1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" 2 "http://www.w3.org/TR/html4/strict.dtd"> 3 <html> 4 <head> 5 <title>LLVM Assembly Language Reference Manual</title> 6 <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> 7 <meta name="author" content="Chris Lattner"> 8 <meta name="description" 9 content="LLVM Assembly Language Reference Manual."> 10 <link rel="stylesheet" href="llvm.css" type="text/css"> 11 </head> 12 13 <body> 14 15 <h1>LLVM Language Reference Manual</h1> 16 <ol> 17 <li><a href="#abstract">Abstract</a></li> 18 <li><a href="#introduction">Introduction</a></li> 19 <li><a href="#identifiers">Identifiers</a></li> 20 <li><a href="#highlevel">High Level Structure</a> 21 <ol> 22 <li><a href="#modulestructure">Module Structure</a></li> 23 <li><a href="#linkage">Linkage Types</a> 24 <ol> 25 <li><a href="#linkage_private">'<tt>private</tt>' Linkage</a></li> 26 <li><a href="#linkage_linker_private">'<tt>linker_private</tt>' Linkage</a></li> 27 <li><a href="#linkage_linker_private_weak">'<tt>linker_private_weak</tt>' Linkage</a></li> 28 <li><a href="#linkage_linker_private_weak_def_auto">'<tt>linker_private_weak_def_auto</tt>' Linkage</a></li> 29 <li><a href="#linkage_internal">'<tt>internal</tt>' Linkage</a></li> 30 <li><a href="#linkage_available_externally">'<tt>available_externally</tt>' Linkage</a></li> 31 <li><a href="#linkage_linkonce">'<tt>linkonce</tt>' Linkage</a></li> 32 <li><a href="#linkage_common">'<tt>common</tt>' Linkage</a></li> 33 <li><a href="#linkage_weak">'<tt>weak</tt>' Linkage</a></li> 34 <li><a href="#linkage_appending">'<tt>appending</tt>' Linkage</a></li> 35 <li><a href="#linkage_externweak">'<tt>extern_weak</tt>' Linkage</a></li> 36 <li><a href="#linkage_linkonce_odr">'<tt>linkonce_odr</tt>' Linkage</a></li> 37 <li><a href="#linkage_weak">'<tt>weak_odr</tt>' Linkage</a></li> 38 <li><a href="#linkage_external">'<tt>external</tt>' Linkage</a></li> 39 <li><a href="#linkage_dllimport">'<tt>dllimport</tt>' Linkage</a></li> 40 <li><a href="#linkage_dllexport">'<tt>dllexport</tt>' Linkage</a></li> 41 </ol> 42 </li> 43 <li><a href="#callingconv">Calling Conventions</a></li> 44 <li><a href="#namedtypes">Named Types</a></li> 45 <li><a href="#globalvars">Global Variables</a></li> 46 <li><a href="#functionstructure">Functions</a></li> 47 <li><a href="#aliasstructure">Aliases</a></li> 48 <li><a href="#namedmetadatastructure">Named Metadata</a></li> 49 <li><a href="#paramattrs">Parameter Attributes</a></li> 50 <li><a href="#fnattrs">Function Attributes</a></li> 51 <li><a href="#gc">Garbage Collector Names</a></li> 52 <li><a href="#moduleasm">Module-Level Inline Assembly</a></li> 53 <li><a href="#datalayout">Data Layout</a></li> 54 <li><a href="#pointeraliasing">Pointer Aliasing Rules</a></li> 55 <li><a href="#volatile">Volatile Memory Accesses</a></li> 56 <li><a href="#memmodel">Memory Model for Concurrent Operations</a></li> 57 <li><a href="#ordering">Atomic Memory Ordering Constraints</a></li> 58 </ol> 59 </li> 60 <li><a href="#typesystem">Type System</a> 61 <ol> 62 <li><a href="#t_classifications">Type Classifications</a></li> 63 <li><a href="#t_primitive">Primitive Types</a> 64 <ol> 65 <li><a href="#t_integer">Integer Type</a></li> 66 <li><a href="#t_floating">Floating Point Types</a></li> 67 <li><a href="#t_x86mmx">X86mmx Type</a></li> 68 <li><a href="#t_void">Void Type</a></li> 69 <li><a href="#t_label">Label Type</a></li> 70 <li><a href="#t_metadata">Metadata Type</a></li> 71 </ol> 72 </li> 73 <li><a href="#t_derived">Derived Types</a> 74 <ol> 75 <li><a href="#t_aggregate">Aggregate Types</a> 76 <ol> 77 <li><a href="#t_array">Array Type</a></li> 78 <li><a href="#t_struct">Structure Type</a></li> 79 <li><a href="#t_opaque">Opaque Structure Types</a></li> 80 <li><a href="#t_vector">Vector Type</a></li> 81 </ol> 82 </li> 83 <li><a href="#t_function">Function Type</a></li> 84 <li><a href="#t_pointer">Pointer Type</a></li> 85 </ol> 86 </li> 87 </ol> 88 </li> 89 <li><a href="#constants">Constants</a> 90 <ol> 91 <li><a href="#simpleconstants">Simple Constants</a></li> 92 <li><a href="#complexconstants">Complex Constants</a></li> 93 <li><a href="#globalconstants">Global Variable and Function Addresses</a></li> 94 <li><a href="#undefvalues">Undefined Values</a></li> 95 <li><a href="#trapvalues">Trap Values</a></li> 96 <li><a href="#blockaddress">Addresses of Basic Blocks</a></li> 97 <li><a href="#constantexprs">Constant Expressions</a></li> 98 </ol> 99 </li> 100 <li><a href="#othervalues">Other Values</a> 101 <ol> 102 <li><a href="#inlineasm">Inline Assembler Expressions</a></li> 103 <li><a href="#metadata">Metadata Nodes and Metadata Strings</a></li> 104 </ol> 105 </li> 106 <li><a href="#intrinsic_globals">Intrinsic Global Variables</a> 107 <ol> 108 <li><a href="#intg_used">The '<tt>llvm.used</tt>' Global Variable</a></li> 109 <li><a href="#intg_compiler_used">The '<tt>llvm.compiler.used</tt>' 110 Global Variable</a></li> 111 <li><a href="#intg_global_ctors">The '<tt>llvm.global_ctors</tt>' 112 Global Variable</a></li> 113 <li><a href="#intg_global_dtors">The '<tt>llvm.global_dtors</tt>' 114 Global Variable</a></li> 115 </ol> 116 </li> 117 <li><a href="#instref">Instruction Reference</a> 118 <ol> 119 <li><a href="#terminators">Terminator Instructions</a> 120 <ol> 121 <li><a href="#i_ret">'<tt>ret</tt>' Instruction</a></li> 122 <li><a href="#i_br">'<tt>br</tt>' Instruction</a></li> 123 <li><a href="#i_switch">'<tt>switch</tt>' Instruction</a></li> 124 <li><a href="#i_indirectbr">'<tt>indirectbr</tt>' Instruction</a></li> 125 <li><a href="#i_invoke">'<tt>invoke</tt>' Instruction</a></li> 126 <li><a href="#i_unwind">'<tt>unwind</tt>' Instruction</a></li> 127 <li><a href="#i_resume">'<tt>resume</tt>' Instruction</a></li> 128 <li><a href="#i_unreachable">'<tt>unreachable</tt>' Instruction</a></li> 129 </ol> 130 </li> 131 <li><a href="#binaryops">Binary Operations</a> 132 <ol> 133 <li><a href="#i_add">'<tt>add</tt>' Instruction</a></li> 134 <li><a href="#i_fadd">'<tt>fadd</tt>' Instruction</a></li> 135 <li><a href="#i_sub">'<tt>sub</tt>' Instruction</a></li> 136 <li><a href="#i_fsub">'<tt>fsub</tt>' Instruction</a></li> 137 <li><a href="#i_mul">'<tt>mul</tt>' Instruction</a></li> 138 <li><a href="#i_fmul">'<tt>fmul</tt>' Instruction</a></li> 139 <li><a href="#i_udiv">'<tt>udiv</tt>' Instruction</a></li> 140 <li><a href="#i_sdiv">'<tt>sdiv</tt>' Instruction</a></li> 141 <li><a href="#i_fdiv">'<tt>fdiv</tt>' Instruction</a></li> 142 <li><a href="#i_urem">'<tt>urem</tt>' Instruction</a></li> 143 <li><a href="#i_srem">'<tt>srem</tt>' Instruction</a></li> 144 <li><a href="#i_frem">'<tt>frem</tt>' Instruction</a></li> 145 </ol> 146 </li> 147 <li><a href="#bitwiseops">Bitwise Binary Operations</a> 148 <ol> 149 <li><a href="#i_shl">'<tt>shl</tt>' Instruction</a></li> 150 <li><a href="#i_lshr">'<tt>lshr</tt>' Instruction</a></li> 151 <li><a href="#i_ashr">'<tt>ashr</tt>' Instruction</a></li> 152 <li><a href="#i_and">'<tt>and</tt>' Instruction</a></li> 153 <li><a href="#i_or">'<tt>or</tt>' Instruction</a></li> 154 <li><a href="#i_xor">'<tt>xor</tt>' Instruction</a></li> 155 </ol> 156 </li> 157 <li><a href="#vectorops">Vector Operations</a> 158 <ol> 159 <li><a href="#i_extractelement">'<tt>extractelement</tt>' Instruction</a></li> 160 <li><a href="#i_insertelement">'<tt>insertelement</tt>' Instruction</a></li> 161 <li><a href="#i_shufflevector">'<tt>shufflevector</tt>' Instruction</a></li> 162 </ol> 163 </li> 164 <li><a href="#aggregateops">Aggregate Operations</a> 165 <ol> 166 <li><a href="#i_extractvalue">'<tt>extractvalue</tt>' Instruction</a></li> 167 <li><a href="#i_insertvalue">'<tt>insertvalue</tt>' Instruction</a></li> 168 </ol> 169 </li> 170 <li><a href="#memoryops">Memory Access and Addressing Operations</a> 171 <ol> 172 <li><a href="#i_alloca">'<tt>alloca</tt>' Instruction</a></li> 173 <li><a href="#i_load">'<tt>load</tt>' Instruction</a></li> 174 <li><a href="#i_store">'<tt>store</tt>' Instruction</a></li> 175 <li><a href="#i_fence">'<tt>fence</tt>' Instruction</a></li> 176 <li><a href="#i_cmpxchg">'<tt>cmpxchg</tt>' Instruction</a></li> 177 <li><a href="#i_atomicrmw">'<tt>atomicrmw</tt>' Instruction</a></li> 178 <li><a href="#i_getelementptr">'<tt>getelementptr</tt>' Instruction</a></li> 179 </ol> 180 </li> 181 <li><a href="#convertops">Conversion Operations</a> 182 <ol> 183 <li><a href="#i_trunc">'<tt>trunc .. to</tt>' Instruction</a></li> 184 <li><a href="#i_zext">'<tt>zext .. to</tt>' Instruction</a></li> 185 <li><a href="#i_sext">'<tt>sext .. to</tt>' Instruction</a></li> 186 <li><a href="#i_fptrunc">'<tt>fptrunc .. to</tt>' Instruction</a></li> 187 <li><a href="#i_fpext">'<tt>fpext .. to</tt>' Instruction</a></li> 188 <li><a href="#i_fptoui">'<tt>fptoui .. to</tt>' Instruction</a></li> 189 <li><a href="#i_fptosi">'<tt>fptosi .. to</tt>' Instruction</a></li> 190 <li><a href="#i_uitofp">'<tt>uitofp .. to</tt>' Instruction</a></li> 191 <li><a href="#i_sitofp">'<tt>sitofp .. to</tt>' Instruction</a></li> 192 <li><a href="#i_ptrtoint">'<tt>ptrtoint .. to</tt>' Instruction</a></li> 193 <li><a href="#i_inttoptr">'<tt>inttoptr .. to</tt>' Instruction</a></li> 194 <li><a href="#i_bitcast">'<tt>bitcast .. to</tt>' Instruction</a></li> 195 </ol> 196 </li> 197 <li><a href="#otherops">Other Operations</a> 198 <ol> 199 <li><a href="#i_icmp">'<tt>icmp</tt>' Instruction</a></li> 200 <li><a href="#i_fcmp">'<tt>fcmp</tt>' Instruction</a></li> 201 <li><a href="#i_phi">'<tt>phi</tt>' Instruction</a></li> 202 <li><a href="#i_select">'<tt>select</tt>' Instruction</a></li> 203 <li><a href="#i_call">'<tt>call</tt>' Instruction</a></li> 204 <li><a href="#i_va_arg">'<tt>va_arg</tt>' Instruction</a></li> 205 <li><a href="#i_landingpad">'<tt>landingpad</tt>' Instruction</a></li> 206 </ol> 207 </li> 208 </ol> 209 </li> 210 <li><a href="#intrinsics">Intrinsic Functions</a> 211 <ol> 212 <li><a href="#int_varargs">Variable Argument Handling Intrinsics</a> 213 <ol> 214 <li><a href="#int_va_start">'<tt>llvm.va_start</tt>' Intrinsic</a></li> 215 <li><a href="#int_va_end">'<tt>llvm.va_end</tt>' Intrinsic</a></li> 216 <li><a href="#int_va_copy">'<tt>llvm.va_copy</tt>' Intrinsic</a></li> 217 </ol> 218 </li> 219 <li><a href="#int_gc">Accurate Garbage Collection Intrinsics</a> 220 <ol> 221 <li><a href="#int_gcroot">'<tt>llvm.gcroot</tt>' Intrinsic</a></li> 222 <li><a href="#int_gcread">'<tt>llvm.gcread</tt>' Intrinsic</a></li> 223 <li><a href="#int_gcwrite">'<tt>llvm.gcwrite</tt>' Intrinsic</a></li> 224 </ol> 225 </li> 226 <li><a href="#int_codegen">Code Generator Intrinsics</a> 227 <ol> 228 <li><a href="#int_returnaddress">'<tt>llvm.returnaddress</tt>' Intrinsic</a></li> 229 <li><a href="#int_frameaddress">'<tt>llvm.frameaddress</tt>' Intrinsic</a></li> 230 <li><a href="#int_stacksave">'<tt>llvm.stacksave</tt>' Intrinsic</a></li> 231 <li><a href="#int_stackrestore">'<tt>llvm.stackrestore</tt>' Intrinsic</a></li> 232 <li><a href="#int_prefetch">'<tt>llvm.prefetch</tt>' Intrinsic</a></li> 233 <li><a href="#int_pcmarker">'<tt>llvm.pcmarker</tt>' Intrinsic</a></li> 234 <li><a href="#int_readcyclecounter">'<tt>llvm.readcyclecounter</tt>' Intrinsic</a></li> 235 </ol> 236 </li> 237 <li><a href="#int_libc">Standard C Library Intrinsics</a> 238 <ol> 239 <li><a href="#int_memcpy">'<tt>llvm.memcpy.*</tt>' Intrinsic</a></li> 240 <li><a href="#int_memmove">'<tt>llvm.memmove.*</tt>' Intrinsic</a></li> 241 <li><a href="#int_memset">'<tt>llvm.memset.*</tt>' Intrinsic</a></li> 242 <li><a href="#int_sqrt">'<tt>llvm.sqrt.*</tt>' Intrinsic</a></li> 243 <li><a href="#int_powi">'<tt>llvm.powi.*</tt>' Intrinsic</a></li> 244 <li><a href="#int_sin">'<tt>llvm.sin.*</tt>' Intrinsic</a></li> 245 <li><a href="#int_cos">'<tt>llvm.cos.*</tt>' Intrinsic</a></li> 246 <li><a href="#int_pow">'<tt>llvm.pow.*</tt>' Intrinsic</a></li> 247 <li><a href="#int_exp">'<tt>llvm.exp.*</tt>' Intrinsic</a></li> 248 <li><a href="#int_log">'<tt>llvm.log.*</tt>' Intrinsic</a></li> 249 <li><a href="#int_fma">'<tt>llvm.fma.*</tt>' Intrinsic</a></li> 250 </ol> 251 </li> 252 <li><a href="#int_manip">Bit Manipulation Intrinsics</a> 253 <ol> 254 <li><a href="#int_bswap">'<tt>llvm.bswap.*</tt>' Intrinsics</a></li> 255 <li><a href="#int_ctpop">'<tt>llvm.ctpop.*</tt>' Intrinsic </a></li> 256 <li><a href="#int_ctlz">'<tt>llvm.ctlz.*</tt>' Intrinsic </a></li> 257 <li><a href="#int_cttz">'<tt>llvm.cttz.*</tt>' Intrinsic </a></li> 258 </ol> 259 </li> 260 <li><a href="#int_overflow">Arithmetic with Overflow Intrinsics</a> 261 <ol> 262 <li><a href="#int_sadd_overflow">'<tt>llvm.sadd.with.overflow.*</tt> Intrinsics</a></li> 263 <li><a href="#int_uadd_overflow">'<tt>llvm.uadd.with.overflow.*</tt> Intrinsics</a></li> 264 <li><a href="#int_ssub_overflow">'<tt>llvm.ssub.with.overflow.*</tt> Intrinsics</a></li> 265 <li><a href="#int_usub_overflow">'<tt>llvm.usub.with.overflow.*</tt> Intrinsics</a></li> 266 <li><a href="#int_smul_overflow">'<tt>llvm.smul.with.overflow.*</tt> Intrinsics</a></li> 267 <li><a href="#int_umul_overflow">'<tt>llvm.umul.with.overflow.*</tt> Intrinsics</a></li> 268 </ol> 269 </li> 270 <li><a href="#int_fp16">Half Precision Floating Point Intrinsics</a> 271 <ol> 272 <li><a href="#int_convert_to_fp16">'<tt>llvm.convert.to.fp16</tt>' Intrinsic</a></li> 273 <li><a href="#int_convert_from_fp16">'<tt>llvm.convert.from.fp16</tt>' Intrinsic</a></li> 274 </ol> 275 </li> 276 <li><a href="#int_debugger">Debugger intrinsics</a></li> 277 <li><a href="#int_eh">Exception Handling intrinsics</a></li> 278 <li><a href="#int_trampoline">Trampoline Intrinsics</a> 279 <ol> 280 <li><a href="#int_it">'<tt>llvm.init.trampoline</tt>' Intrinsic</a></li> 281 <li><a href="#int_at">'<tt>llvm.adjust.trampoline</tt>' Intrinsic</a></li> 282 </ol> 283 </li> 284 <li><a href="#int_memorymarkers">Memory Use Markers</a> 285 <ol> 286 <li><a href="#int_lifetime_start"><tt>llvm.lifetime.start</tt></a></li> 287 <li><a href="#int_lifetime_end"><tt>llvm.lifetime.end</tt></a></li> 288 <li><a href="#int_invariant_start"><tt>llvm.invariant.start</tt></a></li> 289 <li><a href="#int_invariant_end"><tt>llvm.invariant.end</tt></a></li> 290 </ol> 291 </li> 292 <li><a href="#int_general">General intrinsics</a> 293 <ol> 294 <li><a href="#int_var_annotation"> 295 '<tt>llvm.var.annotation</tt>' Intrinsic</a></li> 296 <li><a href="#int_annotation"> 297 '<tt>llvm.annotation.*</tt>' Intrinsic</a></li> 298 <li><a href="#int_trap"> 299 '<tt>llvm.trap</tt>' Intrinsic</a></li> 300 <li><a href="#int_stackprotector"> 301 '<tt>llvm.stackprotector</tt>' Intrinsic</a></li> 302 <li><a href="#int_objectsize"> 303 '<tt>llvm.objectsize</tt>' Intrinsic</a></li> 304 </ol> 305 </li> 306 </ol> 307 </li> 308 </ol> 309 310 <div class="doc_author"> 311 <p>Written by <a href="mailto:sabre (a] nondot.org">Chris Lattner</a> 312 and <a href="mailto:vadve (a] cs.uiuc.edu">Vikram Adve</a></p> 313 </div> 314 315 <!-- *********************************************************************** --> 316 <h2><a name="abstract">Abstract</a></h2> 317 <!-- *********************************************************************** --> 318 319 <div> 320 321 <p>This document is a reference manual for the LLVM assembly language. LLVM is 322 a Static Single Assignment (SSA) based representation that provides type 323 safety, low-level operations, flexibility, and the capability of representing 324 'all' high-level languages cleanly. It is the common code representation 325 used throughout all phases of the LLVM compilation strategy.</p> 326 327 </div> 328 329 <!-- *********************************************************************** --> 330 <h2><a name="introduction">Introduction</a></h2> 331 <!-- *********************************************************************** --> 332 333 <div> 334 335 <p>The LLVM code representation is designed to be used in three different forms: 336 as an in-memory compiler IR, as an on-disk bitcode representation (suitable 337 for fast loading by a Just-In-Time compiler), and as a human readable 338 assembly language representation. This allows LLVM to provide a powerful 339 intermediate representation for efficient compiler transformations and 340 analysis, while providing a natural means to debug and visualize the 341 transformations. The three different forms of LLVM are all equivalent. This 342 document describes the human readable representation and notation.</p> 343 344 <p>The LLVM representation aims to be light-weight and low-level while being 345 expressive, typed, and extensible at the same time. It aims to be a 346 "universal IR" of sorts, by being at a low enough level that high-level ideas 347 may be cleanly mapped to it (similar to how microprocessors are "universal 348 IR's", allowing many source languages to be mapped to them). By providing 349 type information, LLVM can be used as the target of optimizations: for 350 example, through pointer analysis, it can be proven that a C automatic 351 variable is never accessed outside of the current function, allowing it to 352 be promoted to a simple SSA value instead of a memory location.</p> 353 354 <!-- _______________________________________________________________________ --> 355 <h4> 356 <a name="wellformed">Well-Formedness</a> 357 </h4> 358 359 <div> 360 361 <p>It is important to note that this document describes 'well formed' LLVM 362 assembly language. There is a difference between what the parser accepts and 363 what is considered 'well formed'. For example, the following instruction is 364 syntactically okay, but not well formed:</p> 365 366 <pre class="doc_code"> 367 %x = <a href="#i_add">add</a> i32 1, %x 368 </pre> 369 370 <p>because the definition of <tt>%x</tt> does not dominate all of its uses. The 371 LLVM infrastructure provides a verification pass that may be used to verify 372 that an LLVM module is well formed. This pass is automatically run by the 373 parser after parsing input assembly and by the optimizer before it outputs 374 bitcode. The violations pointed out by the verifier pass indicate bugs in 375 transformation passes or input to the parser.</p> 376 377 </div> 378 379 </div> 380 381 <!-- Describe the typesetting conventions here. --> 382 383 <!-- *********************************************************************** --> 384 <h2><a name="identifiers">Identifiers</a></h2> 385 <!-- *********************************************************************** --> 386 387 <div> 388 389 <p>LLVM identifiers come in two basic types: global and local. Global 390 identifiers (functions, global variables) begin with the <tt>'@'</tt> 391 character. Local identifiers (register names, types) begin with 392 the <tt>'%'</tt> character. Additionally, there are three different formats 393 for identifiers, for different purposes:</p> 394 395 <ol> 396 <li>Named values are represented as a string of characters with their prefix. 397 For example, <tt>%foo</tt>, <tt>@DivisionByZero</tt>, 398 <tt>%a.really.long.identifier</tt>. The actual regular expression used is 399 '<tt>[%@][a-zA-Z$._][a-zA-Z$._0-9]*</tt>'. Identifiers which require 400 other characters in their names can be surrounded with quotes. Special 401 characters may be escaped using <tt>"\xx"</tt> where <tt>xx</tt> is the 402 ASCII code for the character in hexadecimal. In this way, any character 403 can be used in a name value, even quotes themselves.</li> 404 405 <li>Unnamed values are represented as an unsigned numeric value with their 406 prefix. For example, <tt>%12</tt>, <tt>@2</tt>, <tt>%44</tt>.</li> 407 408 <li>Constants, which are described in a <a href="#constants">section about 409 constants</a>, below.</li> 410 </ol> 411 412 <p>LLVM requires that values start with a prefix for two reasons: Compilers 413 don't need to worry about name clashes with reserved words, and the set of 414 reserved words may be expanded in the future without penalty. Additionally, 415 unnamed identifiers allow a compiler to quickly come up with a temporary 416 variable without having to avoid symbol table conflicts.</p> 417 418 <p>Reserved words in LLVM are very similar to reserved words in other 419 languages. There are keywords for different opcodes 420 ('<tt><a href="#i_add">add</a></tt>', 421 '<tt><a href="#i_bitcast">bitcast</a></tt>', 422 '<tt><a href="#i_ret">ret</a></tt>', etc...), for primitive type names 423 ('<tt><a href="#t_void">void</a></tt>', 424 '<tt><a href="#t_primitive">i32</a></tt>', etc...), and others. These 425 reserved words cannot conflict with variable names, because none of them 426 start with a prefix character (<tt>'%'</tt> or <tt>'@'</tt>).</p> 427 428 <p>Here is an example of LLVM code to multiply the integer variable 429 '<tt>%X</tt>' by 8:</p> 430 431 <p>The easy way:</p> 432 433 <pre class="doc_code"> 434 %result = <a href="#i_mul">mul</a> i32 %X, 8 435 </pre> 436 437 <p>After strength reduction:</p> 438 439 <pre class="doc_code"> 440 %result = <a href="#i_shl">shl</a> i32 %X, i8 3 441 </pre> 442 443 <p>And the hard way:</p> 444 445 <pre class="doc_code"> 446 %0 = <a href="#i_add">add</a> i32 %X, %X <i>; yields {i32}:%0</i> 447 %1 = <a href="#i_add">add</a> i32 %0, %0 <i>; yields {i32}:%1</i> 448 %result = <a href="#i_add">add</a> i32 %1, %1 449 </pre> 450 451 <p>This last way of multiplying <tt>%X</tt> by 8 illustrates several important 452 lexical features of LLVM:</p> 453 454 <ol> 455 <li>Comments are delimited with a '<tt>;</tt>' and go until the end of 456 line.</li> 457 458 <li>Unnamed temporaries are created when the result of a computation is not 459 assigned to a named value.</li> 460 461 <li>Unnamed temporaries are numbered sequentially</li> 462 </ol> 463 464 <p>It also shows a convention that we follow in this document. When 465 demonstrating instructions, we will follow an instruction with a comment that 466 defines the type and name of value produced. Comments are shown in italic 467 text.</p> 468 469 </div> 470 471 <!-- *********************************************************************** --> 472 <h2><a name="highlevel">High Level Structure</a></h2> 473 <!-- *********************************************************************** --> 474 <div> 475 <!-- ======================================================================= --> 476 <h3> 477 <a name="modulestructure">Module Structure</a> 478 </h3> 479 480 <div> 481 482 <p>LLVM programs are composed of "Module"s, each of which is a translation unit 483 of the input programs. Each module consists of functions, global variables, 484 and symbol table entries. Modules may be combined together with the LLVM 485 linker, which merges function (and global variable) definitions, resolves 486 forward declarations, and merges symbol table entries. Here is an example of 487 the "hello world" module:</p> 488 489 <pre class="doc_code"> 490 <i>; Declare the string constant as a global constant.</i> 491 <a href="#identifiers">@.LC0</a> = <a href="#linkage_internal">internal</a> <a href="#globalvars">constant</a> <a href="#t_array">[13 x i8]</a> c"hello world\0A\00" <i>; [13 x i8]*</i> 492 493 <i>; External declaration of the puts function</i> 494 <a href="#functionstructure">declare</a> i32 @puts(i8*) <i>; i32 (i8*)* </i> 495 496 <i>; Definition of main function</i> 497 define i32 @main() { <i>; i32()* </i> 498 <i>; Convert [13 x i8]* to i8 *...</i> 499 %cast210 = <a href="#i_getelementptr">getelementptr</a> [13 x i8]* @.LC0, i64 0, i64 0 <i>; i8*</i> 500 501 <i>; Call puts function to write out the string to stdout.</i> 502 <a href="#i_call">call</a> i32 @puts(i8* %cast210) <i>; i32</i> 503 <a href="#i_ret">ret</a> i32 0 504 } 505 506 <i>; Named metadata</i> 507 !1 = metadata !{i32 41} 508 !foo = !{!1, null} 509 </pre> 510 511 <p>This example is made up of a <a href="#globalvars">global variable</a> named 512 "<tt>.LC0</tt>", an external declaration of the "<tt>puts</tt>" function, 513 a <a href="#functionstructure">function definition</a> for 514 "<tt>main</tt>" and <a href="#namedmetadatastructure">named metadata</a> 515 "<tt>foo"</tt>.</p> 516 517 <p>In general, a module is made up of a list of global values, where both 518 functions and global variables are global values. Global values are 519 represented by a pointer to a memory location (in this case, a pointer to an 520 array of char, and a pointer to a function), and have one of the 521 following <a href="#linkage">linkage types</a>.</p> 522 523 </div> 524 525 <!-- ======================================================================= --> 526 <h3> 527 <a name="linkage">Linkage Types</a> 528 </h3> 529 530 <div> 531 532 <p>All Global Variables and Functions have one of the following types of 533 linkage:</p> 534 535 <dl> 536 <dt><tt><b><a name="linkage_private">private</a></b></tt></dt> 537 <dd>Global values with "<tt>private</tt>" linkage are only directly accessible 538 by objects in the current module. In particular, linking code into a 539 module with an private global value may cause the private to be renamed as 540 necessary to avoid collisions. Because the symbol is private to the 541 module, all references can be updated. This doesn't show up in any symbol 542 table in the object file.</dd> 543 544 <dt><tt><b><a name="linkage_linker_private">linker_private</a></b></tt></dt> 545 <dd>Similar to <tt>private</tt>, but the symbol is passed through the 546 assembler and evaluated by the linker. Unlike normal strong symbols, they 547 are removed by the linker from the final linked image (executable or 548 dynamic library).</dd> 549 550 <dt><tt><b><a name="linkage_linker_private_weak">linker_private_weak</a></b></tt></dt> 551 <dd>Similar to "<tt>linker_private</tt>", but the symbol is weak. Note that 552 <tt>linker_private_weak</tt> symbols are subject to coalescing by the 553 linker. The symbols are removed by the linker from the final linked image 554 (executable or dynamic library).</dd> 555 556 <dt><tt><b><a name="linkage_linker_private_weak_def_auto">linker_private_weak_def_auto</a></b></tt></dt> 557 <dd>Similar to "<tt>linker_private_weak</tt>", but it's known that the address 558 of the object is not taken. For instance, functions that had an inline 559 definition, but the compiler decided not to inline it. Note, 560 unlike <tt>linker_private</tt> and <tt>linker_private_weak</tt>, 561 <tt>linker_private_weak_def_auto</tt> may have only <tt>default</tt> 562 visibility. The symbols are removed by the linker from the final linked 563 image (executable or dynamic library).</dd> 564 565 <dt><tt><b><a name="linkage_internal">internal</a></b></tt></dt> 566 <dd>Similar to private, but the value shows as a local symbol 567 (<tt>STB_LOCAL</tt> in the case of ELF) in the object file. This 568 corresponds to the notion of the '<tt>static</tt>' keyword in C.</dd> 569 570 <dt><tt><b><a name="linkage_available_externally">available_externally</a></b></tt></dt> 571 <dd>Globals with "<tt>available_externally</tt>" linkage are never emitted 572 into the object file corresponding to the LLVM module. They exist to 573 allow inlining and other optimizations to take place given knowledge of 574 the definition of the global, which is known to be somewhere outside the 575 module. Globals with <tt>available_externally</tt> linkage are allowed to 576 be discarded at will, and are otherwise the same as <tt>linkonce_odr</tt>. 577 This linkage type is only allowed on definitions, not declarations.</dd> 578 579 <dt><tt><b><a name="linkage_linkonce">linkonce</a></b></tt></dt> 580 <dd>Globals with "<tt>linkonce</tt>" linkage are merged with other globals of 581 the same name when linkage occurs. This can be used to implement 582 some forms of inline functions, templates, or other code which must be 583 generated in each translation unit that uses it, but where the body may 584 be overridden with a more definitive definition later. Unreferenced 585 <tt>linkonce</tt> globals are allowed to be discarded. Note that 586 <tt>linkonce</tt> linkage does not actually allow the optimizer to 587 inline the body of this function into callers because it doesn't know if 588 this definition of the function is the definitive definition within the 589 program or whether it will be overridden by a stronger definition. 590 To enable inlining and other optimizations, use "<tt>linkonce_odr</tt>" 591 linkage.</dd> 592 593 <dt><tt><b><a name="linkage_weak">weak</a></b></tt></dt> 594 <dd>"<tt>weak</tt>" linkage has the same merging semantics as 595 <tt>linkonce</tt> linkage, except that unreferenced globals with 596 <tt>weak</tt> linkage may not be discarded. This is used for globals that 597 are declared "weak" in C source code.</dd> 598 599 <dt><tt><b><a name="linkage_common">common</a></b></tt></dt> 600 <dd>"<tt>common</tt>" linkage is most similar to "<tt>weak</tt>" linkage, but 601 they are used for tentative definitions in C, such as "<tt>int X;</tt>" at 602 global scope. 603 Symbols with "<tt>common</tt>" linkage are merged in the same way as 604 <tt>weak symbols</tt>, and they may not be deleted if unreferenced. 605 <tt>common</tt> symbols may not have an explicit section, 606 must have a zero initializer, and may not be marked '<a 607 href="#globalvars"><tt>constant</tt></a>'. Functions and aliases may not 608 have common linkage.</dd> 609 610 611 <dt><tt><b><a name="linkage_appending">appending</a></b></tt></dt> 612 <dd>"<tt>appending</tt>" linkage may only be applied to global variables of 613 pointer to array type. When two global variables with appending linkage 614 are linked together, the two global arrays are appended together. This is 615 the LLVM, typesafe, equivalent of having the system linker append together 616 "sections" with identical names when .o files are linked.</dd> 617 618 <dt><tt><b><a name="linkage_externweak">extern_weak</a></b></tt></dt> 619 <dd>The semantics of this linkage follow the ELF object file model: the symbol 620 is weak until linked, if not linked, the symbol becomes null instead of 621 being an undefined reference.</dd> 622 623 <dt><tt><b><a name="linkage_linkonce_odr">linkonce_odr</a></b></tt></dt> 624 <dt><tt><b><a name="linkage_weak_odr">weak_odr</a></b></tt></dt> 625 <dd>Some languages allow differing globals to be merged, such as two functions 626 with different semantics. Other languages, such as <tt>C++</tt>, ensure 627 that only equivalent globals are ever merged (the "one definition rule" 628 — "ODR"). Such languages can use the <tt>linkonce_odr</tt> 629 and <tt>weak_odr</tt> linkage types to indicate that the global will only 630 be merged with equivalent globals. These linkage types are otherwise the 631 same as their non-<tt>odr</tt> versions.</dd> 632 633 <dt><tt><b><a name="linkage_external">external</a></b></tt>:</dt> 634 <dd>If none of the above identifiers are used, the global is externally 635 visible, meaning that it participates in linkage and can be used to 636 resolve external symbol references.</dd> 637 </dl> 638 639 <p>The next two types of linkage are targeted for Microsoft Windows platform 640 only. They are designed to support importing (exporting) symbols from (to) 641 DLLs (Dynamic Link Libraries).</p> 642 643 <dl> 644 <dt><tt><b><a name="linkage_dllimport">dllimport</a></b></tt></dt> 645 <dd>"<tt>dllimport</tt>" linkage causes the compiler to reference a function 646 or variable via a global pointer to a pointer that is set up by the DLL 647 exporting the symbol. On Microsoft Windows targets, the pointer name is 648 formed by combining <code>__imp_</code> and the function or variable 649 name.</dd> 650 651 <dt><tt><b><a name="linkage_dllexport">dllexport</a></b></tt></dt> 652 <dd>"<tt>dllexport</tt>" linkage causes the compiler to provide a global 653 pointer to a pointer in a DLL, so that it can be referenced with the 654 <tt>dllimport</tt> attribute. On Microsoft Windows targets, the pointer 655 name is formed by combining <code>__imp_</code> and the function or 656 variable name.</dd> 657 </dl> 658 659 <p>For example, since the "<tt>.LC0</tt>" variable is defined to be internal, if 660 another module defined a "<tt>.LC0</tt>" variable and was linked with this 661 one, one of the two would be renamed, preventing a collision. Since 662 "<tt>main</tt>" and "<tt>puts</tt>" are external (i.e., lacking any linkage 663 declarations), they are accessible outside of the current module.</p> 664 665 <p>It is illegal for a function <i>declaration</i> to have any linkage type 666 other than <tt>external</tt>, <tt>dllimport</tt> 667 or <tt>extern_weak</tt>.</p> 668 669 <p>Aliases can have only <tt>external</tt>, <tt>internal</tt>, <tt>weak</tt> 670 or <tt>weak_odr</tt> linkages.</p> 671 672 </div> 673 674 <!-- ======================================================================= --> 675 <h3> 676 <a name="callingconv">Calling Conventions</a> 677 </h3> 678 679 <div> 680 681 <p>LLVM <a href="#functionstructure">functions</a>, <a href="#i_call">calls</a> 682 and <a href="#i_invoke">invokes</a> can all have an optional calling 683 convention specified for the call. The calling convention of any pair of 684 dynamic caller/callee must match, or the behavior of the program is 685 undefined. The following calling conventions are supported by LLVM, and more 686 may be added in the future:</p> 687 688 <dl> 689 <dt><b>"<tt>ccc</tt>" - The C calling convention</b>:</dt> 690 <dd>This calling convention (the default if no other calling convention is 691 specified) matches the target C calling conventions. This calling 692 convention supports varargs function calls and tolerates some mismatch in 693 the declared prototype and implemented declaration of the function (as 694 does normal C).</dd> 695 696 <dt><b>"<tt>fastcc</tt>" - The fast calling convention</b>:</dt> 697 <dd>This calling convention attempts to make calls as fast as possible 698 (e.g. by passing things in registers). This calling convention allows the 699 target to use whatever tricks it wants to produce fast code for the 700 target, without having to conform to an externally specified ABI 701 (Application Binary Interface). 702 <a href="CodeGenerator.html#tailcallopt">Tail calls can only be optimized 703 when this or the GHC convention is used.</a> This calling convention 704 does not support varargs and requires the prototype of all callees to 705 exactly match the prototype of the function definition.</dd> 706 707 <dt><b>"<tt>coldcc</tt>" - The cold calling convention</b>:</dt> 708 <dd>This calling convention attempts to make code in the caller as efficient 709 as possible under the assumption that the call is not commonly executed. 710 As such, these calls often preserve all registers so that the call does 711 not break any live ranges in the caller side. This calling convention 712 does not support varargs and requires the prototype of all callees to 713 exactly match the prototype of the function definition.</dd> 714 715 <dt><b>"<tt>cc <em>10</em></tt>" - GHC convention</b>:</dt> 716 <dd>This calling convention has been implemented specifically for use by the 717 <a href="http://www.haskell.org/ghc">Glasgow Haskell Compiler (GHC)</a>. 718 It passes everything in registers, going to extremes to achieve this by 719 disabling callee save registers. This calling convention should not be 720 used lightly but only for specific situations such as an alternative to 721 the <em>register pinning</em> performance technique often used when 722 implementing functional programming languages.At the moment only X86 723 supports this convention and it has the following limitations: 724 <ul> 725 <li>On <em>X86-32</em> only supports up to 4 bit type parameters. No 726 floating point types are supported.</li> 727 <li>On <em>X86-64</em> only supports up to 10 bit type parameters and 728 6 floating point parameters.</li> 729 </ul> 730 This calling convention supports 731 <a href="CodeGenerator.html#tailcallopt">tail call optimization</a> but 732 requires both the caller and callee are using it. 733 </dd> 734 735 <dt><b>"<tt>cc <<em>n</em>></tt>" - Numbered convention</b>:</dt> 736 <dd>Any calling convention may be specified by number, allowing 737 target-specific calling conventions to be used. Target specific calling 738 conventions start at 64.</dd> 739 </dl> 740 741 <p>More calling conventions can be added/defined on an as-needed basis, to 742 support Pascal conventions or any other well-known target-independent 743 convention.</p> 744 745 </div> 746 747 <!-- ======================================================================= --> 748 <h3> 749 <a name="visibility">Visibility Styles</a> 750 </h3> 751 752 <div> 753 754 <p>All Global Variables and Functions have one of the following visibility 755 styles:</p> 756 757 <dl> 758 <dt><b>"<tt>default</tt>" - Default style</b>:</dt> 759 <dd>On targets that use the ELF object file format, default visibility means 760 that the declaration is visible to other modules and, in shared libraries, 761 means that the declared entity may be overridden. On Darwin, default 762 visibility means that the declaration is visible to other modules. Default 763 visibility corresponds to "external linkage" in the language.</dd> 764 765 <dt><b>"<tt>hidden</tt>" - Hidden style</b>:</dt> 766 <dd>Two declarations of an object with hidden visibility refer to the same 767 object if they are in the same shared object. Usually, hidden visibility 768 indicates that the symbol will not be placed into the dynamic symbol 769 table, so no other module (executable or shared library) can reference it 770 directly.</dd> 771 772 <dt><b>"<tt>protected</tt>" - Protected style</b>:</dt> 773 <dd>On ELF, protected visibility indicates that the symbol will be placed in 774 the dynamic symbol table, but that references within the defining module 775 will bind to the local symbol. That is, the symbol cannot be overridden by 776 another module.</dd> 777 </dl> 778 779 </div> 780 781 <!-- ======================================================================= --> 782 <h3> 783 <a name="namedtypes">Named Types</a> 784 </h3> 785 786 <div> 787 788 <p>LLVM IR allows you to specify name aliases for certain types. This can make 789 it easier to read the IR and make the IR more condensed (particularly when 790 recursive types are involved). An example of a name specification is:</p> 791 792 <pre class="doc_code"> 793 %mytype = type { %mytype*, i32 } 794 </pre> 795 796 <p>You may give a name to any <a href="#typesystem">type</a> except 797 "<a href="#t_void">void</a>". Type name aliases may be used anywhere a type 798 is expected with the syntax "%mytype".</p> 799 800 <p>Note that type names are aliases for the structural type that they indicate, 801 and that you can therefore specify multiple names for the same type. This 802 often leads to confusing behavior when dumping out a .ll file. Since LLVM IR 803 uses structural typing, the name is not part of the type. When printing out 804 LLVM IR, the printer will pick <em>one name</em> to render all types of a 805 particular shape. This means that if you have code where two different 806 source types end up having the same LLVM type, that the dumper will sometimes 807 print the "wrong" or unexpected type. This is an important design point and 808 isn't going to change.</p> 809 810 </div> 811 812 <!-- ======================================================================= --> 813 <h3> 814 <a name="globalvars">Global Variables</a> 815 </h3> 816 817 <div> 818 819 <p>Global variables define regions of memory allocated at compilation time 820 instead of run-time. Global variables may optionally be initialized, may 821 have an explicit section to be placed in, and may have an optional explicit 822 alignment specified. A variable may be defined as "thread_local", which 823 means that it will not be shared by threads (each thread will have a 824 separated copy of the variable). A variable may be defined as a global 825 "constant," which indicates that the contents of the variable 826 will <b>never</b> be modified (enabling better optimization, allowing the 827 global data to be placed in the read-only section of an executable, etc). 828 Note that variables that need runtime initialization cannot be marked 829 "constant" as there is a store to the variable.</p> 830 831 <p>LLVM explicitly allows <em>declarations</em> of global variables to be marked 832 constant, even if the final definition of the global is not. This capability 833 can be used to enable slightly better optimization of the program, but 834 requires the language definition to guarantee that optimizations based on the 835 'constantness' are valid for the translation units that do not include the 836 definition.</p> 837 838 <p>As SSA values, global variables define pointer values that are in scope 839 (i.e. they dominate) all basic blocks in the program. Global variables 840 always define a pointer to their "content" type because they describe a 841 region of memory, and all memory objects in LLVM are accessed through 842 pointers.</p> 843 844 <p>Global variables can be marked with <tt>unnamed_addr</tt> which indicates 845 that the address is not significant, only the content. Constants marked 846 like this can be merged with other constants if they have the same 847 initializer. Note that a constant with significant address <em>can</em> 848 be merged with a <tt>unnamed_addr</tt> constant, the result being a 849 constant whose address is significant.</p> 850 851 <p>A global variable may be declared to reside in a target-specific numbered 852 address space. For targets that support them, address spaces may affect how 853 optimizations are performed and/or what target instructions are used to 854 access the variable. The default address space is zero. The address space 855 qualifier must precede any other attributes.