1 ==============================
2 LLVM Language Reference Manual
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12 This document is a reference manual for the LLVM assembly language. LLVM
13 is a Static Single Assignment (SSA) based representation that provides
14 type safety, low-level operations, flexibility, and the capability of
15 representing 'all' high-level languages cleanly. It is the common code
16 representation used throughout all phases of the LLVM compilation
22 The LLVM code representation is designed to be used in three different
23 forms: as an in-memory compiler IR, as an on-disk bitcode representation
24 (suitable for fast loading by a Just-In-Time compiler), and as a human
25 readable assembly language representation. This allows LLVM to provide a
26 powerful intermediate representation for efficient compiler
27 transformations and analysis, while providing a natural means to debug
28 and visualize the transformations. The three different forms of LLVM are
29 all equivalent. This document describes the human readable
30 representation and notation.
32 The LLVM representation aims to be light-weight and low-level while
33 being expressive, typed, and extensible at the same time. It aims to be
34 a "universal IR" of sorts, by being at a low enough level that
35 high-level ideas may be cleanly mapped to it (similar to how
36 microprocessors are "universal IR's", allowing many source languages to
37 be mapped to them). By providing type information, LLVM can be used as
38 the target of optimizations: for example, through pointer analysis, it
39 can be proven that a C automatic variable is never accessed outside of
40 the current function, allowing it to be promoted to a simple SSA value
41 instead of a memory location.
48 It is important to note that this document describes 'well formed' LLVM
49 assembly language. There is a difference between what the parser accepts
50 and what is considered 'well formed'. For example, the following
51 instruction is syntactically okay, but not well formed:
57 because the definition of ``%x`` does not dominate all of its uses. The
58 LLVM infrastructure provides a verification pass that may be used to
59 verify that an LLVM module is well formed. This pass is automatically
60 run by the parser after parsing input assembly and by the optimizer
61 before it outputs bitcode. The violations pointed out by the verifier
62 pass indicate bugs in transformation passes or input to the parser.
69 LLVM identifiers come in two basic types: global and local. Global
70 identifiers (functions, global variables) begin with the ``'@'``
71 character. Local identifiers (register names, types) begin with the
72 ``'%'`` character. Additionally, there are three different formats for
73 identifiers, for different purposes:
75 #. Named values are represented as a string of characters with their
76 prefix. For example, ``%foo``, ``@DivisionByZero``,
77 ``%a.really.long.identifier``. The actual regular expression used is
78 '``[%@][-a-zA-Z$._][-a-zA-Z$._0-9]*``'. Identifiers that require other
79 characters in their names can be surrounded with quotes. Special
80 characters may be escaped using ``"\xx"`` where ``xx`` is the ASCII
81 code for the character in hexadecimal. In this way, any character can
82 be used in a name value, even quotes themselves. The ``"\01"`` prefix
83 can be used on global variables to suppress mangling.
84 #. Unnamed values are represented as an unsigned numeric value with
85 their prefix. For example, ``%12``, ``@2``, ``%44``.
86 #. Constants, which are described in the section Constants_ below.
88 LLVM requires that values start with a prefix for two reasons: Compilers
89 don't need to worry about name clashes with reserved words, and the set
90 of reserved words may be expanded in the future without penalty.
91 Additionally, unnamed identifiers allow a compiler to quickly come up
92 with a temporary variable without having to avoid symbol table
95 Reserved words in LLVM are very similar to reserved words in other
96 languages. There are keywords for different opcodes ('``add``',
97 '``bitcast``', '``ret``', etc...), for primitive type names ('``void``',
98 '``i32``', etc...), and others. These reserved words cannot conflict
99 with variable names, because none of them start with a prefix character
100 (``'%'`` or ``'@'``).
102 Here is an example of LLVM code to multiply the integer variable
109 %result = mul i32 %X, 8
111 After strength reduction:
115 %result = shl i32 %X, 3
121 %0 = add i32 %X, %X ; yields i32:%0
122 %1 = add i32 %0, %0 ; yields i32:%1
123 %result = add i32 %1, %1
125 This last way of multiplying ``%X`` by 8 illustrates several important
126 lexical features of LLVM:
128 #. Comments are delimited with a '``;``' and go until the end of line.
129 #. Unnamed temporaries are created when the result of a computation is
130 not assigned to a named value.
131 #. Unnamed temporaries are numbered sequentially (using a per-function
132 incrementing counter, starting with 0). Note that basic blocks and unnamed
133 function parameters are included in this numbering. For example, if the
134 entry basic block is not given a label name and all function parameters are
135 named, then it will get number 0.
137 It also shows a convention that we follow in this document. When
138 demonstrating instructions, we will follow an instruction with a comment
139 that defines the type and name of value produced.
147 LLVM programs are composed of ``Module``'s, each of which is a
148 translation unit of the input programs. Each module consists of
149 functions, global variables, and symbol table entries. Modules may be
150 combined together with the LLVM linker, which merges function (and
151 global variable) definitions, resolves forward declarations, and merges
152 symbol table entries. Here is an example of the "hello world" module:
156 ; Declare the string constant as a global constant.
157 @.str = private unnamed_addr constant [13 x i8] c"hello world\0A\00"
159 ; External declaration of the puts function
160 declare i32 @puts(i8* nocapture) nounwind
162 ; Definition of main function
163 define i32 @main() { ; i32()*
164 ; Convert [13 x i8]* to i8 *...
165 %cast210 = getelementptr [13 x i8]* @.str, i64 0, i64 0
167 ; Call puts function to write out the string to stdout.
168 call i32 @puts(i8* %cast210)
173 !0 = !{i32 42, null, !"string"}
176 This example is made up of a :ref:`global variable <globalvars>` named
177 "``.str``", an external declaration of the "``puts``" function, a
178 :ref:`function definition <functionstructure>` for "``main``" and
179 :ref:`named metadata <namedmetadatastructure>` "``foo``".
181 In general, a module is made up of a list of global values (where both
182 functions and global variables are global values). Global values are
183 represented by a pointer to a memory location (in this case, a pointer
184 to an array of char, and a pointer to a function), and have one of the
185 following :ref:`linkage types <linkage>`.
192 All Global Variables and Functions have one of the following types of
196 Global values with "``private``" linkage are only directly
197 accessible by objects in the current module. In particular, linking
198 code into a module with an private global value may cause the
199 private to be renamed as necessary to avoid collisions. Because the
200 symbol is private to the module, all references can be updated. This
201 doesn't show up in any symbol table in the object file.
203 Similar to private, but the value shows as a local symbol
204 (``STB_LOCAL`` in the case of ELF) in the object file. This
205 corresponds to the notion of the '``static``' keyword in C.
206 ``available_externally``
207 Globals with "``available_externally``" linkage are never emitted
208 into the object file corresponding to the LLVM module. They exist to
209 allow inlining and other optimizations to take place given knowledge
210 of the definition of the global, which is known to be somewhere
211 outside the module. Globals with ``available_externally`` linkage
212 are allowed to be discarded at will, and are otherwise the same as
213 ``linkonce_odr``. This linkage type is only allowed on definitions,
216 Globals with "``linkonce``" linkage are merged with other globals of
217 the same name when linkage occurs. This can be used to implement
218 some forms of inline functions, templates, or other code which must
219 be generated in each translation unit that uses it, but where the
220 body may be overridden with a more definitive definition later.
221 Unreferenced ``linkonce`` globals are allowed to be discarded. Note
222 that ``linkonce`` linkage does not actually allow the optimizer to
223 inline the body of this function into callers because it doesn't
224 know if this definition of the function is the definitive definition
225 within the program or whether it will be overridden by a stronger
226 definition. To enable inlining and other optimizations, use
227 "``linkonce_odr``" linkage.
229 "``weak``" linkage has the same merging semantics as ``linkonce``
230 linkage, except that unreferenced globals with ``weak`` linkage may
231 not be discarded. This is used for globals that are declared "weak"
234 "``common``" linkage is most similar to "``weak``" linkage, but they
235 are used for tentative definitions in C, such as "``int X;``" at
236 global scope. Symbols with "``common``" linkage are merged in the
237 same way as ``weak symbols``, and they may not be deleted if
238 unreferenced. ``common`` symbols may not have an explicit section,
239 must have a zero initializer, and may not be marked
240 ':ref:`constant <globalvars>`'. Functions and aliases may not have
243 .. _linkage_appending:
246 "``appending``" linkage may only be applied to global variables of
247 pointer to array type. When two global variables with appending
248 linkage are linked together, the two global arrays are appended
249 together. This is the LLVM, typesafe, equivalent of having the
250 system linker append together "sections" with identical names when
253 The semantics of this linkage follow the ELF object file model: the
254 symbol is weak until linked, if not linked, the symbol becomes null
255 instead of being an undefined reference.
256 ``linkonce_odr``, ``weak_odr``
257 Some languages allow differing globals to be merged, such as two
258 functions with different semantics. Other languages, such as
259 ``C++``, ensure that only equivalent globals are ever merged (the
260 "one definition rule" --- "ODR"). Such languages can use the
261 ``linkonce_odr`` and ``weak_odr`` linkage types to indicate that the
262 global will only be merged with equivalent globals. These linkage
263 types are otherwise the same as their non-``odr`` versions.
265 If none of the above identifiers are used, the global is externally
266 visible, meaning that it participates in linkage and can be used to
267 resolve external symbol references.
269 It is illegal for a function *declaration* to have any linkage type
270 other than ``external`` or ``extern_weak``.
277 LLVM :ref:`functions <functionstructure>`, :ref:`calls <i_call>` and
278 :ref:`invokes <i_invoke>` can all have an optional calling convention
279 specified for the call. The calling convention of any pair of dynamic
280 caller/callee must match, or the behavior of the program is undefined.
281 The following calling conventions are supported by LLVM, and more may be
284 "``ccc``" - The C calling convention
285 This calling convention (the default if no other calling convention
286 is specified) matches the target C calling conventions. This calling
287 convention supports varargs function calls and tolerates some
288 mismatch in the declared prototype and implemented declaration of
289 the function (as does normal C).
290 "``fastcc``" - The fast calling convention
291 This calling convention attempts to make calls as fast as possible
292 (e.g. by passing things in registers). This calling convention
293 allows the target to use whatever tricks it wants to produce fast
294 code for the target, without having to conform to an externally
295 specified ABI (Application Binary Interface). `Tail calls can only
296 be optimized when this, the GHC or the HiPE convention is
297 used. <CodeGenerator.html#id80>`_ This calling convention does not
298 support varargs and requires the prototype of all callees to exactly
299 match the prototype of the function definition.
300 "``coldcc``" - The cold calling convention
301 This calling convention attempts to make code in the caller as
302 efficient as possible under the assumption that the call is not
303 commonly executed. As such, these calls often preserve all registers
304 so that the call does not break any live ranges in the caller side.
305 This calling convention does not support varargs and requires the
306 prototype of all callees to exactly match the prototype of the
307 function definition. Furthermore the inliner doesn't consider such function
309 "``cc 10``" - GHC convention
310 This calling convention has been implemented specifically for use by
311 the `Glasgow Haskell Compiler (GHC) <http://www.haskell.org/ghc>`_.
312 It passes everything in registers, going to extremes to achieve this
313 by disabling callee save registers. This calling convention should
314 not be used lightly but only for specific situations such as an
315 alternative to the *register pinning* performance technique often
316 used when implementing functional programming languages. At the
317 moment only X86 supports this convention and it has the following
320 - On *X86-32* only supports up to 4 bit type parameters. No
321 floating point types are supported.
322 - On *X86-64* only supports up to 10 bit type parameters and 6
323 floating point parameters.
325 This calling convention supports `tail call
326 optimization <CodeGenerator.html#id80>`_ but requires both the
327 caller and callee are using it.
328 "``cc 11``" - The HiPE calling convention
329 This calling convention has been implemented specifically for use by
330 the `High-Performance Erlang
331 (HiPE) <http://www.it.uu.se/research/group/hipe/>`_ compiler, *the*
332 native code compiler of the `Ericsson's Open Source Erlang/OTP
333 system <http://www.erlang.org/download.shtml>`_. It uses more
334 registers for argument passing than the ordinary C calling
335 convention and defines no callee-saved registers. The calling
336 convention properly supports `tail call
337 optimization <CodeGenerator.html#id80>`_ but requires that both the
338 caller and the callee use it. It uses a *register pinning*
339 mechanism, similar to GHC's convention, for keeping frequently
340 accessed runtime components pinned to specific hardware registers.
341 At the moment only X86 supports this convention (both 32 and 64
343 "``webkit_jscc``" - WebKit's JavaScript calling convention
344 This calling convention has been implemented for `WebKit FTL JIT
345 <https://trac.webkit.org/wiki/FTLJIT>`_. It passes arguments on the
346 stack right to left (as cdecl does), and returns a value in the
347 platform's customary return register.
348 "``anyregcc``" - Dynamic calling convention for code patching
349 This is a special convention that supports patching an arbitrary code
350 sequence in place of a call site. This convention forces the call
351 arguments into registers but allows them to be dynamcially
352 allocated. This can currently only be used with calls to
353 llvm.experimental.patchpoint because only this intrinsic records
354 the location of its arguments in a side table. See :doc:`StackMaps`.
355 "``preserve_mostcc``" - The `PreserveMost` calling convention
356 This calling convention attempts to make the code in the caller as little
357 intrusive as possible. This calling convention behaves identical to the `C`
358 calling convention on how arguments and return values are passed, but it
359 uses a different set of caller/callee-saved registers. This alleviates the
360 burden of saving and recovering a large register set before and after the
361 call in the caller. If the arguments are passed in callee-saved registers,
362 then they will be preserved by the callee across the call. This doesn't
363 apply for values returned in callee-saved registers.
365 - On X86-64 the callee preserves all general purpose registers, except for
366 R11. R11 can be used as a scratch register. Floating-point registers
367 (XMMs/YMMs) are not preserved and need to be saved by the caller.
369 The idea behind this convention is to support calls to runtime functions
370 that have a hot path and a cold path. The hot path is usually a small piece
371 of code that doesn't use many registers. The cold path might need to call out to
372 another function and therefore only needs to preserve the caller-saved
373 registers, which haven't already been saved by the caller. The
374 `PreserveMost` calling convention is very similar to the `cold` calling
375 convention in terms of caller/callee-saved registers, but they are used for
376 different types of function calls. `coldcc` is for function calls that are
377 rarely executed, whereas `preserve_mostcc` function calls are intended to be
378 on the hot path and definitely executed a lot. Furthermore `preserve_mostcc`
379 doesn't prevent the inliner from inlining the function call.
381 This calling convention will be used by a future version of the ObjectiveC
382 runtime and should therefore still be considered experimental at this time.
383 Although this convention was created to optimize certain runtime calls to
384 the ObjectiveC runtime, it is not limited to this runtime and might be used
385 by other runtimes in the future too. The current implementation only
386 supports X86-64, but the intention is to support more architectures in the
388 "``preserve_allcc``" - The `PreserveAll` calling convention
389 This calling convention attempts to make the code in the caller even less
390 intrusive than the `PreserveMost` calling convention. This calling
391 convention also behaves identical to the `C` calling convention on how
392 arguments and return values are passed, but it uses a different set of
393 caller/callee-saved registers. This removes the burden of saving and
394 recovering a large register set before and after the call in the caller. If
395 the arguments are passed in callee-saved registers, then they will be
396 preserved by the callee across the call. This doesn't apply for values
397 returned in callee-saved registers.
399 - On X86-64 the callee preserves all general purpose registers, except for
400 R11. R11 can be used as a scratch register. Furthermore it also preserves
401 all floating-point registers (XMMs/YMMs).
403 The idea behind this convention is to support calls to runtime functions
404 that don't need to call out to any other functions.
406 This calling convention, like the `PreserveMost` calling convention, will be
407 used by a future version of the ObjectiveC runtime and should be considered
408 experimental at this time.
409 "``cc <n>``" - Numbered convention
410 Any calling convention may be specified by number, allowing
411 target-specific calling conventions to be used. Target specific
412 calling conventions start at 64.
414 More calling conventions can be added/defined on an as-needed basis, to
415 support Pascal conventions or any other well-known target-independent
418 .. _visibilitystyles:
423 All Global Variables and Functions have one of the following visibility
426 "``default``" - Default style
427 On targets that use the ELF object file format, default visibility
428 means that the declaration is visible to other modules and, in
429 shared libraries, means that the declared entity may be overridden.
430 On Darwin, default visibility means that the declaration is visible
431 to other modules. Default visibility corresponds to "external
432 linkage" in the language.
433 "``hidden``" - Hidden style
434 Two declarations of an object with hidden visibility refer to the
435 same object if they are in the same shared object. Usually, hidden
436 visibility indicates that the symbol will not be placed into the
437 dynamic symbol table, so no other module (executable or shared
438 library) can reference it directly.
439 "``protected``" - Protected style
440 On ELF, protected visibility indicates that the symbol will be
441 placed in the dynamic symbol table, but that references within the
442 defining module will bind to the local symbol. That is, the symbol
443 cannot be overridden by another module.
445 A symbol with ``internal`` or ``private`` linkage must have ``default``
453 All Global Variables, Functions and Aliases can have one of the following
457 "``dllimport``" causes the compiler to reference a function or variable via
458 a global pointer to a pointer that is set up by the DLL exporting the
459 symbol. On Microsoft Windows targets, the pointer name is formed by
460 combining ``__imp_`` and the function or variable name.
462 "``dllexport``" causes the compiler to provide a global pointer to a pointer
463 in a DLL, so that it can be referenced with the ``dllimport`` attribute. On
464 Microsoft Windows targets, the pointer name is formed by combining
465 ``__imp_`` and the function or variable name. Since this storage class
466 exists for defining a dll interface, the compiler, assembler and linker know
467 it is externally referenced and must refrain from deleting the symbol.
471 Thread Local Storage Models
472 ---------------------------
474 A variable may be defined as ``thread_local``, which means that it will
475 not be shared by threads (each thread will have a separated copy of the
476 variable). Not all targets support thread-local variables. Optionally, a
477 TLS model may be specified:
480 For variables that are only used within the current shared library.
482 For variables in modules that will not be loaded dynamically.
484 For variables defined in the executable and only used within it.
486 If no explicit model is given, the "general dynamic" model is used.
488 The models correspond to the ELF TLS models; see `ELF Handling For
489 Thread-Local Storage <http://people.redhat.com/drepper/tls.pdf>`_ for
490 more information on under which circumstances the different models may
491 be used. The target may choose a different TLS model if the specified
492 model is not supported, or if a better choice of model can be made.
494 A model can also be specified in a alias, but then it only governs how
495 the alias is accessed. It will not have any effect in the aliasee.
502 LLVM IR allows you to specify both "identified" and "literal" :ref:`structure
503 types <t_struct>`. Literal types are uniqued structurally, but identified types
504 are never uniqued. An :ref:`opaque structural type <t_opaque>` can also be used
505 to forward declare a type that is not yet available.
507 An example of a identified structure specification is:
511 %mytype = type { %mytype*, i32 }
513 Prior to the LLVM 3.0 release, identified types were structurally uniqued. Only
514 literal types are uniqued in recent versions of LLVM.
521 Global variables define regions of memory allocated at compilation time
524 Global variable definitions must be initialized.
526 Global variables in other translation units can also be declared, in which
527 case they don't have an initializer.
529 Either global variable definitions or declarations may have an explicit section
530 to be placed in and may have an optional explicit alignment specified.
532 A variable may be defined as a global ``constant``, which indicates that
533 the contents of the variable will **never** be modified (enabling better
534 optimization, allowing the global data to be placed in the read-only
535 section of an executable, etc). Note that variables that need runtime
536 initialization cannot be marked ``constant`` as there is a store to the
539 LLVM explicitly allows *declarations* of global variables to be marked
540 constant, even if the final definition of the global is not. This
541 capability can be used to enable slightly better optimization of the
542 program, but requires the language definition to guarantee that
543 optimizations based on the 'constantness' are valid for the translation
544 units that do not include the definition.
546 As SSA values, global variables define pointer values that are in scope
547 (i.e. they dominate) all basic blocks in the program. Global variables
548 always define a pointer to their "content" type because they describe a
549 region of memory, and all memory objects in LLVM are accessed through
552 Global variables can be marked with ``unnamed_addr`` which indicates
553 that the address is not significant, only the content. Constants marked
554 like this can be merged with other constants if they have the same
555 initializer. Note that a constant with significant address *can* be
556 merged with a ``unnamed_addr`` constant, the result being a constant
557 whose address is significant.
559 A global variable may be declared to reside in a target-specific
560 numbered address space. For targets that support them, address spaces
561 may affect how optimizations are performed and/or what target
562 instructions are used to access the variable. The default address space
563 is zero. The address space qualifier must precede any other attributes.
565 LLVM allows an explicit section to be specified for globals. If the
566 target supports it, it will emit globals to the section specified.
567 Additionally, the global can placed in a comdat if the target has the necessary
570 By default, global initializers are optimized by assuming that global
571 variables defined within the module are not modified from their
572 initial values before the start of the global initializer. This is
573 true even for variables potentially accessible from outside the
574 module, including those with external linkage or appearing in
575 ``@llvm.used`` or dllexported variables. This assumption may be suppressed
576 by marking the variable with ``externally_initialized``.
578 An explicit alignment may be specified for a global, which must be a
579 power of 2. If not present, or if the alignment is set to zero, the
580 alignment of the global is set by the target to whatever it feels
581 convenient. If an explicit alignment is specified, the global is forced
582 to have exactly that alignment. Targets and optimizers are not allowed
583 to over-align the global if the global has an assigned section. In this
584 case, the extra alignment could be observable: for example, code could
585 assume that the globals are densely packed in their section and try to
586 iterate over them as an array, alignment padding would break this
587 iteration. The maximum alignment is ``1 << 29``.
589 Globals can also have a :ref:`DLL storage class <dllstorageclass>`.
591 Variables and aliases can have a
592 :ref:`Thread Local Storage Model <tls_model>`.
596 [@<GlobalVarName> =] [Linkage] [Visibility] [DLLStorageClass] [ThreadLocal]
597 [unnamed_addr] [AddrSpace] [ExternallyInitialized]
598 <global | constant> <Type> [<InitializerConstant>]
599 [, section "name"] [, comdat [($name)]]
600 [, align <Alignment>]
602 For example, the following defines a global in a numbered address space
603 with an initializer, section, and alignment:
607 @G = addrspace(5) constant float 1.0, section "foo", align 4
609 The following example just declares a global variable
613 @G = external global i32
615 The following example defines a thread-local global with the
616 ``initialexec`` TLS model:
620 @G = thread_local(initialexec) global i32 0, align 4
622 .. _functionstructure:
627 LLVM function definitions consist of the "``define``" keyword, an
628 optional :ref:`linkage type <linkage>`, an optional :ref:`visibility
629 style <visibility>`, an optional :ref:`DLL storage class <dllstorageclass>`,
630 an optional :ref:`calling convention <callingconv>`,
631 an optional ``unnamed_addr`` attribute, a return type, an optional
632 :ref:`parameter attribute <paramattrs>` for the return type, a function
633 name, a (possibly empty) argument list (each with optional :ref:`parameter
634 attributes <paramattrs>`), optional :ref:`function attributes <fnattrs>`,
635 an optional section, an optional alignment,
636 an optional :ref:`comdat <langref_comdats>`,
637 an optional :ref:`garbage collector name <gc>`, an optional :ref:`prefix <prefixdata>`,
638 an optional :ref:`prologue <prologuedata>`, an opening
639 curly brace, a list of basic blocks, and a closing curly brace.
641 LLVM function declarations consist of the "``declare``" keyword, an
642 optional :ref:`linkage type <linkage>`, an optional :ref:`visibility
643 style <visibility>`, an optional :ref:`DLL storage class <dllstorageclass>`,
644 an optional :ref:`calling convention <callingconv>`,
645 an optional ``unnamed_addr`` attribute, a return type, an optional
646 :ref:`parameter attribute <paramattrs>` for the return type, a function
647 name, a possibly empty list of arguments, an optional alignment, an optional
648 :ref:`garbage collector name <gc>`, an optional :ref:`prefix <prefixdata>`,
649 and an optional :ref:`prologue <prologuedata>`.
651 A function definition contains a list of basic blocks, forming the CFG (Control
652 Flow Graph) for the function. Each basic block may optionally start with a label
653 (giving the basic block a symbol table entry), contains a list of instructions,
654 and ends with a :ref:`terminator <terminators>` instruction (such as a branch or
655 function return). If an explicit label is not provided, a block is assigned an
656 implicit numbered label, using the next value from the same counter as used for
657 unnamed temporaries (:ref:`see above<identifiers>`). For example, if a function
658 entry block does not have an explicit label, it will be assigned label "%0",
659 then the first unnamed temporary in that block will be "%1", etc.
661 The first basic block in a function is special in two ways: it is
662 immediately executed on entrance to the function, and it is not allowed
663 to have predecessor basic blocks (i.e. there can not be any branches to
664 the entry block of a function). Because the block can have no
665 predecessors, it also cannot have any :ref:`PHI nodes <i_phi>`.
667 LLVM allows an explicit section to be specified for functions. If the
668 target supports it, it will emit functions to the section specified.
669 Additionally, the function can be placed in a COMDAT.
671 An explicit alignment may be specified for a function. If not present,
672 or if the alignment is set to zero, the alignment of the function is set
673 by the target to whatever it feels convenient. If an explicit alignment
674 is specified, the function is forced to have at least that much
675 alignment. All alignments must be a power of 2.
677 If the ``unnamed_addr`` attribute is given, the address is known to not
678 be significant and two identical functions can be merged.
682 define [linkage] [visibility] [DLLStorageClass]
684 <ResultType> @<FunctionName> ([argument list])
685 [unnamed_addr] [fn Attrs] [section "name"] [comdat [($name)]]
686 [align N] [gc] [prefix Constant] [prologue Constant] { ... }
688 The argument list is a comma seperated sequence of arguments where each
689 argument is of the following form
693 <type> [parameter Attrs] [name]
701 Aliases, unlike function or variables, don't create any new data. They
702 are just a new symbol and metadata for an existing position.
704 Aliases have a name and an aliasee that is either a global value or a
707 Aliases may have an optional :ref:`linkage type <linkage>`, an optional
708 :ref:`visibility style <visibility>`, an optional :ref:`DLL storage class
709 <dllstorageclass>` and an optional :ref:`tls model <tls_model>`.
713 @<Name> = [Linkage] [Visibility] [DLLStorageClass] [ThreadLocal] [unnamed_addr] alias <AliaseeTy> @<Aliasee>
715 The linkage must be one of ``private``, ``internal``, ``linkonce``, ``weak``,
716 ``linkonce_odr``, ``weak_odr``, ``external``. Note that some system linkers
717 might not correctly handle dropping a weak symbol that is aliased.
719 Aliases that are not ``unnamed_addr`` are guaranteed to have the same address as
720 the aliasee expression. ``unnamed_addr`` ones are only guaranteed to point
723 Since aliases are only a second name, some restrictions apply, of which
724 some can only be checked when producing an object file:
726 * The expression defining the aliasee must be computable at assembly
727 time. Since it is just a name, no relocations can be used.
729 * No alias in the expression can be weak as the possibility of the
730 intermediate alias being overridden cannot be represented in an
733 * No global value in the expression can be a declaration, since that
734 would require a relocation, which is not possible.
741 Comdat IR provides access to COFF and ELF object file COMDAT functionality.
743 Comdats have a name which represents the COMDAT key. All global objects that
744 specify this key will only end up in the final object file if the linker chooses
745 that key over some other key. Aliases are placed in the same COMDAT that their
746 aliasee computes to, if any.
748 Comdats have a selection kind to provide input on how the linker should
749 choose between keys in two different object files.
753 $<Name> = comdat SelectionKind
755 The selection kind must be one of the following:
758 The linker may choose any COMDAT key, the choice is arbitrary.
760 The linker may choose any COMDAT key but the sections must contain the
763 The linker will choose the section containing the largest COMDAT key.
765 The linker requires that only section with this COMDAT key exist.
767 The linker may choose any COMDAT key but the sections must contain the
770 Note that the Mach-O platform doesn't support COMDATs and ELF only supports
771 ``any`` as a selection kind.
773 Here is an example of a COMDAT group where a function will only be selected if
774 the COMDAT key's section is the largest:
778 $foo = comdat largest
779 @foo = global i32 2, comdat($foo)
781 define void @bar() comdat($foo) {
785 As a syntactic sugar the ``$name`` can be omitted if the name is the same as
791 @foo = global i32 2, comdat
794 In a COFF object file, this will create a COMDAT section with selection kind
795 ``IMAGE_COMDAT_SELECT_LARGEST`` containing the contents of the ``@foo`` symbol
796 and another COMDAT section with selection kind
797 ``IMAGE_COMDAT_SELECT_ASSOCIATIVE`` which is associated with the first COMDAT
798 section and contains the contents of the ``@bar`` symbol.
800 There are some restrictions on the properties of the global object.
801 It, or an alias to it, must have the same name as the COMDAT group when
803 The contents and size of this object may be used during link-time to determine
804 which COMDAT groups get selected depending on the selection kind.
805 Because the name of the object must match the name of the COMDAT group, the
806 linkage of the global object must not be local; local symbols can get renamed
807 if a collision occurs in the symbol table.
809 The combined use of COMDATS and section attributes may yield surprising results.
816 @g1 = global i32 42, section "sec", comdat($foo)
817 @g2 = global i32 42, section "sec", comdat($bar)
819 From the object file perspective, this requires the creation of two sections
820 with the same name. This is necessary because both globals belong to different
821 COMDAT groups and COMDATs, at the object file level, are represented by
824 Note that certain IR constructs like global variables and functions may create
825 COMDATs in the object file in addition to any which are specified using COMDAT
826 IR. This arises, for example, when a global variable has linkonce_odr linkage.
828 .. _namedmetadatastructure:
833 Named metadata is a collection of metadata. :ref:`Metadata
834 nodes <metadata>` (but not metadata strings) are the only valid
835 operands for a named metadata.
839 ; Some unnamed metadata nodes, which are referenced by the named metadata.
844 !name = !{!0, !1, !2}
851 The return type and each parameter of a function type may have a set of
852 *parameter attributes* associated with them. Parameter attributes are
853 used to communicate additional information about the result or
854 parameters of a function. Parameter attributes are considered to be part
855 of the function, not of the function type, so functions with different
856 parameter attributes can have the same function type.
858 Parameter attributes are simple keywords that follow the type specified.
859 If multiple parameter attributes are needed, they are space separated.
864 declare i32 @printf(i8* noalias nocapture, ...)
865 declare i32 @atoi(i8 zeroext)
866 declare signext i8 @returns_signed_char()
868 Note that any attributes for the function result (``nounwind``,
869 ``readonly``) come immediately after the argument list.
871 Currently, only the following parameter attributes are defined:
874 This indicates to the code generator that the parameter or return
875 value should be zero-extended to the extent required by the target's
876 ABI (which is usually 32-bits, but is 8-bits for a i1 on x86-64) by
877 the caller (for a parameter) or the callee (for a return value).
879 This indicates to the code generator that the parameter or return
880 value should be sign-extended to the extent required by the target's
881 ABI (which is usually 32-bits) by the caller (for a parameter) or
882 the callee (for a return value).
884 This indicates that this parameter or return value should be treated
885 in a special target-dependent fashion during while emitting code for
886 a function call or return (usually, by putting it in a register as
887 opposed to memory, though some targets use it to distinguish between
888 two different kinds of registers). Use of this attribute is
891 This indicates that the pointer parameter should really be passed by
892 value to the function. The attribute implies that a hidden copy of
893 the pointee is made between the caller and the callee, so the callee
894 is unable to modify the value in the caller. This attribute is only
895 valid on LLVM pointer arguments. It is generally used to pass
896 structs and arrays by value, but is also valid on pointers to
897 scalars. The copy is considered to belong to the caller not the
898 callee (for example, ``readonly`` functions should not write to
899 ``byval`` parameters). This is not a valid attribute for return
902 The byval attribute also supports specifying an alignment with the
903 align attribute. It indicates the alignment of the stack slot to
904 form and the known alignment of the pointer specified to the call
905 site. If the alignment is not specified, then the code generator
906 makes a target-specific assumption.
912 The ``inalloca`` argument attribute allows the caller to take the
913 address of outgoing stack arguments. An ``inalloca`` argument must
914 be a pointer to stack memory produced by an ``alloca`` instruction.
915 The alloca, or argument allocation, must also be tagged with the
916 inalloca keyword. Only the last argument may have the ``inalloca``
917 attribute, and that argument is guaranteed to be passed in memory.
919 An argument allocation may be used by a call at most once because
920 the call may deallocate it. The ``inalloca`` attribute cannot be
921 used in conjunction with other attributes that affect argument
922 storage, like ``inreg``, ``nest``, ``sret``, or ``byval``. The
923 ``inalloca`` attribute also disables LLVM's implicit lowering of
924 large aggregate return values, which means that frontend authors
925 must lower them with ``sret`` pointers.
927 When the call site is reached, the argument allocation must have
928 been the most recent stack allocation that is still live, or the
929 results are undefined. It is possible to allocate additional stack
930 space after an argument allocation and before its call site, but it
931 must be cleared off with :ref:`llvm.stackrestore
934 See :doc:`InAlloca` for more information on how to use this
938 This indicates that the pointer parameter specifies the address of a
939 structure that is the return value of the function in the source
940 program. This pointer must be guaranteed by the caller to be valid:
941 loads and stores to the structure may be assumed by the callee
942 not to trap and to be properly aligned. This may only be applied to
943 the first parameter. This is not a valid attribute for return
947 This indicates that the pointer value may be assumed by the optimizer to
948 have the specified alignment.
950 Note that this attribute has additional semantics when combined with the
956 This indicates that objects accessed via pointer values
957 :ref:`based <pointeraliasing>` on the argument or return value are not also
958 accessed, during the execution of the function, via pointer values not
959 *based* on the argument or return value. The attribute on a return value
960 also has additional semantics described below. The caller shares the
961 responsibility with the callee for ensuring that these requirements are met.
962 For further details, please see the discussion of the NoAlias response in
963 :ref:`alias analysis <Must, May, or No>`.
965 Note that this definition of ``noalias`` is intentionally similar
966 to the definition of ``restrict`` in C99 for function arguments.
968 For function return values, C99's ``restrict`` is not meaningful,
969 while LLVM's ``noalias`` is. Furthermore, the semantics of the ``noalias``
970 attribute on return values are stronger than the semantics of the attribute
971 when used on function arguments. On function return values, the ``noalias``
972 attribute indicates that the function acts like a system memory allocation
973 function, returning a pointer to allocated storage disjoint from the
974 storage for any other object accessible to the caller.
977 This indicates that the callee does not make any copies of the
978 pointer that outlive the callee itself. This is not a valid
979 attribute for return values.
984 This indicates that the pointer parameter can be excised using the
985 :ref:`trampoline intrinsics <int_trampoline>`. This is not a valid
986 attribute for return values and can only be applied to one parameter.
989 This indicates that the function always returns the argument as its return
990 value. This is an optimization hint to the code generator when generating
991 the caller, allowing tail call optimization and omission of register saves
992 and restores in some cases; it is not checked or enforced when generating
993 the callee. The parameter and the function return type must be valid
994 operands for the :ref:`bitcast instruction <i_bitcast>`. This is not a
995 valid attribute for return values and can only be applied to one parameter.
998 This indicates that the parameter or return pointer is not null. This
999 attribute may only be applied to pointer typed parameters. This is not
1000 checked or enforced by LLVM, the caller must ensure that the pointer
1001 passed in is non-null, or the callee must ensure that the returned pointer
1004 ``dereferenceable(<n>)``
1005 This indicates that the parameter or return pointer is dereferenceable. This
1006 attribute may only be applied to pointer typed parameters. A pointer that
1007 is dereferenceable can be loaded from speculatively without a risk of
1008 trapping. The number of bytes known to be dereferenceable must be provided
1009 in parentheses. It is legal for the number of bytes to be less than the
1010 size of the pointee type. The ``nonnull`` attribute does not imply
1011 dereferenceability (consider a pointer to one element past the end of an
1012 array), however ``dereferenceable(<n>)`` does imply ``nonnull`` in
1013 ``addrspace(0)`` (which is the default address space).
1017 Garbage Collector Strategy Names
1018 --------------------------------
1020 Each function may specify a garbage collector strategy name, which is simply a
1023 .. code-block:: llvm
1025 define void @f() gc "name" { ... }
1027 The supported values of *name* includes those :ref:`built in to LLVM
1028 <builtin-gc-strategies>` and any provided by loaded plugins. Specifying a GC
1029 strategy will cause the compiler to alter its output in order to support the
1030 named garbage collection algorithm. Note that LLVM itself does not contain a
1031 garbage collector, this functionality is restricted to generating machine code
1032 which can interoperate with a collector provided externally.
1039 Prefix data is data associated with a function which the code
1040 generator will emit immediately before the function's entrypoint.
1041 The purpose of this feature is to allow frontends to associate
1042 language-specific runtime metadata with specific functions and make it
1043 available through the function pointer while still allowing the
1044 function pointer to be called.
1046 To access the data for a given function, a program may bitcast the
1047 function pointer to a pointer to the constant's type and dereference
1048 index -1. This implies that the IR symbol points just past the end of
1049 the prefix data. For instance, take the example of a function annotated
1050 with a single ``i32``,
1052 .. code-block:: llvm
1054 define void @f() prefix i32 123 { ... }
1056 The prefix data can be referenced as,
1058 .. code-block:: llvm
1060 %0 = bitcast *void () @f to *i32
1061 %a = getelementptr inbounds *i32 %0, i32 -1
1064 Prefix data is laid out as if it were an initializer for a global variable
1065 of the prefix data's type. The function will be placed such that the
1066 beginning of the prefix data is aligned. This means that if the size
1067 of the prefix data is not a multiple of the alignment size, the
1068 function's entrypoint will not be aligned. If alignment of the
1069 function's entrypoint is desired, padding must be added to the prefix
1072 A function may have prefix data but no body. This has similar semantics
1073 to the ``available_externally`` linkage in that the data may be used by the
1074 optimizers but will not be emitted in the object file.
1081 The ``prologue`` attribute allows arbitrary code (encoded as bytes) to
1082 be inserted prior to the function body. This can be used for enabling
1083 function hot-patching and instrumentation.
