1============================== 2LLVM Language Reference Manual 3============================== 4 5.. contents:: 6 :local: 7 :depth: 4 8 9Abstract 10======== 11 12This document is a reference manual for the LLVM assembly language. LLVM 13is a Static Single Assignment (SSA) based representation that provides 14type safety, low-level operations, flexibility, and the capability of 15representing 'all' high-level languages cleanly. It is the common code 16representation used throughout all phases of the LLVM compilation 17strategy. 18 19Introduction 20============ 21 22The LLVM code representation is designed to be used in three different 23forms: 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 25readable assembly language representation. This allows LLVM to provide a 26powerful intermediate representation for efficient compiler 27transformations and analysis, while providing a natural means to debug 28and visualize the transformations. The three different forms of LLVM are 29all equivalent. This document describes the human readable 30representation and notation. 31 32The LLVM representation aims to be light-weight and low-level while 33being expressive, typed, and extensible at the same time. It aims to be 34a "universal IR" of sorts, by being at a low enough level that 35high-level ideas may be cleanly mapped to it (similar to how 36microprocessors are "universal IR's", allowing many source languages to 37be mapped to them). By providing type information, LLVM can be used as 38the target of optimizations: for example, through pointer analysis, it 39can be proven that a C automatic variable is never accessed outside of 40the current function, allowing it to be promoted to a simple SSA value 41instead of a memory location. 42 43.. _wellformed: 44 45Well-Formedness 46--------------- 47 48It is important to note that this document describes 'well formed' LLVM 49assembly language. There is a difference between what the parser accepts 50and what is considered 'well formed'. For example, the following 51instruction is syntactically okay, but not well formed: 52 53.. code-block:: llvm 54 55 %x = add i32 1, %x 56 57because the definition of ``%x`` does not dominate all of its uses. The 58LLVM infrastructure provides a verification pass that may be used to 59verify that an LLVM module is well formed. This pass is automatically 60run by the parser after parsing input assembly and by the optimizer 61before it outputs bitcode. The violations pointed out by the verifier 62pass indicate bugs in transformation passes or input to the parser. 63 64.. _identifiers: 65 66Identifiers 67=========== 68 69LLVM identifiers come in two basic types: global and local. Global 70identifiers (functions, global variables) begin with the ``'@'`` 71character. Local identifiers (register names, types) begin with the 72``'%'`` character. Additionally, there are three different formats for 73identifiers, for different purposes: 74 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. 87 88LLVM requires that values start with a prefix for two reasons: Compilers 89don't need to worry about name clashes with reserved words, and the set 90of reserved words may be expanded in the future without penalty. 91Additionally, unnamed identifiers allow a compiler to quickly come up 92with a temporary variable without having to avoid symbol table 93conflicts. 94 95Reserved words in LLVM are very similar to reserved words in other 96languages. 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 99with variable names, because none of them start with a prefix character 100(``'%'`` or ``'@'``). 101 102Here is an example of LLVM code to multiply the integer variable 103'``%X``' by 8: 104 105The easy way: 106 107.. code-block:: llvm 108 109 %result = mul i32 %X, 8 110 111After strength reduction: 112 113.. code-block:: llvm 114 115 %result = shl i32 %X, 3 116 117And the hard way: 118 119.. code-block:: llvm 120 121 %0 = add i32 %X, %X ; yields i32:%0 122 %1 = add i32 %0, %0 ; yields i32:%1 123 %result = add i32 %1, %1 124 125This last way of multiplying ``%X`` by 8 illustrates several important 126lexical features of LLVM: 127 128#. 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. 136 137It also shows a convention that we follow in this document. When 138demonstrating instructions, we will follow an instruction with a comment 139that defines the type and name of value produced. 140 141High Level Structure 142==================== 143 144Module Structure 145---------------- 146 147LLVM programs are composed of ``Module``'s, each of which is a 148translation unit of the input programs. Each module consists of 149functions, global variables, and symbol table entries. Modules may be 150combined together with the LLVM linker, which merges function (and 151global variable) definitions, resolves forward declarations, and merges 152symbol table entries. Here is an example of the "hello world" module: 153 154.. code-block:: llvm 155 156 ; Declare the string constant as a global constant. 157 @.str = private unnamed_addr constant [13 x i8] c"hello world\0A\00" 158 159 ; External declaration of the puts function 160 declare i32 @puts(i8* nocapture) nounwind 161 162 ; 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 0 166 167 ; Call puts function to write out the string to stdout. 168 call i32 @puts(i8* %cast210) 169 ret i32 0 170 } 171 172 ; Named metadata 173 !0 = !{i32 42, null, !"string"} 174 !foo = !{!0} 175 176This 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``". 180 181In general, a module is made up of a list of global values (where both 182functions and global variables are global values). Global values are 183represented by a pointer to a memory location (in this case, a pointer 184to an array of char, and a pointer to a function), and have one of the 185following :ref:`linkage types <linkage>`. 186 187.. _linkage: 188 189Linkage Types 190------------- 191 192All Global Variables and Functions have one of the following types of 193linkage: 194 195``private`` 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. 202``internal`` 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 into 208 the object file corresponding to the LLVM module. From the linker's 209 perspective, an ``available_externally`` global is equivalent to 210 an external declaration. They exist to allow inlining and other 211 optimizations to take place given knowledge of the definition of the 212 global, which is known to be somewhere outside the module. Globals 213 with ``available_externally`` linkage are allowed to be discarded at 214 will, and allow inlining and other optimizations. This linkage type is 215 only allowed on definitions, not declarations. 216``linkonce`` 217 Globals with "``linkonce``" linkage are merged with other globals of 218 the same name when linkage occurs. This can be used to implement 219 some forms of inline functions, templates, or other code which must 220 be generated in each translation unit that uses it, but where the 221 body may be overridden with a more definitive definition later. 222 Unreferenced ``linkonce`` globals are allowed to be discarded. Note 223 that ``linkonce`` linkage does not actually allow the optimizer to 224 inline the body of this function into callers because it doesn't 225 know if this definition of the function is the definitive definition 226 within the program or whether it will be overridden by a stronger 227 definition. To enable inlining and other optimizations, use 228 "``linkonce_odr``" linkage. 229``weak`` 230 "``weak``" linkage has the same merging semantics as ``linkonce`` 231 linkage, except that unreferenced globals with ``weak`` linkage may 232 not be discarded. This is used for globals that are declared "weak" 233 in C source code. 234``common`` 235 "``common``" linkage is most similar to "``weak``" linkage, but they 236 are used for tentative definitions in C, such as "``int X;``" at 237 global scope. Symbols with "``common``" linkage are merged in the 238 same way as ``weak symbols``, and they may not be deleted if 239 unreferenced. ``common`` symbols may not have an explicit section, 240 must have a zero initializer, and may not be marked 241 ':ref:`constant <globalvars>`'. Functions and aliases may not have 242 common linkage. 243 244.. _linkage_appending: 245 246``appending`` 247 "``appending``" linkage may only be applied to global variables of 248 pointer to array type. When two global variables with appending 249 linkage are linked together, the two global arrays are appended 250 together. This is the LLVM, typesafe, equivalent of having the 251 system linker append together "sections" with identical names when 252 .o files are linked. 253 254 Unfortunately this doesn't correspond to any feature in .o files, so it 255 can only be used for variables like ``llvm.global_ctors`` which llvm 256 interprets specially. 257 258``extern_weak`` 259 The semantics of this linkage follow the ELF object file model: the 260 symbol is weak until linked, if not linked, the symbol becomes null 261 instead of being an undefined reference. 262``linkonce_odr``, ``weak_odr`` 263 Some languages allow differing globals to be merged, such as two 264 functions with different semantics. Other languages, such as 265 ``C++``, ensure that only equivalent globals are ever merged (the 266 "one definition rule" --- "ODR"). Such languages can use the 267 ``linkonce_odr`` and ``weak_odr`` linkage types to indicate that the 268 global will only be merged with equivalent globals. These linkage 269 types are otherwise the same as their non-``odr`` versions. 270``external`` 271 If none of the above identifiers are used, the global is externally 272 visible, meaning that it participates in linkage and can be used to 273 resolve external symbol references. 274 275It is illegal for a function *declaration* to have any linkage type 276other than ``external`` or ``extern_weak``. 277 278.. _callingconv: 279 280Calling Conventions 281------------------- 282 283LLVM :ref:`functions <functionstructure>`, :ref:`calls <i_call>` and 284:ref:`invokes <i_invoke>` can all have an optional calling convention 285specified for the call. The calling convention of any pair of dynamic 286caller/callee must match, or the behavior of the program is undefined. 287The following calling conventions are supported by LLVM, and more may be 288added in the future: 289 290"``ccc``" - The C calling convention 291 This calling convention (the default if no other calling convention 292 is specified) matches the target C calling conventions. This calling 293 convention supports varargs function calls and tolerates some 294 mismatch in the declared prototype and implemented declaration of 295 the function (as does normal C). 296"``fastcc``" - The fast calling convention 297 This calling convention attempts to make calls as fast as possible 298 (e.g. by passing things in registers). This calling convention 299 allows the target to use whatever tricks it wants to produce fast 300 code for the target, without having to conform to an externally 301 specified ABI (Application Binary Interface). `Tail calls can only 302 be optimized when this, the GHC or the HiPE convention is 303 used. <CodeGenerator.html#id80>`_ This calling convention does not 304 support varargs and requires the prototype of all callees to exactly 305 match the prototype of the function definition. 306"``coldcc``" - The cold calling convention 307 This calling convention attempts to make code in the caller as 308 efficient as possible under the assumption that the call is not 309 commonly executed. As such, these calls often preserve all registers 310 so that the call does not break any live ranges in the caller side. 311 This calling convention does not support varargs and requires the 312 prototype of all callees to exactly match the prototype of the 313 function definition. Furthermore the inliner doesn't consider such function 314 calls for inlining. 315"``cc 10``" - GHC convention 316 This calling convention has been implemented specifically for use by 317 the `Glasgow Haskell Compiler (GHC) <http://www.haskell.org/ghc>`_. 318 It passes everything in registers, going to extremes to achieve this 319 by disabling callee save registers. This calling convention should 320 not be used lightly but only for specific situations such as an 321 alternative to the *register pinning* performance technique often 322 used when implementing functional programming languages. At the 323 moment only X86 supports this convention and it has the following 324 limitations: 325 326 - On *X86-32* only supports up to 4 bit type parameters. No 327 floating point types are supported. 328 - On *X86-64* only supports up to 10 bit type parameters and 6 329 floating point parameters. 330 331 This calling convention supports `tail call 332 optimization <CodeGenerator.html#id80>`_ but requires both the 333 caller and callee are using it. 334"``cc 11``" - The HiPE calling convention 335 This calling convention has been implemented specifically for use by 336 the `High-Performance Erlang 337 (HiPE) <http://www.it.uu.se/research/group/hipe/>`_ compiler, *the* 338 native code compiler of the `Ericsson's Open Source Erlang/OTP 339 system <http://www.erlang.org/download.shtml>`_. It uses more 340 registers for argument passing than the ordinary C calling 341 convention and defines no callee-saved registers. The calling 342 convention properly supports `tail call 343 optimization <CodeGenerator.html#id80>`_ but requires that both the 344 caller and the callee use it. It uses a *register pinning* 345 mechanism, similar to GHC's convention, for keeping frequently 346 accessed runtime components pinned to specific hardware registers. 347 At the moment only X86 supports this convention (both 32 and 64 348 bit). 349"``webkit_jscc``" - WebKit's JavaScript calling convention 350 This calling convention has been implemented for `WebKit FTL JIT 351 <https://trac.webkit.org/wiki/FTLJIT>`_. It passes arguments on the 352 stack right to left (as cdecl does), and returns a value in the 353 platform's customary return register. 354"``anyregcc``" - Dynamic calling convention for code patching 355 This is a special convention that supports patching an arbitrary code 356 sequence in place of a call site. This convention forces the call 357 arguments into registers but allows them to be dynamically 358 allocated. This can currently only be used with calls to 359 llvm.experimental.patchpoint because only this intrinsic records 360 the location of its arguments in a side table. See :doc:`StackMaps`. 361"``preserve_mostcc``" - The `PreserveMost` calling convention 362 This calling convention attempts to make the code in the caller as 363 unintrusive as possible. This convention behaves identically to the `C` 364 calling convention on how arguments and return values are passed, but it 365 uses a different set of caller/callee-saved registers. This alleviates the 366 burden of saving and recovering a large register set before and after the 367 call in the caller. If the arguments are passed in callee-saved registers, 368 then they will be preserved by the callee across the call. This doesn't 369 apply for values returned in callee-saved registers. 370 371 - On X86-64 the callee preserves all general purpose registers, except for 372 R11. R11 can be used as a scratch register. Floating-point registers 373 (XMMs/YMMs) are not preserved and need to be saved by the caller. 374 375 The idea behind this convention is to support calls to runtime functions 376 that have a hot path and a cold path. The hot path is usually a small piece 377 of code that doesn't use many registers. The cold path might need to call out to 378 another function and therefore only needs to preserve the caller-saved 379 registers, which haven't already been saved by the caller. The 380 `PreserveMost` calling convention is very similar to the `cold` calling 381 convention in terms of caller/callee-saved registers, but they are used for 382 different types of function calls. `coldcc` is for function calls that are 383 rarely executed, whereas `preserve_mostcc` function calls are intended to be 384 on the hot path and definitely executed a lot. Furthermore `preserve_mostcc` 385 doesn't prevent the inliner from inlining the function call. 386 387 This calling convention will be used by a future version of the ObjectiveC 388 runtime and should therefore still be considered experimental at this time. 389 Although this convention was created to optimize certain runtime calls to 390 the ObjectiveC runtime, it is not limited to this runtime and might be used 391 by other runtimes in the future too. The current implementation only 392 supports X86-64, but the intention is to support more architectures in the 393 future. 394"``preserve_allcc``" - The `PreserveAll` calling convention 395 This calling convention attempts to make the code in the caller even less 396 intrusive than the `PreserveMost` calling convention. This calling 397 convention also behaves identical to the `C` calling convention on how 398 arguments and return values are passed, but it uses a different set of 399 caller/callee-saved registers. This removes the burden of saving and 400 recovering a large register set before and after the call in the caller. If 401 the arguments are passed in callee-saved registers, then they will be 402 preserved by the callee across the call. This doesn't apply for values 403 returned in callee-saved registers. 404 405 - On X86-64 the callee preserves all general purpose registers, except for 406 R11. R11 can be used as a scratch register. Furthermore it also preserves 407 all floating-point registers (XMMs/YMMs). 408 409 The idea behind this convention is to support calls to runtime functions 410 that don't need to call out to any other functions. 411 412 This calling convention, like the `PreserveMost` calling convention, will be 413 used by a future version of the ObjectiveC runtime and should be considered 414 experimental at this time. 415"``cxx_fast_tlscc``" - The `CXX_FAST_TLS` calling convention for access functions 416 Clang generates an access function to access C++-style TLS. The access 417 function generally has an entry block, an exit block and an initialization 418 block that is run at the first time. The entry and exit blocks can access 419 a few TLS IR variables, each access will be lowered to a platform-specific 420 sequence. 421 422 This calling convention aims to minimize overhead in the caller by 423 preserving as many registers as possible (all the registers that are 424 perserved on the fast path, composed of the entry and exit blocks). 425 426 This calling convention behaves identical to the `C` calling convention on 427 how arguments and return values are passed, but it uses a different set of 428 caller/callee-saved registers. 429 430 Given that each platform has its own lowering sequence, hence its own set 431 of preserved registers, we can't use the existing `PreserveMost`. 432 433 - On X86-64 the callee preserves all general purpose registers, except for 434 RDI and RAX. 435"``swiftcc``" - This calling convention is used for Swift language. 436 - On X86-64 RCX and R8 are available for additional integer returns, and 437 XMM2 and XMM3 are available for additional FP/vector returns. 438 - On iOS platforms, we use AAPCS-VFP calling convention. 439"``cc <n>``" - Numbered convention 440 Any calling convention may be specified by number, allowing 441 target-specific calling conventions to be used. Target specific 442 calling conventions start at 64. 443 444More calling conventions can be added/defined on an as-needed basis, to 445support Pascal conventions or any other well-known target-independent 446convention. 447 448.. _visibilitystyles: 449 450Visibility Styles 451----------------- 452 453All Global Variables and Functions have one of the following visibility 454styles: 455 456"``default``" - Default style 457 On targets that use the ELF object file format, default visibility 458 means that the declaration is visible to other modules and, in 459 shared libraries, means that the declared entity may be overridden. 460 On Darwin, default visibility means that the declaration is visible 461 to other modules. Default visibility corresponds to "external 462 linkage" in the language. 463"``hidden``" - Hidden style 464 Two declarations of an object with hidden visibility refer to the 465 same object if they are in the same shared object. Usually, hidden 466 visibility indicates that the symbol will not be placed into the 467 dynamic symbol table, so no other module (executable or shared 468 library) can reference it directly. 469"``protected``" - Protected style 470 On ELF, protected visibility indicates that the symbol will be 471 placed in the dynamic symbol table, but that references within the 472 defining module will bind to the local symbol. That is, the symbol 473 cannot be overridden by another module. 474 475A symbol with ``internal`` or ``private`` linkage must have ``default`` 476visibility. 477 478.. _dllstorageclass: 479 480DLL Storage Classes 481------------------- 482 483All Global Variables, Functions and Aliases can have one of the following 484DLL storage class: 485 486``dllimport`` 487 "``dllimport``" causes the compiler to reference a function or variable via 488 a global pointer to a pointer that is set up by the DLL exporting the 489 symbol. On Microsoft Windows targets, the pointer name is formed by 490 combining ``__imp_`` and the function or variable name. 491``dllexport`` 492 "``dllexport``" causes the compiler to provide a global pointer to a pointer 493 in a DLL, so that it can be referenced with the ``dllimport`` attribute. On 494 Microsoft Windows targets, the pointer name is formed by combining 495 ``__imp_`` and the function or variable name. Since this storage class 496 exists for defining a dll interface, the compiler, assembler and linker know 497 it is externally referenced and must refrain from deleting the symbol. 498 499.. _tls_model: 500 501Thread Local Storage Models 502--------------------------- 503 504A variable may be defined as ``thread_local``, which means that it will 505not be shared by threads (each thread will have a separated copy of the 506variable). Not all targets support thread-local variables. Optionally, a 507TLS model may be specified: 508 509``localdynamic`` 510 For variables that are only used within the current shared library. 511``initialexec`` 512 For variables in modules that will not be loaded dynamically. 513``localexec`` 514 For variables defined in the executable and only used within it. 515 516If no explicit model is given, the "general dynamic" model is used. 517 518The models correspond to the ELF TLS models; see `ELF Handling For 519Thread-Local Storage <http://people.redhat.com/drepper/tls.pdf>`_ for 520more information on under which circumstances the different models may 521be used. The target may choose a different TLS model if the specified 522model is not supported, or if a better choice of model can be made. 523 524A model can also be specified in an alias, but then it only governs how 525the alias is accessed. It will not have any effect in the aliasee. 526 527For platforms without linker support of ELF TLS model, the -femulated-tls 528flag can be used to generate GCC compatible emulated TLS code. 529 530.. _namedtypes: 531 532Structure Types 533--------------- 534 535LLVM IR allows you to specify both "identified" and "literal" :ref:`structure 536types <t_struct>`. Literal types are uniqued structurally, but identified types 537are never uniqued. An :ref:`opaque structural type <t_opaque>` can also be used 538to forward declare a type that is not yet available. 539 540An example of an identified structure specification is: 541 542.. code-block:: llvm 543 544 %mytype = type { %mytype*, i32 } 545 546Prior to the LLVM 3.0 release, identified types were structurally uniqued. Only 547literal types are uniqued in recent versions of LLVM. 548 549.. _globalvars: 550 551Global Variables 552---------------- 553 554Global variables define regions of memory allocated at compilation time 555instead of run-time. 556 557Global variable definitions must be initialized. 558 559Global variables in other translation units can also be declared, in which 560case they don't have an initializer. 561 562Either global variable definitions or declarations may have an explicit section 563to be placed in and may have an optional explicit alignment specified. 564 565A variable may be defined as a global ``constant``, which indicates that 566the contents of the variable will **never** be modified (enabling better 567optimization, allowing the global data to be placed in the read-only 568section of an executable, etc). Note that variables that need runtime 569initialization cannot be marked ``constant`` as there is a store to the 570variable. 571 572LLVM explicitly allows *declarations* of global variables to be marked 573constant, even if the final definition of the global is not. This 574capability can be used to enable slightly better optimization of the 575program, but requires the language definition to guarantee that 576optimizations based on the 'constantness' are valid for the translation 577units that do not include the definition. 578 579As SSA values, global variables define pointer values that are in scope 580(i.e. they dominate) all basic blocks in the program. Global variables 581always define a pointer to their "content" type because they describe a 582region of memory, and all memory objects in LLVM are accessed through 583pointers. 584 585Global variables can be marked with ``unnamed_addr`` which indicates 586that the address is not significant, only the content. Constants marked 587like this can be merged with other constants if they have the same 588initializer. Note that a constant with significant address *can* be 589merged with a ``unnamed_addr`` constant, the result being a constant 590whose address is significant. 591 592If the ``local_unnamed_addr`` attribute is given, the address is known to 593not be significant within the module. 594 595A global variable may be declared to reside in a target-specific 596numbered address space. For targets that support them, address spaces 597may affect how optimizations are performed and/or what target 598instructions are used to access the variable. The default address space 599is zero. The address space qualifier must precede any other attributes. 600 601LLVM allows an explicit section to be specified for globals. If the 602target supports it, it will emit globals to the section specified. 603Additionally, the global can placed in a comdat if the target has the necessary 604support. 605 606By default, global initializers are optimized by assuming that global 607variables defined within the module are not modified from their 608initial values before the start of the global initializer. This is 609true even for variables potentially accessible from outside the 610module, including those with external linkage or appearing in 611``@llvm.used`` or dllexported variables. This assumption may be suppressed 612by marking the variable with ``externally_initialized``. 613 614An explicit alignment may be specified for a global, which must be a 615power of 2. If not present, or if the alignment is set to zero, the 616alignment of the global is set by the target to whatever it feels 617convenient. If an explicit alignment is specified, the global is forced 618to have exactly that alignment. Targets and optimizers are not allowed 619to over-align the global if the global has an assigned section. In this 620case, the extra alignment could be observable: for example, code could 621assume that the globals are densely packed in their section and try to 622iterate over them as an array, alignment padding would break this 623iteration. The maximum alignment is ``1 << 29``. 624 625Globals can also have a :ref:`DLL storage class <dllstorageclass>` and 626an optional list of attached :ref:`metadata <metadata>`, 627 628Variables and aliases can have a 629:ref:`Thread Local Storage Model <tls_model>`. 630 631Syntax:: 632 633 @<GlobalVarName> = [Linkage] [Visibility] [DLLStorageClass] [ThreadLocal] 634 [(unnamed_addr|local_unnamed_addr)] [AddrSpace] 635 [ExternallyInitialized] 636 <global | constant> <Type> [<InitializerConstant>] 637 [, section "name"] [, comdat [($name)]] 638 [, align <Alignment>] (, !name !N)* 639 640For example, the following defines a global in a numbered address space 641with an initializer, section, and alignment: 642 643.. code-block:: llvm 644 645 @G = addrspace(5) constant float 1.0, section "foo", align 4 646 647The following example just declares a global variable 648 649.. code-block:: llvm 650 651 @G = external global i32 652 653The following example defines a thread-local global with the 654``initialexec`` TLS model: 655 656.. code-block:: llvm 657 658 @G = thread_local(initialexec) global i32 0, align 4 659 660.. _functionstructure: 661 662Functions 663--------- 664 665LLVM function definitions consist of the "``define``" keyword, an 666optional :ref:`linkage type <linkage>`, an optional :ref:`visibility 667style <visibility>`, an optional :ref:`DLL storage class <dllstorageclass>`, 668an optional :ref:`calling convention <callingconv>`, 669an optional ``unnamed_addr`` attribute, a return type, an optional 670:ref:`parameter attribute <paramattrs>` for the return type, a function 671name, a (possibly empty) argument list (each with optional :ref:`parameter 672attributes <paramattrs>`), optional :ref:`function attributes <fnattrs>`, 673an optional section, an optional alignment, 674an optional :ref:`comdat <langref_comdats>`, 675an optional :ref:`garbage collector name <gc>`, an optional :ref:`prefix <prefixdata>`, 676an optional :ref:`prologue <prologuedata>`, 677an optional :ref:`personality <personalityfn>`, 678an optional list of attached :ref:`metadata <metadata>`, 679an opening curly brace, a list of basic blocks, and a closing curly brace. 680 681LLVM function declarations consist of the "``declare``" keyword, an 682optional :ref:`linkage type <linkage>`, an optional :ref:`visibility style 683<visibility>`, an optional :ref:`DLL storage class <dllstorageclass>`, an 684optional :ref:`calling convention <callingconv>`, an optional ``unnamed_addr`` 685or ``local_unnamed_addr`` attribute, a return type, an optional :ref:`parameter 686attribute <paramattrs>` for the return type, a function name, a possibly 687empty list of arguments, an optional alignment, an optional :ref:`garbage 688collector name <gc>`, an optional :ref:`prefix <prefixdata>`, and an optional 689:ref:`prologue <prologuedata>`. 690 691A function definition contains a list of basic blocks, forming the CFG (Control 692Flow Graph) for the function. Each basic block may optionally start with a label 693(giving the basic block a symbol table entry), contains a list of instructions, 694and ends with a :ref:`terminator <terminators>` instruction (such as a branch or 695function return). If an explicit label is not provided, a block is assigned an 696implicit numbered label, using the next value from the same counter as used for 697unnamed temporaries (:ref:`see above<identifiers>`). For example, if a function 698entry block does not have an explicit label, it will be assigned label "%0", 699then the first unnamed temporary in that block will be "%1", etc. 700 701The first basic block in a function is special in two ways: it is 702immediately executed on entrance to the function, and it is not allowed 703to have predecessor basic blocks (i.e. there can not be any branches to 704the entry block of a function). Because the block can have no 705predecessors, it also cannot have any :ref:`PHI nodes <i_phi>`. 706 707LLVM allows an explicit section to be specified for functions. If the 708target supports it, it will emit functions to the section specified. 709Additionally, the function can be placed in a COMDAT. 710 711An explicit alignment may be specified for a function. If not present, 712or if the alignment is set to zero, the alignment of the function is set 713by the target to whatever it feels convenient. If an explicit alignment 714is specified, the function is forced to have at least that much 715alignment. All alignments must be a power of 2. 716 717If the ``unnamed_addr`` attribute is given, the address is known to not 718be significant and two identical functions can be merged. 719 720If the ``local_unnamed_addr`` attribute is given, the address is known to 721not be significant within the module. 722 723Syntax:: 724 725 define [linkage] [visibility] [DLLStorageClass] 726 [cconv] [ret attrs] 727 <ResultType> @<FunctionName> ([argument list]) 728 [(unnamed_addr|local_unnamed_addr)] [fn Attrs] [section "name"] 729 [comdat [($name)]] [align N] [gc] [prefix Constant] 730 [prologue Constant] [personality Constant] (!name !N)* { ... } 731 732The argument list is a comma separated sequence of arguments where each 733argument is of the following form: 734 735Syntax:: 736 737 <type> [parameter Attrs] [name] 738 739 740.. _langref_aliases: 741 742Aliases 743------- 744 745Aliases, unlike function or variables, don't create any new data. They 746are just a new symbol and metadata for an existing position. 747 748Aliases have a name and an aliasee that is either a global value or a 749constant expression. 750 751Aliases may have an optional :ref:`linkage type <linkage>`, an optional 752:ref:`visibility style <visibility>`, an optional :ref:`DLL storage class 753<dllstorageclass>` and an optional :ref:`tls model <tls_model>`. 754 755Syntax:: 756 757 @<Name> = [Linkage] [Visibility] [DLLStorageClass] [ThreadLocal] [(unnamed_addr|local_unnamed_addr)] alias <AliaseeTy>, <AliaseeTy>* @<Aliasee> 758 759The linkage must be one of ``private``, ``internal``, ``linkonce``, ``weak``, 760``linkonce_odr``, ``weak_odr``, ``external``. Note that some system linkers 761might not correctly handle dropping a weak symbol that is aliased. 762 763Aliases that are not ``unnamed_addr`` are guaranteed to have the same address as 764the aliasee expression. ``unnamed_addr`` ones are only guaranteed to point 765to the same content. 766 767If the ``local_unnamed_addr`` attribute is given, the address is known to 768not be significant within the module. 769 770Since aliases are only a second name, some restrictions apply, of which 771some can only be checked when producing an object file: 772 773* The expression defining the aliasee must be computable at assembly 774 time. Since it is just a name, no relocations can be used. 775 776* No alias in the expression can be weak as the possibility of the 777 intermediate alias being overridden cannot be represented in an 778 object file. 779 780* No global value in the expression can be a declaration, since that 781 would require a relocation, which is not possible. 782 783.. _langref_ifunc: 784 785IFuncs 786------- 787 788IFuncs, like as aliases, don't create any new data or func. They are just a new 789symbol that dynamic linker resolves at runtime by calling a resolver function. 790 791IFuncs have a name and a resolver that is a function called by dynamic linker 792that returns address of another function associated with the name. 793 794IFunc may have an optional :ref:`linkage type <linkage>` and an optional 795:ref:`visibility style <visibility>`. 796 797Syntax:: 798 799 @<Name> = [Linkage] [Visibility] ifunc <IFuncTy>, <ResolverTy>* @<Resolver> 800 801 802.. _langref_comdats: 803 804Comdats 805------- 806 807Comdat IR provides access to COFF and ELF object file COMDAT functionality. 808 809Comdats have a name which represents the COMDAT key. All global objects that 810specify this key will only end up in the final object file if the linker chooses 811that key over some other key. Aliases are placed in the same COMDAT that their 812aliasee computes to, if any. 813 814Comdats have a selection kind to provide input on how the linker should 815choose between keys in two different object files. 816 817Syntax:: 818 819 $<Name> = comdat SelectionKind 820 821The selection kind must be one of the following: 822 823``any`` 824 The linker may choose any COMDAT key, the choice is arbitrary. 825``exactmatch`` 826 The linker may choose any COMDAT key but the sections must contain the 827 same data. 828``largest`` 829 The linker will choose the section containing the largest COMDAT key. 830``noduplicates`` 831 The linker requires that only section with this COMDAT key exist. 832``samesize`` 833 The linker may choose any COMDAT key but the sections must contain the 834 same amount of data. 835 836Note that the Mach-O platform doesn't support COMDATs and ELF only supports 837``any`` as a selection kind. 838 839Here is an example of a COMDAT group where a function will only be selected if 840the COMDAT key's section is the largest: 841 842.. code-block:: llvm 843 844 $foo = comdat largest 845 @foo = global i32 2, comdat($foo) 846 847 define void @bar() comdat($foo) { 848 ret void 849 } 850 851As a syntactic sugar the ``$name`` can be omitted if the name is the same as 852the global name: 853 854.. code-block:: llvm 855 856 $foo = comdat any 857 @foo = global i32 2, comdat 858 859 860In a COFF object file, this will create a COMDAT section with selection kind 861``IMAGE_COMDAT_SELECT_LARGEST`` containing the contents of the ``@foo`` symbol 862and another COMDAT section with selection kind 863``IMAGE_COMDAT_SELECT_ASSOCIATIVE`` which is associated with the first COMDAT 864section and contains the contents of the ``@bar`` symbol. 865 866There are some restrictions on the properties of the global object. 867It, or an alias to it, must have the same name as the COMDAT group when 868targeting COFF. 869The contents and size of this object may be used during link-time to determine 870which COMDAT groups get selected depending on the selection kind. 871Because the name of the object must match the name of the COMDAT group, the 872linkage of the global object must not be local; local symbols can get renamed 873if a collision occurs in the symbol table. 874 875The combined use of COMDATS and section attributes may yield surprising results. 876For example: 877 878.. code-block:: llvm 879 880 $foo = comdat any 881 $bar = comdat any 882 @g1 = global i32 42, section "sec", comdat($foo) 883 @g2 = global i32 42, section "sec", comdat($bar) 884 885From the object file perspective, this requires the creation of two sections 886with the same name. This is necessary because both globals belong to different 887COMDAT groups and COMDATs, at the object file level, are represented by 888sections. 889 890Note that certain IR constructs like global variables and functions may 891create COMDATs in the object file in addition to any which are specified using 892COMDAT IR. This arises when the code generator is configured to emit globals 893in individual sections (e.g. when `-data-sections` or `-function-sections` 894is supplied to `llc`). 895 896.. _namedmetadatastructure: 897 898Named Metadata 899-------------- 900 901Named metadata is a collection of metadata. :ref:`Metadata 902nodes <metadata>` (but not metadata strings) are the only valid 903operands for a named metadata. 904 905#. Named metadata are represented as a string of characters with the 906 metadata prefix. The rules for metadata names are the same as for 907 identifiers, but quoted names are not allowed. ``"\xx"`` type escapes 908 are still valid, which allows any character to be part of a name. 909 910Syntax:: 911 912 ; Some unnamed metadata nodes, which are referenced by the named metadata. 913 !0 = !{!"zero"} 914 !1 = !{!"one"} 915 !2 = !{!"two"} 916 ; A named metadata. 917 !name = !{!0, !1, !2} 918 919.. _paramattrs: 920 921Parameter Attributes 922-------------------- 923 924The return type and each parameter of a function type may have a set of 925*parameter attributes* associated with them. Parameter attributes are 926used to communicate additional information about the result or 927parameters of a function. Parameter attributes are considered to be part 928of the function, not of the function type, so functions with different 929parameter attributes can have the same function type. 930 931Parameter attributes are simple keywords that follow the type specified. 932If multiple parameter attributes are needed, they are space separated. 933For example: 934 935.. code-block:: llvm 936 937 declare i32 @printf(i8* noalias nocapture, ...) 938 declare i32 @atoi(i8 zeroext) 939 declare signext i8 @returns_signed_char() 940 941Note that any attributes for the function result (``nounwind``, 942``readonly``) come immediately after the argument list. 943 944Currently, only the following parameter attributes are defined: 945 946``zeroext`` 947 This indicates to the code generator that the parameter or return 948 value should be zero-extended to the extent required by the target's 949 ABI by the caller (for a parameter) or the callee (for a return value). 950``signext`` 951 This indicates to the code generator that the parameter or return 952 value should be sign-extended to the extent required by the target's 953 ABI (which is usually 32-bits) by the caller (for a parameter) or 954 the callee (for a return value). 955``inreg`` 956 This indicates that this parameter or return value should be treated 957 in a special target-dependent fashion while emitting code for 958 a function call or return (usually, by putting it in a register as 959 opposed to memory, though some targets use it to distinguish between 960 two different kinds of registers). Use of this attribute is 961 target-specific. 962``byval`` 963 This indicates that the pointer parameter should really be passed by 964 value to the function. The attribute implies that a hidden copy of 965 the pointee is made between the caller and the callee, so the callee 966 is unable to modify the value in the caller. This attribute is only 967 valid on LLVM pointer arguments. It is generally used to pass 968 structs and arrays by value, but is also valid on pointers to 969 scalars. The copy is considered to belong to the caller not the 970 callee (for example, ``readonly`` functions should not write to 971 ``byval`` parameters). This is not a valid attribute for return 972 values. 973 974 The byval attribute also supports specifying an alignment with the 975 align attribute. It indicates the alignment of the stack slot to 976 form and the known alignment of the pointer specified to the call 977 site. If the alignment is not specified, then the code generator 978 makes a target-specific assumption. 979 980.. _attr_inalloca: 981 982``inalloca`` 983 984 The ``inalloca`` argument attribute allows the caller to take the 985 address of outgoing stack arguments. An ``inalloca`` argument must 986 be a pointer to stack memory produced by an ``alloca`` instruction. 987 The alloca, or argument allocation, must also be tagged with the 988 inalloca keyword. Only the last argument may have the ``inalloca`` 989 attribute, and that argument is guaranteed to be passed in memory. 990 991 An argument allocation may be used by a call at most once because 992 the call may deallocate it. The ``inalloca`` attribute cannot be 993 used in conjunction with other attributes that affect argument 994 storage, like ``inreg``, ``nest``, ``sret``, or ``byval``. The 995 ``inalloca`` attribute also disables LLVM's implicit lowering of 996 large aggregate return values, which means that frontend authors 997 must lower them with ``sret`` pointers. 998 999 When the call site is reached, the argument allocation must have 1000 been the most recent stack allocation that is still live, or the 1001 results are undefined. It is possible to allocate additional stack 1002 space after an argument allocation and before its call site, but it 1003 must be cleared off with :ref:`llvm.stackrestore 1004 <int_stackrestore>`. 1005 1006 See :doc:`InAlloca` for more information on how to use this 1007 attribute. 1008 1009``sret`` 1010 This indicates that the pointer parameter specifies the address of a 1011 structure that is the return value of the function in the source 1012 program. This pointer must be guaranteed by the caller to be valid: 1013 loads and stores to the structure may be assumed by the callee 1014 not to trap and to be properly aligned. This may only be applied to 1015 the first parameter. This is not a valid attribute for return 1016 values. 1017 1018``align <n>`` 1019 This indicates that the pointer value may be assumed by the optimizer to 1020 have the specified alignment. 1021 1022 Note that this attribute has additional semantics when combined with the 1023 ``byval`` attribute. 1024 1025.. _noalias: 1026 1027``noalias`` 1028 This indicates that objects accessed via pointer values 1029 :ref:`based <pointeraliasing>` on the argument or return value are not also 1030 accessed, during the execution of the function, via pointer values not 1031 *based* on the argument or return value. The attribute on a return value 1032 also has additional semantics described below. The caller shares the 1033 responsibility with the callee for ensuring that these requirements are met. 1034 For further details, please see the discussion of the NoAlias response in 1035 :ref:`alias analysis <Must, May, or No>`. 1036 1037 Note that this definition of ``noalias`` is intentionally similar 1038 to the definition of ``restrict`` in C99 for function arguments. 1039 1040 For function return values, C99's ``restrict`` is not meaningful, 1041 while LLVM's ``noalias`` is. Furthermore, the semantics of the ``noalias`` 1042 attribute on return values are stronger than the semantics of the attribute 1043 when used on function arguments. On function return values, the ``noalias`` 1044 attribute indicates that the function acts like a system memory allocation 1045 function, returning a pointer to allocated storage disjoint from the 1046 storage for any other object accessible to the caller. 1047 1048``nocapture`` 1049 This indicates that the callee does not make any copies of the 1050 pointer that outlive the callee itself. This is not a valid 1051 attribute for return values. Addresses used in volatile operations 1052 are considered to be captured. 1053 1054.. _nest: 1055 1056``nest`` 1057 This indicates that the pointer parameter can be excised using the 1058 :ref:`trampoline intrinsics <int_trampoline>`. This is not a valid 1059 attribute for return values and can only be applied to one parameter. 1060 1061``returned`` 1062 This indicates that the function always returns the argument as its return 1063 value. This is a hint to the optimizer and code generator used when 1064 generating the caller, allowing value propagation, tail call optimization, 1065 and omission of register saves and restores in some cases; it is not 1066 checked or enforced when generating the callee. The parameter and the 1067 function return type must be valid operands for the 1068 :ref:`bitcast instruction <i_bitcast>`. This is not a valid attribute for 1069 return values and can only be applied to one parameter. 1070 1071``nonnull`` 1072 This indicates that the parameter or return pointer is not null. This 1073 attribute may only be applied to pointer typed parameters. This is not 1074 checked or enforced by LLVM, the caller must ensure that the pointer 1075 passed in is non-null, or the callee must ensure that the returned pointer 1076 is non-null. 1077 1078``dereferenceable(<n>)`` 1079 This indicates that the parameter or return pointer is dereferenceable. This 1080 attribute may only be applied to pointer typed parameters. A pointer that 1081 is dereferenceable can be loaded from speculatively without a risk of 1082 trapping. The number of bytes known to be dereferenceable must be provided 1083 in parentheses. It is legal for the number of bytes to be less than the 1084 size of the pointee type. The ``nonnull`` attribute does not imply 1085 dereferenceability (consider a pointer to one element past the end of an 1086 array), however ``dereferenceable(<n>)`` does imply ``nonnull`` in 1087 ``addrspace(0)`` (which is the default address space). 1088 1089``dereferenceable_or_null(<n>)`` 1090 This indicates that the parameter or return value isn't both 1091 non-null and non-dereferenceable (up to ``<n>`` bytes) at the same 1092 time. All non-null pointers tagged with 1093 ``dereferenceable_or_null(<n>)`` are ``dereferenceable(<n>)``. 1094 For address space 0 ``dereferenceable_or_null(<n>)`` implies that 1095 a pointer is exactly one of ``dereferenceable(<n>)`` or ``null``, 1096 and in other address spaces ``dereferenceable_or_null(<n>)`` 1097 implies that a pointer is at least one of ``dereferenceable(<n>)`` 1098 or ``null`` (i.e. it may be both ``null`` and 1099 ``dereferenceable(<n>)``). This attribute may only be applied to 1100 pointer typed parameters. 1101 1102``swiftself`` 1103 This indicates that the parameter is the self/context parameter. This is not 1104 a valid attribute for return values and can only be applied to one 1105 parameter. 1106 1107``swifterror`` 1108 This attribute is motivated to model and optimize Swift error handling. It 1109 can be applied to a parameter with pointer to pointer type or a 1110 pointer-sized alloca. At the call site, the actual argument that corresponds 1111 to a ``swifterror`` parameter has to come from a ``swifterror`` alloca. A 1112 ``swifterror`` value (either the parameter or the alloca) can only be loaded 1113 and stored from, or used as a ``swifterror`` argument. This is not a valid 1114 attribute for return values and can only be applied to one parameter. 1115 1116 These constraints allow the calling convention to optimize access to 1117 ``swifterror`` variables by associating them with a specific register at 1118 call boundaries rather than placing them in memory. Since this does change 1119 the calling convention, a function which uses the ``swifterror`` attribute 1120 on a parameter is not ABI-compatible with one which does not. 1121 1122 These constraints also allow LLVM to assume that a ``swifterror`` argument 1123 does not alias any other memory visible within a function and that a 1124 ``swifterror`` alloca passed as an argument does not escape. 1125 1126.. _gc: 1127 1128Garbage Collector Strategy Names 1129-------------------------------- 1130 1131Each function may specify a garbage collector strategy name, which is simply a 1132string: 1133 1134.. code-block:: llvm 1135 1136 define void @f() gc "name" { ... } 1137 1138The supported values of *name* includes those :ref:`built in to LLVM 1139<builtin-gc-strategies>` and any provided by loaded plugins. Specifying a GC 1140strategy will cause the compiler to alter its output in order to support the 1141named garbage collection algorithm. Note that LLVM itself does not contain a 1142garbage collector, this functionality is restricted to generating machine code 1143which can interoperate with a collector provided externally. 1144 1145.. _prefixdata: 1146 1147Prefix Data 1148----------- 1149 1150Prefix data is data associated with a function which the code 1151generator will emit immediately before the function's entrypoint. 1152The purpose of this feature is to allow frontends to associate 1153language-specific runtime metadata with specific functions and make it 1154available through the function pointer while still allowing the 1155function pointer to be called. 1156 1157To access the data for a given function, a program may bitcast the 1158function pointer to a pointer to the constant's type and dereference 1159index -1. This implies that the IR symbol points just past the end of 1160the prefix data. For instance, take the example of a function annotated 1161with a single ``i32``, 1162 1163.. code-block:: llvm 1164 1165 define void @f() prefix i32 123 { ... } 1166 1167The prefix data can be referenced as, 1168 1169.. code-block:: llvm 1170 1171 %0 = bitcast void* () @f to i32* 1172 %a = getelementptr inbounds i32, i32* %0, i32 -1 1173 %b = load i32, i32* %a 1174 1175Prefix data is laid out as if it were an initializer for a global variable 1176of the prefix data's type. The function will be placed such that the 1177beginning of the prefix data is aligned. This means that if the size 1178of the prefix data is not a multiple of the alignment size, the 1179function's entrypoint will not be aligned. If alignment of the 1180function's entrypoint is desired, padding must be added to the prefix 1181data. 1182 1183A function may have prefix data but no body. This has similar semantics 1184to the ``available_externally`` linkage in that the data may be used by the 1185optimizers but will not be emitted in the object file. 1186 1187.. _prologuedata: 1188 1189Prologue Data 1190------------- 1191 1192The ``prologue`` attribute allows arbitrary code (encoded as bytes) to 1193be inserted prior to the function body. This can be used for enabling 1194function hot-patching and instrumentation. 1195 1196To maintain the semantics of ordinary function calls, the prologue data must 1197have a particular format. Specifically, it must begin with a sequence of 1198bytes which decode to a sequence of machine instructions, valid for the 1199module's target, which transfer control to the point immediately succeeding 1200the prologue data, without performing any other visible action. This allows 1201the inliner and other passes to reason about the semantics of the function 1202definition without needing to reason about the prologue data. Obviously this 1203makes the format of the prologue data highly target dependent. 1204 1205A trivial example of valid prologue data for the x86 architecture is ``i8 144``, 1206which encodes the ``nop`` instruction: 1207 1208.. code-block:: llvm 1209 1210 define void @f() prologue i8 144 { ... } 1211 1212Generally prologue data can be formed by encoding a relative branch instruction 1213which skips the metadata, as in this example of valid prologue data for the 1214x86_64 architecture, where the first two bytes encode ``jmp .+10``: 1215 1216.. code-block:: llvm 1217 1218 %0 = type <{ i8, i8, i8* }> 1219 1220 define void @f() prologue %0 <{ i8 235, i8 8, i8* @md}> { ... } 1221 1222A function may have prologue data but no body. This has similar semantics 1223to the ``available_externally`` linkage in that the data may be used by the 1224optimizers but will not be emitted in the object file. 1225 1226.. _personalityfn: 1227 1228Personality Function 1229-------------------- 1230 1231The ``personality`` attribute permits functions to specify what function 1232to use for exception handling. 1233 1234.. _attrgrp: 1235 1236Attribute Groups 1237---------------- 1238 1239Attribute groups are groups of attributes that are referenced by objects within 1240the IR. They are important for keeping ``.ll`` files readable, because a lot of 1241functions will use the same set of attributes. In the degenerative case of a 1242``.ll`` file that corresponds to a single ``.c`` file, the single attribute 1243group will capture the important command line flags used to build that file. 1244 1245An attribute group is a module-level object. To use an attribute group, an 1246object references the attribute group's ID (e.g. ``#37``). An object may refer 1247to more than one attribute group. In that situation, the attributes from the 1248different groups are merged. 1249 1250Here is an example of attribute groups for a function that should always be 1251inlined, has a stack alignment of 4, and which shouldn't use SSE instructions: 1252 1253.. code-block:: llvm 1254 1255 ; Target-independent attributes: 1256 attributes #0 = { alwaysinline alignstack=4 } 1257 1258 ; Target-dependent attributes: 1259 attributes #1 = { "no-sse" } 1260 1261 ; Function @f has attributes: alwaysinline, alignstack=4, and "no-sse". 1262 define void @f() #0 #1 { ... } 1263 1264.. _fnattrs: 1265 1266Function Attributes 1267------------------- 1268 1269Function attributes are set to communicate additional information about 1270a function. Function attributes are considered to be part of the 1271function, not of the function type, so functions with different function 1272attributes can have the same function type. 1273 1274Function attributes are simple keywords that follow the type specified. 1275If multiple attributes are needed, they are space separated. For 1276example: 1277 1278.. code-block:: llvm 1279 1280 define void @f() noinline { ... } 1281 define void @f() alwaysinline { ... } 1282 define void @f() alwaysinline optsize { ... } 1283 define void @f() optsize { ... } 1284 1285``alignstack(<n>)`` 1286 This attribute indicates that, when emitting the prologue and 1287 epilogue, the backend should forcibly align the stack pointer. 1288 Specify the desired alignment, which must be a power of two, in 1289 parentheses. 1290``allocsize(<EltSizeParam>[, <NumEltsParam>])`` 1291 This attribute indicates that the annotated function will always return at 1292 least a given number of bytes (or null). Its arguments are zero-indexed 1293 parameter numbers; if one argument is provided, then it's assumed that at 1294 least ``CallSite.Args[EltSizeParam]`` bytes will be available at the 1295 returned pointer. If two are provided, then it's assumed that 1296 ``CallSite.Args[EltSizeParam] * CallSite.Args[NumEltsParam]`` bytes are 1297 available. The referenced parameters must be integer types. No assumptions 1298 are made about the contents of the returned block of memory. 1299``alwaysinline`` 1300 This attribute indicates that the inliner should attempt to inline 1301 this function into callers whenever possible, ignoring any active 1302 inlining size threshold for this caller. 1303``builtin`` 1304 This indicates that the callee function at a call site should be 1305 recognized as a built-in function, even though the function's declaration 1306 uses the ``nobuiltin`` attribute. This is only valid at call sites for 1307 direct calls to functions that are declared with the ``nobuiltin`` 1308 attribute. 1309``cold`` 1310 This attribute indicates that this function is rarely called. When 1311 computing edge weights, basic blocks post-dominated by a cold 1312 function call are also considered to be cold; and, thus, given low 1313 weight. 1314``convergent`` 1315 In some parallel execution models, there exist operations that cannot be 1316 made control-dependent on any additional values. We call such operations 1317 ``convergent``, and mark them with this attribute. 1318 1319 The ``convergent`` attribute may appear on functions or call/invoke 1320 instructions. When it appears on a function, it indicates that calls to 1321 this function should not be made control-dependent on additional values. 1322 For example, the intrinsic ``llvm.nvvm.barrier0`` is ``convergent``, so 1323 calls to this intrinsic cannot be made control-dependent on additional 1324 values. 1325 1326 When it appears on a call/invoke, the ``convergent`` attribute indicates 1327 that we should treat the call as though we're calling a convergent 1328 function. This is particularly useful on indirect calls; without this we 1329 may treat such calls as though the target is non-convergent. 1330 1331 The optimizer may remove the ``convergent`` attribute on functions when it 1332 can prove that the function does not execute any convergent operations. 1333 Similarly, the optimizer may remove ``convergent`` on calls/invokes when it 1334 can prove that the call/invoke cannot call a convergent function. 1335``inaccessiblememonly`` 1336 This attribute indicates that the function may only access memory that 1337 is not accessible by the module being compiled. This is a weaker form 1338 of ``readnone``. 1339``inaccessiblemem_or_argmemonly`` 1340 This attribute indicates that the function may only access memory that is 1341 either not accessible by the module being compiled, or is pointed to 1342 by its pointer arguments. This is a weaker form of ``argmemonly`` 1343``inlinehint`` 1344 This attribute indicates that the source code contained a hint that 1345 inlining this function is desirable (such as the "inline" keyword in 1346 C/C++). It is just a hint; it imposes no requirements on the 1347 inliner. 