1 ==============================
2 LLVM Language Reference Manual
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12 This document is a reference manual for the LLVM assembly language. LLVM
13 is a Static Single Assignment (SSA) based representation that provides
14 type safety, low-level operations, flexibility, and the capability of
15 representing 'all' high-level languages cleanly. It is the common code
16 representation used throughout all phases of the LLVM compilation
22 The LLVM code representation is designed to be used in three different
23 forms: as an in-memory compiler IR, as an on-disk bitcode representation
24 (suitable for fast loading by a Just-In-Time compiler), and as a human
25 readable assembly language representation. This allows LLVM to provide a
26 powerful intermediate representation for efficient compiler
27 transformations and analysis, while providing a natural means to debug
28 and visualize the transformations. The three different forms of LLVM are
29 all equivalent. This document describes the human readable
30 representation and notation.
32 The LLVM representation aims to be light-weight and low-level while
33 being expressive, typed, and extensible at the same time. It aims to be
34 a "universal IR" of sorts, by being at a low enough level that
35 high-level ideas may be cleanly mapped to it (similar to how
36 microprocessors are "universal IR's", allowing many source languages to
37 be mapped to them). By providing type information, LLVM can be used as
38 the target of optimizations: for example, through pointer analysis, it
39 can be proven that a C automatic variable is never accessed outside of
40 the current function, allowing it to be promoted to a simple SSA value
41 instead of a memory location.
48 It is important to note that this document describes 'well formed' LLVM
49 assembly language. There is a difference between what the parser accepts
50 and what is considered 'well formed'. For example, the following
51 instruction is syntactically okay, but not well formed:
57 because the definition of ``%x`` does not dominate all of its uses. The
58 LLVM infrastructure provides a verification pass that may be used to
59 verify that an LLVM module is well formed. This pass is automatically
60 run by the parser after parsing input assembly and by the optimizer
61 before it outputs bitcode. The violations pointed out by the verifier
62 pass indicate bugs in transformation passes or input to the parser.
69 LLVM identifiers come in two basic types: global and local. Global
70 identifiers (functions, global variables) begin with the ``'@'``
71 character. Local identifiers (register names, types) begin with the
72 ``'%'`` character. Additionally, there are three different formats for
73 identifiers, for different purposes:
75 #. Named values are represented as a string of characters with their
76 prefix. For example, ``%foo``, ``@DivisionByZero``,
77 ``%a.really.long.identifier``. The actual regular expression used is
78 '``[%@][-a-zA-Z$._][-a-zA-Z$._0-9]*``'. Identifiers that require other
79 characters in their names can be surrounded with quotes. Special
80 characters may be escaped using ``"\xx"`` where ``xx`` is the ASCII
81 code for the character in hexadecimal. In this way, any character can
82 be used in a name value, even quotes themselves. The ``"\01"`` prefix
83 can be used on global variables to suppress mangling.
84 #. Unnamed values are represented as an unsigned numeric value with
85 their prefix. For example, ``%12``, ``@2``, ``%44``.
86 #. Constants, which are described in the section Constants_ below.
88 LLVM requires that values start with a prefix for two reasons: Compilers
89 don't need to worry about name clashes with reserved words, and the set
90 of reserved words may be expanded in the future without penalty.
91 Additionally, unnamed identifiers allow a compiler to quickly come up
92 with a temporary variable without having to avoid symbol table
95 Reserved words in LLVM are very similar to reserved words in other
96 languages. There are keywords for different opcodes ('``add``',
97 '``bitcast``', '``ret``', etc...), for primitive type names ('``void``',
98 '``i32``', etc...), and others. These reserved words cannot conflict
99 with variable names, because none of them start with a prefix character
100 (``'%'`` or ``'@'``).
102 Here is an example of LLVM code to multiply the integer variable
109 %result = mul i32 %X, 8
111 After strength reduction:
115 %result = shl i32 %X, 3
121 %0 = add i32 %X, %X ; yields i32:%0
122 %1 = add i32 %0, %0 ; yields i32:%1
123 %result = add i32 %1, %1
125 This last way of multiplying ``%X`` by 8 illustrates several important
126 lexical features of LLVM:
128 #. Comments are delimited with a '``;``' and go until the end of line.
129 #. Unnamed temporaries are created when the result of a computation is
130 not assigned to a named value.
131 #. Unnamed temporaries are numbered sequentially (using a per-function
132 incrementing counter, starting with 0). Note that basic blocks and unnamed
133 function parameters are included in this numbering. For example, if the
134 entry basic block is not given a label name and all function parameters are
135 named, then it will get number 0.
137 It also shows a convention that we follow in this document. When
138 demonstrating instructions, we will follow an instruction with a comment
139 that defines the type and name of value produced.
147 LLVM programs are composed of ``Module``'s, each of which is a
148 translation unit of the input programs. Each module consists of
149 functions, global variables, and symbol table entries. Modules may be
150 combined together with the LLVM linker, which merges function (and
151 global variable) definitions, resolves forward declarations, and merges
152 symbol table entries. Here is an example of the "hello world" module:
156 ; Declare the string constant as a global constant.
157 @.str = private unnamed_addr constant [13 x i8] c"hello world\0A\00"
159 ; External declaration of the puts function
160 declare i32 @puts(i8* nocapture) nounwind
162 ; Definition of main function
163 define i32 @main() { ; i32()*
164 ; Convert [13 x i8]* to i8 *...
165 %cast210 = getelementptr [13 x i8], [13 x i8]* @.str, i64 0, i64 0
167 ; Call puts function to write out the string to stdout.
168 call i32 @puts(i8* %cast210)
173 !0 = !{i32 42, null, !"string"}
176 This example is made up of a :ref:`global variable <globalvars>` named
177 "``.str``", an external declaration of the "``puts``" function, a
178 :ref:`function definition <functionstructure>` for "``main``" and
179 :ref:`named metadata <namedmetadatastructure>` "``foo``".
181 In general, a module is made up of a list of global values (where both
182 functions and global variables are global values). Global values are
183 represented by a pointer to a memory location (in this case, a pointer
184 to an array of char, and a pointer to a function), and have one of the
185 following :ref:`linkage types <linkage>`.
192 All Global Variables and Functions have one of the following types of
196 Global values with "``private``" linkage are only directly
197 accessible by objects in the current module. In particular, linking
198 code into a module with an private global value may cause the
199 private to be renamed as necessary to avoid collisions. Because the
200 symbol is private to the module, all references can be updated. This
201 doesn't show up in any symbol table in the object file.
203 Similar to private, but the value shows as a local symbol
204 (``STB_LOCAL`` in the case of ELF) in the object file. This
205 corresponds to the notion of the '``static``' keyword in C.
206 ``available_externally``
207 Globals with "``available_externally``" linkage are never emitted
208 into the object file corresponding to the LLVM module. They exist to
209 allow inlining and other optimizations to take place given knowledge
210 of the definition of the global, which is known to be somewhere
211 outside the module. Globals with ``available_externally`` linkage
212 are allowed to be discarded at will, and are otherwise the same as
213 ``linkonce_odr``. This linkage type is only allowed on definitions,
216 Globals with "``linkonce``" linkage are merged with other globals of
217 the same name when linkage occurs. This can be used to implement
218 some forms of inline functions, templates, or other code which must
219 be generated in each translation unit that uses it, but where the
220 body may be overridden with a more definitive definition later.
221 Unreferenced ``linkonce`` globals are allowed to be discarded. Note
222 that ``linkonce`` linkage does not actually allow the optimizer to
223 inline the body of this function into callers because it doesn't
224 know if this definition of the function is the definitive definition
225 within the program or whether it will be overridden by a stronger
226 definition. To enable inlining and other optimizations, use
227 "``linkonce_odr``" linkage.
229 "``weak``" linkage has the same merging semantics as ``linkonce``
230 linkage, except that unreferenced globals with ``weak`` linkage may
231 not be discarded. This is used for globals that are declared "weak"
234 "``common``" linkage is most similar to "``weak``" linkage, but they
235 are used for tentative definitions in C, such as "``int X;``" at
236 global scope. Symbols with "``common``" linkage are merged in the
237 same way as ``weak symbols``, and they may not be deleted if
238 unreferenced. ``common`` symbols may not have an explicit section,
239 must have a zero initializer, and may not be marked
240 ':ref:`constant <globalvars>`'. Functions and aliases may not have
243 .. _linkage_appending:
246 "``appending``" linkage may only be applied to global variables of
247 pointer to array type. When two global variables with appending
248 linkage are linked together, the two global arrays are appended
249 together. This is the LLVM, typesafe, equivalent of having the
250 system linker append together "sections" with identical names when
253 The semantics of this linkage follow the ELF object file model: the
254 symbol is weak until linked, if not linked, the symbol becomes null
255 instead of being an undefined reference.
256 ``linkonce_odr``, ``weak_odr``
257 Some languages allow differing globals to be merged, such as two
258 functions with different semantics. Other languages, such as
259 ``C++``, ensure that only equivalent globals are ever merged (the
260 "one definition rule" --- "ODR"). Such languages can use the
261 ``linkonce_odr`` and ``weak_odr`` linkage types to indicate that the
262 global will only be merged with equivalent globals. These linkage
263 types are otherwise the same as their non-``odr`` versions.
265 If none of the above identifiers are used, the global is externally
266 visible, meaning that it participates in linkage and can be used to
267 resolve external symbol references.
269 It is illegal for a function *declaration* to have any linkage type
270 other than ``external`` or ``extern_weak``.
277 LLVM :ref:`functions <functionstructure>`, :ref:`calls <i_call>` and
278 :ref:`invokes <i_invoke>` can all have an optional calling convention
279 specified for the call. The calling convention of any pair of dynamic
280 caller/callee must match, or the behavior of the program is undefined.
281 The following calling conventions are supported by LLVM, and more may be
284 "``ccc``" - The C calling convention
285 This calling convention (the default if no other calling convention
286 is specified) matches the target C calling conventions. This calling
287 convention supports varargs function calls and tolerates some
288 mismatch in the declared prototype and implemented declaration of
289 the function (as does normal C).
290 "``fastcc``" - The fast calling convention
291 This calling convention attempts to make calls as fast as possible
292 (e.g. by passing things in registers). This calling convention
293 allows the target to use whatever tricks it wants to produce fast
294 code for the target, without having to conform to an externally
295 specified ABI (Application Binary Interface). `Tail calls can only
296 be optimized when this, the GHC or the HiPE convention is
297 used. <CodeGenerator.html#id80>`_ This calling convention does not
298 support varargs and requires the prototype of all callees to exactly
299 match the prototype of the function definition.
300 "``coldcc``" - The cold calling convention
301 This calling convention attempts to make code in the caller as
302 efficient as possible under the assumption that the call is not
303 commonly executed. As such, these calls often preserve all registers
304 so that the call does not break any live ranges in the caller side.
305 This calling convention does not support varargs and requires the
306 prototype of all callees to exactly match the prototype of the
307 function definition. Furthermore the inliner doesn't consider such function
309 "``cc 10``" - GHC convention
310 This calling convention has been implemented specifically for use by
311 the `Glasgow Haskell Compiler (GHC) <http://www.haskell.org/ghc>`_.
312 It passes everything in registers, going to extremes to achieve this
313 by disabling callee save registers. This calling convention should
314 not be used lightly but only for specific situations such as an
315 alternative to the *register pinning* performance technique often
316 used when implementing functional programming languages. At the
317 moment only X86 supports this convention and it has the following
320 - On *X86-32* only supports up to 4 bit type parameters. No
321 floating point types are supported.
322 - On *X86-64* only supports up to 10 bit type parameters and 6
323 floating point parameters.
325 This calling convention supports `tail call
326 optimization <CodeGenerator.html#id80>`_ but requires both the
327 caller and callee are using it.
328 "``cc 11``" - The HiPE calling convention
329 This calling convention has been implemented specifically for use by
330 the `High-Performance Erlang
331 (HiPE) <http://www.it.uu.se/research/group/hipe/>`_ compiler, *the*
332 native code compiler of the `Ericsson's Open Source Erlang/OTP
333 system <http://www.erlang.org/download.shtml>`_. It uses more
334 registers for argument passing than the ordinary C calling
335 convention and defines no callee-saved registers. The calling
336 convention properly supports `tail call
337 optimization <CodeGenerator.html#id80>`_ but requires that both the
338 caller and the callee use it. It uses a *register pinning*
339 mechanism, similar to GHC's convention, for keeping frequently
340 accessed runtime components pinned to specific hardware registers.
341 At the moment only X86 supports this convention (both 32 and 64
343 "``webkit_jscc``" - WebKit's JavaScript calling convention
344 This calling convention has been implemented for `WebKit FTL JIT
345 <https://trac.webkit.org/wiki/FTLJIT>`_. It passes arguments on the
346 stack right to left (as cdecl does), and returns a value in the
347 platform's customary return register.
348 "``anyregcc``" - Dynamic calling convention for code patching
349 This is a special convention that supports patching an arbitrary code
350 sequence in place of a call site. This convention forces the call
351 arguments into registers but allows them to be dynamically
352 allocated. This can currently only be used with calls to
353 llvm.experimental.patchpoint because only this intrinsic records
354 the location of its arguments in a side table. See :doc:`StackMaps`.
355 "``preserve_mostcc``" - The `PreserveMost` calling convention
356 This calling convention attempts to make the code in the caller as
357 unintrusive as possible. This convention behaves identically to the `C`
358 calling convention on how arguments and return values are passed, but it
359 uses a different set of caller/callee-saved registers. This alleviates the
360 burden of saving and recovering a large register set before and after the
361 call in the caller. If the arguments are passed in callee-saved registers,
362 then they will be preserved by the callee across the call. This doesn't
363 apply for values returned in callee-saved registers.
365 - On X86-64 the callee preserves all general purpose registers, except for
366 R11. R11 can be used as a scratch register. Floating-point registers
367 (XMMs/YMMs) are not preserved and need to be saved by the caller.
369 The idea behind this convention is to support calls to runtime functions
370 that have a hot path and a cold path. The hot path is usually a small piece
371 of code that doesn't use many registers. The cold path might need to call out to
372 another function and therefore only needs to preserve the caller-saved
373 registers, which haven't already been saved by the caller. The
374 `PreserveMost` calling convention is very similar to the `cold` calling
375 convention in terms of caller/callee-saved registers, but they are used for
376 different types of function calls. `coldcc` is for function calls that are
377 rarely executed, whereas `preserve_mostcc` function calls are intended to be
378 on the hot path and definitely executed a lot. Furthermore `preserve_mostcc`
379 doesn't prevent the inliner from inlining the function call.
381 This calling convention will be used by a future version of the ObjectiveC
382 runtime and should therefore still be considered experimental at this time.
383 Although this convention was created to optimize certain runtime calls to
384 the ObjectiveC runtime, it is not limited to this runtime and might be used
385 by other runtimes in the future too. The current implementation only
386 supports X86-64, but the intention is to support more architectures in the
388 "``preserve_allcc``" - The `PreserveAll` calling convention
389 This calling convention attempts to make the code in the caller even less
390 intrusive than the `PreserveMost` calling convention. This calling
391 convention also behaves identical to the `C` calling convention on how
392 arguments and return values are passed, but it uses a different set of
393 caller/callee-saved registers. This removes the burden of saving and
394 recovering a large register set before and after the call in the caller. If
395 the arguments are passed in callee-saved registers, then they will be
396 preserved by the callee across the call. This doesn't apply for values
397 returned in callee-saved registers.
399 - On X86-64 the callee preserves all general purpose registers, except for
400 R11. R11 can be used as a scratch register. Furthermore it also preserves
401 all floating-point registers (XMMs/YMMs).
403 The idea behind this convention is to support calls to runtime functions
404 that don't need to call out to any other functions.
406 This calling convention, like the `PreserveMost` calling convention, will be
407 used by a future version of the ObjectiveC runtime and should be considered
408 experimental at this time.
409 "``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 an alias, but then it only governs how
495 the alias is accessed. It will not have any effect in the aliasee.
497 For platforms without linker support of ELF TLS model, the -femulated-tls
498 flag can be used to generate GCC compatible emulated TLS code.
505 LLVM IR allows you to specify both "identified" and "literal" :ref:`structure
506 types <t_struct>`. Literal types are uniqued structurally, but identified types
507 are never uniqued. An :ref:`opaque structural type <t_opaque>` can also be used
508 to forward declare a type that is not yet available.
510 An example of an identified structure specification is:
514 %mytype = type { %mytype*, i32 }
516 Prior to the LLVM 3.0 release, identified types were structurally uniqued. Only
517 literal types are uniqued in recent versions of LLVM.
524 Global variables define regions of memory allocated at compilation time
527 Global variable definitions must be initialized.
529 Global variables in other translation units can also be declared, in which
530 case they don't have an initializer.
532 Either global variable definitions or declarations may have an explicit section
533 to be placed in and may have an optional explicit alignment specified.
535 A variable may be defined as a global ``constant``, which indicates that
536 the contents of the variable will **never** be modified (enabling better
537 optimization, allowing the global data to be placed in the read-only
538 section of an executable, etc). Note that variables that need runtime
539 initialization cannot be marked ``constant`` as there is a store to the
542 LLVM explicitly allows *declarations* of global variables to be marked
543 constant, even if the final definition of the global is not. This
544 capability can be used to enable slightly better optimization of the
545 program, but requires the language definition to guarantee that
546 optimizations based on the 'constantness' are valid for the translation
547 units that do not include the definition.
549 As SSA values, global variables define pointer values that are in scope
550 (i.e. they dominate) all basic blocks in the program. Global variables
551 always define a pointer to their "content" type because they describe a
552 region of memory, and all memory objects in LLVM are accessed through
555 Global variables can be marked with ``unnamed_addr`` which indicates
556 that the address is not significant, only the content. Constants marked
557 like this can be merged with other constants if they have the same
558 initializer. Note that a constant with significant address *can* be
559 merged with a ``unnamed_addr`` constant, the result being a constant
560 whose address is significant.
562 A global variable may be declared to reside in a target-specific
563 numbered address space. For targets that support them, address spaces
564 may affect how optimizations are performed and/or what target
565 instructions are used to access the variable. The default address space
566 is zero. The address space qualifier must precede any other attributes.
568 LLVM allows an explicit section to be specified for globals. If the
569 target supports it, it will emit globals to the section specified.
570 Additionally, the global can placed in a comdat if the target has the necessary
573 By default, global initializers are optimized by assuming that global
574 variables defined within the module are not modified from their
575 initial values before the start of the global initializer. This is
576 true even for variables potentially accessible from outside the
577 module, including those with external linkage or appearing in
578 ``@llvm.used`` or dllexported variables. This assumption may be suppressed
579 by marking the variable with ``externally_initialized``.
581 An explicit alignment may be specified for a global, which must be a
582 power of 2. If not present, or if the alignment is set to zero, the
583 alignment of the global is set by the target to whatever it feels
584 convenient. If an explicit alignment is specified, the global is forced
585 to have exactly that alignment. Targets and optimizers are not allowed
586 to over-align the global if the global has an assigned section. In this
587 case, the extra alignment could be observable: for example, code could
588 assume that the globals are densely packed in their section and try to
589 iterate over them as an array, alignment padding would break this
590 iteration. The maximum alignment is ``1 << 29``.
592 Globals can also have a :ref:`DLL storage class <dllstorageclass>`.
594 Variables and aliases can have a
595 :ref:`Thread Local Storage Model <tls_model>`.
599 [@<GlobalVarName> =] [Linkage] [Visibility] [DLLStorageClass] [ThreadLocal]
600 [unnamed_addr] [AddrSpace] [ExternallyInitialized]
601 <global | constant> <Type> [<InitializerConstant>]
602 [, section "name"] [, comdat [($name)]]
603 [, align <Alignment>]
605 For example, the following defines a global in a numbered address space
606 with an initializer, section, and alignment:
610 @G = addrspace(5) constant float 1.0, section "foo", align 4
612 The following example just declares a global variable
616 @G = external global i32
618 The following example defines a thread-local global with the
619 ``initialexec`` TLS model:
623 @G = thread_local(initialexec) global i32 0, align 4
625 .. _functionstructure:
630 LLVM function definitions consist of the "``define``" keyword, an
631 optional :ref:`linkage type <linkage>`, an optional :ref:`visibility
632 style <visibility>`, an optional :ref:`DLL storage class <dllstorageclass>`,
633 an optional :ref:`calling convention <callingconv>`,
634 an optional ``unnamed_addr`` attribute, a return type, an optional
635 :ref:`parameter attribute <paramattrs>` for the return type, a function
636 name, a (possibly empty) argument list (each with optional :ref:`parameter
637 attributes <paramattrs>`), optional :ref:`function attributes <fnattrs>`,
638 an optional section, an optional alignment,
639 an optional :ref:`comdat <langref_comdats>`,
640 an optional :ref:`garbage collector name <gc>`, an optional :ref:`prefix <prefixdata>`,
641 an optional :ref:`prologue <prologuedata>`,
642 an optional :ref:`personality <personalityfn>`,
643 an opening curly brace, a list of basic blocks, and a closing curly brace.
645 LLVM function declarations consist of the "``declare``" keyword, an
646 optional :ref:`linkage type <linkage>`, an optional :ref:`visibility
647 style <visibility>`, an optional :ref:`DLL storage class <dllstorageclass>`,
648 an optional :ref:`calling convention <callingconv>`,
649 an optional ``unnamed_addr`` attribute, a return type, an optional
650 :ref:`parameter attribute <paramattrs>` for the return type, a function
651 name, a possibly empty list of arguments, an optional alignment, an optional
652 :ref:`garbage collector name <gc>`, an optional :ref:`prefix <prefixdata>`,
653 and an optional :ref:`prologue <prologuedata>`.
655 A function definition contains a list of basic blocks, forming the CFG (Control
656 Flow Graph) for the function. Each basic block may optionally start with a label
657 (giving the basic block a symbol table entry), contains a list of instructions,
658 and ends with a :ref:`terminator <terminators>` instruction (such as a branch or
659 function return). If an explicit label is not provided, a block is assigned an
660 implicit numbered label, using the next value from the same counter as used for
661 unnamed temporaries (:ref:`see above<identifiers>`). For example, if a function
662 entry block does not have an explicit label, it will be assigned label "%0",
663 then the first unnamed temporary in that block will be "%1", etc.
665 The first basic block in a function is special in two ways: it is
666 immediately executed on entrance to the function, and it is not allowed
667 to have predecessor basic blocks (i.e. there can not be any branches to
668 the entry block of a function). Because the block can have no
669 predecessors, it also cannot have any :ref:`PHI nodes <i_phi>`.
671 LLVM allows an explicit section to be specified for functions. If the
672 target supports it, it will emit functions to the section specified.
673 Additionally, the function can be placed in a COMDAT.
675 An explicit alignment may be specified for a function. If not present,
676 or if the alignment is set to zero, the alignment of the function is set
677 by the target to whatever it feels convenient. If an explicit alignment
678 is specified, the function is forced to have at least that much
679 alignment. All alignments must be a power of 2.
681 If the ``unnamed_addr`` attribute is given, the address is known to not
682 be significant and two identical functions can be merged.
686 define [linkage] [visibility] [DLLStorageClass]
688 <ResultType> @<FunctionName> ([argument list])
689 [unnamed_addr] [fn Attrs] [section "name"] [comdat [($name)]]
690 [align N] [gc] [prefix Constant] [prologue Constant]
691 [personality Constant] { ... }
693 The argument list is a comma separated sequence of arguments where each
694 argument is of the following form:
698 <type> [parameter Attrs] [name]
706 Aliases, unlike function or variables, don't create any new data. They
707 are just a new symbol and metadata for an existing position.
709 Aliases have a name and an aliasee that is either a global value or a
712 Aliases may have an optional :ref:`linkage type <linkage>`, an optional
713 :ref:`visibility style <visibility>`, an optional :ref:`DLL storage class
714 <dllstorageclass>` and an optional :ref:`tls model <tls_model>`.
718 @<Name> = [Linkage] [Visibility] [DLLStorageClass] [ThreadLocal] [unnamed_addr] alias <AliaseeTy> @<Aliasee>
720 The linkage must be one of ``private``, ``internal``, ``linkonce``, ``weak``,
721 ``linkonce_odr``, ``weak_odr``, ``external``. Note that some system linkers
722 might not correctly handle dropping a weak symbol that is aliased.
724 Aliases that are not ``unnamed_addr`` are guaranteed to have the same address as
725 the aliasee expression. ``unnamed_addr`` ones are only guaranteed to point
728 Since aliases are only a second name, some restrictions apply, of which
729 some can only be checked when producing an object file:
731 * The expression defining the aliasee must be computable at assembly
732 time. Since it is just a name, no relocations can be used.
734 * No alias in the expression can be weak as the possibility of the
735 intermediate alias being overridden cannot be represented in an
738 * No global value in the expression can be a declaration, since that
739 would require a relocation, which is not possible.
746 Comdat IR provides access to COFF and ELF object file COMDAT functionality.
748 Comdats have a name which represents the COMDAT key. All global objects that
749 specify this key will only end up in the final object file if the linker chooses
750 that key over some other key. Aliases are placed in the same COMDAT that their
751 aliasee computes to, if any.
753 Comdats have a selection kind to provide input on how the linker should
754 choose between keys in two different object files.
758 $<Name> = comdat SelectionKind
760 The selection kind must be one of the following:
763 The linker may choose any COMDAT key, the choice is arbitrary.
765 The linker may choose any COMDAT key but the sections must contain the
768 The linker will choose the section containing the largest COMDAT key.
770 The linker requires that only section with this COMDAT key exist.
772 The linker may choose any COMDAT key but the sections must contain the
775 Note that the Mach-O platform doesn't support COMDATs and ELF only supports
776 ``any`` as a selection kind.
778 Here is an example of a COMDAT group where a function will only be selected if
779 the COMDAT key's section is the largest:
783 $foo = comdat largest
784 @foo = global i32 2, comdat($foo)
786 define void @bar() comdat($foo) {
790 As a syntactic sugar the ``$name`` can be omitted if the name is the same as
796 @foo = global i32 2, comdat
799 In a COFF object file, this will create a COMDAT section with selection kind
800 ``IMAGE_COMDAT_SELECT_LARGEST`` containing the contents of the ``@foo`` symbol
801 and another COMDAT section with selection kind
802 ``IMAGE_COMDAT_SELECT_ASSOCIATIVE`` which is associated with the first COMDAT
803 section and contains the contents of the ``@bar`` symbol.
805 There are some restrictions on the properties of the global object.
806 It, or an alias to it, must have the same name as the COMDAT group when
808 The contents and size of this object may be used during link-time to determine
809 which COMDAT groups get selected depending on the selection kind.
810 Because the name of the object must match the name of the COMDAT group, the
811 linkage of the global object must not be local; local symbols can get renamed
812 if a collision occurs in the symbol table.
814 The combined use of COMDATS and section attributes may yield surprising results.
821 @g1 = global i32 42, section "sec", comdat($foo)
822 @g2 = global i32 42, section "sec", comdat($bar)
824 From the object file perspective, this requires the creation of two sections
825 with the same name. This is necessary because both globals belong to different
826 COMDAT groups and COMDATs, at the object file level, are represented by
829 Note that certain IR constructs like global variables and functions may
830 create COMDATs in the object file in addition to any which are specified using
831 COMDAT IR. This arises when the code generator is configured to emit globals
832 in individual sections (e.g. when `-data-sections` or `-function-sections`
833 is supplied to `llc`).
835 .. _namedmetadatastructure:
840 Named metadata is a collection of metadata. :ref:`Metadata
841 nodes <metadata>` (but not metadata strings) are the only valid
842 operands for a named metadata.
844 #. Named metadata are represented as a string of characters with the
845 metadata prefix. The rules for metadata names are the same as for
846 identifiers, but quoted names are not allowed. ``"\xx"`` type escapes
847 are still valid, which allows any character to be part of a name.
851 ; Some unnamed metadata nodes, which are referenced by the named metadata.
856 !name = !{!0, !1, !2}
863 The return type and each parameter of a function type may have a set of
864 *parameter attributes* associated with them. Parameter attributes are
865 used to communicate additional information about the result or
866 parameters of a function. Parameter attributes are considered to be part
867 of the function, not of the function type, so functions with different
868 parameter attributes can have the same function type.
870 Parameter attributes are simple keywords that follow the type specified.
871 If multiple parameter attributes are needed, they are space separated.
876 declare i32 @printf(i8* noalias nocapture, ...)
877 declare i32 @atoi(i8 zeroext)
878 declare signext i8 @returns_signed_char()
880 Note that any attributes for the function result (``nounwind``,
881 ``readonly``) come immediately after the argument list.
883 Currently, only the following parameter attributes are defined:
886 This indicates to the code generator that the parameter or return
887 value should be zero-extended to the extent required by the target's
888 ABI (which is usually 32-bits, but is 8-bits for a i1 on x86-64) by
889 the caller (for a parameter) or the callee (for a return value).
891 This indicates to the code generator that the parameter or return
892 value should be sign-extended to the extent required by the target's
893 ABI (which is usually 32-bits) by the caller (for a parameter) or
894 the callee (for a return value).
896 This indicates that this parameter or return value should be treated
897 in a special target-dependent fashion while emitting code for
898 a function call or return (usually, by putting it in a register as
899 opposed to memory, though some targets use it to distinguish between
900 two different kinds of registers). Use of this attribute is
903 This indicates that the pointer parameter should really be passed by
904 value to the function. The attribute implies that a hidden copy of
905 the pointee is made between the caller and the callee, so the callee
906 is unable to modify the value in the caller. This attribute is only
907 valid on LLVM pointer arguments. It is generally used to pass
908 structs and arrays by value, but is also valid on pointers to
909 scalars. The copy is considered to belong to the caller not the
910 callee (for example, ``readonly`` functions should not write to
911 ``byval`` parameters). This is not a valid attribute for return
914 The byval attribute also supports specifying an alignment with the
915 align attribute. It indicates the alignment of the stack slot to
916 form and the known alignment of the pointer specified to the call
917 site. If the alignment is not specified, then the code generator
918 makes a target-specific assumption.
924 The ``inalloca`` argument attribute allows the caller to take the
925 address of outgoing stack arguments. An ``inalloca`` argument must
926 be a pointer to stack memory produced by an ``alloca`` instruction.
927 The alloca, or argument allocation, must also be tagged with the
928 inalloca keyword. Only the last argument may have the ``inalloca``
929 attribute, and that argument is guaranteed to be passed in memory.
931 An argument allocation may be used by a call at most once because
932 the call may deallocate it. The ``inalloca`` attribute cannot be
933 used in conjunction with other attributes that affect argument
934 storage, like ``inreg``, ``nest``, ``sret``, or ``byval``. The
935 ``inalloca`` attribute also disables LLVM's implicit lowering of
936 large aggregate return values, which means that frontend authors
937 must lower them with ``sret`` pointers.
939 When the call site is reached, the argument allocation must have
940 been the most recent stack allocation that is still live, or the
941 results are undefined. It is possible to allocate additional stack
942 space after an argument allocation and before its call site, but it
943 must be cleared off with :ref:`llvm.stackrestore
946 See :doc:`InAlloca` for more information on how to use this
950 This indicates that the pointer parameter specifies the address of a
951 structure that is the return value of the function in the source
952 program. This pointer must be guaranteed by the caller to be valid:
953 loads and stores to the structure may be assumed by the callee
954 not to trap and to be properly aligned. This may only be applied to
955 the first parameter. This is not a valid attribute for return
959 This indicates that the pointer value may be assumed by the optimizer to
960 have the specified alignment.
962 Note that this attribute has additional semantics when combined with the
968 This indicates that objects accessed via pointer values
969 :ref:`based <pointeraliasing>` on the argument or return value are not also
970 accessed, during the execution of the function, via pointer values not
971 *based* on the argument or return value. The attribute on a return value
972 also has additional semantics described below. The caller shares the
973 responsibility with the callee for ensuring that these requirements are met.
974 For further details, please see the discussion of the NoAlias response in
975 :ref:`alias analysis <Must, May, or No>`.
977 Note that this definition of ``noalias`` is intentionally similar
978 to the definition of ``restrict`` in C99 for function arguments.
980 For function return values, C99's ``restrict`` is not meaningful,
981 while LLVM's ``noalias`` is. Furthermore, the semantics of the ``noalias``
982 attribute on return values are stronger than the semantics of the attribute
983 when used on function arguments. On function return values, the ``noalias``
984 attribute indicates that the function acts like a system memory allocation
985 function, returning a pointer to allocated storage disjoint from the
986 storage for any other object accessible to the caller.
989 This indicates that the callee does not make any copies of the
990 pointer that outlive the callee itself. This is not a valid
991 attribute for return values.
996 This indicates that the pointer parameter can be excised using the
997 :ref:`trampoline intrinsics <int_trampoline>`. This is not a valid
998 attribute for return values and can only be applied to one parameter.
1001 This indicates that the function always returns the argument as its return
1002 value. This is an optimization hint to the code generator when generating
1003 the caller, allowing tail call optimization and omission of register saves
1004 and restores in some cases; it is not checked or enforced when generating
1005 the callee. The parameter and the function return type must be valid
1006 operands for the :ref:`bitcast instruction <i_bitcast>`. This is not a
1007 valid attribute for return values and can only be applied to one parameter.
1010 This indicates that the parameter or return pointer is not null. This
1011 attribute may only be applied to pointer typed parameters. This is not
1012 checked or enforced by LLVM, the caller must ensure that the pointer
1013 passed in is non-null, or the callee must ensure that the returned pointer
1016 ``dereferenceable(<n>)``
1017 This indicates that the parameter or return pointer is dereferenceable. This
1018 attribute may only be applied to pointer typed parameters. A pointer that
1019 is dereferenceable can be loaded from speculatively without a risk of
1020 trapping. The number of bytes known to be dereferenceable must be provided
1021 in parentheses. It is legal for the number of bytes to be less than the
1022 size of the pointee type. The ``nonnull`` attribute does not imply
1023 dereferenceability (consider a pointer to one element past the end of an
1024 array), however ``dereferenceable(<n>)`` does imply ``nonnull`` in
1025 ``addrspace(0)`` (which is the default address space).
1027 ``dereferenceable_or_null(<n>)``
1028 This indicates that the parameter or return value isn't both
1029 non-null and non-dereferenceable (up to ``<n>`` bytes) at the same
1030 time. All non-null pointers tagged with
1031 ``dereferenceable_or_null(<n>)`` are ``dereferenceable(<n>)``.
1032 For address space 0 ``dereferenceable_or_null(<n>)`` implies that
1033 a pointer is exactly one of ``dereferenceable(<n>)`` or ``null``,
1034 and in other address spaces ``dereferenceable_or_null(<n>)``
1035 implies that a pointer is at least one of ``dereferenceable(<n>)``
1036 or ``null`` (i.e. it may be both ``null`` and
1037 ``dereferenceable(<n>)``). This attribute may only be applied to
1038 pointer typed parameters.
1042 Garbage Collector Strategy Names
1043 --------------------------------
1045 Each function may specify a garbage collector strategy name, which is simply a
1048 .. code-block:: llvm
1050 define void @f() gc "name" { ... }
1052 The supported values of *name* includes those :ref:`built in to LLVM
1053 <builtin-gc-strategies>` and any provided by loaded plugins. Specifying a GC
1054 strategy will cause the compiler to alter its output in order to support the
1055 named garbage collection algorithm. Note that LLVM itself does not contain a
1056 garbage collector, this functionality is restricted to generating machine code
1057 which can interoperate with a collector provided externally.
1064 Prefix data is data associated with a function which the code
1065 generator will emit immediately before the function's entrypoint.
1066 The purpose of this feature is to allow frontends to associate
1067 language-specific runtime metadata with specific functions and make it
1068 available through the function pointer while still allowing the
1069 function pointer to be called.
1071 To access the data for a given function, a program may bitcast the
1072 function pointer to a pointer to the constant's type and dereference
1073 index -1. This implies that the IR symbol points just past the end of
1074 the prefix data. For instance, take the example of a function annotated
1075 with a single ``i32``,
1077 .. code-block:: llvm
1079 define void @f() prefix i32 123 { ... }
1081 The prefix data can be referenced as,
1083 .. code-block:: llvm
1085 %0 = bitcast void* () @f to i32*
1086 %a = getelementptr inbounds i32, i32* %0, i32 -1
1087 %b = load i32, i32* %a
1089 Prefix data is laid out as if it were an initializer for a global variable
1090 of the prefix data's type. The function will be placed such that the
1091 beginning of the prefix data is aligned. This means that if the size
1092 of the prefix data is not a multiple of the alignment size, the
1093 function's entrypoint will not be aligned. If alignment of the
1094 function's entrypoint is desired, padding must be added to the prefix
1097 A function may have prefix data but no body. This has similar semantics
1098 to the ``available_externally`` linkage in that the data may be used by the
1099 optimizers but will not be emitted in the object file.
1106 The ``prologue`` attribute allows arbitrary code (encoded as bytes) to
1107 be inserted prior to the function body. This can be used for enabling
1108 function hot-patching and instrumentation.
1110 To maintain the semantics of ordinary function calls, the prologue data must
1111 have a particular format. Specifically, it must begin with a sequence of
1112 bytes which decode to a sequence of machine instructions, valid for the
1113 module's target, which transfer control to the point immediately succeeding
1114 the prologue data, without performing any other visible action. This allows
1115 the inliner and other passes to reason about the semantics of the function
1116 definition without needing to reason about the prologue data. Obviously this
1117 makes the format of the prologue data highly target dependent.
1119 A trivial example of valid prologue data for the x86 architecture is ``i8 144``,
1120 which encodes the ``nop`` instruction:
1122 .. code-block:: llvm
1124 define void @f() prologue i8 144 { ... }
1126 Generally prologue data can be formed by encoding a relative branch instruction
1127 which skips the metadata, as in this example of valid prologue data for the
1128 x86_64 architecture, where the first two bytes encode ``jmp .+10``:
1130 .. code-block:: llvm
1132 %0 = type <{ i8, i8, i8* }>
1134 define void @f() prologue %0 <{ i8 235, i8 8, i8* @md}> { ... }
1136 A function may have prologue data but no body. This has similar semantics
1137 to the ``available_externally`` linkage in that the data may be used by the
1138 optimizers but will not be emitted in the object file.
1142 Personality Function
1143 --------------------
1145 The ``personality`` attribute permits functions to specify what function
1146 to use for exception handling.
1153 Attribute groups are groups of attributes that are referenced by objects within
1154 the IR. They are important for keeping ``.ll`` files readable, because a lot of
1155 functions will use the same set of attributes. In the degenerative case of a
1156 ``.ll`` file that corresponds to a single ``.c`` file, the single attribute
1157 group will capture the important command line flags used to build that file.
1159 An attribute group is a module-level object. To use an attribute group, an
1160 object references the attribute group's ID (e.g. ``#37``). An object may refer
1161 to more than one attribute group. In that situation, the attributes from the
1162 different groups are merged.
1164 Here is an example of attribute groups for a function that should always be
1165 inlined, has a stack alignment of 4, and which shouldn't use SSE instructions:
1167 .. code-block:: llvm
1169 ; Target-independent attributes:
1170 attributes #0 = { alwaysinline alignstack=4 }
1172 ; Target-dependent attributes:
1173 attributes #1 = { "no-sse" }
1175 ; Function @f has attributes: alwaysinline, alignstack=4, and "no-sse".
1176 define void @f() #0 #1 { ... }
1183 Function attributes are set to communicate additional information about
1184 a function. Function attributes are considered to be part of the
1185 function, not of the function type, so functions with different function
1186 attributes can have the same function type.
1188 Function attributes are simple keywords that follow the type specified.
1189 If multiple attributes are needed, they are space separated. For
1192 .. code-block:: llvm
1194 define void @f() noinline { ... }
1195 define void @f() alwaysinline { ... }
1196 define void @f() alwaysinline optsize { ... }
1197 define void @f() optsize { ... }
1200 This attribute indicates that, when emitting the prologue and
1201 epilogue, the backend should forcibly align the stack pointer.
1202 Specify the desired alignment, which must be a power of two, in
1205 This attribute indicates that the inliner should attempt to inline
1206 this function into callers whenever possible, ignoring any active
1207 inlining size threshold for this caller.
1209 This indicates that the callee function at a call site should be
1210 recognized as a built-in function, even though the function's declaration
1211 uses the ``nobuiltin`` attribute. This is only valid at call sites for
1212 direct calls to functions that are declared with the ``nobuiltin``
1215 This attribute indicates that this function is rarely called. When
1216 computing edge weights, basic blocks post-dominated by a cold
1217 function call are also considered to be cold; and, thus, given low
1220 This attribute indicates that the callee is dependent on a convergent
1221 thread execution pattern under certain parallel execution models.
1222 Transformations that are execution model agnostic may only move or
1223 tranform this call if the final location is control equivalent to its
1224 original position in the program, where control equivalence is defined as
1225 A dominates B and B post-dominates A, or vice versa.
1227 This attribute indicates that the source code contained a hint that
1228 inlining this function is desirable (such as the "inline" keyword in
1229 C/C++). It is just a hint; it imposes no requirements on the
1232 This attribute indicates that the function should be added to a
1233 jump-instruction table at code-generation time, and that all address-taken
1234 references to this function should be replaced with a reference to the
1235 appropriate jump-instruction-table function pointer. Note that this creates
1236 a new pointer for the original function, which means that code that depends
1237 on function-pointer identity can break. So, any function annotated with
1238 ``jumptable`` must also be ``unnamed_addr``.
1240 This attribute suggests that optimization passes and code generator
1241 passes make choices that keep the code size of this function as small
1242 as possible and perform optimizations that may sacrifice runtime
1243 performance in order to minimize the size of the generated code.
1245 This attribute disables prologue / epilogue emission for the
1246 function. This can have very system-specific consequences.
1248 This indicates that the callee function at a call site is not recognized as
1249 a built-in function. LLVM will retain the original call and not replace it
1250 with equivalent code based on the semantics of the built-in function, unless
1251 the call site uses the ``builtin`` attribute. This is valid at call sites
1252 and on function declarations and definitions.
1254 This attribute indicates that calls to the function cannot be
1255 duplicated. A call to a ``noduplicate`` function may be moved
1256 within its parent function, but may not be duplicated within
1257 its parent function.
1259 A function containing a ``noduplicate`` call may still
1260 be an inlining candidate, provided that the call is not
1261 duplicated by inlining. That implies that the function has
1262 internal linkage and only has one call site, so the original
1263 call is dead after inlining.
1265 This attributes disables implicit floating point instructions.
1267 This attribute indicates that the inliner should never inline this
1268 function in any situation. This attribute may not be used together
1269 with the ``alwaysinline`` attribute.
1271 This attribute suppresses lazy symbol binding for the function. This
1272 may make calls to the function faster, at the cost of extra program
1273 startup time if the function is not called during program startup.
1275 This attribute indicates that the code generator should not use a
1276 red zone, even if the target-specific ABI normally permits it.
1278 This function attribute indicates that the function never returns
1279 normally. This produces undefined behavior at runtime if the
1280 function ever does dynamically return.
1282 This function attribute indicates that the function never raises an
1283 exception. If the function does raise an exception, its runtime
1284 behavior is undefined. However, functions marked nounwind may still
1285 trap or generate asynchronous exceptions. Exception handling schemes
1286 that are recognized by LLVM to handle asynchronous exceptions, such
1287 as SEH, will still provide their implementation defined semantics.
1289 This function attribute indicates that the function is not optimized
1290 by any optimization or code generator passes with the
1291 exception of interprocedural optimization passes.
1292 This attribute cannot be used together with the ``alwaysinline``
1293 attribute; this attribute is also incompatible
1294 with the ``minsize`` attribute and the ``optsize`` attribute.
1296 This attribute requires the ``noinline`` attribute to be specified on
1297 the function as well, so the function is never inlined into any caller.
1298 Only functions with the ``alwaysinline`` attribute are valid
1299 candidates for inlining into the body of this function.
1301 This attribute suggests that optimization passes and code generator
1302 passes make choices that keep the code size of this function low,
1303 and otherwise do optimizations specifically to reduce code size as
1304 long as they do not significantly impact runtime performance.
1306 On a function, this attribute indicates that the function computes its
1307 result (or decides to unwind an exception) based strictly on its arguments,
1308 without dereferencing any pointer arguments or otherwise accessing
1309 any mutable state (e.g. memory, control registers, etc) visible to
1310 caller functions. It does not write through any pointer arguments
1311 (including ``byval`` arguments) and never changes any state visible
1312 to callers. This means that it cannot unwind exceptions by calling
1313 the ``C++`` exception throwing methods.
1315 On an argument, this attribute indicates that the function does not
1316 dereference that pointer argument, even though it may read or write the
1317 memory that the pointer points to if accessed through other pointers.
1319 On a function, this attribute indicates that the function does not write
1320 through any pointer arguments (including ``byval`` arguments) or otherwise
1321 modify any state (e.g. memory, control registers, etc) visible to
1322 caller functions. It may dereference pointer arguments and read
1323 state that may be set in the caller. A readonly function always
1324 returns the same value (or unwinds an exception identically) when
1325 called with the same set of arguments and global state. It cannot
1326 unwind an exception by calling the ``C++`` exception throwing
1329 On an argument, this attribute indicates that the function does not write
1330 through this pointer argument, even though it may write to the memory that
1331 the pointer points to.
1333 This attribute indicates that the only memory accesses inside function are
1334 loads and stores from objects pointed to by its pointer-typed arguments,
1335 with arbitrary offsets. Or in other words, all memory operations in the
1336 function can refer to memory only using pointers based on its function
1338 Note that ``argmemonly`` can be used together with ``readonly`` attribute
1339 in order to specify that function reads only from its arguments.
1341 This attribute indicates that this function can return twice. The C
1342 ``setjmp`` is an example of such a function. The compiler disables
1343 some optimizations (like tail calls) in the caller of these
1346 This attribute indicates that
1347 `SafeStack <http://clang.llvm.org/docs/SafeStack.html>`_
1348 protection is enabled for this function.
1350 If a function that has a ``safestack`` attribute is inlined into a
1351 function that doesn't have a ``safestack`` attribute or which has an
1352 ``ssp``, ``sspstrong`` or ``sspreq`` attribute, then the resulting
1353 function will have a ``safestack`` attribute.
1354 ``sanitize_address``
1355 This attribute indicates that AddressSanitizer checks
1356 (dynamic address safety analysis) are enabled for this function.
1358 This attribute indicates that MemorySanitizer checks (dynamic detection
1359 of accesses to uninitialized memory) are enabled for this function.
1361 This attribute indicates that ThreadSanitizer checks
1362 (dynamic thread safety analysis) are enabled for this function.