1085 To maintain the semantics of ordinary function calls, the prologue data must
1086 have a particular format. Specifically, it must begin with a sequence of
1087 bytes which decode to a sequence of machine instructions, valid for the
1088 module's target, which transfer control to the point immediately succeeding
1089 the prologue data, without performing any other visible action. This allows
1090 the inliner and other passes to reason about the semantics of the function
1091 definition without needing to reason about the prologue data. Obviously this
1092 makes the format of the prologue data highly target dependent.
1094 A trivial example of valid prologue data for the x86 architecture is ``i8 144``,
1095 which encodes the ``nop`` instruction:
1097 .. code-block:: llvm
1099 define void @f() prologue i8 144 { ... }
1101 Generally prologue data can be formed by encoding a relative branch instruction
1102 which skips the metadata, as in this example of valid prologue data for the
1103 x86_64 architecture, where the first two bytes encode ``jmp .+10``:
1105 .. code-block:: llvm
1107 %0 = type <{ i8, i8, i8* }>
1109 define void @f() prologue %0 <{ i8 235, i8 8, i8* @md}> { ... }
1111 A function may have prologue data but no body. This has similar semantics
1112 to the ``available_externally`` linkage in that the data may be used by the
1113 optimizers but will not be emitted in the object file.
1120 Attribute groups are groups of attributes that are referenced by objects within
1121 the IR. They are important for keeping ``.ll`` files readable, because a lot of
1122 functions will use the same set of attributes. In the degenerative case of a
1123 ``.ll`` file that corresponds to a single ``.c`` file, the single attribute
1124 group will capture the important command line flags used to build that file.
1126 An attribute group is a module-level object. To use an attribute group, an
1127 object references the attribute group's ID (e.g. ``#37``). An object may refer
1128 to more than one attribute group. In that situation, the attributes from the
1129 different groups are merged.
1131 Here is an example of attribute groups for a function that should always be
1132 inlined, has a stack alignment of 4, and which shouldn't use SSE instructions:
1134 .. code-block:: llvm
1136 ; Target-independent attributes:
1137 attributes #0 = { alwaysinline alignstack=4 }
1139 ; Target-dependent attributes:
1140 attributes #1 = { "no-sse" }
1142 ; Function @f has attributes: alwaysinline, alignstack=4, and "no-sse".
1143 define void @f() #0 #1 { ... }
1150 Function attributes are set to communicate additional information about
1151 a function. Function attributes are considered to be part of the
1152 function, not of the function type, so functions with different function
1153 attributes can have the same function type.
1155 Function attributes are simple keywords that follow the type specified.
1156 If multiple attributes are needed, they are space separated. For
1159 .. code-block:: llvm
1161 define void @f() noinline { ... }
1162 define void @f() alwaysinline { ... }
1163 define void @f() alwaysinline optsize { ... }
1164 define void @f() optsize { ... }
1167 This attribute indicates that, when emitting the prologue and
1168 epilogue, the backend should forcibly align the stack pointer.
1169 Specify the desired alignment, which must be a power of two, in
1172 This attribute indicates that the inliner should attempt to inline
1173 this function into callers whenever possible, ignoring any active
1174 inlining size threshold for this caller.
1176 This indicates that the callee function at a call site should be
1177 recognized as a built-in function, even though the function's declaration
1178 uses the ``nobuiltin`` attribute. This is only valid at call sites for
1179 direct calls to functions that are declared with the ``nobuiltin``
1182 This attribute indicates that this function is rarely called. When
1183 computing edge weights, basic blocks post-dominated by a cold
1184 function call are also considered to be cold; and, thus, given low
1187 This attribute indicates that the source code contained a hint that
1188 inlining this function is desirable (such as the "inline" keyword in
1189 C/C++). It is just a hint; it imposes no requirements on the
1192 This attribute indicates that the function should be added to a
1193 jump-instruction table at code-generation time, and that all address-taken
1194 references to this function should be replaced with a reference to the
1195 appropriate jump-instruction-table function pointer. Note that this creates
1196 a new pointer for the original function, which means that code that depends
1197 on function-pointer identity can break. So, any function annotated with
1198 ``jumptable`` must also be ``unnamed_addr``.
1200 This attribute suggests that optimization passes and code generator
1201 passes make choices that keep the code size of this function as small
1202 as possible and perform optimizations that may sacrifice runtime
1203 performance in order to minimize the size of the generated code.
1205 This attribute disables prologue / epilogue emission for the
1206 function. This can have very system-specific consequences.
1208 This indicates that the callee function at a call site is not recognized as
1209 a built-in function. LLVM will retain the original call and not replace it
1210 with equivalent code based on the semantics of the built-in function, unless
1211 the call site uses the ``builtin`` attribute. This is valid at call sites
1212 and on function declarations and definitions.
1214 This attribute indicates that calls to the function cannot be
1215 duplicated. A call to a ``noduplicate`` function may be moved
1216 within its parent function, but may not be duplicated within
1217 its parent function.
1219 A function containing a ``noduplicate`` call may still
1220 be an inlining candidate, provided that the call is not
1221 duplicated by inlining. That implies that the function has
1222 internal linkage and only has one call site, so the original
1223 call is dead after inlining.
1225 This attributes disables implicit floating point instructions.
1227 This attribute indicates that the inliner should never inline this
1228 function in any situation. This attribute may not be used together
1229 with the ``alwaysinline`` attribute.
1231 This attribute suppresses lazy symbol binding for the function. This
1232 may make calls to the function faster, at the cost of extra program
1233 startup time if the function is not called during program startup.
1235 This attribute indicates that the code generator should not use a
1236 red zone, even if the target-specific ABI normally permits it.
1238 This function attribute indicates that the function never returns
1239 normally. This produces undefined behavior at runtime if the
1240 function ever does dynamically return.
1242 This function attribute indicates that the function never raises an
1243 exception. If the function does raise an exception, its runtime
1244 behavior is undefined. However, functions marked nounwind may still
1245 trap or generate asynchronous exceptions. Exception handling schemes
1246 that are recognized by LLVM to handle asynchronous exceptions, such
1247 as SEH, will still provide their implementation defined semantics.
1249 This function attribute indicates that the function is not optimized
1250 by any optimization or code generator passes with the
1251 exception of interprocedural optimization passes.
1252 This attribute cannot be used together with the ``alwaysinline``
1253 attribute; this attribute is also incompatible
1254 with the ``minsize`` attribute and the ``optsize`` attribute.
1256 This attribute requires the ``noinline`` attribute to be specified on
1257 the function as well, so the function is never inlined into any caller.
1258 Only functions with the ``alwaysinline`` attribute are valid
1259 candidates for inlining into the body of this function.
1261 This attribute suggests that optimization passes and code generator
1262 passes make choices that keep the code size of this function low,
1263 and otherwise do optimizations specifically to reduce code size as
1264 long as they do not significantly impact runtime performance.
1266 On a function, this attribute indicates that the function computes its
1267 result (or decides to unwind an exception) based strictly on its arguments,
1268 without dereferencing any pointer arguments or otherwise accessing
1269 any mutable state (e.g. memory, control registers, etc) visible to
1270 caller functions. It does not write through any pointer arguments
1271 (including ``byval`` arguments) and never changes any state visible
1272 to callers. This means that it cannot unwind exceptions by calling
1273 the ``C++`` exception throwing methods.
1275 On an argument, this attribute indicates that the function does not
1276 dereference that pointer argument, even though it may read or write the
1277 memory that the pointer points to if accessed through other pointers.
1279 On a function, this attribute indicates that the function does not write
1280 through any pointer arguments (including ``byval`` arguments) or otherwise
1281 modify any state (e.g. memory, control registers, etc) visible to
1282 caller functions. It may dereference pointer arguments and read
1283 state that may be set in the caller. A readonly function always
1284 returns the same value (or unwinds an exception identically) when
1285 called with the same set of arguments and global state. It cannot
1286 unwind an exception by calling the ``C++`` exception throwing
1289 On an argument, this attribute indicates that the function does not write
1290 through this pointer argument, even though it may write to the memory that
1291 the pointer points to.
1293 This attribute indicates that this function can return twice. The C
1294 ``setjmp`` is an example of such a function. The compiler disables
1295 some optimizations (like tail calls) in the caller of these
1297 ``sanitize_address``
1298 This attribute indicates that AddressSanitizer checks
1299 (dynamic address safety analysis) are enabled for this function.
1301 This attribute indicates that MemorySanitizer checks (dynamic detection
1302 of accesses to uninitialized memory) are enabled for this function.
1304 This attribute indicates that ThreadSanitizer checks
1305 (dynamic thread safety analysis) are enabled for this function.
1307 This attribute indicates that the function should emit a stack
1308 smashing protector. It is in the form of a "canary" --- a random value
1309 placed on the stack before the local variables that's checked upon
1310 return from the function to see if it has been overwritten. A
1311 heuristic is used to determine if a function needs stack protectors
1312 or not. The heuristic used will enable protectors for functions with:
1314 - Character arrays larger than ``ssp-buffer-size`` (default 8).
1315 - Aggregates containing character arrays larger than ``ssp-buffer-size``.
1316 - Calls to alloca() with variable sizes or constant sizes greater than
1317 ``ssp-buffer-size``.
1319 Variables that are identified as requiring a protector will be arranged
1320 on the stack such that they are adjacent to the stack protector guard.
1322 If a function that has an ``ssp`` attribute is inlined into a
1323 function that doesn't have an ``ssp`` attribute, then the resulting
1324 function will have an ``ssp`` attribute.
1326 This attribute indicates that the function should *always* emit a
1327 stack smashing protector. This overrides the ``ssp`` function
1330 Variables that are identified as requiring a protector will be arranged
1331 on the stack such that they are adjacent to the stack protector guard.
1332 The specific layout rules are:
1334 #. Large arrays and structures containing large arrays
1335 (``>= ssp-buffer-size``) are closest to the stack protector.
1336 #. Small arrays and structures containing small arrays
1337 (``< ssp-buffer-size``) are 2nd closest to the protector.
1338 #. Variables that have had their address taken are 3rd closest to the
1341 If a function that has an ``sspreq`` attribute is inlined into a
1342 function that doesn't have an ``sspreq`` attribute or which has an
1343 ``ssp`` or ``sspstrong`` attribute, then the resulting function will have
1344 an ``sspreq`` attribute.
1346 This attribute indicates that the function should emit a stack smashing
1347 protector. This attribute causes a strong heuristic to be used when
1348 determining if a function needs stack protectors. The strong heuristic
1349 will enable protectors for functions with:
1351 - Arrays of any size and type
1352 - Aggregates containing an array of any size and type.
1353 - Calls to alloca().
1354 - Local variables that have had their address taken.
1356 Variables that are identified as requiring a protector will be arranged
1357 on the stack such that they are adjacent to the stack protector guard.
1358 The specific layout rules are:
1360 #. Large arrays and structures containing large arrays
1361 (``>= ssp-buffer-size``) are closest to the stack protector.
1362 #. Small arrays and structures containing small arrays
1363 (``< ssp-buffer-size``) are 2nd closest to the protector.
1364 #. Variables that have had their address taken are 3rd closest to the
1367 This overrides the ``ssp`` function attribute.
1369 If a function that has an ``sspstrong`` attribute is inlined into a
1370 function that doesn't have an ``sspstrong`` attribute, then the
1371 resulting function will have an ``sspstrong`` attribute.
1373 This attribute indicates that the ABI being targeted requires that
1374 an unwind table entry be produce for this function even if we can
1375 show that no exceptions passes by it. This is normally the case for
1376 the ELF x86-64 abi, but it can be disabled for some compilation
1381 Module-Level Inline Assembly
1382 ----------------------------
1384 Modules may contain "module-level inline asm" blocks, which corresponds
1385 to the GCC "file scope inline asm" blocks. These blocks are internally
1386 concatenated by LLVM and treated as a single unit, but may be separated
1387 in the ``.ll`` file if desired. The syntax is very simple:
1389 .. code-block:: llvm
1391 module asm "inline asm code goes here"
1392 module asm "more can go here"
1394 The strings can contain any character by escaping non-printable
1395 characters. The escape sequence used is simply "\\xx" where "xx" is the
1396 two digit hex code for the number.
1398 The inline asm code is simply printed to the machine code .s file when
1399 assembly code is generated.
1401 .. _langref_datalayout:
1406 A module may specify a target specific data layout string that specifies
1407 how data is to be laid out in memory. The syntax for the data layout is
1410 .. code-block:: llvm
1412 target datalayout = "layout specification"
1414 The *layout specification* consists of a list of specifications
1415 separated by the minus sign character ('-'). Each specification starts
1416 with a letter and may include other information after the letter to
1417 define some aspect of the data layout. The specifications accepted are
1421 Specifies that the target lays out data in big-endian form. That is,
1422 the bits with the most significance have the lowest address
1425 Specifies that the target lays out data in little-endian form. That
1426 is, the bits with the least significance have the lowest address
1429 Specifies the natural alignment of the stack in bits. Alignment
1430 promotion of stack variables is limited to the natural stack
1431 alignment to avoid dynamic stack realignment. The stack alignment
1432 must be a multiple of 8-bits. If omitted, the natural stack
1433 alignment defaults to "unspecified", which does not prevent any
1434 alignment promotions.
1435 ``p[n]:<size>:<abi>:<pref>``
1436 This specifies the *size* of a pointer and its ``<abi>`` and
1437 ``<pref>``\erred alignments for address space ``n``. All sizes are in
1438 bits. The address space, ``n`` is optional, and if not specified,
1439 denotes the default address space 0. The value of ``n`` must be
1440 in the range [1,2^23).
1441 ``i<size>:<abi>:<pref>``
1442 This specifies the alignment for an integer type of a given bit
1443 ``<size>``. The value of ``<size>`` must be in the range [1,2^23).
1444 ``v<size>:<abi>:<pref>``
1445 This specifies the alignment for a vector type of a given bit
1447 ``f<size>:<abi>:<pref>``
1448 This specifies the alignment for a floating point type of a given bit
1449 ``<size>``. Only values of ``<size>`` that are supported by the target
1450 will work. 32 (float) and 64 (double) are supported on all targets; 80
1451 or 128 (different flavors of long double) are also supported on some
1454 This specifies the alignment for an object of aggregate type.
1456 If present, specifies that llvm names are mangled in the output. The
1459 * ``e``: ELF mangling: Private symbols get a ``.L`` prefix.
1460 * ``m``: Mips mangling: Private symbols get a ``$`` prefix.
1461 * ``o``: Mach-O mangling: Private symbols get ``L`` prefix. Other
1462 symbols get a ``_`` prefix.
1463 * ``w``: Windows COFF prefix: Similar to Mach-O, but stdcall and fastcall
1464 functions also get a suffix based on the frame size.
1465 ``n<size1>:<size2>:<size3>...``
1466 This specifies a set of native integer widths for the target CPU in
1467 bits. For example, it might contain ``n32`` for 32-bit PowerPC,
1468 ``n32:64`` for PowerPC 64, or ``n8:16:32:64`` for X86-64. Elements of
1469 this set are considered to support most general arithmetic operations
1472 On every specification that takes a ``<abi>:<pref>``, specifying the
1473 ``<pref>`` alignment is optional. If omitted, the preceding ``:``
1474 should be omitted too and ``<pref>`` will be equal to ``<abi>``.
1476 When constructing the data layout for a given target, LLVM starts with a
1477 default set of specifications which are then (possibly) overridden by
1478 the specifications in the ``datalayout`` keyword. The default
1479 specifications are given in this list:
1481 - ``E`` - big endian
1482 - ``p:64:64:64`` - 64-bit pointers with 64-bit alignment.
1483 - ``p[n]:64:64:64`` - Other address spaces are assumed to be the
1484 same as the default address space.
1485 - ``S0`` - natural stack alignment is unspecified
1486 - ``i1:8:8`` - i1 is 8-bit (byte) aligned
1487 - ``i8:8:8`` - i8 is 8-bit (byte) aligned
1488 - ``i16:16:16`` - i16 is 16-bit aligned
1489 - ``i32:32:32`` - i32 is 32-bit aligned
1490 - ``i64:32:64`` - i64 has ABI alignment of 32-bits but preferred
1491 alignment of 64-bits
1492 - ``f16:16:16`` - half is 16-bit aligned
1493 - ``f32:32:32`` - float is 32-bit aligned
1494 - ``f64:64:64`` - double is 64-bit aligned
1495 - ``f128:128:128`` - quad is 128-bit aligned
1496 - ``v64:64:64`` - 64-bit vector is 64-bit aligned
1497 - ``v128:128:128`` - 128-bit vector is 128-bit aligned
1498 - ``a:0:64`` - aggregates are 64-bit aligned
1500 When LLVM is determining the alignment for a given type, it uses the
1503 #. If the type sought is an exact match for one of the specifications,
1504 that specification is used.
1505 #. If no match is found, and the type sought is an integer type, then
1506 the smallest integer type that is larger than the bitwidth of the
1507 sought type is used. If none of the specifications are larger than
1508 the bitwidth then the largest integer type is used. For example,
1509 given the default specifications above, the i7 type will use the
1510 alignment of i8 (next largest) while both i65 and i256 will use the
1511 alignment of i64 (largest specified).
1512 #. If no match is found, and the type sought is a vector type, then the
1513 largest vector type that is smaller than the sought vector type will
1514 be used as a fall back. This happens because <128 x double> can be
1515 implemented in terms of 64 <2 x double>, for example.
1517 The function of the data layout string may not be what you expect.
1518 Notably, this is not a specification from the frontend of what alignment
1519 the code generator should use.
1521 Instead, if specified, the target data layout is required to match what
1522 the ultimate *code generator* expects. This string is used by the
1523 mid-level optimizers to improve code, and this only works if it matches
1524 what the ultimate code generator uses. If you would like to generate IR
1525 that does not embed this target-specific detail into the IR, then you
1526 don't have to specify the string. This will disable some optimizations
1527 that require precise layout information, but this also prevents those
1528 optimizations from introducing target specificity into the IR.
1535 A module may specify a target triple string that describes the target
1536 host. The syntax for the target triple is simply:
1538 .. code-block:: llvm
1540 target triple = "x86_64-apple-macosx10.7.0"
1542 The *target triple* string consists of a series of identifiers delimited
1543 by the minus sign character ('-'). The canonical forms are:
1547 ARCHITECTURE-VENDOR-OPERATING_SYSTEM
1548 ARCHITECTURE-VENDOR-OPERATING_SYSTEM-ENVIRONMENT
1550 This information is passed along to the backend so that it generates
1551 code for the proper architecture. It's possible to override this on the
1552 command line with the ``-mtriple`` command line option.
1554 .. _pointeraliasing:
1556 Pointer Aliasing Rules
1557 ----------------------
1559 Any memory access must be done through a pointer value associated with
1560 an address range of the memory access, otherwise the behavior is
1561 undefined. Pointer values are associated with address ranges according
1562 to the following rules:
1564 - A pointer value is associated with the addresses associated with any
1565 value it is *based* on.
1566 - An address of a global variable is associated with the address range
1567 of the variable's storage.
1568 - The result value of an allocation instruction is associated with the
1569 address range of the allocated storage.
1570 - A null pointer in the default address-space is associated with no
1572 - An integer constant other than zero or a pointer value returned from
1573 a function not defined within LLVM may be associated with address
1574 ranges allocated through mechanisms other than those provided by
1575 LLVM. Such ranges shall not overlap with any ranges of addresses
1576 allocated by mechanisms provided by LLVM.
1578 A pointer value is *based* on another pointer value according to the
1581 - A pointer value formed from a ``getelementptr`` operation is *based*
1582 on the first operand of the ``getelementptr``.
1583 - The result value of a ``bitcast`` is *based* on the operand of the
1585 - A pointer value formed by an ``inttoptr`` is *based* on all pointer
1586 values that contribute (directly or indirectly) to the computation of
1587 the pointer's value.
1588 - The "*based* on" relationship is transitive.
1590 Note that this definition of *"based"* is intentionally similar to the
1591 definition of *"based"* in C99, though it is slightly weaker.
1593 LLVM IR does not associate types with memory. The result type of a
1594 ``load`` merely indicates the size and alignment of the memory from
1595 which to load, as well as the interpretation of the value. The first
1596 operand type of a ``store`` similarly only indicates the size and
1597 alignment of the store.
1599 Consequently, type-based alias analysis, aka TBAA, aka
1600 ``-fstrict-aliasing``, is not applicable to general unadorned LLVM IR.
1601 :ref:`Metadata <metadata>` may be used to encode additional information
1602 which specialized optimization passes may use to implement type-based
1607 Volatile Memory Accesses
1608 ------------------------
1610 Certain memory accesses, such as :ref:`load <i_load>`'s,
1611 :ref:`store <i_store>`'s, and :ref:`llvm.memcpy <int_memcpy>`'s may be
1612 marked ``volatile``. The optimizers must not change the number of
1613 volatile operations or change their order of execution relative to other
1614 volatile operations. The optimizers *may* change the order of volatile
1615 operations relative to non-volatile operations. This is not Java's
1616 "volatile" and has no cross-thread synchronization behavior.
1618 IR-level volatile loads and stores cannot safely be optimized into
1619 llvm.memcpy or llvm.memmove intrinsics even when those intrinsics are
1620 flagged volatile. Likewise, the backend should never split or merge
1621 target-legal volatile load/store instructions.
1623 .. admonition:: Rationale
1625 Platforms may rely on volatile loads and stores of natively supported
1626 data width to be executed as single instruction. For example, in C
1627 this holds for an l-value of volatile primitive type with native
1628 hardware support, but not necessarily for aggregate types. The
1629 frontend upholds these expectations, which are intentionally
1630 unspecified in the IR. The rules above ensure that IR transformation
1631 do not violate the frontend's contract with the language.
1635 Memory Model for Concurrent Operations
1636 --------------------------------------
1638 The LLVM IR does not define any way to start parallel threads of
1639 execution or to register signal handlers. Nonetheless, there are
1640 platform-specific ways to create them, and we define LLVM IR's behavior
1641 in their presence. This model is inspired by the C++0x memory model.
1643 For a more informal introduction to this model, see the :doc:`Atomics`.
1645 We define a *happens-before* partial order as the least partial order
1648 - Is a superset of single-thread program order, and
1649 - When a *synchronizes-with* ``b``, includes an edge from ``a`` to
1650 ``b``. *Synchronizes-with* pairs are introduced by platform-specific
1651 techniques, like pthread locks, thread creation, thread joining,
1652 etc., and by atomic instructions. (See also :ref:`Atomic Memory Ordering
1653 Constraints <ordering>`).
1655 Note that program order does not introduce *happens-before* edges
1656 between a thread and signals executing inside that thread.
1658 Every (defined) read operation (load instructions, memcpy, atomic
1659 loads/read-modify-writes, etc.) R reads a series of bytes written by
1660 (defined) write operations (store instructions, atomic
1661 stores/read-modify-writes, memcpy, etc.). For the purposes of this
1662 section, initialized globals are considered to have a write of the
1663 initializer which is atomic and happens before any other read or write
1664 of the memory in question. For each byte of a read R, R\ :sub:`byte`
1665 may see any write to the same byte, except:
1667 - If write\ :sub:`1` happens before write\ :sub:`2`, and
1668 write\ :sub:`2` happens before R\ :sub:`byte`, then
1669 R\ :sub:`byte` does not see write\ :sub:`1`.
1670 - If R\ :sub:`byte` happens before write\ :sub:`3`, then
1671 R\ :sub:`byte` does not see write\ :sub:`3`.
1673 Given that definition, R\ :sub:`byte` is defined as follows:
1675 - If R is volatile, the result is target-dependent. (Volatile is
1676 supposed to give guarantees which can support ``sig_atomic_t`` in
1677 C/C++, and may be used for accesses to addresses that do not behave
1678 like normal memory. It does not generally provide cross-thread
1680 - Otherwise, if there is no write to the same byte that happens before
1681 R\ :sub:`byte`, R\ :sub:`byte` returns ``undef`` for that byte.
1682 - Otherwise, if R\ :sub:`byte` may see exactly one write,
1683 R\ :sub:`byte` returns the value written by that write.
1684 - Otherwise, if R is atomic, and all the writes R\ :sub:`byte` may
1685 see are atomic, it chooses one of the values written. See the :ref:`Atomic
1686 Memory Ordering Constraints <ordering>` section for additional
1687 constraints on how the choice is made.
1688 - Otherwise R\ :sub:`byte` returns ``undef``.
1690 R returns the value composed of the series of bytes it read. This
1691 implies that some bytes within the value may be ``undef`` **without**
1692 the entire value being ``undef``. Note that this only defines the
1693 semantics of the operation; it doesn't mean that targets will emit more
1694 than one instruction to read the series of bytes.
1696 Note that in cases where none of the atomic intrinsics are used, this
1697 model places only one restriction on IR transformations on top of what
1698 is required for single-threaded execution: introducing a store to a byte
1699 which might not otherwise be stored is not allowed in general.
1700 (Specifically, in the case where another thread might write to and read
1701 from an address, introducing a store can change a load that may see
1702 exactly one write into a load that may see multiple writes.)
1706 Atomic Memory Ordering Constraints
1707 ----------------------------------
1709 Atomic instructions (:ref:`cmpxchg <i_cmpxchg>`,
1710 :ref:`atomicrmw <i_atomicrmw>`, :ref:`fence <i_fence>`,
1711 :ref:`atomic load <i_load>`, and :ref:`atomic store <i_store>`) take
1712 ordering parameters that determine which other atomic instructions on
1713 the same address they *synchronize with*. These semantics are borrowed
1714 from Java and C++0x, but are somewhat more colloquial. If these
1715 descriptions aren't precise enough, check those specs (see spec
1716 references in the :doc:`atomics guide <Atomics>`).
1717 :ref:`fence <i_fence>` instructions treat these orderings somewhat
1718 differently since they don't take an address. See that instruction's
1719 documentation for details.
1721 For a simpler introduction to the ordering constraints, see the
1725 The set of values that can be read is governed by the happens-before
1726 partial order. A value cannot be read unless some operation wrote
1727 it. This is intended to provide a guarantee strong enough to model
1728 Java's non-volatile shared variables. This ordering cannot be
1729 specified for read-modify-write operations; it is not strong enough
1730 to make them atomic in any interesting way.
1732 In addition to the guarantees of ``unordered``, there is a single
1733 total order for modifications by ``monotonic`` operations on each
1734 address. All modification orders must be compatible with the
1735 happens-before order. There is no guarantee that the modification
1736 orders can be combined to a global total order for the whole program
1737 (and this often will not be possible). The read in an atomic
1738 read-modify-write operation (:ref:`cmpxchg <i_cmpxchg>` and
1739 :ref:`atomicrmw <i_atomicrmw>`) reads the value in the modification
1740 order immediately before the value it writes. If one atomic read
1741 happens before another atomic read of the same address, the later
1742 read must see the same value or a later value in the address's
1743 modification order. This disallows reordering of ``monotonic`` (or
1744 stronger) operations on the same address. If an address is written
1745 ``monotonic``-ally by one thread, and other threads ``monotonic``-ally
1746 read that address repeatedly, the other threads must eventually see
1747 the write. This corresponds to the C++0x/C1x
1748 ``memory_order_relaxed``.
1750 In addition to the guarantees of ``monotonic``, a
1751 *synchronizes-with* edge may be formed with a ``release`` operation.
1752 This is intended to model C++'s ``memory_order_acquire``.
1754 In addition to the guarantees of ``monotonic``, if this operation
1755 writes a value which is subsequently read by an ``acquire``
1756 operation, it *synchronizes-with* that operation. (This isn't a
1757 complete description; see the C++0x definition of a release
1758 sequence.) This corresponds to the C++0x/C1x
1759 ``memory_order_release``.
1760 ``acq_rel`` (acquire+release)
1761 Acts as both an ``acquire`` and ``release`` operation on its
1762 address. This corresponds to the C++0x/C1x ``memory_order_acq_rel``.
1763 ``seq_cst`` (sequentially consistent)
1764 In addition to the guarantees of ``acq_rel`` (``acquire`` for an
1765 operation that only reads, ``release`` for an operation that only
1766 writes), there is a global total order on all
1767 sequentially-consistent operations on all addresses, which is
1768 consistent with the *happens-before* partial order and with the
1769 modification orders of all the affected addresses. Each
1770 sequentially-consistent read sees the last preceding write to the
1771 same address in this global order. This corresponds to the C++0x/C1x
1772 ``memory_order_seq_cst`` and Java volatile.
1776 If an atomic operation is marked ``singlethread``, it only *synchronizes
1777 with* or participates in modification and seq\_cst total orderings with
1778 other operations running in the same thread (for example, in signal
1786 LLVM IR floating-point binary ops (:ref:`fadd <i_fadd>`,
1787 :ref:`fsub <i_fsub>`, :ref:`fmul <i_fmul>`, :ref:`fdiv <i_fdiv>`,
1788 :ref:`frem <i_frem>`) have the following flags that can be set to enable
1789 otherwise unsafe floating point operations
1792 No NaNs - Allow optimizations to assume the arguments and result are not
1793 NaN. Such optimizations are required to retain defined behavior over
1794 NaNs, but the value of the result is undefined.
1797 No Infs - Allow optimizations to assume the arguments and result are not
1798 +/-Inf. Such optimizations are required to retain defined behavior over
1799 +/-Inf, but the value of the result is undefined.
1802 No Signed Zeros - Allow optimizations to treat the sign of a zero
1803 argument or result as insignificant.
1806 Allow Reciprocal - Allow optimizations to use the reciprocal of an
1807 argument rather than perform division.
1810 Fast - Allow algebraically equivalent transformations that may
1811 dramatically change results in floating point (e.g. reassociate). This
1812 flag implies all the others.
1816 Use-list Order Directives
1817 -------------------------
1819 Use-list directives encode the in-memory order of each use-list, allowing the
1820 order to be recreated. ``<order-indexes>`` is a comma-separated list of
1821 indexes that are assigned to the referenced value's uses. The referenced
1822 value's use-list is immediately sorted by these indexes.
1824 Use-list directives may appear at function scope or global scope. They are not
1825 instructions, and have no effect on the semantics of the IR. When they're at
1826 function scope, they must appear after the terminator of the final basic block.
1828 If basic blocks have their address taken via ``blockaddress()`` expressions,
1829 ``uselistorder_bb`` can be used to reorder their use-lists from outside their
1836 uselistorder <ty> <value>, { <order-indexes> }
1837 uselistorder_bb @function, %block { <order-indexes> }
1843 define void @foo(i32 %arg1, i32 %arg2) {
1845 ; ... instructions ...
1847 ; ... instructions ...
1849 ; At function scope.
1850 uselistorder i32 %arg1, { 1, 0, 2 }
1851 uselistorder label %bb, { 1, 0 }
1855 uselistorder i32* @global, { 1, 2, 0 }
1856 uselistorder i32 7, { 1, 0 }
1857 uselistorder i32 (i32) @bar, { 1, 0 }
1858 uselistorder_bb @foo, %bb, { 5, 1, 3, 2, 0, 4 }
1865 The LLVM type system is one of the most important features of the
1866 intermediate representation. Being typed enables a number of
1867 optimizations to be performed on the intermediate representation
1868 directly, without having to do extra analyses on the side before the
1869 transformation. A strong type system makes it easier to read the
1870 generated code and enables novel analyses and transformations that are
1871 not feasible to perform on normal three address code representations.
1881 The void type does not represent any value and has no size.
1899 The function type can be thought of as a function signature. It consists of a
1900 return type and a list of formal parameter types. The return type of a function
1901 type is a void type or first class type --- except for :ref:`label <t_label>`
1902 and :ref:`metadata <t_metadata>` types.
1908 <returntype> (<parameter list>)
1910 ...where '``<parameter list>``' is a comma-separated list of type
1911 specifiers. Optionally, the parameter list may include a type ``...``, which
1912 indicates that the function takes a variable number of arguments. Variable
1913 argument functions can access their arguments with the :ref:`variable argument
1914 handling intrinsic <int_varargs>` functions. '``<returntype>``' is any type
1915 except :ref:`label <t_label>` and :ref:`metadata <t_metadata>`.
1919 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1920 | ``i32 (i32)`` | function taking an ``i32``, returning an ``i32`` |
1921 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1922 | ``float (i16, i32 *) *`` | :ref:`Pointer <t_pointer>` to a function that takes an ``i16`` and a :ref:`pointer <t_pointer>` to ``i32``, returning ``float``. |
1923 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1924 | ``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. |
1925 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1926 | ``{i32, i32} (i32)`` | A function taking an ``i32``, returning a :ref:`structure <t_struct>` containing two ``i32`` values |
1927 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1934 The :ref:`first class <t_firstclass>` types are perhaps the most important.
1935 Values of these types are the only ones which can be produced by
1943 These are the types that are valid in registers from CodeGen's perspective.
1952 The integer type is a very simple type that simply specifies an
1953 arbitrary bit width for the integer type desired. Any bit width from 1
1954 bit to 2\ :sup:`23`\ -1 (about 8 million) can be specified.
1962 The number of bits the integer will occupy is specified by the ``N``
1968 +----------------+------------------------------------------------+
1969 | ``i1`` | a single-bit integer. |
1970 +----------------+------------------------------------------------+
1971 | ``i32`` | a 32-bit integer. |
1972 +----------------+------------------------------------------------+
1973 | ``i1942652`` | a really big integer of over 1 million bits. |
1974 +----------------+------------------------------------------------+
1978 Floating Point Types
1979 """"""""""""""""""""
1988 - 16-bit floating point value
1991 - 32-bit floating point value
1994 - 64-bit floating point value
1997 - 128-bit floating point value (112-bit mantissa)
2000 - 80-bit floating point value (X87)
2003 - 128-bit floating point value (two 64-bits)
2010 The x86_mmx type represents a value held in an MMX register on an x86
2011 machine. The operations allowed on it are quite limited: parameters and
2012 return values, load and store, and bitcast. User-specified MMX
2013 instructions are represented as intrinsic or asm calls with arguments
2014 and/or results of this type. There are no arrays, vectors or constants
2031 The pointer type is used to specify memory locations. Pointers are
2032 commonly used to reference objects in memory.
2034 Pointer types may have an optional address space attribute defining the
2035 numbered address space where the pointed-to object resides. The default
2036 address space is number zero. The semantics of non-zero address spaces
2037 are target-specific.
2039 Note that LLVM does not permit pointers to void (``void*``) nor does it
2040 permit pointers to labels (``label*``). Use ``i8*`` instead.
2050 +-------------------------+--------------------------------------------------------------------------------------------------------------+
2051 | ``[4 x i32]*`` | A :ref:`pointer <t_pointer>` to :ref:`array <t_array>` of four ``i32`` values. |
2052 +-------------------------+--------------------------------------------------------------------------------------------------------------+
2053 | ``i32 (i32*) *`` | A :ref:`pointer <t_pointer>` to a :ref:`function <t_function>` that takes an ``i32*``, returning an ``i32``. |
2054 +-------------------------+--------------------------------------------------------------------------------------------------------------+
2055 | ``i32 addrspace(5)*`` | A :ref:`pointer <t_pointer>` to an ``i32`` value that resides in address space #5. |
2056 +-------------------------+--------------------------------------------------------------------------------------------------------------+
2065 A vector type is a simple derived type that represents a vector of
2066 elements. Vector types are used when multiple primitive data are
2067 operated in parallel using a single instruction (SIMD). A vector type
2068 requires a size (number of elements) and an underlying primitive data
2069 type. Vector types are considered :ref:`first class <t_firstclass>`.
2075 < <# elements> x <elementtype> >
2077 The number of elements is a constant integer value larger than 0;
2078 elementtype may be any integer, floating point or pointer type. Vectors
2079 of size zero are not allowed.
2083 +-------------------+--------------------------------------------------+
2084 | ``<4 x i32>`` | Vector of 4 32-bit integer values. |
2085 +-------------------+--------------------------------------------------+
2086 | ``<8 x float>`` | Vector of 8 32-bit floating-point values. |
2087 +-------------------+--------------------------------------------------+
2088 | ``<2 x i64>`` | Vector of 2 64-bit integer values. |
2089 +-------------------+--------------------------------------------------+
2090 | ``<4 x i64*>`` | Vector of 4 pointers to 64-bit integer values. |
2091 +-------------------+--------------------------------------------------+
2100 The label type represents code labels.
2115 The metadata type represents embedded metadata. No derived types may be
2116 created from metadata except for :ref:`function <t_function>` arguments.
2129 Aggregate Types are a subset of derived types that can contain multiple
2130 member types. :ref:`Arrays <t_array>` and :ref:`structs <t_struct>` are
2131 aggregate types. :ref:`Vectors <t_vector>` are not considered to be
2141 The array type is a very simple derived type that arranges elements
2142 sequentially in memory. The array type requires a size (number of
2143 elements) and an underlying data type.
2149 [<# elements> x <elementtype>]
2151 The number of elements is a constant integer value; ``elementtype`` may
2152 be any type with a size.
2156 +------------------+--------------------------------------+
2157 | ``[40 x i32]`` | Array of 40 32-bit integer values. |
2158 +------------------+--------------------------------------+
2159 | ``[41 x i32]`` | Array of 41 32-bit integer values. |
2160 +------------------+--------------------------------------+
2161 | ``[4 x i8]`` | Array of 4 8-bit integer values. |
2162 +------------------+--------------------------------------+
2164 Here are some examples of multidimensional arrays:
2166 +-----------------------------+----------------------------------------------------------+
2167 | ``[3 x [4 x i32]]`` | 3x4 array of 32-bit integer values. |
2168 +-----------------------------+----------------------------------------------------------+
2169 | ``[12 x [10 x float]]`` | 12x10 array of single precision floating point values. |
2170 +-----------------------------+----------------------------------------------------------+
2171 | ``[2 x [3 x [4 x i16]]]`` | 2x3x4 array of 16-bit integer values. |
2172 +-----------------------------+----------------------------------------------------------+
2174 There is no restriction on indexing beyond the end of the array implied
2175 by a static type (though there are restrictions on indexing beyond the
2176 bounds of an allocated object in some cases). This means that
2177 single-dimension 'variable sized array' addressing can be implemented in
2178 LLVM with a zero length array type. An implementation of 'pascal style
2179 arrays' in LLVM could use the type "``{ i32, [0 x float]}``", for
2189 The structure type is used to represent a collection of data members
2190 together in memory. The elements of a structure may be any type that has
2193 Structures in memory are accessed using '``load``' and '``store``' by
2194 getting a pointer to a field with the '``getelementptr``' instruction.
