[www-releases] r321287 - Add 5.0.1 docs
Tom Stellard via llvm-commits
llvm-commits at lists.llvm.org
Thu Dec 21 10:09:58 PST 2017
Added: www-releases/trunk/5.0.1/docs/_sources/LangRef.rst.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.1/docs/_sources/LangRef.rst.txt?rev=321287&view=auto
==============================================================================
--- www-releases/trunk/5.0.1/docs/_sources/LangRef.rst.txt (added)
+++ www-releases/trunk/5.0.1/docs/_sources/LangRef.rst.txt Thu Dec 21 10:09:53 2017
@@ -0,0 +1,14339 @@
+==============================
+LLVM Language Reference Manual
+==============================
+
+.. contents::
+ :local:
+ :depth: 4
+
+Abstract
+========
+
+This document is a reference manual for the LLVM assembly language. LLVM
+is a Static Single Assignment (SSA) based representation that provides
+type safety, low-level operations, flexibility, and the capability of
+representing 'all' high-level languages cleanly. It is the common code
+representation used throughout all phases of the LLVM compilation
+strategy.
+
+Introduction
+============
+
+The LLVM code representation is designed to be used in three different
+forms: as an in-memory compiler IR, as an on-disk bitcode representation
+(suitable for fast loading by a Just-In-Time compiler), and as a human
+readable assembly language representation. This allows LLVM to provide a
+powerful intermediate representation for efficient compiler
+transformations and analysis, while providing a natural means to debug
+and visualize the transformations. The three different forms of LLVM are
+all equivalent. This document describes the human readable
+representation and notation.
+
+The LLVM representation aims to be light-weight and low-level while
+being expressive, typed, and extensible at the same time. It aims to be
+a "universal IR" of sorts, by being at a low enough level that
+high-level ideas may be cleanly mapped to it (similar to how
+microprocessors are "universal IR's", allowing many source languages to
+be mapped to them). By providing type information, LLVM can be used as
+the target of optimizations: for example, through pointer analysis, it
+can be proven that a C automatic variable is never accessed outside of
+the current function, allowing it to be promoted to a simple SSA value
+instead of a memory location.
+
+.. _wellformed:
+
+Well-Formedness
+---------------
+
+It is important to note that this document describes 'well formed' LLVM
+assembly language. There is a difference between what the parser accepts
+and what is considered 'well formed'. For example, the following
+instruction is syntactically okay, but not well formed:
+
+.. code-block:: llvm
+
+ %x = add i32 1, %x
+
+because the definition of ``%x`` does not dominate all of its uses. The
+LLVM infrastructure provides a verification pass that may be used to
+verify that an LLVM module is well formed. This pass is automatically
+run by the parser after parsing input assembly and by the optimizer
+before it outputs bitcode. The violations pointed out by the verifier
+pass indicate bugs in transformation passes or input to the parser.
+
+.. _identifiers:
+
+Identifiers
+===========
+
+LLVM identifiers come in two basic types: global and local. Global
+identifiers (functions, global variables) begin with the ``'@'``
+character. Local identifiers (register names, types) begin with the
+``'%'`` character. Additionally, there are three different formats for
+identifiers, for different purposes:
+
+#. Named values are represented as a string of characters with their
+ prefix. For example, ``%foo``, ``@DivisionByZero``,
+ ``%a.really.long.identifier``. The actual regular expression used is
+ '``[%@][-a-zA-Z$._][-a-zA-Z$._0-9]*``'. Identifiers that require other
+ characters in their names can be surrounded with quotes. Special
+ characters may be escaped using ``"\xx"`` where ``xx`` is the ASCII
+ code for the character in hexadecimal. In this way, any character can
+ be used in a name value, even quotes themselves. The ``"\01"`` prefix
+ can be used on global variables to suppress mangling.
+#. Unnamed values are represented as an unsigned numeric value with
+ their prefix. For example, ``%12``, ``@2``, ``%44``.
+#. Constants, which are described in the section Constants_ below.
+
+LLVM requires that values start with a prefix for two reasons: Compilers
+don't need to worry about name clashes with reserved words, and the set
+of reserved words may be expanded in the future without penalty.
+Additionally, unnamed identifiers allow a compiler to quickly come up
+with a temporary variable without having to avoid symbol table
+conflicts.
+
+Reserved words in LLVM are very similar to reserved words in other
+languages. There are keywords for different opcodes ('``add``',
+'``bitcast``', '``ret``', etc...), for primitive type names ('``void``',
+'``i32``', etc...), and others. These reserved words cannot conflict
+with variable names, because none of them start with a prefix character
+(``'%'`` or ``'@'``).
+
+Here is an example of LLVM code to multiply the integer variable
+'``%X``' by 8:
+
+The easy way:
+
+.. code-block:: llvm
+
+ %result = mul i32 %X, 8
+
+After strength reduction:
+
+.. code-block:: llvm
+
+ %result = shl i32 %X, 3
+
+And the hard way:
+
+.. code-block:: llvm
+
+ %0 = add i32 %X, %X ; yields i32:%0
+ %1 = add i32 %0, %0 ; yields i32:%1
+ %result = add i32 %1, %1
+
+This last way of multiplying ``%X`` by 8 illustrates several important
+lexical features of LLVM:
+
+#. Comments are delimited with a '``;``' and go until the end of line.
+#. Unnamed temporaries are created when the result of a computation is
+ not assigned to a named value.
+#. Unnamed temporaries are numbered sequentially (using a per-function
+ incrementing counter, starting with 0). Note that basic blocks and unnamed
+ function parameters are included in this numbering. For example, if the
+ entry basic block is not given a label name and all function parameters are
+ named, then it will get number 0.
+
+It also shows a convention that we follow in this document. When
+demonstrating instructions, we will follow an instruction with a comment
+that defines the type and name of value produced.
+
+High Level Structure
+====================
+
+Module Structure
+----------------
+
+LLVM programs are composed of ``Module``'s, each of which is a
+translation unit of the input programs. Each module consists of
+functions, global variables, and symbol table entries. Modules may be
+combined together with the LLVM linker, which merges function (and
+global variable) definitions, resolves forward declarations, and merges
+symbol table entries. Here is an example of the "hello world" module:
+
+.. code-block:: llvm
+
+ ; Declare the string constant as a global constant.
+ @.str = private unnamed_addr constant [13 x i8] c"hello world\0A\00"
+
+ ; External declaration of the puts function
+ declare i32 @puts(i8* nocapture) nounwind
+
+ ; Definition of main function
+ define i32 @main() { ; i32()*
+ ; Convert [13 x i8]* to i8*...
+ %cast210 = getelementptr [13 x i8], [13 x i8]* @.str, i64 0, i64 0
+
+ ; Call puts function to write out the string to stdout.
+ call i32 @puts(i8* %cast210)
+ ret i32 0
+ }
+
+ ; Named metadata
+ !0 = !{i32 42, null, !"string"}
+ !foo = !{!0}
+
+This example is made up of a :ref:`global variable <globalvars>` named
+"``.str``", an external declaration of the "``puts``" function, a
+:ref:`function definition <functionstructure>` for "``main``" and
+:ref:`named metadata <namedmetadatastructure>` "``foo``".
+
+In general, a module is made up of a list of global values (where both
+functions and global variables are global values). Global values are
+represented by a pointer to a memory location (in this case, a pointer
+to an array of char, and a pointer to a function), and have one of the
+following :ref:`linkage types <linkage>`.
+
+.. _linkage:
+
+Linkage Types
+-------------
+
+All Global Variables and Functions have one of the following types of
+linkage:
+
+``private``
+ Global values with "``private``" linkage are only directly
+ accessible by objects in the current module. In particular, linking
+ code into a module with a private global value may cause the
+ private to be renamed as necessary to avoid collisions. Because the
+ symbol is private to the module, all references can be updated. This
+ doesn't show up in any symbol table in the object file.
+``internal``
+ Similar to private, but the value shows as a local symbol
+ (``STB_LOCAL`` in the case of ELF) in the object file. This
+ corresponds to the notion of the '``static``' keyword in C.
+``available_externally``
+ Globals with "``available_externally``" linkage are never emitted into
+ the object file corresponding to the LLVM module. From the linker's
+ perspective, an ``available_externally`` global is equivalent to
+ an external declaration. They exist to allow inlining and other
+ optimizations to take place given knowledge of the definition of the
+ global, which is known to be somewhere outside the module. Globals
+ with ``available_externally`` linkage are allowed to be discarded at
+ will, and allow inlining and other optimizations. This linkage type is
+ only allowed on definitions, not declarations.
+``linkonce``
+ Globals with "``linkonce``" linkage are merged with other globals of
+ the same name when linkage occurs. This can be used to implement
+ some forms of inline functions, templates, or other code which must
+ be generated in each translation unit that uses it, but where the
+ body may be overridden with a more definitive definition later.
+ Unreferenced ``linkonce`` globals are allowed to be discarded. Note
+ that ``linkonce`` linkage does not actually allow the optimizer to
+ inline the body of this function into callers because it doesn't
+ know if this definition of the function is the definitive definition
+ within the program or whether it will be overridden by a stronger
+ definition. To enable inlining and other optimizations, use
+ "``linkonce_odr``" linkage.
+``weak``
+ "``weak``" linkage has the same merging semantics as ``linkonce``
+ linkage, except that unreferenced globals with ``weak`` linkage may
+ not be discarded. This is used for globals that are declared "weak"
+ in C source code.
+``common``
+ "``common``" linkage is most similar to "``weak``" linkage, but they
+ are used for tentative definitions in C, such as "``int X;``" at
+ global scope. Symbols with "``common``" linkage are merged in the
+ same way as ``weak symbols``, and they may not be deleted if
+ unreferenced. ``common`` symbols may not have an explicit section,
+ must have a zero initializer, and may not be marked
+ ':ref:`constant <globalvars>`'. Functions and aliases may not have
+ common linkage.
+
+.. _linkage_appending:
+
+``appending``
+ "``appending``" linkage may only be applied to global variables of
+ pointer to array type. When two global variables with appending
+ linkage are linked together, the two global arrays are appended
+ together. This is the LLVM, typesafe, equivalent of having the
+ system linker append together "sections" with identical names when
+ .o files are linked.
+
+ Unfortunately this doesn't correspond to any feature in .o files, so it
+ can only be used for variables like ``llvm.global_ctors`` which llvm
+ interprets specially.
+
+``extern_weak``
+ The semantics of this linkage follow the ELF object file model: the
+ symbol is weak until linked, if not linked, the symbol becomes null
+ instead of being an undefined reference.
+``linkonce_odr``, ``weak_odr``
+ Some languages allow differing globals to be merged, such as two
+ functions with different semantics. Other languages, such as
+ ``C++``, ensure that only equivalent globals are ever merged (the
+ "one definition rule" --- "ODR"). Such languages can use the
+ ``linkonce_odr`` and ``weak_odr`` linkage types to indicate that the
+ global will only be merged with equivalent globals. These linkage
+ types are otherwise the same as their non-``odr`` versions.
+``external``
+ If none of the above identifiers are used, the global is externally
+ visible, meaning that it participates in linkage and can be used to
+ resolve external symbol references.
+
+It is illegal for a function *declaration* to have any linkage type
+other than ``external`` or ``extern_weak``.
+
+.. _callingconv:
+
+Calling Conventions
+-------------------
+
+LLVM :ref:`functions <functionstructure>`, :ref:`calls <i_call>` and
+:ref:`invokes <i_invoke>` can all have an optional calling convention
+specified for the call. The calling convention of any pair of dynamic
+caller/callee must match, or the behavior of the program is undefined.
+The following calling conventions are supported by LLVM, and more may be
+added in the future:
+
+"``ccc``" - The C calling convention
+ This calling convention (the default if no other calling convention
+ is specified) matches the target C calling conventions. This calling
+ convention supports varargs function calls and tolerates some
+ mismatch in the declared prototype and implemented declaration of
+ the function (as does normal C).
+"``fastcc``" - The fast calling convention
+ This calling convention attempts to make calls as fast as possible
+ (e.g. by passing things in registers). This calling convention
+ allows the target to use whatever tricks it wants to produce fast
+ code for the target, without having to conform to an externally
+ specified ABI (Application Binary Interface). `Tail calls can only
+ be optimized when this, the GHC or the HiPE convention is
+ used. <CodeGenerator.html#id80>`_ This calling convention does not
+ support varargs and requires the prototype of all callees to exactly
+ match the prototype of the function definition.
+"``coldcc``" - The cold calling convention
+ This calling convention attempts to make code in the caller as
+ efficient as possible under the assumption that the call is not
+ commonly executed. As such, these calls often preserve all registers
+ so that the call does not break any live ranges in the caller side.
+ This calling convention does not support varargs and requires the
+ prototype of all callees to exactly match the prototype of the
+ function definition. Furthermore the inliner doesn't consider such function
+ calls for inlining.
+"``cc 10``" - GHC convention
+ This calling convention has been implemented specifically for use by
+ the `Glasgow Haskell Compiler (GHC) <http://www.haskell.org/ghc>`_.
+ It passes everything in registers, going to extremes to achieve this
+ by disabling callee save registers. This calling convention should
+ not be used lightly but only for specific situations such as an
+ alternative to the *register pinning* performance technique often
+ used when implementing functional programming languages. At the
+ moment only X86 supports this convention and it has the following
+ limitations:
+
+ - On *X86-32* only supports up to 4 bit type parameters. No
+ floating point types are supported.
+ - On *X86-64* only supports up to 10 bit type parameters and 6
+ floating point parameters.
+
+ This calling convention supports `tail call
+ optimization <CodeGenerator.html#id80>`_ but requires both the
+ caller and callee are using it.
+"``cc 11``" - The HiPE calling convention
+ This calling convention has been implemented specifically for use by
+ the `High-Performance Erlang
+ (HiPE) <http://www.it.uu.se/research/group/hipe/>`_ compiler, *the*
+ native code compiler of the `Ericsson's Open Source Erlang/OTP
+ system <http://www.erlang.org/download.shtml>`_. It uses more
+ registers for argument passing than the ordinary C calling
+ convention and defines no callee-saved registers. The calling
+ convention properly supports `tail call
+ optimization <CodeGenerator.html#id80>`_ but requires that both the
+ caller and the callee use it. It uses a *register pinning*
+ mechanism, similar to GHC's convention, for keeping frequently
+ accessed runtime components pinned to specific hardware registers.
+ At the moment only X86 supports this convention (both 32 and 64
+ bit).
+"``webkit_jscc``" - WebKit's JavaScript calling convention
+ This calling convention has been implemented for `WebKit FTL JIT
+ <https://trac.webkit.org/wiki/FTLJIT>`_. It passes arguments on the
+ stack right to left (as cdecl does), and returns a value in the
+ platform's customary return register.
+"``anyregcc``" - Dynamic calling convention for code patching
+ This is a special convention that supports patching an arbitrary code
+ sequence in place of a call site. This convention forces the call
+ arguments into registers but allows them to be dynamically
+ allocated. This can currently only be used with calls to
+ llvm.experimental.patchpoint because only this intrinsic records
+ the location of its arguments in a side table. See :doc:`StackMaps`.
+"``preserve_mostcc``" - The `PreserveMost` calling convention
+ This calling convention attempts to make the code in the caller as
+ unintrusive as possible. This convention behaves identically to the `C`
+ calling convention on how arguments and return values are passed, but it
+ uses a different set of caller/callee-saved registers. This alleviates the
+ burden of saving and recovering a large register set before and after the
+ call in the caller. If the arguments are passed in callee-saved registers,
+ then they will be preserved by the callee across the call. This doesn't
+ apply for values returned in callee-saved registers.
+
+ - On X86-64 the callee preserves all general purpose registers, except for
+ R11. R11 can be used as a scratch register. Floating-point registers
+ (XMMs/YMMs) are not preserved and need to be saved by the caller.
+
+ The idea behind this convention is to support calls to runtime functions
+ that have a hot path and a cold path. The hot path is usually a small piece
+ of code that doesn't use many registers. The cold path might need to call out to
+ another function and therefore only needs to preserve the caller-saved
+ registers, which haven't already been saved by the caller. The
+ `PreserveMost` calling convention is very similar to the `cold` calling
+ convention in terms of caller/callee-saved registers, but they are used for
+ different types of function calls. `coldcc` is for function calls that are
+ rarely executed, whereas `preserve_mostcc` function calls are intended to be
+ on the hot path and definitely executed a lot. Furthermore `preserve_mostcc`
+ doesn't prevent the inliner from inlining the function call.
+
+ This calling convention will be used by a future version of the ObjectiveC
+ runtime and should therefore still be considered experimental at this time.
+ Although this convention was created to optimize certain runtime calls to
+ the ObjectiveC runtime, it is not limited to this runtime and might be used
+ by other runtimes in the future too. The current implementation only
+ supports X86-64, but the intention is to support more architectures in the
+ future.
+"``preserve_allcc``" - The `PreserveAll` calling convention
+ This calling convention attempts to make the code in the caller even less
+ intrusive than the `PreserveMost` calling convention. This calling
+ convention also behaves identical to the `C` calling convention on how
+ arguments and return values are passed, but it uses a different set of
+ caller/callee-saved registers. This removes the burden of saving and
+ recovering a large register set before and after the call in the caller. If
+ the arguments are passed in callee-saved registers, then they will be
+ preserved by the callee across the call. This doesn't apply for values
+ returned in callee-saved registers.
+
+ - On X86-64 the callee preserves all general purpose registers, except for
+ R11. R11 can be used as a scratch register. Furthermore it also preserves
+ all floating-point registers (XMMs/YMMs).
+
+ The idea behind this convention is to support calls to runtime functions
+ that don't need to call out to any other functions.
+
+ This calling convention, like the `PreserveMost` calling convention, will be
+ used by a future version of the ObjectiveC runtime and should be considered
+ experimental at this time.
+"``cxx_fast_tlscc``" - The `CXX_FAST_TLS` calling convention for access functions
+ Clang generates an access function to access C++-style TLS. The access
+ function generally has an entry block, an exit block and an initialization
+ block that is run at the first time. The entry and exit blocks can access
+ a few TLS IR variables, each access will be lowered to a platform-specific
+ sequence.
+
+ This calling convention aims to minimize overhead in the caller by
+ preserving as many registers as possible (all the registers that are
+ perserved on the fast path, composed of the entry and exit blocks).
+
+ This calling convention behaves identical to the `C` calling convention on
+ how arguments and return values are passed, but it uses a different set of
+ caller/callee-saved registers.
+
+ Given that each platform has its own lowering sequence, hence its own set
+ of preserved registers, we can't use the existing `PreserveMost`.
+
+ - On X86-64 the callee preserves all general purpose registers, except for
+ RDI and RAX.
+"``swiftcc``" - This calling convention is used for Swift language.
+ - On X86-64 RCX and R8 are available for additional integer returns, and
+ XMM2 and XMM3 are available for additional FP/vector returns.
+ - On iOS platforms, we use AAPCS-VFP calling convention.
+"``cc <n>``" - Numbered convention
+ Any calling convention may be specified by number, allowing
+ target-specific calling conventions to be used. Target specific
+ calling conventions start at 64.
+
+More calling conventions can be added/defined on an as-needed basis, to
+support Pascal conventions or any other well-known target-independent
+convention.
+
+.. _visibilitystyles:
+
+Visibility Styles
+-----------------
+
+All Global Variables and Functions have one of the following visibility
+styles:
+
+"``default``" - Default style
+ On targets that use the ELF object file format, default visibility
+ means that the declaration is visible to other modules and, in
+ shared libraries, means that the declared entity may be overridden.
+ On Darwin, default visibility means that the declaration is visible
+ to other modules. Default visibility corresponds to "external
+ linkage" in the language.
+"``hidden``" - Hidden style
+ Two declarations of an object with hidden visibility refer to the
+ same object if they are in the same shared object. Usually, hidden
+ visibility indicates that the symbol will not be placed into the
+ dynamic symbol table, so no other module (executable or shared
+ library) can reference it directly.
+"``protected``" - Protected style
+ On ELF, protected visibility indicates that the symbol will be
+ placed in the dynamic symbol table, but that references within the
+ defining module will bind to the local symbol. That is, the symbol
+ cannot be overridden by another module.
+
+A symbol with ``internal`` or ``private`` linkage must have ``default``
+visibility.
+
+.. _dllstorageclass:
+
+DLL Storage Classes
+-------------------
+
+All Global Variables, Functions and Aliases can have one of the following
+DLL storage class:
+
+``dllimport``
+ "``dllimport``" causes the compiler to reference a function or variable via
+ a global pointer to a pointer that is set up by the DLL exporting the
+ symbol. On Microsoft Windows targets, the pointer name is formed by
+ combining ``__imp_`` and the function or variable name.
+``dllexport``
+ "``dllexport``" causes the compiler to provide a global pointer to a pointer
+ in a DLL, so that it can be referenced with the ``dllimport`` attribute. On
+ Microsoft Windows targets, the pointer name is formed by combining
+ ``__imp_`` and the function or variable name. Since this storage class
+ exists for defining a dll interface, the compiler, assembler and linker know
+ it is externally referenced and must refrain from deleting the symbol.
+
+.. _tls_model:
+
+Thread Local Storage Models
+---------------------------
+
+A variable may be defined as ``thread_local``, which means that it will
+not be shared by threads (each thread will have a separated copy of the
+variable). Not all targets support thread-local variables. Optionally, a
+TLS model may be specified:
+
+``localdynamic``
+ For variables that are only used within the current shared library.
+``initialexec``
+ For variables in modules that will not be loaded dynamically.
+``localexec``
+ For variables defined in the executable and only used within it.
+
+If no explicit model is given, the "general dynamic" model is used.
+
+The models correspond to the ELF TLS models; see `ELF Handling For
+Thread-Local Storage <http://people.redhat.com/drepper/tls.pdf>`_ for
+more information on under which circumstances the different models may
+be used. The target may choose a different TLS model if the specified
+model is not supported, or if a better choice of model can be made.
+
+A model can also be specified in an alias, but then it only governs how
+the alias is accessed. It will not have any effect in the aliasee.
+
+For platforms without linker support of ELF TLS model, the -femulated-tls
+flag can be used to generate GCC compatible emulated TLS code.
+
+.. _namedtypes:
+
+Structure Types
+---------------
+
+LLVM IR allows you to specify both "identified" and "literal" :ref:`structure
+types <t_struct>`. Literal types are uniqued structurally, but identified types
+are never uniqued. An :ref:`opaque structural type <t_opaque>` can also be used
+to forward declare a type that is not yet available.
+
+An example of an identified structure specification is:
+
+.. code-block:: llvm
+
+ %mytype = type { %mytype*, i32 }
+
+Prior to the LLVM 3.0 release, identified types were structurally uniqued. Only
+literal types are uniqued in recent versions of LLVM.
+
+.. _nointptrtype:
+
+Non-Integral Pointer Type
+-------------------------
+
+Note: non-integral pointer types are a work in progress, and they should be
+considered experimental at this time.
+
+LLVM IR optionally allows the frontend to denote pointers in certain address
+spaces as "non-integral" via the :ref:`datalayout string<langref_datalayout>`.
+Non-integral pointer types represent pointers that have an *unspecified* bitwise
+representation; that is, the integral representation may be target dependent or
+unstable (not backed by a fixed integer).
+
+``inttoptr`` instructions converting integers to non-integral pointer types are
+ill-typed, and so are ``ptrtoint`` instructions converting values of
+non-integral pointer types to integers. Vector versions of said instructions
+are ill-typed as well.
+
+.. _globalvars:
+
+Global Variables
+----------------
+
+Global variables define regions of memory allocated at compilation time
+instead of run-time.
+
+Global variable definitions must be initialized.
+
+Global variables in other translation units can also be declared, in which
+case they don't have an initializer.
+
+Either global variable definitions or declarations may have an explicit section
+to be placed in and may have an optional explicit alignment specified.
+
+A variable may be defined as a global ``constant``, which indicates that
+the contents of the variable will **never** be modified (enabling better
+optimization, allowing the global data to be placed in the read-only
+section of an executable, etc). Note that variables that need runtime
+initialization cannot be marked ``constant`` as there is a store to the
+variable.
+
+LLVM explicitly allows *declarations* of global variables to be marked
+constant, even if the final definition of the global is not. This
+capability can be used to enable slightly better optimization of the
+program, but requires the language definition to guarantee that
+optimizations based on the 'constantness' are valid for the translation
+units that do not include the definition.
+
+As SSA values, global variables define pointer values that are in scope
+(i.e. they dominate) all basic blocks in the program. Global variables
+always define a pointer to their "content" type because they describe a
+region of memory, and all memory objects in LLVM are accessed through
+pointers.
+
+Global variables can be marked with ``unnamed_addr`` which indicates
+that the address is not significant, only the content. Constants marked
+like this can be merged with other constants if they have the same
+initializer. Note that a constant with significant address *can* be
+merged with a ``unnamed_addr`` constant, the result being a constant
+whose address is significant.
+
+If the ``local_unnamed_addr`` attribute is given, the address is known to
+not be significant within the module.
+
+A global variable may be declared to reside in a target-specific
+numbered address space. For targets that support them, address spaces
+may affect how optimizations are performed and/or what target
+instructions are used to access the variable. The default address space
+is zero. The address space qualifier must precede any other attributes.
+
+LLVM allows an explicit section to be specified for globals. If the
+target supports it, it will emit globals to the section specified.
+Additionally, the global can placed in a comdat if the target has the necessary
+support.
+
+By default, global initializers are optimized by assuming that global
+variables defined within the module are not modified from their
+initial values before the start of the global initializer. This is
+true even for variables potentially accessible from outside the
+module, including those with external linkage or appearing in
+``@llvm.used`` or dllexported variables. This assumption may be suppressed
+by marking the variable with ``externally_initialized``.
+
+An explicit alignment may be specified for a global, which must be a
+power of 2. If not present, or if the alignment is set to zero, the
+alignment of the global is set by the target to whatever it feels
+convenient. If an explicit alignment is specified, the global is forced
+to have exactly that alignment. Targets and optimizers are not allowed
+to over-align the global if the global has an assigned section. In this
+case, the extra alignment could be observable: for example, code could
+assume that the globals are densely packed in their section and try to
+iterate over them as an array, alignment padding would break this
+iteration. The maximum alignment is ``1 << 29``.
+
+Globals can also have a :ref:`DLL storage class <dllstorageclass>`,
+an optional :ref:`global attributes <glattrs>` and
+an optional list of attached :ref:`metadata <metadata>`.
+
+Variables and aliases can have a
+:ref:`Thread Local Storage Model <tls_model>`.
+
+Syntax::
+
+ @<GlobalVarName> = [Linkage] [Visibility] [DLLStorageClass] [ThreadLocal]
+ [(unnamed_addr|local_unnamed_addr)] [AddrSpace]
+ [ExternallyInitialized]
+ <global | constant> <Type> [<InitializerConstant>]
+ [, section "name"] [, comdat [($name)]]
+ [, align <Alignment>] (, !name !N)*
+
+For example, the following defines a global in a numbered address space
+with an initializer, section, and alignment:
+
+.. code-block:: llvm
+
+ @G = addrspace(5) constant float 1.0, section "foo", align 4
+
+The following example just declares a global variable
+
+.. code-block:: llvm
+
+ @G = external global i32
+
+The following example defines a thread-local global with the
+``initialexec`` TLS model:
+
+.. code-block:: llvm
+
+ @G = thread_local(initialexec) global i32 0, align 4
+
+.. _functionstructure:
+
+Functions
+---------
+
+LLVM function definitions consist of the "``define``" keyword, an
+optional :ref:`linkage type <linkage>`, an optional :ref:`visibility
+style <visibility>`, an optional :ref:`DLL storage class <dllstorageclass>`,
+an optional :ref:`calling convention <callingconv>`,
+an optional ``unnamed_addr`` attribute, a return type, an optional
+:ref:`parameter attribute <paramattrs>` for the return type, a function
+name, a (possibly empty) argument list (each with optional :ref:`parameter
+attributes <paramattrs>`), optional :ref:`function attributes <fnattrs>`,
+an optional section, an optional alignment,
+an optional :ref:`comdat <langref_comdats>`,
+an optional :ref:`garbage collector name <gc>`, an optional :ref:`prefix <prefixdata>`,
+an optional :ref:`prologue <prologuedata>`,
+an optional :ref:`personality <personalityfn>`,
+an optional list of attached :ref:`metadata <metadata>`,
+an opening curly brace, a list of basic blocks, and a closing curly brace.
+
+LLVM function declarations consist of the "``declare``" keyword, an
+optional :ref:`linkage type <linkage>`, an optional :ref:`visibility style
+<visibility>`, an optional :ref:`DLL storage class <dllstorageclass>`, an
+optional :ref:`calling convention <callingconv>`, an optional ``unnamed_addr``
+or ``local_unnamed_addr`` attribute, a return type, an optional :ref:`parameter
+attribute <paramattrs>` for the return type, a function name, a possibly
+empty list of arguments, an optional alignment, an optional :ref:`garbage
+collector name <gc>`, an optional :ref:`prefix <prefixdata>`, and an optional
+:ref:`prologue <prologuedata>`.
+
+A function definition contains a list of basic blocks, forming the CFG (Control
+Flow Graph) for the function. Each basic block may optionally start with a label
+(giving the basic block a symbol table entry), contains a list of instructions,
+and ends with a :ref:`terminator <terminators>` instruction (such as a branch or
+function return). If an explicit label is not provided, a block is assigned an
+implicit numbered label, using the next value from the same counter as used for
+unnamed temporaries (:ref:`see above<identifiers>`). For example, if a function
+entry block does not have an explicit label, it will be assigned label "%0",
+then the first unnamed temporary in that block will be "%1", etc.
+
+The first basic block in a function is special in two ways: it is
+immediately executed on entrance to the function, and it is not allowed
+to have predecessor basic blocks (i.e. there can not be any branches to
+the entry block of a function). Because the block can have no
+predecessors, it also cannot have any :ref:`PHI nodes <i_phi>`.
+
+LLVM allows an explicit section to be specified for functions. If the
+target supports it, it will emit functions to the section specified.
+Additionally, the function can be placed in a COMDAT.
+
+An explicit alignment may be specified for a function. If not present,
+or if the alignment is set to zero, the alignment of the function is set
+by the target to whatever it feels convenient. If an explicit alignment
+is specified, the function is forced to have at least that much
+alignment. All alignments must be a power of 2.
+
+If the ``unnamed_addr`` attribute is given, the address is known to not
+be significant and two identical functions can be merged.
+
+If the ``local_unnamed_addr`` attribute is given, the address is known to
+not be significant within the module.
+
+Syntax::
+
+ define [linkage] [visibility] [DLLStorageClass]
+ [cconv] [ret attrs]
+ <ResultType> @<FunctionName> ([argument list])
+ [(unnamed_addr|local_unnamed_addr)] [fn Attrs] [section "name"]
+ [comdat [($name)]] [align N] [gc] [prefix Constant]
+ [prologue Constant] [personality Constant] (!name !N)* { ... }
+
+The argument list is a comma separated sequence of arguments where each
+argument is of the following form:
+
+Syntax::
+
+ <type> [parameter Attrs] [name]
+
+
+.. _langref_aliases:
+
+Aliases
+-------
+
+Aliases, unlike function or variables, don't create any new data. They
+are just a new symbol and metadata for an existing position.
+
+Aliases have a name and an aliasee that is either a global value or a
+constant expression.
+
+Aliases may have an optional :ref:`linkage type <linkage>`, an optional
+:ref:`visibility style <visibility>`, an optional :ref:`DLL storage class
+<dllstorageclass>` and an optional :ref:`tls model <tls_model>`.
+
+Syntax::
+
+ @<Name> = [Linkage] [Visibility] [DLLStorageClass] [ThreadLocal] [(unnamed_addr|local_unnamed_addr)] alias <AliaseeTy>, <AliaseeTy>* @<Aliasee>
+
+The linkage must be one of ``private``, ``internal``, ``linkonce``, ``weak``,
+``linkonce_odr``, ``weak_odr``, ``external``. Note that some system linkers
+might not correctly handle dropping a weak symbol that is aliased.
+
+Aliases that are not ``unnamed_addr`` are guaranteed to have the same address as
+the aliasee expression. ``unnamed_addr`` ones are only guaranteed to point
+to the same content.
+
+If the ``local_unnamed_addr`` attribute is given, the address is known to
+not be significant within the module.
+
+Since aliases are only a second name, some restrictions apply, of which
+some can only be checked when producing an object file:
+
+* The expression defining the aliasee must be computable at assembly
+ time. Since it is just a name, no relocations can be used.
+
+* No alias in the expression can be weak as the possibility of the
+ intermediate alias being overridden cannot be represented in an
+ object file.
+
+* No global value in the expression can be a declaration, since that
+ would require a relocation, which is not possible.
+
+.. _langref_ifunc:
+
+IFuncs
+-------
+
+IFuncs, like as aliases, don't create any new data or func. They are just a new
+symbol that dynamic linker resolves at runtime by calling a resolver function.
+
+IFuncs have a name and a resolver that is a function called by dynamic linker
+that returns address of another function associated with the name.
+
+IFunc may have an optional :ref:`linkage type <linkage>` and an optional
+:ref:`visibility style <visibility>`.
+
+Syntax::
+
+ @<Name> = [Linkage] [Visibility] ifunc <IFuncTy>, <ResolverTy>* @<Resolver>
+
+
+.. _langref_comdats:
+
+Comdats
+-------
+
+Comdat IR provides access to COFF and ELF object file COMDAT functionality.
+
+Comdats have a name which represents the COMDAT key. All global objects that
+specify this key will only end up in the final object file if the linker chooses
+that key over some other key. Aliases are placed in the same COMDAT that their
+aliasee computes to, if any.
+
+Comdats have a selection kind to provide input on how the linker should
+choose between keys in two different object files.
+
+Syntax::
+
+ $<Name> = comdat SelectionKind
+
+The selection kind must be one of the following:
+
+``any``
+ The linker may choose any COMDAT key, the choice is arbitrary.
+``exactmatch``
+ The linker may choose any COMDAT key but the sections must contain the
+ same data.
+``largest``
+ The linker will choose the section containing the largest COMDAT key.
+``noduplicates``
+ The linker requires that only section with this COMDAT key exist.
+``samesize``
+ The linker may choose any COMDAT key but the sections must contain the
+ same amount of data.
+
+Note that the Mach-O platform doesn't support COMDATs and ELF only supports
+``any`` as a selection kind.
+
+Here is an example of a COMDAT group where a function will only be selected if
+the COMDAT key's section is the largest:
+
+.. code-block:: text
+
+ $foo = comdat largest
+ @foo = global i32 2, comdat($foo)
+
+ define void @bar() comdat($foo) {
+ ret void
+ }
+
+As a syntactic sugar the ``$name`` can be omitted if the name is the same as
+the global name:
+
+.. code-block:: text
+
+ $foo = comdat any
+ @foo = global i32 2, comdat
+
+
+In a COFF object file, this will create a COMDAT section with selection kind
+``IMAGE_COMDAT_SELECT_LARGEST`` containing the contents of the ``@foo`` symbol
+and another COMDAT section with selection kind
+``IMAGE_COMDAT_SELECT_ASSOCIATIVE`` which is associated with the first COMDAT
+section and contains the contents of the ``@bar`` symbol.
+
+There are some restrictions on the properties of the global object.
+It, or an alias to it, must have the same name as the COMDAT group when
+targeting COFF.
+The contents and size of this object may be used during link-time to determine
+which COMDAT groups get selected depending on the selection kind.
+Because the name of the object must match the name of the COMDAT group, the
+linkage of the global object must not be local; local symbols can get renamed
+if a collision occurs in the symbol table.
+
+The combined use of COMDATS and section attributes may yield surprising results.
+For example:
+
+.. code-block:: text
+
+ $foo = comdat any
+ $bar = comdat any
+ @g1 = global i32 42, section "sec", comdat($foo)
+ @g2 = global i32 42, section "sec", comdat($bar)
+
+From the object file perspective, this requires the creation of two sections
+with the same name. This is necessary because both globals belong to different
+COMDAT groups and COMDATs, at the object file level, are represented by
+sections.
+
+Note that certain IR constructs like global variables and functions may
+create COMDATs in the object file in addition to any which are specified using
+COMDAT IR. This arises when the code generator is configured to emit globals
+in individual sections (e.g. when `-data-sections` or `-function-sections`
+is supplied to `llc`).
+
+.. _namedmetadatastructure:
+
+Named Metadata
+--------------
+
+Named metadata is a collection of metadata. :ref:`Metadata
+nodes <metadata>` (but not metadata strings) are the only valid
+operands for a named metadata.
+
+#. Named metadata are represented as a string of characters with the
+ metadata prefix. The rules for metadata names are the same as for
+ identifiers, but quoted names are not allowed. ``"\xx"`` type escapes
+ are still valid, which allows any character to be part of a name.
+
+Syntax::
+
+ ; Some unnamed metadata nodes, which are referenced by the named metadata.
+ !0 = !{!"zero"}
+ !1 = !{!"one"}
+ !2 = !{!"two"}
+ ; A named metadata.
+ !name = !{!0, !1, !2}
+
+.. _paramattrs:
+
+Parameter Attributes
+--------------------
+
+The return type and each parameter of a function type may have a set of
+*parameter attributes* associated with them. Parameter attributes are
+used to communicate additional information about the result or
+parameters of a function. Parameter attributes are considered to be part
+of the function, not of the function type, so functions with different
+parameter attributes can have the same function type.
+
+Parameter attributes are simple keywords that follow the type specified.
+If multiple parameter attributes are needed, they are space separated.
+For example:
+
+.. code-block:: llvm
+
+ declare i32 @printf(i8* noalias nocapture, ...)
+ declare i32 @atoi(i8 zeroext)
+ declare signext i8 @returns_signed_char()
+
+Note that any attributes for the function result (``nounwind``,
+``readonly``) come immediately after the argument list.
+
+Currently, only the following parameter attributes are defined:
+
+``zeroext``
+ This indicates to the code generator that the parameter or return
+ value should be zero-extended to the extent required by the target's
+ ABI by the caller (for a parameter) or the callee (for a return value).
+``signext``
+ This indicates to the code generator that the parameter or return
+ value should be sign-extended to the extent required by the target's
+ ABI (which is usually 32-bits) by the caller (for a parameter) or
+ the callee (for a return value).
+``inreg``
+ This indicates that this parameter or return value should be treated
+ in a special target-dependent fashion while emitting code for
+ a function call or return (usually, by putting it in a register as
+ opposed to memory, though some targets use it to distinguish between
+ two different kinds of registers). Use of this attribute is
+ target-specific.
+``byval``
+ This indicates that the pointer parameter should really be passed by
+ value to the function. The attribute implies that a hidden copy of
+ the pointee is made between the caller and the callee, so the callee
+ is unable to modify the value in the caller. This attribute is only
+ valid on LLVM pointer arguments. It is generally used to pass
+ structs and arrays by value, but is also valid on pointers to
+ scalars. The copy is considered to belong to the caller not the
+ callee (for example, ``readonly`` functions should not write to
+ ``byval`` parameters). This is not a valid attribute for return
+ values.
+
+ The byval attribute also supports specifying an alignment with the
+ align attribute. It indicates the alignment of the stack slot to
+ form and the known alignment of the pointer specified to the call
+ site. If the alignment is not specified, then the code generator
+ makes a target-specific assumption.
+
+.. _attr_inalloca:
+
+``inalloca``
+
+ The ``inalloca`` argument attribute allows the caller to take the
+ address of outgoing stack arguments. An ``inalloca`` argument must
+ be a pointer to stack memory produced by an ``alloca`` instruction.
+ The alloca, or argument allocation, must also be tagged with the
+ inalloca keyword. Only the last argument may have the ``inalloca``
+ attribute, and that argument is guaranteed to be passed in memory.
+
+ An argument allocation may be used by a call at most once because
+ the call may deallocate it. The ``inalloca`` attribute cannot be
+ used in conjunction with other attributes that affect argument
+ storage, like ``inreg``, ``nest``, ``sret``, or ``byval``. The
+ ``inalloca`` attribute also disables LLVM's implicit lowering of
+ large aggregate return values, which means that frontend authors
+ must lower them with ``sret`` pointers.
+
+ When the call site is reached, the argument allocation must have
+ been the most recent stack allocation that is still live, or the
+ results are undefined. It is possible to allocate additional stack
+ space after an argument allocation and before its call site, but it
+ must be cleared off with :ref:`llvm.stackrestore
+ <int_stackrestore>`.
+
+ See :doc:`InAlloca` for more information on how to use this
+ attribute.
+
+``sret``
+ This indicates that the pointer parameter specifies the address of a
+ structure that is the return value of the function in the source
+ program. This pointer must be guaranteed by the caller to be valid:
+ loads and stores to the structure may be assumed by the callee not
+ to trap and to be properly aligned. This is not a valid attribute
+ for return values.
+
+``align <n>``
+ This indicates that the pointer value may be assumed by the optimizer to
+ have the specified alignment.
+
+ Note that this attribute has additional semantics when combined with the
+ ``byval`` attribute.
+
+.. _noalias:
+
+``noalias``
+ This indicates that objects accessed via pointer values
+ :ref:`based <pointeraliasing>` on the argument or return value are not also
+ accessed, during the execution of the function, via pointer values not
+ *based* on the argument or return value. The attribute on a return value
+ also has additional semantics described below. The caller shares the
+ responsibility with the callee for ensuring that these requirements are met.
+ For further details, please see the discussion of the NoAlias response in
+ :ref:`alias analysis <Must, May, or No>`.
+
+ Note that this definition of ``noalias`` is intentionally similar
+ to the definition of ``restrict`` in C99 for function arguments.
+
+ For function return values, C99's ``restrict`` is not meaningful,
+ while LLVM's ``noalias`` is. Furthermore, the semantics of the ``noalias``
+ attribute on return values are stronger than the semantics of the attribute
+ when used on function arguments. On function return values, the ``noalias``
+ attribute indicates that the function acts like a system memory allocation
+ function, returning a pointer to allocated storage disjoint from the
+ storage for any other object accessible to the caller.
+
+``nocapture``
+ This indicates that the callee does not make any copies of the
+ pointer that outlive the callee itself. This is not a valid
+ attribute for return values. Addresses used in volatile operations
+ are considered to be captured.
+
+.. _nest:
+
+``nest``
+ This indicates that the pointer parameter can be excised using the
+ :ref:`trampoline intrinsics <int_trampoline>`. This is not a valid
+ attribute for return values and can only be applied to one parameter.
+
+``returned``
+ This indicates that the function always returns the argument as its return
+ value. This is a hint to the optimizer and code generator used when
+ generating the caller, allowing value propagation, tail call optimization,
+ and omission of register saves and restores in some cases; it is not
+ checked or enforced when generating the callee. The parameter and the
+ function return type must be valid operands for the
+ :ref:`bitcast instruction <i_bitcast>`. This is not a valid attribute for
+ return values and can only be applied to one parameter.
+
+``nonnull``
+ This indicates that the parameter or return pointer is not null. This
+ attribute may only be applied to pointer typed parameters. This is not
+ checked or enforced by LLVM, the caller must ensure that the pointer
+ passed in is non-null, or the callee must ensure that the returned pointer
+ is non-null.
+
+``dereferenceable(<n>)``
+ This indicates that the parameter or return pointer is dereferenceable. This
+ attribute may only be applied to pointer typed parameters. A pointer that
+ is dereferenceable can be loaded from speculatively without a risk of
+ trapping. The number of bytes known to be dereferenceable must be provided
+ in parentheses. It is legal for the number of bytes to be less than the
+ size of the pointee type. The ``nonnull`` attribute does not imply
+ dereferenceability (consider a pointer to one element past the end of an
+ array), however ``dereferenceable(<n>)`` does imply ``nonnull`` in
+ ``addrspace(0)`` (which is the default address space).
+
+``dereferenceable_or_null(<n>)``
+ This indicates that the parameter or return value isn't both
+ non-null and non-dereferenceable (up to ``<n>`` bytes) at the same
+ time. All non-null pointers tagged with
+ ``dereferenceable_or_null(<n>)`` are ``dereferenceable(<n>)``.
+ For address space 0 ``dereferenceable_or_null(<n>)`` implies that
+ a pointer is exactly one of ``dereferenceable(<n>)`` or ``null``,
+ and in other address spaces ``dereferenceable_or_null(<n>)``
+ implies that a pointer is at least one of ``dereferenceable(<n>)``
+ or ``null`` (i.e. it may be both ``null`` and
+ ``dereferenceable(<n>)``). This attribute may only be applied to
+ pointer typed parameters.
+
+``swiftself``
+ This indicates that the parameter is the self/context parameter. This is not
+ a valid attribute for return values and can only be applied to one
+ parameter.
+
+``swifterror``
+ This attribute is motivated to model and optimize Swift error handling. It
+ can be applied to a parameter with pointer to pointer type or a
+ pointer-sized alloca. At the call site, the actual argument that corresponds
+ to a ``swifterror`` parameter has to come from a ``swifterror`` alloca or
+ the ``swifterror`` parameter of the caller. A ``swifterror`` value (either
+ the parameter or the alloca) can only be loaded and stored from, or used as
+ a ``swifterror`` argument. This is not a valid attribute for return values
+ and can only be applied to one parameter.
+
+ These constraints allow the calling convention to optimize access to
+ ``swifterror`` variables by associating them with a specific register at
+ call boundaries rather than placing them in memory. Since this does change
+ the calling convention, a function which uses the ``swifterror`` attribute
+ on a parameter is not ABI-compatible with one which does not.
+
+ These constraints also allow LLVM to assume that a ``swifterror`` argument
+ does not alias any other memory visible within a function and that a
+ ``swifterror`` alloca passed as an argument does not escape.
+
+.. _gc:
+
+Garbage Collector Strategy Names
+--------------------------------
+
+Each function may specify a garbage collector strategy name, which is simply a
+string:
+
+.. code-block:: llvm
+
+ define void @f() gc "name" { ... }
+
+The supported values of *name* includes those :ref:`built in to LLVM
+<builtin-gc-strategies>` and any provided by loaded plugins. Specifying a GC
+strategy will cause the compiler to alter its output in order to support the
+named garbage collection algorithm. Note that LLVM itself does not contain a
+garbage collector, this functionality is restricted to generating machine code
+which can interoperate with a collector provided externally.
+
+.. _prefixdata:
+
+Prefix Data
+-----------
+
+Prefix data is data associated with a function which the code
+generator will emit immediately before the function's entrypoint.
+The purpose of this feature is to allow frontends to associate
+language-specific runtime metadata with specific functions and make it
+available through the function pointer while still allowing the
+function pointer to be called.
+
+To access the data for a given function, a program may bitcast the
+function pointer to a pointer to the constant's type and dereference
+index -1. This implies that the IR symbol points just past the end of
+the prefix data. For instance, take the example of a function annotated
+with a single ``i32``,
+
+.. code-block:: llvm
+
+ define void @f() prefix i32 123 { ... }
+
+The prefix data can be referenced as,
+
+.. code-block:: llvm
+
+ %0 = bitcast void* () @f to i32*
+ %a = getelementptr inbounds i32, i32* %0, i32 -1
+ %b = load i32, i32* %a
+
+Prefix data is laid out as if it were an initializer for a global variable
+of the prefix data's type. The function will be placed such that the
+beginning of the prefix data is aligned. This means that if the size
+of the prefix data is not a multiple of the alignment size, the
+function's entrypoint will not be aligned. If alignment of the
+function's entrypoint is desired, padding must be added to the prefix
+data.
+
+A function may have prefix data but no body. This has similar semantics
+to the ``available_externally`` linkage in that the data may be used by the
+optimizers but will not be emitted in the object file.
+
+.. _prologuedata:
+
+Prologue Data
+-------------
+
+The ``prologue`` attribute allows arbitrary code (encoded as bytes) to
+be inserted prior to the function body. This can be used for enabling
+function hot-patching and instrumentation.
+
+To maintain the semantics of ordinary function calls, the prologue data must
+have a particular format. Specifically, it must begin with a sequence of
+bytes which decode to a sequence of machine instructions, valid for the
+module's target, which transfer control to the point immediately succeeding
+the prologue data, without performing any other visible action. This allows
+the inliner and other passes to reason about the semantics of the function
+definition without needing to reason about the prologue data. Obviously this
+makes the format of the prologue data highly target dependent.
+
+A trivial example of valid prologue data for the x86 architecture is ``i8 144``,
+which encodes the ``nop`` instruction:
+
+.. code-block:: text
+
+ define void @f() prologue i8 144 { ... }
+
+Generally prologue data can be formed by encoding a relative branch instruction
+which skips the metadata, as in this example of valid prologue data for the
+x86_64 architecture, where the first two bytes encode ``jmp .+10``:
+
+.. code-block:: text
+
+ %0 = type <{ i8, i8, i8* }>
+
+ define void @f() prologue %0 <{ i8 235, i8 8, i8* @md}> { ... }
+
+A function may have prologue data but no body. This has similar semantics
+to the ``available_externally`` linkage in that the data may be used by the
+optimizers but will not be emitted in the object file.
+
+.. _personalityfn:
+
+Personality Function
+--------------------
+
+The ``personality`` attribute permits functions to specify what function
+to use for exception handling.
+
+.. _attrgrp:
+
+Attribute Groups
+----------------
+
+Attribute groups are groups of attributes that are referenced by objects within
+the IR. They are important for keeping ``.ll`` files readable, because a lot of
+functions will use the same set of attributes. In the degenerative case of a
+``.ll`` file that corresponds to a single ``.c`` file, the single attribute
+group will capture the important command line flags used to build that file.
+
+An attribute group is a module-level object. To use an attribute group, an
+object references the attribute group's ID (e.g. ``#37``). An object may refer
+to more than one attribute group. In that situation, the attributes from the
+different groups are merged.
+
+Here is an example of attribute groups for a function that should always be
+inlined, has a stack alignment of 4, and which shouldn't use SSE instructions:
+
+.. code-block:: llvm
+
+ ; Target-independent attributes:
+ attributes #0 = { alwaysinline alignstack=4 }
+
+ ; Target-dependent attributes:
+ attributes #1 = { "no-sse" }
+
+ ; Function @f has attributes: alwaysinline, alignstack=4, and "no-sse".
+ define void @f() #0 #1 { ... }
+
+.. _fnattrs:
+
+Function Attributes
+-------------------
+
+Function attributes are set to communicate additional information about
+a function. Function attributes are considered to be part of the
+function, not of the function type, so functions with different function
+attributes can have the same function type.
+
+Function attributes are simple keywords that follow the type specified.
+If multiple attributes are needed, they are space separated. For
+example:
+
+.. code-block:: llvm
+
+ define void @f() noinline { ... }
+ define void @f() alwaysinline { ... }
+ define void @f() alwaysinline optsize { ... }
+ define void @f() optsize { ... }
+
+``alignstack(<n>)``
+ This attribute indicates that, when emitting the prologue and
+ epilogue, the backend should forcibly align the stack pointer.
+ Specify the desired alignment, which must be a power of two, in
+ parentheses.
+``allocsize(<EltSizeParam>[, <NumEltsParam>])``
+ This attribute indicates that the annotated function will always return at
+ least a given number of bytes (or null). Its arguments are zero-indexed
+ parameter numbers; if one argument is provided, then it's assumed that at
+ least ``CallSite.Args[EltSizeParam]`` bytes will be available at the
+ returned pointer. If two are provided, then it's assumed that
+ ``CallSite.Args[EltSizeParam] * CallSite.Args[NumEltsParam]`` bytes are
+ available. The referenced parameters must be integer types. No assumptions
+ are made about the contents of the returned block of memory.
+``alwaysinline``
+ This attribute indicates that the inliner should attempt to inline
+ this function into callers whenever possible, ignoring any active
+ inlining size threshold for this caller.
+``builtin``
+ This indicates that the callee function at a call site should be
+ recognized as a built-in function, even though the function's declaration
+ uses the ``nobuiltin`` attribute. This is only valid at call sites for
+ direct calls to functions that are declared with the ``nobuiltin``
+ attribute.
+``cold``
+ This attribute indicates that this function is rarely called. When
+ computing edge weights, basic blocks post-dominated by a cold
+ function call are also considered to be cold; and, thus, given low
+ weight.
+``convergent``
+ In some parallel execution models, there exist operations that cannot be
+ made control-dependent on any additional values. We call such operations
+ ``convergent``, and mark them with this attribute.
+
+ The ``convergent`` attribute may appear on functions or call/invoke
+ instructions. When it appears on a function, it indicates that calls to
+ this function should not be made control-dependent on additional values.
+ For example, the intrinsic ``llvm.nvvm.barrier0`` is ``convergent``, so
+ calls to this intrinsic cannot be made control-dependent on additional
+ values.
+
+ When it appears on a call/invoke, the ``convergent`` attribute indicates
+ that we should treat the call as though we're calling a convergent
+ function. This is particularly useful on indirect calls; without this we
+ may treat such calls as though the target is non-convergent.
+
+ The optimizer may remove the ``convergent`` attribute on functions when it
+ can prove that the function does not execute any convergent operations.
+ Similarly, the optimizer may remove ``convergent`` on calls/invokes when it
+ can prove that the call/invoke cannot call a convergent function.
+``inaccessiblememonly``
+ This attribute indicates that the function may only access memory that
+ is not accessible by the module being compiled. This is a weaker form
+ of ``readnone``.
+``inaccessiblemem_or_argmemonly``
+ This attribute indicates that the function may only access memory that is
+ either not accessible by the module being compiled, or is pointed to
+ by its pointer arguments. This is a weaker form of ``argmemonly``
+``inlinehint``
+ This attribute indicates that the source code contained a hint that
+ inlining this function is desirable (such as the "inline" keyword in
+ C/C++). It is just a hint; it imposes no requirements on the
+ inliner.
+``jumptable``
+ This attribute indicates that the function should be added to a
+ jump-instruction table at code-generation time, and that all address-taken
+ references to this function should be replaced with a reference to the
+ appropriate jump-instruction-table function pointer. Note that this creates
+ a new pointer for the original function, which means that code that depends
+ on function-pointer identity can break. So, any function annotated with
+ ``jumptable`` must also be ``unnamed_addr``.
+``minsize``
+ This attribute suggests that optimization passes and code generator
+ passes make choices that keep the code size of this function as small
+ as possible and perform optimizations that may sacrifice runtime
+ performance in order to minimize the size of the generated code.
+``naked``
+ This attribute disables prologue / epilogue emission for the
+ function. This can have very system-specific consequences.
+``nobuiltin``
+ This indicates that the callee function at a call site is not recognized as
+ a built-in function. LLVM will retain the original call and not replace it
+ with equivalent code based on the semantics of the built-in function, unless
+ the call site uses the ``builtin`` attribute. This is valid at call sites
+ and on function declarations and definitions.
+``noduplicate``
+ This attribute indicates that calls to the function cannot be
+ duplicated. A call to a ``noduplicate`` function may be moved
+ within its parent function, but may not be duplicated within
+ its parent function.
+
+ A function containing a ``noduplicate`` call may still
+ be an inlining candidate, provided that the call is not
+ duplicated by inlining. That implies that the function has
+ internal linkage and only has one call site, so the original
+ call is dead after inlining.
+``noimplicitfloat``
+ This attributes disables implicit floating point instructions.
+``noinline``
+ This attribute indicates that the inliner should never inline this
+ function in any situation. This attribute may not be used together
+ with the ``alwaysinline`` attribute.
+``nonlazybind``
+ This attribute suppresses lazy symbol binding for the function. This
+ may make calls to the function faster, at the cost of extra program
+ startup time if the function is not called during program startup.
+``noredzone``
+ This attribute indicates that the code generator should not use a
+ red zone, even if the target-specific ABI normally permits it.
+``noreturn``
+ This function attribute indicates that the function never returns
+ normally. This produces undefined behavior at runtime if the
+ function ever does dynamically return.
+``norecurse``
+ This function attribute indicates that the function does not call itself
+ either directly or indirectly down any possible call path. This produces
+ undefined behavior at runtime if the function ever does recurse.
+``nounwind``
+ This function attribute indicates that the function never raises an
+ exception. If the function does raise an exception, its runtime
+ behavior is undefined. However, functions marked nounwind may still
+ trap or generate asynchronous exceptions. Exception handling schemes
+ that are recognized by LLVM to handle asynchronous exceptions, such
+ as SEH, will still provide their implementation defined semantics.
+``optnone``
+ This function attribute indicates that most optimization passes will skip
+ this function, with the exception of interprocedural optimization passes.
+ Code generation defaults to the "fast" instruction selector.
+ This attribute cannot be used together with the ``alwaysinline``
+ attribute; this attribute is also incompatible
+ with the ``minsize`` attribute and the ``optsize`` attribute.
+
+ This attribute requires the ``noinline`` attribute to be specified on
+ the function as well, so the function is never inlined into any caller.
+ Only functions with the ``alwaysinline`` attribute are valid
+ candidates for inlining into the body of this function.
+``optsize``
+ This attribute suggests that optimization passes and code generator
+ passes make choices that keep the code size of this function low,
+ and otherwise do optimizations specifically to reduce code size as
+ long as they do not significantly impact runtime performance.
+``"patchable-function"``
+ This attribute tells the code generator that the code
+ generated for this function needs to follow certain conventions that
+ make it possible for a runtime function to patch over it later.
+ The exact effect of this attribute depends on its string value,
+ for which there currently is one legal possibility:
+
+ * ``"prologue-short-redirect"`` - This style of patchable
+ function is intended to support patching a function prologue to
+ redirect control away from the function in a thread safe
+ manner. It guarantees that the first instruction of the
+ function will be large enough to accommodate a short jump
+ instruction, and will be sufficiently aligned to allow being
+ fully changed via an atomic compare-and-swap instruction.
+ While the first requirement can be satisfied by inserting large
+ enough NOP, LLVM can and will try to re-purpose an existing
+ instruction (i.e. one that would have to be emitted anyway) as
+ the patchable instruction larger than a short jump.
+
+ ``"prologue-short-redirect"`` is currently only supported on
+ x86-64.
+
+ This attribute by itself does not imply restrictions on
+ inter-procedural optimizations. All of the semantic effects the
+ patching may have to be separately conveyed via the linkage type.
+``"probe-stack"``
+ This attribute indicates that the function will trigger a guard region
+ in the end of the stack. It ensures that accesses to the stack must be
+ no further apart than the size of the guard region to a previous
+ access of the stack. It takes one required string value, the name of
+ the stack probing function that will be called.
+
+ If a function that has a ``"probe-stack"`` attribute is inlined into
+ a function with another ``"probe-stack"`` attribute, the resulting
+ function has the ``"probe-stack"`` attribute of the caller. If a
+ function that has a ``"probe-stack"`` attribute is inlined into a
+ function that has no ``"probe-stack"`` attribute at all, the resulting
+ function has the ``"probe-stack"`` attribute of the callee.
+``readnone``
+ On a function, this attribute indicates that the function computes its
+ result (or decides to unwind an exception) based strictly on its arguments,
+ without dereferencing any pointer arguments or otherwise accessing
+ any mutable state (e.g. memory, control registers, etc) visible to
+ caller functions. It does not write through any pointer arguments
+ (including ``byval`` arguments) and never changes any state visible
+ to callers. This means while it cannot unwind exceptions by calling
+ the ``C++`` exception throwing methods (since they write to memory), there may
+ be non-``C++`` mechanisms that throw exceptions without writing to LLVM
+ visible memory.
+
+ On an argument, this attribute indicates that the function does not
+ dereference that pointer argument, even though it may read or write the
+ memory that the pointer points to if accessed through other pointers.
+``readonly``
+ On a function, this attribute indicates that the function does not write
+ through any pointer arguments (including ``byval`` arguments) or otherwise
+ modify any state (e.g. memory, control registers, etc) visible to
+ caller functions. It may dereference pointer arguments and read
+ state that may be set in the caller. A readonly function always
+ returns the same value (or unwinds an exception identically) when
+ called with the same set of arguments and global state. This means while it
+ cannot unwind exceptions by calling the ``C++`` exception throwing methods
+ (since they write to memory), there may be non-``C++`` mechanisms that throw
+ exceptions without writing to LLVM visible memory.
+
+ On an argument, this attribute indicates that the function does not write
+ through this pointer argument, even though it may write to the memory that
+ the pointer points to.
+``"stack-probe-size"``
+ This attribute controls the behavior of stack probes: either
+ the ``"probe-stack"`` attribute, or ABI-required stack probes, if any.
+ It defines the size of the guard region. It ensures that if the function
+ may use more stack space than the size of the guard region, stack probing
+ sequence will be emitted. It takes one required integer value, which
+ is 4096 by default.
+
+ If a function that has a ``"stack-probe-size"`` attribute is inlined into
+ a function with another ``"stack-probe-size"`` attribute, the resulting
+ function has the ``"stack-probe-size"`` attribute that has the lower
+ numeric value. If a function that has a ``"stack-probe-size"`` attribute is
+ inlined into a function that has no ``"stack-probe-size"`` attribute
+ at all, the resulting function has the ``"stack-probe-size"`` attribute
+ of the callee.
+``writeonly``
+ On a function, this attribute indicates that the function may write to but
+ does not read from memory.
+
+ On an argument, this attribute indicates that the function may write to but
+ does not read through this pointer argument (even though it may read from
+ the memory that the pointer points to).
+``argmemonly``
+ This attribute indicates that the only memory accesses inside function are
+ loads and stores from objects pointed to by its pointer-typed arguments,
+ with arbitrary offsets. Or in other words, all memory operations in the
+ function can refer to memory only using pointers based on its function
+ arguments.
+ Note that ``argmemonly`` can be used together with ``readonly`` attribute
+ in order to specify that function reads only from its arguments.
+``returns_twice``
+ This attribute indicates that this function can return twice. The C
+ ``setjmp`` is an example of such a function. The compiler disables
+ some optimizations (like tail calls) in the caller of these
+ functions.
+``safestack``
+ This attribute indicates that
+ `SafeStack <http://clang.llvm.org/docs/SafeStack.html>`_
+ protection is enabled for this function.
+
+ If a function that has a ``safestack`` attribute is inlined into a
+ function that doesn't have a ``safestack`` attribute or which has an
+ ``ssp``, ``sspstrong`` or ``sspreq`` attribute, then the resulting
+ function will have a ``safestack`` attribute.
+``sanitize_address``
+ This attribute indicates that AddressSanitizer checks
+ (dynamic address safety analysis) are enabled for this function.
+``sanitize_memory``
+ This attribute indicates that MemorySanitizer checks (dynamic detection
+ of accesses to uninitialized memory) are enabled for this function.
+``sanitize_thread``
+ This attribute indicates that ThreadSanitizer checks
+ (dynamic thread safety analysis) are enabled for this function.
+``speculatable``
+ This function attribute indicates that the function does not have any
+ effects besides calculating its result and does not have undefined behavior.
+ Note that ``speculatable`` is not enough to conclude that along any
+ particular execution path the number of calls to this function will not be
+ externally observable. This attribute is only valid on functions
+ and declarations, not on individual call sites. If a function is
+ incorrectly marked as speculatable and really does exhibit
+ undefined behavior, the undefined behavior may be observed even
+ if the call site is dead code.
+
+``ssp``
+ This attribute indicates that the function should emit a stack
+ smashing protector. It is in the form of a "canary" --- a random value
+ placed on the stack before the local variables that's checked upon
+ return from the function to see if it has been overwritten. A
+ heuristic is used to determine if a function needs stack protectors
+ or not. The heuristic used will enable protectors for functions with:
+
+ - Character arrays larger than ``ssp-buffer-size`` (default 8).
+ - Aggregates containing character arrays larger than ``ssp-buffer-size``.
+ - Calls to alloca() with variable sizes or constant sizes greater than
+ ``ssp-buffer-size``.
+
+ Variables that are identified as requiring a protector will be arranged
+ on the stack such that they are adjacent to the stack protector guard.
+
+ If a function that has an ``ssp`` attribute is inlined into a
+ function that doesn't have an ``ssp`` attribute, then the resulting
+ function will have an ``ssp`` attribute.
+``sspreq``
+ This attribute indicates that the function should *always* emit a
+ stack smashing protector. This overrides the ``ssp`` function
+ attribute.
+
+ Variables that are identified as requiring a protector will be arranged
+ on the stack such that they are adjacent to the stack protector guard.
+ The specific layout rules are:
+
+ #. Large arrays and structures containing large arrays
+ (``>= ssp-buffer-size``) are closest to the stack protector.
+ #. Small arrays and structures containing small arrays
+ (``< ssp-buffer-size``) are 2nd closest to the protector.
+ #. Variables that have had their address taken are 3rd closest to the
+ protector.
+
+ If a function that has an ``sspreq`` attribute is inlined into a
+ function that doesn't have an ``sspreq`` attribute or which has an
+ ``ssp`` or ``sspstrong`` attribute, then the resulting function will have
+ an ``sspreq`` attribute.
+``sspstrong``
+ This attribute indicates that the function should emit a stack smashing
+ protector. This attribute causes a strong heuristic to be used when
+ determining if a function needs stack protectors. The strong heuristic
+ will enable protectors for functions with:
+
+ - Arrays of any size and type
+ - Aggregates containing an array of any size and type.
+ - Calls to alloca().
+ - Local variables that have had their address taken.
+
+ Variables that are identified as requiring a protector will be arranged
+ on the stack such that they are adjacent to the stack protector guard.
+ The specific layout rules are:
+
+ #. Large arrays and structures containing large arrays
+ (``>= ssp-buffer-size``) are closest to the stack protector.
+ #. Small arrays and structures containing small arrays
+ (``< ssp-buffer-size``) are 2nd closest to the protector.
+ #. Variables that have had their address taken are 3rd closest to the
+ protector.
+
+ This overrides the ``ssp`` function attribute.
+
+ If a function that has an ``sspstrong`` attribute is inlined into a
+ function that doesn't have an ``sspstrong`` attribute, then the
+ resulting function will have an ``sspstrong`` attribute.
+``"thunk"``
+ This attribute indicates that the function will delegate to some other
+ function with a tail call. The prototype of a thunk should not be used for
+ optimization purposes. The caller is expected to cast the thunk prototype to
+ match the thunk target prototype.
+``uwtable``
+ This attribute indicates that the ABI being targeted requires that
+ an unwind table entry be produced for this function even if we can
+ show that no exceptions passes by it. This is normally the case for
+ the ELF x86-64 abi, but it can be disabled for some compilation
+ units.
+
+.. _glattrs:
+
+Global Attributes
+-----------------
+
+Attributes may be set to communicate additional information about a global variable.
+Unlike :ref:`function attributes <fnattrs>`, attributes on a global variable
+are grouped into a single :ref:`attribute group <attrgrp>`.
+
+.. _opbundles:
+
+Operand Bundles
+---------------
+
+Operand bundles are tagged sets of SSA values that can be associated
+with certain LLVM instructions (currently only ``call`` s and
+``invoke`` s). In a way they are like metadata, but dropping them is
+incorrect and will change program semantics.
+
+Syntax::
+
+ operand bundle set ::= '[' operand bundle (, operand bundle )* ']'
+ operand bundle ::= tag '(' [ bundle operand ] (, bundle operand )* ')'
+ bundle operand ::= SSA value
+ tag ::= string constant
+
+Operand bundles are **not** part of a function's signature, and a
+given function may be called from multiple places with different kinds
+of operand bundles. This reflects the fact that the operand bundles
+are conceptually a part of the ``call`` (or ``invoke``), not the
+callee being dispatched to.
+
+Operand bundles are a generic mechanism intended to support
+runtime-introspection-like functionality for managed languages. While
+the exact semantics of an operand bundle depend on the bundle tag,
+there are certain limitations to how much the presence of an operand
+bundle can influence the semantics of a program. These restrictions
+are described as the semantics of an "unknown" operand bundle. As
+long as the behavior of an operand bundle is describable within these
+restrictions, LLVM does not need to have special knowledge of the
+operand bundle to not miscompile programs containing it.
+
+- The bundle operands for an unknown operand bundle escape in unknown
+ ways before control is transferred to the callee or invokee.
+- Calls and invokes with operand bundles have unknown read / write
+ effect on the heap on entry and exit (even if the call target is
+ ``readnone`` or ``readonly``), unless they're overridden with
+ callsite specific attributes.
+- An operand bundle at a call site cannot change the implementation
+ of the called function. Inter-procedural optimizations work as
+ usual as long as they take into account the first two properties.
+
+More specific types of operand bundles are described below.
+
+.. _deopt_opbundles:
+
+Deoptimization Operand Bundles
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Deoptimization operand bundles are characterized by the ``"deopt"``
+operand bundle tag. These operand bundles represent an alternate
+"safe" continuation for the call site they're attached to, and can be
+used by a suitable runtime to deoptimize the compiled frame at the
+specified call site. There can be at most one ``"deopt"`` operand
+bundle attached to a call site. Exact details of deoptimization is
+out of scope for the language reference, but it usually involves
+rewriting a compiled frame into a set of interpreted frames.
+
+From the compiler's perspective, deoptimization operand bundles make
+the call sites they're attached to at least ``readonly``. They read
+through all of their pointer typed operands (even if they're not
+otherwise escaped) and the entire visible heap. Deoptimization
+operand bundles do not capture their operands except during
+deoptimization, in which case control will not be returned to the
+compiled frame.
+
+The inliner knows how to inline through calls that have deoptimization
+operand bundles. Just like inlining through a normal call site
+involves composing the normal and exceptional continuations, inlining
+through a call site with a deoptimization operand bundle needs to
+appropriately compose the "safe" deoptimization continuation. The
+inliner does this by prepending the parent's deoptimization
+continuation to every deoptimization continuation in the inlined body.
+E.g. inlining ``@f`` into ``@g`` in the following example
+
+.. code-block:: llvm
+
+ define void @f() {
+ call void @x() ;; no deopt state
+ call void @y() [ "deopt"(i32 10) ]
+ call void @y() [ "deopt"(i32 10), "unknown"(i8* null) ]
+ ret void
+ }
+
+ define void @g() {
+ call void @f() [ "deopt"(i32 20) ]
+ ret void
+ }
+
+will result in
+
+.. code-block:: llvm
+
+ define void @g() {
+ call void @x() ;; still no deopt state
+ call void @y() [ "deopt"(i32 20, i32 10) ]
+ call void @y() [ "deopt"(i32 20, i32 10), "unknown"(i8* null) ]
+ ret void
+ }
+
+It is the frontend's responsibility to structure or encode the
+deoptimization state in a way that syntactically prepending the
+caller's deoptimization state to the callee's deoptimization state is
+semantically equivalent to composing the caller's deoptimization
+continuation after the callee's deoptimization continuation.
+
+.. _ob_funclet:
+
+Funclet Operand Bundles
+^^^^^^^^^^^^^^^^^^^^^^^
+
+Funclet operand bundles are characterized by the ``"funclet"``
+operand bundle tag. These operand bundles indicate that a call site
+is within a particular funclet. There can be at most one
+``"funclet"`` operand bundle attached to a call site and it must have
+exactly one bundle operand.
+
+If any funclet EH pads have been "entered" but not "exited" (per the
+`description in the EH doc\ <ExceptionHandling.html#wineh-constraints>`_),
+it is undefined behavior to execute a ``call`` or ``invoke`` which:
+
+* does not have a ``"funclet"`` bundle and is not a ``call`` to a nounwind
+ intrinsic, or
+* has a ``"funclet"`` bundle whose operand is not the most-recently-entered
+ not-yet-exited funclet EH pad.
+
+Similarly, if no funclet EH pads have been entered-but-not-yet-exited,
+executing a ``call`` or ``invoke`` with a ``"funclet"`` bundle is undefined behavior.
+
+GC Transition Operand Bundles
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+GC transition operand bundles are characterized by the
+``"gc-transition"`` operand bundle tag. These operand bundles mark a
+call as a transition between a function with one GC strategy to a
+function with a different GC strategy. If coordinating the transition
+between GC strategies requires additional code generation at the call
+site, these bundles may contain any values that are needed by the
+generated code. For more details, see :ref:`GC Transitions
+<gc_transition_args>`.
+
+.. _moduleasm:
+
+Module-Level Inline Assembly
+----------------------------
+
+Modules may contain "module-level inline asm" blocks, which corresponds
+to the GCC "file scope inline asm" blocks. These blocks are internally
+concatenated by LLVM and treated as a single unit, but may be separated
+in the ``.ll`` file if desired. The syntax is very simple:
+
+.. code-block:: llvm
+
+ module asm "inline asm code goes here"
+ module asm "more can go here"
+
+The strings can contain any character by escaping non-printable
+characters. The escape sequence used is simply "\\xx" where "xx" is the
+two digit hex code for the number.
+
+Note that the assembly string *must* be parseable by LLVM's integrated assembler
+(unless it is disabled), even when emitting a ``.s`` file.
+
+.. _langref_datalayout:
+
+Data Layout
+-----------
+
+A module may specify a target specific data layout string that specifies
+how data is to be laid out in memory. The syntax for the data layout is
+simply:
+
+.. code-block:: llvm
+
+ target datalayout = "layout specification"
+
+The *layout specification* consists of a list of specifications
+separated by the minus sign character ('-'). Each specification starts
+with a letter and may include other information after the letter to
+define some aspect of the data layout. The specifications accepted are
+as follows:
+
+``E``
+ Specifies that the target lays out data in big-endian form. That is,
+ the bits with the most significance have the lowest address
+ location.
+``e``
+ Specifies that the target lays out data in little-endian form. That
+ is, the bits with the least significance have the lowest address
+ location.
+``S<size>``
+ Specifies the natural alignment of the stack in bits. Alignment
+ promotion of stack variables is limited to the natural stack
+ alignment to avoid dynamic stack realignment. The stack alignment
+ must be a multiple of 8-bits. If omitted, the natural stack
+ alignment defaults to "unspecified", which does not prevent any
+ alignment promotions.
+``A<address space>``
+ Specifies the address space of objects created by '``alloca``'.
+ Defaults to the default address space of 0.
+``p[n]:<size>:<abi>:<pref>``
+ This specifies the *size* of a pointer and its ``<abi>`` and
+ ``<pref>``\erred alignments for address space ``n``. All sizes are in
+ bits. The address space, ``n``, is optional, and if not specified,
+ denotes the default address space 0. The value of ``n`` must be
+ in the range [1,2^23).
+``i<size>:<abi>:<pref>``
+ This specifies the alignment for an integer type of a given bit
+ ``<size>``. The value of ``<size>`` must be in the range [1,2^23).
+``v<size>:<abi>:<pref>``
+ This specifies the alignment for a vector type of a given bit
+ ``<size>``.
+``f<size>:<abi>:<pref>``
+ This specifies the alignment for a floating point type of a given bit
+ ``<size>``. Only values of ``<size>`` that are supported by the target
+ will work. 32 (float) and 64 (double) are supported on all targets; 80
+ or 128 (different flavors of long double) are also supported on some
+ targets.
+``a:<abi>:<pref>``
+ This specifies the alignment for an object of aggregate type.
+``m:<mangling>``
+ If present, specifies that llvm names are mangled in the output. The
+ options are
+
+ * ``e``: ELF mangling: Private symbols get a ``.L`` prefix.
+ * ``m``: Mips mangling: Private symbols get a ``$`` prefix.
+ * ``o``: Mach-O mangling: Private symbols get ``L`` prefix. Other
+ symbols get a ``_`` prefix.
+ * ``w``: Windows COFF prefix: Similar to Mach-O, but stdcall and fastcall
+ functions also get a suffix based on the frame size.
+ * ``x``: Windows x86 COFF prefix: Similar to Windows COFF, but use a ``_``
+ prefix for ``__cdecl`` functions.
+``n<size1>:<size2>:<size3>...``
+ This specifies a set of native integer widths for the target CPU in
+ bits. For example, it might contain ``n32`` for 32-bit PowerPC,
+ ``n32:64`` for PowerPC 64, or ``n8:16:32:64`` for X86-64. Elements of
+ this set are considered to support most general arithmetic operations
+ efficiently.
+``ni:<address space0>:<address space1>:<address space2>...``
+ This specifies pointer types with the specified address spaces
+ as :ref:`Non-Integral Pointer Type <nointptrtype>` s. The ``0``
+ address space cannot be specified as non-integral.
+
+On every specification that takes a ``<abi>:<pref>``, specifying the
+``<pref>`` alignment is optional. If omitted, the preceding ``:``
+should be omitted too and ``<pref>`` will be equal to ``<abi>``.
+
+When constructing the data layout for a given target, LLVM starts with a
+default set of specifications which are then (possibly) overridden by
+the specifications in the ``datalayout`` keyword. The default
+specifications are given in this list:
+
+- ``E`` - big endian
+- ``p:64:64:64`` - 64-bit pointers with 64-bit alignment.
+- ``p[n]:64:64:64`` - Other address spaces are assumed to be the
+ same as the default address space.
+- ``S0`` - natural stack alignment is unspecified
+- ``i1:8:8`` - i1 is 8-bit (byte) aligned
+- ``i8:8:8`` - i8 is 8-bit (byte) aligned
+- ``i16:16:16`` - i16 is 16-bit aligned
+- ``i32:32:32`` - i32 is 32-bit aligned
+- ``i64:32:64`` - i64 has ABI alignment of 32-bits but preferred
+ alignment of 64-bits
+- ``f16:16:16`` - half is 16-bit aligned
+- ``f32:32:32`` - float is 32-bit aligned
+- ``f64:64:64`` - double is 64-bit aligned
+- ``f128:128:128`` - quad is 128-bit aligned
+- ``v64:64:64`` - 64-bit vector is 64-bit aligned
+- ``v128:128:128`` - 128-bit vector is 128-bit aligned
+- ``a:0:64`` - aggregates are 64-bit aligned
+
+When LLVM is determining the alignment for a given type, it uses the
+following rules:
+
+#. If the type sought is an exact match for one of the specifications,
+ that specification is used.
+#. If no match is found, and the type sought is an integer type, then
+ the smallest integer type that is larger than the bitwidth of the
+ sought type is used. If none of the specifications are larger than
+ the bitwidth then the largest integer type is used. For example,
+ given the default specifications above, the i7 type will use the
+ alignment of i8 (next largest) while both i65 and i256 will use the
+ alignment of i64 (largest specified).
+#. If no match is found, and the type sought is a vector type, then the
+ largest vector type that is smaller than the sought vector type will
+ be used as a fall back. This happens because <128 x double> can be
+ implemented in terms of 64 <2 x double>, for example.
+
+The function of the data layout string may not be what you expect.
+Notably, this is not a specification from the frontend of what alignment
+the code generator should use.
+
+Instead, if specified, the target data layout is required to match what
+the ultimate *code generator* expects. This string is used by the
+mid-level optimizers to improve code, and this only works if it matches
+what the ultimate code generator uses. There is no way to generate IR
+that does not embed this target-specific detail into the IR. If you
+don't specify the string, the default specifications will be used to
+generate a Data Layout and the optimization phases will operate
+accordingly and introduce target specificity into the IR with respect to
+these default specifications.
+
+.. _langref_triple:
+
+Target Triple
+-------------
+
+A module may specify a target triple string that describes the target
+host. The syntax for the target triple is simply:
+
+.. code-block:: llvm
+
+ target triple = "x86_64-apple-macosx10.7.0"
+
+The *target triple* string consists of a series of identifiers delimited
+by the minus sign character ('-'). The canonical forms are:
+
+::
+
+ ARCHITECTURE-VENDOR-OPERATING_SYSTEM
+ ARCHITECTURE-VENDOR-OPERATING_SYSTEM-ENVIRONMENT
+
+This information is passed along to the backend so that it generates
+code for the proper architecture. It's possible to override this on the
+command line with the ``-mtriple`` command line option.
+
+.. _pointeraliasing:
+
+Pointer Aliasing Rules
+----------------------
+
+Any memory access must be done through a pointer value associated with
+an address range of the memory access, otherwise the behavior is
+undefined. Pointer values are associated with address ranges according
+to the following rules:
+
+- A pointer value is associated with the addresses associated with any
+ value it is *based* on.
+- An address of a global variable is associated with the address range
+ of the variable's storage.
+- The result value of an allocation instruction is associated with the
+ address range of the allocated storage.
+- A null pointer in the default address-space is associated with no
+ address.
+- An integer constant other than zero or a pointer value returned from
+ a function not defined within LLVM may be associated with address
+ ranges allocated through mechanisms other than those provided by
+ LLVM. Such ranges shall not overlap with any ranges of addresses
+ allocated by mechanisms provided by LLVM.
+
+A pointer value is *based* on another pointer value according to the
+following rules:
+
+- A pointer value formed from a ``getelementptr`` operation is *based*
+ on the second value operand of the ``getelementptr``.
+- The result value of a ``bitcast`` is *based* on the operand of the
+ ``bitcast``.
+- A pointer value formed by an ``inttoptr`` is *based* on all pointer
+ values that contribute (directly or indirectly) to the computation of
+ the pointer's value.
+- The "*based* on" relationship is transitive.
+
+Note that this definition of *"based"* is intentionally similar to the
+definition of *"based"* in C99, though it is slightly weaker.
+
+LLVM IR does not associate types with memory. The result type of a
+``load`` merely indicates the size and alignment of the memory from
+which to load, as well as the interpretation of the value. The first
+operand type of a ``store`` similarly only indicates the size and
+alignment of the store.
+
+Consequently, type-based alias analysis, aka TBAA, aka
+``-fstrict-aliasing``, is not applicable to general unadorned LLVM IR.
+:ref:`Metadata <metadata>` may be used to encode additional information
+which specialized optimization passes may use to implement type-based
+alias analysis.
+
+.. _volatile:
+
+Volatile Memory Accesses
+------------------------
+
+Certain memory accesses, such as :ref:`load <i_load>`'s,
+:ref:`store <i_store>`'s, and :ref:`llvm.memcpy <int_memcpy>`'s may be
+marked ``volatile``. The optimizers must not change the number of
+volatile operations or change their order of execution relative to other
+volatile operations. The optimizers *may* change the order of volatile
+operations relative to non-volatile operations. This is not Java's
+"volatile" and has no cross-thread synchronization behavior.
+
+IR-level volatile loads and stores cannot safely be optimized into
+llvm.memcpy or llvm.memmove intrinsics even when those intrinsics are
+flagged volatile. Likewise, the backend should never split or merge
+target-legal volatile load/store instructions.
+
+.. admonition:: Rationale
+
+ Platforms may rely on volatile loads and stores of natively supported
+ data width to be executed as single instruction. For example, in C
+ this holds for an l-value of volatile primitive type with native
+ hardware support, but not necessarily for aggregate types. The
+ frontend upholds these expectations, which are intentionally
+ unspecified in the IR. The rules above ensure that IR transformations
+ do not violate the frontend's contract with the language.
+
+.. _memmodel:
+
+Memory Model for Concurrent Operations
+--------------------------------------
+
+The LLVM IR does not define any way to start parallel threads of
+execution or to register signal handlers. Nonetheless, there are
+platform-specific ways to create them, and we define LLVM IR's behavior
+in their presence. This model is inspired by the C++0x memory model.
+
+For a more informal introduction to this model, see the :doc:`Atomics`.
+
+We define a *happens-before* partial order as the least partial order
+that
+
+- Is a superset of single-thread program order, and
+- When a *synchronizes-with* ``b``, includes an edge from ``a`` to
+ ``b``. *Synchronizes-with* pairs are introduced by platform-specific
+ techniques, like pthread locks, thread creation, thread joining,
+ etc., and by atomic instructions. (See also :ref:`Atomic Memory Ordering
+ Constraints <ordering>`).
+
+Note that program order does not introduce *happens-before* edges
+between a thread and signals executing inside that thread.
+
+Every (defined) read operation (load instructions, memcpy, atomic
+loads/read-modify-writes, etc.) R reads a series of bytes written by
+(defined) write operations (store instructions, atomic
+stores/read-modify-writes, memcpy, etc.). For the purposes of this
+section, initialized globals are considered to have a write of the
+initializer which is atomic and happens before any other read or write
+of the memory in question. For each byte of a read R, R\ :sub:`byte`
+may see any write to the same byte, except:
+
+- If write\ :sub:`1` happens before write\ :sub:`2`, and
+ write\ :sub:`2` happens before R\ :sub:`byte`, then
+ R\ :sub:`byte` does not see write\ :sub:`1`.
+- If R\ :sub:`byte` happens before write\ :sub:`3`, then
+ R\ :sub:`byte` does not see write\ :sub:`3`.
+
+Given that definition, R\ :sub:`byte` is defined as follows:
+
+- If R is volatile, the result is target-dependent. (Volatile is
+ supposed to give guarantees which can support ``sig_atomic_t`` in
+ C/C++, and may be used for accesses to addresses that do not behave
+ like normal memory. It does not generally provide cross-thread
+ synchronization.)
+- Otherwise, if there is no write to the same byte that happens before
+ R\ :sub:`byte`, R\ :sub:`byte` returns ``undef`` for that byte.
+- Otherwise, if R\ :sub:`byte` may see exactly one write,
+ R\ :sub:`byte` returns the value written by that write.
+- Otherwise, if R is atomic, and all the writes R\ :sub:`byte` may
+ see are atomic, it chooses one of the values written. See the :ref:`Atomic
+ Memory Ordering Constraints <ordering>` section for additional
+ constraints on how the choice is made.
+- Otherwise R\ :sub:`byte` returns ``undef``.
+
+R returns the value composed of the series of bytes it read. This
+implies that some bytes within the value may be ``undef`` **without**
+the entire value being ``undef``. Note that this only defines the
+semantics of the operation; it doesn't mean that targets will emit more
+than one instruction to read the series of bytes.
+
+Note that in cases where none of the atomic intrinsics are used, this
+model places only one restriction on IR transformations on top of what
+is required for single-threaded execution: introducing a store to a byte
+which might not otherwise be stored is not allowed in general.
+(Specifically, in the case where another thread might write to and read
+from an address, introducing a store can change a load that may see
+exactly one write into a load that may see multiple writes.)
+
+.. _ordering:
+
+Atomic Memory Ordering Constraints
+----------------------------------
+
+Atomic instructions (:ref:`cmpxchg <i_cmpxchg>`,
+:ref:`atomicrmw <i_atomicrmw>`, :ref:`fence <i_fence>`,
+:ref:`atomic load <i_load>`, and :ref:`atomic store <i_store>`) take
+ordering parameters that determine which other atomic instructions on
+the same address they *synchronize with*. These semantics are borrowed
+from Java and C++0x, but are somewhat more colloquial. If these
+descriptions aren't precise enough, check those specs (see spec
+references in the :doc:`atomics guide <Atomics>`).
+:ref:`fence <i_fence>` instructions treat these orderings somewhat
+differently since they don't take an address. See that instruction's
+documentation for details.
+
+For a simpler introduction to the ordering constraints, see the
+:doc:`Atomics`.
+
+``unordered``
+ The set of values that can be read is governed by the happens-before
+ partial order. A value cannot be read unless some operation wrote
+ it. This is intended to provide a guarantee strong enough to model
+ Java's non-volatile shared variables. This ordering cannot be
+ specified for read-modify-write operations; it is not strong enough
+ to make them atomic in any interesting way.
+``monotonic``
+ In addition to the guarantees of ``unordered``, there is a single
+ total order for modifications by ``monotonic`` operations on each
+ address. All modification orders must be compatible with the
+ happens-before order. There is no guarantee that the modification
+ orders can be combined to a global total order for the whole program
+ (and this often will not be possible). The read in an atomic
+ read-modify-write operation (:ref:`cmpxchg <i_cmpxchg>` and
+ :ref:`atomicrmw <i_atomicrmw>`) reads the value in the modification
+ order immediately before the value it writes. If one atomic read
+ happens before another atomic read of the same address, the later
+ read must see the same value or a later value in the address's
+ modification order. This disallows reordering of ``monotonic`` (or
+ stronger) operations on the same address. If an address is written
+ ``monotonic``-ally by one thread, and other threads ``monotonic``-ally
+ read that address repeatedly, the other threads must eventually see
+ the write. This corresponds to the C++0x/C1x
+ ``memory_order_relaxed``.
+``acquire``
+ In addition to the guarantees of ``monotonic``, a
+ *synchronizes-with* edge may be formed with a ``release`` operation.
+ This is intended to model C++'s ``memory_order_acquire``.
+``release``
+ In addition to the guarantees of ``monotonic``, if this operation
+ writes a value which is subsequently read by an ``acquire``
+ operation, it *synchronizes-with* that operation. (This isn't a
+ complete description; see the C++0x definition of a release
+ sequence.) This corresponds to the C++0x/C1x
+ ``memory_order_release``.
+``acq_rel`` (acquire+release)
+ Acts as both an ``acquire`` and ``release`` operation on its
+ address. This corresponds to the C++0x/C1x ``memory_order_acq_rel``.
+``seq_cst`` (sequentially consistent)
+ In addition to the guarantees of ``acq_rel`` (``acquire`` for an
+ operation that only reads, ``release`` for an operation that only
+ writes), there is a global total order on all
+ sequentially-consistent operations on all addresses, which is
+ consistent with the *happens-before* partial order and with the
+ modification orders of all the affected addresses. Each
+ sequentially-consistent read sees the last preceding write to the
+ same address in this global order. This corresponds to the C++0x/C1x
+ ``memory_order_seq_cst`` and Java volatile.
+
+.. _syncscope:
+
+If an atomic operation is marked ``syncscope("singlethread")``, it only
+*synchronizes with* and only participates in the seq\_cst total orderings of
+other operations running in the same thread (for example, in signal handlers).
+
+If an atomic operation is marked ``syncscope("<target-scope>")``, where
+``<target-scope>`` is a target specific synchronization scope, then it is target
+dependent if it *synchronizes with* and participates in the seq\_cst total
+orderings of other operations.
+
+Otherwise, an atomic operation that is not marked ``syncscope("singlethread")``
+or ``syncscope("<target-scope>")`` *synchronizes with* and participates in the
+seq\_cst total orderings of other operations that are not marked
+``syncscope("singlethread")`` or ``syncscope("<target-scope>")``.
+
+.. _fastmath:
+
+Fast-Math Flags
+---------------
+
+LLVM IR floating-point binary ops (:ref:`fadd <i_fadd>`,
+:ref:`fsub <i_fsub>`, :ref:`fmul <i_fmul>`, :ref:`fdiv <i_fdiv>`,
+:ref:`frem <i_frem>`, :ref:`fcmp <i_fcmp>`) and :ref:`call <i_call>`
+instructions have the following flags that can be set to enable
+otherwise unsafe floating point transformations.
+
+``nnan``
+ No NaNs - Allow optimizations to assume the arguments and result are not
+ NaN. Such optimizations are required to retain defined behavior over
+ NaNs, but the value of the result is undefined.
+
+``ninf``
+ No Infs - Allow optimizations to assume the arguments and result are not
+ +/-Inf. Such optimizations are required to retain defined behavior over
+ +/-Inf, but the value of the result is undefined.
+
+``nsz``
+ No Signed Zeros - Allow optimizations to treat the sign of a zero
+ argument or result as insignificant.
+
+``arcp``
+ Allow Reciprocal - Allow optimizations to use the reciprocal of an
+ argument rather than perform division.
+
+``contract``
+ Allow floating-point contraction (e.g. fusing a multiply followed by an
+ addition into a fused multiply-and-add).
+
+``fast``
+ Fast - Allow algebraically equivalent transformations that may
+ dramatically change results in floating point (e.g. reassociate). This
+ flag implies all the others.
+
+.. _uselistorder:
+
+Use-list Order Directives
+-------------------------
+
+Use-list directives encode the in-memory order of each use-list, allowing the
+order to be recreated. ``<order-indexes>`` is a comma-separated list of
+indexes that are assigned to the referenced value's uses. The referenced
+value's use-list is immediately sorted by these indexes.
+
+Use-list directives may appear at function scope or global scope. They are not
+instructions, and have no effect on the semantics of the IR. When they're at
+function scope, they must appear after the terminator of the final basic block.
+
+If basic blocks have their address taken via ``blockaddress()`` expressions,
+``uselistorder_bb`` can be used to reorder their use-lists from outside their
+function's scope.
+
+:Syntax:
+
+::
+
+ uselistorder <ty> <value>, { <order-indexes> }
+ uselistorder_bb @function, %block { <order-indexes> }
+
+:Examples:
+
+::
+
+ define void @foo(i32 %arg1, i32 %arg2) {
+ entry:
+ ; ... instructions ...
+ bb:
+ ; ... instructions ...
+
+ ; At function scope.
+ uselistorder i32 %arg1, { 1, 0, 2 }
+ uselistorder label %bb, { 1, 0 }
+ }
+
+ ; At global scope.
+ uselistorder i32* @global, { 1, 2, 0 }
+ uselistorder i32 7, { 1, 0 }
+ uselistorder i32 (i32) @bar, { 1, 0 }
+ uselistorder_bb @foo, %bb, { 5, 1, 3, 2, 0, 4 }
+
+.. _source_filename:
+
+Source Filename
+---------------
+
+The *source filename* string is set to the original module identifier,
+which will be the name of the compiled source file when compiling from
+source through the clang front end, for example. It is then preserved through
+the IR and bitcode.
+
+This is currently necessary to generate a consistent unique global
+identifier for local functions used in profile data, which prepends the
+source file name to the local function name.
+
+The syntax for the source file name is simply:
+
+.. code-block:: text
+
+ source_filename = "/path/to/source.c"
+
+.. _typesystem:
+
+Type System
+===========
+
+The LLVM type system is one of the most important features of the
+intermediate representation. Being typed enables a number of
+optimizations to be performed on the intermediate representation
+directly, without having to do extra analyses on the side before the
+transformation. A strong type system makes it easier to read the
+generated code and enables novel analyses and transformations that are
+not feasible to perform on normal three address code representations.
+
+.. _t_void:
+
+Void Type
+---------
+
+:Overview:
+
+
+The void type does not represent any value and has no size.
+
+:Syntax:
+
+
+::
+
+ void
+
+
+.. _t_function:
+
+Function Type
+-------------
+
+:Overview:
+
+
+The function type can be thought of as a function signature. It consists of a
+return type and a list of formal parameter types. The return type of a function
+type is a void type or first class type --- except for :ref:`label <t_label>`
+and :ref:`metadata <t_metadata>` types.
+
+:Syntax:
+
+::
+
+ <returntype> (<parameter list>)
+
+...where '``<parameter list>``' is a comma-separated list of type
+specifiers. Optionally, the parameter list may include a type ``...``, which
+indicates that the function takes a variable number of arguments. Variable
+argument functions can access their arguments with the :ref:`variable argument
+handling intrinsic <int_varargs>` functions. '``<returntype>``' is any type
+except :ref:`label <t_label>` and :ref:`metadata <t_metadata>`.
+
+:Examples:
+
++---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
+| ``i32 (i32)`` | function taking an ``i32``, returning an ``i32`` |
++---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
+| ``float (i16, i32 *) *`` | :ref:`Pointer <t_pointer>` to a function that takes an ``i16`` and a :ref:`pointer <t_pointer>` to ``i32``, returning ``float``. |
++---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
+| ``i32 (i8*, ...)`` | A vararg function that takes at least one :ref:`pointer <t_pointer>` to ``i8`` (char in C), which returns an integer. This is the signature for ``printf`` in LLVM. |
++---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
+| ``{i32, i32} (i32)`` | A function taking an ``i32``, returning a :ref:`structure <t_struct>` containing two ``i32`` values |
++---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
+
+.. _t_firstclass:
+
+First Class Types
+-----------------
+
+The :ref:`first class <t_firstclass>` types are perhaps the most important.
+Values of these types are the only ones which can be produced by
+instructions.
+
+.. _t_single_value:
+
+Single Value Types
+^^^^^^^^^^^^^^^^^^
+
+These are the types that are valid in registers from CodeGen's perspective.
+
+.. _t_integer:
+
+Integer Type
+""""""""""""
+
+:Overview:
+
+The integer type is a very simple type that simply specifies an
+arbitrary bit width for the integer type desired. Any bit width from 1
+bit to 2\ :sup:`23`\ -1 (about 8 million) can be specified.
+
+:Syntax:
+
+::
+
+ iN
+
+The number of bits the integer will occupy is specified by the ``N``
+value.
+
+Examples:
+*********
+
++----------------+------------------------------------------------+
+| ``i1`` | a single-bit integer. |
++----------------+------------------------------------------------+
+| ``i32`` | a 32-bit integer. |
++----------------+------------------------------------------------+
+| ``i1942652`` | a really big integer of over 1 million bits. |
++----------------+------------------------------------------------+
+
+.. _t_floating:
+
+Floating Point Types
+""""""""""""""""""""
+
+.. list-table::
+ :header-rows: 1
+
+ * - Type
+ - Description
+
+ * - ``half``
+ - 16-bit floating point value
+
+ * - ``float``
+ - 32-bit floating point value
+
+ * - ``double``
+ - 64-bit floating point value
+
+ * - ``fp128``
+ - 128-bit floating point value (112-bit mantissa)
+
+ * - ``x86_fp80``
+ - 80-bit floating point value (X87)
+
+ * - ``ppc_fp128``
+ - 128-bit floating point value (two 64-bits)
+
+X86_mmx Type
+""""""""""""
+
+:Overview:
+
+The x86_mmx type represents a value held in an MMX register on an x86
+machine. The operations allowed on it are quite limited: parameters and
+return values, load and store, and bitcast. User-specified MMX
+instructions are represented as intrinsic or asm calls with arguments
+and/or results of this type. There are no arrays, vectors or constants
+of this type.
+
+:Syntax:
+
+::
+
+ x86_mmx
+
+
+.. _t_pointer:
+
+Pointer Type
+""""""""""""
+
+:Overview:
+
+The pointer type is used to specify memory locations. Pointers are
+commonly used to reference objects in memory.
+
+Pointer types may have an optional address space attribute defining the
+numbered address space where the pointed-to object resides. The default
+address space is number zero. The semantics of non-zero address spaces
+are target-specific.
+
+Note that LLVM does not permit pointers to void (``void*``) nor does it
+permit pointers to labels (``label*``). Use ``i8*`` instead.
+
+:Syntax:
+
+::
+
+ <type> *
+
+:Examples:
+
++-------------------------+--------------------------------------------------------------------------------------------------------------+
+| ``[4 x i32]*`` | A :ref:`pointer <t_pointer>` to :ref:`array <t_array>` of four ``i32`` values. |
++-------------------------+--------------------------------------------------------------------------------------------------------------+
+| ``i32 (i32*) *`` | A :ref:`pointer <t_pointer>` to a :ref:`function <t_function>` that takes an ``i32*``, returning an ``i32``. |
++-------------------------+--------------------------------------------------------------------------------------------------------------+
+| ``i32 addrspace(5)*`` | A :ref:`pointer <t_pointer>` to an ``i32`` value that resides in address space #5. |
++-------------------------+--------------------------------------------------------------------------------------------------------------+
+
+.. _t_vector:
+
+Vector Type
+"""""""""""
+
+:Overview:
+
+A vector type is a simple derived type that represents a vector of
+elements. Vector types are used when multiple primitive data are
+operated in parallel using a single instruction (SIMD). A vector type
+requires a size (number of elements) and an underlying primitive data
+type. Vector types are considered :ref:`first class <t_firstclass>`.
+
+:Syntax:
+
+::
+
+ < <# elements> x <elementtype> >
+
+The number of elements is a constant integer value larger than 0;
+elementtype may be any integer, floating point or pointer type. Vectors
+of size zero are not allowed.
+
+:Examples:
+
++-------------------+--------------------------------------------------+
+| ``<4 x i32>`` | Vector of 4 32-bit integer values. |
++-------------------+--------------------------------------------------+
+| ``<8 x float>`` | Vector of 8 32-bit floating-point values. |
++-------------------+--------------------------------------------------+
+| ``<2 x i64>`` | Vector of 2 64-bit integer values. |
++-------------------+--------------------------------------------------+
+| ``<4 x i64*>`` | Vector of 4 pointers to 64-bit integer values. |
++-------------------+--------------------------------------------------+
+
+.. _t_label:
+
+Label Type
+^^^^^^^^^^
+
+:Overview:
+
+The label type represents code labels.
+
+:Syntax:
+
+::
+
+ label
+
+.. _t_token:
+
+Token Type
+^^^^^^^^^^
+
+:Overview:
+
+The token type is used when a value is associated with an instruction
+but all uses of the value must not attempt to introspect or obscure it.
+As such, it is not appropriate to have a :ref:`phi <i_phi>` or
+:ref:`select <i_select>` of type token.
+
+:Syntax:
+
+::
+
+ token
+
+
+
+.. _t_metadata:
+
+Metadata Type
+^^^^^^^^^^^^^
+
+:Overview:
+
+The metadata type represents embedded metadata. No derived types may be
+created from metadata except for :ref:`function <t_function>` arguments.
+
+:Syntax:
+
+::
+
+ metadata
+
+.. _t_aggregate:
+
+Aggregate Types
+^^^^^^^^^^^^^^^
+
+Aggregate Types are a subset of derived types that can contain multiple
+member types. :ref:`Arrays <t_array>` and :ref:`structs <t_struct>` are
+aggregate types. :ref:`Vectors <t_vector>` are not considered to be
+aggregate types.
+
+.. _t_array:
+
+Array Type
+""""""""""
+
+:Overview:
+
+The array type is a very simple derived type that arranges elements
+sequentially in memory. The array type requires a size (number of
+elements) and an underlying data type.
+
+:Syntax:
+
+::
+
+ [<# elements> x <elementtype>]
+
+The number of elements is a constant integer value; ``elementtype`` may
+be any type with a size.
+
+:Examples:
+
++------------------+--------------------------------------+
+| ``[40 x i32]`` | Array of 40 32-bit integer values. |
++------------------+--------------------------------------+
+| ``[41 x i32]`` | Array of 41 32-bit integer values. |
++------------------+--------------------------------------+
+| ``[4 x i8]`` | Array of 4 8-bit integer values. |
++------------------+--------------------------------------+
+
+Here are some examples of multidimensional arrays:
+
++-----------------------------+----------------------------------------------------------+
+| ``[3 x [4 x i32]]`` | 3x4 array of 32-bit integer values. |
++-----------------------------+----------------------------------------------------------+
+| ``[12 x [10 x float]]`` | 12x10 array of single precision floating point values. |
++-----------------------------+----------------------------------------------------------+
+| ``[2 x [3 x [4 x i16]]]`` | 2x3x4 array of 16-bit integer values. |
++-----------------------------+----------------------------------------------------------+
+
+There is no restriction on indexing beyond the end of the array implied
+by a static type (though there are restrictions on indexing beyond the
+bounds of an allocated object in some cases). This means that
+single-dimension 'variable sized array' addressing can be implemented in
+LLVM with a zero length array type. An implementation of 'pascal style
+arrays' in LLVM could use the type "``{ i32, [0 x float]}``", for
+example.
+
+.. _t_struct:
+
+Structure Type
+""""""""""""""
+
+:Overview:
+
+The structure type is used to represent a collection of data members
+together in memory. The elements of a structure may be any type that has
+a size.
+
+Structures in memory are accessed using '``load``' and '``store``' by
+getting a pointer to a field with the '``getelementptr``' instruction.
+Structures in registers are accessed using the '``extractvalue``' and
+'``insertvalue``' instructions.
+
+Structures may optionally be "packed" structures, which indicate that
+the alignment of the struct is one byte, and that there is no padding
+between the elements. In non-packed structs, padding between field types
+is inserted as defined by the DataLayout string in the module, which is
+required to match what the underlying code generator expects.
+
+Structures can either be "literal" or "identified". A literal structure
+is defined inline with other types (e.g. ``{i32, i32}*``) whereas
+identified types are always defined at the top level with a name.
+Literal types are uniqued by their contents and can never be recursive
+or opaque since there is no way to write one. Identified types can be
+recursive, can be opaqued, and are never uniqued.
+
+:Syntax:
+
+::
+
+ %T1 = type { <type list> } ; Identified normal struct type
+ %T2 = type <{ <type list> }> ; Identified packed struct type
+
+:Examples:
+
++------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
+| ``{ i32, i32, i32 }`` | A triple of three ``i32`` values |
++------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
+| ``{ float, i32 (i32) * }`` | A pair, where the first element is a ``float`` and the second element is a :ref:`pointer <t_pointer>` to a :ref:`function <t_function>` that takes an ``i32``, returning an ``i32``. |
++------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
+| ``<{ i8, i32 }>`` | A packed struct known to be 5 bytes in size. |
++------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
+
+.. _t_opaque:
+
+Opaque Structure Types
+""""""""""""""""""""""
+
+:Overview:
+
+Opaque structure types are used to represent named structure types that
+do not have a body specified. This corresponds (for example) to the C
+notion of a forward declared structure.
+
+:Syntax:
+
+::
+
+ %X = type opaque
+ %52 = type opaque
+
+:Examples:
+
++--------------+-------------------+
+| ``opaque`` | An opaque type. |
++--------------+-------------------+
+
+.. _constants:
+
+Constants
+=========
+
+LLVM has several different basic types of constants. This section
+describes them all and their syntax.
+
+Simple Constants
+----------------
+
+**Boolean constants**
+ The two strings '``true``' and '``false``' are both valid constants
+ of the ``i1`` type.
+**Integer constants**
+ Standard integers (such as '4') are constants of the
+ :ref:`integer <t_integer>` type. Negative numbers may be used with
+ integer types.
+**Floating point constants**
+ Floating point constants use standard decimal notation (e.g.
+ 123.421), exponential notation (e.g. 1.23421e+2), or a more precise
+ hexadecimal notation (see below). The assembler requires the exact
+ decimal value of a floating-point constant. For example, the
+ assembler accepts 1.25 but rejects 1.3 because 1.3 is a repeating
+ decimal in binary. Floating point constants must have a :ref:`floating
+ point <t_floating>` type.
+**Null pointer constants**
+ The identifier '``null``' is recognized as a null pointer constant
+ and must be of :ref:`pointer type <t_pointer>`.
+**Token constants**
+ The identifier '``none``' is recognized as an empty token constant
+ and must be of :ref:`token type <t_token>`.
+
+The one non-intuitive notation for constants is the hexadecimal form of
+floating point constants. For example, the form
+'``double 0x432ff973cafa8000``' is equivalent to (but harder to read
+than) '``double 4.5e+15``'. The only time hexadecimal floating point
+constants are required (and the only time that they are generated by the
+disassembler) is when a floating point constant must be emitted but it
+cannot be represented as a decimal floating point number in a reasonable
+number of digits. For example, NaN's, infinities, and other special
+values are represented in their IEEE hexadecimal format so that assembly
+and disassembly do not cause any bits to change in the constants.
+
+When using the hexadecimal form, constants of types half, float, and
+double are represented using the 16-digit form shown above (which
+matches the IEEE754 representation for double); half and float values
+must, however, be exactly representable as IEEE 754 half and single
+precision, respectively. Hexadecimal format is always used for long
+double, and there are three forms of long double. The 80-bit format used
+by x86 is represented as ``0xK`` followed by 20 hexadecimal digits. The
+128-bit format used by PowerPC (two adjacent doubles) is represented by
+``0xM`` followed by 32 hexadecimal digits. The IEEE 128-bit format is
+represented by ``0xL`` followed by 32 hexadecimal digits. Long doubles
+will only work if they match the long double format on your target.
+The IEEE 16-bit format (half precision) is represented by ``0xH``
+followed by 4 hexadecimal digits. All hexadecimal formats are big-endian
+(sign bit at the left).
+
+There are no constants of type x86_mmx.
+
+.. _complexconstants:
+
+Complex Constants
+-----------------
+
+Complex constants are a (potentially recursive) combination of simple
+constants and smaller complex constants.
+
+**Structure constants**
+ Structure constants are represented with notation similar to
+ structure type definitions (a comma separated list of elements,
+ surrounded by braces (``{}``)). For example:
+ "``{ i32 4, float 17.0, i32* @G }``", where "``@G``" is declared as
+ "``@G = external global i32``". Structure constants must have
+ :ref:`structure type <t_struct>`, and the number and types of elements
+ must match those specified by the type.
+**Array constants**
+ Array constants are represented with notation similar to array type
+ definitions (a comma separated list of elements, surrounded by
+ square brackets (``[]``)). For example:
+ "``[ i32 42, i32 11, i32 74 ]``". Array constants must have
+ :ref:`array type <t_array>`, and the number and types of elements must
+ match those specified by the type. As a special case, character array
+ constants may also be represented as a double-quoted string using the ``c``
+ prefix. For example: "``c"Hello World\0A\00"``".
+**Vector constants**
+ Vector constants are represented with notation similar to vector
+ type definitions (a comma separated list of elements, surrounded by
+ less-than/greater-than's (``<>``)). For example:
+ "``< i32 42, i32 11, i32 74, i32 100 >``". Vector constants
+ must have :ref:`vector type <t_vector>`, and the number and types of
+ elements must match those specified by the type.
+**Zero initialization**
+ The string '``zeroinitializer``' can be used to zero initialize a
+ value to zero of *any* type, including scalar and
+ :ref:`aggregate <t_aggregate>` types. This is often used to avoid
+ having to print large zero initializers (e.g. for large arrays) and
+ is always exactly equivalent to using explicit zero initializers.
+**Metadata node**
+ A metadata node is a constant tuple without types. For example:
+ "``!{!0, !{!2, !0}, !"test"}``". Metadata can reference constant values,
+ for example: "``!{!0, i32 0, i8* @global, i64 (i64)* @function, !"str"}``".
+ Unlike other typed constants that are meant to be interpreted as part of
+ the instruction stream, metadata is a place to attach additional
+ information such as debug info.
+
+Global Variable and Function Addresses
+--------------------------------------
+
+The addresses of :ref:`global variables <globalvars>` and
+:ref:`functions <functionstructure>` are always implicitly valid
+(link-time) constants. These constants are explicitly referenced when
+the :ref:`identifier for the global <identifiers>` is used and always have
+:ref:`pointer <t_pointer>` type. For example, the following is a legal LLVM
+file:
+
+.. code-block:: llvm
+
+ @X = global i32 17
+ @Y = global i32 42
+ @Z = global [2 x i32*] [ i32* @X, i32* @Y ]
+
+.. _undefvalues:
+
+Undefined Values
+----------------
+
+The string '``undef``' can be used anywhere a constant is expected, and
+indicates that the user of the value may receive an unspecified
+bit-pattern. Undefined values may be of any type (other than '``label``'
+or '``void``') and be used anywhere a constant is permitted.
+
+Undefined values are useful because they indicate to the compiler that
+the program is well defined no matter what value is used. This gives the
+compiler more freedom to optimize. Here are some examples of
+(potentially surprising) transformations that are valid (in pseudo IR):
+
+.. code-block:: llvm
+
+ %A = add %X, undef
+ %B = sub %X, undef
+ %C = xor %X, undef
+ Safe:
+ %A = undef
+ %B = undef
+ %C = undef
+
+This is safe because all of the output bits are affected by the undef
+bits. Any output bit can have a zero or one depending on the input bits.
+
+.. code-block:: llvm
+
+ %A = or %X, undef
+ %B = and %X, undef
+ Safe:
+ %A = -1
+ %B = 0
+ Safe:
+ %A = %X ;; By choosing undef as 0
+ %B = %X ;; By choosing undef as -1
+ Unsafe:
+ %A = undef
+ %B = undef
+
+These logical operations have bits that are not always affected by the
+input. For example, if ``%X`` has a zero bit, then the output of the
+'``and``' operation will always be a zero for that bit, no matter what
+the corresponding bit from the '``undef``' is. As such, it is unsafe to
+optimize or assume that the result of the '``and``' is '``undef``'.