1364 This attribute indicates that the function should emit a stack
1365 smashing protector. It is in the form of a "canary" --- a random value
1366 placed on the stack before the local variables that's checked upon
1367 return from the function to see if it has been overwritten. A
1368 heuristic is used to determine if a function needs stack protectors
1369 or not. The heuristic used will enable protectors for functions with:
1371 - Character arrays larger than ``ssp-buffer-size`` (default 8).
1372 - Aggregates containing character arrays larger than ``ssp-buffer-size``.
1373 - Calls to alloca() with variable sizes or constant sizes greater than
1374 ``ssp-buffer-size``.
1376 Variables that are identified as requiring a protector will be arranged
1377 on the stack such that they are adjacent to the stack protector guard.
1379 If a function that has an ``ssp`` attribute is inlined into a
1380 function that doesn't have an ``ssp`` attribute, then the resulting
1381 function will have an ``ssp`` attribute.
1383 This attribute indicates that the function should *always* emit a
1384 stack smashing protector. This overrides the ``ssp`` function
1387 Variables that are identified as requiring a protector will be arranged
1388 on the stack such that they are adjacent to the stack protector guard.
1389 The specific layout rules are:
1391 #. Large arrays and structures containing large arrays
1392 (``>= ssp-buffer-size``) are closest to the stack protector.
1393 #. Small arrays and structures containing small arrays
1394 (``< ssp-buffer-size``) are 2nd closest to the protector.
1395 #. Variables that have had their address taken are 3rd closest to the
1398 If a function that has an ``sspreq`` attribute is inlined into a
1399 function that doesn't have an ``sspreq`` attribute or which has an
1400 ``ssp`` or ``sspstrong`` attribute, then the resulting function will have
1401 an ``sspreq`` attribute.
1403 This attribute indicates that the function should emit a stack smashing
1404 protector. This attribute causes a strong heuristic to be used when
1405 determining if a function needs stack protectors. The strong heuristic
1406 will enable protectors for functions with:
1408 - Arrays of any size and type
1409 - Aggregates containing an array of any size and type.
1410 - Calls to alloca().
1411 - Local variables that have had their address taken.
1413 Variables that are identified as requiring a protector will be arranged
1414 on the stack such that they are adjacent to the stack protector guard.
1415 The specific layout rules are:
1417 #. Large arrays and structures containing large arrays
1418 (``>= ssp-buffer-size``) are closest to the stack protector.
1419 #. Small arrays and structures containing small arrays
1420 (``< ssp-buffer-size``) are 2nd closest to the protector.
1421 #. Variables that have had their address taken are 3rd closest to the
1424 This overrides the ``ssp`` function attribute.
1426 If a function that has an ``sspstrong`` attribute is inlined into a
1427 function that doesn't have an ``sspstrong`` attribute, then the
1428 resulting function will have an ``sspstrong`` attribute.
1430 This attribute indicates that the function will delegate to some other
1431 function with a tail call. The prototype of a thunk should not be used for
1432 optimization purposes. The caller is expected to cast the thunk prototype to
1433 match the thunk target prototype.
1435 This attribute indicates that the ABI being targeted requires that
1436 an unwind table entry be produced for this function even if we can
1437 show that no exceptions passes by it. This is normally the case for
1438 the ELF x86-64 abi, but it can be disabled for some compilation
1443 Module-Level Inline Assembly
1444 ----------------------------
1446 Modules may contain "module-level inline asm" blocks, which corresponds
1447 to the GCC "file scope inline asm" blocks. These blocks are internally
1448 concatenated by LLVM and treated as a single unit, but may be separated
1449 in the ``.ll`` file if desired. The syntax is very simple:
1451 .. code-block:: llvm
1453 module asm "inline asm code goes here"
1454 module asm "more can go here"
1456 The strings can contain any character by escaping non-printable
1457 characters. The escape sequence used is simply "\\xx" where "xx" is the
1458 two digit hex code for the number.
1460 Note that the assembly string *must* be parseable by LLVM's integrated assembler
1461 (unless it is disabled), even when emitting a ``.s`` file.
1463 .. _langref_datalayout:
1468 A module may specify a target specific data layout string that specifies
1469 how data is to be laid out in memory. The syntax for the data layout is
1472 .. code-block:: llvm
1474 target datalayout = "layout specification"
1476 The *layout specification* consists of a list of specifications
1477 separated by the minus sign character ('-'). Each specification starts
1478 with a letter and may include other information after the letter to
1479 define some aspect of the data layout. The specifications accepted are
1483 Specifies that the target lays out data in big-endian form. That is,
1484 the bits with the most significance have the lowest address
1487 Specifies that the target lays out data in little-endian form. That
1488 is, the bits with the least significance have the lowest address
1491 Specifies the natural alignment of the stack in bits. Alignment
1492 promotion of stack variables is limited to the natural stack
1493 alignment to avoid dynamic stack realignment. The stack alignment
1494 must be a multiple of 8-bits. If omitted, the natural stack
1495 alignment defaults to "unspecified", which does not prevent any
1496 alignment promotions.
1497 ``p[n]:<size>:<abi>:<pref>``
1498 This specifies the *size* of a pointer and its ``<abi>`` and
1499 ``<pref>``\erred alignments for address space ``n``. All sizes are in
1500 bits. The address space, ``n``, is optional, and if not specified,
1501 denotes the default address space 0. The value of ``n`` must be
1502 in the range [1,2^23).
1503 ``i<size>:<abi>:<pref>``
1504 This specifies the alignment for an integer type of a given bit
1505 ``<size>``. The value of ``<size>`` must be in the range [1,2^23).
1506 ``v<size>:<abi>:<pref>``
1507 This specifies the alignment for a vector type of a given bit
1509 ``f<size>:<abi>:<pref>``
1510 This specifies the alignment for a floating point type of a given bit
1511 ``<size>``. Only values of ``<size>`` that are supported by the target
1512 will work. 32 (float) and 64 (double) are supported on all targets; 80
1513 or 128 (different flavors of long double) are also supported on some
1516 This specifies the alignment for an object of aggregate type.
1518 If present, specifies that llvm names are mangled in the output. The
1521 * ``e``: ELF mangling: Private symbols get a ``.L`` prefix.
1522 * ``m``: Mips mangling: Private symbols get a ``$`` prefix.
1523 * ``o``: Mach-O mangling: Private symbols get ``L`` prefix. Other
1524 symbols get a ``_`` prefix.
1525 * ``w``: Windows COFF prefix: Similar to Mach-O, but stdcall and fastcall
1526 functions also get a suffix based on the frame size.
1527 ``n<size1>:<size2>:<size3>...``
1528 This specifies a set of native integer widths for the target CPU in
1529 bits. For example, it might contain ``n32`` for 32-bit PowerPC,
1530 ``n32:64`` for PowerPC 64, or ``n8:16:32:64`` for X86-64. Elements of
1531 this set are considered to support most general arithmetic operations
1534 On every specification that takes a ``<abi>:<pref>``, specifying the
1535 ``<pref>`` alignment is optional. If omitted, the preceding ``:``
1536 should be omitted too and ``<pref>`` will be equal to ``<abi>``.
1538 When constructing the data layout for a given target, LLVM starts with a
1539 default set of specifications which are then (possibly) overridden by
1540 the specifications in the ``datalayout`` keyword. The default
1541 specifications are given in this list:
1543 - ``E`` - big endian
1544 - ``p:64:64:64`` - 64-bit pointers with 64-bit alignment.
1545 - ``p[n]:64:64:64`` - Other address spaces are assumed to be the
1546 same as the default address space.
1547 - ``S0`` - natural stack alignment is unspecified
1548 - ``i1:8:8`` - i1 is 8-bit (byte) aligned
1549 - ``i8:8:8`` - i8 is 8-bit (byte) aligned
1550 - ``i16:16:16`` - i16 is 16-bit aligned
1551 - ``i32:32:32`` - i32 is 32-bit aligned
1552 - ``i64:32:64`` - i64 has ABI alignment of 32-bits but preferred
1553 alignment of 64-bits
1554 - ``f16:16:16`` - half is 16-bit aligned
1555 - ``f32:32:32`` - float is 32-bit aligned
1556 - ``f64:64:64`` - double is 64-bit aligned
1557 - ``f128:128:128`` - quad is 128-bit aligned
1558 - ``v64:64:64`` - 64-bit vector is 64-bit aligned
1559 - ``v128:128:128`` - 128-bit vector is 128-bit aligned
1560 - ``a:0:64`` - aggregates are 64-bit aligned
1562 When LLVM is determining the alignment for a given type, it uses the
1565 #. If the type sought is an exact match for one of the specifications,
1566 that specification is used.
1567 #. If no match is found, and the type sought is an integer type, then
1568 the smallest integer type that is larger than the bitwidth of the
1569 sought type is used. If none of the specifications are larger than
1570 the bitwidth then the largest integer type is used. For example,
1571 given the default specifications above, the i7 type will use the
1572 alignment of i8 (next largest) while both i65 and i256 will use the
1573 alignment of i64 (largest specified).
1574 #. If no match is found, and the type sought is a vector type, then the
1575 largest vector type that is smaller than the sought vector type will
1576 be used as a fall back. This happens because <128 x double> can be
1577 implemented in terms of 64 <2 x double>, for example.
1579 The function of the data layout string may not be what you expect.
1580 Notably, this is not a specification from the frontend of what alignment
1581 the code generator should use.
1583 Instead, if specified, the target data layout is required to match what
1584 the ultimate *code generator* expects. This string is used by the
1585 mid-level optimizers to improve code, and this only works if it matches
1586 what the ultimate code generator uses. There is no way to generate IR
1587 that does not embed this target-specific detail into the IR. If you
1588 don't specify the string, the default specifications will be used to
1589 generate a Data Layout and the optimization phases will operate
1590 accordingly and introduce target specificity into the IR with respect to
1591 these default specifications.
1598 A module may specify a target triple string that describes the target
1599 host. The syntax for the target triple is simply:
1601 .. code-block:: llvm
1603 target triple = "x86_64-apple-macosx10.7.0"
1605 The *target triple* string consists of a series of identifiers delimited
1606 by the minus sign character ('-'). The canonical forms are:
1610 ARCHITECTURE-VENDOR-OPERATING_SYSTEM
1611 ARCHITECTURE-VENDOR-OPERATING_SYSTEM-ENVIRONMENT
1613 This information is passed along to the backend so that it generates
1614 code for the proper architecture. It's possible to override this on the
1615 command line with the ``-mtriple`` command line option.
1617 .. _pointeraliasing:
1619 Pointer Aliasing Rules
1620 ----------------------
1622 Any memory access must be done through a pointer value associated with
1623 an address range of the memory access, otherwise the behavior is
1624 undefined. Pointer values are associated with address ranges according
1625 to the following rules:
1627 - A pointer value is associated with the addresses associated with any
1628 value it is *based* on.
1629 - An address of a global variable is associated with the address range
1630 of the variable's storage.
1631 - The result value of an allocation instruction is associated with the
1632 address range of the allocated storage.
1633 - A null pointer in the default address-space is associated with no
1635 - An integer constant other than zero or a pointer value returned from
1636 a function not defined within LLVM may be associated with address
1637 ranges allocated through mechanisms other than those provided by
1638 LLVM. Such ranges shall not overlap with any ranges of addresses
1639 allocated by mechanisms provided by LLVM.
1641 A pointer value is *based* on another pointer value according to the
1644 - A pointer value formed from a ``getelementptr`` operation is *based*
1645 on the first value operand of the ``getelementptr``.
1646 - The result value of a ``bitcast`` is *based* on the operand of the
1648 - A pointer value formed by an ``inttoptr`` is *based* on all pointer
1649 values that contribute (directly or indirectly) to the computation of
1650 the pointer's value.
1651 - The "*based* on" relationship is transitive.
1653 Note that this definition of *"based"* is intentionally similar to the
1654 definition of *"based"* in C99, though it is slightly weaker.
1656 LLVM IR does not associate types with memory. The result type of a
1657 ``load`` merely indicates the size and alignment of the memory from
1658 which to load, as well as the interpretation of the value. The first
1659 operand type of a ``store`` similarly only indicates the size and
1660 alignment of the store.
1662 Consequently, type-based alias analysis, aka TBAA, aka
1663 ``-fstrict-aliasing``, is not applicable to general unadorned LLVM IR.
1664 :ref:`Metadata <metadata>` may be used to encode additional information
1665 which specialized optimization passes may use to implement type-based
1670 Volatile Memory Accesses
1671 ------------------------
1673 Certain memory accesses, such as :ref:`load <i_load>`'s,
1674 :ref:`store <i_store>`'s, and :ref:`llvm.memcpy <int_memcpy>`'s may be
1675 marked ``volatile``. The optimizers must not change the number of
1676 volatile operations or change their order of execution relative to other
1677 volatile operations. The optimizers *may* change the order of volatile
1678 operations relative to non-volatile operations. This is not Java's
1679 "volatile" and has no cross-thread synchronization behavior.
1681 IR-level volatile loads and stores cannot safely be optimized into
1682 llvm.memcpy or llvm.memmove intrinsics even when those intrinsics are
1683 flagged volatile. Likewise, the backend should never split or merge
1684 target-legal volatile load/store instructions.
1686 .. admonition:: Rationale
1688 Platforms may rely on volatile loads and stores of natively supported
1689 data width to be executed as single instruction. For example, in C
1690 this holds for an l-value of volatile primitive type with native
1691 hardware support, but not necessarily for aggregate types. The
1692 frontend upholds these expectations, which are intentionally
1693 unspecified in the IR. The rules above ensure that IR transformations
1694 do not violate the frontend's contract with the language.
1698 Memory Model for Concurrent Operations
1699 --------------------------------------
1701 The LLVM IR does not define any way to start parallel threads of
1702 execution or to register signal handlers. Nonetheless, there are
1703 platform-specific ways to create them, and we define LLVM IR's behavior
1704 in their presence. This model is inspired by the C++0x memory model.
1706 For a more informal introduction to this model, see the :doc:`Atomics`.
1708 We define a *happens-before* partial order as the least partial order
1711 - Is a superset of single-thread program order, and
1712 - When a *synchronizes-with* ``b``, includes an edge from ``a`` to
1713 ``b``. *Synchronizes-with* pairs are introduced by platform-specific
1714 techniques, like pthread locks, thread creation, thread joining,
1715 etc., and by atomic instructions. (See also :ref:`Atomic Memory Ordering
1716 Constraints <ordering>`).
1718 Note that program order does not introduce *happens-before* edges
1719 between a thread and signals executing inside that thread.
1721 Every (defined) read operation (load instructions, memcpy, atomic
1722 loads/read-modify-writes, etc.) R reads a series of bytes written by
1723 (defined) write operations (store instructions, atomic
1724 stores/read-modify-writes, memcpy, etc.). For the purposes of this
1725 section, initialized globals are considered to have a write of the
1726 initializer which is atomic and happens before any other read or write
1727 of the memory in question. For each byte of a read R, R\ :sub:`byte`
1728 may see any write to the same byte, except:
1730 - If write\ :sub:`1` happens before write\ :sub:`2`, and
1731 write\ :sub:`2` happens before R\ :sub:`byte`, then
1732 R\ :sub:`byte` does not see write\ :sub:`1`.
1733 - If R\ :sub:`byte` happens before write\ :sub:`3`, then
1734 R\ :sub:`byte` does not see write\ :sub:`3`.
1736 Given that definition, R\ :sub:`byte` is defined as follows:
1738 - If R is volatile, the result is target-dependent. (Volatile is
1739 supposed to give guarantees which can support ``sig_atomic_t`` in
1740 C/C++, and may be used for accesses to addresses that do not behave
1741 like normal memory. It does not generally provide cross-thread
1743 - Otherwise, if there is no write to the same byte that happens before
1744 R\ :sub:`byte`, R\ :sub:`byte` returns ``undef`` for that byte.
1745 - Otherwise, if R\ :sub:`byte` may see exactly one write,
1746 R\ :sub:`byte` returns the value written by that write.
1747 - Otherwise, if R is atomic, and all the writes R\ :sub:`byte` may
1748 see are atomic, it chooses one of the values written. See the :ref:`Atomic
1749 Memory Ordering Constraints <ordering>` section for additional
1750 constraints on how the choice is made.
1751 - Otherwise R\ :sub:`byte` returns ``undef``.
1753 R returns the value composed of the series of bytes it read. This
1754 implies that some bytes within the value may be ``undef`` **without**
1755 the entire value being ``undef``. Note that this only defines the
1756 semantics of the operation; it doesn't mean that targets will emit more
1757 than one instruction to read the series of bytes.
1759 Note that in cases where none of the atomic intrinsics are used, this
1760 model places only one restriction on IR transformations on top of what
1761 is required for single-threaded execution: introducing a store to a byte
1762 which might not otherwise be stored is not allowed in general.
1763 (Specifically, in the case where another thread might write to and read
1764 from an address, introducing a store can change a load that may see
1765 exactly one write into a load that may see multiple writes.)
1769 Atomic Memory Ordering Constraints
1770 ----------------------------------
1772 Atomic instructions (:ref:`cmpxchg <i_cmpxchg>`,
1773 :ref:`atomicrmw <i_atomicrmw>`, :ref:`fence <i_fence>`,
1774 :ref:`atomic load <i_load>`, and :ref:`atomic store <i_store>`) take
1775 ordering parameters that determine which other atomic instructions on
1776 the same address they *synchronize with*. These semantics are borrowed
1777 from Java and C++0x, but are somewhat more colloquial. If these
1778 descriptions aren't precise enough, check those specs (see spec
1779 references in the :doc:`atomics guide <Atomics>`).
1780 :ref:`fence <i_fence>` instructions treat these orderings somewhat
1781 differently since they don't take an address. See that instruction's
1782 documentation for details.
1784 For a simpler introduction to the ordering constraints, see the
1788 The set of values that can be read is governed by the happens-before
1789 partial order. A value cannot be read unless some operation wrote
1790 it. This is intended to provide a guarantee strong enough to model
1791 Java's non-volatile shared variables. This ordering cannot be
1792 specified for read-modify-write operations; it is not strong enough
1793 to make them atomic in any interesting way.
1795 In addition to the guarantees of ``unordered``, there is a single
1796 total order for modifications by ``monotonic`` operations on each
1797 address. All modification orders must be compatible with the
1798 happens-before order. There is no guarantee that the modification
1799 orders can be combined to a global total order for the whole program
1800 (and this often will not be possible). The read in an atomic
1801 read-modify-write operation (:ref:`cmpxchg <i_cmpxchg>` and
1802 :ref:`atomicrmw <i_atomicrmw>`) reads the value in the modification
1803 order immediately before the value it writes. If one atomic read
1804 happens before another atomic read of the same address, the later
1805 read must see the same value or a later value in the address's
1806 modification order. This disallows reordering of ``monotonic`` (or
1807 stronger) operations on the same address. If an address is written
1808 ``monotonic``-ally by one thread, and other threads ``monotonic``-ally
1809 read that address repeatedly, the other threads must eventually see
1810 the write. This corresponds to the C++0x/C1x
1811 ``memory_order_relaxed``.
1813 In addition to the guarantees of ``monotonic``, a
1814 *synchronizes-with* edge may be formed with a ``release`` operation.
1815 This is intended to model C++'s ``memory_order_acquire``.
1817 In addition to the guarantees of ``monotonic``, if this operation
1818 writes a value which is subsequently read by an ``acquire``
1819 operation, it *synchronizes-with* that operation. (This isn't a
1820 complete description; see the C++0x definition of a release
1821 sequence.) This corresponds to the C++0x/C1x
1822 ``memory_order_release``.
1823 ``acq_rel`` (acquire+release)
1824 Acts as both an ``acquire`` and ``release`` operation on its
1825 address. This corresponds to the C++0x/C1x ``memory_order_acq_rel``.
1826 ``seq_cst`` (sequentially consistent)
1827 In addition to the guarantees of ``acq_rel`` (``acquire`` for an
1828 operation that only reads, ``release`` for an operation that only
1829 writes), there is a global total order on all
1830 sequentially-consistent operations on all addresses, which is
1831 consistent with the *happens-before* partial order and with the
1832 modification orders of all the affected addresses. Each
1833 sequentially-consistent read sees the last preceding write to the
1834 same address in this global order. This corresponds to the C++0x/C1x
1835 ``memory_order_seq_cst`` and Java volatile.
1839 If an atomic operation is marked ``singlethread``, it only *synchronizes
1840 with* or participates in modification and seq\_cst total orderings with
1841 other operations running in the same thread (for example, in signal
1849 LLVM IR floating-point binary ops (:ref:`fadd <i_fadd>`,
1850 :ref:`fsub <i_fsub>`, :ref:`fmul <i_fmul>`, :ref:`fdiv <i_fdiv>`,
1851 :ref:`frem <i_frem>`, :ref:`fcmp <i_fcmp>`) have the following flags that can
1852 be set to enable otherwise unsafe floating point operations
1855 No NaNs - Allow optimizations to assume the arguments and result are not
1856 NaN. Such optimizations are required to retain defined behavior over
1857 NaNs, but the value of the result is undefined.
1860 No Infs - Allow optimizations to assume the arguments and result are not
1861 +/-Inf. Such optimizations are required to retain defined behavior over
1862 +/-Inf, but the value of the result is undefined.
1865 No Signed Zeros - Allow optimizations to treat the sign of a zero
1866 argument or result as insignificant.
1869 Allow Reciprocal - Allow optimizations to use the reciprocal of an
1870 argument rather than perform division.
1873 Fast - Allow algebraically equivalent transformations that may
1874 dramatically change results in floating point (e.g. reassociate). This
1875 flag implies all the others.
1879 Use-list Order Directives
1880 -------------------------
1882 Use-list directives encode the in-memory order of each use-list, allowing the
1883 order to be recreated. ``<order-indexes>`` is a comma-separated list of
1884 indexes that are assigned to the referenced value's uses. The referenced
1885 value's use-list is immediately sorted by these indexes.
1887 Use-list directives may appear at function scope or global scope. They are not
1888 instructions, and have no effect on the semantics of the IR. When they're at
1889 function scope, they must appear after the terminator of the final basic block.
1891 If basic blocks have their address taken via ``blockaddress()`` expressions,
1892 ``uselistorder_bb`` can be used to reorder their use-lists from outside their
1899 uselistorder <ty> <value>, { <order-indexes> }
1900 uselistorder_bb @function, %block { <order-indexes> }
1906 define void @foo(i32 %arg1, i32 %arg2) {
1908 ; ... instructions ...
1910 ; ... instructions ...
1912 ; At function scope.
1913 uselistorder i32 %arg1, { 1, 0, 2 }
1914 uselistorder label %bb, { 1, 0 }
1918 uselistorder i32* @global, { 1, 2, 0 }
1919 uselistorder i32 7, { 1, 0 }
1920 uselistorder i32 (i32) @bar, { 1, 0 }
1921 uselistorder_bb @foo, %bb, { 5, 1, 3, 2, 0, 4 }
1928 The LLVM type system is one of the most important features of the
1929 intermediate representation. Being typed enables a number of
1930 optimizations to be performed on the intermediate representation
1931 directly, without having to do extra analyses on the side before the
1932 transformation. A strong type system makes it easier to read the
1933 generated code and enables novel analyses and transformations that are
1934 not feasible to perform on normal three address code representations.
1944 The void type does not represent any value and has no size.
1962 The function type can be thought of as a function signature. It consists of a
1963 return type and a list of formal parameter types. The return type of a function
1964 type is a void type or first class type --- except for :ref:`label <t_label>`
1965 and :ref:`metadata <t_metadata>` types.
1971 <returntype> (<parameter list>)
1973 ...where '``<parameter list>``' is a comma-separated list of type
1974 specifiers. Optionally, the parameter list may include a type ``...``, which
1975 indicates that the function takes a variable number of arguments. Variable
1976 argument functions can access their arguments with the :ref:`variable argument
1977 handling intrinsic <int_varargs>` functions. '``<returntype>``' is any type
1978 except :ref:`label <t_label>` and :ref:`metadata <t_metadata>`.
1982 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1983 | ``i32 (i32)`` | function taking an ``i32``, returning an ``i32`` |
1984 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1985 | ``float (i16, i32 *) *`` | :ref:`Pointer <t_pointer>` to a function that takes an ``i16`` and a :ref:`pointer <t_pointer>` to ``i32``, returning ``float``. |
1986 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1987 | ``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. |
1988 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1989 | ``{i32, i32} (i32)`` | A function taking an ``i32``, returning a :ref:`structure <t_struct>` containing two ``i32`` values |
1990 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1997 The :ref:`first class <t_firstclass>` types are perhaps the most important.
1998 Values of these types are the only ones which can be produced by
2006 These are the types that are valid in registers from CodeGen's perspective.
2015 The integer type is a very simple type that simply specifies an
2016 arbitrary bit width for the integer type desired. Any bit width from 1
2017 bit to 2\ :sup:`23`\ -1 (about 8 million) can be specified.
2025 The number of bits the integer will occupy is specified by the ``N``
2031 +----------------+------------------------------------------------+
2032 | ``i1`` | a single-bit integer. |
2033 +----------------+------------------------------------------------+
2034 | ``i32`` | a 32-bit integer. |
2035 +----------------+------------------------------------------------+
2036 | ``i1942652`` | a really big integer of over 1 million bits. |
2037 +----------------+------------------------------------------------+
2041 Floating Point Types
2042 """"""""""""""""""""
2051 - 16-bit floating point value
2054 - 32-bit floating point value
2057 - 64-bit floating point value
2060 - 128-bit floating point value (112-bit mantissa)
2063 - 80-bit floating point value (X87)
2066 - 128-bit floating point value (two 64-bits)
2073 The x86_mmx type represents a value held in an MMX register on an x86
2074 machine. The operations allowed on it are quite limited: parameters and
2075 return values, load and store, and bitcast. User-specified MMX
2076 instructions are represented as intrinsic or asm calls with arguments
2077 and/or results of this type. There are no arrays, vectors or constants
2094 The pointer type is used to specify memory locations. Pointers are
2095 commonly used to reference objects in memory.
2097 Pointer types may have an optional address space attribute defining the
2098 numbered address space where the pointed-to object resides. The default
2099 address space is number zero. The semantics of non-zero address spaces
2100 are target-specific.
2102 Note that LLVM does not permit pointers to void (``void*``) nor does it
2103 permit pointers to labels (``label*``). Use ``i8*`` instead.
2113 +-------------------------+--------------------------------------------------------------------------------------------------------------+
2114 | ``[4 x i32]*`` | A :ref:`pointer <t_pointer>` to :ref:`array <t_array>` of four ``i32`` values. |
2115 +-------------------------+--------------------------------------------------------------------------------------------------------------+
2116 | ``i32 (i32*) *`` | A :ref:`pointer <t_pointer>` to a :ref:`function <t_function>` that takes an ``i32*``, returning an ``i32``. |
2117 +-------------------------+--------------------------------------------------------------------------------------------------------------+
2118 | ``i32 addrspace(5)*`` | A :ref:`pointer <t_pointer>` to an ``i32`` value that resides in address space #5. |
2119 +-------------------------+--------------------------------------------------------------------------------------------------------------+
2128 A vector type is a simple derived type that represents a vector of
2129 elements. Vector types are used when multiple primitive data are
2130 operated in parallel using a single instruction (SIMD). A vector type
2131 requires a size (number of elements) and an underlying primitive data
2132 type. Vector types are considered :ref:`first class <t_firstclass>`.
2138 < <# elements> x <elementtype> >
2140 The number of elements is a constant integer value larger than 0;
2141 elementtype may be any integer, floating point or pointer type. Vectors
2142 of size zero are not allowed.
2146 +-------------------+--------------------------------------------------+
2147 | ``<4 x i32>`` | Vector of 4 32-bit integer values. |
2148 +-------------------+--------------------------------------------------+
2149 | ``<8 x float>`` | Vector of 8 32-bit floating-point values. |
2150 +-------------------+--------------------------------------------------+
2151 | ``<2 x i64>`` | Vector of 2 64-bit integer values. |
2152 +-------------------+--------------------------------------------------+
2153 | ``<4 x i64*>`` | Vector of 4 pointers to 64-bit integer values. |
2154 +-------------------+--------------------------------------------------+
2163 The label type represents code labels.
2178 The token type is used when a value is associated with an instruction
2179 but all uses of the value must not attempt to introspect or obscure it.
2180 As such, it is not appropriate to have a :ref:`phi <i_phi>` or
2181 :ref:`select <i_select>` of type token.
2198 The metadata type represents embedded metadata. No derived types may be
2199 created from metadata except for :ref:`function <t_function>` arguments.
2212 Aggregate Types are a subset of derived types that can contain multiple
2213 member types. :ref:`Arrays <t_array>` and :ref:`structs <t_struct>` are
2214 aggregate types. :ref:`Vectors <t_vector>` are not considered to be
2224 The array type is a very simple derived type that arranges elements
2225 sequentially in memory. The array type requires a size (number of
2226 elements) and an underlying data type.
2232 [<# elements> x <elementtype>]
2234 The number of elements is a constant integer value; ``elementtype`` may
2235 be any type with a size.
2239 +------------------+--------------------------------------+
2240 | ``[40 x i32]`` | Array of 40 32-bit integer values. |
2241 +------------------+--------------------------------------+
2242 | ``[41 x i32]`` | Array of 41 32-bit integer values. |
2243 +------------------+--------------------------------------+
2244 | ``[4 x i8]`` | Array of 4 8-bit integer values. |
2245 +------------------+--------------------------------------+
2247 Here are some examples of multidimensional arrays:
2249 +-----------------------------+----------------------------------------------------------+
2250 | ``[3 x [4 x i32]]`` | 3x4 array of 32-bit integer values. |
2251 +-----------------------------+----------------------------------------------------------+
2252 | ``[12 x [10 x float]]`` | 12x10 array of single precision floating point values. |
2253 +-----------------------------+----------------------------------------------------------+
2254 | ``[2 x [3 x [4 x i16]]]`` | 2x3x4 array of 16-bit integer values. |
2255 +-----------------------------+----------------------------------------------------------+
2257 There is no restriction on indexing beyond the end of the array implied
2258 by a static type (though there are restrictions on indexing beyond the
2259 bounds of an allocated object in some cases). This means that
2260 single-dimension 'variable sized array' addressing can be implemented in
2261 LLVM with a zero length array type. An implementation of 'pascal style
2262 arrays' in LLVM could use the type "``{ i32, [0 x float]}``", for
2272 The structure type is used to represent a collection of data members
2273 together in memory. The elements of a structure may be any type that has
2276 Structures in memory are accessed using '``load``' and '``store``' by
2277 getting a pointer to a field with the '``getelementptr``' instruction.
2278 Structures in registers are accessed using the '``extractvalue``' and
2279 '``insertvalue``' instructions.
2281 Structures may optionally be "packed" structures, which indicate that
2282 the alignment of the struct is one byte, and that there is no padding
2283 between the elements. In non-packed structs, padding between field types
2284 is inserted as defined by the DataLayout string in the module, which is
2285 required to match what the underlying code generator expects.
2287 Structures can either be "literal" or "identified". A literal structure
2288 is defined inline with other types (e.g. ``{i32, i32}*``) whereas
2289 identified types are always defined at the top level with a name.
2290 Literal types are uniqued by their contents and can never be recursive
2291 or opaque since there is no way to write one. Identified types can be
2292 recursive, can be opaqued, and are never uniqued.
2298 %T1 = type { <type list> } ; Identified normal struct type
2299 %T2 = type <{ <type list> }> ; Identified packed struct type
2303 +------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
2304 | ``{ i32, i32, i32 }`` | A triple of three ``i32`` values |
2305 +------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
2306 | ``{ 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``. |
2307 +------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
2308 | ``<{ i8, i32 }>`` | A packed struct known to be 5 bytes in size. |
2309 +------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
2313 Opaque Structure Types
2314 """"""""""""""""""""""
2318 Opaque structure types are used to represent named structure types that
2319 do not have a body specified. This corresponds (for example) to the C
2320 notion of a forward declared structure.
2331 +--------------+-------------------+
2332 | ``opaque`` | An opaque type. |
2333 +--------------+-------------------+
2340 LLVM has several different basic types of constants. This section
2341 describes them all and their syntax.
2346 **Boolean constants**
2347 The two strings '``true``' and '``false``' are both valid constants
2349 **Integer constants**
2350 Standard integers (such as '4') are constants of the
2351 :ref:`integer <t_integer>` type. Negative numbers may be used with
2353 **Floating point constants**
2354 Floating point constants use standard decimal notation (e.g.
2355 123.421), exponential notation (e.g. 1.23421e+2), or a more precise
2356 hexadecimal notation (see below). The assembler requires the exact
2357 decimal value of a floating-point constant. For example, the
2358 assembler accepts 1.25 but rejects 1.3 because 1.3 is a repeating
2359 decimal in binary. Floating point constants must have a :ref:`floating
2360 point <t_floating>` type.
2361 **Null pointer constants**
2362 The identifier '``null``' is recognized as a null pointer constant
2363 and must be of :ref:`pointer type <t_pointer>`.
2365 The one non-intuitive notation for constants is the hexadecimal form of
2366 floating point constants. For example, the form
2367 '``double 0x432ff973cafa8000``' is equivalent to (but harder to read
2368 than) '``double 4.5e+15``'. The only time hexadecimal floating point
2369 constants are required (and the only time that they are generated by the
2370 disassembler) is when a floating point constant must be emitted but it
2371 cannot be represented as a decimal floating point number in a reasonable
2372 number of digits. For example, NaN's, infinities, and other special
2373 values are represented in their IEEE hexadecimal format so that assembly
2374 and disassembly do not cause any bits to change in the constants.
2376 When using the hexadecimal form, constants of types half, float, and
2377 double are represented using the 16-digit form shown above (which
2378 matches the IEEE754 representation for double); half and float values
2379 must, however, be exactly representable as IEEE 754 half and single
2380 precision, respectively. Hexadecimal format is always used for long
2381 double, and there are three forms of long double. The 80-bit format used
2382 by x86 is represented as ``0xK`` followed by 20 hexadecimal digits. The
2383 128-bit format used by PowerPC (two adjacent doubles) is represented by
2384 ``0xM`` followed by 32 hexadecimal digits. The IEEE 128-bit format is
2385 represented by ``0xL`` followed by 32 hexadecimal digits. Long doubles
2386 will only work if they match the long double format on your target.
2387 The IEEE 16-bit format (half precision) is represented by ``0xH``
2388 followed by 4 hexadecimal digits. All hexadecimal formats are big-endian
2389 (sign bit at the left).
2391 There are no constants of type x86_mmx.
2393 .. _complexconstants:
2398 Complex constants are a (potentially recursive) combination of simple
2399 constants and smaller complex constants.
2401 **Structure constants**
2402 Structure constants are represented with notation similar to
2403 structure type definitions (a comma separated list of elements,
2404 surrounded by braces (``{}``)). For example:
2405 "``{ i32 4, float 17.0, i32* @G }``", where "``@G``" is declared as
2406 "``@G = external global i32``". Structure constants must have
2407 :ref:`structure type <t_struct>`, and the number and types of elements
2408 must match those specified by the type.
2410 Array constants are represented with notation similar to array type
2411 definitions (a comma separated list of elements, surrounded by
2412 square brackets (``[]``)). For example:
2413 "``[ i32 42, i32 11, i32 74 ]``". Array constants must have
2414 :ref:`array type <t_array>`, and the number and types of elements must
2415 match those specified by the type. As a special case, character array
2416 constants may also be represented as a double-quoted string using the ``c``
2417 prefix. For example: "``c"Hello World\0A\00"``".
2418 **Vector constants**
2419 Vector constants are represented with notation similar to vector
2420 type definitions (a comma separated list of elements, surrounded by
2421 less-than/greater-than's (``<>``)). For example:
2422 "``< i32 42, i32 11, i32 74, i32 100 >``". Vector constants
2423 must have :ref:`vector type <t_vector>`, and the number and types of
2424 elements must match those specified by the type.
2425 **Zero initialization**
2426 The string '``zeroinitializer``' can be used to zero initialize a
2427 value to zero of *any* type, including scalar and
2428 :ref:`aggregate <t_aggregate>` types. This is often used to avoid
2429 having to print large zero initializers (e.g. for large arrays) and
2430 is always exactly equivalent to using explicit zero initializers.
2432 A metadata node is a constant tuple without types. For example:
2433 "``!{!0, !{!2, !0}, !"test"}``". Metadata can reference constant values,
2434 for example: "``!{!0, i32 0, i8* @global, i64 (i64)* @function, !"str"}``".
2435 Unlike other typed constants that are meant to be interpreted as part of
2436 the instruction stream, metadata is a place to attach additional
2437 information such as debug info.
2439 Global Variable and Function Addresses
2440 --------------------------------------
2442 The addresses of :ref:`global variables <globalvars>` and
2443 :ref:`functions <functionstructure>` are always implicitly valid
2444 (link-time) constants. These constants are explicitly referenced when
2445 the :ref:`identifier for the global <identifiers>` is used and always have
2446 :ref:`pointer <t_pointer>` type. For example, the following is a legal LLVM
2449 .. code-block:: llvm
2453 @Z = global [2 x i32*] [ i32* @X, i32* @Y ]
2460 The string '``undef``' can be used anywhere a constant is expected, and
2461 indicates that the user of the value may receive an unspecified
2462 bit-pattern. Undefined values may be of any type (other than '``label``'
2463 or '``void``') and be used anywhere a constant is permitted.
2465 Undefined values are useful because they indicate to the compiler that
2466 the program is well defined no matter what value is used. This gives the
2467 compiler more freedom to optimize. Here are some examples of
2468 (potentially surprising) transformations that are valid (in pseudo IR):
2470 .. code-block:: llvm
2480 This is safe because all of the output bits are affected by the undef
2481 bits. Any output bit can have a zero or one depending on the input bits.
2483 .. code-block:: llvm
2494 These logical operations have bits that are not always affected by the
2495 input. For example, if ``%X`` has a zero bit, then the output of the
2496 '``and``' operation will always be a zero for that bit, no matter what
2497 the corresponding bit from the '``undef``' is. As such, it is unsafe to
2498 optimize or assume that the result of the '``and``' is '``undef``'.
2499 However, it is safe to assume that all bits of the '``undef``' could be
2500 0, and optimize the '``and``' to 0. Likewise, it is safe to assume that
2501 all the bits of the '``undef``' operand to the '``or``' could be set,
2502 allowing the '``or``' to be folded to -1.
2504 .. code-block:: llvm
2506 %A = select undef, %X, %Y
2507 %B = select undef, 42, %Y
2508 %C = select %X, %Y, undef
2518 This set of examples shows that undefined '``select``' (and conditional
2519 branch) conditions can go *either way*, but they have to come from one
2520 of the two operands. In the ``%A`` example, if ``%X`` and ``%Y`` were
2521 both known to have a clear low bit, then ``%A`` would have to have a
2522 cleared low bit. However, in the ``%C`` example, the optimizer is
2523 allowed to assume that the '``undef``' operand could be the same as
2524 ``%Y``, allowing the whole '``select``' to be eliminated.
2526 .. code-block:: llvm
2528 %A = xor undef, undef
2545 This example points out that two '``undef``' operands are not
2546 necessarily the same. This can be surprising to people (and also matches
2547 C semantics) where they assume that "``X^X``" is always zero, even if
2548 ``X`` is undefined. This isn't true for a number of reasons, but the
2549 short answer is that an '``undef``' "variable" can arbitrarily change
2550 its value over its "live range". This is true because the variable
2551 doesn't actually *have a live range*. Instead, the value is logically
2552 read from arbitrary registers that happen to be around when needed, so
2553 the value is not necessarily consistent over time. In fact, ``%A`` and
2554 ``%C`` need to have the same semantics or the core LLVM "replace all
2555 uses with" concept would not hold.
2557 .. code-block:: llvm
2565 These examples show the crucial difference between an *undefined value*
2566 and *undefined behavior*. An undefined value (like '``undef``') is
2567 allowed to have an arbitrary bit-pattern. This means that the ``%A``
2568 operation can be constant folded to '``undef``', because the '``undef``'
2569 could be an SNaN, and ``fdiv`` is not (currently) defined on SNaN's.
2570 However, in the second example, we can make a more aggressive
2571 assumption: because the ``undef`` is allowed to be an arbitrary value,
2572 we are allowed to assume that it could be zero. Since a divide by zero
2573 has *undefined behavior*, we are allowed to assume that the operation
2574 does not execute at all. This allows us to delete the divide and all
2575 code after it. Because the undefined operation "can't happen", the
2576 optimizer can assume that it occurs in dead code.
2578 .. code-block:: llvm
2580 a: store undef -> %X
2581 b: store %X -> undef
2586 These examples reiterate the ``fdiv`` example: a store *of* an undefined
2587 value can be assumed to not have any effect; we can assume that the
2588 value is overwritten with bits that happen to match what was already
2589 there. However, a store *to* an undefined location could clobber
2590 arbitrary memory, therefore, it has undefined behavior.
2597 Poison values are similar to :ref:`undef values <undefvalues>`, however
2598 they also represent the fact that an instruction or constant expression
2599 that cannot evoke side effects has nevertheless detected a condition
2600 that results in undefined behavior.
2602 There is currently no way of representing a poison value in the IR; they
2603 only exist when produced by operations such as :ref:`add <i_add>` with
2606 Poison value behavior is defined in terms of value *dependence*:
2608 - Values other than :ref:`phi <i_phi>` nodes depend on their operands.
2609 - :ref:`Phi <i_phi>` nodes depend on the operand corresponding to
2610 their dynamic predecessor basic block.
2611 - Function arguments depend on the corresponding actual argument values
2612 in the dynamic callers of their functions.
2613 - :ref:`Call <i_call>` instructions depend on the :ref:`ret <i_ret>`
2614 instructions that dynamically transfer control back to them.
2615 - :ref:`Invoke <i_invoke>` instructions depend on the
2616 :ref:`ret <i_ret>`, :ref:`resume <i_resume>`, or exception-throwing
2617 call instructions that dynamically transfer control back to them.
2618 - Non-volatile loads and stores depend on the most recent stores to all
2619 of the referenced memory addresses, following the order in the IR
2620 (including loads and stores implied by intrinsics such as
2621 :ref:`@llvm.memcpy <int_memcpy>`.)
2622 - An instruction with externally visible side effects depends on the
2623 most recent preceding instruction with externally visible side
2624 effects, following the order in the IR. (This includes :ref:`volatile
2625 operations <volatile>`.)
2626 - An instruction *control-depends* on a :ref:`terminator
2627 instruction <terminators>` if the terminator instruction has
2628 multiple successors and the instruction is always executed when
2629 control transfers to one of the successors, and may not be executed
2630 when control is transferred to another.
2631 - Additionally, an instruction also *control-depends* on a terminator
2632 instruction if the set of instructions it otherwise depends on would
2633 be different if the terminator had transferred control to a different
2635 - Dependence is transitive.
2637 Poison values have the same behavior as :ref:`undef values <undefvalues>`,
2638 with the additional effect that any instruction that has a *dependence*
2639 on a poison value has undefined behavior.
2641 Here are some examples:
2643 .. code-block:: llvm
2646 %poison = sub nuw i32 0, 1 ; Results in a poison value.
2647 %still_poison = and i32 %poison, 0 ; 0, but also poison.
2648 %poison_yet_again = getelementptr i32, i32* @h, i32 %still_poison
2649 store i32 0, i32* %poison_yet_again ; memory at @h[0] is poisoned
2651 store i32 %poison, i32* @g ; Poison value stored to memory.
2652 %poison2 = load i32, i32* @g ; Poison value loaded back from memory.
2654 store volatile i32 %poison, i32* @g ; External observation; undefined behavior.
2656 %narrowaddr = bitcast i32* @g to i16*
2657 %wideaddr = bitcast i32* @g to i64*
2658 %poison3 = load i16, i16* %narrowaddr ; Returns a poison value.
2659 %poison4 = load i64, i64* %wideaddr ; Returns a poison value.
2661 %cmp = icmp slt i32 %poison, 0 ; Returns a poison value.
2662 br i1 %cmp, label %true, label %end ; Branch to either destination.
2665 store volatile i32 0, i32* @g ; This is control-dependent on %cmp, so
2666 ; it has undefined behavior.
2670 %p = phi i32 [ 0, %entry ], [ 1, %true ]
2671 ; Both edges into this PHI are
2672 ; control-dependent on %cmp, so this
2673 ; always results in a poison value.
2675 store volatile i32 0, i32* @g ; This would depend on the store in %true
2676 ; if %cmp is true, or the store in %entry
2677 ; otherwise, so this is undefined behavior.
2679 br i1 %cmp, label %second_true, label %second_end
2680 ; The same branch again, but this time the
2681 ; true block doesn't have side effects.
2688 store volatile i32 0, i32* @g ; This time, the instruction always depends
2689 ; on the store in %end. Also, it is
2690 ; control-equivalent to %end, so this is
2691 ; well-defined (ignoring earlier undefined
2692 ; behavior in this example).
2696 Addresses of Basic Blocks
2697 -------------------------
2699 ``blockaddress(@function, %block)``
2701 The '``blockaddress``' constant computes the address of the specified
2702 basic block in the specified function, and always has an ``i8*`` type.
2703 Taking the address of the entry block is illegal.
2705 This value only has defined behavior when used as an operand to the
2706 ':ref:`indirectbr <i_indirectbr>`' instruction, or for comparisons
2707 against null. Pointer equality tests between labels addresses results in
2708 undefined behavior --- though, again, comparison against null is ok, and
2709 no label is equal to the null pointer. This may be passed around as an
2710 opaque pointer sized value as long as the bits are not inspected. This
2711 allows ``ptrtoint`` and arithmetic to be performed on these values so
2712 long as the original value is reconstituted before the ``indirectbr``
2715 Finally, some targets may provide defined semantics when using the value
2716 as the operand to an inline assembly, but that is target specific.
2720 Constant Expressions
2721 --------------------
2723 Constant expressions are used to allow expressions involving other
2724 constants to be used as constants. Constant expressions may be of any
2725 :ref:`first class <t_firstclass>` type and may involve any LLVM operation
2726 that does not have side effects (e.g. load and call are not supported).
2727 The following is the syntax for constant expressions:
2729 ``trunc (CST to TYPE)``
2730 Truncate a constant to another type. The bit size of CST must be
2731 larger than the bit size of TYPE. Both types must be integers.
2732 ``zext (CST to TYPE)``
2733 Zero extend a constant to another type. The bit size of CST must be
2734 smaller than the bit size of TYPE. Both types must be integers.
2735 ``sext (CST to TYPE)``
2736 Sign extend a constant to another type. The bit size of CST must be
2737 smaller than the bit size of TYPE. Both types must be integers.