1348``jumptable`` 1349 This attribute indicates that the function should be added to a 1350 jump-instruction table at code-generation time, and that all address-taken 1351 references to this function should be replaced with a reference to the 1352 appropriate jump-instruction-table function pointer. Note that this creates 1353 a new pointer for the original function, which means that code that depends 1354 on function-pointer identity can break. So, any function annotated with 1355 ``jumptable`` must also be ``unnamed_addr``. 1356``minsize`` 1357 This attribute suggests that optimization passes and code generator 1358 passes make choices that keep the code size of this function as small 1359 as possible and perform optimizations that may sacrifice runtime 1360 performance in order to minimize the size of the generated code. 1361``naked`` 1362 This attribute disables prologue / epilogue emission for the 1363 function. This can have very system-specific consequences. 1364``nobuiltin`` 1365 This indicates that the callee function at a call site is not recognized as 1366 a built-in function. LLVM will retain the original call and not replace it 1367 with equivalent code based on the semantics of the built-in function, unless 1368 the call site uses the ``builtin`` attribute. This is valid at call sites 1369 and on function declarations and definitions. 1370``noduplicate`` 1371 This attribute indicates that calls to the function cannot be 1372 duplicated. A call to a ``noduplicate`` function may be moved 1373 within its parent function, but may not be duplicated within 1374 its parent function. 1375 1376 A function containing a ``noduplicate`` call may still 1377 be an inlining candidate, provided that the call is not 1378 duplicated by inlining. That implies that the function has 1379 internal linkage and only has one call site, so the original 1380 call is dead after inlining. 1381``noimplicitfloat`` 1382 This attributes disables implicit floating point instructions. 1383``noinline`` 1384 This attribute indicates that the inliner should never inline this 1385 function in any situation. This attribute may not be used together 1386 with the ``alwaysinline`` attribute. 1387``nonlazybind`` 1388 This attribute suppresses lazy symbol binding for the function. This 1389 may make calls to the function faster, at the cost of extra program 1390 startup time if the function is not called during program startup. 1391``noredzone`` 1392 This attribute indicates that the code generator should not use a 1393 red zone, even if the target-specific ABI normally permits it. 1394``noreturn`` 1395 This function attribute indicates that the function never returns 1396 normally. This produces undefined behavior at runtime if the 1397 function ever does dynamically return. 1398``norecurse`` 1399 This function attribute indicates that the function does not call itself 1400 either directly or indirectly down any possible call path. This produces 1401 undefined behavior at runtime if the function ever does recurse. 1402``nounwind`` 1403 This function attribute indicates that the function never raises an 1404 exception. If the function does raise an exception, its runtime 1405 behavior is undefined. However, functions marked nounwind may still 1406 trap or generate asynchronous exceptions. Exception handling schemes 1407 that are recognized by LLVM to handle asynchronous exceptions, such 1408 as SEH, will still provide their implementation defined semantics. 1409``optnone`` 1410 This function attribute indicates that most optimization passes will skip 1411 this function, with the exception of interprocedural optimization passes. 1412 Code generation defaults to the "fast" instruction selector. 1413 This attribute cannot be used together with the ``alwaysinline`` 1414 attribute; this attribute is also incompatible 1415 with the ``minsize`` attribute and the ``optsize`` attribute. 1416 1417 This attribute requires the ``noinline`` attribute to be specified on 1418 the function as well, so the function is never inlined into any caller. 1419 Only functions with the ``alwaysinline`` attribute are valid 1420 candidates for inlining into the body of this function. 1421``optsize`` 1422 This attribute suggests that optimization passes and code generator 1423 passes make choices that keep the code size of this function low, 1424 and otherwise do optimizations specifically to reduce code size as 1425 long as they do not significantly impact runtime performance. 1426``"patchable-function"`` 1427 This attribute tells the code generator that the code 1428 generated for this function needs to follow certain conventions that 1429 make it possible for a runtime function to patch over it later. 1430 The exact effect of this attribute depends on its string value, 1431 for which there currently is one legal possibility: 1432 1433 * ``"prologue-short-redirect"`` - This style of patchable 1434 function is intended to support patching a function prologue to 1435 redirect control away from the function in a thread safe 1436 manner. It guarantees that the first instruction of the 1437 function will be large enough to accommodate a short jump 1438 instruction, and will be sufficiently aligned to allow being 1439 fully changed via an atomic compare-and-swap instruction. 1440 While the first requirement can be satisfied by inserting large 1441 enough NOP, LLVM can and will try to re-purpose an existing 1442 instruction (i.e. one that would have to be emitted anyway) as 1443 the patchable instruction larger than a short jump. 1444 1445 ``"prologue-short-redirect"`` is currently only supported on 1446 x86-64. 1447 1448 This attribute by itself does not imply restrictions on 1449 inter-procedural optimizations. All of the semantic effects the 1450 patching may have to be separately conveyed via the linkage type. 1451``readnone`` 1452 On a function, this attribute indicates that the function computes its 1453 result (or decides to unwind an exception) based strictly on its arguments, 1454 without dereferencing any pointer arguments or otherwise accessing 1455 any mutable state (e.g. memory, control registers, etc) visible to 1456 caller functions. It does not write through any pointer arguments 1457 (including ``byval`` arguments) and never changes any state visible 1458 to callers. This means that it cannot unwind exceptions by calling 1459 the ``C++`` exception throwing methods. 1460 1461 On an argument, this attribute indicates that the function does not 1462 dereference that pointer argument, even though it may read or write the 1463 memory that the pointer points to if accessed through other pointers. 1464``readonly`` 1465 On a function, this attribute indicates that the function does not write 1466 through any pointer arguments (including ``byval`` arguments) or otherwise 1467 modify any state (e.g. memory, control registers, etc) visible to 1468 caller functions. It may dereference pointer arguments and read 1469 state that may be set in the caller. A readonly function always 1470 returns the same value (or unwinds an exception identically) when 1471 called with the same set of arguments and global state. It cannot 1472 unwind an exception by calling the ``C++`` exception throwing 1473 methods. 1474 1475 On an argument, this attribute indicates that the function does not write 1476 through this pointer argument, even though it may write to the memory that 1477 the pointer points to. 1478``writeonly`` 1479 On a function, this attribute indicates that the function may write to but 1480 does not read from memory. 1481 1482 On an argument, this attribute indicates that the function may write to but 1483 does not read through this pointer argument (even though it may read from 1484 the memory that the pointer points to). 1485``argmemonly`` 1486 This attribute indicates that the only memory accesses inside function are 1487 loads and stores from objects pointed to by its pointer-typed arguments, 1488 with arbitrary offsets. Or in other words, all memory operations in the 1489 function can refer to memory only using pointers based on its function 1490 arguments. 1491 Note that ``argmemonly`` can be used together with ``readonly`` attribute 1492 in order to specify that function reads only from its arguments. 1493``returns_twice`` 1494 This attribute indicates that this function can return twice. The C 1495 ``setjmp`` is an example of such a function. The compiler disables 1496 some optimizations (like tail calls) in the caller of these 1497 functions. 1498``safestack`` 1499 This attribute indicates that 1500 `SafeStack <http://clang.llvm.org/docs/SafeStack.html>`_ 1501 protection is enabled for this function. 1502 1503 If a function that has a ``safestack`` attribute is inlined into a 1504 function that doesn't have a ``safestack`` attribute or which has an 1505 ``ssp``, ``sspstrong`` or ``sspreq`` attribute, then the resulting 1506 function will have a ``safestack`` attribute. 1507``sanitize_address`` 1508 This attribute indicates that AddressSanitizer checks 1509 (dynamic address safety analysis) are enabled for this function. 1510``sanitize_memory`` 1511 This attribute indicates that MemorySanitizer checks (dynamic detection 1512 of accesses to uninitialized memory) are enabled for this function. 1513``sanitize_thread`` 1514 This attribute indicates that ThreadSanitizer checks 1515 (dynamic thread safety analysis) are enabled for this function. 1516``ssp`` 1517 This attribute indicates that the function should emit a stack 1518 smashing protector. It is in the form of a "canary" --- a random value 1519 placed on the stack before the local variables that's checked upon 1520 return from the function to see if it has been overwritten. A 1521 heuristic is used to determine if a function needs stack protectors 1522 or not. The heuristic used will enable protectors for functions with: 1523 1524 - Character arrays larger than ``ssp-buffer-size`` (default 8). 1525 - Aggregates containing character arrays larger than ``ssp-buffer-size``. 1526 - Calls to alloca() with variable sizes or constant sizes greater than 1527 ``ssp-buffer-size``. 1528 1529 Variables that are identified as requiring a protector will be arranged 1530 on the stack such that they are adjacent to the stack protector guard. 1531 1532 If a function that has an ``ssp`` attribute is inlined into a 1533 function that doesn't have an ``ssp`` attribute, then the resulting 1534 function will have an ``ssp`` attribute. 1535``sspreq`` 1536 This attribute indicates that the function should *always* emit a 1537 stack smashing protector. This overrides the ``ssp`` function 1538 attribute. 1539 1540 Variables that are identified as requiring a protector will be arranged 1541 on the stack such that they are adjacent to the stack protector guard. 1542 The specific layout rules are: 1543 1544 #. Large arrays and structures containing large arrays 1545 (``>= ssp-buffer-size``) are closest to the stack protector. 1546 #. Small arrays and structures containing small arrays 1547 (``< ssp-buffer-size``) are 2nd closest to the protector. 1548 #. Variables that have had their address taken are 3rd closest to the 1549 protector. 1550 1551 If a function that has an ``sspreq`` attribute is inlined into a 1552 function that doesn't have an ``sspreq`` attribute or which has an 1553 ``ssp`` or ``sspstrong`` attribute, then the resulting function will have 1554 an ``sspreq`` attribute. 1555``sspstrong`` 1556 This attribute indicates that the function should emit a stack smashing 1557 protector. This attribute causes a strong heuristic to be used when 1558 determining if a function needs stack protectors. The strong heuristic 1559 will enable protectors for functions with: 1560 1561 - Arrays of any size and type 1562 - Aggregates containing an array of any size and type. 1563 - Calls to alloca(). 1564 - Local variables that have had their address taken. 1565 1566 Variables that are identified as requiring a protector will be arranged 1567 on the stack such that they are adjacent to the stack protector guard. 1568 The specific layout rules are: 1569 1570 #. Large arrays and structures containing large arrays 1571 (``>= ssp-buffer-size``) are closest to the stack protector. 1572 #. Small arrays and structures containing small arrays 1573 (``< ssp-buffer-size``) are 2nd closest to the protector. 1574 #. Variables that have had their address taken are 3rd closest to the 1575 protector. 1576 1577 This overrides the ``ssp`` function attribute. 1578 1579 If a function that has an ``sspstrong`` attribute is inlined into a 1580 function that doesn't have an ``sspstrong`` attribute, then the 1581 resulting function will have an ``sspstrong`` attribute. 1582``"thunk"`` 1583 This attribute indicates that the function will delegate to some other 1584 function with a tail call. The prototype of a thunk should not be used for 1585 optimization purposes. The caller is expected to cast the thunk prototype to 1586 match the thunk target prototype. 1587``uwtable`` 1588 This attribute indicates that the ABI being targeted requires that 1589 an unwind table entry be produced for this function even if we can 1590 show that no exceptions passes by it. This is normally the case for 1591 the ELF x86-64 abi, but it can be disabled for some compilation 1592 units. 1593 1594 1595.. _opbundles: 1596 1597Operand Bundles 1598--------------- 1599 1600Note: operand bundles are a work in progress, and they should be 1601considered experimental at this time. 1602 1603Operand bundles are tagged sets of SSA values that can be associated 1604with certain LLVM instructions (currently only ``call`` s and 1605``invoke`` s). In a way they are like metadata, but dropping them is 1606incorrect and will change program semantics. 1607 1608Syntax:: 1609 1610 operand bundle set ::= '[' operand bundle (, operand bundle )* ']' 1611 operand bundle ::= tag '(' [ bundle operand ] (, bundle operand )* ')' 1612 bundle operand ::= SSA value 1613 tag ::= string constant 1614 1615Operand bundles are **not** part of a function's signature, and a 1616given function may be called from multiple places with different kinds 1617of operand bundles. This reflects the fact that the operand bundles 1618are conceptually a part of the ``call`` (or ``invoke``), not the 1619callee being dispatched to. 1620 1621Operand bundles are a generic mechanism intended to support 1622runtime-introspection-like functionality for managed languages. While 1623the exact semantics of an operand bundle depend on the bundle tag, 1624there are certain limitations to how much the presence of an operand 1625bundle can influence the semantics of a program. These restrictions 1626are described as the semantics of an "unknown" operand bundle. As 1627long as the behavior of an operand bundle is describable within these 1628restrictions, LLVM does not need to have special knowledge of the 1629operand bundle to not miscompile programs containing it. 1630 1631- The bundle operands for an unknown operand bundle escape in unknown 1632 ways before control is transferred to the callee or invokee. 1633- Calls and invokes with operand bundles have unknown read / write 1634 effect on the heap on entry and exit (even if the call target is 1635 ``readnone`` or ``readonly``), unless they're overridden with 1636 callsite specific attributes. 1637- An operand bundle at a call site cannot change the implementation 1638 of the called function. Inter-procedural optimizations work as 1639 usual as long as they take into account the first two properties. 1640 1641More specific types of operand bundles are described below. 1642 1643.. _deopt_opbundles: 1644 1645Deoptimization Operand Bundles 1646^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 1647 1648Deoptimization operand bundles are characterized by the ``"deopt"`` 1649operand bundle tag. These operand bundles represent an alternate 1650"safe" continuation for the call site they're attached to, and can be 1651used by a suitable runtime to deoptimize the compiled frame at the 1652specified call site. There can be at most one ``"deopt"`` operand 1653bundle attached to a call site. Exact details of deoptimization is 1654out of scope for the language reference, but it usually involves 1655rewriting a compiled frame into a set of interpreted frames. 1656 1657From the compiler's perspective, deoptimization operand bundles make 1658the call sites they're attached to at least ``readonly``. They read 1659through all of their pointer typed operands (even if they're not 1660otherwise escaped) and the entire visible heap. Deoptimization 1661operand bundles do not capture their operands except during 1662deoptimization, in which case control will not be returned to the 1663compiled frame. 1664 1665The inliner knows how to inline through calls that have deoptimization 1666operand bundles. Just like inlining through a normal call site 1667involves composing the normal and exceptional continuations, inlining 1668through a call site with a deoptimization operand bundle needs to 1669appropriately compose the "safe" deoptimization continuation. The 1670inliner does this by prepending the parent's deoptimization 1671continuation to every deoptimization continuation in the inlined body. 1672E.g. inlining ``@f`` into ``@g`` in the following example 1673 1674.. code-block:: llvm 1675 1676 define void @f() { 1677 call void @x() ;; no deopt state 1678 call void @y() [ "deopt"(i32 10) ] 1679 call void @y() [ "deopt"(i32 10), "unknown"(i8* null) ] 1680 ret void 1681 } 1682 1683 define void @g() { 1684 call void @f() [ "deopt"(i32 20) ] 1685 ret void 1686 } 1687 1688will result in 1689 1690.. code-block:: llvm 1691 1692 define void @g() { 1693 call void @x() ;; still no deopt state 1694 call void @y() [ "deopt"(i32 20, i32 10) ] 1695 call void @y() [ "deopt"(i32 20, i32 10), "unknown"(i8* null) ] 1696 ret void 1697 } 1698 1699It is the frontend's responsibility to structure or encode the 1700deoptimization state in a way that syntactically prepending the 1701caller's deoptimization state to the callee's deoptimization state is 1702semantically equivalent to composing the caller's deoptimization 1703continuation after the callee's deoptimization continuation. 1704 1705.. _ob_funclet: 1706 1707Funclet Operand Bundles 1708^^^^^^^^^^^^^^^^^^^^^^^ 1709 1710Funclet operand bundles are characterized by the ``"funclet"`` 1711operand bundle tag. These operand bundles indicate that a call site 1712is within a particular funclet. There can be at most one 1713``"funclet"`` operand bundle attached to a call site and it must have 1714exactly one bundle operand. 1715 1716If any funclet EH pads have been "entered" but not "exited" (per the 1717`description in the EH doc\ <ExceptionHandling.html#wineh-constraints>`_), 1718it is undefined behavior to execute a ``call`` or ``invoke`` which: 1719 1720* does not have a ``"funclet"`` bundle and is not a ``call`` to a nounwind 1721 intrinsic, or 1722* has a ``"funclet"`` bundle whose operand is not the most-recently-entered 1723 not-yet-exited funclet EH pad. 1724 1725Similarly, if no funclet EH pads have been entered-but-not-yet-exited, 1726executing a ``call`` or ``invoke`` with a ``"funclet"`` bundle is undefined behavior. 1727 1728GC Transition Operand Bundles 1729^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 1730 1731GC transition operand bundles are characterized by the 1732``"gc-transition"`` operand bundle tag. These operand bundles mark a 1733call as a transition between a function with one GC strategy to a 1734function with a different GC strategy. If coordinating the transition 1735between GC strategies requires additional code generation at the call 1736site, these bundles may contain any values that are needed by the 1737generated code. For more details, see :ref:`GC Transitions 1738<gc_transition_args>`. 1739 1740.. _moduleasm: 1741 1742Module-Level Inline Assembly 1743---------------------------- 1744 1745Modules may contain "module-level inline asm" blocks, which corresponds 1746to the GCC "file scope inline asm" blocks. These blocks are internally 1747concatenated by LLVM and treated as a single unit, but may be separated 1748in the ``.ll`` file if desired. The syntax is very simple: 1749 1750.. code-block:: llvm 1751 1752 module asm "inline asm code goes here" 1753 module asm "more can go here" 1754 1755The strings can contain any character by escaping non-printable 1756characters. The escape sequence used is simply "\\xx" where "xx" is the 1757two digit hex code for the number. 1758 1759Note that the assembly string *must* be parseable by LLVM's integrated assembler 1760(unless it is disabled), even when emitting a ``.s`` file. 1761 1762.. _langref_datalayout: 1763 1764Data Layout 1765----------- 1766 1767A module may specify a target specific data layout string that specifies 1768how data is to be laid out in memory. The syntax for the data layout is 1769simply: 1770 1771.. code-block:: llvm 1772 1773 target datalayout = "layout specification" 1774 1775The *layout specification* consists of a list of specifications 1776separated by the minus sign character ('-'). Each specification starts 1777with a letter and may include other information after the letter to 1778define some aspect of the data layout. The specifications accepted are 1779as follows: 1780 1781``E`` 1782 Specifies that the target lays out data in big-endian form. That is, 1783 the bits with the most significance have the lowest address 1784 location. 1785``e`` 1786 Specifies that the target lays out data in little-endian form. That 1787 is, the bits with the least significance have the lowest address 1788 location. 1789``S<size>`` 1790 Specifies the natural alignment of the stack in bits. Alignment 1791 promotion of stack variables is limited to the natural stack 1792 alignment to avoid dynamic stack realignment. The stack alignment 1793 must be a multiple of 8-bits. If omitted, the natural stack 1794 alignment defaults to "unspecified", which does not prevent any 1795 alignment promotions. 1796``p[n]:<size>:<abi>:<pref>`` 1797 This specifies the *size* of a pointer and its ``<abi>`` and 1798 ``<pref>``\erred alignments for address space ``n``. All sizes are in 1799 bits. The address space, ``n``, is optional, and if not specified, 1800 denotes the default address space 0. The value of ``n`` must be 1801 in the range [1,2^23). 1802``i<size>:<abi>:<pref>`` 1803 This specifies the alignment for an integer type of a given bit 1804 ``<size>``. The value of ``<size>`` must be in the range [1,2^23). 1805``v<size>:<abi>:<pref>`` 1806 This specifies the alignment for a vector type of a given bit 1807 ``<size>``. 1808``f<size>:<abi>:<pref>`` 1809 This specifies the alignment for a floating point type of a given bit 1810 ``<size>``. Only values of ``<size>`` that are supported by the target 1811 will work. 32 (float) and 64 (double) are supported on all targets; 80 1812 or 128 (different flavors of long double) are also supported on some 1813 targets. 1814``a:<abi>:<pref>`` 1815 This specifies the alignment for an object of aggregate type. 1816``m:<mangling>`` 1817 If present, specifies that llvm names are mangled in the output. The 1818 options are 1819 1820 * ``e``: ELF mangling: Private symbols get a ``.L`` prefix. 1821 * ``m``: Mips mangling: Private symbols get a ``$`` prefix. 1822 * ``o``: Mach-O mangling: Private symbols get ``L`` prefix. Other 1823 symbols get a ``_`` prefix. 1824 * ``w``: Windows COFF prefix: Similar to Mach-O, but stdcall and fastcall 1825 functions also get a suffix based on the frame size. 1826 * ``x``: Windows x86 COFF prefix: Similar to Windows COFF, but use a ``_`` 1827 prefix for ``__cdecl`` functions. 1828``n<size1>:<size2>:<size3>...`` 1829 This specifies a set of native integer widths for the target CPU in 1830 bits. For example, it might contain ``n32`` for 32-bit PowerPC, 1831 ``n32:64`` for PowerPC 64, or ``n8:16:32:64`` for X86-64. Elements of 1832 this set are considered to support most general arithmetic operations 1833 efficiently. 1834 1835On every specification that takes a ``<abi>:<pref>``, specifying the 1836``<pref>`` alignment is optional. If omitted, the preceding ``:`` 1837should be omitted too and ``<pref>`` will be equal to ``<abi>``. 1838 1839When constructing the data layout for a given target, LLVM starts with a 1840default set of specifications which are then (possibly) overridden by 1841the specifications in the ``datalayout`` keyword. The default 1842specifications are given in this list: 1843 1844- ``E`` - big endian 1845- ``p:64:64:64`` - 64-bit pointers with 64-bit alignment. 1846- ``p[n]:64:64:64`` - Other address spaces are assumed to be the 1847 same as the default address space. 1848- ``S0`` - natural stack alignment is unspecified 1849- ``i1:8:8`` - i1 is 8-bit (byte) aligned 1850- ``i8:8:8`` - i8 is 8-bit (byte) aligned 1851- ``i16:16:16`` - i16 is 16-bit aligned 1852- ``i32:32:32`` - i32 is 32-bit aligned 1853- ``i64:32:64`` - i64 has ABI alignment of 32-bits but preferred 1854 alignment of 64-bits 1855- ``f16:16:16`` - half is 16-bit aligned 1856- ``f32:32:32`` - float is 32-bit aligned 1857- ``f64:64:64`` - double is 64-bit aligned 1858- ``f128:128:128`` - quad is 128-bit aligned 1859- ``v64:64:64`` - 64-bit vector is 64-bit aligned 1860- ``v128:128:128`` - 128-bit vector is 128-bit aligned 1861- ``a:0:64`` - aggregates are 64-bit aligned 1862 1863When LLVM is determining the alignment for a given type, it uses the 1864following rules: 1865 1866#. If the type sought is an exact match for one of the specifications, 1867 that specification is used. 1868#. If no match is found, and the type sought is an integer type, then 1869 the smallest integer type that is larger than the bitwidth of the 1870 sought type is used. If none of the specifications are larger than 1871 the bitwidth then the largest integer type is used. For example, 1872 given the default specifications above, the i7 type will use the 1873 alignment of i8 (next largest) while both i65 and i256 will use the 1874 alignment of i64 (largest specified). 1875#. If no match is found, and the type sought is a vector type, then the 1876 largest vector type that is smaller than the sought vector type will 1877 be used as a fall back. This happens because <128 x double> can be 1878 implemented in terms of 64 <2 x double>, for example. 1879 1880The function of the data layout string may not be what you expect. 1881Notably, this is not a specification from the frontend of what alignment 1882the code generator should use. 1883 1884Instead, if specified, the target data layout is required to match what 1885the ultimate *code generator* expects. This string is used by the 1886mid-level optimizers to improve code, and this only works if it matches 1887what the ultimate code generator uses. There is no way to generate IR 1888that does not embed this target-specific detail into the IR. If you 1889don't specify the string, the default specifications will be used to 1890generate a Data Layout and the optimization phases will operate 1891accordingly and introduce target specificity into the IR with respect to 1892these default specifications. 1893 1894.. _langref_triple: 1895 1896Target Triple 1897------------- 1898 1899A module may specify a target triple string that describes the target 1900host. The syntax for the target triple is simply: 1901 1902.. code-block:: llvm 1903 1904 target triple = "x86_64-apple-macosx10.7.0" 1905 1906The *target triple* string consists of a series of identifiers delimited 1907by the minus sign character ('-'). The canonical forms are: 1908 1909:: 1910 1911 ARCHITECTURE-VENDOR-OPERATING_SYSTEM 1912 ARCHITECTURE-VENDOR-OPERATING_SYSTEM-ENVIRONMENT 1913 1914This information is passed along to the backend so that it generates 1915code for the proper architecture. It's possible to override this on the 1916command line with the ``-mtriple`` command line option. 1917 1918.. _pointeraliasing: 1919 1920Pointer Aliasing Rules 1921---------------------- 1922 1923Any memory access must be done through a pointer value associated with 1924an address range of the memory access, otherwise the behavior is 1925undefined. Pointer values are associated with address ranges according 1926to the following rules: 1927 1928- A pointer value is associated with the addresses associated with any 1929 value it is *based* on. 1930- An address of a global variable is associated with the address range 1931 of the variable's storage. 1932- The result value of an allocation instruction is associated with the 1933 address range of the allocated storage. 1934- A null pointer in the default address-space is associated with no 1935 address. 1936- An integer constant other than zero or a pointer value returned from 1937 a function not defined within LLVM may be associated with address 1938 ranges allocated through mechanisms other than those provided by 1939 LLVM. Such ranges shall not overlap with any ranges of addresses 1940 allocated by mechanisms provided by LLVM. 1941 1942A pointer value is *based* on another pointer value according to the 1943following rules: 1944 1945- A pointer value formed from a ``getelementptr`` operation is *based* 1946 on the first value operand of the ``getelementptr``. 1947- The result value of a ``bitcast`` is *based* on the operand of the 1948 ``bitcast``. 1949- A pointer value formed by an ``inttoptr`` is *based* on all pointer 1950 values that contribute (directly or indirectly) to the computation of 1951 the pointer's value. 1952- The "*based* on" relationship is transitive. 1953 1954Note that this definition of *"based"* is intentionally similar to the 1955definition of *"based"* in C99, though it is slightly weaker. 1956 1957LLVM IR does not associate types with memory. The result type of a 1958``load`` merely indicates the size and alignment of the memory from 1959which to load, as well as the interpretation of the value. The first 1960operand type of a ``store`` similarly only indicates the size and 1961alignment of the store. 1962 1963Consequently, type-based alias analysis, aka TBAA, aka 1964``-fstrict-aliasing``, is not applicable to general unadorned LLVM IR. 1965:ref:`Metadata <metadata>` may be used to encode additional information 1966which specialized optimization passes may use to implement type-based 1967alias analysis. 1968 1969.. _volatile: 1970 1971Volatile Memory Accesses 1972------------------------ 1973 1974Certain memory accesses, such as :ref:`load <i_load>`'s, 1975:ref:`store <i_store>`'s, and :ref:`llvm.memcpy <int_memcpy>`'s may be 1976marked ``volatile``. The optimizers must not change the number of 1977volatile operations or change their order of execution relative to other 1978volatile operations. The optimizers *may* change the order of volatile 1979operations relative to non-volatile operations. This is not Java's 1980"volatile" and has no cross-thread synchronization behavior. 1981 1982IR-level volatile loads and stores cannot safely be optimized into 1983llvm.memcpy or llvm.memmove intrinsics even when those intrinsics are 1984flagged volatile. Likewise, the backend should never split or merge 1985target-legal volatile load/store instructions. 1986 1987.. admonition:: Rationale 1988 1989 Platforms may rely on volatile loads and stores of natively supported 1990 data width to be executed as single instruction. For example, in C 1991 this holds for an l-value of volatile primitive type with native 1992 hardware support, but not necessarily for aggregate types. The 1993 frontend upholds these expectations, which are intentionally 1994 unspecified in the IR. The rules above ensure that IR transformations 1995 do not violate the frontend's contract with the language. 1996 1997.. _memmodel: 1998 1999Memory Model for Concurrent Operations 2000-------------------------------------- 2001 2002The LLVM IR does not define any way to start parallel threads of 2003execution or to register signal handlers. Nonetheless, there are 2004platform-specific ways to create them, and we define LLVM IR's behavior 2005in their presence. This model is inspired by the C++0x memory model. 2006 2007For a more informal introduction to this model, see the :doc:`Atomics`. 2008 2009We define a *happens-before* partial order as the least partial order 2010that 2011 2012- Is a superset of single-thread program order, and 2013- When a *synchronizes-with* ``b``, includes an edge from ``a`` to 2014 ``b``. *Synchronizes-with* pairs are introduced by platform-specific 2015 techniques, like pthread locks, thread creation, thread joining, 2016 etc., and by atomic instructions. (See also :ref:`Atomic Memory Ordering 2017 Constraints <ordering>`). 2018 2019Note that program order does not introduce *happens-before* edges 2020between a thread and signals executing inside that thread. 2021 2022Every (defined) read operation (load instructions, memcpy, atomic 2023loads/read-modify-writes, etc.) R reads a series of bytes written by 2024(defined) write operations (store instructions, atomic 2025stores/read-modify-writes, memcpy, etc.). For the purposes of this 2026section, initialized globals are considered to have a write of the 2027initializer which is atomic and happens before any other read or write 2028of the memory in question. For each byte of a read R, R\ :sub:`byte` 2029may see any write to the same byte, except: 2030 2031- If write\ :sub:`1` happens before write\ :sub:`2`, and 2032 write\ :sub:`2` happens before R\ :sub:`byte`, then 2033 R\ :sub:`byte` does not see write\ :sub:`1`. 2034- If R\ :sub:`byte` happens before write\ :sub:`3`, then 2035 R\ :sub:`byte` does not see write\ :sub:`3`. 2036 2037Given that definition, R\ :sub:`byte` is defined as follows: 2038 2039- If R is volatile, the result is target-dependent. (Volatile is 2040 supposed to give guarantees which can support ``sig_atomic_t`` in 2041 C/C++, and may be used for accesses to addresses that do not behave 2042 like normal memory. It does not generally provide cross-thread 2043 synchronization.) 2044- Otherwise, if there is no write to the same byte that happens before 2045 R\ :sub:`byte`, R\ :sub:`byte` returns ``undef`` for that byte. 2046- Otherwise, if R\ :sub:`byte` may see exactly one write, 2047 R\ :sub:`byte` returns the value written by that write. 2048- Otherwise, if R is atomic, and all the writes R\ :sub:`byte` may 2049 see are atomic, it chooses one of the values written. See the :ref:`Atomic 2050 Memory Ordering Constraints <ordering>` section for additional 2051 constraints on how the choice is made. 2052- Otherwise R\ :sub:`byte` returns ``undef``. 2053 2054R returns the value composed of the series of bytes it read. This 2055implies that some bytes within the value may be ``undef`` **without** 2056the entire value being ``undef``. Note that this only defines the 2057semantics of the operation; it doesn't mean that targets will emit more 2058than one instruction to read the series of bytes. 2059 2060Note that in cases where none of the atomic intrinsics are used, this 2061model places only one restriction on IR transformations on top of what 2062is required for single-threaded execution: introducing a store to a byte 2063which might not otherwise be stored is not allowed in general. 2064(Specifically, in the case where another thread might write to and read 2065from an address, introducing a store can change a load that may see 2066exactly one write into a load that may see multiple writes.) 2067 2068.. _ordering: 2069 2070Atomic Memory Ordering Constraints 2071---------------------------------- 2072 2073Atomic instructions (:ref:`cmpxchg <i_cmpxchg>`, 2074:ref:`atomicrmw <i_atomicrmw>`, :ref:`fence <i_fence>`, 2075:ref:`atomic load <i_load>`, and :ref:`atomic store <i_store>`) take 2076ordering parameters that determine which other atomic instructions on 2077the same address they *synchronize with*. These semantics are borrowed 2078from Java and C++0x, but are somewhat more colloquial. If these 2079descriptions aren't precise enough, check those specs (see spec 2080references in the :doc:`atomics guide <Atomics>`). 2081:ref:`fence <i_fence>` instructions treat these orderings somewhat 2082differently since they don't take an address. See that instruction's 2083documentation for details. 2084 2085For a simpler introduction to the ordering constraints, see the 2086:doc:`Atomics`. 2087 2088``unordered`` 2089 The set of values that can be read is governed by the happens-before 2090 partial order. A value cannot be read unless some operation wrote 2091 it. This is intended to provide a guarantee strong enough to model 2092 Java's non-volatile shared variables. This ordering cannot be 2093 specified for read-modify-write operations; it is not strong enough 2094 to make them atomic in any interesting way. 2095``monotonic`` 2096 In addition to the guarantees of ``unordered``, there is a single 2097 total order for modifications by ``monotonic`` operations on each 2098 address. All modification orders must be compatible with the 2099 happens-before order. There is no guarantee that the modification 2100 orders can be combined to a global total order for the whole program 2101 (and this often will not be possible). The read in an atomic 2102 read-modify-write operation (:ref:`cmpxchg <i_cmpxchg>` and 2103 :ref:`atomicrmw <i_atomicrmw>`) reads the value in the modification 2104 order immediately before the value it writes. If one atomic read 2105 happens before another atomic read of the same address, the later 2106 read must see the same value or a later value in the address's 2107 modification order. This disallows reordering of ``monotonic`` (or 2108 stronger) operations on the same address. If an address is written 2109 ``monotonic``-ally by one thread, and other threads ``monotonic``-ally 2110 read that address repeatedly, the other threads must eventually see 2111 the write. This corresponds to the C++0x/C1x 2112 ``memory_order_relaxed``. 2113``acquire`` 2114 In addition to the guarantees of ``monotonic``, a 2115 *synchronizes-with* edge may be formed with a ``release`` operation. 2116 This is intended to model C++'s ``memory_order_acquire``. 2117``release`` 2118 In addition to the guarantees of ``monotonic``, if this operation 2119 writes a value which is subsequently read by an ``acquire`` 2120 operation, it *synchronizes-with* that operation. (This isn't a 2121 complete description; see the C++0x definition of a release 2122 sequence.) This corresponds to the C++0x/C1x 2123 ``memory_order_release``. 2124``acq_rel`` (acquire+release) 2125 Acts as both an ``acquire`` and ``release`` operation on its 2126 address. This corresponds to the C++0x/C1x ``memory_order_acq_rel``. 2127``seq_cst`` (sequentially consistent) 2128 In addition to the guarantees of ``acq_rel`` (``acquire`` for an 2129 operation that only reads, ``release`` for an operation that only 2130 writes), there is a global total order on all 2131 sequentially-consistent operations on all addresses, which is 2132 consistent with the *happens-before* partial order and with the 2133 modification orders of all the affected addresses. Each 2134 sequentially-consistent read sees the last preceding write to the 2135 same address in this global order. This corresponds to the C++0x/C1x 2136 ``memory_order_seq_cst`` and Java volatile. 2137 2138.. _singlethread: 2139 2140If an atomic operation is marked ``singlethread``, it only *synchronizes 2141with* or participates in modification and seq\_cst total orderings with 2142other operations running in the same thread (for example, in signal 2143handlers). 2144 2145.. _fastmath: 2146 2147Fast-Math Flags 2148--------------- 2149 2150LLVM IR floating-point binary ops (:ref:`fadd <i_fadd>`, 2151:ref:`fsub <i_fsub>`, :ref:`fmul <i_fmul>`, :ref:`fdiv <i_fdiv>`, 2152:ref:`frem <i_frem>`, :ref:`fcmp <i_fcmp>`) have the following flags that can 2153be set to enable otherwise unsafe floating point operations 2154 2155``nnan`` 2156 No NaNs - Allow optimizations to assume the arguments and result are not 2157 NaN. Such optimizations are required to retain defined behavior over 2158 NaNs, but the value of the result is undefined. 2159 2160``ninf`` 2161 No Infs - Allow optimizations to assume the arguments and result are not 2162 +/-Inf. Such optimizations are required to retain defined behavior over 2163 +/-Inf, but the value of the result is undefined. 2164 2165``nsz`` 2166 No Signed Zeros - Allow optimizations to treat the sign of a zero 2167 argument or result as insignificant. 2168 2169``arcp`` 2170 Allow Reciprocal - Allow optimizations to use the reciprocal of an 2171 argument rather than perform division. 2172 2173``fast`` 2174 Fast - Allow algebraically equivalent transformations that may 2175 dramatically change results in floating point (e.g. reassociate). This 2176 flag implies all the others. 2177 2178.. _uselistorder: 2179 2180Use-list Order Directives 2181------------------------- 2182 2183Use-list directives encode the in-memory order of each use-list, allowing the 2184order to be recreated. ``<order-indexes>`` is a comma-separated list of 2185indexes that are assigned to the referenced value's uses. The referenced 2186value's use-list is immediately sorted by these indexes. 2187 2188Use-list directives may appear at function scope or global scope. They are not 2189instructions, and have no effect on the semantics of the IR. When they're at 2190function scope, they must appear after the terminator of the final basic block. 2191 2192If basic blocks have their address taken via ``blockaddress()`` expressions, 2193``uselistorder_bb`` can be used to reorder their use-lists from outside their 2194function's scope. 2195 2196:Syntax: 2197 2198:: 2199 2200 uselistorder <ty> <value>, { <order-indexes> } 2201 uselistorder_bb @function, %block { <order-indexes> } 2202 2203:Examples: 2204 2205:: 2206 2207 define void @foo(i32 %arg1, i32 %arg2) { 2208 entry: 2209 ; ... instructions ... 2210 bb: 2211 ; ... instructions ... 2212 2213 ; At function scope. 2214 uselistorder i32 %arg1, { 1, 0, 2 } 2215 uselistorder label %bb, { 1, 0 } 2216 } 2217 2218 ; At global scope. 2219 uselistorder i32* @global, { 1, 2, 0 } 2220 uselistorder i32 7, { 1, 0 } 2221 uselistorder i32 (i32) @bar, { 1, 0 } 2222 uselistorder_bb @foo, %bb, { 5, 1, 3, 2, 0, 4 } 2223 2224.. _source_filename: 2225 2226Source Filename 2227--------------- 2228 2229The *source filename* string is set to the original module identifier, 2230which will be the name of the compiled source file when compiling from 2231source through the clang front end, for example. It is then preserved through 2232the IR and bitcode. 2233 2234This is currently necessary to generate a consistent unique global 2235identifier for local functions used in profile data, which prepends the 2236source file name to the local function name. 2237 2238The syntax for the source file name is simply: 2239 2240.. code-block:: llvm 2241 2242 source_filename = "/path/to/source.c" 2243 2244.. _typesystem: 2245 2246Type System 2247=========== 2248 2249The LLVM type system is one of the most important features of the 2250intermediate representation. Being typed enables a number of 2251optimizations to be performed on the intermediate representation 2252directly, without having to do extra analyses on the side before the 2253transformation. A strong type system makes it easier to read the 2254generated code and enables novel analyses and transformations that are 2255not feasible to perform on normal three address code representations. 2256 2257.. _t_void: 2258 2259Void Type 2260--------- 2261 2262:Overview: 2263 2264 2265The void type does not represent any value and has no size. 2266 2267:Syntax: 2268 2269 2270:: 2271 2272 void 2273 2274 2275.. _t_function: 2276 2277Function Type 2278------------- 2279 2280:Overview: 2281 2282 2283The function type can be thought of as a function signature. It consists of a 2284return type and a list of formal parameter types. The return type of a function 2285type is a void type or first class type --- except for :ref:`label <t_label>` 2286and :ref:`metadata <t_metadata>` types. 2287 2288:Syntax: 2289 2290:: 2291 2292 <returntype> (<parameter list>) 2293 2294...where '``<parameter list>``' is a comma-separated list of type 2295specifiers. Optionally, the parameter list may include a type ``...``, which 2296indicates that the function takes a variable number of arguments. Variable 2297argument functions can access their arguments with the :ref:`variable argument 2298handling intrinsic <int_varargs>` functions. '``<returntype>``' is any type 2299except :ref:`label <t_label>` and :ref:`metadata <t_metadata>`. 2300 2301:Examples: 2302 2303+---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 2304| ``i32 (i32)`` | function taking an ``i32``, returning an ``i32`` | 2305+---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 2306| ``float (i16, i32 *) *`` | :ref:`Pointer <t_pointer>` to a function that takes an ``i16`` and a :ref:`pointer <t_pointer>` to ``i32``, returning ``float``. | 2307+---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 2308| ``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. | 2309+---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 2310| ``{i32, i32} (i32)`` | A function taking an ``i32``, returning a :ref:`structure <t_struct>` containing two ``i32`` values | 2311+---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 2312 2313.. _t_firstclass: 2314 2315First Class Types 2316----------------- 2317 2318The :ref:`first class <t_firstclass>` types are perhaps the most important. 2319Values of these types are the only ones which can be produced by 2320instructions. 2321 2322.. _t_single_value: 2323 2324Single Value Types 2325^^^^^^^^^^^^^^^^^^ 2326 2327These are the types that are valid in registers from CodeGen's perspective. 2328 2329.. _t_integer: 2330 2331Integer Type 2332"""""""""""" 2333 2334:Overview: 2335 2336The integer type is a very simple type that simply specifies an 2337arbitrary bit width for the integer type desired. Any bit width from 1 2338bit to 2\ :sup:`23`\ -1 (about 8 million) can be specified. 2339 2340:Syntax: 2341 2342:: 2343 2344 iN 2345 2346The number of bits the integer will occupy is specified by the ``N`` 2347value. 2348 2349Examples: 2350********* 2351 2352+----------------+------------------------------------------------+ 2353| ``i1`` | a single-bit integer. | 2354+----------------+------------------------------------------------+ 2355| ``i32`` | a 32-bit integer. | 2356+----------------+------------------------------------------------+ 2357| ``i1942652`` | a really big integer of over 1 million bits. | 2358+----------------+------------------------------------------------+ 2359 2360.. _t_floating: 2361 2362Floating Point Types 2363"""""""""""""""""""" 2364 2365.. list-table:: 2366 :header-rows: 1 2367 2368 * - Type 2369 - Description 2370 2371 * - ``half`` 2372 - 16-bit floating point value 2373 2374 * - ``float`` 2375 - 32-bit floating point value 2376 2377 * - ``double`` 2378 - 64-bit floating point value 2379 2380 * - ``fp128`` 2381 - 128-bit floating point value (112-bit mantissa) 2382 2383 * - ``x86_fp80`` 2384 - 80-bit floating point value (X87) 2385 2386 * - ``ppc_fp128`` 2387 - 128-bit floating point value (two 64-bits) 2388 2389X86_mmx Type 2390"""""""""""" 2391 2392:Overview: 2393 2394The x86_mmx type represents a value held in an MMX register on an x86 2395machine. The operations allowed on it are quite limited: parameters and 2396return values, load and store, and bitcast. User-specified MMX 2397instructions are represented as intrinsic or asm calls with arguments 2398and/or results of this type. There are no arrays, vectors or constants 2399of this type. 2400 2401:Syntax: 2402 2403:: 2404 2405 x86_mmx 2406 2407 2408.. _t_pointer: 2409 2410Pointer Type 2411"""""""""""" 2412 2413:Overview: 2414 2415The pointer type is used to specify memory locations. Pointers are 2416commonly used to reference objects in memory. 2417 2418Pointer types may have an optional address space attribute defining the 2419numbered address space where the pointed-to object resides. The default 2420address space is number zero. The semantics of non-zero address spaces 2421are target-specific. 2422 2423Note that LLVM does not permit pointers to void (``void*``) nor does it 2424permit pointers to labels (``label*``). Use ``i8*`` instead. 2425 2426:Syntax: 2427 2428:: 2429 2430 <type> * 2431 2432:Examples: 2433 2434+-------------------------+--------------------------------------------------------------------------------------------------------------+ 2435| ``[4 x i32]*`` | A :ref:`pointer <t_pointer>` to :ref:`array <t_array>` of four ``i32`` values. | 2436+-------------------------+--------------------------------------------------------------------------------------------------------------+ 2437| ``i32 (i32*) *`` | A :ref:`pointer <t_pointer>` to a :ref:`function <t_function>` that takes an ``i32*``, returning an ``i32``. | 2438+-------------------------+--------------------------------------------------------------------------------------------------------------+ 2439| ``i32 addrspace(5)*`` | A :ref:`pointer <t_pointer>` to an ``i32`` value that resides in address space #5. | 2440+-------------------------+--------------------------------------------------------------------------------------------------------------+ 2441 2442.. _t_vector: 2443 2444Vector Type 2445""""""""""" 2446 2447:Overview: 2448 2449A vector type is a simple derived type that represents a vector of 2450elements. Vector types are used when multiple primitive data are 2451operated in parallel using a single instruction (SIMD). A vector type 2452requires a size (number of elements) and an underlying primitive data 2453type. Vector types are considered :ref:`first class <t_firstclass>`. 2454 2455:Syntax: 2456 2457:: 2458 2459 < <# elements> x <elementtype> > 2460 2461The number of elements is a constant integer value larger than 0; 2462elementtype may be any integer, floating point or pointer type. Vectors 2463of size zero are not allowed. 2464 2465:Examples: 2466 2467+-------------------+--------------------------------------------------+ 2468| ``<4 x i32>`` | Vector of 4 32-bit integer values. | 2469+-------------------+--------------------------------------------------+ 2470| ``<8 x float>`` | Vector of 8 32-bit floating-point values. | 2471+-------------------+--------------------------------------------------+ 2472| ``<2 x i64>`` | Vector of 2 64-bit integer values. | 2473+-------------------+--------------------------------------------------+ 2474| ``<4 x i64*>`` | Vector of 4 pointers to 64-bit integer values. | 2475+-------------------+--------------------------------------------------+ 2476 2477.. _t_label: 2478 2479Label Type 2480^^^^^^^^^^ 2481 2482:Overview: 2483 2484The label type represents code labels. 2485 2486:Syntax: 2487 2488:: 2489 2490 label 2491 2492.. _t_token: 2493 2494Token Type 2495^^^^^^^^^^ 2496 2497:Overview: 2498 2499The token type is used when a value is associated with an instruction 2500but all uses of the value must not attempt to introspect or obscure it. 2501As such, it is not appropriate to have a :ref:`phi <i_phi>` or 2502:ref:`select <i_select>` of type token. 2503 2504:Syntax: 2505 2506:: 2507 2508 token 2509 2510 2511 2512.. _t_metadata: 2513 2514Metadata Type 2515^^^^^^^^^^^^^ 2516 2517:Overview: 2518 2519The metadata type represents embedded metadata. No derived types may be 2520created from metadata except for :ref:`function <t_function>` arguments. 2521 2522:Syntax: 2523 2524:: 2525 2526 metadata 2527 2528.. _t_aggregate: 2529 2530Aggregate Types 2531^^^^^^^^^^^^^^^ 2532 2533Aggregate Types are a subset of derived types that can contain multiple 2534member types. :ref:`Arrays <t_array>` and :ref:`structs <t_struct>` are 2535aggregate types. :ref:`Vectors <t_vector>` are not considered to be 2536aggregate types. 2537 2538.. _t_array: 2539 2540Array Type 2541"""""""""" 2542 2543:Overview: 2544 2545The array type is a very simple derived type that arranges elements 2546sequentially in memory. The array type requires a size (number of 2547elements) and an underlying data type. 2548 2549:Syntax: 2550 2551:: 2552 2553 [<# elements> x <elementtype>] 2554 2555The number of elements is a constant integer value; ``elementtype`` may 2556be any type with a size. 2557 2558:Examples: 2559 2560+------------------+--------------------------------------+ 2561| ``[40 x i32]`` | Array of 40 32-bit integer values. | 2562+------------------+--------------------------------------+ 2563| ``[41 x i32]`` | Array of 41 32-bit integer values. | 2564+------------------+--------------------------------------+ 2565| ``[4 x i8]`` | Array of 4 8-bit integer values. | 2566+------------------+--------------------------------------+ 2567 2568Here are some examples of multidimensional arrays: 2569 2570+-----------------------------+----------------------------------------------------------+ 2571| ``[3 x [4 x i32]]`` | 3x4 array of 32-bit integer values. | 2572+-----------------------------+----------------------------------------------------------+ 2573| ``[12 x [10 x float]]`` | 12x10 array of single precision floating point values. | 2574+-----------------------------+----------------------------------------------------------+ 2575| ``[2 x [3 x [4 x i16]]]`` | 2x3x4 array of 16-bit integer values. | 2576+-----------------------------+----------------------------------------------------------+ 2577 2578There is no restriction on indexing beyond the end of the array implied 2579by a static type (though there are restrictions on indexing beyond the 2580bounds of an allocated object in some cases). This means that 2581single-dimension 'variable sized array' addressing can be implemented in 2582LLVM with a zero length array type. An implementation of 'pascal style 2583arrays' in LLVM could use the type "``{ i32, [0 x float]}``", for 2584example. 2585 2586.. _t_struct: 2587 2588Structure Type 2589"""""""""""""" 2590 2591:Overview: 2592 2593The structure type is used to represent a collection of data members 2594together in memory. The elements of a structure may be any type that has 2595a size. 2596 2597Structures in memory are accessed using '``load``' and '``store``' by 2598getting a pointer to a field with the '``getelementptr``' instruction. 2599Structures in registers are accessed using the '``extractvalue``' and 2600'``insertvalue``' instructions. 2601 2602Structures may optionally be "packed" structures, which indicate that 2603the alignment of the struct is one byte, and that there is no padding 2604between the elements. In non-packed structs, padding between field types 2605is inserted as defined by the DataLayout string in the module, which is 2606required to match what the underlying code generator expects. 2607 2608Structures can either be "literal" or "identified". A literal structure 2609is defined inline with other types (e.g. ``{i32, i32}*``) whereas 2610identified types are always defined at the top level with a name. 2611Literal types are uniqued by their contents and can never be recursive 2612or opaque since there is no way to write one. Identified types can be 2613recursive, can be opaqued, and are never uniqued. 2614 2615:Syntax: 2616 2617:: 2618 2619 %T1 = type { <type list> } ; Identified normal struct type 2620 %T2 = type <{ <type list> }> ; Identified packed struct type 2621 2622:Examples: 2623 2624+------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 2625| ``{ i32, i32, i32 }`` | A triple of three ``i32`` values | 2626+------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 2627| ``{ 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``. | 2628+------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 2629| ``<{ i8, i32 }>`` | A packed struct known to be 5 bytes in size. | 2630+------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 2631 2632.. _t_opaque: 2633 2634Opaque Structure Types 2635"""""""""""""""""""""" 2636 2637:Overview: 2638 2639Opaque structure types are used to represent named structure types that 2640do not have a body specified. This corresponds (for example) to the C 2641notion of a forward declared structure. 2642 2643:Syntax: 2644 2645:: 2646 2647 %X = type opaque 2648 %52 = type opaque 2649 2650:Examples: 2651 2652+--------------+-------------------+ 2653| ``opaque`` | An opaque type. | 2654+--------------+-------------------+ 2655 2656.. _constants: 2657 2658Constants 2659========= 2660 2661LLVM has several different basic types of constants. This section 2662describes them all and their syntax. 2663 2664Simple Constants 2665---------------- 2666 2667**Boolean constants** 2668 The two strings '``true``' and '``false``' are both valid constants 2669 of the ``i1`` type. 2670**Integer constants** 2671 Standard integers (such as '4') are constants of the 2672 :ref:`integer <t_integer>` type. Negative numbers may be used with 2673 integer types. 2674**Floating point constants** 2675 Floating point constants use standard decimal notation (e.g. 2676 123.421), exponential notation (e.g. 1.23421e+2), or a more precise 2677 hexadecimal notation (see below). The assembler requires the exact 2678 decimal value of a floating-point constant. For example, the 2679 assembler accepts 1.25 but rejects 1.3 because 1.3 is a repeating 2680 decimal in binary. Floating point constants must have a :ref:`floating 2681 point <t_floating>` type. 2682**Null pointer constants** 2683 The identifier '``null``' is recognized as a null pointer constant 2684 and must be of :ref:`pointer type <t_pointer>`. 2685**Token constants** 2686 The identifier '``none``' is recognized as an empty token constant 2687 and must be of :ref:`token type <t_token>`. 2688 2689The one non-intuitive notation for constants is the hexadecimal form of 2690floating point constants. For example, the form 2691'``double 0x432ff973cafa8000``' is equivalent to (but harder to read 2692than) '``double 4.5e+15``'. The only time hexadecimal floating point 2693constants are required (and the only time that they are generated by the 2694disassembler) is when a floating point constant must be emitted but it 2695cannot be represented as a decimal floating point number in a reasonable 2696number of digits. For example, NaN's, infinities, and other special 2697values are represented in their IEEE hexadecimal format so that assembly 2698and disassembly do not cause any bits to change in the constants. 2699 2700When using the hexadecimal form, constants of types half, float, and 2701double are represented using the 16-digit form shown above (which 2702matches the IEEE754 representation for double); half and float values 2703must, however, be exactly representable as IEEE 754 half and single 2704precision, respectively. Hexadecimal format is always used for long 2705double, and there are three forms of long double. The 80-bit format used 2706by x86 is represented as ``0xK`` followed by 20 hexadecimal digits. The 2707128-bit format used by PowerPC (two adjacent doubles) is represented by 2708``0xM`` followed by 32 hexadecimal digits. The IEEE 128-bit format is 2709represented by ``0xL`` followed by 32 hexadecimal digits. Long doubles 2710will only work if they match the long double format on your target. 2711The IEEE 16-bit format (half precision) is represented by ``0xH`` 2712followed by 4 hexadecimal digits. All hexadecimal formats are big-endian 2713(sign bit at the left). 2714 2715There are no constants of type x86_mmx. 2716 2717.. _complexconstants: 2718 2719Complex Constants 2720----------------- 2721 2722Complex constants are a (potentially recursive) combination of simple 2723constants and smaller complex constants. 