</p> 856 857 <p>LLVM allows an explicit section to be specified for globals. If the target 858 supports it, it will emit globals to the section specified.</p> 859 860 <p>An explicit alignment may be specified for a global, which must be a power 861 of 2. If not present, or if the alignment is set to zero, the alignment of 862 the global is set by the target to whatever it feels convenient. If an 863 explicit alignment is specified, the global is forced to have exactly that 864 alignment. Targets and optimizers are not allowed to over-align the global 865 if the global has an assigned section. In this case, the extra alignment 866 could be observable: for example, code could assume that the globals are 867 densely packed in their section and try to iterate over them as an array, 868 alignment padding would break this iteration.</p> 869 870 <p>For example, the following defines a global in a numbered address space with 871 an initializer, section, and alignment:</p> 872 873 <pre class="doc_code"> 874 @G = addrspace(5) constant float 1.0, section "foo", align 4 875 </pre> 876 877 </div> 878 879 880 <!-- ======================================================================= --> 881 <h3> 882 <a name="functionstructure">Functions</a> 883 </h3> 884 885 <div> 886 887 <p>LLVM function definitions consist of the "<tt>define</tt>" keyword, an 888 optional <a href="#linkage">linkage type</a>, an optional 889 <a href="#visibility">visibility style</a>, an optional 890 <a href="#callingconv">calling convention</a>, 891 an optional <tt>unnamed_addr</tt> attribute, a return type, an optional 892 <a href="#paramattrs">parameter attribute</a> for the return type, a function 893 name, a (possibly empty) argument list (each with optional 894 <a href="#paramattrs">parameter attributes</a>), optional 895 <a href="#fnattrs">function attributes</a>, an optional section, an optional 896 alignment, an optional <a href="#gc">garbage collector name</a>, an opening 897 curly brace, a list of basic blocks, and a closing curly brace.</p> 898 899 <p>LLVM function declarations consist of the "<tt>declare</tt>" keyword, an 900 optional <a href="#linkage">linkage type</a>, an optional 901 <a href="#visibility">visibility style</a>, an optional 902 <a href="#callingconv">calling convention</a>, 903 an optional <tt>unnamed_addr</tt> attribute, a return type, an optional 904 <a href="#paramattrs">parameter attribute</a> for the return type, a function 905 name, a possibly empty list of arguments, an optional alignment, and an 906 optional <a href="#gc">garbage collector name</a>.</p> 907 908 <p>A function definition contains a list of basic blocks, forming the CFG 909 (Control Flow Graph) for the function. Each basic block may optionally start 910 with a label (giving the basic block a symbol table entry), contains a list 911 of instructions, and ends with a <a href="#terminators">terminator</a> 912 instruction (such as a branch or function return).</p> 913 914 <p>The first basic block in a function is special in two ways: it is immediately 915 executed on entrance to the function, and it is not allowed to have 916 predecessor basic blocks (i.e. there can not be any branches to the entry 917 block of a function). Because the block can have no predecessors, it also 918 cannot have any <a href="#i_phi">PHI nodes</a>.</p> 919 920 <p>LLVM allows an explicit section to be specified for functions. If the target 921 supports it, it will emit functions to the section specified.</p> 922 923 <p>An explicit alignment may be specified for a function. If not present, or if 924 the alignment is set to zero, the alignment of the function is set by the 925 target to whatever it feels convenient. If an explicit alignment is 926 specified, the function is forced to have at least that much alignment. All 927 alignments must be a power of 2.</p> 928 929 <p>If the <tt>unnamed_addr</tt> attribute is given, the address is know to not 930 be significant and two identical functions can be merged</p>. 931 932 <h5>Syntax:</h5> 933 <pre class="doc_code"> 934 define [<a href="#linkage">linkage</a>] [<a href="#visibility">visibility</a>] 935 [<a href="#callingconv">cconv</a>] [<a href="#paramattrs">ret attrs</a>] 936 <ResultType> @<FunctionName> ([argument list]) 937 [<a href="#fnattrs">fn Attrs</a>] [section "name"] [align N] 938 [<a href="#gc">gc</a>] { ... } 939 </pre> 940 941 </div> 942 943 <!-- ======================================================================= --> 944 <h3> 945 <a name="aliasstructure">Aliases</a> 946 </h3> 947 948 <div> 949 950 <p>Aliases act as "second name" for the aliasee value (which can be either 951 function, global variable, another alias or bitcast of global value). Aliases 952 may have an optional <a href="#linkage">linkage type</a>, and an 953 optional <a href="#visibility">visibility style</a>.</p> 954 955 <h5>Syntax:</h5> 956 <pre class="doc_code"> 957 @<Name> = alias [Linkage] [Visibility] <AliaseeTy> @<Aliasee> 958 </pre> 959 960 </div> 961 962 <!-- ======================================================================= --> 963 <h3> 964 <a name="namedmetadatastructure">Named Metadata</a> 965 </h3> 966 967 <div> 968 969 <p>Named metadata is a collection of metadata. <a href="#metadata">Metadata 970 nodes</a> (but not metadata strings) are the only valid operands for 971 a named metadata.</p> 972 973 <h5>Syntax:</h5> 974 <pre class="doc_code"> 975 ; Some unnamed metadata nodes, which are referenced by the named metadata. 976 !0 = metadata !{metadata !"zero"} 977 !1 = metadata !{metadata !"one"} 978 !2 = metadata !{metadata !"two"} 979 ; A named metadata. 980 !name = !{!0, !1, !2} 981 </pre> 982 983 </div> 984 985 <!-- ======================================================================= --> 986 <h3> 987 <a name="paramattrs">Parameter Attributes</a> 988 </h3> 989 990 <div> 991 992 <p>The return type and each parameter of a function type may have a set of 993 <i>parameter attributes</i> associated with them. Parameter attributes are 994 used to communicate additional information about the result or parameters of 995 a function. Parameter attributes are considered to be part of the function, 996 not of the function type, so functions with different parameter attributes 997 can have the same function type.</p> 998 999 <p>Parameter attributes are simple keywords that follow the type specified. If 1000 multiple parameter attributes are needed, they are space separated. For 1001 example:</p> 1002 1003 <pre class="doc_code"> 1004 declare i32 @printf(i8* noalias nocapture, ...) 1005 declare i32 @atoi(i8 zeroext) 1006 declare signext i8 @returns_signed_char() 1007 </pre> 1008 1009 <p>Note that any attributes for the function result (<tt>nounwind</tt>, 1010 <tt>readonly</tt>) come immediately after the argument list.</p> 1011 1012 <p>Currently, only the following parameter attributes are defined:</p> 1013 1014 <dl> 1015 <dt><tt><b>zeroext</b></tt></dt> 1016 <dd>This indicates to the code generator that the parameter or return value 1017 should be zero-extended to the extent required by the target's ABI (which 1018 is usually 32-bits, but is 8-bits for a i1 on x86-64) by the caller (for a 1019 parameter) or the callee (for a return value).</dd> 1020 1021 <dt><tt><b>signext</b></tt></dt> 1022 <dd>This indicates to the code generator that the parameter or return value 1023 should be sign-extended to the extent required by the target's ABI (which 1024 is usually 32-bits) by the caller (for a parameter) or the callee (for a 1025 return value).</dd> 1026 1027 <dt><tt><b>inreg</b></tt></dt> 1028 <dd>This indicates that this parameter or return value should be treated in a 1029 special target-dependent fashion during while emitting code for a function 1030 call or return (usually, by putting it in a register as opposed to memory, 1031 though some targets use it to distinguish between two different kinds of 1032 registers). Use of this attribute is target-specific.</dd> 1033 1034 <dt><tt><b><a name="byval">byval</a></b></tt></dt> 1035 <dd><p>This indicates that the pointer parameter should really be passed by 1036 value to the function. The attribute implies that a hidden copy of the 1037 pointee 1038 is made between the caller and the callee, so the callee is unable to 1039 modify the value in the callee. This attribute is only valid on LLVM 1040 pointer arguments. It is generally used to pass structs and arrays by 1041 value, but is also valid on pointers to scalars. The copy is considered 1042 to belong to the caller not the callee (for example, 1043 <tt><a href="#readonly">readonly</a></tt> functions should not write to 1044 <tt>byval</tt> parameters). This is not a valid attribute for return 1045 values.</p> 1046 1047 <p>The byval attribute also supports specifying an alignment with 1048 the align attribute. It indicates the alignment of the stack slot to 1049 form and the known alignment of the pointer specified to the call site. If 1050 the alignment is not specified, then the code generator makes a 1051 target-specific assumption.</p></dd> 1052 1053 <dt><tt><b><a name="sret">sret</a></b></tt></dt> 1054 <dd>This indicates that the pointer parameter specifies the address of a 1055 structure that is the return value of the function in the source program. 1056 This pointer must be guaranteed by the caller to be valid: loads and 1057 stores to the structure may be assumed by the callee to not to trap. This 1058 may only be applied to the first parameter. This is not a valid attribute 1059 for return values. </dd> 1060 1061 <dt><tt><b><a name="noalias">noalias</a></b></tt></dt> 1062 <dd>This indicates that pointer values 1063 <a href="#pointeraliasing"><i>based</i></a> on the argument or return 1064 value do not alias pointer values which are not <i>based</i> on it, 1065 ignoring certain "irrelevant" dependencies. 1066 For a call to the parent function, dependencies between memory 1067 references from before or after the call and from those during the call 1068 are "irrelevant" to the <tt>noalias</tt> keyword for the arguments and 1069 return value used in that call. 1070 The caller shares the responsibility with the callee for ensuring that 1071 these requirements are met. 1072 For further details, please see the discussion of the NoAlias response in 1073 <a href="AliasAnalysis.html#MustMayNo">alias analysis</a>.<br> 1074 <br> 1075 Note that this definition of <tt>noalias</tt> is intentionally 1076 similar to the definition of <tt>restrict</tt> in C99 for function 1077 arguments, though it is slightly weaker. 1078 <br> 1079 For function return values, C99's <tt>restrict</tt> is not meaningful, 1080 while LLVM's <tt>noalias</tt> is. 1081 </dd> 1082 1083 <dt><tt><b><a name="nocapture">nocapture</a></b></tt></dt> 1084 <dd>This indicates that the callee does not make any copies of the pointer 1085 that outlive the callee itself. This is not a valid attribute for return 1086 values.</dd> 1087 1088 <dt><tt><b><a name="nest">nest</a></b></tt></dt> 1089 <dd>This indicates that the pointer parameter can be excised using the 1090 <a href="#int_trampoline">trampoline intrinsics</a>. This is not a valid 1091 attribute for return values.</dd> 1092 </dl> 1093 1094 </div> 1095 1096 <!-- ======================================================================= --> 1097 <h3> 1098 <a name="gc">Garbage Collector Names</a> 1099 </h3> 1100 1101 <div> 1102 1103 <p>Each function may specify a garbage collector name, which is simply a 1104 string:</p> 1105 1106 <pre class="doc_code"> 1107 define void @f() gc "name" { ... } 1108 </pre> 1109 1110 <p>The compiler declares the supported values of <i>name</i>. Specifying a 1111 collector which will cause the compiler to alter its output in order to 1112 support the named garbage collection algorithm.</p> 1113 1114 </div> 1115 1116 <!-- ======================================================================= --> 1117 <h3> 1118 <a name="fnattrs">Function Attributes</a> 1119 </h3> 1120 1121 <div> 1122 1123 <p>Function attributes are set to communicate additional information about a 1124 function. Function attributes are considered to be part of the function, not 1125 of the function type, so functions with different parameter attributes can 1126 have the same function type.</p> 1127 1128 <p>Function attributes are simple keywords that follow the type specified. If 1129 multiple attributes are needed, they are space separated. For example:</p> 1130 1131 <pre class="doc_code"> 1132 define void @f() noinline { ... } 1133 define void @f() alwaysinline { ... } 1134 define void @f() alwaysinline optsize { ... } 1135 define void @f() optsize { ... } 1136 </pre> 1137 1138 <dl> 1139 <dt><tt><b>alignstack(<<em>n</em>>)</b></tt></dt> 1140 <dd>This attribute indicates that, when emitting the prologue and epilogue, 1141 the backend should forcibly align the stack pointer. Specify the 1142 desired alignment, which must be a power of two, in parentheses. 1143 1144 <dt><tt><b>alwaysinline</b></tt></dt> 1145 <dd>This attribute indicates that the inliner should attempt to inline this 1146 function into callers whenever possible, ignoring any active inlining size 1147 threshold for this caller.</dd> 1148 1149 <dt><tt><b>nonlazybind</b></tt></dt> 1150 <dd>This attribute suppresses lazy symbol binding for the function. This 1151 may make calls to the function faster, at the cost of extra program 1152 startup time if the function is not called during program startup.</dd> 1153 1154 <dt><tt><b>inlinehint</b></tt></dt> 1155 <dd>This attribute indicates that the source code contained a hint that inlining 1156 this function is desirable (such as the "inline" keyword in C/C++). It 1157 is just a hint; it imposes no requirements on the inliner.</dd> 1158 1159 <dt><tt><b>naked</b></tt></dt> 1160 <dd>This attribute disables prologue / epilogue emission for the function. 1161 This can have very system-specific consequences.</dd> 1162 1163 <dt><tt><b>noimplicitfloat</b></tt></dt> 1164 <dd>This attributes disables implicit floating point instructions.</dd> 1165 1166 <dt><tt><b>noinline</b></tt></dt> 1167 <dd>This attribute indicates that the inliner should never inline this 1168 function in any situation. This attribute may not be used together with 1169 the <tt>alwaysinline</tt> attribute.</dd> 1170 1171 <dt><tt><b>noredzone</b></tt></dt> 1172 <dd>This attribute indicates that the code generator should not use a red 1173 zone, even if the target-specific ABI normally permits it.</dd> 1174 1175 <dt><tt><b>noreturn</b></tt></dt> 1176 <dd>This function attribute indicates that the function never returns 1177 normally. This produces undefined behavior at runtime if the function 1178 ever does dynamically return.</dd> 1179 1180 <dt><tt><b>nounwind</b></tt></dt> 1181 <dd>This function attribute indicates that the function never returns with an 1182 unwind or exceptional control flow. If the function does unwind, its 1183 runtime behavior is undefined.</dd> 1184 1185 <dt><tt><b>optsize</b></tt></dt> 1186 <dd>This attribute suggests that optimization passes and code generator passes 1187 make choices that keep the code size of this function low, and otherwise 1188 do optimizations specifically to reduce code size.</dd> 1189 1190 <dt><tt><b>readnone</b></tt></dt> 1191 <dd>This attribute indicates that the function computes its result (or decides 1192 to unwind an exception) based strictly on its arguments, without 1193 dereferencing any pointer arguments or otherwise accessing any mutable 1194 state (e.g. memory, control registers, etc) visible to caller functions. 1195 It does not write through any pointer arguments 1196 (including <tt><a href="#byval">byval</a></tt> arguments) and never 1197 changes any state visible to callers. This means that it cannot unwind 1198 exceptions by calling the <tt>C++</tt> exception throwing methods, but 1199 could use the <tt>unwind</tt> instruction.</dd> 1200 1201 <dt><tt><b><a name="readonly">readonly</a></b></tt></dt> 1202 <dd>This attribute indicates that the function does not write through any 1203 pointer arguments (including <tt><a href="#byval">byval</a></tt> 1204 arguments) or otherwise modify any state (e.g. memory, control registers, 1205 etc) visible to caller functions. It may dereference pointer arguments 1206 and read state that may be set in the caller. A readonly function always 1207 returns the same value (or unwinds an exception identically) when called 1208 with the same set of arguments and global state. It cannot unwind an 1209 exception by calling the <tt>C++</tt> exception throwing methods, but may 1210 use the <tt>unwind</tt> instruction.</dd> 1211 1212 <dt><tt><b><a name="ssp">ssp</a></b></tt></dt> 1213 <dd>This attribute indicates that the function should emit a stack smashing 1214 protector. It is in the form of a "canary"—a random value placed on 1215 the stack before the local variables that's checked upon return from the 1216 function to see if it has been overwritten. A heuristic is used to 1217 determine if a function needs stack protectors or not.<br> 1218 <br> 1219 If a function that has an <tt>ssp</tt> attribute is inlined into a 1220 function that doesn't have an <tt>ssp</tt> attribute, then the resulting 1221 function will have an <tt>ssp</tt> attribute.</dd> 1222 1223 <dt><tt><b>sspreq</b></tt></dt> 1224 <dd>This attribute indicates that the function should <em>always</em> emit a 1225 stack smashing protector. This overrides 1226 the <tt><a href="#ssp">ssp</a></tt> function attribute.<br> 1227 <br> 1228 If a function that has an <tt>sspreq</tt> attribute is inlined into a 1229 function that doesn't have an <tt>sspreq</tt> attribute or which has 1230 an <tt>ssp</tt> attribute, then the resulting function will have 1231 an <tt>sspreq</tt> attribute.</dd> 1232 1233 <dt><tt><b><a name="uwtable">uwtable</a></b></tt></dt> 1234 <dd>This attribute indicates that the ABI being targeted requires that 1235 an unwind table entry be produce for this function even if we can 1236 show that no exceptions passes by it. This is normally the case for 1237 the ELF x86-64 abi, but it can be disabled for some compilation 1238 units.</dd> 1239 1240 <dt><tt><b><a name="returns_twice">returns_twice</a></b></tt></dt> 1241 <dd>This attribute indicates that this function can return 1242 twice. The C <code>setjmp</code> is an example of such a function. 1243 The compiler disables some optimizations (like tail calls) in the caller of 1244 these functions.</dd> 1245 </dl> 1246 1247 </div> 1248 1249 <!-- ======================================================================= --> 1250 <h3> 1251 <a name="moduleasm">Module-Level Inline Assembly</a> 1252 </h3> 1253 1254 <div> 1255 1256 <p>Modules may contain "module-level inline asm" blocks, which corresponds to 1257 the GCC "file scope inline asm" blocks. These blocks are internally 1258 concatenated by LLVM and treated as a single unit, but may be separated in 1259 the <tt>.ll</tt> file if desired. The syntax is very simple:</p> 1260 1261 <pre class="doc_code"> 1262 module asm "inline asm code goes here" 1263 module asm "more can go here" 1264 </pre> 1265 1266 <p>The strings can contain any character by escaping non-printable characters. 1267 The escape sequence used is simply "\xx" where "xx" is the two digit hex code 1268 for the number.</p> 1269 1270 <p>The inline asm code is simply printed to the machine code .s file when 1271 assembly code is generated.</p> 1272 1273 </div> 1274 1275 <!-- ======================================================================= --> 1276 <h3> 1277 <a name="datalayout">Data Layout</a> 1278 </h3> 1279 1280 <div> 1281 1282 <p>A module may specify a target specific data layout string that specifies how 1283 data is to be laid out in memory. The syntax for the data layout is 1284 simply:</p> 1285 1286 <pre class="doc_code"> 1287 target datalayout = "<i>layout specification</i>" 1288 </pre> 1289 1290 <p>The <i>layout specification</i> consists of a list of specifications 1291 separated by the minus sign character ('-'). Each specification starts with 1292 a letter and may include other information after the letter to define some 1293 aspect of the data layout. The specifications accepted are as follows:</p> 1294 1295 <dl> 1296 <dt><tt>E</tt></dt> 1297 <dd>Specifies that the target lays out data in big-endian form. That is, the 1298 bits with the most significance have the lowest address location.</dd> 1299 1300 <dt><tt>e</tt></dt> 1301 <dd>Specifies that the target lays out data in little-endian form. That is, 1302 the bits with the least significance have the lowest address 1303 location.</dd> 1304 1305 <dt><tt>S<i>size</i></tt></dt> 1306 <dd>Specifies the natural alignment of the stack in bits. Alignment promotion 1307 of stack variables is limited to the natural stack alignment to avoid 1308 dynamic stack realignment. The stack alignment must be a multiple of 1309 8-bits. If omitted, the natural stack alignment defaults to "unspecified", 1310 which does not prevent any alignment promotions.</dd> 1311 1312 <dt><tt>p:<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt> 1313 <dd>This specifies the <i>size</i> of a pointer and its <i>abi</i> and 1314 <i>preferred</i> alignments. All sizes are in bits. Specifying 1315 the <i>pref</i> alignment is optional. If omitted, the 1316 preceding <tt>:</tt> should be omitted too.</dd> 1317 1318 <dt><tt>i<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt> 1319 <dd>This specifies the alignment for an integer type of a given bit 1320 <i>size</i>. The value of <i>size</i> must be in the range [1,2^23).</dd> 1321 1322 <dt><tt>v<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt> 1323 <dd>This specifies the alignment for a vector type of a given bit 1324 <i>size</i>.</dd> 1325 1326 <dt><tt>f<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt> 1327 <dd>This specifies the alignment for a floating point type of a given bit 1328 <i>size</i>. Only values of <i>size</i> that are supported by the target 1329 will work. 32 (float) and 64 (double) are supported on all targets; 1330 80 or 128 (different flavors of long double) are also supported on some 1331 targets. 1332 1333 <dt><tt>a<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt> 1334 <dd>This specifies the alignment for an aggregate type of a given bit 1335 <i>size</i>.</dd> 1336 1337 <dt><tt>s<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt> 1338 <dd>This specifies the alignment for a stack object of a given bit 1339 <i>size</i>.</dd> 1340 1341 <dt><tt>n<i>size1</i>:<i>size2</i>:<i>size3</i>...</tt></dt> 1342 <dd>This specifies a set of native integer widths for the target CPU 1343 in bits. For example, it might contain "n32" for 32-bit PowerPC, 1344 "n32:64" for PowerPC 64, or "n8:16:32:64" for X86-64. Elements of 1345 this set are considered to support most general arithmetic 1346 operations efficiently.</dd> 1347 </dl> 1348 1349 <p>When constructing the data layout for a given target, LLVM starts with a 1350 default set of specifications which are then (possibly) overridden by the 1351 specifications in the <tt>datalayout</tt> keyword. The default specifications 1352 are given in this list:</p> 1353 1354 <ul> 1355 <li><tt>E</tt> - big endian</li> 1356 <li><tt>p:64:64:64</tt> - 64-bit pointers with 64-bit alignment</li> 1357 <li><tt>i1:8:8</tt> - i1 is 8-bit (byte) aligned</li> 1358 <li><tt>i8:8:8</tt> - i8 is 8-bit (byte) aligned</li> 1359 <li><tt>i16:16:16</tt> - i16 is 16-bit aligned</li> 1360 <li><tt>i32:32:32</tt> - i32 is 32-bit aligned</li> 1361 <li><tt>i64:32:64</tt> - i64 has ABI alignment of 32-bits but preferred 1362 alignment of 64-bits</li> 1363 <li><tt>f32:32:32</tt> - float is 32-bit aligned</li> 1364 <li><tt>f64:64:64</tt> - double is 64-bit aligned</li> 1365 <li><tt>v64:64:64</tt> - 64-bit vector is 64-bit aligned</li> 1366 <li><tt>v128:128:128</tt> - 128-bit vector is 128-bit aligned</li> 1367 <li><tt>a0:0:1</tt> - aggregates are 8-bit aligned</li> 1368 <li><tt>s0:64:64</tt> - stack objects are 64-bit aligned</li> 1369 </ul> 1370 1371 <p>When LLVM is determining the alignment for a given type, it uses the 1372 following rules:</p> 1373 1374 <ol> 1375 <li>If the type sought is an exact match for one of the specifications, that 1376 specification is used.</li> 1377 1378 <li>If no match is found, and the type sought is an integer type, then the 1379 smallest integer type that is larger than the bitwidth of the sought type 1380 is used. If none of the specifications are larger than the bitwidth then 1381 the the largest integer type is used. For example, given the default 1382 specifications above, the i7 type will use the alignment of i8 (next 1383 largest) while both i65 and i256 will use the alignment of i64 (largest 1384 specified).</li> 1385 1386 <li>If no match is found, and the type sought is a vector type, then the 1387 largest vector type that is smaller than the sought vector type will be 1388 used as a fall back. This happens because <128 x double> can be 1389 implemented in terms of 64 <2 x double>, for example.</li> 1390 </ol> 1391 1392 <p>The function of the data layout string may not be what you expect. Notably, 1393 this is not a specification from the frontend of what alignment the code 1394 generator should use.</p> 1395 1396 <p>Instead, if specified, the target data layout is required to match what the 1397 ultimate <em>code generator</em> expects. This string is used by the 1398 mid-level optimizers to 1399 improve code, and this only works if it matches what the ultimate code 1400 generator uses. If you would like to generate IR that does not embed this 1401 target-specific detail into the IR, then you don't have to specify the 1402 string. This will disable some optimizations that require precise layout 1403 information, but this also prevents those optimizations from introducing 1404 target specificity into the IR.</p> 1405 1406 1407 1408 </div> 1409 1410 <!-- ======================================================================= --> 1411 <h3> 1412 <a name="pointeraliasing">Pointer Aliasing Rules</a> 1413 </h3> 1414 1415 <div> 1416 1417 <p>Any memory access must be done through a pointer value associated 1418 with an address range of the memory access, otherwise the behavior 1419 is undefined. Pointer values are associated with address ranges 1420 according to the following rules:</p> 1421 1422 <ul> 1423 <li>A pointer value is associated with the addresses associated with 1424 any value it is <i>based</i> on. 1425 <li>An address of a global variable is associated with the address 1426 range of the variable's storage.</li> 1427 <li>The result value of an allocation instruction is associated with 1428 the address range of the allocated storage.</li> 1429 <li>A null pointer in the default address-space is associated with 1430 no address.</li> 1431 <li>An integer constant other than zero or a pointer value returned 1432 from a function not defined within LLVM may be associated with address 1433 ranges allocated through mechanisms other than those provided by 1434 LLVM. Such ranges shall not overlap with any ranges of addresses 1435 allocated by mechanisms provided by LLVM.</li> 1436 </ul> 1437 1438 <p>A pointer value is <i>based</i> on another pointer value according 1439 to the following rules:</p> 1440 1441 <ul> 1442 <li>A pointer value formed from a 1443 <tt><a href="#i_getelementptr">getelementptr</a></tt> operation 1444 is <i>based</i> on the first operand of the <tt>getelementptr</tt>.</li> 1445 <li>The result value of a 1446 <tt><a href="#i_bitcast">bitcast</a></tt> is <i>based</i> on the operand 1447 of the <tt>bitcast</tt>.</li> 1448 <li>A pointer value formed by an 1449 <tt><a href="#i_inttoptr">inttoptr</a></tt> is <i>based</i> on all 1450 pointer values that contribute (directly or indirectly) to the 1451 computation of the pointer's value.</li> 1452 <li>The "<i>based</i> on" relationship is transitive.</li> 1453 </ul> 1454 1455 <p>Note that this definition of <i>"based"</i> is intentionally 1456 similar to the definition of <i>"based"</i> in C99, though it is 1457 slightly weaker.</p> 1458 1459 <p>LLVM IR does not associate types with memory. The result type of a 1460 <tt><a href="#i_load">load</a></tt> merely indicates the size and 1461 alignment of the memory from which to load, as well as the 1462 interpretation of the value. The first operand type of a 1463 <tt><a href="#i_store">store</a></tt> similarly only indicates the size 1464 and alignment of the store.</p> 1465 1466 <p>Consequently, type-based alias analysis, aka TBAA, aka 1467 <tt>-fstrict-aliasing</tt>, is not applicable to general unadorned 1468 LLVM IR. <a href="#metadata">Metadata</a> may be used to encode 1469 additional information which specialized optimization passes may use 1470 to implement type-based alias analysis.</p> 1471 1472 </div> 1473 1474 <!-- ======================================================================= --> 1475 <h3> 1476 <a name="volatile">Volatile Memory Accesses</a> 1477 </h3> 1478 1479 <div> 1480 1481 <p>Certain memory accesses, such as <a href="#i_load"><tt>load</tt></a>s, <a 1482 href="#i_store"><tt>store</tt></a>s, and <a 1483 href="#int_memcpy"><tt>llvm.memcpy</tt></a>s may be marked <tt>volatile</tt>. 1484 The optimizers must not change the number of volatile operations or change their 1485 order of execution relative to other volatile operations. The optimizers 1486 <i>may</i> change the order of volatile operations relative to non-volatile 1487 operations. This is not Java's "volatile" and has no cross-thread 1488 synchronization behavior.</p> 1489 1490 </div> 1491 1492 <!-- ======================================================================= --> 1493 <h3> 1494 <a name="memmodel">Memory Model for Concurrent Operations</a> 1495 </h3> 1496 1497 <div> 1498 1499 <p>The LLVM IR does not define any way to start parallel threads of execution 1500 or to register signal handlers. Nonetheless, there are platform-specific 1501 ways to create them, and we define LLVM IR's behavior in their presence. This 1502 model is inspired by the C++0x memory model.</p> 1503 1504 <p>For a more informal introduction to this model, see the 1505 <a href="Atomics.html">LLVM Atomic Instructions and Concurrency Guide</a>. 1506 1507 <p>We define a <i>happens-before</i> partial order as the least partial order 1508 that</p> 1509 <ul> 1510 <li>Is a superset of single-thread program order, and</li> 1511 <li>When a <i>synchronizes-with</i> <tt>b</tt>, includes an edge from 1512 <tt>a</tt> to <tt>b</tt>. <i>Synchronizes-with</i> pairs are introduced 1513 by platform-specific techniques, like pthread locks, thread 1514 creation, thread joining, etc., and by atomic instructions. 1515 (See also <a href="#ordering">Atomic Memory Ordering Constraints</a>). 1516 </li> 1517 </ul> 1518 1519 <p>Note that program order does not introduce <i>happens-before</i> edges 1520 between a thread and signals executing inside that thread.</p> 1521 1522 <p>Every (defined) read operation (load instructions, memcpy, atomic 1523 loads/read-modify-writes, etc.) <var>R</var> reads a series of bytes written by 1524 (defined) write operations (store instructions, atomic 1525 stores/read-modify-writes, memcpy, etc.). For the purposes of this section, 1526 initialized globals are considered to have a write of the initializer which is 1527 atomic and happens before any other read or write of the memory in question. 1528 For each byte of a read <var>R</var>, <var>R<sub>byte</sub></var> may see 1529 any write to the same byte, except:</p> 1530 1531 <ul> 1532 <li>If <var>write<sub>1</sub></var> happens before 1533 <var>write<sub>2</sub></var>, and <var>write<sub>2</sub></var> happens 1534 before <var>R<sub>byte</sub></var>, then <var>R<sub>byte</sub></var> 1535 does not see <var>write<sub>1</sub></var>. 1536 <li>If <var>R<sub>byte</sub></var> happens before 1537 <var>write<sub>3</sub></var>, then <var>R<sub>byte</sub></var> does not 1538 see <var>write<sub>3</sub></var>. 1539 </ul> 1540 1541 <p>Given that definition, <var>R<sub>byte</sub></var> is defined as follows: 1542 <ul> 1543 <li>If <var>R</var> is volatile, the result is target-dependent. (Volatile 1544 is supposed to give guarantees which can support 1545 <code>sig_atomic_t</code> in C/C++, and may be used for accesses to 1546 addresses which do not behave like normal memory. It does not generally 1547 provide cross-thread synchronization.) 1548 <li>Otherwise, if there is no write to the same byte that happens before 1549 <var>R<sub>byte</sub></var>, <var>R<sub>byte</sub></var> returns 1550 <tt>undef</tt> for that byte. 1551 <li>Otherwise, if <var>R<sub>byte</sub></var> may see exactly one write, 1552 <var>R<sub>byte</sub></var> returns the value written by that 1553 write.</li> 1554 <li>Otherwise, if <var>R</var> is atomic, and all the writes 1555 <var>R<sub>byte</sub></var> may see are atomic, it chooses one of the 1556 values written. See the <a href="#ordering">Atomic Memory Ordering 1557 Constraints</a> section for additional constraints on how the choice 1558 is made. 1559 <li>Otherwise <var>R<sub>byte</sub></var> returns <tt>undef</tt>.</li> 1560 </ul> 1561 1562 <p><var>R</var> returns the value composed of the series of bytes it read. 1563 This implies that some bytes within the value may be <tt>undef</tt> 1564 <b>without</b> the entire value being <tt>undef</tt>. Note that this only 1565 defines the semantics of the operation; it doesn't mean that targets will 1566 emit more than one instruction to read the series of bytes.</p> 1567 1568 <p>Note that in cases where none of the atomic intrinsics are used, this model 1569 places only one restriction on IR transformations on top of what is required 1570 for single-threaded execution: introducing a store to a byte which might not 1571 otherwise be stored is not allowed in general. (Specifically, in the case 1572 where another thread might write to and read from an address, introducing a 1573 store can change a load that may see exactly one write into a load that may 1574 see multiple writes.)</p> 1575 1576 <!-- FIXME: This model assumes all targets where concurrency is relevant have 1577 a byte-size store which doesn't affect adjacent bytes. As far as I can tell, 1578 none of the backends currently in the tree fall into this category; however, 1579 there might be targets which care. If there are, we want a paragraph 1580 like the following: 1581 1582 Targets may specify that stores narrower than a certain width are not 1583 available; on such a target, for the purposes of this model, treat any 1584 non-atomic write with an alignment or width less than the minimum width 1585 as if it writes to the relevant surrounding bytes. 1586 --> 1587 1588 </div> 1589 1590 <!-- ======================================================================= --> 1591 <h3> 1592 <a name="ordering">Atomic Memory Ordering Constraints</a> 1593 </h3> 1594 1595 <div> 1596 1597 <p>Atomic instructions (<a href="#i_cmpxchg"><code>cmpxchg</code></a>, 1598 <a href="#i_atomicrmw"><code>atomicrmw</code></a>, 1599 <a href="#i_fence"><code>fence</code></a>, 1600 <a href="#i_load"><code>atomic load</code></a>, and 1601 <a href="#i_store"><code>atomic store</code></a>) take an ordering parameter 1602 that determines which other atomic instructions on the same address they 1603 <i>synchronize with</i>. These semantics are borrowed from Java and C++0x, 1604 but are somewhat more colloquial. If these descriptions aren't precise enough, 1605 check those specs (see spec references in the 1606 <a href="Atomic.html#introduction">atomics guide</a>). 1607 <a href="#i_fence"><code>fence</code></a> instructions 1608 treat these orderings somewhat differently since they don't take an address. 1609 See that instruction's documentation for details.</p> 1610 1611 <p>For a simpler introduction to the ordering constraints, see the 1612 <a href="Atomics.html">LLVM Atomic Instructions and Concurrency Guide</a>.</p> 1613 1614 <dl> 1615 <dt><code>unordered</code></dt> 1616 <dd>The set of values that can be read is governed by the happens-before 1617 partial order. A value cannot be read unless some operation wrote it. 1618 This is intended to provide a guarantee strong enough to model Java's 1619 non-volatile shared variables. This ordering cannot be specified for 1620 read-modify-write operations; it is not strong enough to make them atomic 1621 in any interesting way.</dd> 1622 <dt><code>monotonic</code></dt> 1623 <dd>In addition to the guarantees of <code>unordered</code>, there is a single 1624 total order for modifications by <code>monotonic</code> operations on each 1625 address. All modification orders must be compatible with the happens-before 1626 order. There is no guarantee that the modification orders can be combined to 1627 a global total order for the whole program (and this often will not be 1628 possible). The read in an atomic read-modify-write operation 1629 (<a href="#i_cmpxchg"><code>cmpxchg</code></a> and 1630 <a href="#i_atomicrmw"><code>atomicrmw</code></a>) 1631 reads the value in the modification order immediately before the value it 1632 writes. If one atomic read happens before another atomic read of the same 1633 address, the later read must see the same value or a later value in the 1634 address's modification order. This disallows reordering of 1635 <code>monotonic</code> (or stronger) operations on the same address. If an 1636 address is written <code>monotonic</code>ally by one thread, and other threads 1637 <code>monotonic</code>ally read that address repeatedly, the other threads must 1638 eventually see the write. This corresponds to the C++0x/C1x 1639 <code>memory_order_relaxed</code>.</dd> 1640 <dt><code>acquire</code></dt> 1641 <dd>In addition to the guarantees of <code>monotonic</code>, 1642 a <i>synchronizes-with</i> edge may be formed with a <code>release</code> 1643 operation. This is intended to model C++'s <code>memory_order_acquire</code>.</dd> 1644 <dt><code>release</code></dt> 1645 <dd>In addition to the guarantees of <code>monotonic</code>, if this operation 1646 writes a value which is subsequently read by an <code>acquire</code> operation, 1647 it <i>synchronizes-with</i> that operation. (This isn't a complete 1648 description; see the C++0x definition of a release sequence.) This corresponds 1649 to the C++0x/C1x <code>memory_order_release</code>.</dd> 1650 <dt><code>acq_rel</code> (acquire+release)</dt><dd>Acts as both an 1651 <code>acquire</code> and <code>release</code> operation on its address. 1652 This corresponds to the C++0x/C1x <code>memory_order_acq_rel</code>.</dd> 1653 <dt><code>seq_cst</code> (sequentially consistent)</dt><dd> 1654 <dd>In addition to the guarantees of <code>acq_rel</code> 1655 (<code>acquire</code> for an operation which only reads, <code>release</code> 1656 for an operation which only writes), there is a global total order on all 1657 sequentially-consistent operations on all addresses, which is consistent with 1658 the <i>happens-before</i> partial order and with the modification orders of 1659 all the affected addresses. Each sequentially-consistent read sees the last 1660 preceding write to the same address in this global order. This corresponds 1661 to the C++0x/C1x <code>memory_order_seq_cst</code> and Java volatile.</dd> 1662 </dl> 1663 1664 <p id="singlethread">If an atomic operation is marked <code>singlethread</code>, 1665 it only <i>synchronizes with</i> or participates in modification and seq_cst 1666 total orderings with other operations running in the same thread (for example, 1667 in signal handlers).</p> 1668 1669 </div> 1670 1671 </div> 1672 1673 <!-- *********************************************************************** --> 1674 <h2><a name="typesystem">Type System</a></h2> 1675 <!-- *********************************************************************** --> 1676 1677 <div> 1678 1679 <p>The LLVM type system is one of the most important features of the 1680 intermediate representation. Being typed enables a number of optimizations 1681 to be performed on the intermediate representation directly, without having 1682 to do extra analyses on the side before the transformation. A strong type 1683 system makes it easier to read the generated code and enables novel analyses 1684 and transformations that are not feasible to perform on normal three address 1685 code representations.</p> 1686 1687 <!-- ======================================================================= --> 1688 <h3> 1689 <a name="t_classifications">Type Classifications</a> 1690 </h3> 1691 1692 <div> 1693 1694 <p>The types fall into a few useful classifications:</p> 1695 1696 <table border="1" cellspacing="0" cellpadding="4"> 1697 <tbody> 1698 <tr><th>Classification</th><th>Types</th></tr> 1699 <tr> 1700 <td><a href="#t_integer">integer</a></td> 1701 <td><tt>i1, i2, i3, ... i8, ... i16, ... i32, ... i64, ... </tt></td> 1702 </tr> 1703 <tr> 1704 <td><a href="#t_floating">floating point</a></td> 1705 <td><tt>float, double, x86_fp80, fp128, ppc_fp128</tt></td> 1706 </tr> 1707 <tr> 1708 <td><a name="t_firstclass">first class</a></td> 1709 <td><a href="#t_integer">integer</a>, 1710 <a href="#t_floating">floating point</a>, 1711 <a href="#t_pointer">pointer</a>, 1712 <a href="#t_vector">vector</a>, 1713 <a href="#t_struct">structure</a>, 1714 <a href="#t_array">array</a>, 1715 <a href="#t_label">label</a>, 1716 <a href="#t_metadata">metadata</a>. 1717 </td> 1718 </tr> 1719 <tr> 1720 <td><a href="#t_primitive">primitive</a></td> 1721 <td><a href="#t_label">label</a>, 1722 <a href="#t_void">void</a>, 1723 <a href="#t_integer">integer</a>, 1724 <a href="#t_floating">floating point</a>, 1725 <a href="#t_x86mmx">x86mmx</a>, 1726 <a href="#t_metadata">metadata</a>.