1 ============================== 2 LLVM Language Reference Manual 3 ============================== 4 5 .. contents:: 6 :local: 7 :depth: 3 8 9 Abstract 10 ======== 11 12 This document is a reference manual for the LLVM assembly language. LLVM 13 is a Static Single Assignment (SSA) based representation that provides 14 type safety, low-level operations, flexibility, and the capability of 15 representing 'all' high-level languages cleanly. It is the common code 16 representation used throughout all phases of the LLVM compilation 17 strategy. 18 19 Introduction 20 ============ 21 22 The LLVM code representation is designed to be used in three different 23 forms: as an in-memory compiler IR, as an on-disk bitcode representation 24 (suitable for fast loading by a Just-In-Time compiler), and as a human 25 readable assembly language representation. This allows LLVM to provide a 26 powerful intermediate representation for efficient compiler 27 transformations and analysis, while providing a natural means to debug 28 and visualize the transformations. The three different forms of LLVM are 29 all equivalent. This document describes the human readable 30 representation and notation. 31 32 The LLVM representation aims to be light-weight and low-level while 33 being expressive, typed, and extensible at the same time. It aims to be 34 a "universal IR" of sorts, by being at a low enough level that 35 high-level ideas may be cleanly mapped to it (similar to how 36 microprocessors are "universal IR's", allowing many source languages to 37 be mapped to them). By providing type information, LLVM can be used as 38 the target of optimizations: for example, through pointer analysis, it 39 can be proven that a C automatic variable is never accessed outside of 40 the current function, allowing it to be promoted to a simple SSA value 41 instead of a memory location. 42 43 .. _wellformed: 44 45 Well-Formedness 46 --------------- 47 48 It is important to note that this document describes 'well formed' LLVM 49 assembly language. There is a difference between what the parser accepts 50 and what is considered 'well formed'. For example, the following 51 instruction is syntactically okay, but not well formed: 52 53 .. code-block:: llvm 54 55 %x = add i32 1, %x 56 57 because the definition of ``%x`` does not dominate all of its uses. The 58 LLVM infrastructure provides a verification pass that may be used to 59 verify that an LLVM module is well formed. This pass is automatically 60 run by the parser after parsing input assembly and by the optimizer 61 before it outputs bitcode. The violations pointed out by the verifier 62 pass indicate bugs in transformation passes or input to the parser. 63 64 .. _identifiers: 65 66 Identifiers 67 =========== 68 69 LLVM identifiers come in two basic types: global and local. Global 70 identifiers (functions, global variables) begin with the ``'@'`` 71 character. Local identifiers (register names, types) begin with the 72 ``'%'`` character. Additionally, there are three different formats for 73 identifiers, for different purposes: 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 which require other 79 characters in their names can be surrounded with quotes. Special 80 characters may be escaped using ``"\xx"`` where ``xx`` is the ASCII 81 code for the character in hexadecimal. In this way, any character can 82 be used in a name value, even quotes themselves. 83 #. Unnamed values are represented as an unsigned numeric value with 84 their prefix. For example, ``%12``, ``@2``, ``%44``. 85 #. Constants, which are described in the section Constants_ below. 86 87 LLVM requires that values start with a prefix for two reasons: Compilers 88 don't need to worry about name clashes with reserved words, and the set 89 of reserved words may be expanded in the future without penalty. 90 Additionally, unnamed identifiers allow a compiler to quickly come up 91 with a temporary variable without having to avoid symbol table 92 conflicts. 93 94 Reserved words in LLVM are very similar to reserved words in other 95 languages. There are keywords for different opcodes ('``add``', 96 '``bitcast``', '``ret``', etc...), for primitive type names ('``void``', 97 '``i32``', etc...), and others. These reserved words cannot conflict 98 with variable names, because none of them start with a prefix character 99 (``'%'`` or ``'@'``). 100 101 Here is an example of LLVM code to multiply the integer variable 102 '``%X``' by 8: 103 104 The easy way: 105 106 .. code-block:: llvm 107 108 %result = mul i32 %X, 8 109 110 After strength reduction: 111 112 .. code-block:: llvm 113 114 %result = shl i32 %X, 3 115 116 And the hard way: 117 118 .. code-block:: llvm 119 120 %0 = add i32 %X, %X ; yields {i32}:%0 121 %1 = add i32 %0, %0 ; yields {i32}:%1 122 %result = add i32 %1, %1 123 124 This last way of multiplying ``%X`` by 8 illustrates several important 125 lexical features of LLVM: 126 127 #. Comments are delimited with a '``;``' and go until the end of line. 128 #. Unnamed temporaries are created when the result of a computation is 129 not assigned to a named value. 130 #. Unnamed temporaries are numbered sequentially (using a per-function 131 incrementing counter, starting with 0). 132 133 It also shows a convention that we follow in this document. When 134 demonstrating instructions, we will follow an instruction with a comment 135 that defines the type and name of value produced. 136 137 High Level Structure 138 ==================== 139 140 Module Structure 141 ---------------- 142 143 LLVM programs are composed of ``Module``'s, each of which is a 144 translation unit of the input programs. Each module consists of 145 functions, global variables, and symbol table entries. Modules may be 146 combined together with the LLVM linker, which merges function (and 147 global variable) definitions, resolves forward declarations, and merges 148 symbol table entries. Here is an example of the "hello world" module: 149 150 .. code-block:: llvm 151 152 ; Declare the string constant as a global constant. 153 @.str = private unnamed_addr constant [13 x i8] c"hello world\0A\00" 154 155 ; External declaration of the puts function 156 declare i32 @puts(i8* nocapture) nounwind 157 158 ; Definition of main function 159 define i32 @main() { ; i32()* 160 ; Convert [13 x i8]* to i8 *... 161 %cast210 = getelementptr [13 x i8]* @.str, i64 0, i64 0 162 163 ; Call puts function to write out the string to stdout. 164 call i32 @puts(i8* %cast210) 165 ret i32 0 166 } 167 168 ; Named metadata 169 !1 = metadata !{i32 42} 170 !foo = !{!1, null} 171 172 This example is made up of a :ref:`global variable <globalvars>` named 173 "``.str``", an external declaration of the "``puts``" function, a 174 :ref:`function definition <functionstructure>` for "``main``" and 175 :ref:`named metadata <namedmetadatastructure>` "``foo``". 176 177 In general, a module is made up of a list of global values (where both 178 functions and global variables are global values). Global values are 179 represented by a pointer to a memory location (in this case, a pointer 180 to an array of char, and a pointer to a function), and have one of the 181 following :ref:`linkage types <linkage>`. 182 183 .. _linkage: 184 185 Linkage Types 186 ------------- 187 188 All Global Variables and Functions have one of the following types of 189 linkage: 190 191 ``private`` 192 Global values with "``private``" linkage are only directly 193 accessible by objects in the current module. In particular, linking 194 code into a module with an private global value may cause the 195 private to be renamed as necessary to avoid collisions. Because the 196 symbol is private to the module, all references can be updated. This 197 doesn't show up in any symbol table in the object file. 198 ``linker_private`` 199 Similar to ``private``, but the symbol is passed through the 200 assembler and evaluated by the linker. Unlike normal strong symbols, 201 they are removed by the linker from the final linked image 202 (executable or dynamic library). 203 ``linker_private_weak`` 204 Similar to "``linker_private``", but the symbol is weak. Note that 205 ``linker_private_weak`` symbols are subject to coalescing by the 206 linker. The symbols are removed by the linker from the final linked 207 image (executable or dynamic library). 208 ``internal`` 209 Similar to private, but the value shows as a local symbol 210 (``STB_LOCAL`` in the case of ELF) in the object file. This 211 corresponds to the notion of the '``static``' keyword in C. 212 ``available_externally`` 213 Globals with "``available_externally``" linkage are never emitted 214 into the object file corresponding to the LLVM module. They exist to 215 allow inlining and other optimizations to take place given knowledge 216 of the definition of the global, which is known to be somewhere 217 outside the module. Globals with ``available_externally`` linkage 218 are allowed to be discarded at will, and are otherwise the same as 219 ``linkonce_odr``. This linkage type is only allowed on definitions, 220 not declarations. 221 ``linkonce`` 222 Globals with "``linkonce``" linkage are merged with other globals of 223 the same name when linkage occurs. This can be used to implement 224 some forms of inline functions, templates, or other code which must 225 be generated in each translation unit that uses it, but where the 226 body may be overridden with a more definitive definition later. 227 Unreferenced ``linkonce`` globals are allowed to be discarded. Note 228 that ``linkonce`` linkage does not actually allow the optimizer to 229 inline the body of this function into callers because it doesn't 230 know if this definition of the function is the definitive definition 231 within the program or whether it will be overridden by a stronger 232 definition. To enable inlining and other optimizations, use 233 "``linkonce_odr``" linkage. 234 ``weak`` 235 "``weak``" linkage has the same merging semantics as ``linkonce`` 236 linkage, except that unreferenced globals with ``weak`` linkage may 237 not be discarded. This is used for globals that are declared "weak" 238 in C source code. 239 ``common`` 240 "``common``" linkage is most similar to "``weak``" linkage, but they 241 are used for tentative definitions in C, such as "``int X;``" at 242 global scope. Symbols with "``common``" linkage are merged in the 243 same way as ``weak symbols``, and they may not be deleted if 244 unreferenced. ``common`` symbols may not have an explicit section, 245 must have a zero initializer, and may not be marked 246 ':ref:`constant <globalvars>`'. Functions and aliases may not have 247 common linkage. 248 249 .. _linkage_appending: 250 251 ``appending`` 252 "``appending``" linkage may only be applied to global variables of 253 pointer to array type. When two global variables with appending 254 linkage are linked together, the two global arrays are appended 255 together. This is the LLVM, typesafe, equivalent of having the 256 system linker append together "sections" with identical names when 257 .o files are linked. 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 ``linkonce_odr_auto_hide`` 271 Similar to "``linkonce_odr``", but nothing in the translation unit 272 takes the address of this definition. For instance, functions that 273 had an inline definition, but the compiler decided not to inline it. 274 ``linkonce_odr_auto_hide`` may have only ``default`` visibility. The 275 symbols are removed by the linker from the final linked image 276 (executable or dynamic library). 277 ``external`` 278 If none of the above identifiers are used, the global is externally 279 visible, meaning that it participates in linkage and can be used to 280 resolve external symbol references. 281 282 The next two types of linkage are targeted for Microsoft Windows 283 platform only. They are designed to support importing (exporting) 284 symbols from (to) DLLs (Dynamic Link Libraries). 285 286 ``dllimport`` 287 "``dllimport``" linkage causes the compiler to reference a function 288 or variable via a global pointer to a pointer that is set up by the 289 DLL exporting the symbol. On Microsoft Windows targets, the pointer 290 name is formed by combining ``__imp_`` and the function or variable 291 name. 292 ``dllexport`` 293 "``dllexport``" linkage causes the compiler to provide a global 294 pointer to a pointer in a DLL, so that it can be referenced with the 295 ``dllimport`` attribute. On Microsoft Windows targets, the pointer 296 name is formed by combining ``__imp_`` and the function or variable 297 name. 298 299 For example, since the "``.LC0``" variable is defined to be internal, if 300 another module defined a "``.LC0``" variable and was linked with this 301 one, one of the two would be renamed, preventing a collision. Since 302 "``main``" and "``puts``" are external (i.e., lacking any linkage 303 declarations), they are accessible outside of the current module. 304 305 It is illegal for a function *declaration* to have any linkage type 306 other than ``external``, ``dllimport`` or ``extern_weak``. 307 308 Aliases can have only ``external``, ``internal``, ``weak`` or 309 ``weak_odr`` linkages. 310 311 .. _callingconv: 312 313 Calling Conventions 314 ------------------- 315 316 LLVM :ref:`functions <functionstructure>`, :ref:`calls <i_call>` and 317 :ref:`invokes <i_invoke>` can all have an optional calling convention 318 specified for the call. The calling convention of any pair of dynamic 319 caller/callee must match, or the behavior of the program is undefined. 320 The following calling conventions are supported by LLVM, and more may be 321 added in the future: 322 323 "``ccc``" - The C calling convention 324 This calling convention (the default if no other calling convention 325 is specified) matches the target C calling conventions. This calling 326 convention supports varargs function calls and tolerates some 327 mismatch in the declared prototype and implemented declaration of 328 the function (as does normal C). 329 "``fastcc``" - The fast calling convention 330 This calling convention attempts to make calls as fast as possible 331 (e.g. by passing things in registers). This calling convention 332 allows the target to use whatever tricks it wants to produce fast 333 code for the target, without having to conform to an externally 334 specified ABI (Application Binary Interface). `Tail calls can only 335 be optimized when this, the GHC or the HiPE convention is 336 used. <CodeGenerator.html#id80>`_ This calling convention does not 337 support varargs and requires the prototype of all callees to exactly 338 match the prototype of the function definition. 339 "``coldcc``" - The cold calling convention 340 This calling convention attempts to make code in the caller as 341 efficient as possible under the assumption that the call is not 342 commonly executed. As such, these calls often preserve all registers 343 so that the call does not break any live ranges in the caller side. 344 This calling convention does not support varargs and requires the 345 prototype of all callees to exactly match the prototype of the 346 function definition. 347 "``cc 10``" - GHC convention 348 This calling convention has been implemented specifically for use by 349 the `Glasgow Haskell Compiler (GHC) <http://www.haskell.org/ghc>`_. 350 It passes everything in registers, going to extremes to achieve this 351 by disabling callee save registers. This calling convention should 352 not be used lightly but only for specific situations such as an 353 alternative to the *register pinning* performance technique often 354 used when implementing functional programming languages. At the 355 moment only X86 supports this convention and it has the following 356 limitations: 357 358 - On *X86-32* only supports up to 4 bit type parameters. No 359 floating point types are supported. 360 - On *X86-64* only supports up to 10 bit type parameters and 6 361 floating point parameters. 362 363 This calling convention supports `tail call 364 optimization <CodeGenerator.html#id80>`_ but requires both the 365 caller and callee are using it. 366 "``cc 11``" - The HiPE calling convention 367 This calling convention has been implemented specifically for use by 368 the `High-Performance Erlang 369 (HiPE) <http://www.it.uu.se/research/group/hipe/>`_ compiler, *the* 370 native code compiler of the `Ericsson's Open Source Erlang/OTP 371 system <http://www.erlang.org/download.shtml>`_. It uses more 372 registers for argument passing than the ordinary C calling 373 convention and defines no callee-saved registers. The calling 374 convention properly supports `tail call 375 optimization <CodeGenerator.html#id80>`_ but requires that both the 376 caller and the callee use it. It uses a *register pinning* 377 mechanism, similar to GHC's convention, for keeping frequently 378 accessed runtime components pinned to specific hardware registers. 379 At the moment only X86 supports this convention (both 32 and 64 380 bit). 381 "``cc <n>``" - Numbered convention 382 Any calling convention may be specified by number, allowing 383 target-specific calling conventions to be used. Target specific 384 calling conventions start at 64. 385 386 More calling conventions can be added/defined on an as-needed basis, to 387 support Pascal conventions or any other well-known target-independent 388 convention. 389 390 .. _visibilitystyles: 391 392 Visibility Styles 393 ----------------- 394 395 All Global Variables and Functions have one of the following visibility 396 styles: 397 398 "``default``" - Default style 399 On targets that use the ELF object file format, default visibility 400 means that the declaration is visible to other modules and, in 401 shared libraries, means that the declared entity may be overridden. 402 On Darwin, default visibility means that the declaration is visible 403 to other modules. Default visibility corresponds to "external 404 linkage" in the language. 405 "``hidden``" - Hidden style 406 Two declarations of an object with hidden visibility refer to the 407 same object if they are in the same shared object. Usually, hidden 408 visibility indicates that the symbol will not be placed into the 409 dynamic symbol table, so no other module (executable or shared 410 library) can reference it directly. 411 "``protected``" - Protected style 412 On ELF, protected visibility indicates that the symbol will be 413 placed in the dynamic symbol table, but that references within the 414 defining module will bind to the local symbol. That is, the symbol 415 cannot be overridden by another module. 416 417 .. _namedtypes: 418 419 Named Types 420 ----------- 421 422 LLVM IR allows you to specify name aliases for certain types. This can 423 make it easier to read the IR and make the IR more condensed 424 (particularly when recursive types are involved). An example of a name 425 specification is: 426 427 .. code-block:: llvm 428 429 %mytype = type { %mytype*, i32 } 430 431 You may give a name to any :ref:`type <typesystem>` except 432 ":ref:`void <t_void>`". Type name aliases may be used anywhere a type is 433 expected with the syntax "%mytype". 434 435 Note that type names are aliases for the structural type that they 436 indicate, and that you can therefore specify multiple names for the same 437 type. This often leads to confusing behavior when dumping out a .ll 438 file. Since LLVM IR uses structural typing, the name is not part of the 439 type. When printing out LLVM IR, the printer will pick *one name* to 440 render all types of a particular shape. This means that if you have code 441 where two different source types end up having the same LLVM type, that 442 the dumper will sometimes print the "wrong" or unexpected type. This is 443 an important design point and isn't going to change. 444 445 .. _globalvars: 446 447 Global Variables 448 ---------------- 449 450 Global variables define regions of memory allocated at compilation time 451 instead of run-time. Global variables may optionally be initialized, may 452 have an explicit section to be placed in, and may have an optional 453 explicit alignment specified. 454 455 A variable may be defined as ``thread_local``, which means that it will 456 not be shared by threads (each thread will have a separated copy of the 457 variable). Not all targets support thread-local variables. Optionally, a 458 TLS model may be specified: 459 460 ``localdynamic`` 461 For variables that are only used within the current shared library. 462 ``initialexec`` 463 For variables in modules that will not be loaded dynamically. 464 ``localexec`` 465 For variables defined in the executable and only used within it. 466 467 The models correspond to the ELF TLS models; see `ELF Handling For 468 Thread-Local Storage <http://people.redhat.com/drepper/tls.pdf>`_ for 469 more information on under which circumstances the different models may 470 be used. The target may choose a different TLS model if the specified 471 model is not supported, or if a better choice of model can be made. 472 473 A variable may be defined as a global ``constant``, which indicates that 474 the contents of the variable will **never** be modified (enabling better 475 optimization, allowing the global data to be placed in the read-only 476 section of an executable, etc). Note that variables that need runtime 477 initialization cannot be marked ``constant`` as there is a store to the 478 variable. 479 480 LLVM explicitly allows *declarations* of global variables to be marked 481 constant, even if the final definition of the global is not. This 482 capability can be used to enable slightly better optimization of the 483 program, but requires the language definition to guarantee that 484 optimizations based on the 'constantness' are valid for the translation 485 units that do not include the definition. 486 487 As SSA values, global variables define pointer values that are in scope 488 (i.e. they dominate) all basic blocks in the program. Global variables 489 always define a pointer to their "content" type because they describe a 490 region of memory, and all memory objects in LLVM are accessed through 491 pointers. 492 493 Global variables can be marked with ``unnamed_addr`` which indicates 494 that the address is not significant, only the content. Constants marked 495 like this can be merged with other constants if they have the same 496 initializer. Note that a constant with significant address *can* be 497 merged with a ``unnamed_addr`` constant, the result being a constant 498 whose address is significant. 499 500 A global variable may be declared to reside in a target-specific 501 numbered address space. For targets that support them, address spaces 502 may affect how optimizations are performed and/or what target 503 instructions are used to access the variable. The default address space 504 is zero. The address space qualifier must precede any other attributes. 505 506 LLVM allows an explicit section to be specified for globals. If the 507 target supports it, it will emit globals to the section specified. 508 509 By default, global initializers are optimized by assuming that global 510 variables defined within the module are not modified from their 511 initial values before the start of the global initializer. This is 512 true even for variables potentially accessible from outside the 513 module, including those with external linkage or appearing in 514 ``@llvm.used``. This assumption may be suppressed by marking the 515 variable with ``externally_initialized``. 516 517 An explicit alignment may be specified for a global, which must be a 518 power of 2. If not present, or if the alignment is set to zero, the 519 alignment of the global is set by the target to whatever it feels 520 convenient. If an explicit alignment is specified, the global is forced 521 to have exactly that alignment. Targets and optimizers are not allowed 522 to over-align the global if the global has an assigned section. In this 523 case, the extra alignment could be observable: for example, code could 524 assume that the globals are densely packed in their section and try to 525 iterate over them as an array, alignment padding would break this 526 iteration. 527 528 For example, the following defines a global in a numbered address space 529 with an initializer, section, and alignment: 530 531 .. code-block:: llvm 532 533 @G = addrspace(5) constant float 1.0, section "foo", align 4 534 535 The following example defines a thread-local global with the 536 ``initialexec`` TLS model: 537 538 .. code-block:: llvm 539 540 @G = thread_local(initialexec) global i32 0, align 4 541 542 .. _functionstructure: 543 544 Functions 545 --------- 546 547 LLVM function definitions consist of the "``define``" keyword, an 548 optional :ref:`linkage type <linkage>`, an optional :ref:`visibility 549 style <visibility>`, an optional :ref:`calling convention <callingconv>`, 550 an optional ``unnamed_addr`` attribute, a return type, an optional 551 :ref:`parameter attribute <paramattrs>` for the return type, a function 552 name, a (possibly empty) argument list (each with optional :ref:`parameter 553 attributes <paramattrs>`), optional :ref:`function attributes <fnattrs>`, 554 an optional section, an optional alignment, an optional :ref:`garbage 555 collector name <gc>`, an opening curly brace, a list of basic blocks, 556 and a closing curly brace. 557 558 LLVM function declarations consist of the "``declare``" keyword, an 559 optional :ref:`linkage type <linkage>`, an optional :ref:`visibility 560 style <visibility>`, an optional :ref:`calling convention <callingconv>`, 561 an optional ``unnamed_addr`` attribute, a return type, an optional 562 :ref:`parameter attribute <paramattrs>` for the return type, a function 563 name, a possibly empty list of arguments, an optional alignment, and an 564 optional :ref:`garbage collector name <gc>`. 565 566 A function definition contains a list of basic blocks, forming the CFG 567 (Control Flow Graph) for the function. Each basic block may optionally 568 start with a label (giving the basic block a symbol table entry), 569 contains a list of instructions, and ends with a 570 :ref:`terminator <terminators>` instruction (such as a branch or function 571 return). If explicit label is not provided, a block is assigned an 572 implicit numbered label, using a next value from the same counter as used 573 for unnamed temporaries (:ref:`see above<identifiers>`). For example, if a 574 function entry block does not have explicit label, it will be assigned 575 label "%0", then first unnamed temporary in that block will be "%1", etc. 576 577 The first basic block in a function is special in two ways: it is 578 immediately executed on entrance to the function, and it is not allowed 579 to have predecessor basic blocks (i.e. there can not be any branches to 580 the entry block of a function). Because the block can have no 581 predecessors, it also cannot have any :ref:`PHI nodes <i_phi>`. 582 583 LLVM allows an explicit section to be specified for functions. If the 584 target supports it, it will emit functions to the section specified. 585 586 An explicit alignment may be specified for a function. If not present, 587 or if the alignment is set to zero, the alignment of the function is set 588 by the target to whatever it feels convenient. If an explicit alignment 589 is specified, the function is forced to have at least that much 590 alignment. All alignments must be a power of 2. 591 592 If the ``unnamed_addr`` attribute is given, the address is know to not 593 be significant and two identical functions can be merged. 594 595 Syntax:: 596 597 define [linkage] [visibility] 598 [cconv] [ret attrs] 599 <ResultType> @<FunctionName> ([argument list]) 600 [fn Attrs] [section "name"] [align N] 601 [gc] { ... } 602 603 .. _langref_aliases: 604 605 Aliases 606 ------- 607 608 Aliases act as "second name" for the aliasee value (which can be either 609 function, global variable, another alias or bitcast of global value). 610 Aliases may have an optional :ref:`linkage type <linkage>`, and an optional 611 :ref:`visibility style <visibility>`. 612 613 Syntax:: 614 615 @<Name> = alias [Linkage] [Visibility] <AliaseeTy> @<Aliasee> 616 617 .. _namedmetadatastructure: 618 619 Named Metadata 620 -------------- 621 622 Named metadata is a collection of metadata. :ref:`Metadata 623 nodes <metadata>` (but not metadata strings) are the only valid 624 operands for a named metadata. 625 626 Syntax:: 627 628 ; Some unnamed metadata nodes, which are referenced by the named metadata. 629 !0 = metadata !{metadata !"zero"} 630 !1 = metadata !{metadata !"one"} 631 !2 = metadata !{metadata !"two"} 632 ; A named metadata. 633 !name = !{!0, !1, !2} 634 635 .. _paramattrs: 636 637 Parameter Attributes 638 -------------------- 639 640 The return type and each parameter of a function type may have a set of 641 *parameter attributes* associated with them. Parameter attributes are 642 used to communicate additional information about the result or 643 parameters of a function. Parameter attributes are considered to be part 644 of the function, not of the function type, so functions with different 645 parameter attributes can have the same function type. 646 647 Parameter attributes are simple keywords that follow the type specified. 648 If multiple parameter attributes are needed, they are space separated. 649 For example: 650 651 .. code-block:: llvm 652 653 declare i32 @printf(i8* noalias nocapture, ...) 654 declare i32 @atoi(i8 zeroext) 655 declare signext i8 @returns_signed_char() 656 657 Note that any attributes for the function result (``nounwind``, 658 ``readonly``) come immediately after the argument list. 659 660 Currently, only the following parameter attributes are defined: 661 662 ``zeroext`` 663 This indicates to the code generator that the parameter or return 664 value should be zero-extended to the extent required by the target's 665 ABI (which is usually 32-bits, but is 8-bits for a i1 on x86-64) by 666 the caller (for a parameter) or the callee (for a return value). 667 ``signext`` 668 This indicates to the code generator that the parameter or return 669 value should be sign-extended to the extent required by the target's 670 ABI (which is usually 32-bits) by the caller (for a parameter) or 671 the callee (for a return value). 672 ``inreg`` 673 This indicates that this parameter or return value should be treated 674 in a special target-dependent fashion during while emitting code for 675 a function call or return (usually, by putting it in a register as 676 opposed to memory, though some targets use it to distinguish between 677 two different kinds of registers). Use of this attribute is 678 target-specific. 679 ``byval`` 680 This indicates that the pointer parameter should really be passed by 681 value to the function. The attribute implies that a hidden copy of 682 the pointee is made between the caller and the callee, so the callee 683 is unable to modify the value in the caller. This attribute is only 684 valid on LLVM pointer arguments. It is generally used to pass 685 structs and arrays by value, but is also valid on pointers to 686 scalars. The copy is considered to belong to the caller not the 687 callee (for example, ``readonly`` functions should not write to 688 ``byval`` parameters). This is not a valid attribute for return 689 values. 690 691 The byval attribute also supports specifying an alignment with the 692 align attribute. It indicates the alignment of the stack slot to 693 form and the known alignment of the pointer specified to the call 694 site. If the alignment is not specified, then the code generator 695 makes a target-specific assumption. 696 697 ``sret`` 698 This indicates that the pointer parameter specifies the address of a 699 structure that is the return value of the function in the source 700 program. This pointer must be guaranteed by the caller to be valid: 701 loads and stores to the structure may be assumed by the callee 702 not to trap and to be properly aligned. This may only be applied to 703 the first parameter. This is not a valid attribute for return 704 values. 705 ``noalias`` 706 This indicates that pointer values :ref:`based <pointeraliasing>` on 707 the argument or return value do not alias pointer values which are 708 not *based* on it, ignoring certain "irrelevant" dependencies. For a 709 call to the parent function, dependencies between memory references 710 from before or after the call and from those during the call are 711 "irrelevant" to the ``noalias`` keyword for the arguments and return 712 value used in that call. The caller shares the responsibility with 713 the callee for ensuring that these requirements are met. For further 714 details, please see the discussion of the NoAlias response in `alias 715 analysis <AliasAnalysis.html#MustMayNo>`_. 716 717 Note that this definition of ``noalias`` is intentionally similar 718 to the definition of ``restrict`` in C99 for function arguments, 719 though it is slightly weaker. 720 721 For function return values, C99's ``restrict`` is not meaningful, 722 while LLVM's ``noalias`` is. 723 ``nocapture`` 724 This indicates that the callee does not make any copies of the 725 pointer that outlive the callee itself. This is not a valid 726 attribute for return values. 727 728 .. _nest: 729 730 ``nest`` 731 This indicates that the pointer parameter can be excised using the 732 :ref:`trampoline intrinsics <int_trampoline>`. This is not a valid 733 attribute for return values and can only be applied to one parameter. 734 735 ``returned`` 736 This indicates that the function always returns the argument as its return 737 value. This is an optimization hint to the code generator when generating 738 the caller, allowing tail call optimization and omission of register saves 739 and restores in some cases; it is not checked or enforced when generating 740 the callee. The parameter and the function return type must be valid 741 operands for the :ref:`bitcast instruction <i_bitcast>`. This is not a 742 valid attribute for return values and can only be applied to one parameter. 743 744 .. _gc: 745 746 Garbage Collector Names 747 ----------------------- 748 749 Each function may specify a garbage collector name, which is simply a 750 string: 751 752 .. code-block:: llvm 753 754 define void @f() gc "name" { ... } 755 756 The compiler declares the supported values of *name*. Specifying a 757 collector which will cause the compiler to alter its output in order to 758 support the named garbage collection algorithm. 759 760 .. _attrgrp: 761 762 Attribute Groups 763 ---------------- 764 765 Attribute groups are groups of attributes that are referenced by objects within 766 the IR. They are important for keeping ``.ll`` files readable, because a lot of 767 functions will use the same set of attributes. In the degenerative case of a 768 ``.ll`` file that corresponds to a single ``.c`` file, the single attribute 769 group will capture the important command line flags used to build that file. 770 771 An attribute group is a module-level object. To use an attribute group, an 772 object references the attribute group's ID (e.g. ``#37``). An object may refer 773 to more than one attribute group. In that situation, the attributes from the 774 different groups are merged. 775 776 Here is an example of attribute groups for a function that should always be 777 inlined, has a stack alignment of 4, and which shouldn't use SSE instructions: 778 779 .. code-block:: llvm 780 781 ; Target-independent attributes: 782 attributes #0 = { alwaysinline alignstack=4 } 783 784 ; Target-dependent attributes: 785 attributes #1 = { "no-sse" } 786 787 ; Function @f has attributes: alwaysinline, alignstack=4, and "no-sse". 788 define void @f() #0 #1 { ... } 789 790 .. _fnattrs: 791 792 Function Attributes 793 ------------------- 794 795 Function attributes are set to communicate additional information about 796 a function. Function attributes are considered to be part of the 797 function, not of the function type, so functions with different function 798 attributes can have the same function type. 799 800 Function attributes are simple keywords that follow the type specified. 801 If multiple attributes are needed, they are space separated. For 802 example: 803 804 .. code-block:: llvm 805 806 define void @f() noinline { ... } 807 define void @f() alwaysinline { ... } 808 define void @f() alwaysinline optsize { ... } 809 define void @f() optsize { ... } 810 811 ``alignstack(<n>)`` 812 This attribute indicates that, when emitting the prologue and 813 epilogue, the backend should forcibly align the stack pointer. 814 Specify the desired alignment, which must be a power of two, in 815 parentheses. 816 ``alwaysinline`` 817 This attribute indicates that the inliner should attempt to inline 818 this function into callers whenever possible, ignoring any active 819 inlining size threshold for this caller. 820 ``builtin`` 821 This indicates that the callee function at a call site should be 822 recognized as a built-in function, even though the function's declaration 823 uses the ``nobuiltin`` attribute. This is only valid at call sites for 824 direct calls to functions which are declared with the ``nobuiltin`` 825 attribute. 826 ``cold`` 827 This attribute indicates that this function is rarely called. When 828 computing edge weights, basic blocks post-dominated by a cold 829 function call are also considered to be cold; and, thus, given low 830 weight. 831 ``inlinehint`` 832 This attribute indicates that the source code contained a hint that 833 inlining this function is desirable (such as the "inline" keyword in 834 C/C++). It is just a hint; it imposes no requirements on the 835 inliner. 836 ``naked`` 837 This attribute disables prologue / epilogue emission for the 838 function. This can have very system-specific consequences. 839 ``nobuiltin`` 840 This indicates that the callee function at a call site is not recognized as 841 a built-in function. LLVM will retain the original call and not replace it 842 with equivalent code based on the semantics of the built-in function, unless 843 the call site uses the ``builtin`` attribute. This is valid at call sites 844 and on function declarations and definitions. 845 ``noduplicate`` 846 This attribute indicates that calls to the function cannot be 847 duplicated. A call to a ``noduplicate`` function may be moved 848 within its parent function, but may not be duplicated within 849 its parent function. 850 851 A function containing a ``noduplicate`` call may still 852 be an inlining candidate, provided that the call is not 853 duplicated by inlining. That implies that the function has 854 internal linkage and only has one call site, so the original 855 call is dead after inlining. 856 ``noimplicitfloat`` 857 This attributes disables implicit floating point instructions. 858 ``noinline`` 859 This attribute indicates that the inliner should never inline this 860 function in any situation. This attribute may not be used together 861 with the ``alwaysinline`` attribute. 862 ``nonlazybind`` 863 This attribute suppresses lazy symbol binding for the function. This 864 may make calls to the function faster, at the cost of extra program 865 startup time if the function is not called during program startup. 866 ``noredzone`` 867 This attribute indicates that the code generator should not use a 868 red zone, even if the target-specific ABI normally permits it. 869 ``noreturn`` 870 This function attribute indicates that the function never returns 871 normally. This produces undefined behavior at runtime if the 872 function ever does dynamically return. 873 ``nounwind`` 874 This function attribute indicates that the function never returns 875 with an unwind or exceptional control flow. If the function does 876 unwind, its runtime behavior is undefined. 