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 which 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.
83 #. Unnamed values are represented as an unsigned numeric value with
84 their prefix. For example, ``%12``, ``@2``, ``%44``.
85 #. Constants, which are described in the section Constants_ below.
87 LLVM requires that values start with a prefix for two reasons: Compilers
88 don't need to worry about name clashes with reserved words, and the set
89 of reserved words may be expanded in the future without penalty.
90 Additionally, unnamed identifiers allow a compiler to quickly come up
91 with a temporary variable without having to avoid symbol table
94 Reserved words in LLVM are very similar to reserved words in other
95 languages. There are keywords for different opcodes ('``add``',
96 '``bitcast``', '``ret``', etc...), for primitive type names ('``void``',
97 '``i32``', etc...), and others. These reserved words cannot conflict
98 with variable names, because none of them start with a prefix character
101 Here is an example of LLVM code to multiply the integer variable
108 %result = mul i32 %X, 8
110 After strength reduction:
114 %result = shl i32 %X, 3
120 %0 = add i32 %X, %X ; yields {i32}:%0
121 %1 = add i32 %0, %0 ; yields {i32}:%1
122 %result = add i32 %1, %1
124 This last way of multiplying ``%X`` by 8 illustrates several important
125 lexical features of LLVM:
127 #. Comments are delimited with a '``;``' and go until the end of line.
128 #. Unnamed temporaries are created when the result of a computation is
129 not assigned to a named value.
130 #. Unnamed temporaries are numbered sequentially (using a per-function
131 incrementing counter, starting with 0). Note that basic blocks are
132 included in this numbering. For example, if the entry basic block is not
133 given a label name, then it will get number 0.
135 It also shows a convention that we follow in this document. When
136 demonstrating instructions, we will follow an instruction with a comment
137 that defines the type and name of value produced.
145 LLVM programs are composed of ``Module``'s, each of which is a
146 translation unit of the input programs. Each module consists of
147 functions, global variables, and symbol table entries. Modules may be
148 combined together with the LLVM linker, which merges function (and
149 global variable) definitions, resolves forward declarations, and merges
150 symbol table entries. Here is an example of the "hello world" module:
154 ; Declare the string constant as a global constant.
155 @.str = private unnamed_addr constant [13 x i8] c"hello world\0A\00"
157 ; External declaration of the puts function
158 declare i32 @puts(i8* nocapture) nounwind
160 ; Definition of main function
161 define i32 @main() { ; i32()*
162 ; Convert [13 x i8]* to i8 *...
163 %cast210 = getelementptr [13 x i8]* @.str, i64 0, i64 0
165 ; Call puts function to write out the string to stdout.
166 call i32 @puts(i8* %cast210)
171 !1 = metadata !{i32 42}
174 This example is made up of a :ref:`global variable <globalvars>` named
175 "``.str``", an external declaration of the "``puts``" function, a
176 :ref:`function definition <functionstructure>` for "``main``" and
177 :ref:`named metadata <namedmetadatastructure>` "``foo``".
179 In general, a module is made up of a list of global values (where both
180 functions and global variables are global values). Global values are
181 represented by a pointer to a memory location (in this case, a pointer
182 to an array of char, and a pointer to a function), and have one of the
183 following :ref:`linkage types <linkage>`.
190 All Global Variables and Functions have one of the following types of
194 Global values with "``private``" linkage are only directly
195 accessible by objects in the current module. In particular, linking
196 code into a module with an private global value may cause the
197 private to be renamed as necessary to avoid collisions. Because the
198 symbol is private to the module, all references can be updated. This
199 doesn't show up in any symbol table in the object file.
201 Similar to ``private``, but the symbol is passed through the
202 assembler and evaluated by the linker. Unlike normal strong symbols,
203 they are removed by the linker from the final linked image
204 (executable or dynamic library).
205 ``linker_private_weak``
206 Similar to "``linker_private``", but the symbol is weak. Note that
207 ``linker_private_weak`` symbols are subject to coalescing by the
208 linker. The symbols are removed by the linker from the final linked
209 image (executable or dynamic library).
211 Similar to private, but the value shows as a local symbol
212 (``STB_LOCAL`` in the case of ELF) in the object file. This
213 corresponds to the notion of the '``static``' keyword in C.
214 ``available_externally``
215 Globals with "``available_externally``" linkage are never emitted
216 into the object file corresponding to the LLVM module. They exist to
217 allow inlining and other optimizations to take place given knowledge
218 of the definition of the global, which is known to be somewhere
219 outside the module. Globals with ``available_externally`` linkage
220 are allowed to be discarded at will, and are otherwise the same as
221 ``linkonce_odr``. This linkage type is only allowed on definitions,
224 Globals with "``linkonce``" linkage are merged with other globals of
225 the same name when linkage occurs. This can be used to implement
226 some forms of inline functions, templates, or other code which must
227 be generated in each translation unit that uses it, but where the
228 body may be overridden with a more definitive definition later.
229 Unreferenced ``linkonce`` globals are allowed to be discarded. Note
230 that ``linkonce`` linkage does not actually allow the optimizer to
231 inline the body of this function into callers because it doesn't
232 know if this definition of the function is the definitive definition
233 within the program or whether it will be overridden by a stronger
234 definition. To enable inlining and other optimizations, use
235 "``linkonce_odr``" linkage.
237 "``weak``" linkage has the same merging semantics as ``linkonce``
238 linkage, except that unreferenced globals with ``weak`` linkage may
239 not be discarded. This is used for globals that are declared "weak"
242 "``common``" linkage is most similar to "``weak``" linkage, but they
243 are used for tentative definitions in C, such as "``int X;``" at
244 global scope. Symbols with "``common``" linkage are merged in the
245 same way as ``weak symbols``, and they may not be deleted if
246 unreferenced. ``common`` symbols may not have an explicit section,
247 must have a zero initializer, and may not be marked
248 ':ref:`constant <globalvars>`'. Functions and aliases may not have
251 .. _linkage_appending:
254 "``appending``" linkage may only be applied to global variables of
255 pointer to array type. When two global variables with appending
256 linkage are linked together, the two global arrays are appended
257 together. This is the LLVM, typesafe, equivalent of having the
258 system linker append together "sections" with identical names when
261 The semantics of this linkage follow the ELF object file model: the
262 symbol is weak until linked, if not linked, the symbol becomes null
263 instead of being an undefined reference.
264 ``linkonce_odr``, ``weak_odr``
265 Some languages allow differing globals to be merged, such as two
266 functions with different semantics. Other languages, such as
267 ``C++``, ensure that only equivalent globals are ever merged (the
268 "one definition rule" --- "ODR"). Such languages can use the
269 ``linkonce_odr`` and ``weak_odr`` linkage types to indicate that the
270 global will only be merged with equivalent globals. These linkage
271 types are otherwise the same as their non-``odr`` versions.
273 If none of the above identifiers are used, the global is externally
274 visible, meaning that it participates in linkage and can be used to
275 resolve external symbol references.
277 It is illegal for a function *declaration* to have any linkage type
278 other than ``external`` or ``extern_weak``.
285 LLVM :ref:`functions <functionstructure>`, :ref:`calls <i_call>` and
286 :ref:`invokes <i_invoke>` can all have an optional calling convention
287 specified for the call. The calling convention of any pair of dynamic
288 caller/callee must match, or the behavior of the program is undefined.
289 The following calling conventions are supported by LLVM, and more may be
292 "``ccc``" - The C calling convention
293 This calling convention (the default if no other calling convention
294 is specified) matches the target C calling conventions. This calling
295 convention supports varargs function calls and tolerates some
296 mismatch in the declared prototype and implemented declaration of
297 the function (as does normal C).
298 "``fastcc``" - The fast calling convention
299 This calling convention attempts to make calls as fast as possible
300 (e.g. by passing things in registers). This calling convention
301 allows the target to use whatever tricks it wants to produce fast
302 code for the target, without having to conform to an externally
303 specified ABI (Application Binary Interface). `Tail calls can only
304 be optimized when this, the GHC or the HiPE convention is
305 used. <CodeGenerator.html#id80>`_ This calling convention does not
306 support varargs and requires the prototype of all callees to exactly
307 match the prototype of the function definition.
308 "``coldcc``" - The cold calling convention
309 This calling convention attempts to make code in the caller as
310 efficient as possible under the assumption that the call is not
311 commonly executed. As such, these calls often preserve all registers
312 so that the call does not break any live ranges in the caller side.
313 This calling convention does not support varargs and requires the
314 prototype of all callees to exactly match the prototype of the
315 function definition. Furthermore the inliner doesn't consider such function
317 "``cc 10``" - GHC convention
318 This calling convention has been implemented specifically for use by
319 the `Glasgow Haskell Compiler (GHC) <http://www.haskell.org/ghc>`_.
320 It passes everything in registers, going to extremes to achieve this
321 by disabling callee save registers. This calling convention should
322 not be used lightly but only for specific situations such as an
323 alternative to the *register pinning* performance technique often
324 used when implementing functional programming languages. At the
325 moment only X86 supports this convention and it has the following
328 - On *X86-32* only supports up to 4 bit type parameters. No
329 floating point types are supported.
330 - On *X86-64* only supports up to 10 bit type parameters and 6
331 floating point parameters.
333 This calling convention supports `tail call
334 optimization <CodeGenerator.html#id80>`_ but requires both the
335 caller and callee are using it.
336 "``cc 11``" - The HiPE calling convention
337 This calling convention has been implemented specifically for use by
338 the `High-Performance Erlang
339 (HiPE) <http://www.it.uu.se/research/group/hipe/>`_ compiler, *the*
340 native code compiler of the `Ericsson's Open Source Erlang/OTP
341 system <http://www.erlang.org/download.shtml>`_. It uses more
342 registers for argument passing than the ordinary C calling
343 convention and defines no callee-saved registers. The calling
344 convention properly supports `tail call
345 optimization <CodeGenerator.html#id80>`_ but requires that both the
346 caller and the callee use it. It uses a *register pinning*
347 mechanism, similar to GHC's convention, for keeping frequently
348 accessed runtime components pinned to specific hardware registers.
349 At the moment only X86 supports this convention (both 32 and 64
351 "``webkit_jscc``" - WebKit's JavaScript calling convention
352 This calling convention has been implemented for `WebKit FTL JIT
353 <https://trac.webkit.org/wiki/FTLJIT>`_. It passes arguments on the
354 stack right to left (as cdecl does), and returns a value in the
355 platform's customary return register.
356 "``anyregcc``" - Dynamic calling convention for code patching
357 This is a special convention that supports patching an arbitrary code
358 sequence in place of a call site. This convention forces the call
359 arguments into registers but allows them to be dynamcially
360 allocated. This can currently only be used with calls to
361 llvm.experimental.patchpoint because only this intrinsic records
362 the location of its arguments in a side table. See :doc:`StackMaps`.
363 "``preserve_mostcc``" - The `PreserveMost` calling convention
364 This calling convention attempts to make the code in the caller as little
365 intrusive as possible. This calling convention behaves identical to the `C`
366 calling convention on how arguments and return values are passed, but it
367 uses a different set of caller/callee-saved registers. This alleviates the
368 burden of saving and recovering a large register set before and after the
369 call in the caller. If the arguments are passed in callee-saved registers,
370 then they will be preserved by the callee across the call. This doesn't
371 apply for values returned in callee-saved registers.
373 - On X86-64 the callee preserves all general purpose registers, except for
374 R11. R11 can be used as a scratch register. Floating-point registers
375 (XMMs/YMMs) are not preserved and need to be saved by the caller.
377 The idea behind this convention is to support calls to runtime functions
378 that have a hot path and a cold path. The hot path is usually a small piece
379 of code that doesn't many registers. The cold path might need to call out to
380 another function and therefore only needs to preserve the caller-saved
381 registers, which haven't already been saved by the caller. The
382 `PreserveMost` calling convention is very similar to the `cold` calling
383 convention in terms of caller/callee-saved registers, but they are used for
384 different types of function calls. `coldcc` is for function calls that are
385 rarely executed, whereas `preserve_mostcc` function calls are intended to be
386 on the hot path and definitely executed a lot. Furthermore `preserve_mostcc`
387 doesn't prevent the inliner from inlining the function call.
389 This calling convention will be used by a future version of the ObjectiveC
390 runtime and should therefore still be considered experimental at this time.
391 Although this convention was created to optimize certain runtime calls to
392 the ObjectiveC runtime, it is not limited to this runtime and might be used
393 by other runtimes in the future too. The current implementation only
394 supports X86-64, but the intention is to support more architectures in the
396 "``preserve_allcc``" - The `PreserveAll` calling convention
397 This calling convention attempts to make the code in the caller even less
398 intrusive than the `PreserveMost` calling convention. This calling
399 convention also behaves identical to the `C` calling convention on how
400 arguments and return values are passed, but it uses a different set of
401 caller/callee-saved registers. This removes the burden of saving and
402 recovering a large register set before and after the call in the caller. If
403 the arguments are passed in callee-saved registers, then they will be
404 preserved by the callee across the call. This doesn't apply for values
405 returned in callee-saved registers.
407 - On X86-64 the callee preserves all general purpose registers, except for
408 R11. R11 can be used as a scratch register. Furthermore it also preserves
409 all floating-point registers (XMMs/YMMs).
411 The idea behind this convention is to support calls to runtime functions
412 that don't need to call out to any other functions.
414 This calling convention, like the `PreserveMost` calling convention, will be
415 used by a future version of the ObjectiveC runtime and should be considered
416 experimental at this time.
417 "``cc <n>``" - Numbered convention
418 Any calling convention may be specified by number, allowing
419 target-specific calling conventions to be used. Target specific
420 calling conventions start at 64.
422 More calling conventions can be added/defined on an as-needed basis, to
423 support Pascal conventions or any other well-known target-independent
426 .. _visibilitystyles:
431 All Global Variables and Functions have one of the following visibility
434 "``default``" - Default style
435 On targets that use the ELF object file format, default visibility
436 means that the declaration is visible to other modules and, in
437 shared libraries, means that the declared entity may be overridden.
438 On Darwin, default visibility means that the declaration is visible
439 to other modules. Default visibility corresponds to "external
440 linkage" in the language.
441 "``hidden``" - Hidden style
442 Two declarations of an object with hidden visibility refer to the
443 same object if they are in the same shared object. Usually, hidden
444 visibility indicates that the symbol will not be placed into the
445 dynamic symbol table, so no other module (executable or shared
446 library) can reference it directly.
447 "``protected``" - Protected style
448 On ELF, protected visibility indicates that the symbol will be
449 placed in the dynamic symbol table, but that references within the
450 defining module will bind to the local symbol. That is, the symbol
451 cannot be overridden by another module.
458 All Global Variables, Functions and Aliases can have one of the following
462 "``dllimport``" causes the compiler to reference a function or variable via
463 a global pointer to a pointer that is set up by the DLL exporting the
464 symbol. On Microsoft Windows targets, the pointer name is formed by
465 combining ``__imp_`` and the function or variable name.
467 "``dllexport``" causes the compiler to provide a global pointer to a pointer
468 in a DLL, so that it can be referenced with the ``dllimport`` attribute. On
469 Microsoft Windows targets, the pointer name is formed by combining
470 ``__imp_`` and the function or variable name. Since this storage class
471 exists for defining a dll interface, the compiler, assembler and linker know
472 it is externally referenced and must refrain from deleting the symbol.
477 LLVM IR allows you to specify both "identified" and "literal" :ref:`structure
478 types <t_struct>`. Literal types are uniqued structurally, but identified types
479 are never uniqued. An :ref:`opaque structural type <t_opaque>` can also be used
480 to forward declare a type which is not yet available.
482 An example of a identified structure specification is:
486 %mytype = type { %mytype*, i32 }
488 Prior to the LLVM 3.0 release, identified types were structurally uniqued. Only
489 literal types are uniqued in recent versions of LLVM.
496 Global variables define regions of memory allocated at compilation time
499 Global variables definitions must be initialized, may have an explicit section
500 to be placed in, and may have an optional explicit alignment specified.
502 Global variables in other translation units can also be declared, in which
503 case they don't have an initializer.
505 A variable may be defined as ``thread_local``, which means that it will
506 not be shared by threads (each thread will have a separated copy of the
507 variable). Not all targets support thread-local variables. Optionally, a
508 TLS model may be specified:
511 For variables that are only used within the current shared library.
513 For variables in modules that will not be loaded dynamically.
515 For variables defined in the executable and only used within it.
517 The models correspond to the ELF TLS models; see `ELF Handling For
518 Thread-Local Storage <http://people.redhat.com/drepper/tls.pdf>`_ for
519 more information on under which circumstances the different models may
520 be used. The target may choose a different TLS model if the specified
521 model is not supported, or if a better choice of model can be made.
523 A variable may be defined as a global ``constant``, which indicates that
524 the contents of the variable will **never** be modified (enabling better
525 optimization, allowing the global data to be placed in the read-only
526 section of an executable, etc). Note that variables that need runtime
527 initialization cannot be marked ``constant`` as there is a store to the
530 LLVM explicitly allows *declarations* of global variables to be marked
531 constant, even if the final definition of the global is not. This
532 capability can be used to enable slightly better optimization of the
533 program, but requires the language definition to guarantee that
534 optimizations based on the 'constantness' are valid for the translation
535 units that do not include the definition.
537 As SSA values, global variables define pointer values that are in scope
538 (i.e. they dominate) all basic blocks in the program. Global variables
539 always define a pointer to their "content" type because they describe a
540 region of memory, and all memory objects in LLVM are accessed through
543 Global variables can be marked with ``unnamed_addr`` which indicates
544 that the address is not significant, only the content. Constants marked
545 like this can be merged with other constants if they have the same
546 initializer. Note that a constant with significant address *can* be
547 merged with a ``unnamed_addr`` constant, the result being a constant
548 whose address is significant.
550 A global variable may be declared to reside in a target-specific
551 numbered address space. For targets that support them, address spaces
552 may affect how optimizations are performed and/or what target
553 instructions are used to access the variable. The default address space
554 is zero. The address space qualifier must precede any other attributes.
556 LLVM allows an explicit section to be specified for globals. If the
557 target supports it, it will emit globals to the section specified.
559 By default, global initializers are optimized by assuming that global
560 variables defined within the module are not modified from their
561 initial values before the start of the global initializer. This is
562 true even for variables potentially accessible from outside the
563 module, including those with external linkage or appearing in
564 ``@llvm.used`` or dllexported variables. This assumption may be suppressed
565 by marking the variable with ``externally_initialized``.
567 An explicit alignment may be specified for a global, which must be a
568 power of 2. If not present, or if the alignment is set to zero, the
569 alignment of the global is set by the target to whatever it feels
570 convenient. If an explicit alignment is specified, the global is forced
571 to have exactly that alignment. Targets and optimizers are not allowed
572 to over-align the global if the global has an assigned section. In this
573 case, the extra alignment could be observable: for example, code could
574 assume that the globals are densely packed in their section and try to
575 iterate over them as an array, alignment padding would break this
578 Globals can also have a :ref:`DLL storage class <dllstorageclass>`.
582 [@<GlobalVarName> =] [Linkage] [Visibility] [DLLStorageClass] [ThreadLocal]
583 [AddrSpace] [unnamed_addr] [ExternallyInitialized]
584 <global | constant> <Type>
585 [, section "name"] [, align <Alignment>]
587 For example, the following defines a global in a numbered address space
588 with an initializer, section, and alignment:
592 @G = addrspace(5) constant float 1.0, section "foo", align 4
594 The following example just declares a global variable
598 @G = external global i32
600 The following example defines a thread-local global with the
601 ``initialexec`` TLS model:
605 @G = thread_local(initialexec) global i32 0, align 4
607 .. _functionstructure:
612 LLVM function definitions consist of the "``define``" keyword, an
613 optional :ref:`linkage type <linkage>`, an optional :ref:`visibility
614 style <visibility>`, an optional :ref:`DLL storage class <dllstorageclass>`,
615 an optional :ref:`calling convention <callingconv>`,
616 an optional ``unnamed_addr`` attribute, a return type, an optional
617 :ref:`parameter attribute <paramattrs>` for the return type, a function
618 name, a (possibly empty) argument list (each with optional :ref:`parameter
619 attributes <paramattrs>`), optional :ref:`function attributes <fnattrs>`,
620 an optional section, an optional alignment, an optional :ref:`garbage
621 collector name <gc>`, an optional :ref:`prefix <prefixdata>`, an opening
622 curly brace, a list of basic blocks, and a closing curly brace.
624 LLVM function declarations consist of the "``declare``" keyword, an
625 optional :ref:`linkage type <linkage>`, an optional :ref:`visibility
626 style <visibility>`, an optional :ref:`DLL storage class <dllstorageclass>`,
627 an optional :ref:`calling convention <callingconv>`,
628 an optional ``unnamed_addr`` attribute, a return type, an optional
629 :ref:`parameter attribute <paramattrs>` for the return type, a function
630 name, a possibly empty list of arguments, an optional alignment, an optional
631 :ref:`garbage collector name <gc>` and an optional :ref:`prefix <prefixdata>`.
633 A function definition contains a list of basic blocks, forming the CFG (Control
634 Flow Graph) for the function. Each basic block may optionally start with a label
635 (giving the basic block a symbol table entry), contains a list of instructions,
636 and ends with a :ref:`terminator <terminators>` instruction (such as a branch or
637 function return). If an explicit label is not provided, a block is assigned an
638 implicit numbered label, using the next value from the same counter as used for
639 unnamed temporaries (:ref:`see above<identifiers>`). For example, if a function
640 entry block does not have an explicit label, it will be assigned label "%0",
641 then the first unnamed temporary in that block will be "%1", etc.
643 The first basic block in a function is special in two ways: it is
644 immediately executed on entrance to the function, and it is not allowed
645 to have predecessor basic blocks (i.e. there can not be any branches to
646 the entry block of a function). Because the block can have no
647 predecessors, it also cannot have any :ref:`PHI nodes <i_phi>`.
649 LLVM allows an explicit section to be specified for functions. If the
650 target supports it, it will emit functions to the section specified.
652 An explicit alignment may be specified for a function. If not present,
653 or if the alignment is set to zero, the alignment of the function is set
654 by the target to whatever it feels convenient. If an explicit alignment
655 is specified, the function is forced to have at least that much
656 alignment. All alignments must be a power of 2.
658 If the ``unnamed_addr`` attribute is given, the address is know to not
659 be significant and two identical functions can be merged.
663 define [linkage] [visibility] [DLLStorageClass]
665 <ResultType> @<FunctionName> ([argument list])
666 [unnamed_addr] [fn Attrs] [section "name"] [align N]
667 [gc] [prefix Constant] { ... }
674 Aliases act as "second name" for the aliasee value (which can be either
675 function, global variable, another alias or bitcast of global value).
676 Aliases may have an optional :ref:`linkage type <linkage>`, an optional
677 :ref:`visibility style <visibility>`, and an optional :ref:`DLL storage class
682 @<Name> = [Visibility] [DLLStorageClass] alias [Linkage] <AliaseeTy> @<Aliasee>
684 The linkage must be one of ``private``, ``linker_private``,
685 ``linker_private_weak``, ``internal``, ``linkonce``, ``weak``,
686 ``linkonce_odr``, ``weak_odr``, ``external``. Note that some system linkers
687 might not correctly handle dropping a weak symbol that is aliased by a non-weak
690 .. _namedmetadatastructure:
695 Named metadata is a collection of metadata. :ref:`Metadata
696 nodes <metadata>` (but not metadata strings) are the only valid
697 operands for a named metadata.
701 ; Some unnamed metadata nodes, which are referenced by the named metadata.
702 !0 = metadata !{metadata !"zero"}
703 !1 = metadata !{metadata !"one"}
704 !2 = metadata !{metadata !"two"}
706 !name = !{!0, !1, !2}
713 The return type and each parameter of a function type may have a set of
714 *parameter attributes* associated with them. Parameter attributes are
715 used to communicate additional information about the result or
716 parameters of a function. Parameter attributes are considered to be part
717 of the function, not of the function type, so functions with different
718 parameter attributes can have the same function type.
720 Parameter attributes are simple keywords that follow the type specified.
721 If multiple parameter attributes are needed, they are space separated.
726 declare i32 @printf(i8* noalias nocapture, ...)
727 declare i32 @atoi(i8 zeroext)
728 declare signext i8 @returns_signed_char()
730 Note that any attributes for the function result (``nounwind``,
731 ``readonly``) come immediately after the argument list.
733 Currently, only the following parameter attributes are defined:
736 This indicates to the code generator that the parameter or return
737 value should be zero-extended to the extent required by the target's
738 ABI (which is usually 32-bits, but is 8-bits for a i1 on x86-64) by
739 the caller (for a parameter) or the callee (for a return value).
741 This indicates to the code generator that the parameter or return
742 value should be sign-extended to the extent required by the target's
743 ABI (which is usually 32-bits) by the caller (for a parameter) or
744 the callee (for a return value).
746 This indicates that this parameter or return value should be treated
747 in a special target-dependent fashion during while emitting code for
748 a function call or return (usually, by putting it in a register as
749 opposed to memory, though some targets use it to distinguish between
750 two different kinds of registers). Use of this attribute is
753 This indicates that the pointer parameter should really be passed by
754 value to the function. The attribute implies that a hidden copy of
755 the pointee is made between the caller and the callee, so the callee
756 is unable to modify the value in the caller. This attribute is only
757 valid on LLVM pointer arguments. It is generally used to pass
758 structs and arrays by value, but is also valid on pointers to
759 scalars. The copy is considered to belong to the caller not the
760 callee (for example, ``readonly`` functions should not write to
761 ``byval`` parameters). This is not a valid attribute for return
764 The byval attribute also supports specifying an alignment with the
765 align attribute. It indicates the alignment of the stack slot to
766 form and the known alignment of the pointer specified to the call
767 site. If the alignment is not specified, then the code generator
768 makes a target-specific assumption.
774 .. Warning:: This feature is unstable and not fully implemented.
776 The ``inalloca`` argument attribute allows the caller to take the
777 address of outgoing stack arguments. An ``inalloca`` argument must
778 be a pointer to stack memory produced by an ``alloca`` instruction.
779 The alloca, or argument allocation, must also be tagged with the
780 inalloca keyword. Only the past argument may have the ``inalloca``
781 attribute, and that argument is guaranteed to be passed in memory.
783 An argument allocation may be used by a call at most once because
784 the call may deallocate it. The ``inalloca`` attribute cannot be
785 used in conjunction with other attributes that affect argument
786 storage, like ``inreg``, ``nest``, ``sret``, or ``byval``. The
787 ``inalloca`` attribute also disables LLVM's implicit lowering of
788 large aggregate return values, which means that frontend authors
789 must lower them with ``sret`` pointers.
791 When the call site is reached, the argument allocation must have
792 been the most recent stack allocation that is still live, or the
793 results are undefined. It is possible to allocate additional stack
794 space after an argument allocation and before its call site, but it
795 must be cleared off with :ref:`llvm.stackrestore
798 See :doc:`InAlloca` for more information on how to use this
802 This indicates that the pointer parameter specifies the address of a
803 structure that is the return value of the function in the source
804 program. This pointer must be guaranteed by the caller to be valid:
805 loads and stores to the structure may be assumed by the callee
806 not to trap and to be properly aligned. This may only be applied to
807 the first parameter. This is not a valid attribute for return
810 This indicates that pointer values :ref:`based <pointeraliasing>` on
811 the argument or return value do not alias pointer values which are
812 not *based* on it, ignoring certain "irrelevant" dependencies. For a
813 call to the parent function, dependencies between memory references
814 from before or after the call and from those during the call are
815 "irrelevant" to the ``noalias`` keyword for the arguments and return
816 value used in that call. The caller shares the responsibility with
817 the callee for ensuring that these requirements are met. For further
818 details, please see the discussion of the NoAlias response in `alias
819 analysis <AliasAnalysis.html#MustMayNo>`_.
821 Note that this definition of ``noalias`` is intentionally similar
822 to the definition of ``restrict`` in C99 for function arguments,
823 though it is slightly weaker.
825 For function return values, C99's ``restrict`` is not meaningful,
826 while LLVM's ``noalias`` is.
828 This indicates that the callee does not make any copies of the
829 pointer that outlive the callee itself. This is not a valid
830 attribute for return values.
835 This indicates that the pointer parameter can be excised using the
836 :ref:`trampoline intrinsics <int_trampoline>`. This is not a valid
837 attribute for return values and can only be applied to one parameter.
840 This indicates that the function always returns the argument as its return
841 value. This is an optimization hint to the code generator when generating
842 the caller, allowing tail call optimization and omission of register saves
843 and restores in some cases; it is not checked or enforced when generating
844 the callee. The parameter and the function return type must be valid
845 operands for the :ref:`bitcast instruction <i_bitcast>`. This is not a
846 valid attribute for return values and can only be applied to one parameter.
850 Garbage Collector Names
851 -----------------------
853 Each function may specify a garbage collector name, which is simply a
858 define void @f() gc "name" { ... }
860 The compiler declares the supported values of *name*. Specifying a
861 collector which will cause the compiler to alter its output in order to
862 support the named garbage collection algorithm.
869 Prefix data is data associated with a function which the code generator
870 will emit immediately before the function body. The purpose of this feature
871 is to allow frontends to associate language-specific runtime metadata with
872 specific functions and make it available through the function pointer while
873 still allowing the function pointer to be called. To access the data for a
874 given function, a program may bitcast the function pointer to a pointer to
875 the constant's type. This implies that the IR symbol points to the start
878 To maintain the semantics of ordinary function calls, the prefix data must
879 have a particular format. Specifically, it must begin with a sequence of
880 bytes which decode to a sequence of machine instructions, valid for the
881 module's target, which transfer control to the point immediately succeeding
882 the prefix data, without performing any other visible action. This allows
883 the inliner and other passes to reason about the semantics of the function
884 definition without needing to reason about the prefix data. Obviously this
885 makes the format of the prefix data highly target dependent.
887 Prefix data is laid out as if it were an initializer for a global variable
888 of the prefix data's type. No padding is automatically placed between the
889 prefix data and the function body. If padding is required, it must be part
892 A trivial example of valid prefix data for the x86 architecture is ``i8 144``,
893 which encodes the ``nop`` instruction:
897 define void @f() prefix i8 144 { ... }
899 Generally prefix data can be formed by encoding a relative branch instruction
900 which skips the metadata, as in this example of valid prefix data for the
901 x86_64 architecture, where the first two bytes encode ``jmp .+10``:
905 %0 = type <{ i8, i8, i8* }>
907 define void @f() prefix %0 <{ i8 235, i8 8, i8* @md}> { ... }
909 A function may have prefix data but no body. This has similar semantics
910 to the ``available_externally`` linkage in that the data may be used by the
911 optimizers but will not be emitted in the object file.
918 Attribute groups are groups of attributes that are referenced by objects within
919 the IR. They are important for keeping ``.ll`` files readable, because a lot of
920 functions will use the same set of attributes. In the degenerative case of a
921 ``.ll`` file that corresponds to a single ``.c`` file, the single attribute
922 group will capture the important command line flags used to build that file.
924 An attribute group is a module-level object. To use an attribute group, an
925 object references the attribute group's ID (e.g. ``#37``). An object may refer
926 to more than one attribute group. In that situation, the attributes from the
927 different groups are merged.
929 Here is an example of attribute groups for a function that should always be
930 inlined, has a stack alignment of 4, and which shouldn't use SSE instructions:
934 ; Target-independent attributes:
935 attributes #0 = { alwaysinline alignstack=4 }
937 ; Target-dependent attributes:
938 attributes #1 = { "no-sse" }
940 ; Function @f has attributes: alwaysinline, alignstack=4, and "no-sse".
941 define void @f() #0 #1 { ... }
948 Function attributes are set to communicate additional information about
949 a function. Function attributes are considered to be part of the
950 function, not of the function type, so functions with different function
951 attributes can have the same function type.
953 Function attributes are simple keywords that follow the type specified.
954 If multiple attributes are needed, they are space separated. For
959 define void @f() noinline { ... }
960 define void @f() alwaysinline { ... }
961 define void @f() alwaysinline optsize { ... }
962 define void @f() optsize { ... }
965 This attribute indicates that, when emitting the prologue and
966 epilogue, the backend should forcibly align the stack pointer.
967 Specify the desired alignment, which must be a power of two, in
970 This attribute indicates that the inliner should attempt to inline
971 this function into callers whenever possible, ignoring any active
972 inlining size threshold for this caller.
974 This indicates that the callee function at a call site should be
975 recognized as a built-in function, even though the function's declaration
976 uses the ``nobuiltin`` attribute. This is only valid at call sites for
977 direct calls to functions which are declared with the ``nobuiltin``
980 This attribute indicates that this function is rarely called. When
981 computing edge weights, basic blocks post-dominated by a cold
982 function call are also considered to be cold; and, thus, given low
985 This attribute indicates that the source code contained a hint that
986 inlining this function is desirable (such as the "inline" keyword in
987 C/C++). It is just a hint; it imposes no requirements on the
990 This attribute suggests that optimization passes and code generator
991 passes make choices that keep the code size of this function as small
992 as possible and perform optimizations that may sacrifice runtime
993 performance in order to minimize the size of the generated code.
995 This attribute disables prologue / epilogue emission for the
996 function. This can have very system-specific consequences.
998 This indicates that the callee function at a call site is not recognized as
999 a built-in function. LLVM will retain the original call and not replace it
1000 with equivalent code based on the semantics of the built-in function, unless
1001 the call site uses the ``builtin`` attribute. This is valid at call sites
1002 and on function declarations and definitions.
1004 This attribute indicates that calls to the function cannot be
1005 duplicated. A call to a ``noduplicate`` function may be moved
1006 within its parent function, but may not be duplicated within
1007 its parent function.
1009 A function containing a ``noduplicate`` call may still
1010 be an inlining candidate, provided that the call is not
1011 duplicated by inlining. That implies that the function has
1012 internal linkage and only has one call site, so the original
1013 call is dead after inlining.
1015 This attributes disables implicit floating point instructions.
1017 This attribute indicates that the inliner should never inline this
1018 function in any situation. This attribute may not be used together
1019 with the ``alwaysinline`` attribute.