</td> 1727 </tr> 1728 <tr> 1729 <td><a href="#t_derived">derived</a></td> 1730 <td><a href="#t_array">array</a>, 1731 <a href="#t_function">function</a>, 1732 <a href="#t_pointer">pointer</a>, 1733 <a href="#t_struct">structure</a>, 1734 <a href="#t_vector">vector</a>, 1735 <a href="#t_opaque">opaque</a>. 1736 </td> 1737 </tr> 1738 </tbody> 1739 </table> 1740 1741 <p>The <a href="#t_firstclass">first class</a> types are perhaps the most 1742 important. Values of these types are the only ones which can be produced by 1743 instructions.</p> 1744 1745 </div> 1746 1747 <!-- ======================================================================= --> 1748 <h3> 1749 <a name="t_primitive">Primitive Types</a> 1750 </h3> 1751 1752 <div> 1753 1754 <p>The primitive types are the fundamental building blocks of the LLVM 1755 system.</p> 1756 1757 <!-- _______________________________________________________________________ --> 1758 <h4> 1759 <a name="t_integer">Integer Type</a> 1760 </h4> 1761 1762 <div> 1763 1764 <h5>Overview:</h5> 1765 <p>The integer type is a very simple type that simply specifies an arbitrary 1766 bit width for the integer type desired. Any bit width from 1 bit to 1767 2<sup>23</sup>-1 (about 8 million) can be specified.</p> 1768 1769 <h5>Syntax:</h5> 1770 <pre> 1771 iN 1772 </pre> 1773 1774 <p>The number of bits the integer will occupy is specified by the <tt>N</tt> 1775 value.</p> 1776 1777 <h5>Examples:</h5> 1778 <table class="layout"> 1779 <tr class="layout"> 1780 <td class="left"><tt>i1</tt></td> 1781 <td class="left">a single-bit integer.</td> 1782 </tr> 1783 <tr class="layout"> 1784 <td class="left"><tt>i32</tt></td> 1785 <td class="left">a 32-bit integer.</td> 1786 </tr> 1787 <tr class="layout"> 1788 <td class="left"><tt>i1942652</tt></td> 1789 <td class="left">a really big integer of over 1 million bits.</td> 1790 </tr> 1791 </table> 1792 1793 </div> 1794 1795 <!-- _______________________________________________________________________ --> 1796 <h4> 1797 <a name="t_floating">Floating Point Types</a> 1798 </h4> 1799 1800 <div> 1801 1802 <table> 1803 <tbody> 1804 <tr><th>Type</th><th>Description</th></tr> 1805 <tr><td><tt>float</tt></td><td>32-bit floating point value</td></tr> 1806 <tr><td><tt>double</tt></td><td>64-bit floating point value</td></tr> 1807 <tr><td><tt>fp128</tt></td><td>128-bit floating point value (112-bit mantissa)</td></tr> 1808 <tr><td><tt>x86_fp80</tt></td><td>80-bit floating point value (X87)</td></tr> 1809 <tr><td><tt>ppc_fp128</tt></td><td>128-bit floating point value (two 64-bits)</td></tr> 1810 </tbody> 1811 </table> 1812 1813 </div> 1814 1815 <!-- _______________________________________________________________________ --> 1816 <h4> 1817 <a name="t_x86mmx">X86mmx Type</a> 1818 </h4> 1819 1820 <div> 1821 1822 <h5>Overview:</h5> 1823 <p>The x86mmx type represents a value held in an MMX register on an x86 machine. The operations allowed on it are quite limited: parameters and return values, load and store, and bitcast. User-specified MMX instructions are represented as intrinsic or asm calls with arguments and/or results of this type. There are no arrays, vectors or constants of this type.</p> 1824 1825 <h5>Syntax:</h5> 1826 <pre> 1827 x86mmx 1828 </pre> 1829 1830 </div> 1831 1832 <!-- _______________________________________________________________________ --> 1833 <h4> 1834 <a name="t_void">Void Type</a> 1835 </h4> 1836 1837 <div> 1838 1839 <h5>Overview:</h5> 1840 <p>The void type does not represent any value and has no size.</p> 1841 1842 <h5>Syntax:</h5> 1843 <pre> 1844 void 1845 </pre> 1846 1847 </div> 1848 1849 <!-- _______________________________________________________________________ --> 1850 <h4> 1851 <a name="t_label">Label Type</a> 1852 </h4> 1853 1854 <div> 1855 1856 <h5>Overview:</h5> 1857 <p>The label type represents code labels.</p> 1858 1859 <h5>Syntax:</h5> 1860 <pre> 1861 label 1862 </pre> 1863 1864 </div> 1865 1866 <!-- _______________________________________________________________________ --> 1867 <h4> 1868 <a name="t_metadata">Metadata Type</a> 1869 </h4> 1870 1871 <div> 1872 1873 <h5>Overview:</h5> 1874 <p>The metadata type represents embedded metadata. No derived types may be 1875 created from metadata except for <a href="#t_function">function</a> 1876 arguments. 1877 1878 <h5>Syntax:</h5> 1879 <pre> 1880 metadata 1881 </pre> 1882 1883 </div> 1884 1885 </div> 1886 1887 <!-- ======================================================================= --> 1888 <h3> 1889 <a name="t_derived">Derived Types</a> 1890 </h3> 1891 1892 <div> 1893 1894 <p>The real power in LLVM comes from the derived types in the system. This is 1895 what allows a programmer to represent arrays, functions, pointers, and other 1896 useful types. Each of these types contain one or more element types which 1897 may be a primitive type, or another derived type. For example, it is 1898 possible to have a two dimensional array, using an array as the element type 1899 of another array.</p> 1900 1901 </div> 1902 1903 1904 <!-- _______________________________________________________________________ --> 1905 <h4> 1906 <a name="t_aggregate">Aggregate Types</a> 1907 </h4> 1908 1909 <div> 1910 1911 <p>Aggregate Types are a subset of derived types that can contain multiple 1912 member types. <a href="#t_array">Arrays</a>, 1913 <a href="#t_struct">structs</a>, and <a href="#t_vector">vectors</a> are 1914 aggregate types.</p> 1915 1916 </div> 1917 1918 <!-- _______________________________________________________________________ --> 1919 <h4> 1920 <a name="t_array">Array Type</a> 1921 </h4> 1922 1923 <div> 1924 1925 <h5>Overview:</h5> 1926 <p>The array type is a very simple derived type that arranges elements 1927 sequentially in memory. The array type requires a size (number of elements) 1928 and an underlying data type.</p> 1929 1930 <h5>Syntax:</h5> 1931 <pre> 1932 [<# elements> x <elementtype>] 1933 </pre> 1934 1935 <p>The number of elements is a constant integer value; <tt>elementtype</tt> may 1936 be any type with a size.</p> 1937 1938 <h5>Examples:</h5> 1939 <table class="layout"> 1940 <tr class="layout"> 1941 <td class="left"><tt>[40 x i32]</tt></td> 1942 <td class="left">Array of 40 32-bit integer values.</td> 1943 </tr> 1944 <tr class="layout"> 1945 <td class="left"><tt>[41 x i32]</tt></td> 1946 <td class="left">Array of 41 32-bit integer values.</td> 1947 </tr> 1948 <tr class="layout"> 1949 <td class="left"><tt>[4 x i8]</tt></td> 1950 <td class="left">Array of 4 8-bit integer values.</td> 1951 </tr> 1952 </table> 1953 <p>Here are some examples of multidimensional arrays:</p> 1954 <table class="layout"> 1955 <tr class="layout"> 1956 <td class="left"><tt>[3 x [4 x i32]]</tt></td> 1957 <td class="left">3x4 array of 32-bit integer values.</td> 1958 </tr> 1959 <tr class="layout"> 1960 <td class="left"><tt>[12 x [10 x float]]</tt></td> 1961 <td class="left">12x10 array of single precision floating point values.</td> 1962 </tr> 1963 <tr class="layout"> 1964 <td class="left"><tt>[2 x [3 x [4 x i16]]]</tt></td> 1965 <td class="left">2x3x4 array of 16-bit integer values.</td> 1966 </tr> 1967 </table> 1968 1969 <p>There is no restriction on indexing beyond the end of the array implied by 1970 a static type (though there are restrictions on indexing beyond the bounds 1971 of an allocated object in some cases). This means that single-dimension 1972 'variable sized array' addressing can be implemented in LLVM with a zero 1973 length array type. An implementation of 'pascal style arrays' in LLVM could 1974 use the type "<tt>{ i32, [0 x float]}</tt>", for example.</p> 1975 1976 </div> 1977 1978 <!-- _______________________________________________________________________ --> 1979 <h4> 1980 <a name="t_function">Function Type</a> 1981 </h4> 1982 1983 <div> 1984 1985 <h5>Overview:</h5> 1986 <p>The function type can be thought of as a function signature. It consists of 1987 a return type and a list of formal parameter types. The return type of a 1988 function type is a first class type or a void type.</p> 1989 1990 <h5>Syntax:</h5> 1991 <pre> 1992 <returntype> (<parameter list>) 1993 </pre> 1994 1995 <p>...where '<tt><parameter list></tt>' is a comma-separated list of type 1996 specifiers. Optionally, the parameter list may include a type <tt>...</tt>, 1997 which indicates that the function takes a variable number of arguments. 1998 Variable argument functions can access their arguments with 1999 the <a href="#int_varargs">variable argument handling intrinsic</a> 2000 functions. '<tt><returntype></tt>' is any type except 2001 <a href="#t_label">label</a>.</p> 2002 2003 <h5>Examples:</h5> 2004 <table class="layout"> 2005 <tr class="layout"> 2006 <td class="left"><tt>i32 (i32)</tt></td> 2007 <td class="left">function taking an <tt>i32</tt>, returning an <tt>i32</tt> 2008 </td> 2009 </tr><tr class="layout"> 2010 <td class="left"><tt>float (i16, i32 *) * 2011 </tt></td> 2012 <td class="left"><a href="#t_pointer">Pointer</a> to a function that takes 2013 an <tt>i16</tt> and a <a href="#t_pointer">pointer</a> to <tt>i32</tt>, 2014 returning <tt>float</tt>. 2015 </td> 2016 </tr><tr class="layout"> 2017 <td class="left"><tt>i32 (i8*, ...)</tt></td> 2018 <td class="left">A vararg function that takes at least one 2019 <a href="#t_pointer">pointer</a> to <tt>i8 </tt> (char in C), 2020 which returns an integer. This is the signature for <tt>printf</tt> in 2021 LLVM. 2022 </td> 2023 </tr><tr class="layout"> 2024 <td class="left"><tt>{i32, i32} (i32)</tt></td> 2025 <td class="left">A function taking an <tt>i32</tt>, returning a 2026 <a href="#t_struct">structure</a> containing two <tt>i32</tt> values 2027 </td> 2028 </tr> 2029 </table> 2030 2031 </div> 2032 2033 <!-- _______________________________________________________________________ --> 2034 <h4> 2035 <a name="t_struct">Structure Type</a> 2036 </h4> 2037 2038 <div> 2039 2040 <h5>Overview:</h5> 2041 <p>The structure type is used to represent a collection of data members together 2042 in memory. The elements of a structure may be any type that has a size.</p> 2043 2044 <p>Structures in memory are accessed using '<tt><a href="#i_load">load</a></tt>' 2045 and '<tt><a href="#i_store">store</a></tt>' by getting a pointer to a field 2046 with the '<tt><a href="#i_getelementptr">getelementptr</a></tt>' instruction. 2047 Structures in registers are accessed using the 2048 '<tt><a href="#i_extractvalue">extractvalue</a></tt>' and 2049 '<tt><a href="#i_insertvalue">insertvalue</a></tt>' instructions.</p> 2050 2051 <p>Structures may optionally be "packed" structures, which indicate that the 2052 alignment of the struct is one byte, and that there is no padding between 2053 the elements. In non-packed structs, padding between field types is inserted 2054 as defined by the TargetData string in the module, which is required to match 2055 what the underlying code generator expects.</p> 2056 2057 <p>Structures can either be "literal" or "identified". A literal structure is 2058 defined inline with other types (e.g. <tt>{i32, i32}*</tt>) whereas identified 2059 types are always defined at the top level with a name. Literal types are 2060 uniqued by their contents and can never be recursive or opaque since there is 2061 no way to write one. Identified types can be recursive, can be opaqued, and are 2062 never uniqued. 2063 </p> 2064 2065 <h5>Syntax:</h5> 2066 <pre> 2067 %T1 = type { <type list> } <i>; Identified normal struct type</i> 2068 %T2 = type <{ <type list> }> <i>; Identified packed struct type</i> 2069 </pre> 2070 2071 <h5>Examples:</h5> 2072 <table class="layout"> 2073 <tr class="layout"> 2074 <td class="left"><tt>{ i32, i32, i32 }</tt></td> 2075 <td class="left">A triple of three <tt>i32</tt> values</td> 2076 </tr> 2077 <tr class="layout"> 2078 <td class="left"><tt>{ float, i32 (i32) * }</tt></td> 2079 <td class="left">A pair, where the first element is a <tt>float</tt> and the 2080 second element is a <a href="#t_pointer">pointer</a> to a 2081 <a href="#t_function">function</a> that takes an <tt>i32</tt>, returning 2082 an <tt>i32</tt>.</td> 2083 </tr> 2084 <tr class="layout"> 2085 <td class="left"><tt><{ i8, i32 }></tt></td> 2086 <td class="left">A packed struct known to be 5 bytes in size.</td> 2087 </tr> 2088 </table> 2089 2090 </div> 2091 2092 <!-- _______________________________________________________________________ --> 2093 <h4> 2094 <a name="t_opaque">Opaque Structure Types</a> 2095 </h4> 2096 2097 <div> 2098 2099 <h5>Overview:</h5> 2100 <p>Opaque structure types are used to represent named structure types that do 2101 not have a body specified. This corresponds (for example) to the C notion of 2102 a forward declared structure.</p> 2103 2104 <h5>Syntax:</h5> 2105 <pre> 2106 %X = type opaque 2107 %52 = type opaque 2108 </pre> 2109 2110 <h5>Examples:</h5> 2111 <table class="layout"> 2112 <tr class="layout"> 2113 <td class="left"><tt>opaque</tt></td> 2114 <td class="left">An opaque type.</td> 2115 </tr> 2116 </table> 2117 2118 </div> 2119 2120 2121 2122 <!-- _______________________________________________________________________ --> 2123 <h4> 2124 <a name="t_pointer">Pointer Type</a> 2125 </h4> 2126 2127 <div> 2128 2129 <h5>Overview:</h5> 2130 <p>The pointer type is used to specify memory locations. 2131 Pointers are commonly used to reference objects in memory.</p> 2132 2133 <p>Pointer types may have an optional address space attribute defining the 2134 numbered address space where the pointed-to object resides. The default 2135 address space is number zero. The semantics of non-zero address 2136 spaces are target-specific.</p> 2137 2138 <p>Note that LLVM does not permit pointers to void (<tt>void*</tt>) nor does it 2139 permit pointers to labels (<tt>label*</tt>). Use <tt>i8*</tt> instead.</p> 2140 2141 <h5>Syntax:</h5> 2142 <pre> 2143 <type> * 2144 </pre> 2145 2146 <h5>Examples:</h5> 2147 <table class="layout"> 2148 <tr class="layout"> 2149 <td class="left"><tt>[4 x i32]*</tt></td> 2150 <td class="left">A <a href="#t_pointer">pointer</a> to <a 2151 href="#t_array">array</a> of four <tt>i32</tt> values.</td> 2152 </tr> 2153 <tr class="layout"> 2154 <td class="left"><tt>i32 (i32*) *</tt></td> 2155 <td class="left"> A <a href="#t_pointer">pointer</a> to a <a 2156 href="#t_function">function</a> that takes an <tt>i32*</tt>, returning an 2157 <tt>i32</tt>.</td> 2158 </tr> 2159 <tr class="layout"> 2160 <td class="left"><tt>i32 addrspace(5)*</tt></td> 2161 <td class="left">A <a href="#t_pointer">pointer</a> to an <tt>i32</tt> value 2162 that resides in address space #5.</td> 2163 </tr> 2164 </table> 2165 2166 </div> 2167 2168 <!-- _______________________________________________________________________ --> 2169 <h4> 2170 <a name="t_vector">Vector Type</a> 2171 </h4> 2172 2173 <div> 2174 2175 <h5>Overview:</h5> 2176 <p>A vector type is a simple derived type that represents a vector of elements. 2177 Vector types are used when multiple primitive data are operated in parallel 2178 using a single instruction (SIMD). A vector type requires a size (number of 2179 elements) and an underlying primitive data type. Vector types are considered 2180 <a href="#t_firstclass">first class</a>.</p> 2181 2182 <h5>Syntax:</h5> 2183 <pre> 2184 < <# elements> x <elementtype> > 2185 </pre> 2186 2187 <p>The number of elements is a constant integer value larger than 0; elementtype 2188 may be any integer or floating point type. Vectors of size zero are not 2189 allowed, and pointers are not allowed as the element type.</p> 2190 2191 <h5>Examples:</h5> 2192 <table class="layout"> 2193 <tr class="layout"> 2194 <td class="left"><tt><4 x i32></tt></td> 2195 <td class="left">Vector of 4 32-bit integer values.</td> 2196 </tr> 2197 <tr class="layout"> 2198 <td class="left"><tt><8 x float></tt></td> 2199 <td class="left">Vector of 8 32-bit floating-point values.</td> 2200 </tr> 2201 <tr class="layout"> 2202 <td class="left"><tt><2 x i64></tt></td> 2203 <td class="left">Vector of 2 64-bit integer values.</td> 2204 </tr> 2205 </table> 2206 2207 </div> 2208 2209 </div> 2210 2211 <!-- *********************************************************************** --> 2212 <h2><a name="constants">Constants</a></h2> 2213 <!-- *********************************************************************** --> 2214 2215 <div> 2216 2217 <p>LLVM has several different basic types of constants. This section describes 2218 them all and their syntax.</p> 2219 2220 <!-- ======================================================================= --> 2221 <h3> 2222 <a name="simpleconstants">Simple Constants</a> 2223 </h3> 2224 2225 <div> 2226 2227 <dl> 2228 <dt><b>Boolean constants</b></dt> 2229 <dd>The two strings '<tt>true</tt>' and '<tt>false</tt>' are both valid 2230 constants of the <tt><a href="#t_integer">i1</a></tt> type.</dd> 2231 2232 <dt><b>Integer constants</b></dt> 2233 <dd>Standard integers (such as '4') are constants of 2234 the <a href="#t_integer">integer</a> type. Negative numbers may be used 2235 with integer types.</dd> 2236 2237 <dt><b>Floating point constants</b></dt> 2238 <dd>Floating point constants use standard decimal notation (e.g. 123.421), 2239 exponential notation (e.g. 1.23421e+2), or a more precise hexadecimal 2240 notation (see below). The assembler requires the exact decimal value of a 2241 floating-point constant. For example, the assembler accepts 1.25 but 2242 rejects 1.3 because 1.3 is a repeating decimal in binary. Floating point 2243 constants must have a <a href="#t_floating">floating point</a> type. </dd> 2244 2245 <dt><b>Null pointer constants</b></dt> 2246 <dd>The identifier '<tt>null</tt>' is recognized as a null pointer constant 2247 and must be of <a href="#t_pointer">pointer type</a>.</dd> 2248 </dl> 2249 2250 <p>The one non-intuitive notation for constants is the hexadecimal form of 2251 floating point constants. For example, the form '<tt>double 2252 0x432ff973cafa8000</tt>' is equivalent to (but harder to read than) 2253 '<tt>double 4.5e+15</tt>'. The only time hexadecimal floating point 2254 constants are required (and the only time that they are generated by the 2255 disassembler) is when a floating point constant must be emitted but it cannot 2256 be represented as a decimal floating point number in a reasonable number of 2257 digits. For example, NaN's, infinities, and other special values are 2258 represented in their IEEE hexadecimal format so that assembly and disassembly 2259 do not cause any bits to change in the constants.</p> 2260 2261 <p>When using the hexadecimal form, constants of types float and double are 2262 represented using the 16-digit form shown above (which matches the IEEE754 2263 representation for double); float values must, however, be exactly 2264 representable as IEE754 single precision. Hexadecimal format is always used 2265 for long double, and there are three forms of long double. The 80-bit format 2266 used by x86 is represented as <tt>0xK</tt> followed by 20 hexadecimal digits. 2267 The 128-bit format used by PowerPC (two adjacent doubles) is represented 2268 by <tt>0xM</tt> followed by 32 hexadecimal digits. The IEEE 128-bit format 2269 is represented by <tt>0xL</tt> followed by 32 hexadecimal digits; no 2270 currently supported target uses this format. Long doubles will only work if 2271 they match the long double format on your target. All hexadecimal formats 2272 are big-endian (sign bit at the left).</p> 2273 2274 <p>There are no constants of type x86mmx.</p> 2275 </div> 2276 2277 <!-- ======================================================================= --> 2278 <h3> 2279 <a name="aggregateconstants"></a> <!-- old anchor --> 2280 <a name="complexconstants">Complex Constants</a> 2281 </h3> 2282 2283 <div> 2284 2285 <p>Complex constants are a (potentially recursive) combination of simple 2286 constants and smaller complex constants.</p> 2287 2288 <dl> 2289 <dt><b>Structure constants</b></dt> 2290 <dd>Structure constants are represented with notation similar to structure 2291 type definitions (a comma separated list of elements, surrounded by braces 2292 (<tt>{}</tt>)). For example: "<tt>{ i32 4, float 17.0, i32* @G }</tt>", 2293 where "<tt>@G</tt>" is declared as "<tt>@G = external global i32</tt>". 2294 Structure constants must have <a href="#t_struct">structure type</a>, and 2295 the number and types of elements must match those specified by the 2296 type.</dd> 2297 2298 <dt><b>Array constants</b></dt> 2299 <dd>Array constants are represented with notation similar to array type 2300 definitions (a comma separated list of elements, surrounded by square 2301 brackets (<tt>[]</tt>)). For example: "<tt>[ i32 42, i32 11, i32 74 2302 ]</tt>". Array constants must have <a href="#t_array">array type</a>, and 2303 the number and types of elements must match those specified by the 2304 type.</dd> 2305 2306 <dt><b>Vector constants</b></dt> 2307 <dd>Vector constants are represented with notation similar to vector type 2308 definitions (a comma separated list of elements, surrounded by 2309 less-than/greater-than's (<tt><></tt>)). For example: "<tt>< i32 2310 42, i32 11, i32 74, i32 100 ></tt>". Vector constants must 2311 have <a href="#t_vector">vector type</a>, and the number and types of 2312 elements must match those specified by the type.</dd> 2313 2314 <dt><b>Zero initialization</b></dt> 2315 <dd>The string '<tt>zeroinitializer</tt>' can be used to zero initialize a 2316 value to zero of <em>any</em> type, including scalar and 2317 <a href="#t_aggregate">aggregate</a> types. 2318 This is often used to avoid having to print large zero initializers 2319 (e.g. for large arrays) and is always exactly equivalent to using explicit 2320 zero initializers.</dd> 2321 2322 <dt><b>Metadata node</b></dt> 2323 <dd>A metadata node is a structure-like constant with 2324 <a href="#t_metadata">metadata type</a>. For example: "<tt>metadata !{ 2325 i32 0, metadata !"test" }</tt>". Unlike other constants that are meant to 2326 be interpreted as part of the instruction stream, metadata is a place to 2327 attach additional information such as debug info.</dd> 2328 </dl> 2329 2330 </div> 2331 2332 <!-- ======================================================================= --> 2333 <h3> 2334 <a name="globalconstants">Global Variable and Function Addresses</a> 2335 </h3> 2336 2337 <div> 2338 2339 <p>The addresses of <a href="#globalvars">global variables</a> 2340 and <a href="#functionstructure">functions</a> are always implicitly valid 2341 (link-time) constants. These constants are explicitly referenced when 2342 the <a href="#identifiers">identifier for the global</a> is used and always 2343 have <a href="#t_pointer">pointer</a> type. For example, the following is a 2344 legal LLVM file:</p> 2345 2346 <pre class="doc_code"> 2347 @X = global i32 17 2348 @Y = global i32 42 2349 @Z = global [2 x i32*] [ i32* @X, i32* @Y ] 2350 </pre> 2351 2352 </div> 2353 2354 <!-- ======================================================================= --> 2355 <h3> 2356 <a name="undefvalues">Undefined Values</a> 2357 </h3> 2358 2359 <div> 2360 2361 <p>The string '<tt>undef</tt>' can be used anywhere a constant is expected, and 2362 indicates that the user of the value may receive an unspecified bit-pattern. 2363 Undefined values may be of any type (other than '<tt>label</tt>' 2364 or '<tt>void</tt>') and be used anywhere a constant is permitted.</p> 2365 2366 <p>Undefined values are useful because they indicate to the compiler that the 2367 program is well defined no matter what value is used. This gives the 2368 compiler more freedom to optimize. Here are some examples of (potentially 2369 surprising) transformations that are valid (in pseudo IR):</p> 2370 2371 2372 <pre class="doc_code"> 2373 %A = add %X, undef 2374 %B = sub %X, undef 2375 %C = xor %X, undef 2376 Safe: 2377 %A = undef 2378 %B = undef 2379 %C = undef 2380 </pre> 2381 2382 <p>This is safe because all of the output bits are affected by the undef bits. 2383 Any output bit can have a zero or one depending on the input bits.</p> 2384 2385 <pre class="doc_code"> 2386 %A = or %X, undef 2387 %B = and %X, undef 2388 Safe: 2389 %A = -1 2390 %B = 0 2391 Unsafe: 2392 %A = undef 2393 %B = undef 2394 </pre> 2395 2396 <p>These logical operations have bits that are not always affected by the input. 2397 For example, if <tt>%X</tt> has a zero bit, then the output of the 2398 '<tt>and</tt>' operation will always be a zero for that bit, no matter what 2399 the corresponding bit from the '<tt>undef</tt>' is. As such, it is unsafe to 2400 optimize or assume that the result of the '<tt>and</tt>' is '<tt>undef</tt>'. 2401 However, it is safe to assume that all bits of the '<tt>undef</tt>' could be 2402 0, and optimize the '<tt>and</tt>' to 0. Likewise, it is safe to assume that 2403 all the bits of the '<tt>undef</tt>' operand to the '<tt>or</tt>' could be 2404 set, allowing the '<tt>or</tt>' to be folded to -1.</p> 2405 2406 <pre class="doc_code"> 2407 %A = select undef, %X, %Y 2408 %B = select undef, 42, %Y 2409 %C = select %X, %Y, undef 2410 Safe: 2411 %A = %X (or %Y) 2412 %B = 42 (or %Y) 2413 %C = %Y 2414 Unsafe: 2415 %A = undef 2416 %B = undef 2417 %C = undef 2418 </pre> 2419 2420 <p>This set of examples shows that undefined '<tt>select</tt>' (and conditional 2421 branch) conditions can go <em>either way</em>, but they have to come from one 2422 of the two operands. In the <tt>%A</tt> example, if <tt>%X</tt> and 2423 <tt>%Y</tt> were both known to have a clear low bit, then <tt>%A</tt> would 2424 have to have a cleared low bit. However, in the <tt>%C</tt> example, the 2425 optimizer is allowed to assume that the '<tt>undef</tt>' operand could be the 2426 same as <tt>%Y</tt>, allowing the whole '<tt>select</tt>' to be 2427 eliminated.</p> 2428 2429 <pre class="doc_code"> 2430 %A = xor undef, undef 2431 2432 %B = undef 2433 %C = xor %B, %B 2434 2435 %D = undef 2436 %E = icmp lt %D, 4 2437 %F = icmp gte %D, 4 2438 2439 Safe: 2440 %A = undef 2441 %B = undef 2442 %C = undef 2443 %D = undef 2444 %E = undef 2445 %F = undef 2446 </pre> 2447 2448 <p>This example points out that two '<tt>undef</tt>' operands are not 2449 necessarily the same. This can be surprising to people (and also matches C 2450 semantics) where they assume that "<tt>X^X</tt>" is always zero, even 2451 if <tt>X</tt> is undefined. This isn't true for a number of reasons, but the 2452 short answer is that an '<tt>undef</tt>' "variable" can arbitrarily change 2453 its value over its "live range". This is true because the variable doesn't 2454 actually <em>have a live range</em>. Instead, the value is logically read 2455 from arbitrary registers that happen to be around when needed, so the value 2456 is not necessarily consistent over time. In fact, <tt>%A</tt> and <tt>%C</tt> 2457 need to have the same semantics or the core LLVM "replace all uses with" 2458 concept would not hold.</p> 2459 2460 <pre class="doc_code"> 2461 %A = fdiv undef, %X 2462 %B = fdiv %X, undef 2463 Safe: 2464 %A = undef 2465 b: unreachable 2466 </pre> 2467 2468 <p>These examples show the crucial difference between an <em>undefined 2469 value</em> and <em>undefined behavior</em>. An undefined value (like 2470 '<tt>undef</tt>') is allowed to have an arbitrary bit-pattern. This means that 2471 the <tt>%A</tt> operation can be constant folded to '<tt>undef</tt>', because 2472 the '<tt>undef</tt>' could be an SNaN, and <tt>fdiv</tt> is not (currently) 2473 defined on SNaN's. However, in the second example, we can make a more 2474 aggressive assumption: because the <tt>undef</tt> is allowed to be an 2475 arbitrary value, we are allowed to assume that it could be zero. Since a 2476 divide by zero has <em>undefined behavior</em>, we are allowed to assume that 2477 the operation does not execute at all. This allows us to delete the divide and 2478 all code after it. Because the undefined operation "can't happen", the 2479 optimizer can assume that it occurs in dead code.</p> 2480 2481 <pre class="doc_code"> 2482 a: store undef -> %X 2483 b: store %X -> undef 2484 Safe: 2485 a: <deleted> 2486 b: unreachable 2487 </pre> 2488 2489 <p>These examples reiterate the <tt>fdiv</tt> example: a store <em>of</em> an 2490 undefined value can be assumed to not have any effect; we can assume that the 2491 value is overwritten with bits that happen to match what was already there. 2492 However, a store <em>to</em> an undefined location could clobber arbitrary 2493 memory, therefore, it has undefined behavior.</p> 2494 2495 </div> 2496 2497 <!-- ======================================================================= --> 2498 <h3> 2499 <a name="trapvalues">Trap Values</a> 2500 </h3> 2501 2502 <div> 2503 2504 <p>Trap values are similar to <a href="#undefvalues">undef values</a>, however 2505 instead of representing an unspecified bit pattern, they represent the 2506 fact that an instruction or constant expression which cannot evoke side 2507 effects has nevertheless detected a condition which results in undefined 2508 behavior.</p> 2509 2510 <p>There is currently no way of representing a trap value in the IR; they 2511 only exist when produced by operations such as 2512 <a href="#i_add"><tt>add</tt></a> with the <tt>nsw</tt> flag.</p> 2513 2514 <p>Trap value behavior is defined in terms of value <i>dependence</i>:</p> 2515 2516 <ul> 2517 <li>Values other than <a href="#i_phi"><tt>phi</tt></a> nodes depend on 2518 their operands.</li> 2519 2520 <li><a href="#i_phi"><tt>Phi</tt></a> nodes depend on the operand corresponding 2521 to their dynamic predecessor basic block.</li> 2522 2523 <li>Function arguments depend on the corresponding actual argument values in 2524 the dynamic callers of their functions.</li> 2525 2526 <li><a href="#i_call"><tt>Call</tt></a> instructions depend on the 2527 <a href="#i_ret"><tt>ret</tt></a> instructions that dynamically transfer 2528 control back to them.</li> 2529 2530 <li><a href="#i_invoke"><tt>Invoke</tt></a> instructions depend on the 2531 <a href="#i_ret"><tt>ret</tt></a>, <a href="#i_unwind"><tt>unwind</tt></a>, 2532 or exception-throwing call instructions that dynamically transfer control 2533 back to them.</li> 2534 2535 <li>Non-volatile loads and stores depend on the most recent stores to all of the 2536 referenced memory addresses, following the order in the IR 2537 (including loads and stores implied by intrinsics such as 2538 <a href="#int_memcpy"><tt>@llvm.memcpy</tt></a>.)</li> 2539 2540 <!-- TODO: In the case of multiple threads, this only applies if the store 2541 "happens-before" the load or store. --> 2542 2543 <!-- TODO: floating-point exception state --> 2544 2545 <li>An instruction with externally visible side effects depends on the most 2546 recent preceding instruction with externally visible side effects, following 2547 the order in the IR. (This includes 2548 <a href="#volatile">volatile operations</a>.)</li> 2549 2550 <li>An instruction <i>control-depends</i> on a 2551 <a href="#terminators">terminator instruction</a> 2552 if the terminator instruction has multiple successors and the instruction 2553 is always executed when control transfers to one of the successors, and 2554 may not be executed when control is transferred to another.</li> 2555 2556 <li>Additionally, an instruction also <i>control-depends</i> on a terminator 2557 instruction if the set of instructions it otherwise depends on would be 2558 different if the terminator had transferred control to a different 2559 successor.</li> 2560 2561 <li>Dependence is transitive.</li> 2562 2563 </ul> 2564 2565 <p>Whenever a trap value is generated, all values which depend on it evaluate 2566 to trap. If they have side effects, they evoke their side effects as if each 2567 operand with a trap value were undef. If they have externally-visible side 2568 effects, the behavior is undefined.</p> 2569 2570 <p>Here are some examples:</p> 2571 2572 <pre class="doc_code"> 2573 entry: 2574 %trap = sub nuw i32 0, 1 ; Results in a trap value. 2575 %still_trap = and i32 %trap, 0 ; Whereas (and i32 undef, 0) would return 0. 2576 %trap_yet_again = getelementptr i32* @h, i32 %still_trap 2577 store i32 0, i32* %trap_yet_again ; undefined behavior 2578 2579 store i32 %trap, i32* @g ; Trap value conceptually stored to memory. 2580 %trap2 = load i32* @g ; Returns a trap value, not just undef. 2581 2582 volatile store i32 %trap, i32* @g ; External observation; undefined behavior. 2583 2584 %narrowaddr = bitcast i32* @g to i16* 2585 %wideaddr = bitcast i32* @g to i64* 2586 %trap3 = load i16* %narrowaddr ; Returns a trap value. 2587 %trap4 = load i64* %wideaddr ; Returns a trap value. 2588 2589 %cmp = icmp slt i32 %trap, 0 ; Returns a trap value. 2590 br i1 %cmp, label %true, label %end ; Branch to either destination. 2591 2592 true: 2593 volatile store i32 0, i32* @g ; This is control-dependent on %cmp, so 2594 ; it has undefined behavior. 2595 br label %end 2596 2597 end: 2598 %p = phi i32 [ 0, %entry ], [ 1, %true ] 2599 ; Both edges into this PHI are 2600 ; control-dependent on %cmp, so this 2601 ; always results in a trap value. 2602 2603 volatile store i32 0, i32* @g ; This would depend on the store in %true 2604 ; if %cmp is true, or the store in %entry 2605 ; otherwise, so this is undefined behavior. 2606 2607 br i1 %cmp, label %second_true, label %second_end 2608 ; The same branch again, but this time the 2609 ; true block doesn't have side effects. 2610 2611 second_true: 2612 ; No side effects! 2613 ret void 2614 2615 second_end: 2616 volatile store i32 0, i32* @g ; This time, the instruction always depends 2617 ; on the store in %end. Also, it is 2618 ; control-equivalent to %end, so this is 2619 ; well-defined (again, ignoring earlier 2620 ; undefined behavior in this example). 2621 </pre> 2622 2623 </div> 2624 2625 <!-- ======================================================================= --> 2626 <h3> 2627 <a name="blockaddress">Addresses of Basic Blocks</a> 2628 </h3> 2629 2630 <div> 2631 2632 <p><b><tt>blockaddress(@function, %block)</tt></b></p> 2633 2634 <p>The '<tt>blockaddress</tt>' constant computes the address of the specified 2635 basic block in the specified function, and always has an i8* type. Taking 2636 the address of the entry block is illegal.</p> 2637 2638 <p>This value only has defined behavior when used as an operand to the 2639 '<a href="#i_indirectbr"><tt>indirectbr</tt></a>' instruction, or for 2640 comparisons against null. Pointer equality tests between labels addresses 2641 results in undefined behavior — though, again, comparison against null 2642 is ok, and no label is equal to the null pointer. This may be passed around 2643 as an opaque pointer sized value as long as the bits are not inspected. This 2644 allows <tt>ptrtoint</tt> and arithmetic to be performed on these values so 2645 long as the original value is reconstituted before the <tt>indirectbr</tt> 2646 instruction.</p> 2647 2648 <p>Finally, some targets may provide defined semantics when using the value as 2649 the operand to an inline assembly, but that is target specific.</p> 2650 2651 </div> 2652 2653 2654 <!-- ======================================================================= --> 2655 <h3> 2656 <a name="constantexprs">Constant Expressions</a> 2657 </h3> 2658 2659 <div> 2660 2661 <p>Constant expressions are used to allow expressions involving other constants 2662 to be used as constants. Constant expressions may be of 2663 any <a href="#t_firstclass">first class</a> type and may involve any LLVM 2664 operation that does not have side effects (e.g. load and call are not 2665 supported). The following is the syntax for constant expressions:</p> 2666 2667 <dl> 2668 <dt><b><tt>trunc (CST to TYPE)</tt></b></dt> 2669 <dd>Truncate a constant to another type. The bit size of CST must be larger 2670 than the bit size of TYPE. Both types must be integers.</dd> 2671 2672 <dt><b><tt>zext (CST to TYPE)</tt></b></dt> 2673 <dd>Zero extend a constant to another type. The bit size of CST must be 2674 smaller than the bit size of TYPE. Both types must be integers.</dd> 2675 2676 <dt><b><tt>sext (CST to TYPE)</tt></b></dt> 2677 <dd>Sign extend a constant to another type. The bit size of CST must be 2678 smaller than the bit size of TYPE. Both types must be integers.</dd> 2679 2680 <dt><b><tt>fptrunc (CST to TYPE)</tt></b></dt> 2681 <dd>Truncate a floating point constant to another floating point type. The 2682 size of CST must be larger than the size of TYPE. Both types must be 2683 floating point.</dd> 2684 2685 <dt><b><tt>fpext (CST to TYPE)</tt></b></dt> 2686 <dd>Floating point extend a constant to another type. The size of CST must be 2687 smaller or equal to the size of TYPE. Both types must be floating 2688 point.</dd> 2689 2690 <dt><b><tt>fptoui (CST to TYPE)</tt></b></dt> 2691 <dd>Convert a floating point constant to the corresponding unsigned integer 2692 constant. TYPE must be a scalar or vector integer type. CST must be of 2693 scalar or vector floating point type. Both CST and TYPE must be scalars, 2694 or vectors of the same number of elements. If the value won't fit in the 2695 integer type, the results are undefined.</dd> 2696 2697 <dt><b><tt>fptosi (CST to TYPE)</tt></b></dt> 2698 <dd>Convert a floating point constant to the corresponding signed integer 2699 constant. TYPE must be a scalar or vector integer type. CST must be of 2700 scalar or vector floating point type. Both CST and TYPE must be scalars, 2701 or vectors of the same number of elements. If the value won't fit in the 2702 integer type, the results are undefined.</dd> 2703 2704 <dt><b><tt>uitofp (CST to TYPE)</tt></b></dt> 2705 <dd>Convert an unsigned integer constant to the corresponding floating point 2706 constant. TYPE must be a scalar or vector floating point type. CST must be 2707 of scalar or vector integer type. Both CST and TYPE must be scalars, or 2708 vectors of the same number of elements. If the value won't fit in the 2709 floating point type, the results are undefined.</dd> 2710 2711 <dt><b><tt>sitofp (CST to TYPE)</tt></b></dt> 2712 <dd>Convert a signed integer constant to the corresponding floating point 2713 constant. TYPE must be a scalar or vector floating point type. CST must be 2714 of scalar or vector integer type. Both CST and TYPE must be scalars, or 2715 vectors of the same number of elements. If the value won't fit in the 2716 floating point type, the results are undefined.</dd> 2717 2718 <dt><b><tt>ptrtoint (CST to TYPE)</tt></b></dt> 2719 <dd>Convert a pointer typed constant to the corresponding integer constant 2720 <tt>TYPE</tt> must be an integer type. <tt>CST</tt> must be of pointer 2721 type. The <tt>CST</tt> value is zero extended, truncated, or unchanged to 2722 make it fit in <tt>TYPE</tt>.</dd> 2723 2724 <dt><b><tt>inttoptr (CST to TYPE)</tt></b></dt> 2725 <dd>Convert a integer constant to a pointer constant. TYPE must be a pointer 2726 type. CST must be of integer type. The CST value is zero extended, 2727 truncated, or unchanged to make it fit in a pointer size. This one is 2728 <i>really</i> dangerous!</dd> 2729 2730 <dt><b><tt>bitcast (CST to TYPE)</tt></b></dt> 2731 <dd>Convert a constant, CST, to another TYPE. The constraints of the operands 2732 are the same as those for the <a href="#i_bitcast">bitcast 2733 instruction</a>.</dd> 2734 2735 <dt><b><tt>getelementptr (CSTPTR, IDX0, IDX1, ...)</tt></b></dt> 2736 <dt><b><tt>getelementptr inbounds (CSTPTR, IDX0, IDX1, ...)</tt></b></dt> 2737 <dd>Perform the <a href="#i_getelementptr">getelementptr operation</a> on 2738 constants. As with the <a href="#i_getelementptr">getelementptr</a> 2739 instruction, the index list may have zero or more indexes, which are 2740 required to make sense for the type of "CSTPTR".</dd> 2741 2742 <dt><b><tt>select (COND, VAL1, VAL2)</tt></b></dt> 2743 <dd>Perform the <a href="#i_select">select operation</a> on constants.</dd> 2744 2745 <dt><b><tt>icmp COND (VAL1, VAL2)</tt></b></dt> 2746 <dd>Performs the <a href="#i_icmp">icmp operation</a> on constants.</dd> 2747 2748 <dt><b><tt>fcmp COND (VAL1, VAL2)</tt></b></dt> 2749 <dd>Performs the <a href="#i_fcmp">fcmp operation</a> on constants.</dd> 2750 2751 <dt><b><tt>extractelement (VAL, IDX)</tt></b></dt> 2752 <dd>Perform the <a href="#i_extractelement">extractelement operation</a> on 2753 constants.</dd> 2754 2755 <dt><b><tt>insertelement (VAL, ELT, IDX)</tt></b></dt> 2756 <dd>Perform the <a href="#i_insertelement">insertelement operation</a> on 2757 constants.</dd> 2758 2759 <dt><b><tt>shufflevector (VEC1, VEC2, IDXMASK)</tt></b></dt> 2760 <dd>Perform the <a href="#i_shufflevector">shufflevector operation</a> on 2761 constants.</dd> 2762 2763 <dt><b><tt>extractvalue (VAL, IDX0, IDX1, ...)</tt></b></dt> 2764 <dd>Perform the <a href="#i_extractvalue">extractvalue operation</a> on 2765 constants. The index list is interpreted in a similar manner as indices in 2766 a '<a href="#i_getelementptr">getelementptr</a>' operation. At least one 2767 index value must be specified.</dd> 2768 2769 <dt><b><tt>insertvalue (VAL, ELT, IDX0, IDX1, ...)</tt></b></dt> 2770 <dd>Perform the <a href="#i_insertvalue">insertvalue operation</a> on 2771 constants. The index list is interpreted in a similar manner as indices in 2772 a '<a href="#i_getelementptr">getelementptr</a>' operation. At least one 2773 index value must be specified.</dd> 2774 2775 <dt><b><tt>OPCODE (LHS, RHS)</tt></b></dt> 2776 <dd>Perform the specified operation of the LHS and RHS constants. OPCODE may 2777 be any of the <a href="#binaryops">binary</a> 2778 or <a href="#bitwiseops">bitwise binary</a> operations. The constraints 2779 on operands are the same as those for the corresponding instruction 2780 (e.g. no bitwise operations on floating point values are allowed).