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7 <meta name="author" content="Chris Lattner">
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9 content="LLVM Assembly Language Reference Manual.">
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15 <h1>LLVM Language Reference Manual</h1>
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>
22 <li><a href="#modulestructure">Module Structure</a></li>
23 <li><a href="#linkage">Linkage Types</a>
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>externally visible</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>
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>
60 <li><a href="#typesystem">Type System</a>
62 <li><a href="#t_classifications">Type Classifications</a></li>
63 <li><a href="#t_primitive">Primitive Types</a>
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>
73 <li><a href="#t_derived">Derived Types</a>
75 <li><a href="#t_aggregate">Aggregate Types</a>
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>
83 <li><a href="#t_function">Function Type</a></li>
84 <li><a href="#t_pointer">Pointer Type</a></li>
89 <li><a href="#constants">Constants</a>
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>
100 <li><a href="#othervalues">Other Values</a>
102 <li><a href="#inlineasm">Inline Assembler Expressions</a></li>
103 <li><a href="#metadata">Metadata Nodes and Metadata Strings</a></li>
106 <li><a href="#intrinsic_globals">Intrinsic Global Variables</a>
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>
117 <li><a href="#instref">Instruction Reference</a>
119 <li><a href="#terminators">Terminator Instructions</a>
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>
131 <li><a href="#binaryops">Binary Operations</a>
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>
147 <li><a href="#bitwiseops">Bitwise Binary Operations</a>
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>
157 <li><a href="#vectorops">Vector Operations</a>
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>
164 <li><a href="#aggregateops">Aggregate Operations</a>
166 <li><a href="#i_extractvalue">'<tt>extractvalue</tt>' Instruction</a></li>
167 <li><a href="#i_insertvalue">'<tt>insertvalue</tt>' Instruction</a></li>
170 <li><a href="#memoryops">Memory Access and Addressing Operations</a>
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>
181 <li><a href="#convertops">Conversion Operations</a>
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>
197 <li><a href="#otherops">Other Operations</a>
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>
209 <li><a href="#intrinsics">Intrinsic Functions</a>
211 <li><a href="#int_varargs">Variable Argument Handling Intrinsics</a>
213 <li><a href="#int_va_start">'<tt>llvm.va_start</tt>' Intrinsic</a></li>
214 <li><a href="#int_va_end">'<tt>llvm.va_end</tt>' Intrinsic</a></li>
215 <li><a href="#int_va_copy">'<tt>llvm.va_copy</tt>' Intrinsic</a></li>
218 <li><a href="#int_gc">Accurate Garbage Collection Intrinsics</a>
220 <li><a href="#int_gcroot">'<tt>llvm.gcroot</tt>' Intrinsic</a></li>
221 <li><a href="#int_gcread">'<tt>llvm.gcread</tt>' Intrinsic</a></li>
222 <li><a href="#int_gcwrite">'<tt>llvm.gcwrite</tt>' Intrinsic</a></li>
225 <li><a href="#int_codegen">Code Generator Intrinsics</a>
227 <li><a href="#int_returnaddress">'<tt>llvm.returnaddress</tt>' Intrinsic</a></li>
228 <li><a href="#int_frameaddress">'<tt>llvm.frameaddress</tt>' Intrinsic</a></li>
229 <li><a href="#int_stacksave">'<tt>llvm.stacksave</tt>' Intrinsic</a></li>
230 <li><a href="#int_stackrestore">'<tt>llvm.stackrestore</tt>' Intrinsic</a></li>