2738 ``fptrunc (CST to TYPE)``
2739 Truncate a floating point constant to another floating point type.
2740 The size of CST must be larger than the size of TYPE. Both types
2741 must be floating point.
2742 ``fpext (CST to TYPE)``
2743 Floating point extend a constant to another type. The size of CST
2744 must be smaller or equal to the size of TYPE. Both types must be
2746 ``fptoui (CST to TYPE)``
2747 Convert a floating point constant to the corresponding unsigned
2748 integer constant. TYPE must be a scalar or vector integer type. CST
2749 must be of scalar or vector floating point type. Both CST and TYPE
2750 must be scalars, or vectors of the same number of elements. If the
2751 value won't fit in the integer type, the results are undefined.
2752 ``fptosi (CST to TYPE)``
2753 Convert a floating point constant to the corresponding signed
2754 integer constant. TYPE must be a scalar or vector integer type. CST
2755 must be of scalar or vector floating point type. Both CST and TYPE
2756 must be scalars, or vectors of the same number of elements. If the
2757 value won't fit in the integer type, the results are undefined.
2758 ``uitofp (CST to TYPE)``
2759 Convert an unsigned integer constant to the corresponding floating
2760 point constant. TYPE must be a scalar or vector floating point type.
2761 CST must be of scalar or vector integer type. Both CST and TYPE must
2762 be scalars, or vectors of the same number of elements. If the value
2763 won't fit in the floating point type, the results are undefined.
2764 ``sitofp (CST to TYPE)``
2765 Convert a signed integer constant to the corresponding floating
2766 point constant. TYPE must be a scalar or vector floating point type.
2767 CST must be of scalar or vector integer type. Both CST and TYPE must
2768 be scalars, or vectors of the same number of elements. If the value
2769 won't fit in the floating point type, the results are undefined.
2770 ``ptrtoint (CST to TYPE)``
2771 Convert a pointer typed constant to the corresponding integer
2772 constant. ``TYPE`` must be an integer type. ``CST`` must be of
2773 pointer type. The ``CST`` value is zero extended, truncated, or
2774 unchanged to make it fit in ``TYPE``.
2775 ``inttoptr (CST to TYPE)``
2776 Convert an integer constant to a pointer constant. TYPE must be a
2777 pointer type. CST must be of integer type. The CST value is zero
2778 extended, truncated, or unchanged to make it fit in a pointer size.
2779 This one is *really* dangerous!
2780 ``bitcast (CST to TYPE)``
2781 Convert a constant, CST, to another TYPE. The constraints of the
2782 operands are the same as those for the :ref:`bitcast
2783 instruction <i_bitcast>`.
2784 ``addrspacecast (CST to TYPE)``
2785 Convert a constant pointer or constant vector of pointer, CST, to another
2786 TYPE in a different address space. The constraints of the operands are the
2787 same as those for the :ref:`addrspacecast instruction <i_addrspacecast>`.
2788 ``getelementptr (TY, CSTPTR, IDX0, IDX1, ...)``, ``getelementptr inbounds (TY, CSTPTR, IDX0, IDX1, ...)``
2789 Perform the :ref:`getelementptr operation <i_getelementptr>` on
2790 constants. As with the :ref:`getelementptr <i_getelementptr>`
2791 instruction, the index list may have zero or more indexes, which are
2792 required to make sense for the type of "pointer to TY".
2793 ``select (COND, VAL1, VAL2)``
2794 Perform the :ref:`select operation <i_select>` on constants.
2795 ``icmp COND (VAL1, VAL2)``
2796 Performs the :ref:`icmp operation <i_icmp>` on constants.
2797 ``fcmp COND (VAL1, VAL2)``
2798 Performs the :ref:`fcmp operation <i_fcmp>` on constants.
2799 ``extractelement (VAL, IDX)``
2800 Perform the :ref:`extractelement operation <i_extractelement>` on
2802 ``insertelement (VAL, ELT, IDX)``
2803 Perform the :ref:`insertelement operation <i_insertelement>` on
2805 ``shufflevector (VEC1, VEC2, IDXMASK)``
2806 Perform the :ref:`shufflevector operation <i_shufflevector>` on
2808 ``extractvalue (VAL, IDX0, IDX1, ...)``
2809 Perform the :ref:`extractvalue operation <i_extractvalue>` on
2810 constants. The index list is interpreted in a similar manner as
2811 indices in a ':ref:`getelementptr <i_getelementptr>`' operation. At
2812 least one index value must be specified.
2813 ``insertvalue (VAL, ELT, IDX0, IDX1, ...)``
2814 Perform the :ref:`insertvalue operation <i_insertvalue>` on constants.
2815 The index list is interpreted in a similar manner as indices in a
2816 ':ref:`getelementptr <i_getelementptr>`' operation. At least one index
2817 value must be specified.
2818 ``OPCODE (LHS, RHS)``
2819 Perform the specified operation of the LHS and RHS constants. OPCODE
2820 may be any of the :ref:`binary <binaryops>` or :ref:`bitwise
2821 binary <bitwiseops>` operations. The constraints on operands are
2822 the same as those for the corresponding instruction (e.g. no bitwise
2823 operations on floating point values are allowed).
2830 Inline Assembler Expressions
2831 ----------------------------
2833 LLVM supports inline assembler expressions (as opposed to :ref:`Module-Level
2834 Inline Assembly <moduleasm>`) through the use of a special value. This value
2835 represents the inline assembler as a template string (containing the
2836 instructions to emit), a list of operand constraints (stored as a string), a
2837 flag that indicates whether or not the inline asm expression has side effects,
2838 and a flag indicating whether the function containing the asm needs to align its
2839 stack conservatively.
2841 The template string supports argument substitution of the operands using "``$``"
2842 followed by a number, to indicate substitution of the given register/memory
2843 location, as specified by the constraint string. "``${NUM:MODIFIER}``" may also
2844 be used, where ``MODIFIER`` is a target-specific annotation for how to print the
2845 operand (See :ref:`inline-asm-modifiers`).
2847 A literal "``$``" may be included by using "``$$``" in the template. To include
2848 other special characters into the output, the usual "``\XX``" escapes may be
2849 used, just as in other strings. Note that after template substitution, the
2850 resulting assembly string is parsed by LLVM's integrated assembler unless it is
2851 disabled -- even when emitting a ``.s`` file -- and thus must contain assembly
2852 syntax known to LLVM.
2854 LLVM's support for inline asm is modeled closely on the requirements of Clang's
2855 GCC-compatible inline-asm support. Thus, the feature-set and the constraint and
2856 modifier codes listed here are similar or identical to those in GCC's inline asm
2857 support. However, to be clear, the syntax of the template and constraint strings
2858 described here is *not* the same as the syntax accepted by GCC and Clang, and,
2859 while most constraint letters are passed through as-is by Clang, some get
2860 translated to other codes when converting from the C source to the LLVM
2863 An example inline assembler expression is:
2865 .. code-block:: llvm
2867 i32 (i32) asm "bswap $0", "=r,r"
2869 Inline assembler expressions may **only** be used as the callee operand
2870 of a :ref:`call <i_call>` or an :ref:`invoke <i_invoke>` instruction.
2871 Thus, typically we have:
2873 .. code-block:: llvm
2875 %X = call i32 asm "bswap $0", "=r,r"(i32 %Y)
2877 Inline asms with side effects not visible in the constraint list must be
2878 marked as having side effects. This is done through the use of the
2879 '``sideeffect``' keyword, like so:
2881 .. code-block:: llvm
2883 call void asm sideeffect "eieio", ""()
2885 In some cases inline asms will contain code that will not work unless
2886 the stack is aligned in some way, such as calls or SSE instructions on
2887 x86, yet will not contain code that does that alignment within the asm.
2888 The compiler should make conservative assumptions about what the asm
2889 might contain and should generate its usual stack alignment code in the
2890 prologue if the '``alignstack``' keyword is present:
2892 .. code-block:: llvm
2894 call void asm alignstack "eieio", ""()
2896 Inline asms also support using non-standard assembly dialects. The
2897 assumed dialect is ATT. When the '``inteldialect``' keyword is present,
2898 the inline asm is using the Intel dialect. Currently, ATT and Intel are
2899 the only supported dialects. An example is:
2901 .. code-block:: llvm
2903 call void asm inteldialect "eieio", ""()
2905 If multiple keywords appear the '``sideeffect``' keyword must come
2906 first, the '``alignstack``' keyword second and the '``inteldialect``'
2909 Inline Asm Constraint String
2910 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2912 The constraint list is a comma-separated string, each element containing one or
2913 more constraint codes.
2915 For each element in the constraint list an appropriate register or memory
2916 operand will be chosen, and it will be made available to assembly template
2917 string expansion as ``$0`` for the first constraint in the list, ``$1`` for the
2920 There are three different types of constraints, which are distinguished by a
2921 prefix symbol in front of the constraint code: Output, Input, and Clobber. The
2922 constraints must always be given in that order: outputs first, then inputs, then
2923 clobbers. They cannot be intermingled.
2925 There are also three different categories of constraint codes:
2927 - Register constraint. This is either a register class, or a fixed physical
2928 register. This kind of constraint will allocate a register, and if necessary,
2929 bitcast the argument or result to the appropriate type.
2930 - Memory constraint. This kind of constraint is for use with an instruction
2931 taking a memory operand. Different constraints allow for different addressing
2932 modes used by the target.
2933 - Immediate value constraint. This kind of constraint is for an integer or other
2934 immediate value which can be rendered directly into an instruction. The
2935 various target-specific constraints allow the selection of a value in the
2936 proper range for the instruction you wish to use it with.
2941 Output constraints are specified by an "``=``" prefix (e.g. "``=r``"). This
2942 indicates that the assembly will write to this operand, and the operand will
2943 then be made available as a return value of the ``asm`` expression. Output
2944 constraints do not consume an argument from the call instruction. (Except, see
2945 below about indirect outputs).
2947 Normally, it is expected that no output locations are written to by the assembly
2948 expression until *all* of the inputs have been read. As such, LLVM may assign
2949 the same register to an output and an input. If this is not safe (e.g. if the
2950 assembly contains two instructions, where the first writes to one output, and
2951 the second reads an input and writes to a second output), then the "``&``"
2952 modifier must be used (e.g. "``=&r``") to specify that the output is an
2953 "early-clobber" output. Marking an ouput as "early-clobber" ensures that LLVM
2954 will not use the same register for any inputs (other than an input tied to this
2960 Input constraints do not have a prefix -- just the constraint codes. Each input
2961 constraint will consume one argument from the call instruction. It is not
2962 permitted for the asm to write to any input register or memory location (unless
2963 that input is tied to an output). Note also that multiple inputs may all be
2964 assigned to the same register, if LLVM can determine that they necessarily all
2965 contain the same value.
2967 Instead of providing a Constraint Code, input constraints may also "tie"
2968 themselves to an output constraint, by providing an integer as the constraint
2969 string. Tied inputs still consume an argument from the call instruction, and
2970 take up a position in the asm template numbering as is usual -- they will simply
2971 be constrained to always use the same register as the output they've been tied
2972 to. For example, a constraint string of "``=r,0``" says to assign a register for
2973 output, and use that register as an input as well (it being the 0'th
2976 It is permitted to tie an input to an "early-clobber" output. In that case, no
2977 *other* input may share the same register as the input tied to the early-clobber
2978 (even when the other input has the same value).
2980 You may only tie an input to an output which has a register constraint, not a
2981 memory constraint. Only a single input may be tied to an output.
2983 There is also an "interesting" feature which deserves a bit of explanation: if a
2984 register class constraint allocates a register which is too small for the value
2985 type operand provided as input, the input value will be split into multiple
2986 registers, and all of them passed to the inline asm.
2988 However, this feature is often not as useful as you might think.
2990 Firstly, the registers are *not* guaranteed to be consecutive. So, on those
2991 architectures that have instructions which operate on multiple consecutive
2992 instructions, this is not an appropriate way to support them. (e.g. the 32-bit
2993 SparcV8 has a 64-bit load, which instruction takes a single 32-bit register. The
2994 hardware then loads into both the named register, and the next register. This
2995 feature of inline asm would not be useful to support that.)
2997 A few of the targets provide a template string modifier allowing explicit access
2998 to the second register of a two-register operand (e.g. MIPS ``L``, ``M``, and
2999 ``D``). On such an architecture, you can actually access the second allocated
3000 register (yet, still, not any subsequent ones). But, in that case, you're still
3001 probably better off simply splitting the value into two separate operands, for
3002 clarity. (e.g. see the description of the ``A`` constraint on X86, which,
3003 despite existing only for use with this feature, is not really a good idea to
3006 Indirect inputs and outputs
3007 """""""""""""""""""""""""""
3009 Indirect output or input constraints can be specified by the "``*``" modifier
3010 (which goes after the "``=``" in case of an output). This indicates that the asm
3011 will write to or read from the contents of an *address* provided as an input
3012 argument. (Note that in this way, indirect outputs act more like an *input* than
3013 an output: just like an input, they consume an argument of the call expression,
3014 rather than producing a return value. An indirect output constraint is an
3015 "output" only in that the asm is expected to write to the contents of the input
3016 memory location, instead of just read from it).
3018 This is most typically used for memory constraint, e.g. "``=*m``", to pass the
3019 address of a variable as a value.
3021 It is also possible to use an indirect *register* constraint, but only on output
3022 (e.g. "``=*r``"). This will cause LLVM to allocate a register for an output
3023 value normally, and then, separately emit a store to the address provided as
3024 input, after the provided inline asm. (It's not clear what value this
3025 functionality provides, compared to writing the store explicitly after the asm
3026 statement, and it can only produce worse code, since it bypasses many
3027 optimization passes. I would recommend not using it.)
3033 A clobber constraint is indicated by a "``~``" prefix. A clobber does not
3034 consume an input operand, nor generate an output. Clobbers cannot use any of the
3035 general constraint code letters -- they may use only explicit register
3036 constraints, e.g. "``~{eax}``". The one exception is that a clobber string of
3037 "``~{memory}``" indicates that the assembly writes to arbitrary undeclared
3038 memory locations -- not only the memory pointed to by a declared indirect
3044 After a potential prefix comes constraint code, or codes.
3046 A Constraint Code is either a single letter (e.g. "``r``"), a "``^``" character
3047 followed by two letters (e.g. "``^wc``"), or "``{``" register-name "``}``"
3050 The one and two letter constraint codes are typically chosen to be the same as
3051 GCC's constraint codes.
3053 A single constraint may include one or more than constraint code in it, leaving
3054 it up to LLVM to choose which one to use. This is included mainly for
3055 compatibility with the translation of GCC inline asm coming from clang.
3057 There are two ways to specify alternatives, and either or both may be used in an
3058 inline asm constraint list:
3060 1) Append the codes to each other, making a constraint code set. E.g. "``im``"
3061 or "``{eax}m``". This means "choose any of the options in the set". The
3062 choice of constraint is made independently for each constraint in the
3065 2) Use "``|``" between constraint code sets, creating alternatives. Every
3066 constraint in the constraint list must have the same number of alternative
3067 sets. With this syntax, the same alternative in *all* of the items in the
3068 constraint list will be chosen together.
3070 Putting those together, you might have a two operand constraint string like
3071 ``"rm|r,ri|rm"``. This indicates that if operand 0 is ``r`` or ``m``, then
3072 operand 1 may be one of ``r`` or ``i``. If operand 0 is ``r``, then operand 1
3073 may be one of ``r`` or ``m``. But, operand 0 and 1 cannot both be of type m.
3075 However, the use of either of the alternatives features is *NOT* recommended, as
3076 LLVM is not able to make an intelligent choice about which one to use. (At the
3077 point it currently needs to choose, not enough information is available to do so
3078 in a smart way.) Thus, it simply tries to make a choice that's most likely to
3079 compile, not one that will be optimal performance. (e.g., given "``rm``", it'll
3080 always choose to use memory, not registers). And, if given multiple registers,
3081 or multiple register classes, it will simply choose the first one. (In fact, it
3082 doesn't currently even ensure explicitly specified physical registers are
3083 unique, so specifying multiple physical registers as alternatives, like
3084 ``{r11}{r12},{r11}{r12}``, will assign r11 to both operands, not at all what was
3087 Supported Constraint Code List
3088 """"""""""""""""""""""""""""""
3090 The constraint codes are, in general, expected to behave the same way they do in
3091 GCC. LLVM's support is often implemented on an 'as-needed' basis, to support C
3092 inline asm code which was supported by GCC. A mismatch in behavior between LLVM
3093 and GCC likely indicates a bug in LLVM.
3095 Some constraint codes are typically supported by all targets:
3097 - ``r``: A register in the target's general purpose register class.
3098 - ``m``: A memory address operand. It is target-specific what addressing modes
3099 are supported, typical examples are register, or register + register offset,
3100 or register + immediate offset (of some target-specific size).
3101 - ``i``: An integer constant (of target-specific width). Allows either a simple
3102 immediate, or a relocatable value.
3103 - ``n``: An integer constant -- *not* including relocatable values.
3104 - ``s``: An integer constant, but allowing *only* relocatable values.
3105 - ``X``: Allows an operand of any kind, no constraint whatsoever. Typically
3106 useful to pass a label for an asm branch or call.
3108 .. FIXME: but that surely isn't actually okay to jump out of an asm
3109 block without telling llvm about the control transfer???)
3111 - ``{register-name}``: Requires exactly the named physical register.
3113 Other constraints are target-specific:
3117 - ``z``: An immediate integer 0. Outputs ``WZR`` or ``XZR``, as appropriate.
3118 - ``I``: An immediate integer valid for an ``ADD`` or ``SUB`` instruction,
3119 i.e. 0 to 4095 with optional shift by 12.
3120 - ``J``: An immediate integer that, when negated, is valid for an ``ADD`` or
3121 ``SUB`` instruction, i.e. -1 to -4095 with optional left shift by 12.
3122 - ``K``: An immediate integer that is valid for the 'bitmask immediate 32' of a
3123 logical instruction like ``AND``, ``EOR``, or ``ORR`` with a 32-bit register.
3124 - ``L``: An immediate integer that is valid for the 'bitmask immediate 64' of a
3125 logical instruction like ``AND``, ``EOR``, or ``ORR`` with a 64-bit register.
3126 - ``M``: An immediate integer for use with the ``MOV`` assembly alias on a
3127 32-bit register. This is a superset of ``K``: in addition to the bitmask
3128 immediate, also allows immediate integers which can be loaded with a single
3129 ``MOVZ`` or ``MOVL`` instruction.
3130 - ``N``: An immediate integer for use with the ``MOV`` assembly alias on a
3131 64-bit register. This is a superset of ``L``.
3132 - ``Q``: Memory address operand must be in a single register (no
3133 offsets). (However, LLVM currently does this for the ``m`` constraint as
3135 - ``r``: A 32 or 64-bit integer register (W* or X*).
3136 - ``w``: A 32, 64, or 128-bit floating-point/SIMD register.
3137 - ``x``: A lower 128-bit floating-point/SIMD register (``V0`` to ``V15``).
3141 - ``r``: A 32 or 64-bit integer register.
3142 - ``[0-9]v``: The 32-bit VGPR register, number 0-9.
3143 - ``[0-9]s``: The 32-bit SGPR register, number 0-9.
3148 - ``Q``, ``Um``, ``Un``, ``Uq``, ``Us``, ``Ut``, ``Uv``, ``Uy``: Memory address
3149 operand. Treated the same as operand ``m``, at the moment.
3151 ARM and ARM's Thumb2 mode:
3153 - ``j``: An immediate integer between 0 and 65535 (valid for ``MOVW``)
3154 - ``I``: An immediate integer valid for a data-processing instruction.
3155 - ``J``: An immediate integer between -4095 and 4095.
3156 - ``K``: An immediate integer whose bitwise inverse is valid for a
3157 data-processing instruction. (Can be used with template modifier "``B``" to
3158 print the inverted value).
3159 - ``L``: An immediate integer whose negation is valid for a data-processing
3160 instruction. (Can be used with template modifier "``n``" to print the negated
3162 - ``M``: A power of two or a integer between 0 and 32.
3163 - ``N``: Invalid immediate constraint.
3164 - ``O``: Invalid immediate constraint.
3165 - ``r``: A general-purpose 32-bit integer register (``r0-r15``).
3166 - ``l``: In Thumb2 mode, low 32-bit GPR registers (``r0-r7``). In ARM mode, same
3168 - ``h``: In Thumb2 mode, a high 32-bit GPR register (``r8-r15``). In ARM mode,
3170 - ``w``: A 32, 64, or 128-bit floating-point/SIMD register: ``s0-s31``,
3171 ``d0-d31``, or ``q0-q15``.
3172 - ``x``: A 32, 64, or 128-bit floating-point/SIMD register: ``s0-s15``,
3173 ``d0-d7``, or ``q0-q3``.
3174 - ``t``: A floating-point/SIMD register, only supports 32-bit values:
3179 - ``I``: An immediate integer between 0 and 255.
3180 - ``J``: An immediate integer between -255 and -1.
3181 - ``K``: An immediate integer between 0 and 255, with optional left-shift by
3183 - ``L``: An immediate integer between -7 and 7.
3184 - ``M``: An immediate integer which is a multiple of 4 between 0 and 1020.
3185 - ``N``: An immediate integer between 0 and 31.
3186 - ``O``: An immediate integer which is a multiple of 4 between -508 and 508.
3187 - ``r``: A low 32-bit GPR register (``r0-r7``).
3188 - ``l``: A low 32-bit GPR register (``r0-r7``).
3189 - ``h``: A high GPR register (``r0-r7``).
3190 - ``w``: A 32, 64, or 128-bit floating-point/SIMD register: ``s0-s31``,
3191 ``d0-d31``, or ``q0-q15``.
3192 - ``x``: A 32, 64, or 128-bit floating-point/SIMD register: ``s0-s15``,
3193 ``d0-d7``, or ``q0-q3``.
3194 - ``t``: A floating-point/SIMD register, only supports 32-bit values:
3200 - ``o``, ``v``: A memory address operand, treated the same as constraint ``m``,
3202 - ``r``: A 32 or 64-bit register.
3206 - ``r``: An 8 or 16-bit register.
3210 - ``I``: An immediate signed 16-bit integer.
3211 - ``J``: An immediate integer zero.
3212 - ``K``: An immediate unsigned 16-bit integer.
3213 - ``L``: An immediate 32-bit integer, where the lower 16 bits are 0.
3214 - ``N``: An immediate integer between -65535 and -1.
3215 - ``O``: An immediate signed 15-bit integer.
3216 - ``P``: An immediate integer between 1 and 65535.
3217 - ``m``: A memory address operand. In MIPS-SE mode, allows a base address
3218 register plus 16-bit immediate offset. In MIPS mode, just a base register.
3219 - ``R``: A memory address operand. In MIPS-SE mode, allows a base address
3220 register plus a 9-bit signed offset. In MIPS mode, the same as constraint
3222 - ``ZC``: A memory address operand, suitable for use in a ``pref``, ``ll``, or
3223 ``sc`` instruction on the given subtarget (details vary).
3224 - ``r``, ``d``, ``y``: A 32 or 64-bit GPR register.
3225 - ``f``: A 32 or 64-bit FPU register (``F0-F31``), or a 128-bit MSA register
3226 (``W0-W31``). In the case of MSA registers, it is recommended to use the ``w``
3227 argument modifier for compatibility with GCC.
3228 - ``c``: A 32-bit or 64-bit GPR register suitable for indirect jump (always
3230 - ``l``: The ``lo`` register, 32 or 64-bit.
3235 - ``b``: A 1-bit integer register.
3236 - ``c`` or ``h``: A 16-bit integer register.
3237 - ``r``: A 32-bit integer register.
3238 - ``l`` or ``N``: A 64-bit integer register.
3239 - ``f``: A 32-bit float register.
3240 - ``d``: A 64-bit float register.
3245 - ``I``: An immediate signed 16-bit integer.
3246 - ``J``: An immediate unsigned 16-bit integer, shifted left 16 bits.
3247 - ``K``: An immediate unsigned 16-bit integer.
3248 - ``L``: An immediate signed 16-bit integer, shifted left 16 bits.
3249 - ``M``: An immediate integer greater than 31.
3250 - ``N``: An immediate integer that is an exact power of 2.
3251 - ``O``: The immediate integer constant 0.
3252 - ``P``: An immediate integer constant whose negation is a signed 16-bit
3254 - ``es``, ``o``, ``Q``, ``Z``, ``Zy``: A memory address operand, currently
3255 treated the same as ``m``.
3256 - ``r``: A 32 or 64-bit integer register.
3257 - ``b``: A 32 or 64-bit integer register, excluding ``R0`` (that is:
3259 - ``f``: A 32 or 64-bit float register (``F0-F31``), or when QPX is enabled, a
3260 128 or 256-bit QPX register (``Q0-Q31``; aliases the ``F`` registers).
3261 - ``v``: For ``4 x f32`` or ``4 x f64`` types, when QPX is enabled, a
3262 128 or 256-bit QPX register (``Q0-Q31``), otherwise a 128-bit
3263 altivec vector register (``V0-V31``).
3265 .. FIXME: is this a bug that v accepts QPX registers? I think this
3266 is supposed to only use the altivec vector registers?
3268 - ``y``: Condition register (``CR0-CR7``).
3269 - ``wc``: An individual CR bit in a CR register.
3270 - ``wa``, ``wd``, ``wf``: Any 128-bit VSX vector register, from the full VSX
3271 register set (overlapping both the floating-point and vector register files).
3272 - ``ws``: A 32 or 64-bit floating point register, from the full VSX register
3277 - ``I``: An immediate 13-bit signed integer.
3278 - ``r``: A 32-bit integer register.
3282 - ``I``: An immediate unsigned 8-bit integer.
3283 - ``J``: An immediate unsigned 12-bit integer.
3284 - ``K``: An immediate signed 16-bit integer.
3285 - ``L``: An immediate signed 20-bit integer.
3286 - ``M``: An immediate integer 0x7fffffff.
3287 - ``Q``, ``R``, ``S``, ``T``: A memory address operand, treated the same as
3288 ``m``, at the moment.
3289 - ``r`` or ``d``: A 32, 64, or 128-bit integer register.
3290 - ``a``: A 32, 64, or 128-bit integer address register (excludes R0, which in an
3291 address context evaluates as zero).
3292 - ``h``: A 32-bit value in the high part of a 64bit data register
3294 - ``f``: A 32, 64, or 128-bit floating point register.
3298 - ``I``: An immediate integer between 0 and 31.
3299 - ``J``: An immediate integer between 0 and 64.
3300 - ``K``: An immediate signed 8-bit integer.
3301 - ``L``: An immediate integer, 0xff or 0xffff or (in 64-bit mode only)
3303 - ``M``: An immediate integer between 0 and 3.
3304 - ``N``: An immediate unsigned 8-bit integer.
3305 - ``O``: An immediate integer between 0 and 127.
3306 - ``e``: An immediate 32-bit signed integer.
3307 - ``Z``: An immediate 32-bit unsigned integer.
3308 - ``o``, ``v``: Treated the same as ``m``, at the moment.
3309 - ``q``: An 8, 16, 32, or 64-bit register which can be accessed as an 8-bit
3310 ``l`` integer register. On X86-32, this is the ``a``, ``b``, ``c``, and ``d``
3311 registers, and on X86-64, it is all of the integer registers.
3312 - ``Q``: An 8, 16, 32, or 64-bit register which can be accessed as an 8-bit
3313 ``h`` integer register. This is the ``a``, ``b``, ``c``, and ``d`` registers.
3314 - ``r`` or ``l``: An 8, 16, 32, or 64-bit integer register.
3315 - ``R``: An 8, 16, 32, or 64-bit "legacy" integer register -- one which has
3316 existed since i386, and can be accessed without the REX prefix.
3317 - ``f``: A 32, 64, or 80-bit '387 FPU stack pseudo-register.
3318 - ``y``: A 64-bit MMX register, if MMX is enabled.
3319 - ``x``: If SSE is enabled: a 32 or 64-bit scalar operand, or 128-bit vector
3320 operand in a SSE register. If AVX is also enabled, can also be a 256-bit
3321 vector operand in an AVX register. If AVX-512 is also enabled, can also be a
3322 512-bit vector operand in an AVX512 register, Otherwise, an error.
3323 - ``Y``: The same as ``x``, if *SSE2* is enabled, otherwise an error.
3324 - ``A``: Special case: allocates EAX first, then EDX, for a single operand (in
3325 32-bit mode, a 64-bit integer operand will get split into two registers). It
3326 is not recommended to use this constraint, as in 64-bit mode, the 64-bit
3327 operand will get allocated only to RAX -- if two 32-bit operands are needed,
3328 you're better off splitting it yourself, before passing it to the asm
3333 - ``r``: A 32-bit integer register.
3336 .. _inline-asm-modifiers:
3338 Asm template argument modifiers
3339 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
3341 In the asm template string, modifiers can be used on the operand reference, like
3344 The modifiers are, in general, expected to behave the same way they do in
3345 GCC. LLVM's support is often implemented on an 'as-needed' basis, to support C
3346 inline asm code which was supported by GCC. A mismatch in behavior between LLVM
3347 and GCC likely indicates a bug in LLVM.
3351 - ``c``: Print an immediate integer constant unadorned, without
3352 the target-specific immediate punctuation (e.g. no ``$`` prefix).
3353 - ``n``: Negate and print immediate integer constant unadorned, without the
3354 target-specific immediate punctuation (e.g. no ``$`` prefix).
3355 - ``l``: Print as an unadorned label, without the target-specific label
3356 punctuation (e.g. no ``$`` prefix).
3360 - ``w``: Print a GPR register with a ``w*`` name instead of ``x*`` name. E.g.,
3361 instead of ``x30``, print ``w30``.
3362 - ``x``: Print a GPR register with a ``x*`` name. (this is the default, anyhow).
3363 - ``b``, ``h``, ``s``, ``d``, ``q``: Print a floating-point/SIMD register with a
3364 ``b*``, ``h*``, ``s*``, ``d*``, or ``q*`` name, rather than the default of
3373 - ``a``: Print an operand as an address (with ``[`` and ``]`` surrounding a
3377 - ``y``: Print a VFP single-precision register as an indexed double (e.g. print
3378 as ``d4[1]`` instead of ``s9``)
3379 - ``B``: Bitwise invert and print an immediate integer constant without ``#``
3381 - ``L``: Print the low 16-bits of an immediate integer constant.
3382 - ``M``: Print as a register set suitable for ldm/stm. Also prints *all*
3383 register operands subsequent to the specified one (!), so use carefully.
3384 - ``Q``: Print the low-order register of a register-pair, or the low-order
3385 register of a two-register operand.
3386 - ``R``: Print the high-order register of a register-pair, or the high-order
3387 register of a two-register operand.
3388 - ``H``: Print the second register of a register-pair. (On a big-endian system,
3389 ``H`` is equivalent to ``Q``, and on little-endian system, ``H`` is equivalent
3392 .. FIXME: H doesn't currently support printing the second register
3393 of a two-register operand.
3395 - ``e``: Print the low doubleword register of a NEON quad register.
3396 - ``f``: Print the high doubleword register of a NEON quad register.
3397 - ``m``: Print the base register of a memory operand without the ``[`` and ``]``
3402 - ``L``: Print the second register of a two-register operand. Requires that it
3403 has been allocated consecutively to the first.
3405 .. FIXME: why is it restricted to consecutive ones? And there's
3406 nothing that ensures that happens, is there?
3408 - ``I``: Print the letter 'i' if the operand is an integer constant, otherwise
3409 nothing. Used to print 'addi' vs 'add' instructions.
3413 No additional modifiers.
3417 - ``X``: Print an immediate integer as hexadecimal
3418 - ``x``: Print the low 16 bits of an immediate integer as hexadecimal.
3419 - ``d``: Print an immediate integer as decimal.
3420 - ``m``: Subtract one and print an immediate integer as decimal.
3421 - ``z``: Print $0 if an immediate zero, otherwise print normally.
3422 - ``L``: Print the low-order register of a two-register operand, or prints the
3423 address of the low-order word of a double-word memory operand.
3425 .. FIXME: L seems to be missing memory operand support.
3427 - ``M``: Print the high-order register of a two-register operand, or prints the
3428 address of the high-order word of a double-word memory operand.
3430 .. FIXME: M seems to be missing memory operand support.
3432 - ``D``: Print the second register of a two-register operand, or prints the
3433 second word of a double-word memory operand. (On a big-endian system, ``D`` is
3434 equivalent to ``L``, and on little-endian system, ``D`` is equivalent to
3436 - ``w``: No effect. Provided for compatibility with GCC which requires this
3437 modifier in order to print MSA registers (``W0-W31``) with the ``f``
3446 - ``L``: Print the second register of a two-register operand. Requires that it
3447 has been allocated consecutively to the first.
3449 .. FIXME: why is it restricted to consecutive ones? And there's
3450 nothing that ensures that happens, is there?
3452 - ``I``: Print the letter 'i' if the operand is an integer constant, otherwise
3453 nothing. Used to print 'addi' vs 'add' instructions.
3454 - ``y``: For a memory operand, prints formatter for a two-register X-form
3455 instruction. (Currently always prints ``r0,OPERAND``).
3456 - ``U``: Prints 'u' if the memory operand is an update form, and nothing
3457 otherwise. (NOTE: LLVM does not support update form, so this will currently
3458 always print nothing)
3459 - ``X``: Prints 'x' if the memory operand is an indexed form. (NOTE: LLVM does
3460 not support indexed form, so this will currently always print nothing)
3468 SystemZ implements only ``n``, and does *not* support any of the other
3469 target-independent modifiers.
3473 - ``c``: Print an unadorned integer or symbol name. (The latter is
3474 target-specific behavior for this typically target-independent modifier).
3475 - ``A``: Print a register name with a '``*``' before it.
3476 - ``b``: Print an 8-bit register name (e.g. ``al``); do nothing on a memory
3478 - ``h``: Print the upper 8-bit register name (e.g. ``ah``); do nothing on a
3480 - ``w``: Print the 16-bit register name (e.g. ``ax``); do nothing on a memory
3482 - ``k``: Print the 32-bit register name (e.g. ``eax``); do nothing on a memory
3484 - ``q``: Print the 64-bit register name (e.g. ``rax``), if 64-bit registers are
3485 available, otherwise the 32-bit register name; do nothing on a memory operand.
3486 - ``n``: Negate and print an unadorned integer, or, for operands other than an
3487 immediate integer (e.g. a relocatable symbol expression), print a '-' before
3488 the operand. (The behavior for relocatable symbol expressions is a
3489 target-specific behavior for this typically target-independent modifier)
3490 - ``H``: Print a memory reference with additional offset +8.
3491 - ``P``: Print a memory reference or operand for use as the argument of a call
3492 instruction. (E.g. omit ``(rip)``, even though it's PC-relative.)
3496 No additional modifiers.
3502 The call instructions that wrap inline asm nodes may have a
3503 "``!srcloc``" MDNode attached to it that contains a list of constant
3504 integers. If present, the code generator will use the integer as the
3505 location cookie value when report errors through the ``LLVMContext``
3506 error reporting mechanisms. This allows a front-end to correlate backend
3507 errors that occur with inline asm back to the source code that produced
3510 .. code-block:: llvm
3512 call void asm sideeffect "something bad", ""(), !srcloc !42
3514 !42 = !{ i32 1234567 }
3516 It is up to the front-end to make sense of the magic numbers it places
3517 in the IR. If the MDNode contains multiple constants, the code generator
3518 will use the one that corresponds to the line of the asm that the error
3526 LLVM IR allows metadata to be attached to instructions in the program
3527 that can convey extra information about the code to the optimizers and
3528 code generator. One example application of metadata is source-level
3529 debug information. There are two metadata primitives: strings and nodes.
3531 Metadata does not have a type, and is not a value. If referenced from a
3532 ``call`` instruction, it uses the ``metadata`` type.
3534 All metadata are identified in syntax by a exclamation point ('``!``').
3536 .. _metadata-string:
3538 Metadata Nodes and Metadata Strings
3539 -----------------------------------
3541 A metadata string is a string surrounded by double quotes. It can
3542 contain any character by escaping non-printable characters with
3543 "``\xx``" where "``xx``" is the two digit hex code. For example:
3546 Metadata nodes are represented with notation similar to structure
3547 constants (a comma separated list of elements, surrounded by braces and
3548 preceded by an exclamation point). Metadata nodes can have any values as
3549 their operand. For example:
3551 .. code-block:: llvm
3553 !{ !"test\00", i32 10}
3555 Metadata nodes that aren't uniqued use the ``distinct`` keyword. For example:
3557 .. code-block:: llvm
3559 !0 = distinct !{!"test\00", i32 10}
3561 ``distinct`` nodes are useful when nodes shouldn't be merged based on their
3562 content. They can also occur when transformations cause uniquing collisions
3563 when metadata operands change.
3565 A :ref:`named metadata <namedmetadatastructure>` is a collection of
3566 metadata nodes, which can be looked up in the module symbol table. For
3569 .. code-block:: llvm
3573 Metadata can be used as function arguments. Here ``llvm.dbg.value``
3574 function is using two metadata arguments:
3576 .. code-block:: llvm
3578 call void @llvm.dbg.value(metadata !24, i64 0, metadata !25)
3580 Metadata can be attached with an instruction. Here metadata ``!21`` is
3581 attached to the ``add`` instruction using the ``!dbg`` identifier:
3583 .. code-block:: llvm
3585 %indvar.next = add i64 %indvar, 1, !dbg !21
3587 More information about specific metadata nodes recognized by the
3588 optimizers and code generator is found below.
3590 .. _specialized-metadata:
3592 Specialized Metadata Nodes
3593 ^^^^^^^^^^^^^^^^^^^^^^^^^^
3595 Specialized metadata nodes are custom data structures in metadata (as opposed
3596 to generic tuples). Their fields are labelled, and can be specified in any
3599 These aren't inherently debug info centric, but currently all the specialized
3600 metadata nodes are related to debug info.
3607 ``DICompileUnit`` nodes represent a compile unit. The ``enums:``,
3608 ``retainedTypes:``, ``subprograms:``, ``globals:`` and ``imports:`` fields are
3609 tuples containing the debug info to be emitted along with the compile unit,
3610 regardless of code optimizations (some nodes are only emitted if there are
3611 references to them from instructions).
3613 .. code-block:: llvm
3615 !0 = !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang",
3616 isOptimized: true, flags: "-O2", runtimeVersion: 2,
3617 splitDebugFilename: "abc.debug", emissionKind: 1,
3618 enums: !2, retainedTypes: !3, subprograms: !4,
3619 globals: !5, imports: !6)
3621 Compile unit descriptors provide the root scope for objects declared in a
3622 specific compilation unit. File descriptors are defined using this scope.
3623 These descriptors are collected by a named metadata ``!llvm.dbg.cu``. They
3624 keep track of subprograms, global variables, type information, and imported
3625 entities (declarations and namespaces).
3632 ``DIFile`` nodes represent files. The ``filename:`` can include slashes.
3634 .. code-block:: llvm
3636 !0 = !DIFile(filename: "path/to/file", directory: "/path/to/dir")
3638 Files are sometimes used in ``scope:`` fields, and are the only valid target
3639 for ``file:`` fields.
3646 ``DIBasicType`` nodes represent primitive types, such as ``int``, ``bool`` and
3647 ``float``. ``tag:`` defaults to ``DW_TAG_base_type``.
3649 .. code-block:: llvm
3651 !0 = !DIBasicType(name: "unsigned char", size: 8, align: 8,
3652 encoding: DW_ATE_unsigned_char)
3653 !1 = !DIBasicType(tag: DW_TAG_unspecified_type, name: "decltype(nullptr)")
3655 The ``encoding:`` describes the details of the type. Usually it's one of the
3658 .. code-block:: llvm
3664 DW_ATE_signed_char = 6
3666 DW_ATE_unsigned_char = 8
3668 .. _DISubroutineType:
3673 ``DISubroutineType`` nodes represent subroutine types. Their ``types:`` field
3674 refers to a tuple; the first operand is the return type, while the rest are the
3675 types of the formal arguments in order. If the first operand is ``null``, that
3676 represents a function with no return value (such as ``void foo() {}`` in C++).
3678 .. code-block:: llvm
3680 !0 = !BasicType(name: "int", size: 32, align: 32, DW_ATE_signed)
3681 !1 = !BasicType(name: "char", size: 8, align: 8, DW_ATE_signed_char)
3682 !2 = !DISubroutineType(types: !{null, !0, !1}) ; void (int, char)
3689 ``DIDerivedType`` nodes represent types derived from other types, such as
3692 .. code-block:: llvm
3694 !0 = !DIBasicType(name: "unsigned char", size: 8, align: 8,
3695 encoding: DW_ATE_unsigned_char)
3696 !1 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !0, size: 32,
3699 The following ``tag:`` values are valid:
3701 .. code-block:: llvm
3703 DW_TAG_formal_parameter = 5
3705 DW_TAG_pointer_type = 15
3706 DW_TAG_reference_type = 16
3708 DW_TAG_ptr_to_member_type = 31
3709 DW_TAG_const_type = 38
3710 DW_TAG_volatile_type = 53
3711 DW_TAG_restrict_type = 55
3713 ``DW_TAG_member`` is used to define a member of a :ref:`composite type
3714 <DICompositeType>` or :ref:`subprogram <DISubprogram>`. The type of the member
3715 is the ``baseType:``. The ``offset:`` is the member's bit offset.
3716 ``DW_TAG_formal_parameter`` is used to define a member which is a formal
3717 argument of a subprogram.
3719 ``DW_TAG_typedef`` is used to provide a name for the ``baseType:``.
3721 ``DW_TAG_pointer_type``, ``DW_TAG_reference_type``, ``DW_TAG_const_type``,
3722 ``DW_TAG_volatile_type`` and ``DW_TAG_restrict_type`` are used to qualify the
3725 Note that the ``void *`` type is expressed as a type derived from NULL.
3727 .. _DICompositeType:
3732 ``DICompositeType`` nodes represent types composed of other types, like
3733 structures and unions. ``elements:`` points to a tuple of the composed types.
3735 If the source language supports ODR, the ``identifier:`` field gives the unique
3736 identifier used for type merging between modules. When specified, other types
3737 can refer to composite types indirectly via a :ref:`metadata string
3738 <metadata-string>` that matches their identifier.
3740 .. code-block:: llvm
3742 !0 = !DIEnumerator(name: "SixKind", value: 7)
3743 !1 = !DIEnumerator(name: "SevenKind", value: 7)
3744 !2 = !DIEnumerator(name: "NegEightKind", value: -8)
3745 !3 = !DICompositeType(tag: DW_TAG_enumeration_type, name: "Enum", file: !12,
3746 line: 2, size: 32, align: 32, identifier: "_M4Enum",
3747 elements: !{!0, !1, !2})
3749 The following ``tag:`` values are valid:
3751 .. code-block:: llvm
3753 DW_TAG_array_type = 1
3754 DW_TAG_class_type = 2
3755 DW_TAG_enumeration_type = 4
3756 DW_TAG_structure_type = 19
3757 DW_TAG_union_type = 23
3758 DW_TAG_subroutine_type = 21
3759 DW_TAG_inheritance = 28
3762 For ``DW_TAG_array_type``, the ``elements:`` should be :ref:`subrange
3763 descriptors <DISubrange>`, each representing the range of subscripts at that
3764 level of indexing. The ``DIFlagVector`` flag to ``flags:`` indicates that an
3765 array type is a native packed vector.
3767 For ``DW_TAG_enumeration_type``, the ``elements:`` should be :ref:`enumerator
3768 descriptors <DIEnumerator>`, each representing the definition of an enumeration
3769 value for the set. All enumeration type descriptors are collected in the
3770 ``enums:`` field of the :ref:`compile unit <DICompileUnit>`.
3772 For ``DW_TAG_structure_type``, ``DW_TAG_class_type``, and
3773 ``DW_TAG_union_type``, the ``elements:`` should be :ref:`derived types
3774 <DIDerivedType>` with ``tag: DW_TAG_member`` or ``tag: DW_TAG_inheritance``.
3781 ``DISubrange`` nodes are the elements for ``DW_TAG_array_type`` variants of
3782 :ref:`DICompositeType`. ``count: -1`` indicates an empty array.
3784 .. code-block:: llvm
3786 !0 = !DISubrange(count: 5, lowerBound: 0) ; array counting from 0
3787 !1 = !DISubrange(count: 5, lowerBound: 1) ; array counting from 1
3788 !2 = !DISubrange(count: -1) ; empty array.
3795 ``DIEnumerator`` nodes are the elements for ``DW_TAG_enumeration_type``
3796 variants of :ref:`DICompositeType`.
3798 .. code-block:: llvm
3800 !0 = !DIEnumerator(name: "SixKind", value: 7)
3801 !1 = !DIEnumerator(name: "SevenKind", value: 7)
3802 !2 = !DIEnumerator(name: "NegEightKind", value: -8)
3804 DITemplateTypeParameter
3805 """""""""""""""""""""""
3807 ``DITemplateTypeParameter`` nodes represent type parameters to generic source
3808 language constructs. They are used (optionally) in :ref:`DICompositeType` and
3809 :ref:`DISubprogram` ``templateParams:`` fields.
3811 .. code-block:: llvm
3813 !0 = !DITemplateTypeParameter(name: "Ty", type: !1)
3815 DITemplateValueParameter
3816 """"""""""""""""""""""""
3818 ``DITemplateValueParameter`` nodes represent value parameters to generic source
3819 language constructs. ``tag:`` defaults to ``DW_TAG_template_value_parameter``,
3820 but if specified can also be set to ``DW_TAG_GNU_template_template_param`` or
3821 ``DW_TAG_GNU_template_param_pack``. They are used (optionally) in
3822 :ref:`DICompositeType` and :ref:`DISubprogram` ``templateParams:`` fields.
3824 .. code-block:: llvm
3826 !0 = !DITemplateValueParameter(name: "Ty", type: !1, value: i32 7)
3831 ``DINamespace`` nodes represent namespaces in the source language.
3833 .. code-block:: llvm
3835 !0 = !DINamespace(name: "myawesomeproject", scope: !1, file: !2, line: 7)
3840 ``DIGlobalVariable`` nodes represent global variables in the source language.
3842 .. code-block:: llvm
3844 !0 = !DIGlobalVariable(name: "foo", linkageName: "foo", scope: !1,
3845 file: !2, line: 7, type: !3, isLocal: true,
3846 isDefinition: false, variable: i32* @foo,
3849 All global variables should be referenced by the `globals:` field of a
3850 :ref:`compile unit <DICompileUnit>`.
3857 ``DISubprogram`` nodes represent functions from the source language. The
3858 ``variables:`` field points at :ref:`variables <DILocalVariable>` that must be
3859 retained, even if their IR counterparts are optimized out of the IR. The
3860 ``type:`` field must point at an :ref:`DISubroutineType`.