877 ``optsize`` 878 This attribute suggests that optimization passes and code generator 879 passes make choices that keep the code size of this function low, 880 and otherwise do optimizations specifically to reduce code size. 881 ``readnone`` 882 On a function, this attribute indicates that the function computes its 883 result (or decides to unwind an exception) based strictly on its arguments, 884 without dereferencing any pointer arguments or otherwise accessing 885 any mutable state (e.g. memory, control registers, etc) visible to 886 caller functions. It does not write through any pointer arguments 887 (including ``byval`` arguments) and never changes any state visible 888 to callers. This means that it cannot unwind exceptions by calling 889 the ``C++`` exception throwing methods. 890 891 On an argument, this attribute indicates that the function does not 892 dereference that pointer argument, even though it may read or write the 893 memory that the pointer points to if accessed through other pointers. 894 ``readonly`` 895 On a function, this attribute indicates that the function does not write 896 through any pointer arguments (including ``byval`` arguments) or otherwise 897 modify any state (e.g. memory, control registers, etc) visible to 898 caller functions. It may dereference pointer arguments and read 899 state that may be set in the caller. A readonly function always 900 returns the same value (or unwinds an exception identically) when 901 called with the same set of arguments and global state. It cannot 902 unwind an exception by calling the ``C++`` exception throwing 903 methods. 904 905 On an argument, this attribute indicates that the function does not write 906 through this pointer argument, even though it may write to the memory that 907 the pointer points to. 908 ``returns_twice`` 909 This attribute indicates that this function can return twice. The C 910 ``setjmp`` is an example of such a function. The compiler disables 911 some optimizations (like tail calls) in the caller of these 912 functions. 913 ``sanitize_address`` 914 This attribute indicates that AddressSanitizer checks 915 (dynamic address safety analysis) are enabled for this function. 916 ``sanitize_memory`` 917 This attribute indicates that MemorySanitizer checks (dynamic detection 918 of accesses to uninitialized memory) are enabled for this function. 919 ``sanitize_thread`` 920 This attribute indicates that ThreadSanitizer checks 921 (dynamic thread safety analysis) are enabled for this function. 922 ``ssp`` 923 This attribute indicates that the function should emit a stack 924 smashing protector. It is in the form of a "canary" --- a random value 925 placed on the stack before the local variables that's checked upon 926 return from the function to see if it has been overwritten. A 927 heuristic is used to determine if a function needs stack protectors 928 or not. The heuristic used will enable protectors for functions with: 929 930 - Character arrays larger than ``ssp-buffer-size`` (default 8). 931 - Aggregates containing character arrays larger than ``ssp-buffer-size``. 932 - Calls to alloca() with variable sizes or constant sizes greater than 933 ``ssp-buffer-size``. 934 935 If a function that has an ``ssp`` attribute is inlined into a 936 function that doesn't have an ``ssp`` attribute, then the resulting 937 function will have an ``ssp`` attribute. 938 ``sspreq`` 939 This attribute indicates that the function should *always* emit a 940 stack smashing protector. This overrides the ``ssp`` function 941 attribute. 942 943 If a function that has an ``sspreq`` attribute is inlined into a 944 function that doesn't have an ``sspreq`` attribute or which has an 945 ``ssp`` or ``sspstrong`` attribute, then the resulting function will have 946 an ``sspreq`` attribute. 947 ``sspstrong`` 948 This attribute indicates that the function should emit a stack smashing 949 protector. This attribute causes a strong heuristic to be used when 950 determining if a function needs stack protectors. The strong heuristic 951 will enable protectors for functions with: 952 953 - Arrays of any size and type 954 - Aggregates containing an array of any size and type. 955 - Calls to alloca(). 956 - Local variables that have had their address taken. 957 958 This overrides the ``ssp`` function attribute. 959 960 If a function that has an ``sspstrong`` attribute is inlined into a 961 function that doesn't have an ``sspstrong`` attribute, then the 962 resulting function will have an ``sspstrong`` attribute. 963 ``uwtable`` 964 This attribute indicates that the ABI being targeted requires that 965 an unwind table entry be produce for this function even if we can 966 show that no exceptions passes by it. This is normally the case for 967 the ELF x86-64 abi, but it can be disabled for some compilation 968 units. 969 970 .. _moduleasm: 971 972 Module-Level Inline Assembly 973 ---------------------------- 974 975 Modules may contain "module-level inline asm" blocks, which corresponds 976 to the GCC "file scope inline asm" blocks. These blocks are internally 977 concatenated by LLVM and treated as a single unit, but may be separated 978 in the ``.ll`` file if desired. The syntax is very simple: 979 980 .. code-block:: llvm 981 982 module asm "inline asm code goes here" 983 module asm "more can go here" 984 985 The strings can contain any character by escaping non-printable 986 characters. The escape sequence used is simply "\\xx" where "xx" is the 987 two digit hex code for the number. 988 989 The inline asm code is simply printed to the machine code .s file when 990 assembly code is generated. 991 992 .. _langref_datalayout: 993 994 Data Layout 995 ----------- 996 997 A module may specify a target specific data layout string that specifies 998 how data is to be laid out in memory. The syntax for the data layout is 999 simply: 1000 1001 .. code-block:: llvm 1002 1003 target datalayout = "layout specification" 1004 1005 The *layout specification* consists of a list of specifications 1006 separated by the minus sign character ('-'). Each specification starts 1007 with a letter and may include other information after the letter to 1008 define some aspect of the data layout. The specifications accepted are 1009 as follows: 1010 1011 ``E`` 1012 Specifies that the target lays out data in big-endian form. That is, 1013 the bits with the most significance have the lowest address 1014 location. 1015 ``e`` 1016 Specifies that the target lays out data in little-endian form. That 1017 is, the bits with the least significance have the lowest address 1018 location. 1019 ``S<size>`` 1020 Specifies the natural alignment of the stack in bits. Alignment 1021 promotion of stack variables is limited to the natural stack 1022 alignment to avoid dynamic stack realignment. The stack alignment 1023 must be a multiple of 8-bits. If omitted, the natural stack 1024 alignment defaults to "unspecified", which does not prevent any 1025 alignment promotions. 1026 ``p[n]:<size>:<abi>:<pref>`` 1027 This specifies the *size* of a pointer and its ``<abi>`` and 1028 ``<pref>``\erred alignments for address space ``n``. All sizes are in 1029 bits. Specifying the ``<pref>`` alignment is optional. If omitted, the 1030 preceding ``:`` should be omitted too. The address space, ``n`` is 1031 optional, and if not specified, denotes the default address space 0. 1032 The value of ``n`` must be in the range [1,2^23). 1033 ``i<size>:<abi>:<pref>`` 1034 This specifies the alignment for an integer type of a given bit 1035 ``<size>``. The value of ``<size>`` must be in the range [1,2^23). 1036 ``v<size>:<abi>:<pref>`` 1037 This specifies the alignment for a vector type of a given bit 1038 ``<size>``. 1039 ``f<size>:<abi>:<pref>`` 1040 This specifies the alignment for a floating point type of a given bit 1041 ``<size>``. Only values of ``<size>`` that are supported by the target 1042 will work. 32 (float) and 64 (double) are supported on all targets; 80 1043 or 128 (different flavors of long double) are also supported on some 1044 targets. 1045 ``a<size>:<abi>:<pref>`` 1046 This specifies the alignment for an aggregate type of a given bit 1047 ``<size>``. 1048 ``s<size>:<abi>:<pref>`` 1049 This specifies the alignment for a stack object of a given bit 1050 ``<size>``. 1051 ``n<size1>:<size2>:<size3>...`` 1052 This specifies a set of native integer widths for the target CPU in 1053 bits. For example, it might contain ``n32`` for 32-bit PowerPC, 1054 ``n32:64`` for PowerPC 64, or ``n8:16:32:64`` for X86-64. Elements of 1055 this set are considered to support most general arithmetic operations 1056 efficiently. 1057 1058 When constructing the data layout for a given target, LLVM starts with a 1059 default set of specifications which are then (possibly) overridden by 1060 the specifications in the ``datalayout`` keyword. The default 1061 specifications are given in this list: 1062 1063 - ``E`` - big endian 1064 - ``p:64:64:64`` - 64-bit pointers with 64-bit alignment. 1065 - ``p[n]:64:64:64`` - Other address spaces are assumed to be the 1066 same as the default address space. 1067 - ``S0`` - natural stack alignment is unspecified 1068 - ``i1:8:8`` - i1 is 8-bit (byte) aligned 1069 - ``i8:8:8`` - i8 is 8-bit (byte) aligned 1070 - ``i16:16:16`` - i16 is 16-bit aligned 1071 - ``i32:32:32`` - i32 is 32-bit aligned 1072 - ``i64:32:64`` - i64 has ABI alignment of 32-bits but preferred 1073 alignment of 64-bits 1074 - ``f16:16:16`` - half is 16-bit aligned 1075 - ``f32:32:32`` - float is 32-bit aligned 1076 - ``f64:64:64`` - double is 64-bit aligned 1077 - ``f128:128:128`` - quad is 128-bit aligned 1078 - ``v64:64:64`` - 64-bit vector is 64-bit aligned 1079 - ``v128:128:128`` - 128-bit vector is 128-bit aligned 1080 - ``a0:0:64`` - aggregates are 64-bit aligned 1081 1082 When LLVM is determining the alignment for a given type, it uses the 1083 following rules: 1084 1085 #. If the type sought is an exact match for one of the specifications, 1086 that specification is used. 1087 #. If no match is found, and the type sought is an integer type, then 1088 the smallest integer type that is larger than the bitwidth of the 1089 sought type is used. If none of the specifications are larger than 1090 the bitwidth then the largest integer type is used. For example, 1091 given the default specifications above, the i7 type will use the 1092 alignment of i8 (next largest) while both i65 and i256 will use the 1093 alignment of i64 (largest specified). 1094 #. If no match is found, and the type sought is a vector type, then the 1095 largest vector type that is smaller than the sought vector type will 1096 be used as a fall back. This happens because <128 x double> can be 1097 implemented in terms of 64 <2 x double>, for example. 1098 1099 The function of the data layout string may not be what you expect. 1100 Notably, this is not a specification from the frontend of what alignment 1101 the code generator should use. 1102 1103 Instead, if specified, the target data layout is required to match what 1104 the ultimate *code generator* expects. This string is used by the 1105 mid-level optimizers to improve code, and this only works if it matches 1106 what the ultimate code generator uses. If you would like to generate IR 1107 that does not embed this target-specific detail into the IR, then you 1108 don't have to specify the string. This will disable some optimizations 1109 that require precise layout information, but this also prevents those 1110 optimizations from introducing target specificity into the IR. 1111 1112 .. _pointeraliasing: 1113 1114 Pointer Aliasing Rules 1115 ---------------------- 1116 1117 Any memory access must be done through a pointer value associated with 1118 an address range of the memory access, otherwise the behavior is 1119 undefined. Pointer values are associated with address ranges according 1120 to the following rules: 1121 1122 - A pointer value is associated with the addresses associated with any 1123 value it is *based* on. 1124 - An address of a global variable is associated with the address range 1125 of the variable's storage. 1126 - The result value of an allocation instruction is associated with the 1127 address range of the allocated storage. 1128 - A null pointer in the default address-space is associated with no 1129 address. 1130 - An integer constant other than zero or a pointer value returned from 1131 a function not defined within LLVM may be associated with address 1132 ranges allocated through mechanisms other than those provided by 1133 LLVM. Such ranges shall not overlap with any ranges of addresses 1134 allocated by mechanisms provided by LLVM. 1135 1136 A pointer value is *based* on another pointer value according to the 1137 following rules: 1138 1139 - A pointer value formed from a ``getelementptr`` operation is *based* 1140 on the first operand of the ``getelementptr``. 1141 - The result value of a ``bitcast`` is *based* on the operand of the 1142 ``bitcast``. 1143 - A pointer value formed by an ``inttoptr`` is *based* on all pointer 1144 values that contribute (directly or indirectly) to the computation of 1145 the pointer's value. 1146 - The "*based* on" relationship is transitive. 1147 1148 Note that this definition of *"based"* is intentionally similar to the 1149 definition of *"based"* in C99, though it is slightly weaker. 1150 1151 LLVM IR does not associate types with memory. The result type of a 1152 ``load`` merely indicates the size and alignment of the memory from 1153 which to load, as well as the interpretation of the value. The first 1154 operand type of a ``store`` similarly only indicates the size and 1155 alignment of the store. 1156 1157 Consequently, type-based alias analysis, aka TBAA, aka 1158 ``-fstrict-aliasing``, is not applicable to general unadorned LLVM IR. 1159 :ref:`Metadata <metadata>` may be used to encode additional information 1160 which specialized optimization passes may use to implement type-based 1161 alias analysis. 1162 1163 .. _volatile: 1164 1165 Volatile Memory Accesses 1166 ------------------------ 1167 1168 Certain memory accesses, such as :ref:`load <i_load>`'s, 1169 :ref:`store <i_store>`'s, and :ref:`llvm.memcpy <int_memcpy>`'s may be 1170 marked ``volatile``. The optimizers must not change the number of 1171 volatile operations or change their order of execution relative to other 1172 volatile operations. The optimizers *may* change the order of volatile 1173 operations relative to non-volatile operations. This is not Java's 1174 "volatile" and has no cross-thread synchronization behavior. 1175 1176 IR-level volatile loads and stores cannot safely be optimized into 1177 llvm.memcpy or llvm.memmove intrinsics even when those intrinsics are 1178 flagged volatile. Likewise, the backend should never split or merge 1179 target-legal volatile load/store instructions. 1180 1181 .. admonition:: Rationale 1182 1183 Platforms may rely on volatile loads and stores of natively supported 1184 data width to be executed as single instruction. For example, in C 1185 this holds for an l-value of volatile primitive type with native 1186 hardware support, but not necessarily for aggregate types. The 1187 frontend upholds these expectations, which are intentionally 1188 unspecified in the IR. The rules above ensure that IR transformation 1189 do not violate the frontend's contract with the language. 1190 1191 .. _memmodel: 1192 1193 Memory Model for Concurrent Operations 1194 -------------------------------------- 1195 1196 The LLVM IR does not define any way to start parallel threads of 1197 execution or to register signal handlers. Nonetheless, there are 1198 platform-specific ways to create them, and we define LLVM IR's behavior 1199 in their presence. This model is inspired by the C++0x memory model. 1200 1201 For a more informal introduction to this model, see the :doc:`Atomics`. 1202 1203 We define a *happens-before* partial order as the least partial order 1204 that 1205 1206 - Is a superset of single-thread program order, and 1207 - When a *synchronizes-with* ``b``, includes an edge from ``a`` to 1208 ``b``. *Synchronizes-with* pairs are introduced by platform-specific 1209 techniques, like pthread locks, thread creation, thread joining, 1210 etc., and by atomic instructions. (See also :ref:`Atomic Memory Ordering 1211 Constraints <ordering>`). 1212 1213 Note that program order does not introduce *happens-before* edges 1214 between a thread and signals executing inside that thread. 1215 1216 Every (defined) read operation (load instructions, memcpy, atomic 1217 loads/read-modify-writes, etc.) R reads a series of bytes written by 1218 (defined) write operations (store instructions, atomic 1219 stores/read-modify-writes, memcpy, etc.). For the purposes of this 1220 section, initialized globals are considered to have a write of the 1221 initializer which is atomic and happens before any other read or write 1222 of the memory in question. For each byte of a read R, R\ :sub:`byte` 1223 may see any write to the same byte, except: 1224 1225 - If write\ :sub:`1` happens before write\ :sub:`2`, and 1226 write\ :sub:`2` happens before R\ :sub:`byte`, then 1227 R\ :sub:`byte` does not see write\ :sub:`1`. 1228 - If R\ :sub:`byte` happens before write\ :sub:`3`, then 1229 R\ :sub:`byte` does not see write\ :sub:`3`. 1230 1231 Given that definition, R\ :sub:`byte` is defined as follows: 1232 1233 - If R is volatile, the result is target-dependent. (Volatile is 1234 supposed to give guarantees which can support ``sig_atomic_t`` in 1235 C/C++, and may be used for accesses to addresses which do not behave 1236 like normal memory. It does not generally provide cross-thread 1237 synchronization.) 1238 - Otherwise, if there is no write to the same byte that happens before 1239 R\ :sub:`byte`, R\ :sub:`byte` returns ``undef`` for that byte. 1240 - Otherwise, if R\ :sub:`byte` may see exactly one write, 1241 R\ :sub:`byte` returns the value written by that write. 1242 - Otherwise, if R is atomic, and all the writes R\ :sub:`byte` may 1243 see are atomic, it chooses one of the values written. See the :ref:`Atomic 1244 Memory Ordering Constraints <ordering>` section for additional 1245 constraints on how the choice is made. 1246 - Otherwise R\ :sub:`byte` returns ``undef``. 1247 1248 R returns the value composed of the series of bytes it read. This 1249 implies that some bytes within the value may be ``undef`` **without** 1250 the entire value being ``undef``. Note that this only defines the 1251 semantics of the operation; it doesn't mean that targets will emit more 1252 than one instruction to read the series of bytes. 1253 1254 Note that in cases where none of the atomic intrinsics are used, this 1255 model places only one restriction on IR transformations on top of what 1256 is required for single-threaded execution: introducing a store to a byte 1257 which might not otherwise be stored is not allowed in general. 1258 (Specifically, in the case where another thread might write to and read 1259 from an address, introducing a store can change a load that may see 1260 exactly one write into a load that may see multiple writes.) 1261 1262 .. _ordering: 1263 1264 Atomic Memory Ordering Constraints 1265 ---------------------------------- 1266 1267 Atomic instructions (:ref:`cmpxchg <i_cmpxchg>`, 1268 :ref:`atomicrmw <i_atomicrmw>`, :ref:`fence <i_fence>`, 1269 :ref:`atomic load <i_load>`, and :ref:`atomic store <i_store>`) take 1270 an ordering parameter that determines which other atomic instructions on 1271 the same address they *synchronize with*. These semantics are borrowed 1272 from Java and C++0x, but are somewhat more colloquial. If these 1273 descriptions aren't precise enough, check those specs (see spec 1274 references in the :doc:`atomics guide <Atomics>`). 1275 :ref:`fence <i_fence>` instructions treat these orderings somewhat 1276 differently since they don't take an address. See that instruction's 1277 documentation for details. 1278 1279 For a simpler introduction to the ordering constraints, see the 1280 :doc:`Atomics`. 1281 1282 ``unordered`` 1283 The set of values that can be read is governed by the happens-before 1284 partial order. A value cannot be read unless some operation wrote 1285 it. This is intended to provide a guarantee strong enough to model 1286 Java's non-volatile shared variables. This ordering cannot be 1287 specified for read-modify-write operations; it is not strong enough 1288 to make them atomic in any interesting way. 1289 ``monotonic`` 1290 In addition to the guarantees of ``unordered``, there is a single 1291 total order for modifications by ``monotonic`` operations on each 1292 address. All modification orders must be compatible with the 1293 happens-before order. There is no guarantee that the modification 1294 orders can be combined to a global total order for the whole program 1295 (and this often will not be possible). The read in an atomic 1296 read-modify-write operation (:ref:`cmpxchg <i_cmpxchg>` and 1297 :ref:`atomicrmw <i_atomicrmw>`) reads the value in the modification 1298 order immediately before the value it writes. If one atomic read 1299 happens before another atomic read of the same address, the later 1300 read must see the same value or a later value in the address's 1301 modification order. This disallows reordering of ``monotonic`` (or 1302 stronger) operations on the same address. If an address is written 1303 ``monotonic``-ally by one thread, and other threads ``monotonic``-ally 1304 read that address repeatedly, the other threads must eventually see 1305 the write. This corresponds to the C++0x/C1x 1306 ``memory_order_relaxed``. 1307 ``acquire`` 1308 In addition to the guarantees of ``monotonic``, a 1309 *synchronizes-with* edge may be formed with a ``release`` operation. 1310 This is intended to model C++'s ``memory_order_acquire``. 1311 ``release`` 1312 In addition to the guarantees of ``monotonic``, if this operation 1313 writes a value which is subsequently read by an ``acquire`` 1314 operation, it *synchronizes-with* that operation. (This isn't a 1315 complete description; see the C++0x definition of a release 1316 sequence.) This corresponds to the C++0x/C1x 1317 ``memory_order_release``. 1318 ``acq_rel`` (acquire+release) 1319 Acts as both an ``acquire`` and ``release`` operation on its 1320 address. This corresponds to the C++0x/C1x ``memory_order_acq_rel``. 1321 ``seq_cst`` (sequentially consistent) 1322 In addition to the guarantees of ``acq_rel`` (``acquire`` for an 1323 operation which only reads, ``release`` for an operation which only 1324 writes), there is a global total order on all 1325 sequentially-consistent operations on all addresses, which is 1326 consistent with the *happens-before* partial order and with the 1327 modification orders of all the affected addresses. Each 1328 sequentially-consistent read sees the last preceding write to the 1329 same address in this global order. This corresponds to the C++0x/C1x 1330 ``memory_order_seq_cst`` and Java volatile. 1331 1332 .. _singlethread: 1333 1334 If an atomic operation is marked ``singlethread``, it only *synchronizes 1335 with* or participates in modification and seq\_cst total orderings with 1336 other operations running in the same thread (for example, in signal 1337 handlers). 1338 1339 .. _fastmath: 1340 1341 Fast-Math Flags 1342 --------------- 1343 1344 LLVM IR floating-point binary ops (:ref:`fadd <i_fadd>`, 1345 :ref:`fsub <i_fsub>`, :ref:`fmul <i_fmul>`, :ref:`fdiv <i_fdiv>`, 1346 :ref:`frem <i_frem>`) have the following flags that can set to enable 1347 otherwise unsafe floating point operations 1348 1349 ``nnan`` 1350 No NaNs - Allow optimizations to assume the arguments and result are not 1351 NaN. Such optimizations are required to retain defined behavior over 1352 NaNs, but the value of the result is undefined. 1353 1354 ``ninf`` 1355 No Infs - Allow optimizations to assume the arguments and result are not 1356 +/-Inf. Such optimizations are required to retain defined behavior over 1357 +/-Inf, but the value of the result is undefined. 1358 1359 ``nsz`` 1360 No Signed Zeros - Allow optimizations to treat the sign of a zero 1361 argument or result as insignificant. 1362 1363 ``arcp`` 1364 Allow Reciprocal - Allow optimizations to use the reciprocal of an 1365 argument rather than perform division. 1366 1367 ``fast`` 1368 Fast - Allow algebraically equivalent transformations that may 1369 dramatically change results in floating point (e.g. reassociate). This 1370 flag implies all the others. 1371 1372 .. _typesystem: 1373 1374 Type System 1375 =========== 1376 1377 The LLVM type system is one of the most important features of the 1378 intermediate representation. Being typed enables a number of 1379 optimizations to be performed on the intermediate representation 1380 directly, without having to do extra analyses on the side before the 1381 transformation. A strong type system makes it easier to read the 1382 generated code and enables novel analyses and transformations that are 1383 not feasible to perform on normal three address code representations. 1384 1385 .. _typeclassifications: 1386 1387 Type Classifications 1388 -------------------- 1389 1390 The types fall into a few useful classifications: 1391 1392 1393 .. list-table:: 1394 :header-rows: 1 1395 1396 * - Classification 1397 - Types 1398 1399 * - :ref:`integer <t_integer>` 1400 - ``i1``, ``i2``, ``i3``, ... ``i8``, ... ``i16``, ... ``i32``, ... 1401 ``i64``, ... 1402 1403 * - :ref:`floating point <t_floating>` 1404 - ``half``, ``float``, ``double``, ``x86_fp80``, ``fp128``, 1405 ``ppc_fp128`` 1406 1407 1408 * - first class 1409 1410 .. _t_firstclass: 1411 1412 - :ref:`integer <t_integer>`, :ref:`floating point <t_floating>`, 1413 :ref:`pointer <t_pointer>`, :ref:`vector <t_vector>`, 1414 :ref:`structure <t_struct>`, :ref:`array <t_array>`, 1415 :ref:`label <t_label>`, :ref:`metadata <t_metadata>`. 1416 1417 * - :ref:`primitive <t_primitive>` 1418 - :ref:`label <t_label>`, 1419 :ref:`void <t_void>`, 1420 :ref:`integer <t_integer>`, 1421 :ref:`floating point <t_floating>`, 1422 :ref:`x86mmx <t_x86mmx>`, 1423 :ref:`metadata <t_metadata>`. 1424 1425 * - :ref:`derived <t_derived>` 1426 - :ref:`array <t_array>`, 1427 :ref:`function <t_function>`, 1428 :ref:`pointer <t_pointer>`, 1429 :ref:`structure <t_struct>`, 1430 :ref:`vector <t_vector>`, 1431 :ref:`opaque <t_opaque>`. 1432 1433 The :ref:`first class <t_firstclass>` types are perhaps the most important. 1434 Values of these types are the only ones which can be produced by 1435 instructions. 1436 1437 .. _t_primitive: 1438 1439 Primitive Types 1440 --------------- 1441 1442 The primitive types are the fundamental building blocks of the LLVM 1443 system. 1444 1445 .. _t_integer: 1446 1447 Integer Type 1448 ^^^^^^^^^^^^ 1449 1450 Overview: 1451 """"""""" 1452 1453 The integer type is a very simple type that simply specifies an 1454 arbitrary bit width for the integer type desired. Any bit width from 1 1455 bit to 2\ :sup:`23`\ -1 (about 8 million) can be specified. 1456 1457 Syntax: 1458 """"""" 1459 1460 :: 1461 1462 iN 1463 1464 The number of bits the integer will occupy is specified by the ``N`` 1465 value. 1466 1467 Examples: 1468 """"""""" 1469 1470 +----------------+------------------------------------------------+ 1471 | ``i1`` | a single-bit integer. | 1472 +----------------+------------------------------------------------+ 1473 | ``i32`` | a 32-bit integer. | 1474 +----------------+------------------------------------------------+ 1475 | ``i1942652`` | a really big integer of over 1 million bits. | 1476 +----------------+------------------------------------------------+ 1477 1478 .. _t_floating: 1479 1480 Floating Point Types 1481 ^^^^^^^^^^^^^^^^^^^^ 1482 1483 .. list-table:: 1484 :header-rows: 1 1485 1486 * - Type 1487 - Description 1488 1489 * - ``half`` 1490 - 16-bit floating point value 1491 1492 * - ``float`` 1493 - 32-bit floating point value 1494 1495 * - ``double`` 1496 - 64-bit floating point value 1497 1498 * - ``fp128`` 1499 - 128-bit floating point value (112-bit mantissa) 1500 1501 * - ``x86_fp80`` 1502 - 80-bit floating point value (X87) 1503 1504 * - ``ppc_fp128`` 1505 - 128-bit floating point value (two 64-bits) 1506 1507 .. _t_x86mmx: 1508 1509 X86mmx Type 1510 ^^^^^^^^^^^ 1511 1512 Overview: 1513 """"""""" 1514 1515 The x86mmx type represents a value held in an MMX register on an x86 1516 machine. The operations allowed on it are quite limited: parameters and 1517 return values, load and store, and bitcast. User-specified MMX 1518 instructions are represented as intrinsic or asm calls with arguments 1519 and/or results of this type. There are no arrays, vectors or constants 1520 of this type. 1521 1522 Syntax: 1523 """"""" 1524 1525 :: 1526 1527 x86mmx 1528 1529 .. _t_void: 1530 1531 Void Type 1532 ^^^^^^^^^ 1533 1534 Overview: 1535 """"""""" 1536 1537 The void type does not represent any value and has no size. 1538 1539 Syntax: 1540 """"""" 1541 1542 :: 1543 1544 void 1545 1546 .. _t_label: 1547 1548 Label Type 1549 ^^^^^^^^^^ 1550 1551 Overview: 1552 """"""""" 1553 1554 The label type represents code labels. 1555 1556 Syntax: 1557 """"""" 1558 1559 :: 1560 1561 label 1562 1563 .. _t_metadata: 1564 1565 Metadata Type 1566 ^^^^^^^^^^^^^ 1567 1568 Overview: 1569 """"""""" 1570 1571 The metadata type represents embedded metadata. No derived types may be 1572 created from metadata except for :ref:`function <t_function>` arguments. 1573 1574 Syntax: 1575 """"""" 1576 1577 :: 1578 1579 metadata 1580 1581 .. _t_derived: 1582 1583 Derived Types 1584 ------------- 1585 1586 The real power in LLVM comes from the derived types in the system. This 1587 is what allows a programmer to represent arrays, functions, pointers, 1588 and other useful types. Each of these types contain one or more element 1589 types which may be a primitive type, or another derived type. For 1590 example, it is possible to have a two dimensional array, using an array 1591 as the element type of another array. 1592 1593 .. _t_aggregate: 1594 1595 Aggregate Types 1596 ^^^^^^^^^^^^^^^ 1597 1598 Aggregate Types are a subset of derived types that can contain multiple 1599 member types. :ref:`Arrays <t_array>` and :ref:`structs <t_struct>` are 1600 aggregate types. :ref:`Vectors <t_vector>` are not considered to be 1601 aggregate types. 1602 1603 .. _t_array: 1604 1605 Array Type 1606 ^^^^^^^^^^ 1607 1608 Overview: 1609 """"""""" 1610 1611 The array type is a very simple derived type that arranges elements 1612 sequentially in memory. The array type requires a size (number of 1613 elements) and an underlying data type. 1614 1615 Syntax: 1616 """"""" 1617 1618 :: 1619 1620 [<# elements> x <elementtype>] 1621 1622 The number of elements is a constant integer value; ``elementtype`` may 1623 be any type with a size. 1624 1625 Examples: 1626 """"""""" 1627 1628 +------------------+--------------------------------------+ 1629 | ``[40 x i32]`` | Array of 40 32-bit integer values. | 1630 +------------------+--------------------------------------+ 1631 | ``[41 x i32]`` | Array of 41 32-bit integer values. | 1632 +------------------+--------------------------------------+ 1633 | ``[4 x i8]`` | Array of 4 8-bit integer values. | 1634 +------------------+--------------------------------------+ 1635 1636 Here are some examples of multidimensional arrays: 1637 1638 +-----------------------------+----------------------------------------------------------+ 1639 | ``[3 x [4 x i32]]`` | 3x4 array of 32-bit integer values. | 1640 +-----------------------------+----------------------------------------------------------+ 1641 | ``[12 x [10 x float]]`` | 12x10 array of single precision floating point values. | 1642 +-----------------------------+----------------------------------------------------------+ 1643 | ``[2 x [3 x [4 x i16]]]`` | 2x3x4 array of 16-bit integer values. | 1644 +-----------------------------+----------------------------------------------------------+ 1645 1646 There is no restriction on indexing beyond the end of the array implied 1647 by a static type (though there are restrictions on indexing beyond the 1648 bounds of an allocated object in some cases). This means that 1649 single-dimension 'variable sized array' addressing can be implemented in 1650 LLVM with a zero length array type. An implementation of 'pascal style 1651 arrays' in LLVM could use the type "``{ i32, [0 x float]}``", for 1652 example. 1653 1654 .. _t_function: 1655 1656 Function Type 1657 ^^^^^^^^^^^^^ 1658 1659 Overview: 1660 """"""""" 1661 1662 The function type can be thought of as a function signature. It consists 1663 of a return type and a list of formal parameter types. The return type 1664 of a function type is a first class type or a void type. 1665 1666 Syntax: 1667 """"""" 1668 1669 :: 1670 1671 <returntype> (<parameter list>) 1672 1673 ...where '``<parameter list>``' is a comma-separated list of type 1674 specifiers. Optionally, the parameter list may include a type ``...``, 1675 which indicates that the function takes a variable number of arguments. 1676 Variable argument functions can access their arguments with the 1677 :ref:`variable argument handling intrinsic <int_varargs>` functions. 1678 '``<returntype>``' is any type except :ref:`label <t_label>`. 1679 1680 Examples: 1681 """"""""" 1682 1683 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 1684 | ``i32 (i32)`` | function taking an ``i32``, returning an ``i32`` | 1685 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 1686 | ``float (i16, i32 *) *`` | :ref:`Pointer <t_pointer>` to a function that takes an ``i16`` and a :ref:`pointer <t_pointer>` to ``i32``, returning ``float``. | 1687 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 1688 | ``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. | 1689 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 1690 | ``{i32, i32} (i32)`` | A function taking an ``i32``, returning a :ref:`structure <t_struct>` containing two ``i32`` values | 1691 +---------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 1692 1693 .. _t_struct: 1694 1695 Structure Type 1696 ^^^^^^^^^^^^^^ 1697 1698 Overview: 1699 """"""""" 1700 1701 The structure type is used to represent a collection of data members 1702 together in memory. The elements of a structure may be any type that has 1703 a size. 1704 1705 Structures in memory are accessed using '``load``' and '``store``' by 1706 getting a pointer to a field with the '``getelementptr``' instruction. 1707 Structures in registers are accessed using the '``extractvalue``' and 1708 '``insertvalue``' instructions. 1709 1710 Structures may optionally be "packed" structures, which indicate that 1711 the alignment of the struct is one byte, and that there is no padding 1712 between the elements. In non-packed structs, padding between field types 1713 is inserted as defined by the DataLayout string in the module, which is 1714 required to match what the underlying code generator expects. 1715 1716 Structures can either be "literal" or "identified". A literal structure 1717 is defined inline with other types (e.g. ``{i32, i32}*``) whereas 1718 identified types are always defined at the top level with a name. 1719 Literal types are uniqued by their contents and can never be recursive 1720 or opaque since there is no way to write one. Identified types can be 1721 recursive, can be opaqued, and are never uniqued. 1722 1723 Syntax: 1724 """"""" 1725 1726 :: 1727 1728 %T1 = type { <type list> } ; Identified normal struct type 1729 %T2 = type <{ <type list> }> ; Identified packed struct type 1730 1731 Examples: 1732 """"""""" 1733 1734 +------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 1735 | ``{ i32, i32, i32 }`` | A triple of three ``i32`` values | 1736 +------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 1737 | ``{ 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``. | 1738 +------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 1739 | ``<{ i8, i32 }>`` | A packed struct known to be 5 bytes in size. | 1740 +------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 1741 1742 .. _t_opaque: 1743 1744 Opaque Structure Types 1745 ^^^^^^^^^^^^^^^^^^^^^^ 1746 1747 Overview: 1748 """"""""" 1749 1750 Opaque structure types are used to represent named structure types that 1751 do not have a body specified. This corresponds (for example) to the C 1752 notion of a forward declared structure. 1753 1754 Syntax: 1755 """"""" 1756 1757 :: 1758 1759 %X = type opaque 1760 %52 = type opaque 1761 1762 Examples: 1763 """"""""" 1764 1765 +--------------+-------------------+ 1766 | ``opaque`` | An opaque type. | 1767 +--------------+-------------------+ 1768 1769 .. _t_pointer: 1770 1771 Pointer Type 1772 ^^^^^^^^^^^^ 1773 1774 Overview: 1775 """"""""" 1776 1777 The pointer type is used to specify memory locations. Pointers are 1778 commonly used to reference objects in memory. 1779 1780 Pointer types may have an optional address space attribute defining the 1781 numbered address space where the pointed-to object resides. The default 1782 address space is number zero. The semantics of non-zero address spaces 1783 are target-specific. 1784 1785 Note that LLVM does not permit pointers to void (``void*``) nor does it 1786 permit pointers to labels (``label*``). Use ``i8*`` instead. 1787 1788 Syntax: 1789 """"""" 1790 1791 :: 1792 1793 <type> * 1794 1795 Examples: 1796 """"""""" 1797 1798 +-------------------------+--------------------------------------------------------------------------------------------------------------+ 1799 | ``[4 x i32]*`` | A :ref:`pointer <t_pointer>` to :ref:`array <t_array>` of four ``i32`` values. | 1800 +-------------------------+--------------------------------------------------------------------------------------------------------------+ 1801 | ``i32 (i32*) *`` | A :ref:`pointer <t_pointer>` to a :ref:`function <t_function>` that takes an ``i32*``, returning an ``i32``. | 1802 +-------------------------+--------------------------------------------------------------------------------------------------------------+ 1803 | ``i32 addrspace(5)*`` | A :ref:`pointer <t_pointer>` to an ``i32`` value that resides in address space #5. | 1804 +-------------------------+--------------------------------------------------------------------------------------------------------------+ 1805 1806 .. _t_vector: 1807 1808 Vector Type 1809 ^^^^^^^^^^^ 1810 1811 Overview: 1812 """"""""" 1813 1814 A vector type is a simple derived type that represents a vector of 1815 elements. Vector types are used when multiple primitive data are 1816 operated in parallel using a single instruction (SIMD). A vector type 1817 requires a size (number of elements) and an underlying primitive data 1818 type. Vector types are considered :ref:`first class <t_firstclass>`. 1819 1820 Syntax: 1821 """"""" 1822 1823 :: 1824 1825 < <# elements> x <elementtype> > 1826 1827 The number of elements is a constant integer value larger than 0; 1828 elementtype may be any integer or floating point type, or a pointer to 1829 these types. Vectors of size zero are not allowed. 1830 1831 Examples: 1832 """"""""" 1833 1834 +-------------------+--------------------------------------------------+ 1835 | ``<4 x i32>`` | Vector of 4 32-bit integer values. | 1836 +-------------------+--------------------------------------------------+ 1837 | ``<8 x float>`` | Vector of 8 32-bit floating-point values. | 1838 +-------------------+--------------------------------------------------+ 1839 | ``<2 x i64>`` | Vector of 2 64-bit integer values. | 1840 +-------------------+--------------------------------------------------+ 1841 | ``<4 x i64*>`` | Vector of 4 pointers to 64-bit integer values. | 1842 +-------------------+--------------------------------------------------+ 1843 1844 Constants 1845 ========= 1846 1847 LLVM has several different basic types of constants. This section 1848 describes them all and their syntax. 1849 1850 Simple Constants 1851 ---------------- 1852 1853 **Boolean constants** 1854 The two strings '``true``' and '``false``' are both valid constants 1855 of the ``i1`` type. 1856 **Integer constants** 1857 Standard integers (such as '4') are constants of the 1858 :ref:`integer <t_integer>` type. Negative numbers may be used with 1859 integer types. 