1021 This attribute suppresses lazy symbol binding for the function. This
1022 may make calls to the function faster, at the cost of extra program
1023 startup time if the function is not called during program startup.
1025 This attribute indicates that the code generator should not use a
1026 red zone, even if the target-specific ABI normally permits it.
1028 This function attribute indicates that the function never returns
1029 normally. This produces undefined behavior at runtime if the
1030 function ever does dynamically return.
1032 This function attribute indicates that the function never returns
1033 with an unwind or exceptional control flow. If the function does
1034 unwind, its runtime behavior is undefined.
1036 This function attribute indicates that the function is not optimized
1037 by any optimization or code generator passes with the
1038 exception of interprocedural optimization passes.
1039 This attribute cannot be used together with the ``alwaysinline``
1040 attribute; this attribute is also incompatible
1041 with the ``minsize`` attribute and the ``optsize`` attribute.
1043 This attribute requires the ``noinline`` attribute to be specified on
1044 the function as well, so the function is never inlined into any caller.
1045 Only functions with the ``alwaysinline`` attribute are valid
1046 candidates for inlining into the body of this function.
1048 This attribute suggests that optimization passes and code generator
1049 passes make choices that keep the code size of this function low,
1050 and otherwise do optimizations specifically to reduce code size as
1051 long as they do not significantly impact runtime performance.
1053 On a function, this attribute indicates that the function computes its
1054 result (or decides to unwind an exception) based strictly on its arguments,
1055 without dereferencing any pointer arguments or otherwise accessing
1056 any mutable state (e.g. memory, control registers, etc) visible to
1057 caller functions. It does not write through any pointer arguments
1058 (including ``byval`` arguments) and never changes any state visible
1059 to callers. This means that it cannot unwind exceptions by calling
1060 the ``C++`` exception throwing methods.
1062 On an argument, this attribute indicates that the function does not
1063 dereference that pointer argument, even though it may read or write the
1064 memory that the pointer points to if accessed through other pointers.
1066 On a function, this attribute indicates that the function does not write
1067 through any pointer arguments (including ``byval`` arguments) or otherwise
1068 modify any state (e.g. memory, control registers, etc) visible to
1069 caller functions. It may dereference pointer arguments and read
1070 state that may be set in the caller. A readonly function always
1071 returns the same value (or unwinds an exception identically) when
1072 called with the same set of arguments and global state. It cannot
1073 unwind an exception by calling the ``C++`` exception throwing
1076 On an argument, this attribute indicates that the function does not write
1077 through this pointer argument, even though it may write to the memory that
1078 the pointer points to.
1080 This attribute indicates that this function can return twice. The C
1081 ``setjmp`` is an example of such a function. The compiler disables
1082 some optimizations (like tail calls) in the caller of these
1084 ``sanitize_address``
1085 This attribute indicates that AddressSanitizer checks
1086 (dynamic address safety analysis) are enabled for this function.
1088 This attribute indicates that MemorySanitizer checks (dynamic detection
1089 of accesses to uninitialized memory) are enabled for this function.
1091 This attribute indicates that ThreadSanitizer checks
1092 (dynamic thread safety analysis) are enabled for this function.
1094 This attribute indicates that the function should emit a stack
1095 smashing protector. It is in the form of a "canary" --- a random value
1096 placed on the stack before the local variables that's checked upon
1097 return from the function to see if it has been overwritten. A
1098 heuristic is used to determine if a function needs stack protectors
1099 or not. The heuristic used will enable protectors for functions with:
1101 - Character arrays larger than ``ssp-buffer-size`` (default 8).
1102 - Aggregates containing character arrays larger than ``ssp-buffer-size``.
1103 - Calls to alloca() with variable sizes or constant sizes greater than
1104 ``ssp-buffer-size``.
1106 Variables that are identified as requiring a protector will be arranged
1107 on the stack such that they are adjacent to the stack protector guard.
1109 If a function that has an ``ssp`` attribute is inlined into a
1110 function that doesn't have an ``ssp`` attribute, then the resulting
1111 function will have an ``ssp`` attribute.
1113 This attribute indicates that the function should *always* emit a
1114 stack smashing protector. This overrides the ``ssp`` function
1117 Variables that are identified as requiring a protector will be arranged
1118 on the stack such that they are adjacent to the stack protector guard.
1119 The specific layout rules are:
1121 #. Large arrays and structures containing large arrays
1122 (``>= ssp-buffer-size``) are closest to the stack protector.
1123 #. Small arrays and structures containing small arrays
1124 (``< ssp-buffer-size``) are 2nd closest to the protector.
1125 #. Variables that have had their address taken are 3rd closest to the
1128 If a function that has an ``sspreq`` attribute is inlined into a
1129 function that doesn't have an ``sspreq`` attribute or which has an
1130 ``ssp`` or ``sspstrong`` attribute, then the resulting function will have
1131 an ``sspreq`` attribute.
1133 This attribute indicates that the function should emit a stack smashing
1134 protector. This attribute causes a strong heuristic to be used when
1135 determining if a function needs stack protectors. The strong heuristic
1136 will enable protectors for functions with:
1138 - Arrays of any size and type
1139 - Aggregates containing an array of any size and type.
1140 - Calls to alloca().
1141 - Local variables that have had their address taken.
1143 Variables that are identified as requiring a protector will be arranged
1144 on the stack such that they are adjacent to the stack protector guard.
1145 The specific layout rules are:
1147 #. Large arrays and structures containing large arrays
1148 (``>= ssp-buffer-size``) are closest to the stack protector.
1149 #. Small arrays and structures containing small arrays
1150 (``< ssp-buffer-size``) are 2nd closest to the protector.
1151 #. Variables that have had their address taken are 3rd closest to the
1154 This overrides the ``ssp`` function attribute.
1156 If a function that has an ``sspstrong`` attribute is inlined into a
1157 function that doesn't have an ``sspstrong`` attribute, then the
1158 resulting function will have an ``sspstrong`` attribute.
1160 This attribute indicates that the ABI being targeted requires that
1161 an unwind table entry be produce for this function even if we can
1162 show that no exceptions passes by it. This is normally the case for
1163 the ELF x86-64 abi, but it can be disabled for some compilation
1168 Module-Level Inline Assembly
1169 ----------------------------
1171 Modules may contain "module-level inline asm" blocks, which corresponds
1172 to the GCC "file scope inline asm" blocks. These blocks are internally
1173 concatenated by LLVM and treated as a single unit, but may be separated
1174 in the ``.ll`` file if desired. The syntax is very simple:
1176 .. code-block:: llvm
1178 module asm "inline asm code goes here"
1179 module asm "more can go here"
1181 The strings can contain any character by escaping non-printable
1182 characters. The escape sequence used is simply "\\xx" where "xx" is the
1183 two digit hex code for the number.
1185 The inline asm code is simply printed to the machine code .s file when
1186 assembly code is generated.
1188 .. _langref_datalayout:
1193 A module may specify a target specific data layout string that specifies
1194 how data is to be laid out in memory. The syntax for the data layout is
1197 .. code-block:: llvm
1199 target datalayout = "layout specification"
1201 The *layout specification* consists of a list of specifications
1202 separated by the minus sign character ('-'). Each specification starts
1203 with a letter and may include other information after the letter to
1204 define some aspect of the data layout. The specifications accepted are
1208 Specifies that the target lays out data in big-endian form. That is,
1209 the bits with the most significance have the lowest address
1212 Specifies that the target lays out data in little-endian form. That
1213 is, the bits with the least significance have the lowest address
1216 Specifies the natural alignment of the stack in bits. Alignment
1217 promotion of stack variables is limited to the natural stack
1218 alignment to avoid dynamic stack realignment. The stack alignment
1219 must be a multiple of 8-bits. If omitted, the natural stack
1220 alignment defaults to "unspecified", which does not prevent any
1221 alignment promotions.
1222 ``p[n]:<size>:<abi>:<pref>``
1223 This specifies the *size* of a pointer and its ``<abi>`` and
1224 ``<pref>``\erred alignments for address space ``n``. All sizes are in
1225 bits. The address space, ``n`` is optional, and if not specified,
1226 denotes the default address space 0. The value of ``n`` must be
1227 in the range [1,2^23).
1228 ``i<size>:<abi>:<pref>``
1229 This specifies the alignment for an integer type of a given bit
1230 ``<size>``. The value of ``<size>`` must be in the range [1,2^23).
1231 ``v<size>:<abi>:<pref>``
1232 This specifies the alignment for a vector type of a given bit
1234 ``f<size>:<abi>:<pref>``
1235 This specifies the alignment for a floating point type of a given bit
1236 ``<size>``. Only values of ``<size>`` that are supported by the target
1237 will work. 32 (float) and 64 (double) are supported on all targets; 80
1238 or 128 (different flavors of long double) are also supported on some
1241 This specifies the alignment for an object of aggregate type.
1243 If present, specifies that llvm names are mangled in the output. The
1246 * ``e``: ELF mangling: Private symbols get a ``.L`` prefix.
1247 * ``m``: Mips mangling: Private symbols get a ``$`` prefix.
1248 * ``o``: Mach-O mangling: Private symbols get ``L`` prefix. Other
1249 symbols get a ``_`` prefix.
1250 * ``w``: Windows COFF prefix: Similar to Mach-O, but stdcall and fastcall
1251 functions also get a suffix based on the frame size.
1252 ``n<size1>:<size2>:<size3>...``
1253 This specifies a set of native integer widths for the target CPU in
1254 bits. For example, it might contain ``n32`` for 32-bit PowerPC,
1255 ``n32:64`` for PowerPC 64, or ``n8:16:32:64`` for X86-64. Elements of
1256 this set are considered to support most general arithmetic operations
1259 On every specification that takes a ``<abi>:<pref>``, specifying the
1260 ``<pref>`` alignment is optional. If omitted, the preceding ``:``
1261 should be omitted too and ``<pref>`` will be equal to ``<abi>``.
1263 When constructing the data layout for a given target, LLVM starts with a
1264 default set of specifications which are then (possibly) overridden by
1265 the specifications in the ``datalayout`` keyword. The default
1266 specifications are given in this list:
1268 - ``E`` - big endian
1269 - ``p:64:64:64`` - 64-bit pointers with 64-bit alignment.
1270 - ``p[n]:64:64:64`` - Other address spaces are assumed to be the
1271 same as the default address space.
1272 - ``S0`` - natural stack alignment is unspecified
1273 - ``i1:8:8`` - i1 is 8-bit (byte) aligned
1274 - ``i8:8:8`` - i8 is 8-bit (byte) aligned
1275 - ``i16:16:16`` - i16 is 16-bit aligned
1276 - ``i32:32:32`` - i32 is 32-bit aligned
1277 - ``i64:32:64`` - i64 has ABI alignment of 32-bits but preferred
1278 alignment of 64-bits
1279 - ``f16:16:16`` - half is 16-bit aligned
1280 - ``f32:32:32`` - float is 32-bit aligned
1281 - ``f64:64:64`` - double is 64-bit aligned
1282 - ``f128:128:128`` - quad is 128-bit aligned
1283 - ``v64:64:64`` - 64-bit vector is 64-bit aligned
1284 - ``v128:128:128`` - 128-bit vector is 128-bit aligned
1285 - ``a:0:64`` - aggregates are 64-bit aligned
1287 When LLVM is determining the alignment for a given type, it uses the
1290 #. If the type sought is an exact match for one of the specifications,
1291 that specification is used.
1292 #. If no match is found, and the type sought is an integer type, then
1293 the smallest integer type that is larger than the bitwidth of the
1294 sought type is used. If none of the specifications are larger than
1295 the bitwidth then the largest integer type is used. For example,
1296 given the default specifications above, the i7 type will use the
1297 alignment of i8 (next largest) while both i65 and i256 will use the
1298 alignment of i64 (largest specified).
1299 #. If no match is found, and the type sought is a vector type, then the
1300 largest vector type that is smaller than the sought vector type will
1301 be used as a fall back. This happens because <128 x double> can be
1302 implemented in terms of 64 <2 x double>, for example.
1304 The function of the data layout string may not be what you expect.
1305 Notably, this is not a specification from the frontend of what alignment
1306 the code generator should use.
1308 Instead, if specified, the target data layout is required to match what
1309 the ultimate *code generator* expects. This string is used by the
1310 mid-level optimizers to improve code, and this only works if it matches
1311 what the ultimate code generator uses. If you would like to generate IR
1312 that does not embed this target-specific detail into the IR, then you
1313 don't have to specify the string. This will disable some optimizations
1314 that require precise layout information, but this also prevents those
1315 optimizations from introducing target specificity into the IR.
1322 A module may specify a target triple string that describes the target
1323 host. The syntax for the target triple is simply:
1325 .. code-block:: llvm
1327 target triple = "x86_64-apple-macosx10.7.0"
1329 The *target triple* string consists of a series of identifiers delimited
1330 by the minus sign character ('-'). The canonical forms are:
1334 ARCHITECTURE-VENDOR-OPERATING_SYSTEM
1335 ARCHITECTURE-VENDOR-OPERATING_SYSTEM-ENVIRONMENT
1337 This information is passed along to the backend so that it generates
1338 code for the proper architecture. It's possible to override this on the
1339 command line with the ``-mtriple`` command line option.
1341 .. _pointeraliasing:
1343 Pointer Aliasing Rules
1344 ----------------------
1346 Any memory access must be done through a pointer value associated with
1347 an address range of the memory access, otherwise the behavior is
1348 undefined. Pointer values are associated with address ranges according
1349 to the following rules:
1351 - A pointer value is associated with the addresses associated with any
1352 value it is *based* on.
1353 - An address of a global variable is associated with the address range
1354 of the variable's storage.
1355 - The result value of an allocation instruction is associated with the
1356 address range of the allocated storage.
1357 - A null pointer in the default address-space is associated with no
1359 - An integer constant other than zero or a pointer value returned from
1360 a function not defined within LLVM may be associated with address
1361 ranges allocated through mechanisms other than those provided by
1362 LLVM. Such ranges shall not overlap with any ranges of addresses
1363 allocated by mechanisms provided by LLVM.
1365 A pointer value is *based* on another pointer value according to the
1368 - A pointer value formed from a ``getelementptr`` operation is *based*
1369 on the first operand of the ``getelementptr``.
1370 - The result value of a ``bitcast`` is *based* on the operand of the
1372 - A pointer value formed by an ``inttoptr`` is *based* on all pointer
1373 values that contribute (directly or indirectly) to the computation of
1374 the pointer's value.
1375 - The "*based* on" relationship is transitive.
1377 Note that this definition of *"based"* is intentionally similar to the
1378 definition of *"based"* in C99, though it is slightly weaker.
1380 LLVM IR does not associate types with memory. The result type of a
1381 ``load`` merely indicates the size and alignment of the memory from
1382 which to load, as well as the interpretation of the value. The first
1383 operand type of a ``store`` similarly only indicates the size and
1384 alignment of the store.
1386 Consequently, type-based alias analysis, aka TBAA, aka
1387 ``-fstrict-aliasing``, is not applicable to general unadorned LLVM IR.
1388 :ref:`Metadata <metadata>` may be used to encode additional information
1389 which specialized optimization passes may use to implement type-based
1394 Volatile Memory Accesses
1395 ------------------------
1397 Certain memory accesses, such as :ref:`load <i_load>`'s,
1398 :ref:`store <i_store>`'s, and :ref:`llvm.memcpy <int_memcpy>`'s may be
1399 marked ``volatile``. The optimizers must not change the number of
1400 volatile operations or change their order of execution relative to other
1401 volatile operations. The optimizers *may* change the order of volatile
1402 operations relative to non-volatile operations. This is not Java's
1403 "volatile" and has no cross-thread synchronization behavior.
1405 IR-level volatile loads and stores cannot safely be optimized into
1406 llvm.memcpy or llvm.memmove intrinsics even when those intrinsics are
1407 flagged volatile. Likewise, the backend should never split or merge
1408 target-legal volatile load/store instructions.
1410 .. admonition:: Rationale
1412 Platforms may rely on volatile loads and stores of natively supported
1413 data width to be executed as single instruction. For example, in C
1414 this holds for an l-value of volatile primitive type with native
1415 hardware support, but not necessarily for aggregate types. The
1416 frontend upholds these expectations, which are intentionally
1417 unspecified in the IR. The rules above ensure that IR transformation
1418 do not violate the frontend's contract with the language.
1422 Memory Model for Concurrent Operations
1423 --------------------------------------
1425 The LLVM IR does not define any way to start parallel threads of
1426 execution or to register signal handlers. Nonetheless, there are
1427 platform-specific ways to create them, and we define LLVM IR's behavior
1428 in their presence. This model is inspired by the C++0x memory model.
1430 For a more informal introduction to this model, see the :doc:`Atomics`.
1432 We define a *happens-before* partial order as the least partial order
1435 - Is a superset of single-thread program order, and
1436 - When a *synchronizes-with* ``b``, includes an edge from ``a`` to
1437 ``b``. *Synchronizes-with* pairs are introduced by platform-specific
1438 techniques, like pthread locks, thread creation, thread joining,
1439 etc., and by atomic instructions. (See also :ref:`Atomic Memory Ordering
1440 Constraints <ordering>`).
1442 Note that program order does not introduce *happens-before* edges
1443 between a thread and signals executing inside that thread.
1445 Every (defined) read operation (load instructions, memcpy, atomic
1446 loads/read-modify-writes, etc.) R reads a series of bytes written by
1447 (defined) write operations (store instructions, atomic
1448 stores/read-modify-writes, memcpy, etc.). For the purposes of this
1449 section, initialized globals are considered to have a write of the
1450 initializer which is atomic and happens before any other read or write
1451 of the memory in question. For each byte of a read R, R\ :sub:`byte`
1452 may see any write to the same byte, except:
1454 - If write\ :sub:`1` happens before write\ :sub:`2`, and
1455 write\ :sub:`2` happens before R\ :sub:`byte`, then
1456 R\ :sub:`byte` does not see write\ :sub:`1`.
1457 - If R\ :sub:`byte` happens before write\ :sub:`3`, then
1458 R\ :sub:`byte` does not see write\ :sub:`3`.
1460 Given that definition, R\ :sub:`byte` is defined as follows:
1462 - If R is volatile, the result is target-dependent. (Volatile is
1463 supposed to give guarantees which can support ``sig_atomic_t`` in
1464 C/C++, and may be used for accesses to addresses which do not behave
1465 like normal memory. It does not generally provide cross-thread
1467 - Otherwise, if there is no write to the same byte that happens before
1468 R\ :sub:`byte`, R\ :sub:`byte` returns ``undef`` for that byte.
1469 - Otherwise, if R\ :sub:`byte` may see exactly one write,
1470 R\ :sub:`byte` returns the value written by that write.
1471 - Otherwise, if R is atomic, and all the writes R\ :sub:`byte` may
1472 see are atomic, it chooses one of the values written. See the :ref:`Atomic
1473 Memory Ordering Constraints <ordering>` section for additional
1474 constraints on how the choice is made.
1475 - Otherwise R\ :sub:`byte` returns ``undef``.
1477 R returns the value composed of the series of bytes it read. This
1478 implies that some bytes within the value may be ``undef`` **without**
1479 the entire value being ``undef``. Note that this only defines the
1480 semantics of the operation; it doesn't mean that targets will emit more
1481 than one instruction to read the series of bytes.
1483 Note that in cases where none of the atomic intrinsics are used, this
1484 model places only one restriction on IR transformations on top of what
1485 is required for single-threaded execution: introducing a store to a byte
1486 which might not otherwise be stored is not allowed in general.
1487 (Specifically, in the case where another thread might write to and read
1488 from an address, introducing a store can change a load that may see
1489 exactly one write into a load that may see multiple writes.)
1493 Atomic Memory Ordering Constraints
1494 ----------------------------------
1496 Atomic instructions (:ref:`cmpxchg <i_cmpxchg>`,
1497 :ref:`atomicrmw <i_atomicrmw>`, :ref:`fence <i_fence>`,
1498 :ref:`atomic load <i_load>`, and :ref:`atomic store <i_store>`) take
1499 an ordering parameter that determines which other atomic instructions on
1500 the same address they *synchronize with*. These semantics are borrowed
1501 from Java and C++0x, but are somewhat more colloquial. If these
1502 descriptions aren't precise enough, check those specs (see spec
1503 references in the :doc:`atomics guide <Atomics>`).
1504 :ref:`fence <i_fence>` instructions treat these orderings somewhat
1505 differently since they don't take an address. See that instruction's
1506 documentation for details.
1508 For a simpler introduction to the ordering constraints, see the
1512 The set of values that can be read is governed by the happens-before
1513 partial order. A value cannot be read unless some operation wrote
1514 it. This is intended to provide a guarantee strong enough to model
1515 Java's non-volatile shared variables. This ordering cannot be
1516 specified for read-modify-write operations; it is not strong enough
1517 to make them atomic in any interesting way.
1519 In addition to the guarantees of ``unordered``, there is a single
1520 total order for modifications by ``monotonic`` operations on each
1521 address. All modification orders must be compatible with the
1522 happens-before order. There is no guarantee that the modification
1523 orders can be combined to a global total order for the whole program
1524 (and this often will not be possible). The read in an atomic
1525 read-modify-write operation (:ref:`cmpxchg <i_cmpxchg>` and
1526 :ref:`atomicrmw <i_atomicrmw>`) reads the value in the modification
1527 order immediately before the value it writes. If one atomic read
1528 happens before another atomic read of the same address, the later
1529 read must see the same value or a later value in the address's
1530 modification order. This disallows reordering of ``monotonic`` (or
1531 stronger) operations on the same address. If an address is written
1532 ``monotonic``-ally by one thread, and other threads ``monotonic``-ally
1533 read that address repeatedly, the other threads must eventually see
1534 the write. This corresponds to the C++0x/C1x
1535 ``memory_order_relaxed``.
1537 In addition to the guarantees of ``monotonic``, a
1538 *synchronizes-with* edge may be formed with a ``release`` operation.
1539 This is intended to model C++'s ``memory_order_acquire``.
1541 In addition to the guarantees of ``monotonic``, if this operation
1542 writes a value which is subsequently read by an ``acquire``
1543 operation, it *synchronizes-with* that operation. (This isn't a
1544 complete description; see the C++0x definition of a release
1545 sequence.) This corresponds to the C++0x/C1x
1546 ``memory_order_release``.
1547 ``acq_rel`` (acquire+release)
1548 Acts as both an ``acquire`` and ``release`` operation on its
1549 address. This corresponds to the C++0x/C1x ``memory_order_acq_rel``.
1550 ``seq_cst`` (sequentially consistent)
1551 In addition to the guarantees of ``acq_rel`` (``acquire`` for an
1552 operation which only reads, ``release`` for an operation which only
1553 writes), there is a global total order on all
1554 sequentially-consistent operations on all addresses, which is
1555 consistent with the *happens-before* partial order and with the
1556 modification orders of all the affected addresses. Each
1557 sequentially-consistent read sees the last preceding write to the
1558 same address in this global order. This corresponds to the C++0x/C1x
1559 ``memory_order_seq_cst`` and Java volatile.
1563 If an atomic operation is marked ``singlethread``, it only *synchronizes
1564 with* or participates in modification and seq\_cst total orderings with
1565 other operations running in the same thread (for example, in signal
1573 LLVM IR floating-point binary ops (:ref:`fadd <i_fadd>`,
1574 :ref:`fsub <i_fsub>`, :ref:`fmul <i_fmul>`, :ref:`fdiv <i_fdiv>`,
1575 :ref:`frem <i_frem>`) have the following flags that can set to enable
1576 otherwise unsafe floating point operations
1579 No NaNs - Allow optimizations to assume the arguments and result are not
1580 NaN. Such optimizations are required to retain defined behavior over
1581 NaNs, but the value of the result is undefined.
1584 No Infs - Allow optimizations to assume the arguments and result are not
1585 +/-Inf. Such optimizations are required to retain defined behavior over
1586 +/-Inf, but the value of the result is undefined.
1589 No Signed Zeros - Allow optimizations to treat the sign of a zero
1590 argument or result as insignificant.
1593 Allow Reciprocal - Allow optimizations to use the reciprocal of an
1594 argument rather than perform division.
1597 Fast - Allow algebraically equivalent transformations that may
1598 dramatically change results in floating point (e.g. reassociate). This
1599 flag implies all the others.
1606 The LLVM type system is one of the most important features of the
1607 intermediate representation. Being typed enables a number of
1608 optimizations to be performed on the intermediate representation
1609 directly, without having to do extra analyses on the side before the
1610 transformation. A strong type system makes it easier to read the
1611 generated code and enables novel analyses and transformations that are
1612 not feasible to perform on normal three address code representations.
1622 The void type does not represent any value and has no size.
1640 The function type can be thought of as a function signature. It consists of a
1641 return type and a list of formal parameter types. The return type of a function
1642 type is a void type or first class type --- except for :ref:`label <t_label>`
1643 and :ref:`metadata <t_metadata>` types.
1649 <returntype> (<parameter list>)
1651 ...where '``<parameter list>``' is a comma-separated list of type
1652 specifiers. Optionally, the parameter list may include a type ``...``, which
1653 indicates that the function takes a variable number of arguments. Variable
1654 argument functions can access their arguments with the :ref:`variable argument
1655 handling intrinsic <int_varargs>` functions. '``<returntype>``' is any type
1656 except :ref:`label <t_label>` and :ref:`metadata <t_metadata>`.
1660 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1661 | ``i32 (i32)`` | function taking an ``i32``, returning an ``i32`` |
1662 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1663 | ``float (i16, i32 *) *`` | :ref:`Pointer <t_pointer>` to a function that takes an ``i16`` and a :ref:`pointer <t_pointer>` to ``i32``, returning ``float``. |
1664 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1665 | ``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. |
1666 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1667 | ``{i32, i32} (i32)`` | A function taking an ``i32``, returning a :ref:`structure <t_struct>` containing two ``i32`` values |
1668 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1675 The :ref:`first class <t_firstclass>` types are perhaps the most important.
1676 Values of these types are the only ones which can be produced by
1684 These are the types that are valid in registers from CodeGen's perspective.
1693 The integer type is a very simple type that simply specifies an
1694 arbitrary bit width for the integer type desired. Any bit width from 1
1695 bit to 2\ :sup:`23`\ -1 (about 8 million) can be specified.
1703 The number of bits the integer will occupy is specified by the ``N``
1709 +----------------+------------------------------------------------+
1710 | ``i1`` | a single-bit integer. |
1711 +----------------+------------------------------------------------+
1712 | ``i32`` | a 32-bit integer. |
1713 +----------------+------------------------------------------------+
1714 | ``i1942652`` | a really big integer of over 1 million bits. |
1715 +----------------+------------------------------------------------+
1719 Floating Point Types
1720 """"""""""""""""""""
1729 - 16-bit floating point value
1732 - 32-bit floating point value
1735 - 64-bit floating point value
1738 - 128-bit floating point value (112-bit mantissa)
1741 - 80-bit floating point value (X87)
1744 - 128-bit floating point value (two 64-bits)
1751 The x86_mmx type represents a value held in an MMX register on an x86
1752 machine. The operations allowed on it are quite limited: parameters and
1753 return values, load and store, and bitcast. User-specified MMX
1754 instructions are represented as intrinsic or asm calls with arguments
1755 and/or results of this type. There are no arrays, vectors or constants
1772 The pointer type is used to specify memory locations. Pointers are
1773 commonly used to reference objects in memory.
1775 Pointer types may have an optional address space attribute defining the
1776 numbered address space where the pointed-to object resides. The default
1777 address space is number zero. The semantics of non-zero address spaces
1778 are target-specific.
1780 Note that LLVM does not permit pointers to void (``void*``) nor does it
1781 permit pointers to labels (``label*``). Use ``i8*`` instead.
1791 +-------------------------+--------------------------------------------------------------------------------------------------------------+
1792 | ``[4 x i32]*`` | A :ref:`pointer <t_pointer>` to :ref:`array <t_array>` of four ``i32`` values. |
1793 +-------------------------+--------------------------------------------------------------------------------------------------------------+
1794 | ``i32 (i32*) *`` | A :ref:`pointer <t_pointer>` to a :ref:`function <t_function>` that takes an ``i32*``, returning an ``i32``. |
1795 +-------------------------+--------------------------------------------------------------------------------------------------------------+
1796 | ``i32 addrspace(5)*`` | A :ref:`pointer <t_pointer>` to an ``i32`` value that resides in address space #5. |
1797 +-------------------------+--------------------------------------------------------------------------------------------------------------+
1806 A vector type is a simple derived type that represents a vector of
1807 elements. Vector types are used when multiple primitive data are
1808 operated in parallel using a single instruction (SIMD). A vector type
1809 requires a size (number of elements) and an underlying primitive data
1810 type. Vector types are considered :ref:`first class <t_firstclass>`.
1816 < <# elements> x <elementtype> >
1818 The number of elements is a constant integer value larger than 0;
1819 elementtype may be any integer or floating point type, or a pointer to
1820 these types. Vectors of size zero are not allowed.
1824 +-------------------+--------------------------------------------------+
1825 | ``<4 x i32>`` | Vector of 4 32-bit integer values. |
1826 +-------------------+--------------------------------------------------+
1827 | ``<8 x float>`` | Vector of 8 32-bit floating-point values. |
1828 +-------------------+--------------------------------------------------+
1829 | ``<2 x i64>`` | Vector of 2 64-bit integer values. |
1830 +-------------------+--------------------------------------------------+
1831 | ``<4 x i64*>`` | Vector of 4 pointers to 64-bit integer values. |
1832 +-------------------+--------------------------------------------------+
1841 The label type represents code labels.
1856 The metadata type represents embedded metadata. No derived types may be
1857 created from metadata except for :ref:`function <t_function>` arguments.
1870 Aggregate Types are a subset of derived types that can contain multiple
1871 member types. :ref:`Arrays <t_array>` and :ref:`structs <t_struct>` are
1872 aggregate types. :ref:`Vectors <t_vector>` are not considered to be
1882 The array type is a very simple derived type that arranges elements
1883 sequentially in memory. The array type requires a size (number of
1884 elements) and an underlying data type.
1890 [<# elements> x <elementtype>]
1892 The number of elements is a constant integer value; ``elementtype`` may
1893 be any type with a size.
1897 +------------------+--------------------------------------+
1898 | ``[40 x i32]`` | Array of 40 32-bit integer values. |
1899 +------------------+--------------------------------------+
1900 | ``[41 x i32]`` | Array of 41 32-bit integer values. |
1901 +------------------+--------------------------------------+
1902 | ``[4 x i8]`` | Array of 4 8-bit integer values. |
1903 +------------------+--------------------------------------+
1905 Here are some examples of multidimensional arrays:
1907 +-----------------------------+----------------------------------------------------------+
1908 | ``[3 x [4 x i32]]`` | 3x4 array of 32-bit integer values. |
1909 +-----------------------------+----------------------------------------------------------+
1910 | ``[12 x [10 x float]]`` | 12x10 array of single precision floating point values. |
1911 +-----------------------------+----------------------------------------------------------+
1912 | ``[2 x [3 x [4 x i16]]]`` | 2x3x4 array of 16-bit integer values. |
1913 +-----------------------------+----------------------------------------------------------+
1915 There is no restriction on indexing beyond the end of the array implied
1916 by a static type (though there are restrictions on indexing beyond the
1917 bounds of an allocated object in some cases). This means that
1918 single-dimension 'variable sized array' addressing can be implemented in
1919 LLVM with a zero length array type. An implementation of 'pascal style
1920 arrays' in LLVM could use the type "``{ i32, [0 x float]}``", for
1930 The structure type is used to represent a collection of data members
1931 together in memory. The elements of a structure may be any type that has
1934 Structures in memory are accessed using '``load``' and '``store``' by
1935 getting a pointer to a field with the '``getelementptr``' instruction.
1936 Structures in registers are accessed using the '``extractvalue``' and
1937 '``insertvalue``' instructions.
1939 Structures may optionally be "packed" structures, which indicate that
1940 the alignment of the struct is one byte, and that there is no padding
1941 between the elements. In non-packed structs, padding between field types
1942 is inserted as defined by the DataLayout string in the module, which is
1943 required to match what the underlying code generator expects.
1945 Structures can either be "literal" or "identified". A literal structure
1946 is defined inline with other types (e.g. ``{i32, i32}*``) whereas
1947 identified types are always defined at the top level with a name.
1948 Literal types are uniqued by their contents and can never be recursive
1949 or opaque since there is no way to write one. Identified types can be
1950 recursive, can be opaqued, and are never uniqued.
1956 %T1 = type { <type list> } ; Identified normal struct type
1957 %T2 = type <{ <type list> }> ; Identified packed struct type
1961 +------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1962 | ``{ i32, i32, i32 }`` | A triple of three ``i32`` values |
1963 +------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1964 | ``{ 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``. |
1965 +------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1966 | ``<{ i8, i32 }>`` | A packed struct known to be 5 bytes in size. |
1967 +------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1971 Opaque Structure Types
1972 """"""""""""""""""""""
1976 Opaque structure types are used to represent named structure types that
1977 do not have a body specified. This corresponds (for example) to the C
1978 notion of a forward declared structure.
1989 +--------------+-------------------+
1990 | ``opaque`` | An opaque type. |
1991 +--------------+-------------------+
1996 LLVM has several different basic types of constants. This section
1997 describes them all and their syntax.
2002 **Boolean constants**
2003 The two strings '``true``' and '``false``' are both valid constants
2005 **Integer constants**
2006 Standard integers (such as '4') are constants of the
2007 :ref:`integer <t_integer>` type. Negative numbers may be used with
2009 **Floating point constants**
2010 Floating point constants use standard decimal notation (e.g.
2011 123.421), exponential notation (e.g. 1.23421e+2), or a more precise
2012 hexadecimal notation (see below). The assembler requires the exact
2013 decimal value of a floating-point constant. For example, the
2014 assembler accepts 1.25 but rejects 1.3 because 1.3 is a repeating
2015 decimal in binary. Floating point constants must have a :ref:`floating
2016 point <t_floating>` type.