3862 .. code-block:: llvm
3864 !0 = !DISubprogram(name: "foo", linkageName: "_Zfoov", scope: !1,
3865 file: !2, line: 7, type: !3, isLocal: true,
3866 isDefinition: false, scopeLine: 8, containingType: !4,
3867 virtuality: DW_VIRTUALITY_pure_virtual, virtualIndex: 10,
3868 flags: DIFlagPrototyped, isOptimized: true,
3869 function: void ()* @_Z3foov,
3870 templateParams: !5, declaration: !6, variables: !7)
3877 ``DILexicalBlock`` nodes describe nested blocks within a :ref:`subprogram
3878 <DISubprogram>`. The line number and column numbers are used to dinstinguish
3879 two lexical blocks at same depth. They are valid targets for ``scope:``
3882 .. code-block:: llvm
3884 !0 = distinct !DILexicalBlock(scope: !1, file: !2, line: 7, column: 35)
3886 Usually lexical blocks are ``distinct`` to prevent node merging based on
3889 .. _DILexicalBlockFile:
3894 ``DILexicalBlockFile`` nodes are used to discriminate between sections of a
3895 :ref:`lexical block <DILexicalBlock>`. The ``file:`` field can be changed to
3896 indicate textual inclusion, or the ``discriminator:`` field can be used to
3897 discriminate between control flow within a single block in the source language.
3899 .. code-block:: llvm
3901 !0 = !DILexicalBlock(scope: !3, file: !4, line: 7, column: 35)
3902 !1 = !DILexicalBlockFile(scope: !0, file: !4, discriminator: 0)
3903 !2 = !DILexicalBlockFile(scope: !0, file: !4, discriminator: 1)
3910 ``DILocation`` nodes represent source debug locations. The ``scope:`` field is
3911 mandatory, and points at an :ref:`DILexicalBlockFile`, an
3912 :ref:`DILexicalBlock`, or an :ref:`DISubprogram`.
3914 .. code-block:: llvm
3916 !0 = !DILocation(line: 2900, column: 42, scope: !1, inlinedAt: !2)
3918 .. _DILocalVariable:
3923 ``DILocalVariable`` nodes represent local variables in the source language. If
3924 the ``arg:`` field is set to non-zero, then this variable is a subprogram
3925 parameter, and it will be included in the ``variables:`` field of its
3926 :ref:`DISubprogram`.
3928 .. code-block:: llvm
3930 !0 = !DILocalVariable(name: "this", arg: 1, scope: !3, file: !2, line: 7,
3931 type: !3, flags: DIFlagArtificial)
3932 !1 = !DILocalVariable(name: "x", arg: 2, scope: !4, file: !2, line: 7,
3934 !2 = !DILocalVariable(name: "y", scope: !5, file: !2, line: 7, type: !3)
3939 ``DIExpression`` nodes represent DWARF expression sequences. They are used in
3940 :ref:`debug intrinsics<dbg_intrinsics>` (such as ``llvm.dbg.declare``) to
3941 describe how the referenced LLVM variable relates to the source language
3944 The current supported vocabulary is limited:
3946 - ``DW_OP_deref`` dereferences the working expression.
3947 - ``DW_OP_plus, 93`` adds ``93`` to the working expression.
3948 - ``DW_OP_bit_piece, 16, 8`` specifies the offset and size (``16`` and ``8``
3949 here, respectively) of the variable piece from the working expression.
3951 .. code-block:: llvm
3953 !0 = !DIExpression(DW_OP_deref)
3954 !1 = !DIExpression(DW_OP_plus, 3)
3955 !2 = !DIExpression(DW_OP_bit_piece, 3, 7)
3956 !3 = !DIExpression(DW_OP_deref, DW_OP_plus, 3, DW_OP_bit_piece, 3, 7)
3961 ``DIObjCProperty`` nodes represent Objective-C property nodes.
3963 .. code-block:: llvm
3965 !3 = !DIObjCProperty(name: "foo", file: !1, line: 7, setter: "setFoo",
3966 getter: "getFoo", attributes: 7, type: !2)
3971 ``DIImportedEntity`` nodes represent entities (such as modules) imported into a
3974 .. code-block:: llvm
3976 !2 = !DIImportedEntity(tag: DW_TAG_imported_module, name: "foo", scope: !0,
3977 entity: !1, line: 7)
3982 In LLVM IR, memory does not have types, so LLVM's own type system is not
3983 suitable for doing TBAA. Instead, metadata is added to the IR to
3984 describe a type system of a higher level language. This can be used to
3985 implement typical C/C++ TBAA, but it can also be used to implement
3986 custom alias analysis behavior for other languages.
3988 The current metadata format is very simple. TBAA metadata nodes have up
3989 to three fields, e.g.:
3991 .. code-block:: llvm
3993 !0 = !{ !"an example type tree" }
3994 !1 = !{ !"int", !0 }
3995 !2 = !{ !"float", !0 }
3996 !3 = !{ !"const float", !2, i64 1 }
3998 The first field is an identity field. It can be any value, usually a
3999 metadata string, which uniquely identifies the type. The most important
4000 name in the tree is the name of the root node. Two trees with different
4001 root node names are entirely disjoint, even if they have leaves with
4004 The second field identifies the type's parent node in the tree, or is
4005 null or omitted for a root node. A type is considered to alias all of
4006 its descendants and all of its ancestors in the tree. Also, a type is
4007 considered to alias all types in other trees, so that bitcode produced
4008 from multiple front-ends is handled conservatively.
4010 If the third field is present, it's an integer which if equal to 1
4011 indicates that the type is "constant" (meaning
4012 ``pointsToConstantMemory`` should return true; see `other useful
4013 AliasAnalysis methods <AliasAnalysis.html#OtherItfs>`_).
4015 '``tbaa.struct``' Metadata
4016 ^^^^^^^^^^^^^^^^^^^^^^^^^^
4018 The :ref:`llvm.memcpy <int_memcpy>` is often used to implement
4019 aggregate assignment operations in C and similar languages, however it
4020 is defined to copy a contiguous region of memory, which is more than
4021 strictly necessary for aggregate types which contain holes due to
4022 padding. Also, it doesn't contain any TBAA information about the fields
4025 ``!tbaa.struct`` metadata can describe which memory subregions in a
4026 memcpy are padding and what the TBAA tags of the struct are.
4028 The current metadata format is very simple. ``!tbaa.struct`` metadata
4029 nodes are a list of operands which are in conceptual groups of three.
4030 For each group of three, the first operand gives the byte offset of a
4031 field in bytes, the second gives its size in bytes, and the third gives
4034 .. code-block:: llvm
4036 !4 = !{ i64 0, i64 4, !1, i64 8, i64 4, !2 }
4038 This describes a struct with two fields. The first is at offset 0 bytes
4039 with size 4 bytes, and has tbaa tag !1. The second is at offset 8 bytes
4040 and has size 4 bytes and has tbaa tag !2.
4042 Note that the fields need not be contiguous. In this example, there is a
4043 4 byte gap between the two fields. This gap represents padding which
4044 does not carry useful data and need not be preserved.
4046 '``noalias``' and '``alias.scope``' Metadata
4047 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4049 ``noalias`` and ``alias.scope`` metadata provide the ability to specify generic
4050 noalias memory-access sets. This means that some collection of memory access
4051 instructions (loads, stores, memory-accessing calls, etc.) that carry
4052 ``noalias`` metadata can specifically be specified not to alias with some other
4053 collection of memory access instructions that carry ``alias.scope`` metadata.
4054 Each type of metadata specifies a list of scopes where each scope has an id and
4055 a domain. When evaluating an aliasing query, if for some domain, the set
4056 of scopes with that domain in one instruction's ``alias.scope`` list is a
4057 subset of (or equal to) the set of scopes for that domain in another
4058 instruction's ``noalias`` list, then the two memory accesses are assumed not to
4061 The metadata identifying each domain is itself a list containing one or two
4062 entries. The first entry is the name of the domain. Note that if the name is a
4063 string then it can be combined accross functions and translation units. A
4064 self-reference can be used to create globally unique domain names. A
4065 descriptive string may optionally be provided as a second list entry.
4067 The metadata identifying each scope is also itself a list containing two or
4068 three entries. The first entry is the name of the scope. Note that if the name
4069 is a string then it can be combined accross functions and translation units. A
4070 self-reference can be used to create globally unique scope names. A metadata
4071 reference to the scope's domain is the second entry. A descriptive string may
4072 optionally be provided as a third list entry.
4076 .. code-block:: llvm
4078 ; Two scope domains:
4082 ; Some scopes in these domains:
4088 !5 = !{!4} ; A list containing only scope !4
4092 ; These two instructions don't alias:
4093 %0 = load float, float* %c, align 4, !alias.scope !5
4094 store float %0, float* %arrayidx.i, align 4, !noalias !5
4096 ; These two instructions also don't alias (for domain !1, the set of scopes
4097 ; in the !alias.scope equals that in the !noalias list):
4098 %2 = load float, float* %c, align 4, !alias.scope !5
4099 store float %2, float* %arrayidx.i2, align 4, !noalias !6
4101 ; These two instructions may alias (for domain !0, the set of scopes in
4102 ; the !noalias list is not a superset of, or equal to, the scopes in the
4103 ; !alias.scope list):
4104 %2 = load float, float* %c, align 4, !alias.scope !6
4105 store float %0, float* %arrayidx.i, align 4, !noalias !7
4107 '``fpmath``' Metadata
4108 ^^^^^^^^^^^^^^^^^^^^^
4110 ``fpmath`` metadata may be attached to any instruction of floating point
4111 type. It can be used to express the maximum acceptable error in the
4112 result of that instruction, in ULPs, thus potentially allowing the
4113 compiler to use a more efficient but less accurate method of computing
4114 it. ULP is defined as follows:
4116 If ``x`` is a real number that lies between two finite consecutive
4117 floating-point numbers ``a`` and ``b``, without being equal to one
4118 of them, then ``ulp(x) = |b - a|``, otherwise ``ulp(x)`` is the
4119 distance between the two non-equal finite floating-point numbers
4120 nearest ``x``. Moreover, ``ulp(NaN)`` is ``NaN``.
4122 The metadata node shall consist of a single positive floating point
4123 number representing the maximum relative error, for example:
4125 .. code-block:: llvm
4127 !0 = !{ float 2.5 } ; maximum acceptable inaccuracy is 2.5 ULPs
4131 '``range``' Metadata
4132 ^^^^^^^^^^^^^^^^^^^^
4134 ``range`` metadata may be attached only to ``load``, ``call`` and ``invoke`` of
4135 integer types. It expresses the possible ranges the loaded value or the value
4136 returned by the called function at this call site is in. The ranges are
4137 represented with a flattened list of integers. The loaded value or the value
4138 returned is known to be in the union of the ranges defined by each consecutive
4139 pair. Each pair has the following properties:
4141 - The type must match the type loaded by the instruction.
4142 - The pair ``a,b`` represents the range ``[a,b)``.
4143 - Both ``a`` and ``b`` are constants.
4144 - The range is allowed to wrap.
4145 - The range should not represent the full or empty set. That is,
4148 In addition, the pairs must be in signed order of the lower bound and
4149 they must be non-contiguous.
4153 .. code-block:: llvm
4155 %a = load i8, i8* %x, align 1, !range !0 ; Can only be 0 or 1
4156 %b = load i8, i8* %y, align 1, !range !1 ; Can only be 255 (-1), 0 or 1
4157 %c = call i8 @foo(), !range !2 ; Can only be 0, 1, 3, 4 or 5
4158 %d = invoke i8 @bar() to label %cont
4159 unwind label %lpad, !range !3 ; Can only be -2, -1, 3, 4 or 5
4161 !0 = !{ i8 0, i8 2 }
4162 !1 = !{ i8 255, i8 2 }
4163 !2 = !{ i8 0, i8 2, i8 3, i8 6 }
4164 !3 = !{ i8 -2, i8 0, i8 3, i8 6 }
4169 It is sometimes useful to attach information to loop constructs. Currently,
4170 loop metadata is implemented as metadata attached to the branch instruction
4171 in the loop latch block. This type of metadata refer to a metadata node that is
4172 guaranteed to be separate for each loop. The loop identifier metadata is
4173 specified with the name ``llvm.loop``.
4175 The loop identifier metadata is implemented using a metadata that refers to
4176 itself to avoid merging it with any other identifier metadata, e.g.,
4177 during module linkage or function inlining. That is, each loop should refer
4178 to their own identification metadata even if they reside in separate functions.
4179 The following example contains loop identifier metadata for two separate loop
4182 .. code-block:: llvm
4187 The loop identifier metadata can be used to specify additional
4188 per-loop metadata. Any operands after the first operand can be treated
4189 as user-defined metadata. For example the ``llvm.loop.unroll.count``
4190 suggests an unroll factor to the loop unroller:
4192 .. code-block:: llvm
4194 br i1 %exitcond, label %._crit_edge, label %.lr.ph, !llvm.loop !0
4197 !1 = !{!"llvm.loop.unroll.count", i32 4}
4199 '``llvm.loop.vectorize``' and '``llvm.loop.interleave``'
4200 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4202 Metadata prefixed with ``llvm.loop.vectorize`` or ``llvm.loop.interleave`` are
4203 used to control per-loop vectorization and interleaving parameters such as
4204 vectorization width and interleave count. These metadata should be used in
4205 conjunction with ``llvm.loop`` loop identification metadata. The
4206 ``llvm.loop.vectorize`` and ``llvm.loop.interleave`` metadata are only
4207 optimization hints and the optimizer will only interleave and vectorize loops if
4208 it believes it is safe to do so. The ``llvm.mem.parallel_loop_access`` metadata
4209 which contains information about loop-carried memory dependencies can be helpful
4210 in determining the safety of these transformations.
4212 '``llvm.loop.interleave.count``' Metadata
4213 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4215 This metadata suggests an interleave count to the loop interleaver.
4216 The first operand is the string ``llvm.loop.interleave.count`` and the
4217 second operand is an integer specifying the interleave count. For
4220 .. code-block:: llvm
4222 !0 = !{!"llvm.loop.interleave.count", i32 4}
4224 Note that setting ``llvm.loop.interleave.count`` to 1 disables interleaving
4225 multiple iterations of the loop. If ``llvm.loop.interleave.count`` is set to 0
4226 then the interleave count will be determined automatically.
4228 '``llvm.loop.vectorize.enable``' Metadata
4229 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4231 This metadata selectively enables or disables vectorization for the loop. The
4232 first operand is the string ``llvm.loop.vectorize.enable`` and the second operand
4233 is a bit. If the bit operand value is 1 vectorization is enabled. A value of
4234 0 disables vectorization:
4236 .. code-block:: llvm
4238 !0 = !{!"llvm.loop.vectorize.enable", i1 0}
4239 !1 = !{!"llvm.loop.vectorize.enable", i1 1}
4241 '``llvm.loop.vectorize.width``' Metadata
4242 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4244 This metadata sets the target width of the vectorizer. The first
4245 operand is the string ``llvm.loop.vectorize.width`` and the second
4246 operand is an integer specifying the width. For example:
4248 .. code-block:: llvm
4250 !0 = !{!"llvm.loop.vectorize.width", i32 4}
4252 Note that setting ``llvm.loop.vectorize.width`` to 1 disables
4253 vectorization of the loop. If ``llvm.loop.vectorize.width`` is set to
4254 0 or if the loop does not have this metadata the width will be
4255 determined automatically.
4257 '``llvm.loop.unroll``'
4258 ^^^^^^^^^^^^^^^^^^^^^^
4260 Metadata prefixed with ``llvm.loop.unroll`` are loop unrolling
4261 optimization hints such as the unroll factor. ``llvm.loop.unroll``
4262 metadata should be used in conjunction with ``llvm.loop`` loop
4263 identification metadata. The ``llvm.loop.unroll`` metadata are only
4264 optimization hints and the unrolling will only be performed if the
4265 optimizer believes it is safe to do so.
4267 '``llvm.loop.unroll.count``' Metadata
4268 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4270 This metadata suggests an unroll factor to the loop unroller. The
4271 first operand is the string ``llvm.loop.unroll.count`` and the second
4272 operand is a positive integer specifying the unroll factor. For
4275 .. code-block:: llvm
4277 !0 = !{!"llvm.loop.unroll.count", i32 4}
4279 If the trip count of the loop is less than the unroll count the loop
4280 will be partially unrolled.
4282 '``llvm.loop.unroll.disable``' Metadata
4283 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4285 This metadata disables loop unrolling. The metadata has a single operand
4286 which is the string ``llvm.loop.unroll.disable``. For example:
4288 .. code-block:: llvm
4290 !0 = !{!"llvm.loop.unroll.disable"}
4292 '``llvm.loop.unroll.runtime.disable``' Metadata
4293 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4295 This metadata disables runtime loop unrolling. The metadata has a single
4296 operand which is the string ``llvm.loop.unroll.runtime.disable``. For example:
4298 .. code-block:: llvm
4300 !0 = !{!"llvm.loop.unroll.runtime.disable"}
4302 '``llvm.loop.unroll.enable``' Metadata
4303 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4305 This metadata suggests that the loop should be fully unrolled if the trip count
4306 is known at compile time and partially unrolled if the trip count is not known
4307 at compile time. The metadata has a single operand which is the string
4308 ``llvm.loop.unroll.enable``. For example:
4310 .. code-block:: llvm
4312 !0 = !{!"llvm.loop.unroll.enable"}
4314 '``llvm.loop.unroll.full``' Metadata
4315 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4317 This metadata suggests that the loop should be unrolled fully. The
4318 metadata has a single operand which is the string ``llvm.loop.unroll.full``.
4321 .. code-block:: llvm
4323 !0 = !{!"llvm.loop.unroll.full"}
4328 Metadata types used to annotate memory accesses with information helpful
4329 for optimizations are prefixed with ``llvm.mem``.
4331 '``llvm.mem.parallel_loop_access``' Metadata
4332 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4334 The ``llvm.mem.parallel_loop_access`` metadata refers to a loop identifier,
4335 or metadata containing a list of loop identifiers for nested loops.
4336 The metadata is attached to memory accessing instructions and denotes that
4337 no loop carried memory dependence exist between it and other instructions denoted
4338 with the same loop identifier.
4340 Precisely, given two instructions ``m1`` and ``m2`` that both have the
4341 ``llvm.mem.parallel_loop_access`` metadata, with ``L1`` and ``L2`` being the
4342 set of loops associated with that metadata, respectively, then there is no loop
4343 carried dependence between ``m1`` and ``m2`` for loops in both ``L1`` and
4346 As a special case, if all memory accessing instructions in a loop have
4347 ``llvm.mem.parallel_loop_access`` metadata that refers to that loop, then the
4348 loop has no loop carried memory dependences and is considered to be a parallel
4351 Note that if not all memory access instructions have such metadata referring to
4352 the loop, then the loop is considered not being trivially parallel. Additional
4353 memory dependence analysis is required to make that determination. As a fail
4354 safe mechanism, this causes loops that were originally parallel to be considered
4355 sequential (if optimization passes that are unaware of the parallel semantics
4356 insert new memory instructions into the loop body).
4358 Example of a loop that is considered parallel due to its correct use of
4359 both ``llvm.loop`` and ``llvm.mem.parallel_loop_access``
4360 metadata types that refer to the same loop identifier metadata.
4362 .. code-block:: llvm
4366 %val0 = load i32, i32* %arrayidx, !llvm.mem.parallel_loop_access !0
4368 store i32 %val0, i32* %arrayidx1, !llvm.mem.parallel_loop_access !0
4370 br i1 %exitcond, label %for.end, label %for.body, !llvm.loop !0
4376 It is also possible to have nested parallel loops. In that case the
4377 memory accesses refer to a list of loop identifier metadata nodes instead of
4378 the loop identifier metadata node directly:
4380 .. code-block:: llvm
4384 %val1 = load i32, i32* %arrayidx3, !llvm.mem.parallel_loop_access !2
4386 br label %inner.for.body
4390 %val0 = load i32, i32* %arrayidx1, !llvm.mem.parallel_loop_access !0
4392 store i32 %val0, i32* %arrayidx2, !llvm.mem.parallel_loop_access !0
4394 br i1 %exitcond, label %inner.for.end, label %inner.for.body, !llvm.loop !1
4398 store i32 %val1, i32* %arrayidx4, !llvm.mem.parallel_loop_access !2
4400 br i1 %exitcond, label %outer.for.end, label %outer.for.body, !llvm.loop !2
4402 outer.for.end: ; preds = %for.body
4404 !0 = !{!1, !2} ; a list of loop identifiers
4405 !1 = !{!1} ; an identifier for the inner loop
4406 !2 = !{!2} ; an identifier for the outer loop
4411 The ``llvm.bitsets`` global metadata is used to implement
4412 :doc:`bitsets <BitSets>`.
4414 Module Flags Metadata
4415 =====================
4417 Information about the module as a whole is difficult to convey to LLVM's
4418 subsystems. The LLVM IR isn't sufficient to transmit this information.
4419 The ``llvm.module.flags`` named metadata exists in order to facilitate
4420 this. These flags are in the form of key / value pairs --- much like a
4421 dictionary --- making it easy for any subsystem who cares about a flag to
4424 The ``llvm.module.flags`` metadata contains a list of metadata triplets.
4425 Each triplet has the following form:
4427 - The first element is a *behavior* flag, which specifies the behavior
4428 when two (or more) modules are merged together, and it encounters two
4429 (or more) metadata with the same ID. The supported behaviors are
4431 - The second element is a metadata string that is a unique ID for the
4432 metadata. Each module may only have one flag entry for each unique ID (not
4433 including entries with the **Require** behavior).
4434 - The third element is the value of the flag.
4436 When two (or more) modules are merged together, the resulting
4437 ``llvm.module.flags`` metadata is the union of the modules' flags. That is, for
4438 each unique metadata ID string, there will be exactly one entry in the merged
4439 modules ``llvm.module.flags`` metadata table, and the value for that entry will
4440 be determined by the merge behavior flag, as described below. The only exception
4441 is that entries with the *Require* behavior are always preserved.
4443 The following behaviors are supported:
4454 Emits an error if two values disagree, otherwise the resulting value
4455 is that of the operands.
4459 Emits a warning if two values disagree. The result value will be the
4460 operand for the flag from the first module being linked.
4464 Adds a requirement that another module flag be present and have a
4465 specified value after linking is performed. The value must be a
4466 metadata pair, where the first element of the pair is the ID of the
4467 module flag to be restricted, and the second element of the pair is
4468 the value the module flag should be restricted to. This behavior can
4469 be used to restrict the allowable results (via triggering of an
4470 error) of linking IDs with the **Override** behavior.
4474 Uses the specified value, regardless of the behavior or value of the
4475 other module. If both modules specify **Override**, but the values
4476 differ, an error will be emitted.
4480 Appends the two values, which are required to be metadata nodes.
4484 Appends the two values, which are required to be metadata
4485 nodes. However, duplicate entries in the second list are dropped
4486 during the append operation.
4488 It is an error for a particular unique flag ID to have multiple behaviors,
4489 except in the case of **Require** (which adds restrictions on another metadata
4490 value) or **Override**.
4492 An example of module flags:
4494 .. code-block:: llvm
4496 !0 = !{ i32 1, !"foo", i32 1 }
4497 !1 = !{ i32 4, !"bar", i32 37 }
4498 !2 = !{ i32 2, !"qux", i32 42 }
4499 !3 = !{ i32 3, !"qux",
4504 !llvm.module.flags = !{ !0, !1, !2, !3 }
4506 - Metadata ``!0`` has the ID ``!"foo"`` and the value '1'. The behavior
4507 if two or more ``!"foo"`` flags are seen is to emit an error if their
4508 values are not equal.
4510 - Metadata ``!1`` has the ID ``!"bar"`` and the value '37'. The
4511 behavior if two or more ``!"bar"`` flags are seen is to use the value
4514 - Metadata ``!2`` has the ID ``!"qux"`` and the value '42'. The
4515 behavior if two or more ``!"qux"`` flags are seen is to emit a
4516 warning if their values are not equal.
4518 - Metadata ``!3`` has the ID ``!"qux"`` and the value:
4524 The behavior is to emit an error if the ``llvm.module.flags`` does not
4525 contain a flag with the ID ``!"foo"`` that has the value '1' after linking is
4528 Objective-C Garbage Collection Module Flags Metadata
4529 ----------------------------------------------------
4531 On the Mach-O platform, Objective-C stores metadata about garbage
4532 collection in a special section called "image info". The metadata
4533 consists of a version number and a bitmask specifying what types of
4534 garbage collection are supported (if any) by the file. If two or more
4535 modules are linked together their garbage collection metadata needs to
4536 be merged rather than appended together.
4538 The Objective-C garbage collection module flags metadata consists of the
4539 following key-value pairs:
4548 * - ``Objective-C Version``
4549 - **[Required]** --- The Objective-C ABI version. Valid values are 1 and 2.
4551 * - ``Objective-C Image Info Version``
4552 - **[Required]** --- The version of the image info section. Currently
4555 * - ``Objective-C Image Info Section``
4556 - **[Required]** --- The section to place the metadata. Valid values are
4557 ``"__OBJC, __image_info, regular"`` for Objective-C ABI version 1, and
4558 ``"__DATA,__objc_imageinfo, regular, no_dead_strip"`` for
4559 Objective-C ABI version 2.
4561 * - ``Objective-C Garbage Collection``
4562 - **[Required]** --- Specifies whether garbage collection is supported or
4563 not. Valid values are 0, for no garbage collection, and 2, for garbage
4564 collection supported.
4566 * - ``Objective-C GC Only``
4567 - **[Optional]** --- Specifies that only garbage collection is supported.
4568 If present, its value must be 6. This flag requires that the
4569 ``Objective-C Garbage Collection`` flag have the value 2.
4571 Some important flag interactions:
4573 - If a module with ``Objective-C Garbage Collection`` set to 0 is
4574 merged with a module with ``Objective-C Garbage Collection`` set to
4575 2, then the resulting module has the
4576 ``Objective-C Garbage Collection`` flag set to 0.
4577 - A module with ``Objective-C Garbage Collection`` set to 0 cannot be
4578 merged with a module with ``Objective-C GC Only`` set to 6.
4580 Automatic Linker Flags Module Flags Metadata
4581 --------------------------------------------
4583 Some targets support embedding flags to the linker inside individual object
4584 files. Typically this is used in conjunction with language extensions which
4585 allow source files to explicitly declare the libraries they depend on, and have
4586 these automatically be transmitted to the linker via object files.
4588 These flags are encoded in the IR using metadata in the module flags section,
4589 using the ``Linker Options`` key. The merge behavior for this flag is required
4590 to be ``AppendUnique``, and the value for the key is expected to be a metadata
4591 node which should be a list of other metadata nodes, each of which should be a
4592 list of metadata strings defining linker options.
4594 For example, the following metadata section specifies two separate sets of
4595 linker options, presumably to link against ``libz`` and the ``Cocoa``
4598 !0 = !{ i32 6, !"Linker Options",
4601 !{ !"-framework", !"Cocoa" } } }
4602 !llvm.module.flags = !{ !0 }
4604 The metadata encoding as lists of lists of options, as opposed to a collapsed
4605 list of options, is chosen so that the IR encoding can use multiple option
4606 strings to specify e.g., a single library, while still having that specifier be
4607 preserved as an atomic element that can be recognized by a target specific
4608 assembly writer or object file emitter.
4610 Each individual option is required to be either a valid option for the target's
4611 linker, or an option that is reserved by the target specific assembly writer or
4612 object file emitter. No other aspect of these options is defined by the IR.
4614 C type width Module Flags Metadata
4615 ----------------------------------
4617 The ARM backend emits a section into each generated object file describing the
4618 options that it was compiled with (in a compiler-independent way) to prevent
4619 linking incompatible objects, and to allow automatic library selection. Some
4620 of these options are not visible at the IR level, namely wchar_t width and enum
4623 To pass this information to the backend, these options are encoded in module
4624 flags metadata, using the following key-value pairs:
4634 - * 0 --- sizeof(wchar_t) == 4
4635 * 1 --- sizeof(wchar_t) == 2
4638 - * 0 --- Enums are at least as large as an ``int``.
4639 * 1 --- Enums are stored in the smallest integer type which can
4640 represent all of its values.
4642 For example, the following metadata section specifies that the module was
4643 compiled with a ``wchar_t`` width of 4 bytes, and the underlying type of an
4644 enum is the smallest type which can represent all of its values::
4646 !llvm.module.flags = !{!0, !1}
4647 !0 = !{i32 1, !"short_wchar", i32 1}
4648 !1 = !{i32 1, !"short_enum", i32 0}
4650 .. _intrinsicglobalvariables:
4652 Intrinsic Global Variables
4653 ==========================
4655 LLVM has a number of "magic" global variables that contain data that
4656 affect code generation or other IR semantics. These are documented here.
4657 All globals of this sort should have a section specified as
4658 "``llvm.metadata``". This section and all globals that start with
4659 "``llvm.``" are reserved for use by LLVM.
4663 The '``llvm.used``' Global Variable
4664 -----------------------------------
4666 The ``@llvm.used`` global is an array which has
4667 :ref:`appending linkage <linkage_appending>`. This array contains a list of
4668 pointers to named global variables, functions and aliases which may optionally
4669 have a pointer cast formed of bitcast or getelementptr. For example, a legal
4672 .. code-block:: llvm
4677 @llvm.used = appending global [2 x i8*] [
4679 i8* bitcast (i32* @Y to i8*)
4680 ], section "llvm.metadata"
4682 If a symbol appears in the ``@llvm.used`` list, then the compiler, assembler,
4683 and linker are required to treat the symbol as if there is a reference to the
4684 symbol that it cannot see (which is why they have to be named). For example, if
4685 a variable has internal linkage and no references other than that from the
4686 ``@llvm.used`` list, it cannot be deleted. This is commonly used to represent
4687 references from inline asms and other things the compiler cannot "see", and
4688 corresponds to "``attribute((used))``" in GNU C.
4690 On some targets, the code generator must emit a directive to the
4691 assembler or object file to prevent the assembler and linker from
4692 molesting the symbol.
4694 .. _gv_llvmcompilerused:
4696 The '``llvm.compiler.used``' Global Variable
4697 --------------------------------------------
4699 The ``@llvm.compiler.used`` directive is the same as the ``@llvm.used``
4700 directive, except that it only prevents the compiler from touching the
4701 symbol. On targets that support it, this allows an intelligent linker to
4702 optimize references to the symbol without being impeded as it would be
4705 This is a rare construct that should only be used in rare circumstances,
4706 and should not be exposed to source languages.
4708 .. _gv_llvmglobalctors:
4710 The '``llvm.global_ctors``' Global Variable
4711 -------------------------------------------
4713 .. code-block:: llvm
4715 %0 = type { i32, void ()*, i8* }
4716 @llvm.global_ctors = appending global [1 x %0] [%0 { i32 65535, void ()* @ctor, i8* @data }]
4718 The ``@llvm.global_ctors`` array contains a list of constructor
4719 functions, priorities, and an optional associated global or function.
4720 The functions referenced by this array will be called in ascending order
4721 of priority (i.e. lowest first) when the module is loaded. The order of
4722 functions with the same priority is not defined.
4724 If the third field is present, non-null, and points to a global variable
4725 or function, the initializer function will only run if the associated
4726 data from the current module is not discarded.
4728 .. _llvmglobaldtors:
4730 The '``llvm.global_dtors``' Global Variable
4731 -------------------------------------------
4733 .. code-block:: llvm
4735 %0 = type { i32, void ()*, i8* }
4736 @llvm.global_dtors = appending global [1 x %0] [%0 { i32 65535, void ()* @dtor, i8* @data }]
4738 The ``@llvm.global_dtors`` array contains a list of destructor
4739 functions, priorities, and an optional associated global or function.
4740 The functions referenced by this array will be called in descending
4741 order of priority (i.e. highest first) when the module is unloaded. The
4742 order of functions with the same priority is not defined.
4744 If the third field is present, non-null, and points to a global variable
4745 or function, the destructor function will only run if the associated
4746 data from the current module is not discarded.
4748 Instruction Reference
4749 =====================
4751 The LLVM instruction set consists of several different classifications
4752 of instructions: :ref:`terminator instructions <terminators>`, :ref:`binary
4753 instructions <binaryops>`, :ref:`bitwise binary
4754 instructions <bitwiseops>`, :ref:`memory instructions <memoryops>`, and
4755 :ref:`other instructions <otherops>`.
4759 Terminator Instructions
4760 -----------------------
4762 As mentioned :ref:`previously <functionstructure>`, every basic block in a
4763 program ends with a "Terminator" instruction, which indicates which
4764 block should be executed after the current block is finished. These
4765 terminator instructions typically yield a '``void``' value: they produce
4766 control flow, not values (the one exception being the
4767 ':ref:`invoke <i_invoke>`' instruction).
4769 The terminator instructions are: ':ref:`ret <i_ret>`',
4770 ':ref:`br <i_br>`', ':ref:`switch <i_switch>`',
4771 ':ref:`indirectbr <i_indirectbr>`', ':ref:`invoke <i_invoke>`',
4772 ':ref:`resume <i_resume>`', ':ref:`catchpad <i_catchpad>`',
4773 ':ref:`catchendpad <i_catchendpad>`',
4774 ':ref:`catchret <i_catchret>`',
4775 ':ref:`cleanupret <i_cleanupret>`',
4776 ':ref:`terminatepad <i_terminatepad>`',
4777 and ':ref:`unreachable <i_unreachable>`'.
4781 '``ret``' Instruction
4782 ^^^^^^^^^^^^^^^^^^^^^
4789 ret <type> <value> ; Return a value from a non-void function
4790 ret void ; Return from void function
4795 The '``ret``' instruction is used to return control flow (and optionally
4796 a value) from a function back to the caller.
4798 There are two forms of the '``ret``' instruction: one that returns a
4799 value and then causes control flow, and one that just causes control
4805 The '``ret``' instruction optionally accepts a single argument, the
4806 return value. The type of the return value must be a ':ref:`first
4807 class <t_firstclass>`' type.
4809 A function is not :ref:`well formed <wellformed>` if it it has a non-void
4810 return type and contains a '``ret``' instruction with no return value or
4811 a return value with a type that does not match its type, or if it has a
4812 void return type and contains a '``ret``' instruction with a return
4818 When the '``ret``' instruction is executed, control flow returns back to
4819 the calling function's context. If the caller is a
4820 ":ref:`call <i_call>`" instruction, execution continues at the
4821 instruction after the call. If the caller was an
4822 ":ref:`invoke <i_invoke>`" instruction, execution continues at the
4823 beginning of the "normal" destination block. If the instruction returns
4824 a value, that value shall set the call or invoke instruction's return
4830 .. code-block:: llvm
4832 ret i32 5 ; Return an integer value of 5
4833 ret void ; Return from a void function
4834 ret { i32, i8 } { i32 4, i8 2 } ; Return a struct of values 4 and 2
4838 '``br``' Instruction
4839 ^^^^^^^^^^^^^^^^^^^^
4846 br i1 <cond>, label <iftrue>, label <iffalse>
4847 br label <dest> ; Unconditional branch
4852 The '``br``' instruction is used to cause control flow to transfer to a
4853 different basic block in the current function. There are two forms of
4854 this instruction, corresponding to a conditional branch and an
4855 unconditional branch.
4860 The conditional branch form of the '``br``' instruction takes a single
4861 '``i1``' value and two '``label``' values. The unconditional form of the
4862 '``br``' instruction takes a single '``label``' value as a target.
4867 Upon execution of a conditional '``br``' instruction, the '``i1``'
4868 argument is evaluated. If the value is ``true``, control flows to the
4869 '``iftrue``' ``label`` argument. If "cond" is ``false``, control flows
4870 to the '``iffalse``' ``label`` argument.
4875 .. code-block:: llvm
4878 %cond = icmp eq i32 %a, %b
4879 br i1 %cond, label %IfEqual, label %IfUnequal
4887 '``switch``' Instruction
4888 ^^^^^^^^^^^^^^^^^^^^^^^^
4895 switch <intty> <value>, label <defaultdest> [ <intty> <val>, label <dest> ... ]
4900 The '``switch``' instruction is used to transfer control flow to one of
4901 several different places. It is a generalization of the '``br``'
4902 instruction, allowing a branch to occur to one of many possible
4908 The '``switch``' instruction uses three parameters: an integer
4909 comparison value '``value``', a default '``label``' destination, and an
4910 array of pairs of comparison value constants and '``label``'s. The table
4911 is not allowed to contain duplicate constant entries.
4916 The ``switch`` instruction specifies a table of values and destinations.
4917 When the '``switch``' instruction is executed, this table is searched
4918 for the given value. If the value is found, control flow is transferred
4919 to the corresponding destination; otherwise, control flow is transferred
4920 to the default destination.
4925 Depending on properties of the target machine and the particular
4926 ``switch`` instruction, this instruction may be code generated in
4927 different ways. For example, it could be generated as a series of
4928 chained conditional branches or with a lookup table.
4933 .. code-block:: llvm
4935 ; Emulate a conditional br instruction
4936 %Val = zext i1 %value to i32
4937 switch i32 %Val, label %truedest [ i32 0, label %falsedest ]
4939 ; Emulate an unconditional br instruction
4940 switch i32 0, label %dest [ ]
4942 ; Implement a jump table:
4943 switch i32 %val, label %otherwise [ i32 0, label %onzero
4945 i32 2, label %ontwo ]
4949 '``indirectbr``' Instruction
4950 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4957 indirectbr <somety>* <address>, [ label <dest1>, label <dest2>, ... ]
4962 The '``indirectbr``' instruction implements an indirect branch to a
4963 label within the current function, whose address is specified by
4964 "``address``". Address must be derived from a
4965 :ref:`blockaddress <blockaddress>` constant.
4970 The '``address``' argument is the address of the label to jump to. The
4971 rest of the arguments indicate the full set of possible destinations
4972 that the address may point to. Blocks are allowed to occur multiple
4973 times in the destination list, though this isn't particularly useful.
4975 This destination list is required so that dataflow analysis has an
4976 accurate understanding of the CFG.
4981 Control transfers to the block specified in the address argument. All
4982 possible destination blocks must be listed in the label list, otherwise
4983 this instruction has undefined behavior. This implies that jumps to
4984 labels defined in other functions have undefined behavior as well.
4989 This is typically implemented with a jump through a register.
4994 .. code-block:: llvm
4996 indirectbr i8* %Addr, [ label %bb1, label %bb2, label %bb3 ]
5000 '``invoke``' Instruction
5001 ^^^^^^^^^^^^^^^^^^^^^^^^
5008 <result> = invoke [cconv] [ret attrs] <ptr to function ty> <function ptr val>(<function args>) [fn attrs]
5009 to label <normal label> unwind label <exception label>
5014 The '``invoke``' instruction causes control to transfer to a specified
5015 function, with the possibility of control flow transfer to either the
5016 '``normal``' label or the '``exception``' label. If the callee function
5017 returns with the "``ret``" instruction, control flow will return to the
5018 "normal" label. If the callee (or any indirect callees) returns via the
5019 ":ref:`resume <i_resume>`" instruction or other exception handling
5020 mechanism, control is interrupted and continued at the dynamically
5021 nearest "exception" label.
5023 The '``exception``' label is a `landing
5024 pad <ExceptionHandling.html#overview>`_ for the exception. As such,
5025 '``exception``' label is required to have the
5026 ":ref:`landingpad <i_landingpad>`" instruction, which contains the
5027 information about the behavior of the program after unwinding happens,
5028 as its first non-PHI instruction. The restrictions on the
5029 "``landingpad``" instruction's tightly couples it to the "``invoke``"
5030 instruction, so that the important information contained within the
5031 "``landingpad``" instruction can't be lost through normal code motion.
5036 This instruction requires several arguments:
5038 #. The optional "cconv" marker indicates which :ref:`calling
5039 convention <callingconv>` the call should use. If none is
5040 specified, the call defaults to using C calling conventions.
5041 #. The optional :ref:`Parameter Attributes <paramattrs>` list for return
5042 values. Only '``zeroext``', '``signext``', and '``inreg``' attributes
5044 #. '``ptr to function ty``': shall be the signature of the pointer to
5045 function value being invoked. In most cases, this is a direct
5046 function invocation, but indirect ``invoke``'s are just as possible,
5047 branching off an arbitrary pointer to function value.
5048 #. '``function ptr val``': An LLVM value containing a pointer to a
5049 function to be invoked.
5050 #. '``function args``': argument list whose types match the function
5051 signature argument types and parameter attributes. All arguments must
5052 be of :ref:`first class <t_firstclass>` type. If the function signature
5053 indicates the function accepts a variable number of arguments, the
5054 extra arguments can be specified.
5055 #. '``normal label``': the label reached when the called function
5056 executes a '``ret``' instruction.
5057 #. '``exception label``': the label reached when a callee returns via
5058 the :ref:`resume <i_resume>` instruction or other exception handling
5060 #. The optional :ref:`function attributes <fnattrs>` list. Only
5061 '``noreturn``', '``nounwind``', '``readonly``' and '``readnone``'
5062 attributes are valid here.
5067 This instruction is designed to operate as a standard '``call``'
5068 instruction in most regards. The primary difference is that it
5069 establishes an association with a label, which is used by the runtime
5070 library to unwind the stack.
5072 This instruction is used in languages with destructors to ensure that
5073 proper cleanup is performed in the case of either a ``longjmp`` or a
5074 thrown exception. Additionally, this is important for implementation of
5075 '``catch``' clauses in high-level languages that support them.
5077 For the purposes of the SSA form, the definition of the value returned
5078 by the '``invoke``' instruction is deemed to occur on the edge from the
5079 current block to the "normal" label. If the callee unwinds then no
5080 return value is available.
5085 .. code-block:: llvm
5087 %retval = invoke i32 @Test(i32 15) to label %Continue
5088 unwind label %TestCleanup ; i32:retval set
5089 %retval = invoke coldcc i32 %Testfnptr(i32 15) to label %Continue
5090 unwind label %TestCleanup ; i32:retval set
5094 '``resume``' Instruction
5095 ^^^^^^^^^^^^^^^^^^^^^^^^
5102 resume <type> <value>
5107 The '``resume``' instruction is a terminator instruction that has no
5113 The '``resume``' instruction requires one argument, which must have the
5114 same type as the result of any '``landingpad``' instruction in the same
5120 The '``resume``' instruction resumes propagation of an existing
5121 (in-flight) exception whose unwinding was interrupted with a
5122 :ref:`landingpad <i_landingpad>` instruction.
5127 .. code-block:: llvm
5129 resume { i8*, i32 } %exn
5133 '``catchpad``' Instruction
5134 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5141 <resultval> = catchpad [<args>*]
5142 to label <normal label> unwind label <exception label>
5147 The '``catchpad``' instruction is used by `LLVM's exception handling
5148 system <ExceptionHandling.html#overview>`_ to specify that a basic block
5149 is a catch block --- one where a personality routine attempts to transfer
5150 control to catch an exception.
5151 The ``args`` correspond to whatever information the personality
5152 routine requires to know if this is an appropriate place to catch the
5153 exception. Control is tranfered to the ``exception`` label if the
5154 ``catchpad`` is not an appropriate handler for the in-flight exception.
5155 The ``normal`` label should contain the code found in the ``catch``
5156 portion of a ``try``/``catch`` sequence. The ``resultval`` has the type
5157 :ref:`token <t_token>` and is used to match the ``catchpad`` to
5158 corresponding :ref:`catchrets <i_catchret>`.
5163 The instruction takes a list of arbitrary values which are interpreted
5164 by the :ref:`personality function <personalityfn>`.
5166 The ``catchpad`` must be provided a ``normal`` label to transfer control
5167 to if the ``catchpad`` matches the exception and an ``exception``
5168 label to transfer control to if it doesn't.
5173 When the call stack is being unwound due to an exception being thrown,
5174 the exception is compared against the ``args``. If it doesn't match,
5175 then control is transfered to the ``exception`` basic block.
5176 As with calling conventions, how the personality function results are
5177 represented in LLVM IR is target specific.
5179 The ``catchpad`` instruction has several restrictions:
5181 - A catch block is a basic block which is the unwind destination of
5182 an exceptional instruction.
5183 - A catch block must have a '``catchpad``' instruction as its
5184 first non-PHI instruction.
5185 - A catch block's ``exception`` edge must refer to a catch block or a
5187 - There can be only one '``catchpad``' instruction within the
5189 - A basic block that is not a catch block may not include a
5190 '``catchpad``' instruction.
5191 - A catch block which has another catch block as a predecessor may not have
5192 any other predecessors.
5193 - It is undefined behavior for control to transfer from a ``catchpad`` to a
5194 ``ret`` without first executing a ``catchret`` that consumes the
5195 ``catchpad`` or unwinding through its ``catchendpad``.
5196 - It is undefined behavior for control to transfer from a ``catchpad`` to
5197 itself without first executing a ``catchret`` that consumes the
5198 ``catchpad`` or unwinding through its ``catchendpad``.
5203 .. code-block:: llvm
5205 ;; A catch block which can catch an integer.
5206 %tok = catchpad [i8** @_ZTIi]
5207 to label %int.handler unwind label %terminate
5211 '``catchendpad``' Instruction
5212 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5219 catchendpad unwind label <nextaction>
5220 catchendpad unwind to caller
5225 The '``catchendpad``' instruction is used by `LLVM's exception handling
5226 system <ExceptionHandling.html#overview>`_ to communicate to the
5227 :ref:`personality function <personalityfn>` which invokes are associated
5228 with a chain of :ref:`catchpad <i_catchpad>` instructions.
5230 The ``nextaction`` label indicates where control should transfer to if
5231 none of the ``catchpad`` instructions are suitable for catching the
5232 in-flight exception.
5234 If a ``nextaction`` label is not present, the instruction unwinds out of
5235 its parent function. The
5236 :ref:`personality function <personalityfn>` will continue processing
5237 exception handling actions in the caller.
5242 The instruction optionally takes a label, ``nextaction``, indicating
5243 where control should transfer to if none of the preceding
5244 ``catchpad`` instructions are suitable for the in-flight exception.
5249 When the call stack is being unwound due to an exception being thrown
5250 and none of the constituent ``catchpad`` instructions match, then
5251 control is transfered to ``nextaction`` if it is present. If it is not
5252 present, control is transfered to the caller.
5254 The ``catchendpad`` instruction has several restrictions:
5256 - A catch-end block is a basic block which is the unwind destination of
5257 an exceptional instruction.
5258 - A catch-end block must have a '``catchendpad``' instruction as its
5259 first non-PHI instruction.
5260 - There can be only one '``catchendpad``' instruction within the
5262 - A basic block that is not a catch-end block may not include a
5263 '``catchendpad``' instruction.