</dd> 2781 </dl> 2782 2783 </div> 2784 2785 </div> 2786 2787 <!-- *********************************************************************** --> 2788 <h2><a name="othervalues">Other Values</a></h2> 2789 <!-- *********************************************************************** --> 2790 <div> 2791 <!-- ======================================================================= --> 2792 <h3> 2793 <a name="inlineasm">Inline Assembler Expressions</a> 2794 </h3> 2795 2796 <div> 2797 2798 <p>LLVM supports inline assembler expressions (as opposed 2799 to <a href="#moduleasm"> Module-Level Inline Assembly</a>) through the use of 2800 a special value. This value represents the inline assembler as a string 2801 (containing the instructions to emit), a list of operand constraints (stored 2802 as a string), a flag that indicates whether or not the inline asm 2803 expression has side effects, and a flag indicating whether the function 2804 containing the asm needs to align its stack conservatively. An example 2805 inline assembler expression is:</p> 2806 2807 <pre class="doc_code"> 2808 i32 (i32) asm "bswap $0", "=r,r" 2809 </pre> 2810 2811 <p>Inline assembler expressions may <b>only</b> be used as the callee operand of 2812 a <a href="#i_call"><tt>call</tt> instruction</a>. Thus, typically we 2813 have:</p> 2814 2815 <pre class="doc_code"> 2816 %X = call i32 asm "<a href="#int_bswap">bswap</a> $0", "=r,r"(i32 %Y) 2817 </pre> 2818 2819 <p>Inline asms with side effects not visible in the constraint list must be 2820 marked as having side effects. This is done through the use of the 2821 '<tt>sideeffect</tt>' keyword, like so:</p> 2822 2823 <pre class="doc_code"> 2824 call void asm sideeffect "eieio", ""() 2825 </pre> 2826 2827 <p>In some cases inline asms will contain code that will not work unless the 2828 stack is aligned in some way, such as calls or SSE instructions on x86, 2829 yet will not contain code that does that alignment within the asm. 2830 The compiler should make conservative assumptions about what the asm might 2831 contain and should generate its usual stack alignment code in the prologue 2832 if the '<tt>alignstack</tt>' keyword is present:</p> 2833 2834 <pre class="doc_code"> 2835 call void asm alignstack "eieio", ""() 2836 </pre> 2837 2838 <p>If both keywords appear the '<tt>sideeffect</tt>' keyword must come 2839 first.</p> 2840 2841 <p>TODO: The format of the asm and constraints string still need to be 2842 documented here. Constraints on what can be done (e.g. duplication, moving, 2843 etc need to be documented). This is probably best done by reference to 2844 another document that covers inline asm from a holistic perspective.</p> 2845 2846 <h4> 2847 <a name="inlineasm_md">Inline Asm Metadata</a> 2848 </h4> 2849 2850 <div> 2851 2852 <p>The call instructions that wrap inline asm nodes may have a "!srcloc" MDNode 2853 attached to it that contains a list of constant integers. If present, the 2854 code generator will use the integer as the location cookie value when report 2855 errors through the LLVMContext error reporting mechanisms. This allows a 2856 front-end to correlate backend errors that occur with inline asm back to the 2857 source code that produced it. For example:</p> 2858 2859 <pre class="doc_code"> 2860 call void asm sideeffect "something bad", ""()<b>, !srcloc !42</b> 2861 ... 2862 !42 = !{ i32 1234567 } 2863 </pre> 2864 2865 <p>It is up to the front-end to make sense of the magic numbers it places in the 2866 IR. If the MDNode contains multiple constants, the code generator will use 2867 the one that corresponds to the line of the asm that the error occurs on.</p> 2868 2869 </div> 2870 2871 </div> 2872 2873 <!-- ======================================================================= --> 2874 <h3> 2875 <a name="metadata">Metadata Nodes and Metadata Strings</a> 2876 </h3> 2877 2878 <div> 2879 2880 <p>LLVM IR allows metadata to be attached to instructions in the program that 2881 can convey extra information about the code to the optimizers and code 2882 generator. One example application of metadata is source-level debug 2883 information. There are two metadata primitives: strings and nodes. All 2884 metadata has the <tt>metadata</tt> type and is identified in syntax by a 2885 preceding exclamation point ('<tt>!</tt>').</p> 2886 2887 <p>A metadata string is a string surrounded by double quotes. It can contain 2888 any character by escaping non-printable characters with "\xx" where "xx" is 2889 the two digit hex code. For example: "<tt>!"test\00"</tt>".</p> 2890 2891 <p>Metadata nodes are represented with notation similar to structure constants 2892 (a comma separated list of elements, surrounded by braces and preceded by an 2893 exclamation point). For example: "<tt>!{ metadata !"test\00", i32 2894 10}</tt>". Metadata nodes can have any values as their operand.</p> 2895 2896 <p>A <a href="#namedmetadatastructure">named metadata</a> is a collection of 2897 metadata nodes, which can be looked up in the module symbol table. For 2898 example: "<tt>!foo = metadata !{!4, !3}</tt>". 2899 2900 <p>Metadata can be used as function arguments. Here <tt>llvm.dbg.value</tt> 2901 function is using two metadata arguments.</p> 2902 2903 <div class="doc_code"> 2904 <pre> 2905 call void @llvm.dbg.value(metadata !24, i64 0, metadata !25) 2906 </pre> 2907 </div> 2908 2909 <p>Metadata can be attached with an instruction. Here metadata <tt>!21</tt> is 2910 attached with <tt>add</tt> instruction using <tt>!dbg</tt> identifier.</p> 2911 2912 <div class="doc_code"> 2913 <pre> 2914 %indvar.next = add i64 %indvar, 1, !dbg !21 2915 </pre> 2916 </div> 2917 2918 </div> 2919 2920 </div> 2921 2922 <!-- *********************************************************************** --> 2923 <h2> 2924 <a name="intrinsic_globals">Intrinsic Global Variables</a> 2925 </h2> 2926 <!-- *********************************************************************** --> 2927 <div> 2928 <p>LLVM has a number of "magic" global variables that contain data that affect 2929 code generation or other IR semantics. These are documented here. All globals 2930 of this sort should have a section specified as "<tt>llvm.metadata</tt>". This 2931 section and all globals that start with "<tt>llvm.</tt>" are reserved for use 2932 by LLVM.</p> 2933 2934 <!-- ======================================================================= --> 2935 <h3> 2936 <a name="intg_used">The '<tt>llvm.used</tt>' Global Variable</a> 2937 </h3> 2938 2939 <div> 2940 2941 <p>The <tt>@llvm.used</tt> global is an array with i8* element type which has <a 2942 href="#linkage_appending">appending linkage</a>. This array contains a list of 2943 pointers to global variables and functions which may optionally have a pointer 2944 cast formed of bitcast or getelementptr. For example, a legal use of it is:</p> 2945 2946 <pre> 2947 @X = global i8 4 2948 @Y = global i32 123 2949 2950 @llvm.used = appending global [2 x i8*] [ 2951 i8* @X, 2952 i8* bitcast (i32* @Y to i8*) 2953 ], section "llvm.metadata" 2954 </pre> 2955 2956 <p>If a global variable appears in the <tt>@llvm.used</tt> list, then the 2957 compiler, assembler, and linker are required to treat the symbol as if there is 2958 a reference to the global that it cannot see. For example, if a variable has 2959 internal linkage and no references other than that from the <tt>@llvm.used</tt> 2960 list, it cannot be deleted. This is commonly used to represent references from 2961 inline asms and other things the compiler cannot "see", and corresponds to 2962 "attribute((used))" in GNU C.</p> 2963 2964 <p>On some targets, the code generator must emit a directive to the assembler or 2965 object file to prevent the assembler and linker from molesting the symbol.</p> 2966 2967 </div> 2968 2969 <!-- ======================================================================= --> 2970 <h3> 2971 <a name="intg_compiler_used"> 2972 The '<tt>llvm.compiler.used</tt>' Global Variable 2973 </a> 2974 </h3> 2975 2976 <div> 2977 2978 <p>The <tt>@llvm.compiler.used</tt> directive is the same as the 2979 <tt>@llvm.used</tt> directive, except that it only prevents the compiler from 2980 touching the symbol. On targets that support it, this allows an intelligent 2981 linker to optimize references to the symbol without being impeded as it would be 2982 by <tt>@llvm.used</tt>.</p> 2983 2984 <p>This is a rare construct that should only be used in rare circumstances, and 2985 should not be exposed to source languages.</p> 2986 2987 </div> 2988 2989 <!-- ======================================================================= --> 2990 <h3> 2991 <a name="intg_global_ctors">The '<tt>llvm.global_ctors</tt>' Global Variable</a> 2992 </h3> 2993 2994 <div> 2995 <pre> 2996 %0 = type { i32, void ()* } 2997 @llvm.global_ctors = appending global [1 x %0] [%0 { i32 65535, void ()* @ctor }] 2998 </pre> 2999 <p>The <tt>@llvm.global_ctors</tt> array contains a list of constructor functions and associated priorities. The functions referenced by this array will be called in ascending order of priority (i.e. lowest first) when the module is loaded. The order of functions with the same priority is not defined. 3000 </p> 3001 3002 </div> 3003 3004 <!-- ======================================================================= --> 3005 <h3> 3006 <a name="intg_global_dtors">The '<tt>llvm.global_dtors</tt>' Global Variable</a> 3007 </h3> 3008 3009 <div> 3010 <pre> 3011 %0 = type { i32, void ()* } 3012 @llvm.global_dtors = appending global [1 x %0] [%0 { i32 65535, void ()* @dtor }] 3013 </pre> 3014 3015 <p>The <tt>@llvm.global_dtors</tt> array contains a list of destructor functions and associated priorities. The functions referenced by this array will be called in descending order of priority (i.e. highest first) when the module is loaded. The order of functions with the same priority is not defined. 3016 </p> 3017 3018 </div> 3019 3020 </div> 3021 3022 <!-- *********************************************************************** --> 3023 <h2><a name="instref">Instruction Reference</a></h2> 3024 <!-- *********************************************************************** --> 3025 3026 <div> 3027 3028 <p>The LLVM instruction set consists of several different classifications of 3029 instructions: <a href="#terminators">terminator 3030 instructions</a>, <a href="#binaryops">binary instructions</a>, 3031 <a href="#bitwiseops">bitwise binary instructions</a>, 3032 <a href="#memoryops">memory instructions</a>, and 3033 <a href="#otherops">other instructions</a>.</p> 3034 3035 <!-- ======================================================================= --> 3036 <h3> 3037 <a name="terminators">Terminator Instructions</a> 3038 </h3> 3039 3040 <div> 3041 3042 <p>As mentioned <a href="#functionstructure">previously</a>, every basic block 3043 in a program ends with a "Terminator" instruction, which indicates which 3044 block should be executed after the current block is finished. These 3045 terminator instructions typically yield a '<tt>void</tt>' value: they produce 3046 control flow, not values (the one exception being the 3047 '<a href="#i_invoke"><tt>invoke</tt></a>' instruction).</p> 3048 3049 <p>The terminator instructions are: 3050 '<a href="#i_ret"><tt>ret</tt></a>', 3051 '<a href="#i_br"><tt>br</tt></a>', 3052 '<a href="#i_switch"><tt>switch</tt></a>', 3053 '<a href="#i_indirectbr"><tt>indirectbr</tt></a>', 3054 '<a href="#i_invoke"><tt>invoke</tt></a>', 3055 '<a href="#i_unwind"><tt>unwind</tt></a>', 3056 '<a href="#i_resume"><tt>resume</tt></a>', and 3057 '<a href="#i_unreachable"><tt>unreachable</tt></a>'.</p> 3058 3059 <!-- _______________________________________________________________________ --> 3060 <h4> 3061 <a name="i_ret">'<tt>ret</tt>' Instruction</a> 3062 </h4> 3063 3064 <div> 3065 3066 <h5>Syntax:</h5> 3067 <pre> 3068 ret <type> <value> <i>; Return a value from a non-void function</i> 3069 ret void <i>; Return from void function</i> 3070 </pre> 3071 3072 <h5>Overview:</h5> 3073 <p>The '<tt>ret</tt>' instruction is used to return control flow (and optionally 3074 a value) from a function back to the caller.</p> 3075 3076 <p>There are two forms of the '<tt>ret</tt>' instruction: one that returns a 3077 value and then causes control flow, and one that just causes control flow to 3078 occur.</p> 3079 3080 <h5>Arguments:</h5> 3081 <p>The '<tt>ret</tt>' instruction optionally accepts a single argument, the 3082 return value. The type of the return value must be a 3083 '<a href="#t_firstclass">first class</a>' type.</p> 3084 3085 <p>A function is not <a href="#wellformed">well formed</a> if it it has a 3086 non-void return type and contains a '<tt>ret</tt>' instruction with no return 3087 value or a return value with a type that does not match its type, or if it 3088 has a void return type and contains a '<tt>ret</tt>' instruction with a 3089 return value.</p> 3090 3091 <h5>Semantics:</h5> 3092 <p>When the '<tt>ret</tt>' instruction is executed, control flow returns back to 3093 the calling function's context. If the caller is a 3094 "<a href="#i_call"><tt>call</tt></a>" instruction, execution continues at the 3095 instruction after the call. If the caller was an 3096 "<a href="#i_invoke"><tt>invoke</tt></a>" instruction, execution continues at 3097 the beginning of the "normal" destination block. If the instruction returns 3098 a value, that value shall set the call or invoke instruction's return 3099 value.</p> 3100 3101 <h5>Example:</h5> 3102 <pre> 3103 ret i32 5 <i>; Return an integer value of 5</i> 3104 ret void <i>; Return from a void function</i> 3105 ret { i32, i8 } { i32 4, i8 2 } <i>; Return a struct of values 4 and 2</i> 3106 </pre> 3107 3108 </div> 3109 <!-- _______________________________________________________________________ --> 3110 <h4> 3111 <a name="i_br">'<tt>br</tt>' Instruction</a> 3112 </h4> 3113 3114 <div> 3115 3116 <h5>Syntax:</h5> 3117 <pre> 3118 br i1 <cond>, label <iftrue>, label <iffalse> 3119 br label <dest> <i>; Unconditional branch</i> 3120 </pre> 3121 3122 <h5>Overview:</h5> 3123 <p>The '<tt>br</tt>' instruction is used to cause control flow to transfer to a 3124 different basic block in the current function. There are two forms of this 3125 instruction, corresponding to a conditional branch and an unconditional 3126 branch.</p> 3127 3128 <h5>Arguments:</h5> 3129 <p>The conditional branch form of the '<tt>br</tt>' instruction takes a single 3130 '<tt>i1</tt>' value and two '<tt>label</tt>' values. The unconditional form 3131 of the '<tt>br</tt>' instruction takes a single '<tt>label</tt>' value as a 3132 target.</p> 3133 3134 <h5>Semantics:</h5> 3135 <p>Upon execution of a conditional '<tt>br</tt>' instruction, the '<tt>i1</tt>' 3136 argument is evaluated. If the value is <tt>true</tt>, control flows to the 3137 '<tt>iftrue</tt>' <tt>label</tt> argument. If "cond" is <tt>false</tt>, 3138 control flows to the '<tt>iffalse</tt>' <tt>label</tt> argument.</p> 3139 3140 <h5>Example:</h5> 3141 <pre> 3142 Test: 3143 %cond = <a href="#i_icmp">icmp</a> eq i32 %a, %b 3144 br i1 %cond, label %IfEqual, label %IfUnequal 3145 IfEqual: 3146 <a href="#i_ret">ret</a> i32 1 3147 IfUnequal: 3148 <a href="#i_ret">ret</a> i32 0 3149 </pre> 3150 3151 </div> 3152 3153 <!-- _______________________________________________________________________ --> 3154 <h4> 3155 <a name="i_switch">'<tt>switch</tt>' Instruction</a> 3156 </h4> 3157 3158 <div> 3159 3160 <h5>Syntax:</h5> 3161 <pre> 3162 switch <intty> <value>, label <defaultdest> [ <intty> <val>, label <dest> ... ] 3163 </pre> 3164 3165 <h5>Overview:</h5> 3166 <p>The '<tt>switch</tt>' instruction is used to transfer control flow to one of 3167 several different places. It is a generalization of the '<tt>br</tt>' 3168 instruction, allowing a branch to occur to one of many possible 3169 destinations.</p> 3170 3171 <h5>Arguments:</h5> 3172 <p>The '<tt>switch</tt>' instruction uses three parameters: an integer 3173 comparison value '<tt>value</tt>', a default '<tt>label</tt>' destination, 3174 and an array of pairs of comparison value constants and '<tt>label</tt>'s. 3175 The table is not allowed to contain duplicate constant entries.</p> 3176 3177 <h5>Semantics:</h5> 3178 <p>The <tt>switch</tt> instruction specifies a table of values and 3179 destinations. When the '<tt>switch</tt>' instruction is executed, this table 3180 is searched for the given value. If the value is found, control flow is 3181 transferred to the corresponding destination; otherwise, control flow is 3182 transferred to the default destination.</p> 3183 3184 <h5>Implementation:</h5> 3185 <p>Depending on properties of the target machine and the particular 3186 <tt>switch</tt> instruction, this instruction may be code generated in 3187 different ways. For example, it could be generated as a series of chained 3188 conditional branches or with a lookup table.</p> 3189 3190 <h5>Example:</h5> 3191 <pre> 3192 <i>; Emulate a conditional br instruction</i> 3193 %Val = <a href="#i_zext">zext</a> i1 %value to i32 3194 switch i32 %Val, label %truedest [ i32 0, label %falsedest ] 3195 3196 <i>; Emulate an unconditional br instruction</i> 3197 switch i32 0, label %dest [ ] 3198 3199 <i>; Implement a jump table:</i> 3200 switch i32 %val, label %otherwise [ i32 0, label %onzero 3201 i32 1, label %onone 3202 i32 2, label %ontwo ] 3203 </pre> 3204 3205 </div> 3206 3207 3208 <!-- _______________________________________________________________________ --> 3209 <h4> 3210 <a name="i_indirectbr">'<tt>indirectbr</tt>' Instruction</a> 3211 </h4> 3212 3213 <div> 3214 3215 <h5>Syntax:</h5> 3216 <pre> 3217 indirectbr <somety>* <address>, [ label <dest1>, label <dest2>, ... ] 3218 </pre> 3219 3220 <h5>Overview:</h5> 3221 3222 <p>The '<tt>indirectbr</tt>' instruction implements an indirect branch to a label 3223 within the current function, whose address is specified by 3224 "<tt>address</tt>". Address must be derived from a <a 3225 href="#blockaddress">blockaddress</a> constant.</p> 3226 3227 <h5>Arguments:</h5> 3228 3229 <p>The '<tt>address</tt>' argument is the address of the label to jump to. The 3230 rest of the arguments indicate the full set of possible destinations that the 3231 address may point to. Blocks are allowed to occur multiple times in the 3232 destination list, though this isn't particularly useful.</p> 3233 3234 <p>This destination list is required so that dataflow analysis has an accurate 3235 understanding of the CFG.</p> 3236 3237 <h5>Semantics:</h5> 3238 3239 <p>Control transfers to the block specified in the address argument. All 3240 possible destination blocks must be listed in the label list, otherwise this 3241 instruction has undefined behavior. This implies that jumps to labels 3242 defined in other functions have undefined behavior as well.</p> 3243 3244 <h5>Implementation:</h5> 3245 3246 <p>This is typically implemented with a jump through a register.</p> 3247 3248 <h5>Example:</h5> 3249 <pre> 3250 indirectbr i8* %Addr, [ label %bb1, label %bb2, label %bb3 ] 3251 </pre> 3252 3253 </div> 3254 3255 3256 <!-- _______________________________________________________________________ --> 3257 <h4> 3258 <a name="i_invoke">'<tt>invoke</tt>' Instruction</a> 3259 </h4> 3260 3261 <div> 3262 3263 <h5>Syntax:</h5> 3264 <pre> 3265 <result> = invoke [<a href="#callingconv">cconv</a>] [<a href="#paramattrs">ret attrs</a>] <ptr to function ty> <function ptr val>(<function args>) [<a href="#fnattrs">fn attrs</a>] 3266 to label <normal label> unwind label <exception label> 3267 </pre> 3268 3269 <h5>Overview:</h5> 3270 <p>The '<tt>invoke</tt>' instruction causes control to transfer to a specified 3271 function, with the possibility of control flow transfer to either the 3272 '<tt>normal</tt>' label or the '<tt>exception</tt>' label. If the callee 3273 function returns with the "<tt><a href="#i_ret">ret</a></tt>" instruction, 3274 control flow will return to the "normal" label. If the callee (or any 3275 indirect callees) returns with the "<a href="#i_unwind"><tt>unwind</tt></a>" 3276 instruction, control is interrupted and continued at the dynamically nearest 3277 "exception" label.</p> 3278 3279 <p>The '<tt>exception</tt>' label is a 3280 <i><a href="ExceptionHandling.html#overview">landing pad</a></i> for the 3281 exception. As such, '<tt>exception</tt>' label is required to have the 3282 "<a href="#i_landingpad"><tt>landingpad</tt></a>" instruction, which contains 3283 the information about about the behavior of the program after unwinding 3284 happens, as its first non-PHI instruction. The restrictions on the 3285 "<tt>landingpad</tt>" instruction's tightly couples it to the 3286 "<tt>invoke</tt>" instruction, so that the important information contained 3287 within the "<tt>landingpad</tt>" instruction can't be lost through normal 3288 code motion.</p> 3289 3290 <h5>Arguments:</h5> 3291 <p>This instruction requires several arguments:</p> 3292 3293 <ol> 3294 <li>The optional "cconv" marker indicates which <a href="#callingconv">calling 3295 convention</a> the call should use. If none is specified, the call 3296 defaults to using C calling conventions.</li> 3297 3298 <li>The optional <a href="#paramattrs">Parameter Attributes</a> list for 3299 return values. Only '<tt>zeroext</tt>', '<tt>signext</tt>', and 3300 '<tt>inreg</tt>' attributes are valid here.</li> 3301 3302 <li>'<tt>ptr to function ty</tt>': shall be the signature of the pointer to 3303 function value being invoked. In most cases, this is a direct function 3304 invocation, but indirect <tt>invoke</tt>s are just as possible, branching 3305 off an arbitrary pointer to function value.</li> 3306 3307 <li>'<tt>function ptr val</tt>': An LLVM value containing a pointer to a 3308 function to be invoked. </li> 3309 3310 <li>'<tt>function args</tt>': argument list whose types match the function 3311 signature argument types and parameter attributes. All arguments must be 3312 of <a href="#t_firstclass">first class</a> type. If the function 3313 signature indicates the function accepts a variable number of arguments, 3314 the extra arguments can be specified.</li> 3315 3316 <li>'<tt>normal label</tt>': the label reached when the called function 3317 executes a '<tt><a href="#i_ret">ret</a></tt>' instruction. </li> 3318 3319 <li>'<tt>exception label</tt>': the label reached when a callee returns with 3320 the <a href="#i_unwind"><tt>unwind</tt></a> instruction. </li> 3321 3322 <li>The optional <a href="#fnattrs">function attributes</a> list. Only 3323 '<tt>noreturn</tt>', '<tt>nounwind</tt>', '<tt>readonly</tt>' and 3324 '<tt>readnone</tt>' attributes are valid here.</li> 3325 </ol> 3326 3327 <h5>Semantics:</h5> 3328 <p>This instruction is designed to operate as a standard 3329 '<tt><a href="#i_call">call</a></tt>' instruction in most regards. The 3330 primary difference is that it establishes an association with a label, which 3331 is used by the runtime library to unwind the stack.</p> 3332 3333 <p>This instruction is used in languages with destructors to ensure that proper 3334 cleanup is performed in the case of either a <tt>longjmp</tt> or a thrown 3335 exception. Additionally, this is important for implementation of 3336 '<tt>catch</tt>' clauses in high-level languages that support them.</p> 3337 3338 <p>For the purposes of the SSA form, the definition of the value returned by the 3339 '<tt>invoke</tt>' instruction is deemed to occur on the edge from the current 3340 block to the "normal" label. If the callee unwinds then no return value is 3341 available.</p> 3342 3343 <p>Note that the code generator does not yet completely support unwind, and 3344 that the invoke/unwind semantics are likely to change in future versions.</p> 3345 3346 <h5>Example:</h5> 3347 <pre> 3348 %retval = invoke i32 @Test(i32 15) to label %Continue 3349 unwind label %TestCleanup <i>; {i32}:retval set</i> 3350 %retval = invoke <a href="#callingconv">coldcc</a> i32 %Testfnptr(i32 15) to label %Continue 3351 unwind label %TestCleanup <i>; {i32}:retval set</i> 3352 </pre> 3353 3354 </div> 3355 3356 <!-- _______________________________________________________________________ --> 3357 3358 <h4> 3359 <a name="i_unwind">'<tt>unwind</tt>' Instruction</a> 3360 </h4> 3361 3362 <div> 3363 3364 <h5>Syntax:</h5> 3365 <pre> 3366 unwind 3367 </pre> 3368 3369 <h5>Overview:</h5> 3370 <p>The '<tt>unwind</tt>' instruction unwinds the stack, continuing control flow 3371 at the first callee in the dynamic call stack which used 3372 an <a href="#i_invoke"><tt>invoke</tt></a> instruction to perform the call. 3373 This is primarily used to implement exception handling.</p> 3374 3375 <h5>Semantics:</h5> 3376 <p>The '<tt>unwind</tt>' instruction causes execution of the current function to 3377 immediately halt. The dynamic call stack is then searched for the 3378 first <a href="#i_invoke"><tt>invoke</tt></a> instruction on the call stack. 3379 Once found, execution continues at the "exceptional" destination block 3380 specified by the <tt>invoke</tt> instruction. If there is no <tt>invoke</tt> 3381 instruction in the dynamic call chain, undefined behavior results.</p> 3382 3383 <p>Note that the code generator does not yet completely support unwind, and 3384 that the invoke/unwind semantics are likely to change in future versions.</p> 3385 3386 </div> 3387 3388 <!-- _______________________________________________________________________ --> 3389 3390 <h4> 3391 <a name="i_resume">'<tt>resume</tt>' Instruction</a> 3392 </h4> 3393 3394 <div> 3395 3396 <h5>Syntax:</h5> 3397 <pre> 3398 resume <type> <value> 3399 </pre> 3400 3401 <h5>Overview:</h5> 3402 <p>The '<tt>resume</tt>' instruction is a terminator instruction that has no 3403 successors.</p> 3404 3405 <h5>Arguments:</h5> 3406 <p>The '<tt>resume</tt>' instruction requires one argument, which must have the 3407 same type as the result of any '<tt>landingpad</tt>' instruction in the same 3408 function.</p> 3409 3410 <h5>Semantics:</h5> 3411 <p>The '<tt>resume</tt>' instruction resumes propagation of an existing 3412 (in-flight) exception whose unwinding was interrupted with 3413 a <a href="#i_landingpad"><tt>landingpad</tt></a> instruction.</p> 3414 3415 <h5>Example:</h5> 3416 <pre> 3417 resume { i8*, i32 } %exn 3418 </pre> 3419 3420 </div> 3421 3422 <!-- _______________________________________________________________________ --> 3423 3424 <h4> 3425 <a name="i_unreachable">'<tt>unreachable</tt>' Instruction</a> 3426 </h4> 3427 3428 <div> 3429 3430 <h5>Syntax:</h5> 3431 <pre> 3432 unreachable 3433 </pre> 3434 3435 <h5>Overview:</h5> 3436 <p>The '<tt>unreachable</tt>' instruction has no defined semantics. This 3437 instruction is used to inform the optimizer that a particular portion of the 3438 code is not reachable. This can be used to indicate that the code after a 3439 no-return function cannot be reached, and other facts.</p> 3440 3441 <h5>Semantics:</h5> 3442 <p>The '<tt>unreachable</tt>' instruction has no defined semantics.</p> 3443 3444 </div> 3445 3446 </div> 3447 3448 <!-- ======================================================================= --> 3449 <h3> 3450 <a name="binaryops">Binary Operations</a> 3451 </h3> 3452 3453 <div> 3454 3455 <p>Binary operators are used to do most of the computation in a program. They 3456 require two operands of the same type, execute an operation on them, and 3457 produce a single value. The operands might represent multiple data, as is 3458 the case with the <a href="#t_vector">vector</a> data type. The result value 3459 has the same type as its operands.</p> 3460 3461 <p>There are several different binary operators:</p> 3462 3463 <!-- _______________________________________________________________________ --> 3464 <h4> 3465 <a name="i_add">'<tt>add</tt>' Instruction</a> 3466 </h4> 3467 3468 <div> 3469 3470 <h5>Syntax:</h5> 3471 <pre> 3472 <result> = add <ty> <op1>, <op2> <i>; yields {ty}:result</i> 3473 <result> = add nuw <ty> <op1>, <op2> <i>; yields {ty}:result</i> 3474 <result> = add nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i> 3475 <result> = add nuw nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i> 3476 </pre> 3477 3478 <h5>Overview:</h5> 3479 <p>The '<tt>add</tt>' instruction returns the sum of its two operands.</p> 3480 3481 <h5>Arguments:</h5> 3482 <p>The two arguments to the '<tt>add</tt>' instruction must 3483 be <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of 3484 integer values. Both arguments must have identical types.</p> 3485 3486 <h5>Semantics:</h5> 3487 <p>The value produced is the integer sum of the two operands.</p> 3488 3489 <p>If the sum has unsigned overflow, the result returned is the mathematical 3490 result modulo 2<sup>n</sup>, where n is the bit width of the result.</p> 3491 3492 <p>Because LLVM integers use a two's complement representation, this instruction 3493 is appropriate for both signed and unsigned integers.</p> 3494 3495 <p><tt>nuw</tt> and <tt>nsw</tt> stand for "No Unsigned Wrap" 3496 and "No Signed Wrap", respectively. If the <tt>nuw</tt> and/or 3497 <tt>nsw</tt> keywords are present, the result value of the <tt>add</tt> 3498 is a <a href="#trapvalues">trap value</a> if unsigned and/or signed overflow, 3499 respectively, occurs.</p> 3500 3501 <h5>Example:</h5> 3502 <pre> 3503 <result> = add i32 4, %var <i>; yields {i32}:result = 4 + %var</i> 3504 </pre> 3505 3506 </div> 3507 3508 <!-- _______________________________________________________________________ --> 3509 <h4> 3510 <a name="i_fadd">'<tt>fadd</tt>' Instruction</a> 3511 </h4> 3512 3513 <div> 3514 3515 <h5>Syntax:</h5> 3516 <pre> 3517 <result> = fadd <ty> <op1>, <op2> <i>; yields {ty}:result</i> 3518 </pre> 3519 3520 <h5>Overview:</h5> 3521 <p>The '<tt>fadd</tt>' instruction returns the sum of its two operands.</p> 3522 3523 <h5>Arguments:</h5> 3524 <p>The two arguments to the '<tt>fadd</tt>' instruction must be 3525 <a href="#t_floating">floating point</a> or <a href="#t_vector">vector</a> of 3526 floating point values. Both arguments must have identical types.</p> 3527 3528 <h5>Semantics:</h5> 3529 <p>The value produced is the floating point sum of the two operands.</p> 3530 3531 <h5>Example:</h5> 3532 <pre> 3533 <result> = fadd float 4.0, %var <i>; yields {float}:result = 4.0 + %var</i> 3534 </pre> 3535 3536 </div> 3537 3538 <!-- _______________________________________________________________________ --> 3539 <h4> 3540 <a name="i_sub">'<tt>sub</tt>' Instruction</a> 3541 </h4> 3542 3543 <div> 3544 3545 <h5>Syntax:</h5> 3546 <pre> 3547 <result> = sub <ty> <op1>, <op2> <i>; yields {ty}:result</i> 3548 <result> = sub nuw <ty> <op1>, <op2> <i>; yields {ty}:result</i> 3549 <result> = sub nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i> 3550 <result> = sub nuw nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i> 3551 </pre> 3552 3553 <h5>Overview:</h5> 3554 <p>The '<tt>sub</tt>' instruction returns the difference of its two 3555 operands.</p> 3556 3557 <p>Note that the '<tt>sub</tt>' instruction is used to represent the 3558 '<tt>neg</tt>' instruction present in most other intermediate 3559 representations.</p> 3560 3561 <h5>Arguments:</h5> 3562 <p>The two arguments to the '<tt>sub</tt>' instruction must 3563 be <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of 3564 integer values. Both arguments must have identical types.</p> 3565 3566 <h5>Semantics:</h5> 3567 <p>The value produced is the integer difference of the two operands.</p> 3568 3569 <p>If the difference has unsigned overflow, the result returned is the 3570 mathematical result modulo 2<sup>n</sup>, where n is the bit width of the 3571 result.</p> 3572 3573 <p>Because LLVM integers use a two's complement representation, this instruction 3574 is appropriate for both signed and unsigned integers.</p> 3575 3576 <p><tt>nuw</tt> and <tt>nsw</tt> stand for "No Unsigned Wrap" 3577 and "No Signed Wrap", respectively. If the <tt>nuw</tt> and/or 3578 <tt>nsw</tt> keywords are present, the result value of the <tt>sub</tt> 3579 is a <a href="#trapvalues">trap value</a> if unsigned and/or signed overflow, 3580 respectively, occurs.</p> 3581 3582 <h5>Example:</h5> 3583 <pre> 3584 <result> = sub i32 4, %var <i>; yields {i32}:result = 4 - %var</i> 3585 <result> = sub i32 0, %val <i>; yields {i32}:result = -%var</i> 3586 </pre> 3587 3588 </div> 3589 3590 <!-- _______________________________________________________________________ --> 3591 <h4> 3592 <a name="i_fsub">'<tt>fsub</tt>' Instruction</a> 3593 </h4> 3594 3595 <div> 3596 3597 <h5>Syntax:</h5> 3598 <pre> 3599 <result> = fsub <ty> <op1>, <op2> <i>; yields {ty}:result</i> 3600 </pre> 3601 3602 <h5>Overview:</h5> 3603 <p>The '<tt>fsub</tt>' instruction returns the difference of its two 3604 operands.</p> 3605 3606 <p>Note that the '<tt>fsub</tt>' instruction is used to represent the 3607 '<tt>fneg</tt>' instruction present in most other intermediate 3608 representations.</p> 3609 3610 <h5>Arguments:</h5> 3611 <p>The two arguments to the '<tt>fsub</tt>' instruction must be 3612 <a href="#t_floating">floating point</a> or <a href="#t_vector">vector</a> of 3613 floating point values. Both arguments must have identical types.</p> 3614 3615 <h5>Semantics:</h5> 3616 <p>The value produced is the floating point difference of the two operands.</p> 3617 3618 <h5>Example:</h5> 3619 <pre> 3620 <result> = fsub float 4.0, %var <i>; yields {float}:result = 4.0 - %var</i> 3621 <result> = fsub float -0.0, %val <i>; yields {float}:result = -%var</i> 3622 </pre> 3623 3624 </div> 3625 3626 <!-- _______________________________________________________________________ --> 3627 <h4> 3628 <a name="i_mul">'<tt>mul</tt>' Instruction</a> 3629 </h4> 3630 3631 <div> 3632 3633 <h5>Syntax:</h5> 3634 <pre> 3635 <result> = mul <ty> <op1>, <op2> <i>; yields {ty}:result</i> 3636 <result> = mul nuw <ty> <op1>, <op2> <i>; yields {ty}:result</i> 3637 <result> = mul nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i> 3638 <result> = mul nuw nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i> 3639 </pre> 3640 3641 <h5>Overview:</h5> 3642 <p>The '<tt>mul</tt>' instruction returns the product of its two operands.</p> 3643 3644 <h5>Arguments:</h5> 3645 <p>The two arguments to the '<tt>mul</tt>' instruction must 3646 be <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of 3647 integer values. Both arguments must have identical types.</p> 3648 3649 <h5>Semantics:</h5> 3650 <p>The value produced is the integer product of the two operands.</p> 3651 3652 <p>If the result of the multiplication has unsigned overflow, the result 3653 returned is the mathematical result modulo 2<sup>n</sup>, where n is the bit 3654 width of the result.</p> 3655 3656 <p>Because LLVM integers use a two's complement representation, and the result 3657 is the same width as the operands, this instruction returns the correct 3658 result for both signed and unsigned integers. If a full product 3659 (e.g. <tt>i32</tt>x<tt>i32</tt>-><tt>i64</tt>) is needed, the operands should 3660 be sign-extended or zero-extended as appropriate to the width of the full 3661 product.</p> 3662 3663 <p><tt>nuw</tt> and <tt>nsw</tt> stand for "No Unsigned Wrap" 3664 and "No Signed Wrap", respectively. If the <tt>nuw</tt> and/or 3665 <tt>nsw</tt> keywords are present, the result value of the <tt>mul</tt> 3666 is a <a href="#trapvalues">trap value</a> if unsigned and/or signed overflow, 3667 respectively, occurs.</p> 3668 3669 <h5>Example:</h5> 3670 <pre> 3671 <result> = mul i32 4, %var <i>; yields {i32}:result = 4 * %var</i> 3672 </pre> 3673 3674 </div> 3675 3676 <!-- _______________________________________________________________________ --> 3677 <h4> 3678 <a name="i_fmul">'<tt>fmul</tt>' Instruction</a> 3679 </h4> 3680 3681 <div> 3682 3683 <h5>Syntax:</h5> 3684 <pre> 3685 <result> = fmul <ty> <op1>, <op2> <i>; yields {ty}:result</i> 3686 </pre> 3687 3688 <h5>Overview:</h5> 3689 <p>The '<tt>fmul</tt>' instruction returns the product of its two operands.</p> 3690 3691 <h5>Arguments:</h5> 3692 <p>The two arguments to the '<tt>fmul</tt>' instruction must be 3693 <a href="#t_floating">floating point</a> or <a href="#t_vector">vector</a> of 3694 floating point values. Both arguments must have identical types.</p> 3695 3696 <h5>Semantics:</h5> 3697 <p>The value produced is the floating point product of the two operands.</p> 3698 3699 <h5>Example:</h5> 3700 <pre> 3701 <result> = fmul float 4.0, %var <i>; yields {float}:result = 4.0 * %var</i> 3702 </pre> 3703 3704 </div> 3705 3706 <!-- _______________________________________________________________________ --> 3707 <h4> 3708 <a name="i_udiv">'<tt>udiv</tt>' Instruction</a> 3709 </h4> 3710 3711 <div> 3712 3713 <h5>Syntax:</h5> 3714 <pre> 3715 <result> = udiv <ty> <op1>, <op2> <i>; yields {ty}:result</i> 3716 <result> = udiv exact <ty> <op1>, <op2> <i>; yields {ty}:result</i> 3717 </pre> 3718 3719 <h5>Overview:</h5> 3720 <p>The '<tt>udiv</tt>' instruction returns the quotient of its two operands.</p> 3721 3722 <h5>Arguments:</h5> 3723 <p>The two arguments to the '<tt>udiv</tt>' instruction must be 3724 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer 3725 values. Both arguments must have identical types.</p> 3726 3727 <h5>Semantics:</h5> 3728 <p>The value produced is the unsigned integer quotient of the two operands.</p> 3729 3730 <p>Note that unsigned integer division and signed integer division are distinct 3731 operations; for signed integer division, use '<tt>sdiv</tt>'.</p> 3732 3733 <p>Division by zero leads to undefined behavior.</p> 3734 3735 <p>If the <tt>exact</tt> keyword is present, the result value of the 3736 <tt>udiv</tt> is a <a href="#trapvalues">trap value</a> if %op1 is not a 3737 multiple of %op2 (as such, "((a udiv exact b) mul b) == a").</p> 3738 3739 3740 <h5>Example:</h5> 3741 <pre> 3742 <result> = udiv i32 4, %var <i>; yields {i32}:result = 4 / %var</i> 3743 </pre> 3744 3745 </div> 3746 3747 <!-- _______________________________________________________________________ --> 3748 <h4> 3749 <a name="i_sdiv">'<tt>sdiv</tt>' Instruction</a> 3750 </h4> 3751 3752 <div> 3753 3754 <h5>Syntax:</h5> 3755 <pre> 3756 <result> = sdiv <ty> <op1>, <op2> <i>; yields {ty}:result</i> 3757 <result> = sdiv exact <ty> <op1>, <op2> <i>; yields {ty}:result</i> 3758 </pre> 3759 3760 <h5>Overview:</h5> 3761 <p>The '<tt>sdiv</tt>' instruction returns the quotient of its two operands.</p> 3762 3763 <h5>Arguments:</h5> 3764 <p>The two arguments to the '<tt>sdiv</tt>' instruction must be 3765 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer 3766 values. Both arguments must have identical types.</p> 3767 3768 <h5>Semantics:</h5> 3769 <p>The value produced is the signed integer quotient of the two operands rounded 3770 towards zero.</p> 3771 3772 <p>Note that signed integer division and unsigned integer division are distinct 3773 operations; for unsigned integer division, use '<tt>udiv</tt>'.</p> 3774 3775 <p>Division by zero leads to undefined behavior. Overflow also leads to 3776 undefined behavior; this is a rare case, but can occur, for example, by doing 3777 a 32-bit division of -2147483648 by -1.</p> 3778 3779 <p>If the <tt>exact</tt> keyword is present, the result value of the 3780 <tt>sdiv</tt> is a <a href="#trapvalues">trap value</a> if the result would 3781 be rounded.</p> 3782 3783 <h5>Example:</h5> 3784 <pre> 3785 <result> = sdiv i32 4, %var <i>; yields {i32}:result = 4 / %var</i> 3786 </pre> 3787 3788 </div> 3789 3790 <!-- _______________________________________________________________________ --> 3791 <h4> 3792 <a name="i_fdiv">'<tt>fdiv</tt>' Instruction</a> 3793 </h4> 3794 3795 <div> 3796 3797 <h5>Syntax:</h5> 3798 <pre> 3799 <result> = fdiv <ty> <op1>, <op2> <i>; yields {ty}:result</i> 3800 </pre> 3801 3802 <h5>Overview:</h5> 3803 <p>The '<tt>fdiv</tt>' instruction returns the quotient of its two operands.</p> 3804 3805 <h5>Arguments:</h5> 3806 <p>The two arguments to the '<tt>fdiv</tt>' instruction must be 3807 <a href="#t_floating">floating point</a> or <a href="#t_vector">vector</a> of 3808 floating point values. Both arguments must have identical types.</p> 3809 3810 <h5>Semantics:</h5> 3811 <p>The value produced is the floating point quotient of the two operands.</p> 3812 3813 <h5>Example:</h5> 3814 <pre> 3815 <result> = fdiv float 4.0, %var <i>; yields {float}:result = 4.0 / %var</i> 3816 </pre> 3817 3818 </div> 3819 3820 <!-- _______________________________________________________________________ --> 3821 <h4> 3822 <a name="i_urem">'<tt>urem</tt>' Instruction</a> 3823 </h4> 3824 3825 <div> 3826 3827 <h5>Syntax:</h5> 3828 <pre> 3829 <result> = urem <ty> <op1>, <op2> <i>; yields {ty}:result</i> 3830 </pre> 3831 3832 <h5>Overview:</h5> 3833 <p>The '<tt>urem</tt>' instruction returns the remainder from the unsigned 3834 division of its two arguments.</p> 3835 3836 <h5>Arguments:</h5> 3837 <p>The two arguments to the '<tt>urem</tt>' instruction must be 3838 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer 3839 values. Both arguments must have identical types.</p> 3840 3841 <h5>Semantics:</h5> 3842 <p>This instruction returns the unsigned integer <i>remainder</i> of a division. 3843 This instruction always performs an unsigned division to get the 3844 remainder.</p> 3845 3846 <p>Note that unsigned integer remainder and signed integer remainder are 3847 distinct operations; for signed integer remainder, use '<tt>srem</tt>'.</p> 3848 3849 <p>Taking the remainder of a division by zero leads to undefined behavior.</p> 3850 3851 <h5>Example:</h5> 3852 <pre> 3853 <result> = urem i32 4, %var <i>; yields {i32}:result = 4 % %var</i> 3854 </pre> 3855 3856 </div> 3857 3858 <!