2724 2725**Structure constants** 2726 Structure constants are represented with notation similar to 2727 structure type definitions (a comma separated list of elements, 2728 surrounded by braces (``{}``)). For example: 2729 "``{ i32 4, float 17.0, i32* @G }``", where "``@G``" is declared as 2730 "``@G = external global i32``". Structure constants must have 2731 :ref:`structure type <t_struct>`, and the number and types of elements 2732 must match those specified by the type. 2733**Array constants** 2734 Array constants are represented with notation similar to array type 2735 definitions (a comma separated list of elements, surrounded by 2736 square brackets (``[]``)). For example: 2737 "``[ i32 42, i32 11, i32 74 ]``". Array constants must have 2738 :ref:`array type <t_array>`, and the number and types of elements must 2739 match those specified by the type. As a special case, character array 2740 constants may also be represented as a double-quoted string using the ``c`` 2741 prefix. For example: "``c"Hello World\0A\00"``". 2742**Vector constants** 2743 Vector constants are represented with notation similar to vector 2744 type definitions (a comma separated list of elements, surrounded by 2745 less-than/greater-than's (``<>``)). For example: 2746 "``< i32 42, i32 11, i32 74, i32 100 >``". Vector constants 2747 must have :ref:`vector type <t_vector>`, and the number and types of 2748 elements must match those specified by the type. 2749**Zero initialization** 2750 The string '``zeroinitializer``' can be used to zero initialize a 2751 value to zero of *any* type, including scalar and 2752 :ref:`aggregate <t_aggregate>` types. This is often used to avoid 2753 having to print large zero initializers (e.g. for large arrays) and 2754 is always exactly equivalent to using explicit zero initializers. 2755**Metadata node** 2756 A metadata node is a constant tuple without types. For example: 2757 "``!{!0, !{!2, !0}, !"test"}``". Metadata can reference constant values, 2758 for example: "``!{!0, i32 0, i8* @global, i64 (i64)* @function, !"str"}``". 2759 Unlike other typed constants that are meant to be interpreted as part of 2760 the instruction stream, metadata is a place to attach additional 2761 information such as debug info. 2762 2763Global Variable and Function Addresses 2764-------------------------------------- 2765 2766The addresses of :ref:`global variables <globalvars>` and 2767:ref:`functions <functionstructure>` are always implicitly valid 2768(link-time) constants. These constants are explicitly referenced when 2769the :ref:`identifier for the global <identifiers>` is used and always have 2770:ref:`pointer <t_pointer>` type. For example, the following is a legal LLVM 2771file: 2772 2773.. code-block:: llvm 2774 2775 @X = global i32 17 2776 @Y = global i32 42 2777 @Z = global [2 x i32*] [ i32* @X, i32* @Y ] 2778 2779.. _undefvalues: 2780 2781Undefined Values 2782---------------- 2783 2784The string '``undef``' can be used anywhere a constant is expected, and 2785indicates that the user of the value may receive an unspecified 2786bit-pattern. Undefined values may be of any type (other than '``label``' 2787or '``void``') and be used anywhere a constant is permitted. 2788 2789Undefined values are useful because they indicate to the compiler that 2790the program is well defined no matter what value is used. This gives the 2791compiler more freedom to optimize. Here are some examples of 2792(potentially surprising) transformations that are valid (in pseudo IR): 2793 2794.. code-block:: llvm 2795 2796 %A = add %X, undef 2797 %B = sub %X, undef 2798 %C = xor %X, undef 2799 Safe: 2800 %A = undef 2801 %B = undef 2802 %C = undef 2803 2804This is safe because all of the output bits are affected by the undef 2805bits. Any output bit can have a zero or one depending on the input bits. 2806 2807.. code-block:: llvm 2808 2809 %A = or %X, undef 2810 %B = and %X, undef 2811 Safe: 2812 %A = -1 2813 %B = 0 2814 Unsafe: 2815 %A = undef 2816 %B = undef 2817 2818These logical operations have bits that are not always affected by the 2819input. For example, if ``%X`` has a zero bit, then the output of the 2820'``and``' operation will always be a zero for that bit, no matter what 2821the corresponding bit from the '``undef``' is. As such, it is unsafe to 2822optimize or assume that the result of the '``and``' is '``undef``'. 2823However, it is safe to assume that all bits of the '``undef``' could be 28240, and optimize the '``and``' to 0. Likewise, it is safe to assume that 2825all the bits of the '``undef``' operand to the '``or``' could be set, 2826allowing the '``or``' to be folded to -1. 2827 2828.. code-block:: llvm 2829 2830 %A = select undef, %X, %Y 2831 %B = select undef, 42, %Y 2832 %C = select %X, %Y, undef 2833 Safe: 2834 %A = %X (or %Y) 2835 %B = 42 (or %Y) 2836 %C = %Y 2837 Unsafe: 2838 %A = undef 2839 %B = undef 2840 %C = undef 2841 2842This set of examples shows that undefined '``select``' (and conditional 2843branch) conditions can go *either way*, but they have to come from one 2844of the two operands. In the ``%A`` example, if ``%X`` and ``%Y`` were 2845both known to have a clear low bit, then ``%A`` would have to have a 2846cleared low bit. However, in the ``%C`` example, the optimizer is 2847allowed to assume that the '``undef``' operand could be the same as 2848``%Y``, allowing the whole '``select``' to be eliminated. 2849 2850.. code-block:: llvm 2851 2852 %A = xor undef, undef 2853 2854 %B = undef 2855 %C = xor %B, %B 2856 2857 %D = undef 2858 %E = icmp slt %D, 4 2859 %F = icmp gte %D, 4 2860 2861 Safe: 2862 %A = undef 2863 %B = undef 2864 %C = undef 2865 %D = undef 2866 %E = undef 2867 %F = undef 2868 2869This example points out that two '``undef``' operands are not 2870necessarily the same. This can be surprising to people (and also matches 2871C semantics) where they assume that "``X^X``" is always zero, even if 2872``X`` is undefined. This isn't true for a number of reasons, but the 2873short answer is that an '``undef``' "variable" can arbitrarily change 2874its value over its "live range". This is true because the variable 2875doesn't actually *have a live range*. Instead, the value is logically 2876read from arbitrary registers that happen to be around when needed, so 2877the value is not necessarily consistent over time. In fact, ``%A`` and 2878``%C`` need to have the same semantics or the core LLVM "replace all 2879uses with" concept would not hold. 2880 2881.. code-block:: llvm 2882 2883 %A = fdiv undef, %X 2884 %B = fdiv %X, undef 2885 Safe: 2886 %A = undef 2887 b: unreachable 2888 2889These examples show the crucial difference between an *undefined value* 2890and *undefined behavior*. An undefined value (like '``undef``') is 2891allowed to have an arbitrary bit-pattern. This means that the ``%A`` 2892operation can be constant folded to '``undef``', because the '``undef``' 2893could be an SNaN, and ``fdiv`` is not (currently) defined on SNaN's. 2894However, in the second example, we can make a more aggressive 2895assumption: because the ``undef`` is allowed to be an arbitrary value, 2896we are allowed to assume that it could be zero. Since a divide by zero 2897has *undefined behavior*, we are allowed to assume that the operation 2898does not execute at all. This allows us to delete the divide and all 2899code after it. Because the undefined operation "can't happen", the 2900optimizer can assume that it occurs in dead code. 2901 2902.. code-block:: llvm 2903 2904 a: store undef -> %X 2905 b: store %X -> undef 2906 Safe: 2907 a: <deleted> 2908 b: unreachable 2909 2910These examples reiterate the ``fdiv`` example: a store *of* an undefined 2911value can be assumed to not have any effect; we can assume that the 2912value is overwritten with bits that happen to match what was already 2913there. However, a store *to* an undefined location could clobber 2914arbitrary memory, therefore, it has undefined behavior. 2915 2916.. _poisonvalues: 2917 2918Poison Values 2919------------- 2920 2921Poison values are similar to :ref:`undef values <undefvalues>`, however 2922they also represent the fact that an instruction or constant expression 2923that cannot evoke side effects has nevertheless detected a condition 2924that results in undefined behavior. 2925 2926There is currently no way of representing a poison value in the IR; they 2927only exist when produced by operations such as :ref:`add <i_add>` with 2928the ``nsw`` flag. 2929 2930Poison value behavior is defined in terms of value *dependence*: 2931 2932- Values other than :ref:`phi <i_phi>` nodes depend on their operands. 2933- :ref:`Phi <i_phi>` nodes depend on the operand corresponding to 2934 their dynamic predecessor basic block. 2935- Function arguments depend on the corresponding actual argument values 2936 in the dynamic callers of their functions. 2937- :ref:`Call <i_call>` instructions depend on the :ref:`ret <i_ret>` 2938 instructions that dynamically transfer control back to them. 2939- :ref:`Invoke <i_invoke>` instructions depend on the 2940 :ref:`ret <i_ret>`, :ref:`resume <i_resume>`, or exception-throwing 2941 call instructions that dynamically transfer control back to them. 2942- Non-volatile loads and stores depend on the most recent stores to all 2943 of the referenced memory addresses, following the order in the IR 2944 (including loads and stores implied by intrinsics such as 2945 :ref:`@llvm.memcpy <int_memcpy>`.) 2946- An instruction with externally visible side effects depends on the 2947 most recent preceding instruction with externally visible side 2948 effects, following the order in the IR. (This includes :ref:`volatile 2949 operations <volatile>`.) 2950- An instruction *control-depends* on a :ref:`terminator 2951 instruction <terminators>` if the terminator instruction has 2952 multiple successors and the instruction is always executed when 2953 control transfers to one of the successors, and may not be executed 2954 when control is transferred to another. 2955- Additionally, an instruction also *control-depends* on a terminator 2956 instruction if the set of instructions it otherwise depends on would 2957 be different if the terminator had transferred control to a different 2958 successor. 2959- Dependence is transitive. 2960 2961Poison values have the same behavior as :ref:`undef values <undefvalues>`, 2962with the additional effect that any instruction that has a *dependence* 2963on a poison value has undefined behavior. 2964 2965Here are some examples: 2966 2967.. code-block:: llvm 2968 2969 entry: 2970 %poison = sub nuw i32 0, 1 ; Results in a poison value. 2971 %still_poison = and i32 %poison, 0 ; 0, but also poison. 2972 %poison_yet_again = getelementptr i32, i32* @h, i32 %still_poison 2973 store i32 0, i32* %poison_yet_again ; memory at @h[0] is poisoned 2974 2975 store i32 %poison, i32* @g ; Poison value stored to memory. 2976 %poison2 = load i32, i32* @g ; Poison value loaded back from memory. 2977 2978 store volatile i32 %poison, i32* @g ; External observation; undefined behavior. 2979 2980 %narrowaddr = bitcast i32* @g to i16* 2981 %wideaddr = bitcast i32* @g to i64* 2982 %poison3 = load i16, i16* %narrowaddr ; Returns a poison value. 2983 %poison4 = load i64, i64* %wideaddr ; Returns a poison value. 2984 2985 %cmp = icmp slt i32 %poison, 0 ; Returns a poison value. 2986 br i1 %cmp, label %true, label %end ; Branch to either destination. 2987 2988 true: 2989 store volatile i32 0, i32* @g ; This is control-dependent on %cmp, so 2990 ; it has undefined behavior. 2991 br label %end 2992 2993 end: 2994 %p = phi i32 [ 0, %entry ], [ 1, %true ] 2995 ; Both edges into this PHI are 2996 ; control-dependent on %cmp, so this 2997 ; always results in a poison value. 2998 2999 store volatile i32 0, i32* @g ; This would depend on the store in %true 3000 ; if %cmp is true, or the store in %entry 3001 ; otherwise, so this is undefined behavior. 3002 3003 br i1 %cmp, label %second_true, label %second_end 3004 ; The same branch again, but this time the 3005 ; true block doesn't have side effects. 3006 3007 second_true: 3008 ; No side effects! 3009 ret void 3010 3011 second_end: 3012 store volatile i32 0, i32* @g ; This time, the instruction always depends 3013 ; on the store in %end. Also, it is 3014 ; control-equivalent to %end, so this is 3015 ; well-defined (ignoring earlier undefined 3016 ; behavior in this example). 3017 3018.. _blockaddress: 3019 3020Addresses of Basic Blocks 3021------------------------- 3022 3023``blockaddress(@function, %block)`` 3024 3025The '``blockaddress``' constant computes the address of the specified 3026basic block in the specified function, and always has an ``i8*`` type. 3027Taking the address of the entry block is illegal. 3028 3029This value only has defined behavior when used as an operand to the 3030':ref:`indirectbr <i_indirectbr>`' instruction, or for comparisons 3031against null. Pointer equality tests between labels addresses results in 3032undefined behavior --- though, again, comparison against null is ok, and 3033no label is equal to the null pointer. This may be passed around as an 3034opaque pointer sized value as long as the bits are not inspected. This 3035allows ``ptrtoint`` and arithmetic to be performed on these values so 3036long as the original value is reconstituted before the ``indirectbr`` 3037instruction. 3038 3039Finally, some targets may provide defined semantics when using the value 3040as the operand to an inline assembly, but that is target specific. 3041 3042.. _constantexprs: 3043 3044Constant Expressions 3045-------------------- 3046 3047Constant expressions are used to allow expressions involving other 3048constants to be used as constants. Constant expressions may be of any 3049:ref:`first class <t_firstclass>` type and may involve any LLVM operation 3050that does not have side effects (e.g. load and call are not supported). 3051The following is the syntax for constant expressions: 3052 3053``trunc (CST to TYPE)`` 3054 Truncate a constant to another type. The bit size of CST must be 3055 larger than the bit size of TYPE. Both types must be integers. 3056``zext (CST to TYPE)`` 3057 Zero extend a constant to another type. The bit size of CST must be 3058 smaller than the bit size of TYPE. Both types must be integers. 3059``sext (CST to TYPE)`` 3060 Sign extend a constant to another type. The bit size of CST must be 3061 smaller than the bit size of TYPE. Both types must be integers. 3062``fptrunc (CST to TYPE)`` 3063 Truncate a floating point constant to another floating point type. 3064 The size of CST must be larger than the size of TYPE. Both types 3065 must be floating point. 3066``fpext (CST to TYPE)`` 3067 Floating point extend a constant to another type. The size of CST 3068 must be smaller or equal to the size of TYPE. Both types must be 3069 floating point. 3070``fptoui (CST to TYPE)`` 3071 Convert a floating point constant to the corresponding unsigned 3072 integer constant. TYPE must be a scalar or vector integer type. CST 3073 must be of scalar or vector floating point type. Both CST and TYPE 3074 must be scalars, or vectors of the same number of elements. If the 3075 value won't fit in the integer type, the results are undefined. 3076``fptosi (CST to TYPE)`` 3077 Convert a floating point constant to the corresponding signed 3078 integer constant. TYPE must be a scalar or vector integer type. CST 3079 must be of scalar or vector floating point type. Both CST and TYPE 3080 must be scalars, or vectors of the same number of elements. If the 3081 value won't fit in the integer type, the results are undefined. 3082``uitofp (CST to TYPE)`` 3083 Convert an unsigned integer constant to the corresponding floating 3084 point constant. TYPE must be a scalar or vector floating point type. 3085 CST must be of scalar or vector integer type. Both CST and TYPE must 3086 be scalars, or vectors of the same number of elements. If the value 3087 won't fit in the floating point type, the results are undefined. 3088``sitofp (CST to TYPE)`` 3089 Convert a signed integer constant to the corresponding floating 3090 point constant. TYPE must be a scalar or vector floating point type. 3091 CST must be of scalar or vector integer type. Both CST and TYPE must 3092 be scalars, or vectors of the same number of elements. If the value 3093 won't fit in the floating point type, the results are undefined. 3094``ptrtoint (CST to TYPE)`` 3095 Convert a pointer typed constant to the corresponding integer 3096 constant. ``TYPE`` must be an integer type. ``CST`` must be of 3097 pointer type. The ``CST`` value is zero extended, truncated, or 3098 unchanged to make it fit in ``TYPE``. 3099``inttoptr (CST to TYPE)`` 3100 Convert an integer constant to a pointer constant. TYPE must be a 3101 pointer type. CST must be of integer type. The CST value is zero 3102 extended, truncated, or unchanged to make it fit in a pointer size. 3103 This one is *really* dangerous! 3104``bitcast (CST to TYPE)`` 3105 Convert a constant, CST, to another TYPE. The constraints of the 3106 operands are the same as those for the :ref:`bitcast 3107 instruction <i_bitcast>`. 3108``addrspacecast (CST to TYPE)`` 3109 Convert a constant pointer or constant vector of pointer, CST, to another 3110 TYPE in a different address space. The constraints of the operands are the 3111 same as those for the :ref:`addrspacecast instruction <i_addrspacecast>`. 3112``getelementptr (TY, CSTPTR, IDX0, IDX1, ...)``, ``getelementptr inbounds (TY, CSTPTR, IDX0, IDX1, ...)`` 3113 Perform the :ref:`getelementptr operation <i_getelementptr>` on 3114 constants. As with the :ref:`getelementptr <i_getelementptr>` 3115 instruction, the index list may have zero or more indexes, which are 3116 required to make sense for the type of "pointer to TY". 3117``select (COND, VAL1, VAL2)`` 3118 Perform the :ref:`select operation <i_select>` on constants. 3119``icmp COND (VAL1, VAL2)`` 3120 Performs the :ref:`icmp operation <i_icmp>` on constants. 3121``fcmp COND (VAL1, VAL2)`` 3122 Performs the :ref:`fcmp operation <i_fcmp>` on constants. 3123``extractelement (VAL, IDX)`` 3124 Perform the :ref:`extractelement operation <i_extractelement>` on 3125 constants. 3126``insertelement (VAL, ELT, IDX)`` 3127 Perform the :ref:`insertelement operation <i_insertelement>` on 3128 constants. 3129``shufflevector (VEC1, VEC2, IDXMASK)`` 3130 Perform the :ref:`shufflevector operation <i_shufflevector>` on 3131 constants. 3132``extractvalue (VAL, IDX0, IDX1, ...)`` 3133 Perform the :ref:`extractvalue operation <i_extractvalue>` on 3134 constants. The index list is interpreted in a similar manner as 3135 indices in a ':ref:`getelementptr <i_getelementptr>`' operation. At 3136 least one index value must be specified. 3137``insertvalue (VAL, ELT, IDX0, IDX1, ...)`` 3138 Perform the :ref:`insertvalue operation <i_insertvalue>` on constants. 3139 The index list is interpreted in a similar manner as indices in a 3140 ':ref:`getelementptr <i_getelementptr>`' operation. At least one index 3141 value must be specified. 3142``OPCODE (LHS, RHS)`` 3143 Perform the specified operation of the LHS and RHS constants. OPCODE 3144 may be any of the :ref:`binary <binaryops>` or :ref:`bitwise 3145 binary <bitwiseops>` operations. The constraints on operands are 3146 the same as those for the corresponding instruction (e.g. no bitwise 3147 operations on floating point values are allowed). 3148 3149Other Values 3150============ 3151 3152.. _inlineasmexprs: 3153 3154Inline Assembler Expressions 3155---------------------------- 3156 3157LLVM supports inline assembler expressions (as opposed to :ref:`Module-Level 3158Inline Assembly <moduleasm>`) through the use of a special value. This value 3159represents the inline assembler as a template string (containing the 3160instructions to emit), a list of operand constraints (stored as a string), a 3161flag that indicates whether or not the inline asm expression has side effects, 3162and a flag indicating whether the function containing the asm needs to align its 3163stack conservatively. 3164 3165The template string supports argument substitution of the operands using "``$``" 3166followed by a number, to indicate substitution of the given register/memory 3167location, as specified by the constraint string. "``${NUM:MODIFIER}``" may also 3168be used, where ``MODIFIER`` is a target-specific annotation for how to print the 3169operand (See :ref:`inline-asm-modifiers`). 3170 3171A literal "``$``" may be included by using "``$$``" in the template. To include 3172other special characters into the output, the usual "``\XX``" escapes may be 3173used, just as in other strings. Note that after template substitution, the 3174resulting assembly string is parsed by LLVM's integrated assembler unless it is 3175disabled -- even when emitting a ``.s`` file -- and thus must contain assembly 3176syntax known to LLVM. 3177 3178LLVM's support for inline asm is modeled closely on the requirements of Clang's 3179GCC-compatible inline-asm support. Thus, the feature-set and the constraint and 3180modifier codes listed here are similar or identical to those in GCC's inline asm 3181support. However, to be clear, the syntax of the template and constraint strings 3182described here is *not* the same as the syntax accepted by GCC and Clang, and, 3183while most constraint letters are passed through as-is by Clang, some get 3184translated to other codes when converting from the C source to the LLVM 3185assembly. 3186 3187An example inline assembler expression is: 3188 3189.. code-block:: llvm 3190 3191 i32 (i32) asm "bswap $0", "=r,r" 3192 3193Inline assembler expressions may **only** be used as the callee operand 3194of a :ref:`call <i_call>` or an :ref:`invoke <i_invoke>` instruction. 3195Thus, typically we have: 3196 3197.. code-block:: llvm 3198 3199 %X = call i32 asm "bswap $0", "=r,r"(i32 %Y) 3200 3201Inline asms with side effects not visible in the constraint list must be 3202marked as having side effects. This is done through the use of the 3203'``sideeffect``' keyword, like so: 3204 3205.. code-block:: llvm 3206 3207 call void asm sideeffect "eieio", ""() 3208 3209In some cases inline asms will contain code that will not work unless 3210the stack is aligned in some way, such as calls or SSE instructions on 3211x86, yet will not contain code that does that alignment within the asm. 3212The compiler should make conservative assumptions about what the asm 3213might contain and should generate its usual stack alignment code in the 3214prologue if the '``alignstack``' keyword is present: 3215 3216.. code-block:: llvm 3217 3218 call void asm alignstack "eieio", ""() 3219 3220Inline asms also support using non-standard assembly dialects. The 3221assumed dialect is ATT. When the '``inteldialect``' keyword is present, 3222the inline asm is using the Intel dialect. Currently, ATT and Intel are 3223the only supported dialects. An example is: 3224 3225.. code-block:: llvm 3226 3227 call void asm inteldialect "eieio", ""() 3228 3229If multiple keywords appear the '``sideeffect``' keyword must come 3230first, the '``alignstack``' keyword second and the '``inteldialect``' 3231keyword last. 3232 3233Inline Asm Constraint String 3234^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 3235 3236The constraint list is a comma-separated string, each element containing one or 3237more constraint codes. 3238 3239For each element in the constraint list an appropriate register or memory 3240operand will be chosen, and it will be made available to assembly template 3241string expansion as ``$0`` for the first constraint in the list, ``$1`` for the 3242second, etc. 3243 3244There are three different types of constraints, which are distinguished by a 3245prefix symbol in front of the constraint code: Output, Input, and Clobber. The 3246constraints must always be given in that order: outputs first, then inputs, then 3247clobbers. They cannot be intermingled. 3248 3249There are also three different categories of constraint codes: 3250 3251- Register constraint. This is either a register class, or a fixed physical 3252 register. This kind of constraint will allocate a register, and if necessary, 3253 bitcast the argument or result to the appropriate type. 3254- Memory constraint. This kind of constraint is for use with an instruction 3255 taking a memory operand. Different constraints allow for different addressing 3256 modes used by the target. 3257- Immediate value constraint. This kind of constraint is for an integer or other 3258 immediate value which can be rendered directly into an instruction. The 3259 various target-specific constraints allow the selection of a value in the 3260 proper range for the instruction you wish to use it with. 3261 3262Output constraints 3263"""""""""""""""""" 3264 3265Output constraints are specified by an "``=``" prefix (e.g. "``=r``"). This 3266indicates that the assembly will write to this operand, and the operand will 3267then be made available as a return value of the ``asm`` expression. Output 3268constraints do not consume an argument from the call instruction. (Except, see 3269below about indirect outputs). 3270 3271Normally, it is expected that no output locations are written to by the assembly 3272expression until *all* of the inputs have been read. As such, LLVM may assign 3273the same register to an output and an input. If this is not safe (e.g. if the 3274assembly contains two instructions, where the first writes to one output, and 3275the second reads an input and writes to a second output), then the "``&``" 3276modifier must be used (e.g. "``=&r``") to specify that the output is an 3277"early-clobber" output. Marking an output as "early-clobber" ensures that LLVM 3278will not use the same register for any inputs (other than an input tied to this 3279output). 3280 3281Input constraints 3282""""""""""""""""" 3283 3284Input constraints do not have a prefix -- just the constraint codes. Each input 3285constraint will consume one argument from the call instruction. It is not 3286permitted for the asm to write to any input register or memory location (unless 3287that input is tied to an output). Note also that multiple inputs may all be 3288assigned to the same register, if LLVM can determine that they necessarily all 3289contain the same value. 3290 3291Instead of providing a Constraint Code, input constraints may also "tie" 3292themselves to an output constraint, by providing an integer as the constraint 3293string. Tied inputs still consume an argument from the call instruction, and 3294take up a position in the asm template numbering as is usual -- they will simply 3295be constrained to always use the same register as the output they've been tied 3296to. For example, a constraint string of "``=r,0``" says to assign a register for 3297output, and use that register as an input as well (it being the 0'th 3298constraint). 3299 3300It is permitted to tie an input to an "early-clobber" output. In that case, no 3301*other* input may share the same register as the input tied to the early-clobber 3302(even when the other input has the same value). 3303 3304You may only tie an input to an output which has a register constraint, not a 3305memory constraint. Only a single input may be tied to an output. 3306 3307There is also an "interesting" feature which deserves a bit of explanation: if a 3308register class constraint allocates a register which is too small for the value 3309type operand provided as input, the input value will be split into multiple 3310registers, and all of them passed to the inline asm. 3311 3312However, this feature is often not as useful as you might think. 3313 3314Firstly, the registers are *not* guaranteed to be consecutive. So, on those 3315architectures that have instructions which operate on multiple consecutive 3316instructions, this is not an appropriate way to support them. (e.g. the 32-bit 3317SparcV8 has a 64-bit load, which instruction takes a single 32-bit register. The 3318hardware then loads into both the named register, and the next register. This 3319feature of inline asm would not be useful to support that.) 3320 3321A few of the targets provide a template string modifier allowing explicit access 3322to the second register of a two-register operand (e.g. MIPS ``L``, ``M``, and 3323``D``). On such an architecture, you can actually access the second allocated 3324register (yet, still, not any subsequent ones). But, in that case, you're still 3325probably better off simply splitting the value into two separate operands, for 3326clarity. (e.g. see the description of the ``A`` constraint on X86, which, 3327despite existing only for use with this feature, is not really a good idea to 3328use) 3329 3330Indirect inputs and outputs 3331""""""""""""""""""""""""""" 3332 3333Indirect output or input constraints can be specified by the "``*``" modifier 3334(which goes after the "``=``" in case of an output). This indicates that the asm 3335will write to or read from the contents of an *address* provided as an input 3336argument. (Note that in this way, indirect outputs act more like an *input* than 3337an output: just like an input, they consume an argument of the call expression, 3338rather than producing a return value. An indirect output constraint is an 3339"output" only in that the asm is expected to write to the contents of the input 3340memory location, instead of just read from it). 3341 3342This is most typically used for memory constraint, e.g. "``=*m``", to pass the 3343address of a variable as a value. 3344 3345It is also possible to use an indirect *register* constraint, but only on output 3346(e.g. "``=*r``"). This will cause LLVM to allocate a register for an output 3347value normally, and then, separately emit a store to the address provided as 3348input, after the provided inline asm. (It's not clear what value this 3349functionality provides, compared to writing the store explicitly after the asm 3350statement, and it can only produce worse code, since it bypasses many 3351optimization passes. I would recommend not using it.) 3352 3353 3354Clobber constraints 3355""""""""""""""""""" 3356 3357A clobber constraint is indicated by a "``~``" prefix. A clobber does not 3358consume an input operand, nor generate an output. Clobbers cannot use any of the 3359general constraint code letters -- they may use only explicit register 3360constraints, e.g. "``~{eax}``". The one exception is that a clobber string of 3361"``~{memory}``" indicates that the assembly writes to arbitrary undeclared 3362memory locations -- not only the memory pointed to by a declared indirect 3363output. 3364 3365 3366Constraint Codes 3367"""""""""""""""" 3368After a potential prefix comes constraint code, or codes. 3369 3370A Constraint Code is either a single letter (e.g. "``r``"), a "``^``" character 3371followed by two letters (e.g. "``^wc``"), or "``{``" register-name "``}``" 3372(e.g. "``{eax}``"). 3373 3374The one and two letter constraint codes are typically chosen to be the same as 3375GCC's constraint codes. 3376 3377A single constraint may include one or more than constraint code in it, leaving 3378it up to LLVM to choose which one to use. This is included mainly for 3379compatibility with the translation of GCC inline asm coming from clang. 3380 3381There are two ways to specify alternatives, and either or both may be used in an 3382inline asm constraint list: 3383 33841) Append the codes to each other, making a constraint code set. E.g. "``im``" 3385 or "``{eax}m``". This means "choose any of the options in the set". The 3386 choice of constraint is made independently for each constraint in the 3387 constraint list. 3388 33892) Use "``|``" between constraint code sets, creating alternatives. Every 3390 constraint in the constraint list must have the same number of alternative 3391 sets. With this syntax, the same alternative in *all* of the items in the 3392 constraint list will be chosen together. 3393 3394Putting those together, you might have a two operand constraint string like 3395``"rm|r,ri|rm"``. This indicates that if operand 0 is ``r`` or ``m``, then 3396operand 1 may be one of ``r`` or ``i``. If operand 0 is ``r``, then operand 1 3397may be one of ``r`` or ``m``. But, operand 0 and 1 cannot both be of type m. 3398 3399However, the use of either of the alternatives features is *NOT* recommended, as 3400LLVM is not able to make an intelligent choice about which one to use. (At the 3401point it currently needs to choose, not enough information is available to do so 3402in a smart way.) Thus, it simply tries to make a choice that's most likely to 3403compile, not one that will be optimal performance. (e.g., given "``rm``", it'll 3404always choose to use memory, not registers). And, if given multiple registers, 3405or multiple register classes, it will simply choose the first one. (In fact, it 3406doesn't currently even ensure explicitly specified physical registers are 3407unique, so specifying multiple physical registers as alternatives, like 3408``{r11}{r12},{r11}{r12}``, will assign r11 to both operands, not at all what was 3409intended.) 3410 3411Supported Constraint Code List 3412"""""""""""""""""""""""""""""" 3413 3414The constraint codes are, in general, expected to behave the same way they do in 3415GCC. LLVM's support is often implemented on an 'as-needed' basis, to support C 3416inline asm code which was supported by GCC. A mismatch in behavior between LLVM 3417and GCC likely indicates a bug in LLVM. 3418 3419Some constraint codes are typically supported by all targets: 3420 3421- ``r``: A register in the target's general purpose register class. 3422- ``m``: A memory address operand. It is target-specific what addressing modes 3423 are supported, typical examples are register, or register + register offset, 3424 or register + immediate offset (of some target-specific size). 3425- ``i``: An integer constant (of target-specific width). Allows either a simple 3426 immediate, or a relocatable value. 3427- ``n``: An integer constant -- *not* including relocatable values. 3428- ``s``: An integer constant, but allowing *only* relocatable values. 3429- ``X``: Allows an operand of any kind, no constraint whatsoever. Typically 3430 useful to pass a label for an asm branch or call. 3431 3432 .. FIXME: but that surely isn't actually okay to jump out of an asm 3433 block without telling llvm about the control transfer???) 3434 3435- ``{register-name}``: Requires exactly the named physical register. 3436 3437Other constraints are target-specific: 3438 3439AArch64: 3440 3441- ``z``: An immediate integer 0. Outputs ``WZR`` or ``XZR``, as appropriate. 3442- ``I``: An immediate integer valid for an ``ADD`` or ``SUB`` instruction, 3443 i.e. 0 to 4095 with optional shift by 12. 3444- ``J``: An immediate integer that, when negated, is valid for an ``ADD`` or 3445 ``SUB`` instruction, i.e. -1 to -4095 with optional left shift by 12. 3446- ``K``: An immediate integer that is valid for the 'bitmask immediate 32' of a 3447 logical instruction like ``AND``, ``EOR``, or ``ORR`` with a 32-bit register. 3448- ``L``: An immediate integer that is valid for the 'bitmask immediate 64' of a 3449 logical instruction like ``AND``, ``EOR``, or ``ORR`` with a 64-bit register. 3450- ``M``: An immediate integer for use with the ``MOV`` assembly alias on a 3451 32-bit register. This is a superset of ``K``: in addition to the bitmask 3452 immediate, also allows immediate integers which can be loaded with a single 3453 ``MOVZ`` or ``MOVL`` instruction. 3454- ``N``: An immediate integer for use with the ``MOV`` assembly alias on a 3455 64-bit register. This is a superset of ``L``. 3456- ``Q``: Memory address operand must be in a single register (no 3457 offsets). (However, LLVM currently does this for the ``m`` constraint as 3458 well.) 3459- ``r``: A 32 or 64-bit integer register (W* or X*). 3460- ``w``: A 32, 64, or 128-bit floating-point/SIMD register. 3461- ``x``: A lower 128-bit floating-point/SIMD register (``V0`` to ``V15``). 3462 3463AMDGPU: 3464 3465- ``r``: A 32 or 64-bit integer register. 3466- ``[0-9]v``: The 32-bit VGPR register, number 0-9. 3467- ``[0-9]s``: The 32-bit SGPR register, number 0-9. 3468 3469 3470All ARM modes: 3471 3472- ``Q``, ``Um``, ``Un``, ``Uq``, ``Us``, ``Ut``, ``Uv``, ``Uy``: Memory address 3473 operand. Treated the same as operand ``m``, at the moment. 3474 3475ARM and ARM's Thumb2 mode: 3476 3477- ``j``: An immediate integer between 0 and 65535 (valid for ``MOVW``) 3478- ``I``: An immediate integer valid for a data-processing instruction. 3479- ``J``: An immediate integer between -4095 and 4095. 3480- ``K``: An immediate integer whose bitwise inverse is valid for a 3481 data-processing instruction. (Can be used with template modifier "``B``" to 3482 print the inverted value). 3483- ``L``: An immediate integer whose negation is valid for a data-processing 3484 instruction. (Can be used with template modifier "``n``" to print the negated 3485 value). 3486- ``M``: A power of two or a integer between 0 and 32. 3487- ``N``: Invalid immediate constraint. 3488- ``O``: Invalid immediate constraint. 3489- ``r``: A general-purpose 32-bit integer register (``r0-r15``). 3490- ``l``: In Thumb2 mode, low 32-bit GPR registers (``r0-r7``). In ARM mode, same 3491 as ``r``. 3492- ``h``: In Thumb2 mode, a high 32-bit GPR register (``r8-r15``). In ARM mode, 3493 invalid. 3494- ``w``: A 32, 64, or 128-bit floating-point/SIMD register: ``s0-s31``, 3495 ``d0-d31``, or ``q0-q15``. 3496- ``x``: A 32, 64, or 128-bit floating-point/SIMD register: ``s0-s15``, 3497 ``d0-d7``, or ``q0-q3``. 3498- ``t``: A floating-point/SIMD register, only supports 32-bit values: 3499 ``s0-s31``. 3500 3501ARM's Thumb1 mode: 3502 3503- ``I``: An immediate integer between 0 and 255. 3504- ``J``: An immediate integer between -255 and -1. 3505- ``K``: An immediate integer between 0 and 255, with optional left-shift by 3506 some amount. 3507- ``L``: An immediate integer between -7 and 7. 3508- ``M``: An immediate integer which is a multiple of 4 between 0 and 1020. 3509- ``N``: An immediate integer between 0 and 31. 3510- ``O``: An immediate integer which is a multiple of 4 between -508 and 508. 3511- ``r``: A low 32-bit GPR register (``r0-r7``). 3512- ``l``: A low 32-bit GPR register (``r0-r7``). 3513- ``h``: A high GPR register (``r0-r7``). 3514- ``w``: A 32, 64, or 128-bit floating-point/SIMD register: ``s0-s31``, 3515 ``d0-d31``, or ``q0-q15``. 3516- ``x``: A 32, 64, or 128-bit floating-point/SIMD register: ``s0-s15``, 3517 ``d0-d7``, or ``q0-q3``. 3518- ``t``: A floating-point/SIMD register, only supports 32-bit values: 3519 ``s0-s31``. 3520 3521 3522Hexagon: 3523 3524- ``o``, ``v``: A memory address operand, treated the same as constraint ``m``, 3525 at the moment. 3526- ``r``: A 32 or 64-bit register. 3527 3528MSP430: 3529 3530- ``r``: An 8 or 16-bit register. 3531 3532MIPS: 3533 3534- ``I``: An immediate signed 16-bit integer. 3535- ``J``: An immediate integer zero. 3536- ``K``: An immediate unsigned 16-bit integer. 3537- ``L``: An immediate 32-bit integer, where the lower 16 bits are 0. 3538- ``N``: An immediate integer between -65535 and -1. 3539- ``O``: An immediate signed 15-bit integer. 3540- ``P``: An immediate integer between 1 and 65535. 3541- ``m``: A memory address operand. In MIPS-SE mode, allows a base address 3542 register plus 16-bit immediate offset. In MIPS mode, just a base register. 3543- ``R``: A memory address operand. In MIPS-SE mode, allows a base address 3544 register plus a 9-bit signed offset. In MIPS mode, the same as constraint 3545 ``m``. 3546- ``ZC``: A memory address operand, suitable for use in a ``pref``, ``ll``, or 3547 ``sc`` instruction on the given subtarget (details vary). 3548- ``r``, ``d``, ``y``: A 32 or 64-bit GPR register. 3549- ``f``: A 32 or 64-bit FPU register (``F0-F31``), or a 128-bit MSA register 3550 (``W0-W31``). In the case of MSA registers, it is recommended to use the ``w`` 3551 argument modifier for compatibility with GCC. 3552- ``c``: A 32-bit or 64-bit GPR register suitable for indirect jump (always 3553 ``25``). 3554- ``l``: The ``lo`` register, 32 or 64-bit. 3555- ``x``: Invalid. 3556 3557NVPTX: 3558 3559- ``b``: A 1-bit integer register. 3560- ``c`` or ``h``: A 16-bit integer register. 3561- ``r``: A 32-bit integer register. 3562- ``l`` or ``N``: A 64-bit integer register. 3563- ``f``: A 32-bit float register. 3564- ``d``: A 64-bit float register. 3565 3566 3567PowerPC: 3568 3569- ``I``: An immediate signed 16-bit integer. 3570- ``J``: An immediate unsigned 16-bit integer, shifted left 16 bits. 3571- ``K``: An immediate unsigned 16-bit integer. 3572- ``L``: An immediate signed 16-bit integer, shifted left 16 bits. 3573- ``M``: An immediate integer greater than 31. 3574- ``N``: An immediate integer that is an exact power of 2. 3575- ``O``: The immediate integer constant 0. 3576- ``P``: An immediate integer constant whose negation is a signed 16-bit 3577 constant. 3578- ``es``, ``o``, ``Q``, ``Z``, ``Zy``: A memory address operand, currently 3579 treated the same as ``m``. 3580- ``r``: A 32 or 64-bit integer register. 3581- ``b``: A 32 or 64-bit integer register, excluding ``R0`` (that is: 3582 ``R1-R31``). 3583- ``f``: A 32 or 64-bit float register (``F0-F31``), or when QPX is enabled, a 3584 128 or 256-bit QPX register (``Q0-Q31``; aliases the ``F`` registers). 3585- ``v``: For ``4 x f32`` or ``4 x f64`` types, when QPX is enabled, a 3586 128 or 256-bit QPX register (``Q0-Q31``), otherwise a 128-bit 3587 altivec vector register (``V0-V31``). 3588 3589 .. FIXME: is this a bug that v accepts QPX registers? I think this 3590 is supposed to only use the altivec vector registers? 3591 3592- ``y``: Condition register (``CR0-CR7``). 3593- ``wc``: An individual CR bit in a CR register. 3594- ``wa``, ``wd``, ``wf``: Any 128-bit VSX vector register, from the full VSX 3595 register set (overlapping both the floating-point and vector register files). 3596- ``ws``: A 32 or 64-bit floating point register, from the full VSX register 3597 set. 3598 3599Sparc: 3600 3601- ``I``: An immediate 13-bit signed integer. 3602- ``r``: A 32-bit integer register. 3603 3604SystemZ: 3605 3606- ``I``: An immediate unsigned 8-bit integer. 3607- ``J``: An immediate unsigned 12-bit integer. 3608- ``K``: An immediate signed 16-bit integer. 3609- ``L``: An immediate signed 20-bit integer. 3610- ``M``: An immediate integer 0x7fffffff. 3611- ``Q``: A memory address operand with a base address and a 12-bit immediate 3612 unsigned displacement. 3613- ``R``: A memory address operand with a base address, a 12-bit immediate 3614 unsigned displacement, and an index register. 3615- ``S``: A memory address operand with a base address and a 20-bit immediate 3616 signed displacement. 3617- ``T``: A memory address operand with a base address, a 20-bit immediate 3618 signed displacement, and an index register. 3619- ``r`` or ``d``: A 32, 64, or 128-bit integer register. 3620- ``a``: A 32, 64, or 128-bit integer address register (excludes R0, which in an 3621 address context evaluates as zero). 3622- ``h``: A 32-bit value in the high part of a 64bit data register 3623 (LLVM-specific) 3624- ``f``: A 32, 64, or 128-bit floating point register. 3625 3626X86: 3627 3628- ``I``: An immediate integer between 0 and 31. 3629- ``J``: An immediate integer between 0 and 64. 3630- ``K``: An immediate signed 8-bit integer. 3631- ``L``: An immediate integer, 0xff or 0xffff or (in 64-bit mode only) 3632 0xffffffff. 3633- ``M``: An immediate integer between 0 and 3. 3634- ``N``: An immediate unsigned 8-bit integer. 3635- ``O``: An immediate integer between 0 and 127. 3636- ``e``: An immediate 32-bit signed integer. 3637- ``Z``: An immediate 32-bit unsigned integer. 3638- ``o``, ``v``: Treated the same as ``m``, at the moment. 3639- ``q``: An 8, 16, 32, or 64-bit register which can be accessed as an 8-bit 3640 ``l`` integer register. On X86-32, this is the ``a``, ``b``, ``c``, and ``d`` 3641 registers, and on X86-64, it is all of the integer registers. 3642- ``Q``: An 8, 16, 32, or 64-bit register which can be accessed as an 8-bit 3643 ``h`` integer register. This is the ``a``, ``b``, ``c``, and ``d`` registers. 3644- ``r`` or ``l``: An 8, 16, 32, or 64-bit integer register. 3645- ``R``: An 8, 16, 32, or 64-bit "legacy" integer register -- one which has 3646 existed since i386, and can be accessed without the REX prefix. 3647- ``f``: A 32, 64, or 80-bit '387 FPU stack pseudo-register. 3648- ``y``: A 64-bit MMX register, if MMX is enabled. 3649- ``x``: If SSE is enabled: a 32 or 64-bit scalar operand, or 128-bit vector 3650 operand in a SSE register. If AVX is also enabled, can also be a 256-bit 3651 vector operand in an AVX register. If AVX-512 is also enabled, can also be a 3652 512-bit vector operand in an AVX512 register, Otherwise, an error. 3653- ``Y``: The same as ``x``, if *SSE2* is enabled, otherwise an error. 3654- ``A``: Special case: allocates EAX first, then EDX, for a single operand (in 3655 32-bit mode, a 64-bit integer operand will get split into two registers). It 3656 is not recommended to use this constraint, as in 64-bit mode, the 64-bit 3657 operand will get allocated only to RAX -- if two 32-bit operands are needed, 3658 you're better off splitting it yourself, before passing it to the asm 3659 statement. 3660 3661XCore: 3662 3663- ``r``: A 32-bit integer register. 3664 3665 3666.. _inline-asm-modifiers: 3667 3668Asm template argument modifiers 3669^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 3670 3671In the asm template string, modifiers can be used on the operand reference, like 3672"``${0:n}``". 3673 3674The modifiers are, in general, expected to behave the same way they do in 3675GCC. LLVM's support is often implemented on an 'as-needed' basis, to support C 3676inline asm code which was supported by GCC. A mismatch in behavior between LLVM 3677and GCC likely indicates a bug in LLVM. 3678 3679Target-independent: 3680 3681- ``c``: Print an immediate integer constant unadorned, without 3682 the target-specific immediate punctuation (e.g. no ``$`` prefix). 3683- ``n``: Negate and print immediate integer constant unadorned, without the 3684 target-specific immediate punctuation (e.g. no ``$`` prefix). 3685- ``l``: Print as an unadorned label, without the target-specific label 3686 punctuation (e.g. no ``$`` prefix). 3687 3688AArch64: 3689 3690- ``w``: Print a GPR register with a ``w*`` name instead of ``x*`` name. E.g., 3691 instead of ``x30``, print ``w30``. 3692- ``x``: Print a GPR register with a ``x*`` name. (this is the default, anyhow). 3693- ``b``, ``h``, ``s``, ``d``, ``q``: Print a floating-point/SIMD register with a 3694 ``b*``, ``h*``, ``s*``, ``d*``, or ``q*`` name, rather than the default of 3695 ``v*``. 3696 3697AMDGPU: 3698 3699- ``r``: No effect. 3700 3701ARM: 3702 3703- ``a``: Print an operand as an address (with ``[`` and ``]`` surrounding a 3704 register). 3705- ``P``: No effect. 3706- ``q``: No effect. 3707- ``y``: Print a VFP single-precision register as an indexed double (e.g. print 3708 as ``d4[1]`` instead of ``s9``) 3709- ``B``: Bitwise invert and print an immediate integer constant without ``#`` 3710 prefix. 3711- ``L``: Print the low 16-bits of an immediate integer constant. 3712- ``M``: Print as a register set suitable for ldm/stm. Also prints *all* 3713 register operands subsequent to the specified one (!), so use carefully. 3714- ``Q``: Print the low-order register of a register-pair, or the low-order 3715 register of a two-register operand. 3716- ``R``: Print the high-order register of a register-pair, or the high-order 3717 register of a two-register operand. 3718- ``H``: Print the second register of a register-pair. (On a big-endian system, 3719 ``H`` is equivalent to ``Q``, and on little-endian system, ``H`` is equivalent 3720 to ``R``.) 3721 3722 .. FIXME: H doesn't currently support printing the second register 3723 of a two-register operand. 3724 3725- ``e``: Print the low doubleword register of a NEON quad register. 3726- ``f``: Print the high doubleword register of a NEON quad register. 3727- ``m``: Print the base register of a memory operand without the ``[`` and ``]`` 3728 adornment. 3729 3730Hexagon: 3731 3732- ``L``: Print the second register of a two-register operand. Requires that it 3733 has been allocated consecutively to the first. 3734 3735 .. FIXME: why is it restricted to consecutive ones? And there's 3736 nothing that ensures that happens, is there? 3737 3738- ``I``: Print the letter 'i' if the operand is an integer constant, otherwise 3739 nothing. Used to print 'addi' vs 'add' instructions. 3740 3741MSP430: 3742 3743No additional modifiers. 3744 3745MIPS: 3746 3747- ``X``: Print an immediate integer as hexadecimal 3748- ``x``: Print the low 16 bits of an immediate integer as hexadecimal. 3749- ``d``: Print an immediate integer as decimal. 3750- ``m``: Subtract one and print an immediate integer as decimal. 3751- ``z``: Print $0 if an immediate zero, otherwise print normally. 3752- ``L``: Print the low-order register of a two-register operand, or prints the 3753 address of the low-order word of a double-word memory operand. 3754 3755 .. FIXME: L seems to be missing memory operand support. 3756 3757- ``M``: Print the high-order register of a two-register operand, or prints the 3758 address of the high-order word of a double-word memory operand. 3759 3760 .. FIXME: M seems to be missing memory operand support. 3761 3762- ``D``: Print the second register of a two-register operand, or prints the 3763 second word of a double-word memory operand. (On a big-endian system, ``D`` is 3764 equivalent to ``L``, and on little-endian system, ``D`` is equivalent to 3765 ``M``.) 3766- ``w``: No effect. Provided for compatibility with GCC which requires this 3767 modifier in order to print MSA registers (``W0-W31``) with the ``f`` 3768 constraint. 3769 3770NVPTX: 3771 3772- ``r``: No effect. 3773 3774PowerPC: 3775 3776- ``L``: Print the second register of a two-register operand. Requires that it 3777 has been allocated consecutively to the first. 3778 3779 .. FIXME: why is it restricted to consecutive ones? And there's 3780 nothing that ensures that happens, is there? 3781 3782- ``I``: Print the letter 'i' if the operand is an integer constant, otherwise 3783 nothing. Used to print 'addi' vs 'add' instructions. 3784- ``y``: For a memory operand, prints formatter for a two-register X-form 3785 instruction. (Currently always prints ``r0,OPERAND``). 3786- ``U``: Prints 'u' if the memory operand is an update form, and nothing 3787 otherwise. (NOTE: LLVM does not support update form, so this will currently 3788 always print nothing) 3789- ``X``: Prints 'x' if the memory operand is an indexed form. (NOTE: LLVM does 3790 not support indexed form, so this will currently always print nothing) 3791 3792Sparc: 3793 3794- ``r``: No effect. 3795 3796SystemZ: 3797 3798SystemZ implements only ``n``, and does *not* support any of the other 3799target-independent modifiers. 3800 3801X86: 3802 3803- ``c``: Print an unadorned integer or symbol name. (The latter is 3804 target-specific behavior for this typically target-independent modifier). 3805- ``A``: Print a register name with a '``*``' before it. 3806- ``b``: Print an 8-bit register name (e.g. ``al``); do nothing on a memory 3807 operand. 3808- ``h``: Print the upper 8-bit register name (e.g. ``ah``); do nothing on a 3809 memory operand. 3810- ``w``: Print the 16-bit register name (e.g. ``ax``); do nothing on a memory 3811 operand. 3812- ``k``: Print the 32-bit register name (e.g. ``eax``); do nothing on a memory 3813 operand. 3814- ``q``: Print the 64-bit register name (e.g. ``rax``), if 64-bit registers are 3815 available, otherwise the 32-bit register name; do nothing on a memory operand. 3816- ``n``: Negate and print an unadorned integer, or, for operands other than an 3817 immediate integer (e.g. a relocatable symbol expression), print a '-' before 3818 the operand. (The behavior for relocatable symbol expressions is a 3819 target-specific behavior for this typically target-independent modifier) 3820- ``H``: Print a memory reference with additional offset +8. 3821- ``P``: Print a memory reference or operand for use as the argument of a call 3822 instruction. (E.g. omit ``(rip)``, even though it's PC-relative.) 3823 3824XCore: 3825 3826No additional modifiers. 3827 3828 3829Inline Asm Metadata 3830^^^^^^^^^^^^^^^^^^^ 3831 3832The call instructions that wrap inline asm nodes may have a 3833"``!srcloc``" MDNode attached to it that contains a list of constant 3834integers. If present, the code generator will use the integer as the 3835location cookie value when report errors through the ``LLVMContext`` 3836error reporting mechanisms. This allows a front-end to correlate backend 3837errors that occur with inline asm back to the source code that produced 3838it. For example: 3839 3840.. code-block:: llvm 3841 3842 call void asm sideeffect "something bad", ""(), !srcloc !42 3843 ... 3844 !42 = !{ i32 1234567 } 3845 3846It is up to the front-end to make sense of the magic numbers it places 3847in the IR. If the MDNode contains multiple constants, the code generator 3848will use the one that corresponds to the line of the asm that the error 3849occurs on. 3850 3851.. _metadata: 3852 3853Metadata 3854======== 3855 3856LLVM IR allows metadata to be attached to instructions in the program 3857that can convey extra information about the code to the optimizers and 3858code generator. One example application of metadata is source-level 3859debug information. There are two metadata primitives: strings and nodes. 3860 3861Metadata does not have a type, and is not a value. If referenced from a 3862``call`` instruction, it uses the ``metadata`` type. 3863 3864All metadata are identified in syntax by a exclamation point ('``!``'). 3865 3866.. _metadata-string: 3867 3868Metadata Nodes and Metadata Strings 3869----------------------------------- 3870 3871A metadata string is a string surrounded by double quotes. It can 3872contain any character by escaping non-printable characters with 3873"``\xx``" where "``xx``" is the two digit hex code. For example: 3874"``!"test\00"``". 3875 3876Metadata nodes are represented with notation similar to structure 3877constants (a comma separated list of elements, surrounded by braces and 3878preceded by an exclamation point). Metadata nodes can have any values as 3879their operand. For example: 3880 3881.. code-block:: llvm 3882 3883 !{ !"test\00", i32 10} 3884 3885Metadata nodes that aren't uniqued use the ``distinct`` keyword. For example: 3886 3887.. code-block:: llvm 3888 3889 !0 = distinct !{!"test\00", i32 10} 3890 3891``distinct`` nodes are useful when nodes shouldn't be merged based on their 3892content. They can also occur when transformations cause uniquing collisions 3893when metadata operands change. 3894 3895A :ref:`named metadata <namedmetadatastructure>` is a collection of 3896metadata nodes, which can be looked up in the module symbol table. For 3897example: 3898 3899.. code-block:: llvm 3900 3901 !foo = !{!4, !3} 3902 3903Metadata can be used as function arguments. Here ``llvm.dbg.value`` 3904function is using two metadata arguments: 3905 3906.. code-block:: llvm 3907 3908 call void @llvm.dbg.value(metadata !24, i64 0, metadata !25) 3909 3910Metadata can be attached to an instruction. Here metadata ``!21`` is attached 3911to the ``add`` instruction using the ``!dbg`` identifier: 3912 3913.. code-block:: llvm 3914 3915 %indvar.next = add i64 %indvar, 1, !dbg !21 3916 3917Metadata can also be attached to a function definition. Here metadata ``!22`` 3918is attached to the ``foo`` function using the ``!dbg`` identifier: 3919 3920.. code-block:: llvm 3921 3922 define void @foo() !dbg !22 { 3923 ret void 3924 } 3925 3926More information about specific metadata nodes recognized by the 3927optimizers and code generator is found below. 3928 3929.. _specialized-metadata: 3930 3931Specialized Metadata Nodes 3932^^^^^^^^^^^^^^^^^^^^^^^^^^ 3933 3934Specialized metadata nodes are custom data structures in metadata (as opposed 3935to generic tuples). Their fields are labelled, and can be specified in any 3936order. 3937 3938These aren't inherently debug info centric, but currently all the specialized 3939metadata nodes are related to debug info. 3940 3941.. _DICompileUnit: 3942 3943DICompileUnit 3944""""""""""""" 3945 3946``DICompileUnit`` nodes represent a compile unit. The ``enums:``, 3947``retainedTypes:``, ``subprograms:``, ``globals:``, ``imports:`` and ``macros:`` 3948fields are tuples containing the debug info to be emitted along with the compile 3949unit, regardless of code optimizations (some nodes are only emitted if there are 3950references to them from instructions). 3951 3952.. code-block:: llvm 3953 3954 !0 = !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang", 3955 isOptimized: true, flags: "-O2", runtimeVersion: 2, 3956 splitDebugFilename: "abc.debug", emissionKind: FullDebug, 3957 enums: !2, retainedTypes: !3, subprograms: !4, 3958 globals: !5, imports: !6, macros: !7, dwoId: 0x0abcd) 3959 3960Compile unit descriptors provide the root scope for objects declared in a 3961specific compilation unit. File descriptors are defined using this scope. 3962These descriptors are collected by a named metadata ``!llvm.dbg.cu``. They 3963keep track of subprograms, global variables, type information, and imported 3964entities (declarations and namespaces). 3965 3966.. _DIFile: 3967 3968DIFile 3969"""""" 3970 3971``DIFile`` nodes represent files. The ``filename:`` can include slashes. 3972 3973.. code-block:: llvm 3974 3975 !0 = !DIFile(filename: "path/to/file", directory: "/path/to/dir") 3976 3977Files are sometimes used in ``scope:`` fields, and are the only valid target 3978for ``file:`` fields. 3979 3980.. _DIBasicType: 3981 3982DIBasicType 3983""""""""""" 3984 3985``DIBasicType`` nodes represent primitive types, such as ``int``, ``bool`` and 3986``float``. ``tag:`` defaults to ``DW_TAG_base_type``. 3987 3988.. code-block:: llvm 3989 3990 !0 = !DIBasicType(name: "unsigned char", size: 8, align: 8, 3991 encoding: DW_ATE_unsigned_char) 3992 !1 = !DIBasicType(tag: DW_TAG_unspecified_type, name: "decltype(nullptr)") 3993 3994The ``encoding:`` describes the details of the type. Usually it's one of the 3995following: 3996 3997.. code-block:: llvm 3998 3999 DW_ATE_address = 1 4000 DW_ATE_boolean = 2 4001 DW_ATE_float = 4 4002 DW_ATE_signed = 5 4003 DW_ATE_signed_char = 6 4004 DW_ATE_unsigned = 7 4005 DW_ATE_unsigned_char = 8 4006 4007.. _DISubroutineType: 4008 4009DISubroutineType 4010"""""""""""""""" 4011 4012``DISubroutineType`` nodes represent subroutine types. Their ``types:`` field 4013refers to a tuple; the first operand is the return type, while the rest are the 4014types of the formal arguments in order. If the first operand is ``null``, that 4015represents a function with no return value (such as ``void foo() {}`` in C++). 4016 4017.. code-block:: llvm 4018 4019 !0 = !BasicType(name: "int", size: 32, align: 32, DW_ATE_signed) 4020 !1 = !BasicType(name: "char", size: 8, align: 8, DW_ATE_signed_char) 4021 !2 = !DISubroutineType(types: !{null, !0, !1}) ; void (int, char) 4022 4023.. _DIDerivedType: 4024 4025DIDerivedType 4026""""""""""""" 4027 4028``DIDerivedType`` nodes represent types derived from other types, such as 4029qualified types. 4030 4031.. code-block:: llvm 4032 4033 !0 = !DIBasicType(name: "unsigned char", size: 8, align: 8, 4034 encoding: DW_ATE_unsigned_char) 4035 !1 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !0, size: 32, 4036 align: 32) 4037 4038The following ``tag:`` values are valid: 4039 4040.. code-block:: llvm 4041 4042 DW_TAG_member = 13 4043 DW_TAG_pointer_type = 15 4044 DW_TAG_reference_type = 16 4045 DW_TAG_typedef = 22 4046 DW_TAG_inheritance = 28 4047 DW_TAG_ptr_to_member_type = 31 4048 DW_TAG_const_type = 38 4049 DW_TAG_friend = 42 4050 DW_TAG_volatile_type = 53 4051 DW_TAG_restrict_type = 55 4052 4053.. _DIDerivedTypeMember: 4054 4055``DW_TAG_member`` is used to define a member of a :ref:`composite type 4056<DICompositeType>`. The type of the member is the ``baseType:``. The 4057``offset:`` is the member's bit offset. If the composite type has an ODR 4058``identifier:`` and does not set ``flags: DIFwdDecl``, then the member is 4059uniqued based only on its ``name:`` and ``scope:``. 