1860 **Floating point constants** 1861 Floating point constants use standard decimal notation (e.g. 1862 123.421), exponential notation (e.g. 1.23421e+2), or a more precise 1863 hexadecimal notation (see below). The assembler requires the exact 1864 decimal value of a floating-point constant. For example, the 1865 assembler accepts 1.25 but rejects 1.3 because 1.3 is a repeating 1866 decimal in binary. Floating point constants must have a :ref:`floating 1867 point <t_floating>` type. 1868 **Null pointer constants** 1869 The identifier '``null``' is recognized as a null pointer constant 1870 and must be of :ref:`pointer type <t_pointer>`. 1871 1872 The one non-intuitive notation for constants is the hexadecimal form of 1873 floating point constants. For example, the form 1874 '``double 0x432ff973cafa8000``' is equivalent to (but harder to read 1875 than) '``double 4.5e+15``'. The only time hexadecimal floating point 1876 constants are required (and the only time that they are generated by the 1877 disassembler) is when a floating point constant must be emitted but it 1878 cannot be represented as a decimal floating point number in a reasonable 1879 number of digits. For example, NaN's, infinities, and other special 1880 values are represented in their IEEE hexadecimal format so that assembly 1881 and disassembly do not cause any bits to change in the constants. 1882 1883 When using the hexadecimal form, constants of types half, float, and 1884 double are represented using the 16-digit form shown above (which 1885 matches the IEEE754 representation for double); half and float values 1886 must, however, be exactly representable as IEEE 754 half and single 1887 precision, respectively. Hexadecimal format is always used for long 1888 double, and there are three forms of long double. The 80-bit format used 1889 by x86 is represented as ``0xK`` followed by 20 hexadecimal digits. The 1890 128-bit format used by PowerPC (two adjacent doubles) is represented by 1891 ``0xM`` followed by 32 hexadecimal digits. The IEEE 128-bit format is 1892 represented by ``0xL`` followed by 32 hexadecimal digits. Long doubles 1893 will only work if they match the long double format on your target. 1894 The IEEE 16-bit format (half precision) is represented by ``0xH`` 1895 followed by 4 hexadecimal digits. All hexadecimal formats are big-endian 1896 (sign bit at the left). 1897 1898 There are no constants of type x86mmx. 1899 1900 .. _complexconstants: 1901 1902 Complex Constants 1903 ----------------- 1904 1905 Complex constants are a (potentially recursive) combination of simple 1906 constants and smaller complex constants. 1907 1908 **Structure constants** 1909 Structure constants are represented with notation similar to 1910 structure type definitions (a comma separated list of elements, 1911 surrounded by braces (``{}``)). For example: 1912 "``{ i32 4, float 17.0, i32* @G }``", where "``@G``" is declared as 1913 "``@G = external global i32``". Structure constants must have 1914 :ref:`structure type <t_struct>`, and the number and types of elements 1915 must match those specified by the type. 1916 **Array constants** 1917 Array constants are represented with notation similar to array type 1918 definitions (a comma separated list of elements, surrounded by 1919 square brackets (``[]``)). For example: 1920 "``[ i32 42, i32 11, i32 74 ]``". Array constants must have 1921 :ref:`array type <t_array>`, and the number and types of elements must 1922 match those specified by the type. 1923 **Vector constants** 1924 Vector constants are represented with notation similar to vector 1925 type definitions (a comma separated list of elements, surrounded by 1926 less-than/greater-than's (``<>``)). For example: 1927 "``< i32 42, i32 11, i32 74, i32 100 >``". Vector constants 1928 must have :ref:`vector type <t_vector>`, and the number and types of 1929 elements must match those specified by the type. 1930 **Zero initialization** 1931 The string '``zeroinitializer``' can be used to zero initialize a 1932 value to zero of *any* type, including scalar and 1933 :ref:`aggregate <t_aggregate>` types. This is often used to avoid 1934 having to print large zero initializers (e.g. for large arrays) and 1935 is always exactly equivalent to using explicit zero initializers. 1936 **Metadata node** 1937 A metadata node is a structure-like constant with :ref:`metadata 1938 type <t_metadata>`. For example: 1939 "``metadata !{ i32 0, metadata !"test" }``". Unlike other 1940 constants that are meant to be interpreted as part of the 1941 instruction stream, metadata is a place to attach additional 1942 information such as debug info. 1943 1944 Global Variable and Function Addresses 1945 -------------------------------------- 1946 1947 The addresses of :ref:`global variables <globalvars>` and 1948 :ref:`functions <functionstructure>` are always implicitly valid 1949 (link-time) constants. These constants are explicitly referenced when 1950 the :ref:`identifier for the global <identifiers>` is used and always have 1951 :ref:`pointer <t_pointer>` type. For example, the following is a legal LLVM 1952 file: 1953 1954 .. code-block:: llvm 1955 1956 @X = global i32 17 1957 @Y = global i32 42 1958 @Z = global [2 x i32*] [ i32* @X, i32* @Y ] 1959 1960 .. _undefvalues: 1961 1962 Undefined Values 1963 ---------------- 1964 1965 The string '``undef``' can be used anywhere a constant is expected, and 1966 indicates that the user of the value may receive an unspecified 1967 bit-pattern. Undefined values may be of any type (other than '``label``' 1968 or '``void``') and be used anywhere a constant is permitted. 1969 1970 Undefined values are useful because they indicate to the compiler that 1971 the program is well defined no matter what value is used. This gives the 1972 compiler more freedom to optimize. Here are some examples of 1973 (potentially surprising) transformations that are valid (in pseudo IR): 1974 1975 .. code-block:: llvm 1976 1977 %A = add %X, undef 1978 %B = sub %X, undef 1979 %C = xor %X, undef 1980 Safe: 1981 %A = undef 1982 %B = undef 1983 %C = undef 1984 1985 This is safe because all of the output bits are affected by the undef 1986 bits. Any output bit can have a zero or one depending on the input bits. 1987 1988 .. code-block:: llvm 1989 1990 %A = or %X, undef 1991 %B = and %X, undef 1992 Safe: 1993 %A = -1 1994 %B = 0 1995 Unsafe: 1996 %A = undef 1997 %B = undef 1998 1999 These logical operations have bits that are not always affected by the 2000 input. For example, if ``%X`` has a zero bit, then the output of the 2001 '``and``' operation will always be a zero for that bit, no matter what 2002 the corresponding bit from the '``undef``' is. As such, it is unsafe to 2003 optimize or assume that the result of the '``and``' is '``undef``'. 2004 However, it is safe to assume that all bits of the '``undef``' could be 2005 0, and optimize the '``and``' to 0. Likewise, it is safe to assume that 2006 all the bits of the '``undef``' operand to the '``or``' could be set, 2007 allowing the '``or``' to be folded to -1. 2008 2009 .. code-block:: llvm 2010 2011 %A = select undef, %X, %Y 2012 %B = select undef, 42, %Y 2013 %C = select %X, %Y, undef 2014 Safe: 2015 %A = %X (or %Y) 2016 %B = 42 (or %Y) 2017 %C = %Y 2018 Unsafe: 2019 %A = undef 2020 %B = undef 2021 %C = undef 2022 2023 This set of examples shows that undefined '``select``' (and conditional 2024 branch) conditions can go *either way*, but they have to come from one 2025 of the two operands. In the ``%A`` example, if ``%X`` and ``%Y`` were 2026 both known to have a clear low bit, then ``%A`` would have to have a 2027 cleared low bit. However, in the ``%C`` example, the optimizer is 2028 allowed to assume that the '``undef``' operand could be the same as 2029 ``%Y``, allowing the whole '``select``' to be eliminated. 2030 2031 .. code-block:: llvm 2032 2033 %A = xor undef, undef 2034 2035 %B = undef 2036 %C = xor %B, %B 2037 2038 %D = undef 2039 %E = icmp lt %D, 4 2040 %F = icmp gte %D, 4 2041 2042 Safe: 2043 %A = undef 2044 %B = undef 2045 %C = undef 2046 %D = undef 2047 %E = undef 2048 %F = undef 2049 2050 This example points out that two '``undef``' operands are not 2051 necessarily the same. This can be surprising to people (and also matches 2052 C semantics) where they assume that "``X^X``" is always zero, even if 2053 ``X`` is undefined. This isn't true for a number of reasons, but the 2054 short answer is that an '``undef``' "variable" can arbitrarily change 2055 its value over its "live range". This is true because the variable 2056 doesn't actually *have a live range*. Instead, the value is logically 2057 read from arbitrary registers that happen to be around when needed, so 2058 the value is not necessarily consistent over time. In fact, ``%A`` and 2059 ``%C`` need to have the same semantics or the core LLVM "replace all 2060 uses with" concept would not hold. 2061 2062 .. code-block:: llvm 2063 2064 %A = fdiv undef, %X 2065 %B = fdiv %X, undef 2066 Safe: 2067 %A = undef 2068 b: unreachable 2069 2070 These examples show the crucial difference between an *undefined value* 2071 and *undefined behavior*. An undefined value (like '``undef``') is 2072 allowed to have an arbitrary bit-pattern. This means that the ``%A`` 2073 operation can be constant folded to '``undef``', because the '``undef``' 2074 could be an SNaN, and ``fdiv`` is not (currently) defined on SNaN's. 2075 However, in the second example, we can make a more aggressive 2076 assumption: because the ``undef`` is allowed to be an arbitrary value, 2077 we are allowed to assume that it could be zero. Since a divide by zero 2078 has *undefined behavior*, we are allowed to assume that the operation 2079 does not execute at all. This allows us to delete the divide and all 2080 code after it. Because the undefined operation "can't happen", the 2081 optimizer can assume that it occurs in dead code. 2082 2083 .. code-block:: llvm 2084 2085 a: store undef -> %X 2086 b: store %X -> undef 2087 Safe: 2088 a: <deleted> 2089 b: unreachable 2090 2091 These examples reiterate the ``fdiv`` example: a store *of* an undefined 2092 value can be assumed to not have any effect; we can assume that the 2093 value is overwritten with bits that happen to match what was already 2094 there. However, a store *to* an undefined location could clobber 2095 arbitrary memory, therefore, it has undefined behavior. 2096 2097 .. _poisonvalues: 2098 2099 Poison Values 2100 ------------- 2101 2102 Poison values are similar to :ref:`undef values <undefvalues>`, however 2103 they also represent the fact that an instruction or constant expression 2104 which cannot evoke side effects has nevertheless detected a condition 2105 which results in undefined behavior. 2106 2107 There is currently no way of representing a poison value in the IR; they 2108 only exist when produced by operations such as :ref:`add <i_add>` with 2109 the ``nsw`` flag. 2110 2111 Poison value behavior is defined in terms of value *dependence*: 2112 2113 - Values other than :ref:`phi <i_phi>` nodes depend on their operands. 2114 - :ref:`Phi <i_phi>` nodes depend on the operand corresponding to 2115 their dynamic predecessor basic block. 2116 - Function arguments depend on the corresponding actual argument values 2117 in the dynamic callers of their functions. 2118 - :ref:`Call <i_call>` instructions depend on the :ref:`ret <i_ret>` 2119 instructions that dynamically transfer control back to them. 2120 - :ref:`Invoke <i_invoke>` instructions depend on the 2121 :ref:`ret <i_ret>`, :ref:`resume <i_resume>`, or exception-throwing 2122 call instructions that dynamically transfer control back to them. 2123 - Non-volatile loads and stores depend on the most recent stores to all 2124 of the referenced memory addresses, following the order in the IR 2125 (including loads and stores implied by intrinsics such as 2126 :ref:`@llvm.memcpy <int_memcpy>`.) 2127 - An instruction with externally visible side effects depends on the 2128 most recent preceding instruction with externally visible side 2129 effects, following the order in the IR. (This includes :ref:`volatile 2130 operations <volatile>`.) 2131 - An instruction *control-depends* on a :ref:`terminator 2132 instruction <terminators>` if the terminator instruction has 2133 multiple successors and the instruction is always executed when 2134 control transfers to one of the successors, and may not be executed 2135 when control is transferred to another. 2136 - Additionally, an instruction also *control-depends* on a terminator 2137 instruction if the set of instructions it otherwise depends on would 2138 be different if the terminator had transferred control to a different 2139 successor. 2140 - Dependence is transitive. 2141 2142 Poison Values have the same behavior as :ref:`undef values <undefvalues>`, 2143 with the additional affect that any instruction which has a *dependence* 2144 on a poison value has undefined behavior. 2145 2146 Here are some examples: 2147 2148 .. code-block:: llvm 2149 2150 entry: 2151 %poison = sub nuw i32 0, 1 ; Results in a poison value. 2152 %still_poison = and i32 %poison, 0 ; 0, but also poison. 2153 %poison_yet_again = getelementptr i32* @h, i32 %still_poison 2154 store i32 0, i32* %poison_yet_again ; memory at @h[0] is poisoned 2155 2156 store i32 %poison, i32* @g ; Poison value stored to memory. 2157 %poison2 = load i32* @g ; Poison value loaded back from memory. 2158 2159 store volatile i32 %poison, i32* @g ; External observation; undefined behavior. 2160 2161 %narrowaddr = bitcast i32* @g to i16* 2162 %wideaddr = bitcast i32* @g to i64* 2163 %poison3 = load i16* %narrowaddr ; Returns a poison value. 2164 %poison4 = load i64* %wideaddr ; Returns a poison value. 2165 2166 %cmp = icmp slt i32 %poison, 0 ; Returns a poison value. 2167 br i1 %cmp, label %true, label %end ; Branch to either destination. 2168 2169 true: 2170 store volatile i32 0, i32* @g ; This is control-dependent on %cmp, so 2171 ; it has undefined behavior. 2172 br label %end 2173 2174 end: 2175 %p = phi i32 [ 0, %entry ], [ 1, %true ] 2176 ; Both edges into this PHI are 2177 ; control-dependent on %cmp, so this 2178 ; always results in a poison value. 2179 2180 store volatile i32 0, i32* @g ; This would depend on the store in %true 2181 ; if %cmp is true, or the store in %entry 2182 ; otherwise, so this is undefined behavior. 2183 2184 br i1 %cmp, label %second_true, label %second_end 2185 ; The same branch again, but this time the 2186 ; true block doesn't have side effects. 2187 2188 second_true: 2189 ; No side effects! 2190 ret void 2191 2192 second_end: 2193 store volatile i32 0, i32* @g ; This time, the instruction always depends 2194 ; on the store in %end. Also, it is 2195 ; control-equivalent to %end, so this is 2196 ; well-defined (ignoring earlier undefined 2197 ; behavior in this example). 2198 2199 .. _blockaddress: 2200 2201 Addresses of Basic Blocks 2202 ------------------------- 2203 2204 ``blockaddress(@function, %block)`` 2205 2206 The '``blockaddress``' constant computes the address of the specified 2207 basic block in the specified function, and always has an ``i8*`` type. 2208 Taking the address of the entry block is illegal. 2209 2210 This value only has defined behavior when used as an operand to the 2211 ':ref:`indirectbr <i_indirectbr>`' instruction, or for comparisons 2212 against null. Pointer equality tests between labels addresses results in 2213 undefined behavior --- though, again, comparison against null is ok, and 2214 no label is equal to the null pointer. This may be passed around as an 2215 opaque pointer sized value as long as the bits are not inspected. This 2216 allows ``ptrtoint`` and arithmetic to be performed on these values so 2217 long as the original value is reconstituted before the ``indirectbr`` 2218 instruction. 2219 2220 Finally, some targets may provide defined semantics when using the value 2221 as the operand to an inline assembly, but that is target specific. 2222 2223 .. _constantexprs: 2224 2225 Constant Expressions 2226 -------------------- 2227 2228 Constant expressions are used to allow expressions involving other 2229 constants to be used as constants. Constant expressions may be of any 2230 :ref:`first class <t_firstclass>` type and may involve any LLVM operation 2231 that does not have side effects (e.g. load and call are not supported). 2232 The following is the syntax for constant expressions: 2233 2234 ``trunc (CST to TYPE)`` 2235 Truncate a constant to another type. The bit size of CST must be 2236 larger than the bit size of TYPE. Both types must be integers. 2237 ``zext (CST to TYPE)`` 2238 Zero extend a constant to another type. The bit size of CST must be 2239 smaller than the bit size of TYPE. Both types must be integers. 2240 ``sext (CST to TYPE)`` 2241 Sign extend a constant to another type. The bit size of CST must be 2242 smaller than the bit size of TYPE. Both types must be integers. 2243 ``fptrunc (CST to TYPE)`` 2244 Truncate a floating point constant to another floating point type. 2245 The size of CST must be larger than the size of TYPE. Both types 2246 must be floating point. 2247 ``fpext (CST to TYPE)`` 2248 Floating point extend a constant to another type. The size of CST 2249 must be smaller or equal to the size of TYPE. Both types must be 2250 floating point. 2251 ``fptoui (CST to TYPE)`` 2252 Convert a floating point constant to the corresponding unsigned 2253 integer constant. TYPE must be a scalar or vector integer type. CST 2254 must be of scalar or vector floating point type. Both CST and TYPE 2255 must be scalars, or vectors of the same number of elements. If the 2256 value won't fit in the integer type, the results are undefined. 2257 ``fptosi (CST to TYPE)`` 2258 Convert a floating point constant to the corresponding signed 2259 integer constant. TYPE must be a scalar or vector integer type. CST 2260 must be of scalar or vector floating point type. Both CST and TYPE 2261 must be scalars, or vectors of the same number of elements. If the 2262 value won't fit in the integer type, the results are undefined. 2263 ``uitofp (CST to TYPE)`` 2264 Convert an unsigned integer constant to the corresponding floating 2265 point constant. TYPE must be a scalar or vector floating point type. 2266 CST must be of scalar or vector integer type. Both CST and TYPE must 2267 be scalars, or vectors of the same number of elements. If the value 2268 won't fit in the floating point type, the results are undefined. 2269 ``sitofp (CST to TYPE)`` 2270 Convert a signed integer constant to the corresponding floating 2271 point constant. TYPE must be a scalar or vector floating point type. 2272 CST must be of scalar or vector integer type. Both CST and TYPE must 2273 be scalars, or vectors of the same number of elements. If the value 2274 won't fit in the floating point type, the results are undefined. 2275 ``ptrtoint (CST to TYPE)`` 2276 Convert a pointer typed constant to the corresponding integer 2277 constant. ``TYPE`` must be an integer type. ``CST`` must be of 2278 pointer type. The ``CST`` value is zero extended, truncated, or 2279 unchanged to make it fit in ``TYPE``. 2280 ``inttoptr (CST to TYPE)`` 2281 Convert an integer constant to a pointer constant. TYPE must be a 2282 pointer type. CST must be of integer type. The CST value is zero 2283 extended, truncated, or unchanged to make it fit in a pointer size. 2284 This one is *really* dangerous! 2285 ``bitcast (CST to TYPE)`` 2286 Convert a constant, CST, to another TYPE. The constraints of the 2287 operands are the same as those for the :ref:`bitcast 2288 instruction <i_bitcast>`. 2289 ``getelementptr (CSTPTR, IDX0, IDX1, ...)``, ``getelementptr inbounds (CSTPTR, IDX0, IDX1, ...)`` 2290 Perform the :ref:`getelementptr operation <i_getelementptr>` on 2291 constants. As with the :ref:`getelementptr <i_getelementptr>` 2292 instruction, the index list may have zero or more indexes, which are 2293 required to make sense for the type of "CSTPTR". 2294 ``select (COND, VAL1, VAL2)`` 2295 Perform the :ref:`select operation <i_select>` on constants. 2296 ``icmp COND (VAL1, VAL2)`` 2297 Performs the :ref:`icmp operation <i_icmp>` on constants. 2298 ``fcmp COND (VAL1, VAL2)`` 2299 Performs the :ref:`fcmp operation <i_fcmp>` on constants. 2300 ``extractelement (VAL, IDX)`` 2301 Perform the :ref:`extractelement operation <i_extractelement>` on 2302 constants. 2303 ``insertelement (VAL, ELT, IDX)`` 2304 Perform the :ref:`insertelement operation <i_insertelement>` on 2305 constants. 2306 ``shufflevector (VEC1, VEC2, IDXMASK)`` 2307 Perform the :ref:`shufflevector operation <i_shufflevector>` on 2308 constants. 2309 ``extractvalue (VAL, IDX0, IDX1, ...)`` 2310 Perform the :ref:`extractvalue operation <i_extractvalue>` on 2311 constants. The index list is interpreted in a similar manner as 2312 indices in a ':ref:`getelementptr <i_getelementptr>`' operation. At 2313 least one index value must be specified. 2314 ``insertvalue (VAL, ELT, IDX0, IDX1, ...)`` 2315 Perform the :ref:`insertvalue operation <i_insertvalue>` on constants. 2316 The index list is interpreted in a similar manner as indices in a 2317 ':ref:`getelementptr <i_getelementptr>`' operation. At least one index 2318 value must be specified. 2319 ``OPCODE (LHS, RHS)`` 2320 Perform the specified operation of the LHS and RHS constants. OPCODE 2321 may be any of the :ref:`binary <binaryops>` or :ref:`bitwise 2322 binary <bitwiseops>` operations. The constraints on operands are 2323 the same as those for the corresponding instruction (e.g. no bitwise 2324 operations on floating point values are allowed). 2325 2326 Other Values 2327 ============ 2328 2329 .. _inlineasmexprs: 2330 2331 Inline Assembler Expressions 2332 ---------------------------- 2333 2334 LLVM supports inline assembler expressions (as opposed to :ref:`Module-Level 2335 Inline Assembly <moduleasm>`) through the use of a special value. This 2336 value represents the inline assembler as a string (containing the 2337 instructions to emit), a list of operand constraints (stored as a 2338 string), a flag that indicates whether or not the inline asm expression 2339 has side effects, and a flag indicating whether the function containing 2340 the asm needs to align its stack conservatively. An example inline 2341 assembler expression is: 2342 2343 .. code-block:: llvm 2344 2345 i32 (i32) asm "bswap $0", "=r,r" 2346 2347 Inline assembler expressions may **only** be used as the callee operand 2348 of a :ref:`call <i_call>` or an :ref:`invoke <i_invoke>` instruction. 2349 Thus, typically we have: 2350 2351 .. code-block:: llvm 2352 2353 %X = call i32 asm "bswap $0", "=r,r"(i32 %Y) 2354 2355 Inline asms with side effects not visible in the constraint list must be 2356 marked as having side effects. This is done through the use of the 2357 '``sideeffect``' keyword, like so: 2358 2359 .. code-block:: llvm 2360 2361 call void asm sideeffect "eieio", ""() 2362 2363 In some cases inline asms will contain code that will not work unless 2364 the stack is aligned in some way, such as calls or SSE instructions on 2365 x86, yet will not contain code that does that alignment within the asm. 2366 The compiler should make conservative assumptions about what the asm 2367 might contain and should generate its usual stack alignment code in the 2368 prologue if the '``alignstack``' keyword is present: 2369 2370 .. code-block:: llvm 2371 2372 call void asm alignstack "eieio", ""() 2373 2374 Inline asms also support using non-standard assembly dialects. The 2375 assumed dialect is ATT. When the '``inteldialect``' keyword is present, 2376 the inline asm is using the Intel dialect. Currently, ATT and Intel are 2377 the only supported dialects. An example is: 2378 2379 .. code-block:: llvm 2380 2381 call void asm inteldialect "eieio", ""() 2382 2383 If multiple keywords appear the '``sideeffect``' keyword must come 2384 first, the '``alignstack``' keyword second and the '``inteldialect``' 2385 keyword last. 2386 2387 Inline Asm Metadata 2388 ^^^^^^^^^^^^^^^^^^^ 2389 2390 The call instructions that wrap inline asm nodes may have a 2391 "``!srcloc``" MDNode attached to it that contains a list of constant 2392 integers. If present, the code generator will use the integer as the 2393 location cookie value when report errors through the ``LLVMContext`` 2394 error reporting mechanisms. This allows a front-end to correlate backend 2395 errors that occur with inline asm back to the source code that produced 2396 it. For example: 2397 2398 .. code-block:: llvm 2399 2400 call void asm sideeffect "something bad", ""(), !srcloc !42 2401 ... 2402 !42 = !{ i32 1234567 } 2403 2404 It is up to the front-end to make sense of the magic numbers it places 2405 in the IR. If the MDNode contains multiple constants, the code generator 2406 will use the one that corresponds to the line of the asm that the error 2407 occurs on. 2408 2409 .. _metadata: 2410 2411 Metadata Nodes and Metadata Strings 2412 ----------------------------------- 2413 2414 LLVM IR allows metadata to be attached to instructions in the program 2415 that can convey extra information about the code to the optimizers and 2416 code generator. One example application of metadata is source-level 2417 debug information. There are two metadata primitives: strings and nodes. 2418 All metadata has the ``metadata`` type and is identified in syntax by a 2419 preceding exclamation point ('``!``'). 2420 2421 A metadata string is a string surrounded by double quotes. It can 2422 contain any character by escaping non-printable characters with 2423 "``\xx``" where "``xx``" is the two digit hex code. For example: 2424 "``!"test\00"``". 2425 2426 Metadata nodes are represented with notation similar to structure 2427 constants (a comma separated list of elements, surrounded by braces and 2428 preceded by an exclamation point). Metadata nodes can have any values as 2429 their operand. For example: 2430 2431 .. code-block:: llvm 2432 2433 !{ metadata !"test\00", i32 10} 2434 2435 A :ref:`named metadata <namedmetadatastructure>` is a collection of 2436 metadata nodes, which can be looked up in the module symbol table. For 2437 example: 2438 2439 .. code-block:: llvm 2440 2441 !foo = metadata !{!4, !3} 2442 2443 Metadata can be used as function arguments. Here ``llvm.dbg.value`` 2444 function is using two metadata arguments: 2445 2446 .. code-block:: llvm 2447 2448 call void @llvm.dbg.value(metadata !24, i64 0, metadata !25) 2449 2450 Metadata can be attached with an instruction. Here metadata ``!21`` is 2451 attached to the ``add`` instruction using the ``!dbg`` identifier: 2452 2453 .. code-block:: llvm 2454 2455 %indvar.next = add i64 %indvar, 1, !dbg !21 2456 2457 More information about specific metadata nodes recognized by the 2458 optimizers and code generator is found below. 2459 2460 '``tbaa``' Metadata 2461 ^^^^^^^^^^^^^^^^^^^ 2462 2463 In LLVM IR, memory does not have types, so LLVM's own type system is not 2464 suitable for doing TBAA. Instead, metadata is added to the IR to 2465 describe a type system of a higher level language. This can be used to 2466 implement typical C/C++ TBAA, but it can also be used to implement 2467 custom alias analysis behavior for other languages. 2468 2469 The current metadata format is very simple. TBAA metadata nodes have up 2470 to three fields, e.g.: 2471 2472 .. code-block:: llvm 2473 2474 !0 = metadata !{ metadata !"an example type tree" } 2475 !1 = metadata !{ metadata !"int", metadata !0 } 2476 !2 = metadata !{ metadata !"float", metadata !0 } 2477 !3 = metadata !{ metadata !"const float", metadata !2, i64 1 } 2478 2479 The first field is an identity field. It can be any value, usually a 2480 metadata string, which uniquely identifies the type. The most important 2481 name in the tree is the name of the root node. Two trees with different 2482 root node names are entirely disjoint, even if they have leaves with 2483 common names. 2484 2485 The second field identifies the type's parent node in the tree, or is 2486 null or omitted for a root node. A type is considered to alias all of 2487 its descendants and all of its ancestors in the tree. Also, a type is 2488 considered to alias all types in other trees, so that bitcode produced 2489 from multiple front-ends is handled conservatively. 2490 2491 If the third field is present, it's an integer which if equal to 1 2492 indicates that the type is "constant" (meaning 2493 ``pointsToConstantMemory`` should return true; see `other useful 2494 AliasAnalysis methods <AliasAnalysis.html#OtherItfs>`_). 2495 2496 '``tbaa.struct``' Metadata 2497 ^^^^^^^^^^^^^^^^^^^^^^^^^^ 2498 2499 The :ref:`llvm.memcpy <int_memcpy>` is often used to implement 2500 aggregate assignment operations in C and similar languages, however it 2501 is defined to copy a contiguous region of memory, which is more than 2502 strictly necessary for aggregate types which contain holes due to 2503 padding. Also, it doesn't contain any TBAA information about the fields 2504 of the aggregate. 2505 2506 ``!tbaa.struct`` metadata can describe which memory subregions in a 2507 memcpy are padding and what the TBAA tags of the struct are. 2508 2509 The current metadata format is very simple. ``!tbaa.struct`` metadata 2510 nodes are a list of operands which are in conceptual groups of three. 2511 For each group of three, the first operand gives the byte offset of a 2512 field in bytes, the second gives its size in bytes, and the third gives 2513 its tbaa tag. e.g.: 2514 2515 .. code-block:: llvm 2516 2517 !4 = metadata !{ i64 0, i64 4, metadata !1, i64 8, i64 4, metadata !2 } 2518 2519 This describes a struct with two fields. The first is at offset 0 bytes 2520 with size 4 bytes, and has tbaa tag !1. The second is at offset 8 bytes 2521 and has size 4 bytes and has tbaa tag !2. 2522 2523 Note that the fields need not be contiguous. In this example, there is a 2524 4 byte gap between the two fields. This gap represents padding which 2525 does not carry useful data and need not be preserved. 2526 2527 '``fpmath``' Metadata 2528 ^^^^^^^^^^^^^^^^^^^^^ 2529 2530 ``fpmath`` metadata may be attached to any instruction of floating point 2531 type. It can be used to express the maximum acceptable error in the 2532 result of that instruction, in ULPs, thus potentially allowing the 2533 compiler to use a more efficient but less accurate method of computing 2534 it. ULP is defined as follows: 2535 2536 If ``x`` is a real number that lies between two finite consecutive 2537 floating-point numbers ``a`` and ``b``, without being equal to one 2538 of them, then ``ulp(x) = |b - a|``, otherwise ``ulp(x)`` is the 2539 distance between the two non-equal finite floating-point numbers 2540 nearest ``x``. Moreover, ``ulp(NaN)`` is ``NaN``. 2541 2542 The metadata node shall consist of a single positive floating point 2543 number representing the maximum relative error, for example: 2544 2545 .. code-block:: llvm 2546 2547 !0 = metadata !{ float 2.5 } ; maximum acceptable inaccuracy is 2.5 ULPs 2548 2549 '``range``' Metadata 2550 ^^^^^^^^^^^^^^^^^^^^ 2551 2552 ``range`` metadata may be attached only to loads of integer types. It 2553 expresses the possible ranges the loaded value is in. The ranges are 2554 represented with a flattened list of integers. The loaded value is known 2555 to be in the union of the ranges defined by each consecutive pair. Each 2556 pair has the following properties: 2557 2558 - The type must match the type loaded by the instruction. 2559 - The pair ``a,b`` represents the range ``[a,b)``. 2560 - Both ``a`` and ``b`` are constants. 2561 - The range is allowed to wrap. 2562 - The range should not represent the full or empty set. That is, 2563 ``a!=b``. 2564 2565 In addition, the pairs must be in signed order of the lower bound and 2566 they must be non-contiguous. 2567 2568 Examples: 2569 2570 .. code-block:: llvm 2571 2572 %a = load i8* %x, align 1, !range !0 ; Can only be 0 or 1 2573 %b = load i8* %y, align 1, !range !1 ; Can only be 255 (-1), 0 or 1 2574 %c = load i8* %z, align 1, !range !2 ; Can only be 0, 1, 3, 4 or 5 2575 %d = load i8* %z, align 1, !range !3 ; Can only be -2, -1, 3, 4 or 5 2576 ... 2577 !0 = metadata !{ i8 0, i8 2 } 2578 !1 = metadata !{ i8 255, i8 2 } 2579 !2 = metadata !{ i8 0, i8 2, i8 3, i8 6 } 2580 !3 = metadata !{ i8 -2, i8 0, i8 3, i8 6 } 2581 2582 '``llvm.loop``' 2583 ^^^^^^^^^^^^^^^ 2584 2585 It is sometimes useful to attach information to loop constructs. Currently, 2586 loop metadata is implemented as metadata attached to the branch instruction 2587 in the loop latch block. This type of metadata refer to a metadata node that is 2588 guaranteed to be separate for each loop. The loop identifier metadata is 2589 specified with the name ``llvm.loop``. 2590 2591 The loop identifier metadata is implemented using a metadata that refers to 2592 itself to avoid merging it with any other identifier metadata, e.g., 2593 during module linkage or function inlining. That is, each loop should refer 2594 to their own identification metadata even if they reside in separate functions. 2595 The following example contains loop identifier metadata for two separate loop 2596 constructs: 2597 2598 .. code-block:: llvm 2599 2600 !0 = metadata !{ metadata !0 } 2601 !1 = metadata !{ metadata !1 } 2602 2603 The loop identifier metadata can be used to specify additional per-loop 2604 metadata. Any operands after the first operand can be treated as user-defined 2605 metadata. For example the ``llvm.vectorizer.unroll`` metadata is understood 2606 by the loop vectorizer to indicate how many times to unroll the loop: 2607 2608 .. code-block:: llvm 2609 2610 br i1 %exitcond, label %._crit_edge, label %.lr.ph, !llvm.loop !0 2611 ... 2612 !0 = metadata !{ metadata !0, metadata !1 } 2613 !1 = metadata !{ metadata !"llvm.vectorizer.unroll", i32 2 } 2614 2615 '``llvm.mem``' 2616 ^^^^^^^^^^^^^^^ 2617 2618 Metadata types used to annotate memory accesses with information helpful 2619 for optimizations are prefixed with ``llvm.mem``. 2620 2621 '``llvm.mem.parallel_loop_access``' Metadata 2622 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 2623 2624 For a loop to be parallel, in addition to using 2625 the ``llvm.loop`` metadata to mark the loop latch branch instruction, 2626 also all of the memory accessing instructions in the loop body need to be 2627 marked with the ``llvm.mem.parallel_loop_access`` metadata. If there 2628 is at least one memory accessing instruction not marked with the metadata, 2629 the loop must be considered a sequential loop. This causes parallel loops to be 2630 converted to sequential loops due to optimization passes that are unaware of 2631 the parallel semantics and that insert new memory instructions to the loop 2632 body. 2633 2634 Example of a loop that is considered parallel due to its correct use of 2635 both ``llvm.loop`` and ``llvm.mem.parallel_loop_access`` 2636 metadata types that refer to the same loop identifier metadata. 2637 2638 .. code-block:: llvm 2639 2640 for.body: 2641 ... 2642 %0 = load i32* %arrayidx, align 4, !llvm.mem.parallel_loop_access !0 2643 ... 2644 store i32 %0, i32* %arrayidx4, align 4, !llvm.mem.parallel_loop_access !0 2645 ... 2646 br i1 %exitcond, label %for.end, label %for.body, !llvm.loop !0 2647 2648 for.end: 2649 ... 2650 !0 = metadata !{ metadata !0 } 2651 2652 It is also possible to have nested parallel loops. In that case the 2653 memory accesses refer to a list of loop identifier metadata nodes instead of 2654 the loop identifier metadata node directly: 2655 2656 .. code-block:: llvm 2657 2658 outer.for.body: 2659 ... 2660 2661 inner.for.body: 2662 ... 2663 %0 = load i32* %arrayidx, align 4, !llvm.mem.parallel_loop_access !0 2664 ... 2665 store i32 %0, i32* %arrayidx4, align 4, !llvm.mem.parallel_loop_access !0 2666 ... 2667 br i1 %exitcond, label %inner.for.end, label %inner.for.body, !llvm.loop !1 2668 2669 inner.for.end: 2670 ... 2671 %0 = load i32* %arrayidx, align 4, !llvm.mem.parallel_loop_access !0 2672 ... 2673 store i32 %0, i32* %arrayidx4, align 4, !llvm.mem.parallel_loop_access !0 2674 ... 2675 br i1 %exitcond, label %outer.for.end, label %outer.for.body, !llvm.loop !2 2676 2677 outer.for.end: ; preds = %for.body 2678 ... 2679 !0 = metadata !{ metadata !1, metadata !2 } ; a list of loop identifiers 2680 !1 = metadata !{ metadata !1 } ; an identifier for the inner loop 2681 !2 = metadata !{ metadata !2 } ; an identifier for the outer loop 2682 2683 '``llvm.vectorizer``' 2684 ^^^^^^^^^^^^^^^^^^^^^ 2685 2686 Metadata prefixed with ``llvm.vectorizer`` is used to control per-loop 2687 vectorization parameters such as vectorization factor and unroll factor. 2688 2689 ``llvm.vectorizer`` metadata should be used in conjunction with ``llvm.loop`` 2690 loop identification metadata. 2691 2692 '``llvm.vectorizer.unroll``' Metadata 2693 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 2694 2695 This metadata instructs the loop vectorizer to unroll the specified 2696 loop exactly ``N`` times. 2697 2698 The first operand is the string ``llvm.vectorizer.unroll`` and the second 2699 operand is an integer specifying the unroll factor. For example: 2700 2701 .. code-block:: llvm 2702 2703 !0 = metadata !{ metadata !"llvm.vectorizer.unroll", i32 4 } 2704 2705 Note that setting ``llvm.vectorizer.unroll`` to 1 disables unrolling of the 2706 loop. 2707 2708 If ``llvm.vectorizer.unroll`` is set to 0 then the amount of unrolling will be 2709 determined automatically. 2710 2711 '``llvm.vectorizer.width``' Metadata 2712 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 2713 2714 This metadata sets the target width of the vectorizer to ``N``. Without 2715 this metadata, the vectorizer will choose a width automatically. 2716 Regardless of this metadata, the vectorizer will only vectorize loops if 2717 it believes it is valid to do so. 2718 2719 The first operand is the string ``llvm.vectorizer.width`` and the second 2720 operand is an integer specifying the width. For example: 2721 2722 .. code-block:: llvm 2723 2724 !0 = metadata !{ metadata !"llvm.vectorizer.width", i32 4 } 2725 2726 Note that setting ``llvm.vectorizer.width`` to 1 disables vectorization of the 2727 loop. 2728 2729 If ``llvm.vectorizer.width`` is set to 0 then the width will be determined 2730 automatically. 2731 2732 Module Flags Metadata 2733 ===================== 2734 2735 Information about the module as a whole is difficult to convey to LLVM's 2736 subsystems. The LLVM IR isn't sufficient to transmit this information. 2737 The ``llvm.module.flags`` named metadata exists in order to facilitate 2738 this. These flags are in the form of key / value pairs --- much like a 2739 dictionary --- making it easy for any subsystem who cares about a flag to 2740 look it up. 2741 2742 The ``llvm.module.flags`` metadata contains a list of metadata triplets. 2743 Each triplet has the following form: 2744 2745 - The first element is a *behavior* flag, which specifies the behavior 2746 when two (or more) modules are merged together, and it encounters two 2747 (or more) metadata with the same ID. The supported behaviors are 2748 described below. 2749 - The second element is a metadata string that is a unique ID for the 2750 metadata. Each module may only have one flag entry for each unique ID (not 2751 including entries with the **Require** behavior). 2752 - The third element is the value of the flag. 2753 2754 When two (or more) modules are merged together, the resulting 2755 ``llvm.module.flags`` metadata is the union of the modules' flags. That is, for 2756 each unique metadata ID string, there will be exactly one entry in the merged 2757 modules ``llvm.module.flags`` metadata table, and the value for that entry will 2758 be determined by the merge behavior flag, as described below. The only exception 2759 is that entries with the *Require* behavior are always preserved. 2760 2761 The following behaviors are supported: 2762 2763 .. list-table:: 2764 :header-rows: 1 2765 :widths: 10 90 2766 2767 * - Value 2768 - Behavior 2769 2770 * - 1 2771 - **Error** 2772 Emits an error if two values disagree, otherwise the resulting value 2773 is that of the operands. 