5264 - Exactly one catch block may unwind to a ``catchendpad``.
5265 - The unwind target of invokes between a ``catchpad`` and a
5266 corresponding ``catchret`` must be its ``catchendpad`` or
5272 .. code-block:: llvm
5274 catchendpad unwind label %terminate
5275 catchendpad unwind to caller
5279 '``catchret``' Instruction
5280 ^^^^^^^^^^^^^^^^^^^^^^^^^^
5287 catchret <value> to label <normal>
5292 The '``catchret``' instruction is a terminator instruction that has a
5299 The first argument to a '``catchret``' indicates which ``catchpad`` it
5300 exits. It must be a :ref:`catchpad <i_catchpad>`.
5301 The second argument to a '``catchret``' specifies where control will
5307 The '``catchret``' instruction ends the existing (in-flight) exception
5308 whose unwinding was interrupted with a
5309 :ref:`catchpad <i_catchpad>` instruction.
5310 The :ref:`personality function <personalityfn>` gets a chance to execute
5311 arbitrary code to, for example, run a C++ destructor.
5312 Control then transfers to ``normal``.
5313 It may be passed an optional, personality specific, value.
5314 It is undefined behavior to execute a ``catchret`` whose ``catchpad`` has
5316 It is undefined behavior to execute a ``catchret`` if any ``catchpad`` or
5317 ``cleanuppad`` has been executed, without subsequently executing a
5318 corresponding ``catchret``/``cleanupret`` or unwinding out of the inner
5319 pad, following the most recent execution of the ``catchret``'s corresponding
5326 .. code-block:: llvm
5328 catchret %catch label %continue
5332 '``cleanupret``' Instruction
5333 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5340 cleanupret <value> unwind label <continue>
5341 cleanupret <value> unwind to caller
5346 The '``cleanupret``' instruction is a terminator instruction that has
5347 an optional successor.
5353 The '``cleanupret``' instruction requires one argument, which indicates
5354 which ``cleanuppad`` it exits, and must be a :ref:`cleanuppad <i_cleanuppad>`.
5355 It also has an optional successor, ``continue``.
5360 The '``cleanupret``' instruction indicates to the
5361 :ref:`personality function <personalityfn>` that one
5362 :ref:`cleanuppad <i_cleanuppad>` it transferred control to has ended.
5363 It transfers control to ``continue`` or unwinds out of the function.
5364 It is undefined behavior to execute a ``cleanupret`` whose ``cleanuppad`` has
5366 It is undefined behavior to execute a ``cleanupret`` if any ``catchpad`` or
5367 ``cleanuppad`` has been executed, without subsequently executing a
5368 corresponding ``catchret``/``cleanupret`` or unwinding out of the inner pad,
5369 following the most recent execution of the ``cleanupret``'s corresponding
5375 .. code-block:: llvm
5377 cleanupret %cleanup unwind to caller
5378 cleanupret %cleanup unwind label %continue
5382 '``terminatepad``' Instruction
5383 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5390 terminatepad [<args>*] unwind label <exception label>
5391 terminatepad [<args>*] unwind to caller
5396 The '``terminatepad``' instruction is used by `LLVM's exception handling
5397 system <ExceptionHandling.html#overview>`_ to specify that a basic block
5398 is a terminate block --- one where a personality routine may decide to
5399 terminate the program.
5400 The ``args`` correspond to whatever information the personality
5401 routine requires to know if this is an appropriate place to terminate the
5402 program. Control is transferred to the ``exception`` label if the
5403 personality routine decides not to terminate the program for the
5404 in-flight exception.
5409 The instruction takes a list of arbitrary values which are interpreted
5410 by the :ref:`personality function <personalityfn>`.
5412 The ``terminatepad`` may be given an ``exception`` label to
5413 transfer control to if the in-flight exception matches the ``args``.
5418 When the call stack is being unwound due to an exception being thrown,
5419 the exception is compared against the ``args``. If it matches,
5420 then control is transfered to the ``exception`` basic block. Otherwise,
5421 the program is terminated via personality-specific means. Typically,
5422 the first argument to ``terminatepad`` specifies what function the
5423 personality should defer to in order to terminate the program.
5425 The ``terminatepad`` instruction has several restrictions:
5427 - A terminate block is a basic block which is the unwind destination of
5428 an exceptional instruction.
5429 - A terminate block must have a '``terminatepad``' instruction as its
5430 first non-PHI instruction.
5431 - There can be only one '``terminatepad``' instruction within the
5433 - A basic block that is not a terminate block may not include a
5434 '``terminatepad``' instruction.
5439 .. code-block:: llvm
5441 ;; A terminate block which only permits integers.
5442 terminatepad [i8** @_ZTIi] unwind label %continue
5446 '``unreachable``' Instruction
5447 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5459 The '``unreachable``' instruction has no defined semantics. This
5460 instruction is used to inform the optimizer that a particular portion of
5461 the code is not reachable. This can be used to indicate that the code
5462 after a no-return function cannot be reached, and other facts.
5467 The '``unreachable``' instruction has no defined semantics.
5474 Binary operators are used to do most of the computation in a program.
5475 They require two operands of the same type, execute an operation on
5476 them, and produce a single value. The operands might represent multiple
5477 data, as is the case with the :ref:`vector <t_vector>` data type. The
5478 result value has the same type as its operands.
5480 There are several different binary operators:
5484 '``add``' Instruction
5485 ^^^^^^^^^^^^^^^^^^^^^
5492 <result> = add <ty> <op1>, <op2> ; yields ty:result
5493 <result> = add nuw <ty> <op1>, <op2> ; yields ty:result
5494 <result> = add nsw <ty> <op1>, <op2> ; yields ty:result
5495 <result> = add nuw nsw <ty> <op1>, <op2> ; yields ty:result
5500 The '``add``' instruction returns the sum of its two operands.
5505 The two arguments to the '``add``' instruction must be
5506 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
5507 arguments must have identical types.
5512 The value produced is the integer sum of the two operands.
5514 If the sum has unsigned overflow, the result returned is the
5515 mathematical result modulo 2\ :sup:`n`\ , where n is the bit width of
5518 Because LLVM integers use a two's complement representation, this
5519 instruction is appropriate for both signed and unsigned integers.
5521 ``nuw`` and ``nsw`` stand for "No Unsigned Wrap" and "No Signed Wrap",
5522 respectively. If the ``nuw`` and/or ``nsw`` keywords are present, the
5523 result value of the ``add`` is a :ref:`poison value <poisonvalues>` if
5524 unsigned and/or signed overflow, respectively, occurs.
5529 .. code-block:: llvm
5531 <result> = add i32 4, %var ; yields i32:result = 4 + %var
5535 '``fadd``' Instruction
5536 ^^^^^^^^^^^^^^^^^^^^^^
5543 <result> = fadd [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
5548 The '``fadd``' instruction returns the sum of its two operands.
5553 The two arguments to the '``fadd``' instruction must be :ref:`floating
5554 point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
5555 Both arguments must have identical types.
5560 The value produced is the floating point sum of the two operands. This
5561 instruction can also take any number of :ref:`fast-math flags <fastmath>`,
5562 which are optimization hints to enable otherwise unsafe floating point
5568 .. code-block:: llvm
5570 <result> = fadd float 4.0, %var ; yields float:result = 4.0 + %var
5572 '``sub``' Instruction
5573 ^^^^^^^^^^^^^^^^^^^^^
5580 <result> = sub <ty> <op1>, <op2> ; yields ty:result
5581 <result> = sub nuw <ty> <op1>, <op2> ; yields ty:result
5582 <result> = sub nsw <ty> <op1>, <op2> ; yields ty:result
5583 <result> = sub nuw nsw <ty> <op1>, <op2> ; yields ty:result
5588 The '``sub``' instruction returns the difference of its two operands.
5590 Note that the '``sub``' instruction is used to represent the '``neg``'
5591 instruction present in most other intermediate representations.
5596 The two arguments to the '``sub``' instruction must be
5597 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
5598 arguments must have identical types.
5603 The value produced is the integer difference of the two operands.
5605 If the difference has unsigned overflow, the result returned is the
5606 mathematical result modulo 2\ :sup:`n`\ , where n is the bit width of
5609 Because LLVM integers use a two's complement representation, this
5610 instruction is appropriate for both signed and unsigned integers.
5612 ``nuw`` and ``nsw`` stand for "No Unsigned Wrap" and "No Signed Wrap",
5613 respectively. If the ``nuw`` and/or ``nsw`` keywords are present, the
5614 result value of the ``sub`` is a :ref:`poison value <poisonvalues>` if
5615 unsigned and/or signed overflow, respectively, occurs.
5620 .. code-block:: llvm
5622 <result> = sub i32 4, %var ; yields i32:result = 4 - %var
5623 <result> = sub i32 0, %val ; yields i32:result = -%var
5627 '``fsub``' Instruction
5628 ^^^^^^^^^^^^^^^^^^^^^^
5635 <result> = fsub [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
5640 The '``fsub``' instruction returns the difference of its two operands.
5642 Note that the '``fsub``' instruction is used to represent the '``fneg``'
5643 instruction present in most other intermediate representations.
5648 The two arguments to the '``fsub``' instruction must be :ref:`floating
5649 point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
5650 Both arguments must have identical types.
5655 The value produced is the floating point difference of the two operands.
5656 This instruction can also take any number of :ref:`fast-math
5657 flags <fastmath>`, which are optimization hints to enable otherwise
5658 unsafe floating point optimizations:
5663 .. code-block:: llvm
5665 <result> = fsub float 4.0, %var ; yields float:result = 4.0 - %var
5666 <result> = fsub float -0.0, %val ; yields float:result = -%var
5668 '``mul``' Instruction
5669 ^^^^^^^^^^^^^^^^^^^^^
5676 <result> = mul <ty> <op1>, <op2> ; yields ty:result
5677 <result> = mul nuw <ty> <op1>, <op2> ; yields ty:result
5678 <result> = mul nsw <ty> <op1>, <op2> ; yields ty:result
5679 <result> = mul nuw nsw <ty> <op1>, <op2> ; yields ty:result
5684 The '``mul``' instruction returns the product of its two operands.
5689 The two arguments to the '``mul``' instruction must be
5690 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
5691 arguments must have identical types.
5696 The value produced is the integer product of the two operands.
5698 If the result of the multiplication has unsigned overflow, the result
5699 returned is the mathematical result modulo 2\ :sup:`n`\ , where n is the
5700 bit width of the result.
5702 Because LLVM integers use a two's complement representation, and the
5703 result is the same width as the operands, this instruction returns the
5704 correct result for both signed and unsigned integers. If a full product
5705 (e.g. ``i32`` * ``i32`` -> ``i64``) is needed, the operands should be
5706 sign-extended or zero-extended as appropriate to the width of the full
5709 ``nuw`` and ``nsw`` stand for "No Unsigned Wrap" and "No Signed Wrap",
5710 respectively. If the ``nuw`` and/or ``nsw`` keywords are present, the
5711 result value of the ``mul`` is a :ref:`poison value <poisonvalues>` if
5712 unsigned and/or signed overflow, respectively, occurs.
5717 .. code-block:: llvm
5719 <result> = mul i32 4, %var ; yields i32:result = 4 * %var
5723 '``fmul``' Instruction
5724 ^^^^^^^^^^^^^^^^^^^^^^
5731 <result> = fmul [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
5736 The '``fmul``' instruction returns the product of its two operands.
5741 The two arguments to the '``fmul``' instruction must be :ref:`floating
5742 point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
5743 Both arguments must have identical types.
5748 The value produced is the floating point product of the two operands.
5749 This instruction can also take any number of :ref:`fast-math
5750 flags <fastmath>`, which are optimization hints to enable otherwise
5751 unsafe floating point optimizations:
5756 .. code-block:: llvm
5758 <result> = fmul float 4.0, %var ; yields float:result = 4.0 * %var
5760 '``udiv``' Instruction
5761 ^^^^^^^^^^^^^^^^^^^^^^
5768 <result> = udiv <ty> <op1>, <op2> ; yields ty:result
5769 <result> = udiv exact <ty> <op1>, <op2> ; yields ty:result
5774 The '``udiv``' instruction returns the quotient of its two operands.
5779 The two arguments to the '``udiv``' instruction must be
5780 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
5781 arguments must have identical types.
5786 The value produced is the unsigned integer quotient of the two operands.
5788 Note that unsigned integer division and signed integer division are
5789 distinct operations; for signed integer division, use '``sdiv``'.
5791 Division by zero leads to undefined behavior.
5793 If the ``exact`` keyword is present, the result value of the ``udiv`` is
5794 a :ref:`poison value <poisonvalues>` if %op1 is not a multiple of %op2 (as
5795 such, "((a udiv exact b) mul b) == a").
5800 .. code-block:: llvm
5802 <result> = udiv i32 4, %var ; yields i32:result = 4 / %var
5804 '``sdiv``' Instruction
5805 ^^^^^^^^^^^^^^^^^^^^^^
5812 <result> = sdiv <ty> <op1>, <op2> ; yields ty:result
5813 <result> = sdiv exact <ty> <op1>, <op2> ; yields ty:result
5818 The '``sdiv``' instruction returns the quotient of its two operands.
5823 The two arguments to the '``sdiv``' instruction must be
5824 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
5825 arguments must have identical types.
5830 The value produced is the signed integer quotient of the two operands
5831 rounded towards zero.
5833 Note that signed integer division and unsigned integer division are
5834 distinct operations; for unsigned integer division, use '``udiv``'.
5836 Division by zero leads to undefined behavior. Overflow also leads to
5837 undefined behavior; this is a rare case, but can occur, for example, by
5838 doing a 32-bit division of -2147483648 by -1.
5840 If the ``exact`` keyword is present, the result value of the ``sdiv`` is
5841 a :ref:`poison value <poisonvalues>` if the result would be rounded.
5846 .. code-block:: llvm
5848 <result> = sdiv i32 4, %var ; yields i32:result = 4 / %var
5852 '``fdiv``' Instruction
5853 ^^^^^^^^^^^^^^^^^^^^^^
5860 <result> = fdiv [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
5865 The '``fdiv``' instruction returns the quotient of its two operands.
5870 The two arguments to the '``fdiv``' instruction must be :ref:`floating
5871 point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
5872 Both arguments must have identical types.
5877 The value produced is the floating point quotient of the two operands.
5878 This instruction can also take any number of :ref:`fast-math
5879 flags <fastmath>`, which are optimization hints to enable otherwise
5880 unsafe floating point optimizations:
5885 .. code-block:: llvm
5887 <result> = fdiv float 4.0, %var ; yields float:result = 4.0 / %var
5889 '``urem``' Instruction
5890 ^^^^^^^^^^^^^^^^^^^^^^
5897 <result> = urem <ty> <op1>, <op2> ; yields ty:result
5902 The '``urem``' instruction returns the remainder from the unsigned
5903 division of its two arguments.
5908 The two arguments to the '``urem``' instruction must be
5909 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
5910 arguments must have identical types.
5915 This instruction returns the unsigned integer *remainder* of a division.
5916 This instruction always performs an unsigned division to get the
5919 Note that unsigned integer remainder and signed integer remainder are
5920 distinct operations; for signed integer remainder, use '``srem``'.
5922 Taking the remainder of a division by zero leads to undefined behavior.
5927 .. code-block:: llvm
5929 <result> = urem i32 4, %var ; yields i32:result = 4 % %var
5931 '``srem``' Instruction
5932 ^^^^^^^^^^^^^^^^^^^^^^
5939 <result> = srem <ty> <op1>, <op2> ; yields ty:result
5944 The '``srem``' instruction returns the remainder from the signed
5945 division of its two operands. This instruction can also take
5946 :ref:`vector <t_vector>` versions of the values in which case the elements
5952 The two arguments to the '``srem``' instruction must be
5953 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
5954 arguments must have identical types.
5959 This instruction returns the *remainder* of a division (where the result
5960 is either zero or has the same sign as the dividend, ``op1``), not the
5961 *modulo* operator (where the result is either zero or has the same sign
5962 as the divisor, ``op2``) of a value. For more information about the
5963 difference, see `The Math
5964 Forum <http://mathforum.org/dr.math/problems/anne.4.28.99.html>`_. For a
5965 table of how this is implemented in various languages, please see
5967 operation <http://en.wikipedia.org/wiki/Modulo_operation>`_.
5969 Note that signed integer remainder and unsigned integer remainder are
5970 distinct operations; for unsigned integer remainder, use '``urem``'.
5972 Taking the remainder of a division by zero leads to undefined behavior.
5973 Overflow also leads to undefined behavior; this is a rare case, but can
5974 occur, for example, by taking the remainder of a 32-bit division of
5975 -2147483648 by -1. (The remainder doesn't actually overflow, but this
5976 rule lets srem be implemented using instructions that return both the
5977 result of the division and the remainder.)
5982 .. code-block:: llvm
5984 <result> = srem i32 4, %var ; yields i32:result = 4 % %var
5988 '``frem``' Instruction
5989 ^^^^^^^^^^^^^^^^^^^^^^
5996 <result> = frem [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result
6001 The '``frem``' instruction returns the remainder from the division of
6007 The two arguments to the '``frem``' instruction must be :ref:`floating
6008 point <t_floating>` or :ref:`vector <t_vector>` of floating point values.
6009 Both arguments must have identical types.
6014 This instruction returns the *remainder* of a division. The remainder
6015 has the same sign as the dividend. This instruction can also take any
6016 number of :ref:`fast-math flags <fastmath>`, which are optimization hints
6017 to enable otherwise unsafe floating point optimizations:
6022 .. code-block:: llvm
6024 <result> = frem float 4.0, %var ; yields float:result = 4.0 % %var
6028 Bitwise Binary Operations
6029 -------------------------
6031 Bitwise binary operators are used to do various forms of bit-twiddling
6032 in a program. They are generally very efficient instructions and can
6033 commonly be strength reduced from other instructions. They require two
6034 operands of the same type, execute an operation on them, and produce a
6035 single value. The resulting value is the same type as its operands.
6037 '``shl``' Instruction
6038 ^^^^^^^^^^^^^^^^^^^^^
6045 <result> = shl <ty> <op1>, <op2> ; yields ty:result
6046 <result> = shl nuw <ty> <op1>, <op2> ; yields ty:result
6047 <result> = shl nsw <ty> <op1>, <op2> ; yields ty:result
6048 <result> = shl nuw nsw <ty> <op1>, <op2> ; yields ty:result
6053 The '``shl``' instruction returns the first operand shifted to the left
6054 a specified number of bits.
6059 Both arguments to the '``shl``' instruction must be the same
6060 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer type.
6061 '``op2``' is treated as an unsigned value.
6066 The value produced is ``op1`` \* 2\ :sup:`op2` mod 2\ :sup:`n`,
6067 where ``n`` is the width of the result. If ``op2`` is (statically or
6068 dynamically) equal to or larger than the number of bits in
6069 ``op1``, the result is undefined. If the arguments are vectors, each
6070 vector element of ``op1`` is shifted by the corresponding shift amount
6073 If the ``nuw`` keyword is present, then the shift produces a :ref:`poison
6074 value <poisonvalues>` if it shifts out any non-zero bits. If the
6075 ``nsw`` keyword is present, then the shift produces a :ref:`poison
6076 value <poisonvalues>` if it shifts out any bits that disagree with the
6077 resultant sign bit. As such, NUW/NSW have the same semantics as they
6078 would if the shift were expressed as a mul instruction with the same
6079 nsw/nuw bits in (mul %op1, (shl 1, %op2)).
6084 .. code-block:: llvm
6086 <result> = shl i32 4, %var ; yields i32: 4 << %var
6087 <result> = shl i32 4, 2 ; yields i32: 16
6088 <result> = shl i32 1, 10 ; yields i32: 1024
6089 <result> = shl i32 1, 32 ; undefined
6090 <result> = shl <2 x i32> < i32 1, i32 1>, < i32 1, i32 2> ; yields: result=<2 x i32> < i32 2, i32 4>
6092 '``lshr``' Instruction
6093 ^^^^^^^^^^^^^^^^^^^^^^
6100 <result> = lshr <ty> <op1>, <op2> ; yields ty:result
6101 <result> = lshr exact <ty> <op1>, <op2> ; yields ty:result
6106 The '``lshr``' instruction (logical shift right) returns the first
6107 operand shifted to the right a specified number of bits with zero fill.
6112 Both arguments to the '``lshr``' instruction must be the same
6113 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer type.
6114 '``op2``' is treated as an unsigned value.
6119 This instruction always performs a logical shift right operation. The
6120 most significant bits of the result will be filled with zero bits after
6121 the shift. If ``op2`` is (statically or dynamically) equal to or larger
6122 than the number of bits in ``op1``, the result is undefined. If the
6123 arguments are vectors, each vector element of ``op1`` is shifted by the
6124 corresponding shift amount in ``op2``.
6126 If the ``exact`` keyword is present, the result value of the ``lshr`` is
6127 a :ref:`poison value <poisonvalues>` if any of the bits shifted out are
6133 .. code-block:: llvm
6135 <result> = lshr i32 4, 1 ; yields i32:result = 2
6136 <result> = lshr i32 4, 2 ; yields i32:result = 1
6137 <result> = lshr i8 4, 3 ; yields i8:result = 0
6138 <result> = lshr i8 -2, 1 ; yields i8:result = 0x7F
6139 <result> = lshr i32 1, 32 ; undefined
6140 <result> = lshr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 2> ; yields: result=<2 x i32> < i32 0x7FFFFFFF, i32 1>
6142 '``ashr``' Instruction
6143 ^^^^^^^^^^^^^^^^^^^^^^
6150 <result> = ashr <ty> <op1>, <op2> ; yields ty:result
6151 <result> = ashr exact <ty> <op1>, <op2> ; yields ty:result
6156 The '``ashr``' instruction (arithmetic shift right) returns the first
6157 operand shifted to the right a specified number of bits with sign
6163 Both arguments to the '``ashr``' instruction must be the same
6164 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer type.
6165 '``op2``' is treated as an unsigned value.
6170 This instruction always performs an arithmetic shift right operation,
6171 The most significant bits of the result will be filled with the sign bit
6172 of ``op1``. If ``op2`` is (statically or dynamically) equal to or larger
6173 than the number of bits in ``op1``, the result is undefined. If the
6174 arguments are vectors, each vector element of ``op1`` is shifted by the
6175 corresponding shift amount in ``op2``.
6177 If the ``exact`` keyword is present, the result value of the ``ashr`` is
6178 a :ref:`poison value <poisonvalues>` if any of the bits shifted out are
6184 .. code-block:: llvm
6186 <result> = ashr i32 4, 1 ; yields i32:result = 2
6187 <result> = ashr i32 4, 2 ; yields i32:result = 1
6188 <result> = ashr i8 4, 3 ; yields i8:result = 0
6189 <result> = ashr i8 -2, 1 ; yields i8:result = -1
6190 <result> = ashr i32 1, 32 ; undefined
6191 <result> = ashr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 3> ; yields: result=<2 x i32> < i32 -1, i32 0>
6193 '``and``' Instruction
6194 ^^^^^^^^^^^^^^^^^^^^^
6201 <result> = and <ty> <op1>, <op2> ; yields ty:result
6206 The '``and``' instruction returns the bitwise logical and of its two
6212 The two arguments to the '``and``' instruction must be
6213 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
6214 arguments must have identical types.
6219 The truth table used for the '``and``' instruction is:
6236 .. code-block:: llvm
6238 <result> = and i32 4, %var ; yields i32:result = 4 & %var
6239 <result> = and i32 15, 40 ; yields i32:result = 8
6240 <result> = and i32 4, 8 ; yields i32:result = 0
6242 '``or``' Instruction
6243 ^^^^^^^^^^^^^^^^^^^^
6250 <result> = or <ty> <op1>, <op2> ; yields ty:result
6255 The '``or``' instruction returns the bitwise logical inclusive or of its
6261 The two arguments to the '``or``' instruction must be
6262 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
6263 arguments must have identical types.
6268 The truth table used for the '``or``' instruction is:
6287 <result> = or i32 4, %var ; yields i32:result = 4 | %var
6288 <result> = or i32 15, 40 ; yields i32:result = 47
6289 <result> = or i32 4, 8 ; yields i32:result = 12
6291 '``xor``' Instruction
6292 ^^^^^^^^^^^^^^^^^^^^^
6299 <result> = xor <ty> <op1>, <op2> ; yields ty:result
6304 The '``xor``' instruction returns the bitwise logical exclusive or of
6305 its two operands. The ``xor`` is used to implement the "one's
6306 complement" operation, which is the "~" operator in C.
6311 The two arguments to the '``xor``' instruction must be
6312 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both
6313 arguments must have identical types.
6318 The truth table used for the '``xor``' instruction is:
6335 .. code-block:: llvm
6337 <result> = xor i32 4, %var ; yields i32:result = 4 ^ %var
6338 <result> = xor i32 15, 40 ; yields i32:result = 39
6339 <result> = xor i32 4, 8 ; yields i32:result = 12
6340 <result> = xor i32 %V, -1 ; yields i32:result = ~%V
6345 LLVM supports several instructions to represent vector operations in a
6346 target-independent manner. These instructions cover the element-access
6347 and vector-specific operations needed to process vectors effectively.
6348 While LLVM does directly support these vector operations, many
6349 sophisticated algorithms will want to use target-specific intrinsics to
6350 take full advantage of a specific target.
6352 .. _i_extractelement:
6354 '``extractelement``' Instruction
6355 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6362 <result> = extractelement <n x <ty>> <val>, <ty2> <idx> ; yields <ty>
6367 The '``extractelement``' instruction extracts a single scalar element
6368 from a vector at a specified index.
6373 The first operand of an '``extractelement``' instruction is a value of
6374 :ref:`vector <t_vector>` type. The second operand is an index indicating
6375 the position from which to extract the element. The index may be a
6376 variable of any integer type.
6381 The result is a scalar of the same type as the element type of ``val``.
6382 Its value is the value at position ``idx`` of ``val``. If ``idx``
6383 exceeds the length of ``val``, the results are undefined.
6388 .. code-block:: llvm
6390 <result> = extractelement <4 x i32> %vec, i32 0 ; yields i32
6392 .. _i_insertelement:
6394 '``insertelement``' Instruction
6395 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6402 <result> = insertelement <n x <ty>> <val>, <ty> <elt>, <ty2> <idx> ; yields <n x <ty>>
6407 The '``insertelement``' instruction inserts a scalar element into a
6408 vector at a specified index.
6413 The first operand of an '``insertelement``' instruction is a value of
6414 :ref:`vector <t_vector>` type. The second operand is a scalar value whose
6415 type must equal the element type of the first operand. The third operand
6416 is an index indicating the position at which to insert the value. The
6417 index may be a variable of any integer type.
6422 The result is a vector of the same type as ``val``. Its element values
6423 are those of ``val`` except at position ``idx``, where it gets the value
6424 ``elt``. If ``idx`` exceeds the length of ``val``, the results are
6430 .. code-block:: llvm
6432 <result> = insertelement <4 x i32> %vec, i32 1, i32 0 ; yields <4 x i32>
6434 .. _i_shufflevector:
6436 '``shufflevector``' Instruction
6437 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6444 <result> = shufflevector <n x <ty>> <v1>, <n x <ty>> <v2>, <m x i32> <mask> ; yields <m x <ty>>
6449 The '``shufflevector``' instruction constructs a permutation of elements
6450 from two input vectors, returning a vector with the same element type as
6451 the input and length that is the same as the shuffle mask.
6456 The first two operands of a '``shufflevector``' instruction are vectors
6457 with the same type. The third argument is a shuffle mask whose element
6458 type is always 'i32'. The result of the instruction is a vector whose
6459 length is the same as the shuffle mask and whose element type is the
6460 same as the element type of the first two operands.
6462 The shuffle mask operand is required to be a constant vector with either
6463 constant integer or undef values.
6468 The elements of the two input vectors are numbered from left to right
6469 across both of the vectors. The shuffle mask operand specifies, for each
6470 element of the result vector, which element of the two input vectors the
6471 result element gets. The element selector may be undef (meaning "don't
6472 care") and the second operand may be undef if performing a shuffle from
6478 .. code-block:: llvm
6480 <result> = shufflevector <4 x i32> %v1, <4 x i32> %v2,
6481 <4 x i32> <i32 0, i32 4, i32 1, i32 5> ; yields <4 x i32>
6482 <result> = shufflevector <4 x i32> %v1, <4 x i32> undef,
6483 <4 x i32> <i32 0, i32 1, i32 2, i32 3> ; yields <4 x i32> - Identity shuffle.
6484 <result> = shufflevector <8 x i32> %v1, <8 x i32> undef,
6485 <4 x i32> <i32 0, i32 1, i32 2, i32 3> ; yields <4 x i32>
6486 <result> = shufflevector <4 x i32> %v1, <4 x i32> %v2,
6487 <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7 > ; yields <8 x i32>
6489 Aggregate Operations
6490 --------------------
6492 LLVM supports several instructions for working with
6493 :ref:`aggregate <t_aggregate>` values.
6497 '``extractvalue``' Instruction
6498 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6505 <result> = extractvalue <aggregate type> <val>, <idx>{, <idx>}*
6510 The '``extractvalue``' instruction extracts the value of a member field
6511 from an :ref:`aggregate <t_aggregate>` value.
6516 The first operand of an '``extractvalue``' instruction is a value of
6517 :ref:`struct <t_struct>` or :ref:`array <t_array>` type. The operands are
6518 constant indices to specify which value to extract in a similar manner
6519 as indices in a '``getelementptr``' instruction.
6521 The major differences to ``getelementptr`` indexing are:
6523 - Since the value being indexed is not a pointer, the first index is
6524 omitted and assumed to be zero.
6525 - At least one index must be specified.
6526 - Not only struct indices but also array indices must be in bounds.
6531 The result is the value at the position in the aggregate specified by
6537 .. code-block:: llvm
6539 <result> = extractvalue {i32, float} %agg, 0 ; yields i32
6543 '``insertvalue``' Instruction
6544 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
6551 <result> = insertvalue <aggregate type> <val>, <ty> <elt>, <idx>{, <idx>}* ; yields <aggregate type>
6556 The '``insertvalue``' instruction inserts a value into a member field in
6557 an :ref:`aggregate <t_aggregate>` value.
6562 The first operand of an '``insertvalue``' instruction is a value of
6563 :ref:`struct <t_struct>` or :ref:`array <t_array>` type. The second operand is
6564 a first-class value to insert. The following operands are constant
6565 indices indicating the position at which to insert the value in a
6566 similar manner as indices in a '``extractvalue``' instruction. The value
6567 to insert must have the same type as the value identified by the
6573 The result is an aggregate of the same type as ``val``. Its value is
6574 that of ``val`` except that the value at the position specified by the
6575 indices is that of ``elt``.
6580 .. code-block:: llvm
6582 %agg1 = insertvalue {i32, float} undef, i32 1, 0 ; yields {i32 1, float undef}
6583 %agg2 = insertvalue {i32, float} %agg1, float %val, 1 ; yields {i32 1, float %val}
6584 %agg3 = insertvalue {i32, {float}} undef, float %val, 1, 0 ; yields {i32 undef, {float %val}}
6588 Memory Access and Addressing Operations
6589 ---------------------------------------
6591 A key design point of an SSA-based representation is how it represents
6592 memory. In LLVM, no memory locations are in SSA form, which makes things
6593 very simple. This section describes how to read, write, and allocate
6598 '``alloca``' Instruction
6599 ^^^^^^^^^^^^^^^^^^^^^^^^
6606 <result> = alloca [inalloca] <type> [, <ty> <NumElements>] [, align <alignment>] ; yields type*:result
6611 The '``alloca``' instruction allocates memory on the stack frame of the
6612 currently executing function, to be automatically released when this
6613 function returns to its caller. The object is always allocated in the
6614 generic address space (address space zero).
6619 The '``alloca``' instruction allocates ``sizeof(<type>)*NumElements``
6620 bytes of memory on the runtime stack, returning a pointer of the
6621 appropriate type to the program. If "NumElements" is specified, it is
6622 the number of elements allocated, otherwise "NumElements" is defaulted
6623 to be one. If a constant alignment is specified, the value result of the
6624 allocation is guaranteed to be aligned to at least that boundary. The
6625 alignment may not be greater than ``1 << 29``. If not specified, or if
6626 zero, the target can choose to align the allocation on any convenient
6627 boundary compatible with the type.
6629 '``type``' may be any sized type.
6634 Memory is allocated; a pointer is returned. The operation is undefined
6635 if there is insufficient stack space for the allocation. '``alloca``'d
6636 memory is automatically released when the function returns. The
6637 '``alloca``' instruction is commonly used to represent automatic
6638 variables that must have an address available. When the function returns
6639 (either with the ``ret`` or ``resume`` instructions), the memory is
6640 reclaimed. Allocating zero bytes is legal, but the result is undefined.
6641 The order in which memory is allocated (ie., which way the stack grows)
6647 .. code-block:: llvm
6649 %ptr = alloca i32 ; yields i32*:ptr
6650 %ptr = alloca i32, i32 4 ; yields i32*:ptr
6651 %ptr = alloca i32, i32 4, align 1024 ; yields i32*:ptr
6652 %ptr = alloca i32, align 1024 ; yields i32*:ptr
6656 '``load``' Instruction
6657 ^^^^^^^^^^^^^^^^^^^^^^
6664 <result> = load [volatile] <ty>, <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>][, !invariant.load !<index>][, !nonnull !<index>][, !dereferenceable !<index>][, !dereferenceable_or_null !<index>]
6665 <result> = load atomic [volatile] <ty>* <pointer> [singlethread] <ordering>, align <alignment>
6666 !<index> = !{ i32 1 }
6671 The '``load``' instruction is used to read from memory.
6676 The argument to the ``load`` instruction specifies the memory address
6677 from which to load. The type specified must be a :ref:`first
6678 class <t_firstclass>` type. If the ``load`` is marked as ``volatile``,
6679 then the optimizer is not allowed to modify the number or order of
6680 execution of this ``load`` with other :ref:`volatile
6681 operations <volatile>`.
6683 If the ``load`` is marked as ``atomic``, it takes an extra
6684 :ref:`ordering <ordering>` and optional ``singlethread`` argument. The
6685 ``release`` and ``acq_rel`` orderings are not valid on ``load``
6686 instructions. Atomic loads produce :ref:`defined <memmodel>` results
6687 when they may see multiple atomic stores. The type of the pointee must
6688 be an integer type whose bit width is a power of two greater than or
6689 equal to eight and less than or equal to a target-specific size limit.
6690 ``align`` must be explicitly specified on atomic loads, and the load has
6691 undefined behavior if the alignment is not set to a value which is at
6692 least the size in bytes of the pointee. ``!nontemporal`` does not have
6693 any defined semantics for atomic loads.
6695 The optional constant ``align`` argument specifies the alignment of the
6696 operation (that is, the alignment of the memory address). A value of 0
6697 or an omitted ``align`` argument means that the operation has the ABI
6698 alignment for the target. It is the responsibility of the code emitter
6699 to ensure that the alignment information is correct. Overestimating the
6700 alignment results in undefined behavior. Underestimating the alignment
6701 may produce less efficient code. An alignment of 1 is always safe. The
6702 maximum possible alignment is ``1 << 29``.
6704 The optional ``!nontemporal`` metadata must reference a single
6705 metadata name ``<index>`` corresponding to a metadata node with one
6706 ``i32`` entry of value 1. The existence of the ``!nontemporal``
6707 metadata on the instruction tells the optimizer and code generator
6708 that this load is not expected to be reused in the cache. The code
6709 generator may select special instructions to save cache bandwidth, such
6710 as the ``MOVNT`` instruction on x86.
6712 The optional ``!invariant.load`` metadata must reference a single
6713 metadata name ``<index>`` corresponding to a metadata node with no
6714 entries. The existence of the ``!invariant.load`` metadata on the
6715 instruction tells the optimizer and code generator that the address
6716 operand to this load points to memory which can be assumed unchanged.
6717 Being invariant does not imply that a location is dereferenceable,
6718 but it does imply that once the location is known dereferenceable
6719 its value is henceforth unchanging.
6721 The optional ``!nonnull`` metadata must reference a single
6722 metadata name ``<index>`` corresponding to a metadata node with no
6723 entries. The existence of the ``!nonnull`` metadata on the
6724 instruction tells the optimizer that the value loaded is known to
6725 never be null. This is analogous to the ''nonnull'' attribute
6726 on parameters and return values. This metadata can only be applied
6727 to loads of a pointer type.
6729 The optional ``!dereferenceable`` metadata must reference a single
6730 metadata name ``<index>`` corresponding to a metadata node with one ``i64``
6731 entry. The existence of the ``!dereferenceable`` metadata on the instruction
6732 tells the optimizer that the value loaded is known to be dereferenceable.
6733 The number of bytes known to be dereferenceable is specified by the integer
6734 value in the metadata node. This is analogous to the ''dereferenceable''
6735 attribute on parameters and return values. This metadata can only be applied
6736 to loads of a pointer type.
6738 The optional ``!dereferenceable_or_null`` metadata must reference a single
6739 metadata name ``<index>`` corresponding to a metadata node with one ``i64``
6740 entry. The existence of the ``!dereferenceable_or_null`` metadata on the
6741 instruction tells the optimizer that the value loaded is known to be either
6742 dereferenceable or null.
6743 The number of bytes known to be dereferenceable is specified by the integer
6744 value in the metadata node. This is analogous to the ''dereferenceable_or_null''
6745 attribute on parameters and return values. This metadata can only be applied
6746 to loads of a pointer type.
6751 The location of memory pointed to is loaded. If the value being loaded
6752 is of scalar type then the number of bytes read does not exceed the
6753 minimum number of bytes needed to hold all bits of the type. For
6754 example, loading an ``i24`` reads at most three bytes. When loading a
6755 value of a type like ``i20`` with a size that is not an integral number
6756 of bytes, the result is undefined if the value was not originally
6757 written using a store of the same type.
6762 .. code-block:: llvm
6764 %ptr = alloca i32 ; yields i32*:ptr
6765 store i32 3, i32* %ptr ; yields void
6766 %val = load i32, i32* %ptr ; yields i32:val = i32 3
6770 '``store``' Instruction
6771 ^^^^^^^^^^^^^^^^^^^^^^^
6778 store [volatile] <ty> <value>, <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>] ; yields void
6779 store atomic [volatile] <ty> <value>, <ty>* <pointer> [singlethread] <ordering>, align <alignment> ; yields void
6784 The '``store``' instruction is used to write to memory.
6789 There are two arguments to the ``store`` instruction: a value to store
6790 and an address at which to store it. The type of the ``<pointer>``
6791 operand must be a pointer to the :ref:`first class <t_firstclass>` type of
6792 the ``<value>`` operand. If the ``store`` is marked as ``volatile``,
6793 then the optimizer is not allowed to modify the number or order of
6794 execution of this ``store`` with other :ref:`volatile
6795 operations <volatile>`.
6797 If the ``store`` is marked as ``atomic``, it takes an extra
6798 :ref:`ordering <ordering>` and optional ``singlethread`` argument. The
6799 ``acquire`` and ``acq_rel`` orderings aren't valid on ``store``
6800 instructions. Atomic loads produce :ref:`defined <memmodel>` results
6801 when they may see multiple atomic stores. The type of the pointee must
6802 be an integer type whose bit width is a power of two greater than or
6803 equal to eight and less than or equal to a target-specific size limit.
6804 ``align`` must be explicitly specified on atomic stores, and the store
6805 has undefined behavior if the alignment is not set to a value which is
6806 at least the size in bytes of the pointee. ``!nontemporal`` does not
6807 have any defined semantics for atomic stores.
6809 The optional constant ``align`` argument specifies the alignment of the
6810 operation (that is, the alignment of the memory address). A value of 0
6811 or an omitted ``align`` argument means that the operation has the ABI
6812 alignment for the target. It is the responsibility of the code emitter
6813 to ensure that the alignment information is correct. Overestimating the
6814 alignment results in undefined behavior. Underestimating the
6815 alignment may produce less efficient code. An alignment of 1 is always
6816 safe. The maximum possible alignment is ``1 << 29``.
6818 The optional ``!nontemporal`` metadata must reference a single metadata
6819 name ``<index>`` corresponding to a metadata node with one ``i32`` entry of
6820 value 1. The existence of the ``!nontemporal`` metadata on the instruction
6821 tells the optimizer and code generator that this load is not expected to
6822 be reused in the cache. The code generator may select special
6823 instructions to save cache bandwidth, such as the MOVNT instruction on
6829 The contents of memory are updated to contain ``<value>`` at the
6830 location specified by the ``<pointer>`` operand. If ``<value>`` is
6831 of scalar type then the number of bytes written does not exceed the
6832 minimum number of bytes needed to hold all bits of the type. For
6833 example, storing an ``i24`` writes at most three bytes. When writing a
6834 value of a type like ``i20`` with a size that is not an integral number
6835 of bytes, it is unspecified what happens to the extra bits that do not
6836 belong to the type, but they will typically be overwritten.
6841 .. code-block:: llvm
6843 %ptr = alloca i32 ; yields i32*:ptr
6844 store i32 3, i32* %ptr ; yields void
6845 %val = load i32, i32* %ptr ; yields i32:val = i32 3
6849 '``fence``' Instruction
6850 ^^^^^^^^^^^^^^^^^^^^^^^
6857 fence [singlethread] <ordering> ; yields void
6862 The '``fence``' instruction is used to introduce happens-before edges
6868 '``fence``' instructions take an :ref:`ordering <ordering>` argument which
6869 defines what *synchronizes-with* edges they add. They can only be given
6870 ``acquire``, ``release``, ``acq_rel``, and ``seq_cst`` orderings.
6875 A fence A which has (at least) ``release`` ordering semantics
6876 *synchronizes with* a fence B with (at least) ``acquire`` ordering
6877 semantics if and only if there exist atomic operations X and Y, both
6878 operating on some atomic object M, such that A is sequenced before X, X
6879 modifies M (either directly or through some side effect of a sequence
6880 headed by X), Y is sequenced before B, and Y observes M. This provides a
6881 *happens-before* dependency between A and B. Rather than an explicit
6882 ``fence``, one (but not both) of the atomic operations X or Y might
6883 provide a ``release`` or ``acquire`` (resp.) ordering constraint and
6884 still *synchronize-with* the explicit ``fence`` and establish the
6885 *happens-before* edge.
6887 A ``fence`` which has ``seq_cst`` ordering, in addition to having both
6888 ``acquire`` and ``release`` semantics specified above, participates in
6889 the global program order of other ``seq_cst`` operations and/or fences.
6891 The optional ":ref:`singlethread <singlethread>`" argument specifies
6892 that the fence only synchronizes with other fences in the same thread.
6893 (This is useful for interacting with signal handlers.)
6898 .. code-block:: llvm
6900 fence acquire ; yields void
6901 fence singlethread seq_cst ; yields void
6905 '``cmpxchg``' Instruction
6906 ^^^^^^^^^^^^^^^^^^^^^^^^^
6913 cmpxchg [weak] [volatile] <ty>* <pointer>, <ty> <cmp>, <ty> <new> [singlethread] <success ordering> <failure ordering> ; yields { ty, i1 }
6918 The '``cmpxchg``' instruction is used to atomically modify memory. It
6919 loads a value in memory and compares it to a given value. If they are
6920 equal, it tries to store a new value into the memory.
6925 There are three arguments to the '``cmpxchg``' instruction: an address
6926 to operate on, a value to compare to the value currently be at that
6927 address, and a new value to place at that address if the compared values
6928 are equal. The type of '<cmp>' must be an integer type whose bit width
6929 is a power of two greater than or equal to eight and less than or equal
6930 to a target-specific size limit. '<cmp>' and '<new>' must have the same
6931 type, and the type of '<pointer>' must be a pointer to that type. If the
6932 ``cmpxchg`` is marked as ``volatile``, then the optimizer is not allowed
6933 to modify the number or order of execution of this ``cmpxchg`` with
6934 other :ref:`volatile operations <volatile>`.
6936 The success and failure :ref:`ordering <ordering>` arguments specify how this
6937 ``cmpxchg`` synchronizes with other atomic operations. Both ordering parameters
6938 must be at least ``monotonic``, the ordering constraint on failure must be no
6939 stronger than that on success, and the failure ordering cannot be either
6940 ``release`` or ``acq_rel``.
6942 The optional "``singlethread``" argument declares that the ``cmpxchg``
6943 is only atomic with respect to code (usually signal handlers) running in
6944 the same thread as the ``cmpxchg``. Otherwise the cmpxchg is atomic with
6945 respect to all other code in the system.
6947 The pointer passed into cmpxchg must have alignment greater than or
6948 equal to the size in memory of the operand.
6953 The contents of memory at the location specified by the '``<pointer>``' operand
6954 is read and compared to '``<cmp>``'; if the read value is the equal, the
6955 '``<new>``' is written. The original value at the location is returned, together
6956 with a flag indicating success (true) or failure (false).
6958 If the cmpxchg operation is marked as ``weak`` then a spurious failure is
6959 permitted: the operation may not write ``<new>`` even if the comparison
6962 If the cmpxchg operation is strong (the default), the i1 value is 1 if and only
6963 if the value loaded equals ``cmp``.
6965 A successful ``cmpxchg`` is a read-modify-write instruction for the purpose of
6966 identifying release sequences. A failed ``cmpxchg`` is equivalent to an atomic
6967 load with an ordering parameter determined the second ordering parameter.
6972 .. code-block:: llvm
6975 %orig = atomic load i32, i32* %ptr unordered ; yields i32
6979 %cmp = phi i32 [ %orig, %entry ], [%old, %loop]
6980 %squared = mul i32 %cmp, %cmp
6981 %val_success = cmpxchg i32* %ptr, i32 %cmp, i32 %squared acq_rel monotonic ; yields { i32, i1 }
6982 %value_loaded = extractvalue { i32, i1 } %val_success, 0
6983 %success = extractvalue { i32, i1 } %val_success, 1
6984 br i1 %success, label %done, label %loop
6991 '``atomicrmw``' Instruction
6992 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
6999 atomicrmw [volatile] <operation> <ty>* <pointer>, <ty> <value> [singlethread] <ordering> ; yields ty
7004 The '``atomicrmw``' instruction is used to atomically modify memory.
7009 There are three arguments to the '``atomicrmw``' instruction: an
7010 operation to apply, an address whose value to modify, an argument to the
7011 operation. The operation must be one of the following keywords:
7025 The type of '<value>' must be an integer type whose bit width is a power
7026 of two greater than or equal to eight and less than or equal to a
7027 target-specific size limit. The type of the '``<pointer>``' operand must
7028 be a pointer to that type. If the ``atomicrmw`` is marked as
7029 ``volatile``, then the optimizer is not allowed to modify the number or
7030 order of execution of this ``atomicrmw`` with other :ref:`volatile
7031 operations <volatile>`.