2017 **Null pointer constants**
2018 The identifier '``null``' is recognized as a null pointer constant
2019 and must be of :ref:`pointer type <t_pointer>`.
2021 The one non-intuitive notation for constants is the hexadecimal form of
2022 floating point constants. For example, the form
2023 '``double 0x432ff973cafa8000``' is equivalent to (but harder to read
2024 than) '``double 4.5e+15``'. The only time hexadecimal floating point
2025 constants are required (and the only time that they are generated by the
2026 disassembler) is when a floating point constant must be emitted but it
2027 cannot be represented as a decimal floating point number in a reasonable
2028 number of digits. For example, NaN's, infinities, and other special
2029 values are represented in their IEEE hexadecimal format so that assembly
2030 and disassembly do not cause any bits to change in the constants.
2032 When using the hexadecimal form, constants of types half, float, and
2033 double are represented using the 16-digit form shown above (which
2034 matches the IEEE754 representation for double); half and float values
2035 must, however, be exactly representable as IEEE 754 half and single
2036 precision, respectively. Hexadecimal format is always used for long
2037 double, and there are three forms of long double. The 80-bit format used
2038 by x86 is represented as ``0xK`` followed by 20 hexadecimal digits. The
2039 128-bit format used by PowerPC (two adjacent doubles) is represented by
2040 ``0xM`` followed by 32 hexadecimal digits. The IEEE 128-bit format is
2041 represented by ``0xL`` followed by 32 hexadecimal digits. Long doubles
2042 will only work if they match the long double format on your target.
2043 The IEEE 16-bit format (half precision) is represented by ``0xH``
2044 followed by 4 hexadecimal digits. All hexadecimal formats are big-endian
2045 (sign bit at the left).
2047 There are no constants of type x86_mmx.
2049 .. _complexconstants:
2054 Complex constants are a (potentially recursive) combination of simple
2055 constants and smaller complex constants.
2057 **Structure constants**
2058 Structure constants are represented with notation similar to
2059 structure type definitions (a comma separated list of elements,
2060 surrounded by braces (``{}``)). For example:
2061 "``{ i32 4, float 17.0, i32* @G }``", where "``@G``" is declared as
2062 "``@G = external global i32``". Structure constants must have
2063 :ref:`structure type <t_struct>`, and the number and types of elements
2064 must match those specified by the type.
2066 Array constants are represented with notation similar to array type
2067 definitions (a comma separated list of elements, surrounded by
2068 square brackets (``[]``)). For example:
2069 "``[ i32 42, i32 11, i32 74 ]``". Array constants must have
2070 :ref:`array type <t_array>`, and the number and types of elements must
2071 match those specified by the type.
2072 **Vector constants**
2073 Vector constants are represented with notation similar to vector
2074 type definitions (a comma separated list of elements, surrounded by
2075 less-than/greater-than's (``<>``)). For example:
2076 "``< i32 42, i32 11, i32 74, i32 100 >``". Vector constants
2077 must have :ref:`vector type <t_vector>`, and the number and types of
2078 elements must match those specified by the type.
2079 **Zero initialization**
2080 The string '``zeroinitializer``' can be used to zero initialize a
2081 value to zero of *any* type, including scalar and
2082 :ref:`aggregate <t_aggregate>` types. This is often used to avoid
2083 having to print large zero initializers (e.g. for large arrays) and
2084 is always exactly equivalent to using explicit zero initializers.
2086 A metadata node is a structure-like constant with :ref:`metadata
2087 type <t_metadata>`. For example:
2088 "``metadata !{ i32 0, metadata !"test" }``". Unlike other
2089 constants that are meant to be interpreted as part of the
2090 instruction stream, metadata is a place to attach additional
2091 information such as debug info.
2093 Global Variable and Function Addresses
2094 --------------------------------------
2096 The addresses of :ref:`global variables <globalvars>` and
2097 :ref:`functions <functionstructure>` are always implicitly valid
2098 (link-time) constants. These constants are explicitly referenced when
2099 the :ref:`identifier for the global <identifiers>` is used and always have
2100 :ref:`pointer <t_pointer>` type. For example, the following is a legal LLVM
2103 .. code-block:: llvm
2107 @Z = global [2 x i32*] [ i32* @X, i32* @Y ]
2114 The string '``undef``' can be used anywhere a constant is expected, and
2115 indicates that the user of the value may receive an unspecified
2116 bit-pattern. Undefined values may be of any type (other than '``label``'
2117 or '``void``') and be used anywhere a constant is permitted.
2119 Undefined values are useful because they indicate to the compiler that
2120 the program is well defined no matter what value is used. This gives the
2121 compiler more freedom to optimize. Here are some examples of
2122 (potentially surprising) transformations that are valid (in pseudo IR):
2124 .. code-block:: llvm
2134 This is safe because all of the output bits are affected by the undef
2135 bits. Any output bit can have a zero or one depending on the input bits.
2137 .. code-block:: llvm
2148 These logical operations have bits that are not always affected by the
2149 input. For example, if ``%X`` has a zero bit, then the output of the
2150 '``and``' operation will always be a zero for that bit, no matter what
2151 the corresponding bit from the '``undef``' is. As such, it is unsafe to
2152 optimize or assume that the result of the '``and``' is '``undef``'.
2153 However, it is safe to assume that all bits of the '``undef``' could be
2154 0, and optimize the '``and``' to 0. Likewise, it is safe to assume that
2155 all the bits of the '``undef``' operand to the '``or``' could be set,
2156 allowing the '``or``' to be folded to -1.
2158 .. code-block:: llvm
2160 %A = select undef, %X, %Y
2161 %B = select undef, 42, %Y
2162 %C = select %X, %Y, undef
2172 This set of examples shows that undefined '``select``' (and conditional
2173 branch) conditions can go *either way*, but they have to come from one
2174 of the two operands. In the ``%A`` example, if ``%X`` and ``%Y`` were
2175 both known to have a clear low bit, then ``%A`` would have to have a
2176 cleared low bit. However, in the ``%C`` example, the optimizer is
2177 allowed to assume that the '``undef``' operand could be the same as
2178 ``%Y``, allowing the whole '``select``' to be eliminated.
2180 .. code-block:: llvm
2182 %A = xor undef, undef
2199 This example points out that two '``undef``' operands are not
2200 necessarily the same. This can be surprising to people (and also matches
2201 C semantics) where they assume that "``X^X``" is always zero, even if
2202 ``X`` is undefined. This isn't true for a number of reasons, but the
2203 short answer is that an '``undef``' "variable" can arbitrarily change
2204 its value over its "live range". This is true because the variable
2205 doesn't actually *have a live range*. Instead, the value is logically
2206 read from arbitrary registers that happen to be around when needed, so
2207 the value is not necessarily consistent over time. In fact, ``%A`` and
2208 ``%C`` need to have the same semantics or the core LLVM "replace all
2209 uses with" concept would not hold.
2211 .. code-block:: llvm
2219 These examples show the crucial difference between an *undefined value*
2220 and *undefined behavior*. An undefined value (like '``undef``') is
2221 allowed to have an arbitrary bit-pattern. This means that the ``%A``
2222 operation can be constant folded to '``undef``', because the '``undef``'
2223 could be an SNaN, and ``fdiv`` is not (currently) defined on SNaN's.
2224 However, in the second example, we can make a more aggressive
2225 assumption: because the ``undef`` is allowed to be an arbitrary value,
2226 we are allowed to assume that it could be zero. Since a divide by zero
2227 has *undefined behavior*, we are allowed to assume that the operation
2228 does not execute at all. This allows us to delete the divide and all
2229 code after it. Because the undefined operation "can't happen", the
2230 optimizer can assume that it occurs in dead code.
2232 .. code-block:: llvm
2234 a: store undef -> %X
2235 b: store %X -> undef
2240 These examples reiterate the ``fdiv`` example: a store *of* an undefined
2241 value can be assumed to not have any effect; we can assume that the
2242 value is overwritten with bits that happen to match what was already
2243 there. However, a store *to* an undefined location could clobber
2244 arbitrary memory, therefore, it has undefined behavior.
2251 Poison values are similar to :ref:`undef values <undefvalues>`, however
2252 they also represent the fact that an instruction or constant expression
2253 which cannot evoke side effects has nevertheless detected a condition
2254 which results in undefined behavior.
2256 There is currently no way of representing a poison value in the IR; they
2257 only exist when produced by operations such as :ref:`add <i_add>` with
2260 Poison value behavior is defined in terms of value *dependence*:
2262 - Values other than :ref:`phi <i_phi>` nodes depend on their operands.
2263 - :ref:`Phi <i_phi>` nodes depend on the operand corresponding to
2264 their dynamic predecessor basic block.
2265 - Function arguments depend on the corresponding actual argument values
2266 in the dynamic callers of their functions.
2267 - :ref:`Call <i_call>` instructions depend on the :ref:`ret <i_ret>`
2268 instructions that dynamically transfer control back to them.
2269 - :ref:`Invoke <i_invoke>` instructions depend on the
2270 :ref:`ret <i_ret>`, :ref:`resume <i_resume>`, or exception-throwing
2271 call instructions that dynamically transfer control back to them.
2272 - Non-volatile loads and stores depend on the most recent stores to all
2273 of the referenced memory addresses, following the order in the IR
2274 (including loads and stores implied by intrinsics such as
2275 :ref:`@llvm.memcpy <int_memcpy>`.)
2276 - An instruction with externally visible side effects depends on the
2277 most recent preceding instruction with externally visible side
2278 effects, following the order in the IR. (This includes :ref:`volatile
2279 operations <volatile>`.)
2280 - An instruction *control-depends* on a :ref:`terminator
2281 instruction <terminators>` if the terminator instruction has
2282 multiple successors and the instruction is always executed when
2283 control transfers to one of the successors, and may not be executed
2284 when control is transferred to another.
2285 - Additionally, an instruction also *control-depends* on a terminator
2286 instruction if the set of instructions it otherwise depends on would
2287 be different if the terminator had transferred control to a different
2289 - Dependence is transitive.
2291 Poison Values have the same behavior as :ref:`undef values <undefvalues>`,
2292 with the additional affect that any instruction which has a *dependence*
2293 on a poison value has undefined behavior.
2295 Here are some examples:
2297 .. code-block:: llvm
2300 %poison = sub nuw i32 0, 1 ; Results in a poison value.
2301 %still_poison = and i32 %poison, 0 ; 0, but also poison.
2302 %poison_yet_again = getelementptr i32* @h, i32 %still_poison
2303 store i32 0, i32* %poison_yet_again ; memory at @h[0] is poisoned
2305 store i32 %poison, i32* @g ; Poison value stored to memory.
2306 %poison2 = load i32* @g ; Poison value loaded back from memory.
2308 store volatile i32 %poison, i32* @g ; External observation; undefined behavior.
2310 %narrowaddr = bitcast i32* @g to i16*
2311 %wideaddr = bitcast i32* @g to i64*
2312 %poison3 = load i16* %narrowaddr ; Returns a poison value.
2313 %poison4 = load i64* %wideaddr ; Returns a poison value.
2315 %cmp = icmp slt i32 %poison, 0 ; Returns a poison value.
2316 br i1 %cmp, label %true, label %end ; Branch to either destination.
2319 store volatile i32 0, i32* @g ; This is control-dependent on %cmp, so
2320 ; it has undefined behavior.
2324 %p = phi i32 [ 0, %entry ], [ 1, %true ]
2325 ; Both edges into this PHI are
2326 ; control-dependent on %cmp, so this
2327 ; always results in a poison value.
2329 store volatile i32 0, i32* @g ; This would depend on the store in %true
2330 ; if %cmp is true, or the store in %entry
2331 ; otherwise, so this is undefined behavior.
2333 br i1 %cmp, label %second_true, label %second_end
2334 ; The same branch again, but this time the
2335 ; true block doesn't have side effects.
2342 store volatile i32 0, i32* @g ; This time, the instruction always depends
2343 ; on the store in %end. Also, it is
2344 ; control-equivalent to %end, so this is
2345 ; well-defined (ignoring earlier undefined
2346 ; behavior in this example).
2350 Addresses of Basic Blocks
2351 -------------------------
2353 ``blockaddress(@function, %block)``
2355 The '``blockaddress``' constant computes the address of the specified
2356 basic block in the specified function, and always has an ``i8*`` type.
2357 Taking the address of the entry block is illegal.
2359 This value only has defined behavior when used as an operand to the
2360 ':ref:`indirectbr <i_indirectbr>`' instruction, or for comparisons
2361 against null. Pointer equality tests between labels addresses results in
2362 undefined behavior --- though, again, comparison against null is ok, and
2363 no label is equal to the null pointer. This may be passed around as an
2364 opaque pointer sized value as long as the bits are not inspected. This
2365 allows ``ptrtoint`` and arithmetic to be performed on these values so
2366 long as the original value is reconstituted before the ``indirectbr``
2369 Finally, some targets may provide defined semantics when using the value
2370 as the operand to an inline assembly, but that is target specific.
2374 Constant Expressions
2375 --------------------
2377 Constant expressions are used to allow expressions involving other
2378 constants to be used as constants. Constant expressions may be of any
2379 :ref:`first class <t_firstclass>` type and may involve any LLVM operation
2380 that does not have side effects (e.g. load and call are not supported).
2381 The following is the syntax for constant expressions:
2383 ``trunc (CST to TYPE)``
2384 Truncate a constant to another type. The bit size of CST must be
2385 larger than the bit size of TYPE. Both types must be integers.
2386 ``zext (CST to TYPE)``
2387 Zero extend a constant to another type. The bit size of CST must be
2388 smaller than the bit size of TYPE. Both types must be integers.
2389 ``sext (CST to TYPE)``
2390 Sign extend a constant to another type. The bit size of CST must be
2391 smaller than the bit size of TYPE. Both types must be integers.
2392 ``fptrunc (CST to TYPE)``
2393 Truncate a floating point constant to another floating point type.
2394 The size of CST must be larger than the size of TYPE. Both types
2395 must be floating point.
2396 ``fpext (CST to TYPE)``
2397 Floating point extend a constant to another type. The size of CST
2398 must be smaller or equal to the size of TYPE. Both types must be
2400 ``fptoui (CST to TYPE)``
2401 Convert a floating point constant to the corresponding unsigned
2402 integer constant. TYPE must be a scalar or vector integer type. CST
2403 must be of scalar or vector floating point type. Both CST and TYPE
2404 must be scalars, or vectors of the same number of elements. If the
2405 value won't fit in the integer type, the results are undefined.
2406 ``fptosi (CST to TYPE)``
2407 Convert a floating point constant to the corresponding signed
2408 integer constant. TYPE must be a scalar or vector integer type. CST
2409 must be of scalar or vector floating point type. Both CST and TYPE
2410 must be scalars, or vectors of the same number of elements. If the
2411 value won't fit in the integer type, the results are undefined.
2412 ``uitofp (CST to TYPE)``
2413 Convert an unsigned integer constant to the corresponding floating
2414 point constant. TYPE must be a scalar or vector floating point type.
2415 CST must be of scalar or vector integer type. Both CST and TYPE must
2416 be scalars, or vectors of the same number of elements. If the value
2417 won't fit in the floating point type, the results are undefined.
2418 ``sitofp (CST to TYPE)``
2419 Convert a signed integer constant to the corresponding floating
2420 point constant. TYPE must be a scalar or vector floating point type.
2421 CST must be of scalar or vector integer type. Both CST and TYPE must
2422 be scalars, or vectors of the same number of elements. If the value
2423 won't fit in the floating point type, the results are undefined.
2424 ``ptrtoint (CST to TYPE)``
2425 Convert a pointer typed constant to the corresponding integer
2426 constant. ``TYPE`` must be an integer type. ``CST`` must be of
2427 pointer type. The ``CST`` value is zero extended, truncated, or
2428 unchanged to make it fit in ``TYPE``.
2429 ``inttoptr (CST to TYPE)``
2430 Convert an integer constant to a pointer constant. TYPE must be a
2431 pointer type. CST must be of integer type. The CST value is zero
2432 extended, truncated, or unchanged to make it fit in a pointer size.
2433 This one is *really* dangerous!
2434 ``bitcast (CST to TYPE)``
2435 Convert a constant, CST, to another TYPE. The constraints of the
2436 operands are the same as those for the :ref:`bitcast
2437 instruction <i_bitcast>`.
2438 ``addrspacecast (CST to TYPE)``
2439 Convert a constant pointer or constant vector of pointer, CST, to another
2440 TYPE in a different address space. The constraints of the operands are the
2441 same as those for the :ref:`addrspacecast instruction <i_addrspacecast>`.
2442 ``getelementptr (CSTPTR, IDX0, IDX1, ...)``, ``getelementptr inbounds (CSTPTR, IDX0, IDX1, ...)``
2443 Perform the :ref:`getelementptr operation <i_getelementptr>` on
2444 constants. As with the :ref:`getelementptr <i_getelementptr>`
2445 instruction, the index list may have zero or more indexes, which are
2446 required to make sense for the type of "CSTPTR".
2447 ``select (COND, VAL1, VAL2)``
2448 Perform the :ref:`select operation <i_select>` on constants.
2449 ``icmp COND (VAL1, VAL2)``
2450 Performs the :ref:`icmp operation <i_icmp>` on constants.
2451 ``fcmp COND (VAL1, VAL2)``
2452 Performs the :ref:`fcmp operation <i_fcmp>` on constants.
2453 ``extractelement (VAL, IDX)``
2454 Perform the :ref:`extractelement operation <i_extractelement>` on
2456 ``insertelement (VAL, ELT, IDX)``
2457 Perform the :ref:`insertelement operation <i_insertelement>` on
2459 ``shufflevector (VEC1, VEC2, IDXMASK)``
2460 Perform the :ref:`shufflevector operation <i_shufflevector>` on
2462 ``extractvalue (VAL, IDX0, IDX1, ...)``
2463 Perform the :ref:`extractvalue operation <i_extractvalue>` on
2464 constants. The index list is interpreted in a similar manner as
2465 indices in a ':ref:`getelementptr <i_getelementptr>`' operation. At
2466 least one index value must be specified.
2467 ``insertvalue (VAL, ELT, IDX0, IDX1, ...)``
2468 Perform the :ref:`insertvalue operation <i_insertvalue>` on constants.
2469 The index list is interpreted in a similar manner as indices in a
2470 ':ref:`getelementptr <i_getelementptr>`' operation. At least one index
2471 value must be specified.
2472 ``OPCODE (LHS, RHS)``
2473 Perform the specified operation of the LHS and RHS constants. OPCODE
2474 may be any of the :ref:`binary <binaryops>` or :ref:`bitwise
2475 binary <bitwiseops>` operations. The constraints on operands are
2476 the same as those for the corresponding instruction (e.g. no bitwise
2477 operations on floating point values are allowed).
2484 Inline Assembler Expressions
2485 ----------------------------
2487 LLVM supports inline assembler expressions (as opposed to :ref:`Module-Level
2488 Inline Assembly <moduleasm>`) through the use of a special value. This
2489 value represents the inline assembler as a string (containing the
2490 instructions to emit), a list of operand constraints (stored as a
2491 string), a flag that indicates whether or not the inline asm expression
2492 has side effects, and a flag indicating whether the function containing
2493 the asm needs to align its stack conservatively. An example inline
2494 assembler expression is:
2496 .. code-block:: llvm
2498 i32 (i32) asm "bswap $0", "=r,r"
2500 Inline assembler expressions may **only** be used as the callee operand
2501 of a :ref:`call <i_call>` or an :ref:`invoke <i_invoke>` instruction.
2502 Thus, typically we have:
2504 .. code-block:: llvm
2506 %X = call i32 asm "bswap $0", "=r,r"(i32 %Y)
2508 Inline asms with side effects not visible in the constraint list must be
2509 marked as having side effects. This is done through the use of the
2510 '``sideeffect``' keyword, like so:
2512 .. code-block:: llvm
2514 call void asm sideeffect "eieio", ""()
2516 In some cases inline asms will contain code that will not work unless
2517 the stack is aligned in some way, such as calls or SSE instructions on
2518 x86, yet will not contain code that does that alignment within the asm.
2519 The compiler should make conservative assumptions about what the asm
2520 might contain and should generate its usual stack alignment code in the
2521 prologue if the '``alignstack``' keyword is present:
2523 .. code-block:: llvm
2525 call void asm alignstack "eieio", ""()
2527 Inline asms also support using non-standard assembly dialects. The
2528 assumed dialect is ATT. When the '``inteldialect``' keyword is present,
2529 the inline asm is using the Intel dialect. Currently, ATT and Intel are
2530 the only supported dialects. An example is:
2532 .. code-block:: llvm
2534 call void asm inteldialect "eieio", ""()
2536 If multiple keywords appear the '``sideeffect``' keyword must come
2537 first, the '``alignstack``' keyword second and the '``inteldialect``'
2543 The call instructions that wrap inline asm nodes may have a
2544 "``!srcloc``" MDNode attached to it that contains a list of constant
2545 integers. If present, the code generator will use the integer as the
2546 location cookie value when report errors through the ``LLVMContext``
2547 error reporting mechanisms. This allows a front-end to correlate backend
2548 errors that occur with inline asm back to the source code that produced
2551 .. code-block:: llvm
2553 call void asm sideeffect "something bad", ""(), !srcloc !42
2555 !42 = !{ i32 1234567 }
2557 It is up to the front-end to make sense of the magic numbers it places
2558 in the IR. If the MDNode contains multiple constants, the code generator
2559 will use the one that corresponds to the line of the asm that the error
2564 Metadata Nodes and Metadata Strings
2565 -----------------------------------
2567 LLVM IR allows metadata to be attached to instructions in the program
2568 that can convey extra information about the code to the optimizers and
2569 code generator. One example application of metadata is source-level
2570 debug information. There are two metadata primitives: strings and nodes.
2571 All metadata has the ``metadata`` type and is identified in syntax by a
2572 preceding exclamation point ('``!``').
2574 A metadata string is a string surrounded by double quotes. It can
2575 contain any character by escaping non-printable characters with
2576 "``\xx``" where "``xx``" is the two digit hex code. For example:
2579 Metadata nodes are represented with notation similar to structure
2580 constants (a comma separated list of elements, surrounded by braces and
2581 preceded by an exclamation point). Metadata nodes can have any values as
2582 their operand. For example:
2584 .. code-block:: llvm
2586 !{ metadata !"test\00", i32 10}
2588 A :ref:`named metadata <namedmetadatastructure>` is a collection of
2589 metadata nodes, which can be looked up in the module symbol table. For
2592 .. code-block:: llvm
2594 !foo = metadata !{!4, !3}
2596 Metadata can be used as function arguments. Here ``llvm.dbg.value``
2597 function is using two metadata arguments:
2599 .. code-block:: llvm
2601 call void @llvm.dbg.value(metadata !24, i64 0, metadata !25)
2603 Metadata can be attached with an instruction. Here metadata ``!21`` is
2604 attached to the ``add`` instruction using the ``!dbg`` identifier:
2606 .. code-block:: llvm
2608 %indvar.next = add i64 %indvar, 1, !dbg !21
2610 More information about specific metadata nodes recognized by the
2611 optimizers and code generator is found below.
2616 In LLVM IR, memory does not have types, so LLVM's own type system is not
2617 suitable for doing TBAA. Instead, metadata is added to the IR to
2618 describe a type system of a higher level language. This can be used to
2619 implement typical C/C++ TBAA, but it can also be used to implement
2620 custom alias analysis behavior for other languages.
2622 The current metadata format is very simple. TBAA metadata nodes have up
2623 to three fields, e.g.:
2625 .. code-block:: llvm
2627 !0 = metadata !{ metadata !"an example type tree" }
2628 !1 = metadata !{ metadata !"int", metadata !0 }
2629 !2 = metadata !{ metadata !"float", metadata !0 }
2630 !3 = metadata !{ metadata !"const float", metadata !2, i64 1 }
2632 The first field is an identity field. It can be any value, usually a
2633 metadata string, which uniquely identifies the type. The most important
2634 name in the tree is the name of the root node. Two trees with different
2635 root node names are entirely disjoint, even if they have leaves with
2638 The second field identifies the type's parent node in the tree, or is
2639 null or omitted for a root node. A type is considered to alias all of
2640 its descendants and all of its ancestors in the tree. Also, a type is
2641 considered to alias all types in other trees, so that bitcode produced
2642 from multiple front-ends is handled conservatively.
2644 If the third field is present, it's an integer which if equal to 1
2645 indicates that the type is "constant" (meaning
2646 ``pointsToConstantMemory`` should return true; see `other useful
2647 AliasAnalysis methods <AliasAnalysis.html#OtherItfs>`_).
2649 '``tbaa.struct``' Metadata
2650 ^^^^^^^^^^^^^^^^^^^^^^^^^^
2652 The :ref:`llvm.memcpy <int_memcpy>` is often used to implement
2653 aggregate assignment operations in C and similar languages, however it
2654 is defined to copy a contiguous region of memory, which is more than
2655 strictly necessary for aggregate types which contain holes due to
2656 padding. Also, it doesn't contain any TBAA information about the fields
2659 ``!tbaa.struct`` metadata can describe which memory subregions in a
2660 memcpy are padding and what the TBAA tags of the struct are.
2662 The current metadata format is very simple. ``!tbaa.struct`` metadata
2663 nodes are a list of operands which are in conceptual groups of three.
2664 For each group of three, the first operand gives the byte offset of a
2665 field in bytes, the second gives its size in bytes, and the third gives
2668 .. code-block:: llvm
2670 !4 = metadata !{ i64 0, i64 4, metadata !1, i64 8, i64 4, metadata !2 }
2672 This describes a struct with two fields. The first is at offset 0 bytes
2673 with size 4 bytes, and has tbaa tag !1. The second is at offset 8 bytes
2674 and has size 4 bytes and has tbaa tag !2.
2676 Note that the fields need not be contiguous. In this example, there is a
2677 4 byte gap between the two fields. This gap represents padding which
2678 does not carry useful data and need not be preserved.
2680 '``fpmath``' Metadata
2681 ^^^^^^^^^^^^^^^^^^^^^
2683 ``fpmath`` metadata may be attached to any instruction of floating point
2684 type. It can be used to express the maximum acceptable error in the
2685 result of that instruction, in ULPs, thus potentially allowing the
2686 compiler to use a more efficient but less accurate method of computing
2687 it. ULP is defined as follows:
2689 If ``x`` is a real number that lies between two finite consecutive
2690 floating-point numbers ``a`` and ``b``, without being equal to one
2691 of them, then ``ulp(x) = |b - a|``, otherwise ``ulp(x)`` is the
2692 distance between the two non-equal finite floating-point numbers
2693 nearest ``x``. Moreover, ``ulp(NaN)`` is ``NaN``.
2695 The metadata node shall consist of a single positive floating point
2696 number representing the maximum relative error, for example:
2698 .. code-block:: llvm
2700 !0 = metadata !{ float 2.5 } ; maximum acceptable inaccuracy is 2.5 ULPs
2702 '``range``' Metadata
2703 ^^^^^^^^^^^^^^^^^^^^
2705 ``range`` metadata may be attached only to loads of integer types. It
2706 expresses the possible ranges the loaded value is in. The ranges are
2707 represented with a flattened list of integers. The loaded value is known
2708 to be in the union of the ranges defined by each consecutive pair. Each
2709 pair has the following properties:
2711 - The type must match the type loaded by the instruction.
2712 - The pair ``a,b`` represents the range ``[a,b)``.
2713 - Both ``a`` and ``b`` are constants.
2714 - The range is allowed to wrap.
2715 - The range should not represent the full or empty set. That is,
2718 In addition, the pairs must be in signed order of the lower bound and
2719 they must be non-contiguous.
2723 .. code-block:: llvm
2725 %a = load i8* %x, align 1, !range !0 ; Can only be 0 or 1
2726 %b = load i8* %y, align 1, !range !1 ; Can only be 255 (-1), 0 or 1
2727 %c = load i8* %z, align 1, !range !2 ; Can only be 0, 1, 3, 4 or 5
2728 %d = load i8* %z, align 1, !range !3 ; Can only be -2, -1, 3, 4 or 5
2730 !0 = metadata !{ i8 0, i8 2 }
2731 !1 = metadata !{ i8 255, i8 2 }
2732 !2 = metadata !{ i8 0, i8 2, i8 3, i8 6 }
2733 !3 = metadata !{ i8 -2, i8 0, i8 3, i8 6 }
2738 It is sometimes useful to attach information to loop constructs. Currently,
2739 loop metadata is implemented as metadata attached to the branch instruction
2740 in the loop latch block. This type of metadata refer to a metadata node that is
2741 guaranteed to be separate for each loop. The loop identifier metadata is
2742 specified with the name ``llvm.loop``.
2744 The loop identifier metadata is implemented using a metadata that refers to
2745 itself to avoid merging it with any other identifier metadata, e.g.,
2746 during module linkage or function inlining. That is, each loop should refer
2747 to their own identification metadata even if they reside in separate functions.
2748 The following example contains loop identifier metadata for two separate loop
2751 .. code-block:: llvm
2753 !0 = metadata !{ metadata !0 }
2754 !1 = metadata !{ metadata !1 }
2756 The loop identifier metadata can be used to specify additional per-loop
2757 metadata. Any operands after the first operand can be treated as user-defined
2758 metadata. For example the ``llvm.vectorizer.unroll`` metadata is understood
2759 by the loop vectorizer to indicate how many times to unroll the loop:
2761 .. code-block:: llvm
2763 br i1 %exitcond, label %._crit_edge, label %.lr.ph, !llvm.loop !0
2765 !0 = metadata !{ metadata !0, metadata !1 }
2766 !1 = metadata !{ metadata !"llvm.vectorizer.unroll", i32 2 }
2771 Metadata types used to annotate memory accesses with information helpful
2772 for optimizations are prefixed with ``llvm.mem``.
2774 '``llvm.mem.parallel_loop_access``' Metadata
2775 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2777 For a loop to be parallel, in addition to using
2778 the ``llvm.loop`` metadata to mark the loop latch branch instruction,
2779 also all of the memory accessing instructions in the loop body need to be
2780 marked with the ``llvm.mem.parallel_loop_access`` metadata. If there
2781 is at least one memory accessing instruction not marked with the metadata,
2782 the loop must be considered a sequential loop. This causes parallel loops to be
2783 converted to sequential loops due to optimization passes that are unaware of
2784 the parallel semantics and that insert new memory instructions to the loop
2787 Example of a loop that is considered parallel due to its correct use of
2788 both ``llvm.loop`` and ``llvm.mem.parallel_loop_access``
2789 metadata types that refer to the same loop identifier metadata.
2791 .. code-block:: llvm
2795 %val0 = load i32* %arrayidx, !llvm.mem.parallel_loop_access !0
2797 store i32 %val0, i32* %arrayidx1, !llvm.mem.parallel_loop_access !0
2799 br i1 %exitcond, label %for.end, label %for.body, !llvm.loop !0
2803 !0 = metadata !{ metadata !0 }
2805 It is also possible to have nested parallel loops. In that case the
2806 memory accesses refer to a list of loop identifier metadata nodes instead of
2807 the loop identifier metadata node directly:
2809 .. code-block:: llvm
2813 %val1 = load i32* %arrayidx3, !llvm.mem.parallel_loop_access !2
2815 br label %inner.for.body
2819 %val0 = load i32* %arrayidx1, !llvm.mem.parallel_loop_access !0
2821 store i32 %val0, i32* %arrayidx2, !llvm.mem.parallel_loop_access !0
2823 br i1 %exitcond, label %inner.for.end, label %inner.for.body, !llvm.loop !1
2827 store i32 %val1, i32* %arrayidx4, !llvm.mem.parallel_loop_access !2
2829 br i1 %exitcond, label %outer.for.end, label %outer.for.body, !llvm.loop !2
2831 outer.for.end: ; preds = %for.body
2833 !0 = metadata !{ metadata !1, metadata !2 } ; a list of loop identifiers
2834 !1 = metadata !{ metadata !1 } ; an identifier for the inner loop
2835 !2 = metadata !{ metadata !2 } ; an identifier for the outer loop
2837 '``llvm.vectorizer``'
2838 ^^^^^^^^^^^^^^^^^^^^^
2840 Metadata prefixed with ``llvm.vectorizer`` is used to control per-loop
2841 vectorization parameters such as vectorization factor and unroll factor.
2843 ``llvm.vectorizer`` metadata should be used in conjunction with ``llvm.loop``
2844 loop identification metadata.
2846 '``llvm.vectorizer.unroll``' Metadata
2847 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2849 This metadata instructs the loop vectorizer to unroll the specified
2850 loop exactly ``N`` times.
2852 The first operand is the string ``llvm.vectorizer.unroll`` and the second
2853 operand is an integer specifying the unroll factor. For example:
2855 .. code-block:: llvm
2857 !0 = metadata !{ metadata !"llvm.vectorizer.unroll", i32 4 }
2859 Note that setting ``llvm.vectorizer.unroll`` to 1 disables unrolling of the
2862 If ``llvm.vectorizer.unroll`` is set to 0 then the amount of unrolling will be
2863 determined automatically.
2865 '``llvm.vectorizer.width``' Metadata
2866 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2868 This metadata sets the target width of the vectorizer to ``N``. Without
2869 this metadata, the vectorizer will choose a width automatically.
2870 Regardless of this metadata, the vectorizer will only vectorize loops if
2871 it believes it is valid to do so.
2873 The first operand is the string ``llvm.vectorizer.width`` and the second
2874 operand is an integer specifying the width. For example:
2876 .. code-block:: llvm
2878 !0 = metadata !{ metadata !"llvm.vectorizer.width", i32 4 }
2880 Note that setting ``llvm.vectorizer.width`` to 1 disables vectorization of the
2883 If ``llvm.vectorizer.width`` is set to 0 then the width will be determined
2886 Module Flags Metadata
2887 =====================
2889 Information about the module as a whole is difficult to convey to LLVM's
2890 subsystems. The LLVM IR isn't sufficient to transmit this information.