2774 2775 * - 2 2776 - **Warning** 2777 Emits a warning if two values disagree. The result value will be the 2778 operand for the flag from the first module being linked. 2779 2780 * - 3 2781 - **Require** 2782 Adds a requirement that another module flag be present and have a 2783 specified value after linking is performed. The value must be a 2784 metadata pair, where the first element of the pair is the ID of the 2785 module flag to be restricted, and the second element of the pair is 2786 the value the module flag should be restricted to. This behavior can 2787 be used to restrict the allowable results (via triggering of an 2788 error) of linking IDs with the **Override** behavior. 2789 2790 * - 4 2791 - **Override** 2792 Uses the specified value, regardless of the behavior or value of the 2793 other module. If both modules specify **Override**, but the values 2794 differ, an error will be emitted. 2795 2796 * - 5 2797 - **Append** 2798 Appends the two values, which are required to be metadata nodes. 2799 2800 * - 6 2801 - **AppendUnique** 2802 Appends the two values, which are required to be metadata 2803 nodes. However, duplicate entries in the second list are dropped 2804 during the append operation. 2805 2806 It is an error for a particular unique flag ID to have multiple behaviors, 2807 except in the case of **Require** (which adds restrictions on another metadata 2808 value) or **Override**. 2809 2810 An example of module flags: 2811 2812 .. code-block:: llvm 2813 2814 !0 = metadata !{ i32 1, metadata !"foo", i32 1 } 2815 !1 = metadata !{ i32 4, metadata !"bar", i32 37 } 2816 !2 = metadata !{ i32 2, metadata !"qux", i32 42 } 2817 !3 = metadata !{ i32 3, metadata !"qux", 2818 metadata !{ 2819 metadata !"foo", i32 1 2820 } 2821 } 2822 !llvm.module.flags = !{ !0, !1, !2, !3 } 2823 2824 - Metadata ``!0`` has the ID ``!"foo"`` and the value '1'. The behavior 2825 if two or more ``!"foo"`` flags are seen is to emit an error if their 2826 values are not equal. 2827 2828 - Metadata ``!1`` has the ID ``!"bar"`` and the value '37'. The 2829 behavior if two or more ``!"bar"`` flags are seen is to use the value 2830 '37'. 2831 2832 - Metadata ``!2`` has the ID ``!"qux"`` and the value '42'. The 2833 behavior if two or more ``!"qux"`` flags are seen is to emit a 2834 warning if their values are not equal. 2835 2836 - Metadata ``!3`` has the ID ``!"qux"`` and the value: 2837 2838 :: 2839 2840 metadata !{ metadata !"foo", i32 1 } 2841 2842 The behavior is to emit an error if the ``llvm.module.flags`` does not 2843 contain a flag with the ID ``!"foo"`` that has the value '1' after linking is 2844 performed. 2845 2846 Objective-C Garbage Collection Module Flags Metadata 2847 ---------------------------------------------------- 2848 2849 On the Mach-O platform, Objective-C stores metadata about garbage 2850 collection in a special section called "image info". The metadata 2851 consists of a version number and a bitmask specifying what types of 2852 garbage collection are supported (if any) by the file. If two or more 2853 modules are linked together their garbage collection metadata needs to 2854 be merged rather than appended together. 2855 2856 The Objective-C garbage collection module flags metadata consists of the 2857 following key-value pairs: 2858 2859 .. list-table:: 2860 :header-rows: 1 2861 :widths: 30 70 2862 2863 * - Key 2864 - Value 2865 2866 * - ``Objective-C Version`` 2867 - **[Required]** --- The Objective-C ABI version. Valid values are 1 and 2. 2868 2869 * - ``Objective-C Image Info Version`` 2870 - **[Required]** --- The version of the image info section. Currently 2871 always 0. 2872 2873 * - ``Objective-C Image Info Section`` 2874 - **[Required]** --- The section to place the metadata. Valid values are 2875 ``"__OBJC, __image_info, regular"`` for Objective-C ABI version 1, and 2876 ``"__DATA,__objc_imageinfo, regular, no_dead_strip"`` for 2877 Objective-C ABI version 2. 2878 2879 * - ``Objective-C Garbage Collection`` 2880 - **[Required]** --- Specifies whether garbage collection is supported or 2881 not. Valid values are 0, for no garbage collection, and 2, for garbage 2882 collection supported. 2883 2884 * - ``Objective-C GC Only`` 2885 - **[Optional]** --- Specifies that only garbage collection is supported. 2886 If present, its value must be 6. This flag requires that the 2887 ``Objective-C Garbage Collection`` flag have the value 2. 2888 2889 Some important flag interactions: 2890 2891 - If a module with ``Objective-C Garbage Collection`` set to 0 is 2892 merged with a module with ``Objective-C Garbage Collection`` set to 2893 2, then the resulting module has the 2894 ``Objective-C Garbage Collection`` flag set to 0. 2895 - A module with ``Objective-C Garbage Collection`` set to 0 cannot be 2896 merged with a module with ``Objective-C GC Only`` set to 6. 2897 2898 Automatic Linker Flags Module Flags Metadata 2899 -------------------------------------------- 2900 2901 Some targets support embedding flags to the linker inside individual object 2902 files. Typically this is used in conjunction with language extensions which 2903 allow source files to explicitly declare the libraries they depend on, and have 2904 these automatically be transmitted to the linker via object files. 2905 2906 These flags are encoded in the IR using metadata in the module flags section, 2907 using the ``Linker Options`` key. The merge behavior for this flag is required 2908 to be ``AppendUnique``, and the value for the key is expected to be a metadata 2909 node which should be a list of other metadata nodes, each of which should be a 2910 list of metadata strings defining linker options. 2911 2912 For example, the following metadata section specifies two separate sets of 2913 linker options, presumably to link against ``libz`` and the ``Cocoa`` 2914 framework:: 2915 2916 !0 = metadata !{ i32 6, metadata !"Linker Options", 2917 metadata !{ 2918 metadata !{ metadata !"-lz" }, 2919 metadata !{ metadata !"-framework", metadata !"Cocoa" } } } 2920 !llvm.module.flags = !{ !0 } 2921 2922 The metadata encoding as lists of lists of options, as opposed to a collapsed 2923 list of options, is chosen so that the IR encoding can use multiple option 2924 strings to specify e.g., a single library, while still having that specifier be 2925 preserved as an atomic element that can be recognized by a target specific 2926 assembly writer or object file emitter. 2927 2928 Each individual option is required to be either a valid option for the target's 2929 linker, or an option that is reserved by the target specific assembly writer or 2930 object file emitter. No other aspect of these options is defined by the IR. 2931 2932 .. _intrinsicglobalvariables: 2933 2934 Intrinsic Global Variables 2935 ========================== 2936 2937 LLVM has a number of "magic" global variables that contain data that 2938 affect code generation or other IR semantics. These are documented here. 2939 All globals of this sort should have a section specified as 2940 "``llvm.metadata``". This section and all globals that start with 2941 "``llvm.``" are reserved for use by LLVM. 2942 2943 .. _gv_llvmused: 2944 2945 The '``llvm.used``' Global Variable 2946 ----------------------------------- 2947 2948 The ``@llvm.used`` global is an array which has 2949 :ref:`appending linkage <linkage_appending>`. This array contains a list of 2950 pointers to named global variables, functions and aliases which may optionally 2951 have a pointer cast formed of bitcast or getelementptr. For example, a legal 2952 use of it is: 2953 2954 .. code-block:: llvm 2955 2956 @X = global i8 4 2957 @Y = global i32 123 2958 2959 @llvm.used = appending global [2 x i8*] [ 2960 i8* @X, 2961 i8* bitcast (i32* @Y to i8*) 2962 ], section "llvm.metadata" 2963 2964 If a symbol appears in the ``@llvm.used`` list, then the compiler, assembler, 2965 and linker are required to treat the symbol as if there is a reference to the 2966 symbol that it cannot see (which is why they have to be named). For example, if 2967 a variable has internal linkage and no references other than that from the 2968 ``@llvm.used`` list, it cannot be deleted. This is commonly used to represent 2969 references from inline asms and other things the compiler cannot "see", and 2970 corresponds to "``attribute((used))``" in GNU C. 2971 2972 On some targets, the code generator must emit a directive to the 2973 assembler or object file to prevent the assembler and linker from 2974 molesting the symbol. 2975 2976 .. _gv_llvmcompilerused: 2977 2978 The '``llvm.compiler.used``' Global Variable 2979 -------------------------------------------- 2980 2981 The ``@llvm.compiler.used`` directive is the same as the ``@llvm.used`` 2982 directive, except that it only prevents the compiler from touching the 2983 symbol. On targets that support it, this allows an intelligent linker to 2984 optimize references to the symbol without being impeded as it would be 2985 by ``@llvm.used``. 2986 2987 This is a rare construct that should only be used in rare circumstances, 2988 and should not be exposed to source languages. 2989 2990 .. _gv_llvmglobalctors: 2991 2992 The '``llvm.global_ctors``' Global Variable 2993 ------------------------------------------- 2994 2995 .. code-block:: llvm 2996 2997 %0 = type { i32, void ()* } 2998 @llvm.global_ctors = appending global [1 x %0] [%0 { i32 65535, void ()* @ctor }] 2999 3000 The ``@llvm.global_ctors`` array contains a list of constructor 3001 functions and associated priorities. The functions referenced by this 3002 array will be called in ascending order of priority (i.e. lowest first) 3003 when the module is loaded. The order of functions with the same priority 3004 is not defined. 3005 3006 .. _llvmglobaldtors: 3007 3008 The '``llvm.global_dtors``' Global Variable 3009 ------------------------------------------- 3010 3011 .. code-block:: llvm 3012 3013 %0 = type { i32, void ()* } 3014 @llvm.global_dtors = appending global [1 x %0] [%0 { i32 65535, void ()* @dtor }] 3015 3016 The ``@llvm.global_dtors`` array contains a list of destructor functions 3017 and associated priorities. The functions referenced by this array will 3018 be called in descending order of priority (i.e. highest first) when the 3019 module is loaded. The order of functions with the same priority is not 3020 defined. 3021 3022 Instruction Reference 3023 ===================== 3024 3025 The LLVM instruction set consists of several different classifications 3026 of instructions: :ref:`terminator instructions <terminators>`, :ref:`binary 3027 instructions <binaryops>`, :ref:`bitwise binary 3028 instructions <bitwiseops>`, :ref:`memory instructions <memoryops>`, and 3029 :ref:`other instructions <otherops>`. 3030 3031 .. _terminators: 3032 3033 Terminator Instructions 3034 ----------------------- 3035 3036 As mentioned :ref:`previously <functionstructure>`, every basic block in a 3037 program ends with a "Terminator" instruction, which indicates which 3038 block should be executed after the current block is finished. These 3039 terminator instructions typically yield a '``void``' value: they produce 3040 control flow, not values (the one exception being the 3041 ':ref:`invoke <i_invoke>`' instruction). 3042 3043 The terminator instructions are: ':ref:`ret <i_ret>`', 3044 ':ref:`br <i_br>`', ':ref:`switch <i_switch>`', 3045 ':ref:`indirectbr <i_indirectbr>`', ':ref:`invoke <i_invoke>`', 3046 ':ref:`resume <i_resume>`', and ':ref:`unreachable <i_unreachable>`'. 3047 3048 .. _i_ret: 3049 3050 '``ret``' Instruction 3051 ^^^^^^^^^^^^^^^^^^^^^ 3052 3053 Syntax: 3054 """"""" 3055 3056 :: 3057 3058 ret <type> <value> ; Return a value from a non-void function 3059 ret void ; Return from void function 3060 3061 Overview: 3062 """"""""" 3063 3064 The '``ret``' instruction is used to return control flow (and optionally 3065 a value) from a function back to the caller. 3066 3067 There are two forms of the '``ret``' instruction: one that returns a 3068 value and then causes control flow, and one that just causes control 3069 flow to occur. 3070 3071 Arguments: 3072 """""""""" 3073 3074 The '``ret``' instruction optionally accepts a single argument, the 3075 return value. The type of the return value must be a ':ref:`first 3076 class <t_firstclass>`' type. 3077 3078 A function is not :ref:`well formed <wellformed>` if it it has a non-void 3079 return type and contains a '``ret``' instruction with no return value or 3080 a return value with a type that does not match its type, or if it has a 3081 void return type and contains a '``ret``' instruction with a return 3082 value. 3083 3084 Semantics: 3085 """""""""" 3086 3087 When the '``ret``' instruction is executed, control flow returns back to 3088 the calling function's context. If the caller is a 3089 ":ref:`call <i_call>`" instruction, execution continues at the 3090 instruction after the call. If the caller was an 3091 ":ref:`invoke <i_invoke>`" instruction, execution continues at the 3092 beginning of the "normal" destination block. If the instruction returns 3093 a value, that value shall set the call or invoke instruction's return 3094 value. 3095 3096 Example: 3097 """""""" 3098 3099 .. code-block:: llvm 3100 3101 ret i32 5 ; Return an integer value of 5 3102 ret void ; Return from a void function 3103 ret { i32, i8 } { i32 4, i8 2 } ; Return a struct of values 4 and 2 3104 3105 .. _i_br: 3106 3107 '``br``' Instruction 3108 ^^^^^^^^^^^^^^^^^^^^ 3109 3110 Syntax: 3111 """"""" 3112 3113 :: 3114 3115 br i1 <cond>, label <iftrue>, label <iffalse> 3116 br label <dest> ; Unconditional branch 3117 3118 Overview: 3119 """"""""" 3120 3121 The '``br``' instruction is used to cause control flow to transfer to a 3122 different basic block in the current function. There are two forms of 3123 this instruction, corresponding to a conditional branch and an 3124 unconditional branch. 3125 3126 Arguments: 3127 """""""""" 3128 3129 The conditional branch form of the '``br``' instruction takes a single 3130 '``i1``' value and two '``label``' values. The unconditional form of the 3131 '``br``' instruction takes a single '``label``' value as a target. 3132 3133 Semantics: 3134 """""""""" 3135 3136 Upon execution of a conditional '``br``' instruction, the '``i1``' 3137 argument is evaluated. If the value is ``true``, control flows to the 3138 '``iftrue``' ``label`` argument. If "cond" is ``false``, control flows 3139 to the '``iffalse``' ``label`` argument. 3140 3141 Example: 3142 """""""" 3143 3144 .. code-block:: llvm 3145 3146 Test: 3147 %cond = icmp eq i32 %a, %b 3148 br i1 %cond, label %IfEqual, label %IfUnequal 3149 IfEqual: 3150 ret i32 1 3151 IfUnequal: 3152 ret i32 0 3153 3154 .. _i_switch: 3155 3156 '``switch``' Instruction 3157 ^^^^^^^^^^^^^^^^^^^^^^^^ 3158 3159 Syntax: 3160 """"""" 3161 3162 :: 3163 3164 switch <intty> <value>, label <defaultdest> [ <intty> <val>, label <dest> ... ] 3165 3166 Overview: 3167 """"""""" 3168 3169 The '``switch``' instruction is used to transfer control flow to one of 3170 several different places. It is a generalization of the '``br``' 3171 instruction, allowing a branch to occur to one of many possible 3172 destinations. 3173 3174 Arguments: 3175 """""""""" 3176 3177 The '``switch``' instruction uses three parameters: an integer 3178 comparison value '``value``', a default '``label``' destination, and an 3179 array of pairs of comparison value constants and '``label``'s. The table 3180 is not allowed to contain duplicate constant entries. 3181 3182 Semantics: 3183 """""""""" 3184 3185 The ``switch`` instruction specifies a table of values and destinations. 3186 When the '``switch``' instruction is executed, this table is searched 3187 for the given value. If the value is found, control flow is transferred 3188 to the corresponding destination; otherwise, control flow is transferred 3189 to the default destination. 3190 3191 Implementation: 3192 """"""""""""""" 3193 3194 Depending on properties of the target machine and the particular 3195 ``switch`` instruction, this instruction may be code generated in 3196 different ways. For example, it could be generated as a series of 3197 chained conditional branches or with a lookup table. 3198 3199 Example: 3200 """""""" 3201 3202 .. code-block:: llvm 3203 3204 ; Emulate a conditional br instruction 3205 %Val = zext i1 %value to i32 3206 switch i32 %Val, label %truedest [ i32 0, label %falsedest ] 3207 3208 ; Emulate an unconditional br instruction 3209 switch i32 0, label %dest [ ] 3210 3211 ; Implement a jump table: 3212 switch i32 %val, label %otherwise [ i32 0, label %onzero 3213 i32 1, label %onone 3214 i32 2, label %ontwo ] 3215 3216 .. _i_indirectbr: 3217 3218 '``indirectbr``' Instruction 3219 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 3220 3221 Syntax: 3222 """"""" 3223 3224 :: 3225 3226 indirectbr <somety>* <address>, [ label <dest1>, label <dest2>, ... ] 3227 3228 Overview: 3229 """"""""" 3230 3231 The '``indirectbr``' instruction implements an indirect branch to a 3232 label within the current function, whose address is specified by 3233 "``address``". Address must be derived from a 3234 :ref:`blockaddress <blockaddress>` constant. 3235 3236 Arguments: 3237 """""""""" 3238 3239 The '``address``' argument is the address of the label to jump to. The 3240 rest of the arguments indicate the full set of possible destinations 3241 that the address may point to. Blocks are allowed to occur multiple 3242 times in the destination list, though this isn't particularly useful. 3243 3244 This destination list is required so that dataflow analysis has an 3245 accurate understanding of the CFG. 3246 3247 Semantics: 3248 """""""""" 3249 3250 Control transfers to the block specified in the address argument. All 3251 possible destination blocks must be listed in the label list, otherwise 3252 this instruction has undefined behavior. This implies that jumps to 3253 labels defined in other functions have undefined behavior as well. 3254 3255 Implementation: 3256 """"""""""""""" 3257 3258 This is typically implemented with a jump through a register. 3259 3260 Example: 3261 """""""" 3262 3263 .. code-block:: llvm 3264 3265 indirectbr i8* %Addr, [ label %bb1, label %bb2, label %bb3 ] 3266 3267 .. _i_invoke: 3268 3269 '``invoke``' Instruction 3270 ^^^^^^^^^^^^^^^^^^^^^^^^ 3271 3272 Syntax: 3273 """"""" 3274 3275 :: 3276 3277 <result> = invoke [cconv] [ret attrs] <ptr to function ty> <function ptr val>(<function args>) [fn attrs] 3278 to label <normal label> unwind label <exception label> 3279 3280 Overview: 3281 """"""""" 3282 3283 The '``invoke``' instruction causes control to transfer to a specified 3284 function, with the possibility of control flow transfer to either the 3285 '``normal``' label or the '``exception``' label. If the callee function 3286 returns with the "``ret``" instruction, control flow will return to the 3287 "normal" label. If the callee (or any indirect callees) returns via the 3288 ":ref:`resume <i_resume>`" instruction or other exception handling 3289 mechanism, control is interrupted and continued at the dynamically 3290 nearest "exception" label. 3291 3292 The '``exception``' label is a `landing 3293 pad <ExceptionHandling.html#overview>`_ for the exception. As such, 3294 '``exception``' label is required to have the 3295 ":ref:`landingpad <i_landingpad>`" instruction, which contains the 3296 information about the behavior of the program after unwinding happens, 3297 as its first non-PHI instruction. The restrictions on the 3298 "``landingpad``" instruction's tightly couples it to the "``invoke``" 3299 instruction, so that the important information contained within the 3300 "``landingpad``" instruction can't be lost through normal code motion. 3301 3302 Arguments: 3303 """""""""" 3304 3305 This instruction requires several arguments: 3306 3307 #. The optional "cconv" marker indicates which :ref:`calling 3308 convention <callingconv>` the call should use. If none is 3309 specified, the call defaults to using C calling conventions. 3310 #. The optional :ref:`Parameter Attributes <paramattrs>` list for return 3311 values. Only '``zeroext``', '``signext``', and '``inreg``' attributes 3312 are valid here. 3313 #. '``ptr to function ty``': shall be the signature of the pointer to 3314 function value being invoked. In most cases, this is a direct 3315 function invocation, but indirect ``invoke``'s are just as possible, 3316 branching off an arbitrary pointer to function value. 3317 #. '``function ptr val``': An LLVM value containing a pointer to a 3318 function to be invoked. 3319 #. '``function args``': argument list whose types match the function 3320 signature argument types and parameter attributes. All arguments must 3321 be of :ref:`first class <t_firstclass>` type. If the function signature 3322 indicates the function accepts a variable number of arguments, the 3323 extra arguments can be specified. 3324 #. '``normal label``': the label reached when the called function 3325 executes a '``ret``' instruction. 3326 #. '``exception label``': the label reached when a callee returns via 3327 the :ref:`resume <i_resume>` instruction or other exception handling 3328 mechanism. 3329 #. The optional :ref:`function attributes <fnattrs>` list. Only 3330 '``noreturn``', '``nounwind``', '``readonly``' and '``readnone``' 3331 attributes are valid here. 3332 3333 Semantics: 3334 """""""""" 3335 3336 This instruction is designed to operate as a standard '``call``' 3337 instruction in most regards. The primary difference is that it 3338 establishes an association with a label, which is used by the runtime 3339 library to unwind the stack. 3340 3341 This instruction is used in languages with destructors to ensure that 3342 proper cleanup is performed in the case of either a ``longjmp`` or a 3343 thrown exception. Additionally, this is important for implementation of 3344 '``catch``' clauses in high-level languages that support them. 3345 3346 For the purposes of the SSA form, the definition of the value returned 3347 by the '``invoke``' instruction is deemed to occur on the edge from the 3348 current block to the "normal" label. If the callee unwinds then no 3349 return value is available. 3350 3351 Example: 3352 """""""" 3353 3354 .. code-block:: llvm 3355 3356 %retval = invoke i32 @Test(i32 15) to label %Continue 3357 unwind label %TestCleanup ; {i32}:retval set 3358 %retval = invoke coldcc i32 %Testfnptr(i32 15) to label %Continue 3359 unwind label %TestCleanup ; {i32}:retval set 3360 3361 .. _i_resume: 3362 3363 '``resume``' Instruction 3364 ^^^^^^^^^^^^^^^^^^^^^^^^ 3365 3366 Syntax: 3367 """"""" 3368 3369 :: 3370 3371 resume <type> <value> 3372 3373 Overview: 3374 """"""""" 3375 3376 The '``resume``' instruction is a terminator instruction that has no 3377 successors. 3378 3379 Arguments: 3380 """""""""" 3381 3382 The '``resume``' instruction requires one argument, which must have the 3383 same type as the result of any '``landingpad``' instruction in the same 3384 function. 3385 3386 Semantics: 3387 """""""""" 3388 3389 The '``resume``' instruction resumes propagation of an existing 3390 (in-flight) exception whose unwinding was interrupted with a 3391 :ref:`landingpad <i_landingpad>` instruction. 3392 3393 Example: 3394 """""""" 3395 3396 .. code-block:: llvm 3397 3398 resume { i8*, i32 } %exn 3399 3400 .. _i_unreachable: 3401 3402 '``unreachable``' Instruction 3403 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 3404 3405 Syntax: 3406 """"""" 3407 3408 :: 3409 3410 unreachable 3411 3412 Overview: 3413 """"""""" 3414 3415 The '``unreachable``' instruction has no defined semantics. This 3416 instruction is used to inform the optimizer that a particular portion of 3417 the code is not reachable. This can be used to indicate that the code 3418 after a no-return function cannot be reached, and other facts. 3419 3420 Semantics: 3421 """""""""" 3422 3423 The '``unreachable``' instruction has no defined semantics. 3424 3425 .. _binaryops: 3426 3427 Binary Operations 3428 ----------------- 3429 3430 Binary operators are used to do most of the computation in a program. 3431 They require two operands of the same type, execute an operation on 3432 them, and produce a single value. The operands might represent multiple 3433 data, as is the case with the :ref:`vector <t_vector>` data type. The 3434 result value has the same type as its operands. 3435 3436 There are several different binary operators: 3437 3438 .. _i_add: 3439 3440 '``add``' Instruction 3441 ^^^^^^^^^^^^^^^^^^^^^ 3442 3443 Syntax: 3444 """"""" 3445 3446 :: 3447 3448 <result> = add <ty> <op1>, <op2> ; yields {ty}:result 3449 <result> = add nuw <ty> <op1>, <op2> ; yields {ty}:result 3450 <result> = add nsw <ty> <op1>, <op2> ; yields {ty}:result 3451 <result> = add nuw nsw <ty> <op1>, <op2> ; yields {ty}:result 3452 3453 Overview: 3454 """"""""" 3455 3456 The '``add``' instruction returns the sum of its two operands. 3457 3458 Arguments: 3459 """""""""" 3460 3461 The two arguments to the '``add``' instruction must be 3462 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both 3463 arguments must have identical types. 3464 3465 Semantics: 3466 """""""""" 3467 3468 The value produced is the integer sum of the two operands. 3469 3470 If the sum has unsigned overflow, the result returned is the 3471 mathematical result modulo 2\ :sup:`n`\ , where n is the bit width of 3472 the result. 3473 3474 Because LLVM integers use a two's complement representation, this 3475 instruction is appropriate for both signed and unsigned integers. 3476 3477 ``nuw`` and ``nsw`` stand for "No Unsigned Wrap" and "No Signed Wrap", 3478 respectively. If the ``nuw`` and/or ``nsw`` keywords are present, the 3479 result value of the ``add`` is a :ref:`poison value <poisonvalues>` if 3480 unsigned and/or signed overflow, respectively, occurs. 3481 3482 Example: 3483 """""""" 3484 3485 .. code-block:: llvm 3486 3487 <result> = add i32 4, %var ; yields {i32}:result = 4 + %var 3488 3489 .. _i_fadd: 3490 3491 '``fadd``' Instruction 3492 ^^^^^^^^^^^^^^^^^^^^^^ 3493 3494 Syntax: 3495 """"""" 3496 3497 :: 3498 3499 <result> = fadd [fast-math flags]* <ty> <op1>, <op2> ; yields {ty}:result 3500 3501 Overview: 3502 """"""""" 3503 3504 The '``fadd``' instruction returns the sum of its two operands. 3505 3506 Arguments: 3507 """""""""" 3508 3509 The two arguments to the '``fadd``' instruction must be :ref:`floating 3510 point <t_floating>` or :ref:`vector <t_vector>` of floating point values. 3511 Both arguments must have identical types. 3512 3513 Semantics: 3514 """""""""" 3515 3516 The value produced is the floating point sum of the two operands. This 3517 instruction can also take any number of :ref:`fast-math flags <fastmath>`, 3518 which are optimization hints to enable otherwise unsafe floating point 3519 optimizations: 3520 3521 Example: 3522 """""""" 3523 3524 .. code-block:: llvm 3525 3526 <result> = fadd float 4.0, %var ; yields {float}:result = 4.0 + %var 3527 3528 '``sub``' Instruction 3529 ^^^^^^^^^^^^^^^^^^^^^ 3530 3531 Syntax: 3532 """"""" 3533 3534 :: 3535 3536 <result> = sub <ty> <op1>, <op2> ; yields {ty}:result 3537 <result> = sub nuw <ty> <op1>, <op2> ; yields {ty}:result 3538 <result> = sub nsw <ty> <op1>, <op2> ; yields {ty}:result 3539 <result> = sub nuw nsw <ty> <op1>, <op2> ; yields {ty}:result 3540 3541 Overview: 3542 """"""""" 3543 3544 The '``sub``' instruction returns the difference of its two operands. 3545 3546 Note that the '``sub``' instruction is used to represent the '``neg``' 3547 instruction present in most other intermediate representations. 3548 3549 Arguments: 3550 """""""""" 3551 3552 The two arguments to the '``sub``' instruction must be 3553 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both 3554 arguments must have identical types. 3555 3556 Semantics: 3557 """""""""" 3558 3559 The value produced is the integer difference of the two operands. 3560 3561 If the difference has unsigned overflow, the result returned is the 3562 mathematical result modulo 2\ :sup:`n`\ , where n is the bit width of 3563 the result. 3564 3565 Because LLVM integers use a two's complement representation, this 3566 instruction is appropriate for both signed and unsigned integers. 3567 3568 ``nuw`` and ``nsw`` stand for "No Unsigned Wrap" and "No Signed Wrap", 3569 respectively. If the ``nuw`` and/or ``nsw`` keywords are present, the 3570 result value of the ``sub`` is a :ref:`poison value <poisonvalues>` if 3571 unsigned and/or signed overflow, respectively, occurs. 3572 3573 Example: 3574 """""""" 3575 3576 .. code-block:: llvm 3577 3578 <result> = sub i32 4, %var ; yields {i32}:result = 4 - %var 3579 <result> = sub i32 0, %val ; yields {i32}:result = -%var 3580 3581 .. _i_fsub: 3582 3583 '``fsub``' Instruction 3584 ^^^^^^^^^^^^^^^^^^^^^^ 3585 3586 Syntax: 3587 """"""" 3588 3589 :: 3590 3591 <result> = fsub [fast-math flags]* <ty> <op1>, <op2> ; yields {ty}:result 3592 3593 Overview: 3594 """"""""" 3595 3596 The '``fsub``' instruction returns the difference of its two operands. 3597 3598 Note that the '``fsub``' instruction is used to represent the '``fneg``' 3599 instruction present in most other intermediate representations. 3600 3601 Arguments: 3602 """""""""" 3603 3604 The two arguments to the '``fsub``' instruction must be :ref:`floating 3605 point <t_floating>` or :ref:`vector <t_vector>` of floating point values. 3606 Both arguments must have identical types. 3607 3608 Semantics: 3609 """""""""" 3610 3611 The value produced is the floating point difference of the two operands. 3612 This instruction can also take any number of :ref:`fast-math 3613 flags <fastmath>`, which are optimization hints to enable otherwise 3614 unsafe floating point optimizations: 3615 3616 Example: 3617 """""""" 3618 3619 .. code-block:: llvm 3620 3621 <result> = fsub float 4.0, %var ; yields {float}:result = 4.0 - %var 3622 <result> = fsub float -0.0, %val ; yields {float}:result = -%var 3623 3624 '``mul``' Instruction 3625 ^^^^^^^^^^^^^^^^^^^^^ 3626 3627 Syntax: 3628 """"""" 3629 3630 :: 3631 3632 <result> = mul <ty> <op1>, <op2> ; yields {ty}:result 3633 <result> = mul nuw <ty> <op1>, <op2> ; yields {ty}:result 3634 <result> = mul nsw <ty> <op1>, <op2> ; yields {ty}:result 3635 <result> = mul nuw nsw <ty> <op1>, <op2> ; yields {ty}:result 3636 3637 Overview: 3638 """"""""" 3639 3640 The '``mul``' instruction returns the product of its two operands. 3641 3642 Arguments: 3643 """""""""" 3644 3645 The two arguments to the '``mul``' instruction must be 3646 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both 3647 arguments must have identical types. 3648 3649 Semantics: 3650 """""""""" 3651 3652 The value produced is the integer product of the two operands. 3653 3654 If the result of the multiplication has unsigned overflow, the result 3655 returned is the mathematical result modulo 2\ :sup:`n`\ , where n is the 3656 bit width of the result. 3657 3658 Because LLVM integers use a two's complement representation, and the 3659 result is the same width as the operands, this instruction returns the 3660 correct result for both signed and unsigned integers. If a full product 3661 (e.g. ``i32`` * ``i32`` -> ``i64``) is needed, the operands should be 3662 sign-extended or zero-extended as appropriate to the width of the full 3663 product. 3664 3665 ``nuw`` and ``nsw`` stand for "No Unsigned Wrap" and "No Signed Wrap", 3666 respectively. If the ``nuw`` and/or ``nsw`` keywords are present, the 3667 result value of the ``mul`` is a :ref:`poison value <poisonvalues>` if 3668 unsigned and/or signed overflow, respectively, occurs. 3669 3670 Example: 3671 """""""" 3672 3673 .. code-block:: llvm 3674 3675 <result> = mul i32 4, %var ; yields {i32}:result = 4 * %var 3676 3677 .. _i_fmul: 3678 3679 '``fmul``' Instruction 3680 ^^^^^^^^^^^^^^^^^^^^^^ 3681 3682 Syntax: 3683 """"""" 3684 3685 :: 3686 3687 <result> = fmul [fast-math flags]* <ty> <op1>, <op2> ; yields {ty}:result 3688 3689 Overview: 3690 """"""""" 3691 3692 The '``fmul``' instruction returns the product of its two operands. 3693 3694 Arguments: 3695 """""""""" 3696 3697 The two arguments to the '``fmul``' instruction must be :ref:`floating 3698 point <t_floating>` or :ref:`vector <t_vector>` of floating point values. 3699 Both arguments must have identical types. 3700 3701 Semantics: 3702 """""""""" 3703 3704 The value produced is the floating point product of the two operands. 3705 This instruction can also take any number of :ref:`fast-math 3706 flags <fastmath>`, which are optimization hints to enable otherwise 3707 unsafe floating point optimizations: 3708 3709 Example: 3710 """""""" 3711 3712 .. code-block:: llvm 3713 3714 <result> = fmul float 4.0, %var ; yields {float}:result = 4.0 * %var 3715 3716 '``udiv``' Instruction 3717 ^^^^^^^^^^^^^^^^^^^^^^ 3718 3719 Syntax: 3720 """"""" 3721 3722 :: 3723 3724 <result> = udiv <ty> <op1>, <op2> ; yields {ty}:result 3725 <result> = udiv exact <ty> <op1>, <op2> ; yields {ty}:result 3726 3727 Overview: 3728 """"""""" 3729 3730 The '``udiv``' instruction returns the quotient of its two operands. 3731 3732 Arguments: 3733 """""""""" 3734 3735 The two arguments to the '``udiv``' instruction must be 3736 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both 3737 arguments must have identical types. 3738 3739 Semantics: 3740 """""""""" 3741 3742 The value produced is the unsigned integer quotient of the two operands. 3743 3744 Note that unsigned integer division and signed integer division are 3745 distinct operations; for signed integer division, use '``sdiv``'. 3746 3747 Division by zero leads to undefined behavior. 3748 3749 If the ``exact`` keyword is present, the result value of the ``udiv`` is 3750 a :ref:`poison value <poisonvalues>` if %op1 is not a multiple of %op2 (as 3751 such, "((a udiv exact b) mul b) == a"). 3752 3753 Example: 3754 """""""" 3755 3756 .. code-block:: llvm 3757 3758 <result> = udiv i32 4, %var ; yields {i32}:result = 4 / %var 3759 3760 '``sdiv``' Instruction 3761 ^^^^^^^^^^^^^^^^^^^^^^ 3762 3763 Syntax: 3764 """"""" 3765 3766 :: 3767 3768 <result> = sdiv <ty> <op1>, <op2> ; yields {ty}:result 3769 <result> = sdiv exact <ty> <op1>, <op2> ; yields {ty}:result 3770 3771 Overview: 3772 """"""""" 3773 3774 The '``sdiv``' instruction returns the quotient of its two operands. 3775 3776 Arguments: 3777 """""""""" 3778 3779 The two arguments to the '``sdiv``' instruction must be 3780 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both 3781 arguments must have identical types. 3782 3783 Semantics: 3784 """""""""" 3785 3786 The value produced is the signed integer quotient of the two operands 3787 rounded towards zero. 3788 3789 Note that signed integer division and unsigned integer division are 3790 distinct operations; for unsigned integer division, use '``udiv``'. 3791 3792 Division by zero leads to undefined behavior. Overflow also leads to 3793 undefined behavior; this is a rare case, but can occur, for example, by 3794 doing a 32-bit division of -2147483648 by -1. 3795 3796 If the ``exact`` keyword is present, the result value of the ``sdiv`` is 3797 a :ref:`poison value <poisonvalues>` if the result would be rounded. 3798 3799 Example: 3800 """""""" 3801 3802 .. code-block:: llvm 3803 3804 <result> = sdiv i32 4, %var ; yields {i32}:result = 4 / %var 3805 3806 .. _i_fdiv: 3807 3808 '``fdiv``' Instruction 3809 ^^^^^^^^^^^^^^^^^^^^^^ 3810 3811 Syntax: 3812 """"""" 3813 3814 :: 3815 3816 <result> = fdiv [fast-math flags]* <ty> <op1>, <op2> ; yields {ty}:result 3817 3818 Overview: 3819 """"""""" 3820 3821 The '``fdiv``' instruction returns the quotient of its two operands. 3822 3823 Arguments: 3824 """""""""" 3825 3826 The two arguments to the '``fdiv``' instruction must be :ref:`floating 3827 point <t_floating>` or :ref:`vector <t_vector>` of floating point values. 3828 Both arguments must have identical types. 3829 3830 Semantics: 3831 """""""""" 3832 3833 The value produced is the floating point quotient of the two operands. 3834 This instruction can also take any number of :ref:`fast-math 3835 flags <fastmath>`, which are optimization hints to enable otherwise 3836 unsafe floating point optimizations: 3837 3838 Example: 3839 """""""" 3840 3841 .. code-block:: llvm 3842 3843 <result> = fdiv float 4.0, %var ; yields {float}:result = 4.0 / %var 3844 3845 '``urem``' Instruction 3846 ^^^^^^^^^^^^^^^^^^^^^^ 3847 3848 Syntax: 3849 """"""" 3850 3851 :: 3852 3853 <result> = urem <ty> <op1>, <op2> ; yields {ty}:result 3854 3855 Overview: 3856 """"""""" 3857 3858 The '``urem``' instruction returns the remainder from the unsigned 3859 division of its two arguments. 3860 3861 Arguments: 3862 """""""""" 3863 3864 The two arguments to the '``urem``' instruction must be 3865 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both 3866 arguments must have identical types. 3867 3868 Semantics: 3869 """""""""" 3870 3871 This instruction returns the unsigned integer *remainder* of a division. 3872 This instruction always performs an unsigned division to get the 3873 remainder. 3874 3875 Note that unsigned integer remainder and signed integer remainder are 3876 distinct operations; for signed integer remainder, use '``srem``'. 3877 3878 Taking the remainder of a division by zero leads to undefined behavior. 3879 3880 Example: 3881 """""""" 3882 3883 .. code-block:: llvm 3884 3885 <result> = urem i32 4, %var ; yields {i32}:result = 4 % %var 3886 3887 '``srem``' Instruction 3888 ^^^^^^^^^^^^^^^^^^^^^^ 3889 3890 Syntax: 3891 """"""" 3892 3893 :: 3894 3895 <result> = srem <ty> <op1>, <op2> ; yields {ty}:result 3896 3897 Overview: 3898 """"""""" 3899 3900 The '``srem``' instruction returns the remainder from the signed 3901 division of its two operands. This instruction can also take 3902 :ref:`vector <t_vector>` versions of the values in which case the elements 3903 must be integers. 3904 3905 Arguments: 3906 """""""""" 3907 3908 The two arguments to the '``srem``' instruction must be 3909 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both 3910 arguments must have identical types. 3911 3912 Semantics: 3913 """""""""" 3914 3915 This instruction returns the *remainder* of a division (where the result 3916 is either zero or has the same sign as the dividend, ``op1``), not the 3917 *modulo* operator (where the result is either zero or has the same sign 3918 as the divisor, ``op2``) of a value. For more information about the 3919 difference, see `The Math 3920 Forum <http://mathforum.org/dr.math/problems/anne.4.28.99.html>`_. For a 3921 table of how this is implemented in various languages, please see 3922 `Wikipedia: modulo 3923 operation <http://en.wikipedia.org/wiki/Modulo_operation>`_. 3924 3925 Note that signed integer remainder and unsigned integer remainder are 3926 distinct operations; for unsigned integer remainder, use '``urem``'. 3927 3928 Taking the remainder of a division by zero leads to undefined behavior. 3929 Overflow also leads to undefined behavior; this is a rare case, but can 3930 occur, for example, by taking the remainder of a 32-bit division of 3931 -2147483648 by -1. (The remainder doesn't actually overflow, but this 3932 rule lets srem be implemented using instructions that return both the 3933 result of the division and the remainder.) 3934 3935 Example: 3936 """""""" 3937 3938 .. code-block:: llvm 3939 3940 <result> = srem i32 4, %var ; yields {i32}:result = 4 % %var 3941 3942 .. _i_frem: 3943 3944 '``frem``' Instruction 3945 ^^^^^^^^^^^^^^^^^^^^^^ 3946 3947 Syntax: 3948 """"""" 3949 3950 :: 3951 3952 <result> = frem [fast-math flags]* <ty> <op1>, <op2> ; yields {ty}:result 3953 3954 Overview: 3955 """"""""" 3956 3957 The '``frem``' instruction returns the remainder from the division of 3958 its two operands. 3959 3960 Arguments: 3961 """""""""" 3962 3963 The two arguments to the '``frem``' instruction must be :ref:`floating 3964 point <t_floating>` or :ref:`vector <t_vector>` of floating point values. 3965 Both arguments must have identical types. 