1 ==============================
2 LLVM Language Reference Manual
3 ==============================
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 = metadata !{i32 42, null, metadata !"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 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 variables 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 aliasaes 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"] [, align <Alignment>]
601 For example, the following defines a global in a numbered address space
602 with an initializer, section, and alignment:
606 @G = addrspace(5) constant float 1.0, section "foo", align 4
608 The following example just declares a global variable
612 @G = external global i32
614 The following example defines a thread-local global with the
615 ``initialexec`` TLS model:
619 @G = thread_local(initialexec) global i32 0, align 4
621 .. _functionstructure:
626 LLVM function definitions consist of the "``define``" keyword, an
627 optional :ref:`linkage type <linkage>`, an optional :ref:`visibility
628 style <visibility>`, an optional :ref:`DLL storage class <dllstorageclass>`,
629 an optional :ref:`calling convention <callingconv>`,
630 an optional ``unnamed_addr`` attribute, a return type, an optional
631 :ref:`parameter attribute <paramattrs>` for the return type, a function
632 name, a (possibly empty) argument list (each with optional :ref:`parameter
633 attributes <paramattrs>`), optional :ref:`function attributes <fnattrs>`,
634 an optional section, an optional alignment,
635 an optional :ref:`comdat <langref_comdats>`,
636 an optional :ref:`garbage collector name <gc>`, an optional :ref:`prefix <prefixdata>`, an opening
637 curly brace, a list of basic blocks, and a closing curly brace.
639 LLVM function declarations consist of the "``declare``" keyword, an
640 optional :ref:`linkage type <linkage>`, an optional :ref:`visibility
641 style <visibility>`, an optional :ref:`DLL storage class <dllstorageclass>`,
642 an optional :ref:`calling convention <callingconv>`,
643 an optional ``unnamed_addr`` attribute, a return type, an optional
644 :ref:`parameter attribute <paramattrs>` for the return type, a function
645 name, a possibly empty list of arguments, an optional alignment, an optional
646 :ref:`garbage collector name <gc>` and an optional :ref:`prefix <prefixdata>`.
648 A function definition contains a list of basic blocks, forming the CFG (Control
649 Flow Graph) for the function. Each basic block may optionally start with a label
650 (giving the basic block a symbol table entry), contains a list of instructions,
651 and ends with a :ref:`terminator <terminators>` instruction (such as a branch or
652 function return). If an explicit label is not provided, a block is assigned an
653 implicit numbered label, using the next value from the same counter as used for
654 unnamed temporaries (:ref:`see above<identifiers>`). For example, if a function
655 entry block does not have an explicit label, it will be assigned label "%0",
656 then the first unnamed temporary in that block will be "%1", etc.
658 The first basic block in a function is special in two ways: it is
659 immediately executed on entrance to the function, and it is not allowed
660 to have predecessor basic blocks (i.e. there can not be any branches to
661 the entry block of a function). Because the block can have no
662 predecessors, it also cannot have any :ref:`PHI nodes <i_phi>`.
664 LLVM allows an explicit section to be specified for functions. If the
665 target supports it, it will emit functions to the section specified.
666 Additionally, the function can placed in a COMDAT.
668 An explicit alignment may be specified for a function. If not present,
669 or if the alignment is set to zero, the alignment of the function is set
670 by the target to whatever it feels convenient. If an explicit alignment
671 is specified, the function is forced to have at least that much
672 alignment. All alignments must be a power of 2.
674 If the ``unnamed_addr`` attribute is given, the address is know to not
675 be significant and two identical functions can be merged.
679 define [linkage] [visibility] [DLLStorageClass]
681 <ResultType> @<FunctionName> ([argument list])
682 [unnamed_addr] [fn Attrs] [section "name"] [comdat $<ComdatName>]
683 [align N] [gc] [prefix Constant] { ... }
685 The argument list is a comma seperated sequence of arguments where each
686 argument is of the following form
690 <type> [parameter Attrs] [name]
698 Aliases, unlike function or variables, don't create any new data. They
699 are just a new symbol and metadata for an existing position.
701 Aliases have a name and an aliasee that is either a global value or a
704 Aliases may have an optional :ref:`linkage type <linkage>`, an optional
705 :ref:`visibility style <visibility>`, an optional :ref:`DLL storage class
706 <dllstorageclass>` and an optional :ref:`tls model <tls_model>`.
710 @<Name> = [Linkage] [Visibility] [DLLStorageClass] [ThreadLocal] [unnamed_addr] alias <AliaseeTy> @<Aliasee>
712 The linkage must be one of ``private``, ``internal``, ``linkonce``, ``weak``,
713 ``linkonce_odr``, ``weak_odr``, ``external``. Note that some system linkers
714 might not correctly handle dropping a weak symbol that is aliased.
716 Alias that are not ``unnamed_addr`` are guaranteed to have the same address as
717 the aliasee expression. ``unnamed_addr`` ones are only guaranteed to point
720 Since aliases are only a second name, some restrictions apply, of which
721 some can only be checked when producing an object file:
723 * The expression defining the aliasee must be computable at assembly
724 time. Since it is just a name, no relocations can be used.
726 * No alias in the expression can be weak as the possibility of the
727 intermediate alias being overridden cannot be represented in an
730 * No global value in the expression can be a declaration, since that
731 would require a relocation, which is not possible.
738 Comdat IR provides access to COFF and ELF object file COMDAT functionality.
740 Comdats have a name which represents the COMDAT key. All global objects that
741 specify this key will only end up in the final object file if the linker chooses
742 that key over some other key. Aliases are placed in the same COMDAT that their
743 aliasee computes to, if any.
745 Comdats have a selection kind to provide input on how the linker should
746 choose between keys in two different object files.
750 $<Name> = comdat SelectionKind
752 The selection kind must be one of the following:
755 The linker may choose any COMDAT key, the choice is arbitrary.
757 The linker may choose any COMDAT key but the sections must contain the
760 The linker will choose the section containing the largest COMDAT key.
762 The linker requires that only section with this COMDAT key exist.
764 The linker may choose any COMDAT key but the sections must contain the
767 Note that the Mach-O platform doesn't support COMDATs and ELF only supports
768 ``any`` as a selection kind.
770 Here is an example of a COMDAT group where a function will only be selected if
771 the COMDAT key's section is the largest:
775 $foo = comdat largest
776 @foo = global i32 2, comdat $foo
778 define void @bar() comdat $foo {
782 In a COFF object file, this will create a COMDAT section with selection kind
783 ``IMAGE_COMDAT_SELECT_LARGEST`` containing the contents of the ``@foo`` symbol
784 and another COMDAT section with selection kind
785 ``IMAGE_COMDAT_SELECT_ASSOCIATIVE`` which is associated with the first COMDAT
786 section and contains the contents of the ``@bar`` symbol.
788 There are some restrictions on the properties of the global object.
789 It, or an alias to it, must have the same name as the COMDAT group when
791 The contents and size of this object may be used during link-time to determine
792 which COMDAT groups get selected depending on the selection kind.
793 Because the name of the object must match the name of the COMDAT group, the
794 linkage of the global object must not be local; local symbols can get renamed
795 if a collision occurs in the symbol table.
797 The combined use of COMDATS and section attributes may yield surprising results.
804 @g1 = global i32 42, section "sec", comdat $foo
805 @g2 = global i32 42, section "sec", comdat $bar
807 From the object file perspective, this requires the creation of two sections
808 with the same name. This is necessary because both globals belong to different
809 COMDAT groups and COMDATs, at the object file level, are represented by
812 Note that certain IR constructs like global variables and functions may create
813 COMDATs in the object file in addition to any which are specified using COMDAT
814 IR. This arises, for example, when a global variable has linkonce_odr linkage.
816 .. _namedmetadatastructure:
821 Named metadata is a collection of metadata. :ref:`Metadata
822 nodes <metadata>` (but not metadata strings) are the only valid
823 operands for a named metadata.
827 ; Some unnamed metadata nodes, which are referenced by the named metadata.
828 !0 = metadata !{metadata !"zero"}
829 !1 = metadata !{metadata !"one"}
830 !2 = metadata !{metadata !"two"}
832 !name = !{!0, !1, !2}
839 The return type and each parameter of a function type may have a set of
840 *parameter attributes* associated with them. Parameter attributes are
841 used to communicate additional information about the result or
842 parameters of a function. Parameter attributes are considered to be part
843 of the function, not of the function type, so functions with different
844 parameter attributes can have the same function type.
846 Parameter attributes are simple keywords that follow the type specified.
847 If multiple parameter attributes are needed, they are space separated.
852 declare i32 @printf(i8* noalias nocapture, ...)
853 declare i32 @atoi(i8 zeroext)
854 declare signext i8 @returns_signed_char()
856 Note that any attributes for the function result (``nounwind``,
857 ``readonly``) come immediately after the argument list.
859 Currently, only the following parameter attributes are defined:
862 This indicates to the code generator that the parameter or return
863 value should be zero-extended to the extent required by the target's
864 ABI (which is usually 32-bits, but is 8-bits for a i1 on x86-64) by
865 the caller (for a parameter) or the callee (for a return value).
867 This indicates to the code generator that the parameter or return
868 value should be sign-extended to the extent required by the target's
869 ABI (which is usually 32-bits) by the caller (for a parameter) or
870 the callee (for a return value).
872 This indicates that this parameter or return value should be treated
873 in a special target-dependent fashion during while emitting code for
874 a function call or return (usually, by putting it in a register as
875 opposed to memory, though some targets use it to distinguish between
876 two different kinds of registers). Use of this attribute is
879 This indicates that the pointer parameter should really be passed by
880 value to the function. The attribute implies that a hidden copy of
881 the pointee is made between the caller and the callee, so the callee
882 is unable to modify the value in the caller. This attribute is only
883 valid on LLVM pointer arguments. It is generally used to pass
884 structs and arrays by value, but is also valid on pointers to
885 scalars. The copy is considered to belong to the caller not the
886 callee (for example, ``readonly`` functions should not write to
887 ``byval`` parameters). This is not a valid attribute for return
890 The byval attribute also supports specifying an alignment with the
891 align attribute. It indicates the alignment of the stack slot to
892 form and the known alignment of the pointer specified to the call
893 site. If the alignment is not specified, then the code generator
894 makes a target-specific assumption.
900 The ``inalloca`` argument attribute allows the caller to take the
901 address of outgoing stack arguments. An ``inalloca`` argument must
902 be a pointer to stack memory produced by an ``alloca`` instruction.
903 The alloca, or argument allocation, must also be tagged with the
904 inalloca keyword. Only the last argument may have the ``inalloca``
905 attribute, and that argument is guaranteed to be passed in memory.
907 An argument allocation may be used by a call at most once because
908 the call may deallocate it. The ``inalloca`` attribute cannot be
909 used in conjunction with other attributes that affect argument
910 storage, like ``inreg``, ``nest``, ``sret``, or ``byval``. The
911 ``inalloca`` attribute also disables LLVM's implicit lowering of
912 large aggregate return values, which means that frontend authors
913 must lower them with ``sret`` pointers.
915 When the call site is reached, the argument allocation must have
916 been the most recent stack allocation that is still live, or the
917 results are undefined. It is possible to allocate additional stack
918 space after an argument allocation and before its call site, but it
919 must be cleared off with :ref:`llvm.stackrestore
922 See :doc:`InAlloca` for more information on how to use this
926 This indicates that the pointer parameter specifies the address of a
927 structure that is the return value of the function in the source
928 program. This pointer must be guaranteed by the caller to be valid:
929 loads and stores to the structure may be assumed by the callee
930 not to trap and to be properly aligned. This may only be applied to
931 the first parameter. This is not a valid attribute for return
935 This indicates that the pointer value may be assumed by the optimizer to
936 have the specified alignment.
938 Note that this attribute has additional semantics when combined with the
944 This indicates that pointer values :ref:`based <pointeraliasing>` on
945 the argument or return value do not alias pointer values that are
946 not *based* on it, ignoring certain "irrelevant" dependencies. For a
947 call to the parent function, dependencies between memory references
948 from before or after the call and from those during the call are
949 "irrelevant" to the ``noalias`` keyword for the arguments and return
950 value used in that call. The caller shares the responsibility with
951 the callee for ensuring that these requirements are met. For further
952 details, please see the discussion of the NoAlias response in :ref:`alias
953 analysis <Must, May, or No>`.
955 Note that this definition of ``noalias`` is intentionally similar
956 to the definition of ``restrict`` in C99 for function arguments,
957 though it is slightly weaker.
959 For function return values, C99's ``restrict`` is not meaningful,
960 while LLVM's ``noalias`` is.
962 This indicates that the callee does not make any copies of the
963 pointer that outlive the callee itself. This is not a valid
964 attribute for return values.
969 This indicates that the pointer parameter can be excised using the
970 :ref:`trampoline intrinsics <int_trampoline>`. This is not a valid
971 attribute for return values and can only be applied to one parameter.
974 This indicates that the function always returns the argument as its return
975 value. This is an optimization hint to the code generator when generating
976 the caller, allowing tail call optimization and omission of register saves
977 and restores in some cases; it is not checked or enforced when generating
978 the callee. The parameter and the function return type must be valid
979 operands for the :ref:`bitcast instruction <i_bitcast>`. This is not a
980 valid attribute for return values and can only be applied to one parameter.
983 This indicates that the parameter or return pointer is not null. This
984 attribute may only be applied to pointer typed parameters. This is not
985 checked or enforced by LLVM, the caller must ensure that the pointer
986 passed in is non-null, or the callee must ensure that the returned pointer
989 ``dereferenceable(<n>)``
990 This indicates that the parameter or return pointer is dereferenceable. This
991 attribute may only be applied to pointer typed parameters. A pointer that
992 is dereferenceable can be loaded from speculatively without a risk of
993 trapping. The number of bytes known to be dereferenceable must be provided
994 in parentheses. It is legal for the number of bytes to be less than the
995 size of the pointee type. The ``nonnull`` attribute does not imply
996 dereferenceability (consider a pointer to one element past the end of an
997 array), however ``dereferenceable(<n>)`` does imply ``nonnull`` in
998 ``addrspace(0)`` (which is the default address space).
1002 Garbage Collector Names
1003 -----------------------
1005 Each function may specify a garbage collector name, which is simply a
1008 .. code-block:: llvm
1010 define void @f() gc "name" { ... }
1012 The compiler declares the supported values of *name*. Specifying a
1013 collector will cause the compiler to alter its output in order to
1014 support the named garbage collection algorithm.
1021 Prefix data is data associated with a function which the code generator
1022 will emit immediately before the function body. The purpose of this feature
1023 is to allow frontends to associate language-specific runtime metadata with
1024 specific functions and make it available through the function pointer while
1025 still allowing the function pointer to be called. To access the data for a
1026 given function, a program may bitcast the function pointer to a pointer to
1027 the constant's type. This implies that the IR symbol points to the start
1030 To maintain the semantics of ordinary function calls, the prefix data must
1031 have a particular format. Specifically, it must begin with a sequence of
1032 bytes which decode to a sequence of machine instructions, valid for the
1033 module's target, which transfer control to the point immediately succeeding
1034 the prefix data, without performing any other visible action. This allows
1035 the inliner and other passes to reason about the semantics of the function
1036 definition without needing to reason about the prefix data. Obviously this
1037 makes the format of the prefix data highly target dependent.
1039 Prefix data is laid out as if it were an initializer for a global variable
1040 of the prefix data's type. No padding is automatically placed between the
1041 prefix data and the function body. If padding is required, it must be part
1044 A trivial example of valid prefix data for the x86 architecture is ``i8 144``,
1045 which encodes the ``nop`` instruction:
1047 .. code-block:: llvm
1049 define void @f() prefix i8 144 { ... }
1051 Generally prefix data can be formed by encoding a relative branch instruction
1052 which skips the metadata, as in this example of valid prefix data for the
1053 x86_64 architecture, where the first two bytes encode ``jmp .+10``:
1055 .. code-block:: llvm
1057 %0 = type <{ i8, i8, i8* }>
1059 define void @f() prefix %0 <{ i8 235, i8 8, i8* @md}> { ... }
1061 A function may have prefix data but no body. This has similar semantics
1062 to the ``available_externally`` linkage in that the data may be used by the
1063 optimizers but will not be emitted in the object file.
1070 Attribute groups are groups of attributes that are referenced by objects within
1071 the IR. They are important for keeping ``.ll`` files readable, because a lot of
1072 functions will use the same set of attributes. In the degenerative case of a
1073 ``.ll`` file that corresponds to a single ``.c`` file, the single attribute
1074 group will capture the important command line flags used to build that file.
1076 An attribute group is a module-level object. To use an attribute group, an
1077 object references the attribute group's ID (e.g. ``#37``). An object may refer
1078 to more than one attribute group. In that situation, the attributes from the
1079 different groups are merged.
1081 Here is an example of attribute groups for a function that should always be
1082 inlined, has a stack alignment of 4, and which shouldn't use SSE instructions:
1084 .. code-block:: llvm
1086 ; Target-independent attributes:
1087 attributes #0 = { alwaysinline alignstack=4 }
1089 ; Target-dependent attributes:
1090 attributes #1 = { "no-sse" }
1092 ; Function @f has attributes: alwaysinline, alignstack=4, and "no-sse".
1093 define void @f() #0 #1 { ... }
1100 Function attributes are set to communicate additional information about
1101 a function. Function attributes are considered to be part of the
1102 function, not of the function type, so functions with different function
1103 attributes can have the same function type.
1105 Function attributes are simple keywords that follow the type specified.
1106 If multiple attributes are needed, they are space separated. For
1109 .. code-block:: llvm
1111 define void @f() noinline { ... }
1112 define void @f() alwaysinline { ... }
1113 define void @f() alwaysinline optsize { ... }
1114 define void @f() optsize { ... }
1117 This attribute indicates that, when emitting the prologue and
1118 epilogue, the backend should forcibly align the stack pointer.
1119 Specify the desired alignment, which must be a power of two, in
1122 This attribute indicates that the inliner should attempt to inline
1123 this function into callers whenever possible, ignoring any active
1124 inlining size threshold for this caller.
1126 This indicates that the callee function at a call site should be
1127 recognized as a built-in function, even though the function's declaration
1128 uses the ``nobuiltin`` attribute. This is only valid at call sites for
1129 direct calls to functions that are declared with the ``nobuiltin``
1132 This attribute indicates that this function is rarely called. When
1133 computing edge weights, basic blocks post-dominated by a cold
1134 function call are also considered to be cold; and, thus, given low
1137 This attribute indicates that the source code contained a hint that
1138 inlining this function is desirable (such as the "inline" keyword in
1139 C/C++). It is just a hint; it imposes no requirements on the
1142 This attribute indicates that the function should be added to a
1143 jump-instruction table at code-generation time, and that all address-taken
1144 references to this function should be replaced with a reference to the
1145 appropriate jump-instruction-table function pointer. Note that this creates
1146 a new pointer for the original function, which means that code that depends
1147 on function-pointer identity can break. So, any function annotated with
1148 ``jumptable`` must also be ``unnamed_addr``.
1150 This attribute suggests that optimization passes and code generator
1151 passes make choices that keep the code size of this function as small
1152 as possible and perform optimizations that may sacrifice runtime
1153 performance in order to minimize the size of the generated code.
1155 This attribute disables prologue / epilogue emission for the
1156 function. This can have very system-specific consequences.
1158 This indicates that the callee function at a call site is not recognized as
1159 a built-in function. LLVM will retain the original call and not replace it
1160 with equivalent code based on the semantics of the built-in function, unless
1161 the call site uses the ``builtin`` attribute. This is valid at call sites
1162 and on function declarations and definitions.
1164 This attribute indicates that calls to the function cannot be
1165 duplicated. A call to a ``noduplicate`` function may be moved
1166 within its parent function, but may not be duplicated within
1167 its parent function.
1169 A function containing a ``noduplicate`` call may still
1170 be an inlining candidate, provided that the call is not
1171 duplicated by inlining. That implies that the function has
1172 internal linkage and only has one call site, so the original
1173 call is dead after inlining.
1175 This attributes disables implicit floating point instructions.
1177 This attribute indicates that the inliner should never inline this
1178 function in any situation. This attribute may not be used together
1179 with the ``alwaysinline`` attribute.
1181 This attribute suppresses lazy symbol binding for the function. This
1182 may make calls to the function faster, at the cost of extra program
1183 startup time if the function is not called during program startup.
1185 This attribute indicates that the code generator should not use a
1186 red zone, even if the target-specific ABI normally permits it.
1188 This function attribute indicates that the function never returns
1189 normally. This produces undefined behavior at runtime if the
1190 function ever does dynamically return.
1192 This function attribute indicates that the function never returns
1193 with an unwind or exceptional control flow. If the function does
1194 unwind, its runtime behavior is undefined.
1196 This function attribute indicates that the function is not optimized
1197 by any optimization or code generator passes with the
1198 exception of interprocedural optimization passes.
1199 This attribute cannot be used together with the ``alwaysinline``
1200 attribute; this attribute is also incompatible
1201 with the ``minsize`` attribute and the ``optsize`` attribute.
1203 This attribute requires the ``noinline`` attribute to be specified on
1204 the function as well, so the function is never inlined into any caller.
1205 Only functions with the ``alwaysinline`` attribute are valid
1206 candidates for inlining into the body of this function.
1208 This attribute suggests that optimization passes and code generator
1209 passes make choices that keep the code size of this function low,
1210 and otherwise do optimizations specifically to reduce code size as
1211 long as they do not significantly impact runtime performance.
1213 On a function, this attribute indicates that the function computes its
1214 result (or decides to unwind an exception) based strictly on its arguments,
1215 without dereferencing any pointer arguments or otherwise accessing
1216 any mutable state (e.g. memory, control registers, etc) visible to
1217 caller functions. It does not write through any pointer arguments
1218 (including ``byval`` arguments) and never changes any state visible
1219 to callers. This means that it cannot unwind exceptions by calling
1220 the ``C++`` exception throwing methods.
1222 On an argument, this attribute indicates that the function does not
1223 dereference that pointer argument, even though it may read or write the
1224 memory that the pointer points to if accessed through other pointers.
1226 On a function, this attribute indicates that the function does not write
1227 through any pointer arguments (including ``byval`` arguments) or otherwise
1228 modify any state (e.g. memory, control registers, etc) visible to
1229 caller functions. It may dereference pointer arguments and read
1230 state that may be set in the caller. A readonly function always
1231 returns the same value (or unwinds an exception identically) when
1232 called with the same set of arguments and global state. It cannot
1233 unwind an exception by calling the ``C++`` exception throwing
1236 On an argument, this attribute indicates that the function does not write
1237 through this pointer argument, even though it may write to the memory that
1238 the pointer points to.
1240 This attribute indicates that this function can return twice. The C
1241 ``setjmp`` is an example of such a function. The compiler disables
1242 some optimizations (like tail calls) in the caller of these
1244 ``sanitize_address``
1245 This attribute indicates that AddressSanitizer checks
1246 (dynamic address safety analysis) are enabled for this function.
1248 This attribute indicates that MemorySanitizer checks (dynamic detection
1249 of accesses to uninitialized memory) are enabled for this function.
1251 This attribute indicates that ThreadSanitizer checks
1252 (dynamic thread safety analysis) are enabled for this function.
1254 This attribute indicates that the function should emit a stack
1255 smashing protector. It is in the form of a "canary" --- a random value
1256 placed on the stack before the local variables that's checked upon
1257 return from the function to see if it has been overwritten. A
1258 heuristic is used to determine if a function needs stack protectors
1259 or not. The heuristic used will enable protectors for functions with:
1261 - Character arrays larger than ``ssp-buffer-size`` (default 8).
1262 - Aggregates containing character arrays larger than ``ssp-buffer-size``.
1263 - Calls to alloca() with variable sizes or constant sizes greater than
1264 ``ssp-buffer-size``.
1266 Variables that are identified as requiring a protector will be arranged
1267 on the stack such that they are adjacent to the stack protector guard.
1269 If a function that has an ``ssp`` attribute is inlined into a
1270 function that doesn't have an ``ssp`` attribute, then the resulting
1271 function will have an ``ssp`` attribute.
1273 This attribute indicates that the function should *always* emit a
1274 stack smashing protector. This overrides the ``ssp`` function
1277 Variables that are identified as requiring a protector will be arranged
1278 on the stack such that they are adjacent to the stack protector guard.
1279 The specific layout rules are:
1281 #. Large arrays and structures containing large arrays
1282 (``>= ssp-buffer-size``) are closest to the stack protector.
1283 #. Small arrays and structures containing small arrays
1284 (``< ssp-buffer-size``) are 2nd closest to the protector.
1285 #. Variables that have had their address taken are 3rd closest to the
1288 If a function that has an ``sspreq`` attribute is inlined into a
1289 function that doesn't have an ``sspreq`` attribute or which has an
1290 ``ssp`` or ``sspstrong`` attribute, then the resulting function will have
1291 an ``sspreq`` attribute.
1293 This attribute indicates that the function should emit a stack smashing
1294 protector. This attribute causes a strong heuristic to be used when
1295 determining if a function needs stack protectors. The strong heuristic
1296 will enable protectors for functions with:
1298 - Arrays of any size and type
1299 - Aggregates containing an array of any size and type.
1300 - Calls to alloca().
1301 - Local variables that have had their address taken.
1303 Variables that are identified as requiring a protector will be arranged
1304 on the stack such that they are adjacent to the stack protector guard.
1305 The specific layout rules are:
1307 #. Large arrays and structures containing large arrays
1308 (``>= ssp-buffer-size``) are closest to the stack protector.
1309 #. Small arrays and structures containing small arrays
1310 (``< ssp-buffer-size``) are 2nd closest to the protector.
1311 #. Variables that have had their address taken are 3rd closest to the
1314 This overrides the ``ssp`` function attribute.
1316 If a function that has an ``sspstrong`` attribute is inlined into a
1317 function that doesn't have an ``sspstrong`` attribute, then the
1318 resulting function will have an ``sspstrong`` attribute.
1320 This attribute indicates that the ABI being targeted requires that
1321 an unwind table entry be produce for this function even if we can
1322 show that no exceptions passes by it. This is normally the case for
1323 the ELF x86-64 abi, but it can be disabled for some compilation
1328 Module-Level Inline Assembly
1329 ----------------------------
1331 Modules may contain "module-level inline asm" blocks, which corresponds
1332 to the GCC "file scope inline asm" blocks. These blocks are internally
1333 concatenated by LLVM and treated as a single unit, but may be separated
1334 in the ``.ll`` file if desired. The syntax is very simple:
1336 .. code-block:: llvm
1338 module asm "inline asm code goes here"
1339 module asm "more can go here"
1341 The strings can contain any character by escaping non-printable
1342 characters. The escape sequence used is simply "\\xx" where "xx" is the
1343 two digit hex code for the number.
1345 The inline asm code is simply printed to the machine code .s file when
1346 assembly code is generated.
1348 .. _langref_datalayout:
1353 A module may specify a target specific data layout string that specifies
1354 how data is to be laid out in memory. The syntax for the data layout is
1357 .. code-block:: llvm
1359 target datalayout = "layout specification"
1361 The *layout specification* consists of a list of specifications
1362 separated by the minus sign character ('-'). Each specification starts
1363 with a letter and may include other information after the letter to
1364 define some aspect of the data layout. The specifications accepted are
1368 Specifies that the target lays out data in big-endian form. That is,
1369 the bits with the most significance have the lowest address
1372 Specifies that the target lays out data in little-endian form. That
1373 is, the bits with the least significance have the lowest address
1376 Specifies the natural alignment of the stack in bits. Alignment
1377 promotion of stack variables is limited to the natural stack
1378 alignment to avoid dynamic stack realignment. The stack alignment
1379 must be a multiple of 8-bits. If omitted, the natural stack
1380 alignment defaults to "unspecified", which does not prevent any
1381 alignment promotions.
1382 ``p[n]:<size>:<abi>:<pref>``
1383 This specifies the *size* of a pointer and its ``<abi>`` and
1384 ``<pref>``\erred alignments for address space ``n``. All sizes are in
1385 bits. The address space, ``n`` is optional, and if not specified,
1386 denotes the default address space 0. The value of ``n`` must be
1387 in the range [1,2^23).
1388 ``i<size>:<abi>:<pref>``
1389 This specifies the alignment for an integer type of a given bit
1390 ``<size>``. The value of ``<size>`` must be in the range [1,2^23).
1391 ``v<size>:<abi>:<pref>``
1392 This specifies the alignment for a vector type of a given bit
1394 ``f<size>:<abi>:<pref>``
1395 This specifies the alignment for a floating point type of a given bit
1396 ``<size>``. Only values of ``<size>`` that are supported by the target
1397 will work. 32 (float) and 64 (double) are supported on all targets; 80
1398 or 128 (different flavors of long double) are also supported on some
1401 This specifies the alignment for an object of aggregate type.
1403 If present, specifies that llvm names are mangled in the output. The
1406 * ``e``: ELF mangling: Private symbols get a ``.L`` prefix.
1407 * ``m``: Mips mangling: Private symbols get a ``$`` prefix.
1408 * ``o``: Mach-O mangling: Private symbols get ``L`` prefix. Other
1409 symbols get a ``_`` prefix.
1410 * ``w``: Windows COFF prefix: Similar to Mach-O, but stdcall and fastcall
1411 functions also get a suffix based on the frame size.
1412 ``n<size1>:<size2>:<size3>...``
1413 This specifies a set of native integer widths for the target CPU in
1414 bits. For example, it might contain ``n32`` for 32-bit PowerPC,
1415 ``n32:64`` for PowerPC 64, or ``n8:16:32:64`` for X86-64. Elements of
1416 this set are considered to support most general arithmetic operations
1419 On every specification that takes a ``<abi>:<pref>``, specifying the
1420 ``<pref>`` alignment is optional. If omitted, the preceding ``:``
1421 should be omitted too and ``<pref>`` will be equal to ``<abi>``.
1423 When constructing the data layout for a given target, LLVM starts with a
1424 default set of specifications which are then (possibly) overridden by
1425 the specifications in the ``datalayout`` keyword. The default
1426 specifications are given in this list:
1428 - ``E`` - big endian
1429 - ``p:64:64:64`` - 64-bit pointers with 64-bit alignment.
1430 - ``p[n]:64:64:64`` - Other address spaces are assumed to be the
1431 same as the default address space.
1432 - ``S0`` - natural stack alignment is unspecified
1433 - ``i1:8:8`` - i1 is 8-bit (byte) aligned
1434 - ``i8:8:8`` - i8 is 8-bit (byte) aligned
1435 - ``i16:16:16`` - i16 is 16-bit aligned
1436 - ``i32:32:32`` - i32 is 32-bit aligned
1437 - ``i64:32:64`` - i64 has ABI alignment of 32-bits but preferred
1438 alignment of 64-bits
1439 - ``f16:16:16`` - half is 16-bit aligned
1440 - ``f32:32:32`` - float is 32-bit aligned
1441 - ``f64:64:64`` - double is 64-bit aligned
1442 - ``f128:128:128`` - quad is 128-bit aligned
1443 - ``v64:64:64`` - 64-bit vector is 64-bit aligned
1444 - ``v128:128:128`` - 128-bit vector is 128-bit aligned
1445 - ``a:0:64`` - aggregates are 64-bit aligned
1447 When LLVM is determining the alignment for a given type, it uses the
1450 #. If the type sought is an exact match for one of the specifications,
1451 that specification is used.
1452 #. If no match is found, and the type sought is an integer type, then
1453 the smallest integer type that is larger than the bitwidth of the
1454 sought type is used. If none of the specifications are larger than
1455 the bitwidth then the largest integer type is used. For example,
1456 given the default specifications above, the i7 type will use the
1457 alignment of i8 (next largest) while both i65 and i256 will use the
1458 alignment of i64 (largest specified).
1459 #. If no match is found, and the type sought is a vector type, then the
1460 largest vector type that is smaller than the sought vector type will
1461 be used as a fall back. This happens because <128 x double> can be
1462 implemented in terms of 64 <2 x double>, for example.
1464 The function of the data layout string may not be what you expect.
1465 Notably, this is not a specification from the frontend of what alignment
1466 the code generator should use.
1468 Instead, if specified, the target data layout is required to match what
1469 the ultimate *code generator* expects. This string is used by the
1470 mid-level optimizers to improve code, and this only works if it matches
1471 what the ultimate code generator uses. If you would like to generate IR
1472 that does not embed this target-specific detail into the IR, then you
1473 don't have to specify the string. This will disable some optimizations
1474 that require precise layout information, but this also prevents those
1475 optimizations from introducing target specificity into the IR.
1482 A module may specify a target triple string that describes the target
1483 host. The syntax for the target triple is simply:
1485 .. code-block:: llvm
1487 target triple = "x86_64-apple-macosx10.7.0"
1489 The *target triple* string consists of a series of identifiers delimited
1490 by the minus sign character ('-'). The canonical forms are:
1494 ARCHITECTURE-VENDOR-OPERATING_SYSTEM
1495 ARCHITECTURE-VENDOR-OPERATING_SYSTEM-ENVIRONMENT
1497 This information is passed along to the backend so that it generates
1498 code for the proper architecture. It's possible to override this on the
1499 command line with the ``-mtriple`` command line option.
1501 .. _pointeraliasing:
1503 Pointer Aliasing Rules
1504 ----------------------
1506 Any memory access must be done through a pointer value associated with
1507 an address range of the memory access, otherwise the behavior is
1508 undefined. Pointer values are associated with address ranges according
1509 to the following rules:
1511 - A pointer value is associated with the addresses associated with any
1512 value it is *based* on.
1513 - An address of a global variable is associated with the address range
1514 of the variable's storage.
1515 - The result value of an allocation instruction is associated with the
1516 address range of the allocated storage.
1517 - A null pointer in the default address-space is associated with no
1519 - An integer constant other than zero or a pointer value returned from
1520 a function not defined within LLVM may be associated with address
1521 ranges allocated through mechanisms other than those provided by
1522 LLVM. Such ranges shall not overlap with any ranges of addresses
1523 allocated by mechanisms provided by LLVM.