2891 The ``llvm.module.flags`` named metadata exists in order to facilitate
2892 this. These flags are in the form of key / value pairs --- much like a
2893 dictionary --- making it easy for any subsystem who cares about a flag to
2896 The ``llvm.module.flags`` metadata contains a list of metadata triplets.
2897 Each triplet has the following form:
2899 - The first element is a *behavior* flag, which specifies the behavior
2900 when two (or more) modules are merged together, and it encounters two
2901 (or more) metadata with the same ID. The supported behaviors are
2903 - The second element is a metadata string that is a unique ID for the
2904 metadata. Each module may only have one flag entry for each unique ID (not
2905 including entries with the **Require** behavior).
2906 - The third element is the value of the flag.
2908 When two (or more) modules are merged together, the resulting
2909 ``llvm.module.flags`` metadata is the union of the modules' flags. That is, for
2910 each unique metadata ID string, there will be exactly one entry in the merged
2911 modules ``llvm.module.flags`` metadata table, and the value for that entry will
2912 be determined by the merge behavior flag, as described below. The only exception
2913 is that entries with the *Require* behavior are always preserved.
2915 The following behaviors are supported:
2926 Emits an error if two values disagree, otherwise the resulting value
2927 is that of the operands.
2931 Emits a warning if two values disagree. The result value will be the
2932 operand for the flag from the first module being linked.
2936 Adds a requirement that another module flag be present and have a
2937 specified value after linking is performed. The value must be a
2938 metadata pair, where the first element of the pair is the ID of the
2939 module flag to be restricted, and the second element of the pair is
2940 the value the module flag should be restricted to. This behavior can
2941 be used to restrict the allowable results (via triggering of an
2942 error) of linking IDs with the **Override** behavior.
2946 Uses the specified value, regardless of the behavior or value of the
2947 other module. If both modules specify **Override**, but the values
2948 differ, an error will be emitted.
2952 Appends the two values, which are required to be metadata nodes.
2956 Appends the two values, which are required to be metadata
2957 nodes. However, duplicate entries in the second list are dropped
2958 during the append operation.
2960 It is an error for a particular unique flag ID to have multiple behaviors,
2961 except in the case of **Require** (which adds restrictions on another metadata
2962 value) or **Override**.
2964 An example of module flags:
2966 .. code-block:: llvm
2968 !0 = metadata !{ i32 1, metadata !"foo", i32 1 }
2969 !1 = metadata !{ i32 4, metadata !"bar", i32 37 }
2970 !2 = metadata !{ i32 2, metadata !"qux", i32 42 }
2971 !3 = metadata !{ i32 3, metadata !"qux",
2973 metadata !"foo", i32 1
2976 !llvm.module.flags = !{ !0, !1, !2, !3 }
2978 - Metadata ``!0`` has the ID ``!"foo"`` and the value '1'. The behavior
2979 if two or more ``!"foo"`` flags are seen is to emit an error if their
2980 values are not equal.
2982 - Metadata ``!1`` has the ID ``!"bar"`` and the value '37'. The
2983 behavior if two or more ``!"bar"`` flags are seen is to use the value
2986 - Metadata ``!2`` has the ID ``!"qux"`` and the value '42'. The
2987 behavior if two or more ``!"qux"`` flags are seen is to emit a
2988 warning if their values are not equal.
2990 - Metadata ``!3`` has the ID ``!"qux"`` and the value:
2994 metadata !{ metadata !"foo", i32 1 }
2996 The behavior is to emit an error if the ``llvm.module.flags`` does not
2997 contain a flag with the ID ``!"foo"`` that has the value '1' after linking is
3000 Objective-C Garbage Collection Module Flags Metadata
3001 ----------------------------------------------------
3003 On the Mach-O platform, Objective-C stores metadata about garbage
3004 collection in a special section called "image info". The metadata
3005 consists of a version number and a bitmask specifying what types of
3006 garbage collection are supported (if any) by the file. If two or more
3007 modules are linked together their garbage collection metadata needs to
3008 be merged rather than appended together.
3010 The Objective-C garbage collection module flags metadata consists of the
3011 following key-value pairs:
3020 * - ``Objective-C Version``
3021 - **[Required]** --- The Objective-C ABI version. Valid values are 1 and 2.
3023 * - ``Objective-C Image Info Version``
3024 - **[Required]** --- The version of the image info section. Currently
3027 * - ``Objective-C Image Info Section``
3028 - **[Required]** --- The section to place the metadata. Valid values are
3029 ``"__OBJC, __image_info, regular"`` for Objective-C ABI version 1, and
3030 ``"__DATA,__objc_imageinfo, regular, no_dead_strip"`` for
3031 Objective-C ABI version 2.
3033 * - ``Objective-C Garbage Collection``
3034 - **[Required]** --- Specifies whether garbage collection is supported or
3035 not. Valid values are 0, for no garbage collection, and 2, for garbage
3036 collection supported.
3038 * - ``Objective-C GC Only``
3039 - **[Optional]** --- Specifies that only garbage collection is supported.
3040 If present, its value must be 6. This flag requires that the
3041 ``Objective-C Garbage Collection`` flag have the value 2.
3043 Some important flag interactions:
3045 - If a module with ``Objective-C Garbage Collection`` set to 0 is
3046 merged with a module with ``Objective-C Garbage Collection`` set to
3047 2, then the resulting module has the
3048 ``Objective-C Garbage Collection`` flag set to 0.
3049 - A module with ``Objective-C Garbage Collection`` set to 0 cannot be
3050 merged with a module with ``Objective-C GC Only`` set to 6.
3052 Automatic Linker Flags Module Flags Metadata
3053 --------------------------------------------
3055 Some targets support embedding flags to the linker inside individual object
3056 files. Typically this is used in conjunction with language extensions which
3057 allow source files to explicitly declare the libraries they depend on, and have
3058 these automatically be transmitted to the linker via object files.
3060 These flags are encoded in the IR using metadata in the module flags section,
3061 using the ``Linker Options`` key. The merge behavior for this flag is required
3062 to be ``AppendUnique``, and the value for the key is expected to be a metadata
3063 node which should be a list of other metadata nodes, each of which should be a
3064 list of metadata strings defining linker options.
3066 For example, the following metadata section specifies two separate sets of
3067 linker options, presumably to link against ``libz`` and the ``Cocoa``
3070 !0 = metadata !{ i32 6, metadata !"Linker Options",
3072 metadata !{ metadata !"-lz" },
3073 metadata !{ metadata !"-framework", metadata !"Cocoa" } } }
3074 !llvm.module.flags = !{ !0 }
3076 The metadata encoding as lists of lists of options, as opposed to a collapsed
3077 list of options, is chosen so that the IR encoding can use multiple option
3078 strings to specify e.g., a single library, while still having that specifier be
3079 preserved as an atomic element that can be recognized by a target specific
3080 assembly writer or object file emitter.
3082 Each individual option is required to be either a valid option for the target's
3083 linker, or an option that is reserved by the target specific assembly writer or
3084 object file emitter. No other aspect of these options is defined by the IR.
3086 .. _intrinsicglobalvariables:
3088 Intrinsic Global Variables
3089 ==========================
3091 LLVM has a number of "magic" global variables that contain data that
3092 affect code generation or other IR semantics. These are documented here.
3093 All globals of this sort should have a section specified as
3094 "``llvm.metadata``". This section and all globals that start with
3095 "``llvm.``" are reserved for use by LLVM.
3099 The '``llvm.used``' Global Variable
3100 -----------------------------------
3102 The ``@llvm.used`` global is an array which has
3103 :ref:`appending linkage <linkage_appending>`. This array contains a list of
3104 pointers to named global variables, functions and aliases which may optionally
3105 have a pointer cast formed of bitcast or getelementptr. For example, a legal
3108 .. code-block:: llvm
3113 @llvm.used = appending global [2 x i8*] [
3115 i8* bitcast (i32* @Y to i8*)
3116 ], section "llvm.metadata"
3118 If a symbol appears in the ``@llvm.used`` list, then the compiler, assembler,
3119 and linker are required to treat the symbol as if there is a reference to the
3120 symbol that it cannot see (which is why they have to be named). For example, if
3121 a variable has internal linkage and no references other than that from the
3122 ``@llvm.used`` list, it cannot be deleted. This is commonly used to represent
3123 references from inline asms and other things the compiler cannot "see", and
3124 corresponds to "``attribute((used))``" in GNU C.
3126 On some targets, the code generator must emit a directive to the
3127 assembler or object file to prevent the assembler and linker from
3128 molesting the symbol.
3130 .. _gv_llvmcompilerused:
3132 The '``llvm.compiler.used``' Global Variable
3133 --------------------------------------------
3135 The ``@llvm.compiler.used`` directive is the same as the ``@llvm.used``
3136 directive, except that it only prevents the compiler from touching the
3137 symbol. On targets that support it, this allows an intelligent linker to
3138 optimize references to the symbol without being impeded as it would be
3141 This is a rare construct that should only be used in rare circumstances,
3142 and should not be exposed to source languages.
3144 .. _gv_llvmglobalctors:
3146 The '``llvm.global_ctors``' Global Variable
3147 -------------------------------------------
3149 .. code-block:: llvm
3151 %0 = type { i32, void ()* }
3152 @llvm.global_ctors = appending global [1 x %0] [%0 { i32 65535, void ()* @ctor }]
3154 The ``@llvm.global_ctors`` array contains a list of constructor
3155 functions and associated priorities. The functions referenced by this
3156 array will be called in ascending order of priority (i.e. lowest first)
3157 when the module is loaded. The order of functions with the same priority
3160 .. _llvmglobaldtors:
3162 The '``llvm.global_dtors``' Global Variable
3163 -------------------------------------------
3165 .. code-block:: llvm
3167 %0 = type { i32, void ()* }
3168 @llvm.global_dtors = appending global [1 x %0] [%0 { i32 65535, void ()* @dtor }]
3170 The ``@llvm.global_dtors`` array contains a list of destructor functions
3171 and associated priorities. The functions referenced by this array will
3172 be called in descending order of priority (i.e. highest first) when the
3173 module is loaded. The order of functions with the same priority is not
3176 Instruction Reference
3177 =====================
3179 The LLVM instruction set consists of several different classifications
3180 of instructions: :ref:`terminator instructions <terminators>`, :ref:`binary
3181 instructions <binaryops>`, :ref:`bitwise binary
3182 instructions <bitwiseops>`, :ref:`memory instructions <memoryops>`, and
3183 :ref:`other instructions <otherops>`.
3187 Terminator Instructions
3188 -----------------------
3190 As mentioned :ref:`previously <functionstructure>`, every basic block in a
3191 program ends with a "Terminator" instruction, which indicates which
3192 block should be executed after the current block is finished. These
3193 terminator instructions typically yield a '``void``' value: they produce
3194 control flow, not values (the one exception being the
3195 ':ref:`invoke <i_invoke>`' instruction).
3197 The terminator instructions are: ':ref:`ret <i_ret>`',
3198 ':ref:`br <i_br>`', ':ref:`switch <i_switch>`',
3199 ':ref:`indirectbr <i_indirectbr>`', ':ref:`invoke <i_invoke>`',
3200 ':ref:`resume <i_resume>`', and ':ref:`unreachable <i_unreachable>`'.
3204 '``ret``' Instruction
3205 ^^^^^^^^^^^^^^^^^^^^^
3212 ret <type> <value> ; Return a value from a non-void function
3213 ret void ; Return from void function
3218 The '``ret``' instruction is used to return control flow (and optionally
3219 a value) from a function back to the caller.
3221 There are two forms of the '``ret``' instruction: one that returns a
3222 value and then causes control flow, and one that just causes control
3228 The '``ret``' instruction optionally accepts a single argument, the
3229 return value. The type of the return value must be a ':ref:`first
3230 class <t_firstclass>`' type.
3232 A function is not :ref:`well formed <wellformed>` if it it has a non-void
3233 return type and contains a '``ret``' instruction with no return value or
3234 a return value with a type that does not match its type, or if it has a
3235 void return type and contains a '``ret``' instruction with a return
3241 When the '``ret``' instruction is executed, control flow returns back to
3242 the calling function's context. If the caller is a
3243 ":ref:`call <i_call>`" instruction, execution continues at the
3244 instruction after the call. If the caller was an
3245 ":ref:`invoke <i_invoke>`" instruction, execution continues at the
3246 beginning of the "normal" destination block. If the instruction returns
3247 a value, that value shall set the call or invoke instruction's return
3253 .. code-block:: llvm
3255 ret i32 5 ; Return an integer value of 5
3256 ret void ; Return from a void function
3257 ret { i32, i8 } { i32 4, i8 2 } ; Return a struct of values 4 and 2
3261 '``br``' Instruction
3262 ^^^^^^^^^^^^^^^^^^^^
3269 br i1 <cond>, label <iftrue>, label <iffalse>
3270 br label <dest> ; Unconditional branch
3275 The '``br``' instruction is used to cause control flow to transfer to a
3276 different basic block in the current function. There are two forms of
3277 this instruction, corresponding to a conditional branch and an
3278 unconditional branch.
3283 The conditional branch form of the '``br``' instruction takes a single
3284 '``i1``' value and two '``label``' values. The unconditional form of the
3285 '``br``' instruction takes a single '``label``' value as a target.
3290 Upon execution of a conditional '``br``' instruction, the '``i1``'
3291 argument is evaluated. If the value is ``true``, control flows to the
3292 '``iftrue``' ``label`` argument. If "cond" is ``false``, control flows
3293 to the '``iffalse``' ``label`` argument.
3298 .. code-block:: llvm
3301 %cond = icmp eq i32 %a, %b
3302 br i1 %cond, label %IfEqual, label %IfUnequal
3310 '``switch``' Instruction
3311 ^^^^^^^^^^^^^^^^^^^^^^^^
3318 switch <intty> <value>, label <defaultdest> [ <intty> <val>, label <dest> ... ]
3323 The '``switch``' instruction is used to transfer control flow to one of
3324 several different places. It is a generalization of the '``br``'
3325 instruction, allowing a branch to occur to one of many possible
3331 The '``switch``' instruction uses three parameters: an integer
3332 comparison value '``value``', a default '``label``' destination, and an
3333 array of pairs of comparison value constants and '``label``'s. The table
3334 is not allowed to contain duplicate constant entries.
3339 The ``switch`` instruction specifies a table of values and destinations.
3340 When the '``switch``' instruction is executed, this table is searched
3341 for the given value. If the value is found, control flow is transferred
3342 to the corresponding destination; otherwise, control flow is transferred
3343 to the default destination.
3348 Depending on properties of the target machine and the particular
3349 ``switch`` instruction, this instruction may be code generated in
3350 different ways. For example, it could be generated as a series of
3351 chained conditional branches or with a lookup table.
3356 .. code-block:: llvm
3358 ; Emulate a conditional br instruction
3359 %Val = zext i1 %value to i32
3360 switch i32 %Val, label %truedest [ i32 0, label %falsedest ]
3362 ; Emulate an unconditional br instruction
3363 switch i32 0, label %dest [ ]
3365 ; Implement a jump table:
3366 switch i32 %val, label %otherwise [ i32 0, label %onzero
3368 i32 2, label %ontwo ]
3372 '``indirectbr``' Instruction
3373 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
3380 indirectbr <somety>* <address>, [ label <dest1>, label <dest2>, ... ]
3385 The '``indirectbr``' instruction implements an indirect branch to a
3386 label within the current function, whose address is specified by
3387 "``address``". Address must be derived from a
3388 :ref:`blockaddress <blockaddress>` constant.
3393 The '``address``' argument is the address of the label to jump to. The
3394 rest of the arguments indicate the full set of possible destinations
3395 that the address may point to. Blocks are allowed to occur multiple
3396 times in the destination list, though this isn't particularly useful.
3398 This destination list is required so that dataflow analysis has an
3399 accurate understanding of the CFG.
3404 Control transfers to the block specified in the address argument. All
3405 possible destination blocks must be listed in the label list, otherwise
3406 this instruction has undefined behavior. This implies that jumps to
3407 labels defined in other functions have undefined behavior as well.
3412 This is typically implemented with a jump through a register.
3417 .. code-block:: llvm
3419 indirectbr i8* %Addr, [ label %bb1, label %bb2, label %bb3 ]
3423 '``invoke``' Instruction
3424 ^^^^^^^^^^^^^^^^^^^^^^^^
3431 <result> = invoke [cconv] [ret attrs] <ptr to function ty> <function ptr val>(<function args>) [fn attrs]
3432 to label <normal label> unwind label <exception label>
3437 The '``invoke``' instruction causes control to transfer to a specified
3438 function, with the possibility of control flow transfer to either the
3439 '``normal``' label or the '``exception``' label. If the callee function
3440 returns with the "``ret``" instruction, control flow will return to the
3441 "normal" label. If the callee (or any indirect callees) returns via the
3442 ":ref:`resume <i_resume>`" instruction or other exception handling
3443 mechanism, control is interrupted and continued at the dynamically
3444 nearest "exception" label.
3446 The '``exception``' label is a `landing
3447 pad <ExceptionHandling.html#overview>`_ for the exception. As such,
3448 '``exception``' label is required to have the
3449 ":ref:`landingpad <i_landingpad>`" instruction, which contains the
3450 information about the behavior of the program after unwinding happens,
3451 as its first non-PHI instruction. The restrictions on the
3452 "``landingpad``" instruction's tightly couples it to the "``invoke``"
3453 instruction, so that the important information contained within the
3454 "``landingpad``" instruction can't be lost through normal code motion.
3459 This instruction requires several arguments:
3461 #. The optional "cconv" marker indicates which :ref:`calling
3462 convention <callingconv>` the call should use. If none is
3463 specified, the call defaults to using C calling conventions.
3464 #. The optional :ref:`Parameter Attributes <paramattrs>` list for return
3465 values. Only '``zeroext``', '``signext``', and '``inreg``' attributes
3467 #. '``ptr to function ty``': shall be the signature of the pointer to
3468 function value being invoked. In most cases, this is a direct
3469 function invocation, but indirect ``invoke``'s are just as possible,
3470 branching off an arbitrary pointer to function value.
3471 #. '``function ptr val``': An LLVM value containing a pointer to a
3472 function to be invoked.
3473 #. '``function args``': argument list whose types match the function
3474 signature argument types and parameter attributes. All arguments must
3475 be of :ref:`first class <t_firstclass>` type. If the function signature
3476 indicates the function accepts a variable number of arguments, the
3477 extra arguments can be specified.
3478 #. '``normal label``': the label reached when the called function
3479 executes a '``ret``' instruction.
3480 #. '``exception label``': the label reached when a callee returns via
3481 the :ref:`resume <i_resume>` instruction or other exception handling
3483 #. The optional :ref:`function attributes <fnattrs>` list. Only
3484 '``noreturn``', '``nounwind``', '``readonly``' and '``readnone``'
3485 attributes are valid here.
3490 This instruction is designed to operate as a standard '``call``'
3491 instruction in most regards. The primary difference is that it
3492 establishes an association with a label, which is used by the runtime
3493 library to unwind the stack.
3495 This instruction is used in languages with destructors to ensure that
3496 proper cleanup is performed in the case of either a ``longjmp`` or a
3497 thrown exception. Additionally, this is important for implementation of
3498 '``catch``' clauses in high-level languages that support them.
3500 For the purposes of the SSA form, the definition of the value returned
3501 by the '``invoke``' instruction is deemed to occur on the edge from the
3502 current block to the "normal" label. If the callee unwinds then no
3503 return value is available.
3508 .. code-block:: llvm
3510 %retval = invoke i32 @Test(i32 15) to label %Continue
3511 unwind label %TestCleanup ; {i32}:retval set
3512 %retval = invoke coldcc i32 %Testfnptr(i32 15) to label %Continue
3513 unwind label %TestCleanup ; {i32}:retval set
3517 '``resume``' Instruction
3518 ^^^^^^^^^^^^^^^^^^^^^^^^
3525 resume <type> <value>
3530 The '``resume``' instruction is a terminator instruction that has no
3536 The '``resume``' instruction requires one argument, which must have the
3537 same type as the result of any '``landingpad``' instruction in the same
3543 The '``resume``' instruction resumes propagation of an existing
3544 (in-flight) exception whose unwinding was interrupted with a
3545 :ref:`landingpad <i_landingpad>` instruction.
3550 .. code-block:: llvm
3552 resume { i8*, i32 } %exn
3556 '``unreachable``' Instruction
3557 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
3569 The '``unreachable``' instruction has no defined semantics. This
3570 instruction is used to inform the optimizer that a particular portion of
3571 the code is not reachable. This can be used to indicate that the code
3572 after a no-return function cannot be reached, and other facts.
3577 The '``unreachable``' instruction has no defined semantics.
3584 Binary operators are used to do most of the computation in a program.
3585 They require two operands of the same type, execute an operation on
3586 them, and produce a single value. The operands might represent multiple
3587 data, as is the case with the :ref:`vector <t_vector>` data type. The
3588 result value has the same type as its operands.
3590 There are several different binary operators:
3594 '``add``' Instruction
3595 ^^^^^^^^^^^^^^^^^^^^^
3602 <result> = add <ty> <op1>, <op2> ; yields {ty}:result
3603 <result> = add nuw <ty> <op1>, <op2> ; yields {ty}:result
3604 <result> = add nsw <ty> <op1>, <op2> ; yields {ty}:result
3605 <result> = add nuw nsw <ty> <op1>, <op2> ; yields {ty}:result
3610 The '``add``' instruction returns the sum of its two operands.
3615 The two arguments to the '``add``' instruction must be
3616 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
3617 arguments must have identical types.
3622 The value produced is the integer sum of the two operands.
3624 If the sum has unsigned overflow, the result returned is the
3625 mathematical result modulo 2\ :sup:`n`\ , where n is the bit width of
3628 Because LLVM integers use a two's complement representation, this
3629 instruction is appropriate for both signed and unsigned integers.
3631 ``nuw`` and ``nsw`` stand for "No Unsigned Wrap" and "No Signed Wrap",
3632 respectively. If the ``nuw`` and/or ``nsw`` keywords are present, the
3633 result value of the ``add`` is a :ref:`poison value <poisonvalues>` if
3634 unsigned and/or signed overflow, respectively, occurs.
3639 .. code-block:: llvm
3641 <result> = add i32 4, %var ; yields {i32}:result = 4 + %var
3645 '``fadd``' Instruction
3646 ^^^^^^^^^^^^^^^^^^^^^^
3653 <result> = fadd [fast-math flags]* <ty> <op1>, <op2> ; yields {ty}:result
3658 The '``fadd``' instruction returns the sum of its two operands.
3663 The two arguments to the '``fadd``' instruction must be :ref:`floating
3664 point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
3665 Both arguments must have identical types.
3670 The value produced is the floating point sum of the two operands. This
3671 instruction can also take any number of :ref:`fast-math flags <fastmath>`,
3672 which are optimization hints to enable otherwise unsafe floating point
3678 .. code-block:: llvm
3680 <result> = fadd float 4.0, %var ; yields {float}:result = 4.0 + %var
3682 '``sub``' Instruction
3683 ^^^^^^^^^^^^^^^^^^^^^
3690 <result> = sub <ty> <op1>, <op2> ; yields {ty}:result
3691 <result> = sub nuw <ty> <op1>, <op2> ; yields {ty}:result
3692 <result> = sub nsw <ty> <op1>, <op2> ; yields {ty}:result
3693 <result> = sub nuw nsw <ty> <op1>, <op2> ; yields {ty}:result
3698 The '``sub``' instruction returns the difference of its two operands.
3700 Note that the '``sub``' instruction is used to represent the '``neg``'
3701 instruction present in most other intermediate representations.
3706 The two arguments to the '``sub``' instruction must be
3707 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
3708 arguments must have identical types.
3713 The value produced is the integer difference of the two operands.
3715 If the difference has unsigned overflow, the result returned is the
3716 mathematical result modulo 2\ :sup:`n`\ , where n is the bit width of
3719 Because LLVM integers use a two's complement representation, this
3720 instruction is appropriate for both signed and unsigned integers.
3722 ``nuw`` and ``nsw`` stand for "No Unsigned Wrap" and "No Signed Wrap",
3723 respectively. If the ``nuw`` and/or ``nsw`` keywords are present, the
3724 result value of the ``sub`` is a :ref:`poison value <poisonvalues>` if
3725 unsigned and/or signed overflow, respectively, occurs.
3730 .. code-block:: llvm
3732 <result> = sub i32 4, %var ; yields {i32}:result = 4 - %var
3733 <result> = sub i32 0, %val ; yields {i32}:result = -%var
3737 '``fsub``' Instruction
3738 ^^^^^^^^^^^^^^^^^^^^^^
3745 <result> = fsub [fast-math flags]* <ty> <op1>, <op2> ; yields {ty}:result
3750 The '``fsub``' instruction returns the difference of its two operands.
3752 Note that the '``fsub``' instruction is used to represent the '``fneg``'
3753 instruction present in most other intermediate representations.
3758 The two arguments to the '``fsub``' instruction must be :ref:`floating
3759 point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
3760 Both arguments must have identical types.
3765 The value produced is the floating point difference of the two operands.
3766 This instruction can also take any number of :ref:`fast-math
3767 flags <fastmath>`, which are optimization hints to enable otherwise
3768 unsafe floating point optimizations:
3773 .. code-block:: llvm
3775 <result> = fsub float 4.0, %var ; yields {float}:result = 4.0 - %var
3776 <result> = fsub float -0.0, %val ; yields {float}:result = -%var
3778 '``mul``' Instruction
3779 ^^^^^^^^^^^^^^^^^^^^^
3786 <result> = mul <ty> <op1>, <op2> ; yields {ty}:result
3787 <result> = mul nuw <ty> <op1>, <op2> ; yields {ty}:result
3788 <result> = mul nsw <ty> <op1>, <op2> ; yields {ty}:result
3789 <result> = mul nuw nsw <ty> <op1>, <op2> ; yields {ty}:result
3794 The '``mul``' instruction returns the product of its two operands.
3799 The two arguments to the '``mul``' instruction must be
3800 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
3801 arguments must have identical types.
3806 The value produced is the integer product of the two operands.
3808 If the result of the multiplication has unsigned overflow, the result
3809 returned is the mathematical result modulo 2\ :sup:`n`\ , where n is the
3810 bit width of the result.
3812 Because LLVM integers use a two's complement representation, and the
3813 result is the same width as the operands, this instruction returns the
3814 correct result for both signed and unsigned integers. If a full product
3815 (e.g. ``i32`` * ``i32`` -> ``i64``) is needed, the operands should be
3816 sign-extended or zero-extended as appropriate to the width of the full
3819 ``nuw`` and ``nsw`` stand for "No Unsigned Wrap" and "No Signed Wrap",
3820 respectively. If the ``nuw`` and/or ``nsw`` keywords are present, the
3821 result value of the ``mul`` is a :ref:`poison value <poisonvalues>` if
3822 unsigned and/or signed overflow, respectively, occurs.
3827 .. code-block:: llvm
3829 <result> = mul i32 4, %var ; yields {i32}:result = 4 * %var
3833 '``fmul``' Instruction
3834 ^^^^^^^^^^^^^^^^^^^^^^
3841 <result> = fmul [fast-math flags]* <ty> <op1>, <op2> ; yields {ty}:result
3846 The '``fmul``' instruction returns the product of its two operands.
3851 The two arguments to the '``fmul``' instruction must be :ref:`floating
3852 point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
3853 Both arguments must have identical types.
3858 The value produced is the floating point product of the two operands.
3859 This instruction can also take any number of :ref:`fast-math
3860 flags <fastmath>`, which are optimization hints to enable otherwise
3861 unsafe floating point optimizations:
3866 .. code-block:: llvm
3868 <result> = fmul float 4.0, %var ; yields {float}:result = 4.0 * %var
3870 '``udiv``' Instruction
3871 ^^^^^^^^^^^^^^^^^^^^^^
3878 <result> = udiv <ty> <op1>, <op2> ; yields {ty}:result
3879 <result> = udiv exact <ty> <op1>, <op2> ; yields {ty}:result
3884 The '``udiv``' instruction returns the quotient of its two operands.
3889 The two arguments to the '``udiv``' instruction must be
3890 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
3891 arguments must have identical types.
3896 The value produced is the unsigned integer quotient of the two operands.
3898 Note that unsigned integer division and signed integer division are
3899 distinct operations; for signed integer division, use '``sdiv``'.
3901 Division by zero leads to undefined behavior.
3903 If the ``exact`` keyword is present, the result value of the ``udiv`` is
3904 a :ref:`poison value <poisonvalues>` if %op1 is not a multiple of %op2 (as
3905 such, "((a udiv exact b) mul b) == a").
3910 .. code-block:: llvm
3912 <result> = udiv i32 4, %var ; yields {i32}:result = 4 / %var
3914 '``sdiv``' Instruction
3915 ^^^^^^^^^^^^^^^^^^^^^^
3922 <result> = sdiv <ty> <op1>, <op2> ; yields {ty}:result
3923 <result> = sdiv exact <ty> <op1>, <op2> ; yields {ty}:result
3928 The '``sdiv``' instruction returns the quotient of its two operands.
3933 The two arguments to the '``sdiv``' instruction must be
3934 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
3935 arguments must have identical types.
3940 The value produced is the signed integer quotient of the two operands
3941 rounded towards zero.
3943 Note that signed integer division and unsigned integer division are
3944 distinct operations; for unsigned integer division, use '``udiv``'.
3946 Division by zero leads to undefined behavior. Overflow also leads to
3947 undefined behavior; this is a rare case, but can occur, for example, by
3948 doing a 32-bit division of -2147483648 by -1.
3950 If the ``exact`` keyword is present, the result value of the ``sdiv`` is
3951 a :ref:`poison value <poisonvalues>` if the result would be rounded.
3956 .. code-block:: llvm
3958 <result> = sdiv i32 4, %var ; yields {i32}:result = 4 / %var
3962 '``fdiv``' Instruction
3963 ^^^^^^^^^^^^^^^^^^^^^^
3970 <result> = fdiv [fast-math flags]* <ty> <op1>, <op2> ; yields {ty}:result
3975 The '``fdiv``' instruction returns the quotient of its two operands.
3980 The two arguments to the '``fdiv``' instruction must be :ref:`floating
3981 point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
3982 Both arguments must have identical types.
3987 The value produced is the floating point quotient of the two operands.
3988 This instruction can also take any number of :ref:`fast-math
3989 flags <fastmath>`, which are optimization hints to enable otherwise
3990 unsafe floating point optimizations:
3995 .. code-block:: llvm
3997 <result> = fdiv float 4.0, %var ; yields {float}:result = 4.0 / %var
3999 '``urem``' Instruction
4000 ^^^^^^^^^^^^^^^^^^^^^^
4007 <result> = urem <ty> <op1>, <op2> ; yields {ty}:result
4012 The '``urem``' instruction returns the remainder from the unsigned
4013 division of its two arguments.
4018 The two arguments to the '``urem``' instruction must be
4019 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
4020 arguments must have identical types.
4025 This instruction returns the unsigned integer *remainder* of a division.
4026 This instruction always performs an unsigned division to get the
4029 Note that unsigned integer remainder and signed integer remainder are
4030 distinct operations; for signed integer remainder, use '``srem``'.
4032 Taking the remainder of a division by zero leads to undefined behavior.
4037 .. code-block:: llvm
4039 <result> = urem i32 4, %var ; yields {i32}:result = 4 % %var
4041 '``srem``' Instruction
4042 ^^^^^^^^^^^^^^^^^^^^^^
4049 <result> = srem <ty> <op1>, <op2> ; yields {ty}:result
4054 The '``srem``' instruction returns the remainder from the signed
4055 division of its two operands. This instruction can also take
4056 :ref:`vector <t_vector>` versions of the values in which case the elements
4062 The two arguments to the '``srem``' instruction must be
4063 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
4064 arguments must have identical types.
4069 This instruction returns the *remainder* of a division (where the result
4070 is either zero or has the same sign as the dividend, ``op1``), not the
4071 *modulo* operator (where the result is either zero or has the same sign
4072 as the divisor, ``op2``) of a value. For more information about the
4073 difference, see `The Math
4074 Forum <http://mathforum.org/dr.math/problems/anne.4.28.99.html>`_. For a
4075 table of how this is implemented in various languages, please see
4077 operation <http://en.wikipedia.org/wiki/Modulo_operation>`_.
4079 Note that signed integer remainder and unsigned integer remainder are
4080 distinct operations; for unsigned integer remainder, use '``urem``'.
4082 Taking the remainder of a division by zero leads to undefined behavior.
4083 Overflow also leads to undefined behavior; this is a rare case, but can
4084 occur, for example, by taking the remainder of a 32-bit division of
4085 -2147483648 by -1. (The remainder doesn't actually overflow, but this
4086 rule lets srem be implemented using instructions that return both the
4087 result of the division and the remainder.)
4092 .. code-block:: llvm
4094 <result> = srem i32 4, %var ; yields {i32}:result = 4 % %var
4098 '``frem``' Instruction
4099 ^^^^^^^^^^^^^^^^^^^^^^
4106 <result> = frem [fast-math flags]* <ty> <op1>, <op2> ; yields {ty}:result
4111 The '``frem``' instruction returns the remainder from the division of
4117 The two arguments to the '``frem``' instruction must be :ref:`floating
4118 point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
4119 Both arguments must have identical types.
4124 This instruction returns the *remainder* of a division. The remainder
4125 has the same sign as the dividend. This instruction can also take any
4126 number of :ref:`fast-math flags <fastmath>`, which are optimization hints
4127 to enable otherwise unsafe floating point optimizations:
4132 .. code-block:: llvm
4134 <result> = frem float 4.0, %var ; yields {float}:result = 4.0 % %var
4138 Bitwise Binary Operations
4139 -------------------------
4141 Bitwise binary operators are used to do various forms of bit-twiddling
4142 in a program. They are generally very efficient instructions and can
4143 commonly be strength reduced from other instructions. They require two
4144 operands of the same type, execute an operation on them, and produce a
4145 single value. The resulting value is the same type as its operands.
4147 '``shl``' Instruction
4148 ^^^^^^^^^^^^^^^^^^^^^
4155 <result> = shl <ty> <op1>, <op2> ; yields {ty}:result
4156 <result> = shl nuw <ty> <op1>, <op2> ; yields {ty}:result
4157 <result> = shl nsw <ty> <op1>, <op2> ; yields {ty}:result
4158 <result> = shl nuw nsw <ty> <op1>, <op2> ; yields {ty}:result
4163 The '``shl``' instruction returns the first operand shifted to the left
4164 a specified number of bits.
