1 ==============================
2 LLVM Language Reference Manual
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12 This document is a reference manual for the LLVM assembly language. LLVM
13 is a Static Single Assignment (SSA) based representation that provides
14 type safety, low-level operations, flexibility, and the capability of
15 representing 'all' high-level languages cleanly. It is the common code
16 representation used throughout all phases of the LLVM compilation
22 The LLVM code representation is designed to be used in three different
23 forms: as an in-memory compiler IR, as an on-disk bitcode representation
24 (suitable for fast loading by a Just-In-Time compiler), and as a human
25 readable assembly language representation. This allows LLVM to provide a
26 powerful intermediate representation for efficient compiler
27 transformations and analysis, while providing a natural means to debug
28 and visualize the transformations. The three different forms of LLVM are
29 all equivalent. This document describes the human readable
30 representation and notation.
32 The LLVM representation aims to be light-weight and low-level while
33 being expressive, typed, and extensible at the same time. It aims to be
34 a "universal IR" of sorts, by being at a low enough level that
35 high-level ideas may be cleanly mapped to it (similar to how
36 microprocessors are "universal IR's", allowing many source languages to
37 be mapped to them). By providing type information, LLVM can be used as
38 the target of optimizations: for example, through pointer analysis, it
39 can be proven that a C automatic variable is never accessed outside of
40 the current function, allowing it to be promoted to a simple SSA value
41 instead of a memory location.
48 It is important to note that this document describes 'well formed' LLVM
49 assembly language. There is a difference between what the parser accepts
50 and what is considered 'well formed'. For example, the following
51 instruction is syntactically okay, but not well formed:
57 because the definition of ``%x`` does not dominate all of its uses. The
58 LLVM infrastructure provides a verification pass that may be used to
59 verify that an LLVM module is well formed. This pass is automatically
60 run by the parser after parsing input assembly and by the optimizer
61 before it outputs bitcode. The violations pointed out by the verifier
62 pass indicate bugs in transformation passes or input to the parser.
69 LLVM identifiers come in two basic types: global and local. Global
70 identifiers (functions, global variables) begin with the ``'@'``
71 character. Local identifiers (register names, types) begin with the
72 ``'%'`` character. Additionally, there are three different formats for
73 identifiers, for different purposes:
75 #. Named values are represented as a string of characters with their
76 prefix. For example, ``%foo``, ``@DivisionByZero``,
77 ``%a.really.long.identifier``. The actual regular expression used is
78 '``[%@][-a-zA-Z$._][-a-zA-Z$._0-9]*``'. Identifiers that require other
79 characters in their names can be surrounded with quotes. Special
80 characters may be escaped using ``"\xx"`` where ``xx`` is the ASCII
81 code for the character in hexadecimal. In this way, any character can
82 be used in a name value, even quotes themselves. The ``"\01"`` prefix
83 can be used on global variables to suppress mangling.
84 #. Unnamed values are represented as an unsigned numeric value with
85 their prefix. For example, ``%12``, ``@2``, ``%44``.
86 #. Constants, which are described in the section Constants_ below.
88 LLVM requires that values start with a prefix for two reasons: Compilers
89 don't need to worry about name clashes with reserved words, and the set
90 of reserved words may be expanded in the future without penalty.
91 Additionally, unnamed identifiers allow a compiler to quickly come up
92 with a temporary variable without having to avoid symbol table
95 Reserved words in LLVM are very similar to reserved words in other
96 languages. There are keywords for different opcodes ('``add``',
97 '``bitcast``', '``ret``', etc...), for primitive type names ('``void``',
98 '``i32``', etc...), and others. These reserved words cannot conflict
99 with variable names, because none of them start with a prefix character
100 (``'%'`` or ``'@'``).
102 Here is an example of LLVM code to multiply the integer variable
109 %result = mul i32 %X, 8
111 After strength reduction:
115 %result = shl i32 %X, 3
121 %0 = add i32 %X, %X ; yields i32:%0
122 %1 = add i32 %0, %0 ; yields i32:%1
123 %result = add i32 %1, %1
125 This last way of multiplying ``%X`` by 8 illustrates several important
126 lexical features of LLVM:
128 #. Comments are delimited with a '``;``' and go until the end of line.
129 #. Unnamed temporaries are created when the result of a computation is
130 not assigned to a named value.
131 #. Unnamed temporaries are numbered sequentially (using a per-function
132 incrementing counter, starting with 0). Note that basic blocks and unnamed
133 function parameters are included in this numbering. For example, if the
134 entry basic block is not given a label name and all function parameters are
135 named, then it will get number 0.
137 It also shows a convention that we follow in this document. When
138 demonstrating instructions, we will follow an instruction with a comment
139 that defines the type and name of value produced.
147 LLVM programs are composed of ``Module``'s, each of which is a
148 translation unit of the input programs. Each module consists of
149 functions, global variables, and symbol table entries. Modules may be
150 combined together with the LLVM linker, which merges function (and
151 global variable) definitions, resolves forward declarations, and merges
152 symbol table entries. Here is an example of the "hello world" module:
156 ; Declare the string constant as a global constant.
157 @.str = private unnamed_addr constant [13 x i8] c"hello world\0A\00"
159 ; External declaration of the puts function
160 declare i32 @puts(i8* nocapture) nounwind
162 ; Definition of main function
163 define i32 @main() { ; i32()*
164 ; Convert [13 x i8]* to i8 *...
165 %cast210 = getelementptr [13 x i8], [13 x i8]* @.str, i64 0, i64 0
167 ; Call puts function to write out the string to stdout.
168 call i32 @puts(i8* %cast210)
173 !0 = !{i32 42, null, !"string"}
176 This example is made up of a :ref:`global variable <globalvars>` named
177 "``.str``", an external declaration of the "``puts``" function, a
178 :ref:`function definition <functionstructure>` for "``main``" and
179 :ref:`named metadata <namedmetadatastructure>` "``foo``".
181 In general, a module is made up of a list of global values (where both
182 functions and global variables are global values). Global values are
183 represented by a pointer to a memory location (in this case, a pointer
184 to an array of char, and a pointer to a function), and have one of the
185 following :ref:`linkage types <linkage>`.
192 All Global Variables and Functions have one of the following types of
196 Global values with "``private``" linkage are only directly
197 accessible by objects in the current module. In particular, linking
198 code into a module with an private global value may cause the
199 private to be renamed as necessary to avoid collisions. Because the
200 symbol is private to the module, all references can be updated. This
201 doesn't show up in any symbol table in the object file.
203 Similar to private, but the value shows as a local symbol
204 (``STB_LOCAL`` in the case of ELF) in the object file. This
205 corresponds to the notion of the '``static``' keyword in C.
206 ``available_externally``
207 Globals with "``available_externally``" linkage are never emitted
208 into the object file corresponding to the LLVM module. They exist to
209 allow inlining and other optimizations to take place given knowledge
210 of the definition of the global, which is known to be somewhere
211 outside the module. Globals with ``available_externally`` linkage
212 are allowed to be discarded at will, and are otherwise the same as
213 ``linkonce_odr``. This linkage type is only allowed on definitions,
216 Globals with "``linkonce``" linkage are merged with other globals of
217 the same name when linkage occurs. This can be used to implement
218 some forms of inline functions, templates, or other code which must
219 be generated in each translation unit that uses it, but where the
220 body may be overridden with a more definitive definition later.
221 Unreferenced ``linkonce`` globals are allowed to be discarded. Note
222 that ``linkonce`` linkage does not actually allow the optimizer to
223 inline the body of this function into callers because it doesn't
224 know if this definition of the function is the definitive definition
225 within the program or whether it will be overridden by a stronger
226 definition. To enable inlining and other optimizations, use
227 "``linkonce_odr``" linkage.
229 "``weak``" linkage has the same merging semantics as ``linkonce``
230 linkage, except that unreferenced globals with ``weak`` linkage may
231 not be discarded. This is used for globals that are declared "weak"
234 "``common``" linkage is most similar to "``weak``" linkage, but they
235 are used for tentative definitions in C, such as "``int X;``" at
236 global scope. Symbols with "``common``" linkage are merged in the
237 same way as ``weak symbols``, and they may not be deleted if
238 unreferenced. ``common`` symbols may not have an explicit section,
239 must have a zero initializer, and may not be marked
240 ':ref:`constant <globalvars>`'. Functions and aliases may not have
243 .. _linkage_appending:
246 "``appending``" linkage may only be applied to global variables of
247 pointer to array type. When two global variables with appending
248 linkage are linked together, the two global arrays are appended
249 together. This is the LLVM, typesafe, equivalent of having the
250 system linker append together "sections" with identical names when
253 The semantics of this linkage follow the ELF object file model: the
254 symbol is weak until linked, if not linked, the symbol becomes null
255 instead of being an undefined reference.
256 ``linkonce_odr``, ``weak_odr``
257 Some languages allow differing globals to be merged, such as two
258 functions with different semantics. Other languages, such as
259 ``C++``, ensure that only equivalent globals are ever merged (the
260 "one definition rule" --- "ODR"). Such languages can use the
261 ``linkonce_odr`` and ``weak_odr`` linkage types to indicate that the
262 global will only be merged with equivalent globals. These linkage
263 types are otherwise the same as their non-``odr`` versions.
265 If none of the above identifiers are used, the global is externally
266 visible, meaning that it participates in linkage and can be used to
267 resolve external symbol references.
269 It is illegal for a function *declaration* to have any linkage type
270 other than ``external`` or ``extern_weak``.
277 LLVM :ref:`functions <functionstructure>`, :ref:`calls <i_call>` and
278 :ref:`invokes <i_invoke>` can all have an optional calling convention
279 specified for the call. The calling convention of any pair of dynamic
280 caller/callee must match, or the behavior of the program is undefined.
281 The following calling conventions are supported by LLVM, and more may be
284 "``ccc``" - The C calling convention
285 This calling convention (the default if no other calling convention
286 is specified) matches the target C calling conventions. This calling
287 convention supports varargs function calls and tolerates some
288 mismatch in the declared prototype and implemented declaration of
289 the function (as does normal C).
290 "``fastcc``" - The fast calling convention
291 This calling convention attempts to make calls as fast as possible
292 (e.g. by passing things in registers). This calling convention
293 allows the target to use whatever tricks it wants to produce fast
294 code for the target, without having to conform to an externally
295 specified ABI (Application Binary Interface). `Tail calls can only
296 be optimized when this, the GHC or the HiPE convention is
297 used. <CodeGenerator.html#id80>`_ This calling convention does not
298 support varargs and requires the prototype of all callees to exactly
299 match the prototype of the function definition.
300 "``coldcc``" - The cold calling convention
301 This calling convention attempts to make code in the caller as
302 efficient as possible under the assumption that the call is not
303 commonly executed. As such, these calls often preserve all registers
304 so that the call does not break any live ranges in the caller side.
305 This calling convention does not support varargs and requires the
306 prototype of all callees to exactly match the prototype of the
307 function definition. Furthermore the inliner doesn't consider such function
309 "``cc 10``" - GHC convention
310 This calling convention has been implemented specifically for use by
311 the `Glasgow Haskell Compiler (GHC) <http://www.haskell.org/ghc>`_.
312 It passes everything in registers, going to extremes to achieve this
313 by disabling callee save registers. This calling convention should
314 not be used lightly but only for specific situations such as an
315 alternative to the *register pinning* performance technique often
316 used when implementing functional programming languages. At the
317 moment only X86 supports this convention and it has the following
320 - On *X86-32* only supports up to 4 bit type parameters. No
321 floating point types are supported.
322 - On *X86-64* only supports up to 10 bit type parameters and 6
323 floating point parameters.
325 This calling convention supports `tail call
326 optimization <CodeGenerator.html#id80>`_ but requires both the
327 caller and callee are using it.
328 "``cc 11``" - The HiPE calling convention
329 This calling convention has been implemented specifically for use by
330 the `High-Performance Erlang
331 (HiPE) <http://www.it.uu.se/research/group/hipe/>`_ compiler, *the*
332 native code compiler of the `Ericsson's Open Source Erlang/OTP
333 system <http://www.erlang.org/download.shtml>`_. It uses more
334 registers for argument passing than the ordinary C calling
335 convention and defines no callee-saved registers. The calling
336 convention properly supports `tail call
337 optimization <CodeGenerator.html#id80>`_ but requires that both the
338 caller and the callee use it. It uses a *register pinning*
339 mechanism, similar to GHC's convention, for keeping frequently
340 accessed runtime components pinned to specific hardware registers.
341 At the moment only X86 supports this convention (both 32 and 64
343 "``webkit_jscc``" - WebKit's JavaScript calling convention
344 This calling convention has been implemented for `WebKit FTL JIT
345 <https://trac.webkit.org/wiki/FTLJIT>`_. It passes arguments on the
346 stack right to left (as cdecl does), and returns a value in the
347 platform's customary return register.
348 "``anyregcc``" - Dynamic calling convention for code patching
349 This is a special convention that supports patching an arbitrary code
350 sequence in place of a call site. This convention forces the call
351 arguments into registers but allows them to be dynamically
352 allocated. This can currently only be used with calls to
353 llvm.experimental.patchpoint because only this intrinsic records
354 the location of its arguments in a side table. See :doc:`StackMaps`.
355 "``preserve_mostcc``" - The `PreserveMost` calling convention
356 This calling convention attempts to make the code in the caller as
357 unintrusive as possible. This convention behaves identically to the `C`
358 calling convention on how arguments and return values are passed, but it
359 uses a different set of caller/callee-saved registers. This alleviates the
360 burden of saving and recovering a large register set before and after the
361 call in the caller. If the arguments are passed in callee-saved registers,
362 then they will be preserved by the callee across the call. This doesn't
363 apply for values returned in callee-saved registers.
365 - On X86-64 the callee preserves all general purpose registers, except for
366 R11. R11 can be used as a scratch register. Floating-point registers
367 (XMMs/YMMs) are not preserved and need to be saved by the caller.
369 The idea behind this convention is to support calls to runtime functions
370 that have a hot path and a cold path. The hot path is usually a small piece
371 of code that doesn't use many registers. The cold path might need to call out to
372 another function and therefore only needs to preserve the caller-saved
373 registers, which haven't already been saved by the caller. The
374 `PreserveMost` calling convention is very similar to the `cold` calling
375 convention in terms of caller/callee-saved registers, but they are used for
376 different types of function calls. `coldcc` is for function calls that are
377 rarely executed, whereas `preserve_mostcc` function calls are intended to be
378 on the hot path and definitely executed a lot. Furthermore `preserve_mostcc`
379 doesn't prevent the inliner from inlining the function call.
381 This calling convention will be used by a future version of the ObjectiveC
382 runtime and should therefore still be considered experimental at this time.
383 Although this convention was created to optimize certain runtime calls to
384 the ObjectiveC runtime, it is not limited to this runtime and might be used
385 by other runtimes in the future too. The current implementation only
386 supports X86-64, but the intention is to support more architectures in the
388 "``preserve_allcc``" - The `PreserveAll` calling convention
389 This calling convention attempts to make the code in the caller even less
390 intrusive than the `PreserveMost` calling convention. This calling
391 convention also behaves identical to the `C` calling convention on how
392 arguments and return values are passed, but it uses a different set of
393 caller/callee-saved registers. This removes the burden of saving and
394 recovering a large register set before and after the call in the caller. If
395 the arguments are passed in callee-saved registers, then they will be
396 preserved by the callee across the call. This doesn't apply for values
397 returned in callee-saved registers.
399 - On X86-64 the callee preserves all general purpose registers, except for
400 R11. R11 can be used as a scratch register. Furthermore it also preserves
401 all floating-point registers (XMMs/YMMs).
403 The idea behind this convention is to support calls to runtime functions
404 that don't need to call out to any other functions.
406 This calling convention, like the `PreserveMost` calling convention, will be
407 used by a future version of the ObjectiveC runtime and should be considered
408 experimental at this time.
409 "``cxx_fast_tlscc``" - The `CXX_FAST_TLS` calling convention for access functions
410 Clang generates an access function to access C++-style TLS. The access
411 function generally has an entry block, an exit block and an initialization
412 block that is run at the first time. The entry and exit blocks can access
413 a few TLS IR variables, each access will be lowered to a platform-specific
416 This calling convention aims to minimize overhead in the caller by
417 preserving as many registers as possible (all the registers that are
418 perserved on the fast path, composed of the entry and exit blocks).
420 This calling convention behaves identical to the `C` calling convention on
421 how arguments and return values are passed, but it uses a different set of
422 caller/callee-saved registers.
424 Given that each platform has its own lowering sequence, hence its own set
425 of preserved registers, we can't use the existing `PreserveMost`.
427 - On X86-64 the callee preserves all general purpose registers, except for
429 "``cc <n>``" - Numbered convention
430 Any calling convention may be specified by number, allowing
431 target-specific calling conventions to be used. Target specific
432 calling conventions start at 64.
434 More calling conventions can be added/defined on an as-needed basis, to
435 support Pascal conventions or any other well-known target-independent
438 .. _visibilitystyles:
443 All Global Variables and Functions have one of the following visibility
446 "``default``" - Default style
447 On targets that use the ELF object file format, default visibility
448 means that the declaration is visible to other modules and, in
449 shared libraries, means that the declared entity may be overridden.
450 On Darwin, default visibility means that the declaration is visible
451 to other modules. Default visibility corresponds to "external
452 linkage" in the language.
453 "``hidden``" - Hidden style
454 Two declarations of an object with hidden visibility refer to the
455 same object if they are in the same shared object. Usually, hidden
456 visibility indicates that the symbol will not be placed into the
457 dynamic symbol table, so no other module (executable or shared
458 library) can reference it directly.
459 "``protected``" - Protected style
460 On ELF, protected visibility indicates that the symbol will be
461 placed in the dynamic symbol table, but that references within the
462 defining module will bind to the local symbol. That is, the symbol
463 cannot be overridden by another module.
465 A symbol with ``internal`` or ``private`` linkage must have ``default``
473 All Global Variables, Functions and Aliases can have one of the following
477 "``dllimport``" causes the compiler to reference a function or variable via
478 a global pointer to a pointer that is set up by the DLL exporting the
479 symbol. On Microsoft Windows targets, the pointer name is formed by
480 combining ``__imp_`` and the function or variable name.
482 "``dllexport``" causes the compiler to provide a global pointer to a pointer
483 in a DLL, so that it can be referenced with the ``dllimport`` attribute. On
484 Microsoft Windows targets, the pointer name is formed by combining
485 ``__imp_`` and the function or variable name. Since this storage class
486 exists for defining a dll interface, the compiler, assembler and linker know
487 it is externally referenced and must refrain from deleting the symbol.
491 Thread Local Storage Models
492 ---------------------------
494 A variable may be defined as ``thread_local``, which means that it will
495 not be shared by threads (each thread will have a separated copy of the
496 variable). Not all targets support thread-local variables. Optionally, a
497 TLS model may be specified:
500 For variables that are only used within the current shared library.
502 For variables in modules that will not be loaded dynamically.
504 For variables defined in the executable and only used within it.
506 If no explicit model is given, the "general dynamic" model is used.
508 The models correspond to the ELF TLS models; see `ELF Handling For
509 Thread-Local Storage <http://people.redhat.com/drepper/tls.pdf>`_ for
510 more information on under which circumstances the different models may
511 be used. The target may choose a different TLS model if the specified
512 model is not supported, or if a better choice of model can be made.
514 A model can also be specified in an alias, but then it only governs how
515 the alias is accessed. It will not have any effect in the aliasee.
517 For platforms without linker support of ELF TLS model, the -femulated-tls
518 flag can be used to generate GCC compatible emulated TLS code.
525 LLVM IR allows you to specify both "identified" and "literal" :ref:`structure
526 types <t_struct>`. Literal types are uniqued structurally, but identified types
527 are never uniqued. An :ref:`opaque structural type <t_opaque>` can also be used
528 to forward declare a type that is not yet available.
530 An example of an identified structure specification is:
534 %mytype = type { %mytype*, i32 }
536 Prior to the LLVM 3.0 release, identified types were structurally uniqued. Only
537 literal types are uniqued in recent versions of LLVM.
544 Global variables define regions of memory allocated at compilation time
547 Global variable definitions must be initialized.
549 Global variables in other translation units can also be declared, in which
550 case they don't have an initializer.
552 Either global variable definitions or declarations may have an explicit section
553 to be placed in and may have an optional explicit alignment specified.
555 A variable may be defined as a global ``constant``, which indicates that
556 the contents of the variable will **never** be modified (enabling better
557 optimization, allowing the global data to be placed in the read-only
558 section of an executable, etc). Note that variables that need runtime
559 initialization cannot be marked ``constant`` as there is a store to the
562 LLVM explicitly allows *declarations* of global variables to be marked
563 constant, even if the final definition of the global is not. This
564 capability can be used to enable slightly better optimization of the
565 program, but requires the language definition to guarantee that
566 optimizations based on the 'constantness' are valid for the translation
567 units that do not include the definition.
569 As SSA values, global variables define pointer values that are in scope
570 (i.e. they dominate) all basic blocks in the program. Global variables
571 always define a pointer to their "content" type because they describe a
572 region of memory, and all memory objects in LLVM are accessed through
575 Global variables can be marked with ``unnamed_addr`` which indicates
576 that the address is not significant, only the content. Constants marked
577 like this can be merged with other constants if they have the same
578 initializer. Note that a constant with significant address *can* be
579 merged with a ``unnamed_addr`` constant, the result being a constant
580 whose address is significant.
582 A global variable may be declared to reside in a target-specific
583 numbered address space. For targets that support them, address spaces
584 may affect how optimizations are performed and/or what target
585 instructions are used to access the variable. The default address space
586 is zero. The address space qualifier must precede any other attributes.
588 LLVM allows an explicit section to be specified for globals. If the
589 target supports it, it will emit globals to the section specified.
590 Additionally, the global can placed in a comdat if the target has the necessary
593 By default, global initializers are optimized by assuming that global
594 variables defined within the module are not modified from their
595 initial values before the start of the global initializer. This is
596 true even for variables potentially accessible from outside the
597 module, including those with external linkage or appearing in
598 ``@llvm.used`` or dllexported variables. This assumption may be suppressed
599 by marking the variable with ``externally_initialized``.
601 An explicit alignment may be specified for a global, which must be a
602 power of 2. If not present, or if the alignment is set to zero, the
603 alignment of the global is set by the target to whatever it feels
604 convenient. If an explicit alignment is specified, the global is forced
605 to have exactly that alignment. Targets and optimizers are not allowed
606 to over-align the global if the global has an assigned section. In this
607 case, the extra alignment could be observable: for example, code could
608 assume that the globals are densely packed in their section and try to
609 iterate over them as an array, alignment padding would break this
610 iteration. The maximum alignment is ``1 << 29``.
612 Globals can also have a :ref:`DLL storage class <dllstorageclass>`.
614 Variables and aliases can have a
615 :ref:`Thread Local Storage Model <tls_model>`.
619 [@<GlobalVarName> =] [Linkage] [Visibility] [DLLStorageClass] [ThreadLocal]
620 [unnamed_addr] [AddrSpace] [ExternallyInitialized]
621 <global | constant> <Type> [<InitializerConstant>]
622 [, section "name"] [, comdat [($name)]]
623 [, align <Alignment>]
625 For example, the following defines a global in a numbered address space
626 with an initializer, section, and alignment:
630 @G = addrspace(5) constant float 1.0, section "foo", align 4
632 The following example just declares a global variable
636 @G = external global i32
638 The following example defines a thread-local global with the
639 ``initialexec`` TLS model:
643 @G = thread_local(initialexec) global i32 0, align 4
645 .. _functionstructure:
650 LLVM function definitions consist of the "``define``" keyword, an
651 optional :ref:`linkage type <linkage>`, an optional :ref:`visibility
652 style <visibility>`, an optional :ref:`DLL storage class <dllstorageclass>`,
653 an optional :ref:`calling convention <callingconv>`,
654 an optional ``unnamed_addr`` attribute, a return type, an optional
655 :ref:`parameter attribute <paramattrs>` for the return type, a function
656 name, a (possibly empty) argument list (each with optional :ref:`parameter
657 attributes <paramattrs>`), optional :ref:`function attributes <fnattrs>`,
658 an optional section, an optional alignment,
659 an optional :ref:`comdat <langref_comdats>`,
660 an optional :ref:`garbage collector name <gc>`, an optional :ref:`prefix <prefixdata>`,
661 an optional :ref:`prologue <prologuedata>`,
662 an optional :ref:`personality <personalityfn>`,
663 an optional list of attached :ref:`metadata <metadata>`,
664 an opening curly brace, a list of basic blocks, and a closing curly brace.
666 LLVM function declarations consist of the "``declare``" keyword, an
667 optional :ref:`linkage type <linkage>`, an optional :ref:`visibility
668 style <visibility>`, an optional :ref:`DLL storage class <dllstorageclass>`,
669 an optional :ref:`calling convention <callingconv>`,
670 an optional ``unnamed_addr`` attribute, a return type, an optional
671 :ref:`parameter attribute <paramattrs>` for the return type, a function
672 name, a possibly empty list of arguments, an optional alignment, an optional
673 :ref:`garbage collector name <gc>`, an optional :ref:`prefix <prefixdata>`,
674 and an optional :ref:`prologue <prologuedata>`.
676 A function definition contains a list of basic blocks, forming the CFG (Control
677 Flow Graph) for the function. Each basic block may optionally start with a label
678 (giving the basic block a symbol table entry), contains a list of instructions,
679 and ends with a :ref:`terminator <terminators>` instruction (such as a branch or
680 function return). If an explicit label is not provided, a block is assigned an
681 implicit numbered label, using the next value from the same counter as used for
682 unnamed temporaries (:ref:`see above<identifiers>`). For example, if a function
683 entry block does not have an explicit label, it will be assigned label "%0",
684 then the first unnamed temporary in that block will be "%1", etc.
686 The first basic block in a function is special in two ways: it is
687 immediately executed on entrance to the function, and it is not allowed
688 to have predecessor basic blocks (i.e. there can not be any branches to
689 the entry block of a function). Because the block can have no
690 predecessors, it also cannot have any :ref:`PHI nodes <i_phi>`.
692 LLVM allows an explicit section to be specified for functions. If the
693 target supports it, it will emit functions to the section specified.
694 Additionally, the function can be placed in a COMDAT.
696 An explicit alignment may be specified for a function. If not present,
697 or if the alignment is set to zero, the alignment of the function is set
698 by the target to whatever it feels convenient. If an explicit alignment
699 is specified, the function is forced to have at least that much
700 alignment. All alignments must be a power of 2.
702 If the ``unnamed_addr`` attribute is given, the address is known to not
703 be significant and two identical functions can be merged.
707 define [linkage] [visibility] [DLLStorageClass]
709 <ResultType> @<FunctionName> ([argument list])
710 [unnamed_addr] [fn Attrs] [section "name"] [comdat [($name)]]
711 [align N] [gc] [prefix Constant] [prologue Constant]
712 [personality Constant] (!name !N)* { ... }
714 The argument list is a comma separated sequence of arguments where each
715 argument is of the following form:
719 <type> [parameter Attrs] [name]
727 Aliases, unlike function or variables, don't create any new data. They
728 are just a new symbol and metadata for an existing position.
730 Aliases have a name and an aliasee that is either a global value or a
733 Aliases may have an optional :ref:`linkage type <linkage>`, an optional
734 :ref:`visibility style <visibility>`, an optional :ref:`DLL storage class
735 <dllstorageclass>` and an optional :ref:`tls model <tls_model>`.
739 @<Name> = [Linkage] [Visibility] [DLLStorageClass] [ThreadLocal] [unnamed_addr] alias <AliaseeTy>, <AliaseeTy>* @<Aliasee>
741 The linkage must be one of ``private``, ``internal``, ``linkonce``, ``weak``,
742 ``linkonce_odr``, ``weak_odr``, ``external``. Note that some system linkers
743 might not correctly handle dropping a weak symbol that is aliased.
745 Aliases that are not ``unnamed_addr`` are guaranteed to have the same address as
746 the aliasee expression. ``unnamed_addr`` ones are only guaranteed to point
749 Since aliases are only a second name, some restrictions apply, of which
750 some can only be checked when producing an object file:
752 * The expression defining the aliasee must be computable at assembly
753 time. Since it is just a name, no relocations can be used.
755 * No alias in the expression can be weak as the possibility of the
756 intermediate alias being overridden cannot be represented in an
759 * No global value in the expression can be a declaration, since that
760 would require a relocation, which is not possible.
767 Comdat IR provides access to COFF and ELF object file COMDAT functionality.
769 Comdats have a name which represents the COMDAT key. All global objects that
770 specify this key will only end up in the final object file if the linker chooses
771 that key over some other key. Aliases are placed in the same COMDAT that their
772 aliasee computes to, if any.
774 Comdats have a selection kind to provide input on how the linker should
775 choose between keys in two different object files.
779 $<Name> = comdat SelectionKind
781 The selection kind must be one of the following:
784 The linker may choose any COMDAT key, the choice is arbitrary.
786 The linker may choose any COMDAT key but the sections must contain the
789 The linker will choose the section containing the largest COMDAT key.
791 The linker requires that only section with this COMDAT key exist.
793 The linker may choose any COMDAT key but the sections must contain the
796 Note that the Mach-O platform doesn't support COMDATs and ELF only supports
797 ``any`` as a selection kind.
799 Here is an example of a COMDAT group where a function will only be selected if
800 the COMDAT key's section is the largest:
804 $foo = comdat largest
805 @foo = global i32 2, comdat($foo)
807 define void @bar() comdat($foo) {
811 As a syntactic sugar the ``$name`` can be omitted if the name is the same as
817 @foo = global i32 2, comdat
820 In a COFF object file, this will create a COMDAT section with selection kind
821 ``IMAGE_COMDAT_SELECT_LARGEST`` containing the contents of the ``@foo`` symbol
822 and another COMDAT section with selection kind
823 ``IMAGE_COMDAT_SELECT_ASSOCIATIVE`` which is associated with the first COMDAT
824 section and contains the contents of the ``@bar`` symbol.
826 There are some restrictions on the properties of the global object.
827 It, or an alias to it, must have the same name as the COMDAT group when
829 The contents and size of this object may be used during link-time to determine
830 which COMDAT groups get selected depending on the selection kind.
831 Because the name of the object must match the name of the COMDAT group, the
832 linkage of the global object must not be local; local symbols can get renamed
833 if a collision occurs in the symbol table.
835 The combined use of COMDATS and section attributes may yield surprising results.
842 @g1 = global i32 42, section "sec", comdat($foo)
843 @g2 = global i32 42, section "sec", comdat($bar)
845 From the object file perspective, this requires the creation of two sections
846 with the same name. This is necessary because both globals belong to different
847 COMDAT groups and COMDATs, at the object file level, are represented by
850 Note that certain IR constructs like global variables and functions may
851 create COMDATs in the object file in addition to any which are specified using
852 COMDAT IR. This arises when the code generator is configured to emit globals
853 in individual sections (e.g. when `-data-sections` or `-function-sections`
854 is supplied to `llc`).
856 .. _namedmetadatastructure:
861 Named metadata is a collection of metadata. :ref:`Metadata
862 nodes <metadata>` (but not metadata strings) are the only valid
863 operands for a named metadata.
865 #. Named metadata are represented as a string of characters with the
866 metadata prefix. The rules for metadata names are the same as for
867 identifiers, but quoted names are not allowed. ``"\xx"`` type escapes
868 are still valid, which allows any character to be part of a name.
872 ; Some unnamed metadata nodes, which are referenced by the named metadata.
877 !name = !{!0, !1, !2}
884 The return type and each parameter of a function type may have a set of
885 *parameter attributes* associated with them. Parameter attributes are
886 used to communicate additional information about the result or
887 parameters of a function. Parameter attributes are considered to be part
888 of the function, not of the function type, so functions with different
889 parameter attributes can have the same function type.
891 Parameter attributes are simple keywords that follow the type specified.
892 If multiple parameter attributes are needed, they are space separated.
897 declare i32 @printf(i8* noalias nocapture, ...)
898 declare i32 @atoi(i8 zeroext)
899 declare signext i8 @returns_signed_char()
901 Note that any attributes for the function result (``nounwind``,
902 ``readonly``) come immediately after the argument list.
904 Currently, only the following parameter attributes are defined:
907 This indicates to the code generator that the parameter or return
908 value should be zero-extended to the extent required by the target's
909 ABI (which is usually 32-bits, but is 8-bits for a i1 on x86-64) by
910 the caller (for a parameter) or the callee (for a return value).
912 This indicates to the code generator that the parameter or return
913 value should be sign-extended to the extent required by the target's
914 ABI (which is usually 32-bits) by the caller (for a parameter) or
915 the callee (for a return value).
917 This indicates that this parameter or return value should be treated
918 in a special target-dependent fashion while emitting code for
919 a function call or return (usually, by putting it in a register as
920 opposed to memory, though some targets use it to distinguish between
921 two different kinds of registers). Use of this attribute is
924 This indicates that the pointer parameter should really be passed by
925 value to the function. The attribute implies that a hidden copy of
926 the pointee is made between the caller and the callee, so the callee
927 is unable to modify the value in the caller. This attribute is only
928 valid on LLVM pointer arguments. It is generally used to pass
929 structs and arrays by value, but is also valid on pointers to
930 scalars. The copy is considered to belong to the caller not the
931 callee (for example, ``readonly`` functions should not write to
932 ``byval`` parameters). This is not a valid attribute for return
935 The byval attribute also supports specifying an alignment with the
936 align attribute. It indicates the alignment of the stack slot to
937 form and the known alignment of the pointer specified to the call
938 site. If the alignment is not specified, then the code generator
939 makes a target-specific assumption.
945 The ``inalloca`` argument attribute allows the caller to take the
946 address of outgoing stack arguments. An ``inalloca`` argument must
947 be a pointer to stack memory produced by an ``alloca`` instruction.
948 The alloca, or argument allocation, must also be tagged with the
949 inalloca keyword. Only the last argument may have the ``inalloca``
950 attribute, and that argument is guaranteed to be passed in memory.
952 An argument allocation may be used by a call at most once because
953 the call may deallocate it. The ``inalloca`` attribute cannot be
954 used in conjunction with other attributes that affect argument
955 storage, like ``inreg``, ``nest``, ``sret``, or ``byval``. The
956 ``inalloca`` attribute also disables LLVM's implicit lowering of
957 large aggregate return values, which means that frontend authors
958 must lower them with ``sret`` pointers.
960 When the call site is reached, the argument allocation must have
961 been the most recent stack allocation that is still live, or the
962 results are undefined. It is possible to allocate additional stack
963 space after an argument allocation and before its call site, but it
964 must be cleared off with :ref:`llvm.stackrestore
967 See :doc:`InAlloca` for more information on how to use this
971 This indicates that the pointer parameter specifies the address of a
972 structure that is the return value of the function in the source
973 program. This pointer must be guaranteed by the caller to be valid:
974 loads and stores to the structure may be assumed by the callee
975 not to trap and to be properly aligned. This may only be applied to
976 the first parameter. This is not a valid attribute for return
980 This indicates that the pointer value may be assumed by the optimizer to
981 have the specified alignment.
983 Note that this attribute has additional semantics when combined with the
989 This indicates that objects accessed via pointer values
990 :ref:`based <pointeraliasing>` on the argument or return value are not also
991 accessed, during the execution of the function, via pointer values not
992 *based* on the argument or return value. The attribute on a return value
993 also has additional semantics described below. The caller shares the
994 responsibility with the callee for ensuring that these requirements are met.
995 For further details, please see the discussion of the NoAlias response in
996 :ref:`alias analysis <Must, May, or No>`.
998 Note that this definition of ``noalias`` is intentionally similar
999 to the definition of ``restrict`` in C99 for function arguments.
1001 For function return values, C99's ``restrict`` is not meaningful,
1002 while LLVM's ``noalias`` is. Furthermore, the semantics of the ``noalias``
1003 attribute on return values are stronger than the semantics of the attribute
1004 when used on function arguments. On function return values, the ``noalias``
1005 attribute indicates that the function acts like a system memory allocation
1006 function, returning a pointer to allocated storage disjoint from the
1007 storage for any other object accessible to the caller.
1010 This indicates that the callee does not make any copies of the
1011 pointer that outlive the callee itself. This is not a valid
1012 attribute for return values.
1017 This indicates that the pointer parameter can be excised using the
1018 :ref:`trampoline intrinsics <int_trampoline>`. This is not a valid
1019 attribute for return values and can only be applied to one parameter.
1022 This indicates that the function always returns the argument as its return
1023 value. This is an optimization hint to the code generator when generating
1024 the caller, allowing tail call optimization and omission of register saves
1025 and restores in some cases; it is not checked or enforced when generating
1026 the callee. The parameter and the function return type must be valid
1027 operands for the :ref:`bitcast instruction <i_bitcast>`. This is not a
1028 valid attribute for return values and can only be applied to one parameter.
1031 This indicates that the parameter or return pointer is not null. This
1032 attribute may only be applied to pointer typed parameters. This is not
1033 checked or enforced by LLVM, the caller must ensure that the pointer
1034 passed in is non-null, or the callee must ensure that the returned pointer
1037 ``dereferenceable(<n>)``
1038 This indicates that the parameter or return pointer is dereferenceable. This
1039 attribute may only be applied to pointer typed parameters. A pointer that
1040 is dereferenceable can be loaded from speculatively without a risk of
1041 trapping. The number of bytes known to be dereferenceable must be provided
1042 in parentheses. It is legal for the number of bytes to be less than the
1043 size of the pointee type. The ``nonnull`` attribute does not imply
1044 dereferenceability (consider a pointer to one element past the end of an
1045 array), however ``dereferenceable(<n>)`` does imply ``nonnull`` in
1046 ``addrspace(0)`` (which is the default address space).
1048 ``dereferenceable_or_null(<n>)``
1049 This indicates that the parameter or return value isn't both
1050 non-null and non-dereferenceable (up to ``<n>`` bytes) at the same
1051 time. All non-null pointers tagged with
1052 ``dereferenceable_or_null(<n>)`` are ``dereferenceable(<n>)``.
1053 For address space 0 ``dereferenceable_or_null(<n>)`` implies that
1054 a pointer is exactly one of ``dereferenceable(<n>)`` or ``null``,
1055 and in other address spaces ``dereferenceable_or_null(<n>)``
1056 implies that a pointer is at least one of ``dereferenceable(<n>)``
1057 or ``null`` (i.e. it may be both ``null`` and
1058 ``dereferenceable(<n>)``). This attribute may only be applied to
1059 pointer typed parameters.
1063 Garbage Collector Strategy Names
1064 --------------------------------
1066 Each function may specify a garbage collector strategy name, which is simply a
1069 .. code-block:: llvm
1071 define void @f() gc "name" { ... }
1073 The supported values of *name* includes those :ref:`built in to LLVM
1074 <builtin-gc-strategies>` and any provided by loaded plugins. Specifying a GC
1075 strategy will cause the compiler to alter its output in order to support the
1076 named garbage collection algorithm. Note that LLVM itself does not contain a
1077 garbage collector, this functionality is restricted to generating machine code
1078 which can interoperate with a collector provided externally.
1085 Prefix data is data associated with a function which the code
1086 generator will emit immediately before the function's entrypoint.
1087 The purpose of this feature is to allow frontends to associate
1088 language-specific runtime metadata with specific functions and make it
1089 available through the function pointer while still allowing the
1090 function pointer to be called.
1092 To access the data for a given function, a program may bitcast the
1093 function pointer to a pointer to the constant's type and dereference
1094 index -1. This implies that the IR symbol points just past the end of
1095 the prefix data. For instance, take the example of a function annotated
1096 with a single ``i32``,
1098 .. code-block:: llvm
1100 define void @f() prefix i32 123 { ... }
1102 The prefix data can be referenced as,
1104 .. code-block:: llvm
1106 %0 = bitcast void* () @f to i32*
1107 %a = getelementptr inbounds i32, i32* %0, i32 -1
1108 %b = load i32, i32* %a
1110 Prefix data is laid out as if it were an initializer for a global variable
1111 of the prefix data's type. The function will be placed such that the
1112 beginning of the prefix data is aligned. This means that if the size
1113 of the prefix data is not a multiple of the alignment size, the
1114 function's entrypoint will not be aligned. If alignment of the
1115 function's entrypoint is desired, padding must be added to the prefix
1118 A function may have prefix data but no body. This has similar semantics
1119 to the ``available_externally`` linkage in that the data may be used by the
1120 optimizers but will not be emitted in the object file.
1127 The ``prologue`` attribute allows arbitrary code (encoded as bytes) to
1128 be inserted prior to the function body. This can be used for enabling
1129 function hot-patching and instrumentation.
1131 To maintain the semantics of ordinary function calls, the prologue data must
1132 have a particular format. Specifically, it must begin with a sequence of
1133 bytes which decode to a sequence of machine instructions, valid for the
1134 module's target, which transfer control to the point immediately succeeding
1135 the prologue data, without performing any other visible action. This allows
1136 the inliner and other passes to reason about the semantics of the function
1137 definition without needing to reason about the prologue data. Obviously this
1138 makes the format of the prologue data highly target dependent.
1140 A trivial example of valid prologue data for the x86 architecture is ``i8 144``,
1141 which encodes the ``nop`` instruction:
1143 .. code-block:: llvm
1145 define void @f() prologue i8 144 { ... }
1147 Generally prologue data can be formed by encoding a relative branch instruction
1148 which skips the metadata, as in this example of valid prologue data for the
1149 x86_64 architecture, where the first two bytes encode ``jmp .+10``:
1151 .. code-block:: llvm
1153 %0 = type <{ i8, i8, i8* }>
1155 define void @f() prologue %0 <{ i8 235, i8 8, i8* @md}> { ... }
1157 A function may have prologue data but no body. This has similar semantics
1158 to the ``available_externally`` linkage in that the data may be used by the
1159 optimizers but will not be emitted in the object file.
1163 Personality Function
1164 --------------------
1166 The ``personality`` attribute permits functions to specify what function
1167 to use for exception handling.
1174 Attribute groups are groups of attributes that are referenced by objects within
1175 the IR. They are important for keeping ``.ll`` files readable, because a lot of
1176 functions will use the same set of attributes. In the degenerative case of a
1177 ``.ll`` file that corresponds to a single ``.c`` file, the single attribute
1178 group will capture the important command line flags used to build that file.
1180 An attribute group is a module-level object. To use an attribute group, an
1181 object references the attribute group's ID (e.g. ``#37``). An object may refer
1182 to more than one attribute group. In that situation, the attributes from the
1183 different groups are merged.
1185 Here is an example of attribute groups for a function that should always be
1186 inlined, has a stack alignment of 4, and which shouldn't use SSE instructions:
1188 .. code-block:: llvm
1190 ; Target-independent attributes:
1191 attributes #0 = { alwaysinline alignstack=4 }
1193 ; Target-dependent attributes:
1194 attributes #1 = { "no-sse" }
1196 ; Function @f has attributes: alwaysinline, alignstack=4, and "no-sse".
1197 define void @f() #0 #1 { ... }
1204 Function attributes are set to communicate additional information about
1205 a function. Function attributes are considered to be part of the
1206 function, not of the function type, so functions with different function
1207 attributes can have the same function type.
1209 Function attributes are simple keywords that follow the type specified.
1210 If multiple attributes are needed, they are space separated. For
1213 .. code-block:: llvm
1215 define void @f() noinline { ... }
1216 define void @f() alwaysinline { ... }
1217 define void @f() alwaysinline optsize { ... }
1218 define void @f() optsize { ... }
1221 This attribute indicates that, when emitting the prologue and
1222 epilogue, the backend should forcibly align the stack pointer.
1223 Specify the desired alignment, which must be a power of two, in
1226 This attribute indicates that the inliner should attempt to inline
1227 this function into callers whenever possible, ignoring any active
1228 inlining size threshold for this caller.
1230 This indicates that the callee function at a call site should be
1231 recognized as a built-in function, even though the function's declaration
1232 uses the ``nobuiltin`` attribute. This is only valid at call sites for
1233 direct calls to functions that are declared with the ``nobuiltin``
1236 This attribute indicates that this function is rarely called. When
1237 computing edge weights, basic blocks post-dominated by a cold
1238 function call are also considered to be cold; and, thus, given low
1241 This attribute indicates that the callee is dependent on a convergent
1242 thread execution pattern under certain parallel execution models.
1243 Transformations that are execution model agnostic may not make the execution
1244 of a convergent operation control dependent on any additional values.
1246 This attribute indicates that the source code contained a hint that
1247 inlining this function is desirable (such as the "inline" keyword in
1248 C/C++). It is just a hint; it imposes no requirements on the
1251 This attribute indicates that the function should be added to a
1252 jump-instruction table at code-generation time, and that all address-taken
1253 references to this function should be replaced with a reference to the
1254 appropriate jump-instruction-table function pointer. Note that this creates
1255 a new pointer for the original function, which means that code that depends
1256 on function-pointer identity can break. So, any function annotated with
1257 ``jumptable`` must also be ``unnamed_addr``.
1259 This attribute suggests that optimization passes and code generator
1260 passes make choices that keep the code size of this function as small
1261 as possible and perform optimizations that may sacrifice runtime
1262 performance in order to minimize the size of the generated code.
1264 This attribute disables prologue / epilogue emission for the
1265 function. This can have very system-specific consequences.
1267 This indicates that the callee function at a call site is not recognized as
1268 a built-in function. LLVM will retain the original call and not replace it
1269 with equivalent code based on the semantics of the built-in function, unless
1270 the call site uses the ``builtin`` attribute. This is valid at call sites
1271 and on function declarations and definitions.
1273 This attribute indicates that calls to the function cannot be
1274 duplicated. A call to a ``noduplicate`` function may be moved
1275 within its parent function, but may not be duplicated within
1276 its parent function.
1278 A function containing a ``noduplicate`` call may still
1279 be an inlining candidate, provided that the call is not
1280 duplicated by inlining. That implies that the function has
1281 internal linkage and only has one call site, so the original
1282 call is dead after inlining.
1284 This attributes disables implicit floating point instructions.
1286 This attribute indicates that the inliner should never inline this
1287 function in any situation. This attribute may not be used together
1288 with the ``alwaysinline`` attribute.
1290 This attribute suppresses lazy symbol binding for the function. This
1291 may make calls to the function faster, at the cost of extra program
1292 startup time if the function is not called during program startup.
1294 This attribute indicates that the code generator should not use a
1295 red zone, even if the target-specific ABI normally permits it.
1297 This function attribute indicates that the function never returns
1298 normally. This produces undefined behavior at runtime if the
1299 function ever does dynamically return.
1301 This function attribute indicates that the function does not call itself
1302 either directly or indirectly down any possible call path. This produces
1303 undefined behavior at runtime if the function ever does recurse.
1305 This function attribute indicates that the function never raises an
1306 exception. If the function does raise an exception, its runtime
1307 behavior is undefined. However, functions marked nounwind may still
1308 trap or generate asynchronous exceptions. Exception handling schemes
1309 that are recognized by LLVM to handle asynchronous exceptions, such
1310 as SEH, will still provide their implementation defined semantics.
1312 This function attribute indicates that most optimization passes will skip
1313 this function, with the exception of interprocedural optimization passes.
1314 Code generation defaults to the "fast" instruction selector.
1315 This attribute cannot be used together with the ``alwaysinline``
1316 attribute; this attribute is also incompatible
1317 with the ``minsize`` attribute and the ``optsize`` attribute.
1319 This attribute requires the ``noinline`` attribute to be specified on
1320 the function as well, so the function is never inlined into any caller.
1321 Only functions with the ``alwaysinline`` attribute are valid
1322 candidates for inlining into the body of this function.
1324 This attribute suggests that optimization passes and code generator
1325 passes make choices that keep the code size of this function low,
1326 and otherwise do optimizations specifically to reduce code size as
1327 long as they do not significantly impact runtime performance.