4060 4061``DW_TAG_inheritance`` and ``DW_TAG_friend`` are used in the ``elements:`` 4062field of :ref:`composite types <DICompositeType>` to describe parents and 4063friends. 4064 4065``DW_TAG_typedef`` is used to provide a name for the ``baseType:``. 4066 4067``DW_TAG_pointer_type``, ``DW_TAG_reference_type``, ``DW_TAG_const_type``, 4068``DW_TAG_volatile_type`` and ``DW_TAG_restrict_type`` are used to qualify the 4069``baseType:``. 4070 4071Note that the ``void *`` type is expressed as a type derived from NULL. 4072 4073.. _DICompositeType: 4074 4075DICompositeType 4076""""""""""""""" 4077 4078``DICompositeType`` nodes represent types composed of other types, like 4079structures and unions. ``elements:`` points to a tuple of the composed types. 4080 4081If the source language supports ODR, the ``identifier:`` field gives the unique 4082identifier used for type merging between modules. When specified, 4083:ref:`subprogram declarations <DISubprogramDeclaration>` and :ref:`member 4084derived types <DIDerivedTypeMember>` that reference the ODR-type in their 4085``scope:`` change uniquing rules. 4086 4087For a given ``identifier:``, there should only be a single composite type that 4088does not have ``flags: DIFlagFwdDecl`` set. LLVM tools that link modules 4089together will unique such definitions at parse time via the ``identifier:`` 4090field, even if the nodes are ``distinct``. 4091 4092.. code-block:: llvm 4093 4094 !0 = !DIEnumerator(name: "SixKind", value: 7) 4095 !1 = !DIEnumerator(name: "SevenKind", value: 7) 4096 !2 = !DIEnumerator(name: "NegEightKind", value: -8) 4097 !3 = !DICompositeType(tag: DW_TAG_enumeration_type, name: "Enum", file: !12, 4098 line: 2, size: 32, align: 32, identifier: "_M4Enum", 4099 elements: !{!0, !1, !2}) 4100 4101The following ``tag:`` values are valid: 4102 4103.. code-block:: llvm 4104 4105 DW_TAG_array_type = 1 4106 DW_TAG_class_type = 2 4107 DW_TAG_enumeration_type = 4 4108 DW_TAG_structure_type = 19 4109 DW_TAG_union_type = 23 4110 4111For ``DW_TAG_array_type``, the ``elements:`` should be :ref:`subrange 4112descriptors <DISubrange>`, each representing the range of subscripts at that 4113level of indexing. The ``DIFlagVector`` flag to ``flags:`` indicates that an 4114array type is a native packed vector. 4115 4116For ``DW_TAG_enumeration_type``, the ``elements:`` should be :ref:`enumerator 4117descriptors <DIEnumerator>`, each representing the definition of an enumeration 4118value for the set. All enumeration type descriptors are collected in the 4119``enums:`` field of the :ref:`compile unit <DICompileUnit>`. 4120 4121For ``DW_TAG_structure_type``, ``DW_TAG_class_type``, and 4122``DW_TAG_union_type``, the ``elements:`` should be :ref:`derived types 4123<DIDerivedType>` with ``tag: DW_TAG_member``, ``tag: DW_TAG_inheritance``, or 4124``tag: DW_TAG_friend``; or :ref:`subprograms <DISubprogram>` with 4125``isDefinition: false``. 4126 4127.. _DISubrange: 4128 4129DISubrange 4130"""""""""" 4131 4132``DISubrange`` nodes are the elements for ``DW_TAG_array_type`` variants of 4133:ref:`DICompositeType`. ``count: -1`` indicates an empty array. 4134 4135.. code-block:: llvm 4136 4137 !0 = !DISubrange(count: 5, lowerBound: 0) ; array counting from 0 4138 !1 = !DISubrange(count: 5, lowerBound: 1) ; array counting from 1 4139 !2 = !DISubrange(count: -1) ; empty array. 4140 4141.. _DIEnumerator: 4142 4143DIEnumerator 4144"""""""""""" 4145 4146``DIEnumerator`` nodes are the elements for ``DW_TAG_enumeration_type`` 4147variants of :ref:`DICompositeType`. 4148 4149.. code-block:: llvm 4150 4151 !0 = !DIEnumerator(name: "SixKind", value: 7) 4152 !1 = !DIEnumerator(name: "SevenKind", value: 7) 4153 !2 = !DIEnumerator(name: "NegEightKind", value: -8) 4154 4155DITemplateTypeParameter 4156""""""""""""""""""""""" 4157 4158``DITemplateTypeParameter`` nodes represent type parameters to generic source 4159language constructs. They are used (optionally) in :ref:`DICompositeType` and 4160:ref:`DISubprogram` ``templateParams:`` fields. 4161 4162.. code-block:: llvm 4163 4164 !0 = !DITemplateTypeParameter(name: "Ty", type: !1) 4165 4166DITemplateValueParameter 4167"""""""""""""""""""""""" 4168 4169``DITemplateValueParameter`` nodes represent value parameters to generic source 4170language constructs. ``tag:`` defaults to ``DW_TAG_template_value_parameter``, 4171but if specified can also be set to ``DW_TAG_GNU_template_template_param`` or 4172``DW_TAG_GNU_template_param_pack``. They are used (optionally) in 4173:ref:`DICompositeType` and :ref:`DISubprogram` ``templateParams:`` fields. 4174 4175.. code-block:: llvm 4176 4177 !0 = !DITemplateValueParameter(name: "Ty", type: !1, value: i32 7) 4178 4179DINamespace 4180""""""""""" 4181 4182``DINamespace`` nodes represent namespaces in the source language. 4183 4184.. code-block:: llvm 4185 4186 !0 = !DINamespace(name: "myawesomeproject", scope: !1, file: !2, line: 7) 4187 4188DIGlobalVariable 4189"""""""""""""""" 4190 4191``DIGlobalVariable`` nodes represent global variables in the source language. 4192 4193.. code-block:: llvm 4194 4195 !0 = !DIGlobalVariable(name: "foo", linkageName: "foo", scope: !1, 4196 file: !2, line: 7, type: !3, isLocal: true, 4197 isDefinition: false, variable: i32* @foo, 4198 declaration: !4) 4199 4200All global variables should be referenced by the `globals:` field of a 4201:ref:`compile unit <DICompileUnit>`. 4202 4203.. _DISubprogram: 4204 4205DISubprogram 4206"""""""""""" 4207 4208``DISubprogram`` nodes represent functions from the source language. A 4209``DISubprogram`` may be attached to a function definition using ``!dbg`` 4210metadata. The ``variables:`` field points at :ref:`variables <DILocalVariable>` 4211that must be retained, even if their IR counterparts are optimized out of 4212the IR. The ``type:`` field must point at an :ref:`DISubroutineType`. 4213 4214.. _DISubprogramDeclaration: 4215 4216When ``isDefinition: false``, subprograms describe a declaration in the type 4217tree as opposed to a definition of a function. If the scope is a composite 4218type with an ODR ``identifier:`` and that does not set ``flags: DIFwdDecl``, 4219then the subprogram declaration is uniqued based only on its ``linkageName:`` 4220and ``scope:``. 4221 4222.. code-block:: llvm 4223 4224 define void @_Z3foov() !dbg !0 { 4225 ... 4226 } 4227 4228 !0 = distinct !DISubprogram(name: "foo", linkageName: "_Zfoov", scope: !1, 4229 file: !2, line: 7, type: !3, isLocal: true, 4230 isDefinition: true, scopeLine: 8, 4231 containingType: !4, 4232 virtuality: DW_VIRTUALITY_pure_virtual, 4233 virtualIndex: 10, flags: DIFlagPrototyped, 4234 isOptimized: true, templateParams: !5, 4235 declaration: !6, variables: !7) 4236 4237.. _DILexicalBlock: 4238 4239DILexicalBlock 4240"""""""""""""" 4241 4242``DILexicalBlock`` nodes describe nested blocks within a :ref:`subprogram 4243<DISubprogram>`. The line number and column numbers are used to distinguish 4244two lexical blocks at same depth. They are valid targets for ``scope:`` 4245fields. 4246 4247.. code-block:: llvm 4248 4249 !0 = distinct !DILexicalBlock(scope: !1, file: !2, line: 7, column: 35) 4250 4251Usually lexical blocks are ``distinct`` to prevent node merging based on 4252operands. 4253 4254.. _DILexicalBlockFile: 4255 4256DILexicalBlockFile 4257"""""""""""""""""" 4258 4259``DILexicalBlockFile`` nodes are used to discriminate between sections of a 4260:ref:`lexical block <DILexicalBlock>`. The ``file:`` field can be changed to 4261indicate textual inclusion, or the ``discriminator:`` field can be used to 4262discriminate between control flow within a single block in the source language. 4263 4264.. code-block:: llvm 4265 4266 !0 = !DILexicalBlock(scope: !3, file: !4, line: 7, column: 35) 4267 !1 = !DILexicalBlockFile(scope: !0, file: !4, discriminator: 0) 4268 !2 = !DILexicalBlockFile(scope: !0, file: !4, discriminator: 1) 4269 4270.. _DILocation: 4271 4272DILocation 4273"""""""""" 4274 4275``DILocation`` nodes represent source debug locations. The ``scope:`` field is 4276mandatory, and points at an :ref:`DILexicalBlockFile`, an 4277:ref:`DILexicalBlock`, or an :ref:`DISubprogram`. 4278 4279.. code-block:: llvm 4280 4281 !0 = !DILocation(line: 2900, column: 42, scope: !1, inlinedAt: !2) 4282 4283.. _DILocalVariable: 4284 4285DILocalVariable 4286""""""""""""""" 4287 4288``DILocalVariable`` nodes represent local variables in the source language. If 4289the ``arg:`` field is set to non-zero, then this variable is a subprogram 4290parameter, and it will be included in the ``variables:`` field of its 4291:ref:`DISubprogram`. 4292 4293.. code-block:: llvm 4294 4295 !0 = !DILocalVariable(name: "this", arg: 1, scope: !3, file: !2, line: 7, 4296 type: !3, flags: DIFlagArtificial) 4297 !1 = !DILocalVariable(name: "x", arg: 2, scope: !4, file: !2, line: 7, 4298 type: !3) 4299 !2 = !DILocalVariable(name: "y", scope: !5, file: !2, line: 7, type: !3) 4300 4301DIExpression 4302"""""""""""" 4303 4304``DIExpression`` nodes represent DWARF expression sequences. They are used in 4305:ref:`debug intrinsics<dbg_intrinsics>` (such as ``llvm.dbg.declare``) to 4306describe how the referenced LLVM variable relates to the source language 4307variable. 4308 4309The current supported vocabulary is limited: 4310 4311- ``DW_OP_deref`` dereferences the working expression. 4312- ``DW_OP_plus, 93`` adds ``93`` to the working expression. 4313- ``DW_OP_bit_piece, 16, 8`` specifies the offset and size (``16`` and ``8`` 4314 here, respectively) of the variable piece from the working expression. 4315 4316.. code-block:: llvm 4317 4318 !0 = !DIExpression(DW_OP_deref) 4319 !1 = !DIExpression(DW_OP_plus, 3) 4320 !2 = !DIExpression(DW_OP_bit_piece, 3, 7) 4321 !3 = !DIExpression(DW_OP_deref, DW_OP_plus, 3, DW_OP_bit_piece, 3, 7) 4322 4323DIObjCProperty 4324"""""""""""""" 4325 4326``DIObjCProperty`` nodes represent Objective-C property nodes. 4327 4328.. code-block:: llvm 4329 4330 !3 = !DIObjCProperty(name: "foo", file: !1, line: 7, setter: "setFoo", 4331 getter: "getFoo", attributes: 7, type: !2) 4332 4333DIImportedEntity 4334"""""""""""""""" 4335 4336``DIImportedEntity`` nodes represent entities (such as modules) imported into a 4337compile unit. 4338 4339.. code-block:: llvm 4340 4341 !2 = !DIImportedEntity(tag: DW_TAG_imported_module, name: "foo", scope: !0, 4342 entity: !1, line: 7) 4343 4344DIMacro 4345""""""" 4346 4347``DIMacro`` nodes represent definition or undefinition of a macro identifiers. 4348The ``name:`` field is the macro identifier, followed by macro parameters when 4349defining a function-like macro, and the ``value`` field is the token-string 4350used to expand the macro identifier. 4351 4352.. code-block:: llvm 4353 4354 !2 = !DIMacro(macinfo: DW_MACINFO_define, line: 7, name: "foo(x)", 4355 value: "((x) + 1)") 4356 !3 = !DIMacro(macinfo: DW_MACINFO_undef, line: 30, name: "foo") 4357 4358DIMacroFile 4359""""""""""" 4360 4361``DIMacroFile`` nodes represent inclusion of source files. 4362The ``nodes:`` field is a list of ``DIMacro`` and ``DIMacroFile`` nodes that 4363appear in the included source file. 4364 4365.. code-block:: llvm 4366 4367 !2 = !DIMacroFile(macinfo: DW_MACINFO_start_file, line: 7, file: !2, 4368 nodes: !3) 4369 4370'``tbaa``' Metadata 4371^^^^^^^^^^^^^^^^^^^ 4372 4373In LLVM IR, memory does not have types, so LLVM's own type system is not 4374suitable for doing TBAA. Instead, metadata is added to the IR to 4375describe a type system of a higher level language. This can be used to 4376implement typical C/C++ TBAA, but it can also be used to implement 4377custom alias analysis behavior for other languages. 4378 4379The current metadata format is very simple. TBAA metadata nodes have up 4380to three fields, e.g.: 4381 4382.. code-block:: llvm 4383 4384 !0 = !{ !"an example type tree" } 4385 !1 = !{ !"int", !0 } 4386 !2 = !{ !"float", !0 } 4387 !3 = !{ !"const float", !2, i64 1 } 4388 4389The first field is an identity field. It can be any value, usually a 4390metadata string, which uniquely identifies the type. The most important 4391name in the tree is the name of the root node. Two trees with different 4392root node names are entirely disjoint, even if they have leaves with 4393common names. 4394 4395The second field identifies the type's parent node in the tree, or is 4396null or omitted for a root node. A type is considered to alias all of 4397its descendants and all of its ancestors in the tree. Also, a type is 4398considered to alias all types in other trees, so that bitcode produced 4399from multiple front-ends is handled conservatively. 4400 4401If the third field is present, it's an integer which if equal to 1 4402indicates that the type is "constant" (meaning 4403``pointsToConstantMemory`` should return true; see `other useful 4404AliasAnalysis methods <AliasAnalysis.html#OtherItfs>`_). 4405 4406'``tbaa.struct``' Metadata 4407^^^^^^^^^^^^^^^^^^^^^^^^^^ 4408 4409The :ref:`llvm.memcpy <int_memcpy>` is often used to implement 4410aggregate assignment operations in C and similar languages, however it 4411is defined to copy a contiguous region of memory, which is more than 4412strictly necessary for aggregate types which contain holes due to 4413padding. Also, it doesn't contain any TBAA information about the fields 4414of the aggregate. 4415 4416``!tbaa.struct`` metadata can describe which memory subregions in a 4417memcpy are padding and what the TBAA tags of the struct are. 4418 4419The current metadata format is very simple. ``!tbaa.struct`` metadata 4420nodes are a list of operands which are in conceptual groups of three. 4421For each group of three, the first operand gives the byte offset of a 4422field in bytes, the second gives its size in bytes, and the third gives 4423its tbaa tag. e.g.: 4424 4425.. code-block:: llvm 4426 4427 !4 = !{ i64 0, i64 4, !1, i64 8, i64 4, !2 } 4428 4429This describes a struct with two fields. The first is at offset 0 bytes 4430with size 4 bytes, and has tbaa tag !1. The second is at offset 8 bytes 4431and has size 4 bytes and has tbaa tag !2. 4432 4433Note that the fields need not be contiguous. In this example, there is a 44344 byte gap between the two fields. This gap represents padding which 4435does not carry useful data and need not be preserved. 4436 4437'``noalias``' and '``alias.scope``' Metadata 4438^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 4439 4440``noalias`` and ``alias.scope`` metadata provide the ability to specify generic 4441noalias memory-access sets. This means that some collection of memory access 4442instructions (loads, stores, memory-accessing calls, etc.) that carry 4443``noalias`` metadata can specifically be specified not to alias with some other 4444collection of memory access instructions that carry ``alias.scope`` metadata. 4445Each type of metadata specifies a list of scopes where each scope has an id and 4446a domain. 4447 4448When evaluating an aliasing query, if for some domain, the set 4449of scopes with that domain in one instruction's ``alias.scope`` list is a 4450subset of (or equal to) the set of scopes for that domain in another 4451instruction's ``noalias`` list, then the two memory accesses are assumed not to 4452alias. 4453 4454Because scopes in one domain don't affect scopes in other domains, separate 4455domains can be used to compose multiple independent noalias sets. This is 4456used for example during inlining. As the noalias function parameters are 4457turned into noalias scope metadata, a new domain is used every time the 4458function is inlined. 4459 4460The metadata identifying each domain is itself a list containing one or two 4461entries. The first entry is the name of the domain. Note that if the name is a 4462string then it can be combined across functions and translation units. A 4463self-reference can be used to create globally unique domain names. A 4464descriptive string may optionally be provided as a second list entry. 4465 4466The metadata identifying each scope is also itself a list containing two or 4467three entries. The first entry is the name of the scope. Note that if the name 4468is a string then it can be combined across functions and translation units. A 4469self-reference can be used to create globally unique scope names. A metadata 4470reference to the scope's domain is the second entry. A descriptive string may 4471optionally be provided as a third list entry. 4472 4473For example, 4474 4475.. code-block:: llvm 4476 4477 ; Two scope domains: 4478 !0 = !{!0} 4479 !1 = !{!1} 4480 4481 ; Some scopes in these domains: 4482 !2 = !{!2, !0} 4483 !3 = !{!3, !0} 4484 !4 = !{!4, !1} 4485 4486 ; Some scope lists: 4487 !5 = !{!4} ; A list containing only scope !4 4488 !6 = !{!4, !3, !2} 4489 !7 = !{!3} 4490 4491 ; These two instructions don't alias: 4492 %0 = load float, float* %c, align 4, !alias.scope !5 4493 store float %0, float* %arrayidx.i, align 4, !noalias !5 4494 4495 ; These two instructions also don't alias (for domain !1, the set of scopes 4496 ; in the !alias.scope equals that in the !noalias list): 4497 %2 = load float, float* %c, align 4, !alias.scope !5 4498 store float %2, float* %arrayidx.i2, align 4, !noalias !6 4499 4500 ; These two instructions may alias (for domain !0, the set of scopes in 4501 ; the !noalias list is not a superset of, or equal to, the scopes in the 4502 ; !alias.scope list): 4503 %2 = load float, float* %c, align 4, !alias.scope !6 4504 store float %0, float* %arrayidx.i, align 4, !noalias !7 4505 4506'``fpmath``' Metadata 4507^^^^^^^^^^^^^^^^^^^^^ 4508 4509``fpmath`` metadata may be attached to any instruction of floating point 4510type. It can be used to express the maximum acceptable error in the 4511result of that instruction, in ULPs, thus potentially allowing the 4512compiler to use a more efficient but less accurate method of computing 4513it. ULP is defined as follows: 4514 4515 If ``x`` is a real number that lies between two finite consecutive 4516 floating-point numbers ``a`` and ``b``, without being equal to one 4517 of them, then ``ulp(x) = |b - a|``, otherwise ``ulp(x)`` is the 4518 distance between the two non-equal finite floating-point numbers 4519 nearest ``x``. Moreover, ``ulp(NaN)`` is ``NaN``. 4520 4521The metadata node shall consist of a single positive float type number 4522representing the maximum relative error, for example: 4523 4524.. code-block:: llvm 4525 4526 !0 = !{ float 2.5 } ; maximum acceptable inaccuracy is 2.5 ULPs 4527 4528.. _range-metadata: 4529 4530'``range``' Metadata 4531^^^^^^^^^^^^^^^^^^^^ 4532 4533``range`` metadata may be attached only to ``load``, ``call`` and ``invoke`` of 4534integer types. It expresses the possible ranges the loaded value or the value 4535returned by the called function at this call site is in. The ranges are 4536represented with a flattened list of integers. The loaded value or the value 4537returned is known to be in the union of the ranges defined by each consecutive 4538pair. Each pair has the following properties: 4539 4540- The type must match the type loaded by the instruction. 4541- The pair ``a,b`` represents the range ``[a,b)``. 4542- Both ``a`` and ``b`` are constants. 4543- The range is allowed to wrap. 4544- The range should not represent the full or empty set. That is, 4545 ``a!=b``. 4546 4547In addition, the pairs must be in signed order of the lower bound and 4548they must be non-contiguous. 4549 4550Examples: 4551 4552.. code-block:: llvm 4553 4554 %a = load i8, i8* %x, align 1, !range !0 ; Can only be 0 or 1 4555 %b = load i8, i8* %y, align 1, !range !1 ; Can only be 255 (-1), 0 or 1 4556 %c = call i8 @foo(), !range !2 ; Can only be 0, 1, 3, 4 or 5 4557 %d = invoke i8 @bar() to label %cont 4558 unwind label %lpad, !range !3 ; Can only be -2, -1, 3, 4 or 5 4559 ... 4560 !0 = !{ i8 0, i8 2 } 4561 !1 = !{ i8 255, i8 2 } 4562 !2 = !{ i8 0, i8 2, i8 3, i8 6 } 4563 !3 = !{ i8 -2, i8 0, i8 3, i8 6 } 4564 4565'``unpredictable``' Metadata 4566^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 4567 4568``unpredictable`` metadata may be attached to any branch or switch 4569instruction. It can be used to express the unpredictability of control 4570flow. Similar to the llvm.expect intrinsic, it may be used to alter 4571optimizations related to compare and branch instructions. The metadata 4572is treated as a boolean value; if it exists, it signals that the branch 4573or switch that it is attached to is completely unpredictable. 4574 4575'``llvm.loop``' 4576^^^^^^^^^^^^^^^ 4577 4578It is sometimes useful to attach information to loop constructs. Currently, 4579loop metadata is implemented as metadata attached to the branch instruction 4580in the loop latch block. This type of metadata refer to a metadata node that is 4581guaranteed to be separate for each loop. The loop identifier metadata is 4582specified with the name ``llvm.loop``. 4583 4584The loop identifier metadata is implemented using a metadata that refers to 4585itself to avoid merging it with any other identifier metadata, e.g., 4586during module linkage or function inlining. That is, each loop should refer 4587to their own identification metadata even if they reside in separate functions. 4588The following example contains loop identifier metadata for two separate loop 4589constructs: 4590 4591.. code-block:: llvm 4592 4593 !0 = !{!0} 4594 !1 = !{!1} 4595 4596The loop identifier metadata can be used to specify additional 4597per-loop metadata. Any operands after the first operand can be treated 4598as user-defined metadata. For example the ``llvm.loop.unroll.count`` 4599suggests an unroll factor to the loop unroller: 4600 4601.. code-block:: llvm 4602 4603 br i1 %exitcond, label %._crit_edge, label %.lr.ph, !llvm.loop !0 4604 ... 4605 !0 = !{!0, !1} 4606 !1 = !{!"llvm.loop.unroll.count", i32 4} 4607 4608'``llvm.loop.vectorize``' and '``llvm.loop.interleave``' 4609^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 4610 4611Metadata prefixed with ``llvm.loop.vectorize`` or ``llvm.loop.interleave`` are 4612used to control per-loop vectorization and interleaving parameters such as 4613vectorization width and interleave count. These metadata should be used in 4614conjunction with ``llvm.loop`` loop identification metadata. The 4615``llvm.loop.vectorize`` and ``llvm.loop.interleave`` metadata are only 4616optimization hints and the optimizer will only interleave and vectorize loops if 4617it believes it is safe to do so. The ``llvm.mem.parallel_loop_access`` metadata 4618which contains information about loop-carried memory dependencies can be helpful 4619in determining the safety of these transformations. 4620 4621'``llvm.loop.interleave.count``' Metadata 4622^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 4623 4624This metadata suggests an interleave count to the loop interleaver. 4625The first operand is the string ``llvm.loop.interleave.count`` and the 4626second operand is an integer specifying the interleave count. For 4627example: 4628 4629.. code-block:: llvm 4630 4631 !0 = !{!"llvm.loop.interleave.count", i32 4} 4632 4633Note that setting ``llvm.loop.interleave.count`` to 1 disables interleaving 4634multiple iterations of the loop. If ``llvm.loop.interleave.count`` is set to 0 4635then the interleave count will be determined automatically. 4636 4637'``llvm.loop.vectorize.enable``' Metadata 4638^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 4639 4640This metadata selectively enables or disables vectorization for the loop. The 4641first operand is the string ``llvm.loop.vectorize.enable`` and the second operand 4642is a bit. If the bit operand value is 1 vectorization is enabled. A value of 46430 disables vectorization: 4644 4645.. code-block:: llvm 4646 4647 !0 = !{!"llvm.loop.vectorize.enable", i1 0} 4648 !1 = !{!"llvm.loop.vectorize.enable", i1 1} 4649 4650'``llvm.loop.vectorize.width``' Metadata 4651^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 4652 4653This metadata sets the target width of the vectorizer. The first 4654operand is the string ``llvm.loop.vectorize.width`` and the second 4655operand is an integer specifying the width. For example: 4656 4657.. code-block:: llvm 4658 4659 !0 = !{!"llvm.loop.vectorize.width", i32 4} 4660 4661Note that setting ``llvm.loop.vectorize.width`` to 1 disables 4662vectorization of the loop. If ``llvm.loop.vectorize.width`` is set to 46630 or if the loop does not have this metadata the width will be 4664determined automatically. 4665 4666'``llvm.loop.unroll``' 4667^^^^^^^^^^^^^^^^^^^^^^ 4668 4669Metadata prefixed with ``llvm.loop.unroll`` are loop unrolling 4670optimization hints such as the unroll factor. ``llvm.loop.unroll`` 4671metadata should be used in conjunction with ``llvm.loop`` loop 4672identification metadata. The ``llvm.loop.unroll`` metadata are only 4673optimization hints and the unrolling will only be performed if the 4674optimizer believes it is safe to do so. 4675 4676'``llvm.loop.unroll.count``' Metadata 4677^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 4678 4679This metadata suggests an unroll factor to the loop unroller. The 4680first operand is the string ``llvm.loop.unroll.count`` and the second 4681operand is a positive integer specifying the unroll factor. For 4682example: 4683 4684.. code-block:: llvm 4685 4686 !0 = !{!"llvm.loop.unroll.count", i32 4} 4687 4688If the trip count of the loop is less than the unroll count the loop 4689will be partially unrolled. 4690 4691'``llvm.loop.unroll.disable``' Metadata 4692^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 4693 4694This metadata disables loop unrolling. The metadata has a single operand 4695which is the string ``llvm.loop.unroll.disable``. For example: 4696 4697.. code-block:: llvm 4698 4699 !0 = !{!"llvm.loop.unroll.disable"} 4700 4701'``llvm.loop.unroll.runtime.disable``' Metadata 4702^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 4703 4704This metadata disables runtime loop unrolling. The metadata has a single 4705operand which is the string ``llvm.loop.unroll.runtime.disable``. For example: 4706 4707.. code-block:: llvm 4708 4709 !0 = !{!"llvm.loop.unroll.runtime.disable"} 4710 4711'``llvm.loop.unroll.enable``' Metadata 4712^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 4713 4714This metadata suggests that the loop should be fully unrolled if the trip count 4715is known at compile time and partially unrolled if the trip count is not known 4716at compile time. The metadata has a single operand which is the string 4717``llvm.loop.unroll.enable``. For example: 4718 4719.. code-block:: llvm 4720 4721 !0 = !{!"llvm.loop.unroll.enable"} 4722 4723'``llvm.loop.unroll.full``' Metadata 4724^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 4725 4726This metadata suggests that the loop should be unrolled fully. The 4727metadata has a single operand which is the string ``llvm.loop.unroll.full``. 4728For example: 4729 4730.. code-block:: llvm 4731 4732 !0 = !{!"llvm.loop.unroll.full"} 4733 4734'``llvm.loop.licm_versioning.disable``' Metadata 4735^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 4736 4737This metadata indicates that the loop should not be versioned for the purpose 4738of enabling loop-invariant code motion (LICM). The metadata has a single operand 4739which is the string ``llvm.loop.licm_versioning.disable``. For example: 4740 4741.. code-block:: llvm 4742 4743 !0 = !{!"llvm.loop.licm_versioning.disable"} 4744 4745'``llvm.loop.distribute.enable``' Metadata 4746^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 4747 4748Loop distribution allows splitting a loop into multiple loops. Currently, 4749this is only performed if the entire loop cannot be vectorized due to unsafe 4750memory dependencies. The transformation will atempt to isolate the unsafe 4751dependencies into their own loop. 4752 4753This metadata can be used to selectively enable or disable distribution of the 4754loop. The first operand is the string ``llvm.loop.distribute.enable`` and the 4755second operand is a bit. If the bit operand value is 1 distribution is 4756enabled. A value of 0 disables distribution: 4757 4758.. code-block:: llvm 4759 4760 !0 = !{!"llvm.loop.distribute.enable", i1 0} 4761 !1 = !{!"llvm.loop.distribute.enable", i1 1} 4762 4763This metadata should be used in conjunction with ``llvm.loop`` loop 4764identification metadata. 4765 4766'``llvm.mem``' 4767^^^^^^^^^^^^^^^ 4768 4769Metadata types used to annotate memory accesses with information helpful 4770for optimizations are prefixed with ``llvm.mem``. 4771 4772'``llvm.mem.parallel_loop_access``' Metadata 4773^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 4774 4775The ``llvm.mem.parallel_loop_access`` metadata refers to a loop identifier, 4776or metadata containing a list of loop identifiers for nested loops. 4777The metadata is attached to memory accessing instructions and denotes that 4778no loop carried memory dependence exist between it and other instructions denoted 4779with the same loop identifier. The metadata on memory reads also implies that 4780if conversion (i.e. speculative execution within a loop iteration) is safe. 4781 4782Precisely, given two instructions ``m1`` and ``m2`` that both have the 4783``llvm.mem.parallel_loop_access`` metadata, with ``L1`` and ``L2`` being the 4784set of loops associated with that metadata, respectively, then there is no loop 4785carried dependence between ``m1`` and ``m2`` for loops in both ``L1`` and 4786``L2``. 4787 4788As a special case, if all memory accessing instructions in a loop have 4789``llvm.mem.parallel_loop_access`` metadata that refers to that loop, then the 4790loop has no loop carried memory dependences and is considered to be a parallel 4791loop. 4792 4793Note that if not all memory access instructions have such metadata referring to 4794the loop, then the loop is considered not being trivially parallel. Additional 4795memory dependence analysis is required to make that determination. As a fail 4796safe mechanism, this causes loops that were originally parallel to be considered 4797sequential (if optimization passes that are unaware of the parallel semantics 4798insert new memory instructions into the loop body). 4799 4800Example of a loop that is considered parallel due to its correct use of 4801both ``llvm.loop`` and ``llvm.mem.parallel_loop_access`` 4802metadata types that refer to the same loop identifier metadata. 4803 4804.. code-block:: llvm 4805 4806 for.body: 4807 ... 4808 %val0 = load i32, i32* %arrayidx, !llvm.mem.parallel_loop_access !0 4809 ... 4810 store i32 %val0, i32* %arrayidx1, !llvm.mem.parallel_loop_access !0 4811 ... 4812 br i1 %exitcond, label %for.end, label %for.body, !llvm.loop !0 4813 4814 for.end: 4815 ... 4816 !0 = !{!0} 4817 4818It is also possible to have nested parallel loops. In that case the 4819memory accesses refer to a list of loop identifier metadata nodes instead of 4820the loop identifier metadata node directly: 4821 4822.. code-block:: llvm 4823 4824 outer.for.body: 4825 ... 4826 %val1 = load i32, i32* %arrayidx3, !llvm.mem.parallel_loop_access !2 4827 ... 4828 br label %inner.for.body 4829 4830 inner.for.body: 4831 ... 4832 %val0 = load i32, i32* %arrayidx1, !llvm.mem.parallel_loop_access !0 4833 ... 4834 store i32 %val0, i32* %arrayidx2, !llvm.mem.parallel_loop_access !0 4835 ... 4836 br i1 %exitcond, label %inner.for.end, label %inner.for.body, !llvm.loop !1 4837 4838 inner.for.end: 4839 ... 4840 store i32 %val1, i32* %arrayidx4, !llvm.mem.parallel_loop_access !2 4841 ... 4842 br i1 %exitcond, label %outer.for.end, label %outer.for.body, !llvm.loop !2 4843 4844 outer.for.end: ; preds = %for.body 4845 ... 4846 !0 = !{!1, !2} ; a list of loop identifiers 4847 !1 = !{!1} ; an identifier for the inner loop 4848 !2 = !{!2} ; an identifier for the outer loop 4849 4850'``invariant.group``' Metadata 4851^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 4852 4853The ``invariant.group`` metadata may be attached to ``load``/``store`` instructions. 4854The existence of the ``invariant.group`` metadata on the instruction tells 4855the optimizer that every ``load`` and ``store`` to the same pointer operand 4856within the same invariant group can be assumed to load or store the same 4857value (but see the ``llvm.invariant.group.barrier`` intrinsic which affects 4858when two pointers are considered the same). 4859 4860Examples: 4861 4862.. code-block:: llvm 4863 4864 @unknownPtr = external global i8 4865 ... 4866 %ptr = alloca i8 4867 store i8 42, i8* %ptr, !invariant.group !0 4868 call void @foo(i8* %ptr) 4869 4870 %a = load i8, i8* %ptr, !invariant.group !0 ; Can assume that value under %ptr didn't change 4871 call void @foo(i8* %ptr) 4872 %b = load i8, i8* %ptr, !invariant.group !1 ; Can't assume anything, because group changed 4873 4874 %newPtr = call i8* @getPointer(i8* %ptr) 4875 %c = load i8, i8* %newPtr, !invariant.group !0 ; Can't assume anything, because we only have information about %ptr 4876 4877 %unknownValue = load i8, i8* @unknownPtr 4878 store i8 %unknownValue, i8* %ptr, !invariant.group !0 ; Can assume that %unknownValue == 42 4879 4880 call void @foo(i8* %ptr) 4881 %newPtr2 = call i8* @llvm.invariant.group.barrier(i8* %ptr) 4882 %d = load i8, i8* %newPtr2, !invariant.group !0 ; Can't step through invariant.group.barrier to get value of %ptr 4883 4884 ... 4885 declare void @foo(i8*) 4886 declare i8* @getPointer(i8*) 4887 declare i8* @llvm.invariant.group.barrier(i8*) 4888 4889 !0 = !{!"magic ptr"} 4890 !1 = !{!"other ptr"} 4891 4892 4893 4894Module Flags Metadata 4895===================== 4896 4897Information about the module as a whole is difficult to convey to LLVM's 4898subsystems. The LLVM IR isn't sufficient to transmit this information. 4899The ``llvm.module.flags`` named metadata exists in order to facilitate 4900this. These flags are in the form of key / value pairs --- much like a 4901dictionary --- making it easy for any subsystem who cares about a flag to 4902look it up. 4903 4904The ``llvm.module.flags`` metadata contains a list of metadata triplets. 4905Each triplet has the following form: 4906 4907- The first element is a *behavior* flag, which specifies the behavior 4908 when two (or more) modules are merged together, and it encounters two 4909 (or more) metadata with the same ID. The supported behaviors are 4910 described below. 4911- The second element is a metadata string that is a unique ID for the 4912 metadata. Each module may only have one flag entry for each unique ID (not 4913 including entries with the **Require** behavior). 4914- The third element is the value of the flag. 4915 4916When two (or more) modules are merged together, the resulting 4917``llvm.module.flags`` metadata is the union of the modules' flags. That is, for 4918each unique metadata ID string, there will be exactly one entry in the merged 4919modules ``llvm.module.flags`` metadata table, and the value for that entry will 4920be determined by the merge behavior flag, as described below. The only exception 4921is that entries with the *Require* behavior are always preserved. 4922 4923The following behaviors are supported: 4924 4925.. list-table:: 4926 :header-rows: 1 4927 :widths: 10 90 4928 4929 * - Value 4930 - Behavior 4931 4932 * - 1 4933 - **Error** 4934 Emits an error if two values disagree, otherwise the resulting value 4935 is that of the operands. 4936 4937 * - 2 4938 - **Warning** 4939 Emits a warning if two values disagree. The result value will be the 4940 operand for the flag from the first module being linked. 4941 4942 * - 3 4943 - **Require** 4944 Adds a requirement that another module flag be present and have a 4945 specified value after linking is performed. The value must be a 4946 metadata pair, where the first element of the pair is the ID of the 4947 module flag to be restricted, and the second element of the pair is 4948 the value the module flag should be restricted to. This behavior can 4949 be used to restrict the allowable results (via triggering of an 4950 error) of linking IDs with the **Override** behavior. 4951 4952 * - 4 4953 - **Override** 4954 Uses the specified value, regardless of the behavior or value of the 4955 other module. If both modules specify **Override**, but the values 4956 differ, an error will be emitted. 4957 4958 * - 5 4959 - **Append** 4960 Appends the two values, which are required to be metadata nodes. 4961 4962 * - 6 4963 - **AppendUnique** 4964 Appends the two values, which are required to be metadata 4965 nodes. However, duplicate entries in the second list are dropped 4966 during the append operation. 4967 4968It is an error for a particular unique flag ID to have multiple behaviors, 4969except in the case of **Require** (which adds restrictions on another metadata 4970value) or **Override**. 4971 4972An example of module flags: 4973 4974.. code-block:: llvm 4975 4976 !0 = !{ i32 1, !"foo", i32 1 } 4977 !1 = !{ i32 4, !"bar", i32 37 } 4978 !2 = !{ i32 2, !"qux", i32 42 } 4979 !3 = !{ i32 3, !"qux", 4980 !{ 4981 !"foo", i32 1 4982 } 4983 } 4984 !llvm.module.flags = !{ !0, !1, !2, !3 } 4985 4986- Metadata ``!0`` has the ID ``!"foo"`` and the value '1'. The behavior 4987 if two or more ``!"foo"`` flags are seen is to emit an error if their 4988 values are not equal. 4989 4990- Metadata ``!1`` has the ID ``!"bar"`` and the value '37'. The 4991 behavior if two or more ``!"bar"`` flags are seen is to use the value 4992 '37'. 4993 4994- Metadata ``!2`` has the ID ``!"qux"`` and the value '42'. The 4995 behavior if two or more ``!"qux"`` flags are seen is to emit a 4996 warning if their values are not equal. 4997 4998- Metadata ``!3`` has the ID ``!"qux"`` and the value: 4999 5000 :: 5001 5002 !{ !"foo", i32 1 } 5003 5004 The behavior is to emit an error if the ``llvm.module.flags`` does not 5005 contain a flag with the ID ``!"foo"`` that has the value '1' after linking is 5006 performed. 5007 5008Objective-C Garbage Collection Module Flags Metadata 5009---------------------------------------------------- 5010 5011On the Mach-O platform, Objective-C stores metadata about garbage 5012collection in a special section called "image info". The metadata 5013consists of a version number and a bitmask specifying what types of 5014garbage collection are supported (if any) by the file. If two or more 5015modules are linked together their garbage collection metadata needs to 5016be merged rather than appended together. 5017 5018The Objective-C garbage collection module flags metadata consists of the 5019following key-value pairs: 5020 5021.. list-table:: 5022 :header-rows: 1 5023 :widths: 30 70 5024 5025 * - Key 5026 - Value 5027 5028 * - ``Objective-C Version`` 5029 - **[Required]** --- The Objective-C ABI version. Valid values are 1 and 2. 5030 5031 * - ``Objective-C Image Info Version`` 5032 - **[Required]** --- The version of the image info section. Currently 5033 always 0. 5034 5035 * - ``Objective-C Image Info Section`` 5036 - **[Required]** --- The section to place the metadata. Valid values are 5037 ``"__OBJC, __image_info, regular"`` for Objective-C ABI version 1, and 5038 ``"__DATA,__objc_imageinfo, regular, no_dead_strip"`` for 5039 Objective-C ABI version 2. 5040 5041 * - ``Objective-C Garbage Collection`` 5042 - **[Required]** --- Specifies whether garbage collection is supported or 5043 not. Valid values are 0, for no garbage collection, and 2, for garbage 5044 collection supported. 5045 5046 * - ``Objective-C GC Only`` 5047 - **[Optional]** --- Specifies that only garbage collection is supported. 5048 If present, its value must be 6. This flag requires that the 5049 ``Objective-C Garbage Collection`` flag have the value 2. 5050 5051Some important flag interactions: 5052 5053- If a module with ``Objective-C Garbage Collection`` set to 0 is 5054 merged with a module with ``Objective-C Garbage Collection`` set to 5055 2, then the resulting module has the 5056 ``Objective-C Garbage Collection`` flag set to 0. 5057- A module with ``Objective-C Garbage Collection`` set to 0 cannot be 5058 merged with a module with ``Objective-C GC Only`` set to 6. 5059 5060Automatic Linker Flags Module Flags Metadata 5061-------------------------------------------- 5062 5063Some targets support embedding flags to the linker inside individual object 5064files. Typically this is used in conjunction with language extensions which 5065allow source files to explicitly declare the libraries they depend on, and have 5066these automatically be transmitted to the linker via object files. 5067 5068These flags are encoded in the IR using metadata in the module flags section, 5069using the ``Linker Options`` key. The merge behavior for this flag is required 5070to be ``AppendUnique``, and the value for the key is expected to be a metadata 5071node which should be a list of other metadata nodes, each of which should be a 5072list of metadata strings defining linker options. 5073 5074For example, the following metadata section specifies two separate sets of 5075linker options, presumably to link against ``libz`` and the ``Cocoa`` 5076framework:: 5077 5078 !0 = !{ i32 6, !"Linker Options", 5079 !{ 5080 !{ !"-lz" }, 5081 !{ !"-framework", !"Cocoa" } } } 5082 !llvm.module.flags = !{ !0 } 5083 5084The metadata encoding as lists of lists of options, as opposed to a collapsed 5085list of options, is chosen so that the IR encoding can use multiple option 5086strings to specify e.g., a single library, while still having that specifier be 5087preserved as an atomic element that can be recognized by a target specific 5088assembly writer or object file emitter. 5089 5090Each individual option is required to be either a valid option for the target's 5091linker, or an option that is reserved by the target specific assembly writer or 5092object file emitter. No other aspect of these options is defined by the IR. 5093 5094C type width Module Flags Metadata 5095---------------------------------- 5096 5097The ARM backend emits a section into each generated object file describing the 5098options that it was compiled with (in a compiler-independent way) to prevent 5099linking incompatible objects, and to allow automatic library selection. Some 5100of these options are not visible at the IR level, namely wchar_t width and enum 5101width. 5102 5103To pass this information to the backend, these options are encoded in module 5104flags metadata, using the following key-value pairs: 5105 5106.. list-table:: 5107 :header-rows: 1 5108 :widths: 30 70 5109 5110 * - Key 5111 - Value 5112 5113 * - short_wchar 5114 - * 0 --- sizeof(wchar_t) == 4 5115 * 1 --- sizeof(wchar_t) == 2 5116 5117 * - short_enum 5118 - * 0 --- Enums are at least as large as an ``int``. 5119 * 1 --- Enums are stored in the smallest integer type which can 5120 represent all of its values. 5121 5122For example, the following metadata section specifies that the module was 5123compiled with a ``wchar_t`` width of 4 bytes, and the underlying type of an 5124enum is the smallest type which can represent all of its values:: 5125 5126 !llvm.module.flags = !{!0, !1} 5127 !0 = !{i32 1, !"short_wchar", i32 1} 5128 !1 = !{i32 1, !"short_enum", i32 0} 5129 5130.. _intrinsicglobalvariables: 5131 5132Intrinsic Global Variables 5133========================== 5134 5135LLVM has a number of "magic" global variables that contain data that 5136affect code generation or other IR semantics. These are documented here. 5137All globals of this sort should have a section specified as 5138"``llvm.metadata``". This section and all globals that start with 5139"``llvm.``" are reserved for use by LLVM. 5140 5141.. _gv_llvmused: 5142 5143The '``llvm.used``' Global Variable 5144----------------------------------- 5145 5146The ``@llvm.used`` global is an array which has 5147:ref:`appending linkage <linkage_appending>`. This array contains a list of 5148pointers to named global variables, functions and aliases which may optionally 5149have a pointer cast formed of bitcast or getelementptr. For example, a legal 5150use of it is: 5151 5152.. code-block:: llvm 5153 5154 @X = global i8 4 5155 @Y = global i32 123 5156 5157 @llvm.used = appending global [2 x i8*] [ 5158 i8* @X, 5159 i8* bitcast (i32* @Y to i8*) 5160 ], section "llvm.metadata" 5161 5162If a symbol appears in the ``@llvm.used`` list, then the compiler, assembler, 5163and linker are required to treat the symbol as if there is a reference to the 5164symbol that it cannot see (which is why they have to be named). For example, if 5165a variable has internal linkage and no references other than that from the 5166``@llvm.used`` list, it cannot be deleted. This is commonly used to represent 5167references from inline asms and other things the compiler cannot "see", and 5168corresponds to "``attribute((used))``" in GNU C. 5169 5170On some targets, the code generator must emit a directive to the 5171assembler or object file to prevent the assembler and linker from 5172molesting the symbol. 5173 5174.. _gv_llvmcompilerused: 5175 5176The '``llvm.compiler.used``' Global Variable 5177-------------------------------------------- 5178 5179The ``@llvm.compiler.used`` directive is the same as the ``@llvm.used`` 5180directive, except that it only prevents the compiler from touching the 5181symbol. On targets that support it, this allows an intelligent linker to 5182optimize references to the symbol without being impeded as it would be 5183by ``@llvm.used``. 5184 5185This is a rare construct that should only be used in rare circumstances, 5186and should not be exposed to source languages. 5187 5188.. _gv_llvmglobalctors: 5189 5190The '``llvm.global_ctors``' Global Variable 5191------------------------------------------- 5192 5193.. code-block:: llvm 5194 5195 %0 = type { i32, void ()*, i8* } 5196 @llvm.global_ctors = appending global [1 x %0] [%0 { i32 65535, void ()* @ctor, i8* @data }] 5197 5198The ``@llvm.global_ctors`` array contains a list of constructor 5199functions, priorities, and an optional associated global or function. 5200The functions referenced by this array will be called in ascending order 5201of priority (i.e. lowest first) when the module is loaded. The order of 5202functions with the same priority is not defined. 5203 5204If the third field is present, non-null, and points to a global variable 5205or function, the initializer function will only run if the associated 5206data from the current module is not discarded. 5207 5208.. _llvmglobaldtors: 5209 5210The '``llvm.global_dtors``' Global Variable 5211------------------------------------------- 5212 5213.. code-block:: llvm 5214 5215 %0 = type { i32, void ()*, i8* } 5216 @llvm.global_dtors = appending global [1 x %0] [%0 { i32 65535, void ()* @dtor, i8* @data }] 5217 5218The ``@llvm.global_dtors`` array contains a list of destructor 5219functions, priorities, and an optional associated global or function. 5220The functions referenced by this array will be called in descending 5221order of priority (i.e. highest first) when the module is unloaded. The 5222order of functions with the same priority is not defined. 5223 5224If the third field is present, non-null, and points to a global variable 5225or function, the destructor function will only run if the associated 5226data from the current module is not discarded. 5227 5228Instruction Reference 5229===================== 5230 5231The LLVM instruction set consists of several different classifications 5232of instructions: :ref:`terminator instructions <terminators>`, :ref:`binary 5233instructions <binaryops>`, :ref:`bitwise binary 5234instructions <bitwiseops>`, :ref:`memory instructions <memoryops>`, and 5235:ref:`other instructions <otherops>`. 5236 5237.. _terminators: 5238 5239Terminator Instructions 5240----------------------- 5241 5242As mentioned :ref:`previously <functionstructure>`, every basic block in a 5243program ends with a "Terminator" instruction, which indicates which 5244block should be executed after the current block is finished. These 5245terminator instructions typically yield a '``void``' value: they produce 5246control flow, not values (the one exception being the 5247':ref:`invoke <i_invoke>`' instruction). 5248 5249The terminator instructions are: ':ref:`ret <i_ret>`', 5250':ref:`br <i_br>`', ':ref:`switch <i_switch>`', 5251':ref:`indirectbr <i_indirectbr>`', ':ref:`invoke <i_invoke>`', 5252':ref:`resume <i_resume>`', ':ref:`catchswitch <i_catchswitch>`', 5253':ref:`catchret <i_catchret>`', 5254':ref:`cleanupret <i_cleanupret>`', 5255and ':ref:`unreachable <i_unreachable>`'. 5256 5257.. _i_ret: 5258 5259'``ret``' Instruction 5260^^^^^^^^^^^^^^^^^^^^^ 5261 5262Syntax: 5263""""""" 5264 5265:: 5266 5267 ret <type> <value> ; Return a value from a non-void function 5268 ret void ; Return from void function 5269 5270Overview: 5271""""""""" 5272 5273The '``ret``' instruction is used to return control flow (and optionally 5274a value) from a function back to the caller. 5275 5276There are two forms of the '``ret``' instruction: one that returns a 5277value and then causes control flow, and one that just causes control 5278flow to occur. 5279 5280Arguments: 5281"""""""""" 5282 5283The '``ret``' instruction optionally accepts a single argument, the 5284return value. The type of the return value must be a ':ref:`first 5285class <t_firstclass>`' type. 5286 5287A function is not :ref:`well formed <wellformed>` if it it has a non-void 5288return type and contains a '``ret``' instruction with no return value or 5289a return value with a type that does not match its type, or if it has a 5290void return type and contains a '``ret``' instruction with a return 5291value. 5292 5293Semantics: 5294"""""""""" 5295 5296When the '``ret``' instruction is executed, control flow returns back to 5297the calling function's context. If the caller is a 5298":ref:`call <i_call>`" instruction, execution continues at the 5299instruction after the call. If the caller was an 5300":ref:`invoke <i_invoke>`" instruction, execution continues at the 5301beginning of the "normal" destination block. If the instruction returns 5302a value, that value shall set the call or invoke instruction's return 5303value. 5304 5305Example: 5306"""""""" 5307 5308.. code-block:: llvm 5309 5310 ret i32 5 ; Return an integer value of 5 5311 ret void ; Return from a void function 5312 ret { i32, i8 } { i32 4, i8 2 } ; Return a struct of values 4 and 2 5313 5314.. _i_br: 5315 5316'``br``' Instruction 5317^^^^^^^^^^^^^^^^^^^^ 5318 5319Syntax: 5320""""""" 5321 5322:: 5323 5324 br i1 <cond>, label <iftrue>, label <iffalse> 5325 br label <dest> ; Unconditional branch 5326 5327Overview: 5328""""""""" 5329 5330The '``br``' instruction is used to cause control flow to transfer to a 5331different basic block in the current function. There are two forms of 5332this instruction, corresponding to a conditional branch and an 5333unconditional branch. 5334 5335Arguments: 5336"""""""""" 5337 5338The conditional branch form of the '``br``' instruction takes a single 5339'``i1``' value and two '``label``' values. The unconditional form of the 5340'``br``' instruction takes a single '``label``' value as a target. 5341 5342Semantics: 5343"""""""""" 5344 5345Upon execution of a conditional '``br``' instruction, the '``i1``' 5346argument is evaluated. If the value is ``true``, control flows to the 5347'``iftrue``' ``label`` argument. If "cond" is ``false``, control flows 5348to the '``iffalse``' ``label`` argument. 5349 5350Example: 5351"""""""" 5352 5353.. code-block:: llvm 5354 5355 Test: 5356 %cond = icmp eq i32 %a, %b 5357 br i1 %cond, label %IfEqual, label %IfUnequal 5358 IfEqual: 5359 ret i32 1 5360 IfUnequal: 5361 ret i32 0 5362 5363.. _i_switch: 5364 5365'``switch``' Instruction 5366^^^^^^^^^^^^^^^^^^^^^^^^ 5367 5368Syntax: 5369""""""" 5370 5371:: 5372 5373 switch <intty> <value>, label <defaultdest> [ <intty> <val>, label <dest> ... ] 5374 5375Overview: 5376""""""""" 5377 5378The '``switch``' instruction is used to transfer control flow to one of 5379several different places. It is a generalization of the '``br``' 5380instruction, allowing a branch to occur to one of many possible 5381destinations. 5382 5383Arguments: 5384"""""""""" 5385 5386The '``switch``' instruction uses three parameters: an integer 5387comparison value '``value``', a default '``label``' destination, and an 5388array of pairs of comparison value constants and '``label``'s. The table 5389is not allowed to contain duplicate constant entries. 5390 5391Semantics: 5392"""""""""" 5393 5394The ``switch`` instruction specifies a table of values and destinations. 5395When the '``switch``' instruction is executed, this table is searched 5396for the given value. If the value is found, control flow is transferred 5397to the corresponding destination; otherwise, control flow is transferred 5398to the default destination. 5399 5400Implementation: 5401""""""""""""""" 5402 5403Depending on properties of the target machine and the particular 5404``switch`` instruction, this instruction may be code generated in 5405different ways. For example, it could be generated as a series of 5406chained conditional branches or with a lookup table. 5407 5408Example: 5409"""""""" 5410 5411.. code-block:: llvm 5412 5413 ; Emulate a conditional br instruction 5414 %Val = zext i1 %value to i32 5415 switch i32 %Val, label %truedest [ i32 0, label %falsedest ] 5416 5417 ; Emulate an unconditional br instruction 5418 switch i32 0, label %dest [ ] 5419 5420 ; Implement a jump table: 5421 switch i32 %val, label %otherwise [ i32 0, label %onzero 5422 i32 1, label %onone 5423 i32 2, label %ontwo ] 5424 5425.. _i_indirectbr: 5426 5427'``indirectbr``' Instruction 5428^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 5429 5430Syntax: 5431""""""" 5432 5433:: 5434 5435 indirectbr <somety>* <address>, [ label <dest1>, label <dest2>, ... ] 5436 5437Overview: 5438""""""""" 5439 5440The '``indirectbr``' instruction implements an indirect branch to a 5441label within the current function, whose address is specified by 5442"``address``". Address must be derived from a 5443:ref:`blockaddress <blockaddress>` constant. 5444 5445Arguments: 5446"""""""""" 5447 5448The '``address``' argument is the address of the label to jump to. The 5449rest of the arguments indicate the full set of possible destinations 5450that the address may point to. Blocks are allowed to occur multiple 5451times in the destination list, though this isn't particularly useful. 5452 5453This destination list is required so that dataflow analysis has an 5454accurate understanding of the CFG. 5455 5456Semantics: 5457"""""""""" 5458 5459Control transfers to the block specified in the address argument. All 5460possible destination blocks must be listed in the label list, otherwise 5461this instruction has undefined behavior. This implies that jumps to 5462labels defined in other functions have undefined behavior as well. 5463 5464Implementation: 5465""""""""""""""" 5466 5467This is typically implemented with a jump through a register. 5468 5469Example: 5470"""""""" 5471 5472.. code-block:: llvm 5473 5474 indirectbr i8* %Addr, [ label %bb1, label %bb2, label %bb3 ] 5475 5476.. _i_invoke: 5477 5478'``invoke``' Instruction 5479^^^^^^^^^^^^^^^^^^^^^^^^ 5480 5481Syntax: 5482""""""" 5483 5484:: 5485 5486 <result> = invoke [cconv] [ret attrs] <ty>|<fnty> <fnptrval>(<function args>) [fn attrs] 5487 [operand bundles] to label <normal label> unwind label <exception label> 5488 5489Overview: 5490""""""""" 5491 5492The '``invoke``' instruction causes control to transfer to a specified 5493function, with the possibility of control flow transfer to either the 5494'``normal``' label or the '``exception``' label. If the callee function 5495returns with the "``ret``" instruction, control flow will return to the 5496"normal" label. If the callee (or any indirect callees) returns via the 5497":ref:`resume <i_resume>`" instruction or other exception handling 5498mechanism, control is interrupted and continued at the dynamically 5499nearest "exception" label. 5500 5501The '``exception``' label is a `landing 5502pad <ExceptionHandling.html#overview>`_ for the exception. As such, 5503'``exception``' label is required to have the 5504":ref:`landingpad <i_landingpad>`" instruction, which contains the 5505information about the behavior of the program after unwinding happens, 5506as its first non-PHI instruction. The restrictions on the 5507"``landingpad``" instruction's tightly couples it to the "``invoke``" 5508instruction, so that the important information contained within the 5509"``landingpad``" instruction can't be lost through normal code motion. 5510 5511Arguments: 5512"""""""""" 5513 5514This instruction requires several arguments: 5515 5516#. The optional "cconv" marker indicates which :ref:`calling 5517 convention <callingconv>` the call should use. If none is 5518 specified, the call defaults to using C calling conventions. 5519#. The optional :ref:`Parameter Attributes <paramattrs>` list for return 5520 values. Only '``zeroext``', '``signext``', and '``inreg``' attributes 5521 are valid here. 5522#. '``ty``': the type of the call instruction itself which is also the 5523 type of the return value. Functions that return no value are marked 5524 ``void``. 5525#. '``fnty``': shall be the signature of the function being invoked. The 5526 argument types must match the types implied by this signature. This 5527 type can be omitted if the function is not varargs. 5528#. '``fnptrval``': An LLVM value containing a pointer to a function to 5529 be invoked. In most cases, this is a direct function invocation, but 5530 indirect ``invoke``'s are just as possible, calling an arbitrary pointer 5531 to function value. 5532#. '``function args``': argument list whose types match the function 5533 signature argument types and parameter attributes. All arguments must 5534 be of :ref:`first class <t_firstclass>` type. If the function signature 5535 indicates the function accepts a variable number of arguments, the 5536 extra arguments can be specified. 5537#. '``normal label``': the label reached when the called function 5538 executes a '``ret``' instruction. 5539#. '``exception label``': the label reached when a callee returns via 5540 the :ref:`resume <i_resume>` instruction or other exception handling 5541 mechanism. 5542#. The optional :ref:`function attributes <fnattrs>` list. Only 5543 '``noreturn``', '``nounwind``', '``readonly``' and '``readnone``' 5544 attributes are valid here. 5545#. The optional :ref:`operand bundles <opbundles>` list. 5546 5547Semantics: 5548"""""""""" 5549 5550This instruction is designed to operate as a standard '``call``' 5551instruction in most regards. The primary difference is that it 5552establishes an association with a label, which is used by the runtime 5553library to unwind the stack. 5554 5555This instruction is used in languages with destructors to ensure that 5556proper cleanup is performed in the case of either a ``longjmp`` or a 5557thrown exception. Additionally, this is important for implementation of 5558'``catch``' clauses in high-level languages that support them. 5559 5560For the purposes of the SSA form, the definition of the value returned 5561by the '``invoke``' instruction is deemed to occur on the edge from the 5562current block to the "normal" label. If the callee unwinds then no 5563return value is available. 5564 5565Example: 5566"""""""" 5567 5568.. code-block:: llvm 5569 5570 %retval = invoke i32 @Test(i32 15) to label %Continue 5571 unwind label %TestCleanup ; i32:retval set 5572 %retval = invoke coldcc i32 %Testfnptr(i32 15) to label %Continue 5573 unwind label %TestCleanup ; i32:retval set 5574 5575.. _i_resume: 5576 5577'``resume``' Instruction 5578^^^^^^^^^^^^^^^^^^^^^^^^ 5579 5580Syntax: 5581""""""" 5582 5583:: 5584 5585 resume <type> <value> 5586 5587Overview: 5588""""""""" 5589 5590The '``resume``' instruction is a terminator instruction that has no 5591successors. 5592 5593Arguments: 5594"""""""""" 5595 5596The '``resume``' instruction requires one argument, which must have the 5597same type as the result of any '``landingpad``' instruction in the same 5598function. 