+However, it is safe to assume that all bits of the '``undef``' could be
+0, and optimize the '``and``' to 0. Likewise, it is safe to assume that
+all the bits of the '``undef``' operand to the '``or``' could be set,
+allowing the '``or``' to be folded to -1.
+
+.. code-block:: llvm
+
+ %A = select undef, %X, %Y
+ %B = select undef, 42, %Y
+ %C = select %X, %Y, undef
+ Safe:
+ %A = %X (or %Y)
+ %B = 42 (or %Y)
+ %C = %Y
+ Unsafe:
+ %A = undef
+ %B = undef
+ %C = undef
+
+This set of examples shows that undefined '``select``' (and conditional
+branch) conditions can go *either way*, but they have to come from one
+of the two operands. In the ``%A`` example, if ``%X`` and ``%Y`` were
+both known to have a clear low bit, then ``%A`` would have to have a
+cleared low bit. However, in the ``%C`` example, the optimizer is
+allowed to assume that the '``undef``' operand could be the same as
+``%Y``, allowing the whole '``select``' to be eliminated.
+
+.. code-block:: text
+
+ %A = xor undef, undef
+
+ %B = undef
+ %C = xor %B, %B
+
+ %D = undef
+ %E = icmp slt %D, 4
+ %F = icmp gte %D, 4
+
+ Safe:
+ %A = undef
+ %B = undef
+ %C = undef
+ %D = undef
+ %E = undef
+ %F = undef
+
+This example points out that two '``undef``' operands are not
+necessarily the same. This can be surprising to people (and also matches
+C semantics) where they assume that "``X^X``" is always zero, even if
+``X`` is undefined. This isn't true for a number of reasons, but the
+short answer is that an '``undef``' "variable" can arbitrarily change
+its value over its "live range". This is true because the variable
+doesn't actually *have a live range*. Instead, the value is logically
+read from arbitrary registers that happen to be around when needed, so
+the value is not necessarily consistent over time. In fact, ``%A`` and
+``%C`` need to have the same semantics or the core LLVM "replace all
+uses with" concept would not hold.
+
+.. code-block:: llvm
+
+ %A = fdiv undef, %X
+ %B = fdiv %X, undef
+ Safe:
+ %A = undef
+ b: unreachable
+
+These examples show the crucial difference between an *undefined value*
+and *undefined behavior*. An undefined value (like '``undef``') is
+allowed to have an arbitrary bit-pattern. This means that the ``%A``
+operation can be constant folded to '``undef``', because the '``undef``'
+could be an SNaN, and ``fdiv`` is not (currently) defined on SNaN's.
+However, in the second example, we can make a more aggressive
+assumption: because the ``undef`` is allowed to be an arbitrary value,
+we are allowed to assume that it could be zero. Since a divide by zero
+has *undefined behavior*, we are allowed to assume that the operation
+does not execute at all. This allows us to delete the divide and all
+code after it. Because the undefined operation "can't happen", the
+optimizer can assume that it occurs in dead code.
+
+.. code-block:: text
+
+ a: store undef -> %X
+ b: store %X -> undef
+ Safe:
+ a: <deleted>
+ b: unreachable
+
+These examples reiterate the ``fdiv`` example: a store *of* an undefined
+value can be assumed to not have any effect; we can assume that the
+value is overwritten with bits that happen to match what was already
+there. However, a store *to* an undefined location could clobber
+arbitrary memory, therefore, it has undefined behavior.
+
+.. _poisonvalues:
+
+Poison Values
+-------------
+
+Poison values are similar to :ref:`undef values <undefvalues>`, however
+they also represent the fact that an instruction or constant expression
+that cannot evoke side effects has nevertheless detected a condition
+that results in undefined behavior.
+
+There is currently no way of representing a poison value in the IR; they
+only exist when produced by operations such as :ref:`add <i_add>` with
+the ``nsw`` flag.
+
+Poison value behavior is defined in terms of value *dependence*:
+
+- Values other than :ref:`phi <i_phi>` nodes depend on their operands.
+- :ref:`Phi <i_phi>` nodes depend on the operand corresponding to
+ their dynamic predecessor basic block.
+- Function arguments depend on the corresponding actual argument values
+ in the dynamic callers of their functions.
+- :ref:`Call <i_call>` instructions depend on the :ref:`ret <i_ret>`
+ instructions that dynamically transfer control back to them.
+- :ref:`Invoke <i_invoke>` instructions depend on the
+ :ref:`ret <i_ret>`, :ref:`resume <i_resume>`, or exception-throwing
+ call instructions that dynamically transfer control back to them.
+- Non-volatile loads and stores depend on the most recent stores to all
+ of the referenced memory addresses, following the order in the IR
+ (including loads and stores implied by intrinsics such as
+ :ref:`@llvm.memcpy <int_memcpy>`.)
+- An instruction with externally visible side effects depends on the
+ most recent preceding instruction with externally visible side
+ effects, following the order in the IR. (This includes :ref:`volatile
+ operations <volatile>`.)
+- An instruction *control-depends* on a :ref:`terminator
+ instruction <terminators>` if the terminator instruction has
+ multiple successors and the instruction is always executed when
+ control transfers to one of the successors, and may not be executed
+ when control is transferred to another.
+- Additionally, an instruction also *control-depends* on a terminator
+ instruction if the set of instructions it otherwise depends on would
+ be different if the terminator had transferred control to a different
+ successor.
+- Dependence is transitive.
+
+Poison values have the same behavior as :ref:`undef values <undefvalues>`,
+with the additional effect that any instruction that has a *dependence*
+on a poison value has undefined behavior.
+
+Here are some examples:
+
+.. code-block:: llvm
+
+ entry:
+ %poison = sub nuw i32 0, 1 ; Results in a poison value.
+ %still_poison = and i32 %poison, 0 ; 0, but also poison.
+ %poison_yet_again = getelementptr i32, i32* @h, i32 %still_poison
+ store i32 0, i32* %poison_yet_again ; memory at @h[0] is poisoned
+
+ store i32 %poison, i32* @g ; Poison value stored to memory.
+ %poison2 = load i32, i32* @g ; Poison value loaded back from memory.
+
+ store volatile i32 %poison, i32* @g ; External observation; undefined behavior.
+
+ %narrowaddr = bitcast i32* @g to i16*
+ %wideaddr = bitcast i32* @g to i64*
+ %poison3 = load i16, i16* %narrowaddr ; Returns a poison value.
+ %poison4 = load i64, i64* %wideaddr ; Returns a poison value.
+
+ %cmp = icmp slt i32 %poison, 0 ; Returns a poison value.
+ br i1 %cmp, label %true, label %end ; Branch to either destination.
+
+ true:
+ store volatile i32 0, i32* @g ; This is control-dependent on %cmp, so
+ ; it has undefined behavior.
+ br label %end
+
+ end:
+ %p = phi i32 [ 0, %entry ], [ 1, %true ]
+ ; Both edges into this PHI are
+ ; control-dependent on %cmp, so this
+ ; always results in a poison value.
+
+ store volatile i32 0, i32* @g ; This would depend on the store in %true
+ ; if %cmp is true, or the store in %entry
+ ; otherwise, so this is undefined behavior.
+
+ br i1 %cmp, label %second_true, label %second_end
+ ; The same branch again, but this time the
+ ; true block doesn't have side effects.
+
+ second_true:
+ ; No side effects!
+ ret void
+
+ second_end:
+ store volatile i32 0, i32* @g ; This time, the instruction always depends
+ ; on the store in %end. Also, it is
+ ; control-equivalent to %end, so this is
+ ; well-defined (ignoring earlier undefined
+ ; behavior in this example).
+
+.. _blockaddress:
+
+Addresses of Basic Blocks
+-------------------------
+
+``blockaddress(@function, %block)``
+
+The '``blockaddress``' constant computes the address of the specified
+basic block in the specified function, and always has an ``i8*`` type.
+Taking the address of the entry block is illegal.
+
+This value only has defined behavior when used as an operand to the
+':ref:`indirectbr <i_indirectbr>`' instruction, or for comparisons
+against null. Pointer equality tests between labels addresses results in
+undefined behavior --- though, again, comparison against null is ok, and
+no label is equal to the null pointer. This may be passed around as an
+opaque pointer sized value as long as the bits are not inspected. This
+allows ``ptrtoint`` and arithmetic to be performed on these values so
+long as the original value is reconstituted before the ``indirectbr``
+instruction.
+
+Finally, some targets may provide defined semantics when using the value
+as the operand to an inline assembly, but that is target specific.
+
+.. _constantexprs:
+
+Constant Expressions
+--------------------
+
+Constant expressions are used to allow expressions involving other
+constants to be used as constants. Constant expressions may be of any
+:ref:`first class <t_firstclass>` type and may involve any LLVM operation
+that does not have side effects (e.g. load and call are not supported).
+The following is the syntax for constant expressions:
+
+``trunc (CST to TYPE)``
+ Truncate a constant to another type. The bit size of CST must be
+ larger than the bit size of TYPE. Both types must be integers.
+``zext (CST to TYPE)``
+ Zero extend a constant to another type. The bit size of CST must be
+ smaller than the bit size of TYPE. Both types must be integers.
+``sext (CST to TYPE)``
+ Sign extend a constant to another type. The bit size of CST must be
+ smaller than the bit size of TYPE. Both types must be integers.
+``fptrunc (CST to TYPE)``
+ Truncate a floating point constant to another floating point type.
+ The size of CST must be larger than the size of TYPE. Both types
+ must be floating point.
+``fpext (CST to TYPE)``
+ Floating point extend a constant to another type. The size of CST
+ must be smaller or equal to the size of TYPE. Both types must be
+ floating point.
+``fptoui (CST to TYPE)``
+ Convert a floating point constant to the corresponding unsigned
+ integer constant. TYPE must be a scalar or vector integer type. CST
+ must be of scalar or vector floating point type. Both CST and TYPE
+ must be scalars, or vectors of the same number of elements. If the
+ value won't fit in the integer type, the results are undefined.
+``fptosi (CST to TYPE)``
+ Convert a floating point constant to the corresponding signed
+ integer constant. TYPE must be a scalar or vector integer type. CST
+ must be of scalar or vector floating point type. Both CST and TYPE
+ must be scalars, or vectors of the same number of elements. If the
+ value won't fit in the integer type, the results are undefined.
+``uitofp (CST to TYPE)``
+ Convert an unsigned integer constant to the corresponding floating
+ point constant. TYPE must be a scalar or vector floating point type.
+ CST must be of scalar or vector integer type. Both CST and TYPE must
+ be scalars, or vectors of the same number of elements. If the value
+ won't fit in the floating point type, the results are undefined.
+``sitofp (CST to TYPE)``
+ Convert a signed integer constant to the corresponding floating
+ point constant. TYPE must be a scalar or vector floating point type.
+ CST must be of scalar or vector integer type. Both CST and TYPE must
+ be scalars, or vectors of the same number of elements. If the value
+ won't fit in the floating point type, the results are undefined.
+``ptrtoint (CST to TYPE)``
+ Convert a pointer typed constant to the corresponding integer
+ constant. ``TYPE`` must be an integer type. ``CST`` must be of
+ pointer type. The ``CST`` value is zero extended, truncated, or
+ unchanged to make it fit in ``TYPE``.
+``inttoptr (CST to TYPE)``
+ Convert an integer constant to a pointer constant. TYPE must be a
+ pointer type. CST must be of integer type. The CST value is zero
+ extended, truncated, or unchanged to make it fit in a pointer size.
+ This one is *really* dangerous!
+``bitcast (CST to TYPE)``
+ Convert a constant, CST, to another TYPE. The constraints of the
+ operands are the same as those for the :ref:`bitcast
+ instruction <i_bitcast>`.
+``addrspacecast (CST to TYPE)``
+ Convert a constant pointer or constant vector of pointer, CST, to another
+ TYPE in a different address space. The constraints of the operands are the
+ same as those for the :ref:`addrspacecast instruction <i_addrspacecast>`.
+``getelementptr (TY, CSTPTR, IDX0, IDX1, ...)``, ``getelementptr inbounds (TY, CSTPTR, IDX0, IDX1, ...)``
+ Perform the :ref:`getelementptr operation <i_getelementptr>` on
+ constants. As with the :ref:`getelementptr <i_getelementptr>`
+ instruction, the index list may have one or more indexes, which are
+ required to make sense for the type of "pointer to TY".
+``select (COND, VAL1, VAL2)``
+ Perform the :ref:`select operation <i_select>` on constants.
+``icmp COND (VAL1, VAL2)``
+ Performs the :ref:`icmp operation <i_icmp>` on constants.
+``fcmp COND (VAL1, VAL2)``
+ Performs the :ref:`fcmp operation <i_fcmp>` on constants.
+``extractelement (VAL, IDX)``
+ Perform the :ref:`extractelement operation <i_extractelement>` on
+ constants.
+``insertelement (VAL, ELT, IDX)``
+ Perform the :ref:`insertelement operation <i_insertelement>` on
+ constants.
+``shufflevector (VEC1, VEC2, IDXMASK)``
+ Perform the :ref:`shufflevector operation <i_shufflevector>` on
+ constants.
+``extractvalue (VAL, IDX0, IDX1, ...)``
+ Perform the :ref:`extractvalue operation <i_extractvalue>` on
+ constants. The index list is interpreted in a similar manner as
+ indices in a ':ref:`getelementptr <i_getelementptr>`' operation. At
+ least one index value must be specified.
+``insertvalue (VAL, ELT, IDX0, IDX1, ...)``
+ Perform the :ref:`insertvalue operation <i_insertvalue>` on constants.
+ The index list is interpreted in a similar manner as indices in a
+ ':ref:`getelementptr <i_getelementptr>`' operation. At least one index
+ value must be specified.
+``OPCODE (LHS, RHS)``
+ Perform the specified operation of the LHS and RHS constants. OPCODE
+ may be any of the :ref:`binary <binaryops>` or :ref:`bitwise
+ binary <bitwiseops>` operations. The constraints on operands are
+ the same as those for the corresponding instruction (e.g. no bitwise
+ operations on floating point values are allowed).
+
+Other Values
+============
+
+.. _inlineasmexprs:
+
+Inline Assembler Expressions
+----------------------------
+
+LLVM supports inline assembler expressions (as opposed to :ref:`Module-Level
+Inline Assembly <moduleasm>`) through the use of a special value. This value
+represents the inline assembler as a template string (containing the
+instructions to emit), a list of operand constraints (stored as a string), a
+flag that indicates whether or not the inline asm expression has side effects,
+and a flag indicating whether the function containing the asm needs to align its
+stack conservatively.
+
+The template string supports argument substitution of the operands using "``$``"
+followed by a number, to indicate substitution of the given register/memory
+location, as specified by the constraint string. "``${NUM:MODIFIER}``" may also
+be used, where ``MODIFIER`` is a target-specific annotation for how to print the
+operand (See :ref:`inline-asm-modifiers`).
+
+A literal "``$``" may be included by using "``$$``" in the template. To include
+other special characters into the output, the usual "``\XX``" escapes may be
+used, just as in other strings. Note that after template substitution, the
+resulting assembly string is parsed by LLVM's integrated assembler unless it is
+disabled -- even when emitting a ``.s`` file -- and thus must contain assembly
+syntax known to LLVM.
+
+LLVM also supports a few more substitions useful for writing inline assembly:
+
+- ``${:uid}``: Expands to a decimal integer unique to this inline assembly blob.
+ This substitution is useful when declaring a local label. Many standard
+ compiler optimizations, such as inlining, may duplicate an inline asm blob.
+ Adding a blob-unique identifier ensures that the two labels will not conflict
+ during assembly. This is used to implement `GCC's %= special format
+ string <https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html>`_.
+- ``${:comment}``: Expands to the comment character of the current target's
+ assembly dialect. This is usually ``#``, but many targets use other strings,
+ such as ``;``, ``//``, or ``!``.
+- ``${:private}``: Expands to the assembler private label prefix. Labels with
+ this prefix will not appear in the symbol table of the assembled object.
+ Typically the prefix is ``L``, but targets may use other strings. ``.L`` is
+ relatively popular.
+
+LLVM's support for inline asm is modeled closely on the requirements of Clang's
+GCC-compatible inline-asm support. Thus, the feature-set and the constraint and
+modifier codes listed here are similar or identical to those in GCC's inline asm
+support. However, to be clear, the syntax of the template and constraint strings
+described here is *not* the same as the syntax accepted by GCC and Clang, and,
+while most constraint letters are passed through as-is by Clang, some get
+translated to other codes when converting from the C source to the LLVM
+assembly.
+
+An example inline assembler expression is:
+
+.. code-block:: llvm
+
+ i32 (i32) asm "bswap $0", "=r,r"
+
+Inline assembler expressions may **only** be used as the callee operand
+of a :ref:`call <i_call>` or an :ref:`invoke <i_invoke>` instruction.
+Thus, typically we have:
+
+.. code-block:: llvm
+
+ %X = call i32 asm "bswap $0", "=r,r"(i32 %Y)
+
+Inline asms with side effects not visible in the constraint list must be
+marked as having side effects. This is done through the use of the
+'``sideeffect``' keyword, like so:
+
+.. code-block:: llvm
+
+ call void asm sideeffect "eieio", ""()
+
+In some cases inline asms will contain code that will not work unless
+the stack is aligned in some way, such as calls or SSE instructions on
+x86, yet will not contain code that does that alignment within the asm.
+The compiler should make conservative assumptions about what the asm
+might contain and should generate its usual stack alignment code in the
+prologue if the '``alignstack``' keyword is present:
+
+.. code-block:: llvm
+
+ call void asm alignstack "eieio", ""()
+
+Inline asms also support using non-standard assembly dialects. The
+assumed dialect is ATT. When the '``inteldialect``' keyword is present,
+the inline asm is using the Intel dialect. Currently, ATT and Intel are
+the only supported dialects. An example is:
+
+.. code-block:: llvm
+
+ call void asm inteldialect "eieio", ""()
+
+If multiple keywords appear the '``sideeffect``' keyword must come
+first, the '``alignstack``' keyword second and the '``inteldialect``'
+keyword last.
+
+Inline Asm Constraint String
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The constraint list is a comma-separated string, each element containing one or
+more constraint codes.
+
+For each element in the constraint list an appropriate register or memory
+operand will be chosen, and it will be made available to assembly template
+string expansion as ``$0`` for the first constraint in the list, ``$1`` for the
+second, etc.
+
+There are three different types of constraints, which are distinguished by a
+prefix symbol in front of the constraint code: Output, Input, and Clobber. The
+constraints must always be given in that order: outputs first, then inputs, then
+clobbers. They cannot be intermingled.
+
+There are also three different categories of constraint codes:
+
+- Register constraint. This is either a register class, or a fixed physical
+ register. This kind of constraint will allocate a register, and if necessary,
+ bitcast the argument or result to the appropriate type.
+- Memory constraint. This kind of constraint is for use with an instruction
+ taking a memory operand. Different constraints allow for different addressing
+ modes used by the target.
+- Immediate value constraint. This kind of constraint is for an integer or other
+ immediate value which can be rendered directly into an instruction. The
+ various target-specific constraints allow the selection of a value in the
+ proper range for the instruction you wish to use it with.
+
+Output constraints
+""""""""""""""""""
+
+Output constraints are specified by an "``=``" prefix (e.g. "``=r``"). This
+indicates that the assembly will write to this operand, and the operand will
+then be made available as a return value of the ``asm`` expression. Output
+constraints do not consume an argument from the call instruction. (Except, see
+below about indirect outputs).
+
+Normally, it is expected that no output locations are written to by the assembly
+expression until *all* of the inputs have been read. As such, LLVM may assign
+the same register to an output and an input. If this is not safe (e.g. if the
+assembly contains two instructions, where the first writes to one output, and
+the second reads an input and writes to a second output), then the "``&``"
+modifier must be used (e.g. "``=&r``") to specify that the output is an
+"early-clobber" output. Marking an output as "early-clobber" ensures that LLVM
+will not use the same register for any inputs (other than an input tied to this
+output).
+
+Input constraints
+"""""""""""""""""
+
+Input constraints do not have a prefix -- just the constraint codes. Each input
+constraint will consume one argument from the call instruction. It is not
+permitted for the asm to write to any input register or memory location (unless
+that input is tied to an output). Note also that multiple inputs may all be
+assigned to the same register, if LLVM can determine that they necessarily all
+contain the same value.
+
+Instead of providing a Constraint Code, input constraints may also "tie"
+themselves to an output constraint, by providing an integer as the constraint
+string. Tied inputs still consume an argument from the call instruction, and
+take up a position in the asm template numbering as is usual -- they will simply
+be constrained to always use the same register as the output they've been tied
+to. For example, a constraint string of "``=r,0``" says to assign a register for
+output, and use that register as an input as well (it being the 0'th
+constraint).
+
+It is permitted to tie an input to an "early-clobber" output. In that case, no
+*other* input may share the same register as the input tied to the early-clobber
+(even when the other input has the same value).
+
+You may only tie an input to an output which has a register constraint, not a
+memory constraint. Only a single input may be tied to an output.
+
+There is also an "interesting" feature which deserves a bit of explanation: if a
+register class constraint allocates a register which is too small for the value
+type operand provided as input, the input value will be split into multiple
+registers, and all of them passed to the inline asm.
+
+However, this feature is often not as useful as you might think.
+
+Firstly, the registers are *not* guaranteed to be consecutive. So, on those
+architectures that have instructions which operate on multiple consecutive
+instructions, this is not an appropriate way to support them. (e.g. the 32-bit
+SparcV8 has a 64-bit load, which instruction takes a single 32-bit register. The
+hardware then loads into both the named register, and the next register. This
+feature of inline asm would not be useful to support that.)
+
+A few of the targets provide a template string modifier allowing explicit access
+to the second register of a two-register operand (e.g. MIPS ``L``, ``M``, and
+``D``). On such an architecture, you can actually access the second allocated
+register (yet, still, not any subsequent ones). But, in that case, you're still
+probably better off simply splitting the value into two separate operands, for
+clarity. (e.g. see the description of the ``A`` constraint on X86, which,
+despite existing only for use with this feature, is not really a good idea to
+use)
+
+Indirect inputs and outputs
+"""""""""""""""""""""""""""
+
+Indirect output or input constraints can be specified by the "``*``" modifier
+(which goes after the "``=``" in case of an output). This indicates that the asm
+will write to or read from the contents of an *address* provided as an input
+argument. (Note that in this way, indirect outputs act more like an *input* than
+an output: just like an input, they consume an argument of the call expression,
+rather than producing a return value. An indirect output constraint is an
+"output" only in that the asm is expected to write to the contents of the input
+memory location, instead of just read from it).
+
+This is most typically used for memory constraint, e.g. "``=*m``", to pass the
+address of a variable as a value.
+
+It is also possible to use an indirect *register* constraint, but only on output
+(e.g. "``=*r``"). This will cause LLVM to allocate a register for an output
+value normally, and then, separately emit a store to the address provided as
+input, after the provided inline asm. (It's not clear what value this
+functionality provides, compared to writing the store explicitly after the asm
+statement, and it can only produce worse code, since it bypasses many
+optimization passes. I would recommend not using it.)
+
+
+Clobber constraints
+"""""""""""""""""""
+
+A clobber constraint is indicated by a "``~``" prefix. A clobber does not
+consume an input operand, nor generate an output. Clobbers cannot use any of the
+general constraint code letters -- they may use only explicit register
+constraints, e.g. "``~{eax}``". The one exception is that a clobber string of
+"``~{memory}``" indicates that the assembly writes to arbitrary undeclared
+memory locations -- not only the memory pointed to by a declared indirect
+output.
+
+Note that clobbering named registers that are also present in output
+constraints is not legal.
+
+
+Constraint Codes
+""""""""""""""""
+After a potential prefix comes constraint code, or codes.
+
+A Constraint Code is either a single letter (e.g. "``r``"), a "``^``" character
+followed by two letters (e.g. "``^wc``"), or "``{``" register-name "``}``"
+(e.g. "``{eax}``").
+
+The one and two letter constraint codes are typically chosen to be the same as
+GCC's constraint codes.
+
+A single constraint may include one or more than constraint code in it, leaving
+it up to LLVM to choose which one to use. This is included mainly for
+compatibility with the translation of GCC inline asm coming from clang.
+
+There are two ways to specify alternatives, and either or both may be used in an
+inline asm constraint list:
+
+1) Append the codes to each other, making a constraint code set. E.g. "``im``"
+ or "``{eax}m``". This means "choose any of the options in the set". The
+ choice of constraint is made independently for each constraint in the
+ constraint list.
+
+2) Use "``|``" between constraint code sets, creating alternatives. Every
+ constraint in the constraint list must have the same number of alternative
+ sets. With this syntax, the same alternative in *all* of the items in the
+ constraint list will be chosen together.
+
+Putting those together, you might have a two operand constraint string like
+``"rm|r,ri|rm"``. This indicates that if operand 0 is ``r`` or ``m``, then
+operand 1 may be one of ``r`` or ``i``. If operand 0 is ``r``, then operand 1
+may be one of ``r`` or ``m``. But, operand 0 and 1 cannot both be of type m.
+
+However, the use of either of the alternatives features is *NOT* recommended, as
+LLVM is not able to make an intelligent choice about which one to use. (At the
+point it currently needs to choose, not enough information is available to do so
+in a smart way.) Thus, it simply tries to make a choice that's most likely to
+compile, not one that will be optimal performance. (e.g., given "``rm``", it'll
+always choose to use memory, not registers). And, if given multiple registers,
+or multiple register classes, it will simply choose the first one. (In fact, it
+doesn't currently even ensure explicitly specified physical registers are
+unique, so specifying multiple physical registers as alternatives, like
+``{r11}{r12},{r11}{r12}``, will assign r11 to both operands, not at all what was
+intended.)
+
+Supported Constraint Code List
+""""""""""""""""""""""""""""""
+
+The constraint codes are, in general, expected to behave the same way they do in
+GCC. LLVM's support is often implemented on an 'as-needed' basis, to support C
+inline asm code which was supported by GCC. A mismatch in behavior between LLVM
+and GCC likely indicates a bug in LLVM.
+
+Some constraint codes are typically supported by all targets:
+
+- ``r``: A register in the target's general purpose register class.
+- ``m``: A memory address operand. It is target-specific what addressing modes
+ are supported, typical examples are register, or register + register offset,
+ or register + immediate offset (of some target-specific size).
+- ``i``: An integer constant (of target-specific width). Allows either a simple
+ immediate, or a relocatable value.
+- ``n``: An integer constant -- *not* including relocatable values.
+- ``s``: An integer constant, but allowing *only* relocatable values.
+- ``X``: Allows an operand of any kind, no constraint whatsoever. Typically
+ useful to pass a label for an asm branch or call.
+
+ .. FIXME: but that surely isn't actually okay to jump out of an asm
+ block without telling llvm about the control transfer???)
+
+- ``{register-name}``: Requires exactly the named physical register.
+
+Other constraints are target-specific:
+
+AArch64:
+
+- ``z``: An immediate integer 0. Outputs ``WZR`` or ``XZR``, as appropriate.
+- ``I``: An immediate integer valid for an ``ADD`` or ``SUB`` instruction,
+ i.e. 0 to 4095 with optional shift by 12.
+- ``J``: An immediate integer that, when negated, is valid for an ``ADD`` or
+ ``SUB`` instruction, i.e. -1 to -4095 with optional left shift by 12.
+- ``K``: An immediate integer that is valid for the 'bitmask immediate 32' of a
+ logical instruction like ``AND``, ``EOR``, or ``ORR`` with a 32-bit register.
+- ``L``: An immediate integer that is valid for the 'bitmask immediate 64' of a
+ logical instruction like ``AND``, ``EOR``, or ``ORR`` with a 64-bit register.
+- ``M``: An immediate integer for use with the ``MOV`` assembly alias on a
+ 32-bit register. This is a superset of ``K``: in addition to the bitmask
+ immediate, also allows immediate integers which can be loaded with a single
+ ``MOVZ`` or ``MOVL`` instruction.
+- ``N``: An immediate integer for use with the ``MOV`` assembly alias on a
+ 64-bit register. This is a superset of ``L``.
+- ``Q``: Memory address operand must be in a single register (no
+ offsets). (However, LLVM currently does this for the ``m`` constraint as
+ well.)
+- ``r``: A 32 or 64-bit integer register (W* or X*).
+- ``w``: A 32, 64, or 128-bit floating-point/SIMD register.
+- ``x``: A lower 128-bit floating-point/SIMD register (``V0`` to ``V15``).
+
+AMDGPU:
+
+- ``r``: A 32 or 64-bit integer register.
+- ``[0-9]v``: The 32-bit VGPR register, number 0-9.
+- ``[0-9]s``: The 32-bit SGPR register, number 0-9.
+
+
+All ARM modes:
+
+- ``Q``, ``Um``, ``Un``, ``Uq``, ``Us``, ``Ut``, ``Uv``, ``Uy``: Memory address
+ operand. Treated the same as operand ``m``, at the moment.
+
+ARM and ARM's Thumb2 mode:
+
+- ``j``: An immediate integer between 0 and 65535 (valid for ``MOVW``)
+- ``I``: An immediate integer valid for a data-processing instruction.
+- ``J``: An immediate integer between -4095 and 4095.
+- ``K``: An immediate integer whose bitwise inverse is valid for a
+ data-processing instruction. (Can be used with template modifier "``B``" to
+ print the inverted value).
+- ``L``: An immediate integer whose negation is valid for a data-processing
+ instruction. (Can be used with template modifier "``n``" to print the negated
+ value).
+- ``M``: A power of two or a integer between 0 and 32.
+- ``N``: Invalid immediate constraint.
+- ``O``: Invalid immediate constraint.
+- ``r``: A general-purpose 32-bit integer register (``r0-r15``).
+- ``l``: In Thumb2 mode, low 32-bit GPR registers (``r0-r7``). In ARM mode, same
+ as ``r``.
+- ``h``: In Thumb2 mode, a high 32-bit GPR register (``r8-r15``). In ARM mode,
+ invalid.
+- ``w``: A 32, 64, or 128-bit floating-point/SIMD register: ``s0-s31``,
+ ``d0-d31``, or ``q0-q15``.
+- ``x``: A 32, 64, or 128-bit floating-point/SIMD register: ``s0-s15``,
+ ``d0-d7``, or ``q0-q3``.
+- ``t``: A floating-point/SIMD register, only supports 32-bit values:
+ ``s0-s31``.
+
+ARM's Thumb1 mode:
+
+- ``I``: An immediate integer between 0 and 255.
+- ``J``: An immediate integer between -255 and -1.
+- ``K``: An immediate integer between 0 and 255, with optional left-shift by
+ some amount.
+- ``L``: An immediate integer between -7 and 7.
+- ``M``: An immediate integer which is a multiple of 4 between 0 and 1020.
+- ``N``: An immediate integer between 0 and 31.
+- ``O``: An immediate integer which is a multiple of 4 between -508 and 508.
+- ``r``: A low 32-bit GPR register (``r0-r7``).
+- ``l``: A low 32-bit GPR register (``r0-r7``).
+- ``h``: A high GPR register (``r0-r7``).
+- ``w``: A 32, 64, or 128-bit floating-point/SIMD register: ``s0-s31``,
+ ``d0-d31``, or ``q0-q15``.
+- ``x``: A 32, 64, or 128-bit floating-point/SIMD register: ``s0-s15``,
+ ``d0-d7``, or ``q0-q3``.
+- ``t``: A floating-point/SIMD register, only supports 32-bit values:
+ ``s0-s31``.
+
+
+Hexagon:
+
+- ``o``, ``v``: A memory address operand, treated the same as constraint ``m``,
+ at the moment.
+- ``r``: A 32 or 64-bit register.
+
+MSP430:
+
+- ``r``: An 8 or 16-bit register.
+
+MIPS:
+
+- ``I``: An immediate signed 16-bit integer.
+- ``J``: An immediate integer zero.
+- ``K``: An immediate unsigned 16-bit integer.
+- ``L``: An immediate 32-bit integer, where the lower 16 bits are 0.
+- ``N``: An immediate integer between -65535 and -1.
+- ``O``: An immediate signed 15-bit integer.
+- ``P``: An immediate integer between 1 and 65535.
+- ``m``: A memory address operand. In MIPS-SE mode, allows a base address
+ register plus 16-bit immediate offset. In MIPS mode, just a base register.
+- ``R``: A memory address operand. In MIPS-SE mode, allows a base address
+ register plus a 9-bit signed offset. In MIPS mode, the same as constraint
+ ``m``.
+- ``ZC``: A memory address operand, suitable for use in a ``pref``, ``ll``, or
+ ``sc`` instruction on the given subtarget (details vary).
+- ``r``, ``d``, ``y``: A 32 or 64-bit GPR register.
+- ``f``: A 32 or 64-bit FPU register (``F0-F31``), or a 128-bit MSA register
+ (``W0-W31``). In the case of MSA registers, it is recommended to use the ``w``
+ argument modifier for compatibility with GCC.
+- ``c``: A 32-bit or 64-bit GPR register suitable for indirect jump (always
+ ``25``).
+- ``l``: The ``lo`` register, 32 or 64-bit.
+- ``x``: Invalid.
+
+NVPTX:
+
+- ``b``: A 1-bit integer register.
+- ``c`` or ``h``: A 16-bit integer register.
+- ``r``: A 32-bit integer register.
+- ``l`` or ``N``: A 64-bit integer register.
+- ``f``: A 32-bit float register.
+- ``d``: A 64-bit float register.
+
+
+PowerPC:
+
+- ``I``: An immediate signed 16-bit integer.
+- ``J``: An immediate unsigned 16-bit integer, shifted left 16 bits.
+- ``K``: An immediate unsigned 16-bit integer.
+- ``L``: An immediate signed 16-bit integer, shifted left 16 bits.
+- ``M``: An immediate integer greater than 31.
+- ``N``: An immediate integer that is an exact power of 2.
+- ``O``: The immediate integer constant 0.
+- ``P``: An immediate integer constant whose negation is a signed 16-bit
+ constant.
+- ``es``, ``o``, ``Q``, ``Z``, ``Zy``: A memory address operand, currently
+ treated the same as ``m``.
+- ``r``: A 32 or 64-bit integer register.
+- ``b``: A 32 or 64-bit integer register, excluding ``R0`` (that is:
+ ``R1-R31``).
+- ``f``: A 32 or 64-bit float register (``F0-F31``), or when QPX is enabled, a
+ 128 or 256-bit QPX register (``Q0-Q31``; aliases the ``F`` registers).
+- ``v``: For ``4 x f32`` or ``4 x f64`` types, when QPX is enabled, a
+ 128 or 256-bit QPX register (``Q0-Q31``), otherwise a 128-bit
+ altivec vector register (``V0-V31``).
+
+ .. FIXME: is this a bug that v accepts QPX registers? I think this
+ is supposed to only use the altivec vector registers?
+
+- ``y``: Condition register (``CR0-CR7``).
+- ``wc``: An individual CR bit in a CR register.
+- ``wa``, ``wd``, ``wf``: Any 128-bit VSX vector register, from the full VSX
+ register set (overlapping both the floating-point and vector register files).
+- ``ws``: A 32 or 64-bit floating point register, from the full VSX register
+ set.
+
+Sparc:
+
+- ``I``: An immediate 13-bit signed integer.
+- ``r``: A 32-bit integer register.
+- ``f``: Any floating-point register on SparcV8, or a floating point
+ register in the "low" half of the registers on SparcV9.
+- ``e``: Any floating point register. (Same as ``f`` on SparcV8.)
+
+SystemZ:
+
+- ``I``: An immediate unsigned 8-bit integer.
+- ``J``: An immediate unsigned 12-bit integer.
+- ``K``: An immediate signed 16-bit integer.
+- ``L``: An immediate signed 20-bit integer.
+- ``M``: An immediate integer 0x7fffffff.
+- ``Q``: A memory address operand with a base address and a 12-bit immediate
+ unsigned displacement.
+- ``R``: A memory address operand with a base address, a 12-bit immediate
+ unsigned displacement, and an index register.
+- ``S``: A memory address operand with a base address and a 20-bit immediate
+ signed displacement.
+- ``T``: A memory address operand with a base address, a 20-bit immediate
+ signed displacement, and an index register.
+- ``r`` or ``d``: A 32, 64, or 128-bit integer register.
+- ``a``: A 32, 64, or 128-bit integer address register (excludes R0, which in an
+ address context evaluates as zero).
+- ``h``: A 32-bit value in the high part of a 64bit data register
+ (LLVM-specific)
+- ``f``: A 32, 64, or 128-bit floating point register.
+
+X86:
+
+- ``I``: An immediate integer between 0 and 31.
+- ``J``: An immediate integer between 0 and 64.
+- ``K``: An immediate signed 8-bit integer.
+- ``L``: An immediate integer, 0xff or 0xffff or (in 64-bit mode only)
+ 0xffffffff.
+- ``M``: An immediate integer between 0 and 3.
+- ``N``: An immediate unsigned 8-bit integer.
+- ``O``: An immediate integer between 0 and 127.
+- ``e``: An immediate 32-bit signed integer.
+- ``Z``: An immediate 32-bit unsigned integer.
+- ``o``, ``v``: Treated the same as ``m``, at the moment.
+- ``q``: An 8, 16, 32, or 64-bit register which can be accessed as an 8-bit
+ ``l`` integer register. On X86-32, this is the ``a``, ``b``, ``c``, and ``d``
+ registers, and on X86-64, it is all of the integer registers.
+- ``Q``: An 8, 16, 32, or 64-bit register which can be accessed as an 8-bit
+ ``h`` integer register. This is the ``a``, ``b``, ``c``, and ``d`` registers.
+- ``r`` or ``l``: An 8, 16, 32, or 64-bit integer register.
+- ``R``: An 8, 16, 32, or 64-bit "legacy" integer register -- one which has
+ existed since i386, and can be accessed without the REX prefix.
+- ``f``: A 32, 64, or 80-bit '387 FPU stack pseudo-register.
+- ``y``: A 64-bit MMX register, if MMX is enabled.
+- ``x``: If SSE is enabled: a 32 or 64-bit scalar operand, or 128-bit vector
+ operand in a SSE register. If AVX is also enabled, can also be a 256-bit
+ vector operand in an AVX register. If AVX-512 is also enabled, can also be a
+ 512-bit vector operand in an AVX512 register, Otherwise, an error.
+- ``Y``: The same as ``x``, if *SSE2* is enabled, otherwise an error.
+- ``A``: Special case: allocates EAX first, then EDX, for a single operand (in
+ 32-bit mode, a 64-bit integer operand will get split into two registers). It
+ is not recommended to use this constraint, as in 64-bit mode, the 64-bit
+ operand will get allocated only to RAX -- if two 32-bit operands are needed,
+ you're better off splitting it yourself, before passing it to the asm
+ statement.
+
+XCore:
+
+- ``r``: A 32-bit integer register.
+
+
+.. _inline-asm-modifiers:
+
+Asm template argument modifiers
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+In the asm template string, modifiers can be used on the operand reference, like
+"``${0:n}``".
+
+The modifiers are, in general, expected to behave the same way they do in
+GCC. LLVM's support is often implemented on an 'as-needed' basis, to support C
+inline asm code which was supported by GCC. A mismatch in behavior between LLVM
+and GCC likely indicates a bug in LLVM.
+
+Target-independent:
+
+- ``c``: Print an immediate integer constant unadorned, without
+ the target-specific immediate punctuation (e.g. no ``$`` prefix).
+- ``n``: Negate and print immediate integer constant unadorned, without the
+ target-specific immediate punctuation (e.g. no ``$`` prefix).
+- ``l``: Print as an unadorned label, without the target-specific label
+ punctuation (e.g. no ``$`` prefix).
+
+AArch64:
+
+- ``w``: Print a GPR register with a ``w*`` name instead of ``x*`` name. E.g.,
+ instead of ``x30``, print ``w30``.
+- ``x``: Print a GPR register with a ``x*`` name. (this is the default, anyhow).
+- ``b``, ``h``, ``s``, ``d``, ``q``: Print a floating-point/SIMD register with a
+ ``b*``, ``h*``, ``s*``, ``d*``, or ``q*`` name, rather than the default of
+ ``v*``.
+
+AMDGPU:
+
+- ``r``: No effect.
+
+ARM:
+
+- ``a``: Print an operand as an address (with ``[`` and ``]`` surrounding a
+ register).
+- ``P``: No effect.
+- ``q``: No effect.
+- ``y``: Print a VFP single-precision register as an indexed double (e.g. print
+ as ``d4[1]`` instead of ``s9``)
+- ``B``: Bitwise invert and print an immediate integer constant without ``#``
+ prefix.
+- ``L``: Print the low 16-bits of an immediate integer constant.
+- ``M``: Print as a register set suitable for ldm/stm. Also prints *all*
+ register operands subsequent to the specified one (!), so use carefully.
+- ``Q``: Print the low-order register of a register-pair, or the low-order
+ register of a two-register operand.
+- ``R``: Print the high-order register of a register-pair, or the high-order
+ register of a two-register operand.
+- ``H``: Print the second register of a register-pair. (On a big-endian system,
+ ``H`` is equivalent to ``Q``, and on little-endian system, ``H`` is equivalent
+ to ``R``.)
+
+ .. FIXME: H doesn't currently support printing the second register
+ of a two-register operand.
+
+- ``e``: Print the low doubleword register of a NEON quad register.
+- ``f``: Print the high doubleword register of a NEON quad register.
+- ``m``: Print the base register of a memory operand without the ``[`` and ``]``
+ adornment.
+
+Hexagon:
+
+- ``L``: Print the second register of a two-register operand. Requires that it
+ has been allocated consecutively to the first.
+
+ .. FIXME: why is it restricted to consecutive ones? And there's
+ nothing that ensures that happens, is there?
+
+- ``I``: Print the letter 'i' if the operand is an integer constant, otherwise
+ nothing. Used to print 'addi' vs 'add' instructions.
+
+MSP430:
+
+No additional modifiers.
+
+MIPS:
+
+- ``X``: Print an immediate integer as hexadecimal
+- ``x``: Print the low 16 bits of an immediate integer as hexadecimal.
+- ``d``: Print an immediate integer as decimal.
+- ``m``: Subtract one and print an immediate integer as decimal.
+- ``z``: Print $0 if an immediate zero, otherwise print normally.
+- ``L``: Print the low-order register of a two-register operand, or prints the
+ address of the low-order word of a double-word memory operand.
+
+ .. FIXME: L seems to be missing memory operand support.
+
+- ``M``: Print the high-order register of a two-register operand, or prints the
+ address of the high-order word of a double-word memory operand.
+
+ .. FIXME: M seems to be missing memory operand support.
+
+- ``D``: Print the second register of a two-register operand, or prints the
+ second word of a double-word memory operand. (On a big-endian system, ``D`` is
+ equivalent to ``L``, and on little-endian system, ``D`` is equivalent to
+ ``M``.)
+- ``w``: No effect. Provided for compatibility with GCC which requires this
+ modifier in order to print MSA registers (``W0-W31``) with the ``f``
+ constraint.
+
+NVPTX:
+
+- ``r``: No effect.
+
+PowerPC:
+
+- ``L``: Print the second register of a two-register operand. Requires that it
+ has been allocated consecutively to the first.
+
+ .. FIXME: why is it restricted to consecutive ones? And there's
+ nothing that ensures that happens, is there?
+
+- ``I``: Print the letter 'i' if the operand is an integer constant, otherwise
+ nothing. Used to print 'addi' vs 'add' instructions.
+- ``y``: For a memory operand, prints formatter for a two-register X-form
+ instruction. (Currently always prints ``r0,OPERAND``).
+- ``U``: Prints 'u' if the memory operand is an update form, and nothing
+ otherwise. (NOTE: LLVM does not support update form, so this will currently
+ always print nothing)
+- ``X``: Prints 'x' if the memory operand is an indexed form. (NOTE: LLVM does
+ not support indexed form, so this will currently always print nothing)
+
+Sparc:
+
+- ``r``: No effect.
+
+SystemZ:
+
+SystemZ implements only ``n``, and does *not* support any of the other
+target-independent modifiers.
+
+X86:
+
+- ``c``: Print an unadorned integer or symbol name. (The latter is
+ target-specific behavior for this typically target-independent modifier).
+- ``A``: Print a register name with a '``*``' before it.
+- ``b``: Print an 8-bit register name (e.g. ``al``); do nothing on a memory
+ operand.
+- ``h``: Print the upper 8-bit register name (e.g. ``ah``); do nothing on a
+ memory operand.
+- ``w``: Print the 16-bit register name (e.g. ``ax``); do nothing on a memory
+ operand.
+- ``k``: Print the 32-bit register name (e.g. ``eax``); do nothing on a memory
+ operand.
+- ``q``: Print the 64-bit register name (e.g. ``rax``), if 64-bit registers are
+ available, otherwise the 32-bit register name; do nothing on a memory operand.
+- ``n``: Negate and print an unadorned integer, or, for operands other than an
+ immediate integer (e.g. a relocatable symbol expression), print a '-' before
+ the operand. (The behavior for relocatable symbol expressions is a
+ target-specific behavior for this typically target-independent modifier)
+- ``H``: Print a memory reference with additional offset +8.
+- ``P``: Print a memory reference or operand for use as the argument of a call
+ instruction. (E.g. omit ``(rip)``, even though it's PC-relative.)
+
+XCore:
+
+No additional modifiers.
+
+
+Inline Asm Metadata
+^^^^^^^^^^^^^^^^^^^
+
+The call instructions that wrap inline asm nodes may have a
+"``!srcloc``" MDNode attached to it that contains a list of constant
+integers. If present, the code generator will use the integer as the
+location cookie value when report errors through the ``LLVMContext``
+error reporting mechanisms. This allows a front-end to correlate backend
+errors that occur with inline asm back to the source code that produced
+it. For example:
+
+.. code-block:: llvm
+
+ call void asm sideeffect "something bad", ""(), !srcloc !42
+ ...
+ !42 = !{ i32 1234567 }
+
+It is up to the front-end to make sense of the magic numbers it places
+in the IR. If the MDNode contains multiple constants, the code generator
+will use the one that corresponds to the line of the asm that the error
+occurs on.
+
+.. _metadata:
+
+Metadata
+========
+
+LLVM IR allows metadata to be attached to instructions in the program
+that can convey extra information about the code to the optimizers and
+code generator. One example application of metadata is source-level
+debug information. There are two metadata primitives: strings and nodes.
+
+Metadata does not have a type, and is not a value. If referenced from a
+``call`` instruction, it uses the ``metadata`` type.
+
+All metadata are identified in syntax by a exclamation point ('``!``').
+
+.. _metadata-string:
+
+Metadata Nodes and Metadata Strings
+-----------------------------------
+
+A metadata string is a string surrounded by double quotes. It can
+contain any character by escaping non-printable characters with
+"``\xx``" where "``xx``" is the two digit hex code. For example:
+"``!"test\00"``".
+
+Metadata nodes are represented with notation similar to structure
+constants (a comma separated list of elements, surrounded by braces and
+preceded by an exclamation point). Metadata nodes can have any values as
+their operand. For example:
+
+.. code-block:: llvm
+
+ !{ !"test\00", i32 10}
+
+Metadata nodes that aren't uniqued use the ``distinct`` keyword. For example:
+
+.. code-block:: text
+
+ !0 = distinct !{!"test\00", i32 10}
+
+``distinct`` nodes are useful when nodes shouldn't be merged based on their
+content. They can also occur when transformations cause uniquing collisions
+when metadata operands change.
+
+A :ref:`named metadata <namedmetadatastructure>` is a collection of
+metadata nodes, which can be looked up in the module symbol table. For
+example:
+
+.. code-block:: llvm
+
+ !foo = !{!4, !3}
+
+Metadata can be used as function arguments. Here ``llvm.dbg.value``
+function is using two metadata arguments:
+
+.. code-block:: llvm
+
+ call void @llvm.dbg.value(metadata !24, i64 0, metadata !25)
+
+Metadata can be attached to an instruction. Here metadata ``!21`` is attached
+to the ``add`` instruction using the ``!dbg`` identifier:
+
+.. code-block:: llvm
+
+ %indvar.next = add i64 %indvar, 1, !dbg !21
+
+Metadata can also be attached to a function or a global variable. Here metadata
+``!22`` is attached to the ``f1`` and ``f2 functions, and the globals ``g1``
+and ``g2`` using the ``!dbg`` identifier:
+
+.. code-block:: llvm
+
+ declare !dbg !22 void @f1()
+ define void @f2() !dbg !22 {
+ ret void
+ }
+
+ @g1 = global i32 0, !dbg !22
+ @g2 = external global i32, !dbg !22
+
+A transformation is required to drop any metadata attachment that it does not
+know or know it can't preserve. Currently there is an exception for metadata
+attachment to globals for ``!type`` and ``!absolute_symbol`` which can't be
+unconditionally dropped unless the global is itself deleted.
+
+Metadata attached to a module using named metadata may not be dropped, with
+the exception of debug metadata (named metadata with the name ``!llvm.dbg.*``).
+
+More information about specific metadata nodes recognized by the
+optimizers and code generator is found below.
+
+.. _specialized-metadata:
+
+Specialized Metadata Nodes
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Specialized metadata nodes are custom data structures in metadata (as opposed
+to generic tuples). Their fields are labelled, and can be specified in any
+order.
+
+These aren't inherently debug info centric, but currently all the specialized
+metadata nodes are related to debug info.
+
+.. _DICompileUnit:
+
+DICompileUnit
+"""""""""""""
+
+``DICompileUnit`` nodes represent a compile unit. The ``enums:``,
+``retainedTypes:``, ``globals:``, ``imports:`` and ``macros:`` fields are tuples
+containing the debug info to be emitted along with the compile unit, regardless
+of code optimizations (some nodes are only emitted if there are references to
+them from instructions). The ``debugInfoForProfiling:`` field is a boolean
+indicating whether or not line-table discriminators are updated to provide
+more-accurate debug info for profiling results.
+
+.. code-block:: text
+
+ !0 = !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang",
+ isOptimized: true, flags: "-O2", runtimeVersion: 2,
+ splitDebugFilename: "abc.debug", emissionKind: FullDebug,
+ enums: !2, retainedTypes: !3, globals: !4, imports: !5,
+ macros: !6, dwoId: 0x0abcd)
+
+Compile unit descriptors provide the root scope for objects declared in a
+specific compilation unit. File descriptors are defined using this scope. These
+descriptors are collected by a named metadata node ``!llvm.dbg.cu``. They keep
+track of global variables, type information, and imported entities (declarations
+and namespaces).
+
+.. _DIFile:
+
+DIFile
+""""""
+
+``DIFile`` nodes represent files. The ``filename:`` can include slashes.
+
+.. code-block:: none
+
+ !0 = !DIFile(filename: "path/to/file", directory: "/path/to/dir",
+ checksumkind: CSK_MD5,
+ checksum: "000102030405060708090a0b0c0d0e0f")
+
+Files are sometimes used in ``scope:`` fields, and are the only valid target
+for ``file:`` fields.
+Valid values for ``checksumkind:`` field are: {CSK_None, CSK_MD5, CSK_SHA1}
+
+.. _DIBasicType:
+
+DIBasicType
+"""""""""""
+
+``DIBasicType`` nodes represent primitive types, such as ``int``, ``bool`` and
+``float``. ``tag:`` defaults to ``DW_TAG_base_type``.
+
+.. code-block:: text
+
+ !0 = !DIBasicType(name: "unsigned char", size: 8, align: 8,
+ encoding: DW_ATE_unsigned_char)
+ !1 = !DIBasicType(tag: DW_TAG_unspecified_type, name: "decltype(nullptr)")
+
+The ``encoding:`` describes the details of the type. Usually it's one of the
+following:
+
+.. code-block:: text
+
+ DW_ATE_address = 1
+ DW_ATE_boolean = 2
+ DW_ATE_float = 4
+ DW_ATE_signed = 5
+ DW_ATE_signed_char = 6
+ DW_ATE_unsigned = 7
+ DW_ATE_unsigned_char = 8
+
+.. _DISubroutineType:
+
+DISubroutineType
+""""""""""""""""
+
+``DISubroutineType`` nodes represent subroutine types. Their ``types:`` field
+refers to a tuple; the first operand is the return type, while the rest are the
+types of the formal arguments in order. If the first operand is ``null``, that
+represents a function with no return value (such as ``void foo() {}`` in C++).
+
+.. code-block:: text
+
+ !0 = !BasicType(name: "int", size: 32, align: 32, DW_ATE_signed)
+ !1 = !BasicType(name: "char", size: 8, align: 8, DW_ATE_signed_char)
+ !2 = !DISubroutineType(types: !{null, !0, !1}) ; void (int, char)
+
+.. _DIDerivedType:
+
+DIDerivedType
+"""""""""""""
+
+``DIDerivedType`` nodes represent types derived from other types, such as
+qualified types.
+
+.. code-block:: text
+
+ !0 = !DIBasicType(name: "unsigned char", size: 8, align: 8,
+ encoding: DW_ATE_unsigned_char)
+ !1 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !0, size: 32,
+ align: 32)
+
+The following ``tag:`` values are valid:
+
+.. code-block:: text
+
+ DW_TAG_member = 13
+ DW_TAG_pointer_type = 15
+ DW_TAG_reference_type = 16
+ DW_TAG_typedef = 22
+ DW_TAG_inheritance = 28
+ DW_TAG_ptr_to_member_type = 31
+ DW_TAG_const_type = 38
+ DW_TAG_friend = 42
+ DW_TAG_volatile_type = 53
+ DW_TAG_restrict_type = 55
+ DW_TAG_atomic_type = 71
+
+.. _DIDerivedTypeMember:
+
+``DW_TAG_member`` is used to define a member of a :ref:`composite type
+<DICompositeType>`. The type of the member is the ``baseType:``. The
+``offset:`` is the member's bit offset. If the composite type has an ODR
+``identifier:`` and does not set ``flags: DIFwdDecl``, then the member is
+uniqued based only on its ``name:`` and ``scope:``.
+
+``DW_TAG_inheritance`` and ``DW_TAG_friend`` are used in the ``elements:``
+field of :ref:`composite types <DICompositeType>` to describe parents and
+friends.
+
+``DW_TAG_typedef`` is used to provide a name for the ``baseType:``.
+
+``DW_TAG_pointer_type``, ``DW_TAG_reference_type``, ``DW_TAG_const_type``,
+``DW_TAG_volatile_type``, ``DW_TAG_restrict_type`` and ``DW_TAG_atomic_type``
+are used to qualify the ``baseType:``.
+
+Note that the ``void *`` type is expressed as a type derived from NULL.
+
+.. _DICompositeType:
+
+DICompositeType
+"""""""""""""""
+
+``DICompositeType`` nodes represent types composed of other types, like
+structures and unions. ``elements:`` points to a tuple of the composed types.
+
+If the source language supports ODR, the ``identifier:`` field gives the unique
+identifier used for type merging between modules. When specified,
+:ref:`subprogram declarations <DISubprogramDeclaration>` and :ref:`member
+derived types <DIDerivedTypeMember>` that reference the ODR-type in their
+``scope:`` change uniquing rules.
+
+For a given ``identifier:``, there should only be a single composite type that
+does not have ``flags: DIFlagFwdDecl`` set. LLVM tools that link modules
+together will unique such definitions at parse time via the ``identifier:``
+field, even if the nodes are ``distinct``.
+
+.. code-block:: text
+
+ !0 = !DIEnumerator(name: "SixKind", value: 7)
+ !1 = !DIEnumerator(name: "SevenKind", value: 7)
+ !2 = !DIEnumerator(name: "NegEightKind", value: -8)
+ !3 = !DICompositeType(tag: DW_TAG_enumeration_type, name: "Enum", file: !12,
+ line: 2, size: 32, align: 32, identifier: "_M4Enum",
+ elements: !{!0, !1, !2})
+
+The following ``tag:`` values are valid:
+
+.. code-block:: text
+
+ DW_TAG_array_type = 1
+ DW_TAG_class_type = 2
+ DW_TAG_enumeration_type = 4
+ DW_TAG_structure_type = 19
+ DW_TAG_union_type = 23
+
+For ``DW_TAG_array_type``, the ``elements:`` should be :ref:`subrange
+descriptors <DISubrange>`, each representing the range of subscripts at that
+level of indexing. The ``DIFlagVector`` flag to ``flags:`` indicates that an
+array type is a native packed vector.
+
+For ``DW_TAG_enumeration_type``, the ``elements:`` should be :ref:`enumerator
+descriptors <DIEnumerator>`, each representing the definition of an enumeration
+value for the set. All enumeration type descriptors are collected in the
+``enums:`` field of the :ref:`compile unit <DICompileUnit>`.
+
+For ``DW_TAG_structure_type``, ``DW_TAG_class_type``, and
+``DW_TAG_union_type``, the ``elements:`` should be :ref:`derived types
+<DIDerivedType>` with ``tag: DW_TAG_member``, ``tag: DW_TAG_inheritance``, or
+``tag: DW_TAG_friend``; or :ref:`subprograms <DISubprogram>` with
+``isDefinition: false``.
+
+.. _DISubrange:
+
+DISubrange
+""""""""""
+
+``DISubrange`` nodes are the elements for ``DW_TAG_array_type`` variants of
+:ref:`DICompositeType`. ``count: -1`` indicates an empty array.
+
+.. code-block:: llvm
+
+ !0 = !DISubrange(count: 5, lowerBound: 0) ; array counting from 0
+ !1 = !DISubrange(count: 5, lowerBound: 1) ; array counting from 1
+ !2 = !DISubrange(count: -1) ; empty array.
+
+.. _DIEnumerator:
+
+DIEnumerator
+""""""""""""
+
+``DIEnumerator`` nodes are the elements for ``DW_TAG_enumeration_type``
+variants of :ref:`DICompositeType`.
+
+.. code-block:: llvm
+
+ !0 = !DIEnumerator(name: "SixKind", value: 7)
+ !1 = !DIEnumerator(name: "SevenKind", value: 7)
+ !2 = !DIEnumerator(name: "NegEightKind", value: -8)
+
+DITemplateTypeParameter
+"""""""""""""""""""""""
+
+``DITemplateTypeParameter`` nodes represent type parameters to generic source
+language constructs. They are used (optionally) in :ref:`DICompositeType` and
+:ref:`DISubprogram` ``templateParams:`` fields.
+
+.. code-block:: llvm
+
+ !0 = !DITemplateTypeParameter(name: "Ty", type: !1)
+
+DITemplateValueParameter
+""""""""""""""""""""""""
+
+``DITemplateValueParameter`` nodes represent value parameters to generic source
+language constructs. ``tag:`` defaults to ``DW_TAG_template_value_parameter``,
+but if specified can also be set to ``DW_TAG_GNU_template_template_param`` or
+``DW_TAG_GNU_template_param_pack``. They are used (optionally) in
+:ref:`DICompositeType` and :ref:`DISubprogram` ``templateParams:`` fields.
+
+.. code-block:: llvm
+
+ !0 = !DITemplateValueParameter(name: "Ty", type: !1, value: i32 7)
+
+DINamespace
+"""""""""""
+
+``DINamespace`` nodes represent namespaces in the source language.
+
+.. code-block:: llvm
+
+ !0 = !DINamespace(name: "myawesomeproject", scope: !1, file: !2, line: 7)
+
+DIGlobalVariable
+""""""""""""""""
+
+``DIGlobalVariable`` nodes represent global variables in the source language.
+
+.. code-block:: llvm
+
+ !0 = !DIGlobalVariable(name: "foo", linkageName: "foo", scope: !1,
+ file: !2, line: 7, type: !3, isLocal: true,
+ isDefinition: false, variable: i32* @foo,
+ declaration: !4)
+
+All global variables should be referenced by the `globals:` field of a
+:ref:`compile unit <DICompileUnit>`.
+
+.. _DISubprogram:
+
+DISubprogram
+""""""""""""
+
+``DISubprogram`` nodes represent functions from the source language. A
+``DISubprogram`` may be attached to a function definition using ``!dbg``
+metadata. The ``variables:`` field points at :ref:`variables <DILocalVariable>`
+that must be retained, even if their IR counterparts are optimized out of
+the IR. The ``type:`` field must point at an :ref:`DISubroutineType`.
+
+.. _DISubprogramDeclaration:
+
+When ``isDefinition: false``, subprograms describe a declaration in the type
+tree as opposed to a definition of a function. If the scope is a composite
+type with an ODR ``identifier:`` and that does not set ``flags: DIFwdDecl``,
+then the subprogram declaration is uniqued based only on its ``linkageName:``
+and ``scope:``.
+
+.. code-block:: text
+
+ define void @_Z3foov() !dbg !0 {
+ ...
+ }
+
+ !0 = distinct !DISubprogram(name: "foo", linkageName: "_Zfoov", scope: !1,
+ file: !2, line: 7, type: !3, isLocal: true,
+ isDefinition: true, scopeLine: 8,
+ containingType: !4,
+ virtuality: DW_VIRTUALITY_pure_virtual,
+ virtualIndex: 10, flags: DIFlagPrototyped,
+ isOptimized: true, unit: !5, templateParams: !6,
+ declaration: !7, variables: !8, thrownTypes: !9)
+
+.. _DILexicalBlock:
+
+DILexicalBlock
+""""""""""""""
+
+``DILexicalBlock`` nodes describe nested blocks within a :ref:`subprogram
+<DISubprogram>`. The line number and column numbers are used to distinguish
+two lexical blocks at same depth. They are valid targets for ``scope:``
+fields.
+
+.. code-block:: text
+
+ !0 = distinct !DILexicalBlock(scope: !1, file: !2, line: 7, column: 35)
+
+Usually lexical blocks are ``distinct`` to prevent node merging based on
+operands.
+
+.. _DILexicalBlockFile:
+
+DILexicalBlockFile
+""""""""""""""""""
+
+``DILexicalBlockFile`` nodes are used to discriminate between sections of a
+:ref:`lexical block <DILexicalBlock>`. The ``file:`` field can be changed to
+indicate textual inclusion, or the ``discriminator:`` field can be used to
+discriminate between control flow within a single block in the source language.
+
+.. code-block:: llvm
+
+ !0 = !DILexicalBlock(scope: !3, file: !4, line: 7, column: 35)
+ !1 = !DILexicalBlockFile(scope: !0, file: !4, discriminator: 0)
+ !2 = !DILexicalBlockFile(scope: !0, file: !4, discriminator: 1)
+
+.. _DILocation:
+
+DILocation
+""""""""""
+
+``DILocation`` nodes represent source debug locations. The ``scope:`` field is
+mandatory, and points at an :ref:`DILexicalBlockFile`, an
+:ref:`DILexicalBlock`, or an :ref:`DISubprogram`.
+
+.. code-block:: llvm
+
+ !0 = !DILocation(line: 2900, column: 42, scope: !1, inlinedAt: !2)
+
+.. _DILocalVariable:
+
+DILocalVariable
+"""""""""""""""
+
+``DILocalVariable`` nodes represent local variables in the source language. If
+the ``arg:`` field is set to non-zero, then this variable is a subprogram
+parameter, and it will be included in the ``variables:`` field of its
+:ref:`DISubprogram`.
+
+.. code-block:: text
+
+ !0 = !DILocalVariable(name: "this", arg: 1, scope: !3, file: !2, line: 7,
+ type: !3, flags: DIFlagArtificial)
+ !1 = !DILocalVariable(name: "x", arg: 2, scope: !4, file: !2, line: 7,
+ type: !3)
+ !2 = !DILocalVariable(name: "y", scope: !5, file: !2, line: 7, type: !3)
+
+DIExpression
+""""""""""""
+
+``DIExpression`` nodes represent expressions that are inspired by the DWARF
+expression language. They are used in :ref:`debug intrinsics<dbg_intrinsics>`
+(such as ``llvm.dbg.declare`` and ``llvm.dbg.value``) to describe how the
+referenced LLVM variable relates to the source language variable.
+
+The current supported vocabulary is limited:
+
+- ``DW_OP_deref`` dereferences the top of the expression stack.
+- ``DW_OP_plus`` pops the last two entries from the expression stack, adds
+ them together and appends the result to the expression stack.
+- ``DW_OP_minus`` pops the last two entries from the expression stack, subtracts
+ the last entry from the second last entry and appends the result to the
+ expression stack.
+- ``DW_OP_plus_uconst, 93`` adds ``93`` to the working expression.
+- ``DW_OP_LLVM_fragment, 16, 8`` specifies the offset and size (``16`` and ``8``
+ here, respectively) of the variable fragment from the working expression. Note
+ that contrary to DW_OP_bit_piece, the offset is describing the the location
+ within the described source variable.
+- ``DW_OP_swap`` swaps top two stack entries.
+- ``DW_OP_xderef`` provides extended dereference mechanism. The entry at the top
+ of the stack is treated as an address. The second stack entry is treated as an
+ address space identifier.
+- ``DW_OP_stack_value`` marks a constant value.
+
+DWARF specifies three kinds of simple location descriptions: Register, memory,
+and implicit location descriptions. Register and memory location descriptions
+describe the *location* of a source variable (in the sense that a debugger might
+modify its value), whereas implicit locations describe merely the *value* of a
+source variable. DIExpressions also follow this model: A DIExpression that
+doesn't have a trailing ``DW_OP_stack_value`` will describe an *address* when
+combined with a concrete location.
+
+.. code-block:: llvm
+
+ !0 = !DIExpression(DW_OP_deref)
+ !1 = !DIExpression(DW_OP_plus_uconst, 3)
+ !1 = !DIExpression(DW_OP_constu, 3, DW_OP_plus)
+ !2 = !DIExpression(DW_OP_bit_piece, 3, 7)
+ !3 = !DIExpression(DW_OP_deref, DW_OP_constu, 3, DW_OP_plus, DW_OP_LLVM_fragment, 3, 7)
+ !4 = !DIExpression(DW_OP_constu, 2, DW_OP_swap, DW_OP_xderef)
+ !5 = !DIExpression(DW_OP_constu, 42, DW_OP_stack_value)
+
+DIObjCProperty
+""""""""""""""
+
+``DIObjCProperty`` nodes represent Objective-C property nodes.
+
+.. code-block:: llvm
+
+ !3 = !DIObjCProperty(name: "foo", file: !1, line: 7, setter: "setFoo",
+ getter: "getFoo", attributes: 7, type: !2)
+
+DIImportedEntity
+""""""""""""""""
+
+``DIImportedEntity`` nodes represent entities (such as modules) imported into a
+compile unit.
+
+.. code-block:: text
+
+ !2 = !DIImportedEntity(tag: DW_TAG_imported_module, name: "foo", scope: !0,
+ entity: !1, line: 7)
+
+DIMacro
+"""""""
+
+``DIMacro`` nodes represent definition or undefinition of a macro identifiers.
+The ``name:`` field is the macro identifier, followed by macro parameters when
+defining a function-like macro, and the ``value`` field is the token-string
+used to expand the macro identifier.
+
+.. code-block:: text
+
+ !2 = !DIMacro(macinfo: DW_MACINFO_define, line: 7, name: "foo(x)",
+ value: "((x) + 1)")
+ !3 = !DIMacro(macinfo: DW_MACINFO_undef, line: 30, name: "foo")
+
+DIMacroFile
+"""""""""""
+
+``DIMacroFile`` nodes represent inclusion of source files.
+The ``nodes:`` field is a list of ``DIMacro`` and ``DIMacroFile`` nodes that
+appear in the included source file.
+
+.. code-block:: text
+
+ !2 = !DIMacroFile(macinfo: DW_MACINFO_start_file, line: 7, file: !2,
+ nodes: !3)
+
+'``tbaa``' Metadata
+^^^^^^^^^^^^^^^^^^^
+
+In LLVM IR, memory does not have types, so LLVM's own type system is not
+suitable for doing type based alias analysis (TBAA). Instead, metadata is
+added to the IR to describe a type system of a higher level language. This
+can be used to implement C/C++ strict type aliasing rules, but it can also
+be used to implement custom alias analysis behavior for other languages.
+
+This description of LLVM's TBAA system is broken into two parts:
+:ref:`Semantics<tbaa_node_semantics>` talks about high level issues, and
+:ref:`Representation<tbaa_node_representation>` talks about the metadata
+encoding of various entities.
+
+It is always possible to trace any TBAA node to a "root" TBAA node (details
+in the :ref:`Representation<tbaa_node_representation>` section). TBAA
+nodes with different roots have an unknown aliasing relationship, and LLVM
+conservatively infers ``MayAlias`` between them. The rules mentioned in
+this section only pertain to TBAA nodes living under the same root.
+
+.. _tbaa_node_semantics:
+
+Semantics
+"""""""""
+
+The TBAA metadata system, referred to as "struct path TBAA" (not to be
+confused with ``tbaa.struct``), consists of the following high level
+concepts: *Type Descriptors*, further subdivided into scalar type
+descriptors and struct type descriptors; and *Access Tags*.
+
+**Type descriptors** describe the type system of the higher level language
+being compiled. **Scalar type descriptors** describe types that do not
+contain other types. Each scalar type has a parent type, which must also
+be a scalar type or the TBAA root. Via this parent relation, scalar types
+within a TBAA root form a tree. **Struct type descriptors** denote types
+that contain a sequence of other type descriptors, at known offsets. These
+contained type descriptors can either be struct type descriptors themselves
+or scalar type descriptors.
+
+**Access tags** are metadata nodes attached to load and store instructions.
+Access tags use type descriptors to describe the *location* being accessed
+in terms of the type system of the higher level language. Access tags are
+tuples consisting of a base type, an access type and an offset. The base
+type is a scalar type descriptor or a struct type descriptor, the access
+type is a scalar type descriptor, and the offset is a constant integer.
+
+The access tag ``(BaseTy, AccessTy, Offset)`` can describe one of two
+things:
+
+ * If ``BaseTy`` is a struct type, the tag describes a memory access (load
+ or store) of a value of type ``AccessTy`` contained in the struct type
+ ``BaseTy`` at offset ``Offset``.
+
+ * If ``BaseTy`` is a scalar type, ``Offset`` must be 0 and ``BaseTy`` and
+ ``AccessTy`` must be the same; and the access tag describes a scalar
+ access with scalar type ``AccessTy``.
+
+We first define an ``ImmediateParent`` relation on ``(BaseTy, Offset)``
+tuples this way:
+
+ * If ``BaseTy`` is a scalar type then ``ImmediateParent(BaseTy, 0)`` is
+ ``(ParentTy, 0)`` where ``ParentTy`` is the parent of the scalar type as
+ described in the TBAA metadata. ``ImmediateParent(BaseTy, Offset)`` is
+ undefined if ``Offset`` is non-zero.
+
+ * If ``BaseTy`` is a struct type then ``ImmediateParent(BaseTy, Offset)``
+ is ``(NewTy, NewOffset)`` where ``NewTy`` is the type contained in
+ ``BaseTy`` at offset ``Offset`` and ``NewOffset`` is ``Offset`` adjusted
+ to be relative within that inner type.
+
+A memory access with an access tag ``(BaseTy1, AccessTy1, Offset1)``
+aliases a memory access with an access tag ``(BaseTy2, AccessTy2,
+Offset2)`` if either ``(BaseTy1, Offset1)`` is reachable from ``(Base2,
+Offset2)`` via the ``Parent`` relation or vice versa.
+
+As a concrete example, the type descriptor graph for the following program
+
+.. code-block:: c
+
+ struct Inner {
+ int i; // offset 0
+ float f; // offset 4
+ };
+
+ struct Outer {
+ float f; // offset 0
+ double d; // offset 4
+ struct Inner inner_a; // offset 12
+ };
+
+ void f(struct Outer* outer, struct Inner* inner, float* f, int* i, char* c) {
+ outer->f = 0; // tag0: (OuterStructTy, FloatScalarTy, 0)
+ outer->inner_a.i = 0; // tag1: (OuterStructTy, IntScalarTy, 12)
+ outer->inner_a.f = 0.0; // tag2: (OuterStructTy, IntScalarTy, 16)
+ *f = 0.0; // tag3: (FloatScalarTy, FloatScalarTy, 0)
+ }
+
+is (note that in C and C++, ``char`` can be used to access any arbitrary
+type):
+
+.. code-block:: text
+
+ Root = "TBAA Root"
+ CharScalarTy = ("char", Root, 0)
+ FloatScalarTy = ("float", CharScalarTy, 0)
+ DoubleScalarTy = ("double", CharScalarTy, 0)
+ IntScalarTy = ("int", CharScalarTy, 0)
+ InnerStructTy = {"Inner" (IntScalarTy, 0), (FloatScalarTy, 4)}
+ OuterStructTy = {"Outer", (FloatScalarTy, 0), (DoubleScalarTy, 4),
+ (InnerStructTy, 12)}
+
+
+with (e.g.) ``ImmediateParent(OuterStructTy, 12)`` = ``(InnerStructTy,
+0)``, ``ImmediateParent(InnerStructTy, 0)`` = ``(IntScalarTy, 0)``, and
+``ImmediateParent(IntScalarTy, 0)`` = ``(CharScalarTy, 0)``.
+
+.. _tbaa_node_representation:
+
+Representation
+""""""""""""""
+
+The root node of a TBAA type hierarchy is an ``MDNode`` with 0 operands or
+with exactly one ``MDString`` operand.
+
+Scalar type descriptors are represented as an ``MDNode`` s with two
+operands. The first operand is an ``MDString`` denoting the name of the
+struct type. LLVM does not assign meaning to the value of this operand, it
+only cares about it being an ``MDString``. The second operand is an
+``MDNode`` which points to the parent for said scalar type descriptor,
+which is either another scalar type descriptor or the TBAA root. Scalar
+type descriptors can have an optional third argument, but that must be the
+constant integer zero.
+
+Struct type descriptors are represented as ``MDNode`` s with an odd number
+of operands greater than 1. The first operand is an ``MDString`` denoting
+the name of the struct type. Like in scalar type descriptors the actual
+value of this name operand is irrelevant to LLVM. After the name operand,
+the struct type descriptors have a sequence of alternating ``MDNode`` and
+``ConstantInt`` operands. With N starting from 1, the 2N - 1 th operand,
+an ``MDNode``, denotes a contained field, and the 2N th operand, a
+``ConstantInt``, is the offset of the said contained field. The offsets
+must be in non-decreasing order.
+
+Access tags are represented as ``MDNode`` s with either 3 or 4 operands.
+The first operand is an ``MDNode`` pointing to the node representing the
+base type. The second operand is an ``MDNode`` pointing to the node
+representing the access type. The third operand is a ``ConstantInt`` that
+states the offset of the access. If a fourth field is present, it must be
+a ``ConstantInt`` valued at 0 or 1. If it is 1 then the access tag states
+that the location being accessed is "constant" (meaning
+``pointsToConstantMemory`` should return true; see `other useful
+AliasAnalysis methods <AliasAnalysis.html#OtherItfs>`_). The TBAA root of
+the access type and the base type of an access tag must be the same, and
+that is the TBAA root of the access tag.
+
+'``tbaa.struct``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The :ref:`llvm.memcpy <int_memcpy>` is often used to implement
+aggregate assignment operations in C and similar languages, however it
+is defined to copy a contiguous region of memory, which is more than
+strictly necessary for aggregate types which contain holes due to
+padding. Also, it doesn't contain any TBAA information about the fields
+of the aggregate.
+
+``!tbaa.struct`` metadata can describe which memory subregions in a
+memcpy are padding and what the TBAA tags of the struct are.
+
+The current metadata format is very simple. ``!tbaa.struct`` metadata
+nodes are a list of operands which are in conceptual groups of three.
+For each group of three, the first operand gives the byte offset of a
+field in bytes, the second gives its size in bytes, and the third gives
+its tbaa tag. e.g.:
+
+.. code-block:: llvm
+
+ !4 = !{ i64 0, i64 4, !1, i64 8, i64 4, !2 }
+
+This describes a struct with two fields. The first is at offset 0 bytes
+with size 4 bytes, and has tbaa tag !1. The second is at offset 8 bytes
+and has size 4 bytes and has tbaa tag !2.
+
+Note that the fields need not be contiguous. In this example, there is a
+4 byte gap between the two fields. This gap represents padding which
+does not carry useful data and need not be preserved.
+
+'``noalias``' and '``alias.scope``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+``noalias`` and ``alias.scope`` metadata provide the ability to specify generic
+noalias memory-access sets. This means that some collection of memory access
+instructions (loads, stores, memory-accessing calls, etc.) that carry
+``noalias`` metadata can specifically be specified not to alias with some other
+collection of memory access instructions that carry ``alias.scope`` metadata.
+Each type of metadata specifies a list of scopes where each scope has an id and
+a domain.
+
+When evaluating an aliasing query, if for some domain, the set
+of scopes with that domain in one instruction's ``alias.scope`` list is a
+subset of (or equal to) the set of scopes for that domain in another
+instruction's ``noalias`` list, then the two memory accesses are assumed not to
+alias.
+
+Because scopes in one domain don't affect scopes in other domains, separate
+domains can be used to compose multiple independent noalias sets. This is
+used for example during inlining. As the noalias function parameters are
+turned into noalias scope metadata, a new domain is used every time the
+function is inlined.
+
+The metadata identifying each domain is itself a list containing one or two
+entries. The first entry is the name of the domain. Note that if the name is a
+string then it can be combined across functions and translation units. A
+self-reference can be used to create globally unique domain names. A
+descriptive string may optionally be provided as a second list entry.
+
+The metadata identifying each scope is also itself a list containing two or
+three entries. The first entry is the name of the scope. Note that if the name
+is a string then it can be combined across functions and translation units. A
+self-reference can be used to create globally unique scope names. A metadata
+reference to the scope's domain is the second entry. A descriptive string may
+optionally be provided as a third list entry.
+
+For example,
+
+.. code-block:: llvm
+
+ ; Two scope domains:
+ !0 = !{!0}
+ !1 = !{!1}
+
+ ; Some scopes in these domains:
+ !2 = !{!2, !0}
+ !3 = !{!3, !0}
+ !4 = !{!4, !1}
+
+ ; Some scope lists:
+ !5 = !{!4} ; A list containing only scope !4
+ !6 = !{!4, !3, !2}
+ !7 = !{!3}
+
+ ; These two instructions don't alias:
+ %0 = load float, float* %c, align 4, !alias.scope !5
+ store float %0, float* %arrayidx.i, align 4, !noalias !5
+
+ ; These two instructions also don't alias (for domain !1, the set of scopes
+ ; in the !alias.scope equals that in the !noalias list):
+ %2 = load float, float* %c, align 4, !alias.scope !5
+ store float %2, float* %arrayidx.i2, align 4, !noalias !6
+
+ ; These two instructions may alias (for domain !0, the set of scopes in
+ ; the !noalias list is not a superset of, or equal to, the scopes in the
+ ; !alias.scope list):
+ %2 = load float, float* %c, align 4, !alias.scope !6
+ store float %0, float* %arrayidx.i, align 4, !noalias !7
+
+'``fpmath``' Metadata
+^^^^^^^^^^^^^^^^^^^^^
+
+``fpmath`` metadata may be attached to any instruction of floating point
+type. It can be used to express the maximum acceptable error in the
+result of that instruction, in ULPs, thus potentially allowing the
+compiler to use a more efficient but less accurate method of computing
+it. ULP is defined as follows:
+
+ If ``x`` is a real number that lies between two finite consecutive
+ floating-point numbers ``a`` and ``b``, without being equal to one
+ of them, then ``ulp(x) = |b - a|``, otherwise ``ulp(x)`` is the
+ distance between the two non-equal finite floating-point numbers
+ nearest ``x``. Moreover, ``ulp(NaN)`` is ``NaN``.
+
+The metadata node shall consist of a single positive float type number
+representing the maximum relative error, for example:
+
+.. code-block:: llvm
+
+ !0 = !{ float 2.5 } ; maximum acceptable inaccuracy is 2.5 ULPs
+
+.. _range-metadata:
+
+'``range``' Metadata
+^^^^^^^^^^^^^^^^^^^^
+
+``range`` metadata may be attached only to ``load``, ``call`` and ``invoke`` of
+integer types. It expresses the possible ranges the loaded value or the value
+returned by the called function at this call site is in. The ranges are
+represented with a flattened list of integers. The loaded value or the value
+returned is known to be in the union of the ranges defined by each consecutive
+pair. Each pair has the following properties:
+
+- The type must match the type loaded by the instruction.
+- The pair ``a,b`` represents the range ``[a,b)``.
+- Both ``a`` and ``b`` are constants.
+- The range is allowed to wrap.
+- The range should not represent the full or empty set. That is,
+ ``a!=b``.
+
+In addition, the pairs must be in signed order of the lower bound and
+they must be non-contiguous.
+
+Examples:
+
+.. code-block:: llvm
+
+ %a = load i8, i8* %x, align 1, !range !0 ; Can only be 0 or 1
+ %b = load i8, i8* %y, align 1, !range !1 ; Can only be 255 (-1), 0 or 1
+ %c = call i8 @foo(), !range !2 ; Can only be 0, 1, 3, 4 or 5
+ %d = invoke i8 @bar() to label %cont
+ unwind label %lpad, !range !3 ; Can only be -2, -1, 3, 4 or 5
+ ...
+ !0 = !{ i8 0, i8 2 }
+ !1 = !{ i8 255, i8 2 }
+ !2 = !{ i8 0, i8 2, i8 3, i8 6 }
+ !3 = !{ i8 -2, i8 0, i8 3, i8 6 }
+
+'``absolute_symbol``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+``absolute_symbol`` metadata may be attached to a global variable
+declaration. It marks the declaration as a reference to an absolute symbol,
+which causes the backend to use absolute relocations for the symbol even
+in position independent code, and expresses the possible ranges that the
+global variable's *address* (not its value) is in, in the same format as
+``range`` metadata, with the extension that the pair ``all-ones,all-ones``
+may be used to represent the full set.
+
+Example (assuming 64-bit pointers):
+
+.. code-block:: llvm
+
+ @a = external global i8, !absolute_symbol !0 ; Absolute symbol in range [0,256)
+ @b = external global i8, !absolute_symbol !1 ; Absolute symbol in range [0,2^64)
+
+ ...
+ !0 = !{ i64 0, i64 256 }
+ !1 = !{ i64 -1, i64 -1 }
+
+'``unpredictable``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+``unpredictable`` metadata may be attached to any branch or switch
+instruction. It can be used to express the unpredictability of control
+flow. Similar to the llvm.expect intrinsic, it may be used to alter
+optimizations related to compare and branch instructions. The metadata
+is treated as a boolean value; if it exists, it signals that the branch
+or switch that it is attached to is completely unpredictable.
+
+'``llvm.loop``'
+^^^^^^^^^^^^^^^
+
+It is sometimes useful to attach information to loop constructs. Currently,
+loop metadata is implemented as metadata attached to the branch instruction
+in the loop latch block. This type of metadata refer to a metadata node that is
+guaranteed to be separate for each loop. The loop identifier metadata is
+specified with the name ``llvm.loop``.
+
+The loop identifier metadata is implemented using a metadata that refers to
+itself to avoid merging it with any other identifier metadata, e.g.,
+during module linkage or function inlining. That is, each loop should refer
+to their own identification metadata even if they reside in separate functions.
+The following example contains loop identifier metadata for two separate loop
+constructs:
+
+.. code-block:: llvm
+
+ !0 = !{!0}
+ !1 = !{!1}
+
+The loop identifier metadata can be used to specify additional
+per-loop metadata. Any operands after the first operand can be treated
+as user-defined metadata. For example the ``llvm.loop.unroll.count``
+suggests an unroll factor to the loop unroller:
+
+.. code-block:: llvm
+
+ br i1 %exitcond, label %._crit_edge, label %.lr.ph, !llvm.loop !0
+ ...
+ !0 = !{!0, !1}
+ !1 = !{!"llvm.loop.unroll.count", i32 4}
+
+'``llvm.loop.vectorize``' and '``llvm.loop.interleave``'
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Metadata prefixed with ``llvm.loop.vectorize`` or ``llvm.loop.interleave`` are
+used to control per-loop vectorization and interleaving parameters such as
+vectorization width and interleave count. These metadata should be used in
+conjunction with ``llvm.loop`` loop identification metadata. The
+``llvm.loop.vectorize`` and ``llvm.loop.interleave`` metadata are only
+optimization hints and the optimizer will only interleave and vectorize loops if
+it believes it is safe to do so. The ``llvm.mem.parallel_loop_access`` metadata
+which contains information about loop-carried memory dependencies can be helpful
+in determining the safety of these transformations.
+
+'``llvm.loop.interleave.count``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This metadata suggests an interleave count to the loop interleaver.
+The first operand is the string ``llvm.loop.interleave.count`` and the
+second operand is an integer specifying the interleave count. For
+example:
+
+.. code-block:: llvm
+
+ !0 = !{!"llvm.loop.interleave.count", i32 4}
+
+Note that setting ``llvm.loop.interleave.count`` to 1 disables interleaving
+multiple iterations of the loop. If ``llvm.loop.interleave.count`` is set to 0
+then the interleave count will be determined automatically.
+
+'``llvm.loop.vectorize.enable``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This metadata selectively enables or disables vectorization for the loop. The
+first operand is the string ``llvm.loop.vectorize.enable`` and the second operand
+is a bit. If the bit operand value is 1 vectorization is enabled. A value of
+0 disables vectorization:
+
+.. code-block:: llvm
+
+ !0 = !{!"llvm.loop.vectorize.enable", i1 0}
+ !1 = !{!"llvm.loop.vectorize.enable", i1 1}
+
+'``llvm.loop.vectorize.width``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This metadata sets the target width of the vectorizer. The first
+operand is the string ``llvm.loop.vectorize.width`` and the second
+operand is an integer specifying the width. For example:
+
+.. code-block:: llvm
+
+ !0 = !{!"llvm.loop.vectorize.width", i32 4}
+
+Note that setting ``llvm.loop.vectorize.width`` to 1 disables
+vectorization of the loop. If ``llvm.loop.vectorize.width`` is set to
+0 or if the loop does not have this metadata the width will be
+determined automatically.
+
+'``llvm.loop.unroll``'
+^^^^^^^^^^^^^^^^^^^^^^
+
+Metadata prefixed with ``llvm.loop.unroll`` are loop unrolling
+optimization hints such as the unroll factor. ``llvm.loop.unroll``
+metadata should be used in conjunction with ``llvm.loop`` loop
+identification metadata. The ``llvm.loop.unroll`` metadata are only
+optimization hints and the unrolling will only be performed if the
+optimizer believes it is safe to do so.
+
+'``llvm.loop.unroll.count``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This metadata suggests an unroll factor to the loop unroller. The
+first operand is the string ``llvm.loop.unroll.count`` and the second
+operand is a positive integer specifying the unroll factor. For
+example:
+
+.. code-block:: llvm
+
+ !0 = !{!"llvm.loop.unroll.count", i32 4}
+
+If the trip count of the loop is less than the unroll count the loop
+will be partially unrolled.
+
+'``llvm.loop.unroll.disable``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This metadata disables loop unrolling. The metadata has a single operand
+which is the string ``llvm.loop.unroll.disable``. For example:
+
+.. code-block:: llvm
+
+ !0 = !{!"llvm.loop.unroll.disable"}
+
+'``llvm.loop.unroll.runtime.disable``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This metadata disables runtime loop unrolling. The metadata has a single
+operand which is the string ``llvm.loop.unroll.runtime.disable``. For example:
+
+.. code-block:: llvm
+
+ !0 = !{!"llvm.loop.unroll.runtime.disable"}
+
+'``llvm.loop.unroll.enable``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This metadata suggests that the loop should be fully unrolled if the trip count
+is known at compile time and partially unrolled if the trip count is not known
+at compile time. The metadata has a single operand which is the string
+``llvm.loop.unroll.enable``. For example:
+
+.. code-block:: llvm
+
+ !0 = !{!"llvm.loop.unroll.enable"}
+
+'``llvm.loop.unroll.full``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This metadata suggests that the loop should be unrolled fully. The
+metadata has a single operand which is the string ``llvm.loop.unroll.full``.
+For example:
+
+.. code-block:: llvm
+
+ !0 = !{!"llvm.loop.unroll.full"}
+
+'``llvm.loop.licm_versioning.disable``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This metadata indicates that the loop should not be versioned for the purpose
+of enabling loop-invariant code motion (LICM). The metadata has a single operand
+which is the string ``llvm.loop.licm_versioning.disable``. For example:
+
+.. code-block:: llvm
+
+ !0 = !{!"llvm.loop.licm_versioning.disable"}
+
+'``llvm.loop.distribute.enable``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Loop distribution allows splitting a loop into multiple loops. Currently,
+this is only performed if the entire loop cannot be vectorized due to unsafe
+memory dependencies. The transformation will attempt to isolate the unsafe
+dependencies into their own loop.
+
+This metadata can be used to selectively enable or disable distribution of the
+loop. The first operand is the string ``llvm.loop.distribute.enable`` and the
+second operand is a bit. If the bit operand value is 1 distribution is
+enabled. A value of 0 disables distribution:
+
+.. code-block:: llvm
+
+ !0 = !{!"llvm.loop.distribute.enable", i1 0}
+ !1 = !{!"llvm.loop.distribute.enable", i1 1}
+
+This metadata should be used in conjunction with ``llvm.loop`` loop
+identification metadata.
+
+'``llvm.mem``'
+^^^^^^^^^^^^^^^
+
+Metadata types used to annotate memory accesses with information helpful
+for optimizations are prefixed with ``llvm.mem``.
+
+'``llvm.mem.parallel_loop_access``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The ``llvm.mem.parallel_loop_access`` metadata refers to a loop identifier,
+or metadata containing a list of loop identifiers for nested loops.
+The metadata is attached to memory accessing instructions and denotes that
+no loop carried memory dependence exist between it and other instructions denoted
+with the same loop identifier. The metadata on memory reads also implies that
+if conversion (i.e. speculative execution within a loop iteration) is safe.
+
+Precisely, given two instructions ``m1`` and ``m2`` that both have the
+``llvm.mem.parallel_loop_access`` metadata, with ``L1`` and ``L2`` being the
+set of loops associated with that metadata, respectively, then there is no loop
+carried dependence between ``m1`` and ``m2`` for loops in both ``L1`` and
+``L2``.
+
+As a special case, if all memory accessing instructions in a loop have
+``llvm.mem.parallel_loop_access`` metadata that refers to that loop, then the
+loop has no loop carried memory dependences and is considered to be a parallel
+loop.
+
+Note that if not all memory access instructions have such metadata referring to
+the loop, then the loop is considered not being trivially parallel. Additional
+memory dependence analysis is required to make that determination. As a fail
+safe mechanism, this causes loops that were originally parallel to be considered
+sequential (if optimization passes that are unaware of the parallel semantics
+insert new memory instructions into the loop body).
+
+Example of a loop that is considered parallel due to its correct use of
+both ``llvm.loop`` and ``llvm.mem.parallel_loop_access``
+metadata types that refer to the same loop identifier metadata.
+
+.. code-block:: llvm
+
+ for.body:
+ ...
+ %val0 = load i32, i32* %arrayidx, !llvm.mem.parallel_loop_access !0
+ ...
+ store i32 %val0, i32* %arrayidx1, !llvm.mem.parallel_loop_access !0
+ ...
+ br i1 %exitcond, label %for.end, label %for.body, !llvm.loop !0
+
+ for.end:
+ ...
+ !0 = !{!0}
+
+It is also possible to have nested parallel loops. In that case the
+memory accesses refer to a list of loop identifier metadata nodes instead of
+the loop identifier metadata node directly:
+
+.. code-block:: llvm
+
+ outer.for.body:
+ ...
+ %val1 = load i32, i32* %arrayidx3, !llvm.mem.parallel_loop_access !2
+ ...
+ br label %inner.for.body
+
+ inner.for.body:
+ ...
+ %val0 = load i32, i32* %arrayidx1, !llvm.mem.parallel_loop_access !0
+ ...
+ store i32 %val0, i32* %arrayidx2, !llvm.mem.parallel_loop_access !0
+ ...
+ br i1 %exitcond, label %inner.for.end, label %inner.for.body, !llvm.loop !1
+
+ inner.for.end:
+ ...
+ store i32 %val1, i32* %arrayidx4, !llvm.mem.parallel_loop_access !2
+ ...
+ br i1 %exitcond, label %outer.for.end, label %outer.for.body, !llvm.loop !2
+
+ outer.for.end: ; preds = %for.body
+ ...
+ !0 = !{!1, !2} ; a list of loop identifiers
+ !1 = !{!1} ; an identifier for the inner loop
+ !2 = !{!2} ; an identifier for the outer loop
+
+'``invariant.group``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The ``invariant.group`` metadata may be attached to ``load``/``store`` instructions.
+The existence of the ``invariant.group`` metadata on the instruction tells
+the optimizer that every ``load`` and ``store`` to the same pointer operand
+within the same invariant group can be assumed to load or store the same
+value (but see the ``llvm.invariant.group.barrier`` intrinsic which affects
+when two pointers are considered the same). Pointers returned by bitcast or
+getelementptr with only zero indices are considered the same.
+
+Examples:
+
+.. code-block:: llvm
+
+ @unknownPtr = external global i8
+ ...
+ %ptr = alloca i8
+ store i8 42, i8* %ptr, !invariant.group !0
+ call void @foo(i8* %ptr)
+
+ %a = load i8, i8* %ptr, !invariant.group !0 ; Can assume that value under %ptr didn't change
+ call void @foo(i8* %ptr)
+ %b = load i8, i8* %ptr, !invariant.group !1 ; Can't assume anything, because group changed
+
+ %newPtr = call i8* @getPointer(i8* %ptr)
+ %c = load i8, i8* %newPtr, !invariant.group !0 ; Can't assume anything, because we only have information about %ptr
+
+ %unknownValue = load i8, i8* @unknownPtr
+ store i8 %unknownValue, i8* %ptr, !invariant.group !0 ; Can assume that %unknownValue == 42
+
+ call void @foo(i8* %ptr)
+ %newPtr2 = call i8* @llvm.invariant.group.barrier(i8* %ptr)
+ %d = load i8, i8* %newPtr2, !invariant.group !0 ; Can't step through invariant.group.barrier to get value of %ptr
+
+ ...
+ declare void @foo(i8*)
+ declare i8* @getPointer(i8*)
+ declare i8* @llvm.invariant.group.barrier(i8*)
+
+ !0 = !{!"magic ptr"}
+ !1 = !{!"other ptr"}
+
+The invariant.group metadata must be dropped when replacing one pointer by
+another based on aliasing information. This is because invariant.group is tied
+to the SSA value of the pointer operand.
+
+.. code-block:: llvm
+
+ %v = load i8, i8* %x, !invariant.group !0
+ ; if %x mustalias %y then we can replace the above instruction with
+ %v = load i8, i8* %y
+
+
+'``type``' Metadata
+^^^^^^^^^^^^^^^^^^^
+
+See :doc:`TypeMetadata`.
+
+'``associated``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The ``associated`` metadata may be attached to a global object
+declaration with a single argument that references another global object.
+
+This metadata prevents discarding of the global object in linker GC
+unless the referenced object is also discarded. The linker support for
+this feature is spotty. For best compatibility, globals carrying this
+metadata may also:
+
+- Be in a comdat with the referenced global.
+- Be in @llvm.compiler.used.
+- Have an explicit section with a name which is a valid C identifier.
+
+It does not have any effect on non-ELF targets.
+
+Example:
+
+.. code-block:: llvm
+
+ $a = comdat any
+ @a = global i32 1, comdat $a
+ @b = internal global i32 2, comdat $a, section "abc", !associated !0
+ !0 = !{i32* @a}
+
+
+'``prof``' Metadata
+^^^^^^^^^^^^^^^^^^^
+
+The ``prof`` metadata is used to record profile data in the IR.
+The first operand of the metadata node indicates the profile metadata
+type. There are currently 3 types:
+:ref:`branch_weights<prof_node_branch_weights>`,
+:ref:`function_entry_count<prof_node_function_entry_count>`, and
+:ref:`VP<prof_node_VP>`.
+
+.. _prof_node_branch_weights:
+
+branch_weights
+""""""""""""""
+
+Branch weight metadata attached to a branch, select, switch or call instruction
+represents the likeliness of the associated branch being taken.
+For more information, see :doc:`BranchWeightMetadata`.
+
+.. _prof_node_function_entry_count:
+
+function_entry_count
+""""""""""""""""""""
+
+Function entry count metadata can be attached to function definitions
+to record the number of times the function is called. Used with BFI
+information, it is also used to derive the basic block profile count.
+For more information, see :doc:`BranchWeightMetadata`.
+
+.. _prof_node_VP:
+
+VP
+""
+
+VP (value profile) metadata can be attached to instructions that have
+value profile information. Currently this is indirect calls (where it
+records the hottest callees) and calls to memory intrinsics such as memcpy,
+memmove, and memset (where it records the hottest byte lengths).
+
+Each VP metadata node contains "VP" string, then a uint32_t value for the value
+profiling kind, a uint64_t value for the total number of times the instruction
+is executed, followed by uint64_t value and execution count pairs.
+The value profiling kind is 0 for indirect call targets and 1 for memory
+operations. For indirect call targets, each profile value is a hash
+of the callee function name, and for memory operations each value is the
+byte length.
+
+Note that the value counts do not need to add up to the total count
+listed in the third operand (in practice only the top hottest values
+are tracked and reported).
+
+Indirect call example:
+
+.. code-block:: llvm
+
+ call void %f(), !prof !1
+ !1 = !{!"VP", i32 0, i64 1600, i64 7651369219802541373, i64 1030, i64 -4377547752858689819, i64 410}
+
+Note that the VP type is 0 (the second operand), which indicates this is
+an indirect call value profile data. The third operand indicates that the
+indirect call executed 1600 times. The 4th and 6th operands give the
+hashes of the 2 hottest target functions' names (this is the same hash used
+to represent function names in the profile database), and the 5th and 7th
+operands give the execution count that each of the respective prior target
+functions was called.
+
+Module Flags Metadata
+=====================
+
+Information about the module as a whole is difficult to convey to LLVM's
+subsystems. The LLVM IR isn't sufficient to transmit this information.
+The ``llvm.module.flags`` named metadata exists in order to facilitate
+this. These flags are in the form of key / value pairs --- much like a
+dictionary --- making it easy for any subsystem who cares about a flag to
+look it up.
+
+The ``llvm.module.flags`` metadata contains a list of metadata triplets.
+Each triplet has the following form:
+
+- The first element is a *behavior* flag, which specifies the behavior
+ when two (or more) modules are merged together, and it encounters two
+ (or more) metadata with the same ID. The supported behaviors are
+ described below.
+- The second element is a metadata string that is a unique ID for the
+ metadata. Each module may only have one flag entry for each unique ID (not
+ including entries with the **Require** behavior).
+- The third element is the value of the flag.
+
+When two (or more) modules are merged together, the resulting
+``llvm.module.flags`` metadata is the union of the modules' flags. That is, for
+each unique metadata ID string, there will be exactly one entry in the merged
+modules ``llvm.module.flags`` metadata table, and the value for that entry will
+be determined by the merge behavior flag, as described below. The only exception
+is that entries with the *Require* behavior are always preserved.
+
+The following behaviors are supported:
+
+.. list-table::
+ :header-rows: 1
+ :widths: 10 90
+
+ * - Value
+ - Behavior
+
+ * - 1
+ - **Error**
+ Emits an error if two values disagree, otherwise the resulting value
+ is that of the operands.
+
+ * - 2
+ - **Warning**
+ Emits a warning if two values disagree. The result value will be the
+ operand for the flag from the first module being linked.
+
+ * - 3
+ - **Require**
+ Adds a requirement that another module flag be present and have a
+ specified value after linking is performed. The value must be a
+ metadata pair, where the first element of the pair is the ID of the
+ module flag to be restricted, and the second element of the pair is
+ the value the module flag should be restricted to. This behavior can
+ be used to restrict the allowable results (via triggering of an
+ error) of linking IDs with the **Override** behavior.
+
+ * - 4
+ - **Override**
+ Uses the specified value, regardless of the behavior or value of the
+ other module. If both modules specify **Override**, but the values
+ differ, an error will be emitted.
+
+ * - 5
+ - **Append**
+ Appends the two values, which are required to be metadata nodes.
+
+ * - 6
+ - **AppendUnique**
+ Appends the two values, which are required to be metadata
+ nodes. However, duplicate entries in the second list are dropped
+ during the append operation.
+
+ * - 7
+ - **Max**
+ Takes the max of the two values, which are required to be integers.
+
+It is an error for a particular unique flag ID to have multiple behaviors,
+except in the case of **Require** (which adds restrictions on another metadata
+value) or **Override**.
+
+An example of module flags:
+
+.. code-block:: llvm
+
+ !0 = !{ i32 1, !"foo", i32 1 }
+ !1 = !{ i32 4, !"bar", i32 37 }
+ !2 = !{ i32 2, !"qux", i32 42 }
+ !3 = !{ i32 3, !"qux",
+ !{
+ !"foo", i32 1
+ }
+ }
+ !llvm.module.flags = !{ !0, !1, !2, !3 }
+
+- Metadata ``!0`` has the ID ``!"foo"`` and the value '1'. The behavior
+ if two or more ``!"foo"`` flags are seen is to emit an error if their
+ values are not equal.
+
+- Metadata ``!1`` has the ID ``!"bar"`` and the value '37'. The
+ behavior if two or more ``!"bar"`` flags are seen is to use the value
+ '37'.
+
+- Metadata ``!2`` has the ID ``!"qux"`` and the value '42'. The
+ behavior if two or more ``!"qux"`` flags are seen is to emit a
+ warning if their values are not equal.
+
+- Metadata ``!3`` has the ID ``!"qux"`` and the value:
+
+ ::
+
+ !{ !"foo", i32 1 }
+
+ The behavior is to emit an error if the ``llvm.module.flags`` does not
+ contain a flag with the ID ``!"foo"`` that has the value '1' after linking is
+ performed.
+
+Objective-C Garbage Collection Module Flags Metadata
+----------------------------------------------------
+
+On the Mach-O platform, Objective-C stores metadata about garbage
+collection in a special section called "image info". The metadata
+consists of a version number and a bitmask specifying what types of
+garbage collection are supported (if any) by the file. If two or more
+modules are linked together their garbage collection metadata needs to
+be merged rather than appended together.
+
+The Objective-C garbage collection module flags metadata consists of the
+following key-value pairs:
+
+.. list-table::
+ :header-rows: 1
+ :widths: 30 70
+
+ * - Key
+ - Value
+
+ * - ``Objective-C Version``
+ - **[Required]** --- The Objective-C ABI version. Valid values are 1 and 2.
+
+ * - ``Objective-C Image Info Version``
+ - **[Required]** --- The version of the image info section. Currently
+ always 0.
+
+ * - ``Objective-C Image Info Section``
+ - **[Required]** --- The section to place the metadata. Valid values are
+ ``"__OBJC, __image_info, regular"`` for Objective-C ABI version 1, and
+ ``"__DATA,__objc_imageinfo, regular, no_dead_strip"`` for
+ Objective-C ABI version 2.
+
+ * - ``Objective-C Garbage Collection``
+ - **[Required]** --- Specifies whether garbage collection is supported or
+ not. Valid values are 0, for no garbage collection, and 2, for garbage
+ collection supported.
+
+ * - ``Objective-C GC Only``
+ - **[Optional]** --- Specifies that only garbage collection is supported.
+ If present, its value must be 6. This flag requires that the
+ ``Objective-C Garbage Collection`` flag have the value 2.
+
+Some important flag interactions:
+
+- If a module with ``Objective-C Garbage Collection`` set to 0 is
+ merged with a module with ``Objective-C Garbage Collection`` set to
+ 2, then the resulting module has the
+ ``Objective-C Garbage Collection`` flag set to 0.
+- A module with ``Objective-C Garbage Collection`` set to 0 cannot be
+ merged with a module with ``Objective-C GC Only`` set to 6.
+
+C type width Module Flags Metadata
+----------------------------------
+
+The ARM backend emits a section into each generated object file describing the
+options that it was compiled with (in a compiler-independent way) to prevent
+linking incompatible objects, and to allow automatic library selection. Some
+of these options are not visible at the IR level, namely wchar_t width and enum
+width.
+
+To pass this information to the backend, these options are encoded in module
+flags metadata, using the following key-value pairs:
+
+.. list-table::
+ :header-rows: 1
+ :widths: 30 70
+
+ * - Key
+ - Value
+
+ * - short_wchar
+ - * 0 --- sizeof(wchar_t) == 4
+ * 1 --- sizeof(wchar_t) == 2
+
+ * - short_enum
+ - * 0 --- Enums are at least as large as an ``int``.
+ * 1 --- Enums are stored in the smallest integer type which can
+ represent all of its values.
+
+For example, the following metadata section specifies that the module was
+compiled with a ``wchar_t`` width of 4 bytes, and the underlying type of an
+enum is the smallest type which can represent all of its values::
+
+ !llvm.module.flags = !{!0, !1}
+ !0 = !{i32 1, !"short_wchar", i32 1}
+ !1 = !{i32 1, !"short_enum", i32 0}
+
+Automatic Linker Flags Named Metadata
+=====================================
+
+Some targets support embedding flags to the linker inside individual object
+files. Typically this is used in conjunction with language extensions which
+allow source files to explicitly declare the libraries they depend on, and have
+these automatically be transmitted to the linker via object files.
+
+These flags are encoded in the IR using named metadata with the name
+``!llvm.linker.options``. Each operand is expected to be a metadata node
+which should be a list of other metadata nodes, each of which should be a
+list of metadata strings defining linker options.
+
+For example, the following metadata section specifies two separate sets of
+linker options, presumably to link against ``libz`` and the ``Cocoa``
+framework::
+
+ !0 = !{ !"-lz" },
+ !1 = !{ !"-framework", !"Cocoa" } } }
+ !llvm.linker.options = !{ !0, !1 }
+
+The metadata encoding as lists of lists of options, as opposed to a collapsed
+list of options, is chosen so that the IR encoding can use multiple option
+strings to specify e.g., a single library, while still having that specifier be
+preserved as an atomic element that can be recognized by a target specific
+assembly writer or object file emitter.
+
+Each individual option is required to be either a valid option for the target's
+linker, or an option that is reserved by the target specific assembly writer or
+object file emitter. No other aspect of these options is defined by the IR.
+
+.. _intrinsicglobalvariables:
+
+Intrinsic Global Variables
+==========================
+
+LLVM has a number of "magic" global variables that contain data that
+affect code generation or other IR semantics. These are documented here.
+All globals of this sort should have a section specified as
+"``llvm.metadata``". This section and all globals that start with
+"``llvm.``" are reserved for use by LLVM.
+
+.. _gv_llvmused:
+
+The '``llvm.used``' Global Variable
+-----------------------------------
+
+The ``@llvm.used`` global is an array which has
+:ref:`appending linkage <linkage_appending>`. This array contains a list of
+pointers to named global variables, functions and aliases which may optionally
+have a pointer cast formed of bitcast or getelementptr. For example, a legal
+use of it is:
+
+.. code-block:: llvm
+
+ @X = global i8 4
+ @Y = global i32 123
+
+ @llvm.used = appending global [2 x i8*] [
+ i8* @X,
+ i8* bitcast (i32* @Y to i8*)
+ ], section "llvm.metadata"
+
+If a symbol appears in the ``@llvm.used`` list, then the compiler, assembler,
+and linker are required to treat the symbol as if there is a reference to the
+symbol that it cannot see (which is why they have to be named). For example, if
+a variable has internal linkage and no references other than that from the
+``@llvm.used`` list, it cannot be deleted. This is commonly used to represent
+references from inline asms and other things the compiler cannot "see", and
+corresponds to "``attribute((used))``" in GNU C.
+
+On some targets, the code generator must emit a directive to the
+assembler or object file to prevent the assembler and linker from
+molesting the symbol.
+
+.. _gv_llvmcompilerused:
+
+The '``llvm.compiler.used``' Global Variable
+--------------------------------------------
+
+The ``@llvm.compiler.used`` directive is the same as the ``@llvm.used``
+directive, except that it only prevents the compiler from touching the
+symbol. On targets that support it, this allows an intelligent linker to
+optimize references to the symbol without being impeded as it would be
+by ``@llvm.used``.
+
+This is a rare construct that should only be used in rare circumstances,
+and should not be exposed to source languages.
+
+.. _gv_llvmglobalctors:
+
+The '``llvm.global_ctors``' Global Variable
+-------------------------------------------
+
+.. code-block:: llvm
+
+ %0 = type { i32, void ()*, i8* }
+ @llvm.global_ctors = appending global [1 x %0] [%0 { i32 65535, void ()* @ctor, i8* @data }]
+
+The ``@llvm.global_ctors`` array contains a list of constructor
+functions, priorities, and an optional associated global or function.
+The functions referenced by this array will be called in ascending order
+of priority (i.e. lowest first) when the module is loaded. The order of
+functions with the same priority is not defined.
+
+If the third field is present, non-null, and points to a global variable
+or function, the initializer function will only run if the associated
+data from the current module is not discarded.
+
+.. _llvmglobaldtors:
+
+The '``llvm.global_dtors``' Global Variable
+-------------------------------------------
+
+.. code-block:: llvm
+
+ %0 = type { i32, void ()*, i8* }
+ @llvm.global_dtors = appending global [1 x %0] [%0 { i32 65535, void ()* @dtor, i8* @data }]
+
+The ``@llvm.global_dtors`` array contains a list of destructor
+functions, priorities, and an optional associated global or function.
+The functions referenced by this array will be called in descending
+order of priority (i.e. highest first) when the module is unloaded. The
+order of functions with the same priority is not defined.
+
+If the third field is present, non-null, and points to a global variable
+or function, the destructor function will only run if the associated
+data from the current module is not discarded.
+
+Instruction Reference
+=====================
+
+The LLVM instruction set consists of several different classifications
+of instructions: :ref:`terminator instructions <terminators>`, :ref:`binary
+instructions <binaryops>`, :ref:`bitwise binary
+instructions <bitwiseops>`, :ref:`memory instructions <memoryops>`, and
+:ref:`other instructions <otherops>`.
+
+.. _terminators:
+
+Terminator Instructions
+-----------------------
+
+As mentioned :ref:`previously <functionstructure>`, every basic block in a
+program ends with a "Terminator" instruction, which indicates which
+block should be executed after the current block is finished. These
+terminator instructions typically yield a '``void``' value: they produce
+control flow, not values (the one exception being the
+':ref:`invoke <i_invoke>`' instruction).
+
+The terminator instructions are: ':ref:`ret <i_ret>`',
+':ref:`br <i_br>`', ':ref:`switch <i_switch>`',
+':ref:`indirectbr <i_indirectbr>`', ':ref:`invoke <i_invoke>`',
+':ref:`resume <i_resume>`', ':ref:`catchswitch <i_catchswitch>`',
+':ref:`catchret <i_catchret>`',
+':ref:`cleanupret <i_cleanupret>`',
+and ':ref:`unreachable <i_unreachable>`'.
+
+.. _i_ret:
+
+'``ret``' Instruction
+^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ ret <type> <value> ; Return a value from a non-void function
+ ret void ; Return from void function
+
+Overview:
+"""""""""
+
+The '``ret``' instruction is used to return control flow (and optionally
+a value) from a function back to the caller.
+
+There are two forms of the '``ret``' instruction: one that returns a
+value and then causes control flow, and one that just causes control
+flow to occur.