231 <li><a href="#int_prefetch">'<tt>llvm.prefetch</tt>' Intrinsic</a></li>
232 <li><a href="#int_pcmarker">'<tt>llvm.pcmarker</tt>' Intrinsic</a></li>
233 <li><a href="#int_readcyclecounter">'<tt>llvm.readcyclecounter</tt>' Intrinsic</a></li>
236 <li><a href="#int_libc">Standard C Library Intrinsics</a>
238 <li><a href="#int_memcpy">'<tt>llvm.memcpy.*</tt>' Intrinsic</a></li>
239 <li><a href="#int_memmove">'<tt>llvm.memmove.*</tt>' Intrinsic</a></li>
240 <li><a href="#int_memset">'<tt>llvm.memset.*</tt>' Intrinsic</a></li>
241 <li><a href="#int_sqrt">'<tt>llvm.sqrt.*</tt>' Intrinsic</a></li>
242 <li><a href="#int_powi">'<tt>llvm.powi.*</tt>' Intrinsic</a></li>
243 <li><a href="#int_sin">'<tt>llvm.sin.*</tt>' Intrinsic</a></li>
244 <li><a href="#int_cos">'<tt>llvm.cos.*</tt>' Intrinsic</a></li>
245 <li><a href="#int_pow">'<tt>llvm.pow.*</tt>' Intrinsic</a></li>
246 <li><a href="#int_exp">'<tt>llvm.exp.*</tt>' Intrinsic</a></li>
247 <li><a href="#int_log">'<tt>llvm.log.*</tt>' Intrinsic</a></li>
248 <li><a href="#int_fma">'<tt>llvm.fma.*</tt>' Intrinsic</a></li>
251 <li><a href="#int_manip">Bit Manipulation Intrinsics</a>
253 <li><a href="#int_bswap">'<tt>llvm.bswap.*</tt>' Intrinsics</a></li>
254 <li><a href="#int_ctpop">'<tt>llvm.ctpop.*</tt>' Intrinsic </a></li>
255 <li><a href="#int_ctlz">'<tt>llvm.ctlz.*</tt>' Intrinsic </a></li>
256 <li><a href="#int_cttz">'<tt>llvm.cttz.*</tt>' Intrinsic </a></li>
259 <li><a href="#int_overflow">Arithmetic with Overflow Intrinsics</a>
261 <li><a href="#int_sadd_overflow">'<tt>llvm.sadd.with.overflow.*</tt> Intrinsics</a></li>
262 <li><a href="#int_uadd_overflow">'<tt>llvm.uadd.with.overflow.*</tt> Intrinsics</a></li>
263 <li><a href="#int_ssub_overflow">'<tt>llvm.ssub.with.overflow.*</tt> Intrinsics</a></li>
264 <li><a href="#int_usub_overflow">'<tt>llvm.usub.with.overflow.*</tt> Intrinsics</a></li>
265 <li><a href="#int_smul_overflow">'<tt>llvm.smul.with.overflow.*</tt> Intrinsics</a></li>
266 <li><a href="#int_umul_overflow">'<tt>llvm.umul.with.overflow.*</tt> Intrinsics</a></li>
269 <li><a href="#int_fp16">Half Precision Floating Point Intrinsics</a>
271 <li><a href="#int_convert_to_fp16">'<tt>llvm.convert.to.fp16</tt>' Intrinsic</a></li>
272 <li><a href="#int_convert_from_fp16">'<tt>llvm.convert.from.fp16</tt>' Intrinsic</a></li>
275 <li><a href="#int_debugger">Debugger intrinsics</a></li>
276 <li><a href="#int_eh">Exception Handling intrinsics</a></li>
277 <li><a href="#int_trampoline">Trampoline Intrinsic</a>
279 <li><a href="#int_it">'<tt>llvm.init.trampoline</tt>' Intrinsic</a></li>
282 <li><a href="#int_atomics">Atomic intrinsics</a>
284 <li><a href="#int_memory_barrier"><tt>llvm.memory_barrier</tt></a></li>
285 <li><a href="#int_atomic_cmp_swap"><tt>llvm.atomic.cmp.swap</tt></a></li>
286 <li><a href="#int_atomic_swap"><tt>llvm.atomic.swap</tt></a></li>
287 <li><a href="#int_atomic_load_add"><tt>llvm.atomic.load.add</tt></a></li>
288 <li><a href="#int_atomic_load_sub"><tt>llvm.atomic.load.sub</tt></a></li>
289 <li><a href="#int_atomic_load_and"><tt>llvm.atomic.load.and</tt></a></li>
290 <li><a href="#int_atomic_load_nand"><tt>llvm.atomic.load.nand</tt></a></li>
291 <li><a href="#int_atomic_load_or"><tt>llvm.atomic.load.or</tt></a></li>
292 <li><a href="#int_atomic_load_xor"><tt>llvm.atomic.load.xor</tt></a></li>
293 <li><a href="#int_atomic_load_max"><tt>llvm.atomic.load.max</tt></a></li>
294 <li><a href="#int_atomic_load_min"><tt>llvm.atomic.load.min</tt></a></li>
295 <li><a href="#int_atomic_load_umax"><tt>llvm.atomic.load.umax</tt></a></li>