2195 Structures in registers are accessed using the '``extractvalue``' and
2196 '``insertvalue``' instructions.
2198 Structures may optionally be "packed" structures, which indicate that
2199 the alignment of the struct is one byte, and that there is no padding
2200 between the elements. In non-packed structs, padding between field types
2201 is inserted as defined by the DataLayout string in the module, which is
2202 required to match what the underlying code generator expects.
2204 Structures can either be "literal" or "identified". A literal structure
2205 is defined inline with other types (e.g. ``{i32, i32}*``) whereas
2206 identified types are always defined at the top level with a name.
2207 Literal types are uniqued by their contents and can never be recursive
2208 or opaque since there is no way to write one. Identified types can be
2209 recursive, can be opaqued, and are never uniqued.
2215 %T1 = type { <type list> } ; Identified normal struct type
2216 %T2 = type <{ <type list> }> ; Identified packed struct type
2220 +------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
2221 | ``{ i32, i32, i32 }`` | A triple of three ``i32`` values |
2222 +------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
2223 | ``{ 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``. |
2224 +------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
2225 | ``<{ i8, i32 }>`` | A packed struct known to be 5 bytes in size. |
2226 +------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
2230 Opaque Structure Types
2231 """"""""""""""""""""""
2235 Opaque structure types are used to represent named structure types that
2236 do not have a body specified. This corresponds (for example) to the C
2237 notion of a forward declared structure.
2248 +--------------+-------------------+
2249 | ``opaque`` | An opaque type. |
2250 +--------------+-------------------+
2257 LLVM has several different basic types of constants. This section
2258 describes them all and their syntax.
2263 **Boolean constants**
2264 The two strings '``true``' and '``false``' are both valid constants
2266 **Integer constants**
2267 Standard integers (such as '4') are constants of the
2268 :ref:`integer <t_integer>` type. Negative numbers may be used with
2270 **Floating point constants**
2271 Floating point constants use standard decimal notation (e.g.
2272 123.421), exponential notation (e.g. 1.23421e+2), or a more precise
2273 hexadecimal notation (see below). The assembler requires the exact
2274 decimal value of a floating-point constant. For example, the
2275 assembler accepts 1.25 but rejects 1.3 because 1.3 is a repeating
2276 decimal in binary. Floating point constants must have a :ref:`floating
2277 point <t_floating>` type.
2278 **Null pointer constants**
2279 The identifier '``null``' is recognized as a null pointer constant
2280 and must be of :ref:`pointer type <t_pointer>`.
2282 The one non-intuitive notation for constants is the hexadecimal form of
2283 floating point constants. For example, the form
2284 '``double 0x432ff973cafa8000``' is equivalent to (but harder to read
2285 than) '``double 4.5e+15``'. The only time hexadecimal floating point
2286 constants are required (and the only time that they are generated by the
2287 disassembler) is when a floating point constant must be emitted but it
2288 cannot be represented as a decimal floating point number in a reasonable
2289 number of digits. For example, NaN's, infinities, and other special
2290 values are represented in their IEEE hexadecimal format so that assembly
2291 and disassembly do not cause any bits to change in the constants.
2293 When using the hexadecimal form, constants of types half, float, and
2294 double are represented using the 16-digit form shown above (which
2295 matches the IEEE754 representation for double); half and float values
2296 must, however, be exactly representable as IEEE 754 half and single
2297 precision, respectively. Hexadecimal format is always used for long
2298 double, and there are three forms of long double. The 80-bit format used
2299 by x86 is represented as ``0xK`` followed by 20 hexadecimal digits. The
2300 128-bit format used by PowerPC (two adjacent doubles) is represented by
2301 ``0xM`` followed by 32 hexadecimal digits. The IEEE 128-bit format is
2302 represented by ``0xL`` followed by 32 hexadecimal digits. Long doubles
2303 will only work if they match the long double format on your target.
2304 The IEEE 16-bit format (half precision) is represented by ``0xH``
2305 followed by 4 hexadecimal digits. All hexadecimal formats are big-endian
2306 (sign bit at the left).
2308 There are no constants of type x86_mmx.
2310 .. _complexconstants:
2315 Complex constants are a (potentially recursive) combination of simple
2316 constants and smaller complex constants.
2318 **Structure constants**
2319 Structure constants are represented with notation similar to
2320 structure type definitions (a comma separated list of elements,
2321 surrounded by braces (``{}``)). For example:
2322 "``{ i32 4, float 17.0, i32* @G }``", where "``@G``" is declared as
2323 "``@G = external global i32``". Structure constants must have
2324 :ref:`structure type <t_struct>`, and the number and types of elements
2325 must match those specified by the type.
2327 Array constants are represented with notation similar to array type
2328 definitions (a comma separated list of elements, surrounded by
2329 square brackets (``[]``)). For example:
2330 "``[ i32 42, i32 11, i32 74 ]``". Array constants must have
2331 :ref:`array type <t_array>`, and the number and types of elements must
2332 match those specified by the type. As a special case, character array
2333 constants may also be represented as a double-quoted string using the ``c``
2334 prefix. For example: "``c"Hello World\0A\00"``".
2335 **Vector constants**
2336 Vector constants are represented with notation similar to vector
2337 type definitions (a comma separated list of elements, surrounded by
2338 less-than/greater-than's (``<>``)). For example:
2339 "``< i32 42, i32 11, i32 74, i32 100 >``". Vector constants
2340 must have :ref:`vector type <t_vector>`, and the number and types of
2341 elements must match those specified by the type.
2342 **Zero initialization**
2343 The string '``zeroinitializer``' can be used to zero initialize a
2344 value to zero of *any* type, including scalar and
2345 :ref:`aggregate <t_aggregate>` types. This is often used to avoid
2346 having to print large zero initializers (e.g. for large arrays) and
2347 is always exactly equivalent to using explicit zero initializers.
2349 A metadata node is a constant tuple without types. For example:
2350 "``!{!0, !{!2, !0}, !"test"}``". Metadata can reference constant values,
2351 for example: "``!{!0, i32 0, i8* @global, i64 (i64)* @function, !"str"}``".
2352 Unlike other typed constants that are meant to be interpreted as part of
2353 the instruction stream, metadata is a place to attach additional
2354 information such as debug info.
2356 Global Variable and Function Addresses
2357 --------------------------------------
2359 The addresses of :ref:`global variables <globalvars>` and
2360 :ref:`functions <functionstructure>` are always implicitly valid
2361 (link-time) constants. These constants are explicitly referenced when
2362 the :ref:`identifier for the global <identifiers>` is used and always have
2363 :ref:`pointer <t_pointer>` type. For example, the following is a legal LLVM
2366 .. code-block:: llvm
2370 @Z = global [2 x i32*] [ i32* @X, i32* @Y ]
2377 The string '``undef``' can be used anywhere a constant is expected, and
2378 indicates that the user of the value may receive an unspecified
2379 bit-pattern. Undefined values may be of any type (other than '``label``'
2380 or '``void``') and be used anywhere a constant is permitted.
2382 Undefined values are useful because they indicate to the compiler that
2383 the program is well defined no matter what value is used. This gives the
2384 compiler more freedom to optimize. Here are some examples of
2385 (potentially surprising) transformations that are valid (in pseudo IR):
2387 .. code-block:: llvm
2397 This is safe because all of the output bits are affected by the undef
2398 bits. Any output bit can have a zero or one depending on the input bits.
2400 .. code-block:: llvm
2411 These logical operations have bits that are not always affected by the
2412 input. For example, if ``%X`` has a zero bit, then the output of the
2413 '``and``' operation will always be a zero for that bit, no matter what
2414 the corresponding bit from the '``undef``' is. As such, it is unsafe to
2415 optimize or assume that the result of the '``and``' is '``undef``'.
2416 However, it is safe to assume that all bits of the '``undef``' could be
2417 0, and optimize the '``and``' to 0. Likewise, it is safe to assume that
2418 all the bits of the '``undef``' operand to the '``or``' could be set,
2419 allowing the '``or``' to be folded to -1.
2421 .. code-block:: llvm
2423 %A = select undef, %X, %Y
2424 %B = select undef, 42, %Y
2425 %C = select %X, %Y, undef
2435 This set of examples shows that undefined '``select``' (and conditional
2436 branch) conditions can go *either way*, but they have to come from one
2437 of the two operands. In the ``%A`` example, if ``%X`` and ``%Y`` were
2438 both known to have a clear low bit, then ``%A`` would have to have a
2439 cleared low bit. However, in the ``%C`` example, the optimizer is
2440 allowed to assume that the '``undef``' operand could be the same as
2441 ``%Y``, allowing the whole '``select``' to be eliminated.
2443 .. code-block:: llvm
2445 %A = xor undef, undef
2462 This example points out that two '``undef``' operands are not
2463 necessarily the same. This can be surprising to people (and also matches
2464 C semantics) where they assume that "``X^X``" is always zero, even if
2465 ``X`` is undefined. This isn't true for a number of reasons, but the
2466 short answer is that an '``undef``' "variable" can arbitrarily change
2467 its value over its "live range". This is true because the variable
2468 doesn't actually *have a live range*. Instead, the value is logically
2469 read from arbitrary registers that happen to be around when needed, so
2470 the value is not necessarily consistent over time. In fact, ``%A`` and
2471 ``%C`` need to have the same semantics or the core LLVM "replace all
2472 uses with" concept would not hold.
2474 .. code-block:: llvm
2482 These examples show the crucial difference between an *undefined value*
2483 and *undefined behavior*. An undefined value (like '``undef``') is
2484 allowed to have an arbitrary bit-pattern. This means that the ``%A``
2485 operation can be constant folded to '``undef``', because the '``undef``'
2486 could be an SNaN, and ``fdiv`` is not (currently) defined on SNaN's.
2487 However, in the second example, we can make a more aggressive
2488 assumption: because the ``undef`` is allowed to be an arbitrary value,
2489 we are allowed to assume that it could be zero. Since a divide by zero
2490 has *undefined behavior*, we are allowed to assume that the operation
2491 does not execute at all. This allows us to delete the divide and all
2492 code after it. Because the undefined operation "can't happen", the
2493 optimizer can assume that it occurs in dead code.
2495 .. code-block:: llvm
2497 a: store undef -> %X
2498 b: store %X -> undef
2503 These examples reiterate the ``fdiv`` example: a store *of* an undefined
2504 value can be assumed to not have any effect; we can assume that the
2505 value is overwritten with bits that happen to match what was already
2506 there. However, a store *to* an undefined location could clobber
2507 arbitrary memory, therefore, it has undefined behavior.
2514 Poison values are similar to :ref:`undef values <undefvalues>`, however
2515 they also represent the fact that an instruction or constant expression
2516 that cannot evoke side effects has nevertheless detected a condition
2517 that results in undefined behavior.
2519 There is currently no way of representing a poison value in the IR; they
2520 only exist when produced by operations such as :ref:`add <i_add>` with
2523 Poison value behavior is defined in terms of value *dependence*:
2525 - Values other than :ref:`phi <i_phi>` nodes depend on their operands.
2526 - :ref:`Phi <i_phi>` nodes depend on the operand corresponding to
2527 their dynamic predecessor basic block.
2528 - Function arguments depend on the corresponding actual argument values
2529 in the dynamic callers of their functions.
2530 - :ref:`Call <i_call>` instructions depend on the :ref:`ret <i_ret>`
2531 instructions that dynamically transfer control back to them.
2532 - :ref:`Invoke <i_invoke>` instructions depend on the
2533 :ref:`ret <i_ret>`, :ref:`resume <i_resume>`, or exception-throwing
2534 call instructions that dynamically transfer control back to them.
2535 - Non-volatile loads and stores depend on the most recent stores to all
2536 of the referenced memory addresses, following the order in the IR
2537 (including loads and stores implied by intrinsics such as
2538 :ref:`@llvm.memcpy <int_memcpy>`.)
2539 - An instruction with externally visible side effects depends on the
2540 most recent preceding instruction with externally visible side
2541 effects, following the order in the IR. (This includes :ref:`volatile
2542 operations <volatile>`.)
2543 - An instruction *control-depends* on a :ref:`terminator
2544 instruction <terminators>` if the terminator instruction has
2545 multiple successors and the instruction is always executed when
2546 control transfers to one of the successors, and may not be executed
2547 when control is transferred to another.
2548 - Additionally, an instruction also *control-depends* on a terminator
2549 instruction if the set of instructions it otherwise depends on would
2550 be different if the terminator had transferred control to a different
2552 - Dependence is transitive.
2554 Poison values have the same behavior as :ref:`undef values <undefvalues>`,
2555 with the additional effect that any instruction that has a *dependence*
2556 on a poison value has undefined behavior.
2558 Here are some examples:
2560 .. code-block:: llvm
2563 %poison = sub nuw i32 0, 1 ; Results in a poison value.
2564 %still_poison = and i32 %poison, 0 ; 0, but also poison.
2565 %poison_yet_again = getelementptr i32* @h, i32 %still_poison
2566 store i32 0, i32* %poison_yet_again ; memory at @h[0] is poisoned
2568 store i32 %poison, i32* @g ; Poison value stored to memory.
2569 %poison2 = load i32* @g ; Poison value loaded back from memory.
2571 store volatile i32 %poison, i32* @g ; External observation; undefined behavior.
2573 %narrowaddr = bitcast i32* @g to i16*
2574 %wideaddr = bitcast i32* @g to i64*
2575 %poison3 = load i16* %narrowaddr ; Returns a poison value.
2576 %poison4 = load i64* %wideaddr ; Returns a poison value.
2578 %cmp = icmp slt i32 %poison, 0 ; Returns a poison value.
2579 br i1 %cmp, label %true, label %end ; Branch to either destination.
2582 store volatile i32 0, i32* @g ; This is control-dependent on %cmp, so
2583 ; it has undefined behavior.
2587 %p = phi i32 [ 0, %entry ], [ 1, %true ]
2588 ; Both edges into this PHI are
2589 ; control-dependent on %cmp, so this
2590 ; always results in a poison value.
2592 store volatile i32 0, i32* @g ; This would depend on the store in %true
2593 ; if %cmp is true, or the store in %entry
2594 ; otherwise, so this is undefined behavior.
2596 br i1 %cmp, label %second_true, label %second_end
2597 ; The same branch again, but this time the
2598 ; true block doesn't have side effects.
2605 store volatile i32 0, i32* @g ; This time, the instruction always depends
2606 ; on the store in %end. Also, it is
2607 ; control-equivalent to %end, so this is
2608 ; well-defined (ignoring earlier undefined
2609 ; behavior in this example).
2613 Addresses of Basic Blocks
2614 -------------------------
2616 ``blockaddress(@function, %block)``
2618 The '``blockaddress``' constant computes the address of the specified
2619 basic block in the specified function, and always has an ``i8*`` type.
2620 Taking the address of the entry block is illegal.
2622 This value only has defined behavior when used as an operand to the
2623 ':ref:`indirectbr <i_indirectbr>`' instruction, or for comparisons
2624 against null. Pointer equality tests between labels addresses results in
2625 undefined behavior --- though, again, comparison against null is ok, and
2626 no label is equal to the null pointer. This may be passed around as an
2627 opaque pointer sized value as long as the bits are not inspected. This
2628 allows ``ptrtoint`` and arithmetic to be performed on these values so
2629 long as the original value is reconstituted before the ``indirectbr``
2632 Finally, some targets may provide defined semantics when using the value
2633 as the operand to an inline assembly, but that is target specific.
2637 Constant Expressions
2638 --------------------
2640 Constant expressions are used to allow expressions involving other
2641 constants to be used as constants. Constant expressions may be of any
2642 :ref:`first class <t_firstclass>` type and may involve any LLVM operation
2643 that does not have side effects (e.g. load and call are not supported).
2644 The following is the syntax for constant expressions:
2646 ``trunc (CST to TYPE)``
2647 Truncate a constant to another type. The bit size of CST must be
2648 larger than the bit size of TYPE. Both types must be integers.
2649 ``zext (CST to TYPE)``
2650 Zero extend a constant to another type. The bit size of CST must be
2651 smaller than the bit size of TYPE. Both types must be integers.
2652 ``sext (CST to TYPE)``
2653 Sign extend a constant to another type. The bit size of CST must be
2654 smaller than the bit size of TYPE. Both types must be integers.
2655 ``fptrunc (CST to TYPE)``
2656 Truncate a floating point constant to another floating point type.
2657 The size of CST must be larger than the size of TYPE. Both types
2658 must be floating point.
2659 ``fpext (CST to TYPE)``
2660 Floating point extend a constant to another type. The size of CST
2661 must be smaller or equal to the size of TYPE. Both types must be
2663 ``fptoui (CST to TYPE)``
2664 Convert a floating point constant to the corresponding unsigned
2665 integer constant. TYPE must be a scalar or vector integer type. CST
2666 must be of scalar or vector floating point type. Both CST and TYPE
2667 must be scalars, or vectors of the same number of elements. If the
2668 value won't fit in the integer type, the results are undefined.
2669 ``fptosi (CST to TYPE)``
2670 Convert a floating point constant to the corresponding signed
2671 integer constant. TYPE must be a scalar or vector integer type. CST
2672 must be of scalar or vector floating point type. Both CST and TYPE
2673 must be scalars, or vectors of the same number of elements. If the
2674 value won't fit in the integer type, the results are undefined.
2675 ``uitofp (CST to TYPE)``
2676 Convert an unsigned integer constant to the corresponding floating
2677 point constant. TYPE must be a scalar or vector floating point type.
2678 CST must be of scalar or vector integer type. Both CST and TYPE must
2679 be scalars, or vectors of the same number of elements. If the value
2680 won't fit in the floating point type, the results are undefined.
2681 ``sitofp (CST to TYPE)``
2682 Convert a signed integer constant to the corresponding floating
2683 point constant. TYPE must be a scalar or vector floating point type.
2684 CST must be of scalar or vector integer type. Both CST and TYPE must
2685 be scalars, or vectors of the same number of elements. If the value
2686 won't fit in the floating point type, the results are undefined.
2687 ``ptrtoint (CST to TYPE)``
2688 Convert a pointer typed constant to the corresponding integer
2689 constant. ``TYPE`` must be an integer type. ``CST`` must be of
2690 pointer type. The ``CST`` value is zero extended, truncated, or
2691 unchanged to make it fit in ``TYPE``.
2692 ``inttoptr (CST to TYPE)``
2693 Convert an integer constant to a pointer constant. TYPE must be a
2694 pointer type. CST must be of integer type. The CST value is zero
2695 extended, truncated, or unchanged to make it fit in a pointer size.
2696 This one is *really* dangerous!
2697 ``bitcast (CST to TYPE)``
2698 Convert a constant, CST, to another TYPE. The constraints of the
2699 operands are the same as those for the :ref:`bitcast
2700 instruction <i_bitcast>`.
2701 ``addrspacecast (CST to TYPE)``
2702 Convert a constant pointer or constant vector of pointer, CST, to another
2703 TYPE in a different address space. The constraints of the operands are the
2704 same as those for the :ref:`addrspacecast instruction <i_addrspacecast>`.
2705 ``getelementptr (CSTPTR, IDX0, IDX1, ...)``, ``getelementptr inbounds (CSTPTR, IDX0, IDX1, ...)``
2706 Perform the :ref:`getelementptr operation <i_getelementptr>` on
2707 constants. As with the :ref:`getelementptr <i_getelementptr>`
2708 instruction, the index list may have zero or more indexes, which are
2709 required to make sense for the type of "CSTPTR".
2710 ``select (COND, VAL1, VAL2)``
2711 Perform the :ref:`select operation <i_select>` on constants.
2712 ``icmp COND (VAL1, VAL2)``
2713 Performs the :ref:`icmp operation <i_icmp>` on constants.
2714 ``fcmp COND (VAL1, VAL2)``
2715 Performs the :ref:`fcmp operation <i_fcmp>` on constants.
2716 ``extractelement (VAL, IDX)``
2717 Perform the :ref:`extractelement operation <i_extractelement>` on
2719 ``insertelement (VAL, ELT, IDX)``
2720 Perform the :ref:`insertelement operation <i_insertelement>` on
2722 ``shufflevector (VEC1, VEC2, IDXMASK)``
2723 Perform the :ref:`shufflevector operation <i_shufflevector>` on
2725 ``extractvalue (VAL, IDX0, IDX1, ...)``
2726 Perform the :ref:`extractvalue operation <i_extractvalue>` on
2727 constants. The index list is interpreted in a similar manner as
2728 indices in a ':ref:`getelementptr <i_getelementptr>`' operation. At
2729 least one index value must be specified.
2730 ``insertvalue (VAL, ELT, IDX0, IDX1, ...)``
2731 Perform the :ref:`insertvalue operation <i_insertvalue>` on constants.
2732 The index list is interpreted in a similar manner as indices in a
2733 ':ref:`getelementptr <i_getelementptr>`' operation. At least one index
2734 value must be specified.
2735 ``OPCODE (LHS, RHS)``
2736 Perform the specified operation of the LHS and RHS constants. OPCODE
2737 may be any of the :ref:`binary <binaryops>` or :ref:`bitwise
2738 binary <bitwiseops>` operations. The constraints on operands are
2739 the same as those for the corresponding instruction (e.g. no bitwise
2740 operations on floating point values are allowed).
2747 Inline Assembler Expressions
2748 ----------------------------
2750 LLVM supports inline assembler expressions (as opposed to :ref:`Module-Level
2751 Inline Assembly <moduleasm>`) through the use of a special value. This
2752 value represents the inline assembler as a string (containing the
2753 instructions to emit), a list of operand constraints (stored as a
2754 string), a flag that indicates whether or not the inline asm expression
2755 has side effects, and a flag indicating whether the function containing
2756 the asm needs to align its stack conservatively. An example inline
2757 assembler expression is:
2759 .. code-block:: llvm
2761 i32 (i32) asm "bswap $0", "=r,r"
2763 Inline assembler expressions may **only** be used as the callee operand
2764 of a :ref:`call <i_call>` or an :ref:`invoke <i_invoke>` instruction.
2765 Thus, typically we have:
2767 .. code-block:: llvm
2769 %X = call i32 asm "bswap $0", "=r,r"(i32 %Y)
2771 Inline asms with side effects not visible in the constraint list must be
2772 marked as having side effects. This is done through the use of the
2773 '``sideeffect``' keyword, like so:
2775 .. code-block:: llvm
2777 call void asm sideeffect "eieio", ""()
2779 In some cases inline asms will contain code that will not work unless
2780 the stack is aligned in some way, such as calls or SSE instructions on
2781 x86, yet will not contain code that does that alignment within the asm.
2782 The compiler should make conservative assumptions about what the asm
2783 might contain and should generate its usual stack alignment code in the
2784 prologue if the '``alignstack``' keyword is present:
2786 .. code-block:: llvm
2788 call void asm alignstack "eieio", ""()
2790 Inline asms also support using non-standard assembly dialects. The
2791 assumed dialect is ATT. When the '``inteldialect``' keyword is present,
2792 the inline asm is using the Intel dialect. Currently, ATT and Intel are
2793 the only supported dialects. An example is:
2795 .. code-block:: llvm
2797 call void asm inteldialect "eieio", ""()
2799 If multiple keywords appear the '``sideeffect``' keyword must come
2800 first, the '``alignstack``' keyword second and the '``inteldialect``'
2806 The call instructions that wrap inline asm nodes may have a
2807 "``!srcloc``" MDNode attached to it that contains a list of constant
2808 integers. If present, the code generator will use the integer as the
2809 location cookie value when report errors through the ``LLVMContext``
2810 error reporting mechanisms. This allows a front-end to correlate backend
2811 errors that occur with inline asm back to the source code that produced
2814 .. code-block:: llvm
2816 call void asm sideeffect "something bad", ""(), !srcloc !42
2818 !42 = !{ i32 1234567 }
2820 It is up to the front-end to make sense of the magic numbers it places
2821 in the IR. If the MDNode contains multiple constants, the code generator
2822 will use the one that corresponds to the line of the asm that the error
2830 LLVM IR allows metadata to be attached to instructions in the program
2831 that can convey extra information about the code to the optimizers and
2832 code generator. One example application of metadata is source-level
2833 debug information. There are two metadata primitives: strings and nodes.
2835 Metadata does not have a type, and is not a value. If referenced from a
2836 ``call`` instruction, it uses the ``metadata`` type.
2838 All metadata are identified in syntax by a exclamation point ('``!``').
2840 Metadata Nodes and Metadata Strings
2841 -----------------------------------
2843 A metadata string is a string surrounded by double quotes. It can
2844 contain any character by escaping non-printable characters with
2845 "``\xx``" where "``xx``" is the two digit hex code. For example:
2848 Metadata nodes are represented with notation similar to structure
2849 constants (a comma separated list of elements, surrounded by braces and
2850 preceded by an exclamation point). Metadata nodes can have any values as
2851 their operand. For example:
2853 .. code-block:: llvm
2855 !{ !"test\00", i32 10}
2857 Metadata nodes that aren't uniqued use the ``distinct`` keyword. For example:
2859 .. code-block:: llvm
2861 !0 = distinct !{!"test\00", i32 10}
2863 ``distinct`` nodes are useful when nodes shouldn't be merged based on their
2864 content. They can also occur when transformations cause uniquing collisions
2865 when metadata operands change.
2867 A :ref:`named metadata <namedmetadatastructure>` is a collection of
2868 metadata nodes, which can be looked up in the module symbol table. For
2871 .. code-block:: llvm
2875 Metadata can be used as function arguments. Here ``llvm.dbg.value``
2876 function is using two metadata arguments:
2878 .. code-block:: llvm
2880 call void @llvm.dbg.value(metadata !24, i64 0, metadata !25)
2882 Metadata can be attached with an instruction. Here metadata ``!21`` is
2883 attached to the ``add`` instruction using the ``!dbg`` identifier:
2885 .. code-block:: llvm
2887 %indvar.next = add i64 %indvar, 1, !dbg !21
2889 More information about specific metadata nodes recognized by the
2890 optimizers and code generator is found below.
2892 Specialized Metadata Nodes
2893 ^^^^^^^^^^^^^^^^^^^^^^^^^^
2895 Specialized metadata nodes are custom data structures in metadata (as opposed
2896 to generic tuples). Their fields are labelled, and can be specified in any
2902 ``MDLocation`` nodes represent source debug locations. The ``scope:`` field is
2905 .. code-block:: llvm
2907 !0 = !MDLocation(line: 2900, column: 42, scope: !1, inlinedAt: !2)
2912 In LLVM IR, memory does not have types, so LLVM's own type system is not
2913 suitable for doing TBAA. Instead, metadata is added to the IR to
2914 describe a type system of a higher level language. This can be used to
2915 implement typical C/C++ TBAA, but it can also be used to implement
2916 custom alias analysis behavior for other languages.
2918 The current metadata format is very simple. TBAA metadata nodes have up
2919 to three fields, e.g.:
2921 .. code-block:: llvm
2923 !0 = !{ !"an example type tree" }
2924 !1 = !{ !"int", !0 }
2925 !2 = !{ !"float", !0 }
2926 !3 = !{ !"const float", !2, i64 1 }
2928 The first field is an identity field. It can be any value, usually a
2929 metadata string, which uniquely identifies the type. The most important
2930 name in the tree is the name of the root node. Two trees with different
2931 root node names are entirely disjoint, even if they have leaves with
2934 The second field identifies the type's parent node in the tree, or is
2935 null or omitted for a root node. A type is considered to alias all of
2936 its descendants and all of its ancestors in the tree. Also, a type is
2937 considered to alias all types in other trees, so that bitcode produced
2938 from multiple front-ends is handled conservatively.
2940 If the third field is present, it's an integer which if equal to 1
2941 indicates that the type is "constant" (meaning
2942 ``pointsToConstantMemory`` should return true; see `other useful
2943 AliasAnalysis methods <AliasAnalysis.html#OtherItfs>`_).
2945 '``tbaa.struct``' Metadata
2946 ^^^^^^^^^^^^^^^^^^^^^^^^^^
2948 The :ref:`llvm.memcpy <int_memcpy>` is often used to implement
2949 aggregate assignment operations in C and similar languages, however it
2950 is defined to copy a contiguous region of memory, which is more than
2951 strictly necessary for aggregate types which contain holes due to
2952 padding. Also, it doesn't contain any TBAA information about the fields
2955 ``!tbaa.struct`` metadata can describe which memory subregions in a
2956 memcpy are padding and what the TBAA tags of the struct are.
2958 The current metadata format is very simple. ``!tbaa.struct`` metadata
2959 nodes are a list of operands which are in conceptual groups of three.
2960 For each group of three, the first operand gives the byte offset of a
2961 field in bytes, the second gives its size in bytes, and the third gives
2964 .. code-block:: llvm
2966 !4 = !{ i64 0, i64 4, !1, i64 8, i64 4, !2 }
2968 This describes a struct with two fields. The first is at offset 0 bytes
2969 with size 4 bytes, and has tbaa tag !1. The second is at offset 8 bytes
2970 and has size 4 bytes and has tbaa tag !2.
2972 Note that the fields need not be contiguous. In this example, there is a
2973 4 byte gap between the two fields. This gap represents padding which
2974 does not carry useful data and need not be preserved.
2976 '``noalias``' and '``alias.scope``' Metadata
2977 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2979 ``noalias`` and ``alias.scope`` metadata provide the ability to specify generic
2980 noalias memory-access sets. This means that some collection of memory access
2981 instructions (loads, stores, memory-accessing calls, etc.) that carry
2982 ``noalias`` metadata can specifically be specified not to alias with some other
2983 collection of memory access instructions that carry ``alias.scope`` metadata.
2984 Each type of metadata specifies a list of scopes where each scope has an id and
2985 a domain. When evaluating an aliasing query, if for some some domain, the set
2986 of scopes with that domain in one instruction's ``alias.scope`` list is a
2987 subset of (or equal to) the set of scopes for that domain in another
2988 instruction's ``noalias`` list, then the two memory accesses are assumed not to
2991 The metadata identifying each domain is itself a list containing one or two
2992 entries. The first entry is the name of the domain. Note that if the name is a
2993 string then it can be combined accross functions and translation units. A
2994 self-reference can be used to create globally unique domain names. A
2995 descriptive string may optionally be provided as a second list entry.
2997 The metadata identifying each scope is also itself a list containing two or
2998 three entries. The first entry is the name of the scope. Note that if the name
2999 is a string then it can be combined accross functions and translation units. A
3000 self-reference can be used to create globally unique scope names. A metadata
3001 reference to the scope's domain is the second entry. A descriptive string may
3002 optionally be provided as a third list entry.
3006 .. code-block:: llvm
3008 ; Two scope domains:
3012 ; Some scopes in these domains:
3018 !5 = !{!4} ; A list containing only scope !4
3022 ; These two instructions don't alias:
3023 %0 = load float* %c, align 4, !alias.scope !5
3024 store float %0, float* %arrayidx.i, align 4, !noalias !5
3026 ; These two instructions also don't alias (for domain !1, the set of scopes
3027 ; in the !alias.scope equals that in the !noalias list):
3028 %2 = load float* %c, align 4, !alias.scope !5
3029 store float %2, float* %arrayidx.i2, align 4, !noalias !6
3031 ; These two instructions don't alias (for domain !0, the set of scopes in
3032 ; the !noalias list is not a superset of, or equal to, the scopes in the
3033 ; !alias.scope list):
3034 %2 = load float* %c, align 4, !alias.scope !6
3035 store float %0, float* %arrayidx.i, align 4, !noalias !7
3037 '``fpmath``' Metadata
3038 ^^^^^^^^^^^^^^^^^^^^^
3040 ``fpmath`` metadata may be attached to any instruction of floating point
3041 type. It can be used to express the maximum acceptable error in the
3042 result of that instruction, in ULPs, thus potentially allowing the
3043 compiler to use a more efficient but less accurate method of computing
3044 it. ULP is defined as follows:
3046 If ``x`` is a real number that lies between two finite consecutive
3047 floating-point numbers ``a`` and ``b``, without being equal to one
3048 of them, then ``ulp(x) = |b - a|``, otherwise ``ulp(x)`` is the
3049 distance between the two non-equal finite floating-point numbers
3050 nearest ``x``. Moreover, ``ulp(NaN)`` is ``NaN``.
3052 The metadata node shall consist of a single positive floating point
3053 number representing the maximum relative error, for example:
3055 .. code-block:: llvm
3057 !0 = !{ float 2.5 } ; maximum acceptable inaccuracy is 2.5 ULPs
3059 '``range``' Metadata
3060 ^^^^^^^^^^^^^^^^^^^^
3062 ``range`` metadata may be attached only to ``load``, ``call`` and ``invoke`` of
3063 integer types. It expresses the possible ranges the loaded value or the value
3064 returned by the called function at this call site is in. The ranges are
3065 represented with a flattened list of integers. The loaded value or the value
3066 returned is known to be in the union of the ranges defined by each consecutive
3067 pair. Each pair has the following properties:
3069 - The type must match the type loaded by the instruction.
3070 - The pair ``a,b`` represents the range ``[a,b)``.
3071 - Both ``a`` and ``b`` are constants.
3072 - The range is allowed to wrap.
3073 - The range should not represent the full or empty set. That is,
3076 In addition, the pairs must be in signed order of the lower bound and
3077 they must be non-contiguous.
3081 .. code-block:: llvm
3083 %a = load i8* %x, align 1, !range !0 ; Can only be 0 or 1
3084 %b = load i8* %y, align 1, !range !1 ; Can only be 255 (-1), 0 or 1
3085 %c = call i8 @foo(), !range !2 ; Can only be 0, 1, 3, 4 or 5
3086 %d = invoke i8 @bar() to label %cont
3087 unwind label %lpad, !range !3 ; Can only be -2, -1, 3, 4 or 5
3089 !0 = !{ i8 0, i8 2 }
3090 !1 = !{ i8 255, i8 2 }
3091 !2 = !{ i8 0, i8 2, i8 3, i8 6 }
3092 !3 = !{ i8 -2, i8 0, i8 3, i8 6 }
3097 It is sometimes useful to attach information to loop constructs. Currently,
3098 loop metadata is implemented as metadata attached to the branch instruction
3099 in the loop latch block. This type of metadata refer to a metadata node that is
3100 guaranteed to be separate for each loop. The loop identifier metadata is
3101 specified with the name ``llvm.loop``.
3103 The loop identifier metadata is implemented using a metadata that refers to
3104 itself to avoid merging it with any other identifier metadata, e.g.,
3105 during module linkage or function inlining. That is, each loop should refer
3106 to their own identification metadata even if they reside in separate functions.
3107 The following example contains loop identifier metadata for two separate loop
3110 .. code-block:: llvm
3115 The loop identifier metadata can be used to specify additional
3116 per-loop metadata. Any operands after the first operand can be treated
3117 as user-defined metadata. For example the ``llvm.loop.unroll.count``
3118 suggests an unroll factor to the loop unroller:
3120 .. code-block:: llvm
3122 br i1 %exitcond, label %._crit_edge, label %.lr.ph, !llvm.loop !0
3125 !1 = !{!"llvm.loop.unroll.count", i32 4}
3127 '``llvm.loop.vectorize``' and '``llvm.loop.interleave``'
3128 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
3130 Metadata prefixed with ``llvm.loop.vectorize`` or ``llvm.loop.interleave`` are
3131 used to control per-loop vectorization and interleaving parameters such as
3132 vectorization width and interleave count. These metadata should be used in
3133 conjunction with ``llvm.loop`` loop identification metadata. The
3134 ``llvm.loop.vectorize`` and ``llvm.loop.interleave`` metadata are only
3135 optimization hints and the optimizer will only interleave and vectorize loops if
3136 it believes it is safe to do so. The ``llvm.mem.parallel_loop_access`` metadata
3137 which contains information about loop-carried memory dependencies can be helpful
3138 in determining the safety of these transformations.
3140 '``llvm.loop.interleave.count``' Metadata
3141 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
3143 This metadata suggests an interleave count to the loop interleaver.
3144 The first operand is the string ``llvm.loop.interleave.count`` and the
3145 second operand is an integer specifying the interleave count. For
3148 .. code-block:: llvm
3150 !0 = !{!"llvm.loop.interleave.count", i32 4}
3152 Note that setting ``llvm.loop.interleave.count`` to 1 disables interleaving
3153 multiple iterations of the loop. If ``llvm.loop.interleave.count`` is set to 0
3154 then the interleave count will be determined automatically.
3156 '``llvm.loop.vectorize.enable``' Metadata
3157 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
3159 This metadata selectively enables or disables vectorization for the loop. The
3160 first operand is the string ``llvm.loop.vectorize.enable`` and the second operand
3161 is a bit. If the bit operand value is 1 vectorization is enabled. A value of
3162 0 disables vectorization:
3164 .. code-block:: llvm
3166 !0 = !{!"llvm.loop.vectorize.enable", i1 0}
3167 !1 = !{!"llvm.loop.vectorize.enable", i1 1}
3169 '``llvm.loop.vectorize.width``' Metadata
3170 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
3172 This metadata sets the target width of the vectorizer. The first
3173 operand is the string ``llvm.loop.vectorize.width`` and the second
3174 operand is an integer specifying the width. For example:
3176 .. code-block:: llvm
3178 !0 = !{!"llvm.loop.vectorize.width", i32 4}
3180 Note that setting ``llvm.loop.vectorize.width`` to 1 disables
3181 vectorization of the loop. If ``llvm.loop.vectorize.width`` is set to
3182 0 or if the loop does not have this metadata the width will be
3183 determined automatically.
3185 '``llvm.loop.unroll``'
3186 ^^^^^^^^^^^^^^^^^^^^^^
3188 Metadata prefixed with ``llvm.loop.unroll`` are loop unrolling
3189 optimization hints such as the unroll factor. ``llvm.loop.unroll``
3190 metadata should be used in conjunction with ``llvm.loop`` loop
3191 identification metadata. The ``llvm.loop.unroll`` metadata are only
3192 optimization hints and the unrolling will only be performed if the
3193 optimizer believes it is safe to do so.