-- _______________________________________________________________________ --> 3859 <h4> 3860 <a name="i_srem">'<tt>srem</tt>' Instruction</a> 3861 </h4> 3862 3863 <div> 3864 3865 <h5>Syntax:</h5> 3866 <pre> 3867 <result> = srem <ty> <op1>, <op2> <i>; yields {ty}:result</i> 3868 </pre> 3869 3870 <h5>Overview:</h5> 3871 <p>The '<tt>srem</tt>' instruction returns the remainder from the signed 3872 division of its two operands. This instruction can also take 3873 <a href="#t_vector">vector</a> versions of the values in which case the 3874 elements must be integers.</p> 3875 3876 <h5>Arguments:</h5> 3877 <p>The two arguments to the '<tt>srem</tt>' instruction must be 3878 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer 3879 values. Both arguments must have identical types.</p> 3880 3881 <h5>Semantics:</h5> 3882 <p>This instruction returns the <i>remainder</i> of a division (where the result 3883 is either zero or has the same sign as the dividend, <tt>op1</tt>), not the 3884 <i>modulo</i> operator (where the result is either zero or has the same sign 3885 as the divisor, <tt>op2</tt>) of a value. 3886 For more information about the difference, 3887 see <a href="http://mathforum.org/dr.math/problems/anne.4.28.99.html">The 3888 Math Forum</a>. For a table of how this is implemented in various languages, 3889 please see <a href="http://en.wikipedia.org/wiki/Modulo_operation"> 3890 Wikipedia: modulo operation</a>.</p> 3891 3892 <p>Note that signed integer remainder and unsigned integer remainder are 3893 distinct operations; for unsigned integer remainder, use '<tt>urem</tt>'.</p> 3894 3895 <p>Taking the remainder of a division by zero leads to undefined behavior. 3896 Overflow also leads to undefined behavior; this is a rare case, but can 3897 occur, for example, by taking the remainder of a 32-bit division of 3898 -2147483648 by -1. (The remainder doesn't actually overflow, but this rule 3899 lets srem be implemented using instructions that return both the result of 3900 the division and the remainder.)</p> 3901 3902 <h5>Example:</h5> 3903 <pre> 3904 <result> = srem i32 4, %var <i>; yields {i32}:result = 4 % %var</i> 3905 </pre> 3906 3907 </div> 3908 3909 <!-- _______________________________________________________________________ --> 3910 <h4> 3911 <a name="i_frem">'<tt>frem</tt>' Instruction</a> 3912 </h4> 3913 3914 <div> 3915 3916 <h5>Syntax:</h5> 3917 <pre> 3918 <result> = frem <ty> <op1>, <op2> <i>; yields {ty}:result</i> 3919 </pre> 3920 3921 <h5>Overview:</h5> 3922 <p>The '<tt>frem</tt>' instruction returns the remainder from the division of 3923 its two operands.</p> 3924 3925 <h5>Arguments:</h5> 3926 <p>The two arguments to the '<tt>frem</tt>' instruction must be 3927 <a href="#t_floating">floating point</a> or <a href="#t_vector">vector</a> of 3928 floating point values. Both arguments must have identical types.</p> 3929 3930 <h5>Semantics:</h5> 3931 <p>This instruction returns the <i>remainder</i> of a division. The remainder 3932 has the same sign as the dividend.</p> 3933 3934 <h5>Example:</h5> 3935 <pre> 3936 <result> = frem float 4.0, %var <i>; yields {float}:result = 4.0 % %var</i> 3937 </pre> 3938 3939 </div> 3940 3941 </div> 3942 3943 <!-- ======================================================================= --> 3944 <h3> 3945 <a name="bitwiseops">Bitwise Binary Operations</a> 3946 </h3> 3947 3948 <div> 3949 3950 <p>Bitwise binary operators are used to do various forms of bit-twiddling in a 3951 program. They are generally very efficient instructions and can commonly be 3952 strength reduced from other instructions. They require two operands of the 3953 same type, execute an operation on them, and produce a single value. The 3954 resulting value is the same type as its operands.</p> 3955 3956 <!-- _______________________________________________________________________ --> 3957 <h4> 3958 <a name="i_shl">'<tt>shl</tt>' Instruction</a> 3959 </h4> 3960 3961 <div> 3962 3963 <h5>Syntax:</h5> 3964 <pre> 3965 <result> = shl <ty> <op1>, <op2> <i>; yields {ty}:result</i> 3966 <result> = shl nuw <ty> <op1>, <op2> <i>; yields {ty}:result</i> 3967 <result> = shl nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i> 3968 <result> = shl nuw nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i> 3969 </pre> 3970 3971 <h5>Overview:</h5> 3972 <p>The '<tt>shl</tt>' instruction returns the first operand shifted to the left 3973 a specified number of bits.</p> 3974 3975 <h5>Arguments:</h5> 3976 <p>Both arguments to the '<tt>shl</tt>' instruction must be the 3977 same <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of 3978 integer type. '<tt>op2</tt>' is treated as an unsigned value.</p> 3979 3980 <h5>Semantics:</h5> 3981 <p>The value produced is <tt>op1</tt> * 2<sup><tt>op2</tt></sup> mod 3982 2<sup>n</sup>, where <tt>n</tt> is the width of the result. If <tt>op2</tt> 3983 is (statically or dynamically) negative or equal to or larger than the number 3984 of bits in <tt>op1</tt>, the result is undefined. If the arguments are 3985 vectors, each vector element of <tt>op1</tt> is shifted by the corresponding 3986 shift amount in <tt>op2</tt>.</p> 3987 3988 <p>If the <tt>nuw</tt> keyword is present, then the shift produces a 3989 <a href="#trapvalues">trap value</a> if it shifts out any non-zero bits. If 3990 the <tt>nsw</tt> keyword is present, then the shift produces a 3991 <a href="#trapvalues">trap value</a> if it shifts out any bits that disagree 3992 with the resultant sign bit. As such, NUW/NSW have the same semantics as 3993 they would if the shift were expressed as a mul instruction with the same 3994 nsw/nuw bits in (mul %op1, (shl 1, %op2)).</p> 3995 3996 <h5>Example:</h5> 3997 <pre> 3998 <result> = shl i32 4, %var <i>; yields {i32}: 4 << %var</i> 3999 <result> = shl i32 4, 2 <i>; yields {i32}: 16</i> 4000 <result> = shl i32 1, 10 <i>; yields {i32}: 1024</i> 4001 <result> = shl i32 1, 32 <i>; undefined</i> 4002 <result> = shl <2 x i32> < i32 1, i32 1>, < i32 1, i32 2> <i>; yields: result=<2 x i32> < i32 2, i32 4></i> 4003 </pre> 4004 4005 </div> 4006 4007 <!-- _______________________________________________________________________ --> 4008 <h4> 4009 <a name="i_lshr">'<tt>lshr</tt>' Instruction</a> 4010 </h4> 4011 4012 <div> 4013 4014 <h5>Syntax:</h5> 4015 <pre> 4016 <result> = lshr <ty> <op1>, <op2> <i>; yields {ty}:result</i> 4017 <result> = lshr exact <ty> <op1>, <op2> <i>; yields {ty}:result</i> 4018 </pre> 4019 4020 <h5>Overview:</h5> 4021 <p>The '<tt>lshr</tt>' instruction (logical shift right) returns the first 4022 operand shifted to the right a specified number of bits with zero fill.</p> 4023 4024 <h5>Arguments:</h5> 4025 <p>Both arguments to the '<tt>lshr</tt>' instruction must be the same 4026 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer 4027 type. '<tt>op2</tt>' is treated as an unsigned value.</p> 4028 4029 <h5>Semantics:</h5> 4030 <p>This instruction always performs a logical shift right operation. The most 4031 significant bits of the result will be filled with zero bits after the shift. 4032 If <tt>op2</tt> is (statically or dynamically) equal to or larger than the 4033 number of bits in <tt>op1</tt>, the result is undefined. If the arguments are 4034 vectors, each vector element of <tt>op1</tt> is shifted by the corresponding 4035 shift amount in <tt>op2</tt>.</p> 4036 4037 <p>If the <tt>exact</tt> keyword is present, the result value of the 4038 <tt>lshr</tt> is a <a href="#trapvalues">trap value</a> if any of the bits 4039 shifted out are non-zero.</p> 4040 4041 4042 <h5>Example:</h5> 4043 <pre> 4044 <result> = lshr i32 4, 1 <i>; yields {i32}:result = 2</i> 4045 <result> = lshr i32 4, 2 <i>; yields {i32}:result = 1</i> 4046 <result> = lshr i8 4, 3 <i>; yields {i8}:result = 0</i> 4047 <result> = lshr i8 -2, 1 <i>; yields {i8}:result = 0x7FFFFFFF </i> 4048 <result> = lshr i32 1, 32 <i>; undefined</i> 4049 <result> = lshr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 2> <i>; yields: result=<2 x i32> < i32 0x7FFFFFFF, i32 1></i> 4050 </pre> 4051 4052 </div> 4053 4054 <!-- _______________________________________________________________________ --> 4055 <h4> 4056 <a name="i_ashr">'<tt>ashr</tt>' Instruction</a> 4057 </h4> 4058 4059 <div> 4060 4061 <h5>Syntax:</h5> 4062 <pre> 4063 <result> = ashr <ty> <op1>, <op2> <i>; yields {ty}:result</i> 4064 <result> = ashr exact <ty> <op1>, <op2> <i>; yields {ty}:result</i> 4065 </pre> 4066 4067 <h5>Overview:</h5> 4068 <p>The '<tt>ashr</tt>' instruction (arithmetic shift right) returns the first 4069 operand shifted to the right a specified number of bits with sign 4070 extension.</p> 4071 4072 <h5>Arguments:</h5> 4073 <p>Both arguments to the '<tt>ashr</tt>' instruction must be the same 4074 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer 4075 type. '<tt>op2</tt>' is treated as an unsigned value.</p> 4076 4077 <h5>Semantics:</h5> 4078 <p>This instruction always performs an arithmetic shift right operation, The 4079 most significant bits of the result will be filled with the sign bit 4080 of <tt>op1</tt>. If <tt>op2</tt> is (statically or dynamically) equal to or 4081 larger than the number of bits in <tt>op1</tt>, the result is undefined. If 4082 the arguments are vectors, each vector element of <tt>op1</tt> is shifted by 4083 the corresponding shift amount in <tt>op2</tt>.</p> 4084 4085 <p>If the <tt>exact</tt> keyword is present, the result value of the 4086 <tt>ashr</tt> is a <a href="#trapvalues">trap value</a> if any of the bits 4087 shifted out are non-zero.</p> 4088 4089 <h5>Example:</h5> 4090 <pre> 4091 <result> = ashr i32 4, 1 <i>; yields {i32}:result = 2</i> 4092 <result> = ashr i32 4, 2 <i>; yields {i32}:result = 1</i> 4093 <result> = ashr i8 4, 3 <i>; yields {i8}:result = 0</i> 4094 <result> = ashr i8 -2, 1 <i>; yields {i8}:result = -1</i> 4095 <result> = ashr i32 1, 32 <i>; undefined</i> 4096 <result> = ashr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 3> <i>; yields: result=<2 x i32> < i32 -1, i32 0></i> 4097 </pre> 4098 4099 </div> 4100 4101 <!-- _______________________________________________________________________ --> 4102 <h4> 4103 <a name="i_and">'<tt>and</tt>' Instruction</a> 4104 </h4> 4105 4106 <div> 4107 4108 <h5>Syntax:</h5> 4109 <pre> 4110 <result> = and <ty> <op1>, <op2> <i>; yields {ty}:result</i> 4111 </pre> 4112 4113 <h5>Overview:</h5> 4114 <p>The '<tt>and</tt>' instruction returns the bitwise logical and of its two 4115 operands.</p> 4116 4117 <h5>Arguments:</h5> 4118 <p>The two arguments to the '<tt>and</tt>' instruction must be 4119 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer 4120 values. Both arguments must have identical types.</p> 4121 4122 <h5>Semantics:</h5> 4123 <p>The truth table used for the '<tt>and</tt>' instruction is:</p> 4124 4125 <table border="1" cellspacing="0" cellpadding="4"> 4126 <tbody> 4127 <tr> 4128 <td>In0</td> 4129 <td>In1</td> 4130 <td>Out</td> 4131 </tr> 4132 <tr> 4133 <td>0</td> 4134 <td>0</td> 4135 <td>0</td> 4136 </tr> 4137 <tr> 4138 <td>0</td> 4139 <td>1</td> 4140 <td>0</td> 4141 </tr> 4142 <tr> 4143 <td>1</td> 4144 <td>0</td> 4145 <td>0</td> 4146 </tr> 4147 <tr> 4148 <td>1</td> 4149 <td>1</td> 4150 <td>1</td> 4151 </tr> 4152 </tbody> 4153 </table> 4154 4155 <h5>Example:</h5> 4156 <pre> 4157 <result> = and i32 4, %var <i>; yields {i32}:result = 4 & %var</i> 4158 <result> = and i32 15, 40 <i>; yields {i32}:result = 8</i> 4159 <result> = and i32 4, 8 <i>; yields {i32}:result = 0</i> 4160 </pre> 4161 </div> 4162 <!-- _______________________________________________________________________ --> 4163 <h4> 4164 <a name="i_or">'<tt>or</tt>' Instruction</a> 4165 </h4> 4166 4167 <div> 4168 4169 <h5>Syntax:</h5> 4170 <pre> 4171 <result> = or <ty> <op1>, <op2> <i>; yields {ty}:result</i> 4172 </pre> 4173 4174 <h5>Overview:</h5> 4175 <p>The '<tt>or</tt>' instruction returns the bitwise logical inclusive or of its 4176 two operands.</p> 4177 4178 <h5>Arguments:</h5> 4179 <p>The two arguments to the '<tt>or</tt>' instruction must be 4180 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer 4181 values. Both arguments must have identical types.</p> 4182 4183 <h5>Semantics:</h5> 4184 <p>The truth table used for the '<tt>or</tt>' instruction is:</p> 4185 4186 <table border="1" cellspacing="0" cellpadding="4"> 4187 <tbody> 4188 <tr> 4189 <td>In0</td> 4190 <td>In1</td> 4191 <td>Out</td> 4192 </tr> 4193 <tr> 4194 <td>0</td> 4195 <td>0</td> 4196 <td>0</td> 4197 </tr> 4198 <tr> 4199 <td>0</td> 4200 <td>1</td> 4201 <td>1</td> 4202 </tr> 4203 <tr> 4204 <td>1</td> 4205 <td>0</td> 4206 <td>1</td> 4207 </tr> 4208 <tr> 4209 <td>1</td> 4210 <td>1</td> 4211 <td>1</td> 4212 </tr> 4213 </tbody> 4214 </table> 4215 4216 <h5>Example:</h5> 4217 <pre> 4218 <result> = or i32 4, %var <i>; yields {i32}:result = 4 | %var</i> 4219 <result> = or i32 15, 40 <i>; yields {i32}:result = 47</i> 4220 <result> = or i32 4, 8 <i>; yields {i32}:result = 12</i> 4221 </pre> 4222 4223 </div> 4224 4225 <!-- _______________________________________________________________________ --> 4226 <h4> 4227 <a name="i_xor">'<tt>xor</tt>' Instruction</a> 4228 </h4> 4229 4230 <div> 4231 4232 <h5>Syntax:</h5> 4233 <pre> 4234 <result> = xor <ty> <op1>, <op2> <i>; yields {ty}:result</i> 4235 </pre> 4236 4237 <h5>Overview:</h5> 4238 <p>The '<tt>xor</tt>' instruction returns the bitwise logical exclusive or of 4239 its two operands. The <tt>xor</tt> is used to implement the "one's 4240 complement" operation, which is the "~" operator in C.</p> 4241 4242 <h5>Arguments:</h5> 4243 <p>The two arguments to the '<tt>xor</tt>' instruction must be 4244 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer 4245 values. Both arguments must have identical types.</p> 4246 4247 <h5>Semantics:</h5> 4248 <p>The truth table used for the '<tt>xor</tt>' instruction is:</p> 4249 4250 <table border="1" cellspacing="0" cellpadding="4"> 4251 <tbody> 4252 <tr> 4253 <td>In0</td> 4254 <td>In1</td> 4255 <td>Out</td> 4256 </tr> 4257 <tr> 4258 <td>0</td> 4259 <td>0</td> 4260 <td>0</td> 4261 </tr> 4262 <tr> 4263 <td>0</td> 4264 <td>1</td> 4265 <td>1</td> 4266 </tr> 4267 <tr> 4268 <td>1</td> 4269 <td>0</td> 4270 <td>1</td> 4271 </tr> 4272 <tr> 4273 <td>1</td> 4274 <td>1</td> 4275 <td>0</td> 4276 </tr> 4277 </tbody> 4278 </table> 4279 4280 <h5>Example:</h5> 4281 <pre> 4282 <result> = xor i32 4, %var <i>; yields {i32}:result = 4 ^ %var</i> 4283 <result> = xor i32 15, 40 <i>; yields {i32}:result = 39</i> 4284 <result> = xor i32 4, 8 <i>; yields {i32}:result = 12</i> 4285 <result> = xor i32 %V, -1 <i>; yields {i32}:result = ~%V</i> 4286 </pre> 4287 4288 </div> 4289 4290 </div> 4291 4292 <!-- ======================================================================= --> 4293 <h3> 4294 <a name="vectorops">Vector Operations</a> 4295 </h3> 4296 4297 <div> 4298 4299 <p>LLVM supports several instructions to represent vector operations in a 4300 target-independent manner. These instructions cover the element-access and 4301 vector-specific operations needed to process vectors effectively. While LLVM 4302 does directly support these vector operations, many sophisticated algorithms 4303 will want to use target-specific intrinsics to take full advantage of a 4304 specific target.</p> 4305 4306 <!-- _______________________________________________________________________ --> 4307 <h4> 4308 <a name="i_extractelement">'<tt>extractelement</tt>' Instruction</a> 4309 </h4> 4310 4311 <div> 4312 4313 <h5>Syntax:</h5> 4314 <pre> 4315 <result> = extractelement <n x <ty>> <val>, i32 <idx> <i>; yields <ty></i> 4316 </pre> 4317 4318 <h5>Overview:</h5> 4319 <p>The '<tt>extractelement</tt>' instruction extracts a single scalar element 4320 from a vector at a specified index.</p> 4321 4322 4323 <h5>Arguments:</h5> 4324 <p>The first operand of an '<tt>extractelement</tt>' instruction is a value 4325 of <a href="#t_vector">vector</a> type. The second operand is an index 4326 indicating the position from which to extract the element. The index may be 4327 a variable.</p> 4328 4329 <h5>Semantics:</h5> 4330 <p>The result is a scalar of the same type as the element type of 4331 <tt>val</tt>. Its value is the value at position <tt>idx</tt> of 4332 <tt>val</tt>. If <tt>idx</tt> exceeds the length of <tt>val</tt>, the 4333 results are undefined.</p> 4334 4335 <h5>Example:</h5> 4336 <pre> 4337 <result> = extractelement <4 x i32> %vec, i32 0 <i>; yields i32</i> 4338 </pre> 4339 4340 </div> 4341 4342 <!-- _______________________________________________________________________ --> 4343 <h4> 4344 <a name="i_insertelement">'<tt>insertelement</tt>' Instruction</a> 4345 </h4> 4346 4347 <div> 4348 4349 <h5>Syntax:</h5> 4350 <pre> 4351 <result> = insertelement <n x <ty>> <val>, <ty> <elt>, i32 <idx> <i>; yields <n x <ty>></i> 4352 </pre> 4353 4354 <h5>Overview:</h5> 4355 <p>The '<tt>insertelement</tt>' instruction inserts a scalar element into a 4356 vector at a specified index.</p> 4357 4358 <h5>Arguments:</h5> 4359 <p>The first operand of an '<tt>insertelement</tt>' instruction is a value 4360 of <a href="#t_vector">vector</a> type. The second operand is a scalar value 4361 whose type must equal the element type of the first operand. The third 4362 operand is an index indicating the position at which to insert the value. 4363 The index may be a variable.</p> 4364 4365 <h5>Semantics:</h5> 4366 <p>The result is a vector of the same type as <tt>val</tt>. Its element values 4367 are those of <tt>val</tt> except at position <tt>idx</tt>, where it gets the 4368 value <tt>elt</tt>. If <tt>idx</tt> exceeds the length of <tt>val</tt>, the 4369 results are undefined.</p> 4370 4371 <h5>Example:</h5> 4372 <pre> 4373 <result> = insertelement <4 x i32> %vec, i32 1, i32 0 <i>; yields <4 x i32></i> 4374 </pre> 4375 4376 </div> 4377 4378 <!-- _______________________________________________________________________ --> 4379 <h4> 4380 <a name="i_shufflevector">'<tt>shufflevector</tt>' Instruction</a> 4381 </h4> 4382 4383 <div> 4384 4385 <h5>Syntax:</h5> 4386 <pre> 4387 <result> = shufflevector <n x <ty>> <v1>, <n x <ty>> <v2>, <m x i32> <mask> <i>; yields <m x <ty>></i> 4388 </pre> 4389 4390 <h5>Overview:</h5> 4391 <p>The '<tt>shufflevector</tt>' instruction constructs a permutation of elements 4392 from two input vectors, returning a vector with the same element type as the 4393 input and length that is the same as the shuffle mask.</p> 4394 4395 <h5>Arguments:</h5> 4396 <p>The first two operands of a '<tt>shufflevector</tt>' instruction are vectors 4397 with types that match each other. The third argument is a shuffle mask whose 4398 element type is always 'i32'. The result of the instruction is a vector 4399 whose length is the same as the shuffle mask and whose element type is the 4400 same as the element type of the first two operands.</p> 4401 4402 <p>The shuffle mask operand is required to be a constant vector with either 4403 constant integer or undef values.</p> 4404 4405 <h5>Semantics:</h5> 4406 <p>The elements of the two input vectors are numbered from left to right across 4407 both of the vectors. The shuffle mask operand specifies, for each element of 4408 the result vector, which element of the two input vectors the result element 4409 gets. The element selector may be undef (meaning "don't care") and the 4410 second operand may be undef if performing a shuffle from only one vector.</p> 4411 4412 <h5>Example:</h5> 4413 <pre> 4414 <result> = shufflevector <4 x i32> %v1, <4 x i32> %v2, 4415 <4 x i32> <i32 0, i32 4, i32 1, i32 5> <i>; yields <4 x i32></i> 4416 <result> = shufflevector <4 x i32> %v1, <4 x i32> undef, 4417 <4 x i32> <i32 0, i32 1, i32 2, i32 3> <i>; yields <4 x i32></i> - Identity shuffle. 4418 <result> = shufflevector <8 x i32> %v1, <8 x i32> undef, 4419 <4 x i32> <i32 0, i32 1, i32 2, i32 3> <i>; yields <4 x i32></i> 4420 <result> = shufflevector <4 x i32> %v1, <4 x i32> %v2, 4421 <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7 > <i>; yields <8 x i32></i> 4422 </pre> 4423 4424 </div> 4425 4426 </div> 4427 4428 <!-- ======================================================================= --> 4429 <h3> 4430 <a name="aggregateops">Aggregate Operations</a> 4431 </h3> 4432 4433 <div> 4434 4435 <p>LLVM supports several instructions for working with 4436 <a href="#t_aggregate">aggregate</a> values.</p> 4437 4438 <!-- _______________________________________________________________________ --> 4439 <h4> 4440 <a name="i_extractvalue">'<tt>extractvalue</tt>' Instruction</a> 4441 </h4> 4442 4443 <div> 4444 4445 <h5>Syntax:</h5> 4446 <pre> 4447 <result> = extractvalue <aggregate type> <val>, <idx>{, <idx>}* 4448 </pre> 4449 4450 <h5>Overview:</h5> 4451 <p>The '<tt>extractvalue</tt>' instruction extracts the value of a member field 4452 from an <a href="#t_aggregate">aggregate</a> value.</p> 4453 4454 <h5>Arguments:</h5> 4455 <p>The first operand of an '<tt>extractvalue</tt>' instruction is a value 4456 of <a href="#t_struct">struct</a> or 4457 <a href="#t_array">array</a> type. The operands are constant indices to 4458 specify which value to extract in a similar manner as indices in a 4459 '<tt><a href="#i_getelementptr">getelementptr</a></tt>' instruction.</p> 4460 <p>The major differences to <tt>getelementptr</tt> indexing are:</p> 4461 <ul> 4462 <li>Since the value being indexed is not a pointer, the first index is 4463 omitted and assumed to be zero.</li> 4464 <li>At least one index must be specified.</li> 4465 <li>Not only struct indices but also array indices must be in 4466 bounds.</li> 4467 </ul> 4468 4469 <h5>Semantics:</h5> 4470 <p>The result is the value at the position in the aggregate specified by the 4471 index operands.</p> 4472 4473 <h5>Example:</h5> 4474 <pre> 4475 <result> = extractvalue {i32, float} %agg, 0 <i>; yields i32</i> 4476 </pre> 4477 4478 </div> 4479 4480 <!-- _______________________________________________________________________ --> 4481 <h4> 4482 <a name="i_insertvalue">'<tt>insertvalue</tt>' Instruction</a> 4483 </h4> 4484 4485 <div> 4486 4487 <h5>Syntax:</h5> 4488 <pre> 4489 <result> = insertvalue <aggregate type> <val>, <ty> <elt>, <idx>{, <idx>}* <i>; yields <aggregate type></i> 4490 </pre> 4491 4492 <h5>Overview:</h5> 4493 <p>The '<tt>insertvalue</tt>' instruction inserts a value into a member field 4494 in an <a href="#t_aggregate">aggregate</a> value.</p> 4495 4496 <h5>Arguments:</h5> 4497 <p>The first operand of an '<tt>insertvalue</tt>' instruction is a value 4498 of <a href="#t_struct">struct</a> or 4499 <a href="#t_array">array</a> type. The second operand is a first-class 4500 value to insert. The following operands are constant indices indicating 4501 the position at which to insert the value in a similar manner as indices in a 4502 '<tt><a href="#i_extractvalue">extractvalue</a></tt>' instruction. The 4503 value to insert must have the same type as the value identified by the 4504 indices.</p> 4505 4506 <h5>Semantics:</h5> 4507 <p>The result is an aggregate of the same type as <tt>val</tt>. Its value is 4508 that of <tt>val</tt> except that the value at the position specified by the 4509 indices is that of <tt>elt</tt>.</p> 4510 4511 <h5>Example:</h5> 4512 <pre> 4513 %agg1 = insertvalue {i32, float} undef, i32 1, 0 <i>; yields {i32 1, float undef}</i> 4514 %agg2 = insertvalue {i32, float} %agg1, float %val, 1 <i>; yields {i32 1, float %val}</i> 4515 %agg3 = insertvalue {i32, {float}} %agg1, float %val, 1, 0 <i>; yields {i32 1, float %val}</i> 4516 </pre> 4517 4518 </div> 4519 4520 </div> 4521 4522 <!-- ======================================================================= --> 4523 <h3> 4524 <a name="memoryops">Memory Access and Addressing Operations</a> 4525 </h3> 4526 4527 <div> 4528 4529 <p>A key design point of an SSA-based representation is how it represents 4530 memory. In LLVM, no memory locations are in SSA form, which makes things 4531 very simple. This section describes how to read, write, and allocate 4532 memory in LLVM.</p> 4533 4534 <!-- _______________________________________________________________________ --> 4535 <h4> 4536 <a name="i_alloca">'<tt>alloca</tt>' Instruction</a> 4537 </h4> 4538 4539 <div> 4540 4541 <h5>Syntax:</h5> 4542 <pre> 4543 <result> = alloca <type>[, <ty> <NumElements>][, align <alignment>] <i>; yields {type*}:result</i> 4544 </pre> 4545 4546 <h5>Overview:</h5> 4547 <p>The '<tt>alloca</tt>' instruction allocates memory on the stack frame of the 4548 currently executing function, to be automatically released when this function 4549 returns to its caller. The object is always allocated in the generic address 4550 space (address space zero).</p> 4551 4552 <h5>Arguments:</h5> 4553 <p>The '<tt>alloca</tt>' instruction 4554 allocates <tt>sizeof(<type>)*NumElements</tt> bytes of memory on the 4555 runtime stack, returning a pointer of the appropriate type to the program. 4556 If "NumElements" is specified, it is the number of elements allocated, 4557 otherwise "NumElements" is defaulted to be one. If a constant alignment is 4558 specified, the value result of the allocation is guaranteed to be aligned to 4559 at least that boundary. If not specified, or if zero, the target can choose 4560 to align the allocation on any convenient boundary compatible with the 4561 type.</p> 4562 4563 <p>'<tt>type</tt>' may be any sized type.</p> 4564 4565 <h5>Semantics:</h5> 4566 <p>Memory is allocated; a pointer is returned. The operation is undefined if 4567 there is insufficient stack space for the allocation. '<tt>alloca</tt>'d 4568 memory is automatically released when the function returns. The 4569 '<tt>alloca</tt>' instruction is commonly used to represent automatic 4570 variables that must have an address available. When the function returns 4571 (either with the <tt><a href="#i_ret">ret</a></tt> 4572 or <tt><a href="#i_unwind">unwind</a></tt> instructions), the memory is 4573 reclaimed. Allocating zero bytes is legal, but the result is undefined.</p> 4574 4575 <h5>Example:</h5> 4576 <pre> 4577 %ptr = alloca i32 <i>; yields {i32*}:ptr</i> 4578 %ptr = alloca i32, i32 4 <i>; yields {i32*}:ptr</i> 4579 %ptr = alloca i32, i32 4, align 1024 <i>; yields {i32*}:ptr</i> 4580 %ptr = alloca i32, align 1024 <i>; yields {i32*}:ptr</i> 4581 </pre> 4582 4583 </div> 4584 4585 <!-- _______________________________________________________________________ --> 4586 <h4> 4587 <a name="i_load">'<tt>load</tt>' Instruction</a> 4588 </h4> 4589 4590 <div> 4591 4592 <h5>Syntax:</h5> 4593 <pre> 4594 <result> = load [volatile] <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>] 4595 <result> = load atomic [volatile] <ty>* <pointer> [singlethread] <ordering>, align <alignment> 4596 !<index> = !{ i32 1 } 4597 </pre> 4598 4599 <h5>Overview:</h5> 4600 <p>The '<tt>load</tt>' instruction is used to read from memory.</p> 4601 4602 <h5>Arguments:</h5> 4603 <p>The argument to the '<tt>load</tt>' instruction specifies the memory address 4604 from which to load. The pointer must point to 4605 a <a href="#t_firstclass">first class</a> type. If the <tt>load</tt> is 4606 marked as <tt>volatile</tt>, then the optimizer is not allowed to modify the 4607 number or order of execution of this <tt>load</tt> with other <a 4608 href="#volatile">volatile operations</a>.</p> 4609 4610 <p>If the <code>load</code> is marked as <code>atomic</code>, it takes an extra 4611 <a href="#ordering">ordering</a> and optional <code>singlethread</code> 4612 argument. The <code>release</code> and <code>acq_rel</code> orderings are 4613 not valid on <code>load</code> instructions. Atomic loads produce <a 4614 href="#memorymodel">defined</a> results when they may see multiple atomic 4615 stores. The type of the pointee must be an integer type whose bit width 4616 is a power of two greater than or equal to eight and less than or equal 4617 to a target-specific size limit. <code>align</code> must be explicitly 4618 specified on atomic loads, and the load has undefined behavior if the 4619 alignment is not set to a value which is at least the size in bytes of 4620 the pointee. <code>!nontemporal</code> does not have any defined semantics 4621 for atomic loads.</p> 4622 4623 <p>The optional constant <tt>align</tt> argument specifies the alignment of the 4624 operation (that is, the alignment of the memory address). A value of 0 or an 4625 omitted <tt>align</tt> argument means that the operation has the preferential 4626 alignment for the target. It is the responsibility of the code emitter to 4627 ensure that the alignment information is correct. Overestimating the 4628 alignment results in undefined behavior. Underestimating the alignment may 4629 produce less efficient code. An alignment of 1 is always safe.</p> 4630 4631 <p>The optional <tt>!nontemporal</tt> metadata must reference a single 4632 metatadata name <index> corresponding to a metadata node with 4633 one <tt>i32</tt> entry of value 1. The existence of 4634 the <tt>!nontemporal</tt> metatadata on the instruction tells the optimizer 4635 and code generator that this load is not expected to be reused in the cache. 4636 The code generator may select special instructions to save cache bandwidth, 4637 such as the <tt>MOVNT</tt> instruction on x86.</p> 4638 4639 <h5>Semantics:</h5> 4640 <p>The location of memory pointed to is loaded. If the value being loaded is of 4641 scalar type then the number of bytes read does not exceed the minimum number 4642 of bytes needed to hold all bits of the type. For example, loading an 4643 <tt>i24</tt> reads at most three bytes. When loading a value of a type like 4644 <tt>i20</tt> with a size that is not an integral number of bytes, the result 4645 is undefined if the value was not originally written using a store of the 4646 same type.</p> 4647 4648 <h5>Examples:</h5> 4649 <pre> 4650 %ptr = <a href="#i_alloca">alloca</a> i32 <i>; yields {i32*}:ptr</i> 4651 <a href="#i_store">store</a> i32 3, i32* %ptr <i>; yields {void}</i> 4652 %val = load i32* %ptr <i>; yields {i32}:val = i32 3</i> 4653 </pre> 4654 4655 </div> 4656 4657 <!-- _______________________________________________________________________ --> 4658 <h4> 4659 <a name="i_store">'<tt>store</tt>' Instruction</a> 4660 </h4> 4661 4662 <div> 4663 4664 <h5>Syntax:</h5> 4665 <pre> 4666 store [volatile] <ty> <value>, <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>] <i>; yields {void}</i> 4667 store atomic [volatile] <ty> <value>, <ty>* <pointer> [singlethread] <ordering>, align <alignment> <i>; yields {void}</i> 4668 </pre> 4669 4670 <h5>Overview:</h5> 4671 <p>The '<tt>store</tt>' instruction is used to write to memory.</p> 4672 4673 <h5>Arguments:</h5> 4674 <p>There are two arguments to the '<tt>store</tt>' instruction: a value to store 4675 and an address at which to store it. The type of the 4676 '<tt><pointer></tt>' operand must be a pointer to 4677 the <a href="#t_firstclass">first class</a> type of the 4678 '<tt><value></tt>' operand. If the <tt>store</tt> is marked as 4679 <tt>volatile</tt>, then the optimizer is not allowed to modify the number or 4680 order of execution of this <tt>store</tt> with other <a 4681 href="#volatile">volatile operations</a>.</p> 4682 4683 <p>If the <code>store</code> is marked as <code>atomic</code>, it takes an extra 4684 <a href="#ordering">ordering</a> and optional <code>singlethread</code> 4685 argument. The <code>acquire</code> and <code>acq_rel</code> orderings aren't 4686 valid on <code>store</code> instructions. Atomic loads produce <a 4687 href="#memorymodel">defined</a> results when they may see multiple atomic 4688 stores. The type of the pointee must be an integer type whose bit width 4689 is a power of two greater than or equal to eight and less than or equal 4690 to a target-specific size limit. <code>align</code> must be explicitly 4691 specified on atomic stores, and the store has undefined behavior if the 4692 alignment is not set to a value which is at least the size in bytes of 4693 the pointee. <code>!nontemporal</code> does not have any defined semantics 4694 for atomic stores.</p> 4695 4696 <p>The optional constant "align" argument specifies the alignment of the 4697 operation (that is, the alignment of the memory address). A value of 0 or an 4698 omitted "align" argument means that the operation has the preferential 4699 alignment for the target. It is the responsibility of the code emitter to 4700 ensure that the alignment information is correct. Overestimating the 4701 alignment results in an undefined behavior. Underestimating the alignment may 4702 produce less efficient code. An alignment of 1 is always safe.</p> 4703 4704 <p>The optional !nontemporal metadata must reference a single metatadata 4705 name <index> corresponding to a metadata node with one i32 entry of 4706 value 1. The existence of the !nontemporal metatadata on the 4707 instruction tells the optimizer and code generator that this load is 4708 not expected to be reused in the cache. The code generator may 4709 select special instructions to save cache bandwidth, such as the 4710 MOVNT instruction on x86.</p> 4711 4712 4713 <h5>Semantics:</h5> 4714 <p>The contents of memory are updated to contain '<tt><value></tt>' at the 4715 location specified by the '<tt><pointer></tt>' operand. If 4716 '<tt><value></tt>' is of scalar type then the number of bytes written 4717 does not exceed the minimum number of bytes needed to hold all bits of the 4718 type. For example, storing an <tt>i24</tt> writes at most three bytes. When 4719 writing a value of a type like <tt>i20</tt> with a size that is not an 4720 integral number of bytes, it is unspecified what happens to the extra bits 4721 that do not belong to the type, but they will typically be overwritten.</p> 4722 4723 <h5>Example:</h5> 4724 <pre> 4725 %ptr = <a href="#i_alloca">alloca</a> i32 <i>; yields {i32*}:ptr</i> 4726 store i32 3, i32* %ptr <i>; yields {void}</i> 4727 %val = <a href="#i_load">load</a> i32* %ptr <i>; yields {i32}:val = i32 3</i> 4728 </pre> 4729 4730 </div> 4731 4732 <!-- _______________________________________________________________________ --> 4733 <h4> 4734 <a name="i_fence">'<tt>fence</tt>' Instruction</a> 4735 </h4> 4736 4737 <div> 4738 4739 <h5>Syntax:</h5> 4740 <pre> 4741 fence [singlethread] <ordering> <i>; yields {void}</i> 4742 </pre> 4743 4744 <h5>Overview:</h5> 4745 <p>The '<tt>fence</tt>' instruction is used to introduce happens-before edges 4746 between operations.</p> 4747 4748 <h5>Arguments:</h5> <p>'<code>fence</code>' instructions take an <a 4749 href="#ordering">ordering</a> argument which defines what 4750 <i>synchronizes-with</i> edges they add. They can only be given 4751 <code>acquire</code>, <code>release</code>, <code>acq_rel</code>, and 4752 <code>seq_cst</code> orderings.</p> 4753 4754 <h5>Semantics:</h5> 4755 <p>A fence <var>A</var> which has (at least) <code>release</code> ordering 4756 semantics <i>synchronizes with</i> a fence <var>B</var> with (at least) 4757 <code>acquire</code> ordering semantics if and only if there exist atomic 4758 operations <var>X</var> and <var>Y</var>, both operating on some atomic object 4759 <var>M</var>, such that <var>A</var> is sequenced before <var>X</var>, 4760 <var>X</var> modifies <var>M</var> (either directly or through some side effect 4761 of a sequence headed by <var>X</var>), <var>Y</var> is sequenced before 4762 <var>B</var>, and <var>Y</var> observes <var>M</var>. This provides a 4763 <i>happens-before</i> dependency between <var>A</var> and <var>B</var>. Rather 4764 than an explicit <code>fence</code>, one (but not both) of the atomic operations 4765 <var>X</var> or <var>Y</var> might provide a <code>release</code> or 4766 <code>acquire</code> (resp.) ordering constraint and still 4767 <i>synchronize-with</i> the explicit <code>fence</code> and establish the 4768 <i>happens-before</i> edge.</p> 4769 4770 <p>A <code>fence</code> which has <code>seq_cst</code> ordering, in addition to 4771 having both <code>acquire</code> and <code>release</code> semantics specified 4772 above, participates in the global program order of other <code>seq_cst</code> 4773 operations and/or fences.</p> 4774 4775 <p>The optional "<a href="#singlethread"><code>singlethread</code></a>" argument 4776 specifies that the fence only synchronizes with other fences in the same 4777 thread. (This is useful for interacting with signal handlers.)</p> 4778 4779 <h5>Example:</h5> 4780 <pre> 4781 fence acquire <i>; yields {void}</i> 4782 fence singlethread seq_cst <i>; yields {void}</i> 4783 </pre> 4784 4785 </div> 4786 4787 <!-- _______________________________________________________________________ --> 4788 <h4> 4789 <a name="i_cmpxchg">'<tt>cmpxchg</tt>' Instruction</a> 4790 </h4> 4791 4792 <div> 4793 4794 <h5>Syntax:</h5> 4795 <pre> 4796 cmpxchg [volatile] <ty>* <pointer>, <ty> <cmp>, <ty> <new> [singlethread] <ordering> <i>; yields {ty}</i> 4797 </pre> 4798 4799 <h5>Overview:</h5> 4800 <p>The '<tt>cmpxchg</tt>' instruction is used to atomically modify memory. 4801 It loads a value in memory and compares it to a given value. If they are 4802 equal, it stores a new value into the memory.</p> 4803 4804 <h5>Arguments:</h5> 4805 <p>There are three arguments to the '<code>cmpxchg</code>' instruction: an 4806 address to operate on, a value to compare to the value currently be at that 4807 address, and a new value to place at that address if the compared values are 4808 equal. The type of '<var><cmp></var>' must be an integer type whose 4809 bit width is a power of two greater than or equal to eight and less than 4810 or equal to a target-specific size limit. '<var><cmp></var>' and 4811 '<var><new></var>' must have the same type, and the type of 4812 '<var><pointer></var>' must be a pointer to that type. If the 4813 <code>cmpxchg</code> is marked as <code>volatile</code>, then the 4814 optimizer is not allowed to modify the number or order of execution 4815 of this <code>cmpxchg</code> with other <a href="#volatile">volatile 4816 operations</a>.</p> 4817 4818 <!-- FIXME: Extend allowed types. --> 4819 4820 <p>The <a href="#ordering"><var>ordering</var></a> argument specifies how this 4821 <code>cmpxchg</code> synchronizes with other atomic operations.</p> 4822 4823 <p>The optional "<code>singlethread</code>" argument declares that the 4824 <code>cmpxchg</code> is only atomic with respect to code (usually signal 4825 handlers) running in the same thread as the <code>cmpxchg</code>. Otherwise the 4826 cmpxchg is atomic with respect to all other code in the system.</p> 4827 4828 <p>The pointer passed into cmpxchg must have alignment greater than or equal to 4829 the size in memory of the operand. 4830 4831 <h5>Semantics:</h5> 4832 <p>The contents of memory at the location specified by the 4833 '<tt><pointer></tt>' operand is read and compared to 4834 '<tt><cmp></tt>'; if the read value is the equal, 4835 '<tt><new></tt>' is written. The original value at the location 4836 is returned. 4837 4838 <p>A successful <code>cmpxchg</code> is a read-modify-write instruction for the 4839 purpose of identifying <a href="#release_sequence">release sequences</a>. A 4840 failed <code>cmpxchg</code> is equivalent to an atomic load with an ordering 4841 parameter determined by dropping any <code>release</code> part of the 4842 <code>cmpxchg</code>'s ordering.</p> 4843 4844 <!-- 4845 FIXME: Is compare_exchange_weak() necessary? (Consider after we've done 4846 optimization work on ARM.) 4847 4848 FIXME: Is a weaker ordering constraint on failure helpful in practice? 4849 --> 4850 4851 <h5>Example:</h5> 4852 <pre> 4853 entry: 4854 %orig = atomic <a href="#i_load">load</a> i32* %ptr unordered <i>; yields {i32}</i> 4855 <a href="#i_br">br</a> label %loop 4856 4857 loop: 4858 %cmp = <a href="#i_phi">phi</a> i32 [ %orig, %entry ], [%old, %loop] 4859 %squared = <a href="#i_mul">mul</a> i32 %cmp, %cmp 4860 %old = cmpxchg i32* %ptr, i32 %cmp, i32 %squared <i>; yields {i32}</i> 4861 %success = <a href="#i_icmp">icmp</a> eq i32 %cmp, %old 4862 <a href="#i_br">br</a> i1 %success, label %done, label %loop 4863 4864 done: 4865 ... 4866 </pre> 4867 4868 </div> 4869 4870 <!-- _______________________________________________________________________ --> 4871 <h4> 4872 <a name="i_atomicrmw">'<tt>atomicrmw</tt>' Instruction</a> 4873 </h4> 4874 4875 <div> 4876 4877 <h5>Syntax:</h5> 4878 <pre> 4879 atomicrmw [volatile] <operation> <ty>* <pointer>, <ty> <value> [singlethread] <ordering> <i>; yields {ty}</i> 4880 </pre> 4881 4882 <h5>Overview:</h5> 4883 <p>The '<tt>atomicrmw</tt>' instruction is used to atomically modify memory.</p> 4884 4885 <h5>Arguments:</h5> 4886 <p>There are three arguments to the '<code>atomicrmw</code>' instruction: an 4887 operation to apply, an address whose value to modify, an argument to the 4888 operation. The operation must be one of the following keywords:</p> 4889 <ul> 4890 <li>xchg</li> 4891 <li>add</li> 4892 <li>sub</li> 4893 <li>and</li> 4894 <li>nand</li> 4895 <li>or</li> 4896 <li>xor</li> 4897 <li>max</li> 4898 <li>min</li> 4899 <li>umax</li> 4900 <li>umin</li> 4901 </ul> 4902 4903 <p>The type of '<var><value></var>' must be an integer type whose 4904 bit width is a power of two greater than or equal to eight and less than 4905 or equal to a target-specific size limit. The type of the 4906 '<code><pointer></code>' operand must be a pointer to that type. 4907 If the <code>atomicrmw</code> is marked as <code>volatile</code>, then the 4908 optimizer is not allowed to modify the number or order of execution of this 4909 <code>atomicrmw</code> with other <a href="#volatile">volatile 4910 operations</a>.</p> 4911 4912 <!