1525 A pointer value is *based* on another pointer value according to the
1528 - A pointer value formed from a ``getelementptr`` operation is *based*
1529 on the first operand of the ``getelementptr``.
1530 - The result value of a ``bitcast`` is *based* on the operand of the
1532 - A pointer value formed by an ``inttoptr`` is *based* on all pointer
1533 values that contribute (directly or indirectly) to the computation of
1534 the pointer's value.
1535 - The "*based* on" relationship is transitive.
1537 Note that this definition of *"based"* is intentionally similar to the
1538 definition of *"based"* in C99, though it is slightly weaker.
1540 LLVM IR does not associate types with memory. The result type of a
1541 ``load`` merely indicates the size and alignment of the memory from
1542 which to load, as well as the interpretation of the value. The first
1543 operand type of a ``store`` similarly only indicates the size and
1544 alignment of the store.
1546 Consequently, type-based alias analysis, aka TBAA, aka
1547 ``-fstrict-aliasing``, is not applicable to general unadorned LLVM IR.
1548 :ref:`Metadata <metadata>` may be used to encode additional information
1549 which specialized optimization passes may use to implement type-based
1554 Volatile Memory Accesses
1555 ------------------------
1557 Certain memory accesses, such as :ref:`load <i_load>`'s,
1558 :ref:`store <i_store>`'s, and :ref:`llvm.memcpy <int_memcpy>`'s may be
1559 marked ``volatile``. The optimizers must not change the number of
1560 volatile operations or change their order of execution relative to other
1561 volatile operations. The optimizers *may* change the order of volatile
1562 operations relative to non-volatile operations. This is not Java's
1563 "volatile" and has no cross-thread synchronization behavior.
1565 IR-level volatile loads and stores cannot safely be optimized into
1566 llvm.memcpy or llvm.memmove intrinsics even when those intrinsics are
1567 flagged volatile. Likewise, the backend should never split or merge
1568 target-legal volatile load/store instructions.
1570 .. admonition:: Rationale
1572 Platforms may rely on volatile loads and stores of natively supported
1573 data width to be executed as single instruction. For example, in C
1574 this holds for an l-value of volatile primitive type with native
1575 hardware support, but not necessarily for aggregate types. The
1576 frontend upholds these expectations, which are intentionally
1577 unspecified in the IR. The rules above ensure that IR transformation
1578 do not violate the frontend's contract with the language.
1582 Memory Model for Concurrent Operations
1583 --------------------------------------
1585 The LLVM IR does not define any way to start parallel threads of
1586 execution or to register signal handlers. Nonetheless, there are
1587 platform-specific ways to create them, and we define LLVM IR's behavior
1588 in their presence. This model is inspired by the C++0x memory model.
1590 For a more informal introduction to this model, see the :doc:`Atomics`.
1592 We define a *happens-before* partial order as the least partial order
1595 - Is a superset of single-thread program order, and
1596 - When a *synchronizes-with* ``b``, includes an edge from ``a`` to
1597 ``b``. *Synchronizes-with* pairs are introduced by platform-specific
1598 techniques, like pthread locks, thread creation, thread joining,
1599 etc., and by atomic instructions. (See also :ref:`Atomic Memory Ordering
1600 Constraints <ordering>`).
1602 Note that program order does not introduce *happens-before* edges
1603 between a thread and signals executing inside that thread.
1605 Every (defined) read operation (load instructions, memcpy, atomic
1606 loads/read-modify-writes, etc.) R reads a series of bytes written by
1607 (defined) write operations (store instructions, atomic
1608 stores/read-modify-writes, memcpy, etc.). For the purposes of this
1609 section, initialized globals are considered to have a write of the
1610 initializer which is atomic and happens before any other read or write
1611 of the memory in question. For each byte of a read R, R\ :sub:`byte`
1612 may see any write to the same byte, except:
1614 - If write\ :sub:`1` happens before write\ :sub:`2`, and
1615 write\ :sub:`2` happens before R\ :sub:`byte`, then
1616 R\ :sub:`byte` does not see write\ :sub:`1`.
1617 - If R\ :sub:`byte` happens before write\ :sub:`3`, then
1618 R\ :sub:`byte` does not see write\ :sub:`3`.
1620 Given that definition, R\ :sub:`byte` is defined as follows:
1622 - If R is volatile, the result is target-dependent. (Volatile is
1623 supposed to give guarantees which can support ``sig_atomic_t`` in
1624 C/C++, and may be used for accesses to addresses that do not behave
1625 like normal memory. It does not generally provide cross-thread
1627 - Otherwise, if there is no write to the same byte that happens before
1628 R\ :sub:`byte`, R\ :sub:`byte` returns ``undef`` for that byte.
1629 - Otherwise, if R\ :sub:`byte` may see exactly one write,
1630 R\ :sub:`byte` returns the value written by that write.
1631 - Otherwise, if R is atomic, and all the writes R\ :sub:`byte` may
1632 see are atomic, it chooses one of the values written. See the :ref:`Atomic
1633 Memory Ordering Constraints <ordering>` section for additional
1634 constraints on how the choice is made.
1635 - Otherwise R\ :sub:`byte` returns ``undef``.
1637 R returns the value composed of the series of bytes it read. This
1638 implies that some bytes within the value may be ``undef`` **without**
1639 the entire value being ``undef``. Note that this only defines the
1640 semantics of the operation; it doesn't mean that targets will emit more
1641 than one instruction to read the series of bytes.
1643 Note that in cases where none of the atomic intrinsics are used, this
1644 model places only one restriction on IR transformations on top of what
1645 is required for single-threaded execution: introducing a store to a byte
1646 which might not otherwise be stored is not allowed in general.
1647 (Specifically, in the case where another thread might write to and read
1648 from an address, introducing a store can change a load that may see
1649 exactly one write into a load that may see multiple writes.)
1653 Atomic Memory Ordering Constraints
1654 ----------------------------------
1656 Atomic instructions (:ref:`cmpxchg <i_cmpxchg>`,
1657 :ref:`atomicrmw <i_atomicrmw>`, :ref:`fence <i_fence>`,
1658 :ref:`atomic load <i_load>`, and :ref:`atomic store <i_store>`) take
1659 ordering parameters that determine which other atomic instructions on
1660 the same address they *synchronize with*. These semantics are borrowed
1661 from Java and C++0x, but are somewhat more colloquial. If these
1662 descriptions aren't precise enough, check those specs (see spec
1663 references in the :doc:`atomics guide <Atomics>`).
1664 :ref:`fence <i_fence>` instructions treat these orderings somewhat
1665 differently since they don't take an address. See that instruction's
1666 documentation for details.
1668 For a simpler introduction to the ordering constraints, see the
1672 The set of values that can be read is governed by the happens-before
1673 partial order. A value cannot be read unless some operation wrote
1674 it. This is intended to provide a guarantee strong enough to model
1675 Java's non-volatile shared variables. This ordering cannot be
1676 specified for read-modify-write operations; it is not strong enough
1677 to make them atomic in any interesting way.
1679 In addition to the guarantees of ``unordered``, there is a single
1680 total order for modifications by ``monotonic`` operations on each
1681 address. All modification orders must be compatible with the
1682 happens-before order. There is no guarantee that the modification
1683 orders can be combined to a global total order for the whole program
1684 (and this often will not be possible). The read in an atomic
1685 read-modify-write operation (:ref:`cmpxchg <i_cmpxchg>` and
1686 :ref:`atomicrmw <i_atomicrmw>`) reads the value in the modification
1687 order immediately before the value it writes. If one atomic read
1688 happens before another atomic read of the same address, the later
1689 read must see the same value or a later value in the address's
1690 modification order. This disallows reordering of ``monotonic`` (or
1691 stronger) operations on the same address. If an address is written
1692 ``monotonic``-ally by one thread, and other threads ``monotonic``-ally
1693 read that address repeatedly, the other threads must eventually see
1694 the write. This corresponds to the C++0x/C1x
1695 ``memory_order_relaxed``.
1697 In addition to the guarantees of ``monotonic``, a
1698 *synchronizes-with* edge may be formed with a ``release`` operation.
1699 This is intended to model C++'s ``memory_order_acquire``.
1701 In addition to the guarantees of ``monotonic``, if this operation
1702 writes a value which is subsequently read by an ``acquire``
1703 operation, it *synchronizes-with* that operation. (This isn't a
1704 complete description; see the C++0x definition of a release
1705 sequence.) This corresponds to the C++0x/C1x
1706 ``memory_order_release``.
1707 ``acq_rel`` (acquire+release)
1708 Acts as both an ``acquire`` and ``release`` operation on its
1709 address. This corresponds to the C++0x/C1x ``memory_order_acq_rel``.
1710 ``seq_cst`` (sequentially consistent)
1711 In addition to the guarantees of ``acq_rel`` (``acquire`` for an
1712 operation that only reads, ``release`` for an operation that only
1713 writes), there is a global total order on all
1714 sequentially-consistent operations on all addresses, which is
1715 consistent with the *happens-before* partial order and with the
1716 modification orders of all the affected addresses. Each
1717 sequentially-consistent read sees the last preceding write to the
1718 same address in this global order. This corresponds to the C++0x/C1x
1719 ``memory_order_seq_cst`` and Java volatile.
1723 If an atomic operation is marked ``singlethread``, it only *synchronizes
1724 with* or participates in modification and seq\_cst total orderings with
1725 other operations running in the same thread (for example, in signal
1733 LLVM IR floating-point binary ops (:ref:`fadd <i_fadd>`,
1734 :ref:`fsub <i_fsub>`, :ref:`fmul <i_fmul>`, :ref:`fdiv <i_fdiv>`,
1735 :ref:`frem <i_frem>`) have the following flags that can set to enable
1736 otherwise unsafe floating point operations
1739 No NaNs - Allow optimizations to assume the arguments and result are not
1740 NaN. Such optimizations are required to retain defined behavior over
1741 NaNs, but the value of the result is undefined.
1744 No Infs - Allow optimizations to assume the arguments and result are not
1745 +/-Inf. Such optimizations are required to retain defined behavior over
1746 +/-Inf, but the value of the result is undefined.
1749 No Signed Zeros - Allow optimizations to treat the sign of a zero
1750 argument or result as insignificant.
1753 Allow Reciprocal - Allow optimizations to use the reciprocal of an
1754 argument rather than perform division.
1757 Fast - Allow algebraically equivalent transformations that may
1758 dramatically change results in floating point (e.g. reassociate). This
1759 flag implies all the others.
1763 Use-list Order Directives
1764 -------------------------
1766 Use-list directives encode the in-memory order of each use-list, allowing the
1767 order to be recreated. ``<order-indexes>`` is a comma-separated list of
1768 indexes that are assigned to the referenced value's uses. The referenced
1769 value's use-list is immediately sorted by these indexes.
1771 Use-list directives may appear at function scope or global scope. They are not
1772 instructions, and have no effect on the semantics of the IR. When they're at
1773 function scope, they must appear after the terminator of the final basic block.
1775 If basic blocks have their address taken via ``blockaddress()`` expressions,
1776 ``uselistorder_bb`` can be used to reorder their use-lists from outside their
1783 uselistorder <ty> <value>, { <order-indexes> }
1784 uselistorder_bb @function, %block { <order-indexes> }
1790 define void @foo(i32 %arg1, i32 %arg2) {
1792 ; ... instructions ...
1794 ; ... instructions ...
1796 ; At function scope.
1797 uselistorder i32 %arg1, { 1, 0, 2 }
1798 uselistorder label %bb, { 1, 0 }
1802 uselistorder i32* @global, { 1, 2, 0 }
1803 uselistorder i32 7, { 1, 0 }
1804 uselistorder i32 (i32) @bar, { 1, 0 }
1805 uselistorder_bb @foo, %bb, { 5, 1, 3, 2, 0, 4 }
1812 The LLVM type system is one of the most important features of the
1813 intermediate representation. Being typed enables a number of
1814 optimizations to be performed on the intermediate representation
1815 directly, without having to do extra analyses on the side before the
1816 transformation. A strong type system makes it easier to read the
1817 generated code and enables novel analyses and transformations that are
1818 not feasible to perform on normal three address code representations.
1828 The void type does not represent any value and has no size.
1846 The function type can be thought of as a function signature. It consists of a
1847 return type and a list of formal parameter types. The return type of a function
1848 type is a void type or first class type --- except for :ref:`label <t_label>`
1849 and :ref:`metadata <t_metadata>` types.
1855 <returntype> (<parameter list>)
1857 ...where '``<parameter list>``' is a comma-separated list of type
1858 specifiers. Optionally, the parameter list may include a type ``...``, which
1859 indicates that the function takes a variable number of arguments. Variable
1860 argument functions can access their arguments with the :ref:`variable argument
1861 handling intrinsic <int_varargs>` functions. '``<returntype>``' is any type
1862 except :ref:`label <t_label>` and :ref:`metadata <t_metadata>`.
1866 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1867 | ``i32 (i32)`` | function taking an ``i32``, returning an ``i32`` |
1868 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1869 | ``float (i16, i32 *) *`` | :ref:`Pointer <t_pointer>` to a function that takes an ``i16`` and a :ref:`pointer <t_pointer>` to ``i32``, returning ``float``. |
1870 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1871 | ``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. |
1872 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1873 | ``{i32, i32} (i32)`` | A function taking an ``i32``, returning a :ref:`structure <t_struct>` containing two ``i32`` values |
1874 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1881 The :ref:`first class <t_firstclass>` types are perhaps the most important.
1882 Values of these types are the only ones which can be produced by
1890 These are the types that are valid in registers from CodeGen's perspective.
1899 The integer type is a very simple type that simply specifies an
1900 arbitrary bit width for the integer type desired. Any bit width from 1
1901 bit to 2\ :sup:`23`\ -1 (about 8 million) can be specified.
1909 The number of bits the integer will occupy is specified by the ``N``
1915 +----------------+------------------------------------------------+
1916 | ``i1`` | a single-bit integer. |
1917 +----------------+------------------------------------------------+
1918 | ``i32`` | a 32-bit integer. |
1919 +----------------+------------------------------------------------+
1920 | ``i1942652`` | a really big integer of over 1 million bits. |
1921 +----------------+------------------------------------------------+
1925 Floating Point Types
1926 """"""""""""""""""""
1935 - 16-bit floating point value
1938 - 32-bit floating point value
1941 - 64-bit floating point value
1944 - 128-bit floating point value (112-bit mantissa)
1947 - 80-bit floating point value (X87)
1950 - 128-bit floating point value (two 64-bits)
1957 The x86_mmx type represents a value held in an MMX register on an x86
1958 machine. The operations allowed on it are quite limited: parameters and
1959 return values, load and store, and bitcast. User-specified MMX
1960 instructions are represented as intrinsic or asm calls with arguments
1961 and/or results of this type. There are no arrays, vectors or constants
1978 The pointer type is used to specify memory locations. Pointers are
1979 commonly used to reference objects in memory.
1981 Pointer types may have an optional address space attribute defining the
1982 numbered address space where the pointed-to object resides. The default
1983 address space is number zero. The semantics of non-zero address spaces
1984 are target-specific.
1986 Note that LLVM does not permit pointers to void (``void*``) nor does it
1987 permit pointers to labels (``label*``). Use ``i8*`` instead.
1997 +-------------------------+--------------------------------------------------------------------------------------------------------------+
1998 | ``[4 x i32]*`` | A :ref:`pointer <t_pointer>` to :ref:`array <t_array>` of four ``i32`` values. |
1999 +-------------------------+--------------------------------------------------------------------------------------------------------------+
2000 | ``i32 (i32*) *`` | A :ref:`pointer <t_pointer>` to a :ref:`function <t_function>` that takes an ``i32*``, returning an ``i32``. |
2001 +-------------------------+--------------------------------------------------------------------------------------------------------------+
2002 | ``i32 addrspace(5)*`` | A :ref:`pointer <t_pointer>` to an ``i32`` value that resides in address space #5. |
2003 +-------------------------+--------------------------------------------------------------------------------------------------------------+
2012 A vector type is a simple derived type that represents a vector of
2013 elements. Vector types are used when multiple primitive data are
2014 operated in parallel using a single instruction (SIMD). A vector type
2015 requires a size (number of elements) and an underlying primitive data
2016 type. Vector types are considered :ref:`first class <t_firstclass>`.
2022 < <# elements> x <elementtype> >
2024 The number of elements is a constant integer value larger than 0;
2025 elementtype may be any integer, floating point or pointer type. Vectors
2026 of size zero are not allowed.
2030 +-------------------+--------------------------------------------------+
2031 | ``<4 x i32>`` | Vector of 4 32-bit integer values. |
2032 +-------------------+--------------------------------------------------+
2033 | ``<8 x float>`` | Vector of 8 32-bit floating-point values. |
2034 +-------------------+--------------------------------------------------+
2035 | ``<2 x i64>`` | Vector of 2 64-bit integer values. |
2036 +-------------------+--------------------------------------------------+
2037 | ``<4 x i64*>`` | Vector of 4 pointers to 64-bit integer values. |
2038 +-------------------+--------------------------------------------------+
2047 The label type represents code labels.
2062 The metadata type represents embedded metadata. No derived types may be
2063 created from metadata except for :ref:`function <t_function>` arguments.
2076 Aggregate Types are a subset of derived types that can contain multiple
2077 member types. :ref:`Arrays <t_array>` and :ref:`structs <t_struct>` are
2078 aggregate types. :ref:`Vectors <t_vector>` are not considered to be
2088 The array type is a very simple derived type that arranges elements
2089 sequentially in memory. The array type requires a size (number of
2090 elements) and an underlying data type.
2096 [<# elements> x <elementtype>]
2098 The number of elements is a constant integer value; ``elementtype`` may
2099 be any type with a size.
2103 +------------------+--------------------------------------+
2104 | ``[40 x i32]`` | Array of 40 32-bit integer values. |
2105 +------------------+--------------------------------------+
2106 | ``[41 x i32]`` | Array of 41 32-bit integer values. |
2107 +------------------+--------------------------------------+
2108 | ``[4 x i8]`` | Array of 4 8-bit integer values. |
2109 +------------------+--------------------------------------+
2111 Here are some examples of multidimensional arrays:
2113 +-----------------------------+----------------------------------------------------------+
2114 | ``[3 x [4 x i32]]`` | 3x4 array of 32-bit integer values. |
2115 +-----------------------------+----------------------------------------------------------+
2116 | ``[12 x [10 x float]]`` | 12x10 array of single precision floating point values. |
2117 +-----------------------------+----------------------------------------------------------+
2118 | ``[2 x [3 x [4 x i16]]]`` | 2x3x4 array of 16-bit integer values. |
2119 +-----------------------------+----------------------------------------------------------+
2121 There is no restriction on indexing beyond the end of the array implied
2122 by a static type (though there are restrictions on indexing beyond the
2123 bounds of an allocated object in some cases). This means that
2124 single-dimension 'variable sized array' addressing can be implemented in
2125 LLVM with a zero length array type. An implementation of 'pascal style
2126 arrays' in LLVM could use the type "``{ i32, [0 x float]}``", for
2136 The structure type is used to represent a collection of data members
2137 together in memory. The elements of a structure may be any type that has
2140 Structures in memory are accessed using '``load``' and '``store``' by
2141 getting a pointer to a field with the '``getelementptr``' instruction.
2142 Structures in registers are accessed using the '``extractvalue``' and
2143 '``insertvalue``' instructions.
2145 Structures may optionally be "packed" structures, which indicate that
2146 the alignment of the struct is one byte, and that there is no padding
2147 between the elements. In non-packed structs, padding between field types
2148 is inserted as defined by the DataLayout string in the module, which is
2149 required to match what the underlying code generator expects.
2151 Structures can either be "literal" or "identified". A literal structure
2152 is defined inline with other types (e.g. ``{i32, i32}*``) whereas
2153 identified types are always defined at the top level with a name.
2154 Literal types are uniqued by their contents and can never be recursive
2155 or opaque since there is no way to write one. Identified types can be
2156 recursive, can be opaqued, and are never uniqued.
2162 %T1 = type { <type list> } ; Identified normal struct type
2163 %T2 = type <{ <type list> }> ; Identified packed struct type
2167 +------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
2168 | ``{ i32, i32, i32 }`` | A triple of three ``i32`` values |
2169 +------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
2170 | ``{ 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``. |
2171 +------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
2172 | ``<{ i8, i32 }>`` | A packed struct known to be 5 bytes in size. |
2173 +------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
2177 Opaque Structure Types
2178 """"""""""""""""""""""
2182 Opaque structure types are used to represent named structure types that
2183 do not have a body specified. This corresponds (for example) to the C
2184 notion of a forward declared structure.
2195 +--------------+-------------------+
2196 | ``opaque`` | An opaque type. |
2197 +--------------+-------------------+
2204 LLVM has several different basic types of constants. This section
2205 describes them all and their syntax.
2210 **Boolean constants**
2211 The two strings '``true``' and '``false``' are both valid constants
2213 **Integer constants**
2214 Standard integers (such as '4') are constants of the
2215 :ref:`integer <t_integer>` type. Negative numbers may be used with
2217 **Floating point constants**
2218 Floating point constants use standard decimal notation (e.g.
2219 123.421), exponential notation (e.g. 1.23421e+2), or a more precise
2220 hexadecimal notation (see below). The assembler requires the exact
2221 decimal value of a floating-point constant. For example, the
2222 assembler accepts 1.25 but rejects 1.3 because 1.3 is a repeating
2223 decimal in binary. Floating point constants must have a :ref:`floating
2224 point <t_floating>` type.
2225 **Null pointer constants**
2226 The identifier '``null``' is recognized as a null pointer constant
2227 and must be of :ref:`pointer type <t_pointer>`.
2229 The one non-intuitive notation for constants is the hexadecimal form of
2230 floating point constants. For example, the form
2231 '``double 0x432ff973cafa8000``' is equivalent to (but harder to read
2232 than) '``double 4.5e+15``'. The only time hexadecimal floating point
2233 constants are required (and the only time that they are generated by the
2234 disassembler) is when a floating point constant must be emitted but it
2235 cannot be represented as a decimal floating point number in a reasonable
2236 number of digits. For example, NaN's, infinities, and other special
2237 values are represented in their IEEE hexadecimal format so that assembly
2238 and disassembly do not cause any bits to change in the constants.
2240 When using the hexadecimal form, constants of types half, float, and
2241 double are represented using the 16-digit form shown above (which
2242 matches the IEEE754 representation for double); half and float values
2243 must, however, be exactly representable as IEEE 754 half and single
2244 precision, respectively. Hexadecimal format is always used for long
2245 double, and there are three forms of long double. The 80-bit format used
2246 by x86 is represented as ``0xK`` followed by 20 hexadecimal digits. The
2247 128-bit format used by PowerPC (two adjacent doubles) is represented by
2248 ``0xM`` followed by 32 hexadecimal digits. The IEEE 128-bit format is
2249 represented by ``0xL`` followed by 32 hexadecimal digits. Long doubles
2250 will only work if they match the long double format on your target.
2251 The IEEE 16-bit format (half precision) is represented by ``0xH``
2252 followed by 4 hexadecimal digits. All hexadecimal formats are big-endian
2253 (sign bit at the left).
2255 There are no constants of type x86_mmx.
2257 .. _complexconstants:
2262 Complex constants are a (potentially recursive) combination of simple
2263 constants and smaller complex constants.
2265 **Structure constants**
2266 Structure constants are represented with notation similar to
2267 structure type definitions (a comma separated list of elements,
2268 surrounded by braces (``{}``)). For example:
2269 "``{ i32 4, float 17.0, i32* @G }``", where "``@G``" is declared as
2270 "``@G = external global i32``". Structure constants must have
2271 :ref:`structure type <t_struct>`, and the number and types of elements
2272 must match those specified by the type.
2274 Array constants are represented with notation similar to array type
2275 definitions (a comma separated list of elements, surrounded by
2276 square brackets (``[]``)). For example:
2277 "``[ i32 42, i32 11, i32 74 ]``". Array constants must have
2278 :ref:`array type <t_array>`, and the number and types of elements must
2279 match those specified by the type. As a special case, character array
2280 constants may also be represented as a double-quoted string using the ``c``
2281 prefix. For example: "``c"Hello World\0A\00"``".
2282 **Vector constants**
2283 Vector constants are represented with notation similar to vector
2284 type definitions (a comma separated list of elements, surrounded by
2285 less-than/greater-than's (``<>``)). For example:
2286 "``< i32 42, i32 11, i32 74, i32 100 >``". Vector constants
2287 must have :ref:`vector type <t_vector>`, and the number and types of
2288 elements must match those specified by the type.
2289 **Zero initialization**
2290 The string '``zeroinitializer``' can be used to zero initialize a
2291 value to zero of *any* type, including scalar and
2292 :ref:`aggregate <t_aggregate>` types. This is often used to avoid
2293 having to print large zero initializers (e.g. for large arrays) and
2294 is always exactly equivalent to using explicit zero initializers.
2296 A metadata node is a structure-like constant with :ref:`metadata
2297 type <t_metadata>`. For example:
2298 "``metadata !{ i32 0, metadata !"test" }``". Unlike other
2299 constants that are meant to be interpreted as part of the
2300 instruction stream, metadata is a place to attach additional
2301 information such as debug info.
2303 Global Variable and Function Addresses
2304 --------------------------------------
2306 The addresses of :ref:`global variables <globalvars>` and
2307 :ref:`functions <functionstructure>` are always implicitly valid
2308 (link-time) constants. These constants are explicitly referenced when
2309 the :ref:`identifier for the global <identifiers>` is used and always have
2310 :ref:`pointer <t_pointer>` type. For example, the following is a legal LLVM
2313 .. code-block:: llvm
2317 @Z = global [2 x i32*] [ i32* @X, i32* @Y ]
2324 The string '``undef``' can be used anywhere a constant is expected, and
2325 indicates that the user of the value may receive an unspecified
2326 bit-pattern. Undefined values may be of any type (other than '``label``'
2327 or '``void``') and be used anywhere a constant is permitted.
2329 Undefined values are useful because they indicate to the compiler that
2330 the program is well defined no matter what value is used. This gives the
2331 compiler more freedom to optimize. Here are some examples of
2332 (potentially surprising) transformations that are valid (in pseudo IR):
2334 .. code-block:: llvm
2344 This is safe because all of the output bits are affected by the undef
2345 bits. Any output bit can have a zero or one depending on the input bits.
2347 .. code-block:: llvm
2358 These logical operations have bits that are not always affected by the
2359 input. For example, if ``%X`` has a zero bit, then the output of the
2360 '``and``' operation will always be a zero for that bit, no matter what
2361 the corresponding bit from the '``undef``' is. As such, it is unsafe to
2362 optimize or assume that the result of the '``and``' is '``undef``'.
2363 However, it is safe to assume that all bits of the '``undef``' could be
2364 0, and optimize the '``and``' to 0. Likewise, it is safe to assume that
2365 all the bits of the '``undef``' operand to the '``or``' could be set,
2366 allowing the '``or``' to be folded to -1.
2368 .. code-block:: llvm
2370 %A = select undef, %X, %Y
2371 %B = select undef, 42, %Y
2372 %C = select %X, %Y, undef
2382 This set of examples shows that undefined '``select``' (and conditional
2383 branch) conditions can go *either way*, but they have to come from one
2384 of the two operands. In the ``%A`` example, if ``%X`` and ``%Y`` were
2385 both known to have a clear low bit, then ``%A`` would have to have a
2386 cleared low bit. However, in the ``%C`` example, the optimizer is
2387 allowed to assume that the '``undef``' operand could be the same as
2388 ``%Y``, allowing the whole '``select``' to be eliminated.
2390 .. code-block:: llvm
2392 %A = xor undef, undef
2409 This example points out that two '``undef``' operands are not
2410 necessarily the same. This can be surprising to people (and also matches
2411 C semantics) where they assume that "``X^X``" is always zero, even if
2412 ``X`` is undefined. This isn't true for a number of reasons, but the
2413 short answer is that an '``undef``' "variable" can arbitrarily change
2414 its value over its "live range". This is true because the variable
2415 doesn't actually *have a live range*. Instead, the value is logically
2416 read from arbitrary registers that happen to be around when needed, so
2417 the value is not necessarily consistent over time. In fact, ``%A`` and
2418 ``%C`` need to have the same semantics or the core LLVM "replace all
2419 uses with" concept would not hold.
2421 .. code-block:: llvm
2429 These examples show the crucial difference between an *undefined value*
2430 and *undefined behavior*. An undefined value (like '``undef``') is
2431 allowed to have an arbitrary bit-pattern. This means that the ``%A``
2432 operation can be constant folded to '``undef``', because the '``undef``'
2433 could be an SNaN, and ``fdiv`` is not (currently) defined on SNaN's.
2434 However, in the second example, we can make a more aggressive
2435 assumption: because the ``undef`` is allowed to be an arbitrary value,
2436 we are allowed to assume that it could be zero. Since a divide by zero
2437 has *undefined behavior*, we are allowed to assume that the operation
2438 does not execute at all. This allows us to delete the divide and all
2439 code after it. Because the undefined operation "can't happen", the
2440 optimizer can assume that it occurs in dead code.
2442 .. code-block:: llvm
2444 a: store undef -> %X
2445 b: store %X -> undef
2450 These examples reiterate the ``fdiv`` example: a store *of* an undefined
2451 value can be assumed to not have any effect; we can assume that the
2452 value is overwritten with bits that happen to match what was already
2453 there. However, a store *to* an undefined location could clobber
2454 arbitrary memory, therefore, it has undefined behavior.
2461 Poison values are similar to :ref:`undef values <undefvalues>`, however
2462 they also represent the fact that an instruction or constant expression
2463 that cannot evoke side effects has nevertheless detected a condition
2464 that results in undefined behavior.
2466 There is currently no way of representing a poison value in the IR; they
2467 only exist when produced by operations such as :ref:`add <i_add>` with
2470 Poison value behavior is defined in terms of value *dependence*:
2472 - Values other than :ref:`phi <i_phi>` nodes depend on their operands.
2473 - :ref:`Phi <i_phi>` nodes depend on the operand corresponding to
2474 their dynamic predecessor basic block.
2475 - Function arguments depend on the corresponding actual argument values
2476 in the dynamic callers of their functions.
2477 - :ref:`Call <i_call>` instructions depend on the :ref:`ret <i_ret>`
2478 instructions that dynamically transfer control back to them.
2479 - :ref:`Invoke <i_invoke>` instructions depend on the
2480 :ref:`ret <i_ret>`, :ref:`resume <i_resume>`, or exception-throwing
2481 call instructions that dynamically transfer control back to them.
2482 - Non-volatile loads and stores depend on the most recent stores to all
2483 of the referenced memory addresses, following the order in the IR
2484 (including loads and stores implied by intrinsics such as
2485 :ref:`@llvm.memcpy <int_memcpy>`.)
2486 - An instruction with externally visible side effects depends on the
2487 most recent preceding instruction with externally visible side
2488 effects, following the order in the IR. (This includes :ref:`volatile
2489 operations <volatile>`.)
2490 - An instruction *control-depends* on a :ref:`terminator
2491 instruction <terminators>` if the terminator instruction has
2492 multiple successors and the instruction is always executed when
2493 control transfers to one of the successors, and may not be executed
2494 when control is transferred to another.
2495 - Additionally, an instruction also *control-depends* on a terminator
2496 instruction if the set of instructions it otherwise depends on would
2497 be different if the terminator had transferred control to a different
2499 - Dependence is transitive.
2501 Poison values have the same behavior as :ref:`undef values <undefvalues>`,
2502 with the additional effect that any instruction that has a *dependence*
2503 on a poison value has undefined behavior.
2505 Here are some examples:
2507 .. code-block:: llvm
2510 %poison = sub nuw i32 0, 1 ; Results in a poison value.
2511 %still_poison = and i32 %poison, 0 ; 0, but also poison.
2512 %poison_yet_again = getelementptr i32* @h, i32 %still_poison
2513 store i32 0, i32* %poison_yet_again ; memory at @h[0] is poisoned
2515 store i32 %poison, i32* @g ; Poison value stored to memory.
2516 %poison2 = load i32* @g ; Poison value loaded back from memory.
2518 store volatile i32 %poison, i32* @g ; External observation; undefined behavior.
2520 %narrowaddr = bitcast i32* @g to i16*
2521 %wideaddr = bitcast i32* @g to i64*
2522 %poison3 = load i16* %narrowaddr ; Returns a poison value.
2523 %poison4 = load i64* %wideaddr ; Returns a poison value.
2525 %cmp = icmp slt i32 %poison, 0 ; Returns a poison value.
2526 br i1 %cmp, label %true, label %end ; Branch to either destination.
2529 store volatile i32 0, i32* @g ; This is control-dependent on %cmp, so
2530 ; it has undefined behavior.
2534 %p = phi i32 [ 0, %entry ], [ 1, %true ]
2535 ; Both edges into this PHI are
2536 ; control-dependent on %cmp, so this
2537 ; always results in a poison value.
2539 store volatile i32 0, i32* @g ; This would depend on the store in %true
2540 ; if %cmp is true, or the store in %entry
2541 ; otherwise, so this is undefined behavior.
2543 br i1 %cmp, label %second_true, label %second_end
2544 ; The same branch again, but this time the
2545 ; true block doesn't have side effects.
2552 store volatile i32 0, i32* @g ; This time, the instruction always depends
2553 ; on the store in %end. Also, it is
2554 ; control-equivalent to %end, so this is
2555 ; well-defined (ignoring earlier undefined
2556 ; behavior in this example).
2560 Addresses of Basic Blocks
2561 -------------------------
2563 ``blockaddress(@function, %block)``
2565 The '``blockaddress``' constant computes the address of the specified
2566 basic block in the specified function, and always has an ``i8*`` type.