1329 On a function, this attribute indicates that the function computes its
1330 result (or decides to unwind an exception) based strictly on its arguments,
1331 without dereferencing any pointer arguments or otherwise accessing
1332 any mutable state (e.g. memory, control registers, etc) visible to
1333 caller functions. It does not write through any pointer arguments
1334 (including ``byval`` arguments) and never changes any state visible
1335 to callers. This means that it cannot unwind exceptions by calling
1336 the ``C++`` exception throwing methods.
1338 On an argument, this attribute indicates that the function does not
1339 dereference that pointer argument, even though it may read or write the
1340 memory that the pointer points to if accessed through other pointers.
1342 On a function, this attribute indicates that the function does not write
1343 through any pointer arguments (including ``byval`` arguments) or otherwise
1344 modify any state (e.g. memory, control registers, etc) visible to
1345 caller functions. It may dereference pointer arguments and read
1346 state that may be set in the caller. A readonly function always
1347 returns the same value (or unwinds an exception identically) when
1348 called with the same set of arguments and global state. It cannot
1349 unwind an exception by calling the ``C++`` exception throwing
1352 On an argument, this attribute indicates that the function does not write
1353 through this pointer argument, even though it may write to the memory that
1354 the pointer points to.
1356 This attribute indicates that the only memory accesses inside function are
1357 loads and stores from objects pointed to by its pointer-typed arguments,
1358 with arbitrary offsets. Or in other words, all memory operations in the
1359 function can refer to memory only using pointers based on its function
1361 Note that ``argmemonly`` can be used together with ``readonly`` attribute
1362 in order to specify that function reads only from its arguments.
1364 This attribute indicates that this function can return twice. The C
1365 ``setjmp`` is an example of such a function. The compiler disables
1366 some optimizations (like tail calls) in the caller of these
1369 This attribute indicates that
1370 `SafeStack <http://clang.llvm.org/docs/SafeStack.html>`_
1371 protection is enabled for this function.
1373 If a function that has a ``safestack`` attribute is inlined into a
1374 function that doesn't have a ``safestack`` attribute or which has an
1375 ``ssp``, ``sspstrong`` or ``sspreq`` attribute, then the resulting
1376 function will have a ``safestack`` attribute.
1377 ``sanitize_address``
1378 This attribute indicates that AddressSanitizer checks
1379 (dynamic address safety analysis) are enabled for this function.
1381 This attribute indicates that MemorySanitizer checks (dynamic detection
1382 of accesses to uninitialized memory) are enabled for this function.
1384 This attribute indicates that ThreadSanitizer checks
1385 (dynamic thread safety analysis) are enabled for this function.
1387 This attribute indicates that the function should emit a stack
1388 smashing protector. It is in the form of a "canary" --- a random value
1389 placed on the stack before the local variables that's checked upon
1390 return from the function to see if it has been overwritten. A
1391 heuristic is used to determine if a function needs stack protectors
1392 or not. The heuristic used will enable protectors for functions with:
1394 - Character arrays larger than ``ssp-buffer-size`` (default 8).
1395 - Aggregates containing character arrays larger than ``ssp-buffer-size``.
1396 - Calls to alloca() with variable sizes or constant sizes greater than
1397 ``ssp-buffer-size``.
1399 Variables that are identified as requiring a protector will be arranged
1400 on the stack such that they are adjacent to the stack protector guard.
1402 If a function that has an ``ssp`` attribute is inlined into a
1403 function that doesn't have an ``ssp`` attribute, then the resulting
1404 function will have an ``ssp`` attribute.
1406 This attribute indicates that the function should *always* emit a
1407 stack smashing protector. This overrides the ``ssp`` function
1410 Variables that are identified as requiring a protector will be arranged
1411 on the stack such that they are adjacent to the stack protector guard.
1412 The specific layout rules are:
1414 #. Large arrays and structures containing large arrays
1415 (``>= ssp-buffer-size``) are closest to the stack protector.
1416 #. Small arrays and structures containing small arrays
1417 (``< ssp-buffer-size``) are 2nd closest to the protector.
1418 #. Variables that have had their address taken are 3rd closest to the
1421 If a function that has an ``sspreq`` attribute is inlined into a
1422 function that doesn't have an ``sspreq`` attribute or which has an
1423 ``ssp`` or ``sspstrong`` attribute, then the resulting function will have
1424 an ``sspreq`` attribute.
1426 This attribute indicates that the function should emit a stack smashing
1427 protector. This attribute causes a strong heuristic to be used when
1428 determining if a function needs stack protectors. The strong heuristic
1429 will enable protectors for functions with:
1431 - Arrays of any size and type
1432 - Aggregates containing an array of any size and type.
1433 - Calls to alloca().
1434 - Local variables that have had their address taken.
1436 Variables that are identified as requiring a protector will be arranged
1437 on the stack such that they are adjacent to the stack protector guard.
1438 The specific layout rules are:
1440 #. Large arrays and structures containing large arrays
1441 (``>= ssp-buffer-size``) are closest to the stack protector.
1442 #. Small arrays and structures containing small arrays
1443 (``< ssp-buffer-size``) are 2nd closest to the protector.
1444 #. Variables that have had their address taken are 3rd closest to the
1447 This overrides the ``ssp`` function attribute.
1449 If a function that has an ``sspstrong`` attribute is inlined into a
1450 function that doesn't have an ``sspstrong`` attribute, then the
1451 resulting function will have an ``sspstrong`` attribute.
1453 This attribute indicates that the function will delegate to some other
1454 function with a tail call. The prototype of a thunk should not be used for
1455 optimization purposes. The caller is expected to cast the thunk prototype to
1456 match the thunk target prototype.
1458 This attribute indicates that the ABI being targeted requires that
1459 an unwind table entry be produced for this function even if we can
1460 show that no exceptions passes by it. This is normally the case for
1461 the ELF x86-64 abi, but it can be disabled for some compilation
1470 Note: operand bundles are a work in progress, and they should be
1471 considered experimental at this time.
1473 Operand bundles are tagged sets of SSA values that can be associated
1474 with certain LLVM instructions (currently only ``call`` s and
1475 ``invoke`` s). In a way they are like metadata, but dropping them is
1476 incorrect and will change program semantics.
1480 operand bundle set ::= '[' operand bundle (, operand bundle )* ']'
1481 operand bundle ::= tag '(' [ bundle operand ] (, bundle operand )* ')'
1482 bundle operand ::= SSA value
1483 tag ::= string constant
1485 Operand bundles are **not** part of a function's signature, and a
1486 given function may be called from multiple places with different kinds
1487 of operand bundles. This reflects the fact that the operand bundles
1488 are conceptually a part of the ``call`` (or ``invoke``), not the
1489 callee being dispatched to.
1491 Operand bundles are a generic mechanism intended to support
1492 runtime-introspection-like functionality for managed languages. While
1493 the exact semantics of an operand bundle depend on the bundle tag,
1494 there are certain limitations to how much the presence of an operand
1495 bundle can influence the semantics of a program. These restrictions
1496 are described as the semantics of an "unknown" operand bundle. As
1497 long as the behavior of an operand bundle is describable within these
1498 restrictions, LLVM does not need to have special knowledge of the
1499 operand bundle to not miscompile programs containing it.
1501 - The bundle operands for an unknown operand bundle escape in unknown
1502 ways before control is transferred to the callee or invokee.
1503 - Calls and invokes with operand bundles have unknown read / write
1504 effect on the heap on entry and exit (even if the call target is
1505 ``readnone`` or ``readonly``), unless they're overriden with
1506 callsite specific attributes.
1507 - An operand bundle at a call site cannot change the implementation
1508 of the called function. Inter-procedural optimizations work as
1509 usual as long as they take into account the first two properties.
1511 More specific types of operand bundles are described below.
1513 Deoptimization Operand Bundles
1514 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
1516 Deoptimization operand bundles are characterized by the ``"deopt"``
1517 operand bundle tag. These operand bundles represent an alternate
1518 "safe" continuation for the call site they're attached to, and can be
1519 used by a suitable runtime to deoptimize the compiled frame at the
1520 specified call site. There can be at most one ``"deopt"`` operand
1521 bundle attached to a call site. Exact details of deoptimization is
1522 out of scope for the language reference, but it usually involves
1523 rewriting a compiled frame into a set of interpreted frames.
1525 From the compiler's perspective, deoptimization operand bundles make
1526 the call sites they're attached to at least ``readonly``. They read
1527 through all of their pointer typed operands (even if they're not
1528 otherwise escaped) and the entire visible heap. Deoptimization
1529 operand bundles do not capture their operands except during
1530 deoptimization, in which case control will not be returned to the
1533 The inliner knows how to inline through calls that have deoptimization
1534 operand bundles. Just like inlining through a normal call site
1535 involves composing the normal and exceptional continuations, inlining
1536 through a call site with a deoptimization operand bundle needs to
1537 appropriately compose the "safe" deoptimization continuation. The
1538 inliner does this by prepending the parent's deoptimization
1539 continuation to every deoptimization continuation in the inlined body.
1540 E.g. inlining ``@f`` into ``@g`` in the following example
1542 .. code-block:: llvm
1545 call void @x() ;; no deopt state
1546 call void @y() [ "deopt"(i32 10) ]
1547 call void @y() [ "deopt"(i32 10), "unknown"(i8* null) ]
1552 call void @f() [ "deopt"(i32 20) ]
1558 .. code-block:: llvm
1561 call void @x() ;; still no deopt state
1562 call void @y() [ "deopt"(i32 20, i32 10) ]
1563 call void @y() [ "deopt"(i32 20, i32 10), "unknown"(i8* null) ]
1567 It is the frontend's responsibility to structure or encode the
1568 deoptimization state in a way that syntactically prepending the
1569 caller's deoptimization state to the callee's deoptimization state is
1570 semantically equivalent to composing the caller's deoptimization
1571 continuation after the callee's deoptimization continuation.
1575 Module-Level Inline Assembly
1576 ----------------------------
1578 Modules may contain "module-level inline asm" blocks, which corresponds
1579 to the GCC "file scope inline asm" blocks. These blocks are internally
1580 concatenated by LLVM and treated as a single unit, but may be separated
1581 in the ``.ll`` file if desired. The syntax is very simple:
1583 .. code-block:: llvm
1585 module asm "inline asm code goes here"
1586 module asm "more can go here"
1588 The strings can contain any character by escaping non-printable
1589 characters. The escape sequence used is simply "\\xx" where "xx" is the
1590 two digit hex code for the number.
1592 Note that the assembly string *must* be parseable by LLVM's integrated assembler
1593 (unless it is disabled), even when emitting a ``.s`` file.
1595 .. _langref_datalayout:
1600 A module may specify a target specific data layout string that specifies
1601 how data is to be laid out in memory. The syntax for the data layout is
1604 .. code-block:: llvm
1606 target datalayout = "layout specification"
1608 The *layout specification* consists of a list of specifications
1609 separated by the minus sign character ('-'). Each specification starts
1610 with a letter and may include other information after the letter to
1611 define some aspect of the data layout. The specifications accepted are
1615 Specifies that the target lays out data in big-endian form. That is,
1616 the bits with the most significance have the lowest address
1619 Specifies that the target lays out data in little-endian form. That
1620 is, the bits with the least significance have the lowest address
1623 Specifies the natural alignment of the stack in bits. Alignment
1624 promotion of stack variables is limited to the natural stack
1625 alignment to avoid dynamic stack realignment. The stack alignment
1626 must be a multiple of 8-bits. If omitted, the natural stack
1627 alignment defaults to "unspecified", which does not prevent any
1628 alignment promotions.
1629 ``p[n]:<size>:<abi>:<pref>``
1630 This specifies the *size* of a pointer and its ``<abi>`` and
1631 ``<pref>``\erred alignments for address space ``n``. All sizes are in
1632 bits. The address space, ``n``, is optional, and if not specified,
1633 denotes the default address space 0. The value of ``n`` must be
1634 in the range [1,2^23).
1635 ``i<size>:<abi>:<pref>``
1636 This specifies the alignment for an integer type of a given bit
1637 ``<size>``. The value of ``<size>`` must be in the range [1,2^23).
1638 ``v<size>:<abi>:<pref>``
1639 This specifies the alignment for a vector type of a given bit
1641 ``f<size>:<abi>:<pref>``
1642 This specifies the alignment for a floating point type of a given bit
1643 ``<size>``. Only values of ``<size>`` that are supported by the target
1644 will work. 32 (float) and 64 (double) are supported on all targets; 80
1645 or 128 (different flavors of long double) are also supported on some
1648 This specifies the alignment for an object of aggregate type.
1650 If present, specifies that llvm names are mangled in the output. The
1653 * ``e``: ELF mangling: Private symbols get a ``.L`` prefix.
1654 * ``m``: Mips mangling: Private symbols get a ``$`` prefix.
1655 * ``o``: Mach-O mangling: Private symbols get ``L`` prefix. Other
1656 symbols get a ``_`` prefix.
1657 * ``w``: Windows COFF prefix: Similar to Mach-O, but stdcall and fastcall
1658 functions also get a suffix based on the frame size.
1659 * ``x``: Windows x86 COFF prefix: Similar to Windows COFF, but use a ``_``
1660 prefix for ``__cdecl`` functions.
1661 ``n<size1>:<size2>:<size3>...``
1662 This specifies a set of native integer widths for the target CPU in
1663 bits. For example, it might contain ``n32`` for 32-bit PowerPC,
1664 ``n32:64`` for PowerPC 64, or ``n8:16:32:64`` for X86-64. Elements of
1665 this set are considered to support most general arithmetic operations
1668 On every specification that takes a ``<abi>:<pref>``, specifying the
1669 ``<pref>`` alignment is optional. If omitted, the preceding ``:``
1670 should be omitted too and ``<pref>`` will be equal to ``<abi>``.
1672 When constructing the data layout for a given target, LLVM starts with a
1673 default set of specifications which are then (possibly) overridden by
1674 the specifications in the ``datalayout`` keyword. The default
1675 specifications are given in this list:
1677 - ``E`` - big endian
1678 - ``p:64:64:64`` - 64-bit pointers with 64-bit alignment.
1679 - ``p[n]:64:64:64`` - Other address spaces are assumed to be the
1680 same as the default address space.
1681 - ``S0`` - natural stack alignment is unspecified
1682 - ``i1:8:8`` - i1 is 8-bit (byte) aligned
1683 - ``i8:8:8`` - i8 is 8-bit (byte) aligned
1684 - ``i16:16:16`` - i16 is 16-bit aligned
1685 - ``i32:32:32`` - i32 is 32-bit aligned
1686 - ``i64:32:64`` - i64 has ABI alignment of 32-bits but preferred
1687 alignment of 64-bits
1688 - ``f16:16:16`` - half is 16-bit aligned
1689 - ``f32:32:32`` - float is 32-bit aligned
1690 - ``f64:64:64`` - double is 64-bit aligned
1691 - ``f128:128:128`` - quad is 128-bit aligned
1692 - ``v64:64:64`` - 64-bit vector is 64-bit aligned
1693 - ``v128:128:128`` - 128-bit vector is 128-bit aligned
1694 - ``a:0:64`` - aggregates are 64-bit aligned
1696 When LLVM is determining the alignment for a given type, it uses the
1699 #. If the type sought is an exact match for one of the specifications,
1700 that specification is used.
1701 #. If no match is found, and the type sought is an integer type, then
1702 the smallest integer type that is larger than the bitwidth of the
1703 sought type is used. If none of the specifications are larger than
1704 the bitwidth then the largest integer type is used. For example,
1705 given the default specifications above, the i7 type will use the
1706 alignment of i8 (next largest) while both i65 and i256 will use the
1707 alignment of i64 (largest specified).
1708 #. If no match is found, and the type sought is a vector type, then the
1709 largest vector type that is smaller than the sought vector type will
1710 be used as a fall back. This happens because <128 x double> can be
1711 implemented in terms of 64 <2 x double>, for example.
1713 The function of the data layout string may not be what you expect.
1714 Notably, this is not a specification from the frontend of what alignment
1715 the code generator should use.
1717 Instead, if specified, the target data layout is required to match what
1718 the ultimate *code generator* expects. This string is used by the
1719 mid-level optimizers to improve code, and this only works if it matches
1720 what the ultimate code generator uses. There is no way to generate IR
1721 that does not embed this target-specific detail into the IR. If you
1722 don't specify the string, the default specifications will be used to
1723 generate a Data Layout and the optimization phases will operate
1724 accordingly and introduce target specificity into the IR with respect to
1725 these default specifications.
1732 A module may specify a target triple string that describes the target
1733 host. The syntax for the target triple is simply:
1735 .. code-block:: llvm
1737 target triple = "x86_64-apple-macosx10.7.0"
1739 The *target triple* string consists of a series of identifiers delimited
1740 by the minus sign character ('-'). The canonical forms are:
1744 ARCHITECTURE-VENDOR-OPERATING_SYSTEM
1745 ARCHITECTURE-VENDOR-OPERATING_SYSTEM-ENVIRONMENT
1747 This information is passed along to the backend so that it generates
1748 code for the proper architecture. It's possible to override this on the
1749 command line with the ``-mtriple`` command line option.
1751 .. _pointeraliasing:
1753 Pointer Aliasing Rules
1754 ----------------------
1756 Any memory access must be done through a pointer value associated with
1757 an address range of the memory access, otherwise the behavior is
1758 undefined. Pointer values are associated with address ranges according
1759 to the following rules:
1761 - A pointer value is associated with the addresses associated with any
1762 value it is *based* on.
1763 - An address of a global variable is associated with the address range
1764 of the variable's storage.
1765 - The result value of an allocation instruction is associated with the
1766 address range of the allocated storage.
1767 - A null pointer in the default address-space is associated with no
1769 - An integer constant other than zero or a pointer value returned from
1770 a function not defined within LLVM may be associated with address
1771 ranges allocated through mechanisms other than those provided by
1772 LLVM. Such ranges shall not overlap with any ranges of addresses
1773 allocated by mechanisms provided by LLVM.
1775 A pointer value is *based* on another pointer value according to the
1778 - A pointer value formed from a ``getelementptr`` operation is *based*
1779 on the first value operand of the ``getelementptr``.
1780 - The result value of a ``bitcast`` is *based* on the operand of the
1782 - A pointer value formed by an ``inttoptr`` is *based* on all pointer
1783 values that contribute (directly or indirectly) to the computation of
1784 the pointer's value.
1785 - The "*based* on" relationship is transitive.
1787 Note that this definition of *"based"* is intentionally similar to the
1788 definition of *"based"* in C99, though it is slightly weaker.
1790 LLVM IR does not associate types with memory. The result type of a
1791 ``load`` merely indicates the size and alignment of the memory from
1792 which to load, as well as the interpretation of the value. The first
1793 operand type of a ``store`` similarly only indicates the size and
1794 alignment of the store.
1796 Consequently, type-based alias analysis, aka TBAA, aka
1797 ``-fstrict-aliasing``, is not applicable to general unadorned LLVM IR.
1798 :ref:`Metadata <metadata>` may be used to encode additional information
1799 which specialized optimization passes may use to implement type-based
1804 Volatile Memory Accesses
1805 ------------------------
1807 Certain memory accesses, such as :ref:`load <i_load>`'s,
1808 :ref:`store <i_store>`'s, and :ref:`llvm.memcpy <int_memcpy>`'s may be
1809 marked ``volatile``. The optimizers must not change the number of
1810 volatile operations or change their order of execution relative to other
1811 volatile operations. The optimizers *may* change the order of volatile
1812 operations relative to non-volatile operations. This is not Java's
1813 "volatile" and has no cross-thread synchronization behavior.
1815 IR-level volatile loads and stores cannot safely be optimized into
1816 llvm.memcpy or llvm.memmove intrinsics even when those intrinsics are
1817 flagged volatile. Likewise, the backend should never split or merge
1818 target-legal volatile load/store instructions.
1820 .. admonition:: Rationale
1822 Platforms may rely on volatile loads and stores of natively supported
1823 data width to be executed as single instruction. For example, in C
1824 this holds for an l-value of volatile primitive type with native
1825 hardware support, but not necessarily for aggregate types. The
1826 frontend upholds these expectations, which are intentionally
1827 unspecified in the IR. The rules above ensure that IR transformations
1828 do not violate the frontend's contract with the language.
1832 Memory Model for Concurrent Operations
1833 --------------------------------------
1835 The LLVM IR does not define any way to start parallel threads of
1836 execution or to register signal handlers. Nonetheless, there are
1837 platform-specific ways to create them, and we define LLVM IR's behavior
1838 in their presence. This model is inspired by the C++0x memory model.
1840 For a more informal introduction to this model, see the :doc:`Atomics`.
1842 We define a *happens-before* partial order as the least partial order
1845 - Is a superset of single-thread program order, and
1846 - When a *synchronizes-with* ``b``, includes an edge from ``a`` to
1847 ``b``. *Synchronizes-with* pairs are introduced by platform-specific
1848 techniques, like pthread locks, thread creation, thread joining,
1849 etc., and by atomic instructions. (See also :ref:`Atomic Memory Ordering
1850 Constraints <ordering>`).
1852 Note that program order does not introduce *happens-before* edges
1853 between a thread and signals executing inside that thread.
1855 Every (defined) read operation (load instructions, memcpy, atomic
1856 loads/read-modify-writes, etc.) R reads a series of bytes written by
1857 (defined) write operations (store instructions, atomic
1858 stores/read-modify-writes, memcpy, etc.). For the purposes of this
1859 section, initialized globals are considered to have a write of the
1860 initializer which is atomic and happens before any other read or write
1861 of the memory in question. For each byte of a read R, R\ :sub:`byte`
1862 may see any write to the same byte, except:
1864 - If write\ :sub:`1` happens before write\ :sub:`2`, and
1865 write\ :sub:`2` happens before R\ :sub:`byte`, then
1866 R\ :sub:`byte` does not see write\ :sub:`1`.
1867 - If R\ :sub:`byte` happens before write\ :sub:`3`, then
1868 R\ :sub:`byte` does not see write\ :sub:`3`.
1870 Given that definition, R\ :sub:`byte` is defined as follows:
1872 - If R is volatile, the result is target-dependent. (Volatile is
1873 supposed to give guarantees which can support ``sig_atomic_t`` in
1874 C/C++, and may be used for accesses to addresses that do not behave
1875 like normal memory. It does not generally provide cross-thread
1877 - Otherwise, if there is no write to the same byte that happens before
1878 R\ :sub:`byte`, R\ :sub:`byte` returns ``undef`` for that byte.
1879 - Otherwise, if R\ :sub:`byte` may see exactly one write,
1880 R\ :sub:`byte` returns the value written by that write.
1881 - Otherwise, if R is atomic, and all the writes R\ :sub:`byte` may
1882 see are atomic, it chooses one of the values written. See the :ref:`Atomic
1883 Memory Ordering Constraints <ordering>` section for additional
1884 constraints on how the choice is made.
1885 - Otherwise R\ :sub:`byte` returns ``undef``.
1887 R returns the value composed of the series of bytes it read. This
1888 implies that some bytes within the value may be ``undef`` **without**
1889 the entire value being ``undef``. Note that this only defines the
1890 semantics of the operation; it doesn't mean that targets will emit more
1891 than one instruction to read the series of bytes.
1893 Note that in cases where none of the atomic intrinsics are used, this
1894 model places only one restriction on IR transformations on top of what
1895 is required for single-threaded execution: introducing a store to a byte
1896 which might not otherwise be stored is not allowed in general.
1897 (Specifically, in the case where another thread might write to and read
1898 from an address, introducing a store can change a load that may see
1899 exactly one write into a load that may see multiple writes.)
1903 Atomic Memory Ordering Constraints
1904 ----------------------------------
1906 Atomic instructions (:ref:`cmpxchg <i_cmpxchg>`,
1907 :ref:`atomicrmw <i_atomicrmw>`, :ref:`fence <i_fence>`,
1908 :ref:`atomic load <i_load>`, and :ref:`atomic store <i_store>`) take
1909 ordering parameters that determine which other atomic instructions on
1910 the same address they *synchronize with*. These semantics are borrowed
1911 from Java and C++0x, but are somewhat more colloquial. If these
1912 descriptions aren't precise enough, check those specs (see spec
1913 references in the :doc:`atomics guide <Atomics>`).
1914 :ref:`fence <i_fence>` instructions treat these orderings somewhat
1915 differently since they don't take an address. See that instruction's
1916 documentation for details.
1918 For a simpler introduction to the ordering constraints, see the
1922 The set of values that can be read is governed by the happens-before
1923 partial order. A value cannot be read unless some operation wrote
1924 it. This is intended to provide a guarantee strong enough to model
1925 Java's non-volatile shared variables. This ordering cannot be
1926 specified for read-modify-write operations; it is not strong enough
1927 to make them atomic in any interesting way.
1929 In addition to the guarantees of ``unordered``, there is a single
1930 total order for modifications by ``monotonic`` operations on each
1931 address. All modification orders must be compatible with the
1932 happens-before order. There is no guarantee that the modification
1933 orders can be combined to a global total order for the whole program
1934 (and this often will not be possible). The read in an atomic
1935 read-modify-write operation (:ref:`cmpxchg <i_cmpxchg>` and
1936 :ref:`atomicrmw <i_atomicrmw>`) reads the value in the modification
1937 order immediately before the value it writes. If one atomic read
1938 happens before another atomic read of the same address, the later
1939 read must see the same value or a later value in the address's
1940 modification order. This disallows reordering of ``monotonic`` (or
1941 stronger) operations on the same address. If an address is written
1942 ``monotonic``-ally by one thread, and other threads ``monotonic``-ally
1943 read that address repeatedly, the other threads must eventually see
1944 the write. This corresponds to the C++0x/C1x
1945 ``memory_order_relaxed``.
1947 In addition to the guarantees of ``monotonic``, a
1948 *synchronizes-with* edge may be formed with a ``release`` operation.
1949 This is intended to model C++'s ``memory_order_acquire``.
1951 In addition to the guarantees of ``monotonic``, if this operation
1952 writes a value which is subsequently read by an ``acquire``
1953 operation, it *synchronizes-with* that operation. (This isn't a
1954 complete description; see the C++0x definition of a release
1955 sequence.) This corresponds to the C++0x/C1x
1956 ``memory_order_release``.
1957 ``acq_rel`` (acquire+release)
1958 Acts as both an ``acquire`` and ``release`` operation on its
1959 address. This corresponds to the C++0x/C1x ``memory_order_acq_rel``.
1960 ``seq_cst`` (sequentially consistent)
1961 In addition to the guarantees of ``acq_rel`` (``acquire`` for an
1962 operation that only reads, ``release`` for an operation that only
1963 writes), there is a global total order on all
1964 sequentially-consistent operations on all addresses, which is
1965 consistent with the *happens-before* partial order and with the
1966 modification orders of all the affected addresses. Each
1967 sequentially-consistent read sees the last preceding write to the
1968 same address in this global order. This corresponds to the C++0x/C1x
1969 ``memory_order_seq_cst`` and Java volatile.
1973 If an atomic operation is marked ``singlethread``, it only *synchronizes
1974 with* or participates in modification and seq\_cst total orderings with
1975 other operations running in the same thread (for example, in signal
1983 LLVM IR floating-point binary ops (:ref:`fadd <i_fadd>`,
1984 :ref:`fsub <i_fsub>`, :ref:`fmul <i_fmul>`, :ref:`fdiv <i_fdiv>`,
1985 :ref:`frem <i_frem>`, :ref:`fcmp <i_fcmp>`) have the following flags that can
1986 be set to enable otherwise unsafe floating point operations
1989 No NaNs - Allow optimizations to assume the arguments and result are not
1990 NaN. Such optimizations are required to retain defined behavior over
1991 NaNs, but the value of the result is undefined.
1994 No Infs - Allow optimizations to assume the arguments and result are not
1995 +/-Inf. Such optimizations are required to retain defined behavior over
1996 +/-Inf, but the value of the result is undefined.
1999 No Signed Zeros - Allow optimizations to treat the sign of a zero
2000 argument or result as insignificant.
2003 Allow Reciprocal - Allow optimizations to use the reciprocal of an
2004 argument rather than perform division.
2007 Fast - Allow algebraically equivalent transformations that may
2008 dramatically change results in floating point (e.g. reassociate). This
2009 flag implies all the others.
2013 Use-list Order Directives
2014 -------------------------
2016 Use-list directives encode the in-memory order of each use-list, allowing the
2017 order to be recreated. ``<order-indexes>`` is a comma-separated list of
2018 indexes that are assigned to the referenced value's uses. The referenced
2019 value's use-list is immediately sorted by these indexes.
2021 Use-list directives may appear at function scope or global scope. They are not
2022 instructions, and have no effect on the semantics of the IR. When they're at
2023 function scope, they must appear after the terminator of the final basic block.
2025 If basic blocks have their address taken via ``blockaddress()`` expressions,
2026 ``uselistorder_bb`` can be used to reorder their use-lists from outside their
2033 uselistorder <ty> <value>, { <order-indexes> }
2034 uselistorder_bb @function, %block { <order-indexes> }
2040 define void @foo(i32 %arg1, i32 %arg2) {
2042 ; ... instructions ...
2044 ; ... instructions ...
2046 ; At function scope.
2047 uselistorder i32 %arg1, { 1, 0, 2 }
2048 uselistorder label %bb, { 1, 0 }
2052 uselistorder i32* @global, { 1, 2, 0 }
2053 uselistorder i32 7, { 1, 0 }
2054 uselistorder i32 (i32) @bar, { 1, 0 }
2055 uselistorder_bb @foo, %bb, { 5, 1, 3, 2, 0, 4 }
2062 The LLVM type system is one of the most important features of the
2063 intermediate representation. Being typed enables a number of
2064 optimizations to be performed on the intermediate representation
2065 directly, without having to do extra analyses on the side before the
2066 transformation. A strong type system makes it easier to read the
2067 generated code and enables novel analyses and transformations that are
2068 not feasible to perform on normal three address code representations.
2078 The void type does not represent any value and has no size.
2096 The function type can be thought of as a function signature. It consists of a
2097 return type and a list of formal parameter types. The return type of a function
2098 type is a void type or first class type --- except for :ref:`label <t_label>`
2099 and :ref:`metadata <t_metadata>` types.
2105 <returntype> (<parameter list>)
2107 ...where '``<parameter list>``' is a comma-separated list of type
2108 specifiers. Optionally, the parameter list may include a type ``...``, which
2109 indicates that the function takes a variable number of arguments. Variable
2110 argument functions can access their arguments with the :ref:`variable argument
2111 handling intrinsic <int_varargs>` functions. '``<returntype>``' is any type
2112 except :ref:`label <t_label>` and :ref:`metadata <t_metadata>`.
2116 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
2117 | ``i32 (i32)`` | function taking an ``i32``, returning an ``i32`` |
2118 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
2119 | ``float (i16, i32 *) *`` | :ref:`Pointer <t_pointer>` to a function that takes an ``i16`` and a :ref:`pointer <t_pointer>` to ``i32``, returning ``float``. |
2120 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
2121 | ``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. |
2122 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
2123 | ``{i32, i32} (i32)`` | A function taking an ``i32``, returning a :ref:`structure <t_struct>` containing two ``i32`` values |
2124 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
2131 The :ref:`first class <t_firstclass>` types are perhaps the most important.
2132 Values of these types are the only ones which can be produced by
2140 These are the types that are valid in registers from CodeGen's perspective.
2149 The integer type is a very simple type that simply specifies an
2150 arbitrary bit width for the integer type desired. Any bit width from 1
2151 bit to 2\ :sup:`23`\ -1 (about 8 million) can be specified.
2159 The number of bits the integer will occupy is specified by the ``N``
2165 +----------------+------------------------------------------------+
2166 | ``i1`` | a single-bit integer. |
2167 +----------------+------------------------------------------------+
2168 | ``i32`` | a 32-bit integer. |
2169 +----------------+------------------------------------------------+
2170 | ``i1942652`` | a really big integer of over 1 million bits. |
2171 +----------------+------------------------------------------------+
2175 Floating Point Types
2176 """"""""""""""""""""
2185 - 16-bit floating point value
2188 - 32-bit floating point value
2191 - 64-bit floating point value
2194 - 128-bit floating point value (112-bit mantissa)
2197 - 80-bit floating point value (X87)
2200 - 128-bit floating point value (two 64-bits)
2207 The x86_mmx type represents a value held in an MMX register on an x86
2208 machine. The operations allowed on it are quite limited: parameters and
2209 return values, load and store, and bitcast. User-specified MMX
2210 instructions are represented as intrinsic or asm calls with arguments
2211 and/or results of this type. There are no arrays, vectors or constants
2228 The pointer type is used to specify memory locations. Pointers are
2229 commonly used to reference objects in memory.
2231 Pointer types may have an optional address space attribute defining the
2232 numbered address space where the pointed-to object resides. The default
2233 address space is number zero. The semantics of non-zero address spaces
2234 are target-specific.
2236 Note that LLVM does not permit pointers to void (``void*``) nor does it
2237 permit pointers to labels (``label*``). Use ``i8*`` instead.
2247 +-------------------------+--------------------------------------------------------------------------------------------------------------+
2248 | ``[4 x i32]*`` | A :ref:`pointer <t_pointer>` to :ref:`array <t_array>` of four ``i32`` values. |
2249 +-------------------------+--------------------------------------------------------------------------------------------------------------+
2250 | ``i32 (i32*) *`` | A :ref:`pointer <t_pointer>` to a :ref:`function <t_function>` that takes an ``i32*``, returning an ``i32``. |
2251 +-------------------------+--------------------------------------------------------------------------------------------------------------+
2252 | ``i32 addrspace(5)*`` | A :ref:`pointer <t_pointer>` to an ``i32`` value that resides in address space #5. |
2253 +-------------------------+--------------------------------------------------------------------------------------------------------------+
2262 A vector type is a simple derived type that represents a vector of
2263 elements. Vector types are used when multiple primitive data are
2264 operated in parallel using a single instruction (SIMD). A vector type
2265 requires a size (number of elements) and an underlying primitive data
2266 type. Vector types are considered :ref:`first class <t_firstclass>`.
2272 < <# elements> x <elementtype> >
2274 The number of elements is a constant integer value larger than 0;
2275 elementtype may be any integer, floating point or pointer type. Vectors
2276 of size zero are not allowed.
2280 +-------------------+--------------------------------------------------+
2281 | ``<4 x i32>`` | Vector of 4 32-bit integer values. |
2282 +-------------------+--------------------------------------------------+
2283 | ``<8 x float>`` | Vector of 8 32-bit floating-point values. |
2284 +-------------------+--------------------------------------------------+
2285 | ``<2 x i64>`` | Vector of 2 64-bit integer values. |
2286 +-------------------+--------------------------------------------------+
2287 | ``<4 x i64*>`` | Vector of 4 pointers to 64-bit integer values. |
2288 +-------------------+--------------------------------------------------+
2297 The label type represents code labels.
2312 The token type is used when a value is associated with an instruction
2313 but all uses of the value must not attempt to introspect or obscure it.
2314 As such, it is not appropriate to have a :ref:`phi <i_phi>` or
2315 :ref:`select <i_select>` of type token.
2332 The metadata type represents embedded metadata. No derived types may be
2333 created from metadata except for :ref:`function <t_function>` arguments.
2346 Aggregate Types are a subset of derived types that can contain multiple
2347 member types. :ref:`Arrays <t_array>` and :ref:`structs <t_struct>` are
2348 aggregate types. :ref:`Vectors <t_vector>` are not considered to be
2358 The array type is a very simple derived type that arranges elements
2359 sequentially in memory. The array type requires a size (number of
2360 elements) and an underlying data type.
2366 [<# elements> x <elementtype>]
2368 The number of elements is a constant integer value; ``elementtype`` may
2369 be any type with a size.
2373 +------------------+--------------------------------------+
2374 | ``[40 x i32]`` | Array of 40 32-bit integer values. |
2375 +------------------+--------------------------------------+
2376 | ``[41 x i32]`` | Array of 41 32-bit integer values. |
2377 +------------------+--------------------------------------+
2378 | ``[4 x i8]`` | Array of 4 8-bit integer values. |
2379 +------------------+--------------------------------------+
2381 Here are some examples of multidimensional arrays:
2383 +-----------------------------+----------------------------------------------------------+
2384 | ``[3 x [4 x i32]]`` | 3x4 array of 32-bit integer values. |
2385 +-----------------------------+----------------------------------------------------------+
2386 | ``[12 x [10 x float]]`` | 12x10 array of single precision floating point values. |
2387 +-----------------------------+----------------------------------------------------------+
2388 | ``[2 x [3 x [4 x i16]]]`` | 2x3x4 array of 16-bit integer values. |
2389 +-----------------------------+----------------------------------------------------------+
2391 There is no restriction on indexing beyond the end of the array implied
2392 by a static type (though there are restrictions on indexing beyond the
2393 bounds of an allocated object in some cases). This means that
2394 single-dimension 'variable sized array' addressing can be implemented in
2395 LLVM with a zero length array type. An implementation of 'pascal style
2396 arrays' in LLVM could use the type "``{ i32, [0 x float]}``", for
2406 The structure type is used to represent a collection of data members
2407 together in memory. The elements of a structure may be any type that has
2410 Structures in memory are accessed using '``load``' and '``store``' by
2411 getting a pointer to a field with the '``getelementptr``' instruction.
2412 Structures in registers are accessed using the '``extractvalue``' and
2413 '``insertvalue``' instructions.
2415 Structures may optionally be "packed" structures, which indicate that
2416 the alignment of the struct is one byte, and that there is no padding
2417 between the elements. In non-packed structs, padding between field types
2418 is inserted as defined by the DataLayout string in the module, which is
2419 required to match what the underlying code generator expects.
2421 Structures can either be "literal" or "identified". A literal structure
2422 is defined inline with other types (e.g. ``{i32, i32}*``) whereas
2423 identified types are always defined at the top level with a name.
2424 Literal types are uniqued by their contents and can never be recursive
2425 or opaque since there is no way to write one. Identified types can be
2426 recursive, can be opaqued, and are never uniqued.
2432 %T1 = type { <type list> } ; Identified normal struct type
2433 %T2 = type <{ <type list> }> ; Identified packed struct type
2437 +------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
2438 | ``{ i32, i32, i32 }`` | A triple of three ``i32`` values |
2439 +------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
2440 | ``{ 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``. |
2441 +------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
2442 | ``<{ i8, i32 }>`` | A packed struct known to be 5 bytes in size. |
2443 +------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
2447 Opaque Structure Types
2448 """"""""""""""""""""""
2452 Opaque structure types are used to represent named structure types that
2453 do not have a body specified. This corresponds (for example) to the C
2454 notion of a forward declared structure.
2465 +--------------+-------------------+
2466 | ``opaque`` | An opaque type. |
2467 +--------------+-------------------+
2474 LLVM has several different basic types of constants. This section
2475 describes them all and their syntax.
2480 **Boolean constants**
2481 The two strings '``true``' and '``false``' are both valid constants
2483 **Integer constants**
2484 Standard integers (such as '4') are constants of the
2485 :ref:`integer <t_integer>` type. Negative numbers may be used with
2487 **Floating point constants**
2488 Floating point constants use standard decimal notation (e.g.
2489 123.421), exponential notation (e.g. 1.23421e+2), or a more precise
2490 hexadecimal notation (see below). The assembler requires the exact
2491 decimal value of a floating-point constant. For example, the
2492 assembler accepts 1.25 but rejects 1.3 because 1.3 is a repeating
2493 decimal in binary. Floating point constants must have a :ref:`floating
2494 point <t_floating>` type.
2495 **Null pointer constants**
2496 The identifier '``null``' is recognized as a null pointer constant
2497 and must be of :ref:`pointer type <t_pointer>`.
2499 The identifier '``none``' is recognized as an empty token constant
2500 and must be of :ref:`token type <t_token>`.
2502 The one non-intuitive notation for constants is the hexadecimal form of
2503 floating point constants. For example, the form
2504 '``double 0x432ff973cafa8000``' is equivalent to (but harder to read
2505 than) '``double 4.5e+15``'. The only time hexadecimal floating point
2506 constants are required (and the only time that they are generated by the
2507 disassembler) is when a floating point constant must be emitted but it
2508 cannot be represented as a decimal floating point number in a reasonable
2509 number of digits. For example, NaN's, infinities, and other special
2510 values are represented in their IEEE hexadecimal format so that assembly
2511 and disassembly do not cause any bits to change in the constants.
2513 When using the hexadecimal form, constants of types half, float, and
2514 double are represented using the 16-digit form shown above (which
2515 matches the IEEE754 representation for double); half and float values
2516 must, however, be exactly representable as IEEE 754 half and single
2517 precision, respectively. Hexadecimal format is always used for long
2518 double, and there are three forms of long double. The 80-bit format used
2519 by x86 is represented as ``0xK`` followed by 20 hexadecimal digits. The
2520 128-bit format used by PowerPC (two adjacent doubles) is represented by
2521 ``0xM`` followed by 32 hexadecimal digits. The IEEE 128-bit format is
2522 represented by ``0xL`` followed by 32 hexadecimal digits. Long doubles
2523 will only work if they match the long double format on your target.
2524 The IEEE 16-bit format (half precision) is represented by ``0xH``
2525 followed by 4 hexadecimal digits. All hexadecimal formats are big-endian
2526 (sign bit at the left).
2528 There are no constants of type x86_mmx.
2530 .. _complexconstants:
2535 Complex constants are a (potentially recursive) combination of simple
2536 constants and smaller complex constants.
2538 **Structure constants**
2539 Structure constants are represented with notation similar to
2540 structure type definitions (a comma separated list of elements,
2541 surrounded by braces (``{}``)). For example:
2542 "``{ i32 4, float 17.0, i32* @G }``", where "``@G``" is declared as
2543 "``@G = external global i32``". Structure constants must have
2544 :ref:`structure type <t_struct>`, and the number and types of elements
2545 must match those specified by the type.
2547 Array constants are represented with notation similar to array type
2548 definitions (a comma separated list of elements, surrounded by
2549 square brackets (``[]``)). For example:
2550 "``[ i32 42, i32 11, i32 74 ]``". Array constants must have
2551 :ref:`array type <t_array>`, and the number and types of elements must
2552 match those specified by the type. As a special case, character array
2553 constants may also be represented as a double-quoted string using the ``c``
2554 prefix. For example: "``c"Hello World\0A\00"``".
2555 **Vector constants**
2556 Vector constants are represented with notation similar to vector
2557 type definitions (a comma separated list of elements, surrounded by
2558 less-than/greater-than's (``<>``)). For example:
2559 "``< i32 42, i32 11, i32 74, i32 100 >``". Vector constants
2560 must have :ref:`vector type <t_vector>`, and the number and types of
2561 elements must match those specified by the type.
2562 **Zero initialization**
2563 The string '``zeroinitializer``' can be used to zero initialize a
2564 value to zero of *any* type, including scalar and
2565 :ref:`aggregate <t_aggregate>` types. This is often used to avoid
2566 having to print large zero initializers (e.g. for large arrays) and
2567 is always exactly equivalent to using explicit zero initializers.
2569 A metadata node is a constant tuple without types. For example:
2570 "``!{!0, !{!2, !0}, !"test"}``". Metadata can reference constant values,
2571 for example: "``!{!0, i32 0, i8* @global, i64 (i64)* @function, !"str"}``".
2572 Unlike other typed constants that are meant to be interpreted as part of
2573 the instruction stream, metadata is a place to attach additional
2574 information such as debug info.
2576 Global Variable and Function Addresses
2577 --------------------------------------
2579 The addresses of :ref:`global variables <globalvars>` and
2580 :ref:`functions <functionstructure>` are always implicitly valid
2581 (link-time) constants. These constants are explicitly referenced when
2582 the :ref:`identifier for the global <identifiers>` is used and always have
2583 :ref:`pointer <t_pointer>` type. For example, the following is a legal LLVM
2586 .. code-block:: llvm
2590 @Z = global [2 x i32*] [ i32* @X, i32* @Y ]
2597 The string '``undef``' can be used anywhere a constant is expected, and
2598 indicates that the user of the value may receive an unspecified
2599 bit-pattern. Undefined values may be of any type (other than '``label``'
2600 or '``void``') and be used anywhere a constant is permitted.
2602 Undefined values are useful because they indicate to the compiler that
2603 the program is well defined no matter what value is used. This gives the
2604 compiler more freedom to optimize. Here are some examples of
2605 (potentially surprising) transformations that are valid (in pseudo IR):
2607 .. code-block:: llvm
2617 This is safe because all of the output bits are affected by the undef
2618 bits. Any output bit can have a zero or one depending on the input bits.
2620 .. code-block:: llvm
2631 These logical operations have bits that are not always affected by the
2632 input. For example, if ``%X`` has a zero bit, then the output of the
2633 '``and``' operation will always be a zero for that bit, no matter what
2634 the corresponding bit from the '``undef``' is. As such, it is unsafe to
2635 optimize or assume that the result of the '``and``' is '``undef``'.
2636 However, it is safe to assume that all bits of the '``undef``' could be
2637 0, and optimize the '``and``' to 0. Likewise, it is safe to assume that
2638 all the bits of the '``undef``' operand to the '``or``' could be set,
2639 allowing the '``or``' to be folded to -1.
2641 .. code-block:: llvm
2643 %A = select undef, %X, %Y
2644 %B = select undef, 42, %Y
2645 %C = select %X, %Y, undef
2655 This set of examples shows that undefined '``select``' (and conditional
2656 branch) conditions can go *either way*, but they have to come from one
2657 of the two operands. In the ``%A`` example, if ``%X`` and ``%Y`` were
2658 both known to have a clear low bit, then ``%A`` would have to have a
2659 cleared low bit. However, in the ``%C`` example, the optimizer is
2660 allowed to assume that the '``undef``' operand could be the same as
2661 ``%Y``, allowing the whole '``select``' to be eliminated.
2663 .. code-block:: llvm
2665 %A = xor undef, undef
2682 This example points out that two '``undef``' operands are not
2683 necessarily the same. This can be surprising to people (and also matches
2684 C semantics) where they assume that "``X^X``" is always zero, even if
2685 ``X`` is undefined. This isn't true for a number of reasons, but the
2686 short answer is that an '``undef``' "variable" can arbitrarily change
2687 its value over its "live range". This is true because the variable
2688 doesn't actually *have a live range*. Instead, the value is logically
2689 read from arbitrary registers that happen to be around when needed, so
2690 the value is not necessarily consistent over time. In fact, ``%A`` and
2691 ``%C`` need to have the same semantics or the core LLVM "replace all
2692 uses with" concept would not hold.
2694 .. code-block:: llvm
2702 These examples show the crucial difference between an *undefined value*
2703 and *undefined behavior*. An undefined value (like '``undef``') is
2704 allowed to have an arbitrary bit-pattern. This means that the ``%A``
2705 operation can be constant folded to '``undef``', because the '``undef``'
2706 could be an SNaN, and ``fdiv`` is not (currently) defined on SNaN's.
2707 However, in the second example, we can make a more aggressive
2708 assumption: because the ``undef`` is allowed to be an arbitrary value,
2709 we are allowed to assume that it could be zero. Since a divide by zero
2710 has *undefined behavior*, we are allowed to assume that the operation
2711 does not execute at all. This allows us to delete the divide and all
2712 code after it. Because the undefined operation "can't happen", the
2713 optimizer can assume that it occurs in dead code.
2715 .. code-block:: llvm
2717 a: store undef -> %X
2718 b: store %X -> undef
2723 These examples reiterate the ``fdiv`` example: a store *of* an undefined
2724 value can be assumed to not have any effect; we can assume that the
2725 value is overwritten with bits that happen to match what was already
2726 there. However, a store *to* an undefined location could clobber
2727 arbitrary memory, therefore, it has undefined behavior.
2734 Poison values are similar to :ref:`undef values <undefvalues>`, however
2735 they also represent the fact that an instruction or constant expression
2736 that cannot evoke side effects has nevertheless detected a condition
2737 that results in undefined behavior.