5599 5600Semantics: 5601"""""""""" 5602 5603The '``resume``' instruction resumes propagation of an existing 5604(in-flight) exception whose unwinding was interrupted with a 5605:ref:`landingpad <i_landingpad>` instruction. 5606 5607Example: 5608"""""""" 5609 5610.. code-block:: llvm 5611 5612 resume { i8*, i32 } %exn 5613 5614.. _i_catchswitch: 5615 5616'``catchswitch``' Instruction 5617^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 5618 5619Syntax: 5620""""""" 5621 5622:: 5623 5624 <resultval> = catchswitch within <parent> [ label <handler1>, label <handler2>, ... ] unwind to caller 5625 <resultval> = catchswitch within <parent> [ label <handler1>, label <handler2>, ... ] unwind label <default> 5626 5627Overview: 5628""""""""" 5629 5630The '``catchswitch``' instruction is used by `LLVM's exception handling system 5631<ExceptionHandling.html#overview>`_ to describe the set of possible catch handlers 5632that may be executed by the :ref:`EH personality routine <personalityfn>`. 5633 5634Arguments: 5635"""""""""" 5636 5637The ``parent`` argument is the token of the funclet that contains the 5638``catchswitch`` instruction. If the ``catchswitch`` is not inside a funclet, 5639this operand may be the token ``none``. 5640 5641The ``default`` argument is the label of another basic block beginning with 5642either a ``cleanuppad`` or ``catchswitch`` instruction. This unwind destination 5643must be a legal target with respect to the ``parent`` links, as described in 5644the `exception handling documentation\ <ExceptionHandling.html#wineh-constraints>`_. 5645 5646The ``handlers`` are a nonempty list of successor blocks that each begin with a 5647:ref:`catchpad <i_catchpad>` instruction. 5648 5649Semantics: 5650"""""""""" 5651 5652Executing this instruction transfers control to one of the successors in 5653``handlers``, if appropriate, or continues to unwind via the unwind label if 5654present. 5655 5656The ``catchswitch`` is both a terminator and a "pad" instruction, meaning that 5657it must be both the first non-phi instruction and last instruction in the basic 5658block. Therefore, it must be the only non-phi instruction in the block. 5659 5660Example: 5661"""""""" 5662 5663.. code-block:: llvm 5664 5665 dispatch1: 5666 %cs1 = catchswitch within none [label %handler0, label %handler1] unwind to caller 5667 dispatch2: 5668 %cs2 = catchswitch within %parenthandler [label %handler0] unwind label %cleanup 5669 5670.. _i_catchret: 5671 5672'``catchret``' Instruction 5673^^^^^^^^^^^^^^^^^^^^^^^^^^ 5674 5675Syntax: 5676""""""" 5677 5678:: 5679 5680 catchret from <token> to label <normal> 5681 5682Overview: 5683""""""""" 5684 5685The '``catchret``' instruction is a terminator instruction that has a 5686single successor. 5687 5688 5689Arguments: 5690"""""""""" 5691 5692The first argument to a '``catchret``' indicates which ``catchpad`` it 5693exits. It must be a :ref:`catchpad <i_catchpad>`. 5694The second argument to a '``catchret``' specifies where control will 5695transfer to next. 5696 5697Semantics: 5698"""""""""" 5699 5700The '``catchret``' instruction ends an existing (in-flight) exception whose 5701unwinding was interrupted with a :ref:`catchpad <i_catchpad>` instruction. The 5702:ref:`personality function <personalityfn>` gets a chance to execute arbitrary 5703code to, for example, destroy the active exception. Control then transfers to 5704``normal``. 5705 5706The ``token`` argument must be a token produced by a ``catchpad`` instruction. 5707If the specified ``catchpad`` is not the most-recently-entered not-yet-exited 5708funclet pad (as described in the `EH documentation\ <ExceptionHandling.html#wineh-constraints>`_), 5709the ``catchret``'s behavior is undefined. 5710 5711Example: 5712"""""""" 5713 5714.. code-block:: llvm 5715 5716 catchret from %catch label %continue 5717 5718.. _i_cleanupret: 5719 5720'``cleanupret``' Instruction 5721^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 5722 5723Syntax: 5724""""""" 5725 5726:: 5727 5728 cleanupret from <value> unwind label <continue> 5729 cleanupret from <value> unwind to caller 5730 5731Overview: 5732""""""""" 5733 5734The '``cleanupret``' instruction is a terminator instruction that has 5735an optional successor. 5736 5737 5738Arguments: 5739"""""""""" 5740 5741The '``cleanupret``' instruction requires one argument, which indicates 5742which ``cleanuppad`` it exits, and must be a :ref:`cleanuppad <i_cleanuppad>`. 5743If the specified ``cleanuppad`` is not the most-recently-entered not-yet-exited 5744funclet pad (as described in the `EH documentation\ <ExceptionHandling.html#wineh-constraints>`_), 5745the ``cleanupret``'s behavior is undefined. 5746 5747The '``cleanupret``' instruction also has an optional successor, ``continue``, 5748which must be the label of another basic block beginning with either a 5749``cleanuppad`` or ``catchswitch`` instruction. This unwind destination must 5750be a legal target with respect to the ``parent`` links, as described in the 5751`exception handling documentation\ <ExceptionHandling.html#wineh-constraints>`_. 5752 5753Semantics: 5754"""""""""" 5755 5756The '``cleanupret``' instruction indicates to the 5757:ref:`personality function <personalityfn>` that one 5758:ref:`cleanuppad <i_cleanuppad>` it transferred control to has ended. 5759It transfers control to ``continue`` or unwinds out of the function. 5760 5761Example: 5762"""""""" 5763 5764.. code-block:: llvm 5765 5766 cleanupret from %cleanup unwind to caller 5767 cleanupret from %cleanup unwind label %continue 5768 5769.. _i_unreachable: 5770 5771'``unreachable``' Instruction 5772^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 5773 5774Syntax: 5775""""""" 5776 5777:: 5778 5779 unreachable 5780 5781Overview: 5782""""""""" 5783 5784The '``unreachable``' instruction has no defined semantics. This 5785instruction is used to inform the optimizer that a particular portion of 5786the code is not reachable. This can be used to indicate that the code 5787after a no-return function cannot be reached, and other facts. 5788 5789Semantics: 5790"""""""""" 5791 5792The '``unreachable``' instruction has no defined semantics. 5793 5794.. _binaryops: 5795 5796Binary Operations 5797----------------- 5798 5799Binary operators are used to do most of the computation in a program. 5800They require two operands of the same type, execute an operation on 5801them, and produce a single value. The operands might represent multiple 5802data, as is the case with the :ref:`vector <t_vector>` data type. The 5803result value has the same type as its operands. 5804 5805There are several different binary operators: 5806 5807.. _i_add: 5808 5809'``add``' Instruction 5810^^^^^^^^^^^^^^^^^^^^^ 5811 5812Syntax: 5813""""""" 5814 5815:: 5816 5817 <result> = add <ty> <op1>, <op2> ; yields ty:result 5818 <result> = add nuw <ty> <op1>, <op2> ; yields ty:result 5819 <result> = add nsw <ty> <op1>, <op2> ; yields ty:result 5820 <result> = add nuw nsw <ty> <op1>, <op2> ; yields ty:result 5821 5822Overview: 5823""""""""" 5824 5825The '``add``' instruction returns the sum of its two operands. 5826 5827Arguments: 5828"""""""""" 5829 5830The two arguments to the '``add``' instruction must be 5831:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both 5832arguments must have identical types. 5833 5834Semantics: 5835"""""""""" 5836 5837The value produced is the integer sum of the two operands. 5838 5839If the sum has unsigned overflow, the result returned is the 5840mathematical result modulo 2\ :sup:`n`\ , where n is the bit width of 5841the result. 5842 5843Because LLVM integers use a two's complement representation, this 5844instruction is appropriate for both signed and unsigned integers. 5845 5846``nuw`` and ``nsw`` stand for "No Unsigned Wrap" and "No Signed Wrap", 5847respectively. If the ``nuw`` and/or ``nsw`` keywords are present, the 5848result value of the ``add`` is a :ref:`poison value <poisonvalues>` if 5849unsigned and/or signed overflow, respectively, occurs. 5850 5851Example: 5852"""""""" 5853 5854.. code-block:: llvm 5855 5856 <result> = add i32 4, %var ; yields i32:result = 4 + %var 5857 5858.. _i_fadd: 5859 5860'``fadd``' Instruction 5861^^^^^^^^^^^^^^^^^^^^^^ 5862 5863Syntax: 5864""""""" 5865 5866:: 5867 5868 <result> = fadd [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result 5869 5870Overview: 5871""""""""" 5872 5873The '``fadd``' instruction returns the sum of its two operands. 5874 5875Arguments: 5876"""""""""" 5877 5878The two arguments to the '``fadd``' instruction must be :ref:`floating 5879point <t_floating>` or :ref:`vector <t_vector>` of floating point values. 5880Both arguments must have identical types. 5881 5882Semantics: 5883"""""""""" 5884 5885The value produced is the floating point sum of the two operands. This 5886instruction can also take any number of :ref:`fast-math flags <fastmath>`, 5887which are optimization hints to enable otherwise unsafe floating point 5888optimizations: 5889 5890Example: 5891"""""""" 5892 5893.. code-block:: llvm 5894 5895 <result> = fadd float 4.0, %var ; yields float:result = 4.0 + %var 5896 5897'``sub``' Instruction 5898^^^^^^^^^^^^^^^^^^^^^ 5899 5900Syntax: 5901""""""" 5902 5903:: 5904 5905 <result> = sub <ty> <op1>, <op2> ; yields ty:result 5906 <result> = sub nuw <ty> <op1>, <op2> ; yields ty:result 5907 <result> = sub nsw <ty> <op1>, <op2> ; yields ty:result 5908 <result> = sub nuw nsw <ty> <op1>, <op2> ; yields ty:result 5909 5910Overview: 5911""""""""" 5912 5913The '``sub``' instruction returns the difference of its two operands. 5914 5915Note that the '``sub``' instruction is used to represent the '``neg``' 5916instruction present in most other intermediate representations. 5917 5918Arguments: 5919"""""""""" 5920 5921The two arguments to the '``sub``' instruction must be 5922:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both 5923arguments must have identical types. 5924 5925Semantics: 5926"""""""""" 5927 5928The value produced is the integer difference of the two operands. 5929 5930If the difference has unsigned overflow, the result returned is the 5931mathematical result modulo 2\ :sup:`n`\ , where n is the bit width of 5932the result. 5933 5934Because LLVM integers use a two's complement representation, this 5935instruction is appropriate for both signed and unsigned integers. 5936 5937``nuw`` and ``nsw`` stand for "No Unsigned Wrap" and "No Signed Wrap", 5938respectively. If the ``nuw`` and/or ``nsw`` keywords are present, the 5939result value of the ``sub`` is a :ref:`poison value <poisonvalues>` if 5940unsigned and/or signed overflow, respectively, occurs. 5941 5942Example: 5943"""""""" 5944 5945.. code-block:: llvm 5946 5947 <result> = sub i32 4, %var ; yields i32:result = 4 - %var 5948 <result> = sub i32 0, %val ; yields i32:result = -%var 5949 5950.. _i_fsub: 5951 5952'``fsub``' Instruction 5953^^^^^^^^^^^^^^^^^^^^^^ 5954 5955Syntax: 5956""""""" 5957 5958:: 5959 5960 <result> = fsub [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result 5961 5962Overview: 5963""""""""" 5964 5965The '``fsub``' instruction returns the difference of its two operands. 5966 5967Note that the '``fsub``' instruction is used to represent the '``fneg``' 5968instruction present in most other intermediate representations. 5969 5970Arguments: 5971"""""""""" 5972 5973The two arguments to the '``fsub``' instruction must be :ref:`floating 5974point <t_floating>` or :ref:`vector <t_vector>` of floating point values. 5975Both arguments must have identical types. 5976 5977Semantics: 5978"""""""""" 5979 5980The value produced is the floating point difference of the two operands. 5981This instruction can also take any number of :ref:`fast-math 5982flags <fastmath>`, which are optimization hints to enable otherwise 5983unsafe floating point optimizations: 5984 5985Example: 5986"""""""" 5987 5988.. code-block:: llvm 5989 5990 <result> = fsub float 4.0, %var ; yields float:result = 4.0 - %var 5991 <result> = fsub float -0.0, %val ; yields float:result = -%var 5992 5993'``mul``' Instruction 5994^^^^^^^^^^^^^^^^^^^^^ 5995 5996Syntax: 5997""""""" 5998 5999:: 6000 6001 <result> = mul <ty> <op1>, <op2> ; yields ty:result 6002 <result> = mul nuw <ty> <op1>, <op2> ; yields ty:result 6003 <result> = mul nsw <ty> <op1>, <op2> ; yields ty:result 6004 <result> = mul nuw nsw <ty> <op1>, <op2> ; yields ty:result 6005 6006Overview: 6007""""""""" 6008 6009The '``mul``' instruction returns the product of its two operands. 6010 6011Arguments: 6012"""""""""" 6013 6014The two arguments to the '``mul``' instruction must be 6015:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both 6016arguments must have identical types. 6017 6018Semantics: 6019"""""""""" 6020 6021The value produced is the integer product of the two operands. 6022 6023If the result of the multiplication has unsigned overflow, the result 6024returned is the mathematical result modulo 2\ :sup:`n`\ , where n is the 6025bit width of the result. 6026 6027Because LLVM integers use a two's complement representation, and the 6028result is the same width as the operands, this instruction returns the 6029correct result for both signed and unsigned integers. If a full product 6030(e.g. ``i32`` * ``i32`` -> ``i64``) is needed, the operands should be 6031sign-extended or zero-extended as appropriate to the width of the full 6032product. 6033 6034``nuw`` and ``nsw`` stand for "No Unsigned Wrap" and "No Signed Wrap", 6035respectively. If the ``nuw`` and/or ``nsw`` keywords are present, the 6036result value of the ``mul`` is a :ref:`poison value <poisonvalues>` if 6037unsigned and/or signed overflow, respectively, occurs. 6038 6039Example: 6040"""""""" 6041 6042.. code-block:: llvm 6043 6044 <result> = mul i32 4, %var ; yields i32:result = 4 * %var 6045 6046.. _i_fmul: 6047 6048'``fmul``' Instruction 6049^^^^^^^^^^^^^^^^^^^^^^ 6050 6051Syntax: 6052""""""" 6053 6054:: 6055 6056 <result> = fmul [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result 6057 6058Overview: 6059""""""""" 6060 6061The '``fmul``' instruction returns the product of its two operands. 6062 6063Arguments: 6064"""""""""" 6065 6066The two arguments to the '``fmul``' instruction must be :ref:`floating 6067point <t_floating>` or :ref:`vector <t_vector>` of floating point values. 6068Both arguments must have identical types. 6069 6070Semantics: 6071"""""""""" 6072 6073The value produced is the floating point product of the two operands. 6074This instruction can also take any number of :ref:`fast-math 6075flags <fastmath>`, which are optimization hints to enable otherwise 6076unsafe floating point optimizations: 6077 6078Example: 6079"""""""" 6080 6081.. code-block:: llvm 6082 6083 <result> = fmul float 4.0, %var ; yields float:result = 4.0 * %var 6084 6085'``udiv``' Instruction 6086^^^^^^^^^^^^^^^^^^^^^^ 6087 6088Syntax: 6089""""""" 6090 6091:: 6092 6093 <result> = udiv <ty> <op1>, <op2> ; yields ty:result 6094 <result> = udiv exact <ty> <op1>, <op2> ; yields ty:result 6095 6096Overview: 6097""""""""" 6098 6099The '``udiv``' instruction returns the quotient of its two operands. 6100 6101Arguments: 6102"""""""""" 6103 6104The two arguments to the '``udiv``' instruction must be 6105:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both 6106arguments must have identical types. 6107 6108Semantics: 6109"""""""""" 6110 6111The value produced is the unsigned integer quotient of the two operands. 6112 6113Note that unsigned integer division and signed integer division are 6114distinct operations; for signed integer division, use '``sdiv``'. 6115 6116Division by zero leads to undefined behavior. 6117 6118If the ``exact`` keyword is present, the result value of the ``udiv`` is 6119a :ref:`poison value <poisonvalues>` if %op1 is not a multiple of %op2 (as 6120such, "((a udiv exact b) mul b) == a"). 6121 6122Example: 6123"""""""" 6124 6125.. code-block:: llvm 6126 6127 <result> = udiv i32 4, %var ; yields i32:result = 4 / %var 6128 6129'``sdiv``' Instruction 6130^^^^^^^^^^^^^^^^^^^^^^ 6131 6132Syntax: 6133""""""" 6134 6135:: 6136 6137 <result> = sdiv <ty> <op1>, <op2> ; yields ty:result 6138 <result> = sdiv exact <ty> <op1>, <op2> ; yields ty:result 6139 6140Overview: 6141""""""""" 6142 6143The '``sdiv``' instruction returns the quotient of its two operands. 6144 6145Arguments: 6146"""""""""" 6147 6148The two arguments to the '``sdiv``' instruction must be 6149:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both 6150arguments must have identical types. 6151 6152Semantics: 6153"""""""""" 6154 6155The value produced is the signed integer quotient of the two operands 6156rounded towards zero. 6157 6158Note that signed integer division and unsigned integer division are 6159distinct operations; for unsigned integer division, use '``udiv``'. 6160 6161Division by zero leads to undefined behavior. Overflow also leads to 6162undefined behavior; this is a rare case, but can occur, for example, by 6163doing a 32-bit division of -2147483648 by -1. 6164 6165If the ``exact`` keyword is present, the result value of the ``sdiv`` is 6166a :ref:`poison value <poisonvalues>` if the result would be rounded. 6167 6168Example: 6169"""""""" 6170 6171.. code-block:: llvm 6172 6173 <result> = sdiv i32 4, %var ; yields i32:result = 4 / %var 6174 6175.. _i_fdiv: 6176 6177'``fdiv``' Instruction 6178^^^^^^^^^^^^^^^^^^^^^^ 6179 6180Syntax: 6181""""""" 6182 6183:: 6184 6185 <result> = fdiv [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result 6186 6187Overview: 6188""""""""" 6189 6190The '``fdiv``' instruction returns the quotient of its two operands. 6191 6192Arguments: 6193"""""""""" 6194 6195The two arguments to the '``fdiv``' instruction must be :ref:`floating 6196point <t_floating>` or :ref:`vector <t_vector>` of floating point values. 6197Both arguments must have identical types. 6198 6199Semantics: 6200"""""""""" 6201 6202The value produced is the floating point quotient of the two operands. 6203This instruction can also take any number of :ref:`fast-math 6204flags <fastmath>`, which are optimization hints to enable otherwise 6205unsafe floating point optimizations: 6206 6207Example: 6208"""""""" 6209 6210.. code-block:: llvm 6211 6212 <result> = fdiv float 4.0, %var ; yields float:result = 4.0 / %var 6213 6214'``urem``' Instruction 6215^^^^^^^^^^^^^^^^^^^^^^ 6216 6217Syntax: 6218""""""" 6219 6220:: 6221 6222 <result> = urem <ty> <op1>, <op2> ; yields ty:result 6223 6224Overview: 6225""""""""" 6226 6227The '``urem``' instruction returns the remainder from the unsigned 6228division of its two arguments. 6229 6230Arguments: 6231"""""""""" 6232 6233The two arguments to the '``urem``' instruction must be 6234:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both 6235arguments must have identical types. 6236 6237Semantics: 6238"""""""""" 6239 6240This instruction returns the unsigned integer *remainder* of a division. 6241This instruction always performs an unsigned division to get the 6242remainder. 6243 6244Note that unsigned integer remainder and signed integer remainder are 6245distinct operations; for signed integer remainder, use '``srem``'. 6246 6247Taking the remainder of a division by zero leads to undefined behavior. 6248 6249Example: 6250"""""""" 6251 6252.. code-block:: llvm 6253 6254 <result> = urem i32 4, %var ; yields i32:result = 4 % %var 6255 6256'``srem``' Instruction 6257^^^^^^^^^^^^^^^^^^^^^^ 6258 6259Syntax: 6260""""""" 6261 6262:: 6263 6264 <result> = srem <ty> <op1>, <op2> ; yields ty:result 6265 6266Overview: 6267""""""""" 6268 6269The '``srem``' instruction returns the remainder from the signed 6270division of its two operands. This instruction can also take 6271:ref:`vector <t_vector>` versions of the values in which case the elements 6272must be integers. 6273 6274Arguments: 6275"""""""""" 6276 6277The two arguments to the '``srem``' instruction must be 6278:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both 6279arguments must have identical types. 6280 6281Semantics: 6282"""""""""" 6283 6284This instruction returns the *remainder* of a division (where the result 6285is either zero or has the same sign as the dividend, ``op1``), not the 6286*modulo* operator (where the result is either zero or has the same sign 6287as the divisor, ``op2``) of a value. For more information about the 6288difference, see `The Math 6289Forum <http://mathforum.org/dr.math/problems/anne.4.28.99.html>`_. For a 6290table of how this is implemented in various languages, please see 6291`Wikipedia: modulo 6292operation <http://en.wikipedia.org/wiki/Modulo_operation>`_. 6293 6294Note that signed integer remainder and unsigned integer remainder are 6295distinct operations; for unsigned integer remainder, use '``urem``'. 6296 6297Taking the remainder of a division by zero leads to undefined behavior. 6298Overflow also leads to undefined behavior; this is a rare case, but can 6299occur, for example, by taking the remainder of a 32-bit division of 6300-2147483648 by -1. (The remainder doesn't actually overflow, but this 6301rule lets srem be implemented using instructions that return both the 6302result of the division and the remainder.) 6303 6304Example: 6305"""""""" 6306 6307.. code-block:: llvm 6308 6309 <result> = srem i32 4, %var ; yields i32:result = 4 % %var 6310 6311.. _i_frem: 6312 6313'``frem``' Instruction 6314^^^^^^^^^^^^^^^^^^^^^^ 6315 6316Syntax: 6317""""""" 6318 6319:: 6320 6321 <result> = frem [fast-math flags]* <ty> <op1>, <op2> ; yields ty:result 6322 6323Overview: 6324""""""""" 6325 6326The '``frem``' instruction returns the remainder from the division of 6327its two operands. 6328 6329Arguments: 6330"""""""""" 6331 6332The two arguments to the '``frem``' instruction must be :ref:`floating 6333point <t_floating>` or :ref:`vector <t_vector>` of floating point values. 6334Both arguments must have identical types. 6335 6336Semantics: 6337"""""""""" 6338 6339This instruction returns the *remainder* of a division. The remainder 6340has the same sign as the dividend. This instruction can also take any 6341number of :ref:`fast-math flags <fastmath>`, which are optimization hints 6342to enable otherwise unsafe floating point optimizations: 6343 6344Example: 6345"""""""" 6346 6347.. code-block:: llvm 6348 6349 <result> = frem float 4.0, %var ; yields float:result = 4.0 % %var 6350 6351.. _bitwiseops: 6352 6353Bitwise Binary Operations 6354------------------------- 6355 6356Bitwise binary operators are used to do various forms of bit-twiddling 6357in a program. They are generally very efficient instructions and can 6358commonly be strength reduced from other instructions. They require two 6359operands of the same type, execute an operation on them, and produce a 6360single value. The resulting value is the same type as its operands. 6361 6362'``shl``' Instruction 6363^^^^^^^^^^^^^^^^^^^^^ 6364 6365Syntax: 6366""""""" 6367 6368:: 6369 6370 <result> = shl <ty> <op1>, <op2> ; yields ty:result 6371 <result> = shl nuw <ty> <op1>, <op2> ; yields ty:result 6372 <result> = shl nsw <ty> <op1>, <op2> ; yields ty:result 6373 <result> = shl nuw nsw <ty> <op1>, <op2> ; yields ty:result 6374 6375Overview: 6376""""""""" 6377 6378The '``shl``' instruction returns the first operand shifted to the left 6379a specified number of bits. 6380 6381Arguments: 6382"""""""""" 6383 6384Both arguments to the '``shl``' instruction must be the same 6385:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer type. 6386'``op2``' is treated as an unsigned value. 6387 6388Semantics: 6389"""""""""" 6390 6391The value produced is ``op1`` \* 2\ :sup:`op2` mod 2\ :sup:`n`, 6392where ``n`` is the width of the result. If ``op2`` is (statically or 6393dynamically) equal to or larger than the number of bits in 6394``op1``, the result is undefined. If the arguments are vectors, each 6395vector element of ``op1`` is shifted by the corresponding shift amount 6396in ``op2``. 6397 6398If the ``nuw`` keyword is present, then the shift produces a :ref:`poison 6399value <poisonvalues>` if it shifts out any non-zero bits. If the 6400``nsw`` keyword is present, then the shift produces a :ref:`poison 6401value <poisonvalues>` if it shifts out any bits that disagree with the 6402resultant sign bit. As such, NUW/NSW have the same semantics as they 6403would if the shift were expressed as a mul instruction with the same 6404nsw/nuw bits in (mul %op1, (shl 1, %op2)). 6405 6406Example: 6407"""""""" 6408 6409.. code-block:: llvm 6410 6411 <result> = shl i32 4, %var ; yields i32: 4 << %var 6412 <result> = shl i32 4, 2 ; yields i32: 16 6413 <result> = shl i32 1, 10 ; yields i32: 1024 6414 <result> = shl i32 1, 32 ; undefined 6415 <result> = shl <2 x i32> < i32 1, i32 1>, < i32 1, i32 2> ; yields: result=<2 x i32> < i32 2, i32 4> 6416 6417'``lshr``' Instruction 6418^^^^^^^^^^^^^^^^^^^^^^ 6419 6420Syntax: 6421""""""" 6422 6423:: 6424 6425 <result> = lshr <ty> <op1>, <op2> ; yields ty:result 6426 <result> = lshr exact <ty> <op1>, <op2> ; yields ty:result 6427 6428Overview: 6429""""""""" 6430 6431The '``lshr``' instruction (logical shift right) returns the first 6432operand shifted to the right a specified number of bits with zero fill. 6433 6434Arguments: 6435"""""""""" 6436 6437Both arguments to the '``lshr``' instruction must be the same 6438:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer type. 6439'``op2``' is treated as an unsigned value. 6440 6441Semantics: 6442"""""""""" 6443 6444This instruction always performs a logical shift right operation. The 6445most significant bits of the result will be filled with zero bits after 6446the shift. If ``op2`` is (statically or dynamically) equal to or larger 6447than the number of bits in ``op1``, the result is undefined. If the 6448arguments are vectors, each vector element of ``op1`` is shifted by the 6449corresponding shift amount in ``op2``. 6450 6451If the ``exact`` keyword is present, the result value of the ``lshr`` is 6452a :ref:`poison value <poisonvalues>` if any of the bits shifted out are 6453non-zero. 6454 6455Example: 6456"""""""" 6457 6458.. code-block:: llvm 6459 6460 <result> = lshr i32 4, 1 ; yields i32:result = 2 6461 <result> = lshr i32 4, 2 ; yields i32:result = 1 6462 <result> = lshr i8 4, 3 ; yields i8:result = 0 6463 <result> = lshr i8 -2, 1 ; yields i8:result = 0x7F 6464 <result> = lshr i32 1, 32 ; undefined 6465 <result> = lshr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 2> ; yields: result=<2 x i32> < i32 0x7FFFFFFF, i32 1> 6466 6467'``ashr``' Instruction 6468^^^^^^^^^^^^^^^^^^^^^^ 6469 6470Syntax: 6471""""""" 6472 6473:: 6474 6475 <result> = ashr <ty> <op1>, <op2> ; yields ty:result 6476 <result> = ashr exact <ty> <op1>, <op2> ; yields ty:result 6477 6478Overview: 6479""""""""" 6480 6481The '``ashr``' instruction (arithmetic shift right) returns the first 6482operand shifted to the right a specified number of bits with sign 6483extension. 6484 6485Arguments: 6486"""""""""" 6487 6488Both arguments to the '``ashr``' instruction must be the same 6489:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer type. 6490'``op2``' is treated as an unsigned value. 6491 6492Semantics: 6493"""""""""" 6494 6495This instruction always performs an arithmetic shift right operation, 6496The most significant bits of the result will be filled with the sign bit 6497of ``op1``. If ``op2`` is (statically or dynamically) equal to or larger 6498than the number of bits in ``op1``, the result is undefined. If the 6499arguments are vectors, each vector element of ``op1`` is shifted by the 6500corresponding shift amount in ``op2``. 6501 6502If the ``exact`` keyword is present, the result value of the ``ashr`` is 6503a :ref:`poison value <poisonvalues>` if any of the bits shifted out are 6504non-zero. 6505 6506Example: 6507"""""""" 6508 6509.. code-block:: llvm 6510 6511 <result> = ashr i32 4, 1 ; yields i32:result = 2 6512 <result> = ashr i32 4, 2 ; yields i32:result = 1 6513 <result> = ashr i8 4, 3 ; yields i8:result = 0 6514 <result> = ashr i8 -2, 1 ; yields i8:result = -1 6515 <result> = ashr i32 1, 32 ; undefined 6516 <result> = ashr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 3> ; yields: result=<2 x i32> < i32 -1, i32 0> 6517 6518'``and``' Instruction 6519^^^^^^^^^^^^^^^^^^^^^ 6520 6521Syntax: 6522""""""" 6523 6524:: 6525 6526 <result> = and <ty> <op1>, <op2> ; yields ty:result 6527 6528Overview: 6529""""""""" 6530 6531The '``and``' instruction returns the bitwise logical and of its two 6532operands. 6533 6534Arguments: 6535"""""""""" 6536 6537The two arguments to the '``and``' instruction must be 6538:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both 6539arguments must have identical types. 6540 6541Semantics: 6542"""""""""" 6543 6544The truth table used for the '``and``' instruction is: 6545 6546+-----+-----+-----+ 6547| In0 | In1 | Out | 6548+-----+-----+-----+ 6549| 0 | 0 | 0 | 6550+-----+-----+-----+ 6551| 0 | 1 | 0 | 6552+-----+-----+-----+ 6553| 1 | 0 | 0 | 6554+-----+-----+-----+ 6555| 1 | 1 | 1 | 6556+-----+-----+-----+ 6557 6558Example: 6559"""""""" 6560 6561.. code-block:: llvm 6562 6563 <result> = and i32 4, %var ; yields i32:result = 4 & %var 6564 <result> = and i32 15, 40 ; yields i32:result = 8 6565 <result> = and i32 4, 8 ; yields i32:result = 0 6566 6567'``or``' Instruction 6568^^^^^^^^^^^^^^^^^^^^ 6569 6570Syntax: 6571""""""" 6572 6573:: 6574 6575 <result> = or <ty> <op1>, <op2> ; yields ty:result 6576 6577Overview: 6578""""""""" 6579 6580The '``or``' instruction returns the bitwise logical inclusive or of its 6581two operands. 6582 6583Arguments: 6584"""""""""" 6585 6586The two arguments to the '``or``' instruction must be 6587:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both 6588arguments must have identical types. 6589 6590Semantics: 6591"""""""""" 6592 6593The truth table used for the '``or``' instruction is: 6594 6595+-----+-----+-----+ 6596| In0 | In1 | Out | 6597+-----+-----+-----+ 6598| 0 | 0 | 0 | 6599+-----+-----+-----+ 6600| 0 | 1 | 1 | 6601+-----+-----+-----+ 6602| 1 | 0 | 1 | 6603+-----+-----+-----+ 6604| 1 | 1 | 1 | 6605+-----+-----+-----+ 6606 6607Example: 6608"""""""" 6609 6610:: 6611 6612 <result> = or i32 4, %var ; yields i32:result = 4 | %var 6613 <result> = or i32 15, 40 ; yields i32:result = 47 6614 <result> = or i32 4, 8 ; yields i32:result = 12 6615 6616'``xor``' Instruction 6617^^^^^^^^^^^^^^^^^^^^^ 6618 6619Syntax: 6620""""""" 6621 6622:: 6623 6624 <result> = xor <ty> <op1>, <op2> ; yields ty:result 6625 6626Overview: 6627""""""""" 6628 6629The '``xor``' instruction returns the bitwise logical exclusive or of 6630its two operands. The ``xor`` is used to implement the "one's 6631complement" operation, which is the "~" operator in C. 6632 6633Arguments: 6634"""""""""" 6635 6636The two arguments to the '``xor``' instruction must be 6637:ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both 6638arguments must have identical types. 6639 6640Semantics: 6641"""""""""" 6642 6643The truth table used for the '``xor``' instruction is: 6644 6645+-----+-----+-----+ 6646| In0 | In1 | Out | 6647+-----+-----+-----+ 6648| 0 | 0 | 0 | 6649+-----+-----+-----+ 6650| 0 | 1 | 1 | 6651+-----+-----+-----+ 6652| 1 | 0 | 1 | 6653+-----+-----+-----+ 6654| 1 | 1 | 0 | 6655+-----+-----+-----+ 6656 6657Example: 6658"""""""" 6659 6660.. code-block:: llvm 6661 6662 <result> = xor i32 4, %var ; yields i32:result = 4 ^ %var 6663 <result> = xor i32 15, 40 ; yields i32:result = 39 6664 <result> = xor i32 4, 8 ; yields i32:result = 12 6665 <result> = xor i32 %V, -1 ; yields i32:result = ~%V 6666 6667Vector Operations 6668----------------- 6669 6670LLVM supports several instructions to represent vector operations in a 6671target-independent manner. These instructions cover the element-access 6672and vector-specific operations needed to process vectors effectively. 6673While LLVM does directly support these vector operations, many 6674sophisticated algorithms will want to use target-specific intrinsics to 6675take full advantage of a specific target. 6676 6677.. _i_extractelement: 6678 6679'``extractelement``' Instruction 6680^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 6681 6682Syntax: 6683""""""" 6684 6685:: 6686 6687 <result> = extractelement <n x <ty>> <val>, <ty2> <idx> ; yields <ty> 6688 6689Overview: 6690""""""""" 6691 6692The '``extractelement``' instruction extracts a single scalar element 6693from a vector at a specified index. 6694 6695Arguments: 6696"""""""""" 6697 6698The first operand of an '``extractelement``' instruction is a value of 6699:ref:`vector <t_vector>` type. The second operand is an index indicating 6700the position from which to extract the element. The index may be a 6701variable of any integer type. 6702 6703Semantics: 6704"""""""""" 6705 6706The result is a scalar of the same type as the element type of ``val``. 6707Its value is the value at position ``idx`` of ``val``. If ``idx`` 6708exceeds the length of ``val``, the results are undefined. 6709 6710Example: 6711"""""""" 6712 6713.. code-block:: llvm 6714 6715 <result> = extractelement <4 x i32> %vec, i32 0 ; yields i32 6716 6717.. _i_insertelement: 6718 6719'``insertelement``' Instruction 6720^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 6721 6722Syntax: 6723""""""" 6724 6725:: 6726 6727 <result> = insertelement <n x <ty>> <val>, <ty> <elt>, <ty2> <idx> ; yields <n x <ty>> 6728 6729Overview: 6730""""""""" 6731 6732The '``insertelement``' instruction inserts a scalar element into a 6733vector at a specified index. 6734 6735Arguments: 6736"""""""""" 6737 6738The first operand of an '``insertelement``' instruction is a value of 6739:ref:`vector <t_vector>` type. The second operand is a scalar value whose 6740type must equal the element type of the first operand. The third operand 6741is an index indicating the position at which to insert the value. The 6742index may be a variable of any integer type. 6743 6744Semantics: 6745"""""""""" 6746 6747The result is a vector of the same type as ``val``. Its element values 6748are those of ``val`` except at position ``idx``, where it gets the value 6749``elt``. If ``idx`` exceeds the length of ``val``, the results are 6750undefined. 6751 6752Example: 6753"""""""" 6754 6755.. code-block:: llvm 6756 6757 <result> = insertelement <4 x i32> %vec, i32 1, i32 0 ; yields <4 x i32> 6758 6759.. _i_shufflevector: 6760 6761'``shufflevector``' Instruction 6762^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 6763 6764Syntax: 6765""""""" 6766 6767:: 6768 6769 <result> = shufflevector <n x <ty>> <v1>, <n x <ty>> <v2>, <m x i32> <mask> ; yields <m x <ty>> 6770 6771Overview: 6772""""""""" 6773 6774The '``shufflevector``' instruction constructs a permutation of elements 6775from two input vectors, returning a vector with the same element type as 6776the input and length that is the same as the shuffle mask. 6777 6778Arguments: 6779"""""""""" 6780 6781The first two operands of a '``shufflevector``' instruction are vectors 6782with the same type. The third argument is a shuffle mask whose element 6783type is always 'i32'. The result of the instruction is a vector whose 6784length is the same as the shuffle mask and whose element type is the 6785same as the element type of the first two operands. 6786 6787The shuffle mask operand is required to be a constant vector with either 6788constant integer or undef values. 6789 6790Semantics: 6791"""""""""" 6792 6793The elements of the two input vectors are numbered from left to right 6794across both of the vectors. The shuffle mask operand specifies, for each 6795element of the result vector, which element of the two input vectors the 6796result element gets. The element selector may be undef (meaning "don't 6797care") and the second operand may be undef if performing a shuffle from 6798only one vector. 6799 6800Example: 6801"""""""" 6802 6803.. code-block:: llvm 6804 6805 <result> = shufflevector <4 x i32> %v1, <4 x i32> %v2, 6806 <4 x i32> <i32 0, i32 4, i32 1, i32 5> ; yields <4 x i32> 6807 <result> = shufflevector <4 x i32> %v1, <4 x i32> undef, 6808 <4 x i32> <i32 0, i32 1, i32 2, i32 3> ; yields <4 x i32> - Identity shuffle. 6809 <result> = shufflevector <8 x i32> %v1, <8 x i32> undef, 6810 <4 x i32> <i32 0, i32 1, i32 2, i32 3> ; yields <4 x i32> 6811 <result> = shufflevector <4 x i32> %v1, <4 x i32> %v2, 6812 <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7 > ; yields <8 x i32> 6813 6814Aggregate Operations 6815-------------------- 6816 6817LLVM supports several instructions for working with 6818:ref:`aggregate <t_aggregate>` values. 6819 6820.. _i_extractvalue: 6821 6822'``extractvalue``' Instruction 6823^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 6824 6825Syntax: 6826""""""" 6827 6828:: 6829 6830 <result> = extractvalue <aggregate type> <val>, <idx>{, <idx>}* 6831 6832Overview: 6833""""""""" 6834 6835The '``extractvalue``' instruction extracts the value of a member field 6836from an :ref:`aggregate <t_aggregate>` value. 6837 6838Arguments: 6839"""""""""" 6840 6841The first operand of an '``extractvalue``' instruction is a value of 6842:ref:`struct <t_struct>` or :ref:`array <t_array>` type. The other operands are 6843constant indices to specify which value to extract in a similar manner 6844as indices in a '``getelementptr``' instruction. 6845 6846The major differences to ``getelementptr`` indexing are: 6847 6848- Since the value being indexed is not a pointer, the first index is 6849 omitted and assumed to be zero. 6850- At least one index must be specified. 6851- Not only struct indices but also array indices must be in bounds. 6852 6853Semantics: 6854"""""""""" 6855 6856The result is the value at the position in the aggregate specified by 6857the index operands. 6858 6859Example: 6860"""""""" 6861 6862.. code-block:: llvm 6863 6864 <result> = extractvalue {i32, float} %agg, 0 ; yields i32 6865 6866.. _i_insertvalue: 6867 6868'``insertvalue``' Instruction 6869^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 6870 6871Syntax: 6872""""""" 6873 6874:: 6875 6876 <result> = insertvalue <aggregate type> <val>, <ty> <elt>, <idx>{, <idx>}* ; yields <aggregate type> 6877 6878Overview: 6879""""""""" 6880 6881The '``insertvalue``' instruction inserts a value into a member field in 6882an :ref:`aggregate <t_aggregate>` value. 6883 6884Arguments: 6885"""""""""" 6886 6887The first operand of an '``insertvalue``' instruction is a value of 6888:ref:`struct <t_struct>` or :ref:`array <t_array>` type. The second operand is 6889a first-class value to insert. The following operands are constant 6890indices indicating the position at which to insert the value in a 6891similar manner as indices in a '``extractvalue``' instruction. The value 6892to insert must have the same type as the value identified by the 6893indices. 6894 6895Semantics: 6896"""""""""" 6897 6898The result is an aggregate of the same type as ``val``. Its value is 6899that of ``val`` except that the value at the position specified by the 6900indices is that of ``elt``. 6901 6902Example: 6903"""""""" 6904 6905.. code-block:: llvm 6906 6907 %agg1 = insertvalue {i32, float} undef, i32 1, 0 ; yields {i32 1, float undef} 6908 %agg2 = insertvalue {i32, float} %agg1, float %val, 1 ; yields {i32 1, float %val} 6909 %agg3 = insertvalue {i32, {float}} undef, float %val, 1, 0 ; yields {i32 undef, {float %val}} 6910 6911.. _memoryops: 6912 6913Memory Access and Addressing Operations 6914--------------------------------------- 6915 6916A key design point of an SSA-based representation is how it represents 6917memory. In LLVM, no memory locations are in SSA form, which makes things 6918very simple. This section describes how to read, write, and allocate 6919memory in LLVM. 6920 6921.. _i_alloca: 6922 6923'``alloca``' Instruction 6924^^^^^^^^^^^^^^^^^^^^^^^^ 6925 6926Syntax: 6927""""""" 6928 6929:: 6930 6931 <result> = alloca [inalloca] <type> [, <ty> <NumElements>] [, align <alignment>] ; yields type*:result 6932 6933Overview: 6934""""""""" 6935 6936The '``alloca``' instruction allocates memory on the stack frame of the 6937currently executing function, to be automatically released when this 6938function returns to its caller. The object is always allocated in the 6939generic address space (address space zero). 6940 6941Arguments: 6942"""""""""" 6943 6944The '``alloca``' instruction allocates ``sizeof(<type>)*NumElements`` 6945bytes of memory on the runtime stack, returning a pointer of the 6946appropriate type to the program. If "NumElements" is specified, it is 6947the number of elements allocated, otherwise "NumElements" is defaulted 6948to be one. If a constant alignment is specified, the value result of the 6949allocation is guaranteed to be aligned to at least that boundary. The 6950alignment may not be greater than ``1 << 29``. If not specified, or if 6951zero, the target can choose to align the allocation on any convenient 6952boundary compatible with the type. 6953 6954'``type``' may be any sized type. 6955 6956Semantics: 6957"""""""""" 6958 6959Memory is allocated; a pointer is returned. The operation is undefined 6960if there is insufficient stack space for the allocation. '``alloca``'d 6961memory is automatically released when the function returns. The 6962'``alloca``' instruction is commonly used to represent automatic 6963variables that must have an address available. When the function returns 6964(either with the ``ret`` or ``resume`` instructions), the memory is 6965reclaimed. Allocating zero bytes is legal, but the result is undefined. 6966The order in which memory is allocated (ie., which way the stack grows) 6967is not specified. 6968 6969Example: 6970"""""""" 6971 6972.. code-block:: llvm 6973 6974 %ptr = alloca i32 ; yields i32*:ptr 6975 %ptr = alloca i32, i32 4 ; yields i32*:ptr 6976 %ptr = alloca i32, i32 4, align 1024 ; yields i32*:ptr 6977 %ptr = alloca i32, align 1024 ; yields i32*:ptr 6978 6979.. _i_load: 6980 6981'``load``' Instruction 6982^^^^^^^^^^^^^^^^^^^^^^ 6983 6984Syntax: 6985""""""" 6986 6987:: 6988 6989 <result> = load [volatile] <ty>, <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>][, !invariant.load !<index>][, !invariant.group !<index>][, !nonnull !<index>][, !dereferenceable !<deref_bytes_node>][, !dereferenceable_or_null !<deref_bytes_node>][, !align !<align_node>] 6990 <result> = load atomic [volatile] <ty>, <ty>* <pointer> [singlethread] <ordering>, align <alignment> [, !invariant.group !<index>] 6991 !<index> = !{ i32 1 } 6992 !<deref_bytes_node> = !{i64 <dereferenceable_bytes>} 6993 !<align_node> = !{ i64 <value_alignment> } 6994 6995Overview: 6996""""""""" 6997 6998The '``load``' instruction is used to read from memory. 6999 7000Arguments: 7001"""""""""" 7002 7003The argument to the ``load`` instruction specifies the memory address from which 7004to load. The type specified must be a :ref:`first class <t_firstclass>` type of 7005known size (i.e. not containing an :ref:`opaque structural type <t_opaque>`). If 7006the ``load`` is marked as ``volatile``, then the optimizer is not allowed to 7007modify the number or order of execution of this ``load`` with other 7008:ref:`volatile operations <volatile>`. 7009 7010If the ``load`` is marked as ``atomic``, it takes an extra :ref:`ordering 7011<ordering>` and optional ``singlethread`` argument. The ``release`` and 7012``acq_rel`` orderings are not valid on ``load`` instructions. Atomic loads 7013produce :ref:`defined <memmodel>` results when they may see multiple atomic 7014stores. The type of the pointee must be an integer, pointer, or floating-point 7015type whose bit width is a power of two greater than or equal to eight and less 7016than or equal to a target-specific size limit. ``align`` must be explicitly 7017specified on atomic loads, and the load has undefined behavior if the alignment 7018is not set to a value which is at least the size in bytes of the 7019pointee. ``!nontemporal`` does not have any defined semantics for atomic loads. 7020 7021The optional constant ``align`` argument specifies the alignment of the 7022operation (that is, the alignment of the memory address). A value of 0 7023or an omitted ``align`` argument means that the operation has the ABI 7024alignment for the target. It is the responsibility of the code emitter 7025to ensure that the alignment information is correct. Overestimating the 7026alignment results in undefined behavior. Underestimating the alignment 7027may produce less efficient code. An alignment of 1 is always safe. The 7028maximum possible alignment is ``1 << 29``. An alignment value higher 7029than the size of the loaded type implies memory up to the alignment 7030value bytes can be safely loaded without trapping in the default 7031address space. Access of the high bytes can interfere with debugging 7032tools, so should not be accessed if the function has the 7033``sanitize_thread`` or ``sanitize_address`` attributes. 7034 7035The optional ``!nontemporal`` metadata must reference a single 7036metadata name ``<index>`` corresponding to a metadata node with one 7037``i32`` entry of value 1. The existence of the ``!nontemporal`` 7038metadata on the instruction tells the optimizer and code generator 7039that this load is not expected to be reused in the cache. The code 7040generator may select special instructions to save cache bandwidth, such 7041as the ``MOVNT`` instruction on x86. 7042 7043The optional ``!invariant.load`` metadata must reference a single 7044metadata name ``<index>`` corresponding to a metadata node with no 7045entries. The existence of the ``!invariant.load`` metadata on the 7046instruction tells the optimizer and code generator that the address 7047operand to this load points to memory which can be assumed unchanged. 7048Being invariant does not imply that a location is dereferenceable, 7049but it does imply that once the location is known dereferenceable 7050its value is henceforth unchanging. 7051 7052The optional ``!invariant.group`` metadata must reference a single metadata name 7053 ``<index>`` corresponding to a metadata node. See ``invariant.group`` metadata. 7054 7055The optional ``!nonnull`` metadata must reference a single 7056metadata name ``<index>`` corresponding to a metadata node with no 7057entries. The existence of the ``!nonnull`` metadata on the 7058instruction tells the optimizer that the value loaded is known to 7059never be null. This is analogous to the ``nonnull`` attribute 7060on parameters and return values. This metadata can only be applied 7061to loads of a pointer type. 7062 7063The optional ``!dereferenceable`` metadata must reference a single metadata 7064name ``<deref_bytes_node>`` corresponding to a metadata node with one ``i64`` 7065entry. The existence of the ``!dereferenceable`` metadata on the instruction 7066tells the optimizer that the value loaded is known to be dereferenceable. 7067The number of bytes known to be dereferenceable is specified by the integer 7068value in the metadata node. This is analogous to the ''dereferenceable'' 7069attribute on parameters and return values. This metadata can only be applied 7070to loads of a pointer type. 7071 7072The optional ``!dereferenceable_or_null`` metadata must reference a single 7073metadata name ``<deref_bytes_node>`` corresponding to a metadata node with one 7074``i64`` entry. The existence of the ``!dereferenceable_or_null`` metadata on the 7075instruction tells the optimizer that the value loaded is known to be either 7076dereferenceable or null. 7077The number of bytes known to be dereferenceable is specified by the integer 7078value in the metadata node. This is analogous to the ''dereferenceable_or_null'' 7079attribute on parameters and return values. This metadata can only be applied 7080to loads of a pointer type. 7081 7082The optional ``!align`` metadata must reference a single metadata name 7083``<align_node>`` corresponding to a metadata node with one ``i64`` entry. 7084The existence of the ``!align`` metadata on the instruction tells the 7085optimizer that the value loaded is known to be aligned to a boundary specified 7086by the integer value in the metadata node. The alignment must be a power of 2. 7087This is analogous to the ''align'' attribute on parameters and return values. 7088This metadata can only be applied to loads of a pointer type. 7089 7090Semantics: 7091"""""""""" 7092 7093The location of memory pointed to is loaded. If the value being loaded 7094is of scalar type then the number of bytes read does not exceed the 7095minimum number of bytes needed to hold all bits of the type. For 7096example, loading an ``i24`` reads at most three bytes. When loading a 7097value of a type like ``i20`` with a size that is not an integral number 7098of bytes, the result is undefined if the value was not originally 7099written using a store of the same type. 7100 7101Examples: 7102""""""""" 7103 7104.. code-block:: llvm 7105 7106 %ptr = alloca i32 ; yields i32*:ptr 7107 store i32 3, i32* %ptr ; yields void 7108 %val = load i32, i32* %ptr ; yields i32:val = i32 3 7109 7110.. _i_store: 7111 7112'``store``' Instruction 7113^^^^^^^^^^^^^^^^^^^^^^^ 7114 7115Syntax: 7116""""""" 7117 7118:: 7119 7120 store [volatile] <ty> <value>, <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>][, !invariant.group !<index>] ; yields void 7121 store atomic [volatile] <ty> <value>, <ty>* <pointer> [singlethread] <ordering>, align <alignment> [, !invariant.group !<index>] ; yields void 7122 7123Overview: 7124""""""""" 7125 7126The '``store``' instruction is used to write to memory. 7127 7128Arguments: 7129"""""""""" 7130 7131There are two arguments to the ``store`` instruction: a value to store and an 7132address at which to store it. The type of the ``<pointer>`` operand must be a 7133pointer to the :ref:`first class <t_firstclass>` type of the ``<value>`` 7134operand. If the ``store`` is marked as ``volatile``, then the optimizer is not 7135allowed to modify the number or order of execution of this ``store`` with other 7136:ref:`volatile operations <volatile>`. Only values of :ref:`first class 7137<t_firstclass>` types of known size (i.e. not containing an :ref:`opaque 7138structural type <t_opaque>`) can be stored. 7139 7140If the ``store`` is marked as ``atomic``, it takes an extra :ref:`ordering 7141<ordering>` and optional ``singlethread`` argument. The ``acquire`` and 7142``acq_rel`` orderings aren't valid on ``store`` instructions. Atomic loads 7143produce :ref:`defined <memmodel>` results when they may see multiple atomic 7144stores. The type of the pointee must be an integer, pointer, or floating-point 7145type whose bit width is a power of two greater than or equal to eight and less 7146than or equal to a target-specific size limit. ``align`` must be explicitly 7147specified on atomic stores, and the store has undefined behavior if the 7148alignment is not set to a value which is at least the size in bytes of the 7149pointee. ``!nontemporal`` does not have any defined semantics for atomic stores. 7150 7151The optional constant ``align`` argument specifies the alignment of the 7152operation (that is, the alignment of the memory address). A value of 0 7153or an omitted ``align`` argument means that the operation has the ABI 7154alignment for the target. It is the responsibility of the code emitter 7155to ensure that the alignment information is correct. Overestimating the 7156alignment results in undefined behavior. Underestimating the 7157alignment may produce less efficient code. An alignment of 1 is always 7158safe. The maximum possible alignment is ``1 << 29``. An alignment 7159value higher than the size of the stored type implies memory up to the 7160alignment value bytes can be stored to without trapping in the default 7161address space. Storing to the higher bytes however may result in data 7162races if another thread can access the same address. Introducing a 7163data race is not allowed. Storing to the extra bytes is not allowed 7164even in situations where a data race is known to not exist if the 7165function has the ``sanitize_address`` attribute. 7166 7167The optional ``!nontemporal`` metadata must reference a single metadata 7168name ``<index>`` corresponding to a metadata node with one ``i32`` entry of 7169value 1. The existence of the ``!nontemporal`` metadata on the instruction 7170tells the optimizer and code generator that this load is not expected to 7171be reused in the cache. The code generator may select special 7172instructions to save cache bandwidth, such as the ``MOVNT`` instruction on 7173x86. 7174 7175The optional ``!invariant.group`` metadata must reference a 7176single metadata name ``<index>``. See ``invariant.group`` metadata. 7177 7178Semantics: 7179"""""""""" 7180 7181The contents of memory are updated to contain ``<value>`` at the 7182location specified by the ``<pointer>`` operand. If ``<value>`` is 7183of scalar type then the number of bytes written does not exceed the 7184minimum number of bytes needed to hold all bits of the type. For 7185example, storing an ``i24`` writes at most three bytes. When writing a 7186value of a type like ``i20`` with a size that is not an integral number 7187of bytes, it is unspecified what happens to the extra bits that do not 7188belong to the type, but they will typically be overwritten. 7189 7190Example: 7191"""""""" 7192 7193.. code-block:: llvm 7194 7195 %ptr = alloca i32 ; yields i32*:ptr 7196 store i32 3, i32* %ptr ; yields void 7197 %val = load i32, i32* %ptr ; yields i32:val = i32 3 7198 7199.. _i_fence: 7200 7201'``fence``' Instruction 7202^^^^^^^^^^^^^^^^^^^^^^^ 7203 7204Syntax: 7205""""""" 7206 7207:: 7208 7209 fence [singlethread] <ordering> ; yields void 7210 7211Overview: 7212""""""""" 7213 7214The '``fence``' instruction is used to introduce happens-before edges 7215between operations. 7216 7217Arguments: 7218"""""""""" 7219 7220'``fence``' instructions take an :ref:`ordering <ordering>` argument which 7221defines what *synchronizes-with* edges they add. They can only be given 7222``acquire``, ``release``, ``acq_rel``, and ``seq_cst`` orderings. 7223 7224Semantics: 7225"""""""""" 7226 7227A fence A which has (at least) ``release`` ordering semantics 7228*synchronizes with* a fence B with (at least) ``acquire`` ordering 7229semantics if and only if there exist atomic operations X and Y, both 7230operating on some atomic object M, such that A is sequenced before X, X 7231modifies M (either directly or through some side effect of a sequence 7232headed by X), Y is sequenced before B, and Y observes M. This provides a 7233*happens-before* dependency between A and B. Rather than an explicit 7234``fence``, one (but not both) of the atomic operations X or Y might 7235provide a ``release`` or ``acquire`` (resp.) ordering constraint and 7236still *synchronize-with* the explicit ``fence`` and establish the 7237*happens-before* edge. 7238 7239A ``fence`` which has ``seq_cst`` ordering, in addition to having both 7240``acquire`` and ``release`` semantics specified above, participates in 7241the global program order of other ``seq_cst`` operations and/or fences. 7242 7243The optional ":ref:`singlethread <singlethread>`" argument specifies 7244that the fence only synchronizes with other fences in the same thread. 7245(This is useful for interacting with signal handlers.) 7246 7247Example: 7248"""""""" 7249 7250.. code-block:: llvm 7251 7252 fence acquire ; yields void 7253 fence singlethread seq_cst ; yields void 7254 7255.. _i_cmpxchg: 7256 7257'``cmpxchg``' Instruction 7258^^^^^^^^^^^^^^^^^^^^^^^^^ 7259 7260Syntax: 7261""""""" 7262 7263:: 7264 7265 cmpxchg [weak] [volatile] <ty>* <pointer>, <ty> <cmp>, <ty> <new> [singlethread] <success ordering> <failure ordering> ; yields { ty, i1 } 7266 7267Overview: 7268""""""""" 7269 7270The '``cmpxchg``' instruction is used to atomically modify memory. It 7271loads a value in memory and compares it to a given value. If they are 7272equal, it tries to store a new value into the memory. 7273 7274Arguments: 7275"""""""""" 7276 7277There are three arguments to the '``cmpxchg``' instruction: an address 7278to operate on, a value to compare to the value currently be at that 7279address, and a new value to place at that address if the compared values 7280are equal. The type of '<cmp>' must be an integer or pointer type whose 7281bit width is a power of two greater than or equal to eight and less 7282than or equal to a target-specific size limit. '<cmp>' and '<new>' must 7283have the same type, and the type of '<pointer>' must be a pointer to 7284that type. If the ``cmpxchg`` is marked as ``volatile``, then the 7285optimizer is not allowed to modify the number or order of execution of 7286this ``cmpxchg`` with other :ref:`volatile operations <volatile>`. 7287 7288The success and failure :ref:`ordering <ordering>` arguments specify how this 7289``cmpxchg`` synchronizes with other atomic operations. Both ordering parameters 7290must be at least ``monotonic``, the ordering constraint on failure must be no 7291stronger than that on success, and the failure ordering cannot be either 7292``release`` or ``acq_rel``. 7293 7294The optional "``singlethread``" argument declares that the ``cmpxchg`` 7295is only atomic with respect to code (usually signal handlers) running in 7296the same thread as the ``cmpxchg``. Otherwise the cmpxchg is atomic with 7297respect to all other code in the system. 7298 7299The pointer passed into cmpxchg must have alignment greater than or 7300equal to the size in memory of the operand. 7301 7302Semantics: 7303"""""""""" 7304 7305The contents of memory at the location specified by the '``<pointer>``' operand 7306is read and compared to '``<cmp>``'; if the read value is the equal, the 7307'``<new>``' is written. The original value at the location is returned, together 7308with a flag indicating success (true) or failure (false). 7309 7310If the cmpxchg operation is marked as ``weak`` then a spurious failure is 7311permitted: the operation may not write ``<new>`` even if the comparison 7312matched. 7313 7314If the cmpxchg operation is strong (the default), the i1 value is 1 if and only 7315if the value loaded equals ``cmp``. 7316 7317A successful ``cmpxchg`` is a read-modify-write instruction for the purpose of 7318identifying release sequences. A failed ``cmpxchg`` is equivalent to an atomic 7319load with an ordering parameter determined the second ordering parameter. 7320 7321Example: 7322"""""""" 7323 7324.. code-block:: llvm 7325 7326 entry: 7327 %orig = load atomic i32, i32* %ptr unordered, align 4 ; yields i32 7328 br label %loop 7329 7330 loop: 7331 %cmp = phi i32 [ %orig, %entry ], [%value_loaded, %loop] 7332 %squared = mul i32 %cmp, %cmp 7333 %val_success = cmpxchg i32* %ptr, i32 %cmp, i32 %squared acq_rel monotonic ; yields { i32, i1 } 7334 %value_loaded = extractvalue { i32, i1 } %val_success, 0 7335 %success = extractvalue { i32, i1 } %val_success, 1 7336 br i1 %success, label %done, label %loop 7337 7338 done: 7339 ... 7340 7341.. _i_atomicrmw: 7342 7343'``atomicrmw``' Instruction 7344^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7345 7346Syntax: 7347""""""" 7348 7349:: 7350 7351 atomicrmw [volatile] <operation> <ty>* <pointer>, <ty> <value> [singlethread] <ordering> ; yields ty 7352 7353Overview: 7354""""""""" 7355 7356The '``atomicrmw``' instruction is used to atomically modify memory. 7357 7358Arguments: 7359"""""""""" 7360 7361There are three arguments to the '``atomicrmw``' instruction: an 7362operation to apply, an address whose value to modify, an argument to the 7363operation. The operation must be one of the following keywords: 7364 7365- xchg 7366- add 7367- sub 7368- and 7369- nand 7370- or 7371- xor 7372- max 7373- min 7374- umax 7375- umin 7376 7377The type of '<value>' must be an integer type whose bit width is a power 7378of two greater than or equal to eight and less than or equal to a 7379target-specific size limit. The type of the '``<pointer>``' operand must 7380be a pointer to that type. If the ``atomicrmw`` is marked as 7381``volatile``, then the optimizer is not allowed to modify the number or 7382order of execution of this ``atomicrmw`` with other :ref:`volatile 7383operations <volatile>`. 