4169 Both arguments to the '``shl``' instruction must be the same
4170 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer type.
4171 '``op2``' is treated as an unsigned value.
4176 The value produced is ``op1`` \* 2\ :sup:`op2` mod 2\ :sup:`n`,
4177 where ``n`` is the width of the result. If ``op2`` is (statically or
4178 dynamically) negative or equal to or larger than the number of bits in
4179 ``op1``, the result is undefined. If the arguments are vectors, each
4180 vector element of ``op1`` is shifted by the corresponding shift amount
4183 If the ``nuw`` keyword is present, then the shift produces a :ref:`poison
4184 value <poisonvalues>` if it shifts out any non-zero bits. If the
4185 ``nsw`` keyword is present, then the shift produces a :ref:`poison
4186 value <poisonvalues>` if it shifts out any bits that disagree with the
4187 resultant sign bit. As such, NUW/NSW have the same semantics as they
4188 would if the shift were expressed as a mul instruction with the same
4189 nsw/nuw bits in (mul %op1, (shl 1, %op2)).
4194 .. code-block:: llvm
4196 <result> = shl i32 4, %var ; yields {i32}: 4 << %var
4197 <result> = shl i32 4, 2 ; yields {i32}: 16
4198 <result> = shl i32 1, 10 ; yields {i32}: 1024
4199 <result> = shl i32 1, 32 ; undefined
4200 <result> = shl <2 x i32> < i32 1, i32 1>, < i32 1, i32 2> ; yields: result=<2 x i32> < i32 2, i32 4>
4202 '``lshr``' Instruction
4203 ^^^^^^^^^^^^^^^^^^^^^^
4210 <result> = lshr <ty> <op1>, <op2> ; yields {ty}:result
4211 <result> = lshr exact <ty> <op1>, <op2> ; yields {ty}:result
4216 The '``lshr``' instruction (logical shift right) returns the first
4217 operand shifted to the right a specified number of bits with zero fill.
4222 Both arguments to the '``lshr``' instruction must be the same
4223 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer type.
4224 '``op2``' is treated as an unsigned value.
4229 This instruction always performs a logical shift right operation. The
4230 most significant bits of the result will be filled with zero bits after
4231 the shift. If ``op2`` is (statically or dynamically) equal to or larger
4232 than the number of bits in ``op1``, the result is undefined. If the
4233 arguments are vectors, each vector element of ``op1`` is shifted by the
4234 corresponding shift amount in ``op2``.
4236 If the ``exact`` keyword is present, the result value of the ``lshr`` is
4237 a :ref:`poison value <poisonvalues>` if any of the bits shifted out are
4243 .. code-block:: llvm
4245 <result> = lshr i32 4, 1 ; yields {i32}:result = 2
4246 <result> = lshr i32 4, 2 ; yields {i32}:result = 1
4247 <result> = lshr i8 4, 3 ; yields {i8}:result = 0
4248 <result> = lshr i8 -2, 1 ; yields {i8}:result = 0x7F
4249 <result> = lshr i32 1, 32 ; undefined
4250 <result> = lshr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 2> ; yields: result=<2 x i32> < i32 0x7FFFFFFF, i32 1>
4252 '``ashr``' Instruction
4253 ^^^^^^^^^^^^^^^^^^^^^^
4260 <result> = ashr <ty> <op1>, <op2> ; yields {ty}:result
4261 <result> = ashr exact <ty> <op1>, <op2> ; yields {ty}:result
4266 The '``ashr``' instruction (arithmetic shift right) returns the first
4267 operand shifted to the right a specified number of bits with sign
4273 Both arguments to the '``ashr``' instruction must be the same
4274 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer type.
4275 '``op2``' is treated as an unsigned value.
4280 This instruction always performs an arithmetic shift right operation,
4281 The most significant bits of the result will be filled with the sign bit
4282 of ``op1``. If ``op2`` is (statically or dynamically) equal to or larger
4283 than the number of bits in ``op1``, the result is undefined. If the
4284 arguments are vectors, each vector element of ``op1`` is shifted by the
4285 corresponding shift amount in ``op2``.
4287 If the ``exact`` keyword is present, the result value of the ``ashr`` is
4288 a :ref:`poison value <poisonvalues>` if any of the bits shifted out are
4294 .. code-block:: llvm
4296 <result> = ashr i32 4, 1 ; yields {i32}:result = 2
4297 <result> = ashr i32 4, 2 ; yields {i32}:result = 1
4298 <result> = ashr i8 4, 3 ; yields {i8}:result = 0
4299 <result> = ashr i8 -2, 1 ; yields {i8}:result = -1
4300 <result> = ashr i32 1, 32 ; undefined
4301 <result> = ashr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 3> ; yields: result=<2 x i32> < i32 -1, i32 0>
4303 '``and``' Instruction
4304 ^^^^^^^^^^^^^^^^^^^^^
4311 <result> = and <ty> <op1>, <op2> ; yields {ty}:result
4316 The '``and``' instruction returns the bitwise logical and of its two
4322 The two arguments to the '``and``' instruction must be
4323 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
4324 arguments must have identical types.
4329 The truth table used for the '``and``' instruction is:
4346 .. code-block:: llvm
4348 <result> = and i32 4, %var ; yields {i32}:result = 4 & %var
4349 <result> = and i32 15, 40 ; yields {i32}:result = 8
4350 <result> = and i32 4, 8 ; yields {i32}:result = 0
4352 '``or``' Instruction
4353 ^^^^^^^^^^^^^^^^^^^^
4360 <result> = or <ty> <op1>, <op2> ; yields {ty}:result
4365 The '``or``' instruction returns the bitwise logical inclusive or of its
4371 The two arguments to the '``or``' instruction must be
4372 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
4373 arguments must have identical types.
4378 The truth table used for the '``or``' instruction is:
4397 <result> = or i32 4, %var ; yields {i32}:result = 4 | %var
4398 <result> = or i32 15, 40 ; yields {i32}:result = 47
4399 <result> = or i32 4, 8 ; yields {i32}:result = 12
4401 '``xor``' Instruction
4402 ^^^^^^^^^^^^^^^^^^^^^
4409 <result> = xor <ty> <op1>, <op2> ; yields {ty}:result
4414 The '``xor``' instruction returns the bitwise logical exclusive or of
4415 its two operands. The ``xor`` is used to implement the "one's
4416 complement" operation, which is the "~" operator in C.
4421 The two arguments to the '``xor``' instruction must be
4422 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
4423 arguments must have identical types.
4428 The truth table used for the '``xor``' instruction is:
4445 .. code-block:: llvm
4447 <result> = xor i32 4, %var ; yields {i32}:result = 4 ^ %var
4448 <result> = xor i32 15, 40 ; yields {i32}:result = 39
4449 <result> = xor i32 4, 8 ; yields {i32}:result = 12
4450 <result> = xor i32 %V, -1 ; yields {i32}:result = ~%V
4455 LLVM supports several instructions to represent vector operations in a
4456 target-independent manner. These instructions cover the element-access
4457 and vector-specific operations needed to process vectors effectively.
4458 While LLVM does directly support these vector operations, many
4459 sophisticated algorithms will want to use target-specific intrinsics to
4460 take full advantage of a specific target.
4462 .. _i_extractelement:
4464 '``extractelement``' Instruction
4465 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4472 <result> = extractelement <n x <ty>> <val>, i32 <idx> ; yields <ty>
4477 The '``extractelement``' instruction extracts a single scalar element
4478 from a vector at a specified index.
4483 The first operand of an '``extractelement``' instruction is a value of
4484 :ref:`vector <t_vector>` type. The second operand is an index indicating
4485 the position from which to extract the element. The index may be a
4491 The result is a scalar of the same type as the element type of ``val``.
4492 Its value is the value at position ``idx`` of ``val``. If ``idx``
4493 exceeds the length of ``val``, the results are undefined.
4498 .. code-block:: llvm
4500 <result> = extractelement <4 x i32> %vec, i32 0 ; yields i32
4502 .. _i_insertelement:
4504 '``insertelement``' Instruction
4505 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4512 <result> = insertelement <n x <ty>> <val>, <ty> <elt>, i32 <idx> ; yields <n x <ty>>
4517 The '``insertelement``' instruction inserts a scalar element into a
4518 vector at a specified index.
4523 The first operand of an '``insertelement``' instruction is a value of
4524 :ref:`vector <t_vector>` type. The second operand is a scalar value whose
4525 type must equal the element type of the first operand. The third operand
4526 is an index indicating the position at which to insert the value. The
4527 index may be a variable.
4532 The result is a vector of the same type as ``val``. Its element values
4533 are those of ``val`` except at position ``idx``, where it gets the value
4534 ``elt``. If ``idx`` exceeds the length of ``val``, the results are
4540 .. code-block:: llvm
4542 <result> = insertelement <4 x i32> %vec, i32 1, i32 0 ; yields <4 x i32>
4544 .. _i_shufflevector:
4546 '``shufflevector``' Instruction
4547 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4554 <result> = shufflevector <n x <ty>> <v1>, <n x <ty>> <v2>, <m x i32> <mask> ; yields <m x <ty>>
4559 The '``shufflevector``' instruction constructs a permutation of elements
4560 from two input vectors, returning a vector with the same element type as
4561 the input and length that is the same as the shuffle mask.
4566 The first two operands of a '``shufflevector``' instruction are vectors
4567 with the same type. The third argument is a shuffle mask whose element
4568 type is always 'i32'. The result of the instruction is a vector whose
4569 length is the same as the shuffle mask and whose element type is the
4570 same as the element type of the first two operands.
4572 The shuffle mask operand is required to be a constant vector with either
4573 constant integer or undef values.
4578 The elements of the two input vectors are numbered from left to right
4579 across both of the vectors. The shuffle mask operand specifies, for each
4580 element of the result vector, which element of the two input vectors the
4581 result element gets. The element selector may be undef (meaning "don't
4582 care") and the second operand may be undef if performing a shuffle from
4588 .. code-block:: llvm
4590 <result> = shufflevector <4 x i32> %v1, <4 x i32> %v2,
4591 <4 x i32> <i32 0, i32 4, i32 1, i32 5> ; yields <4 x i32>
4592 <result> = shufflevector <4 x i32> %v1, <4 x i32> undef,
4593 <4 x i32> <i32 0, i32 1, i32 2, i32 3> ; yields <4 x i32> - Identity shuffle.
4594 <result> = shufflevector <8 x i32> %v1, <8 x i32> undef,
4595 <4 x i32> <i32 0, i32 1, i32 2, i32 3> ; yields <4 x i32>
4596 <result> = shufflevector <4 x i32> %v1, <4 x i32> %v2,
4597 <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7 > ; yields <8 x i32>
4599 Aggregate Operations
4600 --------------------
4602 LLVM supports several instructions for working with
4603 :ref:`aggregate <t_aggregate>` values.
4607 '``extractvalue``' Instruction
4608 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4615 <result> = extractvalue <aggregate type> <val>, <idx>{, <idx>}*
4620 The '``extractvalue``' instruction extracts the value of a member field
4621 from an :ref:`aggregate <t_aggregate>` value.
4626 The first operand of an '``extractvalue``' instruction is a value of
4627 :ref:`struct <t_struct>` or :ref:`array <t_array>` type. The operands are
4628 constant indices to specify which value to extract in a similar manner
4629 as indices in a '``getelementptr``' instruction.
4631 The major differences to ``getelementptr`` indexing are:
4633 - Since the value being indexed is not a pointer, the first index is
4634 omitted and assumed to be zero.
4635 - At least one index must be specified.
4636 - Not only struct indices but also array indices must be in bounds.
4641 The result is the value at the position in the aggregate specified by
4647 .. code-block:: llvm
4649 <result> = extractvalue {i32, float} %agg, 0 ; yields i32
4653 '``insertvalue``' Instruction
4654 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4661 <result> = insertvalue <aggregate type> <val>, <ty> <elt>, <idx>{, <idx>}* ; yields <aggregate type>
4666 The '``insertvalue``' instruction inserts a value into a member field in
4667 an :ref:`aggregate <t_aggregate>` value.
4672 The first operand of an '``insertvalue``' instruction is a value of
4673 :ref:`struct <t_struct>` or :ref:`array <t_array>` type. The second operand is
4674 a first-class value to insert. The following operands are constant
4675 indices indicating the position at which to insert the value in a
4676 similar manner as indices in a '``extractvalue``' instruction. The value
4677 to insert must have the same type as the value identified by the
4683 The result is an aggregate of the same type as ``val``. Its value is
4684 that of ``val`` except that the value at the position specified by the
4685 indices is that of ``elt``.
4690 .. code-block:: llvm
4692 %agg1 = insertvalue {i32, float} undef, i32 1, 0 ; yields {i32 1, float undef}
4693 %agg2 = insertvalue {i32, float} %agg1, float %val, 1 ; yields {i32 1, float %val}
4694 %agg3 = insertvalue {i32, {float}} %agg1, float %val, 1, 0 ; yields {i32 1, float %val}
4698 Memory Access and Addressing Operations
4699 ---------------------------------------
4701 A key design point of an SSA-based representation is how it represents
4702 memory. In LLVM, no memory locations are in SSA form, which makes things
4703 very simple. This section describes how to read, write, and allocate
4708 '``alloca``' Instruction
4709 ^^^^^^^^^^^^^^^^^^^^^^^^
4716 <result> = alloca <type>[, inalloca][, <ty> <NumElements>][, align <alignment>] ; yields {type*}:result
4721 The '``alloca``' instruction allocates memory on the stack frame of the
4722 currently executing function, to be automatically released when this
4723 function returns to its caller. The object is always allocated in the
4724 generic address space (address space zero).
4729 The '``alloca``' instruction allocates ``sizeof(<type>)*NumElements``
4730 bytes of memory on the runtime stack, returning a pointer of the
4731 appropriate type to the program. If "NumElements" is specified, it is
4732 the number of elements allocated, otherwise "NumElements" is defaulted
4733 to be one. If a constant alignment is specified, the value result of the
4734 allocation is guaranteed to be aligned to at least that boundary. If not
4735 specified, or if zero, the target can choose to align the allocation on
4736 any convenient boundary compatible with the type.
4738 '``type``' may be any sized type.
4743 Memory is allocated; a pointer is returned. The operation is undefined
4744 if there is insufficient stack space for the allocation. '``alloca``'d
4745 memory is automatically released when the function returns. The
4746 '``alloca``' instruction is commonly used to represent automatic
4747 variables that must have an address available. When the function returns
4748 (either with the ``ret`` or ``resume`` instructions), the memory is
4749 reclaimed. Allocating zero bytes is legal, but the result is undefined.
4750 The order in which memory is allocated (ie., which way the stack grows)
4756 .. code-block:: llvm
4758 %ptr = alloca i32 ; yields {i32*}:ptr
4759 %ptr = alloca i32, i32 4 ; yields {i32*}:ptr
4760 %ptr = alloca i32, i32 4, align 1024 ; yields {i32*}:ptr
4761 %ptr = alloca i32, align 1024 ; yields {i32*}:ptr
4765 '``load``' Instruction
4766 ^^^^^^^^^^^^^^^^^^^^^^
4773 <result> = load [volatile] <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>][, !invariant.load !<index>]
4774 <result> = load atomic [volatile] <ty>* <pointer> [singlethread] <ordering>, align <alignment>
4775 !<index> = !{ i32 1 }
4780 The '``load``' instruction is used to read from memory.
4785 The argument to the ``load`` instruction specifies the memory address
4786 from which to load. The pointer must point to a :ref:`first
4787 class <t_firstclass>` type. If the ``load`` is marked as ``volatile``,
4788 then the optimizer is not allowed to modify the number or order of
4789 execution of this ``load`` with other :ref:`volatile
4790 operations <volatile>`.
4792 If the ``load`` is marked as ``atomic``, it takes an extra
4793 :ref:`ordering <ordering>` and optional ``singlethread`` argument. The
4794 ``release`` and ``acq_rel`` orderings are not valid on ``load``
4795 instructions. Atomic loads produce :ref:`defined <memmodel>` results
4796 when they may see multiple atomic stores. The type of the pointee must
4797 be an integer type whose bit width is a power of two greater than or
4798 equal to eight and less than or equal to a target-specific size limit.
4799 ``align`` must be explicitly specified on atomic loads, and the load has
4800 undefined behavior if the alignment is not set to a value which is at
4801 least the size in bytes of the pointee. ``!nontemporal`` does not have
4802 any defined semantics for atomic loads.
4804 The optional constant ``align`` argument specifies the alignment of the
4805 operation (that is, the alignment of the memory address). A value of 0
4806 or an omitted ``align`` argument means that the operation has the ABI
4807 alignment for the target. It is the responsibility of the code emitter
4808 to ensure that the alignment information is correct. Overestimating the
4809 alignment results in undefined behavior. Underestimating the alignment
4810 may produce less efficient code. An alignment of 1 is always safe.
4812 The optional ``!nontemporal`` metadata must reference a single
4813 metadata name ``<index>`` corresponding to a metadata node with one
4814 ``i32`` entry of value 1. The existence of the ``!nontemporal``
4815 metadata on the instruction tells the optimizer and code generator
4816 that this load is not expected to be reused in the cache. The code
4817 generator may select special instructions to save cache bandwidth, such
4818 as the ``MOVNT`` instruction on x86.
4820 The optional ``!invariant.load`` metadata must reference a single
4821 metadata name ``<index>`` corresponding to a metadata node with no
4822 entries. The existence of the ``!invariant.load`` metadata on the
4823 instruction tells the optimizer and code generator that this load
4824 address points to memory which does not change value during program
4825 execution. The optimizer may then move this load around, for example, by
4826 hoisting it out of loops using loop invariant code motion.
4831 The location of memory pointed to is loaded. If the value being loaded
4832 is of scalar type then the number of bytes read does not exceed the
4833 minimum number of bytes needed to hold all bits of the type. For
4834 example, loading an ``i24`` reads at most three bytes. When loading a
4835 value of a type like ``i20`` with a size that is not an integral number
4836 of bytes, the result is undefined if the value was not originally
4837 written using a store of the same type.
4842 .. code-block:: llvm
4844 %ptr = alloca i32 ; yields {i32*}:ptr
4845 store i32 3, i32* %ptr ; yields {void}
4846 %val = load i32* %ptr ; yields {i32}:val = i32 3
4850 '``store``' Instruction
4851 ^^^^^^^^^^^^^^^^^^^^^^^
4858 store [volatile] <ty> <value>, <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>] ; yields {void}
4859 store atomic [volatile] <ty> <value>, <ty>* <pointer> [singlethread] <ordering>, align <alignment> ; yields {void}
4864 The '``store``' instruction is used to write to memory.
4869 There are two arguments to the ``store`` instruction: a value to store
4870 and an address at which to store it. The type of the ``<pointer>``
4871 operand must be a pointer to the :ref:`first class <t_firstclass>` type of
4872 the ``<value>`` operand. If the ``store`` is marked as ``volatile``,
4873 then the optimizer is not allowed to modify the number or order of
4874 execution of this ``store`` with other :ref:`volatile
4875 operations <volatile>`.
4877 If the ``store`` is marked as ``atomic``, it takes an extra
4878 :ref:`ordering <ordering>` and optional ``singlethread`` argument. The
4879 ``acquire`` and ``acq_rel`` orderings aren't valid on ``store``
4880 instructions. Atomic loads produce :ref:`defined <memmodel>` results
4881 when they may see multiple atomic stores. The type of the pointee must
4882 be an integer type whose bit width is a power of two greater than or
4883 equal to eight and less than or equal to a target-specific size limit.
4884 ``align`` must be explicitly specified on atomic stores, and the store
4885 has undefined behavior if the alignment is not set to a value which is
4886 at least the size in bytes of the pointee. ``!nontemporal`` does not
4887 have any defined semantics for atomic stores.
4889 The optional constant ``align`` argument specifies the alignment of the
4890 operation (that is, the alignment of the memory address). A value of 0
4891 or an omitted ``align`` argument means that the operation has the ABI
4892 alignment for the target. It is the responsibility of the code emitter
4893 to ensure that the alignment information is correct. Overestimating the
4894 alignment results in undefined behavior. Underestimating the
4895 alignment may produce less efficient code. An alignment of 1 is always
4898 The optional ``!nontemporal`` metadata must reference a single metadata
4899 name ``<index>`` corresponding to a metadata node with one ``i32`` entry of
4900 value 1. The existence of the ``!nontemporal`` metadata on the instruction
4901 tells the optimizer and code generator that this load is not expected to
4902 be reused in the cache. The code generator may select special
4903 instructions to save cache bandwidth, such as the MOVNT instruction on
4909 The contents of memory are updated to contain ``<value>`` at the
4910 location specified by the ``<pointer>`` operand. If ``<value>`` is
4911 of scalar type then the number of bytes written does not exceed the
4912 minimum number of bytes needed to hold all bits of the type. For
4913 example, storing an ``i24`` writes at most three bytes. When writing a
4914 value of a type like ``i20`` with a size that is not an integral number
4915 of bytes, it is unspecified what happens to the extra bits that do not
4916 belong to the type, but they will typically be overwritten.
4921 .. code-block:: llvm
4923 %ptr = alloca i32 ; yields {i32*}:ptr
4924 store i32 3, i32* %ptr ; yields {void}
4925 %val = load i32* %ptr ; yields {i32}:val = i32 3
4929 '``fence``' Instruction
4930 ^^^^^^^^^^^^^^^^^^^^^^^
4937 fence [singlethread] <ordering> ; yields {void}
4942 The '``fence``' instruction is used to introduce happens-before edges
4948 '``fence``' instructions take an :ref:`ordering <ordering>` argument which
4949 defines what *synchronizes-with* edges they add. They can only be given
4950 ``acquire``, ``release``, ``acq_rel``, and ``seq_cst`` orderings.
4955 A fence A which has (at least) ``release`` ordering semantics
4956 *synchronizes with* a fence B with (at least) ``acquire`` ordering
4957 semantics if and only if there exist atomic operations X and Y, both
4958 operating on some atomic object M, such that A is sequenced before X, X
4959 modifies M (either directly or through some side effect of a sequence
4960 headed by X), Y is sequenced before B, and Y observes M. This provides a
4961 *happens-before* dependency between A and B. Rather than an explicit
4962 ``fence``, one (but not both) of the atomic operations X or Y might
4963 provide a ``release`` or ``acquire`` (resp.) ordering constraint and
4964 still *synchronize-with* the explicit ``fence`` and establish the
4965 *happens-before* edge.
4967 A ``fence`` which has ``seq_cst`` ordering, in addition to having both
4968 ``acquire`` and ``release`` semantics specified above, participates in
4969 the global program order of other ``seq_cst`` operations and/or fences.
4971 The optional ":ref:`singlethread <singlethread>`" argument specifies
4972 that the fence only synchronizes with other fences in the same thread.
4973 (This is useful for interacting with signal handlers.)
4978 .. code-block:: llvm
4980 fence acquire ; yields {void}
4981 fence singlethread seq_cst ; yields {void}
4985 '``cmpxchg``' Instruction
4986 ^^^^^^^^^^^^^^^^^^^^^^^^^
4993 cmpxchg [volatile] <ty>* <pointer>, <ty> <cmp>, <ty> <new> [singlethread] <ordering> ; yields {ty}
4998 The '``cmpxchg``' instruction is used to atomically modify memory. It
4999 loads a value in memory and compares it to a given value. If they are
5000 equal, it stores a new value into the memory.
5005 There are three arguments to the '``cmpxchg``' instruction: an address
5006 to operate on, a value to compare to the value currently be at that
5007 address, and a new value to place at that address if the compared values
5008 are equal. The type of '<cmp>' must be an integer type whose bit width
5009 is a power of two greater than or equal to eight and less than or equal
5010 to a target-specific size limit. '<cmp>' and '<new>' must have the same
5011 type, and the type of '<pointer>' must be a pointer to that type. If the
5012 ``cmpxchg`` is marked as ``volatile``, then the optimizer is not allowed
5013 to modify the number or order of execution of this ``cmpxchg`` with
5014 other :ref:`volatile operations <volatile>`.
5016 The :ref:`ordering <ordering>` argument specifies how this ``cmpxchg``
5017 synchronizes with other atomic operations.
5019 The optional "``singlethread``" argument declares that the ``cmpxchg``
5020 is only atomic with respect to code (usually signal handlers) running in
5021 the same thread as the ``cmpxchg``. Otherwise the cmpxchg is atomic with
5022 respect to all other code in the system.
5024 The pointer passed into cmpxchg must have alignment greater than or
5025 equal to the size in memory of the operand.
5030 The contents of memory at the location specified by the '``<pointer>``'
5031 operand is read and compared to '``<cmp>``'; if the read value is the
5032 equal, '``<new>``' is written. The original value at the location is
5035 A successful ``cmpxchg`` is a read-modify-write instruction for the purpose
5036 of identifying release sequences. A failed ``cmpxchg`` is equivalent to an
5037 atomic load with an ordering parameter determined by dropping any
5038 ``release`` part of the ``cmpxchg``'s ordering.
5043 .. code-block:: llvm
5046 %orig = atomic load i32* %ptr unordered ; yields {i32}
5050 %cmp = phi i32 [ %orig, %entry ], [%old, %loop]
5051 %squared = mul i32 %cmp, %cmp
5052 %old = cmpxchg i32* %ptr, i32 %cmp, i32 %squared ; yields {i32}
5053 %success = icmp eq i32 %cmp, %old
5054 br i1 %success, label %done, label %loop
5061 '``atomicrmw``' Instruction
5062 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
5069 atomicrmw [volatile] <operation> <ty>* <pointer>, <ty> <value> [singlethread] <ordering> ; yields {ty}
5074 The '``atomicrmw``' instruction is used to atomically modify memory.
5079 There are three arguments to the '``atomicrmw``' instruction: an
5080 operation to apply, an address whose value to modify, an argument to the
5081 operation. The operation must be one of the following keywords:
5095 The type of '<value>' must be an integer type whose bit width is a power
5096 of two greater than or equal to eight and less than or equal to a
5097 target-specific size limit. The type of the '``<pointer>``' operand must
5098 be a pointer to that type. If the ``atomicrmw`` is marked as
5099 ``volatile``, then the optimizer is not allowed to modify the number or
5100 order of execution of this ``atomicrmw`` with other :ref:`volatile
5101 operations <volatile>`.
5106 The contents of memory at the location specified by the '``<pointer>``'
5107 operand are atomically read, modified, and written back. The original
5108 value at the location is returned. The modification is specified by the
5111 - xchg: ``*ptr = val``
5112 - add: ``*ptr = *ptr + val``
5113 - sub: ``*ptr = *ptr - val``
5114 - and: ``*ptr = *ptr & val``
5115 - nand: ``*ptr = ~(*ptr & val)``
5116 - or: ``*ptr = *ptr | val``
5117 - xor: ``*ptr = *ptr ^ val``
5118 - max: ``*ptr = *ptr > val ? *ptr : val`` (using a signed comparison)
5119 - min: ``*ptr = *ptr < val ? *ptr : val`` (using a signed comparison)
5120 - umax: ``*ptr = *ptr > val ? *ptr : val`` (using an unsigned
5122 - umin: ``*ptr = *ptr < val ? *ptr : val`` (using an unsigned
5128 .. code-block:: llvm
5130 %old = atomicrmw add i32* %ptr, i32 1 acquire ; yields {i32}
5132 .. _i_getelementptr:
5134 '``getelementptr``' Instruction
5135 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5142 <result> = getelementptr <pty>* <ptrval>{, <ty> <idx>}*
5143 <result> = getelementptr inbounds <pty>* <ptrval>{, <ty> <idx>}*
5144 <result> = getelementptr <ptr vector> ptrval, <vector index type> idx
5149 The '``getelementptr``' instruction is used to get the address of a
5150 subelement of an :ref:`aggregate <t_aggregate>` data structure. It performs
5151 address calculation only and does not access memory.
5156 The first argument is always a pointer or a vector of pointers, and
5157 forms the basis of the calculation. The remaining arguments are indices
5158 that indicate which of the elements of the aggregate object are indexed.
5159 The interpretation of each index is dependent on the type being indexed
5160 into. The first index always indexes the pointer value given as the
5161 first argument, the second index indexes a value of the type pointed to
5162 (not necessarily the value directly pointed to, since the first index
5163 can be non-zero), etc. The first type indexed into must be a pointer
5164 value, subsequent types can be arrays, vectors, and structs. Note that
5165 subsequent types being indexed into can never be pointers, since that
5166 would require loading the pointer before continuing calculation.
5168 The type of each index argument depends on the type it is indexing into.
5169 When indexing into a (optionally packed) structure, only ``i32`` integer
5170 **constants** are allowed (when using a vector of indices they must all
5171 be the **same** ``i32`` integer constant). When indexing into an array,
5172 pointer or vector, integers of any width are allowed, and they are not
5173 required to be constant. These integers are treated as signed values
5176 For example, let's consider a C code fragment and how it gets compiled
5192 int *foo(struct ST *s) {
5193 return &s[1].Z.B[5][13];
5196 The LLVM code generated by Clang is:
5198 .. code-block:: llvm
5200 %struct.RT = type { i8, [10 x [20 x i32]], i8 }
5201 %struct.ST = type { i32, double, %struct.RT }
5203 define i32* @foo(%struct.ST* %s) nounwind uwtable readnone optsize ssp {
5205 %arrayidx = getelementptr inbounds %struct.ST* %s, i64 1, i32 2, i32 1, i64 5, i64 13
5212 In the example above, the first index is indexing into the
5213 '``%struct.ST*``' type, which is a pointer, yielding a '``%struct.ST``'
5214 = '``{ i32, double, %struct.RT }``' type, a structure. The second index
5215 indexes into the third element of the structure, yielding a
5216 '``%struct.RT``' = '``{ i8 , [10 x [20 x i32]], i8 }``' type, another
5217 structure. The third index indexes into the second element of the
5218 structure, yielding a '``[10 x [20 x i32]]``' type, an array. The two
5219 dimensions of the array are subscripted into, yielding an '``i32``'
5220 type. The '``getelementptr``' instruction returns a pointer to this
5221 element, thus computing a value of '``i32*``' type.
5223 Note that it is perfectly legal to index partially through a structure,
5224 returning a pointer to an inner element. Because of this, the LLVM code
5225 for the given testcase is equivalent to:
5227 .. code-block:: llvm
5229 define i32* @foo(%struct.ST* %s) {
5230 %t1 = getelementptr %struct.ST* %s, i32 1 ; yields %struct.ST*:%t1
5231 %t2 = getelementptr %struct.ST* %t1, i32 0, i32 2 ; yields %struct.RT*:%t2
5232 %t3 = getelementptr %struct.RT* %t2, i32 0, i32 1 ; yields [10 x [20 x i32]]*:%t3
5233 %t4 = getelementptr [10 x [20 x i32]]* %t3, i32 0, i32 5 ; yields [20 x i32]*:%t4
5234 %t5 = getelementptr [20 x i32]* %t4, i32 0, i32 13 ; yields i32*:%t5
5238 If the ``inbounds`` keyword is present, the result value of the
5239 ``getelementptr`` is a :ref:`poison value <poisonvalues>` if the base
5240 pointer is not an *in bounds* address of an allocated object, or if any
5241 of the addresses that would be formed by successive addition of the
5242 offsets implied by the indices to the base address with infinitely
5243 precise signed arithmetic are not an *in bounds* address of that
5244 allocated object. The *in bounds* addresses for an allocated object are
5245 all the addresses that point into the object, plus the address one byte
5246 past the end. In cases where the base is a vector of pointers the
5247 ``inbounds`` keyword applies to each of the computations element-wise.
5249 If the ``inbounds`` keyword is not present, the offsets are added to the
5250 base address with silently-wrapping two's complement arithmetic. If the
5251 offsets have a different width from the pointer, they are sign-extended
5252 or truncated to the width of the pointer. The result value of the
5253 ``getelementptr`` may be outside the object pointed to by the base
5254 pointer. The result value may not necessarily be used to access memory
5255 though, even if it happens to point into allocated storage. See the
5256 :ref:`Pointer Aliasing Rules <pointeraliasing>` section for more
5259 The getelementptr instruction is often confusing. For some more insight
5260 into how it works, see :doc:`the getelementptr FAQ <GetElementPtr>`.
5265 .. code-block:: llvm
5267 ; yields [12 x i8]*:aptr
5268 %aptr = getelementptr {i32, [12 x i8]}* %saptr, i64 0, i32 1
5270 %vptr = getelementptr {i32, <2 x i8>}* %svptr, i64 0, i32 1, i32 1
5272 %eptr = getelementptr [12 x i8]* %aptr, i64 0, i32 1
5274 %iptr = getelementptr [10 x i32]* @arr, i16 0, i16 0
5276 In cases where the pointer argument is a vector of pointers, each index
5277 must be a vector with the same number of elements. For example:
5279 .. code-block:: llvm
5281 %A = getelementptr <4 x i8*> %ptrs, <4 x i64> %offsets,
5283 Conversion Operations
5284 ---------------------
5286 The instructions in this category are the conversion instructions
5287 (casting) which all take a single operand and a type. They perform
5288 various bit conversions on the operand.
5290 '``trunc .. to``' Instruction
5291 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5298 <result> = trunc <ty> <value> to <ty2> ; yields ty2
5303 The '``trunc``' instruction truncates its operand to the type ``ty2``.
5308 The '``trunc``' instruction takes a value to trunc, and a type to trunc
5309 it to. Both types must be of :ref:`integer <t_integer>` types, or vectors
5310 of the same number of integers. The bit size of the ``value`` must be
5311 larger than the bit size of the destination type, ``ty2``. Equal sized
5312 types are not allowed.
5317 The '``trunc``' instruction truncates the high order bits in ``value``
5318 and converts the remaining bits to ``ty2``. Since the source size must
5319 be larger than the destination size, ``trunc`` cannot be a *no-op cast*.