2739 There is currently no way of representing a poison value in the IR; they
2740 only exist when produced by operations such as :ref:`add <i_add>` with
2743 Poison value behavior is defined in terms of value *dependence*:
2745 - Values other than :ref:`phi <i_phi>` nodes depend on their operands.
2746 - :ref:`Phi <i_phi>` nodes depend on the operand corresponding to
2747 their dynamic predecessor basic block.
2748 - Function arguments depend on the corresponding actual argument values
2749 in the dynamic callers of their functions.
2750 - :ref:`Call <i_call>` instructions depend on the :ref:`ret <i_ret>`
2751 instructions that dynamically transfer control back to them.
2752 - :ref:`Invoke <i_invoke>` instructions depend on the
2753 :ref:`ret <i_ret>`, :ref:`resume <i_resume>`, or exception-throwing
2754 call instructions that dynamically transfer control back to them.
2755 - Non-volatile loads and stores depend on the most recent stores to all
2756 of the referenced memory addresses, following the order in the IR
2757 (including loads and stores implied by intrinsics such as
2758 :ref:`@llvm.memcpy <int_memcpy>`.)
2759 - An instruction with externally visible side effects depends on the
2760 most recent preceding instruction with externally visible side
2761 effects, following the order in the IR. (This includes :ref:`volatile
2762 operations <volatile>`.)
2763 - An instruction *control-depends* on a :ref:`terminator
2764 instruction <terminators>` if the terminator instruction has
2765 multiple successors and the instruction is always executed when
2766 control transfers to one of the successors, and may not be executed
2767 when control is transferred to another.
2768 - Additionally, an instruction also *control-depends* on a terminator
2769 instruction if the set of instructions it otherwise depends on would
2770 be different if the terminator had transferred control to a different
2772 - Dependence is transitive.
2774 Poison values have the same behavior as :ref:`undef values <undefvalues>`,
2775 with the additional effect that any instruction that has a *dependence*
2776 on a poison value has undefined behavior.
2778 Here are some examples:
2780 .. code-block:: llvm
2783 %poison = sub nuw i32 0, 1 ; Results in a poison value.
2784 %still_poison = and i32 %poison, 0 ; 0, but also poison.
2785 %poison_yet_again = getelementptr i32, i32* @h, i32 %still_poison
2786 store i32 0, i32* %poison_yet_again ; memory at @h[0] is poisoned
2788 store i32 %poison, i32* @g ; Poison value stored to memory.
2789 %poison2 = load i32, i32* @g ; Poison value loaded back from memory.
2791 store volatile i32 %poison, i32* @g ; External observation; undefined behavior.
2793 %narrowaddr = bitcast i32* @g to i16*
2794 %wideaddr = bitcast i32* @g to i64*
2795 %poison3 = load i16, i16* %narrowaddr ; Returns a poison value.
2796 %poison4 = load i64, i64* %wideaddr ; Returns a poison value.
2798 %cmp = icmp slt i32 %poison, 0 ; Returns a poison value.
2799 br i1 %cmp, label %true, label %end ; Branch to either destination.
2802 store volatile i32 0, i32* @g ; This is control-dependent on %cmp, so
2803 ; it has undefined behavior.
2807 %p = phi i32 [ 0, %entry ], [ 1, %true ]
2808 ; Both edges into this PHI are
2809 ; control-dependent on %cmp, so this
2810 ; always results in a poison value.
2812 store volatile i32 0, i32* @g ; This would depend on the store in %true
2813 ; if %cmp is true, or the store in %entry
2814 ; otherwise, so this is undefined behavior.
2816 br i1 %cmp, label %second_true, label %second_end
2817 ; The same branch again, but this time the
2818 ; true block doesn't have side effects.
2825 store volatile i32 0, i32* @g ; This time, the instruction always depends
2826 ; on the store in %end. Also, it is
2827 ; control-equivalent to %end, so this is
2828 ; well-defined (ignoring earlier undefined
2829 ; behavior in this example).
2833 Addresses of Basic Blocks
2834 -------------------------
2836 ``blockaddress(@function, %block)``
2838 The '``blockaddress``' constant computes the address of the specified
2839 basic block in the specified function, and always has an ``i8*`` type.
2840 Taking the address of the entry block is illegal.
2842 This value only has defined behavior when used as an operand to the
2843 ':ref:`indirectbr <i_indirectbr>`' instruction, or for comparisons
2844 against null. Pointer equality tests between labels addresses results in
2845 undefined behavior --- though, again, comparison against null is ok, and
2846 no label is equal to the null pointer. This may be passed around as an
2847 opaque pointer sized value as long as the bits are not inspected. This
2848 allows ``ptrtoint`` and arithmetic to be performed on these values so
2849 long as the original value is reconstituted before the ``indirectbr``
2852 Finally, some targets may provide defined semantics when using the value
2853 as the operand to an inline assembly, but that is target specific.
2857 Constant Expressions
2858 --------------------
2860 Constant expressions are used to allow expressions involving other
2861 constants to be used as constants. Constant expressions may be of any
2862 :ref:`first class <t_firstclass>` type and may involve any LLVM operation
2863 that does not have side effects (e.g. load and call are not supported).
2864 The following is the syntax for constant expressions:
2866 ``trunc (CST to TYPE)``
2867 Truncate a constant to another type. The bit size of CST must be
2868 larger than the bit size of TYPE. Both types must be integers.
2869 ``zext (CST to TYPE)``
2870 Zero extend a constant to another type. The bit size of CST must be
2871 smaller than the bit size of TYPE. Both types must be integers.
2872 ``sext (CST to TYPE)``
2873 Sign extend a constant to another type. The bit size of CST must be
2874 smaller than the bit size of TYPE. Both types must be integers.
2875 ``fptrunc (CST to TYPE)``
2876 Truncate a floating point constant to another floating point type.
2877 The size of CST must be larger than the size of TYPE. Both types
2878 must be floating point.
2879 ``fpext (CST to TYPE)``
2880 Floating point extend a constant to another type. The size of CST
2881 must be smaller or equal to the size of TYPE. Both types must be
2883 ``fptoui (CST to TYPE)``
2884 Convert a floating point constant to the corresponding unsigned
2885 integer constant. TYPE must be a scalar or vector integer type. CST
2886 must be of scalar or vector floating point type. Both CST and TYPE
2887 must be scalars, or vectors of the same number of elements. If the
2888 value won't fit in the integer type, the results are undefined.
2889 ``fptosi (CST to TYPE)``
2890 Convert a floating point constant to the corresponding signed
2891 integer constant. TYPE must be a scalar or vector integer type. CST
2892 must be of scalar or vector floating point type. Both CST and TYPE
2893 must be scalars, or vectors of the same number of elements. If the
2894 value won't fit in the integer type, the results are undefined.
2895 ``uitofp (CST to TYPE)``
2896 Convert an unsigned integer constant to the corresponding floating
2897 point constant. TYPE must be a scalar or vector floating point type.
2898 CST must be of scalar or vector integer type. Both CST and TYPE must
2899 be scalars, or vectors of the same number of elements. If the value
2900 won't fit in the floating point type, the results are undefined.
2901 ``sitofp (CST to TYPE)``
2902 Convert a signed integer constant to the corresponding floating
2903 point constant. TYPE must be a scalar or vector floating point type.
2904 CST must be of scalar or vector integer type. Both CST and TYPE must
2905 be scalars, or vectors of the same number of elements. If the value
2906 won't fit in the floating point type, the results are undefined.
2907 ``ptrtoint (CST to TYPE)``
2908 Convert a pointer typed constant to the corresponding integer
2909 constant. ``TYPE`` must be an integer type. ``CST`` must be of
2910 pointer type. The ``CST`` value is zero extended, truncated, or
2911 unchanged to make it fit in ``TYPE``.
2912 ``inttoptr (CST to TYPE)``
2913 Convert an integer constant to a pointer constant. TYPE must be a
2914 pointer type. CST must be of integer type. The CST value is zero
2915 extended, truncated, or unchanged to make it fit in a pointer size.
2916 This one is *really* dangerous!
2917 ``bitcast (CST to TYPE)``
2918 Convert a constant, CST, to another TYPE. The constraints of the
2919 operands are the same as those for the :ref:`bitcast
2920 instruction <i_bitcast>`.
2921 ``addrspacecast (CST to TYPE)``
2922 Convert a constant pointer or constant vector of pointer, CST, to another
2923 TYPE in a different address space. The constraints of the operands are the
2924 same as those for the :ref:`addrspacecast instruction <i_addrspacecast>`.
2925 ``getelementptr (TY, CSTPTR, IDX0, IDX1, ...)``, ``getelementptr inbounds (TY, CSTPTR, IDX0, IDX1, ...)``
2926 Perform the :ref:`getelementptr operation <i_getelementptr>` on
2927 constants. As with the :ref:`getelementptr <i_getelementptr>`
2928 instruction, the index list may have zero or more indexes, which are
2929 required to make sense for the type of "pointer to TY".
2930 ``select (COND, VAL1, VAL2)``
2931 Perform the :ref:`select operation <i_select>` on constants.
2932 ``icmp COND (VAL1, VAL2)``
2933 Performs the :ref:`icmp operation <i_icmp>` on constants.
2934 ``fcmp COND (VAL1, VAL2)``
2935 Performs the :ref:`fcmp operation <i_fcmp>` on constants.
2936 ``extractelement (VAL, IDX)``
2937 Perform the :ref:`extractelement operation <i_extractelement>` on
2939 ``insertelement (VAL, ELT, IDX)``
2940 Perform the :ref:`insertelement operation <i_insertelement>` on
2942 ``shufflevector (VEC1, VEC2, IDXMASK)``
2943 Perform the :ref:`shufflevector operation <i_shufflevector>` on
2945 ``extractvalue (VAL, IDX0, IDX1, ...)``
2946 Perform the :ref:`extractvalue operation <i_extractvalue>` on
2947 constants. The index list is interpreted in a similar manner as
2948 indices in a ':ref:`getelementptr <i_getelementptr>`' operation. At
2949 least one index value must be specified.
2950 ``insertvalue (VAL, ELT, IDX0, IDX1, ...)``
2951 Perform the :ref:`insertvalue operation <i_insertvalue>` on constants.
2952 The index list is interpreted in a similar manner as indices in a
2953 ':ref:`getelementptr <i_getelementptr>`' operation. At least one index
2954 value must be specified.
2955 ``OPCODE (LHS, RHS)``
2956 Perform the specified operation of the LHS and RHS constants. OPCODE
2957 may be any of the :ref:`binary <binaryops>` or :ref:`bitwise
2958 binary <bitwiseops>` operations. The constraints on operands are
2959 the same as those for the corresponding instruction (e.g. no bitwise
2960 operations on floating point values are allowed).
2967 Inline Assembler Expressions
2968 ----------------------------
2970 LLVM supports inline assembler expressions (as opposed to :ref:`Module-Level
2971 Inline Assembly <moduleasm>`) through the use of a special value. This value
2972 represents the inline assembler as a template string (containing the
2973 instructions to emit), a list of operand constraints (stored as a string), a
2974 flag that indicates whether or not the inline asm expression has side effects,
2975 and a flag indicating whether the function containing the asm needs to align its
2976 stack conservatively.
2978 The template string supports argument substitution of the operands using "``$``"
2979 followed by a number, to indicate substitution of the given register/memory
2980 location, as specified by the constraint string. "``${NUM:MODIFIER}``" may also
2981 be used, where ``MODIFIER`` is a target-specific annotation for how to print the
2982 operand (See :ref:`inline-asm-modifiers`).
2984 A literal "``$``" may be included by using "``$$``" in the template. To include
2985 other special characters into the output, the usual "``\XX``" escapes may be
2986 used, just as in other strings. Note that after template substitution, the
2987 resulting assembly string is parsed by LLVM's integrated assembler unless it is
2988 disabled -- even when emitting a ``.s`` file -- and thus must contain assembly
2989 syntax known to LLVM.
2991 LLVM's support for inline asm is modeled closely on the requirements of Clang's
2992 GCC-compatible inline-asm support. Thus, the feature-set and the constraint and
2993 modifier codes listed here are similar or identical to those in GCC's inline asm
2994 support. However, to be clear, the syntax of the template and constraint strings
2995 described here is *not* the same as the syntax accepted by GCC and Clang, and,
2996 while most constraint letters are passed through as-is by Clang, some get
2997 translated to other codes when converting from the C source to the LLVM
3000 An example inline assembler expression is:
3002 .. code-block:: llvm
3004 i32 (i32) asm "bswap $0", "=r,r"
3006 Inline assembler expressions may **only** be used as the callee operand
3007 of a :ref:`call <i_call>` or an :ref:`invoke <i_invoke>` instruction.
3008 Thus, typically we have:
3010 .. code-block:: llvm
3012 %X = call i32 asm "bswap $0", "=r,r"(i32 %Y)
3014 Inline asms with side effects not visible in the constraint list must be
3015 marked as having side effects. This is done through the use of the
3016 '``sideeffect``' keyword, like so:
3018 .. code-block:: llvm
3020 call void asm sideeffect "eieio", ""()
3022 In some cases inline asms will contain code that will not work unless
3023 the stack is aligned in some way, such as calls or SSE instructions on
3024 x86, yet will not contain code that does that alignment within the asm.
3025 The compiler should make conservative assumptions about what the asm
3026 might contain and should generate its usual stack alignment code in the
3027 prologue if the '``alignstack``' keyword is present:
3029 .. code-block:: llvm
3031 call void asm alignstack "eieio", ""()
3033 Inline asms also support using non-standard assembly dialects. The
3034 assumed dialect is ATT. When the '``inteldialect``' keyword is present,
3035 the inline asm is using the Intel dialect. Currently, ATT and Intel are
3036 the only supported dialects. An example is:
3038 .. code-block:: llvm
3040 call void asm inteldialect "eieio", ""()
3042 If multiple keywords appear the '``sideeffect``' keyword must come
3043 first, the '``alignstack``' keyword second and the '``inteldialect``'
3046 Inline Asm Constraint String
3047 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
3049 The constraint list is a comma-separated string, each element containing one or
3050 more constraint codes.
3052 For each element in the constraint list an appropriate register or memory
3053 operand will be chosen, and it will be made available to assembly template
3054 string expansion as ``$0`` for the first constraint in the list, ``$1`` for the
3057 There are three different types of constraints, which are distinguished by a
3058 prefix symbol in front of the constraint code: Output, Input, and Clobber. The
3059 constraints must always be given in that order: outputs first, then inputs, then
3060 clobbers. They cannot be intermingled.
3062 There are also three different categories of constraint codes:
3064 - Register constraint. This is either a register class, or a fixed physical
3065 register. This kind of constraint will allocate a register, and if necessary,
3066 bitcast the argument or result to the appropriate type.
3067 - Memory constraint. This kind of constraint is for use with an instruction
3068 taking a memory operand. Different constraints allow for different addressing
3069 modes used by the target.
3070 - Immediate value constraint. This kind of constraint is for an integer or other
3071 immediate value which can be rendered directly into an instruction. The
3072 various target-specific constraints allow the selection of a value in the
3073 proper range for the instruction you wish to use it with.
3078 Output constraints are specified by an "``=``" prefix (e.g. "``=r``"). This
3079 indicates that the assembly will write to this operand, and the operand will
3080 then be made available as a return value of the ``asm`` expression. Output
3081 constraints do not consume an argument from the call instruction. (Except, see
3082 below about indirect outputs).
3084 Normally, it is expected that no output locations are written to by the assembly
3085 expression until *all* of the inputs have been read. As such, LLVM may assign
3086 the same register to an output and an input. If this is not safe (e.g. if the
3087 assembly contains two instructions, where the first writes to one output, and
3088 the second reads an input and writes to a second output), then the "``&``"
3089 modifier must be used (e.g. "``=&r``") to specify that the output is an
3090 "early-clobber" output. Marking an ouput as "early-clobber" ensures that LLVM
3091 will not use the same register for any inputs (other than an input tied to this
3097 Input constraints do not have a prefix -- just the constraint codes. Each input
3098 constraint will consume one argument from the call instruction. It is not
3099 permitted for the asm to write to any input register or memory location (unless
3100 that input is tied to an output). Note also that multiple inputs may all be
3101 assigned to the same register, if LLVM can determine that they necessarily all
3102 contain the same value.
3104 Instead of providing a Constraint Code, input constraints may also "tie"
3105 themselves to an output constraint, by providing an integer as the constraint
3106 string. Tied inputs still consume an argument from the call instruction, and
3107 take up a position in the asm template numbering as is usual -- they will simply
3108 be constrained to always use the same register as the output they've been tied
3109 to. For example, a constraint string of "``=r,0``" says to assign a register for
3110 output, and use that register as an input as well (it being the 0'th
3113 It is permitted to tie an input to an "early-clobber" output. In that case, no
3114 *other* input may share the same register as the input tied to the early-clobber
3115 (even when the other input has the same value).
3117 You may only tie an input to an output which has a register constraint, not a
3118 memory constraint. Only a single input may be tied to an output.
3120 There is also an "interesting" feature which deserves a bit of explanation: if a
3121 register class constraint allocates a register which is too small for the value
3122 type operand provided as input, the input value will be split into multiple
3123 registers, and all of them passed to the inline asm.
3125 However, this feature is often not as useful as you might think.
3127 Firstly, the registers are *not* guaranteed to be consecutive. So, on those
3128 architectures that have instructions which operate on multiple consecutive
3129 instructions, this is not an appropriate way to support them. (e.g. the 32-bit
3130 SparcV8 has a 64-bit load, which instruction takes a single 32-bit register. The
3131 hardware then loads into both the named register, and the next register. This
3132 feature of inline asm would not be useful to support that.)
3134 A few of the targets provide a template string modifier allowing explicit access
3135 to the second register of a two-register operand (e.g. MIPS ``L``, ``M``, and
3136 ``D``). On such an architecture, you can actually access the second allocated
3137 register (yet, still, not any subsequent ones). But, in that case, you're still
3138 probably better off simply splitting the value into two separate operands, for
3139 clarity. (e.g. see the description of the ``A`` constraint on X86, which,
3140 despite existing only for use with this feature, is not really a good idea to
3143 Indirect inputs and outputs
3144 """""""""""""""""""""""""""
3146 Indirect output or input constraints can be specified by the "``*``" modifier
3147 (which goes after the "``=``" in case of an output). This indicates that the asm
3148 will write to or read from the contents of an *address* provided as an input
3149 argument. (Note that in this way, indirect outputs act more like an *input* than
3150 an output: just like an input, they consume an argument of the call expression,
3151 rather than producing a return value. An indirect output constraint is an
3152 "output" only in that the asm is expected to write to the contents of the input
3153 memory location, instead of just read from it).
3155 This is most typically used for memory constraint, e.g. "``=*m``", to pass the
3156 address of a variable as a value.
3158 It is also possible to use an indirect *register* constraint, but only on output
3159 (e.g. "``=*r``"). This will cause LLVM to allocate a register for an output
3160 value normally, and then, separately emit a store to the address provided as
3161 input, after the provided inline asm. (It's not clear what value this
3162 functionality provides, compared to writing the store explicitly after the asm
3163 statement, and it can only produce worse code, since it bypasses many
3164 optimization passes. I would recommend not using it.)
3170 A clobber constraint is indicated by a "``~``" prefix. A clobber does not
3171 consume an input operand, nor generate an output. Clobbers cannot use any of the
3172 general constraint code letters -- they may use only explicit register
3173 constraints, e.g. "``~{eax}``". The one exception is that a clobber string of
3174 "``~{memory}``" indicates that the assembly writes to arbitrary undeclared
3175 memory locations -- not only the memory pointed to by a declared indirect
3181 After a potential prefix comes constraint code, or codes.
3183 A Constraint Code is either a single letter (e.g. "``r``"), a "``^``" character
3184 followed by two letters (e.g. "``^wc``"), or "``{``" register-name "``}``"
3187 The one and two letter constraint codes are typically chosen to be the same as
3188 GCC's constraint codes.
3190 A single constraint may include one or more than constraint code in it, leaving
3191 it up to LLVM to choose which one to use. This is included mainly for
3192 compatibility with the translation of GCC inline asm coming from clang.
3194 There are two ways to specify alternatives, and either or both may be used in an
3195 inline asm constraint list:
3197 1) Append the codes to each other, making a constraint code set. E.g. "``im``"
3198 or "``{eax}m``". This means "choose any of the options in the set". The
3199 choice of constraint is made independently for each constraint in the
3202 2) Use "``|``" between constraint code sets, creating alternatives. Every
3203 constraint in the constraint list must have the same number of alternative
3204 sets. With this syntax, the same alternative in *all* of the items in the
3205 constraint list will be chosen together.
3207 Putting those together, you might have a two operand constraint string like
3208 ``"rm|r,ri|rm"``. This indicates that if operand 0 is ``r`` or ``m``, then
3209 operand 1 may be one of ``r`` or ``i``. If operand 0 is ``r``, then operand 1
3210 may be one of ``r`` or ``m``. But, operand 0 and 1 cannot both be of type m.
3212 However, the use of either of the alternatives features is *NOT* recommended, as
3213 LLVM is not able to make an intelligent choice about which one to use. (At the
3214 point it currently needs to choose, not enough information is available to do so
3215 in a smart way.) Thus, it simply tries to make a choice that's most likely to
3216 compile, not one that will be optimal performance. (e.g., given "``rm``", it'll
3217 always choose to use memory, not registers). And, if given multiple registers,
3218 or multiple register classes, it will simply choose the first one. (In fact, it
3219 doesn't currently even ensure explicitly specified physical registers are
3220 unique, so specifying multiple physical registers as alternatives, like
3221 ``{r11}{r12},{r11}{r12}``, will assign r11 to both operands, not at all what was
3224 Supported Constraint Code List
3225 """"""""""""""""""""""""""""""
3227 The constraint codes are, in general, expected to behave the same way they do in
3228 GCC. LLVM's support is often implemented on an 'as-needed' basis, to support C
3229 inline asm code which was supported by GCC. A mismatch in behavior between LLVM
3230 and GCC likely indicates a bug in LLVM.
3232 Some constraint codes are typically supported by all targets:
3234 - ``r``: A register in the target's general purpose register class.
3235 - ``m``: A memory address operand. It is target-specific what addressing modes
3236 are supported, typical examples are register, or register + register offset,
3237 or register + immediate offset (of some target-specific size).
3238 - ``i``: An integer constant (of target-specific width). Allows either a simple
3239 immediate, or a relocatable value.
3240 - ``n``: An integer constant -- *not* including relocatable values.
3241 - ``s``: An integer constant, but allowing *only* relocatable values.
3242 - ``X``: Allows an operand of any kind, no constraint whatsoever. Typically
3243 useful to pass a label for an asm branch or call.
3245 .. FIXME: but that surely isn't actually okay to jump out of an asm
3246 block without telling llvm about the control transfer???)
3248 - ``{register-name}``: Requires exactly the named physical register.
3250 Other constraints are target-specific:
3254 - ``z``: An immediate integer 0. Outputs ``WZR`` or ``XZR``, as appropriate.
3255 - ``I``: An immediate integer valid for an ``ADD`` or ``SUB`` instruction,
3256 i.e. 0 to 4095 with optional shift by 12.
3257 - ``J``: An immediate integer that, when negated, is valid for an ``ADD`` or
3258 ``SUB`` instruction, i.e. -1 to -4095 with optional left shift by 12.
3259 - ``K``: An immediate integer that is valid for the 'bitmask immediate 32' of a
3260 logical instruction like ``AND``, ``EOR``, or ``ORR`` with a 32-bit register.
3261 - ``L``: An immediate integer that is valid for the 'bitmask immediate 64' of a
3262 logical instruction like ``AND``, ``EOR``, or ``ORR`` with a 64-bit register.
3263 - ``M``: An immediate integer for use with the ``MOV`` assembly alias on a
3264 32-bit register. This is a superset of ``K``: in addition to the bitmask
3265 immediate, also allows immediate integers which can be loaded with a single
3266 ``MOVZ`` or ``MOVL`` instruction.
3267 - ``N``: An immediate integer for use with the ``MOV`` assembly alias on a
3268 64-bit register. This is a superset of ``L``.
3269 - ``Q``: Memory address operand must be in a single register (no
3270 offsets). (However, LLVM currently does this for the ``m`` constraint as
3272 - ``r``: A 32 or 64-bit integer register (W* or X*).
3273 - ``w``: A 32, 64, or 128-bit floating-point/SIMD register.
3274 - ``x``: A lower 128-bit floating-point/SIMD register (``V0`` to ``V15``).
3278 - ``r``: A 32 or 64-bit integer register.
3279 - ``[0-9]v``: The 32-bit VGPR register, number 0-9.
3280 - ``[0-9]s``: The 32-bit SGPR register, number 0-9.
3285 - ``Q``, ``Um``, ``Un``, ``Uq``, ``Us``, ``Ut``, ``Uv``, ``Uy``: Memory address
3286 operand. Treated the same as operand ``m``, at the moment.
3288 ARM and ARM's Thumb2 mode:
3290 - ``j``: An immediate integer between 0 and 65535 (valid for ``MOVW``)
3291 - ``I``: An immediate integer valid for a data-processing instruction.
3292 - ``J``: An immediate integer between -4095 and 4095.
3293 - ``K``: An immediate integer whose bitwise inverse is valid for a
3294 data-processing instruction. (Can be used with template modifier "``B``" to
3295 print the inverted value).
3296 - ``L``: An immediate integer whose negation is valid for a data-processing
3297 instruction. (Can be used with template modifier "``n``" to print the negated
3299 - ``M``: A power of two or a integer between 0 and 32.
3300 - ``N``: Invalid immediate constraint.
3301 - ``O``: Invalid immediate constraint.
3302 - ``r``: A general-purpose 32-bit integer register (``r0-r15``).
3303 - ``l``: In Thumb2 mode, low 32-bit GPR registers (``r0-r7``). In ARM mode, same
3305 - ``h``: In Thumb2 mode, a high 32-bit GPR register (``r8-r15``). In ARM mode,
3307 - ``w``: A 32, 64, or 128-bit floating-point/SIMD register: ``s0-s31``,
3308 ``d0-d31``, or ``q0-q15``.
3309 - ``x``: A 32, 64, or 128-bit floating-point/SIMD register: ``s0-s15``,
3310 ``d0-d7``, or ``q0-q3``.
3311 - ``t``: A floating-point/SIMD register, only supports 32-bit values:
3316 - ``I``: An immediate integer between 0 and 255.
3317 - ``J``: An immediate integer between -255 and -1.
3318 - ``K``: An immediate integer between 0 and 255, with optional left-shift by
3320 - ``L``: An immediate integer between -7 and 7.
3321 - ``M``: An immediate integer which is a multiple of 4 between 0 and 1020.
3322 - ``N``: An immediate integer between 0 and 31.
3323 - ``O``: An immediate integer which is a multiple of 4 between -508 and 508.
3324 - ``r``: A low 32-bit GPR register (``r0-r7``).
3325 - ``l``: A low 32-bit GPR register (``r0-r7``).
3326 - ``h``: A high GPR register (``r0-r7``).
3327 - ``w``: A 32, 64, or 128-bit floating-point/SIMD register: ``s0-s31``,
3328 ``d0-d31``, or ``q0-q15``.
3329 - ``x``: A 32, 64, or 128-bit floating-point/SIMD register: ``s0-s15``,
3330 ``d0-d7``, or ``q0-q3``.
3331 - ``t``: A floating-point/SIMD register, only supports 32-bit values:
3337 - ``o``, ``v``: A memory address operand, treated the same as constraint ``m``,
3339 - ``r``: A 32 or 64-bit register.
3343 - ``r``: An 8 or 16-bit register.
3347 - ``I``: An immediate signed 16-bit integer.
3348 - ``J``: An immediate integer zero.
3349 - ``K``: An immediate unsigned 16-bit integer.
3350 - ``L``: An immediate 32-bit integer, where the lower 16 bits are 0.
3351 - ``N``: An immediate integer between -65535 and -1.
3352 - ``O``: An immediate signed 15-bit integer.
3353 - ``P``: An immediate integer between 1 and 65535.
3354 - ``m``: A memory address operand. In MIPS-SE mode, allows a base address
3355 register plus 16-bit immediate offset. In MIPS mode, just a base register.
3356 - ``R``: A memory address operand. In MIPS-SE mode, allows a base address
3357 register plus a 9-bit signed offset. In MIPS mode, the same as constraint
3359 - ``ZC``: A memory address operand, suitable for use in a ``pref``, ``ll``, or
3360 ``sc`` instruction on the given subtarget (details vary).
3361 - ``r``, ``d``, ``y``: A 32 or 64-bit GPR register.
3362 - ``f``: A 32 or 64-bit FPU register (``F0-F31``), or a 128-bit MSA register
3363 (``W0-W31``). In the case of MSA registers, it is recommended to use the ``w``
3364 argument modifier for compatibility with GCC.
3365 - ``c``: A 32-bit or 64-bit GPR register suitable for indirect jump (always
3367 - ``l``: The ``lo`` register, 32 or 64-bit.
3372 - ``b``: A 1-bit integer register.
3373 - ``c`` or ``h``: A 16-bit integer register.
3374 - ``r``: A 32-bit integer register.
3375 - ``l`` or ``N``: A 64-bit integer register.
3376 - ``f``: A 32-bit float register.
3377 - ``d``: A 64-bit float register.
3382 - ``I``: An immediate signed 16-bit integer.
3383 - ``J``: An immediate unsigned 16-bit integer, shifted left 16 bits.
3384 - ``K``: An immediate unsigned 16-bit integer.
3385 - ``L``: An immediate signed 16-bit integer, shifted left 16 bits.
3386 - ``M``: An immediate integer greater than 31.
3387 - ``N``: An immediate integer that is an exact power of 2.
3388 - ``O``: The immediate integer constant 0.
3389 - ``P``: An immediate integer constant whose negation is a signed 16-bit
3391 - ``es``, ``o``, ``Q``, ``Z``, ``Zy``: A memory address operand, currently
3392 treated the same as ``m``.
3393 - ``r``: A 32 or 64-bit integer register.
3394 - ``b``: A 32 or 64-bit integer register, excluding ``R0`` (that is:
3396 - ``f``: A 32 or 64-bit float register (``F0-F31``), or when QPX is enabled, a
3397 128 or 256-bit QPX register (``Q0-Q31``; aliases the ``F`` registers).
3398 - ``v``: For ``4 x f32`` or ``4 x f64`` types, when QPX is enabled, a
3399 128 or 256-bit QPX register (``Q0-Q31``), otherwise a 128-bit
3400 altivec vector register (``V0-V31``).
3402 .. FIXME: is this a bug that v accepts QPX registers? I think this
3403 is supposed to only use the altivec vector registers?
3405 - ``y``: Condition register (``CR0-CR7``).
3406 - ``wc``: An individual CR bit in a CR register.
3407 - ``wa``, ``wd``, ``wf``: Any 128-bit VSX vector register, from the full VSX
3408 register set (overlapping both the floating-point and vector register files).
3409 - ``ws``: A 32 or 64-bit floating point register, from the full VSX register
3414 - ``I``: An immediate 13-bit signed integer.
3415 - ``r``: A 32-bit integer register.
3419 - ``I``: An immediate unsigned 8-bit integer.
3420 - ``J``: An immediate unsigned 12-bit integer.
3421 - ``K``: An immediate signed 16-bit integer.
3422 - ``L``: An immediate signed 20-bit integer.
3423 - ``M``: An immediate integer 0x7fffffff.
3424 - ``Q``, ``R``, ``S``, ``T``: A memory address operand, treated the same as
3425 ``m``, at the moment.
3426 - ``r`` or ``d``: A 32, 64, or 128-bit integer register.
3427 - ``a``: A 32, 64, or 128-bit integer address register (excludes R0, which in an
3428 address context evaluates as zero).
3429 - ``h``: A 32-bit value in the high part of a 64bit data register
3431 - ``f``: A 32, 64, or 128-bit floating point register.
3435 - ``I``: An immediate integer between 0 and 31.
3436 - ``J``: An immediate integer between 0 and 64.
3437 - ``K``: An immediate signed 8-bit integer.
3438 - ``L``: An immediate integer, 0xff or 0xffff or (in 64-bit mode only)
3440 - ``M``: An immediate integer between 0 and 3.
3441 - ``N``: An immediate unsigned 8-bit integer.
3442 - ``O``: An immediate integer between 0 and 127.
3443 - ``e``: An immediate 32-bit signed integer.
3444 - ``Z``: An immediate 32-bit unsigned integer.
3445 - ``o``, ``v``: Treated the same as ``m``, at the moment.
3446 - ``q``: An 8, 16, 32, or 64-bit register which can be accessed as an 8-bit
3447 ``l`` integer register. On X86-32, this is the ``a``, ``b``, ``c``, and ``d``
3448 registers, and on X86-64, it is all of the integer registers.
3449 - ``Q``: An 8, 16, 32, or 64-bit register which can be accessed as an 8-bit
3450 ``h`` integer register. This is the ``a``, ``b``, ``c``, and ``d`` registers.
3451 - ``r`` or ``l``: An 8, 16, 32, or 64-bit integer register.
3452 - ``R``: An 8, 16, 32, or 64-bit "legacy" integer register -- one which has
3453 existed since i386, and can be accessed without the REX prefix.
3454 - ``f``: A 32, 64, or 80-bit '387 FPU stack pseudo-register.
3455 - ``y``: A 64-bit MMX register, if MMX is enabled.
3456 - ``x``: If SSE is enabled: a 32 or 64-bit scalar operand, or 128-bit vector
3457 operand in a SSE register. If AVX is also enabled, can also be a 256-bit
3458 vector operand in an AVX register. If AVX-512 is also enabled, can also be a
3459 512-bit vector operand in an AVX512 register, Otherwise, an error.
3460 - ``Y``: The same as ``x``, if *SSE2* is enabled, otherwise an error.
3461 - ``A``: Special case: allocates EAX first, then EDX, for a single operand (in
3462 32-bit mode, a 64-bit integer operand will get split into two registers). It
3463 is not recommended to use this constraint, as in 64-bit mode, the 64-bit
3464 operand will get allocated only to RAX -- if two 32-bit operands are needed,
3465 you're better off splitting it yourself, before passing it to the asm
3470 - ``r``: A 32-bit integer register.
3473 .. _inline-asm-modifiers:
3475 Asm template argument modifiers
3476 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
3478 In the asm template string, modifiers can be used on the operand reference, like
3481 The modifiers are, in general, expected to behave the same way they do in
3482 GCC. LLVM's support is often implemented on an 'as-needed' basis, to support C
3483 inline asm code which was supported by GCC. A mismatch in behavior between LLVM
3484 and GCC likely indicates a bug in LLVM.
3488 - ``c``: Print an immediate integer constant unadorned, without
3489 the target-specific immediate punctuation (e.g. no ``$`` prefix).
3490 - ``n``: Negate and print immediate integer constant unadorned, without the
3491 target-specific immediate punctuation (e.g. no ``$`` prefix).
3492 - ``l``: Print as an unadorned label, without the target-specific label
3493 punctuation (e.g. no ``$`` prefix).
3497 - ``w``: Print a GPR register with a ``w*`` name instead of ``x*`` name. E.g.,
3498 instead of ``x30``, print ``w30``.
3499 - ``x``: Print a GPR register with a ``x*`` name. (this is the default, anyhow).
3500 - ``b``, ``h``, ``s``, ``d``, ``q``: Print a floating-point/SIMD register with a
3501 ``b*``, ``h*``, ``s*``, ``d*``, or ``q*`` name, rather than the default of
3510 - ``a``: Print an operand as an address (with ``[`` and ``]`` surrounding a
3514 - ``y``: Print a VFP single-precision register as an indexed double (e.g. print
3515 as ``d4[1]`` instead of ``s9``)
3516 - ``B``: Bitwise invert and print an immediate integer constant without ``#``
3518 - ``L``: Print the low 16-bits of an immediate integer constant.
3519 - ``M``: Print as a register set suitable for ldm/stm. Also prints *all*
3520 register operands subsequent to the specified one (!), so use carefully.
3521 - ``Q``: Print the low-order register of a register-pair, or the low-order
3522 register of a two-register operand.
3523 - ``R``: Print the high-order register of a register-pair, or the high-order
3524 register of a two-register operand.
3525 - ``H``: Print the second register of a register-pair. (On a big-endian system,
3526 ``H`` is equivalent to ``Q``, and on little-endian system, ``H`` is equivalent
3529 .. FIXME: H doesn't currently support printing the second register
3530 of a two-register operand.
3532 - ``e``: Print the low doubleword register of a NEON quad register.
3533 - ``f``: Print the high doubleword register of a NEON quad register.
3534 - ``m``: Print the base register of a memory operand without the ``[`` and ``]``
3539 - ``L``: Print the second register of a two-register operand. Requires that it
3540 has been allocated consecutively to the first.
3542 .. FIXME: why is it restricted to consecutive ones? And there's
3543 nothing that ensures that happens, is there?
3545 - ``I``: Print the letter 'i' if the operand is an integer constant, otherwise
3546 nothing. Used to print 'addi' vs 'add' instructions.
3550 No additional modifiers.
3554 - ``X``: Print an immediate integer as hexadecimal
3555 - ``x``: Print the low 16 bits of an immediate integer as hexadecimal.
3556 - ``d``: Print an immediate integer as decimal.
3557 - ``m``: Subtract one and print an immediate integer as decimal.
3558 - ``z``: Print $0 if an immediate zero, otherwise print normally.
3559 - ``L``: Print the low-order register of a two-register operand, or prints the
3560 address of the low-order word of a double-word memory operand.
3562 .. FIXME: L seems to be missing memory operand support.
3564 - ``M``: Print the high-order register of a two-register operand, or prints the
3565 address of the high-order word of a double-word memory operand.
3567 .. FIXME: M seems to be missing memory operand support.
3569 - ``D``: Print the second register of a two-register operand, or prints the
3570 second word of a double-word memory operand. (On a big-endian system, ``D`` is
3571 equivalent to ``L``, and on little-endian system, ``D`` is equivalent to
3573 - ``w``: No effect. Provided for compatibility with GCC which requires this
3574 modifier in order to print MSA registers (``W0-W31``) with the ``f``
3583 - ``L``: Print the second register of a two-register operand. Requires that it
3584 has been allocated consecutively to the first.
3586 .. FIXME: why is it restricted to consecutive ones? And there's
3587 nothing that ensures that happens, is there?
3589 - ``I``: Print the letter 'i' if the operand is an integer constant, otherwise
3590 nothing. Used to print 'addi' vs 'add' instructions.
3591 - ``y``: For a memory operand, prints formatter for a two-register X-form
3592 instruction. (Currently always prints ``r0,OPERAND``).
3593 - ``U``: Prints 'u' if the memory operand is an update form, and nothing
3594 otherwise. (NOTE: LLVM does not support update form, so this will currently
3595 always print nothing)
3596 - ``X``: Prints 'x' if the memory operand is an indexed form. (NOTE: LLVM does
3597 not support indexed form, so this will currently always print nothing)
3605 SystemZ implements only ``n``, and does *not* support any of the other
3606 target-independent modifiers.
3610 - ``c``: Print an unadorned integer or symbol name. (The latter is
3611 target-specific behavior for this typically target-independent modifier).
3612 - ``A``: Print a register name with a '``*``' before it.
3613 - ``b``: Print an 8-bit register name (e.g. ``al``); do nothing on a memory
3615 - ``h``: Print the upper 8-bit register name (e.g. ``ah``); do nothing on a
3617 - ``w``: Print the 16-bit register name (e.g. ``ax``); do nothing on a memory
3619 - ``k``: Print the 32-bit register name (e.g. ``eax``); do nothing on a memory
3621 - ``q``: Print the 64-bit register name (e.g. ``rax``), if 64-bit registers are
3622 available, otherwise the 32-bit register name; do nothing on a memory operand.
3623 - ``n``: Negate and print an unadorned integer, or, for operands other than an
3624 immediate integer (e.g. a relocatable symbol expression), print a '-' before
3625 the operand. (The behavior for relocatable symbol expressions is a
3626 target-specific behavior for this typically target-independent modifier)
3627 - ``H``: Print a memory reference with additional offset +8.
3628 - ``P``: Print a memory reference or operand for use as the argument of a call
3629 instruction. (E.g. omit ``(rip)``, even though it's PC-relative.)
3633 No additional modifiers.
3639 The call instructions that wrap inline asm nodes may have a
3640 "``!srcloc``" MDNode attached to it that contains a list of constant
3641 integers. If present, the code generator will use the integer as the
3642 location cookie value when report errors through the ``LLVMContext``
3643 error reporting mechanisms. This allows a front-end to correlate backend
3644 errors that occur with inline asm back to the source code that produced
3647 .. code-block:: llvm
3649 call void asm sideeffect "something bad", ""(), !srcloc !42
3651 !42 = !{ i32 1234567 }
3653 It is up to the front-end to make sense of the magic numbers it places
3654 in the IR. If the MDNode contains multiple constants, the code generator
3655 will use the one that corresponds to the line of the asm that the error
3663 LLVM IR allows metadata to be attached to instructions in the program
3664 that can convey extra information about the code to the optimizers and
3665 code generator. One example application of metadata is source-level
3666 debug information. There are two metadata primitives: strings and nodes.
3668 Metadata does not have a type, and is not a value. If referenced from a
3669 ``call`` instruction, it uses the ``metadata`` type.
3671 All metadata are identified in syntax by a exclamation point ('``!``').
3673 .. _metadata-string:
3675 Metadata Nodes and Metadata Strings
3676 -----------------------------------
3678 A metadata string is a string surrounded by double quotes. It can
3679 contain any character by escaping non-printable characters with
3680 "``\xx``" where "``xx``" is the two digit hex code. For example:
3683 Metadata nodes are represented with notation similar to structure
3684 constants (a comma separated list of elements, surrounded by braces and
3685 preceded by an exclamation point). Metadata nodes can have any values as
3686 their operand. For example:
3688 .. code-block:: llvm
3690 !{ !"test\00", i32 10}
3692 Metadata nodes that aren't uniqued use the ``distinct`` keyword. For example:
3694 .. code-block:: llvm
3696 !0 = distinct !{!"test\00", i32 10}
3698 ``distinct`` nodes are useful when nodes shouldn't be merged based on their
3699 content. They can also occur when transformations cause uniquing collisions
3700 when metadata operands change.
3702 A :ref:`named metadata <namedmetadatastructure>` is a collection of
3703 metadata nodes, which can be looked up in the module symbol table. For
3706 .. code-block:: llvm
3710 Metadata can be used as function arguments. Here ``llvm.dbg.value``
3711 function is using two metadata arguments:
3713 .. code-block:: llvm
3715 call void @llvm.dbg.value(metadata !24, i64 0, metadata !25)
3717 Metadata can be attached to an instruction. Here metadata ``!21`` is attached
3718 to the ``add`` instruction using the ``!dbg`` identifier:
3720 .. code-block:: llvm
3722 %indvar.next = add i64 %indvar, 1, !dbg !21
3724 Metadata can also be attached to a function definition. Here metadata ``!22``
3725 is attached to the ``foo`` function using the ``!dbg`` identifier:
3727 .. code-block:: llvm
3729 define void @foo() !dbg !22 {
3733 More information about specific metadata nodes recognized by the
3734 optimizers and code generator is found below.
3736 .. _specialized-metadata:
3738 Specialized Metadata Nodes
3739 ^^^^^^^^^^^^^^^^^^^^^^^^^^
3741 Specialized metadata nodes are custom data structures in metadata (as opposed
3742 to generic tuples). Their fields are labelled, and can be specified in any
3745 These aren't inherently debug info centric, but currently all the specialized
3746 metadata nodes are related to debug info.
3753 ``DICompileUnit`` nodes represent a compile unit. The ``enums:``,
3754 ``retainedTypes:``, ``subprograms:``, ``globals:``, ``imports:`` and ``macros:``
3755 fields are tuples containing the debug info to be emitted along with the compile
3756 unit, regardless of code optimizations (some nodes are only emitted if there are
3757 references to them from instructions).
3759 .. code-block:: llvm
3761 !0 = !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang",
3762 isOptimized: true, flags: "-O2", runtimeVersion: 2,
3763 splitDebugFilename: "abc.debug", emissionKind: 1,
3764 enums: !2, retainedTypes: !3, subprograms: !4,
3765 globals: !5, imports: !6, macros: !7, dwoId: 0x0abcd)
3767 Compile unit descriptors provide the root scope for objects declared in a
3768 specific compilation unit. File descriptors are defined using this scope.
3769 These descriptors are collected by a named metadata ``!llvm.dbg.cu``. They
3770 keep track of subprograms, global variables, type information, and imported
3771 entities (declarations and namespaces).
3778 ``DIFile`` nodes represent files. The ``filename:`` can include slashes.
3780 .. code-block:: llvm
3782 !0 = !DIFile(filename: "path/to/file", directory: "/path/to/dir")
3784 Files are sometimes used in ``scope:`` fields, and are the only valid target
3785 for ``file:`` fields.
3792 ``DIBasicType`` nodes represent primitive types, such as ``int``, ``bool`` and
3793 ``float``. ``tag:`` defaults to ``DW_TAG_base_type``.
3795 .. code-block:: llvm
3797 !0 = !DIBasicType(name: "unsigned char", size: 8, align: 8,
3798 encoding: DW_ATE_unsigned_char)
3799 !1 = !DIBasicType(tag: DW_TAG_unspecified_type, name: "decltype(nullptr)")
3801 The ``encoding:`` describes the details of the type. Usually it's one of the
3804 .. code-block:: llvm
3810 DW_ATE_signed_char = 6
3812 DW_ATE_unsigned_char = 8
3814 .. _DISubroutineType:
3819 ``DISubroutineType`` nodes represent subroutine types. Their ``types:`` field
3820 refers to a tuple; the first operand is the return type, while the rest are the
3821 types of the formal arguments in order. If the first operand is ``null``, that
3822 represents a function with no return value (such as ``void foo() {}`` in C++).
3824 .. code-block:: llvm
3826 !0 = !BasicType(name: "int", size: 32, align: 32, DW_ATE_signed)
3827 !1 = !BasicType(name: "char", size: 8, align: 8, DW_ATE_signed_char)
3828 !2 = !DISubroutineType(types: !{null, !0, !1}) ; void (int, char)
3835 ``DIDerivedType`` nodes represent types derived from other types, such as
3838 .. code-block:: llvm
3840 !0 = !DIBasicType(name: "unsigned char", size: 8, align: 8,
3841 encoding: DW_ATE_unsigned_char)
3842 !1 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !0, size: 32,
3845 The following ``tag:`` values are valid:
3847 .. code-block:: llvm
3849 DW_TAG_formal_parameter = 5
3851 DW_TAG_pointer_type = 15
3852 DW_TAG_reference_type = 16
3854 DW_TAG_ptr_to_member_type = 31
3855 DW_TAG_const_type = 38
3856 DW_TAG_volatile_type = 53
3857 DW_TAG_restrict_type = 55
3859 ``DW_TAG_member`` is used to define a member of a :ref:`composite type
3860 <DICompositeType>` or :ref:`subprogram <DISubprogram>`. The type of the member
3861 is the ``baseType:``. The ``offset:`` is the member's bit offset.
3862 ``DW_TAG_formal_parameter`` is used to define a member which is a formal
3863 argument of a subprogram.
3865 ``DW_TAG_typedef`` is used to provide a name for the ``baseType:``.
3867 ``DW_TAG_pointer_type``, ``DW_TAG_reference_type``, ``DW_TAG_const_type``,
3868 ``DW_TAG_volatile_type`` and ``DW_TAG_restrict_type`` are used to qualify the
3871 Note that the ``void *`` type is expressed as a type derived from NULL.
3873 .. _DICompositeType:
3878 ``DICompositeType`` nodes represent types composed of other types, like
3879 structures and unions. ``elements:`` points to a tuple of the composed types.
3881 If the source language supports ODR, the ``identifier:`` field gives the unique
3882 identifier used for type merging between modules. When specified, other types
3883 can refer to composite types indirectly via a :ref:`metadata string
3884 <metadata-string>` that matches their identifier.