7384 7385Semantics: 7386"""""""""" 7387 7388The contents of memory at the location specified by the '``<pointer>``' 7389operand are atomically read, modified, and written back. The original 7390value at the location is returned. The modification is specified by the 7391operation argument: 7392 7393- xchg: ``*ptr = val`` 7394- add: ``*ptr = *ptr + val`` 7395- sub: ``*ptr = *ptr - val`` 7396- and: ``*ptr = *ptr & val`` 7397- nand: ``*ptr = ~(*ptr & val)`` 7398- or: ``*ptr = *ptr | val`` 7399- xor: ``*ptr = *ptr ^ val`` 7400- max: ``*ptr = *ptr > val ? *ptr : val`` (using a signed comparison) 7401- min: ``*ptr = *ptr < val ? *ptr : val`` (using a signed comparison) 7402- umax: ``*ptr = *ptr > val ? *ptr : val`` (using an unsigned 7403 comparison) 7404- umin: ``*ptr = *ptr < val ? *ptr : val`` (using an unsigned 7405 comparison) 7406 7407Example: 7408"""""""" 7409 7410.. code-block:: llvm 7411 7412 %old = atomicrmw add i32* %ptr, i32 1 acquire ; yields i32 7413 7414.. _i_getelementptr: 7415 7416'``getelementptr``' Instruction 7417^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7418 7419Syntax: 7420""""""" 7421 7422:: 7423 7424 <result> = getelementptr <ty>, <ty>* <ptrval>{, <ty> <idx>}* 7425 <result> = getelementptr inbounds <ty>, <ty>* <ptrval>{, <ty> <idx>}* 7426 <result> = getelementptr <ty>, <ptr vector> <ptrval>, <vector index type> <idx> 7427 7428Overview: 7429""""""""" 7430 7431The '``getelementptr``' instruction is used to get the address of a 7432subelement of an :ref:`aggregate <t_aggregate>` data structure. It performs 7433address calculation only and does not access memory. The instruction can also 7434be used to calculate a vector of such addresses. 7435 7436Arguments: 7437"""""""""" 7438 7439The first argument is always a type used as the basis for the calculations. 7440The second argument is always a pointer or a vector of pointers, and is the 7441base address to start from. The remaining arguments are indices 7442that indicate which of the elements of the aggregate object are indexed. 7443The interpretation of each index is dependent on the type being indexed 7444into. The first index always indexes the pointer value given as the 7445first argument, the second index indexes a value of the type pointed to 7446(not necessarily the value directly pointed to, since the first index 7447can be non-zero), etc. The first type indexed into must be a pointer 7448value, subsequent types can be arrays, vectors, and structs. Note that 7449subsequent types being indexed into can never be pointers, since that 7450would require loading the pointer before continuing calculation. 7451 7452The type of each index argument depends on the type it is indexing into. 7453When indexing into a (optionally packed) structure, only ``i32`` integer 7454**constants** are allowed (when using a vector of indices they must all 7455be the **same** ``i32`` integer constant). When indexing into an array, 7456pointer or vector, integers of any width are allowed, and they are not 7457required to be constant. These integers are treated as signed values 7458where relevant. 7459 7460For example, let's consider a C code fragment and how it gets compiled 7461to LLVM: 7462 7463.. code-block:: c 7464 7465 struct RT { 7466 char A; 7467 int B[10][20]; 7468 char C; 7469 }; 7470 struct ST { 7471 int X; 7472 double Y; 7473 struct RT Z; 7474 }; 7475 7476 int *foo(struct ST *s) { 7477 return &s[1].Z.B[5][13]; 7478 } 7479 7480The LLVM code generated by Clang is: 7481 7482.. code-block:: llvm 7483 7484 %struct.RT = type { i8, [10 x [20 x i32]], i8 } 7485 %struct.ST = type { i32, double, %struct.RT } 7486 7487 define i32* @foo(%struct.ST* %s) nounwind uwtable readnone optsize ssp { 7488 entry: 7489 %arrayidx = getelementptr inbounds %struct.ST, %struct.ST* %s, i64 1, i32 2, i32 1, i64 5, i64 13 7490 ret i32* %arrayidx 7491 } 7492 7493Semantics: 7494"""""""""" 7495 7496In the example above, the first index is indexing into the 7497'``%struct.ST*``' type, which is a pointer, yielding a '``%struct.ST``' 7498= '``{ i32, double, %struct.RT }``' type, a structure. The second index 7499indexes into the third element of the structure, yielding a 7500'``%struct.RT``' = '``{ i8 , [10 x [20 x i32]], i8 }``' type, another 7501structure. The third index indexes into the second element of the 7502structure, yielding a '``[10 x [20 x i32]]``' type, an array. The two 7503dimensions of the array are subscripted into, yielding an '``i32``' 7504type. The '``getelementptr``' instruction returns a pointer to this 7505element, thus computing a value of '``i32*``' type. 7506 7507Note that it is perfectly legal to index partially through a structure, 7508returning a pointer to an inner element. Because of this, the LLVM code 7509for the given testcase is equivalent to: 7510 7511.. code-block:: llvm 7512 7513 define i32* @foo(%struct.ST* %s) { 7514 %t1 = getelementptr %struct.ST, %struct.ST* %s, i32 1 ; yields %struct.ST*:%t1 7515 %t2 = getelementptr %struct.ST, %struct.ST* %t1, i32 0, i32 2 ; yields %struct.RT*:%t2 7516 %t3 = getelementptr %struct.RT, %struct.RT* %t2, i32 0, i32 1 ; yields [10 x [20 x i32]]*:%t3 7517 %t4 = getelementptr [10 x [20 x i32]], [10 x [20 x i32]]* %t3, i32 0, i32 5 ; yields [20 x i32]*:%t4 7518 %t5 = getelementptr [20 x i32], [20 x i32]* %t4, i32 0, i32 13 ; yields i32*:%t5 7519 ret i32* %t5 7520 } 7521 7522If the ``inbounds`` keyword is present, the result value of the 7523``getelementptr`` is a :ref:`poison value <poisonvalues>` if the base 7524pointer is not an *in bounds* address of an allocated object, or if any 7525of the addresses that would be formed by successive addition of the 7526offsets implied by the indices to the base address with infinitely 7527precise signed arithmetic are not an *in bounds* address of that 7528allocated object. The *in bounds* addresses for an allocated object are 7529all the addresses that point into the object, plus the address one byte 7530past the end. In cases where the base is a vector of pointers the 7531``inbounds`` keyword applies to each of the computations element-wise. 7532 7533If the ``inbounds`` keyword is not present, the offsets are added to the 7534base address with silently-wrapping two's complement arithmetic. If the 7535offsets have a different width from the pointer, they are sign-extended 7536or truncated to the width of the pointer. The result value of the 7537``getelementptr`` may be outside the object pointed to by the base 7538pointer. The result value may not necessarily be used to access memory 7539though, even if it happens to point into allocated storage. See the 7540:ref:`Pointer Aliasing Rules <pointeraliasing>` section for more 7541information. 7542 7543The getelementptr instruction is often confusing. For some more insight 7544into how it works, see :doc:`the getelementptr FAQ <GetElementPtr>`. 7545 7546Example: 7547"""""""" 7548 7549.. code-block:: llvm 7550 7551 ; yields [12 x i8]*:aptr 7552 %aptr = getelementptr {i32, [12 x i8]}, {i32, [12 x i8]}* %saptr, i64 0, i32 1 7553 ; yields i8*:vptr 7554 %vptr = getelementptr {i32, <2 x i8>}, {i32, <2 x i8>}* %svptr, i64 0, i32 1, i32 1 7555 ; yields i8*:eptr 7556 %eptr = getelementptr [12 x i8], [12 x i8]* %aptr, i64 0, i32 1 7557 ; yields i32*:iptr 7558 %iptr = getelementptr [10 x i32], [10 x i32]* @arr, i16 0, i16 0 7559 7560Vector of pointers: 7561""""""""""""""""""" 7562 7563The ``getelementptr`` returns a vector of pointers, instead of a single address, 7564when one or more of its arguments is a vector. In such cases, all vector 7565arguments should have the same number of elements, and every scalar argument 7566will be effectively broadcast into a vector during address calculation. 7567 7568.. code-block:: llvm 7569 7570 ; All arguments are vectors: 7571 ; A[i] = ptrs[i] + offsets[i]*sizeof(i8) 7572 %A = getelementptr i8, <4 x i8*> %ptrs, <4 x i64> %offsets 7573 7574 ; Add the same scalar offset to each pointer of a vector: 7575 ; A[i] = ptrs[i] + offset*sizeof(i8) 7576 %A = getelementptr i8, <4 x i8*> %ptrs, i64 %offset 7577 7578 ; Add distinct offsets to the same pointer: 7579 ; A[i] = ptr + offsets[i]*sizeof(i8) 7580 %A = getelementptr i8, i8* %ptr, <4 x i64> %offsets 7581 7582 ; In all cases described above the type of the result is <4 x i8*> 7583 7584The two following instructions are equivalent: 7585 7586.. code-block:: llvm 7587 7588 getelementptr %struct.ST, <4 x %struct.ST*> %s, <4 x i64> %ind1, 7589 <4 x i32> <i32 2, i32 2, i32 2, i32 2>, 7590 <4 x i32> <i32 1, i32 1, i32 1, i32 1>, 7591 <4 x i32> %ind4, 7592 <4 x i64> <i64 13, i64 13, i64 13, i64 13> 7593 7594 getelementptr %struct.ST, <4 x %struct.ST*> %s, <4 x i64> %ind1, 7595 i32 2, i32 1, <4 x i32> %ind4, i64 13 7596 7597Let's look at the C code, where the vector version of ``getelementptr`` 7598makes sense: 7599 7600.. code-block:: c 7601 7602 // Let's assume that we vectorize the following loop: 7603 double *A, B; int *C; 7604 for (int i = 0; i < size; ++i) { 7605 A[i] = B[C[i]]; 7606 } 7607 7608.. code-block:: llvm 7609 7610 ; get pointers for 8 elements from array B 7611 %ptrs = getelementptr double, double* %B, <8 x i32> %C 7612 ; load 8 elements from array B into A 7613 %A = call <8 x double> @llvm.masked.gather.v8f64(<8 x double*> %ptrs, 7614 i32 8, <8 x i1> %mask, <8 x double> %passthru) 7615 7616Conversion Operations 7617--------------------- 7618 7619The instructions in this category are the conversion instructions 7620(casting) which all take a single operand and a type. They perform 7621various bit conversions on the operand. 7622 7623'``trunc .. to``' Instruction 7624^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7625 7626Syntax: 7627""""""" 7628 7629:: 7630 7631 <result> = trunc <ty> <value> to <ty2> ; yields ty2 7632 7633Overview: 7634""""""""" 7635 7636The '``trunc``' instruction truncates its operand to the type ``ty2``. 7637 7638Arguments: 7639"""""""""" 7640 7641The '``trunc``' instruction takes a value to trunc, and a type to trunc 7642it to. Both types must be of :ref:`integer <t_integer>` types, or vectors 7643of the same number of integers. The bit size of the ``value`` must be 7644larger than the bit size of the destination type, ``ty2``. Equal sized 7645types are not allowed. 7646 7647Semantics: 7648"""""""""" 7649 7650The '``trunc``' instruction truncates the high order bits in ``value`` 7651and converts the remaining bits to ``ty2``. Since the source size must 7652be larger than the destination size, ``trunc`` cannot be a *no-op cast*. 7653It will always truncate bits. 7654 7655Example: 7656"""""""" 7657 7658.. code-block:: llvm 7659 7660 %X = trunc i32 257 to i8 ; yields i8:1 7661 %Y = trunc i32 123 to i1 ; yields i1:true 7662 %Z = trunc i32 122 to i1 ; yields i1:false 7663 %W = trunc <2 x i16> <i16 8, i16 7> to <2 x i8> ; yields <i8 8, i8 7> 7664 7665'``zext .. to``' Instruction 7666^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7667 7668Syntax: 7669""""""" 7670 7671:: 7672 7673 <result> = zext <ty> <value> to <ty2> ; yields ty2 7674 7675Overview: 7676""""""""" 7677 7678The '``zext``' instruction zero extends its operand to type ``ty2``. 7679 7680Arguments: 7681"""""""""" 7682 7683The '``zext``' instruction takes a value to cast, and a type to cast it 7684to. Both types must be of :ref:`integer <t_integer>` types, or vectors of 7685the same number of integers. The bit size of the ``value`` must be 7686smaller than the bit size of the destination type, ``ty2``. 7687 7688Semantics: 7689"""""""""" 7690 7691The ``zext`` fills the high order bits of the ``value`` with zero bits 7692until it reaches the size of the destination type, ``ty2``. 7693 7694When zero extending from i1, the result will always be either 0 or 1. 7695 7696Example: 7697"""""""" 7698 7699.. code-block:: llvm 7700 7701 %X = zext i32 257 to i64 ; yields i64:257 7702 %Y = zext i1 true to i32 ; yields i32:1 7703 %Z = zext <2 x i16> <i16 8, i16 7> to <2 x i32> ; yields <i32 8, i32 7> 7704 7705'``sext .. to``' Instruction 7706^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7707 7708Syntax: 7709""""""" 7710 7711:: 7712 7713 <result> = sext <ty> <value> to <ty2> ; yields ty2 7714 7715Overview: 7716""""""""" 7717 7718The '``sext``' sign extends ``value`` to the type ``ty2``. 7719 7720Arguments: 7721"""""""""" 7722 7723The '``sext``' instruction takes a value to cast, and a type to cast it 7724to. Both types must be of :ref:`integer <t_integer>` types, or vectors of 7725the same number of integers. The bit size of the ``value`` must be 7726smaller than the bit size of the destination type, ``ty2``. 7727 7728Semantics: 7729"""""""""" 7730 7731The '``sext``' instruction performs a sign extension by copying the sign 7732bit (highest order bit) of the ``value`` until it reaches the bit size 7733of the type ``ty2``. 7734 7735When sign extending from i1, the extension always results in -1 or 0. 7736 7737Example: 7738"""""""" 7739 7740.. code-block:: llvm 7741 7742 %X = sext i8 -1 to i16 ; yields i16 :65535 7743 %Y = sext i1 true to i32 ; yields i32:-1 7744 %Z = sext <2 x i16> <i16 8, i16 7> to <2 x i32> ; yields <i32 8, i32 7> 7745 7746'``fptrunc .. to``' Instruction 7747^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7748 7749Syntax: 7750""""""" 7751 7752:: 7753 7754 <result> = fptrunc <ty> <value> to <ty2> ; yields ty2 7755 7756Overview: 7757""""""""" 7758 7759The '``fptrunc``' instruction truncates ``value`` to type ``ty2``. 7760 7761Arguments: 7762"""""""""" 7763 7764The '``fptrunc``' instruction takes a :ref:`floating point <t_floating>` 7765value to cast and a :ref:`floating point <t_floating>` type to cast it to. 7766The size of ``value`` must be larger than the size of ``ty2``. This 7767implies that ``fptrunc`` cannot be used to make a *no-op cast*. 7768 7769Semantics: 7770"""""""""" 7771 7772The '``fptrunc``' instruction casts a ``value`` from a larger 7773:ref:`floating point <t_floating>` type to a smaller :ref:`floating 7774point <t_floating>` type. If the value cannot fit (i.e. overflows) within the 7775destination type, ``ty2``, then the results are undefined. If the cast produces 7776an inexact result, how rounding is performed (e.g. truncation, also known as 7777round to zero) is undefined. 7778 7779Example: 7780"""""""" 7781 7782.. code-block:: llvm 7783 7784 %X = fptrunc double 123.0 to float ; yields float:123.0 7785 %Y = fptrunc double 1.0E+300 to float ; yields undefined 7786 7787'``fpext .. to``' Instruction 7788^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7789 7790Syntax: 7791""""""" 7792 7793:: 7794 7795 <result> = fpext <ty> <value> to <ty2> ; yields ty2 7796 7797Overview: 7798""""""""" 7799 7800The '``fpext``' extends a floating point ``value`` to a larger floating 7801point value. 7802 7803Arguments: 7804"""""""""" 7805 7806The '``fpext``' instruction takes a :ref:`floating point <t_floating>` 7807``value`` to cast, and a :ref:`floating point <t_floating>` type to cast it 7808to. The source type must be smaller than the destination type. 7809 7810Semantics: 7811"""""""""" 7812 7813The '``fpext``' instruction extends the ``value`` from a smaller 7814:ref:`floating point <t_floating>` type to a larger :ref:`floating 7815point <t_floating>` type. The ``fpext`` cannot be used to make a 7816*no-op cast* because it always changes bits. Use ``bitcast`` to make a 7817*no-op cast* for a floating point cast. 7818 7819Example: 7820"""""""" 7821 7822.. code-block:: llvm 7823 7824 %X = fpext float 3.125 to double ; yields double:3.125000e+00 7825 %Y = fpext double %X to fp128 ; yields fp128:0xL00000000000000004000900000000000 7826 7827'``fptoui .. to``' Instruction 7828^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7829 7830Syntax: 7831""""""" 7832 7833:: 7834 7835 <result> = fptoui <ty> <value> to <ty2> ; yields ty2 7836 7837Overview: 7838""""""""" 7839 7840The '``fptoui``' converts a floating point ``value`` to its unsigned 7841integer equivalent of type ``ty2``. 7842 7843Arguments: 7844"""""""""" 7845 7846The '``fptoui``' instruction takes a value to cast, which must be a 7847scalar or vector :ref:`floating point <t_floating>` value, and a type to 7848cast it to ``ty2``, which must be an :ref:`integer <t_integer>` type. If 7849``ty`` is a vector floating point type, ``ty2`` must be a vector integer 7850type with the same number of elements as ``ty`` 7851 7852Semantics: 7853"""""""""" 7854 7855The '``fptoui``' instruction converts its :ref:`floating 7856point <t_floating>` operand into the nearest (rounding towards zero) 7857unsigned integer value. If the value cannot fit in ``ty2``, the results 7858are undefined. 7859 7860Example: 7861"""""""" 7862 7863.. code-block:: llvm 7864 7865 %X = fptoui double 123.0 to i32 ; yields i32:123 7866 %Y = fptoui float 1.0E+300 to i1 ; yields undefined:1 7867 %Z = fptoui float 1.04E+17 to i8 ; yields undefined:1 7868 7869'``fptosi .. to``' Instruction 7870^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7871 7872Syntax: 7873""""""" 7874 7875:: 7876 7877 <result> = fptosi <ty> <value> to <ty2> ; yields ty2 7878 7879Overview: 7880""""""""" 7881 7882The '``fptosi``' instruction converts :ref:`floating point <t_floating>` 7883``value`` to type ``ty2``. 7884 7885Arguments: 7886"""""""""" 7887 7888The '``fptosi``' instruction takes a value to cast, which must be a 7889scalar or vector :ref:`floating point <t_floating>` value, and a type to 7890cast it to ``ty2``, which must be an :ref:`integer <t_integer>` type. If 7891``ty`` is a vector floating point type, ``ty2`` must be a vector integer 7892type with the same number of elements as ``ty`` 7893 7894Semantics: 7895"""""""""" 7896 7897The '``fptosi``' instruction converts its :ref:`floating 7898point <t_floating>` operand into the nearest (rounding towards zero) 7899signed integer value. If the value cannot fit in ``ty2``, the results 7900are undefined. 7901 7902Example: 7903"""""""" 7904 7905.. code-block:: llvm 7906 7907 %X = fptosi double -123.0 to i32 ; yields i32:-123 7908 %Y = fptosi float 1.0E-247 to i1 ; yields undefined:1 7909 %Z = fptosi float 1.04E+17 to i8 ; yields undefined:1 7910 7911'``uitofp .. to``' Instruction 7912^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7913 7914Syntax: 7915""""""" 7916 7917:: 7918 7919 <result> = uitofp <ty> <value> to <ty2> ; yields ty2 7920 7921Overview: 7922""""""""" 7923 7924The '``uitofp``' instruction regards ``value`` as an unsigned integer 7925and converts that value to the ``ty2`` type. 7926 7927Arguments: 7928"""""""""" 7929 7930The '``uitofp``' instruction takes a value to cast, which must be a 7931scalar or vector :ref:`integer <t_integer>` value, and a type to cast it to 7932``ty2``, which must be an :ref:`floating point <t_floating>` type. If 7933``ty`` is a vector integer type, ``ty2`` must be a vector floating point 7934type with the same number of elements as ``ty`` 7935 7936Semantics: 7937"""""""""" 7938 7939The '``uitofp``' instruction interprets its operand as an unsigned 7940integer quantity and converts it to the corresponding floating point 7941value. If the value cannot fit in the floating point value, the results 7942are undefined. 7943 7944Example: 7945"""""""" 7946 7947.. code-block:: llvm 7948 7949 %X = uitofp i32 257 to float ; yields float:257.0 7950 %Y = uitofp i8 -1 to double ; yields double:255.0 7951 7952'``sitofp .. to``' Instruction 7953^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7954 7955Syntax: 7956""""""" 7957 7958:: 7959 7960 <result> = sitofp <ty> <value> to <ty2> ; yields ty2 7961 7962Overview: 7963""""""""" 7964 7965The '``sitofp``' instruction regards ``value`` as a signed integer and 7966converts that value to the ``ty2`` type. 7967 7968Arguments: 7969"""""""""" 7970 7971The '``sitofp``' instruction takes a value to cast, which must be a 7972scalar or vector :ref:`integer <t_integer>` value, and a type to cast it to 7973``ty2``, which must be an :ref:`floating point <t_floating>` type. If 7974``ty`` is a vector integer type, ``ty2`` must be a vector floating point 7975type with the same number of elements as ``ty`` 7976 7977Semantics: 7978"""""""""" 7979 7980The '``sitofp``' instruction interprets its operand as a signed integer 7981quantity and converts it to the corresponding floating point value. If 7982the value cannot fit in the floating point value, the results are 7983undefined. 7984 7985Example: 7986"""""""" 7987 7988.. code-block:: llvm 7989 7990 %X = sitofp i32 257 to float ; yields float:257.0 7991 %Y = sitofp i8 -1 to double ; yields double:-1.0 7992 7993.. _i_ptrtoint: 7994 7995'``ptrtoint .. to``' Instruction 7996^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7997 7998Syntax: 7999""""""" 8000 8001:: 8002 8003 <result> = ptrtoint <ty> <value> to <ty2> ; yields ty2 8004 8005Overview: 8006""""""""" 8007 8008The '``ptrtoint``' instruction converts the pointer or a vector of 8009pointers ``value`` to the integer (or vector of integers) type ``ty2``. 8010 8011Arguments: 8012"""""""""" 8013 8014The '``ptrtoint``' instruction takes a ``value`` to cast, which must be 8015a value of type :ref:`pointer <t_pointer>` or a vector of pointers, and a 8016type to cast it to ``ty2``, which must be an :ref:`integer <t_integer>` or 8017a vector of integers type. 8018 8019Semantics: 8020"""""""""" 8021 8022The '``ptrtoint``' instruction converts ``value`` to integer type 8023``ty2`` by interpreting the pointer value as an integer and either 8024truncating or zero extending that value to the size of the integer type. 8025If ``value`` is smaller than ``ty2`` then a zero extension is done. If 8026``value`` is larger than ``ty2`` then a truncation is done. If they are 8027the same size, then nothing is done (*no-op cast*) other than a type 8028change. 8029 8030Example: 8031"""""""" 8032 8033.. code-block:: llvm 8034 8035 %X = ptrtoint i32* %P to i8 ; yields truncation on 32-bit architecture 8036 %Y = ptrtoint i32* %P to i64 ; yields zero extension on 32-bit architecture 8037 %Z = ptrtoint <4 x i32*> %P to <4 x i64>; yields vector zero extension for a vector of addresses on 32-bit architecture 8038 8039.. _i_inttoptr: 8040 8041'``inttoptr .. to``' Instruction 8042^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 8043 8044Syntax: 8045""""""" 8046 8047:: 8048 8049 <result> = inttoptr <ty> <value> to <ty2> ; yields ty2 8050 8051Overview: 8052""""""""" 8053 8054The '``inttoptr``' instruction converts an integer ``value`` to a 8055pointer type, ``ty2``. 8056 8057Arguments: 8058"""""""""" 8059 8060The '``inttoptr``' instruction takes an :ref:`integer <t_integer>` value to 8061cast, and a type to cast it to, which must be a :ref:`pointer <t_pointer>` 8062type. 8063 8064Semantics: 8065"""""""""" 8066 8067The '``inttoptr``' instruction converts ``value`` to type ``ty2`` by 8068applying either a zero extension or a truncation depending on the size 8069of the integer ``value``. If ``value`` is larger than the size of a 8070pointer then a truncation is done. If ``value`` is smaller than the size 8071of a pointer then a zero extension is done. If they are the same size, 8072nothing is done (*no-op cast*). 8073 8074Example: 8075"""""""" 8076 8077.. code-block:: llvm 8078 8079 %X = inttoptr i32 255 to i32* ; yields zero extension on 64-bit architecture 8080 %Y = inttoptr i32 255 to i32* ; yields no-op on 32-bit architecture 8081 %Z = inttoptr i64 0 to i32* ; yields truncation on 32-bit architecture 8082 %Z = inttoptr <4 x i32> %G to <4 x i8*>; yields truncation of vector G to four pointers 8083 8084.. _i_bitcast: 8085 8086'``bitcast .. to``' Instruction 8087^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 8088 8089Syntax: 8090""""""" 8091 8092:: 8093 8094 <result> = bitcast <ty> <value> to <ty2> ; yields ty2 8095 8096Overview: 8097""""""""" 8098 8099The '``bitcast``' instruction converts ``value`` to type ``ty2`` without 8100changing any bits. 8101 8102Arguments: 8103"""""""""" 8104 8105The '``bitcast``' instruction takes a value to cast, which must be a 8106non-aggregate first class value, and a type to cast it to, which must 8107also be a non-aggregate :ref:`first class <t_firstclass>` type. The 8108bit sizes of ``value`` and the destination type, ``ty2``, must be 8109identical. If the source type is a pointer, the destination type must 8110also be a pointer of the same size. This instruction supports bitwise 8111conversion of vectors to integers and to vectors of other types (as 8112long as they have the same size). 8113 8114Semantics: 8115"""""""""" 8116 8117The '``bitcast``' instruction converts ``value`` to type ``ty2``. It 8118is always a *no-op cast* because no bits change with this 8119conversion. The conversion is done as if the ``value`` had been stored 8120to memory and read back as type ``ty2``. Pointer (or vector of 8121pointers) types may only be converted to other pointer (or vector of 8122pointers) types with the same address space through this instruction. 8123To convert pointers to other types, use the :ref:`inttoptr <i_inttoptr>` 8124or :ref:`ptrtoint <i_ptrtoint>` instructions first. 8125 8126Example: 8127"""""""" 8128 8129.. code-block:: llvm 8130 8131 %X = bitcast i8 255 to i8 ; yields i8 :-1 8132 %Y = bitcast i32* %x to sint* ; yields sint*:%x 8133 %Z = bitcast <2 x int> %V to i64; ; yields i64: %V 8134 %Z = bitcast <2 x i32*> %V to <2 x i64*> ; yields <2 x i64*> 8135 8136.. _i_addrspacecast: 8137 8138'``addrspacecast .. to``' Instruction 8139^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 8140 8141Syntax: 8142""""""" 8143 8144:: 8145 8146 <result> = addrspacecast <pty> <ptrval> to <pty2> ; yields pty2 8147 8148Overview: 8149""""""""" 8150 8151The '``addrspacecast``' instruction converts ``ptrval`` from ``pty`` in 8152address space ``n`` to type ``pty2`` in address space ``m``. 8153 8154Arguments: 8155"""""""""" 8156 8157The '``addrspacecast``' instruction takes a pointer or vector of pointer value 8158to cast and a pointer type to cast it to, which must have a different 8159address space. 8160 8161Semantics: 8162"""""""""" 8163 8164The '``addrspacecast``' instruction converts the pointer value 8165``ptrval`` to type ``pty2``. It can be a *no-op cast* or a complex 8166value modification, depending on the target and the address space 8167pair. Pointer conversions within the same address space must be 8168performed with the ``bitcast`` instruction. Note that if the address space 8169conversion is legal then both result and operand refer to the same memory 8170location. 8171 8172Example: 8173"""""""" 8174 8175.. code-block:: llvm 8176 8177 %X = addrspacecast i32* %x to i32 addrspace(1)* ; yields i32 addrspace(1)*:%x 8178 %Y = addrspacecast i32 addrspace(1)* %y to i64 addrspace(2)* ; yields i64 addrspace(2)*:%y 8179 %Z = addrspacecast <4 x i32*> %z to <4 x float addrspace(3)*> ; yields <4 x float addrspace(3)*>:%z 8180 8181.. _otherops: 8182 8183Other Operations 8184---------------- 8185 8186The instructions in this category are the "miscellaneous" instructions, 8187which defy better classification. 8188 8189.. _i_icmp: 8190 8191'``icmp``' Instruction 8192^^^^^^^^^^^^^^^^^^^^^^ 8193 8194Syntax: 8195""""""" 8196 8197:: 8198 8199 <result> = icmp <cond> <ty> <op1>, <op2> ; yields i1 or <N x i1>:result 8200 8201Overview: 8202""""""""" 8203 8204The '``icmp``' instruction returns a boolean value or a vector of 8205boolean values based on comparison of its two integer, integer vector, 8206pointer, or pointer vector operands. 8207 8208Arguments: 8209"""""""""" 8210 8211The '``icmp``' instruction takes three operands. The first operand is 8212the condition code indicating the kind of comparison to perform. It is 8213not a value, just a keyword. The possible condition codes are: 8214 8215#. ``eq``: equal 8216#. ``ne``: not equal 8217#. ``ugt``: unsigned greater than 8218#. ``uge``: unsigned greater or equal 8219#. ``ult``: unsigned less than 8220#. ``ule``: unsigned less or equal 8221#. ``sgt``: signed greater than 8222#. ``sge``: signed greater or equal 8223#. ``slt``: signed less than 8224#. ``sle``: signed less or equal 8225 8226The remaining two arguments must be :ref:`integer <t_integer>` or 8227:ref:`pointer <t_pointer>` or integer :ref:`vector <t_vector>` typed. They 8228must also be identical types. 8229 8230Semantics: 8231"""""""""" 8232 8233The '``icmp``' compares ``op1`` and ``op2`` according to the condition 8234code given as ``cond``. The comparison performed always yields either an 8235:ref:`i1 <t_integer>` or vector of ``i1`` result, as follows: 8236 8237#. ``eq``: yields ``true`` if the operands are equal, ``false`` 8238 otherwise. No sign interpretation is necessary or performed. 8239#. ``ne``: yields ``true`` if the operands are unequal, ``false`` 8240 otherwise. No sign interpretation is necessary or performed. 8241#. ``ugt``: interprets the operands as unsigned values and yields 8242 ``true`` if ``op1`` is greater than ``op2``. 8243#. ``uge``: interprets the operands as unsigned values and yields 8244 ``true`` if ``op1`` is greater than or equal to ``op2``. 8245#. ``ult``: interprets the operands as unsigned values and yields 8246 ``true`` if ``op1`` is less than ``op2``. 8247#. ``ule``: interprets the operands as unsigned values and yields 8248 ``true`` if ``op1`` is less than or equal to ``op2``. 8249#. ``sgt``: interprets the operands as signed values and yields ``true`` 8250 if ``op1`` is greater than ``op2``. 8251#. ``sge``: interprets the operands as signed values and yields ``true`` 8252 if ``op1`` is greater than or equal to ``op2``. 8253#. ``slt``: interprets the operands as signed values and yields ``true`` 8254 if ``op1`` is less than ``op2``. 8255#. ``sle``: interprets the operands as signed values and yields ``true`` 8256 if ``op1`` is less than or equal to ``op2``. 8257 8258If the operands are :ref:`pointer <t_pointer>` typed, the pointer values 8259are compared as if they were integers. 8260 8261If the operands are integer vectors, then they are compared element by 8262element. The result is an ``i1`` vector with the same number of elements 8263as the values being compared. Otherwise, the result is an ``i1``. 8264 8265Example: 8266"""""""" 8267 8268.. code-block:: llvm 8269 8270 <result> = icmp eq i32 4, 5 ; yields: result=false 8271 <result> = icmp ne float* %X, %X ; yields: result=false 8272 <result> = icmp ult i16 4, 5 ; yields: result=true 8273 <result> = icmp sgt i16 4, 5 ; yields: result=false 8274 <result> = icmp ule i16 -4, 5 ; yields: result=false 8275 <result> = icmp sge i16 4, 5 ; yields: result=false 8276 8277.. _i_fcmp: 8278 8279'``fcmp``' Instruction 8280^^^^^^^^^^^^^^^^^^^^^^ 8281 8282Syntax: 8283""""""" 8284 8285:: 8286 8287 <result> = fcmp [fast-math flags]* <cond> <ty> <op1>, <op2> ; yields i1 or <N x i1>:result 8288 8289Overview: 8290""""""""" 8291 8292The '``fcmp``' instruction returns a boolean value or vector of boolean 8293values based on comparison of its operands. 8294 8295If the operands are floating point scalars, then the result type is a 8296boolean (:ref:`i1 <t_integer>`). 8297 8298If the operands are floating point vectors, then the result type is a 8299vector of boolean with the same number of elements as the operands being 8300compared. 8301 8302Arguments: 8303"""""""""" 8304 8305The '``fcmp``' instruction takes three operands. The first operand is 8306the condition code indicating the kind of comparison to perform. It is 8307not a value, just a keyword. The possible condition codes are: 8308 8309#. ``false``: no comparison, always returns false 8310#. ``oeq``: ordered and equal 8311#. ``ogt``: ordered and greater than 8312#. ``oge``: ordered and greater than or equal 8313#. ``olt``: ordered and less than 8314#. ``ole``: ordered and less than or equal 8315#. ``one``: ordered and not equal 8316#. ``ord``: ordered (no nans) 8317#. ``ueq``: unordered or equal 8318#. ``ugt``: unordered or greater than 8319#. ``uge``: unordered or greater than or equal 8320#. ``ult``: unordered or less than 8321#. ``ule``: unordered or less than or equal 8322#. ``une``: unordered or not equal 8323#. ``uno``: unordered (either nans) 8324#. ``true``: no comparison, always returns true 8325 8326*Ordered* means that neither operand is a QNAN while *unordered* means 8327that either operand may be a QNAN. 8328 8329Each of ``val1`` and ``val2`` arguments must be either a :ref:`floating 8330point <t_floating>` type or a :ref:`vector <t_vector>` of floating point 8331type. They must have identical types. 8332 8333Semantics: 8334"""""""""" 8335 8336The '``fcmp``' instruction compares ``op1`` and ``op2`` according to the 8337condition code given as ``cond``. If the operands are vectors, then the 8338vectors are compared element by element. Each comparison performed 8339always yields an :ref:`i1 <t_integer>` result, as follows: 8340 8341#. ``false``: always yields ``false``, regardless of operands. 8342#. ``oeq``: yields ``true`` if both operands are not a QNAN and ``op1`` 8343 is equal to ``op2``. 8344#. ``ogt``: yields ``true`` if both operands are not a QNAN and ``op1`` 8345 is greater than ``op2``. 8346#. ``oge``: yields ``true`` if both operands are not a QNAN and ``op1`` 8347 is greater than or equal to ``op2``. 8348#. ``olt``: yields ``true`` if both operands are not a QNAN and ``op1`` 8349 is less than ``op2``. 8350#. ``ole``: yields ``true`` if both operands are not a QNAN and ``op1`` 8351 is less than or equal to ``op2``. 8352#. ``one``: yields ``true`` if both operands are not a QNAN and ``op1`` 8353 is not equal to ``op2``. 8354#. ``ord``: yields ``true`` if both operands are not a QNAN. 8355#. ``ueq``: yields ``true`` if either operand is a QNAN or ``op1`` is 8356 equal to ``op2``. 8357#. ``ugt``: yields ``true`` if either operand is a QNAN or ``op1`` is 8358 greater than ``op2``. 8359#. ``uge``: yields ``true`` if either operand is a QNAN or ``op1`` is 8360 greater than or equal to ``op2``. 8361#. ``ult``: yields ``true`` if either operand is a QNAN or ``op1`` is 8362 less than ``op2``. 8363#. ``ule``: yields ``true`` if either operand is a QNAN or ``op1`` is 8364 less than or equal to ``op2``. 8365#. ``une``: yields ``true`` if either operand is a QNAN or ``op1`` is 8366 not equal to ``op2``. 8367#. ``uno``: yields ``true`` if either operand is a QNAN. 8368#. ``true``: always yields ``true``, regardless of operands. 8369 8370The ``fcmp`` instruction can also optionally take any number of 8371:ref:`fast-math flags <fastmath>`, which are optimization hints to enable 8372otherwise unsafe floating point optimizations. 8373 8374Any set of fast-math flags are legal on an ``fcmp`` instruction, but the 8375only flags that have any effect on its semantics are those that allow 8376assumptions to be made about the values of input arguments; namely 8377``nnan``, ``ninf``, and ``nsz``. See :ref:`fastmath` for more information. 8378 8379Example: 8380"""""""" 8381 8382.. code-block:: llvm 8383 8384 <result> = fcmp oeq float 4.0, 5.0 ; yields: result=false 8385 <result> = fcmp one float 4.0, 5.0 ; yields: result=true 8386 <result> = fcmp olt float 4.0, 5.0 ; yields: result=true 8387 <result> = fcmp ueq double 1.0, 2.0 ; yields: result=false 8388 8389.. _i_phi: 8390 8391'``phi``' Instruction 8392^^^^^^^^^^^^^^^^^^^^^ 8393 8394Syntax: 8395""""""" 8396 8397:: 8398 8399 <result> = phi <ty> [ <val0>, <label0>], ... 8400 8401Overview: 8402""""""""" 8403 8404The '``phi``' instruction is used to implement the φ node in the SSA 8405graph representing the function. 8406 8407Arguments: 8408"""""""""" 8409 8410The type of the incoming values is specified with the first type field. 8411After this, the '``phi``' instruction takes a list of pairs as 8412arguments, with one pair for each predecessor basic block of the current 8413block. Only values of :ref:`first class <t_firstclass>` type may be used as 8414the value arguments to the PHI node. Only labels may be used as the 8415label arguments. 8416 8417There must be no non-phi instructions between the start of a basic block 8418and the PHI instructions: i.e. PHI instructions must be first in a basic 8419block. 8420 8421For the purposes of the SSA form, the use of each incoming value is 8422deemed to occur on the edge from the corresponding predecessor block to 8423the current block (but after any definition of an '``invoke``' 8424instruction's return value on the same edge). 8425 8426Semantics: 8427"""""""""" 8428 8429At runtime, the '``phi``' instruction logically takes on the value 8430specified by the pair corresponding to the predecessor basic block that 8431executed just prior to the current block. 8432 8433Example: 8434"""""""" 8435 8436.. code-block:: llvm 8437 8438 Loop: ; Infinite loop that counts from 0 on up... 8439 %indvar = phi i32 [ 0, %LoopHeader ], [ %nextindvar, %Loop ] 8440 %nextindvar = add i32 %indvar, 1 8441 br label %Loop 8442 8443.. _i_select: 8444 8445'``select``' Instruction 8446^^^^^^^^^^^^^^^^^^^^^^^^ 8447 8448Syntax: 8449""""""" 8450 8451:: 8452 8453 <result> = select selty <cond>, <ty> <val1>, <ty> <val2> ; yields ty 8454 8455 selty is either i1 or {<N x i1>} 8456 8457Overview: 8458""""""""" 8459 8460The '``select``' instruction is used to choose one value based on a 8461condition, without IR-level branching. 8462 8463Arguments: 8464"""""""""" 8465 8466The '``select``' instruction requires an 'i1' value or a vector of 'i1' 8467values indicating the condition, and two values of the same :ref:`first 8468class <t_firstclass>` type. 8469 8470Semantics: 8471"""""""""" 8472 8473If the condition is an i1 and it evaluates to 1, the instruction returns 8474the first value argument; otherwise, it returns the second value 8475argument. 8476 8477If the condition is a vector of i1, then the value arguments must be 8478vectors of the same size, and the selection is done element by element. 8479 8480If the condition is an i1 and the value arguments are vectors of the 8481same size, then an entire vector is selected. 8482 8483Example: 8484"""""""" 8485 8486.. code-block:: llvm 8487 8488 %X = select i1 true, i8 17, i8 42 ; yields i8:17 8489 8490.. _i_call: 8491 8492'``call``' Instruction 8493^^^^^^^^^^^^^^^^^^^^^^ 8494 8495Syntax: 8496""""""" 8497 8498:: 8499 8500 <result> = [tail | musttail | notail ] call [fast-math flags] [cconv] [ret attrs] <ty>|<fnty> <fnptrval>(<function args>) [fn attrs] 8501 [ operand bundles ] 8502 8503Overview: 8504""""""""" 8505 8506The '``call``' instruction represents a simple function call. 8507 8508Arguments: 8509"""""""""" 8510 8511This instruction requires several arguments: 8512 8513#. The optional ``tail`` and ``musttail`` markers indicate that the optimizers 8514 should perform tail call optimization. The ``tail`` marker is a hint that 8515 `can be ignored <CodeGenerator.html#sibcallopt>`_. The ``musttail`` marker 8516 means that the call must be tail call optimized in order for the program to 8517 be correct. The ``musttail`` marker provides these guarantees: 8518 8519 #. The call will not cause unbounded stack growth if it is part of a 8520 recursive cycle in the call graph. 8521 #. Arguments with the :ref:`inalloca <attr_inalloca>` attribute are 8522 forwarded in place. 8523 8524 Both markers imply that the callee does not access allocas or varargs from 8525 the caller. Calls marked ``musttail`` must obey the following additional 8526 rules: 8527 8528 - The call must immediately precede a :ref:`ret <i_ret>` instruction, 8529 or a pointer bitcast followed by a ret instruction. 8530 - The ret instruction must return the (possibly bitcasted) value 8531 produced by the call or void. 8532 - The caller and callee prototypes must match. Pointer types of 8533 parameters or return types may differ in pointee type, but not 8534 in address space. 8535 - The calling conventions of the caller and callee must match. 8536 - All ABI-impacting function attributes, such as sret, byval, inreg, 8537 returned, and inalloca, must match. 8538 - The callee must be varargs iff the caller is varargs. Bitcasting a 8539 non-varargs function to the appropriate varargs type is legal so 8540 long as the non-varargs prefixes obey the other rules. 8541 8542 Tail call optimization for calls marked ``tail`` is guaranteed to occur if 8543 the following conditions are met: 8544 8545 - Caller and callee both have the calling convention ``fastcc``. 8546 - The call is in tail position (ret immediately follows call and ret 8547 uses value of call or is void). 8548 - Option ``-tailcallopt`` is enabled, or 8549 ``llvm::GuaranteedTailCallOpt`` is ``true``. 8550 - `Platform-specific constraints are 8551 met. <CodeGenerator.html#tailcallopt>`_ 8552 8553#. The optional ``notail`` marker indicates that the optimizers should not add 8554 ``tail`` or ``musttail`` markers to the call. It is used to prevent tail 8555 call optimization from being performed on the call. 8556 8557#. The optional ``fast-math flags`` marker indicates that the call has one or more 8558 :ref:`fast-math flags <fastmath>`, which are optimization hints to enable 8559 otherwise unsafe floating-point optimizations. Fast-math flags are only valid 8560 for calls that return a floating-point scalar or vector type. 8561 8562#. The optional "cconv" marker indicates which :ref:`calling 8563 convention <callingconv>` the call should use. If none is 8564 specified, the call defaults to using C calling conventions. The 8565 calling convention of the call must match the calling convention of 8566 the target function, or else the behavior is undefined. 8567#. The optional :ref:`Parameter Attributes <paramattrs>` list for return 8568 values. Only '``zeroext``', '``signext``', and '``inreg``' attributes 8569 are valid here. 8570#. '``ty``': the type of the call instruction itself which is also the 8571 type of the return value. Functions that return no value are marked 8572 ``void``. 8573#. '``fnty``': shall be the signature of the function being called. The 8574 argument types must match the types implied by this signature. This 8575 type can be omitted if the function is not varargs. 8576#. '``fnptrval``': An LLVM value containing a pointer to a function to 8577 be called. In most cases, this is a direct function call, but 8578 indirect ``call``'s are just as possible, calling an arbitrary pointer 8579 to function value. 8580#. '``function args``': argument list whose types match the function 8581 signature argument types and parameter attributes. All arguments must 8582 be of :ref:`first class <t_firstclass>` type. If the function signature 8583 indicates the function accepts a variable number of arguments, the 8584 extra arguments can be specified. 8585#. The optional :ref:`function attributes <fnattrs>` list. Only 8586 '``noreturn``', '``nounwind``', '``readonly``' , '``readnone``', 8587 and '``convergent``' attributes are valid here. 8588#. The optional :ref:`operand bundles <opbundles>` list. 8589 8590Semantics: 8591"""""""""" 8592 8593The '``call``' instruction is used to cause control flow to transfer to 8594a specified function, with its incoming arguments bound to the specified 8595values. Upon a '``ret``' instruction in the called function, control 8596flow continues with the instruction after the function call, and the 8597return value of the function is bound to the result argument. 8598 8599Example: 8600"""""""" 8601 8602.. code-block:: llvm 8603 8604 %retval = call i32 @test(i32 %argc) 8605 call i32 (i8*, ...)* @printf(i8* %msg, i32 12, i8 42) ; yields i32 8606 %X = tail call i32 @foo() ; yields i32 8607 %Y = tail call fastcc i32 @foo() ; yields i32 8608 call void %foo(i8 97 signext) 8609 8610 %struct.A = type { i32, i8 } 8611 %r = call %struct.A @foo() ; yields { i32, i8 } 8612 %gr = extractvalue %struct.A %r, 0 ; yields i32 8613 %gr1 = extractvalue %struct.A %r, 1 ; yields i8 8614 %Z = call void @foo() noreturn ; indicates that %foo never returns normally 8615 %ZZ = call zeroext i32 @bar() ; Return value is %zero extended 8616 8617llvm treats calls to some functions with names and arguments that match 8618the standard C99 library as being the C99 library functions, and may 8619perform optimizations or generate code for them under that assumption. 8620This is something we'd like to change in the future to provide better 8621support for freestanding environments and non-C-based languages. 8622 8623.. _i_va_arg: 8624 8625'``va_arg``' Instruction 8626^^^^^^^^^^^^^^^^^^^^^^^^ 8627 8628Syntax: 8629""""""" 8630 8631:: 8632 8633 <resultval> = va_arg <va_list*> <arglist>, <argty> 8634 8635Overview: 8636""""""""" 8637 8638The '``va_arg``' instruction is used to access arguments passed through 8639the "variable argument" area of a function call. It is used to implement 8640the ``va_arg`` macro in C. 8641 8642Arguments: 8643"""""""""" 8644 8645This instruction takes a ``va_list*`` value and the type of the 8646argument. It returns a value of the specified argument type and 8647increments the ``va_list`` to point to the next argument. The actual 8648type of ``va_list`` is target specific. 8649 8650Semantics: 8651"""""""""" 8652 8653The '``va_arg``' instruction loads an argument of the specified type 8654from the specified ``va_list`` and causes the ``va_list`` to point to 8655the next argument. For more information, see the variable argument 8656handling :ref:`Intrinsic Functions <int_varargs>`. 8657 8658It is legal for this instruction to be called in a function which does 8659not take a variable number of arguments, for example, the ``vfprintf`` 8660function. 8661 8662``va_arg`` is an LLVM instruction instead of an :ref:`intrinsic 8663function <intrinsics>` because it takes a type as an argument. 8664 8665Example: 8666"""""""" 8667 8668See the :ref:`variable argument processing <int_varargs>` section. 8669 8670Note that the code generator does not yet fully support va\_arg on many 8671targets. Also, it does not currently support va\_arg with aggregate 8672types on any target. 8673 8674.. _i_landingpad: 8675 8676'``landingpad``' Instruction 8677^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 8678 8679Syntax: 8680""""""" 8681 8682:: 8683 8684 <resultval> = landingpad <resultty> <clause>+ 8685 <resultval> = landingpad <resultty> cleanup <clause>* 8686 8687 <clause> := catch <type> <value> 8688 <clause> := filter <array constant type> <array constant> 8689 8690Overview: 8691""""""""" 8692 8693The '``landingpad``' instruction is used by `LLVM's exception handling 8694system <ExceptionHandling.html#overview>`_ to specify that a basic block 8695is a landing pad --- one where the exception lands, and corresponds to the 8696code found in the ``catch`` portion of a ``try``/``catch`` sequence. It 8697defines values supplied by the :ref:`personality function <personalityfn>` upon 8698re-entry to the function. The ``resultval`` has the type ``resultty``. 8699 8700Arguments: 8701"""""""""" 8702 8703The optional 8704``cleanup`` flag indicates that the landing pad block is a cleanup. 8705 8706A ``clause`` begins with the clause type --- ``catch`` or ``filter`` --- and 8707contains the global variable representing the "type" that may be caught 8708or filtered respectively. Unlike the ``catch`` clause, the ``filter`` 8709clause takes an array constant as its argument. Use 8710"``[0 x i8**] undef``" for a filter which cannot throw. The 8711'``landingpad``' instruction must contain *at least* one ``clause`` or 8712the ``cleanup`` flag. 8713 8714Semantics: 8715"""""""""" 8716 8717The '``landingpad``' instruction defines the values which are set by the 8718:ref:`personality function <personalityfn>` upon re-entry to the function, and 8719therefore the "result type" of the ``landingpad`` instruction. As with 8720calling conventions, how the personality function results are 8721represented in LLVM IR is target specific. 8722 8723The clauses are applied in order from top to bottom. If two 8724``landingpad`` instructions are merged together through inlining, the 8725clauses from the calling function are appended to the list of clauses. 8726When the call stack is being unwound due to an exception being thrown, 8727the exception is compared against each ``clause`` in turn. If it doesn't 8728match any of the clauses, and the ``cleanup`` flag is not set, then 8729unwinding continues further up the call stack. 8730 8731The ``landingpad`` instruction has several restrictions: 8732 8733- A landing pad block is a basic block which is the unwind destination 8734 of an '``invoke``' instruction. 8735- A landing pad block must have a '``landingpad``' instruction as its 8736 first non-PHI instruction. 8737- There can be only one '``landingpad``' instruction within the landing 8738 pad block. 8739- A basic block that is not a landing pad block may not include a 8740 '``landingpad``' instruction. 8741 8742Example: 8743"""""""" 8744 8745.. code-block:: llvm 8746 8747 ;; A landing pad which can catch an integer. 8748 %res = landingpad { i8*, i32 } 8749 catch i8** @_ZTIi 8750 ;; A landing pad that is a cleanup. 8751 %res = landingpad { i8*, i32 } 8752 cleanup 8753 ;; A landing pad which can catch an integer and can only throw a double. 8754 %res = landingpad { i8*, i32 } 8755 catch i8** @_ZTIi 8756 filter [1 x i8**] [@_ZTId] 8757 8758.. _i_catchpad: 8759 8760'``catchpad``' Instruction 8761^^^^^^^^^^^^^^^^^^^^^^^^^^ 8762 8763Syntax: 8764""""""" 8765 8766:: 8767 8768 <resultval> = catchpad within <catchswitch> [<args>*] 8769 8770Overview: 8771""""""""" 8772 8773The '``catchpad``' instruction is used by `LLVM's exception handling 8774system <ExceptionHandling.html#overview>`_ to specify that a basic block 8775begins a catch handler --- one where a personality routine attempts to transfer 8776control to catch an exception. 8777 8778Arguments: 8779"""""""""" 8780 8781The ``catchswitch`` operand must always be a token produced by a 8782:ref:`catchswitch <i_catchswitch>` instruction in a predecessor block. This 8783ensures that each ``catchpad`` has exactly one predecessor block, and it always 8784terminates in a ``catchswitch``. 8785 8786The ``args`` correspond to whatever information the personality routine 8787requires to know if this is an appropriate handler for the exception. Control 8788will transfer to the ``catchpad`` if this is the first appropriate handler for 8789the exception. 8790 8791The ``resultval`` has the type :ref:`token <t_token>` and is used to match the 8792``catchpad`` to corresponding :ref:`catchrets <i_catchret>` and other nested EH 8793pads. 8794 8795Semantics: 8796"""""""""" 8797 8798When the call stack is being unwound due to an exception being thrown, the 8799exception is compared against the ``args``. If it doesn't match, control will 8800not reach the ``catchpad`` instruction. The representation of ``args`` is 8801entirely target and personality function-specific. 8802 8803Like the :ref:`landingpad <i_landingpad>` instruction, the ``catchpad`` 8804instruction must be the first non-phi of its parent basic block. 8805 8806The meaning of the tokens produced and consumed by ``catchpad`` and other "pad" 8807instructions is described in the 8808`Windows exception handling documentation\ <ExceptionHandling.html#wineh>`_. 8809 8810When a ``catchpad`` has been "entered" but not yet "exited" (as 8811described in the `EH documentation\ <ExceptionHandling.html#wineh-constraints>`_), 8812it is undefined behavior to execute a :ref:`call <i_call>` or :ref:`invoke <i_invoke>` 8813that does not carry an appropriate :ref:`"funclet" bundle <ob_funclet>`. 8814 8815Example: 8816"""""""" 8817 8818.. code-block:: llvm 8819 8820 dispatch: 8821 %cs = catchswitch within none [label %handler0] unwind to caller 8822 ;; A catch block which can catch an integer. 8823 handler0: 8824 %tok = catchpad within %cs [i8** @_ZTIi] 8825 8826.. _i_cleanuppad: 8827 8828'``cleanuppad``' Instruction 8829^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 8830 8831Syntax: 8832""""""" 8833 8834:: 8835 8836 <resultval> = cleanuppad within <parent> [<args>*] 8837 8838Overview: 8839""""""""" 8840 8841The '``cleanuppad``' instruction is used by `LLVM's exception handling 8842system <ExceptionHandling.html#overview>`_ to specify that a basic block 8843is a cleanup block --- one where a personality routine attempts to 8844transfer control to run cleanup actions. 8845The ``args`` correspond to whatever additional 8846information the :ref:`personality function <personalityfn>` requires to 8847execute the cleanup. 8848The ``resultval`` has the type :ref:`token <t_token>` and is used to 8849match the ``cleanuppad`` to corresponding :ref:`cleanuprets <i_cleanupret>`. 8850The ``parent`` argument is the token of the funclet that contains the 8851``cleanuppad`` instruction. If the ``cleanuppad`` is not inside a funclet, 8852this operand may be the token ``none``. 8853 8854Arguments: 8855"""""""""" 8856 8857The instruction takes a list of arbitrary values which are interpreted 8858by the :ref:`personality function <personalityfn>`. 8859 8860Semantics: 8861"""""""""" 8862 8863When the call stack is being unwound due to an exception being thrown, 8864the :ref:`personality function <personalityfn>` transfers control to the 8865``cleanuppad`` with the aid of the personality-specific arguments. 8866As with calling conventions, how the personality function results are 8867represented in LLVM IR is target specific. 8868 8869The ``cleanuppad`` instruction has several restrictions: 8870 8871- A cleanup block is a basic block which is the unwind destination of 8872 an exceptional instruction. 8873- A cleanup block must have a '``cleanuppad``' instruction as its 8874 first non-PHI instruction. 8875- There can be only one '``cleanuppad``' instruction within the 8876 cleanup block. 8877- A basic block that is not a cleanup block may not include a 8878 '``cleanuppad``' instruction. 8879 8880When a ``cleanuppad`` has been "entered" but not yet "exited" (as 8881described in the `EH documentation\ <ExceptionHandling.html#wineh-constraints>`_), 8882it is undefined behavior to execute a :ref:`call <i_call>` or :ref:`invoke <i_invoke>` 8883that does not carry an appropriate :ref:`"funclet" bundle <ob_funclet>`. 8884 8885Example: 8886"""""""" 8887 8888.. code-block:: llvm 8889 8890 %tok = cleanuppad within %cs [] 8891 8892.. _intrinsics: 8893 8894Intrinsic Functions 8895=================== 8896 8897LLVM supports the notion of an "intrinsic function". These functions 8898have well known names and semantics and are required to follow certain 8899restrictions. Overall, these intrinsics represent an extension mechanism 8900for the LLVM language that does not require changing all of the 8901transformations in LLVM when adding to the language (or the bitcode 8902reader/writer, the parser, etc...). 8903 8904Intrinsic function names must all start with an "``llvm.``" prefix. This 8905prefix is reserved in LLVM for intrinsic names; thus, function names may 8906not begin with this prefix. Intrinsic functions must always be external 8907functions: you cannot define the body of intrinsic functions. Intrinsic 8908functions may only be used in call or invoke instructions: it is illegal 8909to take the address of an intrinsic function. Additionally, because 8910intrinsic functions are part of the LLVM language, it is required if any 8911are added that they be documented here. 8912 8913Some intrinsic functions can be overloaded, i.e., the intrinsic 8914represents a family of functions that perform the same operation but on 8915different data types. Because LLVM can represent over 8 million 8916different integer types, overloading is used commonly to allow an 8917intrinsic function to operate on any integer type. One or more of the 8918argument types or the result type can be overloaded to accept any 8919integer type. Argument types may also be defined as exactly matching a 8920previous argument's type or the result type. This allows an intrinsic 8921function which accepts multiple arguments, but needs all of them to be 8922of the same type, to only be overloaded with respect to a single 8923argument or the result. 8924 8925Overloaded intrinsics will have the names of its overloaded argument 8926types encoded into its function name, each preceded by a period. Only 8927those types which are overloaded result in a name suffix. Arguments 8928whose type is matched against another type do not. For example, the 8929``llvm.ctpop`` function can take an integer of any width and returns an 8930integer of exactly the same integer width. This leads to a family of 8931functions such as ``i8 @llvm.ctpop.i8(i8 %val)`` and 8932``i29 @llvm.ctpop.i29(i29 %val)``. Only one type, the return type, is 8933overloaded, and only one type suffix is required. Because the argument's 8934type is matched against the return type, it does not require its own 8935name suffix. 8936 8937To learn how to add an intrinsic function, please see the `Extending 8938LLVM Guide <ExtendingLLVM.html>`_. 8939 8940.. _int_varargs: 8941 8942Variable Argument Handling Intrinsics 8943------------------------------------- 8944 8945Variable argument support is defined in LLVM with the 8946:ref:`va_arg <i_va_arg>` instruction and these three intrinsic 8947functions. These functions are related to the similarly named macros 8948defined in the ``<stdarg.h>`` header file. 8949 8950All of these functions operate on arguments that use a target-specific 8951value type "``va_list``". The LLVM assembly language reference manual 8952does not define what this type is, so all transformations should be 8953prepared to handle these functions regardless of the type used. 8954 8955This example shows how the :ref:`va_arg <i_va_arg>` instruction and the 8956variable argument handling intrinsic functions are used. 8957 8958.. code-block:: llvm 8959 8960 ; This struct is different for every platform. For most platforms, 8961 ; it is merely an i8*. 8962 %struct.va_list = type { i8* } 8963 8964 ; For Unix x86_64 platforms, va_list is the following struct: 8965 ; %struct.va_list = type { i32, i32, i8*, i8* } 8966 8967 define i32 @test(i32 %X, ...) { 8968 ; Initialize variable argument processing 8969 %ap = alloca %struct.va_list 8970 %ap2 = bitcast %struct.va_list* %ap to i8* 8971 call void @llvm.va_start(i8* %ap2) 8972 8973 ; Read a single integer argument 8974 %tmp = va_arg i8* %ap2, i32 8975 8976 ; Demonstrate usage of llvm.va_copy and llvm.va_end 8977 %aq = alloca i8* 8978 %aq2 = bitcast i8** %aq to i8* 8979 call void @llvm.va_copy(i8* %aq2, i8* %ap2) 8980 call void @llvm.va_end(i8* %aq2) 8981 8982 ; Stop processing of arguments. 8983 call void @llvm.va_end(i8* %ap2) 8984 ret i32 %tmp 8985 } 8986 8987 declare void @llvm.va_start(i8*) 8988 declare void @llvm.va_copy(i8*, i8*) 8989 declare void @llvm.va_end(i8*) 8990 8991.. _int_va_start: 8992 8993'``llvm.va_start``' Intrinsic 8994^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 8995 8996Syntax: 8997""""""" 8998 8999:: 9000 9001 declare void @llvm.va_start(i8* <arglist>) 9002 9003Overview: 9004""""""""" 9005 9006The '``llvm.va_start``' intrinsic initializes ``*<arglist>`` for 9007subsequent use by ``va_arg``. 9008 9009Arguments: 9010"""""""""" 9011 9012The argument is a pointer to a ``va_list`` element to initialize. 9013 9014Semantics: 9015"""""""""" 9016 9017The '``llvm.va_start``' intrinsic works just like the ``va_start`` macro 9018available in C. In a target-dependent way, it initializes the 9019``va_list`` element to which the argument points, so that the next call 9020to ``va_arg`` will produce the first variable argument passed to the 9021function. Unlike the C ``va_start`` macro, this intrinsic does not need 9022to know the last argument of the function as the compiler can figure 9023that out. 9024 9025'``llvm.va_end``' Intrinsic 9026^^^^^^^^^^^^^^^^^^^^^^^^^^^ 9027 9028Syntax: 9029""""""" 9030 9031:: 9032 9033 declare void @llvm.va_end(i8* <arglist>) 9034 9035Overview: 9036""""""""" 9037 9038The '``llvm.va_end``' intrinsic destroys ``*<arglist>``, which has been 9039initialized previously with ``llvm.va_start`` or ``llvm.va_copy``. 9040 9041Arguments: 9042"""""""""" 9043 9044The argument is a pointer to a ``va_list`` to destroy. 9045 9046Semantics: 9047"""""""""" 9048 9049The '``llvm.va_end``' intrinsic works just like the ``va_end`` macro 9050available in C. In a target-dependent way, it destroys the ``va_list`` 9051element to which the argument points. Calls to 9052:ref:`llvm.va_start <int_va_start>` and 9053:ref:`llvm.va_copy <int_va_copy>` must be matched exactly with calls to 9054``llvm.va_end``. 