5320 It will always truncate bits.
5325 .. code-block:: llvm
5327 %X = trunc i32 257 to i8 ; yields i8:1
5328 %Y = trunc i32 123 to i1 ; yields i1:true
5329 %Z = trunc i32 122 to i1 ; yields i1:false
5330 %W = trunc <2 x i16> <i16 8, i16 7> to <2 x i8> ; yields <i8 8, i8 7>
5332 '``zext .. to``' Instruction
5333 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5340 <result> = zext <ty> <value> to <ty2> ; yields ty2
5345 The '``zext``' instruction zero extends its operand to type ``ty2``.
5350 The '``zext``' instruction takes a value to cast, and a type to cast it
5351 to. Both types must be of :ref:`integer <t_integer>` types, or vectors of
5352 the same number of integers. The bit size of the ``value`` must be
5353 smaller than the bit size of the destination type, ``ty2``.
5358 The ``zext`` fills the high order bits of the ``value`` with zero bits
5359 until it reaches the size of the destination type, ``ty2``.
5361 When zero extending from i1, the result will always be either 0 or 1.
5366 .. code-block:: llvm
5368 %X = zext i32 257 to i64 ; yields i64:257
5369 %Y = zext i1 true to i32 ; yields i32:1
5370 %Z = zext <2 x i16> <i16 8, i16 7> to <2 x i32> ; yields <i32 8, i32 7>
5372 '``sext .. to``' Instruction
5373 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5380 <result> = sext <ty> <value> to <ty2> ; yields ty2
5385 The '``sext``' sign extends ``value`` to the type ``ty2``.
5390 The '``sext``' instruction takes a value to cast, and a type to cast it
5391 to. Both types must be of :ref:`integer <t_integer>` types, or vectors of
5392 the same number of integers. The bit size of the ``value`` must be
5393 smaller than the bit size of the destination type, ``ty2``.
5398 The '``sext``' instruction performs a sign extension by copying the sign
5399 bit (highest order bit) of the ``value`` until it reaches the bit size
5400 of the type ``ty2``.
5402 When sign extending from i1, the extension always results in -1 or 0.
5407 .. code-block:: llvm
5409 %X = sext i8 -1 to i16 ; yields i16 :65535
5410 %Y = sext i1 true to i32 ; yields i32:-1
5411 %Z = sext <2 x i16> <i16 8, i16 7> to <2 x i32> ; yields <i32 8, i32 7>
5413 '``fptrunc .. to``' Instruction
5414 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5421 <result> = fptrunc <ty> <value> to <ty2> ; yields ty2
5426 The '``fptrunc``' instruction truncates ``value`` to type ``ty2``.
5431 The '``fptrunc``' instruction takes a :ref:`floating point <t_floating>`
5432 value to cast and a :ref:`floating point <t_floating>` type to cast it to.
5433 The size of ``value`` must be larger than the size of ``ty2``. This
5434 implies that ``fptrunc`` cannot be used to make a *no-op cast*.
5439 The '``fptrunc``' instruction truncates a ``value`` from a larger
5440 :ref:`floating point <t_floating>` type to a smaller :ref:`floating
5441 point <t_floating>` type. If the value cannot fit within the
5442 destination type, ``ty2``, then the results are undefined.
5447 .. code-block:: llvm
5449 %X = fptrunc double 123.0 to float ; yields float:123.0
5450 %Y = fptrunc double 1.0E+300 to float ; yields undefined
5452 '``fpext .. to``' Instruction
5453 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5460 <result> = fpext <ty> <value> to <ty2> ; yields ty2
5465 The '``fpext``' extends a floating point ``value`` to a larger floating
5471 The '``fpext``' instruction takes a :ref:`floating point <t_floating>`
5472 ``value`` to cast, and a :ref:`floating point <t_floating>` type to cast it
5473 to. The source type must be smaller than the destination type.
5478 The '``fpext``' instruction extends the ``value`` from a smaller
5479 :ref:`floating point <t_floating>` type to a larger :ref:`floating
5480 point <t_floating>` type. The ``fpext`` cannot be used to make a
5481 *no-op cast* because it always changes bits. Use ``bitcast`` to make a
5482 *no-op cast* for a floating point cast.
5487 .. code-block:: llvm
5489 %X = fpext float 3.125 to double ; yields double:3.125000e+00
5490 %Y = fpext double %X to fp128 ; yields fp128:0xL00000000000000004000900000000000
5492 '``fptoui .. to``' Instruction
5493 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5500 <result> = fptoui <ty> <value> to <ty2> ; yields ty2
5505 The '``fptoui``' converts a floating point ``value`` to its unsigned
5506 integer equivalent of type ``ty2``.
5511 The '``fptoui``' instruction takes a value to cast, which must be a
5512 scalar or vector :ref:`floating point <t_floating>` value, and a type to
5513 cast it to ``ty2``, which must be an :ref:`integer <t_integer>` type. If
5514 ``ty`` is a vector floating point type, ``ty2`` must be a vector integer
5515 type with the same number of elements as ``ty``
5520 The '``fptoui``' instruction converts its :ref:`floating
5521 point <t_floating>` operand into the nearest (rounding towards zero)
5522 unsigned integer value. If the value cannot fit in ``ty2``, the results
5528 .. code-block:: llvm
5530 %X = fptoui double 123.0 to i32 ; yields i32:123
5531 %Y = fptoui float 1.0E+300 to i1 ; yields undefined:1
5532 %Z = fptoui float 1.04E+17 to i8 ; yields undefined:1
5534 '``fptosi .. to``' Instruction
5535 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5542 <result> = fptosi <ty> <value> to <ty2> ; yields ty2
5547 The '``fptosi``' instruction converts :ref:`floating point <t_floating>`
5548 ``value`` to type ``ty2``.
5553 The '``fptosi``' instruction takes a value to cast, which must be a
5554 scalar or vector :ref:`floating point <t_floating>` value, and a type to
5555 cast it to ``ty2``, which must be an :ref:`integer <t_integer>` type. If
5556 ``ty`` is a vector floating point type, ``ty2`` must be a vector integer
5557 type with the same number of elements as ``ty``
5562 The '``fptosi``' instruction converts its :ref:`floating
5563 point <t_floating>` operand into the nearest (rounding towards zero)
5564 signed integer value. If the value cannot fit in ``ty2``, the results
5570 .. code-block:: llvm
5572 %X = fptosi double -123.0 to i32 ; yields i32:-123
5573 %Y = fptosi float 1.0E-247 to i1 ; yields undefined:1
5574 %Z = fptosi float 1.04E+17 to i8 ; yields undefined:1
5576 '``uitofp .. to``' Instruction
5577 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5584 <result> = uitofp <ty> <value> to <ty2> ; yields ty2
5589 The '``uitofp``' instruction regards ``value`` as an unsigned integer
5590 and converts that value to the ``ty2`` type.
5595 The '``uitofp``' instruction takes a value to cast, which must be a
5596 scalar or vector :ref:`integer <t_integer>` value, and a type to cast it to
5597 ``ty2``, which must be an :ref:`floating point <t_floating>` type. If
5598 ``ty`` is a vector integer type, ``ty2`` must be a vector floating point
5599 type with the same number of elements as ``ty``
5604 The '``uitofp``' instruction interprets its operand as an unsigned
5605 integer quantity and converts it to the corresponding floating point
5606 value. If the value cannot fit in the floating point value, the results
5612 .. code-block:: llvm
5614 %X = uitofp i32 257 to float ; yields float:257.0
5615 %Y = uitofp i8 -1 to double ; yields double:255.0
5617 '``sitofp .. to``' Instruction
5618 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5625 <result> = sitofp <ty> <value> to <ty2> ; yields ty2
5630 The '``sitofp``' instruction regards ``value`` as a signed integer and
5631 converts that value to the ``ty2`` type.
5636 The '``sitofp``' instruction takes a value to cast, which must be a
5637 scalar or vector :ref:`integer <t_integer>` value, and a type to cast it to
5638 ``ty2``, which must be an :ref:`floating point <t_floating>` type. If
5639 ``ty`` is a vector integer type, ``ty2`` must be a vector floating point
5640 type with the same number of elements as ``ty``
5645 The '``sitofp``' instruction interprets its operand as a signed integer
5646 quantity and converts it to the corresponding floating point value. If
5647 the value cannot fit in the floating point value, the results are
5653 .. code-block:: llvm
5655 %X = sitofp i32 257 to float ; yields float:257.0
5656 %Y = sitofp i8 -1 to double ; yields double:-1.0
5660 '``ptrtoint .. to``' Instruction
5661 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5668 <result> = ptrtoint <ty> <value> to <ty2> ; yields ty2
5673 The '``ptrtoint``' instruction converts the pointer or a vector of
5674 pointers ``value`` to the integer (or vector of integers) type ``ty2``.
5679 The '``ptrtoint``' instruction takes a ``value`` to cast, which must be
5680 a a value of type :ref:`pointer <t_pointer>` or a vector of pointers, and a
5681 type to cast it to ``ty2``, which must be an :ref:`integer <t_integer>` or
5682 a vector of integers type.
5687 The '``ptrtoint``' instruction converts ``value`` to integer type
5688 ``ty2`` by interpreting the pointer value as an integer and either
5689 truncating or zero extending that value to the size of the integer type.
5690 If ``value`` is smaller than ``ty2`` then a zero extension is done. If
5691 ``value`` is larger than ``ty2`` then a truncation is done. If they are
5692 the same size, then nothing is done (*no-op cast*) other than a type
5698 .. code-block:: llvm
5700 %X = ptrtoint i32* %P to i8 ; yields truncation on 32-bit architecture
5701 %Y = ptrtoint i32* %P to i64 ; yields zero extension on 32-bit architecture
5702 %Z = ptrtoint <4 x i32*> %P to <4 x i64>; yields vector zero extension for a vector of addresses on 32-bit architecture
5706 '``inttoptr .. to``' Instruction
5707 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5714 <result> = inttoptr <ty> <value> to <ty2> ; yields ty2
5719 The '``inttoptr``' instruction converts an integer ``value`` to a
5720 pointer type, ``ty2``.
5725 The '``inttoptr``' instruction takes an :ref:`integer <t_integer>` value to
5726 cast, and a type to cast it to, which must be a :ref:`pointer <t_pointer>`
5732 The '``inttoptr``' instruction converts ``value`` to type ``ty2`` by
5733 applying either a zero extension or a truncation depending on the size
5734 of the integer ``value``. If ``value`` is larger than the size of a
5735 pointer then a truncation is done. If ``value`` is smaller than the size
5736 of a pointer then a zero extension is done. If they are the same size,
5737 nothing is done (*no-op cast*).
5742 .. code-block:: llvm
5744 %X = inttoptr i32 255 to i32* ; yields zero extension on 64-bit architecture
5745 %Y = inttoptr i32 255 to i32* ; yields no-op on 32-bit architecture
5746 %Z = inttoptr i64 0 to i32* ; yields truncation on 32-bit architecture
5747 %Z = inttoptr <4 x i32> %G to <4 x i8*>; yields truncation of vector G to four pointers
5751 '``bitcast .. to``' Instruction
5752 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5759 <result> = bitcast <ty> <value> to <ty2> ; yields ty2
5764 The '``bitcast``' instruction converts ``value`` to type ``ty2`` without
5770 The '``bitcast``' instruction takes a value to cast, which must be a
5771 non-aggregate first class value, and a type to cast it to, which must
5772 also be a non-aggregate :ref:`first class <t_firstclass>` type. The
5773 bit sizes of ``value`` and the destination type, ``ty2``, must be
5774 identical. If the source type is a pointer, the destination type must
5775 also be a pointer of the same size. This instruction supports bitwise
5776 conversion of vectors to integers and to vectors of other types (as
5777 long as they have the same size).
5782 The '``bitcast``' instruction converts ``value`` to type ``ty2``. It
5783 is always a *no-op cast* because no bits change with this
5784 conversion. The conversion is done as if the ``value`` had been stored
5785 to memory and read back as type ``ty2``. Pointer (or vector of
5786 pointers) types may only be converted to other pointer (or vector of
5787 pointers) types with the same address space through this instruction.
5788 To convert pointers to other types, use the :ref:`inttoptr <i_inttoptr>`
5789 or :ref:`ptrtoint <i_ptrtoint>` instructions first.
5794 .. code-block:: llvm
5796 %X = bitcast i8 255 to i8 ; yields i8 :-1
5797 %Y = bitcast i32* %x to sint* ; yields sint*:%x
5798 %Z = bitcast <2 x int> %V to i64; ; yields i64: %V
5799 %Z = bitcast <2 x i32*> %V to <2 x i64*> ; yields <2 x i64*>
5801 .. _i_addrspacecast:
5803 '``addrspacecast .. to``' Instruction
5804 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5811 <result> = addrspacecast <pty> <ptrval> to <pty2> ; yields pty2
5816 The '``addrspacecast``' instruction converts ``ptrval`` from ``pty`` in
5817 address space ``n`` to type ``pty2`` in address space ``m``.
5822 The '``addrspacecast``' instruction takes a pointer or vector of pointer value
5823 to cast and a pointer type to cast it to, which must have a different
5829 The '``addrspacecast``' instruction converts the pointer value
5830 ``ptrval`` to type ``pty2``. It can be a *no-op cast* or a complex
5831 value modification, depending on the target and the address space
5832 pair. Pointer conversions within the same address space must be
5833 performed with the ``bitcast`` instruction. Note that if the address space
5834 conversion is legal then both result and operand refer to the same memory
5840 .. code-block:: llvm
5842 %X = addrspacecast i32* %x to i32 addrspace(1)* ; yields i32 addrspace(1)*:%x
5843 %Y = addrspacecast i32 addrspace(1)* %y to i64 addrspace(2)* ; yields i64 addrspace(2)*:%y
5844 %Z = addrspacecast <4 x i32*> %z to <4 x float addrspace(3)*> ; yields <4 x float addrspace(3)*>:%z
5851 The instructions in this category are the "miscellaneous" instructions,
5852 which defy better classification.
5856 '``icmp``' Instruction
5857 ^^^^^^^^^^^^^^^^^^^^^^
5864 <result> = icmp <cond> <ty> <op1>, <op2> ; yields {i1} or {<N x i1>}:result
5869 The '``icmp``' instruction returns a boolean value or a vector of
5870 boolean values based on comparison of its two integer, integer vector,
5871 pointer, or pointer vector operands.
5876 The '``icmp``' instruction takes three operands. The first operand is
5877 the condition code indicating the kind of comparison to perform. It is
5878 not a value, just a keyword. The possible condition code are:
5881 #. ``ne``: not equal
5882 #. ``ugt``: unsigned greater than
5883 #. ``uge``: unsigned greater or equal
5884 #. ``ult``: unsigned less than
5885 #. ``ule``: unsigned less or equal
5886 #. ``sgt``: signed greater than
5887 #. ``sge``: signed greater or equal
5888 #. ``slt``: signed less than
5889 #. ``sle``: signed less or equal
5891 The remaining two arguments must be :ref:`integer <t_integer>` or
5892 :ref:`pointer <t_pointer>` or integer :ref:`vector <t_vector>` typed. They
5893 must also be identical types.
5898 The '``icmp``' compares ``op1`` and ``op2`` according to the condition
5899 code given as ``cond``. The comparison performed always yields either an
5900 :ref:`i1 <t_integer>` or vector of ``i1`` result, as follows:
5902 #. ``eq``: yields ``true`` if the operands are equal, ``false``
5903 otherwise. No sign interpretation is necessary or performed.
5904 #. ``ne``: yields ``true`` if the operands are unequal, ``false``
5905 otherwise. No sign interpretation is necessary or performed.
5906 #. ``ugt``: interprets the operands as unsigned values and yields
5907 ``true`` if ``op1`` is greater than ``op2``.
5908 #. ``uge``: interprets the operands as unsigned values and yields
5909 ``true`` if ``op1`` is greater than or equal to ``op2``.
5910 #. ``ult``: interprets the operands as unsigned values and yields
5911 ``true`` if ``op1`` is less than ``op2``.
5912 #. ``ule``: interprets the operands as unsigned values and yields
5913 ``true`` if ``op1`` is less than or equal to ``op2``.
5914 #. ``sgt``: interprets the operands as signed values and yields ``true``
5915 if ``op1`` is greater than ``op2``.
5916 #. ``sge``: interprets the operands as signed values and yields ``true``
5917 if ``op1`` is greater than or equal to ``op2``.
5918 #. ``slt``: interprets the operands as signed values and yields ``true``
5919 if ``op1`` is less than ``op2``.
5920 #. ``sle``: interprets the operands as signed values and yields ``true``
5921 if ``op1`` is less than or equal to ``op2``.
5923 If the operands are :ref:`pointer <t_pointer>` typed, the pointer values
5924 are compared as if they were integers.
5926 If the operands are integer vectors, then they are compared element by
5927 element. The result is an ``i1`` vector with the same number of elements
5928 as the values being compared. Otherwise, the result is an ``i1``.
5933 .. code-block:: llvm
5935 <result> = icmp eq i32 4, 5 ; yields: result=false
5936 <result> = icmp ne float* %X, %X ; yields: result=false
5937 <result> = icmp ult i16 4, 5 ; yields: result=true
5938 <result> = icmp sgt i16 4, 5 ; yields: result=false
5939 <result> = icmp ule i16 -4, 5 ; yields: result=false
5940 <result> = icmp sge i16 4, 5 ; yields: result=false
5942 Note that the code generator does not yet support vector types with the
5943 ``icmp`` instruction.
5947 '``fcmp``' Instruction
5948 ^^^^^^^^^^^^^^^^^^^^^^
5955 <result> = fcmp <cond> <ty> <op1>, <op2> ; yields {i1} or {<N x i1>}:result
5960 The '``fcmp``' instruction returns a boolean value or vector of boolean
5961 values based on comparison of its operands.
5963 If the operands are floating point scalars, then the result type is a
5964 boolean (:ref:`i1 <t_integer>`).
5966 If the operands are floating point vectors, then the result type is a
5967 vector of boolean with the same number of elements as the operands being
5973 The '``fcmp``' instruction takes three operands. The first operand is
5974 the condition code indicating the kind of comparison to perform. It is
5975 not a value, just a keyword. The possible condition code are:
5977 #. ``false``: no comparison, always returns false
5978 #. ``oeq``: ordered and equal
5979 #. ``ogt``: ordered and greater than
5980 #. ``oge``: ordered and greater than or equal
5981 #. ``olt``: ordered and less than
5982 #. ``ole``: ordered and less than or equal
5983 #. ``one``: ordered and not equal
5984 #. ``ord``: ordered (no nans)
5985 #. ``ueq``: unordered or equal
5986 #. ``ugt``: unordered or greater than
5987 #. ``uge``: unordered or greater than or equal
5988 #. ``ult``: unordered or less than
5989 #. ``ule``: unordered or less than or equal
5990 #. ``une``: unordered or not equal
5991 #. ``uno``: unordered (either nans)
5992 #. ``true``: no comparison, always returns true
5994 *Ordered* means that neither operand is a QNAN while *unordered* means
5995 that either operand may be a QNAN.
5997 Each of ``val1`` and ``val2`` arguments must be either a :ref:`floating
5998 point <t_floating>` type or a :ref:`vector <t_vector>` of floating point
5999 type. They must have identical types.
6004 The '``fcmp``' instruction compares ``op1`` and ``op2`` according to the
6005 condition code given as ``cond``. If the operands are vectors, then the
6006 vectors are compared element by element. Each comparison performed
6007 always yields an :ref:`i1 <t_integer>` result, as follows:
6009 #. ``false``: always yields ``false``, regardless of operands.
6010 #. ``oeq``: yields ``true`` if both operands are not a QNAN and ``op1``
6011 is equal to ``op2``.
6012 #. ``ogt``: yields ``true`` if both operands are not a QNAN and ``op1``
6013 is greater than ``op2``.
6014 #. ``oge``: yields ``true`` if both operands are not a QNAN and ``op1``
6015 is greater than or equal to ``op2``.
6016 #. ``olt``: yields ``true`` if both operands are not a QNAN and ``op1``
6017 is less than ``op2``.
6018 #. ``ole``: yields ``true`` if both operands are not a QNAN and ``op1``
6019 is less than or equal to ``op2``.
6020 #. ``one``: yields ``true`` if both operands are not a QNAN and ``op1``
6021 is not equal to ``op2``.
6022 #. ``ord``: yields ``true`` if both operands are not a QNAN.
6023 #. ``ueq``: yields ``true`` if either operand is a QNAN or ``op1`` is
6025 #. ``ugt``: yields ``true`` if either operand is a QNAN or ``op1`` is
6026 greater than ``op2``.
6027 #. ``uge``: yields ``true`` if either operand is a QNAN or ``op1`` is
6028 greater than or equal to ``op2``.
6029 #. ``ult``: yields ``true`` if either operand is a QNAN or ``op1`` is
6031 #. ``ule``: yields ``true`` if either operand is a QNAN or ``op1`` is
6032 less than or equal to ``op2``.
6033 #. ``une``: yields ``true`` if either operand is a QNAN or ``op1`` is
6034 not equal to ``op2``.
6035 #. ``uno``: yields ``true`` if either operand is a QNAN.
6036 #. ``true``: always yields ``true``, regardless of operands.
6041 .. code-block:: llvm
6043 <result> = fcmp oeq float 4.0, 5.0 ; yields: result=false
6044 <result> = fcmp one float 4.0, 5.0 ; yields: result=true
6045 <result> = fcmp olt float 4.0, 5.0 ; yields: result=true
6046 <result> = fcmp ueq double 1.0, 2.0 ; yields: result=false
6048 Note that the code generator does not yet support vector types with the
6049 ``fcmp`` instruction.
6053 '``phi``' Instruction
6054 ^^^^^^^^^^^^^^^^^^^^^
6061 <result> = phi <ty> [ <val0>, <label0>], ...
6066 The '``phi``' instruction is used to implement the φ node in the SSA
6067 graph representing the function.
6072 The type of the incoming values is specified with the first type field.
6073 After this, the '``phi``' instruction takes a list of pairs as
6074 arguments, with one pair for each predecessor basic block of the current
6075 block. Only values of :ref:`first class <t_firstclass>` type may be used as
6076 the value arguments to the PHI node. Only labels may be used as the
6079 There must be no non-phi instructions between the start of a basic block
6080 and the PHI instructions: i.e. PHI instructions must be first in a basic
6083 For the purposes of the SSA form, the use of each incoming value is
6084 deemed to occur on the edge from the corresponding predecessor block to
6085 the current block (but after any definition of an '``invoke``'
6086 instruction's return value on the same edge).
6091 At runtime, the '``phi``' instruction logically takes on the value
6092 specified by the pair corresponding to the predecessor basic block that
6093 executed just prior to the current block.
6098 .. code-block:: llvm
6100 Loop: ; Infinite loop that counts from 0 on up...
6101 %indvar = phi i32 [ 0, %LoopHeader ], [ %nextindvar, %Loop ]
6102 %nextindvar = add i32 %indvar, 1
6107 '``select``' Instruction
6108 ^^^^^^^^^^^^^^^^^^^^^^^^
6115 <result> = select selty <cond>, <ty> <val1>, <ty> <val2> ; yields ty
6117 selty is either i1 or {<N x i1>}
6122 The '``select``' instruction is used to choose one value based on a
6123 condition, without branching.
6128 The '``select``' instruction requires an 'i1' value or a vector of 'i1'
6129 values indicating the condition, and two values of the same :ref:`first
6130 class <t_firstclass>` type. If the val1/val2 are vectors and the
6131 condition is a scalar, then entire vectors are selected, not individual
6137 If the condition is an i1 and it evaluates to 1, the instruction returns
6138 the first value argument; otherwise, it returns the second value
6141 If the condition is a vector of i1, then the value arguments must be
6142 vectors of the same size, and the selection is done element by element.
6147 .. code-block:: llvm
6149 %X = select i1 true, i8 17, i8 42 ; yields i8:17
6153 '``call``' Instruction
6154 ^^^^^^^^^^^^^^^^^^^^^^
6161 <result> = [tail] call [cconv] [ret attrs] <ty> [<fnty>*] <fnptrval>(<function args>) [fn attrs]
6166 The '``call``' instruction represents a simple function call.
6171 This instruction requires several arguments:
6173 #. The optional "tail" marker indicates that the callee function does
6174 not access any allocas or varargs in the caller. Note that calls may
6175 be marked "tail" even if they do not occur before a
6176 :ref:`ret <i_ret>` instruction. If the "tail" marker is present, the
6177 function call is eligible for tail call optimization, but `might not
6178 in fact be optimized into a jump <CodeGenerator.html#tailcallopt>`_.
6179 The code generator may optimize calls marked "tail" with either 1)
6180 automatic `sibling call
6181 optimization <CodeGenerator.html#sibcallopt>`_ when the caller and
6182 callee have matching signatures, or 2) forced tail call optimization
6183 when the following extra requirements are met:
6185 - Caller and callee both have the calling convention ``fastcc``.
6186 - The call is in tail position (ret immediately follows call and ret
6187 uses value of call or is void).
6188 - Option ``-tailcallopt`` is enabled, or
6189 ``llvm::GuaranteedTailCallOpt`` is ``true``.
6190 - `Platform specific constraints are
6191 met. <CodeGenerator.html#tailcallopt>`_
6193 #. The optional "cconv" marker indicates which :ref:`calling
6194 convention <callingconv>` the call should use. If none is
6195 specified, the call defaults to using C calling conventions. The
6196 calling convention of the call must match the calling convention of
6197 the target function, or else the behavior is undefined.
6198 #. The optional :ref:`Parameter Attributes <paramattrs>` list for return
6199 values. Only '``zeroext``', '``signext``', and '``inreg``' attributes
6201 #. '``ty``': the type of the call instruction itself which is also the
6202 type of the return value. Functions that return no value are marked
6204 #. '``fnty``': shall be the signature of the pointer to function value
6205 being invoked. The argument types must match the types implied by
6206 this signature. This type can be omitted if the function is not
6207 varargs and if the function type does not return a pointer to a
6209 #. '``fnptrval``': An LLVM value containing a pointer to a function to
6210 be invoked. In most cases, this is a direct function invocation, but
6211 indirect ``call``'s are just as possible, calling an arbitrary pointer
6213 #. '``function args``': argument list whose types match the function
6214 signature argument types and parameter attributes. All arguments must
6215 be of :ref:`first class <t_firstclass>` type. If the function signature
6216 indicates the function accepts a variable number of arguments, the
6217 extra arguments can be specified.
6218 #. The optional :ref:`function attributes <fnattrs>` list. Only
6219 '``noreturn``', '``nounwind``', '``readonly``' and '``readnone``'
6220 attributes are valid here.
6225 The '``call``' instruction is used to cause control flow to transfer to
6226 a specified function, with its incoming arguments bound to the specified
6227 values. Upon a '``ret``' instruction in the called function, control
6228 flow continues with the instruction after the function call, and the
6229 return value of the function is bound to the result argument.
6234 .. code-block:: llvm
6236 %retval = call i32 @test(i32 %argc)
6237 call i32 (i8*, ...)* @printf(i8* %msg, i32 12, i8 42) ; yields i32
6238 %X = tail call i32 @foo() ; yields i32
6239 %Y = tail call fastcc i32 @foo() ; yields i32
6240 call void %foo(i8 97 signext)
6242 %struct.A = type { i32, i8 }
6243 %r = call %struct.A @foo() ; yields { 32, i8 }
6244 %gr = extractvalue %struct.A %r, 0 ; yields i32
6245 %gr1 = extractvalue %struct.A %r, 1 ; yields i8
6246 %Z = call void @foo() noreturn ; indicates that %foo never returns normally
6247 %ZZ = call zeroext i32 @bar() ; Return value is %zero extended
6249 llvm treats calls to some functions with names and arguments that match
6250 the standard C99 library as being the C99 library functions, and may
6251 perform optimizations or generate code for them under that assumption.
6252 This is something we'd like to change in the future to provide better
6253 support for freestanding environments and non-C-based languages.
6257 '``va_arg``' Instruction
6258 ^^^^^^^^^^^^^^^^^^^^^^^^
6265 <resultval> = va_arg <va_list*> <arglist>, <argty>
6270 The '``va_arg``' instruction is used to access arguments passed through
6271 the "variable argument" area of a function call. It is used to implement
6272 the ``va_arg`` macro in C.
6277 This instruction takes a ``va_list*`` value and the type of the
6278 argument. It returns a value of the specified argument type and
6279 increments the ``va_list`` to point to the next argument. The actual
6280 type of ``va_list`` is target specific.
6285 The '``va_arg``' instruction loads an argument of the specified type
6286 from the specified ``va_list`` and causes the ``va_list`` to point to
6287 the next argument. For more information, see the variable argument
6288 handling :ref:`Intrinsic Functions <int_varargs>`.
6290 It is legal for this instruction to be called in a function which does
6291 not take a variable number of arguments, for example, the ``vfprintf``
6294 ``va_arg`` is an LLVM instruction instead of an :ref:`intrinsic
6295 function <intrinsics>` because it takes a type as an argument.
6300 See the :ref:`variable argument processing <int_varargs>` section.
6302 Note that the code generator does not yet fully support va\_arg on many
6303 targets. Also, it does not currently support va\_arg with aggregate
6304 types on any target.
6308 '``landingpad``' Instruction
6309 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6316 <resultval> = landingpad <resultty> personality <type> <pers_fn> <clause>+
6317 <resultval> = landingpad <resultty> personality <type> <pers_fn> cleanup <clause>*
6319 <clause> := catch <type> <value>
6320 <clause> := filter <array constant type> <array constant>
6325 The '``landingpad``' instruction is used by `LLVM's exception handling
6326 system <ExceptionHandling.html#overview>`_ to specify that a basic block
6327 is a landing pad --- one where the exception lands, and corresponds to the
6328 code found in the ``catch`` portion of a ``try``/``catch`` sequence. It
6329 defines values supplied by the personality function (``pers_fn``) upon
6330 re-entry to the function. The ``resultval`` has the type ``resultty``.
6335 This instruction takes a ``pers_fn`` value. This is the personality
6336 function associated with the unwinding mechanism. The optional
6337 ``cleanup`` flag indicates that the landing pad block is a cleanup.
6339 A ``clause`` begins with the clause type --- ``catch`` or ``filter`` --- and
6340 contains the global variable representing the "type" that may be caught
6341 or filtered respectively. Unlike the ``catch`` clause, the ``filter``
6342 clause takes an array constant as its argument. Use
6343 "``[0 x i8**] undef``" for a filter which cannot throw. The
6344 '``landingpad``' instruction must contain *at least* one ``clause`` or
6345 the ``cleanup`` flag.
6350 The '``landingpad``' instruction defines the values which are set by the
6351 personality function (``pers_fn``) upon re-entry to the function, and
6352 therefore the "result type" of the ``landingpad`` instruction. As with
6353 calling conventions, how the personality function results are
6354 represented in LLVM IR is target specific.
6356 The clauses are applied in order from top to bottom. If two
6357 ``landingpad`` instructions are merged together through inlining, the
6358 clauses from the calling function are appended to the list of clauses.
6359 When the call stack is being unwound due to an exception being thrown,
6360 the exception is compared against each ``clause`` in turn. If it doesn't
6361 match any of the clauses, and the ``cleanup`` flag is not set, then
6362 unwinding continues further up the call stack.
6364 The ``landingpad`` instruction has several restrictions:
6366 - A landing pad block is a basic block which is the unwind destination
6367 of an '``invoke``' instruction.
6368 - A landing pad block must have a '``landingpad``' instruction as its
6369 first non-PHI instruction.
6370 - There can be only one '``landingpad``' instruction within the landing
6372 - A basic block that is not a landing pad block may not include a
6373 '``landingpad``' instruction.
6374 - All '``landingpad``' instructions in a function must have the same
6375 personality function.
6380 .. code-block:: llvm
6382 ;; A landing pad which can catch an integer.
6383 %res = landingpad { i8*, i32 } personality i32 (...)* @__gxx_personality_v0
6385 ;; A landing pad that is a cleanup.
6386 %res = landingpad { i8*, i32 } personality i32 (...)* @__gxx_personality_v0
6388 ;; A landing pad which can catch an integer and can only throw a double.
6389 %res = landingpad { i8*, i32 } personality i32 (...)* @__gxx_personality_v0
6391 filter [1 x i8**] [@_ZTId]
6398 LLVM supports the notion of an "intrinsic function". These functions
6399 have well known names and semantics and are required to follow certain
6400 restrictions. Overall, these intrinsics represent an extension mechanism
6401 for the LLVM language that does not require changing all of the
6402 transformations in LLVM when adding to the language (or the bitcode
6403 reader/writer, the parser, etc...).
6405 Intrinsic function names must all start with an "``llvm.``" prefix. This
6406 prefix is reserved in LLVM for intrinsic names; thus, function names may
6407 not begin with this prefix. Intrinsic functions must always be external
6408 functions: you cannot define the body of intrinsic functions. Intrinsic
6409 functions may only be used in call or invoke instructions: it is illegal
6410 to take the address of an intrinsic function. Additionally, because
6411 intrinsic functions are part of the LLVM language, it is required if any
6412 are added that they be documented here.
6414 Some intrinsic functions can be overloaded, i.e., the intrinsic
6415 represents a family of functions that perform the same operation but on
6416 different data types. Because LLVM can represent over 8 million
6417 different integer types, overloading is used commonly to allow an
6418 intrinsic function to operate on any integer type. One or more of the
6419 argument types or the result type can be overloaded to accept any
6420 integer type. Argument types may also be defined as exactly matching a
6421 previous argument's type or the result type. This allows an intrinsic
6422 function which accepts multiple arguments, but needs all of them to be
6423 of the same type, to only be overloaded with respect to a single
6424 argument or the result.