-- FIXME: Extend allowed types. --> 4913 4914 <h5>Semantics:</h5> 4915 <p>The contents of memory at the location specified by the 4916 '<tt><pointer></tt>' operand are atomically read, modified, and written 4917 back. The original value at the location is returned. The modification is 4918 specified by the <var>operation</var> argument:</p> 4919 4920 <ul> 4921 <li>xchg: <code>*ptr = val</code></li> 4922 <li>add: <code>*ptr = *ptr + val</code></li> 4923 <li>sub: <code>*ptr = *ptr - val</code></li> 4924 <li>and: <code>*ptr = *ptr & val</code></li> 4925 <li>nand: <code>*ptr = ~(*ptr & val)</code></li> 4926 <li>or: <code>*ptr = *ptr | val</code></li> 4927 <li>xor: <code>*ptr = *ptr ^ val</code></li> 4928 <li>max: <code>*ptr = *ptr > val ? *ptr : val</code> (using a signed comparison)</li> 4929 <li>min: <code>*ptr = *ptr < val ? *ptr : val</code> (using a signed comparison)</li> 4930 <li>umax: <code>*ptr = *ptr > val ? *ptr : val</code> (using an unsigned comparison)</li> 4931 <li>umin: <code>*ptr = *ptr < val ? *ptr : val</code> (using an unsigned comparison)</li> 4932 </ul> 4933 4934 <h5>Example:</h5> 4935 <pre> 4936 %old = atomicrmw add i32* %ptr, i32 1 acquire <i>; yields {i32}</i> 4937 </pre> 4938 4939 </div> 4940 4941 <!-- _______________________________________________________________________ --> 4942 <h4> 4943 <a name="i_getelementptr">'<tt>getelementptr</tt>' Instruction</a> 4944 </h4> 4945 4946 <div> 4947 4948 <h5>Syntax:</h5> 4949 <pre> 4950 <result> = getelementptr <pty>* <ptrval>{, <ty> <idx>}* 4951 <result> = getelementptr inbounds <pty>* <ptrval>{, <ty> <idx>}* 4952 </pre> 4953 4954 <h5>Overview:</h5> 4955 <p>The '<tt>getelementptr</tt>' instruction is used to get the address of a 4956 subelement of an <a href="#t_aggregate">aggregate</a> data structure. 4957 It performs address calculation only and does not access memory.</p> 4958 4959 <h5>Arguments:</h5> 4960 <p>The first argument is always a pointer, and forms the basis of the 4961 calculation. The remaining arguments are indices that indicate which of the 4962 elements of the aggregate object are indexed. The interpretation of each 4963 index is dependent on the type being indexed into. The first index always 4964 indexes the pointer value given as the first argument, the second index 4965 indexes a value of the type pointed to (not necessarily the value directly 4966 pointed to, since the first index can be non-zero), etc. The first type 4967 indexed into must be a pointer value, subsequent types can be arrays, 4968 vectors, and structs. Note that subsequent types being indexed into 4969 can never be pointers, since that would require loading the pointer before 4970 continuing calculation.</p> 4971 4972 <p>The type of each index argument depends on the type it is indexing into. 4973 When indexing into a (optionally packed) structure, only <tt>i32</tt> 4974 integer <b>constants</b> are allowed. When indexing into an array, pointer 4975 or vector, integers of any width are allowed, and they are not required to be 4976 constant. These integers are treated as signed values where relevant.</p> 4977 4978 <p>For example, let's consider a C code fragment and how it gets compiled to 4979 LLVM:</p> 4980 4981 <pre class="doc_code"> 4982 struct RT { 4983 char A; 4984 int B[10][20]; 4985 char C; 4986 }; 4987 struct ST { 4988 int X; 4989 double Y; 4990 struct RT Z; 4991 }; 4992 4993 int *foo(struct ST *s) { 4994 return &s[1].Z.B[5][13]; 4995 } 4996 </pre> 4997 4998 <p>The LLVM code generated by the GCC frontend is:</p> 4999 5000 <pre class="doc_code"> 5001 %RT = <a href="#namedtypes">type</a> { i8 , [10 x [20 x i32]], i8 } 5002 %ST = <a href="#namedtypes">type</a> { i32, double, %RT } 5003 5004 define i32* @foo(%ST* %s) { 5005 entry: 5006 %reg = getelementptr %ST* %s, i32 1, i32 2, i32 1, i32 5, i32 13 5007 ret i32* %reg 5008 } 5009 </pre> 5010 5011 <h5>Semantics:</h5> 5012 <p>In the example above, the first index is indexing into the '<tt>%ST*</tt>' 5013 type, which is a pointer, yielding a '<tt>%ST</tt>' = '<tt>{ i32, double, %RT 5014 }</tt>' type, a structure. The second index indexes into the third element 5015 of the structure, yielding a '<tt>%RT</tt>' = '<tt>{ i8 , [10 x [20 x i32]], 5016 i8 }</tt>' type, another structure. The third index indexes into the second 5017 element of the structure, yielding a '<tt>[10 x [20 x i32]]</tt>' type, an 5018 array. The two dimensions of the array are subscripted into, yielding an 5019 '<tt>i32</tt>' type. The '<tt>getelementptr</tt>' instruction returns a 5020 pointer to this element, thus computing a value of '<tt>i32*</tt>' type.</p> 5021 5022 <p>Note that it is perfectly legal to index partially through a structure, 5023 returning a pointer to an inner element. Because of this, the LLVM code for 5024 the given testcase is equivalent to:</p> 5025 5026 <pre> 5027 define i32* @foo(%ST* %s) { 5028 %t1 = getelementptr %ST* %s, i32 1 <i>; yields %ST*:%t1</i> 5029 %t2 = getelementptr %ST* %t1, i32 0, i32 2 <i>; yields %RT*:%t2</i> 5030 %t3 = getelementptr %RT* %t2, i32 0, i32 1 <i>; yields [10 x [20 x i32]]*:%t3</i> 5031 %t4 = getelementptr [10 x [20 x i32]]* %t3, i32 0, i32 5 <i>; yields [20 x i32]*:%t4</i> 5032 %t5 = getelementptr [20 x i32]* %t4, i32 0, i32 13 <i>; yields i32*:%t5</i> 5033 ret i32* %t5 5034 } 5035 </pre> 5036 5037 <p>If the <tt>inbounds</tt> keyword is present, the result value of the 5038 <tt>getelementptr</tt> is a <a href="#trapvalues">trap value</a> if the 5039 base pointer is not an <i>in bounds</i> address of an allocated object, 5040 or if any of the addresses that would be formed by successive addition of 5041 the offsets implied by the indices to the base address with infinitely 5042 precise signed arithmetic are not an <i>in bounds</i> address of that 5043 allocated object. The <i>in bounds</i> addresses for an allocated object 5044 are all the addresses that point into the object, plus the address one 5045 byte past the end.</p> 5046 5047 <p>If the <tt>inbounds</tt> keyword is not present, the offsets are added to 5048 the base address with silently-wrapping two's complement arithmetic. If the 5049 offsets have a different width from the pointer, they are sign-extended or 5050 truncated to the width of the pointer. The result value of the 5051 <tt>getelementptr</tt> may be outside the object pointed to by the base 5052 pointer. The result value may not necessarily be used to access memory 5053 though, even if it happens to point into allocated storage. See the 5054 <a href="#pointeraliasing">Pointer Aliasing Rules</a> section for more 5055 information.</p> 5056 5057 <p>The getelementptr instruction is often confusing. For some more insight into 5058 how it works, see <a href="GetElementPtr.html">the getelementptr FAQ</a>.</p> 5059 5060 <h5>Example:</h5> 5061 <pre> 5062 <i>; yields [12 x i8]*:aptr</i> 5063 %aptr = getelementptr {i32, [12 x i8]}* %saptr, i64 0, i32 1 5064 <i>; yields i8*:vptr</i> 5065 %vptr = getelementptr {i32, <2 x i8>}* %svptr, i64 0, i32 1, i32 1 5066 <i>; yields i8*:eptr</i> 5067 %eptr = getelementptr [12 x i8]* %aptr, i64 0, i32 1 5068 <i>; yields i32*:iptr</i> 5069 %iptr = getelementptr [10 x i32]* @arr, i16 0, i16 0 5070 </pre> 5071 5072 </div> 5073 5074 </div> 5075 5076 <!-- ======================================================================= --> 5077 <h3> 5078 <a name="convertops">Conversion Operations</a> 5079 </h3> 5080 5081 <div> 5082 5083 <p>The instructions in this category are the conversion instructions (casting) 5084 which all take a single operand and a type. They perform various bit 5085 conversions on the operand.</p> 5086 5087 <!-- _______________________________________________________________________ --> 5088 <h4> 5089 <a name="i_trunc">'<tt>trunc .. to</tt>' Instruction</a> 5090 </h4> 5091 5092 <div> 5093 5094 <h5>Syntax:</h5> 5095 <pre> 5096 <result> = trunc <ty> <value> to <ty2> <i>; yields ty2</i> 5097 </pre> 5098 5099 <h5>Overview:</h5> 5100 <p>The '<tt>trunc</tt>' instruction truncates its operand to the 5101 type <tt>ty2</tt>.</p> 5102 5103 <h5>Arguments:</h5> 5104 <p>The '<tt>trunc</tt>' instruction takes a value to trunc, and a type to trunc it to. 5105 Both types must be of <a href="#t_integer">integer</a> types, or vectors 5106 of the same number of integers. 5107 The bit size of the <tt>value</tt> must be larger than 5108 the bit size of the destination type, <tt>ty2</tt>. 5109 Equal sized types are not allowed.</p> 5110 5111 <h5>Semantics:</h5> 5112 <p>The '<tt>trunc</tt>' instruction truncates the high order bits 5113 in <tt>value</tt> and converts the remaining bits to <tt>ty2</tt>. Since the 5114 source size must be larger than the destination size, <tt>trunc</tt> cannot 5115 be a <i>no-op cast</i>. It will always truncate bits.</p> 5116 5117 <h5>Example:</h5> 5118 <pre> 5119 %X = trunc i32 257 to i8 <i>; yields i8:1</i> 5120 %Y = trunc i32 123 to i1 <i>; yields i1:true</i> 5121 %Z = trunc i32 122 to i1 <i>; yields i1:false</i> 5122 %W = trunc <2 x i16> <i16 8, i16 7> to <2 x i8> <i>; yields <i8 8, i8 7></i> 5123 </pre> 5124 5125 </div> 5126 5127 <!-- _______________________________________________________________________ --> 5128 <h4> 5129 <a name="i_zext">'<tt>zext .. to</tt>' Instruction</a> 5130 </h4> 5131 5132 <div> 5133 5134 <h5>Syntax:</h5> 5135 <pre> 5136 <result> = zext <ty> <value> to <ty2> <i>; yields ty2</i> 5137 </pre> 5138 5139 <h5>Overview:</h5> 5140 <p>The '<tt>zext</tt>' instruction zero extends its operand to type 5141 <tt>ty2</tt>.</p> 5142 5143 5144 <h5>Arguments:</h5> 5145 <p>The '<tt>zext</tt>' instruction takes a value to cast, and a type to cast it to. 5146 Both types must be of <a href="#t_integer">integer</a> types, or vectors 5147 of the same number of integers. 5148 The bit size of the <tt>value</tt> must be smaller than 5149 the bit size of the destination type, 5150 <tt>ty2</tt>.</p> 5151 5152 <h5>Semantics:</h5> 5153 <p>The <tt>zext</tt> fills the high order bits of the <tt>value</tt> with zero 5154 bits until it reaches the size of the destination type, <tt>ty2</tt>.</p> 5155 5156 <p>When zero extending from i1, the result will always be either 0 or 1.</p> 5157 5158 <h5>Example:</h5> 5159 <pre> 5160 %X = zext i32 257 to i64 <i>; yields i64:257</i> 5161 %Y = zext i1 true to i32 <i>; yields i32:1</i> 5162 %Z = zext <2 x i16> <i16 8, i16 7> to <2 x i32> <i>; yields <i32 8, i32 7></i> 5163 </pre> 5164 5165 </div> 5166 5167 <!-- _______________________________________________________________________ --> 5168 <h4> 5169 <a name="i_sext">'<tt>sext .. to</tt>' Instruction</a> 5170 </h4> 5171 5172 <div> 5173 5174 <h5>Syntax:</h5> 5175 <pre> 5176 <result> = sext <ty> <value> to <ty2> <i>; yields ty2</i> 5177 </pre> 5178 5179 <h5>Overview:</h5> 5180 <p>The '<tt>sext</tt>' sign extends <tt>value</tt> to the type <tt>ty2</tt>.</p> 5181 5182 <h5>Arguments:</h5> 5183 <p>The '<tt>sext</tt>' instruction takes a value to cast, and a type to cast it to. 5184 Both types must be of <a href="#t_integer">integer</a> types, or vectors 5185 of the same number of integers. 5186 The bit size of the <tt>value</tt> must be smaller than 5187 the bit size of the destination type, 5188 <tt>ty2</tt>.</p> 5189 5190 <h5>Semantics:</h5> 5191 <p>The '<tt>sext</tt>' instruction performs a sign extension by copying the sign 5192 bit (highest order bit) of the <tt>value</tt> until it reaches the bit size 5193 of the type <tt>ty2</tt>.</p> 5194 5195 <p>When sign extending from i1, the extension always results in -1 or 0.</p> 5196 5197 <h5>Example:</h5> 5198 <pre> 5199 %X = sext i8 -1 to i16 <i>; yields i16 :65535</i> 5200 %Y = sext i1 true to i32 <i>; yields i32:-1</i> 5201 %Z = sext <2 x i16> <i16 8, i16 7> to <2 x i32> <i>; yields <i32 8, i32 7></i> 5202 </pre> 5203 5204 </div> 5205 5206 <!-- _______________________________________________________________________ --> 5207 <h4> 5208 <a name="i_fptrunc">'<tt>fptrunc .. to</tt>' Instruction</a> 5209 </h4> 5210 5211 <div> 5212 5213 <h5>Syntax:</h5> 5214 <pre> 5215 <result> = fptrunc <ty> <value> to <ty2> <i>; yields ty2</i> 5216 </pre> 5217 5218 <h5>Overview:</h5> 5219 <p>The '<tt>fptrunc</tt>' instruction truncates <tt>value</tt> to type 5220 <tt>ty2</tt>.</p> 5221 5222 <h5>Arguments:</h5> 5223 <p>The '<tt>fptrunc</tt>' instruction takes a <a href="#t_floating">floating 5224 point</a> value to cast and a <a href="#t_floating">floating point</a> type 5225 to cast it to. The size of <tt>value</tt> must be larger than the size of 5226 <tt>ty2</tt>. This implies that <tt>fptrunc</tt> cannot be used to make a 5227 <i>no-op cast</i>.</p> 5228 5229 <h5>Semantics:</h5> 5230 <p>The '<tt>fptrunc</tt>' instruction truncates a <tt>value</tt> from a larger 5231 <a href="#t_floating">floating point</a> type to a smaller 5232 <a href="#t_floating">floating point</a> type. If the value cannot fit 5233 within the destination type, <tt>ty2</tt>, then the results are 5234 undefined.</p> 5235 5236 <h5>Example:</h5> 5237 <pre> 5238 %X = fptrunc double 123.0 to float <i>; yields float:123.0</i> 5239 %Y = fptrunc double 1.0E+300 to float <i>; yields undefined</i> 5240 </pre> 5241 5242 </div> 5243 5244 <!-- _______________________________________________________________________ --> 5245 <h4> 5246 <a name="i_fpext">'<tt>fpext .. to</tt>' Instruction</a> 5247 </h4> 5248 5249 <div> 5250 5251 <h5>Syntax:</h5> 5252 <pre> 5253 <result> = fpext <ty> <value> to <ty2> <i>; yields ty2</i> 5254 </pre> 5255 5256 <h5>Overview:</h5> 5257 <p>The '<tt>fpext</tt>' extends a floating point <tt>value</tt> to a larger 5258 floating point value.</p> 5259 5260 <h5>Arguments:</h5> 5261 <p>The '<tt>fpext</tt>' instruction takes a 5262 <a href="#t_floating">floating point</a> <tt>value</tt> to cast, and 5263 a <a href="#t_floating">floating point</a> type to cast it to. The source 5264 type must be smaller than the destination type.</p> 5265 5266 <h5>Semantics:</h5> 5267 <p>The '<tt>fpext</tt>' instruction extends the <tt>value</tt> from a smaller 5268 <a href="#t_floating">floating point</a> type to a larger 5269 <a href="#t_floating">floating point</a> type. The <tt>fpext</tt> cannot be 5270 used to make a <i>no-op cast</i> because it always changes bits. Use 5271 <tt>bitcast</tt> to make a <i>no-op cast</i> for a floating point cast.</p> 5272 5273 <h5>Example:</h5> 5274 <pre> 5275 %X = fpext float 3.125 to double <i>; yields double:3.125000e+00</i> 5276 %Y = fpext double %X to fp128 <i>; yields fp128:0xL00000000000000004000900000000000</i> 5277 </pre> 5278 5279 </div> 5280 5281 <!-- _______________________________________________________________________ --> 5282 <h4> 5283 <a name="i_fptoui">'<tt>fptoui .. to</tt>' Instruction</a> 5284 </h4> 5285 5286 <div> 5287 5288 <h5>Syntax:</h5> 5289 <pre> 5290 <result> = fptoui <ty> <value> to <ty2> <i>; yields ty2</i> 5291 </pre> 5292 5293 <h5>Overview:</h5> 5294 <p>The '<tt>fptoui</tt>' converts a floating point <tt>value</tt> to its 5295 unsigned integer equivalent of type <tt>ty2</tt>.</p> 5296 5297 <h5>Arguments:</h5> 5298 <p>The '<tt>fptoui</tt>' instruction takes a value to cast, which must be a 5299 scalar or vector <a href="#t_floating">floating point</a> value, and a type 5300 to cast it to <tt>ty2</tt>, which must be an <a href="#t_integer">integer</a> 5301 type. If <tt>ty</tt> is a vector floating point type, <tt>ty2</tt> must be a 5302 vector integer type with the same number of elements as <tt>ty</tt></p> 5303 5304 <h5>Semantics:</h5> 5305 <p>The '<tt>fptoui</tt>' instruction converts its 5306 <a href="#t_floating">floating point</a> operand into the nearest (rounding 5307 towards zero) unsigned integer value. If the value cannot fit 5308 in <tt>ty2</tt>, the results are undefined.</p> 5309 5310 <h5>Example:</h5> 5311 <pre> 5312 %X = fptoui double 123.0 to i32 <i>; yields i32:123</i> 5313 %Y = fptoui float 1.0E+300 to i1 <i>; yields undefined:1</i> 5314 %Z = fptoui float 1.04E+17 to i8 <i>; yields undefined:1</i> 5315 </pre> 5316 5317 </div> 5318 5319 <!-- _______________________________________________________________________ --> 5320 <h4> 5321 <a name="i_fptosi">'<tt>fptosi .. to</tt>' Instruction</a> 5322 </h4> 5323 5324 <div> 5325 5326 <h5>Syntax:</h5> 5327 <pre> 5328 <result> = fptosi <ty> <value> to <ty2> <i>; yields ty2</i> 5329 </pre> 5330 5331 <h5>Overview:</h5> 5332 <p>The '<tt>fptosi</tt>' instruction converts 5333 <a href="#t_floating">floating point</a> <tt>value</tt> to 5334 type <tt>ty2</tt>.</p> 5335 5336 <h5>Arguments:</h5> 5337 <p>The '<tt>fptosi</tt>' instruction takes a value to cast, which must be a 5338 scalar or vector <a href="#t_floating">floating point</a> value, and a type 5339 to cast it to <tt>ty2</tt>, which must be an <a href="#t_integer">integer</a> 5340 type. If <tt>ty</tt> is a vector floating point type, <tt>ty2</tt> must be a 5341 vector integer type with the same number of elements as <tt>ty</tt></p> 5342 5343 <h5>Semantics:</h5> 5344 <p>The '<tt>fptosi</tt>' instruction converts its 5345 <a href="#t_floating">floating point</a> operand into the nearest (rounding 5346 towards zero) signed integer value. If the value cannot fit in <tt>ty2</tt>, 5347 the results are undefined.</p> 5348 5349 <h5>Example:</h5> 5350 <pre> 5351 %X = fptosi double -123.0 to i32 <i>; yields i32:-123</i> 5352 %Y = fptosi float 1.0E-247 to i1 <i>; yields undefined:1</i> 5353 %Z = fptosi float 1.04E+17 to i8 <i>; yields undefined:1</i> 5354 </pre> 5355 5356 </div> 5357 5358 <!-- _______________________________________________________________________ --> 5359 <h4> 5360 <a name="i_uitofp">'<tt>uitofp .. to</tt>' Instruction</a> 5361 </h4> 5362 5363 <div> 5364 5365 <h5>Syntax:</h5> 5366 <pre> 5367 <result> = uitofp <ty> <value> to <ty2> <i>; yields ty2</i> 5368 </pre> 5369 5370 <h5>Overview:</h5> 5371 <p>The '<tt>uitofp</tt>' instruction regards <tt>value</tt> as an unsigned 5372 integer and converts that value to the <tt>ty2</tt> type.</p> 5373 5374 <h5>Arguments:</h5> 5375 <p>The '<tt>uitofp</tt>' instruction takes a value to cast, which must be a 5376 scalar or vector <a href="#t_integer">integer</a> value, and a type to cast 5377 it to <tt>ty2</tt>, which must be an <a href="#t_floating">floating point</a> 5378 type. If <tt>ty</tt> is a vector integer type, <tt>ty2</tt> must be a vector 5379 floating point type with the same number of elements as <tt>ty</tt></p> 5380 5381 <h5>Semantics:</h5> 5382 <p>The '<tt>uitofp</tt>' instruction interprets its operand as an unsigned 5383 integer quantity and converts it to the corresponding floating point 5384 value. If the value cannot fit in the floating point value, the results are 5385 undefined.</p> 5386 5387 <h5>Example:</h5> 5388 <pre> 5389 %X = uitofp i32 257 to float <i>; yields float:257.0</i> 5390 %Y = uitofp i8 -1 to double <i>; yields double:255.0</i> 5391 </pre> 5392 5393 </div> 5394 5395 <!-- _______________________________________________________________________ --> 5396 <h4> 5397 <a name="i_sitofp">'<tt>sitofp .. to</tt>' Instruction</a> 5398 </h4> 5399 5400 <div> 5401 5402 <h5>Syntax:</h5> 5403 <pre> 5404 <result> = sitofp <ty> <value> to <ty2> <i>; yields ty2</i> 5405 </pre> 5406 5407 <h5>Overview:</h5> 5408 <p>The '<tt>sitofp</tt>' instruction regards <tt>value</tt> as a signed integer 5409 and converts that value to the <tt>ty2</tt> type.</p> 5410 5411 <h5>Arguments:</h5> 5412 <p>The '<tt>sitofp</tt>' instruction takes a value to cast, which must be a 5413 scalar or vector <a href="#t_integer">integer</a> value, and a type to cast 5414 it to <tt>ty2</tt>, which must be an <a href="#t_floating">floating point</a> 5415 type. If <tt>ty</tt> is a vector integer type, <tt>ty2</tt> must be a vector 5416 floating point type with the same number of elements as <tt>ty</tt></p> 5417 5418 <h5>Semantics:</h5> 5419 <p>The '<tt>sitofp</tt>' instruction interprets its operand as a signed integer 5420 quantity and converts it to the corresponding floating point value. If the 5421 value cannot fit in the floating point value, the results are undefined.</p> 5422 5423 <h5>Example:</h5> 5424 <pre> 5425 %X = sitofp i32 257 to float <i>; yields float:257.0</i> 5426 %Y = sitofp i8 -1 to double <i>; yields double:-1.0</i> 5427 </pre> 5428 5429 </div> 5430 5431 <!-- _______________________________________________________________________ --> 5432 <h4> 5433 <a name="i_ptrtoint">'<tt>ptrtoint .. to</tt>' Instruction</a> 5434 </h4> 5435 5436 <div> 5437 5438 <h5>Syntax:</h5> 5439 <pre> 5440 <result> = ptrtoint <ty> <value> to <ty2> <i>; yields ty2</i> 5441 </pre> 5442 5443 <h5>Overview:</h5> 5444 <p>The '<tt>ptrtoint</tt>' instruction converts the pointer <tt>value</tt> to 5445 the integer type <tt>ty2</tt>.</p> 5446 5447 <h5>Arguments:</h5> 5448 <p>The '<tt>ptrtoint</tt>' instruction takes a <tt>value</tt> to cast, which 5449 must be a <a href="#t_pointer">pointer</a> value, and a type to cast it to 5450 <tt>ty2</tt>, which must be an <a href="#t_integer">integer</a> type.</p> 5451 5452 <h5>Semantics:</h5> 5453 <p>The '<tt>ptrtoint</tt>' instruction converts <tt>value</tt> to integer type 5454 <tt>ty2</tt> by interpreting the pointer value as an integer and either 5455 truncating or zero extending that value to the size of the integer type. If 5456 <tt>value</tt> is smaller than <tt>ty2</tt> then a zero extension is done. If 5457 <tt>value</tt> is larger than <tt>ty2</tt> then a truncation is done. If they 5458 are the same size, then nothing is done (<i>no-op cast</i>) other than a type 5459 change.</p> 5460 5461 <h5>Example:</h5> 5462 <pre> 5463 %X = ptrtoint i32* %X to i8 <i>; yields truncation on 32-bit architecture</i> 5464 %Y = ptrtoint i32* %x to i64 <i>; yields zero extension on 32-bit architecture</i> 5465 </pre> 5466 5467 </div> 5468 5469 <!-- _______________________________________________________________________ --> 5470 <h4> 5471 <a name="i_inttoptr">'<tt>inttoptr .. to</tt>' Instruction</a> 5472 </h4> 5473 5474 <div> 5475 5476 <h5>Syntax:</h5> 5477 <pre> 5478 <result> = inttoptr <ty> <value> to <ty2> <i>; yields ty2</i> 5479 </pre> 5480 5481 <h5>Overview:</h5> 5482 <p>The '<tt>inttoptr</tt>' instruction converts an integer <tt>value</tt> to a 5483 pointer type, <tt>ty2</tt>.</p> 5484 5485 <h5>Arguments:</h5> 5486 <p>The '<tt>inttoptr</tt>' instruction takes an <a href="#t_integer">integer</a> 5487 value to cast, and a type to cast it to, which must be a 5488 <a href="#t_pointer">pointer</a> type.</p> 5489 5490 <h5>Semantics:</h5> 5491 <p>The '<tt>inttoptr</tt>' instruction converts <tt>value</tt> to type 5492 <tt>ty2</tt> by applying either a zero extension or a truncation depending on 5493 the size of the integer <tt>value</tt>. If <tt>value</tt> is larger than the 5494 size of a pointer then a truncation is done. If <tt>value</tt> is smaller 5495 than the size of a pointer then a zero extension is done. If they are the 5496 same size, nothing is done (<i>no-op cast</i>).</p> 5497 5498 <h5>Example:</h5> 5499 <pre> 5500 %X = inttoptr i32 255 to i32* <i>; yields zero extension on 64-bit architecture</i> 5501 %Y = inttoptr i32 255 to i32* <i>; yields no-op on 32-bit architecture</i> 5502 %Z = inttoptr i64 0 to i32* <i>; yields truncation on 32-bit architecture</i> 5503 </pre> 5504 5505 </div> 5506 5507 <!-- _______________________________________________________________________ --> 5508 <h4> 5509 <a name="i_bitcast">'<tt>bitcast .. to</tt>' Instruction</a> 5510 </h4> 5511 5512 <div> 5513 5514 <h5>Syntax:</h5> 5515 <pre> 5516 <result> = bitcast <ty> <value> to <ty2> <i>; yields ty2</i> 5517 </pre> 5518 5519 <h5>Overview:</h5> 5520 <p>The '<tt>bitcast</tt>' instruction converts <tt>value</tt> to type 5521 <tt>ty2</tt> without changing any bits.</p> 5522 5523 <h5>Arguments:</h5> 5524 <p>The '<tt>bitcast</tt>' instruction takes a value to cast, which must be a 5525 non-aggregate first class value, and a type to cast it to, which must also be 5526 a non-aggregate <a href="#t_firstclass">first class</a> type. The bit sizes 5527 of <tt>value</tt> and the destination type, <tt>ty2</tt>, must be 5528 identical. If the source type is a pointer, the destination type must also be 5529 a pointer. This instruction supports bitwise conversion of vectors to 5530 integers and to vectors of other types (as long as they have the same 5531 size).</p> 5532 5533 <h5>Semantics:</h5> 5534 <p>The '<tt>bitcast</tt>' instruction converts <tt>value</tt> to type 5535 <tt>ty2</tt>. It is always a <i>no-op cast</i> because no bits change with 5536 this conversion. The conversion is done as if the <tt>value</tt> had been 5537 stored to memory and read back as type <tt>ty2</tt>. Pointer types may only 5538 be converted to other pointer types with this instruction. To convert 5539 pointers to other types, use the <a href="#i_inttoptr">inttoptr</a> or 5540 <a href="#i_ptrtoint">ptrtoint</a> instructions first.</p> 5541 5542 <h5>Example:</h5> 5543 <pre> 5544 %X = bitcast i8 255 to i8 <i>; yields i8 :-1</i> 5545 %Y = bitcast i32* %x to sint* <i>; yields sint*:%x</i> 5546 %Z = bitcast <2 x int> %V to i64; <i>; yields i64: %V</i> 5547 </pre> 5548 5549 </div> 5550 5551 </div> 5552 5553 <!-- ======================================================================= --> 5554 <h3> 5555 <a name="otherops">Other Operations</a> 5556 </h3> 5557 5558 <div> 5559 5560 <p>The instructions in this category are the "miscellaneous" instructions, which 5561 defy better classification.</p> 5562 5563 <!-- _______________________________________________________________________ --> 5564 <h4> 5565 <a name="i_icmp">'<tt>icmp</tt>' Instruction</a> 5566 </h4> 5567 5568 <div> 5569 5570 <h5>Syntax:</h5> 5571 <pre> 5572 <result> = icmp <cond> <ty> <op1>, <op2> <i>; yields {i1} or {<N x i1>}:result</i> 5573 </pre> 5574 5575 <h5>Overview:</h5> 5576 <p>The '<tt>icmp</tt>' instruction returns a boolean value or a vector of 5577 boolean values based on comparison of its two integer, integer vector, or 5578 pointer operands.</p> 5579 5580 <h5>Arguments:</h5> 5581 <p>The '<tt>icmp</tt>' instruction takes three operands. The first operand is 5582 the condition code indicating the kind of comparison to perform. It is not a 5583 value, just a keyword. The possible condition code are:</p> 5584 5585 <ol> 5586 <li><tt>eq</tt>: equal</li> 5587 <li><tt>ne</tt>: not equal </li> 5588 <li><tt>ugt</tt>: unsigned greater than</li> 5589 <li><tt>uge</tt>: unsigned greater or equal</li> 5590 <li><tt>ult</tt>: unsigned less than</li> 5591 <li><tt>ule</tt>: unsigned less or equal</li> 5592 <li><tt>sgt</tt>: signed greater than</li> 5593 <li><tt>sge</tt>: signed greater or equal</li> 5594 <li><tt>slt</tt>: signed less than</li> 5595 <li><tt>sle</tt>: signed less or equal</li> 5596 </ol> 5597 5598 <p>The remaining two arguments must be <a href="#t_integer">integer</a> or 5599 <a href="#t_pointer">pointer</a> or integer <a href="#t_vector">vector</a> 5600 typed. They must also be identical types.</p> 5601 5602 <h5>Semantics:</h5> 5603 <p>The '<tt>icmp</tt>' compares <tt>op1</tt> and <tt>op2</tt> according to the 5604 condition code given as <tt>cond</tt>. The comparison performed always yields 5605 either an <a href="#t_integer"><tt>i1</tt></a> or vector of <tt>i1</tt> 5606 result, as follows:</p> 5607 5608 <ol> 5609 <li><tt>eq</tt>: yields <tt>true</tt> if the operands are equal, 5610 <tt>false</tt> otherwise. No sign interpretation is necessary or 5611 performed.</li> 5612 5613 <li><tt>ne</tt>: yields <tt>true</tt> if the operands are unequal, 5614 <tt>false</tt> otherwise. No sign interpretation is necessary or 5615 performed.</li> 5616 5617 <li><tt>ugt</tt>: interprets the operands as unsigned values and yields 5618 <tt>true</tt> if <tt>op1</tt> is greater than <tt>op2</tt>.</li> 5619 5620 <li><tt>uge</tt>: interprets the operands as unsigned values and yields 5621 <tt>true</tt> if <tt>op1</tt> is greater than or equal 5622 to <tt>op2</tt>.</li> 5623 5624 <li><tt>ult</tt>: interprets the operands as unsigned values and yields 5625 <tt>true</tt> if <tt>op1</tt> is less than <tt>op2</tt>.</li> 5626 5627 <li><tt>ule</tt>: interprets the operands as unsigned values and yields 5628 <tt>true</tt> if <tt>op1</tt> is less than or equal to <tt>op2</tt>.</li> 5629 5630 <li><tt>sgt</tt>: interprets the operands as signed values and yields 5631 <tt>true</tt> if <tt>op1</tt> is greater than <tt>op2</tt>.</li> 5632 5633 <li><tt>sge</tt>: interprets the operands as signed values and yields 5634 <tt>true</tt> if <tt>op1</tt> is greater than or equal 5635 to <tt>op2</tt>.</li> 5636 5637 <li><tt>slt</tt>: interprets the operands as signed values and yields 5638 <tt>true</tt> if <tt>op1</tt> is less than <tt>op2</tt>.</li> 5639 5640 <li><tt>sle</tt>: interprets the operands as signed values and yields 5641 <tt>true</tt> if <tt>op1</tt> is less than or equal to <tt>op2</tt>.</li> 5642 </ol> 5643 5644 <p>If the operands are <a href="#t_pointer">pointer</a> typed, the pointer 5645 values are compared as if they were integers.</p> 5646 5647 <p>If the operands are integer vectors, then they are compared element by 5648 element. The result is an <tt>i1</tt> vector with the same number of elements 5649 as the values being compared. Otherwise, the result is an <tt>i1</tt>.</p> 5650 5651 <h5>Example:</h5> 5652 <pre> 5653 <result> = icmp eq i32 4, 5 <i>; yields: result=false</i> 5654 <result> = icmp ne float* %X, %X <i>; yields: result=false</i> 5655 <result> = icmp ult i16 4, 5 <i>; yields: result=true</i> 5656 <result> = icmp sgt i16 4, 5 <i>; yields: result=false</i> 5657 <result> = icmp ule i16 -4, 5 <i>; yields: result=false</i> 5658 <result> = icmp sge i16 4, 5 <i>; yields: result=false</i> 5659 </pre> 5660 5661 <p>Note that the code generator does not yet support vector types with 5662 the <tt>icmp</tt> instruction.</p> 5663 5664 </div> 5665 5666 <!-- _______________________________________________________________________ --> 5667 <h4> 5668 <a name="i_fcmp">'<tt>fcmp</tt>' Instruction</a> 5669 </h4> 5670 5671 <div> 5672 5673 <h5>Syntax:</h5> 5674 <pre> 5675 <result> = fcmp <cond> <ty> <op1>, <op2> <i>; yields {i1} or {<N x i1>}:result</i> 5676 </pre> 5677 5678 <h5>Overview:</h5> 5679 <p>The '<tt>fcmp</tt>' instruction returns a boolean value or vector of boolean 5680 values based on comparison of its operands.</p> 5681 5682 <p>If the operands are floating point scalars, then the result type is a boolean 5683 (<a href="#t_integer"><tt>i1</tt></a>).</p> 5684 5685 <p>If the operands are floating point vectors, then the result type is a vector 5686 of boolean with the same number of elements as the operands being 5687 compared.</p> 5688 5689 <h5>Arguments:</h5> 5690 <p>The '<tt>fcmp</tt>' instruction takes three operands. The first operand is 5691 the condition code indicating the kind of comparison to perform. It is not a 5692 value, just a keyword. The possible condition code are:</p> 5693 5694 <ol> 5695 <li><tt>false</tt>: no comparison, always returns false</li> 5696 <li><tt>oeq</tt>: ordered and equal</li> 5697 <li><tt>ogt</tt>: ordered and greater than </li> 5698 <li><tt>oge</tt>: ordered and greater than or equal</li> 5699 <li><tt>olt</tt>: ordered and less than </li> 5700 <li><tt>ole</tt>: ordered and less than or equal</li> 5701 <li><tt>one</tt>: ordered and not equal</li> 5702 <li><tt>ord</tt>: ordered (no nans)</li> 5703 <li><tt>ueq</tt>: unordered or equal</li> 5704 <li><tt>ugt</tt>: unordered or greater than </li> 5705 <li><tt>uge</tt>: unordered or greater than or equal</li> 5706 <li><tt>ult</tt>: unordered or less than </li> 5707 <li><tt>ule</tt>: unordered or less than or equal</li> 5708 <li><tt>une</tt>: unordered or not equal</li> 5709 <li><tt>uno</tt>: unordered (either nans)</li> 5710 <li><tt>true</tt>: no comparison, always returns true</li> 5711 </ol> 5712 5713 <p><i>Ordered</i> means that neither operand is a QNAN while 5714 <i>unordered</i> means that either operand may be a QNAN.</p> 5715 5716 <p>Each of <tt>val1</tt> and <tt>val2</tt> arguments must be either 5717 a <a href="#t_floating">floating point</a> type or 5718 a <a href="#t_vector">vector</a> of floating point type. They must have 5719 identical types.</p> 5720 5721 <h5>Semantics:</h5> 5722 <p>The '<tt>fcmp</tt>' instruction compares <tt>op1</tt> and <tt>op2</tt> 5723 according to the condition code given as <tt>cond</tt>. If the operands are 5724 vectors, then the vectors are compared element by element. Each comparison 5725 performed always yields an <a href="#t_integer">i1</a> result, as 5726 follows:</p> 5727 5728 <ol> 5729 <li><tt>false</tt>: always yields <tt>false</tt>, regardless of operands.</li> 5730 5731 <li><tt>oeq</tt>: yields <tt>true</tt> if both operands are not a QNAN and 5732 <tt>op1</tt> is equal to <tt>op2</tt>.</li> 5733 5734 <li><tt>ogt</tt>: yields <tt>true</tt> if both operands are not a QNAN and 5735 <tt>op1</tt> is greater than <tt>op2</tt>.</li> 5736 5737 <li><tt>oge</tt>: yields <tt>true</tt> if both operands are not a QNAN and 5738 <tt>op1</tt> is greater than or equal to <tt>op2</tt>.</li> 5739 5740 <li><tt>olt</tt>: yields <tt>true</tt> if both operands are not a QNAN and 5741 <tt>op1</tt> is less than <tt>op2</tt>.</li> 5742 5743 <li><tt>ole</tt>: yields <tt>true</tt> if both operands are not a QNAN and 5744 <tt>op1</tt> is less than or equal to <tt>op2</tt>.</li> 5745 5746 <li><tt>one</tt>: yields <tt>true</tt> if both operands are not a QNAN and 5747 <tt>op1</tt> is not equal to <tt>op2</tt>.</li> 5748 5749 <li><tt>ord</tt>: yields <tt>true</tt> if both operands are not a QNAN.</li> 5750 5751 <li><tt>ueq</tt>: yields <tt>true</tt> if either operand is a QNAN or 5752 <tt>op1</tt> is equal to <tt>op2</tt>.</li> 5753 5754 <li><tt>ugt</tt>: yields <tt>true</tt> if either operand is a QNAN or 5755 <tt>op1</tt> is greater than <tt>op2</tt>.</li> 5756 5757 <li><tt>uge</tt>: yields <tt>true</tt> if either operand is a QNAN or 5758 <tt>op1</tt> is greater than or equal to <tt>op2</tt>.</li> 5759 5760 <li><tt>ult</tt>: yields <tt>true</tt> if either operand is a QNAN or 5761 <tt>op1</tt> is less than <tt>op2</tt>.</li> 5762 5763 <li><tt>ule</tt>: yields <tt>true</tt> if either operand is a QNAN or 5764 <tt>op1</tt> is less than or equal to <tt>op2</tt>.</li> 5765 5766 <li><tt>une</tt>: yields <tt>true</tt> if either operand is a QNAN or 5767 <tt>op1</tt> is not equal to <tt>op2</tt>.</li> 5768 5769 <li><tt>uno</tt>: yields <tt>true</tt> if either operand is a QNAN.</li> 5770 5771 <li><tt>true</tt>: always yields <tt>true</tt>, regardless of operands.</li> 5772 </ol> 5773 5774 <h5>Example:</h5> 5775 <pre> 5776 <result> = fcmp oeq float 4.0, 5.0 <i>; yields: result=false</i> 5777 <result> = fcmp one float 4.0, 5.0 <i>; yields: result=true</i> 5778 <result> = fcmp olt float 4.0, 5.0 <i>; yields: result=true</i> 5779 <result> = fcmp ueq double 1.0, 2.0 <i>; yields: result=false</i> 5780 </pre> 5781 5782 <p>Note that the code generator does not yet support vector types with 5783 the <tt>fcmp</tt> instruction.</p> 5784 5785 </div> 5786 5787 <!-- _______________________________________________________________________ --> 5788 <h4> 5789 <a name="i_phi">'<tt>phi</tt>' Instruction</a> 5790 </h4> 5791 5792 <div> 5793 5794 <h5>Syntax:</h5> 5795 <pre> 5796 <result> = phi <ty> [ <val0>, <label0>], ... 5797 </pre> 5798 5799 <h5>Overview:</h5> 5800 <p>The '<tt>phi</tt>' instruction is used to implement the φ node in the 5801 SSA graph representing the function.</p> 5802 5803 <h5>Arguments:</h5> 5804 <p>The type of the incoming values is specified with the first type field. After 5805 this, the '<tt>phi</tt>' instruction takes a list of pairs as arguments, with 5806 one pair for each predecessor basic block of the current block. Only values 5807 of <a href="#t_firstclass">first class</a> type may be used as the value 5808 arguments to the PHI node. Only labels may be used as the label 5809 arguments.</p> 5810 5811 <p>There must be no non-phi instructions between the start of a basic block and 5812 the PHI instructions: i.e. PHI instructions must be first in a basic 5813 block.</p> 5814 5815 <p>For the purposes of the SSA form, the use of each incoming value is deemed to 5816 occur on the edge from the corresponding predecessor block to the current 5817 block (but after any definition of an '<tt>invoke</tt>' instruction's return 5818 value on the same edge).</p> 5819 5820 <h5>Semantics:</h5> 5821 <p>At runtime, the '<tt>phi</tt>' instruction logically takes on the value 5822 specified by the pair corresponding to the predecessor basic block that 5823 executed just prior to the current block.</p> 5824 5825 <h5>Example:</h5> 5826 <pre> 5827 Loop: ; Infinite loop that counts from 0 on up... 5828 %indvar = phi i32 [ 0, %LoopHeader ], [ %nextindvar, %Loop ] 5829 %nextindvar = add i32 %indvar, 1 5830 br label %Loop 5831 </pre> 5832 5833 </div> 5834 5835 <!-- _______________________________________________________________________ --> 5836 <h4> 5837 <a name="i_select">'<tt>select</tt>' Instruction</a> 5838 </h4> 5839 5840 <div> 5841 5842 <h5>Syntax:</h5> 5843 <pre> 5844 <result> = select <i>selty</i> <cond>, <ty> <val1>, <ty> <val2> <i>; yields ty</i> 5845 5846 <i>selty</i> is either i1 or {<N x i1>} 5847 </pre> 5848 5849 <h5>Overview:</h5> 5850 <p>The '<tt>select</tt>' instruction is used to choose one value based on a 5851 condition, without branching.</p> 5852 5853 5854 <h5>Arguments:</h5> 5855 <p>The '<tt>select</tt>' instruction requires an 'i1' value or a vector of 'i1' 5856 values indicating the condition, and two values of the 5857 same <a href="#t_firstclass">first class</a> type. If the val1/val2 are 5858 vectors and the condition is a scalar, then entire vectors are selected, not 5859 individual elements.</p> 5860 5861 <h5>Semantics:</h5> 5862 <p>If the condition is an i1 and it evaluates to 1, the instruction returns the 5863 first value argument; otherwise, it returns the second value argument.</p> 5864 5865 <p>If the condition is a vector of i1, then the value arguments must be vectors 5866 of the same size, and the selection is done element by element.</p> 5867 5868 <h5>Example:</h5> 5869 <pre> 5870 %X = select i1 true, i8 17, i8 42 <i>; yields i8:17</i> 5871 </pre> 5872 5873 <p>Note that the code generator does not yet support conditions 5874 with vector type.</p> 5875 5876 </div> 5877 5878 <!-- _______________________________________________________________________ --> 5879 <h4> 5880 <a name="i_call">'<tt>call</tt>' Instruction</a> 5881 </h4> 5882 5883 <div> 5884 5885 <h5>Syntax:</h5> 5886 <pre> 5887 <result> = [tail] call [<a href="#callingconv">cconv</a>] [<a href="#paramattrs">ret attrs</a>] <ty> [<fnty>*] <fnptrval>(<function args>) [<a href="#fnattrs">fn attrs</a>] 5888 </pre> 5889 5890 <h5>Overview:</h5> 5891 <p>The '<tt>call</tt>' instruction represents a simple function call.</p> 5892 5893 <h5>Arguments:</h5> 5894 <p>This instruction requires several arguments:</p> 5895 5896 <ol> 5897 <li>The optional "tail" marker indicates that the callee function does not 5898 access any allocas or varargs in the caller. Note that calls may be 5899 marked "tail" even if they do not occur before 5900 a <a href="#i_ret"><tt>ret</tt></a> instruction. If the "tail" marker is 5901 present, the function call is eligible for tail call optimization, 5902 but <a href="CodeGenerator.html#tailcallopt">might not in fact be 5903 optimized into a jump</a>. The code generator may optimize calls marked 5904 "tail" with either 1) automatic <a href="CodeGenerator.html#sibcallopt"> 5905 sibling call optimization</a> when the caller and callee have 5906 matching signatures, or 2) forced tail call optimization when the 5907 following extra requirements are met: 5908 <ul> 5909 <li>Caller and callee both have the calling 5910 convention <tt>fastcc</tt>.</li> 5911 <li>The call is in tail position (ret immediately follows call and ret 5912 uses value of call or is void).</li> 5913 <li>Option <tt>-tailcallopt</tt> is enabled, 5914 or <code>llvm::GuaranteedTailCallOpt</code> is <code>true</code>.</li> 5915 <li><a href="CodeGenerator.html#tailcallopt">Platform specific 5916 constraints are met.</a></li> 5917 </ul> 5918 </li> 5919 5920 <li>The optional "cconv" marker indicates which <a href="#callingconv">calling 5921 convention</a> the call should use. If none is specified, the call 5922 defaults to using C calling conventions. The calling convention of the 5923 call must match the calling convention of the target function, or else the 5924 behavior is undefined.</li> 5925 5926 <li>The optional <a href="#paramattrs">Parameter Attributes</a> list for 5927 return values. Only '<tt>zeroext</tt>', '<tt>signext</tt>', and 5928 '<tt>inreg</tt>' attributes are valid here.</li> 5929 5930 <li>'<tt>ty</tt>': the type of the call instruction itself which is also the 5931 type of the return value. Functions that return no value are marked 5932 <tt><a href="#t_void">void</a></tt>.</li> 5933 5934 <li>'<tt>fnty</tt>': shall be the signature of the pointer to function value 5935 being invoked. The argument types must match the types implied by this 5936 signature. This type can be omitted if the function is not varargs and if 5937 the function type does not return a pointer to a function.</li> 5938 5939 <li>'<tt>fnptrval</tt>': An LLVM value containing a pointer to a function to 5940 be invoked. In most cases, this is a direct function invocation, but 5941 indirect <tt>call</tt>s are just as possible, calling an arbitrary pointer 5942 to function value.</li> 5943 5944 <li>'<tt>function args</tt>': argument list whose types match the function 5945 signature argument types and parameter attributes. All arguments must be 5946 of <a href="#t_firstclass">first class</a> type. If the function 5947 signature indicates the function accepts a variable number of arguments, 5948 the extra arguments can be specified.