9055 9056.. _int_va_copy: 9057 9058'``llvm.va_copy``' Intrinsic 9059^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 9060 9061Syntax: 9062""""""" 9063 9064:: 9065 9066 declare void @llvm.va_copy(i8* <destarglist>, i8* <srcarglist>) 9067 9068Overview: 9069""""""""" 9070 9071The '``llvm.va_copy``' intrinsic copies the current argument position 9072from the source argument list to the destination argument list. 9073 9074Arguments: 9075"""""""""" 9076 9077The first argument is a pointer to a ``va_list`` element to initialize. 9078The second argument is a pointer to a ``va_list`` element to copy from. 9079 9080Semantics: 9081"""""""""" 9082 9083The '``llvm.va_copy``' intrinsic works just like the ``va_copy`` macro 9084available in C. In a target-dependent way, it copies the source 9085``va_list`` element into the destination ``va_list`` element. This 9086intrinsic is necessary because the `` llvm.va_start`` intrinsic may be 9087arbitrarily complex and require, for example, memory allocation. 9088 9089Accurate Garbage Collection Intrinsics 9090-------------------------------------- 9091 9092LLVM's support for `Accurate Garbage Collection <GarbageCollection.html>`_ 9093(GC) requires the frontend to generate code containing appropriate intrinsic 9094calls and select an appropriate GC strategy which knows how to lower these 9095intrinsics in a manner which is appropriate for the target collector. 9096 9097These intrinsics allow identification of :ref:`GC roots on the 9098stack <int_gcroot>`, as well as garbage collector implementations that 9099require :ref:`read <int_gcread>` and :ref:`write <int_gcwrite>` barriers. 9100Frontends for type-safe garbage collected languages should generate 9101these intrinsics to make use of the LLVM garbage collectors. For more 9102details, see `Garbage Collection with LLVM <GarbageCollection.html>`_. 9103 9104Experimental Statepoint Intrinsics 9105^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 9106 9107LLVM provides an second experimental set of intrinsics for describing garbage 9108collection safepoints in compiled code. These intrinsics are an alternative 9109to the ``llvm.gcroot`` intrinsics, but are compatible with the ones for 9110:ref:`read <int_gcread>` and :ref:`write <int_gcwrite>` barriers. The 9111differences in approach are covered in the `Garbage Collection with LLVM 9112<GarbageCollection.html>`_ documentation. The intrinsics themselves are 9113described in :doc:`Statepoints`. 9114 9115.. _int_gcroot: 9116 9117'``llvm.gcroot``' Intrinsic 9118^^^^^^^^^^^^^^^^^^^^^^^^^^^ 9119 9120Syntax: 9121""""""" 9122 9123:: 9124 9125 declare void @llvm.gcroot(i8** %ptrloc, i8* %metadata) 9126 9127Overview: 9128""""""""" 9129 9130The '``llvm.gcroot``' intrinsic declares the existence of a GC root to 9131the code generator, and allows some metadata to be associated with it. 9132 9133Arguments: 9134"""""""""" 9135 9136The first argument specifies the address of a stack object that contains 9137the root pointer. The second pointer (which must be either a constant or 9138a global value address) contains the meta-data to be associated with the 9139root. 9140 9141Semantics: 9142"""""""""" 9143 9144At runtime, a call to this intrinsic stores a null pointer into the 9145"ptrloc" location. At compile-time, the code generator generates 9146information to allow the runtime to find the pointer at GC safe points. 9147The '``llvm.gcroot``' intrinsic may only be used in a function which 9148:ref:`specifies a GC algorithm <gc>`. 9149 9150.. _int_gcread: 9151 9152'``llvm.gcread``' Intrinsic 9153^^^^^^^^^^^^^^^^^^^^^^^^^^^ 9154 9155Syntax: 9156""""""" 9157 9158:: 9159 9160 declare i8* @llvm.gcread(i8* %ObjPtr, i8** %Ptr) 9161 9162Overview: 9163""""""""" 9164 9165The '``llvm.gcread``' intrinsic identifies reads of references from heap 9166locations, allowing garbage collector implementations that require read 9167barriers. 9168 9169Arguments: 9170"""""""""" 9171 9172The second argument is the address to read from, which should be an 9173address allocated from the garbage collector. The first object is a 9174pointer to the start of the referenced object, if needed by the language 9175runtime (otherwise null). 9176 9177Semantics: 9178"""""""""" 9179 9180The '``llvm.gcread``' intrinsic has the same semantics as a load 9181instruction, but may be replaced with substantially more complex code by 9182the garbage collector runtime, as needed. The '``llvm.gcread``' 9183intrinsic may only be used in a function which :ref:`specifies a GC 9184algorithm <gc>`. 9185 9186.. _int_gcwrite: 9187 9188'``llvm.gcwrite``' Intrinsic 9189^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 9190 9191Syntax: 9192""""""" 9193 9194:: 9195 9196 declare void @llvm.gcwrite(i8* %P1, i8* %Obj, i8** %P2) 9197 9198Overview: 9199""""""""" 9200 9201The '``llvm.gcwrite``' intrinsic identifies writes of references to heap 9202locations, allowing garbage collector implementations that require write 9203barriers (such as generational or reference counting collectors). 9204 9205Arguments: 9206"""""""""" 9207 9208The first argument is the reference to store, the second is the start of 9209the object to store it to, and the third is the address of the field of 9210Obj to store to. If the runtime does not require a pointer to the 9211object, Obj may be null. 9212 9213Semantics: 9214"""""""""" 9215 9216The '``llvm.gcwrite``' intrinsic has the same semantics as a store 9217instruction, but may be replaced with substantially more complex code by 9218the garbage collector runtime, as needed. The '``llvm.gcwrite``' 9219intrinsic may only be used in a function which :ref:`specifies a GC 9220algorithm <gc>`. 9221 9222Code Generator Intrinsics 9223------------------------- 9224 9225These intrinsics are provided by LLVM to expose special features that 9226may only be implemented with code generator support. 9227 9228'``llvm.returnaddress``' Intrinsic 9229^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 9230 9231Syntax: 9232""""""" 9233 9234:: 9235 9236 declare i8 *@llvm.returnaddress(i32 <level>) 9237 9238Overview: 9239""""""""" 9240 9241The '``llvm.returnaddress``' intrinsic attempts to compute a 9242target-specific value indicating the return address of the current 9243function or one of its callers. 9244 9245Arguments: 9246"""""""""" 9247 9248The argument to this intrinsic indicates which function to return the 9249address for. Zero indicates the calling function, one indicates its 9250caller, etc. The argument is **required** to be a constant integer 9251value. 9252 9253Semantics: 9254"""""""""" 9255 9256The '``llvm.returnaddress``' intrinsic either returns a pointer 9257indicating the return address of the specified call frame, or zero if it 9258cannot be identified. The value returned by this intrinsic is likely to 9259be incorrect or 0 for arguments other than zero, so it should only be 9260used for debugging purposes. 9261 9262Note that calling this intrinsic does not prevent function inlining or 9263other aggressive transformations, so the value returned may not be that 9264of the obvious source-language caller. 9265 9266'``llvm.frameaddress``' Intrinsic 9267^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 9268 9269Syntax: 9270""""""" 9271 9272:: 9273 9274 declare i8* @llvm.frameaddress(i32 <level>) 9275 9276Overview: 9277""""""""" 9278 9279The '``llvm.frameaddress``' intrinsic attempts to return the 9280target-specific frame pointer value for the specified stack frame. 9281 9282Arguments: 9283"""""""""" 9284 9285The argument to this intrinsic indicates which function to return the 9286frame pointer for. Zero indicates the calling function, one indicates 9287its caller, etc. The argument is **required** to be a constant integer 9288value. 9289 9290Semantics: 9291"""""""""" 9292 9293The '``llvm.frameaddress``' intrinsic either returns a pointer 9294indicating the frame address of the specified call frame, or zero if it 9295cannot be identified. The value returned by this intrinsic is likely to 9296be incorrect or 0 for arguments other than zero, so it should only be 9297used for debugging purposes. 9298 9299Note that calling this intrinsic does not prevent function inlining or 9300other aggressive transformations, so the value returned may not be that 9301of the obvious source-language caller. 9302 9303'``llvm.localescape``' and '``llvm.localrecover``' Intrinsics 9304^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 9305 9306Syntax: 9307""""""" 9308 9309:: 9310 9311 declare void @llvm.localescape(...) 9312 declare i8* @llvm.localrecover(i8* %func, i8* %fp, i32 %idx) 9313 9314Overview: 9315""""""""" 9316 9317The '``llvm.localescape``' intrinsic escapes offsets of a collection of static 9318allocas, and the '``llvm.localrecover``' intrinsic applies those offsets to a 9319live frame pointer to recover the address of the allocation. The offset is 9320computed during frame layout of the caller of ``llvm.localescape``. 9321 9322Arguments: 9323"""""""""" 9324 9325All arguments to '``llvm.localescape``' must be pointers to static allocas or 9326casts of static allocas. Each function can only call '``llvm.localescape``' 9327once, and it can only do so from the entry block. 9328 9329The ``func`` argument to '``llvm.localrecover``' must be a constant 9330bitcasted pointer to a function defined in the current module. The code 9331generator cannot determine the frame allocation offset of functions defined in 9332other modules. 9333 9334The ``fp`` argument to '``llvm.localrecover``' must be a frame pointer of a 9335call frame that is currently live. The return value of '``llvm.localaddress``' 9336is one way to produce such a value, but various runtimes also expose a suitable 9337pointer in platform-specific ways. 9338 9339The ``idx`` argument to '``llvm.localrecover``' indicates which alloca passed to 9340'``llvm.localescape``' to recover. It is zero-indexed. 9341 9342Semantics: 9343"""""""""" 9344 9345These intrinsics allow a group of functions to share access to a set of local 9346stack allocations of a one parent function. The parent function may call the 9347'``llvm.localescape``' intrinsic once from the function entry block, and the 9348child functions can use '``llvm.localrecover``' to access the escaped allocas. 9349The '``llvm.localescape``' intrinsic blocks inlining, as inlining changes where 9350the escaped allocas are allocated, which would break attempts to use 9351'``llvm.localrecover``'. 9352 9353.. _int_read_register: 9354.. _int_write_register: 9355 9356'``llvm.read_register``' and '``llvm.write_register``' Intrinsics 9357^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 9358 9359Syntax: 9360""""""" 9361 9362:: 9363 9364 declare i32 @llvm.read_register.i32(metadata) 9365 declare i64 @llvm.read_register.i64(metadata) 9366 declare void @llvm.write_register.i32(metadata, i32 @value) 9367 declare void @llvm.write_register.i64(metadata, i64 @value) 9368 !0 = !{!"sp\00"} 9369 9370Overview: 9371""""""""" 9372 9373The '``llvm.read_register``' and '``llvm.write_register``' intrinsics 9374provides access to the named register. The register must be valid on 9375the architecture being compiled to. The type needs to be compatible 9376with the register being read. 9377 9378Semantics: 9379"""""""""" 9380 9381The '``llvm.read_register``' intrinsic returns the current value of the 9382register, where possible. The '``llvm.write_register``' intrinsic sets 9383the current value of the register, where possible. 9384 9385This is useful to implement named register global variables that need 9386to always be mapped to a specific register, as is common practice on 9387bare-metal programs including OS kernels. 9388 9389The compiler doesn't check for register availability or use of the used 9390register in surrounding code, including inline assembly. Because of that, 9391allocatable registers are not supported. 9392 9393Warning: So far it only works with the stack pointer on selected 9394architectures (ARM, AArch64, PowerPC and x86_64). Significant amount of 9395work is needed to support other registers and even more so, allocatable 9396registers. 9397 9398.. _int_stacksave: 9399 9400'``llvm.stacksave``' Intrinsic 9401^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 9402 9403Syntax: 9404""""""" 9405 9406:: 9407 9408 declare i8* @llvm.stacksave() 9409 9410Overview: 9411""""""""" 9412 9413The '``llvm.stacksave``' intrinsic is used to remember the current state 9414of the function stack, for use with 9415:ref:`llvm.stackrestore <int_stackrestore>`. This is useful for 9416implementing language features like scoped automatic variable sized 9417arrays in C99. 9418 9419Semantics: 9420"""""""""" 9421 9422This intrinsic returns a opaque pointer value that can be passed to 9423:ref:`llvm.stackrestore <int_stackrestore>`. When an 9424``llvm.stackrestore`` intrinsic is executed with a value saved from 9425``llvm.stacksave``, it effectively restores the state of the stack to 9426the state it was in when the ``llvm.stacksave`` intrinsic executed. In 9427practice, this pops any :ref:`alloca <i_alloca>` blocks from the stack that 9428were allocated after the ``llvm.stacksave`` was executed. 9429 9430.. _int_stackrestore: 9431 9432'``llvm.stackrestore``' Intrinsic 9433^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 9434 9435Syntax: 9436""""""" 9437 9438:: 9439 9440 declare void @llvm.stackrestore(i8* %ptr) 9441 9442Overview: 9443""""""""" 9444 9445The '``llvm.stackrestore``' intrinsic is used to restore the state of 9446the function stack to the state it was in when the corresponding 9447:ref:`llvm.stacksave <int_stacksave>` intrinsic executed. This is 9448useful for implementing language features like scoped automatic variable 9449sized arrays in C99. 9450 9451Semantics: 9452"""""""""" 9453 9454See the description for :ref:`llvm.stacksave <int_stacksave>`. 9455 9456.. _int_get_dynamic_area_offset: 9457 9458'``llvm.get.dynamic.area.offset``' Intrinsic 9459^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 9460 9461Syntax: 9462""""""" 9463 9464:: 9465 9466 declare i32 @llvm.get.dynamic.area.offset.i32() 9467 declare i64 @llvm.get.dynamic.area.offset.i64() 9468 9469 Overview: 9470 """"""""" 9471 9472 The '``llvm.get.dynamic.area.offset.*``' intrinsic family is used to 9473 get the offset from native stack pointer to the address of the most 9474 recent dynamic alloca on the caller's stack. These intrinsics are 9475 intendend for use in combination with 9476 :ref:`llvm.stacksave <int_stacksave>` to get a 9477 pointer to the most recent dynamic alloca. This is useful, for example, 9478 for AddressSanitizer's stack unpoisoning routines. 9479 9480Semantics: 9481"""""""""" 9482 9483 These intrinsics return a non-negative integer value that can be used to 9484 get the address of the most recent dynamic alloca, allocated by :ref:`alloca <i_alloca>` 9485 on the caller's stack. In particular, for targets where stack grows downwards, 9486 adding this offset to the native stack pointer would get the address of the most 9487 recent dynamic alloca. For targets where stack grows upwards, the situation is a bit more 9488 complicated, because substracting this value from stack pointer would get the address 9489 one past the end of the most recent dynamic alloca. 9490 9491 Although for most targets `llvm.get.dynamic.area.offset <int_get_dynamic_area_offset>` 9492 returns just a zero, for others, such as PowerPC and PowerPC64, it returns a 9493 compile-time-known constant value. 9494 9495 The return value type of :ref:`llvm.get.dynamic.area.offset <int_get_dynamic_area_offset>` 9496 must match the target's generic address space's (address space 0) pointer type. 9497 9498'``llvm.prefetch``' Intrinsic 9499^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 9500 9501Syntax: 9502""""""" 9503 9504:: 9505 9506 declare void @llvm.prefetch(i8* <address>, i32 <rw>, i32 <locality>, i32 <cache type>) 9507 9508Overview: 9509""""""""" 9510 9511The '``llvm.prefetch``' intrinsic is a hint to the code generator to 9512insert a prefetch instruction if supported; otherwise, it is a noop. 9513Prefetches have no effect on the behavior of the program but can change 9514its performance characteristics. 9515 9516Arguments: 9517"""""""""" 9518 9519``address`` is the address to be prefetched, ``rw`` is the specifier 9520determining if the fetch should be for a read (0) or write (1), and 9521``locality`` is a temporal locality specifier ranging from (0) - no 9522locality, to (3) - extremely local keep in cache. The ``cache type`` 9523specifies whether the prefetch is performed on the data (1) or 9524instruction (0) cache. The ``rw``, ``locality`` and ``cache type`` 9525arguments must be constant integers. 9526 9527Semantics: 9528"""""""""" 9529 9530This intrinsic does not modify the behavior of the program. In 9531particular, prefetches cannot trap and do not produce a value. On 9532targets that support this intrinsic, the prefetch can provide hints to 9533the processor cache for better performance. 9534 9535'``llvm.pcmarker``' Intrinsic 9536^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 9537 9538Syntax: 9539""""""" 9540 9541:: 9542 9543 declare void @llvm.pcmarker(i32 <id>) 9544 9545Overview: 9546""""""""" 9547 9548The '``llvm.pcmarker``' intrinsic is a method to export a Program 9549Counter (PC) in a region of code to simulators and other tools. The 9550method is target specific, but it is expected that the marker will use 9551exported symbols to transmit the PC of the marker. The marker makes no 9552guarantees that it will remain with any specific instruction after 9553optimizations. It is possible that the presence of a marker will inhibit 9554optimizations. The intended use is to be inserted after optimizations to 9555allow correlations of simulation runs. 9556 9557Arguments: 9558"""""""""" 9559 9560``id`` is a numerical id identifying the marker. 9561 9562Semantics: 9563"""""""""" 9564 9565This intrinsic does not modify the behavior of the program. Backends 9566that do not support this intrinsic may ignore it. 9567 9568'``llvm.readcyclecounter``' Intrinsic 9569^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 9570 9571Syntax: 9572""""""" 9573 9574:: 9575 9576 declare i64 @llvm.readcyclecounter() 9577 9578Overview: 9579""""""""" 9580 9581The '``llvm.readcyclecounter``' intrinsic provides access to the cycle 9582counter register (or similar low latency, high accuracy clocks) on those 9583targets that support it. On X86, it should map to RDTSC. On Alpha, it 9584should map to RPCC. As the backing counters overflow quickly (on the 9585order of 9 seconds on alpha), this should only be used for small 9586timings. 9587 9588Semantics: 9589"""""""""" 9590 9591When directly supported, reading the cycle counter should not modify any 9592memory. Implementations are allowed to either return a application 9593specific value or a system wide value. On backends without support, this 9594is lowered to a constant 0. 9595 9596Note that runtime support may be conditional on the privilege-level code is 9597running at and the host platform. 9598 9599'``llvm.clear_cache``' Intrinsic 9600^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 9601 9602Syntax: 9603""""""" 9604 9605:: 9606 9607 declare void @llvm.clear_cache(i8*, i8*) 9608 9609Overview: 9610""""""""" 9611 9612The '``llvm.clear_cache``' intrinsic ensures visibility of modifications 9613in the specified range to the execution unit of the processor. On 9614targets with non-unified instruction and data cache, the implementation 9615flushes the instruction cache. 9616 9617Semantics: 9618"""""""""" 9619 9620On platforms with coherent instruction and data caches (e.g. x86), this 9621intrinsic is a nop. On platforms with non-coherent instruction and data 9622cache (e.g. ARM, MIPS), the intrinsic is lowered either to appropriate 9623instructions or a system call, if cache flushing requires special 9624privileges. 9625 9626The default behavior is to emit a call to ``__clear_cache`` from the run 9627time library. 9628 9629This instrinsic does *not* empty the instruction pipeline. Modifications 9630of the current function are outside the scope of the intrinsic. 9631 9632'``llvm.instrprof_increment``' Intrinsic 9633^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 9634 9635Syntax: 9636""""""" 9637 9638:: 9639 9640 declare void @llvm.instrprof_increment(i8* <name>, i64 <hash>, 9641 i32 <num-counters>, i32 <index>) 9642 9643Overview: 9644""""""""" 9645 9646The '``llvm.instrprof_increment``' intrinsic can be emitted by a 9647frontend for use with instrumentation based profiling. These will be 9648lowered by the ``-instrprof`` pass to generate execution counts of a 9649program at runtime. 9650 9651Arguments: 9652"""""""""" 9653 9654The first argument is a pointer to a global variable containing the 9655name of the entity being instrumented. This should generally be the 9656(mangled) function name for a set of counters. 9657 9658The second argument is a hash value that can be used by the consumer 9659of the profile data to detect changes to the instrumented source, and 9660the third is the number of counters associated with ``name``. It is an 9661error if ``hash`` or ``num-counters`` differ between two instances of 9662``instrprof_increment`` that refer to the same name. 9663 9664The last argument refers to which of the counters for ``name`` should 9665be incremented. It should be a value between 0 and ``num-counters``. 9666 9667Semantics: 9668"""""""""" 9669 9670This intrinsic represents an increment of a profiling counter. It will 9671cause the ``-instrprof`` pass to generate the appropriate data 9672structures and the code to increment the appropriate value, in a 9673format that can be written out by a compiler runtime and consumed via 9674the ``llvm-profdata`` tool. 9675 9676'``llvm.instrprof_value_profile``' Intrinsic 9677^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 9678 9679Syntax: 9680""""""" 9681 9682:: 9683 9684 declare void @llvm.instrprof_value_profile(i8* <name>, i64 <hash>, 9685 i64 <value>, i32 <value_kind>, 9686 i32 <index>) 9687 9688Overview: 9689""""""""" 9690 9691The '``llvm.instrprof_value_profile``' intrinsic can be emitted by a 9692frontend for use with instrumentation based profiling. This will be 9693lowered by the ``-instrprof`` pass to find out the target values, 9694instrumented expressions take in a program at runtime. 9695 9696Arguments: 9697"""""""""" 9698 9699The first argument is a pointer to a global variable containing the 9700name of the entity being instrumented. ``name`` should generally be the 9701(mangled) function name for a set of counters. 9702 9703The second argument is a hash value that can be used by the consumer 9704of the profile data to detect changes to the instrumented source. It 9705is an error if ``hash`` differs between two instances of 9706``llvm.instrprof_*`` that refer to the same name. 9707 9708The third argument is the value of the expression being profiled. The profiled 9709expression's value should be representable as an unsigned 64-bit value. The 9710fourth argument represents the kind of value profiling that is being done. The 9711supported value profiling kinds are enumerated through the 9712``InstrProfValueKind`` type declared in the 9713``<include/llvm/ProfileData/InstrProf.h>`` header file. The last argument is the 9714index of the instrumented expression within ``name``. It should be >= 0. 9715 9716Semantics: 9717"""""""""" 9718 9719This intrinsic represents the point where a call to a runtime routine 9720should be inserted for value profiling of target expressions. ``-instrprof`` 9721pass will generate the appropriate data structures and replace the 9722``llvm.instrprof_value_profile`` intrinsic with the call to the profile 9723runtime library with proper arguments. 9724 9725'``llvm.thread.pointer``' Intrinsic 9726^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 9727 9728Syntax: 9729""""""" 9730 9731:: 9732 9733 declare i8* @llvm.thread.pointer() 9734 9735Overview: 9736""""""""" 9737 9738The '``llvm.thread.pointer``' intrinsic returns the value of the thread 9739pointer. 9740 9741Semantics: 9742"""""""""" 9743 9744The '``llvm.thread.pointer``' intrinsic returns a pointer to the TLS area 9745for the current thread. The exact semantics of this value are target 9746specific: it may point to the start of TLS area, to the end, or somewhere 9747in the middle. Depending on the target, this intrinsic may read a register, 9748call a helper function, read from an alternate memory space, or perform 9749other operations necessary to locate the TLS area. Not all targets support 9750this intrinsic. 9751 9752Standard C Library Intrinsics 9753----------------------------- 9754 9755LLVM provides intrinsics for a few important standard C library 9756functions. These intrinsics allow source-language front-ends to pass 9757information about the alignment of the pointer arguments to the code 9758generator, providing opportunity for more efficient code generation. 9759 9760.. _int_memcpy: 9761 9762'``llvm.memcpy``' Intrinsic 9763^^^^^^^^^^^^^^^^^^^^^^^^^^^ 9764 9765Syntax: 9766""""""" 9767 9768This is an overloaded intrinsic. You can use ``llvm.memcpy`` on any 9769integer bit width and for different address spaces. Not all targets 9770support all bit widths however. 9771 9772:: 9773 9774 declare void @llvm.memcpy.p0i8.p0i8.i32(i8* <dest>, i8* <src>, 9775 i32 <len>, i32 <align>, i1 <isvolatile>) 9776 declare void @llvm.memcpy.p0i8.p0i8.i64(i8* <dest>, i8* <src>, 9777 i64 <len>, i32 <align>, i1 <isvolatile>) 9778 9779Overview: 9780""""""""" 9781 9782The '``llvm.memcpy.*``' intrinsics copy a block of memory from the 9783source location to the destination location. 9784 9785Note that, unlike the standard libc function, the ``llvm.memcpy.*`` 9786intrinsics do not return a value, takes extra alignment/isvolatile 9787arguments and the pointers can be in specified address spaces. 9788 9789Arguments: 9790"""""""""" 9791 9792The first argument is a pointer to the destination, the second is a 9793pointer to the source. The third argument is an integer argument 9794specifying the number of bytes to copy, the fourth argument is the 9795alignment of the source and destination locations, and the fifth is a 9796boolean indicating a volatile access. 9797 9798If the call to this intrinsic has an alignment value that is not 0 or 1, 9799then the caller guarantees that both the source and destination pointers 9800are aligned to that boundary. 9801 9802If the ``isvolatile`` parameter is ``true``, the ``llvm.memcpy`` call is 9803a :ref:`volatile operation <volatile>`. The detailed access behavior is not 9804very cleanly specified and it is unwise to depend on it. 9805 9806Semantics: 9807"""""""""" 9808 9809The '``llvm.memcpy.*``' intrinsics copy a block of memory from the 9810source location to the destination location, which are not allowed to 9811overlap. It copies "len" bytes of memory over. If the argument is known 9812to be aligned to some boundary, this can be specified as the fourth 9813argument, otherwise it should be set to 0 or 1 (both meaning no alignment). 9814 9815'``llvm.memmove``' Intrinsic 9816^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 9817 9818Syntax: 9819""""""" 9820 9821This is an overloaded intrinsic. You can use llvm.memmove on any integer 9822bit width and for different address space. Not all targets support all 9823bit widths however. 9824 9825:: 9826 9827 declare void @llvm.memmove.p0i8.p0i8.i32(i8* <dest>, i8* <src>, 9828 i32 <len>, i32 <align>, i1 <isvolatile>) 9829 declare void @llvm.memmove.p0i8.p0i8.i64(i8* <dest>, i8* <src>, 9830 i64 <len>, i32 <align>, i1 <isvolatile>) 9831 9832Overview: 9833""""""""" 9834 9835The '``llvm.memmove.*``' intrinsics move a block of memory from the 9836source location to the destination location. It is similar to the 9837'``llvm.memcpy``' intrinsic but allows the two memory locations to 9838overlap. 9839 9840Note that, unlike the standard libc function, the ``llvm.memmove.*`` 9841intrinsics do not return a value, takes extra alignment/isvolatile 9842arguments and the pointers can be in specified address spaces. 9843 9844Arguments: 9845"""""""""" 9846 9847The first argument is a pointer to the destination, the second is a 9848pointer to the source. The third argument is an integer argument 9849specifying the number of bytes to copy, the fourth argument is the 9850alignment of the source and destination locations, and the fifth is a 9851boolean indicating a volatile access. 9852 9853If the call to this intrinsic has an alignment value that is not 0 or 1, 9854then the caller guarantees that the source and destination pointers are 9855aligned to that boundary. 9856 9857If the ``isvolatile`` parameter is ``true``, the ``llvm.memmove`` call 9858is a :ref:`volatile operation <volatile>`. The detailed access behavior is 9859not very cleanly specified and it is unwise to depend on it. 9860 9861Semantics: 9862"""""""""" 9863 9864The '``llvm.memmove.*``' intrinsics copy a block of memory from the 9865source location to the destination location, which may overlap. It 9866copies "len" bytes of memory over. If the argument is known to be 9867aligned to some boundary, this can be specified as the fourth argument, 9868otherwise it should be set to 0 or 1 (both meaning no alignment). 9869 9870'``llvm.memset.*``' Intrinsics 9871^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 9872 9873Syntax: 9874""""""" 9875 9876This is an overloaded intrinsic. You can use llvm.memset on any integer 9877bit width and for different address spaces. However, not all targets 9878support all bit widths. 9879 9880:: 9881 9882 declare void @llvm.memset.p0i8.i32(i8* <dest>, i8 <val>, 9883 i32 <len>, i32 <align>, i1 <isvolatile>) 9884 declare void @llvm.memset.p0i8.i64(i8* <dest>, i8 <val>, 9885 i64 <len>, i32 <align>, i1 <isvolatile>) 9886 9887Overview: 9888""""""""" 9889 9890The '``llvm.memset.*``' intrinsics fill a block of memory with a 9891particular byte value. 9892 9893Note that, unlike the standard libc function, the ``llvm.memset`` 9894intrinsic does not return a value and takes extra alignment/volatile 9895arguments. Also, the destination can be in an arbitrary address space. 9896 9897Arguments: 9898"""""""""" 9899 9900The first argument is a pointer to the destination to fill, the second 9901is the byte value with which to fill it, the third argument is an 9902integer argument specifying the number of bytes to fill, and the fourth 9903argument is the known alignment of the destination location. 9904 9905If the call to this intrinsic has an alignment value that is not 0 or 1, 9906then the caller guarantees that the destination pointer is aligned to 9907that boundary. 9908 9909If the ``isvolatile`` parameter is ``true``, the ``llvm.memset`` call is 9910a :ref:`volatile operation <volatile>`. The detailed access behavior is not 9911very cleanly specified and it is unwise to depend on it. 9912 9913Semantics: 9914"""""""""" 9915 9916The '``llvm.memset.*``' intrinsics fill "len" bytes of memory starting 9917at the destination location. If the argument is known to be aligned to 9918some boundary, this can be specified as the fourth argument, otherwise 9919it should be set to 0 or 1 (both meaning no alignment). 9920 9921'``llvm.sqrt.*``' Intrinsic 9922^^^^^^^^^^^^^^^^^^^^^^^^^^^ 9923 9924Syntax: 9925""""""" 9926 9927This is an overloaded intrinsic. You can use ``llvm.sqrt`` on any 9928floating point or vector of floating point type. Not all targets support 9929all types however. 9930 9931:: 9932 9933 declare float @llvm.sqrt.f32(float %Val) 9934 declare double @llvm.sqrt.f64(double %Val) 9935 declare x86_fp80 @llvm.sqrt.f80(x86_fp80 %Val) 9936 declare fp128 @llvm.sqrt.f128(fp128 %Val) 9937 declare ppc_fp128 @llvm.sqrt.ppcf128(ppc_fp128 %Val) 9938 9939Overview: 9940""""""""" 9941 9942The '``llvm.sqrt``' intrinsics return the sqrt of the specified operand, 9943returning the same value as the libm '``sqrt``' functions would. Unlike 9944``sqrt`` in libm, however, ``llvm.sqrt`` has undefined behavior for 9945negative numbers other than -0.0 (which allows for better optimization, 9946because there is no need to worry about errno being set). 9947``llvm.sqrt(-0.0)`` is defined to return -0.0 like IEEE sqrt. 9948 9949Arguments: 9950"""""""""" 9951 9952The argument and return value are floating point numbers of the same 9953type. 9954 9955Semantics: 9956"""""""""" 9957 9958This function returns the sqrt of the specified operand if it is a 9959nonnegative floating point number. 9960 9961'``llvm.powi.*``' Intrinsic 9962^^^^^^^^^^^^^^^^^^^^^^^^^^^ 9963 9964Syntax: 9965""""""" 9966 9967This is an overloaded intrinsic. You can use ``llvm.powi`` on any 9968floating point or vector of floating point type. Not all targets support 9969all types however. 9970 9971:: 9972 9973 declare float @llvm.powi.f32(float %Val, i32 %power) 9974 declare double @llvm.powi.f64(double %Val, i32 %power) 9975 declare x86_fp80 @llvm.powi.f80(x86_fp80 %Val, i32 %power) 9976 declare fp128 @llvm.powi.f128(fp128 %Val, i32 %power) 9977 declare ppc_fp128 @llvm.powi.ppcf128(ppc_fp128 %Val, i32 %power) 9978 9979Overview: 9980""""""""" 9981 9982The '``llvm.powi.*``' intrinsics return the first operand raised to the 9983specified (positive or negative) power. The order of evaluation of 9984multiplications is not defined. When a vector of floating point type is 9985used, the second argument remains a scalar integer value. 9986 9987Arguments: 9988"""""""""" 9989 9990The second argument is an integer power, and the first is a value to 9991raise to that power. 9992 9993Semantics: 9994"""""""""" 9995 9996This function returns the first value raised to the second power with an 9997unspecified sequence of rounding operations. 9998 9999'``llvm.sin.*``' Intrinsic 10000^^^^^^^^^^^^^^^^^^^^^^^^^^ 10001 10002Syntax: 10003""""""" 10004 10005This is an overloaded intrinsic. You can use ``llvm.sin`` on any 10006floating point or vector of floating point type. Not all targets support 10007all types however. 10008 10009:: 10010 10011 declare float @llvm.sin.f32(float %Val) 10012 declare double @llvm.sin.f64(double %Val) 10013 declare x86_fp80 @llvm.sin.f80(x86_fp80 %Val) 10014 declare fp128 @llvm.sin.f128(fp128 %Val) 10015 declare ppc_fp128 @llvm.sin.ppcf128(ppc_fp128 %Val) 10016 10017Overview: 10018""""""""" 10019 10020The '``llvm.sin.*``' intrinsics return the sine of the operand. 10021 10022Arguments: 10023"""""""""" 10024 10025The argument and return value are floating point numbers of the same 10026type. 10027 10028Semantics: 10029"""""""""" 10030 10031This function returns the sine of the specified operand, returning the 10032same values as the libm ``sin`` functions would, and handles error 10033conditions in the same way. 10034 10035'``llvm.cos.*``' Intrinsic 10036^^^^^^^^^^^^^^^^^^^^^^^^^^ 10037 10038Syntax: 10039""""""" 10040 10041This is an overloaded intrinsic. You can use ``llvm.cos`` on any 10042floating point or vector of floating point type. Not all targets support 10043all types however. 10044 10045:: 10046 10047 declare float @llvm.cos.f32(float %Val) 10048 declare double @llvm.cos.f64(double %Val) 10049 declare x86_fp80 @llvm.cos.f80(x86_fp80 %Val) 10050 declare fp128 @llvm.cos.f128(fp128 %Val) 10051 declare ppc_fp128 @llvm.cos.ppcf128(ppc_fp128 %Val) 10052 10053Overview: 10054""""""""" 10055 10056The '``llvm.cos.*``' intrinsics return the cosine of the operand. 10057 10058Arguments: 10059"""""""""" 10060 10061The argument and return value are floating point numbers of the same 10062type. 10063 10064Semantics: 10065"""""""""" 10066 10067This function returns the cosine of the specified operand, returning the 10068same values as the libm ``cos`` functions would, and handles error 10069conditions in the same way. 10070 10071'``llvm.pow.*``' Intrinsic 10072^^^^^^^^^^^^^^^^^^^^^^^^^^ 10073 10074Syntax: 10075""""""" 10076 10077This is an overloaded intrinsic. You can use ``llvm.pow`` on any 10078floating point or vector of floating point type. Not all targets support 10079all types however. 10080 10081:: 10082 10083 declare float @llvm.pow.f32(float %Val, float %Power) 10084 declare double @llvm.pow.f64(double %Val, double %Power) 10085 declare x86_fp80 @llvm.pow.f80(x86_fp80 %Val, x86_fp80 %Power) 10086 declare fp128 @llvm.pow.f128(fp128 %Val, fp128 %Power) 10087 declare ppc_fp128 @llvm.pow.ppcf128(ppc_fp128 %Val, ppc_fp128 Power) 10088 10089Overview: 10090""""""""" 10091 10092The '``llvm.pow.*``' intrinsics return the first operand raised to the 10093specified (positive or negative) power. 10094 10095Arguments: 10096"""""""""" 10097 10098The second argument is a floating point power, and the first is a value 10099to raise to that power. 10100 10101Semantics: 10102"""""""""" 10103 10104This function returns the first value raised to the second power, 10105returning the same values as the libm ``pow`` functions would, and 10106handles error conditions in the same way. 10107 10108'``llvm.exp.*``' Intrinsic 10109^^^^^^^^^^^^^^^^^^^^^^^^^^ 10110 10111Syntax: 10112""""""" 10113 10114This is an overloaded intrinsic. You can use ``llvm.exp`` on any 10115floating point or vector of floating point type. Not all targets support 10116all types however. 10117 10118:: 10119 10120 declare float @llvm.exp.f32(float %Val) 10121 declare double @llvm.exp.f64(double %Val) 10122 declare x86_fp80 @llvm.exp.f80(x86_fp80 %Val) 10123 declare fp128 @llvm.exp.f128(fp128 %Val) 10124 declare ppc_fp128 @llvm.exp.ppcf128(ppc_fp128 %Val) 10125 10126Overview: 10127""""""""" 10128 10129The '``llvm.exp.*``' intrinsics perform the exp function. 10130 10131Arguments: 10132"""""""""" 10133 10134The argument and return value are floating point numbers of the same 10135type. 10136 10137Semantics: 10138"""""""""" 10139 10140This function returns the same values as the libm ``exp`` functions 10141would, and handles error conditions in the same way. 10142 10143'``llvm.exp2.*``' Intrinsic 10144^^^^^^^^^^^^^^^^^^^^^^^^^^^ 10145 10146Syntax: 10147""""""" 10148 10149This is an overloaded intrinsic. You can use ``llvm.exp2`` on any 10150floating point or vector of floating point type. Not all targets support 10151all types however. 10152 10153:: 10154 10155 declare float @llvm.exp2.f32(float %Val) 10156 declare double @llvm.exp2.f64(double %Val) 10157 declare x86_fp80 @llvm.exp2.f80(x86_fp80 %Val) 10158 declare fp128 @llvm.exp2.f128(fp128 %Val) 10159 declare ppc_fp128 @llvm.exp2.ppcf128(ppc_fp128 %Val) 10160 10161Overview: 10162""""""""" 10163 10164The '``llvm.exp2.*``' intrinsics perform the exp2 function. 10165 10166Arguments: 10167"""""""""" 10168 10169The argument and return value are floating point numbers of the same 10170type. 10171 10172Semantics: 10173"""""""""" 10174 10175This function returns the same values as the libm ``exp2`` functions 10176would, and handles error conditions in the same way. 10177 10178'``llvm.log.*``' Intrinsic 10179^^^^^^^^^^^^^^^^^^^^^^^^^^ 10180 10181Syntax: 10182""""""" 10183 10184This is an overloaded intrinsic. You can use ``llvm.log`` on any 10185floating point or vector of floating point type. Not all targets support 10186all types however. 10187 10188:: 10189 10190 declare float @llvm.log.f32(float %Val) 10191 declare double @llvm.log.f64(double %Val) 10192 declare x86_fp80 @llvm.log.f80(x86_fp80 %Val) 10193 declare fp128 @llvm.log.f128(fp128 %Val) 10194 declare ppc_fp128 @llvm.log.ppcf128(ppc_fp128 %Val) 10195 10196Overview: 10197""""""""" 10198 10199The '``llvm.log.*``' intrinsics perform the log function. 10200 10201Arguments: 10202"""""""""" 10203 10204The argument and return value are floating point numbers of the same 10205type. 10206 10207Semantics: 10208"""""""""" 10209 10210This function returns the same values as the libm ``log`` functions 10211would, and handles error conditions in the same way. 10212 10213'``llvm.log10.*``' Intrinsic 10214^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 10215 10216Syntax: 10217""""""" 10218 10219This is an overloaded intrinsic. You can use ``llvm.log10`` on any 10220floating point or vector of floating point type. Not all targets support 10221all types however. 10222 10223:: 10224 10225 declare float @llvm.log10.f32(float %Val) 10226 declare double @llvm.log10.f64(double %Val) 10227 declare x86_fp80 @llvm.log10.f80(x86_fp80 %Val) 10228 declare fp128 @llvm.log10.f128(fp128 %Val) 10229 declare ppc_fp128 @llvm.log10.ppcf128(ppc_fp128 %Val) 10230 10231Overview: 10232""""""""" 10233 10234The '``llvm.log10.*``' intrinsics perform the log10 function. 10235 10236Arguments: 10237"""""""""" 10238 10239The argument and return value are floating point numbers of the same 10240type. 10241 10242Semantics: 10243"""""""""" 10244 10245This function returns the same values as the libm ``log10`` functions 10246would, and handles error conditions in the same way. 10247 10248'``llvm.log2.*``' Intrinsic 10249^^^^^^^^^^^^^^^^^^^^^^^^^^^ 10250 10251Syntax: 10252""""""" 10253 10254This is an overloaded intrinsic. You can use ``llvm.log2`` on any 10255floating point or vector of floating point type. Not all targets support 10256all types however. 10257 10258:: 10259 10260 declare float @llvm.log2.f32(float %Val) 10261 declare double @llvm.log2.f64(double %Val) 10262 declare x86_fp80 @llvm.log2.f80(x86_fp80 %Val) 10263 declare fp128 @llvm.log2.f128(fp128 %Val) 10264 declare ppc_fp128 @llvm.log2.ppcf128(ppc_fp128 %Val) 10265 10266Overview: 10267""""""""" 10268 10269The '``llvm.log2.*``' intrinsics perform the log2 function. 10270 10271Arguments: 10272"""""""""" 10273 10274The argument and return value are floating point numbers of the same 10275type. 10276 10277Semantics: 10278"""""""""" 10279 10280This function returns the same values as the libm ``log2`` functions 10281would, and handles error conditions in the same way. 10282 10283'``llvm.fma.*``' Intrinsic 10284^^^^^^^^^^^^^^^^^^^^^^^^^^ 10285 10286Syntax: 10287""""""" 10288 10289This is an overloaded intrinsic. You can use ``llvm.fma`` on any 10290floating point or vector of floating point type. Not all targets support 10291all types however. 10292 10293:: 10294 10295 declare float @llvm.fma.f32(float %a, float %b, float %c) 10296 declare double @llvm.fma.f64(double %a, double %b, double %c) 10297 declare x86_fp80 @llvm.fma.f80(x86_fp80 %a, x86_fp80 %b, x86_fp80 %c) 10298 declare fp128 @llvm.fma.f128(fp128 %a, fp128 %b, fp128 %c) 10299 declare ppc_fp128 @llvm.fma.ppcf128(ppc_fp128 %a, ppc_fp128 %b, ppc_fp128 %c) 10300 10301Overview: 10302""""""""" 10303 10304The '``llvm.fma.*``' intrinsics perform the fused multiply-add 10305operation. 10306 10307Arguments: 10308"""""""""" 10309 10310The argument and return value are floating point numbers of the same 10311type. 10312 10313Semantics: 10314"""""""""" 10315 10316This function returns the same values as the libm ``fma`` functions 10317would, and does not set errno. 10318 10319'``llvm.fabs.*``' Intrinsic 10320^^^^^^^^^^^^^^^^^^^^^^^^^^^ 10321 10322Syntax: 10323""""""" 10324 10325This is an overloaded intrinsic. You can use ``llvm.fabs`` on any 10326floating point or vector of floating point type. Not all targets support 10327all types however. 10328 10329:: 10330 10331 declare float @llvm.fabs.f32(float %Val) 10332 declare double @llvm.fabs.f64(double %Val) 10333 declare x86_fp80 @llvm.fabs.f80(x86_fp80 %Val) 10334 declare fp128 @llvm.fabs.f128(fp128 %Val) 10335 declare ppc_fp128 @llvm.fabs.ppcf128(ppc_fp128 %Val) 10336 10337Overview: 10338""""""""" 10339 10340The '``llvm.fabs.*``' intrinsics return the absolute value of the 10341operand. 10342 10343Arguments: 10344"""""""""" 10345 10346The argument and return value are floating point numbers of the same 10347type. 10348 10349Semantics: 10350"""""""""" 10351 10352This function returns the same values as the libm ``fabs`` functions 10353would, and handles error conditions in the same way. 10354 10355'``llvm.minnum.*``' Intrinsic 10356^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 10357 10358Syntax: 10359""""""" 10360 10361This is an overloaded intrinsic. You can use ``llvm.minnum`` on any 10362floating point or vector of floating point type. Not all targets support 10363all types however. 10364 10365:: 10366 10367 declare float @llvm.minnum.f32(float %Val0, float %Val1) 10368 declare double @llvm.minnum.f64(double %Val0, double %Val1) 10369 declare x86_fp80 @llvm.minnum.f80(x86_fp80 %Val0, x86_fp80 %Val1) 10370 declare fp128 @llvm.minnum.f128(fp128 %Val0, fp128 %Val1) 10371 declare ppc_fp128 @llvm.minnum.ppcf128(ppc_fp128 %Val0, ppc_fp128 %Val1) 10372 10373Overview: 10374""""""""" 10375 10376The '``llvm.minnum.*``' intrinsics return the minimum of the two 10377arguments. 10378 10379 10380Arguments: 10381"""""""""" 10382 10383The arguments and return value are floating point numbers of the same 10384type. 10385 10386Semantics: 10387"""""""""" 10388 10389Follows the IEEE-754 semantics for minNum, which also match for libm's 10390fmin. 10391 10392If either operand is a NaN, returns the other non-NaN operand. Returns 10393NaN only if both operands are NaN. If the operands compare equal, 10394returns a value that compares equal to both operands. This means that 10395fmin(+/-0.0, +/-0.0) could return either -0.0 or 0.0. 10396 10397'``llvm.maxnum.*``' Intrinsic 10398^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 10399 10400Syntax: 10401""""""" 10402 10403This is an overloaded intrinsic. You can use ``llvm.maxnum`` on any 10404floating point or vector of floating point type. Not all targets support 10405all types however. 10406 10407:: 10408 10409 declare float @llvm.maxnum.f32(float %Val0, float %Val1l) 10410 declare double @llvm.maxnum.f64(double %Val0, double %Val1) 10411 declare x86_fp80 @llvm.maxnum.f80(x86_fp80 %Val0, x86_fp80 %Val1) 10412 declare fp128 @llvm.maxnum.f128(fp128 %Val0, fp128 %Val1) 10413 declare ppc_fp128 @llvm.maxnum.ppcf128(ppc_fp128 %Val0, ppc_fp128 %Val1) 10414 10415Overview: 10416""""""""" 10417 10418The '``llvm.maxnum.*``' intrinsics return the maximum of the two 10419arguments. 10420 10421 10422Arguments: 10423"""""""""" 10424 10425The arguments and return value are floating point numbers of the same 10426type. 10427 10428Semantics: 10429"""""""""" 10430Follows the IEEE-754 semantics for maxNum, which also match for libm's 10431fmax. 10432 10433If either operand is a NaN, returns the other non-NaN operand. Returns 10434NaN only if both operands are NaN. If the operands compare equal, 10435returns a value that compares equal to both operands. This means that 10436fmax(+/-0.0, +/-0.0) could return either -0.0 or 0.0. 10437 10438'``llvm.copysign.*``' Intrinsic 10439^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 10440 10441Syntax: 10442""""""" 10443 10444This is an overloaded intrinsic. You can use ``llvm.copysign`` on any 10445floating point or vector of floating point type. Not all targets support 10446all types however. 10447 10448:: 10449 10450 declare float @llvm.copysign.f32(float %Mag, float %Sgn) 10451 declare double @llvm.copysign.f64(double %Mag, double %Sgn) 10452 declare x86_fp80 @llvm.copysign.f80(x86_fp80 %Mag, x86_fp80 %Sgn) 10453 declare fp128 @llvm.copysign.f128(fp128 %Mag, fp128 %Sgn) 10454 declare ppc_fp128 @llvm.copysign.ppcf128(ppc_fp128 %Mag, ppc_fp128 %Sgn) 10455 10456Overview: 10457""""""""" 10458 10459The '``llvm.copysign.*``' intrinsics return a value with the magnitude of the 10460first operand and the sign of the second operand. 10461 10462Arguments: 10463"""""""""" 10464 10465The arguments and return value are floating point numbers of the same 10466type. 10467 10468Semantics: 10469"""""""""" 10470 10471This function returns the same values as the libm ``copysign`` 10472functions would, and handles error conditions in the same way. 10473 10474'``llvm.floor.*``' Intrinsic 10475^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 10476 10477Syntax: 10478""""""" 10479 10480This is an overloaded intrinsic. You can use ``llvm.floor`` on any 10481floating point or vector of floating point type. Not all targets support 10482all types however. 10483 10484:: 10485 10486 declare float @llvm.floor.f32(float %Val) 10487 declare double @llvm.floor.f64(double %Val) 10488 declare x86_fp80 @llvm.floor.f80(x86_fp80 %Val) 10489 declare fp128 @llvm.floor.f128(fp128 %Val) 10490 declare ppc_fp128 @llvm.floor.ppcf128(ppc_fp128 %Val) 10491 10492Overview: 10493""""""""" 10494 10495The '``llvm.floor.*``' intrinsics return the floor of the operand. 10496 10497Arguments: 10498"""""""""" 10499 10500The argument and return value are floating point numbers of the same 10501type. 10502 10503Semantics: 10504"""""""""" 10505 10506This function returns the same values as the libm ``floor`` functions 10507would, and handles error conditions in the same way. 10508 10509'``llvm.ceil.*``' Intrinsic 10510^^^^^^^^^^^^^^^^^^^^^^^^^^^ 10511 10512Syntax: 10513""""""" 10514 10515This is an overloaded intrinsic. You can use ``llvm.ceil`` on any 10516floating point or vector of floating point type. Not all targets support 10517all types however. 10518 10519:: 10520 10521 declare float @llvm.ceil.f32(float %Val) 10522 declare double @llvm.ceil.f64(double %Val) 10523 declare x86_fp80 @llvm.ceil.f80(x86_fp80 %Val) 10524 declare fp128 @llvm.ceil.f128(fp128 %Val) 10525 declare ppc_fp128 @llvm.ceil.ppcf128(ppc_fp128 %Val) 10526 10527Overview: 10528""""""""" 10529 10530The '``llvm.ceil.*``' intrinsics return the ceiling of the operand. 10531 10532Arguments: 10533"""""""""" 10534 10535The argument and return value are floating point numbers of the same 10536type. 10537 10538Semantics: 10539"""""""""" 10540 10541This function returns the same values as the libm ``ceil`` functions 10542would, and handles error conditions in the same way. 10543 10544'``llvm.trunc.*``' Intrinsic 10545^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 10546 10547Syntax: 10548""""""" 10549 10550This is an overloaded intrinsic. You can use ``llvm.trunc`` on any 10551floating point or vector of floating point type. Not all targets support 10552all types however. 10553 10554:: 10555 10556 declare float @llvm.trunc.f32(float %Val) 10557 declare double @llvm.trunc.f64(double %Val) 10558 declare x86_fp80 @llvm.trunc.f80(x86_fp80 %Val) 10559 declare fp128 @llvm.trunc.f128(fp128 %Val) 10560 declare ppc_fp128 @llvm.trunc.ppcf128(ppc_fp128 %Val) 10561 10562Overview: 10563""""""""" 10564 10565The '``llvm.trunc.*``' intrinsics returns the operand rounded to the 10566nearest integer not larger in magnitude than the operand. 10567 10568Arguments: 10569"""""""""" 10570 10571The argument and return value are floating point numbers of the same 10572type. 10573 10574Semantics: 10575"""""""""" 10576 10577This function returns the same values as the libm ``trunc`` functions 10578would, and handles error conditions in the same way. 10579 10580'``llvm.rint.*``' Intrinsic 10581^^^^^^^^^^^^^^^^^^^^^^^^^^^ 10582 10583Syntax: 10584""""""" 10585 10586This is an overloaded intrinsic. You can use ``llvm.rint`` on any 10587floating point or vector of floating point type. Not all targets support 10588all types however. 10589 10590:: 10591 10592 declare float @llvm.rint.f32(float %Val) 10593 declare double @llvm.rint.f64(double %Val) 10594 declare x86_fp80 @llvm.rint.f80(x86_fp80 %Val) 10595 declare fp128 @llvm.rint.f128(fp128 %Val) 10596 declare ppc_fp128 @llvm.rint.ppcf128(ppc_fp128 %Val) 10597 10598Overview: 10599""""""""" 10600 10601The '``llvm.rint.*``' intrinsics returns the operand rounded to the 10602nearest integer. It may raise an inexact floating-point exception if the 10603operand isn't an integer. 10604 10605Arguments: 10606"""""""""" 10607 10608The argument and return value are floating point numbers of the same 10609type. 10610 10611Semantics: 10612"""""""""" 10613 10614This function returns the same values as the libm ``rint`` functions 10615would, and handles error conditions in the same way. 10616 10617'``llvm.nearbyint.*``' Intrinsic 10618^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 10619 10620Syntax: 10621""""""" 10622 10623This is an overloaded intrinsic. You can use ``llvm.nearbyint`` on any 10624floating point or vector of floating point type. Not all targets support 10625all types however. 10626 10627:: 10628 10629 declare float @llvm.nearbyint.f32(float %Val) 10630 declare double @llvm.nearbyint.f64(double %Val) 10631 declare x86_fp80 @llvm.nearbyint.f80(x86_fp80 %Val) 10632 declare fp128 @llvm.nearbyint.f128(fp128 %Val) 10633 declare ppc_fp128 @llvm.nearbyint.ppcf128(ppc_fp128 %Val) 10634 10635Overview: 10636""""""""" 10637 10638The '``llvm.nearbyint.*``' intrinsics returns the operand rounded to the 10639nearest integer. 10640 10641Arguments: 10642"""""""""" 10643 10644The argument and return value are floating point numbers of the same 10645type. 10646 10647Semantics: 10648"""""""""" 10649 10650This function returns the same values as the libm ``nearbyint`` 10651functions would, and handles error conditions in the same way. 10652 10653'``llvm.round.*``' Intrinsic 10654^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 10655 10656Syntax: 10657""""""" 10658 10659This is an overloaded intrinsic. You can use ``llvm.round`` on any 10660floating point or vector of floating point type. Not all targets support 10661all types however. 10662 10663:: 10664 10665 declare float @llvm.round.f32(float %Val) 10666 declare double @llvm.round.f64(double %Val) 10667 declare x86_fp80 @llvm.round.f80(x86_fp80 %Val) 10668 declare fp128 @llvm.round.f128(fp128 %Val) 10669 declare ppc_fp128 @llvm.round.ppcf128(ppc_fp128 %Val) 10670 10671Overview: 10672""""""""" 10673 10674The '``llvm.round.*``' intrinsics returns the operand rounded to the 10675nearest integer. 10676 10677Arguments: 10678"""""""""" 10679 10680The argument and return value are floating point numbers of the same 10681type. 10682 10683Semantics: 10684"""""""""" 10685 10686This function returns the same values as the libm ``round`` 10687functions would, and handles error conditions in the same way. 10688 10689Bit Manipulation Intrinsics 10690--------------------------- 10691 10692LLVM provides intrinsics for a few important bit manipulation 10693operations. These allow efficient code generation for some algorithms. 10694 10695'``llvm.bitreverse.*``' Intrinsics 10696^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 10697 10698Syntax: 10699""""""" 10700 10701This is an overloaded intrinsic function. You can use bitreverse on any 10702integer type. 10703 10704:: 10705 10706 declare i16 @llvm.bitreverse.i16(i16 <id>) 10707 declare i32 @llvm.bitreverse.i32(i32 <id>) 10708 declare i64 @llvm.bitreverse.i64(i64 <id>) 10709 10710Overview: 10711""""""""" 10712 10713The '``llvm.bitreverse``' family of intrinsics is used to reverse the 10714bitpattern of an integer value; for example ``0b10110110`` becomes 10715``0b01101101``. 10716 10717Semantics: 10718"""""""""" 10719 10720The ``llvm.bitreverse.iN`` intrinsic returns an i16 value that has bit 10721``M`` in the input moved to bit ``N-M`` in the output. 10722 10723'``llvm.bswap.*``' Intrinsics 10724^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 10725 10726Syntax: 10727""""""" 10728 10729This is an overloaded intrinsic function. You can use bswap on any 10730integer type that is an even number of bytes (i.e. BitWidth % 16 == 0). 10731 10732:: 10733 10734 declare i16 @llvm.bswap.i16(i16 <id>) 10735 declare i32 @llvm.bswap.i32(i32 <id>) 10736 declare i64 @llvm.bswap.i64(i64 <id>) 10737 10738Overview: 10739""""""""" 10740 10741The '``llvm.bswap``' family of intrinsics is used to byte swap integer 10742values with an even number of bytes (positive multiple of 16 bits). 10743These are useful for performing operations on data that is not in the 10744target's native byte order. 10745 10746Semantics: 10747"""""""""" 10748 10749The ``llvm.bswap.i16`` intrinsic returns an i16 value that has the high 10750and low byte of the input i16 swapped. Similarly, the ``llvm.bswap.i32`` 10751intrinsic returns an i32 value that has the four bytes of the input i32 10752swapped, so that if the input bytes are numbered 0, 1, 2, 3 then the 10753returned i32 will have its bytes in 3, 2, 1, 0 order. The 10754``llvm.bswap.i48``, ``llvm.bswap.i64`` and other intrinsics extend this 10755concept to additional even-byte lengths (6 bytes, 8 bytes and more, 10756respectively). 10757 10758'``llvm.ctpop.*``' Intrinsic 10759^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 10760 10761Syntax: 10762""""""" 10763 10764This is an overloaded intrinsic. You can use llvm.ctpop on any integer 10765bit width, or on any vector with integer elements. Not all targets 10766support all bit widths or vector types, however. 10767 10768:: 10769 10770 declare i8 @llvm.ctpop.i8(i8 <src>) 10771 declare i16 @llvm.ctpop.i16(i16 <src>) 10772 declare i32 @llvm.ctpop.i32(i32 <src>) 10773 declare i64 @llvm.ctpop.i64(i64 <src>) 10774 declare i256 @llvm.ctpop.i256(i256 <src>) 10775 declare <2 x i32> @llvm.ctpop.v2i32(<2 x i32> <src>) 10776 10777Overview: 10778""""""""" 10779 10780The '``llvm.ctpop``' family of intrinsics counts the number of bits set 10781in a value. 10782 10783Arguments: 10784"""""""""" 10785 10786The only argument is the value to be counted. The argument may be of any 10787integer type, or a vector with integer elements. The return type must 10788match the argument type. 10789 10790Semantics: 10791"""""""""" 10792 10793The '``llvm.ctpop``' intrinsic counts the 1's in a variable, or within 10794each element of a vector. 10795 10796'``llvm.ctlz.*``' Intrinsic 10797^^^^^^^^^^^^^^^^^^^^^^^^^^^ 10798 10799Syntax: 10800""""""" 10801 10802This is an overloaded intrinsic. You can use ``llvm.ctlz`` on any 10803integer bit width, or any vector whose elements are integers. Not all 10804targets support all bit widths or vector types, however. 10805 10806:: 10807 10808 declare i8 @llvm.ctlz.i8 (i8 <src>, i1 <is_zero_undef>) 10809 declare i16 @llvm.ctlz.i16 (i16 <src>, i1 <is_zero_undef>) 10810 declare i32 @llvm.ctlz.i32 (i32 <src>, i1 <is_zero_undef>) 10811 declare i64 @llvm.ctlz.i64 (i64 <src>, i1 <is_zero_undef>) 10812 declare i256 @llvm.ctlz.i256(i256 <src>, i1 <is_zero_undef>) 10813 declare <2 x i32> @llvm.ctlz.v2i32(<2 x i32> <src>, i1 <is_zero_undef>) 10814 10815Overview: 10816""""""""" 10817 10818The '``llvm.ctlz``' family of intrinsic functions counts the number of 10819leading zeros in a variable. 10820 10821Arguments: 10822"""""""""" 10823 10824The first argument is the value to be counted. This argument may be of 10825any integer type, or a vector with integer element type. The return 10826type must match the first argument type. 10827 10828The second argument must be a constant and is a flag to indicate whether 10829the intrinsic should ensure that a zero as the first argument produces a 10830defined result. Historically some architectures did not provide a 10831defined result for zero values as efficiently, and many algorithms are 10832now predicated on avoiding zero-value inputs. 10833 10834Semantics: 10835"""""""""" 10836 10837The '``llvm.ctlz``' intrinsic counts the leading (most significant) 10838zeros in a variable, or within each element of the vector. If 10839``src == 0`` then the result is the size in bits of the type of ``src`` 10840if ``is_zero_undef == 0`` and ``undef`` otherwise. For example, 10841``llvm.ctlz(i32 2) = 30``. 10842 10843'``llvm.cttz.*``' Intrinsic 10844^^^^^^^^^^^^^^^^^^^^^^^^^^^ 10845 10846Syntax: 10847""""""" 10848 10849This is an overloaded intrinsic. You can use ``llvm.cttz`` on any 10850integer bit width, or any vector of integer elements. Not all targets 10851support all bit widths or vector types, however. 10852 10853:: 10854 10855 declare i8 @llvm.cttz.i8 (i8 <src>, i1 <is_zero_undef>) 10856 declare i16 @llvm.cttz.i16 (i16 <src>, i1 <is_zero_undef>) 10857 declare i32 @llvm.cttz.i32 (i32 <src>, i1 <is_zero_undef>) 10858 declare i64 @llvm.cttz.i64 (i64 <src>, i1 <is_zero_undef>) 10859 declare i256 @llvm.cttz.i256(i256 <src>, i1 <is_zero_undef>) 10860 declare <2 x i32> @llvm.cttz.v2i32(<2 x i32> <src>, i1 <is_zero_undef>) 10861 10862Overview: 10863""""""""" 10864 10865The '``llvm.cttz``' family of intrinsic functions counts the number of 10866trailing zeros. 