+
+Arguments:
+""""""""""
+
+The '``ret``' instruction optionally accepts a single argument, the
+return value. The type of the return value must be a ':ref:`first
+class <t_firstclass>`' type.
+
+A function is not :ref:`well formed <wellformed>` if it it has a non-void
+return type and contains a '``ret``' instruction with no return value or
+a return value with a type that does not match its type, or if it has a
+void return type and contains a '``ret``' instruction with a return
+value.
+
+Semantics:
+""""""""""
+
+When the '``ret``' instruction is executed, control flow returns back to
+the calling function's context. If the caller is a
+":ref:`call <i_call>`" instruction, execution continues at the
+instruction after the call. If the caller was an
+":ref:`invoke <i_invoke>`" instruction, execution continues at the
+beginning of the "normal" destination block. If the instruction returns
+a value, that value shall set the call or invoke instruction's return
+value.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ ret i32 5 ; Return an integer value of 5
+ ret void ; Return from a void function
+ ret { i32, i8 } { i32 4, i8 2 } ; Return a struct of values 4 and 2
+
+.. _i_br:
+
+'``br``' Instruction
+^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ br i1 <cond>, label <iftrue>, label <iffalse>
+ br label <dest> ; Unconditional branch
+
+Overview:
+"""""""""
+
+The '``br``' instruction is used to cause control flow to transfer to a
+different basic block in the current function. There are two forms of
+this instruction, corresponding to a conditional branch and an
+unconditional branch.
+
+Arguments:
+""""""""""
+
+The conditional branch form of the '``br``' instruction takes a single
+'``i1``' value and two '``label``' values. The unconditional form of the
+'``br``' instruction takes a single '``label``' value as a target.
+
+Semantics:
+""""""""""
+
+Upon execution of a conditional '``br``' instruction, the '``i1``'
+argument is evaluated. If the value is ``true``, control flows to the
+'``iftrue``' ``label`` argument. If "cond" is ``false``, control flows
+to the '``iffalse``' ``label`` argument.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ Test:
+ %cond = icmp eq i32 %a, %b
+ br i1 %cond, label %IfEqual, label %IfUnequal
+ IfEqual:
+ ret i32 1
+ IfUnequal:
+ ret i32 0
+
+.. _i_switch:
+
+'``switch``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ switch <intty> <value>, label <defaultdest> [ <intty> <val>, label <dest> ... ]
+
+Overview:
+"""""""""
+
+The '``switch``' instruction is used to transfer control flow to one of
+several different places. It is a generalization of the '``br``'
+instruction, allowing a branch to occur to one of many possible
+destinations.
+
+Arguments:
+""""""""""
+
+The '``switch``' instruction uses three parameters: an integer
+comparison value '``value``', a default '``label``' destination, and an
+array of pairs of comparison value constants and '``label``'s. The table
+is not allowed to contain duplicate constant entries.
+
+Semantics:
+""""""""""
+
+The ``switch`` instruction specifies a table of values and destinations.
+When the '``switch``' instruction is executed, this table is searched
+for the given value. If the value is found, control flow is transferred
+to the corresponding destination; otherwise, control flow is transferred
+to the default destination.
+
+Implementation:
+"""""""""""""""
+
+Depending on properties of the target machine and the particular
+``switch`` instruction, this instruction may be code generated in
+different ways. For example, it could be generated as a series of
+chained conditional branches or with a lookup table.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ ; Emulate a conditional br instruction
+ %Val = zext i1 %value to i32
+ switch i32 %Val, label %truedest [ i32 0, label %falsedest ]
+
+ ; Emulate an unconditional br instruction
+ switch i32 0, label %dest [ ]
+
+ ; Implement a jump table:
+ switch i32 %val, label %otherwise [ i32 0, label %onzero
+ i32 1, label %onone
+ i32 2, label %ontwo ]
+
+.. _i_indirectbr:
+
+'``indirectbr``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ indirectbr <somety>* <address>, [ label <dest1>, label <dest2>, ... ]
+
+Overview:
+"""""""""
+
+The '``indirectbr``' instruction implements an indirect branch to a
+label within the current function, whose address is specified by
+"``address``". Address must be derived from a
+:ref:`blockaddress <blockaddress>` constant.
+
+Arguments:
+""""""""""
+
+The '``address``' argument is the address of the label to jump to. The
+rest of the arguments indicate the full set of possible destinations
+that the address may point to. Blocks are allowed to occur multiple
+times in the destination list, though this isn't particularly useful.
+
+This destination list is required so that dataflow analysis has an
+accurate understanding of the CFG.
+
+Semantics:
+""""""""""
+
+Control transfers to the block specified in the address argument. All
+possible destination blocks must be listed in the label list, otherwise
+this instruction has undefined behavior. This implies that jumps to
+labels defined in other functions have undefined behavior as well.
+
+Implementation:
+"""""""""""""""
+
+This is typically implemented with a jump through a register.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ indirectbr i8* %Addr, [ label %bb1, label %bb2, label %bb3 ]
+
+.. _i_invoke:
+
+'``invoke``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = invoke [cconv] [ret attrs] <ty>|<fnty> <fnptrval>(<function args>) [fn attrs]
+ [operand bundles] to label <normal label> unwind label <exception label>
+
+Overview:
+"""""""""
+
+The '``invoke``' instruction causes control to transfer to a specified
+function, with the possibility of control flow transfer to either the
+'``normal``' label or the '``exception``' label. If the callee function
+returns with the "``ret``" instruction, control flow will return to the
+"normal" label. If the callee (or any indirect callees) returns via the
+":ref:`resume <i_resume>`" instruction or other exception handling
+mechanism, control is interrupted and continued at the dynamically
+nearest "exception" label.
+
+The '``exception``' label is a `landing
+pad <ExceptionHandling.html#overview>`_ for the exception. As such,
+'``exception``' label is required to have the
+":ref:`landingpad <i_landingpad>`" instruction, which contains the
+information about the behavior of the program after unwinding happens,
+as its first non-PHI instruction. The restrictions on the
+"``landingpad``" instruction's tightly couples it to the "``invoke``"
+instruction, so that the important information contained within the
+"``landingpad``" instruction can't be lost through normal code motion.
+
+Arguments:
+""""""""""
+
+This instruction requires several arguments:
+
+#. The optional "cconv" marker indicates which :ref:`calling
+ convention <callingconv>` the call should use. If none is
+ specified, the call defaults to using C calling conventions.
+#. The optional :ref:`Parameter Attributes <paramattrs>` list for return
+ values. Only '``zeroext``', '``signext``', and '``inreg``' attributes
+ are valid here.
+#. '``ty``': the type of the call instruction itself which is also the
+ type of the return value. Functions that return no value are marked
+ ``void``.
+#. '``fnty``': shall be the signature of the function being invoked. The
+ argument types must match the types implied by this signature. This
+ type can be omitted if the function is not varargs.
+#. '``fnptrval``': An LLVM value containing a pointer to a function to
+ be invoked. In most cases, this is a direct function invocation, but
+ indirect ``invoke``'s are just as possible, calling an arbitrary pointer
+ to function value.
+#. '``function args``': argument list whose types match the function
+ signature argument types and parameter attributes. All arguments must
+ be of :ref:`first class <t_firstclass>` type. If the function signature
+ indicates the function accepts a variable number of arguments, the
+ extra arguments can be specified.
+#. '``normal label``': the label reached when the called function
+ executes a '``ret``' instruction.
+#. '``exception label``': the label reached when a callee returns via
+ the :ref:`resume <i_resume>` instruction or other exception handling
+ mechanism.
+#. The optional :ref:`function attributes <fnattrs>` list.
+#. The optional :ref:`operand bundles <opbundles>` list.
+
+Semantics:
+""""""""""
+
+This instruction is designed to operate as a standard '``call``'
+instruction in most regards. The primary difference is that it
+establishes an association with a label, which is used by the runtime
+library to unwind the stack.
+
+This instruction is used in languages with destructors to ensure that
+proper cleanup is performed in the case of either a ``longjmp`` or a
+thrown exception. Additionally, this is important for implementation of
+'``catch``' clauses in high-level languages that support them.
+
+For the purposes of the SSA form, the definition of the value returned
+by the '``invoke``' instruction is deemed to occur on the edge from the
+current block to the "normal" label. If the callee unwinds then no
+return value is available.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %retval = invoke i32 @Test(i32 15) to label %Continue
+ unwind label %TestCleanup ; i32:retval set
+ %retval = invoke coldcc i32 %Testfnptr(i32 15) to label %Continue
+ unwind label %TestCleanup ; i32:retval set
+
+.. _i_resume:
+
+'``resume``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ resume <type> <value>
+
+Overview:
+"""""""""
+
+The '``resume``' instruction is a terminator instruction that has no
+successors.
+
+Arguments:
+""""""""""
+
+The '``resume``' instruction requires one argument, which must have the
+same type as the result of any '``landingpad``' instruction in the same
+function.
+
+Semantics:
+""""""""""
+
+The '``resume``' instruction resumes propagation of an existing
+(in-flight) exception whose unwinding was interrupted with a
+:ref:`landingpad <i_landingpad>` instruction.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ resume { i8*, i32 } %exn
+
+.. _i_catchswitch:
+
+'``catchswitch``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <resultval> = catchswitch within <parent> [ label <handler1>, label <handler2>, ... ] unwind to caller
+ <resultval> = catchswitch within <parent> [ label <handler1>, label <handler2>, ... ] unwind label <default>
+
+Overview:
+"""""""""
+
+The '``catchswitch``' instruction is used by `LLVM's exception handling system
+<ExceptionHandling.html#overview>`_ to describe the set of possible catch handlers
+that may be executed by the :ref:`EH personality routine <personalityfn>`.
+
+Arguments:
+""""""""""
+
+The ``parent`` argument is the token of the funclet that contains the
+``catchswitch`` instruction. If the ``catchswitch`` is not inside a funclet,
+this operand may be the token ``none``.
+
+The ``default`` argument is the label of another basic block beginning with
+either a ``cleanuppad`` or ``catchswitch`` instruction. This unwind destination
+must be a legal target with respect to the ``parent`` links, as described in
+the `exception handling documentation\ <ExceptionHandling.html#wineh-constraints>`_.
+
+The ``handlers`` are a nonempty list of successor blocks that each begin with a
+:ref:`catchpad <i_catchpad>` instruction.
+
+Semantics:
+""""""""""
+
+Executing this instruction transfers control to one of the successors in
+``handlers``, if appropriate, or continues to unwind via the unwind label if
+present.
+
+The ``catchswitch`` is both a terminator and a "pad" instruction, meaning that
+it must be both the first non-phi instruction and last instruction in the basic
+block. Therefore, it must be the only non-phi instruction in the block.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ dispatch1:
+ %cs1 = catchswitch within none [label %handler0, label %handler1] unwind to caller
+ dispatch2:
+ %cs2 = catchswitch within %parenthandler [label %handler0] unwind label %cleanup
+
+.. _i_catchret:
+
+'``catchret``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ catchret from <token> to label <normal>
+
+Overview:
+"""""""""
+
+The '``catchret``' instruction is a terminator instruction that has a
+single successor.
+
+
+Arguments:
+""""""""""
+
+The first argument to a '``catchret``' indicates which ``catchpad`` it
+exits. It must be a :ref:`catchpad <i_catchpad>`.
+The second argument to a '``catchret``' specifies where control will
+transfer to next.
+
+Semantics:
+""""""""""
+
+The '``catchret``' instruction ends an existing (in-flight) exception whose
+unwinding was interrupted with a :ref:`catchpad <i_catchpad>` instruction. The
+:ref:`personality function <personalityfn>` gets a chance to execute arbitrary
+code to, for example, destroy the active exception. Control then transfers to
+``normal``.
+
+The ``token`` argument must be a token produced by a ``catchpad`` instruction.
+If the specified ``catchpad`` is not the most-recently-entered not-yet-exited
+funclet pad (as described in the `EH documentation\ <ExceptionHandling.html#wineh-constraints>`_),
+the ``catchret``'s behavior is undefined.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ catchret from %catch label %continue
+
+.. _i_cleanupret:
+
+'``cleanupret``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ cleanupret from <value> unwind label <continue>
+ cleanupret from <value> unwind to caller
+
+Overview:
+"""""""""
+
+The '``cleanupret``' instruction is a terminator instruction that has
+an optional successor.
+
+
+Arguments:
+""""""""""
+
+The '``cleanupret``' instruction requires one argument, which indicates
+which ``cleanuppad`` it exits, and must be a :ref:`cleanuppad <i_cleanuppad>`.
+If the specified ``cleanuppad`` is not the most-recently-entered not-yet-exited
+funclet pad (as described in the `EH documentation\ <ExceptionHandling.html#wineh-constraints>`_),
+the ``cleanupret``'s behavior is undefined.
+
+The '``cleanupret``' instruction also has an optional successor, ``continue``,
+which must be the label of another basic block beginning with either a
+``cleanuppad`` or ``catchswitch`` instruction. This unwind destination must
+be a legal target with respect to the ``parent`` links, as described in the
+`exception handling documentation\ <ExceptionHandling.html#wineh-constraints>`_.
+
+Semantics:
+""""""""""
+
+The '``cleanupret``' instruction indicates to the
+:ref:`personality function <personalityfn>` that one
+:ref:`cleanuppad <i_cleanuppad>` it transferred control to has ended.
+It transfers control to ``continue`` or unwinds out of the function.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ cleanupret from %cleanup unwind to caller
+ cleanupret from %cleanup unwind label %continue
+
+.. _i_unreachable:
+
+'``unreachable``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ unreachable
+
+Overview:
+"""""""""
+
+The '``unreachable``' instruction has no defined semantics. This
+instruction is used to inform the optimizer that a particular portion of
+the code is not reachable. This can be used to indicate that the code
+after a no-return function cannot be reached, and other facts.
+
+Semantics:
+""""""""""
+
+The '``unreachable``' instruction has no defined semantics.
+
+.. _binaryops:
+
+Binary Operations
+-----------------
+
+Binary operators are used to do most of the computation in a program.
+They require two operands of the same type, execute an operation on
+them, and produce a single value. The operands might represent multiple
+data, as is the case with the :ref:`vector <t_vector>` data type. The
+result value has the same type as its operands.
+
+There are several different binary operators:
+
+.. _i_add:
+
+'``add``' Instruction
+^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = add <ty> <op1>, <op2> ; yields ty:result
+ <result> = add nuw <ty> <op1>, <op2> ; yields ty:result
+ <result> = add nsw <ty> <op1>, <op2> ; yields ty:result
+ <result> = add nuw nsw <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``add``' instruction returns the sum of its two operands.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``add``' instruction must be
+:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
+arguments must have identical types.
+
+Semantics:
+""""""""""
+
+The value produced is the integer sum of the two operands.
+
+If the sum has unsigned overflow, the result returned is the
+mathematical result modulo 2\ :sup:`n`\ , where n is the bit width of
+the result.
+
+Because LLVM integers use a two's complement representation, this
+instruction is appropriate for both signed and unsigned integers.
+
+``nuw`` and ``nsw`` stand for "No Unsigned Wrap" and "No Signed Wrap",
+respectively. If the ``nuw`` and/or ``nsw`` keywords are present, the
+result value of the ``add`` is a :ref:`poison value <poisonvalues>` if
+unsigned and/or signed overflow, respectively, occurs.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = add i32 4, %var ; yields i32:result = 4 + %var
+
+.. _i_fadd:
+
+'``fadd``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = fadd [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``fadd``' instruction returns the sum of its two operands.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``fadd``' instruction must be :ref:`floating
+point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
+Both arguments must have identical types.
+
+Semantics:
+""""""""""
+
+The value produced is the floating point sum of the two operands. This
+instruction can also take any number of :ref:`fast-math flags <fastmath>`,
+which are optimization hints to enable otherwise unsafe floating point
+optimizations:
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = fadd float 4.0, %var ; yields float:result = 4.0 + %var
+
+'``sub``' Instruction
+^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = sub <ty> <op1>, <op2> ; yields ty:result
+ <result> = sub nuw <ty> <op1>, <op2> ; yields ty:result
+ <result> = sub nsw <ty> <op1>, <op2> ; yields ty:result
+ <result> = sub nuw nsw <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``sub``' instruction returns the difference of its two operands.
+
+Note that the '``sub``' instruction is used to represent the '``neg``'
+instruction present in most other intermediate representations.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``sub``' instruction must be
+:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
+arguments must have identical types.
+
+Semantics:
+""""""""""
+
+The value produced is the integer difference of the two operands.
+
+If the difference has unsigned overflow, the result returned is the
+mathematical result modulo 2\ :sup:`n`\ , where n is the bit width of
+the result.
+
+Because LLVM integers use a two's complement representation, this
+instruction is appropriate for both signed and unsigned integers.
+
+``nuw`` and ``nsw`` stand for "No Unsigned Wrap" and "No Signed Wrap",
+respectively. If the ``nuw`` and/or ``nsw`` keywords are present, the
+result value of the ``sub`` is a :ref:`poison value <poisonvalues>` if
+unsigned and/or signed overflow, respectively, occurs.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = sub i32 4, %var ; yields i32:result = 4 - %var
+ <result> = sub i32 0, %val ; yields i32:result = -%var
+
+.. _i_fsub:
+
+'``fsub``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = fsub [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``fsub``' instruction returns the difference of its two operands.
+
+Note that the '``fsub``' instruction is used to represent the '``fneg``'
+instruction present in most other intermediate representations.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``fsub``' instruction must be :ref:`floating
+point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
+Both arguments must have identical types.
+
+Semantics:
+""""""""""
+
+The value produced is the floating point difference of the two operands.
+This instruction can also take any number of :ref:`fast-math
+flags <fastmath>`, which are optimization hints to enable otherwise
+unsafe floating point optimizations:
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = fsub float 4.0, %var ; yields float:result = 4.0 - %var
+ <result> = fsub float -0.0, %val ; yields float:result = -%var
+
+'``mul``' Instruction
+^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = mul <ty> <op1>, <op2> ; yields ty:result
+ <result> = mul nuw <ty> <op1>, <op2> ; yields ty:result
+ <result> = mul nsw <ty> <op1>, <op2> ; yields ty:result
+ <result> = mul nuw nsw <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``mul``' instruction returns the product of its two operands.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``mul``' instruction must be
+:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
+arguments must have identical types.
+
+Semantics:
+""""""""""
+
+The value produced is the integer product of the two operands.
+
+If the result of the multiplication has unsigned overflow, the result
+returned is the mathematical result modulo 2\ :sup:`n`\ , where n is the
+bit width of the result.
+
+Because LLVM integers use a two's complement representation, and the
+result is the same width as the operands, this instruction returns the
+correct result for both signed and unsigned integers. If a full product
+(e.g. ``i32`` * ``i32`` -> ``i64``) is needed, the operands should be
+sign-extended or zero-extended as appropriate to the width of the full
+product.
+
+``nuw`` and ``nsw`` stand for "No Unsigned Wrap" and "No Signed Wrap",
+respectively. If the ``nuw`` and/or ``nsw`` keywords are present, the
+result value of the ``mul`` is a :ref:`poison value <poisonvalues>` if
+unsigned and/or signed overflow, respectively, occurs.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = mul i32 4, %var ; yields i32:result = 4 * %var
+
+.. _i_fmul:
+
+'``fmul``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = fmul [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``fmul``' instruction returns the product of its two operands.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``fmul``' instruction must be :ref:`floating
+point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
+Both arguments must have identical types.
+
+Semantics:
+""""""""""
+
+The value produced is the floating point product of the two operands.
+This instruction can also take any number of :ref:`fast-math
+flags <fastmath>`, which are optimization hints to enable otherwise
+unsafe floating point optimizations:
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = fmul float 4.0, %var ; yields float:result = 4.0 * %var
+
+'``udiv``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = udiv <ty> <op1>, <op2> ; yields ty:result
+ <result> = udiv exact <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``udiv``' instruction returns the quotient of its two operands.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``udiv``' instruction must be
+:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
+arguments must have identical types.
+
+Semantics:
+""""""""""
+
+The value produced is the unsigned integer quotient of the two operands.
+
+Note that unsigned integer division and signed integer division are
+distinct operations; for signed integer division, use '``sdiv``'.
+
+Division by zero is undefined behavior. For vectors, if any element
+of the divisor is zero, the operation has undefined behavior.
+
+
+If the ``exact`` keyword is present, the result value of the ``udiv`` is
+a :ref:`poison value <poisonvalues>` if %op1 is not a multiple of %op2 (as
+such, "((a udiv exact b) mul b) == a").
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = udiv i32 4, %var ; yields i32:result = 4 / %var
+
+'``sdiv``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = sdiv <ty> <op1>, <op2> ; yields ty:result
+ <result> = sdiv exact <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``sdiv``' instruction returns the quotient of its two operands.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``sdiv``' instruction must be
+:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
+arguments must have identical types.
+
+Semantics:
+""""""""""
+
+The value produced is the signed integer quotient of the two operands
+rounded towards zero.
+
+Note that signed integer division and unsigned integer division are
+distinct operations; for unsigned integer division, use '``udiv``'.
+
+Division by zero is undefined behavior. For vectors, if any element
+of the divisor is zero, the operation has undefined behavior.
+Overflow also leads to undefined behavior; this is a rare case, but can
+occur, for example, by doing a 32-bit division of -2147483648 by -1.
+
+If the ``exact`` keyword is present, the result value of the ``sdiv`` is
+a :ref:`poison value <poisonvalues>` if the result would be rounded.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = sdiv i32 4, %var ; yields i32:result = 4 / %var
+
+.. _i_fdiv:
+
+'``fdiv``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = fdiv [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``fdiv``' instruction returns the quotient of its two operands.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``fdiv``' instruction must be :ref:`floating
+point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
+Both arguments must have identical types.
+
+Semantics:
+""""""""""
+
+The value produced is the floating point quotient of the two operands.
+This instruction can also take any number of :ref:`fast-math
+flags <fastmath>`, which are optimization hints to enable otherwise
+unsafe floating point optimizations:
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = fdiv float 4.0, %var ; yields float:result = 4.0 / %var
+
+'``urem``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = urem <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``urem``' instruction returns the remainder from the unsigned
+division of its two arguments.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``urem``' instruction must be
+:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
+arguments must have identical types.
+
+Semantics:
+""""""""""
+
+This instruction returns the unsigned integer *remainder* of a division.
+This instruction always performs an unsigned division to get the
+remainder.
+
+Note that unsigned integer remainder and signed integer remainder are
+distinct operations; for signed integer remainder, use '``srem``'.
+
+Taking the remainder of a division by zero is undefined behavior.
+For vectors, if any element of the divisor is zero, the operation has
+undefined behavior.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = urem i32 4, %var ; yields i32:result = 4 % %var
+
+'``srem``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = srem <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``srem``' instruction returns the remainder from the signed
+division of its two operands. This instruction can also take
+:ref:`vector <t_vector>` versions of the values in which case the elements
+must be integers.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``srem``' instruction must be
+:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
+arguments must have identical types.
+
+Semantics:
+""""""""""
+
+This instruction returns the *remainder* of a division (where the result
+is either zero or has the same sign as the dividend, ``op1``), not the
+*modulo* operator (where the result is either zero or has the same sign
+as the divisor, ``op2``) of a value. For more information about the
+difference, see `The Math
+Forum <http://mathforum.org/dr.math/problems/anne.4.28.99.html>`_. For a
+table of how this is implemented in various languages, please see
+`Wikipedia: modulo
+operation <http://en.wikipedia.org/wiki/Modulo_operation>`_.
+
+Note that signed integer remainder and unsigned integer remainder are
+distinct operations; for unsigned integer remainder, use '``urem``'.
+
+Taking the remainder of a division by zero is undefined behavior.
+For vectors, if any element of the divisor is zero, the operation has
+undefined behavior.
+Overflow also leads to undefined behavior; this is a rare case, but can
+occur, for example, by taking the remainder of a 32-bit division of
+-2147483648 by -1. (The remainder doesn't actually overflow, but this
+rule lets srem be implemented using instructions that return both the
+result of the division and the remainder.)
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = srem i32 4, %var ; yields i32:result = 4 % %var
+
+.. _i_frem:
+
+'``frem``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = frem [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``frem``' instruction returns the remainder from the division of
+its two operands.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``frem``' instruction must be :ref:`floating
+point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
+Both arguments must have identical types.
+
+Semantics:
+""""""""""
+
+This instruction returns the *remainder* of a division. The remainder
+has the same sign as the dividend. This instruction can also take any
+number of :ref:`fast-math flags <fastmath>`, which are optimization hints
+to enable otherwise unsafe floating point optimizations:
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = frem float 4.0, %var ; yields float:result = 4.0 % %var
+
+.. _bitwiseops:
+
+Bitwise Binary Operations
+-------------------------
+
+Bitwise binary operators are used to do various forms of bit-twiddling
+in a program. They are generally very efficient instructions and can
+commonly be strength reduced from other instructions. They require two
+operands of the same type, execute an operation on them, and produce a
+single value. The resulting value is the same type as its operands.
+
+'``shl``' Instruction
+^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = shl <ty> <op1>, <op2> ; yields ty:result
+ <result> = shl nuw <ty> <op1>, <op2> ; yields ty:result
+ <result> = shl nsw <ty> <op1>, <op2> ; yields ty:result
+ <result> = shl nuw nsw <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``shl``' instruction returns the first operand shifted to the left
+a specified number of bits.
+
+Arguments:
+""""""""""
+
+Both arguments to the '``shl``' instruction must be the same
+:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer type.
+'``op2``' is treated as an unsigned value.
+
+Semantics:
+""""""""""
+
+The value produced is ``op1`` \* 2\ :sup:`op2` mod 2\ :sup:`n`,
+where ``n`` is the width of the result. If ``op2`` is (statically or
+dynamically) equal to or larger than the number of bits in
+``op1``, this instruction returns a :ref:`poison value <poisonvalues>`.
+If the arguments are vectors, each vector element of ``op1`` is shifted
+by the corresponding shift amount in ``op2``.
+
+If the ``nuw`` keyword is present, then the shift produces a poison
+value if it shifts out any non-zero bits.
+If the ``nsw`` keyword is present, then the shift produces a poison
+value it shifts out any bits that disagree with the resultant sign bit.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = shl i32 4, %var ; yields i32: 4 << %var
+ <result> = shl i32 4, 2 ; yields i32: 16
+ <result> = shl i32 1, 10 ; yields i32: 1024
+ <result> = shl i32 1, 32 ; undefined
+ <result> = shl <2 x i32> < i32 1, i32 1>, < i32 1, i32 2> ; yields: result=<2 x i32> < i32 2, i32 4>
+
+'``lshr``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = lshr <ty> <op1>, <op2> ; yields ty:result
+ <result> = lshr exact <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``lshr``' instruction (logical shift right) returns the first
+operand shifted to the right a specified number of bits with zero fill.
+
+Arguments:
+""""""""""
+
+Both arguments to the '``lshr``' instruction must be the same
+:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer type.
+'``op2``' is treated as an unsigned value.
+
+Semantics:
+""""""""""
+
+This instruction always performs a logical shift right operation. The
+most significant bits of the result will be filled with zero bits after
+the shift. If ``op2`` is (statically or dynamically) equal to or larger
+than the number of bits in ``op1``, this instruction returns a :ref:`poison
+value <poisonvalues>`. If the arguments are vectors, each vector element
+of ``op1`` is shifted by the corresponding shift amount in ``op2``.
+
+If the ``exact`` keyword is present, the result value of the ``lshr`` is
+a poison value if any of the bits shifted out are non-zero.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = lshr i32 4, 1 ; yields i32:result = 2
+ <result> = lshr i32 4, 2 ; yields i32:result = 1
+ <result> = lshr i8 4, 3 ; yields i8:result = 0
+ <result> = lshr i8 -2, 1 ; yields i8:result = 0x7F
+ <result> = lshr i32 1, 32 ; undefined
+ <result> = lshr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 2> ; yields: result=<2 x i32> < i32 0x7FFFFFFF, i32 1>
+
+'``ashr``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = ashr <ty> <op1>, <op2> ; yields ty:result
+ <result> = ashr exact <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``ashr``' instruction (arithmetic shift right) returns the first
+operand shifted to the right a specified number of bits with sign
+extension.
+
+Arguments:
+""""""""""
+
+Both arguments to the '``ashr``' instruction must be the same
+:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer type.
+'``op2``' is treated as an unsigned value.
+
+Semantics:
+""""""""""
+
+This instruction always performs an arithmetic shift right operation,
+The most significant bits of the result will be filled with the sign bit
+of ``op1``. If ``op2`` is (statically or dynamically) equal to or larger
+than the number of bits in ``op1``, this instruction returns a :ref:`poison
+value <poisonvalues>`. If the arguments are vectors, each vector element
+of ``op1`` is shifted by the corresponding shift amount in ``op2``.
+
+If the ``exact`` keyword is present, the result value of the ``ashr`` is
+a poison value if any of the bits shifted out are non-zero.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = ashr i32 4, 1 ; yields i32:result = 2
+ <result> = ashr i32 4, 2 ; yields i32:result = 1
+ <result> = ashr i8 4, 3 ; yields i8:result = 0
+ <result> = ashr i8 -2, 1 ; yields i8:result = -1
+ <result> = ashr i32 1, 32 ; undefined
+ <result> = ashr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 3> ; yields: result=<2 x i32> < i32 -1, i32 0>
+
+'``and``' Instruction
+^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = and <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``and``' instruction returns the bitwise logical and of its two
+operands.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``and``' instruction must be
+:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
+arguments must have identical types.
+
+Semantics:
+""""""""""
+
+The truth table used for the '``and``' instruction is:
+
++-----+-----+-----+
+| In0 | In1 | Out |
++-----+-----+-----+
+| 0 | 0 | 0 |
++-----+-----+-----+
+| 0 | 1 | 0 |
++-----+-----+-----+
+| 1 | 0 | 0 |
++-----+-----+-----+
+| 1 | 1 | 1 |
++-----+-----+-----+
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = and i32 4, %var ; yields i32:result = 4 & %var
+ <result> = and i32 15, 40 ; yields i32:result = 8
+ <result> = and i32 4, 8 ; yields i32:result = 0
+
+'``or``' Instruction
+^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = or <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``or``' instruction returns the bitwise logical inclusive or of its
+two operands.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``or``' instruction must be
+:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
+arguments must have identical types.
+
+Semantics:
+""""""""""
+
+The truth table used for the '``or``' instruction is:
+
++-----+-----+-----+
+| In0 | In1 | Out |
++-----+-----+-----+
+| 0 | 0 | 0 |
++-----+-----+-----+
+| 0 | 1 | 1 |
++-----+-----+-----+
+| 1 | 0 | 1 |
++-----+-----+-----+
+| 1 | 1 | 1 |
++-----+-----+-----+
+
+Example:
+""""""""
+
+::
+
+ <result> = or i32 4, %var ; yields i32:result = 4 | %var
+ <result> = or i32 15, 40 ; yields i32:result = 47
+ <result> = or i32 4, 8 ; yields i32:result = 12
+
+'``xor``' Instruction
+^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = xor <ty> <op1>, <op2> ; yields ty:result
+
+Overview:
+"""""""""
+
+The '``xor``' instruction returns the bitwise logical exclusive or of
+its two operands. The ``xor`` is used to implement the "one's
+complement" operation, which is the "~" operator in C.
+
+Arguments:
+""""""""""
+
+The two arguments to the '``xor``' instruction must be
+:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
+arguments must have identical types.
+
+Semantics:
+""""""""""
+
+The truth table used for the '``xor``' instruction is:
+
++-----+-----+-----+
+| In0 | In1 | Out |
++-----+-----+-----+
+| 0 | 0 | 0 |
++-----+-----+-----+
+| 0 | 1 | 1 |
++-----+-----+-----+
+| 1 | 0 | 1 |
++-----+-----+-----+
+| 1 | 1 | 0 |
++-----+-----+-----+
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = xor i32 4, %var ; yields i32:result = 4 ^ %var
+ <result> = xor i32 15, 40 ; yields i32:result = 39
+ <result> = xor i32 4, 8 ; yields i32:result = 12
+ <result> = xor i32 %V, -1 ; yields i32:result = ~%V
+
+Vector Operations
+-----------------
+
+LLVM supports several instructions to represent vector operations in a
+target-independent manner. These instructions cover the element-access
+and vector-specific operations needed to process vectors effectively.
+While LLVM does directly support these vector operations, many
+sophisticated algorithms will want to use target-specific intrinsics to
+take full advantage of a specific target.
+
+.. _i_extractelement:
+
+'``extractelement``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = extractelement <n x <ty>> <val>, <ty2> <idx> ; yields <ty>
+
+Overview:
+"""""""""
+
+The '``extractelement``' instruction extracts a single scalar element
+from a vector at a specified index.
+
+Arguments:
+""""""""""
+
+The first operand of an '``extractelement``' instruction is a value of
+:ref:`vector <t_vector>` type. The second operand is an index indicating
+the position from which to extract the element. The index may be a
+variable of any integer type.
+
+Semantics:
+""""""""""
+
+The result is a scalar of the same type as the element type of ``val``.
+Its value is the value at position ``idx`` of ``val``. If ``idx``
+exceeds the length of ``val``, the results are undefined.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = extractelement <4 x i32> %vec, i32 0 ; yields i32
+
+.. _i_insertelement:
+
+'``insertelement``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = insertelement <n x <ty>> <val>, <ty> <elt>, <ty2> <idx> ; yields <n x <ty>>
+
+Overview:
+"""""""""
+
+The '``insertelement``' instruction inserts a scalar element into a
+vector at a specified index.
+
+Arguments:
+""""""""""
+
+The first operand of an '``insertelement``' instruction is a value of
+:ref:`vector <t_vector>` type. The second operand is a scalar value whose
+type must equal the element type of the first operand. The third operand
+is an index indicating the position at which to insert the value. The
+index may be a variable of any integer type.
+
+Semantics:
+""""""""""
+
+The result is a vector of the same type as ``val``. Its element values
+are those of ``val`` except at position ``idx``, where it gets the value
+``elt``. If ``idx`` exceeds the length of ``val``, the results are
+undefined.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = insertelement <4 x i32> %vec, i32 1, i32 0 ; yields <4 x i32>
+
+.. _i_shufflevector:
+
+'``shufflevector``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = shufflevector <n x <ty>> <v1>, <n x <ty>> <v2>, <m x i32> <mask> ; yields <m x <ty>>
+
+Overview:
+"""""""""
+
+The '``shufflevector``' instruction constructs a permutation of elements
+from two input vectors, returning a vector with the same element type as
+the input and length that is the same as the shuffle mask.
+
+Arguments:
+""""""""""
+
+The first two operands of a '``shufflevector``' instruction are vectors
+with the same type. The third argument is a shuffle mask whose element
+type is always 'i32'. The result of the instruction is a vector whose
+length is the same as the shuffle mask and whose element type is the
+same as the element type of the first two operands.
+
+The shuffle mask operand is required to be a constant vector with either
+constant integer or undef values.
+
+Semantics:
+""""""""""
+
+The elements of the two input vectors are numbered from left to right
+across both of the vectors. The shuffle mask operand specifies, for each
+element of the result vector, which element of the two input vectors the
+result element gets. If the shuffle mask is undef, the result vector is
+undef. If any element of the mask operand is undef, that element of the
+result is undef. If the shuffle mask selects an undef element from one
+of the input vectors, the resulting element is undef.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = shufflevector <4 x i32> %v1, <4 x i32> %v2,
+ <4 x i32> <i32 0, i32 4, i32 1, i32 5> ; yields <4 x i32>
+ <result> = shufflevector <4 x i32> %v1, <4 x i32> undef,
+ <4 x i32> <i32 0, i32 1, i32 2, i32 3> ; yields <4 x i32> - Identity shuffle.
+ <result> = shufflevector <8 x i32> %v1, <8 x i32> undef,
+ <4 x i32> <i32 0, i32 1, i32 2, i32 3> ; yields <4 x i32>
+ <result> = shufflevector <4 x i32> %v1, <4 x i32> %v2,
+ <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7 > ; yields <8 x i32>
+
+Aggregate Operations
+--------------------
+
+LLVM supports several instructions for working with
+:ref:`aggregate <t_aggregate>` values.
+
+.. _i_extractvalue:
+
+'``extractvalue``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = extractvalue <aggregate type> <val>, <idx>{, <idx>}*
+
+Overview:
+"""""""""
+
+The '``extractvalue``' instruction extracts the value of a member field
+from an :ref:`aggregate <t_aggregate>` value.
+
+Arguments:
+""""""""""
+
+The first operand of an '``extractvalue``' instruction is a value of
+:ref:`struct <t_struct>` or :ref:`array <t_array>` type. The other operands are
+constant indices to specify which value to extract in a similar manner
+as indices in a '``getelementptr``' instruction.
+
+The major differences to ``getelementptr`` indexing are:
+
+- Since the value being indexed is not a pointer, the first index is
+ omitted and assumed to be zero.
+- At least one index must be specified.
+- Not only struct indices but also array indices must be in bounds.
+
+Semantics:
+""""""""""
+
+The result is the value at the position in the aggregate specified by
+the index operands.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = extractvalue {i32, float} %agg, 0 ; yields i32
+
+.. _i_insertvalue:
+
+'``insertvalue``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = insertvalue <aggregate type> <val>, <ty> <elt>, <idx>{, <idx>}* ; yields <aggregate type>
+
+Overview:
+"""""""""
+
+The '``insertvalue``' instruction inserts a value into a member field in
+an :ref:`aggregate <t_aggregate>` value.
+
+Arguments:
+""""""""""
+
+The first operand of an '``insertvalue``' instruction is a value of
+:ref:`struct <t_struct>` or :ref:`array <t_array>` type. The second operand is
+a first-class value to insert. The following operands are constant
+indices indicating the position at which to insert the value in a
+similar manner as indices in a '``extractvalue``' instruction. The value
+to insert must have the same type as the value identified by the
+indices.
+
+Semantics:
+""""""""""
+
+The result is an aggregate of the same type as ``val``. Its value is
+that of ``val`` except that the value at the position specified by the
+indices is that of ``elt``.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %agg1 = insertvalue {i32, float} undef, i32 1, 0 ; yields {i32 1, float undef}
+ %agg2 = insertvalue {i32, float} %agg1, float %val, 1 ; yields {i32 1, float %val}
+ %agg3 = insertvalue {i32, {float}} undef, float %val, 1, 0 ; yields {i32 undef, {float %val}}
+
+.. _memoryops:
+
+Memory Access and Addressing Operations
+---------------------------------------
+
+A key design point of an SSA-based representation is how it represents
+memory. In LLVM, no memory locations are in SSA form, which makes things
+very simple. This section describes how to read, write, and allocate
+memory in LLVM.
+
+.. _i_alloca:
+
+'``alloca``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = alloca [inalloca] <type> [, <ty> <NumElements>] [, align <alignment>] [, addrspace(<num>)] ; yields type addrspace(num)*:result
+
+Overview:
+"""""""""
+
+The '``alloca``' instruction allocates memory on the stack frame of the
+currently executing function, to be automatically released when this
+function returns to its caller. The object is always allocated in the
+address space for allocas indicated in the datalayout.
+
+Arguments:
+""""""""""
+
+The '``alloca``' instruction allocates ``sizeof(<type>)*NumElements``
+bytes of memory on the runtime stack, returning a pointer of the
+appropriate type to the program. If "NumElements" is specified, it is
+the number of elements allocated, otherwise "NumElements" is defaulted
+to be one. If a constant alignment is specified, the value result of the
+allocation is guaranteed to be aligned to at least that boundary. The
+alignment may not be greater than ``1 << 29``. If not specified, or if
+zero, the target can choose to align the allocation on any convenient
+boundary compatible with the type.
+
+'``type``' may be any sized type.
+
+Semantics:
+""""""""""
+
+Memory is allocated; a pointer is returned. The operation is undefined
+if there is insufficient stack space for the allocation. '``alloca``'d
+memory is automatically released when the function returns. The
+'``alloca``' instruction is commonly used to represent automatic
+variables that must have an address available. When the function returns
+(either with the ``ret`` or ``resume`` instructions), the memory is
+reclaimed. Allocating zero bytes is legal, but the result is undefined.
+The order in which memory is allocated (ie., which way the stack grows)
+is not specified.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %ptr = alloca i32 ; yields i32*:ptr
+ %ptr = alloca i32, i32 4 ; yields i32*:ptr
+ %ptr = alloca i32, i32 4, align 1024 ; yields i32*:ptr
+ %ptr = alloca i32, align 1024 ; yields i32*:ptr
+
+.. _i_load:
+
+'``load``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = load [volatile] <ty>, <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>][, !invariant.load !<index>][, !invariant.group !<index>][, !nonnull !<index>][, !dereferenceable !<deref_bytes_node>][, !dereferenceable_or_null !<deref_bytes_node>][, !align !<align_node>]
+ <result> = load atomic [volatile] <ty>, <ty>* <pointer> [syncscope("<target-scope>")] <ordering>, align <alignment> [, !invariant.group !<index>]
+ !<index> = !{ i32 1 }
+ !<deref_bytes_node> = !{i64 <dereferenceable_bytes>}
+ !<align_node> = !{ i64 <value_alignment> }
+
+Overview:
+"""""""""
+
+The '``load``' instruction is used to read from memory.
+
+Arguments:
+""""""""""
+
+The argument to the ``load`` instruction specifies the memory address from which
+to load. The type specified must be a :ref:`first class <t_firstclass>` type of
+known size (i.e. not containing an :ref:`opaque structural type <t_opaque>`). If
+the ``load`` is marked as ``volatile``, then the optimizer is not allowed to
+modify the number or order of execution of this ``load`` with other
+:ref:`volatile operations <volatile>`.
+
+If the ``load`` is marked as ``atomic``, it takes an extra :ref:`ordering
+<ordering>` and optional ``syncscope("<target-scope>")`` argument. The
+``release`` and ``acq_rel`` orderings are not valid on ``load`` instructions.
+Atomic loads produce :ref:`defined <memmodel>` results when they may see
+multiple atomic stores. The type of the pointee must be an integer, pointer, or
+floating-point type whose bit width is a power of two greater than or equal to
+eight and less than or equal to a target-specific size limit. ``align`` must be
+explicitly specified on atomic loads, and the load has undefined behavior if the
+alignment is not set to a value which is at least the size in bytes of the
+pointee. ``!nontemporal`` does not have any defined semantics for atomic loads.
+
+The optional constant ``align`` argument specifies the alignment of the
+operation (that is, the alignment of the memory address). A value of 0
+or an omitted ``align`` argument means that the operation has the ABI
+alignment for the target. It is the responsibility of the code emitter
+to ensure that the alignment information is correct. Overestimating the
+alignment results in undefined behavior. Underestimating the alignment
+may produce less efficient code. An alignment of 1 is always safe. The
+maximum possible alignment is ``1 << 29``. An alignment value higher
+than the size of the loaded type implies memory up to the alignment
+value bytes can be safely loaded without trapping in the default
+address space. Access of the high bytes can interfere with debugging
+tools, so should not be accessed if the function has the
+``sanitize_thread`` or ``sanitize_address`` attributes.
+
+The optional ``!nontemporal`` metadata must reference a single
+metadata name ``<index>`` corresponding to a metadata node with one
+``i32`` entry of value 1. The existence of the ``!nontemporal``
+metadata on the instruction tells the optimizer and code generator
+that this load is not expected to be reused in the cache. The code
+generator may select special instructions to save cache bandwidth, such
+as the ``MOVNT`` instruction on x86.
+
+The optional ``!invariant.load`` metadata must reference a single
+metadata name ``<index>`` corresponding to a metadata node with no
+entries. If a load instruction tagged with the ``!invariant.load``
+metadata is executed, the optimizer may assume the memory location
+referenced by the load contains the same value at all points in the
+program where the memory location is known to be dereferenceable.
+
+The optional ``!invariant.group`` metadata must reference a single metadata name
+ ``<index>`` corresponding to a metadata node. See ``invariant.group`` metadata.
+
+The optional ``!nonnull`` metadata must reference a single
+metadata name ``<index>`` corresponding to a metadata node with no
+entries. The existence of the ``!nonnull`` metadata on the
+instruction tells the optimizer that the value loaded is known to
+never be null. This is analogous to the ``nonnull`` attribute
+on parameters and return values. This metadata can only be applied
+to loads of a pointer type.
+
+The optional ``!dereferenceable`` metadata must reference a single metadata
+name ``<deref_bytes_node>`` corresponding to a metadata node with one ``i64``
+entry. The existence of the ``!dereferenceable`` metadata on the instruction
+tells the optimizer that the value loaded is known to be dereferenceable.
+The number of bytes known to be dereferenceable is specified by the integer
+value in the metadata node. This is analogous to the ''dereferenceable''
+attribute on parameters and return values. This metadata can only be applied
+to loads of a pointer type.
+
+The optional ``!dereferenceable_or_null`` metadata must reference a single
+metadata name ``<deref_bytes_node>`` corresponding to a metadata node with one
+``i64`` entry. The existence of the ``!dereferenceable_or_null`` metadata on the
+instruction tells the optimizer that the value loaded is known to be either
+dereferenceable or null.
+The number of bytes known to be dereferenceable is specified by the integer
+value in the metadata node. This is analogous to the ''dereferenceable_or_null''
+attribute on parameters and return values. This metadata can only be applied
+to loads of a pointer type.
+
+The optional ``!align`` metadata must reference a single metadata name
+``<align_node>`` corresponding to a metadata node with one ``i64`` entry.
+The existence of the ``!align`` metadata on the instruction tells the
+optimizer that the value loaded is known to be aligned to a boundary specified
+by the integer value in the metadata node. The alignment must be a power of 2.
+This is analogous to the ''align'' attribute on parameters and return values.
+This metadata can only be applied to loads of a pointer type.
+
+Semantics:
+""""""""""
+
+The location of memory pointed to is loaded. If the value being loaded
+is of scalar type then the number of bytes read does not exceed the
+minimum number of bytes needed to hold all bits of the type. For
+example, loading an ``i24`` reads at most three bytes. When loading a
+value of a type like ``i20`` with a size that is not an integral number
+of bytes, the result is undefined if the value was not originally
+written using a store of the same type.
+
+Examples:
+"""""""""
+
+.. code-block:: llvm
+
+ %ptr = alloca i32 ; yields i32*:ptr
+ store i32 3, i32* %ptr ; yields void
+ %val = load i32, i32* %ptr ; yields i32:val = i32 3
+
+.. _i_store:
+
+'``store``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ store [volatile] <ty> <value>, <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>][, !invariant.group !<index>] ; yields void
+ store atomic [volatile] <ty> <value>, <ty>* <pointer> [syncscope("<target-scope>")] <ordering>, align <alignment> [, !invariant.group !<index>] ; yields void
+
+Overview:
+"""""""""
+
+The '``store``' instruction is used to write to memory.
+
+Arguments:
+""""""""""
+
+There are two arguments to the ``store`` instruction: a value to store and an
+address at which to store it. The type of the ``<pointer>`` operand must be a
+pointer to the :ref:`first class <t_firstclass>` type of the ``<value>``
+operand. If the ``store`` is marked as ``volatile``, then the optimizer is not
+allowed to modify the number or order of execution of this ``store`` with other
+:ref:`volatile operations <volatile>`. Only values of :ref:`first class
+<t_firstclass>` types of known size (i.e. not containing an :ref:`opaque
+structural type <t_opaque>`) can be stored.
+
+If the ``store`` is marked as ``atomic``, it takes an extra :ref:`ordering
+<ordering>` and optional ``syncscope("<target-scope>")`` argument. The
+``acquire`` and ``acq_rel`` orderings aren't valid on ``store`` instructions.
+Atomic loads produce :ref:`defined <memmodel>` results when they may see
+multiple atomic stores. The type of the pointee must be an integer, pointer, or
+floating-point type whose bit width is a power of two greater than or equal to
+eight and less than or equal to a target-specific size limit. ``align`` must be
+explicitly specified on atomic stores, and the store has undefined behavior if
+the alignment is not set to a value which is at least the size in bytes of the
+pointee. ``!nontemporal`` does not have any defined semantics for atomic stores.
+
+The optional constant ``align`` argument specifies the alignment of the
+operation (that is, the alignment of the memory address). A value of 0
+or an omitted ``align`` argument means that the operation has the ABI
+alignment for the target. It is the responsibility of the code emitter
+to ensure that the alignment information is correct. Overestimating the
+alignment results in undefined behavior. Underestimating the
+alignment may produce less efficient code. An alignment of 1 is always
+safe. The maximum possible alignment is ``1 << 29``. An alignment
+value higher than the size of the stored type implies memory up to the
+alignment value bytes can be stored to without trapping in the default
+address space. Storing to the higher bytes however may result in data
+races if another thread can access the same address. Introducing a
+data race is not allowed. Storing to the extra bytes is not allowed
+even in situations where a data race is known to not exist if the
+function has the ``sanitize_address`` attribute.
+
+The optional ``!nontemporal`` metadata must reference a single metadata
+name ``<index>`` corresponding to a metadata node with one ``i32`` entry of
+value 1. The existence of the ``!nontemporal`` metadata on the instruction
+tells the optimizer and code generator that this load is not expected to
+be reused in the cache. The code generator may select special
+instructions to save cache bandwidth, such as the ``MOVNT`` instruction on
+x86.
+
+The optional ``!invariant.group`` metadata must reference a
+single metadata name ``<index>``. See ``invariant.group`` metadata.
+
+Semantics:
+""""""""""
+
+The contents of memory are updated to contain ``<value>`` at the
+location specified by the ``<pointer>`` operand. If ``<value>`` is
+of scalar type then the number of bytes written does not exceed the
+minimum number of bytes needed to hold all bits of the type. For
+example, storing an ``i24`` writes at most three bytes. When writing a
+value of a type like ``i20`` with a size that is not an integral number
+of bytes, it is unspecified what happens to the extra bits that do not
+belong to the type, but they will typically be overwritten.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %ptr = alloca i32 ; yields i32*:ptr
+ store i32 3, i32* %ptr ; yields void
+ %val = load i32, i32* %ptr ; yields i32:val = i32 3
+
+.. _i_fence:
+
+'``fence``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ fence [syncscope("<target-scope>")] <ordering> ; yields void
+
+Overview:
+"""""""""
+
+The '``fence``' instruction is used to introduce happens-before edges
+between operations.
+
+Arguments:
+""""""""""
+
+'``fence``' instructions take an :ref:`ordering <ordering>` argument which
+defines what *synchronizes-with* edges they add. They can only be given
+``acquire``, ``release``, ``acq_rel``, and ``seq_cst`` orderings.
+
+Semantics:
+""""""""""
+
+A fence A which has (at least) ``release`` ordering semantics
+*synchronizes with* a fence B with (at least) ``acquire`` ordering
+semantics if and only if there exist atomic operations X and Y, both
+operating on some atomic object M, such that A is sequenced before X, X
+modifies M (either directly or through some side effect of a sequence
+headed by X), Y is sequenced before B, and Y observes M. This provides a
+*happens-before* dependency between A and B. Rather than an explicit
+``fence``, one (but not both) of the atomic operations X or Y might
+provide a ``release`` or ``acquire`` (resp.) ordering constraint and
+still *synchronize-with* the explicit ``fence`` and establish the
+*happens-before* edge.
+
+A ``fence`` which has ``seq_cst`` ordering, in addition to having both
+``acquire`` and ``release`` semantics specified above, participates in
+the global program order of other ``seq_cst`` operations and/or fences.
+
+A ``fence`` instruction can also take an optional
+":ref:`syncscope <syncscope>`" argument.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ fence acquire ; yields void
+ fence syncscope("singlethread") seq_cst ; yields void
+ fence syncscope("agent") seq_cst ; yields void
+
+.. _i_cmpxchg:
+
+'``cmpxchg``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ cmpxchg [weak] [volatile] <ty>* <pointer>, <ty> <cmp>, <ty> <new> [syncscope("<target-scope>")] <success ordering> <failure ordering> ; yields { ty, i1 }
+
+Overview:
+"""""""""
+
+The '``cmpxchg``' instruction is used to atomically modify memory. It
+loads a value in memory and compares it to a given value. If they are
+equal, it tries to store a new value into the memory.
+
+Arguments:
+""""""""""
+
+There are three arguments to the '``cmpxchg``' instruction: an address
+to operate on, a value to compare to the value currently be at that
+address, and a new value to place at that address if the compared values
+are equal. The type of '<cmp>' must be an integer or pointer type whose
+bit width is a power of two greater than or equal to eight and less
+than or equal to a target-specific size limit. '<cmp>' and '<new>' must
+have the same type, and the type of '<pointer>' must be a pointer to
+that type. If the ``cmpxchg`` is marked as ``volatile``, then the
+optimizer is not allowed to modify the number or order of execution of
+this ``cmpxchg`` with other :ref:`volatile operations <volatile>`.
+
+The success and failure :ref:`ordering <ordering>` arguments specify how this
+``cmpxchg`` synchronizes with other atomic operations. Both ordering parameters
+must be at least ``monotonic``, the ordering constraint on failure must be no
+stronger than that on success, and the failure ordering cannot be either
+``release`` or ``acq_rel``.
+
+A ``cmpxchg`` instruction can also take an optional
+":ref:`syncscope <syncscope>`" argument.
+
+The pointer passed into cmpxchg must have alignment greater than or
+equal to the size in memory of the operand.
+
+Semantics:
+""""""""""
+
+The contents of memory at the location specified by the '``<pointer>``' operand
+is read and compared to '``<cmp>``'; if the read value is the equal, the
+'``<new>``' is written. The original value at the location is returned, together
+with a flag indicating success (true) or failure (false).
+
+If the cmpxchg operation is marked as ``weak`` then a spurious failure is
+permitted: the operation may not write ``<new>`` even if the comparison
+matched.
+
+If the cmpxchg operation is strong (the default), the i1 value is 1 if and only
+if the value loaded equals ``cmp``.
+
+A successful ``cmpxchg`` is a read-modify-write instruction for the purpose of
+identifying release sequences. A failed ``cmpxchg`` is equivalent to an atomic
+load with an ordering parameter determined the second ordering parameter.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ entry:
+ %orig = load atomic i32, i32* %ptr unordered, align 4 ; yields i32
+ br label %loop
+
+ loop:
+ %cmp = phi i32 [ %orig, %entry ], [%value_loaded, %loop]
+ %squared = mul i32 %cmp, %cmp
+ %val_success = cmpxchg i32* %ptr, i32 %cmp, i32 %squared acq_rel monotonic ; yields { i32, i1 }
+ %value_loaded = extractvalue { i32, i1 } %val_success, 0
+ %success = extractvalue { i32, i1 } %val_success, 1
+ br i1 %success, label %done, label %loop
+
+ done:
+ ...
+
+.. _i_atomicrmw:
+
+'``atomicrmw``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ atomicrmw [volatile] <operation> <ty>* <pointer>, <ty> <value> [syncscope("<target-scope>")] <ordering> ; yields ty
+
+Overview:
+"""""""""
+
+The '``atomicrmw``' instruction is used to atomically modify memory.
+
+Arguments:
+""""""""""
+
+There are three arguments to the '``atomicrmw``' instruction: an
+operation to apply, an address whose value to modify, an argument to the
+operation. The operation must be one of the following keywords:
+
+- xchg
+- add
+- sub
+- and
+- nand
+- or
+- xor
+- max
+- min
+- umax
+- umin
+
+The type of '<value>' must be an integer type whose bit width is a power
+of two greater than or equal to eight and less than or equal to a
+target-specific size limit. The type of the '``<pointer>``' operand must
+be a pointer to that type. If the ``atomicrmw`` is marked as
+``volatile``, then the optimizer is not allowed to modify the number or
+order of execution of this ``atomicrmw`` with other :ref:`volatile
+operations <volatile>`.
+
+A ``atomicrmw`` instruction can also take an optional
+":ref:`syncscope <syncscope>`" argument.
+
+Semantics:
+""""""""""
+
+The contents of memory at the location specified by the '``<pointer>``'
+operand are atomically read, modified, and written back. The original
+value at the location is returned. The modification is specified by the
+operation argument:
+
+- xchg: ``*ptr = val``
+- add: ``*ptr = *ptr + val``
+- sub: ``*ptr = *ptr - val``
+- and: ``*ptr = *ptr & val``
+- nand: ``*ptr = ~(*ptr & val)``
+- or: ``*ptr = *ptr | val``
+- xor: ``*ptr = *ptr ^ val``
+- max: ``*ptr = *ptr > val ? *ptr : val`` (using a signed comparison)
+- min: ``*ptr = *ptr < val ? *ptr : val`` (using a signed comparison)
+- umax: ``*ptr = *ptr > val ? *ptr : val`` (using an unsigned
+ comparison)
+- umin: ``*ptr = *ptr < val ? *ptr : val`` (using an unsigned
+ comparison)
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %old = atomicrmw add i32* %ptr, i32 1 acquire ; yields i32
+
+.. _i_getelementptr:
+
+'``getelementptr``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = getelementptr <ty>, <ty>* <ptrval>{, [inrange] <ty> <idx>}*
+ <result> = getelementptr inbounds <ty>, <ty>* <ptrval>{, [inrange] <ty> <idx>}*
+ <result> = getelementptr <ty>, <ptr vector> <ptrval>, [inrange] <vector index type> <idx>
+
+Overview:
+"""""""""
+
+The '``getelementptr``' instruction is used to get the address of a
+subelement of an :ref:`aggregate <t_aggregate>` data structure. It performs
+address calculation only and does not access memory. The instruction can also
+be used to calculate a vector of such addresses.
+
+Arguments:
+""""""""""
+
+The first argument is always a type used as the basis for the calculations.
+The second argument is always a pointer or a vector of pointers, and is the
+base address to start from. The remaining arguments are indices
+that indicate which of the elements of the aggregate object are indexed.
+The interpretation of each index is dependent on the type being indexed
+into. The first index always indexes the pointer value given as the
+second argument, the second index indexes a value of the type pointed to
+(not necessarily the value directly pointed to, since the first index
+can be non-zero), etc. The first type indexed into must be a pointer
+value, subsequent types can be arrays, vectors, and structs. Note that
+subsequent types being indexed into can never be pointers, since that
+would require loading the pointer before continuing calculation.
+
+The type of each index argument depends on the type it is indexing into.
+When indexing into a (optionally packed) structure, only ``i32`` integer
+**constants** are allowed (when using a vector of indices they must all
+be the **same** ``i32`` integer constant). When indexing into an array,
+pointer or vector, integers of any width are allowed, and they are not
+required to be constant. These integers are treated as signed values
+where relevant.
+
+For example, let's consider a C code fragment and how it gets compiled
+to LLVM:
+
+.. code-block:: c
+
+ struct RT {
+ char A;
+ int B[10][20];
+ char C;
+ };
+ struct ST {
+ int X;
+ double Y;
+ struct RT Z;
+ };
+
+ int *foo(struct ST *s) {
+ return &s[1].Z.B[5][13];
+ }
+
+The LLVM code generated by Clang is:
+
+.. code-block:: llvm
+
+ %struct.RT = type { i8, [10 x [20 x i32]], i8 }
+ %struct.ST = type { i32, double, %struct.RT }
+
+ define i32* @foo(%struct.ST* %s) nounwind uwtable readnone optsize ssp {
+ entry:
+ %arrayidx = getelementptr inbounds %struct.ST, %struct.ST* %s, i64 1, i32 2, i32 1, i64 5, i64 13
+ ret i32* %arrayidx
+ }
+
+Semantics:
+""""""""""
+
+In the example above, the first index is indexing into the
+'``%struct.ST*``' type, which is a pointer, yielding a '``%struct.ST``'
+= '``{ i32, double, %struct.RT }``' type, a structure. The second index
+indexes into the third element of the structure, yielding a
+'``%struct.RT``' = '``{ i8 , [10 x [20 x i32]], i8 }``' type, another
+structure. The third index indexes into the second element of the
+structure, yielding a '``[10 x [20 x i32]]``' type, an array. The two
+dimensions of the array are subscripted into, yielding an '``i32``'
+type. The '``getelementptr``' instruction returns a pointer to this
+element, thus computing a value of '``i32*``' type.
+
+Note that it is perfectly legal to index partially through a structure,
+returning a pointer to an inner element. Because of this, the LLVM code
+for the given testcase is equivalent to:
+
+.. code-block:: llvm
+
+ define i32* @foo(%struct.ST* %s) {
+ %t1 = getelementptr %struct.ST, %struct.ST* %s, i32 1 ; yields %struct.ST*:%t1
+ %t2 = getelementptr %struct.ST, %struct.ST* %t1, i32 0, i32 2 ; yields %struct.RT*:%t2
+ %t3 = getelementptr %struct.RT, %struct.RT* %t2, i32 0, i32 1 ; yields [10 x [20 x i32]]*:%t3
+ %t4 = getelementptr [10 x [20 x i32]], [10 x [20 x i32]]* %t3, i32 0, i32 5 ; yields [20 x i32]*:%t4
+ %t5 = getelementptr [20 x i32], [20 x i32]* %t4, i32 0, i32 13 ; yields i32*:%t5
+ ret i32* %t5
+ }
+
+If the ``inbounds`` keyword is present, the result value of the
+``getelementptr`` is a :ref:`poison value <poisonvalues>` if the base
+pointer is not an *in bounds* address of an allocated object, or if any
+of the addresses that would be formed by successive addition of the
+offsets implied by the indices to the base address with infinitely
+precise signed arithmetic are not an *in bounds* address of that
+allocated object. The *in bounds* addresses for an allocated object are
+all the addresses that point into the object, plus the address one byte
+past the end. The only *in bounds* address for a null pointer in the
+default address-space is the null pointer itself. In cases where the
+base is a vector of pointers the ``inbounds`` keyword applies to each
+of the computations element-wise.
+
+If the ``inbounds`` keyword is not present, the offsets are added to the
+base address with silently-wrapping two's complement arithmetic. If the
+offsets have a different width from the pointer, they are sign-extended
+or truncated to the width of the pointer. The result value of the
+``getelementptr`` may be outside the object pointed to by the base
+pointer. The result value may not necessarily be used to access memory
+though, even if it happens to point into allocated storage. See the
+:ref:`Pointer Aliasing Rules <pointeraliasing>` section for more
+information.
+
+If the ``inrange`` keyword is present before any index, loading from or
+storing to any pointer derived from the ``getelementptr`` has undefined
+behavior if the load or store would access memory outside of the bounds of
+the element selected by the index marked as ``inrange``. The result of a
+pointer comparison or ``ptrtoint`` (including ``ptrtoint``-like operations
+involving memory) involving a pointer derived from a ``getelementptr`` with
+the ``inrange`` keyword is undefined, with the exception of comparisons
+in the case where both operands are in the range of the element selected
+by the ``inrange`` keyword, inclusive of the address one past the end of
+that element. Note that the ``inrange`` keyword is currently only allowed
+in constant ``getelementptr`` expressions.
+
+The getelementptr instruction is often confusing. For some more insight
+into how it works, see :doc:`the getelementptr FAQ <GetElementPtr>`.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ ; yields [12 x i8]*:aptr
+ %aptr = getelementptr {i32, [12 x i8]}, {i32, [12 x i8]}* %saptr, i64 0, i32 1
+ ; yields i8*:vptr
+ %vptr = getelementptr {i32, <2 x i8>}, {i32, <2 x i8>}* %svptr, i64 0, i32 1, i32 1
+ ; yields i8*:eptr
+ %eptr = getelementptr [12 x i8], [12 x i8]* %aptr, i64 0, i32 1
+ ; yields i32*:iptr
+ %iptr = getelementptr [10 x i32], [10 x i32]* @arr, i16 0, i16 0
+
+Vector of pointers:
+"""""""""""""""""""
+
+The ``getelementptr`` returns a vector of pointers, instead of a single address,
+when one or more of its arguments is a vector. In such cases, all vector
+arguments should have the same number of elements, and every scalar argument
+will be effectively broadcast into a vector during address calculation.
+
+.. code-block:: llvm
+
+ ; All arguments are vectors:
+ ; A[i] = ptrs[i] + offsets[i]*sizeof(i8)
+ %A = getelementptr i8, <4 x i8*> %ptrs, <4 x i64> %offsets
+
+ ; Add the same scalar offset to each pointer of a vector:
+ ; A[i] = ptrs[i] + offset*sizeof(i8)
+ %A = getelementptr i8, <4 x i8*> %ptrs, i64 %offset
+
+ ; Add distinct offsets to the same pointer:
+ ; A[i] = ptr + offsets[i]*sizeof(i8)
+ %A = getelementptr i8, i8* %ptr, <4 x i64> %offsets
+
+ ; In all cases described above the type of the result is <4 x i8*>
+
+The two following instructions are equivalent:
+
+.. code-block:: llvm
+
+ getelementptr %struct.ST, <4 x %struct.ST*> %s, <4 x i64> %ind1,
+ <4 x i32> <i32 2, i32 2, i32 2, i32 2>,
+ <4 x i32> <i32 1, i32 1, i32 1, i32 1>,
+ <4 x i32> %ind4,
+ <4 x i64> <i64 13, i64 13, i64 13, i64 13>
+
+ getelementptr %struct.ST, <4 x %struct.ST*> %s, <4 x i64> %ind1,
+ i32 2, i32 1, <4 x i32> %ind4, i64 13
+
+Let's look at the C code, where the vector version of ``getelementptr``
+makes sense:
+
+.. code-block:: c
+
+ // Let's assume that we vectorize the following loop:
+ double *A, *B; int *C;
+ for (int i = 0; i < size; ++i) {
+ A[i] = B[C[i]];
+ }
+
+.. code-block:: llvm
+
+ ; get pointers for 8 elements from array B
+ %ptrs = getelementptr double, double* %B, <8 x i32> %C
+ ; load 8 elements from array B into A
+ %A = call <8 x double> @llvm.masked.gather.v8f64.v8p0f64(<8 x double*> %ptrs,
+ i32 8, <8 x i1> %mask, <8 x double> %passthru)
+
+Conversion Operations
+---------------------
+
+The instructions in this category are the conversion instructions
+(casting) which all take a single operand and a type. They perform
+various bit conversions on the operand.
+
+'``trunc .. to``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = trunc <ty> <value> to <ty2> ; yields ty2
+
+Overview:
+"""""""""
+
+The '``trunc``' instruction truncates its operand to the type ``ty2``.
+
+Arguments:
+""""""""""
+
+The '``trunc``' instruction takes a value to trunc, and a type to trunc
+it to. Both types must be of :ref:`integer <t_integer>` types, or vectors
+of the same number of integers. The bit size of the ``value`` must be
+larger than the bit size of the destination type, ``ty2``. Equal sized
+types are not allowed.
+
+Semantics:
+""""""""""
+
+The '``trunc``' instruction truncates the high order bits in ``value``
+and converts the remaining bits to ``ty2``. Since the source size must
+be larger than the destination size, ``trunc`` cannot be a *no-op cast*.
+It will always truncate bits.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %X = trunc i32 257 to i8 ; yields i8:1
+ %Y = trunc i32 123 to i1 ; yields i1:true
+ %Z = trunc i32 122 to i1 ; yields i1:false
+ %W = trunc <2 x i16> <i16 8, i16 7> to <2 x i8> ; yields <i8 8, i8 7>
+
+'``zext .. to``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = zext <ty> <value> to <ty2> ; yields ty2
+
+Overview:
+"""""""""
+
+The '``zext``' instruction zero extends its operand to type ``ty2``.
+
+Arguments:
+""""""""""
+
+The '``zext``' instruction takes a value to cast, and a type to cast it
+to. Both types must be of :ref:`integer <t_integer>` types, or vectors of
+the same number of integers. The bit size of the ``value`` must be
+smaller than the bit size of the destination type, ``ty2``.
+
+Semantics:
+""""""""""
+
+The ``zext`` fills the high order bits of the ``value`` with zero bits
+until it reaches the size of the destination type, ``ty2``.
+
+When zero extending from i1, the result will always be either 0 or 1.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %X = zext i32 257 to i64 ; yields i64:257
+ %Y = zext i1 true to i32 ; yields i32:1
+ %Z = zext <2 x i16> <i16 8, i16 7> to <2 x i32> ; yields <i32 8, i32 7>
+
+'``sext .. to``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = sext <ty> <value> to <ty2> ; yields ty2
+
+Overview:
+"""""""""
+
+The '``sext``' sign extends ``value`` to the type ``ty2``.
+
+Arguments:
+""""""""""
+
+The '``sext``' instruction takes a value to cast, and a type to cast it
+to. Both types must be of :ref:`integer <t_integer>` types, or vectors of
+the same number of integers. The bit size of the ``value`` must be
+smaller than the bit size of the destination type, ``ty2``.
+
+Semantics:
+""""""""""
+
+The '``sext``' instruction performs a sign extension by copying the sign
+bit (highest order bit) of the ``value`` until it reaches the bit size
+of the type ``ty2``.
+
+When sign extending from i1, the extension always results in -1 or 0.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %X = sext i8 -1 to i16 ; yields i16 :65535
+ %Y = sext i1 true to i32 ; yields i32:-1
+ %Z = sext <2 x i16> <i16 8, i16 7> to <2 x i32> ; yields <i32 8, i32 7>
+
+'``fptrunc .. to``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = fptrunc <ty> <value> to <ty2> ; yields ty2
+
+Overview:
+"""""""""
+
+The '``fptrunc``' instruction truncates ``value`` to type ``ty2``.
+
+Arguments:
+""""""""""
+
+The '``fptrunc``' instruction takes a :ref:`floating point <t_floating>`
+value to cast and a :ref:`floating point <t_floating>` type to cast it to.
+The size of ``value`` must be larger than the size of ``ty2``. This
+implies that ``fptrunc`` cannot be used to make a *no-op cast*.
+
+Semantics:
+""""""""""
+
+The '``fptrunc``' instruction casts a ``value`` from a larger
+:ref:`floating point <t_floating>` type to a smaller :ref:`floating
+point <t_floating>` type. If the value cannot fit (i.e. overflows) within the
+destination type, ``ty2``, then the results are undefined. If the cast produces
+an inexact result, how rounding is performed (e.g. truncation, also known as
+round to zero) is undefined.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %X = fptrunc double 123.0 to float ; yields float:123.0
+ %Y = fptrunc double 1.0E+300 to float ; yields undefined
+
+'``fpext .. to``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = fpext <ty> <value> to <ty2> ; yields ty2
+
+Overview:
+"""""""""
+
+The '``fpext``' extends a floating point ``value`` to a larger floating
+point value.
+
+Arguments:
+""""""""""
+
+The '``fpext``' instruction takes a :ref:`floating point <t_floating>`
+``value`` to cast, and a :ref:`floating point <t_floating>` type to cast it
+to. The source type must be smaller than the destination type.
+
+Semantics:
+""""""""""
+
+The '``fpext``' instruction extends the ``value`` from a smaller
+:ref:`floating point <t_floating>` type to a larger :ref:`floating
+point <t_floating>` type. The ``fpext`` cannot be used to make a
+*no-op cast* because it always changes bits. Use ``bitcast`` to make a
+*no-op cast* for a floating point cast.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %X = fpext float 3.125 to double ; yields double:3.125000e+00
+ %Y = fpext double %X to fp128 ; yields fp128:0xL00000000000000004000900000000000
+
+'``fptoui .. to``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = fptoui <ty> <value> to <ty2> ; yields ty2
+
+Overview:
+"""""""""
+
+The '``fptoui``' converts a floating point ``value`` to its unsigned
+integer equivalent of type ``ty2``.
+
+Arguments:
+""""""""""
+
+The '``fptoui``' instruction takes a value to cast, which must be a
+scalar or vector :ref:`floating point <t_floating>` value, and a type to
+cast it to ``ty2``, which must be an :ref:`integer <t_integer>` type. If
+``ty`` is a vector floating point type, ``ty2`` must be a vector integer
+type with the same number of elements as ``ty``
+
+Semantics:
+""""""""""
+
+The '``fptoui``' instruction converts its :ref:`floating
+point <t_floating>` operand into the nearest (rounding towards zero)
+unsigned integer value. If the value cannot fit in ``ty2``, the results
+are undefined.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %X = fptoui double 123.0 to i32 ; yields i32:123
+ %Y = fptoui float 1.0E+300 to i1 ; yields undefined:1
+ %Z = fptoui float 1.04E+17 to i8 ; yields undefined:1
+
+'``fptosi .. to``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = fptosi <ty> <value> to <ty2> ; yields ty2
+
+Overview:
+"""""""""
+
+The '``fptosi``' instruction converts :ref:`floating point <t_floating>`
+``value`` to type ``ty2``.
+
+Arguments:
+""""""""""
+
+The '``fptosi``' instruction takes a value to cast, which must be a
+scalar or vector :ref:`floating point <t_floating>` value, and a type to
+cast it to ``ty2``, which must be an :ref:`integer <t_integer>` type. If
+``ty`` is a vector floating point type, ``ty2`` must be a vector integer
+type with the same number of elements as ``ty``
+
+Semantics:
+""""""""""
+
+The '``fptosi``' instruction converts its :ref:`floating
+point <t_floating>` operand into the nearest (rounding towards zero)
+signed integer value. If the value cannot fit in ``ty2``, the results
+are undefined.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %X = fptosi double -123.0 to i32 ; yields i32:-123
+ %Y = fptosi float 1.0E-247 to i1 ; yields undefined:1
+ %Z = fptosi float 1.04E+17 to i8 ; yields undefined:1
+
+'``uitofp .. to``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = uitofp <ty> <value> to <ty2> ; yields ty2
+
+Overview:
+"""""""""
+
+The '``uitofp``' instruction regards ``value`` as an unsigned integer
+and converts that value to the ``ty2`` type.
+
+Arguments:
+""""""""""
+
+The '``uitofp``' instruction takes a value to cast, which must be a
+scalar or vector :ref:`integer <t_integer>` value, and a type to cast it to
+``ty2``, which must be an :ref:`floating point <t_floating>` type. If
+``ty`` is a vector integer type, ``ty2`` must be a vector floating point
+type with the same number of elements as ``ty``
+
+Semantics:
+""""""""""
+
+The '``uitofp``' instruction interprets its operand as an unsigned
+integer quantity and converts it to the corresponding floating point
+value. If the value cannot fit in the floating point value, the results
+are undefined.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %X = uitofp i32 257 to float ; yields float:257.0
+ %Y = uitofp i8 -1 to double ; yields double:255.0
+
+'``sitofp .. to``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = sitofp <ty> <value> to <ty2> ; yields ty2
+
+Overview:
+"""""""""
+
+The '``sitofp``' instruction regards ``value`` as a signed integer and
+converts that value to the ``ty2`` type.
+
+Arguments:
+""""""""""
+
+The '``sitofp``' instruction takes a value to cast, which must be a
+scalar or vector :ref:`integer <t_integer>` value, and a type to cast it to
+``ty2``, which must be an :ref:`floating point <t_floating>` type. If
+``ty`` is a vector integer type, ``ty2`` must be a vector floating point
+type with the same number of elements as ``ty``
+
+Semantics:
+""""""""""
+
+The '``sitofp``' instruction interprets its operand as a signed integer
+quantity and converts it to the corresponding floating point value. If
+the value cannot fit in the floating point value, the results are
+undefined.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %X = sitofp i32 257 to float ; yields float:257.0
+ %Y = sitofp i8 -1 to double ; yields double:-1.0
+
+.. _i_ptrtoint:
+
+'``ptrtoint .. to``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = ptrtoint <ty> <value> to <ty2> ; yields ty2
+
+Overview:
+"""""""""
+
+The '``ptrtoint``' instruction converts the pointer or a vector of
+pointers ``value`` to the integer (or vector of integers) type ``ty2``.
+
+Arguments:
+""""""""""
+
+The '``ptrtoint``' instruction takes a ``value`` to cast, which must be
+a value of type :ref:`pointer <t_pointer>` or a vector of pointers, and a
+type to cast it to ``ty2``, which must be an :ref:`integer <t_integer>` or
+a vector of integers type.
+
+Semantics:
+""""""""""
+
+The '``ptrtoint``' instruction converts ``value`` to integer type
+``ty2`` by interpreting the pointer value as an integer and either
+truncating or zero extending that value to the size of the integer type.
+If ``value`` is smaller than ``ty2`` then a zero extension is done. If
+``value`` is larger than ``ty2`` then a truncation is done. If they are
+the same size, then nothing is done (*no-op cast*) other than a type
+change.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %X = ptrtoint i32* %P to i8 ; yields truncation on 32-bit architecture
+ %Y = ptrtoint i32* %P to i64 ; yields zero extension on 32-bit architecture
+ %Z = ptrtoint <4 x i32*> %P to <4 x i64>; yields vector zero extension for a vector of addresses on 32-bit architecture
+
+.. _i_inttoptr:
+
+'``inttoptr .. to``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = inttoptr <ty> <value> to <ty2> ; yields ty2
+
+Overview:
+"""""""""
+
+The '``inttoptr``' instruction converts an integer ``value`` to a
+pointer type, ``ty2``.
+
+Arguments:
+""""""""""
+
+The '``inttoptr``' instruction takes an :ref:`integer <t_integer>` value to
+cast, and a type to cast it to, which must be a :ref:`pointer <t_pointer>`
+type.
+
+Semantics:
+""""""""""
+
+The '``inttoptr``' instruction converts ``value`` to type ``ty2`` by
+applying either a zero extension or a truncation depending on the size
+of the integer ``value``. If ``value`` is larger than the size of a
+pointer then a truncation is done. If ``value`` is smaller than the size
+of a pointer then a zero extension is done. If they are the same size,
+nothing is done (*no-op cast*).
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %X = inttoptr i32 255 to i32* ; yields zero extension on 64-bit architecture
+ %Y = inttoptr i32 255 to i32* ; yields no-op on 32-bit architecture
+ %Z = inttoptr i64 0 to i32* ; yields truncation on 32-bit architecture
+ %Z = inttoptr <4 x i32> %G to <4 x i8*>; yields truncation of vector G to four pointers
+
+.. _i_bitcast:
+
+'``bitcast .. to``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = bitcast <ty> <value> to <ty2> ; yields ty2
+
+Overview:
+"""""""""
+
+The '``bitcast``' instruction converts ``value`` to type ``ty2`` without
+changing any bits.
+
+Arguments:
+""""""""""
+
+The '``bitcast``' instruction takes a value to cast, which must be a
+non-aggregate first class value, and a type to cast it to, which must
+also be a non-aggregate :ref:`first class <t_firstclass>` type. The
+bit sizes of ``value`` and the destination type, ``ty2``, must be
+identical. If the source type is a pointer, the destination type must
+also be a pointer of the same size. This instruction supports bitwise
+conversion of vectors to integers and to vectors of other types (as
+long as they have the same size).
+
+Semantics:
+""""""""""
+
+The '``bitcast``' instruction converts ``value`` to type ``ty2``. It
+is always a *no-op cast* because no bits change with this
+conversion. The conversion is done as if the ``value`` had been stored
+to memory and read back as type ``ty2``. Pointer (or vector of
+pointers) types may only be converted to other pointer (or vector of
+pointers) types with the same address space through this instruction.
+To convert pointers to other types, use the :ref:`inttoptr <i_inttoptr>`
+or :ref:`ptrtoint <i_ptrtoint>` instructions first.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ %X = bitcast i8 255 to i8 ; yields i8 :-1
+ %Y = bitcast i32* %x to sint* ; yields sint*:%x
+ %Z = bitcast <2 x int> %V to i64; ; yields i64: %V
+ %Z = bitcast <2 x i32*> %V to <2 x i64*> ; yields <2 x i64*>
+
+.. _i_addrspacecast:
+
+'``addrspacecast .. to``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = addrspacecast <pty> <ptrval> to <pty2> ; yields pty2
+
+Overview:
+"""""""""
+
+The '``addrspacecast``' instruction converts ``ptrval`` from ``pty`` in
+address space ``n`` to type ``pty2`` in address space ``m``.
+
+Arguments:
+""""""""""
+
+The '``addrspacecast``' instruction takes a pointer or vector of pointer value
+to cast and a pointer type to cast it to, which must have a different
+address space.
+
+Semantics:
+""""""""""
+
+The '``addrspacecast``' instruction converts the pointer value
+``ptrval`` to type ``pty2``. It can be a *no-op cast* or a complex
+value modification, depending on the target and the address space
+pair. Pointer conversions within the same address space must be
+performed with the ``bitcast`` instruction. Note that if the address space
+conversion is legal then both result and operand refer to the same memory
+location.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %X = addrspacecast i32* %x to i32 addrspace(1)* ; yields i32 addrspace(1)*:%x
+ %Y = addrspacecast i32 addrspace(1)* %y to i64 addrspace(2)* ; yields i64 addrspace(2)*:%y
+ %Z = addrspacecast <4 x i32*> %z to <4 x float addrspace(3)*> ; yields <4 x float addrspace(3)*>:%z
+
+.. _otherops:
+
+Other Operations
+----------------
+
+The instructions in this category are the "miscellaneous" instructions,
+which defy better classification.
+
+.. _i_icmp:
+
+'``icmp``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = icmp <cond> <ty> <op1>, <op2> ; yields i1 or <N x i1>:result
+
+Overview:
+"""""""""
+
+The '``icmp``' instruction returns a boolean value or a vector of
+boolean values based on comparison of its two integer, integer vector,
+pointer, or pointer vector operands.
+
+Arguments:
+""""""""""
+
+The '``icmp``' instruction takes three operands. The first operand is
+the condition code indicating the kind of comparison to perform. It is
+not a value, just a keyword. The possible condition codes are:
+
+#. ``eq``: equal
+#. ``ne``: not equal
+#. ``ugt``: unsigned greater than
+#. ``uge``: unsigned greater or equal
+#. ``ult``: unsigned less than
+#. ``ule``: unsigned less or equal
+#. ``sgt``: signed greater than
+#. ``sge``: signed greater or equal
+#. ``slt``: signed less than
+#. ``sle``: signed less or equal
+
+The remaining two arguments must be :ref:`integer <t_integer>` or
+:ref:`pointer <t_pointer>` or integer :ref:`vector <t_vector>` typed. They
+must also be identical types.
+
+Semantics:
+""""""""""
+
+The '``icmp``' compares ``op1`` and ``op2`` according to the condition
+code given as ``cond``. The comparison performed always yields either an
+:ref:`i1 <t_integer>` or vector of ``i1`` result, as follows:
+
+#. ``eq``: yields ``true`` if the operands are equal, ``false``
+ otherwise. No sign interpretation is necessary or performed.
+#. ``ne``: yields ``true`` if the operands are unequal, ``false``
+ otherwise. No sign interpretation is necessary or performed.
+#. ``ugt``: interprets the operands as unsigned values and yields
+ ``true`` if ``op1`` is greater than ``op2``.
+#. ``uge``: interprets the operands as unsigned values and yields
+ ``true`` if ``op1`` is greater than or equal to ``op2``.
+#. ``ult``: interprets the operands as unsigned values and yields
+ ``true`` if ``op1`` is less than ``op2``.
+#. ``ule``: interprets the operands as unsigned values and yields
+ ``true`` if ``op1`` is less than or equal to ``op2``.
+#. ``sgt``: interprets the operands as signed values and yields ``true``
+ if ``op1`` is greater than ``op2``.
+#. ``sge``: interprets the operands as signed values and yields ``true``
+ if ``op1`` is greater than or equal to ``op2``.
+#. ``slt``: interprets the operands as signed values and yields ``true``
+ if ``op1`` is less than ``op2``.
+#. ``sle``: interprets the operands as signed values and yields ``true``
+ if ``op1`` is less than or equal to ``op2``.
+
+If the operands are :ref:`pointer <t_pointer>` typed, the pointer values
+are compared as if they were integers.
+
+If the operands are integer vectors, then they are compared element by
+element. The result is an ``i1`` vector with the same number of elements
+as the values being compared. Otherwise, the result is an ``i1``.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = icmp eq i32 4, 5 ; yields: result=false
+ <result> = icmp ne float* %X, %X ; yields: result=false
+ <result> = icmp ult i16 4, 5 ; yields: result=true
+ <result> = icmp sgt i16 4, 5 ; yields: result=false
+ <result> = icmp ule i16 -4, 5 ; yields: result=false
+ <result> = icmp sge i16 4, 5 ; yields: result=false
+
+.. _i_fcmp:
+
+'``fcmp``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = fcmp [fast-math flags]* <cond> <ty> <op1>, <op2> ; yields i1 or <N x i1>:result
+
+Overview:
+"""""""""
+
+The '``fcmp``' instruction returns a boolean value or vector of boolean
+values based on comparison of its operands.
+
+If the operands are floating point scalars, then the result type is a
+boolean (:ref:`i1 <t_integer>`).
+
+If the operands are floating point vectors, then the result type is a
+vector of boolean with the same number of elements as the operands being
+compared.
+
+Arguments:
+""""""""""
+
+The '``fcmp``' instruction takes three operands. The first operand is
+the condition code indicating the kind of comparison to perform. It is
+not a value, just a keyword. The possible condition codes are:
+
+#. ``false``: no comparison, always returns false
+#. ``oeq``: ordered and equal
+#. ``ogt``: ordered and greater than
+#. ``oge``: ordered and greater than or equal
+#. ``olt``: ordered and less than
+#. ``ole``: ordered and less than or equal
+#. ``one``: ordered and not equal
+#. ``ord``: ordered (no nans)
+#. ``ueq``: unordered or equal
+#. ``ugt``: unordered or greater than
+#. ``uge``: unordered or greater than or equal
+#. ``ult``: unordered or less than
+#. ``ule``: unordered or less than or equal
+#. ``une``: unordered or not equal
+#. ``uno``: unordered (either nans)
+#. ``true``: no comparison, always returns true
+
+*Ordered* means that neither operand is a QNAN while *unordered* means
+that either operand may be a QNAN.
+
+Each of ``val1`` and ``val2`` arguments must be either a :ref:`floating
+point <t_floating>` type or a :ref:`vector <t_vector>` of floating point
+type. They must have identical types.
+
+Semantics:
+""""""""""
+
+The '``fcmp``' instruction compares ``op1`` and ``op2`` according to the
+condition code given as ``cond``. If the operands are vectors, then the
+vectors are compared element by element. Each comparison performed
+always yields an :ref:`i1 <t_integer>` result, as follows:
+
+#. ``false``: always yields ``false``, regardless of operands.
+#. ``oeq``: yields ``true`` if both operands are not a QNAN and ``op1``
+ is equal to ``op2``.
+#. ``ogt``: yields ``true`` if both operands are not a QNAN and ``op1``
+ is greater than ``op2``.
+#. ``oge``: yields ``true`` if both operands are not a QNAN and ``op1``
+ is greater than or equal to ``op2``.
+#. ``olt``: yields ``true`` if both operands are not a QNAN and ``op1``
+ is less than ``op2``.
+#. ``ole``: yields ``true`` if both operands are not a QNAN and ``op1``
+ is less than or equal to ``op2``.
+#. ``one``: yields ``true`` if both operands are not a QNAN and ``op1``
+ is not equal to ``op2``.
+#. ``ord``: yields ``true`` if both operands are not a QNAN.
+#. ``ueq``: yields ``true`` if either operand is a QNAN or ``op1`` is
+ equal to ``op2``.
+#. ``ugt``: yields ``true`` if either operand is a QNAN or ``op1`` is
+ greater than ``op2``.
+#. ``uge``: yields ``true`` if either operand is a QNAN or ``op1`` is
+ greater than or equal to ``op2``.
+#. ``ult``: yields ``true`` if either operand is a QNAN or ``op1`` is
+ less than ``op2``.
+#. ``ule``: yields ``true`` if either operand is a QNAN or ``op1`` is
+ less than or equal to ``op2``.
+#. ``une``: yields ``true`` if either operand is a QNAN or ``op1`` is
+ not equal to ``op2``.
+#. ``uno``: yields ``true`` if either operand is a QNAN.
+#. ``true``: always yields ``true``, regardless of operands.
+
+The ``fcmp`` instruction can also optionally take any number of
+:ref:`fast-math flags <fastmath>`, which are optimization hints to enable
+otherwise unsafe floating point optimizations.
+
+Any set of fast-math flags are legal on an ``fcmp`` instruction, but the
+only flags that have any effect on its semantics are those that allow
+assumptions to be made about the values of input arguments; namely
+``nnan``, ``ninf``, and ``nsz``. See :ref:`fastmath` for more information.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ <result> = fcmp oeq float 4.0, 5.0 ; yields: result=false
+ <result> = fcmp one float 4.0, 5.0 ; yields: result=true
+ <result> = fcmp olt float 4.0, 5.0 ; yields: result=true
+ <result> = fcmp ueq double 1.0, 2.0 ; yields: result=false
+
+.. _i_phi:
+
+'``phi``' Instruction
+^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = phi <ty> [ <val0>, <label0>], ...
+
+Overview:
+"""""""""
+
+The '``phi``' instruction is used to implement the Ï node in the SSA
+graph representing the function.
+
+Arguments:
+""""""""""
+
+The type of the incoming values is specified with the first type field.
+After this, the '``phi``' instruction takes a list of pairs as
+arguments, with one pair for each predecessor basic block of the current
+block. Only values of :ref:`first class <t_firstclass>` type may be used as
+the value arguments to the PHI node. Only labels may be used as the
+label arguments.
+
+There must be no non-phi instructions between the start of a basic block
+and the PHI instructions: i.e. PHI instructions must be first in a basic
+block.
+
+For the purposes of the SSA form, the use of each incoming value is
+deemed to occur on the edge from the corresponding predecessor block to
+the current block (but after any definition of an '``invoke``'
+instruction's return value on the same edge).
+
+Semantics:
+""""""""""
+
+At runtime, the '``phi``' instruction logically takes on the value
+specified by the pair corresponding to the predecessor basic block that
+executed just prior to the current block.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ Loop: ; Infinite loop that counts from 0 on up...
+ %indvar = phi i32 [ 0, %LoopHeader ], [ %nextindvar, %Loop ]
+ %nextindvar = add i32 %indvar, 1
+ br label %Loop
+
+.. _i_select:
+
+'``select``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = select selty <cond>, <ty> <val1>, <ty> <val2> ; yields ty
+
+ selty is either i1 or {<N x i1>}
+
+Overview:
+"""""""""
+
+The '``select``' instruction is used to choose one value based on a
+condition, without IR-level branching.
+
+Arguments:
+""""""""""
+
+The '``select``' instruction requires an 'i1' value or a vector of 'i1'
+values indicating the condition, and two values of the same :ref:`first
+class <t_firstclass>` type.
+
+Semantics:
+""""""""""
+
+If the condition is an i1 and it evaluates to 1, the instruction returns
+the first value argument; otherwise, it returns the second value
+argument.
+
+If the condition is a vector of i1, then the value arguments must be
+vectors of the same size, and the selection is done element by element.
+
+If the condition is an i1 and the value arguments are vectors of the
+same size, then an entire vector is selected.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %X = select i1 true, i8 17, i8 42 ; yields i8:17
+
+.. _i_call:
+
+'``call``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <result> = [tail | musttail | notail ] call [fast-math flags] [cconv] [ret attrs] <ty>|<fnty> <fnptrval>(<function args>) [fn attrs]
+ [ operand bundles ]
+
+Overview:
+"""""""""
+
+The '``call``' instruction represents a simple function call.
+
+Arguments:
+""""""""""
+
+This instruction requires several arguments:
+
+#. The optional ``tail`` and ``musttail`` markers indicate that the optimizers
+ should perform tail call optimization. The ``tail`` marker is a hint that
+ `can be ignored <CodeGenerator.html#sibcallopt>`_. The ``musttail`` marker
+ means that the call must be tail call optimized in order for the program to
+ be correct. The ``musttail`` marker provides these guarantees:
+
+ #. The call will not cause unbounded stack growth if it is part of a
+ recursive cycle in the call graph.
+ #. Arguments with the :ref:`inalloca <attr_inalloca>` attribute are
+ forwarded in place.
+
+ Both markers imply that the callee does not access allocas or varargs from
+ the caller. Calls marked ``musttail`` must obey the following additional
+ rules:
+
+ - The call must immediately precede a :ref:`ret <i_ret>` instruction,
+ or a pointer bitcast followed by a ret instruction.
+ - The ret instruction must return the (possibly bitcasted) value
+ produced by the call or void.
+ - The caller and callee prototypes must match. Pointer types of
+ parameters or return types may differ in pointee type, but not
+ in address space.
+ - The calling conventions of the caller and callee must match.
+ - All ABI-impacting function attributes, such as sret, byval, inreg,
+ returned, and inalloca, must match.
+ - The callee must be varargs iff the caller is varargs. Bitcasting a
+ non-varargs function to the appropriate varargs type is legal so
+ long as the non-varargs prefixes obey the other rules.
+
+ Tail call optimization for calls marked ``tail`` is guaranteed to occur if
+ the following conditions are met:
+
+ - Caller and callee both have the calling convention ``fastcc``.
+ - The call is in tail position (ret immediately follows call and ret
+ uses value of call or is void).
+ - Option ``-tailcallopt`` is enabled, or
+ ``llvm::GuaranteedTailCallOpt`` is ``true``.
+ - `Platform-specific constraints are
+ met. <CodeGenerator.html#tailcallopt>`_
+
+#. The optional ``notail`` marker indicates that the optimizers should not add
+ ``tail`` or ``musttail`` markers to the call. It is used to prevent tail
+ call optimization from being performed on the call.
+
+#. The optional ``fast-math flags`` marker indicates that the call has one or more
+ :ref:`fast-math flags <fastmath>`, which are optimization hints to enable
+ otherwise unsafe floating-point optimizations. Fast-math flags are only valid
+ for calls that return a floating-point scalar or vector type.
+
+#. The optional "cconv" marker indicates which :ref:`calling
+ convention <callingconv>` the call should use. If none is
+ specified, the call defaults to using C calling conventions. The
+ calling convention of the call must match the calling convention of
+ the target function, or else the behavior is undefined.
+#. The optional :ref:`Parameter Attributes <paramattrs>` list for return
+ values. Only '``zeroext``', '``signext``', and '``inreg``' attributes
+ are valid here.
+#. '``ty``': the type of the call instruction itself which is also the
+ type of the return value. Functions that return no value are marked
+ ``void``.
+#. '``fnty``': shall be the signature of the function being called. The
+ argument types must match the types implied by this signature. This
+ type can be omitted if the function is not varargs.
+#. '``fnptrval``': An LLVM value containing a pointer to a function to
+ be called. In most cases, this is a direct function call, but
+ indirect ``call``'s are just as possible, calling an arbitrary pointer
+ to function value.
+#. '``function args``': argument list whose types match the function
+ signature argument types and parameter attributes. All arguments must
+ be of :ref:`first class <t_firstclass>` type. If the function signature
+ indicates the function accepts a variable number of arguments, the
+ extra arguments can be specified.
+#. The optional :ref:`function attributes <fnattrs>` list.
+#. The optional :ref:`operand bundles <opbundles>` list.
+
+Semantics:
+""""""""""
+
+The '``call``' instruction is used to cause control flow to transfer to
+a specified function, with its incoming arguments bound to the specified
+values. Upon a '``ret``' instruction in the called function, control
+flow continues with the instruction after the function call, and the
+return value of the function is bound to the result argument.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ %retval = call i32 @test(i32 %argc)
+ call i32 (i8*, ...)* @printf(i8* %msg, i32 12, i8 42) ; yields i32
+ %X = tail call i32 @foo() ; yields i32
+ %Y = tail call fastcc i32 @foo() ; yields i32
+ call void %foo(i8 97 signext)
+
+ %struct.A = type { i32, i8 }
+ %r = call %struct.A @foo() ; yields { i32, i8 }
+ %gr = extractvalue %struct.A %r, 0 ; yields i32
+ %gr1 = extractvalue %struct.A %r, 1 ; yields i8
+ %Z = call void @foo() noreturn ; indicates that %foo never returns normally
+ %ZZ = call zeroext i32 @bar() ; Return value is %zero extended
+
+llvm treats calls to some functions with names and arguments that match
+the standard C99 library as being the C99 library functions, and may
+perform optimizations or generate code for them under that assumption.
+This is something we'd like to change in the future to provide better
+support for freestanding environments and non-C-based languages.
+
+.. _i_va_arg:
+
+'``va_arg``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <resultval> = va_arg <va_list*> <arglist>, <argty>
+
+Overview:
+"""""""""
+
+The '``va_arg``' instruction is used to access arguments passed through
+the "variable argument" area of a function call. It is used to implement
+the ``va_arg`` macro in C.
+
+Arguments:
+""""""""""
+
+This instruction takes a ``va_list*`` value and the type of the
+argument. It returns a value of the specified argument type and
+increments the ``va_list`` to point to the next argument. The actual
+type of ``va_list`` is target specific.
+
+Semantics:
+""""""""""
+
+The '``va_arg``' instruction loads an argument of the specified type
+from the specified ``va_list`` and causes the ``va_list`` to point to
+the next argument. For more information, see the variable argument
+handling :ref:`Intrinsic Functions <int_varargs>`.
+
+It is legal for this instruction to be called in a function which does
+not take a variable number of arguments, for example, the ``vfprintf``
+function.
+
+``va_arg`` is an LLVM instruction instead of an :ref:`intrinsic
+function <intrinsics>` because it takes a type as an argument.
+
+Example:
+""""""""
+
+See the :ref:`variable argument processing <int_varargs>` section.
+
+Note that the code generator does not yet fully support va\_arg on many
+targets. Also, it does not currently support va\_arg with aggregate
+types on any target.
+
+.. _i_landingpad:
+
+'``landingpad``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <resultval> = landingpad <resultty> <clause>+
+ <resultval> = landingpad <resultty> cleanup <clause>*
+
+ <clause> := catch <type> <value>
+ <clause> := filter <array constant type> <array constant>
+
+Overview:
+"""""""""
+
+The '``landingpad``' instruction is used by `LLVM's exception handling
+system <ExceptionHandling.html#overview>`_ to specify that a basic block
+is a landing pad --- one where the exception lands, and corresponds to the
+code found in the ``catch`` portion of a ``try``/``catch`` sequence. It
+defines values supplied by the :ref:`personality function <personalityfn>` upon
+re-entry to the function. The ``resultval`` has the type ``resultty``.
+
+Arguments:
+""""""""""
+
+The optional
+``cleanup`` flag indicates that the landing pad block is a cleanup.
+
+A ``clause`` begins with the clause type --- ``catch`` or ``filter`` --- and
+contains the global variable representing the "type" that may be caught
+or filtered respectively. Unlike the ``catch`` clause, the ``filter``
+clause takes an array constant as its argument. Use
+"``[0 x i8**] undef``" for a filter which cannot throw. The
+'``landingpad``' instruction must contain *at least* one ``clause`` or
+the ``cleanup`` flag.
+
+Semantics:
+""""""""""
+
+The '``landingpad``' instruction defines the values which are set by the
+:ref:`personality function <personalityfn>` upon re-entry to the function, and
+therefore the "result type" of the ``landingpad`` instruction. As with
+calling conventions, how the personality function results are
+represented in LLVM IR is target specific.
+
+The clauses are applied in order from top to bottom. If two
+``landingpad`` instructions are merged together through inlining, the
+clauses from the calling function are appended to the list of clauses.
+When the call stack is being unwound due to an exception being thrown,
+the exception is compared against each ``clause`` in turn. If it doesn't
+match any of the clauses, and the ``cleanup`` flag is not set, then
+unwinding continues further up the call stack.
+
+The ``landingpad`` instruction has several restrictions:
+
+- A landing pad block is a basic block which is the unwind destination
+ of an '``invoke``' instruction.
+- A landing pad block must have a '``landingpad``' instruction as its
+ first non-PHI instruction.
+- There can be only one '``landingpad``' instruction within the landing
+ pad block.
+- A basic block that is not a landing pad block may not include a
+ '``landingpad``' instruction.
+
+Example:
+""""""""
+
+.. code-block:: llvm
+
+ ;; A landing pad which can catch an integer.
+ %res = landingpad { i8*, i32 }
+ catch i8** @_ZTIi
+ ;; A landing pad that is a cleanup.
+ %res = landingpad { i8*, i32 }
+ cleanup
+ ;; A landing pad which can catch an integer and can only throw a double.
+ %res = landingpad { i8*, i32 }
+ catch i8** @_ZTIi
+ filter [1 x i8**] [@_ZTId]
+
+.. _i_catchpad:
+
+'``catchpad``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <resultval> = catchpad within <catchswitch> [<args>*]
+
+Overview:
+"""""""""
+
+The '``catchpad``' instruction is used by `LLVM's exception handling
+system <ExceptionHandling.html#overview>`_ to specify that a basic block
+begins a catch handler --- one where a personality routine attempts to transfer
+control to catch an exception.
+
+Arguments:
+""""""""""
+
+The ``catchswitch`` operand must always be a token produced by a
+:ref:`catchswitch <i_catchswitch>` instruction in a predecessor block. This
+ensures that each ``catchpad`` has exactly one predecessor block, and it always
+terminates in a ``catchswitch``.
+
+The ``args`` correspond to whatever information the personality routine
+requires to know if this is an appropriate handler for the exception. Control
+will transfer to the ``catchpad`` if this is the first appropriate handler for
+the exception.
+
+The ``resultval`` has the type :ref:`token <t_token>` and is used to match the
+``catchpad`` to corresponding :ref:`catchrets <i_catchret>` and other nested EH
+pads.
+
+Semantics:
+""""""""""
+
+When the call stack is being unwound due to an exception being thrown, the
+exception is compared against the ``args``. If it doesn't match, control will
+not reach the ``catchpad`` instruction. The representation of ``args`` is
+entirely target and personality function-specific.
+
+Like the :ref:`landingpad <i_landingpad>` instruction, the ``catchpad``
+instruction must be the first non-phi of its parent basic block.
+
+The meaning of the tokens produced and consumed by ``catchpad`` and other "pad"
+instructions is described in the
+`Windows exception handling documentation\ <ExceptionHandling.html#wineh>`_.
+
+When a ``catchpad`` has been "entered" but not yet "exited" (as
+described in the `EH documentation\ <ExceptionHandling.html#wineh-constraints>`_),
+it is undefined behavior to execute a :ref:`call <i_call>` or :ref:`invoke <i_invoke>`
+that does not carry an appropriate :ref:`"funclet" bundle <ob_funclet>`.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ dispatch:
+ %cs = catchswitch within none [label %handler0] unwind to caller
+ ;; A catch block which can catch an integer.
+ handler0:
+ %tok = catchpad within %cs [i8** @_ZTIi]
+
+.. _i_cleanuppad:
+
+'``cleanuppad``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ <resultval> = cleanuppad within <parent> [<args>*]
+
+Overview:
+"""""""""
+
+The '``cleanuppad``' instruction is used by `LLVM's exception handling
+system <ExceptionHandling.html#overview>`_ to specify that a basic block
+is a cleanup block --- one where a personality routine attempts to
+transfer control to run cleanup actions.
+The ``args`` correspond to whatever additional
+information the :ref:`personality function <personalityfn>` requires to
+execute the cleanup.
+The ``resultval`` has the type :ref:`token <t_token>` and is used to
+match the ``cleanuppad`` to corresponding :ref:`cleanuprets <i_cleanupret>`.
+The ``parent`` argument is the token of the funclet that contains the
+``cleanuppad`` instruction. If the ``cleanuppad`` is not inside a funclet,
+this operand may be the token ``none``.
+
+Arguments:
+""""""""""
+
+The instruction takes a list of arbitrary values which are interpreted
+by the :ref:`personality function <personalityfn>`.
+
+Semantics:
+""""""""""
+
+When the call stack is being unwound due to an exception being thrown,
+the :ref:`personality function <personalityfn>` transfers control to the
+``cleanuppad`` with the aid of the personality-specific arguments.
+As with calling conventions, how the personality function results are
+represented in LLVM IR is target specific.
+
+The ``cleanuppad`` instruction has several restrictions:
+
+- A cleanup block is a basic block which is the unwind destination of
+ an exceptional instruction.
+- A cleanup block must have a '``cleanuppad``' instruction as its
+ first non-PHI instruction.
+- There can be only one '``cleanuppad``' instruction within the
+ cleanup block.
+- A basic block that is not a cleanup block may not include a
+ '``cleanuppad``' instruction.
+
+When a ``cleanuppad`` has been "entered" but not yet "exited" (as
+described in the `EH documentation\ <ExceptionHandling.html#wineh-constraints>`_),
+it is undefined behavior to execute a :ref:`call <i_call>` or :ref:`invoke <i_invoke>`
+that does not carry an appropriate :ref:`"funclet" bundle <ob_funclet>`.
+
+Example:
+""""""""
+
+.. code-block:: text
+
+ %tok = cleanuppad within %cs []
+
+.. _intrinsics:
+
+Intrinsic Functions
+===================
+
+LLVM supports the notion of an "intrinsic function". These functions
+have well known names and semantics and are required to follow certain
+restrictions. Overall, these intrinsics represent an extension mechanism
+for the LLVM language that does not require changing all of the
+transformations in LLVM when adding to the language (or the bitcode
+reader/writer, the parser, etc...).
+
+Intrinsic function names must all start with an "``llvm.``" prefix. This
+prefix is reserved in LLVM for intrinsic names; thus, function names may
+not begin with this prefix. Intrinsic functions must always be external
+functions: you cannot define the body of intrinsic functions. Intrinsic
+functions may only be used in call or invoke instructions: it is illegal
+to take the address of an intrinsic function. Additionally, because
+intrinsic functions are part of the LLVM language, it is required if any
+are added that they be documented here.
+
+Some intrinsic functions can be overloaded, i.e., the intrinsic
+represents a family of functions that perform the same operation but on
+different data types. Because LLVM can represent over 8 million
+different integer types, overloading is used commonly to allow an
+intrinsic function to operate on any integer type. One or more of the
+argument types or the result type can be overloaded to accept any
+integer type. Argument types may also be defined as exactly matching a
+previous argument's type or the result type. This allows an intrinsic
+function which accepts multiple arguments, but needs all of them to be
+of the same type, to only be overloaded with respect to a single
+argument or the result.
+
+Overloaded intrinsics will have the names of its overloaded argument
+types encoded into its function name, each preceded by a period. Only
+those types which are overloaded result in a name suffix. Arguments
+whose type is matched against another type do not. For example, the
+``llvm.ctpop`` function can take an integer of any width and returns an
+integer of exactly the same integer width. This leads to a family of
+functions such as ``i8 @llvm.ctpop.i8(i8 %val)`` and
+``i29 @llvm.ctpop.i29(i29 %val)``. Only one type, the return type, is
+overloaded, and only one type suffix is required. Because the argument's
+type is matched against the return type, it does not require its own
+name suffix.
+
+To learn how to add an intrinsic function, please see the `Extending
+LLVM Guide <ExtendingLLVM.html>`_.
+
+.. _int_varargs:
+
+Variable Argument Handling Intrinsics
+-------------------------------------
+
+Variable argument support is defined in LLVM with the
+:ref:`va_arg <i_va_arg>` instruction and these three intrinsic
+functions. These functions are related to the similarly named macros
+defined in the ``<stdarg.h>`` header file.
+
+All of these functions operate on arguments that use a target-specific
+value type "``va_list``". The LLVM assembly language reference manual
+does not define what this type is, so all transformations should be
+prepared to handle these functions regardless of the type used.
+
+This example shows how the :ref:`va_arg <i_va_arg>` instruction and the
+variable argument handling intrinsic functions are used.
+
+.. code-block:: llvm
+
+ ; This struct is different for every platform. For most platforms,
+ ; it is merely an i8*.
+ %struct.va_list = type { i8* }
+
+ ; For Unix x86_64 platforms, va_list is the following struct:
+ ; %struct.va_list = type { i32, i32, i8*, i8* }
+
+ define i32 @test(i32 %X, ...) {
+ ; Initialize variable argument processing
+ %ap = alloca %struct.va_list
+ %ap2 = bitcast %struct.va_list* %ap to i8*
+ call void @llvm.va_start(i8* %ap2)
+
+ ; Read a single integer argument
+ %tmp = va_arg i8* %ap2, i32
+
+ ; Demonstrate usage of llvm.va_copy and llvm.va_end
+ %aq = alloca i8*
+ %aq2 = bitcast i8** %aq to i8*
+ call void @llvm.va_copy(i8* %aq2, i8* %ap2)
+ call void @llvm.va_end(i8* %aq2)
+
+ ; Stop processing of arguments.
+ call void @llvm.va_end(i8* %ap2)
+ ret i32 %tmp
+ }
+
+ declare void @llvm.va_start(i8*)
+ declare void @llvm.va_copy(i8*, i8*)
+ declare void @llvm.va_end(i8*)
+
+.. _int_va_start:
+
+'``llvm.va_start``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.va_start(i8* <arglist>)
+
+Overview:
+"""""""""
+
+The '``llvm.va_start``' intrinsic initializes ``*<arglist>`` for
+subsequent use by ``va_arg``.
+
+Arguments:
+""""""""""
+
+The argument is a pointer to a ``va_list`` element to initialize.
+
+Semantics:
+""""""""""
+
+The '``llvm.va_start``' intrinsic works just like the ``va_start`` macro
+available in C. In a target-dependent way, it initializes the
+``va_list`` element to which the argument points, so that the next call
+to ``va_arg`` will produce the first variable argument passed to the
+function. Unlike the C ``va_start`` macro, this intrinsic does not need
+to know the last argument of the function as the compiler can figure
+that out.
+
+'``llvm.va_end``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.va_end(i8* <arglist>)
+
+Overview:
+"""""""""
+
+The '``llvm.va_end``' intrinsic destroys ``*<arglist>``, which has been
+initialized previously with ``llvm.va_start`` or ``llvm.va_copy``.
+
+Arguments:
+""""""""""
+
+The argument is a pointer to a ``va_list`` to destroy.
+
+Semantics:
+""""""""""
+
+The '``llvm.va_end``' intrinsic works just like the ``va_end`` macro
+available in C. In a target-dependent way, it destroys the ``va_list``
+element to which the argument points. Calls to
+:ref:`llvm.va_start <int_va_start>` and
+:ref:`llvm.va_copy <int_va_copy>` must be matched exactly with calls to
+``llvm.va_end``.
+
+.. _int_va_copy:
+
+'``llvm.va_copy``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.va_copy(i8* <destarglist>, i8* <srcarglist>)
+
+Overview:
+"""""""""
+
+The '``llvm.va_copy``' intrinsic copies the current argument position
+from the source argument list to the destination argument list.
+
+Arguments:
+""""""""""
+
+The first argument is a pointer to a ``va_list`` element to initialize.
+The second argument is a pointer to a ``va_list`` element to copy from.
+
+Semantics:
+""""""""""
+
+The '``llvm.va_copy``' intrinsic works just like the ``va_copy`` macro
+available in C. In a target-dependent way, it copies the source
+``va_list`` element into the destination ``va_list`` element. This
+intrinsic is necessary because the `` llvm.va_start`` intrinsic may be
+arbitrarily complex and require, for example, memory allocation.
+
+Accurate Garbage Collection Intrinsics
+--------------------------------------
+
+LLVM's support for `Accurate Garbage Collection <GarbageCollection.html>`_
+(GC) requires the frontend to generate code containing appropriate intrinsic
+calls and select an appropriate GC strategy which knows how to lower these
+intrinsics in a manner which is appropriate for the target collector.
+
+These intrinsics allow identification of :ref:`GC roots on the
+stack <int_gcroot>`, as well as garbage collector implementations that
+require :ref:`read <int_gcread>` and :ref:`write <int_gcwrite>` barriers.