</li> 5949 5950 <li>The optional <a href="#fnattrs">function attributes</a> list. Only 5951 '<tt>noreturn</tt>', '<tt>nounwind</tt>', '<tt>readonly</tt>' and 5952 '<tt>readnone</tt>' attributes are valid here.</li> 5953 </ol> 5954 5955 <h5>Semantics:</h5> 5956 <p>The '<tt>call</tt>' instruction is used to cause control flow to transfer to 5957 a specified function, with its incoming arguments bound to the specified 5958 values. Upon a '<tt><a href="#i_ret">ret</a></tt>' instruction in the called 5959 function, control flow continues with the instruction after the function 5960 call, and the return value of the function is bound to the result 5961 argument.</p> 5962 5963 <h5>Example:</h5> 5964 <pre> 5965 %retval = call i32 @test(i32 %argc) 5966 call i32 (i8*, ...)* @printf(i8* %msg, i32 12, i8 42) <i>; yields i32</i> 5967 %X = tail call i32 @foo() <i>; yields i32</i> 5968 %Y = tail call <a href="#callingconv">fastcc</a> i32 @foo() <i>; yields i32</i> 5969 call void %foo(i8 97 signext) 5970 5971 %struct.A = type { i32, i8 } 5972 %r = call %struct.A @foo() <i>; yields { 32, i8 }</i> 5973 %gr = extractvalue %struct.A %r, 0 <i>; yields i32</i> 5974 %gr1 = extractvalue %struct.A %r, 1 <i>; yields i8</i> 5975 %Z = call void @foo() noreturn <i>; indicates that %foo never returns normally</i> 5976 %ZZ = call zeroext i32 @bar() <i>; Return value is %zero extended</i> 5977 </pre> 5978 5979 <p>llvm treats calls to some functions with names and arguments that match the 5980 standard C99 library as being the C99 library functions, and may perform 5981 optimizations or generate code for them under that assumption. This is 5982 something we'd like to change in the future to provide better support for 5983 freestanding environments and non-C-based languages.</p> 5984 5985 </div> 5986 5987 <!-- _______________________________________________________________________ --> 5988 <h4> 5989 <a name="i_va_arg">'<tt>va_arg</tt>' Instruction</a> 5990 </h4> 5991 5992 <div> 5993 5994 <h5>Syntax:</h5> 5995 <pre> 5996 <resultval> = va_arg <va_list*> <arglist>, <argty> 5997 </pre> 5998 5999 <h5>Overview:</h5> 6000 <p>The '<tt>va_arg</tt>' instruction is used to access arguments passed through 6001 the "variable argument" area of a function call. It is used to implement the 6002 <tt>va_arg</tt> macro in C.</p> 6003 6004 <h5>Arguments:</h5> 6005 <p>This instruction takes a <tt>va_list*</tt> value and the type of the 6006 argument. It returns a value of the specified argument type and increments 6007 the <tt>va_list</tt> to point to the next argument. The actual type 6008 of <tt>va_list</tt> is target specific.</p> 6009 6010 <h5>Semantics:</h5> 6011 <p>The '<tt>va_arg</tt>' instruction loads an argument of the specified type 6012 from the specified <tt>va_list</tt> and causes the <tt>va_list</tt> to point 6013 to the next argument. For more information, see the variable argument 6014 handling <a href="#int_varargs">Intrinsic Functions</a>.</p> 6015 6016 <p>It is legal for this instruction to be called in a function which does not 6017 take a variable number of arguments, for example, the <tt>vfprintf</tt> 6018 function.</p> 6019 6020 <p><tt>va_arg</tt> is an LLVM instruction instead of 6021 an <a href="#intrinsics">intrinsic function</a> because it takes a type as an 6022 argument.</p> 6023 6024 <h5>Example:</h5> 6025 <p>See the <a href="#int_varargs">variable argument processing</a> section.</p> 6026 6027 <p>Note that the code generator does not yet fully support va_arg on many 6028 targets. Also, it does not currently support va_arg with aggregate types on 6029 any target.</p> 6030 6031 </div> 6032 6033 <!-- _______________________________________________________________________ --> 6034 <h4> 6035 <a name="i_landingpad">'<tt>landingpad</tt>' Instruction</a> 6036 </h4> 6037 6038 <div> 6039 6040 <h5>Syntax:</h5> 6041 <pre> 6042 <resultval> = landingpad <somety> personality <type> <pers_fn> <clause>+ 6043 <resultval> = landingpad <somety> personality <type> <pers_fn> cleanup <clause>* 6044 6045 <clause> := catch <type> <value> 6046 <clause> := filter <array constant type> <array constant> 6047 </pre> 6048 6049 <h5>Overview:</h5> 6050 <p>The '<tt>landingpad</tt>' instruction is used by 6051 <a href="ExceptionHandling.html#overview">LLVM's exception handling 6052 system</a> to specify that a basic block is a landing pad — one where 6053 the exception lands, and corresponds to the code found in the 6054 <i><tt>catch</tt></i> portion of a <i><tt>try/catch</tt></i> sequence. It 6055 defines values supplied by the personality function (<tt>pers_fn</tt>) upon 6056 re-entry to the function. The <tt>resultval</tt> has the 6057 type <tt>somety</tt>.</p> 6058 6059 <h5>Arguments:</h5> 6060 <p>This instruction takes a <tt>pers_fn</tt> value. This is the personality 6061 function associated with the unwinding mechanism. The optional 6062 <tt>cleanup</tt> flag indicates that the landing pad block is a cleanup.</p> 6063 6064 <p>A <tt>clause</tt> begins with the clause type — <tt>catch</tt> 6065 or <tt>filter</tt> — and contains the global variable representing the 6066 "type" that may be caught or filtered respectively. Unlike the 6067 <tt>catch</tt> clause, the <tt>filter</tt> clause takes an array constant as 6068 its argument. Use "<tt>[0 x i8**] undef</tt>" for a filter which cannot 6069 throw. The '<tt>landingpad</tt>' instruction must contain <em>at least</em> 6070 one <tt>clause</tt> or the <tt>cleanup</tt> flag.</p> 6071 6072 <h5>Semantics:</h5> 6073 <p>The '<tt>landingpad</tt>' instruction defines the values which are set by the 6074 personality function (<tt>pers_fn</tt>) upon re-entry to the function, and 6075 therefore the "result type" of the <tt>landingpad</tt> instruction. As with 6076 calling conventions, how the personality function results are represented in 6077 LLVM IR is target specific.</p> 6078 6079 <p>The clauses are applied in order from top to bottom. If two 6080 <tt>landingpad</tt> instructions are merged together through inlining, the 6081 clauses from the calling function are appended to the list of clauses.</p> 6082 6083 <p>The <tt>landingpad</tt> instruction has several restrictions:</p> 6084 6085 <ul> 6086 <li>A landing pad block is a basic block which is the unwind destination of an 6087 '<tt>invoke</tt>' instruction.</li> 6088 <li>A landing pad block must have a '<tt>landingpad</tt>' instruction as its 6089 first non-PHI instruction.</li> 6090 <li>There can be only one '<tt>landingpad</tt>' instruction within the landing 6091 pad block.</li> 6092 <li>A basic block that is not a landing pad block may not include a 6093 '<tt>landingpad</tt>' instruction.</li> 6094 <li>All '<tt>landingpad</tt>' instructions in a function must have the same 6095 personality function.</li> 6096 </ul> 6097 6098 <h5>Example:</h5> 6099 <pre> 6100 ;; A landing pad which can catch an integer. 6101 %res = landingpad { i8*, i32 } personality i32 (...)* @__gxx_personality_v0 6102 catch i8** @_ZTIi 6103 ;; A landing pad that is a cleanup. 6104 %res = landingpad { i8*, i32 } personality i32 (...)* @__gxx_personality_v0 6105 cleanup 6106 ;; A landing pad which can catch an integer and can only throw a double. 6107 %res = landingpad { i8*, i32 } personality i32 (...)* @__gxx_personality_v0 6108 catch i8** @_ZTIi 6109 filter [1 x i8**] [@_ZTId] 6110 </pre> 6111 6112 </div> 6113 6114 </div> 6115 6116 </div> 6117 6118 <!-- *********************************************************************** --> 6119 <h2><a name="intrinsics">Intrinsic Functions</a></h2> 6120 <!-- *********************************************************************** --> 6121 6122 <div> 6123 6124 <p>LLVM supports the notion of an "intrinsic function". These functions have 6125 well known names and semantics and are required to follow certain 6126 restrictions. Overall, these intrinsics represent an extension mechanism for 6127 the LLVM language that does not require changing all of the transformations 6128 in LLVM when adding to the language (or the bitcode reader/writer, the 6129 parser, etc...).</p> 6130 6131 <p>Intrinsic function names must all start with an "<tt>llvm.</tt>" prefix. This 6132 prefix is reserved in LLVM for intrinsic names; thus, function names may not 6133 begin with this prefix. Intrinsic functions must always be external 6134 functions: you cannot define the body of intrinsic functions. Intrinsic 6135 functions may only be used in call or invoke instructions: it is illegal to 6136 take the address of an intrinsic function. Additionally, because intrinsic 6137 functions are part of the LLVM language, it is required if any are added that 6138 they be documented here.</p> 6139 6140 <p>Some intrinsic functions can be overloaded, i.e., the intrinsic represents a 6141 family of functions that perform the same operation but on different data 6142 types. Because LLVM can represent over 8 million different integer types, 6143 overloading is used commonly to allow an intrinsic function to operate on any 6144 integer type. One or more of the argument types or the result type can be 6145 overloaded to accept any integer type. Argument types may also be defined as 6146 exactly matching a previous argument's type or the result type. This allows 6147 an intrinsic function which accepts multiple arguments, but needs all of them 6148 to be of the same type, to only be overloaded with respect to a single 6149 argument or the result.</p> 6150 6151 <p>Overloaded intrinsics will have the names of its overloaded argument types 6152 encoded into its function name, each preceded by a period. Only those types 6153 which are overloaded result in a name suffix. Arguments whose type is matched 6154 against another type do not. For example, the <tt>llvm.ctpop</tt> function 6155 can take an integer of any width and returns an integer of exactly the same 6156 integer width. This leads to a family of functions such as 6157 <tt>i8 @llvm.ctpop.i8(i8 %val)</tt> and <tt>i29 @llvm.ctpop.i29(i29 6158 %val)</tt>. Only one type, the return type, is overloaded, and only one type 6159 suffix is required. Because the argument's type is matched against the return 6160 type, it does not require its own name suffix.</p> 6161 6162 <p>To learn how to add an intrinsic function, please see the 6163 <a href="ExtendingLLVM.html">Extending LLVM Guide</a>.</p> 6164 6165 <!-- ======================================================================= --> 6166 <h3> 6167 <a name="int_varargs">Variable Argument Handling Intrinsics</a> 6168 </h3> 6169 6170 <div> 6171 6172 <p>Variable argument support is defined in LLVM with 6173 the <a href="#i_va_arg"><tt>va_arg</tt></a> instruction and these three 6174 intrinsic functions. These functions are related to the similarly named 6175 macros defined in the <tt><stdarg.h></tt> header file.</p> 6176 6177 <p>All of these functions operate on arguments that use a target-specific value 6178 type "<tt>va_list</tt>". The LLVM assembly language reference manual does 6179 not define what this type is, so all transformations should be prepared to 6180 handle these functions regardless of the type used.</p> 6181 6182 <p>This example shows how the <a href="#i_va_arg"><tt>va_arg</tt></a> 6183 instruction and the variable argument handling intrinsic functions are 6184 used.</p> 6185 6186 <pre class="doc_code"> 6187 define i32 @test(i32 %X, ...) { 6188 ; Initialize variable argument processing 6189 %ap = alloca i8* 6190 %ap2 = bitcast i8** %ap to i8* 6191 call void @llvm.va_start(i8* %ap2) 6192 6193 ; Read a single integer argument 6194 %tmp = va_arg i8** %ap, i32 6195 6196 ; Demonstrate usage of llvm.va_copy and llvm.va_end 6197 %aq = alloca i8* 6198 %aq2 = bitcast i8** %aq to i8* 6199 call void @llvm.va_copy(i8* %aq2, i8* %ap2) 6200 call void @llvm.va_end(i8* %aq2) 6201 6202 ; Stop processing of arguments. 6203 call void @llvm.va_end(i8* %ap2) 6204 ret i32 %tmp 6205 } 6206 6207 declare void @llvm.va_start(i8*) 6208 declare void @llvm.va_copy(i8*, i8*) 6209 declare void @llvm.va_end(i8*) 6210 </pre> 6211 6212 <!-- _______________________________________________________________________ --> 6213 <h4> 6214 <a name="int_va_start">'<tt>llvm.va_start</tt>' Intrinsic</a> 6215 </h4> 6216 6217 6218 <div> 6219 6220 <h5>Syntax:</h5> 6221 <pre> 6222 declare void %llvm.va_start(i8* <arglist>) 6223 </pre> 6224 6225 <h5>Overview:</h5> 6226 <p>The '<tt>llvm.va_start</tt>' intrinsic initializes <tt>*<arglist></tt> 6227 for subsequent use by <tt><a href="#i_va_arg">va_arg</a></tt>.</p> 6228 6229 <h5>Arguments:</h5> 6230 <p>The argument is a pointer to a <tt>va_list</tt> element to initialize.</p> 6231 6232 <h5>Semantics:</h5> 6233 <p>The '<tt>llvm.va_start</tt>' intrinsic works just like the <tt>va_start</tt> 6234 macro available in C. In a target-dependent way, it initializes 6235 the <tt>va_list</tt> element to which the argument points, so that the next 6236 call to <tt>va_arg</tt> will produce the first variable argument passed to 6237 the function. Unlike the C <tt>va_start</tt> macro, this intrinsic does not 6238 need to know the last argument of the function as the compiler can figure 6239 that out.</p> 6240 6241 </div> 6242 6243 <!-- _______________________________________________________________________ --> 6244 <h4> 6245 <a name="int_va_end">'<tt>llvm.va_end</tt>' Intrinsic</a> 6246 </h4> 6247 6248 <div> 6249 6250 <h5>Syntax:</h5> 6251 <pre> 6252 declare void @llvm.va_end(i8* <arglist>) 6253 </pre> 6254 6255 <h5>Overview:</h5> 6256 <p>The '<tt>llvm.va_end</tt>' intrinsic destroys <tt>*<arglist></tt>, 6257 which has been initialized previously 6258 with <tt><a href="#int_va_start">llvm.va_start</a></tt> 6259 or <tt><a href="#i_va_copy">llvm.va_copy</a></tt>.</p> 6260 6261 <h5>Arguments:</h5> 6262 <p>The argument is a pointer to a <tt>va_list</tt> to destroy.</p> 6263 6264 <h5>Semantics:</h5> 6265 <p>The '<tt>llvm.va_end</tt>' intrinsic works just like the <tt>va_end</tt> 6266 macro available in C. In a target-dependent way, it destroys 6267 the <tt>va_list</tt> element to which the argument points. Calls 6268 to <a href="#int_va_start"><tt>llvm.va_start</tt></a> 6269 and <a href="#int_va_copy"> <tt>llvm.va_copy</tt></a> must be matched exactly 6270 with calls to <tt>llvm.va_end</tt>.</p> 6271 6272 </div> 6273 6274 <!-- _______________________________________________________________________ --> 6275 <h4> 6276 <a name="int_va_copy">'<tt>llvm.va_copy</tt>' Intrinsic</a> 6277 </h4> 6278 6279 <div> 6280 6281 <h5>Syntax:</h5> 6282 <pre> 6283 declare void @llvm.va_copy(i8* <destarglist>, i8* <srcarglist>) 6284 </pre> 6285 6286 <h5>Overview:</h5> 6287 <p>The '<tt>llvm.va_copy</tt>' intrinsic copies the current argument position 6288 from the source argument list to the destination argument list.</p> 6289 6290 <h5>Arguments:</h5> 6291 <p>The first argument is a pointer to a <tt>va_list</tt> element to initialize. 6292 The second argument is a pointer to a <tt>va_list</tt> element to copy 6293 from.</p> 6294 6295 <h5>Semantics:</h5> 6296 <p>The '<tt>llvm.va_copy</tt>' intrinsic works just like the <tt>va_copy</tt> 6297 macro available in C. In a target-dependent way, it copies the 6298 source <tt>va_list</tt> element into the destination <tt>va_list</tt> 6299 element. This intrinsic is necessary because 6300 the <tt><a href="#int_va_start"> llvm.va_start</a></tt> intrinsic may be 6301 arbitrarily complex and require, for example, memory allocation.</p> 6302 6303 </div> 6304 6305 </div> 6306 6307 </div> 6308 6309 <!-- ======================================================================= --> 6310 <h3> 6311 <a name="int_gc">Accurate Garbage Collection Intrinsics</a> 6312 </h3> 6313 6314 <div> 6315 6316 <p>LLVM support for <a href="GarbageCollection.html">Accurate Garbage 6317 Collection</a> (GC) requires the implementation and generation of these 6318 intrinsics. These intrinsics allow identification of <a href="#int_gcroot">GC 6319 roots on the stack</a>, as well as garbage collector implementations that 6320 require <a href="#int_gcread">read</a> and <a href="#int_gcwrite">write</a> 6321 barriers. Front-ends for type-safe garbage collected languages should generate 6322 these intrinsics to make use of the LLVM garbage collectors. For more details, 6323 see <a href="GarbageCollection.html">Accurate Garbage Collection with 6324 LLVM</a>.</p> 6325 6326 <p>The garbage collection intrinsics only operate on objects in the generic 6327 address space (address space zero).</p> 6328 6329 <!-- _______________________________________________________________________ --> 6330 <h4> 6331 <a name="int_gcroot">'<tt>llvm.gcroot</tt>' Intrinsic</a> 6332 </h4> 6333 6334 <div> 6335 6336 <h5>Syntax:</h5> 6337 <pre> 6338 declare void @llvm.gcroot(i8** %ptrloc, i8* %metadata) 6339 </pre> 6340 6341 <h5>Overview:</h5> 6342 <p>The '<tt>llvm.gcroot</tt>' intrinsic declares the existence of a GC root to 6343 the code generator, and allows some metadata to be associated with it.</p> 6344 6345 <h5>Arguments:</h5> 6346 <p>The first argument specifies the address of a stack object that contains the 6347 root pointer. The second pointer (which must be either a constant or a 6348 global value address) contains the meta-data to be associated with the 6349 root.</p> 6350 6351 <h5>Semantics:</h5> 6352 <p>At runtime, a call to this intrinsic stores a null pointer into the "ptrloc" 6353 location. At compile-time, the code generator generates information to allow 6354 the runtime to find the pointer at GC safe points. The '<tt>llvm.gcroot</tt>' 6355 intrinsic may only be used in a function which <a href="#gc">specifies a GC 6356 algorithm</a>.</p> 6357 6358 </div> 6359 6360 <!-- _______________________________________________________________________ --> 6361 <h4> 6362 <a name="int_gcread">'<tt>llvm.gcread</tt>' Intrinsic</a> 6363 </h4> 6364 6365 <div> 6366 6367 <h5>Syntax:</h5> 6368 <pre> 6369 declare i8* @llvm.gcread(i8* %ObjPtr, i8** %Ptr) 6370 </pre> 6371 6372 <h5>Overview:</h5> 6373 <p>The '<tt>llvm.gcread</tt>' intrinsic identifies reads of references from heap 6374 locations, allowing garbage collector implementations that require read 6375 barriers.</p> 6376 6377 <h5>Arguments:</h5> 6378 <p>The second argument is the address to read from, which should be an address 6379 allocated from the garbage collector. The first object is a pointer to the 6380 start of the referenced object, if needed by the language runtime (otherwise 6381 null).</p> 6382 6383 <h5>Semantics:</h5> 6384 <p>The '<tt>llvm.gcread</tt>' intrinsic has the same semantics as a load 6385 instruction, but may be replaced with substantially more complex code by the 6386 garbage collector runtime, as needed. The '<tt>llvm.gcread</tt>' intrinsic 6387 may only be used in a function which <a href="#gc">specifies a GC 6388 algorithm</a>.</p> 6389 6390 </div> 6391 6392 <!-- _______________________________________________________________________ --> 6393 <h4> 6394 <a name="int_gcwrite">'<tt>llvm.gcwrite</tt>' Intrinsic</a> 6395 </h4> 6396 6397 <div> 6398 6399 <h5>Syntax:</h5> 6400 <pre> 6401 declare void @llvm.gcwrite(i8* %P1, i8* %Obj, i8** %P2) 6402 </pre> 6403 6404 <h5>Overview:</h5> 6405 <p>The '<tt>llvm.gcwrite</tt>' intrinsic identifies writes of references to heap 6406 locations, allowing garbage collector implementations that require write 6407 barriers (such as generational or reference counting collectors).</p> 6408 6409 <h5>Arguments:</h5> 6410 <p>The first argument is the reference to store, the second is the start of the 6411 object to store it to, and the third is the address of the field of Obj to 6412 store to. If the runtime does not require a pointer to the object, Obj may 6413 be null.</p> 6414 6415 <h5>Semantics:</h5> 6416 <p>The '<tt>llvm.gcwrite</tt>' intrinsic has the same semantics as a store 6417 instruction, but may be replaced with substantially more complex code by the 6418 garbage collector runtime, as needed. The '<tt>llvm.gcwrite</tt>' intrinsic 6419 may only be used in a function which <a href="#gc">specifies a GC 6420 algorithm</a>.</p> 6421 6422 </div> 6423 6424 </div> 6425 6426 <!-- ======================================================================= --> 6427 <h3> 6428 <a name="int_codegen">Code Generator Intrinsics</a> 6429 </h3> 6430 6431 <div> 6432 6433 <p>These intrinsics are provided by LLVM to expose special features that may 6434 only be implemented with code generator support.</p> 6435 6436 <!-- _______________________________________________________________________ --> 6437 <h4> 6438 <a name="int_returnaddress">'<tt>llvm.returnaddress</tt>' Intrinsic</a> 6439 </h4> 6440 6441 <div> 6442 6443 <h5>Syntax:</h5> 6444 <pre> 6445 declare i8 *@llvm.returnaddress(i32 <level>) 6446 </pre> 6447 6448 <h5>Overview:</h5> 6449 <p>The '<tt>llvm.returnaddress</tt>' intrinsic attempts to compute a 6450 target-specific value indicating the return address of the current function 6451 or one of its callers.</p> 6452 6453 <h5>Arguments:</h5> 6454 <p>The argument to this intrinsic indicates which function to return the address 6455 for. Zero indicates the calling function, one indicates its caller, etc. 6456 The argument is <b>required</b> to be a constant integer value.</p> 6457 6458 <h5>Semantics:</h5> 6459 <p>The '<tt>llvm.returnaddress</tt>' intrinsic either returns a pointer 6460 indicating the return address of the specified call frame, or zero if it 6461 cannot be identified. The value returned by this intrinsic is likely to be 6462 incorrect or 0 for arguments other than zero, so it should only be used for 6463 debugging purposes.</p> 6464 6465 <p>Note that calling this intrinsic does not prevent function inlining or other 6466 aggressive transformations, so the value returned may not be that of the 6467 obvious source-language caller.</p> 6468 6469 </div> 6470 6471 <!-- _______________________________________________________________________ --> 6472 <h4> 6473 <a name="int_frameaddress">'<tt>llvm.frameaddress</tt>' Intrinsic</a> 6474 </h4> 6475 6476 <div> 6477 6478 <h5>Syntax:</h5> 6479 <pre> 6480 declare i8* @llvm.frameaddress(i32 <level>) 6481 </pre> 6482 6483 <h5>Overview:</h5> 6484 <p>The '<tt>llvm.frameaddress</tt>' intrinsic attempts to return the 6485 target-specific frame pointer value for the specified stack frame.</p> 6486 6487 <h5>Arguments:</h5> 6488 <p>The argument to this intrinsic indicates which function to return the frame 6489 pointer for. Zero indicates the calling function, one indicates its caller, 6490 etc. The argument is <b>required</b> to be a constant integer value.</p> 6491 6492 <h5>Semantics:</h5> 6493 <p>The '<tt>llvm.frameaddress</tt>' intrinsic either returns a pointer 6494 indicating the frame address of the specified call frame, or zero if it 6495 cannot be identified. The value returned by this intrinsic is likely to be 6496 incorrect or 0 for arguments other than zero, so it should only be used for 6497 debugging purposes.</p> 6498 6499 <p>Note that calling this intrinsic does not prevent function inlining or other 6500 aggressive transformations, so the value returned may not be that of the 6501 obvious source-language caller.</p> 6502 6503 </div> 6504 6505 <!-- _______________________________________________________________________ --> 6506 <h4> 6507 <a name="int_stacksave">'<tt>llvm.stacksave</tt>' Intrinsic</a> 6508 </h4> 6509 6510 <div> 6511 6512 <h5>Syntax:</h5> 6513 <pre> 6514 declare i8* @llvm.stacksave() 6515 </pre> 6516 6517 <h5>Overview:</h5> 6518 <p>The '<tt>llvm.stacksave</tt>' intrinsic is used to remember the current state 6519 of the function stack, for use 6520 with <a href="#int_stackrestore"> <tt>llvm.stackrestore</tt></a>. This is 6521 useful for implementing language features like scoped automatic variable 6522 sized arrays in C99.</p> 6523 6524 <h5>Semantics:</h5> 6525 <p>This intrinsic returns a opaque pointer value that can be passed 6526 to <a href="#int_stackrestore"><tt>llvm.stackrestore</tt></a>. When 6527 an <tt>llvm.stackrestore</tt> intrinsic is executed with a value saved 6528 from <tt>llvm.stacksave</tt>, it effectively restores the state of the stack 6529 to the state it was in when the <tt>llvm.stacksave</tt> intrinsic executed. 6530 In practice, this pops any <a href="#i_alloca">alloca</a> blocks from the 6531 stack that were allocated after the <tt>llvm.stacksave</tt> was executed.</p> 6532 6533 </div> 6534 6535 <!-- _______________________________________________________________________ --> 6536 <h4> 6537 <a name="int_stackrestore">'<tt>llvm.stackrestore</tt>' Intrinsic</a> 6538 </h4> 6539 6540 <div> 6541 6542 <h5>Syntax:</h5> 6543 <pre> 6544 declare void @llvm.stackrestore(i8* %ptr) 6545 </pre> 6546 6547 <h5>Overview:</h5> 6548 <p>The '<tt>llvm.stackrestore</tt>' intrinsic is used to restore the state of 6549 the function stack to the state it was in when the 6550 corresponding <a href="#int_stacksave"><tt>llvm.stacksave</tt></a> intrinsic 6551 executed. This is useful for implementing language features like scoped 6552 automatic variable sized arrays in C99.</p> 6553 6554 <h5>Semantics:</h5> 6555 <p>See the description 6556 for <a href="#int_stacksave"><tt>llvm.stacksave</tt></a>.</p> 6557 6558 </div> 6559 6560 <!-- _______________________________________________________________________ --> 6561 <h4> 6562 <a name="int_prefetch">'<tt>llvm.prefetch</tt>' Intrinsic</a> 6563 </h4> 6564 6565 <div> 6566 6567 <h5>Syntax:</h5> 6568 <pre> 6569 declare void @llvm.prefetch(i8* <address>, i32 <rw>, i32 <locality>, i32 <cache type>) 6570 </pre> 6571 6572 <h5>Overview:</h5> 6573 <p>The '<tt>llvm.prefetch</tt>' intrinsic is a hint to the code generator to 6574 insert a prefetch instruction if supported; otherwise, it is a noop. 6575 Prefetches have no effect on the behavior of the program but can change its 6576 performance characteristics.</p> 6577 6578 <h5>Arguments:</h5> 6579 <p><tt>address</tt> is the address to be prefetched, <tt>rw</tt> is the 6580 specifier determining if the fetch should be for a read (0) or write (1), 6581 and <tt>locality</tt> is a temporal locality specifier ranging from (0) - no 6582 locality, to (3) - extremely local keep in cache. The <tt>cache type</tt> 6583 specifies whether the prefetch is performed on the data (1) or instruction (0) 6584 cache. The <tt>rw</tt>, <tt>locality</tt> and <tt>cache type</tt> arguments 6585 must be constant integers.</p> 6586 6587 <h5>Semantics:</h5> 6588 <p>This intrinsic does not modify the behavior of the program. In particular, 6589 prefetches cannot trap and do not produce a value. On targets that support 6590 this intrinsic, the prefetch can provide hints to the processor cache for 6591 better performance.</p> 6592 6593 </div> 6594 6595 <!-- _______________________________________________________________________ --> 6596 <h4> 6597 <a name="int_pcmarker">'<tt>llvm.pcmarker</tt>' Intrinsic</a> 6598 </h4> 6599 6600 <div> 6601 6602 <h5>Syntax:</h5> 6603 <pre> 6604 declare void @llvm.pcmarker(i32 <id>) 6605 </pre> 6606 6607 <h5>Overview:</h5> 6608 <p>The '<tt>llvm.pcmarker</tt>' intrinsic is a method to export a Program 6609 Counter (PC) in a region of code to simulators and other tools. The method 6610 is target specific, but it is expected that the marker will use exported 6611 symbols to transmit the PC of the marker. The marker makes no guarantees 6612 that it will remain with any specific instruction after optimizations. It is 6613 possible that the presence of a marker will inhibit optimizations. The 6614 intended use is to be inserted after optimizations to allow correlations of 6615 simulation runs.</p> 6616 6617 <h5>Arguments:</h5> 6618 <p><tt>id</tt> is a numerical id identifying the marker.</p> 6619 6620 <h5>Semantics:</h5> 6621 <p>This intrinsic does not modify the behavior of the program. Backends that do 6622 not support this intrinsic may ignore it.</p> 6623 6624 </div> 6625 6626 <!-- _______________________________________________________________________ --> 6627 <h4> 6628 <a name="int_readcyclecounter">'<tt>llvm.readcyclecounter</tt>' Intrinsic</a> 6629 </h4> 6630 6631 <div> 6632 6633 <h5>Syntax:</h5> 6634 <pre> 6635 declare i64 @llvm.readcyclecounter() 6636 </pre> 6637 6638 <h5>Overview:</h5> 6639 <p>The '<tt>llvm.readcyclecounter</tt>' intrinsic provides access to the cycle 6640 counter register (or similar low latency, high accuracy clocks) on those 6641 targets that support it. On X86, it should map to RDTSC. On Alpha, it 6642 should map to RPCC. As the backing counters overflow quickly (on the order 6643 of 9 seconds on alpha), this should only be used for small timings.</p> 6644 6645 <h5>Semantics:</h5> 6646 <p>When directly supported, reading the cycle counter should not modify any 6647 memory. Implementations are allowed to either return a application specific 6648 value or a system wide value. On backends without support, this is lowered 6649 to a constant 0.</p> 6650 6651 </div> 6652 6653 </div> 6654 6655 <!-- ======================================================================= --> 6656 <h3> 6657 <a name="int_libc">Standard C Library Intrinsics</a> 6658 </h3> 6659 6660 <div> 6661 6662 <p>LLVM provides intrinsics for a few important standard C library functions. 6663 These intrinsics allow source-language front-ends to pass information about 6664 the alignment of the pointer arguments to the code generator, providing 6665 opportunity for more efficient code generation.</p> 6666 6667 <!-- _______________________________________________________________________ --> 6668 <h4> 6669 <a name="int_memcpy">'<tt>llvm.memcpy</tt>' Intrinsic</a> 6670 </h4> 6671 6672 <div> 6673 6674 <h5>Syntax:</h5> 6675 <p>This is an overloaded intrinsic. You can use <tt>llvm.memcpy</tt> on any 6676 integer bit width and for different address spaces. Not all targets support 6677 all bit widths however.</p> 6678 6679 <pre> 6680 declare void @llvm.memcpy.p0i8.p0i8.i32(i8* <dest>, i8* <src>, 6681 i32 <len>, i32 <align>, i1 <isvolatile>) 6682 declare void @llvm.memcpy.p0i8.p0i8.i64(i8* <dest>, i8* <src>, 6683 i64 <len>, i32 <align>, i1 <isvolatile>) 6684 </pre> 6685 6686 <h5>Overview:</h5> 6687 <p>The '<tt>llvm.memcpy.*</tt>' intrinsics copy a block of memory from the 6688 source location to the destination location.</p> 6689 6690 <p>Note that, unlike the standard libc function, the <tt>llvm.memcpy.*</tt> 6691 intrinsics do not return a value, takes extra alignment/isvolatile arguments 6692 and the pointers can be in specified address spaces.</p> 6693 6694 <h5>Arguments:</h5> 6695 6696 <p>The first argument is a pointer to the destination, the second is a pointer 6697 to the source. The third argument is an integer argument specifying the 6698 number of bytes to copy, the fourth argument is the alignment of the 6699 source and destination locations, and the fifth is a boolean indicating a 6700 volatile access.</p> 6701 6702 <p>If the call to this intrinsic has an alignment value that is not 0 or 1, 6703 then the caller guarantees that both the source and destination pointers are 6704 aligned to that boundary.</p> 6705 6706 <p>If the <tt>isvolatile</tt> parameter is <tt>true</tt>, the 6707 <tt>llvm.memcpy</tt> call is a <a href="#volatile">volatile operation</a>. 6708 The detailed access behavior is not very cleanly specified and it is unwise 6709 to depend on it.</p> 6710 6711 <h5>Semantics:</h5> 6712 6713 <p>The '<tt>llvm.memcpy.*</tt>' intrinsics copy a block of memory from the 6714 source location to the destination location, which are not allowed to 6715 overlap. It copies "len" bytes of memory over. If the argument is known to 6716 be aligned to some boundary, this can be specified as the fourth argument, 6717 otherwise it should be set to 0 or 1.</p> 6718 6719 </div> 6720 6721 <!-- _______________________________________________________________________ --> 6722 <h4> 6723 <a name="int_memmove">'<tt>llvm.memmove</tt>' Intrinsic</a> 6724 </h4> 6725 6726 <div> 6727 6728 <h5>Syntax:</h5> 6729 <p>This is an overloaded intrinsic. You can use llvm.memmove on any integer bit 6730 width and for different address space. Not all targets support all bit 6731 widths however.</p> 6732 6733 <pre> 6734 declare void @llvm.memmove.p0i8.p0i8.i32(i8* <dest>, i8* <src>, 6735 i32 <len>, i32 <align>, i1 <isvolatile>) 6736 declare void @llvm.memmove.p0i8.p0i8.i64(i8* <dest>, i8* <src>, 6737 i64 <len>, i32 <align>, i1 <isvolatile>) 6738 </pre> 6739 6740 <h5>Overview:</h5> 6741 <p>The '<tt>llvm.memmove.*</tt>' intrinsics move a block of memory from the 6742 source location to the destination location. It is similar to the 6743 '<tt>llvm.memcpy</tt>' intrinsic but allows the two memory locations to 6744 overlap.</p> 6745 6746 <p>Note that, unlike the standard libc function, the <tt>llvm.memmove.*</tt> 6747 intrinsics do not return a value, takes extra alignment/isvolatile arguments 6748 and the pointers can be in specified address spaces.</p> 6749 6750 <h5>Arguments:</h5> 6751 6752 <p>The first argument is a pointer to the destination, the second is a pointer 6753 to the source. The third argument is an integer argument specifying the 6754 number of bytes to copy, the fourth argument is the alignment of the 6755 source and destination locations, and the fifth is a boolean indicating a 6756 volatile access.</p> 6757 6758 <p>If the call to this intrinsic has an alignment value that is not 0 or 1, 6759 then the caller guarantees that the source and destination pointers are 6760 aligned to that boundary.</p> 6761 6762 <p>If the <tt>isvolatile</tt> parameter is <tt>true</tt>, the 6763 <tt>llvm.memmove</tt> call is a <a href="#volatile">volatile operation</a>. 6764 The detailed access behavior is not very cleanly specified and it is unwise 6765 to depend on it.</p> 6766 6767 <h5>Semantics:</h5> 6768 6769 <p>The '<tt>llvm.memmove.*</tt>' intrinsics copy a block of memory from the 6770 source location to the destination location, which may overlap. It copies 6771 "len" bytes of memory over. If the argument is known to be aligned to some 6772 boundary, this can be specified as the fourth argument, otherwise it should 6773 be set to 0 or 1.</p> 6774 6775 </div> 6776 6777 <!-- _______________________________________________________________________ --> 6778 <h4> 6779 <a name="int_memset">'<tt>llvm.memset.*</tt>' Intrinsics</a> 6780 </h4> 6781 6782 <div> 6783 6784 <h5>Syntax:</h5> 6785 <p>This is an overloaded intrinsic. You can use llvm.memset on any integer bit 6786 width and for different address spaces. However, not all targets support all 6787 bit widths.</p> 6788 6789 <pre> 6790 declare void @llvm.memset.p0i8.i32(i8* <dest>, i8 <val>, 6791 i32 <len>, i32 <align>, i1 <isvolatile>) 6792 declare void @llvm.memset.p0i8.i64(i8* <dest>, i8 <val>, 6793 i64 <len>, i32 <align>, i1 <isvolatile>) 6794 </pre> 6795 6796 <h5>Overview:</h5> 6797 <p>The '<tt>llvm.memset.*</tt>' intrinsics fill a block of memory with a 6798 particular byte value.</p> 6799 6800 <p>Note that, unlike the standard libc function, the <tt>llvm.memset</tt> 6801 intrinsic does not return a value and takes extra alignment/volatile 6802 arguments. Also, the destination can be in an arbitrary address space.</p> 6803 6804 <h5>Arguments:</h5> 6805 <p>The first argument is a pointer to the destination to fill, the second is the 6806 byte value with which to fill it, the third argument is an integer argument 6807 specifying the number of bytes to fill, and the fourth argument is the known 6808 alignment of the destination location.</p> 6809 6810 <p>If the call to this intrinsic has an alignment value that is not 0 or 1, 6811 then the caller guarantees that the destination pointer is aligned to that 6812 boundary.</p> 6813 6814 <p>If the <tt>isvolatile</tt> parameter is <tt>true</tt>, the 6815 <tt>llvm.memset</tt> call is a <a href="#volatile">volatile operation</a>. 6816 The detailed access behavior is not very cleanly specified and it is unwise 6817 to depend on it.</p> 6818 6819 <h5>Semantics:</h5> 6820 <p>The '<tt>llvm.memset.*</tt>' intrinsics fill "len" bytes of memory starting 6821 at the destination location. If the argument is known to be aligned to some 6822 boundary, this can be specified as the fourth argument, otherwise it should 6823 be set to 0 or 1.</p> 6824 6825 </div> 6826 6827 <!-- _______________________________________________________________________ --> 6828 <h4> 6829 <a name="int_sqrt">'<tt>llvm.sqrt.*</tt>' Intrinsic</a> 6830 </h4> 6831 6832 <div> 6833 6834 <h5>Syntax:</h5> 6835 <p>This is an overloaded intrinsic. You can use <tt>llvm.sqrt</tt> on any 6836 floating point or vector of floating point type. Not all targets support all 6837 types however.</p> 6838 6839 <pre> 6840 declare float @llvm.sqrt.f32(float %Val) 6841 declare double @llvm.sqrt.f64(double %Val) 6842 declare x86_fp80 @llvm.sqrt.f80(x86_fp80 %Val) 6843 declare fp128 @llvm.sqrt.f128(fp128 %Val) 6844 declare ppc_fp128 @llvm.sqrt.ppcf128(ppc_fp128 %Val) 6845 </pre> 6846 6847 <h5>Overview:</h5> 6848 <p>The '<tt>llvm.sqrt</tt>' intrinsics return the sqrt of the specified operand, 6849 returning the same value as the libm '<tt>sqrt</tt>' functions would. 6850 Unlike <tt>sqrt</tt> in libm, however, <tt>llvm.sqrt</tt> has undefined 6851 behavior for negative numbers other than -0.0 (which allows for better 6852 optimization, because there is no need to worry about errno being 6853 set). <tt>llvm.sqrt(-0.0)</tt> is defined to return -0.0 like IEEE sqrt.</p> 6854 6855 <h5>Arguments:</h5> 6856 <p>The argument and return value are floating point numbers of the same 6857 type.</p> 6858 6859 <h5>Semantics:</h5> 6860 <p>This function returns the sqrt of the specified operand if it is a 6861 nonnegative floating point number.</p> 6862 6863 </div> 6864 6865 <!-- _______________________________________________________________________ --> 6866 <h4> 6867 <a name="int_powi">'<tt>llvm.powi.*</tt>' Intrinsic</a> 6868 </h4> 6869 6870 <div> 6871 6872 <h5>Syntax:</h5> 6873 <p>This is an overloaded intrinsic. You can use <tt>llvm.powi</tt> on any 6874 floating point or vector of floating point type. Not all targets support all 6875 types however.</p> 6876 6877 <pre> 6878 declare float @llvm.powi.f32(float %Val, i32 %power) 6879 declare double @llvm.powi.f64(double %Val, i32 %power) 6880 declare x86_fp80 @llvm.powi.f80(x86_fp80 %Val, i32 %power) 6881 declare fp128 @llvm.powi.f128(fp128 %Val, i32 %power) 6882 declare ppc_fp128 @llvm.powi.ppcf128(ppc_fp128 %Val, i32 %power) 6883 </pre> 6884 6885 <h5>Overview:</h5> 6886 <p>The '<tt>llvm.powi.*</tt>' intrinsics return the first operand raised to the 6887 specified (positive or negative) power. The order of evaluation of 6888 multiplications is not defined. When a vector of floating point type is 6889 used, the second argument remains a scalar integer value.</p> 6890 6891 <h5>Arguments:</h5> 6892 <p>The second argument is an integer power, and the first is a value to raise to 6893 that power.</p> 6894 6895 <h5>Semantics:</h5> 6896 <p>This function returns the first value raised to the second power with an 6897 unspecified sequence of rounding operations.</p> 6898 6899 </div> 6900 6901 <!-- _______________________________________________________________________ --> 6902 <h4> 6903 <a name="int_sin">'<tt>llvm.sin.*</tt>' Intrinsic</a> 6904 </h4> 6905 6906 <div> 6907 6908 <h5>Syntax:</h5> 6909 <p>This is an overloaded intrinsic. You can use <tt>llvm.sin</tt> on any 6910 floating point or vector of floating point type. Not all targets support all 6911 types however.</p> 6912 6913 <pre> 6914 declare float @llvm.sin.f32(float %Val) 6915 declare double @llvm.sin.f64(double %Val) 6916 declare x86_fp80 @llvm.sin.f80(x86_fp80 %Val) 6917 declare fp128 @llvm.sin.f128(fp128 %Val) 6918 declare ppc_fp128 @llvm.sin.ppcf128(ppc_fp128 %Val) 6919 </pre> 6920 6921 <h5>Overview:</h5> 6922 <p>The '<tt>llvm.sin.*</tt>' intrinsics return the sine of the operand.</p> 6923 6924 <h5>Arguments:</h5> 6925 <p>The argument and return value are floating point numbers of the same 6926 type.</p> 6927 6928 <h5>Semantics:</h5> 6929 <p>This function returns the sine of the specified operand, returning the same 6930 values as the libm <tt>sin</tt> functions would, and handles error conditions 6931 in the same way.</p> 6932 6933 </div> 6934 6935 <!-- _______________________________________________________________________ --> 6936 <h4> 6937 <a name="int_cos">'<tt>llvm.cos.*</tt>' Intrinsic</a> 6938 </h4> 6939 6940 <div> 6941 6942 <h5>Syntax:</h5> 6943 <p>This is an overloaded intrinsic. You can use <tt>llvm.cos</tt> on any 6944 floating point or vector of floating point type. Not all targets support all 6945 types however.</p> 6946 6947 <pre> 6948 declare float @llvm.cos.f32(float %Val) 6949 declare double @llvm.cos.f64(double %Val) 6950 declare x86_fp80 @llvm.cos.f80(x86_fp80 %Val) 6951 declare fp128 @llvm.cos.f128(fp128 %Val) 6952 declare ppc_fp128 @llvm.cos.ppcf128(ppc_fp128 %Val) 6953 </pre> 6954 6955 <h5>Overview:</h5> 6956 <p>The '<tt>llvm.cos.*</tt>' intrinsics return the cosine of the operand.</p> 6957 6958 <h5>Arguments:</h5> 6959 <p>The argument and return value are floating point numbers of the same 6960 type.</p> 6961 6962 <h5>Semantics:</h5> 6963 <p>This function returns the cosine of the specified operand, returning the same 6964 values as the libm <tt>cos</tt> functions would, and handles error conditions 6965 in the same way.</p> 6966 6967 </div> 6968 6969 <!-- _______________________________________________________________________ --> 6970 <h4> 6971 <a name="int_pow">'<tt>llvm.pow.*</tt>' Intrinsic</a> 6972 </h4> 6973 6974 <div> 6975 6976 <h5>Syntax:</h5> 6977 <p>This is an overloaded intrinsic. You can use <tt>llvm.pow</tt> on any 6978 floating point or vector of floating point type. Not all targets support all 6979 types however.