3886 .. code-block:: llvm
3888 !0 = !DIEnumerator(name: "SixKind", value: 7)
3889 !1 = !DIEnumerator(name: "SevenKind", value: 7)
3890 !2 = !DIEnumerator(name: "NegEightKind", value: -8)
3891 !3 = !DICompositeType(tag: DW_TAG_enumeration_type, name: "Enum", file: !12,
3892 line: 2, size: 32, align: 32, identifier: "_M4Enum",
3893 elements: !{!0, !1, !2})
3895 The following ``tag:`` values are valid:
3897 .. code-block:: llvm
3899 DW_TAG_array_type = 1
3900 DW_TAG_class_type = 2
3901 DW_TAG_enumeration_type = 4
3902 DW_TAG_structure_type = 19
3903 DW_TAG_union_type = 23
3904 DW_TAG_subroutine_type = 21
3905 DW_TAG_inheritance = 28
3908 For ``DW_TAG_array_type``, the ``elements:`` should be :ref:`subrange
3909 descriptors <DISubrange>`, each representing the range of subscripts at that
3910 level of indexing. The ``DIFlagVector`` flag to ``flags:`` indicates that an
3911 array type is a native packed vector.
3913 For ``DW_TAG_enumeration_type``, the ``elements:`` should be :ref:`enumerator
3914 descriptors <DIEnumerator>`, each representing the definition of an enumeration
3915 value for the set. All enumeration type descriptors are collected in the
3916 ``enums:`` field of the :ref:`compile unit <DICompileUnit>`.
3918 For ``DW_TAG_structure_type``, ``DW_TAG_class_type``, and
3919 ``DW_TAG_union_type``, the ``elements:`` should be :ref:`derived types
3920 <DIDerivedType>` with ``tag: DW_TAG_member`` or ``tag: DW_TAG_inheritance``.
3927 ``DISubrange`` nodes are the elements for ``DW_TAG_array_type`` variants of
3928 :ref:`DICompositeType`. ``count: -1`` indicates an empty array.
3930 .. code-block:: llvm
3932 !0 = !DISubrange(count: 5, lowerBound: 0) ; array counting from 0
3933 !1 = !DISubrange(count: 5, lowerBound: 1) ; array counting from 1
3934 !2 = !DISubrange(count: -1) ; empty array.
3941 ``DIEnumerator`` nodes are the elements for ``DW_TAG_enumeration_type``
3942 variants of :ref:`DICompositeType`.
3944 .. code-block:: llvm
3946 !0 = !DIEnumerator(name: "SixKind", value: 7)
3947 !1 = !DIEnumerator(name: "SevenKind", value: 7)
3948 !2 = !DIEnumerator(name: "NegEightKind", value: -8)
3950 DITemplateTypeParameter
3951 """""""""""""""""""""""
3953 ``DITemplateTypeParameter`` nodes represent type parameters to generic source
3954 language constructs. They are used (optionally) in :ref:`DICompositeType` and
3955 :ref:`DISubprogram` ``templateParams:`` fields.
3957 .. code-block:: llvm
3959 !0 = !DITemplateTypeParameter(name: "Ty", type: !1)
3961 DITemplateValueParameter
3962 """"""""""""""""""""""""
3964 ``DITemplateValueParameter`` nodes represent value parameters to generic source
3965 language constructs. ``tag:`` defaults to ``DW_TAG_template_value_parameter``,
3966 but if specified can also be set to ``DW_TAG_GNU_template_template_param`` or
3967 ``DW_TAG_GNU_template_param_pack``. They are used (optionally) in
3968 :ref:`DICompositeType` and :ref:`DISubprogram` ``templateParams:`` fields.
3970 .. code-block:: llvm
3972 !0 = !DITemplateValueParameter(name: "Ty", type: !1, value: i32 7)
3977 ``DINamespace`` nodes represent namespaces in the source language.
3979 .. code-block:: llvm
3981 !0 = !DINamespace(name: "myawesomeproject", scope: !1, file: !2, line: 7)
3986 ``DIGlobalVariable`` nodes represent global variables in the source language.
3988 .. code-block:: llvm
3990 !0 = !DIGlobalVariable(name: "foo", linkageName: "foo", scope: !1,
3991 file: !2, line: 7, type: !3, isLocal: true,
3992 isDefinition: false, variable: i32* @foo,
3995 All global variables should be referenced by the `globals:` field of a
3996 :ref:`compile unit <DICompileUnit>`.
4003 ``DISubprogram`` nodes represent functions from the source language. A
4004 ``DISubprogram`` may be attached to a function definition using ``!dbg``
4005 metadata. The ``variables:`` field points at :ref:`variables <DILocalVariable>`
4006 that must be retained, even if their IR counterparts are optimized out of
4007 the IR. The ``type:`` field must point at an :ref:`DISubroutineType`.
4009 .. code-block:: llvm
4011 define void @_Z3foov() !dbg !0 {
4015 !0 = distinct !DISubprogram(name: "foo", linkageName: "_Zfoov", scope: !1,
4016 file: !2, line: 7, type: !3, isLocal: true,
4017 isDefinition: false, scopeLine: 8,
4019 virtuality: DW_VIRTUALITY_pure_virtual,
4020 virtualIndex: 10, flags: DIFlagPrototyped,
4021 isOptimized: true, templateParams: !5,
4022 declaration: !6, variables: !7)
4029 ``DILexicalBlock`` nodes describe nested blocks within a :ref:`subprogram
4030 <DISubprogram>`. The line number and column numbers are used to distinguish
4031 two lexical blocks at same depth. They are valid targets for ``scope:``
4034 .. code-block:: llvm
4036 !0 = distinct !DILexicalBlock(scope: !1, file: !2, line: 7, column: 35)
4038 Usually lexical blocks are ``distinct`` to prevent node merging based on
4041 .. _DILexicalBlockFile:
4046 ``DILexicalBlockFile`` nodes are used to discriminate between sections of a
4047 :ref:`lexical block <DILexicalBlock>`. The ``file:`` field can be changed to
4048 indicate textual inclusion, or the ``discriminator:`` field can be used to
4049 discriminate between control flow within a single block in the source language.
4051 .. code-block:: llvm
4053 !0 = !DILexicalBlock(scope: !3, file: !4, line: 7, column: 35)
4054 !1 = !DILexicalBlockFile(scope: !0, file: !4, discriminator: 0)
4055 !2 = !DILexicalBlockFile(scope: !0, file: !4, discriminator: 1)
4062 ``DILocation`` nodes represent source debug locations. The ``scope:`` field is
4063 mandatory, and points at an :ref:`DILexicalBlockFile`, an
4064 :ref:`DILexicalBlock`, or an :ref:`DISubprogram`.
4066 .. code-block:: llvm
4068 !0 = !DILocation(line: 2900, column: 42, scope: !1, inlinedAt: !2)
4070 .. _DILocalVariable:
4075 ``DILocalVariable`` nodes represent local variables in the source language. If
4076 the ``arg:`` field is set to non-zero, then this variable is a subprogram
4077 parameter, and it will be included in the ``variables:`` field of its
4078 :ref:`DISubprogram`.
4080 .. code-block:: llvm
4082 !0 = !DILocalVariable(name: "this", arg: 1, scope: !3, file: !2, line: 7,
4083 type: !3, flags: DIFlagArtificial)
4084 !1 = !DILocalVariable(name: "x", arg: 2, scope: !4, file: !2, line: 7,
4086 !2 = !DILocalVariable(name: "y", scope: !5, file: !2, line: 7, type: !3)
4091 ``DIExpression`` nodes represent DWARF expression sequences. They are used in
4092 :ref:`debug intrinsics<dbg_intrinsics>` (such as ``llvm.dbg.declare``) to
4093 describe how the referenced LLVM variable relates to the source language
4096 The current supported vocabulary is limited:
4098 - ``DW_OP_deref`` dereferences the working expression.
4099 - ``DW_OP_plus, 93`` adds ``93`` to the working expression.
4100 - ``DW_OP_bit_piece, 16, 8`` specifies the offset and size (``16`` and ``8``
4101 here, respectively) of the variable piece from the working expression.
4103 .. code-block:: llvm
4105 !0 = !DIExpression(DW_OP_deref)
4106 !1 = !DIExpression(DW_OP_plus, 3)
4107 !2 = !DIExpression(DW_OP_bit_piece, 3, 7)
4108 !3 = !DIExpression(DW_OP_deref, DW_OP_plus, 3, DW_OP_bit_piece, 3, 7)
4113 ``DIObjCProperty`` nodes represent Objective-C property nodes.
4115 .. code-block:: llvm
4117 !3 = !DIObjCProperty(name: "foo", file: !1, line: 7, setter: "setFoo",
4118 getter: "getFoo", attributes: 7, type: !2)
4123 ``DIImportedEntity`` nodes represent entities (such as modules) imported into a
4126 .. code-block:: llvm
4128 !2 = !DIImportedEntity(tag: DW_TAG_imported_module, name: "foo", scope: !0,
4129 entity: !1, line: 7)
4134 ``DIMacro`` nodes represent definition or undefinition of a macro identifiers.
4135 The ``name:`` field is the macro identifier, followed by macro parameters when
4136 definining a function-like macro, and the ``value`` field is the token-string
4137 used to expand the macro identifier.
4139 .. code-block:: llvm
4141 !2 = !DIMacro(macinfo: DW_MACINFO_define, line: 7, name: "foo(x)",
4143 !3 = !DIMacro(macinfo: DW_MACINFO_undef, line: 30, name: "foo")
4148 ``DIMacroFile`` nodes represent inclusion of source files.
4149 The ``nodes:`` field is a list of ``DIMacro`` and ``DIMacroFile`` nodes that
4150 appear in the included source file.
4152 .. code-block:: llvm
4154 !2 = !DIMacroFile(macinfo: DW_MACINFO_start_file, line: 7, file: !2,
4160 In LLVM IR, memory does not have types, so LLVM's own type system is not
4161 suitable for doing TBAA. Instead, metadata is added to the IR to
4162 describe a type system of a higher level language. This can be used to
4163 implement typical C/C++ TBAA, but it can also be used to implement
4164 custom alias analysis behavior for other languages.
4166 The current metadata format is very simple. TBAA metadata nodes have up
4167 to three fields, e.g.:
4169 .. code-block:: llvm
4171 !0 = !{ !"an example type tree" }
4172 !1 = !{ !"int", !0 }
4173 !2 = !{ !"float", !0 }
4174 !3 = !{ !"const float", !2, i64 1 }
4176 The first field is an identity field. It can be any value, usually a
4177 metadata string, which uniquely identifies the type. The most important
4178 name in the tree is the name of the root node. Two trees with different
4179 root node names are entirely disjoint, even if they have leaves with
4182 The second field identifies the type's parent node in the tree, or is
4183 null or omitted for a root node. A type is considered to alias all of
4184 its descendants and all of its ancestors in the tree. Also, a type is
4185 considered to alias all types in other trees, so that bitcode produced
4186 from multiple front-ends is handled conservatively.
4188 If the third field is present, it's an integer which if equal to 1
4189 indicates that the type is "constant" (meaning
4190 ``pointsToConstantMemory`` should return true; see `other useful
4191 AliasAnalysis methods <AliasAnalysis.html#OtherItfs>`_).
4193 '``tbaa.struct``' Metadata
4194 ^^^^^^^^^^^^^^^^^^^^^^^^^^
4196 The :ref:`llvm.memcpy <int_memcpy>` is often used to implement
4197 aggregate assignment operations in C and similar languages, however it
4198 is defined to copy a contiguous region of memory, which is more than
4199 strictly necessary for aggregate types which contain holes due to
4200 padding. Also, it doesn't contain any TBAA information about the fields
4203 ``!tbaa.struct`` metadata can describe which memory subregions in a
4204 memcpy are padding and what the TBAA tags of the struct are.
4206 The current metadata format is very simple. ``!tbaa.struct`` metadata
4207 nodes are a list of operands which are in conceptual groups of three.
4208 For each group of three, the first operand gives the byte offset of a
4209 field in bytes, the second gives its size in bytes, and the third gives
4212 .. code-block:: llvm
4214 !4 = !{ i64 0, i64 4, !1, i64 8, i64 4, !2 }
4216 This describes a struct with two fields. The first is at offset 0 bytes
4217 with size 4 bytes, and has tbaa tag !1. The second is at offset 8 bytes
4218 and has size 4 bytes and has tbaa tag !2.
4220 Note that the fields need not be contiguous. In this example, there is a
4221 4 byte gap between the two fields. This gap represents padding which
4222 does not carry useful data and need not be preserved.
4224 '``noalias``' and '``alias.scope``' Metadata
4225 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4227 ``noalias`` and ``alias.scope`` metadata provide the ability to specify generic
4228 noalias memory-access sets. This means that some collection of memory access
4229 instructions (loads, stores, memory-accessing calls, etc.) that carry
4230 ``noalias`` metadata can specifically be specified not to alias with some other
4231 collection of memory access instructions that carry ``alias.scope`` metadata.
4232 Each type of metadata specifies a list of scopes where each scope has an id and
4233 a domain. When evaluating an aliasing query, if for some domain, the set
4234 of scopes with that domain in one instruction's ``alias.scope`` list is a
4235 subset of (or equal to) the set of scopes for that domain in another
4236 instruction's ``noalias`` list, then the two memory accesses are assumed not to
4239 The metadata identifying each domain is itself a list containing one or two
4240 entries. The first entry is the name of the domain. Note that if the name is a
4241 string then it can be combined across functions and translation units. A
4242 self-reference can be used to create globally unique domain names. A
4243 descriptive string may optionally be provided as a second list entry.
4245 The metadata identifying each scope is also itself a list containing two or
4246 three entries. The first entry is the name of the scope. Note that if the name
4247 is a string then it can be combined across functions and translation units. A
4248 self-reference can be used to create globally unique scope names. A metadata
4249 reference to the scope's domain is the second entry. A descriptive string may
4250 optionally be provided as a third list entry.
4254 .. code-block:: llvm
4256 ; Two scope domains:
4260 ; Some scopes in these domains:
4266 !5 = !{!4} ; A list containing only scope !4
4270 ; These two instructions don't alias:
4271 %0 = load float, float* %c, align 4, !alias.scope !5
4272 store float %0, float* %arrayidx.i, align 4, !noalias !5
4274 ; These two instructions also don't alias (for domain !1, the set of scopes
4275 ; in the !alias.scope equals that in the !noalias list):
4276 %2 = load float, float* %c, align 4, !alias.scope !5
4277 store float %2, float* %arrayidx.i2, align 4, !noalias !6
4279 ; These two instructions may alias (for domain !0, the set of scopes in
4280 ; the !noalias list is not a superset of, or equal to, the scopes in the
4281 ; !alias.scope list):
4282 %2 = load float, float* %c, align 4, !alias.scope !6
4283 store float %0, float* %arrayidx.i, align 4, !noalias !7
4285 '``fpmath``' Metadata
4286 ^^^^^^^^^^^^^^^^^^^^^
4288 ``fpmath`` metadata may be attached to any instruction of floating point
4289 type. It can be used to express the maximum acceptable error in the
4290 result of that instruction, in ULPs, thus potentially allowing the
4291 compiler to use a more efficient but less accurate method of computing
4292 it. ULP is defined as follows:
4294 If ``x`` is a real number that lies between two finite consecutive
4295 floating-point numbers ``a`` and ``b``, without being equal to one
4296 of them, then ``ulp(x) = |b - a|``, otherwise ``ulp(x)`` is the
4297 distance between the two non-equal finite floating-point numbers
4298 nearest ``x``. Moreover, ``ulp(NaN)`` is ``NaN``.
4300 The metadata node shall consist of a single positive floating point
4301 number representing the maximum relative error, for example:
4303 .. code-block:: llvm
4305 !0 = !{ float 2.5 } ; maximum acceptable inaccuracy is 2.5 ULPs
4309 '``range``' Metadata
4310 ^^^^^^^^^^^^^^^^^^^^
4312 ``range`` metadata may be attached only to ``load``, ``call`` and ``invoke`` of
4313 integer types. It expresses the possible ranges the loaded value or the value
4314 returned by the called function at this call site is in. The ranges are
4315 represented with a flattened list of integers. The loaded value or the value
4316 returned is known to be in the union of the ranges defined by each consecutive
4317 pair. Each pair has the following properties:
4319 - The type must match the type loaded by the instruction.
4320 - The pair ``a,b`` represents the range ``[a,b)``.
4321 - Both ``a`` and ``b`` are constants.
4322 - The range is allowed to wrap.
4323 - The range should not represent the full or empty set. That is,
4326 In addition, the pairs must be in signed order of the lower bound and
4327 they must be non-contiguous.
4331 .. code-block:: llvm
4333 %a = load i8, i8* %x, align 1, !range !0 ; Can only be 0 or 1
4334 %b = load i8, i8* %y, align 1, !range !1 ; Can only be 255 (-1), 0 or 1
4335 %c = call i8 @foo(), !range !2 ; Can only be 0, 1, 3, 4 or 5
4336 %d = invoke i8 @bar() to label %cont
4337 unwind label %lpad, !range !3 ; Can only be -2, -1, 3, 4 or 5
4339 !0 = !{ i8 0, i8 2 }
4340 !1 = !{ i8 255, i8 2 }
4341 !2 = !{ i8 0, i8 2, i8 3, i8 6 }
4342 !3 = !{ i8 -2, i8 0, i8 3, i8 6 }
4344 '``unpredictable``' Metadata
4345 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4347 ``unpredictable`` metadata may be attached to any branch or switch
4348 instruction. It can be used to express the unpredictability of control
4349 flow. Similar to the llvm.expect intrinsic, it may be used to alter
4350 optimizations related to compare and branch instructions. The metadata
4351 is treated as a boolean value; if it exists, it signals that the branch
4352 or switch that it is attached to is completely unpredictable.
4357 It is sometimes useful to attach information to loop constructs. Currently,
4358 loop metadata is implemented as metadata attached to the branch instruction
4359 in the loop latch block. This type of metadata refer to a metadata node that is
4360 guaranteed to be separate for each loop. The loop identifier metadata is
4361 specified with the name ``llvm.loop``.
4363 The loop identifier metadata is implemented using a metadata that refers to
4364 itself to avoid merging it with any other identifier metadata, e.g.,
4365 during module linkage or function inlining. That is, each loop should refer
4366 to their own identification metadata even if they reside in separate functions.
4367 The following example contains loop identifier metadata for two separate loop
4370 .. code-block:: llvm
4375 The loop identifier metadata can be used to specify additional
4376 per-loop metadata. Any operands after the first operand can be treated
4377 as user-defined metadata. For example the ``llvm.loop.unroll.count``
4378 suggests an unroll factor to the loop unroller:
4380 .. code-block:: llvm
4382 br i1 %exitcond, label %._crit_edge, label %.lr.ph, !llvm.loop !0
4385 !1 = !{!"llvm.loop.unroll.count", i32 4}
4387 '``llvm.loop.vectorize``' and '``llvm.loop.interleave``'
4388 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4390 Metadata prefixed with ``llvm.loop.vectorize`` or ``llvm.loop.interleave`` are
4391 used to control per-loop vectorization and interleaving parameters such as
4392 vectorization width and interleave count. These metadata should be used in
4393 conjunction with ``llvm.loop`` loop identification metadata. The
4394 ``llvm.loop.vectorize`` and ``llvm.loop.interleave`` metadata are only
4395 optimization hints and the optimizer will only interleave and vectorize loops if
4396 it believes it is safe to do so. The ``llvm.mem.parallel_loop_access`` metadata
4397 which contains information about loop-carried memory dependencies can be helpful
4398 in determining the safety of these transformations.
4400 '``llvm.loop.interleave.count``' Metadata
4401 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4403 This metadata suggests an interleave count to the loop interleaver.
4404 The first operand is the string ``llvm.loop.interleave.count`` and the
4405 second operand is an integer specifying the interleave count. For
4408 .. code-block:: llvm
4410 !0 = !{!"llvm.loop.interleave.count", i32 4}
4412 Note that setting ``llvm.loop.interleave.count`` to 1 disables interleaving
4413 multiple iterations of the loop. If ``llvm.loop.interleave.count`` is set to 0
4414 then the interleave count will be determined automatically.
4416 '``llvm.loop.vectorize.enable``' Metadata
4417 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4419 This metadata selectively enables or disables vectorization for the loop. The
4420 first operand is the string ``llvm.loop.vectorize.enable`` and the second operand
4421 is a bit. If the bit operand value is 1 vectorization is enabled. A value of
4422 0 disables vectorization:
4424 .. code-block:: llvm
4426 !0 = !{!"llvm.loop.vectorize.enable", i1 0}
4427 !1 = !{!"llvm.loop.vectorize.enable", i1 1}
4429 '``llvm.loop.vectorize.width``' Metadata
4430 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4432 This metadata sets the target width of the vectorizer. The first
4433 operand is the string ``llvm.loop.vectorize.width`` and the second
4434 operand is an integer specifying the width. For example:
4436 .. code-block:: llvm
4438 !0 = !{!"llvm.loop.vectorize.width", i32 4}
4440 Note that setting ``llvm.loop.vectorize.width`` to 1 disables
4441 vectorization of the loop. If ``llvm.loop.vectorize.width`` is set to
4442 0 or if the loop does not have this metadata the width will be
4443 determined automatically.
4445 '``llvm.loop.unroll``'
4446 ^^^^^^^^^^^^^^^^^^^^^^
4448 Metadata prefixed with ``llvm.loop.unroll`` are loop unrolling
4449 optimization hints such as the unroll factor. ``llvm.loop.unroll``
4450 metadata should be used in conjunction with ``llvm.loop`` loop
4451 identification metadata. The ``llvm.loop.unroll`` metadata are only
4452 optimization hints and the unrolling will only be performed if the
4453 optimizer believes it is safe to do so.
4455 '``llvm.loop.unroll.count``' Metadata
4456 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4458 This metadata suggests an unroll factor to the loop unroller. The
4459 first operand is the string ``llvm.loop.unroll.count`` and the second
4460 operand is a positive integer specifying the unroll factor. For
4463 .. code-block:: llvm
4465 !0 = !{!"llvm.loop.unroll.count", i32 4}
4467 If the trip count of the loop is less than the unroll count the loop
4468 will be partially unrolled.
4470 '``llvm.loop.unroll.disable``' Metadata
4471 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4473 This metadata disables loop unrolling. The metadata has a single operand
4474 which is the string ``llvm.loop.unroll.disable``. For example:
4476 .. code-block:: llvm
4478 !0 = !{!"llvm.loop.unroll.disable"}
4480 '``llvm.loop.unroll.runtime.disable``' Metadata
4481 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4483 This metadata disables runtime loop unrolling. The metadata has a single
4484 operand which is the string ``llvm.loop.unroll.runtime.disable``. For example:
4486 .. code-block:: llvm
4488 !0 = !{!"llvm.loop.unroll.runtime.disable"}
4490 '``llvm.loop.unroll.enable``' Metadata
4491 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4493 This metadata suggests that the loop should be fully unrolled if the trip count
4494 is known at compile time and partially unrolled if the trip count is not known
4495 at compile time. The metadata has a single operand which is the string
4496 ``llvm.loop.unroll.enable``. For example:
4498 .. code-block:: llvm
4500 !0 = !{!"llvm.loop.unroll.enable"}
4502 '``llvm.loop.unroll.full``' Metadata
4503 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4505 This metadata suggests that the loop should be unrolled fully. The
4506 metadata has a single operand which is the string ``llvm.loop.unroll.full``.
4509 .. code-block:: llvm
4511 !0 = !{!"llvm.loop.unroll.full"}
4516 Metadata types used to annotate memory accesses with information helpful
4517 for optimizations are prefixed with ``llvm.mem``.
4519 '``llvm.mem.parallel_loop_access``' Metadata
4520 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4522 The ``llvm.mem.parallel_loop_access`` metadata refers to a loop identifier,
4523 or metadata containing a list of loop identifiers for nested loops.
4524 The metadata is attached to memory accessing instructions and denotes that
4525 no loop carried memory dependence exist between it and other instructions denoted
4526 with the same loop identifier.
4528 Precisely, given two instructions ``m1`` and ``m2`` that both have the
4529 ``llvm.mem.parallel_loop_access`` metadata, with ``L1`` and ``L2`` being the
4530 set of loops associated with that metadata, respectively, then there is no loop
4531 carried dependence between ``m1`` and ``m2`` for loops in both ``L1`` and
4534 As a special case, if all memory accessing instructions in a loop have
4535 ``llvm.mem.parallel_loop_access`` metadata that refers to that loop, then the
4536 loop has no loop carried memory dependences and is considered to be a parallel
4539 Note that if not all memory access instructions have such metadata referring to
4540 the loop, then the loop is considered not being trivially parallel. Additional
4541 memory dependence analysis is required to make that determination. As a fail
4542 safe mechanism, this causes loops that were originally parallel to be considered
4543 sequential (if optimization passes that are unaware of the parallel semantics
4544 insert new memory instructions into the loop body).
4546 Example of a loop that is considered parallel due to its correct use of
4547 both ``llvm.loop`` and ``llvm.mem.parallel_loop_access``
4548 metadata types that refer to the same loop identifier metadata.
4550 .. code-block:: llvm
4554 %val0 = load i32, i32* %arrayidx, !llvm.mem.parallel_loop_access !0
4556 store i32 %val0, i32* %arrayidx1, !llvm.mem.parallel_loop_access !0
4558 br i1 %exitcond, label %for.end, label %for.body, !llvm.loop !0
4564 It is also possible to have nested parallel loops. In that case the
4565 memory accesses refer to a list of loop identifier metadata nodes instead of
4566 the loop identifier metadata node directly:
4568 .. code-block:: llvm
4572 %val1 = load i32, i32* %arrayidx3, !llvm.mem.parallel_loop_access !2
4574 br label %inner.for.body
4578 %val0 = load i32, i32* %arrayidx1, !llvm.mem.parallel_loop_access !0
4580 store i32 %val0, i32* %arrayidx2, !llvm.mem.parallel_loop_access !0
4582 br i1 %exitcond, label %inner.for.end, label %inner.for.body, !llvm.loop !1
4586 store i32 %val1, i32* %arrayidx4, !llvm.mem.parallel_loop_access !2
4588 br i1 %exitcond, label %outer.for.end, label %outer.for.body, !llvm.loop !2
4590 outer.for.end: ; preds = %for.body
4592 !0 = !{!1, !2} ; a list of loop identifiers
4593 !1 = !{!1} ; an identifier for the inner loop
4594 !2 = !{!2} ; an identifier for the outer loop
4599 The ``llvm.bitsets`` global metadata is used to implement
4600 :doc:`bitsets <BitSets>`.
4602 '``invariant.group``' Metadata
4603 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4605 The ``invariant.group`` metadata may be attached to ``load``/``store`` instructions.
4606 The existence of the ``invariant.group`` metadata on the instruction tells
4607 the optimizer that every ``load`` and ``store`` to the same pointer operand
4608 within the same invariant group can be assumed to load or store the same
4609 value (but see the ``llvm.invariant.group.barrier`` intrinsic which affects
4610 when two pointers are considered the same).
4614 .. code-block:: llvm
4616 @unknownPtr = external global i8
4619 store i8 42, i8* %ptr, !invariant.group !0
4620 call void @foo(i8* %ptr)
4622 %a = load i8, i8* %ptr, !invariant.group !0 ; Can assume that value under %ptr didn't change
4623 call void @foo(i8* %ptr)
4624 %b = load i8, i8* %ptr, !invariant.group !1 ; Can't assume anything, because group changed
4626 %newPtr = call i8* @getPointer(i8* %ptr)
4627 %c = load i8, i8* %newPtr, !invariant.group !0 ; Can't assume anything, because we only have information about %ptr
4629 %unknownValue = load i8, i8* @unknownPtr
4630 store i8 %unknownValue, i8* %ptr, !invariant.group !0 ; Can assume that %unknownValue == 42
4632 call void @foo(i8* %ptr)
4633 %newPtr2 = call i8* @llvm.invariant.group.barrier(i8* %ptr)
4634 %d = load i8, i8* %newPtr2, !invariant.group !0 ; Can't step through invariant.group.barrier to get value of %ptr
4637 declare void @foo(i8*)
4638 declare i8* @getPointer(i8*)
4639 declare i8* @llvm.invariant.group.barrier(i8*)
4641 !0 = !{!"magic ptr"}
4642 !1 = !{!"other ptr"}
4646 Module Flags Metadata
4647 =====================
4649 Information about the module as a whole is difficult to convey to LLVM's
4650 subsystems. The LLVM IR isn't sufficient to transmit this information.
4651 The ``llvm.module.flags`` named metadata exists in order to facilitate
4652 this. These flags are in the form of key / value pairs --- much like a
4653 dictionary --- making it easy for any subsystem who cares about a flag to
4656 The ``llvm.module.flags`` metadata contains a list of metadata triplets.
4657 Each triplet has the following form:
4659 - The first element is a *behavior* flag, which specifies the behavior
4660 when two (or more) modules are merged together, and it encounters two
4661 (or more) metadata with the same ID. The supported behaviors are
4663 - The second element is a metadata string that is a unique ID for the
4664 metadata. Each module may only have one flag entry for each unique ID (not
4665 including entries with the **Require** behavior).
4666 - The third element is the value of the flag.
4668 When two (or more) modules are merged together, the resulting
4669 ``llvm.module.flags`` metadata is the union of the modules' flags. That is, for
4670 each unique metadata ID string, there will be exactly one entry in the merged
4671 modules ``llvm.module.flags`` metadata table, and the value for that entry will
4672 be determined by the merge behavior flag, as described below. The only exception
4673 is that entries with the *Require* behavior are always preserved.
4675 The following behaviors are supported:
4686 Emits an error if two values disagree, otherwise the resulting value
4687 is that of the operands.
4691 Emits a warning if two values disagree. The result value will be the
4692 operand for the flag from the first module being linked.
4696 Adds a requirement that another module flag be present and have a
4697 specified value after linking is performed. The value must be a
4698 metadata pair, where the first element of the pair is the ID of the
4699 module flag to be restricted, and the second element of the pair is
4700 the value the module flag should be restricted to. This behavior can
4701 be used to restrict the allowable results (via triggering of an
4702 error) of linking IDs with the **Override** behavior.
4706 Uses the specified value, regardless of the behavior or value of the
4707 other module. If both modules specify **Override**, but the values
4708 differ, an error will be emitted.
4712 Appends the two values, which are required to be metadata nodes.
4716 Appends the two values, which are required to be metadata
4717 nodes. However, duplicate entries in the second list are dropped
4718 during the append operation.
4720 It is an error for a particular unique flag ID to have multiple behaviors,
4721 except in the case of **Require** (which adds restrictions on another metadata
4722 value) or **Override**.
4724 An example of module flags:
4726 .. code-block:: llvm
4728 !0 = !{ i32 1, !"foo", i32 1 }
4729 !1 = !{ i32 4, !"bar", i32 37 }
4730 !2 = !{ i32 2, !"qux", i32 42 }
4731 !3 = !{ i32 3, !"qux",
4736 !llvm.module.flags = !{ !0, !1, !2, !3 }
4738 - Metadata ``!0`` has the ID ``!"foo"`` and the value '1'. The behavior
4739 if two or more ``!"foo"`` flags are seen is to emit an error if their
4740 values are not equal.
4742 - Metadata ``!1`` has the ID ``!"bar"`` and the value '37'. The
4743 behavior if two or more ``!"bar"`` flags are seen is to use the value
4746 - Metadata ``!2`` has the ID ``!"qux"`` and the value '42'. The
4747 behavior if two or more ``!"qux"`` flags are seen is to emit a
4748 warning if their values are not equal.
4750 - Metadata ``!3`` has the ID ``!"qux"`` and the value:
4756 The behavior is to emit an error if the ``llvm.module.flags`` does not
4757 contain a flag with the ID ``!"foo"`` that has the value '1' after linking is
4760 Objective-C Garbage Collection Module Flags Metadata
4761 ----------------------------------------------------
4763 On the Mach-O platform, Objective-C stores metadata about garbage
4764 collection in a special section called "image info". The metadata
4765 consists of a version number and a bitmask specifying what types of
4766 garbage collection are supported (if any) by the file. If two or more
4767 modules are linked together their garbage collection metadata needs to
4768 be merged rather than appended together.
4770 The Objective-C garbage collection module flags metadata consists of the
4771 following key-value pairs:
4780 * - ``Objective-C Version``
4781 - **[Required]** --- The Objective-C ABI version. Valid values are 1 and 2.
4783 * - ``Objective-C Image Info Version``
4784 - **[Required]** --- The version of the image info section. Currently
4787 * - ``Objective-C Image Info Section``
4788 - **[Required]** --- The section to place the metadata. Valid values are
4789 ``"__OBJC, __image_info, regular"`` for Objective-C ABI version 1, and
4790 ``"__DATA,__objc_imageinfo, regular, no_dead_strip"`` for
4791 Objective-C ABI version 2.
4793 * - ``Objective-C Garbage Collection``
4794 - **[Required]** --- Specifies whether garbage collection is supported or
4795 not. Valid values are 0, for no garbage collection, and 2, for garbage
4796 collection supported.
4798 * - ``Objective-C GC Only``
4799 - **[Optional]** --- Specifies that only garbage collection is supported.
4800 If present, its value must be 6. This flag requires that the
4801 ``Objective-C Garbage Collection`` flag have the value 2.
4803 Some important flag interactions:
4805 - If a module with ``Objective-C Garbage Collection`` set to 0 is
4806 merged with a module with ``Objective-C Garbage Collection`` set to
4807 2, then the resulting module has the
4808 ``Objective-C Garbage Collection`` flag set to 0.
4809 - A module with ``Objective-C Garbage Collection`` set to 0 cannot be
4810 merged with a module with ``Objective-C GC Only`` set to 6.
4812 Automatic Linker Flags Module Flags Metadata
4813 --------------------------------------------
4815 Some targets support embedding flags to the linker inside individual object
4816 files. Typically this is used in conjunction with language extensions which
4817 allow source files to explicitly declare the libraries they depend on, and have
4818 these automatically be transmitted to the linker via object files.
4820 These flags are encoded in the IR using metadata in the module flags section,
4821 using the ``Linker Options`` key. The merge behavior for this flag is required
4822 to be ``AppendUnique``, and the value for the key is expected to be a metadata
4823 node which should be a list of other metadata nodes, each of which should be a
4824 list of metadata strings defining linker options.
4826 For example, the following metadata section specifies two separate sets of
4827 linker options, presumably to link against ``libz`` and the ``Cocoa``
4830 !0 = !{ i32 6, !"Linker Options",
4833 !{ !"-framework", !"Cocoa" } } }
4834 !llvm.module.flags = !{ !0 }
4836 The metadata encoding as lists of lists of options, as opposed to a collapsed
4837 list of options, is chosen so that the IR encoding can use multiple option
4838 strings to specify e.g., a single library, while still having that specifier be
4839 preserved as an atomic element that can be recognized by a target specific
4840 assembly writer or object file emitter.
4842 Each individual option is required to be either a valid option for the target's
4843 linker, or an option that is reserved by the target specific assembly writer or
4844 object file emitter. No other aspect of these options is defined by the IR.
4846 C type width Module Flags Metadata
4847 ----------------------------------
4849 The ARM backend emits a section into each generated object file describing the
4850 options that it was compiled with (in a compiler-independent way) to prevent
4851 linking incompatible objects, and to allow automatic library selection. Some
4852 of these options are not visible at the IR level, namely wchar_t width and enum
4855 To pass this information to the backend, these options are encoded in module
4856 flags metadata, using the following key-value pairs:
4866 - * 0 --- sizeof(wchar_t) == 4
4867 * 1 --- sizeof(wchar_t) == 2
4870 - * 0 --- Enums are at least as large as an ``int``.
4871 * 1 --- Enums are stored in the smallest integer type which can
4872 represent all of its values.
4874 For example, the following metadata section specifies that the module was
4875 compiled with a ``wchar_t`` width of 4 bytes, and the underlying type of an
4876 enum is the smallest type which can represent all of its values::
4878 !llvm.module.flags = !{!0, !1}
4879 !0 = !{i32 1, !"short_wchar", i32 1}
4880 !1 = !{i32 1, !"short_enum", i32 0}
4882 .. _intrinsicglobalvariables:
4884 Intrinsic Global Variables
4885 ==========================
4887 LLVM has a number of "magic" global variables that contain data that
4888 affect code generation or other IR semantics. These are documented here.
4889 All globals of this sort should have a section specified as
4890 "``llvm.metadata``". This section and all globals that start with
4891 "``llvm.``" are reserved for use by LLVM.
4895 The '``llvm.used``' Global Variable
4896 -----------------------------------
4898 The ``@llvm.used`` global is an array which has
4899 :ref:`appending linkage <linkage_appending>`. This array contains a list of
4900 pointers to named global variables, functions and aliases which may optionally
4901 have a pointer cast formed of bitcast or getelementptr. For example, a legal
4904 .. code-block:: llvm
4909 @llvm.used = appending global [2 x i8*] [
4911 i8* bitcast (i32* @Y to i8*)
4912 ], section "llvm.metadata"
4914 If a symbol appears in the ``@llvm.used`` list, then the compiler, assembler,
4915 and linker are required to treat the symbol as if there is a reference to the
4916 symbol that it cannot see (which is why they have to be named). For example, if
4917 a variable has internal linkage and no references other than that from the
4918 ``@llvm.used`` list, it cannot be deleted. This is commonly used to represent
4919 references from inline asms and other things the compiler cannot "see", and
4920 corresponds to "``attribute((used))``" in GNU C.
4922 On some targets, the code generator must emit a directive to the
4923 assembler or object file to prevent the assembler and linker from
4924 molesting the symbol.
4926 .. _gv_llvmcompilerused:
4928 The '``llvm.compiler.used``' Global Variable
4929 --------------------------------------------
4931 The ``@llvm.compiler.used`` directive is the same as the ``@llvm.used``
4932 directive, except that it only prevents the compiler from touching the
4933 symbol. On targets that support it, this allows an intelligent linker to
4934 optimize references to the symbol without being impeded as it would be
4937 This is a rare construct that should only be used in rare circumstances,
4938 and should not be exposed to source languages.
4940 .. _gv_llvmglobalctors:
4942 The '``llvm.global_ctors``' Global Variable
4943 -------------------------------------------
4945 .. code-block:: llvm
4947 %0 = type { i32, void ()*, i8* }
4948 @llvm.global_ctors = appending global [1 x %0] [%0 { i32 65535, void ()* @ctor, i8* @data }]
4950 The ``@llvm.global_ctors`` array contains a list of constructor
4951 functions, priorities, and an optional associated global or function.
4952 The functions referenced by this array will be called in ascending order
4953 of priority (i.e. lowest first) when the module is loaded. The order of
4954 functions with the same priority is not defined.
4956 If the third field is present, non-null, and points to a global variable
4957 or function, the initializer function will only run if the associated
4958 data from the current module is not discarded.
4960 .. _llvmglobaldtors:
4962 The '``llvm.global_dtors``' Global Variable
4963 -------------------------------------------
4965 .. code-block:: llvm
4967 %0 = type { i32, void ()*, i8* }
4968 @llvm.global_dtors = appending global [1 x %0] [%0 { i32 65535, void ()* @dtor, i8* @data }]
4970 The ``@llvm.global_dtors`` array contains a list of destructor
4971 functions, priorities, and an optional associated global or function.
4972 The functions referenced by this array will be called in descending
4973 order of priority (i.e. highest first) when the module is unloaded. The
4974 order of functions with the same priority is not defined.
4976 If the third field is present, non-null, and points to a global variable
4977 or function, the destructor function will only run if the associated
4978 data from the current module is not discarded.
4980 Instruction Reference
4981 =====================
4983 The LLVM instruction set consists of several different classifications
4984 of instructions: :ref:`terminator instructions <terminators>`, :ref:`binary
4985 instructions <binaryops>`, :ref:`bitwise binary
4986 instructions <bitwiseops>`, :ref:`memory instructions <memoryops>`, and
4987 :ref:`other instructions <otherops>`.
4991 Terminator Instructions
4992 -----------------------
4994 As mentioned :ref:`previously <functionstructure>`, every basic block in a
4995 program ends with a "Terminator" instruction, which indicates which
4996 block should be executed after the current block is finished. These
4997 terminator instructions typically yield a '``void``' value: they produce
4998 control flow, not values (the one exception being the
4999 ':ref:`invoke <i_invoke>`' instruction).
5001 The terminator instructions are: ':ref:`ret <i_ret>`',
5002 ':ref:`br <i_br>`', ':ref:`switch <i_switch>`',
5003 ':ref:`indirectbr <i_indirectbr>`', ':ref:`invoke <i_invoke>`',
5004 ':ref:`resume <i_resume>`', ':ref:`catchswitch <i_catchswitch>`',
5005 ':ref:`catchret <i_catchret>`',
5006 ':ref:`cleanupret <i_cleanupret>`',
5007 and ':ref:`unreachable <i_unreachable>`'.
5011 '``ret``' Instruction
5012 ^^^^^^^^^^^^^^^^^^^^^
5019 ret <type> <value> ; Return a value from a non-void function
5020 ret void ; Return from void function
5025 The '``ret``' instruction is used to return control flow (and optionally
5026 a value) from a function back to the caller.
5028 There are two forms of the '``ret``' instruction: one that returns a
5029 value and then causes control flow, and one that just causes control
5035 The '``ret``' instruction optionally accepts a single argument, the
5036 return value. The type of the return value must be a ':ref:`first
5037 class <t_firstclass>`' type.
5039 A function is not :ref:`well formed <wellformed>` if it it has a non-void
5040 return type and contains a '``ret``' instruction with no return value or
5041 a return value with a type that does not match its type, or if it has a
5042 void return type and contains a '``ret``' instruction with a return
5048 When the '``ret``' instruction is executed, control flow returns back to
5049 the calling function's context. If the caller is a
5050 ":ref:`call <i_call>`" instruction, execution continues at the
5051 instruction after the call. If the caller was an
5052 ":ref:`invoke <i_invoke>`" instruction, execution continues at the
5053 beginning of the "normal" destination block. If the instruction returns
5054 a value, that value shall set the call or invoke instruction's return
5060 .. code-block:: llvm
5062 ret i32 5 ; Return an integer value of 5
5063 ret void ; Return from a void function
5064 ret { i32, i8 } { i32 4, i8 2 } ; Return a struct of values 4 and 2
5068 '``br``' Instruction
5069 ^^^^^^^^^^^^^^^^^^^^
5076 br i1 <cond>, label <iftrue>, label <iffalse>
5077 br label <dest> ; Unconditional branch
5082 The '``br``' instruction is used to cause control flow to transfer to a
5083 different basic block in the current function. There are two forms of
5084 this instruction, corresponding to a conditional branch and an
5085 unconditional branch.
5090 The conditional branch form of the '``br``' instruction takes a single
5091 '``i1``' value and two '``label``' values. The unconditional form of the
5092 '``br``' instruction takes a single '``label``' value as a target.
5097 Upon execution of a conditional '``br``' instruction, the '``i1``'
5098 argument is evaluated. If the value is ``true``, control flows to the
5099 '``iftrue``' ``label`` argument. If "cond" is ``false``, control flows
5100 to the '``iffalse``' ``label`` argument.
5105 .. code-block:: llvm
5108 %cond = icmp eq i32 %a, %b
5109 br i1 %cond, label %IfEqual, label %IfUnequal
5117 '``switch``' Instruction
5118 ^^^^^^^^^^^^^^^^^^^^^^^^
5125 switch <intty> <value>, label <defaultdest> [ <intty> <val>, label <dest> ... ]
5130 The '``switch``' instruction is used to transfer control flow to one of
5131 several different places. It is a generalization of the '``br``'
5132 instruction, allowing a branch to occur to one of many possible
5138 The '``switch``' instruction uses three parameters: an integer
5139 comparison value '``value``', a default '``label``' destination, and an
5140 array of pairs of comparison value constants and '``label``'s. The table
5141 is not allowed to contain duplicate constant entries.
5146 The ``switch`` instruction specifies a table of values and destinations.
5147 When the '``switch``' instruction is executed, this table is searched
5148 for the given value. If the value is found, control flow is transferred
5149 to the corresponding destination; otherwise, control flow is transferred
5150 to the default destination.
5155 Depending on properties of the target machine and the particular
5156 ``switch`` instruction, this instruction may be code generated in
5157 different ways. For example, it could be generated as a series of
5158 chained conditional branches or with a lookup table.
5163 .. code-block:: llvm
5165 ; Emulate a conditional br instruction
5166 %Val = zext i1 %value to i32
5167 switch i32 %Val, label %truedest [ i32 0, label %falsedest ]
5169 ; Emulate an unconditional br instruction
5170 switch i32 0, label %dest [ ]
5172 ; Implement a jump table:
5173 switch i32 %val, label %otherwise [ i32 0, label %onzero
5175 i32 2, label %ontwo ]
5179 '``indirectbr``' Instruction
5180 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5187 indirectbr <somety>* <address>, [ label <dest1>, label <dest2>, ... ]
5192 The '``indirectbr``' instruction implements an indirect branch to a
5193 label within the current function, whose address is specified by
5194 "``address``". Address must be derived from a
5195 :ref:`blockaddress <blockaddress>` constant.
5200 The '``address``' argument is the address of the label to jump to. The
5201 rest of the arguments indicate the full set of possible destinations
5202 that the address may point to. Blocks are allowed to occur multiple
5203 times in the destination list, though this isn't particularly useful.
5205 This destination list is required so that dataflow analysis has an
5206 accurate understanding of the CFG.
5211 Control transfers to the block specified in the address argument. All
5212 possible destination blocks must be listed in the label list, otherwise
5213 this instruction has undefined behavior. This implies that jumps to
5214 labels defined in other functions have undefined behavior as well.
5219 This is typically implemented with a jump through a register.
5224 .. code-block:: llvm
5226 indirectbr i8* %Addr, [ label %bb1, label %bb2, label %bb3 ]
5230 '``invoke``' Instruction
5231 ^^^^^^^^^^^^^^^^^^^^^^^^
5238 <result> = invoke [cconv] [ret attrs] <ptr to function ty> <function ptr val>(<function args>) [fn attrs]
5239 [operand bundles] to label <normal label> unwind label <exception label>
5244 The '``invoke``' instruction causes control to transfer to a specified
5245 function, with the possibility of control flow transfer to either the
5246 '``normal``' label or the '``exception``' label. If the callee function
5247 returns with the "``ret``" instruction, control flow will return to the
5248 "normal" label. If the callee (or any indirect callees) returns via the
5249 ":ref:`resume <i_resume>`" instruction or other exception handling
5250 mechanism, control is interrupted and continued at the dynamically
5251 nearest "exception" label.
5253 The '``exception``' label is a `landing
5254 pad <ExceptionHandling.html#overview>`_ for the exception. As such,
5255 '``exception``' label is required to have the
5256 ":ref:`landingpad <i_landingpad>`" instruction, which contains the
5257 information about the behavior of the program after unwinding happens,
5258 as its first non-PHI instruction. The restrictions on the
5259 "``landingpad``" instruction's tightly couples it to the "``invoke``"
5260 instruction, so that the important information contained within the
5261 "``landingpad``" instruction can't be lost through normal code motion.
5266 This instruction requires several arguments:
5268 #. The optional "cconv" marker indicates which :ref:`calling
5269 convention <callingconv>` the call should use. If none is
5270 specified, the call defaults to using C calling conventions.
5271 #. The optional :ref:`Parameter Attributes <paramattrs>` list for return
5272 values. Only '``zeroext``', '``signext``', and '``inreg``' attributes
5274 #. '``ptr to function ty``': shall be the signature of the pointer to
5275 function value being invoked. In most cases, this is a direct
5276 function invocation, but indirect ``invoke``'s are just as possible,
5277 branching off an arbitrary pointer to function value.