2567 Taking the address of the entry block is illegal.
2569 This value only has defined behavior when used as an operand to the
2570 ':ref:`indirectbr <i_indirectbr>`' instruction, or for comparisons
2571 against null. Pointer equality tests between labels addresses results in
2572 undefined behavior --- though, again, comparison against null is ok, and
2573 no label is equal to the null pointer. This may be passed around as an
2574 opaque pointer sized value as long as the bits are not inspected. This
2575 allows ``ptrtoint`` and arithmetic to be performed on these values so
2576 long as the original value is reconstituted before the ``indirectbr``
2579 Finally, some targets may provide defined semantics when using the value
2580 as the operand to an inline assembly, but that is target specific.
2584 Constant Expressions
2585 --------------------
2587 Constant expressions are used to allow expressions involving other
2588 constants to be used as constants. Constant expressions may be of any
2589 :ref:`first class <t_firstclass>` type and may involve any LLVM operation
2590 that does not have side effects (e.g. load and call are not supported).
2591 The following is the syntax for constant expressions:
2593 ``trunc (CST to TYPE)``
2594 Truncate a constant to another type. The bit size of CST must be
2595 larger than the bit size of TYPE. Both types must be integers.
2596 ``zext (CST to TYPE)``
2597 Zero extend a constant to another type. The bit size of CST must be
2598 smaller than the bit size of TYPE. Both types must be integers.
2599 ``sext (CST to TYPE)``
2600 Sign extend a constant to another type. The bit size of CST must be
2601 smaller than the bit size of TYPE. Both types must be integers.
2602 ``fptrunc (CST to TYPE)``
2603 Truncate a floating point constant to another floating point type.
2604 The size of CST must be larger than the size of TYPE. Both types
2605 must be floating point.
2606 ``fpext (CST to TYPE)``
2607 Floating point extend a constant to another type. The size of CST
2608 must be smaller or equal to the size of TYPE. Both types must be
2610 ``fptoui (CST to TYPE)``
2611 Convert a floating point constant to the corresponding unsigned
2612 integer constant. TYPE must be a scalar or vector integer type. CST
2613 must be of scalar or vector floating point type. Both CST and TYPE
2614 must be scalars, or vectors of the same number of elements. If the
2615 value won't fit in the integer type, the results are undefined.
2616 ``fptosi (CST to TYPE)``
2617 Convert a floating point constant to the corresponding signed
2618 integer constant. TYPE must be a scalar or vector integer type. CST
2619 must be of scalar or vector floating point type. Both CST and TYPE
2620 must be scalars, or vectors of the same number of elements. If the
2621 value won't fit in the integer type, the results are undefined.
2622 ``uitofp (CST to TYPE)``
2623 Convert an unsigned integer constant to the corresponding floating
2624 point constant. TYPE must be a scalar or vector floating point type.
2625 CST must be of scalar or vector integer type. Both CST and TYPE must
2626 be scalars, or vectors of the same number of elements. If the value
2627 won't fit in the floating point type, the results are undefined.
2628 ``sitofp (CST to TYPE)``
2629 Convert a signed integer constant to the corresponding floating
2630 point constant. TYPE must be a scalar or vector floating point type.
2631 CST must be of scalar or vector integer type. Both CST and TYPE must
2632 be scalars, or vectors of the same number of elements. If the value
2633 won't fit in the floating point type, the results are undefined.
2634 ``ptrtoint (CST to TYPE)``
2635 Convert a pointer typed constant to the corresponding integer
2636 constant. ``TYPE`` must be an integer type. ``CST`` must be of
2637 pointer type. The ``CST`` value is zero extended, truncated, or
2638 unchanged to make it fit in ``TYPE``.
2639 ``inttoptr (CST to TYPE)``
2640 Convert an integer constant to a pointer constant. TYPE must be a
2641 pointer type. CST must be of integer type. The CST value is zero
2642 extended, truncated, or unchanged to make it fit in a pointer size.
2643 This one is *really* dangerous!
2644 ``bitcast (CST to TYPE)``
2645 Convert a constant, CST, to another TYPE. The constraints of the
2646 operands are the same as those for the :ref:`bitcast
2647 instruction <i_bitcast>`.
2648 ``addrspacecast (CST to TYPE)``
2649 Convert a constant pointer or constant vector of pointer, CST, to another
2650 TYPE in a different address space. The constraints of the operands are the
2651 same as those for the :ref:`addrspacecast instruction <i_addrspacecast>`.
2652 ``getelementptr (CSTPTR, IDX0, IDX1, ...)``, ``getelementptr inbounds (CSTPTR, IDX0, IDX1, ...)``
2653 Perform the :ref:`getelementptr operation <i_getelementptr>` on
2654 constants. As with the :ref:`getelementptr <i_getelementptr>`
2655 instruction, the index list may have zero or more indexes, which are
2656 required to make sense for the type of "CSTPTR".
2657 ``select (COND, VAL1, VAL2)``
2658 Perform the :ref:`select operation <i_select>` on constants.
2659 ``icmp COND (VAL1, VAL2)``
2660 Performs the :ref:`icmp operation <i_icmp>` on constants.
2661 ``fcmp COND (VAL1, VAL2)``
2662 Performs the :ref:`fcmp operation <i_fcmp>` on constants.
2663 ``extractelement (VAL, IDX)``
2664 Perform the :ref:`extractelement operation <i_extractelement>` on
2666 ``insertelement (VAL, ELT, IDX)``
2667 Perform the :ref:`insertelement operation <i_insertelement>` on
2669 ``shufflevector (VEC1, VEC2, IDXMASK)``
2670 Perform the :ref:`shufflevector operation <i_shufflevector>` on
2672 ``extractvalue (VAL, IDX0, IDX1, ...)``
2673 Perform the :ref:`extractvalue operation <i_extractvalue>` on
2674 constants. The index list is interpreted in a similar manner as
2675 indices in a ':ref:`getelementptr <i_getelementptr>`' operation. At
2676 least one index value must be specified.
2677 ``insertvalue (VAL, ELT, IDX0, IDX1, ...)``
2678 Perform the :ref:`insertvalue operation <i_insertvalue>` on constants.
2679 The index list is interpreted in a similar manner as indices in a
2680 ':ref:`getelementptr <i_getelementptr>`' operation. At least one index
2681 value must be specified.
2682 ``OPCODE (LHS, RHS)``
2683 Perform the specified operation of the LHS and RHS constants. OPCODE
2684 may be any of the :ref:`binary <binaryops>` or :ref:`bitwise
2685 binary <bitwiseops>` operations. The constraints on operands are
2686 the same as those for the corresponding instruction (e.g. no bitwise
2687 operations on floating point values are allowed).
2694 Inline Assembler Expressions
2695 ----------------------------
2697 LLVM supports inline assembler expressions (as opposed to :ref:`Module-Level
2698 Inline Assembly <moduleasm>`) through the use of a special value. This
2699 value represents the inline assembler as a string (containing the
2700 instructions to emit), a list of operand constraints (stored as a
2701 string), a flag that indicates whether or not the inline asm expression
2702 has side effects, and a flag indicating whether the function containing
2703 the asm needs to align its stack conservatively. An example inline
2704 assembler expression is:
2706 .. code-block:: llvm
2708 i32 (i32) asm "bswap $0", "=r,r"
2710 Inline assembler expressions may **only** be used as the callee operand
2711 of a :ref:`call <i_call>` or an :ref:`invoke <i_invoke>` instruction.
2712 Thus, typically we have:
2714 .. code-block:: llvm
2716 %X = call i32 asm "bswap $0", "=r,r"(i32 %Y)
2718 Inline asms with side effects not visible in the constraint list must be
2719 marked as having side effects. This is done through the use of the
2720 '``sideeffect``' keyword, like so:
2722 .. code-block:: llvm
2724 call void asm sideeffect "eieio", ""()
2726 In some cases inline asms will contain code that will not work unless
2727 the stack is aligned in some way, such as calls or SSE instructions on
2728 x86, yet will not contain code that does that alignment within the asm.
2729 The compiler should make conservative assumptions about what the asm
2730 might contain and should generate its usual stack alignment code in the
2731 prologue if the '``alignstack``' keyword is present:
2733 .. code-block:: llvm
2735 call void asm alignstack "eieio", ""()
2737 Inline asms also support using non-standard assembly dialects. The
2738 assumed dialect is ATT. When the '``inteldialect``' keyword is present,
2739 the inline asm is using the Intel dialect. Currently, ATT and Intel are
2740 the only supported dialects. An example is:
2742 .. code-block:: llvm
2744 call void asm inteldialect "eieio", ""()
2746 If multiple keywords appear the '``sideeffect``' keyword must come
2747 first, the '``alignstack``' keyword second and the '``inteldialect``'
2753 The call instructions that wrap inline asm nodes may have a
2754 "``!srcloc``" MDNode attached to it that contains a list of constant
2755 integers. If present, the code generator will use the integer as the
2756 location cookie value when report errors through the ``LLVMContext``
2757 error reporting mechanisms. This allows a front-end to correlate backend
2758 errors that occur with inline asm back to the source code that produced
2761 .. code-block:: llvm
2763 call void asm sideeffect "something bad", ""(), !srcloc !42
2765 !42 = !{ i32 1234567 }
2767 It is up to the front-end to make sense of the magic numbers it places
2768 in the IR. If the MDNode contains multiple constants, the code generator
2769 will use the one that corresponds to the line of the asm that the error
2774 Metadata Nodes and Metadata Strings
2775 -----------------------------------
2777 LLVM IR allows metadata to be attached to instructions in the program
2778 that can convey extra information about the code to the optimizers and
2779 code generator. One example application of metadata is source-level
2780 debug information. There are two metadata primitives: strings and nodes.
2781 All metadata has the ``metadata`` type and is identified in syntax by a
2782 preceding exclamation point ('``!``').
2784 A metadata string is a string surrounded by double quotes. It can
2785 contain any character by escaping non-printable characters with
2786 "``\xx``" where "``xx``" is the two digit hex code. For example:
2789 Metadata nodes are represented with notation similar to structure
2790 constants (a comma separated list of elements, surrounded by braces and
2791 preceded by an exclamation point). Metadata nodes can have any values as
2792 their operand. For example:
2794 .. code-block:: llvm
2796 !{ metadata !"test\00", i32 10}
2798 A :ref:`named metadata <namedmetadatastructure>` is a collection of
2799 metadata nodes, which can be looked up in the module symbol table. For
2802 .. code-block:: llvm
2804 !foo = metadata !{!4, !3}
2806 Metadata can be used as function arguments. Here ``llvm.dbg.value``
2807 function is using two metadata arguments:
2809 .. code-block:: llvm
2811 call void @llvm.dbg.value(metadata !24, i64 0, metadata !25)
2813 Metadata can be attached with an instruction. Here metadata ``!21`` is
2814 attached to the ``add`` instruction using the ``!dbg`` identifier:
2816 .. code-block:: llvm
2818 %indvar.next = add i64 %indvar, 1, !dbg !21
2820 More information about specific metadata nodes recognized by the
2821 optimizers and code generator is found below.
2826 In LLVM IR, memory does not have types, so LLVM's own type system is not
2827 suitable for doing TBAA. Instead, metadata is added to the IR to
2828 describe a type system of a higher level language. This can be used to
2829 implement typical C/C++ TBAA, but it can also be used to implement
2830 custom alias analysis behavior for other languages.
2832 The current metadata format is very simple. TBAA metadata nodes have up
2833 to three fields, e.g.:
2835 .. code-block:: llvm
2837 !0 = metadata !{ metadata !"an example type tree" }
2838 !1 = metadata !{ metadata !"int", metadata !0 }
2839 !2 = metadata !{ metadata !"float", metadata !0 }
2840 !3 = metadata !{ metadata !"const float", metadata !2, i64 1 }
2842 The first field is an identity field. It can be any value, usually a
2843 metadata string, which uniquely identifies the type. The most important
2844 name in the tree is the name of the root node. Two trees with different
2845 root node names are entirely disjoint, even if they have leaves with
2848 The second field identifies the type's parent node in the tree, or is
2849 null or omitted for a root node. A type is considered to alias all of
2850 its descendants and all of its ancestors in the tree. Also, a type is
2851 considered to alias all types in other trees, so that bitcode produced
2852 from multiple front-ends is handled conservatively.
2854 If the third field is present, it's an integer which if equal to 1
2855 indicates that the type is "constant" (meaning
2856 ``pointsToConstantMemory`` should return true; see `other useful
2857 AliasAnalysis methods <AliasAnalysis.html#OtherItfs>`_).
2859 '``tbaa.struct``' Metadata
2860 ^^^^^^^^^^^^^^^^^^^^^^^^^^
2862 The :ref:`llvm.memcpy <int_memcpy>` is often used to implement
2863 aggregate assignment operations in C and similar languages, however it
2864 is defined to copy a contiguous region of memory, which is more than
2865 strictly necessary for aggregate types which contain holes due to
2866 padding. Also, it doesn't contain any TBAA information about the fields
2869 ``!tbaa.struct`` metadata can describe which memory subregions in a
2870 memcpy are padding and what the TBAA tags of the struct are.
2872 The current metadata format is very simple. ``!tbaa.struct`` metadata
2873 nodes are a list of operands which are in conceptual groups of three.
2874 For each group of three, the first operand gives the byte offset of a
2875 field in bytes, the second gives its size in bytes, and the third gives
2878 .. code-block:: llvm
2880 !4 = metadata !{ i64 0, i64 4, metadata !1, i64 8, i64 4, metadata !2 }
2882 This describes a struct with two fields. The first is at offset 0 bytes
2883 with size 4 bytes, and has tbaa tag !1. The second is at offset 8 bytes
2884 and has size 4 bytes and has tbaa tag !2.
2886 Note that the fields need not be contiguous. In this example, there is a
2887 4 byte gap between the two fields. This gap represents padding which
2888 does not carry useful data and need not be preserved.
2890 '``noalias``' and '``alias.scope``' Metadata
2891 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2893 ``noalias`` and ``alias.scope`` metadata provide the ability to specify generic
2894 noalias memory-access sets. This means that some collection of memory access
2895 instructions (loads, stores, memory-accessing calls, etc.) that carry
2896 ``noalias`` metadata can specifically be specified not to alias with some other
2897 collection of memory access instructions that carry ``alias.scope`` metadata.
2898 Each type of metadata specifies a list of scopes where each scope has an id and
2899 a domain. When evaluating an aliasing query, if for some some domain, the set
2900 of scopes with that domain in one instruction's ``alias.scope`` list is a
2901 subset of (or qual to) the set of scopes for that domain in another
2902 instruction's ``noalias`` list, then the two memory accesses are assumed not to
2905 The metadata identifying each domain is itself a list containing one or two
2906 entries. The first entry is the name of the domain. Note that if the name is a
2907 string then it can be combined accross functions and translation units. A
2908 self-reference can be used to create globally unique domain names. A
2909 descriptive string may optionally be provided as a second list entry.
2911 The metadata identifying each scope is also itself a list containing two or
2912 three entries. The first entry is the name of the scope. Note that if the name
2913 is a string then it can be combined accross functions and translation units. A
2914 self-reference can be used to create globally unique scope names. A metadata
2915 reference to the scope's domain is the second entry. A descriptive string may
2916 optionally be provided as a third list entry.
2920 .. code-block:: llvm
2922 ; Two scope domains:
2923 !0 = metadata !{metadata !0}
2924 !1 = metadata !{metadata !1}
2926 ; Some scopes in these domains:
2927 !2 = metadata !{metadata !2, metadata !0}
2928 !3 = metadata !{metadata !3, metadata !0}
2929 !4 = metadata !{metadata !4, metadata !1}
2932 !5 = metadata !{metadata !4} ; A list containing only scope !4
2933 !6 = metadata !{metadata !4, metadata !3, metadata !2}
2934 !7 = metadata !{metadata !3}
2936 ; These two instructions don't alias:
2937 %0 = load float* %c, align 4, !alias.scope !5
2938 store float %0, float* %arrayidx.i, align 4, !noalias !5
2940 ; These two instructions also don't alias (for domain !1, the set of scopes
2941 ; in the !alias.scope equals that in the !noalias list):
2942 %2 = load float* %c, align 4, !alias.scope !5
2943 store float %2, float* %arrayidx.i2, align 4, !noalias !6
2945 ; These two instructions don't alias (for domain !0, the set of scopes in
2946 ; the !noalias list is not a superset of, or equal to, the scopes in the
2947 ; !alias.scope list):
2948 %2 = load float* %c, align 4, !alias.scope !6
2949 store float %0, float* %arrayidx.i, align 4, !noalias !7
2951 '``fpmath``' Metadata
2952 ^^^^^^^^^^^^^^^^^^^^^
2954 ``fpmath`` metadata may be attached to any instruction of floating point
2955 type. It can be used to express the maximum acceptable error in the
2956 result of that instruction, in ULPs, thus potentially allowing the
2957 compiler to use a more efficient but less accurate method of computing
2958 it. ULP is defined as follows:
2960 If ``x`` is a real number that lies between two finite consecutive
2961 floating-point numbers ``a`` and ``b``, without being equal to one
2962 of them, then ``ulp(x) = |b - a|``, otherwise ``ulp(x)`` is the
2963 distance between the two non-equal finite floating-point numbers
2964 nearest ``x``. Moreover, ``ulp(NaN)`` is ``NaN``.
2966 The metadata node shall consist of a single positive floating point
2967 number representing the maximum relative error, for example:
2969 .. code-block:: llvm
2971 !0 = metadata !{ float 2.5 } ; maximum acceptable inaccuracy is 2.5 ULPs
2973 '``range``' Metadata
2974 ^^^^^^^^^^^^^^^^^^^^
2976 ``range`` metadata may be attached only to ``load``, ``call`` and ``invoke`` of
2977 integer types. It expresses the possible ranges the loaded value or the value
2978 returned by the called function at this call site is in. The ranges are
2979 represented with a flattened list of integers. The loaded value or the value
2980 returned is known to be in the union of the ranges defined by each consecutive
2981 pair. Each pair has the following properties:
2983 - The type must match the type loaded by the instruction.
2984 - The pair ``a,b`` represents the range ``[a,b)``.
2985 - Both ``a`` and ``b`` are constants.
2986 - The range is allowed to wrap.
2987 - The range should not represent the full or empty set. That is,
2990 In addition, the pairs must be in signed order of the lower bound and
2991 they must be non-contiguous.
2995 .. code-block:: llvm
2997 %a = load i8* %x, align 1, !range !0 ; Can only be 0 or 1
2998 %b = load i8* %y, align 1, !range !1 ; Can only be 255 (-1), 0 or 1
2999 %c = call i8 @foo(), !range !2 ; Can only be 0, 1, 3, 4 or 5
3000 %d = invoke i8 @bar() to label %cont
3001 unwind label %lpad, !range !3 ; Can only be -2, -1, 3, 4 or 5
3003 !0 = metadata !{ i8 0, i8 2 }
3004 !1 = metadata !{ i8 255, i8 2 }
3005 !2 = metadata !{ i8 0, i8 2, i8 3, i8 6 }
3006 !3 = metadata !{ i8 -2, i8 0, i8 3, i8 6 }
3011 It is sometimes useful to attach information to loop constructs. Currently,
3012 loop metadata is implemented as metadata attached to the branch instruction
3013 in the loop latch block. This type of metadata refer to a metadata node that is
3014 guaranteed to be separate for each loop. The loop identifier metadata is
3015 specified with the name ``llvm.loop``.
3017 The loop identifier metadata is implemented using a metadata that refers to
3018 itself to avoid merging it with any other identifier metadata, e.g.,
3019 during module linkage or function inlining. That is, each loop should refer
3020 to their own identification metadata even if they reside in separate functions.
3021 The following example contains loop identifier metadata for two separate loop
3024 .. code-block:: llvm
3026 !0 = metadata !{ metadata !0 }
3027 !1 = metadata !{ metadata !1 }
3029 The loop identifier metadata can be used to specify additional
3030 per-loop metadata. Any operands after the first operand can be treated
3031 as user-defined metadata. For example the ``llvm.loop.unroll.count``
3032 suggests an unroll factor to the loop unroller:
3034 .. code-block:: llvm
3036 br i1 %exitcond, label %._crit_edge, label %.lr.ph, !llvm.loop !0
3038 !0 = metadata !{ metadata !0, metadata !1 }
3039 !1 = metadata !{ metadata !"llvm.loop.unroll.count", i32 4 }
3041 '``llvm.loop.vectorize``' and '``llvm.loop.interleave``'
3042 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
3044 Metadata prefixed with ``llvm.loop.vectorize`` or ``llvm.loop.interleave`` are
3045 used to control per-loop vectorization and interleaving parameters such as
3046 vectorization width and interleave count. These metadata should be used in
3047 conjunction with ``llvm.loop`` loop identification metadata. The
3048 ``llvm.loop.vectorize`` and ``llvm.loop.interleave`` metadata are only
3049 optimization hints and the optimizer will only interleave and vectorize loops if
3050 it believes it is safe to do so. The ``llvm.mem.parallel_loop_access`` metadata
3051 which contains information about loop-carried memory dependencies can be helpful
3052 in determining the safety of these transformations.
3054 '``llvm.loop.interleave.count``' Metadata
3055 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
3057 This metadata suggests an interleave count to the loop interleaver.
3058 The first operand is the string ``llvm.loop.interleave.count`` and the
3059 second operand is an integer specifying the interleave count. For
3062 .. code-block:: llvm
3064 !0 = metadata !{ metadata !"llvm.loop.interleave.count", i32 4 }
3066 Note that setting ``llvm.loop.interleave.count`` to 1 disables interleaving
3067 multiple iterations of the loop. If ``llvm.loop.interleave.count`` is set to 0
3068 then the interleave count will be determined automatically.
3070 '``llvm.loop.vectorize.enable``' Metadata
3071 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
3073 This metadata selectively enables or disables vectorization for the loop. The
3074 first operand is the string ``llvm.loop.vectorize.enable`` and the second operand
3075 is a bit. If the bit operand value is 1 vectorization is enabled. A value of
3076 0 disables vectorization:
3078 .. code-block:: llvm
3080 !0 = metadata !{ metadata !"llvm.loop.vectorize.enable", i1 0 }
3081 !1 = metadata !{ metadata !"llvm.loop.vectorize.enable", i1 1 }
3083 '``llvm.loop.vectorize.width``' Metadata
3084 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
3086 This metadata sets the target width of the vectorizer. The first
3087 operand is the string ``llvm.loop.vectorize.width`` and the second
3088 operand is an integer specifying the width. For example:
3090 .. code-block:: llvm
3092 !0 = metadata !{ metadata !"llvm.loop.vectorize.width", i32 4 }
3094 Note that setting ``llvm.loop.vectorize.width`` to 1 disables
3095 vectorization of the loop. If ``llvm.loop.vectorize.width`` is set to
3096 0 or if the loop does not have this metadata the width will be
3097 determined automatically.
3099 '``llvm.loop.unroll``'
3100 ^^^^^^^^^^^^^^^^^^^^^^
3102 Metadata prefixed with ``llvm.loop.unroll`` are loop unrolling
3103 optimization hints such as the unroll factor. ``llvm.loop.unroll``
3104 metadata should be used in conjunction with ``llvm.loop`` loop
3105 identification metadata. The ``llvm.loop.unroll`` metadata are only
3106 optimization hints and the unrolling will only be performed if the
3107 optimizer believes it is safe to do so.
3109 '``llvm.loop.unroll.count``' Metadata
3110 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
3112 This metadata suggests an unroll factor to the loop unroller. The
3113 first operand is the string ``llvm.loop.unroll.count`` and the second
3114 operand is a positive integer specifying the unroll factor. For
3117 .. code-block:: llvm
3119 !0 = metadata !{ metadata !"llvm.loop.unroll.count", i32 4 }
3121 If the trip count of the loop is less than the unroll count the loop
3122 will be partially unrolled.
3124 '``llvm.loop.unroll.disable``' Metadata
3125 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
3127 This metadata either disables loop unrolling. The metadata has a single operand
3128 which is the string ``llvm.loop.unroll.disable``. For example:
3130 .. code-block:: llvm
3132 !0 = metadata !{ metadata !"llvm.loop.unroll.disable" }
3134 '``llvm.loop.unroll.full``' Metadata
3135 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
3137 This metadata either suggests that the loop should be unrolled fully. The
3138 metadata has a single operand which is the string ``llvm.loop.unroll.disable``.
3141 .. code-block:: llvm
3143 !0 = metadata !{ metadata !"llvm.loop.unroll.full" }
3148 Metadata types used to annotate memory accesses with information helpful
3149 for optimizations are prefixed with ``llvm.mem``.
3151 '``llvm.mem.parallel_loop_access``' Metadata
3152 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
3154 The ``llvm.mem.parallel_loop_access`` metadata refers to a loop identifier,
3155 or metadata containing a list of loop identifiers for nested loops.
3156 The metadata is attached to memory accessing instructions and denotes that
3157 no loop carried memory dependence exist between it and other instructions denoted
3158 with the same loop identifier.
3160 Precisely, given two instructions ``m1`` and ``m2`` that both have the
3161 ``llvm.mem.parallel_loop_access`` metadata, with ``L1`` and ``L2`` being the
3162 set of loops associated with that metadata, respectively, then there is no loop
3163 carried dependence between ``m1`` and ``m2`` for loops in both ``L1`` and
3166 As a special case, if all memory accessing instructions in a loop have
3167 ``llvm.mem.parallel_loop_access`` metadata that refers to that loop, then the
3168 loop has no loop carried memory dependences and is considered to be a parallel
3171 Note that if not all memory access instructions have such metadata referring to
3172 the loop, then the loop is considered not being trivially parallel. Additional
3173 memory dependence analysis is required to make that determination. As a fail
3174 safe mechanism, this causes loops that were originally parallel to be considered
3175 sequential (if optimization passes that are unaware of the parallel semantics
3176 insert new memory instructions into the loop body).
3178 Example of a loop that is considered parallel due to its correct use of
3179 both ``llvm.loop`` and ``llvm.mem.parallel_loop_access``
3180 metadata types that refer to the same loop identifier metadata.
3182 .. code-block:: llvm
3186 %val0 = load i32* %arrayidx, !llvm.mem.parallel_loop_access !0
3188 store i32 %val0, i32* %arrayidx1, !llvm.mem.parallel_loop_access !0
3190 br i1 %exitcond, label %for.end, label %for.body, !llvm.loop !0
3194 !0 = metadata !{ metadata !0 }
3196 It is also possible to have nested parallel loops. In that case the
3197 memory accesses refer to a list of loop identifier metadata nodes instead of
3198 the loop identifier metadata node directly:
3200 .. code-block:: llvm
3204 %val1 = load i32* %arrayidx3, !llvm.mem.parallel_loop_access !2
3206 br label %inner.for.body
3210 %val0 = load i32* %arrayidx1, !llvm.mem.parallel_loop_access !0
3212 store i32 %val0, i32* %arrayidx2, !llvm.mem.parallel_loop_access !0
3214 br i1 %exitcond, label %inner.for.end, label %inner.for.body, !llvm.loop !1
3218 store i32 %val1, i32* %arrayidx4, !llvm.mem.parallel_loop_access !2
3220 br i1 %exitcond, label %outer.for.end, label %outer.for.body, !llvm.loop !2
3222 outer.for.end: ; preds = %for.body
3224 !0 = metadata !{ metadata !1, metadata !2 } ; a list of loop identifiers
3225 !1 = metadata !{ metadata !1 } ; an identifier for the inner loop
3226 !2 = metadata !{ metadata !2 } ; an identifier for the outer loop
3228 Module Flags Metadata
3229 =====================
3231 Information about the module as a whole is difficult to convey to LLVM's
3232 subsystems. The LLVM IR isn't sufficient to transmit this information.
3233 The ``llvm.module.flags`` named metadata exists in order to facilitate
3234 this. These flags are in the form of key / value pairs --- much like a
3235 dictionary --- making it easy for any subsystem who cares about a flag to
3238 The ``llvm.module.flags`` metadata contains a list of metadata triplets.
3239 Each triplet has the following form:
3241 - The first element is a *behavior* flag, which specifies the behavior
3242 when two (or more) modules are merged together, and it encounters two
3243 (or more) metadata with the same ID. The supported behaviors are
3245 - The second element is a metadata string that is a unique ID for the
3246 metadata. Each module may only have one flag entry for each unique ID (not
3247 including entries with the **Require** behavior).
3248 - The third element is the value of the flag.
3250 When two (or more) modules are merged together, the resulting
3251 ``llvm.module.flags`` metadata is the union of the modules' flags. That is, for
3252 each unique metadata ID string, there will be exactly one entry in the merged
3253 modules ``llvm.module.flags`` metadata table, and the value for that entry will
3254 be determined by the merge behavior flag, as described below. The only exception
3255 is that entries with the *Require* behavior are always preserved.
3257 The following behaviors are supported:
3268 Emits an error if two values disagree, otherwise the resulting value
3269 is that of the operands.
3273 Emits a warning if two values disagree. The result value will be the
3274 operand for the flag from the first module being linked.
3278 Adds a requirement that another module flag be present and have a
3279 specified value after linking is performed. The value must be a
3280 metadata pair, where the first element of the pair is the ID of the
3281 module flag to be restricted, and the second element of the pair is
3282 the value the module flag should be restricted to. This behavior can
3283 be used to restrict the allowable results (via triggering of an
3284 error) of linking IDs with the **Override** behavior.
3288 Uses the specified value, regardless of the behavior or value of the
3289 other module. If both modules specify **Override**, but the values
3290 differ, an error will be emitted.
3294 Appends the two values, which are required to be metadata nodes.
3298 Appends the two values, which are required to be metadata
3299 nodes. However, duplicate entries in the second list are dropped
3300 during the append operation.
3302 It is an error for a particular unique flag ID to have multiple behaviors,
3303 except in the case of **Require** (which adds restrictions on another metadata
3304 value) or **Override**.
3306 An example of module flags:
3308 .. code-block:: llvm
3310 !0 = metadata !{ i32 1, metadata !"foo", i32 1 }
3311 !1 = metadata !{ i32 4, metadata !"bar", i32 37 }
3312 !2 = metadata !{ i32 2, metadata !"qux", i32 42 }
3313 !3 = metadata !{ i32 3, metadata !"qux",
3315 metadata !"foo", i32 1
3318 !llvm.module.flags = !{ !0, !1, !2, !3 }
3320 - Metadata ``!0`` has the ID ``!"foo"`` and the value '1'. The behavior
3321 if two or more ``!"foo"`` flags are seen is to emit an error if their
3322 values are not equal.
3324 - Metadata ``!1`` has the ID ``!"bar"`` and the value '37'. The
3325 behavior if two or more ``!"bar"`` flags are seen is to use the value
3328 - Metadata ``!2`` has the ID ``!"qux"`` and the value '42'. The
3329 behavior if two or more ``!"qux"`` flags are seen is to emit a
3330 warning if their values are not equal.
3332 - Metadata ``!3`` has the ID ``!"qux"`` and the value:
3336 metadata !{ metadata !"foo", i32 1 }
3338 The behavior is to emit an error if the ``llvm.module.flags`` does not
3339 contain a flag with the ID ``!"foo"`` that has the value '1' after linking is
3342 Objective-C Garbage Collection Module Flags Metadata
3343 ----------------------------------------------------
3345 On the Mach-O platform, Objective-C stores metadata about garbage
3346 collection in a special section called "image info". The metadata
3347 consists of a version number and a bitmask specifying what types of
3348 garbage collection are supported (if any) by the file. If two or more
3349 modules are linked together their garbage collection metadata needs to
3350 be merged rather than appended together.
3352 The Objective-C garbage collection module flags metadata consists of the
3353 following key-value pairs:
3362 * - ``Objective-C Version``
3363 - **[Required]** --- The Objective-C ABI version. Valid values are 1 and 2.
3365 * - ``Objective-C Image Info Version``
3366 - **[Required]** --- The version of the image info section. Currently
3369 * - ``Objective-C Image Info Section``
3370 - **[Required]** --- The section to place the metadata. Valid values are
3371 ``"__OBJC, __image_info, regular"`` for Objective-C ABI version 1, and
3372 ``"__DATA,__objc_imageinfo, regular, no_dead_strip"`` for
3373 Objective-C ABI version 2.
3375 * - ``Objective-C Garbage Collection``
3376 - **[Required]** --- Specifies whether garbage collection is supported or
3377 not. Valid values are 0, for no garbage collection, and 2, for garbage
3378 collection supported.
3380 * - ``Objective-C GC Only``
3381 - **[Optional]** --- Specifies that only garbage collection is supported.
3382 If present, its value must be 6. This flag requires that the
3383 ``Objective-C Garbage Collection`` flag have the value 2.
3385 Some important flag interactions:
3387 - If a module with ``Objective-C Garbage Collection`` set to 0 is
3388 merged with a module with ``Objective-C Garbage Collection`` set to
3389 2, then the resulting module has the
3390 ``Objective-C Garbage Collection`` flag set to 0.
3391 - A module with ``Objective-C Garbage Collection`` set to 0 cannot be
3392 merged with a module with ``Objective-C GC Only`` set to 6.
3394 Automatic Linker Flags Module Flags Metadata
3395 --------------------------------------------
3397 Some targets support embedding flags to the linker inside individual object
3398 files. Typically this is used in conjunction with language extensions which
3399 allow source files to explicitly declare the libraries they depend on, and have
3400 these automatically be transmitted to the linker via object files.
3402 These flags are encoded in the IR using metadata in the module flags section,
3403 using the ``Linker Options`` key. The merge behavior for this flag is required
3404 to be ``AppendUnique``, and the value for the key is expected to be a metadata
3405 node which should be a list of other metadata nodes, each of which should be a
3406 list of metadata strings defining linker options.
3408 For example, the following metadata section specifies two separate sets of
3409 linker options, presumably to link against ``libz`` and the ``Cocoa``
3412 !0 = metadata !{ i32 6, metadata !"Linker Options",
3414 metadata !{ metadata !"-lz" },
3415 metadata !{ metadata !"-framework", metadata !"Cocoa" } } }
3416 !llvm.module.flags = !{ !0 }
3418 The metadata encoding as lists of lists of options, as opposed to a collapsed
3419 list of options, is chosen so that the IR encoding can use multiple option
3420 strings to specify e.g., a single library, while still having that specifier be
3421 preserved as an atomic element that can be recognized by a target specific
3422 assembly writer or object file emitter.