+Frontends for type-safe garbage collected languages should generate
+these intrinsics to make use of the LLVM garbage collectors. For more
+details, see `Garbage Collection with LLVM <GarbageCollection.html>`_.
+
+Experimental Statepoint Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+LLVM provides an second experimental set of intrinsics for describing garbage
+collection safepoints in compiled code. These intrinsics are an alternative
+to the ``llvm.gcroot`` intrinsics, but are compatible with the ones for
+:ref:`read <int_gcread>` and :ref:`write <int_gcwrite>` barriers. The
+differences in approach are covered in the `Garbage Collection with LLVM
+<GarbageCollection.html>`_ documentation. The intrinsics themselves are
+described in :doc:`Statepoints`.
+
+.. _int_gcroot:
+
+'``llvm.gcroot``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.gcroot(i8** %ptrloc, i8* %metadata)
+
+Overview:
+"""""""""
+
+The '``llvm.gcroot``' intrinsic declares the existence of a GC root to
+the code generator, and allows some metadata to be associated with it.
+
+Arguments:
+""""""""""
+
+The first argument specifies the address of a stack object that contains
+the root pointer. The second pointer (which must be either a constant or
+a global value address) contains the meta-data to be associated with the
+root.
+
+Semantics:
+""""""""""
+
+At runtime, a call to this intrinsic stores a null pointer into the
+"ptrloc" location. At compile-time, the code generator generates
+information to allow the runtime to find the pointer at GC safe points.
+The '``llvm.gcroot``' intrinsic may only be used in a function which
+:ref:`specifies a GC algorithm <gc>`.
+
+.. _int_gcread:
+
+'``llvm.gcread``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i8* @llvm.gcread(i8* %ObjPtr, i8** %Ptr)
+
+Overview:
+"""""""""
+
+The '``llvm.gcread``' intrinsic identifies reads of references from heap
+locations, allowing garbage collector implementations that require read
+barriers.
+
+Arguments:
+""""""""""
+
+The second argument is the address to read from, which should be an
+address allocated from the garbage collector. The first object is a
+pointer to the start of the referenced object, if needed by the language
+runtime (otherwise null).
+
+Semantics:
+""""""""""
+
+The '``llvm.gcread``' intrinsic has the same semantics as a load
+instruction, but may be replaced with substantially more complex code by
+the garbage collector runtime, as needed. The '``llvm.gcread``'
+intrinsic may only be used in a function which :ref:`specifies a GC
+algorithm <gc>`.
+
+.. _int_gcwrite:
+
+'``llvm.gcwrite``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.gcwrite(i8* %P1, i8* %Obj, i8** %P2)
+
+Overview:
+"""""""""
+
+The '``llvm.gcwrite``' intrinsic identifies writes of references to heap
+locations, allowing garbage collector implementations that require write
+barriers (such as generational or reference counting collectors).
+
+Arguments:
+""""""""""
+
+The first argument is the reference to store, the second is the start of
+the object to store it to, and the third is the address of the field of
+Obj to store to. If the runtime does not require a pointer to the
+object, Obj may be null.
+
+Semantics:
+""""""""""
+
+The '``llvm.gcwrite``' intrinsic has the same semantics as a store
+instruction, but may be replaced with substantially more complex code by
+the garbage collector runtime, as needed. The '``llvm.gcwrite``'
+intrinsic may only be used in a function which :ref:`specifies a GC
+algorithm <gc>`.
+
+Code Generator Intrinsics
+-------------------------
+
+These intrinsics are provided by LLVM to expose special features that
+may only be implemented with code generator support.
+
+'``llvm.returnaddress``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i8* @llvm.returnaddress(i32 <level>)
+
+Overview:
+"""""""""
+
+The '``llvm.returnaddress``' intrinsic attempts to compute a
+target-specific value indicating the return address of the current
+function or one of its callers.
+
+Arguments:
+""""""""""
+
+The argument to this intrinsic indicates which function to return the
+address for. Zero indicates the calling function, one indicates its
+caller, etc. The argument is **required** to be a constant integer
+value.
+
+Semantics:
+""""""""""
+
+The '``llvm.returnaddress``' intrinsic either returns a pointer
+indicating the return address of the specified call frame, or zero if it
+cannot be identified. The value returned by this intrinsic is likely to
+be incorrect or 0 for arguments other than zero, so it should only be
+used for debugging purposes.
+
+Note that calling this intrinsic does not prevent function inlining or
+other aggressive transformations, so the value returned may not be that
+of the obvious source-language caller.
+
+'``llvm.addressofreturnaddress``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i8* @llvm.addressofreturnaddress()
+
+Overview:
+"""""""""
+
+The '``llvm.addressofreturnaddress``' intrinsic returns a target-specific
+pointer to the place in the stack frame where the return address of the
+current function is stored.
+
+Semantics:
+""""""""""
+
+Note that calling this intrinsic does not prevent function inlining or
+other aggressive transformations, so the value returned may not be that
+of the obvious source-language caller.
+
+This intrinsic is only implemented for x86.
+
+'``llvm.frameaddress``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i8* @llvm.frameaddress(i32 <level>)
+
+Overview:
+"""""""""
+
+The '``llvm.frameaddress``' intrinsic attempts to return the
+target-specific frame pointer value for the specified stack frame.
+
+Arguments:
+""""""""""
+
+The argument to this intrinsic indicates which function to return the
+frame pointer for. Zero indicates the calling function, one indicates
+its caller, etc. The argument is **required** to be a constant integer
+value.
+
+Semantics:
+""""""""""
+
+The '``llvm.frameaddress``' intrinsic either returns a pointer
+indicating the frame address of the specified call frame, or zero if it
+cannot be identified. The value returned by this intrinsic is likely to
+be incorrect or 0 for arguments other than zero, so it should only be
+used for debugging purposes.
+
+Note that calling this intrinsic does not prevent function inlining or
+other aggressive transformations, so the value returned may not be that
+of the obvious source-language caller.
+
+'``llvm.localescape``' and '``llvm.localrecover``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.localescape(...)
+ declare i8* @llvm.localrecover(i8* %func, i8* %fp, i32 %idx)
+
+Overview:
+"""""""""
+
+The '``llvm.localescape``' intrinsic escapes offsets of a collection of static
+allocas, and the '``llvm.localrecover``' intrinsic applies those offsets to a
+live frame pointer to recover the address of the allocation. The offset is
+computed during frame layout of the caller of ``llvm.localescape``.
+
+Arguments:
+""""""""""
+
+All arguments to '``llvm.localescape``' must be pointers to static allocas or
+casts of static allocas. Each function can only call '``llvm.localescape``'
+once, and it can only do so from the entry block.
+
+The ``func`` argument to '``llvm.localrecover``' must be a constant
+bitcasted pointer to a function defined in the current module. The code
+generator cannot determine the frame allocation offset of functions defined in
+other modules.
+
+The ``fp`` argument to '``llvm.localrecover``' must be a frame pointer of a
+call frame that is currently live. The return value of '``llvm.localaddress``'
+is one way to produce such a value, but various runtimes also expose a suitable
+pointer in platform-specific ways.
+
+The ``idx`` argument to '``llvm.localrecover``' indicates which alloca passed to
+'``llvm.localescape``' to recover. It is zero-indexed.
+
+Semantics:
+""""""""""
+
+These intrinsics allow a group of functions to share access to a set of local
+stack allocations of a one parent function. The parent function may call the
+'``llvm.localescape``' intrinsic once from the function entry block, and the
+child functions can use '``llvm.localrecover``' to access the escaped allocas.
+The '``llvm.localescape``' intrinsic blocks inlining, as inlining changes where
+the escaped allocas are allocated, which would break attempts to use
+'``llvm.localrecover``'.
+
+.. _int_read_register:
+.. _int_write_register:
+
+'``llvm.read_register``' and '``llvm.write_register``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i32 @llvm.read_register.i32(metadata)
+ declare i64 @llvm.read_register.i64(metadata)
+ declare void @llvm.write_register.i32(metadata, i32 @value)
+ declare void @llvm.write_register.i64(metadata, i64 @value)
+ !0 = !{!"sp\00"}
+
+Overview:
+"""""""""
+
+The '``llvm.read_register``' and '``llvm.write_register``' intrinsics
+provides access to the named register. The register must be valid on
+the architecture being compiled to. The type needs to be compatible
+with the register being read.
+
+Semantics:
+""""""""""
+
+The '``llvm.read_register``' intrinsic returns the current value of the
+register, where possible. The '``llvm.write_register``' intrinsic sets
+the current value of the register, where possible.
+
+This is useful to implement named register global variables that need
+to always be mapped to a specific register, as is common practice on
+bare-metal programs including OS kernels.
+
+The compiler doesn't check for register availability or use of the used
+register in surrounding code, including inline assembly. Because of that,
+allocatable registers are not supported.
+
+Warning: So far it only works with the stack pointer on selected
+architectures (ARM, AArch64, PowerPC and x86_64). Significant amount of
+work is needed to support other registers and even more so, allocatable
+registers.
+
+.. _int_stacksave:
+
+'``llvm.stacksave``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i8* @llvm.stacksave()
+
+Overview:
+"""""""""
+
+The '``llvm.stacksave``' intrinsic is used to remember the current state
+of the function stack, for use with
+:ref:`llvm.stackrestore <int_stackrestore>`. This is useful for
+implementing language features like scoped automatic variable sized
+arrays in C99.
+
+Semantics:
+""""""""""
+
+This intrinsic returns a opaque pointer value that can be passed to
+:ref:`llvm.stackrestore <int_stackrestore>`. When an
+``llvm.stackrestore`` intrinsic is executed with a value saved from
+``llvm.stacksave``, it effectively restores the state of the stack to
+the state it was in when the ``llvm.stacksave`` intrinsic executed. In
+practice, this pops any :ref:`alloca <i_alloca>` blocks from the stack that
+were allocated after the ``llvm.stacksave`` was executed.
+
+.. _int_stackrestore:
+
+'``llvm.stackrestore``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.stackrestore(i8* %ptr)
+
+Overview:
+"""""""""
+
+The '``llvm.stackrestore``' intrinsic is used to restore the state of
+the function stack to the state it was in when the corresponding
+:ref:`llvm.stacksave <int_stacksave>` intrinsic executed. This is
+useful for implementing language features like scoped automatic variable
+sized arrays in C99.
+
+Semantics:
+""""""""""
+
+See the description for :ref:`llvm.stacksave <int_stacksave>`.
+
+.. _int_get_dynamic_area_offset:
+
+'``llvm.get.dynamic.area.offset``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i32 @llvm.get.dynamic.area.offset.i32()
+ declare i64 @llvm.get.dynamic.area.offset.i64()
+
+Overview:
+"""""""""
+
+ The '``llvm.get.dynamic.area.offset.*``' intrinsic family is used to
+ get the offset from native stack pointer to the address of the most
+ recent dynamic alloca on the caller's stack. These intrinsics are
+ intendend for use in combination with
+ :ref:`llvm.stacksave <int_stacksave>` to get a
+ pointer to the most recent dynamic alloca. This is useful, for example,
+ for AddressSanitizer's stack unpoisoning routines.
+
+Semantics:
+""""""""""
+
+ These intrinsics return a non-negative integer value that can be used to
+ get the address of the most recent dynamic alloca, allocated by :ref:`alloca <i_alloca>`
+ on the caller's stack. In particular, for targets where stack grows downwards,
+ adding this offset to the native stack pointer would get the address of the most
+ recent dynamic alloca. For targets where stack grows upwards, the situation is a bit more
+ complicated, because subtracting this value from stack pointer would get the address
+ one past the end of the most recent dynamic alloca.
+
+ Although for most targets `llvm.get.dynamic.area.offset <int_get_dynamic_area_offset>`
+ returns just a zero, for others, such as PowerPC and PowerPC64, it returns a
+ compile-time-known constant value.
+
+ The return value type of :ref:`llvm.get.dynamic.area.offset <int_get_dynamic_area_offset>`
+ must match the target's default address space's (address space 0) pointer type.
+
+'``llvm.prefetch``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.prefetch(i8* <address>, i32 <rw>, i32 <locality>, i32 <cache type>)
+
+Overview:
+"""""""""
+
+The '``llvm.prefetch``' intrinsic is a hint to the code generator to
+insert a prefetch instruction if supported; otherwise, it is a noop.
+Prefetches have no effect on the behavior of the program but can change
+its performance characteristics.
+
+Arguments:
+""""""""""
+
+``address`` is the address to be prefetched, ``rw`` is the specifier
+determining if the fetch should be for a read (0) or write (1), and
+``locality`` is a temporal locality specifier ranging from (0) - no
+locality, to (3) - extremely local keep in cache. The ``cache type``
+specifies whether the prefetch is performed on the data (1) or
+instruction (0) cache. The ``rw``, ``locality`` and ``cache type``
+arguments must be constant integers.
+
+Semantics:
+""""""""""
+
+This intrinsic does not modify the behavior of the program. In
+particular, prefetches cannot trap and do not produce a value. On
+targets that support this intrinsic, the prefetch can provide hints to
+the processor cache for better performance.
+
+'``llvm.pcmarker``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.pcmarker(i32 <id>)
+
+Overview:
+"""""""""
+
+The '``llvm.pcmarker``' intrinsic is a method to export a Program
+Counter (PC) in a region of code to simulators and other tools. The
+method is target specific, but it is expected that the marker will use
+exported symbols to transmit the PC of the marker. The marker makes no
+guarantees that it will remain with any specific instruction after
+optimizations. It is possible that the presence of a marker will inhibit
+optimizations. The intended use is to be inserted after optimizations to
+allow correlations of simulation runs.
+
+Arguments:
+""""""""""
+
+``id`` is a numerical id identifying the marker.
+
+Semantics:
+""""""""""
+
+This intrinsic does not modify the behavior of the program. Backends
+that do not support this intrinsic may ignore it.
+
+'``llvm.readcyclecounter``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i64 @llvm.readcyclecounter()
+
+Overview:
+"""""""""
+
+The '``llvm.readcyclecounter``' intrinsic provides access to the cycle
+counter register (or similar low latency, high accuracy clocks) on those
+targets that support it. On X86, it should map to RDTSC. On Alpha, it
+should map to RPCC. As the backing counters overflow quickly (on the
+order of 9 seconds on alpha), this should only be used for small
+timings.
+
+Semantics:
+""""""""""
+
+When directly supported, reading the cycle counter should not modify any
+memory. Implementations are allowed to either return a application
+specific value or a system wide value. On backends without support, this
+is lowered to a constant 0.
+
+Note that runtime support may be conditional on the privilege-level code is
+running at and the host platform.
+
+'``llvm.clear_cache``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.clear_cache(i8*, i8*)
+
+Overview:
+"""""""""
+
+The '``llvm.clear_cache``' intrinsic ensures visibility of modifications
+in the specified range to the execution unit of the processor. On
+targets with non-unified instruction and data cache, the implementation
+flushes the instruction cache.
+
+Semantics:
+""""""""""
+
+On platforms with coherent instruction and data caches (e.g. x86), this
+intrinsic is a nop. On platforms with non-coherent instruction and data
+cache (e.g. ARM, MIPS), the intrinsic is lowered either to appropriate
+instructions or a system call, if cache flushing requires special
+privileges.
+
+The default behavior is to emit a call to ``__clear_cache`` from the run
+time library.
+
+This instrinsic does *not* empty the instruction pipeline. Modifications
+of the current function are outside the scope of the intrinsic.
+
+'``llvm.instrprof_increment``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.instrprof_increment(i8* <name>, i64 <hash>,
+ i32 <num-counters>, i32 <index>)
+
+Overview:
+"""""""""
+
+The '``llvm.instrprof_increment``' intrinsic can be emitted by a
+frontend for use with instrumentation based profiling. These will be
+lowered by the ``-instrprof`` pass to generate execution counts of a
+program at runtime.
+
+Arguments:
+""""""""""
+
+The first argument is a pointer to a global variable containing the
+name of the entity being instrumented. This should generally be the
+(mangled) function name for a set of counters.
+
+The second argument is a hash value that can be used by the consumer
+of the profile data to detect changes to the instrumented source, and
+the third is the number of counters associated with ``name``. It is an
+error if ``hash`` or ``num-counters`` differ between two instances of
+``instrprof_increment`` that refer to the same name.
+
+The last argument refers to which of the counters for ``name`` should
+be incremented. It should be a value between 0 and ``num-counters``.
+
+Semantics:
+""""""""""
+
+This intrinsic represents an increment of a profiling counter. It will
+cause the ``-instrprof`` pass to generate the appropriate data
+structures and the code to increment the appropriate value, in a
+format that can be written out by a compiler runtime and consumed via
+the ``llvm-profdata`` tool.
+
+'``llvm.instrprof_increment_step``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.instrprof_increment_step(i8* <name>, i64 <hash>,
+ i32 <num-counters>,
+ i32 <index>, i64 <step>)
+
+Overview:
+"""""""""
+
+The '``llvm.instrprof_increment_step``' intrinsic is an extension to
+the '``llvm.instrprof_increment``' intrinsic with an additional fifth
+argument to specify the step of the increment.
+
+Arguments:
+""""""""""
+The first four arguments are the same as '``llvm.instrprof_increment``'
+instrinsic.
+
+The last argument specifies the value of the increment of the counter variable.
+
+Semantics:
+""""""""""
+See description of '``llvm.instrprof_increment``' instrinsic.
+
+
+'``llvm.instrprof_value_profile``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.instrprof_value_profile(i8* <name>, i64 <hash>,
+ i64 <value>, i32 <value_kind>,
+ i32 <index>)
+
+Overview:
+"""""""""
+
+The '``llvm.instrprof_value_profile``' intrinsic can be emitted by a
+frontend for use with instrumentation based profiling. This will be
+lowered by the ``-instrprof`` pass to find out the target values,
+instrumented expressions take in a program at runtime.
+
+Arguments:
+""""""""""
+
+The first argument is a pointer to a global variable containing the
+name of the entity being instrumented. ``name`` should generally be the
+(mangled) function name for a set of counters.
+
+The second argument is a hash value that can be used by the consumer
+of the profile data to detect changes to the instrumented source. It
+is an error if ``hash`` differs between two instances of
+``llvm.instrprof_*`` that refer to the same name.
+
+The third argument is the value of the expression being profiled. The profiled
+expression's value should be representable as an unsigned 64-bit value. The
+fourth argument represents the kind of value profiling that is being done. The
+supported value profiling kinds are enumerated through the
+``InstrProfValueKind`` type declared in the
+``<include/llvm/ProfileData/InstrProf.h>`` header file. The last argument is the
+index of the instrumented expression within ``name``. It should be >= 0.
+
+Semantics:
+""""""""""
+
+This intrinsic represents the point where a call to a runtime routine
+should be inserted for value profiling of target expressions. ``-instrprof``
+pass will generate the appropriate data structures and replace the
+``llvm.instrprof_value_profile`` intrinsic with the call to the profile
+runtime library with proper arguments.
+
+'``llvm.thread.pointer``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i8* @llvm.thread.pointer()
+
+Overview:
+"""""""""
+
+The '``llvm.thread.pointer``' intrinsic returns the value of the thread
+pointer.
+
+Semantics:
+""""""""""
+
+The '``llvm.thread.pointer``' intrinsic returns a pointer to the TLS area
+for the current thread. The exact semantics of this value are target
+specific: it may point to the start of TLS area, to the end, or somewhere
+in the middle. Depending on the target, this intrinsic may read a register,
+call a helper function, read from an alternate memory space, or perform
+other operations necessary to locate the TLS area. Not all targets support
+this intrinsic.
+
+Standard C Library Intrinsics
+-----------------------------
+
+LLVM provides intrinsics for a few important standard C library
+functions. These intrinsics allow source-language front-ends to pass
+information about the alignment of the pointer arguments to the code
+generator, providing opportunity for more efficient code generation.
+
+.. _int_memcpy:
+
+'``llvm.memcpy``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.memcpy`` on any
+integer bit width and for different address spaces. Not all targets
+support all bit widths however.
+
+::
+
+ declare void @llvm.memcpy.p0i8.p0i8.i32(i8* <dest>, i8* <src>,
+ i32 <len>, i32 <align>, i1 <isvolatile>)
+ declare void @llvm.memcpy.p0i8.p0i8.i64(i8* <dest>, i8* <src>,
+ i64 <len>, i32 <align>, i1 <isvolatile>)
+
+Overview:
+"""""""""
+
+The '``llvm.memcpy.*``' intrinsics copy a block of memory from the
+source location to the destination location.
+
+Note that, unlike the standard libc function, the ``llvm.memcpy.*``
+intrinsics do not return a value, takes extra alignment/isvolatile
+arguments and the pointers can be in specified address spaces.
+
+Arguments:
+""""""""""
+
+The first argument is a pointer to the destination, the second is a
+pointer to the source. The third argument is an integer argument
+specifying the number of bytes to copy, the fourth argument is the
+alignment of the source and destination locations, and the fifth is a
+boolean indicating a volatile access.
+
+If the call to this intrinsic has an alignment value that is not 0 or 1,
+then the caller guarantees that both the source and destination pointers
+are aligned to that boundary.
+
+If the ``isvolatile`` parameter is ``true``, the ``llvm.memcpy`` call is
+a :ref:`volatile operation <volatile>`. The detailed access behavior is not
+very cleanly specified and it is unwise to depend on it.
+
+Semantics:
+""""""""""
+
+The '``llvm.memcpy.*``' intrinsics copy a block of memory from the
+source location to the destination location, which are not allowed to
+overlap. It copies "len" bytes of memory over. If the argument is known
+to be aligned to some boundary, this can be specified as the fourth
+argument, otherwise it should be set to 0 or 1 (both meaning no alignment).
+
+.. _int_memmove:
+
+'``llvm.memmove``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use llvm.memmove on any integer
+bit width and for different address space. Not all targets support all
+bit widths however.
+
+::
+
+ declare void @llvm.memmove.p0i8.p0i8.i32(i8* <dest>, i8* <src>,
+ i32 <len>, i32 <align>, i1 <isvolatile>)
+ declare void @llvm.memmove.p0i8.p0i8.i64(i8* <dest>, i8* <src>,
+ i64 <len>, i32 <align>, i1 <isvolatile>)
+
+Overview:
+"""""""""
+
+The '``llvm.memmove.*``' intrinsics move a block of memory from the
+source location to the destination location. It is similar to the
+'``llvm.memcpy``' intrinsic but allows the two memory locations to
+overlap.
+
+Note that, unlike the standard libc function, the ``llvm.memmove.*``
+intrinsics do not return a value, takes extra alignment/isvolatile
+arguments and the pointers can be in specified address spaces.
+
+Arguments:
+""""""""""
+
+The first argument is a pointer to the destination, the second is a
+pointer to the source. The third argument is an integer argument
+specifying the number of bytes to copy, the fourth argument is the
+alignment of the source and destination locations, and the fifth is a
+boolean indicating a volatile access.
+
+If the call to this intrinsic has an alignment value that is not 0 or 1,
+then the caller guarantees that the source and destination pointers are
+aligned to that boundary.
+
+If the ``isvolatile`` parameter is ``true``, the ``llvm.memmove`` call
+is a :ref:`volatile operation <volatile>`. The detailed access behavior is
+not very cleanly specified and it is unwise to depend on it.
+
+Semantics:
+""""""""""
+
+The '``llvm.memmove.*``' intrinsics copy a block of memory from the
+source location to the destination location, which may overlap. It
+copies "len" bytes of memory over. If the argument is known to be
+aligned to some boundary, this can be specified as the fourth argument,
+otherwise it should be set to 0 or 1 (both meaning no alignment).
+
+.. _int_memset:
+
+'``llvm.memset.*``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use llvm.memset on any integer
+bit width and for different address spaces. However, not all targets
+support all bit widths.
+
+::
+
+ declare void @llvm.memset.p0i8.i32(i8* <dest>, i8 <val>,
+ i32 <len>, i32 <align>, i1 <isvolatile>)
+ declare void @llvm.memset.p0i8.i64(i8* <dest>, i8 <val>,
+ i64 <len>, i32 <align>, i1 <isvolatile>)
+
+Overview:
+"""""""""
+
+The '``llvm.memset.*``' intrinsics fill a block of memory with a
+particular byte value.
+
+Note that, unlike the standard libc function, the ``llvm.memset``
+intrinsic does not return a value and takes extra alignment/volatile
+arguments. Also, the destination can be in an arbitrary address space.
+
+Arguments:
+""""""""""
+
+The first argument is a pointer to the destination to fill, the second
+is the byte value with which to fill it, the third argument is an
+integer argument specifying the number of bytes to fill, and the fourth
+argument is the known alignment of the destination location.
+
+If the call to this intrinsic has an alignment value that is not 0 or 1,
+then the caller guarantees that the destination pointer is aligned to
+that boundary.
+
+If the ``isvolatile`` parameter is ``true``, the ``llvm.memset`` call is
+a :ref:`volatile operation <volatile>`. The detailed access behavior is not
+very cleanly specified and it is unwise to depend on it.
+
+Semantics:
+""""""""""
+
+The '``llvm.memset.*``' intrinsics fill "len" bytes of memory starting
+at the destination location. If the argument is known to be aligned to
+some boundary, this can be specified as the fourth argument, otherwise
+it should be set to 0 or 1 (both meaning no alignment).
+
+'``llvm.sqrt.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.sqrt`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.sqrt.f32(float %Val)
+ declare double @llvm.sqrt.f64(double %Val)
+ declare x86_fp80 @llvm.sqrt.f80(x86_fp80 %Val)
+ declare fp128 @llvm.sqrt.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.sqrt.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.sqrt``' intrinsics return the square root of the specified value,
+returning the same value as the libm '``sqrt``' functions would, but without
+trapping or setting ``errno``.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same type.
+
+Semantics:
+""""""""""
+
+This function returns the square root of the operand if it is a nonnegative
+floating point number.
+
+'``llvm.powi.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.powi`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.powi.f32(float %Val, i32 %power)
+ declare double @llvm.powi.f64(double %Val, i32 %power)
+ declare x86_fp80 @llvm.powi.f80(x86_fp80 %Val, i32 %power)
+ declare fp128 @llvm.powi.f128(fp128 %Val, i32 %power)
+ declare ppc_fp128 @llvm.powi.ppcf128(ppc_fp128 %Val, i32 %power)
+
+Overview:
+"""""""""
+
+The '``llvm.powi.*``' intrinsics return the first operand raised to the
+specified (positive or negative) power. The order of evaluation of
+multiplications is not defined. When a vector of floating point type is
+used, the second argument remains a scalar integer value.
+
+Arguments:
+""""""""""
+
+The second argument is an integer power, and the first is a value to
+raise to that power.
+
+Semantics:
+""""""""""
+
+This function returns the first value raised to the second power with an
+unspecified sequence of rounding operations.
+
+'``llvm.sin.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.sin`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.sin.f32(float %Val)
+ declare double @llvm.sin.f64(double %Val)
+ declare x86_fp80 @llvm.sin.f80(x86_fp80 %Val)
+ declare fp128 @llvm.sin.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.sin.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.sin.*``' intrinsics return the sine of the operand.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same type.
+
+Semantics:
+""""""""""
+
+This function returns the sine of the specified operand, returning the
+same values as the libm ``sin`` functions would, and handles error
+conditions in the same way.
+
+'``llvm.cos.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.cos`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.cos.f32(float %Val)
+ declare double @llvm.cos.f64(double %Val)
+ declare x86_fp80 @llvm.cos.f80(x86_fp80 %Val)
+ declare fp128 @llvm.cos.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.cos.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.cos.*``' intrinsics return the cosine of the operand.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same type.
+
+Semantics:
+""""""""""
+
+This function returns the cosine of the specified operand, returning the
+same values as the libm ``cos`` functions would, and handles error
+conditions in the same way.
+
+'``llvm.pow.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.pow`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.pow.f32(float %Val, float %Power)
+ declare double @llvm.pow.f64(double %Val, double %Power)
+ declare x86_fp80 @llvm.pow.f80(x86_fp80 %Val, x86_fp80 %Power)
+ declare fp128 @llvm.pow.f128(fp128 %Val, fp128 %Power)
+ declare ppc_fp128 @llvm.pow.ppcf128(ppc_fp128 %Val, ppc_fp128 Power)
+
+Overview:
+"""""""""
+
+The '``llvm.pow.*``' intrinsics return the first operand raised to the
+specified (positive or negative) power.
+
+Arguments:
+""""""""""
+
+The second argument is a floating point power, and the first is a value
+to raise to that power.
+
+Semantics:
+""""""""""
+
+This function returns the first value raised to the second power,
+returning the same values as the libm ``pow`` functions would, and
+handles error conditions in the same way.
+
+'``llvm.exp.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.exp`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.exp.f32(float %Val)
+ declare double @llvm.exp.f64(double %Val)
+ declare x86_fp80 @llvm.exp.f80(x86_fp80 %Val)
+ declare fp128 @llvm.exp.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.exp.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.exp.*``' intrinsics compute the base-e exponential of the specified
+value.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same type.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``exp`` functions
+would, and handles error conditions in the same way.
+
+'``llvm.exp2.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.exp2`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.exp2.f32(float %Val)
+ declare double @llvm.exp2.f64(double %Val)
+ declare x86_fp80 @llvm.exp2.f80(x86_fp80 %Val)
+ declare fp128 @llvm.exp2.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.exp2.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.exp2.*``' intrinsics compute the base-2 exponential of the
+specified value.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same type.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``exp2`` functions
+would, and handles error conditions in the same way.
+
+'``llvm.log.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.log`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.log.f32(float %Val)
+ declare double @llvm.log.f64(double %Val)
+ declare x86_fp80 @llvm.log.f80(x86_fp80 %Val)
+ declare fp128 @llvm.log.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.log.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.log.*``' intrinsics compute the base-e logarithm of the specified
+value.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same type.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``log`` functions
+would, and handles error conditions in the same way.
+
+'``llvm.log10.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.log10`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.log10.f32(float %Val)
+ declare double @llvm.log10.f64(double %Val)
+ declare x86_fp80 @llvm.log10.f80(x86_fp80 %Val)
+ declare fp128 @llvm.log10.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.log10.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.log10.*``' intrinsics compute the base-10 logarithm of the
+specified value.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same type.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``log10`` functions
+would, and handles error conditions in the same way.
+
+'``llvm.log2.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.log2`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.log2.f32(float %Val)
+ declare double @llvm.log2.f64(double %Val)
+ declare x86_fp80 @llvm.log2.f80(x86_fp80 %Val)
+ declare fp128 @llvm.log2.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.log2.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.log2.*``' intrinsics compute the base-2 logarithm of the specified
+value.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same type.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``log2`` functions
+would, and handles error conditions in the same way.
+
+'``llvm.fma.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.fma`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.fma.f32(float %a, float %b, float %c)
+ declare double @llvm.fma.f64(double %a, double %b, double %c)
+ declare x86_fp80 @llvm.fma.f80(x86_fp80 %a, x86_fp80 %b, x86_fp80 %c)
+ declare fp128 @llvm.fma.f128(fp128 %a, fp128 %b, fp128 %c)
+ declare ppc_fp128 @llvm.fma.ppcf128(ppc_fp128 %a, ppc_fp128 %b, ppc_fp128 %c)
+
+Overview:
+"""""""""
+
+The '``llvm.fma.*``' intrinsics perform the fused multiply-add
+operation.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same
+type.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``fma`` functions
+would, and does not set errno.
+
+'``llvm.fabs.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.fabs`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.fabs.f32(float %Val)
+ declare double @llvm.fabs.f64(double %Val)
+ declare x86_fp80 @llvm.fabs.f80(x86_fp80 %Val)
+ declare fp128 @llvm.fabs.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.fabs.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.fabs.*``' intrinsics return the absolute value of the
+operand.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same
+type.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``fabs`` functions
+would, and handles error conditions in the same way.
+
+'``llvm.minnum.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.minnum`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.minnum.f32(float %Val0, float %Val1)
+ declare double @llvm.minnum.f64(double %Val0, double %Val1)
+ declare x86_fp80 @llvm.minnum.f80(x86_fp80 %Val0, x86_fp80 %Val1)
+ declare fp128 @llvm.minnum.f128(fp128 %Val0, fp128 %Val1)
+ declare ppc_fp128 @llvm.minnum.ppcf128(ppc_fp128 %Val0, ppc_fp128 %Val1)
+
+Overview:
+"""""""""
+
+The '``llvm.minnum.*``' intrinsics return the minimum of the two
+arguments.
+
+
+Arguments:
+""""""""""
+
+The arguments and return value are floating point numbers of the same
+type.
+
+Semantics:
+""""""""""
+
+Follows the IEEE-754 semantics for minNum, which also match for libm's
+fmin.
+
+If either operand is a NaN, returns the other non-NaN operand. Returns
+NaN only if both operands are NaN. If the operands compare equal,
+returns a value that compares equal to both operands. This means that
+fmin(+/-0.0, +/-0.0) could return either -0.0 or 0.0.
+
+'``llvm.maxnum.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.maxnum`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.maxnum.f32(float %Val0, float %Val1l)
+ declare double @llvm.maxnum.f64(double %Val0, double %Val1)
+ declare x86_fp80 @llvm.maxnum.f80(x86_fp80 %Val0, x86_fp80 %Val1)
+ declare fp128 @llvm.maxnum.f128(fp128 %Val0, fp128 %Val1)
+ declare ppc_fp128 @llvm.maxnum.ppcf128(ppc_fp128 %Val0, ppc_fp128 %Val1)
+
+Overview:
+"""""""""
+
+The '``llvm.maxnum.*``' intrinsics return the maximum of the two
+arguments.
+
+
+Arguments:
+""""""""""
+
+The arguments and return value are floating point numbers of the same
+type.
+
+Semantics:
+""""""""""
+Follows the IEEE-754 semantics for maxNum, which also match for libm's
+fmax.
+
+If either operand is a NaN, returns the other non-NaN operand. Returns
+NaN only if both operands are NaN. If the operands compare equal,
+returns a value that compares equal to both operands. This means that
+fmax(+/-0.0, +/-0.0) could return either -0.0 or 0.0.
+
+'``llvm.copysign.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.copysign`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.copysign.f32(float %Mag, float %Sgn)
+ declare double @llvm.copysign.f64(double %Mag, double %Sgn)
+ declare x86_fp80 @llvm.copysign.f80(x86_fp80 %Mag, x86_fp80 %Sgn)
+ declare fp128 @llvm.copysign.f128(fp128 %Mag, fp128 %Sgn)
+ declare ppc_fp128 @llvm.copysign.ppcf128(ppc_fp128 %Mag, ppc_fp128 %Sgn)
+
+Overview:
+"""""""""
+
+The '``llvm.copysign.*``' intrinsics return a value with the magnitude of the
+first operand and the sign of the second operand.
+
+Arguments:
+""""""""""
+
+The arguments and return value are floating point numbers of the same
+type.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``copysign``
+functions would, and handles error conditions in the same way.
+
+'``llvm.floor.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.floor`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.floor.f32(float %Val)
+ declare double @llvm.floor.f64(double %Val)
+ declare x86_fp80 @llvm.floor.f80(x86_fp80 %Val)
+ declare fp128 @llvm.floor.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.floor.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.floor.*``' intrinsics return the floor of the operand.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same
+type.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``floor`` functions
+would, and handles error conditions in the same way.
+
+'``llvm.ceil.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.ceil`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.ceil.f32(float %Val)
+ declare double @llvm.ceil.f64(double %Val)
+ declare x86_fp80 @llvm.ceil.f80(x86_fp80 %Val)
+ declare fp128 @llvm.ceil.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.ceil.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.ceil.*``' intrinsics return the ceiling of the operand.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same
+type.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``ceil`` functions
+would, and handles error conditions in the same way.
+
+'``llvm.trunc.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.trunc`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.trunc.f32(float %Val)
+ declare double @llvm.trunc.f64(double %Val)
+ declare x86_fp80 @llvm.trunc.f80(x86_fp80 %Val)
+ declare fp128 @llvm.trunc.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.trunc.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.trunc.*``' intrinsics returns the operand rounded to the
+nearest integer not larger in magnitude than the operand.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same
+type.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``trunc`` functions
+would, and handles error conditions in the same way.
+
+'``llvm.rint.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.rint`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.rint.f32(float %Val)
+ declare double @llvm.rint.f64(double %Val)
+ declare x86_fp80 @llvm.rint.f80(x86_fp80 %Val)
+ declare fp128 @llvm.rint.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.rint.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.rint.*``' intrinsics returns the operand rounded to the
+nearest integer. It may raise an inexact floating-point exception if the
+operand isn't an integer.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same
+type.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``rint`` functions
+would, and handles error conditions in the same way.
+
+'``llvm.nearbyint.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.nearbyint`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.nearbyint.f32(float %Val)
+ declare double @llvm.nearbyint.f64(double %Val)
+ declare x86_fp80 @llvm.nearbyint.f80(x86_fp80 %Val)
+ declare fp128 @llvm.nearbyint.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.nearbyint.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.nearbyint.*``' intrinsics returns the operand rounded to the
+nearest integer.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same
+type.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``nearbyint``
+functions would, and handles error conditions in the same way.
+
+'``llvm.round.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.round`` on any
+floating point or vector of floating point type. Not all targets support
+all types however.
+
+::
+
+ declare float @llvm.round.f32(float %Val)
+ declare double @llvm.round.f64(double %Val)
+ declare x86_fp80 @llvm.round.f80(x86_fp80 %Val)
+ declare fp128 @llvm.round.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.round.ppcf128(ppc_fp128 %Val)
+
+Overview:
+"""""""""
+
+The '``llvm.round.*``' intrinsics returns the operand rounded to the
+nearest integer.
+
+Arguments:
+""""""""""
+
+The argument and return value are floating point numbers of the same
+type.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``round``
+functions would, and handles error conditions in the same way.
+
+Bit Manipulation Intrinsics
+---------------------------
+
+LLVM provides intrinsics for a few important bit manipulation
+operations. These allow efficient code generation for some algorithms.
+
+'``llvm.bitreverse.*``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic function. You can use bitreverse on any
+integer type.
+
+::
+
+ declare i16 @llvm.bitreverse.i16(i16 <id>)
+ declare i32 @llvm.bitreverse.i32(i32 <id>)
+ declare i64 @llvm.bitreverse.i64(i64 <id>)
+
+Overview:
+"""""""""
+
+The '``llvm.bitreverse``' family of intrinsics is used to reverse the
+bitpattern of an integer value; for example ``0b10110110`` becomes
+``0b01101101``.
+
+Semantics:
+""""""""""
+
+The ``llvm.bitreverse.iN`` intrinsic returns an iN value that has bit
+``M`` in the input moved to bit ``N-M`` in the output.
+
+'``llvm.bswap.*``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic function. You can use bswap on any
+integer type that is an even number of bytes (i.e. BitWidth % 16 == 0).
+
+::
+
+ declare i16 @llvm.bswap.i16(i16 <id>)
+ declare i32 @llvm.bswap.i32(i32 <id>)
+ declare i64 @llvm.bswap.i64(i64 <id>)
+
+Overview:
+"""""""""
+
+The '``llvm.bswap``' family of intrinsics is used to byte swap integer
+values with an even number of bytes (positive multiple of 16 bits).
+These are useful for performing operations on data that is not in the
+target's native byte order.
+
+Semantics:
+""""""""""
+
+The ``llvm.bswap.i16`` intrinsic returns an i16 value that has the high
+and low byte of the input i16 swapped. Similarly, the ``llvm.bswap.i32``
+intrinsic returns an i32 value that has the four bytes of the input i32
+swapped, so that if the input bytes are numbered 0, 1, 2, 3 then the
+returned i32 will have its bytes in 3, 2, 1, 0 order. The
+``llvm.bswap.i48``, ``llvm.bswap.i64`` and other intrinsics extend this
+concept to additional even-byte lengths (6 bytes, 8 bytes and more,
+respectively).
+
+'``llvm.ctpop.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use llvm.ctpop on any integer
+bit width, or on any vector with integer elements. Not all targets
+support all bit widths or vector types, however.
+
+::
+
+ declare i8 @llvm.ctpop.i8(i8 <src>)
+ declare i16 @llvm.ctpop.i16(i16 <src>)
+ declare i32 @llvm.ctpop.i32(i32 <src>)
+ declare i64 @llvm.ctpop.i64(i64 <src>)
+ declare i256 @llvm.ctpop.i256(i256 <src>)
+ declare <2 x i32> @llvm.ctpop.v2i32(<2 x i32> <src>)
+
+Overview:
+"""""""""
+
+The '``llvm.ctpop``' family of intrinsics counts the number of bits set
+in a value.
+
+Arguments:
+""""""""""
+
+The only argument is the value to be counted. The argument may be of any
+integer type, or a vector with integer elements. The return type must
+match the argument type.
+
+Semantics:
+""""""""""
+
+The '``llvm.ctpop``' intrinsic counts the 1's in a variable, or within
+each element of a vector.
+
+'``llvm.ctlz.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.ctlz`` on any
+integer bit width, or any vector whose elements are integers. Not all
+targets support all bit widths or vector types, however.
+
+::
+
+ declare i8 @llvm.ctlz.i8 (i8 <src>, i1 <is_zero_undef>)
+ declare i16 @llvm.ctlz.i16 (i16 <src>, i1 <is_zero_undef>)
+ declare i32 @llvm.ctlz.i32 (i32 <src>, i1 <is_zero_undef>)
+ declare i64 @llvm.ctlz.i64 (i64 <src>, i1 <is_zero_undef>)
+ declare i256 @llvm.ctlz.i256(i256 <src>, i1 <is_zero_undef>)
+ declare <2 x i32> @llvm.ctlz.v2i32(<2 x i32> <src>, i1 <is_zero_undef>)
+
+Overview:
+"""""""""
+
+The '``llvm.ctlz``' family of intrinsic functions counts the number of
+leading zeros in a variable.
+
+Arguments:
+""""""""""
+
+The first argument is the value to be counted. This argument may be of
+any integer type, or a vector with integer element type. The return
+type must match the first argument type.
+
+The second argument must be a constant and is a flag to indicate whether
+the intrinsic should ensure that a zero as the first argument produces a
+defined result. Historically some architectures did not provide a
+defined result for zero values as efficiently, and many algorithms are
+now predicated on avoiding zero-value inputs.
+
+Semantics:
+""""""""""
+
+The '``llvm.ctlz``' intrinsic counts the leading (most significant)
+zeros in a variable, or within each element of the vector. If
+``src == 0`` then the result is the size in bits of the type of ``src``
+if ``is_zero_undef == 0`` and ``undef`` otherwise. For example,
+``llvm.ctlz(i32 2) = 30``.
+
+'``llvm.cttz.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.cttz`` on any
+integer bit width, or any vector of integer elements. Not all targets
+support all bit widths or vector types, however.
+
+::
+
+ declare i8 @llvm.cttz.i8 (i8 <src>, i1 <is_zero_undef>)
+ declare i16 @llvm.cttz.i16 (i16 <src>, i1 <is_zero_undef>)
+ declare i32 @llvm.cttz.i32 (i32 <src>, i1 <is_zero_undef>)
+ declare i64 @llvm.cttz.i64 (i64 <src>, i1 <is_zero_undef>)
+ declare i256 @llvm.cttz.i256(i256 <src>, i1 <is_zero_undef>)
+ declare <2 x i32> @llvm.cttz.v2i32(<2 x i32> <src>, i1 <is_zero_undef>)
+
+Overview:
+"""""""""
+
+The '``llvm.cttz``' family of intrinsic functions counts the number of
+trailing zeros.
+
+Arguments:
+""""""""""
+
+The first argument is the value to be counted. This argument may be of
+any integer type, or a vector with integer element type. The return
+type must match the first argument type.
+
+The second argument must be a constant and is a flag to indicate whether
+the intrinsic should ensure that a zero as the first argument produces a
+defined result. Historically some architectures did not provide a
+defined result for zero values as efficiently, and many algorithms are
+now predicated on avoiding zero-value inputs.
+
+Semantics:
+""""""""""
+
+The '``llvm.cttz``' intrinsic counts the trailing (least significant)
+zeros in a variable, or within each element of a vector. If ``src == 0``
+then the result is the size in bits of the type of ``src`` if
+``is_zero_undef == 0`` and ``undef`` otherwise. For example,
+``llvm.cttz(2) = 1``.
+
+.. _int_overflow:
+
+Arithmetic with Overflow Intrinsics
+-----------------------------------
+
+LLVM provides intrinsics for fast arithmetic overflow checking.
+
+Each of these intrinsics returns a two-element struct. The first
+element of this struct contains the result of the corresponding
+arithmetic operation modulo 2\ :sup:`n`\ , where n is the bit width of
+the result. Therefore, for example, the first element of the struct
+returned by ``llvm.sadd.with.overflow.i32`` is always the same as the
+result of a 32-bit ``add`` instruction with the same operands, where
+the ``add`` is *not* modified by an ``nsw`` or ``nuw`` flag.
+
+The second element of the result is an ``i1`` that is 1 if the
+arithmetic operation overflowed and 0 otherwise. An operation
+overflows if, for any values of its operands ``A`` and ``B`` and for
+any ``N`` larger than the operands' width, ``ext(A op B) to iN`` is
+not equal to ``(ext(A) to iN) op (ext(B) to iN)`` where ``ext`` is
+``sext`` for signed overflow and ``zext`` for unsigned overflow, and
+``op`` is the underlying arithmetic operation.
+
+The behavior of these intrinsics is well-defined for all argument
+values.
+
+'``llvm.sadd.with.overflow.*``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.sadd.with.overflow``
+on any integer bit width.
+
+::
+
+ declare {i16, i1} @llvm.sadd.with.overflow.i16(i16 %a, i16 %b)
+ declare {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b)
+ declare {i64, i1} @llvm.sadd.with.overflow.i64(i64 %a, i64 %b)
+
+Overview:
+"""""""""
+
+The '``llvm.sadd.with.overflow``' family of intrinsic functions perform
+a signed addition of the two arguments, and indicate whether an overflow
+occurred during the signed summation.
+
+Arguments:
+""""""""""
+
+The arguments (%a and %b) and the first element of the result structure
+may be of integer types of any bit width, but they must have the same
+bit width. The second element of the result structure must be of type
+``i1``. ``%a`` and ``%b`` are the two values that will undergo signed
+addition.
+
+Semantics:
+""""""""""
+
+The '``llvm.sadd.with.overflow``' family of intrinsic functions perform
+a signed addition of the two variables. They return a structure --- the
+first element of which is the signed summation, and the second element
+of which is a bit specifying if the signed summation resulted in an
+overflow.
+
+Examples:
+"""""""""
+
+.. code-block:: llvm
+
+ %res = call {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b)
+ %sum = extractvalue {i32, i1} %res, 0
+ %obit = extractvalue {i32, i1} %res, 1
+ br i1 %obit, label %overflow, label %normal
+
+'``llvm.uadd.with.overflow.*``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.uadd.with.overflow``
+on any integer bit width.
+
+::
+
+ declare {i16, i1} @llvm.uadd.with.overflow.i16(i16 %a, i16 %b)
+ declare {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)
+ declare {i64, i1} @llvm.uadd.with.overflow.i64(i64 %a, i64 %b)
+
+Overview:
+"""""""""
+
+The '``llvm.uadd.with.overflow``' family of intrinsic functions perform
+an unsigned addition of the two arguments, and indicate whether a carry
+occurred during the unsigned summation.
+
+Arguments:
+""""""""""
+
+The arguments (%a and %b) and the first element of the result structure
+may be of integer types of any bit width, but they must have the same
+bit width. The second element of the result structure must be of type
+``i1``. ``%a`` and ``%b`` are the two values that will undergo unsigned
+addition.
+
+Semantics:
+""""""""""
+
+The '``llvm.uadd.with.overflow``' family of intrinsic functions perform
+an unsigned addition of the two arguments. They return a structure --- the
+first element of which is the sum, and the second element of which is a
+bit specifying if the unsigned summation resulted in a carry.
+
+Examples:
+"""""""""
+
+.. code-block:: llvm
+
+ %res = call {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)
+ %sum = extractvalue {i32, i1} %res, 0
+ %obit = extractvalue {i32, i1} %res, 1
+ br i1 %obit, label %carry, label %normal
+
+'``llvm.ssub.with.overflow.*``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.ssub.with.overflow``
+on any integer bit width.
+
+::
+
+ declare {i16, i1} @llvm.ssub.with.overflow.i16(i16 %a, i16 %b)
+ declare {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b)
+ declare {i64, i1} @llvm.ssub.with.overflow.i64(i64 %a, i64 %b)
+
+Overview:
+"""""""""
+
+The '``llvm.ssub.with.overflow``' family of intrinsic functions perform
+a signed subtraction of the two arguments, and indicate whether an
+overflow occurred during the signed subtraction.
+
+Arguments:
+""""""""""
+
+The arguments (%a and %b) and the first element of the result structure
+may be of integer types of any bit width, but they must have the same
+bit width. The second element of the result structure must be of type
+``i1``. ``%a`` and ``%b`` are the two values that will undergo signed
+subtraction.
+
+Semantics:
+""""""""""
+
+The '``llvm.ssub.with.overflow``' family of intrinsic functions perform
+a signed subtraction of the two arguments. They return a structure --- the
+first element of which is the subtraction, and the second element of
+which is a bit specifying if the signed subtraction resulted in an
+overflow.
+
+Examples:
+"""""""""
+
+.. code-block:: llvm
+
+ %res = call {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b)
+ %sum = extractvalue {i32, i1} %res, 0
+ %obit = extractvalue {i32, i1} %res, 1
+ br i1 %obit, label %overflow, label %normal
+
+'``llvm.usub.with.overflow.*``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.usub.with.overflow``
+on any integer bit width.
+
+::
+
+ declare {i16, i1} @llvm.usub.with.overflow.i16(i16 %a, i16 %b)
+ declare {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b)
+ declare {i64, i1} @llvm.usub.with.overflow.i64(i64 %a, i64 %b)
+
+Overview:
+"""""""""
+
+The '``llvm.usub.with.overflow``' family of intrinsic functions perform
+an unsigned subtraction of the two arguments, and indicate whether an
+overflow occurred during the unsigned subtraction.
+
+Arguments:
+""""""""""
+
+The arguments (%a and %b) and the first element of the result structure
+may be of integer types of any bit width, but they must have the same
+bit width. The second element of the result structure must be of type
+``i1``. ``%a`` and ``%b`` are the two values that will undergo unsigned
+subtraction.
+
+Semantics:
+""""""""""
+
+The '``llvm.usub.with.overflow``' family of intrinsic functions perform
+an unsigned subtraction of the two arguments. They return a structure ---
+the first element of which is the subtraction, and the second element of
+which is a bit specifying if the unsigned subtraction resulted in an
+overflow.
+
+Examples:
+"""""""""
+
+.. code-block:: llvm
+
+ %res = call {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b)
+ %sum = extractvalue {i32, i1} %res, 0
+ %obit = extractvalue {i32, i1} %res, 1
+ br i1 %obit, label %overflow, label %normal
+
+'``llvm.smul.with.overflow.*``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.smul.with.overflow``
+on any integer bit width.
+
+::
+
+ declare {i16, i1} @llvm.smul.with.overflow.i16(i16 %a, i16 %b)
+ declare {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b)
+ declare {i64, i1} @llvm.smul.with.overflow.i64(i64 %a, i64 %b)
+
+Overview:
+"""""""""
+
+The '``llvm.smul.with.overflow``' family of intrinsic functions perform
+a signed multiplication of the two arguments, and indicate whether an
+overflow occurred during the signed multiplication.
+
+Arguments:
+""""""""""
+
+The arguments (%a and %b) and the first element of the result structure
+may be of integer types of any bit width, but they must have the same
+bit width. The second element of the result structure must be of type
+``i1``. ``%a`` and ``%b`` are the two values that will undergo signed
+multiplication.
+
+Semantics:
+""""""""""
+
+The '``llvm.smul.with.overflow``' family of intrinsic functions perform
+a signed multiplication of the two arguments. They return a structure ---
+the first element of which is the multiplication, and the second element
+of which is a bit specifying if the signed multiplication resulted in an
+overflow.
+
+Examples:
+"""""""""
+
+.. code-block:: llvm
+
+ %res = call {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b)
+ %sum = extractvalue {i32, i1} %res, 0
+ %obit = extractvalue {i32, i1} %res, 1
+ br i1 %obit, label %overflow, label %normal
+
+'``llvm.umul.with.overflow.*``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.umul.with.overflow``
+on any integer bit width.
+
+::
+
+ declare {i16, i1} @llvm.umul.with.overflow.i16(i16 %a, i16 %b)
+ declare {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b)
+ declare {i64, i1} @llvm.umul.with.overflow.i64(i64 %a, i64 %b)
+
+Overview:
+"""""""""
+
+The '``llvm.umul.with.overflow``' family of intrinsic functions perform
+a unsigned multiplication of the two arguments, and indicate whether an
+overflow occurred during the unsigned multiplication.
+
+Arguments:
+""""""""""
+
+The arguments (%a and %b) and the first element of the result structure
+may be of integer types of any bit width, but they must have the same
+bit width. The second element of the result structure must be of type
+``i1``. ``%a`` and ``%b`` are the two values that will undergo unsigned
+multiplication.
+
+Semantics:
+""""""""""
+
+The '``llvm.umul.with.overflow``' family of intrinsic functions perform
+an unsigned multiplication of the two arguments. They return a structure ---
+the first element of which is the multiplication, and the second
+element of which is a bit specifying if the unsigned multiplication
+resulted in an overflow.
+
+Examples:
+"""""""""
+
+.. code-block:: llvm
+
+ %res = call {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b)
+ %sum = extractvalue {i32, i1} %res, 0
+ %obit = extractvalue {i32, i1} %res, 1
+ br i1 %obit, label %overflow, label %normal
+
+Specialised Arithmetic Intrinsics
+---------------------------------
+
+'``llvm.canonicalize.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare float @llvm.canonicalize.f32(float %a)
+ declare double @llvm.canonicalize.f64(double %b)
+
+Overview:
+"""""""""
+
+The '``llvm.canonicalize.*``' intrinsic returns the platform specific canonical
+encoding of a floating point number. This canonicalization is useful for
+implementing certain numeric primitives such as frexp. The canonical encoding is
+defined by IEEE-754-2008 to be:
+
+::
+
+ 2.1.8 canonical encoding: The preferred encoding of a floating-point
+ representation in a format. Applied to declets, significands of finite
+ numbers, infinities, and NaNs, especially in decimal formats.
+
+This operation can also be considered equivalent to the IEEE-754-2008
+conversion of a floating-point value to the same format. NaNs are handled
+according to section 6.2.
+
+Examples of non-canonical encodings:
+
+- x87 pseudo denormals, pseudo NaNs, pseudo Infinity, Unnormals. These are
+ converted to a canonical representation per hardware-specific protocol.
+- Many normal decimal floating point numbers have non-canonical alternative
+ encodings.
+- Some machines, like GPUs or ARMv7 NEON, do not support subnormal values.
+ These are treated as non-canonical encodings of zero and will be flushed to
+ a zero of the same sign by this operation.
+
+Note that per IEEE-754-2008 6.2, systems that support signaling NaNs with
+default exception handling must signal an invalid exception, and produce a
+quiet NaN result.
+
+This function should always be implementable as multiplication by 1.0, provided
+that the compiler does not constant fold the operation. Likewise, division by
+1.0 and ``llvm.minnum(x, x)`` are possible implementations. Addition with
+-0.0 is also sufficient provided that the rounding mode is not -Infinity.
+
+``@llvm.canonicalize`` must preserve the equality relation. That is:
+
+- ``(@llvm.canonicalize(x) == x)`` is equivalent to ``(x == x)``
+- ``(@llvm.canonicalize(x) == @llvm.canonicalize(y))`` is equivalent to
+ to ``(x == y)``
+
+Additionally, the sign of zero must be conserved:
+``@llvm.canonicalize(-0.0) = -0.0`` and ``@llvm.canonicalize(+0.0) = +0.0``
+
+The payload bits of a NaN must be conserved, with two exceptions.
+First, environments which use only a single canonical representation of NaN
+must perform said canonicalization. Second, SNaNs must be quieted per the
+usual methods.
+
+The canonicalization operation may be optimized away if:
+
+- The input is known to be canonical. For example, it was produced by a
+ floating-point operation that is required by the standard to be canonical.
+- The result is consumed only by (or fused with) other floating-point
+ operations. That is, the bits of the floating point value are not examined.
+
+'``llvm.fmuladd.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare float @llvm.fmuladd.f32(float %a, float %b, float %c)
+ declare double @llvm.fmuladd.f64(double %a, double %b, double %c)
+
+Overview:
+"""""""""
+
+The '``llvm.fmuladd.*``' intrinsic functions represent multiply-add
+expressions that can be fused if the code generator determines that (a) the
+target instruction set has support for a fused operation, and (b) that the
+fused operation is more efficient than the equivalent, separate pair of mul
+and add instructions.
+
+Arguments:
+""""""""""
+
+The '``llvm.fmuladd.*``' intrinsics each take three arguments: two
+multiplicands, a and b, and an addend c.
+
+Semantics:
+""""""""""
+
+The expression:
+
+::
+
+ %0 = call float @llvm.fmuladd.f32(%a, %b, %c)
+
+is equivalent to the expression a \* b + c, except that rounding will
+not be performed between the multiplication and addition steps if the
+code generator fuses the operations. Fusion is not guaranteed, even if
+the target platform supports it. If a fused multiply-add is required the
+corresponding llvm.fma.\* intrinsic function should be used
+instead. This never sets errno, just as '``llvm.fma.*``'.
+
+Examples:
+"""""""""
+
+.. code-block:: llvm
+
+ %r2 = call float @llvm.fmuladd.f32(float %a, float %b, float %c) ; yields float:r2 = (a * b) + c
+
+
+Experimental Vector Reduction Intrinsics
+----------------------------------------
+
+Horizontal reductions of vectors can be expressed using the following
+intrinsics. Each one takes a vector operand as an input and applies its
+respective operation across all elements of the vector, returning a single
+scalar result of the same element type.
+
+
+'``llvm.experimental.vector.reduce.add.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i32 @llvm.experimental.vector.reduce.add.i32.v4i32(<4 x i32> %a)
+ declare i64 @llvm.experimental.vector.reduce.add.i64.v2i64(<2 x i64> %a)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.vector.reduce.add.*``' intrinsics do an integer ``ADD``
+reduction of a vector, returning the result as a scalar. The return type matches
+the element-type of the vector input.
+
+Arguments:
+""""""""""
+The argument to this intrinsic must be a vector of integer values.
+
+'``llvm.experimental.vector.reduce.fadd.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare float @llvm.experimental.vector.reduce.fadd.f32.v4f32(float %acc, <4 x float> %a)
+ declare double @llvm.experimental.vector.reduce.fadd.f64.v2f64(double %acc, <2 x double> %a)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.vector.reduce.fadd.*``' intrinsics do a floating point
+``ADD`` reduction of a vector, returning the result as a scalar. The return type
+matches the element-type of the vector input.
+
+If the intrinsic call has fast-math flags, then the reduction will not preserve
+the associativity of an equivalent scalarized counterpart. If it does not have
+fast-math flags, then the reduction will be *ordered*, implying that the
+operation respects the associativity of a scalarized reduction.
+
+
+Arguments:
+""""""""""
+The first argument to this intrinsic is a scalar accumulator value, which is
+only used when there are no fast-math flags attached. This argument may be undef
+when fast-math flags are used.
+
+The second argument must be a vector of floating point values.
+
+Examples:
+"""""""""
+
+.. code-block:: llvm
+
+ %fast = call fast float @llvm.experimental.vector.reduce.fadd.f32.v4f32(float undef, <4 x float> %input) ; fast reduction
+ %ord = call float @llvm.experimental.vector.reduce.fadd.f32.v4f32(float %acc, <4 x float> %input) ; ordered reduction
+
+
+'``llvm.experimental.vector.reduce.mul.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i32 @llvm.experimental.vector.reduce.mul.i32.v4i32(<4 x i32> %a)
+ declare i64 @llvm.experimental.vector.reduce.mul.i64.v2i64(<2 x i64> %a)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.vector.reduce.mul.*``' intrinsics do an integer ``MUL``
+reduction of a vector, returning the result as a scalar. The return type matches
+the element-type of the vector input.
+
+Arguments:
+""""""""""
+The argument to this intrinsic must be a vector of integer values.
+
+'``llvm.experimental.vector.reduce.fmul.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare float @llvm.experimental.vector.reduce.fmul.f32.v4f32(float %acc, <4 x float> %a)
+ declare double @llvm.experimental.vector.reduce.fmul.f64.v2f64(double %acc, <2 x double> %a)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.vector.reduce.fmul.*``' intrinsics do a floating point
+``MUL`` reduction of a vector, returning the result as a scalar. The return type
+matches the element-type of the vector input.
+
+If the intrinsic call has fast-math flags, then the reduction will not preserve
+the associativity of an equivalent scalarized counterpart. If it does not have
+fast-math flags, then the reduction will be *ordered*, implying that the
+operation respects the associativity of a scalarized reduction.
+
+
+Arguments:
+""""""""""
+The first argument to this intrinsic is a scalar accumulator value, which is
+only used when there are no fast-math flags attached. This argument may be undef
+when fast-math flags are used.
+
+The second argument must be a vector of floating point values.
+
+Examples:
+"""""""""
+
+.. code-block:: llvm
+
+ %fast = call fast float @llvm.experimental.vector.reduce.fmul.f32.v4f32(float undef, <4 x float> %input) ; fast reduction
+ %ord = call float @llvm.experimental.vector.reduce.fmul.f32.v4f32(float %acc, <4 x float> %input) ; ordered reduction
+
+'``llvm.experimental.vector.reduce.and.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i32 @llvm.experimental.vector.reduce.and.i32.v4i32(<4 x i32> %a)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.vector.reduce.and.*``' intrinsics do a bitwise ``AND``
+reduction of a vector, returning the result as a scalar. The return type matches
+the element-type of the vector input.
+
+Arguments:
+""""""""""
+The argument to this intrinsic must be a vector of integer values.
+
+'``llvm.experimental.vector.reduce.or.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i32 @llvm.experimental.vector.reduce.or.i32.v4i32(<4 x i32> %a)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.vector.reduce.or.*``' intrinsics do a bitwise ``OR`` reduction
+of a vector, returning the result as a scalar. The return type matches the
+element-type of the vector input.
+
+Arguments:
+""""""""""
+The argument to this intrinsic must be a vector of integer values.
+
+'``llvm.experimental.vector.reduce.xor.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i32 @llvm.experimental.vector.reduce.xor.i32.v4i32(<4 x i32> %a)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.vector.reduce.xor.*``' intrinsics do a bitwise ``XOR``
+reduction of a vector, returning the result as a scalar. The return type matches
+the element-type of the vector input.
+
+Arguments:
+""""""""""
+The argument to this intrinsic must be a vector of integer values.
+
+'``llvm.experimental.vector.reduce.smax.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i32 @llvm.experimental.vector.reduce.smax.i32.v4i32(<4 x i32> %a)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.vector.reduce.smax.*``' intrinsics do a signed integer
+``MAX`` reduction of a vector, returning the result as a scalar. The return type
+matches the element-type of the vector input.
+
+Arguments:
+""""""""""
+The argument to this intrinsic must be a vector of integer values.
+
+'``llvm.experimental.vector.reduce.smin.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i32 @llvm.experimental.vector.reduce.smin.i32.v4i32(<4 x i32> %a)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.vector.reduce.smin.*``' intrinsics do a signed integer
+``MIN`` reduction of a vector, returning the result as a scalar. The return type
+matches the element-type of the vector input.
+
+Arguments:
+""""""""""
+The argument to this intrinsic must be a vector of integer values.
+
+'``llvm.experimental.vector.reduce.umax.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i32 @llvm.experimental.vector.reduce.umax.i32.v4i32(<4 x i32> %a)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.vector.reduce.umax.*``' intrinsics do an unsigned
+integer ``MAX`` reduction of a vector, returning the result as a scalar. The
+return type matches the element-type of the vector input.
+
+Arguments:
+""""""""""
+The argument to this intrinsic must be a vector of integer values.
+
+'``llvm.experimental.vector.reduce.umin.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i32 @llvm.experimental.vector.reduce.umin.i32.v4i32(<4 x i32> %a)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.vector.reduce.umin.*``' intrinsics do an unsigned
+integer ``MIN`` reduction of a vector, returning the result as a scalar. The
+return type matches the element-type of the vector input.
+
+Arguments:
+""""""""""
+The argument to this intrinsic must be a vector of integer values.
+
+'``llvm.experimental.vector.reduce.fmax.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare float @llvm.experimental.vector.reduce.fmax.f32.v4f32(<4 x float> %a)
+ declare double @llvm.experimental.vector.reduce.fmax.f64.v2f64(<2 x double> %a)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.vector.reduce.fmax.*``' intrinsics do a floating point
+``MAX`` reduction of a vector, returning the result as a scalar. The return type
+matches the element-type of the vector input.
+
+If the intrinsic call has the ``nnan`` fast-math flag then the operation can
+assume that NaNs are not present in the input vector.
+
+Arguments:
+""""""""""
+The argument to this intrinsic must be a vector of floating point values.
+
+'``llvm.experimental.vector.reduce.fmin.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare float @llvm.experimental.vector.reduce.fmin.f32.v4f32(<4 x float> %a)
+ declare double @llvm.experimental.vector.reduce.fmin.f64.v2f64(<2 x double> %a)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.vector.reduce.fmin.*``' intrinsics do a floating point
+``MIN`` reduction of a vector, returning the result as a scalar. The return type
+matches the element-type of the vector input.
+
+If the intrinsic call has the ``nnan`` fast-math flag then the operation can
+assume that NaNs are not present in the input vector.
+
+Arguments:
+""""""""""
+The argument to this intrinsic must be a vector of floating point values.
+
+Half Precision Floating Point Intrinsics
+----------------------------------------
+
+For most target platforms, half precision floating point is a
+storage-only format. This means that it is a dense encoding (in memory)
+but does not support computation in the format.
+
+This means that code must first load the half-precision floating point
+value as an i16, then convert it to float with
+:ref:`llvm.convert.from.fp16 <int_convert_from_fp16>`. Computation can
+then be performed on the float value (including extending to double
+etc). To store the value back to memory, it is first converted to float
+if needed, then converted to i16 with
+:ref:`llvm.convert.to.fp16 <int_convert_to_fp16>`, then storing as an
+i16 value.
+
+.. _int_convert_to_fp16:
+
+'``llvm.convert.to.fp16``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i16 @llvm.convert.to.fp16.f32(float %a)
+ declare i16 @llvm.convert.to.fp16.f64(double %a)
+
+Overview:
+"""""""""
+
+The '``llvm.convert.to.fp16``' intrinsic function performs a conversion from a
+conventional floating point type to half precision floating point format.
+
+Arguments:
+""""""""""
+
+The intrinsic function contains single argument - the value to be
+converted.
+
+Semantics:
+""""""""""
+
+The '``llvm.convert.to.fp16``' intrinsic function performs a conversion from a
+conventional floating point format to half precision floating point format. The
+return value is an ``i16`` which contains the converted number.
+
+Examples:
+"""""""""
+
+.. code-block:: llvm
+
+ %res = call i16 @llvm.convert.to.fp16.f32(float %a)
+ store i16 %res, i16* @x, align 2
+
+.. _int_convert_from_fp16:
+
+'``llvm.convert.from.fp16``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare float @llvm.convert.from.fp16.f32(i16 %a)
+ declare double @llvm.convert.from.fp16.f64(i16 %a)
+
+Overview:
+"""""""""
+
+The '``llvm.convert.from.fp16``' intrinsic function performs a
+conversion from half precision floating point format to single precision
+floating point format.
+
+Arguments:
+""""""""""
+
+The intrinsic function contains single argument - the value to be
+converted.
+
+Semantics:
+""""""""""
+
+The '``llvm.convert.from.fp16``' intrinsic function performs a
+conversion from half single precision floating point format to single
+precision floating point format. The input half-float value is
+represented by an ``i16`` value.
+
+Examples:
+"""""""""
+
+.. code-block:: llvm
+
+ %a = load i16, i16* @x, align 2
+ %res = call float @llvm.convert.from.fp16(i16 %a)
+
+.. _dbg_intrinsics:
+
+Debugger Intrinsics
+-------------------
+
+The LLVM debugger intrinsics (which all start with ``llvm.dbg.``
+prefix), are described in the `LLVM Source Level
+Debugging <SourceLevelDebugging.html#format_common_intrinsics>`_
+document.
+
+Exception Handling Intrinsics
+-----------------------------
+
+The LLVM exception handling intrinsics (which all start with
+``llvm.eh.`` prefix), are described in the `LLVM Exception
+Handling <ExceptionHandling.html#format_common_intrinsics>`_ document.
+
+.. _int_trampoline:
+
+Trampoline Intrinsics
+---------------------
+
+These intrinsics make it possible to excise one parameter, marked with
+the :ref:`nest <nest>` attribute, from a function. The result is a
+callable function pointer lacking the nest parameter - the caller does
+not need to provide a value for it. Instead, the value to use is stored
+in advance in a "trampoline", a block of memory usually allocated on the
+stack, which also contains code to splice the nest value into the
+argument list. This is used to implement the GCC nested function address
+extension.
+
+For example, if the function is ``i32 f(i8* nest %c, i32 %x, i32 %y)``
+then the resulting function pointer has signature ``i32 (i32, i32)*``.
+It can be created as follows:
+
+.. code-block:: llvm
+
+ %tramp = alloca [10 x i8], align 4 ; size and alignment only correct for X86
+ %tramp1 = getelementptr [10 x i8], [10 x i8]* %tramp, i32 0, i32 0
+ call i8* @llvm.init.trampoline(i8* %tramp1, i8* bitcast (i32 (i8*, i32, i32)* @f to i8*), i8* %nval)
+ %p = call i8* @llvm.adjust.trampoline(i8* %tramp1)
+ %fp = bitcast i8* %p to i32 (i32, i32)*
+
+The call ``%val = call i32 %fp(i32 %x, i32 %y)`` is then equivalent to
+``%val = call i32 %f(i8* %nval, i32 %x, i32 %y)``.
+
+.. _int_it:
+
+'``llvm.init.trampoline``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.init.trampoline(i8* <tramp>, i8* <func>, i8* <nval>)
+
+Overview:
+"""""""""
+
+This fills the memory pointed to by ``tramp`` with executable code,
+turning it into a trampoline.
+
+Arguments:
+""""""""""
+
+The ``llvm.init.trampoline`` intrinsic takes three arguments, all
+pointers. The ``tramp`` argument must point to a sufficiently large and
+sufficiently aligned block of memory; this memory is written to by the
+intrinsic. Note that the size and the alignment are target-specific -
+LLVM currently provides no portable way of determining them, so a
+front-end that generates this intrinsic needs to have some
+target-specific knowledge. The ``func`` argument must hold a function
+bitcast to an ``i8*``.
+
+Semantics:
+""""""""""
+
+The block of memory pointed to by ``tramp`` is filled with target
+dependent code, turning it into a function. Then ``tramp`` needs to be
+passed to :ref:`llvm.adjust.trampoline <int_at>` to get a pointer which can
+be :ref:`bitcast (to a new function) and called <int_trampoline>`. The new
+function's signature is the same as that of ``func`` with any arguments
+marked with the ``nest`` attribute removed. At most one such ``nest``
+argument is allowed, and it must be of pointer type. Calling the new
+function is equivalent to calling ``func`` with the same argument list,
+but with ``nval`` used for the missing ``nest`` argument. If, after
+calling ``llvm.init.trampoline``, the memory pointed to by ``tramp`` is
+modified, then the effect of any later call to the returned function
+pointer is undefined.
+
+.. _int_at:
+
+'``llvm.adjust.trampoline``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i8* @llvm.adjust.trampoline(i8* <tramp>)
+
+Overview:
+"""""""""
+
+This performs any required machine-specific adjustment to the address of
+a trampoline (passed as ``tramp``).
+
+Arguments:
+""""""""""
+
+``tramp`` must point to a block of memory which already has trampoline
+code filled in by a previous call to
+:ref:`llvm.init.trampoline <int_it>`.
+
+Semantics:
+""""""""""
+
+On some architectures the address of the code to be executed needs to be
+different than the address where the trampoline is actually stored. This
+intrinsic returns the executable address corresponding to ``tramp``
+after performing the required machine specific adjustments. The pointer
+returned can then be :ref:`bitcast and executed <int_trampoline>`.
+
+.. _int_mload_mstore:
+
+Masked Vector Load and Store Intrinsics
+---------------------------------------
+
+LLVM provides intrinsics for predicated vector load and store operations. The predicate is specified by a mask operand, which holds one bit per vector element, switching the associated vector lane on or off. The memory addresses corresponding to the "off" lanes are not accessed. When all bits of the mask are on, the intrinsic is identical to a regular vector load or store. When all bits are off, no memory is accessed.
+
+.. _int_mload:
+
+'``llvm.masked.load.*``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+This is an overloaded intrinsic. The loaded data is a vector of any integer, floating point or pointer data type.
+
+::
+
+ declare <16 x float> @llvm.masked.load.v16f32.p0v16f32 (<16 x float>* <ptr>, i32 <alignment>, <16 x i1> <mask>, <16 x float> <passthru>)
+ declare <2 x double> @llvm.masked.load.v2f64.p0v2f64 (<2 x double>* <ptr>, i32 <alignment>, <2 x i1> <mask>, <2 x double> <passthru>)
+ ;; The data is a vector of pointers to double
+ declare <8 x double*> @llvm.masked.load.v8p0f64.p0v8p0f64 (<8 x double*>* <ptr>, i32 <alignment>, <8 x i1> <mask>, <8 x double*> <passthru>)
+ ;; The data is a vector of function pointers
+ declare <8 x i32 ()*> @llvm.masked.load.v8p0f_i32f.p0v8p0f_i32f (<8 x i32 ()*>* <ptr>, i32 <alignment>, <8 x i1> <mask>, <8 x i32 ()*> <passthru>)
+
+Overview:
+"""""""""
+
+Reads a vector from memory according to the provided mask. The mask holds a bit for each vector lane, and is used to prevent memory accesses to the masked-off lanes. The masked-off lanes in the result vector are taken from the corresponding lanes of the '``passthru``' operand.
+
+
+Arguments:
+""""""""""
+
+The first operand is the base pointer for the load. The second operand is the alignment of the source location. It must be a constant integer value. The third operand, mask, is a vector of boolean values with the same number of elements as the return type. The fourth is a pass-through value that is used to fill the masked-off lanes of the result. The return type, underlying type of the base pointer and the type of the '``passthru``' operand are the same vector types.
+
+
+Semantics:
+""""""""""
+
+The '``llvm.masked.load``' intrinsic is designed for conditional reading of selected vector elements in a single IR operation. It is useful for targets that support vector masked loads and allows vectorizing predicated basic blocks on these targets. Other targets may support this intrinsic differently, for example by lowering it into a sequence of branches that guard scalar load operations.
+The result of this operation is equivalent to a regular vector load instruction followed by a 'select' between the loaded and the passthru values, predicated on the same mask. However, using this intrinsic prevents exceptions on memory access to masked-off lanes.
+
+
+::
+
+ %res = call <16 x float> @llvm.masked.load.v16f32.p0v16f32 (<16 x float>* %ptr, i32 4, <16 x i1>%mask, <16 x float> %passthru)
+
+ ;; The result of the two following instructions is identical aside from potential memory access exception
+ %loadlal = load <16 x float>, <16 x float>* %ptr, align 4
+ %res = select <16 x i1> %mask, <16 x float> %loadlal, <16 x float> %passthru
+
+.. _int_mstore:
+
+'``llvm.masked.store.*``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+This is an overloaded intrinsic. The data stored in memory is a vector of any integer, floating point or pointer data type.
+
+::
+
+ declare void @llvm.masked.store.v8i32.p0v8i32 (<8 x i32> <value>, <8 x i32>* <ptr>, i32 <alignment>, <8 x i1> <mask>)
+ declare void @llvm.masked.store.v16f32.p0v16f32 (<16 x float> <value>, <16 x float>* <ptr>, i32 <alignment>, <16 x i1> <mask>)
+ ;; The data is a vector of pointers to double
+ declare void @llvm.masked.store.v8p0f64.p0v8p0f64 (<8 x double*> <value>, <8 x double*>* <ptr>, i32 <alignment>, <8 x i1> <mask>)
+ ;; The data is a vector of function pointers
+ declare void @llvm.masked.store.v4p0f_i32f.p0v4p0f_i32f (<4 x i32 ()*> <value>, <4 x i32 ()*>* <ptr>, i32 <alignment>, <4 x i1> <mask>)
+
+Overview:
+"""""""""
+
+Writes a vector to memory according to the provided mask. The mask holds a bit for each vector lane, and is used to prevent memory accesses to the masked-off lanes.
+
+Arguments:
+""""""""""
+
+The first operand is the vector value to be written to memory. The second operand is the base pointer for the store, it has the same underlying type as the value operand. The third operand is the alignment of the destination location. The fourth operand, mask, is a vector of boolean values. The types of the mask and the value operand must have the same number of vector elements.
+
+
+Semantics:
+""""""""""
+
+The '``llvm.masked.store``' intrinsics is designed for conditional writing of selected vector elements in a single IR operation. It is useful for targets that support vector masked store and allows vectorizing predicated basic blocks on these targets. Other targets may support this intrinsic differently, for example by lowering it into a sequence of branches that guard scalar store operations.
+The result of this operation is equivalent to a load-modify-store sequence. However, using this intrinsic prevents exceptions and data races on memory access to masked-off lanes.
+
+::
+
+ call void @llvm.masked.store.v16f32.p0v16f32(<16 x float> %value, <16 x float>* %ptr, i32 4, <16 x i1> %mask)
+
+ ;; The result of the following instructions is identical aside from potential data races and memory access exceptions
+ %oldval = load <16 x float>, <16 x float>* %ptr, align 4
+ %res = select <16 x i1> %mask, <16 x float> %value, <16 x float> %oldval
+ store <16 x float> %res, <16 x float>* %ptr, align 4
+
+
+Masked Vector Gather and Scatter Intrinsics
+-------------------------------------------
+
+LLVM provides intrinsics for vector gather and scatter operations. They are similar to :ref:`Masked Vector Load and Store <int_mload_mstore>`, except they are designed for arbitrary memory accesses, rather than sequential memory accesses. Gather and scatter also employ a mask operand, which holds one bit per vector element, switching the associated vector lane on or off. The memory addresses corresponding to the "off" lanes are not accessed. When all bits are off, no memory is accessed.
+
+.. _int_mgather:
+
+'``llvm.masked.gather.*``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+This is an overloaded intrinsic. The loaded data are multiple scalar values of any integer, floating point or pointer data type gathered together into one vector.
+
+::
+
+ declare <16 x float> @llvm.masked.gather.v16f32.v16p0f32 (<16 x float*> <ptrs>, i32 <alignment>, <16 x i1> <mask>, <16 x float> <passthru>)
+ declare <2 x double> @llvm.masked.gather.v2f64.v2p1f64 (<2 x double addrspace(1)*> <ptrs>, i32 <alignment>, <2 x i1> <mask>, <2 x double> <passthru>)
+ declare <8 x float*> @llvm.masked.gather.v8p0f32.v8p0p0f32 (<8 x float**> <ptrs>, i32 <alignment>, <8 x i1> <mask>, <8 x float*> <passthru>)
+
+Overview:
+"""""""""
+
+Reads scalar values from arbitrary memory locations and gathers them into one vector. The memory locations are provided in the vector of pointers '``ptrs``'. The memory is accessed according to the provided mask. The mask holds a bit for each vector lane, and is used to prevent memory accesses to the masked-off lanes. The masked-off lanes in the result vector are taken from the corresponding lanes of the '``passthru``' operand.
+
+
+Arguments:
+""""""""""
+
+The first operand is a vector of pointers which holds all memory addresses to read. The second operand is an alignment of the source addresses. It must be a constant integer value. The third operand, mask, is a vector of boolean values with the same number of elements as the return type. The fourth is a pass-through value that is used to fill the masked-off lanes of the result. The return type, underlying type of the vector of pointers and the type of the '``passthru``' operand are the same vector types.
+
+
+Semantics:
+""""""""""
+
+The '``llvm.masked.gather``' intrinsic is designed for conditional reading of multiple scalar values from arbitrary memory locations in a single IR operation. It is useful for targets that support vector masked gathers and allows vectorizing basic blocks with data and control divergence. Other targets may support this intrinsic differently, for example by lowering it into a sequence of scalar load operations.
+The semantics of this operation are equivalent to a sequence of conditional scalar loads with subsequent gathering all loaded values into a single vector. The mask restricts memory access to certain lanes and facilitates vectorization of predicated basic blocks.
+
+
+::
+
+ %res = call <4 x double> @llvm.masked.gather.v4f64.v4p0f64 (<4 x double*> %ptrs, i32 8, <4 x i1> <i1 true, i1 true, i1 true, i1 true>, <4 x double> undef)
+
+ ;; The gather with all-true mask is equivalent to the following instruction sequence
+ %ptr0 = extractelement <4 x double*> %ptrs, i32 0
+ %ptr1 = extractelement <4 x double*> %ptrs, i32 1
+ %ptr2 = extractelement <4 x double*> %ptrs, i32 2
+ %ptr3 = extractelement <4 x double*> %ptrs, i32 3
+
+ %val0 = load double, double* %ptr0, align 8
+ %val1 = load double, double* %ptr1, align 8
+ %val2 = load double, double* %ptr2, align 8
+ %val3 = load double, double* %ptr3, align 8
+
+ %vec0 = insertelement <4 x double>undef, %val0, 0
+ %vec01 = insertelement <4 x double>%vec0, %val1, 1
+ %vec012 = insertelement <4 x double>%vec01, %val2, 2
+ %vec0123 = insertelement <4 x double>%vec012, %val3, 3
+
+.. _int_mscatter:
+
+'``llvm.masked.scatter.*``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+This is an overloaded intrinsic. The data stored in memory is a vector of any integer, floating point or pointer data type. Each vector element is stored in an arbitrary memory address. Scatter with overlapping addresses is guaranteed to be ordered from least-significant to most-significant element.
+
+::
+
+ declare void @llvm.masked.scatter.v8i32.v8p0i32 (<8 x i32> <value>, <8 x i32*> <ptrs>, i32 <alignment>, <8 x i1> <mask>)
+ declare void @llvm.masked.scatter.v16f32.v16p1f32 (<16 x float> <value>, <16 x float addrspace(1)*> <ptrs>, i32 <alignment>, <16 x i1> <mask>)
+ declare void @llvm.masked.scatter.v4p0f64.v4p0p0f64 (<4 x double*> <value>, <4 x double**> <ptrs>, i32 <alignment>, <4 x i1> <mask>)
+
+Overview:
+"""""""""
+
+Writes each element from the value vector to the corresponding memory address. The memory addresses are represented as a vector of pointers. Writing is done according to the provided mask. The mask holds a bit for each vector lane, and is used to prevent memory accesses to the masked-off lanes.
+
+Arguments:
+""""""""""
+
+The first operand is a vector value to be written to memory. The second operand is a vector of pointers, pointing to where the value elements should be stored. It has the same underlying type as the value operand. The third operand is an alignment of the destination addresses. The fourth operand, mask, is a vector of boolean values. The types of the mask and the value operand must have the same number of vector elements.
+
+
+Semantics:
+""""""""""
+
+The '``llvm.masked.scatter``' intrinsics is designed for writing selected vector elements to arbitrary memory addresses in a single IR operation. The operation may be conditional, when not all bits in the mask are switched on. It is useful for targets that support vector masked scatter and allows vectorizing basic blocks with data and control divergence. Other targets may support this intrinsic differently, for example by lowering it into a sequence of branches that guard scalar store operations.
+
+::
+
+ ;; This instruction unconditionally stores data vector in multiple addresses
+ call @llvm.masked.scatter.v8i32.v8p0i32 (<8 x i32> %value, <8 x i32*> %ptrs, i32 4, <8 x i1> <true, true, .. true>)
+
+ ;; It is equivalent to a list of scalar stores
+ %val0 = extractelement <8 x i32> %value, i32 0
+ %val1 = extractelement <8 x i32> %value, i32 1
+ ..
+ %val7 = extractelement <8 x i32> %value, i32 7
+ %ptr0 = extractelement <8 x i32*> %ptrs, i32 0
+ %ptr1 = extractelement <8 x i32*> %ptrs, i32 1
+ ..
+ %ptr7 = extractelement <8 x i32*> %ptrs, i32 7
+ ;; Note: the order of the following stores is important when they overlap:
+ store i32 %val0, i32* %ptr0, align 4
+ store i32 %val1, i32* %ptr1, align 4
+ ..
+ store i32 %val7, i32* %ptr7, align 4
+
+
+Memory Use Markers
+------------------
+
+This class of intrinsics provides information about the lifetime of
+memory objects and ranges where variables are immutable.
+
+.. _int_lifestart:
+
+'``llvm.lifetime.start``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.lifetime.start(i64 <size>, i8* nocapture <ptr>)
+
+Overview:
+"""""""""
+
+The '``llvm.lifetime.start``' intrinsic specifies the start of a memory
+object's lifetime.
+
+Arguments:
+""""""""""
+
+The first argument is a constant integer representing the size of the
+object, or -1 if it is variable sized. The second argument is a pointer
+to the object.
+
+Semantics:
+""""""""""
+
+This intrinsic indicates that before this point in the code, the value
+of the memory pointed to by ``ptr`` is dead. This means that it is known
+to never be used and has an undefined value. A load from the pointer
+that precedes this intrinsic can be replaced with ``'undef'``.
+
+.. _int_lifeend:
+
+'``llvm.lifetime.end``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.lifetime.end(i64 <size>, i8* nocapture <ptr>)
+
+Overview:
+"""""""""
+
+The '``llvm.lifetime.end``' intrinsic specifies the end of a memory
+object's lifetime.
+
+Arguments:
+""""""""""
+
+The first argument is a constant integer representing the size of the
+object, or -1 if it is variable sized. The second argument is a pointer
+to the object.
+
+Semantics:
+""""""""""
+
+This intrinsic indicates that after this point in the code, the value of
+the memory pointed to by ``ptr`` is dead. This means that it is known to
+never be used and has an undefined value. Any stores into the memory
+object following this intrinsic may be removed as dead.
+
+'``llvm.invariant.start``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+This is an overloaded intrinsic. The memory object can belong to any address space.
+
+::
+
+ declare {}* @llvm.invariant.start.p0i8(i64 <size>, i8* nocapture <ptr>)
+
+Overview:
+"""""""""
+
+The '``llvm.invariant.start``' intrinsic specifies that the contents of
+a memory object will not change.
+
+Arguments:
+""""""""""
+
+The first argument is a constant integer representing the size of the
+object, or -1 if it is variable sized. The second argument is a pointer
+to the object.
+
+Semantics:
+""""""""""
+
+This intrinsic indicates that until an ``llvm.invariant.end`` that uses
+the return value, the referenced memory location is constant and
+unchanging.
+
+'``llvm.invariant.end``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+This is an overloaded intrinsic. The memory object can belong to any address space.
+
+::
+
+ declare void @llvm.invariant.end.p0i8({}* <start>, i64 <size>, i8* nocapture <ptr>)
+
+Overview:
+"""""""""
+
+The '``llvm.invariant.end``' intrinsic specifies that the contents of a
+memory object are mutable.
+
+Arguments:
+""""""""""
+
+The first argument is the matching ``llvm.invariant.start`` intrinsic.
+The second argument is a constant integer representing the size of the
+object, or -1 if it is variable sized and the third argument is a
+pointer to the object.
+
+Semantics:
+""""""""""
+
+This intrinsic indicates that the memory is mutable again.
+
+'``llvm.invariant.group.barrier``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i8* @llvm.invariant.group.barrier(i8* <ptr>)
+
+Overview:
+"""""""""
+
+The '``llvm.invariant.group.barrier``' intrinsic can be used when an invariant
+established by invariant.group metadata no longer holds, to obtain a new pointer
+value that does not carry the invariant information.
+
+
+Arguments:
+""""""""""
+
+The ``llvm.invariant.group.barrier`` takes only one argument, which is
+the pointer to the memory for which the ``invariant.group`` no longer holds.
+
+Semantics:
+""""""""""
+
+Returns another pointer that aliases its argument but which is considered different
+for the purposes of ``load``/``store`` ``invariant.group`` metadata.
+
+Constrained Floating Point Intrinsics
+-------------------------------------
+
+These intrinsics are used to provide special handling of floating point
+operations when specific rounding mode or floating point exception behavior is
+required. By default, LLVM optimization passes assume that the rounding mode is
+round-to-nearest and that floating point exceptions will not be monitored.
+Constrained FP intrinsics are used to support non-default rounding modes and
+accurately preserve exception behavior without compromising LLVM's ability to
+optimize FP code when the default behavior is used.
+
+Each of these intrinsics corresponds to a normal floating point operation. The
+first two arguments and the return value are the same as the corresponding FP
+operation.
+
+The third argument is a metadata argument specifying the rounding mode to be
+assumed. This argument must be one of the following strings:
+
+::
+
+ "round.dynamic"
+ "round.tonearest"
+ "round.downward"
+ "round.upward"
+ "round.towardzero"
+
+If this argument is "round.dynamic" optimization passes must assume that the
+rounding mode is unknown and may change at runtime. No transformations that
+depend on rounding mode may be performed in this case.
+
+The other possible values for the rounding mode argument correspond to the
+similarly named IEEE rounding modes. If the argument is any of these values
+optimization passes may perform transformations as long as they are consistent
+with the specified rounding mode.
+
+For example, 'x-0'->'x' is not a valid transformation if the rounding mode is
+"round.downward" or "round.dynamic" because if the value of 'x' is +0 then
+'x-0' should evaluate to '-0' when rounding downward. However, this
+transformation is legal for all other rounding modes.
+
+For values other than "round.dynamic" optimization passes may assume that the
+actual runtime rounding mode (as defined in a target-specific manner) matches
+the specified rounding mode, but this is not guaranteed. Using a specific
+non-dynamic rounding mode which does not match the actual rounding mode at
+runtime results in undefined behavior.
+
+The fourth argument to the constrained floating point intrinsics specifies the
+required exception behavior. This argument must be one of the following
+strings:
+
+::
+
+ "fpexcept.ignore"
+ "fpexcept.maytrap"
+ "fpexcept.strict"
+
+If this argument is "fpexcept.ignore" optimization passes may assume that the
+exception status flags will not be read and that floating point exceptions will
+be masked. This allows transformations to be performed that may change the
+exception semantics of the original code. For example, FP operations may be
+speculatively executed in this case whereas they must not be for either of the
+other possible values of this argument.
+
+If the exception behavior argument is "fpexcept.maytrap" optimization passes
+must avoid transformations that may raise exceptions that would not have been
+raised by the original code (such as speculatively executing FP operations), but
+passes are not required to preserve all exceptions that are implied by the
+original code. For example, exceptions may be potentially hidden by constant
+folding.
+
+If the exception behavior argument is "fpexcept.strict" all transformations must
+strictly preserve the floating point exception semantics of the original code.
+Any FP exception that would have been raised by the original code must be raised
+by the transformed code, and the transformed code must not raise any FP
+exceptions that would not have been raised by the original code. This is the
+exception behavior argument that will be used if the code being compiled reads
+the FP exception status flags, but this mode can also be used with code that
+unmasks FP exceptions.
+
+The number and order of floating point exceptions is NOT guaranteed. For
+example, a series of FP operations that each may raise exceptions may be
+vectorized into a single instruction that raises each unique exception a single
+time.
+
+
+'``llvm.experimental.constrained.fadd``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.fadd(<type> <op1>, <type> <op2>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.fadd``' intrinsic returns the sum of its
+two operands.
+
+
+Arguments:
+""""""""""
+
+The first two arguments to the '``llvm.experimental.constrained.fadd``'
+intrinsic must be :ref:`floating point <t_floating>` or :ref:`vector <t_vector>`
+of floating point values. Both arguments must have identical types.
+
+The third and fourth arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+The value produced is the floating point sum of the two value operands and has
+the same type as the operands.
+
+
+'``llvm.experimental.constrained.fsub``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.fsub(<type> <op1>, <type> <op2>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.fsub``' intrinsic returns the difference
+of its two operands.
+
+
+Arguments:
+""""""""""
+
+The first two arguments to the '``llvm.experimental.constrained.fsub``'
+intrinsic must be :ref:`floating point <t_floating>` or :ref:`vector <t_vector>`
+of floating point values. Both arguments must have identical types.
+
+The third and fourth arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+The value produced is the floating point difference of the two value operands
+and has the same type as the operands.
+
+
+'``llvm.experimental.constrained.fmul``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.fmul(<type> <op1>, <type> <op2>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.fmul``' intrinsic returns the product of
+its two operands.
+
+
+Arguments:
+""""""""""
+
+The first two arguments to the '``llvm.experimental.constrained.fmul``'
+intrinsic must be :ref:`floating point <t_floating>` or :ref:`vector <t_vector>`
+of floating point values. Both arguments must have identical types.
+
+The third and fourth arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+The value produced is the floating point product of the two value operands and
+has the same type as the operands.
+
+
+'``llvm.experimental.constrained.fdiv``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.fdiv(<type> <op1>, <type> <op2>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.fdiv``' intrinsic returns the quotient of
+its two operands.
+
+
+Arguments:
+""""""""""
+
+The first two arguments to the '``llvm.experimental.constrained.fdiv``'
+intrinsic must be :ref:`floating point <t_floating>` or :ref:`vector <t_vector>`
+of floating point values. Both arguments must have identical types.
+
+The third and fourth arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+The value produced is the floating point quotient of the two value operands and
+has the same type as the operands.
+
+
+'``llvm.experimental.constrained.frem``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.frem(<type> <op1>, <type> <op2>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.frem``' intrinsic returns the remainder
+from the division of its two operands.
+
+
+Arguments:
+""""""""""
+
+The first two arguments to the '``llvm.experimental.constrained.frem``'
+intrinsic must be :ref:`floating point <t_floating>` or :ref:`vector <t_vector>`
+of floating point values. Both arguments must have identical types.
+
+The third and fourth arguments specify the rounding mode and exception
+behavior as described above. The rounding mode argument has no effect, since
+the result of frem is never rounded, but the argument is included for
+consistency with the other constrained floating point intrinsics.
+
+Semantics:
+""""""""""
+
+The value produced is the floating point remainder from the division of the two
+value operands and has the same type as the operands. The remainder has the
+same sign as the dividend.
+
+
+Constrained libm-equivalent Intrinsics
+--------------------------------------
+
+In addition to the basic floating point operations for which constrained
+intrinsics are described above, there are constrained versions of various
+operations which provide equivalent behavior to a corresponding libm function.
+These intrinsics allow the precise behavior of these operations with respect to
+rounding mode and exception behavior to be controlled.
+
+As with the basic constrained floating point intrinsics, the rounding mode
+and exception behavior arguments only control the behavior of the optimizer.
+They do not change the runtime floating point environment.
+
+
+'``llvm.experimental.constrained.sqrt``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.sqrt(<type> <op1>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.sqrt``' intrinsic returns the square root
+of the specified value, returning the same value as the libm '``sqrt``'
+functions would, but without setting ``errno``.
+
+Arguments:
+""""""""""
+
+The first argument and the return type are floating point numbers of the same
+type.
+
+The second and third arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+This function returns the nonnegative square root of the specified value.
+If the value is less than negative zero, a floating point exception occurs
+and the the return value is architecture specific.
+
+
+'``llvm.experimental.constrained.pow``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.pow(<type> <op1>, <type> <op2>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.pow``' intrinsic returns the first operand
+raised to the (positive or negative) power specified by the second operand.
+
+Arguments:
+""""""""""
+
+The first two arguments and the return value are floating point numbers of the
+same type. The second argument specifies the power to which the first argument
+should be raised.
+
+The third and fourth arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+This function returns the first value raised to the second power,
+returning the same values as the libm ``pow`` functions would, and
+handles error conditions in the same way.
+
+
+'``llvm.experimental.constrained.powi``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.powi(<type> <op1>, i32 <op2>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.powi``' intrinsic returns the first operand
+raised to the (positive or negative) power specified by the second operand. The
+order of evaluation of multiplications is not defined. When a vector of floating
+point type is used, the second argument remains a scalar integer value.
+
+
+Arguments:
+""""""""""
+
+The first argument and the return value are floating point numbers of the same
+type. The second argument is a 32-bit signed integer specifying the power to
+which the first argument should be raised.
+
+The third and fourth arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+This function returns the first value raised to the second power with an
+unspecified sequence of rounding operations.
+
+
+'``llvm.experimental.constrained.sin``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.sin(<type> <op1>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.sin``' intrinsic returns the sine of the
+first operand.
+
+Arguments:
+""""""""""
+
+The first argument and the return type are floating point numbers of the same
+type.
+
+The second and third arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+This function returns the sine of the specified operand, returning the
+same values as the libm ``sin`` functions would, and handles error
+conditions in the same way.
+
+
+'``llvm.experimental.constrained.cos``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.cos(<type> <op1>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.cos``' intrinsic returns the cosine of the
+first operand.
+
+Arguments:
+""""""""""
+
+The first argument and the return type are floating point numbers of the same
+type.
+
+The second and third arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+This function returns the cosine of the specified operand, returning the
+same values as the libm ``cos`` functions would, and handles error
+conditions in the same way.
+
+
+'``llvm.experimental.constrained.exp``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.exp(<type> <op1>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.exp``' intrinsic computes the base-e
+exponential of the specified value.
+
+Arguments:
+""""""""""
+
+The first argument and the return value are floating point numbers of the same
+type.
+
+The second and third arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``exp`` functions
+would, and handles error conditions in the same way.
+
+
+'``llvm.experimental.constrained.exp2``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.exp2(<type> <op1>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.exp2``' intrinsic computes the base-2
+exponential of the specified value.
+
+
+Arguments:
+""""""""""
+
+The first argument and the return value are floating point numbers of the same
+type.
+
+The second and third arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``exp2`` functions
+would, and handles error conditions in the same way.
+
+
+'``llvm.experimental.constrained.log``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.log(<type> <op1>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.log``' intrinsic computes the base-e
+logarithm of the specified value.
+
+Arguments:
+""""""""""
+
+The first argument and the return value are floating point numbers of the same
+type.
+
+The second and third arguments specify the rounding mode and exception
+behavior as described above.
+
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``log`` functions
+would, and handles error conditions in the same way.
+
+
+'``llvm.experimental.constrained.log10``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.log10(<type> <op1>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.log10``' intrinsic computes the base-10
+logarithm of the specified value.
+
+Arguments:
+""""""""""
+
+The first argument and the return value are floating point numbers of the same
+type.
+
+The second and third arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``log10`` functions
+would, and handles error conditions in the same way.
+
+
+'``llvm.experimental.constrained.log2``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.log2(<type> <op1>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.log2``' intrinsic computes the base-2
+logarithm of the specified value.
+
+Arguments:
+""""""""""
+
+The first argument and the return value are floating point numbers of the same
+type.
+
+The second and third arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``log2`` functions
+would, and handles error conditions in the same way.
+
+
+'``llvm.experimental.constrained.rint``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.rint(<type> <op1>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.rint``' intrinsic returns the first
+operand rounded to the nearest integer. It may raise an inexact floating point
+exception if the operand is not an integer.
+
+Arguments:
+""""""""""
+
+The first argument and the return value are floating point numbers of the same
+type.
+
+The second and third arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``rint`` functions
+would, and handles error conditions in the same way. The rounding mode is
+described, not determined, by the rounding mode argument. The actual rounding
+mode is determined by the runtime floating point environment. The rounding
+mode argument is only intended as information to the compiler.
+
+
+'``llvm.experimental.constrained.nearbyint``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare <type>
+ @llvm.experimental.constrained.nearbyint(<type> <op1>,
+ metadata <rounding mode>,
+ metadata <exception behavior>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.constrained.nearbyint``' intrinsic returns the first
+operand rounded to the nearest integer. It will not raise an inexact floating
+point exception if the operand is not an integer.
+
+
+Arguments:
+""""""""""
+
+The first argument and the return value are floating point numbers of the same
+type.
+
+The second and third arguments specify the rounding mode and exception
+behavior as described above.
+
+Semantics:
+""""""""""
+
+This function returns the same values as the libm ``nearbyint`` functions
+would, and handles error conditions in the same way. The rounding mode is
+described, not determined, by the rounding mode argument. The actual rounding
+mode is determined by the runtime floating point environment. The rounding
+mode argument is only intended as information to the compiler.
+
+
+General Intrinsics
+------------------
+
+This class of intrinsics is designed to be generic and has no specific
+purpose.
+
+'``llvm.var.annotation``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.var.annotation(i8* <val>, i8* <str>, i8* <str>, i32 <int>)
+
+Overview:
+"""""""""
+
+The '``llvm.var.annotation``' intrinsic.
+
+Arguments:
+""""""""""
+
+The first argument is a pointer to a value, the second is a pointer to a
+global string, the third is a pointer to a global string which is the
+source file name, and the last argument is the line number.
+
+Semantics:
+""""""""""
+
+This intrinsic allows annotation of local variables with arbitrary
+strings. This can be useful for special purpose optimizations that want
+to look for these annotations. These have no other defined use; they are
+ignored by code generation and optimization.
+
+'``llvm.ptr.annotation.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use '``llvm.ptr.annotation``' on a
+pointer to an integer of any width. *NOTE* you must specify an address space for
+the pointer. The identifier for the default address space is the integer
+'``0``'.
+
+::
+
+ declare i8* @llvm.ptr.annotation.p<address space>i8(i8* <val>, i8* <str>, i8* <str>, i32 <int>)
+ declare i16* @llvm.ptr.annotation.p<address space>i16(i16* <val>, i8* <str>, i8* <str>, i32 <int>)
+ declare i32* @llvm.ptr.annotation.p<address space>i32(i32* <val>, i8* <str>, i8* <str>, i32 <int>)
+ declare i64* @llvm.ptr.annotation.p<address space>i64(i64* <val>, i8* <str>, i8* <str>, i32 <int>)
+ declare i256* @llvm.ptr.annotation.p<address space>i256(i256* <val>, i8* <str>, i8* <str>, i32 <int>)
+
+Overview:
+"""""""""
+
+The '``llvm.ptr.annotation``' intrinsic.
+
+Arguments:
+""""""""""
+
+The first argument is a pointer to an integer value of arbitrary bitwidth
+(result of some expression), the second is a pointer to a global string, the
+third is a pointer to a global string which is the source file name, and the
+last argument is the line number. It returns the value of the first argument.
+
+Semantics:
+""""""""""
+
+This intrinsic allows annotation of a pointer to an integer with arbitrary
+strings. This can be useful for special purpose optimizations that want to look
+for these annotations. These have no other defined use; they are ignored by code
+generation and optimization.
+
+'``llvm.annotation.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use '``llvm.annotation``' on
+any integer bit width.
+
+::
+
+ declare i8 @llvm.annotation.i8(i8 <val>, i8* <str>, i8* <str>, i32 <int>)
+ declare i16 @llvm.annotation.i16(i16 <val>, i8* <str>, i8* <str>, i32 <int>)
+ declare i32 @llvm.annotation.i32(i32 <val>, i8* <str>, i8* <str>, i32 <int>)
+ declare i64 @llvm.annotation.i64(i64 <val>, i8* <str>, i8* <str>, i32 <int>)
+ declare i256 @llvm.annotation.i256(i256 <val>, i8* <str>, i8* <str>, i32 <int>)
+
+Overview:
+"""""""""
+
+The '``llvm.annotation``' intrinsic.
+
+Arguments:
+""""""""""
+
+The first argument is an integer value (result of some expression), the
+second is a pointer to a global string, the third is a pointer to a
+global string which is the source file name, and the last argument is
+the line number. It returns the value of the first argument.
+
+Semantics:
+""""""""""
+
+This intrinsic allows annotations to be put on arbitrary expressions
+with arbitrary strings. This can be useful for special purpose
+optimizations that want to look for these annotations. These have no
+other defined use; they are ignored by code generation and optimization.
+
+'``llvm.trap``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.trap() noreturn nounwind
+
+Overview:
+"""""""""
+
+The '``llvm.trap``' intrinsic.
+
+Arguments:
+""""""""""
+
+None.
+
+Semantics:
+""""""""""
+
+This intrinsic is lowered to the target dependent trap instruction. If
+the target does not have a trap instruction, this intrinsic will be
+lowered to a call of the ``abort()`` function.
+
+'``llvm.debugtrap``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.debugtrap() nounwind
+
+Overview:
+"""""""""
+
+The '``llvm.debugtrap``' intrinsic.
+
+Arguments:
+""""""""""
+
+None.
+
+Semantics:
+""""""""""
+
+This intrinsic is lowered to code which is intended to cause an
+execution trap with the intention of requesting the attention of a
+debugger.
+
+'``llvm.stackprotector``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.stackprotector(i8* <guard>, i8** <slot>)
+
+Overview:
+"""""""""
+
+The ``llvm.stackprotector`` intrinsic takes the ``guard`` and stores it
+onto the stack at ``slot``. The stack slot is adjusted to ensure that it
+is placed on the stack before local variables.
+
+Arguments:
+""""""""""
+
+The ``llvm.stackprotector`` intrinsic requires two pointer arguments.
+The first argument is the value loaded from the stack guard
+``@__stack_chk_guard``. The second variable is an ``alloca`` that has
+enough space to hold the value of the guard.
+
+Semantics:
+""""""""""
+
+This intrinsic causes the prologue/epilogue inserter to force the position of
+the ``AllocaInst`` stack slot to be before local variables on the stack. This is
+to ensure that if a local variable on the stack is overwritten, it will destroy
+the value of the guard. When the function exits, the guard on the stack is
+checked against the original guard by ``llvm.stackprotectorcheck``. If they are
+different, then ``llvm.stackprotectorcheck`` causes the program to abort by
+calling the ``__stack_chk_fail()`` function.
+
+'``llvm.stackguard``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i8* @llvm.stackguard()
+
+Overview:
+"""""""""
+
+The ``llvm.stackguard`` intrinsic returns the system stack guard value.
+
+It should not be generated by frontends, since it is only for internal usage.
+The reason why we create this intrinsic is that we still support IR form Stack
+Protector in FastISel.
+
+Arguments:
+""""""""""
+
+None.
+
+Semantics:
+""""""""""
+
+On some platforms, the value returned by this intrinsic remains unchanged
+between loads in the same thread. On other platforms, it returns the same
+global variable value, if any, e.g. ``@__stack_chk_guard``.
+
+Currently some platforms have IR-level customized stack guard loading (e.g.
+X86 Linux) that is not handled by ``llvm.stackguard()``, while they should be
+in the future.
+
+'``llvm.objectsize``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i32 @llvm.objectsize.i32(i8* <object>, i1 <min>, i1 <nullunknown>)
+ declare i64 @llvm.objectsize.i64(i8* <object>, i1 <min>, i1 <nullunknown>)
+
+Overview:
+"""""""""
+
+The ``llvm.objectsize`` intrinsic is designed to provide information to
+the optimizers to determine at compile time whether a) an operation
+(like memcpy) will overflow a buffer that corresponds to an object, or
+b) that a runtime check for overflow isn't necessary. An object in this
+context means an allocation of a specific class, structure, array, or
+other object.
+
+Arguments:
+""""""""""
+
+The ``llvm.objectsize`` intrinsic takes three arguments. The first argument is
+a pointer to or into the ``object``. The second argument determines whether
+``llvm.objectsize`` returns 0 (if true) or -1 (if false) when the object size
+is unknown. The third argument controls how ``llvm.objectsize`` acts when
+``null`` is used as its pointer argument. If it's true and the pointer is in
+address space 0, ``null`` is treated as an opaque value with an unknown number
+of bytes. Otherwise, ``llvm.objectsize`` reports 0 bytes available when given
+``null``.
+
+The second and third arguments only accept constants.
+
+Semantics:
+""""""""""
+
+The ``llvm.objectsize`` intrinsic is lowered to a constant representing
+the size of the object concerned. If the size cannot be determined at
+compile time, ``llvm.objectsize`` returns ``i32/i64 -1 or 0`` (depending
+on the ``min`` argument).
+
+'``llvm.expect``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.expect`` on any
+integer bit width.
+
+::
+
+ declare i1 @llvm.expect.i1(i1 <val>, i1 <expected_val>)
+ declare i32 @llvm.expect.i32(i32 <val>, i32 <expected_val>)
+ declare i64 @llvm.expect.i64(i64 <val>, i64 <expected_val>)
+
+Overview:
+"""""""""
+
+The ``llvm.expect`` intrinsic provides information about expected (the
+most probable) value of ``val``, which can be used by optimizers.
+
+Arguments:
+""""""""""
+
+The ``llvm.expect`` intrinsic takes two arguments. The first argument is
+a value. The second argument is an expected value, this needs to be a
+constant value, variables are not allowed.
+
+Semantics:
+""""""""""
+
+This intrinsic is lowered to the ``val``.
+
+.. _int_assume:
+
+'``llvm.assume``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.assume(i1 %cond)
+
+Overview:
+"""""""""
+
+The ``llvm.assume`` allows the optimizer to assume that the provided
+condition is true. This information can then be used in simplifying other parts
+of the code.
+
+Arguments:
+""""""""""
+
+The condition which the optimizer may assume is always true.
+
+Semantics:
+""""""""""
+
+The intrinsic allows the optimizer to assume that the provided condition is
+always true whenever the control flow reaches the intrinsic call. No code is
+generated for this intrinsic, and instructions that contribute only to the
+provided condition are not used for code generation. If the condition is
+violated during execution, the behavior is undefined.
+
+Note that the optimizer might limit the transformations performed on values
+used by the ``llvm.assume`` intrinsic in order to preserve the instructions
+only used to form the intrinsic's input argument. This might prove undesirable
+if the extra information provided by the ``llvm.assume`` intrinsic does not cause
+sufficient overall improvement in code quality. For this reason,
+``llvm.assume`` should not be used to document basic mathematical invariants
+that the optimizer can otherwise deduce or facts that are of little use to the
+optimizer.
+
+.. _int_ssa_copy:
+
+'``llvm.ssa_copy``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare type @llvm.ssa_copy(type %operand) returned(1) readnone
+
+Arguments:
+""""""""""
+
+The first argument is an operand which is used as the returned value.
+
+Overview:
+""""""""""
+
+The ``llvm.ssa_copy`` intrinsic can be used to attach information to
+operations by copying them and giving them new names. For example,
+the PredicateInfo utility uses it to build Extended SSA form, and
+attach various forms of information to operands that dominate specific
+uses. It is not meant for general use, only for building temporary
+renaming forms that require value splits at certain points.
+
+.. _type.test:
+
+'``llvm.type.test``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i1 @llvm.type.test(i8* %ptr, metadata %type) nounwind readnone
+
+
+Arguments:
+""""""""""
+
+The first argument is a pointer to be tested. The second argument is a
+metadata object representing a :doc:`type identifier <TypeMetadata>`.
+
+Overview:
+"""""""""
+
+The ``llvm.type.test`` intrinsic tests whether the given pointer is associated
+with the given type identifier.
+
+'``llvm.type.checked.load``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare {i8*, i1} @llvm.type.checked.load(i8* %ptr, i32 %offset, metadata %type) argmemonly nounwind readonly
+
+
+Arguments:
+""""""""""
+
+The first argument is a pointer from which to load a function pointer. The
+second argument is the byte offset from which to load the function pointer. The
+third argument is a metadata object representing a :doc:`type identifier
+<TypeMetadata>`.