3195 '``llvm.loop.unroll.count``' Metadata
3196 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
3198 This metadata suggests an unroll factor to the loop unroller. The
3199 first operand is the string ``llvm.loop.unroll.count`` and the second
3200 operand is a positive integer specifying the unroll factor. For
3203 .. code-block:: llvm
3205 !0 = !{!"llvm.loop.unroll.count", i32 4}
3207 If the trip count of the loop is less than the unroll count the loop
3208 will be partially unrolled.
3210 '``llvm.loop.unroll.disable``' Metadata
3211 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
3213 This metadata either disables loop unrolling. The metadata has a single operand
3214 which is the string ``llvm.loop.unroll.disable``. For example:
3216 .. code-block:: llvm
3218 !0 = !{!"llvm.loop.unroll.disable"}
3220 '``llvm.loop.unroll.full``' Metadata
3221 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
3223 This metadata either suggests that the loop should be unrolled fully. The
3224 metadata has a single operand which is the string ``llvm.loop.unroll.disable``.
3227 .. code-block:: llvm
3229 !0 = !{!"llvm.loop.unroll.full"}
3234 Metadata types used to annotate memory accesses with information helpful
3235 for optimizations are prefixed with ``llvm.mem``.
3237 '``llvm.mem.parallel_loop_access``' Metadata
3238 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
3240 The ``llvm.mem.parallel_loop_access`` metadata refers to a loop identifier,
3241 or metadata containing a list of loop identifiers for nested loops.
3242 The metadata is attached to memory accessing instructions and denotes that
3243 no loop carried memory dependence exist between it and other instructions denoted
3244 with the same loop identifier.
3246 Precisely, given two instructions ``m1`` and ``m2`` that both have the
3247 ``llvm.mem.parallel_loop_access`` metadata, with ``L1`` and ``L2`` being the
3248 set of loops associated with that metadata, respectively, then there is no loop
3249 carried dependence between ``m1`` and ``m2`` for loops in both ``L1`` and
3252 As a special case, if all memory accessing instructions in a loop have
3253 ``llvm.mem.parallel_loop_access`` metadata that refers to that loop, then the
3254 loop has no loop carried memory dependences and is considered to be a parallel
3257 Note that if not all memory access instructions have such metadata referring to
3258 the loop, then the loop is considered not being trivially parallel. Additional
3259 memory dependence analysis is required to make that determination. As a fail
3260 safe mechanism, this causes loops that were originally parallel to be considered
3261 sequential (if optimization passes that are unaware of the parallel semantics
3262 insert new memory instructions into the loop body).
3264 Example of a loop that is considered parallel due to its correct use of
3265 both ``llvm.loop`` and ``llvm.mem.parallel_loop_access``
3266 metadata types that refer to the same loop identifier metadata.
3268 .. code-block:: llvm
3272 %val0 = load i32* %arrayidx, !llvm.mem.parallel_loop_access !0
3274 store i32 %val0, i32* %arrayidx1, !llvm.mem.parallel_loop_access !0
3276 br i1 %exitcond, label %for.end, label %for.body, !llvm.loop !0
3282 It is also possible to have nested parallel loops. In that case the
3283 memory accesses refer to a list of loop identifier metadata nodes instead of
3284 the loop identifier metadata node directly:
3286 .. code-block:: llvm
3290 %val1 = load i32* %arrayidx3, !llvm.mem.parallel_loop_access !2
3292 br label %inner.for.body
3296 %val0 = load i32* %arrayidx1, !llvm.mem.parallel_loop_access !0
3298 store i32 %val0, i32* %arrayidx2, !llvm.mem.parallel_loop_access !0
3300 br i1 %exitcond, label %inner.for.end, label %inner.for.body, !llvm.loop !1
3304 store i32 %val1, i32* %arrayidx4, !llvm.mem.parallel_loop_access !2
3306 br i1 %exitcond, label %outer.for.end, label %outer.for.body, !llvm.loop !2
3308 outer.for.end: ; preds = %for.body
3310 !0 = !{!1, !2} ; a list of loop identifiers
3311 !1 = !{!1} ; an identifier for the inner loop
3312 !2 = !{!2} ; an identifier for the outer loop
3317 The ``llvm.bitsets`` global metadata is used to implement
3318 :doc:`bitsets <BitSets>`.
3320 Module Flags Metadata
3321 =====================
3323 Information about the module as a whole is difficult to convey to LLVM's
3324 subsystems. The LLVM IR isn't sufficient to transmit this information.
3325 The ``llvm.module.flags`` named metadata exists in order to facilitate
3326 this. These flags are in the form of key / value pairs --- much like a
3327 dictionary --- making it easy for any subsystem who cares about a flag to
3330 The ``llvm.module.flags`` metadata contains a list of metadata triplets.
3331 Each triplet has the following form:
3333 - The first element is a *behavior* flag, which specifies the behavior
3334 when two (or more) modules are merged together, and it encounters two
3335 (or more) metadata with the same ID. The supported behaviors are
3337 - The second element is a metadata string that is a unique ID for the
3338 metadata. Each module may only have one flag entry for each unique ID (not
3339 including entries with the **Require** behavior).
3340 - The third element is the value of the flag.
3342 When two (or more) modules are merged together, the resulting
3343 ``llvm.module.flags`` metadata is the union of the modules' flags. That is, for
3344 each unique metadata ID string, there will be exactly one entry in the merged
3345 modules ``llvm.module.flags`` metadata table, and the value for that entry will
3346 be determined by the merge behavior flag, as described below. The only exception
3347 is that entries with the *Require* behavior are always preserved.
3349 The following behaviors are supported:
3360 Emits an error if two values disagree, otherwise the resulting value
3361 is that of the operands.
3365 Emits a warning if two values disagree. The result value will be the
3366 operand for the flag from the first module being linked.
3370 Adds a requirement that another module flag be present and have a
3371 specified value after linking is performed. The value must be a
3372 metadata pair, where the first element of the pair is the ID of the
3373 module flag to be restricted, and the second element of the pair is
3374 the value the module flag should be restricted to. This behavior can
3375 be used to restrict the allowable results (via triggering of an
3376 error) of linking IDs with the **Override** behavior.
3380 Uses the specified value, regardless of the behavior or value of the
3381 other module. If both modules specify **Override**, but the values
3382 differ, an error will be emitted.
3386 Appends the two values, which are required to be metadata nodes.
3390 Appends the two values, which are required to be metadata
3391 nodes. However, duplicate entries in the second list are dropped
3392 during the append operation.
3394 It is an error for a particular unique flag ID to have multiple behaviors,
3395 except in the case of **Require** (which adds restrictions on another metadata
3396 value) or **Override**.
3398 An example of module flags:
3400 .. code-block:: llvm
3402 !0 = !{ i32 1, !"foo", i32 1 }
3403 !1 = !{ i32 4, !"bar", i32 37 }
3404 !2 = !{ i32 2, !"qux", i32 42 }
3405 !3 = !{ i32 3, !"qux",
3410 !llvm.module.flags = !{ !0, !1, !2, !3 }
3412 - Metadata ``!0`` has the ID ``!"foo"`` and the value '1'. The behavior
3413 if two or more ``!"foo"`` flags are seen is to emit an error if their
3414 values are not equal.
3416 - Metadata ``!1`` has the ID ``!"bar"`` and the value '37'. The
3417 behavior if two or more ``!"bar"`` flags are seen is to use the value
3420 - Metadata ``!2`` has the ID ``!"qux"`` and the value '42'. The
3421 behavior if two or more ``!"qux"`` flags are seen is to emit a
3422 warning if their values are not equal.
3424 - Metadata ``!3`` has the ID ``!"qux"`` and the value:
3430 The behavior is to emit an error if the ``llvm.module.flags`` does not
3431 contain a flag with the ID ``!"foo"`` that has the value '1' after linking is
3434 Objective-C Garbage Collection Module Flags Metadata
3435 ----------------------------------------------------
3437 On the Mach-O platform, Objective-C stores metadata about garbage
3438 collection in a special section called "image info". The metadata
3439 consists of a version number and a bitmask specifying what types of
3440 garbage collection are supported (if any) by the file. If two or more
3441 modules are linked together their garbage collection metadata needs to
3442 be merged rather than appended together.
3444 The Objective-C garbage collection module flags metadata consists of the
3445 following key-value pairs:
3454 * - ``Objective-C Version``
3455 - **[Required]** --- The Objective-C ABI version. Valid values are 1 and 2.
3457 * - ``Objective-C Image Info Version``
3458 - **[Required]** --- The version of the image info section. Currently
3461 * - ``Objective-C Image Info Section``
3462 - **[Required]** --- The section to place the metadata. Valid values are
3463 ``"__OBJC, __image_info, regular"`` for Objective-C ABI version 1, and
3464 ``"__DATA,__objc_imageinfo, regular, no_dead_strip"`` for
3465 Objective-C ABI version 2.
3467 * - ``Objective-C Garbage Collection``
3468 - **[Required]** --- Specifies whether garbage collection is supported or
3469 not. Valid values are 0, for no garbage collection, and 2, for garbage
3470 collection supported.
3472 * - ``Objective-C GC Only``
3473 - **[Optional]** --- Specifies that only garbage collection is supported.
3474 If present, its value must be 6. This flag requires that the
3475 ``Objective-C Garbage Collection`` flag have the value 2.
3477 Some important flag interactions:
3479 - If a module with ``Objective-C Garbage Collection`` set to 0 is
3480 merged with a module with ``Objective-C Garbage Collection`` set to
3481 2, then the resulting module has the
3482 ``Objective-C Garbage Collection`` flag set to 0.
3483 - A module with ``Objective-C Garbage Collection`` set to 0 cannot be
3484 merged with a module with ``Objective-C GC Only`` set to 6.
3486 Automatic Linker Flags Module Flags Metadata
3487 --------------------------------------------
3489 Some targets support embedding flags to the linker inside individual object
3490 files. Typically this is used in conjunction with language extensions which
3491 allow source files to explicitly declare the libraries they depend on, and have
3492 these automatically be transmitted to the linker via object files.
3494 These flags are encoded in the IR using metadata in the module flags section,
3495 using the ``Linker Options`` key. The merge behavior for this flag is required
3496 to be ``AppendUnique``, and the value for the key is expected to be a metadata
3497 node which should be a list of other metadata nodes, each of which should be a
3498 list of metadata strings defining linker options.
3500 For example, the following metadata section specifies two separate sets of
3501 linker options, presumably to link against ``libz`` and the ``Cocoa``
3504 !0 = !{ i32 6, !"Linker Options",
3507 !{ !"-framework", !"Cocoa" } } }
3508 !llvm.module.flags = !{ !0 }
3510 The metadata encoding as lists of lists of options, as opposed to a collapsed
3511 list of options, is chosen so that the IR encoding can use multiple option
3512 strings to specify e.g., a single library, while still having that specifier be
3513 preserved as an atomic element that can be recognized by a target specific
3514 assembly writer or object file emitter.
3516 Each individual option is required to be either a valid option for the target's
3517 linker, or an option that is reserved by the target specific assembly writer or
3518 object file emitter. No other aspect of these options is defined by the IR.
3520 C type width Module Flags Metadata
3521 ----------------------------------
3523 The ARM backend emits a section into each generated object file describing the
3524 options that it was compiled with (in a compiler-independent way) to prevent
3525 linking incompatible objects, and to allow automatic library selection. Some
3526 of these options are not visible at the IR level, namely wchar_t width and enum
3529 To pass this information to the backend, these options are encoded in module
3530 flags metadata, using the following key-value pairs:
3540 - * 0 --- sizeof(wchar_t) == 4
3541 * 1 --- sizeof(wchar_t) == 2
3544 - * 0 --- Enums are at least as large as an ``int``.
3545 * 1 --- Enums are stored in the smallest integer type which can
3546 represent all of its values.
3548 For example, the following metadata section specifies that the module was
3549 compiled with a ``wchar_t`` width of 4 bytes, and the underlying type of an
3550 enum is the smallest type which can represent all of its values::
3552 !llvm.module.flags = !{!0, !1}
3553 !0 = !{i32 1, !"short_wchar", i32 1}
3554 !1 = !{i32 1, !"short_enum", i32 0}
3556 .. _intrinsicglobalvariables:
3558 Intrinsic Global Variables
3559 ==========================
3561 LLVM has a number of "magic" global variables that contain data that
3562 affect code generation or other IR semantics. These are documented here.
3563 All globals of this sort should have a section specified as
3564 "``llvm.metadata``". This section and all globals that start with
3565 "``llvm.``" are reserved for use by LLVM.
3569 The '``llvm.used``' Global Variable
3570 -----------------------------------
3572 The ``@llvm.used`` global is an array which has
3573 :ref:`appending linkage <linkage_appending>`. This array contains a list of
3574 pointers to named global variables, functions and aliases which may optionally
3575 have a pointer cast formed of bitcast or getelementptr. For example, a legal
3578 .. code-block:: llvm
3583 @llvm.used = appending global [2 x i8*] [
3585 i8* bitcast (i32* @Y to i8*)
3586 ], section "llvm.metadata"
3588 If a symbol appears in the ``@llvm.used`` list, then the compiler, assembler,
3589 and linker are required to treat the symbol as if there is a reference to the
3590 symbol that it cannot see (which is why they have to be named). For example, if
3591 a variable has internal linkage and no references other than that from the
3592 ``@llvm.used`` list, it cannot be deleted. This is commonly used to represent
3593 references from inline asms and other things the compiler cannot "see", and
3594 corresponds to "``attribute((used))``" in GNU C.
3596 On some targets, the code generator must emit a directive to the
3597 assembler or object file to prevent the assembler and linker from
3598 molesting the symbol.
3600 .. _gv_llvmcompilerused:
3602 The '``llvm.compiler.used``' Global Variable
3603 --------------------------------------------
3605 The ``@llvm.compiler.used`` directive is the same as the ``@llvm.used``
3606 directive, except that it only prevents the compiler from touching the
3607 symbol. On targets that support it, this allows an intelligent linker to
3608 optimize references to the symbol without being impeded as it would be
3611 This is a rare construct that should only be used in rare circumstances,
3612 and should not be exposed to source languages.
3614 .. _gv_llvmglobalctors:
3616 The '``llvm.global_ctors``' Global Variable
3617 -------------------------------------------
3619 .. code-block:: llvm
3621 %0 = type { i32, void ()*, i8* }
3622 @llvm.global_ctors = appending global [1 x %0] [%0 { i32 65535, void ()* @ctor, i8* @data }]
3624 The ``@llvm.global_ctors`` array contains a list of constructor
3625 functions, priorities, and an optional associated global or function.
3626 The functions referenced by this array will be called in ascending order
3627 of priority (i.e. lowest first) when the module is loaded. The order of
3628 functions with the same priority is not defined.
3630 If the third field is present, non-null, and points to a global variable
3631 or function, the initializer function will only run if the associated
3632 data from the current module is not discarded.
3634 .. _llvmglobaldtors:
3636 The '``llvm.global_dtors``' Global Variable
3637 -------------------------------------------
3639 .. code-block:: llvm
3641 %0 = type { i32, void ()*, i8* }
3642 @llvm.global_dtors = appending global [1 x %0] [%0 { i32 65535, void ()* @dtor, i8* @data }]
3644 The ``@llvm.global_dtors`` array contains a list of destructor
3645 functions, priorities, and an optional associated global or function.
3646 The functions referenced by this array will be called in descending
3647 order of priority (i.e. highest first) when the module is unloaded. The
3648 order of functions with the same priority is not defined.
3650 If the third field is present, non-null, and points to a global variable
3651 or function, the destructor function will only run if the associated
3652 data from the current module is not discarded.
3654 Instruction Reference
3655 =====================
3657 The LLVM instruction set consists of several different classifications
3658 of instructions: :ref:`terminator instructions <terminators>`, :ref:`binary
3659 instructions <binaryops>`, :ref:`bitwise binary
3660 instructions <bitwiseops>`, :ref:`memory instructions <memoryops>`, and
3661 :ref:`other instructions <otherops>`.
3665 Terminator Instructions
3666 -----------------------
3668 As mentioned :ref:`previously <functionstructure>`, every basic block in a
3669 program ends with a "Terminator" instruction, which indicates which
3670 block should be executed after the current block is finished. These
3671 terminator instructions typically yield a '``void``' value: they produce
3672 control flow, not values (the one exception being the
3673 ':ref:`invoke <i_invoke>`' instruction).
3675 The terminator instructions are: ':ref:`ret <i_ret>`',
3676 ':ref:`br <i_br>`', ':ref:`switch <i_switch>`',
3677 ':ref:`indirectbr <i_indirectbr>`', ':ref:`invoke <i_invoke>`',
3678 ':ref:`resume <i_resume>`', and ':ref:`unreachable <i_unreachable>`'.
3682 '``ret``' Instruction
3683 ^^^^^^^^^^^^^^^^^^^^^
3690 ret <type> <value> ; Return a value from a non-void function
3691 ret void ; Return from void function
3696 The '``ret``' instruction is used to return control flow (and optionally
3697 a value) from a function back to the caller.
3699 There are two forms of the '``ret``' instruction: one that returns a
3700 value and then causes control flow, and one that just causes control
3706 The '``ret``' instruction optionally accepts a single argument, the
3707 return value. The type of the return value must be a ':ref:`first
3708 class <t_firstclass>`' type.
3710 A function is not :ref:`well formed <wellformed>` if it it has a non-void
3711 return type and contains a '``ret``' instruction with no return value or
3712 a return value with a type that does not match its type, or if it has a
3713 void return type and contains a '``ret``' instruction with a return
3719 When the '``ret``' instruction is executed, control flow returns back to
3720 the calling function's context. If the caller is a
3721 ":ref:`call <i_call>`" instruction, execution continues at the
3722 instruction after the call. If the caller was an
3723 ":ref:`invoke <i_invoke>`" instruction, execution continues at the
3724 beginning of the "normal" destination block. If the instruction returns
3725 a value, that value shall set the call or invoke instruction's return
3731 .. code-block:: llvm
3733 ret i32 5 ; Return an integer value of 5
3734 ret void ; Return from a void function
3735 ret { i32, i8 } { i32 4, i8 2 } ; Return a struct of values 4 and 2
3739 '``br``' Instruction
3740 ^^^^^^^^^^^^^^^^^^^^
3747 br i1 <cond>, label <iftrue>, label <iffalse>
3748 br label <dest> ; Unconditional branch
3753 The '``br``' instruction is used to cause control flow to transfer to a
3754 different basic block in the current function. There are two forms of
3755 this instruction, corresponding to a conditional branch and an
3756 unconditional branch.
3761 The conditional branch form of the '``br``' instruction takes a single
3762 '``i1``' value and two '``label``' values. The unconditional form of the
3763 '``br``' instruction takes a single '``label``' value as a target.
3768 Upon execution of a conditional '``br``' instruction, the '``i1``'
3769 argument is evaluated. If the value is ``true``, control flows to the
3770 '``iftrue``' ``label`` argument. If "cond" is ``false``, control flows
3771 to the '``iffalse``' ``label`` argument.
3776 .. code-block:: llvm
3779 %cond = icmp eq i32 %a, %b
3780 br i1 %cond, label %IfEqual, label %IfUnequal
3788 '``switch``' Instruction
3789 ^^^^^^^^^^^^^^^^^^^^^^^^
3796 switch <intty> <value>, label <defaultdest> [ <intty> <val>, label <dest> ... ]
3801 The '``switch``' instruction is used to transfer control flow to one of
3802 several different places. It is a generalization of the '``br``'
3803 instruction, allowing a branch to occur to one of many possible
3809 The '``switch``' instruction uses three parameters: an integer
3810 comparison value '``value``', a default '``label``' destination, and an
3811 array of pairs of comparison value constants and '``label``'s. The table
3812 is not allowed to contain duplicate constant entries.
3817 The ``switch`` instruction specifies a table of values and destinations.
3818 When the '``switch``' instruction is executed, this table is searched
3819 for the given value. If the value is found, control flow is transferred
3820 to the corresponding destination; otherwise, control flow is transferred
3821 to the default destination.
3826 Depending on properties of the target machine and the particular
3827 ``switch`` instruction, this instruction may be code generated in
3828 different ways. For example, it could be generated as a series of
3829 chained conditional branches or with a lookup table.
3834 .. code-block:: llvm
3836 ; Emulate a conditional br instruction
3837 %Val = zext i1 %value to i32
3838 switch i32 %Val, label %truedest [ i32 0, label %falsedest ]
3840 ; Emulate an unconditional br instruction
3841 switch i32 0, label %dest [ ]
3843 ; Implement a jump table:
3844 switch i32 %val, label %otherwise [ i32 0, label %onzero
3846 i32 2, label %ontwo ]
3850 '``indirectbr``' Instruction
3851 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
3858 indirectbr <somety>* <address>, [ label <dest1>, label <dest2>, ... ]
3863 The '``indirectbr``' instruction implements an indirect branch to a
3864 label within the current function, whose address is specified by
3865 "``address``". Address must be derived from a
3866 :ref:`blockaddress <blockaddress>` constant.
3871 The '``address``' argument is the address of the label to jump to. The
3872 rest of the arguments indicate the full set of possible destinations
3873 that the address may point to. Blocks are allowed to occur multiple
3874 times in the destination list, though this isn't particularly useful.
3876 This destination list is required so that dataflow analysis has an
3877 accurate understanding of the CFG.
3882 Control transfers to the block specified in the address argument. All
3883 possible destination blocks must be listed in the label list, otherwise
3884 this instruction has undefined behavior. This implies that jumps to
3885 labels defined in other functions have undefined behavior as well.
3890 This is typically implemented with a jump through a register.
3895 .. code-block:: llvm
3897 indirectbr i8* %Addr, [ label %bb1, label %bb2, label %bb3 ]
3901 '``invoke``' Instruction
3902 ^^^^^^^^^^^^^^^^^^^^^^^^
3909 <result> = invoke [cconv] [ret attrs] <ptr to function ty> <function ptr val>(<function args>) [fn attrs]
3910 to label <normal label> unwind label <exception label>
3915 The '``invoke``' instruction causes control to transfer to a specified
3916 function, with the possibility of control flow transfer to either the
3917 '``normal``' label or the '``exception``' label. If the callee function
3918 returns with the "``ret``" instruction, control flow will return to the
3919 "normal" label. If the callee (or any indirect callees) returns via the
3920 ":ref:`resume <i_resume>`" instruction or other exception handling
3921 mechanism, control is interrupted and continued at the dynamically
3922 nearest "exception" label.
3924 The '``exception``' label is a `landing
3925 pad <ExceptionHandling.html#overview>`_ for the exception. As such,
3926 '``exception``' label is required to have the
3927 ":ref:`landingpad <i_landingpad>`" instruction, which contains the
3928 information about the behavior of the program after unwinding happens,
3929 as its first non-PHI instruction. The restrictions on the
3930 "``landingpad``" instruction's tightly couples it to the "``invoke``"
3931 instruction, so that the important information contained within the
3932 "``landingpad``" instruction can't be lost through normal code motion.
3937 This instruction requires several arguments:
3939 #. The optional "cconv" marker indicates which :ref:`calling
3940 convention <callingconv>` the call should use. If none is
3941 specified, the call defaults to using C calling conventions.
3942 #. The optional :ref:`Parameter Attributes <paramattrs>` list for return
3943 values. Only '``zeroext``', '``signext``', and '``inreg``' attributes
3945 #. '``ptr to function ty``': shall be the signature of the pointer to
3946 function value being invoked. In most cases, this is a direct
3947 function invocation, but indirect ``invoke``'s are just as possible,
3948 branching off an arbitrary pointer to function value.
3949 #. '``function ptr val``': An LLVM value containing a pointer to a
3950 function to be invoked.
3951 #. '``function args``': argument list whose types match the function
3952 signature argument types and parameter attributes. All arguments must
3953 be of :ref:`first class <t_firstclass>` type. If the function signature
3954 indicates the function accepts a variable number of arguments, the
3955 extra arguments can be specified.
3956 #. '``normal label``': the label reached when the called function
3957 executes a '``ret``' instruction.
3958 #. '``exception label``': the label reached when a callee returns via
3959 the :ref:`resume <i_resume>` instruction or other exception handling
3961 #. The optional :ref:`function attributes <fnattrs>` list. Only
3962 '``noreturn``', '``nounwind``', '``readonly``' and '``readnone``'
3963 attributes are valid here.
3968 This instruction is designed to operate as a standard '``call``'
3969 instruction in most regards. The primary difference is that it
3970 establishes an association with a label, which is used by the runtime
3971 library to unwind the stack.
3973 This instruction is used in languages with destructors to ensure that
3974 proper cleanup is performed in the case of either a ``longjmp`` or a
3975 thrown exception. Additionally, this is important for implementation of
3976 '``catch``' clauses in high-level languages that support them.
3978 For the purposes of the SSA form, the definition of the value returned
3979 by the '``invoke``' instruction is deemed to occur on the edge from the
3980 current block to the "normal" label. If the callee unwinds then no
3981 return value is available.
3986 .. code-block:: llvm
3988 %retval = invoke i32 @Test(i32 15) to label %Continue
3989 unwind label %TestCleanup ; i32:retval set
3990 %retval = invoke coldcc i32 %Testfnptr(i32 15) to label %Continue
3991 unwind label %TestCleanup ; i32:retval set
3995 '``resume``' Instruction
3996 ^^^^^^^^^^^^^^^^^^^^^^^^
4003 resume <type> <value>
4008 The '``resume``' instruction is a terminator instruction that has no
4014 The '``resume``' instruction requires one argument, which must have the
4015 same type as the result of any '``landingpad``' instruction in the same
4021 The '``resume``' instruction resumes propagation of an existing
4022 (in-flight) exception whose unwinding was interrupted with a
4023 :ref:`landingpad <i_landingpad>` instruction.
4028 .. code-block:: llvm
4030 resume { i8*, i32 } %exn
4034 '``unreachable``' Instruction
4035 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4047 The '``unreachable``' instruction has no defined semantics. This
4048 instruction is used to inform the optimizer that a particular portion of
4049 the code is not reachable. This can be used to indicate that the code
4050 after a no-return function cannot be reached, and other facts.
4055 The '``unreachable``' instruction has no defined semantics.
4062 Binary operators are used to do most of the computation in a program.
4063 They require two operands of the same type, execute an operation on
4064 them, and produce a single value. The operands might represent multiple
4065 data, as is the case with the :ref:`vector <t_vector>` data type. The
4066 result value has the same type as its operands.
4068 There are several different binary operators:
4072 '``add``' Instruction
4073 ^^^^^^^^^^^^^^^^^^^^^
4080 <result> = add <ty> <op1>, <op2> ; yields ty:result
4081 <result> = add nuw <ty> <op1>, <op2> ; yields ty:result
4082 <result> = add nsw <ty> <op1>, <op2> ; yields ty:result
4083 <result> = add nuw nsw <ty> <op1>, <op2> ; yields ty:result
4088 The '``add``' instruction returns the sum of its two operands.
4093 The two arguments to the '``add``' instruction must be
4094 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
4095 arguments must have identical types.
4100 The value produced is the integer sum of the two operands.
4102 If the sum has unsigned overflow, the result returned is the
4103 mathematical result modulo 2\ :sup:`n`\ , where n is the bit width of
4106 Because LLVM integers use a two's complement representation, this
4107 instruction is appropriate for both signed and unsigned integers.
4109 ``nuw`` and ``nsw`` stand for "No Unsigned Wrap" and "No Signed Wrap",
4110 respectively. If the ``nuw`` and/or ``nsw`` keywords are present, the
4111 result value of the ``add`` is a :ref:`poison value <poisonvalues>` if
4112 unsigned and/or signed overflow, respectively, occurs.
4117 .. code-block:: llvm
4119 <result> = add i32 4, %var ; yields i32:result = 4 + %var
4123 '``fadd``' Instruction
4124 ^^^^^^^^^^^^^^^^^^^^^^
4131 <result> = fadd [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
4136 The '``fadd``' instruction returns the sum of its two operands.
4141 The two arguments to the '``fadd``' instruction must be :ref:`floating
4142 point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
4143 Both arguments must have identical types.
4148 The value produced is the floating point sum of the two operands. This
4149 instruction can also take any number of :ref:`fast-math flags <fastmath>`,
4150 which are optimization hints to enable otherwise unsafe floating point
4156 .. code-block:: llvm
4158 <result> = fadd float 4.0, %var ; yields float:result = 4.0 + %var
4160 '``sub``' Instruction
4161 ^^^^^^^^^^^^^^^^^^^^^
4168 <result> = sub <ty> <op1>, <op2> ; yields ty:result
4169 <result> = sub nuw <ty> <op1>, <op2> ; yields ty:result
4170 <result> = sub nsw <ty> <op1>, <op2> ; yields ty:result
4171 <result> = sub nuw nsw <ty> <op1>, <op2> ; yields ty:result
4176 The '``sub``' instruction returns the difference of its two operands.
4178 Note that the '``sub``' instruction is used to represent the '``neg``'
4179 instruction present in most other intermediate representations.
4184 The two arguments to the '``sub``' instruction must be
4185 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
4186 arguments must have identical types.
4191 The value produced is the integer difference of the two operands.
4193 If the difference has unsigned overflow, the result returned is the
4194 mathematical result modulo 2\ :sup:`n`\ , where n is the bit width of
4197 Because LLVM integers use a two's complement representation, this
4198 instruction is appropriate for both signed and unsigned integers.
4200 ``nuw`` and ``nsw`` stand for "No Unsigned Wrap" and "No Signed Wrap",
4201 respectively. If the ``nuw`` and/or ``nsw`` keywords are present, the
4202 result value of the ``sub`` is a :ref:`poison value <poisonvalues>` if
4203 unsigned and/or signed overflow, respectively, occurs.
4208 .. code-block:: llvm
4210 <result> = sub i32 4, %var ; yields i32:result = 4 - %var
4211 <result> = sub i32 0, %val ; yields i32:result = -%var
4215 '``fsub``' Instruction
4216 ^^^^^^^^^^^^^^^^^^^^^^
4223 <result> = fsub [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
4228 The '``fsub``' instruction returns the difference of its two operands.
4230 Note that the '``fsub``' instruction is used to represent the '``fneg``'
4231 instruction present in most other intermediate representations.
4236 The two arguments to the '``fsub``' instruction must be :ref:`floating
4237 point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
4238 Both arguments must have identical types.
4243 The value produced is the floating point difference of the two operands.
4244 This instruction can also take any number of :ref:`fast-math
4245 flags <fastmath>`, which are optimization hints to enable otherwise
4246 unsafe floating point optimizations:
4251 .. code-block:: llvm
4253 <result> = fsub float 4.0, %var ; yields float:result = 4.0 - %var
4254 <result> = fsub float -0.0, %val ; yields float:result = -%var
4256 '``mul``' Instruction
4257 ^^^^^^^^^^^^^^^^^^^^^
4264 <result> = mul <ty> <op1>, <op2> ; yields ty:result
4265 <result> = mul nuw <ty> <op1>, <op2> ; yields ty:result
4266 <result> = mul nsw <ty> <op1>, <op2> ; yields ty:result
4267 <result> = mul nuw nsw <ty> <op1>, <op2> ; yields ty:result
4272 The '``mul``' instruction returns the product of its two operands.
4277 The two arguments to the '``mul``' instruction must be
4278 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
4279 arguments must have identical types.
4284 The value produced is the integer product of the two operands.
4286 If the result of the multiplication has unsigned overflow, the result
4287 returned is the mathematical result modulo 2\ :sup:`n`\ , where n is the
4288 bit width of the result.
4290 Because LLVM integers use a two's complement representation, and the
4291 result is the same width as the operands, this instruction returns the
4292 correct result for both signed and unsigned integers. If a full product
4293 (e.g. ``i32`` * ``i32`` -> ``i64``) is needed, the operands should be
4294 sign-extended or zero-extended as appropriate to the width of the full
4297 ``nuw`` and ``nsw`` stand for "No Unsigned Wrap" and "No Signed Wrap",
4298 respectively. If the ``nuw`` and/or ``nsw`` keywords are present, the
4299 result value of the ``mul`` is a :ref:`poison value <poisonvalues>` if
4300 unsigned and/or signed overflow, respectively, occurs.
4305 .. code-block:: llvm
4307 <result> = mul i32 4, %var ; yields i32:result = 4 * %var
4311 '``fmul``' Instruction
4312 ^^^^^^^^^^^^^^^^^^^^^^
4319 <result> = fmul [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
4324 The '``fmul``' instruction returns the product of its two operands.
4329 The two arguments to the '``fmul``' instruction must be :ref:`floating
4330 point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
4331 Both arguments must have identical types.
4336 The value produced is the floating point product of the two operands.
4337 This instruction can also take any number of :ref:`fast-math
4338 flags <fastmath>`, which are optimization hints to enable otherwise
4339 unsafe floating point optimizations:
4344 .. code-block:: llvm
4346 <result> = fmul float 4.0, %var ; yields float:result = 4.0 * %var
4348 '``udiv``' Instruction
4349 ^^^^^^^^^^^^^^^^^^^^^^
4356 <result> = udiv <ty> <op1>, <op2> ; yields ty:result
4357 <result> = udiv exact <ty> <op1>, <op2> ; yields ty:result
4362 The '``udiv``' instruction returns the quotient of its two operands.
4367 The two arguments to the '``udiv``' instruction must be
4368 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
4369 arguments must have identical types.
4374 The value produced is the unsigned integer quotient of the two operands.
4376 Note that unsigned integer division and signed integer division are
4377 distinct operations; for signed integer division, use '``sdiv``'.
4379 Division by zero leads to undefined behavior.
4381 If the ``exact`` keyword is present, the result value of the ``udiv`` is
4382 a :ref:`poison value <poisonvalues>` if %op1 is not a multiple of %op2 (as
4383 such, "((a udiv exact b) mul b) == a").
4388 .. code-block:: llvm
4390 <result> = udiv i32 4, %var ; yields i32:result = 4 / %var
4392 '``sdiv``' Instruction
4393 ^^^^^^^^^^^^^^^^^^^^^^
4400 <result> = sdiv <ty> <op1>, <op2> ; yields ty:result
4401 <result> = sdiv exact <ty> <op1>, <op2> ; yields ty:result
4406 The '``sdiv``' instruction returns the quotient of its two operands.
4411 The two arguments to the '``sdiv``' instruction must be
4412 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
4413 arguments must have identical types.
4418 The value produced is the signed integer quotient of the two operands
4419 rounded towards zero.
4421 Note that signed integer division and unsigned integer division are
4422 distinct operations; for unsigned integer division, use '``udiv``'.
4424 Division by zero leads to undefined behavior. Overflow also leads to
4425 undefined behavior; this is a rare case, but can occur, for example, by
4426 doing a 32-bit division of -2147483648 by -1.
4428 If the ``exact`` keyword is present, the result value of the ``sdiv`` is
4429 a :ref:`poison value <poisonvalues>` if the result would be rounded.
4434 .. code-block:: llvm
4436 <result> = sdiv i32 4, %var ; yields i32:result = 4 / %var
4440 '``fdiv``' Instruction
4441 ^^^^^^^^^^^^^^^^^^^^^^
4448 <result> = fdiv [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
4453 The '``fdiv``' instruction returns the quotient of its two operands.
4458 The two arguments to the '``fdiv``' instruction must be :ref:`floating
4459 point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
4460 Both arguments must have identical types.
4465 The value produced is the floating point quotient of the two operands.
4466 This instruction can also take any number of :ref:`fast-math
4467 flags <fastmath>`, which are optimization hints to enable otherwise
4468 unsafe floating point optimizations:
4473 .. code-block:: llvm
4475 <result> = fdiv float 4.0, %var ; yields float:result = 4.0 / %var
4477 '``urem``' Instruction
4478 ^^^^^^^^^^^^^^^^^^^^^^
4485 <result> = urem <ty> <op1>, <op2> ; yields ty:result
4490 The '``urem``' instruction returns the remainder from the unsigned
4491 division of its two arguments.
4496 The two arguments to the '``urem``' instruction must be
4497 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
4498 arguments must have identical types.
4503 This instruction returns the unsigned integer *remainder* of a division.
4504 This instruction always performs an unsigned division to get the
4507 Note that unsigned integer remainder and signed integer remainder are
4508 distinct operations; for signed integer remainder, use '``srem``'.
4510 Taking the remainder of a division by zero leads to undefined behavior.
4515 .. code-block:: llvm
4517 <result> = urem i32 4, %var ; yields i32:result = 4 % %var
4519 '``srem``' Instruction
4520 ^^^^^^^^^^^^^^^^^^^^^^
4527 <result> = srem <ty> <op1>, <op2> ; yields ty:result
4532 The '``srem``' instruction returns the remainder from the signed
4533 division of its two operands. This instruction can also take
4534 :ref:`vector <t_vector>` versions of the values in which case the elements
4540 The two arguments to the '``srem``' instruction must be
4541 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
4542 arguments must have identical types.
4547 This instruction returns the *remainder* of a division (where the result
4548 is either zero or has the same sign as the dividend, ``op1``), not the
4549 *modulo* operator (where the result is either zero or has the same sign
4550 as the divisor, ``op2``) of a value. For more information about the
4551 difference, see `The Math
4552 Forum <http://mathforum.org/dr.math/problems/anne.4.28.99.html>`_. For a
4553 table of how this is implemented in various languages, please see
4555 operation <http://en.wikipedia.org/wiki/Modulo_operation>`_.
4557 Note that signed integer remainder and unsigned integer remainder are
4558 distinct operations; for unsigned integer remainder, use '``urem``'.
4560 Taking the remainder of a division by zero leads to undefined behavior.
4561 Overflow also leads to undefined behavior; this is a rare case, but can
4562 occur, for example, by taking the remainder of a 32-bit division of
4563 -2147483648 by -1. (The remainder doesn't actually overflow, but this
4564 rule lets srem be implemented using instructions that return both the
4565 result of the division and the remainder.)
4570 .. code-block:: llvm
4572 <result> = srem i32 4, %var ; yields i32:result = 4 % %var
4576 '``frem``' Instruction
4577 ^^^^^^^^^^^^^^^^^^^^^^
4584 <result> = frem [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
4589 The '``frem``' instruction returns the remainder from the division of
4595 The two arguments to the '``frem``' instruction must be :ref:`floating
4596 point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
4597 Both arguments must have identical types.
4602 This instruction returns the *remainder* of a division. The remainder
4603 has the same sign as the dividend. This instruction can also take any
4604 number of :ref:`fast-math flags <fastmath>`, which are optimization hints
4605 to enable otherwise unsafe floating point optimizations:
4610 .. code-block:: llvm
4612 <result> = frem float 4.0, %var ; yields float:result = 4.0 % %var
4616 Bitwise Binary Operations
4617 -------------------------
4619 Bitwise binary operators are used to do various forms of bit-twiddling
4620 in a program. They are generally very efficient instructions and can
4621 commonly be strength reduced from other instructions. They require two
4622 operands of the same type, execute an operation on them, and produce a
4623 single value. The resulting value is the same type as its operands.