296 <li><a href="#int_atomic_load_umin"><tt>llvm.atomic.load.umin</tt></a></li>
299 <li><a href="#int_memorymarkers">Memory Use Markers</a>
301 <li><a href="#int_lifetime_start"><tt>llvm.lifetime.start</tt></a></li>
302 <li><a href="#int_lifetime_end"><tt>llvm.lifetime.end</tt></a></li>
303 <li><a href="#int_invariant_start"><tt>llvm.invariant.start</tt></a></li>
304 <li><a href="#int_invariant_end"><tt>llvm.invariant.end</tt></a></li>
307 <li><a href="#int_general">General intrinsics</a>
309 <li><a href="#int_var_annotation">
310 '<tt>llvm.var.annotation</tt>' Intrinsic</a></li>
311 <li><a href="#int_annotation">
312 '<tt>llvm.annotation.*</tt>' Intrinsic</a></li>
313 <li><a href="#int_trap">
314 '<tt>llvm.trap</tt>' Intrinsic</a></li>
315 <li><a href="#int_stackprotector">
316 '<tt>llvm.stackprotector</tt>' Intrinsic</a></li>
317 <li><a href="#int_objectsize">
318 '<tt>llvm.objectsize</tt>' Intrinsic</a></li>
325 <div class="doc_author">
326 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>
327 and <a href="mailto:vadve@cs.uiuc.edu">Vikram Adve</a></p>
330 <!-- *********************************************************************** -->
331 <h2><a name="abstract">Abstract</a></h2>
332 <!-- *********************************************************************** -->
336 <p>This document is a reference manual for the LLVM assembly language. LLVM is
337 a Static Single Assignment (SSA) based representation that provides type
338 safety, low-level operations, flexibility, and the capability of representing
339 'all' high-level languages cleanly. It is the common code representation
340 used throughout all phases of the LLVM compilation strategy.</p>
344 <!-- *********************************************************************** -->
345 <h2><a name="introduction">Introduction</a></h2>
346 <!-- *********************************************************************** -->
350 <p>The LLVM code representation is designed to be used in three different forms:
351 as an in-memory compiler IR, as an on-disk bitcode representation (suitable
352 for fast loading by a Just-In-Time compiler), and as a human readable
353 assembly language representation. This allows LLVM to provide a powerful
354 intermediate representation for efficient compiler transformations and
355 analysis, while providing a natural means to debug and visualize the
356 transformations. The three different forms of LLVM are all equivalent. This
357 document describes the human readable representation and notation.</p>
359 <p>The LLVM representation aims to be light-weight and low-level while being
360 expressive, typed, and extensible at the same time. It aims to be a
361 "universal IR" of sorts, by being at a low enough level that high-level ideas
362 may be cleanly mapped to it (similar to how microprocessors are "universal
363 IR's", allowing many source languages to be mapped to them). By providing
364 type information, LLVM can be used as the target of optimizations: for
365 example, through pointer analysis, it can be proven that a C automatic
366 variable is never accessed outside of the current function, allowing it to
367 be promoted to a simple SSA value instead of a memory location.</p>
369 <!-- _______________________________________________________________________ -->
371 <a name="wellformed">Well-Formedness</a>
376 <p>It is important to note that this document describes 'well formed' LLVM
377 assembly language. There is a difference between what the parser accepts and
378 what is considered 'well formed'. For example, the following instruction is