3966 3967 Semantics: 3968 """""""""" 3969 3970 This instruction returns the *remainder* of a division. The remainder 3971 has the same sign as the dividend. This instruction can also take any 3972 number of :ref:`fast-math flags <fastmath>`, which are optimization hints 3973 to enable otherwise unsafe floating point optimizations: 3974 3975 Example: 3976 """""""" 3977 3978 .. code-block:: llvm 3979 3980 <result> = frem float 4.0, %var ; yields {float}:result = 4.0 % %var 3981 3982 .. _bitwiseops: 3983 3984 Bitwise Binary Operations 3985 ------------------------- 3986 3987 Bitwise binary operators are used to do various forms of bit-twiddling 3988 in a program. They are generally very efficient instructions and can 3989 commonly be strength reduced from other instructions. They require two 3990 operands of the same type, execute an operation on them, and produce a 3991 single value. The resulting value is the same type as its operands. 3992 3993 '``shl``' Instruction 3994 ^^^^^^^^^^^^^^^^^^^^^ 3995 3996 Syntax: 3997 """"""" 3998 3999 :: 4000 4001 <result> = shl <ty> <op1>, <op2> ; yields {ty}:result 4002 <result> = shl nuw <ty> <op1>, <op2> ; yields {ty}:result 4003 <result> = shl nsw <ty> <op1>, <op2> ; yields {ty}:result 4004 <result> = shl nuw nsw <ty> <op1>, <op2> ; yields {ty}:result 4005 4006 Overview: 4007 """"""""" 4008 4009 The '``shl``' instruction returns the first operand shifted to the left 4010 a specified number of bits. 4011 4012 Arguments: 4013 """""""""" 4014 4015 Both arguments to the '``shl``' instruction must be the same 4016 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer type. 4017 '``op2``' is treated as an unsigned value. 4018 4019 Semantics: 4020 """""""""" 4021 4022 The value produced is ``op1`` \* 2\ :sup:`op2` mod 2\ :sup:`n`, 4023 where ``n`` is the width of the result. If ``op2`` is (statically or 4024 dynamically) negative or equal to or larger than the number of bits in 4025 ``op1``, the result is undefined. If the arguments are vectors, each 4026 vector element of ``op1`` is shifted by the corresponding shift amount 4027 in ``op2``. 4028 4029 If the ``nuw`` keyword is present, then the shift produces a :ref:`poison 4030 value <poisonvalues>` if it shifts out any non-zero bits. If the 4031 ``nsw`` keyword is present, then the shift produces a :ref:`poison 4032 value <poisonvalues>` if it shifts out any bits that disagree with the 4033 resultant sign bit. As such, NUW/NSW have the same semantics as they 4034 would if the shift were expressed as a mul instruction with the same 4035 nsw/nuw bits in (mul %op1, (shl 1, %op2)). 4036 4037 Example: 4038 """""""" 4039 4040 .. code-block:: llvm 4041 4042 <result> = shl i32 4, %var ; yields {i32}: 4 << %var 4043 <result> = shl i32 4, 2 ; yields {i32}: 16 4044 <result> = shl i32 1, 10 ; yields {i32}: 1024 4045 <result> = shl i32 1, 32 ; undefined 4046 <result> = shl <2 x i32> < i32 1, i32 1>, < i32 1, i32 2> ; yields: result=<2 x i32> < i32 2, i32 4> 4047 4048 '``lshr``' Instruction 4049 ^^^^^^^^^^^^^^^^^^^^^^ 4050 4051 Syntax: 4052 """"""" 4053 4054 :: 4055 4056 <result> = lshr <ty> <op1>, <op2> ; yields {ty}:result 4057 <result> = lshr exact <ty> <op1>, <op2> ; yields {ty}:result 4058 4059 Overview: 4060 """"""""" 4061 4062 The '``lshr``' instruction (logical shift right) returns the first 4063 operand shifted to the right a specified number of bits with zero fill. 4064 4065 Arguments: 4066 """""""""" 4067 4068 Both arguments to the '``lshr``' instruction must be the same 4069 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer type. 4070 '``op2``' is treated as an unsigned value. 4071 4072 Semantics: 4073 """""""""" 4074 4075 This instruction always performs a logical shift right operation. The 4076 most significant bits of the result will be filled with zero bits after 4077 the shift. If ``op2`` is (statically or dynamically) equal to or larger 4078 than the number of bits in ``op1``, the result is undefined. If the 4079 arguments are vectors, each vector element of ``op1`` is shifted by the 4080 corresponding shift amount in ``op2``. 4081 4082 If the ``exact`` keyword is present, the result value of the ``lshr`` is 4083 a :ref:`poison value <poisonvalues>` if any of the bits shifted out are 4084 non-zero. 4085 4086 Example: 4087 """""""" 4088 4089 .. code-block:: llvm 4090 4091 <result> = lshr i32 4, 1 ; yields {i32}:result = 2 4092 <result> = lshr i32 4, 2 ; yields {i32}:result = 1 4093 <result> = lshr i8 4, 3 ; yields {i8}:result = 0 4094 <result> = lshr i8 -2, 1 ; yields {i8}:result = 0x7F 4095 <result> = lshr i32 1, 32 ; undefined 4096 <result> = lshr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 2> ; yields: result=<2 x i32> < i32 0x7FFFFFFF, i32 1> 4097 4098 '``ashr``' Instruction 4099 ^^^^^^^^^^^^^^^^^^^^^^ 4100 4101 Syntax: 4102 """"""" 4103 4104 :: 4105 4106 <result> = ashr <ty> <op1>, <op2> ; yields {ty}:result 4107 <result> = ashr exact <ty> <op1>, <op2> ; yields {ty}:result 4108 4109 Overview: 4110 """"""""" 4111 4112 The '``ashr``' instruction (arithmetic shift right) returns the first 4113 operand shifted to the right a specified number of bits with sign 4114 extension. 4115 4116 Arguments: 4117 """""""""" 4118 4119 Both arguments to the '``ashr``' instruction must be the same 4120 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer type. 4121 '``op2``' is treated as an unsigned value. 4122 4123 Semantics: 4124 """""""""" 4125 4126 This instruction always performs an arithmetic shift right operation, 4127 The most significant bits of the result will be filled with the sign bit 4128 of ``op1``. If ``op2`` is (statically or dynamically) equal to or larger 4129 than the number of bits in ``op1``, the result is undefined. If the 4130 arguments are vectors, each vector element of ``op1`` is shifted by the 4131 corresponding shift amount in ``op2``. 4132 4133 If the ``exact`` keyword is present, the result value of the ``ashr`` is 4134 a :ref:`poison value <poisonvalues>` if any of the bits shifted out are 4135 non-zero. 4136 4137 Example: 4138 """""""" 4139 4140 .. code-block:: llvm 4141 4142 <result> = ashr i32 4, 1 ; yields {i32}:result = 2 4143 <result> = ashr i32 4, 2 ; yields {i32}:result = 1 4144 <result> = ashr i8 4, 3 ; yields {i8}:result = 0 4145 <result> = ashr i8 -2, 1 ; yields {i8}:result = -1 4146 <result> = ashr i32 1, 32 ; undefined 4147 <result> = ashr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 3> ; yields: result=<2 x i32> < i32 -1, i32 0> 4148 4149 '``and``' Instruction 4150 ^^^^^^^^^^^^^^^^^^^^^ 4151 4152 Syntax: 4153 """"""" 4154 4155 :: 4156 4157 <result> = and <ty> <op1>, <op2> ; yields {ty}:result 4158 4159 Overview: 4160 """"""""" 4161 4162 The '``and``' instruction returns the bitwise logical and of its two 4163 operands. 4164 4165 Arguments: 4166 """""""""" 4167 4168 The two arguments to the '``and``' instruction must be 4169 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both 4170 arguments must have identical types. 4171 4172 Semantics: 4173 """""""""" 4174 4175 The truth table used for the '``and``' instruction is: 4176 4177 +-----+-----+-----+ 4178 | In0 | In1 | Out | 4179 +-----+-----+-----+ 4180 | 0 | 0 | 0 | 4181 +-----+-----+-----+ 4182 | 0 | 1 | 0 | 4183 +-----+-----+-----+ 4184 | 1 | 0 | 0 | 4185 +-----+-----+-----+ 4186 | 1 | 1 | 1 | 4187 +-----+-----+-----+ 4188 4189 Example: 4190 """""""" 4191 4192 .. code-block:: llvm 4193 4194 <result> = and i32 4, %var ; yields {i32}:result = 4 & %var 4195 <result> = and i32 15, 40 ; yields {i32}:result = 8 4196 <result> = and i32 4, 8 ; yields {i32}:result = 0 4197 4198 '``or``' Instruction 4199 ^^^^^^^^^^^^^^^^^^^^ 4200 4201 Syntax: 4202 """"""" 4203 4204 :: 4205 4206 <result> = or <ty> <op1>, <op2> ; yields {ty}:result 4207 4208 Overview: 4209 """"""""" 4210 4211 The '``or``' instruction returns the bitwise logical inclusive or of its 4212 two operands. 4213 4214 Arguments: 4215 """""""""" 4216 4217 The two arguments to the '``or``' instruction must be 4218 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both 4219 arguments must have identical types. 4220 4221 Semantics: 4222 """""""""" 4223 4224 The truth table used for the '``or``' instruction is: 4225 4226 +-----+-----+-----+ 4227 | In0 | In1 | Out | 4228 +-----+-----+-----+ 4229 | 0 | 0 | 0 | 4230 +-----+-----+-----+ 4231 | 0 | 1 | 1 | 4232 +-----+-----+-----+ 4233 | 1 | 0 | 1 | 4234 +-----+-----+-----+ 4235 | 1 | 1 | 1 | 4236 +-----+-----+-----+ 4237 4238 Example: 4239 """""""" 4240 4241 :: 4242 4243 <result> = or i32 4, %var ; yields {i32}:result = 4 | %var 4244 <result> = or i32 15, 40 ; yields {i32}:result = 47 4245 <result> = or i32 4, 8 ; yields {i32}:result = 12 4246 4247 '``xor``' Instruction 4248 ^^^^^^^^^^^^^^^^^^^^^ 4249 4250 Syntax: 4251 """"""" 4252 4253 :: 4254 4255 <result> = xor <ty> <op1>, <op2> ; yields {ty}:result 4256 4257 Overview: 4258 """"""""" 4259 4260 The '``xor``' instruction returns the bitwise logical exclusive or of 4261 its two operands. The ``xor`` is used to implement the "one's 4262 complement" operation, which is the "~" operator in C. 4263 4264 Arguments: 4265 """""""""" 4266 4267 The two arguments to the '``xor``' instruction must be 4268 :ref:`integer <t_integer>` or :ref:`vector <t_vector>` of integer values. Both 4269 arguments must have identical types. 4270 4271 Semantics: 4272 """""""""" 4273 4274 The truth table used for the '``xor``' instruction is: 4275 4276 +-----+-----+-----+ 4277 | In0 | In1 | Out | 4278 +-----+-----+-----+ 4279 | 0 | 0 | 0 | 4280 +-----+-----+-----+ 4281 | 0 | 1 | 1 | 4282 +-----+-----+-----+ 4283 | 1 | 0 | 1 | 4284 +-----+-----+-----+ 4285 | 1 | 1 | 0 | 4286 +-----+-----+-----+ 4287 4288 Example: 4289 """""""" 4290 4291 .. code-block:: llvm 4292 4293 <result> = xor i32 4, %var ; yields {i32}:result = 4 ^ %var 4294 <result> = xor i32 15, 40 ; yields {i32}:result = 39 4295 <result> = xor i32 4, 8 ; yields {i32}:result = 12 4296 <result> = xor i32 %V, -1 ; yields {i32}:result = ~%V 4297 4298 Vector Operations 4299 ----------------- 4300 4301 LLVM supports several instructions to represent vector operations in a 4302 target-independent manner. These instructions cover the element-access 4303 and vector-specific operations needed to process vectors effectively. 4304 While LLVM does directly support these vector operations, many 4305 sophisticated algorithms will want to use target-specific intrinsics to 4306 take full advantage of a specific target. 4307 4308 .. _i_extractelement: 4309 4310 '``extractelement``' Instruction 4311 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 4312 4313 Syntax: 4314 """"""" 4315 4316 :: 4317 4318 <result> = extractelement <n x <ty>> <val>, i32 <idx> ; yields <ty> 4319 4320 Overview: 4321 """"""""" 4322 4323 The '``extractelement``' instruction extracts a single scalar element 4324 from a vector at a specified index. 4325 4326 Arguments: 4327 """""""""" 4328 4329 The first operand of an '``extractelement``' instruction is a value of 4330 :ref:`vector <t_vector>` type. The second operand is an index indicating 4331 the position from which to extract the element. The index may be a 4332 variable. 4333 4334 Semantics: 4335 """""""""" 4336 4337 The result is a scalar of the same type as the element type of ``val``. 4338 Its value is the value at position ``idx`` of ``val``. If ``idx`` 4339 exceeds the length of ``val``, the results are undefined. 4340 4341 Example: 4342 """""""" 4343 4344 .. code-block:: llvm 4345 4346 <result> = extractelement <4 x i32> %vec, i32 0 ; yields i32 4347 4348 .. _i_insertelement: 4349 4350 '``insertelement``' Instruction 4351 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 4352 4353 Syntax: 4354 """"""" 4355 4356 :: 4357 4358 <result> = insertelement <n x <ty>> <val>, <ty> <elt>, i32 <idx> ; yields <n x <ty>> 4359 4360 Overview: 4361 """"""""" 4362 4363 The '``insertelement``' instruction inserts a scalar element into a 4364 vector at a specified index. 4365 4366 Arguments: 4367 """""""""" 4368 4369 The first operand of an '``insertelement``' instruction is a value of 4370 :ref:`vector <t_vector>` type. The second operand is a scalar value whose 4371 type must equal the element type of the first operand. The third operand 4372 is an index indicating the position at which to insert the value. The 4373 index may be a variable. 4374 4375 Semantics: 4376 """""""""" 4377 4378 The result is a vector of the same type as ``val``. Its element values 4379 are those of ``val`` except at position ``idx``, where it gets the value 4380 ``elt``. If ``idx`` exceeds the length of ``val``, the results are 4381 undefined. 4382 4383 Example: 4384 """""""" 4385 4386 .. code-block:: llvm 4387 4388 <result> = insertelement <4 x i32> %vec, i32 1, i32 0 ; yields <4 x i32> 4389 4390 .. _i_shufflevector: 4391 4392 '``shufflevector``' Instruction 4393 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 4394 4395 Syntax: 4396 """"""" 4397 4398 :: 4399 4400 <result> = shufflevector <n x <ty>> <v1>, <n x <ty>> <v2>, <m x i32> <mask> ; yields <m x <ty>> 4401 4402 Overview: 4403 """"""""" 4404 4405 The '``shufflevector``' instruction constructs a permutation of elements 4406 from two input vectors, returning a vector with the same element type as 4407 the input and length that is the same as the shuffle mask. 4408 4409 Arguments: 4410 """""""""" 4411 4412 The first two operands of a '``shufflevector``' instruction are vectors 4413 with the same type. The third argument is a shuffle mask whose element 4414 type is always 'i32'. The result of the instruction is a vector whose 4415 length is the same as the shuffle mask and whose element type is the 4416 same as the element type of the first two operands. 4417 4418 The shuffle mask operand is required to be a constant vector with either 4419 constant integer or undef values. 4420 4421 Semantics: 4422 """""""""" 4423 4424 The elements of the two input vectors are numbered from left to right 4425 across both of the vectors. The shuffle mask operand specifies, for each 4426 element of the result vector, which element of the two input vectors the 4427 result element gets. The element selector may be undef (meaning "don't 4428 care") and the second operand may be undef if performing a shuffle from 4429 only one vector. 4430 4431 Example: 4432 """""""" 4433 4434 .. code-block:: llvm 4435 4436 <result> = shufflevector <4 x i32> %v1, <4 x i32> %v2, 4437 <4 x i32> <i32 0, i32 4, i32 1, i32 5> ; yields <4 x i32> 4438 <result> = shufflevector <4 x i32> %v1, <4 x i32> undef, 4439 <4 x i32> <i32 0, i32 1, i32 2, i32 3> ; yields <4 x i32> - Identity shuffle. 4440 <result> = shufflevector <8 x i32> %v1, <8 x i32> undef, 4441 <4 x i32> <i32 0, i32 1, i32 2, i32 3> ; yields <4 x i32> 4442 <result> = shufflevector <4 x i32> %v1, <4 x i32> %v2, 4443 <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7 > ; yields <8 x i32> 4444 4445 Aggregate Operations 4446 -------------------- 4447 4448 LLVM supports several instructions for working with 4449 :ref:`aggregate <t_aggregate>` values. 4450 4451 .. _i_extractvalue: 4452 4453 '``extractvalue``' Instruction 4454 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 4455 4456 Syntax: 4457 """"""" 4458 4459 :: 4460 4461 <result> = extractvalue <aggregate type> <val>, <idx>{, <idx>}* 4462 4463 Overview: 4464 """"""""" 4465 4466 The '``extractvalue``' instruction extracts the value of a member field 4467 from an :ref:`aggregate <t_aggregate>` value. 4468 4469 Arguments: 4470 """""""""" 4471 4472 The first operand of an '``extractvalue``' instruction is a value of 4473 :ref:`struct <t_struct>` or :ref:`array <t_array>` type. The operands are 4474 constant indices to specify which value to extract in a similar manner 4475 as indices in a '``getelementptr``' instruction. 4476 4477 The major differences to ``getelementptr`` indexing are: 4478 4479 - Since the value being indexed is not a pointer, the first index is 4480 omitted and assumed to be zero. 4481 - At least one index must be specified. 4482 - Not only struct indices but also array indices must be in bounds. 4483 4484 Semantics: 4485 """""""""" 4486 4487 The result is the value at the position in the aggregate specified by 4488 the index operands. 4489 4490 Example: 4491 """""""" 4492 4493 .. code-block:: llvm 4494 4495 <result> = extractvalue {i32, float} %agg, 0 ; yields i32 4496 4497 .. _i_insertvalue: 4498 4499 '``insertvalue``' Instruction 4500 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 4501 4502 Syntax: 4503 """"""" 4504 4505 :: 4506 4507 <result> = insertvalue <aggregate type> <val>, <ty> <elt>, <idx>{, <idx>}* ; yields <aggregate type> 4508 4509 Overview: 4510 """"""""" 4511 4512 The '``insertvalue``' instruction inserts a value into a member field in 4513 an :ref:`aggregate <t_aggregate>` value. 4514 4515 Arguments: 4516 """""""""" 4517 4518 The first operand of an '``insertvalue``' instruction is a value of 4519 :ref:`struct <t_struct>` or :ref:`array <t_array>` type. The second operand is 4520 a first-class value to insert. The following operands are constant 4521 indices indicating the position at which to insert the value in a 4522 similar manner as indices in a '``extractvalue``' instruction. The value 4523 to insert must have the same type as the value identified by the 4524 indices. 4525 4526 Semantics: 4527 """""""""" 4528 4529 The result is an aggregate of the same type as ``val``. Its value is 4530 that of ``val`` except that the value at the position specified by the 4531 indices is that of ``elt``. 4532 4533 Example: 4534 """""""" 4535 4536 .. code-block:: llvm 4537 4538 %agg1 = insertvalue {i32, float} undef, i32 1, 0 ; yields {i32 1, float undef} 4539 %agg2 = insertvalue {i32, float} %agg1, float %val, 1 ; yields {i32 1, float %val} 4540 %agg3 = insertvalue {i32, {float}} %agg1, float %val, 1, 0 ; yields {i32 1, float %val} 4541 4542 .. _memoryops: 4543 4544 Memory Access and Addressing Operations 4545 --------------------------------------- 4546 4547 A key design point of an SSA-based representation is how it represents 4548 memory. In LLVM, no memory locations are in SSA form, which makes things 4549 very simple. This section describes how to read, write, and allocate 4550 memory in LLVM. 4551 4552 .. _i_alloca: 4553 4554 '``alloca``' Instruction 4555 ^^^^^^^^^^^^^^^^^^^^^^^^ 4556 4557 Syntax: 4558 """"""" 4559 4560 :: 4561 4562 <result> = alloca <type>[, <ty> <NumElements>][, align <alignment>] ; yields {type*}:result 4563 4564 Overview: 4565 """"""""" 4566 4567 The '``alloca``' instruction allocates memory on the stack frame of the 4568 currently executing function, to be automatically released when this 4569 function returns to its caller. The object is always allocated in the 4570 generic address space (address space zero). 4571 4572 Arguments: 4573 """""""""" 4574 4575 The '``alloca``' instruction allocates ``sizeof(<type>)*NumElements`` 4576 bytes of memory on the runtime stack, returning a pointer of the 4577 appropriate type to the program. If "NumElements" is specified, it is 4578 the number of elements allocated, otherwise "NumElements" is defaulted 4579 to be one. If a constant alignment is specified, the value result of the 4580 allocation is guaranteed to be aligned to at least that boundary. If not 4581 specified, or if zero, the target can choose to align the allocation on 4582 any convenient boundary compatible with the type. 4583 4584 '``type``' may be any sized type. 4585 4586 Semantics: 4587 """""""""" 4588 4589 Memory is allocated; a pointer is returned. The operation is undefined 4590 if there is insufficient stack space for the allocation. '``alloca``'d 4591 memory is automatically released when the function returns. The 4592 '``alloca``' instruction is commonly used to represent automatic 4593 variables that must have an address available. When the function returns 4594 (either with the ``ret`` or ``resume`` instructions), the memory is 4595 reclaimed. Allocating zero bytes is legal, but the result is undefined. 4596 The order in which memory is allocated (ie., which way the stack grows) 4597 is not specified. 4598 4599 Example: 4600 """""""" 4601 4602 .. code-block:: llvm 4603 4604 %ptr = alloca i32 ; yields {i32*}:ptr 4605 %ptr = alloca i32, i32 4 ; yields {i32*}:ptr 4606 %ptr = alloca i32, i32 4, align 1024 ; yields {i32*}:ptr 4607 %ptr = alloca i32, align 1024 ; yields {i32*}:ptr 4608 4609 .. _i_load: 4610 4611 '``load``' Instruction 4612 ^^^^^^^^^^^^^^^^^^^^^^ 4613 4614 Syntax: 4615 """"""" 4616 4617 :: 4618 4619 <result> = load [volatile] <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>][, !invariant.load !<index>] 4620 <result> = load atomic [volatile] <ty>* <pointer> [singlethread] <ordering>, align <alignment> 4621 !<index> = !{ i32 1 } 4622 4623 Overview: 4624 """"""""" 4625 4626 The '``load``' instruction is used to read from memory. 4627 4628 Arguments: 4629 """""""""" 4630 4631 The argument to the ``load`` instruction specifies the memory address 4632 from which to load. The pointer must point to a :ref:`first 4633 class <t_firstclass>` type. If the ``load`` is marked as ``volatile``, 4634 then the optimizer is not allowed to modify the number or order of 4635 execution of this ``load`` with other :ref:`volatile 4636 operations <volatile>`. 4637 4638 If the ``load`` is marked as ``atomic``, it takes an extra 4639 :ref:`ordering <ordering>` and optional ``singlethread`` argument. The 4640 ``release`` and ``acq_rel`` orderings are not valid on ``load`` 4641 instructions. Atomic loads produce :ref:`defined <memmodel>` results 4642 when they may see multiple atomic stores. The type of the pointee must 4643 be an integer type whose bit width is a power of two greater than or 4644 equal to eight and less than or equal to a target-specific size limit. 4645 ``align`` must be explicitly specified on atomic loads, and the load has 4646 undefined behavior if the alignment is not set to a value which is at 4647 least the size in bytes of the pointee. ``!nontemporal`` does not have 4648 any defined semantics for atomic loads. 4649 4650 The optional constant ``align`` argument specifies the alignment of the 4651 operation (that is, the alignment of the memory address). A value of 0 4652 or an omitted ``align`` argument means that the operation has the ABI 4653 alignment for the target. It is the responsibility of the code emitter 4654 to ensure that the alignment information is correct. Overestimating the 4655 alignment results in undefined behavior. Underestimating the alignment 4656 may produce less efficient code. An alignment of 1 is always safe. 4657 4658 The optional ``!nontemporal`` metadata must reference a single 4659 metadata name ``<index>`` corresponding to a metadata node with one 4660 ``i32`` entry of value 1. The existence of the ``!nontemporal`` 4661 metadata on the instruction tells the optimizer and code generator 4662 that this load is not expected to be reused in the cache. The code 4663 generator may select special instructions to save cache bandwidth, such 4664 as the ``MOVNT`` instruction on x86. 4665 4666 The optional ``!invariant.load`` metadata must reference a single 4667 metadata name ``<index>`` corresponding to a metadata node with no 4668 entries. The existence of the ``!invariant.load`` metadata on the 4669 instruction tells the optimizer and code generator that this load 4670 address points to memory which does not change value during program 4671 execution. The optimizer may then move this load around, for example, by 4672 hoisting it out of loops using loop invariant code motion. 4673 4674 Semantics: 4675 """""""""" 4676 4677 The location of memory pointed to is loaded. If the value being loaded 4678 is of scalar type then the number of bytes read does not exceed the 4679 minimum number of bytes needed to hold all bits of the type. For 4680 example, loading an ``i24`` reads at most three bytes. When loading a 4681 value of a type like ``i20`` with a size that is not an integral number 4682 of bytes, the result is undefined if the value was not originally 4683 written using a store of the same type. 4684 4685 Examples: 4686 """"""""" 4687 4688 .. code-block:: llvm 4689 4690 %ptr = alloca i32 ; yields {i32*}:ptr 4691 store i32 3, i32* %ptr ; yields {void} 4692 %val = load i32* %ptr ; yields {i32}:val = i32 3 4693 4694 .. _i_store: 4695 4696 '``store``' Instruction 4697 ^^^^^^^^^^^^^^^^^^^^^^^ 4698 4699 Syntax: 4700 """"""" 4701 4702 :: 4703 4704 store [volatile] <ty> <value>, <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>] ; yields {void} 4705 store atomic [volatile] <ty> <value>, <ty>* <pointer> [singlethread] <ordering>, align <alignment> ; yields {void} 4706 4707 Overview: 4708 """"""""" 4709 4710 The '``store``' instruction is used to write to memory. 4711 4712 Arguments: 4713 """""""""" 4714 4715 There are two arguments to the ``store`` instruction: a value to store 4716 and an address at which to store it. The type of the ``<pointer>`` 4717 operand must be a pointer to the :ref:`first class <t_firstclass>` type of 4718 the ``<value>`` operand. If the ``store`` is marked as ``volatile``, 4719 then the optimizer is not allowed to modify the number or order of 4720 execution of this ``store`` with other :ref:`volatile 4721 operations <volatile>`. 4722 4723 If the ``store`` is marked as ``atomic``, it takes an extra 4724 :ref:`ordering <ordering>` and optional ``singlethread`` argument. The 4725 ``acquire`` and ``acq_rel`` orderings aren't valid on ``store`` 4726 instructions. Atomic loads produce :ref:`defined <memmodel>` results 4727 when they may see multiple atomic stores. The type of the pointee must 4728 be an integer type whose bit width is a power of two greater than or 4729 equal to eight and less than or equal to a target-specific size limit. 4730 ``align`` must be explicitly specified on atomic stores, and the store 4731 has undefined behavior if the alignment is not set to a value which is 4732 at least the size in bytes of the pointee. ``!nontemporal`` does not 4733 have any defined semantics for atomic stores. 4734 4735 The optional constant ``align`` argument specifies the alignment of the 4736 operation (that is, the alignment of the memory address). A value of 0 4737 or an omitted ``align`` argument means that the operation has the ABI 4738 alignment for the target. It is the responsibility of the code emitter 4739 to ensure that the alignment information is correct. Overestimating the 4740 alignment results in undefined behavior. Underestimating the 4741 alignment may produce less efficient code. An alignment of 1 is always 4742 safe. 4743 4744 The optional ``!nontemporal`` metadata must reference a single metadata 4745 name ``<index>`` corresponding to a metadata node with one ``i32`` entry of 4746 value 1. The existence of the ``!nontemporal`` metadata on the instruction 4747 tells the optimizer and code generator that this load is not expected to 4748 be reused in the cache. The code generator may select special 4749 instructions to save cache bandwidth, such as the MOVNT instruction on 4750 x86. 4751 4752 Semantics: 4753 """""""""" 4754 4755 The contents of memory are updated to contain ``<value>`` at the 4756 location specified by the ``<pointer>`` operand. If ``<value>`` is 4757 of scalar type then the number of bytes written does not exceed the 4758 minimum number of bytes needed to hold all bits of the type. For 4759 example, storing an ``i24`` writes at most three bytes. When writing a 4760 value of a type like ``i20`` with a size that is not an integral number 4761 of bytes, it is unspecified what happens to the extra bits that do not 4762 belong to the type, but they will typically be overwritten. 4763 4764 Example: 4765 """""""" 4766 4767 .. code-block:: llvm 4768 4769 %ptr = alloca i32 ; yields {i32*}:ptr 4770 store i32 3, i32* %ptr ; yields {void} 4771 %val = load i32* %ptr ; yields {i32}:val = i32 3 4772 4773 .. _i_fence: 4774 4775 '``fence``' Instruction 4776 ^^^^^^^^^^^^^^^^^^^^^^^ 4777 4778 Syntax: 4779 """"""" 4780 4781 :: 4782 4783 fence [singlethread] <ordering> ; yields {void} 4784 4785 Overview: 4786 """"""""" 4787 4788 The '``fence``' instruction is used to introduce happens-before edges 4789 between operations. 4790 4791 Arguments: 4792 """""""""" 4793 4794 '``fence``' instructions take an :ref:`ordering <ordering>` argument which 4795 defines what *synchronizes-with* edges they add. They can only be given 4796 ``acquire``, ``release``, ``acq_rel``, and ``seq_cst`` orderings. 4797 4798 Semantics: 4799 """""""""" 4800 4801 A fence A which has (at least) ``release`` ordering semantics 4802 *synchronizes with* a fence B with (at least) ``acquire`` ordering 4803 semantics if and only if there exist atomic operations X and Y, both 4804 operating on some atomic object M, such that A is sequenced before X, X 4805 modifies M (either directly or through some side effect of a sequence 4806 headed by X), Y is sequenced before B, and Y observes M. This provides a 4807 *happens-before* dependency between A and B. Rather than an explicit 4808 ``fence``, one (but not both) of the atomic operations X or Y might 4809 provide a ``release`` or ``acquire`` (resp.) ordering constraint and 4810 still *synchronize-with* the explicit ``fence`` and establish the 4811 *happens-before* edge. 4812 4813 A ``fence`` which has ``seq_cst`` ordering, in addition to having both 4814 ``acquire`` and ``release`` semantics specified above, participates in 4815 the global program order of other ``seq_cst`` operations and/or fences. 4816 4817 The optional ":ref:`singlethread <singlethread>`" argument specifies 4818 that the fence only synchronizes with other fences in the same thread. 4819 (This is useful for interacting with signal handlers.) 4820 4821 Example: 4822 """""""" 4823 4824 .. code-block:: llvm 4825 4826 fence acquire ; yields {void} 4827 fence singlethread seq_cst ; yields {void} 4828 4829 .. _i_cmpxchg: 4830 4831 '``cmpxchg``' Instruction 4832 ^^^^^^^^^^^^^^^^^^^^^^^^^ 4833 4834 Syntax: 4835 """"""" 4836 4837 :: 4838 4839 cmpxchg [volatile] <ty>* <pointer>, <ty> <cmp>, <ty> <new> [singlethread] <ordering> ; yields {ty} 4840 4841 Overview: 4842 """"""""" 4843 4844 The '``cmpxchg``' instruction is used to atomically modify memory. It 4845 loads a value in memory and compares it to a given value. If they are 4846 equal, it stores a new value into the memory. 4847 4848 Arguments: 4849 """""""""" 4850 4851 There are three arguments to the '``cmpxchg``' instruction: an address 4852 to operate on, a value to compare to the value currently be at that 4853 address, and a new value to place at that address if the compared values 4854 are equal. The type of '<cmp>' must be an integer type whose bit width 4855 is a power of two greater than or equal to eight and less than or equal 4856 to a target-specific size limit. '<cmp>' and '<new>' must have the same 4857 type, and the type of '<pointer>' must be a pointer to that type. If the 4858 ``cmpxchg`` is marked as ``volatile``, then the optimizer is not allowed 4859 to modify the number or order of execution of this ``cmpxchg`` with 4860 other :ref:`volatile operations <volatile>`. 4861 4862 The :ref:`ordering <ordering>` argument specifies how this ``cmpxchg`` 4863 synchronizes with other atomic operations. 4864 4865 The optional "``singlethread``" argument declares that the ``cmpxchg`` 4866 is only atomic with respect to code (usually signal handlers) running in 4867 the same thread as the ``cmpxchg``. Otherwise the cmpxchg is atomic with 4868 respect to all other code in the system. 4869 4870 The pointer passed into cmpxchg must have alignment greater than or 4871 equal to the size in memory of the operand. 4872 4873 Semantics: 4874 """""""""" 4875 4876 The contents of memory at the location specified by the '``<pointer>``' 4877 operand is read and compared to '``<cmp>``'; if the read value is the 4878 equal, '``<new>``' is written. The original value at the location is 4879 returned. 4880 4881 A successful ``cmpxchg`` is a read-modify-write instruction for the purpose 4882 of identifying release sequences. A failed ``cmpxchg`` is equivalent to an 4883 atomic load with an ordering parameter determined by dropping any 4884 ``release`` part of the ``cmpxchg``'s ordering. 4885 4886 Example: 4887 """""""" 4888 4889 .. code-block:: llvm 4890 4891 entry: 4892 %orig = atomic load i32* %ptr unordered ; yields {i32} 4893 br label %loop 4894 4895 loop: 4896 %cmp = phi i32 [ %orig, %entry ], [%old, %loop] 4897 %squared = mul i32 %cmp, %cmp 4898 %old = cmpxchg i32* %ptr, i32 %cmp, i32 %squared ; yields {i32} 4899 %success = icmp eq i32 %cmp, %old 4900 br i1 %success, label %done, label %loop 4901 4902 done: 4903 ... 4904 4905 .. _i_atomicrmw: 4906 4907 '``atomicrmw``' Instruction 4908 ^^^^^^^^^^^^^^^^^^^^^^^^^^^ 4909 4910 Syntax: 4911 """"""" 4912 4913 :: 4914 4915 atomicrmw [volatile] <operation> <ty>* <pointer>, <ty> <value> [singlethread] <ordering> ; yields {ty} 4916 4917 Overview: 4918 """"""""" 4919 4920 The '``atomicrmw``' instruction is used to atomically modify memory. 4921 4922 Arguments: 4923 """""""""" 4924 4925 There are three arguments to the '``atomicrmw``' instruction: an 4926 operation to apply, an address whose value to modify, an argument to the 4927 operation. The operation must be one of the following keywords: 4928 4929 - xchg 4930 - add 4931 - sub 4932 - and 4933 - nand 4934 - or 4935 - xor 4936 - max 4937 - min 4938 - umax 4939 - umin 4940 4941 The type of '<value>' must be an integer type whose bit width is a power 4942 of two greater than or equal to eight and less than or equal to a 4943 target-specific size limit. The type of the '``<pointer>``' operand must 4944 be a pointer to that type. If the ``atomicrmw`` is marked as 4945 ``volatile``, then the optimizer is not allowed to modify the number or 4946 order of execution of this ``atomicrmw`` with other :ref:`volatile 4947 operations <volatile>`. 4948 4949 Semantics: 4950 """""""""" 4951 4952 The contents of memory at the location specified by the '``<pointer>``' 4953 operand are atomically read, modified, and written back. The original 4954 value at the location is returned. The modification is specified by the 4955 operation argument: 4956 4957 - xchg: ``*ptr = val`` 4958 - add: ``*ptr = *ptr + val`` 4959 - sub: ``*ptr = *ptr - val`` 4960 - and: ``*ptr = *ptr & val`` 4961 - nand: ``*ptr = ~(*ptr & val)`` 4962 - or: ``*ptr = *ptr | val`` 4963 - xor: ``*ptr = *ptr ^ val`` 4964 - max: ``*ptr = *ptr > val ? *ptr : val`` (using a signed comparison) 4965 - min: ``*ptr = *ptr < val ? *ptr : val`` (using a signed comparison) 4966 - umax: ``*ptr = *ptr > val ? *ptr : val`` (using an unsigned 4967 comparison) 4968 - umin: ``*ptr = *ptr < val ? *ptr : val`` (using an unsigned 4969 comparison) 4970 4971 Example: 4972 """""""" 4973 4974 .. code-block:: llvm 4975 4976 %old = atomicrmw add i32* %ptr, i32 1 acquire ; yields {i32} 4977 4978 .. _i_getelementptr: 4979 4980 '``getelementptr``' Instruction 4981 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 4982 4983 Syntax: 4984 """"""" 4985 4986 :: 4987 4988 <result> = getelementptr <pty>* <ptrval>{, <ty> <idx>}* 4989 <result> = getelementptr inbounds <pty>* <ptrval>{, <ty> <idx>}* 4990 <result> = getelementptr <ptr vector> ptrval, <vector index type> idx 4991 4992 Overview: 4993 """"""""" 4994 4995 The '``getelementptr``' instruction is used to get the address of a 4996 subelement of an :ref:`aggregate <t_aggregate>` data structure. It performs 4997 address calculation only and does not access memory. 4998 4999 Arguments: 5000 """""""""" 5001 5002 The first argument is always a pointer or a vector of pointers, and 5003 forms the basis of the calculation. The remaining arguments are indices 5004 that indicate which of the elements of the aggregate object are indexed. 5005 The interpretation of each index is dependent on the type being indexed 5006 into. The first index always indexes the pointer value given as the 5007 first argument, the second index indexes a value of the type pointed to 5008 (not necessarily the value directly pointed to, since the first index 5009 can be non-zero), etc. The first type indexed into must be a pointer 5010 value, subsequent types can be arrays, vectors, and structs. Note that 5011 subsequent types being indexed into can never be pointers, since that 5012 would require loading the pointer before continuing calculation. 5013 5014 The type of each index argument depends on the type it is indexing into. 5015 When indexing into a (optionally packed) structure, only ``i32`` integer 5016 **constants** are allowed (when using a vector of indices they must all 5017 be the **same** ``i32`` integer constant). When indexing into an array, 5018 pointer or vector, integers of any width are allowed, and they are not 5019 required to be constant. These integers are treated as signed values 5020 where relevant. 5021 5022 For example, let's consider a C code fragment and how it gets compiled 5023 to LLVM: 5024 5025 .. code-block:: c 5026 5027 struct RT { 5028 char A; 5029 int B[10][20]; 5030 char C; 5031 }; 5032 struct ST { 5033 int X; 5034 double Y; 5035 struct RT Z; 5036 }; 5037 5038 int *foo(struct ST *s) { 5039 return &s[1].Z.B[5][13]; 5040 } 5041 5042 The LLVM code generated by Clang is: 5043 5044 .. code-block:: llvm 5045 5046 %struct.RT = type { i8, [10 x [20 x i32]], i8 } 5047 %struct.ST = type { i32, double, %struct.RT } 5048 5049 define i32* @foo(%struct.ST* %s) nounwind uwtable readnone optsize ssp { 5050 entry: 5051 %arrayidx = getelementptr inbounds %struct.ST* %s, i64 1, i32 2, i32 1, i64 5, i64 13 5052 ret i32* %arrayidx 5053 } 5054 5055 Semantics: 5056 """""""""" 5057 5058 In the example above, the first index is indexing into the 5059 '``%struct.ST*``' type, which is a pointer, yielding a '``%struct.ST``' 5060 = '``{ i32, double, %struct.RT }``' type, a structure. The second index 5061 indexes into the third element of the structure, yielding a 5062 '``%struct.RT``' = '``{ i8 , [10 x [20 x i32]], i8 }``' type, another 5063 structure. The third index indexes into the second element of the 5064 structure, yielding a '``[10 x [20 x i32]]``' type, an array. The two 5065 dimensions of the array are subscripted into, yielding an '``i32``' 5066 type. The '``getelementptr``' instruction returns a pointer to this 5067 element, thus computing a value of '``i32*``' type. 5068 5069 Note that it is perfectly legal to index partially through a structure, 5070 returning a pointer to an inner element. Because of this, the LLVM code 5071 for the given testcase is equivalent to: 5072 5073 .. code-block:: llvm 5074 5075 define i32* @foo(%struct.ST* %s) { 5076 %t1 = getelementptr %struct.ST* %s, i32 1 ; yields %struct.ST*:%t1 5077 %t2 = getelementptr %struct.ST* %t1, i32 0, i32 2 ; yields %struct.RT*:%t2 5078 %t3 = getelementptr %struct.RT* %t2, i32 0, i32 1 ; yields [10 x [20 x i32]]*:%t3 5079 %t4 = getelementptr [10 x [20 x i32]]* %t3, i32 0, i32 5 ; yields [20 x i32]*:%t4 5080 %t5 = getelementptr [20 x i32]* %t4, i32 0, i32 13 ; yields i32*:%t5 5081 ret i32* %t5 5082 } 5083 5084 If the ``inbounds`` keyword is present, the result value of the 5085 ``getelementptr`` is a :ref:`poison value <poisonvalues>` if the base 5086 pointer is not an *in bounds* address of an allocated object, or if any 5087 of the addresses that would be formed by successive addition of the 5088 offsets implied by the indices to the base address with infinitely 5089 precise signed arithmetic are not an *in bounds* address of that 5090 allocated object. The *in bounds* addresses for an allocated object are 5091 all the addresses that point into the object, plus the address one byte 5092 past the end. In cases where the base is a vector of pointers the 5093 ``inbounds`` keyword applies to each of the computations element-wise. 5094 5095 If the ``inbounds`` keyword is not present, the offsets are added to the 5096 base address with silently-wrapping two's complement arithmetic. If the 5097 offsets have a different width from the pointer, they are sign-extended 5098 or truncated to the width of the pointer. The result value of the 5099 ``getelementptr`` may be outside the object pointed to by the base 5100 pointer. The result value may not necessarily be used to access memory 5101 though, even if it happens to point into allocated storage. See the 5102 :ref:`Pointer Aliasing Rules <pointeraliasing>` section for more 5103 information. 