4625 '``shl``' Instruction
4626 ^^^^^^^^^^^^^^^^^^^^^
4633 <result> = shl <ty> <op1>, <op2> ; yields ty:result
4634 <result> = shl nuw <ty> <op1>, <op2> ; yields ty:result
4635 <result> = shl nsw <ty> <op1>, <op2> ; yields ty:result
4636 <result> = shl nuw nsw <ty> <op1>, <op2> ; yields ty:result
4641 The '``shl``' instruction returns the first operand shifted to the left
4642 a specified number of bits.
4647 Both arguments to the '``shl``' instruction must be the same
4648 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer type.
4649 '``op2``' is treated as an unsigned value.
4654 The value produced is ``op1`` \* 2\ :sup:`op2` mod 2\ :sup:`n`,
4655 where ``n`` is the width of the result. If ``op2`` is (statically or
4656 dynamically) negative or equal to or larger than the number of bits in
4657 ``op1``, the result is undefined. If the arguments are vectors, each
4658 vector element of ``op1`` is shifted by the corresponding shift amount
4661 If the ``nuw`` keyword is present, then the shift produces a :ref:`poison
4662 value <poisonvalues>` if it shifts out any non-zero bits. If the
4663 ``nsw`` keyword is present, then the shift produces a :ref:`poison
4664 value <poisonvalues>` if it shifts out any bits that disagree with the
4665 resultant sign bit. As such, NUW/NSW have the same semantics as they
4666 would if the shift were expressed as a mul instruction with the same
4667 nsw/nuw bits in (mul %op1, (shl 1, %op2)).
4672 .. code-block:: llvm
4674 <result> = shl i32 4, %var ; yields i32: 4 << %var
4675 <result> = shl i32 4, 2 ; yields i32: 16
4676 <result> = shl i32 1, 10 ; yields i32: 1024
4677 <result> = shl i32 1, 32 ; undefined
4678 <result> = shl <2 x i32> < i32 1, i32 1>, < i32 1, i32 2> ; yields: result=<2 x i32> < i32 2, i32 4>
4680 '``lshr``' Instruction
4681 ^^^^^^^^^^^^^^^^^^^^^^
4688 <result> = lshr <ty> <op1>, <op2> ; yields ty:result
4689 <result> = lshr exact <ty> <op1>, <op2> ; yields ty:result
4694 The '``lshr``' instruction (logical shift right) returns the first
4695 operand shifted to the right a specified number of bits with zero fill.
4700 Both arguments to the '``lshr``' instruction must be the same
4701 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer type.
4702 '``op2``' is treated as an unsigned value.
4707 This instruction always performs a logical shift right operation. The
4708 most significant bits of the result will be filled with zero bits after
4709 the shift. If ``op2`` is (statically or dynamically) equal to or larger
4710 than the number of bits in ``op1``, the result is undefined. If the
4711 arguments are vectors, each vector element of ``op1`` is shifted by the
4712 corresponding shift amount in ``op2``.
4714 If the ``exact`` keyword is present, the result value of the ``lshr`` is
4715 a :ref:`poison value <poisonvalues>` if any of the bits shifted out are
4721 .. code-block:: llvm
4723 <result> = lshr i32 4, 1 ; yields i32:result = 2
4724 <result> = lshr i32 4, 2 ; yields i32:result = 1
4725 <result> = lshr i8 4, 3 ; yields i8:result = 0
4726 <result> = lshr i8 -2, 1 ; yields i8:result = 0x7F
4727 <result> = lshr i32 1, 32 ; undefined
4728 <result> = lshr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 2> ; yields: result=<2 x i32> < i32 0x7FFFFFFF, i32 1>
4730 '``ashr``' Instruction
4731 ^^^^^^^^^^^^^^^^^^^^^^
4738 <result> = ashr <ty> <op1>, <op2> ; yields ty:result
4739 <result> = ashr exact <ty> <op1>, <op2> ; yields ty:result
4744 The '``ashr``' instruction (arithmetic shift right) returns the first
4745 operand shifted to the right a specified number of bits with sign
4751 Both arguments to the '``ashr``' instruction must be the same
4752 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer type.
4753 '``op2``' is treated as an unsigned value.
4758 This instruction always performs an arithmetic shift right operation,
4759 The most significant bits of the result will be filled with the sign bit
4760 of ``op1``. If ``op2`` is (statically or dynamically) equal to or larger
4761 than the number of bits in ``op1``, the result is undefined. If the
4762 arguments are vectors, each vector element of ``op1`` is shifted by the
4763 corresponding shift amount in ``op2``.
4765 If the ``exact`` keyword is present, the result value of the ``ashr`` is
4766 a :ref:`poison value <poisonvalues>` if any of the bits shifted out are
4772 .. code-block:: llvm
4774 <result> = ashr i32 4, 1 ; yields i32:result = 2
4775 <result> = ashr i32 4, 2 ; yields i32:result = 1
4776 <result> = ashr i8 4, 3 ; yields i8:result = 0
4777 <result> = ashr i8 -2, 1 ; yields i8:result = -1
4778 <result> = ashr i32 1, 32 ; undefined
4779 <result> = ashr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 3> ; yields: result=<2 x i32> < i32 -1, i32 0>
4781 '``and``' Instruction
4782 ^^^^^^^^^^^^^^^^^^^^^
4789 <result> = and <ty> <op1>, <op2> ; yields ty:result
4794 The '``and``' instruction returns the bitwise logical and of its two
4800 The two arguments to the '``and``' instruction must be
4801 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
4802 arguments must have identical types.
4807 The truth table used for the '``and``' instruction is:
4824 .. code-block:: llvm
4826 <result> = and i32 4, %var ; yields i32:result = 4 & %var
4827 <result> = and i32 15, 40 ; yields i32:result = 8
4828 <result> = and i32 4, 8 ; yields i32:result = 0
4830 '``or``' Instruction
4831 ^^^^^^^^^^^^^^^^^^^^
4838 <result> = or <ty> <op1>, <op2> ; yields ty:result
4843 The '``or``' instruction returns the bitwise logical inclusive or of its
4849 The two arguments to the '``or``' instruction must be
4850 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
4851 arguments must have identical types.
4856 The truth table used for the '``or``' instruction is:
4875 <result> = or i32 4, %var ; yields i32:result = 4 | %var
4876 <result> = or i32 15, 40 ; yields i32:result = 47
4877 <result> = or i32 4, 8 ; yields i32:result = 12
4879 '``xor``' Instruction
4880 ^^^^^^^^^^^^^^^^^^^^^
4887 <result> = xor <ty> <op1>, <op2> ; yields ty:result
4892 The '``xor``' instruction returns the bitwise logical exclusive or of
4893 its two operands. The ``xor`` is used to implement the "one's
4894 complement" operation, which is the "~" operator in C.
4899 The two arguments to the '``xor``' instruction must be
4900 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
4901 arguments must have identical types.
4906 The truth table used for the '``xor``' instruction is:
4923 .. code-block:: llvm
4925 <result> = xor i32 4, %var ; yields i32:result = 4 ^ %var
4926 <result> = xor i32 15, 40 ; yields i32:result = 39
4927 <result> = xor i32 4, 8 ; yields i32:result = 12
4928 <result> = xor i32 %V, -1 ; yields i32:result = ~%V
4933 LLVM supports several instructions to represent vector operations in a
4934 target-independent manner. These instructions cover the element-access
4935 and vector-specific operations needed to process vectors effectively.
4936 While LLVM does directly support these vector operations, many
4937 sophisticated algorithms will want to use target-specific intrinsics to
4938 take full advantage of a specific target.
4940 .. _i_extractelement:
4942 '``extractelement``' Instruction
4943 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4950 <result> = extractelement <n x <ty>> <val>, <ty2> <idx> ; yields <ty>
4955 The '``extractelement``' instruction extracts a single scalar element
4956 from a vector at a specified index.
4961 The first operand of an '``extractelement``' instruction is a value of
4962 :ref:`vector <t_vector>` type. The second operand is an index indicating
4963 the position from which to extract the element. The index may be a
4964 variable of any integer type.
4969 The result is a scalar of the same type as the element type of ``val``.
4970 Its value is the value at position ``idx`` of ``val``. If ``idx``
4971 exceeds the length of ``val``, the results are undefined.
4976 .. code-block:: llvm
4978 <result> = extractelement <4 x i32> %vec, i32 0 ; yields i32
4980 .. _i_insertelement:
4982 '``insertelement``' Instruction
4983 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4990 <result> = insertelement <n x <ty>> <val>, <ty> <elt>, <ty2> <idx> ; yields <n x <ty>>
4995 The '``insertelement``' instruction inserts a scalar element into a
4996 vector at a specified index.
5001 The first operand of an '``insertelement``' instruction is a value of
5002 :ref:`vector <t_vector>` type. The second operand is a scalar value whose
5003 type must equal the element type of the first operand. The third operand
5004 is an index indicating the position at which to insert the value. The
5005 index may be a variable of any integer type.
5010 The result is a vector of the same type as ``val``. Its element values
5011 are those of ``val`` except at position ``idx``, where it gets the value
5012 ``elt``. If ``idx`` exceeds the length of ``val``, the results are
5018 .. code-block:: llvm
5020 <result> = insertelement <4 x i32> %vec, i32 1, i32 0 ; yields <4 x i32>
5022 .. _i_shufflevector:
5024 '``shufflevector``' Instruction
5025 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5032 <result> = shufflevector <n x <ty>> <v1>, <n x <ty>> <v2>, <m x i32> <mask> ; yields <m x <ty>>
5037 The '``shufflevector``' instruction constructs a permutation of elements
5038 from two input vectors, returning a vector with the same element type as
5039 the input and length that is the same as the shuffle mask.
5044 The first two operands of a '``shufflevector``' instruction are vectors
5045 with the same type. The third argument is a shuffle mask whose element
5046 type is always 'i32'. The result of the instruction is a vector whose
5047 length is the same as the shuffle mask and whose element type is the
5048 same as the element type of the first two operands.
5050 The shuffle mask operand is required to be a constant vector with either
5051 constant integer or undef values.
5056 The elements of the two input vectors are numbered from left to right
5057 across both of the vectors. The shuffle mask operand specifies, for each
5058 element of the result vector, which element of the two input vectors the
5059 result element gets. The element selector may be undef (meaning "don't
5060 care") and the second operand may be undef if performing a shuffle from
5066 .. code-block:: llvm
5068 <result> = shufflevector <4 x i32> %v1, <4 x i32> %v2,
5069 <4 x i32> <i32 0, i32 4, i32 1, i32 5> ; yields <4 x i32>
5070 <result> = shufflevector <4 x i32> %v1, <4 x i32> undef,
5071 <4 x i32> <i32 0, i32 1, i32 2, i32 3> ; yields <4 x i32> - Identity shuffle.
5072 <result> = shufflevector <8 x i32> %v1, <8 x i32> undef,
5073 <4 x i32> <i32 0, i32 1, i32 2, i32 3> ; yields <4 x i32>
5074 <result> = shufflevector <4 x i32> %v1, <4 x i32> %v2,
5075 <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7 > ; yields <8 x i32>
5077 Aggregate Operations
5078 --------------------
5080 LLVM supports several instructions for working with
5081 :ref:`aggregate <t_aggregate>` values.
5085 '``extractvalue``' Instruction
5086 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5093 <result> = extractvalue <aggregate type> <val>, <idx>{, <idx>}*
5098 The '``extractvalue``' instruction extracts the value of a member field
5099 from an :ref:`aggregate <t_aggregate>` value.
5104 The first operand of an '``extractvalue``' instruction is a value of
5105 :ref:`struct <t_struct>` or :ref:`array <t_array>` type. The operands are
5106 constant indices to specify which value to extract in a similar manner
5107 as indices in a '``getelementptr``' instruction.
5109 The major differences to ``getelementptr`` indexing are:
5111 - Since the value being indexed is not a pointer, the first index is
5112 omitted and assumed to be zero.
5113 - At least one index must be specified.
5114 - Not only struct indices but also array indices must be in bounds.
5119 The result is the value at the position in the aggregate specified by
5125 .. code-block:: llvm
5127 <result> = extractvalue {i32, float} %agg, 0 ; yields i32
5131 '``insertvalue``' Instruction
5132 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5139 <result> = insertvalue <aggregate type> <val>, <ty> <elt>, <idx>{, <idx>}* ; yields <aggregate type>
5144 The '``insertvalue``' instruction inserts a value into a member field in
5145 an :ref:`aggregate <t_aggregate>` value.
5150 The first operand of an '``insertvalue``' instruction is a value of
5151 :ref:`struct <t_struct>` or :ref:`array <t_array>` type. The second operand is
5152 a first-class value to insert. The following operands are constant
5153 indices indicating the position at which to insert the value in a
5154 similar manner as indices in a '``extractvalue``' instruction. The value
5155 to insert must have the same type as the value identified by the
5161 The result is an aggregate of the same type as ``val``. Its value is
5162 that of ``val`` except that the value at the position specified by the
5163 indices is that of ``elt``.
5168 .. code-block:: llvm
5170 %agg1 = insertvalue {i32, float} undef, i32 1, 0 ; yields {i32 1, float undef}
5171 %agg2 = insertvalue {i32, float} %agg1, float %val, 1 ; yields {i32 1, float %val}
5172 %agg3 = insertvalue {i32, {float}} undef, float %val, 1, 0 ; yields {i32 undef, {float %val}}
5176 Memory Access and Addressing Operations
5177 ---------------------------------------
5179 A key design point of an SSA-based representation is how it represents
5180 memory. In LLVM, no memory locations are in SSA form, which makes things
5181 very simple. This section describes how to read, write, and allocate
5186 '``alloca``' Instruction
5187 ^^^^^^^^^^^^^^^^^^^^^^^^
5194 <result> = alloca [inalloca] <type> [, <ty> <NumElements>] [, align <alignment>] ; yields type*:result
5199 The '``alloca``' instruction allocates memory on the stack frame of the
5200 currently executing function, to be automatically released when this
5201 function returns to its caller. The object is always allocated in the
5202 generic address space (address space zero).
5207 The '``alloca``' instruction allocates ``sizeof(<type>)*NumElements``
5208 bytes of memory on the runtime stack, returning a pointer of the
5209 appropriate type to the program. If "NumElements" is specified, it is
5210 the number of elements allocated, otherwise "NumElements" is defaulted
5211 to be one. If a constant alignment is specified, the value result of the
5212 allocation is guaranteed to be aligned to at least that boundary. The
5213 alignment may not be greater than ``1 << 29``. If not specified, or if
5214 zero, the target can choose to align the allocation on any convenient
5215 boundary compatible with the type.
5217 '``type``' may be any sized type.
5222 Memory is allocated; a pointer is returned. The operation is undefined
5223 if there is insufficient stack space for the allocation. '``alloca``'d
5224 memory is automatically released when the function returns. The
5225 '``alloca``' instruction is commonly used to represent automatic
5226 variables that must have an address available. When the function returns
5227 (either with the ``ret`` or ``resume`` instructions), the memory is
5228 reclaimed. Allocating zero bytes is legal, but the result is undefined.
5229 The order in which memory is allocated (ie., which way the stack grows)
5235 .. code-block:: llvm
5237 %ptr = alloca i32 ; yields i32*:ptr
5238 %ptr = alloca i32, i32 4 ; yields i32*:ptr
5239 %ptr = alloca i32, i32 4, align 1024 ; yields i32*:ptr
5240 %ptr = alloca i32, align 1024 ; yields i32*:ptr
5244 '``load``' Instruction
5245 ^^^^^^^^^^^^^^^^^^^^^^
5252 <result> = load [volatile] <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>][, !invariant.load !<index>][, !nonnull !<index>]
5253 <result> = load atomic [volatile] <ty>* <pointer> [singlethread] <ordering>, align <alignment>
5254 !<index> = !{ i32 1 }
5259 The '``load``' instruction is used to read from memory.
5264 The argument to the ``load`` instruction specifies the memory address
5265 from which to load. The pointer must point to a :ref:`first
5266 class <t_firstclass>` type. If the ``load`` is marked as ``volatile``,
5267 then the optimizer is not allowed to modify the number or order of
5268 execution of this ``load`` with other :ref:`volatile
5269 operations <volatile>`.
5271 If the ``load`` is marked as ``atomic``, it takes an extra
5272 :ref:`ordering <ordering>` and optional ``singlethread`` argument. The
5273 ``release`` and ``acq_rel`` orderings are not valid on ``load``
5274 instructions. Atomic loads produce :ref:`defined <memmodel>` results
5275 when they may see multiple atomic stores. The type of the pointee must
5276 be an integer type whose bit width is a power of two greater than or
5277 equal to eight and less than or equal to a target-specific size limit.
5278 ``align`` must be explicitly specified on atomic loads, and the load has
5279 undefined behavior if the alignment is not set to a value which is at
5280 least the size in bytes of the pointee. ``!nontemporal`` does not have
5281 any defined semantics for atomic loads.
5283 The optional constant ``align`` argument specifies the alignment of the
5284 operation (that is, the alignment of the memory address). A value of 0
5285 or an omitted ``align`` argument means that the operation has the ABI
5286 alignment for the target. It is the responsibility of the code emitter
5287 to ensure that the alignment information is correct. Overestimating the
5288 alignment results in undefined behavior. Underestimating the alignment
5289 may produce less efficient code. An alignment of 1 is always safe. The
5290 maximum possible alignment is ``1 << 29``.
5292 The optional ``!nontemporal`` metadata must reference a single
5293 metadata name ``<index>`` corresponding to a metadata node with one
5294 ``i32`` entry of value 1. The existence of the ``!nontemporal``
5295 metadata on the instruction tells the optimizer and code generator
5296 that this load is not expected to be reused in the cache. The code
5297 generator may select special instructions to save cache bandwidth, such
5298 as the ``MOVNT`` instruction on x86.
5300 The optional ``!invariant.load`` metadata must reference a single
5301 metadata name ``<index>`` corresponding to a metadata node with no
5302 entries. The existence of the ``!invariant.load`` metadata on the
5303 instruction tells the optimizer and code generator that the address
5304 operand to this load points to memory which can be assumed unchanged.
5305 Being invariant does not imply that a location is dereferenceable,
5306 but it does imply that once the location is known dereferenceable
5307 its value is henceforth unchanging.
5309 The optional ``!nonnull`` metadata must reference a single
5310 metadata name ``<index>`` corresponding to a metadata node with no
5311 entries. The existence of the ``!nonnull`` metadata on the
5312 instruction tells the optimizer that the value loaded is known to
5313 never be null. This is analogous to the ''nonnull'' attribute
5314 on parameters and return values. This metadata can only be applied
5315 to loads of a pointer type.
5320 The location of memory pointed to is loaded. If the value being loaded
5321 is of scalar type then the number of bytes read does not exceed the
5322 minimum number of bytes needed to hold all bits of the type. For
5323 example, loading an ``i24`` reads at most three bytes. When loading a
5324 value of a type like ``i20`` with a size that is not an integral number
5325 of bytes, the result is undefined if the value was not originally
5326 written using a store of the same type.
5331 .. code-block:: llvm
5333 %ptr = alloca i32 ; yields i32*:ptr
5334 store i32 3, i32* %ptr ; yields void
5335 %val = load i32* %ptr ; yields i32:val = i32 3
5339 '``store``' Instruction
5340 ^^^^^^^^^^^^^^^^^^^^^^^
5347 store [volatile] <ty> <value>, <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>] ; yields void
5348 store atomic [volatile] <ty> <value>, <ty>* <pointer> [singlethread] <ordering>, align <alignment> ; yields void
5353 The '``store``' instruction is used to write to memory.
5358 There are two arguments to the ``store`` instruction: a value to store
5359 and an address at which to store it. The type of the ``<pointer>``
5360 operand must be a pointer to the :ref:`first class <t_firstclass>` type of
5361 the ``<value>`` operand. If the ``store`` is marked as ``volatile``,
5362 then the optimizer is not allowed to modify the number or order of
5363 execution of this ``store`` with other :ref:`volatile
5364 operations <volatile>`.
5366 If the ``store`` is marked as ``atomic``, it takes an extra
5367 :ref:`ordering <ordering>` and optional ``singlethread`` argument. The
5368 ``acquire`` and ``acq_rel`` orderings aren't valid on ``store``
5369 instructions. Atomic loads produce :ref:`defined <memmodel>` results
5370 when they may see multiple atomic stores. The type of the pointee must
5371 be an integer type whose bit width is a power of two greater than or
5372 equal to eight and less than or equal to a target-specific size limit.
5373 ``align`` must be explicitly specified on atomic stores, and the store
5374 has undefined behavior if the alignment is not set to a value which is
5375 at least the size in bytes of the pointee. ``!nontemporal`` does not
5376 have any defined semantics for atomic stores.
5378 The optional constant ``align`` argument specifies the alignment of the
5379 operation (that is, the alignment of the memory address). A value of 0
5380 or an omitted ``align`` argument means that the operation has the ABI
5381 alignment for the target. It is the responsibility of the code emitter
5382 to ensure that the alignment information is correct. Overestimating the
5383 alignment results in undefined behavior. Underestimating the
5384 alignment may produce less efficient code. An alignment of 1 is always
5385 safe. The maximum possible alignment is ``1 << 29``.
5387 The optional ``!nontemporal`` metadata must reference a single metadata
5388 name ``<index>`` corresponding to a metadata node with one ``i32`` entry of
5389 value 1. The existence of the ``!nontemporal`` metadata on the instruction
5390 tells the optimizer and code generator that this load is not expected to
5391 be reused in the cache. The code generator may select special
5392 instructions to save cache bandwidth, such as the MOVNT instruction on
5398 The contents of memory are updated to contain ``<value>`` at the
5399 location specified by the ``<pointer>`` operand. If ``<value>`` is
5400 of scalar type then the number of bytes written does not exceed the
5401 minimum number of bytes needed to hold all bits of the type. For
5402 example, storing an ``i24`` writes at most three bytes. When writing a
5403 value of a type like ``i20`` with a size that is not an integral number
5404 of bytes, it is unspecified what happens to the extra bits that do not
5405 belong to the type, but they will typically be overwritten.
5410 .. code-block:: llvm
5412 %ptr = alloca i32 ; yields i32*:ptr
5413 store i32 3, i32* %ptr ; yields void
5414 %val = load i32* %ptr ; yields i32:val = i32 3
5418 '``fence``' Instruction
5419 ^^^^^^^^^^^^^^^^^^^^^^^
5426 fence [singlethread] <ordering> ; yields void
5431 The '``fence``' instruction is used to introduce happens-before edges
5437 '``fence``' instructions take an :ref:`ordering <ordering>` argument which
5438 defines what *synchronizes-with* edges they add. They can only be given
5439 ``acquire``, ``release``, ``acq_rel``, and ``seq_cst`` orderings.
5444 A fence A which has (at least) ``release`` ordering semantics
5445 *synchronizes with* a fence B with (at least) ``acquire`` ordering
5446 semantics if and only if there exist atomic operations X and Y, both
5447 operating on some atomic object M, such that A is sequenced before X, X
5448 modifies M (either directly or through some side effect of a sequence
5449 headed by X), Y is sequenced before B, and Y observes M. This provides a
5450 *happens-before* dependency between A and B. Rather than an explicit
5451 ``fence``, one (but not both) of the atomic operations X or Y might
5452 provide a ``release`` or ``acquire`` (resp.) ordering constraint and
5453 still *synchronize-with* the explicit ``fence`` and establish the
5454 *happens-before* edge.
5456 A ``fence`` which has ``seq_cst`` ordering, in addition to having both
5457 ``acquire`` and ``release`` semantics specified above, participates in
5458 the global program order of other ``seq_cst`` operations and/or fences.
5460 The optional ":ref:`singlethread <singlethread>`" argument specifies
5461 that the fence only synchronizes with other fences in the same thread.
5462 (This is useful for interacting with signal handlers.)
5467 .. code-block:: llvm
5469 fence acquire ; yields void
5470 fence singlethread seq_cst ; yields void
5474 '``cmpxchg``' Instruction
5475 ^^^^^^^^^^^^^^^^^^^^^^^^^
5482 cmpxchg [weak] [volatile] <ty>* <pointer>, <ty> <cmp>, <ty> <new> [singlethread] <success ordering> <failure ordering> ; yields { ty, i1 }
5487 The '``cmpxchg``' instruction is used to atomically modify memory. It
5488 loads a value in memory and compares it to a given value. If they are
5489 equal, it tries to store a new value into the memory.
5494 There are three arguments to the '``cmpxchg``' instruction: an address
5495 to operate on, a value to compare to the value currently be at that
5496 address, and a new value to place at that address if the compared values
5497 are equal. The type of '<cmp>' must be an integer type whose bit width
5498 is a power of two greater than or equal to eight and less than or equal
5499 to a target-specific size limit. '<cmp>' and '<new>' must have the same
5500 type, and the type of '<pointer>' must be a pointer to that type. If the
5501 ``cmpxchg`` is marked as ``volatile``, then the optimizer is not allowed
5502 to modify the number or order of execution of this ``cmpxchg`` with
5503 other :ref:`volatile operations <volatile>`.
5505 The success and failure :ref:`ordering <ordering>` arguments specify how this
5506 ``cmpxchg`` synchronizes with other atomic operations. Both ordering parameters
5507 must be at least ``monotonic``, the ordering constraint on failure must be no
5508 stronger than that on success, and the failure ordering cannot be either
5509 ``release`` or ``acq_rel``.
5511 The optional "``singlethread``" argument declares that the ``cmpxchg``
5512 is only atomic with respect to code (usually signal handlers) running in
5513 the same thread as the ``cmpxchg``. Otherwise the cmpxchg is atomic with
5514 respect to all other code in the system.
5516 The pointer passed into cmpxchg must have alignment greater than or
5517 equal to the size in memory of the operand.
5522 The contents of memory at the location specified by the '``<pointer>``' operand
5523 is read and compared to '``<cmp>``'; if the read value is the equal, the
5524 '``<new>``' is written. The original value at the location is returned, together
5525 with a flag indicating success (true) or failure (false).
5527 If the cmpxchg operation is marked as ``weak`` then a spurious failure is
5528 permitted: the operation may not write ``<new>`` even if the comparison
5531 If the cmpxchg operation is strong (the default), the i1 value is 1 if and only
5532 if the value loaded equals ``cmp``.
5534 A successful ``cmpxchg`` is a read-modify-write instruction for the purpose of
5535 identifying release sequences. A failed ``cmpxchg`` is equivalent to an atomic
5536 load with an ordering parameter determined the second ordering parameter.
5541 .. code-block:: llvm
5544 %orig = atomic load i32* %ptr unordered ; yields i32
5548 %cmp = phi i32 [ %orig, %entry ], [%old, %loop]
5549 %squared = mul i32 %cmp, %cmp
5550 %val_success = cmpxchg i32* %ptr, i32 %cmp, i32 %squared acq_rel monotonic ; yields { i32, i1 }
5551 %value_loaded = extractvalue { i32, i1 } %val_success, 0
5552 %success = extractvalue { i32, i1 } %val_success, 1
5553 br i1 %success, label %done, label %loop
5560 '``atomicrmw``' Instruction
5561 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
5568 atomicrmw [volatile] <operation> <ty>* <pointer>, <ty> <value> [singlethread] <ordering> ; yields ty
5573 The '``atomicrmw``' instruction is used to atomically modify memory.
5578 There are three arguments to the '``atomicrmw``' instruction: an
5579 operation to apply, an address whose value to modify, an argument to the
5580 operation. The operation must be one of the following keywords:
5594 The type of '<value>' must be an integer type whose bit width is a power
5595 of two greater than or equal to eight and less than or equal to a
5596 target-specific size limit. The type of the '``<pointer>``' operand must
5597 be a pointer to that type. If the ``atomicrmw`` is marked as
5598 ``volatile``, then the optimizer is not allowed to modify the number or
5599 order of execution of this ``atomicrmw`` with other :ref:`volatile
5600 operations <volatile>`.
5605 The contents of memory at the location specified by the '``<pointer>``'
5606 operand are atomically read, modified, and written back. The original
5607 value at the location is returned. The modification is specified by the
5610 - xchg: ``*ptr = val``
5611 - add: ``*ptr = *ptr + val``
5612 - sub: ``*ptr = *ptr - val``
5613 - and: ``*ptr = *ptr & val``
5614 - nand: ``*ptr = ~(*ptr & val)``
5615 - or: ``*ptr = *ptr | val``
5616 - xor: ``*ptr = *ptr ^ val``
5617 - max: ``*ptr = *ptr > val ? *ptr : val`` (using a signed comparison)
5618 - min: ``*ptr = *ptr < val ? *ptr : val`` (using a signed comparison)
5619 - umax: ``*ptr = *ptr > val ? *ptr : val`` (using an unsigned
5621 - umin: ``*ptr = *ptr < val ? *ptr : val`` (using an unsigned
5627 .. code-block:: llvm
5629 %old = atomicrmw add i32* %ptr, i32 1 acquire ; yields i32
5631 .. _i_getelementptr:
5633 '``getelementptr``' Instruction
5634 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5641 <result> = getelementptr <pty>* <ptrval>{, <ty> <idx>}*
5642 <result> = getelementptr inbounds <pty>* <ptrval>{, <ty> <idx>}*
5643 <result> = getelementptr <ptr vector> ptrval, <vector index type> idx
5648 The '``getelementptr``' instruction is used to get the address of a
5649 subelement of an :ref:`aggregate <t_aggregate>` data structure. It performs
5650 address calculation only and does not access memory.
5655 The first argument is always a pointer or a vector of pointers, and
5656 forms the basis of the calculation. The remaining arguments are indices
5657 that indicate which of the elements of the aggregate object are indexed.
5658 The interpretation of each index is dependent on the type being indexed
5659 into. The first index always indexes the pointer value given as the
5660 first argument, the second index indexes a value of the type pointed to
5661 (not necessarily the value directly pointed to, since the first index
5662 can be non-zero), etc. The first type indexed into must be a pointer
5663 value, subsequent types can be arrays, vectors, and structs. Note that
5664 subsequent types being indexed into can never be pointers, since that
5665 would require loading the pointer before continuing calculation.
5667 The type of each index argument depends on the type it is indexing into.
5668 When indexing into a (optionally packed) structure, only ``i32`` integer
5669 **constants** are allowed (when using a vector of indices they must all
5670 be the **same** ``i32`` integer constant). When indexing into an array,
5671 pointer or vector, integers of any width are allowed, and they are not
5672 required to be constant. These integers are treated as signed values
5675 For example, let's consider a C code fragment and how it gets compiled
5691 int *foo(struct ST *s) {
5692 return &s[1].Z.B[5][13];
5695 The LLVM code generated by Clang is:
5697 .. code-block:: llvm
5699 %struct.RT = type { i8, [10 x [20 x i32]], i8 }
5700 %struct.ST = type { i32, double, %struct.RT }
5702 define i32* @foo(%struct.ST* %s) nounwind uwtable readnone optsize ssp {
5704 %arrayidx = getelementptr inbounds %struct.ST* %s, i64 1, i32 2, i32 1, i64 5, i64 13
5711 In the example above, the first index is indexing into the
5712 '``%struct.ST*``' type, which is a pointer, yielding a '``%struct.ST``'
5713 = '``{ i32, double, %struct.RT }``' type, a structure. The second index
5714 indexes into the third element of the structure, yielding a
5715 '``%struct.RT``' = '``{ i8 , [10 x [20 x i32]], i8 }``' type, another
5716 structure. The third index indexes into the second element of the
5717 structure, yielding a '``[10 x [20 x i32]]``' type, an array. The two
5718 dimensions of the array are subscripted into, yielding an '``i32``'
5719 type. The '``getelementptr``' instruction returns a pointer to this
5720 element, thus computing a value of '``i32*``' type.
5722 Note that it is perfectly legal to index partially through a structure,
5723 returning a pointer to an inner element. Because of this, the LLVM code
5724 for the given testcase is equivalent to:
5726 .. code-block:: llvm
5728 define i32* @foo(%struct.ST* %s) {
5729 %t1 = getelementptr %struct.ST* %s, i32 1 ; yields %struct.ST*:%t1
5730 %t2 = getelementptr %struct.ST* %t1, i32 0, i32 2 ; yields %struct.RT*:%t2
5731 %t3 = getelementptr %struct.RT* %t2, i32 0, i32 1 ; yields [10 x [20 x i32]]*:%t3
5732 %t4 = getelementptr [10 x [20 x i32]]* %t3, i32 0, i32 5 ; yields [20 x i32]*:%t4
5733 %t5 = getelementptr [20 x i32]* %t4, i32 0, i32 13 ; yields i32*:%t5
5737 If the ``inbounds`` keyword is present, the result value of the
5738 ``getelementptr`` is a :ref:`poison value <poisonvalues>` if the base
5739 pointer is not an *in bounds* address of an allocated object, or if any
5740 of the addresses that would be formed by successive addition of the
5741 offsets implied by the indices to the base address with infinitely
5742 precise signed arithmetic are not an *in bounds* address of that
5743 allocated object. The *in bounds* addresses for an allocated object are
5744 all the addresses that point into the object, plus the address one byte
5745 past the end. In cases where the base is a vector of pointers the
5746 ``inbounds`` keyword applies to each of the computations element-wise.
5748 If the ``inbounds`` keyword is not present, the offsets are added to the
5749 base address with silently-wrapping two's complement arithmetic. If the
5750 offsets have a different width from the pointer, they are sign-extended
5751 or truncated to the width of the pointer. The result value of the
5752 ``getelementptr`` may be outside the object pointed to by the base
5753 pointer. The result value may not necessarily be used to access memory
5754 though, even if it happens to point into allocated storage. See the
5755 :ref:`Pointer Aliasing Rules <pointeraliasing>` section for more
5758 The getelementptr instruction is often confusing. For some more insight
5759 into how it works, see :doc:`the getelementptr FAQ <GetElementPtr>`.
5764 .. code-block:: llvm
5766 ; yields [12 x i8]*:aptr
5767 %aptr = getelementptr {i32, [12 x i8]}* %saptr, i64 0, i32 1
5769 %vptr = getelementptr {i32, <2 x i8>}* %svptr, i64 0, i32 1, i32 1
5771 %eptr = getelementptr [12 x i8]* %aptr, i64 0, i32 1
5773 %iptr = getelementptr [10 x i32]* @arr, i16 0, i16 0
5775 In cases where the pointer argument is a vector of pointers, each index
5776 must be a vector with the same number of elements. For example:
5778 .. code-block:: llvm
5780 %A = getelementptr <4 x i8*> %ptrs, <4 x i64> %offsets,
5782 Conversion Operations
5783 ---------------------
5785 The instructions in this category are the conversion instructions
5786 (casting) which all take a single operand and a type. They perform
5787 various bit conversions on the operand.
5789 '``trunc .. to``' Instruction
5790 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5797 <result> = trunc <ty> <value> to <ty2> ; yields ty2
5802 The '``trunc``' instruction truncates its operand to the type ``ty2``.
5807 The '``trunc``' instruction takes a value to trunc, and a type to trunc
5808 it to. Both types must be of :ref:`integer <t_integer>` types, or vectors
5809 of the same number of integers. The bit size of the ``value`` must be
5810 larger than the bit size of the destination type, ``ty2``. Equal sized
5811 types are not allowed.
5816 The '``trunc``' instruction truncates the high order bits in ``value``
5817 and converts the remaining bits to ``ty2``. Since the source size must
5818 be larger than the destination size, ``trunc`` cannot be a *no-op cast*.
5819 It will always truncate bits.
5824 .. code-block:: llvm
5826 %X = trunc i32 257 to i8 ; yields i8:1
5827 %Y = trunc i32 123 to i1 ; yields i1:true
5828 %Z = trunc i32 122 to i1 ; yields i1:false
5829 %W = trunc <2 x i16> <i16 8, i16 7> to <2 x i8> ; yields <i8 8, i8 7>
5831 '``zext .. to``' Instruction
5832 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5839 <result> = zext <ty> <value> to <ty2> ; yields ty2
5844 The '``zext``' instruction zero extends its operand to type ``ty2``.
5849 The '``zext``' instruction takes a value to cast, and a type to cast it
5850 to. Both types must be of :ref:`integer <t_integer>` types, or vectors of
5851 the same number of integers. The bit size of the ``value`` must be
5852 smaller than the bit size of the destination type, ``ty2``.
5857 The ``zext`` fills the high order bits of the ``value`` with zero bits
5858 until it reaches the size of the destination type, ``ty2``.
5860 When zero extending from i1, the result will always be either 0 or 1.
5865 .. code-block:: llvm
5867 %X = zext i32 257 to i64 ; yields i64:257
5868 %Y = zext i1 true to i32 ; yields i32:1
5869 %Z = zext <2 x i16> <i16 8, i16 7> to <2 x i32> ; yields <i32 8, i32 7>
5871 '``sext .. to``' Instruction
5872 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5879 <result> = sext <ty> <value> to <ty2> ; yields ty2
5884 The '``sext``' sign extends ``value`` to the type ``ty2``.
5889 The '``sext``' instruction takes a value to cast, and a type to cast it
5890 to. Both types must be of :ref:`integer <t_integer>` types, or vectors of
5891 the same number of integers. The bit size of the ``value`` must be
5892 smaller than the bit size of the destination type, ``ty2``.
5897 The '``sext``' instruction performs a sign extension by copying the sign
5898 bit (highest order bit) of the ``value`` until it reaches the bit size
5899 of the type ``ty2``.
5901 When sign extending from i1, the extension always results in -1 or 0.
5906 .. code-block:: llvm
5908 %X = sext i8 -1 to i16 ; yields i16 :65535
5909 %Y = sext i1 true to i32 ; yields i32:-1
5910 %Z = sext <2 x i16> <i16 8, i16 7> to <2 x i32> ; yields <i32 8, i32 7>
5912 '``fptrunc .. to``' Instruction
5913 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5920 <result> = fptrunc <ty> <value> to <ty2> ; yields ty2
5925 The '``fptrunc``' instruction truncates ``value`` to type ``ty2``.
5930 The '``fptrunc``' instruction takes a :ref:`floating point <t_floating>`
5931 value to cast and a :ref:`floating point <t_floating>` type to cast it to.