5278 #. '``function ptr val``': An LLVM value containing a pointer to a
5279 function to be invoked.
5280 #. '``function args``': argument list whose types match the function
5281 signature argument types and parameter attributes. All arguments must
5282 be of :ref:`first class <t_firstclass>` type. If the function signature
5283 indicates the function accepts a variable number of arguments, the
5284 extra arguments can be specified.
5285 #. '``normal label``': the label reached when the called function
5286 executes a '``ret``' instruction.
5287 #. '``exception label``': the label reached when a callee returns via
5288 the :ref:`resume <i_resume>` instruction or other exception handling
5290 #. The optional :ref:`function attributes <fnattrs>` list. Only
5291 '``noreturn``', '``nounwind``', '``readonly``' and '``readnone``'
5292 attributes are valid here.
5293 #. The optional :ref:`operand bundles <opbundles>` list.
5298 This instruction is designed to operate as a standard '``call``'
5299 instruction in most regards. The primary difference is that it
5300 establishes an association with a label, which is used by the runtime
5301 library to unwind the stack.
5303 This instruction is used in languages with destructors to ensure that
5304 proper cleanup is performed in the case of either a ``longjmp`` or a
5305 thrown exception. Additionally, this is important for implementation of
5306 '``catch``' clauses in high-level languages that support them.
5308 For the purposes of the SSA form, the definition of the value returned
5309 by the '``invoke``' instruction is deemed to occur on the edge from the
5310 current block to the "normal" label. If the callee unwinds then no
5311 return value is available.
5316 .. code-block:: llvm
5318 %retval = invoke i32 @Test(i32 15) to label %Continue
5319 unwind label %TestCleanup ; i32:retval set
5320 %retval = invoke coldcc i32 %Testfnptr(i32 15) to label %Continue
5321 unwind label %TestCleanup ; i32:retval set
5325 '``resume``' Instruction
5326 ^^^^^^^^^^^^^^^^^^^^^^^^
5333 resume <type> <value>
5338 The '``resume``' instruction is a terminator instruction that has no
5344 The '``resume``' instruction requires one argument, which must have the
5345 same type as the result of any '``landingpad``' instruction in the same
5351 The '``resume``' instruction resumes propagation of an existing
5352 (in-flight) exception whose unwinding was interrupted with a
5353 :ref:`landingpad <i_landingpad>` instruction.
5358 .. code-block:: llvm
5360 resume { i8*, i32 } %exn
5364 '``catchswitch``' Instruction
5365 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5372 <resultval> = catchswitch within <parent> [ label <handler1>, label <handler2>, ... ] unwind to caller
5373 <resultval> = catchswitch within <parent> [ label <handler1>, label <handler2>, ... ] unwind label <default>
5378 The '``catchswitch``' instruction is used by `LLVM's exception handling system
5379 <ExceptionHandling.html#overview>`_ to describe the set of possible catch handlers
5380 that may be executed by the :ref:`EH personality routine <personalityfn>`.
5385 The ``parent`` argument is the token of the funclet that contains the
5386 ``catchswitch`` instruction. If the ``catchswitch`` is not inside a funclet,
5387 this operand may be the token ``none``.
5389 The ``default`` argument is the label of another basic block beginning with a
5390 "pad" instruction, one of ``cleanuppad`` or ``catchswitch``.
5392 The ``handlers`` are a list of successor blocks that each begin with a
5393 :ref:`catchpad <i_catchpad>` instruction.
5398 Executing this instruction transfers control to one of the successors in
5399 ``handlers``, if appropriate, or continues to unwind via the unwind label if
5402 The ``catchswitch`` is both a terminator and a "pad" instruction, meaning that
5403 it must be both the first non-phi instruction and last instruction in the basic
5404 block. Therefore, it must be the only non-phi instruction in the block.
5409 .. code-block:: llvm
5412 %cs1 = catchswitch within none [label %handler0, label %handler1] unwind to caller
5414 %cs2 = catchswitch within %parenthandler [label %handler0] unwind label %cleanup
5418 '``catchpad``' Instruction
5419 ^^^^^^^^^^^^^^^^^^^^^^^^^^
5426 <resultval> = catchpad within <catchswitch> [<args>*]
5431 The '``catchpad``' instruction is used by `LLVM's exception handling
5432 system <ExceptionHandling.html#overview>`_ to specify that a basic block
5433 begins a catch handler --- one where a personality routine attempts to transfer
5434 control to catch an exception.
5439 The ``catchswitch`` operand must always be a token produced by a
5440 :ref:`catchswitch <i_catchswitch>` instruction in a predecessor block. This
5441 ensures that each ``catchpad`` has exactly one predecessor block, and it always
5442 terminates in a ``catchswitch``.
5444 The ``args`` correspond to whatever information the personality routine
5445 requires to know if this is an appropriate handler for the exception. Control
5446 will transfer to the ``catchpad`` if this is the first appropriate handler for
5449 The ``resultval`` has the type :ref:`token <t_token>` and is used to match the
5450 ``catchpad`` to corresponding :ref:`catchrets <i_catchret>` and other nested EH
5456 When the call stack is being unwound due to an exception being thrown, the
5457 exception is compared against the ``args``. If it doesn't match, control will
5458 not reach the ``catchpad`` instruction. The representation of ``args`` is
5459 entirely target and personality function-specific.
5461 Like the :ref:`landingpad <i_landingpad>` instruction, the ``catchpad``
5462 instruction must be the first non-phi of its parent basic block.
5464 The meaning of the tokens produced and consumed by ``catchpad`` and other "pad"
5465 instructions is described in the
5466 `Windows exception handling documentation <ExceptionHandling.html#wineh>`.
5468 Executing a ``catchpad`` instruction constitutes "entering" that pad.
5469 The pad may then be "exited" in one of three ways:
5470 1) explicitly via a ``catchret`` that consumes it. Executing such a ``catchret``
5471 is undefined behavior if any descendant pads have been entered but not yet
5473 2) implicitly via a call (which unwinds all the way to the current function's caller),
5474 or via a ``catchswitch`` or a ``cleanupret`` that unwinds to caller.
5475 3) implicitly via an unwind edge whose destination EH pad isn't a descendant of
5476 the ``catchpad``. When the ``catchpad`` is exited in this manner, it is
5477 undefined behavior if the destination EH pad has a parent which is not an
5478 ancestor of the ``catchpad`` being exited.
5483 .. code-block:: llvm
5486 %cs = catchswitch within none [label %handler0] unwind to caller
5487 ;; A catch block which can catch an integer.
5489 %tok = catchpad within %cs [i8** @_ZTIi]
5493 '``catchret``' Instruction
5494 ^^^^^^^^^^^^^^^^^^^^^^^^^^
5501 catchret from <token> to label <normal>
5506 The '``catchret``' instruction is a terminator instruction that has a
5513 The first argument to a '``catchret``' indicates which ``catchpad`` it
5514 exits. It must be a :ref:`catchpad <i_catchpad>`.
5515 The second argument to a '``catchret``' specifies where control will
5521 The '``catchret``' instruction ends an existing (in-flight) exception whose
5522 unwinding was interrupted with a :ref:`catchpad <i_catchpad>` instruction. The
5523 :ref:`personality function <personalityfn>` gets a chance to execute arbitrary
5524 code to, for example, destroy the active exception. Control then transfers to
5527 The ``token`` argument must be a token produced by a dominating ``catchpad``
5528 instruction. The ``catchret`` destroys the physical frame established by
5529 ``catchpad``, so executing multiple returns on the same token without
5530 re-executing the ``catchpad`` will result in undefined behavior.
5531 See :ref:`catchpad <i_catchpad>` for more details.
5536 .. code-block:: llvm
5538 catchret from %catch label %continue
5542 '``cleanupret``' Instruction
5543 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5550 cleanupret from <value> unwind label <continue>
5551 cleanupret from <value> unwind to caller
5556 The '``cleanupret``' instruction is a terminator instruction that has
5557 an optional successor.
5563 The '``cleanupret``' instruction requires one argument, which indicates
5564 which ``cleanuppad`` it exits, and must be a :ref:`cleanuppad <i_cleanuppad>`.
5565 It also has an optional successor, ``continue``.
5570 The '``cleanupret``' instruction indicates to the
5571 :ref:`personality function <personalityfn>` that one
5572 :ref:`cleanuppad <i_cleanuppad>` it transferred control to has ended.
5573 It transfers control to ``continue`` or unwinds out of the function.
5575 The unwind destination ``continue``, if present, must be an EH pad
5576 whose parent is either ``none`` or an ancestor of the ``cleanuppad``
5577 being returned from. This constitutes an exceptional exit from all
5578 ancestors of the completed ``cleanuppad``, up to but not including
5579 the parent of ``continue``.
5580 See :ref:`cleanuppad <i_cleanuppad>` for more details.
5585 .. code-block:: llvm
5587 cleanupret from %cleanup unwind to caller
5588 cleanupret from %cleanup unwind label %continue
5592 '``unreachable``' Instruction
5593 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5605 The '``unreachable``' instruction has no defined semantics. This
5606 instruction is used to inform the optimizer that a particular portion of
5607 the code is not reachable. This can be used to indicate that the code
5608 after a no-return function cannot be reached, and other facts.
5613 The '``unreachable``' instruction has no defined semantics.
5620 Binary operators are used to do most of the computation in a program.
5621 They require two operands of the same type, execute an operation on
5622 them, and produce a single value. The operands might represent multiple
5623 data, as is the case with the :ref:`vector <t_vector>` data type. The
5624 result value has the same type as its operands.
5626 There are several different binary operators:
5630 '``add``' Instruction
5631 ^^^^^^^^^^^^^^^^^^^^^
5638 <result> = add <ty> <op1>, <op2> ; yields ty:result
5639 <result> = add nuw <ty> <op1>, <op2> ; yields ty:result
5640 <result> = add nsw <ty> <op1>, <op2> ; yields ty:result
5641 <result> = add nuw nsw <ty> <op1>, <op2> ; yields ty:result
5646 The '``add``' instruction returns the sum of its two operands.
5651 The two arguments to the '``add``' instruction must be
5652 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
5653 arguments must have identical types.
5658 The value produced is the integer sum of the two operands.
5660 If the sum has unsigned overflow, the result returned is the
5661 mathematical result modulo 2\ :sup:`n`\ , where n is the bit width of
5664 Because LLVM integers use a two's complement representation, this
5665 instruction is appropriate for both signed and unsigned integers.
5667 ``nuw`` and ``nsw`` stand for "No Unsigned Wrap" and "No Signed Wrap",
5668 respectively. If the ``nuw`` and/or ``nsw`` keywords are present, the
5669 result value of the ``add`` is a :ref:`poison value <poisonvalues>` if
5670 unsigned and/or signed overflow, respectively, occurs.
5675 .. code-block:: llvm
5677 <result> = add i32 4, %var ; yields i32:result = 4 + %var
5681 '``fadd``' Instruction
5682 ^^^^^^^^^^^^^^^^^^^^^^
5689 <result> = fadd [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
5694 The '``fadd``' instruction returns the sum of its two operands.
5699 The two arguments to the '``fadd``' instruction must be :ref:`floating
5700 point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
5701 Both arguments must have identical types.
5706 The value produced is the floating point sum of the two operands. This
5707 instruction can also take any number of :ref:`fast-math flags <fastmath>`,
5708 which are optimization hints to enable otherwise unsafe floating point
5714 .. code-block:: llvm
5716 <result> = fadd float 4.0, %var ; yields float:result = 4.0 + %var
5718 '``sub``' Instruction
5719 ^^^^^^^^^^^^^^^^^^^^^
5726 <result> = sub <ty> <op1>, <op2> ; yields ty:result
5727 <result> = sub nuw <ty> <op1>, <op2> ; yields ty:result
5728 <result> = sub nsw <ty> <op1>, <op2> ; yields ty:result
5729 <result> = sub nuw nsw <ty> <op1>, <op2> ; yields ty:result
5734 The '``sub``' instruction returns the difference of its two operands.
5736 Note that the '``sub``' instruction is used to represent the '``neg``'
5737 instruction present in most other intermediate representations.
5742 The two arguments to the '``sub``' instruction must be
5743 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
5744 arguments must have identical types.
5749 The value produced is the integer difference of the two operands.
5751 If the difference has unsigned overflow, the result returned is the
5752 mathematical result modulo 2\ :sup:`n`\ , where n is the bit width of
5755 Because LLVM integers use a two's complement representation, this
5756 instruction is appropriate for both signed and unsigned integers.
5758 ``nuw`` and ``nsw`` stand for "No Unsigned Wrap" and "No Signed Wrap",
5759 respectively. If the ``nuw`` and/or ``nsw`` keywords are present, the
5760 result value of the ``sub`` is a :ref:`poison value <poisonvalues>` if
5761 unsigned and/or signed overflow, respectively, occurs.
5766 .. code-block:: llvm
5768 <result> = sub i32 4, %var ; yields i32:result = 4 - %var
5769 <result> = sub i32 0, %val ; yields i32:result = -%var
5773 '``fsub``' Instruction
5774 ^^^^^^^^^^^^^^^^^^^^^^
5781 <result> = fsub [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
5786 The '``fsub``' instruction returns the difference of its two operands.
5788 Note that the '``fsub``' instruction is used to represent the '``fneg``'
5789 instruction present in most other intermediate representations.
5794 The two arguments to the '``fsub``' instruction must be :ref:`floating
5795 point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
5796 Both arguments must have identical types.
5801 The value produced is the floating point difference of the two operands.
5802 This instruction can also take any number of :ref:`fast-math
5803 flags <fastmath>`, which are optimization hints to enable otherwise
5804 unsafe floating point optimizations:
5809 .. code-block:: llvm
5811 <result> = fsub float 4.0, %var ; yields float:result = 4.0 - %var
5812 <result> = fsub float -0.0, %val ; yields float:result = -%var
5814 '``mul``' Instruction
5815 ^^^^^^^^^^^^^^^^^^^^^
5822 <result> = mul <ty> <op1>, <op2> ; yields ty:result
5823 <result> = mul nuw <ty> <op1>, <op2> ; yields ty:result
5824 <result> = mul nsw <ty> <op1>, <op2> ; yields ty:result
5825 <result> = mul nuw nsw <ty> <op1>, <op2> ; yields ty:result
5830 The '``mul``' instruction returns the product of its two operands.
5835 The two arguments to the '``mul``' instruction must be
5836 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
5837 arguments must have identical types.
5842 The value produced is the integer product of the two operands.
5844 If the result of the multiplication has unsigned overflow, the result
5845 returned is the mathematical result modulo 2\ :sup:`n`\ , where n is the
5846 bit width of the result.
5848 Because LLVM integers use a two's complement representation, and the
5849 result is the same width as the operands, this instruction returns the
5850 correct result for both signed and unsigned integers. If a full product
5851 (e.g. ``i32`` * ``i32`` -> ``i64``) is needed, the operands should be
5852 sign-extended or zero-extended as appropriate to the width of the full
5855 ``nuw`` and ``nsw`` stand for "No Unsigned Wrap" and "No Signed Wrap",
5856 respectively. If the ``nuw`` and/or ``nsw`` keywords are present, the
5857 result value of the ``mul`` is a :ref:`poison value <poisonvalues>` if
5858 unsigned and/or signed overflow, respectively, occurs.
5863 .. code-block:: llvm
5865 <result> = mul i32 4, %var ; yields i32:result = 4 * %var
5869 '``fmul``' Instruction
5870 ^^^^^^^^^^^^^^^^^^^^^^
5877 <result> = fmul [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
5882 The '``fmul``' instruction returns the product of its two operands.
5887 The two arguments to the '``fmul``' instruction must be :ref:`floating
5888 point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
5889 Both arguments must have identical types.
5894 The value produced is the floating point product of the two operands.
5895 This instruction can also take any number of :ref:`fast-math
5896 flags <fastmath>`, which are optimization hints to enable otherwise
5897 unsafe floating point optimizations:
5902 .. code-block:: llvm
5904 <result> = fmul float 4.0, %var ; yields float:result = 4.0 * %var
5906 '``udiv``' Instruction
5907 ^^^^^^^^^^^^^^^^^^^^^^
5914 <result> = udiv <ty> <op1>, <op2> ; yields ty:result
5915 <result> = udiv exact <ty> <op1>, <op2> ; yields ty:result
5920 The '``udiv``' instruction returns the quotient of its two operands.
5925 The two arguments to the '``udiv``' instruction must be
5926 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
5927 arguments must have identical types.
5932 The value produced is the unsigned integer quotient of the two operands.
5934 Note that unsigned integer division and signed integer division are
5935 distinct operations; for signed integer division, use '``sdiv``'.
5937 Division by zero leads to undefined behavior.
5939 If the ``exact`` keyword is present, the result value of the ``udiv`` is
5940 a :ref:`poison value <poisonvalues>` if %op1 is not a multiple of %op2 (as
5941 such, "((a udiv exact b) mul b) == a").
5946 .. code-block:: llvm
5948 <result> = udiv i32 4, %var ; yields i32:result = 4 / %var
5950 '``sdiv``' Instruction
5951 ^^^^^^^^^^^^^^^^^^^^^^
5958 <result> = sdiv <ty> <op1>, <op2> ; yields ty:result
5959 <result> = sdiv exact <ty> <op1>, <op2> ; yields ty:result
5964 The '``sdiv``' instruction returns the quotient of its two operands.
5969 The two arguments to the '``sdiv``' instruction must be
5970 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
5971 arguments must have identical types.
5976 The value produced is the signed integer quotient of the two operands
5977 rounded towards zero.
5979 Note that signed integer division and unsigned integer division are
5980 distinct operations; for unsigned integer division, use '``udiv``'.
5982 Division by zero leads to undefined behavior. Overflow also leads to
5983 undefined behavior; this is a rare case, but can occur, for example, by
5984 doing a 32-bit division of -2147483648 by -1.
5986 If the ``exact`` keyword is present, the result value of the ``sdiv`` is
5987 a :ref:`poison value <poisonvalues>` if the result would be rounded.
5992 .. code-block:: llvm
5994 <result> = sdiv i32 4, %var ; yields i32:result = 4 / %var
5998 '``fdiv``' Instruction
5999 ^^^^^^^^^^^^^^^^^^^^^^
6006 <result> = fdiv [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
6011 The '``fdiv``' instruction returns the quotient of its two operands.
6016 The two arguments to the '``fdiv``' instruction must be :ref:`floating
6017 point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
6018 Both arguments must have identical types.
6023 The value produced is the floating point quotient of the two operands.
6024 This instruction can also take any number of :ref:`fast-math
6025 flags <fastmath>`, which are optimization hints to enable otherwise
6026 unsafe floating point optimizations:
6031 .. code-block:: llvm
6033 <result> = fdiv float 4.0, %var ; yields float:result = 4.0 / %var
6035 '``urem``' Instruction
6036 ^^^^^^^^^^^^^^^^^^^^^^
6043 <result> = urem <ty> <op1>, <op2> ; yields ty:result
6048 The '``urem``' instruction returns the remainder from the unsigned
6049 division of its two arguments.
6054 The two arguments to the '``urem``' instruction must be
6055 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
6056 arguments must have identical types.
6061 This instruction returns the unsigned integer *remainder* of a division.
6062 This instruction always performs an unsigned division to get the
6065 Note that unsigned integer remainder and signed integer remainder are
6066 distinct operations; for signed integer remainder, use '``srem``'.
6068 Taking the remainder of a division by zero leads to undefined behavior.
6073 .. code-block:: llvm
6075 <result> = urem i32 4, %var ; yields i32:result = 4 % %var
6077 '``srem``' Instruction
6078 ^^^^^^^^^^^^^^^^^^^^^^
6085 <result> = srem <ty> <op1>, <op2> ; yields ty:result
6090 The '``srem``' instruction returns the remainder from the signed
6091 division of its two operands. This instruction can also take
6092 :ref:`vector <t_vector>` versions of the values in which case the elements
6098 The two arguments to the '``srem``' instruction must be
6099 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
6100 arguments must have identical types.
6105 This instruction returns the *remainder* of a division (where the result
6106 is either zero or has the same sign as the dividend, ``op1``), not the
6107 *modulo* operator (where the result is either zero or has the same sign
6108 as the divisor, ``op2``) of a value. For more information about the
6109 difference, see `The Math
6110 Forum <http://mathforum.org/dr.math/problems/anne.4.28.99.html>`_. For a
6111 table of how this is implemented in various languages, please see
6113 operation <http://en.wikipedia.org/wiki/Modulo_operation>`_.
6115 Note that signed integer remainder and unsigned integer remainder are
6116 distinct operations; for unsigned integer remainder, use '``urem``'.
6118 Taking the remainder of a division by zero leads to undefined behavior.
6119 Overflow also leads to undefined behavior; this is a rare case, but can
6120 occur, for example, by taking the remainder of a 32-bit division of
6121 -2147483648 by -1. (The remainder doesn't actually overflow, but this
6122 rule lets srem be implemented using instructions that return both the
6123 result of the division and the remainder.)
6128 .. code-block:: llvm
6130 <result> = srem i32 4, %var ; yields i32:result = 4 % %var
6134 '``frem``' Instruction
6135 ^^^^^^^^^^^^^^^^^^^^^^
6142 <result> = frem [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
6147 The '``frem``' instruction returns the remainder from the division of
6153 The two arguments to the '``frem``' instruction must be :ref:`floating
6154 point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
6155 Both arguments must have identical types.
6160 This instruction returns the *remainder* of a division. The remainder
6161 has the same sign as the dividend. This instruction can also take any
6162 number of :ref:`fast-math flags <fastmath>`, which are optimization hints
6163 to enable otherwise unsafe floating point optimizations:
6168 .. code-block:: llvm
6170 <result> = frem float 4.0, %var ; yields float:result = 4.0 % %var
6174 Bitwise Binary Operations
6175 -------------------------
6177 Bitwise binary operators are used to do various forms of bit-twiddling
6178 in a program. They are generally very efficient instructions and can
6179 commonly be strength reduced from other instructions. They require two
6180 operands of the same type, execute an operation on them, and produce a
6181 single value. The resulting value is the same type as its operands.
6183 '``shl``' Instruction
6184 ^^^^^^^^^^^^^^^^^^^^^
6191 <result> = shl <ty> <op1>, <op2> ; yields ty:result
6192 <result> = shl nuw <ty> <op1>, <op2> ; yields ty:result
6193 <result> = shl nsw <ty> <op1>, <op2> ; yields ty:result
6194 <result> = shl nuw nsw <ty> <op1>, <op2> ; yields ty:result
6199 The '``shl``' instruction returns the first operand shifted to the left
6200 a specified number of bits.
6205 Both arguments to the '``shl``' instruction must be the same
6206 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer type.
6207 '``op2``' is treated as an unsigned value.
6212 The value produced is ``op1`` \* 2\ :sup:`op2` mod 2\ :sup:`n`,
6213 where ``n`` is the width of the result. If ``op2`` is (statically or
6214 dynamically) equal to or larger than the number of bits in
6215 ``op1``, the result is undefined. If the arguments are vectors, each
6216 vector element of ``op1`` is shifted by the corresponding shift amount
6219 If the ``nuw`` keyword is present, then the shift produces a :ref:`poison
6220 value <poisonvalues>` if it shifts out any non-zero bits. If the
6221 ``nsw`` keyword is present, then the shift produces a :ref:`poison
6222 value <poisonvalues>` if it shifts out any bits that disagree with the
6223 resultant sign bit. As such, NUW/NSW have the same semantics as they
6224 would if the shift were expressed as a mul instruction with the same
6225 nsw/nuw bits in (mul %op1, (shl 1, %op2)).
6230 .. code-block:: llvm
6232 <result> = shl i32 4, %var ; yields i32: 4 << %var
6233 <result> = shl i32 4, 2 ; yields i32: 16
6234 <result> = shl i32 1, 10 ; yields i32: 1024
6235 <result> = shl i32 1, 32 ; undefined
6236 <result> = shl <2 x i32> < i32 1, i32 1>, < i32 1, i32 2> ; yields: result=<2 x i32> < i32 2, i32 4>
6238 '``lshr``' Instruction
6239 ^^^^^^^^^^^^^^^^^^^^^^
6246 <result> = lshr <ty> <op1>, <op2> ; yields ty:result
6247 <result> = lshr exact <ty> <op1>, <op2> ; yields ty:result
6252 The '``lshr``' instruction (logical shift right) returns the first
6253 operand shifted to the right a specified number of bits with zero fill.
6258 Both arguments to the '``lshr``' instruction must be the same
6259 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer type.
6260 '``op2``' is treated as an unsigned value.
6265 This instruction always performs a logical shift right operation. The
6266 most significant bits of the result will be filled with zero bits after
6267 the shift. If ``op2`` is (statically or dynamically) equal to or larger
6268 than the number of bits in ``op1``, the result is undefined. If the
6269 arguments are vectors, each vector element of ``op1`` is shifted by the
6270 corresponding shift amount in ``op2``.
6272 If the ``exact`` keyword is present, the result value of the ``lshr`` is
6273 a :ref:`poison value <poisonvalues>` if any of the bits shifted out are
6279 .. code-block:: llvm
6281 <result> = lshr i32 4, 1 ; yields i32:result = 2
6282 <result> = lshr i32 4, 2 ; yields i32:result = 1
6283 <result> = lshr i8 4, 3 ; yields i8:result = 0
6284 <result> = lshr i8 -2, 1 ; yields i8:result = 0x7F
6285 <result> = lshr i32 1, 32 ; undefined
6286 <result> = lshr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 2> ; yields: result=<2 x i32> < i32 0x7FFFFFFF, i32 1>
6288 '``ashr``' Instruction
6289 ^^^^^^^^^^^^^^^^^^^^^^
6296 <result> = ashr <ty> <op1>, <op2> ; yields ty:result
6297 <result> = ashr exact <ty> <op1>, <op2> ; yields ty:result
6302 The '``ashr``' instruction (arithmetic shift right) returns the first
6303 operand shifted to the right a specified number of bits with sign
6309 Both arguments to the '``ashr``' instruction must be the same
6310 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer type.
6311 '``op2``' is treated as an unsigned value.
6316 This instruction always performs an arithmetic shift right operation,
6317 The most significant bits of the result will be filled with the sign bit
6318 of ``op1``. If ``op2`` is (statically or dynamically) equal to or larger
6319 than the number of bits in ``op1``, the result is undefined. If the
6320 arguments are vectors, each vector element of ``op1`` is shifted by the
6321 corresponding shift amount in ``op2``.
6323 If the ``exact`` keyword is present, the result value of the ``ashr`` is
6324 a :ref:`poison value <poisonvalues>` if any of the bits shifted out are
6330 .. code-block:: llvm
6332 <result> = ashr i32 4, 1 ; yields i32:result = 2
6333 <result> = ashr i32 4, 2 ; yields i32:result = 1
6334 <result> = ashr i8 4, 3 ; yields i8:result = 0
6335 <result> = ashr i8 -2, 1 ; yields i8:result = -1
6336 <result> = ashr i32 1, 32 ; undefined
6337 <result> = ashr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 3> ; yields: result=<2 x i32> < i32 -1, i32 0>
6339 '``and``' Instruction
6340 ^^^^^^^^^^^^^^^^^^^^^
6347 <result> = and <ty> <op1>, <op2> ; yields ty:result
6352 The '``and``' instruction returns the bitwise logical and of its two
6358 The two arguments to the '``and``' instruction must be
6359 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
6360 arguments must have identical types.
6365 The truth table used for the '``and``' instruction is:
6382 .. code-block:: llvm
6384 <result> = and i32 4, %var ; yields i32:result = 4 & %var
6385 <result> = and i32 15, 40 ; yields i32:result = 8
6386 <result> = and i32 4, 8 ; yields i32:result = 0
6388 '``or``' Instruction
6389 ^^^^^^^^^^^^^^^^^^^^
6396 <result> = or <ty> <op1>, <op2> ; yields ty:result
6401 The '``or``' instruction returns the bitwise logical inclusive or of its
6407 The two arguments to the '``or``' instruction must be
6408 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
6409 arguments must have identical types.
6414 The truth table used for the '``or``' instruction is:
6433 <result> = or i32 4, %var ; yields i32:result = 4 | %var
6434 <result> = or i32 15, 40 ; yields i32:result = 47
6435 <result> = or i32 4, 8 ; yields i32:result = 12
6437 '``xor``' Instruction
6438 ^^^^^^^^^^^^^^^^^^^^^
6445 <result> = xor <ty> <op1>, <op2> ; yields ty:result
6450 The '``xor``' instruction returns the bitwise logical exclusive or of
6451 its two operands. The ``xor`` is used to implement the "one's
6452 complement" operation, which is the "~" operator in C.
6457 The two arguments to the '``xor``' instruction must be
6458 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
6459 arguments must have identical types.
6464 The truth table used for the '``xor``' instruction is:
6481 .. code-block:: llvm
6483 <result> = xor i32 4, %var ; yields i32:result = 4 ^ %var
6484 <result> = xor i32 15, 40 ; yields i32:result = 39
6485 <result> = xor i32 4, 8 ; yields i32:result = 12
6486 <result> = xor i32 %V, -1 ; yields i32:result = ~%V
6491 LLVM supports several instructions to represent vector operations in a
6492 target-independent manner. These instructions cover the element-access
6493 and vector-specific operations needed to process vectors effectively.
6494 While LLVM does directly support these vector operations, many
6495 sophisticated algorithms will want to use target-specific intrinsics to
6496 take full advantage of a specific target.
6498 .. _i_extractelement:
6500 '``extractelement``' Instruction
6501 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6508 <result> = extractelement <n x <ty>> <val>, <ty2> <idx> ; yields <ty>
6513 The '``extractelement``' instruction extracts a single scalar element
6514 from a vector at a specified index.
6519 The first operand of an '``extractelement``' instruction is a value of
6520 :ref:`vector <t_vector>` type. The second operand is an index indicating
6521 the position from which to extract the element. The index may be a
6522 variable of any integer type.
6527 The result is a scalar of the same type as the element type of ``val``.
6528 Its value is the value at position ``idx`` of ``val``. If ``idx``
6529 exceeds the length of ``val``, the results are undefined.
6534 .. code-block:: llvm
6536 <result> = extractelement <4 x i32> %vec, i32 0 ; yields i32
6538 .. _i_insertelement:
6540 '``insertelement``' Instruction
6541 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6548 <result> = insertelement <n x <ty>> <val>, <ty> <elt>, <ty2> <idx> ; yields <n x <ty>>
6553 The '``insertelement``' instruction inserts a scalar element into a
6554 vector at a specified index.
6559 The first operand of an '``insertelement``' instruction is a value of
6560 :ref:`vector <t_vector>` type. The second operand is a scalar value whose
6561 type must equal the element type of the first operand. The third operand
6562 is an index indicating the position at which to insert the value. The
6563 index may be a variable of any integer type.
6568 The result is a vector of the same type as ``val``. Its element values
6569 are those of ``val`` except at position ``idx``, where it gets the value
6570 ``elt``. If ``idx`` exceeds the length of ``val``, the results are
6576 .. code-block:: llvm
6578 <result> = insertelement <4 x i32> %vec, i32 1, i32 0 ; yields <4 x i32>
6580 .. _i_shufflevector:
6582 '``shufflevector``' Instruction
6583 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6590 <result> = shufflevector <n x <ty>> <v1>, <n x <ty>> <v2>, <m x i32> <mask> ; yields <m x <ty>>
6595 The '``shufflevector``' instruction constructs a permutation of elements
6596 from two input vectors, returning a vector with the same element type as
6597 the input and length that is the same as the shuffle mask.
6602 The first two operands of a '``shufflevector``' instruction are vectors
6603 with the same type. The third argument is a shuffle mask whose element
6604 type is always 'i32'. The result of the instruction is a vector whose
6605 length is the same as the shuffle mask and whose element type is the
6606 same as the element type of the first two operands.
6608 The shuffle mask operand is required to be a constant vector with either
6609 constant integer or undef values.
6614 The elements of the two input vectors are numbered from left to right
6615 across both of the vectors. The shuffle mask operand specifies, for each
6616 element of the result vector, which element of the two input vectors the
6617 result element gets. The element selector may be undef (meaning "don't
6618 care") and the second operand may be undef if performing a shuffle from
6624 .. code-block:: llvm
6626 <result> = shufflevector <4 x i32> %v1, <4 x i32> %v2,
6627 <4 x i32> <i32 0, i32 4, i32 1, i32 5> ; yields <4 x i32>
6628 <result> = shufflevector <4 x i32> %v1, <4 x i32> undef,
6629 <4 x i32> <i32 0, i32 1, i32 2, i32 3> ; yields <4 x i32> - Identity shuffle.
6630 <result> = shufflevector <8 x i32> %v1, <8 x i32> undef,
6631 <4 x i32> <i32 0, i32 1, i32 2, i32 3> ; yields <4 x i32>
6632 <result> = shufflevector <4 x i32> %v1, <4 x i32> %v2,
6633 <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7 > ; yields <8 x i32>
6635 Aggregate Operations
6636 --------------------
6638 LLVM supports several instructions for working with
6639 :ref:`aggregate <t_aggregate>` values.
6643 '``extractvalue``' Instruction
6644 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6651 <result> = extractvalue <aggregate type> <val>, <idx>{, <idx>}*
6656 The '``extractvalue``' instruction extracts the value of a member field
6657 from an :ref:`aggregate <t_aggregate>` value.
6662 The first operand of an '``extractvalue``' instruction is a value of
6663 :ref:`struct <t_struct>` or :ref:`array <t_array>` type. The other operands are
6664 constant indices to specify which value to extract in a similar manner
6665 as indices in a '``getelementptr``' instruction.
6667 The major differences to ``getelementptr`` indexing are:
6669 - Since the value being indexed is not a pointer, the first index is
6670 omitted and assumed to be zero.
6671 - At least one index must be specified.
6672 - Not only struct indices but also array indices must be in bounds.
6677 The result is the value at the position in the aggregate specified by
6683 .. code-block:: llvm
6685 <result> = extractvalue {i32, float} %agg, 0 ; yields i32
6689 '``insertvalue``' Instruction
6690 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6697 <result> = insertvalue <aggregate type> <val>, <ty> <elt>, <idx>{, <idx>}* ; yields <aggregate type>
6702 The '``insertvalue``' instruction inserts a value into a member field in
6703 an :ref:`aggregate <t_aggregate>` value.
6708 The first operand of an '``insertvalue``' instruction is a value of
6709 :ref:`struct <t_struct>` or :ref:`array <t_array>` type. The second operand is
6710 a first-class value to insert. The following operands are constant
6711 indices indicating the position at which to insert the value in a
6712 similar manner as indices in a '``extractvalue``' instruction. The value
6713 to insert must have the same type as the value identified by the
6719 The result is an aggregate of the same type as ``val``. Its value is
6720 that of ``val`` except that the value at the position specified by the
6721 indices is that of ``elt``.
6726 .. code-block:: llvm
6728 %agg1 = insertvalue {i32, float} undef, i32 1, 0 ; yields {i32 1, float undef}
6729 %agg2 = insertvalue {i32, float} %agg1, float %val, 1 ; yields {i32 1, float %val}
6730 %agg3 = insertvalue {i32, {float}} undef, float %val, 1, 0 ; yields {i32 undef, {float %val}}
6734 Memory Access and Addressing Operations
6735 ---------------------------------------
6737 A key design point of an SSA-based representation is how it represents
6738 memory. In LLVM, no memory locations are in SSA form, which makes things
6739 very simple. This section describes how to read, write, and allocate
6744 '``alloca``' Instruction
6745 ^^^^^^^^^^^^^^^^^^^^^^^^
6752 <result> = alloca [inalloca] <type> [, <ty> <NumElements>] [, align <alignment>] ; yields type*:result
6757 The '``alloca``' instruction allocates memory on the stack frame of the
6758 currently executing function, to be automatically released when this
6759 function returns to its caller. The object is always allocated in the
6760 generic address space (address space zero).
6765 The '``alloca``' instruction allocates ``sizeof(<type>)*NumElements``
6766 bytes of memory on the runtime stack, returning a pointer of the
6767 appropriate type to the program. If "NumElements" is specified, it is
6768 the number of elements allocated, otherwise "NumElements" is defaulted
6769 to be one. If a constant alignment is specified, the value result of the
6770 allocation is guaranteed to be aligned to at least that boundary. The
6771 alignment may not be greater than ``1 << 29``. If not specified, or if
6772 zero, the target can choose to align the allocation on any convenient
6773 boundary compatible with the type.
6775 '``type``' may be any sized type.
6780 Memory is allocated; a pointer is returned. The operation is undefined
6781 if there is insufficient stack space for the allocation. '``alloca``'d
6782 memory is automatically released when the function returns. The
6783 '``alloca``' instruction is commonly used to represent automatic
6784 variables that must have an address available. When the function returns
6785 (either with the ``ret`` or ``resume`` instructions), the memory is
6786 reclaimed. Allocating zero bytes is legal, but the result is undefined.
6787 The order in which memory is allocated (ie., which way the stack grows)
6793 .. code-block:: llvm
6795 %ptr = alloca i32 ; yields i32*:ptr
6796 %ptr = alloca i32, i32 4 ; yields i32*:ptr
6797 %ptr = alloca i32, i32 4, align 1024 ; yields i32*:ptr
6798 %ptr = alloca i32, align 1024 ; yields i32*:ptr
6802 '``load``' Instruction
6803 ^^^^^^^^^^^^^^^^^^^^^^
6810 <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>]
6811 <result> = load atomic [volatile] <ty>* <pointer> [singlethread] <ordering>, align <alignment> [, !invariant.group !<index>]
6812 !<index> = !{ i32 1 }
6813 !<deref_bytes_node> = !{i64 <dereferenceable_bytes>}
6814 !<align_node> = !{ i64 <value_alignment> }
6819 The '``load``' instruction is used to read from memory.
6824 The argument to the ``load`` instruction specifies the memory address
6825 from which to load. The type specified must be a :ref:`first
6826 class <t_firstclass>` type. If the ``load`` is marked as ``volatile``,
6827 then the optimizer is not allowed to modify the number or order of
6828 execution of this ``load`` with other :ref:`volatile
6829 operations <volatile>`.
6831 If the ``load`` is marked as ``atomic``, it takes an extra
6832 :ref:`ordering <ordering>` and optional ``singlethread`` argument. The
6833 ``release`` and ``acq_rel`` orderings are not valid on ``load``
6834 instructions. Atomic loads produce :ref:`defined <memmodel>` results
6835 when they may see multiple atomic stores. The type of the pointee must
6836 be an integer type whose bit width is a power of two greater than or
6837 equal to eight and less than or equal to a target-specific size limit.
6838 ``align`` must be explicitly specified on atomic loads, and the load has
6839 undefined behavior if the alignment is not set to a value which is at
6840 least the size in bytes of the pointee. ``!nontemporal`` does not have
6841 any defined semantics for atomic loads.
6843 The optional constant ``align`` argument specifies the alignment of the
6844 operation (that is, the alignment of the memory address). A value of 0
6845 or an omitted ``align`` argument means that the operation has the ABI
6846 alignment for the target. It is the responsibility of the code emitter
6847 to ensure that the alignment information is correct. Overestimating the
6848 alignment results in undefined behavior. Underestimating the alignment
6849 may produce less efficient code. An alignment of 1 is always safe. The
6850 maximum possible alignment is ``1 << 29``.
6852 The optional ``!nontemporal`` metadata must reference a single
6853 metadata name ``<index>`` corresponding to a metadata node with one
6854 ``i32`` entry of value 1. The existence of the ``!nontemporal``
6855 metadata on the instruction tells the optimizer and code generator
6856 that this load is not expected to be reused in the cache. The code
6857 generator may select special instructions to save cache bandwidth, such
6858 as the ``MOVNT`` instruction on x86.
6860 The optional ``!invariant.load`` metadata must reference a single
6861 metadata name ``<index>`` corresponding to a metadata node with no
6862 entries. The existence of the ``!invariant.load`` metadata on the
6863 instruction tells the optimizer and code generator that the address
6864 operand to this load points to memory which can be assumed unchanged.
6865 Being invariant does not imply that a location is dereferenceable,
6866 but it does imply that once the location is known dereferenceable
6867 its value is henceforth unchanging.
6869 The optional ``!invariant.group`` metadata must reference a single metadata name
6870 ``<index>`` corresponding to a metadata node. See ``invariant.group`` metadata.
6872 The optional ``!nonnull`` metadata must reference a single
6873 metadata name ``<index>`` corresponding to a metadata node with no
6874 entries. The existence of the ``!nonnull`` metadata on the
6875 instruction tells the optimizer that the value loaded is known to
6876 never be null. This is analogous to the ``nonnull`` attribute
6877 on parameters and return values. This metadata can only be applied
6878 to loads of a pointer type.
6880 The optional ``!dereferenceable`` metadata must reference a single metadata
6881 name ``<deref_bytes_node>`` corresponding to a metadata node with one ``i64``
6882 entry. The existence of the ``!dereferenceable`` metadata on the instruction
6883 tells the optimizer that the value loaded is known to be dereferenceable.
6884 The number of bytes known to be dereferenceable is specified by the integer
6885 value in the metadata node. This is analogous to the ''dereferenceable''
6886 attribute on parameters and return values. This metadata can only be applied
6887 to loads of a pointer type.
6889 The optional ``!dereferenceable_or_null`` metadata must reference a single
6890 metadata name ``<deref_bytes_node>`` corresponding to a metadata node with one
6891 ``i64`` entry. The existence of the ``!dereferenceable_or_null`` metadata on the
6892 instruction tells the optimizer that the value loaded is known to be either
6893 dereferenceable or null.
6894 The number of bytes known to be dereferenceable is specified by the integer
6895 value in the metadata node. This is analogous to the ''dereferenceable_or_null''
6896 attribute on parameters and return values. This metadata can only be applied
6897 to loads of a pointer type.
6899 The optional ``!align`` metadata must reference a single metadata name
6900 ``<align_node>`` corresponding to a metadata node with one ``i64`` entry.
6901 The existence of the ``!align`` metadata on the instruction tells the
6902 optimizer that the value loaded is known to be aligned to a boundary specified
6903 by the integer value in the metadata node. The alignment must be a power of 2.
6904 This is analogous to the ''align'' attribute on parameters and return values.
6905 This metadata can only be applied to loads of a pointer type.
6910 The location of memory pointed to is loaded. If the value being loaded
6911 is of scalar type then the number of bytes read does not exceed the
6912 minimum number of bytes needed to hold all bits of the type. For
6913 example, loading an ``i24`` reads at most three bytes. When loading a
6914 value of a type like ``i20`` with a size that is not an integral number
6915 of bytes, the result is undefined if the value was not originally
6916 written using a store of the same type.
6921 .. code-block:: llvm
6923 %ptr = alloca i32 ; yields i32*:ptr
6924 store i32 3, i32* %ptr ; yields void
6925 %val = load i32, i32* %ptr ; yields i32:val = i32 3
6929 '``store``' Instruction
6930 ^^^^^^^^^^^^^^^^^^^^^^^
6937 store [volatile] <ty> <value>, <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>][, !invariant.group !<index>] ; yields void
6938 store atomic [volatile] <ty> <value>, <ty>* <pointer> [singlethread] <ordering>, align <alignment> [, !invariant.group !<index>] ; yields void
6943 The '``store``' instruction is used to write to memory.
6948 There are two arguments to the ``store`` instruction: a value to store
6949 and an address at which to store it. The type of the ``<pointer>``
6950 operand must be a pointer to the :ref:`first class <t_firstclass>` type of
6951 the ``<value>`` operand. If the ``store`` is marked as ``volatile``,
6952 then the optimizer is not allowed to modify the number or order of
6953 execution of this ``store`` with other :ref:`volatile
6954 operations <volatile>`.
6956 If the ``store`` is marked as ``atomic``, it takes an extra
6957 :ref:`ordering <ordering>` and optional ``singlethread`` argument. The
6958 ``acquire`` and ``acq_rel`` orderings aren't valid on ``store``
6959 instructions. Atomic loads produce :ref:`defined <memmodel>` results
6960 when they may see multiple atomic stores. The type of the pointee must
6961 be an integer type whose bit width is a power of two greater than or
6962 equal to eight and less than or equal to a target-specific size limit.
6963 ``align`` must be explicitly specified on atomic stores, and the store
6964 has undefined behavior if the alignment is not set to a value which is
6965 at least the size in bytes of the pointee. ``!nontemporal`` does not
6966 have any defined semantics for atomic stores.
6968 The optional constant ``align`` argument specifies the alignment of the
6969 operation (that is, the alignment of the memory address). A value of 0
6970 or an omitted ``align`` argument means that the operation has the ABI
6971 alignment for the target. It is the responsibility of the code emitter
6972 to ensure that the alignment information is correct. Overestimating the
6973 alignment results in undefined behavior. Underestimating the
6974 alignment may produce less efficient code. An alignment of 1 is always
6975 safe. The maximum possible alignment is ``1 << 29``.
6977 The optional ``!nontemporal`` metadata must reference a single metadata
6978 name ``<index>`` corresponding to a metadata node with one ``i32`` entry of
6979 value 1. The existence of the ``!nontemporal`` metadata on the instruction
6980 tells the optimizer and code generator that this load is not expected to
6981 be reused in the cache. The code generator may select special
6982 instructions to save cache bandwidth, such as the MOVNT instruction on
6985 The optional ``!invariant.group`` metadata must reference a
6986 single metadata name ``<index>``. See ``invariant.group`` metadata.
6991 The contents of memory are updated to contain ``<value>`` at the
6992 location specified by the ``<pointer>`` operand. If ``<value>`` is
6993 of scalar type then the number of bytes written does not exceed the
6994 minimum number of bytes needed to hold all bits of the type. For
6995 example, storing an ``i24`` writes at most three bytes. When writing a
6996 value of a type like ``i20`` with a size that is not an integral number
6997 of bytes, it is unspecified what happens to the extra bits that do not
6998 belong to the type, but they will typically be overwritten.
7003 .. code-block:: llvm
7005 %ptr = alloca i32 ; yields i32*:ptr
7006 store i32 3, i32* %ptr ; yields void
7007 %val = load i32, i32* %ptr ; yields i32:val = i32 3
7011 '``fence``' Instruction
7012 ^^^^^^^^^^^^^^^^^^^^^^^
7019 fence [singlethread] <ordering> ; yields void
7024 The '``fence``' instruction is used to introduce happens-before edges
7030 '``fence``' instructions take an :ref:`ordering <ordering>` argument which
7031 defines what *synchronizes-with* edges they add. They can only be given
7032 ``acquire``, ``release``, ``acq_rel``, and ``seq_cst`` orderings.
7037 A fence A which has (at least) ``release`` ordering semantics
7038 *synchronizes with* a fence B with (at least) ``acquire`` ordering
7039 semantics if and only if there exist atomic operations X and Y, both
7040 operating on some atomic object M, such that A is sequenced before X, X
7041 modifies M (either directly or through some side effect of a sequence
7042 headed by X), Y is sequenced before B, and Y observes M. This provides a
7043 *happens-before* dependency between A and B. Rather than an explicit
7044 ``fence``, one (but not both) of the atomic operations X or Y might
7045 provide a ``release`` or ``acquire`` (resp.) ordering constraint and
7046 still *synchronize-with* the explicit ``fence`` and establish the
7047 *happens-before* edge.
7049 A ``fence`` which has ``seq_cst`` ordering, in addition to having both
7050 ``acquire`` and ``release`` semantics specified above, participates in
7051 the global program order of other ``seq_cst`` operations and/or fences.
7053 The optional ":ref:`singlethread <singlethread>`" argument specifies
7054 that the fence only synchronizes with other fences in the same thread.
7055 (This is useful for interacting with signal handlers.)