379 syntactically okay, but not well formed:</p>
381 <pre class="doc_code">
382 %x = <a href="#i_add">add</a> i32 1, %x
385 <p>because the definition of <tt>%x</tt> does not dominate all of its uses. The
386 LLVM infrastructure provides a verification pass that may be used to verify
387 that an LLVM module is well formed. This pass is automatically run by the
388 parser after parsing input assembly and by the optimizer before it outputs
389 bitcode. The violations pointed out by the verifier pass indicate bugs in
390 transformation passes or input to the parser.</p>
396 <!-- Describe the typesetting conventions here. -->
398 <!-- *********************************************************************** -->
399 <h2><a name="identifiers">Identifiers</a></h2>
400 <!-- *********************************************************************** -->
404 <p>LLVM identifiers come in two basic types: global and local. Global
405 identifiers (functions, global variables) begin with the <tt>'@'</tt>
406 character. Local identifiers (register names, types) begin with
407 the <tt>'%'</tt> character. Additionally, there are three different formats
408 for identifiers, for different purposes:</p>
411 <li>Named values are represented as a string of characters with their prefix.
412 For example, <tt>%foo</tt>, <tt>@DivisionByZero</tt>,
413 <tt>%a.really.long.identifier</tt>. The actual regular expression used is
414 '<tt>[%@][a-zA-Z$._][a-zA-Z$._0-9]*</tt>'. Identifiers which require
415 other characters in their names can be surrounded with quotes. Special
416 characters may be escaped using <tt>"\xx"</tt> where <tt>xx</tt> is the
417 ASCII code for the character in hexadecimal. In this way, any character
418 can be used in a name value, even quotes themselves.</li>
420 <li>Unnamed values are represented as an unsigned numeric value with their
421 prefix. For example, <tt>%12</tt>, <tt>@2</tt>, <tt>%44</tt>.</li>
423 <li>Constants, which are described in a <a href="#constants">section about
424 constants</a>, below.</li>
427 <p>LLVM requires that values start with a prefix for two reasons: Compilers
428 don't need to worry about name clashes with reserved words, and the set of
429 reserved words may be expanded in the future without penalty. Additionally,
430 unnamed identifiers allow a compiler to quickly come up with a temporary
431 variable without having to avoid symbol table conflicts.</p>
433 <p>Reserved words in LLVM are very similar to reserved words in other
434 languages. There are keywords for different opcodes
435 ('<tt><a href="#i_add">add</a></tt>',
436 '<tt><a href="#i_bitcast">bitcast</a></tt>',
437 '<tt><a href="#i_ret">ret</a></tt>', etc...), for primitive type names
438 ('<tt><a href="#t_void">void</a></tt>',
439 '<tt><a href="#t_primitive">i32</a></tt>', etc...), and others. These
440 reserved words cannot conflict with variable names, because none of them
441 start with a prefix character (<tt>'%'</tt> or <tt>'@'</tt>).</p>
443 <p>Here is an example of LLVM code to multiply the integer variable
444 '<tt>%X</tt>' by 8:</p>
448 <pre class="doc_code">
449 %result = <a href="#i_mul">mul</a> i32 %X, 8
452 <p>After strength reduction:</p>
454 <pre class="doc_code">
455 %result = <a href="#i_shl">shl</a> i32 %X, i8 3
458 <p>And the hard way:</p>
460 <pre class="doc_code">
461 %0 = <a href="#i_add">add</a> i32 %X, %X <i>; yields {i32}:%0</i>
462 %1 = <a href="#i_add">add</a> i32 %0, %0 <i>; yields {i32}:%1</i>
463 %result = <a href="#i_add">add</a> i32 %1, %1
466 <p>This last way of multiplying <tt>%X</tt> by 8 illustrates several important
