '(';
+ args=parse_args [];
+ 'Token.Kwd ')' ?? "expected ')'">] ->
+ Ast.Call (id, Array.of_list (List.rev args))
+
+ (* Simple variable ref. *)
+ | [< >] -> Ast.Variable id
+ in
+ parse_ident id stream
+
+ | [< >] -> raise (Stream.Error "unknown token when expecting an expression.")
+
+ (* binoprhs
+ * ::= ('+' primary)* *)
+ and parse_bin_rhs expr_prec lhs stream =
+ match Stream.peek stream with
+ (* If this is a binop, find its precedence. *)
+ | Some (Token.Kwd c) when Hashtbl.mem binop_precedence c ->
+ let token_prec = precedence c in
+
+ (* If this is a binop that binds at least as tightly as the current binop,
+ * consume it, otherwise we are done. *)
+ if token_prec < expr_prec then lhs else begin
+ (* Eat the binop. *)
+ Stream.junk stream;
+
+ (* Parse the primary expression after the binary operator. *)
+ let rhs = parse_primary stream in
+
+ (* Okay, we know this is a binop. *)
+ let rhs =
+ match Stream.peek stream with
+ | Some (Token.Kwd c2) ->
+ (* If BinOp binds less tightly with rhs than the operator after
+ * rhs, let the pending operator take rhs as its lhs. *)
+ let next_prec = precedence c2 in
+ if token_prec < next_prec
+ then parse_bin_rhs (token_prec + 1) rhs stream
+ else rhs
+ | _ -> rhs
+ in
+
+ (* Merge lhs/rhs. *)
+ let lhs = Ast.Binary (c, lhs, rhs) in
+ parse_bin_rhs expr_prec lhs stream
+ end
+ | _ -> lhs
+
+ (* expression
+ * ::= primary binoprhs *)
+ and parse_expr = parser
+ | [< lhs=parse_primary; stream >] -> parse_bin_rhs 0 lhs stream
+
+ (* prototype
+ * ::= id '(' id* ')' *)
+ let parse_prototype =
+ let rec parse_args accumulator = parser
+ | [< 'Token.Ident id; e=parse_args (id::accumulator) >] -> e
+ | [< >] -> accumulator
+ in
+
+ parser
+ | [< 'Token.Ident id;
+ 'Token.Kwd '(' ?? "expected '(' in prototype";
+ args=parse_args [];
+ 'Token.Kwd ')' ?? "expected ')' in prototype" >] ->
+ (* success. *)
+ Ast.Prototype (id, Array.of_list (List.rev args))
+
+ | [< >] ->
+ raise (Stream.Error "expected function name in prototype")
+
+ (* definition ::= 'def' prototype expression *)
+ let parse_definition = parser
+ | [< 'Token.Def; p=parse_prototype; e=parse_expr >] ->
+ Ast.Function (p, e)
+
+ (* toplevelexpr ::= expression *)
+ let parse_toplevel = parser
+ | [< e=parse_expr >] ->
+ (* Make an anonymous proto. *)
+ Ast.Function (Ast.Prototype ("", [||]), e)
+
+ (* external ::= 'extern' prototype *)
+ let parse_extern = parser
+ | [< 'Token.Extern; e=parse_prototype >] -> e
+
+codegen.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Code Generation
+ *===----------------------------------------------------------------------===*)
+
+ open Llvm
+
+ exception Error of string
+
+ let context = global_context ()
+ let the_module = create_module context "my cool jit"
+ let builder = builder context
+ let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10
+ let double_type = double_type context
+
+ let rec codegen_expr = function
+ | Ast.Number n -> const_float double_type n
+ | Ast.Variable name ->
+ (try Hashtbl.find named_values name with
+ | Not_found -> raise (Error "unknown variable name"))
+ | Ast.Binary (op, lhs, rhs) ->
+ let lhs_val = codegen_expr lhs in
+ let rhs_val = codegen_expr rhs in
+ begin
+ match op with
+ | '+' -> build_add lhs_val rhs_val "addtmp" builder
+ | '-' -> build_sub lhs_val rhs_val "subtmp" builder
+ | '*' -> build_mul lhs_val rhs_val "multmp" builder
+ | '<' ->
+ (* Convert bool 0/1 to double 0.0 or 1.0 *)
+ let i = build_fcmp Fcmp.Ult lhs_val rhs_val "cmptmp" builder in
+ build_uitofp i double_type "booltmp" builder
+ | _ -> raise (Error "invalid binary operator")
+ end
+ | Ast.Call (callee, args) ->
+ (* Look up the name in the module table. *)
+ let callee =
+ match lookup_function callee the_module with
+ | Some callee -> callee
+ | None -> raise (Error "unknown function referenced")
+ in
+ let params = params callee in
+
+ (* If argument mismatch error. *)
+ if Array.length params == Array.length args then () else
+ raise (Error "incorrect # arguments passed");
+ let args = Array.map codegen_expr args in
+ build_call callee args "calltmp" builder
+
+ let codegen_proto = function
+ | Ast.Prototype (name, args) ->
+ (* Make the function type: double(double,double) etc. *)
+ let doubles = Array.make (Array.length args) double_type in
+ let ft = function_type double_type doubles in
+ let f =
+ match lookup_function name the_module with
+ | None -> declare_function name ft the_module
+
+ (* If 'f' conflicted, there was already something named 'name'. If it
+ * has a body, don't allow redefinition or reextern. *)
+ | Some f ->
+ (* If 'f' already has a body, reject this. *)
+ if block_begin f <> At_end f then