5104 5105 The getelementptr instruction is often confusing. For some more insight 5106 into how it works, see :doc:`the getelementptr FAQ <GetElementPtr>`. 5107 5108 Example: 5109 """""""" 5110 5111 .. code-block:: llvm 5112 5113 ; yields [12 x i8]*:aptr 5114 %aptr = getelementptr {i32, [12 x i8]}* %saptr, i64 0, i32 1 5115 ; yields i8*:vptr 5116 %vptr = getelementptr {i32, <2 x i8>}* %svptr, i64 0, i32 1, i32 1 5117 ; yields i8*:eptr 5118 %eptr = getelementptr [12 x i8]* %aptr, i64 0, i32 1 5119 ; yields i32*:iptr 5120 %iptr = getelementptr [10 x i32]* @arr, i16 0, i16 0 5121 5122 In cases where the pointer argument is a vector of pointers, each index 5123 must be a vector with the same number of elements. For example: 5124 5125 .. code-block:: llvm 5126 5127 %A = getelementptr <4 x i8*> %ptrs, <4 x i64> %offsets, 5128 5129 Conversion Operations 5130 --------------------- 5131 5132 The instructions in this category are the conversion instructions 5133 (casting) which all take a single operand and a type. They perform 5134 various bit conversions on the operand. 5135 5136 '``trunc .. to``' Instruction 5137 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 5138 5139 Syntax: 5140 """"""" 5141 5142 :: 5143 5144 <result> = trunc <ty> <value> to <ty2> ; yields ty2 5145 5146 Overview: 5147 """"""""" 5148 5149 The '``trunc``' instruction truncates its operand to the type ``ty2``. 5150 5151 Arguments: 5152 """""""""" 5153 5154 The '``trunc``' instruction takes a value to trunc, and a type to trunc 5155 it to. Both types must be of :ref:`integer <t_integer>` types, or vectors 5156 of the same number of integers. The bit size of the ``value`` must be 5157 larger than the bit size of the destination type, ``ty2``. Equal sized 5158 types are not allowed. 5159 5160 Semantics: 5161 """""""""" 5162 5163 The '``trunc``' instruction truncates the high order bits in ``value`` 5164 and converts the remaining bits to ``ty2``. Since the source size must 5165 be larger than the destination size, ``trunc`` cannot be a *no-op cast*. 5166 It will always truncate bits. 5167 5168 Example: 5169 """""""" 5170 5171 .. code-block:: llvm 5172 5173 %X = trunc i32 257 to i8 ; yields i8:1 5174 %Y = trunc i32 123 to i1 ; yields i1:true 5175 %Z = trunc i32 122 to i1 ; yields i1:false 5176 %W = trunc <2 x i16> <i16 8, i16 7> to <2 x i8> ; yields <i8 8, i8 7> 5177 5178 '``zext .. to``' Instruction 5179 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 5180 5181 Syntax: 5182 """"""" 5183 5184 :: 5185 5186 <result> = zext <ty> <value> to <ty2> ; yields ty2 5187 5188 Overview: 5189 """"""""" 5190 5191 The '``zext``' instruction zero extends its operand to type ``ty2``. 5192 5193 Arguments: 5194 """""""""" 5195 5196 The '``zext``' instruction takes a value to cast, and a type to cast it 5197 to. Both types must be of :ref:`integer <t_integer>` types, or vectors of 5198 the same number of integers. The bit size of the ``value`` must be 5199 smaller than the bit size of the destination type, ``ty2``. 5200 5201 Semantics: 5202 """""""""" 5203 5204 The ``zext`` fills the high order bits of the ``value`` with zero bits 5205 until it reaches the size of the destination type, ``ty2``. 5206 5207 When zero extending from i1, the result will always be either 0 or 1. 5208 5209 Example: 5210 """""""" 5211 5212 .. code-block:: llvm 5213 5214 %X = zext i32 257 to i64 ; yields i64:257 5215 %Y = zext i1 true to i32 ; yields i32:1 5216 %Z = zext <2 x i16> <i16 8, i16 7> to <2 x i32> ; yields <i32 8, i32 7> 5217 5218 '``sext .. to``' Instruction 5219 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 5220 5221 Syntax: 5222 """"""" 5223 5224 :: 5225 5226 <result> = sext <ty> <value> to <ty2> ; yields ty2 5227 5228 Overview: 5229 """"""""" 5230 5231 The '``sext``' sign extends ``value`` to the type ``ty2``. 5232 5233 Arguments: 5234 """""""""" 5235 5236 The '``sext``' instruction takes a value to cast, and a type to cast it 5237 to. Both types must be of :ref:`integer <t_integer>` types, or vectors of 5238 the same number of integers. The bit size of the ``value`` must be 5239 smaller than the bit size of the destination type, ``ty2``. 5240 5241 Semantics: 5242 """""""""" 5243 5244 The '``sext``' instruction performs a sign extension by copying the sign 5245 bit (highest order bit) of the ``value`` until it reaches the bit size 5246 of the type ``ty2``. 5247 5248 When sign extending from i1, the extension always results in -1 or 0. 5249 5250 Example: 5251 """""""" 5252 5253 .. code-block:: llvm 5254 5255 %X = sext i8 -1 to i16 ; yields i16 :65535 5256 %Y = sext i1 true to i32 ; yields i32:-1 5257 %Z = sext <2 x i16> <i16 8, i16 7> to <2 x i32> ; yields <i32 8, i32 7> 5258 5259 '``fptrunc .. to``' Instruction 5260 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 5261 5262 Syntax: 5263 """"""" 5264 5265 :: 5266 5267 <result> = fptrunc <ty> <value> to <ty2> ; yields ty2 5268 5269 Overview: 5270 """"""""" 5271 5272 The '``fptrunc``' instruction truncates ``value`` to type ``ty2``. 5273 5274 Arguments: 5275 """""""""" 5276 5277 The '``fptrunc``' instruction takes a :ref:`floating point <t_floating>` 5278 value to cast and a :ref:`floating point <t_floating>` type to cast it to. 5279 The size of ``value`` must be larger than the size of ``ty2``. This 5280 implies that ``fptrunc`` cannot be used to make a *no-op cast*. 5281 5282 Semantics: 5283 """""""""" 5284 5285 The '``fptrunc``' instruction truncates a ``value`` from a larger 5286 :ref:`floating point <t_floating>` type to a smaller :ref:`floating 5287 point <t_floating>` type. If the value cannot fit within the 5288 destination type, ``ty2``, then the results are undefined. 5289 5290 Example: 5291 """""""" 5292 5293 .. code-block:: llvm 5294 5295 %X = fptrunc double 123.0 to float ; yields float:123.0 5296 %Y = fptrunc double 1.0E+300 to float ; yields undefined 5297 5298 '``fpext .. to``' Instruction 5299 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 5300 5301 Syntax: 5302 """"""" 5303 5304 :: 5305 5306 <result> = fpext <ty> <value> to <ty2> ; yields ty2 5307 5308 Overview: 5309 """"""""" 5310 5311 The '``fpext``' extends a floating point ``value`` to a larger floating 5312 point value. 5313 5314 Arguments: 5315 """""""""" 5316 5317 The '``fpext``' instruction takes a :ref:`floating point <t_floating>` 5318 ``value`` to cast, and a :ref:`floating point <t_floating>` type to cast it 5319 to. The source type must be smaller than the destination type. 5320 5321 Semantics: 5322 """""""""" 5323 5324 The '``fpext``' instruction extends the ``value`` from a smaller 5325 :ref:`floating point <t_floating>` type to a larger :ref:`floating 5326 point <t_floating>` type. The ``fpext`` cannot be used to make a 5327 *no-op cast* because it always changes bits. Use ``bitcast`` to make a 5328 *no-op cast* for a floating point cast. 5329 5330 Example: 5331 """""""" 5332 5333 .. code-block:: llvm 5334 5335 %X = fpext float 3.125 to double ; yields double:3.125000e+00 5336 %Y = fpext double %X to fp128 ; yields fp128:0xL00000000000000004000900000000000 5337 5338 '``fptoui .. to``' Instruction 5339 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 5340 5341 Syntax: 5342 """"""" 5343 5344 :: 5345 5346 <result> = fptoui <ty> <value> to <ty2> ; yields ty2 5347 5348 Overview: 5349 """"""""" 5350 5351 The '``fptoui``' converts a floating point ``value`` to its unsigned 5352 integer equivalent of type ``ty2``. 5353 5354 Arguments: 5355 """""""""" 5356 5357 The '``fptoui``' instruction takes a value to cast, which must be a 5358 scalar or vector :ref:`floating point <t_floating>` value, and a type to 5359 cast it to ``ty2``, which must be an :ref:`integer <t_integer>` type. If 5360 ``ty`` is a vector floating point type, ``ty2`` must be a vector integer 5361 type with the same number of elements as ``ty`` 5362 5363 Semantics: 5364 """""""""" 5365 5366 The '``fptoui``' instruction converts its :ref:`floating 5367 point <t_floating>` operand into the nearest (rounding towards zero) 5368 unsigned integer value. If the value cannot fit in ``ty2``, the results 5369 are undefined. 5370 5371 Example: 5372 """""""" 5373 5374 .. code-block:: llvm 5375 5376 %X = fptoui double 123.0 to i32 ; yields i32:123 5377 %Y = fptoui float 1.0E+300 to i1 ; yields undefined:1 5378 %Z = fptoui float 1.04E+17 to i8 ; yields undefined:1 5379 5380 '``fptosi .. to``' Instruction 5381 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 5382 5383 Syntax: 5384 """"""" 5385 5386 :: 5387 5388 <result> = fptosi <ty> <value> to <ty2> ; yields ty2 5389 5390 Overview: 5391 """"""""" 5392 5393 The '``fptosi``' instruction converts :ref:`floating point <t_floating>` 5394 ``value`` to type ``ty2``. 5395 5396 Arguments: 5397 """""""""" 5398 5399 The '``fptosi``' instruction takes a value to cast, which must be a 5400 scalar or vector :ref:`floating point <t_floating>` value, and a type to 5401 cast it to ``ty2``, which must be an :ref:`integer <t_integer>` type. If 5402 ``ty`` is a vector floating point type, ``ty2`` must be a vector integer 5403 type with the same number of elements as ``ty`` 5404 5405 Semantics: 5406 """""""""" 5407 5408 The '``fptosi``' instruction converts its :ref:`floating 5409 point <t_floating>` operand into the nearest (rounding towards zero) 5410 signed integer value. If the value cannot fit in ``ty2``, the results 5411 are undefined. 5412 5413 Example: 5414 """""""" 5415 5416 .. code-block:: llvm 5417 5418 %X = fptosi double -123.0 to i32 ; yields i32:-123 5419 %Y = fptosi float 1.0E-247 to i1 ; yields undefined:1 5420 %Z = fptosi float 1.04E+17 to i8 ; yields undefined:1 5421 5422 '``uitofp .. to``' Instruction 5423 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 5424 5425 Syntax: 5426 """"""" 5427 5428 :: 5429 5430 <result> = uitofp <ty> <value> to <ty2> ; yields ty2 5431 5432 Overview: 5433 """"""""" 5434 5435 The '``uitofp``' instruction regards ``value`` as an unsigned integer 5436 and converts that value to the ``ty2`` type. 5437 5438 Arguments: 5439 """""""""" 5440 5441 The '``uitofp``' instruction takes a value to cast, which must be a 5442 scalar or vector :ref:`integer <t_integer>` value, and a type to cast it to 5443 ``ty2``, which must be an :ref:`floating point <t_floating>` type. If 5444 ``ty`` is a vector integer type, ``ty2`` must be a vector floating point 5445 type with the same number of elements as ``ty`` 5446 5447 Semantics: 5448 """""""""" 5449 5450 The '``uitofp``' instruction interprets its operand as an unsigned 5451 integer quantity and converts it to the corresponding floating point 5452 value. If the value cannot fit in the floating point value, the results 5453 are undefined. 5454 5455 Example: 5456 """""""" 5457 5458 .. code-block:: llvm 5459 5460 %X = uitofp i32 257 to float ; yields float:257.0 5461 %Y = uitofp i8 -1 to double ; yields double:255.0 5462 5463 '``sitofp .. to``' Instruction 5464 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 5465 5466 Syntax: 5467 """"""" 5468 5469 :: 5470 5471 <result> = sitofp <ty> <value> to <ty2> ; yields ty2 5472 5473 Overview: 5474 """"""""" 5475 5476 The '``sitofp``' instruction regards ``value`` as a signed integer and 5477 converts that value to the ``ty2`` type. 5478 5479 Arguments: 5480 """""""""" 5481 5482 The '``sitofp``' instruction takes a value to cast, which must be a 5483 scalar or vector :ref:`integer <t_integer>` value, and a type to cast it to 5484 ``ty2``, which must be an :ref:`floating point <t_floating>` type. If 5485 ``ty`` is a vector integer type, ``ty2`` must be a vector floating point 5486 type with the same number of elements as ``ty`` 5487 5488 Semantics: 5489 """""""""" 5490 5491 The '``sitofp``' instruction interprets its operand as a signed integer 5492 quantity and converts it to the corresponding floating point value. If 5493 the value cannot fit in the floating point value, the results are 5494 undefined. 5495 5496 Example: 5497 """""""" 5498 5499 .. code-block:: llvm 5500 5501 %X = sitofp i32 257 to float ; yields float:257.0 5502 %Y = sitofp i8 -1 to double ; yields double:-1.0 5503 5504 .. _i_ptrtoint: 5505 5506 '``ptrtoint .. to``' Instruction 5507 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 5508 5509 Syntax: 5510 """"""" 5511 5512 :: 5513 5514 <result> = ptrtoint <ty> <value> to <ty2> ; yields ty2 5515 5516 Overview: 5517 """"""""" 5518 5519 The '``ptrtoint``' instruction converts the pointer or a vector of 5520 pointers ``value`` to the integer (or vector of integers) type ``ty2``. 5521 5522 Arguments: 5523 """""""""" 5524 5525 The '``ptrtoint``' instruction takes a ``value`` to cast, which must be 5526 a a value of type :ref:`pointer <t_pointer>` or a vector of pointers, and a 5527 type to cast it to ``ty2``, which must be an :ref:`integer <t_integer>` or 5528 a vector of integers type. 5529 5530 Semantics: 5531 """""""""" 5532 5533 The '``ptrtoint``' instruction converts ``value`` to integer type 5534 ``ty2`` by interpreting the pointer value as an integer and either 5535 truncating or zero extending that value to the size of the integer type. 5536 If ``value`` is smaller than ``ty2`` then a zero extension is done. If 5537 ``value`` is larger than ``ty2`` then a truncation is done. If they are 5538 the same size, then nothing is done (*no-op cast*) other than a type 5539 change. 5540 5541 Example: 5542 """""""" 5543 5544 .. code-block:: llvm 5545 5546 %X = ptrtoint i32* %P to i8 ; yields truncation on 32-bit architecture 5547 %Y = ptrtoint i32* %P to i64 ; yields zero extension on 32-bit architecture 5548 %Z = ptrtoint <4 x i32*> %P to <4 x i64>; yields vector zero extension for a vector of addresses on 32-bit architecture 5549 5550 .. _i_inttoptr: 5551 5552 '``inttoptr .. to``' Instruction 5553 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 5554 5555 Syntax: 5556 """"""" 5557 5558 :: 5559 5560 <result> = inttoptr <ty> <value> to <ty2> ; yields ty2 5561 5562 Overview: 5563 """"""""" 5564 5565 The '``inttoptr``' instruction converts an integer ``value`` to a 5566 pointer type, ``ty2``. 5567 5568 Arguments: 5569 """""""""" 5570 5571 The '``inttoptr``' instruction takes an :ref:`integer <t_integer>` value to 5572 cast, and a type to cast it to, which must be a :ref:`pointer <t_pointer>` 5573 type. 5574 5575 Semantics: 5576 """""""""" 5577 5578 The '``inttoptr``' instruction converts ``value`` to type ``ty2`` by 5579 applying either a zero extension or a truncation depending on the size 5580 of the integer ``value``. If ``value`` is larger than the size of a 5581 pointer then a truncation is done. If ``value`` is smaller than the size 5582 of a pointer then a zero extension is done. If they are the same size, 5583 nothing is done (*no-op cast*). 5584 5585 Example: 5586 """""""" 5587 5588 .. code-block:: llvm 5589 5590 %X = inttoptr i32 255 to i32* ; yields zero extension on 64-bit architecture 5591 %Y = inttoptr i32 255 to i32* ; yields no-op on 32-bit architecture 5592 %Z = inttoptr i64 0 to i32* ; yields truncation on 32-bit architecture 5593 %Z = inttoptr <4 x i32> %G to <4 x i8*>; yields truncation of vector G to four pointers 5594 5595 .. _i_bitcast: 5596 5597 '``bitcast .. to``' Instruction 5598 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 5599 5600 Syntax: 5601 """"""" 5602 5603 :: 5604 5605 <result> = bitcast <ty> <value> to <ty2> ; yields ty2 5606 5607 Overview: 5608 """"""""" 5609 5610 The '``bitcast``' instruction converts ``value`` to type ``ty2`` without 5611 changing any bits. 5612 5613 Arguments: 5614 """""""""" 5615 5616 The '``bitcast``' instruction takes a value to cast, which must be a 5617 non-aggregate first class value, and a type to cast it to, which must 5618 also be a non-aggregate :ref:`first class <t_firstclass>` type. The 5619 bit sizes of ``value`` and the destination type, ``ty2``, must be 5620 identical. If the source type is a pointer, the destination type must 5621 also be a pointer of the same size. This instruction supports bitwise 5622 conversion of vectors to integers and to vectors of other types (as 5623 long as they have the same size). 5624 5625 Semantics: 5626 """""""""" 5627 5628 The '``bitcast``' instruction converts ``value`` to type ``ty2``. It 5629 is always a *no-op cast* because no bits change with this 5630 conversion. The conversion is done as if the ``value`` had been stored 5631 to memory and read back as type ``ty2``. Pointer (or vector of 5632 pointers) types may only be converted to other pointer (or vector of 5633 pointers) types with this instruction if the pointer sizes are 5634 equal. To convert pointers to other types, use the :ref:`inttoptr 5635 <i_inttoptr>` or :ref:`ptrtoint <i_ptrtoint>` instructions first. 5636 5637 Example: 5638 """""""" 5639 5640 .. code-block:: llvm 5641 5642 %X = bitcast i8 255 to i8 ; yields i8 :-1 5643 %Y = bitcast i32* %x to sint* ; yields sint*:%x 5644 %Z = bitcast <2 x int> %V to i64; ; yields i64: %V 5645 %Z = bitcast <2 x i32*> %V to <2 x i64*> ; yields <2 x i64*> 5646 5647 .. _otherops: 5648 5649 Other Operations 5650 ---------------- 5651 5652 The instructions in this category are the "miscellaneous" instructions, 5653 which defy better classification. 5654 5655 .. _i_icmp: 5656 5657 '``icmp``' Instruction 5658 ^^^^^^^^^^^^^^^^^^^^^^ 5659 5660 Syntax: 5661 """"""" 5662 5663 :: 5664 5665 <result> = icmp <cond> <ty> <op1>, <op2> ; yields {i1} or {<N x i1>}:result 5666 5667 Overview: 5668 """"""""" 5669 5670 The '``icmp``' instruction returns a boolean value or a vector of 5671 boolean values based on comparison of its two integer, integer vector, 5672 pointer, or pointer vector operands. 5673 5674 Arguments: 5675 """""""""" 5676 5677 The '``icmp``' instruction takes three operands. The first operand is 5678 the condition code indicating the kind of comparison to perform. It is 5679 not a value, just a keyword. The possible condition code are: 5680 5681 #. ``eq``: equal 5682 #. ``ne``: not equal 5683 #. ``ugt``: unsigned greater than 5684 #. ``uge``: unsigned greater or equal 5685 #. ``ult``: unsigned less than 5686 #. ``ule``: unsigned less or equal 5687 #. ``sgt``: signed greater than 5688 #. ``sge``: signed greater or equal 5689 #. ``slt``: signed less than 5690 #. ``sle``: signed less or equal 5691 5692 The remaining two arguments must be :ref:`integer <t_integer>` or 5693 :ref:`pointer <t_pointer>` or integer :ref:`vector <t_vector>` typed. They 5694 must also be identical types. 5695 5696 Semantics: 5697 """""""""" 5698 5699 The '``icmp``' compares ``op1`` and ``op2`` according to the condition 5700 code given as ``cond``. The comparison performed always yields either an 5701 :ref:`i1 <t_integer>` or vector of ``i1`` result, as follows: 5702 5703 #. ``eq``: yields ``true`` if the operands are equal, ``false`` 5704 otherwise. No sign interpretation is necessary or performed. 5705 #. ``ne``: yields ``true`` if the operands are unequal, ``false`` 5706 otherwise. No sign interpretation is necessary or performed. 5707 #. ``ugt``: interprets the operands as unsigned values and yields 5708 ``true`` if ``op1`` is greater than ``op2``. 5709 #. ``uge``: interprets the operands as unsigned values and yields 5710 ``true`` if ``op1`` is greater than or equal to ``op2``. 5711 #. ``ult``: interprets the operands as unsigned values and yields 5712 ``true`` if ``op1`` is less than ``op2``. 5713 #. ``ule``: interprets the operands as unsigned values and yields 5714 ``true`` if ``op1`` is less than or equal to ``op2``. 5715 #. ``sgt``: interprets the operands as signed values and yields ``true`` 5716 if ``op1`` is greater than ``op2``. 5717 #. ``sge``: interprets the operands as signed values and yields ``true`` 5718 if ``op1`` is greater than or equal to ``op2``. 5719 #. ``slt``: interprets the operands as signed values and yields ``true`` 5720 if ``op1`` is less than ``op2``. 5721 #. ``sle``: interprets the operands as signed values and yields ``true`` 5722 if ``op1`` is less than or equal to ``op2``. 5723 5724 If the operands are :ref:`pointer <t_pointer>` typed, the pointer values 5725 are compared as if they were integers. 5726 5727 If the operands are integer vectors, then they are compared element by 5728 element. The result is an ``i1`` vector with the same number of elements 5729 as the values being compared. Otherwise, the result is an ``i1``. 5730 5731 Example: 5732 """""""" 5733 5734 .. code-block:: llvm 5735 5736 <result> = icmp eq i32 4, 5 ; yields: result=false 5737 <result> = icmp ne float* %X, %X ; yields: result=false 5738 <result> = icmp ult i16 4, 5 ; yields: result=true 5739 <result> = icmp sgt i16 4, 5 ; yields: result=false 5740 <result> = icmp ule i16 -4, 5 ; yields: result=false 5741 <result> = icmp sge i16 4, 5 ; yields: result=false 5742 5743 Note that the code generator does not yet support vector types with the 5744 ``icmp`` instruction. 5745 5746 .. _i_fcmp: 5747 5748 '``fcmp``' Instruction 5749 ^^^^^^^^^^^^^^^^^^^^^^ 5750 5751 Syntax: 5752 """"""" 5753 5754 :: 5755 5756 <result> = fcmp <cond> <ty> <op1>, <op2> ; yields {i1} or {<N x i1>}:result 5757 5758 Overview: 5759 """"""""" 5760 5761 The '``fcmp``' instruction returns a boolean value or vector of boolean 5762 values based on comparison of its operands. 5763 5764 If the operands are floating point scalars, then the result type is a 5765 boolean (:ref:`i1 <t_integer>`). 5766 5767 If the operands are floating point vectors, then the result type is a 5768 vector of boolean with the same number of elements as the operands being 5769 compared. 5770 5771 Arguments: 5772 """""""""" 5773 5774 The '``fcmp``' instruction takes three operands. The first operand is 5775 the condition code indicating the kind of comparison to perform. It is 5776 not a value, just a keyword. The possible condition code are: 5777 5778 #. ``false``: no comparison, always returns false 5779 #. ``oeq``: ordered and equal 5780 #. ``ogt``: ordered and greater than 5781 #. ``oge``: ordered and greater than or equal 5782 #. ``olt``: ordered and less than 5783 #. ``ole``: ordered and less than or equal 5784 #. ``one``: ordered and not equal 5785 #. ``ord``: ordered (no nans) 5786 #. ``ueq``: unordered or equal 5787 #. ``ugt``: unordered or greater than 5788 #. ``uge``: unordered or greater than or equal 5789 #. ``ult``: unordered or less than 5790 #. ``ule``: unordered or less than or equal 5791 #. ``une``: unordered or not equal 5792 #. ``uno``: unordered (either nans) 5793 #. ``true``: no comparison, always returns true 5794 5795 *Ordered* means that neither operand is a QNAN while *unordered* means 5796 that either operand may be a QNAN. 5797 5798 Each of ``val1`` and ``val2`` arguments must be either a :ref:`floating 5799 point <t_floating>` type or a :ref:`vector <t_vector>` of floating point 5800 type. They must have identical types. 5801 5802 Semantics: 5803 """""""""" 5804 5805 The '``fcmp``' instruction compares ``op1`` and ``op2`` according to the 5806 condition code given as ``cond``. If the operands are vectors, then the 5807 vectors are compared element by element. Each comparison performed 5808 always yields an :ref:`i1 <t_integer>` result, as follows: 5809 5810 #. ``false``: always yields ``false``, regardless of operands. 5811 #. ``oeq``: yields ``true`` if both operands are not a QNAN and ``op1`` 5812 is equal to ``op2``. 5813 #. ``ogt``: yields ``true`` if both operands are not a QNAN and ``op1`` 5814 is greater than ``op2``. 5815 #. ``oge``: yields ``true`` if both operands are not a QNAN and ``op1`` 5816 is greater than or equal to ``op2``. 5817 #. ``olt``: yields ``true`` if both operands are not a QNAN and ``op1`` 5818 is less than ``op2``. 5819 #. ``ole``: yields ``true`` if both operands are not a QNAN and ``op1`` 5820 is less than or equal to ``op2``. 5821 #. ``one``: yields ``true`` if both operands are not a QNAN and ``op1`` 5822 is not equal to ``op2``. 5823 #. ``ord``: yields ``true`` if both operands are not a QNAN. 5824 #. ``ueq``: yields ``true`` if either operand is a QNAN or ``op1`` is 5825 equal to ``op2``. 5826 #. ``ugt``: yields ``true`` if either operand is a QNAN or ``op1`` is 5827 greater than ``op2``. 5828 #. ``uge``: yields ``true`` if either operand is a QNAN or ``op1`` is 5829 greater than or equal to ``op2``. 5830 #. ``ult``: yields ``true`` if either operand is a QNAN or ``op1`` is 5831 less than ``op2``. 5832 #. ``ule``: yields ``true`` if either operand is a QNAN or ``op1`` is 5833 less than or equal to ``op2``. 5834 #. ``une``: yields ``true`` if either operand is a QNAN or ``op1`` is 5835 not equal to ``op2``. 5836 #. ``uno``: yields ``true`` if either operand is a QNAN. 5837 #. ``true``: always yields ``true``, regardless of operands. 5838 5839 Example: 5840 """""""" 5841 5842 .. code-block:: llvm 5843 5844 <result> = fcmp oeq float 4.0, 5.0 ; yields: result=false 5845 <result> = fcmp one float 4.0, 5.0 ; yields: result=true 5846 <result> = fcmp olt float 4.0, 5.0 ; yields: result=true 5847 <result> = fcmp ueq double 1.0, 2.0 ; yields: result=false 5848 5849 Note that the code generator does not yet support vector types with the 5850 ``fcmp`` instruction. 5851 5852 .. _i_phi: 5853 5854 '``phi``' Instruction 5855 ^^^^^^^^^^^^^^^^^^^^^ 5856 5857 Syntax: 5858 """"""" 5859 5860 :: 5861 5862 <result> = phi <ty> [ <val0>, <label0>], ... 5863 5864 Overview: 5865 """"""""" 5866 5867 The '``phi``' instruction is used to implement the node in the SSA 5868 graph representing the function. 5869 5870 Arguments: 5871 """""""""" 5872 5873 The type of the incoming values is specified with the first type field. 5874 After this, the '``phi``' instruction takes a list of pairs as 5875 arguments, with one pair for each predecessor basic block of the current 5876 block. Only values of :ref:`first class <t_firstclass>` type may be used as 5877 the value arguments to the PHI node. Only labels may be used as the 5878 label arguments. 5879 5880 There must be no non-phi instructions between the start of a basic block 5881 and the PHI instructions: i.e. PHI instructions must be first in a basic 5882 block. 5883 5884 For the purposes of the SSA form, the use of each incoming value is 5885 deemed to occur on the edge from the corresponding predecessor block to 5886 the current block (but after any definition of an '``invoke``' 5887 instruction's return value on the same edge). 5888 5889 Semantics: 5890 """""""""" 5891 5892 At runtime, the '``phi``' instruction logically takes on the value 5893 specified by the pair corresponding to the predecessor basic block that 5894 executed just prior to the current block. 5895 5896 Example: 5897 """""""" 5898 5899 .. code-block:: llvm 5900 5901 Loop: ; Infinite loop that counts from 0 on up... 5902 %indvar = phi i32 [ 0, %LoopHeader ], [ %nextindvar, %Loop ] 5903 %nextindvar = add i32 %indvar, 1 5904 br label %Loop 5905 5906 .. _i_select: 5907 5908 '``select``' Instruction 5909 ^^^^^^^^^^^^^^^^^^^^^^^^ 5910 5911 Syntax: 5912 """"""" 5913 5914 :: 5915 5916 <result> = select selty <cond>, <ty> <val1>, <ty> <val2> ; yields ty 5917 5918 selty is either i1 or {<N x i1>} 5919 5920 Overview: 5921 """"""""" 5922 5923 The '``select``' instruction is used to choose one value based on a 5924 condition, without branching. 5925 5926 Arguments: 5927 """""""""" 5928 5929 The '``select``' instruction requires an 'i1' value or a vector of 'i1' 5930 values indicating the condition, and two values of the same :ref:`first 5931 class <t_firstclass>` type. If the val1/val2 are vectors and the 5932 condition is a scalar, then entire vectors are selected, not individual 5933 elements. 5934 5935 Semantics: 5936 """""""""" 5937 5938 If the condition is an i1 and it evaluates to 1, the instruction returns 5939 the first value argument; otherwise, it returns the second value 5940 argument. 5941 5942 If the condition is a vector of i1, then the value arguments must be 5943 vectors of the same size, and the selection is done element by element. 5944 5945 Example: 5946 """""""" 5947 5948 .. code-block:: llvm 5949 5950 %X = select i1 true, i8 17, i8 42 ; yields i8:17 5951 5952 .. _i_call: 5953 5954 '``call``' Instruction 5955 ^^^^^^^^^^^^^^^^^^^^^^ 5956 5957 Syntax: 5958 """"""" 5959 5960 :: 5961 5962 <result> = [tail] call [cconv] [ret attrs] <ty> [<fnty>*] <fnptrval>(<function args>) [fn attrs] 5963 5964 Overview: 5965 """"""""" 5966 5967 The '``call``' instruction represents a simple function call. 5968 5969 Arguments: 5970 """""""""" 5971 5972 This instruction requires several arguments: 5973 5974 #. The optional "tail" marker indicates that the callee function does 5975 not access any allocas or varargs in the caller. Note that calls may 5976 be marked "tail" even if they do not occur before a 5977 :ref:`ret <i_ret>` instruction. If the "tail" marker is present, the 5978 function call is eligible for tail call optimization, but `might not 5979 in fact be optimized into a jump <CodeGenerator.html#tailcallopt>`_. 5980 The code generator may optimize calls marked "tail" with either 1) 5981 automatic `sibling call 5982 optimization <CodeGenerator.html#sibcallopt>`_ when the caller and 5983 callee have matching signatures, or 2) forced tail call optimization 5984 when the following extra requirements are met: 5985 5986 - Caller and callee both have the calling convention ``fastcc``. 5987 - The call is in tail position (ret immediately follows call and ret 5988 uses value of call or is void). 5989 - Option ``-tailcallopt`` is enabled, or 5990 ``llvm::GuaranteedTailCallOpt`` is ``true``. 5991 - `Platform specific constraints are 5992 met. <CodeGenerator.html#tailcallopt>`_ 5993 5994 #. The optional "cconv" marker indicates which :ref:`calling 5995 convention <callingconv>` the call should use. If none is 5996 specified, the call defaults to using C calling conventions. The 5997 calling convention of the call must match the calling convention of 5998 the target function, or else the behavior is undefined. 5999 #. The optional :ref:`Parameter Attributes <paramattrs>` list for return 6000 values. Only '``zeroext``', '``signext``', and '``inreg``' attributes 6001 are valid here. 6002 #. '``ty``': the type of the call instruction itself which is also the 6003 type of the return value. Functions that return no value are marked 6004 ``void``. 6005 #. '``fnty``': shall be the signature of the pointer to function value 6006 being invoked. The argument types must match the types implied by 6007 this signature. This type can be omitted if the function is not 6008 varargs and if the function type does not return a pointer to a 6009 function. 6010 #. '``fnptrval``': An LLVM value containing a pointer to a function to 6011 be invoked. In most cases, this is a direct function invocation, but 6012 indirect ``call``'s are just as possible, calling an arbitrary pointer 6013 to function value. 6014 #. '``function args``': argument list whose types match the function 6015 signature argument types and parameter attributes. All arguments must 6016 be of :ref:`first class <t_firstclass>` type. If the function signature 6017 indicates the function accepts a variable number of arguments, the 6018 extra arguments can be specified. 6019 #. The optional :ref:`function attributes <fnattrs>` list. Only 6020 '``noreturn``', '``nounwind``', '``readonly``' and '``readnone``' 6021 attributes are valid here. 6022 6023 Semantics: 6024 """""""""" 6025 6026 The '``call``' instruction is used to cause control flow to transfer to 6027 a specified function, with its incoming arguments bound to the specified 6028 values. Upon a '``ret``' instruction in the called function, control 6029 flow continues with the instruction after the function call, and the 6030 return value of the function is bound to the result argument. 6031 6032 Example: 6033 """""""" 6034 6035 .. code-block:: llvm 6036 6037 %retval = call i32 @test(i32 %argc) 6038 call i32 (i8*, ...)* @printf(i8* %msg, i32 12, i8 42) ; yields i32 6039 %X = tail call i32 @foo() ; yields i32 6040 %Y = tail call fastcc i32 @foo() ; yields i32 6041 call void %foo(i8 97 signext) 6042 6043 %struct.A = type { i32, i8 } 6044 %r = call %struct.A @foo() ; yields { 32, i8 } 6045 %gr = extractvalue %struct.A %r, 0 ; yields i32 6046 %gr1 = extractvalue %struct.A %r, 1 ; yields i8 6047 %Z = call void @foo() noreturn ; indicates that %foo never returns normally 6048 %ZZ = call zeroext i32 @bar() ; Return value is %zero extended 6049 6050 llvm treats calls to some functions with names and arguments that match 6051 the standard C99 library as being the C99 library functions, and may 6052 perform optimizations or generate code for them under that assumption. 6053 This is something we'd like to change in the future to provide better 6054 support for freestanding environments and non-C-based languages. 6055 6056 .. _i_va_arg: 6057 6058 '``va_arg``' Instruction 6059 ^^^^^^^^^^^^^^^^^^^^^^^^ 6060 6061 Syntax: 6062 """"""" 6063 6064 :: 6065 6066 <resultval> = va_arg <va_list*> <arglist>, <argty> 6067 6068 Overview: 6069 """"""""" 6070 6071 The '``va_arg``' instruction is used to access arguments passed through 6072 the "variable argument" area of a function call. It is used to implement 6073 the ``va_arg`` macro in C. 6074 6075 Arguments: 6076 """""""""" 6077 6078 This instruction takes a ``va_list*`` value and the type of the 6079 argument. It returns a value of the specified argument type and 6080 increments the ``va_list`` to point to the next argument. The actual 6081 type of ``va_list`` is target specific. 6082 6083 Semantics: 6084 """""""""" 6085 6086 The '``va_arg``' instruction loads an argument of the specified type 6087 from the specified ``va_list`` and causes the ``va_list`` to point to 6088 the next argument. For more information, see the variable argument 6089 handling :ref:`Intrinsic Functions <int_varargs>`. 6090 6091 It is legal for this instruction to be called in a function which does 6092 not take a variable number of arguments, for example, the ``vfprintf`` 6093 function. 6094 6095 ``va_arg`` is an LLVM instruction instead of an :ref:`intrinsic 6096 function <intrinsics>` because it takes a type as an argument. 6097 6098 Example: 6099 """""""" 6100 6101 See the :ref:`variable argument processing <int_varargs>` section. 6102 6103 Note that the code generator does not yet fully support va\_arg on many 6104 targets. Also, it does not currently support va\_arg with aggregate 6105 types on any target. 6106 6107 .. _i_landingpad: 6108 6109 '``landingpad``' Instruction 6110 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 6111 6112 Syntax: 6113 """"""" 6114 6115 :: 6116 6117 <resultval> = landingpad <resultty> personality <type> <pers_fn> <clause>+ 6118 <resultval> = landingpad <resultty> personality <type> <pers_fn> cleanup <clause>* 6119 6120 <clause> := catch <type> <value> 6121 <clause> := filter <array constant type> <array constant> 6122 6123 Overview: 6124 """"""""" 6125 6126 The '``landingpad``' instruction is used by `LLVM's exception handling 6127 system <ExceptionHandling.html#overview>`_ to specify that a basic block 6128 is a landing pad --- one where the exception lands, and corresponds to the 6129 code found in the ``catch`` portion of a ``try``/``catch`` sequence. It 6130 defines values supplied by the personality function (``pers_fn``) upon 6131 re-entry to the function. The ``resultval`` has the type ``resultty``. 6132 6133 Arguments: 6134 """""""""" 6135 6136 This instruction takes a ``pers_fn`` value. This is the personality 6137 function associated with the unwinding mechanism. The optional 6138 ``cleanup`` flag indicates that the landing pad block is a cleanup. 6139 6140 A ``clause`` begins with the clause type --- ``catch`` or ``filter`` --- and 6141 contains the global variable representing the "type" that may be caught 6142 or filtered respectively. Unlike the ``catch`` clause, the ``filter`` 6143 clause takes an array constant as its argument. Use 6144 "``[0 x i8**] undef``" for a filter which cannot throw. The 6145 '``landingpad``' instruction must contain *at least* one ``clause`` or 6146 the ``cleanup`` flag. 6147 6148 Semantics: 6149 """""""""" 6150 6151 The '``landingpad``' instruction defines the values which are set by the 6152 personality function (``pers_fn``) upon re-entry to the function, and 6153 therefore the "result type" of the ``landingpad`` instruction. As with 6154 calling conventions, how the personality function results are 6155 represented in LLVM IR is target specific. 6156 6157 The clauses are applied in order from top to bottom. If two 6158 ``landingpad`` instructions are merged together through inlining, the 6159 clauses from the calling function are appended to the list of clauses. 6160 When the call stack is being unwound due to an exception being thrown, 6161 the exception is compared against each ``clause`` in turn. If it doesn't 6162 match any of the clauses, and the ``cleanup`` flag is not set, then 6163 unwinding continues further up the call stack. 6164 6165 The ``landingpad`` instruction has several restrictions: 6166 6167 - A landing pad block is a basic block which is the unwind destination 6168 of an '``invoke``' instruction. 6169 - A landing pad block must have a '``landingpad``' instruction as its 6170 first non-PHI instruction. 6171 - There can be only one '``landingpad``' instruction within the landing 6172 pad block. 6173 - A basic block that is not a landing pad block may not include a 6174 '``landingpad``' instruction. 6175 - All '``landingpad``' instructions in a function must have the same 6176 personality function. 6177 6178 Example: 6179 """""""" 6180 6181 .. code-block:: llvm 6182 6183 ;; A landing pad which can catch an integer. 6184 %res = landingpad { i8*, i32 } personality i32 (...)* @__gxx_personality_v0 6185 catch i8** @_ZTIi 6186 ;; A landing pad that is a cleanup. 6187 %res = landingpad { i8*, i32 } personality i32 (...)* @__gxx_personality_v0 6188 cleanup 6189 ;; A landing pad which can catch an integer and can only throw a double. 6190 %res = landingpad { i8*, i32 } personality i32 (...)* @__gxx_personality_v0 6191 catch i8** @_ZTIi 6192 filter [1 x i8**] [@_ZTId] 6193 6194 .. _intrinsics: 6195 6196 Intrinsic Functions 6197 =================== 6198 6199 LLVM supports the notion of an "intrinsic function". These functions 6200 have well known names and semantics and are required to follow certain 6201 restrictions. Overall, these intrinsics represent an extension mechanism 6202 for the LLVM language that does not require changing all of the 6203 transformations in LLVM when adding to the language (or the bitcode 6204 reader/writer, the parser, etc...). 6205 6206 Intrinsic function names must all start with an "``llvm.``" prefix. This 6207 prefix is reserved in LLVM for intrinsic names; thus, function names may 6208 not begin with this prefix. Intrinsic functions must always be external 6209 functions: you cannot define the body of intrinsic functions. Intrinsic 6210 functions may only be used in call or invoke instructions: it is illegal 6211 to take the address of an intrinsic function. Additionally, because 6212 intrinsic functions are part of the LLVM language, it is required if any 6213 are added that they be documented here. 6214 6215 Some intrinsic functions can be overloaded, i.e., the intrinsic 6216 represents a family of functions that perform the same operation but on 6217 different data types. Because LLVM can represent over 8 million 6218 different integer types, overloading is used commonly to allow an 6219 intrinsic function to operate on any integer type. One or more of the 6220 argument types or the result type can be overloaded to accept any 6221 integer type. Argument types may also be defined as exactly matching a 6222 previous argument's type or the result type. This allows an intrinsic 6223 function which accepts multiple arguments, but needs all of them to be 6224 of the same type, to only be overloaded with respect to a single 6225 argument or the result. 