3424 Each individual option is required to be either a valid option for the target's
3425 linker, or an option that is reserved by the target specific assembly writer or
3426 object file emitter. No other aspect of these options is defined by the IR.
3428 C type width Module Flags Metadata
3429 ----------------------------------
3431 The ARM backend emits a section into each generated object file describing the
3432 options that it was compiled with (in a compiler-independent way) to prevent
3433 linking incompatible objects, and to allow automatic library selection. Some
3434 of these options are not visible at the IR level, namely wchar_t width and enum
3437 To pass this information to the backend, these options are encoded in module
3438 flags metadata, using the following key-value pairs:
3448 - * 0 --- sizeof(wchar_t) == 4
3449 * 1 --- sizeof(wchar_t) == 2
3452 - * 0 --- Enums are at least as large as an ``int``.
3453 * 1 --- Enums are stored in the smallest integer type which can
3454 represent all of its values.
3456 For example, the following metadata section specifies that the module was
3457 compiled with a ``wchar_t`` width of 4 bytes, and the underlying type of an
3458 enum is the smallest type which can represent all of its values::
3460 !llvm.module.flags = !{!0, !1}
3461 !0 = metadata !{i32 1, metadata !"short_wchar", i32 1}
3462 !1 = metadata !{i32 1, metadata !"short_enum", i32 0}
3464 .. _intrinsicglobalvariables:
3466 Intrinsic Global Variables
3467 ==========================
3469 LLVM has a number of "magic" global variables that contain data that
3470 affect code generation or other IR semantics. These are documented here.
3471 All globals of this sort should have a section specified as
3472 "``llvm.metadata``". This section and all globals that start with
3473 "``llvm.``" are reserved for use by LLVM.
3477 The '``llvm.used``' Global Variable
3478 -----------------------------------
3480 The ``@llvm.used`` global is an array which has
3481 :ref:`appending linkage <linkage_appending>`. This array contains a list of
3482 pointers to named global variables, functions and aliases which may optionally
3483 have a pointer cast formed of bitcast or getelementptr. For example, a legal
3486 .. code-block:: llvm
3491 @llvm.used = appending global [2 x i8*] [
3493 i8* bitcast (i32* @Y to i8*)
3494 ], section "llvm.metadata"
3496 If a symbol appears in the ``@llvm.used`` list, then the compiler, assembler,
3497 and linker are required to treat the symbol as if there is a reference to the
3498 symbol that it cannot see (which is why they have to be named). For example, if
3499 a variable has internal linkage and no references other than that from the
3500 ``@llvm.used`` list, it cannot be deleted. This is commonly used to represent
3501 references from inline asms and other things the compiler cannot "see", and
3502 corresponds to "``attribute((used))``" in GNU C.
3504 On some targets, the code generator must emit a directive to the
3505 assembler or object file to prevent the assembler and linker from
3506 molesting the symbol.
3508 .. _gv_llvmcompilerused:
3510 The '``llvm.compiler.used``' Global Variable
3511 --------------------------------------------
3513 The ``@llvm.compiler.used`` directive is the same as the ``@llvm.used``
3514 directive, except that it only prevents the compiler from touching the
3515 symbol. On targets that support it, this allows an intelligent linker to
3516 optimize references to the symbol without being impeded as it would be
3519 This is a rare construct that should only be used in rare circumstances,
3520 and should not be exposed to source languages.
3522 .. _gv_llvmglobalctors:
3524 The '``llvm.global_ctors``' Global Variable
3525 -------------------------------------------
3527 .. code-block:: llvm
3529 %0 = type { i32, void ()*, i8* }
3530 @llvm.global_ctors = appending global [1 x %0] [%0 { i32 65535, void ()* @ctor, i8* @data }]
3532 The ``@llvm.global_ctors`` array contains a list of constructor
3533 functions, priorities, and an optional associated global or function.
3534 The functions referenced by this array will be called in ascending order
3535 of priority (i.e. lowest first) when the module is loaded. The order of
3536 functions with the same priority is not defined.
3538 If the third field is present, non-null, and points to a global variable
3539 or function, the initializer function will only run if the associated
3540 data from the current module is not discarded.
3542 .. _llvmglobaldtors:
3544 The '``llvm.global_dtors``' Global Variable
3545 -------------------------------------------
3547 .. code-block:: llvm
3549 %0 = type { i32, void ()*, i8* }
3550 @llvm.global_dtors = appending global [1 x %0] [%0 { i32 65535, void ()* @dtor, i8* @data }]
3552 The ``@llvm.global_dtors`` array contains a list of destructor
3553 functions, priorities, and an optional associated global or function.
3554 The functions referenced by this array will be called in descending
3555 order of priority (i.e. highest first) when the module is unloaded. The
3556 order of functions with the same priority is not defined.
3558 If the third field is present, non-null, and points to a global variable
3559 or function, the destructor function will only run if the associated
3560 data from the current module is not discarded.
3562 Instruction Reference
3563 =====================
3565 The LLVM instruction set consists of several different classifications
3566 of instructions: :ref:`terminator instructions <terminators>`, :ref:`binary
3567 instructions <binaryops>`, :ref:`bitwise binary
3568 instructions <bitwiseops>`, :ref:`memory instructions <memoryops>`, and
3569 :ref:`other instructions <otherops>`.
3573 Terminator Instructions
3574 -----------------------
3576 As mentioned :ref:`previously <functionstructure>`, every basic block in a
3577 program ends with a "Terminator" instruction, which indicates which
3578 block should be executed after the current block is finished. These
3579 terminator instructions typically yield a '``void``' value: they produce
3580 control flow, not values (the one exception being the
3581 ':ref:`invoke <i_invoke>`' instruction).
3583 The terminator instructions are: ':ref:`ret <i_ret>`',
3584 ':ref:`br <i_br>`', ':ref:`switch <i_switch>`',
3585 ':ref:`indirectbr <i_indirectbr>`', ':ref:`invoke <i_invoke>`',
3586 ':ref:`resume <i_resume>`', and ':ref:`unreachable <i_unreachable>`'.
3590 '``ret``' Instruction
3591 ^^^^^^^^^^^^^^^^^^^^^
3598 ret <type> <value> ; Return a value from a non-void function
3599 ret void ; Return from void function
3604 The '``ret``' instruction is used to return control flow (and optionally
3605 a value) from a function back to the caller.
3607 There are two forms of the '``ret``' instruction: one that returns a
3608 value and then causes control flow, and one that just causes control
3614 The '``ret``' instruction optionally accepts a single argument, the
3615 return value. The type of the return value must be a ':ref:`first
3616 class <t_firstclass>`' type.
3618 A function is not :ref:`well formed <wellformed>` if it it has a non-void
3619 return type and contains a '``ret``' instruction with no return value or
3620 a return value with a type that does not match its type, or if it has a
3621 void return type and contains a '``ret``' instruction with a return
3627 When the '``ret``' instruction is executed, control flow returns back to
3628 the calling function's context. If the caller is a
3629 ":ref:`call <i_call>`" instruction, execution continues at the
3630 instruction after the call. If the caller was an
3631 ":ref:`invoke <i_invoke>`" instruction, execution continues at the
3632 beginning of the "normal" destination block. If the instruction returns
3633 a value, that value shall set the call or invoke instruction's return
3639 .. code-block:: llvm
3641 ret i32 5 ; Return an integer value of 5
3642 ret void ; Return from a void function
3643 ret { i32, i8 } { i32 4, i8 2 } ; Return a struct of values 4 and 2
3647 '``br``' Instruction
3648 ^^^^^^^^^^^^^^^^^^^^
3655 br i1 <cond>, label <iftrue>, label <iffalse>
3656 br label <dest> ; Unconditional branch
3661 The '``br``' instruction is used to cause control flow to transfer to a
3662 different basic block in the current function. There are two forms of
3663 this instruction, corresponding to a conditional branch and an
3664 unconditional branch.
3669 The conditional branch form of the '``br``' instruction takes a single
3670 '``i1``' value and two '``label``' values. The unconditional form of the
3671 '``br``' instruction takes a single '``label``' value as a target.
3676 Upon execution of a conditional '``br``' instruction, the '``i1``'
3677 argument is evaluated. If the value is ``true``, control flows to the
3678 '``iftrue``' ``label`` argument. If "cond" is ``false``, control flows
3679 to the '``iffalse``' ``label`` argument.
3684 .. code-block:: llvm
3687 %cond = icmp eq i32 %a, %b
3688 br i1 %cond, label %IfEqual, label %IfUnequal
3696 '``switch``' Instruction
3697 ^^^^^^^^^^^^^^^^^^^^^^^^
3704 switch <intty> <value>, label <defaultdest> [ <intty> <val>, label <dest> ... ]
3709 The '``switch``' instruction is used to transfer control flow to one of
3710 several different places. It is a generalization of the '``br``'
3711 instruction, allowing a branch to occur to one of many possible
3717 The '``switch``' instruction uses three parameters: an integer
3718 comparison value '``value``', a default '``label``' destination, and an
3719 array of pairs of comparison value constants and '``label``'s. The table
3720 is not allowed to contain duplicate constant entries.
3725 The ``switch`` instruction specifies a table of values and destinations.
3726 When the '``switch``' instruction is executed, this table is searched
3727 for the given value. If the value is found, control flow is transferred
3728 to the corresponding destination; otherwise, control flow is transferred
3729 to the default destination.
3734 Depending on properties of the target machine and the particular
3735 ``switch`` instruction, this instruction may be code generated in
3736 different ways. For example, it could be generated as a series of
3737 chained conditional branches or with a lookup table.
3742 .. code-block:: llvm
3744 ; Emulate a conditional br instruction
3745 %Val = zext i1 %value to i32
3746 switch i32 %Val, label %truedest [ i32 0, label %falsedest ]
3748 ; Emulate an unconditional br instruction
3749 switch i32 0, label %dest [ ]
3751 ; Implement a jump table:
3752 switch i32 %val, label %otherwise [ i32 0, label %onzero
3754 i32 2, label %ontwo ]
3758 '``indirectbr``' Instruction
3759 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
3766 indirectbr <somety>* <address>, [ label <dest1>, label <dest2>, ... ]
3771 The '``indirectbr``' instruction implements an indirect branch to a
3772 label within the current function, whose address is specified by
3773 "``address``". Address must be derived from a
3774 :ref:`blockaddress <blockaddress>` constant.
3779 The '``address``' argument is the address of the label to jump to. The
3780 rest of the arguments indicate the full set of possible destinations
3781 that the address may point to. Blocks are allowed to occur multiple
3782 times in the destination list, though this isn't particularly useful.
3784 This destination list is required so that dataflow analysis has an
3785 accurate understanding of the CFG.
3790 Control transfers to the block specified in the address argument. All
3791 possible destination blocks must be listed in the label list, otherwise
3792 this instruction has undefined behavior. This implies that jumps to
3793 labels defined in other functions have undefined behavior as well.
3798 This is typically implemented with a jump through a register.
3803 .. code-block:: llvm
3805 indirectbr i8* %Addr, [ label %bb1, label %bb2, label %bb3 ]
3809 '``invoke``' Instruction
3810 ^^^^^^^^^^^^^^^^^^^^^^^^
3817 <result> = invoke [cconv] [ret attrs] <ptr to function ty> <function ptr val>(<function args>) [fn attrs]
3818 to label <normal label> unwind label <exception label>
3823 The '``invoke``' instruction causes control to transfer to a specified
3824 function, with the possibility of control flow transfer to either the
3825 '``normal``' label or the '``exception``' label. If the callee function
3826 returns with the "``ret``" instruction, control flow will return to the
3827 "normal" label. If the callee (or any indirect callees) returns via the
3828 ":ref:`resume <i_resume>`" instruction or other exception handling
3829 mechanism, control is interrupted and continued at the dynamically
3830 nearest "exception" label.
3832 The '``exception``' label is a `landing
3833 pad <ExceptionHandling.html#overview>`_ for the exception. As such,
3834 '``exception``' label is required to have the
3835 ":ref:`landingpad <i_landingpad>`" instruction, which contains the
3836 information about the behavior of the program after unwinding happens,
3837 as its first non-PHI instruction. The restrictions on the
3838 "``landingpad``" instruction's tightly couples it to the "``invoke``"
3839 instruction, so that the important information contained within the
3840 "``landingpad``" instruction can't be lost through normal code motion.
3845 This instruction requires several arguments:
3847 #. The optional "cconv" marker indicates which :ref:`calling
3848 convention <callingconv>` the call should use. If none is
3849 specified, the call defaults to using C calling conventions.
3850 #. The optional :ref:`Parameter Attributes <paramattrs>` list for return
3851 values. Only '``zeroext``', '``signext``', and '``inreg``' attributes
3853 #. '``ptr to function ty``': shall be the signature of the pointer to
3854 function value being invoked. In most cases, this is a direct
3855 function invocation, but indirect ``invoke``'s are just as possible,
3856 branching off an arbitrary pointer to function value.
3857 #. '``function ptr val``': An LLVM value containing a pointer to a
3858 function to be invoked.
3859 #. '``function args``': argument list whose types match the function
3860 signature argument types and parameter attributes. All arguments must
3861 be of :ref:`first class <t_firstclass>` type. If the function signature
3862 indicates the function accepts a variable number of arguments, the
3863 extra arguments can be specified.
3864 #. '``normal label``': the label reached when the called function
3865 executes a '``ret``' instruction.
3866 #. '``exception label``': the label reached when a callee returns via
3867 the :ref:`resume <i_resume>` instruction or other exception handling
3869 #. The optional :ref:`function attributes <fnattrs>` list. Only
3870 '``noreturn``', '``nounwind``', '``readonly``' and '``readnone``'
3871 attributes are valid here.
3876 This instruction is designed to operate as a standard '``call``'
3877 instruction in most regards. The primary difference is that it
3878 establishes an association with a label, which is used by the runtime
3879 library to unwind the stack.
3881 This instruction is used in languages with destructors to ensure that
3882 proper cleanup is performed in the case of either a ``longjmp`` or a
3883 thrown exception. Additionally, this is important for implementation of
3884 '``catch``' clauses in high-level languages that support them.
3886 For the purposes of the SSA form, the definition of the value returned
3887 by the '``invoke``' instruction is deemed to occur on the edge from the
3888 current block to the "normal" label. If the callee unwinds then no
3889 return value is available.
3894 .. code-block:: llvm
3896 %retval = invoke i32 @Test(i32 15) to label %Continue
3897 unwind label %TestCleanup ; i32:retval set
3898 %retval = invoke coldcc i32 %Testfnptr(i32 15) to label %Continue
3899 unwind label %TestCleanup ; i32:retval set
3903 '``resume``' Instruction
3904 ^^^^^^^^^^^^^^^^^^^^^^^^
3911 resume <type> <value>
3916 The '``resume``' instruction is a terminator instruction that has no
3922 The '``resume``' instruction requires one argument, which must have the
3923 same type as the result of any '``landingpad``' instruction in the same
3929 The '``resume``' instruction resumes propagation of an existing
3930 (in-flight) exception whose unwinding was interrupted with a
3931 :ref:`landingpad <i_landingpad>` instruction.
3936 .. code-block:: llvm
3938 resume { i8*, i32 } %exn
3942 '``unreachable``' Instruction
3943 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
3955 The '``unreachable``' instruction has no defined semantics. This
3956 instruction is used to inform the optimizer that a particular portion of
3957 the code is not reachable. This can be used to indicate that the code
3958 after a no-return function cannot be reached, and other facts.
3963 The '``unreachable``' instruction has no defined semantics.
3970 Binary operators are used to do most of the computation in a program.
3971 They require two operands of the same type, execute an operation on
3972 them, and produce a single value. The operands might represent multiple
3973 data, as is the case with the :ref:`vector <t_vector>` data type. The
3974 result value has the same type as its operands.
3976 There are several different binary operators:
3980 '``add``' Instruction
3981 ^^^^^^^^^^^^^^^^^^^^^
3988 <result> = add <ty> <op1>, <op2> ; yields ty:result
3989 <result> = add nuw <ty> <op1>, <op2> ; yields ty:result
3990 <result> = add nsw <ty> <op1>, <op2> ; yields ty:result
3991 <result> = add nuw nsw <ty> <op1>, <op2> ; yields ty:result
3996 The '``add``' instruction returns the sum of its two operands.
4001 The two arguments to the '``add``' instruction must be
4002 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
4003 arguments must have identical types.
4008 The value produced is the integer sum of the two operands.
4010 If the sum has unsigned overflow, the result returned is the
4011 mathematical result modulo 2\ :sup:`n`\ , where n is the bit width of
4014 Because LLVM integers use a two's complement representation, this
4015 instruction is appropriate for both signed and unsigned integers.
4017 ``nuw`` and ``nsw`` stand for "No Unsigned Wrap" and "No Signed Wrap",
4018 respectively. If the ``nuw`` and/or ``nsw`` keywords are present, the
4019 result value of the ``add`` is a :ref:`poison value <poisonvalues>` if
4020 unsigned and/or signed overflow, respectively, occurs.
4025 .. code-block:: llvm
4027 <result> = add i32 4, %var ; yields i32:result = 4 + %var
4031 '``fadd``' Instruction
4032 ^^^^^^^^^^^^^^^^^^^^^^
4039 <result> = fadd [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
4044 The '``fadd``' instruction returns the sum of its two operands.
4049 The two arguments to the '``fadd``' instruction must be :ref:`floating
4050 point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
4051 Both arguments must have identical types.
4056 The value produced is the floating point sum of the two operands. This
4057 instruction can also take any number of :ref:`fast-math flags <fastmath>`,
4058 which are optimization hints to enable otherwise unsafe floating point
4064 .. code-block:: llvm
4066 <result> = fadd float 4.0, %var ; yields float:result = 4.0 + %var
4068 '``sub``' Instruction
4069 ^^^^^^^^^^^^^^^^^^^^^
4076 <result> = sub <ty> <op1>, <op2> ; yields ty:result
4077 <result> = sub nuw <ty> <op1>, <op2> ; yields ty:result
4078 <result> = sub nsw <ty> <op1>, <op2> ; yields ty:result
4079 <result> = sub nuw nsw <ty> <op1>, <op2> ; yields ty:result
4084 The '``sub``' instruction returns the difference of its two operands.
4086 Note that the '``sub``' instruction is used to represent the '``neg``'
4087 instruction present in most other intermediate representations.
4092 The two arguments to the '``sub``' instruction must be
4093 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
4094 arguments must have identical types.
4099 The value produced is the integer difference of the two operands.
4101 If the difference has unsigned overflow, the result returned is the
4102 mathematical result modulo 2\ :sup:`n`\ , where n is the bit width of
4105 Because LLVM integers use a two's complement representation, this
4106 instruction is appropriate for both signed and unsigned integers.
4108 ``nuw`` and ``nsw`` stand for "No Unsigned Wrap" and "No Signed Wrap",
4109 respectively. If the ``nuw`` and/or ``nsw`` keywords are present, the
4110 result value of the ``sub`` is a :ref:`poison value <poisonvalues>` if
4111 unsigned and/or signed overflow, respectively, occurs.
4116 .. code-block:: llvm
4118 <result> = sub i32 4, %var ; yields i32:result = 4 - %var
4119 <result> = sub i32 0, %val ; yields i32:result = -%var
4123 '``fsub``' Instruction
4124 ^^^^^^^^^^^^^^^^^^^^^^
4131 <result> = fsub [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
4136 The '``fsub``' instruction returns the difference of its two operands.
4138 Note that the '``fsub``' instruction is used to represent the '``fneg``'
4139 instruction present in most other intermediate representations.
4144 The two arguments to the '``fsub``' instruction must be :ref:`floating
4145 point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
4146 Both arguments must have identical types.
4151 The value produced is the floating point difference of the two operands.
4152 This instruction can also take any number of :ref:`fast-math
4153 flags <fastmath>`, which are optimization hints to enable otherwise
4154 unsafe floating point optimizations:
4159 .. code-block:: llvm
4161 <result> = fsub float 4.0, %var ; yields float:result = 4.0 - %var
4162 <result> = fsub float -0.0, %val ; yields float:result = -%var
4164 '``mul``' Instruction
4165 ^^^^^^^^^^^^^^^^^^^^^
4172 <result> = mul <ty> <op1>, <op2> ; yields ty:result
4173 <result> = mul nuw <ty> <op1>, <op2> ; yields ty:result
4174 <result> = mul nsw <ty> <op1>, <op2> ; yields ty:result
4175 <result> = mul nuw nsw <ty> <op1>, <op2> ; yields ty:result
4180 The '``mul``' instruction returns the product of its two operands.
4185 The two arguments to the '``mul``' instruction must be
4186 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
4187 arguments must have identical types.
4192 The value produced is the integer product of the two operands.
4194 If the result of the multiplication has unsigned overflow, the result
4195 returned is the mathematical result modulo 2\ :sup:`n`\ , where n is the
4196 bit width of the result.
4198 Because LLVM integers use a two's complement representation, and the
4199 result is the same width as the operands, this instruction returns the
4200 correct result for both signed and unsigned integers. If a full product
4201 (e.g. ``i32`` * ``i32`` -> ``i64``) is needed, the operands should be
4202 sign-extended or zero-extended as appropriate to the width of the full
4205 ``nuw`` and ``nsw`` stand for "No Unsigned Wrap" and "No Signed Wrap",
4206 respectively. If the ``nuw`` and/or ``nsw`` keywords are present, the
4207 result value of the ``mul`` is a :ref:`poison value <poisonvalues>` if
4208 unsigned and/or signed overflow, respectively, occurs.
4213 .. code-block:: llvm
4215 <result> = mul i32 4, %var ; yields i32:result = 4 * %var
4219 '``fmul``' Instruction
4220 ^^^^^^^^^^^^^^^^^^^^^^
4227 <result> = fmul [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
4232 The '``fmul``' instruction returns the product of its two operands.
4237 The two arguments to the '``fmul``' instruction must be :ref:`floating
4238 point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
4239 Both arguments must have identical types.
4244 The value produced is the floating point product of the two operands.
4245 This instruction can also take any number of :ref:`fast-math
4246 flags <fastmath>`, which are optimization hints to enable otherwise
4247 unsafe floating point optimizations:
4252 .. code-block:: llvm
4254 <result> = fmul float 4.0, %var ; yields float:result = 4.0 * %var
4256 '``udiv``' Instruction
4257 ^^^^^^^^^^^^^^^^^^^^^^
4264 <result> = udiv <ty> <op1>, <op2> ; yields ty:result
4265 <result> = udiv exact <ty> <op1>, <op2> ; yields ty:result
4270 The '``udiv``' instruction returns the quotient of its two operands.
4275 The two arguments to the '``udiv``' instruction must be
4276 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
4277 arguments must have identical types.
4282 The value produced is the unsigned integer quotient of the two operands.
4284 Note that unsigned integer division and signed integer division are
4285 distinct operations; for signed integer division, use '``sdiv``'.
4287 Division by zero leads to undefined behavior.
4289 If the ``exact`` keyword is present, the result value of the ``udiv`` is
4290 a :ref:`poison value <poisonvalues>` if %op1 is not a multiple of %op2 (as
4291 such, "((a udiv exact b) mul b) == a").
4296 .. code-block:: llvm
4298 <result> = udiv i32 4, %var ; yields i32:result = 4 / %var
4300 '``sdiv``' Instruction
4301 ^^^^^^^^^^^^^^^^^^^^^^
4308 <result> = sdiv <ty> <op1>, <op2> ; yields ty:result
4309 <result> = sdiv exact <ty> <op1>, <op2> ; yields ty:result
4314 The '``sdiv``' instruction returns the quotient of its two operands.
4319 The two arguments to the '``sdiv``' instruction must be
4320 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
4321 arguments must have identical types.
4326 The value produced is the signed integer quotient of the two operands
4327 rounded towards zero.
4329 Note that signed integer division and unsigned integer division are
4330 distinct operations; for unsigned integer division, use '``udiv``'.
4332 Division by zero leads to undefined behavior. Overflow also leads to
4333 undefined behavior; this is a rare case, but can occur, for example, by
4334 doing a 32-bit division of -2147483648 by -1.
4336 If the ``exact`` keyword is present, the result value of the ``sdiv`` is
4337 a :ref:`poison value <poisonvalues>` if the result would be rounded.
4342 .. code-block:: llvm
4344 <result> = sdiv i32 4, %var ; yields i32:result = 4 / %var
4348 '``fdiv``' Instruction
4349 ^^^^^^^^^^^^^^^^^^^^^^
4356 <result> = fdiv [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
4361 The '``fdiv``' instruction returns the quotient of its two operands.
4366 The two arguments to the '``fdiv``' instruction must be :ref:`floating
4367 point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
4368 Both arguments must have identical types.
4373 The value produced is the floating point quotient of the two operands.
4374 This instruction can also take any number of :ref:`fast-math
4375 flags <fastmath>`, which are optimization hints to enable otherwise
4376 unsafe floating point optimizations:
4381 .. code-block:: llvm
4383 <result> = fdiv float 4.0, %var ; yields float:result = 4.0 / %var
4385 '``urem``' Instruction
4386 ^^^^^^^^^^^^^^^^^^^^^^
4393 <result> = urem <ty> <op1>, <op2> ; yields ty:result
4398 The '``urem``' instruction returns the remainder from the unsigned
4399 division of its two arguments.
4404 The two arguments to the '``urem``' instruction must be
4405 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
4406 arguments must have identical types.
4411 This instruction returns the unsigned integer *remainder* of a division.
4412 This instruction always performs an unsigned division to get the
4415 Note that unsigned integer remainder and signed integer remainder are
4416 distinct operations; for signed integer remainder, use '``srem``'.
4418 Taking the remainder of a division by zero leads to undefined behavior.
4423 .. code-block:: llvm
4425 <result> = urem i32 4, %var ; yields i32:result = 4 % %var
4427 '``srem``' Instruction
4428 ^^^^^^^^^^^^^^^^^^^^^^
4435 <result> = srem <ty> <op1>, <op2> ; yields ty:result
4440 The '``srem``' instruction returns the remainder from the signed
4441 division of its two operands. This instruction can also take
4442 :ref:`vector <t_vector>` versions of the values in which case the elements
4448 The two arguments to the '``srem``' instruction must be
4449 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
4450 arguments must have identical types.
4455 This instruction returns the *remainder* of a division (where the result
4456 is either zero or has the same sign as the dividend, ``op1``), not the
4457 *modulo* operator (where the result is either zero or has the same sign
4458 as the divisor, ``op2``) of a value. For more information about the
4459 difference, see `The Math
4460 Forum <http://mathforum.org/dr.math/problems/anne.4.28.99.html>`_. For a
4461 table of how this is implemented in various languages, please see
4463 operation <http://en.wikipedia.org/wiki/Modulo_operation>`_.
4465 Note that signed integer remainder and unsigned integer remainder are
4466 distinct operations; for unsigned integer remainder, use '``urem``'.
4468 Taking the remainder of a division by zero leads to undefined behavior.
4469 Overflow also leads to undefined behavior; this is a rare case, but can
4470 occur, for example, by taking the remainder of a 32-bit division of
4471 -2147483648 by -1. (The remainder doesn't actually overflow, but this
4472 rule lets srem be implemented using instructions that return both the
4473 result of the division and the remainder.)
4478 .. code-block:: llvm
4480 <result> = srem i32 4, %var ; yields i32:result = 4 % %var
4484 '``frem``' Instruction
4485 ^^^^^^^^^^^^^^^^^^^^^^
4492 <result> = frem [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
4497 The '``frem``' instruction returns the remainder from the division of
4503 The two arguments to the '``frem``' instruction must be :ref:`floating
4504 point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
4505 Both arguments must have identical types.
4510 This instruction returns the *remainder* of a division. The remainder
4511 has the same sign as the dividend. This instruction can also take any
4512 number of :ref:`fast-math flags <fastmath>`, which are optimization hints
4513 to enable otherwise unsafe floating point optimizations:
4518 .. code-block:: llvm
4520 <result> = frem float 4.0, %var ; yields float:result = 4.0 % %var
4524 Bitwise Binary Operations
4525 -------------------------
4527 Bitwise binary operators are used to do various forms of bit-twiddling
4528 in a program. They are generally very efficient instructions and can
4529 commonly be strength reduced from other instructions. They require two
4530 operands of the same type, execute an operation on them, and produce a
4531 single value. The resulting value is the same type as its operands.
4533 '``shl``' Instruction
4534 ^^^^^^^^^^^^^^^^^^^^^
4541 <result> = shl <ty> <op1>, <op2> ; yields ty:result
4542 <result> = shl nuw <ty> <op1>, <op2> ; yields ty:result
4543 <result> = shl nsw <ty> <op1>, <op2> ; yields ty:result
4544 <result> = shl nuw nsw <ty> <op1>, <op2> ; yields ty:result
4549 The '``shl``' instruction returns the first operand shifted to the left
4550 a specified number of bits.
4555 Both arguments to the '``shl``' instruction must be the same
4556 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer type.
4557 '``op2``' is treated as an unsigned value.
4562 The value produced is ``op1`` \* 2\ :sup:`op2` mod 2\ :sup:`n`,
4563 where ``n`` is the width of the result. If ``op2`` is (statically or
4564 dynamically) negative or equal to or larger than the number of bits in
4565 ``op1``, the result is undefined. If the arguments are vectors, each
4566 vector element of ``op1`` is shifted by the corresponding shift amount
4569 If the ``nuw`` keyword is present, then the shift produces a :ref:`poison
4570 value <poisonvalues>` if it shifts out any non-zero bits. If the
4571 ``nsw`` keyword is present, then the shift produces a :ref:`poison
4572 value <poisonvalues>` if it shifts out any bits that disagree with the
4573 resultant sign bit. As such, NUW/NSW have the same semantics as they
4574 would if the shift were expressed as a mul instruction with the same
4575 nsw/nuw bits in (mul %op1, (shl 1, %op2)).
4580 .. code-block:: llvm
4582 <result> = shl i32 4, %var ; yields i32: 4 << %var
4583 <result> = shl i32 4, 2 ; yields i32: 16
4584 <result> = shl i32 1, 10 ; yields i32: 1024
4585 <result> = shl i32 1, 32 ; undefined
4586 <result> = shl <2 x i32> < i32 1, i32 1>, < i32 1, i32 2> ; yields: result=<2 x i32> < i32 2, i32 4>
4588 '``lshr``' Instruction
4589 ^^^^^^^^^^^^^^^^^^^^^^
4596 <result> = lshr <ty> <op1>, <op2> ; yields ty:result
4597 <result> = lshr exact <ty> <op1>, <op2> ; yields ty:result
4602 The '``lshr``' instruction (logical shift right) returns the first
4603 operand shifted to the right a specified number of bits with zero fill.
4608 Both arguments to the '``lshr``' instruction must be the same
4609 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer type.
4610 '``op2``' is treated as an unsigned value.
4615 This instruction always performs a logical shift right operation. The
4616 most significant bits of the result will be filled with zero bits after
4617 the shift. If ``op2`` is (statically or dynamically) equal to or larger
4618 than the number of bits in ``op1``, the result is undefined. If the
4619 arguments are vectors, each vector element of ``op1`` is shifted by the
4620 corresponding shift amount in ``op2``.
4622 If the ``exact`` keyword is present, the result value of the ``lshr`` is
4623 a :ref:`poison value <poisonvalues>` if any of the bits shifted out are
4629 .. code-block:: llvm
4631 <result> = lshr i32 4, 1 ; yields i32:result = 2
4632 <result> = lshr i32 4, 2 ; yields i32:result = 1
4633 <result> = lshr i8 4, 3 ; yields i8:result = 0
4634 <result> = lshr i8 -2, 1 ; yields i8:result = 0x7F
4635 <result> = lshr i32 1, 32 ; undefined
4636 <result> = lshr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 2> ; yields: result=<2 x i32> < i32 0x7FFFFFFF, i32 1>
4638 '``ashr``' Instruction
4639 ^^^^^^^^^^^^^^^^^^^^^^
4646 <result> = ashr <ty> <op1>, <op2> ; yields ty:result
4647 <result> = ashr exact <ty> <op1>, <op2> ; yields ty:result
4652 The '``ashr``' instruction (arithmetic shift right) returns the first
4653 operand shifted to the right a specified number of bits with sign
4659 Both arguments to the '``ashr``' instruction must be the same
4660 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer type.
4661 '``op2``' is treated as an unsigned value.
4666 This instruction always performs an arithmetic shift right operation,
4667 The most significant bits of the result will be filled with the sign bit
4668 of ``op1``. If ``op2`` is (statically or dynamically) equal to or larger
4669 than the number of bits in ``op1``, the result is undefined. If the
4670 arguments are vectors, each vector element of ``op1`` is shifted by the
4671 corresponding shift amount in ``op2``.
4673 If the ``exact`` keyword is present, the result value of the ``ashr`` is
4674 a :ref:`poison value <poisonvalues>` if any of the bits shifted out are
4680 .. code-block:: llvm
4682 <result> = ashr i32 4, 1 ; yields i32:result = 2
4683 <result> = ashr i32 4, 2 ; yields i32:result = 1
4684 <result> = ashr i8 4, 3 ; yields i8:result = 0
4685 <result> = ashr i8 -2, 1 ; yields i8:result = -1
4686 <result> = ashr i32 1, 32 ; undefined
4687 <result> = ashr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 3> ; yields: result=<2 x i32> < i32 -1, i32 0>
4689 '``and``' Instruction
4690 ^^^^^^^^^^^^^^^^^^^^^
4697 <result> = and <ty> <op1>, <op2> ; yields ty:result
4702 The '``and``' instruction returns the bitwise logical and of its two
4708 The two arguments to the '``and``' instruction must be
4709 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
4710 arguments must have identical types.