+ raise (Error "redefinition of function");
+
+ (* If 'f' took a different number of arguments, reject. *)
+ if element_type (type_of f) <> ft then
+ raise (Error "redefinition of function with different # args");
+ f
+ in
+
+ (* Set names for all arguments. *)
+ Array.iteri (fun i a ->
+ let n = args.(i) in
+ set_value_name n a;
+ Hashtbl.add named_values n a;
+ ) (params f);
+ f
+
+ let codegen_func the_fpm = function
+ | Ast.Function (proto, body) ->
+ Hashtbl.clear named_values;
+ let the_function = codegen_proto proto in
+
+ (* Create a new basic block to start insertion into. *)
+ let bb = append_block context "entry" the_function in
+ position_at_end bb builder;
+
+ try
+ let ret_val = codegen_expr body in
+
+ (* Finish off the function. *)
+ let _ = build_ret ret_val builder in
+
+ (* Validate the generated code, checking for consistency. *)
+ Llvm_analysis.assert_valid_function the_function;
+
+ (* Optimize the function. *)
+ let _ = PassManager.run_function the_function the_fpm in
+
+ the_function
+ with e ->
+ delete_function the_function;
+ raise e
+
+toplevel.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Top-Level parsing and JIT Driver
+ *===----------------------------------------------------------------------===*)
+
+ open Llvm
+ open Llvm_executionengine
+
+ (* top ::= definition | external | expression | ';' *)
+ let rec main_loop the_fpm the_execution_engine stream =
+ match Stream.peek stream with
+ | None -> ()
+
+ (* ignore top-level semicolons. *)
+ | Some (Token.Kwd ';') ->
+ Stream.junk stream;
+ main_loop the_fpm the_execution_engine stream
+
+ | Some token ->
+ begin
+ try match token with
+ | Token.Def ->
+ let e = Parser.parse_definition stream in
+ print_endline "parsed a function definition.";
+ dump_value (Codegen.codegen_func the_fpm e);
+ | Token.Extern ->
+ let e = Parser.parse_extern stream in
+ print_endline "parsed an extern.";
+ dump_value (Codegen.codegen_proto e);
+ | _ ->
+ (* Evaluate a top-level expression into an anonymous function. *)
+ let e = Parser.parse_toplevel stream in
+ print_endline "parsed a top-level expr";
+ let the_function = Codegen.codegen_func the_fpm e in
+ dump_value the_function;
+
+ (* JIT the function, returning a function pointer. *)
+ let result = ExecutionEngine.run_function the_function [||]
+ the_execution_engine in
+
+ print_string "Evaluated to ";
+ print_float (GenericValue.as_float Codegen.double_type result);
+ print_newline ();
+ with Stream.Error s | Codegen.Error s ->
+ (* Skip token for error recovery. *)
+ Stream.junk stream;
+ print_endline s;
+ end;
+ print_string "ready> "; flush stdout;
+ main_loop the_fpm the_execution_engine stream
+
+toy.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Main driver code.
+ *===----------------------------------------------------------------------===*)
+
+ open Llvm
+ open Llvm_executionengine
+ open Llvm_target
+ open Llvm_scalar_opts
+
+ let main () =
+ ignore (initialize_native_target ());
+
+ (* Install standard binary operators.
+ * 1 is the lowest precedence. *)
+ Hashtbl.add Parser.binop_precedence '<' 10;
+ Hashtbl.add Parser.binop_precedence '+' 20;
+ Hashtbl.add Parser.binop_precedence '-' 20;
+ Hashtbl.add Parser.binop_precedence '*' 40; (* highest. *)
+
+ (* Prime the first token. *)
+ print_string "ready> "; flush stdout;
+ let stream = Lexer.lex (Stream.of_channel stdin) in
+
+ (* Create the JIT. *)
+ let the_execution_engine = ExecutionEngine.create Codegen.the_module in
+ let the_fpm = PassManager.create_function Codegen.the_module in
+
+ (* Set up the optimizer pipeline. Start with registering info about how the
+ * target lays out data structures. *)
+ DataLayout.add (ExecutionEngine.target_data the_execution_engine) the_fpm;
+
+ (* Do simple "peephole" optimizations and bit-twiddling optzn. *)
+ add_instruction_combination the_fpm;
+
+ (* reassociate expressions. *)
+ add_reassociation the_fpm;
+
+ (* Eliminate Common SubExpressions. *)
+ add_gvn the_fpm;
+
+ (* Simplify the control flow graph (deleting unreachable blocks, etc). *)
+ add_cfg_simplification the_fpm;
+
+ ignore (PassManager.initialize the_fpm);
+
+ (* Run the main "interpreter loop" now. *)
+ Toplevel.main_loop the_fpm the_execution_engine stream;
+
+ (* Print out all the generated code. *)
+ dump_module Codegen.the_module
+ ;;
+
+ main ()
+
+bindings.c
+ .. code-block:: c
+
+ #include <stdio.h>
+
+ /* putchard - putchar that takes a double and returns 0. */
+ extern double putchard(double X) {
+ putchar((char)X);
+ return 0;
+ }
+
+`Next: Extending the language: control flow <OCamlLangImpl5.html>`_
+
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