+
+Overview:
+"""""""""
+
+The ``llvm.type.checked.load`` intrinsic safely loads a function pointer from a
+virtual table pointer using type metadata. This intrinsic is used to implement
+control flow integrity in conjunction with virtual call optimization. The
+virtual call optimization pass will optimize away ``llvm.type.checked.load``
+intrinsics associated with devirtualized calls, thereby removing the type
+check in cases where it is not needed to enforce the control flow integrity
+constraint.
+
+If the given pointer is associated with a type metadata identifier, this
+function returns true as the second element of its return value. (Note that
+the function may also return true if the given pointer is not associated
+with a type metadata identifier.) If the function's return value's second
+element is true, the following rules apply to the first element:
+
+- If the given pointer is associated with the given type metadata identifier,
+ it is the function pointer loaded from the given byte offset from the given
+ pointer.
+
+- If the given pointer is not associated with the given type metadata
+ identifier, it is one of the following (the choice of which is unspecified):
+
+ 1. The function pointer that would have been loaded from an arbitrarily chosen
+ (through an unspecified mechanism) pointer associated with the type
+ metadata.
+
+ 2. If the function has a non-void return type, a pointer to a function that
+ returns an unspecified value without causing side effects.
+
+If the function's return value's second element is false, the value of the
+first element is undefined.
+
+
+'``llvm.donothing``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.donothing() nounwind readnone
+
+Overview:
+"""""""""
+
+The ``llvm.donothing`` intrinsic doesn't perform any operation. It's one of only
+three intrinsics (besides ``llvm.experimental.patchpoint`` and
+``llvm.experimental.gc.statepoint``) that can be called with an invoke
+instruction.
+
+Arguments:
+""""""""""
+
+None.
+
+Semantics:
+""""""""""
+
+This intrinsic does nothing, and it's removed by optimizers and ignored
+by codegen.
+
+'``llvm.experimental.deoptimize``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare type @llvm.experimental.deoptimize(...) [ "deopt"(...) ]
+
+Overview:
+"""""""""
+
+This intrinsic, together with :ref:`deoptimization operand bundles
+<deopt_opbundles>`, allow frontends to express transfer of control and
+frame-local state from the currently executing (typically more specialized,
+hence faster) version of a function into another (typically more generic, hence
+slower) version.
+
+In languages with a fully integrated managed runtime like Java and JavaScript
+this intrinsic can be used to implement "uncommon trap" or "side exit" like
+functionality. In unmanaged languages like C and C++, this intrinsic can be
+used to represent the slow paths of specialized functions.
+
+
+Arguments:
+""""""""""
+
+The intrinsic takes an arbitrary number of arguments, whose meaning is
+decided by the :ref:`lowering strategy<deoptimize_lowering>`.
+
+Semantics:
+""""""""""
+
+The ``@llvm.experimental.deoptimize`` intrinsic executes an attached
+deoptimization continuation (denoted using a :ref:`deoptimization
+operand bundle <deopt_opbundles>`) and returns the value returned by
+the deoptimization continuation. Defining the semantic properties of
+the continuation itself is out of scope of the language reference --
+as far as LLVM is concerned, the deoptimization continuation can
+invoke arbitrary side effects, including reading from and writing to
+the entire heap.
+
+Deoptimization continuations expressed using ``"deopt"`` operand bundles always
+continue execution to the end of the physical frame containing them, so all
+calls to ``@llvm.experimental.deoptimize`` must be in "tail position":
+
+ - ``@llvm.experimental.deoptimize`` cannot be invoked.
+ - The call must immediately precede a :ref:`ret <i_ret>` instruction.
+ - The ``ret`` instruction must return the value produced by the
+ ``@llvm.experimental.deoptimize`` call if there is one, or void.
+
+Note that the above restrictions imply that the return type for a call to
+``@llvm.experimental.deoptimize`` will match the return type of its immediate
+caller.
+
+The inliner composes the ``"deopt"`` continuations of the caller into the
+``"deopt"`` continuations present in the inlinee, and also updates calls to this
+intrinsic to return directly from the frame of the function it inlined into.
+
+All declarations of ``@llvm.experimental.deoptimize`` must share the
+same calling convention.
+
+.. _deoptimize_lowering:
+
+Lowering:
+"""""""""
+
+Calls to ``@llvm.experimental.deoptimize`` are lowered to calls to the
+symbol ``__llvm_deoptimize`` (it is the frontend's responsibility to
+ensure that this symbol is defined). The call arguments to
+``@llvm.experimental.deoptimize`` are lowered as if they were formal
+arguments of the specified types, and not as varargs.
+
+
+'``llvm.experimental.guard``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare void @llvm.experimental.guard(i1, ...) [ "deopt"(...) ]
+
+Overview:
+"""""""""
+
+This intrinsic, together with :ref:`deoptimization operand bundles
+<deopt_opbundles>`, allows frontends to express guards or checks on
+optimistic assumptions made during compilation. The semantics of
+``@llvm.experimental.guard`` is defined in terms of
+``@llvm.experimental.deoptimize`` -- its body is defined to be
+equivalent to:
+
+.. code-block:: text
+
+ define void @llvm.experimental.guard(i1 %pred, <args...>) {
+ %realPred = and i1 %pred, undef
+ br i1 %realPred, label %continue, label %leave [, !make.implicit !{}]
+
+ leave:
+ call void @llvm.experimental.deoptimize(<args...>) [ "deopt"() ]
+ ret void
+
+ continue:
+ ret void
+ }
+
+
+with the optional ``[, !make.implicit !{}]`` present if and only if it
+is present on the call site. For more details on ``!make.implicit``,
+see :doc:`FaultMaps`.
+
+In words, ``@llvm.experimental.guard`` executes the attached
+``"deopt"`` continuation if (but **not** only if) its first argument
+is ``false``. Since the optimizer is allowed to replace the ``undef``
+with an arbitrary value, it can optimize guard to fail "spuriously",
+i.e. without the original condition being false (hence the "not only
+if"); and this allows for "check widening" type optimizations.
+
+``@llvm.experimental.guard`` cannot be invoked.
+
+
+'``llvm.load.relative``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+ declare i8* @llvm.load.relative.iN(i8* %ptr, iN %offset) argmemonly nounwind readonly
+
+Overview:
+"""""""""
+
+This intrinsic loads a 32-bit value from the address ``%ptr + %offset``,
+adds ``%ptr`` to that value and returns it. The constant folder specifically
+recognizes the form of this intrinsic and the constant initializers it may
+load from; if a loaded constant initializer is known to have the form
+``i32 trunc(x - %ptr)``, the intrinsic call is folded to ``x``.
+
+LLVM provides that the calculation of such a constant initializer will
+not overflow at link time under the medium code model if ``x`` is an
+``unnamed_addr`` function. However, it does not provide this guarantee for
+a constant initializer folded into a function body. This intrinsic can be
+used to avoid the possibility of overflows when loading from such a constant.
+
+Stack Map Intrinsics
+--------------------
+
+LLVM provides experimental intrinsics to support runtime patching
+mechanisms commonly desired in dynamic language JITs. These intrinsics
+are described in :doc:`StackMaps`.
+
+Element Wise Atomic Memory Intrinsics
+-------------------------------------
+
+These intrinsics are similar to the standard library memory intrinsics except
+that they perform memory transfer as a sequence of atomic memory accesses.
+
+.. _int_memcpy_element_unordered_atomic:
+
+'``llvm.memcpy.element.unordered.atomic``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.memcpy.element.unordered.atomic`` on
+any integer bit width and for different address spaces. Not all targets
+support all bit widths however.
+
+::
+
+ declare void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i32(i8* <dest>,
+ i8* <src>,
+ i32 <len>,
+ i32 <element_size>)
+ declare void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* <dest>,
+ i8* <src>,
+ i64 <len>,
+ i32 <element_size>)
+
+Overview:
+"""""""""
+
+The '``llvm.memcpy.element.unordered.atomic.*``' intrinsic is a specialization of the
+'``llvm.memcpy.*``' intrinsic. It differs in that the ``dest`` and ``src`` are treated
+as arrays with elements that are exactly ``element_size`` bytes, and the copy between
+buffers uses a sequence of :ref:`unordered atomic <ordering>` load/store operations
+that are a positive integer multiple of the ``element_size`` in size.
+
+Arguments:
+""""""""""
+
+The first three arguments are the same as they are in the :ref:`@llvm.memcpy <int_memcpy>`
+intrinsic, with the added constraint that ``len`` is required to be a positive integer
+multiple of the ``element_size``. If ``len`` is not a positive integer multiple of
+``element_size``, then the behaviour of the intrinsic is undefined.
+
+``element_size`` must be a compile-time constant positive power of two no greater than
+target-specific atomic access size limit.
+
+For each of the input pointers ``align`` parameter attribute must be specified. It
+must be a power of two no less than the ``element_size``. Caller guarantees that
+both the source and destination pointers are aligned to that boundary.
+
+Semantics:
+""""""""""
+
+The '``llvm.memcpy.element.unordered.atomic.*``' intrinsic copies ``len`` bytes of
+memory from the source location to the destination location. These locations are not
+allowed to overlap. The memory copy is performed as a sequence of load/store operations
+where each access is guaranteed to be a multiple of ``element_size`` bytes wide and
+aligned at an ``element_size`` boundary.
+
+The order of the copy is unspecified. The same value may be read from the source
+buffer many times, but only one write is issued to the destination buffer per
+element. It is well defined to have concurrent reads and writes to both source and
+destination provided those reads and writes are unordered atomic when specified.
+
+This intrinsic does not provide any additional ordering guarantees over those
+provided by a set of unordered loads from the source location and stores to the
+destination.
+
+Lowering:
+"""""""""
+
+In the most general case call to the '``llvm.memcpy.element.unordered.atomic.*``' is
+lowered to a call to the symbol ``__llvm_memcpy_element_unordered_atomic_*``. Where '*'
+is replaced with an actual element size.
+
+Optimizer is allowed to inline memory copy when it's profitable to do so.
+
+'``llvm.memmove.element.unordered.atomic``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use
+``llvm.memmove.element.unordered.atomic`` on any integer bit width and for
+different address spaces. Not all targets support all bit widths however.
+
+::
+
+ declare void @llvm.memmove.element.unordered.atomic.p0i8.p0i8.i32(i8* <dest>,
+ i8* <src>,
+ i32 <len>,
+ i32 <element_size>)
+ declare void @llvm.memmove.element.unordered.atomic.p0i8.p0i8.i64(i8* <dest>,
+ i8* <src>,
+ i64 <len>,
+ i32 <element_size>)
+
+Overview:
+"""""""""
+
+The '``llvm.memmove.element.unordered.atomic.*``' intrinsic is a specialization
+of the '``llvm.memmove.*``' intrinsic. It differs in that the ``dest`` and
+``src`` are treated as arrays with elements that are exactly ``element_size``
+bytes, and the copy between buffers uses a sequence of
+:ref:`unordered atomic <ordering>` load/store operations that are a positive
+integer multiple of the ``element_size`` in size.
+
+Arguments:
+""""""""""
+
+The first three arguments are the same as they are in the
+:ref:`@llvm.memmove <int_memmove>` intrinsic, with the added constraint that
+``len`` is required to be a positive integer multiple of the ``element_size``.
+If ``len`` is not a positive integer multiple of ``element_size``, then the
+behaviour of the intrinsic is undefined.
+
+``element_size`` must be a compile-time constant positive power of two no
+greater than a target-specific atomic access size limit.
+
+For each of the input pointers the ``align`` parameter attribute must be
+specified. It must be a power of two no less than the ``element_size``. Caller
+guarantees that both the source and destination pointers are aligned to that
+boundary.
+
+Semantics:
+""""""""""
+
+The '``llvm.memmove.element.unordered.atomic.*``' intrinsic copies ``len`` bytes
+of memory from the source location to the destination location. These locations
+are allowed to overlap. The memory copy is performed as a sequence of load/store
+operations where each access is guaranteed to be a multiple of ``element_size``
+bytes wide and aligned at an ``element_size`` boundary.
+
+The order of the copy is unspecified. The same value may be read from the source
+buffer many times, but only one write is issued to the destination buffer per
+element. It is well defined to have concurrent reads and writes to both source
+and destination provided those reads and writes are unordered atomic when
+specified.
+
+This intrinsic does not provide any additional ordering guarantees over those
+provided by a set of unordered loads from the source location and stores to the
+destination.
+
+Lowering:
+"""""""""
+
+In the most general case call to the
+'``llvm.memmove.element.unordered.atomic.*``' is lowered to a call to the symbol
+``__llvm_memmove_element_unordered_atomic_*``. Where '*' is replaced with an
+actual element size.
+
+The optimizer is allowed to inline the memory copy when it's profitable to do so.
+
+.. _int_memset_element_unordered_atomic:
+
+'``llvm.memset.element.unordered.atomic``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.memset.element.unordered.atomic`` on
+any integer bit width and for different address spaces. Not all targets
+support all bit widths however.
+
+::
+
+ declare void @llvm.memset.element.unordered.atomic.p0i8.i32(i8* <dest>,
+ i8 <value>,
+ i32 <len>,
+ i32 <element_size>)
+ declare void @llvm.memset.element.unordered.atomic.p0i8.i64(i8* <dest>,
+ i8 <value>,
+ i64 <len>,
+ i32 <element_size>)
+
+Overview:
+"""""""""
+
+The '``llvm.memset.element.unordered.atomic.*``' intrinsic is a specialization of the
+'``llvm.memset.*``' intrinsic. It differs in that the ``dest`` is treated as an array
+with elements that are exactly ``element_size`` bytes, and the assignment to that array
+uses uses a sequence of :ref:`unordered atomic <ordering>` store operations
+that are a positive integer multiple of the ``element_size`` in size.
+
+Arguments:
+""""""""""
+
+The first three arguments are the same as they are in the :ref:`@llvm.memset <int_memset>`
+intrinsic, with the added constraint that ``len`` is required to be a positive integer
+multiple of the ``element_size``. If ``len`` is not a positive integer multiple of
+``element_size``, then the behaviour of the intrinsic is undefined.
+
+``element_size`` must be a compile-time constant positive power of two no greater than
+target-specific atomic access size limit.
+
+The ``dest`` input pointer must have the ``align`` parameter attribute specified. It
+must be a power of two no less than the ``element_size``. Caller guarantees that
+the destination pointer is aligned to that boundary.
+
+Semantics:
+""""""""""
+
+The '``llvm.memset.element.unordered.atomic.*``' intrinsic sets the ``len`` bytes of
+memory starting at the destination location to the given ``value``. The memory is
+set with a sequence of store operations where each access is guaranteed to be a
+multiple of ``element_size`` bytes wide and aligned at an ``element_size`` boundary.
+
+The order of the assignment is unspecified. Only one write is issued to the
+destination buffer per element. It is well defined to have concurrent reads and
+writes to the destination provided those reads and writes are unordered atomic
+when specified.
+
+This intrinsic does not provide any additional ordering guarantees over those
+provided by a set of unordered stores to the destination.
+
+Lowering:
+"""""""""
+
+In the most general case call to the '``llvm.memset.element.unordered.atomic.*``' is
+lowered to a call to the symbol ``__llvm_memset_element_unordered_atomic_*``. Where '*'
+is replaced with an actual element size.
+
+The optimizer is allowed to inline the memory assignment when it's profitable to do so.
+
Added: www-releases/trunk/5.0.1/docs/_sources/Lexicon.rst.txt
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==============================================================================
--- www-releases/trunk/5.0.1/docs/_sources/Lexicon.rst.txt (added)
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@@ -0,0 +1,282 @@
+================
+The LLVM Lexicon
+================
+
+.. note::
+
+ This document is a work in progress!
+
+Definitions
+===========
+
+A
+-
+
+**ADCE**
+ Aggressive Dead Code Elimination
+
+**AST**
+ Abstract Syntax Tree.
+
+ Due to Clang's influence (mostly the fact that parsing and semantic
+ analysis are so intertwined for C and especially C++), the typical
+ working definition of AST in the LLVM community is roughly "the
+ compiler's first complete symbolic (as opposed to textual)
+ representation of an input program".
+ As such, an "AST" might be a more general graph instead of a "tree"
+ (consider the symbolic representation for the type of a typical "linked
+ list node"). This working definition is closer to what some authors
+ call an "annotated abstract syntax tree".
+
+ Consult your favorite compiler book or search engine for more details.
+
+B
+-
+
+.. _lexicon-bb-vectorization:
+
+**BB Vectorization**
+ Basic-Block Vectorization
+
+**BDCE**
+ Bit-tracking dead code elimination. Some bit-wise instructions (shifts,
+ ands, ors, etc.) "kill" some of their input bits -- that is, they make it
+ such that those bits can be either zero or one without affecting control or
+ data flow of a program. The BDCE pass removes instructions that only
+ compute these dead bits.
+
+**BURS**
+ Bottom Up Rewriting System --- A method of instruction selection for code
+ generation. An example is the `BURG
+ <http://www.program-transformation.org/Transform/BURG>`_ tool.
+
+C
+-
+
+**CFI**
+ Call Frame Information. Used in DWARF debug info and in C++ unwind info
+ to show how the function prolog lays out the stack frame.
+
+**CIE**
+ Common Information Entry. A kind of CFI used to reduce the size of FDEs.
+ The compiler creates a CIE which contains the information common across all
+ the FDEs. Each FDE then points to its CIE.
+
+**CSE**
+ Common Subexpression Elimination. An optimization that removes common
+ subexpression compuation. For example ``(a+b)*(a+b)`` has two subexpressions
+ that are the same: ``(a+b)``. This optimization would perform the addition
+ only once and then perform the multiply (but only if it's computationally
+ correct/safe).
+
+D
+-
+
+**DAG**
+ Directed Acyclic Graph
+
+.. _derived pointer:
+.. _derived pointers:
+
+**Derived Pointer**
+ A pointer to the interior of an object, such that a garbage collector is
+ unable to use the pointer for reachability analysis. While a derived pointer
+ is live, the corresponding object pointer must be kept in a root, otherwise
+ the collector might free the referenced object. With copying collectors,
+ derived pointers pose an additional hazard that they may be invalidated at
+ any `safe point`_. This term is used in opposition to `object pointer`_.
+
+**DSA**
+ Data Structure Analysis
+
+**DSE**
+ Dead Store Elimination
+
+F
+-
+
+**FCA**
+ First Class Aggregate
+
+**FDE**
+ Frame Description Entry. A kind of CFI used to describe the stack frame of
+ one function.
+
+G
+-
+
+**GC**
+ Garbage Collection. The practice of using reachability analysis instead of
+ explicit memory management to reclaim unused memory.
+
+**GVN**
+ Global Value Numbering. GVN is a pass that partitions values computed by a
+ function into congruence classes. Values ending up in the same congruence
+ class are guaranteed to be the same for every execution of the program.
+ In that respect, congruency is a compile-time approximation of equivalence
+ of values at runtime.
+
+H
+-
+
+.. _heap:
+
+**Heap**
+ In garbage collection, the region of memory which is managed using
+ reachability analysis.
+
+I
+-
+
+**IPA**
+ Inter-Procedural Analysis. Refers to any variety of code analysis that
+ occurs between procedures, functions or compilation units (modules).
+
+**IPO**
+ Inter-Procedural Optimization. Refers to any variety of code optimization
+ that occurs between procedures, functions or compilation units (modules).
+
+**ISel**
+ Instruction Selection
+
+L
+-
+
+**LCSSA**
+ Loop-Closed Static Single Assignment Form
+
+**LGTM**
+ "Looks Good To Me". In a review thread, this indicates that the
+ reviewer thinks that the patch is okay to commit.
+
+**LICM**
+ Loop Invariant Code Motion
+
+**LSDA**
+ Language Specific Data Area. C++ "zero cost" unwinding is built on top a
+ generic unwinding mechanism. As the unwinder walks each frame, it calls
+ a "personality" function to do language specific analysis. Each function's
+ FDE points to an optional LSDA which is passed to the personality function.
+ For C++, the LSDA contain info about the type and location of catch
+ statements in that function.
+
+**Load-VN**
+ Load Value Numbering
+
+**LTO**
+ Link-Time Optimization
+
+M
+-
+
+**MC**
+ Machine Code
+
+N
+-
+
+**NFC**
+ "No functional change". Used in a commit message to indicate that a patch
+ is a pure refactoring/cleanup.
+ Usually used in the first line, so it is visible without opening the
+ actual commit email.
+
+O
+-
+.. _object pointer:
+.. _object pointers:
+
+**Object Pointer**
+ A pointer to an object such that the garbage collector is able to trace
+ references contained within the object. This term is used in opposition to
+ `derived pointer`_.
+
+P
+-
+
+**PR**
+ Problem report. A bug filed on `the LLVM Bug Tracking System
+ <https://bugs.llvm.org/enter_bug.cgi>`_.
+
+**PRE**
+ Partial Redundancy Elimination
+
+R
+-
+
+**RAUW**
+
+ Replace All Uses With. The functions ``User::replaceUsesOfWith()``,
+ ``Value::replaceAllUsesWith()``, and
+ ``Constant::replaceUsesOfWithOnConstant()`` implement the replacement of one
+ Value with another by iterating over its def/use chain and fixing up all of
+ the pointers to point to the new value. See
+ also `def/use chains <ProgrammersManual.html#iterating-over-def-use-use-def-chains>`_.
+
+**Reassociation**
+ Rearranging associative expressions to promote better redundancy elimination
+ and other optimization. For example, changing ``(A+B-A)`` into ``(B+A-A)``,
+ permitting it to be optimized into ``(B+0)`` then ``(B)``.
+
+.. _roots:
+.. _stack roots:
+
+**Root**
+ In garbage collection, a pointer variable lying outside of the `heap`_ from
+ which the collector begins its reachability analysis. In the context of code
+ generation, "root" almost always refers to a "stack root" --- a local or
+ temporary variable within an executing function.
+
+**RPO**
+ Reverse postorder
+
+S
+-
+
+.. _safe point:
+
+**Safe Point**
+ In garbage collection, it is necessary to identify `stack roots`_ so that
+ reachability analysis may proceed. It may be infeasible to provide this
+ information for every instruction, so instead the information may is
+ calculated only at designated safe points. With a copying collector,
+ `derived pointers`_ must not be retained across safe points and `object
+ pointers`_ must be reloaded from stack roots.
+
+**SDISel**
+ Selection DAG Instruction Selection.
+
+**SCC**
+ Strongly Connected Component
+
+**SCCP**
+ Sparse Conditional Constant Propagation
+
+**SLP**
+ Superword-Level Parallelism, same as :ref:`Basic-Block Vectorization
+ <lexicon-bb-vectorization>`.
+
+**Splat**
+ Splat refers to a vector of identical scalar elements.
+
+ The term is based on the PowerPC Altivec instructions that provided
+ this functionality in hardware. For example, "vsplth" and the corresponding
+ software intrinsic "vec_splat()". Examples of other hardware names for this
+ action include "duplicate" (ARM) and "broadcast" (x86).
+
+**SRoA**
+ Scalar Replacement of Aggregates
+
+**SSA**
+ Static Single Assignment
+
+**Stack Map**
+ In garbage collection, metadata emitted by the code generator which
+ identifies `roots`_ within the stack frame of an executing function.
+
+T
+-
+
+**TBAA**
+ Type-Based Alias Analysis
+
Added: www-releases/trunk/5.0.1/docs/_sources/LibFuzzer.rst.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.1/docs/_sources/LibFuzzer.rst.txt?rev=321287&view=auto
==============================================================================
--- www-releases/trunk/5.0.1/docs/_sources/LibFuzzer.rst.txt (added)
+++ www-releases/trunk/5.0.1/docs/_sources/LibFuzzer.rst.txt Thu Dec 21 10:09:53 2017
@@ -0,0 +1,812 @@
+=======================================================
+libFuzzer â a library for coverage-guided fuzz testing.
+=======================================================
+.. contents::
+ :local:
+ :depth: 1
+
+Introduction
+============
+
+LibFuzzer is in-process, coverage-guided, evolutionary fuzzing engine.
+
+LibFuzzer is linked with the library under test, and feeds fuzzed inputs to the
+library via a specific fuzzing entrypoint (aka "target function"); the fuzzer
+then tracks which areas of the code are reached, and generates mutations on the
+corpus of input data in order to maximize the code coverage.
+The code coverage
+information for libFuzzer is provided by LLVM's SanitizerCoverage_
+instrumentation.
+
+Contact: libfuzzer(#)googlegroups.com
+
+Versions
+========
+
+LibFuzzer is under active development so you will need the current
+(or at least a very recent) version of the Clang compiler.
+
+(If `building Clang from trunk`_ is too time-consuming or difficult, then
+the Clang binaries that the Chromium developers build are likely to be
+fairly recent:
+
+.. code-block:: console
+
+ mkdir TMP_CLANG
+ cd TMP_CLANG
+ git clone https://chromium.googlesource.com/chromium/src/tools/clang
+ cd ..
+ TMP_CLANG/clang/scripts/update.py
+
+This installs the Clang binary as
+``./third_party/llvm-build/Release+Asserts/bin/clang``)
+
+The libFuzzer code resides in the LLVM repository, and requires a recent Clang
+compiler to build (and is used to `fuzz various parts of LLVM itself`_).
+However the fuzzer itself does not (and should not) depend on any part of LLVM
+infrastructure and can be used for other projects without requiring the rest
+of LLVM.
+
+
+Getting Started
+===============
+
+.. contents::
+ :local:
+ :depth: 1
+
+Fuzz Target
+-----------
+
+The first step in using libFuzzer on a library is to implement a
+*fuzz target* -- a function that accepts an array of bytes and
+does something interesting with these bytes using the API under test.
+Like this:
+
+.. code-block:: c++
+
+ // fuzz_target.cc
+ extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
+ DoSomethingInterestingWithMyAPI(Data, Size);
+ return 0; // Non-zero return values are reserved for future use.
+ }
+
+Note that this fuzz target does not depend on libFuzzer in any way
+and so it is possible and even desirable to use it with other fuzzing engines
+e.g. AFL_ and/or Radamsa_.
+
+Some important things to remember about fuzz targets:
+
+* The fuzzing engine will execute the fuzz target many times with different inputs in the same process.
+* It must tolerate any kind of input (empty, huge, malformed, etc).
+* It must not `exit()` on any input.
+* It may use threads but ideally all threads should be joined at the end of the function.
+* It must be as deterministic as possible. Non-determinism (e.g. random decisions not based on the input bytes) will make fuzzing inefficient.
+* It must be fast. Try avoiding cubic or greater complexity, logging, or excessive memory consumption.
+* Ideally, it should not modify any global state (although that's not strict).
+* Usually, the narrower the target the better. E.g. if your target can parse several data formats, split it into several targets, one per format.
+
+
+Fuzzer Usage
+------------
+
+Very recent versions of Clang (> April 20 2017) include libFuzzer,
+and no installation is necessary.
+In order to fuzz your binary, use the `-fsanitize=fuzzer` flag during the compilation::
+
+ clang -fsanitize=fuzzer,address mytarget.c
+
+Otherwise, build the libFuzzer library as a static archive, without any sanitizer
+options. Note that the libFuzzer library contains the ``main()`` function:
+
+.. code-block:: console
+
+ svn co http://llvm.org/svn/llvm-project/llvm/trunk/lib/Fuzzer # or git clone https://chromium.googlesource.com/chromium/llvm-project/llvm/lib/Fuzzer
+ ./Fuzzer/build.sh # Produces libFuzzer.a
+
+Then build the fuzzing target function and the library under test using
+the SanitizerCoverage_ option, which instruments the code so that the fuzzer
+can retrieve code coverage information (to guide the fuzzing). Linking with
+the libFuzzer code then gives a fuzzer executable.
+
+You should also enable one or more of the *sanitizers*, which help to expose
+latent bugs by making incorrect behavior generate errors at runtime:
+
+ - AddressSanitizer_ (ASAN) detects memory access errors. Use `-fsanitize=address`.
+ - UndefinedBehaviorSanitizer_ (UBSAN) detects the use of various features of C/C++ that are explicitly
+ listed as resulting in undefined behavior. Use `-fsanitize=undefined -fno-sanitize-recover=undefined`
+ or any individual UBSAN check, e.g. `-fsanitize=signed-integer-overflow -fno-sanitize-recover=undefined`.
+ You may combine ASAN and UBSAN in one build.
+ - MemorySanitizer_ (MSAN) detects uninitialized reads: code whose behavior relies on memory
+ contents that have not been initialized to a specific value. Use `-fsanitize=memory`.
+ MSAN can not be combined with other sanirizers and should be used as a seprate build.
+
+Finally, link with ``libFuzzer.a``::
+
+ clang -fsanitize-coverage=trace-pc-guard -fsanitize=address your_lib.cc fuzz_target.cc libFuzzer.a -o my_fuzzer
+
+Corpus
+------
+
+Coverage-guided fuzzers like libFuzzer rely on a corpus of sample inputs for the
+code under test. This corpus should ideally be seeded with a varied collection
+of valid and invalid inputs for the code under test; for example, for a graphics
+library the initial corpus might hold a variety of different small PNG/JPG/GIF
+files. The fuzzer generates random mutations based around the sample inputs in
+the current corpus. If a mutation triggers execution of a previously-uncovered
+path in the code under test, then that mutation is saved to the corpus for
+future variations.
+
+LibFuzzer will work without any initial seeds, but will be less
+efficient if the library under test accepts complex,
+structured inputs.
+
+The corpus can also act as a sanity/regression check, to confirm that the
+fuzzing entrypoint still works and that all of the sample inputs run through
+the code under test without problems.
+
+If you have a large corpus (either generated by fuzzing or acquired by other means)
+you may want to minimize it while still preserving the full coverage. One way to do that
+is to use the `-merge=1` flag:
+
+.. code-block:: console
+
+ mkdir NEW_CORPUS_DIR # Store minimized corpus here.
+ ./my_fuzzer -merge=1 NEW_CORPUS_DIR FULL_CORPUS_DIR
+
+You may use the same flag to add more interesting items to an existing corpus.
+Only the inputs that trigger new coverage will be added to the first corpus.
+
+.. code-block:: console
+
+ ./my_fuzzer -merge=1 CURRENT_CORPUS_DIR NEW_POTENTIALLY_INTERESTING_INPUTS_DIR
+
+
+Running
+-------
+
+To run the fuzzer, first create a Corpus_ directory that holds the
+initial "seed" sample inputs:
+
+.. code-block:: console
+
+ mkdir CORPUS_DIR
+ cp /some/input/samples/* CORPUS_DIR
+
+Then run the fuzzer on the corpus directory:
+
+.. code-block:: console
+
+ ./my_fuzzer CORPUS_DIR # -max_len=1000 -jobs=20 ...
+
+As the fuzzer discovers new interesting test cases (i.e. test cases that
+trigger coverage of new paths through the code under test), those test cases
+will be added to the corpus directory.
+
+By default, the fuzzing process will continue indefinitely â at least until
+a bug is found. Any crashes or sanitizer failures will be reported as usual,
+stopping the fuzzing process, and the particular input that triggered the bug
+will be written to disk (typically as ``crash-<sha1>``, ``leak-<sha1>``,
+or ``timeout-<sha1>``).
+
+
+Parallel Fuzzing
+----------------
+
+Each libFuzzer process is single-threaded, unless the library under test starts
+its own threads. However, it is possible to run multiple libFuzzer processes in
+parallel with a shared corpus directory; this has the advantage that any new
+inputs found by one fuzzer process will be available to the other fuzzer
+processes (unless you disable this with the ``-reload=0`` option).
+
+This is primarily controlled by the ``-jobs=N`` option, which indicates that
+that `N` fuzzing jobs should be run to completion (i.e. until a bug is found or
+time/iteration limits are reached). These jobs will be run across a set of
+worker processes, by default using half of the available CPU cores; the count of
+worker processes can be overridden by the ``-workers=N`` option. For example,
+running with ``-jobs=30`` on a 12-core machine would run 6 workers by default,
+with each worker averaging 5 bugs by completion of the entire process.
+
+
+Options
+=======
+
+To run the fuzzer, pass zero or more corpus directories as command line
+arguments. The fuzzer will read test inputs from each of these corpus
+directories, and any new test inputs that are generated will be written
+back to the first corpus directory:
+
+.. code-block:: console
+
+ ./fuzzer [-flag1=val1 [-flag2=val2 ...] ] [dir1 [dir2 ...] ]
+
+If a list of files (rather than directories) are passed to the fuzzer program,
+then it will re-run those files as test inputs but will not perform any fuzzing.
+In this mode the fuzzer binary can be used as a regression test (e.g. on a
+continuous integration system) to check the target function and saved inputs
+still work.
+
+The most important command line options are:
+
+``-help``
+ Print help message.
+``-seed``
+ Random seed. If 0 (the default), the seed is generated.
+``-runs``
+ Number of individual test runs, -1 (the default) to run indefinitely.
+``-max_len``
+ Maximum length of a test input. If 0 (the default), libFuzzer tries to guess
+ a good value based on the corpus (and reports it).
+``-timeout``
+ Timeout in seconds, default 1200. If an input takes longer than this timeout,
+ the process is treated as a failure case.
+``-rss_limit_mb``
+ Memory usage limit in Mb, default 2048. Use 0 to disable the limit.
+ If an input requires more than this amount of RSS memory to execute,
+ the process is treated as a failure case.
+ The limit is checked in a separate thread every second.
+ If running w/o ASAN/MSAN, you may use 'ulimit -v' instead.
+``-timeout_exitcode``
+ Exit code (default 77) used if libFuzzer reports a timeout.
+``-error_exitcode``
+ Exit code (default 77) used if libFuzzer itself (not a sanitizer) reports a bug (leak, OOM, etc).
+``-max_total_time``
+ If positive, indicates the maximum total time in seconds to run the fuzzer.
+ If 0 (the default), run indefinitely.
+``-merge``
+ If set to 1, any corpus inputs from the 2nd, 3rd etc. corpus directories
+ that trigger new code coverage will be merged into the first corpus
+ directory. Defaults to 0. This flag can be used to minimize a corpus.
+``-minimize_crash``
+ If 1, minimizes the provided crash input.
+ Use with -runs=N or -max_total_time=N to limit the number of attempts.
+``-reload``
+ If set to 1 (the default), the corpus directory is re-read periodically to
+ check for new inputs; this allows detection of new inputs that were discovered
+ by other fuzzing processes.
+``-jobs``
+ Number of fuzzing jobs to run to completion. Default value is 0, which runs a
+ single fuzzing process until completion. If the value is >= 1, then this
+ number of jobs performing fuzzing are run, in a collection of parallel
+ separate worker processes; each such worker process has its
+ ``stdout``/``stderr`` redirected to ``fuzz-<JOB>.log``.
+``-workers``
+ Number of simultaneous worker processes to run the fuzzing jobs to completion
+ in. If 0 (the default), ``min(jobs, NumberOfCpuCores()/2)`` is used.
+``-dict``
+ Provide a dictionary of input keywords; see Dictionaries_.
+``-use_counters``
+ Use `coverage counters`_ to generate approximate counts of how often code
+ blocks are hit; defaults to 1.
+``-use_value_profile``
+ Use `value profile`_ to guide corpus expansion; defaults to 0.
+``-only_ascii``
+ If 1, generate only ASCII (``isprint``+``isspace``) inputs. Defaults to 0.
+``-artifact_prefix``
+ Provide a prefix to use when saving fuzzing artifacts (crash, timeout, or
+ slow inputs) as ``$(artifact_prefix)file``. Defaults to empty.
+``-exact_artifact_path``
+ Ignored if empty (the default). If non-empty, write the single artifact on
+ failure (crash, timeout) as ``$(exact_artifact_path)``. This overrides
+ ``-artifact_prefix`` and will not use checksum in the file name. Do not use
+ the same path for several parallel processes.
+``-print_pcs``
+ If 1, print out newly covered PCs. Defaults to 0.
+``-print_final_stats``
+ If 1, print statistics at exit. Defaults to 0.
+``-detect_leaks``
+ If 1 (default) and if LeakSanitizer is enabled
+ try to detect memory leaks during fuzzing (i.e. not only at shut down).
+``-close_fd_mask``
+ Indicate output streams to close at startup. Be careful, this will
+ remove diagnostic output from target code (e.g. messages on assert failure).
+
+ - 0 (default): close neither ``stdout`` nor ``stderr``
+ - 1 : close ``stdout``
+ - 2 : close ``stderr``
+ - 3 : close both ``stdout`` and ``stderr``.
+``-print_coverage``
+ If 1, print coverage information as text at exit.
+``-dump_coverage``
+ If 1, dump coverage information as a .sancov file at exit.
+
+For the full list of flags run the fuzzer binary with ``-help=1``.
+
+Output
+======
+
+During operation the fuzzer prints information to ``stderr``, for example::
+
+ INFO: Seed: 1523017872
+ INFO: Loaded 1 modules (16 guards): [0x744e60, 0x744ea0),
+ INFO: -max_len is not provided, using 64
+ INFO: A corpus is not provided, starting from an empty corpus
+ #0 READ units: 1
+ #1 INITED cov: 3 ft: 2 corp: 1/1b exec/s: 0 rss: 24Mb
+ #3811 NEW cov: 4 ft: 3 corp: 2/2b exec/s: 0 rss: 25Mb L: 1 MS: 5 ChangeBit-ChangeByte-ChangeBit-ShuffleBytes-ChangeByte-
+ #3827 NEW cov: 5 ft: 4 corp: 3/4b exec/s: 0 rss: 25Mb L: 2 MS: 1 CopyPart-
+ #3963 NEW cov: 6 ft: 5 corp: 4/6b exec/s: 0 rss: 25Mb L: 2 MS: 2 ShuffleBytes-ChangeBit-
+ #4167 NEW cov: 7 ft: 6 corp: 5/9b exec/s: 0 rss: 25Mb L: 3 MS: 1 InsertByte-
+ ...
+
+The early parts of the output include information about the fuzzer options and
+configuration, including the current random seed (in the ``Seed:`` line; this
+can be overridden with the ``-seed=N`` flag).
+
+Further output lines have the form of an event code and statistics. The
+possible event codes are:
+
+``READ``
+ The fuzzer has read in all of the provided input samples from the corpus
+ directories.
+``INITED``
+ The fuzzer has completed initialization, which includes running each of
+ the initial input samples through the code under test.
+``NEW``
+ The fuzzer has created a test input that covers new areas of the code
+ under test. This input will be saved to the primary corpus directory.
+``pulse``
+ The fuzzer has generated 2\ :sup:`n` inputs (generated periodically to reassure
+ the user that the fuzzer is still working).
+``DONE``
+ The fuzzer has completed operation because it has reached the specified
+ iteration limit (``-runs``) or time limit (``-max_total_time``).
+``RELOAD``
+ The fuzzer is performing a periodic reload of inputs from the corpus
+ directory; this allows it to discover any inputs discovered by other
+ fuzzer processes (see `Parallel Fuzzing`_).
+
+Each output line also reports the following statistics (when non-zero):
+
+``cov:``
+ Total number of code blocks or edges covered by the executing the current
+ corpus.
+``ft:``
+ libFuzzer uses different signals to evaluate the code coverage:
+ edge coverage, edge counters, value profiles, indirect caller/callee pairs, etc.
+ These signals combined are called *features* (`ft:`).
+``corp:``
+ Number of entries in the current in-memory test corpus and its size in bytes.
+``exec/s:``
+ Number of fuzzer iterations per second.
+``rss:``
+ Current memory consumption.
+
+For ``NEW`` events, the output line also includes information about the mutation
+operation that produced the new input:
+
+``L:``
+ Size of the new input in bytes.
+``MS: <n> <operations>``
+ Count and list of the mutation operations used to generate the input.
+
+
+Examples
+========
+.. contents::
+ :local:
+ :depth: 1
+
+Toy example
+-----------
+
+A simple function that does something interesting if it receives the input
+"HI!"::
+
+ cat << EOF > test_fuzzer.cc
+ #include <stdint.h>
+ #include <stddef.h>
+ extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+ if (size > 0 && data[0] == 'H')
+ if (size > 1 && data[1] == 'I')
+ if (size > 2 && data[2] == '!')
+ __builtin_trap();
+ return 0;
+ }
+ EOF
+ # Build test_fuzzer.cc with asan and link against libFuzzer.a
+ clang++ -fsanitize=address -fsanitize-coverage=trace-pc-guard test_fuzzer.cc libFuzzer.a
+ # Run the fuzzer with no corpus.
+ ./a.out
+
+You should get an error pretty quickly::
+
+ INFO: Seed: 1523017872
+ INFO: Loaded 1 modules (16 guards): [0x744e60, 0x744ea0),
+ INFO: -max_len is not provided, using 64
+ INFO: A corpus is not provided, starting from an empty corpus
+ #0 READ units: 1
+ #1 INITED cov: 3 ft: 2 corp: 1/1b exec/s: 0 rss: 24Mb
+ #3811 NEW cov: 4 ft: 3 corp: 2/2b exec/s: 0 rss: 25Mb L: 1 MS: 5 ChangeBit-ChangeByte-ChangeBit-ShuffleBytes-ChangeByte-
+ #3827 NEW cov: 5 ft: 4 corp: 3/4b exec/s: 0 rss: 25Mb L: 2 MS: 1 CopyPart-
+ #3963 NEW cov: 6 ft: 5 corp: 4/6b exec/s: 0 rss: 25Mb L: 2 MS: 2 ShuffleBytes-ChangeBit-
+ #4167 NEW cov: 7 ft: 6 corp: 5/9b exec/s: 0 rss: 25Mb L: 3 MS: 1 InsertByte-
+ ==31511== ERROR: libFuzzer: deadly signal
+ ...
+ artifact_prefix='./'; Test unit written to ./crash-b13e8756b13a00cf168300179061fb4b91fefbed
+
+
+More examples
+-------------
+
+Examples of real-life fuzz targets and the bugs they find can be found
+at http://tutorial.libfuzzer.info. Among other things you can learn how
+to detect Heartbleed_ in one second.
+
+
+Advanced features
+=================
+.. contents::
+ :local:
+ :depth: 1
+
+Dictionaries
+------------
+LibFuzzer supports user-supplied dictionaries with input language keywords
+or other interesting byte sequences (e.g. multi-byte magic values).
+Use ``-dict=DICTIONARY_FILE``. For some input languages using a dictionary
+may significantly improve the search speed.
+The dictionary syntax is similar to that used by AFL_ for its ``-x`` option::
+
+ # Lines starting with '#' and empty lines are ignored.
+
+ # Adds "blah" (w/o quotes) to the dictionary.
+ kw1="blah"
+ # Use \\ for backslash and \" for quotes.
+ kw2="\"ac\\dc\""
+ # Use \xAB for hex values
+ kw3="\xF7\xF8"
+ # the name of the keyword followed by '=' may be omitted:
+ "foo\x0Abar"
+
+
+
+Tracing CMP instructions
+------------------------
+
+With an additional compiler flag ``-fsanitize-coverage=trace-cmp``
+(see SanitizerCoverageTraceDataFlow_)
+libFuzzer will intercept CMP instructions and guide mutations based
+on the arguments of intercepted CMP instructions. This may slow down
+the fuzzing but is very likely to improve the results.
+
+Value Profile
+-------------
+
+*EXPERIMENTAL*.
+With ``-fsanitize-coverage=trace-cmp``
+and extra run-time flag ``-use_value_profile=1`` the fuzzer will
+collect value profiles for the parameters of compare instructions
+and treat some new values as new coverage.
+
+The current imlpementation does roughly the following:
+
+* The compiler instruments all CMP instructions with a callback that receives both CMP arguments.
+* The callback computes `(caller_pc&4095) | (popcnt(Arg1 ^ Arg2) << 12)` and uses this value to set a bit in a bitset.
+* Every new observed bit in the bitset is treated as new coverage.
+
+
+This feature has a potential to discover many interesting inputs,
+but there are two downsides.
+First, the extra instrumentation may bring up to 2x additional slowdown.
+Second, the corpus may grow by several times.
+
+Fuzzer-friendly build mode
+---------------------------
+Sometimes the code under test is not fuzzing-friendly. Examples:
+
+ - The target code uses a PRNG seeded e.g. by system time and
+ thus two consequent invocations may potentially execute different code paths
+ even if the end result will be the same. This will cause a fuzzer to treat
+ two similar inputs as significantly different and it will blow up the test corpus.
+ E.g. libxml uses ``rand()`` inside its hash table.
+ - The target code uses checksums to protect from invalid inputs.
+ E.g. png checks CRC for every chunk.
+
+In many cases it makes sense to build a special fuzzing-friendly build
+with certain fuzzing-unfriendly features disabled. We propose to use a common build macro
+for all such cases for consistency: ``FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION``.
+
+.. code-block:: c++
+
+ void MyInitPRNG() {
+ #ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
+ // In fuzzing mode the behavior of the code should be deterministic.
+ srand(0);
+ #else
+ srand(time(0));
+ #endif
+ }
+
+
+
+AFL compatibility
+-----------------
+LibFuzzer can be used together with AFL_ on the same test corpus.
+Both fuzzers expect the test corpus to reside in a directory, one file per input.
+You can run both fuzzers on the same corpus, one after another:
+
+.. code-block:: console
+
+ ./afl-fuzz -i testcase_dir -o findings_dir /path/to/program @@
+ ./llvm-fuzz testcase_dir findings_dir # Will write new tests to testcase_dir
+
+Periodically restart both fuzzers so that they can use each other's findings.
+Currently, there is no simple way to run both fuzzing engines in parallel while sharing the same corpus dir.
+
+You may also use AFL on your target function ``LLVMFuzzerTestOneInput``:
+see an example `here <https://github.com/llvm-mirror/llvm/blob/master/lib/Fuzzer/afl/afl_driver.cpp>`__.
+
+How good is my fuzzer?
+----------------------
+
+Once you implement your target function ``LLVMFuzzerTestOneInput`` and fuzz it to death,
+you will want to know whether the function or the corpus can be improved further.
+One easy to use metric is, of course, code coverage.
+You can get the coverage for your corpus like this:
+
+.. code-block:: console
+
+ ./fuzzer CORPUS_DIR -runs=0 -print_coverage=1
+
+This will run all tests in the CORPUS_DIR but will not perform any fuzzing.
+At the end of the process it will print text describing what code has been covered and what hasn't.
+
+Alternatively, use
+
+.. code-block:: console
+
+ ./fuzzer CORPUS_DIR -runs=0 -dump_coverage=1
+
+which will dump a ``.sancov`` file with coverage information.
+See SanitizerCoverage_ for details on querying the file using the ``sancov`` tool.
+
+You may also use other ways to visualize coverage,
+e.g. using `Clang coverage <http://clang.llvm.org/docs/SourceBasedCodeCoverage.html>`_,
+but those will require
+you to rebuild the code with different compiler flags.
+
+User-supplied mutators
+----------------------
+
+LibFuzzer allows to use custom (user-supplied) mutators,
+see FuzzerInterface.h_
+
+Startup initialization
+----------------------
+If the library being tested needs to be initialized, there are several options.
+
+The simplest way is to have a statically initialized global object inside
+`LLVMFuzzerTestOneInput` (or in global scope if that works for you):
+
+.. code-block:: c++
+
+ extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
+ static bool Initialized = DoInitialization();
+ ...
+
+Alternatively, you may define an optional init function and it will receive
+the program arguments that you can read and modify. Do this **only** if you
+really need to access ``argv``/``argc``.
+
+.. code-block:: c++
+
+ extern "C" int LLVMFuzzerInitialize(int *argc, char ***argv) {
+ ReadAndMaybeModify(argc, argv);
+ return 0;
+ }
+
+
+Leaks
+-----
+
+Binaries built with AddressSanitizer_ or LeakSanitizer_ will try to detect
+memory leaks at the process shutdown.
+For in-process fuzzing this is inconvenient
+since the fuzzer needs to report a leak with a reproducer as soon as the leaky
+mutation is found. However, running full leak detection after every mutation
+is expensive.
+
+By default (``-detect_leaks=1``) libFuzzer will count the number of
+``malloc`` and ``free`` calls when executing every mutation.
+If the numbers don't match (which by itself doesn't mean there is a leak)
+libFuzzer will invoke the more expensive LeakSanitizer_
+pass and if the actual leak is found, it will be reported with the reproducer
+and the process will exit.
+
+If your target has massive leaks and the leak detection is disabled
+you will eventually run out of RAM (see the ``-rss_limit_mb`` flag).
+
+
+Developing libFuzzer
+====================
+
+Building libFuzzer as a part of LLVM project and running its test requires
+fresh clang as the host compiler and special CMake configuration:
+
+.. code-block:: console
+
+ cmake -GNinja -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ -DLLVM_USE_SANITIZER=Address -DLLVM_USE_SANITIZE_COVERAGE=YES -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_ASSERTIONS=ON /path/to/llvm
+ ninja check-fuzzer
+
+
+Fuzzing components of LLVM
+==========================
+.. contents::
+ :local:
+ :depth: 1
+
+To build any of the LLVM fuzz targets use the build instructions above.
+
+clang-format-fuzzer
+-------------------
+The inputs are random pieces of C++-like text.
+
+.. code-block:: console
+
+ ninja clang-format-fuzzer
+ mkdir CORPUS_DIR
+ ./bin/clang-format-fuzzer CORPUS_DIR
+
+Optionally build other kinds of binaries (ASan+Debug, MSan, UBSan, etc).
+
+Tracking bug: https://llvm.org/bugs/show_bug.cgi?id=23052
+
+clang-fuzzer
+------------
+
+The behavior is very similar to ``clang-format-fuzzer``.
+
+Tracking bug: https://llvm.org/bugs/show_bug.cgi?id=23057
+
+llvm-as-fuzzer
+--------------
+
+Tracking bug: https://llvm.org/bugs/show_bug.cgi?id=24639
+
+llvm-mc-fuzzer
+--------------
+
+This tool fuzzes the MC layer. Currently it is only able to fuzz the
+disassembler but it is hoped that assembly, and round-trip verification will be
+added in future.
+
+When run in dissassembly mode, the inputs are opcodes to be disassembled. The
+fuzzer will consume as many instructions as possible and will stop when it
+finds an invalid instruction or runs out of data.
+
+Please note that the command line interface differs slightly from that of other
+fuzzers. The fuzzer arguments should follow ``--fuzzer-args`` and should have
+a single dash, while other arguments control the operation mode and target in a
+similar manner to ``llvm-mc`` and should have two dashes. For example:
+
+.. code-block:: console
+
+ llvm-mc-fuzzer --triple=aarch64-linux-gnu --disassemble --fuzzer-args -max_len=4 -jobs=10
+
+Buildbot
+--------
+
+A buildbot continuously runs the above fuzzers for LLVM components, with results
+shown at http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-fuzzer .
+
+FAQ
+=========================
+
+Q. Why doesn't libFuzzer use any of the LLVM support?
+-----------------------------------------------------
+
+There are two reasons.
+
+First, we want this library to be used outside of the LLVM without users having to
+build the rest of LLVM. This may sound unconvincing for many LLVM folks,
+but in practice the need for building the whole LLVM frightens many potential
+users -- and we want more users to use this code.
+
+Second, there is a subtle technical reason not to rely on the rest of LLVM, or
+any other large body of code (maybe not even STL). When coverage instrumentation
+is enabled, it will also instrument the LLVM support code which will blow up the
+coverage set of the process (since the fuzzer is in-process). In other words, by
+using more external dependencies we will slow down the fuzzer while the main
+reason for it to exist is extreme speed.
+
+Q. What about Windows then? The fuzzer contains code that does not build on Windows.
+------------------------------------------------------------------------------------
+
+Volunteers are welcome.
+
+Q. When libFuzzer is not a good solution for a problem?
+---------------------------------------------------------
+
+* If the test inputs are validated by the target library and the validator
+ asserts/crashes on invalid inputs, in-process fuzzing is not applicable.
+* Bugs in the target library may accumulate without being detected. E.g. a memory
+ corruption that goes undetected at first and then leads to a crash while
+ testing another input. This is why it is highly recommended to run this
+ in-process fuzzer with all sanitizers to detect most bugs on the spot.
+* It is harder to protect the in-process fuzzer from excessive memory
+ consumption and infinite loops in the target library (still possible).
+* The target library should not have significant global state that is not
+ reset between the runs.
+* Many interesting target libraries are not designed in a way that supports
+ the in-process fuzzer interface (e.g. require a file path instead of a
+ byte array).
+* If a single test run takes a considerable fraction of a second (or
+ more) the speed benefit from the in-process fuzzer is negligible.
+* If the target library runs persistent threads (that outlive
+ execution of one test) the fuzzing results will be unreliable.
+
+Q. So, what exactly this Fuzzer is good for?
+--------------------------------------------
+
+This Fuzzer might be a good choice for testing libraries that have relatively
+small inputs, each input takes < 10ms to run, and the library code is not expected
+to crash on invalid inputs.
+Examples: regular expression matchers, text or binary format parsers, compression,
+network, crypto.
+
+
+Trophies
+========
+* GLIBC: https://sourceware.org/glibc/wiki/FuzzingLibc
+
+* MUSL LIBC: `[1] <http://git.musl-libc.org/cgit/musl/commit/?id=39dfd58417ef642307d90306e1c7e50aaec5a35c>`__ `[2] <http://www.openwall.com/lists/oss-security/2015/03/30/3>`__
+
+* `pugixml <https://github.com/zeux/pugixml/issues/39>`_
+
+* PCRE: Search for "LLVM fuzzer" in http://vcs.pcre.org/pcre2/code/trunk/ChangeLog?view=markup;
+ also in `bugzilla <https://bugs.exim.org/buglist.cgi?bug_status=__all__&content=libfuzzer&no_redirect=1&order=Importance&product=PCRE&query_format=specific>`_
+
+* `ICU <http://bugs.icu-project.org/trac/ticket/11838>`_
+
+* `Freetype <https://savannah.nongnu.org/search/?words=LibFuzzer&type_of_search=bugs&Search=Search&exact=1#options>`_
+
+* `Harfbuzz <https://github.com/behdad/harfbuzz/issues/139>`_
+
+* `SQLite <http://www3.sqlite.org/cgi/src/info/088009efdd56160b>`_
+
+* `Python <http://bugs.python.org/issue25388>`_
+
+* OpenSSL/BoringSSL: `[1] <https://boringssl.googlesource.com/boringssl/+/cb852981cd61733a7a1ae4fd8755b7ff950e857d>`_ `[2] <https://openssl.org/news/secadv/20160301.txt>`_ `[3] <https://boringssl.googlesource.com/boringssl/+/2b07fa4b22198ac02e0cee8f37f3337c3dba91bc>`_ `[4] <https://boringssl.googlesource.com/boringssl/+/6b6e0b20893e2be0e68af605a60ffa2cbb0ffa64>`_ `[5] <https://github.com/openssl/openssl/pull/931/commits/dd5ac557f052cc2b7f718ac44a8cb7ac6f77dca8>`_ `[6] <https://github.com/openssl/openssl/pull/931/commits/19b5b9194071d1d84e38ac9a952e715afbc85a81>`_
+
+* `Libxml2
+ <https://bugzilla.gnome.org/buglist.cgi?bug_status=__all__&content=libFuzzer&list_id=68957&order=Importance&product=libxml2&query_format=specific>`_ and `[HT206167] <https://support.apple.com/en-gb/HT206167>`_ (CVE-2015-5312, CVE-2015-7500, CVE-2015-7942)
+
+* `Linux Kernel's BPF verifier <https://github.com/iovisor/bpf-fuzzer>`_
+
+* Capstone: `[1] <https://github.com/aquynh/capstone/issues/600>`__ `[2] <https://github.com/aquynh/capstone/commit/6b88d1d51eadf7175a8f8a11b690684443b11359>`__
+
+* file:`[1] <http://bugs.gw.com/view.php?id=550>`__ `[2] <http://bugs.gw.com/view.php?id=551>`__ `[3] <http://bugs.gw.com/view.php?id=553>`__ `[4] <http://bugs.gw.com/view.php?id=554>`__
+
+* Radare2: `[1] <https://github.com/revskills?tab=contributions&from=2016-04-09>`__
+
+* gRPC: `[1] <https://github.com/grpc/grpc/pull/6071/commits/df04c1f7f6aec6e95722ec0b023a6b29b6ea871c>`__ `[2] <https://github.com/grpc/grpc/pull/6071/commits/22a3dfd95468daa0db7245a4e8e6679a52847579>`__ `[3] <https://github.com/grpc/grpc/pull/6071/commits/9cac2a12d9e181d130841092e9d40fa3309d7aa7>`__ `[4] <https://github.com/grpc/grpc/pull/6012/commits/82a91c91d01ce9b999c8821ed13515883468e203>`__ `[5] <https://github.com/grpc/grpc/pull/6202/commits/2e3e0039b30edaf89fb93bfb2c1d0909098519fa>`__ `[6] <https://github.com/grpc/grpc/pull/6106/files>`__
+
+* WOFF2: `[1] <https://github.com/google/woff2/commit/a15a8ab>`__
+
+* LLVM: `Clang <https://llvm.org/bugs/show_bug.cgi?id=23057>`_, `Clang-format <https://llvm.org/bugs/show_bug.cgi?id=23052>`_, `libc++ <https://llvm.org/bugs/show_bug.cgi?id=24411>`_, `llvm-as <https://llvm.org/bugs/show_bug.cgi?id=24639>`_, `Demangler <https://bugs.chromium.org/p/chromium/issues/detail?id=606626>`_, Disassembler: http://reviews.llvm.org/rL247405, http://reviews.llvm.org/rL247414, http://reviews.llvm.org/rL247416, http://reviews.llvm.org/rL247417, http://reviews.llvm.org/rL247420, http://reviews.llvm.org/rL247422.
+
+* Tensorflow: `[1] <https://da-data.blogspot.com/2017/01/finding-bugs-in-tensorflow-with.html>`__
+
+* Ffmpeg: `[1] <https://github.com/FFmpeg/FFmpeg/commit/c92f55847a3d9cd12db60bfcd0831ff7f089c37c>`__ `[2] <https://github.com/FFmpeg/FFmpeg/commit/25ab1a65f3acb5ec67b53fb7a2463a7368f1ad16>`__ `[3] <https://github.com/FFmpeg/FFmpeg/commit/85d23e5cbc9ad6835eef870a5b4247de78febe56>`__ `[4] <https://github.com/FFmpeg/FFmpeg/commit/04bd1b38ee6b8df410d0ab8d4949546b6c4af26a>`__
+
+* `Wireshark <https://bugs.wireshark.org/bugzilla/buglist.cgi?bug_status=UNCONFIRMED&bug_status=CONFIRMED&bug_status=IN_PROGRESS&bug_status=INCOMPLETE&bug_status=RESOLVED&bug_status=VERIFIED&f0=OP&f1=OP&f2=product&f3=component&f4=alias&f5=short_desc&f7=content&f8=CP&f9=CP&j1=OR&o2=substring&o3=substring&o4=substring&o5=substring&o6=substring&o7=matches&order=bug_id%20DESC&query_format=advanced&v2=libfuzzer&v3=libfuzzer&v4=libfuzzer&v5=libfuzzer&v6=libfuzzer&v7=%22libfuzzer%22>`_
+
+.. _pcre2: http://www.pcre.org/
+.. _AFL: http://lcamtuf.coredump.cx/afl/
+.. _Radamsa: https://github.com/aoh/radamsa
+.. _SanitizerCoverage: http://clang.llvm.org/docs/SanitizerCoverage.html
+.. _SanitizerCoverageTraceDataFlow: http://clang.llvm.org/docs/SanitizerCoverage.html#tracing-data-flow
+.. _AddressSanitizer: http://clang.llvm.org/docs/AddressSanitizer.html
+.. _LeakSanitizer: http://clang.llvm.org/docs/LeakSanitizer.html
+.. _Heartbleed: http://en.wikipedia.org/wiki/Heartbleed
+.. _FuzzerInterface.h: https://github.com/llvm-mirror/llvm/blob/master/lib/Fuzzer/FuzzerInterface.h
+.. _3.7.0: http://llvm.org/releases/3.7.0/docs/LibFuzzer.html
+.. _building Clang from trunk: http://clang.llvm.org/get_started.html
+.. _MemorySanitizer: http://clang.llvm.org/docs/MemorySanitizer.html
+.. _UndefinedBehaviorSanitizer: http://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html
+.. _`coverage counters`: http://clang.llvm.org/docs/SanitizerCoverage.html#coverage-counters
+.. _`value profile`: #value-profile
+.. _`caller-callee pairs`: http://clang.llvm.org/docs/SanitizerCoverage.html#caller-callee-coverage
+.. _BoringSSL: https://boringssl.googlesource.com/boringssl/
+.. _`fuzz various parts of LLVM itself`: `Fuzzing components of LLVM`_
Added: www-releases/trunk/5.0.1/docs/_sources/LinkTimeOptimization.rst.txt
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--- www-releases/trunk/5.0.1/docs/_sources/LinkTimeOptimization.rst.txt (added)
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@@ -0,0 +1,299 @@
+======================================================
+LLVM Link Time Optimization: Design and Implementation
+======================================================
+
+.. contents::
+ :local:
+
+Description
+===========
+
+LLVM features powerful intermodular optimizations which can be used at link
+time. Link Time Optimization (LTO) is another name for intermodular
+optimization when performed during the link stage. This document describes the
+interface and design between the LTO optimizer and the linker.
+
+Design Philosophy
+=================
+
+The LLVM Link Time Optimizer provides complete transparency, while doing
+intermodular optimization, in the compiler tool chain. Its main goal is to let
+the developer take advantage of intermodular optimizations without making any
+significant changes to the developer's makefiles or build system. This is
+achieved through tight integration with the linker. In this model, the linker
+treats LLVM bitcode files like native object files and allows mixing and
+matching among them. The linker uses `libLTO`_, a shared object, to handle LLVM
+bitcode files. This tight integration between the linker and LLVM optimizer
+helps to do optimizations that are not possible in other models. The linker
+input allows the optimizer to avoid relying on conservative escape analysis.
+
+.. _libLTO-example:
+
+Example of link time optimization
+---------------------------------
+
+The following example illustrates the advantages of LTO's integrated approach
+and clean interface. This example requires a system linker which supports LTO
+through the interface described in this document. Here, clang transparently
+invokes system linker.
+
+* Input source file ``a.c`` is compiled into LLVM bitcode form.
+* Input source file ``main.c`` is compiled into native object code.
+
+.. code-block:: c++
+
+ --- a.h ---
+ extern int foo1(void);
+ extern void foo2(void);
+ extern void foo4(void);
+
+ --- a.c ---
+ #include "a.h"
+
+ static signed int i = 0;
+
+ void foo2(void) {
+ i = -1;
+ }
+
+ static int foo3() {
+ foo4();
+ return 10;
+ }
+
+ int foo1(void) {
+ int data = 0;
+
+ if (i < 0)
+ data = foo3();
+
+ data = data + 42;
+ return data;
+ }
+
+ --- main.c ---
+ #include <stdio.h>
+ #include "a.h"
+
+ void foo4(void) {
+ printf("Hi\n");
+ }
+
+ int main() {
+ return foo1();
+ }
+
+To compile, run:
+
+.. code-block:: console
+
+ % clang -flto -c a.c -o a.o # <-- a.o is LLVM bitcode file
+ % clang -c main.c -o main.o # <-- main.o is native object file
+ % clang -flto a.o main.o -o main # <-- standard link command with -flto
+
+* In this example, the linker recognizes that ``foo2()`` is an externally
+ visible symbol defined in LLVM bitcode file. The linker completes its usual
+ symbol resolution pass and finds that ``foo2()`` is not used
+ anywhere. This information is used by the LLVM optimizer and it
+ removes ``foo2()``.
+
+* As soon as ``foo2()`` is removed, the optimizer recognizes that condition ``i
+ < 0`` is always false, which means ``foo3()`` is never used. Hence, the
+ optimizer also removes ``foo3()``.
+
+* And this in turn, enables linker to remove ``foo4()``.
+
+This example illustrates the advantage of tight integration with the
+linker. Here, the optimizer can not remove ``foo3()`` without the linker's
+input.
+
+Alternative Approaches
+----------------------
+
+**Compiler driver invokes link time optimizer separately.**
+ In this model the link time optimizer is not able to take advantage of
+ information collected during the linker's normal symbol resolution phase.
+ In the above example, the optimizer can not remove ``foo2()`` without the
+ linker's input because it is externally visible. This in turn prohibits the
+ optimizer from removing ``foo3()``.
+
+**Use separate tool to collect symbol information from all object files.**
+ In this model, a new, separate, tool or library replicates the linker's
+ capability to collect information for link time optimization. Not only is
+ this code duplication difficult to justify, but it also has several other
+ disadvantages. For example, the linking semantics and the features provided
+ by the linker on various platform are not unique. This means, this new tool
+ needs to support all such features and platforms in one super tool or a
+ separate tool per platform is required. This increases maintenance cost for
+ link time optimizer significantly, which is not necessary. This approach
+ also requires staying synchronized with linker developments on various
+ platforms, which is not the main focus of the link time optimizer. Finally,
+ this approach increases end user's build time due to the duplication of work
+ done by this separate tool and the linker itself.
+
+Multi-phase communication between ``libLTO`` and linker
+=======================================================
+
+The linker collects information about symbol definitions and uses in various
+link objects which is more accurate than any information collected by other
+tools during typical build cycles. The linker collects this information by
+looking at the definitions and uses of symbols in native .o files and using
+symbol visibility information. The linker also uses user-supplied information,
+such as a list of exported symbols. LLVM optimizer collects control flow
+information, data flow information and knows much more about program structure
+from the optimizer's point of view. Our goal is to take advantage of tight
+integration between the linker and the optimizer by sharing this information
+during various linking phases.
+
+Phase 1 : Read LLVM Bitcode Files
+---------------------------------
+
+The linker first reads all object files in natural order and collects symbol
+information. This includes native object files as well as LLVM bitcode files.
+To minimize the cost to the linker in the case that all .o files are native
+object files, the linker only calls ``lto_module_create()`` when a supplied
+object file is found to not be a native object file. If ``lto_module_create()``
+returns that the file is an LLVM bitcode file, the linker then iterates over the
+module using ``lto_module_get_symbol_name()`` and
+``lto_module_get_symbol_attribute()`` to get all symbols defined and referenced.
+This information is added to the linker's global symbol table.
+
+
+The lto* functions are all implemented in a shared object libLTO. This allows
+the LLVM LTO code to be updated independently of the linker tool. On platforms
+that support it, the shared object is lazily loaded.
+
+Phase 2 : Symbol Resolution
+---------------------------
+
+In this stage, the linker resolves symbols using global symbol table. It may
+report undefined symbol errors, read archive members, replace weak symbols, etc.
+The linker is able to do this seamlessly even though it does not know the exact
+content of input LLVM bitcode files. If dead code stripping is enabled then the
+linker collects the list of live symbols.
+
+Phase 3 : Optimize Bitcode Files
+--------------------------------
+
+After symbol resolution, the linker tells the LTO shared object which symbols
+are needed by native object files. In the example above, the linker reports
+that only ``foo1()`` is used by native object files using
+``lto_codegen_add_must_preserve_symbol()``. Next the linker invokes the LLVM
+optimizer and code generators using ``lto_codegen_compile()`` which returns a
+native object file creating by merging the LLVM bitcode files and applying
+various optimization passes.
+
+Phase 4 : Symbol Resolution after optimization
+----------------------------------------------
+
+In this phase, the linker reads optimized a native object file and updates the
+internal global symbol table to reflect any changes. The linker also collects
+information about any changes in use of external symbols by LLVM bitcode
+files. In the example above, the linker notes that ``foo4()`` is not used any
+more. If dead code stripping is enabled then the linker refreshes the live
+symbol information appropriately and performs dead code stripping.
+
+After this phase, the linker continues linking as if it never saw LLVM bitcode
+files.
+
+.. _libLTO:
+
+``libLTO``
+==========
+
+``libLTO`` is a shared object that is part of the LLVM tools, and is intended
+for use by a linker. ``libLTO`` provides an abstract C interface to use the LLVM
+interprocedural optimizer without exposing details of LLVM's internals. The
+intention is to keep the interface as stable as possible even when the LLVM
+optimizer continues to evolve. It should even be possible for a completely
+different compilation technology to provide a different libLTO that works with
+their object files and the standard linker tool.
+
+``lto_module_t``
+----------------
+
+A non-native object file is handled via an ``lto_module_t``. The following
+functions allow the linker to check if a file (on disk or in a memory buffer) is
+a file which libLTO can process:
+
+.. code-block:: c
+
+ lto_module_is_object_file(const char*)
+ lto_module_is_object_file_for_target(const char*, const char*)
+ lto_module_is_object_file_in_memory(const void*, size_t)
+ lto_module_is_object_file_in_memory_for_target(const void*, size_t, const char*)
+
+If the object file can be processed by ``libLTO``, the linker creates a
+``lto_module_t`` by using one of:
+
+.. code-block:: c
+
+ lto_module_create(const char*)
+ lto_module_create_from_memory(const void*, size_t)
+
+and when done, the handle is released via
+
+.. code-block:: c
+
+ lto_module_dispose(lto_module_t)
+
+
+The linker can introspect the non-native object file by getting the number of
+symbols and getting the name and attributes of each symbol via:
+
+.. code-block:: c
+
+ lto_module_get_num_symbols(lto_module_t)
+ lto_module_get_symbol_name(lto_module_t, unsigned int)
+ lto_module_get_symbol_attribute(lto_module_t, unsigned int)
+
+The attributes of a symbol include the alignment, visibility, and kind.
+
+``lto_code_gen_t``
+------------------
+
+Once the linker has loaded each non-native object files into an
+``lto_module_t``, it can request ``libLTO`` to process them all and generate a
+native object file. This is done in a couple of steps. First, a code generator
+is created with:
+
+.. code-block:: c
+
+ lto_codegen_create()
+
+Then, each non-native object file is added to the code generator with:
+
+.. code-block:: c
+
+ lto_codegen_add_module(lto_code_gen_t, lto_module_t)
+
+The linker then has the option of setting some codegen options. Whether or not
+to generate DWARF debug info is set with:
+
+.. code-block:: c
+
+ lto_codegen_set_debug_model(lto_code_gen_t)
+
+which kind of position independence is set with:
+
+.. code-block:: c
+
+ lto_codegen_set_pic_model(lto_code_gen_t)
+
+And each symbol that is referenced by a native object file or otherwise must not
+be optimized away is set with:
+
+.. code-block:: c
+
+ lto_codegen_add_must_preserve_symbol(lto_code_gen_t, const char*)
+
+After all these settings are done, the linker requests that a native object file
+be created from the modules with the settings using:
+
+.. code-block:: c
+
+ lto_codegen_compile(lto_code_gen_t, size*)
+
+which returns a pointer to a buffer containing the generated native object file.
+The linker then parses that and links it with the rest of the native object
+files.
Added: www-releases/trunk/5.0.1/docs/_sources/MCJITDesignAndImplementation.rst.txt
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--- www-releases/trunk/5.0.1/docs/_sources/MCJITDesignAndImplementation.rst.txt (added)
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@@ -0,0 +1,180 @@
+===============================
+MCJIT Design and Implementation
+===============================
+
+Introduction
+============
+
+This document describes the internal workings of the MCJIT execution
+engine and the RuntimeDyld component. It is intended as a high level
+overview of the implementation, showing the flow and interactions of
+objects throughout the code generation and dynamic loading process.
+
+Engine Creation
+===============
+
+In most cases, an EngineBuilder object is used to create an instance of
+the MCJIT execution engine. The EngineBuilder takes an llvm::Module
+object as an argument to its constructor. The client may then set various
+options that we control the later be passed along to the MCJIT engine,
+including the selection of MCJIT as the engine type to be created.
+Of particular interest is the EngineBuilder::setMCJITMemoryManager
+function. If the client does not explicitly create a memory manager at
+this time, a default memory manager (specifically SectionMemoryManager)
+will be created when the MCJIT engine is instantiated.
+
+Once the options have been set, a client calls EngineBuilder::create to
+create an instance of the MCJIT engine. If the client does not use the
+form of this function that takes a TargetMachine as a parameter, a new
+TargetMachine will be created based on the target triple associated with
+the Module that was used to create the EngineBuilder.
+
+.. image:: MCJIT-engine-builder.png
+
+EngineBuilder::create will call the static MCJIT::createJIT function,
+passing in its pointers to the module, memory manager and target machine
+objects, all of which will subsequently be owned by the MCJIT object.
+
+The MCJIT class has a member variable, Dyld, which contains an instance of
+the RuntimeDyld wrapper class. This member will be used for
+communications between MCJIT and the actual RuntimeDyldImpl object that
+gets created when an object is loaded.
+
+.. image:: MCJIT-creation.png
+
+Upon creation, MCJIT holds a pointer to the Module object that it received
+from EngineBuilder but it does not immediately generate code for this
+module. Code generation is deferred until either the
+MCJIT::finalizeObject method is called explicitly or a function such as
+MCJIT::getPointerToFunction is called which requires the code to have been
+generated.
+
+Code Generation
+===============
+
+When code generation is triggered, as described above, MCJIT will first
+attempt to retrieve an object image from its ObjectCache member, if one
+has been set. If a cached object image cannot be retrieved, MCJIT will
+call its emitObject method. MCJIT::emitObject uses a local PassManager
+instance and creates a new ObjectBufferStream instance, both of which it
+passes to TargetMachine::addPassesToEmitMC before calling PassManager::run
+on the Module with which it was created.
+
+.. image:: MCJIT-load.png
+
+The PassManager::run call causes the MC code generation mechanisms to emit
+a complete relocatable binary object image (either in either ELF or MachO
+format, depending on the target) into the ObjectBufferStream object, which
+is flushed to complete the process. If an ObjectCache is being used, the
+image will be passed to the ObjectCache here.
+
+At this point, the ObjectBufferStream contains the raw object image.
+Before the code can be executed, the code and data sections from this
+image must be loaded into suitable memory, relocations must be applied and
+memory permission and code cache invalidation (if required) must be completed.
+
+Object Loading
+==============
+
+Once an object image has been obtained, either through code generation or
+having been retrieved from an ObjectCache, it is passed to RuntimeDyld to
+be loaded. The RuntimeDyld wrapper class examines the object to determine
+its file format and creates an instance of either RuntimeDyldELF or
+RuntimeDyldMachO (both of which derive from the RuntimeDyldImpl base
+class) and calls the RuntimeDyldImpl::loadObject method to perform that
+actual loading.
+
+.. image:: MCJIT-dyld-load.png
+
+RuntimeDyldImpl::loadObject begins by creating an ObjectImage instance
+from the ObjectBuffer it received. ObjectImage, which wraps the
+ObjectFile class, is a helper class which parses the binary object image
+and provides access to the information contained in the format-specific
+headers, including section, symbol and relocation information.
+
+RuntimeDyldImpl::loadObject then iterates through the symbols in the
+image. Information about common symbols is collected for later use. For
+each function or data symbol, the associated section is loaded into memory
+and the symbol is stored in a symbol table map data structure. When the
+iteration is complete, a section is emitted for the common symbols.
+
+Next, RuntimeDyldImpl::loadObject iterates through the sections in the
+object image and for each section iterates through the relocations for
+that sections. For each relocation, it calls the format-specific
+processRelocationRef method, which will examine the relocation and store
+it in one of two data structures, a section-based relocation list map and
+an external symbol relocation map.
+
+.. image:: MCJIT-load-object.png
+
+When RuntimeDyldImpl::loadObject returns, all of the code and data
+sections for the object will have been loaded into memory allocated by the
+memory manager and relocation information will have been prepared, but the
+relocations have not yet been applied and the generated code is still not
+ready to be executed.
+
+[Currently (as of August 2013) the MCJIT engine will immediately apply
+relocations when loadObject completes. However, this shouldn't be
+happening. Because the code may have been generated for a remote target,
+the client should be given a chance to re-map the section addresses before
+relocations are applied. It is possible to apply relocations multiple
+times, but in the case where addresses are to be re-mapped, this first
+application is wasted effort.]
+
+Address Remapping
+=================
+
+At any time after initial code has been generated and before
+finalizeObject is called, the client can remap the address of sections in
+the object. Typically this is done because the code was generated for an
+external process and is being mapped into that process' address space.
+The client remaps the section address by calling MCJIT::mapSectionAddress.
+This should happen before the section memory is copied to its new
+location.
+
+When MCJIT::mapSectionAddress is called, MCJIT passes the call on to
+RuntimeDyldImpl (via its Dyld member). RuntimeDyldImpl stores the new
+address in an internal data structure but does not update the code at this
+time, since other sections are likely to change.
+
+When the client is finished remapping section addresses, it will call
+MCJIT::finalizeObject to complete the remapping process.
+
+Final Preparations
+==================
+
+When MCJIT::finalizeObject is called, MCJIT calls
+RuntimeDyld::resolveRelocations. This function will attempt to locate any
+external symbols and then apply all relocations for the object.
+
+External symbols are resolved by calling the memory manager's
+getPointerToNamedFunction method. The memory manager will return the
+address of the requested symbol in the target address space. (Note, this
+may not be a valid pointer in the host process.) RuntimeDyld will then
+iterate through the list of relocations it has stored which are associated
+with this symbol and invoke the resolveRelocation method which, through an
+format-specific implementation, will apply the relocation to the loaded
+section memory.
+
+Next, RuntimeDyld::resolveRelocations iterates through the list of
+sections and for each section iterates through a list of relocations that
+have been saved which reference that symbol and call resolveRelocation for
+each entry in this list. The relocation list here is a list of
+relocations for which the symbol associated with the relocation is located
+in the section associated with the list. Each of these locations will
+have a target location at which the relocation will be applied that is
+likely located in a different section.
+
+.. image:: MCJIT-resolve-relocations.png
+
+Once relocations have been applied as described above, MCJIT calls
+RuntimeDyld::getEHFrameSection, and if a non-zero result is returned
+passes the section data to the memory manager's registerEHFrames method.
+This allows the memory manager to call any desired target-specific
+functions, such as registering the EH frame information with a debugger.
+
+Finally, MCJIT calls the memory manager's finalizeMemory method. In this
+method, the memory manager will invalidate the target code cache, if
+necessary, and apply final permissions to the memory pages it has
+allocated for code and data memory.
+
Added: www-releases/trunk/5.0.1/docs/_sources/MIRLangRef.rst.txt
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==============================================================================
--- www-releases/trunk/5.0.1/docs/_sources/MIRLangRef.rst.txt (added)
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@@ -0,0 +1,543 @@
+========================================
+Machine IR (MIR) Format Reference Manual
+========================================
+
+.. contents::
+ :local:
+
+.. warning::
+ This is a work in progress.
+
+Introduction
+============
+
+This document is a reference manual for the Machine IR (MIR) serialization
+format. MIR is a human readable serialization format that is used to represent
+LLVM's :ref:`machine specific intermediate representation
+<machine code representation>`.
+
+The MIR serialization format is designed to be used for testing the code
+generation passes in LLVM.
+
+Overview
+========
+
+The MIR serialization format uses a YAML container. YAML is a standard
+data serialization language, and the full YAML language spec can be read at
+`yaml.org
+<http://www.yaml.org/spec/1.2/spec.html#Introduction>`_.
+
+A MIR file is split up into a series of `YAML documents`_. The first document
+can contain an optional embedded LLVM IR module, and the rest of the documents
+contain the serialized machine functions.
+
+.. _YAML documents: http://www.yaml.org/spec/1.2/spec.html#id2800132
+
+MIR Testing Guide
+=================
+
+You can use the MIR format for testing in two different ways:
+
+- You can write MIR tests that invoke a single code generation pass using the
+ ``-run-pass`` option in llc.
+
+- You can use llc's ``-stop-after`` option with existing or new LLVM assembly
+ tests and check the MIR output of a specific code generation pass.
+
+Testing Individual Code Generation Passes
+-----------------------------------------
+
+The ``-run-pass`` option in llc allows you to create MIR tests that invoke just
+a single code generation pass. When this option is used, llc will parse an
+input MIR file, run the specified code generation pass(es), and output the
+resulting MIR code.
+
+You can generate an input MIR file for the test by using the ``-stop-after`` or
+``-stop-before`` option in llc. For example, if you would like to write a test
+for the post register allocation pseudo instruction expansion pass, you can
+specify the machine copy propagation pass in the ``-stop-after`` option, as it
+runs just before the pass that we are trying to test:
+
+ ``llc -stop-after=machine-cp bug-trigger.ll > test.mir``
+
+After generating the input MIR file, you'll have to add a run line that uses
+the ``-run-pass`` option to it. In order to test the post register allocation
+pseudo instruction expansion pass on X86-64, a run line like the one shown
+below can be used:
+
+ ``# RUN: llc -o - %s -mtriple=x86_64-- -run-pass=postrapseudos | FileCheck %s``
+
+The MIR files are target dependent, so they have to be placed in the target
+specific test directories (``lib/CodeGen/TARGETNAME``). They also need to
+specify a target triple or a target architecture either in the run line or in
+the embedded LLVM IR module.
+
+Simplifying MIR files
+^^^^^^^^^^^^^^^^^^^^^
+
+The MIR code coming out of ``-stop-after``/``-stop-before`` is very verbose;
+Tests are more accessible and future proof when simplified:
+
+- Use the ``-simplify-mir`` option with llc.
+
+- Machine function attributes often have default values or the test works just
+ as well with default values. Typical candidates for this are: `alignment:`,
+ `exposesReturnsTwice`, `legalized`, `regBankSelected`, `selected`.
+ The whole `frameInfo` section is often unnecessary if there is no special
+ frame usage in the function. `tracksRegLiveness` on the other hand is often
+ necessary for some passes that care about block livein lists.
+
+- The (global) `liveins:` list is typically only interesting for early
+ instruction selection passes and can be removed when testing later passes.
+ The per-block `liveins:` on the other hand are necessary if
+ `tracksRegLiveness` is true.
+
+- Branch probability data in block `successors:` lists can be dropped if the
+ test doesn't depend on it. Example:
+ `successors: %bb.1(0x40000000), %bb.2(0x40000000)` can be replaced with
+ `successors: %bb.1, %bb.2`.
+
+- MIR code contains a whole IR module. This is necessary because there are
+ no equivalents in MIR for global variables, references to external functions,
+ function attributes, metadata, debug info. Instead some MIR data references
+ the IR constructs. You can often remove them if the test doesn't depend on
+ them.
+
+- Alias Analysis is performed on IR values. These are referenced by memory
+ operands in MIR. Example: `:: (load 8 from %ir.foobar, !alias.scope !9)`.
+ If the test doesn't depend on (good) alias analysis the references can be
+ dropped: `:: (load 8)`
+
+- MIR blocks can reference IR blocks for debug printing, profile information
+ or debug locations. Example: `bb.42.myblock` in MIR references the IR block
+ `myblock`. It is usually possible to drop the `.myblock` reference and simply
+ use `bb.42`.
+
+- If there are no memory operands or blocks referencing the IR then the
+ IR function can be replaced by a parameterless dummy function like
+ `define @func() { ret void }`.
+
+- It is possible to drop the whole IR section of the MIR file if it only
+ contains dummy functions (see above). The .mir loader will create the
+ IR functions automatically in this case.
+
+Limitations
+-----------
+
+Currently the MIR format has several limitations in terms of which state it
+can serialize:
+
+- The target-specific state in the target-specific ``MachineFunctionInfo``
+ subclasses isn't serialized at the moment.
+
+- The target-specific ``MachineConstantPoolValue`` subclasses (in the ARM and
+ SystemZ backends) aren't serialized at the moment.
+
+- The ``MCSymbol`` machine operands are only printed, they can't be parsed.
+
+- A lot of the state in ``MachineModuleInfo`` isn't serialized - only the CFI
+ instructions and the variable debug information from MMI is serialized right
+ now.
+
+These limitations impose restrictions on what you can test with the MIR format.
+For now, tests that would like to test some behaviour that depends on the state
+of certain ``MCSymbol`` operands or the exception handling state in MMI, can't
+use the MIR format. As well as that, tests that test some behaviour that
+depends on the state of the target specific ``MachineFunctionInfo`` or
+``MachineConstantPoolValue`` subclasses can't use the MIR format at the moment.
+
+High Level Structure
+====================
+
+.. _embedded-module:
+
+Embedded Module
+---------------
+
+When the first YAML document contains a `YAML block literal string`_, the MIR
+parser will treat this string as an LLVM assembly language string that
+represents an embedded LLVM IR module.
+Here is an example of a YAML document that contains an LLVM module:
+
+.. code-block:: llvm
+
+ define i32 @inc(i32* %x) {
+ entry:
+ %0 = load i32, i32* %x
+ %1 = add i32 %0, 1
+ store i32 %1, i32* %x
+ ret i32 %1
+ }
+
+.. _YAML block literal string: http://www.yaml.org/spec/1.2/spec.html#id2795688
+
+Machine Functions
+-----------------
+
+The remaining YAML documents contain the machine functions. This is an example
+of such YAML document:
+
+.. code-block:: text
+
+ ---
+ name: inc
+ tracksRegLiveness: true
+ liveins:
+ - { reg: '%rdi' }
+ body: |
+ bb.0.entry:
+ liveins: %rdi
+
+ %eax = MOV32rm %rdi, 1, _, 0, _
+ %eax = INC32r killed %eax, implicit-def dead %eflags
+ MOV32mr killed %rdi, 1, _, 0, _, %eax
+ RETQ %eax
+ ...
+
+The document above consists of attributes that represent the various
+properties and data structures in a machine function.
+
+The attribute ``name`` is required, and its value should be identical to the
+name of a function that this machine function is based on.
+
+The attribute ``body`` is a `YAML block literal string`_. Its value represents
+the function's machine basic blocks and their machine instructions.
+
+Machine Instructions Format Reference
+=====================================
+
+The machine basic blocks and their instructions are represented using a custom,
+human readable serialization language. This language is used in the
+`YAML block literal string`_ that corresponds to the machine function's body.
+
+A source string that uses this language contains a list of machine basic
+blocks, which are described in the section below.
+
+Machine Basic Blocks
+--------------------
+
+A machine basic block is defined in a single block definition source construct
+that contains the block's ID.
+The example below defines two blocks that have an ID of zero and one:
+
+.. code-block:: text
+
+ bb.0:
+ <instructions>
+ bb.1:
+ <instructions>
+
+A machine basic block can also have a name. It should be specified after the ID
+in the block's definition:
+
+.. code-block:: text
+
+ bb.0.entry: ; This block's name is "entry"
+ <instructions>
+
+The block's name should be identical to the name of the IR block that this
+machine block is based on.
+
+Block References
+^^^^^^^^^^^^^^^^
+
+The machine basic blocks are identified by their ID numbers. Individual
+blocks are referenced using the following syntax:
+
+.. code-block:: text
+
+ %bb.<id>[.<name>]
+
+Examples:
+
+.. code-block:: llvm
+
+ %bb.0
+ %bb.1.then
+
+Successors
+^^^^^^^^^^
+
+The machine basic block's successors have to be specified before any of the
+instructions:
+
+.. code-block:: text
+
+ bb.0.entry:
+ successors: %bb.1.then, %bb.2.else
+ <instructions>
+ bb.1.then:
+ <instructions>
+ bb.2.else:
+ <instructions>
+
+The branch weights can be specified in brackets after the successor blocks.
+The example below defines a block that has two successors with branch weights
+of 32 and 16:
+
+.. code-block:: text
+
+ bb.0.entry:
+ successors: %bb.1.then(32), %bb.2.else(16)
+
+.. _bb-liveins:
+
+Live In Registers
+^^^^^^^^^^^^^^^^^
+
+The machine basic block's live in registers have to be specified before any of
+the instructions:
+
+.. code-block:: text
+
+ bb.0.entry:
+ liveins: %edi, %esi
+
+The list of live in registers and successors can be empty. The language also
+allows multiple live in register and successor lists - they are combined into
+one list by the parser.
+
+Miscellaneous Attributes
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+The attributes ``IsAddressTaken``, ``IsLandingPad`` and ``Alignment`` can be
+specified in brackets after the block's definition:
+
+.. code-block:: text
+
+ bb.0.entry (address-taken):
+ <instructions>
+ bb.2.else (align 4):
+ <instructions>
+ bb.3(landing-pad, align 4):
+ <instructions>
+
+.. TODO: Describe the way the reference to an unnamed LLVM IR block can be
+ preserved.
+
+Machine Instructions
+--------------------
+
+A machine instruction is composed of a name,
+:ref:`machine operands <machine-operands>`,
+:ref:`instruction flags <instruction-flags>`, and machine memory operands.
+
+The instruction's name is usually specified before the operands. The example
+below shows an instance of the X86 ``RETQ`` instruction with a single machine
+operand:
+
+.. code-block:: text
+
+ RETQ %eax
+
+However, if the machine instruction has one or more explicitly defined register
+operands, the instruction's name has to be specified after them. The example
+below shows an instance of the AArch64 ``LDPXpost`` instruction with three
+defined register operands:
+
+.. code-block:: text
+
+ %sp, %fp, %lr = LDPXpost %sp, 2
+
+The instruction names are serialized using the exact definitions from the
+target's ``*InstrInfo.td`` files, and they are case sensitive. This means that
+similar instruction names like ``TSTri`` and ``tSTRi`` represent different
+machine instructions.
+
+.. _instruction-flags:
+
+Instruction Flags
+^^^^^^^^^^^^^^^^^
+
+The flag ``frame-setup`` can be specified before the instruction's name:
+
+.. code-block:: text
+
+ %fp = frame-setup ADDXri %sp, 0, 0
+
+.. _registers:
+
+Registers
+---------
+
+Registers are one of the key primitives in the machine instructions
+serialization language. They are primarly used in the
+:ref:`register machine operands <register-operands>`,
+but they can also be used in a number of other places, like the
+:ref:`basic block's live in list <bb-liveins>`.
+
+The physical registers are identified by their name. They use the following
+syntax:
+
+.. code-block:: text
+
+ %<name>
+
+The example below shows three X86 physical registers:
+
+.. code-block:: text
+
+ %eax
+ %r15
+ %eflags
+
+The virtual registers are identified by their ID number. They use the following
+syntax:
+
+.. code-block:: text
+
+ %<id>
+
+Example:
+
+.. code-block:: text
+
+ %0
+
+The null registers are represented using an underscore ('``_``'). They can also be
+represented using a '``%noreg``' named register, although the former syntax
+is preferred.
+
+.. _machine-operands:
+
+Machine Operands
+----------------
+
+There are seventeen different kinds of machine operands, and all of them, except
+the ``MCSymbol`` operand, can be serialized. The ``MCSymbol`` operands are
+just printed out - they can't be parsed back yet.
+
+Immediate Operands
+^^^^^^^^^^^^^^^^^^
+
+The immediate machine operands are untyped, 64-bit signed integers. The
+example below shows an instance of the X86 ``MOV32ri`` instruction that has an
+immediate machine operand ``-42``:
+
+.. code-block:: text
+
+ %eax = MOV32ri -42
+
+.. TODO: Describe the CIMM (Rare) and FPIMM immediate operands.
+
+.. _register-operands:
+
+Register Operands
+^^^^^^^^^^^^^^^^^
+
+The :ref:`register <registers>` primitive is used to represent the register
+machine operands. The register operands can also have optional
+:ref:`register flags <register-flags>`,
+:ref:`a subregister index <subregister-indices>`,
+and a reference to the tied register operand.
+The full syntax of a register operand is shown below:
+
+.. code-block:: text
+
+ [<flags>] <register> [ :<subregister-idx-name> ] [ (tied-def <tied-op>) ]
+
+This example shows an instance of the X86 ``XOR32rr`` instruction that has
+5 register operands with different register flags:
+
+.. code-block:: text
+
+ dead %eax = XOR32rr undef %eax, undef %eax, implicit-def dead %eflags, implicit-def %al
+
+.. _register-flags:
+
+Register Flags
+~~~~~~~~~~~~~~
+
+The table below shows all of the possible register flags along with the
+corresponding internal ``llvm::RegState`` representation:
+
+.. list-table::
+ :header-rows: 1
+
+ * - Flag
+ - Internal Value
+
+ * - ``implicit``
+ - ``RegState::Implicit``
+
+ * - ``implicit-def``
+ - ``RegState::ImplicitDefine``
+
+ * - ``def``
+ - ``RegState::Define``
+
+ * - ``dead``
+ - ``RegState::Dead``
+
+ * - ``killed``
+ - ``RegState::Kill``
+
+ * - ``undef``
+ - ``RegState::Undef``
+
+ * - ``internal``
+ - ``RegState::InternalRead``
+
+ * - ``early-clobber``
+ - ``RegState::EarlyClobber``
+
+ * - ``debug-use``
+ - ``RegState::Debug``
+
+.. _subregister-indices:
+
+Subregister Indices
+~~~~~~~~~~~~~~~~~~~
+
+The register machine operands can reference a portion of a register by using
+the subregister indices. The example below shows an instance of the ``COPY``
+pseudo instruction that uses the X86 ``sub_8bit`` subregister index to copy 8
+lower bits from the 32-bit virtual register 0 to the 8-bit virtual register 1:
+
+.. code-block:: text
+
+ %1 = COPY %0:sub_8bit
+
+The names of the subregister indices are target specific, and are typically
+defined in the target's ``*RegisterInfo.td`` file.
+
+Global Value Operands
+^^^^^^^^^^^^^^^^^^^^^
+
+The global value machine operands reference the global values from the
+:ref:`embedded LLVM IR module <embedded-module>`.
+The example below shows an instance of the X86 ``MOV64rm`` instruction that has
+a global value operand named ``G``:
+
+.. code-block:: text
+
+ %rax = MOV64rm %rip, 1, _, @G, _
+
+The named global values are represented using an identifier with the '@' prefix.
+If the identifier doesn't match the regular expression
+`[-a-zA-Z$._][-a-zA-Z$._0-9]*`, then this identifier must be quoted.
+
+The unnamed global values are represented using an unsigned numeric value with
+the '@' prefix, like in the following examples: ``@0``, ``@989``.
+
+.. TODO: Describe the parsers default behaviour when optional YAML attributes
+ are missing.
+.. TODO: Describe the syntax for the bundled instructions.
+.. TODO: Describe the syntax for virtual register YAML definitions.
+.. TODO: Describe the machine function's YAML flag attributes.
+.. TODO: Describe the syntax for the external symbol and register
+ mask machine operands.
+.. TODO: Describe the frame information YAML mapping.
+.. TODO: Describe the syntax of the stack object machine operands and their
+ YAML definitions.
+.. TODO: Describe the syntax of the constant pool machine operands and their
+ YAML definitions.
+.. TODO: Describe the syntax of the jump table machine operands and their
+ YAML definitions.
+.. TODO: Describe the syntax of the block address machine operands.
+.. TODO: Describe the syntax of the CFI index machine operands.
+.. TODO: Describe the syntax of the metadata machine operands, and the
+ instructions debug location attribute.
+.. TODO: Describe the syntax of the target index machine operands.
+.. TODO: Describe the syntax of the register live out machine operands.
+.. TODO: Describe the syntax of the machine memory operands.
Added: www-releases/trunk/5.0.1/docs/_sources/MarkedUpDisassembly.rst.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.1/docs/_sources/MarkedUpDisassembly.rst.txt?rev=321287&view=auto
==============================================================================
--- www-releases/trunk/5.0.1/docs/_sources/MarkedUpDisassembly.rst.txt (added)
+++ www-releases/trunk/5.0.1/docs/_sources/MarkedUpDisassembly.rst.txt Thu Dec 21 10:09:53 2017
@@ -0,0 +1,86 @@
+=======================================
+LLVM's Optional Rich Disassembly Output
+=======================================
+
+.. contents::
+ :local:
+
+Introduction
+============
+
+LLVM's default disassembly output is raw text. To allow consumers more ability
+to introspect the instructions' textual representation or to reformat for a more
+user friendly display there is an optional rich disassembly output.
+
+This optional output is sufficient to reference into individual portions of the
+instruction text. This is intended for clients like disassemblers, list file
+generators, and pretty-printers, which need more than the raw instructions and
+the ability to print them.
+
+To provide this functionality the assembly text is marked up with annotations.
+The markup is simple enough in syntax to be robust even in the case of version
+mismatches between consumers and producers. That is, the syntax generally does
+not carry semantics beyond "this text has an annotation," so consumers can
+simply ignore annotations they do not understand or do not care about.
+
+After calling ``LLVMCreateDisasm()`` to create a disassembler context the
+optional output is enable with this call:
+
+.. code-block:: c
+
+ LLVMSetDisasmOptions(DC, LLVMDisassembler_Option_UseMarkup);
+
+Then subsequent calls to ``LLVMDisasmInstruction()`` will return output strings
+with the marked up annotations.
+
+Instruction Annotations
+=======================
+
+.. _contextual markups:
+
+Contextual markups
+------------------
+
+Annoated assembly display will supply contextual markup to help clients more
+efficiently implement things like pretty printers. Most markup will be target
+independent, so clients can effectively provide good display without any target
+specific knowledge.
+
+Annotated assembly goes through the normal instruction printer, but optionally
+includes contextual tags on portions of the instruction string. An annotation
+is any '<' '>' delimited section of text(1).
+
+.. code-block:: bat
+
+ annotation: '<' tag-name tag-modifier-list ':' annotated-text '>'
+ tag-name: identifier
+ tag-modifier-list: comma delimited identifier list
+
+The tag-name is an identifier which gives the type of the annotation. For the
+first pass, this will be very simple, with memory references, registers, and
+immediates having the tag names "mem", "reg", and "imm", respectively.
+
+The tag-modifier-list is typically additional target-specific context, such as
+register class.
+
+Clients should accept and ignore any tag-names or tag-modifiers they do not
+understand, allowing the annotations to grow in richness without breaking older
+clients.
+
+For example, a possible annotation of an ARM load of a stack-relative location
+might be annotated as:
+
+.. code-block:: text
+
+ ldr <reg gpr:r0>, <mem regoffset:[<reg gpr:sp>, <imm:#4>]>
+
+
+1: For assembly dialects in which '<' and/or '>' are legal tokens, a literal token is escaped by following immediately with a repeat of the character. For example, a literal '<' character is output as '<<' in an annotated assembly string.
+
+C API Details
+-------------
+
+The intended consumers of this information use the C API, therefore the new C
+API function for the disassembler will be added to provide an option to produce
+disassembled instructions with annotations, ``LLVMSetDisasmOptions()`` and the
+``LLVMDisassembler_Option_UseMarkup`` option (see above).
Added: www-releases/trunk/5.0.1/docs/_sources/MemorySSA.rst.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.1/docs/_sources/MemorySSA.rst.txt?rev=321287&view=auto
==============================================================================
--- www-releases/trunk/5.0.1/docs/_sources/MemorySSA.rst.txt (added)
+++ www-releases/trunk/5.0.1/docs/_sources/MemorySSA.rst.txt Thu Dec 21 10:09:53 2017
@@ -0,0 +1,364 @@
+=========
+MemorySSA
+=========
+
+.. contents::
+ :local:
+
+Introduction
+============
+
+``MemorySSA`` is an analysis that allows us to cheaply reason about the
+interactions between various memory operations. Its goal is to replace
+``MemoryDependenceAnalysis`` for most (if not all) use-cases. This is because,
+unless you're very careful, use of ``MemoryDependenceAnalysis`` can easily
+result in quadratic-time algorithms in LLVM. Additionally, ``MemorySSA`` doesn't
+have as many arbitrary limits as ``MemoryDependenceAnalysis``, so you should get
+better results, too.
+
+At a high level, one of the goals of ``MemorySSA`` is to provide an SSA based
+form for memory, complete with def-use and use-def chains, which
+enables users to quickly find may-def and may-uses of memory operations.
+It can also be thought of as a way to cheaply give versions to the complete
+state of heap memory, and associate memory operations with those versions.
+
+This document goes over how ``MemorySSA`` is structured, and some basic
+intuition on how ``MemorySSA`` works.
+
+A paper on MemorySSA (with notes about how it's implemented in GCC) `can be
+found here <http://www.airs.com/dnovillo/Papers/mem-ssa.pdf>`_. Though, it's
+relatively out-of-date; the paper references multiple heap partitions, but GCC
+eventually swapped to just using one, like we now have in LLVM. Like
+GCC's, LLVM's MemorySSA is intraprocedural.
+
+
+MemorySSA Structure
+===================
+
+MemorySSA is a virtual IR. After it's built, ``MemorySSA`` will contain a
+structure that maps ``Instruction``\ s to ``MemoryAccess``\ es, which are
+``MemorySSA``'s parallel to LLVM ``Instruction``\ s.
+
+Each ``MemoryAccess`` can be one of three types:
+
+- ``MemoryPhi``
+- ``MemoryUse``
+- ``MemoryDef``
+
+``MemoryPhi``\ s are ``PhiNode``\ s, but for memory operations. If at any
+point we have two (or more) ``MemoryDef``\ s that could flow into a
+``BasicBlock``, the block's top ``MemoryAccess`` will be a
+``MemoryPhi``. As in LLVM IR, ``MemoryPhi``\ s don't correspond to any
+concrete operation. As such, ``BasicBlock``\ s are mapped to ``MemoryPhi``\ s
+inside ``MemorySSA``, whereas ``Instruction``\ s are mapped to ``MemoryUse``\ s
+and ``MemoryDef``\ s.
+
+Note also that in SSA, Phi nodes merge must-reach definitions (that is,
+definitions that *must* be new versions of variables). In MemorySSA, PHI nodes
+merge may-reach definitions (that is, until disambiguated, the versions that
+reach a phi node may or may not clobber a given variable).
+
+``MemoryUse``\ s are operations which use but don't modify memory. An example of
+a ``MemoryUse`` is a ``load``, or a ``readonly`` function call.
+
+``MemoryDef``\ s are operations which may either modify memory, or which
+introduce some kind of ordering constraints. Examples of ``MemoryDef``\ s
+include ``store``\ s, function calls, ``load``\ s with ``acquire`` (or higher)
+ordering, volatile operations, memory fences, etc.
+
+Every function that exists has a special ``MemoryDef`` called ``liveOnEntry``.
+It dominates every ``MemoryAccess`` in the function that ``MemorySSA`` is being
+run on, and implies that we've hit the top of the function. It's the only
+``MemoryDef`` that maps to no ``Instruction`` in LLVM IR. Use of
+``liveOnEntry`` implies that the memory being used is either undefined or
+defined before the function begins.
+
+An example of all of this overlaid on LLVM IR (obtained by running ``opt
+-passes='print<memoryssa>' -disable-output`` on an ``.ll`` file) is below. When
+viewing this example, it may be helpful to view it in terms of clobbers. The
+operands of a given ``MemoryAccess`` are all (potential) clobbers of said
+MemoryAccess, and the value produced by a ``MemoryAccess`` can act as a clobber
+for other ``MemoryAccess``\ es. Another useful way of looking at it is in
+terms of heap versions. In that view, operands of of a given
+``MemoryAccess`` are the version of the heap before the operation, and
+if the access produces a value, the value is the new version of the heap
+after the operation.
+
+.. code-block:: llvm
+
+ define void @foo() {
+ entry:
+ %p1 = alloca i8
+ %p2 = alloca i8
+ %p3 = alloca i8
+ ; 1 = MemoryDef(liveOnEntry)
+ store i8 0, i8* %p3
+ br label %while.cond
+
+ while.cond:
+ ; 6 = MemoryPhi({%0,1},{if.end,4})
+ br i1 undef, label %if.then, label %if.else
+
+ if.then:
+ ; 2 = MemoryDef(6)
+ store i8 0, i8* %p1
+ br label %if.end
+
+ if.else:
+ ; 3 = MemoryDef(6)
+ store i8 1, i8* %p2
+ br label %if.end
+
+ if.end:
+ ; 5 = MemoryPhi({if.then,2},{if.else,3})
+ ; MemoryUse(5)
+ %1 = load i8, i8* %p1
+ ; 4 = MemoryDef(5)
+ store i8 2, i8* %p2
+ ; MemoryUse(1)
+ %2 = load i8, i8* %p3
+ br label %while.cond
+ }
+
+The ``MemorySSA`` IR is shown in comments that precede the instructions they map
+to (if such an instruction exists). For example, ``1 = MemoryDef(liveOnEntry)``
+is a ``MemoryAccess`` (specifically, a ``MemoryDef``), and it describes the LLVM
+instruction ``store i8 0, i8* %p3``. Other places in ``MemorySSA`` refer to this
+particular ``MemoryDef`` as ``1`` (much like how one can refer to ``load i8, i8*
+%p1`` in LLVM with ``%1``). Again, ``MemoryPhi``\ s don't correspond to any LLVM
+Instruction, so the line directly below a ``MemoryPhi`` isn't special.
+
+Going from the top down:
+
+- ``6 = MemoryPhi({entry,1},{if.end,4})`` notes that, when entering
+ ``while.cond``, the reaching definition for it is either ``1`` or ``4``. This
+ ``MemoryPhi`` is referred to in the textual IR by the number ``6``.
+- ``2 = MemoryDef(6)`` notes that ``store i8 0, i8* %p1`` is a definition,
+ and its reaching definition before it is ``6``, or the ``MemoryPhi`` after
+ ``while.cond``. (See the `Build-time use optimization`_ and `Precision`_
+ sections below for why this ``MemoryDef`` isn't linked to a separate,
+ disambiguated ``MemoryPhi``.)
+- ``3 = MemoryDef(6)`` notes that ``store i8 0, i8* %p2`` is a definition; its
+ reaching definition is also ``6``.
+- ``5 = MemoryPhi({if.then,2},{if.else,3})`` notes that the clobber before
+ this block could either be ``2`` or ``3``.
+- ``MemoryUse(5)`` notes that ``load i8, i8* %p1`` is a use of memory, and that
+ it's clobbered by ``5``.
+- ``4 = MemoryDef(5)`` notes that ``store i8 2, i8* %p2`` is a definition; it's
+ reaching definition is ``5``.
+- ``MemoryUse(1)`` notes that ``load i8, i8* %p3`` is just a user of memory,
+ and the last thing that could clobber this use is above ``while.cond`` (e.g.
+ the store to ``%p3``). In heap versioning parlance, it really only depends on
+ the heap version 1, and is unaffected by the new heap versions generated since
+ then.
+
+As an aside, ``MemoryAccess`` is a ``Value`` mostly for convenience; it's not
+meant to interact with LLVM IR.
+
+Design of MemorySSA
+===================
+
+``MemorySSA`` is an analysis that can be built for any arbitrary function. When
+it's built, it does a pass over the function's IR in order to build up its
+mapping of ``MemoryAccess``\ es. You can then query ``MemorySSA`` for things
+like the dominance relation between ``MemoryAccess``\ es, and get the
+``MemoryAccess`` for any given ``Instruction`` .
+
+When ``MemorySSA`` is done building, it also hands you a ``MemorySSAWalker``
+that you can use (see below).
+
+
+The walker
+----------
+
+A structure that helps ``MemorySSA`` do its job is the ``MemorySSAWalker``, or
+the walker, for short. The goal of the walker is to provide answers to clobber
+queries beyond what's represented directly by ``MemoryAccess``\ es. For example,
+given:
+
+.. code-block:: llvm
+
+ define void @foo() {
+ %a = alloca i8
+ %b = alloca i8
+
+ ; 1 = MemoryDef(liveOnEntry)
+ store i8 0, i8* %a
+ ; 2 = MemoryDef(1)
+ store i8 0, i8* %b
+ }
+
+The store to ``%a`` is clearly not a clobber for the store to ``%b``. It would
+be the walker's goal to figure this out, and return ``liveOnEntry`` when queried
+for the clobber of ``MemoryAccess`` ``2``.
+
+By default, ``MemorySSA`` provides a walker that can optimize ``MemoryDef``\ s
+and ``MemoryUse``\ s by consulting whatever alias analysis stack you happen to
+be using. Walkers were built to be flexible, though, so it's entirely reasonable
+(and expected) to create more specialized walkers (e.g. one that specifically
+queries ``GlobalsAA``, one that always stops at ``MemoryPhi`` nodes, etc).
+
+
+Locating clobbers yourself
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+If you choose to make your own walker, you can find the clobber for a
+``MemoryAccess`` by walking every ``MemoryDef`` that dominates said
+``MemoryAccess``. The structure of ``MemoryDef``\ s makes this relatively simple;
+they ultimately form a linked list of every clobber that dominates the
+``MemoryAccess`` that you're trying to optimize. In other words, the
+``definingAccess`` of a ``MemoryDef`` is always the nearest dominating
+``MemoryDef`` or ``MemoryPhi`` of said ``MemoryDef``.
+
+
+Build-time use optimization
+---------------------------
+
+``MemorySSA`` will optimize some ``MemoryAccess``\ es at build-time.
+Specifically, we optimize the operand of every ``MemoryUse`` to point to the
+actual clobber of said ``MemoryUse``. This can be seen in the above example; the
+second ``MemoryUse`` in ``if.end`` has an operand of ``1``, which is a
+``MemoryDef`` from the entry block. This is done to make walking,
+value numbering, etc, faster and easier.
+
+It is not possible to optimize ``MemoryDef`` in the same way, as we
+restrict ``MemorySSA`` to one heap variable and, thus, one Phi node
+per block.
+
+
+Invalidation and updating
+-------------------------
+
+Because ``MemorySSA`` keeps track of LLVM IR, it needs to be updated whenever
+the IR is updated. "Update", in this case, includes the addition, deletion, and
+motion of ``Instructions``. The update API is being made on an as-needed basis.
+If you'd like examples, ``GVNHoist`` is a user of ``MemorySSA``\ s update API.
+
+
+Phi placement
+^^^^^^^^^^^^^
+
+``MemorySSA`` only places ``MemoryPhi``\ s where they're actually
+needed. That is, it is a pruned SSA form, like LLVM's SSA form. For
+example, consider:
+
+.. code-block:: llvm
+
+ define void @foo() {
+ entry:
+ %p1 = alloca i8
+ %p2 = alloca i8
+ %p3 = alloca i8
+ ; 1 = MemoryDef(liveOnEntry)
+ store i8 0, i8* %p3
+ br label %while.cond
+
+ while.cond:
+ ; 3 = MemoryPhi({%0,1},{if.end,2})
+ br i1 undef, label %if.then, label %if.else
+
+ if.then:
+ br label %if.end
+
+ if.else:
+ br label %if.end
+
+ if.end:
+ ; MemoryUse(1)
+ %1 = load i8, i8* %p1
+ ; 2 = MemoryDef(3)
+ store i8 2, i8* %p2
+ ; MemoryUse(1)
+ %2 = load i8, i8* %p3
+ br label %while.cond
+ }
+
+Because we removed the stores from ``if.then`` and ``if.else``, a ``MemoryPhi``
+for ``if.end`` would be pointless, so we don't place one. So, if you need to
+place a ``MemoryDef`` in ``if.then`` or ``if.else``, you'll need to also create
+a ``MemoryPhi`` for ``if.end``.
+
+If it turns out that this is a large burden, we can just place ``MemoryPhi``\ s
+everywhere. Because we have Walkers that are capable of optimizing above said
+phis, doing so shouldn't prohibit optimizations.
+
+
+Non-Goals
+---------
+
+``MemorySSA`` is meant to reason about the relation between memory
+operations, and enable quicker querying.