5932 The size of ``value`` must be larger than the size of ``ty2``. This
5933 implies that ``fptrunc`` cannot be used to make a *no-op cast*.
5938 The '``fptrunc``' instruction truncates a ``value`` from a larger
5939 :ref:`floating point <t_floating>` type to a smaller :ref:`floating
5940 point <t_floating>` type. If the value cannot fit within the
5941 destination type, ``ty2``, then the results are undefined.
5946 .. code-block:: llvm
5948 %X = fptrunc double 123.0 to float ; yields float:123.0
5949 %Y = fptrunc double 1.0E+300 to float ; yields undefined
5951 '``fpext .. to``' Instruction
5952 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5959 <result> = fpext <ty> <value> to <ty2> ; yields ty2
5964 The '``fpext``' extends a floating point ``value`` to a larger floating
5970 The '``fpext``' instruction takes a :ref:`floating point <t_floating>`
5971 ``value`` to cast, and a :ref:`floating point <t_floating>` type to cast it
5972 to. The source type must be smaller than the destination type.
5977 The '``fpext``' instruction extends the ``value`` from a smaller
5978 :ref:`floating point <t_floating>` type to a larger :ref:`floating
5979 point <t_floating>` type. The ``fpext`` cannot be used to make a
5980 *no-op cast* because it always changes bits. Use ``bitcast`` to make a
5981 *no-op cast* for a floating point cast.
5986 .. code-block:: llvm
5988 %X = fpext float 3.125 to double ; yields double:3.125000e+00
5989 %Y = fpext double %X to fp128 ; yields fp128:0xL00000000000000004000900000000000
5991 '``fptoui .. to``' Instruction
5992 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5999 <result> = fptoui <ty> <value> to <ty2> ; yields ty2
6004 The '``fptoui``' converts a floating point ``value`` to its unsigned
6005 integer equivalent of type ``ty2``.
6010 The '``fptoui``' instruction takes a value to cast, which must be a
6011 scalar or vector :ref:`floating point <t_floating>` value, and a type to
6012 cast it to ``ty2``, which must be an :ref:`integer <t_integer>` type. If
6013 ``ty`` is a vector floating point type, ``ty2`` must be a vector integer
6014 type with the same number of elements as ``ty``
6019 The '``fptoui``' instruction converts its :ref:`floating
6020 point <t_floating>` operand into the nearest (rounding towards zero)
6021 unsigned integer value. If the value cannot fit in ``ty2``, the results
6027 .. code-block:: llvm
6029 %X = fptoui double 123.0 to i32 ; yields i32:123
6030 %Y = fptoui float 1.0E+300 to i1 ; yields undefined:1
6031 %Z = fptoui float 1.04E+17 to i8 ; yields undefined:1
6033 '``fptosi .. to``' Instruction
6034 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6041 <result> = fptosi <ty> <value> to <ty2> ; yields ty2
6046 The '``fptosi``' instruction converts :ref:`floating point <t_floating>`
6047 ``value`` to type ``ty2``.
6052 The '``fptosi``' instruction takes a value to cast, which must be a
6053 scalar or vector :ref:`floating point <t_floating>` value, and a type to
6054 cast it to ``ty2``, which must be an :ref:`integer <t_integer>` type. If
6055 ``ty`` is a vector floating point type, ``ty2`` must be a vector integer
6056 type with the same number of elements as ``ty``
6061 The '``fptosi``' instruction converts its :ref:`floating
6062 point <t_floating>` operand into the nearest (rounding towards zero)
6063 signed integer value. If the value cannot fit in ``ty2``, the results
6069 .. code-block:: llvm
6071 %X = fptosi double -123.0 to i32 ; yields i32:-123
6072 %Y = fptosi float 1.0E-247 to i1 ; yields undefined:1
6073 %Z = fptosi float 1.04E+17 to i8 ; yields undefined:1
6075 '``uitofp .. to``' Instruction
6076 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6083 <result> = uitofp <ty> <value> to <ty2> ; yields ty2
6088 The '``uitofp``' instruction regards ``value`` as an unsigned integer
6089 and converts that value to the ``ty2`` type.
6094 The '``uitofp``' instruction takes a value to cast, which must be a
6095 scalar or vector :ref:`integer <t_integer>` value, and a type to cast it to
6096 ``ty2``, which must be an :ref:`floating point <t_floating>` type. If
6097 ``ty`` is a vector integer type, ``ty2`` must be a vector floating point
6098 type with the same number of elements as ``ty``
6103 The '``uitofp``' instruction interprets its operand as an unsigned
6104 integer quantity and converts it to the corresponding floating point
6105 value. If the value cannot fit in the floating point value, the results
6111 .. code-block:: llvm
6113 %X = uitofp i32 257 to float ; yields float:257.0
6114 %Y = uitofp i8 -1 to double ; yields double:255.0
6116 '``sitofp .. to``' Instruction
6117 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6124 <result> = sitofp <ty> <value> to <ty2> ; yields ty2
6129 The '``sitofp``' instruction regards ``value`` as a signed integer and
6130 converts that value to the ``ty2`` type.
6135 The '``sitofp``' instruction takes a value to cast, which must be a
6136 scalar or vector :ref:`integer <t_integer>` value, and a type to cast it to
6137 ``ty2``, which must be an :ref:`floating point <t_floating>` type. If
6138 ``ty`` is a vector integer type, ``ty2`` must be a vector floating point
6139 type with the same number of elements as ``ty``
6144 The '``sitofp``' instruction interprets its operand as a signed integer
6145 quantity and converts it to the corresponding floating point value. If
6146 the value cannot fit in the floating point value, the results are
6152 .. code-block:: llvm
6154 %X = sitofp i32 257 to float ; yields float:257.0
6155 %Y = sitofp i8 -1 to double ; yields double:-1.0
6159 '``ptrtoint .. to``' Instruction
6160 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6167 <result> = ptrtoint <ty> <value> to <ty2> ; yields ty2
6172 The '``ptrtoint``' instruction converts the pointer or a vector of
6173 pointers ``value`` to the integer (or vector of integers) type ``ty2``.
6178 The '``ptrtoint``' instruction takes a ``value`` to cast, which must be
6179 a a value of type :ref:`pointer <t_pointer>` or a vector of pointers, and a
6180 type to cast it to ``ty2``, which must be an :ref:`integer <t_integer>` or
6181 a vector of integers type.
6186 The '``ptrtoint``' instruction converts ``value`` to integer type
6187 ``ty2`` by interpreting the pointer value as an integer and either
6188 truncating or zero extending that value to the size of the integer type.
6189 If ``value`` is smaller than ``ty2`` then a zero extension is done. If
6190 ``value`` is larger than ``ty2`` then a truncation is done. If they are
6191 the same size, then nothing is done (*no-op cast*) other than a type
6197 .. code-block:: llvm
6199 %X = ptrtoint i32* %P to i8 ; yields truncation on 32-bit architecture
6200 %Y = ptrtoint i32* %P to i64 ; yields zero extension on 32-bit architecture
6201 %Z = ptrtoint <4 x i32*> %P to <4 x i64>; yields vector zero extension for a vector of addresses on 32-bit architecture
6205 '``inttoptr .. to``' Instruction
6206 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6213 <result> = inttoptr <ty> <value> to <ty2> ; yields ty2
6218 The '``inttoptr``' instruction converts an integer ``value`` to a
6219 pointer type, ``ty2``.
6224 The '``inttoptr``' instruction takes an :ref:`integer <t_integer>` value to
6225 cast, and a type to cast it to, which must be a :ref:`pointer <t_pointer>`
6231 The '``inttoptr``' instruction converts ``value`` to type ``ty2`` by
6232 applying either a zero extension or a truncation depending on the size
6233 of the integer ``value``. If ``value`` is larger than the size of a
6234 pointer then a truncation is done. If ``value`` is smaller than the size
6235 of a pointer then a zero extension is done. If they are the same size,
6236 nothing is done (*no-op cast*).
6241 .. code-block:: llvm
6243 %X = inttoptr i32 255 to i32* ; yields zero extension on 64-bit architecture
6244 %Y = inttoptr i32 255 to i32* ; yields no-op on 32-bit architecture
6245 %Z = inttoptr i64 0 to i32* ; yields truncation on 32-bit architecture
6246 %Z = inttoptr <4 x i32> %G to <4 x i8*>; yields truncation of vector G to four pointers
6250 '``bitcast .. to``' Instruction
6251 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6258 <result> = bitcast <ty> <value> to <ty2> ; yields ty2
6263 The '``bitcast``' instruction converts ``value`` to type ``ty2`` without
6269 The '``bitcast``' instruction takes a value to cast, which must be a
6270 non-aggregate first class value, and a type to cast it to, which must
6271 also be a non-aggregate :ref:`first class <t_firstclass>` type. The
6272 bit sizes of ``value`` and the destination type, ``ty2``, must be
6273 identical. If the source type is a pointer, the destination type must
6274 also be a pointer of the same size. This instruction supports bitwise
6275 conversion of vectors to integers and to vectors of other types (as
6276 long as they have the same size).
6281 The '``bitcast``' instruction converts ``value`` to type ``ty2``. It
6282 is always a *no-op cast* because no bits change with this
6283 conversion. The conversion is done as if the ``value`` had been stored
6284 to memory and read back as type ``ty2``. Pointer (or vector of
6285 pointers) types may only be converted to other pointer (or vector of
6286 pointers) types with the same address space through this instruction.
6287 To convert pointers to other types, use the :ref:`inttoptr <i_inttoptr>`
6288 or :ref:`ptrtoint <i_ptrtoint>` instructions first.
6293 .. code-block:: llvm
6295 %X = bitcast i8 255 to i8 ; yields i8 :-1
6296 %Y = bitcast i32* %x to sint* ; yields sint*:%x
6297 %Z = bitcast <2 x int> %V to i64; ; yields i64: %V
6298 %Z = bitcast <2 x i32*> %V to <2 x i64*> ; yields <2 x i64*>
6300 .. _i_addrspacecast:
6302 '``addrspacecast .. to``' Instruction
6303 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6310 <result> = addrspacecast <pty> <ptrval> to <pty2> ; yields pty2
6315 The '``addrspacecast``' instruction converts ``ptrval`` from ``pty`` in
6316 address space ``n`` to type ``pty2`` in address space ``m``.
6321 The '``addrspacecast``' instruction takes a pointer or vector of pointer value
6322 to cast and a pointer type to cast it to, which must have a different
6328 The '``addrspacecast``' instruction converts the pointer value
6329 ``ptrval`` to type ``pty2``. It can be a *no-op cast* or a complex
6330 value modification, depending on the target and the address space
6331 pair. Pointer conversions within the same address space must be
6332 performed with the ``bitcast`` instruction. Note that if the address space
6333 conversion is legal then both result and operand refer to the same memory
6339 .. code-block:: llvm
6341 %X = addrspacecast i32* %x to i32 addrspace(1)* ; yields i32 addrspace(1)*:%x
6342 %Y = addrspacecast i32 addrspace(1)* %y to i64 addrspace(2)* ; yields i64 addrspace(2)*:%y
6343 %Z = addrspacecast <4 x i32*> %z to <4 x float addrspace(3)*> ; yields <4 x float addrspace(3)*>:%z
6350 The instructions in this category are the "miscellaneous" instructions,
6351 which defy better classification.
6355 '``icmp``' Instruction
6356 ^^^^^^^^^^^^^^^^^^^^^^
6363 <result> = icmp <cond> <ty> <op1>, <op2> ; yields i1 or <N x i1>:result
6368 The '``icmp``' instruction returns a boolean value or a vector of
6369 boolean values based on comparison of its two integer, integer vector,
6370 pointer, or pointer vector operands.
6375 The '``icmp``' instruction takes three operands. The first operand is
6376 the condition code indicating the kind of comparison to perform. It is
6377 not a value, just a keyword. The possible condition code are:
6380 #. ``ne``: not equal
6381 #. ``ugt``: unsigned greater than
6382 #. ``uge``: unsigned greater or equal
6383 #. ``ult``: unsigned less than
6384 #. ``ule``: unsigned less or equal
6385 #. ``sgt``: signed greater than
6386 #. ``sge``: signed greater or equal
6387 #. ``slt``: signed less than
6388 #. ``sle``: signed less or equal
6390 The remaining two arguments must be :ref:`integer <t_integer>` or
6391 :ref:`pointer <t_pointer>` or integer :ref:`vector <t_vector>` typed. They
6392 must also be identical types.
6397 The '``icmp``' compares ``op1`` and ``op2`` according to the condition
6398 code given as ``cond``. The comparison performed always yields either an
6399 :ref:`i1 <t_integer>` or vector of ``i1`` result, as follows:
6401 #. ``eq``: yields ``true`` if the operands are equal, ``false``
6402 otherwise. No sign interpretation is necessary or performed.
6403 #. ``ne``: yields ``true`` if the operands are unequal, ``false``
6404 otherwise. No sign interpretation is necessary or performed.
6405 #. ``ugt``: interprets the operands as unsigned values and yields
6406 ``true`` if ``op1`` is greater than ``op2``.
6407 #. ``uge``: interprets the operands as unsigned values and yields
6408 ``true`` if ``op1`` is greater than or equal to ``op2``.
6409 #. ``ult``: interprets the operands as unsigned values and yields
6410 ``true`` if ``op1`` is less than ``op2``.
6411 #. ``ule``: interprets the operands as unsigned values and yields
6412 ``true`` if ``op1`` is less than or equal to ``op2``.
6413 #. ``sgt``: interprets the operands as signed values and yields ``true``
6414 if ``op1`` is greater than ``op2``.
6415 #. ``sge``: interprets the operands as signed values and yields ``true``
6416 if ``op1`` is greater than or equal to ``op2``.
6417 #. ``slt``: interprets the operands as signed values and yields ``true``
6418 if ``op1`` is less than ``op2``.
6419 #. ``sle``: interprets the operands as signed values and yields ``true``
6420 if ``op1`` is less than or equal to ``op2``.
6422 If the operands are :ref:`pointer <t_pointer>` typed, the pointer values
6423 are compared as if they were integers.
6425 If the operands are integer vectors, then they are compared element by
6426 element. The result is an ``i1`` vector with the same number of elements
6427 as the values being compared. Otherwise, the result is an ``i1``.
6432 .. code-block:: llvm
6434 <result> = icmp eq i32 4, 5 ; yields: result=false
6435 <result> = icmp ne float* %X, %X ; yields: result=false
6436 <result> = icmp ult i16 4, 5 ; yields: result=true
6437 <result> = icmp sgt i16 4, 5 ; yields: result=false
6438 <result> = icmp ule i16 -4, 5 ; yields: result=false
6439 <result> = icmp sge i16 4, 5 ; yields: result=false
6441 Note that the code generator does not yet support vector types with the
6442 ``icmp`` instruction.
6446 '``fcmp``' Instruction
6447 ^^^^^^^^^^^^^^^^^^^^^^
6454 <result> = fcmp <cond> <ty> <op1>, <op2> ; yields i1 or <N x i1>:result
6459 The '``fcmp``' instruction returns a boolean value or vector of boolean
6460 values based on comparison of its operands.
6462 If the operands are floating point scalars, then the result type is a
6463 boolean (:ref:`i1 <t_integer>`).
6465 If the operands are floating point vectors, then the result type is a
6466 vector of boolean with the same number of elements as the operands being
6472 The '``fcmp``' instruction takes three operands. The first operand is
6473 the condition code indicating the kind of comparison to perform. It is
6474 not a value, just a keyword. The possible condition code are:
6476 #. ``false``: no comparison, always returns false
6477 #. ``oeq``: ordered and equal
6478 #. ``ogt``: ordered and greater than
6479 #. ``oge``: ordered and greater than or equal
6480 #. ``olt``: ordered and less than
6481 #. ``ole``: ordered and less than or equal
6482 #. ``one``: ordered and not equal
6483 #. ``ord``: ordered (no nans)
6484 #. ``ueq``: unordered or equal
6485 #. ``ugt``: unordered or greater than
6486 #. ``uge``: unordered or greater than or equal
6487 #. ``ult``: unordered or less than
6488 #. ``ule``: unordered or less than or equal
6489 #. ``une``: unordered or not equal
6490 #. ``uno``: unordered (either nans)
6491 #. ``true``: no comparison, always returns true
6493 *Ordered* means that neither operand is a QNAN while *unordered* means
6494 that either operand may be a QNAN.
6496 Each of ``val1`` and ``val2`` arguments must be either a :ref:`floating
6497 point <t_floating>` type or a :ref:`vector <t_vector>` of floating point
6498 type. They must have identical types.
6503 The '``fcmp``' instruction compares ``op1`` and ``op2`` according to the
6504 condition code given as ``cond``. If the operands are vectors, then the
6505 vectors are compared element by element. Each comparison performed
6506 always yields an :ref:`i1 <t_integer>` result, as follows:
6508 #. ``false``: always yields ``false``, regardless of operands.
6509 #. ``oeq``: yields ``true`` if both operands are not a QNAN and ``op1``
6510 is equal to ``op2``.
6511 #. ``ogt``: yields ``true`` if both operands are not a QNAN and ``op1``
6512 is greater than ``op2``.
6513 #. ``oge``: yields ``true`` if both operands are not a QNAN and ``op1``
6514 is greater than or equal to ``op2``.
6515 #. ``olt``: yields ``true`` if both operands are not a QNAN and ``op1``
6516 is less than ``op2``.
6517 #. ``ole``: yields ``true`` if both operands are not a QNAN and ``op1``
6518 is less than or equal to ``op2``.
6519 #. ``one``: yields ``true`` if both operands are not a QNAN and ``op1``
6520 is not equal to ``op2``.
6521 #. ``ord``: yields ``true`` if both operands are not a QNAN.
6522 #. ``ueq``: yields ``true`` if either operand is a QNAN or ``op1`` is
6524 #. ``ugt``: yields ``true`` if either operand is a QNAN or ``op1`` is
6525 greater than ``op2``.
6526 #. ``uge``: yields ``true`` if either operand is a QNAN or ``op1`` is
6527 greater than or equal to ``op2``.
6528 #. ``ult``: yields ``true`` if either operand is a QNAN or ``op1`` is
6530 #. ``ule``: yields ``true`` if either operand is a QNAN or ``op1`` is
6531 less than or equal to ``op2``.
6532 #. ``une``: yields ``true`` if either operand is a QNAN or ``op1`` is
6533 not equal to ``op2``.
6534 #. ``uno``: yields ``true`` if either operand is a QNAN.
6535 #. ``true``: always yields ``true``, regardless of operands.
6540 .. code-block:: llvm
6542 <result> = fcmp oeq float 4.0, 5.0 ; yields: result=false
6543 <result> = fcmp one float 4.0, 5.0 ; yields: result=true
6544 <result> = fcmp olt float 4.0, 5.0 ; yields: result=true
6545 <result> = fcmp ueq double 1.0, 2.0 ; yields: result=false
6547 Note that the code generator does not yet support vector types with the
6548 ``fcmp`` instruction.
6552 '``phi``' Instruction
6553 ^^^^^^^^^^^^^^^^^^^^^
6560 <result> = phi <ty> [ <val0>, <label0>], ...
6565 The '``phi``' instruction is used to implement the φ node in the SSA
6566 graph representing the function.
6571 The type of the incoming values is specified with the first type field.
6572 After this, the '``phi``' instruction takes a list of pairs as
6573 arguments, with one pair for each predecessor basic block of the current
6574 block. Only values of :ref:`first class <t_firstclass>` type may be used as
6575 the value arguments to the PHI node. Only labels may be used as the
6578 There must be no non-phi instructions between the start of a basic block
6579 and the PHI instructions: i.e. PHI instructions must be first in a basic
6582 For the purposes of the SSA form, the use of each incoming value is
6583 deemed to occur on the edge from the corresponding predecessor block to
6584 the current block (but after any definition of an '``invoke``'
6585 instruction's return value on the same edge).
6590 At runtime, the '``phi``' instruction logically takes on the value
6591 specified by the pair corresponding to the predecessor basic block that
6592 executed just prior to the current block.
6597 .. code-block:: llvm
6599 Loop: ; Infinite loop that counts from 0 on up...
6600 %indvar = phi i32 [ 0, %LoopHeader ], [ %nextindvar, %Loop ]
6601 %nextindvar = add i32 %indvar, 1
6606 '``select``' Instruction
6607 ^^^^^^^^^^^^^^^^^^^^^^^^
6614 <result> = select selty <cond>, <ty> <val1>, <ty> <val2> ; yields ty
6616 selty is either i1 or {<N x i1>}
6621 The '``select``' instruction is used to choose one value based on a
6622 condition, without IR-level branching.
6627 The '``select``' instruction requires an 'i1' value or a vector of 'i1'
6628 values indicating the condition, and two values of the same :ref:`first
6629 class <t_firstclass>` type. If the val1/val2 are vectors and the
6630 condition is a scalar, then entire vectors are selected, not individual
6636 If the condition is an i1 and it evaluates to 1, the instruction returns
6637 the first value argument; otherwise, it returns the second value
6640 If the condition is a vector of i1, then the value arguments must be
6641 vectors of the same size, and the selection is done element by element.
6646 .. code-block:: llvm
6648 %X = select i1 true, i8 17, i8 42 ; yields i8:17
6652 '``call``' Instruction
6653 ^^^^^^^^^^^^^^^^^^^^^^
6660 <result> = [tail | musttail] call [cconv] [ret attrs] <ty> [<fnty>*] <fnptrval>(<function args>) [fn attrs]
6665 The '``call``' instruction represents a simple function call.
6670 This instruction requires several arguments:
6672 #. The optional ``tail`` and ``musttail`` markers indicate that the optimizers
6673 should perform tail call optimization. The ``tail`` marker is a hint that
6674 `can be ignored <CodeGenerator.html#sibcallopt>`_. The ``musttail`` marker
6675 means that the call must be tail call optimized in order for the program to
6676 be correct. The ``musttail`` marker provides these guarantees:
6678 #. The call will not cause unbounded stack growth if it is part of a
6679 recursive cycle in the call graph.
6680 #. Arguments with the :ref:`inalloca <attr_inalloca>` attribute are
6683 Both markers imply that the callee does not access allocas or varargs from
6684 the caller. Calls marked ``musttail`` must obey the following additional
6687 - The call must immediately precede a :ref:`ret <i_ret>` instruction,
6688 or a pointer bitcast followed by a ret instruction.
6689 - The ret instruction must return the (possibly bitcasted) value
6690 produced by the call or void.
6691 - The caller and callee prototypes must match. Pointer types of
6692 parameters or return types may differ in pointee type, but not
6694 - The calling conventions of the caller and callee must match.
6695 - All ABI-impacting function attributes, such as sret, byval, inreg,
6696 returned, and inalloca, must match.
6697 - The callee must be varargs iff the caller is varargs. Bitcasting a
6698 non-varargs function to the appropriate varargs type is legal so
6699 long as the non-varargs prefixes obey the other rules.
6701 Tail call optimization for calls marked ``tail`` is guaranteed to occur if
6702 the following conditions are met:
6704 - Caller and callee both have the calling convention ``fastcc``.
6705 - The call is in tail position (ret immediately follows call and ret
6706 uses value of call or is void).
6707 - Option ``-tailcallopt`` is enabled, or
6708 ``llvm::GuaranteedTailCallOpt`` is ``true``.
6709 - `Platform-specific constraints are
6710 met. <CodeGenerator.html#tailcallopt>`_
6712 #. The optional "cconv" marker indicates which :ref:`calling
6713 convention <callingconv>` the call should use. If none is
6714 specified, the call defaults to using C calling conventions. The
6715 calling convention of the call must match the calling convention of
6716 the target function, or else the behavior is undefined.
6717 #. The optional :ref:`Parameter Attributes <paramattrs>` list for return
6718 values. Only '``zeroext``', '``signext``', and '``inreg``' attributes
6720 #. '``ty``': the type of the call instruction itself which is also the
6721 type of the return value. Functions that return no value are marked
6723 #. '``fnty``': shall be the signature of the pointer to function value
6724 being invoked. The argument types must match the types implied by
6725 this signature. This type can be omitted if the function is not
6726 varargs and if the function type does not return a pointer to a
6728 #. '``fnptrval``': An LLVM value containing a pointer to a function to
6729 be invoked. In most cases, this is a direct function invocation, but
6730 indirect ``call``'s are just as possible, calling an arbitrary pointer
6732 #. '``function args``': argument list whose types match the function
6733 signature argument types and parameter attributes. All arguments must
6734 be of :ref:`first class <t_firstclass>` type. If the function signature
6735 indicates the function accepts a variable number of arguments, the
6736 extra arguments can be specified.
6737 #. The optional :ref:`function attributes <fnattrs>` list. Only
6738 '``noreturn``', '``nounwind``', '``readonly``' and '``readnone``'
6739 attributes are valid here.
6744 The '``call``' instruction is used to cause control flow to transfer to
6745 a specified function, with its incoming arguments bound to the specified
6746 values. Upon a '``ret``' instruction in the called function, control
6747 flow continues with the instruction after the function call, and the
6748 return value of the function is bound to the result argument.
6753 .. code-block:: llvm
6755 %retval = call i32 @test(i32 %argc)
6756 call i32 (i8*, ...)* @printf(i8* %msg, i32 12, i8 42) ; yields i32
6757 %X = tail call i32 @foo() ; yields i32
6758 %Y = tail call fastcc i32 @foo() ; yields i32
6759 call void %foo(i8 97 signext)
6761 %struct.A = type { i32, i8 }
6762 %r = call %struct.A @foo() ; yields { i32, i8 }
6763 %gr = extractvalue %struct.A %r, 0 ; yields i32
6764 %gr1 = extractvalue %struct.A %r, 1 ; yields i8
6765 %Z = call void @foo() noreturn ; indicates that %foo never returns normally
6766 %ZZ = call zeroext i32 @bar() ; Return value is %zero extended
6768 llvm treats calls to some functions with names and arguments that match
6769 the standard C99 library as being the C99 library functions, and may
6770 perform optimizations or generate code for them under that assumption.
6771 This is something we'd like to change in the future to provide better
6772 support for freestanding environments and non-C-based languages.
6776 '``va_arg``' Instruction
6777 ^^^^^^^^^^^^^^^^^^^^^^^^
6784 <resultval> = va_arg <va_list*> <arglist>, <argty>
6789 The '``va_arg``' instruction is used to access arguments passed through
6790 the "variable argument" area of a function call. It is used to implement
6791 the ``va_arg`` macro in C.
6796 This instruction takes a ``va_list*`` value and the type of the
6797 argument. It returns a value of the specified argument type and
6798 increments the ``va_list`` to point to the next argument. The actual
6799 type of ``va_list`` is target specific.
6804 The '``va_arg``' instruction loads an argument of the specified type
6805 from the specified ``va_list`` and causes the ``va_list`` to point to
6806 the next argument. For more information, see the variable argument
6807 handling :ref:`Intrinsic Functions <int_varargs>`.
6809 It is legal for this instruction to be called in a function which does
6810 not take a variable number of arguments, for example, the ``vfprintf``
6813 ``va_arg`` is an LLVM instruction instead of an :ref:`intrinsic
6814 function <intrinsics>` because it takes a type as an argument.
6819 See the :ref:`variable argument processing <int_varargs>` section.
6821 Note that the code generator does not yet fully support va\_arg on many
6822 targets. Also, it does not currently support va\_arg with aggregate
6823 types on any target.
6827 '``landingpad``' Instruction
6828 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6835 <resultval> = landingpad <resultty> personality <type> <pers_fn> <clause>+
6836 <resultval> = landingpad <resultty> personality <type> <pers_fn> cleanup <clause>*
6838 <clause> := catch <type> <value>
6839 <clause> := filter <array constant type> <array constant>
6844 The '``landingpad``' instruction is used by `LLVM's exception handling
6845 system <ExceptionHandling.html#overview>`_ to specify that a basic block
6846 is a landing pad --- one where the exception lands, and corresponds to the
6847 code found in the ``catch`` portion of a ``try``/``catch`` sequence. It
6848 defines values supplied by the personality function (``pers_fn``) upon
6849 re-entry to the function. The ``resultval`` has the type ``resultty``.
6854 This instruction takes a ``pers_fn`` value. This is the personality
6855 function associated with the unwinding mechanism. The optional
6856 ``cleanup`` flag indicates that the landing pad block is a cleanup.
6858 A ``clause`` begins with the clause type --- ``catch`` or ``filter`` --- and
6859 contains the global variable representing the "type" that may be caught
6860 or filtered respectively. Unlike the ``catch`` clause, the ``filter``
6861 clause takes an array constant as its argument. Use
6862 "``[0 x i8**] undef``" for a filter which cannot throw. The
6863 '``landingpad``' instruction must contain *at least* one ``clause`` or
6864 the ``cleanup`` flag.
6869 The '``landingpad``' instruction defines the values which are set by the
6870 personality function (``pers_fn``) upon re-entry to the function, and
6871 therefore the "result type" of the ``landingpad`` instruction. As with
6872 calling conventions, how the personality function results are
6873 represented in LLVM IR is target specific.
6875 The clauses are applied in order from top to bottom. If two
6876 ``landingpad`` instructions are merged together through inlining, the
6877 clauses from the calling function are appended to the list of clauses.
6878 When the call stack is being unwound due to an exception being thrown,
6879 the exception is compared against each ``clause`` in turn. If it doesn't
6880 match any of the clauses, and the ``cleanup`` flag is not set, then
6881 unwinding continues further up the call stack.
6883 The ``landingpad`` instruction has several restrictions:
6885 - A landing pad block is a basic block which is the unwind destination
6886 of an '``invoke``' instruction.
6887 - A landing pad block must have a '``landingpad``' instruction as its
6888 first non-PHI instruction.
6889 - There can be only one '``landingpad``' instruction within the landing
6891 - A basic block that is not a landing pad block may not include a
6892 '``landingpad``' instruction.
6893 - All '``landingpad``' instructions in a function must have the same
6894 personality function.
6899 .. code-block:: llvm
6901 ;; A landing pad which can catch an integer.
6902 %res = landingpad { i8*, i32 } personality i32 (...)* @__gxx_personality_v0
6904 ;; A landing pad that is a cleanup.
6905 %res = landingpad { i8*, i32 } personality i32 (...)* @__gxx_personality_v0
6907 ;; A landing pad which can catch an integer and can only throw a double.
6908 %res = landingpad { i8*, i32 } personality i32 (...)* @__gxx_personality_v0
6910 filter [1 x i8**] [@_ZTId]
6917 LLVM supports the notion of an "intrinsic function". These functions
6918 have well known names and semantics and are required to follow certain
6919 restrictions. Overall, these intrinsics represent an extension mechanism
6920 for the LLVM language that does not require changing all of the
6921 transformations in LLVM when adding to the language (or the bitcode
6922 reader/writer, the parser, etc...).
6924 Intrinsic function names must all start with an "``llvm.``" prefix. This
6925 prefix is reserved in LLVM for intrinsic names; thus, function names may
6926 not begin with this prefix. Intrinsic functions must always be external
6927 functions: you cannot define the body of intrinsic functions. Intrinsic
6928 functions may only be used in call or invoke instructions: it is illegal
6929 to take the address of an intrinsic function. Additionally, because
6930 intrinsic functions are part of the LLVM language, it is required if any
6931 are added that they be documented here.
6933 Some intrinsic functions can be overloaded, i.e., the intrinsic
6934 represents a family of functions that perform the same operation but on
6935 different data types. Because LLVM can represent over 8 million
6936 different integer types, overloading is used commonly to allow an
6937 intrinsic function to operate on any integer type. One or more of the
6938 argument types or the result type can be overloaded to accept any
6939 integer type. Argument types may also be defined as exactly matching a
6940 previous argument's type or the result type. This allows an intrinsic
6941 function which accepts multiple arguments, but needs all of them to be
6942 of the same type, to only be overloaded with respect to a single
6943 argument or the result.
6945 Overloaded intrinsics will have the names of its overloaded argument
6946 types encoded into its function name, each preceded by a period. Only
6947 those types which are overloaded result in a name suffix. Arguments
6948 whose type is matched against another type do not. For example, the
6949 ``llvm.ctpop`` function can take an integer of any width and returns an
6950 integer of exactly the same integer width. This leads to a family of
6951 functions such as ``i8 @llvm.ctpop.i8(i8 %val)`` and
6952 ``i29 @llvm.ctpop.i29(i29 %val)``. Only one type, the return type, is
6953 overloaded, and only one type suffix is required. Because the argument's
6954 type is matched against the return type, it does not require its own
6957 To learn how to add an intrinsic function, please see the `Extending
6958 LLVM Guide <ExtendingLLVM.html>`_.
6962 Variable Argument Handling Intrinsics
6963 -------------------------------------
6965 Variable argument support is defined in LLVM with the
6966 :ref:`va_arg <i_va_arg>` instruction and these three intrinsic
6967 functions. These functions are related to the similarly named macros
6968 defined in the ``<stdarg.h>`` header file.
6970 All of these functions operate on arguments that use a target-specific
6971 value type "``va_list``". The LLVM assembly language reference manual
6972 does not define what this type is, so all transformations should be
6973 prepared to handle these functions regardless of the type used.
6975 This example shows how the :ref:`va_arg <i_va_arg>` instruction and the
6976 variable argument handling intrinsic functions are used.
6978 .. code-block:: llvm
6980 ; This struct is different for every platform. For most platforms,
6981 ; it is merely an i8*.
6982 %struct.va_list = type { i8* }
6984 ; For Unix x86_64 platforms, va_list is the following struct:
6985 ; %struct.va_list = type { i32, i32, i8*, i8* }
6987 define i32 @test(i32 %X, ...) {
6988 ; Initialize variable argument processing
6989 %ap = alloca %struct.va_list
6990 %ap2 = bitcast %struct.va_list* %ap to i8*
6991 call void @llvm.va_start(i8* %ap2)
6993 ; Read a single integer argument
6994 %tmp = va_arg i8* %ap2, i32
6996 ; Demonstrate usage of llvm.va_copy and llvm.va_end
6998 %aq2 = bitcast i8** %aq to i8*
6999 call void @llvm.va_copy(i8* %aq2, i8* %ap2)
7000 call void @llvm.va_end(i8* %aq2)
7002 ; Stop processing of arguments.
7003 call void @llvm.va_end(i8* %ap2)
7007 declare void @llvm.va_start(i8*)
7008 declare void @llvm.va_copy(i8*, i8*)
7009 declare void @llvm.va_end(i8*)
7013 '``llvm.va_start``' Intrinsic
7014 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7021 declare void @llvm.va_start(i8* <arglist>)
7026 The '``llvm.va_start``' intrinsic initializes ``*<arglist>`` for
7027 subsequent use by ``va_arg``.
7032 The argument is a pointer to a ``va_list`` element to initialize.
7037 The '``llvm.va_start``' intrinsic works just like the ``va_start`` macro
7038 available in C. In a target-dependent way, it initializes the
7039 ``va_list`` element to which the argument points, so that the next call
7040 to ``va_arg`` will produce the first variable argument passed to the
7041 function. Unlike the C ``va_start`` macro, this intrinsic does not need
7042 to know the last argument of the function as the compiler can figure
7045 '``llvm.va_end``' Intrinsic
7046 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
7053 declare void @llvm.va_end(i8* <arglist>)
7058 The '``llvm.va_end``' intrinsic destroys ``*<arglist>``, which has been
7059 initialized previously with ``llvm.va_start`` or ``llvm.va_copy``.
7064 The argument is a pointer to a ``va_list`` to destroy.
7069 The '``llvm.va_end``' intrinsic works just like the ``va_end`` macro
7070 available in C. In a target-dependent way, it destroys the ``va_list``
7071 element to which the argument points. Calls to
7072 :ref:`llvm.va_start <int_va_start>` and
7073 :ref:`llvm.va_copy <int_va_copy>` must be matched exactly with calls to
7078 '``llvm.va_copy``' Intrinsic
7079 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7086 declare void @llvm.va_copy(i8* <destarglist>, i8* <srcarglist>)
7091 The '``llvm.va_copy``' intrinsic copies the current argument position
7092 from the source argument list to the destination argument list.
7097 The first argument is a pointer to a ``va_list`` element to initialize.
7098 The second argument is a pointer to a ``va_list`` element to copy from.
7103 The '``llvm.va_copy``' intrinsic works just like the ``va_copy`` macro
7104 available in C. In a target-dependent way, it copies the source
7105 ``va_list`` element into the destination ``va_list`` element. This
7106 intrinsic is necessary because the `` llvm.va_start`` intrinsic may be
7107 arbitrarily complex and require, for example, memory allocation.
7109 Accurate Garbage Collection Intrinsics
7110 --------------------------------------
7112 LLVM's support for `Accurate Garbage Collection <GarbageCollection.html>`_
7113 (GC) requires the frontend to generate code containing appropriate intrinsic
7114 calls and select an appropriate GC strategy which knows how to lower these
7115 intrinsics in a manner which is appropriate for the target collector.
7117 These intrinsics allow identification of :ref:`GC roots on the
7118 stack <int_gcroot>`, as well as garbage collector implementations that
7119 require :ref:`read <int_gcread>` and :ref:`write <int_gcwrite>` barriers.
7120 Frontends for type-safe garbage collected languages should generate
7121 these intrinsics to make use of the LLVM garbage collectors. For more
7122 details, see `Garbage Collection with LLVM <GarbageCollection.html>`_.
7124 Experimental Statepoint Intrinsics
7125 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7127 LLVM provides an second experimental set of intrinsics for describing garbage
7128 collection safepoints in compiled code. These intrinsics are an alternative
7129 to the ``llvm.gcroot`` intrinsics, but are compatible with the ones for
7130 :ref:`read <int_gcread>` and :ref:`write <int_gcwrite>` barriers. The
7131 differences in approach are covered in the `Garbage Collection with LLVM
7132 <GarbageCollection.html>`_ documentation. The intrinsics themselves are
7133 described in :doc:`Statepoints`.