6226 6227 Overloaded intrinsics will have the names of its overloaded argument 6228 types encoded into its function name, each preceded by a period. Only 6229 those types which are overloaded result in a name suffix. Arguments 6230 whose type is matched against another type do not. For example, the 6231 ``llvm.ctpop`` function can take an integer of any width and returns an 6232 integer of exactly the same integer width. This leads to a family of 6233 functions such as ``i8 @llvm.ctpop.i8(i8 %val)`` and 6234 ``i29 @llvm.ctpop.i29(i29 %val)``. Only one type, the return type, is 6235 overloaded, and only one type suffix is required. Because the argument's 6236 type is matched against the return type, it does not require its own 6237 name suffix. 6238 6239 To learn how to add an intrinsic function, please see the `Extending 6240 LLVM Guide <ExtendingLLVM.html>`_. 6241 6242 .. _int_varargs: 6243 6244 Variable Argument Handling Intrinsics 6245 ------------------------------------- 6246 6247 Variable argument support is defined in LLVM with the 6248 :ref:`va_arg <i_va_arg>` instruction and these three intrinsic 6249 functions. These functions are related to the similarly named macros 6250 defined in the ``<stdarg.h>`` header file. 6251 6252 All of these functions operate on arguments that use a target-specific 6253 value type "``va_list``". The LLVM assembly language reference manual 6254 does not define what this type is, so all transformations should be 6255 prepared to handle these functions regardless of the type used. 6256 6257 This example shows how the :ref:`va_arg <i_va_arg>` instruction and the 6258 variable argument handling intrinsic functions are used. 6259 6260 .. code-block:: llvm 6261 6262 define i32 @test(i32 %X, ...) { 6263 ; Initialize variable argument processing 6264 %ap = alloca i8* 6265 %ap2 = bitcast i8** %ap to i8* 6266 call void @llvm.va_start(i8* %ap2) 6267 6268 ; Read a single integer argument 6269 %tmp = va_arg i8** %ap, i32 6270 6271 ; Demonstrate usage of llvm.va_copy and llvm.va_end 6272 %aq = alloca i8* 6273 %aq2 = bitcast i8** %aq to i8* 6274 call void @llvm.va_copy(i8* %aq2, i8* %ap2) 6275 call void @llvm.va_end(i8* %aq2) 6276 6277 ; Stop processing of arguments. 6278 call void @llvm.va_end(i8* %ap2) 6279 ret i32 %tmp 6280 } 6281 6282 declare void @llvm.va_start(i8*) 6283 declare void @llvm.va_copy(i8*, i8*) 6284 declare void @llvm.va_end(i8*) 6285 6286 .. _int_va_start: 6287 6288 '``llvm.va_start``' Intrinsic 6289 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 6290 6291 Syntax: 6292 """"""" 6293 6294 :: 6295 6296 declare void %llvm.va_start(i8* <arglist>) 6297 6298 Overview: 6299 """"""""" 6300 6301 The '``llvm.va_start``' intrinsic initializes ``*<arglist>`` for 6302 subsequent use by ``va_arg``. 6303 6304 Arguments: 6305 """""""""" 6306 6307 The argument is a pointer to a ``va_list`` element to initialize. 6308 6309 Semantics: 6310 """""""""" 6311 6312 The '``llvm.va_start``' intrinsic works just like the ``va_start`` macro 6313 available in C. In a target-dependent way, it initializes the 6314 ``va_list`` element to which the argument points, so that the next call 6315 to ``va_arg`` will produce the first variable argument passed to the 6316 function. Unlike the C ``va_start`` macro, this intrinsic does not need 6317 to know the last argument of the function as the compiler can figure 6318 that out. 6319 6320 '``llvm.va_end``' Intrinsic 6321 ^^^^^^^^^^^^^^^^^^^^^^^^^^^ 6322 6323 Syntax: 6324 """"""" 6325 6326 :: 6327 6328 declare void @llvm.va_end(i8* <arglist>) 6329 6330 Overview: 6331 """"""""" 6332 6333 The '``llvm.va_end``' intrinsic destroys ``*<arglist>``, which has been 6334 initialized previously with ``llvm.va_start`` or ``llvm.va_copy``. 6335 6336 Arguments: 6337 """""""""" 6338 6339 The argument is a pointer to a ``va_list`` to destroy. 6340 6341 Semantics: 6342 """""""""" 6343 6344 The '``llvm.va_end``' intrinsic works just like the ``va_end`` macro 6345 available in C. In a target-dependent way, it destroys the ``va_list`` 6346 element to which the argument points. Calls to 6347 :ref:`llvm.va_start <int_va_start>` and 6348 :ref:`llvm.va_copy <int_va_copy>` must be matched exactly with calls to 6349 ``llvm.va_end``. 6350 6351 .. _int_va_copy: 6352 6353 '``llvm.va_copy``' Intrinsic 6354 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 6355 6356 Syntax: 6357 """"""" 6358 6359 :: 6360 6361 declare void @llvm.va_copy(i8* <destarglist>, i8* <srcarglist>) 6362 6363 Overview: 6364 """"""""" 6365 6366 The '``llvm.va_copy``' intrinsic copies the current argument position 6367 from the source argument list to the destination argument list. 6368 6369 Arguments: 6370 """""""""" 6371 6372 The first argument is a pointer to a ``va_list`` element to initialize. 6373 The second argument is a pointer to a ``va_list`` element to copy from. 6374 6375 Semantics: 6376 """""""""" 6377 6378 The '``llvm.va_copy``' intrinsic works just like the ``va_copy`` macro 6379 available in C. In a target-dependent way, it copies the source 6380 ``va_list`` element into the destination ``va_list`` element. This 6381 intrinsic is necessary because the `` llvm.va_start`` intrinsic may be 6382 arbitrarily complex and require, for example, memory allocation. 6383 6384 Accurate Garbage Collection Intrinsics 6385 -------------------------------------- 6386 6387 LLVM support for `Accurate Garbage Collection <GarbageCollection.html>`_ 6388 (GC) requires the implementation and generation of these intrinsics. 6389 These intrinsics allow identification of :ref:`GC roots on the 6390 stack <int_gcroot>`, as well as garbage collector implementations that 6391 require :ref:`read <int_gcread>` and :ref:`write <int_gcwrite>` barriers. 6392 Front-ends for type-safe garbage collected languages should generate 6393 these intrinsics to make use of the LLVM garbage collectors. For more 6394 details, see `Accurate Garbage Collection with 6395 LLVM <GarbageCollection.html>`_. 6396 6397 The garbage collection intrinsics only operate on objects in the generic 6398 address space (address space zero). 6399 6400 .. _int_gcroot: 6401 6402 '``llvm.gcroot``' Intrinsic 6403 ^^^^^^^^^^^^^^^^^^^^^^^^^^^ 6404 6405 Syntax: 6406 """"""" 6407 6408 :: 6409 6410 declare void @llvm.gcroot(i8** %ptrloc, i8* %metadata) 6411 6412 Overview: 6413 """"""""" 6414 6415 The '``llvm.gcroot``' intrinsic declares the existence of a GC root to 6416 the code generator, and allows some metadata to be associated with it. 6417 6418 Arguments: 6419 """""""""" 6420 6421 The first argument specifies the address of a stack object that contains 6422 the root pointer. The second pointer (which must be either a constant or 6423 a global value address) contains the meta-data to be associated with the 6424 root. 6425 6426 Semantics: 6427 """""""""" 6428 6429 At runtime, a call to this intrinsic stores a null pointer into the 6430 "ptrloc" location. At compile-time, the code generator generates 6431 information to allow the runtime to find the pointer at GC safe points. 6432 The '``llvm.gcroot``' intrinsic may only be used in a function which 6433 :ref:`specifies a GC algorithm <gc>`. 6434 6435 .. _int_gcread: 6436 6437 '``llvm.gcread``' Intrinsic 6438 ^^^^^^^^^^^^^^^^^^^^^^^^^^^ 6439 6440 Syntax: 6441 """"""" 6442 6443 :: 6444 6445 declare i8* @llvm.gcread(i8* %ObjPtr, i8** %Ptr) 6446 6447 Overview: 6448 """"""""" 6449 6450 The '``llvm.gcread``' intrinsic identifies reads of references from heap 6451 locations, allowing garbage collector implementations that require read 6452 barriers. 6453 6454 Arguments: 6455 """""""""" 6456 6457 The second argument is the address to read from, which should be an 6458 address allocated from the garbage collector. The first object is a 6459 pointer to the start of the referenced object, if needed by the language 6460 runtime (otherwise null). 6461 6462 Semantics: 6463 """""""""" 6464 6465 The '``llvm.gcread``' intrinsic has the same semantics as a load 6466 instruction, but may be replaced with substantially more complex code by 6467 the garbage collector runtime, as needed. The '``llvm.gcread``' 6468 intrinsic may only be used in a function which :ref:`specifies a GC 6469 algorithm <gc>`. 6470 6471 .. _int_gcwrite: 6472 6473 '``llvm.gcwrite``' Intrinsic 6474 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 6475 6476 Syntax: 6477 """"""" 6478 6479 :: 6480 6481 declare void @llvm.gcwrite(i8* %P1, i8* %Obj, i8** %P2) 6482 6483 Overview: 6484 """"""""" 6485 6486 The '``llvm.gcwrite``' intrinsic identifies writes of references to heap 6487 locations, allowing garbage collector implementations that require write 6488 barriers (such as generational or reference counting collectors). 6489 6490 Arguments: 6491 """""""""" 6492 6493 The first argument is the reference to store, the second is the start of 6494 the object to store it to, and the third is the address of the field of 6495 Obj to store to. If the runtime does not require a pointer to the 6496 object, Obj may be null. 6497 6498 Semantics: 6499 """""""""" 6500 6501 The '``llvm.gcwrite``' intrinsic has the same semantics as a store 6502 instruction, but may be replaced with substantially more complex code by 6503 the garbage collector runtime, as needed. The '``llvm.gcwrite``' 6504 intrinsic may only be used in a function which :ref:`specifies a GC 6505 algorithm <gc>`. 6506 6507 Code Generator Intrinsics 6508 ------------------------- 6509 6510 These intrinsics are provided by LLVM to expose special features that 6511 may only be implemented with code generator support. 6512 6513 '``llvm.returnaddress``' Intrinsic 6514 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 6515 6516 Syntax: 6517 """"""" 6518 6519 :: 6520 6521 declare i8 *@llvm.returnaddress(i32 <level>) 6522 6523 Overview: 6524 """"""""" 6525 6526 The '``llvm.returnaddress``' intrinsic attempts to compute a 6527 target-specific value indicating the return address of the current 6528 function or one of its callers. 6529 6530 Arguments: 6531 """""""""" 6532 6533 The argument to this intrinsic indicates which function to return the 6534 address for. Zero indicates the calling function, one indicates its 6535 caller, etc. The argument is **required** to be a constant integer 6536 value. 6537 6538 Semantics: 6539 """""""""" 6540 6541 The '``llvm.returnaddress``' intrinsic either returns a pointer 6542 indicating the return address of the specified call frame, or zero if it 6543 cannot be identified. The value returned by this intrinsic is likely to 6544 be incorrect or 0 for arguments other than zero, so it should only be 6545 used for debugging purposes. 6546 6547 Note that calling this intrinsic does not prevent function inlining or 6548 other aggressive transformations, so the value returned may not be that 6549 of the obvious source-language caller. 6550 6551 '``llvm.frameaddress``' Intrinsic 6552 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 6553 6554 Syntax: 6555 """"""" 6556 6557 :: 6558 6559 declare i8* @llvm.frameaddress(i32 <level>) 6560 6561 Overview: 6562 """"""""" 6563 6564 The '``llvm.frameaddress``' intrinsic attempts to return the 6565 target-specific frame pointer value for the specified stack frame. 6566 6567 Arguments: 6568 """""""""" 6569 6570 The argument to this intrinsic indicates which function to return the 6571 frame pointer for. Zero indicates the calling function, one indicates 6572 its caller, etc. The argument is **required** to be a constant integer 6573 value. 6574 6575 Semantics: 6576 """""""""" 6577 6578 The '``llvm.frameaddress``' intrinsic either returns a pointer 6579 indicating the frame address of the specified call frame, or zero if it 6580 cannot be identified. The value returned by this intrinsic is likely to 6581 be incorrect or 0 for arguments other than zero, so it should only be 6582 used for debugging purposes. 6583 6584 Note that calling this intrinsic does not prevent function inlining or 6585 other aggressive transformations, so the value returned may not be that 6586 of the obvious source-language caller. 6587 6588 .. _int_stacksave: 6589 6590 '``llvm.stacksave``' Intrinsic 6591 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 6592 6593 Syntax: 6594 """"""" 6595 6596 :: 6597 6598 declare i8* @llvm.stacksave() 6599 6600 Overview: 6601 """"""""" 6602 6603 The '``llvm.stacksave``' intrinsic is used to remember the current state 6604 of the function stack, for use with 6605 :ref:`llvm.stackrestore <int_stackrestore>`. This is useful for 6606 implementing language features like scoped automatic variable sized 6607 arrays in C99. 6608 6609 Semantics: 6610 """""""""" 6611 6612 This intrinsic returns a opaque pointer value that can be passed to 6613 :ref:`llvm.stackrestore <int_stackrestore>`. When an 6614 ``llvm.stackrestore`` intrinsic is executed with a value saved from 6615 ``llvm.stacksave``, it effectively restores the state of the stack to 6616 the state it was in when the ``llvm.stacksave`` intrinsic executed. In 6617 practice, this pops any :ref:`alloca <i_alloca>` blocks from the stack that 6618 were allocated after the ``llvm.stacksave`` was executed. 6619 6620 .. _int_stackrestore: 6621 6622 '``llvm.stackrestore``' Intrinsic 6623 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 6624 6625 Syntax: 6626 """"""" 6627 6628 :: 6629 6630 declare void @llvm.stackrestore(i8* %ptr) 6631 6632 Overview: 6633 """"""""" 6634 6635 The '``llvm.stackrestore``' intrinsic is used to restore the state of 6636 the function stack to the state it was in when the corresponding 6637 :ref:`llvm.stacksave <int_stacksave>` intrinsic executed. This is 6638 useful for implementing language features like scoped automatic variable 6639 sized arrays in C99. 6640 6641 Semantics: 6642 """""""""" 6643 6644 See the description for :ref:`llvm.stacksave <int_stacksave>`. 6645 6646 '``llvm.prefetch``' Intrinsic 6647 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 6648 6649 Syntax: 6650 """"""" 6651 6652 :: 6653 6654 declare void @llvm.prefetch(i8* <address>, i32 <rw>, i32 <locality>, i32 <cache type>) 6655 6656 Overview: 6657 """"""""" 6658 6659 The '``llvm.prefetch``' intrinsic is a hint to the code generator to 6660 insert a prefetch instruction if supported; otherwise, it is a noop. 6661 Prefetches have no effect on the behavior of the program but can change 6662 its performance characteristics. 6663 6664 Arguments: 6665 """""""""" 6666 6667 ``address`` is the address to be prefetched, ``rw`` is the specifier 6668 determining if the fetch should be for a read (0) or write (1), and 6669 ``locality`` is a temporal locality specifier ranging from (0) - no 6670 locality, to (3) - extremely local keep in cache. The ``cache type`` 6671 specifies whether the prefetch is performed on the data (1) or 6672 instruction (0) cache. The ``rw``, ``locality`` and ``cache type`` 6673 arguments must be constant integers. 6674 6675 Semantics: 6676 """""""""" 6677 6678 This intrinsic does not modify the behavior of the program. In 6679 particular, prefetches cannot trap and do not produce a value. On 6680 targets that support this intrinsic, the prefetch can provide hints to 6681 the processor cache for better performance. 6682 6683 '``llvm.pcmarker``' Intrinsic 6684 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 6685 6686 Syntax: 6687 """"""" 6688 6689 :: 6690 6691 declare void @llvm.pcmarker(i32 <id>) 6692 6693 Overview: 6694 """"""""" 6695 6696 The '``llvm.pcmarker``' intrinsic is a method to export a Program 6697 Counter (PC) in a region of code to simulators and other tools. The 6698 method is target specific, but it is expected that the marker will use 6699 exported symbols to transmit the PC of the marker. The marker makes no 6700 guarantees that it will remain with any specific instruction after 6701 optimizations. It is possible that the presence of a marker will inhibit 6702 optimizations. The intended use is to be inserted after optimizations to 6703 allow correlations of simulation runs. 6704 6705 Arguments: 6706 """""""""" 6707 6708 ``id`` is a numerical id identifying the marker. 6709 6710 Semantics: 6711 """""""""" 6712 6713 This intrinsic does not modify the behavior of the program. Backends 6714 that do not support this intrinsic may ignore it. 6715 6716 '``llvm.readcyclecounter``' Intrinsic 6717 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 6718 6719 Syntax: 6720 """"""" 6721 6722 :: 6723 6724 declare i64 @llvm.readcyclecounter() 6725 6726 Overview: 6727 """"""""" 6728 6729 The '``llvm.readcyclecounter``' intrinsic provides access to the cycle 6730 counter register (or similar low latency, high accuracy clocks) on those 6731 targets that support it. On X86, it should map to RDTSC. On Alpha, it 6732 should map to RPCC. As the backing counters overflow quickly (on the 6733 order of 9 seconds on alpha), this should only be used for small 6734 timings. 6735 6736 Semantics: 6737 """""""""" 6738 6739 When directly supported, reading the cycle counter should not modify any 6740 memory. Implementations are allowed to either return a application 6741 specific value or a system wide value. On backends without support, this 6742 is lowered to a constant 0. 6743 6744 Note that runtime support may be conditional on the privilege-level code is 6745 running at and the host platform. 6746 6747 Standard C Library Intrinsics 6748 ----------------------------- 6749 6750 LLVM provides intrinsics for a few important standard C library 6751 functions. These intrinsics allow source-language front-ends to pass 6752 information about the alignment of the pointer arguments to the code 6753 generator, providing opportunity for more efficient code generation. 6754 6755 .. _int_memcpy: 6756 6757 '``llvm.memcpy``' Intrinsic 6758 ^^^^^^^^^^^^^^^^^^^^^^^^^^^ 6759 6760 Syntax: 6761 """"""" 6762 6763 This is an overloaded intrinsic. You can use ``llvm.memcpy`` on any 6764 integer bit width and for different address spaces. Not all targets 6765 support all bit widths however. 6766 6767 :: 6768 6769 declare void @llvm.memcpy.p0i8.p0i8.i32(i8* <dest>, i8* <src>, 6770 i32 <len>, i32 <align>, i1 <isvolatile>) 6771 declare void @llvm.memcpy.p0i8.p0i8.i64(i8* <dest>, i8* <src>, 6772 i64 <len>, i32 <align>, i1 <isvolatile>) 6773 6774 Overview: 6775 """"""""" 6776 6777 The '``llvm.memcpy.*``' intrinsics copy a block of memory from the 6778 source location to the destination location. 6779 6780 Note that, unlike the standard libc function, the ``llvm.memcpy.*`` 6781 intrinsics do not return a value, takes extra alignment/isvolatile 6782 arguments and the pointers can be in specified address spaces. 6783 6784 Arguments: 6785 """""""""" 6786 6787 The first argument is a pointer to the destination, the second is a 6788 pointer to the source. The third argument is an integer argument 6789 specifying the number of bytes to copy, the fourth argument is the 6790 alignment of the source and destination locations, and the fifth is a 6791 boolean indicating a volatile access. 6792 6793 If the call to this intrinsic has an alignment value that is not 0 or 1, 6794 then the caller guarantees that both the source and destination pointers 6795 are aligned to that boundary. 6796 6797 If the ``isvolatile`` parameter is ``true``, the ``llvm.memcpy`` call is 6798 a :ref:`volatile operation <volatile>`. The detailed access behavior is not 6799 very cleanly specified and it is unwise to depend on it. 6800 6801 Semantics: 6802 """""""""" 6803 6804 The '``llvm.memcpy.*``' intrinsics copy a block of memory from the 6805 source location to the destination location, which are not allowed to 6806 overlap. It copies "len" bytes of memory over. If the argument is known 6807 to be aligned to some boundary, this can be specified as the fourth 6808 argument, otherwise it should be set to 0 or 1. 6809 6810 '``llvm.memmove``' Intrinsic 6811 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 6812 6813 Syntax: 6814 """"""" 6815 6816 This is an overloaded intrinsic. You can use llvm.memmove on any integer 6817 bit width and for different address space. Not all targets support all 6818 bit widths however. 6819 6820 :: 6821 6822 declare void @llvm.memmove.p0i8.p0i8.i32(i8* <dest>, i8* <src>, 6823 i32 <len>, i32 <align>, i1 <isvolatile>) 6824 declare void @llvm.memmove.p0i8.p0i8.i64(i8* <dest>, i8* <src>, 6825 i64 <len>, i32 <align>, i1 <isvolatile>) 6826 6827 Overview: 6828 """"""""" 6829 6830 The '``llvm.memmove.*``' intrinsics move a block of memory from the 6831 source location to the destination location. It is similar to the 6832 '``llvm.memcpy``' intrinsic but allows the two memory locations to 6833 overlap. 6834 6835 Note that, unlike the standard libc function, the ``llvm.memmove.*`` 6836 intrinsics do not return a value, takes extra alignment/isvolatile 6837 arguments and the pointers can be in specified address spaces. 6838 6839 Arguments: 6840 """""""""" 6841 6842 The first argument is a pointer to the destination, the second is a 6843 pointer to the source. The third argument is an integer argument 6844 specifying the number of bytes to copy, the fourth argument is the 6845 alignment of the source and destination locations, and the fifth is a 6846 boolean indicating a volatile access. 6847 6848 If the call to this intrinsic has an alignment value that is not 0 or 1, 6849 then the caller guarantees that the source and destination pointers are 6850 aligned to that boundary. 6851 6852 If the ``isvolatile`` parameter is ``true``, the ``llvm.memmove`` call 6853 is a :ref:`volatile operation <volatile>`. The detailed access behavior is 6854 not very cleanly specified and it is unwise to depend on it. 6855 6856 Semantics: 6857 """""""""" 6858 6859 The '``llvm.memmove.*``' intrinsics copy a block of memory from the 6860 source location to the destination location, which may overlap. It 6861 copies "len" bytes of memory over. If the argument is known to be 6862 aligned to some boundary, this can be specified as the fourth argument, 6863 otherwise it should be set to 0 or 1. 6864 6865 '``llvm.memset.*``' Intrinsics 6866 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 6867 6868 Syntax: 6869 """"""" 6870 6871 This is an overloaded intrinsic. You can use llvm.memset on any integer 6872 bit width and for different address spaces. However, not all targets 6873 support all bit widths. 6874 6875 :: 6876 6877 declare void @llvm.memset.p0i8.i32(i8* <dest>, i8 <val>, 6878 i32 <len>, i32 <align>, i1 <isvolatile>) 6879 declare void @llvm.memset.p0i8.i64(i8* <dest>, i8 <val>, 6880 i64 <len>, i32 <align>, i1 <isvolatile>) 6881 6882 Overview: 6883 """"""""" 6884 6885 The '``llvm.memset.*``' intrinsics fill a block of memory with a 6886 particular byte value. 6887 6888 Note that, unlike the standard libc function, the ``llvm.memset`` 6889 intrinsic does not return a value and takes extra alignment/volatile 6890 arguments. Also, the destination can be in an arbitrary address space. 6891 6892 Arguments: 6893 """""""""" 6894 6895 The first argument is a pointer to the destination to fill, the second 6896 is the byte value with which to fill it, the third argument is an 6897 integer argument specifying the number of bytes to fill, and the fourth 6898 argument is the known alignment of the destination location. 6899 6900 If the call to this intrinsic has an alignment value that is not 0 or 1, 6901 then the caller guarantees that the destination pointer is aligned to 6902 that boundary. 6903 6904 If the ``isvolatile`` parameter is ``true``, the ``llvm.memset`` call is 6905 a :ref:`volatile operation <volatile>`. The detailed access behavior is not 6906 very cleanly specified and it is unwise to depend on it. 6907 6908 Semantics: 6909 """""""""" 6910 6911 The '``llvm.memset.*``' intrinsics fill "len" bytes of memory starting 6912 at the destination location. If the argument is known to be aligned to 6913 some boundary, this can be specified as the fourth argument, otherwise 6914 it should be set to 0 or 1. 6915 6916 '``llvm.sqrt.*``' Intrinsic 6917 ^^^^^^^^^^^^^^^^^^^^^^^^^^^ 6918 6919 Syntax: 6920 """"""" 6921 6922 This is an overloaded intrinsic. You can use ``llvm.sqrt`` on any 6923 floating point or vector of floating point type. Not all targets support 6924 all types however. 6925 6926 :: 6927 6928 declare float @llvm.sqrt.f32(float %Val) 6929 declare double @llvm.sqrt.f64(double %Val) 6930 declare x86_fp80 @llvm.sqrt.f80(x86_fp80 %Val) 6931 declare fp128 @llvm.sqrt.f128(fp128 %Val) 6932 declare ppc_fp128 @llvm.sqrt.ppcf128(ppc_fp128 %Val) 6933 6934 Overview: 6935 """"""""" 6936 6937 The '``llvm.sqrt``' intrinsics return the sqrt of the specified operand, 6938 returning the same value as the libm '``sqrt``' functions would. Unlike 6939 ``sqrt`` in libm, however, ``llvm.sqrt`` has undefined behavior for 6940 negative numbers other than -0.0 (which allows for better optimization, 6941 because there is no need to worry about errno being set). 6942 ``llvm.sqrt(-0.0)`` is defined to return -0.0 like IEEE sqrt. 6943 6944 Arguments: 6945 """""""""" 6946 6947 The argument and return value are floating point numbers of the same 6948 type. 6949 6950 Semantics: 6951 """""""""" 6952 6953 This function returns the sqrt of the specified operand if it is a 6954 nonnegative floating point number. 6955 6956 '``llvm.powi.*``' Intrinsic 6957 ^^^^^^^^^^^^^^^^^^^^^^^^^^^ 6958 6959 Syntax: 6960 """"""" 6961 6962 This is an overloaded intrinsic. You can use ``llvm.powi`` on any 6963 floating point or vector of floating point type. Not all targets support 6964 all types however. 6965 6966 :: 6967 6968 declare float @llvm.powi.f32(float %Val, i32 %power) 6969 declare double @llvm.powi.f64(double %Val, i32 %power) 6970 declare x86_fp80 @llvm.powi.f80(x86_fp80 %Val, i32 %power) 6971 declare fp128 @llvm.powi.f128(fp128 %Val, i32 %power) 6972 declare ppc_fp128 @llvm.powi.ppcf128(ppc_fp128 %Val, i32 %power) 6973 6974 Overview: 6975 """"""""" 6976 6977 The '``llvm.powi.*``' intrinsics return the first operand raised to the 6978 specified (positive or negative) power. The order of evaluation of 6979 multiplications is not defined. When a vector of floating point type is 6980 used, the second argument remains a scalar integer value. 6981 6982 Arguments: 6983 """""""""" 6984 6985 The second argument is an integer power, and the first is a value to 6986 raise to that power. 6987 6988 Semantics: 6989 """""""""" 6990 6991 This function returns the first value raised to the second power with an 6992 unspecified sequence of rounding operations. 6993 6994 '``llvm.sin.*``' Intrinsic 6995 ^^^^^^^^^^^^^^^^^^^^^^^^^^ 6996 6997 Syntax: 6998 """"""" 6999 7000 This is an overloaded intrinsic. You can use ``llvm.sin`` on any 7001 floating point or vector of floating point type. Not all targets support 7002 all types however. 7003 7004 :: 7005 7006 declare float @llvm.sin.f32(float %Val) 7007 declare double @llvm.sin.f64(double %Val) 7008 declare x86_fp80 @llvm.sin.f80(x86_fp80 %Val) 7009 declare fp128 @llvm.sin.f128(fp128 %Val) 7010 declare ppc_fp128 @llvm.sin.ppcf128(ppc_fp128 %Val) 7011 7012 Overview: 7013 """"""""" 7014 7015 The '``llvm.sin.*``' intrinsics return the sine of the operand. 7016 7017 Arguments: 7018 """""""""" 7019 7020 The argument and return value are floating point numbers of the same 7021 type. 7022 7023 Semantics: 7024 """""""""" 7025 7026 This function returns the sine of the specified operand, returning the 7027 same values as the libm ``sin`` functions would, and handles error 7028 conditions in the same way. 7029 7030 '``llvm.cos.*``' Intrinsic 7031 ^^^^^^^^^^^^^^^^^^^^^^^^^^ 7032 7033 Syntax: 7034 """"""" 7035 7036 This is an overloaded intrinsic. You can use ``llvm.cos`` on any 7037 floating point or vector of floating point type. Not all targets support 7038 all types however. 7039 7040 :: 7041 7042 declare float @llvm.cos.f32(float %Val) 7043 declare double @llvm.cos.f64(double %Val) 7044 declare x86_fp80 @llvm.cos.f80(x86_fp80 %Val) 7045 declare fp128 @llvm.cos.f128(fp128 %Val) 7046 declare ppc_fp128 @llvm.cos.ppcf128(ppc_fp128 %Val) 7047 7048 Overview: 7049 """"""""" 7050 7051 The '``llvm.cos.*``' intrinsics return the cosine of the operand. 7052 7053 Arguments: 7054 """""""""" 7055 7056 The argument and return value are floating point numbers of the same 7057 type. 7058 7059 Semantics: 7060 """""""""" 7061 7062 This function returns the cosine of the specified operand, returning the 7063 same values as the libm ``cos`` functions would, and handles error 7064 conditions in the same way. 7065 7066 '``llvm.pow.*``' Intrinsic 7067 ^^^^^^^^^^^^^^^^^^^^^^^^^^ 7068 7069 Syntax: 7070 """"""" 7071 7072 This is an overloaded intrinsic. You can use ``llvm.pow`` on any 7073 floating point or vector of floating point type. Not all targets support 7074 all types however. 7075 7076 :: 7077 7078 declare float @llvm.pow.f32(float %Val, float %Power) 7079 declare double @llvm.pow.f64(double %Val, double %Power) 7080 declare x86_fp80 @llvm.pow.f80(x86_fp80 %Val, x86_fp80 %Power) 7081 declare fp128 @llvm.pow.f128(fp128 %Val, fp128 %Power) 7082 declare ppc_fp128 @llvm.pow.ppcf128(ppc_fp128 %Val, ppc_fp128 Power) 7083 7084 Overview: 7085 """"""""" 7086 7087 The '``llvm.pow.*``' intrinsics return the first operand raised to the 7088 specified (positive or negative) power. 7089 7090 Arguments: 7091 """""""""" 7092 7093 The second argument is a floating point power, and the first is a value 7094 to raise to that power. 7095 7096 Semantics: 7097 """""""""" 7098 7099 This function returns the first value raised to the second power, 7100 returning the same values as the libm ``pow`` functions would, and 7101 handles error conditions in the same way. 7102 7103 '``llvm.exp.*``' Intrinsic 7104 ^^^^^^^^^^^^^^^^^^^^^^^^^^ 7105 7106 Syntax: 7107 """"""" 7108 7109 This is an overloaded intrinsic. You can use ``llvm.exp`` on any 7110 floating point or vector of floating point type. Not all targets support 7111 all types however. 7112 7113 :: 7114 7115 declare float @llvm.exp.f32(float %Val) 7116 declare double @llvm.exp.f64(double %Val) 7117 declare x86_fp80 @llvm.exp.f80(x86_fp80 %Val) 7118 declare fp128 @llvm.exp.f128(fp128 %Val) 7119 declare ppc_fp128 @llvm.exp.ppcf128(ppc_fp128 %Val) 7120 7121 Overview: 7122 """"""""" 7123 7124 The '``llvm.exp.*``' intrinsics perform the exp function. 7125 7126 Arguments: 7127 """""""""" 7128 7129 The argument and return value are floating point numbers of the same 7130 type. 7131 7132 Semantics: 7133 """""""""" 7134 7135 This function returns the same values as the libm ``exp`` functions 7136 would, and handles error conditions in the same way. 7137 7138 '``llvm.exp2.*``' Intrinsic 7139 ^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7140 7141 Syntax: 7142 """"""" 7143 7144 This is an overloaded intrinsic. You can use ``llvm.exp2`` on any 7145 floating point or vector of floating point type. Not all targets support 7146 all types however. 7147 7148 :: 7149 7150 declare float @llvm.exp2.f32(float %Val) 7151 declare double @llvm.exp2.f64(double %Val) 7152 declare x86_fp80 @llvm.exp2.f80(x86_fp80 %Val) 7153 declare fp128 @llvm.exp2.f128(fp128 %Val) 7154 declare ppc_fp128 @llvm.exp2.ppcf128(ppc_fp128 %Val) 7155 7156 Overview: 7157 """"""""" 7158 7159 The '``llvm.exp2.*``' intrinsics perform the exp2 function. 7160 7161 Arguments: 7162 """""""""" 7163 7164 The argument and return value are floating point numbers of the same 7165 type. 7166 7167 Semantics: 7168 """""""""" 7169 7170 This function returns the same values as the libm ``exp2`` functions 7171 would, and handles error conditions in the same way. 7172 7173 '``llvm.log.*``' Intrinsic 7174 ^^^^^^^^^^^^^^^^^^^^^^^^^^ 7175 7176 Syntax: 7177 """"""" 7178 7179 This is an overloaded intrinsic. You can use ``llvm.log`` on any 7180 floating point or vector of floating point type. Not all targets support 7181 all types however. 7182 7183 :: 7184 7185 declare float @llvm.log.f32(float %Val) 7186 declare double @llvm.log.f64(double %Val) 7187 declare x86_fp80 @llvm.log.f80(x86_fp80 %Val) 7188 declare fp128 @llvm.log.f128(fp128 %Val) 7189 declare ppc_fp128 @llvm.log.ppcf128(ppc_fp128 %Val) 7190 7191 Overview: 7192 """"""""" 7193 7194 The '``llvm.log.*``' intrinsics perform the log function. 7195 7196 Arguments: 7197 """""""""" 7198 7199 The argument and return value are floating point numbers of the same 7200 type. 7201 7202 Semantics: 7203 """""""""" 7204 7205 This function returns the same values as the libm ``log`` functions 7206 would, and handles error conditions in the same way. 7207 7208 '``llvm.log10.*``' Intrinsic 7209 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7210 7211 Syntax: 7212 """"""" 7213 7214 This is an overloaded intrinsic. You can use ``llvm.log10`` on any 7215 floating point or vector of floating point type. Not all targets support 7216 all types however. 7217 7218 :: 7219 7220 declare float @llvm.log10.f32(float %Val) 7221 declare double @llvm.log10.f64(double %Val) 7222 declare x86_fp80 @llvm.log10.f80(x86_fp80 %Val) 7223 declare fp128 @llvm.log10.f128(fp128 %Val) 7224 declare ppc_fp128 @llvm.log10.ppcf128(ppc_fp128 %Val) 7225 7226 Overview: 7227 """"""""" 7228 7229 The '``llvm.log10.*``' intrinsics perform the log10 function. 7230 7231 Arguments: 7232 """""""""" 7233 7234 The argument and return value are floating point numbers of the same 7235 type. 7236 7237 Semantics: 7238 """""""""" 7239 7240 This function returns the same values as the libm ``log10`` functions 7241 would, and handles error conditions in the same way. 7242 7243 '``llvm.log2.*``' Intrinsic 7244 ^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7245 7246 Syntax: 7247 """"""" 7248 7249 This is an overloaded intrinsic. You can use ``llvm.log2`` on any 7250 floating point or vector of floating point type. Not all targets support 7251 all types however. 7252 7253 :: 7254 7255 declare float @llvm.log2.f32(float %Val) 7256 declare double @llvm.log2.f64(double %Val) 7257 declare x86_fp80 @llvm.log2.f80(x86_fp80 %Val) 7258 declare fp128 @llvm.log2.f128(fp128 %Val) 7259 declare ppc_fp128 @llvm.log2.ppcf128(ppc_fp128 %Val) 7260 7261 Overview: 7262 """"""""" 7263 7264 The '``llvm.log2.*``' intrinsics perform the log2 function. 7265 7266 Arguments: 7267 """""""""" 7268 7269 The argument and return value are floating point numbers of the same 7270 type. 7271 7272 Semantics: 7273 """""""""" 7274 7275 This function returns the same values as the libm ``log2`` functions 7276 would, and handles error conditions in the same way. 7277 7278 '``llvm.fma.*``' Intrinsic 7279 ^^^^^^^^^^^^^^^^^^^^^^^^^^ 7280 7281 Syntax: 7282 """"""" 7283 7284 This is an overloaded intrinsic. You can use ``llvm.fma`` on any 7285 floating point or vector of floating point type. Not all targets support 7286 all types however. 7287 7288 :: 7289 7290 declare float @llvm.fma.f32(float %a, float %b, float %c) 7291 declare double @llvm.fma.f64(double %a, double %b, double %c) 7292 declare x86_fp80 @llvm.fma.f80(x86_fp80 %a, x86_fp80 %b, x86_fp80 %c) 7293 declare fp128 @llvm.fma.f128(fp128 %a, fp128 %b, fp128 %c) 7294 declare ppc_fp128 @llvm.fma.ppcf128(ppc_fp128 %a, ppc_fp128 %b, ppc_fp128 %c) 7295 7296 Overview: 7297 """"""""" 7298 7299 The '``llvm.fma.*``' intrinsics perform the fused multiply-add 7300 operation. 7301 7302 Arguments: 7303 """""""""" 7304 7305 The argument and return value are floating point numbers of the same 7306 type. 7307 7308 Semantics: 7309 """""""""" 7310 7311 This function returns the same values as the libm ``fma`` functions 7312 would. 7313 7314 '``llvm.fabs.*``' Intrinsic 7315 ^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7316 7317 Syntax: 7318 """"""" 7319 7320 This is an overloaded intrinsic. You can use ``llvm.fabs`` on any 7321 floating point or vector of floating point type. Not all targets support 7322 all types however. 7323 7324 :: 7325 7326 declare float @llvm.fabs.f32(float %Val) 7327 declare double @llvm.fabs.f64(double %Val) 7328 declare x86_fp80 @llvm.fabs.f80(x86_fp80 %Val) 7329 declare fp128 @llvm.fabs.f128(fp128 %Val) 7330 declare ppc_fp128 @llvm.fabs.ppcf128(ppc_fp128 %Val) 7331 7332 Overview: 7333 """"""""" 7334 7335 The '``llvm.fabs.*``' intrinsics return the absolute value of the 7336 operand. 7337 7338 Arguments: 7339 """""""""" 7340 7341 The argument and return value are floating point numbers of the same 7342 type. 7343 7344 Semantics: 7345 """""""""" 7346 7347 This function returns the same values as the libm ``fabs`` functions 7348 would, and handles error conditions in the same way. 7349 7350 '``llvm.floor.*``' Intrinsic 7351 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7352 7353 Syntax: 7354 """"""" 7355 7356 This is an overloaded intrinsic. You can use ``llvm.floor`` on any 7357 floating point or vector of floating point type. Not all targets support 7358 all types however. 7359 7360 :: 7361 7362 declare float @llvm.floor.f32(float %Val) 7363 declare double @llvm.floor.f64(double %Val) 7364 declare x86_fp80 @llvm.floor.f80(x86_fp80 %Val) 7365 declare fp128 @llvm.floor.f128(fp128 %Val) 7366 declare ppc_fp128 @llvm.floor.ppcf128(ppc_fp128 %Val) 7367 7368 Overview: 7369 """"""""" 7370 7371 The '``llvm.floor.*``' intrinsics return the floor of the operand. 7372 7373 Arguments: 7374 """""""""" 7375 7376 The argument and return value are floating point numbers of the same 7377 type. 7378 7379 Semantics: 7380 """""""""" 7381 7382 This function returns the same values as the libm ``floor`` functions 7383 would, and handles error conditions in the same way. 7384 7385 '``llvm.ceil.*``' Intrinsic 7386 ^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7387 7388 Syntax: 7389 """"""" 7390 7391 This is an overloaded intrinsic. You can use ``llvm.ceil`` on any 7392 floating point or vector of floating point type. Not all targets support 7393 all types however. 7394 7395 :: 7396 7397 declare float @llvm.ceil.f32(float %Val) 7398 declare double @llvm.ceil.f64(double %Val) 7399 declare x86_fp80 @llvm.ceil.f80(x86_fp80 %Val) 7400 declare fp128 @llvm.ceil.f128(fp128 %Val) 7401 declare ppc_fp128 @llvm.ceil.ppcf128(ppc_fp128 %Val) 7402 7403 Overview: 7404 """"""""" 7405 7406 The '``llvm.ceil.*``' intrinsics return the ceiling of the operand. 7407 7408 Arguments: 7409 """""""""" 7410 7411 The argument and return value are floating point numbers of the same 7412 type. 7413 7414 Semantics: 7415 """""""""" 7416 7417 This function returns the same values as the libm ``ceil`` functions 7418 would, and handles error conditions in the same way. 7419 7420 '``llvm.trunc.*``' Intrinsic 7421 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7422 7423 Syntax: 7424 """"""" 7425 7426 This is an overloaded intrinsic. You can use ``llvm.trunc`` on any 7427 floating point or vector of floating point type. Not all targets support 7428 all types however. 7429 7430 :: 7431 7432 declare float @llvm.trunc.f32(float %Val) 7433 declare double @llvm.trunc.f64(double %Val) 7434 declare x86_fp80 @llvm.trunc.f80(x86_fp80 %Val) 7435 declare fp128 @llvm.trunc.f128(fp128 %Val) 7436 declare ppc_fp128 @llvm.trunc.ppcf128(ppc_fp128 %Val) 7437 7438 Overview: 7439 """"""""" 7440 7441 The '``llvm.trunc.*``' intrinsics returns the operand rounded to the 7442 nearest integer not larger in magnitude than the operand. 7443 7444 Arguments: 7445 """""""""" 7446 7447 The argument and return value are floating point numbers of the same 7448 type. 7449 7450 Semantics: 7451 """""""""" 7452 7453 This function returns the same values as the libm ``trunc`` functions 7454 would, and handles error conditions in the same way. 7455 7456 '``llvm.rint.*``' Intrinsic 7457 ^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7458 7459 Syntax: 7460 """"""" 7461 7462 This is an overloaded intrinsic. You can use ``llvm.rint`` on any 7463 floating point or vector of floating point type. Not all targets support 7464 all types however. 7465 7466 :: 7467 7468 declare float @llvm.rint.f32(float %Val) 7469 declare double @llvm.rint.f64(double %Val) 7470 declare x86_fp80 @llvm.rint.f80(x86_fp80 %Val) 7471 declare fp128 @llvm.rint.f128(fp128 %Val) 7472 declare ppc_fp128 @llvm.rint.ppcf128(ppc_fp128 %Val) 7473 7474 Overview: 7475 """"""""" 7476 7477 The '``llvm.rint.*``' intrinsics returns the operand rounded to the 7478 nearest integer. It may raise an inexact floating-point exception if the 7479 operand isn't an integer. 