6426 Overloaded intrinsics will have the names of its overloaded argument
6427 types encoded into its function name, each preceded by a period. Only
6428 those types which are overloaded result in a name suffix. Arguments
6429 whose type is matched against another type do not. For example, the
6430 ``llvm.ctpop`` function can take an integer of any width and returns an
6431 integer of exactly the same integer width. This leads to a family of
6432 functions such as ``i8 @llvm.ctpop.i8(i8 %val)`` and
6433 ``i29 @llvm.ctpop.i29(i29 %val)``. Only one type, the return type, is
6434 overloaded, and only one type suffix is required. Because the argument's
6435 type is matched against the return type, it does not require its own
6438 To learn how to add an intrinsic function, please see the `Extending
6439 LLVM Guide <ExtendingLLVM.html>`_.
6443 Variable Argument Handling Intrinsics
6444 -------------------------------------
6446 Variable argument support is defined in LLVM with the
6447 :ref:`va_arg <i_va_arg>` instruction and these three intrinsic
6448 functions. These functions are related to the similarly named macros
6449 defined in the ``<stdarg.h>`` header file.
6451 All of these functions operate on arguments that use a target-specific
6452 value type "``va_list``". The LLVM assembly language reference manual
6453 does not define what this type is, so all transformations should be
6454 prepared to handle these functions regardless of the type used.
6456 This example shows how the :ref:`va_arg <i_va_arg>` instruction and the
6457 variable argument handling intrinsic functions are used.
6459 .. code-block:: llvm
6461 define i32 @test(i32 %X, ...) {
6462 ; Initialize variable argument processing
6464 %ap2 = bitcast i8** %ap to i8*
6465 call void @llvm.va_start(i8* %ap2)
6467 ; Read a single integer argument
6468 %tmp = va_arg i8** %ap, i32
6470 ; Demonstrate usage of llvm.va_copy and llvm.va_end
6472 %aq2 = bitcast i8** %aq to i8*
6473 call void @llvm.va_copy(i8* %aq2, i8* %ap2)
6474 call void @llvm.va_end(i8* %aq2)
6476 ; Stop processing of arguments.
6477 call void @llvm.va_end(i8* %ap2)
6481 declare void @llvm.va_start(i8*)
6482 declare void @llvm.va_copy(i8*, i8*)
6483 declare void @llvm.va_end(i8*)
6487 '``llvm.va_start``' Intrinsic
6488 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6495 declare void @llvm.va_start(i8* <arglist>)
6500 The '``llvm.va_start``' intrinsic initializes ``*<arglist>`` for
6501 subsequent use by ``va_arg``.
6506 The argument is a pointer to a ``va_list`` element to initialize.
6511 The '``llvm.va_start``' intrinsic works just like the ``va_start`` macro
6512 available in C. In a target-dependent way, it initializes the
6513 ``va_list`` element to which the argument points, so that the next call
6514 to ``va_arg`` will produce the first variable argument passed to the
6515 function. Unlike the C ``va_start`` macro, this intrinsic does not need
6516 to know the last argument of the function as the compiler can figure
6519 '``llvm.va_end``' Intrinsic
6520 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
6527 declare void @llvm.va_end(i8* <arglist>)
6532 The '``llvm.va_end``' intrinsic destroys ``*<arglist>``, which has been
6533 initialized previously with ``llvm.va_start`` or ``llvm.va_copy``.
6538 The argument is a pointer to a ``va_list`` to destroy.
6543 The '``llvm.va_end``' intrinsic works just like the ``va_end`` macro
6544 available in C. In a target-dependent way, it destroys the ``va_list``
6545 element to which the argument points. Calls to
6546 :ref:`llvm.va_start <int_va_start>` and
6547 :ref:`llvm.va_copy <int_va_copy>` must be matched exactly with calls to
6552 '``llvm.va_copy``' Intrinsic
6553 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6560 declare void @llvm.va_copy(i8* <destarglist>, i8* <srcarglist>)
6565 The '``llvm.va_copy``' intrinsic copies the current argument position
6566 from the source argument list to the destination argument list.
6571 The first argument is a pointer to a ``va_list`` element to initialize.
6572 The second argument is a pointer to a ``va_list`` element to copy from.
6577 The '``llvm.va_copy``' intrinsic works just like the ``va_copy`` macro
6578 available in C. In a target-dependent way, it copies the source
6579 ``va_list`` element into the destination ``va_list`` element. This
6580 intrinsic is necessary because the `` llvm.va_start`` intrinsic may be
6581 arbitrarily complex and require, for example, memory allocation.
6583 Accurate Garbage Collection Intrinsics
6584 --------------------------------------
6586 LLVM support for `Accurate Garbage Collection <GarbageCollection.html>`_
6587 (GC) requires the implementation and generation of these intrinsics.
6588 These intrinsics allow identification of :ref:`GC roots on the
6589 stack <int_gcroot>`, as well as garbage collector implementations that
6590 require :ref:`read <int_gcread>` and :ref:`write <int_gcwrite>` barriers.
6591 Front-ends for type-safe garbage collected languages should generate
6592 these intrinsics to make use of the LLVM garbage collectors. For more
6593 details, see `Accurate Garbage Collection with
6594 LLVM <GarbageCollection.html>`_.
6596 The garbage collection intrinsics only operate on objects in the generic
6597 address space (address space zero).
6601 '``llvm.gcroot``' Intrinsic
6602 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
6609 declare void @llvm.gcroot(i8** %ptrloc, i8* %metadata)
6614 The '``llvm.gcroot``' intrinsic declares the existence of a GC root to
6615 the code generator, and allows some metadata to be associated with it.
6620 The first argument specifies the address of a stack object that contains
6621 the root pointer. The second pointer (which must be either a constant or
6622 a global value address) contains the meta-data to be associated with the
6628 At runtime, a call to this intrinsic stores a null pointer into the
6629 "ptrloc" location. At compile-time, the code generator generates
6630 information to allow the runtime to find the pointer at GC safe points.
6631 The '``llvm.gcroot``' intrinsic may only be used in a function which
6632 :ref:`specifies a GC algorithm <gc>`.
6636 '``llvm.gcread``' Intrinsic
6637 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
6644 declare i8* @llvm.gcread(i8* %ObjPtr, i8** %Ptr)
6649 The '``llvm.gcread``' intrinsic identifies reads of references from heap
6650 locations, allowing garbage collector implementations that require read
6656 The second argument is the address to read from, which should be an
6657 address allocated from the garbage collector. The first object is a
6658 pointer to the start of the referenced object, if needed by the language
6659 runtime (otherwise null).
6664 The '``llvm.gcread``' intrinsic has the same semantics as a load
6665 instruction, but may be replaced with substantially more complex code by
6666 the garbage collector runtime, as needed. The '``llvm.gcread``'
6667 intrinsic may only be used in a function which :ref:`specifies a GC
6672 '``llvm.gcwrite``' Intrinsic
6673 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6680 declare void @llvm.gcwrite(i8* %P1, i8* %Obj, i8** %P2)
6685 The '``llvm.gcwrite``' intrinsic identifies writes of references to heap
6686 locations, allowing garbage collector implementations that require write
6687 barriers (such as generational or reference counting collectors).
6692 The first argument is the reference to store, the second is the start of
6693 the object to store it to, and the third is the address of the field of
6694 Obj to store to. If the runtime does not require a pointer to the
6695 object, Obj may be null.
6700 The '``llvm.gcwrite``' intrinsic has the same semantics as a store
6701 instruction, but may be replaced with substantially more complex code by
6702 the garbage collector runtime, as needed. The '``llvm.gcwrite``'
6703 intrinsic may only be used in a function which :ref:`specifies a GC
6706 Code Generator Intrinsics
6707 -------------------------
6709 These intrinsics are provided by LLVM to expose special features that
6710 may only be implemented with code generator support.
6712 '``llvm.returnaddress``' Intrinsic
6713 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6720 declare i8 *@llvm.returnaddress(i32 <level>)
6725 The '``llvm.returnaddress``' intrinsic attempts to compute a
6726 target-specific value indicating the return address of the current
6727 function or one of its callers.
6732 The argument to this intrinsic indicates which function to return the
6733 address for. Zero indicates the calling function, one indicates its
6734 caller, etc. The argument is **required** to be a constant integer
6740 The '``llvm.returnaddress``' intrinsic either returns a pointer
6741 indicating the return address of the specified call frame, or zero if it
6742 cannot be identified. The value returned by this intrinsic is likely to
6743 be incorrect or 0 for arguments other than zero, so it should only be
6744 used for debugging purposes.
6746 Note that calling this intrinsic does not prevent function inlining or
6747 other aggressive transformations, so the value returned may not be that
6748 of the obvious source-language caller.
6750 '``llvm.frameaddress``' Intrinsic
6751 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6758 declare i8* @llvm.frameaddress(i32 <level>)
6763 The '``llvm.frameaddress``' intrinsic attempts to return the
6764 target-specific frame pointer value for the specified stack frame.
6769 The argument to this intrinsic indicates which function to return the
6770 frame pointer for. Zero indicates the calling function, one indicates
6771 its caller, etc. The argument is **required** to be a constant integer
6777 The '``llvm.frameaddress``' intrinsic either returns a pointer
6778 indicating the frame address of the specified call frame, or zero if it
6779 cannot be identified. The value returned by this intrinsic is likely to
6780 be incorrect or 0 for arguments other than zero, so it should only be
6781 used for debugging purposes.
6783 Note that calling this intrinsic does not prevent function inlining or
6784 other aggressive transformations, so the value returned may not be that
6785 of the obvious source-language caller.
6789 '``llvm.stacksave``' Intrinsic
6790 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6797 declare i8* @llvm.stacksave()
6802 The '``llvm.stacksave``' intrinsic is used to remember the current state
6803 of the function stack, for use with
6804 :ref:`llvm.stackrestore <int_stackrestore>`. This is useful for
6805 implementing language features like scoped automatic variable sized
6811 This intrinsic returns a opaque pointer value that can be passed to
6812 :ref:`llvm.stackrestore <int_stackrestore>`. When an
6813 ``llvm.stackrestore`` intrinsic is executed with a value saved from
6814 ``llvm.stacksave``, it effectively restores the state of the stack to
6815 the state it was in when the ``llvm.stacksave`` intrinsic executed. In
6816 practice, this pops any :ref:`alloca <i_alloca>` blocks from the stack that
6817 were allocated after the ``llvm.stacksave`` was executed.
6819 .. _int_stackrestore:
6821 '``llvm.stackrestore``' Intrinsic
6822 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6829 declare void @llvm.stackrestore(i8* %ptr)
6834 The '``llvm.stackrestore``' intrinsic is used to restore the state of
6835 the function stack to the state it was in when the corresponding
6836 :ref:`llvm.stacksave <int_stacksave>` intrinsic executed. This is
6837 useful for implementing language features like scoped automatic variable
6838 sized arrays in C99.
6843 See the description for :ref:`llvm.stacksave <int_stacksave>`.
6845 '``llvm.prefetch``' Intrinsic
6846 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6853 declare void @llvm.prefetch(i8* <address>, i32 <rw>, i32 <locality>, i32 <cache type>)
6858 The '``llvm.prefetch``' intrinsic is a hint to the code generator to
6859 insert a prefetch instruction if supported; otherwise, it is a noop.
6860 Prefetches have no effect on the behavior of the program but can change
6861 its performance characteristics.
6866 ``address`` is the address to be prefetched, ``rw`` is the specifier
6867 determining if the fetch should be for a read (0) or write (1), and
6868 ``locality`` is a temporal locality specifier ranging from (0) - no
6869 locality, to (3) - extremely local keep in cache. The ``cache type``
6870 specifies whether the prefetch is performed on the data (1) or
6871 instruction (0) cache. The ``rw``, ``locality`` and ``cache type``
6872 arguments must be constant integers.
6877 This intrinsic does not modify the behavior of the program. In
6878 particular, prefetches cannot trap and do not produce a value. On
6879 targets that support this intrinsic, the prefetch can provide hints to
6880 the processor cache for better performance.
6882 '``llvm.pcmarker``' Intrinsic
6883 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6890 declare void @llvm.pcmarker(i32 <id>)
6895 The '``llvm.pcmarker``' intrinsic is a method to export a Program
6896 Counter (PC) in a region of code to simulators and other tools. The
6897 method is target specific, but it is expected that the marker will use
6898 exported symbols to transmit the PC of the marker. The marker makes no
6899 guarantees that it will remain with any specific instruction after
6900 optimizations. It is possible that the presence of a marker will inhibit
6901 optimizations. The intended use is to be inserted after optimizations to
6902 allow correlations of simulation runs.
6907 ``id`` is a numerical id identifying the marker.
6912 This intrinsic does not modify the behavior of the program. Backends
6913 that do not support this intrinsic may ignore it.
6915 '``llvm.readcyclecounter``' Intrinsic
6916 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6923 declare i64 @llvm.readcyclecounter()
6928 The '``llvm.readcyclecounter``' intrinsic provides access to the cycle
6929 counter register (or similar low latency, high accuracy clocks) on those
6930 targets that support it. On X86, it should map to RDTSC. On Alpha, it
6931 should map to RPCC. As the backing counters overflow quickly (on the
6932 order of 9 seconds on alpha), this should only be used for small
6938 When directly supported, reading the cycle counter should not modify any
6939 memory. Implementations are allowed to either return a application
6940 specific value or a system wide value. On backends without support, this
6941 is lowered to a constant 0.
6943 Note that runtime support may be conditional on the privilege-level code is
6944 running at and the host platform.
6946 Standard C Library Intrinsics
6947 -----------------------------
6949 LLVM provides intrinsics for a few important standard C library
6950 functions. These intrinsics allow source-language front-ends to pass
6951 information about the alignment of the pointer arguments to the code
6952 generator, providing opportunity for more efficient code generation.
6956 '``llvm.memcpy``' Intrinsic
6957 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
6962 This is an overloaded intrinsic. You can use ``llvm.memcpy`` on any
6963 integer bit width and for different address spaces. Not all targets
6964 support all bit widths however.
6968 declare void @llvm.memcpy.p0i8.p0i8.i32(i8* <dest>, i8* <src>,
6969 i32 <len>, i32 <align>, i1 <isvolatile>)
6970 declare void @llvm.memcpy.p0i8.p0i8.i64(i8* <dest>, i8* <src>,
6971 i64 <len>, i32 <align>, i1 <isvolatile>)
6976 The '``llvm.memcpy.*``' intrinsics copy a block of memory from the
6977 source location to the destination location.
6979 Note that, unlike the standard libc function, the ``llvm.memcpy.*``
6980 intrinsics do not return a value, takes extra alignment/isvolatile
6981 arguments and the pointers can be in specified address spaces.
6986 The first argument is a pointer to the destination, the second is a
6987 pointer to the source. The third argument is an integer argument
6988 specifying the number of bytes to copy, the fourth argument is the
6989 alignment of the source and destination locations, and the fifth is a
6990 boolean indicating a volatile access.
6992 If the call to this intrinsic has an alignment value that is not 0 or 1,
6993 then the caller guarantees that both the source and destination pointers
6994 are aligned to that boundary.
6996 If the ``isvolatile`` parameter is ``true``, the ``llvm.memcpy`` call is
6997 a :ref:`volatile operation <volatile>`. The detailed access behavior is not
6998 very cleanly specified and it is unwise to depend on it.
7003 The '``llvm.memcpy.*``' intrinsics copy a block of memory from the
7004 source location to the destination location, which are not allowed to
7005 overlap. It copies "len" bytes of memory over. If the argument is known
7006 to be aligned to some boundary, this can be specified as the fourth
7007 argument, otherwise it should be set to 0 or 1 (both meaning no alignment).
7009 '``llvm.memmove``' Intrinsic
7010 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7015 This is an overloaded intrinsic. You can use llvm.memmove on any integer
7016 bit width and for different address space. Not all targets support all
7021 declare void @llvm.memmove.p0i8.p0i8.i32(i8* <dest>, i8* <src>,
7022 i32 <len>, i32 <align>, i1 <isvolatile>)
7023 declare void @llvm.memmove.p0i8.p0i8.i64(i8* <dest>, i8* <src>,
7024 i64 <len>, i32 <align>, i1 <isvolatile>)
7029 The '``llvm.memmove.*``' intrinsics move a block of memory from the
7030 source location to the destination location. It is similar to the
7031 '``llvm.memcpy``' intrinsic but allows the two memory locations to
7034 Note that, unlike the standard libc function, the ``llvm.memmove.*``
7035 intrinsics do not return a value, takes extra alignment/isvolatile
7036 arguments and the pointers can be in specified address spaces.
7041 The first argument is a pointer to the destination, the second is a
7042 pointer to the source. The third argument is an integer argument
7043 specifying the number of bytes to copy, the fourth argument is the
7044 alignment of the source and destination locations, and the fifth is a
7045 boolean indicating a volatile access.
7047 If the call to this intrinsic has an alignment value that is not 0 or 1,
7048 then the caller guarantees that the source and destination pointers are
7049 aligned to that boundary.
7051 If the ``isvolatile`` parameter is ``true``, the ``llvm.memmove`` call
7052 is a :ref:`volatile operation <volatile>`. The detailed access behavior is
7053 not very cleanly specified and it is unwise to depend on it.
7058 The '``llvm.memmove.*``' intrinsics copy a block of memory from the
7059 source location to the destination location, which may overlap. It
7060 copies "len" bytes of memory over. If the argument is known to be
7061 aligned to some boundary, this can be specified as the fourth argument,
7062 otherwise it should be set to 0 or 1 (both meaning no alignment).
7064 '``llvm.memset.*``' Intrinsics
7065 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7070 This is an overloaded intrinsic. You can use llvm.memset on any integer
7071 bit width and for different address spaces. However, not all targets
7072 support all bit widths.
7076 declare void @llvm.memset.p0i8.i32(i8* <dest>, i8 <val>,
7077 i32 <len>, i32 <align>, i1 <isvolatile>)
7078 declare void @llvm.memset.p0i8.i64(i8* <dest>, i8 <val>,
7079 i64 <len>, i32 <align>, i1 <isvolatile>)
7084 The '``llvm.memset.*``' intrinsics fill a block of memory with a
7085 particular byte value.
7087 Note that, unlike the standard libc function, the ``llvm.memset``
7088 intrinsic does not return a value and takes extra alignment/volatile
7089 arguments. Also, the destination can be in an arbitrary address space.
7094 The first argument is a pointer to the destination to fill, the second
7095 is the byte value with which to fill it, the third argument is an
7096 integer argument specifying the number of bytes to fill, and the fourth
7097 argument is the known alignment of the destination location.
7099 If the call to this intrinsic has an alignment value that is not 0 or 1,
7100 then the caller guarantees that the destination pointer is aligned to
7103 If the ``isvolatile`` parameter is ``true``, the ``llvm.memset`` call is
7104 a :ref:`volatile operation <volatile>`. The detailed access behavior is not
7105 very cleanly specified and it is unwise to depend on it.
7110 The '``llvm.memset.*``' intrinsics fill "len" bytes of memory starting
7111 at the destination location. If the argument is known to be aligned to
7112 some boundary, this can be specified as the fourth argument, otherwise
7113 it should be set to 0 or 1 (both meaning no alignment).
7115 '``llvm.sqrt.*``' Intrinsic
7116 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
7121 This is an overloaded intrinsic. You can use ``llvm.sqrt`` on any
7122 floating point or vector of floating point type. Not all targets support
7127 declare float @llvm.sqrt.f32(float %Val)
7128 declare double @llvm.sqrt.f64(double %Val)
7129 declare x86_fp80 @llvm.sqrt.f80(x86_fp80 %Val)
7130 declare fp128 @llvm.sqrt.f128(fp128 %Val)
7131 declare ppc_fp128 @llvm.sqrt.ppcf128(ppc_fp128 %Val)
7136 The '``llvm.sqrt``' intrinsics return the sqrt of the specified operand,
7137 returning the same value as the libm '``sqrt``' functions would. Unlike
7138 ``sqrt`` in libm, however, ``llvm.sqrt`` has undefined behavior for
7139 negative numbers other than -0.0 (which allows for better optimization,
7140 because there is no need to worry about errno being set).
7141 ``llvm.sqrt(-0.0)`` is defined to return -0.0 like IEEE sqrt.
7146 The argument and return value are floating point numbers of the same
7152 This function returns the sqrt of the specified operand if it is a
7153 nonnegative floating point number.
7155 '``llvm.powi.*``' Intrinsic
7156 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
7161 This is an overloaded intrinsic. You can use ``llvm.powi`` on any
7162 floating point or vector of floating point type. Not all targets support
7167 declare float @llvm.powi.f32(float %Val, i32 %power)
7168 declare double @llvm.powi.f64(double %Val, i32 %power)
7169 declare x86_fp80 @llvm.powi.f80(x86_fp80 %Val, i32 %power)
7170 declare fp128 @llvm.powi.f128(fp128 %Val, i32 %power)
7171 declare ppc_fp128 @llvm.powi.ppcf128(ppc_fp128 %Val, i32 %power)
7176 The '``llvm.powi.*``' intrinsics return the first operand raised to the
7177 specified (positive or negative) power. The order of evaluation of
7178 multiplications is not defined. When a vector of floating point type is
7179 used, the second argument remains a scalar integer value.
7184 The second argument is an integer power, and the first is a value to
7185 raise to that power.
7190 This function returns the first value raised to the second power with an
7191 unspecified sequence of rounding operations.
7193 '``llvm.sin.*``' Intrinsic
7194 ^^^^^^^^^^^^^^^^^^^^^^^^^^
7199 This is an overloaded intrinsic. You can use ``llvm.sin`` on any
7200 floating point or vector of floating point type. Not all targets support
7205 declare float @llvm.sin.f32(float %Val)
7206 declare double @llvm.sin.f64(double %Val)
7207 declare x86_fp80 @llvm.sin.f80(x86_fp80 %Val)
7208 declare fp128 @llvm.sin.f128(fp128 %Val)
7209 declare ppc_fp128 @llvm.sin.ppcf128(ppc_fp128 %Val)
7214 The '``llvm.sin.*``' intrinsics return the sine of the operand.
7219 The argument and return value are floating point numbers of the same
7225 This function returns the sine of the specified operand, returning the
7226 same values as the libm ``sin`` functions would, and handles error
7227 conditions in the same way.
7229 '``llvm.cos.*``' Intrinsic
7230 ^^^^^^^^^^^^^^^^^^^^^^^^^^
7235 This is an overloaded intrinsic. You can use ``llvm.cos`` on any
7236 floating point or vector of floating point type. Not all targets support
7241 declare float @llvm.cos.f32(float %Val)
7242 declare double @llvm.cos.f64(double %Val)
7243 declare x86_fp80 @llvm.cos.f80(x86_fp80 %Val)
7244 declare fp128 @llvm.cos.f128(fp128 %Val)
7245 declare ppc_fp128 @llvm.cos.ppcf128(ppc_fp128 %Val)
7250 The '``llvm.cos.*``' intrinsics return the cosine of the operand.
7255 The argument and return value are floating point numbers of the same
7261 This function returns the cosine of the specified operand, returning the
7262 same values as the libm ``cos`` functions would, and handles error
7263 conditions in the same way.
7265 '``llvm.pow.*``' Intrinsic
7266 ^^^^^^^^^^^^^^^^^^^^^^^^^^
7271 This is an overloaded intrinsic. You can use ``llvm.pow`` on any
7272 floating point or vector of floating point type. Not all targets support
7277 declare float @llvm.pow.f32(float %Val, float %Power)
7278 declare double @llvm.pow.f64(double %Val, double %Power)
7279 declare x86_fp80 @llvm.pow.f80(x86_fp80 %Val, x86_fp80 %Power)
7280 declare fp128 @llvm.pow.f128(fp128 %Val, fp128 %Power)
7281 declare ppc_fp128 @llvm.pow.ppcf128(ppc_fp128 %Val, ppc_fp128 Power)
7286 The '``llvm.pow.*``' intrinsics return the first operand raised to the
7287 specified (positive or negative) power.
7292 The second argument is a floating point power, and the first is a value
7293 to raise to that power.
7298 This function returns the first value raised to the second power,
7299 returning the same values as the libm ``pow`` functions would, and
7300 handles error conditions in the same way.
7302 '``llvm.exp.*``' Intrinsic
7303 ^^^^^^^^^^^^^^^^^^^^^^^^^^
7308 This is an overloaded intrinsic. You can use ``llvm.exp`` on any
7309 floating point or vector of floating point type. Not all targets support
7314 declare float @llvm.exp.f32(float %Val)
7315 declare double @llvm.exp.f64(double %Val)
7316 declare x86_fp80 @llvm.exp.f80(x86_fp80 %Val)
7317 declare fp128 @llvm.exp.f128(fp128 %Val)
7318 declare ppc_fp128 @llvm.exp.ppcf128(ppc_fp128 %Val)
7323 The '``llvm.exp.*``' intrinsics perform the exp function.
7328 The argument and return value are floating point numbers of the same
7334 This function returns the same values as the libm ``exp`` functions
7335 would, and handles error conditions in the same way.
7337 '``llvm.exp2.*``' Intrinsic
7338 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
7343 This is an overloaded intrinsic. You can use ``llvm.exp2`` on any
7344 floating point or vector of floating point type. Not all targets support
7349 declare float @llvm.exp2.f32(float %Val)
7350 declare double @llvm.exp2.f64(double %Val)
7351 declare x86_fp80 @llvm.exp2.f80(x86_fp80 %Val)
7352 declare fp128 @llvm.exp2.f128(fp128 %Val)
7353 declare ppc_fp128 @llvm.exp2.ppcf128(ppc_fp128 %Val)
7358 The '``llvm.exp2.*``' intrinsics perform the exp2 function.
7363 The argument and return value are floating point numbers of the same
7369 This function returns the same values as the libm ``exp2`` functions
7370 would, and handles error conditions in the same way.
7372 '``llvm.log.*``' Intrinsic
7373 ^^^^^^^^^^^^^^^^^^^^^^^^^^
7378 This is an overloaded intrinsic. You can use ``llvm.log`` on any
7379 floating point or vector of floating point type. Not all targets support
7384 declare float @llvm.log.f32(float %Val)
7385 declare double @llvm.log.f64(double %Val)
7386 declare x86_fp80 @llvm.log.f80(x86_fp80 %Val)
7387 declare fp128 @llvm.log.f128(fp128 %Val)
7388 declare ppc_fp128 @llvm.log.ppcf128(ppc_fp128 %Val)
7393 The '``llvm.log.*``' intrinsics perform the log function.
7398 The argument and return value are floating point numbers of the same
7404 This function returns the same values as the libm ``log`` functions
7405 would, and handles error conditions in the same way.
7407 '``llvm.log10.*``' Intrinsic
7408 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7413 This is an overloaded intrinsic. You can use ``llvm.log10`` on any
7414 floating point or vector of floating point type. Not all targets support
7419 declare float @llvm.log10.f32(float %Val)
7420 declare double @llvm.log10.f64(double %Val)
7421 declare x86_fp80 @llvm.log10.f80(x86_fp80 %Val)
7422 declare fp128 @llvm.log10.f128(fp128 %Val)
7423 declare ppc_fp128 @llvm.log10.ppcf128(ppc_fp128 %Val)
7428 The '``llvm.log10.*``' intrinsics perform the log10 function.
7433 The argument and return value are floating point numbers of the same
7439 This function returns the same values as the libm ``log10`` functions
7440 would, and handles error conditions in the same way.
7442 '``llvm.log2.*``' Intrinsic
7443 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
7448 This is an overloaded intrinsic. You can use ``llvm.log2`` on any
7449 floating point or vector of floating point type. Not all targets support
7454 declare float @llvm.log2.f32(float %Val)
7455 declare double @llvm.log2.f64(double %Val)
7456 declare x86_fp80 @llvm.log2.f80(x86_fp80 %Val)
7457 declare fp128 @llvm.log2.f128(fp128 %Val)
7458 declare ppc_fp128 @llvm.log2.ppcf128(ppc_fp128 %Val)
7463 The '``llvm.log2.*``' intrinsics perform the log2 function.
7468 The argument and return value are floating point numbers of the same
7474 This function returns the same values as the libm ``log2`` functions
7475 would, and handles error conditions in the same way.
7477 '``llvm.fma.*``' Intrinsic
7478 ^^^^^^^^^^^^^^^^^^^^^^^^^^
7483 This is an overloaded intrinsic. You can use ``llvm.fma`` on any
7484 floating point or vector of floating point type. Not all targets support
7489 declare float @llvm.fma.f32(float %a, float %b, float %c)
7490 declare double @llvm.fma.f64(double %a, double %b, double %c)
7491 declare x86_fp80 @llvm.fma.f80(x86_fp80 %a, x86_fp80 %b, x86_fp80 %c)
7492 declare fp128 @llvm.fma.f128(fp128 %a, fp128 %b, fp128 %c)
7493 declare ppc_fp128 @llvm.fma.ppcf128(ppc_fp128 %a, ppc_fp128 %b, ppc_fp128 %c)
7498 The '``llvm.fma.*``' intrinsics perform the fused multiply-add
7504 The argument and return value are floating point numbers of the same
7510 This function returns the same values as the libm ``fma`` functions
7511 would, and does not set errno.
7513 '``llvm.fabs.*``' Intrinsic
7514 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
7519 This is an overloaded intrinsic. You can use ``llvm.fabs`` on any
7520 floating point or vector of floating point type. Not all targets support
7525 declare float @llvm.fabs.f32(float %Val)
7526 declare double @llvm.fabs.f64(double %Val)
7527 declare x86_fp80 @llvm.fabs.f80(x86_fp80 %Val)
7528 declare fp128 @llvm.fabs.f128(fp128 %Val)
7529 declare ppc_fp128 @llvm.fabs.ppcf128(ppc_fp128 %Val)
7534 The '``llvm.fabs.*``' intrinsics return the absolute value of the
7540 The argument and return value are floating point numbers of the same
7546 This function returns the same values as the libm ``fabs`` functions
7547 would, and handles error conditions in the same way.
7549 '``llvm.copysign.*``' Intrinsic
7550 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7555 This is an overloaded intrinsic. You can use ``llvm.copysign`` on any
7556 floating point or vector of floating point type. Not all targets support
7561 declare float @llvm.copysign.f32(float %Mag, float %Sgn)
7562 declare double @llvm.copysign.f64(double %Mag, double %Sgn)
7563 declare x86_fp80 @llvm.copysign.f80(x86_fp80 %Mag, x86_fp80 %Sgn)
7564 declare fp128 @llvm.copysign.f128(fp128 %Mag, fp128 %Sgn)
7565 declare ppc_fp128 @llvm.copysign.ppcf128(ppc_fp128 %Mag, ppc_fp128 %Sgn)
7570 The '``llvm.copysign.*``' intrinsics return a value with the magnitude of the
7571 first operand and the sign of the second operand.
7576 The arguments and return value are floating point numbers of the same
7582 This function returns the same values as the libm ``copysign``
7583 functions would, and handles error conditions in the same way.
7585 '``llvm.floor.*``' Intrinsic
7586 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7591 This is an overloaded intrinsic. You can use ``llvm.floor`` on any
7592 floating point or vector of floating point type. Not all targets support
7597 declare float @llvm.floor.f32(float %Val)
7598 declare double @llvm.floor.f64(double %Val)
7599 declare x86_fp80 @llvm.floor.f80(x86_fp80 %Val)
7600 declare fp128 @llvm.floor.f128(fp128 %Val)
7601 declare ppc_fp128 @llvm.floor.ppcf128(ppc_fp128 %Val)
7606 The '``llvm.floor.*``' intrinsics return the floor of the operand.
7611 The argument and return value are floating point numbers of the same
7617 This function returns the same values as the libm ``floor`` functions
7618 would, and handles error conditions in the same way.
7620 '``llvm.ceil.*``' Intrinsic
7621 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
7626 This is an overloaded intrinsic. You can use ``llvm.ceil`` on any
7627 floating point or vector of floating point type. Not all targets support
7632 declare float @llvm.ceil.f32(float %Val)
7633 declare double @llvm.ceil.f64(double %Val)
7634 declare x86_fp80 @llvm.ceil.f80(x86_fp80 %Val)
7635 declare fp128 @llvm.ceil.f128(fp128 %Val)
7636 declare ppc_fp128 @llvm.ceil.ppcf128(ppc_fp128 %Val)
7641 The '``llvm.ceil.*``' intrinsics return the ceiling of the operand.
7646 The argument and return value are floating point numbers of the same
7652 This function returns the same values as the libm ``ceil`` functions
7653 would, and handles error conditions in the same way.
7655 '``llvm.trunc.*``' Intrinsic
7656 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7661 This is an overloaded intrinsic. You can use ``llvm.trunc`` on any
7662 floating point or vector of floating point type. Not all targets support
7667 declare float @llvm.trunc.f32(float %Val)
7668 declare double @llvm.trunc.f64(double %Val)
7669 declare x86_fp80 @llvm.trunc.f80(x86_fp80 %Val)
7670 declare fp128 @llvm.trunc.f128(fp128 %Val)
7671 declare ppc_fp128 @llvm.trunc.ppcf128(ppc_fp128 %Val)
7676 The '``llvm.trunc.*``' intrinsics returns the operand rounded to the
7677 nearest integer not larger in magnitude than the operand.
7682 The argument and return value are floating point numbers of the same
7688 This function returns the same values as the libm ``trunc`` functions
7689 would, and handles error conditions in the same way.
7691 '``llvm.rint.*``' Intrinsic
7692 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
7697 This is an overloaded intrinsic. You can use ``llvm.rint`` on any
7698 floating point or vector of floating point type. Not all targets support
7703 declare float @llvm.rint.f32(float %Val)
7704 declare double @llvm.rint.f64(double %Val)
7705 declare x86_fp80 @llvm.rint.f80(x86_fp80 %Val)
7706 declare fp128 @llvm.rint.f128(fp128 %Val)
7707 declare ppc_fp128 @llvm.rint.ppcf128(ppc_fp128 %Val)
7712 The '``llvm.rint.*``' intrinsics returns the operand rounded to the
7713 nearest integer. It may raise an inexact floating-point exception if the
7714 operand isn't an integer.
7719 The argument and return value are floating point numbers of the same
7725 This function returns the same values as the libm ``rint`` functions
7726 would, and handles error conditions in the same way.