4715 The truth table used for the '``and``' instruction is:
4732 .. code-block:: llvm
4734 <result> = and i32 4, %var ; yields i32:result = 4 & %var
4735 <result> = and i32 15, 40 ; yields i32:result = 8
4736 <result> = and i32 4, 8 ; yields i32:result = 0
4738 '``or``' Instruction
4739 ^^^^^^^^^^^^^^^^^^^^
4746 <result> = or <ty> <op1>, <op2> ; yields ty:result
4751 The '``or``' instruction returns the bitwise logical inclusive or of its
4757 The two arguments to the '``or``' instruction must be
4758 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
4759 arguments must have identical types.
4764 The truth table used for the '``or``' instruction is:
4783 <result> = or i32 4, %var ; yields i32:result = 4 | %var
4784 <result> = or i32 15, 40 ; yields i32:result = 47
4785 <result> = or i32 4, 8 ; yields i32:result = 12
4787 '``xor``' Instruction
4788 ^^^^^^^^^^^^^^^^^^^^^
4795 <result> = xor <ty> <op1>, <op2> ; yields ty:result
4800 The '``xor``' instruction returns the bitwise logical exclusive or of
4801 its two operands. The ``xor`` is used to implement the "one's
4802 complement" operation, which is the "~" operator in C.
4807 The two arguments to the '``xor``' instruction must be
4808 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
4809 arguments must have identical types.
4814 The truth table used for the '``xor``' instruction is:
4831 .. code-block:: llvm
4833 <result> = xor i32 4, %var ; yields i32:result = 4 ^ %var
4834 <result> = xor i32 15, 40 ; yields i32:result = 39
4835 <result> = xor i32 4, 8 ; yields i32:result = 12
4836 <result> = xor i32 %V, -1 ; yields i32:result = ~%V
4841 LLVM supports several instructions to represent vector operations in a
4842 target-independent manner. These instructions cover the element-access
4843 and vector-specific operations needed to process vectors effectively.
4844 While LLVM does directly support these vector operations, many
4845 sophisticated algorithms will want to use target-specific intrinsics to
4846 take full advantage of a specific target.
4848 .. _i_extractelement:
4850 '``extractelement``' Instruction
4851 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4858 <result> = extractelement <n x <ty>> <val>, <ty2> <idx> ; yields <ty>
4863 The '``extractelement``' instruction extracts a single scalar element
4864 from a vector at a specified index.
4869 The first operand of an '``extractelement``' instruction is a value of
4870 :ref:`vector <t_vector>` type. The second operand is an index indicating
4871 the position from which to extract the element. The index may be a
4872 variable of any integer type.
4877 The result is a scalar of the same type as the element type of ``val``.
4878 Its value is the value at position ``idx`` of ``val``. If ``idx``
4879 exceeds the length of ``val``, the results are undefined.
4884 .. code-block:: llvm
4886 <result> = extractelement <4 x i32> %vec, i32 0 ; yields i32
4888 .. _i_insertelement:
4890 '``insertelement``' Instruction
4891 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4898 <result> = insertelement <n x <ty>> <val>, <ty> <elt>, <ty2> <idx> ; yields <n x <ty>>
4903 The '``insertelement``' instruction inserts a scalar element into a
4904 vector at a specified index.
4909 The first operand of an '``insertelement``' instruction is a value of
4910 :ref:`vector <t_vector>` type. The second operand is a scalar value whose
4911 type must equal the element type of the first operand. The third operand
4912 is an index indicating the position at which to insert the value. The
4913 index may be a variable of any integer type.
4918 The result is a vector of the same type as ``val``. Its element values
4919 are those of ``val`` except at position ``idx``, where it gets the value
4920 ``elt``. If ``idx`` exceeds the length of ``val``, the results are
4926 .. code-block:: llvm
4928 <result> = insertelement <4 x i32> %vec, i32 1, i32 0 ; yields <4 x i32>
4930 .. _i_shufflevector:
4932 '``shufflevector``' Instruction
4933 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4940 <result> = shufflevector <n x <ty>> <v1>, <n x <ty>> <v2>, <m x i32> <mask> ; yields <m x <ty>>
4945 The '``shufflevector``' instruction constructs a permutation of elements
4946 from two input vectors, returning a vector with the same element type as
4947 the input and length that is the same as the shuffle mask.
4952 The first two operands of a '``shufflevector``' instruction are vectors
4953 with the same type. The third argument is a shuffle mask whose element
4954 type is always 'i32'. The result of the instruction is a vector whose
4955 length is the same as the shuffle mask and whose element type is the
4956 same as the element type of the first two operands.
4958 The shuffle mask operand is required to be a constant vector with either
4959 constant integer or undef values.
4964 The elements of the two input vectors are numbered from left to right
4965 across both of the vectors. The shuffle mask operand specifies, for each
4966 element of the result vector, which element of the two input vectors the
4967 result element gets. The element selector may be undef (meaning "don't
4968 care") and the second operand may be undef if performing a shuffle from
4974 .. code-block:: llvm
4976 <result> = shufflevector <4 x i32> %v1, <4 x i32> %v2,
4977 <4 x i32> <i32 0, i32 4, i32 1, i32 5> ; yields <4 x i32>
4978 <result> = shufflevector <4 x i32> %v1, <4 x i32> undef,
4979 <4 x i32> <i32 0, i32 1, i32 2, i32 3> ; yields <4 x i32> - Identity shuffle.
4980 <result> = shufflevector <8 x i32> %v1, <8 x i32> undef,
4981 <4 x i32> <i32 0, i32 1, i32 2, i32 3> ; yields <4 x i32>
4982 <result> = shufflevector <4 x i32> %v1, <4 x i32> %v2,
4983 <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7 > ; yields <8 x i32>
4985 Aggregate Operations
4986 --------------------
4988 LLVM supports several instructions for working with
4989 :ref:`aggregate <t_aggregate>` values.
4993 '``extractvalue``' Instruction
4994 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5001 <result> = extractvalue <aggregate type> <val>, <idx>{, <idx>}*
5006 The '``extractvalue``' instruction extracts the value of a member field
5007 from an :ref:`aggregate <t_aggregate>` value.
5012 The first operand of an '``extractvalue``' instruction is a value of
5013 :ref:`struct <t_struct>` or :ref:`array <t_array>` type. The operands are
5014 constant indices to specify which value to extract in a similar manner
5015 as indices in a '``getelementptr``' instruction.
5017 The major differences to ``getelementptr`` indexing are:
5019 - Since the value being indexed is not a pointer, the first index is
5020 omitted and assumed to be zero.
5021 - At least one index must be specified.
5022 - Not only struct indices but also array indices must be in bounds.
5027 The result is the value at the position in the aggregate specified by
5033 .. code-block:: llvm
5035 <result> = extractvalue {i32, float} %agg, 0 ; yields i32
5039 '``insertvalue``' Instruction
5040 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5047 <result> = insertvalue <aggregate type> <val>, <ty> <elt>, <idx>{, <idx>}* ; yields <aggregate type>
5052 The '``insertvalue``' instruction inserts a value into a member field in
5053 an :ref:`aggregate <t_aggregate>` value.
5058 The first operand of an '``insertvalue``' instruction is a value of
5059 :ref:`struct <t_struct>` or :ref:`array <t_array>` type. The second operand is
5060 a first-class value to insert. The following operands are constant
5061 indices indicating the position at which to insert the value in a
5062 similar manner as indices in a '``extractvalue``' instruction. The value
5063 to insert must have the same type as the value identified by the
5069 The result is an aggregate of the same type as ``val``. Its value is
5070 that of ``val`` except that the value at the position specified by the
5071 indices is that of ``elt``.
5076 .. code-block:: llvm
5078 %agg1 = insertvalue {i32, float} undef, i32 1, 0 ; yields {i32 1, float undef}
5079 %agg2 = insertvalue {i32, float} %agg1, float %val, 1 ; yields {i32 1, float %val}
5080 %agg3 = insertvalue {i32, {float}} undef, float %val, 1, 0 ; yields {i32 undef, {float %val}}
5084 Memory Access and Addressing Operations
5085 ---------------------------------------
5087 A key design point of an SSA-based representation is how it represents
5088 memory. In LLVM, no memory locations are in SSA form, which makes things
5089 very simple. This section describes how to read, write, and allocate
5094 '``alloca``' Instruction
5095 ^^^^^^^^^^^^^^^^^^^^^^^^
5102 <result> = alloca [inalloca] <type> [, <ty> <NumElements>] [, align <alignment>] ; yields type*:result
5107 The '``alloca``' instruction allocates memory on the stack frame of the
5108 currently executing function, to be automatically released when this
5109 function returns to its caller. The object is always allocated in the
5110 generic address space (address space zero).
5115 The '``alloca``' instruction allocates ``sizeof(<type>)*NumElements``
5116 bytes of memory on the runtime stack, returning a pointer of the
5117 appropriate type to the program. If "NumElements" is specified, it is
5118 the number of elements allocated, otherwise "NumElements" is defaulted
5119 to be one. If a constant alignment is specified, the value result of the
5120 allocation is guaranteed to be aligned to at least that boundary. The
5121 alignment may not be greater than ``1 << 29``. If not specified, or if
5122 zero, the target can choose to align the allocation on any convenient
5123 boundary compatible with the type.
5125 '``type``' may be any sized type.
5130 Memory is allocated; a pointer is returned. The operation is undefined
5131 if there is insufficient stack space for the allocation. '``alloca``'d
5132 memory is automatically released when the function returns. The
5133 '``alloca``' instruction is commonly used to represent automatic
5134 variables that must have an address available. When the function returns
5135 (either with the ``ret`` or ``resume`` instructions), the memory is
5136 reclaimed. Allocating zero bytes is legal, but the result is undefined.
5137 The order in which memory is allocated (ie., which way the stack grows)
5143 .. code-block:: llvm
5145 %ptr = alloca i32 ; yields i32*:ptr
5146 %ptr = alloca i32, i32 4 ; yields i32*:ptr
5147 %ptr = alloca i32, i32 4, align 1024 ; yields i32*:ptr
5148 %ptr = alloca i32, align 1024 ; yields i32*:ptr
5152 '``load``' Instruction
5153 ^^^^^^^^^^^^^^^^^^^^^^
5160 <result> = load [volatile] <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>][, !invariant.load !<index>]
5161 <result> = load atomic [volatile] <ty>* <pointer> [singlethread] <ordering>, align <alignment>
5162 !<index> = !{ i32 1 }
5167 The '``load``' instruction is used to read from memory.
5172 The argument to the ``load`` instruction specifies the memory address
5173 from which to load. The pointer must point to a :ref:`first
5174 class <t_firstclass>` type. If the ``load`` is marked as ``volatile``,
5175 then the optimizer is not allowed to modify the number or order of
5176 execution of this ``load`` with other :ref:`volatile
5177 operations <volatile>`.
5179 If the ``load`` is marked as ``atomic``, it takes an extra
5180 :ref:`ordering <ordering>` and optional ``singlethread`` argument. The
5181 ``release`` and ``acq_rel`` orderings are not valid on ``load``
5182 instructions. Atomic loads produce :ref:`defined <memmodel>` results
5183 when they may see multiple atomic stores. The type of the pointee must
5184 be an integer type whose bit width is a power of two greater than or
5185 equal to eight and less than or equal to a target-specific size limit.
5186 ``align`` must be explicitly specified on atomic loads, and the load has
5187 undefined behavior if the alignment is not set to a value which is at
5188 least the size in bytes of the pointee. ``!nontemporal`` does not have
5189 any defined semantics for atomic loads.
5191 The optional constant ``align`` argument specifies the alignment of the
5192 operation (that is, the alignment of the memory address). A value of 0
5193 or an omitted ``align`` argument means that the operation has the ABI
5194 alignment for the target. It is the responsibility of the code emitter
5195 to ensure that the alignment information is correct. Overestimating the
5196 alignment results in undefined behavior. Underestimating the alignment
5197 may produce less efficient code. An alignment of 1 is always safe. The
5198 maximum possible alignment is ``1 << 29``.
5200 The optional ``!nontemporal`` metadata must reference a single
5201 metadata name ``<index>`` corresponding to a metadata node with one
5202 ``i32`` entry of value 1. The existence of the ``!nontemporal``
5203 metadata on the instruction tells the optimizer and code generator
5204 that this load is not expected to be reused in the cache. The code
5205 generator may select special instructions to save cache bandwidth, such
5206 as the ``MOVNT`` instruction on x86.
5208 The optional ``!invariant.load`` metadata must reference a single
5209 metadata name ``<index>`` corresponding to a metadata node with no
5210 entries. The existence of the ``!invariant.load`` metadata on the
5211 instruction tells the optimizer and code generator that this load
5212 address points to memory which does not change value during program
5213 execution. The optimizer may then move this load around, for example, by
5214 hoisting it out of loops using loop invariant code motion.
5219 The location of memory pointed to is loaded. If the value being loaded
5220 is of scalar type then the number of bytes read does not exceed the
5221 minimum number of bytes needed to hold all bits of the type. For
5222 example, loading an ``i24`` reads at most three bytes. When loading a
5223 value of a type like ``i20`` with a size that is not an integral number
5224 of bytes, the result is undefined if the value was not originally
5225 written using a store of the same type.
5230 .. code-block:: llvm
5232 %ptr = alloca i32 ; yields i32*:ptr
5233 store i32 3, i32* %ptr ; yields void
5234 %val = load i32* %ptr ; yields i32:val = i32 3
5238 '``store``' Instruction
5239 ^^^^^^^^^^^^^^^^^^^^^^^
5246 store [volatile] <ty> <value>, <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>] ; yields void
5247 store atomic [volatile] <ty> <value>, <ty>* <pointer> [singlethread] <ordering>, align <alignment> ; yields void
5252 The '``store``' instruction is used to write to memory.
5257 There are two arguments to the ``store`` instruction: a value to store
5258 and an address at which to store it. The type of the ``<pointer>``
5259 operand must be a pointer to the :ref:`first class <t_firstclass>` type of
5260 the ``<value>`` operand. If the ``store`` is marked as ``volatile``,
5261 then the optimizer is not allowed to modify the number or order of
5262 execution of this ``store`` with other :ref:`volatile
5263 operations <volatile>`.
5265 If the ``store`` is marked as ``atomic``, it takes an extra
5266 :ref:`ordering <ordering>` and optional ``singlethread`` argument. The
5267 ``acquire`` and ``acq_rel`` orderings aren't valid on ``store``
5268 instructions. Atomic loads produce :ref:`defined <memmodel>` results
5269 when they may see multiple atomic stores. The type of the pointee must
5270 be an integer type whose bit width is a power of two greater than or
5271 equal to eight and less than or equal to a target-specific size limit.
5272 ``align`` must be explicitly specified on atomic stores, and the store
5273 has undefined behavior if the alignment is not set to a value which is
5274 at least the size in bytes of the pointee. ``!nontemporal`` does not
5275 have any defined semantics for atomic stores.
5277 The optional constant ``align`` argument specifies the alignment of the
5278 operation (that is, the alignment of the memory address). A value of 0
5279 or an omitted ``align`` argument means that the operation has the ABI
5280 alignment for the target. It is the responsibility of the code emitter
5281 to ensure that the alignment information is correct. Overestimating the
5282 alignment results in undefined behavior. Underestimating the
5283 alignment may produce less efficient code. An alignment of 1 is always
5284 safe. The maximum possible alignment is ``1 << 29``.
5286 The optional ``!nontemporal`` metadata must reference a single metadata
5287 name ``<index>`` corresponding to a metadata node with one ``i32`` entry of
5288 value 1. The existence of the ``!nontemporal`` metadata on the instruction
5289 tells the optimizer and code generator that this load is not expected to
5290 be reused in the cache. The code generator may select special
5291 instructions to save cache bandwidth, such as the MOVNT instruction on
5297 The contents of memory are updated to contain ``<value>`` at the
5298 location specified by the ``<pointer>`` operand. If ``<value>`` is
5299 of scalar type then the number of bytes written does not exceed the
5300 minimum number of bytes needed to hold all bits of the type. For
5301 example, storing an ``i24`` writes at most three bytes. When writing a
5302 value of a type like ``i20`` with a size that is not an integral number
5303 of bytes, it is unspecified what happens to the extra bits that do not
5304 belong to the type, but they will typically be overwritten.
5309 .. code-block:: llvm
5311 %ptr = alloca i32 ; yields i32*:ptr
5312 store i32 3, i32* %ptr ; yields void
5313 %val = load i32* %ptr ; yields i32:val = i32 3
5317 '``fence``' Instruction
5318 ^^^^^^^^^^^^^^^^^^^^^^^
5325 fence [singlethread] <ordering> ; yields void
5330 The '``fence``' instruction is used to introduce happens-before edges
5336 '``fence``' instructions take an :ref:`ordering <ordering>` argument which
5337 defines what *synchronizes-with* edges they add. They can only be given
5338 ``acquire``, ``release``, ``acq_rel``, and ``seq_cst`` orderings.
5343 A fence A which has (at least) ``release`` ordering semantics
5344 *synchronizes with* a fence B with (at least) ``acquire`` ordering
5345 semantics if and only if there exist atomic operations X and Y, both
5346 operating on some atomic object M, such that A is sequenced before X, X
5347 modifies M (either directly or through some side effect of a sequence
5348 headed by X), Y is sequenced before B, and Y observes M. This provides a
5349 *happens-before* dependency between A and B. Rather than an explicit
5350 ``fence``, one (but not both) of the atomic operations X or Y might
5351 provide a ``release`` or ``acquire`` (resp.) ordering constraint and
5352 still *synchronize-with* the explicit ``fence`` and establish the
5353 *happens-before* edge.
5355 A ``fence`` which has ``seq_cst`` ordering, in addition to having both
5356 ``acquire`` and ``release`` semantics specified above, participates in
5357 the global program order of other ``seq_cst`` operations and/or fences.
5359 The optional ":ref:`singlethread <singlethread>`" argument specifies
5360 that the fence only synchronizes with other fences in the same thread.
5361 (This is useful for interacting with signal handlers.)
5366 .. code-block:: llvm
5368 fence acquire ; yields void
5369 fence singlethread seq_cst ; yields void
5373 '``cmpxchg``' Instruction
5374 ^^^^^^^^^^^^^^^^^^^^^^^^^
5381 cmpxchg [weak] [volatile] <ty>* <pointer>, <ty> <cmp>, <ty> <new> [singlethread] <success ordering> <failure ordering> ; yields { ty, i1 }
5386 The '``cmpxchg``' instruction is used to atomically modify memory. It
5387 loads a value in memory and compares it to a given value. If they are
5388 equal, it tries to store a new value into the memory.
5393 There are three arguments to the '``cmpxchg``' instruction: an address
5394 to operate on, a value to compare to the value currently be at that
5395 address, and a new value to place at that address if the compared values
5396 are equal. The type of '<cmp>' must be an integer type whose bit width
5397 is a power of two greater than or equal to eight and less than or equal
5398 to a target-specific size limit. '<cmp>' and '<new>' must have the same
5399 type, and the type of '<pointer>' must be a pointer to that type. If the
5400 ``cmpxchg`` is marked as ``volatile``, then the optimizer is not allowed
5401 to modify the number or order of execution of this ``cmpxchg`` with
5402 other :ref:`volatile operations <volatile>`.
5404 The success and failure :ref:`ordering <ordering>` arguments specify how this
5405 ``cmpxchg`` synchronizes with other atomic operations. Both ordering parameters
5406 must be at least ``monotonic``, the ordering constraint on failure must be no
5407 stronger than that on success, and the failure ordering cannot be either
5408 ``release`` or ``acq_rel``.
5410 The optional "``singlethread``" argument declares that the ``cmpxchg``
5411 is only atomic with respect to code (usually signal handlers) running in
5412 the same thread as the ``cmpxchg``. Otherwise the cmpxchg is atomic with
5413 respect to all other code in the system.
5415 The pointer passed into cmpxchg must have alignment greater than or
5416 equal to the size in memory of the operand.
5421 The contents of memory at the location specified by the '``<pointer>``' operand
5422 is read and compared to '``<cmp>``'; if the read value is the equal, the
5423 '``<new>``' is written. The original value at the location is returned, together
5424 with a flag indicating success (true) or failure (false).
5426 If the cmpxchg operation is marked as ``weak`` then a spurious failure is
5427 permitted: the operation may not write ``<new>`` even if the comparison
5430 If the cmpxchg operation is strong (the default), the i1 value is 1 if and only
5431 if the value loaded equals ``cmp``.
5433 A successful ``cmpxchg`` is a read-modify-write instruction for the purpose of
5434 identifying release sequences. A failed ``cmpxchg`` is equivalent to an atomic
5435 load with an ordering parameter determined the second ordering parameter.
5440 .. code-block:: llvm
5443 %orig = atomic load i32* %ptr unordered ; yields i32
5447 %cmp = phi i32 [ %orig, %entry ], [%old, %loop]
5448 %squared = mul i32 %cmp, %cmp
5449 %val_success = cmpxchg i32* %ptr, i32 %cmp, i32 %squared acq_rel monotonic ; yields { i32, i1 }
5450 %value_loaded = extractvalue { i32, i1 } %val_success, 0
5451 %success = extractvalue { i32, i1 } %val_success, 1
5452 br i1 %success, label %done, label %loop
5459 '``atomicrmw``' Instruction
5460 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
5467 atomicrmw [volatile] <operation> <ty>* <pointer>, <ty> <value> [singlethread] <ordering> ; yields ty
5472 The '``atomicrmw``' instruction is used to atomically modify memory.
5477 There are three arguments to the '``atomicrmw``' instruction: an
5478 operation to apply, an address whose value to modify, an argument to the
5479 operation. The operation must be one of the following keywords:
5493 The type of '<value>' must be an integer type whose bit width is a power
5494 of two greater than or equal to eight and less than or equal to a
5495 target-specific size limit. The type of the '``<pointer>``' operand must
5496 be a pointer to that type. If the ``atomicrmw`` is marked as
5497 ``volatile``, then the optimizer is not allowed to modify the number or
5498 order of execution of this ``atomicrmw`` with other :ref:`volatile
5499 operations <volatile>`.
5504 The contents of memory at the location specified by the '``<pointer>``'
5505 operand are atomically read, modified, and written back. The original
5506 value at the location is returned. The modification is specified by the
5509 - xchg: ``*ptr = val``
5510 - add: ``*ptr = *ptr + val``
5511 - sub: ``*ptr = *ptr - val``
5512 - and: ``*ptr = *ptr & val``
5513 - nand: ``*ptr = ~(*ptr & val)``
5514 - or: ``*ptr = *ptr | val``
5515 - xor: ``*ptr = *ptr ^ val``
5516 - max: ``*ptr = *ptr > val ? *ptr : val`` (using a signed comparison)
5517 - min: ``*ptr = *ptr < val ? *ptr : val`` (using a signed comparison)
5518 - umax: ``*ptr = *ptr > val ? *ptr : val`` (using an unsigned
5520 - umin: ``*ptr = *ptr < val ? *ptr : val`` (using an unsigned
5526 .. code-block:: llvm
5528 %old = atomicrmw add i32* %ptr, i32 1 acquire ; yields i32
5530 .. _i_getelementptr:
5532 '``getelementptr``' Instruction
5533 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5540 <result> = getelementptr <pty>* <ptrval>{, <ty> <idx>}*
5541 <result> = getelementptr inbounds <pty>* <ptrval>{, <ty> <idx>}*
5542 <result> = getelementptr <ptr vector> ptrval, <vector index type> idx
5547 The '``getelementptr``' instruction is used to get the address of a
5548 subelement of an :ref:`aggregate <t_aggregate>` data structure. It performs
5549 address calculation only and does not access memory.
5554 The first argument is always a pointer or a vector of pointers, and
5555 forms the basis of the calculation. The remaining arguments are indices
5556 that indicate which of the elements of the aggregate object are indexed.
5557 The interpretation of each index is dependent on the type being indexed
5558 into. The first index always indexes the pointer value given as the
5559 first argument, the second index indexes a value of the type pointed to
5560 (not necessarily the value directly pointed to, since the first index
5561 can be non-zero), etc. The first type indexed into must be a pointer
5562 value, subsequent types can be arrays, vectors, and structs. Note that
5563 subsequent types being indexed into can never be pointers, since that
5564 would require loading the pointer before continuing calculation.
5566 The type of each index argument depends on the type it is indexing into.
5567 When indexing into a (optionally packed) structure, only ``i32`` integer
5568 **constants** are allowed (when using a vector of indices they must all
5569 be the **same** ``i32`` integer constant). When indexing into an array,
5570 pointer or vector, integers of any width are allowed, and they are not
5571 required to be constant. These integers are treated as signed values
5574 For example, let's consider a C code fragment and how it gets compiled
5590 int *foo(struct ST *s) {
5591 return &s[1].Z.B[5][13];
5594 The LLVM code generated by Clang is:
5596 .. code-block:: llvm
5598 %struct.RT = type { i8, [10 x [20 x i32]], i8 }
5599 %struct.ST = type { i32, double, %struct.RT }
5601 define i32* @foo(%struct.ST* %s) nounwind uwtable readnone optsize ssp {
5603 %arrayidx = getelementptr inbounds %struct.ST* %s, i64 1, i32 2, i32 1, i64 5, i64 13
5610 In the example above, the first index is indexing into the
5611 '``%struct.ST*``' type, which is a pointer, yielding a '``%struct.ST``'
5612 = '``{ i32, double, %struct.RT }``' type, a structure. The second index
5613 indexes into the third element of the structure, yielding a
5614 '``%struct.RT``' = '``{ i8 , [10 x [20 x i32]], i8 }``' type, another
5615 structure. The third index indexes into the second element of the
5616 structure, yielding a '``[10 x [20 x i32]]``' type, an array. The two
5617 dimensions of the array are subscripted into, yielding an '``i32``'
5618 type. The '``getelementptr``' instruction returns a pointer to this
5619 element, thus computing a value of '``i32*``' type.
5621 Note that it is perfectly legal to index partially through a structure,
5622 returning a pointer to an inner element. Because of this, the LLVM code
5623 for the given testcase is equivalent to:
5625 .. code-block:: llvm
5627 define i32* @foo(%struct.ST* %s) {
5628 %t1 = getelementptr %struct.ST* %s, i32 1 ; yields %struct.ST*:%t1
5629 %t2 = getelementptr %struct.ST* %t1, i32 0, i32 2 ; yields %struct.RT*:%t2
5630 %t3 = getelementptr %struct.RT* %t2, i32 0, i32 1 ; yields [10 x [20 x i32]]*:%t3
5631 %t4 = getelementptr [10 x [20 x i32]]* %t3, i32 0, i32 5 ; yields [20 x i32]*:%t4
5632 %t5 = getelementptr [20 x i32]* %t4, i32 0, i32 13 ; yields i32*:%t5
5636 If the ``inbounds`` keyword is present, the result value of the
5637 ``getelementptr`` is a :ref:`poison value <poisonvalues>` if the base
5638 pointer is not an *in bounds* address of an allocated object, or if any
5639 of the addresses that would be formed by successive addition of the
5640 offsets implied by the indices to the base address with infinitely
5641 precise signed arithmetic are not an *in bounds* address of that
5642 allocated object. The *in bounds* addresses for an allocated object are
5643 all the addresses that point into the object, plus the address one byte
5644 past the end. In cases where the base is a vector of pointers the
5645 ``inbounds`` keyword applies to each of the computations element-wise.
5647 If the ``inbounds`` keyword is not present, the offsets are added to the
5648 base address with silently-wrapping two's complement arithmetic. If the
5649 offsets have a different width from the pointer, they are sign-extended
5650 or truncated to the width of the pointer. The result value of the
5651 ``getelementptr`` may be outside the object pointed to by the base
5652 pointer. The result value may not necessarily be used to access memory
5653 though, even if it happens to point into allocated storage. See the
5654 :ref:`Pointer Aliasing Rules <pointeraliasing>` section for more
5657 The getelementptr instruction is often confusing. For some more insight
5658 into how it works, see :doc:`the getelementptr FAQ <GetElementPtr>`.
5663 .. code-block:: llvm
5665 ; yields [12 x i8]*:aptr
5666 %aptr = getelementptr {i32, [12 x i8]}* %saptr, i64 0, i32 1
5668 %vptr = getelementptr {i32, <2 x i8>}* %svptr, i64 0, i32 1, i32 1
5670 %eptr = getelementptr [12 x i8]* %aptr, i64 0, i32 1
5672 %iptr = getelementptr [10 x i32]* @arr, i16 0, i16 0
5674 In cases where the pointer argument is a vector of pointers, each index
5675 must be a vector with the same number of elements. For example:
5677 .. code-block:: llvm
5679 %A = getelementptr <4 x i8*> %ptrs, <4 x i64> %offsets,
5681 Conversion Operations
5682 ---------------------
5684 The instructions in this category are the conversion instructions
5685 (casting) which all take a single operand and a type. They perform
5686 various bit conversions on the operand.
5688 '``trunc .. to``' Instruction
5689 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5696 <result> = trunc <ty> <value> to <ty2> ; yields ty2
5701 The '``trunc``' instruction truncates its operand to the type ``ty2``.
5706 The '``trunc``' instruction takes a value to trunc, and a type to trunc
5707 it to. Both types must be of :ref:`integer <t_integer>` types, or vectors
5708 of the same number of integers. The bit size of the ``value`` must be
5709 larger than the bit size of the destination type, ``ty2``. Equal sized
5710 types are not allowed.
5715 The '``trunc``' instruction truncates the high order bits in ``value``
5716 and converts the remaining bits to ``ty2``. Since the source size must
5717 be larger than the destination size, ``trunc`` cannot be a *no-op cast*.
5718 It will always truncate bits.
5723 .. code-block:: llvm
5725 %X = trunc i32 257 to i8 ; yields i8:1
5726 %Y = trunc i32 123 to i1 ; yields i1:true
5727 %Z = trunc i32 122 to i1 ; yields i1:false
5728 %W = trunc <2 x i16> <i16 8, i16 7> to <2 x i8> ; yields <i8 8, i8 7>
5730 '``zext .. to``' Instruction
5731 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5738 <result> = zext <ty> <value> to <ty2> ; yields ty2
5743 The '``zext``' instruction zero extends its operand to type ``ty2``.
5748 The '``zext``' instruction takes a value to cast, and a type to cast it
5749 to. Both types must be of :ref:`integer <t_integer>` types, or vectors of
5750 the same number of integers. The bit size of the ``value`` must be
5751 smaller than the bit size of the destination type, ``ty2``.
5756 The ``zext`` fills the high order bits of the ``value`` with zero bits
5757 until it reaches the size of the destination type, ``ty2``.
5759 When zero extending from i1, the result will always be either 0 or 1.
5764 .. code-block:: llvm
5766 %X = zext i32 257 to i64 ; yields i64:257
5767 %Y = zext i1 true to i32 ; yields i32:1
5768 %Z = zext <2 x i16> <i16 8, i16 7> to <2 x i32> ; yields <i32 8, i32 7>
5770 '``sext .. to``' Instruction
5771 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5778 <result> = sext <ty> <value> to <ty2> ; yields ty2
5783 The '``sext``' sign extends ``value`` to the type ``ty2``.
5788 The '``sext``' instruction takes a value to cast, and a type to cast it
5789 to. Both types must be of :ref:`integer <t_integer>` types, or vectors of
5790 the same number of integers. The bit size of the ``value`` must be
5791 smaller than the bit size of the destination type, ``ty2``.
5796 The '``sext``' instruction performs a sign extension by copying the sign
5797 bit (highest order bit) of the ``value`` until it reaches the bit size
5798 of the type ``ty2``.
5800 When sign extending from i1, the extension always results in -1 or 0.
5805 .. code-block:: llvm
5807 %X = sext i8 -1 to i16 ; yields i16 :65535
5808 %Y = sext i1 true to i32 ; yields i32:-1
5809 %Z = sext <2 x i16> <i16 8, i16 7> to <2 x i32> ; yields <i32 8, i32 7>
5811 '``fptrunc .. to``' Instruction
5812 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5819 <result> = fptrunc <ty> <value> to <ty2> ; yields ty2
5824 The '``fptrunc``' instruction truncates ``value`` to type ``ty2``.
5829 The '``fptrunc``' instruction takes a :ref:`floating point <t_floating>`
5830 value to cast and a :ref:`floating point <t_floating>` type to cast it to.
5831 The size of ``value`` must be larger than the size of ``ty2``. This
5832 implies that ``fptrunc`` cannot be used to make a *no-op cast*.
5837 The '``fptrunc``' instruction truncates a ``value`` from a larger
5838 :ref:`floating point <t_floating>` type to a smaller :ref:`floating
5839 point <t_floating>` type. If the value cannot fit within the
5840 destination type, ``ty2``, then the results are undefined.
5845 .. code-block:: llvm
5847 %X = fptrunc double 123.0 to float ; yields float:123.0
5848 %Y = fptrunc double 1.0E+300 to float ; yields undefined
5850 '``fpext .. to``' Instruction
5851 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5858 <result> = fpext <ty> <value> to <ty2> ; yields ty2
5863 The '``fpext``' extends a floating point ``value`` to a larger floating
5869 The '``fpext``' instruction takes a :ref:`floating point <t_floating>`
5870 ``value`` to cast, and a :ref:`floating point <t_floating>` type to cast it
5871 to. The source type must be smaller than the destination type.
5876 The '``fpext``' instruction extends the ``value`` from a smaller
5877 :ref:`floating point <t_floating>` type to a larger :ref:`floating
5878 point <t_floating>` type. The ``fpext`` cannot be used to make a
5879 *no-op cast* because it always changes bits. Use ``bitcast`` to make a
5880 *no-op cast* for a floating point cast.
5885 .. code-block:: llvm
5887 %X = fpext float 3.125 to double ; yields double:3.125000e+00
5888 %Y = fpext double %X to fp128 ; yields fp128:0xL00000000000000004000900000000000
5890 '``fptoui .. to``' Instruction
5891 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5898 <result> = fptoui <ty> <value> to <ty2> ; yields ty2
5903 The '``fptoui``' converts a floating point ``value`` to its unsigned
5904 integer equivalent of type ``ty2``.