7060 .. code-block:: llvm
7062 fence acquire ; yields void
7063 fence singlethread seq_cst ; yields void
7067 '``cmpxchg``' Instruction
7068 ^^^^^^^^^^^^^^^^^^^^^^^^^
7075 cmpxchg [weak] [volatile] <ty>* <pointer>, <ty> <cmp>, <ty> <new> [singlethread] <success ordering> <failure ordering> ; yields { ty, i1 }
7080 The '``cmpxchg``' instruction is used to atomically modify memory. It
7081 loads a value in memory and compares it to a given value. If they are
7082 equal, it tries to store a new value into the memory.
7087 There are three arguments to the '``cmpxchg``' instruction: an address
7088 to operate on, a value to compare to the value currently be at that
7089 address, and a new value to place at that address if the compared values
7090 are equal. The type of '<cmp>' must be an integer type whose bit width
7091 is a power of two greater than or equal to eight and less than or equal
7092 to a target-specific size limit. '<cmp>' and '<new>' must have the same
7093 type, and the type of '<pointer>' must be a pointer to that type. If the
7094 ``cmpxchg`` is marked as ``volatile``, then the optimizer is not allowed
7095 to modify the number or order of execution of this ``cmpxchg`` with
7096 other :ref:`volatile operations <volatile>`.
7098 The success and failure :ref:`ordering <ordering>` arguments specify how this
7099 ``cmpxchg`` synchronizes with other atomic operations. Both ordering parameters
7100 must be at least ``monotonic``, the ordering constraint on failure must be no
7101 stronger than that on success, and the failure ordering cannot be either
7102 ``release`` or ``acq_rel``.
7104 The optional "``singlethread``" argument declares that the ``cmpxchg``
7105 is only atomic with respect to code (usually signal handlers) running in
7106 the same thread as the ``cmpxchg``. Otherwise the cmpxchg is atomic with
7107 respect to all other code in the system.
7109 The pointer passed into cmpxchg must have alignment greater than or
7110 equal to the size in memory of the operand.
7115 The contents of memory at the location specified by the '``<pointer>``' operand
7116 is read and compared to '``<cmp>``'; if the read value is the equal, the
7117 '``<new>``' is written. The original value at the location is returned, together
7118 with a flag indicating success (true) or failure (false).
7120 If the cmpxchg operation is marked as ``weak`` then a spurious failure is
7121 permitted: the operation may not write ``<new>`` even if the comparison
7124 If the cmpxchg operation is strong (the default), the i1 value is 1 if and only
7125 if the value loaded equals ``cmp``.
7127 A successful ``cmpxchg`` is a read-modify-write instruction for the purpose of
7128 identifying release sequences. A failed ``cmpxchg`` is equivalent to an atomic
7129 load with an ordering parameter determined the second ordering parameter.
7134 .. code-block:: llvm
7137 %orig = atomic load i32, i32* %ptr unordered ; yields i32
7141 %cmp = phi i32 [ %orig, %entry ], [%old, %loop]
7142 %squared = mul i32 %cmp, %cmp
7143 %val_success = cmpxchg i32* %ptr, i32 %cmp, i32 %squared acq_rel monotonic ; yields { i32, i1 }
7144 %value_loaded = extractvalue { i32, i1 } %val_success, 0
7145 %success = extractvalue { i32, i1 } %val_success, 1
7146 br i1 %success, label %done, label %loop
7153 '``atomicrmw``' Instruction
7154 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
7161 atomicrmw [volatile] <operation> <ty>* <pointer>, <ty> <value> [singlethread] <ordering> ; yields ty
7166 The '``atomicrmw``' instruction is used to atomically modify memory.
7171 There are three arguments to the '``atomicrmw``' instruction: an
7172 operation to apply, an address whose value to modify, an argument to the
7173 operation. The operation must be one of the following keywords:
7187 The type of '<value>' must be an integer type whose bit width is a power
7188 of two greater than or equal to eight and less than or equal to a
7189 target-specific size limit. The type of the '``<pointer>``' operand must
7190 be a pointer to that type. If the ``atomicrmw`` is marked as
7191 ``volatile``, then the optimizer is not allowed to modify the number or
7192 order of execution of this ``atomicrmw`` with other :ref:`volatile
7193 operations <volatile>`.
7198 The contents of memory at the location specified by the '``<pointer>``'
7199 operand are atomically read, modified, and written back. The original
7200 value at the location is returned. The modification is specified by the
7203 - xchg: ``*ptr = val``
7204 - add: ``*ptr = *ptr + val``
7205 - sub: ``*ptr = *ptr - val``
7206 - and: ``*ptr = *ptr & val``
7207 - nand: ``*ptr = ~(*ptr & val)``
7208 - or: ``*ptr = *ptr | val``
7209 - xor: ``*ptr = *ptr ^ val``
7210 - max: ``*ptr = *ptr > val ? *ptr : val`` (using a signed comparison)
7211 - min: ``*ptr = *ptr < val ? *ptr : val`` (using a signed comparison)
7212 - umax: ``*ptr = *ptr > val ? *ptr : val`` (using an unsigned
7214 - umin: ``*ptr = *ptr < val ? *ptr : val`` (using an unsigned
7220 .. code-block:: llvm
7222 %old = atomicrmw add i32* %ptr, i32 1 acquire ; yields i32
7224 .. _i_getelementptr:
7226 '``getelementptr``' Instruction
7227 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7234 <result> = getelementptr <ty>, <ty>* <ptrval>{, <ty> <idx>}*
7235 <result> = getelementptr inbounds <ty>, <ty>* <ptrval>{, <ty> <idx>}*
7236 <result> = getelementptr <ty>, <ptr vector> <ptrval>, <vector index type> <idx>
7241 The '``getelementptr``' instruction is used to get the address of a
7242 subelement of an :ref:`aggregate <t_aggregate>` data structure. It performs
7243 address calculation only and does not access memory. The instruction can also
7244 be used to calculate a vector of such addresses.
7249 The first argument is always a type used as the basis for the calculations.
7250 The second argument is always a pointer or a vector of pointers, and is the
7251 base address to start from. The remaining arguments are indices
7252 that indicate which of the elements of the aggregate object are indexed.
7253 The interpretation of each index is dependent on the type being indexed
7254 into. The first index always indexes the pointer value given as the
7255 first argument, the second index indexes a value of the type pointed to
7256 (not necessarily the value directly pointed to, since the first index
7257 can be non-zero), etc. The first type indexed into must be a pointer
7258 value, subsequent types can be arrays, vectors, and structs. Note that
7259 subsequent types being indexed into can never be pointers, since that
7260 would require loading the pointer before continuing calculation.
7262 The type of each index argument depends on the type it is indexing into.
7263 When indexing into a (optionally packed) structure, only ``i32`` integer
7264 **constants** are allowed (when using a vector of indices they must all
7265 be the **same** ``i32`` integer constant). When indexing into an array,
7266 pointer or vector, integers of any width are allowed, and they are not
7267 required to be constant. These integers are treated as signed values
7270 For example, let's consider a C code fragment and how it gets compiled
7286 int *foo(struct ST *s) {
7287 return &s[1].Z.B[5][13];
7290 The LLVM code generated by Clang is:
7292 .. code-block:: llvm
7294 %struct.RT = type { i8, [10 x [20 x i32]], i8 }
7295 %struct.ST = type { i32, double, %struct.RT }
7297 define i32* @foo(%struct.ST* %s) nounwind uwtable readnone optsize ssp {
7299 %arrayidx = getelementptr inbounds %struct.ST, %struct.ST* %s, i64 1, i32 2, i32 1, i64 5, i64 13
7306 In the example above, the first index is indexing into the
7307 '``%struct.ST*``' type, which is a pointer, yielding a '``%struct.ST``'
7308 = '``{ i32, double, %struct.RT }``' type, a structure. The second index
7309 indexes into the third element of the structure, yielding a
7310 '``%struct.RT``' = '``{ i8 , [10 x [20 x i32]], i8 }``' type, another
7311 structure. The third index indexes into the second element of the
7312 structure, yielding a '``[10 x [20 x i32]]``' type, an array. The two
7313 dimensions of the array are subscripted into, yielding an '``i32``'
7314 type. The '``getelementptr``' instruction returns a pointer to this
7315 element, thus computing a value of '``i32*``' type.
7317 Note that it is perfectly legal to index partially through a structure,
7318 returning a pointer to an inner element. Because of this, the LLVM code
7319 for the given testcase is equivalent to:
7321 .. code-block:: llvm
7323 define i32* @foo(%struct.ST* %s) {
7324 %t1 = getelementptr %struct.ST, %struct.ST* %s, i32 1 ; yields %struct.ST*:%t1
7325 %t2 = getelementptr %struct.ST, %struct.ST* %t1, i32 0, i32 2 ; yields %struct.RT*:%t2
7326 %t3 = getelementptr %struct.RT, %struct.RT* %t2, i32 0, i32 1 ; yields [10 x [20 x i32]]*:%t3
7327 %t4 = getelementptr [10 x [20 x i32]], [10 x [20 x i32]]* %t3, i32 0, i32 5 ; yields [20 x i32]*:%t4
7328 %t5 = getelementptr [20 x i32], [20 x i32]* %t4, i32 0, i32 13 ; yields i32*:%t5
7332 If the ``inbounds`` keyword is present, the result value of the
7333 ``getelementptr`` is a :ref:`poison value <poisonvalues>` if the base
7334 pointer is not an *in bounds* address of an allocated object, or if any
7335 of the addresses that would be formed by successive addition of the
7336 offsets implied by the indices to the base address with infinitely
7337 precise signed arithmetic are not an *in bounds* address of that
7338 allocated object. The *in bounds* addresses for an allocated object are
7339 all the addresses that point into the object, plus the address one byte
7340 past the end. In cases where the base is a vector of pointers the
7341 ``inbounds`` keyword applies to each of the computations element-wise.
7343 If the ``inbounds`` keyword is not present, the offsets are added to the
7344 base address with silently-wrapping two's complement arithmetic. If the
7345 offsets have a different width from the pointer, they are sign-extended
7346 or truncated to the width of the pointer. The result value of the
7347 ``getelementptr`` may be outside the object pointed to by the base
7348 pointer. The result value may not necessarily be used to access memory
7349 though, even if it happens to point into allocated storage. See the
7350 :ref:`Pointer Aliasing Rules <pointeraliasing>` section for more
7353 The getelementptr instruction is often confusing. For some more insight
7354 into how it works, see :doc:`the getelementptr FAQ <GetElementPtr>`.
7359 .. code-block:: llvm
7361 ; yields [12 x i8]*:aptr
7362 %aptr = getelementptr {i32, [12 x i8]}, {i32, [12 x i8]}* %saptr, i64 0, i32 1
7364 %vptr = getelementptr {i32, <2 x i8>}, {i32, <2 x i8>}* %svptr, i64 0, i32 1, i32 1
7366 %eptr = getelementptr [12 x i8], [12 x i8]* %aptr, i64 0, i32 1
7368 %iptr = getelementptr [10 x i32], [10 x i32]* @arr, i16 0, i16 0
7373 The ``getelementptr`` returns a vector of pointers, instead of a single address,
7374 when one or more of its arguments is a vector. In such cases, all vector
7375 arguments should have the same number of elements, and every scalar argument
7376 will be effectively broadcast into a vector during address calculation.
7378 .. code-block:: llvm
7380 ; All arguments are vectors:
7381 ; A[i] = ptrs[i] + offsets[i]*sizeof(i8)
7382 %A = getelementptr i8, <4 x i8*> %ptrs, <4 x i64> %offsets
7384 ; Add the same scalar offset to each pointer of a vector:
7385 ; A[i] = ptrs[i] + offset*sizeof(i8)
7386 %A = getelementptr i8, <4 x i8*> %ptrs, i64 %offset
7388 ; Add distinct offsets to the same pointer:
7389 ; A[i] = ptr + offsets[i]*sizeof(i8)
7390 %A = getelementptr i8, i8* %ptr, <4 x i64> %offsets
7392 ; In all cases described above the type of the result is <4 x i8*>
7394 The two following instructions are equivalent:
7396 .. code-block:: llvm
7398 getelementptr %struct.ST, <4 x %struct.ST*> %s, <4 x i64> %ind1,
7399 <4 x i32> <i32 2, i32 2, i32 2, i32 2>,
7400 <4 x i32> <i32 1, i32 1, i32 1, i32 1>,
7402 <4 x i64> <i64 13, i64 13, i64 13, i64 13>
7404 getelementptr %struct.ST, <4 x %struct.ST*> %s, <4 x i64> %ind1,
7405 i32 2, i32 1, <4 x i32> %ind4, i64 13
7407 Let's look at the C code, where the vector version of ``getelementptr``
7412 // Let's assume that we vectorize the following loop:
7413 double *A, B; int *C;
7414 for (int i = 0; i < size; ++i) {
7418 .. code-block:: llvm
7420 ; get pointers for 8 elements from array B
7421 %ptrs = getelementptr double, double* %B, <8 x i32> %C
7422 ; load 8 elements from array B into A
7423 %A = call <8 x double> @llvm.masked.gather.v8f64(<8 x double*> %ptrs,
7424 i32 8, <8 x i1> %mask, <8 x double> %passthru)
7426 Conversion Operations
7427 ---------------------
7429 The instructions in this category are the conversion instructions
7430 (casting) which all take a single operand and a type. They perform
7431 various bit conversions on the operand.
7433 '``trunc .. to``' Instruction
7434 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7441 <result> = trunc <ty> <value> to <ty2> ; yields ty2
7446 The '``trunc``' instruction truncates its operand to the type ``ty2``.
7451 The '``trunc``' instruction takes a value to trunc, and a type to trunc
7452 it to. Both types must be of :ref:`integer <t_integer>` types, or vectors
7453 of the same number of integers. The bit size of the ``value`` must be
7454 larger than the bit size of the destination type, ``ty2``. Equal sized
7455 types are not allowed.
7460 The '``trunc``' instruction truncates the high order bits in ``value``
7461 and converts the remaining bits to ``ty2``. Since the source size must
7462 be larger than the destination size, ``trunc`` cannot be a *no-op cast*.
7463 It will always truncate bits.
7468 .. code-block:: llvm
7470 %X = trunc i32 257 to i8 ; yields i8:1
7471 %Y = trunc i32 123 to i1 ; yields i1:true
7472 %Z = trunc i32 122 to i1 ; yields i1:false
7473 %W = trunc <2 x i16> <i16 8, i16 7> to <2 x i8> ; yields <i8 8, i8 7>
7475 '``zext .. to``' Instruction
7476 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7483 <result> = zext <ty> <value> to <ty2> ; yields ty2
7488 The '``zext``' instruction zero extends its operand to type ``ty2``.
7493 The '``zext``' instruction takes a value to cast, and a type to cast it
7494 to. Both types must be of :ref:`integer <t_integer>` types, or vectors of
7495 the same number of integers. The bit size of the ``value`` must be
7496 smaller than the bit size of the destination type, ``ty2``.
7501 The ``zext`` fills the high order bits of the ``value`` with zero bits
7502 until it reaches the size of the destination type, ``ty2``.
7504 When zero extending from i1, the result will always be either 0 or 1.
7509 .. code-block:: llvm
7511 %X = zext i32 257 to i64 ; yields i64:257
7512 %Y = zext i1 true to i32 ; yields i32:1
7513 %Z = zext <2 x i16> <i16 8, i16 7> to <2 x i32> ; yields <i32 8, i32 7>
7515 '``sext .. to``' Instruction
7516 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7523 <result> = sext <ty> <value> to <ty2> ; yields ty2
7528 The '``sext``' sign extends ``value`` to the type ``ty2``.
7533 The '``sext``' instruction takes a value to cast, and a type to cast it
7534 to. Both types must be of :ref:`integer <t_integer>` types, or vectors of
7535 the same number of integers. The bit size of the ``value`` must be
7536 smaller than the bit size of the destination type, ``ty2``.
7541 The '``sext``' instruction performs a sign extension by copying the sign
7542 bit (highest order bit) of the ``value`` until it reaches the bit size
7543 of the type ``ty2``.
7545 When sign extending from i1, the extension always results in -1 or 0.
7550 .. code-block:: llvm
7552 %X = sext i8 -1 to i16 ; yields i16 :65535
7553 %Y = sext i1 true to i32 ; yields i32:-1
7554 %Z = sext <2 x i16> <i16 8, i16 7> to <2 x i32> ; yields <i32 8, i32 7>
7556 '``fptrunc .. to``' Instruction
7557 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7564 <result> = fptrunc <ty> <value> to <ty2> ; yields ty2
7569 The '``fptrunc``' instruction truncates ``value`` to type ``ty2``.
7574 The '``fptrunc``' instruction takes a :ref:`floating point <t_floating>`
7575 value to cast and a :ref:`floating point <t_floating>` type to cast it to.
7576 The size of ``value`` must be larger than the size of ``ty2``. This
7577 implies that ``fptrunc`` cannot be used to make a *no-op cast*.
7582 The '``fptrunc``' instruction casts a ``value`` from a larger
7583 :ref:`floating point <t_floating>` type to a smaller :ref:`floating
7584 point <t_floating>` type. If the value cannot fit (i.e. overflows) within the
7585 destination type, ``ty2``, then the results are undefined. If the cast produces
7586 an inexact result, how rounding is performed (e.g. truncation, also known as
7587 round to zero) is undefined.
7592 .. code-block:: llvm
7594 %X = fptrunc double 123.0 to float ; yields float:123.0
7595 %Y = fptrunc double 1.0E+300 to float ; yields undefined
7597 '``fpext .. to``' Instruction
7598 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7605 <result> = fpext <ty> <value> to <ty2> ; yields ty2
7610 The '``fpext``' extends a floating point ``value`` to a larger floating
7616 The '``fpext``' instruction takes a :ref:`floating point <t_floating>`
7617 ``value`` to cast, and a :ref:`floating point <t_floating>` type to cast it
7618 to. The source type must be smaller than the destination type.
7623 The '``fpext``' instruction extends the ``value`` from a smaller
7624 :ref:`floating point <t_floating>` type to a larger :ref:`floating
7625 point <t_floating>` type. The ``fpext`` cannot be used to make a
7626 *no-op cast* because it always changes bits. Use ``bitcast`` to make a
7627 *no-op cast* for a floating point cast.
7632 .. code-block:: llvm
7634 %X = fpext float 3.125 to double ; yields double:3.125000e+00
7635 %Y = fpext double %X to fp128 ; yields fp128:0xL00000000000000004000900000000000
7637 '``fptoui .. to``' Instruction
7638 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7645 <result> = fptoui <ty> <value> to <ty2> ; yields ty2
7650 The '``fptoui``' converts a floating point ``value`` to its unsigned
7651 integer equivalent of type ``ty2``.
7656 The '``fptoui``' instruction takes a value to cast, which must be a
7657 scalar or vector :ref:`floating point <t_floating>` value, and a type to
7658 cast it to ``ty2``, which must be an :ref:`integer <t_integer>` type. If
7659 ``ty`` is a vector floating point type, ``ty2`` must be a vector integer
7660 type with the same number of elements as ``ty``
7665 The '``fptoui``' instruction converts its :ref:`floating
7666 point <t_floating>` operand into the nearest (rounding towards zero)
7667 unsigned integer value. If the value cannot fit in ``ty2``, the results
7673 .. code-block:: llvm
7675 %X = fptoui double 123.0 to i32 ; yields i32:123
7676 %Y = fptoui float 1.0E+300 to i1 ; yields undefined:1
7677 %Z = fptoui float 1.04E+17 to i8 ; yields undefined:1
7679 '``fptosi .. to``' Instruction
7680 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7687 <result> = fptosi <ty> <value> to <ty2> ; yields ty2
7692 The '``fptosi``' instruction converts :ref:`floating point <t_floating>`
7693 ``value`` to type ``ty2``.
7698 The '``fptosi``' instruction takes a value to cast, which must be a
7699 scalar or vector :ref:`floating point <t_floating>` value, and a type to
7700 cast it to ``ty2``, which must be an :ref:`integer <t_integer>` type. If
7701 ``ty`` is a vector floating point type, ``ty2`` must be a vector integer
7702 type with the same number of elements as ``ty``
7707 The '``fptosi``' instruction converts its :ref:`floating
7708 point <t_floating>` operand into the nearest (rounding towards zero)
7709 signed integer value. If the value cannot fit in ``ty2``, the results
7715 .. code-block:: llvm
7717 %X = fptosi double -123.0 to i32 ; yields i32:-123
7718 %Y = fptosi float 1.0E-247 to i1 ; yields undefined:1
7719 %Z = fptosi float 1.04E+17 to i8 ; yields undefined:1
7721 '``uitofp .. to``' Instruction
7722 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7729 <result> = uitofp <ty> <value> to <ty2> ; yields ty2
7734 The '``uitofp``' instruction regards ``value`` as an unsigned integer
7735 and converts that value to the ``ty2`` type.
7740 The '``uitofp``' instruction takes a value to cast, which must be a
7741 scalar or vector :ref:`integer <t_integer>` value, and a type to cast it to
7742 ``ty2``, which must be an :ref:`floating point <t_floating>` type. If
7743 ``ty`` is a vector integer type, ``ty2`` must be a vector floating point
7744 type with the same number of elements as ``ty``
7749 The '``uitofp``' instruction interprets its operand as an unsigned
7750 integer quantity and converts it to the corresponding floating point
7751 value. If the value cannot fit in the floating point value, the results
7757 .. code-block:: llvm
7759 %X = uitofp i32 257 to float ; yields float:257.0
7760 %Y = uitofp i8 -1 to double ; yields double:255.0
7762 '``sitofp .. to``' Instruction
7763 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7770 <result> = sitofp <ty> <value> to <ty2> ; yields ty2
7775 The '``sitofp``' instruction regards ``value`` as a signed integer and
7776 converts that value to the ``ty2`` type.
7781 The '``sitofp``' instruction takes a value to cast, which must be a
7782 scalar or vector :ref:`integer <t_integer>` value, and a type to cast it to
7783 ``ty2``, which must be an :ref:`floating point <t_floating>` type. If
7784 ``ty`` is a vector integer type, ``ty2`` must be a vector floating point
7785 type with the same number of elements as ``ty``
7790 The '``sitofp``' instruction interprets its operand as a signed integer
7791 quantity and converts it to the corresponding floating point value. If
7792 the value cannot fit in the floating point value, the results are
7798 .. code-block:: llvm
7800 %X = sitofp i32 257 to float ; yields float:257.0
7801 %Y = sitofp i8 -1 to double ; yields double:-1.0
7805 '``ptrtoint .. to``' Instruction
7806 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7813 <result> = ptrtoint <ty> <value> to <ty2> ; yields ty2
7818 The '``ptrtoint``' instruction converts the pointer or a vector of
7819 pointers ``value`` to the integer (or vector of integers) type ``ty2``.
7824 The '``ptrtoint``' instruction takes a ``value`` to cast, which must be
7825 a value of type :ref:`pointer <t_pointer>` or a vector of pointers, and a
7826 type to cast it to ``ty2``, which must be an :ref:`integer <t_integer>` or
7827 a vector of integers type.
7832 The '``ptrtoint``' instruction converts ``value`` to integer type
7833 ``ty2`` by interpreting the pointer value as an integer and either
7834 truncating or zero extending that value to the size of the integer type.
7835 If ``value`` is smaller than ``ty2`` then a zero extension is done. If
7836 ``value`` is larger than ``ty2`` then a truncation is done. If they are
7837 the same size, then nothing is done (*no-op cast*) other than a type
7843 .. code-block:: llvm
7845 %X = ptrtoint i32* %P to i8 ; yields truncation on 32-bit architecture
7846 %Y = ptrtoint i32* %P to i64 ; yields zero extension on 32-bit architecture
7847 %Z = ptrtoint <4 x i32*> %P to <4 x i64>; yields vector zero extension for a vector of addresses on 32-bit architecture
7851 '``inttoptr .. to``' Instruction
7852 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7859 <result> = inttoptr <ty> <value> to <ty2> ; yields ty2
7864 The '``inttoptr``' instruction converts an integer ``value`` to a
7865 pointer type, ``ty2``.
7870 The '``inttoptr``' instruction takes an :ref:`integer <t_integer>` value to
7871 cast, and a type to cast it to, which must be a :ref:`pointer <t_pointer>`
7877 The '``inttoptr``' instruction converts ``value`` to type ``ty2`` by
7878 applying either a zero extension or a truncation depending on the size
7879 of the integer ``value``. If ``value`` is larger than the size of a
7880 pointer then a truncation is done. If ``value`` is smaller than the size
7881 of a pointer then a zero extension is done. If they are the same size,
7882 nothing is done (*no-op cast*).
7887 .. code-block:: llvm
7889 %X = inttoptr i32 255 to i32* ; yields zero extension on 64-bit architecture
7890 %Y = inttoptr i32 255 to i32* ; yields no-op on 32-bit architecture
7891 %Z = inttoptr i64 0 to i32* ; yields truncation on 32-bit architecture
7892 %Z = inttoptr <4 x i32> %G to <4 x i8*>; yields truncation of vector G to four pointers
7896 '``bitcast .. to``' Instruction
7897 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7904 <result> = bitcast <ty> <value> to <ty2> ; yields ty2
7909 The '``bitcast``' instruction converts ``value`` to type ``ty2`` without
7915 The '``bitcast``' instruction takes a value to cast, which must be a
7916 non-aggregate first class value, and a type to cast it to, which must
7917 also be a non-aggregate :ref:`first class <t_firstclass>` type. The
7918 bit sizes of ``value`` and the destination type, ``ty2``, must be
7919 identical. If the source type is a pointer, the destination type must
7920 also be a pointer of the same size. This instruction supports bitwise
7921 conversion of vectors to integers and to vectors of other types (as
7922 long as they have the same size).
7927 The '``bitcast``' instruction converts ``value`` to type ``ty2``. It
7928 is always a *no-op cast* because no bits change with this
7929 conversion. The conversion is done as if the ``value`` had been stored
7930 to memory and read back as type ``ty2``. Pointer (or vector of
7931 pointers) types may only be converted to other pointer (or vector of
7932 pointers) types with the same address space through this instruction.
7933 To convert pointers to other types, use the :ref:`inttoptr <i_inttoptr>`
7934 or :ref:`ptrtoint <i_ptrtoint>` instructions first.
7939 .. code-block:: llvm
7941 %X = bitcast i8 255 to i8 ; yields i8 :-1
7942 %Y = bitcast i32* %x to sint* ; yields sint*:%x
7943 %Z = bitcast <2 x int> %V to i64; ; yields i64: %V
7944 %Z = bitcast <2 x i32*> %V to <2 x i64*> ; yields <2 x i64*>
7946 .. _i_addrspacecast:
7948 '``addrspacecast .. to``' Instruction
7949 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7956 <result> = addrspacecast <pty> <ptrval> to <pty2> ; yields pty2
7961 The '``addrspacecast``' instruction converts ``ptrval`` from ``pty`` in
7962 address space ``n`` to type ``pty2`` in address space ``m``.
7967 The '``addrspacecast``' instruction takes a pointer or vector of pointer value
7968 to cast and a pointer type to cast it to, which must have a different
7974 The '``addrspacecast``' instruction converts the pointer value
7975 ``ptrval`` to type ``pty2``. It can be a *no-op cast* or a complex
7976 value modification, depending on the target and the address space
7977 pair. Pointer conversions within the same address space must be
7978 performed with the ``bitcast`` instruction. Note that if the address space
7979 conversion is legal then both result and operand refer to the same memory
7985 .. code-block:: llvm
7987 %X = addrspacecast i32* %x to i32 addrspace(1)* ; yields i32 addrspace(1)*:%x
7988 %Y = addrspacecast i32 addrspace(1)* %y to i64 addrspace(2)* ; yields i64 addrspace(2)*:%y
7989 %Z = addrspacecast <4 x i32*> %z to <4 x float addrspace(3)*> ; yields <4 x float addrspace(3)*>:%z
7996 The instructions in this category are the "miscellaneous" instructions,
7997 which defy better classification.
8001 '``icmp``' Instruction
8002 ^^^^^^^^^^^^^^^^^^^^^^
8009 <result> = icmp <cond> <ty> <op1>, <op2> ; yields i1 or <N x i1>:result
8014 The '``icmp``' instruction returns a boolean value or a vector of
8015 boolean values based on comparison of its two integer, integer vector,
8016 pointer, or pointer vector operands.
8021 The '``icmp``' instruction takes three operands. The first operand is
8022 the condition code indicating the kind of comparison to perform. It is
8023 not a value, just a keyword. The possible condition code are:
8026 #. ``ne``: not equal
8027 #. ``ugt``: unsigned greater than
8028 #. ``uge``: unsigned greater or equal
8029 #. ``ult``: unsigned less than
8030 #. ``ule``: unsigned less or equal
8031 #. ``sgt``: signed greater than
8032 #. ``sge``: signed greater or equal
8033 #. ``slt``: signed less than
8034 #. ``sle``: signed less or equal
8036 The remaining two arguments must be :ref:`integer <t_integer>` or
8037 :ref:`pointer <t_pointer>` or integer :ref:`vector <t_vector>` typed. They
8038 must also be identical types.
8043 The '``icmp``' compares ``op1`` and ``op2`` according to the condition
8044 code given as ``cond``. The comparison performed always yields either an
8045 :ref:`i1 <t_integer>` or vector of ``i1`` result, as follows:
8047 #. ``eq``: yields ``true`` if the operands are equal, ``false``
8048 otherwise. No sign interpretation is necessary or performed.
8049 #. ``ne``: yields ``true`` if the operands are unequal, ``false``
8050 otherwise. No sign interpretation is necessary or performed.
8051 #. ``ugt``: interprets the operands as unsigned values and yields
8052 ``true`` if ``op1`` is greater than ``op2``.
8053 #. ``uge``: interprets the operands as unsigned values and yields
8054 ``true`` if ``op1`` is greater than or equal to ``op2``.
8055 #. ``ult``: interprets the operands as unsigned values and yields
8056 ``true`` if ``op1`` is less than ``op2``.
8057 #. ``ule``: interprets the operands as unsigned values and yields
8058 ``true`` if ``op1`` is less than or equal to ``op2``.
8059 #. ``sgt``: interprets the operands as signed values and yields ``true``
8060 if ``op1`` is greater than ``op2``.
8061 #. ``sge``: interprets the operands as signed values and yields ``true``
8062 if ``op1`` is greater than or equal to ``op2``.
8063 #. ``slt``: interprets the operands as signed values and yields ``true``
8064 if ``op1`` is less than ``op2``.
8065 #. ``sle``: interprets the operands as signed values and yields ``true``
8066 if ``op1`` is less than or equal to ``op2``.
8068 If the operands are :ref:`pointer <t_pointer>` typed, the pointer values
8069 are compared as if they were integers.
8071 If the operands are integer vectors, then they are compared element by
8072 element. The result is an ``i1`` vector with the same number of elements
8073 as the values being compared. Otherwise, the result is an ``i1``.
8078 .. code-block:: llvm
8080 <result> = icmp eq i32 4, 5 ; yields: result=false
8081 <result> = icmp ne float* %X, %X ; yields: result=false
8082 <result> = icmp ult i16 4, 5 ; yields: result=true
8083 <result> = icmp sgt i16 4, 5 ; yields: result=false
8084 <result> = icmp ule i16 -4, 5 ; yields: result=false
8085 <result> = icmp sge i16 4, 5 ; yields: result=false
8087 Note that the code generator does not yet support vector types with the
8088 ``icmp`` instruction.
8092 '``fcmp``' Instruction
8093 ^^^^^^^^^^^^^^^^^^^^^^
8100 <result> = fcmp [fast-math flags]* <cond> <ty> <op1>, <op2> ; yields i1 or <N x i1>:result
8105 The '``fcmp``' instruction returns a boolean value or vector of boolean
8106 values based on comparison of its operands.
8108 If the operands are floating point scalars, then the result type is a
8109 boolean (:ref:`i1 <t_integer>`).
8111 If the operands are floating point vectors, then the result type is a
8112 vector of boolean with the same number of elements as the operands being
8118 The '``fcmp``' instruction takes three operands. The first operand is
8119 the condition code indicating the kind of comparison to perform. It is
8120 not a value, just a keyword. The possible condition code are:
8122 #. ``false``: no comparison, always returns false
8123 #. ``oeq``: ordered and equal
8124 #. ``ogt``: ordered and greater than
8125 #. ``oge``: ordered and greater than or equal
8126 #. ``olt``: ordered and less than
8127 #. ``ole``: ordered and less than or equal
8128 #. ``one``: ordered and not equal
8129 #. ``ord``: ordered (no nans)
8130 #. ``ueq``: unordered or equal
8131 #. ``ugt``: unordered or greater than
8132 #. ``uge``: unordered or greater than or equal
8133 #. ``ult``: unordered or less than
8134 #. ``ule``: unordered or less than or equal
8135 #. ``une``: unordered or not equal
8136 #. ``uno``: unordered (either nans)
8137 #. ``true``: no comparison, always returns true
8139 *Ordered* means that neither operand is a QNAN while *unordered* means
8140 that either operand may be a QNAN.
8142 Each of ``val1`` and ``val2`` arguments must be either a :ref:`floating
8143 point <t_floating>` type or a :ref:`vector <t_vector>` of floating point
8144 type. They must have identical types.
8149 The '``fcmp``' instruction compares ``op1`` and ``op2`` according to the
8150 condition code given as ``cond``. If the operands are vectors, then the
8151 vectors are compared element by element. Each comparison performed
8152 always yields an :ref:`i1 <t_integer>` result, as follows:
8154 #. ``false``: always yields ``false``, regardless of operands.
8155 #. ``oeq``: yields ``true`` if both operands are not a QNAN and ``op1``
8156 is equal to ``op2``.
8157 #. ``ogt``: yields ``true`` if both operands are not a QNAN and ``op1``
8158 is greater than ``op2``.
8159 #. ``oge``: yields ``true`` if both operands are not a QNAN and ``op1``
8160 is greater than or equal to ``op2``.
8161 #. ``olt``: yields ``true`` if both operands are not a QNAN and ``op1``
8162 is less than ``op2``.
8163 #. ``ole``: yields ``true`` if both operands are not a QNAN and ``op1``
8164 is less than or equal to ``op2``.
8165 #. ``one``: yields ``true`` if both operands are not a QNAN and ``op1``
8166 is not equal to ``op2``.
8167 #. ``ord``: yields ``true`` if both operands are not a QNAN.
8168 #. ``ueq``: yields ``true`` if either operand is a QNAN or ``op1`` is
8170 #. ``ugt``: yields ``true`` if either operand is a QNAN or ``op1`` is
8171 greater than ``op2``.
8172 #. ``uge``: yields ``true`` if either operand is a QNAN or ``op1`` is
8173 greater than or equal to ``op2``.
8174 #. ``ult``: yields ``true`` if either operand is a QNAN or ``op1`` is
8176 #. ``ule``: yields ``true`` if either operand is a QNAN or ``op1`` is
8177 less than or equal to ``op2``.
8178 #. ``une``: yields ``true`` if either operand is a QNAN or ``op1`` is
8179 not equal to ``op2``.
8180 #. ``uno``: yields ``true`` if either operand is a QNAN.
8181 #. ``true``: always yields ``true``, regardless of operands.
8183 The ``fcmp`` instruction can also optionally take any number of
8184 :ref:`fast-math flags <fastmath>`, which are optimization hints to enable
8185 otherwise unsafe floating point optimizations.
8187 Any set of fast-math flags are legal on an ``fcmp`` instruction, but the
8188 only flags that have any effect on its semantics are those that allow
8189 assumptions to be made about the values of input arguments; namely
8190 ``nnan``, ``ninf``, and ``nsz``. See :ref:`fastmath` for more information.
8195 .. code-block:: llvm
8197 <result> = fcmp oeq float 4.0, 5.0 ; yields: result=false
8198 <result> = fcmp one float 4.0, 5.0 ; yields: result=true
8199 <result> = fcmp olt float 4.0, 5.0 ; yields: result=true
8200 <result> = fcmp ueq double 1.0, 2.0 ; yields: result=false
8202 Note that the code generator does not yet support vector types with the
8203 ``fcmp`` instruction.
8207 '``phi``' Instruction
8208 ^^^^^^^^^^^^^^^^^^^^^
8215 <result> = phi <ty> [ <val0>, <label0>], ...
8220 The '``phi``' instruction is used to implement the φ node in the SSA
8221 graph representing the function.
8226 The type of the incoming values is specified with the first type field.
8227 After this, the '``phi``' instruction takes a list of pairs as
8228 arguments, with one pair for each predecessor basic block of the current
8229 block. Only values of :ref:`first class <t_firstclass>` type may be used as
8230 the value arguments to the PHI node. Only labels may be used as the
8233 There must be no non-phi instructions between the start of a basic block
8234 and the PHI instructions: i.e. PHI instructions must be first in a basic
8237 For the purposes of the SSA form, the use of each incoming value is
8238 deemed to occur on the edge from the corresponding predecessor block to
8239 the current block (but after any definition of an '``invoke``'
8240 instruction's return value on the same edge).
8245 At runtime, the '``phi``' instruction logically takes on the value
8246 specified by the pair corresponding to the predecessor basic block that
8247 executed just prior to the current block.
8252 .. code-block:: llvm
8254 Loop: ; Infinite loop that counts from 0 on up...
8255 %indvar = phi i32 [ 0, %LoopHeader ], [ %nextindvar, %Loop ]
8256 %nextindvar = add i32 %indvar, 1
8261 '``select``' Instruction
8262 ^^^^^^^^^^^^^^^^^^^^^^^^
8269 <result> = select selty <cond>, <ty> <val1>, <ty> <val2> ; yields ty
8271 selty is either i1 or {<N x i1>}
8276 The '``select``' instruction is used to choose one value based on a
8277 condition, without IR-level branching.
8282 The '``select``' instruction requires an 'i1' value or a vector of 'i1'
8283 values indicating the condition, and two values of the same :ref:`first
8284 class <t_firstclass>` type.
8289 If the condition is an i1 and it evaluates to 1, the instruction returns
8290 the first value argument; otherwise, it returns the second value
8293 If the condition is a vector of i1, then the value arguments must be
8294 vectors of the same size, and the selection is done element by element.
8296 If the condition is an i1 and the value arguments are vectors of the
8297 same size, then an entire vector is selected.
8302 .. code-block:: llvm
8304 %X = select i1 true, i8 17, i8 42 ; yields i8:17
8308 '``call``' Instruction
8309 ^^^^^^^^^^^^^^^^^^^^^^
8316 <result> = [tail | musttail | notail ] call [cconv] [ret attrs] <ty> [<fnty>*] <fnptrval>(<function args>) [fn attrs]
8322 The '``call``' instruction represents a simple function call.
8327 This instruction requires several arguments:
8329 #. The optional ``tail`` and ``musttail`` markers indicate that the optimizers
8330 should perform tail call optimization. The ``tail`` marker is a hint that
8331 `can be ignored <CodeGenerator.html#sibcallopt>`_. The ``musttail`` marker
8332 means that the call must be tail call optimized in order for the program to
8333 be correct. The ``musttail`` marker provides these guarantees:
8335 #. The call will not cause unbounded stack growth if it is part of a
8336 recursive cycle in the call graph.
8337 #. Arguments with the :ref:`inalloca <attr_inalloca>` attribute are
8340 Both markers imply that the callee does not access allocas or varargs from
8341 the caller. Calls marked ``musttail`` must obey the following additional
8344 - The call must immediately precede a :ref:`ret <i_ret>` instruction,
8345 or a pointer bitcast followed by a ret instruction.
8346 - The ret instruction must return the (possibly bitcasted) value
8347 produced by the call or void.
8348 - The caller and callee prototypes must match. Pointer types of
8349 parameters or return types may differ in pointee type, but not
8351 - The calling conventions of the caller and callee must match.
8352 - All ABI-impacting function attributes, such as sret, byval, inreg,
8353 returned, and inalloca, must match.
8354 - The callee must be varargs iff the caller is varargs. Bitcasting a
8355 non-varargs function to the appropriate varargs type is legal so
8356 long as the non-varargs prefixes obey the other rules.
8358 Tail call optimization for calls marked ``tail`` is guaranteed to occur if
8359 the following conditions are met:
8361 - Caller and callee both have the calling convention ``fastcc``.
8362 - The call is in tail position (ret immediately follows call and ret
8363 uses value of call or is void).
8364 - Option ``-tailcallopt`` is enabled, or
8365 ``llvm::GuaranteedTailCallOpt`` is ``true``.
8366 - `Platform-specific constraints are
8367 met. <CodeGenerator.html#tailcallopt>`_
8369 #. The optional ``notail`` marker indicates that the optimizers should not add
8370 ``tail`` or ``musttail`` markers to the call. It is used to prevent tail
8371 call optimization from being performed on the call.
8373 #. The optional "cconv" marker indicates which :ref:`calling
8374 convention <callingconv>` the call should use. If none is
8375 specified, the call defaults to using C calling conventions. The
8376 calling convention of the call must match the calling convention of
8377 the target function, or else the behavior is undefined.
8378 #. The optional :ref:`Parameter Attributes <paramattrs>` list for return
8379 values. Only '``zeroext``', '``signext``', and '``inreg``' attributes
8381 #. '``ty``': the type of the call instruction itself which is also the
8382 type of the return value. Functions that return no value are marked
8384 #. '``fnty``': shall be the signature of the pointer to function value
8385 being invoked. The argument types must match the types implied by
8386 this signature. This type can be omitted if the function is not
8387 varargs and if the function type does not return a pointer to a
8389 #. '``fnptrval``': An LLVM value containing a pointer to a function to
8390 be invoked. In most cases, this is a direct function invocation, but
8391 indirect ``call``'s are just as possible, calling an arbitrary pointer
8393 #. '``function args``': argument list whose types match the function
8394 signature argument types and parameter attributes. All arguments must
8395 be of :ref:`first class <t_firstclass>` type. If the function signature
8396 indicates the function accepts a variable number of arguments, the
8397 extra arguments can be specified.
8398 #. The optional :ref:`function attributes <fnattrs>` list. Only
8399 '``noreturn``', '``nounwind``', '``readonly``' and '``readnone``'
8400 attributes are valid here.
8401 #. The optional :ref:`operand bundles <opbundles>` list.
8406 The '``call``' instruction is used to cause control flow to transfer to
8407 a specified function, with its incoming arguments bound to the specified
8408 values. Upon a '``ret``' instruction in the called function, control
8409 flow continues with the instruction after the function call, and the
8410 return value of the function is bound to the result argument.
8415 .. code-block:: llvm
8417 %retval = call i32 @test(i32 %argc)
8418 call i32 (i8*, ...)* @printf(i8* %msg, i32 12, i8 42) ; yields i32
8419 %X = tail call i32 @foo() ; yields i32
8420 %Y = tail call fastcc i32 @foo() ; yields i32
8421 call void %foo(i8 97 signext)
8423 %struct.A = type { i32, i8 }
8424 %r = call %struct.A @foo() ; yields { i32, i8 }
8425 %gr = extractvalue %struct.A %r, 0 ; yields i32
8426 %gr1 = extractvalue %struct.A %r, 1 ; yields i8
8427 %Z = call void @foo() noreturn ; indicates that %foo never returns normally
8428 %ZZ = call zeroext i32 @bar() ; Return value is %zero extended
8430 llvm treats calls to some functions with names and arguments that match
8431 the standard C99 library as being the C99 library functions, and may
8432 perform optimizations or generate code for them under that assumption.
8433 This is something we'd like to change in the future to provide better
8434 support for freestanding environments and non-C-based languages.
8438 '``va_arg``' Instruction
8439 ^^^^^^^^^^^^^^^^^^^^^^^^
8446 <resultval> = va_arg <va_list*> <arglist>, <argty>
8451 The '``va_arg``' instruction is used to access arguments passed through
8452 the "variable argument" area of a function call. It is used to implement
8453 the ``va_arg`` macro in C.
8458 This instruction takes a ``va_list*`` value and the type of the
8459 argument. It returns a value of the specified argument type and
8460 increments the ``va_list`` to point to the next argument. The actual
8461 type of ``va_list`` is target specific.
8466 The '``va_arg``' instruction loads an argument of the specified type
8467 from the specified ``va_list`` and causes the ``va_list`` to point to
8468 the next argument. For more information, see the variable argument
8469 handling :ref:`Intrinsic Functions <int_varargs>`.
8471 It is legal for this instruction to be called in a function which does
8472 not take a variable number of arguments, for example, the ``vfprintf``
8475 ``va_arg`` is an LLVM instruction instead of an :ref:`intrinsic
8476 function <intrinsics>` because it takes a type as an argument.
8481 See the :ref:`variable argument processing <int_varargs>` section.
8483 Note that the code generator does not yet fully support va\_arg on many
8484 targets. Also, it does not currently support va\_arg with aggregate
8485 types on any target.
8489 '``landingpad``' Instruction
8490 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8497 <resultval> = landingpad <resultty> <clause>+
8498 <resultval> = landingpad <resultty> cleanup <clause>*
8500 <clause> := catch <type> <value>
8501 <clause> := filter <array constant type> <array constant>
8506 The '``landingpad``' instruction is used by `LLVM's exception handling
8507 system <ExceptionHandling.html#overview>`_ to specify that a basic block
8508 is a landing pad --- one where the exception lands, and corresponds to the
8509 code found in the ``catch`` portion of a ``try``/``catch`` sequence. It
8510 defines values supplied by the :ref:`personality function <personalityfn>` upon
8511 re-entry to the function. The ``resultval`` has the type ``resultty``.
8517 ``cleanup`` flag indicates that the landing pad block is a cleanup.
8519 A ``clause`` begins with the clause type --- ``catch`` or ``filter`` --- and
8520 contains the global variable representing the "type" that may be caught
8521 or filtered respectively. Unlike the ``catch`` clause, the ``filter``
8522 clause takes an array constant as its argument. Use
8523 "``[0 x i8**] undef``" for a filter which cannot throw. The
8524 '``landingpad``' instruction must contain *at least* one ``clause`` or
8525 the ``cleanup`` flag.
8530 The '``landingpad``' instruction defines the values which are set by the
8531 :ref:`personality function <personalityfn>` upon re-entry to the function, and
8532 therefore the "result type" of the ``landingpad`` instruction. As with
8533 calling conventions, how the personality function results are
8534 represented in LLVM IR is target specific.
8536 The clauses are applied in order from top to bottom. If two
8537 ``landingpad`` instructions are merged together through inlining, the
8538 clauses from the calling function are appended to the list of clauses.
8539 When the call stack is being unwound due to an exception being thrown,
8540 the exception is compared against each ``clause`` in turn. If it doesn't
8541 match any of the clauses, and the ``cleanup`` flag is not set, then
8542 unwinding continues further up the call stack.
8544 The ``landingpad`` instruction has several restrictions:
8546 - A landing pad block is a basic block which is the unwind destination
8547 of an '``invoke``' instruction.
8548 - A landing pad block must have a '``landingpad``' instruction as its
8549 first non-PHI instruction.
8550 - There can be only one '``landingpad``' instruction within the landing
8552 - A basic block that is not a landing pad block may not include a
8553 '``landingpad``' instruction.
8558 .. code-block:: llvm
8560 ;; A landing pad which can catch an integer.
8561 %res = landingpad { i8*, i32 }
8563 ;; A landing pad that is a cleanup.
8564 %res = landingpad { i8*, i32 }
8566 ;; A landing pad which can catch an integer and can only throw a double.
8567 %res = landingpad { i8*, i32 }
8569 filter [1 x i8**] [@_ZTId]
8573 '``cleanuppad``' Instruction
8574 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8581 <resultval> = cleanuppad within <parent> [<args>*]
8586 The '``cleanuppad``' instruction is used by `LLVM's exception handling
8587 system <ExceptionHandling.html#overview>`_ to specify that a basic block
8588 is a cleanup block --- one where a personality routine attempts to
8589 transfer control to run cleanup actions.
8590 The ``args`` correspond to whatever additional
8591 information the :ref:`personality function <personalityfn>` requires to
8592 execute the cleanup.
8593 The ``resultval`` has the type :ref:`token <t_token>` and is used to
8594 match the ``cleanuppad`` to corresponding :ref:`cleanuprets <i_cleanupret>`.