7728 '``llvm.nearbyint.*``' Intrinsic
7729 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7734 This is an overloaded intrinsic. You can use ``llvm.nearbyint`` on any
7735 floating point or vector of floating point type. Not all targets support
7740 declare float @llvm.nearbyint.f32(float %Val)
7741 declare double @llvm.nearbyint.f64(double %Val)
7742 declare x86_fp80 @llvm.nearbyint.f80(x86_fp80 %Val)
7743 declare fp128 @llvm.nearbyint.f128(fp128 %Val)
7744 declare ppc_fp128 @llvm.nearbyint.ppcf128(ppc_fp128 %Val)
7749 The '``llvm.nearbyint.*``' intrinsics returns the operand rounded to the
7755 The argument and return value are floating point numbers of the same
7761 This function returns the same values as the libm ``nearbyint``
7762 functions would, and handles error conditions in the same way.
7764 '``llvm.round.*``' Intrinsic
7765 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7770 This is an overloaded intrinsic. You can use ``llvm.round`` on any
7771 floating point or vector of floating point type. Not all targets support
7776 declare float @llvm.round.f32(float %Val)
7777 declare double @llvm.round.f64(double %Val)
7778 declare x86_fp80 @llvm.round.f80(x86_fp80 %Val)
7779 declare fp128 @llvm.round.f128(fp128 %Val)
7780 declare ppc_fp128 @llvm.round.ppcf128(ppc_fp128 %Val)
7785 The '``llvm.round.*``' intrinsics returns the operand rounded to the
7791 The argument and return value are floating point numbers of the same
7797 This function returns the same values as the libm ``round``
7798 functions would, and handles error conditions in the same way.
7800 Bit Manipulation Intrinsics
7801 ---------------------------
7803 LLVM provides intrinsics for a few important bit manipulation
7804 operations. These allow efficient code generation for some algorithms.
7806 '``llvm.bswap.*``' Intrinsics
7807 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7812 This is an overloaded intrinsic function. You can use bswap on any
7813 integer type that is an even number of bytes (i.e. BitWidth % 16 == 0).
7817 declare i16 @llvm.bswap.i16(i16 <id>)
7818 declare i32 @llvm.bswap.i32(i32 <id>)
7819 declare i64 @llvm.bswap.i64(i64 <id>)
7824 The '``llvm.bswap``' family of intrinsics is used to byte swap integer
7825 values with an even number of bytes (positive multiple of 16 bits).
7826 These are useful for performing operations on data that is not in the
7827 target's native byte order.
7832 The ``llvm.bswap.i16`` intrinsic returns an i16 value that has the high
7833 and low byte of the input i16 swapped. Similarly, the ``llvm.bswap.i32``
7834 intrinsic returns an i32 value that has the four bytes of the input i32
7835 swapped, so that if the input bytes are numbered 0, 1, 2, 3 then the
7836 returned i32 will have its bytes in 3, 2, 1, 0 order. The
7837 ``llvm.bswap.i48``, ``llvm.bswap.i64`` and other intrinsics extend this
7838 concept to additional even-byte lengths (6 bytes, 8 bytes and more,
7841 '``llvm.ctpop.*``' Intrinsic
7842 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7847 This is an overloaded intrinsic. You can use llvm.ctpop on any integer
7848 bit width, or on any vector with integer elements. Not all targets
7849 support all bit widths or vector types, however.
7853 declare i8 @llvm.ctpop.i8(i8 <src>)
7854 declare i16 @llvm.ctpop.i16(i16 <src>)
7855 declare i32 @llvm.ctpop.i32(i32 <src>)
7856 declare i64 @llvm.ctpop.i64(i64 <src>)
7857 declare i256 @llvm.ctpop.i256(i256 <src>)
7858 declare <2 x i32> @llvm.ctpop.v2i32(<2 x i32> <src>)
7863 The '``llvm.ctpop``' family of intrinsics counts the number of bits set
7869 The only argument is the value to be counted. The argument may be of any
7870 integer type, or a vector with integer elements. The return type must
7871 match the argument type.
7876 The '``llvm.ctpop``' intrinsic counts the 1's in a variable, or within
7877 each element of a vector.
7879 '``llvm.ctlz.*``' Intrinsic
7880 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
7885 This is an overloaded intrinsic. You can use ``llvm.ctlz`` on any
7886 integer bit width, or any vector whose elements are integers. Not all
7887 targets support all bit widths or vector types, however.
7891 declare i8 @llvm.ctlz.i8 (i8 <src>, i1 <is_zero_undef>)
7892 declare i16 @llvm.ctlz.i16 (i16 <src>, i1 <is_zero_undef>)
7893 declare i32 @llvm.ctlz.i32 (i32 <src>, i1 <is_zero_undef>)
7894 declare i64 @llvm.ctlz.i64 (i64 <src>, i1 <is_zero_undef>)
7895 declare i256 @llvm.ctlz.i256(i256 <src>, i1 <is_zero_undef>)
7896 declase <2 x i32> @llvm.ctlz.v2i32(<2 x i32> <src>, i1 <is_zero_undef>)
7901 The '``llvm.ctlz``' family of intrinsic functions counts the number of
7902 leading zeros in a variable.
7907 The first argument is the value to be counted. This argument may be of
7908 any integer type, or a vectory with integer element type. The return
7909 type must match the first argument type.
7911 The second argument must be a constant and is a flag to indicate whether
7912 the intrinsic should ensure that a zero as the first argument produces a
7913 defined result. Historically some architectures did not provide a
7914 defined result for zero values as efficiently, and many algorithms are
7915 now predicated on avoiding zero-value inputs.
7920 The '``llvm.ctlz``' intrinsic counts the leading (most significant)
7921 zeros in a variable, or within each element of the vector. If
7922 ``src == 0`` then the result is the size in bits of the type of ``src``
7923 if ``is_zero_undef == 0`` and ``undef`` otherwise. For example,
7924 ``llvm.ctlz(i32 2) = 30``.
7926 '``llvm.cttz.*``' Intrinsic
7927 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
7932 This is an overloaded intrinsic. You can use ``llvm.cttz`` on any
7933 integer bit width, or any vector of integer elements. Not all targets
7934 support all bit widths or vector types, however.
7938 declare i8 @llvm.cttz.i8 (i8 <src>, i1 <is_zero_undef>)
7939 declare i16 @llvm.cttz.i16 (i16 <src>, i1 <is_zero_undef>)
7940 declare i32 @llvm.cttz.i32 (i32 <src>, i1 <is_zero_undef>)
7941 declare i64 @llvm.cttz.i64 (i64 <src>, i1 <is_zero_undef>)
7942 declare i256 @llvm.cttz.i256(i256 <src>, i1 <is_zero_undef>)
7943 declase <2 x i32> @llvm.cttz.v2i32(<2 x i32> <src>, i1 <is_zero_undef>)
7948 The '``llvm.cttz``' family of intrinsic functions counts the number of
7954 The first argument is the value to be counted. This argument may be of
7955 any integer type, or a vectory with integer element type. The return
7956 type must match the first argument type.
7958 The second argument must be a constant and is a flag to indicate whether
7959 the intrinsic should ensure that a zero as the first argument produces a
7960 defined result. Historically some architectures did not provide a
7961 defined result for zero values as efficiently, and many algorithms are
7962 now predicated on avoiding zero-value inputs.
7967 The '``llvm.cttz``' intrinsic counts the trailing (least significant)
7968 zeros in a variable, or within each element of a vector. If ``src == 0``
7969 then the result is the size in bits of the type of ``src`` if
7970 ``is_zero_undef == 0`` and ``undef`` otherwise. For example,
7971 ``llvm.cttz(2) = 1``.
7973 Arithmetic with Overflow Intrinsics
7974 -----------------------------------
7976 LLVM provides intrinsics for some arithmetic with overflow operations.
7978 '``llvm.sadd.with.overflow.*``' Intrinsics
7979 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7984 This is an overloaded intrinsic. You can use ``llvm.sadd.with.overflow``
7985 on any integer bit width.
7989 declare {i16, i1} @llvm.sadd.with.overflow.i16(i16 %a, i16 %b)
7990 declare {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b)
7991 declare {i64, i1} @llvm.sadd.with.overflow.i64(i64 %a, i64 %b)
7996 The '``llvm.sadd.with.overflow``' family of intrinsic functions perform
7997 a signed addition of the two arguments, and indicate whether an overflow
7998 occurred during the signed summation.
8003 The arguments (%a and %b) and the first element of the result structure
8004 may be of integer types of any bit width, but they must have the same
8005 bit width. The second element of the result structure must be of type
8006 ``i1``. ``%a`` and ``%b`` are the two values that will undergo signed
8012 The '``llvm.sadd.with.overflow``' family of intrinsic functions perform
8013 a signed addition of the two variables. They return a structure --- the
8014 first element of which is the signed summation, and the second element
8015 of which is a bit specifying if the signed summation resulted in an
8021 .. code-block:: llvm
8023 %res = call {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b)
8024 %sum = extractvalue {i32, i1} %res, 0
8025 %obit = extractvalue {i32, i1} %res, 1
8026 br i1 %obit, label %overflow, label %normal
8028 '``llvm.uadd.with.overflow.*``' Intrinsics
8029 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8034 This is an overloaded intrinsic. You can use ``llvm.uadd.with.overflow``
8035 on any integer bit width.
8039 declare {i16, i1} @llvm.uadd.with.overflow.i16(i16 %a, i16 %b)
8040 declare {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)
8041 declare {i64, i1} @llvm.uadd.with.overflow.i64(i64 %a, i64 %b)
8046 The '``llvm.uadd.with.overflow``' family of intrinsic functions perform
8047 an unsigned addition of the two arguments, and indicate whether a carry
8048 occurred during the unsigned summation.
8053 The arguments (%a and %b) and the first element of the result structure
8054 may be of integer types of any bit width, but they must have the same
8055 bit width. The second element of the result structure must be of type
8056 ``i1``. ``%a`` and ``%b`` are the two values that will undergo unsigned
8062 The '``llvm.uadd.with.overflow``' family of intrinsic functions perform
8063 an unsigned addition of the two arguments. They return a structure --- the
8064 first element of which is the sum, and the second element of which is a
8065 bit specifying if the unsigned summation resulted in a carry.
8070 .. code-block:: llvm
8072 %res = call {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)
8073 %sum = extractvalue {i32, i1} %res, 0
8074 %obit = extractvalue {i32, i1} %res, 1
8075 br i1 %obit, label %carry, label %normal
8077 '``llvm.ssub.with.overflow.*``' Intrinsics
8078 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8083 This is an overloaded intrinsic. You can use ``llvm.ssub.with.overflow``
8084 on any integer bit width.
8088 declare {i16, i1} @llvm.ssub.with.overflow.i16(i16 %a, i16 %b)
8089 declare {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b)
8090 declare {i64, i1} @llvm.ssub.with.overflow.i64(i64 %a, i64 %b)
8095 The '``llvm.ssub.with.overflow``' family of intrinsic functions perform
8096 a signed subtraction of the two arguments, and indicate whether an
8097 overflow occurred during the signed subtraction.
8102 The arguments (%a and %b) and the first element of the result structure
8103 may be of integer types of any bit width, but they must have the same
8104 bit width. The second element of the result structure must be of type
8105 ``i1``. ``%a`` and ``%b`` are the two values that will undergo signed
8111 The '``llvm.ssub.with.overflow``' family of intrinsic functions perform
8112 a signed subtraction of the two arguments. They return a structure --- the
8113 first element of which is the subtraction, and the second element of
8114 which is a bit specifying if the signed subtraction resulted in an
8120 .. code-block:: llvm
8122 %res = call {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b)
8123 %sum = extractvalue {i32, i1} %res, 0
8124 %obit = extractvalue {i32, i1} %res, 1
8125 br i1 %obit, label %overflow, label %normal
8127 '``llvm.usub.with.overflow.*``' Intrinsics
8128 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8133 This is an overloaded intrinsic. You can use ``llvm.usub.with.overflow``
8134 on any integer bit width.
8138 declare {i16, i1} @llvm.usub.with.overflow.i16(i16 %a, i16 %b)
8139 declare {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b)
8140 declare {i64, i1} @llvm.usub.with.overflow.i64(i64 %a, i64 %b)
8145 The '``llvm.usub.with.overflow``' family of intrinsic functions perform
8146 an unsigned subtraction of the two arguments, and indicate whether an
8147 overflow occurred during the unsigned subtraction.
8152 The arguments (%a and %b) and the first element of the result structure
8153 may be of integer types of any bit width, but they must have the same
8154 bit width. The second element of the result structure must be of type
8155 ``i1``. ``%a`` and ``%b`` are the two values that will undergo unsigned
8161 The '``llvm.usub.with.overflow``' family of intrinsic functions perform
8162 an unsigned subtraction of the two arguments. They return a structure ---
8163 the first element of which is the subtraction, and the second element of
8164 which is a bit specifying if the unsigned subtraction resulted in an
8170 .. code-block:: llvm
8172 %res = call {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b)
8173 %sum = extractvalue {i32, i1} %res, 0
8174 %obit = extractvalue {i32, i1} %res, 1
8175 br i1 %obit, label %overflow, label %normal
8177 '``llvm.smul.with.overflow.*``' Intrinsics
8178 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8183 This is an overloaded intrinsic. You can use ``llvm.smul.with.overflow``
8184 on any integer bit width.
8188 declare {i16, i1} @llvm.smul.with.overflow.i16(i16 %a, i16 %b)
8189 declare {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b)
8190 declare {i64, i1} @llvm.smul.with.overflow.i64(i64 %a, i64 %b)
8195 The '``llvm.smul.with.overflow``' family of intrinsic functions perform
8196 a signed multiplication of the two arguments, and indicate whether an
8197 overflow occurred during the signed multiplication.
8202 The arguments (%a and %b) and the first element of the result structure
8203 may be of integer types of any bit width, but they must have the same
8204 bit width. The second element of the result structure must be of type
8205 ``i1``. ``%a`` and ``%b`` are the two values that will undergo signed
8211 The '``llvm.smul.with.overflow``' family of intrinsic functions perform
8212 a signed multiplication of the two arguments. They return a structure ---
8213 the first element of which is the multiplication, and the second element
8214 of which is a bit specifying if the signed multiplication resulted in an
8220 .. code-block:: llvm
8222 %res = call {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b)
8223 %sum = extractvalue {i32, i1} %res, 0
8224 %obit = extractvalue {i32, i1} %res, 1
8225 br i1 %obit, label %overflow, label %normal
8227 '``llvm.umul.with.overflow.*``' Intrinsics
8228 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8233 This is an overloaded intrinsic. You can use ``llvm.umul.with.overflow``
8234 on any integer bit width.
8238 declare {i16, i1} @llvm.umul.with.overflow.i16(i16 %a, i16 %b)
8239 declare {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b)
8240 declare {i64, i1} @llvm.umul.with.overflow.i64(i64 %a, i64 %b)
8245 The '``llvm.umul.with.overflow``' family of intrinsic functions perform
8246 a unsigned multiplication of the two arguments, and indicate whether an
8247 overflow occurred during the unsigned multiplication.
8252 The arguments (%a and %b) and the first element of the result structure
8253 may be of integer types of any bit width, but they must have the same
8254 bit width. The second element of the result structure must be of type
8255 ``i1``. ``%a`` and ``%b`` are the two values that will undergo unsigned
8261 The '``llvm.umul.with.overflow``' family of intrinsic functions perform
8262 an unsigned multiplication of the two arguments. They return a structure ---
8263 the first element of which is the multiplication, and the second
8264 element of which is a bit specifying if the unsigned multiplication
8265 resulted in an overflow.
8270 .. code-block:: llvm
8272 %res = call {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b)
8273 %sum = extractvalue {i32, i1} %res, 0
8274 %obit = extractvalue {i32, i1} %res, 1
8275 br i1 %obit, label %overflow, label %normal
8277 Specialised Arithmetic Intrinsics
8278 ---------------------------------
8280 '``llvm.fmuladd.*``' Intrinsic
8281 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8288 declare float @llvm.fmuladd.f32(float %a, float %b, float %c)
8289 declare double @llvm.fmuladd.f64(double %a, double %b, double %c)
8294 The '``llvm.fmuladd.*``' intrinsic functions represent multiply-add
8295 expressions that can be fused if the code generator determines that (a) the
8296 target instruction set has support for a fused operation, and (b) that the
8297 fused operation is more efficient than the equivalent, separate pair of mul
8298 and add instructions.
8303 The '``llvm.fmuladd.*``' intrinsics each take three arguments: two
8304 multiplicands, a and b, and an addend c.
8313 %0 = call float @llvm.fmuladd.f32(%a, %b, %c)
8315 is equivalent to the expression a \* b + c, except that rounding will
8316 not be performed between the multiplication and addition steps if the
8317 code generator fuses the operations. Fusion is not guaranteed, even if
8318 the target platform supports it. If a fused multiply-add is required the
8319 corresponding llvm.fma.\* intrinsic function should be used
8320 instead. This never sets errno, just as '``llvm.fma.*``'.
8325 .. code-block:: llvm
8327 %r2 = call float @llvm.fmuladd.f32(float %a, float %b, float %c) ; yields {float}:r2 = (a * b) + c
8329 Half Precision Floating Point Intrinsics
8330 ----------------------------------------
8332 For most target platforms, half precision floating point is a
8333 storage-only format. This means that it is a dense encoding (in memory)
8334 but does not support computation in the format.
8336 This means that code must first load the half-precision floating point
8337 value as an i16, then convert it to float with
8338 :ref:`llvm.convert.from.fp16 <int_convert_from_fp16>`. Computation can
8339 then be performed on the float value (including extending to double
8340 etc). To store the value back to memory, it is first converted to float
8341 if needed, then converted to i16 with
8342 :ref:`llvm.convert.to.fp16 <int_convert_to_fp16>`, then storing as an
8345 .. _int_convert_to_fp16:
8347 '``llvm.convert.to.fp16``' Intrinsic
8348 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8355 declare i16 @llvm.convert.to.fp16(f32 %a)
8360 The '``llvm.convert.to.fp16``' intrinsic function performs a conversion
8361 from single precision floating point format to half precision floating
8367 The intrinsic function contains single argument - the value to be
8373 The '``llvm.convert.to.fp16``' intrinsic function performs a conversion
8374 from single precision floating point format to half precision floating
8375 point format. The return value is an ``i16`` which contains the
8381 .. code-block:: llvm
8383 %res = call i16 @llvm.convert.to.fp16(f32 %a)
8384 store i16 %res, i16* @x, align 2
8386 .. _int_convert_from_fp16:
8388 '``llvm.convert.from.fp16``' Intrinsic
8389 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8396 declare f32 @llvm.convert.from.fp16(i16 %a)
8401 The '``llvm.convert.from.fp16``' intrinsic function performs a
8402 conversion from half precision floating point format to single precision
8403 floating point format.
8408 The intrinsic function contains single argument - the value to be
8414 The '``llvm.convert.from.fp16``' intrinsic function performs a
8415 conversion from half single precision floating point format to single
8416 precision floating point format. The input half-float value is
8417 represented by an ``i16`` value.
8422 .. code-block:: llvm
8424 %a = load i16* @x, align 2
8425 %res = call f32 @llvm.convert.from.fp16(i16 %a)
8430 The LLVM debugger intrinsics (which all start with ``llvm.dbg.``
8431 prefix), are described in the `LLVM Source Level
8432 Debugging <SourceLevelDebugging.html#format_common_intrinsics>`_
8435 Exception Handling Intrinsics
8436 -----------------------------
8438 The LLVM exception handling intrinsics (which all start with
8439 ``llvm.eh.`` prefix), are described in the `LLVM Exception
8440 Handling <ExceptionHandling.html#format_common_intrinsics>`_ document.
8444 Trampoline Intrinsics
8445 ---------------------
8447 These intrinsics make it possible to excise one parameter, marked with
8448 the :ref:`nest <nest>` attribute, from a function. The result is a
8449 callable function pointer lacking the nest parameter - the caller does
8450 not need to provide a value for it. Instead, the value to use is stored
8451 in advance in a "trampoline", a block of memory usually allocated on the
8452 stack, which also contains code to splice the nest value into the
8453 argument list. This is used to implement the GCC nested function address
8456 For example, if the function is ``i32 f(i8* nest %c, i32 %x, i32 %y)``
8457 then the resulting function pointer has signature ``i32 (i32, i32)*``.
8458 It can be created as follows:
8460 .. code-block:: llvm
8462 %tramp = alloca [10 x i8], align 4 ; size and alignment only correct for X86
8463 %tramp1 = getelementptr [10 x i8]* %tramp, i32 0, i32 0
8464 call i8* @llvm.init.trampoline(i8* %tramp1, i8* bitcast (i32 (i8*, i32, i32)* @f to i8*), i8* %nval)
8465 %p = call i8* @llvm.adjust.trampoline(i8* %tramp1)
8466 %fp = bitcast i8* %p to i32 (i32, i32)*
8468 The call ``%val = call i32 %fp(i32 %x, i32 %y)`` is then equivalent to
8469 ``%val = call i32 %f(i8* %nval, i32 %x, i32 %y)``.
8473 '``llvm.init.trampoline``' Intrinsic
8474 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8481 declare void @llvm.init.trampoline(i8* <tramp>, i8* <func>, i8* <nval>)
8486 This fills the memory pointed to by ``tramp`` with executable code,
8487 turning it into a trampoline.
8492 The ``llvm.init.trampoline`` intrinsic takes three arguments, all
8493 pointers. The ``tramp`` argument must point to a sufficiently large and
8494 sufficiently aligned block of memory; this memory is written to by the
8495 intrinsic. Note that the size and the alignment are target-specific -
8496 LLVM currently provides no portable way of determining them, so a
8497 front-end that generates this intrinsic needs to have some
8498 target-specific knowledge. The ``func`` argument must hold a function
8499 bitcast to an ``i8*``.
8504 The block of memory pointed to by ``tramp`` is filled with target
8505 dependent code, turning it into a function. Then ``tramp`` needs to be
8506 passed to :ref:`llvm.adjust.trampoline <int_at>` to get a pointer which can
8507 be :ref:`bitcast (to a new function) and called <int_trampoline>`. The new
8508 function's signature is the same as that of ``func`` with any arguments
8509 marked with the ``nest`` attribute removed. At most one such ``nest``
8510 argument is allowed, and it must be of pointer type. Calling the new
8511 function is equivalent to calling ``func`` with the same argument list,
8512 but with ``nval`` used for the missing ``nest`` argument. If, after
8513 calling ``llvm.init.trampoline``, the memory pointed to by ``tramp`` is
8514 modified, then the effect of any later call to the returned function
8515 pointer is undefined.
8519 '``llvm.adjust.trampoline``' Intrinsic
8520 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8527 declare i8* @llvm.adjust.trampoline(i8* <tramp>)
8532 This performs any required machine-specific adjustment to the address of
8533 a trampoline (passed as ``tramp``).
8538 ``tramp`` must point to a block of memory which already has trampoline
8539 code filled in by a previous call to
8540 :ref:`llvm.init.trampoline <int_it>`.
8545 On some architectures the address of the code to be executed needs to be
8546 different to the address where the trampoline is actually stored. This
8547 intrinsic returns the executable address corresponding to ``tramp``
8548 after performing the required machine specific adjustments. The pointer
8549 returned can then be :ref:`bitcast and executed <int_trampoline>`.
8554 This class of intrinsics exists to information about the lifetime of
8555 memory objects and ranges where variables are immutable.
8559 '``llvm.lifetime.start``' Intrinsic
8560 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8567 declare void @llvm.lifetime.start(i64 <size>, i8* nocapture <ptr>)
8572 The '``llvm.lifetime.start``' intrinsic specifies the start of a memory
8578 The first argument is a constant integer representing the size of the
8579 object, or -1 if it is variable sized. The second argument is a pointer
8585 This intrinsic indicates that before this point in the code, the value
8586 of the memory pointed to by ``ptr`` is dead. This means that it is known
8587 to never be used and has an undefined value. A load from the pointer
8588 that precedes this intrinsic can be replaced with ``'undef'``.
8592 '``llvm.lifetime.end``' Intrinsic
8593 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8600 declare void @llvm.lifetime.end(i64 <size>, i8* nocapture <ptr>)
8605 The '``llvm.lifetime.end``' intrinsic specifies the end of a memory
8611 The first argument is a constant integer representing the size of the
8612 object, or -1 if it is variable sized. The second argument is a pointer
8618 This intrinsic indicates that after this point in the code, the value of
8619 the memory pointed to by ``ptr`` is dead. This means that it is known to
8620 never be used and has an undefined value. Any stores into the memory
8621 object following this intrinsic may be removed as dead.
8623 '``llvm.invariant.start``' Intrinsic
8624 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8631 declare {}* @llvm.invariant.start(i64 <size>, i8* nocapture <ptr>)
8636 The '``llvm.invariant.start``' intrinsic specifies that the contents of
8637 a memory object will not change.
8642 The first argument is a constant integer representing the size of the
8643 object, or -1 if it is variable sized. The second argument is a pointer
8649 This intrinsic indicates that until an ``llvm.invariant.end`` that uses
8650 the return value, the referenced memory location is constant and
8653 '``llvm.invariant.end``' Intrinsic
8654 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8661 declare void @llvm.invariant.end({}* <start>, i64 <size>, i8* nocapture <ptr>)
8666 The '``llvm.invariant.end``' intrinsic specifies that the contents of a
8667 memory object are mutable.
8672 The first argument is the matching ``llvm.invariant.start`` intrinsic.
8673 The second argument is a constant integer representing the size of the
8674 object, or -1 if it is variable sized and the third argument is a
8675 pointer to the object.
8680 This intrinsic indicates that the memory is mutable again.
8685 This class of intrinsics is designed to be generic and has no specific
8688 '``llvm.var.annotation``' Intrinsic
8689 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8696 declare void @llvm.var.annotation(i8* <val>, i8* <str>, i8* <str>, i32 <int>)
8701 The '``llvm.var.annotation``' intrinsic.
8706 The first argument is a pointer to a value, the second is a pointer to a
8707 global string, the third is a pointer to a global string which is the
8708 source file name, and the last argument is the line number.
8713 This intrinsic allows annotation of local variables with arbitrary
8714 strings. This can be useful for special purpose optimizations that want
8715 to look for these annotations. These have no other defined use; they are
8716 ignored by code generation and optimization.
8718 '``llvm.ptr.annotation.*``' Intrinsic
8719 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8724 This is an overloaded intrinsic. You can use '``llvm.ptr.annotation``' on a
8725 pointer to an integer of any width. *NOTE* you must specify an address space for
8726 the pointer. The identifier for the default address space is the integer
8731 declare i8* @llvm.ptr.annotation.p<address space>i8(i8* <val>, i8* <str>, i8* <str>, i32 <int>)
8732 declare i16* @llvm.ptr.annotation.p<address space>i16(i16* <val>, i8* <str>, i8* <str>, i32 <int>)
8733 declare i32* @llvm.ptr.annotation.p<address space>i32(i32* <val>, i8* <str>, i8* <str>, i32 <int>)
8734 declare i64* @llvm.ptr.annotation.p<address space>i64(i64* <val>, i8* <str>, i8* <str>, i32 <int>)
8735 declare i256* @llvm.ptr.annotation.p<address space>i256(i256* <val>, i8* <str>, i8* <str>, i32 <int>)
8740 The '``llvm.ptr.annotation``' intrinsic.
8745 The first argument is a pointer to an integer value of arbitrary bitwidth
8746 (result of some expression), the second is a pointer to a global string, the
8747 third is a pointer to a global string which is the source file name, and the
8748 last argument is the line number. It returns the value of the first argument.
8753 This intrinsic allows annotation of a pointer to an integer with arbitrary
8754 strings. This can be useful for special purpose optimizations that want to look
8755 for these annotations. These have no other defined use; they are ignored by code
8756 generation and optimization.
8758 '``llvm.annotation.*``' Intrinsic
8759 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8764 This is an overloaded intrinsic. You can use '``llvm.annotation``' on
8765 any integer bit width.
8769 declare i8 @llvm.annotation.i8(i8 <val>, i8* <str>, i8* <str>, i32 <int>)
8770 declare i16 @llvm.annotation.i16(i16 <val>, i8* <str>, i8* <str>, i32 <int>)
8771 declare i32 @llvm.annotation.i32(i32 <val>, i8* <str>, i8* <str>, i32 <int>)
8772 declare i64 @llvm.annotation.i64(i64 <val>, i8* <str>, i8* <str>, i32 <int>)
8773 declare i256 @llvm.annotation.i256(i256 <val>, i8* <str>, i8* <str>, i32 <int>)
8778 The '``llvm.annotation``' intrinsic.
8783 The first argument is an integer value (result of some expression), the
8784 second is a pointer to a global string, the third is a pointer to a
8785 global string which is the source file name, and the last argument is
8786 the line number. It returns the value of the first argument.
8791 This intrinsic allows annotations to be put on arbitrary expressions
8792 with arbitrary strings. This can be useful for special purpose
8793 optimizations that want to look for these annotations. These have no
8794 other defined use; they are ignored by code generation and optimization.
8796 '``llvm.trap``' Intrinsic
8797 ^^^^^^^^^^^^^^^^^^^^^^^^^
8804 declare void @llvm.trap() noreturn nounwind
8809 The '``llvm.trap``' intrinsic.
8819 This intrinsic is lowered to the target dependent trap instruction. If
8820 the target does not have a trap instruction, this intrinsic will be
8821 lowered to a call of the ``abort()`` function.
8823 '``llvm.debugtrap``' Intrinsic
8824 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8831 declare void @llvm.debugtrap() nounwind
8836 The '``llvm.debugtrap``' intrinsic.
8846 This intrinsic is lowered to code which is intended to cause an
8847 execution trap with the intention of requesting the attention of a
8850 '``llvm.stackprotector``' Intrinsic
8851 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8858 declare void @llvm.stackprotector(i8* <guard>, i8** <slot>)
8863 The ``llvm.stackprotector`` intrinsic takes the ``guard`` and stores it
8864 onto the stack at ``slot``. The stack slot is adjusted to ensure that it
8865 is placed on the stack before local variables.
8870 The ``llvm.stackprotector`` intrinsic requires two pointer arguments.
8871 The first argument is the value loaded from the stack guard
8872 ``@__stack_chk_guard``. The second variable is an ``alloca`` that has
8873 enough space to hold the value of the guard.
8878 This intrinsic causes the prologue/epilogue inserter to force the position of
8879 the ``AllocaInst`` stack slot to be before local variables on the stack. This is
8880 to ensure that if a local variable on the stack is overwritten, it will destroy
8881 the value of the guard. When the function exits, the guard on the stack is
8882 checked against the original guard by ``llvm.stackprotectorcheck``. If they are
8883 different, then ``llvm.stackprotectorcheck`` causes the program to abort by
8884 calling the ``__stack_chk_fail()`` function.
8886 '``llvm.stackprotectorcheck``' Intrinsic
8887 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8894 declare void @llvm.stackprotectorcheck(i8** <guard>)
8899 The ``llvm.stackprotectorcheck`` intrinsic compares ``guard`` against an already
8900 created stack protector and if they are not equal calls the
8901 ``__stack_chk_fail()`` function.
8906 The ``llvm.stackprotectorcheck`` intrinsic requires one pointer argument, the
8907 the variable ``@__stack_chk_guard``.
8912 This intrinsic is provided to perform the stack protector check by comparing
8913 ``guard`` with the stack slot created by ``llvm.stackprotector`` and if the
8914 values do not match call the ``__stack_chk_fail()`` function.
8916 The reason to provide this as an IR level intrinsic instead of implementing it
8917 via other IR operations is that in order to perform this operation at the IR
8918 level without an intrinsic, one would need to create additional basic blocks to
8919 handle the success/failure cases. This makes it difficult to stop the stack
8920 protector check from disrupting sibling tail calls in Codegen. With this
8921 intrinsic, we are able to generate the stack protector basic blocks late in
8922 codegen after the tail call decision has occurred.
8924 '``llvm.objectsize``' Intrinsic
8925 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8932 declare i32 @llvm.objectsize.i32(i8* <object>, i1 <min>)
8933 declare i64 @llvm.objectsize.i64(i8* <object>, i1 <min>)
8938 The ``llvm.objectsize`` intrinsic is designed to provide information to
8939 the optimizers to determine at compile time whether a) an operation
8940 (like memcpy) will overflow a buffer that corresponds to an object, or
8941 b) that a runtime check for overflow isn't necessary. An object in this
8942 context means an allocation of a specific class, structure, array, or
8948 The ``llvm.objectsize`` intrinsic takes two arguments. The first
8949 argument is a pointer to or into the ``object``. The second argument is
8950 a boolean and determines whether ``llvm.objectsize`` returns 0 (if true)
8951 or -1 (if false) when the object size is unknown. The second argument
8952 only accepts constants.
8957 The ``llvm.objectsize`` intrinsic is lowered to a constant representing
8958 the size of the object concerned. If the size cannot be determined at
8959 compile time, ``llvm.objectsize`` returns ``i32/i64 -1 or 0`` (depending
8960 on the ``min`` argument).
8962 '``llvm.expect``' Intrinsic
8963 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
8968 This is an overloaded intrinsic. You can use ``llvm.expect`` on any
8973 declare i1 @llvm.expect.i1(i1 <val>, i1 <expected_val>)
8974 declare i32 @llvm.expect.i32(i32 <val>, i32 <expected_val>)
8975 declare i64 @llvm.expect.i64(i64 <val>, i64 <expected_val>)
8980 The ``llvm.expect`` intrinsic provides information about expected (the
8981 most probable) value of ``val``, which can be used by optimizers.
8986 The ``llvm.expect`` intrinsic takes two arguments. The first argument is
8987 a value. The second argument is an expected value, this needs to be a
8988 constant value, variables are not allowed.
8993 This intrinsic is lowered to the ``val``.
8995 '``llvm.donothing``' Intrinsic
8996 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9003 declare void @llvm.donothing() nounwind readnone
9008 The ``llvm.donothing`` intrinsic doesn't perform any operation. It's the
9009 only intrinsic that can be called with an invoke instruction.
9019 This intrinsic does nothing, and it's removed by optimizers and ignored
9022 Stack Map Intrinsics
9023 --------------------
9025 LLVM provides experimental intrinsics to support runtime patching
9026 mechanisms commonly desired in dynamic language JITs. These intrinsics
9027 are described in :doc:`StackMaps`.