5909 The '``fptoui``' instruction takes a value to cast, which must be a
5910 scalar or vector :ref:`floating point <t_floating>` value, and a type to
5911 cast it to ``ty2``, which must be an :ref:`integer <t_integer>` type. If
5912 ``ty`` is a vector floating point type, ``ty2`` must be a vector integer
5913 type with the same number of elements as ``ty``
5918 The '``fptoui``' instruction converts its :ref:`floating
5919 point <t_floating>` operand into the nearest (rounding towards zero)
5920 unsigned integer value. If the value cannot fit in ``ty2``, the results
5926 .. code-block:: llvm
5928 %X = fptoui double 123.0 to i32 ; yields i32:123
5929 %Y = fptoui float 1.0E+300 to i1 ; yields undefined:1
5930 %Z = fptoui float 1.04E+17 to i8 ; yields undefined:1
5932 '``fptosi .. to``' Instruction
5933 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5940 <result> = fptosi <ty> <value> to <ty2> ; yields ty2
5945 The '``fptosi``' instruction converts :ref:`floating point <t_floating>`
5946 ``value`` to type ``ty2``.
5951 The '``fptosi``' instruction takes a value to cast, which must be a
5952 scalar or vector :ref:`floating point <t_floating>` value, and a type to
5953 cast it to ``ty2``, which must be an :ref:`integer <t_integer>` type. If
5954 ``ty`` is a vector floating point type, ``ty2`` must be a vector integer
5955 type with the same number of elements as ``ty``
5960 The '``fptosi``' instruction converts its :ref:`floating
5961 point <t_floating>` operand into the nearest (rounding towards zero)
5962 signed integer value. If the value cannot fit in ``ty2``, the results
5968 .. code-block:: llvm
5970 %X = fptosi double -123.0 to i32 ; yields i32:-123
5971 %Y = fptosi float 1.0E-247 to i1 ; yields undefined:1
5972 %Z = fptosi float 1.04E+17 to i8 ; yields undefined:1
5974 '``uitofp .. to``' Instruction
5975 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5982 <result> = uitofp <ty> <value> to <ty2> ; yields ty2
5987 The '``uitofp``' instruction regards ``value`` as an unsigned integer
5988 and converts that value to the ``ty2`` type.
5993 The '``uitofp``' instruction takes a value to cast, which must be a
5994 scalar or vector :ref:`integer <t_integer>` value, and a type to cast it to
5995 ``ty2``, which must be an :ref:`floating point <t_floating>` type. If
5996 ``ty`` is a vector integer type, ``ty2`` must be a vector floating point
5997 type with the same number of elements as ``ty``
6002 The '``uitofp``' instruction interprets its operand as an unsigned
6003 integer quantity and converts it to the corresponding floating point
6004 value. If the value cannot fit in the floating point value, the results
6010 .. code-block:: llvm
6012 %X = uitofp i32 257 to float ; yields float:257.0
6013 %Y = uitofp i8 -1 to double ; yields double:255.0
6015 '``sitofp .. to``' Instruction
6016 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6023 <result> = sitofp <ty> <value> to <ty2> ; yields ty2
6028 The '``sitofp``' instruction regards ``value`` as a signed integer and
6029 converts that value to the ``ty2`` type.
6034 The '``sitofp``' instruction takes a value to cast, which must be a
6035 scalar or vector :ref:`integer <t_integer>` value, and a type to cast it to
6036 ``ty2``, which must be an :ref:`floating point <t_floating>` type. If
6037 ``ty`` is a vector integer type, ``ty2`` must be a vector floating point
6038 type with the same number of elements as ``ty``
6043 The '``sitofp``' instruction interprets its operand as a signed integer
6044 quantity and converts it to the corresponding floating point value. If
6045 the value cannot fit in the floating point value, the results are
6051 .. code-block:: llvm
6053 %X = sitofp i32 257 to float ; yields float:257.0
6054 %Y = sitofp i8 -1 to double ; yields double:-1.0
6058 '``ptrtoint .. to``' Instruction
6059 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6066 <result> = ptrtoint <ty> <value> to <ty2> ; yields ty2
6071 The '``ptrtoint``' instruction converts the pointer or a vector of
6072 pointers ``value`` to the integer (or vector of integers) type ``ty2``.
6077 The '``ptrtoint``' instruction takes a ``value`` to cast, which must be
6078 a a value of type :ref:`pointer <t_pointer>` or a vector of pointers, and a
6079 type to cast it to ``ty2``, which must be an :ref:`integer <t_integer>` or
6080 a vector of integers type.
6085 The '``ptrtoint``' instruction converts ``value`` to integer type
6086 ``ty2`` by interpreting the pointer value as an integer and either
6087 truncating or zero extending that value to the size of the integer type.
6088 If ``value`` is smaller than ``ty2`` then a zero extension is done. If
6089 ``value`` is larger than ``ty2`` then a truncation is done. If they are
6090 the same size, then nothing is done (*no-op cast*) other than a type
6096 .. code-block:: llvm
6098 %X = ptrtoint i32* %P to i8 ; yields truncation on 32-bit architecture
6099 %Y = ptrtoint i32* %P to i64 ; yields zero extension on 32-bit architecture
6100 %Z = ptrtoint <4 x i32*> %P to <4 x i64>; yields vector zero extension for a vector of addresses on 32-bit architecture
6104 '``inttoptr .. to``' Instruction
6105 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6112 <result> = inttoptr <ty> <value> to <ty2> ; yields ty2
6117 The '``inttoptr``' instruction converts an integer ``value`` to a
6118 pointer type, ``ty2``.
6123 The '``inttoptr``' instruction takes an :ref:`integer <t_integer>` value to
6124 cast, and a type to cast it to, which must be a :ref:`pointer <t_pointer>`
6130 The '``inttoptr``' instruction converts ``value`` to type ``ty2`` by
6131 applying either a zero extension or a truncation depending on the size
6132 of the integer ``value``. If ``value`` is larger than the size of a
6133 pointer then a truncation is done. If ``value`` is smaller than the size
6134 of a pointer then a zero extension is done. If they are the same size,
6135 nothing is done (*no-op cast*).
6140 .. code-block:: llvm
6142 %X = inttoptr i32 255 to i32* ; yields zero extension on 64-bit architecture
6143 %Y = inttoptr i32 255 to i32* ; yields no-op on 32-bit architecture
6144 %Z = inttoptr i64 0 to i32* ; yields truncation on 32-bit architecture
6145 %Z = inttoptr <4 x i32> %G to <4 x i8*>; yields truncation of vector G to four pointers
6149 '``bitcast .. to``' Instruction
6150 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6157 <result> = bitcast <ty> <value> to <ty2> ; yields ty2
6162 The '``bitcast``' instruction converts ``value`` to type ``ty2`` without
6168 The '``bitcast``' instruction takes a value to cast, which must be a
6169 non-aggregate first class value, and a type to cast it to, which must
6170 also be a non-aggregate :ref:`first class <t_firstclass>` type. The
6171 bit sizes of ``value`` and the destination type, ``ty2``, must be
6172 identical. If the source type is a pointer, the destination type must
6173 also be a pointer of the same size. This instruction supports bitwise
6174 conversion of vectors to integers and to vectors of other types (as
6175 long as they have the same size).
6180 The '``bitcast``' instruction converts ``value`` to type ``ty2``. It
6181 is always a *no-op cast* because no bits change with this
6182 conversion. The conversion is done as if the ``value`` had been stored
6183 to memory and read back as type ``ty2``. Pointer (or vector of
6184 pointers) types may only be converted to other pointer (or vector of
6185 pointers) types with the same address space through this instruction.
6186 To convert pointers to other types, use the :ref:`inttoptr <i_inttoptr>`
6187 or :ref:`ptrtoint <i_ptrtoint>` instructions first.
6192 .. code-block:: llvm
6194 %X = bitcast i8 255 to i8 ; yields i8 :-1
6195 %Y = bitcast i32* %x to sint* ; yields sint*:%x
6196 %Z = bitcast <2 x int> %V to i64; ; yields i64: %V
6197 %Z = bitcast <2 x i32*> %V to <2 x i64*> ; yields <2 x i64*>
6199 .. _i_addrspacecast:
6201 '``addrspacecast .. to``' Instruction
6202 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6209 <result> = addrspacecast <pty> <ptrval> to <pty2> ; yields pty2
6214 The '``addrspacecast``' instruction converts ``ptrval`` from ``pty`` in
6215 address space ``n`` to type ``pty2`` in address space ``m``.
6220 The '``addrspacecast``' instruction takes a pointer or vector of pointer value
6221 to cast and a pointer type to cast it to, which must have a different
6227 The '``addrspacecast``' instruction converts the pointer value
6228 ``ptrval`` to type ``pty2``. It can be a *no-op cast* or a complex
6229 value modification, depending on the target and the address space
6230 pair. Pointer conversions within the same address space must be
6231 performed with the ``bitcast`` instruction. Note that if the address space
6232 conversion is legal then both result and operand refer to the same memory
6238 .. code-block:: llvm
6240 %X = addrspacecast i32* %x to i32 addrspace(1)* ; yields i32 addrspace(1)*:%x
6241 %Y = addrspacecast i32 addrspace(1)* %y to i64 addrspace(2)* ; yields i64 addrspace(2)*:%y
6242 %Z = addrspacecast <4 x i32*> %z to <4 x float addrspace(3)*> ; yields <4 x float addrspace(3)*>:%z
6249 The instructions in this category are the "miscellaneous" instructions,
6250 which defy better classification.
6254 '``icmp``' Instruction
6255 ^^^^^^^^^^^^^^^^^^^^^^
6262 <result> = icmp <cond> <ty> <op1>, <op2> ; yields i1 or <N x i1>:result
6267 The '``icmp``' instruction returns a boolean value or a vector of
6268 boolean values based on comparison of its two integer, integer vector,
6269 pointer, or pointer vector operands.
6274 The '``icmp``' instruction takes three operands. The first operand is
6275 the condition code indicating the kind of comparison to perform. It is
6276 not a value, just a keyword. The possible condition code are:
6279 #. ``ne``: not equal
6280 #. ``ugt``: unsigned greater than
6281 #. ``uge``: unsigned greater or equal
6282 #. ``ult``: unsigned less than
6283 #. ``ule``: unsigned less or equal
6284 #. ``sgt``: signed greater than
6285 #. ``sge``: signed greater or equal
6286 #. ``slt``: signed less than
6287 #. ``sle``: signed less or equal
6289 The remaining two arguments must be :ref:`integer <t_integer>` or
6290 :ref:`pointer <t_pointer>` or integer :ref:`vector <t_vector>` typed. They
6291 must also be identical types.
6296 The '``icmp``' compares ``op1`` and ``op2`` according to the condition
6297 code given as ``cond``. The comparison performed always yields either an
6298 :ref:`i1 <t_integer>` or vector of ``i1`` result, as follows:
6300 #. ``eq``: yields ``true`` if the operands are equal, ``false``
6301 otherwise. No sign interpretation is necessary or performed.
6302 #. ``ne``: yields ``true`` if the operands are unequal, ``false``
6303 otherwise. No sign interpretation is necessary or performed.
6304 #. ``ugt``: interprets the operands as unsigned values and yields
6305 ``true`` if ``op1`` is greater than ``op2``.
6306 #. ``uge``: interprets the operands as unsigned values and yields
6307 ``true`` if ``op1`` is greater than or equal to ``op2``.
6308 #. ``ult``: interprets the operands as unsigned values and yields
6309 ``true`` if ``op1`` is less than ``op2``.
6310 #. ``ule``: interprets the operands as unsigned values and yields
6311 ``true`` if ``op1`` is less than or equal to ``op2``.
6312 #. ``sgt``: interprets the operands as signed values and yields ``true``
6313 if ``op1`` is greater than ``op2``.
6314 #. ``sge``: interprets the operands as signed values and yields ``true``
6315 if ``op1`` is greater than or equal to ``op2``.
6316 #. ``slt``: interprets the operands as signed values and yields ``true``
6317 if ``op1`` is less than ``op2``.
6318 #. ``sle``: interprets the operands as signed values and yields ``true``
6319 if ``op1`` is less than or equal to ``op2``.
6321 If the operands are :ref:`pointer <t_pointer>` typed, the pointer values
6322 are compared as if they were integers.
6324 If the operands are integer vectors, then they are compared element by
6325 element. The result is an ``i1`` vector with the same number of elements
6326 as the values being compared. Otherwise, the result is an ``i1``.
6331 .. code-block:: llvm
6333 <result> = icmp eq i32 4, 5 ; yields: result=false
6334 <result> = icmp ne float* %X, %X ; yields: result=false
6335 <result> = icmp ult i16 4, 5 ; yields: result=true
6336 <result> = icmp sgt i16 4, 5 ; yields: result=false
6337 <result> = icmp ule i16 -4, 5 ; yields: result=false
6338 <result> = icmp sge i16 4, 5 ; yields: result=false
6340 Note that the code generator does not yet support vector types with the
6341 ``icmp`` instruction.
6345 '``fcmp``' Instruction
6346 ^^^^^^^^^^^^^^^^^^^^^^
6353 <result> = fcmp <cond> <ty> <op1>, <op2> ; yields i1 or <N x i1>:result
6358 The '``fcmp``' instruction returns a boolean value or vector of boolean
6359 values based on comparison of its operands.
6361 If the operands are floating point scalars, then the result type is a
6362 boolean (:ref:`i1 <t_integer>`).
6364 If the operands are floating point vectors, then the result type is a
6365 vector of boolean with the same number of elements as the operands being
6371 The '``fcmp``' instruction takes three operands. The first operand is
6372 the condition code indicating the kind of comparison to perform. It is
6373 not a value, just a keyword. The possible condition code are:
6375 #. ``false``: no comparison, always returns false
6376 #. ``oeq``: ordered and equal
6377 #. ``ogt``: ordered and greater than
6378 #. ``oge``: ordered and greater than or equal
6379 #. ``olt``: ordered and less than
6380 #. ``ole``: ordered and less than or equal
6381 #. ``one``: ordered and not equal
6382 #. ``ord``: ordered (no nans)
6383 #. ``ueq``: unordered or equal
6384 #. ``ugt``: unordered or greater than
6385 #. ``uge``: unordered or greater than or equal
6386 #. ``ult``: unordered or less than
6387 #. ``ule``: unordered or less than or equal
6388 #. ``une``: unordered or not equal
6389 #. ``uno``: unordered (either nans)
6390 #. ``true``: no comparison, always returns true
6392 *Ordered* means that neither operand is a QNAN while *unordered* means
6393 that either operand may be a QNAN.
6395 Each of ``val1`` and ``val2`` arguments must be either a :ref:`floating
6396 point <t_floating>` type or a :ref:`vector <t_vector>` of floating point
6397 type. They must have identical types.
6402 The '``fcmp``' instruction compares ``op1`` and ``op2`` according to the
6403 condition code given as ``cond``. If the operands are vectors, then the
6404 vectors are compared element by element. Each comparison performed
6405 always yields an :ref:`i1 <t_integer>` result, as follows:
6407 #. ``false``: always yields ``false``, regardless of operands.
6408 #. ``oeq``: yields ``true`` if both operands are not a QNAN and ``op1``
6409 is equal to ``op2``.
6410 #. ``ogt``: yields ``true`` if both operands are not a QNAN and ``op1``
6411 is greater than ``op2``.
6412 #. ``oge``: yields ``true`` if both operands are not a QNAN and ``op1``
6413 is greater than or equal to ``op2``.
6414 #. ``olt``: yields ``true`` if both operands are not a QNAN and ``op1``
6415 is less than ``op2``.
6416 #. ``ole``: yields ``true`` if both operands are not a QNAN and ``op1``
6417 is less than or equal to ``op2``.
6418 #. ``one``: yields ``true`` if both operands are not a QNAN and ``op1``
6419 is not equal to ``op2``.
6420 #. ``ord``: yields ``true`` if both operands are not a QNAN.
6421 #. ``ueq``: yields ``true`` if either operand is a QNAN or ``op1`` is
6423 #. ``ugt``: yields ``true`` if either operand is a QNAN or ``op1`` is
6424 greater than ``op2``.
6425 #. ``uge``: yields ``true`` if either operand is a QNAN or ``op1`` is
6426 greater than or equal to ``op2``.
6427 #. ``ult``: yields ``true`` if either operand is a QNAN or ``op1`` is
6429 #. ``ule``: yields ``true`` if either operand is a QNAN or ``op1`` is
6430 less than or equal to ``op2``.
6431 #. ``une``: yields ``true`` if either operand is a QNAN or ``op1`` is
6432 not equal to ``op2``.
6433 #. ``uno``: yields ``true`` if either operand is a QNAN.
6434 #. ``true``: always yields ``true``, regardless of operands.
6439 .. code-block:: llvm
6441 <result> = fcmp oeq float 4.0, 5.0 ; yields: result=false
6442 <result> = fcmp one float 4.0, 5.0 ; yields: result=true
6443 <result> = fcmp olt float 4.0, 5.0 ; yields: result=true
6444 <result> = fcmp ueq double 1.0, 2.0 ; yields: result=false
6446 Note that the code generator does not yet support vector types with the
6447 ``fcmp`` instruction.
6451 '``phi``' Instruction
6452 ^^^^^^^^^^^^^^^^^^^^^
6459 <result> = phi <ty> [ <val0>, <label0>], ...
6464 The '``phi``' instruction is used to implement the φ node in the SSA
6465 graph representing the function.
6470 The type of the incoming values is specified with the first type field.
6471 After this, the '``phi``' instruction takes a list of pairs as
6472 arguments, with one pair for each predecessor basic block of the current
6473 block. Only values of :ref:`first class <t_firstclass>` type may be used as
6474 the value arguments to the PHI node. Only labels may be used as the
6477 There must be no non-phi instructions between the start of a basic block
6478 and the PHI instructions: i.e. PHI instructions must be first in a basic
6481 For the purposes of the SSA form, the use of each incoming value is
6482 deemed to occur on the edge from the corresponding predecessor block to
6483 the current block (but after any definition of an '``invoke``'
6484 instruction's return value on the same edge).
6489 At runtime, the '``phi``' instruction logically takes on the value
6490 specified by the pair corresponding to the predecessor basic block that
6491 executed just prior to the current block.
6496 .. code-block:: llvm
6498 Loop: ; Infinite loop that counts from 0 on up...
6499 %indvar = phi i32 [ 0, %LoopHeader ], [ %nextindvar, %Loop ]
6500 %nextindvar = add i32 %indvar, 1
6505 '``select``' Instruction
6506 ^^^^^^^^^^^^^^^^^^^^^^^^
6513 <result> = select selty <cond>, <ty> <val1>, <ty> <val2> ; yields ty
6515 selty is either i1 or {<N x i1>}
6520 The '``select``' instruction is used to choose one value based on a
6521 condition, without IR-level branching.
6526 The '``select``' instruction requires an 'i1' value or a vector of 'i1'
6527 values indicating the condition, and two values of the same :ref:`first
6528 class <t_firstclass>` type. If the val1/val2 are vectors and the
6529 condition is a scalar, then entire vectors are selected, not individual
6535 If the condition is an i1 and it evaluates to 1, the instruction returns
6536 the first value argument; otherwise, it returns the second value
6539 If the condition is a vector of i1, then the value arguments must be
6540 vectors of the same size, and the selection is done element by element.
6545 .. code-block:: llvm
6547 %X = select i1 true, i8 17, i8 42 ; yields i8:17
6551 '``call``' Instruction
6552 ^^^^^^^^^^^^^^^^^^^^^^
6559 <result> = [tail | musttail] call [cconv] [ret attrs] <ty> [<fnty>*] <fnptrval>(<function args>) [fn attrs]
6564 The '``call``' instruction represents a simple function call.
6569 This instruction requires several arguments:
6571 #. The optional ``tail`` and ``musttail`` markers indicate that the optimizers
6572 should perform tail call optimization. The ``tail`` marker is a hint that
6573 `can be ignored <CodeGenerator.html#sibcallopt>`_. The ``musttail`` marker
6574 means that the call must be tail call optimized in order for the program to
6575 be correct. The ``musttail`` marker provides these guarantees:
6577 #. The call will not cause unbounded stack growth if it is part of a
6578 recursive cycle in the call graph.
6579 #. Arguments with the :ref:`inalloca <attr_inalloca>` attribute are
6582 Both markers imply that the callee does not access allocas or varargs from
6583 the caller. Calls marked ``musttail`` must obey the following additional
6586 - The call must immediately precede a :ref:`ret <i_ret>` instruction,
6587 or a pointer bitcast followed by a ret instruction.
6588 - The ret instruction must return the (possibly bitcasted) value
6589 produced by the call or void.
6590 - The caller and callee prototypes must match. Pointer types of
6591 parameters or return types may differ in pointee type, but not
6593 - The calling conventions of the caller and callee must match.
6594 - All ABI-impacting function attributes, such as sret, byval, inreg,
6595 returned, and inalloca, must match.
6596 - The callee must be varargs iff the caller is varargs. Bitcasting a
6597 non-varargs function to the appropriate varargs type is legal so
6598 long as the non-varargs prefixes obey the other rules.
6600 Tail call optimization for calls marked ``tail`` is guaranteed to occur if
6601 the following conditions are met:
6603 - Caller and callee both have the calling convention ``fastcc``.
6604 - The call is in tail position (ret immediately follows call and ret
6605 uses value of call or is void).
6606 - Option ``-tailcallopt`` is enabled, or
6607 ``llvm::GuaranteedTailCallOpt`` is ``true``.
6608 - `Platform-specific constraints are
6609 met. <CodeGenerator.html#tailcallopt>`_
6611 #. The optional "cconv" marker indicates which :ref:`calling
6612 convention <callingconv>` the call should use. If none is
6613 specified, the call defaults to using C calling conventions. The
6614 calling convention of the call must match the calling convention of
6615 the target function, or else the behavior is undefined.
6616 #. The optional :ref:`Parameter Attributes <paramattrs>` list for return
6617 values. Only '``zeroext``', '``signext``', and '``inreg``' attributes
6619 #. '``ty``': the type of the call instruction itself which is also the
6620 type of the return value. Functions that return no value are marked
6622 #. '``fnty``': shall be the signature of the pointer to function value
6623 being invoked. The argument types must match the types implied by
6624 this signature. This type can be omitted if the function is not
6625 varargs and if the function type does not return a pointer to a
6627 #. '``fnptrval``': An LLVM value containing a pointer to a function to
6628 be invoked. In most cases, this is a direct function invocation, but
6629 indirect ``call``'s are just as possible, calling an arbitrary pointer
6631 #. '``function args``': argument list whose types match the function
6632 signature argument types and parameter attributes. All arguments must
6633 be of :ref:`first class <t_firstclass>` type. If the function signature
6634 indicates the function accepts a variable number of arguments, the
6635 extra arguments can be specified.
6636 #. The optional :ref:`function attributes <fnattrs>` list. Only
6637 '``noreturn``', '``nounwind``', '``readonly``' and '``readnone``'
6638 attributes are valid here.
6643 The '``call``' instruction is used to cause control flow to transfer to
6644 a specified function, with its incoming arguments bound to the specified
6645 values. Upon a '``ret``' instruction in the called function, control
6646 flow continues with the instruction after the function call, and the
6647 return value of the function is bound to the result argument.
6652 .. code-block:: llvm
6654 %retval = call i32 @test(i32 %argc)
6655 call i32 (i8*, ...)* @printf(i8* %msg, i32 12, i8 42) ; yields i32
6656 %X = tail call i32 @foo() ; yields i32
6657 %Y = tail call fastcc i32 @foo() ; yields i32
6658 call void %foo(i8 97 signext)
6660 %struct.A = type { i32, i8 }
6661 %r = call %struct.A @foo() ; yields { i32, i8 }
6662 %gr = extractvalue %struct.A %r, 0 ; yields i32
6663 %gr1 = extractvalue %struct.A %r, 1 ; yields i8
6664 %Z = call void @foo() noreturn ; indicates that %foo never returns normally
6665 %ZZ = call zeroext i32 @bar() ; Return value is %zero extended
6667 llvm treats calls to some functions with names and arguments that match
6668 the standard C99 library as being the C99 library functions, and may
6669 perform optimizations or generate code for them under that assumption.
6670 This is something we'd like to change in the future to provide better
6671 support for freestanding environments and non-C-based languages.
6675 '``va_arg``' Instruction
6676 ^^^^^^^^^^^^^^^^^^^^^^^^
6683 <resultval> = va_arg <va_list*> <arglist>, <argty>
6688 The '``va_arg``' instruction is used to access arguments passed through
6689 the "variable argument" area of a function call. It is used to implement
6690 the ``va_arg`` macro in C.
6695 This instruction takes a ``va_list*`` value and the type of the
6696 argument. It returns a value of the specified argument type and
6697 increments the ``va_list`` to point to the next argument. The actual
6698 type of ``va_list`` is target specific.
6703 The '``va_arg``' instruction loads an argument of the specified type
6704 from the specified ``va_list`` and causes the ``va_list`` to point to
6705 the next argument. For more information, see the variable argument
6706 handling :ref:`Intrinsic Functions <int_varargs>`.
6708 It is legal for this instruction to be called in a function which does
6709 not take a variable number of arguments, for example, the ``vfprintf``
6712 ``va_arg`` is an LLVM instruction instead of an :ref:`intrinsic
6713 function <intrinsics>` because it takes a type as an argument.
6718 See the :ref:`variable argument processing <int_varargs>` section.
6720 Note that the code generator does not yet fully support va\_arg on many
6721 targets. Also, it does not currently support va\_arg with aggregate
6722 types on any target.
6726 '``landingpad``' Instruction
6727 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6734 <resultval> = landingpad <resultty> personality <type> <pers_fn> <clause>+
6735 <resultval> = landingpad <resultty> personality <type> <pers_fn> cleanup <clause>*
6737 <clause> := catch <type> <value>
6738 <clause> := filter <array constant type> <array constant>
6743 The '``landingpad``' instruction is used by `LLVM's exception handling
6744 system <ExceptionHandling.html#overview>`_ to specify that a basic block
6745 is a landing pad --- one where the exception lands, and corresponds to the
6746 code found in the ``catch`` portion of a ``try``/``catch`` sequence. It
6747 defines values supplied by the personality function (``pers_fn``) upon
6748 re-entry to the function. The ``resultval`` has the type ``resultty``.
6753 This instruction takes a ``pers_fn`` value. This is the personality
6754 function associated with the unwinding mechanism. The optional
6755 ``cleanup`` flag indicates that the landing pad block is a cleanup.
6757 A ``clause`` begins with the clause type --- ``catch`` or ``filter`` --- and
6758 contains the global variable representing the "type" that may be caught
6759 or filtered respectively. Unlike the ``catch`` clause, the ``filter``
6760 clause takes an array constant as its argument. Use
6761 "``[0 x i8**] undef``" for a filter which cannot throw. The
6762 '``landingpad``' instruction must contain *at least* one ``clause`` or
6763 the ``cleanup`` flag.
6768 The '``landingpad``' instruction defines the values which are set by the
6769 personality function (``pers_fn``) upon re-entry to the function, and
6770 therefore the "result type" of the ``landingpad`` instruction. As with
6771 calling conventions, how the personality function results are
6772 represented in LLVM IR is target specific.
6774 The clauses are applied in order from top to bottom. If two
6775 ``landingpad`` instructions are merged together through inlining, the
6776 clauses from the calling function are appended to the list of clauses.
6777 When the call stack is being unwound due to an exception being thrown,
6778 the exception is compared against each ``clause`` in turn. If it doesn't
6779 match any of the clauses, and the ``cleanup`` flag is not set, then
6780 unwinding continues further up the call stack.
6782 The ``landingpad`` instruction has several restrictions:
6784 - A landing pad block is a basic block which is the unwind destination
6785 of an '``invoke``' instruction.
6786 - A landing pad block must have a '``landingpad``' instruction as its
6787 first non-PHI instruction.
6788 - There can be only one '``landingpad``' instruction within the landing
6790 - A basic block that is not a landing pad block may not include a
6791 '``landingpad``' instruction.
6792 - All '``landingpad``' instructions in a function must have the same
6793 personality function.
6798 .. code-block:: llvm
6800 ;; A landing pad which can catch an integer.
6801 %res = landingpad { i8*, i32 } personality i32 (...)* @__gxx_personality_v0
6803 ;; A landing pad that is a cleanup.
6804 %res = landingpad { i8*, i32 } personality i32 (...)* @__gxx_personality_v0
6806 ;; A landing pad which can catch an integer and can only throw a double.
6807 %res = landingpad { i8*, i32 } personality i32 (...)* @__gxx_personality_v0
6809 filter [1 x i8**] [@_ZTId]
6816 LLVM supports the notion of an "intrinsic function". These functions
6817 have well known names and semantics and are required to follow certain
6818 restrictions. Overall, these intrinsics represent an extension mechanism
6819 for the LLVM language that does not require changing all of the
6820 transformations in LLVM when adding to the language (or the bitcode
6821 reader/writer, the parser, etc...).
6823 Intrinsic function names must all start with an "``llvm.``" prefix. This
6824 prefix is reserved in LLVM for intrinsic names; thus, function names may
6825 not begin with this prefix. Intrinsic functions must always be external
6826 functions: you cannot define the body of intrinsic functions. Intrinsic
6827 functions may only be used in call or invoke instructions: it is illegal
6828 to take the address of an intrinsic function. Additionally, because
6829 intrinsic functions are part of the LLVM language, it is required if any
6830 are added that they be documented here.
6832 Some intrinsic functions can be overloaded, i.e., the intrinsic
6833 represents a family of functions that perform the same operation but on
6834 different data types. Because LLVM can represent over 8 million
6835 different integer types, overloading is used commonly to allow an
6836 intrinsic function to operate on any integer type. One or more of the
6837 argument types or the result type can be overloaded to accept any
6838 integer type. Argument types may also be defined as exactly matching a
6839 previous argument's type or the result type. This allows an intrinsic
6840 function which accepts multiple arguments, but needs all of them to be
6841 of the same type, to only be overloaded with respect to a single
6842 argument or the result.
6844 Overloaded intrinsics will have the names of its overloaded argument
6845 types encoded into its function name, each preceded by a period. Only
6846 those types which are overloaded result in a name suffix. Arguments
6847 whose type is matched against another type do not. For example, the
6848 ``llvm.ctpop`` function can take an integer of any width and returns an
6849 integer of exactly the same integer width. This leads to a family of
6850 functions such as ``i8 @llvm.ctpop.i8(i8 %val)`` and
6851 ``i29 @llvm.ctpop.i29(i29 %val)``. Only one type, the return type, is
6852 overloaded, and only one type suffix is required. Because the argument's
6853 type is matched against the return type, it does not require its own
6856 To learn how to add an intrinsic function, please see the `Extending
6857 LLVM Guide <ExtendingLLVM.html>`_.
6861 Variable Argument Handling Intrinsics
6862 -------------------------------------
6864 Variable argument support is defined in LLVM with the
6865 :ref:`va_arg <i_va_arg>` instruction and these three intrinsic
6866 functions. These functions are related to the similarly named macros
6867 defined in the ``<stdarg.h>`` header file.
6869 All of these functions operate on arguments that use a target-specific
6870 value type "``va_list``". The LLVM assembly language reference manual
6871 does not define what this type is, so all transformations should be
6872 prepared to handle these functions regardless of the type used.
6874 This example shows how the :ref:`va_arg <i_va_arg>` instruction and the
6875 variable argument handling intrinsic functions are used.
6877 .. code-block:: llvm
6879 define i32 @test(i32 %X, ...) {
6880 ; Initialize variable argument processing
6882 %ap2 = bitcast i8** %ap to i8*
6883 call void @llvm.va_start(i8* %ap2)
6885 ; Read a single integer argument
6886 %tmp = va_arg i8** %ap, i32
6888 ; Demonstrate usage of llvm.va_copy and llvm.va_end
6890 %aq2 = bitcast i8** %aq to i8*
6891 call void @llvm.va_copy(i8* %aq2, i8* %ap2)
6892 call void @llvm.va_end(i8* %aq2)
6894 ; Stop processing of arguments.
6895 call void @llvm.va_end(i8* %ap2)
6899 declare void @llvm.va_start(i8*)
6900 declare void @llvm.va_copy(i8*, i8*)
6901 declare void @llvm.va_end(i8*)
6905 '``llvm.va_start``' Intrinsic
6906 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6913 declare void @llvm.va_start(i8* <arglist>)
6918 The '``llvm.va_start``' intrinsic initializes ``*<arglist>`` for
6919 subsequent use by ``va_arg``.
6924 The argument is a pointer to a ``va_list`` element to initialize.
6929 The '``llvm.va_start``' intrinsic works just like the ``va_start`` macro
6930 available in C. In a target-dependent way, it initializes the
6931 ``va_list`` element to which the argument points, so that the next call
6932 to ``va_arg`` will produce the first variable argument passed to the
6933 function. Unlike the C ``va_start`` macro, this intrinsic does not need
6934 to know the last argument of the function as the compiler can figure
6937 '``llvm.va_end``' Intrinsic
6938 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
6945 declare void @llvm.va_end(i8* <arglist>)
6950 The '``llvm.va_end``' intrinsic destroys ``*<arglist>``, which has been
6951 initialized previously with ``llvm.va_start`` or ``llvm.va_copy``.
6956 The argument is a pointer to a ``va_list`` to destroy.
6961 The '``llvm.va_end``' intrinsic works just like the ``va_end`` macro
6962 available in C. In a target-dependent way, it destroys the ``va_list``
6963 element to which the argument points. Calls to
6964 :ref:`llvm.va_start <int_va_start>` and
6965 :ref:`llvm.va_copy <int_va_copy>` must be matched exactly with calls to
6970 '``llvm.va_copy``' Intrinsic
6971 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6978 declare void @llvm.va_copy(i8* <destarglist>, i8* <srcarglist>)
6983 The '``llvm.va_copy``' intrinsic copies the current argument position
6984 from the source argument list to the destination argument list.