+It isn't meant to be the single source of truth for all potential memory-related
+optimizations. Specifically, care must be taken when trying to use ``MemorySSA``
+to reason about atomic or volatile operations, as in:
+
+.. code-block:: llvm
+
+ define i8 @foo(i8* %a) {
+ entry:
+ br i1 undef, label %if.then, label %if.end
+
+ if.then:
+ ; 1 = MemoryDef(liveOnEntry)
+ %0 = load volatile i8, i8* %a
+ br label %if.end
+
+ if.end:
+ %av = phi i8 [0, %entry], [%0, %if.then]
+ ret i8 %av
+ }
+
+Going solely by ``MemorySSA``'s analysis, hoisting the ``load`` to ``entry`` may
+seem legal. Because it's a volatile load, though, it's not.
+
+
+Design tradeoffs
+----------------
+
+Precision
+^^^^^^^^^
+
+``MemorySSA`` in LLVM deliberately trades off precision for speed.
+Let us think about memory variables as if they were disjoint partitions of the
+heap (that is, if you have one variable, as above, it represents the entire
+heap, and if you have multiple variables, each one represents some
+disjoint portion of the heap)
+
+First, because alias analysis results conflict with each other, and
+each result may be what an analysis wants (IE
+TBAA may say no-alias, and something else may say must-alias), it is
+not possible to partition the heap the way every optimization wants.
+Second, some alias analysis results are not transitive (IE A noalias B,
+and B noalias C, does not mean A noalias C), so it is not possible to
+come up with a precise partitioning in all cases without variables to
+represent every pair of possible aliases. Thus, partitioning
+precisely may require introducing at least N^2 new virtual variables,
+phi nodes, etc.
+
+Each of these variables may be clobbered at multiple def sites.
+
+To give an example, if you were to split up struct fields into
+individual variables, all aliasing operations that may-def multiple struct
+fields, will may-def more than one of them. This is pretty common (calls,
+copies, field stores, etc).
+
+Experience with SSA forms for memory in other compilers has shown that
+it is simply not possible to do this precisely, and in fact, doing it
+precisely is not worth it, because now all the optimizations have to
+walk tons and tons of virtual variables and phi nodes.
+
+So we partition. At the point at which you partition, again,
+experience has shown us there is no point in partitioning to more than
+one variable. It simply generates more IR, and optimizations still
+have to query something to disambiguate further anyway.
+
+As a result, LLVM partitions to one variable.
+
+Use Optimization
+^^^^^^^^^^^^^^^^
+
+Unlike other partitioned forms, LLVM's ``MemorySSA`` does make one
+useful guarantee - all loads are optimized to point at the thing that
+actually clobbers them. This gives some nice properties. For example,
+for a given store, you can find all loads actually clobbered by that
+store by walking the immediate uses of the store.
Added: www-releases/trunk/5.0.1/docs/_sources/MergeFunctions.rst.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.1/docs/_sources/MergeFunctions.rst.txt?rev=321287&view=auto
==============================================================================
--- www-releases/trunk/5.0.1/docs/_sources/MergeFunctions.rst.txt (added)
+++ www-releases/trunk/5.0.1/docs/_sources/MergeFunctions.rst.txt Thu Dec 21 10:09:53 2017
@@ -0,0 +1,802 @@
+=================================
+MergeFunctions pass, how it works
+=================================
+
+.. contents::
+ :local:
+
+Introduction
+============
+Sometimes code contains equal functions, or functions that does exactly the same
+thing even though they are non-equal on the IR level (e.g.: multiplication on 2
+and 'shl 1'). It could happen due to several reasons: mainly, the usage of
+templates and automatic code generators. Though, sometimes user itself could
+write the same thing twice :-)
+
+The main purpose of this pass is to recognize such functions and merge them.
+
+Why would I want to read this document?
+---------------------------------------
+Document is the extension to pass comments and describes the pass logic. It
+describes algorithm that is used in order to compare functions, it also
+explains how we could combine equal functions correctly, keeping module valid.
+
+Material is brought in top-down form, so reader could start learn pass from
+ideas and end up with low-level algorithm details, thus preparing him for
+reading the sources.
+
+So main goal is do describe algorithm and logic here; the concept. This document
+is good for you, if you *don't want* to read the source code, but want to
+understand pass algorithms. Author tried not to repeat the source-code and
+cover only common cases, and thus avoid cases when after minor code changes we
+need to update this document.
+
+
+What should I know to be able to follow along with this document?
+-----------------------------------------------------------------
+
+Reader should be familiar with common compile-engineering principles and LLVM
+code fundamentals. In this article we suppose reader is familiar with
+`Single Static Assingment <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_
+concepts. Understanding of
+`IR structure <http://llvm.org/docs/LangRef.html#high-level-structure>`_ is
+also important.
+
+We will use such terms as
+"`module <http://llvm.org/docs/LangRef.html#high-level-structure>`_",
+"`function <http://llvm.org/docs/ProgrammersManual.html#the-function-class>`_",
+"`basic block <http://en.wikipedia.org/wiki/Basic_block>`_",
+"`user <http://llvm.org/docs/ProgrammersManual.html#the-user-class>`_",
+"`value <http://llvm.org/docs/ProgrammersManual.html#the-value-class>`_",
+"`instruction <http://llvm.org/docs/ProgrammersManual.html#the-instruction-class>`_".
+
+As a good start point, Kaleidoscope tutorial could be used:
+
+:doc:`tutorial/index`
+
+Especially it's important to understand chapter 3 of tutorial:
+
+:doc:`tutorial/LangImpl03`
+
+Reader also should know how passes work in LLVM, they could use next article as
+a reference and start point here:
+
+:doc:`WritingAnLLVMPass`
+
+What else? Well perhaps reader also should have some experience in LLVM pass
+debugging and bug-fixing.
+
+What I gain by reading this document?
+-------------------------------------
+Main purpose is to provide reader with comfortable form of algorithms
+description, namely the human reading text. Since it could be hard to
+understand algorithm straight from the source code: pass uses some principles
+that have to be explained first.
+
+Author wishes to everybody to avoid case, when you read code from top to bottom
+again and again, and yet you don't understand why we implemented it that way.
+
+We hope that after this article reader could easily debug and improve
+MergeFunctions pass and thus help LLVM project.
+
+Narrative structure
+-------------------
+Article consists of three parts. First part explains pass functionality on the
+top-level. Second part describes the comparison procedure itself. The third
+part describes the merging process.
+
+In every part author also tried to put the contents into the top-down form.
+First, the top-level methods will be described, while the terminal ones will be
+at the end, in the tail of each part. If reader will see the reference to the
+method that wasn't described yet, they will find its description a bit below.
+
+Basics
+======
+
+How to do it?
+-------------
+Do we need to merge functions? Obvious thing is: yes that's a quite possible
+case, since usually we *do* have duplicates. And it would be good to get rid of
+them. But how to detect such a duplicates? The idea is next: we split functions
+onto small bricks (parts), then we compare "bricks" amount, and if it equal,
+compare "bricks" themselves, and then do our conclusions about functions
+themselves.
+
+What the difference it could be? For example, on machine with 64-bit pointers
+(let's assume we have only one address space), one function stores 64-bit
+integer, while another one stores a pointer. So if the target is a machine
+mentioned above, and if functions are identical, except the parameter type (we
+could consider it as a part of function type), then we can treat ``uint64_t``
+and``void*`` as equal.
+
+It was just an example; possible details are described a bit below.
+
+As another example reader may imagine two more functions. First function
+performs multiplication on 2, while the second one performs arithmetic right
+shift on 1.
+
+Possible solutions
+^^^^^^^^^^^^^^^^^^
+Let's briefly consider possible options about how and what we have to implement
+in order to create full-featured functions merging, and also what it would
+meant for us.
+
+Equal functions detection, obviously supposes "detector" method to be
+implemented, latter should answer the question "whether functions are equal".
+This "detector" method consists of tiny "sub-detectors", each of them answers
+exactly the same question, but for function parts.
+
+As the second step, we should merge equal functions. So it should be a "merger"
+method. "Merger" accepts two functions *F1* and *F2*, and produces *F1F2*
+function, the result of merging.
+
+Having such a routines in our hands, we can process whole module, and merge all
+equal functions.
+
+In this case, we have to compare every function with every another function. As
+reader could notice, this way seems to be quite expensive. Of course we could
+introduce hashing and other helpers, but it is still just an optimization, and
+thus the level of O(N*N) complexity.
+
+Can we reach another level? Could we introduce logarithmical search, or random
+access lookup? The answer is: "yes".
+
+Random-access
+"""""""""""""
+How it could be done? Just convert each function to number, and gather all of
+them in special hash-table. Functions with equal hash are equal. Good hashing
+means, that every function part must be taken into account. That means we have
+to convert every function part into some number, and then add it into hash.
+Lookup-up time would be small, but such approach adds some delay due to hashing
+routine.
+
+Logarithmical search
+""""""""""""""""""""
+We could introduce total ordering among the functions set, once we had it we
+could then implement a logarithmical search. Lookup time still depends on N,
+but adds a little of delay (*log(N)*).
+
+Present state
+"""""""""""""
+Both of approaches (random-access and logarithmical) has been implemented and
+tested. And both of them gave a very good improvement. And what was most
+surprising, logarithmical search was faster; sometimes up to 15%. Hashing needs
+some extra CPU time, and it is the main reason why it works slower; in most of
+cases total "hashing" time was greater than total "logarithmical-search" time.
+
+So, preference has been granted to the "logarithmical search".
+
+Though in the case of need, *logarithmical-search* (read "total-ordering") could
+be used as a milestone on our way to the *random-access* implementation.
+
+Every comparison is based either on the numbers or on flags comparison. In
+*random-access* approach we could use the same comparison algorithm. During
+comparison we exit once we find the difference, but here we might have to scan
+whole function body every time (note, it could be slower). Like in
+"total-ordering", we will track every numbers and flags, but instead of
+comparison, we should get numbers sequence and then create the hash number. So,
+once again, *total-ordering* could be considered as a milestone for even faster
+(in theory) random-access approach.
+
+MergeFunctions, main fields and runOnModule
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+There are two most important fields in class:
+
+``FnTree`` â the set of all unique functions. It keeps items that couldn't be
+merged with each other. It is defined as:
+
+``std::set<FunctionNode> FnTree;``
+
+Here ``FunctionNode`` is a wrapper for ``llvm::Function`` class, with
+implemented â<â operator among the functions set (below we explain how it works
+exactly; this is a key point in fast functions comparison).
+
+``Deferred`` â merging process can affect bodies of functions that are in
+``FnTree`` already. Obviously such functions should be rechecked again. In this
+case we remove them from ``FnTree``, and mark them as to be rescanned, namely
+put them into ``Deferred`` list.
+
+runOnModule
+"""""""""""
+The algorithm is pretty simple:
+
+1. Put all module's functions into the *worklist*.
+
+2. Scan *worklist*'s functions twice: first enumerate only strong functions and
+then only weak ones:
+
+ 2.1. Loop body: take function from *worklist* (call it *FCur*) and try to
+ insert it into *FnTree*: check whether *FCur* is equal to one of functions
+ in *FnTree*. If there *is* equal function in *FnTree* (call it *FExists*):
+ merge function *FCur* with *FExists*. Otherwise add function from *worklist*
+ to *FnTree*.
+
+3. Once *worklist* scanning and merging operations is complete, check *Deferred*
+list. If it is not empty: refill *worklist* contents with *Deferred* list and
+do step 2 again, if *Deferred* is empty, then exit from method.
+
+Comparison and logarithmical search
+"""""""""""""""""""""""""""""""""""
+Let's recall our task: for every function *F* from module *M*, we have to find
+equal functions *F`* in shortest time, and merge them into the single function.
+
+Defining total ordering among the functions set allows to organize functions
+into the binary tree. The lookup procedure complexity would be estimated as
+O(log(N)) in this case. But how to define *total-ordering*?
+
+We have to introduce a single rule applicable to every pair of functions, and
+following this rule then evaluate which of them is greater. What kind of rule
+it could be? Let's declare it as "compare" method, that returns one of 3
+possible values:
+
+-1, left is *less* than right,
+
+0, left and right are *equal*,
+
+1, left is *greater* than right.
+
+Of course it means, that we have to maintain
+*strict and non-strict order relation properties*:
+
+* reflexivity (``a <= a``, ``a == a``, ``a >= a``),
+* antisymmetry (if ``a <= b`` and ``b <= a`` then ``a == b``),
+* transitivity (``a <= b`` and ``b <= c``, then ``a <= c``)
+* asymmetry (if ``a < b``, then ``a > b`` or ``a == b``).
+
+As it was mentioned before, comparison routine consists of
+"sub-comparison-routines", each of them also consists
+"sub-comparison-routines", and so on, finally it ends up with a primitives
+comparison.
+
+Below, we will use the next operations:
+
+#. ``cmpNumbers(number1, number2)`` is method that returns -1 if left is less
+ than right; 0, if left and right are equal; and 1 otherwise.
+
+#. ``cmpFlags(flag1, flag2)`` is hypothetical method that compares two flags.
+ The logic is the same as in ``cmpNumbers``, where ``true`` is 1, and
+ ``false`` is 0.
+
+The rest of article is based on *MergeFunctions.cpp* source code
+(*<llvm_dir>/lib/Transforms/IPO/MergeFunctions.cpp*). We would like to ask
+reader to keep this file open nearby, so we could use it as a reference for
+further explanations.
+
+Now we're ready to proceed to the next chapter and see how it works.
+
+Functions comparison
+====================
+At first, let's define how exactly we compare complex objects.
+
+Complex objects comparison (function, basic-block, etc) is mostly based on its
+sub-objects comparison results. So it is similar to the next "tree" objects
+comparison:
+
+#. For two trees *T1* and *T2* we perform *depth-first-traversal* and have
+ two sequences as a product: "*T1Items*" and "*T2Items*".
+
+#. Then compare chains "*T1Items*" and "*T2Items*" in
+ most-significant-item-first order. Result of items comparison would be the
+ result of *T1* and *T2* comparison itself.
+
+FunctionComparator::compare(void)
+---------------------------------
+Brief look at the source code tells us, that comparison starts in
+â``int FunctionComparator::compare(void)``â method.
+
+1. First parts to be compared are function's attributes and some properties that
+outsides âattributesâ term, but still could make function different without
+changing its body. This part of comparison is usually done within simple
+*cmpNumbers* or *cmpFlags* operations (e.g.
+``cmpFlags(F1->hasGC(), F2->hasGC())``). Below is full list of function's
+properties to be compared on this stage:
+
+ * *Attributes* (those are returned by ``Function::getAttributes()``
+ method).
+
+ * *GC*, for equivalence, *RHS* and *LHS* should be both either without
+ *GC* or with the same one.
+
+ * *Section*, just like a *GC*: *RHS* and *LHS* should be defined in the
+ same section.
+
+ * *Variable arguments*. *LHS* and *RHS* should be both either with or
+ without *var-args*.
+
+ * *Calling convention* should be the same.
+
+2. Function type. Checked by ``FunctionComparator::cmpType(Type*, Type*)``
+method. It checks return type and parameters type; the method itself will be
+described later.
+
+3. Associate function formal parameters with each other. Then comparing function
+bodies, if we see the usage of *LHS*'s *i*-th argument in *LHS*'s body, then,
+we want to see usage of *RHS*'s *i*-th argument at the same place in *RHS*'s
+body, otherwise functions are different. On this stage we grant the preference
+to those we met later in function body (value we met first would be *less*).
+This is done by â``FunctionComparator::cmpValues(const Value*, const Value*)``â
+method (will be described a bit later).
+
+4. Function body comparison. As it written in method comments:
+
+âWe do a CFG-ordered walk since the actual ordering of the blocks in the linked
+list is immaterial. Our walk starts at the entry block for both functions, then
+takes each block from each terminator in order. As an artifact, this also means
+that unreachable blocks are ignored.â
+
+So, using this walk we get BBs from *left* and *right* in the same order, and
+compare them by â``FunctionComparator::compare(const BasicBlock*, const
+BasicBlock*)``â method.
+
+We also associate BBs with each other, like we did it with function formal
+arguments (see ``cmpValues`` method below).
+
+FunctionComparator::cmpType
+---------------------------
+Consider how types comparison works.
+
+1. Coerce pointer to integer. If left type is a pointer, try to coerce it to the
+integer type. It could be done if its address space is 0, or if address spaces
+are ignored at all. Do the same thing for the right type.
+
+2. If left and right types are equal, return 0. Otherwise we need to give
+preference to one of them. So proceed to the next step.
+
+3. If types are of different kind (different type IDs). Return result of type
+IDs comparison, treating them as a numbers (use ``cmpNumbers`` operation).
+
+4. If types are vectors or integers, return result of their pointers comparison,
+comparing them as numbers.
+
+5. Check whether type ID belongs to the next group (call it equivalent-group):
+
+ * Void
+
+ * Float
+
+ * Double
+
+ * X86_FP80
+
+ * FP128
+
+ * PPC_FP128
+
+ * Label
+
+ * Metadata.
+
+ If ID belongs to group above, return 0. Since it's enough to see that
+ types has the same ``TypeID``. No additional information is required.
+
+6. Left and right are pointers. Return result of address space comparison
+(numbers comparison).
+
+7. Complex types (structures, arrays, etc.). Follow complex objects comparison
+technique (see the very first paragraph of this chapter). Both *left* and
+*right* are to be expanded and their element types will be checked the same
+way. If we get -1 or 1 on some stage, return it. Otherwise return 0.
+
+8. Steps 1-6 describe all the possible cases, if we passed steps 1-6 and didn't
+get any conclusions, then invoke ``llvm_unreachable``, since it's quite
+unexpectable case.
+
+cmpValues(const Value*, const Value*)
+-------------------------------------
+Method that compares local values.
+
+This method gives us an answer on a very curious quesion: whether we could treat
+local values as equal, and which value is greater otherwise. It's better to
+start from example:
+
+Consider situation when we're looking at the same place in left function "*FL*"
+and in right function "*FR*". And every part of *left* place is equal to the
+corresponding part of *right* place, and (!) both parts use *Value* instances,
+for example:
+
+.. code-block:: text
+
+ instr0 i32 %LV ; left side, function FL
+ instr0 i32 %RV ; right side, function FR
+
+So, now our conclusion depends on *Value* instances comparison.
+
+Main purpose of this method is to determine relation between such values.
+
+What we expect from equal functions? At the same place, in functions "*FL*" and
+"*FR*" we expect to see *equal* values, or values *defined* at the same place
+in "*FL*" and "*FR*".
+
+Consider small example here:
+
+.. code-block:: text
+
+ define void %f(i32 %pf0, i32 %pf1) {
+ instr0 i32 %pf0 instr1 i32 %pf1 instr2 i32 123
+ }
+
+.. code-block:: text
+
+ define void %g(i32 %pg0, i32 %pg1) {
+ instr0 i32 %pg0 instr1 i32 %pg0 instr2 i32 123
+ }
+
+In this example, *pf0* is associated with *pg0*, *pf1* is associated with *pg1*,
+and we also declare that *pf0* < *pf1*, and thus *pg0* < *pf1*.
+
+Instructions with opcode "*instr0*" would be *equal*, since their types and
+opcodes are equal, and values are *associated*.
+
+Instruction with opcode "*instr1*" from *f* is *greater* than instruction with
+opcode "*instr1*" from *g*; here we have equal types and opcodes, but "*pf1* is
+greater than "*pg0*".
+
+And instructions with opcode "*instr2*" are equal, because their opcodes and
+types are equal, and the same constant is used as a value.
+
+What we assiciate in cmpValues?
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+* Function arguments. *i*-th argument from left function associated with
+ *i*-th argument from right function.
+* BasicBlock instances. In basic-block enumeration loop we associate *i*-th
+ BasicBlock from the left function with *i*-th BasicBlock from the right
+ function.
+* Instructions.
+* Instruction operands. Note, we can meet *Value* here we have never seen
+ before. In this case it is not a function argument, nor *BasicBlock*, nor
+ *Instruction*. It is global value. It is constant, since its the only
+ supposed global here. Method also compares:
+* Constants that are of the same type.
+* If right constant could be losslessly bit-casted to the left one, then we
+ also compare them.
+
+How to implement cmpValues?
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+*Association* is a case of equality for us. We just treat such values as equal.
+But, in general, we need to implement antisymmetric relation. As it was
+mentioned above, to understand what is *less*, we can use order in which we
+meet values. If both of values has the same order in function (met at the same
+time), then treat values as *associated*. Otherwise â it depends on who was
+first.
+
+Every time we run top-level compare method, we initialize two identical maps
+(one for the left side, another one for the right side):
+
+``map<Value, int> sn_mapL, sn_mapR;``
+
+The key of the map is the *Value* itself, the *value* â is its order (call it
+*serial number*).
+
+To add value *V* we need to perform the next procedure:
+
+``sn_map.insert(std::make_pair(V, sn_map.size()));``
+
+For the first *Value*, map will return *0*, for second *Value* map will return
+*1*, and so on.
+
+Then we can check whether left and right values met at the same time with simple
+comparison:
+
+``cmpNumbers(sn_mapL[Left], sn_mapR[Right]);``
+
+Of course, we can combine insertion and comparison:
+
+.. code-block:: c++
+
+ std::pair<iterator, bool>
+ LeftRes = sn_mapL.insert(std::make_pair(Left, sn_mapL.size())), RightRes
+ = sn_mapR.insert(std::make_pair(Right, sn_mapR.size()));
+ return cmpNumbers(LeftRes.first->second, RightRes.first->second);
+
+Let's look, how whole method could be implemented.
+
+1. we have to start from the bad news. Consider function self and
+cross-referencing cases:
+
+.. code-block:: c++
+
+ // self-reference unsigned fact0(unsigned n) { return n > 1 ? n
+ * fact0(n-1) : 1; } unsigned fact1(unsigned n) { return n > 1 ? n *
+ fact1(n-1) : 1; }
+
+ // cross-reference unsigned ping(unsigned n) { return n!= 0 ? pong(n-1) : 0;
+ } unsigned pong(unsigned n) { return n!= 0 ? ping(n-1) : 0; }
+
+..
+
+ This comparison has been implemented in initial *MergeFunctions* pass
+ version. But, unfortunately, it is not transitive. And this is the only case
+ we can't convert to less-equal-greater comparison. It is a seldom case, 4-5
+ functions of 10000 (checked on test-suite), and, we hope, reader would
+ forgive us for such a sacrifice in order to get the O(log(N)) pass time.
+
+2. If left/right *Value* is a constant, we have to compare them. Return 0 if it
+is the same constant, or use ``cmpConstants`` method otherwise.
+
+3. If left/right is *InlineAsm* instance. Return result of *Value* pointers
+comparison.
+
+4. Explicit association of *L* (left value) and *R* (right value). We need to
+find out whether values met at the same time, and thus are *associated*. Or we
+need to put the rule: when we treat *L* < *R*. Now it is easy: just return
+result of numbers comparison:
+
+.. code-block:: c++
+
+ std::pair<iterator, bool>
+ LeftRes = sn_mapL.insert(std::make_pair(Left, sn_mapL.size())),
+ RightRes = sn_mapR.insert(std::make_pair(Right, sn_mapR.size()));
+ if (LeftRes.first->second == RightRes.first->second) return 0;
+ if (LeftRes.first->second < RightRes.first->second) return -1;
+ return 1;
+
+Now when *cmpValues* returns 0, we can proceed comparison procedure. Otherwise,
+if we get (-1 or 1), we need to pass this result to the top level, and finish
+comparison procedure.
+
+cmpConstants
+------------
+Performs constants comparison as follows:
+
+1. Compare constant types using ``cmpType`` method. If result is -1 or 1, goto
+step 2, otherwise proceed to step 3.
+
+2. If types are different, we still can check whether constants could be
+losslessly bitcasted to each other. The further explanation is modification of
+``canLosslesslyBitCastTo`` method.
+
+ 2.1 Check whether constants are of the first class types
+ (``isFirstClassType`` check):
+
+ 2.1.1. If both constants are *not* of the first class type: return result
+ of ``cmpType``.
+
+ 2.1.2. Otherwise, if left type is not of the first class, return -1. If
+ right type is not of the first class, return 1.
+
+ 2.1.3. If both types are of the first class type, proceed to the next step
+ (2.1.3.1).
+
+ 2.1.3.1. If types are vectors, compare their bitwidth using the
+ *cmpNumbers*. If result is not 0, return it.
+
+ 2.1.3.2. Different types, but not a vectors:
+
+ * if both of them are pointers, good for us, we can proceed to step 3.
+ * if one of types is pointer, return result of *isPointer* flags
+ comparison (*cmpFlags* operation).
+ * otherwise we have no methods to prove bitcastability, and thus return
+ result of types comparison (-1 or 1).
+
+Steps below are for the case when types are equal, or case when constants are
+bitcastable:
+
+3. One of constants is a "*null*" value. Return the result of
+``cmpFlags(L->isNullValue, R->isNullValue)`` comparison.
+
+4. Compare value IDs, and return result if it is not 0:
+
+.. code-block:: c++
+
+ if (int Res = cmpNumbers(L->getValueID(), R->getValueID()))
+ return Res;
+
+5. Compare the contents of constants. The comparison depends on kind of
+constants, but on this stage it is just a lexicographical comparison. Just see
+how it was described in the beginning of "*Functions comparison*" paragraph.
+Mathematically it is equal to the next case: we encode left constant and right
+constant (with similar way *bitcode-writer* does). Then compare left code
+sequence and right code sequence.
+
+compare(const BasicBlock*, const BasicBlock*)
+---------------------------------------------
+Compares two *BasicBlock* instances.
+
+It enumerates instructions from left *BB* and right *BB*.
+
+1. It assigns serial numbers to the left and right instructions, using
+``cmpValues`` method.
+
+2. If one of left or right is *GEP* (``GetElementPtr``), then treat *GEP* as
+greater than other instructions, if both instructions are *GEPs* use ``cmpGEP``
+method for comparison. If result is -1 or 1, pass it to the top-level
+comparison (return it).
+
+ 3.1. Compare operations. Call ``cmpOperation`` method. If result is -1 or
+ 1, return it.
+
+ 3.2. Compare number of operands, if result is -1 or 1, return it.
+
+ 3.3. Compare operands themselves, use ``cmpValues`` method. Return result
+ if it is -1 or 1.
+
+ 3.4. Compare type of operands, using ``cmpType`` method. Return result if
+ it is -1 or 1.
+
+ 3.5. Proceed to the next instruction.
+
+4. We can finish instruction enumeration in 3 cases:
+
+ 4.1. We reached the end of both left and right basic-blocks. We didn't
+ exit on steps 1-3, so contents is equal, return 0.
+
+ 4.2. We have reached the end of the left basic-block. Return -1.
+
+ 4.3. Return 1 (the end of the right basic block).
+
+cmpGEP
+------
+Compares two GEPs (``getelementptr`` instructions).
+
+It differs from regular operations comparison with the only thing: possibility
+to use ``accumulateConstantOffset`` method.
+
+So, if we get constant offset for both left and right *GEPs*, then compare it as
+numbers, and return comparison result.
+
+Otherwise treat it like a regular operation (see previous paragraph).
+
+cmpOperation
+------------
+Compares instruction opcodes and some important operation properties.
+
+1. Compare opcodes, if it differs return the result.
+
+2. Compare number of operands. If it differs â return the result.
+
+3. Compare operation types, use *cmpType*. All the same â if types are
+different, return result.
+
+4. Compare *subclassOptionalData*, get it with ``getRawSubclassOptionalData``
+method, and compare it like a numbers.
+
+5. Compare operand types.
+
+6. For some particular instructions check equivalence (relation in our case) of
+some significant attributes. For example we have to compare alignment for
+``load`` instructions.
+
+O(log(N))
+---------
+Methods described above implement order relationship. And latter, could be used
+for nodes comparison in a binary tree. So we can organize functions set into
+the binary tree and reduce the cost of lookup procedure from
+O(N*N) to O(log(N)).
+
+Merging process, mergeTwoFunctions
+==================================
+Once *MergeFunctions* detected that current function (*G*) is equal to one that
+were analyzed before (function *F*) it calls ``mergeTwoFunctions(Function*,
+Function*)``.
+
+Operation affects ``FnTree`` contents with next way: *F* will stay in
+``FnTree``. *G* being equal to *F* will not be added to ``FnTree``. Calls of
+*G* would be replaced with something else. It changes bodies of callers. So,
+functions that calls *G* would be put into ``Deferred`` set and removed from
+``FnTree``, and analyzed again.
+
+The approach is next:
+
+1. Most wished case: when we can use alias and both of *F* and *G* are weak. We
+make both of them with aliases to the third strong function *H*. Actually *H*
+is *F*. See below how it's made (but it's better to look straight into the
+source code). Well, this is a case when we can just replace *G* with *F*
+everywhere, we use ``replaceAllUsesWith`` operation here (*RAUW*).
+
+2. *F* could not be overridden, while *G* could. It would be good to do the
+next: after merging the places where overridable function were used, still use
+overridable stub. So try to make *G* alias to *F*, or create overridable tail
+call wrapper around *F* and replace *G* with that call.
+
+3. Neither *F* nor *G* could be overridden. We can't use *RAUW*. We can just
+change the callers: call *F* instead of *G*. That's what
+``replaceDirectCallers`` does.
+
+Below is detailed body description.
+
+If âFâ may be overridden
+------------------------
+As follows from ``mayBeOverridden`` comments: âwhether the definition of this
+global may be replaced by something non-equivalent at link timeâ. If so, that's
+ok: we can use alias to *F* instead of *G* or change call instructions itself.
+
+HasGlobalAliases, removeUsers
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+First consider the case when we have global aliases of one function name to
+another. Our purpose is make both of them with aliases to the third strong
+function. Though if we keep *F* alive and without major changes we can leave it
+in ``FnTree``. Try to combine these two goals.
+
+Do stub replacement of *F* itself with an alias to *F*.
+
+1. Create stub function *H*, with the same name and attributes like function
+*F*. It takes maximum alignment of *F* and *G*.
+
+2. Replace all uses of function *F* with uses of function *H*. It is the two
+steps procedure instead. First of all, we must take into account, all functions
+from whom *F* is called would be changed: since we change the call argument
+(from *F* to *H*). If so we must to review these caller functions again after
+this procedure. We remove callers from ``FnTree``, method with name
+``removeUsers(F)`` does that (don't confuse with ``replaceAllUsesWith``):
+
+ 2.1. ``Inside removeUsers(Value*
+ V)`` we go through the all values that use value *V* (or *F* in our context).
+ If value is instruction, we go to function that holds this instruction and
+ mark it as to-be-analyzed-again (put to ``Deferred`` set), we also remove
+ caller from ``FnTree``.
+
+ 2.2. Now we can do the replacement: call ``F->replaceAllUsesWith(H)``.
+
+3. *H* (that now "officially" plays *F*'s role) is replaced with alias to *F*.
+Do the same with *G*: replace it with alias to *F*. So finally everywhere *F*
+was used, we use *H* and it is alias to *F*, and everywhere *G* was used we
+also have alias to *F*.
+
+4. Set *F* linkage to private. Make it strong :-)
+
+No global aliases, replaceDirectCallers
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+If global aliases are not supported. We call ``replaceDirectCallers`` then. Just
+go through all calls of *G* and replace it with calls of *F*. If you look into
+method you will see that it scans all uses of *G* too, and if use is callee (if
+user is call instruction and *G* is used as what to be called), we replace it
+with use of *F*.
+
+If âFâ could not be overridden, fix it!
+"""""""""""""""""""""""""""""""""""""""
+
+We call ``writeThunkOrAlias(Function *F, Function *G)``. Here we try to replace
+*G* with alias to *F* first. Next conditions are essential:
+
+* target should support global aliases,
+* the address itself of *G* should be not significant, not named and not
+ referenced anywhere,
+* function should come with external, local or weak linkage.
+
+Otherwise we write thunk: some wrapper that has *G's* interface and calls *F*,
+so *G* could be replaced with this wrapper.
+
+*writeAlias*
+
+As follows from *llvm* reference:
+
+âAliases act as *second name* for the aliasee valueâ. So we just want to create
+second name for *F* and use it instead of *G*:
+
+1. create global alias itself (*GA*),
+
+2. adjust alignment of *F* so it must be maximum of current and *G's* alignment;
+
+3. replace uses of *G*:
+
+ 3.1. first mark all callers of *G* as to-be-analyzed-again, using
+ ``removeUsers`` method (see chapter above),
+
+ 3.2. call ``G->replaceAllUsesWith(GA)``.
+
+4. Get rid of *G*.
+
+*writeThunk*
+
+As it written in method comments:
+
+âReplace G with a simple tail call to bitcast(F). Also replace direct uses of G
+with bitcast(F). Deletes G.â
+
+In general it does the same as usual when we want to replace callee, except the
+first point:
+
+1. We generate tail call wrapper around *F*, but with interface that allows use
+it instead of *G*.
+
+2. âAs-usualâ: ``removeUsers`` and ``replaceAllUsesWith`` then.
+
+3. Get rid of *G*.
+
+That's it.
+==========
+We have described how to detect equal functions, and how to merge them, and in
+first chapter we have described how it works all-together. Author hopes, reader
+have some picture from now, and it helps him improve and debug Âthis pass.
+
+Reader is welcomed to send us any questions and proposals ;-)
Added: www-releases/trunk/5.0.1/docs/_sources/NVPTXUsage.rst.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.1/docs/_sources/NVPTXUsage.rst.txt?rev=321287&view=auto
==============================================================================
--- www-releases/trunk/5.0.1/docs/_sources/NVPTXUsage.rst.txt (added)
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@@ -0,0 +1,972 @@
+=============================
+User Guide for NVPTX Back-end
+=============================
+
+.. contents::
+ :local:
+ :depth: 3
+
+
+Introduction
+============
+
+To support GPU programming, the NVPTX back-end supports a subset of LLVM IR
+along with a defined set of conventions used to represent GPU programming
+concepts. This document provides an overview of the general usage of the back-
+end, including a description of the conventions used and the set of accepted
+LLVM IR.
+
+.. note::
+
+ This document assumes a basic familiarity with CUDA and the PTX
+ assembly language. Information about the CUDA Driver API and the PTX assembly
+ language can be found in the `CUDA documentation
+ <http://docs.nvidia.com/cuda/index.html>`_.
+
+
+
+Conventions
+===========
+
+Marking Functions as Kernels
+----------------------------
+
+In PTX, there are two types of functions: *device functions*, which are only
+callable by device code, and *kernel functions*, which are callable by host
+code. By default, the back-end will emit device functions. Metadata is used to
+declare a function as a kernel function. This metadata is attached to the
+``nvvm.annotations`` named metadata object, and has the following format:
+
+.. code-block:: text
+
+ !0 = !{<function-ref>, metadata !"kernel", i32 1}
+
+The first parameter is a reference to the kernel function. The following
+example shows a kernel function calling a device function in LLVM IR. The
+function ``@my_kernel`` is callable from host code, but ``@my_fmad`` is not.
+
+.. code-block:: llvm
+
+ define float @my_fmad(float %x, float %y, float %z) {
+ %mul = fmul float %x, %y
+ %add = fadd float %mul, %z
+ ret float %add
+ }
+
+ define void @my_kernel(float* %ptr) {
+ %val = load float, float* %ptr
+ %ret = call float @my_fmad(float %val, float %val, float %val)
+ store float %ret, float* %ptr
+ ret void
+ }
+
+ !nvvm.annotations = !{!1}
+ !1 = !{void (float*)* @my_kernel, !"kernel", i32 1}
+
+When compiled, the PTX kernel functions are callable by host-side code.
+
+
+.. _address_spaces:
+
+Address Spaces
+--------------
+
+The NVPTX back-end uses the following address space mapping:
+
+ ============= ======================
+ Address Space Memory Space
+ ============= ======================
+ 0 Generic
+ 1 Global
+ 2 Internal Use
+ 3 Shared
+ 4 Constant
+ 5 Local
+ ============= ======================
+
+Every global variable and pointer type is assigned to one of these address
+spaces, with 0 being the default address space. Intrinsics are provided which
+can be used to convert pointers between the generic and non-generic address
+spaces.
+
+As an example, the following IR will define an array ``@g`` that resides in
+global device memory.
+
+.. code-block:: llvm
+
+ @g = internal addrspace(1) global [4 x i32] [ i32 0, i32 1, i32 2, i32 3 ]
+
+LLVM IR functions can read and write to this array, and host-side code can
+copy data to it by name with the CUDA Driver API.
+
+Note that since address space 0 is the generic space, it is illegal to have
+global variables in address space 0. Address space 0 is the default address
+space in LLVM, so the ``addrspace(N)`` annotation is *required* for global
+variables.
+
+
+Triples
+-------
+
+The NVPTX target uses the module triple to select between 32/64-bit code
+generation and the driver-compiler interface to use. The triple architecture
+can be one of ``nvptx`` (32-bit PTX) or ``nvptx64`` (64-bit PTX). The
+operating system should be one of ``cuda`` or ``nvcl``, which determines the
+interface used by the generated code to communicate with the driver. Most
+users will want to use ``cuda`` as the operating system, which makes the
+generated PTX compatible with the CUDA Driver API.
+
+Example: 32-bit PTX for CUDA Driver API: ``nvptx-nvidia-cuda``
+
+Example: 64-bit PTX for CUDA Driver API: ``nvptx64-nvidia-cuda``
+
+
+
+.. _nvptx_intrinsics:
+
+NVPTX Intrinsics
+================
+
+Address Space Conversion
+------------------------
+
+'``llvm.nvvm.ptr.*.to.gen``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+These are overloaded intrinsics. You can use these on any pointer types.
+
+.. code-block:: llvm
+
+ declare i8* @llvm.nvvm.ptr.global.to.gen.p0i8.p1i8(i8 addrspace(1)*)
+ declare i8* @llvm.nvvm.ptr.shared.to.gen.p0i8.p3i8(i8 addrspace(3)*)
+ declare i8* @llvm.nvvm.ptr.constant.to.gen.p0i8.p4i8(i8 addrspace(4)*)
+ declare i8* @llvm.nvvm.ptr.local.to.gen.p0i8.p5i8(i8 addrspace(5)*)
+
+Overview:
+"""""""""
+
+The '``llvm.nvvm.ptr.*.to.gen``' intrinsics convert a pointer in a non-generic
+address space to a generic address space pointer.
+
+Semantics:
+""""""""""
+
+These intrinsics modify the pointer value to be a valid generic address space
+pointer.
+
+
+'``llvm.nvvm.ptr.gen.to.*``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+These are overloaded intrinsics. You can use these on any pointer types.
+
+.. code-block:: llvm
+
+ declare i8 addrspace(1)* @llvm.nvvm.ptr.gen.to.global.p1i8.p0i8(i8*)
+ declare i8 addrspace(3)* @llvm.nvvm.ptr.gen.to.shared.p3i8.p0i8(i8*)
+ declare i8 addrspace(4)* @llvm.nvvm.ptr.gen.to.constant.p4i8.p0i8(i8*)
+ declare i8 addrspace(5)* @llvm.nvvm.ptr.gen.to.local.p5i8.p0i8(i8*)
+
+Overview:
+"""""""""
+
+The '``llvm.nvvm.ptr.gen.to.*``' intrinsics convert a pointer in the generic
+address space to a pointer in the target address space. Note that these
+intrinsics are only useful if the address space of the target address space of
+the pointer is known. It is not legal to use address space conversion
+intrinsics to convert a pointer from one non-generic address space to another
+non-generic address space.
+
+Semantics:
+""""""""""
+
+These intrinsics modify the pointer value to be a valid pointer in the target
+non-generic address space.
+
+
+Reading PTX Special Registers
+-----------------------------
+
+'``llvm.nvvm.read.ptx.sreg.*``'
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+.. code-block:: llvm
+
+ declare i32 @llvm.nvvm.read.ptx.sreg.tid.x()
+ declare i32 @llvm.nvvm.read.ptx.sreg.tid.y()
+ declare i32 @llvm.nvvm.read.ptx.sreg.tid.z()
+ declare i32 @llvm.nvvm.read.ptx.sreg.ntid.x()
+ declare i32 @llvm.nvvm.read.ptx.sreg.ntid.y()
+ declare i32 @llvm.nvvm.read.ptx.sreg.ntid.z()
+ declare i32 @llvm.nvvm.read.ptx.sreg.ctaid.x()
+ declare i32 @llvm.nvvm.read.ptx.sreg.ctaid.y()
+ declare i32 @llvm.nvvm.read.ptx.sreg.ctaid.z()
+ declare i32 @llvm.nvvm.read.ptx.sreg.nctaid.x()
+ declare i32 @llvm.nvvm.read.ptx.sreg.nctaid.y()
+ declare i32 @llvm.nvvm.read.ptx.sreg.nctaid.z()
+ declare i32 @llvm.nvvm.read.ptx.sreg.warpsize()
+
+Overview:
+"""""""""
+
+The '``@llvm.nvvm.read.ptx.sreg.*``' intrinsics provide access to the PTX
+special registers, in particular the kernel launch bounds. These registers
+map in the following way to CUDA builtins:
+
+ ============ =====================================
+ CUDA Builtin PTX Special Register Intrinsic
+ ============ =====================================
+ ``threadId`` ``@llvm.nvvm.read.ptx.sreg.tid.*``
+ ``blockIdx`` ``@llvm.nvvm.read.ptx.sreg.ctaid.*``
+ ``blockDim`` ``@llvm.nvvm.read.ptx.sreg.ntid.*``
+ ``gridDim`` ``@llvm.nvvm.read.ptx.sreg.nctaid.*``
+ ============ =====================================
+
+
+Barriers
+--------
+
+'``llvm.nvvm.barrier0``'
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+.. code-block:: llvm
+
+ declare void @llvm.nvvm.barrier0()
+
+Overview:
+"""""""""
+
+The '``@llvm.nvvm.barrier0()``' intrinsic emits a PTX ``bar.sync 0``
+instruction, equivalent to the ``__syncthreads()`` call in CUDA.
+
+
+Other Intrinsics
+----------------
+
+For the full set of NVPTX intrinsics, please see the
+``include/llvm/IR/IntrinsicsNVVM.td`` file in the LLVM source tree.
+
+
+.. _libdevice:
+
+Linking with Libdevice
+======================
+
+The CUDA Toolkit comes with an LLVM bitcode library called ``libdevice`` that
+implements many common mathematical functions. This library can be used as a
+high-performance math library for any compilers using the LLVM NVPTX target.
+The library can be found under ``nvvm/libdevice/`` in the CUDA Toolkit and
+there is a separate version for each compute architecture.
+
+For a list of all math functions implemented in libdevice, see
+`libdevice Users Guide <http://docs.nvidia.com/cuda/libdevice-users-guide/index.html>`_.
+
+To accommodate various math-related compiler flags that can affect code
+generation of libdevice code, the library code depends on a special LLVM IR
+pass (``NVVMReflect``) to handle conditional compilation within LLVM IR. This
+pass looks for calls to the ``@__nvvm_reflect`` function and replaces them
+with constants based on the defined reflection parameters. Such conditional
+code often follows a pattern:
+
+.. code-block:: c++
+
+ float my_function(float a) {
+ if (__nvvm_reflect("FASTMATH"))
+ return my_function_fast(a);
+ else
+ return my_function_precise(a);
+ }
+
+The default value for all unspecified reflection parameters is zero.
+
+The ``NVVMReflect`` pass should be executed early in the optimization
+pipeline, immediately after the link stage. The ``internalize`` pass is also
+recommended to remove unused math functions from the resulting PTX. For an
+input IR module ``module.bc``, the following compilation flow is recommended:
+
+1. Save list of external functions in ``module.bc``
+2. Link ``module.bc`` with ``libdevice.compute_XX.YY.bc``
+3. Internalize all functions not in list from (1)
+4. Eliminate all unused internal functions
+5. Run ``NVVMReflect`` pass
+6. Run standard optimization pipeline
+
+.. note::
+
+ ``linkonce`` and ``linkonce_odr`` linkage types are not suitable for the
+ libdevice functions. It is possible to link two IR modules that have been
+ linked against libdevice using different reflection variables.
+
+Since the ``NVVMReflect`` pass replaces conditionals with constants, it will
+often leave behind dead code of the form:
+
+.. code-block:: llvm
+
+ entry:
+ ..
+ br i1 true, label %foo, label %bar
+ foo:
+ ..
+ bar:
+ ; Dead code
+ ..
+
+Therefore, it is recommended that ``NVVMReflect`` is executed early in the
+optimization pipeline before dead-code elimination.
+
+The NVPTX TargetMachine knows how to schedule ``NVVMReflect`` at the beginning
+of your pass manager; just use the following code when setting up your pass
+manager:
+
+.. code-block:: c++
+
+ std::unique_ptr<TargetMachine> TM = ...;
+ PassManagerBuilder PMBuilder(...);
+ if (TM)
+ TM->adjustPassManager(PMBuilder);
+
+Reflection Parameters
+---------------------
+
+The libdevice library currently uses the following reflection parameters to
+control code generation:
+
+==================== ======================================================
+Flag Description
+==================== ======================================================
+``__CUDA_FTZ=[0,1]`` Use optimized code paths that flush subnormals to zero
+==================== ======================================================
+
+The value of this flag is determined by the "nvvm-reflect-ftz" module flag.
+The following sets the ftz flag to 1.
+
+.. code-block:: llvm
+
+ !llvm.module.flag = !{!0}
+ !0 = !{i32 4, !"nvvm-reflect-ftz", i32 1}
+
+(``i32 4`` indicates that the value set here overrides the value in another
+module we link with. See the `LangRef <LangRef.html#module-flags-metadata>`
+for details.)
+
+Executing PTX
+=============
+
+The most common way to execute PTX assembly on a GPU device is to use the CUDA
+Driver API. This API is a low-level interface to the GPU driver and allows for
+JIT compilation of PTX code to native GPU machine code.
+
+Initializing the Driver API:
+
+.. code-block:: c++
+
+ CUdevice device;
+ CUcontext context;
+
+ // Initialize the driver API
+ cuInit(0);
+ // Get a handle to the first compute device
+ cuDeviceGet(&device, 0);
+ // Create a compute device context
+ cuCtxCreate(&context, 0, device);
+
+JIT compiling a PTX string to a device binary:
+
+.. code-block:: c++
+
+ CUmodule module;
+ CUfunction function;
+
+ // JIT compile a null-terminated PTX string
+ cuModuleLoadData(&module, (void*)PTXString);
+
+ // Get a handle to the "myfunction" kernel function
+ cuModuleGetFunction(&function, module, "myfunction");
+
+For full examples of executing PTX assembly, please see the `CUDA Samples
+<https://developer.nvidia.com/cuda-downloads>`_ distribution.
+
+
+Common Issues
+=============
+
+ptxas complains of undefined function: __nvvm_reflect
+-----------------------------------------------------
+
+When linking with libdevice, the ``NVVMReflect`` pass must be used. See
+:ref:`libdevice` for more information.
+
+
+Tutorial: A Simple Compute Kernel
+=================================
+
+To start, let us take a look at a simple compute kernel written directly in
+LLVM IR. The kernel implements vector addition, where each thread computes one
+element of the output vector C from the input vectors A and B. To make this
+easier, we also assume that only a single CTA (thread block) will be launched,
+and that it will be one dimensional.
+
+
+The Kernel
+----------
+
+.. code-block:: llvm
+
+ target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v16:16:16-v32:32:32-v64:64:64-v128:128:128-n16:32:64"
+ target triple = "nvptx64-nvidia-cuda"
+
+ ; Intrinsic to read X component of thread ID
+ declare i32 @llvm.nvvm.read.ptx.sreg.tid.x() readnone nounwind
+
+ define void @kernel(float addrspace(1)* %A,
+ float addrspace(1)* %B,
+ float addrspace(1)* %C) {
+ entry:
+ ; What is my ID?
+ %id = tail call i32 @llvm.nvvm.read.ptx.sreg.tid.x() readnone nounwind
+
+ ; Compute pointers into A, B, and C
+ %ptrA = getelementptr float, float addrspace(1)* %A, i32 %id
+ %ptrB = getelementptr float, float addrspace(1)* %B, i32 %id
+ %ptrC = getelementptr float, float addrspace(1)* %C, i32 %id
+
+ ; Read A, B
+ %valA = load float, float addrspace(1)* %ptrA, align 4
+ %valB = load float, float addrspace(1)* %ptrB, align 4
+
+ ; Compute C = A + B
+ %valC = fadd float %valA, %valB
+
+ ; Store back to C
+ store float %valC, float addrspace(1)* %ptrC, align 4
+
+ ret void
+ }
+
+ !nvvm.annotations = !{!0}
+ !0 = !{void (float addrspace(1)*,
+ float addrspace(1)*,
+ float addrspace(1)*)* @kernel, !"kernel", i32 1}
+
+
+We can use the LLVM ``llc`` tool to directly run the NVPTX code generator:
+
+.. code-block:: text
+
+ # llc -mcpu=sm_20 kernel.ll -o kernel.ptx
+
+
+.. note::
+
+ If you want to generate 32-bit code, change ``p:64:64:64`` to ``p:32:32:32``
+ in the module data layout string and use ``nvptx-nvidia-cuda`` as the
+ target triple.
+
+
+The output we get from ``llc`` (as of LLVM 3.4):
+
+.. code-block:: text
+
+ //
+ // Generated by LLVM NVPTX Back-End
+ //
+
+ .version 3.1
+ .target sm_20
+ .address_size 64
+
+ // .globl kernel
+ // @kernel
+ .visible .entry kernel(
+ .param .u64 kernel_param_0,
+ .param .u64 kernel_param_1,
+ .param .u64 kernel_param_2
+ )
+ {
+ .reg .f32 %f<4>;
+ .reg .s32 %r<2>;
+ .reg .s64 %rl<8>;
+
+ // BB#0: // %entry
+ ld.param.u64 %rl1, [kernel_param_0];
+ mov.u32 %r1, %tid.x;
+ mul.wide.s32 %rl2, %r1, 4;
+ add.s64 %rl3, %rl1, %rl2;
+ ld.param.u64 %rl4, [kernel_param_1];
+ add.s64 %rl5, %rl4, %rl2;
+ ld.param.u64 %rl6, [kernel_param_2];
+ add.s64 %rl7, %rl6, %rl2;
+ ld.global.f32 %f1, [%rl3];
+ ld.global.f32 %f2, [%rl5];
+ add.f32 %f3, %f1, %f2;
+ st.global.f32 [%rl7], %f3;
+ ret;
+ }
+
+
+Dissecting the Kernel
+---------------------
+
+Now let us dissect the LLVM IR that makes up this kernel.
+
+Data Layout
+^^^^^^^^^^^
+
+The data layout string determines the size in bits of common data types, their
+ABI alignment, and their storage size. For NVPTX, you should use one of the
+following:
+
+32-bit PTX:
+
+.. code-block:: llvm
+
+ target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v16:16:16-v32:32:32-v64:64:64-v128:128:128-n16:32:64"
+
+64-bit PTX:
+
+.. code-block:: llvm
+
+ target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v16:16:16-v32:32:32-v64:64:64-v128:128:128-n16:32:64"
+
+
+Target Intrinsics
+^^^^^^^^^^^^^^^^^
+
+In this example, we use the ``@llvm.nvvm.read.ptx.sreg.tid.x`` intrinsic to
+read the X component of the current thread's ID, which corresponds to a read
+of register ``%tid.x`` in PTX. The NVPTX back-end supports a large set of
+intrinsics. A short list is shown below; please see
+``include/llvm/IR/IntrinsicsNVVM.td`` for the full list.
+
+
+================================================ ====================
+Intrinsic CUDA Equivalent
+================================================ ====================
+``i32 @llvm.nvvm.read.ptx.sreg.tid.{x,y,z}`` threadIdx.{x,y,z}
+``i32 @llvm.nvvm.read.ptx.sreg.ctaid.{x,y,z}`` blockIdx.{x,y,z}
+``i32 @llvm.nvvm.read.ptx.sreg.ntid.{x,y,z}`` blockDim.{x,y,z}
+``i32 @llvm.nvvm.read.ptx.sreg.nctaid.{x,y,z}`` gridDim.{x,y,z}
+``void @llvm.nvvm.barrier0()`` __syncthreads()
+================================================ ====================
+
+
+Address Spaces
+^^^^^^^^^^^^^^
+
+You may have noticed that all of the pointer types in the LLVM IR example had
+an explicit address space specifier. What is address space 1? NVIDIA GPU
+devices (generally) have four types of memory:
+
+- Global: Large, off-chip memory
+- Shared: Small, on-chip memory shared among all threads in a CTA
+- Local: Per-thread, private memory
+- Constant: Read-only memory shared across all threads
+
+These different types of memory are represented in LLVM IR as address spaces.
+There is also a fifth address space used by the NVPTX code generator that
+corresponds to the "generic" address space. This address space can represent
+addresses in any other address space (with a few exceptions). This allows
+users to write IR functions that can load/store memory using the same
+instructions. Intrinsics are provided to convert pointers between the generic
+and non-generic address spaces.
+
+See :ref:`address_spaces` and :ref:`nvptx_intrinsics` for more information.
+
+
+Kernel Metadata
+^^^^^^^^^^^^^^^
+
+In PTX, a function can be either a `kernel` function (callable from the host
+program), or a `device` function (callable only from GPU code). You can think
+of `kernel` functions as entry-points in the GPU program. To mark an LLVM IR
+function as a `kernel` function, we make use of special LLVM metadata. The
+NVPTX back-end will look for a named metadata node called
+``nvvm.annotations``. This named metadata must contain a list of metadata that
+describe the IR. For our purposes, we need to declare a metadata node that
+assigns the "kernel" attribute to the LLVM IR function that should be emitted
+as a PTX `kernel` function. These metadata nodes take the form:
+
+.. code-block:: text
+
+ !{<function ref>, metadata !"kernel", i32 1}
+
+For the previous example, we have:
+
+.. code-block:: llvm
+
+ !nvvm.annotations = !{!0}
+ !0 = !{void (float addrspace(1)*,
+ float addrspace(1)*,
+ float addrspace(1)*)* @kernel, !"kernel", i32 1}
+
+Here, we have a single metadata declaration in ``nvvm.annotations``. This
+metadata annotates our ``@kernel`` function with the ``kernel`` attribute.
+
+
+Running the Kernel
+------------------
+
+Generating PTX from LLVM IR is all well and good, but how do we execute it on
+a real GPU device? The CUDA Driver API provides a convenient mechanism for
+loading and JIT compiling PTX to a native GPU device, and launching a kernel.
+The API is similar to OpenCL. A simple example showing how to load and
+execute our vector addition code is shown below. Note that for brevity this
+code does not perform much error checking!
+
+.. note::
+
+ You can also use the ``ptxas`` tool provided by the CUDA Toolkit to offline
+ compile PTX to machine code (SASS) for a specific GPU architecture. Such
+ binaries can be loaded by the CUDA Driver API in the same way as PTX. This
+ can be useful for reducing startup time by precompiling the PTX kernels.
+
+
+.. code-block:: c++
+
+ #include <iostream>
+ #include <fstream>
+ #include <cassert>
+ #include "cuda.h"
+
+
+ void checkCudaErrors(CUresult err) {
+ assert(err == CUDA_SUCCESS);
+ }
+
+ /// main - Program entry point
+ int main(int argc, char **argv) {
+ CUdevice device;
+ CUmodule cudaModule;
+ CUcontext context;
+ CUfunction function;
+ CUlinkState linker;
+ int devCount;
+
+ // CUDA initialization
+ checkCudaErrors(cuInit(0));
+ checkCudaErrors(cuDeviceGetCount(&devCount));
+ checkCudaErrors(cuDeviceGet(&device, 0));
+
+ char name[128];
+ checkCudaErrors(cuDeviceGetName(name, 128, device));
+ std::cout << "Using CUDA Device [0]: " << name << "\n";
+
+ int devMajor, devMinor;
+ checkCudaErrors(cuDeviceComputeCapability(&devMajor, &devMinor, device));
+ std::cout << "Device Compute Capability: "
+ << devMajor << "." << devMinor << "\n";
+ if (devMajor < 2) {
+ std::cerr << "ERROR: Device 0 is not SM 2.0 or greater\n";
+ return 1;
+ }
+
+ std::ifstream t("kernel.ptx");
+ if (!t.is_open()) {
+ std::cerr << "kernel.ptx not found\n";
+ return 1;
+ }
+ std::string str((std::istreambuf_iterator<char>(t)),
+ std::istreambuf_iterator<char>());
+
+ // Create driver context
+ checkCudaErrors(cuCtxCreate(&context, 0, device));
+
+ // Create module for object
+ checkCudaErrors(cuModuleLoadDataEx(&cudaModule, str.c_str(), 0, 0, 0));
+
+ // Get kernel function
+ checkCudaErrors(cuModuleGetFunction(&function, cudaModule, "kernel"));
+
+ // Device data
+ CUdeviceptr devBufferA;
+ CUdeviceptr devBufferB;
+ CUdeviceptr devBufferC;
+
+ checkCudaErrors(cuMemAlloc(&devBufferA, sizeof(float)*16));
+ checkCudaErrors(cuMemAlloc(&devBufferB, sizeof(float)*16));
+ checkCudaErrors(cuMemAlloc(&devBufferC, sizeof(float)*16));
+
+ float* hostA = new float[16];
+ float* hostB = new float[16];
+ float* hostC = new float[16];
+
+ // Populate input
+ for (unsigned i = 0; i != 16; ++i) {
+ hostA[i] = (float)i;
+ hostB[i] = (float)(2*i);
+ hostC[i] = 0.0f;
+ }
+
+ checkCudaErrors(cuMemcpyHtoD(devBufferA, &hostA[0], sizeof(float)*16));
+ checkCudaErrors(cuMemcpyHtoD(devBufferB, &hostB[0], sizeof(float)*16));
+
+
+ unsigned blockSizeX = 16;
+ unsigned blockSizeY = 1;
+ unsigned blockSizeZ = 1;
+ unsigned gridSizeX = 1;
+ unsigned gridSizeY = 1;
+ unsigned gridSizeZ = 1;
+
+ // Kernel parameters
+ void *KernelParams[] = { &devBufferA, &devBufferB, &devBufferC };
+
+ std::cout << "Launching kernel\n";
+
+ // Kernel launch
+ checkCudaErrors(cuLaunchKernel(function, gridSizeX, gridSizeY, gridSizeZ,
+ blockSizeX, blockSizeY, blockSizeZ,
+ 0, NULL, KernelParams, NULL));
+
+ // Retrieve device data
+ checkCudaErrors(cuMemcpyDtoH(&hostC[0], devBufferC, sizeof(float)*16));
+
+
+ std::cout << "Results:\n";
+ for (unsigned i = 0; i != 16; ++i) {
+ std::cout << hostA[i] << " + " << hostB[i] << " = " << hostC[i] << "\n";
+ }
+
+
+ // Clean up after ourselves
+ delete [] hostA;
+ delete [] hostB;
+ delete [] hostC;
+
+ // Clean-up
+ checkCudaErrors(cuMemFree(devBufferA));
+ checkCudaErrors(cuMemFree(devBufferB));
+ checkCudaErrors(cuMemFree(devBufferC));
+ checkCudaErrors(cuModuleUnload(cudaModule));
+ checkCudaErrors(cuCtxDestroy(context));
+
+ return 0;
+ }
+
+
+You will need to link with the CUDA driver and specify the path to cuda.h.
+
+.. code-block:: text
+
+ # clang++ sample.cpp -o sample -O2 -g -I/usr/local/cuda-5.5/include -lcuda
+
+We don't need to specify a path to ``libcuda.so`` since this is installed in a
+system location by the driver, not the CUDA toolkit.
+
+If everything goes as planned, you should see the following output when
+running the compiled program:
+
+.. code-block:: text
+
+ Using CUDA Device [0]: GeForce GTX 680
+ Device Compute Capability: 3.0
+ Launching kernel
+ Results:
+ 0 + 0 = 0
+ 1 + 2 = 3
+ 2 + 4 = 6
+ 3 + 6 = 9
+ 4 + 8 = 12
+ 5 + 10 = 15
+ 6 + 12 = 18
+ 7 + 14 = 21
+ 8 + 16 = 24
+ 9 + 18 = 27
+ 10 + 20 = 30
+ 11 + 22 = 33
+ 12 + 24 = 36
+ 13 + 26 = 39
+ 14 + 28 = 42
+ 15 + 30 = 45
+
+.. note::
+
+ You will likely see a different device identifier based on your hardware
+
+
+Tutorial: Linking with Libdevice
+================================
+
+In this tutorial, we show a simple example of linking LLVM IR with the
+libdevice library. We will use the same kernel as the previous tutorial,
+except that we will compute ``C = pow(A, B)`` instead of ``C = A + B``.
+Libdevice provides an ``__nv_powf`` function that we will use.
+
+.. code-block:: llvm
+
+ target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v16:16:16-v32:32:32-v64:64:64-v128:128:128-n16:32:64"
+ target triple = "nvptx64-nvidia-cuda"
+
+ ; Intrinsic to read X component of thread ID
+ declare i32 @llvm.nvvm.read.ptx.sreg.tid.x() readnone nounwind
+ ; libdevice function
+ declare float @__nv_powf(float, float)
+
+ define void @kernel(float addrspace(1)* %A,
+ float addrspace(1)* %B,
+ float addrspace(1)* %C) {
+ entry:
+ ; What is my ID?
+ %id = tail call i32 @llvm.nvvm.read.ptx.sreg.tid.x() readnone nounwind
+
+ ; Compute pointers into A, B, and C
+ %ptrA = getelementptr float, float addrspace(1)* %A, i32 %id
+ %ptrB = getelementptr float, float addrspace(1)* %B, i32 %id
+ %ptrC = getelementptr float, float addrspace(1)* %C, i32 %id
+
+ ; Read A, B
+ %valA = load float, float addrspace(1)* %ptrA, align 4
+ %valB = load float, float addrspace(1)* %ptrB, align 4
+
+ ; Compute C = pow(A, B)
+ %valC = call float @__nv_powf(float %valA, float %valB)
+
+ ; Store back to C
+ store float %valC, float addrspace(1)* %ptrC, align 4
+
+ ret void
+ }
+
+ !nvvm.annotations = !{!0}
+ !0 = !{void (float addrspace(1)*,
+ float addrspace(1)*,
+ float addrspace(1)*)* @kernel, !"kernel", i32 1}
+
+
+To compile this kernel, we perform the following steps:
+
+1. Link with libdevice
+2. Internalize all but the public kernel function
+3. Run ``NVVMReflect`` and set ``__CUDA_FTZ`` to 0
+4. Optimize the linked module
+5. Codegen the module
+
+
+These steps can be performed by the LLVM ``llvm-link``, ``opt``, and ``llc``
+tools. In a complete compiler, these steps can also be performed entirely
+programmatically by setting up an appropriate pass configuration (see
+:ref:`libdevice`).
+
+.. code-block:: text
+
+ # llvm-link t2.bc libdevice.compute_20.10.bc -o t2.linked.bc
+ # opt -internalize -internalize-public-api-list=kernel -nvvm-reflect-list=__CUDA_FTZ=0 -nvvm-reflect -O3 t2.linked.bc -o t2.opt.bc
+ # llc -mcpu=sm_20 t2.opt.bc -o t2.ptx
+
+.. note::
+
+ The ``-nvvm-reflect-list=_CUDA_FTZ=0`` is not strictly required, as any
+ undefined variables will default to zero. It is shown here for evaluation
+ purposes.
+
+
+This gives us the following PTX (excerpt):
+
+.. code-block:: text
+
+ //
+ // Generated by LLVM NVPTX Back-End
+ //
+
+ .version 3.1
+ .target sm_20
+ .address_size 64
+
+ // .globl kernel
+ // @kernel
+ .visible .entry kernel(
+ .param .u64 kernel_param_0,
+ .param .u64 kernel_param_1,
+ .param .u64 kernel_param_2
+ )
+ {
+ .reg .pred %p<30>;
+ .reg .f32 %f<111>;
+ .reg .s32 %r<21>;
+ .reg .s64 %rl<8>;
+
+ // BB#0: // %entry
+ ld.param.u64 %rl2, [kernel_param_0];
+ mov.u32 %r3, %tid.x;
+ ld.param.u64 %rl3, [kernel_param_1];
+ mul.wide.s32 %rl4, %r3, 4;
+ add.s64 %rl5, %rl2, %rl4;
+ ld.param.u64 %rl6, [kernel_param_2];
+ add.s64 %rl7, %rl3, %rl4;
+ add.s64 %rl1, %rl6, %rl4;
+ ld.global.f32 %f1, [%rl5];
+ ld.global.f32 %f2, [%rl7];
+ setp.eq.f32 %p1, %f1, 0f3F800000;
+ setp.eq.f32 %p2, %f2, 0f00000000;
+ or.pred %p3, %p1, %p2;
+ @%p3 bra BB0_1;
+ bra.uni BB0_2;
+ BB0_1:
+ mov.f32 %f110, 0f3F800000;
+ st.global.f32 [%rl1], %f110;
+ ret;
+ BB0_2: // %__nv_isnanf.exit.i
+ abs.f32 %f4, %f1;
+ setp.gtu.f32 %p4, %f4, 0f7F800000;
+ @%p4 bra BB0_4;
+ // BB#3: // %__nv_isnanf.exit5.i
+ abs.f32 %f5, %f2;
+ setp.le.f32 %p5, %f5, 0f7F800000;
+ @%p5 bra BB0_5;
+ BB0_4: // %.critedge1.i
+ add.f32 %f110, %f1, %f2;
+ st.global.f32 [%rl1], %f110;
+ ret;
+ BB0_5: // %__nv_isinff.exit.i
+
+ ...
+
+ BB0_26: // %__nv_truncf.exit.i.i.i.i.i
+ mul.f32 %f90, %f107, 0f3FB8AA3B;
+ cvt.rzi.f32.f32 %f91, %f90;
+ mov.f32 %f92, 0fBF317200;
+ fma.rn.f32 %f93, %f91, %f92, %f107;
+ mov.f32 %f94, 0fB5BFBE8E;
+ fma.rn.f32 %f95, %f91, %f94, %f93;
+ mul.f32 %f89, %f95, 0f3FB8AA3B;
+ // inline asm
+ ex2.approx.ftz.f32 %f88,%f89;
+ // inline asm
+ add.f32 %f96, %f91, 0f00000000;
+ ex2.approx.f32 %f97, %f96;
+ mul.f32 %f98, %f88, %f97;
+ setp.lt.f32 %p15, %f107, 0fC2D20000;
+ selp.f32 %f99, 0f00000000, %f98, %p15;
+ setp.gt.f32 %p16, %f107, 0f42D20000;
+ selp.f32 %f110, 0f7F800000, %f99, %p16;
+ setp.eq.f32 %p17, %f110, 0f7F800000;
+ @%p17 bra BB0_28;
+ // BB#27:
+ fma.rn.f32 %f110, %f110, %f108, %f110;
+ BB0_28: // %__internal_accurate_powf.exit.i
+ setp.lt.f32 %p18, %f1, 0f00000000;
+ setp.eq.f32 %p19, %f3, 0f3F800000;
+ and.pred %p20, %p18, %p19;
+ @!%p20 bra BB0_30;
+ bra.uni BB0_29;
+ BB0_29:
+ mov.b32 %r9, %f110;
+ xor.b32 %r10, %r9, -2147483648;
+ mov.b32 %f110, %r10;
+ BB0_30: // %__nv_powf.exit
+ st.global.f32 [%rl1], %f110;
+ ret;
+ }
+
Added: www-releases/trunk/5.0.1/docs/_sources/OptBisect.rst.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.1/docs/_sources/OptBisect.rst.txt?rev=321287&view=auto
==============================================================================
--- www-releases/trunk/5.0.1/docs/_sources/OptBisect.rst.txt (added)
+++ www-releases/trunk/5.0.1/docs/_sources/OptBisect.rst.txt Thu Dec 21 10:09:53 2017
@@ -0,0 +1,193 @@
+====================================================
+Using -opt-bisect-limit to debug optimization errors
+====================================================
+.. contents::
+ :local:
+ :depth: 1
+
+Introduction
+============
+
+The -opt-bisect-limit option provides a way to disable all optimization passes
+above a specified limit without modifying the way in which the Pass Managers
+are populated. The intention of this option is to assist in tracking down
+problems where incorrect transformations during optimization result in incorrect
+run-time behavior.
+
+This feature is implemented on an opt-in basis. Passes which can be safely
+skipped while still allowing correct code generation call a function to
+check the opt-bisect limit before performing optimizations. Passes which
+either must be run or do not modify the IR do not perform this check and are
+therefore never skipped. Generally, this means analysis passes, passes
+that are run at CodeGenOpt::None and passes which are required for register
+allocation.
+
+The -opt-bisect-limit option can be used with any tool, including front ends
+such as clang, that uses the core LLVM library for optimization and code
+generation. The exact syntax for invoking the option is discussed below.
+
+This feature is not intended to replace other debugging tools such as bugpoint.
+Rather it provides an alternate course of action when reproducing the problem
+requires a complex build infrastructure that would make using bugpoint
+impractical or when reproducing the failure requires a sequence of
+transformations that is difficult to replicate with tools like opt and llc.
+
+
+Getting Started
+===============
+
+The -opt-bisect-limit command line option can be passed directly to tools such
+as opt, llc and lli. The syntax is as follows:
+
+::
+
+ <tool name> [other options] -opt-bisect-limit=<limit>
+
+If a value of -1 is used the tool will perform all optimizations but a message
+will be printed to stderr for each optimization that could be skipped
+indicating the index value that is associated with that optimization. To skip
+optimizations, pass the value of the last optimization to be performed as the
+opt-bisect-limit. All optimizations with a higher index value will be skipped.
+
+In order to use the -opt-bisect-limit option with a driver that provides a
+wrapper around the LLVM core library, an additional prefix option may be
+required, as defined by the driver. For example, to use this option with
+clang, the "-mllvm" prefix must be used. A typical clang invocation would look
+like this:
+
+::
+
+ clang -O2 -mllvm -opt-bisect-limit=256 my_file.c
+
+The -opt-bisect-limit option may also be applied to link-time optimizations by
+using a prefix to indicate that this is a plug-in option for the linker. The
+following syntax will set a bisect limit for LTO transformations:
+
+::
+
+ # When using lld, or ld64 (macOS)
+ clang -flto -Wl,-mllvm,-opt-bisect-limit=256 my_file.o my_other_file.o
+ # When using Gold
+ clang -flto -Wl,-plugin-opt,-opt-bisect-limit=256 my_file.o my_other_file.o
+
+LTO passes are run by a library instance invoked by the linker. Therefore any
+passes run in the primary driver compilation phase are not affected by options
+passed via '-Wl,-plugin-opt' and LTO passes are not affected by options
+passed to the driver-invoked LLVM invocation via '-mllvm'.
+
+
+Bisection Index Values
+======================
+
+The granularity of the optimizations associated with a single index value is
+variable. Depending on how the optimization pass has been instrumented the
+value may be associated with as much as all transformations that would have
+been performed by an optimization pass on an IR unit for which it is invoked
+(for instance, during a single call of runOnFunction for a FunctionPass) or as
+little as a single transformation. The index values may also be nested so that
+if an invocation of the pass is not skipped individual transformations within
+that invocation may still be skipped.
+
+The order of the values assigned is guaranteed to remain stable and consistent
+from one run to the next up to and including the value specified as the limit.
+Above the limit value skipping of optimizations can cause a change in the
+numbering, but because all optimizations above the limit are skipped this
+is not a problem.
+
+When an opt-bisect index value refers to an entire invocation of the run
+function for a pass, the pass will query whether or not it should be skipped
+each time it is invoked and each invocation will be assigned a unique value.
+For example, if a FunctionPass is used with a module containing three functions
+a different index value will be assigned to the pass for each of the functions
+as the pass is run. The pass may be run on two functions but skipped for the
+third.
+
+If the pass internally performs operations on a smaller IR unit the pass must be
+specifically instrumented to enable bisection at this finer level of granularity
+(see below for details).
+
+
+Example Usage
+=============
+
+.. code-block:: console
+
+ $ opt -O2 -o test-opt.bc -opt-bisect-limit=16 test.ll
+
+ BISECT: running pass (1) Simplify the CFG on function (g)
+ BISECT: running pass (2) SROA on function (g)
+ BISECT: running pass (3) Early CSE on function (g)
+ BISECT: running pass (4) Infer set function attributes on module (test.ll)
+ BISECT: running pass (5) Interprocedural Sparse Conditional Constant Propagation on module (test.ll)
+ BISECT: running pass (6) Global Variable Optimizer on module (test.ll)
+ BISECT: running pass (7) Promote Memory to Register on function (g)
+ BISECT: running pass (8) Dead Argument Elimination on module (test.ll)
+ BISECT: running pass (9) Combine redundant instructions on function (g)
+ BISECT: running pass (10) Simplify the CFG on function (g)
+ BISECT: running pass (11) Remove unused exception handling info on SCC (<<null function>>)
+ BISECT: running pass (12) Function Integration/Inlining on SCC (<<null function>>)
+ BISECT: running pass (13) Deduce function attributes on SCC (<<null function>>)
+ BISECT: running pass (14) Remove unused exception handling info on SCC (f)
+ BISECT: running pass (15) Function Integration/Inlining on SCC (f)
+ BISECT: running pass (16) Deduce function attributes on SCC (f)
+ BISECT: NOT running pass (17) Remove unused exception handling info on SCC (g)
+ BISECT: NOT running pass (18) Function Integration/Inlining on SCC (g)
+ BISECT: NOT running pass (19) Deduce function attributes on SCC (g)
+ BISECT: NOT running pass (20) SROA on function (g)
+ BISECT: NOT running pass (21) Early CSE on function (g)
+ BISECT: NOT running pass (22) Speculatively execute instructions if target has divergent branches on function (g)
+ ... etc. ...
+
+
+Pass Skipping Implementation
+============================
+
+The -opt-bisect-limit implementation depends on individual passes opting in to
+the opt-bisect process. The OptBisect object that manages the process is
+entirely passive and has no knowledge of how any pass is implemented. When a
+pass is run if the pass may be skipped, it should call the OptBisect object to
+see if it should be skipped.
+
+The OptBisect object is intended to be accessed through LLVMContext and each
+Pass base class contains a helper function that abstracts the details in order
+to make this check uniform across all passes. These helper functions are:
+
+.. code-block:: c++
+
+ bool ModulePass::skipModule(Module &M);
+ bool CallGraphSCCPass::skipSCC(CallGraphSCC &SCC);
+ bool FunctionPass::skipFunction(const Function &F);
+ bool BasicBlockPass::skipBasicBlock(const BasicBlock &BB);
+ bool LoopPass::skipLoop(const Loop *L);
+
+A MachineFunctionPass should use FunctionPass::skipFunction() as such:
+
+.. code-block:: c++
+
+ bool MyMachineFunctionPass::runOnMachineFunction(Function &MF) {
+ if (skipFunction(*MF.getFunction())
+ return false;
+ // Otherwise, run the pass normally.
+ }
+
+In addition to checking with the OptBisect class to see if the pass should be
+skipped, the skipFunction(), skipLoop() and skipBasicBlock() helper functions
+also look for the presence of the "optnone" function attribute. The calling
+pass will be unable to determine whether it is being skipped because the
+"optnone" attribute is present or because the opt-bisect-limit has been
+reached. This is desirable because the behavior should be the same in either
+case.
+
+The majority of LLVM passes which can be skipped have already been instrumented
+in the manner described above. If you are adding a new pass or believe you
+have found a pass which is not being included in the opt-bisect process but
+should be, you can add it as described above.
+
+
+Adding Finer Granularity
+========================
+
+Once the pass in which an incorrect transformation is performed has been
+determined, it may be useful to perform further analysis in order to determine
+which specific transformation is causing the problem. Debug counters
+can be used for this purpose.
Added: www-releases/trunk/5.0.1/docs/_sources/PDB/CodeViewSymbols.rst.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.1/docs/_sources/PDB/CodeViewSymbols.rst.txt?rev=321287&view=auto
==============================================================================
--- www-releases/trunk/5.0.1/docs/_sources/PDB/CodeViewSymbols.rst.txt (added)
+++ www-releases/trunk/5.0.1/docs/_sources/PDB/CodeViewSymbols.rst.txt Thu Dec 21 10:09:53 2017
@@ -0,0 +1,4 @@
+=====================================
+CodeView Symbol Records
+=====================================
+
Added: www-releases/trunk/5.0.1/docs/_sources/PDB/CodeViewTypes.rst.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.1/docs/_sources/PDB/CodeViewTypes.rst.txt?rev=321287&view=auto
==============================================================================
--- www-releases/trunk/5.0.1/docs/_sources/PDB/CodeViewTypes.rst.txt (added)
+++ www-releases/trunk/5.0.1/docs/_sources/PDB/CodeViewTypes.rst.txt Thu Dec 21 10:09:53 2017
@@ -0,0 +1,4 @@
+=====================================
+CodeView Type Records
+=====================================
+
Added: www-releases/trunk/5.0.1/docs/_sources/PDB/DbiStream.rst.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.1/docs/_sources/PDB/DbiStream.rst.txt?rev=321287&view=auto
==============================================================================
--- www-releases/trunk/5.0.1/docs/_sources/PDB/DbiStream.rst.txt (added)
+++ www-releases/trunk/5.0.1/docs/_sources/PDB/DbiStream.rst.txt Thu Dec 21 10:09:53 2017
@@ -0,0 +1,445 @@
+=====================================
+The PDB DBI (Debug Info) Stream
+=====================================
+
+.. contents::
+ :local:
+
+.. _dbi_intro:
+
+Introduction
+============
+
+The PDB DBI Stream (Index 3) is one of the largest and most important streams
+in a PDB file. It contains information about how the program was compiled,
+(e.g. compilation flags, etc), the compilands (e.g. object files) that
+were used to link together the program, the source files which were used
+to build the program, as well as references to other streams that contain more
+detailed information about each compiland, such as the CodeView symbol records
+contained within each compiland and the source and line information for
+functions and other symbols within each compiland.
+
+
+.. _dbi_header:
+
+Stream Header
+=============
+At offset 0 of the DBI Stream is a header with the following layout:
+
+
+.. code-block:: c++
+
+ struct DbiStreamHeader {
+ int32_t VersionSignature;
+ uint32_t VersionHeader;
+ uint32_t Age;
+ uint16_t GlobalStreamIndex;
+ uint16_t BuildNumber;
+ uint16_t PublicStreamIndex;
+ uint16_t PdbDllVersion;
+ uint16_t SymRecordStream;
+ uint16_t PdbDllRbld;
+ int32_t ModInfoSize;
+ int32_t SectionContributionSize;
+ int32_t SectionMapSize;
+ int32_t SourceInfoSize;
+ int32_t TypeServerSize;
+ uint32_t MFCTypeServerIndex;
+ int32_t OptionalDbgHeaderSize;
+ int32_t ECSubstreamSize;
+ uint16_t Flags;
+ uint16_t Machine;
+ uint32_t Padding;
+ };
+
+- **VersionSignature** - Unknown meaning. Appears to always be ``-1``.
+
+- **VersionHeader** - A value from the following enum.
+
+.. code-block:: c++
+
+ enum class DbiStreamVersion : uint32_t {
+ VC41 = 930803,
+ V50 = 19960307,
+ V60 = 19970606,
+ V70 = 19990903,
+ V110 = 20091201
+ };
+
+Similar to the :doc:`PDB Stream <PdbStream>`, this value always appears to be
+``V70``, and it is not clear what the other values are for.
+
+- **Age** - The number of times the PDB has been written. Equal to the same
+ field from the :ref:`PDB Stream header <pdb_stream_header>`.
+
+- **GlobalStreamIndex** - The index of the :doc:`Global Symbol Stream <GlobalStream>`,
+ which contains CodeView symbol records for all global symbols. Actual records
+ are stored in the symbol record stream, and are referenced from this stream.
+
+- **BuildNumber** - A bitfield containing values representing the major and minor
+ version number of the toolchain (e.g. 12.0 for MSVC 2013) used to build the
+ program, with the following layout:
+
+.. code-block:: c++
+
+ uint16_t MinorVersion : 8;
+ uint16_t MajorVersion : 7;
+ uint16_t NewVersionFormat : 1;
+
+For the purposes of LLVM, we assume ``NewVersionFormat`` to be always ``true``.
+If it is ``false``, the layout above does not apply and the reader should consult
+the `Microsoft Source Code <https://github.com/Microsoft/microsoft-pdb>`__ for
+further guidance.
+
+- **PublicStreamIndex** - The index of the :doc:`Public Symbol Stream <PublicStream>`,
+ which contains CodeView symbol records for all public symbols. Actual records
+ are stored in the symbol record stream, and are referenced from this stream.
+
+- **PdbDllVersion** - The version number of ``mspdbXXXX.dll`` used to produce this
+ PDB. Note this obviously does not apply for LLVM as LLVM does not use ``mspdb.dll``.
+
+- **SymRecordStream** - The stream containing all CodeView symbol records used
+ by the program. This is used for deduplication, so that many different
+ compilands can refer to the same symbols without having to include the full record
+ content inside of each module stream.
+
+- **PdbDllRbld** - Unknown
+
+- **MFCTypeServerIndex** - The length of the :ref:dbi_mfc_type_server_substream
+
+- **Flags** - A bitfield with the following layout, containing various
+ information about how the program was built:
+
+.. code-block:: c++
+
+ uint16_t WasIncrementallyLinked : 1;
+ uint16_t ArePrivateSymbolsStripped : 1;
+ uint16_t HasConflictingTypes : 1;
+ uint16_t Reserved : 13;
+
+The only one of these that is not self-explanatory is ``HasConflictingTypes``.
+Although undocumented, ``link.exe`` contains a hidden flag ``/DEBUG:CTYPES``.
+If it is passed to ``link.exe``, this field will be set. Otherwise it will
+not be set. It is unclear what this flag does, although it seems to have
+subtle implications on the algorithm used to look up type records.
+
+- **Machine** - A value from the `CV_CPU_TYPE_e <https://msdn.microsoft.com/en-us/library/b2fc64ek.aspx>`__
+ enumeration. Common values are ``0x8664`` (x86-64) and ``0x14C`` (x86).
+
+Immediately after the fixed-size DBI Stream header are ``7`` variable-length
+`substreams`. The following ``7`` fields of the DBI Stream header specify the
+number of bytes of the corresponding substream. Each substream's contents will
+be described in detail :ref:`below <dbi_substreams>`. The length of the entire
+DBI Stream should equal ``64`` (the length of the header above) plus the value
+of each of the following ``7`` fields.
+
+- **ModInfoSize** - The length of the :ref:`dbi_mod_info_substream`.
+
+- **SectionContributionSize** - The length of the :ref:`dbi_sec_contr_substream`.
+
+- **SectionMapSize** - The length of the :ref:`dbi_section_map_substream`.
+
+- **SourceInfoSize** - The length of the :ref:`dbi_file_info_substream`.
+
+- **TypeServerSize** - The length of the :ref:`dbi_type_server_substream`.
+
+- **OptionalDbgHeaderSize** - The length of the :ref:`dbi_optional_dbg_stream`.
+
+- **ECSubstreamSize** - The length of the :ref:`dbi_ec_substream`.
+
+.. _dbi_substreams:
+
+Substreams
+==========
+
+.. _dbi_mod_info_substream:
+
+Module Info Substream
+^^^^^^^^^^^^^^^^^^^^^
+
+Begins at offset ``0`` immediately after the :ref:`header <dbi_header>`. The
+module info substream is an array of variable-length records, each one
+describing a single module (e.g. object file) linked into the program. Each
+record in the array has the format:
+
+.. code-block:: c++
+
+ struct SectionContribEntry {
+ uint16_t Section;
+ char Padding1[2];
+ int32_t Offset;
+ int32_t Size;
+ uint32_t Characteristics;
+ uint16_t ModuleIndex;
+ char Padding2[2];
+ uint32_t DataCrc;
+ uint32_t RelocCrc;
+ };
+
+While most of these are self-explanatory, the ``Characteristics`` field
+warrants some elaboration. It corresponds to the ``Characteristics``
+field of the `IMAGE_SECTION_HEADER <https://msdn.microsoft.com/en-us/library/windows/desktop/ms680341(v=vs.85).aspx>`__
+structure.
+
+.. code-block:: c++
+
+ struct ModInfo {
+ uint32_t Unused1;
+ SectionContribEntry SectionContr;
+ uint16_t Flags;
+ uint16_t ModuleSymStream;
+ uint32_t SymByteSize;
+ uint32_t C11ByteSize;
+ uint32_t C13ByteSize;
+ uint16_t SourceFileCount;
+ char Padding[2];
+ uint32_t Unused2;
+ uint32_t SourceFileNameIndex;
+ uint32_t PdbFilePathNameIndex;
+ char ModuleName[];
+ char ObjFileName[];
+ };
+
+- **SectionContr** - Describes the properties of the section in the final binary
+ which contain the code and data from this module.
+
+- **Flags** - A bitfield with the following format:
+
+.. code-block:: c++
+
+ uint16_t Dirty : 1; // ``true`` if this ModInfo has been written since reading the PDB.
+ uint16_t EC : 1; // ``true`` if EC information is present for this module. It is unknown what EC actually is.
+ uint16_t Unused : 6;
+ uint16_t TSM : 8; // Type Server Index for this module. It is unknown what this is used for, but it is not used by LLVM.
+
+
+- **ModuleSymStream** - The index of the stream that contains symbol information
+ for this module. This includes CodeView symbol information as well as source
+ and line information.
+
+- **SymByteSize** - The number of bytes of data from the stream identified by
+ ``ModuleSymStream`` that represent CodeView symbol records.
+
+- **C11ByteSize** - The number of bytes of data from the stream identified by
+ ``ModuleSymStream`` that represent C11-style CodeView line information.
+
+- **C13ByteSize** - The number of bytes of data from the stream identified by
+ ``ModuleSymStream`` that represent C13-style CodeView line information. At
+ most one of ``C11ByteSize`` and ``C13ByteSize`` will be non-zero.
+
+- **SourceFileCount** - The number of source files that contributed to this
+ module during compilation.
+
+- **SourceFileNameIndex** - The offset in the names buffer of the primary
+ translation unit used to build this module. All PDB files observed to date
+ always have this value equal to 0.
+
+- **PdbFilePathNameIndex** - The offset in the names buffer of the PDB file
+ containing this module's symbol information. This has only been observed
+ to be non-zero for the special ``* Linker *`` module.
+
+- **ModuleName** - The module name. This is usually either a full path to an
+ object file (either directly passed to ``link.exe`` or from an archive) or
+ a string of the form ``Import:<dll name>``.
+
+- **ObjFileName** - The object file name. In the case of an module that is
+ linked directly passed to ``link.exe``, this is the same as **ModuleName**.
+ In the case of a module that comes from an archive, this is usually the full
+ path to the archive.
+
+.. _dbi_sec_contr_substream:
+
+Section Contribution Substream
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+Begins at offset ``0`` immediately after the :ref:`dbi_mod_info_substream` ends,
+and consumes ``Header->SectionContributionSize`` bytes. This substream begins
+with a single ``uint32_t`` which will be one of the following values:
+
+.. code-block:: c++
+
+ enum class SectionContrSubstreamVersion : uint32_t {
+ Ver60 = 0xeffe0000 + 19970605,
+ V2 = 0xeffe0000 + 20140516
+ };
+
+``Ver60`` is the only value which has been observed in a PDB so far. Following
+this ``4`` byte field is an array of fixed-length structures. If the version
+is ``Ver60``, it is an array of ``SectionContribEntry`` structures. If the
+version is ``V2``, it is an array of ``SectionContribEntry2`` structures,
+defined as follows:
+
+.. code-block:: c++
+
+ struct SectionContribEntry2 {
+ SectionContribEntry SC;
+ uint32_t ISectCoff;
+ };
+
+The purpose of the second field is not well understood.
+
+
+.. _dbi_section_map_substream:
+
+Section Map Substream
+^^^^^^^^^^^^^^^^^^^^^
+Begins at offset ``0`` immediately after the :ref:`dbi_sec_contr_substream` ends,
+and consumes ``Header->SectionMapSize`` bytes. This substream begins with an ``8``
+byte header followed by an array of fixed-length records. The header and records
+have the following layout:
+
+.. code-block:: c++
+
+ struct SectionMapHeader {
+ uint16_t Count; // Number of segment descriptors
+ uint16_t LogCount; // Number of logical segment descriptors
+ };
+
+ struct SectionMapEntry {
+ uint16_t Flags; // See the SectionMapEntryFlags enum below.
+ uint16_t Ovl; // Logical overlay number
+ uint16_t Group; // Group index into descriptor array.
+ uint16_t Frame;
+ uint16_t SectionName; // Byte index of segment / group name in string table, or 0xFFFF.
+ uint16_t ClassName; // Byte index of class in string table, or 0xFFFF.
+ uint32_t Offset; // Byte offset of the logical segment within physical segment. If group is set in flags, this is the offset of the group.
+ uint32_t SectionLength; // Byte count of the segment or group.
+ };
+
+ enum class SectionMapEntryFlags : uint16_t {
+ Read = 1 << 0, // Segment is readable.
+ Write = 1 << 1, // Segment is writable.
+ Execute = 1 << 2, // Segment is executable.
+ AddressIs32Bit = 1 << 3, // Descriptor describes a 32-bit linear address.
+ IsSelector = 1 << 8, // Frame represents a selector.
+ IsAbsoluteAddress = 1 << 9, // Frame represents an absolute address.
+ IsGroup = 1 << 10 // If set, descriptor represents a group.
+ };
+
+Many of these fields are not well understood, so will not be discussed further.
+
+.. _dbi_file_info_substream:
+
+File Info Substream
+^^^^^^^^^^^^^^^^^^^
+Begins at offset ``0`` immediately after the :ref:`dbi_section_map_substream` ends,
+and consumes ``Header->SourceInfoSize`` bytes. This substream defines the mapping
+from module to the source files that contribute to that module. Since multiple
+modules can use the same source file (for example, a header file), this substream
+uses a string table to store each unique file name only once, and then have each
+module use offsets into the string table rather than embedding the string's value
+directly. The format of this substream is as follows:
+
+.. code-block:: c++
+
+ struct FileInfoSubstream {
+ uint16_t NumModules;
+ uint16_t NumSourceFiles;
+
+ uint16_t ModIndices[NumModules];
+ uint16_t ModFileCounts[NumModules];
+ uint32_t FileNameOffsets[NumSourceFiles];
+ char NamesBuffer[][NumSourceFiles];
+ };
+
+**NumModules** - The number of modules for which source file information is
+contained within this substream. Should match the corresponding value from the
+ref:`dbi_header`.
+
+**NumSourceFiles**: In theory this is supposed to contain the number of source
+files for which this substream contains information. But that would present a
+problem in that the width of this field being ``16``-bits would prevent one from
+having more than 64K source files in a program. In early versions of the file
+format, this seems to have been the case. In order to support more than this, this
+field of the is simply ignored, and computed dynamically by summing up the values of
+the ``ModFileCounts`` array (discussed below). In short, this value should be
+ignored.
+
+**ModIndices** - This array is present, but does not appear to be useful.
+
+**ModFileCountArray** - An array of ``NumModules`` integers, each one containing
+the number of source files which contribute to the module at the specified index.
+While each individual module is limited to 64K contributing source files, the
+union of all modules' source files may be greater than 64K. The real number of
+source files is thus computed by summing this array. Note that summing this array
+does not give the number of `unique` source files, only the total number of source
+file contributions to modules.
+
+**FileNameOffsets** - An array of **NumSourceFiles** integers (where **NumSourceFiles**
+here refers to the 32-bit value obtained from summing **ModFileCountArray**), where
+each integer is an offset into **NamesBuffer** pointing to a null terminated string.
+
+**NamesBuffer** - An array of null terminated strings containing the actual source
+file names.
+
+.. _dbi_type_server_substream:
+
+Type Server Substream
+^^^^^^^^^^^^^^^^^^^^^
+Begins at offset ``0`` immediately after the :ref:`dbi_file_info_substream` ends,
+and consumes ``Header->TypeServerSize`` bytes. Neither the purpose nor the layout
+of this substream is understood, although it is assumed to related somehow to the
+usage of ``/Zi`` and ``mspdbsrv.exe``. This substream will not be discussed further.
+
+.. _dbi_ec_substream:
+
+EC Substream
+^^^^^^^^^^^^
+Begins at offset ``0`` immediately after the :ref:`dbi_type_server_substream` ends,
+and consumes ``Header->ECSubstreamSize`` bytes. Neither the purpose nor the layout
+of this substream is understood, and it will not be discussed further.
+
+.. _dbi_optional_dbg_stream:
+
+Optional Debug Header Stream
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+Begins at offset ``0`` immediately after the :ref:`dbi_ec_substream` ends, and
+consumes ``Header->OptionalDbgHeaderSize`` bytes. This field is an array of
+stream indices (e.g. ``uint16_t``'s), each of which identifies a stream
+index in the larger MSF file which contains some additional debug information.
+Each position of this array has a special meaning, allowing one to determine
+what kind of debug information is at the referenced stream. ``11`` indices
+are currently understood, although it's possible there may be more. The
+layout of each stream generally corresponds exactly to a particular type
+of debug data directory from the PE/COFF file. The format of these fields
+can be found in the `Microsoft PE/COFF Specification <https://www.microsoft.com/en-us/download/details.aspx?id=19509>`__.
+
+**FPO Data** - ``DbgStreamArray[0]``. The data in the referenced stream is a
+debug data directory of type ``IMAGE_DEBUG_TYPE_FPO``
+
+**Exception Data** - ``DbgStreamArray[1]``. The data in the referenced stream
+is a debug data directory of type ``IMAGE_DEBUG_TYPE_EXCEPTION``.
+
+**Fixup Data** - ``DbgStreamArray[2]``. The data in the referenced stream is a
+debug data directory of type ``IMAGE_DEBUG_TYPE_FIXUP``.
+
+**Omap To Src Data** - ``DbgStreamArray[3]``. The data in the referenced stream
+is a debug data directory of type ``IMAGE_DEBUG_TYPE_OMAP_TO_SRC``. This
+is used for mapping addresses between instrumented and uninstrumented code.
+
+**Omap From Src Data** - ``DbgStreamArray[4]``. The data in the referenced stream
+is a debug data directory of type ``IMAGE_DEBUG_TYPE_OMAP_FROM_SRC``. This
+is used for mapping addresses between instrumented and uninstrumented code.
+
+**Section Header Data** - ``DbgStreamArray[5]``. A dump of all section headers from
+the original executable.
+
+**Token / RID Map** - ``DbgStreamArray[6]``. The layout of this stream is not
+understood, but it is assumed to be a mapping from ``CLR Token`` to
+``CLR Record ID``. Refer to `ECMA 335 <http://www.ecma-international.org/publications/standards/Ecma-335.htm>`__
+for more information.
+
+**Xdata** - ``DbgStreamArray[7]``. A copy of the ``.xdata`` section from the
+executable.
+
+**Pdata** - ``DbgStreamArray[8]``. This is assumed to be a copy of the ``.pdata``
+section from the executable, but that would make it identical to
+``DbgStreamArray[1]``. The difference between these two indices is not well
+understood.
+
+**New FPO Data** - ``DbgStreamArray[9]``. The data in the referenced stream is a
+debug data directory of type ``IMAGE_DEBUG_TYPE_FPO``. It is not clear how this
+differs from ``DbgStreamArray[0]``, but in practice all observed PDB files have
+used the "new" format rather than the "old" format.
+
+**Original Section Header Data** - ``DbgStreamArray[10]``. Assumed to be similar
+to ``DbgStreamArray[5]``, but has not been observed in practice.
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--- www-releases/trunk/5.0.1/docs/_sources/PDB/GlobalStream.rst.txt (added)
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@@ -0,0 +1,3 @@
+=====================================
+The PDB Global Symbol Stream
+=====================================
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--- www-releases/trunk/5.0.1/docs/_sources/PDB/HashStream.rst.txt (added)
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@@ -0,0 +1,3 @@
+=====================================
+The TPI & IPI Hash Streams
+=====================================
Added: www-releases/trunk/5.0.1/docs/_sources/PDB/ModiStream.rst.txt
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--- www-releases/trunk/5.0.1/docs/_sources/PDB/ModiStream.rst.txt (added)
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+=====================================
+The Module Information Stream
+=====================================
+
+.. contents::
+ :local:
+
+.. _modi_stream_intro:
+
+Introduction
+============
+
+The Module Info Stream (henceforth referred to as the Modi stream) contains
+information about a single module (object file, import library, etc that
+contributes to the binary this PDB contains debug information about. There
+is one modi stream for each module, and the mapping between modi stream index
+and module is contained in the :doc:`DBI Stream <DbiStream>`. The modi stream
+for a single module contains line information for the compiland, as well as
+all CodeView information for the symbols defined in the compiland. Finally,
+there is a "global refs" substream which is not well understood.
+
+.. _modi_stream_layout:
+
+Stream Layout
+=============
+
+A modi stream is laid out as follows:
+
+
+.. code-block:: c++
+
+ struct ModiStream {
+ uint32_t Signature;
+ uint8_t Symbols[SymbolSize-4];
+ uint8_t C11LineInfo[C11Size];
+ uint8_t C13LineInfo[C13Size];
+
+ uint32_t GlobalRefsSize;
+ uint8_t GlobalRefs[GlobalRefsSize];
+ };
+
+- **Signature** - Unknown. In practice only the value of ``4`` has been
+ observed. It is hypothesized that this value corresponds to the set of
+ ``CV_SIGNATURE_xx`` defines in ``cvinfo.h``, with the value of ``4``
+ meaning that this module has C13 line information (as opposed to C11 line
+ information). A corollary of this is that we expect to only ever see
+ C13 line info, and that we do not understand the format of C11 line info.
+
+- **Symbols** - The :ref:`CodeView Symbol Substream <modi_symbol_substream>`.
+ ``SymbolSize`` is equal to the value of ``SymByteSize`` for the
+ corresponding module's entry in the :ref:`Module Info Substream <dbi_mod_info_substream>`
+ of the :doc:`DBI Stream <DbiStream>`.
+
+- **C11LineInfo** - A block containing CodeView line information in C11
+ format. ``C11Size`` is equal to the value of ``C11ByteSize`` from the
+ :ref:`Module Info Substream <dbi_mod_info_substream>` of the
+ :doc:`DBI Stream <DbiStream>`. If this value is ``0``, then C11 line
+ information is not present. As mentioned previously, the format of
+ C11 line info is not understood and we assume all line in modern PDBs
+ to be in C13 format.
+
+- **C13LineInfo** - A block containing CodeView line information in C13
+ format. ``C13Size`` is equal to the value of ``C13ByteSize`` from the
+ :ref:`Module Info Substream <dbi_mod_info_substream>` of the
+ :doc:`DBI Stream <DbiStream>`. If this value is ``0``, then C13 line
+ information is not present.
+
+- **GlobalRefs** - The meaning of this substream is not understood.
+
+.. _modi_symbol_substream:
+
+The CodeView Symbol Substream
+=============================
+
+The CodeView Symbol Substream. This is an array of variable length
+records describing the functions, variables, inlining information,
+and other symbols defined in the compiland. The entire array consumes
+``SymbolSize-4`` bytes. The format of a CodeView Symbol Record (and
+thusly, an array of CodeView Symbol Records) is described in
+:doc:`CodeViewSymbols`.
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--- www-releases/trunk/5.0.1/docs/_sources/PDB/MsfFile.rst.txt (added)
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@@ -0,0 +1,121 @@
+=====================================
+The MSF File Format
+=====================================
+
+.. contents::
+ :local:
+
+.. _msf_superblock:
+
+The Superblock
+==============
+At file offset 0 in an MSF file is the MSF *SuperBlock*, which is laid out as
+follows:
+
+.. code-block:: c++
+
+ struct SuperBlock {
+ char FileMagic[sizeof(Magic)];
+ ulittle32_t BlockSize;
+ ulittle32_t FreeBlockMapBlock;
+ ulittle32_t NumBlocks;
+ ulittle32_t NumDirectoryBytes;
+ ulittle32_t Unknown;
+ ulittle32_t BlockMapAddr;
+ };
+
+- **FileMagic** - Must be equal to ``"Microsoft C / C++ MSF 7.00\\r\\n"``
+ followed by the bytes ``1A 44 53 00 00 00``.
+- **BlockSize** - The block size of the internal file system. Valid values are
+ 512, 1024, 2048, and 4096 bytes. Certain aspects of the MSF file layout vary
+ depending on the block sizes. For the purposes of LLVM, we handle only block
+ sizes of 4KiB, and all further discussion assumes a block size of 4KiB.
+- **FreeBlockMapBlock** - The index of a block within the file, at which begins
+ a bitfield representing the set of all blocks within the file which are "free"
+ (i.e. the data within that block is not used). This bitfield is spread across
+ the MSF file at ``BlockSize`` intervals.
+ **Important**: ``FreeBlockMapBlock`` can only be ``1`` or ``2``! This field
+ is designed to support incremental and atomic updates of the underlying MSF
+ file. While writing to an MSF file, if the value of this field is `1`, you
+ can write your new modified bitfield to page 2, and vice versa. Only when
+ you commit the file to disk do you need to swap the value in the SuperBlock
+ to point to the new ``FreeBlockMapBlock``.
+- **NumBlocks** - The total number of blocks in the file. ``NumBlocks * BlockSize``
+ should equal the size of the file on disk.
+- **NumDirectoryBytes** - The size of the stream directory, in bytes. The stream
+ directory contains information about each stream's size and the set of blocks
+ that it occupies. It will be described in more detail later.
+- **BlockMapAddr** - The index of a block within the MSF file. At this block is
+ an array of ``ulittle32_t``'s listing the blocks that the stream directory
+ resides on. For large MSF files, the stream directory (which describes the
+ block layout of each stream) may not fit entirely on a single block. As a
+ result, this extra layer of indirection is introduced, whereby this block
+ contains the list of blocks that the stream directory occupies, and the stream
+ directory itself can be stitched together accordingly. The number of
+ ``ulittle32_t``'s in this array is given by ``ceil(NumDirectoryBytes / BlockSize)``.
+
+The Stream Directory
+====================
+The Stream Directory is the root of all access to the other streams in an MSF
+file. Beginning at byte 0 of the stream directory is the following structure:
+
+.. code-block:: c++
+
+ struct StreamDirectory {
+ ulittle32_t NumStreams;
+ ulittle32_t StreamSizes[NumStreams];
+ ulittle32_t StreamBlocks[NumStreams][];
+ };
+
+And this structure occupies exactly ``SuperBlock->NumDirectoryBytes`` bytes.
+Note that each of the last two arrays is of variable length, and in particular
+that the second array is jagged.
+
+**Example:** Suppose a hypothetical PDB file with a 4KiB block size, and 4
+streams of lengths {1000 bytes, 8000 bytes, 16000 bytes, 9000 bytes}.
+
+Stream 0: ceil(1000 / 4096) = 1 block
+
+Stream 1: ceil(8000 / 4096) = 2 blocks
+
+Stream 2: ceil(16000 / 4096) = 4 blocks
+
+Stream 3: ceil(9000 / 4096) = 3 blocks
+
+In total, 10 blocks are used. Let's see what the stream directory might look
+like:
+
+.. code-block:: c++
+
+ struct StreamDirectory {
+ ulittle32_t NumStreams = 4;
+ ulittle32_t StreamSizes[] = {1000, 8000, 16000, 9000};
+ ulittle32_t StreamBlocks[][] = {
+ {4},
+ {5, 6},
+ {11, 9, 7, 8},
+ {10, 15, 12}
+ };
+ };
+
+In total, this occupies ``15 * 4 = 60`` bytes, so ``SuperBlock->NumDirectoryBytes``
+would equal ``60``, and ``SuperBlock->BlockMapAddr`` would be an array of one
+``ulittle32_t``, since ``60 <= SuperBlock->BlockSize``.
+
+Note also that the streams are discontiguous, and that part of stream 3 is in the
+middle of part of stream 2. You cannot assume anything about the layout of the
+blocks!
+
+Alignment and Block Boundaries
+==============================
+As may be clear by now, it is possible for a single field (whether it be a high
+level record, a long string field, or even a single ``uint16``) to begin and
+end in separate blocks. For example, if the block size is 4096 bytes, and a
+``uint16`` field begins at the last byte of the current block, then it would
+need to end on the first byte of the next block. Since blocks are not
+necessarily contiguously laid out in the file, this means that both the consumer
+and the producer of an MSF file must be prepared to split data apart
+accordingly. In the aforementioned example, the high byte of the ``uint16``
+would be written to the last byte of block N, and the low byte would be written
+to the first byte of block N+1, which could be tens of thousands of bytes later
+(or even earlier!) in the file, depending on what the stream directory says.
Added: www-releases/trunk/5.0.1/docs/_sources/PDB/PdbStream.rst.txt
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--- www-releases/trunk/5.0.1/docs/_sources/PDB/PdbStream.rst.txt (added)
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@@ -0,0 +1,80 @@
+========================================
+The PDB Info Stream (aka the PDB Stream)
+========================================
+
+.. contents::
+ :local:
+
+.. _pdb_stream_header:
+
+Stream Header
+=============
+At offset 0 of the PDB Stream is a header with the following layout:
+
+
+.. code-block:: c++
+
+ struct PdbStreamHeader {
+ ulittle32_t Version;
+ ulittle32_t Signature;
+ ulittle32_t Age;
+ Guid UniqueId;
+ };
+
+- **Version** - A Value from the following enum:
+
+.. code-block:: c++
+
+ enum class PdbStreamVersion : uint32_t {
+ VC2 = 19941610,
+ VC4 = 19950623,
+ VC41 = 19950814,
+ VC50 = 19960307,
+ VC98 = 19970604,
+ VC70Dep = 19990604,
+ VC70 = 20000404,
+ VC80 = 20030901,
+ VC110 = 20091201,
+ VC140 = 20140508,
+ };
+
+While the meaning of this field appears to be obvious, in practice we have
+never observed a value other than ``VC70``, even with modern versions of
+the toolchain, and it is unclear why the other values exist. It is assumed
+that certain aspects of the PDB stream's layout, and perhaps even that of
+the other streams, will change if the value is something other than ``VC70``.
+
+- **Signature** - A 32-bit time-stamp generated with a call to ``time()`` at
+ the time the PDB file is written. Note that due to the inherent uniqueness
+ problems of using a timestamp with 1-second granularity, this field does not
+ really serve its intended purpose, and as such is typically ignored in favor
+ of the ``Guid`` field, described below.
+
+- **Age** - The number of times the PDB file has been written. This can be used
+ along with ``Guid`` to match the PDB to its corresponding executable.
+
+- **Guid** - A 128-bit identifier guaranteed to be unique across space and time.
+ In general, this can be thought of as the result of calling the Win32 API
+ `UuidCreate <https://msdn.microsoft.com/en-us/library/windows/desktop/aa379205(v=vs.85).aspx>`__,
+ although LLVM cannot rely on that, as it must work on non-Windows platforms.
+
+Matching a PDB to its executable
+================================
+The linker is responsible for writing both the PDB and the final executable, and
+as a result is the only entity capable of writing the information necessary to
+match the PDB to the executable.
+
+In order to accomplish this, the linker generates a guid for the PDB (or
+re-uses the existing guid if it is linking incrementally) and increments the Age
+field.
+
+The executable is a PE/COFF file, and part of a PE/COFF file is the presence of
+number of "directories". For our purposes here, we are interested in the "debug
+directory". The exact format of a debug directory is described by the
+`IMAGE_DEBUG_DIRECTORY structure <https://msdn.microsoft.com/en-us/library/windows/desktop/ms680307(v=vs.85).aspx>`__.
+For this particular case, the linker emits a debug directory of type
+``IMAGE_DEBUG_TYPE_CODEVIEW``. The format of this record is defined in
+``llvm/DebugInfo/CodeView/CVDebugRecord.h``, but it suffices to say here only
+that it includes the same ``Guid`` and ``Age`` fields. At runtime, a
+debugger or tool can scan the COFF executable image for the presence of
+a debug directory of the correct type and verify that the Guid and Age match.
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--- www-releases/trunk/5.0.1/docs/_sources/PDB/PublicStream.rst.txt (added)
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@@ -0,0 +1,3 @@
+=====================================
+The PDB Public Symbol Stream
+=====================================
Added: www-releases/trunk/5.0.1/docs/_sources/PDB/TpiStream.rst.txt
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--- www-releases/trunk/5.0.1/docs/_sources/PDB/TpiStream.rst.txt (added)
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@@ -0,0 +1,3 @@
+=====================================
+The PDB TPI Stream
+=====================================
Added: www-releases/trunk/5.0.1/docs/_sources/PDB/index.rst.txt
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--- www-releases/trunk/5.0.1/docs/_sources/PDB/index.rst.txt (added)
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@@ -0,0 +1,167 @@
+=====================================
+The PDB File Format
+=====================================
+
+.. contents::
+ :local:
+
+.. _pdb_intro:
+
+Introduction
+============
+
+PDB (Program Database) is a file format invented by Microsoft and which contains
+debug information that can be consumed by debuggers and other tools. Since
+officially supported APIs exist on Windows for querying debug information from
+PDBs even without the user understanding the internals of the file format, a
+large ecosystem of tools has been built for Windows to consume this format. In
+order for Clang to be able to generate programs that can interoperate with these
+tools, it is necessary for us to generate PDB files ourselves.
+
+At the same time, LLVM has a long history of being able to cross-compile from
+any platform to any platform, and we wish for the same to be true here. So it
+is necessary for us to understand the PDB file format at the byte-level so that
+we can generate PDB files entirely on our own.
+
+This manual describes what we know about the PDB file format today. The layout
+of the file, the various streams contained within, the format of individual
+records within, and more.
+
+We would like to extend our heartfelt gratitude to Microsoft, without whom we
+would not be where we are today. Much of the knowledge contained within this
+manual was learned through reading code published by Microsoft on their `GitHub
+repo <https://github.com/Microsoft/microsoft-pdb>`__.
+
+.. _pdb_layout:
+
+File Layout
+===========
+
+.. important::
+ Unless otherwise specified, all numeric values are encoded in little endian.
+ If you see a type such as ``uint16_t`` or ``uint64_t`` going forward, always
+ assume it is little endian!
+
+.. toctree::
+ :hidden:
+
+ MsfFile
+ PdbStream
+ TpiStream
+ DbiStream
+ ModiStream
+ PublicStream
+ GlobalStream
+ HashStream
+ CodeViewSymbols
+ CodeViewTypes
+
+.. _msf:
+
+The MSF Container
+-----------------
+A PDB file is really just a special case of an MSF (Multi-Stream Format) file.
+An MSF file is actually a miniature "file system within a file". It contains
+multiple streams (aka files) which can represent arbitrary data, and these
+streams are divided into blocks which may not necessarily be contiguously
+laid out within the file (aka fragmented). Additionally, the MSF contains a
+stream directory (aka MFT) which describes how the streams (files) are laid
+out within the MSF.
+
+For more information about the MSF container format, stream directory, and
+block layout, see :doc:`MsfFile`.