467 lexical features of LLVM:</p>
470 <li>Comments are delimited with a '<tt>;</tt>' and go until the end of
473 <li>Unnamed temporaries are created when the result of a computation is not
474 assigned to a named value.</li>
476 <li>Unnamed temporaries are numbered sequentially</li>
479 <p>It also shows a convention that we follow in this document. When
480 demonstrating instructions, we will follow an instruction with a comment that
481 defines the type and name of value produced. Comments are shown in italic
486 <!-- *********************************************************************** -->
487 <h2><a name="highlevel">High Level Structure</a></h2>
488 <!-- *********************************************************************** -->
490 <!-- ======================================================================= -->
492 <a name="modulestructure">Module Structure</a>
497 <p>LLVM programs are composed of "Module"s, each of which is a translation unit
498 of the input programs. Each module consists of functions, global variables,
499 and symbol table entries. Modules may be combined together with the LLVM
500 linker, which merges function (and global variable) definitions, resolves
501 forward declarations, and merges symbol table entries. Here is an example of
502 the "hello world" module:</p>
504 <pre class="doc_code">
505 <i>; Declare the string constant as a global constant.</i>
506 <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>
508 <i>; External declaration of the puts function</i>
509 <a href="#functionstructure">declare</a> i32 @puts(i8*) <i>; i32 (i8*)* </i>
511 <i>; Definition of main function</i>
512 define i32 @main() { <i>; i32()* </i>
513 <i>; Convert [13 x i8]* to i8 *...</i>
514 %cast210 = <a href="#i_getelementptr">getelementptr</a> [13 x i8]* @.LC0, i64 0, i64 0 <i>; i8*</i>
516 <i>; Call puts function to write out the string to stdout.</i>
517 <a href="#i_call">call</a> i32 @puts(i8* %cast210) <i>; i32</i>
518 <a href="#i_ret">ret</a> i32 0
521 <i>; Named metadata</i>
522 !1 = metadata !{i32 41}
526 <p>This example is made up of a <a href="#globalvars">global variable</a> named
527 "<tt>.LC0</tt>", an external declaration of the "<tt>puts</tt>" function,
528 a <a href="#functionstructure">function definition</a> for
529 "<tt>main</tt>" and <a href="#namedmetadatastructure">named metadata</a>
532 <p>In general, a module is made up of a list of global values, where both
533 functions and global variables are global values. Global values are
534 represented by a pointer to a memory location (in this case, a pointer to an
535 array of char, and a pointer to a function), and have one of the
536 following <a href="#linkage">linkage types</a>.</p>
540 <!-- ======================================================================= -->
542 <a name="linkage">Linkage Types</a>
547 <p>All Global Variables and Functions have one of the following types of
551 <dt><tt><b><a name="linkage_private">private</a></b></tt></dt>
552 <dd>Global values with "<tt>private</tt>" linkage are only directly accessible
553 by objects in the current module. In particular, linking code into a
554 module with an private global value may cause the private to be renamed as
555 necessary to avoid collisions. Because the symbol is private to the
556 module, all references can be updated. This doesn't show up in any symbol
557 table in the object file.</dd>
559 <dt><tt><b><a name="linkage_linker_private">linker_private</a></b></tt></dt>
560 <dd>Similar to <tt>private</tt>, but the symbol is passed through the