7137 '``llvm.gcroot``' Intrinsic
7138 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
7145 declare void @llvm.gcroot(i8** %ptrloc, i8* %metadata)
7150 The '``llvm.gcroot``' intrinsic declares the existence of a GC root to
7151 the code generator, and allows some metadata to be associated with it.
7156 The first argument specifies the address of a stack object that contains
7157 the root pointer. The second pointer (which must be either a constant or
7158 a global value address) contains the meta-data to be associated with the
7164 At runtime, a call to this intrinsic stores a null pointer into the
7165 "ptrloc" location. At compile-time, the code generator generates
7166 information to allow the runtime to find the pointer at GC safe points.
7167 The '``llvm.gcroot``' intrinsic may only be used in a function which
7168 :ref:`specifies a GC algorithm <gc>`.
7172 '``llvm.gcread``' Intrinsic
7173 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
7180 declare i8* @llvm.gcread(i8* %ObjPtr, i8** %Ptr)
7185 The '``llvm.gcread``' intrinsic identifies reads of references from heap
7186 locations, allowing garbage collector implementations that require read
7192 The second argument is the address to read from, which should be an
7193 address allocated from the garbage collector. The first object is a
7194 pointer to the start of the referenced object, if needed by the language
7195 runtime (otherwise null).
7200 The '``llvm.gcread``' intrinsic has the same semantics as a load
7201 instruction, but may be replaced with substantially more complex code by
7202 the garbage collector runtime, as needed. The '``llvm.gcread``'
7203 intrinsic may only be used in a function which :ref:`specifies a GC
7208 '``llvm.gcwrite``' Intrinsic
7209 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7216 declare void @llvm.gcwrite(i8* %P1, i8* %Obj, i8** %P2)
7221 The '``llvm.gcwrite``' intrinsic identifies writes of references to heap
7222 locations, allowing garbage collector implementations that require write
7223 barriers (such as generational or reference counting collectors).
7228 The first argument is the reference to store, the second is the start of
7229 the object to store it to, and the third is the address of the field of
7230 Obj to store to. If the runtime does not require a pointer to the
7231 object, Obj may be null.
7236 The '``llvm.gcwrite``' intrinsic has the same semantics as a store
7237 instruction, but may be replaced with substantially more complex code by
7238 the garbage collector runtime, as needed. The '``llvm.gcwrite``'
7239 intrinsic may only be used in a function which :ref:`specifies a GC
7242 Code Generator Intrinsics
7243 -------------------------
7245 These intrinsics are provided by LLVM to expose special features that
7246 may only be implemented with code generator support.
7248 '``llvm.returnaddress``' Intrinsic
7249 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7256 declare i8 *@llvm.returnaddress(i32 <level>)
7261 The '``llvm.returnaddress``' intrinsic attempts to compute a
7262 target-specific value indicating the return address of the current
7263 function or one of its callers.
7268 The argument to this intrinsic indicates which function to return the
7269 address for. Zero indicates the calling function, one indicates its
7270 caller, etc. The argument is **required** to be a constant integer
7276 The '``llvm.returnaddress``' intrinsic either returns a pointer
7277 indicating the return address of the specified call frame, or zero if it
7278 cannot be identified. The value returned by this intrinsic is likely to
7279 be incorrect or 0 for arguments other than zero, so it should only be
7280 used for debugging purposes.
7282 Note that calling this intrinsic does not prevent function inlining or
7283 other aggressive transformations, so the value returned may not be that
7284 of the obvious source-language caller.
7286 '``llvm.frameaddress``' Intrinsic
7287 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7294 declare i8* @llvm.frameaddress(i32 <level>)
7299 The '``llvm.frameaddress``' intrinsic attempts to return the
7300 target-specific frame pointer value for the specified stack frame.
7305 The argument to this intrinsic indicates which function to return the
7306 frame pointer for. Zero indicates the calling function, one indicates
7307 its caller, etc. The argument is **required** to be a constant integer
7313 The '``llvm.frameaddress``' intrinsic either returns a pointer
7314 indicating the frame address of the specified call frame, or zero if it
7315 cannot be identified. The value returned by this intrinsic is likely to
7316 be incorrect or 0 for arguments other than zero, so it should only be
7317 used for debugging purposes.
7319 Note that calling this intrinsic does not prevent function inlining or
7320 other aggressive transformations, so the value returned may not be that
7321 of the obvious source-language caller.
7323 '``llvm.frameallocate``' and '``llvm.framerecover``' Intrinsics
7324 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7331 declare i8* @llvm.frameallocate(i32 %size)
7332 declare i8* @llvm.framerecover(i8* %func, i8* %fp)
7337 The '``llvm.frameallocate``' intrinsic allocates stack memory at some fixed
7338 offset from the frame pointer, and the '``llvm.framerecover``'
7339 intrinsic applies that offset to a live frame pointer to recover the address of
7340 the allocation. The offset is computed during frame layout of the caller of
7341 ``llvm.frameallocate``.
7346 The ``size`` argument to '``llvm.frameallocate``' must be a constant integer
7347 indicating the amount of stack memory to allocate. As with allocas, allocating
7348 zero bytes is legal, but the result is undefined.
7350 The ``func`` argument to '``llvm.framerecover``' must be a constant
7351 bitcasted pointer to a function defined in the current module. The code
7352 generator cannot determine the frame allocation offset of functions defined in
7355 The ``fp`` argument to '``llvm.framerecover``' must be a frame
7356 pointer of a call frame that is currently live. The return value of
7357 '``llvm.frameaddress``' is one way to produce such a value, but most platforms
7358 also expose the frame pointer through stack unwinding mechanisms.
7363 These intrinsics allow a group of functions to access one stack memory
7364 allocation in an ancestor stack frame. The memory returned from
7365 '``llvm.frameallocate``' may be allocated prior to stack realignment, so the
7366 memory is only aligned to the ABI-required stack alignment. Each function may
7367 only call '``llvm.frameallocate``' one or zero times from the function entry
7368 block. The frame allocation intrinsic inhibits inlining, as any frame
7369 allocations in the inlined function frame are likely to be at a different
7370 offset from the one used by '``llvm.framerecover``' called with the
7373 .. _int_read_register:
7374 .. _int_write_register:
7376 '``llvm.read_register``' and '``llvm.write_register``' Intrinsics
7377 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7384 declare i32 @llvm.read_register.i32(metadata)
7385 declare i64 @llvm.read_register.i64(metadata)
7386 declare void @llvm.write_register.i32(metadata, i32 @value)
7387 declare void @llvm.write_register.i64(metadata, i64 @value)
7393 The '``llvm.read_register``' and '``llvm.write_register``' intrinsics
7394 provides access to the named register. The register must be valid on
7395 the architecture being compiled to. The type needs to be compatible
7396 with the register being read.
7401 The '``llvm.read_register``' intrinsic returns the current value of the
7402 register, where possible. The '``llvm.write_register``' intrinsic sets
7403 the current value of the register, where possible.
7405 This is useful to implement named register global variables that need
7406 to always be mapped to a specific register, as is common practice on
7407 bare-metal programs including OS kernels.
7409 The compiler doesn't check for register availability or use of the used
7410 register in surrounding code, including inline assembly. Because of that,
7411 allocatable registers are not supported.
7413 Warning: So far it only works with the stack pointer on selected
7414 architectures (ARM, AArch64, PowerPC and x86_64). Significant amount of
7415 work is needed to support other registers and even more so, allocatable
7420 '``llvm.stacksave``' Intrinsic
7421 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7428 declare i8* @llvm.stacksave()
7433 The '``llvm.stacksave``' intrinsic is used to remember the current state
7434 of the function stack, for use with
7435 :ref:`llvm.stackrestore <int_stackrestore>`. This is useful for
7436 implementing language features like scoped automatic variable sized
7442 This intrinsic returns a opaque pointer value that can be passed to
7443 :ref:`llvm.stackrestore <int_stackrestore>`. When an
7444 ``llvm.stackrestore`` intrinsic is executed with a value saved from
7445 ``llvm.stacksave``, it effectively restores the state of the stack to
7446 the state it was in when the ``llvm.stacksave`` intrinsic executed. In
7447 practice, this pops any :ref:`alloca <i_alloca>` blocks from the stack that
7448 were allocated after the ``llvm.stacksave`` was executed.
7450 .. _int_stackrestore:
7452 '``llvm.stackrestore``' Intrinsic
7453 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7460 declare void @llvm.stackrestore(i8* %ptr)
7465 The '``llvm.stackrestore``' intrinsic is used to restore the state of
7466 the function stack to the state it was in when the corresponding
7467 :ref:`llvm.stacksave <int_stacksave>` intrinsic executed. This is
7468 useful for implementing language features like scoped automatic variable
7469 sized arrays in C99.
7474 See the description for :ref:`llvm.stacksave <int_stacksave>`.
7476 '``llvm.prefetch``' Intrinsic
7477 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7484 declare void @llvm.prefetch(i8* <address>, i32 <rw>, i32 <locality>, i32 <cache type>)
7489 The '``llvm.prefetch``' intrinsic is a hint to the code generator to
7490 insert a prefetch instruction if supported; otherwise, it is a noop.
7491 Prefetches have no effect on the behavior of the program but can change
7492 its performance characteristics.
7497 ``address`` is the address to be prefetched, ``rw`` is the specifier
7498 determining if the fetch should be for a read (0) or write (1), and
7499 ``locality`` is a temporal locality specifier ranging from (0) - no
7500 locality, to (3) - extremely local keep in cache. The ``cache type``
7501 specifies whether the prefetch is performed on the data (1) or
7502 instruction (0) cache. The ``rw``, ``locality`` and ``cache type``
7503 arguments must be constant integers.
7508 This intrinsic does not modify the behavior of the program. In
7509 particular, prefetches cannot trap and do not produce a value. On
7510 targets that support this intrinsic, the prefetch can provide hints to
7511 the processor cache for better performance.
7513 '``llvm.pcmarker``' Intrinsic
7514 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7521 declare void @llvm.pcmarker(i32 <id>)
7526 The '``llvm.pcmarker``' intrinsic is a method to export a Program
7527 Counter (PC) in a region of code to simulators and other tools. The
7528 method is target specific, but it is expected that the marker will use
7529 exported symbols to transmit the PC of the marker. The marker makes no
7530 guarantees that it will remain with any specific instruction after
7531 optimizations. It is possible that the presence of a marker will inhibit
7532 optimizations. The intended use is to be inserted after optimizations to
7533 allow correlations of simulation runs.
7538 ``id`` is a numerical id identifying the marker.
7543 This intrinsic does not modify the behavior of the program. Backends
7544 that do not support this intrinsic may ignore it.
7546 '``llvm.readcyclecounter``' Intrinsic
7547 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7554 declare i64 @llvm.readcyclecounter()
7559 The '``llvm.readcyclecounter``' intrinsic provides access to the cycle
7560 counter register (or similar low latency, high accuracy clocks) on those
7561 targets that support it. On X86, it should map to RDTSC. On Alpha, it
7562 should map to RPCC. As the backing counters overflow quickly (on the
7563 order of 9 seconds on alpha), this should only be used for small
7569 When directly supported, reading the cycle counter should not modify any
7570 memory. Implementations are allowed to either return a application
7571 specific value or a system wide value. On backends without support, this
7572 is lowered to a constant 0.
7574 Note that runtime support may be conditional on the privilege-level code is
7575 running at and the host platform.
7577 '``llvm.clear_cache``' Intrinsic
7578 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7585 declare void @llvm.clear_cache(i8*, i8*)
7590 The '``llvm.clear_cache``' intrinsic ensures visibility of modifications
7591 in the specified range to the execution unit of the processor. On
7592 targets with non-unified instruction and data cache, the implementation
7593 flushes the instruction cache.
7598 On platforms with coherent instruction and data caches (e.g. x86), this
7599 intrinsic is a nop. On platforms with non-coherent instruction and data
7600 cache (e.g. ARM, MIPS), the intrinsic is lowered either to appropriate
7601 instructions or a system call, if cache flushing requires special
7604 The default behavior is to emit a call to ``__clear_cache`` from the run
7607 This instrinsic does *not* empty the instruction pipeline. Modifications
7608 of the current function are outside the scope of the intrinsic.
7610 '``llvm.instrprof_increment``' Intrinsic
7611 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7618 declare void @llvm.instrprof_increment(i8* <name>, i64 <hash>,
7619 i32 <num-counters>, i32 <index>)
7624 The '``llvm.instrprof_increment``' intrinsic can be emitted by a
7625 frontend for use with instrumentation based profiling. These will be
7626 lowered by the ``-instrprof`` pass to generate execution counts of a
7632 The first argument is a pointer to a global variable containing the
7633 name of the entity being instrumented. This should generally be the
7634 (mangled) function name for a set of counters.
7636 The second argument is a hash value that can be used by the consumer
7637 of the profile data to detect changes to the instrumented source, and
7638 the third is the number of counters associated with ``name``. It is an
7639 error if ``hash`` or ``num-counters`` differ between two instances of
7640 ``instrprof_increment`` that refer to the same name.
7642 The last argument refers to which of the counters for ``name`` should
7643 be incremented. It should be a value between 0 and ``num-counters``.
7648 This intrinsic represents an increment of a profiling counter. It will
7649 cause the ``-instrprof`` pass to generate the appropriate data
7650 structures and the code to increment the appropriate value, in a
7651 format that can be written out by a compiler runtime and consumed via
7652 the ``llvm-profdata`` tool.
7654 Standard C Library Intrinsics
7655 -----------------------------
7657 LLVM provides intrinsics for a few important standard C library
7658 functions. These intrinsics allow source-language front-ends to pass
7659 information about the alignment of the pointer arguments to the code
7660 generator, providing opportunity for more efficient code generation.
7664 '``llvm.memcpy``' Intrinsic
7665 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
7670 This is an overloaded intrinsic. You can use ``llvm.memcpy`` on any
7671 integer bit width and for different address spaces. Not all targets
7672 support all bit widths however.
7676 declare void @llvm.memcpy.p0i8.p0i8.i32(i8* <dest>, i8* <src>,
7677 i32 <len>, i32 <align>, i1 <isvolatile>)
7678 declare void @llvm.memcpy.p0i8.p0i8.i64(i8* <dest>, i8* <src>,
7679 i64 <len>, i32 <align>, i1 <isvolatile>)
7684 The '``llvm.memcpy.*``' intrinsics copy a block of memory from the
7685 source location to the destination location.
7687 Note that, unlike the standard libc function, the ``llvm.memcpy.*``
7688 intrinsics do not return a value, takes extra alignment/isvolatile
7689 arguments and the pointers can be in specified address spaces.
7694 The first argument is a pointer to the destination, the second is a
7695 pointer to the source. The third argument is an integer argument
7696 specifying the number of bytes to copy, the fourth argument is the
7697 alignment of the source and destination locations, and the fifth is a
7698 boolean indicating a volatile access.
7700 If the call to this intrinsic has an alignment value that is not 0 or 1,
7701 then the caller guarantees that both the source and destination pointers
7702 are aligned to that boundary.
7704 If the ``isvolatile`` parameter is ``true``, the ``llvm.memcpy`` call is
7705 a :ref:`volatile operation <volatile>`. The detailed access behavior is not
7706 very cleanly specified and it is unwise to depend on it.
7711 The '``llvm.memcpy.*``' intrinsics copy a block of memory from the
7712 source location to the destination location, which are not allowed to
7713 overlap. It copies "len" bytes of memory over. If the argument is known
7714 to be aligned to some boundary, this can be specified as the fourth
7715 argument, otherwise it should be set to 0 or 1 (both meaning no alignment).
7717 '``llvm.memmove``' Intrinsic
7718 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7723 This is an overloaded intrinsic. You can use llvm.memmove on any integer
7724 bit width and for different address space. Not all targets support all
7729 declare void @llvm.memmove.p0i8.p0i8.i32(i8* <dest>, i8* <src>,
7730 i32 <len>, i32 <align>, i1 <isvolatile>)
7731 declare void @llvm.memmove.p0i8.p0i8.i64(i8* <dest>, i8* <src>,
7732 i64 <len>, i32 <align>, i1 <isvolatile>)
7737 The '``llvm.memmove.*``' intrinsics move a block of memory from the
7738 source location to the destination location. It is similar to the
7739 '``llvm.memcpy``' intrinsic but allows the two memory locations to
7742 Note that, unlike the standard libc function, the ``llvm.memmove.*``
7743 intrinsics do not return a value, takes extra alignment/isvolatile
7744 arguments and the pointers can be in specified address spaces.
7749 The first argument is a pointer to the destination, the second is a
7750 pointer to the source. The third argument is an integer argument
7751 specifying the number of bytes to copy, the fourth argument is the
7752 alignment of the source and destination locations, and the fifth is a
7753 boolean indicating a volatile access.
7755 If the call to this intrinsic has an alignment value that is not 0 or 1,
7756 then the caller guarantees that the source and destination pointers are
7757 aligned to that boundary.
7759 If the ``isvolatile`` parameter is ``true``, the ``llvm.memmove`` call
7760 is a :ref:`volatile operation <volatile>`. The detailed access behavior is
7761 not very cleanly specified and it is unwise to depend on it.
7766 The '``llvm.memmove.*``' intrinsics copy a block of memory from the
7767 source location to the destination location, which may overlap. It
7768 copies "len" bytes of memory over. If the argument is known to be
7769 aligned to some boundary, this can be specified as the fourth argument,
7770 otherwise it should be set to 0 or 1 (both meaning no alignment).
7772 '``llvm.memset.*``' Intrinsics
7773 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7778 This is an overloaded intrinsic. You can use llvm.memset on any integer
7779 bit width and for different address spaces. However, not all targets
7780 support all bit widths.
7784 declare void @llvm.memset.p0i8.i32(i8* <dest>, i8 <val>,
7785 i32 <len>, i32 <align>, i1 <isvolatile>)
7786 declare void @llvm.memset.p0i8.i64(i8* <dest>, i8 <val>,
7787 i64 <len>, i32 <align>, i1 <isvolatile>)
7792 The '``llvm.memset.*``' intrinsics fill a block of memory with a
7793 particular byte value.
7795 Note that, unlike the standard libc function, the ``llvm.memset``
7796 intrinsic does not return a value and takes extra alignment/volatile
7797 arguments. Also, the destination can be in an arbitrary address space.
7802 The first argument is a pointer to the destination to fill, the second
7803 is the byte value with which to fill it, the third argument is an
7804 integer argument specifying the number of bytes to fill, and the fourth
7805 argument is the known alignment of the destination location.
7807 If the call to this intrinsic has an alignment value that is not 0 or 1,
7808 then the caller guarantees that the destination pointer is aligned to
7811 If the ``isvolatile`` parameter is ``true``, the ``llvm.memset`` call is
7812 a :ref:`volatile operation <volatile>`. The detailed access behavior is not
7813 very cleanly specified and it is unwise to depend on it.
7818 The '``llvm.memset.*``' intrinsics fill "len" bytes of memory starting
7819 at the destination location. If the argument is known to be aligned to
7820 some boundary, this can be specified as the fourth argument, otherwise
7821 it should be set to 0 or 1 (both meaning no alignment).
7823 '``llvm.sqrt.*``' Intrinsic
7824 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
7829 This is an overloaded intrinsic. You can use ``llvm.sqrt`` on any
7830 floating point or vector of floating point type. Not all targets support
7835 declare float @llvm.sqrt.f32(float %Val)
7836 declare double @llvm.sqrt.f64(double %Val)
7837 declare x86_fp80 @llvm.sqrt.f80(x86_fp80 %Val)
7838 declare fp128 @llvm.sqrt.f128(fp128 %Val)
7839 declare ppc_fp128 @llvm.sqrt.ppcf128(ppc_fp128 %Val)
7844 The '``llvm.sqrt``' intrinsics return the sqrt of the specified operand,
7845 returning the same value as the libm '``sqrt``' functions would. Unlike
7846 ``sqrt`` in libm, however, ``llvm.sqrt`` has undefined behavior for
7847 negative numbers other than -0.0 (which allows for better optimization,
7848 because there is no need to worry about errno being set).
7849 ``llvm.sqrt(-0.0)`` is defined to return -0.0 like IEEE sqrt.
7854 The argument and return value are floating point numbers of the same
7860 This function returns the sqrt of the specified operand if it is a
7861 nonnegative floating point number.
7863 '``llvm.powi.*``' Intrinsic
7864 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
7869 This is an overloaded intrinsic. You can use ``llvm.powi`` on any
7870 floating point or vector of floating point type. Not all targets support
7875 declare float @llvm.powi.f32(float %Val, i32 %power)
7876 declare double @llvm.powi.f64(double %Val, i32 %power)
7877 declare x86_fp80 @llvm.powi.f80(x86_fp80 %Val, i32 %power)
7878 declare fp128 @llvm.powi.f128(fp128 %Val, i32 %power)
7879 declare ppc_fp128 @llvm.powi.ppcf128(ppc_fp128 %Val, i32 %power)
7884 The '``llvm.powi.*``' intrinsics return the first operand raised to the
7885 specified (positive or negative) power. The order of evaluation of
7886 multiplications is not defined. When a vector of floating point type is
7887 used, the second argument remains a scalar integer value.
7892 The second argument is an integer power, and the first is a value to
7893 raise to that power.
7898 This function returns the first value raised to the second power with an
7899 unspecified sequence of rounding operations.
7901 '``llvm.sin.*``' Intrinsic
7902 ^^^^^^^^^^^^^^^^^^^^^^^^^^
7907 This is an overloaded intrinsic. You can use ``llvm.sin`` on any
7908 floating point or vector of floating point type. Not all targets support
7913 declare float @llvm.sin.f32(float %Val)
7914 declare double @llvm.sin.f64(double %Val)
7915 declare x86_fp80 @llvm.sin.f80(x86_fp80 %Val)
7916 declare fp128 @llvm.sin.f128(fp128 %Val)
7917 declare ppc_fp128 @llvm.sin.ppcf128(ppc_fp128 %Val)
7922 The '``llvm.sin.*``' intrinsics return the sine of the operand.
7927 The argument and return value are floating point numbers of the same
7933 This function returns the sine of the specified operand, returning the
7934 same values as the libm ``sin`` functions would, and handles error
7935 conditions in the same way.
7937 '``llvm.cos.*``' Intrinsic
7938 ^^^^^^^^^^^^^^^^^^^^^^^^^^
7943 This is an overloaded intrinsic. You can use ``llvm.cos`` on any
7944 floating point or vector of floating point type. Not all targets support
7949 declare float @llvm.cos.f32(float %Val)
7950 declare double @llvm.cos.f64(double %Val)
7951 declare x86_fp80 @llvm.cos.f80(x86_fp80 %Val)
7952 declare fp128 @llvm.cos.f128(fp128 %Val)
7953 declare ppc_fp128 @llvm.cos.ppcf128(ppc_fp128 %Val)
7958 The '``llvm.cos.*``' intrinsics return the cosine of the operand.
7963 The argument and return value are floating point numbers of the same
7969 This function returns the cosine of the specified operand, returning the
7970 same values as the libm ``cos`` functions would, and handles error
7971 conditions in the same way.
7973 '``llvm.pow.*``' Intrinsic
7974 ^^^^^^^^^^^^^^^^^^^^^^^^^^
7979 This is an overloaded intrinsic. You can use ``llvm.pow`` on any
7980 floating point or vector of floating point type. Not all targets support
7985 declare float @llvm.pow.f32(float %Val, float %Power)
7986 declare double @llvm.pow.f64(double %Val, double %Power)
7987 declare x86_fp80 @llvm.pow.f80(x86_fp80 %Val, x86_fp80 %Power)
7988 declare fp128 @llvm.pow.f128(fp128 %Val, fp128 %Power)
7989 declare ppc_fp128 @llvm.pow.ppcf128(ppc_fp128 %Val, ppc_fp128 Power)
7994 The '``llvm.pow.*``' intrinsics return the first operand raised to the
7995 specified (positive or negative) power.
8000 The second argument is a floating point power, and the first is a value
8001 to raise to that power.
8006 This function returns the first value raised to the second power,
8007 returning the same values as the libm ``pow`` functions would, and
8008 handles error conditions in the same way.
8010 '``llvm.exp.*``' Intrinsic
8011 ^^^^^^^^^^^^^^^^^^^^^^^^^^
8016 This is an overloaded intrinsic. You can use ``llvm.exp`` on any
8017 floating point or vector of floating point type. Not all targets support
8022 declare float @llvm.exp.f32(float %Val)
8023 declare double @llvm.exp.f64(double %Val)
8024 declare x86_fp80 @llvm.exp.f80(x86_fp80 %Val)
8025 declare fp128 @llvm.exp.f128(fp128 %Val)
8026 declare ppc_fp128 @llvm.exp.ppcf128(ppc_fp128 %Val)
8031 The '``llvm.exp.*``' intrinsics perform the exp function.
8036 The argument and return value are floating point numbers of the same
8042 This function returns the same values as the libm ``exp`` functions
8043 would, and handles error conditions in the same way.
8045 '``llvm.exp2.*``' Intrinsic
8046 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
8051 This is an overloaded intrinsic. You can use ``llvm.exp2`` on any
8052 floating point or vector of floating point type. Not all targets support
8057 declare float @llvm.exp2.f32(float %Val)
8058 declare double @llvm.exp2.f64(double %Val)
8059 declare x86_fp80 @llvm.exp2.f80(x86_fp80 %Val)
8060 declare fp128 @llvm.exp2.f128(fp128 %Val)
8061 declare ppc_fp128 @llvm.exp2.ppcf128(ppc_fp128 %Val)
8066 The '``llvm.exp2.*``' intrinsics perform the exp2 function.
8071 The argument and return value are floating point numbers of the same
8077 This function returns the same values as the libm ``exp2`` functions
8078 would, and handles error conditions in the same way.
8080 '``llvm.log.*``' Intrinsic
8081 ^^^^^^^^^^^^^^^^^^^^^^^^^^
8086 This is an overloaded intrinsic. You can use ``llvm.log`` on any
8087 floating point or vector of floating point type. Not all targets support
8092 declare float @llvm.log.f32(float %Val)
8093 declare double @llvm.log.f64(double %Val)
8094 declare x86_fp80 @llvm.log.f80(x86_fp80 %Val)
8095 declare fp128 @llvm.log.f128(fp128 %Val)
8096 declare ppc_fp128 @llvm.log.ppcf128(ppc_fp128 %Val)
8101 The '``llvm.log.*``' intrinsics perform the log function.
8106 The argument and return value are floating point numbers of the same
8112 This function returns the same values as the libm ``log`` functions
8113 would, and handles error conditions in the same way.
8115 '``llvm.log10.*``' Intrinsic
8116 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8121 This is an overloaded intrinsic. You can use ``llvm.log10`` on any
8122 floating point or vector of floating point type. Not all targets support
8127 declare float @llvm.log10.f32(float %Val)
8128 declare double @llvm.log10.f64(double %Val)
8129 declare x86_fp80 @llvm.log10.f80(x86_fp80 %Val)
8130 declare fp128 @llvm.log10.f128(fp128 %Val)
8131 declare ppc_fp128 @llvm.log10.ppcf128(ppc_fp128 %Val)
8136 The '``llvm.log10.*``' intrinsics perform the log10 function.
8141 The argument and return value are floating point numbers of the same
8147 This function returns the same values as the libm ``log10`` functions
8148 would, and handles error conditions in the same way.
8150 '``llvm.log2.*``' Intrinsic
8151 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
8156 This is an overloaded intrinsic. You can use ``llvm.log2`` on any
8157 floating point or vector of floating point type. Not all targets support
8162 declare float @llvm.log2.f32(float %Val)
8163 declare double @llvm.log2.f64(double %Val)
8164 declare x86_fp80 @llvm.log2.f80(x86_fp80 %Val)
8165 declare fp128 @llvm.log2.f128(fp128 %Val)
8166 declare ppc_fp128 @llvm.log2.ppcf128(ppc_fp128 %Val)
8171 The '``llvm.log2.*``' intrinsics perform the log2 function.
8176 The argument and return value are floating point numbers of the same
8182 This function returns the same values as the libm ``log2`` functions
8183 would, and handles error conditions in the same way.
8185 '``llvm.fma.*``' Intrinsic
8186 ^^^^^^^^^^^^^^^^^^^^^^^^^^
8191 This is an overloaded intrinsic. You can use ``llvm.fma`` on any
8192 floating point or vector of floating point type. Not all targets support
8197 declare float @llvm.fma.f32(float %a, float %b, float %c)
8198 declare double @llvm.fma.f64(double %a, double %b, double %c)
8199 declare x86_fp80 @llvm.fma.f80(x86_fp80 %a, x86_fp80 %b, x86_fp80 %c)
8200 declare fp128 @llvm.fma.f128(fp128 %a, fp128 %b, fp128 %c)
8201 declare ppc_fp128 @llvm.fma.ppcf128(ppc_fp128 %a, ppc_fp128 %b, ppc_fp128 %c)
8206 The '``llvm.fma.*``' intrinsics perform the fused multiply-add
8212 The argument and return value are floating point numbers of the same
8218 This function returns the same values as the libm ``fma`` functions
8219 would, and does not set errno.
8221 '``llvm.fabs.*``' Intrinsic
8222 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
8227 This is an overloaded intrinsic. You can use ``llvm.fabs`` on any
8228 floating point or vector of floating point type. Not all targets support
8233 declare float @llvm.fabs.f32(float %Val)
8234 declare double @llvm.fabs.f64(double %Val)
8235 declare x86_fp80 @llvm.fabs.f80(x86_fp80 %Val)
8236 declare fp128 @llvm.fabs.f128(fp128 %Val)
8237 declare ppc_fp128 @llvm.fabs.ppcf128(ppc_fp128 %Val)
8242 The '``llvm.fabs.*``' intrinsics return the absolute value of the
8248 The argument and return value are floating point numbers of the same
8254 This function returns the same values as the libm ``fabs`` functions
8255 would, and handles error conditions in the same way.
8257 '``llvm.minnum.*``' Intrinsic
8258 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8263 This is an overloaded intrinsic. You can use ``llvm.minnum`` on any
8264 floating point or vector of floating point type. Not all targets support
8269 declare float @llvm.minnum.f32(float %Val0, float %Val1)
8270 declare double @llvm.minnum.f64(double %Val0, double %Val1)
8271 declare x86_fp80 @llvm.minnum.f80(x86_fp80 %Val0, x86_fp80 %Val1)
8272 declare fp128 @llvm.minnum.f128(fp128 %Val0, fp128 %Val1)
8273 declare ppc_fp128 @llvm.minnum.ppcf128(ppc_fp128 %Val0, ppc_fp128 %Val1)
8278 The '``llvm.minnum.*``' intrinsics return the minimum of the two
8285 The arguments and return value are floating point numbers of the same
8291 Follows the IEEE-754 semantics for minNum, which also match for libm's
8294 If either operand is a NaN, returns the other non-NaN operand. Returns
8295 NaN only if both operands are NaN. If the operands compare equal,
8296 returns a value that compares equal to both operands. This means that
8297 fmin(+/-0.0, +/-0.0) could return either -0.0 or 0.0.
8299 '``llvm.maxnum.*``' Intrinsic
8300 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8305 This is an overloaded intrinsic. You can use ``llvm.maxnum`` on any
8306 floating point or vector of floating point type. Not all targets support
8311 declare float @llvm.maxnum.f32(float %Val0, float %Val1l)
8312 declare double @llvm.maxnum.f64(double %Val0, double %Val1)
8313 declare x86_fp80 @llvm.maxnum.f80(x86_fp80 %Val0, x86_fp80 %Val1)
8314 declare fp128 @llvm.maxnum.f128(fp128 %Val0, fp128 %Val1)
8315 declare ppc_fp128 @llvm.maxnum.ppcf128(ppc_fp128 %Val0, ppc_fp128 %Val1)
8320 The '``llvm.maxnum.*``' intrinsics return the maximum of the two
8327 The arguments and return value are floating point numbers of the same
8332 Follows the IEEE-754 semantics for maxNum, which also match for libm's
8335 If either operand is a NaN, returns the other non-NaN operand. Returns
8336 NaN only if both operands are NaN. If the operands compare equal,
8337 returns a value that compares equal to both operands. This means that
8338 fmax(+/-0.0, +/-0.0) could return either -0.0 or 0.0.
8340 '``llvm.copysign.*``' Intrinsic
8341 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8346 This is an overloaded intrinsic. You can use ``llvm.copysign`` on any
8347 floating point or vector of floating point type. Not all targets support
8352 declare float @llvm.copysign.f32(float %Mag, float %Sgn)
8353 declare double @llvm.copysign.f64(double %Mag, double %Sgn)
8354 declare x86_fp80 @llvm.copysign.f80(x86_fp80 %Mag, x86_fp80 %Sgn)
8355 declare fp128 @llvm.copysign.f128(fp128 %Mag, fp128 %Sgn)
8356 declare ppc_fp128 @llvm.copysign.ppcf128(ppc_fp128 %Mag, ppc_fp128 %Sgn)
8361 The '``llvm.copysign.*``' intrinsics return a value with the magnitude of the
8362 first operand and the sign of the second operand.
8367 The arguments and return value are floating point numbers of the same
8373 This function returns the same values as the libm ``copysign``
8374 functions would, and handles error conditions in the same way.
8376 '``llvm.floor.*``' Intrinsic
8377 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8382 This is an overloaded intrinsic. You can use ``llvm.floor`` on any
8383 floating point or vector of floating point type. Not all targets support
8388 declare float @llvm.floor.f32(float %Val)
8389 declare double @llvm.floor.f64(double %Val)
8390 declare x86_fp80 @llvm.floor.f80(x86_fp80 %Val)
8391 declare fp128 @llvm.floor.f128(fp128 %Val)
8392 declare ppc_fp128 @llvm.floor.ppcf128(ppc_fp128 %Val)
8397 The '``llvm.floor.*``' intrinsics return the floor of the operand.
8402 The argument and return value are floating point numbers of the same
8408 This function returns the same values as the libm ``floor`` functions
8409 would, and handles error conditions in the same way.
8411 '``llvm.ceil.*``' Intrinsic
8412 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
8417 This is an overloaded intrinsic. You can use ``llvm.ceil`` on any
8418 floating point or vector of floating point type. Not all targets support
8423 declare float @llvm.ceil.f32(float %Val)
8424 declare double @llvm.ceil.f64(double %Val)
8425 declare x86_fp80 @llvm.ceil.f80(x86_fp80 %Val)
8426 declare fp128 @llvm.ceil.f128(fp128 %Val)
8427 declare ppc_fp128 @llvm.ceil.ppcf128(ppc_fp128 %Val)
8432 The '``llvm.ceil.*``' intrinsics return the ceiling of the operand.
8437 The argument and return value are floating point numbers of the same
8443 This function returns the same values as the libm ``ceil`` functions
8444 would, and handles error conditions in the same way.
8446 '``llvm.trunc.*``' Intrinsic
8447 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8452 This is an overloaded intrinsic. You can use ``llvm.trunc`` on any
8453 floating point or vector of floating point type. Not all targets support
8458 declare float @llvm.trunc.f32(float %Val)
8459 declare double @llvm.trunc.f64(double %Val)
8460 declare x86_fp80 @llvm.trunc.f80(x86_fp80 %Val)
8461 declare fp128 @llvm.trunc.f128(fp128 %Val)
8462 declare ppc_fp128 @llvm.trunc.ppcf128(ppc_fp128 %Val)
8467 The '``llvm.trunc.*``' intrinsics returns the operand rounded to the
8468 nearest integer not larger in magnitude than the operand.
8473 The argument and return value are floating point numbers of the same
8479 This function returns the same values as the libm ``trunc`` functions
8480 would, and handles error conditions in the same way.
8482 '``llvm.rint.*``' Intrinsic
8483 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
8488 This is an overloaded intrinsic. You can use ``llvm.rint`` on any
8489 floating point or vector of floating point type. Not all targets support
8494 declare float @llvm.rint.f32(float %Val)
8495 declare double @llvm.rint.f64(double %Val)
8496 declare x86_fp80 @llvm.rint.f80(x86_fp80 %Val)
8497 declare fp128 @llvm.rint.f128(fp128 %Val)
8498 declare ppc_fp128 @llvm.rint.ppcf128(ppc_fp128 %Val)
8503 The '``llvm.rint.*``' intrinsics returns the operand rounded to the
8504 nearest integer. It may raise an inexact floating-point exception if the
8505 operand isn't an integer.
8510 The argument and return value are floating point numbers of the same
8516 This function returns the same values as the libm ``rint`` functions
8517 would, and handles error conditions in the same way.
8519 '``llvm.nearbyint.*``' Intrinsic
8520 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8525 This is an overloaded intrinsic. You can use ``llvm.nearbyint`` on any
8526 floating point or vector of floating point type. Not all targets support
8531 declare float @llvm.nearbyint.f32(float %Val)
8532 declare double @llvm.nearbyint.f64(double %Val)
8533 declare x86_fp80 @llvm.nearbyint.f80(x86_fp80 %Val)
8534 declare fp128 @llvm.nearbyint.f128(fp128 %Val)
8535 declare ppc_fp128 @llvm.nearbyint.ppcf128(ppc_fp128 %Val)
8540 The '``llvm.nearbyint.*``' intrinsics returns the operand rounded to the
8546 The argument and return value are floating point numbers of the same
8552 This function returns the same values as the libm ``nearbyint``
8553 functions would, and handles error conditions in the same way.
8555 '``llvm.round.*``' Intrinsic
8556 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8561 This is an overloaded intrinsic. You can use ``llvm.round`` on any
8562 floating point or vector of floating point type. Not all targets support
8567 declare float @llvm.round.f32(float %Val)
8568 declare double @llvm.round.f64(double %Val)
8569 declare x86_fp80 @llvm.round.f80(x86_fp80 %Val)
8570 declare fp128 @llvm.round.f128(fp128 %Val)
8571 declare ppc_fp128 @llvm.round.ppcf128(ppc_fp128 %Val)
8576 The '``llvm.round.*``' intrinsics returns the operand rounded to the
8582 The argument and return value are floating point numbers of the same
8588 This function returns the same values as the libm ``round``
8589 functions would, and handles error conditions in the same way.
8591 Bit Manipulation Intrinsics
8592 ---------------------------
8594 LLVM provides intrinsics for a few important bit manipulation
8595 operations. These allow efficient code generation for some algorithms.