+
+.. _streams:
+
+Streams
+-------
+The PDB format contains a number of streams which describe various information
+such as the types, symbols, source files, and compilands (e.g. object files)
+of a program, as well as some additional streams containing hash tables that are
+used by debuggers and other tools to provide fast lookup of records and types
+by name, and various other information about how the program was compiled such
+as the specific toolchain used, and more. A summary of streams contained in a
+PDB file is as follows:
+
++--------------------+------------------------------+-------------------------------------------+
+| Name | Stream Index | Contents |
++====================+==============================+===========================================+
+| Old Directory | - Fixed Stream Index 0 | - Previous MSF Stream Directory |
++--------------------+------------------------------+-------------------------------------------+
+| PDB Stream | - Fixed Stream Index 1 | - Basic File Information |
+| | | - Fields to match EXE to this PDB |
+| | | - Map of named streams to stream indices |
++--------------------+------------------------------+-------------------------------------------+
+| TPI Stream | - Fixed Stream Index 2 | - CodeView Type Records |
+| | | - Index of TPI Hash Stream |
++--------------------+------------------------------+-------------------------------------------+
+| DBI Stream | - Fixed Stream Index 3 | - Module/Compiland Information |
+| | | - Indices of individual module streams |
+| | | - Indices of public / global streams |
+| | | - Section Contribution Information |
+| | | - Source File Information |
+| | | - FPO / PGO Data |
++--------------------+------------------------------+-------------------------------------------+
+| IPI Stream | - Fixed Stream Index 4 | - CodeView Type Records |
+| | | - Index of IPI Hash Stream |
++--------------------+------------------------------+-------------------------------------------+
+| /LinkInfo | - Contained in PDB Stream | - Unknown |
+| | Named Stream map | |
++--------------------+------------------------------+-------------------------------------------+
+| /src/headerblock | - Contained in PDB Stream | - Unknown |
+| | Named Stream map | |
++--------------------+------------------------------+-------------------------------------------+
+| /names | - Contained in PDB Stream | - PDB-wide global string table used for |
+| | Named Stream map | string de-duplication |
++--------------------+------------------------------+-------------------------------------------+
+| Module Info Stream | - Contained in DBI Stream | - CodeView Symbol Records for this module |
+| | - One for each compiland | - Line Number Information |
++--------------------+------------------------------+-------------------------------------------+
+| Public Stream | - Contained in DBI Stream | - Public (Exported) Symbol Records |
+| | | - Index of Public Hash Stream |
++--------------------+------------------------------+-------------------------------------------+
+| Global Stream | - Contained in DBI Stream | - Global Symbol Records |
+| | | - Index of Global Hash Stream |
++--------------------+------------------------------+-------------------------------------------+
+| TPI Hash Stream | - Contained in TPI Stream | - Hash table for looking up TPI records |
+| | | by name |
++--------------------+------------------------------+-------------------------------------------+
+| IPI Hash Stream | - Contained in IPI Stream | - Hash table for looking up IPI records |
+| | | by name |
++--------------------+------------------------------+-------------------------------------------+
+
+More information about the structure of each of these can be found on the
+following pages:
+
+:doc:`PdbStream`
+ Information about the PDB Info Stream and how it is used to match PDBs to EXEs.
+
+:doc:`TpiStream`
+ Information about the TPI stream and the CodeView records contained within.
+
+:doc:`DbiStream`
+ Information about the DBI stream and relevant substreams including the Module Substreams,
+ source file information, and CodeView symbol records contained within.
+
+:doc:`ModiStream`
+ Information about the Module Information Stream, of which there is one for each compilation
+ unit and the format of symbols contained within.
+
+:doc:`PublicStream`
+ Information about the Public Symbol Stream.
+
+:doc:`GlobalStream`
+ Information about the Global Symbol Stream.
+
+:doc:`HashStream`
+ Information about the Hash Table stream, and how it can be used to quickly look up records
+ by name.
+
+CodeView
+========
+CodeView is another format which comes into the picture. While MSF defines
+the structure of the overall file, and PDB defines the set of streams that
+appear within the MSF file and the format of those streams, CodeView defines
+the format of **symbol and type records** that appear within specific streams.
+Refer to the pages on :doc:`CodeViewSymbols` and :doc:`CodeViewTypes` for
+more information about the CodeView format.
Added: www-releases/trunk/5.0.1/docs/_sources/Packaging.rst.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.1/docs/_sources/Packaging.rst.txt?rev=321287&view=auto
==============================================================================
--- www-releases/trunk/5.0.1/docs/_sources/Packaging.rst.txt (added)
+++ www-releases/trunk/5.0.1/docs/_sources/Packaging.rst.txt Thu Dec 21 10:09:53 2017
@@ -0,0 +1,73 @@
+========================
+Advice on Packaging LLVM
+========================
+
+.. contents::
+ :local:
+
+Overview
+========
+
+LLVM sets certain default configure options to make sure our developers don't
+break things for constrained platforms. These settings are not optimal for most
+desktop systems, and we hope that packagers (e.g., Redhat, Debian, MacPorts,
+etc.) will tweak them. This document lists settings we suggest you tweak.
+
+LLVM's API changes with each release, so users are likely to want, for example,
+both LLVM-2.6 and LLVM-2.7 installed at the same time to support apps developed
+against each.
+
+Compile Flags
+=============
+
+LLVM runs much more quickly when it's optimized and assertions are removed.
+However, such a build is currently incompatible with users who build without
+defining ``NDEBUG``, and the lack of assertions makes it hard to debug problems
+in user code. We recommend allowing users to install both optimized and debug
+versions of LLVM in parallel. The following configure flags are relevant:
+
+``--disable-assertions``
+ Builds LLVM with ``NDEBUG`` defined. Changes the LLVM ABI. Also available
+ by setting ``DISABLE_ASSERTIONS=0|1`` in ``make``'s environment. This
+ defaults to enabled regardless of the optimization setting, but it slows
+ things down.
+
+``--enable-debug-symbols``
+ Builds LLVM with ``-g``. Also available by setting ``DEBUG_SYMBOLS=0|1`` in
+ ``make``'s environment. This defaults to disabled when optimizing, so you
+ should turn it back on to let users debug their programs.
+
+``--enable-optimized``
+ (For svn checkouts) Builds LLVM with ``-O2`` and, by default, turns off
+ debug symbols. Also available by setting ``ENABLE_OPTIMIZED=0|1`` in
+ ``make``'s environment. This defaults to enabled when not in a
+ checkout.
+
+C++ Features
+============
+
+RTTI
+ LLVM disables RTTI by default. Add ``REQUIRES_RTTI=1`` to your environment
+ while running ``make`` to re-enable it. This will allow users to build with
+ RTTI enabled and still inherit from LLVM classes.
+
+Shared Library
+==============
+
+Configure with ``--enable-shared`` to build
+``libLLVM-<major>.<minor>.(so|dylib)`` and link the tools against it. This
+saves lots of binary size at the cost of some startup time.
+
+Dependencies
+============
+
+``--enable-libffi``
+ Depend on `libffi <http://sources.redhat.com/libffi/>`_ to allow the LLVM
+ interpreter to call external functions.
+
+``--with-oprofile``
+
+ Depend on `libopagent
+ <http://oprofile.sourceforge.net/doc/devel/index.html>`_ (>=version 0.9.4)
+ to let the LLVM JIT tell oprofile about function addresses and line
+ numbers.
Added: www-releases/trunk/5.0.1/docs/_sources/Passes.rst.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.1/docs/_sources/Passes.rst.txt?rev=321287&view=auto
==============================================================================
--- www-releases/trunk/5.0.1/docs/_sources/Passes.rst.txt (added)
+++ www-releases/trunk/5.0.1/docs/_sources/Passes.rst.txt Thu Dec 21 10:09:53 2017
@@ -0,0 +1,1179 @@
+..
+ If Passes.html is up to date, the following "one-liner" should print
+ an empty diff.
+
+ egrep -e '^<tr><td><a href="#.*">-.*</a></td><td>.*</td></tr>$' \
+ -e '^ <a name=".*">.*</a>$' < Passes.html >html; \
+ perl >help <<'EOT' && diff -u help html; rm -f help html
+ open HTML, "<Passes.html" or die "open: Passes.html: $!\n";
+ while (<HTML>) {
+ m:^<tr><td><a href="#(.*)">-.*</a></td><td>.*</td></tr>$: or next;
+ $order{$1} = sprintf("%03d", 1 + int %order);
+ }
+ open HELP, "../Release/bin/opt -help|" or die "open: opt -help: $!\n";
+ while (<HELP>) {
+ m:^ -([^ ]+) +- (.*)$: or next;
+ my $o = $order{$1};
+ $o = "000" unless defined $o;
+ push @x, "$o<tr><td><a href=\"#$1\">-$1</a></td><td>$2</td></tr>\n";
+ push @y, "$o <a name=\"$1\">-$1: $2</a>\n";
+ }
+ @x = map { s/^\d\d\d//; $_ } sort @x;
+ @y = map { s/^\d\d\d//; $_ } sort @y;
+ print @x, @y;
+ EOT
+
+ This (real) one-liner can also be helpful when converting comments to HTML:
+
+ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print " <p>\n" if !$on && $_ =~ /\S/; print " </p>\n" if $on && $_ =~ /^\s*$/; print " $_\n"; $on = ($_ =~ /\S/); } print " </p>\n" if $on'
+
+====================================
+LLVM's Analysis and Transform Passes
+====================================
+
+.. contents::
+ :local:
+
+Introduction
+============
+
+This document serves as a high level summary of the optimization features that
+LLVM provides. Optimizations are implemented as Passes that traverse some
+portion of a program to either collect information or transform the program.
+The table below divides the passes that LLVM provides into three categories.
+Analysis passes compute information that other passes can use or for debugging
+or program visualization purposes. Transform passes can use (or invalidate)
+the analysis passes. Transform passes all mutate the program in some way.
+Utility passes provides some utility but don't otherwise fit categorization.
+For example passes to extract functions to bitcode or write a module to bitcode
+are neither analysis nor transform passes. The table of contents above
+provides a quick summary of each pass and links to the more complete pass
+description later in the document.
+
+Analysis Passes
+===============
+
+This section describes the LLVM Analysis Passes.
+
+``-aa-eval``: Exhaustive Alias Analysis Precision Evaluator
+-----------------------------------------------------------
+
+This is a simple N^2 alias analysis accuracy evaluator. Basically, for each
+function in the program, it simply queries to see how the alias analysis
+implementation answers alias queries between each pair of pointers in the
+function.
+
+This is inspired and adapted from code by: Naveen Neelakantam, Francesco
+Spadini, and Wojciech Stryjewski.
+
+``-basicaa``: Basic Alias Analysis (stateless AA impl)
+------------------------------------------------------
+
+A basic alias analysis pass that implements identities (two different globals
+cannot alias, etc), but does no stateful analysis.
+
+``-basiccg``: Basic CallGraph Construction
+------------------------------------------
+
+Yet to be written.
+
+``-count-aa``: Count Alias Analysis Query Responses
+---------------------------------------------------
+
+A pass which can be used to count how many alias queries are being made and how
+the alias analysis implementation being used responds.
+
+``-da``: Dependence Analysis
+----------------------------
+
+Dependence analysis framework, which is used to detect dependences in memory
+accesses.
+
+``-debug-aa``: AA use debugger
+------------------------------
+
+This simple pass checks alias analysis users to ensure that if they create a
+new value, they do not query AA without informing it of the value. It acts as
+a shim over any other AA pass you want.
+
+Yes keeping track of every value in the program is expensive, but this is a
+debugging pass.
+
+``-domfrontier``: Dominance Frontier Construction
+-------------------------------------------------
+
+This pass is a simple dominator construction algorithm for finding forward
+dominator frontiers.
+
+``-domtree``: Dominator Tree Construction
+-----------------------------------------
+
+This pass is a simple dominator construction algorithm for finding forward
+dominators.
+
+
+``-dot-callgraph``: Print Call Graph to "dot" file
+--------------------------------------------------
+
+This pass, only available in ``opt``, prints the call graph into a ``.dot``
+graph. This graph can then be processed with the "dot" tool to convert it to
+postscript or some other suitable format.
+
+``-dot-cfg``: Print CFG of function to "dot" file
+-------------------------------------------------
+
+This pass, only available in ``opt``, prints the control flow graph into a
+``.dot`` graph. This graph can then be processed with the :program:`dot` tool
+to convert it to postscript or some other suitable format.
+
+``-dot-cfg-only``: Print CFG of function to "dot" file (with no function bodies)
+--------------------------------------------------------------------------------
+
+This pass, only available in ``opt``, prints the control flow graph into a
+``.dot`` graph, omitting the function bodies. This graph can then be processed
+with the :program:`dot` tool to convert it to postscript or some other suitable
+format.
+
+``-dot-dom``: Print dominance tree of function to "dot" file
+------------------------------------------------------------
+
+This pass, only available in ``opt``, prints the dominator tree into a ``.dot``
+graph. This graph can then be processed with the :program:`dot` tool to
+convert it to postscript or some other suitable format.
+
+``-dot-dom-only``: Print dominance tree of function to "dot" file (with no function bodies)
+-------------------------------------------------------------------------------------------
+
+This pass, only available in ``opt``, prints the dominator tree into a ``.dot``
+graph, omitting the function bodies. This graph can then be processed with the
+:program:`dot` tool to convert it to postscript or some other suitable format.
+
+``-dot-postdom``: Print postdominance tree of function to "dot" file
+--------------------------------------------------------------------
+
+This pass, only available in ``opt``, prints the post dominator tree into a
+``.dot`` graph. This graph can then be processed with the :program:`dot` tool
+to convert it to postscript or some other suitable format.
+
+``-dot-postdom-only``: Print postdominance tree of function to "dot" file (with no function bodies)
+---------------------------------------------------------------------------------------------------
+
+This pass, only available in ``opt``, prints the post dominator tree into a
+``.dot`` graph, omitting the function bodies. This graph can then be processed
+with the :program:`dot` tool to convert it to postscript or some other suitable
+format.
+
+``-globalsmodref-aa``: Simple mod/ref analysis for globals
+----------------------------------------------------------
+
+This simple pass provides alias and mod/ref information for global values that
+do not have their address taken, and keeps track of whether functions read or
+write memory (are "pure"). For this simple (but very common) case, we can
+provide pretty accurate and useful information.
+
+``-instcount``: Counts the various types of ``Instruction``\ s
+--------------------------------------------------------------
+
+This pass collects the count of all instructions and reports them.
+
+``-intervals``: Interval Partition Construction
+-----------------------------------------------
+
+This analysis calculates and represents the interval partition of a function,
+or a preexisting interval partition.
+
+In this way, the interval partition may be used to reduce a flow graph down to
+its degenerate single node interval partition (unless it is irreducible).
+
+``-iv-users``: Induction Variable Users
+---------------------------------------
+
+Bookkeeping for "interesting" users of expressions computed from induction
+variables.
+
+``-lazy-value-info``: Lazy Value Information Analysis
+-----------------------------------------------------
+
+Interface for lazy computation of value constraint information.
+
+``-libcall-aa``: LibCall Alias Analysis
+---------------------------------------
+
+LibCall Alias Analysis.
+
+``-lint``: Statically lint-checks LLVM IR
+-----------------------------------------
+
+This pass statically checks for common and easily-identified constructs which
+produce undefined or likely unintended behavior in LLVM IR.
+
+It is not a guarantee of correctness, in two ways. First, it isn't
+comprehensive. There are checks which could be done statically which are not
+yet implemented. Some of these are indicated by TODO comments, but those
+aren't comprehensive either. Second, many conditions cannot be checked
+statically. This pass does no dynamic instrumentation, so it can't check for
+all possible problems.
+
+Another limitation is that it assumes all code will be executed. A store
+through a null pointer in a basic block which is never reached is harmless, but
+this pass will warn about it anyway.
+
+Optimization passes may make conditions that this pass checks for more or less
+obvious. If an optimization pass appears to be introducing a warning, it may
+be that the optimization pass is merely exposing an existing condition in the
+code.
+
+This code may be run before :ref:`instcombine <passes-instcombine>`. In many
+cases, instcombine checks for the same kinds of things and turns instructions
+with undefined behavior into unreachable (or equivalent). Because of this,
+this pass makes some effort to look through bitcasts and so on.
+
+``-loops``: Natural Loop Information
+------------------------------------
+
+This analysis is used to identify natural loops and determine the loop depth of
+various nodes of the CFG. Note that the loops identified may actually be
+several natural loops that share the same header node... not just a single
+natural loop.
+
+``-memdep``: Memory Dependence Analysis
+---------------------------------------
+
+An analysis that determines, for a given memory operation, what preceding
+memory operations it depends on. It builds on alias analysis information, and
+tries to provide a lazy, caching interface to a common kind of alias
+information query.
+
+``-module-debuginfo``: Decodes module-level debug info
+------------------------------------------------------
+
+This pass decodes the debug info metadata in a module and prints in a
+(sufficiently-prepared-) human-readable form.
+
+For example, run this pass from ``opt`` along with the ``-analyze`` option, and
+it'll print to standard output.
+
+``-postdomfrontier``: Post-Dominance Frontier Construction
+----------------------------------------------------------
+
+This pass is a simple post-dominator construction algorithm for finding
+post-dominator frontiers.
+
+``-postdomtree``: Post-Dominator Tree Construction
+--------------------------------------------------
+
+This pass is a simple post-dominator construction algorithm for finding
+post-dominators.
+
+``-print-alias-sets``: Alias Set Printer
+----------------------------------------
+
+Yet to be written.
+
+``-print-callgraph``: Print a call graph
+----------------------------------------
+
+This pass, only available in ``opt``, prints the call graph to standard error
+in a human-readable form.
+
+``-print-callgraph-sccs``: Print SCCs of the Call Graph
+-------------------------------------------------------
+
+This pass, only available in ``opt``, prints the SCCs of the call graph to
+standard error in a human-readable form.
+
+``-print-cfg-sccs``: Print SCCs of each function CFG
+----------------------------------------------------
+
+This pass, only available in ``opt``, printsthe SCCs of each function CFG to
+standard error in a human-readable fom.
+
+``-print-dom-info``: Dominator Info Printer
+-------------------------------------------
+
+Dominator Info Printer.
+
+``-print-externalfnconstants``: Print external fn callsites passed constants
+----------------------------------------------------------------------------
+
+This pass, only available in ``opt``, prints out call sites to external
+functions that are called with constant arguments. This can be useful when
+looking for standard library functions we should constant fold or handle in
+alias analyses.
+
+``-print-function``: Print function to stderr
+---------------------------------------------
+
+The ``PrintFunctionPass`` class is designed to be pipelined with other
+``FunctionPasses``, and prints out the functions of the module as they are
+processed.
+
+``-print-module``: Print module to stderr
+-----------------------------------------
+
+This pass simply prints out the entire module when it is executed.
+
+.. _passes-print-used-types:
+
+``-print-used-types``: Find Used Types
+--------------------------------------
+
+This pass is used to seek out all of the types in use by the program. Note
+that this analysis explicitly does not include types only used by the symbol
+table.
+
+``-regions``: Detect single entry single exit regions
+-----------------------------------------------------
+
+The ``RegionInfo`` pass detects single entry single exit regions in a function,
+where a region is defined as any subgraph that is connected to the remaining
+graph at only two spots. Furthermore, an hierarchical region tree is built.
+
+``-scalar-evolution``: Scalar Evolution Analysis
+------------------------------------------------
+
+The ``ScalarEvolution`` analysis can be used to analyze and catagorize scalar
+expressions in loops. It specializes in recognizing general induction
+variables, representing them with the abstract and opaque ``SCEV`` class.
+Given this analysis, trip counts of loops and other important properties can be
+obtained.
+
+This analysis is primarily useful for induction variable substitution and
+strength reduction.
+
+``-scev-aa``: ScalarEvolution-based Alias Analysis
+--------------------------------------------------
+
+Simple alias analysis implemented in terms of ``ScalarEvolution`` queries.
+
+This differs from traditional loop dependence analysis in that it tests for
+dependencies within a single iteration of a loop, rather than dependencies
+between different iterations.
+
+``ScalarEvolution`` has a more complete understanding of pointer arithmetic
+than ``BasicAliasAnalysis``' collection of ad-hoc analyses.
+
+``-targetdata``: Target Data Layout
+-----------------------------------
+
+Provides other passes access to information on how the size and alignment
+required by the target ABI for various data types.
+
+Transform Passes
+================
+
+This section describes the LLVM Transform Passes.
+
+``-adce``: Aggressive Dead Code Elimination
+-------------------------------------------
+
+ADCE aggressively tries to eliminate code. This pass is similar to :ref:`DCE
+<passes-dce>` but it assumes that values are dead until proven otherwise. This
+is similar to :ref:`SCCP <passes-sccp>`, except applied to the liveness of
+values.
+
+``-always-inline``: Inliner for ``always_inline`` functions
+-----------------------------------------------------------
+
+A custom inliner that handles only functions that are marked as "always
+inline".
+
+``-argpromotion``: Promote 'by reference' arguments to scalars
+--------------------------------------------------------------
+
+This pass promotes "by reference" arguments to be "by value" arguments. In
+practice, this means looking for internal functions that have pointer
+arguments. If it can prove, through the use of alias analysis, that an
+argument is *only* loaded, then it can pass the value into the function instead
+of the address of the value. This can cause recursive simplification of code
+and lead to the elimination of allocas (especially in C++ template code like
+the STL).
+
+This pass also handles aggregate arguments that are passed into a function,
+scalarizing them if the elements of the aggregate are only loaded. Note that
+it refuses to scalarize aggregates which would require passing in more than
+three operands to the function, because passing thousands of operands for a
+large array or structure is unprofitable!
+
+Note that this transformation could also be done for arguments that are only
+stored to (returning the value instead), but does not currently. This case
+would be best handled when and if LLVM starts supporting multiple return values
+from functions.
+
+``-bb-vectorize``: Basic-Block Vectorization
+--------------------------------------------
+
+This pass combines instructions inside basic blocks to form vector
+instructions. It iterates over each basic block, attempting to pair compatible
+instructions, repeating this process until no additional pairs are selected for
+vectorization. When the outputs of some pair of compatible instructions are
+used as inputs by some other pair of compatible instructions, those pairs are
+part of a potential vectorization chain. Instruction pairs are only fused into
+vector instructions when they are part of a chain longer than some threshold
+length. Moreover, the pass attempts to find the best possible chain for each
+pair of compatible instructions. These heuristics are intended to prevent
+vectorization in cases where it would not yield a performance increase of the
+resulting code.
+
+``-block-placement``: Profile Guided Basic Block Placement
+----------------------------------------------------------
+
+This pass is a very simple profile guided basic block placement algorithm. The
+idea is to put frequently executed blocks together at the start of the function
+and hopefully increase the number of fall-through conditional branches. If
+there is no profile information for a particular function, this pass basically
+orders blocks in depth-first order.
+
+``-break-crit-edges``: Break critical edges in CFG
+--------------------------------------------------
+
+Break all of the critical edges in the CFG by inserting a dummy basic block.
+It may be "required" by passes that cannot deal with critical edges. This
+transformation obviously invalidates the CFG, but can update forward dominator
+(set, immediate dominators, tree, and frontier) information.
+
+``-codegenprepare``: Optimize for code generation
+-------------------------------------------------
+
+This pass munges the code in the input function to better prepare it for
+SelectionDAG-based code generation. This works around limitations in its
+basic-block-at-a-time approach. It should eventually be removed.
+
+``-constmerge``: Merge Duplicate Global Constants
+-------------------------------------------------
+
+Merges duplicate global constants together into a single constant that is
+shared. This is useful because some passes (i.e., TraceValues) insert a lot of
+string constants into the program, regardless of whether or not an existing
+string is available.
+
+``-constprop``: Simple constant propagation
+-------------------------------------------
+
+This pass implements constant propagation and merging. It looks for
+instructions involving only constant operands and replaces them with a constant
+value instead of an instruction. For example:
+
+.. code-block:: llvm
+
+ add i32 1, 2
+
+becomes
+
+.. code-block:: llvm
+
+ i32 3
+
+NOTE: this pass has a habit of making definitions be dead. It is a good idea
+to run a :ref:`Dead Instruction Elimination <passes-die>` pass sometime after
+running this pass.
+
+.. _passes-dce:
+
+``-dce``: Dead Code Elimination
+-------------------------------
+
+Dead code elimination is similar to :ref:`dead instruction elimination
+<passes-die>`, but it rechecks instructions that were used by removed
+instructions to see if they are newly dead.
+
+``-deadargelim``: Dead Argument Elimination
+-------------------------------------------
+
+This pass deletes dead arguments from internal functions. Dead argument
+elimination removes arguments which are directly dead, as well as arguments
+only passed into function calls as dead arguments of other functions. This
+pass also deletes dead arguments in a similar way.
+
+This pass is often useful as a cleanup pass to run after aggressive
+interprocedural passes, which add possibly-dead arguments.
+
+``-deadtypeelim``: Dead Type Elimination
+----------------------------------------
+
+This pass is used to cleanup the output of GCC. It eliminate names for types
+that are unused in the entire translation unit, using the :ref:`find used types
+<passes-print-used-types>` pass.
+
+.. _passes-die:
+
+``-die``: Dead Instruction Elimination
+--------------------------------------
+
+Dead instruction elimination performs a single pass over the function, removing
+instructions that are obviously dead.
+
+``-dse``: Dead Store Elimination
+--------------------------------
+
+A trivial dead store elimination that only considers basic-block local
+redundant stores.
+
+.. _passes-functionattrs:
+
+``-functionattrs``: Deduce function attributes
+----------------------------------------------
+
+A simple interprocedural pass which walks the call-graph, looking for functions
+which do not access or only read non-local memory, and marking them
+``readnone``/``readonly``. In addition, it marks function arguments (of
+pointer type) "``nocapture``" if a call to the function does not create any
+copies of the pointer value that outlive the call. This more or less means
+that the pointer is only dereferenced, and not returned from the function or
+stored in a global. This pass is implemented as a bottom-up traversal of the
+call-graph.
+
+``-globaldce``: Dead Global Elimination
+---------------------------------------
+
+This transform is designed to eliminate unreachable internal globals from the
+program. It uses an aggressive algorithm, searching out globals that are known
+to be alive. After it finds all of the globals which are needed, it deletes
+whatever is left over. This allows it to delete recursive chunks of the
+program which are unreachable.
+
+``-globalopt``: Global Variable Optimizer
+-----------------------------------------
+
+This pass transforms simple global variables that never have their address
+taken. If obviously true, it marks read/write globals as constant, deletes
+variables only stored to, etc.
+
+``-gvn``: Global Value Numbering
+--------------------------------
+
+This pass performs global value numbering to eliminate fully and partially
+redundant instructions. It also performs redundant load elimination.
+
+.. _passes-indvars:
+
+``-indvars``: Canonicalize Induction Variables
+----------------------------------------------
+
+This transformation analyzes and transforms the induction variables (and
+computations derived from them) into simpler forms suitable for subsequent
+analysis and transformation.
+
+This transformation makes the following changes to each loop with an
+identifiable induction variable:
+
+* All loops are transformed to have a *single* canonical induction variable
+ which starts at zero and steps by one.
+* The canonical induction variable is guaranteed to be the first PHI node in
+ the loop header block.
+* Any pointer arithmetic recurrences are raised to use array subscripts.
+
+If the trip count of a loop is computable, this pass also makes the following
+changes:
+
+* The exit condition for the loop is canonicalized to compare the induction
+ value against the exit value. This turns loops like:
+
+ .. code-block:: c++
+
+ for (i = 7; i*i < 1000; ++i)
+
+ into
+
+ .. code-block:: c++
+
+ for (i = 0; i != 25; ++i)
+
+* Any use outside of the loop of an expression derived from the indvar is
+ changed to compute the derived value outside of the loop, eliminating the
+ dependence on the exit value of the induction variable. If the only purpose
+ of the loop is to compute the exit value of some derived expression, this
+ transformation will make the loop dead.
+
+This transformation should be followed by strength reduction after all of the
+desired loop transformations have been performed. Additionally, on targets
+where it is profitable, the loop could be transformed to count down to zero
+(the "do loop" optimization).
+
+``-inline``: Function Integration/Inlining
+------------------------------------------
+
+Bottom-up inlining of functions into callees.
+
+.. _passes-instcombine:
+
+``-instcombine``: Combine redundant instructions
+------------------------------------------------
+
+Combine instructions to form fewer, simple instructions. This pass does not
+modify the CFG. This pass is where algebraic simplification happens.
+
+This pass combines things like:
+
+.. code-block:: llvm
+
+ %Y = add i32 %X, 1
+ %Z = add i32 %Y, 1
+
+into:
+
+.. code-block:: llvm
+
+ %Z = add i32 %X, 2
+
+This is a simple worklist driven algorithm.
+
+This pass guarantees that the following canonicalizations are performed on the
+program:
+
+#. If a binary operator has a constant operand, it is moved to the right-hand
+ side.
+#. Bitwise operators with constant operands are always grouped so that shifts
+ are performed first, then ``or``\ s, then ``and``\ s, then ``xor``\ s.
+#. Compare instructions are converted from ``<``, ``>``, ``â¤``, or ``â¥`` to
+ ``=`` or ``â `` if possible.
+#. All ``cmp`` instructions on boolean values are replaced with logical
+ operations.
+#. ``add X, X`` is represented as ``mul X, 2`` â ``shl X, 1``
+#. Multiplies with a constant power-of-two argument are transformed into
+ shifts.
+#. ⦠etc.
+
+This pass can also simplify calls to specific well-known function calls (e.g.
+runtime library functions). For example, a call ``exit(3)`` that occurs within
+the ``main()`` function can be transformed into simply ``return 3``. Whether or
+not library calls are simplified is controlled by the
+:ref:`-functionattrs <passes-functionattrs>` pass and LLVM's knowledge of
+library calls on different targets.
+
+``-internalize``: Internalize Global Symbols
+--------------------------------------------
+
+This pass loops over all of the functions in the input module, looking for a
+main function. If a main function is found, all other functions and all global
+variables with initializers are marked as internal.
+
+``-ipconstprop``: Interprocedural constant propagation
+------------------------------------------------------
+
+This pass implements an *extremely* simple interprocedural constant propagation
+pass. It could certainly be improved in many different ways, like using a
+worklist. This pass makes arguments dead, but does not remove them. The
+existing dead argument elimination pass should be run after this to clean up
+the mess.
+
+``-ipsccp``: Interprocedural Sparse Conditional Constant Propagation
+--------------------------------------------------------------------
+
+An interprocedural variant of :ref:`Sparse Conditional Constant Propagation
+<passes-sccp>`.
+
+``-jump-threading``: Jump Threading
+-----------------------------------
+
+Jump threading tries to find distinct threads of control flow running through a
+basic block. This pass looks at blocks that have multiple predecessors and
+multiple successors. If one or more of the predecessors of the block can be
+proven to always cause a jump to one of the successors, we forward the edge
+from the predecessor to the successor by duplicating the contents of this
+block.
+
+An example of when this can occur is code like this:
+
+.. code-block:: c++
+
+ if () { ...
+ X = 4;
+ }
+ if (X < 3) {
+
+In this case, the unconditional branch at the end of the first if can be
+revectored to the false side of the second if.
+
+``-lcssa``: Loop-Closed SSA Form Pass
+-------------------------------------
+
+This pass transforms loops by placing phi nodes at the end of the loops for all
+values that are live across the loop boundary. For example, it turns the left
+into the right code:
+
+.. code-block:: c++
+
+ for (...) for (...)
+ if (c) if (c)
+ X1 = ... X1 = ...
+ else else
+ X2 = ... X2 = ...
+ X3 = phi(X1, X2) X3 = phi(X1, X2)
+ ... = X3 + 4 X4 = phi(X3)
+ ... = X4 + 4
+
+This is still valid LLVM; the extra phi nodes are purely redundant, and will be
+trivially eliminated by ``InstCombine``. The major benefit of this
+transformation is that it makes many other loop optimizations, such as
+``LoopUnswitch``\ ing, simpler.
+
+.. _passes-licm:
+
+``-licm``: Loop Invariant Code Motion
+-------------------------------------
+
+This pass performs loop invariant code motion, attempting to remove as much
+code from the body of a loop as possible. It does this by either hoisting code
+into the preheader block, or by sinking code to the exit blocks if it is safe.
+This pass also promotes must-aliased memory locations in the loop to live in
+registers, thus hoisting and sinking "invariant" loads and stores.
+
+This pass uses alias analysis for two purposes:
+
+#. Moving loop invariant loads and calls out of loops. If we can determine
+ that a load or call inside of a loop never aliases anything stored to, we
+ can hoist it or sink it like any other instruction.
+
+#. Scalar Promotion of Memory. If there is a store instruction inside of the
+ loop, we try to move the store to happen AFTER the loop instead of inside of
+ the loop. This can only happen if a few conditions are true:
+
+ #. The pointer stored through is loop invariant.
+ #. There are no stores or loads in the loop which *may* alias the pointer.
+ There are no calls in the loop which mod/ref the pointer.
+
+ If these conditions are true, we can promote the loads and stores in the
+ loop of the pointer to use a temporary alloca'd variable. We then use the
+ :ref:`mem2reg <passes-mem2reg>` functionality to construct the appropriate
+ SSA form for the variable.
+
+``-loop-deletion``: Delete dead loops
+-------------------------------------
+
+This file implements the Dead Loop Deletion Pass. This pass is responsible for
+eliminating loops with non-infinite computable trip counts that have no side
+effects or volatile instructions, and do not contribute to the computation of
+the function's return value.
+
+.. _passes-loop-extract:
+
+``-loop-extract``: Extract loops into new functions
+---------------------------------------------------
+
+A pass wrapper around the ``ExtractLoop()`` scalar transformation to extract
+each top-level loop into its own new function. If the loop is the *only* loop
+in a given function, it is not touched. This is a pass most useful for
+debugging via bugpoint.
+
+``-loop-extract-single``: Extract at most one loop into a new function
+----------------------------------------------------------------------
+
+Similar to :ref:`Extract loops into new functions <passes-loop-extract>`, this
+pass extracts one natural loop from the program into a function if it can.
+This is used by :program:`bugpoint`.
+
+``-loop-reduce``: Loop Strength Reduction
+-----------------------------------------
+
+This pass performs a strength reduction on array references inside loops that
+have as one or more of their components the loop induction variable. This is
+accomplished by creating a new value to hold the initial value of the array
+access for the first iteration, and then creating a new GEP instruction in the
+loop to increment the value by the appropriate amount.
+
+``-loop-rotate``: Rotate Loops
+------------------------------
+
+A simple loop rotation transformation.
+
+``-loop-simplify``: Canonicalize natural loops
+----------------------------------------------
+
+This pass performs several transformations to transform natural loops into a
+simpler form, which makes subsequent analyses and transformations simpler and
+more effective.
+
+Loop pre-header insertion guarantees that there is a single, non-critical entry
+edge from outside of the loop to the loop header. This simplifies a number of
+analyses and transformations, such as :ref:`LICM <passes-licm>`.
+
+Loop exit-block insertion guarantees that all exit blocks from the loop (blocks
+which are outside of the loop that have predecessors inside of the loop) only
+have predecessors from inside of the loop (and are thus dominated by the loop
+header). This simplifies transformations such as store-sinking that are built
+into LICM.
+
+This pass also guarantees that loops will have exactly one backedge.
+
+Note that the :ref:`simplifycfg <passes-simplifycfg>` pass will clean up blocks
+which are split out but end up being unnecessary, so usage of this pass should
+not pessimize generated code.
+
+This pass obviously modifies the CFG, but updates loop information and
+dominator information.
+
+``-loop-unroll``: Unroll loops
+------------------------------
+
+This pass implements a simple loop unroller. It works best when loops have
+been canonicalized by the :ref:`indvars <passes-indvars>` pass, allowing it to
+determine the trip counts of loops easily.
+
+``-loop-unswitch``: Unswitch loops
+----------------------------------
+
+This pass transforms loops that contain branches on loop-invariant conditions
+to have multiple loops. For example, it turns the left into the right code:
+
+.. code-block:: c++
+
+ for (...) if (lic)
+ A for (...)
+ if (lic) A; B; C
+ B else
+ C for (...)
+ A; C
+
+This can increase the size of the code exponentially (doubling it every time a
+loop is unswitched) so we only unswitch if the resultant code will be smaller
+than a threshold.
+
+This pass expects :ref:`LICM <passes-licm>` to be run before it to hoist
+invariant conditions out of the loop, to make the unswitching opportunity
+obvious.
+
+``-loweratomic``: Lower atomic intrinsics to non-atomic form
+------------------------------------------------------------
+
+This pass lowers atomic intrinsics to non-atomic form for use in a known
+non-preemptible environment.
+
+The pass does not verify that the environment is non-preemptible (in general
+this would require knowledge of the entire call graph of the program including
+any libraries which may not be available in bitcode form); it simply lowers
+every atomic intrinsic.
+
+``-lowerinvoke``: Lower invokes to calls, for unwindless code generators
+------------------------------------------------------------------------
+
+This transformation is designed for use by code generators which do not yet
+support stack unwinding. This pass converts ``invoke`` instructions to
+``call`` instructions, so that any exception-handling ``landingpad`` blocks
+become dead code (which can be removed by running the ``-simplifycfg`` pass
+afterwards).
+
+``-lowerswitch``: Lower ``SwitchInst``\ s to branches
+-----------------------------------------------------
+
+Rewrites switch instructions with a sequence of branches, which allows targets
+to get away with not implementing the switch instruction until it is
+convenient.
+
+.. _passes-mem2reg:
+
+``-mem2reg``: Promote Memory to Register
+----------------------------------------
+
+This file promotes memory references to be register references. It promotes
+alloca instructions which only have loads and stores as uses. An ``alloca`` is
+transformed by using dominator frontiers to place phi nodes, then traversing
+the function in depth-first order to rewrite loads and stores as appropriate.
+This is just the standard SSA construction algorithm to construct "pruned" SSA
+form.
+
+``-memcpyopt``: MemCpy Optimization
+-----------------------------------
+
+This pass performs various transformations related to eliminating ``memcpy``
+calls, or transforming sets of stores into ``memset``\ s.
+
+``-mergefunc``: Merge Functions
+-------------------------------
+
+This pass looks for equivalent functions that are mergable and folds them.
+
+Total-ordering is introduced among the functions set: we define comparison
+that answers for every two functions which of them is greater. It allows to
+arrange functions into the binary tree.
+
+For every new function we check for equivalent in tree.
+
+If equivalent exists we fold such functions. If both functions are overridable,
+we move the functionality into a new internal function and leave two
+overridable thunks to it.
+
+If there is no equivalent, then we add this function to tree.
+
+Lookup routine has O(log(n)) complexity, while whole merging process has
+complexity of O(n*log(n)).
+
+Read
+:doc:`this <MergeFunctions>`
+article for more details.
+
+``-mergereturn``: Unify function exit nodes
+-------------------------------------------
+
+Ensure that functions have at most one ``ret`` instruction in them.
+Additionally, it keeps track of which node is the new exit node of the CFG.
+
+``-partial-inliner``: Partial Inliner
+-------------------------------------
+
+This pass performs partial inlining, typically by inlining an ``if`` statement
+that surrounds the body of the function.
+
+``-prune-eh``: Remove unused exception handling info
+----------------------------------------------------
+
+This file implements a simple interprocedural pass which walks the call-graph,
+turning invoke instructions into call instructions if and only if the callee
+cannot throw an exception. It implements this as a bottom-up traversal of the
+call-graph.
+
+``-reassociate``: Reassociate expressions
+-----------------------------------------
+
+This pass reassociates commutative expressions in an order that is designed to
+promote better constant propagation, GCSE, :ref:`LICM <passes-licm>`, PRE, etc.
+
+For example: 4 + (x + 5) â x + (4 + 5)
+
+In the implementation of this algorithm, constants are assigned rank = 0,
+function arguments are rank = 1, and other values are assigned ranks
+corresponding to the reverse post order traversal of current function (starting
+at 2), which effectively gives values in deep loops higher rank than values not
+in loops.
+
+``-reg2mem``: Demote all values to stack slots
+----------------------------------------------
+
+This file demotes all registers to memory references. It is intended to be the
+inverse of :ref:`mem2reg <passes-mem2reg>`. By converting to ``load``
+instructions, the only values live across basic blocks are ``alloca``
+instructions and ``load`` instructions before ``phi`` nodes. It is intended
+that this should make CFG hacking much easier. To make later hacking easier,
+the entry block is split into two, such that all introduced ``alloca``
+instructions (and nothing else) are in the entry block.
+
+``-sroa``: Scalar Replacement of Aggregates
+------------------------------------------------------
+
+The well-known scalar replacement of aggregates transformation. This transform
+breaks up ``alloca`` instructions of aggregate type (structure or array) into
+individual ``alloca`` instructions for each member if possible. Then, if
+possible, it transforms the individual ``alloca`` instructions into nice clean
+scalar SSA form.
+
+.. _passes-sccp:
+
+``-sccp``: Sparse Conditional Constant Propagation
+--------------------------------------------------
+
+Sparse conditional constant propagation and merging, which can be summarized
+as:
+
+* Assumes values are constant unless proven otherwise
+* Assumes BasicBlocks are dead unless proven otherwise
+* Proves values to be constant, and replaces them with constants
+* Proves conditional branches to be unconditional
+
+Note that this pass has a habit of making definitions be dead. It is a good
+idea to run a :ref:`DCE <passes-dce>` pass sometime after running this pass.
+
+.. _passes-simplifycfg:
+
+``-simplifycfg``: Simplify the CFG
+----------------------------------
+
+Performs dead code elimination and basic block merging. Specifically:
+
+* Removes basic blocks with no predecessors.
+* Merges a basic block into its predecessor if there is only one and the
+ predecessor only has one successor.
+* Eliminates PHI nodes for basic blocks with a single predecessor.
+* Eliminates a basic block that only contains an unconditional branch.
+
+``-sink``: Code sinking
+-----------------------
+
+This pass moves instructions into successor blocks, when possible, so that they
+aren't executed on paths where their results aren't needed.
+
+``-strip``: Strip all symbols from a module
+-------------------------------------------
+
+Performs code stripping. This transformation can delete:
+
+* names for virtual registers
+* symbols for internal globals and functions
+* debug information
+
+Note that this transformation makes code much less readable, so it should only
+be used in situations where the strip utility would be used, such as reducing
+code size or making it harder to reverse engineer code.
+
+``-strip-dead-debug-info``: Strip debug info for unused symbols
+---------------------------------------------------------------
+
+.. FIXME: this description is the same as for -strip
+
+performs code stripping. this transformation can delete:
+
+* names for virtual registers
+* symbols for internal globals and functions
+* debug information
+
+note that this transformation makes code much less readable, so it should only
+be used in situations where the strip utility would be used, such as reducing
+code size or making it harder to reverse engineer code.
+
+``-strip-dead-prototypes``: Strip Unused Function Prototypes
+------------------------------------------------------------
+
+This pass loops over all of the functions in the input module, looking for dead
+declarations and removes them. Dead declarations are declarations of functions
+for which no implementation is available (i.e., declarations for unused library
+functions).
+
+``-strip-debug-declare``: Strip all ``llvm.dbg.declare`` intrinsics
+-------------------------------------------------------------------
+
+.. FIXME: this description is the same as for -strip
+
+This pass implements code stripping. Specifically, it can delete:
+
+#. names for virtual registers
+#. symbols for internal globals and functions
+#. debug information
+
+Note that this transformation makes code much less readable, so it should only
+be used in situations where the 'strip' utility would be used, such as reducing
+code size or making it harder to reverse engineer code.
+
+``-strip-nondebug``: Strip all symbols, except dbg symbols, from a module
+-------------------------------------------------------------------------
+
+.. FIXME: this description is the same as for -strip
+
+This pass implements code stripping. Specifically, it can delete:
+
+#. names for virtual registers
+#. symbols for internal globals and functions
+#. debug information
+
+Note that this transformation makes code much less readable, so it should only
+be used in situations where the 'strip' utility would be used, such as reducing
+code size or making it harder to reverse engineer code.
+
+``-tailcallelim``: Tail Call Elimination
+----------------------------------------
+
+This file transforms calls of the current function (self recursion) followed by
+a return instruction with a branch to the entry of the function, creating a
+loop. This pass also implements the following extensions to the basic
+algorithm:
+
+#. Trivial instructions between the call and return do not prevent the
+ transformation from taking place, though currently the analysis cannot
+ support moving any really useful instructions (only dead ones).
+#. This pass transforms functions that are prevented from being tail recursive
+ by an associative expression to use an accumulator variable, thus compiling
+ the typical naive factorial or fib implementation into efficient code.
+#. TRE is performed if the function returns void, if the return returns the
+ result returned by the call, or if the function returns a run-time constant
+ on all exits from the function. It is possible, though unlikely, that the
+ return returns something else (like constant 0), and can still be TRE'd. It
+ can be TRE'd if *all other* return instructions in the function return the
+ exact same value.
+#. If it can prove that callees do not access theier caller stack frame, they
+ are marked as eligible for tail call elimination (by the code generator).
+
+Utility Passes
+==============
+
+This section describes the LLVM Utility Passes.
+
+``-deadarghaX0r``: Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)
+------------------------------------------------------------------------
+
+Same as dead argument elimination, but deletes arguments to functions which are
+external. This is only for use by :doc:`bugpoint <Bugpoint>`.
+
+``-extract-blocks``: Extract Basic Blocks From Module (for bugpoint use)
+------------------------------------------------------------------------
+
+This pass is used by bugpoint to extract all blocks from the module into their
+own functions.
+
+``-instnamer``: Assign names to anonymous instructions
+------------------------------------------------------
+
+This is a little utility pass that gives instructions names, this is mostly
+useful when diffing the effect of an optimization because deleting an unnamed
+instruction can change all other instruction numbering, making the diff very
+noisy.
+
+.. _passes-verify:
+
+``-verify``: Module Verifier
+----------------------------
+
+Verifies an LLVM IR code. This is useful to run after an optimization which is
+undergoing testing. Note that llvm-as verifies its input before emitting
+bitcode, and also that malformed bitcode is likely to make LLVM crash. All
+language front-ends are therefore encouraged to verify their output before
+performing optimizing transformations.
+
+#. Both of a binary operator's parameters are of the same type.
+#. Verify that the indices of mem access instructions match other operands.
+#. Verify that arithmetic and other things are only performed on first-class
+ types. Verify that shifts and logicals only happen on integrals f.e.
+#. All of the constants in a switch statement are of the correct type.
+#. The code is in valid SSA form.
+#. It is illegal to put a label into any other type (like a structure) or to
+ return one.
+#. Only phi nodes can be self referential: ``%x = add i32 %x``, ``%x`` is
+ invalid.
+#. PHI nodes must have an entry for each predecessor, with no extras.
+#. PHI nodes must be the first thing in a basic block, all grouped together.
+#. PHI nodes must have at least one entry.
+#. All basic blocks should only end with terminator insts, not contain them.
+#. The entry node to a function must not have predecessors.
+#. All Instructions must be embedded into a basic block.
+#. Functions cannot take a void-typed parameter.
+#. Verify that a function's argument list agrees with its declared type.
+#. It is illegal to specify a name for a void value.
+#. It is illegal to have an internal global value with no initializer.
+#. It is illegal to have a ``ret`` instruction that returns a value that does
+ not agree with the function return value type.
+#. Function call argument types match the function prototype.
+#. All other things that are tested by asserts spread about the code.
+
+Note that this does not provide full security verification (like Java), but
+instead just tries to ensure that code is well-formed.
+
+``-view-cfg``: View CFG of function
+-----------------------------------
+
+Displays the control flow graph using the GraphViz tool.
+
+``-view-cfg-only``: View CFG of function (with no function bodies)
+------------------------------------------------------------------
+
+Displays the control flow graph using the GraphViz tool, but omitting function
+bodies.
+
+``-view-dom``: View dominance tree of function
+----------------------------------------------
+
+Displays the dominator tree using the GraphViz tool.
+
+``-view-dom-only``: View dominance tree of function (with no function bodies)
+-----------------------------------------------------------------------------
+
+Displays the dominator tree using the GraphViz tool, but omitting function
+bodies.
+
+``-view-postdom``: View postdominance tree of function
+------------------------------------------------------
+
+Displays the post dominator tree using the GraphViz tool.
+
+``-view-postdom-only``: View postdominance tree of function (with no function bodies)
+-------------------------------------------------------------------------------------
+
+Displays the post dominator tree using the GraphViz tool, but omitting function
+bodies.
+
Added: www-releases/trunk/5.0.1/docs/_sources/Phabricator.rst.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.1/docs/_sources/Phabricator.rst.txt?rev=321287&view=auto
==============================================================================
--- www-releases/trunk/5.0.1/docs/_sources/Phabricator.rst.txt (added)
+++ www-releases/trunk/5.0.1/docs/_sources/Phabricator.rst.txt Thu Dec 21 10:09:53 2017
@@ -0,0 +1,239 @@
+=============================
+Code Reviews with Phabricator
+=============================
+
+.. contents::
+ :local:
+
+If you prefer to use a web user interface for code reviews, you can now submit
+your patches for Clang and LLVM at `LLVM's Phabricator`_ instance.
+
+While Phabricator is a useful tool for some, the relevant -commits mailing list
+is the system of record for all LLVM code review. The mailing list should be
+added as a subscriber on all reviews, and Phabricator users should be prepared
+to respond to free-form comments in mail sent to the commits list.
+
+Sign up
+-------
+
+To get started with Phabricator, navigate to `http://reviews.llvm.org`_ and
+click the power icon in the top right. You can register with a GitHub account,
+a Google account, or you can create your own profile.
+
+Make *sure* that the email address registered with Phabricator is subscribed
+to the relevant -commits mailing list. If you are not subscribed to the commit
+list, all mail sent by Phabricator on your behalf will be held for moderation.
+
+Note that if you use your Subversion user name as Phabricator user name,
+Phabricator will automatically connect your submits to your Phabricator user in
+the `Code Repository Browser`_.
+
+Requesting a review via the command line
+----------------------------------------
+
+Phabricator has a tool called *Arcanist* to upload patches from
+the command line. To get you set up, follow the
+`Arcanist Quick Start`_ instructions.
+
+You can learn more about how to use arc to interact with
+Phabricator in the `Arcanist User Guide`_.
+
+Requesting a review via the web interface
+-----------------------------------------
+
+The tool to create and review patches in Phabricator is called
+*Differential*.
+
+Note that you can upload patches created through various diff tools,
+including git and svn. To make reviews easier, please always include
+**as much context as possible** with your diff! Don't worry, Phabricator
+will automatically send a diff with a smaller context in the review
+email, but having the full file in the web interface will help the
+reviewer understand your code.
+
+To get a full diff, use one of the following commands (or just use Arcanist
+to upload your patch):
+
+* ``git show HEAD -U999999 > mypatch.patch``
+* ``git format-patch -U999999 @{u}``
+* ``svn diff --diff-cmd=diff -x -U999999``
+
+To upload a new patch:
+
+* Click *Differential*.
+* Click *+ Create Diff*.
+* Paste the text diff or browse to the patch file. Click *Create Diff*.
+* Leave the Repository field blank.
+* Leave the drop down on *Create a new Revision...* and click *Continue*.
+* Enter a descriptive title and summary. The title and summary are usually
+ in the form of a :ref:`commit message <commit messages>`.
+* Add reviewers (see below for advice) and subscribe mailing
+ lists that you want to be included in the review. If your patch is
+ for LLVM, add llvm-commits as a Subscriber; if your patch is for Clang,
+ add cfe-commits.
+* Leave the Repository and Project fields blank.
+* Click *Save*.
+
+To submit an updated patch:
+
+* Click *Differential*.
+* Click *+ Create Diff*.
+* Paste the updated diff or browse to the updated patch file. Click *Create Diff*.
+* Select the review you want to from the *Attach To* dropdown and click
+ *Continue*.
+* Leave the Repository and Project fields blank.
+* Add comments about the changes in the new diff. Click *Save*.
+
+Choosing reviewers: You typically pick one or two people as initial reviewers.
+This choice is not crucial, because you are merely suggesting and not requiring
+them to participate. Many people will see the email notification on cfe-commits
+or llvm-commits, and if the subject line suggests the patch is something they
+should look at, they will.
+
+Here are a couple of ways to pick the initial reviewer(s):
+
+* Use ``svn blame`` and the commit log to find names of people who have
+ recently modified the same area of code that you are modifying.
+* Look in CODE_OWNERS.TXT to see who might be responsible for that area.
+* If you've discussed the change on a dev list, the people who participated
+ might be appropriate reviewers.
+
+Even if you think the code owner is the busiest person in the world, it's still
+okay to put them as a reviewer. Being the code owner means they have accepted
+responsibility for making sure the review happens.
+
+Reviewing code with Phabricator
+-------------------------------
+
+Phabricator allows you to add inline comments as well as overall comments
+to a revision. To add an inline comment, select the lines of code you want
+to comment on by clicking and dragging the line numbers in the diff pane.
+When you have added all your comments, scroll to the bottom of the page and
+click the Submit button.
+
+You can add overall comments in the text box at the bottom of the page.
+When you're done, click the Submit button.
+
+Phabricator has many useful features, for example allowing you to select
+diffs between different versions of the patch as it was reviewed in the
+*Revision Update History*. Most features are self descriptive - explore, and
+if you have a question, drop by on #llvm in IRC to get help.
+
+Note that as e-mail is the system of reference for code reviews, and some
+people prefer it over a web interface, we do not generate automated mail
+when a review changes state, for example by clicking "Accept Revision" in
+the web interface. Thus, please type LGTM into the comment box to accept
+a change from Phabricator.
+
+Committing a change
+-------------------
+
+Once a patch has been reviewed and approved on Phabricator it can then be
+committed to trunk. If you do not have commit access, someone has to
+commit the change for you (with attribution). It is sufficient to add
+a comment to the approved review indicating you cannot commit the patch
+yourself. If you have commit access, there are multiple workflows to commit the
+change. Whichever method you follow it is recommended that your commit message
+ends with the line:
+
+::
+
+ Differential Revision: <URL>
+
+where ``<URL>`` is the URL for the code review, starting with
+``http://reviews.llvm.org/``.
+
+This allows people reading the version history to see the review for
+context. This also allows Phabricator to detect the commit, close the
+review, and add a link from the review to the commit.
+
+Note that if you use the Arcanist tool the ``Differential Revision`` line will
+be added automatically. If you don't want to use Arcanist, you can add the
+``Differential Revision`` line (as the last line) to the commit message
+yourself.
+
+Using the Arcanist tool can simplify the process of committing reviewed code
+as it will retrieve reviewers, the ``Differential Revision``, etc from the review
+and place it in the commit message. Several methods of using Arcanist to commit
+code are given below. If you do not wish to use Arcanist then simply commit
+the reviewed patch as you would normally.
+
+Note that if you commit the change without using Arcanist and forget to add the
+``Differential Revision`` line to your commit message then it is recommended
+that you close the review manually. In the web UI, under "Leap Into Action" put
+the SVN revision number in the Comment, set the Action to "Close Revision" and
+click Submit. Note the review must have been Accepted first.
+
+Subversion and Arcanist
+^^^^^^^^^^^^^^^^^^^^^^^
+
+On a clean Subversion working copy run the following (where ``<Revision>`` is
+the Phabricator review number):
+
+::
+
+ arc patch D<Revision>
+ arc commit --revision D<Revision>
+
+The first command will take the latest version of the reviewed patch and apply it to the working
+copy. The second command will commit this revision to trunk.
+
+git-svn and Arcanist
+^^^^^^^^^^^^^^^^^^^^
+
+This presumes that the git repository has been configured as described in :ref:`developers-work-with-git-svn`.
+
+On a clean Git repository on an up to date ``master`` branch run the
+following (where ``<Revision>`` is the Phabricator review number):
+
+::
+
+ arc patch D<Revision>
+
+
+This will create a new branch called ``arcpatch-D<Revision>`` based on the
+current ``master`` and will create a commit corresponding to ``D<Revision>`` with a
+commit message derived from information in the Phabricator review.
+
+Check you are happy with the commit message and amend it if necessary. Now switch to
+the ``master`` branch and add the new commit to it and commit it to trunk. This
+can be done by running the following:
+
+::
+
+ git checkout master
+ git merge --ff-only arcpatch-D<Revision>
+ git svn dcommit
+
+
+
+Abandoning a change
+-------------------
+
+If you decide you should not commit the patch, you should explicitly abandon
+the review so that reviewers don't think it is still open. In the web UI,
+scroll to the bottom of the page where normally you would enter an overall
+comment. In the drop-down Action list, which defaults to "Comment," you should
+select "Abandon Revision" and then enter a comment explaining why. Click the
+Submit button to finish closing the review.
+
+Status
+------
+
+Please let us know whether you like it and what could be improved! We're still
+working on setting up a bug tracker, but you can email klimek-at-google-dot-com
+and chandlerc-at-gmail-dot-com and CC the llvm-dev mailing list with questions
+until then. We also could use help implementing improvements. This sadly is
+really painful and hard because the Phabricator codebase is in PHP and not as
+testable as you might like. However, we've put exactly what we're deploying up
+on an `llvm-reviews GitHub project`_ where folks can hack on it and post pull
+requests. We're looking into what the right long-term hosting for this is, but
+note that it is a derivative of an existing open source project, and so not
+trivially a good fit for an official LLVM project.
+
+.. _LLVM's Phabricator: http://reviews.llvm.org
+.. _`http://reviews.llvm.org`: http://reviews.llvm.org
+.. _Code Repository Browser: http://reviews.llvm.org/diffusion/
+.. _Arcanist Quick Start: https://secure.phabricator.com/book/phabricator/article/arcanist_quick_start/
+.. _Arcanist User Guide: https://secure.phabricator.com/book/phabricator/article/arcanist/
+.. _llvm-reviews GitHub project: https://github.com/r4nt/llvm-reviews/
Added: www-releases/trunk/5.0.1/docs/_sources/ProgrammersManual.rst.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.1/docs/_sources/ProgrammersManual.rst.txt?rev=321287&view=auto
==============================================================================
--- www-releases/trunk/5.0.1/docs/_sources/ProgrammersManual.rst.txt (added)
+++ www-releases/trunk/5.0.1/docs/_sources/ProgrammersManual.rst.txt Thu Dec 21 10:09:53 2017
@@ -0,0 +1,4117 @@
+========================
+LLVM Programmer's Manual
+========================
+
+.. contents::
+ :local:
+
+.. warning::
+ This is always a work in progress.
+
+.. _introduction:
+
+Introduction
+============
+
+This document is meant to highlight some of the important classes and interfaces
+available in the LLVM source-base. This manual is not intended to explain what
+LLVM is, how it works, and what LLVM code looks like. It assumes that you know
+the basics of LLVM and are interested in writing transformations or otherwise
+analyzing or manipulating the code.
+
+This document should get you oriented so that you can find your way in the
+continuously growing source code that makes up the LLVM infrastructure. Note
+that this manual is not intended to serve as a replacement for reading the
+source code, so if you think there should be a method in one of these classes to
+do something, but it's not listed, check the source. Links to the `doxygen
+<http://llvm.org/doxygen/>`__ sources are provided to make this as easy as
+possible.
+
+The first section of this document describes general information that is useful
+to know when working in the LLVM infrastructure, and the second describes the
+Core LLVM classes. In the future this manual will be extended with information
+describing how to use extension libraries, such as dominator information, CFG
+traversal routines, and useful utilities like the ``InstVisitor`` (`doxygen
+<http://llvm.org/doxygen/InstVisitor_8h_source.html>`__) template.
+
+.. _general:
+
+General Information
+===================
+
+This section contains general information that is useful if you are working in
+the LLVM source-base, but that isn't specific to any particular API.
+
+.. _stl:
+
+The C++ Standard Template Library
+---------------------------------
+
+LLVM makes heavy use of the C++ Standard Template Library (STL), perhaps much
+more than you are used to, or have seen before. Because of this, you might want
+to do a little background reading in the techniques used and capabilities of the
+library. There are many good pages that discuss the STL, and several books on
+the subject that you can get, so it will not be discussed in this document.
+
+Here are some useful links:
+
+#. `cppreference.com
+ <http://en.cppreference.com/w/>`_ - an excellent
+ reference for the STL and other parts of the standard C++ library.
+
+#. `C++ In a Nutshell <http://www.tempest-sw.com/cpp/>`_ - This is an O'Reilly
+ book in the making. It has a decent Standard Library Reference that rivals
+ Dinkumware's, and is unfortunately no longer free since the book has been
+ published.
+
+#. `C++ Frequently Asked Questions <http://www.parashift.com/c++-faq-lite/>`_.
+
+#. `SGI's STL Programmer's Guide <http://www.sgi.com/tech/stl/>`_ - Contains a
+ useful `Introduction to the STL
+ <http://www.sgi.com/tech/stl/stl_introduction.html>`_.
+
+#. `Bjarne Stroustrup's C++ Page
+ <http://www.research.att.com/%7Ebs/C++.html>`_.
+
+#. `Bruce Eckel's Thinking in C++, 2nd ed. Volume 2 Revision 4.0
+ (even better, get the book)
+ <http://www.mindview.net/Books/TICPP/ThinkingInCPP2e.html>`_.
+
+You are also encouraged to take a look at the :doc:`LLVM Coding Standards
+<CodingStandards>` guide which focuses on how to write maintainable code more
+than where to put your curly braces.
+
+.. _resources:
+
+Other useful references
+-----------------------
+
+#. `Using static and shared libraries across platforms
+ <http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html>`_
+
+.. _apis:
+
+Important and useful LLVM APIs
+==============================
+
+Here we highlight some LLVM APIs that are generally useful and good to know
+about when writing transformations.
+
+.. _isa:
+
+The ``isa<>``, ``cast<>`` and ``dyn_cast<>`` templates
+------------------------------------------------------
+
+The LLVM source-base makes extensive use of a custom form of RTTI. These
+templates have many similarities to the C++ ``dynamic_cast<>`` operator, but
+they don't have some drawbacks (primarily stemming from the fact that
+``dynamic_cast<>`` only works on classes that have a v-table). Because they are
+used so often, you must know what they do and how they work. All of these
+templates are defined in the ``llvm/Support/Casting.h`` (`doxygen
+<http://llvm.org/doxygen/Casting_8h_source.html>`__) file (note that you very
+rarely have to include this file directly).
+
+``isa<>``:
+ The ``isa<>`` operator works exactly like the Java "``instanceof``" operator.
+ It returns true or false depending on whether a reference or pointer points to
+ an instance of the specified class. This can be very useful for constraint
+ checking of various sorts (example below).
+
+``cast<>``:
+ The ``cast<>`` operator is a "checked cast" operation. It converts a pointer
+ or reference from a base class to a derived class, causing an assertion
+ failure if it is not really an instance of the right type. This should be
+ used in cases where you have some information that makes you believe that
+ something is of the right type. An example of the ``isa<>`` and ``cast<>``
+ template is:
+
+ .. code-block:: c++
+
+ static bool isLoopInvariant(const Value *V, const Loop *L) {
+ if (isa<Constant>(V) || isa<Argument>(V) || isa<GlobalValue>(V))
+ return true;
+
+ // Otherwise, it must be an instruction...
+ return !L->contains(cast<Instruction>(V)->getParent());
+ }
+
+ Note that you should **not** use an ``isa<>`` test followed by a ``cast<>``,
+ for that use the ``dyn_cast<>`` operator.
+
+``dyn_cast<>``:
+ The ``dyn_cast<>`` operator is a "checking cast" operation. It checks to see
+ if the operand is of the specified type, and if so, returns a pointer to it
+ (this operator does not work with references). If the operand is not of the
+ correct type, a null pointer is returned. Thus, this works very much like
+ the ``dynamic_cast<>`` operator in C++, and should be used in the same
+ circumstances. Typically, the ``dyn_cast<>`` operator is used in an ``if``
+ statement or some other flow control statement like this:
+
+ .. code-block:: c++
+
+ if (auto *AI = dyn_cast<AllocationInst>(Val)) {
+ // ...
+ }
+
+ This form of the ``if`` statement effectively combines together a call to
+ ``isa<>`` and a call to ``cast<>`` into one statement, which is very
+ convenient.
+
+ Note that the ``dyn_cast<>`` operator, like C++'s ``dynamic_cast<>`` or Java's
+ ``instanceof`` operator, can be abused. In particular, you should not use big
+ chained ``if/then/else`` blocks to check for lots of different variants of
+ classes. If you find yourself wanting to do this, it is much cleaner and more
+ efficient to use the ``InstVisitor`` class to dispatch over the instruction
+ type directly.
+
+``cast_or_null<>``:
+ The ``cast_or_null<>`` operator works just like the ``cast<>`` operator,
+ except that it allows for a null pointer as an argument (which it then
+ propagates). This can sometimes be useful, allowing you to combine several
+ null checks into one.
+
+``dyn_cast_or_null<>``:
+ The ``dyn_cast_or_null<>`` operator works just like the ``dyn_cast<>``
+ operator, except that it allows for a null pointer as an argument (which it
+ then propagates). This can sometimes be useful, allowing you to combine
+ several null checks into one.
+
+These five templates can be used with any classes, whether they have a v-table
+or not. If you want to add support for these templates, see the document
+:doc:`How to set up LLVM-style RTTI for your class hierarchy
+<HowToSetUpLLVMStyleRTTI>`
+
+.. _string_apis:
+
+Passing strings (the ``StringRef`` and ``Twine`` classes)
+---------------------------------------------------------
+
+Although LLVM generally does not do much string manipulation, we do have several
+important APIs which take strings. Two important examples are the Value class
+-- which has names for instructions, functions, etc. -- and the ``StringMap``
+class which is used extensively in LLVM and Clang.
+
+These are generic classes, and they need to be able to accept strings which may
+have embedded null characters. Therefore, they cannot simply take a ``const
+char *``, and taking a ``const std::string&`` requires clients to perform a heap
+allocation which is usually unnecessary. Instead, many LLVM APIs use a
+``StringRef`` or a ``const Twine&`` for passing strings efficiently.
+
+.. _StringRef:
+
+The ``StringRef`` class
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The ``StringRef`` data type represents a reference to a constant string (a
+character array and a length) and supports the common operations available on
+``std::string``, but does not require heap allocation.
+
+It can be implicitly constructed using a C style null-terminated string, an
+``std::string``, or explicitly with a character pointer and length. For
+example, the ``StringRef`` find function is declared as:
+
+.. code-block:: c++
+
+ iterator find(StringRef Key);
+
+and clients can call it using any one of:
+
+.. code-block:: c++
+
+ Map.find("foo"); // Lookup "foo"
+ Map.find(std::string("bar")); // Lookup "bar"
+ Map.find(StringRef("\0baz", 4)); // Lookup "\0baz"
+
+Similarly, APIs which need to return a string may return a ``StringRef``
+instance, which can be used directly or converted to an ``std::string`` using
+the ``str`` member function. See ``llvm/ADT/StringRef.h`` (`doxygen
+<http://llvm.org/doxygen/StringRef_8h_source.html>`__) for more
+information.
+
+You should rarely use the ``StringRef`` class directly, because it contains
+pointers to external memory it is not generally safe to store an instance of the
+class (unless you know that the external storage will not be freed).
+``StringRef`` is small and pervasive enough in LLVM that it should always be
+passed by value.
+
+The ``Twine`` class
+^^^^^^^^^^^^^^^^^^^
+
+The ``Twine`` (`doxygen <http://llvm.org/doxygen/classllvm_1_1Twine.html>`__)
+class is an efficient way for APIs to accept concatenated strings. For example,
+a common LLVM paradigm is to name one instruction based on the name of another
+instruction with a suffix, for example:
+
+.. code-block:: c++
+
+ New = CmpInst::Create(..., SO->getName() + ".cmp");
+
+The ``Twine`` class is effectively a lightweight `rope
+<http://en.wikipedia.org/wiki/Rope_(computer_science)>`_ which points to
+temporary (stack allocated) objects. Twines can be implicitly constructed as
+the result of the plus operator applied to strings (i.e., a C strings, an
+``std::string``, or a ``StringRef``). The twine delays the actual concatenation
+of strings until it is actually required, at which point it can be efficiently
+rendered directly into a character array. This avoids unnecessary heap
+allocation involved in constructing the temporary results of string
+concatenation. See ``llvm/ADT/Twine.h`` (`doxygen
+<http://llvm.org/doxygen/Twine_8h_source.html>`__) and :ref:`here <dss_twine>`
+for more information.
+
+As with a ``StringRef``, ``Twine`` objects point to external memory and should
+almost never be stored or mentioned directly. They are intended solely for use
+when defining a function which should be able to efficiently accept concatenated
+strings.
+
+.. _formatting_strings:
+
+Formatting strings (the ``formatv`` function)
+---------------------------------------------
+While LLVM doesn't necessarily do a lot of string manipulation and parsing, it
+does do a lot of string formatting. From diagnostic messages, to llvm tool
+outputs such as ``llvm-readobj`` to printing verbose disassembly listings and
+LLDB runtime logging, the need for string formatting is pervasive.
+
+The ``formatv`` is similar in spirit to ``printf``, but uses a different syntax
+which borrows heavily from Python and C#. Unlike ``printf`` it deduces the type
+to be formatted at compile time, so it does not need a format specifier such as
+``%d``. This reduces the mental overhead of trying to construct portable format
+strings, especially for platform-specific types like ``size_t`` or pointer types.
+Unlike both ``printf`` and Python, it additionally fails to compile if LLVM does
+not know how to format the type. These two properties ensure that the function
+is both safer and simpler to use than traditional formatting methods such as
+the ``printf`` family of functions.
+
+Simple formatting
+^^^^^^^^^^^^^^^^^
+
+A call to ``formatv`` involves a single **format string** consisting of 0 or more
+**replacement sequences**, followed by a variable length list of **replacement values**.
+A replacement sequence is a string of the form ``{N[[,align]:style]}``.
+
+``N`` refers to the 0-based index of the argument from the list of replacement
+values. Note that this means it is possible to reference the same parameter
+multiple times, possibly with different style and/or alignment options, in any order.
+
+``align`` is an optional string specifying the width of the field to format
+the value into, and the alignment of the value within the field. It is specified as
+an optional **alignment style** followed by a positive integral **field width**. The
+alignment style can be one of the characters ``-`` (left align), ``=`` (center align),
+or ``+`` (right align). The default is right aligned.
+
+``style`` is an optional string consisting of a type specific that controls the
+formatting of the value. For example, to format a floating point value as a percentage,
+you can use the style option ``P``.
+
+Custom formatting
+^^^^^^^^^^^^^^^^^
+
+There are two ways to customize the formatting behavior for a type.
+
+1. Provide a template specialization of ``llvm::format_provider<T>`` for your
+ type ``T`` with the appropriate static format method.
+
+ .. code-block:: c++
+
+ namespace llvm {
+ template<>
+ struct format_provider<MyFooBar> {
+ static void format(const MyFooBar &V, raw_ostream &Stream, StringRef Style) {
+ // Do whatever is necessary to format `V` into `Stream`
+ }
+ };
+ void foo() {
+ MyFooBar X;
+ std::string S = formatv("{0}", X);
+ }
+ }
+
+ This is a useful extensibility mechanism for adding support for formatting your own
+ custom types with your own custom Style options. But it does not help when you want
+ to extend the mechanism for formatting a type that the library already knows how to
+ format. For that, we need something else.
+
+2. Provide a **format adapter** inheriting from ``llvm::FormatAdapter<T>``.
+
+ .. code-block:: c++
+
+ namespace anything {
+ struct format_int_custom : public llvm::FormatAdapter<int> {
+ explicit format_int_custom(int N) : llvm::FormatAdapter<int>(N) {}
+ void format(llvm::raw_ostream &Stream, StringRef Style) override {
+ // Do whatever is necessary to format ``this->Item`` into ``Stream``
+ }
+ };
+ }
+ namespace llvm {
+ void foo() {
+ std::string S = formatv("{0}", anything::format_int_custom(42));
+ }
+ }
+
+ If the type is detected to be derived from ``FormatAdapter<T>``, ``formatv``
+ will call the
+ ``format`` method on the argument passing in the specified style. This allows
+ one to provide custom formatting of any type, including one which already has
+ a builtin format provider.
+
+``formatv`` Examples
+^^^^^^^^^^^^^^^^^^^^
+Below is intended to provide an incomplete set of examples demonstrating
+the usage of ``formatv``. More information can be found by reading the
+doxygen documentation or by looking at the unit test suite.
+
+
+.. code-block:: c++
+
+ std::string S;
+ // Simple formatting of basic types and implicit string conversion.
+ S = formatv("{0} ({1:P})", 7, 0.35); // S == "7 (35.00%)"
+
+ // Out-of-order referencing and multi-referencing
+ outs() << formatv("{0} {2} {1} {0}", 1, "test", 3); // prints "1 3 test 1"
+
+ // Left, right, and center alignment
+ S = formatv("{0,7}", 'a'); // S == " a";
+ S = formatv("{0,-7}", 'a'); // S == "a ";
+ S = formatv("{0,=7}", 'a'); // S == " a ";
+ S = formatv("{0,+7}", 'a'); // S == " a";
+
+ // Custom styles
+ S = formatv("{0:N} - {0:x} - {1:E}", 12345, 123908342); // S == "12,345 - 0x3039 - 1.24E8"
+
+ // Adapters
+ S = formatv("{0}", fmt_align(42, AlignStyle::Center, 7)); // S == " 42 "
+ S = formatv("{0}", fmt_repeat("hi", 3)); // S == "hihihi"
+ S = formatv("{0}", fmt_pad("hi", 2, 6)); // S == " hi "
+
+ // Ranges
+ std::vector<int> V = {8, 9, 10};
+ S = formatv("{0}", make_range(V.begin(), V.end())); // S == "8, 9, 10"
+ S = formatv("{0:$[+]}", make_range(V.begin(), V.end())); // S == "8+9+10"
+ S = formatv("{0:$[ + ]@[x]}", make_range(V.begin(), V.end())); // S == "0x8 + 0x9 + 0xA"
+
+.. _error_apis:
+
+Error handling
+--------------
+
+Proper error handling helps us identify bugs in our code, and helps end-users
+understand errors in their tool usage. Errors fall into two broad categories:
+*programmatic* and *recoverable*, with different strategies for handling and
+reporting.
+
+Programmatic Errors
+^^^^^^^^^^^^^^^^^^^
+
+Programmatic errors are violations of program invariants or API contracts, and
+represent bugs within the program itself. Our aim is to document invariants, and
+to abort quickly at the point of failure (providing some basic diagnostic) when
+invariants are broken at runtime.
+
+The fundamental tools for handling programmatic errors are assertions and the
+llvm_unreachable function. Assertions are used to express invariant conditions,
+and should include a message describing the invariant:
+
+.. code-block:: c++
+
+ assert(isPhysReg(R) && "All virt regs should have been allocated already.");
+
+The llvm_unreachable function can be used to document areas of control flow
+that should never be entered if the program invariants hold:
+
+.. code-block:: c++
+
+ enum { Foo, Bar, Baz } X = foo();
+
+ switch (X) {
+ case Foo: /* Handle Foo */; break;
+ case Bar: /* Handle Bar */; break;
+ default:
+ llvm_unreachable("X should be Foo or Bar here");
+ }
+
+Recoverable Errors
+^^^^^^^^^^^^^^^^^^
+
+Recoverable errors represent an error in the program's environment, for example
+a resource failure (a missing file, a dropped network connection, etc.), or
+malformed input. These errors should be detected and communicated to a level of
+the program where they can be handled appropriately. Handling the error may be
+as simple as reporting the issue to the user, or it may involve attempts at
+recovery.
+
+Recoverable errors are modeled using LLVM's ``Error`` scheme. This scheme
+represents errors using function return values, similar to classic C integer
+error codes, or C++'s ``std::error_code``. However, the ``Error`` class is
+actually a lightweight wrapper for user-defined error types, allowing arbitrary
+information to be attached to describe the error. This is similar to the way C++
+exceptions allow throwing of user-defined types.
+
+Success values are created by calling ``Error::success()``, E.g.:
+
+.. code-block:: c++
+
+ Error foo() {
+ // Do something.
+ // Return success.
+ return Error::success();
+ }
+
+Success values are very cheap to construct and return - they have minimal
+impact on program performance.
+
+Failure values are constructed using ``make_error<T>``, where ``T`` is any class
+that inherits from the ErrorInfo utility, E.g.:
+
+.. code-block:: c++
+
+ class BadFileFormat : public ErrorInfo<BadFileFormat> {
+ public:
+ static char ID;
+ std::string Path;
+
+ BadFileFormat(StringRef Path) : Path(Path.str()) {}
+
+ void log(raw_ostream &OS) const override {
+ OS << Path << " is malformed";
+ }
+
+ std::error_code convertToErrorCode() const override {
+ return make_error_code(object_error::parse_failed);
+ }
+ };
+
+ char BadFileFormat::ID; // This should be declared in the C++ file.
+
+ Error printFormattedFile(StringRef Path) {
+ if (<check for valid format>)
+ return make_error<InvalidObjectFile>(Path);
+ // print file contents.
+ return Error::success();
+ }
+
+Error values can be implicitly converted to bool: true for error, false for
+success, enabling the following idiom:
+
+.. code-block:: c++
+
+ Error mayFail();
+
+ Error foo() {
+ if (auto Err = mayFail())
+ return Err;
+ // Success! We can proceed.
+ ...
+
+For functions that can fail but need to return a value the ``Expected<T>``
+utility can be used. Values of this type can be constructed with either a
+``T``, or an ``Error``. Expected<T> values are also implicitly convertible to
+boolean, but with the opposite convention to ``Error``: true for success, false
+for error. If success, the ``T`` value can be accessed via the dereference
+operator. If failure, the ``Error`` value can be extracted using the
+``takeError()`` method. Idiomatic usage looks like:
+
+.. code-block:: c++
+
+ Expected<FormattedFile> openFormattedFile(StringRef Path) {
+ // If badly formatted, return an error.
+ if (auto Err = checkFormat(Path))
+ return std::move(Err);
+ // Otherwise return a FormattedFile instance.
+ return FormattedFile(Path);
+ }
+
+ Error processFormattedFile(StringRef Path) {
+ // Try to open a formatted file
+ if (auto FileOrErr = openFormattedFile(Path)) {
+ // On success, grab a reference to the file and continue.
+ auto &File = *FileOrErr;
+ ...
+ } else
+ // On error, extract the Error value and return it.
+ return FileOrErr.takeError();
+ }
+
+If an ``Expected<T>`` value is in success mode then the ``takeError()`` method
+will return a success value. Using this fact, the above function can be
+rewritten as:
+
+.. code-block:: c++
+
+ Error processFormattedFile(StringRef Path) {
+ // Try to open a formatted file
+ auto FileOrErr = openFormattedFile(Path);
+ if (auto Err = FileOrErr.takeError())
+ // On error, extract the Error value and return it.
+ return Err;
+ // On success, grab a reference to the file and continue.
+ auto &File = *FileOrErr;
+ ...
+ }
+
+This second form is often more readable for functions that involve multiple
+``Expected<T>`` values as it limits the indentation required.
+
+All ``Error`` instances, whether success or failure, must be either checked or
+moved from (via ``std::move`` or a return) before they are destructed.
+Accidentally discarding an unchecked error will cause a program abort at the
+point where the unchecked value's destructor is run, making it easy to identify
+and fix violations of this rule.
+
+Success values are considered checked once they have been tested (by invoking
+the boolean conversion operator):
+
+.. code-block:: c++
+
+ if (auto Err = mayFail(...))
+ return Err; // Failure value - move error to caller.
+
+ // Safe to continue: Err was checked.
+
+In contrast, the following code will always cause an abort, even if ``mayFail``
+returns a success value:
+
+.. code-block:: c++
+
+ mayFail();
+ // Program will always abort here, even if mayFail() returns Success, since
+ // the value is not checked.
+
+Failure values are considered checked once a handler for the error type has
+been activated:
+
+.. code-block:: c++
+
+ handleErrors(
+ processFormattedFile(...),
+ [](const BadFileFormat &BFF) {
+ report("Unable to process " + BFF.Path + ": bad format");
+ },
+ [](const FileNotFound &FNF) {
+ report("File not found " + FNF.Path);
+ });
+
+The ``handleErrors`` function takes an error as its first argument, followed by
+a variadic list of "handlers", each of which must be a callable type (a
+function, lambda, or class with a call operator) with one argument. The
+``handleErrors`` function will visit each handler in the sequence and check its
+argument type against the dynamic type of the error, running the first handler
+that matches. This is the same decision process that is used decide which catch
+clause to run for a C++ exception.
+
+Since the list of handlers passed to ``handleErrors`` may not cover every error
+type that can occur, the ``handleErrors`` function also returns an Error value
+that must be checked or propagated. If the error value that is passed to
+``handleErrors`` does not match any of the handlers it will be returned from
+handleErrors. Idiomatic use of ``handleErrors`` thus looks like:
+
+.. code-block:: c++
+
+ if (auto Err =
+ handleErrors(
+ processFormattedFile(...),
+ [](const BadFileFormat &BFF) {
+ report("Unable to process " + BFF.Path + ": bad format");
+ },
+ [](const FileNotFound &FNF) {
+ report("File not found " + FNF.Path);
+ }))
+ return Err;
+
+In cases where you truly know that the handler list is exhaustive the
+``handleAllErrors`` function can be used instead. This is identical to
+``handleErrors`` except that it will terminate the program if an unhandled
+error is passed in, and can therefore return void. The ``handleAllErrors``
+function should generally be avoided: the introduction of a new error type
+elsewhere in the program can easily turn a formerly exhaustive list of errors
+into a non-exhaustive list, risking unexpected program termination. Where
+possible, use handleErrors and propagate unknown errors up the stack instead.
+
+For tool code, where errors can be handled by printing an error message then
+exiting with an error code, the :ref:`ExitOnError <err_exitonerr>` utility
+may be a better choice than handleErrors, as it simplifies control flow when
+calling fallible functions.
+
+In situations where it is known that a particular call to a fallible function
+will always succeed (for example, a call to a function that can only fail on a
+subset of inputs with an input that is known to be safe) the
+:ref:`cantFail <err_cantfail>` functions can be used to remove the error type,
+simplifying control flow.
+
+StringError
+"""""""""""
+
+Many kinds of errors have no recovery strategy, the only action that can be
+taken is to report them to the user so that the user can attempt to fix the
+environment. In this case representing the error as a string makes perfect
+sense. LLVM provides the ``StringError`` class for this purpose. It takes two
+arguments: A string error message, and an equivalent ``std::error_code`` for
+interoperability:
+
+.. code-block:: c++
+
+ make_error<StringError>("Bad executable",
+ make_error_code(errc::executable_format_error"));
+
+If you're certain that the error you're building will never need to be converted
+to a ``std::error_code`` you can use the ``inconvertibleErrorCode()`` function:
+
+.. code-block:: c++
+
+ make_error<StringError>("Bad executable", inconvertibleErrorCode());
+
+This should be done only after careful consideration. If any attempt is made to
+convert this error to a ``std::error_code`` it will trigger immediate program
+termination. Unless you are certain that your errors will not need
+interoperability you should look for an existing ``std::error_code`` that you
+can convert to, and even (as painful as it is) consider introducing a new one as
+a stopgap measure.
+
+Interoperability with std::error_code and ErrorOr
+"""""""""""""""""""""""""""""""""""""""""""""""""
+
+Many existing LLVM APIs use ``std::error_code`` and its partner ``ErrorOr<T>``
+(which plays the same role as ``Expected<T>``, but wraps a ``std::error_code``
+rather than an ``Error``). The infectious nature of error types means that an
+attempt to change one of these functions to return ``Error`` or ``Expected<T>``
+instead often results in an avalanche of changes to callers, callers of callers,
+and so on. (The first such attempt, returning an ``Error`` from
+MachOObjectFile's constructor, was abandoned after the diff reached 3000 lines,
+impacted half a dozen libraries, and was still growing).
+
+To solve this problem, the ``Error``/``std::error_code`` interoperability requirement was
+introduced. Two pairs of functions allow any ``Error`` value to be converted to a
+``std::error_code``, any ``Expected<T>`` to be converted to an ``ErrorOr<T>``, and vice
+versa:
+
+.. code-block:: c++
+
+ std::error_code errorToErrorCode(Error Err);
+ Error errorCodeToError(std::error_code EC);
+
+ template <typename T> ErrorOr<T> expectedToErrorOr(Expected<T> TOrErr);
+ template <typename T> Expected<T> errorOrToExpected(ErrorOr<T> TOrEC);
+
+
+Using these APIs it is easy to make surgical patches that update individual
+functions from ``std::error_code`` to ``Error``, and from ``ErrorOr<T>`` to
+``Expected<T>``.
+
+Returning Errors from error handlers
+""""""""""""""""""""""""""""""""""""
+
+Error recovery attempts may themselves fail. For that reason, ``handleErrors``
+actually recognises three different forms of handler signature:
+
+.. code-block:: c++
+
+ // Error must be handled, no new errors produced:
+ void(UserDefinedError &E);
+
+ // Error must be handled, new errors can be produced:
+ Error(UserDefinedError &E);
+
+ // Original error can be inspected, then re-wrapped and returned (or a new
+ // error can be produced):
+ Error(std::unique_ptr<UserDefinedError> E);
+
+Any error returned from a handler will be returned from the ``handleErrors``
+function so that it can be handled itself, or propagated up the stack.
+
+.. _err_exitonerr:
+
+Using ExitOnError to simplify tool code
+"""""""""""""""""""""""""""""""""""""""
+
+Library code should never call ``exit`` for a recoverable error, however in tool
+code (especially command line tools) this can be a reasonable approach. Calling
+``exit`` upon encountering an error dramatically simplifies control flow as the
+error no longer needs to be propagated up the stack. This allows code to be
+written in straight-line style, as long as each fallible call is wrapped in a
+check and call to exit. The ``ExitOnError`` class supports this pattern by
+providing call operators that inspect ``Error`` values, stripping the error away
+in the success case and logging to ``stderr`` then exiting in the failure case.
+
+To use this class, declare a global ``ExitOnError`` variable in your program:
+
+.. code-block:: c++
+
+ ExitOnError ExitOnErr;
+
+Calls to fallible functions can then be wrapped with a call to ``ExitOnErr``,
+turning them into non-failing calls:
+
+.. code-block:: c++
+
+ Error mayFail();
+ Expected<int> mayFail2();
+
+ void foo() {
+ ExitOnErr(mayFail());
+ int X = ExitOnErr(mayFail2());
+ }
+
+On failure, the error's log message will be written to ``stderr``, optionally
+preceded by a string "banner" that can be set by calling the setBanner method. A
+mapping can also be supplied from ``Error`` values to exit codes using the
+``setExitCodeMapper`` method:
+
+.. code-block:: c++
+
+ int main(int argc, char *argv[]) {
+ ExitOnErr.setBanner(std::string(argv[0]) + " error:");
+ ExitOnErr.setExitCodeMapper(
+ [](const Error &Err) {
+ if (Err.isA<BadFileFormat>())
+ return 2;
+ return 1;
+ });
+
+Use ``ExitOnError`` in your tool code where possible as it can greatly improve
+readability.
+
+.. _err_cantfail:
+
+Using cantFail to simplify safe callsites
+"""""""""""""""""""""""""""""""""""""""""
+
+Some functions may only fail for a subset of their inputs, so calls using known
+safe inputs can be assumed to succeed.
+
+The cantFail functions encapsulate this by wrapping an assertion that their
+argument is a success value and, in the case of Expected<T>, unwrapping the
+T value:
+
+.. code-block:: c++
+
+ Error onlyFailsForSomeXValues(int X);
+ Expected<int> onlyFailsForSomeXValues2(int X);
+
+ void foo() {
+ cantFail(onlyFailsForSomeXValues(KnownSafeValue));
+ int Y = cantFail(onlyFailsForSomeXValues2(KnownSafeValue));
+ ...
+ }
+
+Like the ExitOnError utility, cantFail simplifies control flow. Their treatment
+of error cases is very different however: Where ExitOnError is guaranteed to
+terminate the program on an error input, cantFile simply asserts that the result
+is success. In debug builds this will result in an assertion failure if an error
+is encountered. In release builds the behavior of cantFail for failure values is
+undefined. As such, care must be taken in the use of cantFail: clients must be
+certain that a cantFail wrapped call really can not fail with the given
+arguments.
+
+Use of the cantFail functions should be rare in library code, but they are
+likely to be of more use in tool and unit-test code where inputs and/or
+mocked-up classes or functions may be known to be safe.
+
+Fallible constructors
+"""""""""""""""""""""
+
+Some classes require resource acquisition or other complex initialization that
+can fail during construction. Unfortunately constructors can't return errors,
+and having clients test objects after they're constructed to ensure that they're
+valid is error prone as it's all too easy to forget the test. To work around
+this, use the named constructor idiom and return an ``Expected<T>``:
+
+.. code-block:: c++
+
+ class Foo {
+ public:
+
+ static Expected<Foo> Create(Resource R1, Resource R2) {
+ Error Err;
+ Foo F(R1, R2, Err);
+ if (Err)
+ return std::move(Err);
+ return std::move(F);
+ }
+
+ private:
+
+ Foo(Resource R1, Resource R2, Error &Err) {
+ ErrorAsOutParameter EAO(&Err);
+ if (auto Err2 = R1.acquire()) {
+ Err = std::move(Err2);
+ return;
+ }
+ Err = R2.acquire();
+ }
+ };
+
+
+Here, the named constructor passes an ``Error`` by reference into the actual
+constructor, which the constructor can then use to return errors. The
+``ErrorAsOutParameter`` utility sets the ``Error`` value's checked flag on entry
+to the constructor so that the error can be assigned to, then resets it on exit
+to force the client (the named constructor) to check the error.
+
+By using this idiom, clients attempting to construct a Foo receive either a
+well-formed Foo or an Error, never an object in an invalid state.
+
+Propagating and consuming errors based on types
+"""""""""""""""""""""""""""""""""""""""""""""""
+
+In some contexts, certain types of error are known to be benign. For example,
+when walking an archive, some clients may be happy to skip over badly formatted
+object files rather than terminating the walk immediately. Skipping badly
+formatted objects could be achieved using an elaborate handler method, but the
+Error.h header provides two utilities that make this idiom much cleaner: the
+type inspection method, ``isA``, and the ``consumeError`` function:
+
+.. code-block:: c++
+
+ Error walkArchive(Archive A) {
+ for (unsigned I = 0; I != A.numMembers(); ++I) {
+ auto ChildOrErr = A.getMember(I);
+ if (auto Err = ChildOrErr.takeError()) {
+ if (Err.isA<BadFileFormat>())
+ consumeError(std::move(Err))
+ else
+ return Err;
+ }
+ auto &Child = *ChildOrErr;
+ // Use Child
+ ...
+ }
+ return Error::success();
+ }
+
+Concatenating Errors with joinErrors
+""""""""""""""""""""""""""""""""""""
+
+In the archive walking example above ``BadFileFormat`` errors are simply
+consumed and ignored. If the client had wanted report these errors after
+completing the walk over the archive they could use the ``joinErrors`` utility:
+
+.. code-block:: c++
+
+ Error walkArchive(Archive A) {
+ Error DeferredErrs = Error::success();
+ for (unsigned I = 0; I != A.numMembers(); ++I) {
+ auto ChildOrErr = A.getMember(I);
+ if (auto Err = ChildOrErr.takeError())
+ if (Err.isA<BadFileFormat>())
+ DeferredErrs = joinErrors(std::move(DeferredErrs), std::move(Err));
+ else
+ return Err;
+ auto &Child = *ChildOrErr;
+ // Use Child
+ ...
+ }
+ return DeferredErrs;
+ }
+
+The ``joinErrors`` routine builds a special error type called ``ErrorList``,
+which holds a list of user defined errors. The ``handleErrors`` routine
+recognizes this type and will attempt to handle each of the contained errors in
+order. If all contained errors can be handled, ``handleErrors`` will return
+``Error::success()``, otherwise ``handleErrors`` will concatenate the remaining
+errors and return the resulting ``ErrorList``.
+
+Building fallible iterators and iterator ranges
+"""""""""""""""""""""""""""""""""""""""""""""""
+
+The archive walking examples above retrieve archive members by index, however
+this requires considerable boiler-plate for iteration and error checking. We can
+clean this up by using ``Error`` with the "fallible iterator" pattern. The usual
+C++ iterator patterns do not allow for failure on increment, but we can
+incorporate support for it by having iterators hold an Error reference through
+which they can report failure. In this pattern, if an increment operation fails
+the failure is recorded via the Error reference and the iterator value is set to
+the end of the range in order to terminate the loop. This ensures that the
+dereference operation is safe anywhere that an ordinary iterator dereference
+would be safe (i.e. when the iterator is not equal to end). Where this pattern
+is followed (as in the ``llvm::object::Archive`` class) the result is much
+cleaner iteration idiom:
+
+.. code-block:: c++
+
+ Error Err;
+ for (auto &Child : Ar->children(Err)) {
+ // Use Child - we only enter the loop when it's valid
+ ...
+ }
+ // Check Err after the loop to ensure it didn't break due to an error.
+ if (Err)
+ return Err;
+
+.. _function_apis:
+
+More information on Error and its related utilities can be found in the
+Error.h header file.
+
+Passing functions and other callable objects
+--------------------------------------------
+
+Sometimes you may want a function to be passed a callback object. In order to
+support lambda expressions and other function objects, you should not use the
+traditional C approach of taking a function pointer and an opaque cookie:
+
+.. code-block:: c++
+
+ void takeCallback(bool (*Callback)(Function *, void *), void *Cookie);
+
+Instead, use one of the following approaches:
+
+Function template
+^^^^^^^^^^^^^^^^^
+
+If you don't mind putting the definition of your function into a header file,
+make it a function template that is templated on the callable type.
+
+.. code-block:: c++
+
+ template<typename Callable>
+ void takeCallback(Callable Callback) {
+ Callback(1, 2, 3);
+ }
+
+The ``function_ref`` class template
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The ``function_ref``
+(`doxygen <http://llvm.org/doxygen/classllvm_1_1function__ref_3_01Ret_07Params_8_8_8_08_4.html>`__) class
+template represents a reference to a callable object, templated over the type
+of the callable. This is a good choice for passing a callback to a function,
+if you don't need to hold onto the callback after the function returns. In this
+way, ``function_ref`` is to ``std::function`` as ``StringRef`` is to
+``std::string``.
+
+``function_ref<Ret(Param1, Param2, ...)>`` can be implicitly constructed from
+any callable object that can be called with arguments of type ``Param1``,
+``Param2``, ..., and returns a value that can be converted to type ``Ret``.
+For example:
+
+.. code-block:: c++
+
+ void visitBasicBlocks(Function *F, function_ref<bool (BasicBlock*)> Callback) {
+ for (BasicBlock &BB : *F)
+ if (Callback(&BB))
+ return;
+ }
+
+can be called using:
+
+.. code-block:: c++
+
+ visitBasicBlocks(F, [&](BasicBlock *BB) {
+ if (process(BB))
+ return isEmpty(BB);
+ return false;
+ });
+
+Note that a ``function_ref`` object contains pointers to external memory, so it
+is not generally safe to store an instance of the class (unless you know that
+the external storage will not be freed). If you need this ability, consider
+using ``std::function``. ``function_ref`` is small enough that it should always
+be passed by value.
+
+.. _DEBUG:
+
+The ``DEBUG()`` macro and ``-debug`` option
+-------------------------------------------
+
+Often when working on your pass you will put a bunch of debugging printouts and
+other code into your pass. After you get it working, you want to remove it, but
+you may need it again in the future (to work out new bugs that you run across).
+
+Naturally, because of this, you don't want to delete the debug printouts, but
+you don't want them to always be noisy. A standard compromise is to comment
+them out, allowing you to enable them if you need them in the future.
+
+The ``llvm/Support/Debug.h`` (`doxygen
+<http://llvm.org/doxygen/Debug_8h_source.html>`__) file provides a macro named
+``DEBUG()`` that is a much nicer solution to this problem. Basically, you can
+put arbitrary code into the argument of the ``DEBUG`` macro, and it is only
+executed if '``opt``' (or any other tool) is run with the '``-debug``' command
+line argument:
+
+.. code-block:: c++
+
+ DEBUG(errs() << "I am here!\n");
+
+Then you can run your pass like this:
+
+.. code-block:: none
+
+ $ opt < a.bc > /dev/null -mypass
+ <no output>
+ $ opt < a.bc > /dev/null -mypass -debug
+ I am here!
+
+Using the ``DEBUG()`` macro instead of a home-brewed solution allows you to not
+have to create "yet another" command line option for the debug output for your
+pass. Note that ``DEBUG()`` macros are disabled for non-asserts builds, so they
+do not cause a performance impact at all (for the same reason, they should also
+not contain side-effects!).
+
+One additional nice thing about the ``DEBUG()`` macro is that you can enable or
+disable it directly in gdb. Just use "``set DebugFlag=0``" or "``set
+DebugFlag=1``" from the gdb if the program is running. If the program hasn't
+been started yet, you can always just run it with ``-debug``.
+
+.. _DEBUG_TYPE:
+
+Fine grained debug info with ``DEBUG_TYPE`` and the ``-debug-only`` option
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Sometimes you may find yourself in a situation where enabling ``-debug`` just
+turns on **too much** information (such as when working on the code generator).
+If you want to enable debug information with more fine-grained control, you
+should define the ``DEBUG_TYPE`` macro and use the ``-debug-only`` option as
+follows:
+
+.. code-block:: c++
+
+ #define DEBUG_TYPE "foo"
+ DEBUG(errs() << "'foo' debug type\n");
+ #undef DEBUG_TYPE
+ #define DEBUG_TYPE "bar"
+ DEBUG(errs() << "'bar' debug type\n"));
+ #undef DEBUG_TYPE
+
+Then you can run your pass like this:
+
+.. code-block:: none
+
+ $ opt < a.bc > /dev/null -mypass
+ <no output>
+ $ opt < a.bc > /dev/null -mypass -debug
+ 'foo' debug type
+ 'bar' debug type
+ $ opt < a.bc > /dev/null -mypass -debug-only=foo
+ 'foo' debug type
+ $ opt < a.bc > /dev/null -mypass -debug-only=bar
+ 'bar' debug type
+ $ opt < a.bc > /dev/null -mypass -debug-only=foo,bar
+ 'foo' debug type
+ 'bar' debug type
+
+Of course, in practice, you should only set ``DEBUG_TYPE`` at the top of a file,
+to specify the debug type for the entire module. Be careful that you only do
+this after including Debug.h and not around any #include of headers. Also, you
+should use names more meaningful than "foo" and "bar", because there is no
+system in place to ensure that names do not conflict. If two different modules
+use the same string, they will all be turned on when the name is specified.
+This allows, for example, all debug information for instruction scheduling to be
+enabled with ``-debug-only=InstrSched``, even if the source lives in multiple
+files. The name must not include a comma (,) as that is used to separate the
+arguments of the ``-debug-only`` option.
+
+For performance reasons, -debug-only is not available in optimized build
+(``--enable-optimized``) of LLVM.
+
+The ``DEBUG_WITH_TYPE`` macro is also available for situations where you would
+like to set ``DEBUG_TYPE``, but only for one specific ``DEBUG`` statement. It
+takes an additional first parameter, which is the type to use. For example, the
+preceding example could be written as:
+
+.. code-block:: c++
+
+ DEBUG_WITH_TYPE("foo", errs() << "'foo' debug type\n");
+ DEBUG_WITH_TYPE("bar", errs() << "'bar' debug type\n"));
+
+.. _Statistic:
+
+The ``Statistic`` class & ``-stats`` option
+-------------------------------------------
+
+The ``llvm/ADT/Statistic.h`` (`doxygen
+<http://llvm.org/doxygen/Statistic_8h_source.html>`__) file provides a class
+named ``Statistic`` that is used as a unified way to keep track of what the LLVM
+compiler is doing and how effective various optimizations are. It is useful to
+see what optimizations are contributing to making a particular program run
+faster.
+
+Often you may run your pass on some big program, and you're interested to see
+how many times it makes a certain transformation. Although you can do this with
+hand inspection, or some ad-hoc method, this is a real pain and not very useful
+for big programs. Using the ``Statistic`` class makes it very easy to keep
+track of this information, and the calculated information is presented in a
+uniform manner with the rest of the passes being executed.
+
+There are many examples of ``Statistic`` uses, but the basics of using it are as
+follows:
+
+Define your statistic like this:
+
+.. code-block:: c++
+
+ #define DEBUG_TYPE "mypassname" // This goes before any #includes.
+ STATISTIC(NumXForms, "The # of times I did stuff");
+
+The ``STATISTIC`` macro defines a static variable, whose name is specified by
+the first argument. The pass name is taken from the ``DEBUG_TYPE`` macro, and
+the description is taken from the second argument. The variable defined
+("NumXForms" in this case) acts like an unsigned integer.
+
+Whenever you make a transformation, bump the counter:
+
+.. code-block:: c++
+
+ ++NumXForms; // I did stuff!
+
+That's all you have to do. To get '``opt``' to print out the statistics
+gathered, use the '``-stats``' option:
+
+.. code-block:: none
+
+ $ opt -stats -mypassname < program.bc > /dev/null
+ ... statistics output ...
+
+Note that in order to use the '``-stats``' option, LLVM must be
+compiled with assertions enabled.
+
+When running ``opt`` on a C file from the SPEC benchmark suite, it gives a
+report that looks like this:
+
+.. code-block:: none
+
+ 7646 bitcodewriter - Number of normal instructions
+ 725 bitcodewriter - Number of oversized instructions
+ 129996 bitcodewriter - Number of bitcode bytes written
+ 2817 raise - Number of insts DCEd or constprop'd
+ 3213 raise - Number of cast-of-self removed
+ 5046 raise - Number of expression trees converted
+ 75 raise - Number of other getelementptr's formed
+ 138 raise - Number of load/store peepholes
+ 42 deadtypeelim - Number of unused typenames removed from symtab
+ 392 funcresolve - Number of varargs functions resolved
+ 27 globaldce - Number of global variables removed
+ 2 adce - Number of basic blocks removed
+ 134 cee - Number of branches revectored
+ 49 cee - Number of setcc instruction eliminated
+ 532 gcse - Number of loads removed
+ 2919 gcse - Number of instructions removed
+ 86 indvars - Number of canonical indvars added
+ 87 indvars - Number of aux indvars removed
+ 25 instcombine - Number of dead inst eliminate
+ 434 instcombine - Number of insts combined
+ 248 licm - Number of load insts hoisted
+ 1298 licm - Number of insts hoisted to a loop pre-header
+ 3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
+ 75 mem2reg - Number of alloca's promoted
+ 1444 cfgsimplify - Number of blocks simplified
+
+Obviously, with so many optimizations, having a unified framework for this stuff
+is very nice. Making your pass fit well into the framework makes it more
+maintainable and useful.
+
+.. _DebugCounters:
+
+Adding debug counters to aid in debugging your code
+---------------------------------------------------
+
+Sometimes, when writing new passes, or trying to track down bugs, it
+is useful to be able to control whether certain things in your pass
+happen or not. For example, there are times the minimization tooling
+can only easily give you large testcases. You would like to narrow
+your bug down to a specific transformation happening or not happening,
+automatically, using bisection. This is where debug counters help.
+They provide a framework for making parts of your code only execute a
+certain number of times.
+
+The ``llvm/Support/DebugCounter.h`` (`doxygen
+<http://llvm.org/doxygen/DebugCounter_8h_source.html>`__) file
+provides a class named ``DebugCounter`` that can be used to create
+command line counter options that control execution of parts of your code.
+
+Define your DebugCounter like this:
+
+.. code-block:: c++
+
+ DEBUG_COUNTER(DeleteAnInstruction, "passname-delete-instruction",
+ "Controls which instructions get delete").
+
+The ``DEBUG_COUNTER`` macro defines a static variable, whose name
+is specified by the first argument. The name of the counter
+(which is used on the command line) is specified by the second
+argument, and the description used in the help is specified by the
+third argument.
+
+Whatever code you want that control, use ``DebugCounter::shouldExecute`` to control it.
+
+.. code-block:: c++
+
+ if (DebugCounter::shouldExecute(DeleteAnInstruction))
+ I->eraseFromParent();
+
+That's all you have to do. Now, using opt, you can control when this code triggers using
+the '``--debug-counter``' option. There are two counters provided, ``skip`` and ``count``.
+``skip`` is the number of times to skip execution of the codepath. ``count`` is the number
+of times, once we are done skipping, to execute the codepath.
+
+.. code-block:: none
+
+ $ opt --debug-counter=passname-delete-instruction-skip=1,passname-delete-instruction-count=2 -passname
+
+This will skip the above code the first time we hit it, then execute it twice, then skip the rest of the executions.
+
+So if executed on the following code:
+
+.. code-block:: llvm
+
+ %1 = add i32 %a, %b
+ %2 = add i32 %a, %b
+ %3 = add i32 %a, %b
+ %4 = add i32 %a, %b
+
+It would delete number ``%2`` and ``%3``.
+
+A utility is provided in `utils/bisect-skip-count` to binary search
+skip and count arguments. It can be used to automatically minimize the
+skip and count for a debug-counter variable.
+
+.. _ViewGraph:
+
+Viewing graphs while debugging code
+-----------------------------------
+
+Several of the important data structures in LLVM are graphs: for example CFGs
+made out of LLVM :ref:`BasicBlocks <BasicBlock>`, CFGs made out of LLVM
+:ref:`MachineBasicBlocks <MachineBasicBlock>`, and :ref:`Instruction Selection
+DAGs <SelectionDAG>`. In many cases, while debugging various parts of the
+compiler, it is nice to instantly visualize these graphs.
+
+LLVM provides several callbacks that are available in a debug build to do
+exactly that. If you call the ``Function::viewCFG()`` method, for example, the
+current LLVM tool will pop up a window containing the CFG for the function where
+each basic block is a node in the graph, and each node contains the instructions
+in the block. Similarly, there also exists ``Function::viewCFGOnly()`` (does
+not include the instructions), the ``MachineFunction::viewCFG()`` and
+``MachineFunction::viewCFGOnly()``, and the ``SelectionDAG::viewGraph()``
+methods. Within GDB, for example, you can usually use something like ``call
+DAG.viewGraph()`` to pop up a window. Alternatively, you can sprinkle calls to
+these functions in your code in places you want to debug.
+
+Getting this to work requires a small amount of setup. On Unix systems
+with X11, install the `graphviz <http://www.graphviz.org>`_ toolkit, and make
+sure 'dot' and 'gv' are in your path. If you are running on Mac OS X, download
+and install the Mac OS X `Graphviz program
+<http://www.pixelglow.com/graphviz/>`_ and add
+``/Applications/Graphviz.app/Contents/MacOS/`` (or wherever you install it) to
+your path. The programs need not be present when configuring, building or
+running LLVM and can simply be installed when needed during an active debug
+session.
+
+``SelectionDAG`` has been extended to make it easier to locate *interesting*
+nodes in large complex graphs. From gdb, if you ``call DAG.setGraphColor(node,
+"color")``, then the next ``call DAG.viewGraph()`` would highlight the node in
+the specified color (choices of colors can be found at `colors
+<http://www.graphviz.org/doc/info/colors.html>`_.) More complex node attributes
+can be provided with ``call DAG.setGraphAttrs(node, "attributes")`` (choices can
+be found at `Graph attributes <http://www.graphviz.org/doc/info/attrs.html>`_.)
+If you want to restart and clear all the current graph attributes, then you can
+``call DAG.clearGraphAttrs()``.
+
+Note that graph visualization features are compiled out of Release builds to
+reduce file size. This means that you need a Debug+Asserts or Release+Asserts
+build to use these features.
+
+.. _datastructure:
+
+Picking the Right Data Structure for a Task
+===========================================
+
+LLVM has a plethora of data structures in the ``llvm/ADT/`` directory, and we
+commonly use STL data structures. This section describes the trade-offs you
+should consider when you pick one.
+
+The first step is a choose your own adventure: do you want a sequential
+container, a set-like container, or a map-like container? The most important
+thing when choosing a container is the algorithmic properties of how you plan to
+access the container. Based on that, you should use:
+
+
+* a :ref:`map-like <ds_map>` container if you need efficient look-up of a
+ value based on another value. Map-like containers also support efficient
+ queries for containment (whether a key is in the map). Map-like containers
+ generally do not support efficient reverse mapping (values to keys). If you
+ need that, use two maps. Some map-like containers also support efficient
+ iteration through the keys in sorted order. Map-like containers are the most
+ expensive sort, only use them if you need one of these capabilities.
+
+* a :ref:`set-like <ds_set>` container if you need to put a bunch of stuff into
+ a container that automatically eliminates duplicates. Some set-like
+ containers support efficient iteration through the elements in sorted order.
+ Set-like containers are more expensive than sequential containers.
+
+* a :ref:`sequential <ds_sequential>` container provides the most efficient way
+ to add elements and keeps track of the order they are added to the collection.
+ They permit duplicates and support efficient iteration, but do not support
+ efficient look-up based on a key.
+
+* a :ref:`string <ds_string>` container is a specialized sequential container or
+ reference structure that is used for character or byte arrays.
+
+* a :ref:`bit <ds_bit>` container provides an efficient way to store and
+ perform set operations on sets of numeric id's, while automatically
+ eliminating duplicates. Bit containers require a maximum of 1 bit for each
+ identifier you want to store.
+
+Once the proper category of container is determined, you can fine tune the
+memory use, constant factors, and cache behaviors of access by intelligently
+picking a member of the category. Note that constant factors and cache behavior
+can be a big deal. If you have a vector that usually only contains a few
+elements (but could contain many), for example, it's much better to use
+:ref:`SmallVector <dss_smallvector>` than :ref:`vector <dss_vector>`. Doing so
+avoids (relatively) expensive malloc/free calls, which dwarf the cost of adding
+the elements to the container.
+
+.. _ds_sequential:
+
+Sequential Containers (std::vector, std::list, etc)
+---------------------------------------------------
+
+There are a variety of sequential containers available for you, based on your
+needs. Pick the first in this section that will do what you want.
+
+.. _dss_arrayref:
+
+llvm/ADT/ArrayRef.h
+^^^^^^^^^^^^^^^^^^^
+
+The ``llvm::ArrayRef`` class is the preferred class to use in an interface that
+accepts a sequential list of elements in memory and just reads from them. By
+taking an ``ArrayRef``, the API can be passed a fixed size array, an
+``std::vector``, an ``llvm::SmallVector`` and anything else that is contiguous
+in memory.
+
+.. _dss_fixedarrays:
+
+Fixed Size Arrays
+^^^^^^^^^^^^^^^^^
+
+Fixed size arrays are very simple and very fast. They are good if you know
+exactly how many elements you have, or you have a (low) upper bound on how many
+you have.
+
+.. _dss_heaparrays:
+
+Heap Allocated Arrays
+^^^^^^^^^^^^^^^^^^^^^
+
+Heap allocated arrays (``new[]`` + ``delete[]``) are also simple. They are good
+if the number of elements is variable, if you know how many elements you will
+need before the array is allocated, and if the array is usually large (if not,
+consider a :ref:`SmallVector <dss_smallvector>`). The cost of a heap allocated
+array is the cost of the new/delete (aka malloc/free). Also note that if you
+are allocating an array of a type with a constructor, the constructor and
+destructors will be run for every element in the array (re-sizable vectors only
+construct those elements actually used).
+
+.. _dss_tinyptrvector:
+
+llvm/ADT/TinyPtrVector.h
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+``TinyPtrVector<Type>`` is a highly specialized collection class that is
+optimized to avoid allocation in the case when a vector has zero or one
+elements. It has two major restrictions: 1) it can only hold values of pointer
+type, and 2) it cannot hold a null pointer.
+
+Since this container is highly specialized, it is rarely used.