7036 The contents of memory at the location specified by the '``<pointer>``'
7037 operand are atomically read, modified, and written back. The original
7038 value at the location is returned. The modification is specified by the
7041 - xchg: ``*ptr = val``
7042 - add: ``*ptr = *ptr + val``
7043 - sub: ``*ptr = *ptr - val``
7044 - and: ``*ptr = *ptr & val``
7045 - nand: ``*ptr = ~(*ptr & val)``
7046 - or: ``*ptr = *ptr | val``
7047 - xor: ``*ptr = *ptr ^ val``
7048 - max: ``*ptr = *ptr > val ? *ptr : val`` (using a signed comparison)
7049 - min: ``*ptr = *ptr < val ? *ptr : val`` (using a signed comparison)
7050 - umax: ``*ptr = *ptr > val ? *ptr : val`` (using an unsigned
7052 - umin: ``*ptr = *ptr < val ? *ptr : val`` (using an unsigned
7058 .. code-block:: llvm
7060 %old = atomicrmw add i32* %ptr, i32 1 acquire ; yields i32
7062 .. _i_getelementptr:
7064 '``getelementptr``' Instruction
7065 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7072 <result> = getelementptr <ty>, <ty>* <ptrval>{, <ty> <idx>}*
7073 <result> = getelementptr inbounds <ty>, <ty>* <ptrval>{, <ty> <idx>}*
7074 <result> = getelementptr <ty>, <ptr vector> <ptrval>, <vector index type> <idx>
7079 The '``getelementptr``' instruction is used to get the address of a
7080 subelement of an :ref:`aggregate <t_aggregate>` data structure. It performs
7081 address calculation only and does not access memory. The instruction can also
7082 be used to calculate a vector of such addresses.
7087 The first argument is always a type used as the basis for the calculations.
7088 The second argument is always a pointer or a vector of pointers, and is the
7089 base address to start from. The remaining arguments are indices
7090 that indicate which of the elements of the aggregate object are indexed.
7091 The interpretation of each index is dependent on the type being indexed
7092 into. The first index always indexes the pointer value given as the
7093 first argument, the second index indexes a value of the type pointed to
7094 (not necessarily the value directly pointed to, since the first index
7095 can be non-zero), etc. The first type indexed into must be a pointer
7096 value, subsequent types can be arrays, vectors, and structs. Note that
7097 subsequent types being indexed into can never be pointers, since that
7098 would require loading the pointer before continuing calculation.
7100 The type of each index argument depends on the type it is indexing into.
7101 When indexing into a (optionally packed) structure, only ``i32`` integer
7102 **constants** are allowed (when using a vector of indices they must all
7103 be the **same** ``i32`` integer constant). When indexing into an array,
7104 pointer or vector, integers of any width are allowed, and they are not
7105 required to be constant. These integers are treated as signed values
7108 For example, let's consider a C code fragment and how it gets compiled
7124 int *foo(struct ST *s) {
7125 return &s[1].Z.B[5][13];
7128 The LLVM code generated by Clang is:
7130 .. code-block:: llvm
7132 %struct.RT = type { i8, [10 x [20 x i32]], i8 }
7133 %struct.ST = type { i32, double, %struct.RT }
7135 define i32* @foo(%struct.ST* %s) nounwind uwtable readnone optsize ssp {
7137 %arrayidx = getelementptr inbounds %struct.ST, %struct.ST* %s, i64 1, i32 2, i32 1, i64 5, i64 13
7144 In the example above, the first index is indexing into the
7145 '``%struct.ST*``' type, which is a pointer, yielding a '``%struct.ST``'
7146 = '``{ i32, double, %struct.RT }``' type, a structure. The second index
7147 indexes into the third element of the structure, yielding a
7148 '``%struct.RT``' = '``{ i8 , [10 x [20 x i32]], i8 }``' type, another
7149 structure. The third index indexes into the second element of the
7150 structure, yielding a '``[10 x [20 x i32]]``' type, an array. The two
7151 dimensions of the array are subscripted into, yielding an '``i32``'
7152 type. The '``getelementptr``' instruction returns a pointer to this
7153 element, thus computing a value of '``i32*``' type.
7155 Note that it is perfectly legal to index partially through a structure,
7156 returning a pointer to an inner element. Because of this, the LLVM code
7157 for the given testcase is equivalent to:
7159 .. code-block:: llvm
7161 define i32* @foo(%struct.ST* %s) {
7162 %t1 = getelementptr %struct.ST, %struct.ST* %s, i32 1 ; yields %struct.ST*:%t1
7163 %t2 = getelementptr %struct.ST, %struct.ST* %t1, i32 0, i32 2 ; yields %struct.RT*:%t2
7164 %t3 = getelementptr %struct.RT, %struct.RT* %t2, i32 0, i32 1 ; yields [10 x [20 x i32]]*:%t3
7165 %t4 = getelementptr [10 x [20 x i32]], [10 x [20 x i32]]* %t3, i32 0, i32 5 ; yields [20 x i32]*:%t4
7166 %t5 = getelementptr [20 x i32], [20 x i32]* %t4, i32 0, i32 13 ; yields i32*:%t5
7170 If the ``inbounds`` keyword is present, the result value of the
7171 ``getelementptr`` is a :ref:`poison value <poisonvalues>` if the base
7172 pointer is not an *in bounds* address of an allocated object, or if any
7173 of the addresses that would be formed by successive addition of the
7174 offsets implied by the indices to the base address with infinitely
7175 precise signed arithmetic are not an *in bounds* address of that
7176 allocated object. The *in bounds* addresses for an allocated object are
7177 all the addresses that point into the object, plus the address one byte
7178 past the end. In cases where the base is a vector of pointers the
7179 ``inbounds`` keyword applies to each of the computations element-wise.
7181 If the ``inbounds`` keyword is not present, the offsets are added to the
7182 base address with silently-wrapping two's complement arithmetic. If the
7183 offsets have a different width from the pointer, they are sign-extended
7184 or truncated to the width of the pointer. The result value of the
7185 ``getelementptr`` may be outside the object pointed to by the base
7186 pointer. The result value may not necessarily be used to access memory
7187 though, even if it happens to point into allocated storage. See the
7188 :ref:`Pointer Aliasing Rules <pointeraliasing>` section for more
7191 The getelementptr instruction is often confusing. For some more insight
7192 into how it works, see :doc:`the getelementptr FAQ <GetElementPtr>`.
7197 .. code-block:: llvm
7199 ; yields [12 x i8]*:aptr
7200 %aptr = getelementptr {i32, [12 x i8]}, {i32, [12 x i8]}* %saptr, i64 0, i32 1
7202 %vptr = getelementptr {i32, <2 x i8>}, {i32, <2 x i8>}* %svptr, i64 0, i32 1, i32 1
7204 %eptr = getelementptr [12 x i8], [12 x i8]* %aptr, i64 0, i32 1
7206 %iptr = getelementptr [10 x i32], [10 x i32]* @arr, i16 0, i16 0
7211 The ``getelementptr`` returns a vector of pointers, instead of a single address,
7212 when one or more of its arguments is a vector. In such cases, all vector
7213 arguments should have the same number of elements, and every scalar argument
7214 will be effectively broadcast into a vector during address calculation.
7216 .. code-block:: llvm
7218 ; All arguments are vectors:
7219 ; A[i] = ptrs[i] + offsets[i]*sizeof(i8)
7220 %A = getelementptr i8, <4 x i8*> %ptrs, <4 x i64> %offsets
7222 ; Add the same scalar offset to each pointer of a vector:
7223 ; A[i] = ptrs[i] + offset*sizeof(i8)
7224 %A = getelementptr i8, <4 x i8*> %ptrs, i64 %offset
7226 ; Add distinct offsets to the same pointer:
7227 ; A[i] = ptr + offsets[i]*sizeof(i8)
7228 %A = getelementptr i8, i8* %ptr, <4 x i64> %offsets
7230 ; In all cases described above the type of the result is <4 x i8*>
7232 The two following instructions are equivalent:
7234 .. code-block:: llvm
7236 getelementptr %struct.ST, <4 x %struct.ST*> %s, <4 x i64> %ind1,
7237 <4 x i32> <i32 2, i32 2, i32 2, i32 2>,
7238 <4 x i32> <i32 1, i32 1, i32 1, i32 1>,
7240 <4 x i64> <i64 13, i64 13, i64 13, i64 13>
7242 getelementptr %struct.ST, <4 x %struct.ST*> %s, <4 x i64> %ind1,
7243 i32 2, i32 1, <4 x i32> %ind4, i64 13
7245 Let's look at the C code, where the vector version of ``getelementptr``
7250 // Let's assume that we vectorize the following loop:
7251 double *A, B; int *C;
7252 for (int i = 0; i < size; ++i) {
7256 .. code-block:: llvm
7258 ; get pointers for 8 elements from array B
7259 %ptrs = getelementptr double, double* %B, <8 x i32> %C
7260 ; load 8 elements from array B into A
7261 %A = call <8 x double> @llvm.masked.gather.v8f64(<8 x double*> %ptrs,
7262 i32 8, <8 x i1> %mask, <8 x double> %passthru)
7264 Conversion Operations
7265 ---------------------
7267 The instructions in this category are the conversion instructions
7268 (casting) which all take a single operand and a type. They perform
7269 various bit conversions on the operand.
7271 '``trunc .. to``' Instruction
7272 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7279 <result> = trunc <ty> <value> to <ty2> ; yields ty2
7284 The '``trunc``' instruction truncates its operand to the type ``ty2``.
7289 The '``trunc``' instruction takes a value to trunc, and a type to trunc
7290 it to. Both types must be of :ref:`integer <t_integer>` types, or vectors
7291 of the same number of integers. The bit size of the ``value`` must be
7292 larger than the bit size of the destination type, ``ty2``. Equal sized
7293 types are not allowed.
7298 The '``trunc``' instruction truncates the high order bits in ``value``
7299 and converts the remaining bits to ``ty2``. Since the source size must
7300 be larger than the destination size, ``trunc`` cannot be a *no-op cast*.
7301 It will always truncate bits.
7306 .. code-block:: llvm
7308 %X = trunc i32 257 to i8 ; yields i8:1
7309 %Y = trunc i32 123 to i1 ; yields i1:true
7310 %Z = trunc i32 122 to i1 ; yields i1:false
7311 %W = trunc <2 x i16> <i16 8, i16 7> to <2 x i8> ; yields <i8 8, i8 7>
7313 '``zext .. to``' Instruction
7314 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7321 <result> = zext <ty> <value> to <ty2> ; yields ty2
7326 The '``zext``' instruction zero extends its operand to type ``ty2``.
7331 The '``zext``' instruction takes a value to cast, and a type to cast it
7332 to. Both types must be of :ref:`integer <t_integer>` types, or vectors of
7333 the same number of integers. The bit size of the ``value`` must be
7334 smaller than the bit size of the destination type, ``ty2``.
7339 The ``zext`` fills the high order bits of the ``value`` with zero bits
7340 until it reaches the size of the destination type, ``ty2``.
7342 When zero extending from i1, the result will always be either 0 or 1.
7347 .. code-block:: llvm
7349 %X = zext i32 257 to i64 ; yields i64:257
7350 %Y = zext i1 true to i32 ; yields i32:1
7351 %Z = zext <2 x i16> <i16 8, i16 7> to <2 x i32> ; yields <i32 8, i32 7>
7353 '``sext .. to``' Instruction
7354 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7361 <result> = sext <ty> <value> to <ty2> ; yields ty2
7366 The '``sext``' sign extends ``value`` to the type ``ty2``.
7371 The '``sext``' instruction takes a value to cast, and a type to cast it
7372 to. Both types must be of :ref:`integer <t_integer>` types, or vectors of
7373 the same number of integers. The bit size of the ``value`` must be
7374 smaller than the bit size of the destination type, ``ty2``.
7379 The '``sext``' instruction performs a sign extension by copying the sign
7380 bit (highest order bit) of the ``value`` until it reaches the bit size
7381 of the type ``ty2``.
7383 When sign extending from i1, the extension always results in -1 or 0.
7388 .. code-block:: llvm
7390 %X = sext i8 -1 to i16 ; yields i16 :65535
7391 %Y = sext i1 true to i32 ; yields i32:-1
7392 %Z = sext <2 x i16> <i16 8, i16 7> to <2 x i32> ; yields <i32 8, i32 7>
7394 '``fptrunc .. to``' Instruction
7395 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7402 <result> = fptrunc <ty> <value> to <ty2> ; yields ty2
7407 The '``fptrunc``' instruction truncates ``value`` to type ``ty2``.
7412 The '``fptrunc``' instruction takes a :ref:`floating point <t_floating>`
7413 value to cast and a :ref:`floating point <t_floating>` type to cast it to.
7414 The size of ``value`` must be larger than the size of ``ty2``. This
7415 implies that ``fptrunc`` cannot be used to make a *no-op cast*.
7420 The '``fptrunc``' instruction truncates a ``value`` from a larger
7421 :ref:`floating point <t_floating>` type to a smaller :ref:`floating
7422 point <t_floating>` type. If the value cannot fit within the
7423 destination type, ``ty2``, then the results are undefined.
7428 .. code-block:: llvm
7430 %X = fptrunc double 123.0 to float ; yields float:123.0
7431 %Y = fptrunc double 1.0E+300 to float ; yields undefined
7433 '``fpext .. to``' Instruction
7434 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7441 <result> = fpext <ty> <value> to <ty2> ; yields ty2
7446 The '``fpext``' extends a floating point ``value`` to a larger floating
7452 The '``fpext``' instruction takes a :ref:`floating point <t_floating>`
7453 ``value`` to cast, and a :ref:`floating point <t_floating>` type to cast it
7454 to. The source type must be smaller than the destination type.
7459 The '``fpext``' instruction extends the ``value`` from a smaller
7460 :ref:`floating point <t_floating>` type to a larger :ref:`floating
7461 point <t_floating>` type. The ``fpext`` cannot be used to make a
7462 *no-op cast* because it always changes bits. Use ``bitcast`` to make a
7463 *no-op cast* for a floating point cast.
7468 .. code-block:: llvm
7470 %X = fpext float 3.125 to double ; yields double:3.125000e+00
7471 %Y = fpext double %X to fp128 ; yields fp128:0xL00000000000000004000900000000000
7473 '``fptoui .. to``' Instruction
7474 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7481 <result> = fptoui <ty> <value> to <ty2> ; yields ty2
7486 The '``fptoui``' converts a floating point ``value`` to its unsigned
7487 integer equivalent of type ``ty2``.
7492 The '``fptoui``' instruction takes a value to cast, which must be a
7493 scalar or vector :ref:`floating point <t_floating>` value, and a type to
7494 cast it to ``ty2``, which must be an :ref:`integer <t_integer>` type. If
7495 ``ty`` is a vector floating point type, ``ty2`` must be a vector integer
7496 type with the same number of elements as ``ty``
7501 The '``fptoui``' instruction converts its :ref:`floating
7502 point <t_floating>` operand into the nearest (rounding towards zero)
7503 unsigned integer value. If the value cannot fit in ``ty2``, the results
7509 .. code-block:: llvm
7511 %X = fptoui double 123.0 to i32 ; yields i32:123
7512 %Y = fptoui float 1.0E+300 to i1 ; yields undefined:1
7513 %Z = fptoui float 1.04E+17 to i8 ; yields undefined:1
7515 '``fptosi .. to``' Instruction
7516 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7523 <result> = fptosi <ty> <value> to <ty2> ; yields ty2
7528 The '``fptosi``' instruction converts :ref:`floating point <t_floating>`
7529 ``value`` to type ``ty2``.
7534 The '``fptosi``' instruction takes a value to cast, which must be a
7535 scalar or vector :ref:`floating point <t_floating>` value, and a type to
7536 cast it to ``ty2``, which must be an :ref:`integer <t_integer>` type. If
7537 ``ty`` is a vector floating point type, ``ty2`` must be a vector integer
7538 type with the same number of elements as ``ty``
7543 The '``fptosi``' instruction converts its :ref:`floating
7544 point <t_floating>` operand into the nearest (rounding towards zero)
7545 signed integer value. If the value cannot fit in ``ty2``, the results
7551 .. code-block:: llvm
7553 %X = fptosi double -123.0 to i32 ; yields i32:-123
7554 %Y = fptosi float 1.0E-247 to i1 ; yields undefined:1
7555 %Z = fptosi float 1.04E+17 to i8 ; yields undefined:1
7557 '``uitofp .. to``' Instruction
7558 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7565 <result> = uitofp <ty> <value> to <ty2> ; yields ty2
7570 The '``uitofp``' instruction regards ``value`` as an unsigned integer
7571 and converts that value to the ``ty2`` type.
7576 The '``uitofp``' instruction takes a value to cast, which must be a
7577 scalar or vector :ref:`integer <t_integer>` value, and a type to cast it to
7578 ``ty2``, which must be an :ref:`floating point <t_floating>` type. If
7579 ``ty`` is a vector integer type, ``ty2`` must be a vector floating point
7580 type with the same number of elements as ``ty``
7585 The '``uitofp``' instruction interprets its operand as an unsigned
7586 integer quantity and converts it to the corresponding floating point
7587 value. If the value cannot fit in the floating point value, the results
7593 .. code-block:: llvm
7595 %X = uitofp i32 257 to float ; yields float:257.0
7596 %Y = uitofp i8 -1 to double ; yields double:255.0
7598 '``sitofp .. to``' Instruction
7599 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7606 <result> = sitofp <ty> <value> to <ty2> ; yields ty2
7611 The '``sitofp``' instruction regards ``value`` as a signed integer and
7612 converts that value to the ``ty2`` type.
7617 The '``sitofp``' instruction takes a value to cast, which must be a
7618 scalar or vector :ref:`integer <t_integer>` value, and a type to cast it to
7619 ``ty2``, which must be an :ref:`floating point <t_floating>` type. If
7620 ``ty`` is a vector integer type, ``ty2`` must be a vector floating point
7621 type with the same number of elements as ``ty``
7626 The '``sitofp``' instruction interprets its operand as a signed integer
7627 quantity and converts it to the corresponding floating point value. If
7628 the value cannot fit in the floating point value, the results are
7634 .. code-block:: llvm
7636 %X = sitofp i32 257 to float ; yields float:257.0
7637 %Y = sitofp i8 -1 to double ; yields double:-1.0
7641 '``ptrtoint .. to``' Instruction
7642 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7649 <result> = ptrtoint <ty> <value> to <ty2> ; yields ty2
7654 The '``ptrtoint``' instruction converts the pointer or a vector of
7655 pointers ``value`` to the integer (or vector of integers) type ``ty2``.
7660 The '``ptrtoint``' instruction takes a ``value`` to cast, which must be
7661 a value of type :ref:`pointer <t_pointer>` or a vector of pointers, and a
7662 type to cast it to ``ty2``, which must be an :ref:`integer <t_integer>` or
7663 a vector of integers type.
7668 The '``ptrtoint``' instruction converts ``value`` to integer type
7669 ``ty2`` by interpreting the pointer value as an integer and either
7670 truncating or zero extending that value to the size of the integer type.
7671 If ``value`` is smaller than ``ty2`` then a zero extension is done. If
7672 ``value`` is larger than ``ty2`` then a truncation is done. If they are
7673 the same size, then nothing is done (*no-op cast*) other than a type
7679 .. code-block:: llvm
7681 %X = ptrtoint i32* %P to i8 ; yields truncation on 32-bit architecture
7682 %Y = ptrtoint i32* %P to i64 ; yields zero extension on 32-bit architecture
7683 %Z = ptrtoint <4 x i32*> %P to <4 x i64>; yields vector zero extension for a vector of addresses on 32-bit architecture
7687 '``inttoptr .. to``' Instruction
7688 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7695 <result> = inttoptr <ty> <value> to <ty2> ; yields ty2
7700 The '``inttoptr``' instruction converts an integer ``value`` to a
7701 pointer type, ``ty2``.
7706 The '``inttoptr``' instruction takes an :ref:`integer <t_integer>` value to
7707 cast, and a type to cast it to, which must be a :ref:`pointer <t_pointer>`
7713 The '``inttoptr``' instruction converts ``value`` to type ``ty2`` by
7714 applying either a zero extension or a truncation depending on the size
7715 of the integer ``value``. If ``value`` is larger than the size of a
7716 pointer then a truncation is done. If ``value`` is smaller than the size
7717 of a pointer then a zero extension is done. If they are the same size,
7718 nothing is done (*no-op cast*).
7723 .. code-block:: llvm
7725 %X = inttoptr i32 255 to i32* ; yields zero extension on 64-bit architecture
7726 %Y = inttoptr i32 255 to i32* ; yields no-op on 32-bit architecture
7727 %Z = inttoptr i64 0 to i32* ; yields truncation on 32-bit architecture
7728 %Z = inttoptr <4 x i32> %G to <4 x i8*>; yields truncation of vector G to four pointers
7732 '``bitcast .. to``' Instruction
7733 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7740 <result> = bitcast <ty> <value> to <ty2> ; yields ty2
7745 The '``bitcast``' instruction converts ``value`` to type ``ty2`` without
7751 The '``bitcast``' instruction takes a value to cast, which must be a
7752 non-aggregate first class value, and a type to cast it to, which must
7753 also be a non-aggregate :ref:`first class <t_firstclass>` type. The
7754 bit sizes of ``value`` and the destination type, ``ty2``, must be
7755 identical. If the source type is a pointer, the destination type must
7756 also be a pointer of the same size. This instruction supports bitwise
7757 conversion of vectors to integers and to vectors of other types (as
7758 long as they have the same size).
7763 The '``bitcast``' instruction converts ``value`` to type ``ty2``. It
7764 is always a *no-op cast* because no bits change with this
7765 conversion. The conversion is done as if the ``value`` had been stored
7766 to memory and read back as type ``ty2``. Pointer (or vector of
7767 pointers) types may only be converted to other pointer (or vector of
7768 pointers) types with the same address space through this instruction.
7769 To convert pointers to other types, use the :ref:`inttoptr <i_inttoptr>`
7770 or :ref:`ptrtoint <i_ptrtoint>` instructions first.
7775 .. code-block:: llvm
7777 %X = bitcast i8 255 to i8 ; yields i8 :-1
7778 %Y = bitcast i32* %x to sint* ; yields sint*:%x
7779 %Z = bitcast <2 x int> %V to i64; ; yields i64: %V
7780 %Z = bitcast <2 x i32*> %V to <2 x i64*> ; yields <2 x i64*>
7782 .. _i_addrspacecast:
7784 '``addrspacecast .. to``' Instruction
7785 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7792 <result> = addrspacecast <pty> <ptrval> to <pty2> ; yields pty2
7797 The '``addrspacecast``' instruction converts ``ptrval`` from ``pty`` in
7798 address space ``n`` to type ``pty2`` in address space ``m``.
7803 The '``addrspacecast``' instruction takes a pointer or vector of pointer value
7804 to cast and a pointer type to cast it to, which must have a different
7810 The '``addrspacecast``' instruction converts the pointer value
7811 ``ptrval`` to type ``pty2``. It can be a *no-op cast* or a complex
7812 value modification, depending on the target and the address space
7813 pair. Pointer conversions within the same address space must be
7814 performed with the ``bitcast`` instruction. Note that if the address space
7815 conversion is legal then both result and operand refer to the same memory
7821 .. code-block:: llvm
7823 %X = addrspacecast i32* %x to i32 addrspace(1)* ; yields i32 addrspace(1)*:%x
7824 %Y = addrspacecast i32 addrspace(1)* %y to i64 addrspace(2)* ; yields i64 addrspace(2)*:%y
7825 %Z = addrspacecast <4 x i32*> %z to <4 x float addrspace(3)*> ; yields <4 x float addrspace(3)*>:%z
7832 The instructions in this category are the "miscellaneous" instructions,
7833 which defy better classification.
7837 '``icmp``' Instruction
7838 ^^^^^^^^^^^^^^^^^^^^^^
7845 <result> = icmp <cond> <ty> <op1>, <op2> ; yields i1 or <N x i1>:result
7850 The '``icmp``' instruction returns a boolean value or a vector of
7851 boolean values based on comparison of its two integer, integer vector,
7852 pointer, or pointer vector operands.
7857 The '``icmp``' instruction takes three operands. The first operand is
7858 the condition code indicating the kind of comparison to perform. It is
7859 not a value, just a keyword. The possible condition code are:
7862 #. ``ne``: not equal
7863 #. ``ugt``: unsigned greater than
7864 #. ``uge``: unsigned greater or equal
7865 #. ``ult``: unsigned less than
7866 #. ``ule``: unsigned less or equal
7867 #. ``sgt``: signed greater than
7868 #. ``sge``: signed greater or equal
7869 #. ``slt``: signed less than
7870 #. ``sle``: signed less or equal
7872 The remaining two arguments must be :ref:`integer <t_integer>` or
7873 :ref:`pointer <t_pointer>` or integer :ref:`vector <t_vector>` typed. They
7874 must also be identical types.
7879 The '``icmp``' compares ``op1`` and ``op2`` according to the condition
7880 code given as ``cond``. The comparison performed always yields either an
7881 :ref:`i1 <t_integer>` or vector of ``i1`` result, as follows:
7883 #. ``eq``: yields ``true`` if the operands are equal, ``false``
7884 otherwise. No sign interpretation is necessary or performed.
7885 #. ``ne``: yields ``true`` if the operands are unequal, ``false``
7886 otherwise. No sign interpretation is necessary or performed.
7887 #. ``ugt``: interprets the operands as unsigned values and yields
7888 ``true`` if ``op1`` is greater than ``op2``.
7889 #. ``uge``: interprets the operands as unsigned values and yields
7890 ``true`` if ``op1`` is greater than or equal to ``op2``.
7891 #. ``ult``: interprets the operands as unsigned values and yields
7892 ``true`` if ``op1`` is less than ``op2``.
7893 #. ``ule``: interprets the operands as unsigned values and yields
7894 ``true`` if ``op1`` is less than or equal to ``op2``.
7895 #. ``sgt``: interprets the operands as signed values and yields ``true``
7896 if ``op1`` is greater than ``op2``.
7897 #. ``sge``: interprets the operands as signed values and yields ``true``
7898 if ``op1`` is greater than or equal to ``op2``.
7899 #. ``slt``: interprets the operands as signed values and yields ``true``
7900 if ``op1`` is less than ``op2``.
7901 #. ``sle``: interprets the operands as signed values and yields ``true``
7902 if ``op1`` is less than or equal to ``op2``.
7904 If the operands are :ref:`pointer <t_pointer>` typed, the pointer values
7905 are compared as if they were integers.
7907 If the operands are integer vectors, then they are compared element by
7908 element. The result is an ``i1`` vector with the same number of elements
7909 as the values being compared. Otherwise, the result is an ``i1``.
7914 .. code-block:: llvm
7916 <result> = icmp eq i32 4, 5 ; yields: result=false
7917 <result> = icmp ne float* %X, %X ; yields: result=false
7918 <result> = icmp ult i16 4, 5 ; yields: result=true
7919 <result> = icmp sgt i16 4, 5 ; yields: result=false
7920 <result> = icmp ule i16 -4, 5 ; yields: result=false
7921 <result> = icmp sge i16 4, 5 ; yields: result=false
7923 Note that the code generator does not yet support vector types with the
7924 ``icmp`` instruction.
7928 '``fcmp``' Instruction
7929 ^^^^^^^^^^^^^^^^^^^^^^
7936 <result> = fcmp [fast-math flags]* <cond> <ty> <op1>, <op2> ; yields i1 or <N x i1>:result
7941 The '``fcmp``' instruction returns a boolean value or vector of boolean
7942 values based on comparison of its operands.
7944 If the operands are floating point scalars, then the result type is a
7945 boolean (:ref:`i1 <t_integer>`).
7947 If the operands are floating point vectors, then the result type is a
7948 vector of boolean with the same number of elements as the operands being
7954 The '``fcmp``' instruction takes three operands. The first operand is
7955 the condition code indicating the kind of comparison to perform. It is
7956 not a value, just a keyword. The possible condition code are:
7958 #. ``false``: no comparison, always returns false
7959 #. ``oeq``: ordered and equal
7960 #. ``ogt``: ordered and greater than
7961 #. ``oge``: ordered and greater than or equal
7962 #. ``olt``: ordered and less than
7963 #. ``ole``: ordered and less than or equal
7964 #. ``one``: ordered and not equal
7965 #. ``ord``: ordered (no nans)
7966 #. ``ueq``: unordered or equal
7967 #. ``ugt``: unordered or greater than
7968 #. ``uge``: unordered or greater than or equal
7969 #. ``ult``: unordered or less than
7970 #. ``ule``: unordered or less than or equal
7971 #. ``une``: unordered or not equal
7972 #. ``uno``: unordered (either nans)
7973 #. ``true``: no comparison, always returns true
7975 *Ordered* means that neither operand is a QNAN while *unordered* means
7976 that either operand may be a QNAN.
7978 Each of ``val1`` and ``val2`` arguments must be either a :ref:`floating
7979 point <t_floating>` type or a :ref:`vector <t_vector>` of floating point
7980 type. They must have identical types.
7985 The '``fcmp``' instruction compares ``op1`` and ``op2`` according to the
7986 condition code given as ``cond``. If the operands are vectors, then the
7987 vectors are compared element by element. Each comparison performed
7988 always yields an :ref:`i1 <t_integer>` result, as follows:
7990 #. ``false``: always yields ``false``, regardless of operands.
7991 #. ``oeq``: yields ``true`` if both operands are not a QNAN and ``op1``
7992 is equal to ``op2``.
7993 #. ``ogt``: yields ``true`` if both operands are not a QNAN and ``op1``
7994 is greater than ``op2``.
7995 #. ``oge``: yields ``true`` if both operands are not a QNAN and ``op1``
7996 is greater than or equal to ``op2``.
7997 #. ``olt``: yields ``true`` if both operands are not a QNAN and ``op1``
7998 is less than ``op2``.
7999 #. ``ole``: yields ``true`` if both operands are not a QNAN and ``op1``
8000 is less than or equal to ``op2``.
8001 #. ``one``: yields ``true`` if both operands are not a QNAN and ``op1``
8002 is not equal to ``op2``.
8003 #. ``ord``: yields ``true`` if both operands are not a QNAN.
8004 #. ``ueq``: yields ``true`` if either operand is a QNAN or ``op1`` is
8006 #. ``ugt``: yields ``true`` if either operand is a QNAN or ``op1`` is
8007 greater than ``op2``.
8008 #. ``uge``: yields ``true`` if either operand is a QNAN or ``op1`` is
8009 greater than or equal to ``op2``.
8010 #. ``ult``: yields ``true`` if either operand is a QNAN or ``op1`` is
8012 #. ``ule``: yields ``true`` if either operand is a QNAN or ``op1`` is
8013 less than or equal to ``op2``.
8014 #. ``une``: yields ``true`` if either operand is a QNAN or ``op1`` is
8015 not equal to ``op2``.
8016 #. ``uno``: yields ``true`` if either operand is a QNAN.
8017 #. ``true``: always yields ``true``, regardless of operands.
8019 The ``fcmp`` instruction can also optionally take any number of
8020 :ref:`fast-math flags <fastmath>`, which are optimization hints to enable
8021 otherwise unsafe floating point optimizations.
8023 Any set of fast-math flags are legal on an ``fcmp`` instruction, but the
8024 only flags that have any effect on its semantics are those that allow
8025 assumptions to be made about the values of input arguments; namely
8026 ``nnan``, ``ninf``, and ``nsz``. See :ref:`fastmath` for more information.
8031 .. code-block:: llvm
8033 <result> = fcmp oeq float 4.0, 5.0 ; yields: result=false
8034 <result> = fcmp one float 4.0, 5.0 ; yields: result=true
8035 <result> = fcmp olt float 4.0, 5.0 ; yields: result=true
8036 <result> = fcmp ueq double 1.0, 2.0 ; yields: result=false
8038 Note that the code generator does not yet support vector types with the
8039 ``fcmp`` instruction.
8043 '``phi``' Instruction
8044 ^^^^^^^^^^^^^^^^^^^^^
8051 <result> = phi <ty> [ <val0>, <label0>], ...
8056 The '``phi``' instruction is used to implement the φ node in the SSA
8057 graph representing the function.
8062 The type of the incoming values is specified with the first type field.
8063 After this, the '``phi``' instruction takes a list of pairs as
8064 arguments, with one pair for each predecessor basic block of the current
8065 block. Only values of :ref:`first class <t_firstclass>` type may be used as
8066 the value arguments to the PHI node. Only labels may be used as the
8069 There must be no non-phi instructions between the start of a basic block
8070 and the PHI instructions: i.e. PHI instructions must be first in a basic
8073 For the purposes of the SSA form, the use of each incoming value is
8074 deemed to occur on the edge from the corresponding predecessor block to
8075 the current block (but after any definition of an '``invoke``'
8076 instruction's return value on the same edge).
8081 At runtime, the '``phi``' instruction logically takes on the value
8082 specified by the pair corresponding to the predecessor basic block that
8083 executed just prior to the current block.
8088 .. code-block:: llvm
8090 Loop: ; Infinite loop that counts from 0 on up...
8091 %indvar = phi i32 [ 0, %LoopHeader ], [ %nextindvar, %Loop ]
8092 %nextindvar = add i32 %indvar, 1
8097 '``select``' Instruction
8098 ^^^^^^^^^^^^^^^^^^^^^^^^
8105 <result> = select selty <cond>, <ty> <val1>, <ty> <val2> ; yields ty
8107 selty is either i1 or {<N x i1>}
8112 The '``select``' instruction is used to choose one value based on a
8113 condition, without IR-level branching.
8118 The '``select``' instruction requires an 'i1' value or a vector of 'i1'
8119 values indicating the condition, and two values of the same :ref:`first
8120 class <t_firstclass>` type.
8125 If the condition is an i1 and it evaluates to 1, the instruction returns
8126 the first value argument; otherwise, it returns the second value
8129 If the condition is a vector of i1, then the value arguments must be
8130 vectors of the same size, and the selection is done element by element.
8132 If the condition is an i1 and the value arguments are vectors of the
8133 same size, then an entire vector is selected.
8138 .. code-block:: llvm
8140 %X = select i1 true, i8 17, i8 42 ; yields i8:17
8144 '``call``' Instruction
8145 ^^^^^^^^^^^^^^^^^^^^^^
8152 <result> = [tail | musttail] call [cconv] [ret attrs] <ty> [<fnty>*] <fnptrval>(<function args>) [fn attrs]
8157 The '``call``' instruction represents a simple function call.
8162 This instruction requires several arguments:
8164 #. The optional ``tail`` and ``musttail`` markers indicate that the optimizers
8165 should perform tail call optimization. The ``tail`` marker is a hint that
8166 `can be ignored <CodeGenerator.html#sibcallopt>`_. The ``musttail`` marker
8167 means that the call must be tail call optimized in order for the program to
8168 be correct. The ``musttail`` marker provides these guarantees:
8170 #. The call will not cause unbounded stack growth if it is part of a
8171 recursive cycle in the call graph.
8172 #. Arguments with the :ref:`inalloca <attr_inalloca>` attribute are
8175 Both markers imply that the callee does not access allocas or varargs from
8176 the caller. Calls marked ``musttail`` must obey the following additional
8179 - The call must immediately precede a :ref:`ret <i_ret>` instruction,
8180 or a pointer bitcast followed by a ret instruction.
8181 - The ret instruction must return the (possibly bitcasted) value
8182 produced by the call or void.
8183 - The caller and callee prototypes must match. Pointer types of
8184 parameters or return types may differ in pointee type, but not
8186 - The calling conventions of the caller and callee must match.
8187 - All ABI-impacting function attributes, such as sret, byval, inreg,
8188 returned, and inalloca, must match.
8189 - The callee must be varargs iff the caller is varargs. Bitcasting a
8190 non-varargs function to the appropriate varargs type is legal so
8191 long as the non-varargs prefixes obey the other rules.
8193 Tail call optimization for calls marked ``tail`` is guaranteed to occur if
8194 the following conditions are met:
8196 - Caller and callee both have the calling convention ``fastcc``.
8197 - The call is in tail position (ret immediately follows call and ret
8198 uses value of call or is void).
8199 - Option ``-tailcallopt`` is enabled, or
8200 ``llvm::GuaranteedTailCallOpt`` is ``true``.
8201 - `Platform-specific constraints are
8202 met. <CodeGenerator.html#tailcallopt>`_
8204 #. The optional "cconv" marker indicates which :ref:`calling
8205 convention <callingconv>` the call should use. If none is
8206 specified, the call defaults to using C calling conventions. The
8207 calling convention of the call must match the calling convention of
8208 the target function, or else the behavior is undefined.
8209 #. The optional :ref:`Parameter Attributes <paramattrs>` list for return
8210 values. Only '``zeroext``', '``signext``', and '``inreg``' attributes
8212 #. '``ty``': the type of the call instruction itself which is also the
8213 type of the return value. Functions that return no value are marked
8215 #. '``fnty``': shall be the signature of the pointer to function value
8216 being invoked. The argument types must match the types implied by
8217 this signature. This type can be omitted if the function is not
8218 varargs and if the function type does not return a pointer to a
8220 #. '``fnptrval``': An LLVM value containing a pointer to a function to
8221 be invoked. In most cases, this is a direct function invocation, but
8222 indirect ``call``'s are just as possible, calling an arbitrary pointer
8224 #. '``function args``': argument list whose types match the function
8225 signature argument types and parameter attributes. All arguments must
8226 be of :ref:`first class <t_firstclass>` type. If the function signature
8227 indicates the function accepts a variable number of arguments, the
8228 extra arguments can be specified.
8229 #. The optional :ref:`function attributes <fnattrs>` list. Only
8230 '``noreturn``', '``nounwind``', '``readonly``' and '``readnone``'
8231 attributes are valid here.
8236 The '``call``' instruction is used to cause control flow to transfer to
8237 a specified function, with its incoming arguments bound to the specified
8238 values. Upon a '``ret``' instruction in the called function, control
8239 flow continues with the instruction after the function call, and the
8240 return value of the function is bound to the result argument.
8245 .. code-block:: llvm
8247 %retval = call i32 @test(i32 %argc)
8248 call i32 (i8*, ...)* @printf(i8* %msg, i32 12, i8 42) ; yields i32
8249 %X = tail call i32 @foo() ; yields i32
8250 %Y = tail call fastcc i32 @foo() ; yields i32
8251 call void %foo(i8 97 signext)
8253 %struct.A = type { i32, i8 }
8254 %r = call %struct.A @foo() ; yields { i32, i8 }
8255 %gr = extractvalue %struct.A %r, 0 ; yields i32
8256 %gr1 = extractvalue %struct.A %r, 1 ; yields i8
8257 %Z = call void @foo() noreturn ; indicates that %foo never returns normally
8258 %ZZ = call zeroext i32 @bar() ; Return value is %zero extended
8260 llvm treats calls to some functions with names and arguments that match
8261 the standard C99 library as being the C99 library functions, and may
8262 perform optimizations or generate code for them under that assumption.
8263 This is something we'd like to change in the future to provide better
8264 support for freestanding environments and non-C-based languages.
8268 '``va_arg``' Instruction
8269 ^^^^^^^^^^^^^^^^^^^^^^^^
8276 <resultval> = va_arg <va_list*> <arglist>, <argty>
8281 The '``va_arg``' instruction is used to access arguments passed through
8282 the "variable argument" area of a function call. It is used to implement
8283 the ``va_arg`` macro in C.
8288 This instruction takes a ``va_list*`` value and the type of the
8289 argument. It returns a value of the specified argument type and
8290 increments the ``va_list`` to point to the next argument. The actual
8291 type of ``va_list`` is target specific.
8296 The '``va_arg``' instruction loads an argument of the specified type
8297 from the specified ``va_list`` and causes the ``va_list`` to point to
8298 the next argument. For more information, see the variable argument
8299 handling :ref:`Intrinsic Functions <int_varargs>`.
8301 It is legal for this instruction to be called in a function which does
8302 not take a variable number of arguments, for example, the ``vfprintf``
8305 ``va_arg`` is an LLVM instruction instead of an :ref:`intrinsic
8306 function <intrinsics>` because it takes a type as an argument.
8311 See the :ref:`variable argument processing <int_varargs>` section.
8313 Note that the code generator does not yet fully support va\_arg on many
8314 targets. Also, it does not currently support va\_arg with aggregate
8315 types on any target.
8319 '``landingpad``' Instruction
8320 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8327 <resultval> = landingpad <resultty> <clause>+
8328 <resultval> = landingpad <resultty> cleanup <clause>*
8330 <clause> := catch <type> <value>
8331 <clause> := filter <array constant type> <array constant>
8336 The '``landingpad``' instruction is used by `LLVM's exception handling
8337 system <ExceptionHandling.html#overview>`_ to specify that a basic block
8338 is a landing pad --- one where the exception lands, and corresponds to the
8339 code found in the ``catch`` portion of a ``try``/``catch`` sequence. It
8340 defines values supplied by the :ref:`personality function <personalityfn>` upon
8341 re-entry to the function. The ``resultval`` has the type ``resultty``.
8347 ``cleanup`` flag indicates that the landing pad block is a cleanup.
8349 A ``clause`` begins with the clause type --- ``catch`` or ``filter`` --- and
8350 contains the global variable representing the "type" that may be caught
8351 or filtered respectively. Unlike the ``catch`` clause, the ``filter``
8352 clause takes an array constant as its argument. Use
8353 "``[0 x i8**] undef``" for a filter which cannot throw. The
8354 '``landingpad``' instruction must contain *at least* one ``clause`` or
8355 the ``cleanup`` flag.
8360 The '``landingpad``' instruction defines the values which are set by the
8361 :ref:`personality function <personalityfn>` upon re-entry to the function, and
8362 therefore the "result type" of the ``landingpad`` instruction. As with
8363 calling conventions, how the personality function results are
8364 represented in LLVM IR is target specific.
8366 The clauses are applied in order from top to bottom. If two
8367 ``landingpad`` instructions are merged together through inlining, the
8368 clauses from the calling function are appended to the list of clauses.
8369 When the call stack is being unwound due to an exception being thrown,
8370 the exception is compared against each ``clause`` in turn. If it doesn't
8371 match any of the clauses, and the ``cleanup`` flag is not set, then
8372 unwinding continues further up the call stack.
8374 The ``landingpad`` instruction has several restrictions:
8376 - A landing pad block is a basic block which is the unwind destination
8377 of an '``invoke``' instruction.
8378 - A landing pad block must have a '``landingpad``' instruction as its
8379 first non-PHI instruction.
8380 - There can be only one '``landingpad``' instruction within the landing
8382 - A basic block that is not a landing pad block may not include a
8383 '``landingpad``' instruction.
8388 .. code-block:: llvm
8390 ;; A landing pad which can catch an integer.
8391 %res = landingpad { i8*, i32 }
8393 ;; A landing pad that is a cleanup.
8394 %res = landingpad { i8*, i32 }
8396 ;; A landing pad which can catch an integer and can only throw a double.
8397 %res = landingpad { i8*, i32 }
8399 filter [1 x i8**] [@_ZTId]
8403 '``cleanuppad``' Instruction
8404 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8411 <resultval> = cleanuppad [<args>*]
8416 The '``cleanuppad``' instruction is used by `LLVM's exception handling
8417 system <ExceptionHandling.html#overview>`_ to specify that a basic block
8418 is a cleanup block --- one where a personality routine attempts to
8419 transfer control to run cleanup actions.
8420 The ``args`` correspond to whatever additional
8421 information the :ref:`personality function <personalityfn>` requires to
8422 execute the cleanup.
8423 The ``resultval`` has the type :ref:`token <t_token>` and is used to
8424 match the ``cleanuppad`` to corresponding :ref:`cleanuprets <i_cleanupret>`.
8429 The instruction takes a list of arbitrary values which are interpreted
8430 by the :ref:`personality function <personalityfn>`.
8435 The '``cleanuppad``' instruction defines the values which are set by the
8436 :ref:`personality function <personalityfn>` upon re-entry to the function.
8437 As with calling conventions, how the personality function results are
8438 represented in LLVM IR is target specific.
8440 When the call stack is being unwound due to an exception being thrown,
8441 the :ref:`personality function <personalityfn>` transfers control to the
8442 ``cleanuppad`` with the aid of the personality-specific arguments.
8444 The ``cleanuppad`` instruction has several restrictions:
8446 - A cleanup block is a basic block which is the unwind destination of
8447 an exceptional instruction.
8448 - A cleanup block must have a '``cleanuppad``' instruction as its
8449 first non-PHI instruction.
8450 - There can be only one '``cleanuppad``' instruction within the
8452 - A basic block that is not a cleanup block may not include a
8453 '``cleanuppad``' instruction.
8454 - All ``cleanupret``s which exit a cleanuppad must have the same
8455 exceptional successor.
8456 - It is undefined behavior for control to transfer from a ``cleanuppad`` to a
8457 ``ret`` without first executing a ``cleanupret`` that consumes the
8458 ``cleanuppad`` or unwinding out of the ``cleanuppad``.
8459 - It is undefined behavior for control to transfer from a ``cleanuppad`` to
8460 itself without first executing a ``cleanupret`` that consumes the
8461 ``cleanuppad`` or unwinding out of the ``cleanuppad``.
8466 .. code-block:: llvm
8468 %tok = cleanuppad []
8475 LLVM supports the notion of an "intrinsic function". These functions
8476 have well known names and semantics and are required to follow certain
8477 restrictions. Overall, these intrinsics represent an extension mechanism
8478 for the LLVM language that does not require changing all of the
8479 transformations in LLVM when adding to the language (or the bitcode
8480 reader/writer, the parser, etc...).
8482 Intrinsic function names must all start with an "``llvm.``" prefix. This
8483 prefix is reserved in LLVM for intrinsic names; thus, function names may
8484 not begin with this prefix. Intrinsic functions must always be external
8485 functions: you cannot define the body of intrinsic functions. Intrinsic
8486 functions may only be used in call or invoke instructions: it is illegal
8487 to take the address of an intrinsic function. Additionally, because
8488 intrinsic functions are part of the LLVM language, it is required if any
8489 are added that they be documented here.
8491 Some intrinsic functions can be overloaded, i.e., the intrinsic
8492 represents a family of functions that perform the same operation but on
8493 different data types. Because LLVM can represent over 8 million
8494 different integer types, overloading is used commonly to allow an
8495 intrinsic function to operate on any integer type. One or more of the
8496 argument types or the result type can be overloaded to accept any
8497 integer type. Argument types may also be defined as exactly matching a
8498 previous argument's type or the result type. This allows an intrinsic
8499 function which accepts multiple arguments, but needs all of them to be
8500 of the same type, to only be overloaded with respect to a single
8501 argument or the result.