8595 The ``parent`` argument is the token of the funclet that contains the
8596 ``cleanuppad`` instruction. If the ``cleanuppad`` is not inside a funclet,
8597 this operand may be the token ``none``.
8602 The instruction takes a list of arbitrary values which are interpreted
8603 by the :ref:`personality function <personalityfn>`.
8608 When the call stack is being unwound due to an exception being thrown,
8609 the :ref:`personality function <personalityfn>` transfers control to the
8610 ``cleanuppad`` with the aid of the personality-specific arguments.
8611 As with calling conventions, how the personality function results are
8612 represented in LLVM IR is target specific.
8614 The ``cleanuppad`` instruction has several restrictions:
8616 - A cleanup block is a basic block which is the unwind destination of
8617 an exceptional instruction.
8618 - A cleanup block must have a '``cleanuppad``' instruction as its
8619 first non-PHI instruction.
8620 - There can be only one '``cleanuppad``' instruction within the
8622 - A basic block that is not a cleanup block may not include a
8623 '``cleanuppad``' instruction.
8625 Executing a ``cleanuppad`` instruction constitutes "entering" that pad.
8626 The pad may then be "exited" in one of three ways:
8627 1) explicitly via a ``cleanupret`` that consumes it. Executing such a ``cleanupret``
8628 is undefined behavior if any descendant pads have been entered but not yet
8630 2) implicitly via a call (which unwinds all the way to the current function's caller),
8631 or via a ``catchswitch`` or a ``cleanupret`` that unwinds to caller.
8632 3) implicitly via an unwind edge whose destination EH pad isn't a descendant of
8633 the ``cleanuppad``. When the ``cleanuppad`` is exited in this manner, it is
8634 undefined behavior if the destination EH pad has a parent which is not an
8635 ancestor of the ``cleanuppad`` being exited.
8637 It is undefined behavior for the ``cleanuppad`` to exit via an unwind edge which
8638 does not transitively unwind to the same destination as a constituent
8644 .. code-block:: llvm
8646 %tok = cleanuppad within %cs []
8653 LLVM supports the notion of an "intrinsic function". These functions
8654 have well known names and semantics and are required to follow certain
8655 restrictions. Overall, these intrinsics represent an extension mechanism
8656 for the LLVM language that does not require changing all of the
8657 transformations in LLVM when adding to the language (or the bitcode
8658 reader/writer, the parser, etc...).
8660 Intrinsic function names must all start with an "``llvm.``" prefix. This
8661 prefix is reserved in LLVM for intrinsic names; thus, function names may
8662 not begin with this prefix. Intrinsic functions must always be external
8663 functions: you cannot define the body of intrinsic functions. Intrinsic
8664 functions may only be used in call or invoke instructions: it is illegal
8665 to take the address of an intrinsic function. Additionally, because
8666 intrinsic functions are part of the LLVM language, it is required if any
8667 are added that they be documented here.
8669 Some intrinsic functions can be overloaded, i.e., the intrinsic
8670 represents a family of functions that perform the same operation but on
8671 different data types. Because LLVM can represent over 8 million
8672 different integer types, overloading is used commonly to allow an
8673 intrinsic function to operate on any integer type. One or more of the
8674 argument types or the result type can be overloaded to accept any
8675 integer type. Argument types may also be defined as exactly matching a
8676 previous argument's type or the result type. This allows an intrinsic
8677 function which accepts multiple arguments, but needs all of them to be
8678 of the same type, to only be overloaded with respect to a single
8679 argument or the result.
8681 Overloaded intrinsics will have the names of its overloaded argument
8682 types encoded into its function name, each preceded by a period. Only
8683 those types which are overloaded result in a name suffix. Arguments
8684 whose type is matched against another type do not. For example, the
8685 ``llvm.ctpop`` function can take an integer of any width and returns an
8686 integer of exactly the same integer width. This leads to a family of
8687 functions such as ``i8 @llvm.ctpop.i8(i8 %val)`` and
8688 ``i29 @llvm.ctpop.i29(i29 %val)``. Only one type, the return type, is
8689 overloaded, and only one type suffix is required. Because the argument's
8690 type is matched against the return type, it does not require its own
8693 To learn how to add an intrinsic function, please see the `Extending
8694 LLVM Guide <ExtendingLLVM.html>`_.
8698 Variable Argument Handling Intrinsics
8699 -------------------------------------
8701 Variable argument support is defined in LLVM with the
8702 :ref:`va_arg <i_va_arg>` instruction and these three intrinsic
8703 functions. These functions are related to the similarly named macros
8704 defined in the ``<stdarg.h>`` header file.
8706 All of these functions operate on arguments that use a target-specific
8707 value type "``va_list``". The LLVM assembly language reference manual
8708 does not define what this type is, so all transformations should be
8709 prepared to handle these functions regardless of the type used.
8711 This example shows how the :ref:`va_arg <i_va_arg>` instruction and the
8712 variable argument handling intrinsic functions are used.
8714 .. code-block:: llvm
8716 ; This struct is different for every platform. For most platforms,
8717 ; it is merely an i8*.
8718 %struct.va_list = type { i8* }
8720 ; For Unix x86_64 platforms, va_list is the following struct:
8721 ; %struct.va_list = type { i32, i32, i8*, i8* }
8723 define i32 @test(i32 %X, ...) {
8724 ; Initialize variable argument processing
8725 %ap = alloca %struct.va_list
8726 %ap2 = bitcast %struct.va_list* %ap to i8*
8727 call void @llvm.va_start(i8* %ap2)
8729 ; Read a single integer argument
8730 %tmp = va_arg i8* %ap2, i32
8732 ; Demonstrate usage of llvm.va_copy and llvm.va_end
8734 %aq2 = bitcast i8** %aq to i8*
8735 call void @llvm.va_copy(i8* %aq2, i8* %ap2)
8736 call void @llvm.va_end(i8* %aq2)
8738 ; Stop processing of arguments.
8739 call void @llvm.va_end(i8* %ap2)
8743 declare void @llvm.va_start(i8*)
8744 declare void @llvm.va_copy(i8*, i8*)
8745 declare void @llvm.va_end(i8*)
8749 '``llvm.va_start``' Intrinsic
8750 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8757 declare void @llvm.va_start(i8* <arglist>)
8762 The '``llvm.va_start``' intrinsic initializes ``*<arglist>`` for
8763 subsequent use by ``va_arg``.
8768 The argument is a pointer to a ``va_list`` element to initialize.
8773 The '``llvm.va_start``' intrinsic works just like the ``va_start`` macro
8774 available in C. In a target-dependent way, it initializes the
8775 ``va_list`` element to which the argument points, so that the next call
8776 to ``va_arg`` will produce the first variable argument passed to the
8777 function. Unlike the C ``va_start`` macro, this intrinsic does not need
8778 to know the last argument of the function as the compiler can figure
8781 '``llvm.va_end``' Intrinsic
8782 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
8789 declare void @llvm.va_end(i8* <arglist>)
8794 The '``llvm.va_end``' intrinsic destroys ``*<arglist>``, which has been
8795 initialized previously with ``llvm.va_start`` or ``llvm.va_copy``.
8800 The argument is a pointer to a ``va_list`` to destroy.
8805 The '``llvm.va_end``' intrinsic works just like the ``va_end`` macro
8806 available in C. In a target-dependent way, it destroys the ``va_list``
8807 element to which the argument points. Calls to
8808 :ref:`llvm.va_start <int_va_start>` and
8809 :ref:`llvm.va_copy <int_va_copy>` must be matched exactly with calls to
8814 '``llvm.va_copy``' Intrinsic
8815 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8822 declare void @llvm.va_copy(i8* <destarglist>, i8* <srcarglist>)
8827 The '``llvm.va_copy``' intrinsic copies the current argument position
8828 from the source argument list to the destination argument list.
8833 The first argument is a pointer to a ``va_list`` element to initialize.
8834 The second argument is a pointer to a ``va_list`` element to copy from.
8839 The '``llvm.va_copy``' intrinsic works just like the ``va_copy`` macro
8840 available in C. In a target-dependent way, it copies the source
8841 ``va_list`` element into the destination ``va_list`` element. This
8842 intrinsic is necessary because the `` llvm.va_start`` intrinsic may be
8843 arbitrarily complex and require, for example, memory allocation.
8845 Accurate Garbage Collection Intrinsics
8846 --------------------------------------
8848 LLVM's support for `Accurate Garbage Collection <GarbageCollection.html>`_
8849 (GC) requires the frontend to generate code containing appropriate intrinsic
8850 calls and select an appropriate GC strategy which knows how to lower these
8851 intrinsics in a manner which is appropriate for the target collector.
8853 These intrinsics allow identification of :ref:`GC roots on the
8854 stack <int_gcroot>`, as well as garbage collector implementations that
8855 require :ref:`read <int_gcread>` and :ref:`write <int_gcwrite>` barriers.
8856 Frontends for type-safe garbage collected languages should generate
8857 these intrinsics to make use of the LLVM garbage collectors. For more
8858 details, see `Garbage Collection with LLVM <GarbageCollection.html>`_.
8860 Experimental Statepoint Intrinsics
8861 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8863 LLVM provides an second experimental set of intrinsics for describing garbage
8864 collection safepoints in compiled code. These intrinsics are an alternative
8865 to the ``llvm.gcroot`` intrinsics, but are compatible with the ones for
8866 :ref:`read <int_gcread>` and :ref:`write <int_gcwrite>` barriers. The
8867 differences in approach are covered in the `Garbage Collection with LLVM
8868 <GarbageCollection.html>`_ documentation. The intrinsics themselves are
8869 described in :doc:`Statepoints`.
8873 '``llvm.gcroot``' Intrinsic
8874 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
8881 declare void @llvm.gcroot(i8** %ptrloc, i8* %metadata)
8886 The '``llvm.gcroot``' intrinsic declares the existence of a GC root to
8887 the code generator, and allows some metadata to be associated with it.
8892 The first argument specifies the address of a stack object that contains
8893 the root pointer. The second pointer (which must be either a constant or
8894 a global value address) contains the meta-data to be associated with the
8900 At runtime, a call to this intrinsic stores a null pointer into the
8901 "ptrloc" location. At compile-time, the code generator generates
8902 information to allow the runtime to find the pointer at GC safe points.
8903 The '``llvm.gcroot``' intrinsic may only be used in a function which
8904 :ref:`specifies a GC algorithm <gc>`.
8908 '``llvm.gcread``' Intrinsic
8909 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
8916 declare i8* @llvm.gcread(i8* %ObjPtr, i8** %Ptr)
8921 The '``llvm.gcread``' intrinsic identifies reads of references from heap
8922 locations, allowing garbage collector implementations that require read
8928 The second argument is the address to read from, which should be an
8929 address allocated from the garbage collector. The first object is a
8930 pointer to the start of the referenced object, if needed by the language
8931 runtime (otherwise null).
8936 The '``llvm.gcread``' intrinsic has the same semantics as a load
8937 instruction, but may be replaced with substantially more complex code by
8938 the garbage collector runtime, as needed. The '``llvm.gcread``'
8939 intrinsic may only be used in a function which :ref:`specifies a GC
8944 '``llvm.gcwrite``' Intrinsic
8945 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8952 declare void @llvm.gcwrite(i8* %P1, i8* %Obj, i8** %P2)
8957 The '``llvm.gcwrite``' intrinsic identifies writes of references to heap
8958 locations, allowing garbage collector implementations that require write
8959 barriers (such as generational or reference counting collectors).
8964 The first argument is the reference to store, the second is the start of
8965 the object to store it to, and the third is the address of the field of
8966 Obj to store to. If the runtime does not require a pointer to the
8967 object, Obj may be null.
8972 The '``llvm.gcwrite``' intrinsic has the same semantics as a store
8973 instruction, but may be replaced with substantially more complex code by
8974 the garbage collector runtime, as needed. The '``llvm.gcwrite``'
8975 intrinsic may only be used in a function which :ref:`specifies a GC
8978 Code Generator Intrinsics
8979 -------------------------
8981 These intrinsics are provided by LLVM to expose special features that
8982 may only be implemented with code generator support.
8984 '``llvm.returnaddress``' Intrinsic
8985 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8992 declare i8 *@llvm.returnaddress(i32 <level>)
8997 The '``llvm.returnaddress``' intrinsic attempts to compute a
8998 target-specific value indicating the return address of the current
8999 function or one of its callers.
9004 The argument to this intrinsic indicates which function to return the
9005 address for. Zero indicates the calling function, one indicates its
9006 caller, etc. The argument is **required** to be a constant integer
9012 The '``llvm.returnaddress``' intrinsic either returns a pointer
9013 indicating the return address of the specified call frame, or zero if it
9014 cannot be identified. The value returned by this intrinsic is likely to
9015 be incorrect or 0 for arguments other than zero, so it should only be
9016 used for debugging purposes.
9018 Note that calling this intrinsic does not prevent function inlining or
9019 other aggressive transformations, so the value returned may not be that
9020 of the obvious source-language caller.
9022 '``llvm.frameaddress``' Intrinsic
9023 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9030 declare i8* @llvm.frameaddress(i32 <level>)
9035 The '``llvm.frameaddress``' intrinsic attempts to return the
9036 target-specific frame pointer value for the specified stack frame.
9041 The argument to this intrinsic indicates which function to return the
9042 frame pointer for. Zero indicates the calling function, one indicates
9043 its caller, etc. The argument is **required** to be a constant integer
9049 The '``llvm.frameaddress``' intrinsic either returns a pointer
9050 indicating the frame address of the specified call frame, or zero if it
9051 cannot be identified. The value returned by this intrinsic is likely to
9052 be incorrect or 0 for arguments other than zero, so it should only be
9053 used for debugging purposes.
9055 Note that calling this intrinsic does not prevent function inlining or
9056 other aggressive transformations, so the value returned may not be that
9057 of the obvious source-language caller.
9059 '``llvm.localescape``' and '``llvm.localrecover``' Intrinsics
9060 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9067 declare void @llvm.localescape(...)
9068 declare i8* @llvm.localrecover(i8* %func, i8* %fp, i32 %idx)
9073 The '``llvm.localescape``' intrinsic escapes offsets of a collection of static
9074 allocas, and the '``llvm.localrecover``' intrinsic applies those offsets to a
9075 live frame pointer to recover the address of the allocation. The offset is
9076 computed during frame layout of the caller of ``llvm.localescape``.
9081 All arguments to '``llvm.localescape``' must be pointers to static allocas or
9082 casts of static allocas. Each function can only call '``llvm.localescape``'
9083 once, and it can only do so from the entry block.
9085 The ``func`` argument to '``llvm.localrecover``' must be a constant
9086 bitcasted pointer to a function defined in the current module. The code
9087 generator cannot determine the frame allocation offset of functions defined in
9090 The ``fp`` argument to '``llvm.localrecover``' must be a frame pointer of a
9091 call frame that is currently live. The return value of '``llvm.localaddress``'
9092 is one way to produce such a value, but various runtimes also expose a suitable
9093 pointer in platform-specific ways.
9095 The ``idx`` argument to '``llvm.localrecover``' indicates which alloca passed to
9096 '``llvm.localescape``' to recover. It is zero-indexed.
9101 These intrinsics allow a group of functions to share access to a set of local
9102 stack allocations of a one parent function. The parent function may call the
9103 '``llvm.localescape``' intrinsic once from the function entry block, and the
9104 child functions can use '``llvm.localrecover``' to access the escaped allocas.
9105 The '``llvm.localescape``' intrinsic blocks inlining, as inlining changes where
9106 the escaped allocas are allocated, which would break attempts to use
9107 '``llvm.localrecover``'.
9109 .. _int_read_register:
9110 .. _int_write_register:
9112 '``llvm.read_register``' and '``llvm.write_register``' Intrinsics
9113 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9120 declare i32 @llvm.read_register.i32(metadata)
9121 declare i64 @llvm.read_register.i64(metadata)
9122 declare void @llvm.write_register.i32(metadata, i32 @value)
9123 declare void @llvm.write_register.i64(metadata, i64 @value)
9129 The '``llvm.read_register``' and '``llvm.write_register``' intrinsics
9130 provides access to the named register. The register must be valid on
9131 the architecture being compiled to. The type needs to be compatible
9132 with the register being read.
9137 The '``llvm.read_register``' intrinsic returns the current value of the
9138 register, where possible. The '``llvm.write_register``' intrinsic sets
9139 the current value of the register, where possible.
9141 This is useful to implement named register global variables that need
9142 to always be mapped to a specific register, as is common practice on
9143 bare-metal programs including OS kernels.
9145 The compiler doesn't check for register availability or use of the used
9146 register in surrounding code, including inline assembly. Because of that,
9147 allocatable registers are not supported.
9149 Warning: So far it only works with the stack pointer on selected
9150 architectures (ARM, AArch64, PowerPC and x86_64). Significant amount of
9151 work is needed to support other registers and even more so, allocatable
9156 '``llvm.stacksave``' Intrinsic
9157 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9164 declare i8* @llvm.stacksave()
9169 The '``llvm.stacksave``' intrinsic is used to remember the current state
9170 of the function stack, for use with
9171 :ref:`llvm.stackrestore <int_stackrestore>`. This is useful for
9172 implementing language features like scoped automatic variable sized
9178 This intrinsic returns a opaque pointer value that can be passed to
9179 :ref:`llvm.stackrestore <int_stackrestore>`. When an
9180 ``llvm.stackrestore`` intrinsic is executed with a value saved from
9181 ``llvm.stacksave``, it effectively restores the state of the stack to
9182 the state it was in when the ``llvm.stacksave`` intrinsic executed. In
9183 practice, this pops any :ref:`alloca <i_alloca>` blocks from the stack that
9184 were allocated after the ``llvm.stacksave`` was executed.
9186 .. _int_stackrestore:
9188 '``llvm.stackrestore``' Intrinsic
9189 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9196 declare void @llvm.stackrestore(i8* %ptr)
9201 The '``llvm.stackrestore``' intrinsic is used to restore the state of
9202 the function stack to the state it was in when the corresponding
9203 :ref:`llvm.stacksave <int_stacksave>` intrinsic executed. This is
9204 useful for implementing language features like scoped automatic variable
9205 sized arrays in C99.
9210 See the description for :ref:`llvm.stacksave <int_stacksave>`.
9212 .. _int_get_dynamic_area_offset:
9214 '``llvm.get.dynamic.area.offset``' Intrinsic
9215 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9222 declare i32 @llvm.get.dynamic.area.offset.i32()
9223 declare i64 @llvm.get.dynamic.area.offset.i64()
9228 The '``llvm.get.dynamic.area.offset.*``' intrinsic family is used to
9229 get the offset from native stack pointer to the address of the most
9230 recent dynamic alloca on the caller's stack. These intrinsics are
9231 intendend for use in combination with
9232 :ref:`llvm.stacksave <int_stacksave>` to get a
9233 pointer to the most recent dynamic alloca. This is useful, for example,
9234 for AddressSanitizer's stack unpoisoning routines.
9239 These intrinsics return a non-negative integer value that can be used to
9240 get the address of the most recent dynamic alloca, allocated by :ref:`alloca <i_alloca>`
9241 on the caller's stack. In particular, for targets where stack grows downwards,
9242 adding this offset to the native stack pointer would get the address of the most
9243 recent dynamic alloca. For targets where stack grows upwards, the situation is a bit more
9244 complicated, because substracting this value from stack pointer would get the address
9245 one past the end of the most recent dynamic alloca.
9247 Although for most targets `llvm.get.dynamic.area.offset <int_get_dynamic_area_offset>`
9248 returns just a zero, for others, such as PowerPC and PowerPC64, it returns a
9249 compile-time-known constant value.
9251 The return value type of :ref:`llvm.get.dynamic.area.offset <int_get_dynamic_area_offset>`
9252 must match the target's generic address space's (address space 0) pointer type.
9254 '``llvm.prefetch``' Intrinsic
9255 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9262 declare void @llvm.prefetch(i8* <address>, i32 <rw>, i32 <locality>, i32 <cache type>)
9267 The '``llvm.prefetch``' intrinsic is a hint to the code generator to
9268 insert a prefetch instruction if supported; otherwise, it is a noop.
9269 Prefetches have no effect on the behavior of the program but can change
9270 its performance characteristics.
9275 ``address`` is the address to be prefetched, ``rw`` is the specifier
9276 determining if the fetch should be for a read (0) or write (1), and
9277 ``locality`` is a temporal locality specifier ranging from (0) - no
9278 locality, to (3) - extremely local keep in cache. The ``cache type``
9279 specifies whether the prefetch is performed on the data (1) or
9280 instruction (0) cache. The ``rw``, ``locality`` and ``cache type``
9281 arguments must be constant integers.
9286 This intrinsic does not modify the behavior of the program. In
9287 particular, prefetches cannot trap and do not produce a value. On
9288 targets that support this intrinsic, the prefetch can provide hints to
9289 the processor cache for better performance.
9291 '``llvm.pcmarker``' Intrinsic
9292 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9299 declare void @llvm.pcmarker(i32 <id>)
9304 The '``llvm.pcmarker``' intrinsic is a method to export a Program
9305 Counter (PC) in a region of code to simulators and other tools. The
9306 method is target specific, but it is expected that the marker will use
9307 exported symbols to transmit the PC of the marker. The marker makes no
9308 guarantees that it will remain with any specific instruction after
9309 optimizations. It is possible that the presence of a marker will inhibit
9310 optimizations. The intended use is to be inserted after optimizations to
9311 allow correlations of simulation runs.
9316 ``id`` is a numerical id identifying the marker.
9321 This intrinsic does not modify the behavior of the program. Backends
9322 that do not support this intrinsic may ignore it.
9324 '``llvm.readcyclecounter``' Intrinsic
9325 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9332 declare i64 @llvm.readcyclecounter()
9337 The '``llvm.readcyclecounter``' intrinsic provides access to the cycle
9338 counter register (or similar low latency, high accuracy clocks) on those
9339 targets that support it. On X86, it should map to RDTSC. On Alpha, it
9340 should map to RPCC. As the backing counters overflow quickly (on the
9341 order of 9 seconds on alpha), this should only be used for small
9347 When directly supported, reading the cycle counter should not modify any
9348 memory. Implementations are allowed to either return a application
9349 specific value or a system wide value. On backends without support, this
9350 is lowered to a constant 0.
9352 Note that runtime support may be conditional on the privilege-level code is
9353 running at and the host platform.
9355 '``llvm.clear_cache``' Intrinsic
9356 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9363 declare void @llvm.clear_cache(i8*, i8*)
9368 The '``llvm.clear_cache``' intrinsic ensures visibility of modifications
9369 in the specified range to the execution unit of the processor. On
9370 targets with non-unified instruction and data cache, the implementation
9371 flushes the instruction cache.
9376 On platforms with coherent instruction and data caches (e.g. x86), this
9377 intrinsic is a nop. On platforms with non-coherent instruction and data
9378 cache (e.g. ARM, MIPS), the intrinsic is lowered either to appropriate
9379 instructions or a system call, if cache flushing requires special
9382 The default behavior is to emit a call to ``__clear_cache`` from the run
9385 This instrinsic does *not* empty the instruction pipeline. Modifications
9386 of the current function are outside the scope of the intrinsic.
9388 '``llvm.instrprof_increment``' Intrinsic
9389 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9396 declare void @llvm.instrprof_increment(i8* <name>, i64 <hash>,
9397 i32 <num-counters>, i32 <index>)
9402 The '``llvm.instrprof_increment``' intrinsic can be emitted by a
9403 frontend for use with instrumentation based profiling. These will be
9404 lowered by the ``-instrprof`` pass to generate execution counts of a
9410 The first argument is a pointer to a global variable containing the
9411 name of the entity being instrumented. This should generally be the
9412 (mangled) function name for a set of counters.
9414 The second argument is a hash value that can be used by the consumer
9415 of the profile data to detect changes to the instrumented source, and
9416 the third is the number of counters associated with ``name``. It is an
9417 error if ``hash`` or ``num-counters`` differ between two instances of
9418 ``instrprof_increment`` that refer to the same name.
9420 The last argument refers to which of the counters for ``name`` should
9421 be incremented. It should be a value between 0 and ``num-counters``.
9426 This intrinsic represents an increment of a profiling counter. It will
9427 cause the ``-instrprof`` pass to generate the appropriate data
9428 structures and the code to increment the appropriate value, in a
9429 format that can be written out by a compiler runtime and consumed via
9430 the ``llvm-profdata`` tool.
9432 '``llvm.instrprof_value_profile``' Intrinsic
9433 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9440 declare void @llvm.instrprof_value_profile(i8* <name>, i64 <hash>,
9441 i64 <value>, i32 <value_kind>,
9447 The '``llvm.instrprof_value_profile``' intrinsic can be emitted by a
9448 frontend for use with instrumentation based profiling. This will be
9449 lowered by the ``-instrprof`` pass to find out the target values,
9450 instrumented expressions take in a program at runtime.
9455 The first argument is a pointer to a global variable containing the
9456 name of the entity being instrumented. ``name`` should generally be the
9457 (mangled) function name for a set of counters.
9459 The second argument is a hash value that can be used by the consumer
9460 of the profile data to detect changes to the instrumented source. It
9461 is an error if ``hash`` differs between two instances of
9462 ``llvm.instrprof_*`` that refer to the same name.
9464 The third argument is the value of the expression being profiled. The profiled
9465 expression's value should be representable as an unsigned 64-bit value. The
9466 fourth argument represents the kind of value profiling that is being done. The
9467 supported value profiling kinds are enumerated through the
9468 ``InstrProfValueKind`` type declared in the
9469 ``<include/llvm/ProfileData/InstrProf.h>`` header file. The last argument is the
9470 index of the instrumented expression within ``name``. It should be >= 0.
9475 This intrinsic represents the point where a call to a runtime routine
9476 should be inserted for value profiling of target expressions. ``-instrprof``
9477 pass will generate the appropriate data structures and replace the
9478 ``llvm.instrprof_value_profile`` intrinsic with the call to the profile
9479 runtime library with proper arguments.
9481 Standard C Library Intrinsics
9482 -----------------------------
9484 LLVM provides intrinsics for a few important standard C library
9485 functions. These intrinsics allow source-language front-ends to pass
9486 information about the alignment of the pointer arguments to the code
9487 generator, providing opportunity for more efficient code generation.
9491 '``llvm.memcpy``' Intrinsic
9492 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
9497 This is an overloaded intrinsic. You can use ``llvm.memcpy`` on any
9498 integer bit width and for different address spaces. Not all targets
9499 support all bit widths however.
9503 declare void @llvm.memcpy.p0i8.p0i8.i32(i8* <dest>, i8* <src>,
9504 i32 <len>, i32 <align>, i1 <isvolatile>)
9505 declare void @llvm.memcpy.p0i8.p0i8.i64(i8* <dest>, i8* <src>,
9506 i64 <len>, i32 <align>, i1 <isvolatile>)
9511 The '``llvm.memcpy.*``' intrinsics copy a block of memory from the
9512 source location to the destination location.
9514 Note that, unlike the standard libc function, the ``llvm.memcpy.*``
9515 intrinsics do not return a value, takes extra alignment/isvolatile
9516 arguments and the pointers can be in specified address spaces.
9521 The first argument is a pointer to the destination, the second is a
9522 pointer to the source. The third argument is an integer argument
9523 specifying the number of bytes to copy, the fourth argument is the
9524 alignment of the source and destination locations, and the fifth is a
9525 boolean indicating a volatile access.
9527 If the call to this intrinsic has an alignment value that is not 0 or 1,
9528 then the caller guarantees that both the source and destination pointers
9529 are aligned to that boundary.
9531 If the ``isvolatile`` parameter is ``true``, the ``llvm.memcpy`` call is
9532 a :ref:`volatile operation <volatile>`. The detailed access behavior is not
9533 very cleanly specified and it is unwise to depend on it.
9538 The '``llvm.memcpy.*``' intrinsics copy a block of memory from the
9539 source location to the destination location, which are not allowed to
9540 overlap. It copies "len" bytes of memory over. If the argument is known
9541 to be aligned to some boundary, this can be specified as the fourth
9542 argument, otherwise it should be set to 0 or 1 (both meaning no alignment).
9544 '``llvm.memmove``' Intrinsic
9545 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9550 This is an overloaded intrinsic. You can use llvm.memmove on any integer
9551 bit width and for different address space. Not all targets support all
9556 declare void @llvm.memmove.p0i8.p0i8.i32(i8* <dest>, i8* <src>,
9557 i32 <len>, i32 <align>, i1 <isvolatile>)
9558 declare void @llvm.memmove.p0i8.p0i8.i64(i8* <dest>, i8* <src>,
9559 i64 <len>, i32 <align>, i1 <isvolatile>)
9564 The '``llvm.memmove.*``' intrinsics move a block of memory from the
9565 source location to the destination location. It is similar to the
9566 '``llvm.memcpy``' intrinsic but allows the two memory locations to
9569 Note that, unlike the standard libc function, the ``llvm.memmove.*``
9570 intrinsics do not return a value, takes extra alignment/isvolatile
9571 arguments and the pointers can be in specified address spaces.
9576 The first argument is a pointer to the destination, the second is a
9577 pointer to the source. The third argument is an integer argument
9578 specifying the number of bytes to copy, the fourth argument is the
9579 alignment of the source and destination locations, and the fifth is a
9580 boolean indicating a volatile access.
9582 If the call to this intrinsic has an alignment value that is not 0 or 1,
9583 then the caller guarantees that the source and destination pointers are
9584 aligned to that boundary.
9586 If the ``isvolatile`` parameter is ``true``, the ``llvm.memmove`` call
9587 is a :ref:`volatile operation <volatile>`. The detailed access behavior is
9588 not very cleanly specified and it is unwise to depend on it.
9593 The '``llvm.memmove.*``' intrinsics copy a block of memory from the
9594 source location to the destination location, which may overlap. It
9595 copies "len" bytes of memory over. If the argument is known to be
9596 aligned to some boundary, this can be specified as the fourth argument,
9597 otherwise it should be set to 0 or 1 (both meaning no alignment).
9599 '``llvm.memset.*``' Intrinsics
9600 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9605 This is an overloaded intrinsic. You can use llvm.memset on any integer
9606 bit width and for different address spaces. However, not all targets
9607 support all bit widths.
9611 declare void @llvm.memset.p0i8.i32(i8* <dest>, i8 <val>,
9612 i32 <len>, i32 <align>, i1 <isvolatile>)
9613 declare void @llvm.memset.p0i8.i64(i8* <dest>, i8 <val>,
9614 i64 <len>, i32 <align>, i1 <isvolatile>)
9619 The '``llvm.memset.*``' intrinsics fill a block of memory with a
9620 particular byte value.
9622 Note that, unlike the standard libc function, the ``llvm.memset``
9623 intrinsic does not return a value and takes extra alignment/volatile
9624 arguments. Also, the destination can be in an arbitrary address space.
9629 The first argument is a pointer to the destination to fill, the second
9630 is the byte value with which to fill it, the third argument is an
9631 integer argument specifying the number of bytes to fill, and the fourth
9632 argument is the known alignment of the destination location.
9634 If the call to this intrinsic has an alignment value that is not 0 or 1,
9635 then the caller guarantees that the destination pointer is aligned to
9638 If the ``isvolatile`` parameter is ``true``, the ``llvm.memset`` call is
9639 a :ref:`volatile operation <volatile>`. The detailed access behavior is not
9640 very cleanly specified and it is unwise to depend on it.
9645 The '``llvm.memset.*``' intrinsics fill "len" bytes of memory starting
9646 at the destination location. If the argument is known to be aligned to
9647 some boundary, this can be specified as the fourth argument, otherwise
9648 it should be set to 0 or 1 (both meaning no alignment).
9650 '``llvm.sqrt.*``' Intrinsic
9651 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
9656 This is an overloaded intrinsic. You can use ``llvm.sqrt`` on any
9657 floating point or vector of floating point type. Not all targets support
9662 declare float @llvm.sqrt.f32(float %Val)
9663 declare double @llvm.sqrt.f64(double %Val)
9664 declare x86_fp80 @llvm.sqrt.f80(x86_fp80 %Val)
9665 declare fp128 @llvm.sqrt.f128(fp128 %Val)
9666 declare ppc_fp128 @llvm.sqrt.ppcf128(ppc_fp128 %Val)
9671 The '``llvm.sqrt``' intrinsics return the sqrt of the specified operand,
9672 returning the same value as the libm '``sqrt``' functions would. Unlike
9673 ``sqrt`` in libm, however, ``llvm.sqrt`` has undefined behavior for
9674 negative numbers other than -0.0 (which allows for better optimization,
9675 because there is no need to worry about errno being set).
9676 ``llvm.sqrt(-0.0)`` is defined to return -0.0 like IEEE sqrt.
9681 The argument and return value are floating point numbers of the same
9687 This function returns the sqrt of the specified operand if it is a
9688 nonnegative floating point number.
9690 '``llvm.powi.*``' Intrinsic
9691 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
9696 This is an overloaded intrinsic. You can use ``llvm.powi`` on any
9697 floating point or vector of floating point type. Not all targets support
9702 declare float @llvm.powi.f32(float %Val, i32 %power)
9703 declare double @llvm.powi.f64(double %Val, i32 %power)
9704 declare x86_fp80 @llvm.powi.f80(x86_fp80 %Val, i32 %power)
9705 declare fp128 @llvm.powi.f128(fp128 %Val, i32 %power)
9706 declare ppc_fp128 @llvm.powi.ppcf128(ppc_fp128 %Val, i32 %power)
9711 The '``llvm.powi.*``' intrinsics return the first operand raised to the
9712 specified (positive or negative) power. The order of evaluation of
9713 multiplications is not defined. When a vector of floating point type is
9714 used, the second argument remains a scalar integer value.
9719 The second argument is an integer power, and the first is a value to
9720 raise to that power.
9725 This function returns the first value raised to the second power with an
9726 unspecified sequence of rounding operations.
9728 '``llvm.sin.*``' Intrinsic
9729 ^^^^^^^^^^^^^^^^^^^^^^^^^^
9734 This is an overloaded intrinsic. You can use ``llvm.sin`` on any
9735 floating point or vector of floating point type. Not all targets support
9740 declare float @llvm.sin.f32(float %Val)
9741 declare double @llvm.sin.f64(double %Val)
9742 declare x86_fp80 @llvm.sin.f80(x86_fp80 %Val)
9743 declare fp128 @llvm.sin.f128(fp128 %Val)
9744 declare ppc_fp128 @llvm.sin.ppcf128(ppc_fp128 %Val)
9749 The '``llvm.sin.*``' intrinsics return the sine of the operand.
9754 The argument and return value are floating point numbers of the same
9760 This function returns the sine of the specified operand, returning the
9761 same values as the libm ``sin`` functions would, and handles error
9762 conditions in the same way.
9764 '``llvm.cos.*``' Intrinsic
9765 ^^^^^^^^^^^^^^^^^^^^^^^^^^
9770 This is an overloaded intrinsic. You can use ``llvm.cos`` on any
9771 floating point or vector of floating point type. Not all targets support
9776 declare float @llvm.cos.f32(float %Val)
9777 declare double @llvm.cos.f64(double %Val)
9778 declare x86_fp80 @llvm.cos.f80(x86_fp80 %Val)
9779 declare fp128 @llvm.cos.f128(fp128 %Val)
9780 declare ppc_fp128 @llvm.cos.ppcf128(ppc_fp128 %Val)
9785 The '``llvm.cos.*``' intrinsics return the cosine of the operand.
9790 The argument and return value are floating point numbers of the same
9796 This function returns the cosine of the specified operand, returning the
9797 same values as the libm ``cos`` functions would, and handles error
9798 conditions in the same way.
9800 '``llvm.pow.*``' Intrinsic
9801 ^^^^^^^^^^^^^^^^^^^^^^^^^^
9806 This is an overloaded intrinsic. You can use ``llvm.pow`` on any
9807 floating point or vector of floating point type. Not all targets support
9812 declare float @llvm.pow.f32(float %Val, float %Power)
9813 declare double @llvm.pow.f64(double %Val, double %Power)
9814 declare x86_fp80 @llvm.pow.f80(x86_fp80 %Val, x86_fp80 %Power)
9815 declare fp128 @llvm.pow.f128(fp128 %Val, fp128 %Power)
9816 declare ppc_fp128 @llvm.pow.ppcf128(ppc_fp128 %Val, ppc_fp128 Power)
9821 The '``llvm.pow.*``' intrinsics return the first operand raised to the
9822 specified (positive or negative) power.
9827 The second argument is a floating point power, and the first is a value
9828 to raise to that power.
9833 This function returns the first value raised to the second power,
9834 returning the same values as the libm ``pow`` functions would, and
9835 handles error conditions in the same way.
9837 '``llvm.exp.*``' Intrinsic
9838 ^^^^^^^^^^^^^^^^^^^^^^^^^^
9843 This is an overloaded intrinsic. You can use ``llvm.exp`` on any
9844 floating point or vector of floating point type. Not all targets support
9849 declare float @llvm.exp.f32(float %Val)
9850 declare double @llvm.exp.f64(double %Val)
9851 declare x86_fp80 @llvm.exp.f80(x86_fp80 %Val)
9852 declare fp128 @llvm.exp.f128(fp128 %Val)
9853 declare ppc_fp128 @llvm.exp.ppcf128(ppc_fp128 %Val)
9858 The '``llvm.exp.*``' intrinsics perform the exp function.
9863 The argument and return value are floating point numbers of the same
9869 This function returns the same values as the libm ``exp`` functions
9870 would, and handles error conditions in the same way.
9872 '``llvm.exp2.*``' Intrinsic
9873 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
9878 This is an overloaded intrinsic. You can use ``llvm.exp2`` on any
9879 floating point or vector of floating point type. Not all targets support
9884 declare float @llvm.exp2.f32(float %Val)
9885 declare double @llvm.exp2.f64(double %Val)
9886 declare x86_fp80 @llvm.exp2.f80(x86_fp80 %Val)
9887 declare fp128 @llvm.exp2.f128(fp128 %Val)
9888 declare ppc_fp128 @llvm.exp2.ppcf128(ppc_fp128 %Val)
9893 The '``llvm.exp2.*``' intrinsics perform the exp2 function.
9898 The argument and return value are floating point numbers of the same
9904 This function returns the same values as the libm ``exp2`` functions
9905 would, and handles error conditions in the same way.
9907 '``llvm.log.*``' Intrinsic
9908 ^^^^^^^^^^^^^^^^^^^^^^^^^^
9913 This is an overloaded intrinsic. You can use ``llvm.log`` on any
9914 floating point or vector of floating point type. Not all targets support
9919 declare float @llvm.log.f32(float %Val)
9920 declare double @llvm.log.f64(double %Val)
9921 declare x86_fp80 @llvm.log.f80(x86_fp80 %Val)
9922 declare fp128 @llvm.log.f128(fp128 %Val)
9923 declare ppc_fp128 @llvm.log.ppcf128(ppc_fp128 %Val)
9928 The '``llvm.log.*``' intrinsics perform the log function.
9933 The argument and return value are floating point numbers of the same
9939 This function returns the same values as the libm ``log`` functions
9940 would, and handles error conditions in the same way.
9942 '``llvm.log10.*``' Intrinsic
9943 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9948 This is an overloaded intrinsic. You can use ``llvm.log10`` on any
9949 floating point or vector of floating point type. Not all targets support
9954 declare float @llvm.log10.f32(float %Val)
9955 declare double @llvm.log10.f64(double %Val)
9956 declare x86_fp80 @llvm.log10.f80(x86_fp80 %Val)
9957 declare fp128 @llvm.log10.f128(fp128 %Val)
9958 declare ppc_fp128 @llvm.log10.ppcf128(ppc_fp128 %Val)
9963 The '``llvm.log10.*``' intrinsics perform the log10 function.
9968 The argument and return value are floating point numbers of the same
9974 This function returns the same values as the libm ``log10`` functions
9975 would, and handles error conditions in the same way.
9977 '``llvm.log2.*``' Intrinsic
9978 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
9983 This is an overloaded intrinsic. You can use ``llvm.log2`` on any
9984 floating point or vector of floating point type. Not all targets support
9989 declare float @llvm.log2.f32(float %Val)
9990 declare double @llvm.log2.f64(double %Val)
9991 declare x86_fp80 @llvm.log2.f80(x86_fp80 %Val)
9992 declare fp128 @llvm.log2.f128(fp128 %Val)
9993 declare ppc_fp128 @llvm.log2.ppcf128(ppc_fp128 %Val)
9998 The '``llvm.log2.*``' intrinsics perform the log2 function.
10003 The argument and return value are floating point numbers of the same
10009 This function returns the same values as the libm ``log2`` functions
10010 would, and handles error conditions in the same way.
10012 '``llvm.fma.*``' Intrinsic
10013 ^^^^^^^^^^^^^^^^^^^^^^^^^^
10018 This is an overloaded intrinsic. You can use ``llvm.fma`` on any
10019 floating point or vector of floating point type. Not all targets support
10024 declare float @llvm.fma.f32(float %a, float %b, float %c)
10025 declare double @llvm.fma.f64(double %a, double %b, double %c)
10026 declare x86_fp80 @llvm.fma.f80(x86_fp80 %a, x86_fp80 %b, x86_fp80 %c)
10027 declare fp128 @llvm.fma.f128(fp128 %a, fp128 %b, fp128 %c)
10028 declare ppc_fp128 @llvm.fma.ppcf128(ppc_fp128 %a, ppc_fp128 %b, ppc_fp128 %c)
10033 The '``llvm.fma.*``' intrinsics perform the fused multiply-add
10039 The argument and return value are floating point numbers of the same
10045 This function returns the same values as the libm ``fma`` functions
10046 would, and does not set errno.
10048 '``llvm.fabs.*``' Intrinsic
10049 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
10054 This is an overloaded intrinsic. You can use ``llvm.fabs`` on any
10055 floating point or vector of floating point type. Not all targets support
10060 declare float @llvm.fabs.f32(float %Val)
10061 declare double @llvm.fabs.f64(double %Val)
10062 declare x86_fp80 @llvm.fabs.f80(x86_fp80 %Val)
10063 declare fp128 @llvm.fabs.f128(fp128 %Val)
10064 declare ppc_fp128 @llvm.fabs.ppcf128(ppc_fp128 %Val)
10069 The '``llvm.fabs.*``' intrinsics return the absolute value of the
10075 The argument and return value are floating point numbers of the same
10081 This function returns the same values as the libm ``fabs`` functions
10082 would, and handles error conditions in the same way.
10084 '``llvm.minnum.*``' Intrinsic
10085 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10090 This is an overloaded intrinsic. You can use ``llvm.minnum`` on any
10091 floating point or vector of floating point type. Not all targets support
10096 declare float @llvm.minnum.f32(float %Val0, float %Val1)
10097 declare double @llvm.minnum.f64(double %Val0, double %Val1)
10098 declare x86_fp80 @llvm.minnum.f80(x86_fp80 %Val0, x86_fp80 %Val1)
10099 declare fp128 @llvm.minnum.f128(fp128 %Val0, fp128 %Val1)
10100 declare ppc_fp128 @llvm.minnum.ppcf128(ppc_fp128 %Val0, ppc_fp128 %Val1)
10105 The '``llvm.minnum.*``' intrinsics return the minimum of the two
10112 The arguments and return value are floating point numbers of the same
10118 Follows the IEEE-754 semantics for minNum, which also match for libm's
10121 If either operand is a NaN, returns the other non-NaN operand. Returns
10122 NaN only if both operands are NaN. If the operands compare equal,
10123 returns a value that compares equal to both operands. This means that
10124 fmin(+/-0.0, +/-0.0) could return either -0.0 or 0.0.
10126 '``llvm.maxnum.*``' Intrinsic
10127 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10132 This is an overloaded intrinsic. You can use ``llvm.maxnum`` on any
10133 floating point or vector of floating point type. Not all targets support
10138 declare float @llvm.maxnum.f32(float %Val0, float %Val1l)
10139 declare double @llvm.maxnum.f64(double %Val0, double %Val1)
10140 declare x86_fp80 @llvm.maxnum.f80(x86_fp80 %Val0, x86_fp80 %Val1)
10141 declare fp128 @llvm.maxnum.f128(fp128 %Val0, fp128 %Val1)
10142 declare ppc_fp128 @llvm.maxnum.ppcf128(ppc_fp128 %Val0, ppc_fp128 %Val1)
10147 The '``llvm.maxnum.*``' intrinsics return the maximum of the two
10154 The arguments and return value are floating point numbers of the same
10159 Follows the IEEE-754 semantics for maxNum, which also match for libm's
10162 If either operand is a NaN, returns the other non-NaN operand. Returns
10163 NaN only if both operands are NaN. If the operands compare equal,
10164 returns a value that compares equal to both operands. This means that
10165 fmax(+/-0.0, +/-0.0) could return either -0.0 or 0.0.
10167 '``llvm.copysign.*``' Intrinsic
10168 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10173 This is an overloaded intrinsic. You can use ``llvm.copysign`` on any
10174 floating point or vector of floating point type. Not all targets support
10179 declare float @llvm.copysign.f32(float %Mag, float %Sgn)
10180 declare double @llvm.copysign.f64(double %Mag, double %Sgn)
10181 declare x86_fp80 @llvm.copysign.f80(x86_fp80 %Mag, x86_fp80 %Sgn)
10182 declare fp128 @llvm.copysign.f128(fp128 %Mag, fp128 %Sgn)
10183 declare ppc_fp128 @llvm.copysign.ppcf128(ppc_fp128 %Mag, ppc_fp128 %Sgn)
10188 The '``llvm.copysign.*``' intrinsics return a value with the magnitude of the
10189 first operand and the sign of the second operand.
10194 The arguments and return value are floating point numbers of the same
10200 This function returns the same values as the libm ``copysign``
10201 functions would, and handles error conditions in the same way.
10203 '``llvm.floor.*``' Intrinsic
10204 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10209 This is an overloaded intrinsic. You can use ``llvm.floor`` on any
10210 floating point or vector of floating point type. Not all targets support
10215 declare float @llvm.floor.f32(float %Val)
10216 declare double @llvm.floor.f64(double %Val)
10217 declare x86_fp80 @llvm.floor.f80(x86_fp80 %Val)
10218 declare fp128 @llvm.floor.f128(fp128 %Val)
10219 declare ppc_fp128 @llvm.floor.ppcf128(ppc_fp128 %Val)
10224 The '``llvm.floor.*``' intrinsics return the floor of the operand.
10229 The argument and return value are floating point numbers of the same
10235 This function returns the same values as the libm ``floor`` functions
10236 would, and handles error conditions in the same way.
10238 '``llvm.ceil.*``' Intrinsic
10239 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
10244 This is an overloaded intrinsic. You can use ``llvm.ceil`` on any
10245 floating point or vector of floating point type. Not all targets support
10250 declare float @llvm.ceil.f32(float %Val)
10251 declare double @llvm.ceil.f64(double %Val)
10252 declare x86_fp80 @llvm.ceil.f80(x86_fp80 %Val)
10253 declare fp128 @llvm.ceil.f128(fp128 %Val)
10254 declare ppc_fp128 @llvm.ceil.ppcf128(ppc_fp128 %Val)
10259 The '``llvm.ceil.*``' intrinsics return the ceiling of the operand.
10264 The argument and return value are floating point numbers of the same
10270 This function returns the same values as the libm ``ceil`` functions
10271 would, and handles error conditions in the same way.
10273 '``llvm.trunc.*``' Intrinsic
10274 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10279 This is an overloaded intrinsic. You can use ``llvm.trunc`` on any
10280 floating point or vector of floating point type. Not all targets support
10285 declare float @llvm.trunc.f32(float %Val)
10286 declare double @llvm.trunc.f64(double %Val)
10287 declare x86_fp80 @llvm.trunc.f80(x86_fp80 %Val)
10288 declare fp128 @llvm.trunc.f128(fp128 %Val)
10289 declare ppc_fp128 @llvm.trunc.ppcf128(ppc_fp128 %Val)
10294 The '``llvm.trunc.*``' intrinsics returns the operand rounded to the
10295 nearest integer not larger in magnitude than the operand.