</p> 6980 6981 <pre> 6982 declare float @llvm.pow.f32(float %Val, float %Power) 6983 declare double @llvm.pow.f64(double %Val, double %Power) 6984 declare x86_fp80 @llvm.pow.f80(x86_fp80 %Val, x86_fp80 %Power) 6985 declare fp128 @llvm.pow.f128(fp128 %Val, fp128 %Power) 6986 declare ppc_fp128 @llvm.pow.ppcf128(ppc_fp128 %Val, ppc_fp128 Power) 6987 </pre> 6988 6989 <h5>Overview:</h5> 6990 <p>The '<tt>llvm.pow.*</tt>' intrinsics return the first operand raised to the 6991 specified (positive or negative) power.</p> 6992 6993 <h5>Arguments:</h5> 6994 <p>The second argument is a floating point power, and the first is a value to 6995 raise to that power.</p> 6996 6997 <h5>Semantics:</h5> 6998 <p>This function returns the first value raised to the second power, returning 6999 the same values as the libm <tt>pow</tt> functions would, and handles error 7000 conditions in the same way.</p> 7001 7002 </div> 7003 7004 </div> 7005 7006 <!-- _______________________________________________________________________ --> 7007 <h4> 7008 <a name="int_exp">'<tt>llvm.exp.*</tt>' Intrinsic</a> 7009 </h4> 7010 7011 <div> 7012 7013 <h5>Syntax:</h5> 7014 <p>This is an overloaded intrinsic. You can use <tt>llvm.exp</tt> on any 7015 floating point or vector of floating point type. Not all targets support all 7016 types however.</p> 7017 7018 <pre> 7019 declare float @llvm.exp.f32(float %Val) 7020 declare double @llvm.exp.f64(double %Val) 7021 declare x86_fp80 @llvm.exp.f80(x86_fp80 %Val) 7022 declare fp128 @llvm.exp.f128(fp128 %Val) 7023 declare ppc_fp128 @llvm.exp.ppcf128(ppc_fp128 %Val) 7024 </pre> 7025 7026 <h5>Overview:</h5> 7027 <p>The '<tt>llvm.exp.*</tt>' intrinsics perform the exp function.</p> 7028 7029 <h5>Arguments:</h5> 7030 <p>The argument and return value are floating point numbers of the same 7031 type.</p> 7032 7033 <h5>Semantics:</h5> 7034 <p>This function returns the same values as the libm <tt>exp</tt> functions 7035 would, and handles error conditions in the same way.</p> 7036 7037 </div> 7038 7039 <!-- _______________________________________________________________________ --> 7040 <h4> 7041 <a name="int_log">'<tt>llvm.log.*</tt>' Intrinsic</a> 7042 </h4> 7043 7044 <div> 7045 7046 <h5>Syntax:</h5> 7047 <p>This is an overloaded intrinsic. You can use <tt>llvm.log</tt> on any 7048 floating point or vector of floating point type. Not all targets support all 7049 types however.</p> 7050 7051 <pre> 7052 declare float @llvm.log.f32(float %Val) 7053 declare double @llvm.log.f64(double %Val) 7054 declare x86_fp80 @llvm.log.f80(x86_fp80 %Val) 7055 declare fp128 @llvm.log.f128(fp128 %Val) 7056 declare ppc_fp128 @llvm.log.ppcf128(ppc_fp128 %Val) 7057 </pre> 7058 7059 <h5>Overview:</h5> 7060 <p>The '<tt>llvm.log.*</tt>' intrinsics perform the log function.</p> 7061 7062 <h5>Arguments:</h5> 7063 <p>The argument and return value are floating point numbers of the same 7064 type.</p> 7065 7066 <h5>Semantics:</h5> 7067 <p>This function returns the same values as the libm <tt>log</tt> functions 7068 would, and handles error conditions in the same way.</p> 7069 7070 <h4> 7071 <a name="int_fma">'<tt>llvm.fma.*</tt>' Intrinsic</a> 7072 </h4> 7073 7074 <div> 7075 7076 <h5>Syntax:</h5> 7077 <p>This is an overloaded intrinsic. You can use <tt>llvm.fma</tt> on any 7078 floating point or vector of floating point type. Not all targets support all 7079 types however.</p> 7080 7081 <pre> 7082 declare float @llvm.fma.f32(float %a, float %b, float %c) 7083 declare double @llvm.fma.f64(double %a, double %b, double %c) 7084 declare x86_fp80 @llvm.fma.f80(x86_fp80 %a, x86_fp80 %b, x86_fp80 %c) 7085 declare fp128 @llvm.fma.f128(fp128 %a, fp128 %b, fp128 %c) 7086 declare ppc_fp128 @llvm.fma.ppcf128(ppc_fp128 %a, ppc_fp128 %b, ppc_fp128 %c) 7087 </pre> 7088 7089 <h5>Overview:</h5> 7090 <p>The '<tt>llvm.fma.*</tt>' intrinsics perform the fused multiply-add 7091 operation.</p> 7092 7093 <h5>Arguments:</h5> 7094 <p>The argument and return value are floating point numbers of the same 7095 type.</p> 7096 7097 <h5>Semantics:</h5> 7098 <p>This function returns the same values as the libm <tt>fma</tt> functions 7099 would.</p> 7100 7101 </div> 7102 7103 <!-- ======================================================================= --> 7104 <h3> 7105 <a name="int_manip">Bit Manipulation Intrinsics</a> 7106 </h3> 7107 7108 <div> 7109 7110 <p>LLVM provides intrinsics for a few important bit manipulation operations. 7111 These allow efficient code generation for some algorithms.</p> 7112 7113 <!-- _______________________________________________________________________ --> 7114 <h4> 7115 <a name="int_bswap">'<tt>llvm.bswap.*</tt>' Intrinsics</a> 7116 </h4> 7117 7118 <div> 7119 7120 <h5>Syntax:</h5> 7121 <p>This is an overloaded intrinsic function. You can use bswap on any integer 7122 type that is an even number of bytes (i.e. BitWidth % 16 == 0).</p> 7123 7124 <pre> 7125 declare i16 @llvm.bswap.i16(i16 <id>) 7126 declare i32 @llvm.bswap.i32(i32 <id>) 7127 declare i64 @llvm.bswap.i64(i64 <id>) 7128 </pre> 7129 7130 <h5>Overview:</h5> 7131 <p>The '<tt>llvm.bswap</tt>' family of intrinsics is used to byte swap integer 7132 values with an even number of bytes (positive multiple of 16 bits). These 7133 are useful for performing operations on data that is not in the target's 7134 native byte order.</p> 7135 7136 <h5>Semantics:</h5> 7137 <p>The <tt>llvm.bswap.i16</tt> intrinsic returns an i16 value that has the high 7138 and low byte of the input i16 swapped. Similarly, 7139 the <tt>llvm.bswap.i32</tt> intrinsic returns an i32 value that has the four 7140 bytes of the input i32 swapped, so that if the input bytes are numbered 0, 1, 7141 2, 3 then the returned i32 will have its bytes in 3, 2, 1, 0 order. 7142 The <tt>llvm.bswap.i48</tt>, <tt>llvm.bswap.i64</tt> and other intrinsics 7143 extend this concept to additional even-byte lengths (6 bytes, 8 bytes and 7144 more, respectively).</p> 7145 7146 </div> 7147 7148 <!-- _______________________________________________________________________ --> 7149 <h4> 7150 <a name="int_ctpop">'<tt>llvm.ctpop.*</tt>' Intrinsic</a> 7151 </h4> 7152 7153 <div> 7154 7155 <h5>Syntax:</h5> 7156 <p>This is an overloaded intrinsic. You can use llvm.ctpop on any integer bit 7157 width, or on any vector with integer elements. Not all targets support all 7158 bit widths or vector types, however.</p> 7159 7160 <pre> 7161 declare i8 @llvm.ctpop.i8(i8 <src>) 7162 declare i16 @llvm.ctpop.i16(i16 <src>) 7163 declare i32 @llvm.ctpop.i32(i32 <src>) 7164 declare i64 @llvm.ctpop.i64(i64 <src>) 7165 declare i256 @llvm.ctpop.i256(i256 <src>) 7166 declare <2 x i32> @llvm.ctpop.v2i32(<2 x i32> <src>) 7167 </pre> 7168 7169 <h5>Overview:</h5> 7170 <p>The '<tt>llvm.ctpop</tt>' family of intrinsics counts the number of bits set 7171 in a value.</p> 7172 7173 <h5>Arguments:</h5> 7174 <p>The only argument is the value to be counted. The argument may be of any 7175 integer type, or a vector with integer elements. 7176 The return type must match the argument type.</p> 7177 7178 <h5>Semantics:</h5> 7179 <p>The '<tt>llvm.ctpop</tt>' intrinsic counts the 1's in a variable, or within each 7180 element of a vector.</p> 7181 7182 </div> 7183 7184 <!-- _______________________________________________________________________ --> 7185 <h4> 7186 <a name="int_ctlz">'<tt>llvm.ctlz.*</tt>' Intrinsic</a> 7187 </h4> 7188 7189 <div> 7190 7191 <h5>Syntax:</h5> 7192 <p>This is an overloaded intrinsic. You can use <tt>llvm.ctlz</tt> on any 7193 integer bit width, or any vector whose elements are integers. Not all 7194 targets support all bit widths or vector types, however.</p> 7195 7196 <pre> 7197 declare i8 @llvm.ctlz.i8 (i8 <src>) 7198 declare i16 @llvm.ctlz.i16(i16 <src>) 7199 declare i32 @llvm.ctlz.i32(i32 <src>) 7200 declare i64 @llvm.ctlz.i64(i64 <src>) 7201 declare i256 @llvm.ctlz.i256(i256 <src>) 7202 declare <2 x i32> @llvm.ctlz.v2i32(<2 x i32> <src;gt) 7203 </pre> 7204 7205 <h5>Overview:</h5> 7206 <p>The '<tt>llvm.ctlz</tt>' family of intrinsic functions counts the number of 7207 leading zeros in a variable.</p> 7208 7209 <h5>Arguments:</h5> 7210 <p>The only argument is the value to be counted. The argument may be of any 7211 integer type, or any vector type with integer element type. 7212 The return type must match the argument type.</p> 7213 7214 <h5>Semantics:</h5> 7215 <p>The '<tt>llvm.ctlz</tt>' intrinsic counts the leading (most significant) 7216 zeros in a variable, or within each element of the vector if the operation 7217 is of vector type. If the src == 0 then the result is the size in bits of 7218 the type of src. For example, <tt>llvm.ctlz(i32 2) = 30</tt>.</p> 7219 7220 </div> 7221 7222 <!-- _______________________________________________________________________ --> 7223 <h4> 7224 <a name="int_cttz">'<tt>llvm.cttz.*</tt>' Intrinsic</a> 7225 </h4> 7226 7227 <div> 7228 7229 <h5>Syntax:</h5> 7230 <p>This is an overloaded intrinsic. You can use <tt>llvm.cttz</tt> on any 7231 integer bit width, or any vector of integer elements. Not all targets 7232 support all bit widths or vector types, however.</p> 7233 7234 <pre> 7235 declare i8 @llvm.cttz.i8 (i8 <src>) 7236 declare i16 @llvm.cttz.i16(i16 <src>) 7237 declare i32 @llvm.cttz.i32(i32 <src>) 7238 declare i64 @llvm.cttz.i64(i64 <src>) 7239 declare i256 @llvm.cttz.i256(i256 <src>) 7240 declase <2 x i32> @llvm.cttz.v2i32(<2 x i32> <src>) 7241 </pre> 7242 7243 <h5>Overview:</h5> 7244 <p>The '<tt>llvm.cttz</tt>' family of intrinsic functions counts the number of 7245 trailing zeros.</p> 7246 7247 <h5>Arguments:</h5> 7248 <p>The only argument is the value to be counted. The argument may be of any 7249 integer type, or a vectory with integer element type.. The return type 7250 must match the argument type.</p> 7251 7252 <h5>Semantics:</h5> 7253 <p>The '<tt>llvm.cttz</tt>' intrinsic counts the trailing (least significant) 7254 zeros in a variable, or within each element of a vector. 7255 If the src == 0 then the result is the size in bits of 7256 the type of src. For example, <tt>llvm.cttz(2) = 1</tt>.</p> 7257 7258 </div> 7259 7260 </div> 7261 7262 <!-- ======================================================================= --> 7263 <h3> 7264 <a name="int_overflow">Arithmetic with Overflow Intrinsics</a> 7265 </h3> 7266 7267 <div> 7268 7269 <p>LLVM provides intrinsics for some arithmetic with overflow operations.</p> 7270 7271 <!-- _______________________________________________________________________ --> 7272 <h4> 7273 <a name="int_sadd_overflow"> 7274 '<tt>llvm.sadd.with.overflow.*</tt>' Intrinsics 7275 </a> 7276 </h4> 7277 7278 <div> 7279 7280 <h5>Syntax:</h5> 7281 <p>This is an overloaded intrinsic. You can use <tt>llvm.sadd.with.overflow</tt> 7282 on any integer bit width.</p> 7283 7284 <pre> 7285 declare {i16, i1} @llvm.sadd.with.overflow.i16(i16 %a, i16 %b) 7286 declare {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b) 7287 declare {i64, i1} @llvm.sadd.with.overflow.i64(i64 %a, i64 %b) 7288 </pre> 7289 7290 <h5>Overview:</h5> 7291 <p>The '<tt>llvm.sadd.with.overflow</tt>' family of intrinsic functions perform 7292 a signed addition of the two arguments, and indicate whether an overflow 7293 occurred during the signed summation.</p> 7294 7295 <h5>Arguments:</h5> 7296 <p>The arguments (%a and %b) and the first element of the result structure may 7297 be of integer types of any bit width, but they must have the same bit 7298 width. The second element of the result structure must be of 7299 type <tt>i1</tt>. <tt>%a</tt> and <tt>%b</tt> are the two values that will 7300 undergo signed addition.</p> 7301 7302 <h5>Semantics:</h5> 7303 <p>The '<tt>llvm.sadd.with.overflow</tt>' family of intrinsic functions perform 7304 a signed addition of the two variables. They return a structure — the 7305 first element of which is the signed summation, and the second element of 7306 which is a bit specifying if the signed summation resulted in an 7307 overflow.</p> 7308 7309 <h5>Examples:</h5> 7310 <pre> 7311 %res = call {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b) 7312 %sum = extractvalue {i32, i1} %res, 0 7313 %obit = extractvalue {i32, i1} %res, 1 7314 br i1 %obit, label %overflow, label %normal 7315 </pre> 7316 7317 </div> 7318 7319 <!-- _______________________________________________________________________ --> 7320 <h4> 7321 <a name="int_uadd_overflow"> 7322 '<tt>llvm.uadd.with.overflow.*</tt>' Intrinsics 7323 </a> 7324 </h4> 7325 7326 <div> 7327 7328 <h5>Syntax:</h5> 7329 <p>This is an overloaded intrinsic. You can use <tt>llvm.uadd.with.overflow</tt> 7330 on any integer bit width.</p> 7331 7332 <pre> 7333 declare {i16, i1} @llvm.uadd.with.overflow.i16(i16 %a, i16 %b) 7334 declare {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b) 7335 declare {i64, i1} @llvm.uadd.with.overflow.i64(i64 %a, i64 %b) 7336 </pre> 7337 7338 <h5>Overview:</h5> 7339 <p>The '<tt>llvm.uadd.with.overflow</tt>' family of intrinsic functions perform 7340 an unsigned addition of the two arguments, and indicate whether a carry 7341 occurred during the unsigned summation.</p> 7342 7343 <h5>Arguments:</h5> 7344 <p>The arguments (%a and %b) and the first element of the result structure may 7345 be of integer types of any bit width, but they must have the same bit 7346 width. The second element of the result structure must be of 7347 type <tt>i1</tt>. <tt>%a</tt> and <tt>%b</tt> are the two values that will 7348 undergo unsigned addition.</p> 7349 7350 <h5>Semantics:</h5> 7351 <p>The '<tt>llvm.uadd.with.overflow</tt>' family of intrinsic functions perform 7352 an unsigned addition of the two arguments. They return a structure — 7353 the first element of which is the sum, and the second element of which is a 7354 bit specifying if the unsigned summation resulted in a carry.</p> 7355 7356 <h5>Examples:</h5> 7357 <pre> 7358 %res = call {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b) 7359 %sum = extractvalue {i32, i1} %res, 0 7360 %obit = extractvalue {i32, i1} %res, 1 7361 br i1 %obit, label %carry, label %normal 7362 </pre> 7363 7364 </div> 7365 7366 <!-- _______________________________________________________________________ --> 7367 <h4> 7368 <a name="int_ssub_overflow"> 7369 '<tt>llvm.ssub.with.overflow.*</tt>' Intrinsics 7370 </a> 7371 </h4> 7372 7373 <div> 7374 7375 <h5>Syntax:</h5> 7376 <p>This is an overloaded intrinsic. You can use <tt>llvm.ssub.with.overflow</tt> 7377 on any integer bit width.</p> 7378 7379 <pre> 7380 declare {i16, i1} @llvm.ssub.with.overflow.i16(i16 %a, i16 %b) 7381 declare {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b) 7382 declare {i64, i1} @llvm.ssub.with.overflow.i64(i64 %a, i64 %b) 7383 </pre> 7384 7385 <h5>Overview:</h5> 7386 <p>The '<tt>llvm.ssub.with.overflow</tt>' family of intrinsic functions perform 7387 a signed subtraction of the two arguments, and indicate whether an overflow 7388 occurred during the signed subtraction.</p> 7389 7390 <h5>Arguments:</h5> 7391 <p>The arguments (%a and %b) and the first element of the result structure may 7392 be of integer types of any bit width, but they must have the same bit 7393 width. The second element of the result structure must be of 7394 type <tt>i1</tt>. <tt>%a</tt> and <tt>%b</tt> are the two values that will 7395 undergo signed subtraction.</p> 7396 7397 <h5>Semantics:</h5> 7398 <p>The '<tt>llvm.ssub.with.overflow</tt>' family of intrinsic functions perform 7399 a signed subtraction of the two arguments. They return a structure — 7400 the first element of which is the subtraction, and the second element of 7401 which is a bit specifying if the signed subtraction resulted in an 7402 overflow.</p> 7403 7404 <h5>Examples:</h5> 7405 <pre> 7406 %res = call {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b) 7407 %sum = extractvalue {i32, i1} %res, 0 7408 %obit = extractvalue {i32, i1} %res, 1 7409 br i1 %obit, label %overflow, label %normal 7410 </pre> 7411 7412 </div> 7413 7414 <!-- _______________________________________________________________________ --> 7415 <h4> 7416 <a name="int_usub_overflow"> 7417 '<tt>llvm.usub.with.overflow.*</tt>' Intrinsics 7418 </a> 7419 </h4> 7420 7421 <div> 7422 7423 <h5>Syntax:</h5> 7424 <p>This is an overloaded intrinsic. You can use <tt>llvm.usub.with.overflow</tt> 7425 on any integer bit width.</p> 7426 7427 <pre> 7428 declare {i16, i1} @llvm.usub.with.overflow.i16(i16 %a, i16 %b) 7429 declare {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b) 7430 declare {i64, i1} @llvm.usub.with.overflow.i64(i64 %a, i64 %b) 7431 </pre> 7432 7433 <h5>Overview:</h5> 7434 <p>The '<tt>llvm.usub.with.overflow</tt>' family of intrinsic functions perform 7435 an unsigned subtraction of the two arguments, and indicate whether an 7436 overflow occurred during the unsigned subtraction.</p> 7437 7438 <h5>Arguments:</h5> 7439 <p>The arguments (%a and %b) and the first element of the result structure may 7440 be of integer types of any bit width, but they must have the same bit 7441 width. The second element of the result structure must be of 7442 type <tt>i1</tt>. <tt>%a</tt> and <tt>%b</tt> are the two values that will 7443 undergo unsigned subtraction.</p> 7444 7445 <h5>Semantics:</h5> 7446 <p>The '<tt>llvm.usub.with.overflow</tt>' family of intrinsic functions perform 7447 an unsigned subtraction of the two arguments. They return a structure — 7448 the first element of which is the subtraction, and the second element of 7449 which is a bit specifying if the unsigned subtraction resulted in an 7450 overflow.</p> 7451 7452 <h5>Examples:</h5> 7453 <pre> 7454 %res = call {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b) 7455 %sum = extractvalue {i32, i1} %res, 0 7456 %obit = extractvalue {i32, i1} %res, 1 7457 br i1 %obit, label %overflow, label %normal 7458 </pre> 7459 7460 </div> 7461 7462 <!-- _______________________________________________________________________ --> 7463 <h4> 7464 <a name="int_smul_overflow"> 7465 '<tt>llvm.smul.with.overflow.*</tt>' Intrinsics 7466 </a> 7467 </h4> 7468 7469 <div> 7470 7471 <h5>Syntax:</h5> 7472 <p>This is an overloaded intrinsic. You can use <tt>llvm.smul.with.overflow</tt> 7473 on any integer bit width.</p> 7474 7475 <pre> 7476 declare {i16, i1} @llvm.smul.with.overflow.i16(i16 %a, i16 %b) 7477 declare {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b) 7478 declare {i64, i1} @llvm.smul.with.overflow.i64(i64 %a, i64 %b) 7479 </pre> 7480 7481 <h5>Overview:</h5> 7482 7483 <p>The '<tt>llvm.smul.with.overflow</tt>' family of intrinsic functions perform 7484 a signed multiplication of the two arguments, and indicate whether an 7485 overflow occurred during the signed multiplication.</p> 7486 7487 <h5>Arguments:</h5> 7488 <p>The arguments (%a and %b) and the first element of the result structure may 7489 be of integer types of any bit width, but they must have the same bit 7490 width. The second element of the result structure must be of 7491 type <tt>i1</tt>. <tt>%a</tt> and <tt>%b</tt> are the two values that will 7492 undergo signed multiplication.</p> 7493 7494 <h5>Semantics:</h5> 7495 <p>The '<tt>llvm.smul.with.overflow</tt>' family of intrinsic functions perform 7496 a signed multiplication of the two arguments. They return a structure — 7497 the first element of which is the multiplication, and the second element of 7498 which is a bit specifying if the signed multiplication resulted in an 7499 overflow.</p> 7500 7501 <h5>Examples:</h5> 7502 <pre> 7503 %res = call {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b) 7504 %sum = extractvalue {i32, i1} %res, 0 7505 %obit = extractvalue {i32, i1} %res, 1 7506 br i1 %obit, label %overflow, label %normal 7507 </pre> 7508 7509 </div> 7510 7511 <!-- _______________________________________________________________________ --> 7512 <h4> 7513 <a name="int_umul_overflow"> 7514 '<tt>llvm.umul.with.overflow.*</tt>' Intrinsics 7515 </a> 7516 </h4> 7517 7518 <div> 7519 7520 <h5>Syntax:</h5> 7521 <p>This is an overloaded intrinsic. You can use <tt>llvm.umul.with.overflow</tt> 7522 on any integer bit width.</p> 7523 7524 <pre> 7525 declare {i16, i1} @llvm.umul.with.overflow.i16(i16 %a, i16 %b) 7526 declare {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b) 7527 declare {i64, i1} @llvm.umul.with.overflow.i64(i64 %a, i64 %b) 7528 </pre> 7529 7530 <h5>Overview:</h5> 7531 <p>The '<tt>llvm.umul.with.overflow</tt>' family of intrinsic functions perform 7532 a unsigned multiplication of the two arguments, and indicate whether an 7533 overflow occurred during the unsigned multiplication.</p> 7534 7535 <h5>Arguments:</h5> 7536 <p>The arguments (%a and %b) and the first element of the result structure may 7537 be of integer types of any bit width, but they must have the same bit 7538 width. The second element of the result structure must be of 7539 type <tt>i1</tt>. <tt>%a</tt> and <tt>%b</tt> are the two values that will 7540 undergo unsigned multiplication.</p> 7541 7542 <h5>Semantics:</h5> 7543 <p>The '<tt>llvm.umul.with.overflow</tt>' family of intrinsic functions perform 7544 an unsigned multiplication of the two arguments. They return a structure 7545 — the first element of which is the multiplication, and the second 7546 element of which is a bit specifying if the unsigned multiplication resulted 7547 in an overflow.</p> 7548 7549 <h5>Examples:</h5> 7550 <pre> 7551 %res = call {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b) 7552 %sum = extractvalue {i32, i1} %res, 0 7553 %obit = extractvalue {i32, i1} %res, 1 7554 br i1 %obit, label %overflow, label %normal 7555 </pre> 7556 7557 </div> 7558 7559 </div> 7560 7561 <!-- ======================================================================= --> 7562 <h3> 7563 <a name="int_fp16">Half Precision Floating Point Intrinsics</a> 7564 </h3> 7565 7566 <div> 7567 7568 <p>Half precision floating point is a storage-only format. This means that it is 7569 a dense encoding (in memory) but does not support computation in the 7570 format.</p> 7571 7572 <p>This means that code must first load the half-precision floating point 7573 value as an i16, then convert it to float with <a 7574 href="#int_convert_from_fp16"><tt>llvm.convert.from.fp16</tt></a>. 7575 Computation can then be performed on the float value (including extending to 7576 double etc). To store the value back to memory, it is first converted to 7577 float if needed, then converted to i16 with 7578 <a href="#int_convert_to_fp16"><tt>llvm.convert.to.fp16</tt></a>, then 7579 storing as an i16 value.</p> 7580 7581 <!-- _______________________________________________________________________ --> 7582 <h4> 7583 <a name="int_convert_to_fp16"> 7584 '<tt>llvm.convert.to.fp16</tt>' Intrinsic 7585 </a> 7586 </h4> 7587 7588 <div> 7589 7590 <h5>Syntax:</h5> 7591 <pre> 7592 declare i16 @llvm.convert.to.fp16(f32 %a) 7593 </pre> 7594 7595 <h5>Overview:</h5> 7596 <p>The '<tt>llvm.convert.to.fp16</tt>' intrinsic function performs 7597 a conversion from single precision floating point format to half precision 7598 floating point format.</p> 7599 7600 <h5>Arguments:</h5> 7601 <p>The intrinsic function contains single argument - the value to be 7602 converted.</p> 7603 7604 <h5>Semantics:</h5> 7605 <p>The '<tt>llvm.convert.to.fp16</tt>' intrinsic function performs 7606 a conversion from single precision floating point format to half precision 7607 floating point format. The return value is an <tt>i16</tt> which 7608 contains the converted number.</p> 7609 7610 <h5>Examples:</h5> 7611 <pre> 7612 %res = call i16 @llvm.convert.to.fp16(f32 %a) 7613 store i16 %res, i16* @x, align 2 7614 </pre> 7615 7616 </div> 7617 7618 <!-- _______________________________________________________________________ --> 7619 <h4> 7620 <a name="int_convert_from_fp16"> 7621 '<tt>llvm.convert.from.fp16</tt>' Intrinsic 7622 </a> 7623 </h4> 7624 7625 <div> 7626 7627 <h5>Syntax:</h5> 7628 <pre> 7629 declare f32 @llvm.convert.from.fp16(i16 %a) 7630 </pre> 7631 7632 <h5>Overview:</h5> 7633 <p>The '<tt>llvm.convert.from.fp16</tt>' intrinsic function performs 7634 a conversion from half precision floating point format to single precision 7635 floating point format.</p> 7636 7637 <h5>Arguments:</h5> 7638 <p>The intrinsic function contains single argument - the value to be 7639 converted.</p> 7640 7641 <h5>Semantics:</h5> 7642 <p>The '<tt>llvm.convert.from.fp16</tt>' intrinsic function performs a 7643 conversion from half single precision floating point format to single 7644 precision floating point format. The input half-float value is represented by 7645 an <tt>i16</tt> value.</p> 7646 7647 <h5>Examples:</h5> 7648 <pre> 7649 %a = load i16* @x, align 2 7650 %res = call f32 @llvm.convert.from.fp16(i16 %a) 7651 </pre> 7652 7653 </div> 7654 7655 </div> 7656 7657 <!-- ======================================================================= --> 7658 <h3> 7659 <a name="int_debugger">Debugger Intrinsics</a> 7660 </h3> 7661 7662 <div> 7663 7664 <p>The LLVM debugger intrinsics (which all start with <tt>llvm.dbg.</tt> 7665 prefix), are described in 7666 the <a href="SourceLevelDebugging.html#format_common_intrinsics">LLVM Source 7667 Level Debugging</a> document.</p> 7668 7669 </div> 7670 7671 <!-- ======================================================================= --> 7672 <h3> 7673 <a name="int_eh">Exception Handling Intrinsics</a> 7674 </h3> 7675 7676 <div> 7677 7678 <p>The LLVM exception handling intrinsics (which all start with 7679 <tt>llvm.eh.</tt> prefix), are described in 7680 the <a href="ExceptionHandling.html#format_common_intrinsics">LLVM Exception 7681 Handling</a> document.</p> 7682 7683 </div> 7684 7685 <!-- ======================================================================= --> 7686 <h3> 7687 <a name="int_trampoline">Trampoline Intrinsics</a> 7688 </h3> 7689 7690 <div> 7691 7692 <p>These intrinsics make it possible to excise one parameter, marked with 7693 the <a href="#nest"><tt>nest</tt></a> attribute, from a function. 7694 The result is a callable 7695 function pointer lacking the nest parameter - the caller does not need to 7696 provide a value for it. Instead, the value to use is stored in advance in a 7697 "trampoline", a block of memory usually allocated on the stack, which also 7698 contains code to splice the nest value into the argument list. This is used 7699 to implement the GCC nested function address extension.</p> 7700 7701 <p>For example, if the function is 7702 <tt>i32 f(i8* nest %c, i32 %x, i32 %y)</tt> then the resulting function 7703 pointer has signature <tt>i32 (i32, i32)*</tt>. It can be created as 7704 follows:</p> 7705 7706 <pre class="doc_code"> 7707 %tramp = alloca [10 x i8], align 4 ; size and alignment only correct for X86 7708 %tramp1 = getelementptr [10 x i8]* %tramp, i32 0, i32 0 7709 call i8* @llvm.init.trampoline(i8* %tramp1, i8* bitcast (i32 (i8*, i32, i32)* @f to i8*), i8* %nval) 7710 %p = call i8* @llvm.adjust.trampoline(i8* %tramp1) 7711 %fp = bitcast i8* %p to i32 (i32, i32)* 7712 </pre> 7713 7714 <p>The call <tt>%val = call i32 %fp(i32 %x, i32 %y)</tt> is then equivalent 7715 to <tt>%val = call i32 %f(i8* %nval, i32 %x, i32 %y)</tt>.</p> 7716 7717 <!-- _______________________________________________________________________ --> 7718 <h4> 7719 <a name="int_it"> 7720 '<tt>llvm.init.trampoline</tt>' Intrinsic 7721 </a> 7722 </h4> 7723 7724 <div> 7725 7726 <h5>Syntax:</h5> 7727 <pre> 7728 declare void @llvm.init.trampoline(i8* <tramp>, i8* <func>, i8* <nval>) 7729 </pre> 7730 7731 <h5>Overview:</h5> 7732 <p>This fills the memory pointed to by <tt>tramp</tt> with executable code, 7733 turning it into a trampoline.</p> 7734 7735 <h5>Arguments:</h5> 7736 <p>The <tt>llvm.init.trampoline</tt> intrinsic takes three arguments, all 7737 pointers. The <tt>tramp</tt> argument must point to a sufficiently large and 7738 sufficiently aligned block of memory; this memory is written to by the 7739 intrinsic. Note that the size and the alignment are target-specific - LLVM 7740 currently provides no portable way of determining them, so a front-end that 7741 generates this intrinsic needs to have some target-specific knowledge. 7742 The <tt>func</tt> argument must hold a function bitcast to 7743 an <tt>i8*</tt>.</p> 7744 7745 <h5>Semantics:</h5> 7746 <p>The block of memory pointed to by <tt>tramp</tt> is filled with target 7747 dependent code, turning it into a function. Then <tt>tramp</tt> needs to be 7748 passed to <a href="#int_at">llvm.adjust.trampoline</a> to get a pointer 7749 which can be <a href="#int_trampoline">bitcast (to a new function) and 7750 called</a>. The new function's signature is the same as that of 7751 <tt>func</tt> with any arguments marked with the <tt>nest</tt> attribute 7752 removed. At most one such <tt>nest</tt> argument is allowed, and it must be of 7753 pointer type. Calling the new function is equivalent to calling <tt>func</tt> 7754 with the same argument list, but with <tt>nval</tt> used for the missing 7755 <tt>nest</tt> argument. If, after calling <tt>llvm.init.trampoline</tt>, the 7756 memory pointed to by <tt>tramp</tt> is modified, then the effect of any later call 7757 to the returned function pointer is undefined.</p> 7758 </div> 7759 7760 <!-- _______________________________________________________________________ --> 7761 <h4> 7762 <a name="int_at"> 7763 '<tt>llvm.adjust.trampoline</tt>' Intrinsic 7764 </a> 7765 </h4> 7766 7767 <div> 7768 7769 <h5>Syntax:</h5> 7770 <pre> 7771 declare i8* @llvm.adjust.trampoline(i8* <tramp>) 7772 </pre> 7773 7774 <h5>Overview:</h5> 7775 <p>This performs any required machine-specific adjustment to the address of a 7776 trampoline (passed as <tt>tramp</tt>).</p> 7777 7778 <h5>Arguments:</h5> 7779 <p><tt>tramp</tt> must point to a block of memory which already has trampoline code 7780 filled in by a previous call to <a href="#int_it"><tt>llvm.init.trampoline</tt> 7781 </a>.</p> 7782 7783 <h5>Semantics:</h5> 7784 <p>On some architectures the address of the code to be executed needs to be 7785 different to the address where the trampoline is actually stored. This 7786 intrinsic returns the executable address corresponding to <tt>tramp</tt> 7787 after performing the required machine specific adjustments. 7788 The pointer returned can then be <a href="#int_trampoline"> bitcast and 7789 executed</a>. 7790 </p> 7791 7792 </div> 7793 7794 </div> 7795 7796 <!-- ======================================================================= --> 7797 <h3> 7798 <a name="int_memorymarkers">Memory Use Markers</a> 7799 </h3> 7800 7801 <div> 7802 7803 <p>This class of intrinsics exists to information about the lifetime of memory 7804 objects and ranges where variables are immutable.</p> 7805 7806 <!-- _______________________________________________________________________ --> 7807 <h4> 7808 <a name="int_lifetime_start">'<tt>llvm.lifetime.start</tt>' Intrinsic</a> 7809 </h4> 7810 7811 <div> 7812 7813 <h5>Syntax:</h5> 7814 <pre> 7815 declare void @llvm.lifetime.start(i64 <size>, i8* nocapture <ptr>) 7816 </pre> 7817 7818 <h5>Overview:</h5> 7819 <p>The '<tt>llvm.lifetime.start</tt>' intrinsic specifies the start of a memory 7820 object's lifetime.</p> 7821 7822 <h5>Arguments:</h5> 7823 <p>The first argument is a constant integer representing the size of the 7824 object, or -1 if it is variable sized. The second argument is a pointer to 7825 the object.</p> 7826 7827 <h5>Semantics:</h5> 7828 <p>This intrinsic indicates that before this point in the code, the value of the 7829 memory pointed to by <tt>ptr</tt> is dead. This means that it is known to 7830 never be used and has an undefined value. A load from the pointer that 7831 precedes this intrinsic can be replaced with 7832 <tt>'<a href="#undefvalues">undef</a>'</tt>.</p> 7833 7834 </div> 7835 7836 <!-- _______________________________________________________________________ --> 7837 <h4> 7838 <a name="int_lifetime_end">'<tt>llvm.lifetime.end</tt>' Intrinsic</a> 7839 </h4> 7840 7841 <div> 7842 7843 <h5>Syntax:</h5> 7844 <pre> 7845 declare void @llvm.lifetime.end(i64 <size>, i8* nocapture <ptr>) 7846 </pre> 7847 7848 <h5>Overview:</h5> 7849 <p>The '<tt>llvm.lifetime.end</tt>' intrinsic specifies the end of a memory 7850 object's lifetime.</p> 7851 7852 <h5>Arguments:</h5> 7853 <p>The first argument is a constant integer representing the size of the 7854 object, or -1 if it is variable sized. The second argument is a pointer to 7855 the object.</p> 7856 7857 <h5>Semantics:</h5> 7858 <p>This intrinsic indicates that after this point in the code, the value of the 7859 memory pointed to by <tt>ptr</tt> is dead. This means that it is known to 7860 never be used and has an undefined value. Any stores into the memory object 7861 following this intrinsic may be removed as dead. 7862 7863 </div> 7864 7865 <!-- _______________________________________________________________________ --> 7866 <h4> 7867 <a name="int_invariant_start">'<tt>llvm.invariant.start</tt>' Intrinsic</a> 7868 </h4> 7869 7870 <div> 7871 7872 <h5>Syntax:</h5> 7873 <pre> 7874 declare {}* @llvm.invariant.start(i64 <size>, i8* nocapture <ptr>) 7875 </pre> 7876 7877 <h5>Overview:</h5> 7878 <p>The '<tt>llvm.invariant.start</tt>' intrinsic specifies that the contents of 7879 a memory object will not change.</p> 7880 7881 <h5>Arguments:</h5> 7882 <p>The first argument is a constant integer representing the size of the 7883 object, or -1 if it is variable sized. The second argument is a pointer to 7884 the object.</p> 7885 7886 <h5>Semantics:</h5> 7887 <p>This intrinsic indicates that until an <tt>llvm.invariant.end</tt> that uses 7888 the return value, the referenced memory location is constant and 7889 unchanging.</p> 7890 7891 </div> 7892 7893 <!-- _______________________________________________________________________ --> 7894 <h4> 7895 <a name="int_invariant_end">'<tt>llvm.invariant.end</tt>' Intrinsic</a> 7896 </h4> 7897 7898 <div> 7899 7900 <h5>Syntax:</h5> 7901 <pre> 7902 declare void @llvm.invariant.end({}* <start>, i64 <size>, i8* nocapture <ptr>) 7903 </pre> 7904 7905 <h5>Overview:</h5> 7906 <p>The '<tt>llvm.invariant.end</tt>' intrinsic specifies that the contents of 7907 a memory object are mutable.</p> 7908 7909 <h5>Arguments:</h5> 7910 <p>The first argument is the matching <tt>llvm.invariant.start</tt> intrinsic. 7911 The second argument is a constant integer representing the size of the 7912 object, or -1 if it is variable sized and the third argument is a pointer 7913 to the object.</p> 7914 7915 <h5>Semantics:</h5> 7916 <p>This intrinsic indicates that the memory is mutable again.</p> 7917 7918 </div> 7919 7920 </div> 7921 7922 <!-- ======================================================================= --> 7923 <h3> 7924 <a name="int_general">General Intrinsics</a> 7925 </h3> 7926 7927 <div> 7928 7929 <p>This class of intrinsics is designed to be generic and has no specific 7930 purpose.</p> 7931 7932 <!-- _______________________________________________________________________ --> 7933 <h4> 7934 <a name="int_var_annotation">'<tt>llvm.var.annotation</tt>' Intrinsic</a> 7935 </h4> 7936 7937 <div> 7938 7939 <h5>Syntax:</h5> 7940 <pre> 7941 declare void @llvm.var.annotation(i8* <val>, i8* <str>, i8* <str>, i32 <int>) 7942 </pre> 7943 7944 <h5>Overview:</h5> 7945 <p>The '<tt>llvm.var.annotation</tt>' intrinsic.</p> 7946 7947 <h5>Arguments:</h5> 7948 <p>The first argument is a pointer to a value, the second is a pointer to a 7949 global string, the third is a pointer to a global string which is the source 7950 file name, and the last argument is the line number.</p> 7951 7952 <h5>Semantics:</h5> 7953 <p>This intrinsic allows annotation of local variables with arbitrary strings. 7954 This can be useful for special purpose optimizations that want to look for 7955 these annotations. These have no other defined use; they are ignored by code 7956 generation and optimization.</p> 7957 7958 </div> 7959 7960 <!-- _______________________________________________________________________ --> 7961 <h4> 7962 <a name="int_annotation">'<tt>llvm.annotation.*</tt>' Intrinsic</a> 7963 </h4> 7964 7965 <div> 7966 7967 <h5>Syntax:</h5> 7968 <p>This is an overloaded intrinsic. You can use '<tt>llvm.annotation</tt>' on 7969 any integer bit width.</p> 7970 7971 <pre> 7972 declare i8 @llvm.annotation.i8(i8 <val>, i8* <str>, i8* <str>, i32 <int>) 7973 declare i16 @llvm.annotation.i16(i16 <val>, i8* <str>, i8* <str>, i32 <int>) 7974 declare i32 @llvm.annotation.i32(i32 <val>, i8* <str>, i8* <str>, i32 <int>) 7975 declare i64 @llvm.annotation.i64(i64 <val>, i8* <str>, i8* <str>, i32 <int>) 7976 declare i256 @llvm.annotation.i256(i256 <val>, i8* <str>, i8* <str>, i32 <int>) 7977 </pre> 7978 7979 <h5>Overview:</h5> 7980 <p>The '<tt>llvm.annotation</tt>' intrinsic.</p> 7981 7982 <h5>Arguments:</h5> 7983 <p>The first argument is an integer value (result of some expression), the 7984 second is a pointer to a global string, the third is a pointer to a global 7985 string which is the source file name, and the last argument is the line 7986 number. It returns the value of the first argument.</p> 7987 7988 <h5>Semantics:</h5> 7989 <p>This intrinsic allows annotations to be put on arbitrary expressions with 7990 arbitrary strings. This can be useful for special purpose optimizations that 7991 want to look for these annotations. These have no other defined use; they 7992 are ignored by code generation and optimization.</p> 7993 7994 </div> 7995 7996 <!-- _______________________________________________________________________ --> 7997 <h4> 7998 <a name="int_trap">'<tt>llvm.trap</tt>' Intrinsic</a> 7999 </h4> 8000 8001 <div> 8002 8003 <h5>Syntax:</h5> 8004 <pre> 8005 declare void @llvm.trap() 8006 </pre> 8007 8008 <h5>Overview:</h5> 8009 <p>The '<tt>llvm.trap</tt>' intrinsic.</p> 8010 8011 <h5>Arguments:</h5> 8012 <p>None.</p> 8013 8014 <h5>Semantics:</h5> 8015 <p>This intrinsics is lowered to the target dependent trap instruction. If the 8016 target does not have a trap instruction, this intrinsic will be lowered to 8017 the call of the <tt>abort()</tt> function.</p> 8018 8019 </div> 8020 8021 <!-- _______________________________________________________________________ --> 8022 <h4> 8023 <a name="int_stackprotector">'<tt>llvm.stackprotector</tt>' Intrinsic</a> 8024 </h4> 8025 8026 <div> 8027 8028 <h5>Syntax:</h5> 8029 <pre> 8030 declare void @llvm.stackprotector(i8* <guard>, i8** <slot>) 8031 </pre> 8032 8033 <h5>Overview:</h5> 8034 <p>The <tt>llvm.stackprotector</tt> intrinsic takes the <tt>guard</tt> and 8035 stores it onto the stack at <tt>slot</tt>. The stack slot is adjusted to 8036 ensure that it is placed on the stack before local variables.</p> 8037 8038 <h5>Arguments:</h5> 8039 <p>The <tt>llvm.stackprotector</tt> intrinsic requires two pointer 8040 arguments. The first argument is the value loaded from the stack 8041 guard <tt>@__stack_chk_guard</tt>. The second variable is an <tt>alloca</tt> 8042 that has enough space to hold the value of the guard.</p> 8043 8044 <h5>Semantics:</h5> 8045 <p>This intrinsic causes the prologue/epilogue inserter to force the position of 8046 the <tt>AllocaInst</tt> stack slot to be before local variables on the 8047 stack. This is to ensure that if a local variable on the stack is 8048 overwritten, it will destroy the value of the guard. When the function exits, 8049 the guard on the stack is checked against the original guard. If they are 8050 different, then the program aborts by calling the <tt>__stack_chk_fail()</tt> 8051 function.</p> 8052 8053 </div> 8054 8055 <!-- _______________________________________________________________________ --> 8056 <h4> 8057 <a name="int_objectsize">'<tt>llvm.objectsize</tt>' Intrinsic</a> 8058 </h4> 8059 8060 <div> 8061 8062 <h5>Syntax:</h5> 8063 <pre> 8064 declare i32 @llvm.objectsize.i32(i8* <object>, i1 <type>) 8065 declare i64 @llvm.objectsize.i64(i8* <object>, i1 <type>) 8066 </pre> 8067 8068 <h5>Overview:</h5> 8069 <p>The <tt>llvm.objectsize</tt> intrinsic is designed to provide information to 8070 the optimizers to determine at compile time whether a) an operation (like 8071 memcpy) will overflow a buffer that corresponds to an object, or b) that a 8072 runtime check for overflow isn't necessary. An object in this context means 8073 an allocation of a specific class, structure, array, or other object.</p> 8074 8075 <h5>Arguments:</h5> 8076 <p>The <tt>llvm.objectsize</tt> intrinsic takes two arguments. The first 8077 argument is a pointer to or into the <tt>object</tt>. The second argument 8078 is a boolean 0 or 1. This argument determines whether you want the 8079 maximum (0) or minimum (1) bytes remaining. This needs to be a literal 0 or 8080 1, variables are not allowed.</p> 8081 8082 <h5>Semantics:</h5> 8083 <p>The <tt>llvm.objectsize</tt> intrinsic is lowered to either a constant 8084 representing the size of the object concerned, or <tt>i32/i64 -1 or 0</tt>, 8085 depending on the <tt>type</tt> argument, if the size cannot be determined at 8086 compile time.</p> 8087 8088 </div> 8089 8090 </div> 8091 8092 </div> 8093 8094 <!-- *********************************************************************** --> 8095 <hr> 8096 <address> 8097 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img 8098 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a> 8099 <a href="http://validator.w3.org/check/referer"><img 8100 src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a> 8101 8102 <a href="mailto:sabre (a] nondot.org">Chris Lattner</a><br> 8103 <a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br> 8104 Last modified: $Date: 2011-10-26 18:35:59 -0400 (Wed, 26 Oct 2011) $ 8105 </address> 8106 8107 </body> 8108 </html> 8109