+
+.. _dss_smallvector:
+
+llvm/ADT/SmallVector.h
+^^^^^^^^^^^^^^^^^^^^^^
+
+``SmallVector<Type, N>`` is a simple class that looks and smells just like
+``vector<Type>``: it supports efficient iteration, lays out elements in memory
+order (so you can do pointer arithmetic between elements), supports efficient
+push_back/pop_back operations, supports efficient random access to its elements,
+etc.
+
+The advantage of SmallVector is that it allocates space for some number of
+elements (N) **in the object itself**. Because of this, if the SmallVector is
+dynamically smaller than N, no malloc is performed. This can be a big win in
+cases where the malloc/free call is far more expensive than the code that
+fiddles around with the elements.
+
+This is good for vectors that are "usually small" (e.g. the number of
+predecessors/successors of a block is usually less than 8). On the other hand,
+this makes the size of the SmallVector itself large, so you don't want to
+allocate lots of them (doing so will waste a lot of space). As such,
+SmallVectors are most useful when on the stack.
+
+SmallVector also provides a nice portable and efficient replacement for
+``alloca``.
+
+.. note::
+
+ Prefer to use ``SmallVectorImpl<T>`` as a parameter type.
+
+ In APIs that don't care about the "small size" (most?), prefer to use
+ the ``SmallVectorImpl<T>`` class, which is basically just the "vector
+ header" (and methods) without the elements allocated after it. Note that
+ ``SmallVector<T, N>`` inherits from ``SmallVectorImpl<T>`` so the
+ conversion is implicit and costs nothing. E.g.
+
+ .. code-block:: c++
+
+ // BAD: Clients cannot pass e.g. SmallVector<Foo, 4>.
+ hardcodedSmallSize(SmallVector<Foo, 2> &Out);
+ // GOOD: Clients can pass any SmallVector<Foo, N>.
+ allowsAnySmallSize(SmallVectorImpl<Foo> &Out);
+
+ void someFunc() {
+ SmallVector<Foo, 8> Vec;
+ hardcodedSmallSize(Vec); // Error.
+ allowsAnySmallSize(Vec); // Works.
+ }
+
+ Even though it has "``Impl``" in the name, this is so widely used that
+ it really isn't "private to the implementation" anymore. A name like
+ ``SmallVectorHeader`` would be more appropriate.
+
+.. _dss_vector:
+
+<vector>
+^^^^^^^^
+
+``std::vector`` is well loved and respected. It is useful when SmallVector
+isn't: when the size of the vector is often large (thus the small optimization
+will rarely be a benefit) or if you will be allocating many instances of the
+vector itself (which would waste space for elements that aren't in the
+container). vector is also useful when interfacing with code that expects
+vectors :).
+
+One worthwhile note about std::vector: avoid code like this:
+
+.. code-block:: c++
+
+ for ( ... ) {
+ std::vector<foo> V;
+ // make use of V.
+ }
+
+Instead, write this as:
+
+.. code-block:: c++
+
+ std::vector<foo> V;
+ for ( ... ) {
+ // make use of V.
+ V.clear();
+ }
+
+Doing so will save (at least) one heap allocation and free per iteration of the
+loop.
+
+.. _dss_deque:
+
+<deque>
+^^^^^^^
+
+``std::deque`` is, in some senses, a generalized version of ``std::vector``.
+Like ``std::vector``, it provides constant time random access and other similar
+properties, but it also provides efficient access to the front of the list. It
+does not guarantee continuity of elements within memory.
+
+In exchange for this extra flexibility, ``std::deque`` has significantly higher
+constant factor costs than ``std::vector``. If possible, use ``std::vector`` or
+something cheaper.
+
+.. _dss_list:
+
+<list>
+^^^^^^
+
+``std::list`` is an extremely inefficient class that is rarely useful. It
+performs a heap allocation for every element inserted into it, thus having an
+extremely high constant factor, particularly for small data types.
+``std::list`` also only supports bidirectional iteration, not random access
+iteration.
+
+In exchange for this high cost, std::list supports efficient access to both ends
+of the list (like ``std::deque``, but unlike ``std::vector`` or
+``SmallVector``). In addition, the iterator invalidation characteristics of
+std::list are stronger than that of a vector class: inserting or removing an
+element into the list does not invalidate iterator or pointers to other elements
+in the list.
+
+.. _dss_ilist:
+
+llvm/ADT/ilist.h
+^^^^^^^^^^^^^^^^
+
+``ilist<T>`` implements an 'intrusive' doubly-linked list. It is intrusive,
+because it requires the element to store and provide access to the prev/next
+pointers for the list.
+
+``ilist`` has the same drawbacks as ``std::list``, and additionally requires an
+``ilist_traits`` implementation for the element type, but it provides some novel
+characteristics. In particular, it can efficiently store polymorphic objects,
+the traits class is informed when an element is inserted or removed from the
+list, and ``ilist``\ s are guaranteed to support a constant-time splice
+operation.
+
+These properties are exactly what we want for things like ``Instruction``\ s and
+basic blocks, which is why these are implemented with ``ilist``\ s.
+
+Related classes of interest are explained in the following subsections:
+
+* :ref:`ilist_traits <dss_ilist_traits>`
+
+* :ref:`iplist <dss_iplist>`
+
+* :ref:`llvm/ADT/ilist_node.h <dss_ilist_node>`
+
+* :ref:`Sentinels <dss_ilist_sentinel>`
+
+.. _dss_packedvector:
+
+llvm/ADT/PackedVector.h
+^^^^^^^^^^^^^^^^^^^^^^^
+
+Useful for storing a vector of values using only a few number of bits for each
+value. Apart from the standard operations of a vector-like container, it can
+also perform an 'or' set operation.
+
+For example:
+
+.. code-block:: c++
+
+ enum State {
+ None = 0x0,
+ FirstCondition = 0x1,
+ SecondCondition = 0x2,
+ Both = 0x3
+ };
+
+ State get() {
+ PackedVector<State, 2> Vec1;
+ Vec1.push_back(FirstCondition);
+
+ PackedVector<State, 2> Vec2;
+ Vec2.push_back(SecondCondition);
+
+ Vec1 |= Vec2;
+ return Vec1[0]; // returns 'Both'.
+ }
+
+.. _dss_ilist_traits:
+
+ilist_traits
+^^^^^^^^^^^^
+
+``ilist_traits<T>`` is ``ilist<T>``'s customization mechanism. ``iplist<T>``
+(and consequently ``ilist<T>``) publicly derive from this traits class.
+
+.. _dss_iplist:
+
+iplist
+^^^^^^
+
+``iplist<T>`` is ``ilist<T>``'s base and as such supports a slightly narrower
+interface. Notably, inserters from ``T&`` are absent.
+
+``ilist_traits<T>`` is a public base of this class and can be used for a wide
+variety of customizations.
+
+.. _dss_ilist_node:
+
+llvm/ADT/ilist_node.h
+^^^^^^^^^^^^^^^^^^^^^
+
+``ilist_node<T>`` implements the forward and backward links that are expected
+by the ``ilist<T>`` (and analogous containers) in the default manner.
+
+``ilist_node<T>``\ s are meant to be embedded in the node type ``T``, usually
+``T`` publicly derives from ``ilist_node<T>``.
+
+.. _dss_ilist_sentinel:
+
+Sentinels
+^^^^^^^^^
+
+``ilist``\ s have another specialty that must be considered. To be a good
+citizen in the C++ ecosystem, it needs to support the standard container
+operations, such as ``begin`` and ``end`` iterators, etc. Also, the
+``operator--`` must work correctly on the ``end`` iterator in the case of
+non-empty ``ilist``\ s.
+
+The only sensible solution to this problem is to allocate a so-called *sentinel*
+along with the intrusive list, which serves as the ``end`` iterator, providing
+the back-link to the last element. However conforming to the C++ convention it
+is illegal to ``operator++`` beyond the sentinel and it also must not be
+dereferenced.
+
+These constraints allow for some implementation freedom to the ``ilist`` how to
+allocate and store the sentinel. The corresponding policy is dictated by
+``ilist_traits<T>``. By default a ``T`` gets heap-allocated whenever the need
+for a sentinel arises.
+
+While the default policy is sufficient in most cases, it may break down when
+``T`` does not provide a default constructor. Also, in the case of many
+instances of ``ilist``\ s, the memory overhead of the associated sentinels is
+wasted. To alleviate the situation with numerous and voluminous
+``T``-sentinels, sometimes a trick is employed, leading to *ghostly sentinels*.
+
+Ghostly sentinels are obtained by specially-crafted ``ilist_traits<T>`` which
+superpose the sentinel with the ``ilist`` instance in memory. Pointer
+arithmetic is used to obtain the sentinel, which is relative to the ``ilist``'s
+``this`` pointer. The ``ilist`` is augmented by an extra pointer, which serves
+as the back-link of the sentinel. This is the only field in the ghostly
+sentinel which can be legally accessed.
+
+.. _dss_other:
+
+Other Sequential Container options
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Other STL containers are available, such as ``std::string``.
+
+There are also various STL adapter classes such as ``std::queue``,
+``std::priority_queue``, ``std::stack``, etc. These provide simplified access
+to an underlying container but don't affect the cost of the container itself.
+
+.. _ds_string:
+
+String-like containers
+----------------------
+
+There are a variety of ways to pass around and use strings in C and C++, and
+LLVM adds a few new options to choose from. Pick the first option on this list
+that will do what you need, they are ordered according to their relative cost.
+
+Note that it is generally preferred to *not* pass strings around as ``const
+char*``'s. These have a number of problems, including the fact that they
+cannot represent embedded nul ("\0") characters, and do not have a length
+available efficiently. The general replacement for '``const char*``' is
+StringRef.
+
+For more information on choosing string containers for APIs, please see
+:ref:`Passing Strings <string_apis>`.
+
+.. _dss_stringref:
+
+llvm/ADT/StringRef.h
+^^^^^^^^^^^^^^^^^^^^
+
+The StringRef class is a simple value class that contains a pointer to a
+character and a length, and is quite related to the :ref:`ArrayRef
+<dss_arrayref>` class (but specialized for arrays of characters). Because
+StringRef carries a length with it, it safely handles strings with embedded nul
+characters in it, getting the length does not require a strlen call, and it even
+has very convenient APIs for slicing and dicing the character range that it
+represents.
+
+StringRef is ideal for passing simple strings around that are known to be live,
+either because they are C string literals, std::string, a C array, or a
+SmallVector. Each of these cases has an efficient implicit conversion to
+StringRef, which doesn't result in a dynamic strlen being executed.
+
+StringRef has a few major limitations which make more powerful string containers
+useful:
+
+#. You cannot directly convert a StringRef to a 'const char*' because there is
+ no way to add a trailing nul (unlike the .c_str() method on various stronger
+ classes).
+
+#. StringRef doesn't own or keep alive the underlying string bytes.
+ As such it can easily lead to dangling pointers, and is not suitable for
+ embedding in datastructures in most cases (instead, use an std::string or
+ something like that).
+
+#. For the same reason, StringRef cannot be used as the return value of a
+ method if the method "computes" the result string. Instead, use std::string.
+
+#. StringRef's do not allow you to mutate the pointed-to string bytes and it
+ doesn't allow you to insert or remove bytes from the range. For editing
+ operations like this, it interoperates with the :ref:`Twine <dss_twine>`
+ class.
+
+Because of its strengths and limitations, it is very common for a function to
+take a StringRef and for a method on an object to return a StringRef that points
+into some string that it owns.
+
+.. _dss_twine:
+
+llvm/ADT/Twine.h
+^^^^^^^^^^^^^^^^
+
+The Twine class is used as an intermediary datatype for APIs that want to take a
+string that can be constructed inline with a series of concatenations. Twine
+works by forming recursive instances of the Twine datatype (a simple value
+object) on the stack as temporary objects, linking them together into a tree
+which is then linearized when the Twine is consumed. Twine is only safe to use
+as the argument to a function, and should always be a const reference, e.g.:
+
+.. code-block:: c++
+
+ void foo(const Twine &T);
+ ...
+ StringRef X = ...
+ unsigned i = ...
+ foo(X + "." + Twine(i));
+
+This example forms a string like "blarg.42" by concatenating the values
+together, and does not form intermediate strings containing "blarg" or "blarg.".
+
+Because Twine is constructed with temporary objects on the stack, and because
+these instances are destroyed at the end of the current statement, it is an
+inherently dangerous API. For example, this simple variant contains undefined
+behavior and will probably crash:
+
+.. code-block:: c++
+
+ void foo(const Twine &T);
+ ...
+ StringRef X = ...
+ unsigned i = ...
+ const Twine &Tmp = X + "." + Twine(i);
+ foo(Tmp);
+
+... because the temporaries are destroyed before the call. That said, Twine's
+are much more efficient than intermediate std::string temporaries, and they work
+really well with StringRef. Just be aware of their limitations.
+
+.. _dss_smallstring:
+
+llvm/ADT/SmallString.h
+^^^^^^^^^^^^^^^^^^^^^^
+
+SmallString is a subclass of :ref:`SmallVector <dss_smallvector>` that adds some
+convenience APIs like += that takes StringRef's. SmallString avoids allocating
+memory in the case when the preallocated space is enough to hold its data, and
+it calls back to general heap allocation when required. Since it owns its data,
+it is very safe to use and supports full mutation of the string.
+
+Like SmallVector's, the big downside to SmallString is their sizeof. While they
+are optimized for small strings, they themselves are not particularly small.
+This means that they work great for temporary scratch buffers on the stack, but
+should not generally be put into the heap: it is very rare to see a SmallString
+as the member of a frequently-allocated heap data structure or returned
+by-value.
+
+.. _dss_stdstring:
+
+std::string
+^^^^^^^^^^^
+
+The standard C++ std::string class is a very general class that (like
+SmallString) owns its underlying data. sizeof(std::string) is very reasonable
+so it can be embedded into heap data structures and returned by-value. On the
+other hand, std::string is highly inefficient for inline editing (e.g.
+concatenating a bunch of stuff together) and because it is provided by the
+standard library, its performance characteristics depend a lot of the host
+standard library (e.g. libc++ and MSVC provide a highly optimized string class,
+GCC contains a really slow implementation).
+
+The major disadvantage of std::string is that almost every operation that makes
+them larger can allocate memory, which is slow. As such, it is better to use
+SmallVector or Twine as a scratch buffer, but then use std::string to persist
+the result.
+
+.. _ds_set:
+
+Set-Like Containers (std::set, SmallSet, SetVector, etc)
+--------------------------------------------------------
+
+Set-like containers are useful when you need to canonicalize multiple values
+into a single representation. There are several different choices for how to do
+this, providing various trade-offs.
+
+.. _dss_sortedvectorset:
+
+A sorted 'vector'
+^^^^^^^^^^^^^^^^^
+
+If you intend to insert a lot of elements, then do a lot of queries, a great
+approach is to use a vector (or other sequential container) with
+std::sort+std::unique to remove duplicates. This approach works really well if
+your usage pattern has these two distinct phases (insert then query), and can be
+coupled with a good choice of :ref:`sequential container <ds_sequential>`.
+
+This combination provides the several nice properties: the result data is
+contiguous in memory (good for cache locality), has few allocations, is easy to
+address (iterators in the final vector are just indices or pointers), and can be
+efficiently queried with a standard binary search (e.g.
+``std::lower_bound``; if you want the whole range of elements comparing
+equal, use ``std::equal_range``).
+
+.. _dss_smallset:
+
+llvm/ADT/SmallSet.h
+^^^^^^^^^^^^^^^^^^^
+
+If you have a set-like data structure that is usually small and whose elements
+are reasonably small, a ``SmallSet<Type, N>`` is a good choice. This set has
+space for N elements in place (thus, if the set is dynamically smaller than N,
+no malloc traffic is required) and accesses them with a simple linear search.
+When the set grows beyond N elements, it allocates a more expensive
+representation that guarantees efficient access (for most types, it falls back
+to :ref:`std::set <dss_set>`, but for pointers it uses something far better,
+:ref:`SmallPtrSet <dss_smallptrset>`.
+
+The magic of this class is that it handles small sets extremely efficiently, but
+gracefully handles extremely large sets without loss of efficiency. The
+drawback is that the interface is quite small: it supports insertion, queries
+and erasing, but does not support iteration.
+
+.. _dss_smallptrset:
+
+llvm/ADT/SmallPtrSet.h
+^^^^^^^^^^^^^^^^^^^^^^
+
+``SmallPtrSet`` has all the advantages of ``SmallSet`` (and a ``SmallSet`` of
+pointers is transparently implemented with a ``SmallPtrSet``), but also supports
+iterators. If more than N insertions are performed, a single quadratically
+probed hash table is allocated and grows as needed, providing extremely
+efficient access (constant time insertion/deleting/queries with low constant
+factors) and is very stingy with malloc traffic.
+
+Note that, unlike :ref:`std::set <dss_set>`, the iterators of ``SmallPtrSet``
+are invalidated whenever an insertion occurs. Also, the values visited by the
+iterators are not visited in sorted order.
+
+.. _dss_stringset:
+
+llvm/ADT/StringSet.h
+^^^^^^^^^^^^^^^^^^^^
+
+``StringSet`` is a thin wrapper around :ref:`StringMap\<char\> <dss_stringmap>`,
+and it allows efficient storage and retrieval of unique strings.
+
+Functionally analogous to ``SmallSet<StringRef>``, ``StringSet`` also supports
+iteration. (The iterator dereferences to a ``StringMapEntry<char>``, so you
+need to call ``i->getKey()`` to access the item of the StringSet.) On the
+other hand, ``StringSet`` doesn't support range-insertion and
+copy-construction, which :ref:`SmallSet <dss_smallset>` and :ref:`SmallPtrSet
+<dss_smallptrset>` do support.
+
+.. _dss_denseset:
+
+llvm/ADT/DenseSet.h
+^^^^^^^^^^^^^^^^^^^
+
+DenseSet is a simple quadratically probed hash table. It excels at supporting
+small values: it uses a single allocation to hold all of the pairs that are
+currently inserted in the set. DenseSet is a great way to unique small values
+that are not simple pointers (use :ref:`SmallPtrSet <dss_smallptrset>` for
+pointers). Note that DenseSet has the same requirements for the value type that
+:ref:`DenseMap <dss_densemap>` has.
+
+.. _dss_sparseset:
+
+llvm/ADT/SparseSet.h
+^^^^^^^^^^^^^^^^^^^^
+
+SparseSet holds a small number of objects identified by unsigned keys of
+moderate size. It uses a lot of memory, but provides operations that are almost
+as fast as a vector. Typical keys are physical registers, virtual registers, or
+numbered basic blocks.
+
+SparseSet is useful for algorithms that need very fast clear/find/insert/erase
+and fast iteration over small sets. It is not intended for building composite
+data structures.
+
+.. _dss_sparsemultiset:
+
+llvm/ADT/SparseMultiSet.h
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+SparseMultiSet adds multiset behavior to SparseSet, while retaining SparseSet's
+desirable attributes. Like SparseSet, it typically uses a lot of memory, but
+provides operations that are almost as fast as a vector. Typical keys are
+physical registers, virtual registers, or numbered basic blocks.
+
+SparseMultiSet is useful for algorithms that need very fast
+clear/find/insert/erase of the entire collection, and iteration over sets of
+elements sharing a key. It is often a more efficient choice than using composite
+data structures (e.g. vector-of-vectors, map-of-vectors). It is not intended for
+building composite data structures.
+
+.. _dss_FoldingSet:
+
+llvm/ADT/FoldingSet.h
+^^^^^^^^^^^^^^^^^^^^^
+
+FoldingSet is an aggregate class that is really good at uniquing
+expensive-to-create or polymorphic objects. It is a combination of a chained
+hash table with intrusive links (uniqued objects are required to inherit from
+FoldingSetNode) that uses :ref:`SmallVector <dss_smallvector>` as part of its ID
+process.
+
+Consider a case where you want to implement a "getOrCreateFoo" method for a
+complex object (for example, a node in the code generator). The client has a
+description of **what** it wants to generate (it knows the opcode and all the
+operands), but we don't want to 'new' a node, then try inserting it into a set
+only to find out it already exists, at which point we would have to delete it
+and return the node that already exists.
+
+To support this style of client, FoldingSet perform a query with a
+FoldingSetNodeID (which wraps SmallVector) that can be used to describe the
+element that we want to query for. The query either returns the element
+matching the ID or it returns an opaque ID that indicates where insertion should
+take place. Construction of the ID usually does not require heap traffic.
+
+Because FoldingSet uses intrusive links, it can support polymorphic objects in
+the set (for example, you can have SDNode instances mixed with LoadSDNodes).
+Because the elements are individually allocated, pointers to the elements are
+stable: inserting or removing elements does not invalidate any pointers to other
+elements.
+
+.. _dss_set:
+
+<set>
+^^^^^
+
+``std::set`` is a reasonable all-around set class, which is decent at many
+things but great at nothing. std::set allocates memory for each element
+inserted (thus it is very malloc intensive) and typically stores three pointers
+per element in the set (thus adding a large amount of per-element space
+overhead). It offers guaranteed log(n) performance, which is not particularly
+fast from a complexity standpoint (particularly if the elements of the set are
+expensive to compare, like strings), and has extremely high constant factors for
+lookup, insertion and removal.
+
+The advantages of std::set are that its iterators are stable (deleting or
+inserting an element from the set does not affect iterators or pointers to other
+elements) and that iteration over the set is guaranteed to be in sorted order.
+If the elements in the set are large, then the relative overhead of the pointers
+and malloc traffic is not a big deal, but if the elements of the set are small,
+std::set is almost never a good choice.
+
+.. _dss_setvector:
+
+llvm/ADT/SetVector.h
+^^^^^^^^^^^^^^^^^^^^
+
+LLVM's ``SetVector<Type>`` is an adapter class that combines your choice of a
+set-like container along with a :ref:`Sequential Container <ds_sequential>` The
+important property that this provides is efficient insertion with uniquing
+(duplicate elements are ignored) with iteration support. It implements this by
+inserting elements into both a set-like container and the sequential container,
+using the set-like container for uniquing and the sequential container for
+iteration.
+
+The difference between SetVector and other sets is that the order of iteration
+is guaranteed to match the order of insertion into the SetVector. This property
+is really important for things like sets of pointers. Because pointer values
+are non-deterministic (e.g. vary across runs of the program on different
+machines), iterating over the pointers in the set will not be in a well-defined
+order.
+
+The drawback of SetVector is that it requires twice as much space as a normal
+set and has the sum of constant factors from the set-like container and the
+sequential container that it uses. Use it **only** if you need to iterate over
+the elements in a deterministic order. SetVector is also expensive to delete
+elements out of (linear time), unless you use its "pop_back" method, which is
+faster.
+
+``SetVector`` is an adapter class that defaults to using ``std::vector`` and a
+size 16 ``SmallSet`` for the underlying containers, so it is quite expensive.
+However, ``"llvm/ADT/SetVector.h"`` also provides a ``SmallSetVector`` class,
+which defaults to using a ``SmallVector`` and ``SmallSet`` of a specified size.
+If you use this, and if your sets are dynamically smaller than ``N``, you will
+save a lot of heap traffic.
+
+.. _dss_uniquevector:
+
+llvm/ADT/UniqueVector.h
+^^^^^^^^^^^^^^^^^^^^^^^
+
+UniqueVector is similar to :ref:`SetVector <dss_setvector>` but it retains a
+unique ID for each element inserted into the set. It internally contains a map
+and a vector, and it assigns a unique ID for each value inserted into the set.
+
+UniqueVector is very expensive: its cost is the sum of the cost of maintaining
+both the map and vector, it has high complexity, high constant factors, and
+produces a lot of malloc traffic. It should be avoided.
+
+.. _dss_immutableset:
+
+llvm/ADT/ImmutableSet.h
+^^^^^^^^^^^^^^^^^^^^^^^
+
+ImmutableSet is an immutable (functional) set implementation based on an AVL
+tree. Adding or removing elements is done through a Factory object and results
+in the creation of a new ImmutableSet object. If an ImmutableSet already exists
+with the given contents, then the existing one is returned; equality is compared
+with a FoldingSetNodeID. The time and space complexity of add or remove
+operations is logarithmic in the size of the original set.
+
+There is no method for returning an element of the set, you can only check for
+membership.
+
+.. _dss_otherset:
+
+Other Set-Like Container Options
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The STL provides several other options, such as std::multiset and the various
+"hash_set" like containers (whether from C++ TR1 or from the SGI library). We
+never use hash_set and unordered_set because they are generally very expensive
+(each insertion requires a malloc) and very non-portable.
+
+std::multiset is useful if you're not interested in elimination of duplicates,
+but has all the drawbacks of :ref:`std::set <dss_set>`. A sorted vector
+(where you don't delete duplicate entries) or some other approach is almost
+always better.
+
+.. _ds_map:
+
+Map-Like Containers (std::map, DenseMap, etc)
+---------------------------------------------
+
+Map-like containers are useful when you want to associate data to a key. As
+usual, there are a lot of different ways to do this. :)
+
+.. _dss_sortedvectormap:
+
+A sorted 'vector'
+^^^^^^^^^^^^^^^^^
+
+If your usage pattern follows a strict insert-then-query approach, you can
+trivially use the same approach as :ref:`sorted vectors for set-like containers
+<dss_sortedvectorset>`. The only difference is that your query function (which
+uses std::lower_bound to get efficient log(n) lookup) should only compare the
+key, not both the key and value. This yields the same advantages as sorted
+vectors for sets.
+
+.. _dss_stringmap:
+
+llvm/ADT/StringMap.h
+^^^^^^^^^^^^^^^^^^^^
+
+Strings are commonly used as keys in maps, and they are difficult to support
+efficiently: they are variable length, inefficient to hash and compare when
+long, expensive to copy, etc. StringMap is a specialized container designed to
+cope with these issues. It supports mapping an arbitrary range of bytes to an
+arbitrary other object.
+
+The StringMap implementation uses a quadratically-probed hash table, where the
+buckets store a pointer to the heap allocated entries (and some other stuff).
+The entries in the map must be heap allocated because the strings are variable
+length. The string data (key) and the element object (value) are stored in the
+same allocation with the string data immediately after the element object.
+This container guarantees the "``(char*)(&Value+1)``" points to the key string
+for a value.
+
+The StringMap is very fast for several reasons: quadratic probing is very cache
+efficient for lookups, the hash value of strings in buckets is not recomputed
+when looking up an element, StringMap rarely has to touch the memory for
+unrelated objects when looking up a value (even when hash collisions happen),
+hash table growth does not recompute the hash values for strings already in the
+table, and each pair in the map is store in a single allocation (the string data
+is stored in the same allocation as the Value of a pair).
+
+StringMap also provides query methods that take byte ranges, so it only ever
+copies a string if a value is inserted into the table.
+
+StringMap iteratation order, however, is not guaranteed to be deterministic, so
+any uses which require that should instead use a std::map.
+
+.. _dss_indexmap:
+
+llvm/ADT/IndexedMap.h
+^^^^^^^^^^^^^^^^^^^^^
+
+IndexedMap is a specialized container for mapping small dense integers (or
+values that can be mapped to small dense integers) to some other type. It is
+internally implemented as a vector with a mapping function that maps the keys
+to the dense integer range.
+
+This is useful for cases like virtual registers in the LLVM code generator: they
+have a dense mapping that is offset by a compile-time constant (the first
+virtual register ID).
+
+.. _dss_densemap:
+
+llvm/ADT/DenseMap.h
+^^^^^^^^^^^^^^^^^^^
+
+DenseMap is a simple quadratically probed hash table. It excels at supporting
+small keys and values: it uses a single allocation to hold all of the pairs
+that are currently inserted in the map. DenseMap is a great way to map
+pointers to pointers, or map other small types to each other.
+
+There are several aspects of DenseMap that you should be aware of, however.
+The iterators in a DenseMap are invalidated whenever an insertion occurs,
+unlike map. Also, because DenseMap allocates space for a large number of
+key/value pairs (it starts with 64 by default), it will waste a lot of space if
+your keys or values are large. Finally, you must implement a partial
+specialization of DenseMapInfo for the key that you want, if it isn't already
+supported. This is required to tell DenseMap about two special marker values
+(which can never be inserted into the map) that it needs internally.
+
+DenseMap's find_as() method supports lookup operations using an alternate key
+type. This is useful in cases where the normal key type is expensive to
+construct, but cheap to compare against. The DenseMapInfo is responsible for
+defining the appropriate comparison and hashing methods for each alternate key
+type used.
+
+.. _dss_valuemap:
+
+llvm/IR/ValueMap.h
+^^^^^^^^^^^^^^^^^^^
+
+ValueMap is a wrapper around a :ref:`DenseMap <dss_densemap>` mapping
+``Value*``\ s (or subclasses) to another type. When a Value is deleted or
+RAUW'ed, ValueMap will update itself so the new version of the key is mapped to
+the same value, just as if the key were a WeakVH. You can configure exactly how
+this happens, and what else happens on these two events, by passing a ``Config``
+parameter to the ValueMap template.
+
+.. _dss_intervalmap:
+
+llvm/ADT/IntervalMap.h
+^^^^^^^^^^^^^^^^^^^^^^
+
+IntervalMap is a compact map for small keys and values. It maps key intervals
+instead of single keys, and it will automatically coalesce adjacent intervals.
+When the map only contains a few intervals, they are stored in the map object
+itself to avoid allocations.
+
+The IntervalMap iterators are quite big, so they should not be passed around as
+STL iterators. The heavyweight iterators allow a smaller data structure.
+
+.. _dss_map:
+
+<map>
+^^^^^
+
+std::map has similar characteristics to :ref:`std::set <dss_set>`: it uses a
+single allocation per pair inserted into the map, it offers log(n) lookup with
+an extremely large constant factor, imposes a space penalty of 3 pointers per
+pair in the map, etc.
+
+std::map is most useful when your keys or values are very large, if you need to
+iterate over the collection in sorted order, or if you need stable iterators
+into the map (i.e. they don't get invalidated if an insertion or deletion of
+another element takes place).
+
+.. _dss_mapvector:
+
+llvm/ADT/MapVector.h
+^^^^^^^^^^^^^^^^^^^^
+
+``MapVector<KeyT,ValueT>`` provides a subset of the DenseMap interface. The
+main difference is that the iteration order is guaranteed to be the insertion
+order, making it an easy (but somewhat expensive) solution for non-deterministic
+iteration over maps of pointers.
+
+It is implemented by mapping from key to an index in a vector of key,value
+pairs. This provides fast lookup and iteration, but has two main drawbacks:
+the key is stored twice and removing elements takes linear time. If it is
+necessary to remove elements, it's best to remove them in bulk using
+``remove_if()``.
+
+.. _dss_inteqclasses:
+
+llvm/ADT/IntEqClasses.h
+^^^^^^^^^^^^^^^^^^^^^^^
+
+IntEqClasses provides a compact representation of equivalence classes of small
+integers. Initially, each integer in the range 0..n-1 has its own equivalence
+class. Classes can be joined by passing two class representatives to the
+join(a, b) method. Two integers are in the same class when findLeader() returns
+the same representative.
+
+Once all equivalence classes are formed, the map can be compressed so each
+integer 0..n-1 maps to an equivalence class number in the range 0..m-1, where m
+is the total number of equivalence classes. The map must be uncompressed before
+it can be edited again.
+
+.. _dss_immutablemap:
+
+llvm/ADT/ImmutableMap.h
+^^^^^^^^^^^^^^^^^^^^^^^
+
+ImmutableMap is an immutable (functional) map implementation based on an AVL
+tree. Adding or removing elements is done through a Factory object and results
+in the creation of a new ImmutableMap object. If an ImmutableMap already exists
+with the given key set, then the existing one is returned; equality is compared
+with a FoldingSetNodeID. The time and space complexity of add or remove
+operations is logarithmic in the size of the original map.
+
+.. _dss_othermap:
+
+Other Map-Like Container Options
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The STL provides several other options, such as std::multimap and the various
+"hash_map" like containers (whether from C++ TR1 or from the SGI library). We
+never use hash_set and unordered_set because they are generally very expensive
+(each insertion requires a malloc) and very non-portable.
+
+std::multimap is useful if you want to map a key to multiple values, but has all
+the drawbacks of std::map. A sorted vector or some other approach is almost
+always better.
+
+.. _ds_bit:
+
+Bit storage containers (BitVector, SparseBitVector)
+---------------------------------------------------
+
+Unlike the other containers, there are only two bit storage containers, and
+choosing when to use each is relatively straightforward.
+
+One additional option is ``std::vector<bool>``: we discourage its use for two
+reasons 1) the implementation in many common compilers (e.g. commonly
+available versions of GCC) is extremely inefficient and 2) the C++ standards
+committee is likely to deprecate this container and/or change it significantly
+somehow. In any case, please don't use it.
+
+.. _dss_bitvector:
+
+BitVector
+^^^^^^^^^
+
+The BitVector container provides a dynamic size set of bits for manipulation.
+It supports individual bit setting/testing, as well as set operations. The set
+operations take time O(size of bitvector), but operations are performed one word
+at a time, instead of one bit at a time. This makes the BitVector very fast for
+set operations compared to other containers. Use the BitVector when you expect
+the number of set bits to be high (i.e. a dense set).
+
+.. _dss_smallbitvector:
+
+SmallBitVector
+^^^^^^^^^^^^^^
+
+The SmallBitVector container provides the same interface as BitVector, but it is
+optimized for the case where only a small number of bits, less than 25 or so,
+are needed. It also transparently supports larger bit counts, but slightly less
+efficiently than a plain BitVector, so SmallBitVector should only be used when
+larger counts are rare.
+
+At this time, SmallBitVector does not support set operations (and, or, xor), and
+its operator[] does not provide an assignable lvalue.
+
+.. _dss_sparsebitvector:
+
+SparseBitVector
+^^^^^^^^^^^^^^^
+
+The SparseBitVector container is much like BitVector, with one major difference:
+Only the bits that are set, are stored. This makes the SparseBitVector much
+more space efficient than BitVector when the set is sparse, as well as making
+set operations O(number of set bits) instead of O(size of universe). The
+downside to the SparseBitVector is that setting and testing of random bits is
+O(N), and on large SparseBitVectors, this can be slower than BitVector. In our
+implementation, setting or testing bits in sorted order (either forwards or
+reverse) is O(1) worst case. Testing and setting bits within 128 bits (depends
+on size) of the current bit is also O(1). As a general statement,
+testing/setting bits in a SparseBitVector is O(distance away from last set bit).
+
+.. _debugging:
+
+Debugging
+=========
+
+A handful of `GDB pretty printers
+<https://sourceware.org/gdb/onlinedocs/gdb/Pretty-Printing.html>`__ are
+provided for some of the core LLVM libraries. To use them, execute the
+following (or add it to your ``~/.gdbinit``)::
+
+ source /path/to/llvm/src/utils/gdb-scripts/prettyprinters.py
+
+It also might be handy to enable the `print pretty
+<http://ftp.gnu.org/old-gnu/Manuals/gdb/html_node/gdb_57.html>`__ option to
+avoid data structures being printed as a big block of text.
+
+.. _common:
+
+Helpful Hints for Common Operations
+===================================
+
+This section describes how to perform some very simple transformations of LLVM
+code. This is meant to give examples of common idioms used, showing the
+practical side of LLVM transformations.
+
+Because this is a "how-to" section, you should also read about the main classes
+that you will be working with. The :ref:`Core LLVM Class Hierarchy Reference
+<coreclasses>` contains details and descriptions of the main classes that you
+should know about.
+
+.. _inspection:
+
+Basic Inspection and Traversal Routines
+---------------------------------------
+
+The LLVM compiler infrastructure have many different data structures that may be
+traversed. Following the example of the C++ standard template library, the
+techniques used to traverse these various data structures are all basically the
+same. For a enumerable sequence of values, the ``XXXbegin()`` function (or
+method) returns an iterator to the start of the sequence, the ``XXXend()``
+function returns an iterator pointing to one past the last valid element of the
+sequence, and there is some ``XXXiterator`` data type that is common between the
+two operations.
+
+Because the pattern for iteration is common across many different aspects of the
+program representation, the standard template library algorithms may be used on
+them, and it is easier to remember how to iterate. First we show a few common
+examples of the data structures that need to be traversed. Other data
+structures are traversed in very similar ways.
+
+.. _iterate_function:
+
+Iterating over the ``BasicBlock`` in a ``Function``
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+It's quite common to have a ``Function`` instance that you'd like to transform
+in some way; in particular, you'd like to manipulate its ``BasicBlock``\ s. To
+facilitate this, you'll need to iterate over all of the ``BasicBlock``\ s that
+constitute the ``Function``. The following is an example that prints the name
+of a ``BasicBlock`` and the number of ``Instruction``\ s it contains:
+
+.. code-block:: c++
+
+ Function &Func = ...
+ for (BasicBlock &BB : Func)
+ // Print out the name of the basic block if it has one, and then the
+ // number of instructions that it contains
+ errs() << "Basic block (name=" << BB.getName() << ") has "
+ << BB.size() << " instructions.\n";
+
+.. _iterate_basicblock:
+
+Iterating over the ``Instruction`` in a ``BasicBlock``
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Just like when dealing with ``BasicBlock``\ s in ``Function``\ s, it's easy to
+iterate over the individual instructions that make up ``BasicBlock``\ s. Here's
+a code snippet that prints out each instruction in a ``BasicBlock``:
+
+.. code-block:: c++
+
+ BasicBlock& BB = ...
+ for (Instruction &I : BB)
+ // The next statement works since operator<<(ostream&,...)
+ // is overloaded for Instruction&
+ errs() << I << "\n";
+
+
+However, this isn't really the best way to print out the contents of a
+``BasicBlock``! Since the ostream operators are overloaded for virtually
+anything you'll care about, you could have just invoked the print routine on the
+basic block itself: ``errs() << BB << "\n";``.
+
+.. _iterate_insiter:
+
+Iterating over the ``Instruction`` in a ``Function``
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+If you're finding that you commonly iterate over a ``Function``'s
+``BasicBlock``\ s and then that ``BasicBlock``'s ``Instruction``\ s,
+``InstIterator`` should be used instead. You'll need to include
+``llvm/IR/InstIterator.h`` (`doxygen
+<http://llvm.org/doxygen/InstIterator_8h.html>`__) and then instantiate
+``InstIterator``\ s explicitly in your code. Here's a small example that shows
+how to dump all instructions in a function to the standard error stream:
+
+.. code-block:: c++
+
+ #include "llvm/IR/InstIterator.h"
+
+ // F is a pointer to a Function instance
+ for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
+ errs() << *I << "\n";
+
+Easy, isn't it? You can also use ``InstIterator``\ s to fill a work list with
+its initial contents. For example, if you wanted to initialize a work list to
+contain all instructions in a ``Function`` F, all you would need to do is
+something like:
+
+.. code-block:: c++
+
+ std::set<Instruction*> worklist;
+ // or better yet, SmallPtrSet<Instruction*, 64> worklist;
+
+ for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
+ worklist.insert(&*I);
+
+The STL set ``worklist`` would now contain all instructions in the ``Function``
+pointed to by F.
+
+.. _iterate_convert:
+
+Turning an iterator into a class pointer (and vice-versa)
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Sometimes, it'll be useful to grab a reference (or pointer) to a class instance
+when all you've got at hand is an iterator. Well, extracting a reference or a
+pointer from an iterator is very straight-forward. Assuming that ``i`` is a
+``BasicBlock::iterator`` and ``j`` is a ``BasicBlock::const_iterator``:
+
+.. code-block:: c++
+
+ Instruction& inst = *i; // Grab reference to instruction reference
+ Instruction* pinst = &*i; // Grab pointer to instruction reference
+ const Instruction& inst = *j;
+
+However, the iterators you'll be working with in the LLVM framework are special:
+they will automatically convert to a ptr-to-instance type whenever they need to.
+Instead of dereferencing the iterator and then taking the address of the result,
+you can simply assign the iterator to the proper pointer type and you get the
+dereference and address-of operation as a result of the assignment (behind the
+scenes, this is a result of overloading casting mechanisms). Thus the second
+line of the last example,
+
+.. code-block:: c++
+
+ Instruction *pinst = &*i;
+
+is semantically equivalent to
+
+.. code-block:: c++
+
+ Instruction *pinst = i;
+
+It's also possible to turn a class pointer into the corresponding iterator, and
+this is a constant time operation (very efficient). The following code snippet
+illustrates use of the conversion constructors provided by LLVM iterators. By
+using these, you can explicitly grab the iterator of something without actually
+obtaining it via iteration over some structure:
+
+.. code-block:: c++
+
+ void printNextInstruction(Instruction* inst) {
+ BasicBlock::iterator it(inst);
+ ++it; // After this line, it refers to the instruction after *inst
+ if (it != inst->getParent()->end()) errs() << *it << "\n";
+ }
+
+Unfortunately, these implicit conversions come at a cost; they prevent these
+iterators from conforming to standard iterator conventions, and thus from being
+usable with standard algorithms and containers. For example, they prevent the
+following code, where ``B`` is a ``BasicBlock``, from compiling:
+
+.. code-block:: c++
+
+ llvm::SmallVector<llvm::Instruction *, 16>(B->begin(), B->end());
+
+Because of this, these implicit conversions may be removed some day, and
+``operator*`` changed to return a pointer instead of a reference.
+
+.. _iterate_complex:
+
+Finding call sites: a slightly more complex example
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Say that you're writing a FunctionPass and would like to count all the locations
+in the entire module (that is, across every ``Function``) where a certain
+function (i.e., some ``Function *``) is already in scope. As you'll learn
+later, you may want to use an ``InstVisitor`` to accomplish this in a much more
+straight-forward manner, but this example will allow us to explore how you'd do
+it if you didn't have ``InstVisitor`` around. In pseudo-code, this is what we
+want to do:
+
+.. code-block:: none
+
+ initialize callCounter to zero
+ for each Function f in the Module
+ for each BasicBlock b in f
+ for each Instruction i in b
+ if (i is a CallInst and calls the given function)
+ increment callCounter
+
+And the actual code is (remember, because we're writing a ``FunctionPass``, our
+``FunctionPass``-derived class simply has to override the ``runOnFunction``
+method):
+
+.. code-block:: c++
+
+ Function* targetFunc = ...;
+
+ class OurFunctionPass : public FunctionPass {
+ public:
+ OurFunctionPass(): callCounter(0) { }
+
+ virtual runOnFunction(Function& F) {
+ for (BasicBlock &B : F) {
+ for (Instruction &I: B) {
+ if (auto *CallInst = dyn_cast<CallInst>(&I)) {
+ // We know we've encountered a call instruction, so we
+ // need to determine if it's a call to the
+ // function pointed to by m_func or not.
+ if (CallInst->getCalledFunction() == targetFunc)
+ ++callCounter;
+ }
+ }
+ }
+ }
+
+ private:
+ unsigned callCounter;
+ };
+
+.. _calls_and_invokes:
+
+Treating calls and invokes the same way
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+You may have noticed that the previous example was a bit oversimplified in that
+it did not deal with call sites generated by 'invoke' instructions. In this,
+and in other situations, you may find that you want to treat ``CallInst``\ s and
+``InvokeInst``\ s the same way, even though their most-specific common base
+class is ``Instruction``, which includes lots of less closely-related things.
+For these cases, LLVM provides a handy wrapper class called ``CallSite``
+(`doxygen <http://llvm.org/doxygen/classllvm_1_1CallSite.html>`__) It is
+essentially a wrapper around an ``Instruction`` pointer, with some methods that
+provide functionality common to ``CallInst``\ s and ``InvokeInst``\ s.
+
+This class has "value semantics": it should be passed by value, not by reference
+and it should not be dynamically allocated or deallocated using ``operator new``
+or ``operator delete``. It is efficiently copyable, assignable and
+constructable, with costs equivalents to that of a bare pointer. If you look at
+its definition, it has only a single pointer member.
+
+.. _iterate_chains:
+
+Iterating over def-use & use-def chains
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Frequently, we might have an instance of the ``Value`` class (`doxygen
+<http://llvm.org/doxygen/classllvm_1_1Value.html>`__) and we want to determine
+which ``User`` s use the ``Value``. The list of all ``User``\ s of a particular
+``Value`` is called a *def-use* chain. For example, let's say we have a
+``Function*`` named ``F`` to a particular function ``foo``. Finding all of the
+instructions that *use* ``foo`` is as simple as iterating over the *def-use*
+chain of ``F``:
+
+.. code-block:: c++
+
+ Function *F = ...;
+
+ for (User *U : F->users()) {
+ if (Instruction *Inst = dyn_cast<Instruction>(U)) {
+ errs() << "F is used in instruction:\n";
+ errs() << *Inst << "\n";
+ }
+
+Alternatively, it's common to have an instance of the ``User`` Class (`doxygen
+<http://llvm.org/doxygen/classllvm_1_1User.html>`__) and need to know what
+``Value``\ s are used by it. The list of all ``Value``\ s used by a ``User`` is
+known as a *use-def* chain. Instances of class ``Instruction`` are common
+``User`` s, so we might want to iterate over all of the values that a particular
+instruction uses (that is, the operands of the particular ``Instruction``):
+
+.. code-block:: c++
+
+ Instruction *pi = ...;
+
+ for (Use &U : pi->operands()) {
+ Value *v = U.get();
+ // ...
+ }
+
+Declaring objects as ``const`` is an important tool of enforcing mutation free
+algorithms (such as analyses, etc.). For this purpose above iterators come in
+constant flavors as ``Value::const_use_iterator`` and
+``Value::const_op_iterator``. They automatically arise when calling
+``use/op_begin()`` on ``const Value*``\ s or ``const User*``\ s respectively.
+Upon dereferencing, they return ``const Use*``\ s. Otherwise the above patterns
+remain unchanged.
+
+.. _iterate_preds:
+
+Iterating over predecessors & successors of blocks
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Iterating over the predecessors and successors of a block is quite easy with the
+routines defined in ``"llvm/IR/CFG.h"``. Just use code like this to
+iterate over all predecessors of BB:
+
+.. code-block:: c++
+
+ #include "llvm/IR/CFG.h"
+ BasicBlock *BB = ...;
+
+ for (BasicBlock *Pred : predecessors(BB)) {
+ // ...
+ }
+
+Similarly, to iterate over successors use ``successors``.
+
+.. _simplechanges:
+
+Making simple changes
+---------------------
+
+There are some primitive transformation operations present in the LLVM
+infrastructure that are worth knowing about. When performing transformations,
+it's fairly common to manipulate the contents of basic blocks. This section
+describes some of the common methods for doing so and gives example code.
+
+.. _schanges_creating:
+
+Creating and inserting new ``Instruction``\ s
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+*Instantiating Instructions*
+
+Creation of ``Instruction``\ s is straight-forward: simply call the constructor
+for the kind of instruction to instantiate and provide the necessary parameters.
+For example, an ``AllocaInst`` only *requires* a (const-ptr-to) ``Type``. Thus:
+
+.. code-block:: c++
+
+ auto *ai = new AllocaInst(Type::Int32Ty);
+
+will create an ``AllocaInst`` instance that represents the allocation of one
+integer in the current stack frame, at run time. Each ``Instruction`` subclass
+is likely to have varying default parameters which change the semantics of the
+instruction, so refer to the `doxygen documentation for the subclass of
+Instruction <http://llvm.org/doxygen/classllvm_1_1Instruction.html>`_ that
+you're interested in instantiating.
+
+*Naming values*
+
+It is very useful to name the values of instructions when you're able to, as
+this facilitates the debugging of your transformations. If you end up looking
+at generated LLVM machine code, you definitely want to have logical names
+associated with the results of instructions! By supplying a value for the
+``Name`` (default) parameter of the ``Instruction`` constructor, you associate a
+logical name with the result of the instruction's execution at run time. For
+example, say that I'm writing a transformation that dynamically allocates space
+for an integer on the stack, and that integer is going to be used as some kind
+of index by some other code. To accomplish this, I place an ``AllocaInst`` at
+the first point in the first ``BasicBlock`` of some ``Function``, and I'm
+intending to use it within the same ``Function``. I might do:
+
+.. code-block:: c++
+
+ auto *pa = new AllocaInst(Type::Int32Ty, 0, "indexLoc");
+
+where ``indexLoc`` is now the logical name of the instruction's execution value,
+which is a pointer to an integer on the run time stack.
+
+*Inserting instructions*
+
+There are essentially three ways to insert an ``Instruction`` into an existing
+sequence of instructions that form a ``BasicBlock``:
+
+* Insertion into an explicit instruction list
+
+ Given a ``BasicBlock* pb``, an ``Instruction* pi`` within that ``BasicBlock``,
+ and a newly-created instruction we wish to insert before ``*pi``, we do the
+ following:
+
+ .. code-block:: c++
+
+ BasicBlock *pb = ...;
+ Instruction *pi = ...;
+ auto *newInst = new Instruction(...);
+
+ pb->getInstList().insert(pi, newInst); // Inserts newInst before pi in pb
+
+ Appending to the end of a ``BasicBlock`` is so common that the ``Instruction``
+ class and ``Instruction``-derived classes provide constructors which take a
+ pointer to a ``BasicBlock`` to be appended to. For example code that looked
+ like:
+
+ .. code-block:: c++
+
+ BasicBlock *pb = ...;
+ auto *newInst = new Instruction(...);
+
+ pb->getInstList().push_back(newInst); // Appends newInst to pb
+
+ becomes:
+
+ .. code-block:: c++
+
+ BasicBlock *pb = ...;
+ auto *newInst = new Instruction(..., pb);
+
+ which is much cleaner, especially if you are creating long instruction
+ streams.
+
+* Insertion into an implicit instruction list
+
+ ``Instruction`` instances that are already in ``BasicBlock``\ s are implicitly
+ associated with an existing instruction list: the instruction list of the
+ enclosing basic block. Thus, we could have accomplished the same thing as the
+ above code without being given a ``BasicBlock`` by doing:
+
+ .. code-block:: c++
+
+ Instruction *pi = ...;
+ auto *newInst = new Instruction(...);
+
+ pi->getParent()->getInstList().insert(pi, newInst);
+
+ In fact, this sequence of steps occurs so frequently that the ``Instruction``
+ class and ``Instruction``-derived classes provide constructors which take (as
+ a default parameter) a pointer to an ``Instruction`` which the newly-created
+ ``Instruction`` should precede. That is, ``Instruction`` constructors are
+ capable of inserting the newly-created instance into the ``BasicBlock`` of a
+ provided instruction, immediately before that instruction. Using an
+ ``Instruction`` constructor with a ``insertBefore`` (default) parameter, the
+ above code becomes:
+
+ .. code-block:: c++
+
+ Instruction* pi = ...;
+ auto *newInst = new Instruction(..., pi);
+
+ which is much cleaner, especially if you're creating a lot of instructions and
+ adding them to ``BasicBlock``\ s.
+
+* Insertion using an instance of ``IRBuilder``
+
+ Inserting several ``Instruction``\ s can be quite laborious using the previous
+ methods. The ``IRBuilder`` is a convenience class that can be used to add
+ several instructions to the end of a ``BasicBlock`` or before a particular
+ ``Instruction``. It also supports constant folding and renaming named
+ registers (see ``IRBuilder``'s template arguments).
+
+ The example below demonstrates a very simple use of the ``IRBuilder`` where
+ three instructions are inserted before the instruction ``pi``. The first two
+ instructions are Call instructions and third instruction multiplies the return
+ value of the two calls.
+
+ .. code-block:: c++
+
+ Instruction *pi = ...;
+ IRBuilder<> Builder(pi);
+ CallInst* callOne = Builder.CreateCall(...);
+ CallInst* callTwo = Builder.CreateCall(...);
+ Value* result = Builder.CreateMul(callOne, callTwo);
+
+ The example below is similar to the above example except that the created
+ ``IRBuilder`` inserts instructions at the end of the ``BasicBlock`` ``pb``.
+
+ .. code-block:: c++
+
+ BasicBlock *pb = ...;
+ IRBuilder<> Builder(pb);
+ CallInst* callOne = Builder.CreateCall(...);
+ CallInst* callTwo = Builder.CreateCall(...);
+ Value* result = Builder.CreateMul(callOne, callTwo);
+
+ See :doc:`tutorial/LangImpl03` for a practical use of the ``IRBuilder``.
+
+
+.. _schanges_deleting:
+
+Deleting Instructions
+^^^^^^^^^^^^^^^^^^^^^
+
+Deleting an instruction from an existing sequence of instructions that form a
+BasicBlock_ is very straight-forward: just call the instruction's
+``eraseFromParent()`` method. For example:
+
+.. code-block:: c++
+
+ Instruction *I = .. ;
+ I->eraseFromParent();
+
+This unlinks the instruction from its containing basic block and deletes it. If
+you'd just like to unlink the instruction from its containing basic block but
+not delete it, you can use the ``removeFromParent()`` method.
+
+.. _schanges_replacing:
+
+Replacing an Instruction with another Value
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Replacing individual instructions
+"""""""""""""""""""""""""""""""""
+
+Including "`llvm/Transforms/Utils/BasicBlockUtils.h
+<http://llvm.org/doxygen/BasicBlockUtils_8h_source.html>`_" permits use of two
+very useful replace functions: ``ReplaceInstWithValue`` and
+``ReplaceInstWithInst``.
+
+.. _schanges_deleting_sub:
+
+Deleting Instructions
+"""""""""""""""""""""
+
+* ``ReplaceInstWithValue``
+
+ This function replaces all uses of a given instruction with a value, and then
+ removes the original instruction. The following example illustrates the
+ replacement of the result of a particular ``AllocaInst`` that allocates memory
+ for a single integer with a null pointer to an integer.
+
+ .. code-block:: c++
+
+ AllocaInst* instToReplace = ...;
+ BasicBlock::iterator ii(instToReplace);
+
+ ReplaceInstWithValue(instToReplace->getParent()->getInstList(), ii,
+ Constant::getNullValue(PointerType::getUnqual(Type::Int32Ty)));
+
+* ``ReplaceInstWithInst``
+
+ This function replaces a particular instruction with another instruction,
+ inserting the new instruction into the basic block at the location where the
+ old instruction was, and replacing any uses of the old instruction with the
+ new instruction. The following example illustrates the replacement of one
+ ``AllocaInst`` with another.
+
+ .. code-block:: c++
+
+ AllocaInst* instToReplace = ...;
+ BasicBlock::iterator ii(instToReplace);
+
+ ReplaceInstWithInst(instToReplace->getParent()->getInstList(), ii,
+ new AllocaInst(Type::Int32Ty, 0, "ptrToReplacedInt"));
+
+
+Replacing multiple uses of Users and Values
+"""""""""""""""""""""""""""""""""""""""""""
+
+You can use ``Value::replaceAllUsesWith`` and ``User::replaceUsesOfWith`` to
+change more than one use at a time. See the doxygen documentation for the
+`Value Class <http://llvm.org/doxygen/classllvm_1_1Value.html>`_ and `User Class
+<http://llvm.org/doxygen/classllvm_1_1User.html>`_, respectively, for more
+information.
+
+.. _schanges_deletingGV:
+
+Deleting GlobalVariables
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+Deleting a global variable from a module is just as easy as deleting an
+Instruction. First, you must have a pointer to the global variable that you
+wish to delete. You use this pointer to erase it from its parent, the module.
+For example:
+
+.. code-block:: c++
+
+ GlobalVariable *GV = .. ;
+
+ GV->eraseFromParent();
+
+
+.. _create_types:
+
+How to Create Types
+-------------------
+
+In generating IR, you may need some complex types. If you know these types
+statically, you can use ``TypeBuilder<...>::get()``, defined in
+``llvm/Support/TypeBuilder.h``, to retrieve them. ``TypeBuilder`` has two forms
+depending on whether you're building types for cross-compilation or native
+library use. ``TypeBuilder<T, true>`` requires that ``T`` be independent of the
+host environment, meaning that it's built out of types from the ``llvm::types``
+(`doxygen <http://llvm.org/doxygen/namespacellvm_1_1types.html>`__) namespace
+and pointers, functions, arrays, etc. built of those. ``TypeBuilder<T, false>``
+additionally allows native C types whose size may depend on the host compiler.
+For example,
+
+.. code-block:: c++
+
+ FunctionType *ft = TypeBuilder<types::i<8>(types::i<32>*), true>::get();
+
+is easier to read and write than the equivalent
+
+.. code-block:: c++
+
+ std::vector<const Type*> params;
+ params.push_back(PointerType::getUnqual(Type::Int32Ty));
+ FunctionType *ft = FunctionType::get(Type::Int8Ty, params, false);
+
+See the `class comment
+<http://llvm.org/doxygen/TypeBuilder_8h_source.html#l00001>`_ for more details.
+
+.. _threading:
+
+Threads and LLVM
+================
+
+This section describes the interaction of the LLVM APIs with multithreading,
+both on the part of client applications, and in the JIT, in the hosted
+application.
+
+Note that LLVM's support for multithreading is still relatively young. Up
+through version 2.5, the execution of threaded hosted applications was
+supported, but not threaded client access to the APIs. While this use case is
+now supported, clients *must* adhere to the guidelines specified below to ensure
+proper operation in multithreaded mode.
+
+Note that, on Unix-like platforms, LLVM requires the presence of GCC's atomic
+intrinsics in order to support threaded operation. If you need a
+multhreading-capable LLVM on a platform without a suitably modern system
+compiler, consider compiling LLVM and LLVM-GCC in single-threaded mode, and
+using the resultant compiler to build a copy of LLVM with multithreading
+support.
+
+.. _shutdown:
+
+Ending Execution with ``llvm_shutdown()``
+-----------------------------------------
+
+When you are done using the LLVM APIs, you should call ``llvm_shutdown()`` to
+deallocate memory used for internal structures.
+
+.. _managedstatic:
+
+Lazy Initialization with ``ManagedStatic``
+------------------------------------------
+
+``ManagedStatic`` is a utility class in LLVM used to implement static
+initialization of static resources, such as the global type tables. In a
+single-threaded environment, it implements a simple lazy initialization scheme.
+When LLVM is compiled with support for multi-threading, however, it uses
+double-checked locking to implement thread-safe lazy initialization.
+
+.. _llvmcontext:
+
+Achieving Isolation with ``LLVMContext``
+----------------------------------------
+
+``LLVMContext`` is an opaque class in the LLVM API which clients can use to
+operate multiple, isolated instances of LLVM concurrently within the same
+address space. For instance, in a hypothetical compile-server, the compilation
+of an individual translation unit is conceptually independent from all the
+others, and it would be desirable to be able to compile incoming translation
+units concurrently on independent server threads. Fortunately, ``LLVMContext``
+exists to enable just this kind of scenario!
+
+Conceptually, ``LLVMContext`` provides isolation. Every LLVM entity
+(``Module``\ s, ``Value``\ s, ``Type``\ s, ``Constant``\ s, etc.) in LLVM's
+in-memory IR belongs to an ``LLVMContext``. Entities in different contexts
+*cannot* interact with each other: ``Module``\ s in different contexts cannot be
+linked together, ``Function``\ s cannot be added to ``Module``\ s in different
+contexts, etc. What this means is that is is safe to compile on multiple
+threads simultaneously, as long as no two threads operate on entities within the
+same context.
+
+In practice, very few places in the API require the explicit specification of a
+``LLVMContext``, other than the ``Type`` creation/lookup APIs. Because every
+``Type`` carries a reference to its owning context, most other entities can
+determine what context they belong to by looking at their own ``Type``. If you
+are adding new entities to LLVM IR, please try to maintain this interface
+design.
+
+.. _jitthreading:
+
+Threads and the JIT
+-------------------
+
+LLVM's "eager" JIT compiler is safe to use in threaded programs. Multiple
+threads can call ``ExecutionEngine::getPointerToFunction()`` or
+``ExecutionEngine::runFunction()`` concurrently, and multiple threads can run
+code output by the JIT concurrently. The user must still ensure that only one
+thread accesses IR in a given ``LLVMContext`` while another thread might be
+modifying it. One way to do that is to always hold the JIT lock while accessing
+IR outside the JIT (the JIT *modifies* the IR by adding ``CallbackVH``\ s).
+Another way is to only call ``getPointerToFunction()`` from the
+``LLVMContext``'s thread.
+
+When the JIT is configured to compile lazily (using
+``ExecutionEngine::DisableLazyCompilation(false)``), there is currently a `race
+condition <https://bugs.llvm.org/show_bug.cgi?id=5184>`_ in updating call sites
+after a function is lazily-jitted. It's still possible to use the lazy JIT in a
+threaded program if you ensure that only one thread at a time can call any
+particular lazy stub and that the JIT lock guards any IR access, but we suggest
+using only the eager JIT in threaded programs.
+
+.. _advanced:
+
+Advanced Topics
+===============
+
+This section describes some of the advanced or obscure API's that most clients
+do not need to be aware of. These API's tend manage the inner workings of the
+LLVM system, and only need to be accessed in unusual circumstances.
+
+.. _SymbolTable:
+
+The ``ValueSymbolTable`` class
+------------------------------
+
+The ``ValueSymbolTable`` (`doxygen
+<http://llvm.org/doxygen/classllvm_1_1ValueSymbolTable.html>`__) class provides
+a symbol table that the :ref:`Function <c_Function>` and Module_ classes use for
+naming value definitions. The symbol table can provide a name for any Value_.
+
+Note that the ``SymbolTable`` class should not be directly accessed by most
+clients. It should only be used when iteration over the symbol table names
+themselves are required, which is very special purpose. Note that not all LLVM
+Value_\ s have names, and those without names (i.e. they have an empty name) do
+not exist in the symbol table.
+
+Symbol tables support iteration over the values in the symbol table with
+``begin/end/iterator`` and supports querying to see if a specific name is in the
+symbol table (with ``lookup``). The ``ValueSymbolTable`` class exposes no
+public mutator methods, instead, simply call ``setName`` on a value, which will
+autoinsert it into the appropriate symbol table.
+
+.. _UserLayout:
+
+The ``User`` and owned ``Use`` classes' memory layout
+-----------------------------------------------------
+
+The ``User`` (`doxygen <http://llvm.org/doxygen/classllvm_1_1User.html>`__)
+class provides a basis for expressing the ownership of ``User`` towards other
+`Value instance <http://llvm.org/doxygen/classllvm_1_1Value.html>`_\ s. The
+``Use`` (`doxygen <http://llvm.org/doxygen/classllvm_1_1Use.html>`__) helper
+class is employed to do the bookkeeping and to facilitate *O(1)* addition and
+removal.
+
+.. _Use2User:
+
+Interaction and relationship between ``User`` and ``Use`` objects
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+A subclass of ``User`` can choose between incorporating its ``Use`` objects or
+refer to them out-of-line by means of a pointer. A mixed variant (some ``Use``
+s inline others hung off) is impractical and breaks the invariant that the
+``Use`` objects belonging to the same ``User`` form a contiguous array.
+
+We have 2 different layouts in the ``User`` (sub)classes:
+
+* Layout a)
+
+ The ``Use`` object(s) are inside (resp. at fixed offset) of the ``User``
+ object and there are a fixed number of them.
+
+* Layout b)
+
+ The ``Use`` object(s) are referenced by a pointer to an array from the
+ ``User`` object and there may be a variable number of them.
+
+As of v2.4 each layout still possesses a direct pointer to the start of the
+array of ``Use``\ s. Though not mandatory for layout a), we stick to this
+redundancy for the sake of simplicity. The ``User`` object also stores the
+number of ``Use`` objects it has. (Theoretically this information can also be
+calculated given the scheme presented below.)
+
+Special forms of allocation operators (``operator new``) enforce the following
+memory layouts:
+
+* Layout a) is modelled by prepending the ``User`` object by the ``Use[]``
+ array.
+
+ .. code-block:: none
+
+ ...---.---.---.---.-------...
+ | P | P | P | P | User
+ '''---'---'---'---'-------'''
+
+* Layout b) is modelled by pointing at the ``Use[]`` array.
+
+ .. code-block:: none
+
+ .-------...
+ | User
+ '-------'''
+ |
+ v
+ .---.---.---.---...
+ | P | P | P | P |
+ '---'---'---'---'''
+
+*(In the above figures* '``P``' *stands for the* ``Use**`` *that is stored in
+each* ``Use`` *object in the member* ``Use::Prev`` *)*
+
+.. _Waymarking:
+
+The waymarking algorithm
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+Since the ``Use`` objects are deprived of the direct (back)pointer to their
+``User`` objects, there must be a fast and exact method to recover it. This is
+accomplished by the following scheme:
+
+A bit-encoding in the 2 LSBits (least significant bits) of the ``Use::Prev``
+allows to find the start of the ``User`` object:
+
+* ``00`` --- binary digit 0
+
+* ``01`` --- binary digit 1
+
+* ``10`` --- stop and calculate (``s``)
+
+* ``11`` --- full stop (``S``)
+
+Given a ``Use*``, all we have to do is to walk till we get a stop and we either
+have a ``User`` immediately behind or we have to walk to the next stop picking
+up digits and calculating the offset:
+
+.. code-block:: none
+
+ .---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.----------------
+ | 1 | s | 1 | 0 | 1 | 0 | s | 1 | 1 | 0 | s | 1 | 1 | s | 1 | S | User (or User*)
+ '---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'----------------
+ |+15 |+10 |+6 |+3 |+1
+ | | | | | __>
+ | | | | __________>
+ | | | ______________________>
+ | | ______________________________________>
+ | __________________________________________________________>
+
+Only the significant number of bits need to be stored between the stops, so that
+the *worst case is 20 memory accesses* when there are 1000 ``Use`` objects
+associated with a ``User``.
+
+.. _ReferenceImpl:
+
+Reference implementation
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+The following literate Haskell fragment demonstrates the concept:
+
+.. code-block:: haskell
+
+ > import Test.QuickCheck
+ >
+ > digits :: Int -> [Char] -> [Char]
+ > digits 0 acc = '0' : acc
+ > digits 1 acc = '1' : acc
+ > digits n acc = digits (n `div` 2) $ digits (n `mod` 2) acc
+ >
+ > dist :: Int -> [Char] -> [Char]
+ > dist 0 [] = ['S']
+ > dist 0 acc = acc
+ > dist 1 acc = let r = dist 0 acc in 's' : digits (length r) r
+ > dist n acc = dist (n - 1) $ dist 1 acc
+ >
+ > takeLast n ss = reverse $ take n $ reverse ss
+ >
+ > test = takeLast 40 $ dist 20 []
+ >
+
+Printing <test> gives: ``"1s100000s11010s10100s1111s1010s110s11s1S"``
+
+The reverse algorithm computes the length of the string just by examining a
+certain prefix:
+
+.. code-block:: haskell
+
+ > pref :: [Char] -> Int
+ > pref "S" = 1
+ > pref ('s':'1':rest) = decode 2 1 rest
+ > pref (_:rest) = 1 + pref rest
+ >
+ > decode walk acc ('0':rest) = decode (walk + 1) (acc * 2) rest
+ > decode walk acc ('1':rest) = decode (walk + 1) (acc * 2 + 1) rest
+ > decode walk acc _ = walk + acc
+ >
+
+Now, as expected, printing <pref test> gives ``40``.
+
+We can *quickCheck* this with following property:
+
+.. code-block:: haskell
+
+ > testcase = dist 2000 []
+ > testcaseLength = length testcase
+ >
+ > identityProp n = n > 0 && n <= testcaseLength ==> length arr == pref arr
+ > where arr = takeLast n testcase
+ >
+
+As expected <quickCheck identityProp> gives:
+
+::
+
+ *Main> quickCheck identityProp
+ OK, passed 100 tests.
+
+Let's be a bit more exhaustive:
+
+.. code-block:: haskell
+
+ >
+ > deepCheck p = check (defaultConfig { configMaxTest = 500 }) p
+ >
+
+And here is the result of <deepCheck identityProp>:
+
+::
+
+ *Main> deepCheck identityProp
+ OK, passed 500 tests.
+
+.. _Tagging:
+
+Tagging considerations
+^^^^^^^^^^^^^^^^^^^^^^
+
+To maintain the invariant that the 2 LSBits of each ``Use**`` in ``Use`` never
+change after being set up, setters of ``Use::Prev`` must re-tag the new
+``Use**`` on every modification. Accordingly getters must strip the tag bits.
+
+For layout b) instead of the ``User`` we find a pointer (``User*`` with LSBit
+set). Following this pointer brings us to the ``User``. A portable trick
+ensures that the first bytes of ``User`` (if interpreted as a pointer) never has
+the LSBit set. (Portability is relying on the fact that all known compilers
+place the ``vptr`` in the first word of the instances.)
+
+.. _polymorphism:
+
+Designing Type Hiercharies and Polymorphic Interfaces
+-----------------------------------------------------
+
+There are two different design patterns that tend to result in the use of
+virtual dispatch for methods in a type hierarchy in C++ programs. The first is
+a genuine type hierarchy where different types in the hierarchy model
+a specific subset of the functionality and semantics, and these types nest
+strictly within each other. Good examples of this can be seen in the ``Value``
+or ``Type`` type hierarchies.
+
+A second is the desire to dispatch dynamically across a collection of
+polymorphic interface implementations. This latter use case can be modeled with
+virtual dispatch and inheritance by defining an abstract interface base class
+which all implementations derive from and override. However, this
+implementation strategy forces an **"is-a"** relationship to exist that is not
+actually meaningful. There is often not some nested hierarchy of useful
+generalizations which code might interact with and move up and down. Instead,
+there is a singular interface which is dispatched across a range of
+implementations.
+
+The preferred implementation strategy for the second use case is that of
+generic programming (sometimes called "compile-time duck typing" or "static
+polymorphism"). For example, a template over some type parameter ``T`` can be
+instantiated across any particular implementation that conforms to the
+interface or *concept*. A good example here is the highly generic properties of
+any type which models a node in a directed graph. LLVM models these primarily
+through templates and generic programming. Such templates include the
+``LoopInfoBase`` and ``DominatorTreeBase``. When this type of polymorphism
+truly needs **dynamic** dispatch you can generalize it using a technique
+called *concept-based polymorphism*. This pattern emulates the interfaces and
+behaviors of templates using a very limited form of virtual dispatch for type
+erasure inside its implementation. You can find examples of this technique in
+the ``PassManager.h`` system, and there is a more detailed introduction to it
+by Sean Parent in several of his talks and papers:
+
+#. `Inheritance Is The Base Class of Evil
+ <http://channel9.msdn.com/Events/GoingNative/2013/Inheritance-Is-The-Base-Class-of-Evil>`_
+ - The GoingNative 2013 talk describing this technique, and probably the best
+ place to start.
+#. `Value Semantics and Concepts-based Polymorphism
+ <http://www.youtube.com/watch?v=_BpMYeUFXv8>`_ - The C++Now! 2012 talk
+ describing this technique in more detail.
+#. `Sean Parent's Papers and Presentations
+ <http://github.com/sean-parent/sean-parent.github.com/wiki/Papers-and-Presentations>`_
+ - A Github project full of links to slides, video, and sometimes code.
+
+When deciding between creating a type hierarchy (with either tagged or virtual
+dispatch) and using templates or concepts-based polymorphism, consider whether
+there is some refinement of an abstract base class which is a semantically
+meaningful type on an interface boundary. If anything more refined than the
+root abstract interface is meaningless to talk about as a partial extension of
+the semantic model, then your use case likely fits better with polymorphism and
+you should avoid using virtual dispatch. However, there may be some exigent
+circumstances that require one technique or the other to be used.
+
+If you do need to introduce a type hierarchy, we prefer to use explicitly
+closed type hierarchies with manual tagged dispatch and/or RTTI rather than the
+open inheritance model and virtual dispatch that is more common in C++ code.
+This is because LLVM rarely encourages library consumers to extend its core
+types, and leverages the closed and tag-dispatched nature of its hierarchies to
+generate significantly more efficient code. We have also found that a large
+amount of our usage of type hierarchies fits better with tag-based pattern
+matching rather than dynamic dispatch across a common interface. Within LLVM we
+have built custom helpers to facilitate this design. See this document's
+section on :ref:`isa and dyn_cast <isa>` and our :doc:`detailed document
+<HowToSetUpLLVMStyleRTTI>` which describes how you can implement this
+pattern for use with the LLVM helpers.
+
+.. _abi_breaking_checks:
+
+ABI Breaking Checks
+-------------------
+
+Checks and asserts that alter the LLVM C++ ABI are predicated on the
+preprocessor symbol `LLVM_ENABLE_ABI_BREAKING_CHECKS` -- LLVM
+libraries built with `LLVM_ENABLE_ABI_BREAKING_CHECKS` are not ABI
+compatible LLVM libraries built without it defined. By default,
+turning on assertions also turns on `LLVM_ENABLE_ABI_BREAKING_CHECKS`
+so a default +Asserts build is not ABI compatible with a
+default -Asserts build. Clients that want ABI compatibility
+between +Asserts and -Asserts builds should use the CMake or autoconf
+build systems to set `LLVM_ENABLE_ABI_BREAKING_CHECKS` independently
+of `LLVM_ENABLE_ASSERTIONS`.
+
+.. _coreclasses:
+
+The Core LLVM Class Hierarchy Reference
+=======================================
+
+``#include "llvm/IR/Type.h"``
+
+header source: `Type.h <http://llvm.org/doxygen/Type_8h_source.html>`_
+
+doxygen info: `Type Clases <http://llvm.org/doxygen/classllvm_1_1Type.html>`_
+
+The Core LLVM classes are the primary means of representing the program being
+inspected or transformed. The core LLVM classes are defined in header files in
+the ``include/llvm/IR`` directory, and implemented in the ``lib/IR``
+directory. It's worth noting that, for historical reasons, this library is
+called ``libLLVMCore.so``, not ``libLLVMIR.so`` as you might expect.
+
+.. _Type:
+
+The Type class and Derived Types
+--------------------------------
+
+``Type`` is a superclass of all type classes. Every ``Value`` has a ``Type``.
+``Type`` cannot be instantiated directly but only through its subclasses.
+Certain primitive types (``VoidType``, ``LabelType``, ``FloatType`` and
+``DoubleType``) have hidden subclasses. They are hidden because they offer no
+useful functionality beyond what the ``Type`` class offers except to distinguish
+themselves from other subclasses of ``Type``.
+
+All other types are subclasses of ``DerivedType``. Types can be named, but this
+is not a requirement. There exists exactly one instance of a given shape at any
+one time. This allows type equality to be performed with address equality of
+the Type Instance. That is, given two ``Type*`` values, the types are identical
+if the pointers are identical.
+
+.. _m_Type:
+
+Important Public Methods
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+* ``bool isIntegerTy() const``: Returns true for any integer type.
+
+* ``bool isFloatingPointTy()``: Return true if this is one of the five
+ floating point types.
+
+* ``bool isSized()``: Return true if the type has known size. Things
+ that don't have a size are abstract types, labels and void.
+
+.. _derivedtypes:
+
+Important Derived Types
+^^^^^^^^^^^^^^^^^^^^^^^
+
+``IntegerType``
+ Subclass of DerivedType that represents integer types of any bit width. Any
+ bit width between ``IntegerType::MIN_INT_BITS`` (1) and
+ ``IntegerType::MAX_INT_BITS`` (~8 million) can be represented.
+
+ * ``static const IntegerType* get(unsigned NumBits)``: get an integer
+ type of a specific bit width.
+
+ * ``unsigned getBitWidth() const``: Get the bit width of an integer type.
+
+``SequentialType``
+ This is subclassed by ArrayType and VectorType.
+
+ * ``const Type * getElementType() const``: Returns the type of each
+ of the elements in the sequential type.
+
+ * ``uint64_t getNumElements() const``: Returns the number of elements
+ in the sequential type.
+
+``ArrayType``
+ This is a subclass of SequentialType and defines the interface for array
+ types.
+
+``PointerType``
+ Subclass of Type for pointer types.
+
+``VectorType``
+ Subclass of SequentialType for vector types. A vector type is similar to an
+ ArrayType but is distinguished because it is a first class type whereas
+ ArrayType is not. Vector types are used for vector operations and are usually
+ small vectors of an integer or floating point type.
+
+``StructType``
+ Subclass of DerivedTypes for struct types.
+
+.. _FunctionType:
+
+``FunctionType``
+ Subclass of DerivedTypes for function types.
+
+ * ``bool isVarArg() const``: Returns true if it's a vararg function.
+
+ * ``const Type * getReturnType() const``: Returns the return type of the
+ function.
+
+ * ``const Type * getParamType (unsigned i)``: Returns the type of the ith
+ parameter.
+
+ * ``const unsigned getNumParams() const``: Returns the number of formal
+ parameters.
+
+.. _Module:
+
+The ``Module`` class
+--------------------
+
+``#include "llvm/IR/Module.h"``
+
+header source: `Module.h <http://llvm.org/doxygen/Module_8h_source.html>`_
+
+doxygen info: `Module Class <http://llvm.org/doxygen/classllvm_1_1Module.html>`_
+
+The ``Module`` class represents the top level structure present in LLVM
+programs. An LLVM module is effectively either a translation unit of the
+original program or a combination of several translation units merged by the
+linker. The ``Module`` class keeps track of a list of :ref:`Function
+<c_Function>`\ s, a list of GlobalVariable_\ s, and a SymbolTable_.
+Additionally, it contains a few helpful member functions that try to make common
+operations easy.
+
+.. _m_Module:
+
+Important Public Members of the ``Module`` class
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+* ``Module::Module(std::string name = "")``
+
+ Constructing a Module_ is easy. You can optionally provide a name for it
+ (probably based on the name of the translation unit).
+
+* | ``Module::iterator`` - Typedef for function list iterator
+ | ``Module::const_iterator`` - Typedef for const_iterator.
+ | ``begin()``, ``end()``, ``size()``, ``empty()``
+
+ These are forwarding methods that make it easy to access the contents of a
+ ``Module`` object's :ref:`Function <c_Function>` list.
+
+* ``Module::FunctionListType &getFunctionList()``
+
+ Returns the list of :ref:`Function <c_Function>`\ s. This is necessary to use
+ when you need to update the list or perform a complex action that doesn't have
+ a forwarding method.
+
+----------------
+
+* | ``Module::global_iterator`` - Typedef for global variable list iterator
+ | ``Module::const_global_iterator`` - Typedef for const_iterator.
+ | ``global_begin()``, ``global_end()``, ``global_size()``, ``global_empty()``
+
+ These are forwarding methods that make it easy to access the contents of a
+ ``Module`` object's GlobalVariable_ list.
+
+* ``Module::GlobalListType &getGlobalList()``
+
+ Returns the list of GlobalVariable_\ s. This is necessary to use when you
+ need to update the list or perform a complex action that doesn't have a
+ forwarding method.
+
+----------------
+
+* ``SymbolTable *getSymbolTable()``
+
+ Return a reference to the SymbolTable_ for this ``Module``.
+
+----------------
+
+* ``Function *getFunction(StringRef Name) const``
+
+ Look up the specified function in the ``Module`` SymbolTable_. If it does not
+ exist, return ``null``.
+
+* ``Function *getOrInsertFunction(const std::string &Name, const FunctionType
+ *T)``
+
+ Look up the specified function in the ``Module`` SymbolTable_. If it does not
+ exist, add an external declaration for the function and return it.
+
+* ``std::string getTypeName(const Type *Ty)``
+
+ If there is at least one entry in the SymbolTable_ for the specified Type_,
+ return it. Otherwise return the empty string.
+
+* ``bool addTypeName(const std::string &Name, const Type *Ty)``
+
+ Insert an entry in the SymbolTable_ mapping ``Name`` to ``Ty``. If there is
+ already an entry for this name, true is returned and the SymbolTable_ is not
+ modified.
+
+.. _Value:
+
+The ``Value`` class
+-------------------
+
+``#include "llvm/IR/Value.h"``
+
+header source: `Value.h <http://llvm.org/doxygen/Value_8h_source.html>`_
+
+doxygen info: `Value Class <http://llvm.org/doxygen/classllvm_1_1Value.html>`_
+
+The ``Value`` class is the most important class in the LLVM Source base. It
+represents a typed value that may be used (among other things) as an operand to
+an instruction. There are many different types of ``Value``\ s, such as
+Constant_\ s, Argument_\ s. Even Instruction_\ s and :ref:`Function
+<c_Function>`\ s are ``Value``\ s.
+
+A particular ``Value`` may be used many times in the LLVM representation for a
+program. For example, an incoming argument to a function (represented with an
+instance of the Argument_ class) is "used" by every instruction in the function
+that references the argument. To keep track of this relationship, the ``Value``
+class keeps a list of all of the ``User``\ s that is using it (the User_ class
+is a base class for all nodes in the LLVM graph that can refer to ``Value``\ s).
+This use list is how LLVM represents def-use information in the program, and is
+accessible through the ``use_*`` methods, shown below.
+
+Because LLVM is a typed representation, every LLVM ``Value`` is typed, and this
+Type_ is available through the ``getType()`` method. In addition, all LLVM
+values can be named. The "name" of the ``Value`` is a symbolic string printed
+in the LLVM code:
+
+.. code-block:: llvm
+
+ %foo = add i32 1, 2
+
+.. _nameWarning:
+
+The name of this instruction is "foo". **NOTE** that the name of any value may
+be missing (an empty string), so names should **ONLY** be used for debugging
+(making the source code easier to read, debugging printouts), they should not be
+used to keep track of values or map between them. For this purpose, use a
+``std::map`` of pointers to the ``Value`` itself instead.
+
+One important aspect of LLVM is that there is no distinction between an SSA
+variable and the operation that produces it. Because of this, any reference to
+the value produced by an instruction (or the value available as an incoming
+argument, for example) is represented as a direct pointer to the instance of the
+class that represents this value. Although this may take some getting used to,
+it simplifies the representation and makes it easier to manipulate.
+
+.. _m_Value:
+
+Important Public Members of the ``Value`` class
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+* | ``Value::use_iterator`` - Typedef for iterator over the use-list
+ | ``Value::const_use_iterator`` - Typedef for const_iterator over the
+ use-list
+ | ``unsigned use_size()`` - Returns the number of users of the value.
+ | ``bool use_empty()`` - Returns true if there are no users.
+ | ``use_iterator use_begin()`` - Get an iterator to the start of the
+ use-list.
+ | ``use_iterator use_end()`` - Get an iterator to the end of the use-list.
+ | ``User *use_back()`` - Returns the last element in the list.
+
+ These methods are the interface to access the def-use information in LLVM.
+ As with all other iterators in LLVM, the naming conventions follow the
+ conventions defined by the STL_.
+
+* ``Type *getType() const``
+ This method returns the Type of the Value.
+
+* | ``bool hasName() const``
+ | ``std::string getName() const``
+ | ``void setName(const std::string &Name)``
+
+ This family of methods is used to access and assign a name to a ``Value``, be
+ aware of the :ref:`precaution above <nameWarning>`.
+
+* ``void replaceAllUsesWith(Value *V)``
+
+ This method traverses the use list of a ``Value`` changing all User_\ s of the
+ current value to refer to "``V``" instead. For example, if you detect that an
+ instruction always produces a constant value (for example through constant
+ folding), you can replace all uses of the instruction with the constant like
+ this:
+
+ .. code-block:: c++
+
+ Inst->replaceAllUsesWith(ConstVal);
+
+.. _User:
+
+The ``User`` class
+------------------
+
+``#include "llvm/IR/User.h"``
+
+header source: `User.h <http://llvm.org/doxygen/User_8h_source.html>`_
+
+doxygen info: `User Class <http://llvm.org/doxygen/classllvm_1_1User.html>`_
+
+Superclass: Value_
+
+The ``User`` class is the common base class of all LLVM nodes that may refer to
+``Value``\ s. It exposes a list of "Operands" that are all of the ``Value``\ s
+that the User is referring to. The ``User`` class itself is a subclass of
+``Value``.
+
+The operands of a ``User`` point directly to the LLVM ``Value`` that it refers
+to. Because LLVM uses Static Single Assignment (SSA) form, there can only be
+one definition referred to, allowing this direct connection. This connection
+provides the use-def information in LLVM.
+
+.. _m_User:
+
+Important Public Members of the ``User`` class
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The ``User`` class exposes the operand list in two ways: through an index access
+interface and through an iterator based interface.
+
+* | ``Value *getOperand(unsigned i)``
+ | ``unsigned getNumOperands()``
+
+ These two methods expose the operands of the ``User`` in a convenient form for
+ direct access.
+
+* | ``User::op_iterator`` - Typedef for iterator over the operand list
+ | ``op_iterator op_begin()`` - Get an iterator to the start of the operand
+ list.
+ | ``op_iterator op_end()`` - Get an iterator to the end of the operand list.
+
+ Together, these methods make up the iterator based interface to the operands
+ of a ``User``.
+
+
+.. _Instruction:
+
+The ``Instruction`` class
+-------------------------
+
+``#include "llvm/IR/Instruction.h"``
+
+header source: `Instruction.h
+<http://llvm.org/doxygen/Instruction_8h_source.html>`_
+
+doxygen info: `Instruction Class
+<http://llvm.org/doxygen/classllvm_1_1Instruction.html>`_
+
+Superclasses: User_, Value_
+
+The ``Instruction`` class is the common base class for all LLVM instructions.
+It provides only a few methods, but is a very commonly used class. The primary
+data tracked by the ``Instruction`` class itself is the opcode (instruction
+type) and the parent BasicBlock_ the ``Instruction`` is embedded into. To
+represent a specific type of instruction, one of many subclasses of
+``Instruction`` are used.
+
+Because the ``Instruction`` class subclasses the User_ class, its operands can
+be accessed in the same way as for other ``User``\ s (with the
+``getOperand()``/``getNumOperands()`` and ``op_begin()``/``op_end()`` methods).
+An important file for the ``Instruction`` class is the ``llvm/Instruction.def``
+file. This file contains some meta-data about the various different types of
+instructions in LLVM. It describes the enum values that are used as opcodes
+(for example ``Instruction::Add`` and ``Instruction::ICmp``), as well as the
+concrete sub-classes of ``Instruction`` that implement the instruction (for
+example BinaryOperator_ and CmpInst_). Unfortunately, the use of macros in this
+file confuses doxygen, so these enum values don't show up correctly in the
+`doxygen output <http://llvm.org/doxygen/classllvm_1_1Instruction.html>`_.
+
+.. _s_Instruction:
+
+Important Subclasses of the ``Instruction`` class
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. _BinaryOperator:
+
+* ``BinaryOperator``
+
+ This subclasses represents all two operand instructions whose operands must be
+ the same type, except for the comparison instructions.
+
+.. _CastInst:
+
+* ``CastInst``
+ This subclass is the parent of the 12 casting instructions. It provides
+ common operations on cast instructions.
+
+.. _CmpInst:
+
+* ``CmpInst``
+
+ This subclass respresents the two comparison instructions,
+ `ICmpInst <LangRef.html#i_icmp>`_ (integer opreands), and
+ `FCmpInst <LangRef.html#i_fcmp>`_ (floating point operands).
+
+.. _TerminatorInst:
+
+* ``TerminatorInst``
+
+ This subclass is the parent of all terminator instructions (those which can
+ terminate a block).
+
+.. _m_Instruction:
+
+Important Public Members of the ``Instruction`` class
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+* ``BasicBlock *getParent()``
+
+ Returns the BasicBlock_ that this
+ ``Instruction`` is embedded into.
+
+* ``bool mayWriteToMemory()``
+
+ Returns true if the instruction writes to memory, i.e. it is a ``call``,
+ ``free``, ``invoke``, or ``store``.
+
+* ``unsigned getOpcode()``
+
+ Returns the opcode for the ``Instruction``.
+
+* ``Instruction *clone() const``
+
+ Returns another instance of the specified instruction, identical in all ways
+ to the original except that the instruction has no parent (i.e. it's not
+ embedded into a BasicBlock_), and it has no name.
+
+.. _Constant:
+
+The ``Constant`` class and subclasses
+-------------------------------------
+
+Constant represents a base class for different types of constants. It is
+subclassed by ConstantInt, ConstantArray, etc. for representing the various
+types of Constants. GlobalValue_ is also a subclass, which represents the
+address of a global variable or function.
+
+.. _s_Constant:
+
+Important Subclasses of Constant
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+* ConstantInt : This subclass of Constant represents an integer constant of
+ any width.
+
+ * ``const APInt& getValue() const``: Returns the underlying
+ value of this constant, an APInt value.
+
+ * ``int64_t getSExtValue() const``: Converts the underlying APInt value to an
+ int64_t via sign extension. If the value (not the bit width) of the APInt
+ is too large to fit in an int64_t, an assertion will result. For this
+ reason, use of this method is discouraged.
+
+ * ``uint64_t getZExtValue() const``: Converts the underlying APInt value
+ to a uint64_t via zero extension. IF the value (not the bit width) of the
+ APInt is too large to fit in a uint64_t, an assertion will result. For this
+ reason, use of this method is discouraged.
+
+ * ``static ConstantInt* get(const APInt& Val)``: Returns the ConstantInt
+ object that represents the value provided by ``Val``. The type is implied
+ as the IntegerType that corresponds to the bit width of ``Val``.
+
+ * ``static ConstantInt* get(const Type *Ty, uint64_t Val)``: Returns the
+ ConstantInt object that represents the value provided by ``Val`` for integer
+ type ``Ty``.
+
+* ConstantFP : This class represents a floating point constant.
+
+ * ``double getValue() const``: Returns the underlying value of this constant.
+
+* ConstantArray : This represents a constant array.
+
+ * ``const std::vector<Use> &getValues() const``: Returns a vector of
+ component constants that makeup this array.
+
+* ConstantStruct : This represents a constant struct.
+
+ * ``const std::vector<Use> &getValues() const``: Returns a vector of
+ component constants that makeup this array.
+
+* GlobalValue : This represents either a global variable or a function. In
+ either case, the value is a constant fixed address (after linking).
+
+.. _GlobalValue:
+
+The ``GlobalValue`` class
+-------------------------
+
+``#include "llvm/IR/GlobalValue.h"``
+
+header source: `GlobalValue.h
+<http://llvm.org/doxygen/GlobalValue_8h_source.html>`_
+
+doxygen info: `GlobalValue Class
+<http://llvm.org/doxygen/classllvm_1_1GlobalValue.html>`_
+
+Superclasses: Constant_, User_, Value_
+
+Global values ( GlobalVariable_\ s or :ref:`Function <c_Function>`\ s) are the
+only LLVM values that are visible in the bodies of all :ref:`Function
+<c_Function>`\ s. Because they are visible at global scope, they are also
+subject to linking with other globals defined in different translation units.
+To control the linking process, ``GlobalValue``\ s know their linkage rules.
+Specifically, ``GlobalValue``\ s know whether they have internal or external
+linkage, as defined by the ``LinkageTypes`` enumeration.
+
+If a ``GlobalValue`` has internal linkage (equivalent to being ``static`` in C),
+it is not visible to code outside the current translation unit, and does not
+participate in linking. If it has external linkage, it is visible to external
+code, and does participate in linking. In addition to linkage information,
+``GlobalValue``\ s keep track of which Module_ they are currently part of.
+
+Because ``GlobalValue``\ s are memory objects, they are always referred to by
+their **address**. As such, the Type_ of a global is always a pointer to its
+contents. It is important to remember this when using the ``GetElementPtrInst``
+instruction because this pointer must be dereferenced first. For example, if
+you have a ``GlobalVariable`` (a subclass of ``GlobalValue)`` that is an array
+of 24 ints, type ``[24 x i32]``, then the ``GlobalVariable`` is a pointer to
+that array. Although the address of the first element of this array and the
+value of the ``GlobalVariable`` are the same, they have different types. The
+``GlobalVariable``'s type is ``[24 x i32]``. The first element's type is
+``i32.`` Because of this, accessing a global value requires you to dereference
+the pointer with ``GetElementPtrInst`` first, then its elements can be accessed.
+This is explained in the `LLVM Language Reference Manual
+<LangRef.html#globalvars>`_.
+
+.. _m_GlobalValue:
+
+Important Public Members of the ``GlobalValue`` class
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+* | ``bool hasInternalLinkage() const``
+ | ``bool hasExternalLinkage() const``
+ | ``void setInternalLinkage(bool HasInternalLinkage)``
+
+ These methods manipulate the linkage characteristics of the ``GlobalValue``.
+
+* ``Module *getParent()``
+
+ This returns the Module_ that the
+ GlobalValue is currently embedded into.
+
+.. _c_Function:
+
+The ``Function`` class
+----------------------
+
+``#include "llvm/IR/Function.h"``
+
+header source: `Function.h <http://llvm.org/doxygen/Function_8h_source.html>`_
+
+doxygen info: `Function Class
+<http://llvm.org/doxygen/classllvm_1_1Function.html>`_
+
+Superclasses: GlobalValue_, Constant_, User_, Value_
+
+The ``Function`` class represents a single procedure in LLVM. It is actually
+one of the more complex classes in the LLVM hierarchy because it must keep track
+of a large amount of data. The ``Function`` class keeps track of a list of
+BasicBlock_\ s, a list of formal Argument_\ s, and a SymbolTable_.
+
+The list of BasicBlock_\ s is the most commonly used part of ``Function``
+objects. The list imposes an implicit ordering of the blocks in the function,
+which indicate how the code will be laid out by the backend. Additionally, the
+first BasicBlock_ is the implicit entry node for the ``Function``. It is not
+legal in LLVM to explicitly branch to this initial block. There are no implicit
+exit nodes, and in fact there may be multiple exit nodes from a single
+``Function``. If the BasicBlock_ list is empty, this indicates that the
+``Function`` is actually a function declaration: the actual body of the function
+hasn't been linked in yet.
+
+In addition to a list of BasicBlock_\ s, the ``Function`` class also keeps track
+of the list of formal Argument_\ s that the function receives. This container
+manages the lifetime of the Argument_ nodes, just like the BasicBlock_ list does
+for the BasicBlock_\ s.
+
+The SymbolTable_ is a very rarely used LLVM feature that is only used when you
+have to look up a value by name. Aside from that, the SymbolTable_ is used
+internally to make sure that there are not conflicts between the names of
+Instruction_\ s, BasicBlock_\ s, or Argument_\ s in the function body.
+
+Note that ``Function`` is a GlobalValue_ and therefore also a Constant_. The
+value of the function is its address (after linking) which is guaranteed to be
+constant.
+
+.. _m_Function:
+
+Important Public Members of the ``Function``
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+* ``Function(const FunctionType *Ty, LinkageTypes Linkage,
+ const std::string &N = "", Module* Parent = 0)``
+
+ Constructor used when you need to create new ``Function``\ s to add the
+ program. The constructor must specify the type of the function to create and
+ what type of linkage the function should have. The FunctionType_ argument
+ specifies the formal arguments and return value for the function. The same
+ FunctionType_ value can be used to create multiple functions. The ``Parent``
+ argument specifies the Module in which the function is defined. If this
+ argument is provided, the function will automatically be inserted into that
+ module's list of functions.
+
+* ``bool isDeclaration()``
+
+ Return whether or not the ``Function`` has a body defined. If the function is
+ "external", it does not have a body, and thus must be resolved by linking with
+ a function defined in a different translation unit.
+
+* | ``Function::iterator`` - Typedef for basic block list iterator
+ | ``Function::const_iterator`` - Typedef for const_iterator.
+ | ``begin()``, ``end()``, ``size()``, ``empty()``
+
+ These are forwarding methods that make it easy to access the contents of a
+ ``Function`` object's BasicBlock_ list.
+
+* ``Function::BasicBlockListType &getBasicBlockList()``
+
+ Returns the list of BasicBlock_\ s. This is necessary to use when you need to
+ update the list or perform a complex action that doesn't have a forwarding
+ method.
+
+* | ``Function::arg_iterator`` - Typedef for the argument list iterator
+ | ``Function::const_arg_iterator`` - Typedef for const_iterator.
+ | ``arg_begin()``, ``arg_end()``, ``arg_size()``, ``arg_empty()``
+
+ These are forwarding methods that make it easy to access the contents of a
+ ``Function`` object's Argument_ list.
+
+* ``Function::ArgumentListType &getArgumentList()``
+
+ Returns the list of Argument_. This is necessary to use when you need to
+ update the list or perform a complex action that doesn't have a forwarding
+ method.
+
+* ``BasicBlock &getEntryBlock()``
+
+ Returns the entry ``BasicBlock`` for the function. Because the entry block
+ for the function is always the first block, this returns the first block of
+ the ``Function``.
+
+* | ``Type *getReturnType()``
+ | ``FunctionType *getFunctionType()``
+
+ This traverses the Type_ of the ``Function`` and returns the return type of
+ the function, or the FunctionType_ of the actual function.
+
+* ``SymbolTable *getSymbolTable()``
+
+ Return a pointer to the SymbolTable_ for this ``Function``.
+
+.. _GlobalVariable:
+
+The ``GlobalVariable`` class
+----------------------------
+
+``#include "llvm/IR/GlobalVariable.h"``
+
+header source: `GlobalVariable.h
+<http://llvm.org/doxygen/GlobalVariable_8h_source.html>`_
+
+doxygen info: `GlobalVariable Class
+<http://llvm.org/doxygen/classllvm_1_1GlobalVariable.html>`_
+
+Superclasses: GlobalValue_, Constant_, User_, Value_
+
+Global variables are represented with the (surprise surprise) ``GlobalVariable``
+class. Like functions, ``GlobalVariable``\ s are also subclasses of
+GlobalValue_, and as such are always referenced by their address (global values
+must live in memory, so their "name" refers to their constant address). See
+GlobalValue_ for more on this. Global variables may have an initial value
+(which must be a Constant_), and if they have an initializer, they may be marked
+as "constant" themselves (indicating that their contents never change at
+runtime).
+
+.. _m_GlobalVariable:
+
+Important Public Members of the ``GlobalVariable`` class
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+* ``GlobalVariable(const Type *Ty, bool isConstant, LinkageTypes &Linkage,
+ Constant *Initializer = 0, const std::string &Name = "", Module* Parent = 0)``
+
+ Create a new global variable of the specified type. If ``isConstant`` is true
+ then the global variable will be marked as unchanging for the program. The
+ Linkage parameter specifies the type of linkage (internal, external, weak,
+ linkonce, appending) for the variable. If the linkage is InternalLinkage,
+ WeakAnyLinkage, WeakODRLinkage, LinkOnceAnyLinkage or LinkOnceODRLinkage, then
+ the resultant global variable will have internal linkage. AppendingLinkage
+ concatenates together all instances (in different translation units) of the
+ variable into a single variable but is only applicable to arrays. See the
+ `LLVM Language Reference <LangRef.html#modulestructure>`_ for further details
+ on linkage types. Optionally an initializer, a name, and the module to put
+ the variable into may be specified for the global variable as well.
+
+* ``bool isConstant() const``
+
+ Returns true if this is a global variable that is known not to be modified at
+ runtime.
+
+* ``bool hasInitializer()``
+
+ Returns true if this ``GlobalVariable`` has an intializer.
+
+* ``Constant *getInitializer()``
+
+ Returns the initial value for a ``GlobalVariable``. It is not legal to call
+ this method if there is no initializer.
+
+.. _BasicBlock:
+
+The ``BasicBlock`` class
+------------------------
+
+``#include "llvm/IR/BasicBlock.h"``
+
+header source: `BasicBlock.h
+<http://llvm.org/doxygen/BasicBlock_8h_source.html>`_
+
+doxygen info: `BasicBlock Class
+<http://llvm.org/doxygen/classllvm_1_1BasicBlock.html>`_
+
+Superclass: Value_
+
+This class represents a single entry single exit section of the code, commonly
+known as a basic block by the compiler community. The ``BasicBlock`` class
+maintains a list of Instruction_\ s, which form the body of the block. Matching
+the language definition, the last element of this list of instructions is always
+a terminator instruction (a subclass of the TerminatorInst_ class).
+
+In addition to tracking the list of instructions that make up the block, the
+``BasicBlock`` class also keeps track of the :ref:`Function <c_Function>` that
+it is embedded into.
+
+Note that ``BasicBlock``\ s themselves are Value_\ s, because they are
+referenced by instructions like branches and can go in the switch tables.
+``BasicBlock``\ s have type ``label``.
+
+.. _m_BasicBlock:
+
+Important Public Members of the ``BasicBlock`` class
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+* ``BasicBlock(const std::string &Name = "", Function *Parent = 0)``
+
+ The ``BasicBlock`` constructor is used to create new basic blocks for
+ insertion into a function. The constructor optionally takes a name for the
+ new block, and a :ref:`Function <c_Function>` to insert it into. If the
+ ``Parent`` parameter is specified, the new ``BasicBlock`` is automatically
+ inserted at the end of the specified :ref:`Function <c_Function>`, if not
+ specified, the BasicBlock must be manually inserted into the :ref:`Function
+ <c_Function>`.
+
+* | ``BasicBlock::iterator`` - Typedef for instruction list iterator
+ | ``BasicBlock::const_iterator`` - Typedef for const_iterator.
+ | ``begin()``, ``end()``, ``front()``, ``back()``,
+ ``size()``, ``empty()``
+ STL-style functions for accessing the instruction list.
+
+ These methods and typedefs are forwarding functions that have the same
+ semantics as the standard library methods of the same names. These methods
+ expose the underlying instruction list of a basic block in a way that is easy
+ to manipulate. To get the full complement of container operations (including
+ operations to update the list), you must use the ``getInstList()`` method.
+
+* ``BasicBlock::InstListType &getInstList()``
+
+ This method is used to get access to the underlying container that actually
+ holds the Instructions. This method must be used when there isn't a
+ forwarding function in the ``BasicBlock`` class for the operation that you
+ would like to perform. Because there are no forwarding functions for
+ "updating" operations, you need to use this if you want to update the contents
+ of a ``BasicBlock``.
+
+* ``Function *getParent()``
+
+ Returns a pointer to :ref:`Function <c_Function>` the block is embedded into,
+ or a null pointer if it is homeless.
+
+* ``TerminatorInst *getTerminator()``
+
+ Returns a pointer to the terminator instruction that appears at the end of the
+ ``BasicBlock``. If there is no terminator instruction, or if the last
+ instruction in the block is not a terminator, then a null pointer is returned.
+
+.. _Argument:
+
+The ``Argument`` class
+----------------------
+
+This subclass of Value defines the interface for incoming formal arguments to a
+function. A Function maintains a list of its formal arguments. An argument has
+a pointer to the parent Function.
+
+
Added: www-releases/trunk/5.0.1/docs/_sources/Projects.rst.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/5.0.1/docs/_sources/Projects.rst.txt?rev=321287&view=auto
==============================================================================
--- www-releases/trunk/5.0.1/docs/_sources/Projects.rst.txt (added)
+++ www-releases/trunk/5.0.1/docs/_sources/Projects.rst.txt Thu Dec 21 10:09:53 2017
@@ -0,0 +1,257 @@
+========================
+Creating an LLVM Project
+========================
+
+.. contents::
+ :local:
+
+Overview
+========
+
+The LLVM build system is designed to facilitate the building of third party
+projects that use LLVM header files, libraries, and tools. In order to use
+these facilities, a ``Makefile`` from a project must do the following things:
+
+* Set ``make`` variables. There are several variables that a ``Makefile`` needs
+ to set to use the LLVM build system:
+
+ * ``PROJECT_NAME`` - The name by which your project is known.
+ * ``LLVM_SRC_ROOT`` - The root of the LLVM source tree.
+ * ``LLVM_OBJ_ROOT`` - The root of the LLVM object tree.
+ * ``PROJ_SRC_ROOT`` - The root of the project's source tree.
+ * ``PROJ_OBJ_ROOT`` - The root of the project's object tree.
+ * ``PROJ_INSTALL_ROOT`` - The root installation directory.
+ * ``LEVEL`` - The relative path from the current directory to the
+ project's root ``($PROJ_OBJ_ROOT)``.
+
+* Include ``Makefile.config`` from ``$(LLVM_OBJ_ROOT)``.
+
+* Include ``Makefile.rules`` from ``$(LLVM_SRC_ROOT)``.
+
+There are two ways that you can set all of these variables:
+
+* You can write your own ``Makefiles`` which hard-code these values.
+
+* You can use the pre-made LLVM sample project. This sample project includes
+ ``Makefiles``, a configure script that can be used to configure the location
+ of LLVM, and the ability to support multiple object directories from a single
+ source directory.
+
+If you want to devise your own build system, studying other projects and LLVM
+``Makefiles`` will probably provide enough information on how to write your own
+``Makefiles``.
+
+Source Tree Layout
+==================
+
+In order to use the LLVM build system, you will want to organize your source
+code so that it can benefit from the build system's features. Mainly, you want
+your source tree layout to look similar to the LLVM source tree layout.
+
+Underneath your top level directory, you should have the following directories:
+
+**lib**
+
+ This subdirectory should contain all of your library source code. For each
+ library that you build, you will have one directory in **lib** that will
+ contain that library's source code.
+
+ Libraries can be object files, archives, or dynamic libraries. The **lib**
+ directory is just a convenient place for libraries as it places them all in
+ a directory from which they can be linked later.
+
+**include**
+
+ This subdirectory should contain any header files that are global to your
+ project. By global, we mean that they are used by more than one library or
+ executable of your project.
+
+ By placing your header files in **include**, they will be found
+ automatically by the LLVM build system. For example, if you have a file
+ **include/jazz/note.h**, then your source files can include it simply with
+ **#include "jazz/note.h"**.
+
+**tools**
+
+ This subdirectory should contain all of your source code for executables.
+ For each program that you build, you will have one directory in **tools**
+ that will contain that program's source code.
+
+**test**
+
+ This subdirectory should contain tests that verify that your code works
+ correctly. Automated tests are especially useful.
+
+ Currently, the LLVM build system provides basic support for tests. The LLVM
+ system provides the following:
+
+* LLVM contains regression tests in ``llvm/test``. These tests are run by the
+ :doc:`Lit <CommandGuide/lit>` testing tool. This test procedure uses ``RUN``
+ lines in the actual test case to determine how to run the test. See the
+ :doc:`TestingGuide` for more details.
+
+* LLVM contains an optional package called ``llvm-test``, which provides
+ benchmarks and programs that are known to compile with the Clang front
+ end. You can use these programs to test your code, gather statistical
+ information, and compare it to the current LLVM performance statistics.
+
+ Currently, there is no way to hook your tests directly into the ``llvm/test``
+ testing harness. You will simply need to find a way to use the source
+ provided within that directory on your own.
+
+Typically, you will want to build your **lib** directory first followed by your
+**tools** directory.
+
+Writing LLVM Style Makefiles
+============================
+
+The LLVM build system provides a convenient way to build libraries and
+executables. Most of your project Makefiles will only need to define a few
+variables. Below is a list of the variables one can set and what they can
+do:
+
+Required Variables
+------------------
+
+``LEVEL``
+
+ This variable is the relative path from this ``Makefile`` to the top
+ directory of your project's source code. For example, if your source code
+ is in ``/tmp/src``, then the ``Makefile`` in ``/tmp/src/jump/high``
+ would set ``LEVEL`` to ``"../.."``.
+
+Variables for Building Subdirectories
+-------------------------------------
+
+``DIRS``
+
+ This is a space separated list of subdirectories that should be built. They
+ will be built, one at a time, in the order specified.
+
+``PARALLEL_DIRS``
+
+ This is a list of directories that can be built in parallel. These will be
+ built after the directories in DIRS have been built.
+
+``OPTIONAL_DIRS``
+
+ This is a list of directories that can be built if they exist, but will not
+ cause an error if they do not exist. They are built serially in the order
+ in which they are listed.
+
+Variables for Building Libraries
+--------------------------------
+
+``LIBRARYNAME``
+
+ This variable contains the base name of the library that will be built. For
+ example, to build a library named ``libsample.a``, ``LIBRARYNAME`` should
+ be set to ``sample``.
+
+``BUILD_ARCHIVE``
+
+ By default, a library is a ``.o`` file that is linked directly into a
+ program. To build an archive (also known as a static library), set the
+ ``BUILD_ARCHIVE`` variable.
+
+``SHARED_LIBRARY``
+
+ If ``SHARED_LIBRARY`` is defined in your Makefile, a shared (or dynamic)
+ library will be built.
+
+Variables for Building Programs
+-------------------------------
+
+``TOOLNAME``
+
+ This variable contains the name of the program that will be built. For
+ example, to build an executable named ``sample``, ``TOOLNAME`` should be set
+ to ``sample``.
+
+``USEDLIBS``
+
+ This variable holds a space separated list of libraries that should be
+ linked into the program. These libraries must be libraries that come from
+ your **lib** directory. The libraries must be specified without their
+ ``lib`` prefix. For example, to link ``libsample.a``, you would set
+ ``USEDLIBS`` to ``sample.a``.
+
+ Note that this works only for statically linked libraries.
+
+``LLVMLIBS``
+
+ This variable holds a space separated list of libraries that should be
+ linked into the program. These libraries must be LLVM libraries. The
+ libraries must be specified without their ``lib`` prefix. For example, to
+ link with a driver that performs an IR transformation you might set
+ ``LLVMLIBS`` to this minimal set of libraries ``LLVMSupport.a LLVMCore.a
+ LLVMBitReader.a LLVMAsmParser.a LLVMAnalysis.a LLVMTransformUtils.a
+ LLVMScalarOpts.a LLVMTarget.a``.
+
+ Note that this works only for statically linked libraries. LLVM is split
+ into a large number of static libraries, and the list of libraries you
+ require may be much longer than the list above. To see a full list of
+ libraries use: ``llvm-config --libs all``. Using ``LINK_COMPONENTS`` as
+ described below, obviates the need to set ``LLVMLIBS``.
+
+``LINK_COMPONENTS``
+
+ This variable holds a space separated list of components that the LLVM
+ ``Makefiles`` pass to the ``llvm-config`` tool to generate a link line for
+ the program. For example, to link with all LLVM libraries use
+ ``LINK_COMPONENTS = all``.
+
+``LIBS``
+
+ To link dynamic libraries, add ``-l<library base name>`` to the ``LIBS``
+ variable. The LLVM build system will look in the same places for dynamic
+ libraries as it does for static libraries.
+
+ For example, to link ``libsample.so``, you would have the following line in
+ your ``Makefile``:
+
+ .. code-block:: makefile
+
+ LIBS += -lsample
+
+Note that ``LIBS`` must occur in the Makefile after the inclusion of
+``Makefile.common``.
+
+Miscellaneous Variables
+-----------------------
+
+``CFLAGS`` & ``CPPFLAGS``
+
+ This variable can be used to add options to the C and C++ compiler,
+ respectively. It is typically used to add options that tell the compiler
+ the location of additional directories to search for header files.
+
+ It is highly suggested that you append to ``CFLAGS`` and ``CPPFLAGS`` as
+ opposed to overwriting them. The master ``Makefiles`` may already have
+ useful options in them that you may not want to overwrite.
+
+Placement of Object Code
+========================
+
+The final location of built libraries and executables will depend upon whether
+you do a ``Debug``, ``Release``, or ``Profile`` build.
+
+Libraries
+
+ All libraries (static and dynamic) will be stored in
+ ``PROJ_OBJ_ROOT/<type>/lib``, where *type* is ``Debug``, ``Release``, or
+ ``Profile`` for a debug, optimized, or profiled build, respectively.
+
+Executables
+
+ All executables will be stored in ``PROJ_OBJ_ROOT/<type>/bin``, where *type*
+ is ``Debug``, ``Release``, or ``Profile`` for a debug, optimized, or
+ profiled build, respectively.
+
+Further Help
+============
+
+If you have any questions or need any help creating an LLVM project, the LLVM
+team would be more than happy to help. You can always post your questions to
+the `LLVM Developers Mailing List
+<http://lists.llvm.org/pipermail/llvm-dev/>`_.
More information about the llvm-commits
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