10300 The argument and return value are floating point numbers of the same
10306 This function returns the same values as the libm ``trunc`` functions
10307 would, and handles error conditions in the same way.
10309 '``llvm.rint.*``' Intrinsic
10310 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
10315 This is an overloaded intrinsic. You can use ``llvm.rint`` on any
10316 floating point or vector of floating point type. Not all targets support
10321 declare float @llvm.rint.f32(float %Val)
10322 declare double @llvm.rint.f64(double %Val)
10323 declare x86_fp80 @llvm.rint.f80(x86_fp80 %Val)
10324 declare fp128 @llvm.rint.f128(fp128 %Val)
10325 declare ppc_fp128 @llvm.rint.ppcf128(ppc_fp128 %Val)
10330 The '``llvm.rint.*``' intrinsics returns the operand rounded to the
10331 nearest integer. It may raise an inexact floating-point exception if the
10332 operand isn't an integer.
10337 The argument and return value are floating point numbers of the same
10343 This function returns the same values as the libm ``rint`` functions
10344 would, and handles error conditions in the same way.
10346 '``llvm.nearbyint.*``' Intrinsic
10347 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10352 This is an overloaded intrinsic. You can use ``llvm.nearbyint`` on any
10353 floating point or vector of floating point type. Not all targets support
10358 declare float @llvm.nearbyint.f32(float %Val)
10359 declare double @llvm.nearbyint.f64(double %Val)
10360 declare x86_fp80 @llvm.nearbyint.f80(x86_fp80 %Val)
10361 declare fp128 @llvm.nearbyint.f128(fp128 %Val)
10362 declare ppc_fp128 @llvm.nearbyint.ppcf128(ppc_fp128 %Val)
10367 The '``llvm.nearbyint.*``' intrinsics returns the operand rounded to the
10373 The argument and return value are floating point numbers of the same
10379 This function returns the same values as the libm ``nearbyint``
10380 functions would, and handles error conditions in the same way.
10382 '``llvm.round.*``' Intrinsic
10383 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10388 This is an overloaded intrinsic. You can use ``llvm.round`` on any
10389 floating point or vector of floating point type. Not all targets support
10394 declare float @llvm.round.f32(float %Val)
10395 declare double @llvm.round.f64(double %Val)
10396 declare x86_fp80 @llvm.round.f80(x86_fp80 %Val)
10397 declare fp128 @llvm.round.f128(fp128 %Val)
10398 declare ppc_fp128 @llvm.round.ppcf128(ppc_fp128 %Val)
10403 The '``llvm.round.*``' intrinsics returns the operand rounded to the
10409 The argument and return value are floating point numbers of the same
10415 This function returns the same values as the libm ``round``
10416 functions would, and handles error conditions in the same way.
10418 Bit Manipulation Intrinsics
10419 ---------------------------
10421 LLVM provides intrinsics for a few important bit manipulation
10422 operations. These allow efficient code generation for some algorithms.
10424 '``llvm.bitreverse.*``' Intrinsics
10425 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10430 This is an overloaded intrinsic function. You can use bitreverse on any
10435 declare i16 @llvm.bitreverse.i16(i16 <id>)
10436 declare i32 @llvm.bitreverse.i32(i32 <id>)
10437 declare i64 @llvm.bitreverse.i64(i64 <id>)
10442 The '``llvm.bitreverse``' family of intrinsics is used to reverse the
10443 bitpattern of an integer value; for example ``0b1234567`` becomes
10449 The ``llvm.bitreverse.iN`` intrinsic returns an i16 value that has bit
10450 ``M`` in the input moved to bit ``N-M`` in the output.
10452 '``llvm.bswap.*``' Intrinsics
10453 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10458 This is an overloaded intrinsic function. You can use bswap on any
10459 integer type that is an even number of bytes (i.e. BitWidth % 16 == 0).
10463 declare i16 @llvm.bswap.i16(i16 <id>)
10464 declare i32 @llvm.bswap.i32(i32 <id>)
10465 declare i64 @llvm.bswap.i64(i64 <id>)
10470 The '``llvm.bswap``' family of intrinsics is used to byte swap integer
10471 values with an even number of bytes (positive multiple of 16 bits).
10472 These are useful for performing operations on data that is not in the
10473 target's native byte order.
10478 The ``llvm.bswap.i16`` intrinsic returns an i16 value that has the high
10479 and low byte of the input i16 swapped. Similarly, the ``llvm.bswap.i32``
10480 intrinsic returns an i32 value that has the four bytes of the input i32
10481 swapped, so that if the input bytes are numbered 0, 1, 2, 3 then the
10482 returned i32 will have its bytes in 3, 2, 1, 0 order. The
10483 ``llvm.bswap.i48``, ``llvm.bswap.i64`` and other intrinsics extend this
10484 concept to additional even-byte lengths (6 bytes, 8 bytes and more,
10487 '``llvm.ctpop.*``' Intrinsic
10488 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10493 This is an overloaded intrinsic. You can use llvm.ctpop on any integer
10494 bit width, or on any vector with integer elements. Not all targets
10495 support all bit widths or vector types, however.
10499 declare i8 @llvm.ctpop.i8(i8 <src>)
10500 declare i16 @llvm.ctpop.i16(i16 <src>)
10501 declare i32 @llvm.ctpop.i32(i32 <src>)
10502 declare i64 @llvm.ctpop.i64(i64 <src>)
10503 declare i256 @llvm.ctpop.i256(i256 <src>)
10504 declare <2 x i32> @llvm.ctpop.v2i32(<2 x i32> <src>)
10509 The '``llvm.ctpop``' family of intrinsics counts the number of bits set
10515 The only argument is the value to be counted. The argument may be of any
10516 integer type, or a vector with integer elements. The return type must
10517 match the argument type.
10522 The '``llvm.ctpop``' intrinsic counts the 1's in a variable, or within
10523 each element of a vector.
10525 '``llvm.ctlz.*``' Intrinsic
10526 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
10531 This is an overloaded intrinsic. You can use ``llvm.ctlz`` on any
10532 integer bit width, or any vector whose elements are integers. Not all
10533 targets support all bit widths or vector types, however.
10537 declare i8 @llvm.ctlz.i8 (i8 <src>, i1 <is_zero_undef>)
10538 declare i16 @llvm.ctlz.i16 (i16 <src>, i1 <is_zero_undef>)
10539 declare i32 @llvm.ctlz.i32 (i32 <src>, i1 <is_zero_undef>)
10540 declare i64 @llvm.ctlz.i64 (i64 <src>, i1 <is_zero_undef>)
10541 declare i256 @llvm.ctlz.i256(i256 <src>, i1 <is_zero_undef>)
10542 declase <2 x i32> @llvm.ctlz.v2i32(<2 x i32> <src>, i1 <is_zero_undef>)
10547 The '``llvm.ctlz``' family of intrinsic functions counts the number of
10548 leading zeros in a variable.
10553 The first argument is the value to be counted. This argument may be of
10554 any integer type, or a vector with integer element type. The return
10555 type must match the first argument type.
10557 The second argument must be a constant and is a flag to indicate whether
10558 the intrinsic should ensure that a zero as the first argument produces a
10559 defined result. Historically some architectures did not provide a
10560 defined result for zero values as efficiently, and many algorithms are
10561 now predicated on avoiding zero-value inputs.
10566 The '``llvm.ctlz``' intrinsic counts the leading (most significant)
10567 zeros in a variable, or within each element of the vector. If
10568 ``src == 0`` then the result is the size in bits of the type of ``src``
10569 if ``is_zero_undef == 0`` and ``undef`` otherwise. For example,
10570 ``llvm.ctlz(i32 2) = 30``.
10572 '``llvm.cttz.*``' Intrinsic
10573 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
10578 This is an overloaded intrinsic. You can use ``llvm.cttz`` on any
10579 integer bit width, or any vector of integer elements. Not all targets
10580 support all bit widths or vector types, however.
10584 declare i8 @llvm.cttz.i8 (i8 <src>, i1 <is_zero_undef>)
10585 declare i16 @llvm.cttz.i16 (i16 <src>, i1 <is_zero_undef>)
10586 declare i32 @llvm.cttz.i32 (i32 <src>, i1 <is_zero_undef>)
10587 declare i64 @llvm.cttz.i64 (i64 <src>, i1 <is_zero_undef>)
10588 declare i256 @llvm.cttz.i256(i256 <src>, i1 <is_zero_undef>)
10589 declase <2 x i32> @llvm.cttz.v2i32(<2 x i32> <src>, i1 <is_zero_undef>)
10594 The '``llvm.cttz``' family of intrinsic functions counts the number of
10600 The first argument is the value to be counted. This argument may be of
10601 any integer type, or a vector with integer element type. The return
10602 type must match the first argument type.
10604 The second argument must be a constant and is a flag to indicate whether
10605 the intrinsic should ensure that a zero as the first argument produces a
10606 defined result. Historically some architectures did not provide a
10607 defined result for zero values as efficiently, and many algorithms are
10608 now predicated on avoiding zero-value inputs.
10613 The '``llvm.cttz``' intrinsic counts the trailing (least significant)
10614 zeros in a variable, or within each element of a vector. If ``src == 0``
10615 then the result is the size in bits of the type of ``src`` if
10616 ``is_zero_undef == 0`` and ``undef`` otherwise. For example,
10617 ``llvm.cttz(2) = 1``.
10621 Arithmetic with Overflow Intrinsics
10622 -----------------------------------
10624 LLVM provides intrinsics for some arithmetic with overflow operations.
10626 '``llvm.sadd.with.overflow.*``' Intrinsics
10627 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10632 This is an overloaded intrinsic. You can use ``llvm.sadd.with.overflow``
10633 on any integer bit width.
10637 declare {i16, i1} @llvm.sadd.with.overflow.i16(i16 %a, i16 %b)
10638 declare {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b)
10639 declare {i64, i1} @llvm.sadd.with.overflow.i64(i64 %a, i64 %b)
10644 The '``llvm.sadd.with.overflow``' family of intrinsic functions perform
10645 a signed addition of the two arguments, and indicate whether an overflow
10646 occurred during the signed summation.
10651 The arguments (%a and %b) and the first element of the result structure
10652 may be of integer types of any bit width, but they must have the same
10653 bit width. The second element of the result structure must be of type
10654 ``i1``. ``%a`` and ``%b`` are the two values that will undergo signed
10660 The '``llvm.sadd.with.overflow``' family of intrinsic functions perform
10661 a signed addition of the two variables. They return a structure --- the
10662 first element of which is the signed summation, and the second element
10663 of which is a bit specifying if the signed summation resulted in an
10669 .. code-block:: llvm
10671 %res = call {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b)
10672 %sum = extractvalue {i32, i1} %res, 0
10673 %obit = extractvalue {i32, i1} %res, 1
10674 br i1 %obit, label %overflow, label %normal
10676 '``llvm.uadd.with.overflow.*``' Intrinsics
10677 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10682 This is an overloaded intrinsic. You can use ``llvm.uadd.with.overflow``
10683 on any integer bit width.
10687 declare {i16, i1} @llvm.uadd.with.overflow.i16(i16 %a, i16 %b)
10688 declare {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)
10689 declare {i64, i1} @llvm.uadd.with.overflow.i64(i64 %a, i64 %b)
10694 The '``llvm.uadd.with.overflow``' family of intrinsic functions perform
10695 an unsigned addition of the two arguments, and indicate whether a carry
10696 occurred during the unsigned summation.
10701 The arguments (%a and %b) and the first element of the result structure
10702 may be of integer types of any bit width, but they must have the same
10703 bit width. The second element of the result structure must be of type
10704 ``i1``. ``%a`` and ``%b`` are the two values that will undergo unsigned
10710 The '``llvm.uadd.with.overflow``' family of intrinsic functions perform
10711 an unsigned addition of the two arguments. They return a structure --- the
10712 first element of which is the sum, and the second element of which is a
10713 bit specifying if the unsigned summation resulted in a carry.
10718 .. code-block:: llvm
10720 %res = call {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)
10721 %sum = extractvalue {i32, i1} %res, 0
10722 %obit = extractvalue {i32, i1} %res, 1
10723 br i1 %obit, label %carry, label %normal
10725 '``llvm.ssub.with.overflow.*``' Intrinsics
10726 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10731 This is an overloaded intrinsic. You can use ``llvm.ssub.with.overflow``
10732 on any integer bit width.
10736 declare {i16, i1} @llvm.ssub.with.overflow.i16(i16 %a, i16 %b)
10737 declare {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b)
10738 declare {i64, i1} @llvm.ssub.with.overflow.i64(i64 %a, i64 %b)
10743 The '``llvm.ssub.with.overflow``' family of intrinsic functions perform
10744 a signed subtraction of the two arguments, and indicate whether an
10745 overflow occurred during the signed subtraction.
10750 The arguments (%a and %b) and the first element of the result structure
10751 may be of integer types of any bit width, but they must have the same
10752 bit width. The second element of the result structure must be of type
10753 ``i1``. ``%a`` and ``%b`` are the two values that will undergo signed
10759 The '``llvm.ssub.with.overflow``' family of intrinsic functions perform
10760 a signed subtraction of the two arguments. They return a structure --- the
10761 first element of which is the subtraction, and the second element of
10762 which is a bit specifying if the signed subtraction resulted in an
10768 .. code-block:: llvm
10770 %res = call {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b)
10771 %sum = extractvalue {i32, i1} %res, 0
10772 %obit = extractvalue {i32, i1} %res, 1
10773 br i1 %obit, label %overflow, label %normal
10775 '``llvm.usub.with.overflow.*``' Intrinsics
10776 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10781 This is an overloaded intrinsic. You can use ``llvm.usub.with.overflow``
10782 on any integer bit width.
10786 declare {i16, i1} @llvm.usub.with.overflow.i16(i16 %a, i16 %b)
10787 declare {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b)
10788 declare {i64, i1} @llvm.usub.with.overflow.i64(i64 %a, i64 %b)
10793 The '``llvm.usub.with.overflow``' family of intrinsic functions perform
10794 an unsigned subtraction of the two arguments, and indicate whether an
10795 overflow occurred during the unsigned subtraction.
10800 The arguments (%a and %b) and the first element of the result structure
10801 may be of integer types of any bit width, but they must have the same
10802 bit width. The second element of the result structure must be of type
10803 ``i1``. ``%a`` and ``%b`` are the two values that will undergo unsigned
10809 The '``llvm.usub.with.overflow``' family of intrinsic functions perform
10810 an unsigned subtraction of the two arguments. They return a structure ---
10811 the first element of which is the subtraction, and the second element of
10812 which is a bit specifying if the unsigned subtraction resulted in an
10818 .. code-block:: llvm
10820 %res = call {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b)
10821 %sum = extractvalue {i32, i1} %res, 0
10822 %obit = extractvalue {i32, i1} %res, 1
10823 br i1 %obit, label %overflow, label %normal
10825 '``llvm.smul.with.overflow.*``' Intrinsics
10826 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10831 This is an overloaded intrinsic. You can use ``llvm.smul.with.overflow``
10832 on any integer bit width.
10836 declare {i16, i1} @llvm.smul.with.overflow.i16(i16 %a, i16 %b)
10837 declare {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b)
10838 declare {i64, i1} @llvm.smul.with.overflow.i64(i64 %a, i64 %b)
10843 The '``llvm.smul.with.overflow``' family of intrinsic functions perform
10844 a signed multiplication of the two arguments, and indicate whether an
10845 overflow occurred during the signed multiplication.
10850 The arguments (%a and %b) and the first element of the result structure
10851 may be of integer types of any bit width, but they must have the same
10852 bit width. The second element of the result structure must be of type
10853 ``i1``. ``%a`` and ``%b`` are the two values that will undergo signed
10859 The '``llvm.smul.with.overflow``' family of intrinsic functions perform
10860 a signed multiplication of the two arguments. They return a structure ---
10861 the first element of which is the multiplication, and the second element
10862 of which is a bit specifying if the signed multiplication resulted in an
10868 .. code-block:: llvm
10870 %res = call {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b)
10871 %sum = extractvalue {i32, i1} %res, 0
10872 %obit = extractvalue {i32, i1} %res, 1
10873 br i1 %obit, label %overflow, label %normal
10875 '``llvm.umul.with.overflow.*``' Intrinsics
10876 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10881 This is an overloaded intrinsic. You can use ``llvm.umul.with.overflow``
10882 on any integer bit width.
10886 declare {i16, i1} @llvm.umul.with.overflow.i16(i16 %a, i16 %b)
10887 declare {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b)
10888 declare {i64, i1} @llvm.umul.with.overflow.i64(i64 %a, i64 %b)
10893 The '``llvm.umul.with.overflow``' family of intrinsic functions perform
10894 a unsigned multiplication of the two arguments, and indicate whether an
10895 overflow occurred during the unsigned multiplication.
10900 The arguments (%a and %b) and the first element of the result structure
10901 may be of integer types of any bit width, but they must have the same
10902 bit width. The second element of the result structure must be of type
10903 ``i1``. ``%a`` and ``%b`` are the two values that will undergo unsigned
10909 The '``llvm.umul.with.overflow``' family of intrinsic functions perform
10910 an unsigned multiplication of the two arguments. They return a structure ---
10911 the first element of which is the multiplication, and the second
10912 element of which is a bit specifying if the unsigned multiplication
10913 resulted in an overflow.
10918 .. code-block:: llvm
10920 %res = call {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b)
10921 %sum = extractvalue {i32, i1} %res, 0
10922 %obit = extractvalue {i32, i1} %res, 1
10923 br i1 %obit, label %overflow, label %normal
10925 Specialised Arithmetic Intrinsics
10926 ---------------------------------
10928 '``llvm.canonicalize.*``' Intrinsic
10929 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10936 declare float @llvm.canonicalize.f32(float %a)
10937 declare double @llvm.canonicalize.f64(double %b)
10942 The '``llvm.canonicalize.*``' intrinsic returns the platform specific canonical
10943 encoding of a floating point number. This canonicalization is useful for
10944 implementing certain numeric primitives such as frexp. The canonical encoding is
10945 defined by IEEE-754-2008 to be:
10949 2.1.8 canonical encoding: The preferred encoding of a floating-point
10950 representation in a format. Applied to declets, significands of finite
10951 numbers, infinities, and NaNs, especially in decimal formats.
10953 This operation can also be considered equivalent to the IEEE-754-2008
10954 conversion of a floating-point value to the same format. NaNs are handled
10955 according to section 6.2.
10957 Examples of non-canonical encodings:
10959 - x87 pseudo denormals, pseudo NaNs, pseudo Infinity, Unnormals. These are
10960 converted to a canonical representation per hardware-specific protocol.
10961 - Many normal decimal floating point numbers have non-canonical alternative
10963 - Some machines, like GPUs or ARMv7 NEON, do not support subnormal values.
10964 These are treated as non-canonical encodings of zero and with be flushed to
10965 a zero of the same sign by this operation.
10967 Note that per IEEE-754-2008 6.2, systems that support signaling NaNs with
10968 default exception handling must signal an invalid exception, and produce a
10971 This function should always be implementable as multiplication by 1.0, provided
10972 that the compiler does not constant fold the operation. Likewise, division by
10973 1.0 and ``llvm.minnum(x, x)`` are possible implementations. Addition with
10974 -0.0 is also sufficient provided that the rounding mode is not -Infinity.
10976 ``@llvm.canonicalize`` must preserve the equality relation. That is:
10978 - ``(@llvm.canonicalize(x) == x)`` is equivalent to ``(x == x)``
10979 - ``(@llvm.canonicalize(x) == @llvm.canonicalize(y))`` is equivalent to
10982 Additionally, the sign of zero must be conserved:
10983 ``@llvm.canonicalize(-0.0) = -0.0`` and ``@llvm.canonicalize(+0.0) = +0.0``
10985 The payload bits of a NaN must be conserved, with two exceptions.
10986 First, environments which use only a single canonical representation of NaN
10987 must perform said canonicalization. Second, SNaNs must be quieted per the
10990 The canonicalization operation may be optimized away if:
10992 - The input is known to be canonical. For example, it was produced by a
10993 floating-point operation that is required by the standard to be canonical.
10994 - The result is consumed only by (or fused with) other floating-point
10995 operations. That is, the bits of the floating point value are not examined.
10997 '``llvm.fmuladd.*``' Intrinsic
10998 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11005 declare float @llvm.fmuladd.f32(float %a, float %b, float %c)
11006 declare double @llvm.fmuladd.f64(double %a, double %b, double %c)
11011 The '``llvm.fmuladd.*``' intrinsic functions represent multiply-add
11012 expressions that can be fused if the code generator determines that (a) the
11013 target instruction set has support for a fused operation, and (b) that the
11014 fused operation is more efficient than the equivalent, separate pair of mul
11015 and add instructions.
11020 The '``llvm.fmuladd.*``' intrinsics each take three arguments: two
11021 multiplicands, a and b, and an addend c.
11030 %0 = call float @llvm.fmuladd.f32(%a, %b, %c)
11032 is equivalent to the expression a \* b + c, except that rounding will
11033 not be performed between the multiplication and addition steps if the
11034 code generator fuses the operations. Fusion is not guaranteed, even if
11035 the target platform supports it. If a fused multiply-add is required the
11036 corresponding llvm.fma.\* intrinsic function should be used
11037 instead. This never sets errno, just as '``llvm.fma.*``'.
11042 .. code-block:: llvm
11044 %r2 = call float @llvm.fmuladd.f32(float %a, float %b, float %c) ; yields float:r2 = (a * b) + c
11046 Half Precision Floating Point Intrinsics
11047 ----------------------------------------
11049 For most target platforms, half precision floating point is a
11050 storage-only format. This means that it is a dense encoding (in memory)
11051 but does not support computation in the format.
11053 This means that code must first load the half-precision floating point
11054 value as an i16, then convert it to float with
11055 :ref:`llvm.convert.from.fp16 <int_convert_from_fp16>`. Computation can
11056 then be performed on the float value (including extending to double
11057 etc). To store the value back to memory, it is first converted to float
11058 if needed, then converted to i16 with
11059 :ref:`llvm.convert.to.fp16 <int_convert_to_fp16>`, then storing as an
11062 .. _int_convert_to_fp16:
11064 '``llvm.convert.to.fp16``' Intrinsic
11065 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11072 declare i16 @llvm.convert.to.fp16.f32(float %a)
11073 declare i16 @llvm.convert.to.fp16.f64(double %a)
11078 The '``llvm.convert.to.fp16``' intrinsic function performs a conversion from a
11079 conventional floating point type to half precision floating point format.
11084 The intrinsic function contains single argument - the value to be
11090 The '``llvm.convert.to.fp16``' intrinsic function performs a conversion from a
11091 conventional floating point format to half precision floating point format. The
11092 return value is an ``i16`` which contains the converted number.
11097 .. code-block:: llvm
11099 %res = call i16 @llvm.convert.to.fp16.f32(float %a)
11100 store i16 %res, i16* @x, align 2
11102 .. _int_convert_from_fp16:
11104 '``llvm.convert.from.fp16``' Intrinsic
11105 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11112 declare float @llvm.convert.from.fp16.f32(i16 %a)
11113 declare double @llvm.convert.from.fp16.f64(i16 %a)
11118 The '``llvm.convert.from.fp16``' intrinsic function performs a
11119 conversion from half precision floating point format to single precision
11120 floating point format.
11125 The intrinsic function contains single argument - the value to be
11131 The '``llvm.convert.from.fp16``' intrinsic function performs a
11132 conversion from half single precision floating point format to single
11133 precision floating point format. The input half-float value is
11134 represented by an ``i16`` value.
11139 .. code-block:: llvm
11141 %a = load i16, i16* @x, align 2
11142 %res = call float @llvm.convert.from.fp16(i16 %a)
11144 .. _dbg_intrinsics:
11146 Debugger Intrinsics
11147 -------------------
11149 The LLVM debugger intrinsics (which all start with ``llvm.dbg.``
11150 prefix), are described in the `LLVM Source Level
11151 Debugging <SourceLevelDebugging.html#format_common_intrinsics>`_
11154 Exception Handling Intrinsics
11155 -----------------------------
11157 The LLVM exception handling intrinsics (which all start with
11158 ``llvm.eh.`` prefix), are described in the `LLVM Exception
11159 Handling <ExceptionHandling.html#format_common_intrinsics>`_ document.
11161 .. _int_trampoline:
11163 Trampoline Intrinsics
11164 ---------------------
11166 These intrinsics make it possible to excise one parameter, marked with
11167 the :ref:`nest <nest>` attribute, from a function. The result is a
11168 callable function pointer lacking the nest parameter - the caller does
11169 not need to provide a value for it. Instead, the value to use is stored
11170 in advance in a "trampoline", a block of memory usually allocated on the
11171 stack, which also contains code to splice the nest value into the
11172 argument list. This is used to implement the GCC nested function address
11175 For example, if the function is ``i32 f(i8* nest %c, i32 %x, i32 %y)``
11176 then the resulting function pointer has signature ``i32 (i32, i32)*``.
11177 It can be created as follows:
11179 .. code-block:: llvm
11181 %tramp = alloca [10 x i8], align 4 ; size and alignment only correct for X86
11182 %tramp1 = getelementptr [10 x i8], [10 x i8]* %tramp, i32 0, i32 0
11183 call i8* @llvm.init.trampoline(i8* %tramp1, i8* bitcast (i32 (i8*, i32, i32)* @f to i8*), i8* %nval)
11184 %p = call i8* @llvm.adjust.trampoline(i8* %tramp1)
11185 %fp = bitcast i8* %p to i32 (i32, i32)*
11187 The call ``%val = call i32 %fp(i32 %x, i32 %y)`` is then equivalent to
11188 ``%val = call i32 %f(i8* %nval, i32 %x, i32 %y)``.
11192 '``llvm.init.trampoline``' Intrinsic
11193 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11200 declare void @llvm.init.trampoline(i8* <tramp>, i8* <func>, i8* <nval>)
11205 This fills the memory pointed to by ``tramp`` with executable code,
11206 turning it into a trampoline.
11211 The ``llvm.init.trampoline`` intrinsic takes three arguments, all
11212 pointers. The ``tramp`` argument must point to a sufficiently large and
11213 sufficiently aligned block of memory; this memory is written to by the
11214 intrinsic. Note that the size and the alignment are target-specific -
11215 LLVM currently provides no portable way of determining them, so a
11216 front-end that generates this intrinsic needs to have some
11217 target-specific knowledge. The ``func`` argument must hold a function
11218 bitcast to an ``i8*``.
11223 The block of memory pointed to by ``tramp`` is filled with target
11224 dependent code, turning it into a function. Then ``tramp`` needs to be
11225 passed to :ref:`llvm.adjust.trampoline <int_at>` to get a pointer which can
11226 be :ref:`bitcast (to a new function) and called <int_trampoline>`. The new
11227 function's signature is the same as that of ``func`` with any arguments
11228 marked with the ``nest`` attribute removed. At most one such ``nest``
11229 argument is allowed, and it must be of pointer type. Calling the new
11230 function is equivalent to calling ``func`` with the same argument list,
11231 but with ``nval`` used for the missing ``nest`` argument. If, after
11232 calling ``llvm.init.trampoline``, the memory pointed to by ``tramp`` is
11233 modified, then the effect of any later call to the returned function
11234 pointer is undefined.
11238 '``llvm.adjust.trampoline``' Intrinsic
11239 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11246 declare i8* @llvm.adjust.trampoline(i8* <tramp>)
11251 This performs any required machine-specific adjustment to the address of
11252 a trampoline (passed as ``tramp``).
11257 ``tramp`` must point to a block of memory which already has trampoline
11258 code filled in by a previous call to
11259 :ref:`llvm.init.trampoline <int_it>`.
11264 On some architectures the address of the code to be executed needs to be
11265 different than the address where the trampoline is actually stored. This
11266 intrinsic returns the executable address corresponding to ``tramp``
11267 after performing the required machine specific adjustments. The pointer
11268 returned can then be :ref:`bitcast and executed <int_trampoline>`.
11270 .. _int_mload_mstore:
11272 Masked Vector Load and Store Intrinsics
11273 ---------------------------------------
11275 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.
11279 '``llvm.masked.load.*``' Intrinsics
11280 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11284 This is an overloaded intrinsic. The loaded data is a vector of any integer, floating point or pointer data type.
11288 declare <16 x float> @llvm.masked.load.v16f32 (<16 x float>* <ptr>, i32 <alignment>, <16 x i1> <mask>, <16 x float> <passthru>)
11289 declare <2 x double> @llvm.masked.load.v2f64 (<2 x double>* <ptr>, i32 <alignment>, <2 x i1> <mask>, <2 x double> <passthru>)
11290 ;; The data is a vector of pointers to double
11291 declare <8 x double*> @llvm.masked.load.v8p0f64 (<8 x double*>* <ptr>, i32 <alignment>, <8 x i1> <mask>, <8 x double*> <passthru>)
11292 ;; The data is a vector of function pointers
11293 declare <8 x i32 ()*> @llvm.masked.load.v8p0f_i32f (<8 x i32 ()*>* <ptr>, i32 <alignment>, <8 x i1> <mask>, <8 x i32 ()*> <passthru>)
11298 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.
11304 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.
11310 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.
11311 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.
11316 %res = call <16 x float> @llvm.masked.load.v16f32 (<16 x float>* %ptr, i32 4, <16 x i1>%mask, <16 x float> %passthru)
11318 ;; The result of the two following instructions is identical aside from potential memory access exception
11319 %loadlal = load <16 x float>, <16 x float>* %ptr, align 4
11320 %res = select <16 x i1> %mask, <16 x float> %loadlal, <16 x float> %passthru
11324 '``llvm.masked.store.*``' Intrinsics
11325 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11329 This is an overloaded intrinsic. The data stored in memory is a vector of any integer, floating point or pointer data type.
11333 declare void @llvm.masked.store.v8i32 (<8 x i32> <value>, <8 x i32>* <ptr>, i32 <alignment>, <8 x i1> <mask>)
11334 declare void @llvm.masked.store.v16f32 (<16 x float> <value>, <16 x float>* <ptr>, i32 <alignment>, <16 x i1> <mask>)
11335 ;; The data is a vector of pointers to double
11336 declare void @llvm.masked.store.v8p0f64 (<8 x double*> <value>, <8 x double*>* <ptr>, i32 <alignment>, <8 x i1> <mask>)
11337 ;; The data is a vector of function pointers
11338 declare void @llvm.masked.store.v4p0f_i32f (<4 x i32 ()*> <value>, <4 x i32 ()*>* <ptr>, i32 <alignment>, <4 x i1> <mask>)
11343 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.
11348 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.
11354 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.
11355 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.
11359 call void @llvm.masked.store.v16f32(<16 x float> %value, <16 x float>* %ptr, i32 4, <16 x i1> %mask)
11361 ;; The result of the following instructions is identical aside from potential data races and memory access exceptions
11362 %oldval = load <16 x float>, <16 x float>* %ptr, align 4
11363 %res = select <16 x i1> %mask, <16 x float> %value, <16 x float> %oldval
11364 store <16 x float> %res, <16 x float>* %ptr, align 4
11367 Masked Vector Gather and Scatter Intrinsics
11368 -------------------------------------------
11370 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.
11374 '``llvm.masked.gather.*``' Intrinsics
11375 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11379 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.
11383 declare <16 x float> @llvm.masked.gather.v16f32 (<16 x float*> <ptrs>, i32 <alignment>, <16 x i1> <mask>, <16 x float> <passthru>)
11384 declare <2 x double> @llvm.masked.gather.v2f64 (<2 x double*> <ptrs>, i32 <alignment>, <2 x i1> <mask>, <2 x double> <passthru>)
11385 declare <8 x float*> @llvm.masked.gather.v8p0f32 (<8 x float**> <ptrs>, i32 <alignment>, <8 x i1> <mask>, <8 x float*> <passthru>)
11390 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.
11396 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.
11402 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.
11403 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.
11408 %res = call <4 x double> @llvm.masked.gather.v4f64 (<4 x double*> %ptrs, i32 8, <4 x i1>%mask, <4 x double> <true, true, true, true>)
11410 ;; The gather with all-true mask is equivalent to the following instruction sequence
11411 %ptr0 = extractelement <4 x double*> %ptrs, i32 0
11412 %ptr1 = extractelement <4 x double*> %ptrs, i32 1
11413 %ptr2 = extractelement <4 x double*> %ptrs, i32 2
11414 %ptr3 = extractelement <4 x double*> %ptrs, i32 3
11416 %val0 = load double, double* %ptr0, align 8
11417 %val1 = load double, double* %ptr1, align 8
11418 %val2 = load double, double* %ptr2, align 8
11419 %val3 = load double, double* %ptr3, align 8
11421 %vec0 = insertelement <4 x double>undef, %val0, 0
11422 %vec01 = insertelement <4 x double>%vec0, %val1, 1
11423 %vec012 = insertelement <4 x double>%vec01, %val2, 2
11424 %vec0123 = insertelement <4 x double>%vec012, %val3, 3
11428 '``llvm.masked.scatter.*``' Intrinsics
11429 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11433 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.
11437 declare void @llvm.masked.scatter.v8i32 (<8 x i32> <value>, <8 x i32*> <ptrs>, i32 <alignment>, <8 x i1> <mask>)
11438 declare void @llvm.masked.scatter.v16f32 (<16 x float> <value>, <16 x float*> <ptrs>, i32 <alignment>, <16 x i1> <mask>)
11439 declare void @llvm.masked.scatter.v4p0f64 (<4 x double*> <value>, <4 x double**> <ptrs>, i32 <alignment>, <4 x i1> <mask>)
11444 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.
11449 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.
11455 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.
11459 ;; This instruction unconditionaly stores data vector in multiple addresses
11460 call @llvm.masked.scatter.v8i32 (<8 x i32> %value, <8 x i32*> %ptrs, i32 4, <8 x i1> <true, true, .. true>)
11462 ;; It is equivalent to a list of scalar stores
11463 %val0 = extractelement <8 x i32> %value, i32 0
11464 %val1 = extractelement <8 x i32> %value, i32 1
11466 %val7 = extractelement <8 x i32> %value, i32 7
11467 %ptr0 = extractelement <8 x i32*> %ptrs, i32 0
11468 %ptr1 = extractelement <8 x i32*> %ptrs, i32 1
11470 %ptr7 = extractelement <8 x i32*> %ptrs, i32 7
11471 ;; Note: the order of the following stores is important when they overlap:
11472 store i32 %val0, i32* %ptr0, align 4
11473 store i32 %val1, i32* %ptr1, align 4
11475 store i32 %val7, i32* %ptr7, align 4
11481 This class of intrinsics provides information about the lifetime of
11482 memory objects and ranges where variables are immutable.
11486 '``llvm.lifetime.start``' Intrinsic
11487 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11494 declare void @llvm.lifetime.start(i64 <size>, i8* nocapture <ptr>)
11499 The '``llvm.lifetime.start``' intrinsic specifies the start of a memory
11505 The first argument is a constant integer representing the size of the
11506 object, or -1 if it is variable sized. The second argument is a pointer
11512 This intrinsic indicates that before this point in the code, the value
11513 of the memory pointed to by ``ptr`` is dead. This means that it is known
11514 to never be used and has an undefined value. A load from the pointer
11515 that precedes this intrinsic can be replaced with ``'undef'``.
11519 '``llvm.lifetime.end``' Intrinsic
11520 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11527 declare void @llvm.lifetime.end(i64 <size>, i8* nocapture <ptr>)
11532 The '``llvm.lifetime.end``' intrinsic specifies the end of a memory
11538 The first argument is a constant integer representing the size of the
11539 object, or -1 if it is variable sized. The second argument is a pointer
11545 This intrinsic indicates that after this point in the code, the value of
11546 the memory pointed to by ``ptr`` is dead. This means that it is known to
11547 never be used and has an undefined value. Any stores into the memory
11548 object following this intrinsic may be removed as dead.
11550 '``llvm.invariant.start``' Intrinsic
11551 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11558 declare {}* @llvm.invariant.start(i64 <size>, i8* nocapture <ptr>)
11563 The '``llvm.invariant.start``' intrinsic specifies that the contents of
11564 a memory object will not change.
11569 The first argument is a constant integer representing the size of the
11570 object, or -1 if it is variable sized. The second argument is a pointer
11576 This intrinsic indicates that until an ``llvm.invariant.end`` that uses
11577 the return value, the referenced memory location is constant and
11580 '``llvm.invariant.end``' Intrinsic
11581 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11588 declare void @llvm.invariant.end({}* <start>, i64 <size>, i8* nocapture <ptr>)
11593 The '``llvm.invariant.end``' intrinsic specifies that the contents of a
11594 memory object are mutable.
11599 The first argument is the matching ``llvm.invariant.start`` intrinsic.
11600 The second argument is a constant integer representing the size of the
11601 object, or -1 if it is variable sized and the third argument is a
11602 pointer to the object.
11607 This intrinsic indicates that the memory is mutable again.
11609 '``llvm.invariant.group.barrier``' Intrinsic
11610 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11617 declare i8* @llvm.invariant.group.barrier(i8* <ptr>)
11622 The '``llvm.invariant.group.barrier``' intrinsic can be used when an invariant
11623 established by invariant.group metadata no longer holds, to obtain a new pointer
11624 value that does not carry the invariant information.
11630 The ``llvm.invariant.group.barrier`` takes only one argument, which is
11631 the pointer to the memory for which the ``invariant.group`` no longer holds.
11636 Returns another pointer that aliases its argument but which is considered different
11637 for the purposes of ``load``/``store`` ``invariant.group`` metadata.
11642 This class of intrinsics is designed to be generic and has no specific
11645 '``llvm.var.annotation``' Intrinsic
11646 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11653 declare void @llvm.var.annotation(i8* <val>, i8* <str>, i8* <str>, i32 <int>)
11658 The '``llvm.var.annotation``' intrinsic.
11663 The first argument is a pointer to a value, the second is a pointer to a
11664 global string, the third is a pointer to a global string which is the
11665 source file name, and the last argument is the line number.
11670 This intrinsic allows annotation of local variables with arbitrary
11671 strings. This can be useful for special purpose optimizations that want
11672 to look for these annotations. These have no other defined use; they are
11673 ignored by code generation and optimization.
11675 '``llvm.ptr.annotation.*``' Intrinsic
11676 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11681 This is an overloaded intrinsic. You can use '``llvm.ptr.annotation``' on a
11682 pointer to an integer of any width. *NOTE* you must specify an address space for
11683 the pointer. The identifier for the default address space is the integer
11688 declare i8* @llvm.ptr.annotation.p<address space>i8(i8* <val>, i8* <str>, i8* <str>, i32 <int>)
11689 declare i16* @llvm.ptr.annotation.p<address space>i16(i16* <val>, i8* <str>, i8* <str>, i32 <int>)
11690 declare i32* @llvm.ptr.annotation.p<address space>i32(i32* <val>, i8* <str>, i8* <str>, i32 <int>)
11691 declare i64* @llvm.ptr.annotation.p<address space>i64(i64* <val>, i8* <str>, i8* <str>, i32 <int>)
11692 declare i256* @llvm.ptr.annotation.p<address space>i256(i256* <val>, i8* <str>, i8* <str>, i32 <int>)
11697 The '``llvm.ptr.annotation``' intrinsic.
11702 The first argument is a pointer to an integer value of arbitrary bitwidth
11703 (result of some expression), the second is a pointer to a global string, the
11704 third is a pointer to a global string which is the source file name, and the
11705 last argument is the line number. It returns the value of the first argument.
11710 This intrinsic allows annotation of a pointer to an integer with arbitrary
11711 strings. This can be useful for special purpose optimizations that want to look
11712 for these annotations. These have no other defined use; they are ignored by code
11713 generation and optimization.
11715 '``llvm.annotation.*``' Intrinsic
11716 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11721 This is an overloaded intrinsic. You can use '``llvm.annotation``' on
11722 any integer bit width.
11726 declare i8 @llvm.annotation.i8(i8 <val>, i8* <str>, i8* <str>, i32 <int>)
11727 declare i16 @llvm.annotation.i16(i16 <val>, i8* <str>, i8* <str>, i32 <int>)
11728 declare i32 @llvm.annotation.i32(i32 <val>, i8* <str>, i8* <str>, i32 <int>)
11729 declare i64 @llvm.annotation.i64(i64 <val>, i8* <str>, i8* <str>, i32 <int>)
11730 declare i256 @llvm.annotation.i256(i256 <val>, i8* <str>, i8* <str>, i32 <int>)
11735 The '``llvm.annotation``' intrinsic.
11740 The first argument is an integer value (result of some expression), the
11741 second is a pointer to a global string, the third is a pointer to a
11742 global string which is the source file name, and the last argument is
11743 the line number. It returns the value of the first argument.
11748 This intrinsic allows annotations to be put on arbitrary expressions
11749 with arbitrary strings. This can be useful for special purpose
11750 optimizations that want to look for these annotations. These have no
11751 other defined use; they are ignored by code generation and optimization.
11753 '``llvm.trap``' Intrinsic
11754 ^^^^^^^^^^^^^^^^^^^^^^^^^
11761 declare void @llvm.trap() noreturn nounwind
11766 The '``llvm.trap``' intrinsic.
11776 This intrinsic is lowered to the target dependent trap instruction. If
11777 the target does not have a trap instruction, this intrinsic will be
11778 lowered to a call of the ``abort()`` function.
11780 '``llvm.debugtrap``' Intrinsic
11781 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11788 declare void @llvm.debugtrap() nounwind
11793 The '``llvm.debugtrap``' intrinsic.
11803 This intrinsic is lowered to code which is intended to cause an
11804 execution trap with the intention of requesting the attention of a
11807 '``llvm.stackprotector``' Intrinsic
11808 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11815 declare void @llvm.stackprotector(i8* <guard>, i8** <slot>)
11820 The ``llvm.stackprotector`` intrinsic takes the ``guard`` and stores it
11821 onto the stack at ``slot``. The stack slot is adjusted to ensure that it
11822 is placed on the stack before local variables.
11827 The ``llvm.stackprotector`` intrinsic requires two pointer arguments.
11828 The first argument is the value loaded from the stack guard
11829 ``@__stack_chk_guard``. The second variable is an ``alloca`` that has
11830 enough space to hold the value of the guard.
11835 This intrinsic causes the prologue/epilogue inserter to force the position of
11836 the ``AllocaInst`` stack slot to be before local variables on the stack. This is
11837 to ensure that if a local variable on the stack is overwritten, it will destroy
11838 the value of the guard. When the function exits, the guard on the stack is
11839 checked against the original guard by ``llvm.stackprotectorcheck``. If they are
11840 different, then ``llvm.stackprotectorcheck`` causes the program to abort by
11841 calling the ``__stack_chk_fail()`` function.
11843 '``llvm.stackprotectorcheck``' Intrinsic
11844 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11851 declare void @llvm.stackprotectorcheck(i8** <guard>)
11856 The ``llvm.stackprotectorcheck`` intrinsic compares ``guard`` against an already
11857 created stack protector and if they are not equal calls the
11858 ``__stack_chk_fail()`` function.
11863 The ``llvm.stackprotectorcheck`` intrinsic requires one pointer argument, the
11864 the variable ``@__stack_chk_guard``.
11869 This intrinsic is provided to perform the stack protector check by comparing
11870 ``guard`` with the stack slot created by ``llvm.stackprotector`` and if the
11871 values do not match call the ``__stack_chk_fail()`` function.
11873 The reason to provide this as an IR level intrinsic instead of implementing it
11874 via other IR operations is that in order to perform this operation at the IR
11875 level without an intrinsic, one would need to create additional basic blocks to
11876 handle the success/failure cases. This makes it difficult to stop the stack
11877 protector check from disrupting sibling tail calls in Codegen. With this
11878 intrinsic, we are able to generate the stack protector basic blocks late in
11879 codegen after the tail call decision has occurred.
11881 '``llvm.objectsize``' Intrinsic
11882 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11889 declare i32 @llvm.objectsize.i32(i8* <object>, i1 <min>)
11890 declare i64 @llvm.objectsize.i64(i8* <object>, i1 <min>)
11895 The ``llvm.objectsize`` intrinsic is designed to provide information to
11896 the optimizers to determine at compile time whether a) an operation
11897 (like memcpy) will overflow a buffer that corresponds to an object, or
11898 b) that a runtime check for overflow isn't necessary. An object in this
11899 context means an allocation of a specific class, structure, array, or
11905 The ``llvm.objectsize`` intrinsic takes two arguments. The first
11906 argument is a pointer to or into the ``object``. The second argument is
11907 a boolean and determines whether ``llvm.objectsize`` returns 0 (if true)
11908 or -1 (if false) when the object size is unknown. The second argument
11909 only accepts constants.
11914 The ``llvm.objectsize`` intrinsic is lowered to a constant representing
11915 the size of the object concerned. If the size cannot be determined at
11916 compile time, ``llvm.objectsize`` returns ``i32/i64 -1 or 0`` (depending
11917 on the ``min`` argument).
11919 '``llvm.expect``' Intrinsic
11920 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
11925 This is an overloaded intrinsic. You can use ``llvm.expect`` on any
11930 declare i1 @llvm.expect.i1(i1 <val>, i1 <expected_val>)
11931 declare i32 @llvm.expect.i32(i32 <val>, i32 <expected_val>)
11932 declare i64 @llvm.expect.i64(i64 <val>, i64 <expected_val>)
11937 The ``llvm.expect`` intrinsic provides information about expected (the
11938 most probable) value of ``val``, which can be used by optimizers.
11943 The ``llvm.expect`` intrinsic takes two arguments. The first argument is
11944 a value. The second argument is an expected value, this needs to be a
11945 constant value, variables are not allowed.
11950 This intrinsic is lowered to the ``val``.
11954 '``llvm.assume``' Intrinsic
11955 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11962 declare void @llvm.assume(i1 %cond)
11967 The ``llvm.assume`` allows the optimizer to assume that the provided
11968 condition is true. This information can then be used in simplifying other parts
11974 The condition which the optimizer may assume is always true.
11979 The intrinsic allows the optimizer to assume that the provided condition is
11980 always true whenever the control flow reaches the intrinsic call. No code is
11981 generated for this intrinsic, and instructions that contribute only to the
11982 provided condition are not used for code generation. If the condition is
11983 violated during execution, the behavior is undefined.
11985 Note that the optimizer might limit the transformations performed on values
11986 used by the ``llvm.assume`` intrinsic in order to preserve the instructions
11987 only used to form the intrinsic's input argument. This might prove undesirable
11988 if the extra information provided by the ``llvm.assume`` intrinsic does not cause
11989 sufficient overall improvement in code quality. For this reason,
11990 ``llvm.assume`` should not be used to document basic mathematical invariants
11991 that the optimizer can otherwise deduce or facts that are of little use to the
11996 '``llvm.bitset.test``' Intrinsic
11997 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
12004 declare i1 @llvm.bitset.test(i8* %ptr, metadata %bitset) nounwind readnone
12010 The first argument is a pointer to be tested. The second argument is a
12011 metadata object representing an identifier for a :doc:`bitset <BitSets>`.
12016 The ``llvm.bitset.test`` intrinsic tests whether the given pointer is a
12017 member of the given bitset.
12019 '``llvm.donothing``' Intrinsic
12020 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
12027 declare void @llvm.donothing() nounwind readnone
12032 The ``llvm.donothing`` intrinsic doesn't perform any operation. It's one of only
12033 two intrinsics (besides ``llvm.experimental.patchpoint``) that can be called
12034 with an invoke instruction.
12044 This intrinsic does nothing, and it's removed by optimizers and ignored
12047 Stack Map Intrinsics
12048 --------------------
12050 LLVM provides experimental intrinsics to support runtime patching
12051 mechanisms commonly desired in dynamic language JITs. These intrinsics
12052 are described in :doc:`StackMaps`.