7480 7481 Arguments: 7482 """""""""" 7483 7484 The argument and return value are floating point numbers of the same 7485 type. 7486 7487 Semantics: 7488 """""""""" 7489 7490 This function returns the same values as the libm ``rint`` functions 7491 would, and handles error conditions in the same way. 7492 7493 '``llvm.nearbyint.*``' Intrinsic 7494 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7495 7496 Syntax: 7497 """"""" 7498 7499 This is an overloaded intrinsic. You can use ``llvm.nearbyint`` on any 7500 floating point or vector of floating point type. Not all targets support 7501 all types however. 7502 7503 :: 7504 7505 declare float @llvm.nearbyint.f32(float %Val) 7506 declare double @llvm.nearbyint.f64(double %Val) 7507 declare x86_fp80 @llvm.nearbyint.f80(x86_fp80 %Val) 7508 declare fp128 @llvm.nearbyint.f128(fp128 %Val) 7509 declare ppc_fp128 @llvm.nearbyint.ppcf128(ppc_fp128 %Val) 7510 7511 Overview: 7512 """"""""" 7513 7514 The '``llvm.nearbyint.*``' intrinsics returns the operand rounded to the 7515 nearest integer. 7516 7517 Arguments: 7518 """""""""" 7519 7520 The argument and return value are floating point numbers of the same 7521 type. 7522 7523 Semantics: 7524 """""""""" 7525 7526 This function returns the same values as the libm ``nearbyint`` 7527 functions would, and handles error conditions in the same way. 7528 7529 Bit Manipulation Intrinsics 7530 --------------------------- 7531 7532 LLVM provides intrinsics for a few important bit manipulation 7533 operations. These allow efficient code generation for some algorithms. 7534 7535 '``llvm.bswap.*``' Intrinsics 7536 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7537 7538 Syntax: 7539 """"""" 7540 7541 This is an overloaded intrinsic function. You can use bswap on any 7542 integer type that is an even number of bytes (i.e. BitWidth % 16 == 0). 7543 7544 :: 7545 7546 declare i16 @llvm.bswap.i16(i16 <id>) 7547 declare i32 @llvm.bswap.i32(i32 <id>) 7548 declare i64 @llvm.bswap.i64(i64 <id>) 7549 7550 Overview: 7551 """"""""" 7552 7553 The '``llvm.bswap``' family of intrinsics is used to byte swap integer 7554 values with an even number of bytes (positive multiple of 16 bits). 7555 These are useful for performing operations on data that is not in the 7556 target's native byte order. 7557 7558 Semantics: 7559 """""""""" 7560 7561 The ``llvm.bswap.i16`` intrinsic returns an i16 value that has the high 7562 and low byte of the input i16 swapped. Similarly, the ``llvm.bswap.i32`` 7563 intrinsic returns an i32 value that has the four bytes of the input i32 7564 swapped, so that if the input bytes are numbered 0, 1, 2, 3 then the 7565 returned i32 will have its bytes in 3, 2, 1, 0 order. The 7566 ``llvm.bswap.i48``, ``llvm.bswap.i64`` and other intrinsics extend this 7567 concept to additional even-byte lengths (6 bytes, 8 bytes and more, 7568 respectively). 7569 7570 '``llvm.ctpop.*``' Intrinsic 7571 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7572 7573 Syntax: 7574 """"""" 7575 7576 This is an overloaded intrinsic. You can use llvm.ctpop on any integer 7577 bit width, or on any vector with integer elements. Not all targets 7578 support all bit widths or vector types, however. 7579 7580 :: 7581 7582 declare i8 @llvm.ctpop.i8(i8 <src>) 7583 declare i16 @llvm.ctpop.i16(i16 <src>) 7584 declare i32 @llvm.ctpop.i32(i32 <src>) 7585 declare i64 @llvm.ctpop.i64(i64 <src>) 7586 declare i256 @llvm.ctpop.i256(i256 <src>) 7587 declare <2 x i32> @llvm.ctpop.v2i32(<2 x i32> <src>) 7588 7589 Overview: 7590 """"""""" 7591 7592 The '``llvm.ctpop``' family of intrinsics counts the number of bits set 7593 in a value. 7594 7595 Arguments: 7596 """""""""" 7597 7598 The only argument is the value to be counted. The argument may be of any 7599 integer type, or a vector with integer elements. The return type must 7600 match the argument type. 7601 7602 Semantics: 7603 """""""""" 7604 7605 The '``llvm.ctpop``' intrinsic counts the 1's in a variable, or within 7606 each element of a vector. 7607 7608 '``llvm.ctlz.*``' Intrinsic 7609 ^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7610 7611 Syntax: 7612 """"""" 7613 7614 This is an overloaded intrinsic. You can use ``llvm.ctlz`` on any 7615 integer bit width, or any vector whose elements are integers. Not all 7616 targets support all bit widths or vector types, however. 7617 7618 :: 7619 7620 declare i8 @llvm.ctlz.i8 (i8 <src>, i1 <is_zero_undef>) 7621 declare i16 @llvm.ctlz.i16 (i16 <src>, i1 <is_zero_undef>) 7622 declare i32 @llvm.ctlz.i32 (i32 <src>, i1 <is_zero_undef>) 7623 declare i64 @llvm.ctlz.i64 (i64 <src>, i1 <is_zero_undef>) 7624 declare i256 @llvm.ctlz.i256(i256 <src>, i1 <is_zero_undef>) 7625 declase <2 x i32> @llvm.ctlz.v2i32(<2 x i32> <src>, i1 <is_zero_undef>) 7626 7627 Overview: 7628 """"""""" 7629 7630 The '``llvm.ctlz``' family of intrinsic functions counts the number of 7631 leading zeros in a variable. 7632 7633 Arguments: 7634 """""""""" 7635 7636 The first argument is the value to be counted. This argument may be of 7637 any integer type, or a vectory with integer element type. The return 7638 type must match the first argument type. 7639 7640 The second argument must be a constant and is a flag to indicate whether 7641 the intrinsic should ensure that a zero as the first argument produces a 7642 defined result. Historically some architectures did not provide a 7643 defined result for zero values as efficiently, and many algorithms are 7644 now predicated on avoiding zero-value inputs. 7645 7646 Semantics: 7647 """""""""" 7648 7649 The '``llvm.ctlz``' intrinsic counts the leading (most significant) 7650 zeros in a variable, or within each element of the vector. If 7651 ``src == 0`` then the result is the size in bits of the type of ``src`` 7652 if ``is_zero_undef == 0`` and ``undef`` otherwise. For example, 7653 ``llvm.ctlz(i32 2) = 30``. 7654 7655 '``llvm.cttz.*``' Intrinsic 7656 ^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7657 7658 Syntax: 7659 """"""" 7660 7661 This is an overloaded intrinsic. You can use ``llvm.cttz`` on any 7662 integer bit width, or any vector of integer elements. Not all targets 7663 support all bit widths or vector types, however. 7664 7665 :: 7666 7667 declare i8 @llvm.cttz.i8 (i8 <src>, i1 <is_zero_undef>) 7668 declare i16 @llvm.cttz.i16 (i16 <src>, i1 <is_zero_undef>) 7669 declare i32 @llvm.cttz.i32 (i32 <src>, i1 <is_zero_undef>) 7670 declare i64 @llvm.cttz.i64 (i64 <src>, i1 <is_zero_undef>) 7671 declare i256 @llvm.cttz.i256(i256 <src>, i1 <is_zero_undef>) 7672 declase <2 x i32> @llvm.cttz.v2i32(<2 x i32> <src>, i1 <is_zero_undef>) 7673 7674 Overview: 7675 """"""""" 7676 7677 The '``llvm.cttz``' family of intrinsic functions counts the number of 7678 trailing zeros. 7679 7680 Arguments: 7681 """""""""" 7682 7683 The first argument is the value to be counted. This argument may be of 7684 any integer type, or a vectory with integer element type. The return 7685 type must match the first argument type. 7686 7687 The second argument must be a constant and is a flag to indicate whether 7688 the intrinsic should ensure that a zero as the first argument produces a 7689 defined result. Historically some architectures did not provide a 7690 defined result for zero values as efficiently, and many algorithms are 7691 now predicated on avoiding zero-value inputs. 7692 7693 Semantics: 7694 """""""""" 7695 7696 The '``llvm.cttz``' intrinsic counts the trailing (least significant) 7697 zeros in a variable, or within each element of a vector. If ``src == 0`` 7698 then the result is the size in bits of the type of ``src`` if 7699 ``is_zero_undef == 0`` and ``undef`` otherwise. For example, 7700 ``llvm.cttz(2) = 1``. 7701 7702 Arithmetic with Overflow Intrinsics 7703 ----------------------------------- 7704 7705 LLVM provides intrinsics for some arithmetic with overflow operations. 7706 7707 '``llvm.sadd.with.overflow.*``' Intrinsics 7708 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7709 7710 Syntax: 7711 """"""" 7712 7713 This is an overloaded intrinsic. You can use ``llvm.sadd.with.overflow`` 7714 on any integer bit width. 7715 7716 :: 7717 7718 declare {i16, i1} @llvm.sadd.with.overflow.i16(i16 %a, i16 %b) 7719 declare {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b) 7720 declare {i64, i1} @llvm.sadd.with.overflow.i64(i64 %a, i64 %b) 7721 7722 Overview: 7723 """"""""" 7724 7725 The '``llvm.sadd.with.overflow``' family of intrinsic functions perform 7726 a signed addition of the two arguments, and indicate whether an overflow 7727 occurred during the signed summation. 7728 7729 Arguments: 7730 """""""""" 7731 7732 The arguments (%a and %b) and the first element of the result structure 7733 may be of integer types of any bit width, but they must have the same 7734 bit width. The second element of the result structure must be of type 7735 ``i1``. ``%a`` and ``%b`` are the two values that will undergo signed 7736 addition. 7737 7738 Semantics: 7739 """""""""" 7740 7741 The '``llvm.sadd.with.overflow``' family of intrinsic functions perform 7742 a signed addition of the two variables. They return a structure --- the 7743 first element of which is the signed summation, and the second element 7744 of which is a bit specifying if the signed summation resulted in an 7745 overflow. 7746 7747 Examples: 7748 """"""""" 7749 7750 .. code-block:: llvm 7751 7752 %res = call {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b) 7753 %sum = extractvalue {i32, i1} %res, 0 7754 %obit = extractvalue {i32, i1} %res, 1 7755 br i1 %obit, label %overflow, label %normal 7756 7757 '``llvm.uadd.with.overflow.*``' Intrinsics 7758 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7759 7760 Syntax: 7761 """"""" 7762 7763 This is an overloaded intrinsic. You can use ``llvm.uadd.with.overflow`` 7764 on any integer bit width. 7765 7766 :: 7767 7768 declare {i16, i1} @llvm.uadd.with.overflow.i16(i16 %a, i16 %b) 7769 declare {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b) 7770 declare {i64, i1} @llvm.uadd.with.overflow.i64(i64 %a, i64 %b) 7771 7772 Overview: 7773 """"""""" 7774 7775 The '``llvm.uadd.with.overflow``' family of intrinsic functions perform 7776 an unsigned addition of the two arguments, and indicate whether a carry 7777 occurred during the unsigned summation. 7778 7779 Arguments: 7780 """""""""" 7781 7782 The arguments (%a and %b) and the first element of the result structure 7783 may be of integer types of any bit width, but they must have the same 7784 bit width. The second element of the result structure must be of type 7785 ``i1``. ``%a`` and ``%b`` are the two values that will undergo unsigned 7786 addition. 7787 7788 Semantics: 7789 """""""""" 7790 7791 The '``llvm.uadd.with.overflow``' family of intrinsic functions perform 7792 an unsigned addition of the two arguments. They return a structure --- the 7793 first element of which is the sum, and the second element of which is a 7794 bit specifying if the unsigned summation resulted in a carry. 7795 7796 Examples: 7797 """"""""" 7798 7799 .. code-block:: llvm 7800 7801 %res = call {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b) 7802 %sum = extractvalue {i32, i1} %res, 0 7803 %obit = extractvalue {i32, i1} %res, 1 7804 br i1 %obit, label %carry, label %normal 7805 7806 '``llvm.ssub.with.overflow.*``' Intrinsics 7807 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7808 7809 Syntax: 7810 """"""" 7811 7812 This is an overloaded intrinsic. You can use ``llvm.ssub.with.overflow`` 7813 on any integer bit width. 7814 7815 :: 7816 7817 declare {i16, i1} @llvm.ssub.with.overflow.i16(i16 %a, i16 %b) 7818 declare {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b) 7819 declare {i64, i1} @llvm.ssub.with.overflow.i64(i64 %a, i64 %b) 7820 7821 Overview: 7822 """"""""" 7823 7824 The '``llvm.ssub.with.overflow``' family of intrinsic functions perform 7825 a signed subtraction of the two arguments, and indicate whether an 7826 overflow occurred during the signed subtraction. 7827 7828 Arguments: 7829 """""""""" 7830 7831 The arguments (%a and %b) and the first element of the result structure 7832 may be of integer types of any bit width, but they must have the same 7833 bit width. The second element of the result structure must be of type 7834 ``i1``. ``%a`` and ``%b`` are the two values that will undergo signed 7835 subtraction. 7836 7837 Semantics: 7838 """""""""" 7839 7840 The '``llvm.ssub.with.overflow``' family of intrinsic functions perform 7841 a signed subtraction of the two arguments. They return a structure --- the 7842 first element of which is the subtraction, and the second element of 7843 which is a bit specifying if the signed subtraction resulted in an 7844 overflow. 7845 7846 Examples: 7847 """"""""" 7848 7849 .. code-block:: llvm 7850 7851 %res = call {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b) 7852 %sum = extractvalue {i32, i1} %res, 0 7853 %obit = extractvalue {i32, i1} %res, 1 7854 br i1 %obit, label %overflow, label %normal 7855 7856 '``llvm.usub.with.overflow.*``' Intrinsics 7857 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7858 7859 Syntax: 7860 """"""" 7861 7862 This is an overloaded intrinsic. You can use ``llvm.usub.with.overflow`` 7863 on any integer bit width. 7864 7865 :: 7866 7867 declare {i16, i1} @llvm.usub.with.overflow.i16(i16 %a, i16 %b) 7868 declare {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b) 7869 declare {i64, i1} @llvm.usub.with.overflow.i64(i64 %a, i64 %b) 7870 7871 Overview: 7872 """"""""" 7873 7874 The '``llvm.usub.with.overflow``' family of intrinsic functions perform 7875 an unsigned subtraction of the two arguments, and indicate whether an 7876 overflow occurred during the unsigned subtraction. 7877 7878 Arguments: 7879 """""""""" 7880 7881 The arguments (%a and %b) and the first element of the result structure 7882 may be of integer types of any bit width, but they must have the same 7883 bit width. The second element of the result structure must be of type 7884 ``i1``. ``%a`` and ``%b`` are the two values that will undergo unsigned 7885 subtraction. 7886 7887 Semantics: 7888 """""""""" 7889 7890 The '``llvm.usub.with.overflow``' family of intrinsic functions perform 7891 an unsigned subtraction of the two arguments. They return a structure --- 7892 the first element of which is the subtraction, and the second element of 7893 which is a bit specifying if the unsigned subtraction resulted in an 7894 overflow. 7895 7896 Examples: 7897 """"""""" 7898 7899 .. code-block:: llvm 7900 7901 %res = call {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b) 7902 %sum = extractvalue {i32, i1} %res, 0 7903 %obit = extractvalue {i32, i1} %res, 1 7904 br i1 %obit, label %overflow, label %normal 7905 7906 '``llvm.smul.with.overflow.*``' Intrinsics 7907 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7908 7909 Syntax: 7910 """"""" 7911 7912 This is an overloaded intrinsic. You can use ``llvm.smul.with.overflow`` 7913 on any integer bit width. 7914 7915 :: 7916 7917 declare {i16, i1} @llvm.smul.with.overflow.i16(i16 %a, i16 %b) 7918 declare {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b) 7919 declare {i64, i1} @llvm.smul.with.overflow.i64(i64 %a, i64 %b) 7920 7921 Overview: 7922 """"""""" 7923 7924 The '``llvm.smul.with.overflow``' family of intrinsic functions perform 7925 a signed multiplication of the two arguments, and indicate whether an 7926 overflow occurred during the signed multiplication. 7927 7928 Arguments: 7929 """""""""" 7930 7931 The arguments (%a and %b) and the first element of the result structure 7932 may be of integer types of any bit width, but they must have the same 7933 bit width. The second element of the result structure must be of type 7934 ``i1``. ``%a`` and ``%b`` are the two values that will undergo signed 7935 multiplication. 7936 7937 Semantics: 7938 """""""""" 7939 7940 The '``llvm.smul.with.overflow``' family of intrinsic functions perform 7941 a signed multiplication of the two arguments. They return a structure --- 7942 the first element of which is the multiplication, and the second element 7943 of which is a bit specifying if the signed multiplication resulted in an 7944 overflow. 7945 7946 Examples: 7947 """"""""" 7948 7949 .. code-block:: llvm 7950 7951 %res = call {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b) 7952 %sum = extractvalue {i32, i1} %res, 0 7953 %obit = extractvalue {i32, i1} %res, 1 7954 br i1 %obit, label %overflow, label %normal 7955 7956 '``llvm.umul.with.overflow.*``' Intrinsics 7957 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 7958 7959 Syntax: 7960 """"""" 7961 7962 This is an overloaded intrinsic. You can use ``llvm.umul.with.overflow`` 7963 on any integer bit width. 7964 7965 :: 7966 7967 declare {i16, i1} @llvm.umul.with.overflow.i16(i16 %a, i16 %b) 7968 declare {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b) 7969 declare {i64, i1} @llvm.umul.with.overflow.i64(i64 %a, i64 %b) 7970 7971 Overview: 7972 """"""""" 7973 7974 The '``llvm.umul.with.overflow``' family of intrinsic functions perform 7975 a unsigned multiplication of the two arguments, and indicate whether an 7976 overflow occurred during the unsigned multiplication. 7977 7978 Arguments: 7979 """""""""" 7980 7981 The arguments (%a and %b) and the first element of the result structure 7982 may be of integer types of any bit width, but they must have the same 7983 bit width. The second element of the result structure must be of type 7984 ``i1``. ``%a`` and ``%b`` are the two values that will undergo unsigned 7985 multiplication. 7986 7987 Semantics: 7988 """""""""" 7989 7990 The '``llvm.umul.with.overflow``' family of intrinsic functions perform 7991 an unsigned multiplication of the two arguments. They return a structure --- 7992 the first element of which is the multiplication, and the second 7993 element of which is a bit specifying if the unsigned multiplication 7994 resulted in an overflow. 7995 7996 Examples: 7997 """"""""" 7998 7999 .. code-block:: llvm 8000 8001 %res = call {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b) 8002 %sum = extractvalue {i32, i1} %res, 0 8003 %obit = extractvalue {i32, i1} %res, 1 8004 br i1 %obit, label %overflow, label %normal 8005 8006 Specialised Arithmetic Intrinsics 8007 --------------------------------- 8008 8009 '``llvm.fmuladd.*``' Intrinsic 8010 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 8011 8012 Syntax: 8013 """"""" 8014 8015 :: 8016 8017 declare float @llvm.fmuladd.f32(float %a, float %b, float %c) 8018 declare double @llvm.fmuladd.f64(double %a, double %b, double %c) 8019 8020 Overview: 8021 """"""""" 8022 8023 The '``llvm.fmuladd.*``' intrinsic functions represent multiply-add 8024 expressions that can be fused if the code generator determines that (a) the 8025 target instruction set has support for a fused operation, and (b) that the 8026 fused operation is more efficient than the equivalent, separate pair of mul 8027 and add instructions. 8028 8029 Arguments: 8030 """""""""" 8031 8032 The '``llvm.fmuladd.*``' intrinsics each take three arguments: two 8033 multiplicands, a and b, and an addend c. 8034 8035 Semantics: 8036 """""""""" 8037 8038 The expression: 8039 8040 :: 8041 8042 %0 = call float @llvm.fmuladd.f32(%a, %b, %c) 8043 8044 is equivalent to the expression a \* b + c, except that rounding will 8045 not be performed between the multiplication and addition steps if the 8046 code generator fuses the operations. Fusion is not guaranteed, even if 8047 the target platform supports it. If a fused multiply-add is required the 8048 corresponding llvm.fma.\* intrinsic function should be used instead. 8049 8050 Examples: 8051 """"""""" 8052 8053 .. code-block:: llvm 8054 8055 %r2 = call float @llvm.fmuladd.f32(float %a, float %b, float %c) ; yields {float}:r2 = (a * b) + c 8056 8057 Half Precision Floating Point Intrinsics 8058 ---------------------------------------- 8059 8060 For most target platforms, half precision floating point is a 8061 storage-only format. This means that it is a dense encoding (in memory) 8062 but does not support computation in the format. 8063 8064 This means that code must first load the half-precision floating point 8065 value as an i16, then convert it to float with 8066 :ref:`llvm.convert.from.fp16 <int_convert_from_fp16>`. Computation can 8067 then be performed on the float value (including extending to double 8068 etc). To store the value back to memory, it is first converted to float 8069 if needed, then converted to i16 with 8070 :ref:`llvm.convert.to.fp16 <int_convert_to_fp16>`, then storing as an 8071 i16 value. 8072 8073 .. _int_convert_to_fp16: 8074 8075 '``llvm.convert.to.fp16``' Intrinsic 8076 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 8077 8078 Syntax: 8079 """"""" 8080 8081 :: 8082 8083 declare i16 @llvm.convert.to.fp16(f32 %a) 8084 8085 Overview: 8086 """"""""" 8087 8088 The '``llvm.convert.to.fp16``' intrinsic function performs a conversion 8089 from single precision floating point format to half precision floating 8090 point format. 8091 8092 Arguments: 8093 """""""""" 8094 8095 The intrinsic function contains single argument - the value to be 8096 converted. 8097 8098 Semantics: 8099 """""""""" 8100 8101 The '``llvm.convert.to.fp16``' intrinsic function performs a conversion 8102 from single precision floating point format to half precision floating 8103 point format. The return value is an ``i16`` which contains the 8104 converted number. 8105 8106 Examples: 8107 """"""""" 8108 8109 .. code-block:: llvm 8110 8111 %res = call i16 @llvm.convert.to.fp16(f32 %a) 8112 store i16 %res, i16* @x, align 2 8113 8114 .. _int_convert_from_fp16: 8115 8116 '``llvm.convert.from.fp16``' Intrinsic 8117 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 8118 8119 Syntax: 8120 """"""" 8121 8122 :: 8123 8124 declare f32 @llvm.convert.from.fp16(i16 %a) 8125 8126 Overview: 8127 """"""""" 8128 8129 The '``llvm.convert.from.fp16``' intrinsic function performs a 8130 conversion from half precision floating point format to single precision 8131 floating point format. 8132 8133 Arguments: 8134 """""""""" 8135 8136 The intrinsic function contains single argument - the value to be 8137 converted. 8138 8139 Semantics: 8140 """""""""" 8141 8142 The '``llvm.convert.from.fp16``' intrinsic function performs a 8143 conversion from half single precision floating point format to single 8144 precision floating point format. The input half-float value is 8145 represented by an ``i16`` value. 8146 8147 Examples: 8148 """"""""" 8149 8150 .. code-block:: llvm 8151 8152 %a = load i16* @x, align 2 8153 %res = call f32 @llvm.convert.from.fp16(i16 %a) 8154 8155 Debugger Intrinsics 8156 ------------------- 8157 8158 The LLVM debugger intrinsics (which all start with ``llvm.dbg.`` 8159 prefix), are described in the `LLVM Source Level 8160 Debugging <SourceLevelDebugging.html#format_common_intrinsics>`_ 8161 document. 8162 8163 Exception Handling Intrinsics 8164 ----------------------------- 8165 8166 The LLVM exception handling intrinsics (which all start with 8167 ``llvm.eh.`` prefix), are described in the `LLVM Exception 8168 Handling <ExceptionHandling.html#format_common_intrinsics>`_ document. 8169 8170 .. _int_trampoline: 8171 8172 Trampoline Intrinsics 8173 --------------------- 8174 8175 These intrinsics make it possible to excise one parameter, marked with 8176 the :ref:`nest <nest>` attribute, from a function. The result is a 8177 callable function pointer lacking the nest parameter - the caller does 8178 not need to provide a value for it. Instead, the value to use is stored 8179 in advance in a "trampoline", a block of memory usually allocated on the 8180 stack, which also contains code to splice the nest value into the 8181 argument list. This is used to implement the GCC nested function address 8182 extension. 8183 8184 For example, if the function is ``i32 f(i8* nest %c, i32 %x, i32 %y)`` 8185 then the resulting function pointer has signature ``i32 (i32, i32)*``. 8186 It can be created as follows: 8187 8188 .. code-block:: llvm 8189 8190 %tramp = alloca [10 x i8], align 4 ; size and alignment only correct for X86 8191 %tramp1 = getelementptr [10 x i8]* %tramp, i32 0, i32 0 8192 call i8* @llvm.init.trampoline(i8* %tramp1, i8* bitcast (i32 (i8*, i32, i32)* @f to i8*), i8* %nval) 8193 %p = call i8* @llvm.adjust.trampoline(i8* %tramp1) 8194 %fp = bitcast i8* %p to i32 (i32, i32)* 8195 8196 The call ``%val = call i32 %fp(i32 %x, i32 %y)`` is then equivalent to 8197 ``%val = call i32 %f(i8* %nval, i32 %x, i32 %y)``. 8198 8199 .. _int_it: 8200 8201 '``llvm.init.trampoline``' Intrinsic 8202 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 8203 8204 Syntax: 8205 """"""" 8206 8207 :: 8208 8209 declare void @llvm.init.trampoline(i8* <tramp>, i8* <func>, i8* <nval>) 8210 8211 Overview: 8212 """"""""" 8213 8214 This fills the memory pointed to by ``tramp`` with executable code, 8215 turning it into a trampoline. 8216 8217 Arguments: 8218 """""""""" 8219 8220 The ``llvm.init.trampoline`` intrinsic takes three arguments, all 8221 pointers. The ``tramp`` argument must point to a sufficiently large and 8222 sufficiently aligned block of memory; this memory is written to by the 8223 intrinsic. Note that the size and the alignment are target-specific - 8224 LLVM currently provides no portable way of determining them, so a 8225 front-end that generates this intrinsic needs to have some 8226 target-specific knowledge. The ``func`` argument must hold a function 8227 bitcast to an ``i8*``. 8228 8229 Semantics: 8230 """""""""" 8231 8232 The block of memory pointed to by ``tramp`` is filled with target 8233 dependent code, turning it into a function. Then ``tramp`` needs to be 8234 passed to :ref:`llvm.adjust.trampoline <int_at>` to get a pointer which can 8235 be :ref:`bitcast (to a new function) and called <int_trampoline>`. The new 8236 function's signature is the same as that of ``func`` with any arguments 8237 marked with the ``nest`` attribute removed. At most one such ``nest`` 8238 argument is allowed, and it must be of pointer type. Calling the new 8239 function is equivalent to calling ``func`` with the same argument list, 8240 but with ``nval`` used for the missing ``nest`` argument. If, after 8241 calling ``llvm.init.trampoline``, the memory pointed to by ``tramp`` is 8242 modified, then the effect of any later call to the returned function 8243 pointer is undefined. 8244 8245 .. _int_at: 8246 8247 '``llvm.adjust.trampoline``' Intrinsic 8248 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 8249 8250 Syntax: 8251 """"""" 8252 8253 :: 8254 8255 declare i8* @llvm.adjust.trampoline(i8* <tramp>) 8256 8257 Overview: 8258 """"""""" 8259 8260 This performs any required machine-specific adjustment to the address of 8261 a trampoline (passed as ``tramp``). 8262 8263 Arguments: 8264 """""""""" 8265 8266 ``tramp`` must point to a block of memory which already has trampoline 8267 code filled in by a previous call to 8268 :ref:`llvm.init.trampoline <int_it>`. 8269 8270 Semantics: 8271 """""""""" 8272 8273 On some architectures the address of the code to be executed needs to be 8274 different to the address where the trampoline is actually stored. This 8275 intrinsic returns the executable address corresponding to ``tramp`` 8276 after performing the required machine specific adjustments. The pointer 8277 returned can then be :ref:`bitcast and executed <int_trampoline>`. 8278 8279 Memory Use Markers 8280 ------------------ 8281 8282 This class of intrinsics exists to information about the lifetime of 8283 memory objects and ranges where variables are immutable. 8284 8285 '``llvm.lifetime.start``' Intrinsic 8286 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 8287 8288 Syntax: 8289 """"""" 8290 8291 :: 8292 8293 declare void @llvm.lifetime.start(i64 <size>, i8* nocapture <ptr>) 8294 8295 Overview: 8296 """"""""" 8297 8298 The '``llvm.lifetime.start``' intrinsic specifies the start of a memory 8299 object's lifetime. 8300 8301 Arguments: 8302 """""""""" 8303 8304 The first argument is a constant integer representing the size of the 8305 object, or -1 if it is variable sized. The second argument is a pointer 8306 to the object. 8307 8308 Semantics: 8309 """""""""" 8310 8311 This intrinsic indicates that before this point in the code, the value 8312 of the memory pointed to by ``ptr`` is dead. This means that it is known 8313 to never be used and has an undefined value. A load from the pointer 8314 that precedes this intrinsic can be replaced with ``'undef'``. 8315 8316 '``llvm.lifetime.end``' Intrinsic 8317 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 8318 8319 Syntax: 8320 """"""" 8321 8322 :: 8323 8324 declare void @llvm.lifetime.end(i64 <size>, i8* nocapture <ptr>) 8325 8326 Overview: 8327 """"""""" 8328 8329 The '``llvm.lifetime.end``' intrinsic specifies the end of a memory 8330 object's lifetime. 8331 8332 Arguments: 8333 """""""""" 8334 8335 The first argument is a constant integer representing the size of the 8336 object, or -1 if it is variable sized. The second argument is a pointer 8337 to the object. 8338 8339 Semantics: 8340 """""""""" 8341 8342 This intrinsic indicates that after this point in the code, the value of 8343 the memory pointed to by ``ptr`` is dead. This means that it is known to 8344 never be used and has an undefined value. Any stores into the memory 8345 object following this intrinsic may be removed as dead. 8346 8347 '``llvm.invariant.start``' Intrinsic 8348 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 8349 8350 Syntax: 8351 """"""" 8352 8353 :: 8354 8355 declare {}* @llvm.invariant.start(i64 <size>, i8* nocapture <ptr>) 8356 8357 Overview: 8358 """"""""" 8359 8360 The '``llvm.invariant.start``' intrinsic specifies that the contents of 8361 a memory object will not change. 8362 8363 Arguments: 8364 """""""""" 8365 8366 The first argument is a constant integer representing the size of the 8367 object, or -1 if it is variable sized. The second argument is a pointer 8368 to the object. 8369 8370 Semantics: 8371 """""""""" 8372 8373 This intrinsic indicates that until an ``llvm.invariant.end`` that uses 8374 the return value, the referenced memory location is constant and 8375 unchanging. 8376 8377 '``llvm.invariant.end``' Intrinsic 8378 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 8379 8380 Syntax: 8381 """"""" 8382 8383 :: 8384 8385 declare void @llvm.invariant.end({}* <start>, i64 <size>, i8* nocapture <ptr>) 8386 8387 Overview: 8388 """"""""" 8389 8390 The '``llvm.invariant.end``' intrinsic specifies that the contents of a 8391 memory object are mutable. 8392 8393 Arguments: 8394 """""""""" 8395 8396 The first argument is the matching ``llvm.invariant.start`` intrinsic. 8397 The second argument is a constant integer representing the size of the 8398 object, or -1 if it is variable sized and the third argument is a 8399 pointer to the object. 8400 8401 Semantics: 8402 """""""""" 8403 8404 This intrinsic indicates that the memory is mutable again. 8405 8406 General Intrinsics 8407 ------------------ 8408 8409 This class of intrinsics is designed to be generic and has no specific 8410 purpose. 8411 8412 '``llvm.var.annotation``' Intrinsic 8413 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 8414 8415 Syntax: 8416 """"""" 8417 8418 :: 8419 8420 declare void @llvm.var.annotation(i8* <val>, i8* <str>, i8* <str>, i32 <int>) 8421 8422 Overview: 8423 """"""""" 8424 8425 The '``llvm.var.annotation``' intrinsic. 8426 8427 Arguments: 8428 """""""""" 8429 8430 The first argument is a pointer to a value, the second is a pointer to a 8431 global string, the third is a pointer to a global string which is the 8432 source file name, and the last argument is the line number. 8433 8434 Semantics: 8435 """""""""" 8436 8437 This intrinsic allows annotation of local variables with arbitrary 8438 strings. This can be useful for special purpose optimizations that want 8439 to look for these annotations. These have no other defined use; they are 8440 ignored by code generation and optimization. 8441 8442 '``llvm.ptr.annotation.*``' Intrinsic 8443 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 8444 8445 Syntax: 8446 """"""" 8447 8448 This is an overloaded intrinsic. You can use '``llvm.ptr.annotation``' on a 8449 pointer to an integer of any width. *NOTE* you must specify an address space for 8450 the pointer. The identifier for the default address space is the integer 8451 '``0``'. 8452 8453 :: 8454 8455 declare i8* @llvm.ptr.annotation.p<address space>i8(i8* <val>, i8* <str>, i8* <str>, i32 <int>) 8456 declare i16* @llvm.ptr.annotation.p<address space>i16(i16* <val>, i8* <str>, i8* <str>, i32 <int>) 8457 declare i32* @llvm.ptr.annotation.p<address space>i32(i32* <val>, i8* <str>, i8* <str>, i32 <int>) 8458 declare i64* @llvm.ptr.annotation.p<address space>i64(i64* <val>, i8* <str>, i8* <str>, i32 <int>) 8459 declare i256* @llvm.ptr.annotation.p<address space>i256(i256* <val>, i8* <str>, i8* <str>, i32 <int>) 8460 8461 Overview: 8462 """"""""" 8463 8464 The '``llvm.ptr.annotation``' intrinsic. 8465 8466 Arguments: 8467 """""""""" 8468 8469 The first argument is a pointer to an integer value of arbitrary bitwidth 8470 (result of some expression), the second is a pointer to a global string, the 8471 third is a pointer to a global string which is the source file name, and the 8472 last argument is the line number. It returns the value of the first argument. 8473 8474 Semantics: 8475 """""""""" 8476 8477 This intrinsic allows annotation of a pointer to an integer with arbitrary 8478 strings. This can be useful for special purpose optimizations that want to look 8479 for these annotations. These have no other defined use; they are ignored by code 8480 generation and optimization. 8481 8482 '``llvm.annotation.*``' Intrinsic 8483 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 8484 8485 Syntax: 8486 """"""" 8487 8488 This is an overloaded intrinsic. You can use '``llvm.annotation``' on 8489 any integer bit width. 8490 8491 :: 8492 8493 declare i8 @llvm.annotation.i8(i8 <val>, i8* <str>, i8* <str>, i32 <int>) 8494 declare i16 @llvm.annotation.i16(i16 <val>, i8* <str>, i8* <str>, i32 <int>) 8495 declare i32 @llvm.annotation.i32(i32 <val>, i8* <str>, i8* <str>, i32 <int>) 8496 declare i64 @llvm.annotation.i64(i64 <val>, i8* <str>, i8* <str>, i32 <int>) 8497 declare i256 @llvm.annotation.i256(i256 <val>, i8* <str>, i8* <str>, i32 <int>) 8498 8499 Overview: 8500 """"""""" 8501 8502 The '``llvm.annotation``' intrinsic. 8503 8504 Arguments: 8505 """""""""" 8506 8507 The first argument is an integer value (result of some expression), the 8508 second is a pointer to a global string, the third is a pointer to a 8509 global string which is the source file name, and the last argument is 8510 the line number. It returns the value of the first argument. 8511 8512 Semantics: 8513 """""""""" 8514 8515 This intrinsic allows annotations to be put on arbitrary expressions 8516 with arbitrary strings. This can be useful for special purpose 8517 optimizations that want to look for these annotations. These have no 8518 other defined use; they are ignored by code generation and optimization. 8519 8520 '``llvm.trap``' Intrinsic 8521 ^^^^^^^^^^^^^^^^^^^^^^^^^ 8522 8523 Syntax: 8524 """"""" 8525 8526 :: 8527 8528 declare void @llvm.trap() noreturn nounwind 8529 8530 Overview: 8531 """"""""" 8532 8533 The '``llvm.trap``' intrinsic. 8534 8535 Arguments: 8536 """""""""" 8537 8538 None. 8539 8540 Semantics: 8541 """""""""" 8542 8543 This intrinsic is lowered to the target dependent trap instruction. If 8544 the target does not have a trap instruction, this intrinsic will be 8545 lowered to a call of the ``abort()`` function. 8546 8547 '``llvm.debugtrap``' Intrinsic 8548 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 8549 8550 Syntax: 8551 """"""" 8552 8553 :: 8554 8555 declare void @llvm.debugtrap() nounwind 8556 8557 Overview: 8558 """"""""" 8559 8560 The '``llvm.debugtrap``' intrinsic. 8561 8562 Arguments: 8563 """""""""" 8564 8565 None. 8566 8567 Semantics: 8568 """""""""" 8569 8570 This intrinsic is lowered to code which is intended to cause an 8571 execution trap with the intention of requesting the attention of a 8572 debugger. 8573 8574 '``llvm.stackprotector``' Intrinsic 8575 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 8576 8577 Syntax: 8578 """"""" 8579 8580 :: 8581 8582 declare void @llvm.stackprotector(i8* <guard>, i8** <slot>) 8583 8584 Overview: 8585 """"""""" 8586 8587 The ``llvm.stackprotector`` intrinsic takes the ``guard`` and stores it 8588 onto the stack at ``slot``. The stack slot is adjusted to ensure that it 8589 is placed on the stack before local variables. 8590 8591 Arguments: 8592 """""""""" 8593 8594 The ``llvm.stackprotector`` intrinsic requires two pointer arguments. 8595 The first argument is the value loaded from the stack guard 8596 ``@__stack_chk_guard``. The second variable is an ``alloca`` that has 8597 enough space to hold the value of the guard. 8598 8599 Semantics: 8600 """""""""" 8601 8602 This intrinsic causes the prologue/epilogue inserter to force the 8603 position of the ``AllocaInst`` stack slot to be before local variables 8604 on the stack. This is to ensure that if a local variable on the stack is 8605 overwritten, it will destroy the value of the guard. When the function 8606 exits, the guard on the stack is checked against the original guard. If 8607 they are different, then the program aborts by calling the 8608 ``__stack_chk_fail()`` function. 8609 8610 '``llvm.objectsize``' Intrinsic 8611 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 8612 8613 Syntax: 8614 """"""" 8615 8616 :: 8617 8618 declare i32 @llvm.objectsize.i32(i8* <object>, i1 <min>) 8619 declare i64 @llvm.objectsize.i64(i8* <object>, i1 <min>) 8620 8621 Overview: 8622 """"""""" 8623 8624 The ``llvm.objectsize`` intrinsic is designed to provide information to 8625 the optimizers to determine at compile time whether a) an operation 8626 (like memcpy) will overflow a buffer that corresponds to an object, or 8627 b) that a runtime check for overflow isn't necessary. An object in this 8628 context means an allocation of a specific class, structure, array, or 8629 other object. 8630 8631 Arguments: 8632 """""""""" 8633 8634 The ``llvm.objectsize`` intrinsic takes two arguments. The first 8635 argument is a pointer to or into the ``object``. The second argument is 8636 a boolean and determines whether ``llvm.objectsize`` returns 0 (if true) 8637 or -1 (if false) when the object size is unknown. The second argument 8638 only accepts constants. 8639 8640 Semantics: 8641 """""""""" 8642 8643 The ``llvm.objectsize`` intrinsic is lowered to a constant representing 8644 the size of the object concerned. If the size cannot be determined at 8645 compile time, ``llvm.objectsize`` returns ``i32/i64 -1 or 0`` (depending 8646 on the ``min`` argument). 8647 8648 '``llvm.expect``' Intrinsic 8649 ^^^^^^^^^^^^^^^^^^^^^^^^^^^ 8650 8651 Syntax: 8652 """"""" 8653 8654 :: 8655 8656 declare i32 @llvm.expect.i32(i32 <val>, i32 <expected_val>) 8657 declare i64 @llvm.expect.i64(i64 <val>, i64 <expected_val>) 8658 8659 Overview: 8660 """"""""" 8661 8662 The ``llvm.expect`` intrinsic provides information about expected (the 8663 most probable) value of ``val``, which can be used by optimizers. 8664 8665 Arguments: 8666 """""""""" 8667 8668 The ``llvm.expect`` intrinsic takes two arguments. The first argument is 8669 a value. The second argument is an expected value, this needs to be a 8670 constant value, variables are not allowed. 8671 8672 Semantics: 8673 """""""""" 8674 8675 This intrinsic is lowered to the ``val``. 8676 8677 '``llvm.donothing``' Intrinsic 8678 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 8679 8680 Syntax: 8681 """"""" 8682 8683 :: 8684 8685 declare void @llvm.donothing() nounwind readnone 8686 8687 Overview: 8688 """"""""" 8689 8690 The ``llvm.donothing`` intrinsic doesn't perform any operation. It's the 8691 only intrinsic that can be called with an invoke instruction. 8692 8693 Arguments: 8694 """""""""" 8695 8696 None. 8697 8698 Semantics: 8699 """""""""" 8700 8701 This intrinsic does nothing, and it's removed by optimizers and ignored 8702 by codegen. 8703