8503 Overloaded intrinsics will have the names of its overloaded argument
8504 types encoded into its function name, each preceded by a period. Only
8505 those types which are overloaded result in a name suffix. Arguments
8506 whose type is matched against another type do not. For example, the
8507 ``llvm.ctpop`` function can take an integer of any width and returns an
8508 integer of exactly the same integer width. This leads to a family of
8509 functions such as ``i8 @llvm.ctpop.i8(i8 %val)`` and
8510 ``i29 @llvm.ctpop.i29(i29 %val)``. Only one type, the return type, is
8511 overloaded, and only one type suffix is required. Because the argument's
8512 type is matched against the return type, it does not require its own
8515 To learn how to add an intrinsic function, please see the `Extending
8516 LLVM Guide <ExtendingLLVM.html>`_.
8520 Variable Argument Handling Intrinsics
8521 -------------------------------------
8523 Variable argument support is defined in LLVM with the
8524 :ref:`va_arg <i_va_arg>` instruction and these three intrinsic
8525 functions. These functions are related to the similarly named macros
8526 defined in the ``<stdarg.h>`` header file.
8528 All of these functions operate on arguments that use a target-specific
8529 value type "``va_list``". The LLVM assembly language reference manual
8530 does not define what this type is, so all transformations should be
8531 prepared to handle these functions regardless of the type used.
8533 This example shows how the :ref:`va_arg <i_va_arg>` instruction and the
8534 variable argument handling intrinsic functions are used.
8536 .. code-block:: llvm
8538 ; This struct is different for every platform. For most platforms,
8539 ; it is merely an i8*.
8540 %struct.va_list = type { i8* }
8542 ; For Unix x86_64 platforms, va_list is the following struct:
8543 ; %struct.va_list = type { i32, i32, i8*, i8* }
8545 define i32 @test(i32 %X, ...) {
8546 ; Initialize variable argument processing
8547 %ap = alloca %struct.va_list
8548 %ap2 = bitcast %struct.va_list* %ap to i8*
8549 call void @llvm.va_start(i8* %ap2)
8551 ; Read a single integer argument
8552 %tmp = va_arg i8* %ap2, i32
8554 ; Demonstrate usage of llvm.va_copy and llvm.va_end
8556 %aq2 = bitcast i8** %aq to i8*
8557 call void @llvm.va_copy(i8* %aq2, i8* %ap2)
8558 call void @llvm.va_end(i8* %aq2)
8560 ; Stop processing of arguments.
8561 call void @llvm.va_end(i8* %ap2)
8565 declare void @llvm.va_start(i8*)
8566 declare void @llvm.va_copy(i8*, i8*)
8567 declare void @llvm.va_end(i8*)
8571 '``llvm.va_start``' Intrinsic
8572 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8579 declare void @llvm.va_start(i8* <arglist>)
8584 The '``llvm.va_start``' intrinsic initializes ``*<arglist>`` for
8585 subsequent use by ``va_arg``.
8590 The argument is a pointer to a ``va_list`` element to initialize.
8595 The '``llvm.va_start``' intrinsic works just like the ``va_start`` macro
8596 available in C. In a target-dependent way, it initializes the
8597 ``va_list`` element to which the argument points, so that the next call
8598 to ``va_arg`` will produce the first variable argument passed to the
8599 function. Unlike the C ``va_start`` macro, this intrinsic does not need
8600 to know the last argument of the function as the compiler can figure
8603 '``llvm.va_end``' Intrinsic
8604 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
8611 declare void @llvm.va_end(i8* <arglist>)
8616 The '``llvm.va_end``' intrinsic destroys ``*<arglist>``, which has been
8617 initialized previously with ``llvm.va_start`` or ``llvm.va_copy``.
8622 The argument is a pointer to a ``va_list`` to destroy.
8627 The '``llvm.va_end``' intrinsic works just like the ``va_end`` macro
8628 available in C. In a target-dependent way, it destroys the ``va_list``
8629 element to which the argument points. Calls to
8630 :ref:`llvm.va_start <int_va_start>` and
8631 :ref:`llvm.va_copy <int_va_copy>` must be matched exactly with calls to
8636 '``llvm.va_copy``' Intrinsic
8637 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8644 declare void @llvm.va_copy(i8* <destarglist>, i8* <srcarglist>)
8649 The '``llvm.va_copy``' intrinsic copies the current argument position
8650 from the source argument list to the destination argument list.
8655 The first argument is a pointer to a ``va_list`` element to initialize.
8656 The second argument is a pointer to a ``va_list`` element to copy from.
8661 The '``llvm.va_copy``' intrinsic works just like the ``va_copy`` macro
8662 available in C. In a target-dependent way, it copies the source
8663 ``va_list`` element into the destination ``va_list`` element. This
8664 intrinsic is necessary because the `` llvm.va_start`` intrinsic may be
8665 arbitrarily complex and require, for example, memory allocation.
8667 Accurate Garbage Collection Intrinsics
8668 --------------------------------------
8670 LLVM's support for `Accurate Garbage Collection <GarbageCollection.html>`_
8671 (GC) requires the frontend to generate code containing appropriate intrinsic
8672 calls and select an appropriate GC strategy which knows how to lower these
8673 intrinsics in a manner which is appropriate for the target collector.
8675 These intrinsics allow identification of :ref:`GC roots on the
8676 stack <int_gcroot>`, as well as garbage collector implementations that
8677 require :ref:`read <int_gcread>` and :ref:`write <int_gcwrite>` barriers.
8678 Frontends for type-safe garbage collected languages should generate
8679 these intrinsics to make use of the LLVM garbage collectors. For more
8680 details, see `Garbage Collection with LLVM <GarbageCollection.html>`_.
8682 Experimental Statepoint Intrinsics
8683 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8685 LLVM provides an second experimental set of intrinsics for describing garbage
8686 collection safepoints in compiled code. These intrinsics are an alternative
8687 to the ``llvm.gcroot`` intrinsics, but are compatible with the ones for
8688 :ref:`read <int_gcread>` and :ref:`write <int_gcwrite>` barriers. The
8689 differences in approach are covered in the `Garbage Collection with LLVM
8690 <GarbageCollection.html>`_ documentation. The intrinsics themselves are
8691 described in :doc:`Statepoints`.
8695 '``llvm.gcroot``' Intrinsic
8696 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
8703 declare void @llvm.gcroot(i8** %ptrloc, i8* %metadata)
8708 The '``llvm.gcroot``' intrinsic declares the existence of a GC root to
8709 the code generator, and allows some metadata to be associated with it.
8714 The first argument specifies the address of a stack object that contains
8715 the root pointer. The second pointer (which must be either a constant or
8716 a global value address) contains the meta-data to be associated with the
8722 At runtime, a call to this intrinsic stores a null pointer into the
8723 "ptrloc" location. At compile-time, the code generator generates
8724 information to allow the runtime to find the pointer at GC safe points.
8725 The '``llvm.gcroot``' intrinsic may only be used in a function which
8726 :ref:`specifies a GC algorithm <gc>`.
8730 '``llvm.gcread``' Intrinsic
8731 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
8738 declare i8* @llvm.gcread(i8* %ObjPtr, i8** %Ptr)
8743 The '``llvm.gcread``' intrinsic identifies reads of references from heap
8744 locations, allowing garbage collector implementations that require read
8750 The second argument is the address to read from, which should be an
8751 address allocated from the garbage collector. The first object is a
8752 pointer to the start of the referenced object, if needed by the language
8753 runtime (otherwise null).
8758 The '``llvm.gcread``' intrinsic has the same semantics as a load
8759 instruction, but may be replaced with substantially more complex code by
8760 the garbage collector runtime, as needed. The '``llvm.gcread``'
8761 intrinsic may only be used in a function which :ref:`specifies a GC
8766 '``llvm.gcwrite``' Intrinsic
8767 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8774 declare void @llvm.gcwrite(i8* %P1, i8* %Obj, i8** %P2)
8779 The '``llvm.gcwrite``' intrinsic identifies writes of references to heap
8780 locations, allowing garbage collector implementations that require write
8781 barriers (such as generational or reference counting collectors).
8786 The first argument is the reference to store, the second is the start of
8787 the object to store it to, and the third is the address of the field of
8788 Obj to store to. If the runtime does not require a pointer to the
8789 object, Obj may be null.
8794 The '``llvm.gcwrite``' intrinsic has the same semantics as a store
8795 instruction, but may be replaced with substantially more complex code by
8796 the garbage collector runtime, as needed. The '``llvm.gcwrite``'
8797 intrinsic may only be used in a function which :ref:`specifies a GC
8800 Code Generator Intrinsics
8801 -------------------------
8803 These intrinsics are provided by LLVM to expose special features that
8804 may only be implemented with code generator support.
8806 '``llvm.returnaddress``' Intrinsic
8807 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8814 declare i8 *@llvm.returnaddress(i32 <level>)
8819 The '``llvm.returnaddress``' intrinsic attempts to compute a
8820 target-specific value indicating the return address of the current
8821 function or one of its callers.
8826 The argument to this intrinsic indicates which function to return the
8827 address for. Zero indicates the calling function, one indicates its
8828 caller, etc. The argument is **required** to be a constant integer
8834 The '``llvm.returnaddress``' intrinsic either returns a pointer
8835 indicating the return address of the specified call frame, or zero if it
8836 cannot be identified. The value returned by this intrinsic is likely to
8837 be incorrect or 0 for arguments other than zero, so it should only be
8838 used for debugging purposes.
8840 Note that calling this intrinsic does not prevent function inlining or
8841 other aggressive transformations, so the value returned may not be that
8842 of the obvious source-language caller.
8844 '``llvm.frameaddress``' Intrinsic
8845 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8852 declare i8* @llvm.frameaddress(i32 <level>)
8857 The '``llvm.frameaddress``' intrinsic attempts to return the
8858 target-specific frame pointer value for the specified stack frame.
8863 The argument to this intrinsic indicates which function to return the
8864 frame pointer for. Zero indicates the calling function, one indicates
8865 its caller, etc. The argument is **required** to be a constant integer
8871 The '``llvm.frameaddress``' intrinsic either returns a pointer
8872 indicating the frame address of the specified call frame, or zero if it
8873 cannot be identified. The value returned by this intrinsic is likely to
8874 be incorrect or 0 for arguments other than zero, so it should only be
8875 used for debugging purposes.
8877 Note that calling this intrinsic does not prevent function inlining or
8878 other aggressive transformations, so the value returned may not be that
8879 of the obvious source-language caller.
8881 '``llvm.localescape``' and '``llvm.localrecover``' Intrinsics
8882 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8889 declare void @llvm.localescape(...)
8890 declare i8* @llvm.localrecover(i8* %func, i8* %fp, i32 %idx)
8895 The '``llvm.localescape``' intrinsic escapes offsets of a collection of static
8896 allocas, and the '``llvm.localrecover``' intrinsic applies those offsets to a
8897 live frame pointer to recover the address of the allocation. The offset is
8898 computed during frame layout of the caller of ``llvm.localescape``.
8903 All arguments to '``llvm.localescape``' must be pointers to static allocas or
8904 casts of static allocas. Each function can only call '``llvm.localescape``'
8905 once, and it can only do so from the entry block.
8907 The ``func`` argument to '``llvm.localrecover``' must be a constant
8908 bitcasted pointer to a function defined in the current module. The code
8909 generator cannot determine the frame allocation offset of functions defined in
8912 The ``fp`` argument to '``llvm.localrecover``' must be a frame pointer of a
8913 call frame that is currently live. The return value of '``llvm.localaddress``'
8914 is one way to produce such a value, but various runtimes also expose a suitable
8915 pointer in platform-specific ways.
8917 The ``idx`` argument to '``llvm.localrecover``' indicates which alloca passed to
8918 '``llvm.localescape``' to recover. It is zero-indexed.
8923 These intrinsics allow a group of functions to share access to a set of local
8924 stack allocations of a one parent function. The parent function may call the
8925 '``llvm.localescape``' intrinsic once from the function entry block, and the
8926 child functions can use '``llvm.localrecover``' to access the escaped allocas.
8927 The '``llvm.localescape``' intrinsic blocks inlining, as inlining changes where
8928 the escaped allocas are allocated, which would break attempts to use
8929 '``llvm.localrecover``'.
8931 .. _int_read_register:
8932 .. _int_write_register:
8934 '``llvm.read_register``' and '``llvm.write_register``' Intrinsics
8935 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8942 declare i32 @llvm.read_register.i32(metadata)
8943 declare i64 @llvm.read_register.i64(metadata)
8944 declare void @llvm.write_register.i32(metadata, i32 @value)
8945 declare void @llvm.write_register.i64(metadata, i64 @value)
8951 The '``llvm.read_register``' and '``llvm.write_register``' intrinsics
8952 provides access to the named register. The register must be valid on
8953 the architecture being compiled to. The type needs to be compatible
8954 with the register being read.
8959 The '``llvm.read_register``' intrinsic returns the current value of the
8960 register, where possible. The '``llvm.write_register``' intrinsic sets
8961 the current value of the register, where possible.
8963 This is useful to implement named register global variables that need
8964 to always be mapped to a specific register, as is common practice on
8965 bare-metal programs including OS kernels.
8967 The compiler doesn't check for register availability or use of the used
8968 register in surrounding code, including inline assembly. Because of that,
8969 allocatable registers are not supported.
8971 Warning: So far it only works with the stack pointer on selected
8972 architectures (ARM, AArch64, PowerPC and x86_64). Significant amount of
8973 work is needed to support other registers and even more so, allocatable
8978 '``llvm.stacksave``' Intrinsic
8979 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8986 declare i8* @llvm.stacksave()
8991 The '``llvm.stacksave``' intrinsic is used to remember the current state
8992 of the function stack, for use with
8993 :ref:`llvm.stackrestore <int_stackrestore>`. This is useful for
8994 implementing language features like scoped automatic variable sized
9000 This intrinsic returns a opaque pointer value that can be passed to
9001 :ref:`llvm.stackrestore <int_stackrestore>`. When an
9002 ``llvm.stackrestore`` intrinsic is executed with a value saved from
9003 ``llvm.stacksave``, it effectively restores the state of the stack to
9004 the state it was in when the ``llvm.stacksave`` intrinsic executed. In
9005 practice, this pops any :ref:`alloca <i_alloca>` blocks from the stack that
9006 were allocated after the ``llvm.stacksave`` was executed.
9008 .. _int_stackrestore:
9010 '``llvm.stackrestore``' Intrinsic
9011 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9018 declare void @llvm.stackrestore(i8* %ptr)
9023 The '``llvm.stackrestore``' intrinsic is used to restore the state of
9024 the function stack to the state it was in when the corresponding
9025 :ref:`llvm.stacksave <int_stacksave>` intrinsic executed. This is
9026 useful for implementing language features like scoped automatic variable
9027 sized arrays in C99.
9032 See the description for :ref:`llvm.stacksave <int_stacksave>`.
9034 '``llvm.prefetch``' Intrinsic
9035 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9042 declare void @llvm.prefetch(i8* <address>, i32 <rw>, i32 <locality>, i32 <cache type>)
9047 The '``llvm.prefetch``' intrinsic is a hint to the code generator to
9048 insert a prefetch instruction if supported; otherwise, it is a noop.
9049 Prefetches have no effect on the behavior of the program but can change
9050 its performance characteristics.
9055 ``address`` is the address to be prefetched, ``rw`` is the specifier
9056 determining if the fetch should be for a read (0) or write (1), and
9057 ``locality`` is a temporal locality specifier ranging from (0) - no
9058 locality, to (3) - extremely local keep in cache. The ``cache type``
9059 specifies whether the prefetch is performed on the data (1) or
9060 instruction (0) cache. The ``rw``, ``locality`` and ``cache type``
9061 arguments must be constant integers.
9066 This intrinsic does not modify the behavior of the program. In
9067 particular, prefetches cannot trap and do not produce a value. On
9068 targets that support this intrinsic, the prefetch can provide hints to
9069 the processor cache for better performance.
9071 '``llvm.pcmarker``' Intrinsic
9072 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9079 declare void @llvm.pcmarker(i32 <id>)
9084 The '``llvm.pcmarker``' intrinsic is a method to export a Program
9085 Counter (PC) in a region of code to simulators and other tools. The
9086 method is target specific, but it is expected that the marker will use
9087 exported symbols to transmit the PC of the marker. The marker makes no
9088 guarantees that it will remain with any specific instruction after
9089 optimizations. It is possible that the presence of a marker will inhibit
9090 optimizations. The intended use is to be inserted after optimizations to
9091 allow correlations of simulation runs.
9096 ``id`` is a numerical id identifying the marker.
9101 This intrinsic does not modify the behavior of the program. Backends
9102 that do not support this intrinsic may ignore it.
9104 '``llvm.readcyclecounter``' Intrinsic
9105 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9112 declare i64 @llvm.readcyclecounter()
9117 The '``llvm.readcyclecounter``' intrinsic provides access to the cycle
9118 counter register (or similar low latency, high accuracy clocks) on those
9119 targets that support it. On X86, it should map to RDTSC. On Alpha, it
9120 should map to RPCC. As the backing counters overflow quickly (on the
9121 order of 9 seconds on alpha), this should only be used for small
9127 When directly supported, reading the cycle counter should not modify any
9128 memory. Implementations are allowed to either return a application
9129 specific value or a system wide value. On backends without support, this
9130 is lowered to a constant 0.
9132 Note that runtime support may be conditional on the privilege-level code is
9133 running at and the host platform.
9135 '``llvm.clear_cache``' Intrinsic
9136 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9143 declare void @llvm.clear_cache(i8*, i8*)
9148 The '``llvm.clear_cache``' intrinsic ensures visibility of modifications
9149 in the specified range to the execution unit of the processor. On
9150 targets with non-unified instruction and data cache, the implementation
9151 flushes the instruction cache.
9156 On platforms with coherent instruction and data caches (e.g. x86), this
9157 intrinsic is a nop. On platforms with non-coherent instruction and data
9158 cache (e.g. ARM, MIPS), the intrinsic is lowered either to appropriate
9159 instructions or a system call, if cache flushing requires special
9162 The default behavior is to emit a call to ``__clear_cache`` from the run
9165 This instrinsic does *not* empty the instruction pipeline. Modifications
9166 of the current function are outside the scope of the intrinsic.
9168 '``llvm.instrprof_increment``' Intrinsic
9169 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9176 declare void @llvm.instrprof_increment(i8* <name>, i64 <hash>,
9177 i32 <num-counters>, i32 <index>)
9182 The '``llvm.instrprof_increment``' intrinsic can be emitted by a
9183 frontend for use with instrumentation based profiling. These will be
9184 lowered by the ``-instrprof`` pass to generate execution counts of a
9190 The first argument is a pointer to a global variable containing the
9191 name of the entity being instrumented. This should generally be the
9192 (mangled) function name for a set of counters.
9194 The second argument is a hash value that can be used by the consumer
9195 of the profile data to detect changes to the instrumented source, and
9196 the third is the number of counters associated with ``name``. It is an
9197 error if ``hash`` or ``num-counters`` differ between two instances of
9198 ``instrprof_increment`` that refer to the same name.
9200 The last argument refers to which of the counters for ``name`` should
9201 be incremented. It should be a value between 0 and ``num-counters``.
9206 This intrinsic represents an increment of a profiling counter. It will
9207 cause the ``-instrprof`` pass to generate the appropriate data
9208 structures and the code to increment the appropriate value, in a
9209 format that can be written out by a compiler runtime and consumed via
9210 the ``llvm-profdata`` tool.
9212 Standard C Library Intrinsics
9213 -----------------------------
9215 LLVM provides intrinsics for a few important standard C library
9216 functions. These intrinsics allow source-language front-ends to pass
9217 information about the alignment of the pointer arguments to the code
9218 generator, providing opportunity for more efficient code generation.
9222 '``llvm.memcpy``' Intrinsic
9223 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
9228 This is an overloaded intrinsic. You can use ``llvm.memcpy`` on any
9229 integer bit width and for different address spaces. Not all targets
9230 support all bit widths however.
9234 declare void @llvm.memcpy.p0i8.p0i8.i32(i8* <dest>, i8* <src>,
9235 i32 <len>, i32 <align>, i1 <isvolatile>)
9236 declare void @llvm.memcpy.p0i8.p0i8.i64(i8* <dest>, i8* <src>,
9237 i64 <len>, i32 <align>, i1 <isvolatile>)
9242 The '``llvm.memcpy.*``' intrinsics copy a block of memory from the
9243 source location to the destination location.
9245 Note that, unlike the standard libc function, the ``llvm.memcpy.*``
9246 intrinsics do not return a value, takes extra alignment/isvolatile
9247 arguments and the pointers can be in specified address spaces.
9252 The first argument is a pointer to the destination, the second is a
9253 pointer to the source. The third argument is an integer argument
9254 specifying the number of bytes to copy, the fourth argument is the
9255 alignment of the source and destination locations, and the fifth is a
9256 boolean indicating a volatile access.
9258 If the call to this intrinsic has an alignment value that is not 0 or 1,
9259 then the caller guarantees that both the source and destination pointers
9260 are aligned to that boundary.
9262 If the ``isvolatile`` parameter is ``true``, the ``llvm.memcpy`` call is
9263 a :ref:`volatile operation <volatile>`. The detailed access behavior is not
9264 very cleanly specified and it is unwise to depend on it.
9269 The '``llvm.memcpy.*``' intrinsics copy a block of memory from the
9270 source location to the destination location, which are not allowed to
9271 overlap. It copies "len" bytes of memory over. If the argument is known
9272 to be aligned to some boundary, this can be specified as the fourth
9273 argument, otherwise it should be set to 0 or 1 (both meaning no alignment).
9275 '``llvm.memmove``' Intrinsic
9276 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9281 This is an overloaded intrinsic. You can use llvm.memmove on any integer
9282 bit width and for different address space. Not all targets support all
9287 declare void @llvm.memmove.p0i8.p0i8.i32(i8* <dest>, i8* <src>,
9288 i32 <len>, i32 <align>, i1 <isvolatile>)
9289 declare void @llvm.memmove.p0i8.p0i8.i64(i8* <dest>, i8* <src>,
9290 i64 <len>, i32 <align>, i1 <isvolatile>)
9295 The '``llvm.memmove.*``' intrinsics move a block of memory from the
9296 source location to the destination location. It is similar to the
9297 '``llvm.memcpy``' intrinsic but allows the two memory locations to
9300 Note that, unlike the standard libc function, the ``llvm.memmove.*``
9301 intrinsics do not return a value, takes extra alignment/isvolatile
9302 arguments and the pointers can be in specified address spaces.
9307 The first argument is a pointer to the destination, the second is a
9308 pointer to the source. The third argument is an integer argument
9309 specifying the number of bytes to copy, the fourth argument is the
9310 alignment of the source and destination locations, and the fifth is a
9311 boolean indicating a volatile access.
9313 If the call to this intrinsic has an alignment value that is not 0 or 1,
9314 then the caller guarantees that the source and destination pointers are
9315 aligned to that boundary.
9317 If the ``isvolatile`` parameter is ``true``, the ``llvm.memmove`` call
9318 is a :ref:`volatile operation <volatile>`. The detailed access behavior is
9319 not very cleanly specified and it is unwise to depend on it.
9324 The '``llvm.memmove.*``' intrinsics copy a block of memory from the
9325 source location to the destination location, which may overlap. It
9326 copies "len" bytes of memory over. If the argument is known to be
9327 aligned to some boundary, this can be specified as the fourth argument,
9328 otherwise it should be set to 0 or 1 (both meaning no alignment).
9330 '``llvm.memset.*``' Intrinsics
9331 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9336 This is an overloaded intrinsic. You can use llvm.memset on any integer
9337 bit width and for different address spaces. However, not all targets
9338 support all bit widths.
9342 declare void @llvm.memset.p0i8.i32(i8* <dest>, i8 <val>,
9343 i32 <len>, i32 <align>, i1 <isvolatile>)
9344 declare void @llvm.memset.p0i8.i64(i8* <dest>, i8 <val>,
9345 i64 <len>, i32 <align>, i1 <isvolatile>)
9350 The '``llvm.memset.*``' intrinsics fill a block of memory with a
9351 particular byte value.
9353 Note that, unlike the standard libc function, the ``llvm.memset``
9354 intrinsic does not return a value and takes extra alignment/volatile
9355 arguments. Also, the destination can be in an arbitrary address space.
9360 The first argument is a pointer to the destination to fill, the second
9361 is the byte value with which to fill it, the third argument is an
9362 integer argument specifying the number of bytes to fill, and the fourth
9363 argument is the known alignment of the destination location.
9365 If the call to this intrinsic has an alignment value that is not 0 or 1,
9366 then the caller guarantees that the destination pointer is aligned to
9369 If the ``isvolatile`` parameter is ``true``, the ``llvm.memset`` call is
9370 a :ref:`volatile operation <volatile>`. The detailed access behavior is not
9371 very cleanly specified and it is unwise to depend on it.
9376 The '``llvm.memset.*``' intrinsics fill "len" bytes of memory starting
9377 at the destination location. If the argument is known to be aligned to
9378 some boundary, this can be specified as the fourth argument, otherwise
9379 it should be set to 0 or 1 (both meaning no alignment).
9381 '``llvm.sqrt.*``' Intrinsic
9382 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
9387 This is an overloaded intrinsic. You can use ``llvm.sqrt`` on any
9388 floating point or vector of floating point type. Not all targets support
9393 declare float @llvm.sqrt.f32(float %Val)
9394 declare double @llvm.sqrt.f64(double %Val)
9395 declare x86_fp80 @llvm.sqrt.f80(x86_fp80 %Val)
9396 declare fp128 @llvm.sqrt.f128(fp128 %Val)
9397 declare ppc_fp128 @llvm.sqrt.ppcf128(ppc_fp128 %Val)
9402 The '``llvm.sqrt``' intrinsics return the sqrt of the specified operand,
9403 returning the same value as the libm '``sqrt``' functions would. Unlike
9404 ``sqrt`` in libm, however, ``llvm.sqrt`` has undefined behavior for
9405 negative numbers other than -0.0 (which allows for better optimization,
9406 because there is no need to worry about errno being set).
9407 ``llvm.sqrt(-0.0)`` is defined to return -0.0 like IEEE sqrt.
9412 The argument and return value are floating point numbers of the same
9418 This function returns the sqrt of the specified operand if it is a
9419 nonnegative floating point number.
9421 '``llvm.powi.*``' Intrinsic
9422 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
9427 This is an overloaded intrinsic. You can use ``llvm.powi`` on any
9428 floating point or vector of floating point type. Not all targets support
9433 declare float @llvm.powi.f32(float %Val, i32 %power)
9434 declare double @llvm.powi.f64(double %Val, i32 %power)
9435 declare x86_fp80 @llvm.powi.f80(x86_fp80 %Val, i32 %power)
9436 declare fp128 @llvm.powi.f128(fp128 %Val, i32 %power)
9437 declare ppc_fp128 @llvm.powi.ppcf128(ppc_fp128 %Val, i32 %power)
9442 The '``llvm.powi.*``' intrinsics return the first operand raised to the
9443 specified (positive or negative) power. The order of evaluation of
9444 multiplications is not defined. When a vector of floating point type is
9445 used, the second argument remains a scalar integer value.
9450 The second argument is an integer power, and the first is a value to
9451 raise to that power.
9456 This function returns the first value raised to the second power with an
9457 unspecified sequence of rounding operations.
9459 '``llvm.sin.*``' Intrinsic
9460 ^^^^^^^^^^^^^^^^^^^^^^^^^^
9465 This is an overloaded intrinsic. You can use ``llvm.sin`` on any
9466 floating point or vector of floating point type. Not all targets support
9471 declare float @llvm.sin.f32(float %Val)
9472 declare double @llvm.sin.f64(double %Val)
9473 declare x86_fp80 @llvm.sin.f80(x86_fp80 %Val)
9474 declare fp128 @llvm.sin.f128(fp128 %Val)
9475 declare ppc_fp128 @llvm.sin.ppcf128(ppc_fp128 %Val)
9480 The '``llvm.sin.*``' intrinsics return the sine of the operand.
9485 The argument and return value are floating point numbers of the same
9491 This function returns the sine of the specified operand, returning the
9492 same values as the libm ``sin`` functions would, and handles error
9493 conditions in the same way.
9495 '``llvm.cos.*``' Intrinsic
9496 ^^^^^^^^^^^^^^^^^^^^^^^^^^
9501 This is an overloaded intrinsic. You can use ``llvm.cos`` on any
9502 floating point or vector of floating point type. Not all targets support
9507 declare float @llvm.cos.f32(float %Val)
9508 declare double @llvm.cos.f64(double %Val)
9509 declare x86_fp80 @llvm.cos.f80(x86_fp80 %Val)
9510 declare fp128 @llvm.cos.f128(fp128 %Val)
9511 declare ppc_fp128 @llvm.cos.ppcf128(ppc_fp128 %Val)
9516 The '``llvm.cos.*``' intrinsics return the cosine of the operand.
9521 The argument and return value are floating point numbers of the same
9527 This function returns the cosine of the specified operand, returning the
9528 same values as the libm ``cos`` functions would, and handles error
9529 conditions in the same way.
9531 '``llvm.pow.*``' Intrinsic
9532 ^^^^^^^^^^^^^^^^^^^^^^^^^^
9537 This is an overloaded intrinsic. You can use ``llvm.pow`` on any
9538 floating point or vector of floating point type. Not all targets support
9543 declare float @llvm.pow.f32(float %Val, float %Power)
9544 declare double @llvm.pow.f64(double %Val, double %Power)
9545 declare x86_fp80 @llvm.pow.f80(x86_fp80 %Val, x86_fp80 %Power)
9546 declare fp128 @llvm.pow.f128(fp128 %Val, fp128 %Power)
9547 declare ppc_fp128 @llvm.pow.ppcf128(ppc_fp128 %Val, ppc_fp128 Power)
9552 The '``llvm.pow.*``' intrinsics return the first operand raised to the
9553 specified (positive or negative) power.
9558 The second argument is a floating point power, and the first is a value
9559 to raise to that power.
9564 This function returns the first value raised to the second power,
9565 returning the same values as the libm ``pow`` functions would, and
9566 handles error conditions in the same way.
9568 '``llvm.exp.*``' Intrinsic
9569 ^^^^^^^^^^^^^^^^^^^^^^^^^^
9574 This is an overloaded intrinsic. You can use ``llvm.exp`` on any
9575 floating point or vector of floating point type. Not all targets support
9580 declare float @llvm.exp.f32(float %Val)
9581 declare double @llvm.exp.f64(double %Val)
9582 declare x86_fp80 @llvm.exp.f80(x86_fp80 %Val)
9583 declare fp128 @llvm.exp.f128(fp128 %Val)
9584 declare ppc_fp128 @llvm.exp.ppcf128(ppc_fp128 %Val)
9589 The '``llvm.exp.*``' intrinsics perform the exp function.
9594 The argument and return value are floating point numbers of the same
9600 This function returns the same values as the libm ``exp`` functions
9601 would, and handles error conditions in the same way.
9603 '``llvm.exp2.*``' Intrinsic
9604 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
9609 This is an overloaded intrinsic. You can use ``llvm.exp2`` on any
9610 floating point or vector of floating point type. Not all targets support
9615 declare float @llvm.exp2.f32(float %Val)
9616 declare double @llvm.exp2.f64(double %Val)
9617 declare x86_fp80 @llvm.exp2.f80(x86_fp80 %Val)
9618 declare fp128 @llvm.exp2.f128(fp128 %Val)
9619 declare ppc_fp128 @llvm.exp2.ppcf128(ppc_fp128 %Val)
9624 The '``llvm.exp2.*``' intrinsics perform the exp2 function.
9629 The argument and return value are floating point numbers of the same
9635 This function returns the same values as the libm ``exp2`` functions
9636 would, and handles error conditions in the same way.
9638 '``llvm.log.*``' Intrinsic
9639 ^^^^^^^^^^^^^^^^^^^^^^^^^^
9644 This is an overloaded intrinsic. You can use ``llvm.log`` on any
9645 floating point or vector of floating point type. Not all targets support
9650 declare float @llvm.log.f32(float %Val)
9651 declare double @llvm.log.f64(double %Val)
9652 declare x86_fp80 @llvm.log.f80(x86_fp80 %Val)
9653 declare fp128 @llvm.log.f128(fp128 %Val)
9654 declare ppc_fp128 @llvm.log.ppcf128(ppc_fp128 %Val)
9659 The '``llvm.log.*``' intrinsics perform the log function.
9664 The argument and return value are floating point numbers of the same
9670 This function returns the same values as the libm ``log`` functions
9671 would, and handles error conditions in the same way.
9673 '``llvm.log10.*``' Intrinsic
9674 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9679 This is an overloaded intrinsic. You can use ``llvm.log10`` on any
9680 floating point or vector of floating point type. Not all targets support
9685 declare float @llvm.log10.f32(float %Val)
9686 declare double @llvm.log10.f64(double %Val)
9687 declare x86_fp80 @llvm.log10.f80(x86_fp80 %Val)
9688 declare fp128 @llvm.log10.f128(fp128 %Val)
9689 declare ppc_fp128 @llvm.log10.ppcf128(ppc_fp128 %Val)
9694 The '``llvm.log10.*``' intrinsics perform the log10 function.
9699 The argument and return value are floating point numbers of the same
9705 This function returns the same values as the libm ``log10`` functions
9706 would, and handles error conditions in the same way.
9708 '``llvm.log2.*``' Intrinsic
9709 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
9714 This is an overloaded intrinsic. You can use ``llvm.log2`` on any
9715 floating point or vector of floating point type. Not all targets support
9720 declare float @llvm.log2.f32(float %Val)
9721 declare double @llvm.log2.f64(double %Val)
9722 declare x86_fp80 @llvm.log2.f80(x86_fp80 %Val)
9723 declare fp128 @llvm.log2.f128(fp128 %Val)
9724 declare ppc_fp128 @llvm.log2.ppcf128(ppc_fp128 %Val)
9729 The '``llvm.log2.*``' intrinsics perform the log2 function.
9734 The argument and return value are floating point numbers of the same
9740 This function returns the same values as the libm ``log2`` functions
9741 would, and handles error conditions in the same way.
9743 '``llvm.fma.*``' Intrinsic
9744 ^^^^^^^^^^^^^^^^^^^^^^^^^^
9749 This is an overloaded intrinsic. You can use ``llvm.fma`` on any
9750 floating point or vector of floating point type. Not all targets support
9755 declare float @llvm.fma.f32(float %a, float %b, float %c)
9756 declare double @llvm.fma.f64(double %a, double %b, double %c)
9757 declare x86_fp80 @llvm.fma.f80(x86_fp80 %a, x86_fp80 %b, x86_fp80 %c)
9758 declare fp128 @llvm.fma.f128(fp128 %a, fp128 %b, fp128 %c)
9759 declare ppc_fp128 @llvm.fma.ppcf128(ppc_fp128 %a, ppc_fp128 %b, ppc_fp128 %c)
9764 The '``llvm.fma.*``' intrinsics perform the fused multiply-add
9770 The argument and return value are floating point numbers of the same
9776 This function returns the same values as the libm ``fma`` functions
9777 would, and does not set errno.
9779 '``llvm.fabs.*``' Intrinsic
9780 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
9785 This is an overloaded intrinsic. You can use ``llvm.fabs`` on any
9786 floating point or vector of floating point type. Not all targets support
9791 declare float @llvm.fabs.f32(float %Val)
9792 declare double @llvm.fabs.f64(double %Val)
9793 declare x86_fp80 @llvm.fabs.f80(x86_fp80 %Val)
9794 declare fp128 @llvm.fabs.f128(fp128 %Val)
9795 declare ppc_fp128 @llvm.fabs.ppcf128(ppc_fp128 %Val)
9800 The '``llvm.fabs.*``' intrinsics return the absolute value of the
9806 The argument and return value are floating point numbers of the same
9812 This function returns the same values as the libm ``fabs`` functions
9813 would, and handles error conditions in the same way.
9815 '``llvm.minnum.*``' Intrinsic
9816 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9821 This is an overloaded intrinsic. You can use ``llvm.minnum`` on any
9822 floating point or vector of floating point type. Not all targets support
9827 declare float @llvm.minnum.f32(float %Val0, float %Val1)
9828 declare double @llvm.minnum.f64(double %Val0, double %Val1)
9829 declare x86_fp80 @llvm.minnum.f80(x86_fp80 %Val0, x86_fp80 %Val1)
9830 declare fp128 @llvm.minnum.f128(fp128 %Val0, fp128 %Val1)
9831 declare ppc_fp128 @llvm.minnum.ppcf128(ppc_fp128 %Val0, ppc_fp128 %Val1)
9836 The '``llvm.minnum.*``' intrinsics return the minimum of the two
9843 The arguments and return value are floating point numbers of the same
9849 Follows the IEEE-754 semantics for minNum, which also match for libm's
9852 If either operand is a NaN, returns the other non-NaN operand. Returns
9853 NaN only if both operands are NaN. If the operands compare equal,
9854 returns a value that compares equal to both operands. This means that
9855 fmin(+/-0.0, +/-0.0) could return either -0.0 or 0.0.
9857 '``llvm.maxnum.*``' Intrinsic
9858 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9863 This is an overloaded intrinsic. You can use ``llvm.maxnum`` on any
9864 floating point or vector of floating point type. Not all targets support
9869 declare float @llvm.maxnum.f32(float %Val0, float %Val1l)
9870 declare double @llvm.maxnum.f64(double %Val0, double %Val1)
9871 declare x86_fp80 @llvm.maxnum.f80(x86_fp80 %Val0, x86_fp80 %Val1)
9872 declare fp128 @llvm.maxnum.f128(fp128 %Val0, fp128 %Val1)
9873 declare ppc_fp128 @llvm.maxnum.ppcf128(ppc_fp128 %Val0, ppc_fp128 %Val1)
9878 The '``llvm.maxnum.*``' intrinsics return the maximum of the two
9885 The arguments and return value are floating point numbers of the same
9890 Follows the IEEE-754 semantics for maxNum, which also match for libm's
9893 If either operand is a NaN, returns the other non-NaN operand. Returns
9894 NaN only if both operands are NaN. If the operands compare equal,
9895 returns a value that compares equal to both operands. This means that
9896 fmax(+/-0.0, +/-0.0) could return either -0.0 or 0.0.
9898 '``llvm.copysign.*``' Intrinsic
9899 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9904 This is an overloaded intrinsic. You can use ``llvm.copysign`` on any
9905 floating point or vector of floating point type. Not all targets support
9910 declare float @llvm.copysign.f32(float %Mag, float %Sgn)
9911 declare double @llvm.copysign.f64(double %Mag, double %Sgn)
9912 declare x86_fp80 @llvm.copysign.f80(x86_fp80 %Mag, x86_fp80 %Sgn)
9913 declare fp128 @llvm.copysign.f128(fp128 %Mag, fp128 %Sgn)
9914 declare ppc_fp128 @llvm.copysign.ppcf128(ppc_fp128 %Mag, ppc_fp128 %Sgn)
9919 The '``llvm.copysign.*``' intrinsics return a value with the magnitude of the
9920 first operand and the sign of the second operand.
9925 The arguments and return value are floating point numbers of the same
9931 This function returns the same values as the libm ``copysign``
9932 functions would, and handles error conditions in the same way.
9934 '``llvm.floor.*``' Intrinsic
9935 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9940 This is an overloaded intrinsic. You can use ``llvm.floor`` on any
9941 floating point or vector of floating point type. Not all targets support
9946 declare float @llvm.floor.f32(float %Val)
9947 declare double @llvm.floor.f64(double %Val)
9948 declare x86_fp80 @llvm.floor.f80(x86_fp80 %Val)
9949 declare fp128 @llvm.floor.f128(fp128 %Val)
9950 declare ppc_fp128 @llvm.floor.ppcf128(ppc_fp128 %Val)
9955 The '``llvm.floor.*``' intrinsics return the floor of the operand.
9960 The argument and return value are floating point numbers of the same
9966 This function returns the same values as the libm ``floor`` functions
9967 would, and handles error conditions in the same way.
9969 '``llvm.ceil.*``' Intrinsic
9970 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
9975 This is an overloaded intrinsic. You can use ``llvm.ceil`` on any
9976 floating point or vector of floating point type. Not all targets support
9981 declare float @llvm.ceil.f32(float %Val)
9982 declare double @llvm.ceil.f64(double %Val)
9983 declare x86_fp80 @llvm.ceil.f80(x86_fp80 %Val)
9984 declare fp128 @llvm.ceil.f128(fp128 %Val)
9985 declare ppc_fp128 @llvm.ceil.ppcf128(ppc_fp128 %Val)
9990 The '``llvm.ceil.*``' intrinsics return the ceiling of the operand.
9995 The argument and return value are floating point numbers of the same
10001 This function returns the same values as the libm ``ceil`` functions
10002 would, and handles error conditions in the same way.
10004 '``llvm.trunc.*``' Intrinsic
10005 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10010 This is an overloaded intrinsic. You can use ``llvm.trunc`` on any
10011 floating point or vector of floating point type. Not all targets support
10016 declare float @llvm.trunc.f32(float %Val)
10017 declare double @llvm.trunc.f64(double %Val)
10018 declare x86_fp80 @llvm.trunc.f80(x86_fp80 %Val)
10019 declare fp128 @llvm.trunc.f128(fp128 %Val)
10020 declare ppc_fp128 @llvm.trunc.ppcf128(ppc_fp128 %Val)
10025 The '``llvm.trunc.*``' intrinsics returns the operand rounded to the
10026 nearest integer not larger in magnitude than the operand.
10031 The argument and return value are floating point numbers of the same
10037 This function returns the same values as the libm ``trunc`` functions
10038 would, and handles error conditions in the same way.
10040 '``llvm.rint.*``' Intrinsic
10041 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
10046 This is an overloaded intrinsic. You can use ``llvm.rint`` on any
10047 floating point or vector of floating point type. Not all targets support
10052 declare float @llvm.rint.f32(float %Val)
10053 declare double @llvm.rint.f64(double %Val)
10054 declare x86_fp80 @llvm.rint.f80(x86_fp80 %Val)
10055 declare fp128 @llvm.rint.f128(fp128 %Val)
10056 declare ppc_fp128 @llvm.rint.ppcf128(ppc_fp128 %Val)
10061 The '``llvm.rint.*``' intrinsics returns the operand rounded to the
10062 nearest integer. It may raise an inexact floating-point exception if the
10063 operand isn't an integer.
10068 The argument and return value are floating point numbers of the same
10074 This function returns the same values as the libm ``rint`` functions
10075 would, and handles error conditions in the same way.
10077 '``llvm.nearbyint.*``' Intrinsic
10078 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10083 This is an overloaded intrinsic. You can use ``llvm.nearbyint`` on any
10084 floating point or vector of floating point type. Not all targets support
10089 declare float @llvm.nearbyint.f32(float %Val)
10090 declare double @llvm.nearbyint.f64(double %Val)
10091 declare x86_fp80 @llvm.nearbyint.f80(x86_fp80 %Val)
10092 declare fp128 @llvm.nearbyint.f128(fp128 %Val)
10093 declare ppc_fp128 @llvm.nearbyint.ppcf128(ppc_fp128 %Val)
10098 The '``llvm.nearbyint.*``' intrinsics returns the operand rounded to the
10104 The argument and return value are floating point numbers of the same
10110 This function returns the same values as the libm ``nearbyint``
10111 functions would, and handles error conditions in the same way.
10113 '``llvm.round.*``' Intrinsic
10114 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10119 This is an overloaded intrinsic. You can use ``llvm.round`` on any
10120 floating point or vector of floating point type. Not all targets support
10125 declare float @llvm.round.f32(float %Val)
10126 declare double @llvm.round.f64(double %Val)
10127 declare x86_fp80 @llvm.round.f80(x86_fp80 %Val)
10128 declare fp128 @llvm.round.f128(fp128 %Val)
10129 declare ppc_fp128 @llvm.round.ppcf128(ppc_fp128 %Val)
10134 The '``llvm.round.*``' intrinsics returns the operand rounded to the
10140 The argument and return value are floating point numbers of the same
10146 This function returns the same values as the libm ``round``
10147 functions would, and handles error conditions in the same way.
10149 Bit Manipulation Intrinsics
10150 ---------------------------
10152 LLVM provides intrinsics for a few important bit manipulation
10153 operations. These allow efficient code generation for some algorithms.
10155 '``llvm.bswap.*``' Intrinsics
10156 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10161 This is an overloaded intrinsic function. You can use bswap on any
10162 integer type that is an even number of bytes (i.e. BitWidth % 16 == 0).
10166 declare i16 @llvm.bswap.i16(i16 <id>)
10167 declare i32 @llvm.bswap.i32(i32 <id>)
10168 declare i64 @llvm.bswap.i64(i64 <id>)
10173 The '``llvm.bswap``' family of intrinsics is used to byte swap integer
10174 values with an even number of bytes (positive multiple of 16 bits).
10175 These are useful for performing operations on data that is not in the
10176 target's native byte order.
10181 The ``llvm.bswap.i16`` intrinsic returns an i16 value that has the high
10182 and low byte of the input i16 swapped. Similarly, the ``llvm.bswap.i32``
10183 intrinsic returns an i32 value that has the four bytes of the input i32
10184 swapped, so that if the input bytes are numbered 0, 1, 2, 3 then the
10185 returned i32 will have its bytes in 3, 2, 1, 0 order. The
10186 ``llvm.bswap.i48``, ``llvm.bswap.i64`` and other intrinsics extend this
10187 concept to additional even-byte lengths (6 bytes, 8 bytes and more,
10190 '``llvm.ctpop.*``' Intrinsic
10191 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10196 This is an overloaded intrinsic. You can use llvm.ctpop on any integer
10197 bit width, or on any vector with integer elements. Not all targets
10198 support all bit widths or vector types, however.
10202 declare i8 @llvm.ctpop.i8(i8 <src>)
10203 declare i16 @llvm.ctpop.i16(i16 <src>)
10204 declare i32 @llvm.ctpop.i32(i32 <src>)
10205 declare i64 @llvm.ctpop.i64(i64 <src>)
10206 declare i256 @llvm.ctpop.i256(i256 <src>)
10207 declare <2 x i32> @llvm.ctpop.v2i32(<2 x i32> <src>)
10212 The '``llvm.ctpop``' family of intrinsics counts the number of bits set
10218 The only argument is the value to be counted. The argument may be of any
10219 integer type, or a vector with integer elements. The return type must
10220 match the argument type.
10225 The '``llvm.ctpop``' intrinsic counts the 1's in a variable, or within
10226 each element of a vector.