8597 '``llvm.bswap.*``' Intrinsics
8598 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8603 This is an overloaded intrinsic function. You can use bswap on any
8604 integer type that is an even number of bytes (i.e. BitWidth % 16 == 0).
8608 declare i16 @llvm.bswap.i16(i16 <id>)
8609 declare i32 @llvm.bswap.i32(i32 <id>)
8610 declare i64 @llvm.bswap.i64(i64 <id>)
8615 The '``llvm.bswap``' family of intrinsics is used to byte swap integer
8616 values with an even number of bytes (positive multiple of 16 bits).
8617 These are useful for performing operations on data that is not in the
8618 target's native byte order.
8623 The ``llvm.bswap.i16`` intrinsic returns an i16 value that has the high
8624 and low byte of the input i16 swapped. Similarly, the ``llvm.bswap.i32``
8625 intrinsic returns an i32 value that has the four bytes of the input i32
8626 swapped, so that if the input bytes are numbered 0, 1, 2, 3 then the
8627 returned i32 will have its bytes in 3, 2, 1, 0 order. The
8628 ``llvm.bswap.i48``, ``llvm.bswap.i64`` and other intrinsics extend this
8629 concept to additional even-byte lengths (6 bytes, 8 bytes and more,
8632 '``llvm.ctpop.*``' Intrinsic
8633 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8638 This is an overloaded intrinsic. You can use llvm.ctpop on any integer
8639 bit width, or on any vector with integer elements. Not all targets
8640 support all bit widths or vector types, however.
8644 declare i8 @llvm.ctpop.i8(i8 <src>)
8645 declare i16 @llvm.ctpop.i16(i16 <src>)
8646 declare i32 @llvm.ctpop.i32(i32 <src>)
8647 declare i64 @llvm.ctpop.i64(i64 <src>)
8648 declare i256 @llvm.ctpop.i256(i256 <src>)
8649 declare <2 x i32> @llvm.ctpop.v2i32(<2 x i32> <src>)
8654 The '``llvm.ctpop``' family of intrinsics counts the number of bits set
8660 The only argument is the value to be counted. The argument may be of any
8661 integer type, or a vector with integer elements. The return type must
8662 match the argument type.
8667 The '``llvm.ctpop``' intrinsic counts the 1's in a variable, or within
8668 each element of a vector.
8670 '``llvm.ctlz.*``' Intrinsic
8671 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
8676 This is an overloaded intrinsic. You can use ``llvm.ctlz`` on any
8677 integer bit width, or any vector whose elements are integers. Not all
8678 targets support all bit widths or vector types, however.
8682 declare i8 @llvm.ctlz.i8 (i8 <src>, i1 <is_zero_undef>)
8683 declare i16 @llvm.ctlz.i16 (i16 <src>, i1 <is_zero_undef>)
8684 declare i32 @llvm.ctlz.i32 (i32 <src>, i1 <is_zero_undef>)
8685 declare i64 @llvm.ctlz.i64 (i64 <src>, i1 <is_zero_undef>)
8686 declare i256 @llvm.ctlz.i256(i256 <src>, i1 <is_zero_undef>)
8687 declase <2 x i32> @llvm.ctlz.v2i32(<2 x i32> <src>, i1 <is_zero_undef>)
8692 The '``llvm.ctlz``' family of intrinsic functions counts the number of
8693 leading zeros in a variable.
8698 The first argument is the value to be counted. This argument may be of
8699 any integer type, or a vector with integer element type. The return
8700 type must match the first argument type.
8702 The second argument must be a constant and is a flag to indicate whether
8703 the intrinsic should ensure that a zero as the first argument produces a
8704 defined result. Historically some architectures did not provide a
8705 defined result for zero values as efficiently, and many algorithms are
8706 now predicated on avoiding zero-value inputs.
8711 The '``llvm.ctlz``' intrinsic counts the leading (most significant)
8712 zeros in a variable, or within each element of the vector. If
8713 ``src == 0`` then the result is the size in bits of the type of ``src``
8714 if ``is_zero_undef == 0`` and ``undef`` otherwise. For example,
8715 ``llvm.ctlz(i32 2) = 30``.
8717 '``llvm.cttz.*``' Intrinsic
8718 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
8723 This is an overloaded intrinsic. You can use ``llvm.cttz`` on any
8724 integer bit width, or any vector of integer elements. Not all targets
8725 support all bit widths or vector types, however.
8729 declare i8 @llvm.cttz.i8 (i8 <src>, i1 <is_zero_undef>)
8730 declare i16 @llvm.cttz.i16 (i16 <src>, i1 <is_zero_undef>)
8731 declare i32 @llvm.cttz.i32 (i32 <src>, i1 <is_zero_undef>)
8732 declare i64 @llvm.cttz.i64 (i64 <src>, i1 <is_zero_undef>)
8733 declare i256 @llvm.cttz.i256(i256 <src>, i1 <is_zero_undef>)
8734 declase <2 x i32> @llvm.cttz.v2i32(<2 x i32> <src>, i1 <is_zero_undef>)
8739 The '``llvm.cttz``' family of intrinsic functions counts the number of
8745 The first argument is the value to be counted. This argument may be of
8746 any integer type, or a vector with integer element type. The return
8747 type must match the first argument type.
8749 The second argument must be a constant and is a flag to indicate whether
8750 the intrinsic should ensure that a zero as the first argument produces a
8751 defined result. Historically some architectures did not provide a
8752 defined result for zero values as efficiently, and many algorithms are
8753 now predicated on avoiding zero-value inputs.
8758 The '``llvm.cttz``' intrinsic counts the trailing (least significant)
8759 zeros in a variable, or within each element of a vector. If ``src == 0``
8760 then the result is the size in bits of the type of ``src`` if
8761 ``is_zero_undef == 0`` and ``undef`` otherwise. For example,
8762 ``llvm.cttz(2) = 1``.
8764 Arithmetic with Overflow Intrinsics
8765 -----------------------------------
8767 LLVM provides intrinsics for some arithmetic with overflow operations.
8769 '``llvm.sadd.with.overflow.*``' Intrinsics
8770 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8775 This is an overloaded intrinsic. You can use ``llvm.sadd.with.overflow``
8776 on any integer bit width.
8780 declare {i16, i1} @llvm.sadd.with.overflow.i16(i16 %a, i16 %b)
8781 declare {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b)
8782 declare {i64, i1} @llvm.sadd.with.overflow.i64(i64 %a, i64 %b)
8787 The '``llvm.sadd.with.overflow``' family of intrinsic functions perform
8788 a signed addition of the two arguments, and indicate whether an overflow
8789 occurred during the signed summation.
8794 The arguments (%a and %b) and the first element of the result structure
8795 may be of integer types of any bit width, but they must have the same
8796 bit width. The second element of the result structure must be of type
8797 ``i1``. ``%a`` and ``%b`` are the two values that will undergo signed
8803 The '``llvm.sadd.with.overflow``' family of intrinsic functions perform
8804 a signed addition of the two variables. They return a structure --- the
8805 first element of which is the signed summation, and the second element
8806 of which is a bit specifying if the signed summation resulted in an
8812 .. code-block:: llvm
8814 %res = call {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b)
8815 %sum = extractvalue {i32, i1} %res, 0
8816 %obit = extractvalue {i32, i1} %res, 1
8817 br i1 %obit, label %overflow, label %normal
8819 '``llvm.uadd.with.overflow.*``' Intrinsics
8820 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8825 This is an overloaded intrinsic. You can use ``llvm.uadd.with.overflow``
8826 on any integer bit width.
8830 declare {i16, i1} @llvm.uadd.with.overflow.i16(i16 %a, i16 %b)
8831 declare {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)
8832 declare {i64, i1} @llvm.uadd.with.overflow.i64(i64 %a, i64 %b)
8837 The '``llvm.uadd.with.overflow``' family of intrinsic functions perform
8838 an unsigned addition of the two arguments, and indicate whether a carry
8839 occurred during the unsigned summation.
8844 The arguments (%a and %b) and the first element of the result structure
8845 may be of integer types of any bit width, but they must have the same
8846 bit width. The second element of the result structure must be of type
8847 ``i1``. ``%a`` and ``%b`` are the two values that will undergo unsigned
8853 The '``llvm.uadd.with.overflow``' family of intrinsic functions perform
8854 an unsigned addition of the two arguments. They return a structure --- the
8855 first element of which is the sum, and the second element of which is a
8856 bit specifying if the unsigned summation resulted in a carry.
8861 .. code-block:: llvm
8863 %res = call {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)
8864 %sum = extractvalue {i32, i1} %res, 0
8865 %obit = extractvalue {i32, i1} %res, 1
8866 br i1 %obit, label %carry, label %normal
8868 '``llvm.ssub.with.overflow.*``' Intrinsics
8869 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8874 This is an overloaded intrinsic. You can use ``llvm.ssub.with.overflow``
8875 on any integer bit width.
8879 declare {i16, i1} @llvm.ssub.with.overflow.i16(i16 %a, i16 %b)
8880 declare {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b)
8881 declare {i64, i1} @llvm.ssub.with.overflow.i64(i64 %a, i64 %b)
8886 The '``llvm.ssub.with.overflow``' family of intrinsic functions perform
8887 a signed subtraction of the two arguments, and indicate whether an
8888 overflow occurred during the signed subtraction.
8893 The arguments (%a and %b) and the first element of the result structure
8894 may be of integer types of any bit width, but they must have the same
8895 bit width. The second element of the result structure must be of type
8896 ``i1``. ``%a`` and ``%b`` are the two values that will undergo signed
8902 The '``llvm.ssub.with.overflow``' family of intrinsic functions perform
8903 a signed subtraction of the two arguments. They return a structure --- the
8904 first element of which is the subtraction, and the second element of
8905 which is a bit specifying if the signed subtraction resulted in an
8911 .. code-block:: llvm
8913 %res = call {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b)
8914 %sum = extractvalue {i32, i1} %res, 0
8915 %obit = extractvalue {i32, i1} %res, 1
8916 br i1 %obit, label %overflow, label %normal
8918 '``llvm.usub.with.overflow.*``' Intrinsics
8919 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8924 This is an overloaded intrinsic. You can use ``llvm.usub.with.overflow``
8925 on any integer bit width.
8929 declare {i16, i1} @llvm.usub.with.overflow.i16(i16 %a, i16 %b)
8930 declare {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b)
8931 declare {i64, i1} @llvm.usub.with.overflow.i64(i64 %a, i64 %b)
8936 The '``llvm.usub.with.overflow``' family of intrinsic functions perform
8937 an unsigned subtraction of the two arguments, and indicate whether an
8938 overflow occurred during the unsigned subtraction.
8943 The arguments (%a and %b) and the first element of the result structure
8944 may be of integer types of any bit width, but they must have the same
8945 bit width. The second element of the result structure must be of type
8946 ``i1``. ``%a`` and ``%b`` are the two values that will undergo unsigned
8952 The '``llvm.usub.with.overflow``' family of intrinsic functions perform
8953 an unsigned subtraction of the two arguments. They return a structure ---
8954 the first element of which is the subtraction, and the second element of
8955 which is a bit specifying if the unsigned subtraction resulted in an
8961 .. code-block:: llvm
8963 %res = call {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b)
8964 %sum = extractvalue {i32, i1} %res, 0
8965 %obit = extractvalue {i32, i1} %res, 1
8966 br i1 %obit, label %overflow, label %normal
8968 '``llvm.smul.with.overflow.*``' Intrinsics
8969 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8974 This is an overloaded intrinsic. You can use ``llvm.smul.with.overflow``
8975 on any integer bit width.
8979 declare {i16, i1} @llvm.smul.with.overflow.i16(i16 %a, i16 %b)
8980 declare {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b)
8981 declare {i64, i1} @llvm.smul.with.overflow.i64(i64 %a, i64 %b)
8986 The '``llvm.smul.with.overflow``' family of intrinsic functions perform
8987 a signed multiplication of the two arguments, and indicate whether an
8988 overflow occurred during the signed multiplication.
8993 The arguments (%a and %b) and the first element of the result structure
8994 may be of integer types of any bit width, but they must have the same
8995 bit width. The second element of the result structure must be of type
8996 ``i1``. ``%a`` and ``%b`` are the two values that will undergo signed
9002 The '``llvm.smul.with.overflow``' family of intrinsic functions perform
9003 a signed multiplication of the two arguments. They return a structure ---
9004 the first element of which is the multiplication, and the second element
9005 of which is a bit specifying if the signed multiplication resulted in an
9011 .. code-block:: llvm
9013 %res = call {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b)
9014 %sum = extractvalue {i32, i1} %res, 0
9015 %obit = extractvalue {i32, i1} %res, 1
9016 br i1 %obit, label %overflow, label %normal
9018 '``llvm.umul.with.overflow.*``' Intrinsics
9019 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9024 This is an overloaded intrinsic. You can use ``llvm.umul.with.overflow``
9025 on any integer bit width.
9029 declare {i16, i1} @llvm.umul.with.overflow.i16(i16 %a, i16 %b)
9030 declare {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b)
9031 declare {i64, i1} @llvm.umul.with.overflow.i64(i64 %a, i64 %b)
9036 The '``llvm.umul.with.overflow``' family of intrinsic functions perform
9037 a unsigned multiplication of the two arguments, and indicate whether an
9038 overflow occurred during the unsigned multiplication.
9043 The arguments (%a and %b) and the first element of the result structure
9044 may be of integer types of any bit width, but they must have the same
9045 bit width. The second element of the result structure must be of type
9046 ``i1``. ``%a`` and ``%b`` are the two values that will undergo unsigned
9052 The '``llvm.umul.with.overflow``' family of intrinsic functions perform
9053 an unsigned multiplication of the two arguments. They return a structure ---
9054 the first element of which is the multiplication, and the second
9055 element of which is a bit specifying if the unsigned multiplication
9056 resulted in an overflow.
9061 .. code-block:: llvm
9063 %res = call {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b)
9064 %sum = extractvalue {i32, i1} %res, 0
9065 %obit = extractvalue {i32, i1} %res, 1
9066 br i1 %obit, label %overflow, label %normal
9068 Specialised Arithmetic Intrinsics
9069 ---------------------------------
9071 '``llvm.fmuladd.*``' Intrinsic
9072 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9079 declare float @llvm.fmuladd.f32(float %a, float %b, float %c)
9080 declare double @llvm.fmuladd.f64(double %a, double %b, double %c)
9085 The '``llvm.fmuladd.*``' intrinsic functions represent multiply-add
9086 expressions that can be fused if the code generator determines that (a) the
9087 target instruction set has support for a fused operation, and (b) that the
9088 fused operation is more efficient than the equivalent, separate pair of mul
9089 and add instructions.
9094 The '``llvm.fmuladd.*``' intrinsics each take three arguments: two
9095 multiplicands, a and b, and an addend c.
9104 %0 = call float @llvm.fmuladd.f32(%a, %b, %c)
9106 is equivalent to the expression a \* b + c, except that rounding will
9107 not be performed between the multiplication and addition steps if the
9108 code generator fuses the operations. Fusion is not guaranteed, even if
9109 the target platform supports it. If a fused multiply-add is required the
9110 corresponding llvm.fma.\* intrinsic function should be used
9111 instead. This never sets errno, just as '``llvm.fma.*``'.
9116 .. code-block:: llvm
9118 %r2 = call float @llvm.fmuladd.f32(float %a, float %b, float %c) ; yields float:r2 = (a * b) + c
9120 Half Precision Floating Point Intrinsics
9121 ----------------------------------------
9123 For most target platforms, half precision floating point is a
9124 storage-only format. This means that it is a dense encoding (in memory)
9125 but does not support computation in the format.
9127 This means that code must first load the half-precision floating point
9128 value as an i16, then convert it to float with
9129 :ref:`llvm.convert.from.fp16 <int_convert_from_fp16>`. Computation can
9130 then be performed on the float value (including extending to double
9131 etc). To store the value back to memory, it is first converted to float
9132 if needed, then converted to i16 with
9133 :ref:`llvm.convert.to.fp16 <int_convert_to_fp16>`, then storing as an
9136 .. _int_convert_to_fp16:
9138 '``llvm.convert.to.fp16``' Intrinsic
9139 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9146 declare i16 @llvm.convert.to.fp16.f32(float %a)
9147 declare i16 @llvm.convert.to.fp16.f64(double %a)
9152 The '``llvm.convert.to.fp16``' intrinsic function performs a conversion from a
9153 conventional floating point type to half precision floating point format.
9158 The intrinsic function contains single argument - the value to be
9164 The '``llvm.convert.to.fp16``' intrinsic function performs a conversion from a
9165 conventional floating point format to half precision floating point format. The
9166 return value is an ``i16`` which contains the converted number.
9171 .. code-block:: llvm
9173 %res = call i16 @llvm.convert.to.fp16.f32(float %a)
9174 store i16 %res, i16* @x, align 2
9176 .. _int_convert_from_fp16:
9178 '``llvm.convert.from.fp16``' Intrinsic
9179 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9186 declare float @llvm.convert.from.fp16.f32(i16 %a)
9187 declare double @llvm.convert.from.fp16.f64(i16 %a)
9192 The '``llvm.convert.from.fp16``' intrinsic function performs a
9193 conversion from half precision floating point format to single precision
9194 floating point format.
9199 The intrinsic function contains single argument - the value to be
9205 The '``llvm.convert.from.fp16``' intrinsic function performs a
9206 conversion from half single precision floating point format to single
9207 precision floating point format. The input half-float value is
9208 represented by an ``i16`` value.
9213 .. code-block:: llvm
9215 %a = load i16* @x, align 2
9216 %res = call float @llvm.convert.from.fp16(i16 %a)
9221 The LLVM debugger intrinsics (which all start with ``llvm.dbg.``
9222 prefix), are described in the `LLVM Source Level
9223 Debugging <SourceLevelDebugging.html#format_common_intrinsics>`_
9226 Exception Handling Intrinsics
9227 -----------------------------
9229 The LLVM exception handling intrinsics (which all start with
9230 ``llvm.eh.`` prefix), are described in the `LLVM Exception
9231 Handling <ExceptionHandling.html#format_common_intrinsics>`_ document.
9235 Trampoline Intrinsics
9236 ---------------------
9238 These intrinsics make it possible to excise one parameter, marked with
9239 the :ref:`nest <nest>` attribute, from a function. The result is a
9240 callable function pointer lacking the nest parameter - the caller does
9241 not need to provide a value for it. Instead, the value to use is stored
9242 in advance in a "trampoline", a block of memory usually allocated on the
9243 stack, which also contains code to splice the nest value into the
9244 argument list. This is used to implement the GCC nested function address
9247 For example, if the function is ``i32 f(i8* nest %c, i32 %x, i32 %y)``
9248 then the resulting function pointer has signature ``i32 (i32, i32)*``.
9249 It can be created as follows:
9251 .. code-block:: llvm
9253 %tramp = alloca [10 x i8], align 4 ; size and alignment only correct for X86
9254 %tramp1 = getelementptr [10 x i8]* %tramp, i32 0, i32 0
9255 call i8* @llvm.init.trampoline(i8* %tramp1, i8* bitcast (i32 (i8*, i32, i32)* @f to i8*), i8* %nval)
9256 %p = call i8* @llvm.adjust.trampoline(i8* %tramp1)
9257 %fp = bitcast i8* %p to i32 (i32, i32)*
9259 The call ``%val = call i32 %fp(i32 %x, i32 %y)`` is then equivalent to
9260 ``%val = call i32 %f(i8* %nval, i32 %x, i32 %y)``.
9264 '``llvm.init.trampoline``' Intrinsic
9265 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9272 declare void @llvm.init.trampoline(i8* <tramp>, i8* <func>, i8* <nval>)
9277 This fills the memory pointed to by ``tramp`` with executable code,
9278 turning it into a trampoline.
9283 The ``llvm.init.trampoline`` intrinsic takes three arguments, all
9284 pointers. The ``tramp`` argument must point to a sufficiently large and
9285 sufficiently aligned block of memory; this memory is written to by the
9286 intrinsic. Note that the size and the alignment are target-specific -
9287 LLVM currently provides no portable way of determining them, so a
9288 front-end that generates this intrinsic needs to have some
9289 target-specific knowledge. The ``func`` argument must hold a function
9290 bitcast to an ``i8*``.
9295 The block of memory pointed to by ``tramp`` is filled with target
9296 dependent code, turning it into a function. Then ``tramp`` needs to be
9297 passed to :ref:`llvm.adjust.trampoline <int_at>` to get a pointer which can
9298 be :ref:`bitcast (to a new function) and called <int_trampoline>`. The new
9299 function's signature is the same as that of ``func`` with any arguments
9300 marked with the ``nest`` attribute removed. At most one such ``nest``
9301 argument is allowed, and it must be of pointer type. Calling the new
9302 function is equivalent to calling ``func`` with the same argument list,
9303 but with ``nval`` used for the missing ``nest`` argument. If, after
9304 calling ``llvm.init.trampoline``, the memory pointed to by ``tramp`` is
9305 modified, then the effect of any later call to the returned function
9306 pointer is undefined.
9310 '``llvm.adjust.trampoline``' Intrinsic
9311 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9318 declare i8* @llvm.adjust.trampoline(i8* <tramp>)
9323 This performs any required machine-specific adjustment to the address of
9324 a trampoline (passed as ``tramp``).
9329 ``tramp`` must point to a block of memory which already has trampoline
9330 code filled in by a previous call to
9331 :ref:`llvm.init.trampoline <int_it>`.
9336 On some architectures the address of the code to be executed needs to be
9337 different than the address where the trampoline is actually stored. This
9338 intrinsic returns the executable address corresponding to ``tramp``
9339 after performing the required machine specific adjustments. The pointer
9340 returned can then be :ref:`bitcast and executed <int_trampoline>`.
9342 Masked Vector Load and Store Intrinsics
9343 ---------------------------------------
9345 LLVM provides intrinsics for predicated vector load and store operations. The predicate is specified by a mask operand, which holds one bit per vector element, switching the associated vector lane on or off. The memory addresses corresponding to the "off" lanes are not accessed. When all bits of the mask are on, the intrinsic is identical to a regular vector load or store. When all bits are off, no memory is accessed.
9349 '``llvm.masked.load.*``' Intrinsics
9350 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9354 This is an overloaded intrinsic. The loaded data is a vector of any integer or floating point data type.
9358 declare <16 x float> @llvm.masked.load.v16f32 (<16 x float>* <ptr>, i32 <alignment>, <16 x i1> <mask>, <16 x float> <passthru>)
9359 declare <2 x double> @llvm.masked.load.v2f64 (<2 x double>* <ptr>, i32 <alignment>, <2 x i1> <mask>, <2 x double> <passthru>)
9364 Reads a vector from memory according to the provided mask. The mask holds a bit for each vector lane, and is used to prevent memory accesses to the masked-off lanes. The masked-off lanes in the result vector are taken from the corresponding lanes in the passthru operand.
9370 The first operand is the base pointer for the load. The second operand is the alignment of the source location. It must be a constant integer value. The third operand, mask, is a vector of boolean 'i1' values with the same number of elements as the return type. The fourth is a pass-through value that is used to fill the masked-off lanes of the result. The return type, underlying type of the base pointer and the type of passthru operand are the same vector types.
9376 The '``llvm.masked.load``' intrinsic is designed for conditional reading of selected vector elements in a single IR operation. It is useful for targets that support vector masked loads and allows vectorizing predicated basic blocks on these targets. Other targets may support this intrinsic differently, for example by lowering it into a sequence of branches that guard scalar load operations.
9377 The result of this operation is equivalent to a regular vector load instruction followed by a 'select' between the loaded and the passthru values, predicated on the same mask. However, using this intrinsic prevents exceptions on memory access to masked-off lanes.
9382 %res = call <16 x float> @llvm.masked.load.v16f32 (<16 x float>* %ptr, i32 4, <16 x i1>%mask, <16 x float> %passthru)
9384 ;; The result of the two following instructions is identical aside from potential memory access exception
9385 %loadlal = load <16 x float>* %ptr, align 4
9386 %res = select <16 x i1> %mask, <16 x float> %loadlal, <16 x float> %passthru
9390 '``llvm.masked.store.*``' Intrinsics
9391 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9395 This is an overloaded intrinsic. The data stored in memory is a vector of any integer or floating point data type.
9399 declare void @llvm.masked.store.v8i32 (<8 x i32> <value>, <8 x i32> * <ptr>, i32 <alignment>, <8 x i1> <mask>)
9400 declare void @llvm.masked.store.v16f32(<16 x i32> <value>, <16 x i32>* <ptr>, i32 <alignment>, <16 x i1> <mask>)
9405 Writes a vector to memory according to the provided mask. The mask holds a bit for each vector lane, and is used to prevent memory accesses to the masked-off lanes.
9410 The first operand is the vector value to be written to memory. The second operand is the base pointer for the store, it has the same underlying type as the value operand. The third operand is the alignment of the destination location. The fourth operand, mask, is a vector of boolean values. The types of the mask and the value operand must have the same number of vector elements.
9416 The '``llvm.masked.store``' intrinsics is designed for conditional writing of selected vector elements in a single IR operation. It is useful for targets that support vector masked store and allows vectorizing predicated basic blocks on these targets. Other targets may support this intrinsic differently, for example by lowering it into a sequence of branches that guard scalar store operations.
9417 The result of this operation is equivalent to a load-modify-store sequence. However, using this intrinsic prevents exceptions and data races on memory access to masked-off lanes.
9421 call void @llvm.masked.store.v16f32(<16 x float> %value, <16 x float>* %ptr, i32 4, <16 x i1> %mask)
9423 ;; The result of the following instructions is identical aside from potential data races and memory access exceptions
9424 %oldval = load <16 x float>* %ptr, align 4
9425 %res = select <16 x i1> %mask, <16 x float> %value, <16 x float> %oldval
9426 store <16 x float> %res, <16 x float>* %ptr, align 4
9432 This class of intrinsics provides information about the lifetime of
9433 memory objects and ranges where variables are immutable.
9437 '``llvm.lifetime.start``' Intrinsic
9438 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9445 declare void @llvm.lifetime.start(i64 <size>, i8* nocapture <ptr>)
9450 The '``llvm.lifetime.start``' intrinsic specifies the start of a memory
9456 The first argument is a constant integer representing the size of the
9457 object, or -1 if it is variable sized. The second argument is a pointer
9463 This intrinsic indicates that before this point in the code, the value
9464 of the memory pointed to by ``ptr`` is dead. This means that it is known
9465 to never be used and has an undefined value. A load from the pointer
9466 that precedes this intrinsic can be replaced with ``'undef'``.
9470 '``llvm.lifetime.end``' Intrinsic
9471 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9478 declare void @llvm.lifetime.end(i64 <size>, i8* nocapture <ptr>)
9483 The '``llvm.lifetime.end``' intrinsic specifies the end of a memory
9489 The first argument is a constant integer representing the size of the
9490 object, or -1 if it is variable sized. The second argument is a pointer
9496 This intrinsic indicates that after this point in the code, the value of
9497 the memory pointed to by ``ptr`` is dead. This means that it is known to
9498 never be used and has an undefined value. Any stores into the memory
9499 object following this intrinsic may be removed as dead.
9501 '``llvm.invariant.start``' Intrinsic
9502 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9509 declare {}* @llvm.invariant.start(i64 <size>, i8* nocapture <ptr>)
9514 The '``llvm.invariant.start``' intrinsic specifies that the contents of
9515 a memory object will not change.
9520 The first argument is a constant integer representing the size of the
9521 object, or -1 if it is variable sized. The second argument is a pointer
9527 This intrinsic indicates that until an ``llvm.invariant.end`` that uses
9528 the return value, the referenced memory location is constant and
9531 '``llvm.invariant.end``' Intrinsic
9532 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9539 declare void @llvm.invariant.end({}* <start>, i64 <size>, i8* nocapture <ptr>)
9544 The '``llvm.invariant.end``' intrinsic specifies that the contents of a
9545 memory object are mutable.
9550 The first argument is the matching ``llvm.invariant.start`` intrinsic.
9551 The second argument is a constant integer representing the size of the
9552 object, or -1 if it is variable sized and the third argument is a
9553 pointer to the object.
9558 This intrinsic indicates that the memory is mutable again.
9563 This class of intrinsics is designed to be generic and has no specific
9566 '``llvm.var.annotation``' Intrinsic
9567 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9574 declare void @llvm.var.annotation(i8* <val>, i8* <str>, i8* <str>, i32 <int>)
9579 The '``llvm.var.annotation``' intrinsic.
9584 The first argument is a pointer to a value, the second is a pointer to a
9585 global string, the third is a pointer to a global string which is the
9586 source file name, and the last argument is the line number.
9591 This intrinsic allows annotation of local variables with arbitrary
9592 strings. This can be useful for special purpose optimizations that want
9593 to look for these annotations. These have no other defined use; they are
9594 ignored by code generation and optimization.
9596 '``llvm.ptr.annotation.*``' Intrinsic
9597 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9602 This is an overloaded intrinsic. You can use '``llvm.ptr.annotation``' on a
9603 pointer to an integer of any width. *NOTE* you must specify an address space for
9604 the pointer. The identifier for the default address space is the integer
9609 declare i8* @llvm.ptr.annotation.p<address space>i8(i8* <val>, i8* <str>, i8* <str>, i32 <int>)
9610 declare i16* @llvm.ptr.annotation.p<address space>i16(i16* <val>, i8* <str>, i8* <str>, i32 <int>)
9611 declare i32* @llvm.ptr.annotation.p<address space>i32(i32* <val>, i8* <str>, i8* <str>, i32 <int>)
9612 declare i64* @llvm.ptr.annotation.p<address space>i64(i64* <val>, i8* <str>, i8* <str>, i32 <int>)
9613 declare i256* @llvm.ptr.annotation.p<address space>i256(i256* <val>, i8* <str>, i8* <str>, i32 <int>)
9618 The '``llvm.ptr.annotation``' intrinsic.
9623 The first argument is a pointer to an integer value of arbitrary bitwidth
9624 (result of some expression), the second is a pointer to a global string, the
9625 third is a pointer to a global string which is the source file name, and the
9626 last argument is the line number. It returns the value of the first argument.
9631 This intrinsic allows annotation of a pointer to an integer with arbitrary
9632 strings. This can be useful for special purpose optimizations that want to look
9633 for these annotations. These have no other defined use; they are ignored by code
9634 generation and optimization.
9636 '``llvm.annotation.*``' Intrinsic
9637 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9642 This is an overloaded intrinsic. You can use '``llvm.annotation``' on
9643 any integer bit width.
9647 declare i8 @llvm.annotation.i8(i8 <val>, i8* <str>, i8* <str>, i32 <int>)
9648 declare i16 @llvm.annotation.i16(i16 <val>, i8* <str>, i8* <str>, i32 <int>)
9649 declare i32 @llvm.annotation.i32(i32 <val>, i8* <str>, i8* <str>, i32 <int>)
9650 declare i64 @llvm.annotation.i64(i64 <val>, i8* <str>, i8* <str>, i32 <int>)
9651 declare i256 @llvm.annotation.i256(i256 <val>, i8* <str>, i8* <str>, i32 <int>)
9656 The '``llvm.annotation``' intrinsic.
9661 The first argument is an integer value (result of some expression), the
9662 second is a pointer to a global string, the third is a pointer to a
9663 global string which is the source file name, and the last argument is
9664 the line number. It returns the value of the first argument.
9669 This intrinsic allows annotations to be put on arbitrary expressions
9670 with arbitrary strings. This can be useful for special purpose
9671 optimizations that want to look for these annotations. These have no
9672 other defined use; they are ignored by code generation and optimization.
9674 '``llvm.trap``' Intrinsic
9675 ^^^^^^^^^^^^^^^^^^^^^^^^^
9682 declare void @llvm.trap() noreturn nounwind
9687 The '``llvm.trap``' intrinsic.
9697 This intrinsic is lowered to the target dependent trap instruction. If
9698 the target does not have a trap instruction, this intrinsic will be
9699 lowered to a call of the ``abort()`` function.
9701 '``llvm.debugtrap``' Intrinsic
9702 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9709 declare void @llvm.debugtrap() nounwind
9714 The '``llvm.debugtrap``' intrinsic.
9724 This intrinsic is lowered to code which is intended to cause an
9725 execution trap with the intention of requesting the attention of a
9728 '``llvm.stackprotector``' Intrinsic
9729 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9736 declare void @llvm.stackprotector(i8* <guard>, i8** <slot>)
9741 The ``llvm.stackprotector`` intrinsic takes the ``guard`` and stores it
9742 onto the stack at ``slot``. The stack slot is adjusted to ensure that it
9743 is placed on the stack before local variables.
9748 The ``llvm.stackprotector`` intrinsic requires two pointer arguments.
9749 The first argument is the value loaded from the stack guard
9750 ``@__stack_chk_guard``. The second variable is an ``alloca`` that has
9751 enough space to hold the value of the guard.
9756 This intrinsic causes the prologue/epilogue inserter to force the position of
9757 the ``AllocaInst`` stack slot to be before local variables on the stack. This is
9758 to ensure that if a local variable on the stack is overwritten, it will destroy
9759 the value of the guard. When the function exits, the guard on the stack is
9760 checked against the original guard by ``llvm.stackprotectorcheck``. If they are
9761 different, then ``llvm.stackprotectorcheck`` causes the program to abort by
9762 calling the ``__stack_chk_fail()`` function.
9764 '``llvm.stackprotectorcheck``' Intrinsic
9765 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9772 declare void @llvm.stackprotectorcheck(i8** <guard>)
9777 The ``llvm.stackprotectorcheck`` intrinsic compares ``guard`` against an already
9778 created stack protector and if they are not equal calls the
9779 ``__stack_chk_fail()`` function.
9784 The ``llvm.stackprotectorcheck`` intrinsic requires one pointer argument, the
9785 the variable ``@__stack_chk_guard``.
9790 This intrinsic is provided to perform the stack protector check by comparing
9791 ``guard`` with the stack slot created by ``llvm.stackprotector`` and if the
9792 values do not match call the ``__stack_chk_fail()`` function.
9794 The reason to provide this as an IR level intrinsic instead of implementing it
9795 via other IR operations is that in order to perform this operation at the IR
9796 level without an intrinsic, one would need to create additional basic blocks to
9797 handle the success/failure cases. This makes it difficult to stop the stack
9798 protector check from disrupting sibling tail calls in Codegen. With this
9799 intrinsic, we are able to generate the stack protector basic blocks late in
9800 codegen after the tail call decision has occurred.
9802 '``llvm.objectsize``' Intrinsic
9803 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9810 declare i32 @llvm.objectsize.i32(i8* <object>, i1 <min>)
9811 declare i64 @llvm.objectsize.i64(i8* <object>, i1 <min>)
9816 The ``llvm.objectsize`` intrinsic is designed to provide information to
9817 the optimizers to determine at compile time whether a) an operation
9818 (like memcpy) will overflow a buffer that corresponds to an object, or
9819 b) that a runtime check for overflow isn't necessary. An object in this
9820 context means an allocation of a specific class, structure, array, or
9826 The ``llvm.objectsize`` intrinsic takes two arguments. The first
9827 argument is a pointer to or into the ``object``. The second argument is
9828 a boolean and determines whether ``llvm.objectsize`` returns 0 (if true)
9829 or -1 (if false) when the object size is unknown. The second argument
9830 only accepts constants.
9835 The ``llvm.objectsize`` intrinsic is lowered to a constant representing
9836 the size of the object concerned. If the size cannot be determined at
9837 compile time, ``llvm.objectsize`` returns ``i32/i64 -1 or 0`` (depending
9838 on the ``min`` argument).
9840 '``llvm.expect``' Intrinsic
9841 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
9846 This is an overloaded intrinsic. You can use ``llvm.expect`` on any
9851 declare i1 @llvm.expect.i1(i1 <val>, i1 <expected_val>)
9852 declare i32 @llvm.expect.i32(i32 <val>, i32 <expected_val>)
9853 declare i64 @llvm.expect.i64(i64 <val>, i64 <expected_val>)
9858 The ``llvm.expect`` intrinsic provides information about expected (the
9859 most probable) value of ``val``, which can be used by optimizers.
9864 The ``llvm.expect`` intrinsic takes two arguments. The first argument is
9865 a value. The second argument is an expected value, this needs to be a
9866 constant value, variables are not allowed.
9871 This intrinsic is lowered to the ``val``.
9873 '``llvm.assume``' Intrinsic
9874 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9881 declare void @llvm.assume(i1 %cond)
9886 The ``llvm.assume`` allows the optimizer to assume that the provided
9887 condition is true. This information can then be used in simplifying other parts
9893 The condition which the optimizer may assume is always true.
9898 The intrinsic allows the optimizer to assume that the provided condition is
9899 always true whenever the control flow reaches the intrinsic call. No code is
9900 generated for this intrinsic, and instructions that contribute only to the
9901 provided condition are not used for code generation. If the condition is
9902 violated during execution, the behavior is undefined.
9904 Note that the optimizer might limit the transformations performed on values
9905 used by the ``llvm.assume`` intrinsic in order to preserve the instructions
9906 only used to form the intrinsic's input argument. This might prove undesirable
9907 if the extra information provided by the ``llvm.assume`` intrinsic does not cause
9908 sufficient overall improvement in code quality. For this reason,
9909 ``llvm.assume`` should not be used to document basic mathematical invariants
9910 that the optimizer can otherwise deduce or facts that are of little use to the
9915 '``llvm.bitset.test``' Intrinsic
9916 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9923 declare i1 @llvm.bitset.test(i8* %ptr, metadata %bitset) nounwind readnone
9929 The first argument is a pointer to be tested. The second argument is a
9930 metadata string containing the name of a :doc:`bitset <BitSets>`.
9935 The ``llvm.bitset.test`` intrinsic tests whether the given pointer is a
9936 member of the given bitset.
9938 '``llvm.donothing``' Intrinsic
9939 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9946 declare void @llvm.donothing() nounwind readnone
9951 The ``llvm.donothing`` intrinsic doesn't perform any operation. It's one of only
9952 two intrinsics (besides ``llvm.experimental.patchpoint``) that can be called
9953 with an invoke instruction.
9963 This intrinsic does nothing, and it's removed by optimizers and ignored
9966 Stack Map Intrinsics
9967 --------------------
9969 LLVM provides experimental intrinsics to support runtime patching
9970 mechanisms commonly desired in dynamic language JITs. These intrinsics
9971 are described in :doc:`StackMaps`.