561 assembler and evaluated by the linker. Unlike normal strong symbols, they
562 are removed by the linker from the final linked image (executable or
563 dynamic library).</dd>
565 <dt><tt><b><a name="linkage_linker_private_weak">linker_private_weak</a></b></tt></dt>
566 <dd>Similar to "<tt>linker_private</tt>", but the symbol is weak. Note that
567 <tt>linker_private_weak</tt> symbols are subject to coalescing by the
568 linker. The symbols are removed by the linker from the final linked image
569 (executable or dynamic library).</dd>
571 <dt><tt><b><a name="linkage_linker_private_weak_def_auto">linker_private_weak_def_auto</a></b></tt></dt>
572 <dd>Similar to "<tt>linker_private_weak</tt>", but it's known that the address
573 of the object is not taken. For instance, functions that had an inline
574 definition, but the compiler decided not to inline it. Note,
575 unlike <tt>linker_private</tt> and <tt>linker_private_weak</tt>,
576 <tt>linker_private_weak_def_auto</tt> may have only <tt>default</tt>
577 visibility. The symbols are removed by the linker from the final linked
578 image (executable or dynamic library).</dd>
580 <dt><tt><b><a name="linkage_internal">internal</a></b></tt></dt>
581 <dd>Similar to private, but the value shows as a local symbol
582 (<tt>STB_LOCAL</tt> in the case of ELF) in the object file. This
583 corresponds to the notion of the '<tt>static</tt>' keyword in C.</dd>
585 <dt><tt><b><a name="linkage_available_externally">available_externally</a></b></tt></dt>
586 <dd>Globals with "<tt>available_externally</tt>" linkage are never emitted
587 into the object file corresponding to the LLVM module. They exist to
588 allow inlining and other optimizations to take place given knowledge of
589 the definition of the global, which is known to be somewhere outside the
590 module. Globals with <tt>available_externally</tt> linkage are allowed to
591 be discarded at will, and are otherwise the same as <tt>linkonce_odr</tt>.
592 This linkage type is only allowed on definitions, not declarations.</dd>
594 <dt><tt><b><a name="linkage_linkonce">linkonce</a></b></tt></dt>
595 <dd>Globals with "<tt>linkonce</tt>" linkage are merged with other globals of
596 the same name when linkage occurs. This can be used to implement
597 some forms of inline functions, templates, or other code which must be
598 generated in each translation unit that uses it, but where the body may
599 be overridden with a more definitive definition later. Unreferenced
600 <tt>linkonce</tt> globals are allowed to be discarded. Note that
601 <tt>linkonce</tt> linkage does not actually allow the optimizer to
602 inline the body of this function into callers because it doesn't know if
603 this definition of the function is the definitive definition within the
604 program or whether it will be overridden by a stronger definition.
605 To enable inlining and other optimizations, use "<tt>linkonce_odr</tt>"
608 <dt><tt><b><a name="linkage_weak">weak</a></b></tt></dt>
609 <dd>"<tt>weak</tt>" linkage has the same merging semantics as
610 <tt>linkonce</tt> linkage, except that unreferenced globals with
611 <tt>weak</tt> linkage may not be discarded. This is used for globals that
612 are declared "weak" in C source code.</dd>
614 <dt><tt><b><a name="linkage_common">common</a></b></tt></dt>
615 <dd>"<tt>common</tt>" linkage is most similar to "<tt>weak</tt>" linkage, but
616 they are used for tentative definitions in C, such as "<tt>int X;</tt>" at
618 Symbols with "<tt>common</tt>" linkage are merged in the same way as
619 <tt>weak symbols</tt>, and they may not be deleted if unreferenced.