10867 10868Arguments: 10869"""""""""" 10870 10871The first argument is the value to be counted. This argument may be of 10872any integer type, or a vector with integer element type. The return 10873type must match the first argument type. 10874 10875The second argument must be a constant and is a flag to indicate whether 10876the intrinsic should ensure that a zero as the first argument produces a 10877defined result. Historically some architectures did not provide a 10878defined result for zero values as efficiently, and many algorithms are 10879now predicated on avoiding zero-value inputs. 10880 10881Semantics: 10882"""""""""" 10883 10884The '``llvm.cttz``' intrinsic counts the trailing (least significant) 10885zeros in a variable, or within each element of a vector. If ``src == 0`` 10886then the result is the size in bits of the type of ``src`` if 10887``is_zero_undef == 0`` and ``undef`` otherwise. For example, 10888``llvm.cttz(2) = 1``. 10889 10890.. _int_overflow: 10891 10892Arithmetic with Overflow Intrinsics 10893----------------------------------- 10894 10895LLVM provides intrinsics for fast arithmetic overflow checking. 10896 10897Each of these intrinsics returns a two-element struct. The first 10898element of this struct contains the result of the corresponding 10899arithmetic operation modulo 2\ :sup:`n`\ , where n is the bit width of 10900the result. Therefore, for example, the first element of the struct 10901returned by ``llvm.sadd.with.overflow.i32`` is always the same as the 10902result of a 32-bit ``add`` instruction with the same operands, where 10903the ``add`` is *not* modified by an ``nsw`` or ``nuw`` flag. 10904 10905The second element of the result is an ``i1`` that is 1 if the 10906arithmetic operation overflowed and 0 otherwise. An operation 10907overflows if, for any values of its operands ``A`` and ``B`` and for 10908any ``N`` larger than the operands' width, ``ext(A op B) to iN`` is 10909not equal to ``(ext(A) to iN) op (ext(B) to iN)`` where ``ext`` is 10910``sext`` for signed overflow and ``zext`` for unsigned overflow, and 10911``op`` is the underlying arithmetic operation. 10912 10913The behavior of these intrinsics is well-defined for all argument 10914values. 10915 10916'``llvm.sadd.with.overflow.*``' Intrinsics 10917^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 10918 10919Syntax: 10920""""""" 10921 10922This is an overloaded intrinsic. You can use ``llvm.sadd.with.overflow`` 10923on any integer bit width. 10924 10925:: 10926 10927 declare {i16, i1} @llvm.sadd.with.overflow.i16(i16 %a, i16 %b) 10928 declare {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b) 10929 declare {i64, i1} @llvm.sadd.with.overflow.i64(i64 %a, i64 %b) 10930 10931Overview: 10932""""""""" 10933 10934The '``llvm.sadd.with.overflow``' family of intrinsic functions perform 10935a signed addition of the two arguments, and indicate whether an overflow 10936occurred during the signed summation. 10937 10938Arguments: 10939"""""""""" 10940 10941The arguments (%a and %b) and the first element of the result structure 10942may be of integer types of any bit width, but they must have the same 10943bit width. The second element of the result structure must be of type 10944``i1``. ``%a`` and ``%b`` are the two values that will undergo signed 10945addition. 10946 10947Semantics: 10948"""""""""" 10949 10950The '``llvm.sadd.with.overflow``' family of intrinsic functions perform 10951a signed addition of the two variables. They return a structure --- the 10952first element of which is the signed summation, and the second element 10953of which is a bit specifying if the signed summation resulted in an 10954overflow. 10955 10956Examples: 10957""""""""" 10958 10959.. code-block:: llvm 10960 10961 %res = call {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b) 10962 %sum = extractvalue {i32, i1} %res, 0 10963 %obit = extractvalue {i32, i1} %res, 1 10964 br i1 %obit, label %overflow, label %normal 10965 10966'``llvm.uadd.with.overflow.*``' Intrinsics 10967^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 10968 10969Syntax: 10970""""""" 10971 10972This is an overloaded intrinsic. You can use ``llvm.uadd.with.overflow`` 10973on any integer bit width. 10974 10975:: 10976 10977 declare {i16, i1} @llvm.uadd.with.overflow.i16(i16 %a, i16 %b) 10978 declare {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b) 10979 declare {i64, i1} @llvm.uadd.with.overflow.i64(i64 %a, i64 %b) 10980 10981Overview: 10982""""""""" 10983 10984The '``llvm.uadd.with.overflow``' family of intrinsic functions perform 10985an unsigned addition of the two arguments, and indicate whether a carry 10986occurred during the unsigned summation. 10987 10988Arguments: 10989"""""""""" 10990 10991The arguments (%a and %b) and the first element of the result structure 10992may be of integer types of any bit width, but they must have the same 10993bit width. The second element of the result structure must be of type 10994``i1``. ``%a`` and ``%b`` are the two values that will undergo unsigned 10995addition. 10996 10997Semantics: 10998"""""""""" 10999 11000The '``llvm.uadd.with.overflow``' family of intrinsic functions perform 11001an unsigned addition of the two arguments. They return a structure --- the 11002first element of which is the sum, and the second element of which is a 11003bit specifying if the unsigned summation resulted in a carry. 11004 11005Examples: 11006""""""""" 11007 11008.. code-block:: llvm 11009 11010 %res = call {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b) 11011 %sum = extractvalue {i32, i1} %res, 0 11012 %obit = extractvalue {i32, i1} %res, 1 11013 br i1 %obit, label %carry, label %normal 11014 11015'``llvm.ssub.with.overflow.*``' Intrinsics 11016^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 11017 11018Syntax: 11019""""""" 11020 11021This is an overloaded intrinsic. You can use ``llvm.ssub.with.overflow`` 11022on any integer bit width. 11023 11024:: 11025 11026 declare {i16, i1} @llvm.ssub.with.overflow.i16(i16 %a, i16 %b) 11027 declare {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b) 11028 declare {i64, i1} @llvm.ssub.with.overflow.i64(i64 %a, i64 %b) 11029 11030Overview: 11031""""""""" 11032 11033The '``llvm.ssub.with.overflow``' family of intrinsic functions perform 11034a signed subtraction of the two arguments, and indicate whether an 11035overflow occurred during the signed subtraction. 11036 11037Arguments: 11038"""""""""" 11039 11040The arguments (%a and %b) and the first element of the result structure 11041may be of integer types of any bit width, but they must have the same 11042bit width. The second element of the result structure must be of type 11043``i1``. ``%a`` and ``%b`` are the two values that will undergo signed 11044subtraction. 11045 11046Semantics: 11047"""""""""" 11048 11049The '``llvm.ssub.with.overflow``' family of intrinsic functions perform 11050a signed subtraction of the two arguments. They return a structure --- the 11051first element of which is the subtraction, and the second element of 11052which is a bit specifying if the signed subtraction resulted in an 11053overflow. 11054 11055Examples: 11056""""""""" 11057 11058.. code-block:: llvm 11059 11060 %res = call {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b) 11061 %sum = extractvalue {i32, i1} %res, 0 11062 %obit = extractvalue {i32, i1} %res, 1 11063 br i1 %obit, label %overflow, label %normal 11064 11065'``llvm.usub.with.overflow.*``' Intrinsics 11066^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 11067 11068Syntax: 11069""""""" 11070 11071This is an overloaded intrinsic. You can use ``llvm.usub.with.overflow`` 11072on any integer bit width. 11073 11074:: 11075 11076 declare {i16, i1} @llvm.usub.with.overflow.i16(i16 %a, i16 %b) 11077 declare {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b) 11078 declare {i64, i1} @llvm.usub.with.overflow.i64(i64 %a, i64 %b) 11079 11080Overview: 11081""""""""" 11082 11083The '``llvm.usub.with.overflow``' family of intrinsic functions perform 11084an unsigned subtraction of the two arguments, and indicate whether an 11085overflow occurred during the unsigned subtraction. 11086 11087Arguments: 11088"""""""""" 11089 11090The arguments (%a and %b) and the first element of the result structure 11091may be of integer types of any bit width, but they must have the same 11092bit width. The second element of the result structure must be of type 11093``i1``. ``%a`` and ``%b`` are the two values that will undergo unsigned 11094subtraction. 11095 11096Semantics: 11097"""""""""" 11098 11099The '``llvm.usub.with.overflow``' family of intrinsic functions perform 11100an unsigned subtraction of the two arguments. They return a structure --- 11101the first element of which is the subtraction, and the second element of 11102which is a bit specifying if the unsigned subtraction resulted in an 11103overflow. 11104 11105Examples: 11106""""""""" 11107 11108.. code-block:: llvm 11109 11110 %res = call {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b) 11111 %sum = extractvalue {i32, i1} %res, 0 11112 %obit = extractvalue {i32, i1} %res, 1 11113 br i1 %obit, label %overflow, label %normal 11114 11115'``llvm.smul.with.overflow.*``' Intrinsics 11116^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 11117 11118Syntax: 11119""""""" 11120 11121This is an overloaded intrinsic. You can use ``llvm.smul.with.overflow`` 11122on any integer bit width. 11123 11124:: 11125 11126 declare {i16, i1} @llvm.smul.with.overflow.i16(i16 %a, i16 %b) 11127 declare {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b) 11128 declare {i64, i1} @llvm.smul.with.overflow.i64(i64 %a, i64 %b) 11129 11130Overview: 11131""""""""" 11132 11133The '``llvm.smul.with.overflow``' family of intrinsic functions perform 11134a signed multiplication of the two arguments, and indicate whether an 11135overflow occurred during the signed multiplication. 11136 11137Arguments: 11138"""""""""" 11139 11140The arguments (%a and %b) and the first element of the result structure 11141may be of integer types of any bit width, but they must have the same 11142bit width. The second element of the result structure must be of type 11143``i1``. ``%a`` and ``%b`` are the two values that will undergo signed 11144multiplication. 11145 11146Semantics: 11147"""""""""" 11148 11149The '``llvm.smul.with.overflow``' family of intrinsic functions perform 11150a signed multiplication of the two arguments. They return a structure --- 11151the first element of which is the multiplication, and the second element 11152of which is a bit specifying if the signed multiplication resulted in an 11153overflow. 11154 11155Examples: 11156""""""""" 11157 11158.. code-block:: llvm 11159 11160 %res = call {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b) 11161 %sum = extractvalue {i32, i1} %res, 0 11162 %obit = extractvalue {i32, i1} %res, 1 11163 br i1 %obit, label %overflow, label %normal 11164 11165'``llvm.umul.with.overflow.*``' Intrinsics 11166^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 11167 11168Syntax: 11169""""""" 11170 11171This is an overloaded intrinsic. You can use ``llvm.umul.with.overflow`` 11172on any integer bit width. 11173 11174:: 11175 11176 declare {i16, i1} @llvm.umul.with.overflow.i16(i16 %a, i16 %b) 11177 declare {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b) 11178 declare {i64, i1} @llvm.umul.with.overflow.i64(i64 %a, i64 %b) 11179 11180Overview: 11181""""""""" 11182 11183The '``llvm.umul.with.overflow``' family of intrinsic functions perform 11184a unsigned multiplication of the two arguments, and indicate whether an 11185overflow occurred during the unsigned multiplication. 11186 11187Arguments: 11188"""""""""" 11189 11190The arguments (%a and %b) and the first element of the result structure 11191may be of integer types of any bit width, but they must have the same 11192bit width. The second element of the result structure must be of type 11193``i1``. ``%a`` and ``%b`` are the two values that will undergo unsigned 11194multiplication. 11195 11196Semantics: 11197"""""""""" 11198 11199The '``llvm.umul.with.overflow``' family of intrinsic functions perform 11200an unsigned multiplication of the two arguments. They return a structure --- 11201the first element of which is the multiplication, and the second 11202element of which is a bit specifying if the unsigned multiplication 11203resulted in an overflow. 11204 11205Examples: 11206""""""""" 11207 11208.. code-block:: llvm 11209 11210 %res = call {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b) 11211 %sum = extractvalue {i32, i1} %res, 0 11212 %obit = extractvalue {i32, i1} %res, 1 11213 br i1 %obit, label %overflow, label %normal 11214 11215Specialised Arithmetic Intrinsics 11216--------------------------------- 11217 11218'``llvm.canonicalize.*``' Intrinsic 11219^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 11220 11221Syntax: 11222""""""" 11223 11224:: 11225 11226 declare float @llvm.canonicalize.f32(float %a) 11227 declare double @llvm.canonicalize.f64(double %b) 11228 11229Overview: 11230""""""""" 11231 11232The '``llvm.canonicalize.*``' intrinsic returns the platform specific canonical 11233encoding of a floating point number. This canonicalization is useful for 11234implementing certain numeric primitives such as frexp. The canonical encoding is 11235defined by IEEE-754-2008 to be: 11236 11237:: 11238 11239 2.1.8 canonical encoding: The preferred encoding of a floating-point 11240 representation in a format. Applied to declets, significands of finite 11241 numbers, infinities, and NaNs, especially in decimal formats. 11242 11243This operation can also be considered equivalent to the IEEE-754-2008 11244conversion of a floating-point value to the same format. NaNs are handled 11245according to section 6.2. 11246 11247Examples of non-canonical encodings: 11248 11249- x87 pseudo denormals, pseudo NaNs, pseudo Infinity, Unnormals. These are 11250 converted to a canonical representation per hardware-specific protocol. 11251- Many normal decimal floating point numbers have non-canonical alternative 11252 encodings. 11253- Some machines, like GPUs or ARMv7 NEON, do not support subnormal values. 11254 These are treated as non-canonical encodings of zero and will be flushed to 11255 a zero of the same sign by this operation. 11256 11257Note that per IEEE-754-2008 6.2, systems that support signaling NaNs with 11258default exception handling must signal an invalid exception, and produce a 11259quiet NaN result. 11260 11261This function should always be implementable as multiplication by 1.0, provided 11262that the compiler does not constant fold the operation. Likewise, division by 112631.0 and ``llvm.minnum(x, x)`` are possible implementations. Addition with 11264-0.0 is also sufficient provided that the rounding mode is not -Infinity. 11265 11266``@llvm.canonicalize`` must preserve the equality relation. That is: 11267 11268- ``(@llvm.canonicalize(x) == x)`` is equivalent to ``(x == x)`` 11269- ``(@llvm.canonicalize(x) == @llvm.canonicalize(y))`` is equivalent to 11270 to ``(x == y)`` 11271 11272Additionally, the sign of zero must be conserved: 11273``@llvm.canonicalize(-0.0) = -0.0`` and ``@llvm.canonicalize(+0.0) = +0.0`` 11274 11275The payload bits of a NaN must be conserved, with two exceptions. 11276First, environments which use only a single canonical representation of NaN 11277must perform said canonicalization. Second, SNaNs must be quieted per the 11278usual methods. 11279 11280The canonicalization operation may be optimized away if: 11281 11282- The input is known to be canonical. For example, it was produced by a 11283 floating-point operation that is required by the standard to be canonical. 11284- The result is consumed only by (or fused with) other floating-point 11285 operations. That is, the bits of the floating point value are not examined. 11286 11287'``llvm.fmuladd.*``' Intrinsic 11288^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 11289 11290Syntax: 11291""""""" 11292 11293:: 11294 11295 declare float @llvm.fmuladd.f32(float %a, float %b, float %c) 11296 declare double @llvm.fmuladd.f64(double %a, double %b, double %c) 11297 11298Overview: 11299""""""""" 11300 11301The '``llvm.fmuladd.*``' intrinsic functions represent multiply-add 11302expressions that can be fused if the code generator determines that (a) the 11303target instruction set has support for a fused operation, and (b) that the 11304fused operation is more efficient than the equivalent, separate pair of mul 11305and add instructions. 11306 11307Arguments: 11308"""""""""" 11309 11310The '``llvm.fmuladd.*``' intrinsics each take three arguments: two 11311multiplicands, a and b, and an addend c. 11312 11313Semantics: 11314"""""""""" 11315 11316The expression: 11317 11318:: 11319 11320 %0 = call float @llvm.fmuladd.f32(%a, %b, %c) 11321 11322is equivalent to the expression a \* b + c, except that rounding will 11323not be performed between the multiplication and addition steps if the 11324code generator fuses the operations. Fusion is not guaranteed, even if 11325the target platform supports it. If a fused multiply-add is required the 11326corresponding llvm.fma.\* intrinsic function should be used 11327instead. This never sets errno, just as '``llvm.fma.*``'. 11328 11329Examples: 11330""""""""" 11331 11332.. code-block:: llvm 11333 11334 %r2 = call float @llvm.fmuladd.f32(float %a, float %b, float %c) ; yields float:r2 = (a * b) + c 11335 11336Half Precision Floating Point Intrinsics 11337---------------------------------------- 11338 11339For most target platforms, half precision floating point is a 11340storage-only format. This means that it is a dense encoding (in memory) 11341but does not support computation in the format. 11342 11343This means that code must first load the half-precision floating point 11344value as an i16, then convert it to float with 11345:ref:`llvm.convert.from.fp16 <int_convert_from_fp16>`. Computation can 11346then be performed on the float value (including extending to double 11347etc). To store the value back to memory, it is first converted to float 11348if needed, then converted to i16 with 11349:ref:`llvm.convert.to.fp16 <int_convert_to_fp16>`, then storing as an 11350i16 value. 11351 11352.. _int_convert_to_fp16: 11353 11354'``llvm.convert.to.fp16``' Intrinsic 11355^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 11356 11357Syntax: 11358""""""" 11359 11360:: 11361 11362 declare i16 @llvm.convert.to.fp16.f32(float %a) 11363 declare i16 @llvm.convert.to.fp16.f64(double %a) 11364 11365Overview: 11366""""""""" 11367 11368The '``llvm.convert.to.fp16``' intrinsic function performs a conversion from a 11369conventional floating point type to half precision floating point format. 11370 11371Arguments: 11372"""""""""" 11373 11374The intrinsic function contains single argument - the value to be 11375converted. 11376 11377Semantics: 11378"""""""""" 11379 11380The '``llvm.convert.to.fp16``' intrinsic function performs a conversion from a 11381conventional floating point format to half precision floating point format. The 11382return value is an ``i16`` which contains the converted number. 11383 11384Examples: 11385""""""""" 11386 11387.. code-block:: llvm 11388 11389 %res = call i16 @llvm.convert.to.fp16.f32(float %a) 11390 store i16 %res, i16* @x, align 2 11391 11392.. _int_convert_from_fp16: 11393 11394'``llvm.convert.from.fp16``' Intrinsic 11395^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 11396 11397Syntax: 11398""""""" 11399 11400:: 11401 11402 declare float @llvm.convert.from.fp16.f32(i16 %a) 11403 declare double @llvm.convert.from.fp16.f64(i16 %a) 11404 11405Overview: 11406""""""""" 11407 11408The '``llvm.convert.from.fp16``' intrinsic function performs a 11409conversion from half precision floating point format to single precision 11410floating point format. 11411 11412Arguments: 11413"""""""""" 11414 11415The intrinsic function contains single argument - the value to be 11416converted. 11417 11418Semantics: 11419"""""""""" 11420 11421The '``llvm.convert.from.fp16``' intrinsic function performs a 11422conversion from half single precision floating point format to single 11423precision floating point format. The input half-float value is 11424represented by an ``i16`` value. 11425 11426Examples: 11427""""""""" 11428 11429.. code-block:: llvm 11430 11431 %a = load i16, i16* @x, align 2 11432 %res = call float @llvm.convert.from.fp16(i16 %a) 11433 11434.. _dbg_intrinsics: 11435 11436Debugger Intrinsics 11437------------------- 11438 11439The LLVM debugger intrinsics (which all start with ``llvm.dbg.`` 11440prefix), are described in the `LLVM Source Level 11441Debugging <SourceLevelDebugging.html#format_common_intrinsics>`_ 11442document. 11443 11444Exception Handling Intrinsics 11445----------------------------- 11446 11447The LLVM exception handling intrinsics (which all start with 11448``llvm.eh.`` prefix), are described in the `LLVM Exception 11449Handling <ExceptionHandling.html#format_common_intrinsics>`_ document. 11450 11451.. _int_trampoline: 11452 11453Trampoline Intrinsics 11454--------------------- 11455 11456These intrinsics make it possible to excise one parameter, marked with 11457the :ref:`nest <nest>` attribute, from a function. The result is a 11458callable function pointer lacking the nest parameter - the caller does 11459not need to provide a value for it. Instead, the value to use is stored 11460in advance in a "trampoline", a block of memory usually allocated on the 11461stack, which also contains code to splice the nest value into the 11462argument list. This is used to implement the GCC nested function address 11463extension. 11464 11465For example, if the function is ``i32 f(i8* nest %c, i32 %x, i32 %y)`` 11466then the resulting function pointer has signature ``i32 (i32, i32)*``. 11467It can be created as follows: 11468 11469.. code-block:: llvm 11470 11471 %tramp = alloca [10 x i8], align 4 ; size and alignment only correct for X86 11472 %tramp1 = getelementptr [10 x i8], [10 x i8]* %tramp, i32 0, i32 0 11473 call i8* @llvm.init.trampoline(i8* %tramp1, i8* bitcast (i32 (i8*, i32, i32)* @f to i8*), i8* %nval) 11474 %p = call i8* @llvm.adjust.trampoline(i8* %tramp1) 11475 %fp = bitcast i8* %p to i32 (i32, i32)* 11476 11477The call ``%val = call i32 %fp(i32 %x, i32 %y)`` is then equivalent to 11478``%val = call i32 %f(i8* %nval, i32 %x, i32 %y)``. 11479 11480.. _int_it: 11481 11482'``llvm.init.trampoline``' Intrinsic 11483^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 11484 11485Syntax: 11486""""""" 11487 11488:: 11489 11490 declare void @llvm.init.trampoline(i8* <tramp>, i8* <func>, i8* <nval>) 11491 11492Overview: 11493""""""""" 11494 11495This fills the memory pointed to by ``tramp`` with executable code, 11496turning it into a trampoline. 11497 11498Arguments: 11499"""""""""" 11500 11501The ``llvm.init.trampoline`` intrinsic takes three arguments, all 11502pointers. The ``tramp`` argument must point to a sufficiently large and 11503sufficiently aligned block of memory; this memory is written to by the 11504intrinsic. Note that the size and the alignment are target-specific - 11505LLVM currently provides no portable way of determining them, so a 11506front-end that generates this intrinsic needs to have some 11507target-specific knowledge. The ``func`` argument must hold a function 11508bitcast to an ``i8*``. 11509 11510Semantics: 11511"""""""""" 11512 11513The block of memory pointed to by ``tramp`` is filled with target 11514dependent code, turning it into a function. Then ``tramp`` needs to be 11515passed to :ref:`llvm.adjust.trampoline <int_at>` to get a pointer which can 11516be :ref:`bitcast (to a new function) and called <int_trampoline>`. The new 11517function's signature is the same as that of ``func`` with any arguments 11518marked with the ``nest`` attribute removed. At most one such ``nest`` 11519argument is allowed, and it must be of pointer type. Calling the new 11520function is equivalent to calling ``func`` with the same argument list, 11521but with ``nval`` used for the missing ``nest`` argument. If, after 11522calling ``llvm.init.trampoline``, the memory pointed to by ``tramp`` is 11523modified, then the effect of any later call to the returned function 11524pointer is undefined. 11525 11526.. _int_at: 11527 11528'``llvm.adjust.trampoline``' Intrinsic 11529^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 11530 11531Syntax: 11532""""""" 11533 11534:: 11535 11536 declare i8* @llvm.adjust.trampoline(i8* <tramp>) 11537 11538Overview: 11539""""""""" 11540 11541This performs any required machine-specific adjustment to the address of 11542a trampoline (passed as ``tramp``). 11543 11544Arguments: 11545"""""""""" 11546 11547``tramp`` must point to a block of memory which already has trampoline 11548code filled in by a previous call to 11549:ref:`llvm.init.trampoline <int_it>`. 11550 11551Semantics: 11552"""""""""" 11553 11554On some architectures the address of the code to be executed needs to be 11555different than the address where the trampoline is actually stored. This 11556intrinsic returns the executable address corresponding to ``tramp`` 11557after performing the required machine specific adjustments. The pointer 11558returned can then be :ref:`bitcast and executed <int_trampoline>`. 11559 11560.. _int_mload_mstore: 11561 11562Masked Vector Load and Store Intrinsics 11563--------------------------------------- 11564 11565LLVM 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. 11566 11567.. _int_mload: 11568 11569'``llvm.masked.load.*``' Intrinsics 11570^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 11571 11572Syntax: 11573""""""" 11574This is an overloaded intrinsic. The loaded data is a vector of any integer, floating point or pointer data type. 11575 11576:: 11577 11578 declare <16 x float> @llvm.masked.load.v16f32.p0v16f32 (<16 x float>* <ptr>, i32 <alignment>, <16 x i1> <mask>, <16 x float> <passthru>) 11579 declare <2 x double> @llvm.masked.load.v2f64.p0v2f64 (<2 x double>* <ptr>, i32 <alignment>, <2 x i1> <mask>, <2 x double> <passthru>) 11580 ;; The data is a vector of pointers to double 11581 declare <8 x double*> @llvm.masked.load.v8p0f64.p0v8p0f64 (<8 x double*>* <ptr>, i32 <alignment>, <8 x i1> <mask>, <8 x double*> <passthru>) 11582 ;; The data is a vector of function pointers 11583 declare <8 x i32 ()*> @llvm.masked.load.v8p0f_i32f.p0v8p0f_i32f (<8 x i32 ()*>* <ptr>, i32 <alignment>, <8 x i1> <mask>, <8 x i32 ()*> <passthru>) 11584 11585Overview: 11586""""""""" 11587 11588Reads 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. 11589 11590 11591Arguments: 11592"""""""""" 11593 11594The 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. 11595 11596 11597Semantics: 11598"""""""""" 11599 11600The '``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. 11601The 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. 11602 11603 11604:: 11605 11606 %res = call <16 x float> @llvm.masked.load.v16f32.p0v16f32 (<16 x float>* %ptr, i32 4, <16 x i1>%mask, <16 x float> %passthru) 11607 11608 ;; The result of the two following instructions is identical aside from potential memory access exception 11609 %loadlal = load <16 x float>, <16 x float>* %ptr, align 4 11610 %res = select <16 x i1> %mask, <16 x float> %loadlal, <16 x float> %passthru 11611 11612.. _int_mstore: 11613 11614'``llvm.masked.store.*``' Intrinsics 11615^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 11616 11617Syntax: 11618""""""" 11619This is an overloaded intrinsic. The data stored in memory is a vector of any integer, floating point or pointer data type. 11620 11621:: 11622 11623 declare void @llvm.masked.store.v8i32.p0v8i32 (<8 x i32> <value>, <8 x i32>* <ptr>, i32 <alignment>, <8 x i1> <mask>) 11624 declare void @llvm.masked.store.v16f32.p0v16f32 (<16 x float> <value>, <16 x float>* <ptr>, i32 <alignment>, <16 x i1> <mask>) 11625 ;; The data is a vector of pointers to double 11626 declare void @llvm.masked.store.v8p0f64.p0v8p0f64 (<8 x double*> <value>, <8 x double*>* <ptr>, i32 <alignment>, <8 x i1> <mask>) 11627 ;; The data is a vector of function pointers 11628 declare void @llvm.masked.store.v4p0f_i32f.p0v4p0f_i32f (<4 x i32 ()*> <value>, <4 x i32 ()*>* <ptr>, i32 <alignment>, <4 x i1> <mask>) 11629 11630Overview: 11631""""""""" 11632 11633Writes 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. 11634 11635Arguments: 11636"""""""""" 11637 11638The 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. 11639 11640 11641Semantics: 11642"""""""""" 11643 11644The '``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. 11645The 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. 11646 11647:: 11648 11649 call void @llvm.masked.store.v16f32.p0v16f32(<16 x float> %value, <16 x float>* %ptr, i32 4, <16 x i1> %mask) 11650 11651 ;; The result of the following instructions is identical aside from potential data races and memory access exceptions 11652 %oldval = load <16 x float>, <16 x float>* %ptr, align 4 11653 %res = select <16 x i1> %mask, <16 x float> %value, <16 x float> %oldval 11654 store <16 x float> %res, <16 x float>* %ptr, align 4 11655 11656 11657Masked Vector Gather and Scatter Intrinsics 11658------------------------------------------- 11659 11660LLVM 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. 11661 11662.. _int_mgather: 11663 11664'``llvm.masked.gather.*``' Intrinsics 11665^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 11666 11667Syntax: 11668""""""" 11669This is an overloaded intrinsic. The loaded data are multiple scalar values of any integer, floating point or pointer data type gathered together into one vector. 11670 11671:: 11672 11673 declare <16 x float> @llvm.masked.gather.v16f32 (<16 x float*> <ptrs>, i32 <alignment>, <16 x i1> <mask>, <16 x float> <passthru>) 11674 declare <2 x double> @llvm.masked.gather.v2f64 (<2 x double*> <ptrs>, i32 <alignment>, <2 x i1> <mask>, <2 x double> <passthru>) 11675 declare <8 x float*> @llvm.masked.gather.v8p0f32 (<8 x float**> <ptrs>, i32 <alignment>, <8 x i1> <mask>, <8 x float*> <passthru>) 11676 11677Overview: 11678""""""""" 11679 11680Reads 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. 11681 11682 11683Arguments: 11684"""""""""" 11685 11686The 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. 11687 11688 11689Semantics: 11690"""""""""" 11691 11692The '``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. 11693The 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. 11694 11695 11696:: 11697 11698 %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>) 11699 11700 ;; The gather with all-true mask is equivalent to the following instruction sequence 11701 %ptr0 = extractelement <4 x double*> %ptrs, i32 0 11702 %ptr1 = extractelement <4 x double*> %ptrs, i32 1 11703 %ptr2 = extractelement <4 x double*> %ptrs, i32 2 11704 %ptr3 = extractelement <4 x double*> %ptrs, i32 3 11705 11706 %val0 = load double, double* %ptr0, align 8 11707 %val1 = load double, double* %ptr1, align 8 11708 %val2 = load double, double* %ptr2, align 8 11709 %val3 = load double, double* %ptr3, align 8 11710 11711 %vec0 = insertelement <4 x double>undef, %val0, 0 11712 %vec01 = insertelement <4 x double>%vec0, %val1, 1 11713 %vec012 = insertelement <4 x double>%vec01, %val2, 2 11714 %vec0123 = insertelement <4 x double>%vec012, %val3, 3 11715 11716.. _int_mscatter: 11717 11718'``llvm.masked.scatter.*``' Intrinsics 11719^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 11720 11721Syntax: 11722""""""" 11723This is an overloaded intrinsic. The data stored in memory is a vector of any integer, floating point or pointer data type. Each vector element is stored in an arbitrary memory address. Scatter with overlapping addresses is guaranteed to be ordered from least-significant to most-significant element. 11724 11725:: 11726 11727 declare void @llvm.masked.scatter.v8i32 (<8 x i32> <value>, <8 x i32*> <ptrs>, i32 <alignment>, <8 x i1> <mask>) 11728 declare void @llvm.masked.scatter.v16f32 (<16 x float> <value>, <16 x float*> <ptrs>, i32 <alignment>, <16 x i1> <mask>) 11729 declare void @llvm.masked.scatter.v4p0f64 (<4 x double*> <value>, <4 x double**> <ptrs>, i32 <alignment>, <4 x i1> <mask>) 11730 11731Overview: 11732""""""""" 11733 11734Writes 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. 11735 11736Arguments: 11737"""""""""" 11738 11739The 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. 11740 11741 11742Semantics: 11743"""""""""" 11744 11745The '``llvm.masked.scatter``' intrinsics is designed for writing selected vector elements to arbitrary memory addresses in a single IR operation. The operation may be conditional, when not all bits in the mask are switched on. It is useful for targets that support vector masked scatter and allows vectorizing basic blocks with data and control divergence. Other targets may support this intrinsic differently, for example by lowering it into a sequence of branches that guard scalar store operations. 11746 11747:: 11748 11749 ;; This instruction unconditionally stores data vector in multiple addresses 11750 call @llvm.masked.scatter.v8i32 (<8 x i32> %value, <8 x i32*> %ptrs, i32 4, <8 x i1> <true, true, .. true>) 11751 11752 ;; It is equivalent to a list of scalar stores 11753 %val0 = extractelement <8 x i32> %value, i32 0 11754 %val1 = extractelement <8 x i32> %value, i32 1 11755 .. 11756 %val7 = extractelement <8 x i32> %value, i32 7 11757 %ptr0 = extractelement <8 x i32*> %ptrs, i32 0 11758 %ptr1 = extractelement <8 x i32*> %ptrs, i32 1 11759 .. 11760 %ptr7 = extractelement <8 x i32*> %ptrs, i32 7 11761 ;; Note: the order of the following stores is important when they overlap: 11762 store i32 %val0, i32* %ptr0, align 4 11763 store i32 %val1, i32* %ptr1, align 4 11764 .. 11765 store i32 %val7, i32* %ptr7, align 4 11766 11767 11768Memory Use Markers 11769------------------ 11770 11771This class of intrinsics provides information about the lifetime of 11772memory objects and ranges where variables are immutable. 11773 11774.. _int_lifestart: 11775 11776'``llvm.lifetime.start``' Intrinsic 11777^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 11778 11779Syntax: 11780""""""" 11781 11782:: 11783 11784 declare void @llvm.lifetime.start(i64 <size>, i8* nocapture <ptr>) 11785 11786Overview: 11787""""""""" 11788 11789The '``llvm.lifetime.start``' intrinsic specifies the start of a memory 11790object's lifetime. 11791 11792Arguments: 11793"""""""""" 11794 11795The first argument is a constant integer representing the size of the 11796object, or -1 if it is variable sized. The second argument is a pointer 11797to the object. 11798 11799Semantics: 11800"""""""""" 11801 11802This intrinsic indicates that before this point in the code, the value 11803of the memory pointed to by ``ptr`` is dead. This means that it is known 11804to never be used and has an undefined value. A load from the pointer 11805that precedes this intrinsic can be replaced with ``'undef'``. 11806 11807.. _int_lifeend: 11808 11809'``llvm.lifetime.end``' Intrinsic 11810^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 11811 11812Syntax: 11813""""""" 11814 11815:: 11816 11817 declare void @llvm.lifetime.end(i64 <size>, i8* nocapture <ptr>) 11818 11819Overview: 11820""""""""" 11821 11822The '``llvm.lifetime.end``' intrinsic specifies the end of a memory 11823object's lifetime. 11824 11825Arguments: 11826"""""""""" 11827 11828The first argument is a constant integer representing the size of the 11829object, or -1 if it is variable sized. The second argument is a pointer 11830to the object. 11831 11832Semantics: 11833"""""""""" 11834 11835This intrinsic indicates that after this point in the code, the value of 11836the memory pointed to by ``ptr`` is dead. This means that it is known to 11837never be used and has an undefined value. Any stores into the memory 11838object following this intrinsic may be removed as dead. 11839 11840'``llvm.invariant.start``' Intrinsic 11841^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 11842 11843Syntax: 11844""""""" 11845 11846:: 11847 11848 declare {}* @llvm.invariant.start(i64 <size>, i8* nocapture <ptr>) 11849 11850Overview: 11851""""""""" 11852 11853The '``llvm.invariant.start``' intrinsic specifies that the contents of 11854a memory object will not change. 11855 11856Arguments: 11857"""""""""" 11858 11859The first argument is a constant integer representing the size of the 11860object, or -1 if it is variable sized. The second argument is a pointer 11861to the object. 11862 11863Semantics: 11864"""""""""" 11865 11866This intrinsic indicates that until an ``llvm.invariant.end`` that uses 11867the return value, the referenced memory location is constant and 11868unchanging. 11869 11870'``llvm.invariant.end``' Intrinsic 11871^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 11872 11873Syntax: 11874""""""" 11875 11876:: 11877 11878 declare void @llvm.invariant.end({}* <start>, i64 <size>, i8* nocapture <ptr>) 11879 11880Overview: 11881""""""""" 11882 11883The '``llvm.invariant.end``' intrinsic specifies that the contents of a 11884memory object are mutable. 11885 11886Arguments: 11887"""""""""" 11888 11889The first argument is the matching ``llvm.invariant.start`` intrinsic. 11890The second argument is a constant integer representing the size of the 11891object, or -1 if it is variable sized and the third argument is a 11892pointer to the object. 11893 11894Semantics: 11895"""""""""" 11896 11897This intrinsic indicates that the memory is mutable again. 11898 11899'``llvm.invariant.group.barrier``' Intrinsic 11900^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 11901 11902Syntax: 11903""""""" 11904 11905:: 11906 11907 declare i8* @llvm.invariant.group.barrier(i8* <ptr>) 11908 11909Overview: 11910""""""""" 11911 11912The '``llvm.invariant.group.barrier``' intrinsic can be used when an invariant 11913established by invariant.group metadata no longer holds, to obtain a new pointer 11914value that does not carry the invariant information. 11915 11916 11917Arguments: 11918"""""""""" 11919 11920The ``llvm.invariant.group.barrier`` takes only one argument, which is 11921the pointer to the memory for which the ``invariant.group`` no longer holds. 11922 11923Semantics: 11924"""""""""" 11925 11926Returns another pointer that aliases its argument but which is considered different 11927for the purposes of ``load``/``store`` ``invariant.group`` metadata. 11928 11929General Intrinsics 11930------------------ 11931 11932This class of intrinsics is designed to be generic and has no specific 11933purpose. 11934 11935'``llvm.var.annotation``' Intrinsic 11936^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 11937 11938Syntax: 11939""""""" 11940 11941:: 11942 11943 declare void @llvm.var.annotation(i8* <val>, i8* <str>, i8* <str>, i32 <int>) 11944 11945Overview: 11946""""""""" 11947 11948The '``llvm.var.annotation``' intrinsic. 11949 11950Arguments: 11951"""""""""" 11952 11953The first argument is a pointer to a value, the second is a pointer to a 11954global string, the third is a pointer to a global string which is the 11955source file name, and the last argument is the line number. 11956 11957Semantics: 11958"""""""""" 11959 11960This intrinsic allows annotation of local variables with arbitrary 11961strings. This can be useful for special purpose optimizations that want 11962to look for these annotations. These have no other defined use; they are 11963ignored by code generation and optimization. 11964 11965'``llvm.ptr.annotation.*``' Intrinsic 11966^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 11967 11968Syntax: 11969""""""" 11970 11971This is an overloaded intrinsic. You can use '``llvm.ptr.annotation``' on a 11972pointer to an integer of any width. *NOTE* you must specify an address space for 11973the pointer. The identifier for the default address space is the integer 11974'``0``'. 11975 11976:: 11977 11978 declare i8* @llvm.ptr.annotation.p<address space>i8(i8* <val>, i8* <str>, i8* <str>, i32 <int>) 11979 declare i16* @llvm.ptr.annotation.p<address space>i16(i16* <val>, i8* <str>, i8* <str>, i32 <int>) 11980 declare i32* @llvm.ptr.annotation.p<address space>i32(i32* <val>, i8* <str>, i8* <str>, i32 <int>) 11981 declare i64* @llvm.ptr.annotation.p<address space>i64(i64* <val>, i8* <str>, i8* <str>, i32 <int>) 11982 declare i256* @llvm.ptr.annotation.p<address space>i256(i256* <val>, i8* <str>, i8* <str>, i32 <int>) 11983 11984Overview: 11985""""""""" 11986 11987The '``llvm.ptr.annotation``' intrinsic. 11988 11989Arguments: 11990"""""""""" 11991 11992The first argument is a pointer to an integer value of arbitrary bitwidth 11993(result of some expression), the second is a pointer to a global string, the 11994third is a pointer to a global string which is the source file name, and the 11995last argument is the line number. It returns the value of the first argument. 11996 11997Semantics: 11998"""""""""" 11999 12000This intrinsic allows annotation of a pointer to an integer with arbitrary 12001strings. This can be useful for special purpose optimizations that want to look 12002for these annotations. These have no other defined use; they are ignored by code 12003generation and optimization. 12004 12005'``llvm.annotation.*``' Intrinsic 12006^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 12007 12008Syntax: 12009""""""" 12010 12011This is an overloaded intrinsic. You can use '``llvm.annotation``' on 12012any integer bit width. 12013 12014:: 12015 12016 declare i8 @llvm.annotation.i8(i8 <val>, i8* <str>, i8* <str>, i32 <int>) 12017 declare i16 @llvm.annotation.i16(i16 <val>, i8* <str>, i8* <str>, i32 <int>) 12018 declare i32 @llvm.annotation.i32(i32 <val>, i8* <str>, i8* <str>, i32 <int>) 12019 declare i64 @llvm.annotation.i64(i64 <val>, i8* <str>, i8* <str>, i32 <int>) 12020 declare i256 @llvm.annotation.i256(i256 <val>, i8* <str>, i8* <str>, i32 <int>) 12021 12022Overview: 12023""""""""" 12024 12025The '``llvm.annotation``' intrinsic. 12026 12027Arguments: 12028"""""""""" 12029 12030The first argument is an integer value (result of some expression), the 12031second is a pointer to a global string, the third is a pointer to a 12032global string which is the source file name, and the last argument is 12033the line number. It returns the value of the first argument. 12034 12035Semantics: 12036"""""""""" 12037 12038This intrinsic allows annotations to be put on arbitrary expressions 12039with arbitrary strings. This can be useful for special purpose 12040optimizations that want to look for these annotations. These have no 12041other defined use; they are ignored by code generation and optimization. 12042 12043'``llvm.trap``' Intrinsic 12044^^^^^^^^^^^^^^^^^^^^^^^^^ 12045 12046Syntax: 12047""""""" 12048 12049:: 12050 12051 declare void @llvm.trap() noreturn nounwind 12052 12053Overview: 12054""""""""" 12055 12056The '``llvm.trap``' intrinsic. 12057 12058Arguments: 12059"""""""""" 12060 12061None. 12062 12063Semantics: 12064"""""""""" 12065 12066This intrinsic is lowered to the target dependent trap instruction. If 12067the target does not have a trap instruction, this intrinsic will be 12068lowered to a call of the ``abort()`` function. 12069 12070'``llvm.debugtrap``' Intrinsic 12071^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 12072 12073Syntax: 12074""""""" 12075 12076:: 12077 12078 declare void @llvm.debugtrap() nounwind 12079 12080Overview: 12081""""""""" 12082 12083The '``llvm.debugtrap``' intrinsic. 12084 12085Arguments: 12086"""""""""" 12087 12088None. 12089 12090Semantics: 12091"""""""""" 12092 12093This intrinsic is lowered to code which is intended to cause an 12094execution trap with the intention of requesting the attention of a 12095debugger. 12096 12097'``llvm.stackprotector``' Intrinsic 12098^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 12099 12100Syntax: 12101""""""" 12102 12103:: 12104 12105 declare void @llvm.stackprotector(i8* <guard>, i8** <slot>) 12106 12107Overview: 12108""""""""" 12109 12110The ``llvm.stackprotector`` intrinsic takes the ``guard`` and stores it 12111onto the stack at ``slot``. The stack slot is adjusted to ensure that it 12112is placed on the stack before local variables. 12113 12114Arguments: 12115"""""""""" 12116 12117The ``llvm.stackprotector`` intrinsic requires two pointer arguments. 12118The first argument is the value loaded from the stack guard 12119``@__stack_chk_guard``. The second variable is an ``alloca`` that has 12120enough space to hold the value of the guard. 12121 12122Semantics: 12123"""""""""" 12124 12125This intrinsic causes the prologue/epilogue inserter to force the position of 12126the ``AllocaInst`` stack slot to be before local variables on the stack. This is 12127to ensure that if a local variable on the stack is overwritten, it will destroy 12128the value of the guard. When the function exits, the guard on the stack is 12129checked against the original guard by ``llvm.stackprotectorcheck``. If they are 12130different, then ``llvm.stackprotectorcheck`` causes the program to abort by 12131calling the ``__stack_chk_fail()`` function. 12132 12133'``llvm.stackguard``' Intrinsic 12134^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 12135 12136Syntax: 12137""""""" 12138 12139:: 12140 12141 declare i8* @llvm.stackguard() 12142 12143Overview: 12144""""""""" 12145 12146The ``llvm.stackguard`` intrinsic returns the system stack guard value. 12147 12148It should not be generated by frontends, since it is only for internal usage. 12149The reason why we create this intrinsic is that we still support IR form Stack 12150Protector in FastISel. 12151 12152Arguments: 12153"""""""""" 12154 12155None. 12156 12157Semantics: 12158"""""""""" 12159 12160On some platforms, the value returned by this intrinsic remains unchanged 12161between loads in the same thread. On other platforms, it returns the same 12162global variable value, if any, e.g. ``@__stack_chk_guard``. 12163 12164Currently some platforms have IR-level customized stack guard loading (e.g. 12165X86 Linux) that is not handled by ``llvm.stackguard()``, while they should be 12166in the future. 12167 12168'``llvm.objectsize``' Intrinsic 12169^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 12170 12171Syntax: 12172""""""" 12173 12174:: 12175 12176 declare i32 @llvm.objectsize.i32(i8* <object>, i1 <min>) 12177 declare i64 @llvm.objectsize.i64(i8* <object>, i1 <min>) 12178 12179Overview: 12180""""""""" 12181 12182The ``llvm.objectsize`` intrinsic is designed to provide information to 12183the optimizers to determine at compile time whether a) an operation 12184(like memcpy) will overflow a buffer that corresponds to an object, or 12185b) that a runtime check for overflow isn't necessary. An object in this 12186context means an allocation of a specific class, structure, array, or 12187other object. 12188 12189Arguments: 12190"""""""""" 12191 12192The ``llvm.objectsize`` intrinsic takes two arguments. The first 12193argument is a pointer to or into the ``object``. The second argument is 12194a boolean and determines whether ``llvm.objectsize`` returns 0 (if true) 12195or -1 (if false) when the object size is unknown. The second argument 12196only accepts constants. 12197 12198Semantics: 12199"""""""""" 12200 12201The ``llvm.objectsize`` intrinsic is lowered to a constant representing 12202the size of the object concerned. If the size cannot be determined at 12203compile time, ``llvm.objectsize`` returns ``i32/i64 -1 or 0`` (depending 12204on the ``min`` argument). 12205 12206'``llvm.expect``' Intrinsic 12207^^^^^^^^^^^^^^^^^^^^^^^^^^^ 12208 12209Syntax: 12210""""""" 12211 12212This is an overloaded intrinsic. You can use ``llvm.expect`` on any 12213integer bit width. 12214 12215:: 12216 12217 declare i1 @llvm.expect.i1(i1 <val>, i1 <expected_val>) 12218 declare i32 @llvm.expect.i32(i32 <val>, i32 <expected_val>) 12219 declare i64 @llvm.expect.i64(i64 <val>, i64 <expected_val>) 12220 12221Overview: 12222""""""""" 12223 12224The ``llvm.expect`` intrinsic provides information about expected (the 12225most probable) value of ``val``, which can be used by optimizers. 12226 12227Arguments: 12228"""""""""" 12229 12230The ``llvm.expect`` intrinsic takes two arguments. The first argument is 12231a value. The second argument is an expected value, this needs to be a 12232constant value, variables are not allowed. 12233 12234Semantics: 12235"""""""""" 12236 12237This intrinsic is lowered to the ``val``. 12238 12239.. _int_assume: 12240 12241'``llvm.assume``' Intrinsic 12242^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 12243 12244Syntax: 12245""""""" 12246 12247:: 12248 12249 declare void @llvm.assume(i1 %cond) 12250 12251Overview: 12252""""""""" 12253 12254The ``llvm.assume`` allows the optimizer to assume that the provided 12255condition is true. This information can then be used in simplifying other parts 12256of the code. 12257 12258Arguments: 12259"""""""""" 12260 12261The condition which the optimizer may assume is always true. 12262 12263Semantics: 12264"""""""""" 12265 12266The intrinsic allows the optimizer to assume that the provided condition is 12267always true whenever the control flow reaches the intrinsic call. No code is 12268generated for this intrinsic, and instructions that contribute only to the 12269provided condition are not used for code generation. If the condition is 12270violated during execution, the behavior is undefined. 12271 12272Note that the optimizer might limit the transformations performed on values 12273used by the ``llvm.assume`` intrinsic in order to preserve the instructions 12274only used to form the intrinsic's input argument. This might prove undesirable 12275if the extra information provided by the ``llvm.assume`` intrinsic does not cause 12276sufficient overall improvement in code quality. For this reason, 12277``llvm.assume`` should not be used to document basic mathematical invariants 12278that the optimizer can otherwise deduce or facts that are of little use to the 12279optimizer. 12280 12281.. _type.test: 12282 12283'``llvm.type.test``' Intrinsic 12284^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 12285 12286Syntax: 12287""""""" 12288 12289:: 12290 12291 declare i1 @llvm.type.test(i8* %ptr, metadata %type) nounwind readnone 12292 12293 12294Arguments: 12295"""""""""" 12296 12297The first argument is a pointer to be tested. The second argument is a 12298metadata object representing a :doc:`type identifier <TypeMetadata>`. 12299 12300Overview: 12301""""""""" 12302 12303The ``llvm.type.test`` intrinsic tests whether the given pointer is associated 12304with the given type identifier. 12305 12306'``llvm.type.checked.load``' Intrinsic 12307^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 12308 12309Syntax: 12310""""""" 12311 12312:: 12313 12314 declare {i8*, i1} @llvm.type.checked.load(i8* %ptr, i32 %offset, metadata %type) argmemonly nounwind readonly 12315 12316 12317Arguments: 12318"""""""""" 12319 12320The first argument is a pointer from which to load a function pointer. The 12321second argument is the byte offset from which to load the function pointer. The 12322third argument is a metadata object representing a :doc:`type identifier 12323<TypeMetadata>`. 12324 12325Overview: 12326""""""""" 12327 12328The ``llvm.type.checked.load`` intrinsic safely loads a function pointer from a 12329virtual table pointer using type metadata. This intrinsic is used to implement 12330control flow integrity in conjunction with virtual call optimization. The 12331virtual call optimization pass will optimize away ``llvm.type.checked.load`` 12332intrinsics associated with devirtualized calls, thereby removing the type 12333check in cases where it is not needed to enforce the control flow integrity 12334constraint. 12335 12336If the given pointer is associated with a type metadata identifier, this 12337function returns true as the second element of its return value. (Note that 12338the function may also return true if the given pointer is not associated 12339with a type metadata identifier.) If the function's return value's second 12340element is true, the following rules apply to the first element: 12341 12342- If the given pointer is associated with the given type metadata identifier, 12343 it is the function pointer loaded from the given byte offset from the given 12344 pointer. 12345 12346- If the given pointer is not associated with the given type metadata 12347 identifier, it is one of the following (the choice of which is unspecified): 12348 12349 1. The function pointer that would have been loaded from an arbitrarily chosen 12350 (through an unspecified mechanism) pointer associated with the type 12351 metadata. 12352 12353 2. If the function has a non-void return type, a pointer to a function that 12354 returns an unspecified value without causing side effects. 12355 12356If the function's return value's second element is false, the value of the 12357first element is undefined. 12358 12359 12360'``llvm.donothing``' Intrinsic 12361^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 12362 12363Syntax: 12364""""""" 12365 12366:: 12367 12368 declare void @llvm.donothing() nounwind readnone 12369 12370Overview: 12371""""""""" 12372 12373The ``llvm.donothing`` intrinsic doesn't perform any operation. It's one of only 12374three intrinsics (besides ``llvm.experimental.patchpoint`` and 12375``llvm.experimental.gc.statepoint``) that can be called with an invoke 12376instruction. 12377 12378Arguments: 12379"""""""""" 12380 12381None. 12382 12383Semantics: 12384"""""""""" 12385 12386This intrinsic does nothing, and it's removed by optimizers and ignored 12387by codegen. 12388 12389'``llvm.experimental.deoptimize``' Intrinsic 12390^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 12391 12392Syntax: 12393""""""" 12394 12395:: 12396 12397 declare type @llvm.experimental.deoptimize(...) [ "deopt"(...) ] 12398 12399Overview: 12400""""""""" 12401 12402This intrinsic, together with :ref:`deoptimization operand bundles 12403<deopt_opbundles>`, allow frontends to express transfer of control and 12404frame-local state from the currently executing (typically more specialized, 12405hence faster) version of a function into another (typically more generic, hence 12406slower) version. 12407 12408In languages with a fully integrated managed runtime like Java and JavaScript 12409this intrinsic can be used to implement "uncommon trap" or "side exit" like 12410functionality. In unmanaged languages like C and C++, this intrinsic can be 12411used to represent the slow paths of specialized functions. 12412 12413 12414Arguments: 12415"""""""""" 12416 12417The intrinsic takes an arbitrary number of arguments, whose meaning is 12418decided by the :ref:`lowering strategy<deoptimize_lowering>`. 12419 12420Semantics: 12421"""""""""" 12422 12423The ``@llvm.experimental.deoptimize`` intrinsic executes an attached 12424deoptimization continuation (denoted using a :ref:`deoptimization 12425operand bundle <deopt_opbundles>`) and returns the value returned by 12426the deoptimization continuation. Defining the semantic properties of 12427the continuation itself is out of scope of the language reference -- 12428as far as LLVM is concerned, the deoptimization continuation can 12429invoke arbitrary side effects, including reading from and writing to 12430the entire heap. 12431 12432Deoptimization continuations expressed using ``"deopt"`` operand bundles always 12433continue execution to the end of the physical frame containing them, so all 12434calls to ``@llvm.experimental.deoptimize`` must be in "tail position": 12435 12436 - ``@llvm.experimental.deoptimize`` cannot be invoked. 12437 - The call must immediately precede a :ref:`ret <i_ret>` instruction. 12438 - The ``ret`` instruction must return the value produced by the 12439 ``@llvm.experimental.deoptimize`` call if there is one, or void. 12440 12441Note that the above restrictions imply that the return type for a call to 12442``@llvm.experimental.deoptimize`` will match the return type of its immediate 12443caller. 12444 12445The inliner composes the ``"deopt"`` continuations of the caller into the 12446``"deopt"`` continuations present in the inlinee, and also updates calls to this 12447intrinsic to return directly from the frame of the function it inlined into. 12448 12449All declarations of ``@llvm.experimental.deoptimize`` must share the 12450same calling convention. 12451 12452.. _deoptimize_lowering: 12453 12454Lowering: 12455""""""""" 12456 12457Calls to ``@llvm.experimental.deoptimize`` are lowered to calls to the 12458symbol ``__llvm_deoptimize`` (it is the frontend's responsibility to 12459ensure that this symbol is defined). The call arguments to 12460``@llvm.experimental.deoptimize`` are lowered as if they were formal 12461arguments of the specified types, and not as varargs. 12462 12463 12464'``llvm.experimental.guard``' Intrinsic 12465^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 12466 12467Syntax: 12468""""""" 12469 12470:: 12471 12472 declare void @llvm.experimental.guard(i1, ...) [ "deopt"(...) ] 12473 12474Overview: 12475""""""""" 12476 12477This intrinsic, together with :ref:`deoptimization operand bundles 12478<deopt_opbundles>`, allows frontends to express guards or checks on 12479optimistic assumptions made during compilation. The semantics of 12480``@llvm.experimental.guard`` is defined in terms of 12481``@llvm.experimental.deoptimize`` -- its body is defined to be 12482equivalent to: 12483 12484.. code-block:: llvm 12485 12486 define void @llvm.experimental.guard(i1 %pred, <args...>) { 12487 %realPred = and i1 %pred, undef 12488 br i1 %realPred, label %continue, label %leave [, !make.implicit !{}] 12489 12490 leave: 12491 call void @llvm.experimental.deoptimize(<args...>) [ "deopt"() ] 12492 ret void 12493 12494 continue: 12495 ret void 12496 } 12497 12498 12499with the optional ``[, !make.implicit !{}]`` present if and only if it 12500is present on the call site. For more details on ``!make.implicit``, 12501see :doc:`FaultMaps`. 12502 12503In words, ``@llvm.experimental.guard`` executes the attached 12504``"deopt"`` continuation if (but **not** only if) its first argument 12505is ``false``. Since the optimizer is allowed to replace the ``undef`` 12506with an arbitrary value, it can optimize guard to fail "spuriously", 12507i.e. without the original condition being false (hence the "not only 12508if"); and this allows for "check widening" type optimizations. 12509 12510``@llvm.experimental.guard`` cannot be invoked. 12511 12512 12513'``llvm.load.relative``' Intrinsic 12514^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 12515 12516Syntax: 12517""""""" 12518 12519:: 12520 12521 declare i8* @llvm.load.relative.iN(i8* %ptr, iN %offset) argmemonly nounwind readonly 12522 12523Overview: 12524""""""""" 12525 12526This intrinsic loads a 32-bit value from the address ``%ptr + %offset``, 12527adds ``%ptr`` to that value and returns it. The constant folder specifically 12528recognizes the form of this intrinsic and the constant initializers it may 12529load from; if a loaded constant initializer is known to have the form 12530``i32 trunc(x - %ptr)``, the intrinsic call is folded to ``x``. 12531 12532LLVM provides that the calculation of such a constant initializer will 12533not overflow at link time under the medium code model if ``x`` is an 12534``unnamed_addr`` function. However, it does not provide this guarantee for 12535a constant initializer folded into a function body. This intrinsic can be 12536used to avoid the possibility of overflows when loading from such a constant. 12537 12538Stack Map Intrinsics 12539-------------------- 12540 12541LLVM provides experimental intrinsics to support runtime patching 12542mechanisms commonly desired in dynamic language JITs. These intrinsics 12543are described in :doc:`StackMaps`. 12544