10228 '``llvm.ctlz.*``' Intrinsic
10229 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
10234 This is an overloaded intrinsic. You can use ``llvm.ctlz`` on any
10235 integer bit width, or any vector whose elements are integers. Not all
10236 targets support all bit widths or vector types, however.
10240 declare i8 @llvm.ctlz.i8 (i8 <src>, i1 <is_zero_undef>)
10241 declare i16 @llvm.ctlz.i16 (i16 <src>, i1 <is_zero_undef>)
10242 declare i32 @llvm.ctlz.i32 (i32 <src>, i1 <is_zero_undef>)
10243 declare i64 @llvm.ctlz.i64 (i64 <src>, i1 <is_zero_undef>)
10244 declare i256 @llvm.ctlz.i256(i256 <src>, i1 <is_zero_undef>)
10245 declase <2 x i32> @llvm.ctlz.v2i32(<2 x i32> <src>, i1 <is_zero_undef>)
10250 The '``llvm.ctlz``' family of intrinsic functions counts the number of
10251 leading zeros in a variable.
10256 The first argument is the value to be counted. This argument may be of
10257 any integer type, or a vector with integer element type. The return
10258 type must match the first argument type.
10260 The second argument must be a constant and is a flag to indicate whether
10261 the intrinsic should ensure that a zero as the first argument produces a
10262 defined result. Historically some architectures did not provide a
10263 defined result for zero values as efficiently, and many algorithms are
10264 now predicated on avoiding zero-value inputs.
10269 The '``llvm.ctlz``' intrinsic counts the leading (most significant)
10270 zeros in a variable, or within each element of the vector. If
10271 ``src == 0`` then the result is the size in bits of the type of ``src``
10272 if ``is_zero_undef == 0`` and ``undef`` otherwise. For example,
10273 ``llvm.ctlz(i32 2) = 30``.
10275 '``llvm.cttz.*``' Intrinsic
10276 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
10281 This is an overloaded intrinsic. You can use ``llvm.cttz`` on any
10282 integer bit width, or any vector of integer elements. Not all targets
10283 support all bit widths or vector types, however.
10287 declare i8 @llvm.cttz.i8 (i8 <src>, i1 <is_zero_undef>)
10288 declare i16 @llvm.cttz.i16 (i16 <src>, i1 <is_zero_undef>)
10289 declare i32 @llvm.cttz.i32 (i32 <src>, i1 <is_zero_undef>)
10290 declare i64 @llvm.cttz.i64 (i64 <src>, i1 <is_zero_undef>)
10291 declare i256 @llvm.cttz.i256(i256 <src>, i1 <is_zero_undef>)
10292 declase <2 x i32> @llvm.cttz.v2i32(<2 x i32> <src>, i1 <is_zero_undef>)
10297 The '``llvm.cttz``' family of intrinsic functions counts the number of
10303 The first argument is the value to be counted. This argument may be of
10304 any integer type, or a vector with integer element type. The return
10305 type must match the first argument type.
10307 The second argument must be a constant and is a flag to indicate whether
10308 the intrinsic should ensure that a zero as the first argument produces a
10309 defined result. Historically some architectures did not provide a
10310 defined result for zero values as efficiently, and many algorithms are
10311 now predicated on avoiding zero-value inputs.
10316 The '``llvm.cttz``' intrinsic counts the trailing (least significant)
10317 zeros in a variable, or within each element of a vector. If ``src == 0``
10318 then the result is the size in bits of the type of ``src`` if
10319 ``is_zero_undef == 0`` and ``undef`` otherwise. For example,
10320 ``llvm.cttz(2) = 1``.
10324 Arithmetic with Overflow Intrinsics
10325 -----------------------------------
10327 LLVM provides intrinsics for some arithmetic with overflow operations.
10329 '``llvm.sadd.with.overflow.*``' Intrinsics
10330 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10335 This is an overloaded intrinsic. You can use ``llvm.sadd.with.overflow``
10336 on any integer bit width.
10340 declare {i16, i1} @llvm.sadd.with.overflow.i16(i16 %a, i16 %b)
10341 declare {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b)
10342 declare {i64, i1} @llvm.sadd.with.overflow.i64(i64 %a, i64 %b)
10347 The '``llvm.sadd.with.overflow``' family of intrinsic functions perform
10348 a signed addition of the two arguments, and indicate whether an overflow
10349 occurred during the signed summation.
10354 The arguments (%a and %b) and the first element of the result structure
10355 may be of integer types of any bit width, but they must have the same
10356 bit width. The second element of the result structure must be of type
10357 ``i1``. ``%a`` and ``%b`` are the two values that will undergo signed
10363 The '``llvm.sadd.with.overflow``' family of intrinsic functions perform
10364 a signed addition of the two variables. They return a structure --- the
10365 first element of which is the signed summation, and the second element
10366 of which is a bit specifying if the signed summation resulted in an
10372 .. code-block:: llvm
10374 %res = call {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b)
10375 %sum = extractvalue {i32, i1} %res, 0
10376 %obit = extractvalue {i32, i1} %res, 1
10377 br i1 %obit, label %overflow, label %normal
10379 '``llvm.uadd.with.overflow.*``' Intrinsics
10380 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10385 This is an overloaded intrinsic. You can use ``llvm.uadd.with.overflow``
10386 on any integer bit width.
10390 declare {i16, i1} @llvm.uadd.with.overflow.i16(i16 %a, i16 %b)
10391 declare {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)
10392 declare {i64, i1} @llvm.uadd.with.overflow.i64(i64 %a, i64 %b)
10397 The '``llvm.uadd.with.overflow``' family of intrinsic functions perform
10398 an unsigned addition of the two arguments, and indicate whether a carry
10399 occurred during the unsigned summation.
10404 The arguments (%a and %b) and the first element of the result structure
10405 may be of integer types of any bit width, but they must have the same
10406 bit width. The second element of the result structure must be of type
10407 ``i1``. ``%a`` and ``%b`` are the two values that will undergo unsigned
10413 The '``llvm.uadd.with.overflow``' family of intrinsic functions perform
10414 an unsigned addition of the two arguments. They return a structure --- the
10415 first element of which is the sum, and the second element of which is a
10416 bit specifying if the unsigned summation resulted in a carry.
10421 .. code-block:: llvm
10423 %res = call {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)
10424 %sum = extractvalue {i32, i1} %res, 0
10425 %obit = extractvalue {i32, i1} %res, 1
10426 br i1 %obit, label %carry, label %normal
10428 '``llvm.ssub.with.overflow.*``' Intrinsics
10429 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10434 This is an overloaded intrinsic. You can use ``llvm.ssub.with.overflow``
10435 on any integer bit width.
10439 declare {i16, i1} @llvm.ssub.with.overflow.i16(i16 %a, i16 %b)
10440 declare {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b)
10441 declare {i64, i1} @llvm.ssub.with.overflow.i64(i64 %a, i64 %b)
10446 The '``llvm.ssub.with.overflow``' family of intrinsic functions perform
10447 a signed subtraction of the two arguments, and indicate whether an
10448 overflow occurred during the signed subtraction.
10453 The arguments (%a and %b) and the first element of the result structure
10454 may be of integer types of any bit width, but they must have the same
10455 bit width. The second element of the result structure must be of type
10456 ``i1``. ``%a`` and ``%b`` are the two values that will undergo signed
10462 The '``llvm.ssub.with.overflow``' family of intrinsic functions perform
10463 a signed subtraction of the two arguments. They return a structure --- the
10464 first element of which is the subtraction, and the second element of
10465 which is a bit specifying if the signed subtraction resulted in an
10471 .. code-block:: llvm
10473 %res = call {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b)
10474 %sum = extractvalue {i32, i1} %res, 0
10475 %obit = extractvalue {i32, i1} %res, 1
10476 br i1 %obit, label %overflow, label %normal
10478 '``llvm.usub.with.overflow.*``' Intrinsics
10479 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10484 This is an overloaded intrinsic. You can use ``llvm.usub.with.overflow``
10485 on any integer bit width.
10489 declare {i16, i1} @llvm.usub.with.overflow.i16(i16 %a, i16 %b)
10490 declare {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b)
10491 declare {i64, i1} @llvm.usub.with.overflow.i64(i64 %a, i64 %b)
10496 The '``llvm.usub.with.overflow``' family of intrinsic functions perform
10497 an unsigned subtraction of the two arguments, and indicate whether an
10498 overflow occurred during the unsigned subtraction.
10503 The arguments (%a and %b) and the first element of the result structure
10504 may be of integer types of any bit width, but they must have the same
10505 bit width. The second element of the result structure must be of type
10506 ``i1``. ``%a`` and ``%b`` are the two values that will undergo unsigned
10512 The '``llvm.usub.with.overflow``' family of intrinsic functions perform
10513 an unsigned subtraction of the two arguments. They return a structure ---
10514 the first element of which is the subtraction, and the second element of
10515 which is a bit specifying if the unsigned subtraction resulted in an
10521 .. code-block:: llvm
10523 %res = call {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b)
10524 %sum = extractvalue {i32, i1} %res, 0
10525 %obit = extractvalue {i32, i1} %res, 1
10526 br i1 %obit, label %overflow, label %normal
10528 '``llvm.smul.with.overflow.*``' Intrinsics
10529 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10534 This is an overloaded intrinsic. You can use ``llvm.smul.with.overflow``
10535 on any integer bit width.
10539 declare {i16, i1} @llvm.smul.with.overflow.i16(i16 %a, i16 %b)
10540 declare {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b)
10541 declare {i64, i1} @llvm.smul.with.overflow.i64(i64 %a, i64 %b)
10546 The '``llvm.smul.with.overflow``' family of intrinsic functions perform
10547 a signed multiplication of the two arguments, and indicate whether an
10548 overflow occurred during the signed multiplication.
10553 The arguments (%a and %b) and the first element of the result structure
10554 may be of integer types of any bit width, but they must have the same
10555 bit width. The second element of the result structure must be of type
10556 ``i1``. ``%a`` and ``%b`` are the two values that will undergo signed
10562 The '``llvm.smul.with.overflow``' family of intrinsic functions perform
10563 a signed multiplication of the two arguments. They return a structure ---
10564 the first element of which is the multiplication, and the second element
10565 of which is a bit specifying if the signed multiplication resulted in an
10571 .. code-block:: llvm
10573 %res = call {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b)
10574 %sum = extractvalue {i32, i1} %res, 0
10575 %obit = extractvalue {i32, i1} %res, 1
10576 br i1 %obit, label %overflow, label %normal
10578 '``llvm.umul.with.overflow.*``' Intrinsics
10579 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10584 This is an overloaded intrinsic. You can use ``llvm.umul.with.overflow``
10585 on any integer bit width.
10589 declare {i16, i1} @llvm.umul.with.overflow.i16(i16 %a, i16 %b)
10590 declare {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b)
10591 declare {i64, i1} @llvm.umul.with.overflow.i64(i64 %a, i64 %b)
10596 The '``llvm.umul.with.overflow``' family of intrinsic functions perform
10597 a unsigned multiplication of the two arguments, and indicate whether an
10598 overflow occurred during the unsigned multiplication.
10603 The arguments (%a and %b) and the first element of the result structure
10604 may be of integer types of any bit width, but they must have the same
10605 bit width. The second element of the result structure must be of type
10606 ``i1``. ``%a`` and ``%b`` are the two values that will undergo unsigned
10612 The '``llvm.umul.with.overflow``' family of intrinsic functions perform
10613 an unsigned multiplication of the two arguments. They return a structure ---
10614 the first element of which is the multiplication, and the second
10615 element of which is a bit specifying if the unsigned multiplication
10616 resulted in an overflow.
10621 .. code-block:: llvm
10623 %res = call {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b)
10624 %sum = extractvalue {i32, i1} %res, 0
10625 %obit = extractvalue {i32, i1} %res, 1
10626 br i1 %obit, label %overflow, label %normal
10628 Specialised Arithmetic Intrinsics
10629 ---------------------------------
10631 '``llvm.canonicalize.*``' Intrinsic
10632 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10639 declare float @llvm.canonicalize.f32(float %a)
10640 declare double @llvm.canonicalize.f64(double %b)
10645 The '``llvm.canonicalize.*``' intrinsic returns the platform specific canonical
10646 encoding of a floating point number. This canonicalization is useful for
10647 implementing certain numeric primitives such as frexp. The canonical encoding is
10648 defined by IEEE-754-2008 to be:
10652 2.1.8 canonical encoding: The preferred encoding of a floating-point
10653 representation in a format. Applied to declets, significands of finite
10654 numbers, infinities, and NaNs, especially in decimal formats.
10656 This operation can also be considered equivalent to the IEEE-754-2008
10657 conversion of a floating-point value to the same format. NaNs are handled
10658 according to section 6.2.
10660 Examples of non-canonical encodings:
10662 - x87 pseudo denormals, pseudo NaNs, pseudo Infinity, Unnormals. These are
10663 converted to a canonical representation per hardware-specific protocol.
10664 - Many normal decimal floating point numbers have non-canonical alternative
10666 - Some machines, like GPUs or ARMv7 NEON, do not support subnormal values.
10667 These are treated as non-canonical encodings of zero and with be flushed to
10668 a zero of the same sign by this operation.
10670 Note that per IEEE-754-2008 6.2, systems that support signaling NaNs with
10671 default exception handling must signal an invalid exception, and produce a
10674 This function should always be implementable as multiplication by 1.0, provided
10675 that the compiler does not constant fold the operation. Likewise, division by
10676 1.0 and ``llvm.minnum(x, x)`` are possible implementations. Addition with
10677 -0.0 is also sufficient provided that the rounding mode is not -Infinity.
10679 ``@llvm.canonicalize`` must preserve the equality relation. That is:
10681 - ``(@llvm.canonicalize(x) == x)`` is equivalent to ``(x == x)``
10682 - ``(@llvm.canonicalize(x) == @llvm.canonicalize(y))`` is equivalent to
10685 Additionally, the sign of zero must be conserved:
10686 ``@llvm.canonicalize(-0.0) = -0.0`` and ``@llvm.canonicalize(+0.0) = +0.0``
10688 The payload bits of a NaN must be conserved, with two exceptions.
10689 First, environments which use only a single canonical representation of NaN
10690 must perform said canonicalization. Second, SNaNs must be quieted per the
10693 The canonicalization operation may be optimized away if:
10695 - The input is known to be canonical. For example, it was produced by a
10696 floating-point operation that is required by the standard to be canonical.
10697 - The result is consumed only by (or fused with) other floating-point
10698 operations. That is, the bits of the floating point value are not examined.
10700 '``llvm.fmuladd.*``' Intrinsic
10701 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10708 declare float @llvm.fmuladd.f32(float %a, float %b, float %c)
10709 declare double @llvm.fmuladd.f64(double %a, double %b, double %c)
10714 The '``llvm.fmuladd.*``' intrinsic functions represent multiply-add
10715 expressions that can be fused if the code generator determines that (a) the
10716 target instruction set has support for a fused operation, and (b) that the
10717 fused operation is more efficient than the equivalent, separate pair of mul
10718 and add instructions.
10723 The '``llvm.fmuladd.*``' intrinsics each take three arguments: two
10724 multiplicands, a and b, and an addend c.
10733 %0 = call float @llvm.fmuladd.f32(%a, %b, %c)
10735 is equivalent to the expression a \* b + c, except that rounding will
10736 not be performed between the multiplication and addition steps if the
10737 code generator fuses the operations. Fusion is not guaranteed, even if
10738 the target platform supports it. If a fused multiply-add is required the
10739 corresponding llvm.fma.\* intrinsic function should be used
10740 instead. This never sets errno, just as '``llvm.fma.*``'.
10745 .. code-block:: llvm
10747 %r2 = call float @llvm.fmuladd.f32(float %a, float %b, float %c) ; yields float:r2 = (a * b) + c
10750 '``llvm.uabsdiff.*``' and '``llvm.sabsdiff.*``' Intrinsics
10751 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10755 This is an overloaded intrinsic. The loaded data is a vector of any integer bit width.
10757 .. code-block:: llvm
10759 declare <4 x integer> @llvm.uabsdiff.v4i32(<4 x integer> %a, <4 x integer> %b)
10765 The ``llvm.uabsdiff`` intrinsic returns a vector result of the absolute difference of
10766 the two operands, treating them both as unsigned integers.
10768 The ``llvm.sabsdiff`` intrinsic returns a vector result of the absolute difference of
10769 the two operands, treating them both as signed integers.
10773 These intrinsics are primarily used during the code generation stage of compilation.
10774 They are generated by compiler passes such as the Loop and SLP vectorizers.it is not
10775 recommended for users to create them manually.
10780 Both intrinsics take two integer of the same bitwidth.
10787 call <4 x i32> @llvm.uabsdiff.v4i32(<4 x i32> %a, <4 x i32> %b)
10791 %sub = sub <4 x i32> %a, %b
10792 %ispos = icmp ugt <4 x i32> %sub, <i32 -1, i32 -1, i32 -1, i32 -1>
10793 %neg = sub <4 x i32> zeroinitializer, %sub
10794 %1 = select <4 x i1> %ispos, <4 x i32> %sub, <4 x i32> %neg
10796 Similarly the expression::
10798 call <4 x i32> @llvm.sabsdiff.v4i32(<4 x i32> %a, <4 x i32> %b)
10802 %sub = sub nsw <4 x i32> %a, %b
10803 %ispos = icmp sgt <4 x i32> %sub, <i32 -1, i32 -1, i32 -1, i32 -1>
10804 %neg = sub nsw <4 x i32> zeroinitializer, %sub
10805 %1 = select <4 x i1> %ispos, <4 x i32> %sub, <4 x i32> %neg
10808 Half Precision Floating Point Intrinsics
10809 ----------------------------------------
10811 For most target platforms, half precision floating point is a
10812 storage-only format. This means that it is a dense encoding (in memory)
10813 but does not support computation in the format.
10815 This means that code must first load the half-precision floating point
10816 value as an i16, then convert it to float with
10817 :ref:`llvm.convert.from.fp16 <int_convert_from_fp16>`. Computation can
10818 then be performed on the float value (including extending to double
10819 etc). To store the value back to memory, it is first converted to float
10820 if needed, then converted to i16 with
10821 :ref:`llvm.convert.to.fp16 <int_convert_to_fp16>`, then storing as an
10824 .. _int_convert_to_fp16:
10826 '``llvm.convert.to.fp16``' Intrinsic
10827 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10834 declare i16 @llvm.convert.to.fp16.f32(float %a)
10835 declare i16 @llvm.convert.to.fp16.f64(double %a)
10840 The '``llvm.convert.to.fp16``' intrinsic function performs a conversion from a
10841 conventional floating point type to half precision floating point format.
10846 The intrinsic function contains single argument - the value to be
10852 The '``llvm.convert.to.fp16``' intrinsic function performs a conversion from a
10853 conventional floating point format to half precision floating point format. The
10854 return value is an ``i16`` which contains the converted number.
10859 .. code-block:: llvm
10861 %res = call i16 @llvm.convert.to.fp16.f32(float %a)
10862 store i16 %res, i16* @x, align 2
10864 .. _int_convert_from_fp16:
10866 '``llvm.convert.from.fp16``' Intrinsic
10867 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10874 declare float @llvm.convert.from.fp16.f32(i16 %a)
10875 declare double @llvm.convert.from.fp16.f64(i16 %a)
10880 The '``llvm.convert.from.fp16``' intrinsic function performs a
10881 conversion from half precision floating point format to single precision
10882 floating point format.
10887 The intrinsic function contains single argument - the value to be
10893 The '``llvm.convert.from.fp16``' intrinsic function performs a
10894 conversion from half single precision floating point format to single
10895 precision floating point format. The input half-float value is
10896 represented by an ``i16`` value.
10901 .. code-block:: llvm
10903 %a = load i16, i16* @x, align 2
10904 %res = call float @llvm.convert.from.fp16(i16 %a)
10906 .. _dbg_intrinsics:
10908 Debugger Intrinsics
10909 -------------------
10911 The LLVM debugger intrinsics (which all start with ``llvm.dbg.``
10912 prefix), are described in the `LLVM Source Level
10913 Debugging <SourceLevelDebugging.html#format_common_intrinsics>`_
10916 Exception Handling Intrinsics
10917 -----------------------------
10919 The LLVM exception handling intrinsics (which all start with
10920 ``llvm.eh.`` prefix), are described in the `LLVM Exception
10921 Handling <ExceptionHandling.html#format_common_intrinsics>`_ document.
10923 .. _int_trampoline:
10925 Trampoline Intrinsics
10926 ---------------------
10928 These intrinsics make it possible to excise one parameter, marked with
10929 the :ref:`nest <nest>` attribute, from a function. The result is a
10930 callable function pointer lacking the nest parameter - the caller does
10931 not need to provide a value for it. Instead, the value to use is stored
10932 in advance in a "trampoline", a block of memory usually allocated on the
10933 stack, which also contains code to splice the nest value into the
10934 argument list. This is used to implement the GCC nested function address
10937 For example, if the function is ``i32 f(i8* nest %c, i32 %x, i32 %y)``
10938 then the resulting function pointer has signature ``i32 (i32, i32)*``.
10939 It can be created as follows:
10941 .. code-block:: llvm
10943 %tramp = alloca [10 x i8], align 4 ; size and alignment only correct for X86
10944 %tramp1 = getelementptr [10 x i8], [10 x i8]* %tramp, i32 0, i32 0
10945 call i8* @llvm.init.trampoline(i8* %tramp1, i8* bitcast (i32 (i8*, i32, i32)* @f to i8*), i8* %nval)
10946 %p = call i8* @llvm.adjust.trampoline(i8* %tramp1)
10947 %fp = bitcast i8* %p to i32 (i32, i32)*
10949 The call ``%val = call i32 %fp(i32 %x, i32 %y)`` is then equivalent to
10950 ``%val = call i32 %f(i8* %nval, i32 %x, i32 %y)``.
10954 '``llvm.init.trampoline``' Intrinsic
10955 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10962 declare void @llvm.init.trampoline(i8* <tramp>, i8* <func>, i8* <nval>)
10967 This fills the memory pointed to by ``tramp`` with executable code,
10968 turning it into a trampoline.
10973 The ``llvm.init.trampoline`` intrinsic takes three arguments, all
10974 pointers. The ``tramp`` argument must point to a sufficiently large and
10975 sufficiently aligned block of memory; this memory is written to by the
10976 intrinsic. Note that the size and the alignment are target-specific -
10977 LLVM currently provides no portable way of determining them, so a
10978 front-end that generates this intrinsic needs to have some
10979 target-specific knowledge. The ``func`` argument must hold a function
10980 bitcast to an ``i8*``.
10985 The block of memory pointed to by ``tramp`` is filled with target
10986 dependent code, turning it into a function. Then ``tramp`` needs to be
10987 passed to :ref:`llvm.adjust.trampoline <int_at>` to get a pointer which can
10988 be :ref:`bitcast (to a new function) and called <int_trampoline>`. The new
10989 function's signature is the same as that of ``func`` with any arguments
10990 marked with the ``nest`` attribute removed. At most one such ``nest``
10991 argument is allowed, and it must be of pointer type. Calling the new
10992 function is equivalent to calling ``func`` with the same argument list,
10993 but with ``nval`` used for the missing ``nest`` argument. If, after
10994 calling ``llvm.init.trampoline``, the memory pointed to by ``tramp`` is
10995 modified, then the effect of any later call to the returned function
10996 pointer is undefined.
11000 '``llvm.adjust.trampoline``' Intrinsic
11001 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11008 declare i8* @llvm.adjust.trampoline(i8* <tramp>)
11013 This performs any required machine-specific adjustment to the address of
11014 a trampoline (passed as ``tramp``).
11019 ``tramp`` must point to a block of memory which already has trampoline
11020 code filled in by a previous call to
11021 :ref:`llvm.init.trampoline <int_it>`.
11026 On some architectures the address of the code to be executed needs to be
11027 different than the address where the trampoline is actually stored. This
11028 intrinsic returns the executable address corresponding to ``tramp``
11029 after performing the required machine specific adjustments. The pointer
11030 returned can then be :ref:`bitcast and executed <int_trampoline>`.
11032 .. _int_mload_mstore:
11034 Masked Vector Load and Store Intrinsics
11035 ---------------------------------------
11037 LLVM provides intrinsics for predicated vector load and store operations. The predicate is specified by a mask operand, which holds one bit per vector element, switching the associated vector lane on or off. The memory addresses corresponding to the "off" lanes are not accessed. When all bits of the mask are on, the intrinsic is identical to a regular vector load or store. When all bits are off, no memory is accessed.
11041 '``llvm.masked.load.*``' Intrinsics
11042 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11046 This is an overloaded intrinsic. The loaded data is a vector of any integer or floating point data type.
11050 declare <16 x float> @llvm.masked.load.v16f32 (<16 x float>* <ptr>, i32 <alignment>, <16 x i1> <mask>, <16 x float> <passthru>)
11051 declare <2 x double> @llvm.masked.load.v2f64 (<2 x double>* <ptr>, i32 <alignment>, <2 x i1> <mask>, <2 x double> <passthru>)
11056 Reads a vector from memory according to the provided mask. The mask holds a bit for each vector lane, and is used to prevent memory accesses to the masked-off lanes. The masked-off lanes in the result vector are taken from the corresponding lanes of the '``passthru``' operand.
11062 The first operand is the base pointer for the load. The second operand is the alignment of the source location. It must be a constant integer value. The third operand, mask, is a vector of boolean values with the same number of elements as the return type. The fourth is a pass-through value that is used to fill the masked-off lanes of the result. The return type, underlying type of the base pointer and the type of the '``passthru``' operand are the same vector types.
11068 The '``llvm.masked.load``' intrinsic is designed for conditional reading of selected vector elements in a single IR operation. It is useful for targets that support vector masked loads and allows vectorizing predicated basic blocks on these targets. Other targets may support this intrinsic differently, for example by lowering it into a sequence of branches that guard scalar load operations.
11069 The result of this operation is equivalent to a regular vector load instruction followed by a 'select' between the loaded and the passthru values, predicated on the same mask. However, using this intrinsic prevents exceptions on memory access to masked-off lanes.
11074 %res = call <16 x float> @llvm.masked.load.v16f32 (<16 x float>* %ptr, i32 4, <16 x i1>%mask, <16 x float> %passthru)
11076 ;; The result of the two following instructions is identical aside from potential memory access exception
11077 %loadlal = load <16 x float>, <16 x float>* %ptr, align 4
11078 %res = select <16 x i1> %mask, <16 x float> %loadlal, <16 x float> %passthru
11082 '``llvm.masked.store.*``' Intrinsics
11083 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11087 This is an overloaded intrinsic. The data stored in memory is a vector of any integer or floating point data type.
11091 declare void @llvm.masked.store.v8i32 (<8 x i32> <value>, <8 x i32> * <ptr>, i32 <alignment>, <8 x i1> <mask>)
11092 declare void @llvm.masked.store.v16f32(<16 x i32> <value>, <16 x i32>* <ptr>, i32 <alignment>, <16 x i1> <mask>)
11097 Writes a vector to memory according to the provided mask. The mask holds a bit for each vector lane, and is used to prevent memory accesses to the masked-off lanes.
11102 The first operand is the vector value to be written to memory. The second operand is the base pointer for the store, it has the same underlying type as the value operand. The third operand is the alignment of the destination location. The fourth operand, mask, is a vector of boolean values. The types of the mask and the value operand must have the same number of vector elements.
11108 The '``llvm.masked.store``' intrinsics is designed for conditional writing of selected vector elements in a single IR operation. It is useful for targets that support vector masked store and allows vectorizing predicated basic blocks on these targets. Other targets may support this intrinsic differently, for example by lowering it into a sequence of branches that guard scalar store operations.
11109 The result of this operation is equivalent to a load-modify-store sequence. However, using this intrinsic prevents exceptions and data races on memory access to masked-off lanes.
11113 call void @llvm.masked.store.v16f32(<16 x float> %value, <16 x float>* %ptr, i32 4, <16 x i1> %mask)
11115 ;; The result of the following instructions is identical aside from potential data races and memory access exceptions
11116 %oldval = load <16 x float>, <16 x float>* %ptr, align 4
11117 %res = select <16 x i1> %mask, <16 x float> %value, <16 x float> %oldval
11118 store <16 x float> %res, <16 x float>* %ptr, align 4
11121 Masked Vector Gather and Scatter Intrinsics
11122 -------------------------------------------
11124 LLVM provides intrinsics for vector gather and scatter operations. They are similar to :ref:`Masked Vector Load and Store <int_mload_mstore>`, except they are designed for arbitrary memory accesses, rather than sequential memory accesses. Gather and scatter also employ a mask operand, which holds one bit per vector element, switching the associated vector lane on or off. The memory addresses corresponding to the "off" lanes are not accessed. When all bits are off, no memory is accessed.
11128 '``llvm.masked.gather.*``' Intrinsics
11129 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11133 This is an overloaded intrinsic. The loaded data are multiple scalar values of any integer or floating point data type gathered together into one vector.
11137 declare <16 x float> @llvm.masked.gather.v16f32 (<16 x float*> <ptrs>, i32 <alignment>, <16 x i1> <mask>, <16 x float> <passthru>)
11138 declare <2 x double> @llvm.masked.gather.v2f64 (<2 x double*> <ptrs>, i32 <alignment>, <2 x i1> <mask>, <2 x double> <passthru>)
11143 Reads scalar values from arbitrary memory locations and gathers them into one vector. The memory locations are provided in the vector of pointers '``ptrs``'. The memory is accessed according to the provided mask. The mask holds a bit for each vector lane, and is used to prevent memory accesses to the masked-off lanes. The masked-off lanes in the result vector are taken from the corresponding lanes of the '``passthru``' operand.
11149 The first operand is a vector of pointers which holds all memory addresses to read. The second operand is an alignment of the source addresses. It must be a constant integer value. The third operand, mask, is a vector of boolean values with the same number of elements as the return type. The fourth is a pass-through value that is used to fill the masked-off lanes of the result. The return type, underlying type of the vector of pointers and the type of the '``passthru``' operand are the same vector types.
11155 The '``llvm.masked.gather``' intrinsic is designed for conditional reading of multiple scalar values from arbitrary memory locations in a single IR operation. It is useful for targets that support vector masked gathers and allows vectorizing basic blocks with data and control divergence. Other targets may support this intrinsic differently, for example by lowering it into a sequence of scalar load operations.
11156 The semantics of this operation are equivalent to a sequence of conditional scalar loads with subsequent gathering all loaded values into a single vector. The mask restricts memory access to certain lanes and facilitates vectorization of predicated basic blocks.
11161 %res = call <4 x double> @llvm.masked.gather.v4f64 (<4 x double*> %ptrs, i32 8, <4 x i1>%mask, <4 x double> <true, true, true, true>)
11163 ;; The gather with all-true mask is equivalent to the following instruction sequence
11164 %ptr0 = extractelement <4 x double*> %ptrs, i32 0
11165 %ptr1 = extractelement <4 x double*> %ptrs, i32 1
11166 %ptr2 = extractelement <4 x double*> %ptrs, i32 2
11167 %ptr3 = extractelement <4 x double*> %ptrs, i32 3
11169 %val0 = load double, double* %ptr0, align 8
11170 %val1 = load double, double* %ptr1, align 8
11171 %val2 = load double, double* %ptr2, align 8
11172 %val3 = load double, double* %ptr3, align 8
11174 %vec0 = insertelement <4 x double>undef, %val0, 0
11175 %vec01 = insertelement <4 x double>%vec0, %val1, 1
11176 %vec012 = insertelement <4 x double>%vec01, %val2, 2
11177 %vec0123 = insertelement <4 x double>%vec012, %val3, 3
11181 '``llvm.masked.scatter.*``' Intrinsics
11182 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11186 This is an overloaded intrinsic. The data stored in memory is a vector of any integer or floating point data type. Each vector element is stored in an arbitrary memory addresses. Scatter with overlapping addresses is guaranteed to be ordered from least-significant to most-significant element.
11190 declare void @llvm.masked.scatter.v8i32 (<8 x i32> <value>, <8 x i32*> <ptrs>, i32 <alignment>, <8 x i1> <mask>)
11191 declare void @llvm.masked.scatter.v16f32(<16 x i32> <value>, <16 x i32*> <ptrs>, i32 <alignment>, <16 x i1> <mask>)
11196 Writes each element from the value vector to the corresponding memory address. The memory addresses are represented as a vector of pointers. Writing is done according to the provided mask. The mask holds a bit for each vector lane, and is used to prevent memory accesses to the masked-off lanes.
11201 The first operand is a vector value to be written to memory. The second operand is a vector of pointers, pointing to where the value elements should be stored. It has the same underlying type as the value operand. The third operand is an alignment of the destination addresses. The fourth operand, mask, is a vector of boolean values. The types of the mask and the value operand must have the same number of vector elements.
11207 The '``llvm.masked.scatter``' intrinsics is designed for writing selected vector elements to arbitrary memory addresses in a single IR operation. The operation may be conditional, when not all bits in the mask are switched on. It is useful for targets that support vector masked scatter and allows vectorizing basic blocks with data and control divergency. Other targets may support this intrinsic differently, for example by lowering it into a sequence of branches that guard scalar store operations.
11211 ;; This instruction unconditionaly stores data vector in multiple addresses
11212 call @llvm.masked.scatter.v8i32 (<8 x i32> %value, <8 x i32*> %ptrs, i32 4, <8 x i1> <true, true, .. true>)
11214 ;; It is equivalent to a list of scalar stores
11215 %val0 = extractelement <8 x i32> %value, i32 0
11216 %val1 = extractelement <8 x i32> %value, i32 1
11218 %val7 = extractelement <8 x i32> %value, i32 7
11219 %ptr0 = extractelement <8 x i32*> %ptrs, i32 0
11220 %ptr1 = extractelement <8 x i32*> %ptrs, i32 1
11222 %ptr7 = extractelement <8 x i32*> %ptrs, i32 7
11223 ;; Note: the order of the following stores is important when they overlap:
11224 store i32 %val0, i32* %ptr0, align 4
11225 store i32 %val1, i32* %ptr1, align 4
11227 store i32 %val7, i32* %ptr7, align 4
11233 This class of intrinsics provides information about the lifetime of
11234 memory objects and ranges where variables are immutable.
11238 '``llvm.lifetime.start``' Intrinsic
11239 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11246 declare void @llvm.lifetime.start(i64 <size>, i8* nocapture <ptr>)
11251 The '``llvm.lifetime.start``' intrinsic specifies the start of a memory
11257 The first argument is a constant integer representing the size of the
11258 object, or -1 if it is variable sized. The second argument is a pointer
11264 This intrinsic indicates that before this point in the code, the value
11265 of the memory pointed to by ``ptr`` is dead. This means that it is known
11266 to never be used and has an undefined value. A load from the pointer
11267 that precedes this intrinsic can be replaced with ``'undef'``.
11271 '``llvm.lifetime.end``' Intrinsic
11272 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11279 declare void @llvm.lifetime.end(i64 <size>, i8* nocapture <ptr>)
11284 The '``llvm.lifetime.end``' intrinsic specifies the end of a memory
11290 The first argument is a constant integer representing the size of the
11291 object, or -1 if it is variable sized. The second argument is a pointer
11297 This intrinsic indicates that after this point in the code, the value of
11298 the memory pointed to by ``ptr`` is dead. This means that it is known to
11299 never be used and has an undefined value. Any stores into the memory
11300 object following this intrinsic may be removed as dead.
11302 '``llvm.invariant.start``' Intrinsic
11303 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11310 declare {}* @llvm.invariant.start(i64 <size>, i8* nocapture <ptr>)
11315 The '``llvm.invariant.start``' intrinsic specifies that the contents of
11316 a memory object will not change.
11321 The first argument is a constant integer representing the size of the
11322 object, or -1 if it is variable sized. The second argument is a pointer
11328 This intrinsic indicates that until an ``llvm.invariant.end`` that uses
11329 the return value, the referenced memory location is constant and
11332 '``llvm.invariant.end``' Intrinsic
11333 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11340 declare void @llvm.invariant.end({}* <start>, i64 <size>, i8* nocapture <ptr>)
11345 The '``llvm.invariant.end``' intrinsic specifies that the contents of a
11346 memory object are mutable.
11351 The first argument is the matching ``llvm.invariant.start`` intrinsic.
11352 The second argument is a constant integer representing the size of the
11353 object, or -1 if it is variable sized and the third argument is a
11354 pointer to the object.
11359 This intrinsic indicates that the memory is mutable again.
11364 This class of intrinsics is designed to be generic and has no specific
11367 '``llvm.var.annotation``' Intrinsic
11368 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11375 declare void @llvm.var.annotation(i8* <val>, i8* <str>, i8* <str>, i32 <int>)
11380 The '``llvm.var.annotation``' intrinsic.
11385 The first argument is a pointer to a value, the second is a pointer to a
11386 global string, the third is a pointer to a global string which is the
11387 source file name, and the last argument is the line number.
11392 This intrinsic allows annotation of local variables with arbitrary
11393 strings. This can be useful for special purpose optimizations that want
11394 to look for these annotations. These have no other defined use; they are
11395 ignored by code generation and optimization.
11397 '``llvm.ptr.annotation.*``' Intrinsic
11398 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11403 This is an overloaded intrinsic. You can use '``llvm.ptr.annotation``' on a
11404 pointer to an integer of any width. *NOTE* you must specify an address space for
11405 the pointer. The identifier for the default address space is the integer
11410 declare i8* @llvm.ptr.annotation.p<address space>i8(i8* <val>, i8* <str>, i8* <str>, i32 <int>)
11411 declare i16* @llvm.ptr.annotation.p<address space>i16(i16* <val>, i8* <str>, i8* <str>, i32 <int>)
11412 declare i32* @llvm.ptr.annotation.p<address space>i32(i32* <val>, i8* <str>, i8* <str>, i32 <int>)
11413 declare i64* @llvm.ptr.annotation.p<address space>i64(i64* <val>, i8* <str>, i8* <str>, i32 <int>)
11414 declare i256* @llvm.ptr.annotation.p<address space>i256(i256* <val>, i8* <str>, i8* <str>, i32 <int>)
11419 The '``llvm.ptr.annotation``' intrinsic.
11424 The first argument is a pointer to an integer value of arbitrary bitwidth
11425 (result of some expression), the second is a pointer to a global string, the
11426 third is a pointer to a global string which is the source file name, and the
11427 last argument is the line number. It returns the value of the first argument.
11432 This intrinsic allows annotation of a pointer to an integer with arbitrary
11433 strings. This can be useful for special purpose optimizations that want to look
11434 for these annotations. These have no other defined use; they are ignored by code
11435 generation and optimization.
11437 '``llvm.annotation.*``' Intrinsic
11438 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11443 This is an overloaded intrinsic. You can use '``llvm.annotation``' on
11444 any integer bit width.
11448 declare i8 @llvm.annotation.i8(i8 <val>, i8* <str>, i8* <str>, i32 <int>)
11449 declare i16 @llvm.annotation.i16(i16 <val>, i8* <str>, i8* <str>, i32 <int>)
11450 declare i32 @llvm.annotation.i32(i32 <val>, i8* <str>, i8* <str>, i32 <int>)
11451 declare i64 @llvm.annotation.i64(i64 <val>, i8* <str>, i8* <str>, i32 <int>)
11452 declare i256 @llvm.annotation.i256(i256 <val>, i8* <str>, i8* <str>, i32 <int>)
11457 The '``llvm.annotation``' intrinsic.
11462 The first argument is an integer value (result of some expression), the
11463 second is a pointer to a global string, the third is a pointer to a
11464 global string which is the source file name, and the last argument is
11465 the line number. It returns the value of the first argument.
11470 This intrinsic allows annotations to be put on arbitrary expressions
11471 with arbitrary strings. This can be useful for special purpose
11472 optimizations that want to look for these annotations. These have no
11473 other defined use; they are ignored by code generation and optimization.
11475 '``llvm.trap``' Intrinsic
11476 ^^^^^^^^^^^^^^^^^^^^^^^^^
11483 declare void @llvm.trap() noreturn nounwind
11488 The '``llvm.trap``' intrinsic.
11498 This intrinsic is lowered to the target dependent trap instruction. If
11499 the target does not have a trap instruction, this intrinsic will be
11500 lowered to a call of the ``abort()`` function.
11502 '``llvm.debugtrap``' Intrinsic
11503 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11510 declare void @llvm.debugtrap() nounwind
11515 The '``llvm.debugtrap``' intrinsic.
11525 This intrinsic is lowered to code which is intended to cause an
11526 execution trap with the intention of requesting the attention of a
11529 '``llvm.stackprotector``' Intrinsic
11530 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11537 declare void @llvm.stackprotector(i8* <guard>, i8** <slot>)
11542 The ``llvm.stackprotector`` intrinsic takes the ``guard`` and stores it
11543 onto the stack at ``slot``. The stack slot is adjusted to ensure that it
11544 is placed on the stack before local variables.
11549 The ``llvm.stackprotector`` intrinsic requires two pointer arguments.
11550 The first argument is the value loaded from the stack guard
11551 ``@__stack_chk_guard``. The second variable is an ``alloca`` that has
11552 enough space to hold the value of the guard.
11557 This intrinsic causes the prologue/epilogue inserter to force the position of
11558 the ``AllocaInst`` stack slot to be before local variables on the stack. This is
11559 to ensure that if a local variable on the stack is overwritten, it will destroy
11560 the value of the guard. When the function exits, the guard on the stack is
11561 checked against the original guard by ``llvm.stackprotectorcheck``. If they are
11562 different, then ``llvm.stackprotectorcheck`` causes the program to abort by
11563 calling the ``__stack_chk_fail()`` function.
11565 '``llvm.stackprotectorcheck``' Intrinsic
11566 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11573 declare void @llvm.stackprotectorcheck(i8** <guard>)
11578 The ``llvm.stackprotectorcheck`` intrinsic compares ``guard`` against an already
11579 created stack protector and if they are not equal calls the
11580 ``__stack_chk_fail()`` function.
11585 The ``llvm.stackprotectorcheck`` intrinsic requires one pointer argument, the
11586 the variable ``@__stack_chk_guard``.
11591 This intrinsic is provided to perform the stack protector check by comparing
11592 ``guard`` with the stack slot created by ``llvm.stackprotector`` and if the
11593 values do not match call the ``__stack_chk_fail()`` function.
11595 The reason to provide this as an IR level intrinsic instead of implementing it
11596 via other IR operations is that in order to perform this operation at the IR
11597 level without an intrinsic, one would need to create additional basic blocks to
11598 handle the success/failure cases. This makes it difficult to stop the stack
11599 protector check from disrupting sibling tail calls in Codegen. With this
11600 intrinsic, we are able to generate the stack protector basic blocks late in
11601 codegen after the tail call decision has occurred.
11603 '``llvm.objectsize``' Intrinsic
11604 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11611 declare i32 @llvm.objectsize.i32(i8* <object>, i1 <min>)
11612 declare i64 @llvm.objectsize.i64(i8* <object>, i1 <min>)
11617 The ``llvm.objectsize`` intrinsic is designed to provide information to
11618 the optimizers to determine at compile time whether a) an operation
11619 (like memcpy) will overflow a buffer that corresponds to an object, or
11620 b) that a runtime check for overflow isn't necessary. An object in this
11621 context means an allocation of a specific class, structure, array, or
11627 The ``llvm.objectsize`` intrinsic takes two arguments. The first
11628 argument is a pointer to or into the ``object``. The second argument is
11629 a boolean and determines whether ``llvm.objectsize`` returns 0 (if true)
11630 or -1 (if false) when the object size is unknown. The second argument
11631 only accepts constants.
11636 The ``llvm.objectsize`` intrinsic is lowered to a constant representing
11637 the size of the object concerned. If the size cannot be determined at
11638 compile time, ``llvm.objectsize`` returns ``i32/i64 -1 or 0`` (depending
11639 on the ``min`` argument).
11641 '``llvm.expect``' Intrinsic
11642 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
11647 This is an overloaded intrinsic. You can use ``llvm.expect`` on any
11652 declare i1 @llvm.expect.i1(i1 <val>, i1 <expected_val>)
11653 declare i32 @llvm.expect.i32(i32 <val>, i32 <expected_val>)
11654 declare i64 @llvm.expect.i64(i64 <val>, i64 <expected_val>)
11659 The ``llvm.expect`` intrinsic provides information about expected (the
11660 most probable) value of ``val``, which can be used by optimizers.
11665 The ``llvm.expect`` intrinsic takes two arguments. The first argument is
11666 a value. The second argument is an expected value, this needs to be a
11667 constant value, variables are not allowed.
11672 This intrinsic is lowered to the ``val``.
11676 '``llvm.assume``' Intrinsic
11677 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11684 declare void @llvm.assume(i1 %cond)
11689 The ``llvm.assume`` allows the optimizer to assume that the provided
11690 condition is true. This information can then be used in simplifying other parts
11696 The condition which the optimizer may assume is always true.
11701 The intrinsic allows the optimizer to assume that the provided condition is
11702 always true whenever the control flow reaches the intrinsic call. No code is
11703 generated for this intrinsic, and instructions that contribute only to the
11704 provided condition are not used for code generation. If the condition is
11705 violated during execution, the behavior is undefined.
11707 Note that the optimizer might limit the transformations performed on values
11708 used by the ``llvm.assume`` intrinsic in order to preserve the instructions
11709 only used to form the intrinsic's input argument. This might prove undesirable
11710 if the extra information provided by the ``llvm.assume`` intrinsic does not cause
11711 sufficient overall improvement in code quality. For this reason,
11712 ``llvm.assume`` should not be used to document basic mathematical invariants
11713 that the optimizer can otherwise deduce or facts that are of little use to the
11718 '``llvm.bitset.test``' Intrinsic
11719 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11726 declare i1 @llvm.bitset.test(i8* %ptr, metadata %bitset) nounwind readnone
11732 The first argument is a pointer to be tested. The second argument is a
11733 metadata string containing the name of a :doc:`bitset <BitSets>`.
11738 The ``llvm.bitset.test`` intrinsic tests whether the given pointer is a
11739 member of the given bitset.
11741 '``llvm.donothing``' Intrinsic
11742 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11749 declare void @llvm.donothing() nounwind readnone
11754 The ``llvm.donothing`` intrinsic doesn't perform any operation. It's one of only
11755 two intrinsics (besides ``llvm.experimental.patchpoint``) that can be called
11756 with an invoke instruction.
11766 This intrinsic does nothing, and it's removed by optimizers and ignored
11769 Stack Map Intrinsics
11770 --------------------
11772 LLVM provides experimental intrinsics to support runtime patching
11773 mechanisms commonly desired in dynamic language JITs. These intrinsics
11774 are described in :doc:`StackMaps`.