6989 The first argument is a pointer to a ``va_list`` element to initialize.
6990 The second argument is a pointer to a ``va_list`` element to copy from.
6995 The '``llvm.va_copy``' intrinsic works just like the ``va_copy`` macro
6996 available in C. In a target-dependent way, it copies the source
6997 ``va_list`` element into the destination ``va_list`` element. This
6998 intrinsic is necessary because the `` llvm.va_start`` intrinsic may be
6999 arbitrarily complex and require, for example, memory allocation.
7001 Accurate Garbage Collection Intrinsics
7002 --------------------------------------
7004 LLVM support for `Accurate Garbage Collection <GarbageCollection.html>`_
7005 (GC) requires the implementation and generation of these intrinsics.
7006 These intrinsics allow identification of :ref:`GC roots on the
7007 stack <int_gcroot>`, as well as garbage collector implementations that
7008 require :ref:`read <int_gcread>` and :ref:`write <int_gcwrite>` barriers.
7009 Front-ends for type-safe garbage collected languages should generate
7010 these intrinsics to make use of the LLVM garbage collectors. For more
7011 details, see `Accurate Garbage Collection with
7012 LLVM <GarbageCollection.html>`_.
7014 The garbage collection intrinsics only operate on objects in the generic
7015 address space (address space zero).
7019 '``llvm.gcroot``' Intrinsic
7020 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
7027 declare void @llvm.gcroot(i8** %ptrloc, i8* %metadata)
7032 The '``llvm.gcroot``' intrinsic declares the existence of a GC root to
7033 the code generator, and allows some metadata to be associated with it.
7038 The first argument specifies the address of a stack object that contains
7039 the root pointer. The second pointer (which must be either a constant or
7040 a global value address) contains the meta-data to be associated with the
7046 At runtime, a call to this intrinsic stores a null pointer into the
7047 "ptrloc" location. At compile-time, the code generator generates
7048 information to allow the runtime to find the pointer at GC safe points.
7049 The '``llvm.gcroot``' intrinsic may only be used in a function which
7050 :ref:`specifies a GC algorithm <gc>`.
7054 '``llvm.gcread``' Intrinsic
7055 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
7062 declare i8* @llvm.gcread(i8* %ObjPtr, i8** %Ptr)
7067 The '``llvm.gcread``' intrinsic identifies reads of references from heap
7068 locations, allowing garbage collector implementations that require read
7074 The second argument is the address to read from, which should be an
7075 address allocated from the garbage collector. The first object is a
7076 pointer to the start of the referenced object, if needed by the language
7077 runtime (otherwise null).
7082 The '``llvm.gcread``' intrinsic has the same semantics as a load
7083 instruction, but may be replaced with substantially more complex code by
7084 the garbage collector runtime, as needed. The '``llvm.gcread``'
7085 intrinsic may only be used in a function which :ref:`specifies a GC
7090 '``llvm.gcwrite``' Intrinsic
7091 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7098 declare void @llvm.gcwrite(i8* %P1, i8* %Obj, i8** %P2)
7103 The '``llvm.gcwrite``' intrinsic identifies writes of references to heap
7104 locations, allowing garbage collector implementations that require write
7105 barriers (such as generational or reference counting collectors).
7110 The first argument is the reference to store, the second is the start of
7111 the object to store it to, and the third is the address of the field of
7112 Obj to store to. If the runtime does not require a pointer to the
7113 object, Obj may be null.
7118 The '``llvm.gcwrite``' intrinsic has the same semantics as a store
7119 instruction, but may be replaced with substantially more complex code by
7120 the garbage collector runtime, as needed. The '``llvm.gcwrite``'
7121 intrinsic may only be used in a function which :ref:`specifies a GC
7124 Code Generator Intrinsics
7125 -------------------------
7127 These intrinsics are provided by LLVM to expose special features that
7128 may only be implemented with code generator support.
7130 '``llvm.returnaddress``' Intrinsic
7131 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7138 declare i8 *@llvm.returnaddress(i32 <level>)
7143 The '``llvm.returnaddress``' intrinsic attempts to compute a
7144 target-specific value indicating the return address of the current
7145 function or one of its callers.
7150 The argument to this intrinsic indicates which function to return the
7151 address for. Zero indicates the calling function, one indicates its
7152 caller, etc. The argument is **required** to be a constant integer
7158 The '``llvm.returnaddress``' intrinsic either returns a pointer
7159 indicating the return address of the specified call frame, or zero if it
7160 cannot be identified. The value returned by this intrinsic is likely to
7161 be incorrect or 0 for arguments other than zero, so it should only be
7162 used for debugging purposes.
7164 Note that calling this intrinsic does not prevent function inlining or
7165 other aggressive transformations, so the value returned may not be that
7166 of the obvious source-language caller.
7168 '``llvm.frameaddress``' Intrinsic
7169 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7176 declare i8* @llvm.frameaddress(i32 <level>)
7181 The '``llvm.frameaddress``' intrinsic attempts to return the
7182 target-specific frame pointer value for the specified stack frame.
7187 The argument to this intrinsic indicates which function to return the
7188 frame pointer for. Zero indicates the calling function, one indicates
7189 its caller, etc. The argument is **required** to be a constant integer
7195 The '``llvm.frameaddress``' intrinsic either returns a pointer
7196 indicating the frame address of the specified call frame, or zero if it
7197 cannot be identified. The value returned by this intrinsic is likely to
7198 be incorrect or 0 for arguments other than zero, so it should only be
7199 used for debugging purposes.
7201 Note that calling this intrinsic does not prevent function inlining or
7202 other aggressive transformations, so the value returned may not be that
7203 of the obvious source-language caller.
7205 .. _int_read_register:
7206 .. _int_write_register:
7208 '``llvm.read_register``' and '``llvm.write_register``' Intrinsics
7209 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7216 declare i32 @llvm.read_register.i32(metadata)
7217 declare i64 @llvm.read_register.i64(metadata)
7218 declare void @llvm.write_register.i32(metadata, i32 @value)
7219 declare void @llvm.write_register.i64(metadata, i64 @value)
7220 !0 = metadata !{metadata !"sp\00"}
7225 The '``llvm.read_register``' and '``llvm.write_register``' intrinsics
7226 provides access to the named register. The register must be valid on
7227 the architecture being compiled to. The type needs to be compatible
7228 with the register being read.
7233 The '``llvm.read_register``' intrinsic returns the current value of the
7234 register, where possible. The '``llvm.write_register``' intrinsic sets
7235 the current value of the register, where possible.
7237 This is useful to implement named register global variables that need
7238 to always be mapped to a specific register, as is common practice on
7239 bare-metal programs including OS kernels.
7241 The compiler doesn't check for register availability or use of the used
7242 register in surrounding code, including inline assembly. Because of that,
7243 allocatable registers are not supported.
7245 Warning: So far it only works with the stack pointer on selected
7246 architectures (ARM, AArch64, PowerPC and x86_64). Significant amount of
7247 work is needed to support other registers and even more so, allocatable
7252 '``llvm.stacksave``' Intrinsic
7253 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7260 declare i8* @llvm.stacksave()
7265 The '``llvm.stacksave``' intrinsic is used to remember the current state
7266 of the function stack, for use with
7267 :ref:`llvm.stackrestore <int_stackrestore>`. This is useful for
7268 implementing language features like scoped automatic variable sized
7274 This intrinsic returns a opaque pointer value that can be passed to
7275 :ref:`llvm.stackrestore <int_stackrestore>`. When an
7276 ``llvm.stackrestore`` intrinsic is executed with a value saved from
7277 ``llvm.stacksave``, it effectively restores the state of the stack to
7278 the state it was in when the ``llvm.stacksave`` intrinsic executed. In
7279 practice, this pops any :ref:`alloca <i_alloca>` blocks from the stack that
7280 were allocated after the ``llvm.stacksave`` was executed.
7282 .. _int_stackrestore:
7284 '``llvm.stackrestore``' Intrinsic
7285 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7292 declare void @llvm.stackrestore(i8* %ptr)
7297 The '``llvm.stackrestore``' intrinsic is used to restore the state of
7298 the function stack to the state it was in when the corresponding
7299 :ref:`llvm.stacksave <int_stacksave>` intrinsic executed. This is
7300 useful for implementing language features like scoped automatic variable
7301 sized arrays in C99.
7306 See the description for :ref:`llvm.stacksave <int_stacksave>`.
7308 '``llvm.prefetch``' Intrinsic
7309 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7316 declare void @llvm.prefetch(i8* <address>, i32 <rw>, i32 <locality>, i32 <cache type>)
7321 The '``llvm.prefetch``' intrinsic is a hint to the code generator to
7322 insert a prefetch instruction if supported; otherwise, it is a noop.
7323 Prefetches have no effect on the behavior of the program but can change
7324 its performance characteristics.
7329 ``address`` is the address to be prefetched, ``rw`` is the specifier
7330 determining if the fetch should be for a read (0) or write (1), and
7331 ``locality`` is a temporal locality specifier ranging from (0) - no
7332 locality, to (3) - extremely local keep in cache. The ``cache type``
7333 specifies whether the prefetch is performed on the data (1) or
7334 instruction (0) cache. The ``rw``, ``locality`` and ``cache type``
7335 arguments must be constant integers.
7340 This intrinsic does not modify the behavior of the program. In
7341 particular, prefetches cannot trap and do not produce a value. On
7342 targets that support this intrinsic, the prefetch can provide hints to
7343 the processor cache for better performance.
7345 '``llvm.pcmarker``' Intrinsic
7346 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7353 declare void @llvm.pcmarker(i32 <id>)
7358 The '``llvm.pcmarker``' intrinsic is a method to export a Program
7359 Counter (PC) in a region of code to simulators and other tools. The
7360 method is target specific, but it is expected that the marker will use
7361 exported symbols to transmit the PC of the marker. The marker makes no
7362 guarantees that it will remain with any specific instruction after
7363 optimizations. It is possible that the presence of a marker will inhibit
7364 optimizations. The intended use is to be inserted after optimizations to
7365 allow correlations of simulation runs.
7370 ``id`` is a numerical id identifying the marker.
7375 This intrinsic does not modify the behavior of the program. Backends
7376 that do not support this intrinsic may ignore it.
7378 '``llvm.readcyclecounter``' Intrinsic
7379 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7386 declare i64 @llvm.readcyclecounter()
7391 The '``llvm.readcyclecounter``' intrinsic provides access to the cycle
7392 counter register (or similar low latency, high accuracy clocks) on those
7393 targets that support it. On X86, it should map to RDTSC. On Alpha, it
7394 should map to RPCC. As the backing counters overflow quickly (on the
7395 order of 9 seconds on alpha), this should only be used for small
7401 When directly supported, reading the cycle counter should not modify any
7402 memory. Implementations are allowed to either return a application
7403 specific value or a system wide value. On backends without support, this
7404 is lowered to a constant 0.
7406 Note that runtime support may be conditional on the privilege-level code is
7407 running at and the host platform.
7409 '``llvm.clear_cache``' Intrinsic
7410 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7417 declare void @llvm.clear_cache(i8*, i8*)
7422 The '``llvm.clear_cache``' intrinsic ensures visibility of modifications
7423 in the specified range to the execution unit of the processor. On
7424 targets with non-unified instruction and data cache, the implementation
7425 flushes the instruction cache.
7430 On platforms with coherent instruction and data caches (e.g. x86), this
7431 intrinsic is a nop. On platforms with non-coherent instruction and data
7432 cache (e.g. ARM, MIPS), the intrinsic is lowered either to appropriate
7433 instructions or a system call, if cache flushing requires special
7436 The default behavior is to emit a call to ``__clear_cache`` from the run
7439 This instrinsic does *not* empty the instruction pipeline. Modifications
7440 of the current function are outside the scope of the intrinsic.
7442 Standard C Library Intrinsics
7443 -----------------------------
7445 LLVM provides intrinsics for a few important standard C library
7446 functions. These intrinsics allow source-language front-ends to pass
7447 information about the alignment of the pointer arguments to the code
7448 generator, providing opportunity for more efficient code generation.
7452 '``llvm.memcpy``' Intrinsic
7453 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
7458 This is an overloaded intrinsic. You can use ``llvm.memcpy`` on any
7459 integer bit width and for different address spaces. Not all targets
7460 support all bit widths however.
7464 declare void @llvm.memcpy.p0i8.p0i8.i32(i8* <dest>, i8* <src>,
7465 i32 <len>, i32 <align>, i1 <isvolatile>)
7466 declare void @llvm.memcpy.p0i8.p0i8.i64(i8* <dest>, i8* <src>,
7467 i64 <len>, i32 <align>, i1 <isvolatile>)
7472 The '``llvm.memcpy.*``' intrinsics copy a block of memory from the
7473 source location to the destination location.
7475 Note that, unlike the standard libc function, the ``llvm.memcpy.*``
7476 intrinsics do not return a value, takes extra alignment/isvolatile
7477 arguments and the pointers can be in specified address spaces.
7482 The first argument is a pointer to the destination, the second is a
7483 pointer to the source. The third argument is an integer argument
7484 specifying the number of bytes to copy, the fourth argument is the
7485 alignment of the source and destination locations, and the fifth is a
7486 boolean indicating a volatile access.
7488 If the call to this intrinsic has an alignment value that is not 0 or 1,
7489 then the caller guarantees that both the source and destination pointers
7490 are aligned to that boundary.
7492 If the ``isvolatile`` parameter is ``true``, the ``llvm.memcpy`` call is
7493 a :ref:`volatile operation <volatile>`. The detailed access behavior is not
7494 very cleanly specified and it is unwise to depend on it.
7499 The '``llvm.memcpy.*``' intrinsics copy a block of memory from the
7500 source location to the destination location, which are not allowed to
7501 overlap. It copies "len" bytes of memory over. If the argument is known
7502 to be aligned to some boundary, this can be specified as the fourth
7503 argument, otherwise it should be set to 0 or 1 (both meaning no alignment).
7505 '``llvm.memmove``' Intrinsic
7506 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7511 This is an overloaded intrinsic. You can use llvm.memmove on any integer
7512 bit width and for different address space. Not all targets support all
7517 declare void @llvm.memmove.p0i8.p0i8.i32(i8* <dest>, i8* <src>,
7518 i32 <len>, i32 <align>, i1 <isvolatile>)
7519 declare void @llvm.memmove.p0i8.p0i8.i64(i8* <dest>, i8* <src>,
7520 i64 <len>, i32 <align>, i1 <isvolatile>)
7525 The '``llvm.memmove.*``' intrinsics move a block of memory from the
7526 source location to the destination location. It is similar to the
7527 '``llvm.memcpy``' intrinsic but allows the two memory locations to
7530 Note that, unlike the standard libc function, the ``llvm.memmove.*``
7531 intrinsics do not return a value, takes extra alignment/isvolatile
7532 arguments and the pointers can be in specified address spaces.
7537 The first argument is a pointer to the destination, the second is a
7538 pointer to the source. The third argument is an integer argument
7539 specifying the number of bytes to copy, the fourth argument is the
7540 alignment of the source and destination locations, and the fifth is a
7541 boolean indicating a volatile access.
7543 If the call to this intrinsic has an alignment value that is not 0 or 1,
7544 then the caller guarantees that the source and destination pointers are
7545 aligned to that boundary.
7547 If the ``isvolatile`` parameter is ``true``, the ``llvm.memmove`` call
7548 is a :ref:`volatile operation <volatile>`. The detailed access behavior is
7549 not very cleanly specified and it is unwise to depend on it.
7554 The '``llvm.memmove.*``' intrinsics copy a block of memory from the
7555 source location to the destination location, which may overlap. It
7556 copies "len" bytes of memory over. If the argument is known to be
7557 aligned to some boundary, this can be specified as the fourth argument,
7558 otherwise it should be set to 0 or 1 (both meaning no alignment).
7560 '``llvm.memset.*``' Intrinsics
7561 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7566 This is an overloaded intrinsic. You can use llvm.memset on any integer
7567 bit width and for different address spaces. However, not all targets
7568 support all bit widths.
7572 declare void @llvm.memset.p0i8.i32(i8* <dest>, i8 <val>,
7573 i32 <len>, i32 <align>, i1 <isvolatile>)
7574 declare void @llvm.memset.p0i8.i64(i8* <dest>, i8 <val>,
7575 i64 <len>, i32 <align>, i1 <isvolatile>)
7580 The '``llvm.memset.*``' intrinsics fill a block of memory with a
7581 particular byte value.
7583 Note that, unlike the standard libc function, the ``llvm.memset``
7584 intrinsic does not return a value and takes extra alignment/volatile
7585 arguments. Also, the destination can be in an arbitrary address space.
7590 The first argument is a pointer to the destination to fill, the second
7591 is the byte value with which to fill it, the third argument is an
7592 integer argument specifying the number of bytes to fill, and the fourth
7593 argument is the known alignment of the destination location.
7595 If the call to this intrinsic has an alignment value that is not 0 or 1,
7596 then the caller guarantees that the destination pointer is aligned to
7599 If the ``isvolatile`` parameter is ``true``, the ``llvm.memset`` call is
7600 a :ref:`volatile operation <volatile>`. The detailed access behavior is not
7601 very cleanly specified and it is unwise to depend on it.
7606 The '``llvm.memset.*``' intrinsics fill "len" bytes of memory starting
7607 at the destination location. If the argument is known to be aligned to
7608 some boundary, this can be specified as the fourth argument, otherwise
7609 it should be set to 0 or 1 (both meaning no alignment).
7611 '``llvm.sqrt.*``' Intrinsic
7612 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
7617 This is an overloaded intrinsic. You can use ``llvm.sqrt`` on any
7618 floating point or vector of floating point type. Not all targets support
7623 declare float @llvm.sqrt.f32(float %Val)
7624 declare double @llvm.sqrt.f64(double %Val)
7625 declare x86_fp80 @llvm.sqrt.f80(x86_fp80 %Val)
7626 declare fp128 @llvm.sqrt.f128(fp128 %Val)
7627 declare ppc_fp128 @llvm.sqrt.ppcf128(ppc_fp128 %Val)
7632 The '``llvm.sqrt``' intrinsics return the sqrt of the specified operand,
7633 returning the same value as the libm '``sqrt``' functions would. Unlike
7634 ``sqrt`` in libm, however, ``llvm.sqrt`` has undefined behavior for
7635 negative numbers other than -0.0 (which allows for better optimization,
7636 because there is no need to worry about errno being set).
7637 ``llvm.sqrt(-0.0)`` is defined to return -0.0 like IEEE sqrt.
7642 The argument and return value are floating point numbers of the same
7648 This function returns the sqrt of the specified operand if it is a
7649 nonnegative floating point number.
7651 '``llvm.powi.*``' Intrinsic
7652 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
7657 This is an overloaded intrinsic. You can use ``llvm.powi`` on any
7658 floating point or vector of floating point type. Not all targets support
7663 declare float @llvm.powi.f32(float %Val, i32 %power)
7664 declare double @llvm.powi.f64(double %Val, i32 %power)
7665 declare x86_fp80 @llvm.powi.f80(x86_fp80 %Val, i32 %power)
7666 declare fp128 @llvm.powi.f128(fp128 %Val, i32 %power)
7667 declare ppc_fp128 @llvm.powi.ppcf128(ppc_fp128 %Val, i32 %power)
7672 The '``llvm.powi.*``' intrinsics return the first operand raised to the
7673 specified (positive or negative) power. The order of evaluation of
7674 multiplications is not defined. When a vector of floating point type is
7675 used, the second argument remains a scalar integer value.
7680 The second argument is an integer power, and the first is a value to
7681 raise to that power.
7686 This function returns the first value raised to the second power with an
7687 unspecified sequence of rounding operations.
7689 '``llvm.sin.*``' Intrinsic
7690 ^^^^^^^^^^^^^^^^^^^^^^^^^^
7695 This is an overloaded intrinsic. You can use ``llvm.sin`` on any
7696 floating point or vector of floating point type. Not all targets support
7701 declare float @llvm.sin.f32(float %Val)
7702 declare double @llvm.sin.f64(double %Val)
7703 declare x86_fp80 @llvm.sin.f80(x86_fp80 %Val)
7704 declare fp128 @llvm.sin.f128(fp128 %Val)
7705 declare ppc_fp128 @llvm.sin.ppcf128(ppc_fp128 %Val)
7710 The '``llvm.sin.*``' intrinsics return the sine of the operand.
7715 The argument and return value are floating point numbers of the same
7721 This function returns the sine of the specified operand, returning the
7722 same values as the libm ``sin`` functions would, and handles error
7723 conditions in the same way.
7725 '``llvm.cos.*``' Intrinsic
7726 ^^^^^^^^^^^^^^^^^^^^^^^^^^
7731 This is an overloaded intrinsic. You can use ``llvm.cos`` on any
7732 floating point or vector of floating point type. Not all targets support
7737 declare float @llvm.cos.f32(float %Val)
7738 declare double @llvm.cos.f64(double %Val)
7739 declare x86_fp80 @llvm.cos.f80(x86_fp80 %Val)
7740 declare fp128 @llvm.cos.f128(fp128 %Val)
7741 declare ppc_fp128 @llvm.cos.ppcf128(ppc_fp128 %Val)
7746 The '``llvm.cos.*``' intrinsics return the cosine of the operand.
7751 The argument and return value are floating point numbers of the same
7757 This function returns the cosine of the specified operand, returning the
7758 same values as the libm ``cos`` functions would, and handles error
7759 conditions in the same way.
7761 '``llvm.pow.*``' Intrinsic
7762 ^^^^^^^^^^^^^^^^^^^^^^^^^^
7767 This is an overloaded intrinsic. You can use ``llvm.pow`` on any
7768 floating point or vector of floating point type. Not all targets support
7773 declare float @llvm.pow.f32(float %Val, float %Power)
7774 declare double @llvm.pow.f64(double %Val, double %Power)
7775 declare x86_fp80 @llvm.pow.f80(x86_fp80 %Val, x86_fp80 %Power)
7776 declare fp128 @llvm.pow.f128(fp128 %Val, fp128 %Power)
7777 declare ppc_fp128 @llvm.pow.ppcf128(ppc_fp128 %Val, ppc_fp128 Power)
7782 The '``llvm.pow.*``' intrinsics return the first operand raised to the
7783 specified (positive or negative) power.
7788 The second argument is a floating point power, and the first is a value
7789 to raise to that power.
7794 This function returns the first value raised to the second power,
7795 returning the same values as the libm ``pow`` functions would, and
7796 handles error conditions in the same way.
7798 '``llvm.exp.*``' Intrinsic
7799 ^^^^^^^^^^^^^^^^^^^^^^^^^^
7804 This is an overloaded intrinsic. You can use ``llvm.exp`` on any
7805 floating point or vector of floating point type. Not all targets support
7810 declare float @llvm.exp.f32(float %Val)
7811 declare double @llvm.exp.f64(double %Val)
7812 declare x86_fp80 @llvm.exp.f80(x86_fp80 %Val)
7813 declare fp128 @llvm.exp.f128(fp128 %Val)
7814 declare ppc_fp128 @llvm.exp.ppcf128(ppc_fp128 %Val)
7819 The '``llvm.exp.*``' intrinsics perform the exp function.
7824 The argument and return value are floating point numbers of the same
7830 This function returns the same values as the libm ``exp`` functions
7831 would, and handles error conditions in the same way.
7833 '``llvm.exp2.*``' Intrinsic
7834 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
7839 This is an overloaded intrinsic. You can use ``llvm.exp2`` on any
7840 floating point or vector of floating point type. Not all targets support
7845 declare float @llvm.exp2.f32(float %Val)
7846 declare double @llvm.exp2.f64(double %Val)
7847 declare x86_fp80 @llvm.exp2.f80(x86_fp80 %Val)
7848 declare fp128 @llvm.exp2.f128(fp128 %Val)
7849 declare ppc_fp128 @llvm.exp2.ppcf128(ppc_fp128 %Val)
7854 The '``llvm.exp2.*``' intrinsics perform the exp2 function.
7859 The argument and return value are floating point numbers of the same
7865 This function returns the same values as the libm ``exp2`` functions
7866 would, and handles error conditions in the same way.
7868 '``llvm.log.*``' Intrinsic
7869 ^^^^^^^^^^^^^^^^^^^^^^^^^^
7874 This is an overloaded intrinsic. You can use ``llvm.log`` on any
7875 floating point or vector of floating point type. Not all targets support
7880 declare float @llvm.log.f32(float %Val)
7881 declare double @llvm.log.f64(double %Val)
7882 declare x86_fp80 @llvm.log.f80(x86_fp80 %Val)
7883 declare fp128 @llvm.log.f128(fp128 %Val)
7884 declare ppc_fp128 @llvm.log.ppcf128(ppc_fp128 %Val)
7889 The '``llvm.log.*``' intrinsics perform the log function.
7894 The argument and return value are floating point numbers of the same
7900 This function returns the same values as the libm ``log`` functions
7901 would, and handles error conditions in the same way.
7903 '``llvm.log10.*``' Intrinsic
7904 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7909 This is an overloaded intrinsic. You can use ``llvm.log10`` on any
7910 floating point or vector of floating point type. Not all targets support
7915 declare float @llvm.log10.f32(float %Val)
7916 declare double @llvm.log10.f64(double %Val)
7917 declare x86_fp80 @llvm.log10.f80(x86_fp80 %Val)
7918 declare fp128 @llvm.log10.f128(fp128 %Val)
7919 declare ppc_fp128 @llvm.log10.ppcf128(ppc_fp128 %Val)
7924 The '``llvm.log10.*``' intrinsics perform the log10 function.
7929 The argument and return value are floating point numbers of the same
7935 This function returns the same values as the libm ``log10`` functions
7936 would, and handles error conditions in the same way.
7938 '``llvm.log2.*``' Intrinsic
7939 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
7944 This is an overloaded intrinsic. You can use ``llvm.log2`` on any
7945 floating point or vector of floating point type. Not all targets support
7950 declare float @llvm.log2.f32(float %Val)
7951 declare double @llvm.log2.f64(double %Val)
7952 declare x86_fp80 @llvm.log2.f80(x86_fp80 %Val)
7953 declare fp128 @llvm.log2.f128(fp128 %Val)
7954 declare ppc_fp128 @llvm.log2.ppcf128(ppc_fp128 %Val)
7959 The '``llvm.log2.*``' intrinsics perform the log2 function.
7964 The argument and return value are floating point numbers of the same
7970 This function returns the same values as the libm ``log2`` functions
7971 would, and handles error conditions in the same way.
7973 '``llvm.fma.*``' Intrinsic
7974 ^^^^^^^^^^^^^^^^^^^^^^^^^^
7979 This is an overloaded intrinsic. You can use ``llvm.fma`` on any
7980 floating point or vector of floating point type. Not all targets support
7985 declare float @llvm.fma.f32(float %a, float %b, float %c)
7986 declare double @llvm.fma.f64(double %a, double %b, double %c)
7987 declare x86_fp80 @llvm.fma.f80(x86_fp80 %a, x86_fp80 %b, x86_fp80 %c)
7988 declare fp128 @llvm.fma.f128(fp128 %a, fp128 %b, fp128 %c)
7989 declare ppc_fp128 @llvm.fma.ppcf128(ppc_fp128 %a, ppc_fp128 %b, ppc_fp128 %c)
7994 The '``llvm.fma.*``' intrinsics perform the fused multiply-add
8000 The argument and return value are floating point numbers of the same
8006 This function returns the same values as the libm ``fma`` functions
8007 would, and does not set errno.
8009 '``llvm.fabs.*``' Intrinsic
8010 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
8015 This is an overloaded intrinsic. You can use ``llvm.fabs`` on any
8016 floating point or vector of floating point type. Not all targets support
8021 declare float @llvm.fabs.f32(float %Val)
8022 declare double @llvm.fabs.f64(double %Val)
8023 declare x86_fp80 @llvm.fabs.f80(x86_fp80 %Val)
8024 declare fp128 @llvm.fabs.f128(fp128 %Val)
8025 declare ppc_fp128 @llvm.fabs.ppcf128(ppc_fp128 %Val)
8030 The '``llvm.fabs.*``' intrinsics return the absolute value of the
8036 The argument and return value are floating point numbers of the same
8042 This function returns the same values as the libm ``fabs`` functions
8043 would, and handles error conditions in the same way.
8045 '``llvm.copysign.*``' Intrinsic
8046 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8051 This is an overloaded intrinsic. You can use ``llvm.copysign`` on any
8052 floating point or vector of floating point type. Not all targets support
8057 declare float @llvm.copysign.f32(float %Mag, float %Sgn)
8058 declare double @llvm.copysign.f64(double %Mag, double %Sgn)
8059 declare x86_fp80 @llvm.copysign.f80(x86_fp80 %Mag, x86_fp80 %Sgn)
8060 declare fp128 @llvm.copysign.f128(fp128 %Mag, fp128 %Sgn)
8061 declare ppc_fp128 @llvm.copysign.ppcf128(ppc_fp128 %Mag, ppc_fp128 %Sgn)
8066 The '``llvm.copysign.*``' intrinsics return a value with the magnitude of the
8067 first operand and the sign of the second operand.
8072 The arguments and return value are floating point numbers of the same
8078 This function returns the same values as the libm ``copysign``
8079 functions would, and handles error conditions in the same way.
8081 '``llvm.floor.*``' Intrinsic
8082 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8087 This is an overloaded intrinsic. You can use ``llvm.floor`` on any
8088 floating point or vector of floating point type. Not all targets support
8093 declare float @llvm.floor.f32(float %Val)
8094 declare double @llvm.floor.f64(double %Val)
8095 declare x86_fp80 @llvm.floor.f80(x86_fp80 %Val)
8096 declare fp128 @llvm.floor.f128(fp128 %Val)
8097 declare ppc_fp128 @llvm.floor.ppcf128(ppc_fp128 %Val)
8102 The '``llvm.floor.*``' intrinsics return the floor of the operand.
8107 The argument and return value are floating point numbers of the same
8113 This function returns the same values as the libm ``floor`` functions
8114 would, and handles error conditions in the same way.
8116 '``llvm.ceil.*``' Intrinsic
8117 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
8122 This is an overloaded intrinsic. You can use ``llvm.ceil`` on any
8123 floating point or vector of floating point type. Not all targets support
8128 declare float @llvm.ceil.f32(float %Val)
8129 declare double @llvm.ceil.f64(double %Val)
8130 declare x86_fp80 @llvm.ceil.f80(x86_fp80 %Val)
8131 declare fp128 @llvm.ceil.f128(fp128 %Val)
8132 declare ppc_fp128 @llvm.ceil.ppcf128(ppc_fp128 %Val)
8137 The '``llvm.ceil.*``' intrinsics return the ceiling of the operand.
8142 The argument and return value are floating point numbers of the same
8148 This function returns the same values as the libm ``ceil`` functions
8149 would, and handles error conditions in the same way.
8151 '``llvm.trunc.*``' Intrinsic
8152 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8157 This is an overloaded intrinsic. You can use ``llvm.trunc`` on any
8158 floating point or vector of floating point type. Not all targets support
8163 declare float @llvm.trunc.f32(float %Val)
8164 declare double @llvm.trunc.f64(double %Val)
8165 declare x86_fp80 @llvm.trunc.f80(x86_fp80 %Val)
8166 declare fp128 @llvm.trunc.f128(fp128 %Val)
8167 declare ppc_fp128 @llvm.trunc.ppcf128(ppc_fp128 %Val)
8172 The '``llvm.trunc.*``' intrinsics returns the operand rounded to the
8173 nearest integer not larger in magnitude than the operand.
8178 The argument and return value are floating point numbers of the same
8184 This function returns the same values as the libm ``trunc`` functions
8185 would, and handles error conditions in the same way.
8187 '``llvm.rint.*``' Intrinsic
8188 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
8193 This is an overloaded intrinsic. You can use ``llvm.rint`` on any
8194 floating point or vector of floating point type. Not all targets support
8199 declare float @llvm.rint.f32(float %Val)
8200 declare double @llvm.rint.f64(double %Val)
8201 declare x86_fp80 @llvm.rint.f80(x86_fp80 %Val)
8202 declare fp128 @llvm.rint.f128(fp128 %Val)
8203 declare ppc_fp128 @llvm.rint.ppcf128(ppc_fp128 %Val)
8208 The '``llvm.rint.*``' intrinsics returns the operand rounded to the
8209 nearest integer. It may raise an inexact floating-point exception if the
8210 operand isn't an integer.
8215 The argument and return value are floating point numbers of the same
8221 This function returns the same values as the libm ``rint`` functions
8222 would, and handles error conditions in the same way.
8224 '``llvm.nearbyint.*``' Intrinsic
8225 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8230 This is an overloaded intrinsic. You can use ``llvm.nearbyint`` on any
8231 floating point or vector of floating point type. Not all targets support
8236 declare float @llvm.nearbyint.f32(float %Val)
8237 declare double @llvm.nearbyint.f64(double %Val)
8238 declare x86_fp80 @llvm.nearbyint.f80(x86_fp80 %Val)
8239 declare fp128 @llvm.nearbyint.f128(fp128 %Val)
8240 declare ppc_fp128 @llvm.nearbyint.ppcf128(ppc_fp128 %Val)
8245 The '``llvm.nearbyint.*``' intrinsics returns the operand rounded to the
8251 The argument and return value are floating point numbers of the same
8257 This function returns the same values as the libm ``nearbyint``
8258 functions would, and handles error conditions in the same way.
8260 '``llvm.round.*``' Intrinsic
8261 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8266 This is an overloaded intrinsic. You can use ``llvm.round`` on any
8267 floating point or vector of floating point type. Not all targets support
8272 declare float @llvm.round.f32(float %Val)
8273 declare double @llvm.round.f64(double %Val)
8274 declare x86_fp80 @llvm.round.f80(x86_fp80 %Val)
8275 declare fp128 @llvm.round.f128(fp128 %Val)
8276 declare ppc_fp128 @llvm.round.ppcf128(ppc_fp128 %Val)
8281 The '``llvm.round.*``' intrinsics returns the operand rounded to the
8287 The argument and return value are floating point numbers of the same
8293 This function returns the same values as the libm ``round``
8294 functions would, and handles error conditions in the same way.