620 <tt>common</tt> symbols may not have an explicit section,
621 must have a zero initializer, and may not be marked '<a
622 href="#globalvars"><tt>constant</tt></a>'. Functions and aliases may not
623 have common linkage.</dd>
626 <dt><tt><b><a name="linkage_appending">appending</a></b></tt></dt>
627 <dd>"<tt>appending</tt>" linkage may only be applied to global variables of
628 pointer to array type. When two global variables with appending linkage
629 are linked together, the two global arrays are appended together. This is
630 the LLVM, typesafe, equivalent of having the system linker append together
631 "sections" with identical names when .o files are linked.</dd>
633 <dt><tt><b><a name="linkage_externweak">extern_weak</a></b></tt></dt>
634 <dd>The semantics of this linkage follow the ELF object file model: the symbol
635 is weak until linked, if not linked, the symbol becomes null instead of
636 being an undefined reference.</dd>
638 <dt><tt><b><a name="linkage_linkonce_odr">linkonce_odr</a></b></tt></dt>
639 <dt><tt><b><a name="linkage_weak_odr">weak_odr</a></b></tt></dt>
640 <dd>Some languages allow differing globals to be merged, such as two functions
641 with different semantics. Other languages, such as <tt>C++</tt>, ensure
642 that only equivalent globals are ever merged (the "one definition rule"
643 — "ODR"). Such languages can use the <tt>linkonce_odr</tt>
644 and <tt>weak_odr</tt> linkage types to indicate that the global will only
645 be merged with equivalent globals. These linkage types are otherwise the
646 same as their non-<tt>odr</tt> versions.</dd>
648 <dt><tt><b><a name="linkage_external">externally visible</a></b></tt>:</dt>
649 <dd>If none of the above identifiers are used, the global is externally
650 visible, meaning that it participates in linkage and can be used to
651 resolve external symbol references.</dd>
654 <p>The next two types of linkage are targeted for Microsoft Windows platform
655 only. They are designed to support importing (exporting) symbols from (to)
656 DLLs (Dynamic Link Libraries).</p>
659 <dt><tt><b><a name="linkage_dllimport">dllimport</a></b></tt></dt>
660 <dd>"<tt>dllimport</tt>" linkage causes the compiler to reference a function
661 or variable via a global pointer to a pointer that is set up by the DLL
662 exporting the symbol. On Microsoft Windows targets, the pointer name is
663 formed by combining <code>__imp_</code> and the function or variable
666 <dt><tt><b><a name="linkage_dllexport">dllexport</a></b></tt></dt>
667 <dd>"<tt>dllexport</tt>" linkage causes the compiler to provide a global
668 pointer to a pointer in a DLL, so that it can be referenced with the
669 <tt>dllimport</tt> attribute. On Microsoft Windows targets, the pointer
670 name is formed by combining <code>__imp_</code> and the function or
674 <p>For example, since the "<tt>.LC0</tt>" variable is defined to be internal, if
675 another module defined a "<tt>.LC0</tt>" variable and was linked with this
676 one, one of the two would be renamed, preventing a collision. Since
677 "<tt>main</tt>" and "<tt>puts</tt>" are external (i.e., lacking any linkage
678 declarations), they are accessible outside of the current module.</p>
680 <p>It is illegal for a function <i>declaration</i> to have any linkage type
681 other than "externally visible", <tt>dllimport</tt>
682 or <tt>extern_weak</tt>.</p>
684 <p>Aliases can have only <tt>external</tt>, <tt>internal</tt>, <tt>weak</tt>
685 or <tt>weak_odr</tt> linkages.</p>
689 <!-- ======================================================================= -->
691 <a name="callingconv">Calling Conventions</a>
696 <p>LLVM <a href="#functionstructure">functions</a>, <a href="#i_call">calls</a>
697 and <a href="#i_invoke">invokes</a> can all have an optional calling
698 convention specified for the call. The calling convention of any pair of
699 dynamic caller/callee must match, or the behavior of the program is
700 undefined. The following calling conventions are supported by LLVM, and more
701 may be added in the future:</p>
704 <dt><b>"<tt>ccc</tt>" - The C calling convention</b>:</dt>
705 <dd>This calling convention (the default if no other calling convention is
706 specified) matches the target C calling conventions. This calling
707 convention supports varargs function calls and tolerates some mismatch in
708 the declared prototype and implemented declaration of the function (as
711 <dt><b>"<tt>fastcc</tt>" - The fast calling convention</b>:</dt>
712 <dd>This calling convention attempts to make calls as fast as possible
713 (e.g. by passing things in registers). This calling convention allows the
714 target to use whatever tricks it wants to produce fast code for the
715 target, without having to conform to an externally specified ABI
716 (Application Binary Interface).