8296 Bit Manipulation Intrinsics
8297 ---------------------------
8299 LLVM provides intrinsics for a few important bit manipulation
8300 operations. These allow efficient code generation for some algorithms.
8302 '``llvm.bswap.*``' Intrinsics
8303 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8308 This is an overloaded intrinsic function. You can use bswap on any
8309 integer type that is an even number of bytes (i.e. BitWidth % 16 == 0).
8313 declare i16 @llvm.bswap.i16(i16 <id>)
8314 declare i32 @llvm.bswap.i32(i32 <id>)
8315 declare i64 @llvm.bswap.i64(i64 <id>)
8320 The '``llvm.bswap``' family of intrinsics is used to byte swap integer
8321 values with an even number of bytes (positive multiple of 16 bits).
8322 These are useful for performing operations on data that is not in the
8323 target's native byte order.
8328 The ``llvm.bswap.i16`` intrinsic returns an i16 value that has the high
8329 and low byte of the input i16 swapped. Similarly, the ``llvm.bswap.i32``
8330 intrinsic returns an i32 value that has the four bytes of the input i32
8331 swapped, so that if the input bytes are numbered 0, 1, 2, 3 then the
8332 returned i32 will have its bytes in 3, 2, 1, 0 order. The
8333 ``llvm.bswap.i48``, ``llvm.bswap.i64`` and other intrinsics extend this
8334 concept to additional even-byte lengths (6 bytes, 8 bytes and more,
8337 '``llvm.ctpop.*``' Intrinsic
8338 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8343 This is an overloaded intrinsic. You can use llvm.ctpop on any integer
8344 bit width, or on any vector with integer elements. Not all targets
8345 support all bit widths or vector types, however.
8349 declare i8 @llvm.ctpop.i8(i8 <src>)
8350 declare i16 @llvm.ctpop.i16(i16 <src>)
8351 declare i32 @llvm.ctpop.i32(i32 <src>)
8352 declare i64 @llvm.ctpop.i64(i64 <src>)
8353 declare i256 @llvm.ctpop.i256(i256 <src>)
8354 declare <2 x i32> @llvm.ctpop.v2i32(<2 x i32> <src>)
8359 The '``llvm.ctpop``' family of intrinsics counts the number of bits set
8365 The only argument is the value to be counted. The argument may be of any
8366 integer type, or a vector with integer elements. The return type must
8367 match the argument type.
8372 The '``llvm.ctpop``' intrinsic counts the 1's in a variable, or within
8373 each element of a vector.
8375 '``llvm.ctlz.*``' Intrinsic
8376 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
8381 This is an overloaded intrinsic. You can use ``llvm.ctlz`` on any
8382 integer bit width, or any vector whose elements are integers. Not all
8383 targets support all bit widths or vector types, however.
8387 declare i8 @llvm.ctlz.i8 (i8 <src>, i1 <is_zero_undef>)
8388 declare i16 @llvm.ctlz.i16 (i16 <src>, i1 <is_zero_undef>)
8389 declare i32 @llvm.ctlz.i32 (i32 <src>, i1 <is_zero_undef>)
8390 declare i64 @llvm.ctlz.i64 (i64 <src>, i1 <is_zero_undef>)
8391 declare i256 @llvm.ctlz.i256(i256 <src>, i1 <is_zero_undef>)
8392 declase <2 x i32> @llvm.ctlz.v2i32(<2 x i32> <src>, i1 <is_zero_undef>)
8397 The '``llvm.ctlz``' family of intrinsic functions counts the number of
8398 leading zeros in a variable.
8403 The first argument is the value to be counted. This argument may be of
8404 any integer type, or a vectory with integer element type. The return
8405 type must match the first argument type.
8407 The second argument must be a constant and is a flag to indicate whether
8408 the intrinsic should ensure that a zero as the first argument produces a
8409 defined result. Historically some architectures did not provide a
8410 defined result for zero values as efficiently, and many algorithms are
8411 now predicated on avoiding zero-value inputs.
8416 The '``llvm.ctlz``' intrinsic counts the leading (most significant)
8417 zeros in a variable, or within each element of the vector. If
8418 ``src == 0`` then the result is the size in bits of the type of ``src``
8419 if ``is_zero_undef == 0`` and ``undef`` otherwise. For example,
8420 ``llvm.ctlz(i32 2) = 30``.
8422 '``llvm.cttz.*``' Intrinsic
8423 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
8428 This is an overloaded intrinsic. You can use ``llvm.cttz`` on any
8429 integer bit width, or any vector of integer elements. Not all targets
8430 support all bit widths or vector types, however.
8434 declare i8 @llvm.cttz.i8 (i8 <src>, i1 <is_zero_undef>)
8435 declare i16 @llvm.cttz.i16 (i16 <src>, i1 <is_zero_undef>)
8436 declare i32 @llvm.cttz.i32 (i32 <src>, i1 <is_zero_undef>)
8437 declare i64 @llvm.cttz.i64 (i64 <src>, i1 <is_zero_undef>)
8438 declare i256 @llvm.cttz.i256(i256 <src>, i1 <is_zero_undef>)
8439 declase <2 x i32> @llvm.cttz.v2i32(<2 x i32> <src>, i1 <is_zero_undef>)
8444 The '``llvm.cttz``' family of intrinsic functions counts the number of
8450 The first argument is the value to be counted. This argument may be of
8451 any integer type, or a vectory with integer element type. The return
8452 type must match the first argument type.
8454 The second argument must be a constant and is a flag to indicate whether
8455 the intrinsic should ensure that a zero as the first argument produces a
8456 defined result. Historically some architectures did not provide a
8457 defined result for zero values as efficiently, and many algorithms are
8458 now predicated on avoiding zero-value inputs.
8463 The '``llvm.cttz``' intrinsic counts the trailing (least significant)
8464 zeros in a variable, or within each element of a vector. If ``src == 0``
8465 then the result is the size in bits of the type of ``src`` if
8466 ``is_zero_undef == 0`` and ``undef`` otherwise. For example,
8467 ``llvm.cttz(2) = 1``.
8469 Arithmetic with Overflow Intrinsics
8470 -----------------------------------
8472 LLVM provides intrinsics for some arithmetic with overflow operations.
8474 '``llvm.sadd.with.overflow.*``' Intrinsics
8475 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8480 This is an overloaded intrinsic. You can use ``llvm.sadd.with.overflow``
8481 on any integer bit width.
8485 declare {i16, i1} @llvm.sadd.with.overflow.i16(i16 %a, i16 %b)
8486 declare {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b)
8487 declare {i64, i1} @llvm.sadd.with.overflow.i64(i64 %a, i64 %b)
8492 The '``llvm.sadd.with.overflow``' family of intrinsic functions perform
8493 a signed addition of the two arguments, and indicate whether an overflow
8494 occurred during the signed summation.
8499 The arguments (%a and %b) and the first element of the result structure
8500 may be of integer types of any bit width, but they must have the same
8501 bit width. The second element of the result structure must be of type
8502 ``i1``. ``%a`` and ``%b`` are the two values that will undergo signed
8508 The '``llvm.sadd.with.overflow``' family of intrinsic functions perform
8509 a signed addition of the two variables. They return a structure --- the
8510 first element of which is the signed summation, and the second element
8511 of which is a bit specifying if the signed summation resulted in an
8517 .. code-block:: llvm
8519 %res = call {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b)
8520 %sum = extractvalue {i32, i1} %res, 0
8521 %obit = extractvalue {i32, i1} %res, 1
8522 br i1 %obit, label %overflow, label %normal
8524 '``llvm.uadd.with.overflow.*``' Intrinsics
8525 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8530 This is an overloaded intrinsic. You can use ``llvm.uadd.with.overflow``
8531 on any integer bit width.
8535 declare {i16, i1} @llvm.uadd.with.overflow.i16(i16 %a, i16 %b)
8536 declare {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)
8537 declare {i64, i1} @llvm.uadd.with.overflow.i64(i64 %a, i64 %b)
8542 The '``llvm.uadd.with.overflow``' family of intrinsic functions perform
8543 an unsigned addition of the two arguments, and indicate whether a carry
8544 occurred during the unsigned summation.
8549 The arguments (%a and %b) and the first element of the result structure
8550 may be of integer types of any bit width, but they must have the same
8551 bit width. The second element of the result structure must be of type
8552 ``i1``. ``%a`` and ``%b`` are the two values that will undergo unsigned
8558 The '``llvm.uadd.with.overflow``' family of intrinsic functions perform
8559 an unsigned addition of the two arguments. They return a structure --- the
8560 first element of which is the sum, and the second element of which is a
8561 bit specifying if the unsigned summation resulted in a carry.
8566 .. code-block:: llvm
8568 %res = call {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)
8569 %sum = extractvalue {i32, i1} %res, 0
8570 %obit = extractvalue {i32, i1} %res, 1
8571 br i1 %obit, label %carry, label %normal
8573 '``llvm.ssub.with.overflow.*``' Intrinsics
8574 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8579 This is an overloaded intrinsic. You can use ``llvm.ssub.with.overflow``
8580 on any integer bit width.
8584 declare {i16, i1} @llvm.ssub.with.overflow.i16(i16 %a, i16 %b)
8585 declare {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b)
8586 declare {i64, i1} @llvm.ssub.with.overflow.i64(i64 %a, i64 %b)
8591 The '``llvm.ssub.with.overflow``' family of intrinsic functions perform
8592 a signed subtraction of the two arguments, and indicate whether an
8593 overflow occurred during the signed subtraction.
8598 The arguments (%a and %b) and the first element of the result structure
8599 may be of integer types of any bit width, but they must have the same
8600 bit width. The second element of the result structure must be of type
8601 ``i1``. ``%a`` and ``%b`` are the two values that will undergo signed
8607 The '``llvm.ssub.with.overflow``' family of intrinsic functions perform
8608 a signed subtraction of the two arguments. They return a structure --- the
8609 first element of which is the subtraction, and the second element of
8610 which is a bit specifying if the signed subtraction resulted in an
8616 .. code-block:: llvm
8618 %res = call {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b)
8619 %sum = extractvalue {i32, i1} %res, 0
8620 %obit = extractvalue {i32, i1} %res, 1
8621 br i1 %obit, label %overflow, label %normal
8623 '``llvm.usub.with.overflow.*``' Intrinsics
8624 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8629 This is an overloaded intrinsic. You can use ``llvm.usub.with.overflow``
8630 on any integer bit width.
8634 declare {i16, i1} @llvm.usub.with.overflow.i16(i16 %a, i16 %b)
8635 declare {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b)
8636 declare {i64, i1} @llvm.usub.with.overflow.i64(i64 %a, i64 %b)
8641 The '``llvm.usub.with.overflow``' family of intrinsic functions perform
8642 an unsigned subtraction of the two arguments, and indicate whether an
8643 overflow occurred during the unsigned subtraction.
8648 The arguments (%a and %b) and the first element of the result structure
8649 may be of integer types of any bit width, but they must have the same
8650 bit width. The second element of the result structure must be of type
8651 ``i1``. ``%a`` and ``%b`` are the two values that will undergo unsigned
8657 The '``llvm.usub.with.overflow``' family of intrinsic functions perform
8658 an unsigned subtraction of the two arguments. They return a structure ---
8659 the first element of which is the subtraction, and the second element of
8660 which is a bit specifying if the unsigned subtraction resulted in an
8666 .. code-block:: llvm
8668 %res = call {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b)
8669 %sum = extractvalue {i32, i1} %res, 0
8670 %obit = extractvalue {i32, i1} %res, 1
8671 br i1 %obit, label %overflow, label %normal
8673 '``llvm.smul.with.overflow.*``' Intrinsics
8674 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8679 This is an overloaded intrinsic. You can use ``llvm.smul.with.overflow``
8680 on any integer bit width.
8684 declare {i16, i1} @llvm.smul.with.overflow.i16(i16 %a, i16 %b)
8685 declare {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b)
8686 declare {i64, i1} @llvm.smul.with.overflow.i64(i64 %a, i64 %b)
8691 The '``llvm.smul.with.overflow``' family of intrinsic functions perform
8692 a signed multiplication of the two arguments, and indicate whether an
8693 overflow occurred during the signed multiplication.
8698 The arguments (%a and %b) and the first element of the result structure
8699 may be of integer types of any bit width, but they must have the same
8700 bit width. The second element of the result structure must be of type
8701 ``i1``. ``%a`` and ``%b`` are the two values that will undergo signed
8707 The '``llvm.smul.with.overflow``' family of intrinsic functions perform
8708 a signed multiplication of the two arguments. They return a structure ---
8709 the first element of which is the multiplication, and the second element
8710 of which is a bit specifying if the signed multiplication resulted in an
8716 .. code-block:: llvm
8718 %res = call {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b)
8719 %sum = extractvalue {i32, i1} %res, 0
8720 %obit = extractvalue {i32, i1} %res, 1
8721 br i1 %obit, label %overflow, label %normal
8723 '``llvm.umul.with.overflow.*``' Intrinsics
8724 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8729 This is an overloaded intrinsic. You can use ``llvm.umul.with.overflow``
8730 on any integer bit width.
8734 declare {i16, i1} @llvm.umul.with.overflow.i16(i16 %a, i16 %b)
8735 declare {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b)
8736 declare {i64, i1} @llvm.umul.with.overflow.i64(i64 %a, i64 %b)
8741 The '``llvm.umul.with.overflow``' family of intrinsic functions perform
8742 a unsigned multiplication of the two arguments, and indicate whether an
8743 overflow occurred during the unsigned multiplication.
8748 The arguments (%a and %b) and the first element of the result structure
8749 may be of integer types of any bit width, but they must have the same
8750 bit width. The second element of the result structure must be of type
8751 ``i1``. ``%a`` and ``%b`` are the two values that will undergo unsigned
8757 The '``llvm.umul.with.overflow``' family of intrinsic functions perform
8758 an unsigned multiplication of the two arguments. They return a structure ---
8759 the first element of which is the multiplication, and the second
8760 element of which is a bit specifying if the unsigned multiplication
8761 resulted in an overflow.
8766 .. code-block:: llvm
8768 %res = call {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b)
8769 %sum = extractvalue {i32, i1} %res, 0
8770 %obit = extractvalue {i32, i1} %res, 1
8771 br i1 %obit, label %overflow, label %normal
8773 Specialised Arithmetic Intrinsics
8774 ---------------------------------
8776 '``llvm.fmuladd.*``' Intrinsic
8777 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8784 declare float @llvm.fmuladd.f32(float %a, float %b, float %c)
8785 declare double @llvm.fmuladd.f64(double %a, double %b, double %c)
8790 The '``llvm.fmuladd.*``' intrinsic functions represent multiply-add
8791 expressions that can be fused if the code generator determines that (a) the
8792 target instruction set has support for a fused operation, and (b) that the
8793 fused operation is more efficient than the equivalent, separate pair of mul
8794 and add instructions.
8799 The '``llvm.fmuladd.*``' intrinsics each take three arguments: two
8800 multiplicands, a and b, and an addend c.
8809 %0 = call float @llvm.fmuladd.f32(%a, %b, %c)
8811 is equivalent to the expression a \* b + c, except that rounding will
8812 not be performed between the multiplication and addition steps if the
8813 code generator fuses the operations. Fusion is not guaranteed, even if
8814 the target platform supports it. If a fused multiply-add is required the
8815 corresponding llvm.fma.\* intrinsic function should be used
8816 instead. This never sets errno, just as '``llvm.fma.*``'.
8821 .. code-block:: llvm
8823 %r2 = call float @llvm.fmuladd.f32(float %a, float %b, float %c) ; yields float:r2 = (a * b) + c
8825 Half Precision Floating Point Intrinsics
8826 ----------------------------------------
8828 For most target platforms, half precision floating point is a
8829 storage-only format. This means that it is a dense encoding (in memory)
8830 but does not support computation in the format.
8832 This means that code must first load the half-precision floating point
8833 value as an i16, then convert it to float with
8834 :ref:`llvm.convert.from.fp16 <int_convert_from_fp16>`. Computation can
8835 then be performed on the float value (including extending to double
8836 etc). To store the value back to memory, it is first converted to float
8837 if needed, then converted to i16 with
8838 :ref:`llvm.convert.to.fp16 <int_convert_to_fp16>`, then storing as an
8841 .. _int_convert_to_fp16:
8843 '``llvm.convert.to.fp16``' Intrinsic
8844 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8851 declare i16 @llvm.convert.to.fp16.f32(float %a)
8852 declare i16 @llvm.convert.to.fp16.f64(double %a)
8857 The '``llvm.convert.to.fp16``' intrinsic function performs a conversion from a
8858 conventional floating point type to half precision floating point format.
8863 The intrinsic function contains single argument - the value to be
8869 The '``llvm.convert.to.fp16``' intrinsic function performs a conversion from a
8870 conventional floating point format to half precision floating point format. The
8871 return value is an ``i16`` which contains the converted number.
8876 .. code-block:: llvm
8878 %res = call i16 @llvm.convert.to.fp16.f32(float %a)
8879 store i16 %res, i16* @x, align 2
8881 .. _int_convert_from_fp16:
8883 '``llvm.convert.from.fp16``' Intrinsic
8884 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8891 declare float @llvm.convert.from.fp16.f32(i16 %a)
8892 declare double @llvm.convert.from.fp16.f64(i16 %a)
8897 The '``llvm.convert.from.fp16``' intrinsic function performs a
8898 conversion from half precision floating point format to single precision
8899 floating point format.
8904 The intrinsic function contains single argument - the value to be
8910 The '``llvm.convert.from.fp16``' intrinsic function performs a
8911 conversion from half single precision floating point format to single
8912 precision floating point format. The input half-float value is
8913 represented by an ``i16`` value.
8918 .. code-block:: llvm
8920 %a = load i16* @x, align 2
8921 %res = call float @llvm.convert.from.fp16(i16 %a)
8926 The LLVM debugger intrinsics (which all start with ``llvm.dbg.``
8927 prefix), are described in the `LLVM Source Level
8928 Debugging <SourceLevelDebugging.html#format_common_intrinsics>`_
8931 Exception Handling Intrinsics
8932 -----------------------------
8934 The LLVM exception handling intrinsics (which all start with
8935 ``llvm.eh.`` prefix), are described in the `LLVM Exception
8936 Handling <ExceptionHandling.html#format_common_intrinsics>`_ document.
8940 Trampoline Intrinsics
8941 ---------------------
8943 These intrinsics make it possible to excise one parameter, marked with
8944 the :ref:`nest <nest>` attribute, from a function. The result is a
8945 callable function pointer lacking the nest parameter - the caller does
8946 not need to provide a value for it. Instead, the value to use is stored
8947 in advance in a "trampoline", a block of memory usually allocated on the
8948 stack, which also contains code to splice the nest value into the
8949 argument list. This is used to implement the GCC nested function address
8952 For example, if the function is ``i32 f(i8* nest %c, i32 %x, i32 %y)``
8953 then the resulting function pointer has signature ``i32 (i32, i32)*``.
8954 It can be created as follows:
8956 .. code-block:: llvm
8958 %tramp = alloca [10 x i8], align 4 ; size and alignment only correct for X86
8959 %tramp1 = getelementptr [10 x i8]* %tramp, i32 0, i32 0
8960 call i8* @llvm.init.trampoline(i8* %tramp1, i8* bitcast (i32 (i8*, i32, i32)* @f to i8*), i8* %nval)
8961 %p = call i8* @llvm.adjust.trampoline(i8* %tramp1)
8962 %fp = bitcast i8* %p to i32 (i32, i32)*
8964 The call ``%val = call i32 %fp(i32 %x, i32 %y)`` is then equivalent to
8965 ``%val = call i32 %f(i8* %nval, i32 %x, i32 %y)``.
8969 '``llvm.init.trampoline``' Intrinsic
8970 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8977 declare void @llvm.init.trampoline(i8* <tramp>, i8* <func>, i8* <nval>)
8982 This fills the memory pointed to by ``tramp`` with executable code,
8983 turning it into a trampoline.
8988 The ``llvm.init.trampoline`` intrinsic takes three arguments, all
8989 pointers. The ``tramp`` argument must point to a sufficiently large and
8990 sufficiently aligned block of memory; this memory is written to by the
8991 intrinsic. Note that the size and the alignment are target-specific -
8992 LLVM currently provides no portable way of determining them, so a
8993 front-end that generates this intrinsic needs to have some
8994 target-specific knowledge. The ``func`` argument must hold a function
8995 bitcast to an ``i8*``.
9000 The block of memory pointed to by ``tramp`` is filled with target
9001 dependent code, turning it into a function. Then ``tramp`` needs to be
9002 passed to :ref:`llvm.adjust.trampoline <int_at>` to get a pointer which can
9003 be :ref:`bitcast (to a new function) and called <int_trampoline>`. The new
9004 function's signature is the same as that of ``func`` with any arguments
9005 marked with the ``nest`` attribute removed. At most one such ``nest``
9006 argument is allowed, and it must be of pointer type. Calling the new
9007 function is equivalent to calling ``func`` with the same argument list,
9008 but with ``nval`` used for the missing ``nest`` argument. If, after
9009 calling ``llvm.init.trampoline``, the memory pointed to by ``tramp`` is
9010 modified, then the effect of any later call to the returned function
9011 pointer is undefined.
9015 '``llvm.adjust.trampoline``' Intrinsic
9016 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9023 declare i8* @llvm.adjust.trampoline(i8* <tramp>)
9028 This performs any required machine-specific adjustment to the address of
9029 a trampoline (passed as ``tramp``).
9034 ``tramp`` must point to a block of memory which already has trampoline
9035 code filled in by a previous call to
9036 :ref:`llvm.init.trampoline <int_it>`.
9041 On some architectures the address of the code to be executed needs to be
9042 different than the address where the trampoline is actually stored. This
9043 intrinsic returns the executable address corresponding to ``tramp``
9044 after performing the required machine specific adjustments. The pointer
9045 returned can then be :ref:`bitcast and executed <int_trampoline>`.
9050 This class of intrinsics provides information about the lifetime of
9051 memory objects and ranges where variables are immutable.
9055 '``llvm.lifetime.start``' Intrinsic
9056 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9063 declare void @llvm.lifetime.start(i64 <size>, i8* nocapture <ptr>)
9068 The '``llvm.lifetime.start``' intrinsic specifies the start of a memory
9074 The first argument is a constant integer representing the size of the
9075 object, or -1 if it is variable sized. The second argument is a pointer
9081 This intrinsic indicates that before this point in the code, the value
9082 of the memory pointed to by ``ptr`` is dead. This means that it is known
9083 to never be used and has an undefined value. A load from the pointer
9084 that precedes this intrinsic can be replaced with ``'undef'``.
9088 '``llvm.lifetime.end``' Intrinsic
9089 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9096 declare void @llvm.lifetime.end(i64 <size>, i8* nocapture <ptr>)
9101 The '``llvm.lifetime.end``' intrinsic specifies the end of a memory
9107 The first argument is a constant integer representing the size of the
9108 object, or -1 if it is variable sized. The second argument is a pointer
9114 This intrinsic indicates that after this point in the code, the value of
9115 the memory pointed to by ``ptr`` is dead. This means that it is known to
9116 never be used and has an undefined value. Any stores into the memory
9117 object following this intrinsic may be removed as dead.
9119 '``llvm.invariant.start``' Intrinsic
9120 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9127 declare {}* @llvm.invariant.start(i64 <size>, i8* nocapture <ptr>)
9132 The '``llvm.invariant.start``' intrinsic specifies that the contents of
9133 a memory object will not change.
9138 The first argument is a constant integer representing the size of the
9139 object, or -1 if it is variable sized. The second argument is a pointer
9145 This intrinsic indicates that until an ``llvm.invariant.end`` that uses
9146 the return value, the referenced memory location is constant and
9149 '``llvm.invariant.end``' Intrinsic
9150 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9157 declare void @llvm.invariant.end({}* <start>, i64 <size>, i8* nocapture <ptr>)
9162 The '``llvm.invariant.end``' intrinsic specifies that the contents of a
9163 memory object are mutable.
9168 The first argument is the matching ``llvm.invariant.start`` intrinsic.
9169 The second argument is a constant integer representing the size of the
9170 object, or -1 if it is variable sized and the third argument is a
9171 pointer to the object.
9176 This intrinsic indicates that the memory is mutable again.
9181 This class of intrinsics is designed to be generic and has no specific
9184 '``llvm.var.annotation``' Intrinsic
9185 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9192 declare void @llvm.var.annotation(i8* <val>, i8* <str>, i8* <str>, i32 <int>)
9197 The '``llvm.var.annotation``' intrinsic.
9202 The first argument is a pointer to a value, the second is a pointer to a
9203 global string, the third is a pointer to a global string which is the
9204 source file name, and the last argument is the line number.
9209 This intrinsic allows annotation of local variables with arbitrary
9210 strings. This can be useful for special purpose optimizations that want
9211 to look for these annotations. These have no other defined use; they are
9212 ignored by code generation and optimization.
9214 '``llvm.ptr.annotation.*``' Intrinsic
9215 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9220 This is an overloaded intrinsic. You can use '``llvm.ptr.annotation``' on a
9221 pointer to an integer of any width. *NOTE* you must specify an address space for
9222 the pointer. The identifier for the default address space is the integer
9227 declare i8* @llvm.ptr.annotation.p<address space>i8(i8* <val>, i8* <str>, i8* <str>, i32 <int>)
9228 declare i16* @llvm.ptr.annotation.p<address space>i16(i16* <val>, i8* <str>, i8* <str>, i32 <int>)
9229 declare i32* @llvm.ptr.annotation.p<address space>i32(i32* <val>, i8* <str>, i8* <str>, i32 <int>)
9230 declare i64* @llvm.ptr.annotation.p<address space>i64(i64* <val>, i8* <str>, i8* <str>, i32 <int>)
9231 declare i256* @llvm.ptr.annotation.p<address space>i256(i256* <val>, i8* <str>, i8* <str>, i32 <int>)
9236 The '``llvm.ptr.annotation``' intrinsic.
9241 The first argument is a pointer to an integer value of arbitrary bitwidth
9242 (result of some expression), the second is a pointer to a global string, the
9243 third is a pointer to a global string which is the source file name, and the
9244 last argument is the line number. It returns the value of the first argument.
9249 This intrinsic allows annotation of a pointer to an integer with arbitrary
9250 strings. This can be useful for special purpose optimizations that want to look
9251 for these annotations. These have no other defined use; they are ignored by code
9252 generation and optimization.
9254 '``llvm.annotation.*``' Intrinsic
9255 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9260 This is an overloaded intrinsic. You can use '``llvm.annotation``' on
9261 any integer bit width.
9265 declare i8 @llvm.annotation.i8(i8 <val>, i8* <str>, i8* <str>, i32 <int>)
9266 declare i16 @llvm.annotation.i16(i16 <val>, i8* <str>, i8* <str>, i32 <int>)
9267 declare i32 @llvm.annotation.i32(i32 <val>, i8* <str>, i8* <str>, i32 <int>)
9268 declare i64 @llvm.annotation.i64(i64 <val>, i8* <str>, i8* <str>, i32 <int>)
9269 declare i256 @llvm.annotation.i256(i256 <val>, i8* <str>, i8* <str>, i32 <int>)
9274 The '``llvm.annotation``' intrinsic.
9279 The first argument is an integer value (result of some expression), the
9280 second is a pointer to a global string, the third is a pointer to a
9281 global string which is the source file name, and the last argument is
9282 the line number. It returns the value of the first argument.
9287 This intrinsic allows annotations to be put on arbitrary expressions
9288 with arbitrary strings. This can be useful for special purpose
9289 optimizations that want to look for these annotations. These have no
9290 other defined use; they are ignored by code generation and optimization.
9292 '``llvm.trap``' Intrinsic
9293 ^^^^^^^^^^^^^^^^^^^^^^^^^
9300 declare void @llvm.trap() noreturn nounwind
9305 The '``llvm.trap``' intrinsic.
9315 This intrinsic is lowered to the target dependent trap instruction. If
9316 the target does not have a trap instruction, this intrinsic will be
9317 lowered to a call of the ``abort()`` function.
9319 '``llvm.debugtrap``' Intrinsic
9320 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9327 declare void @llvm.debugtrap() nounwind
9332 The '``llvm.debugtrap``' intrinsic.
9342 This intrinsic is lowered to code which is intended to cause an
9343 execution trap with the intention of requesting the attention of a
9346 '``llvm.stackprotector``' Intrinsic
9347 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9354 declare void @llvm.stackprotector(i8* <guard>, i8** <slot>)
9359 The ``llvm.stackprotector`` intrinsic takes the ``guard`` and stores it
9360 onto the stack at ``slot``. The stack slot is adjusted to ensure that it
9361 is placed on the stack before local variables.
9366 The ``llvm.stackprotector`` intrinsic requires two pointer arguments.
9367 The first argument is the value loaded from the stack guard
9368 ``@__stack_chk_guard``. The second variable is an ``alloca`` that has
9369 enough space to hold the value of the guard.
9374 This intrinsic causes the prologue/epilogue inserter to force the position of
9375 the ``AllocaInst`` stack slot to be before local variables on the stack. This is
9376 to ensure that if a local variable on the stack is overwritten, it will destroy
9377 the value of the guard. When the function exits, the guard on the stack is
9378 checked against the original guard by ``llvm.stackprotectorcheck``. If they are
9379 different, then ``llvm.stackprotectorcheck`` causes the program to abort by
9380 calling the ``__stack_chk_fail()`` function.
9382 '``llvm.stackprotectorcheck``' Intrinsic
9383 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9390 declare void @llvm.stackprotectorcheck(i8** <guard>)
9395 The ``llvm.stackprotectorcheck`` intrinsic compares ``guard`` against an already
9396 created stack protector and if they are not equal calls the
9397 ``__stack_chk_fail()`` function.
9402 The ``llvm.stackprotectorcheck`` intrinsic requires one pointer argument, the
9403 the variable ``@__stack_chk_guard``.
9408 This intrinsic is provided to perform the stack protector check by comparing
9409 ``guard`` with the stack slot created by ``llvm.stackprotector`` and if the
9410 values do not match call the ``__stack_chk_fail()`` function.
9412 The reason to provide this as an IR level intrinsic instead of implementing it
9413 via other IR operations is that in order to perform this operation at the IR
9414 level without an intrinsic, one would need to create additional basic blocks to
9415 handle the success/failure cases. This makes it difficult to stop the stack
9416 protector check from disrupting sibling tail calls in Codegen. With this
9417 intrinsic, we are able to generate the stack protector basic blocks late in
9418 codegen after the tail call decision has occurred.
9420 '``llvm.objectsize``' Intrinsic
9421 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9428 declare i32 @llvm.objectsize.i32(i8* <object>, i1 <min>)
9429 declare i64 @llvm.objectsize.i64(i8* <object>, i1 <min>)
9434 The ``llvm.objectsize`` intrinsic is designed to provide information to
9435 the optimizers to determine at compile time whether a) an operation
9436 (like memcpy) will overflow a buffer that corresponds to an object, or
9437 b) that a runtime check for overflow isn't necessary. An object in this
9438 context means an allocation of a specific class, structure, array, or
9444 The ``llvm.objectsize`` intrinsic takes two arguments. The first
9445 argument is a pointer to or into the ``object``. The second argument is
9446 a boolean and determines whether ``llvm.objectsize`` returns 0 (if true)
9447 or -1 (if false) when the object size is unknown. The second argument
9448 only accepts constants.
9453 The ``llvm.objectsize`` intrinsic is lowered to a constant representing
9454 the size of the object concerned. If the size cannot be determined at
9455 compile time, ``llvm.objectsize`` returns ``i32/i64 -1 or 0`` (depending
9456 on the ``min`` argument).
9458 '``llvm.expect``' Intrinsic
9459 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
9464 This is an overloaded intrinsic. You can use ``llvm.expect`` on any
9469 declare i1 @llvm.expect.i1(i1 <val>, i1 <expected_val>)
9470 declare i32 @llvm.expect.i32(i32 <val>, i32 <expected_val>)
9471 declare i64 @llvm.expect.i64(i64 <val>, i64 <expected_val>)
9476 The ``llvm.expect`` intrinsic provides information about expected (the
9477 most probable) value of ``val``, which can be used by optimizers.
9482 The ``llvm.expect`` intrinsic takes two arguments. The first argument is
9483 a value. The second argument is an expected value, this needs to be a
9484 constant value, variables are not allowed.
9489 This intrinsic is lowered to the ``val``.
9491 '``llvm.assume``' Intrinsic
9492 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9499 declare void @llvm.assume(i1 %cond)
9504 The ``llvm.assume`` allows the optimizer to assume that the provided
9505 condition is true. This information can then be used in simplifying other parts
9511 The condition which the optimizer may assume is always true.
9516 The intrinsic allows the optimizer to assume that the provided condition is
9517 always true whenever the control flow reaches the intrinsic call. No code is
9518 generated for this intrinsic, and instructions that contribute only to the
9519 provided condition are not used for code generation. If the condition is
9520 violated during execution, the behavior is undefined.
9522 Please note that optimizer might limit the transformations performed on values
9523 used by the ``llvm.assume`` intrinsic in order to preserve the instructions
9524 only used to form the intrinsic's input argument. This might prove undesirable
9525 if the extra information provided by the ``llvm.assume`` intrinsic does cause
9526 sufficient overall improvement in code quality. For this reason,
9527 ``llvm.assume`` should not be used to document basic mathematical invariants
9528 that the optimizer can otherwise deduce or facts that are of little use to the
9531 '``llvm.donothing``' Intrinsic
9532 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9539 declare void @llvm.donothing() nounwind readnone
9544 The ``llvm.donothing`` intrinsic doesn't perform any operation. It's the
9545 only intrinsic that can be called with an invoke instruction.
9555 This intrinsic does nothing, and it's removed by optimizers and ignored
9558 Stack Map Intrinsics
9559 --------------------
9561 LLVM provides experimental intrinsics to support runtime patching
9562 mechanisms commonly desired in dynamic language JITs. These intrinsics
9563 are described in :doc:`StackMaps`.