717 <a href="CodeGenerator.html#tailcallopt">Tail calls can only be optimized
718 when this or the GHC convention is used.</a> This calling convention
719 does not support varargs and requires the prototype of all callees to
720 exactly match the prototype of the function definition.</dd>
722 <dt><b>"<tt>coldcc</tt>" - The cold calling convention</b>:</dt>
723 <dd>This calling convention attempts to make code in the caller as efficient
724 as possible under the assumption that the call is not commonly executed.
725 As such, these calls often preserve all registers so that the call does
726 not break any live ranges in the caller side. This calling convention
727 does not support varargs and requires the prototype of all callees to
728 exactly match the prototype of the function definition.</dd>
730 <dt><b>"<tt>cc <em>10</em></tt>" - GHC convention</b>:</dt>
731 <dd>This calling convention has been implemented specifically for use by the
732 <a href="http://www.haskell.org/ghc">Glasgow Haskell Compiler (GHC)</a>.
733 It passes everything in registers, going to extremes to achieve this by
734 disabling callee save registers. This calling convention should not be
735 used lightly but only for specific situations such as an alternative to
736 the <em>register pinning</em> performance technique often used when
737 implementing functional programming languages.At the moment only X86
738 supports this convention and it has the following limitations:
740 <li>On <em>X86-32</em> only supports up to 4 bit type parameters. No
741 floating point types are supported.</li>
742 <li>On <em>X86-64</em> only supports up to 10 bit type parameters and
743 6 floating point parameters.</li>
745 This calling convention supports
746 <a href="CodeGenerator.html#tailcallopt">tail call optimization</a> but
747 requires both the caller and callee are using it.
750 <dt><b>"<tt>cc <<em>n</em>></tt>" - Numbered convention</b>:</dt>
751 <dd>Any calling convention may be specified by number, allowing
752 target-specific calling conventions to be used. Target specific calling
753 conventions start at 64.</dd>
756 <p>More calling conventions can be added/defined on an as-needed basis, to
757 support Pascal conventions or any other well-known target-independent
762 <!-- ======================================================================= -->
764 <a name="visibility">Visibility Styles</a>
769 <p>All Global Variables and Functions have one of the following visibility
773 <dt><b>"<tt>default</tt>" - Default style</b>:</dt>
774 <dd>On targets that use the ELF object file format, default visibility means
775 that the declaration is visible to other modules and, in shared libraries,
776 means that the declared entity may be overridden. On Darwin, default
777 visibility means that the declaration is visible to other modules. Default
778 visibility corresponds to "external linkage" in the language.</dd>
780 <dt><b>"<tt>hidden</tt>" - Hidden style</b>:</dt>
781 <dd>Two declarations of an object with hidden visibility refer to the same
782 object if they are in the same shared object. Usually, hidden visibility
783 indicates that the symbol will not be placed into the dynamic symbol
784 table, so no other module (executable or shared library) can reference it
787 <dt><b>"<tt>protected</tt>" - Protected style</b>:</dt>
788 <dd>On ELF, protected visibility indicates that the symbol will be placed in
789 the dynamic symbol table, but that references within the defining module
790 will bind to the local symbol. That is, the symbol cannot be overridden by
796 <!-- ======================================================================= -->
798 <a name="namedtypes">Named Types</a>
803 <p>LLVM IR allows you to specify name aliases for certain types. This can make
804 it easier to read the IR and make the IR more condensed (particularly when
805 recursive types are involved). An example of a name specification is:</p>
807 <pre class="doc_code">
808 %mytype = type { %mytype*, i32 }
811 <p>You may give a name to any <a href="#typesystem">type</a> except
812 "<a href="#t_void">void</a>". Type name aliases may be used anywhere a type
813 is expected with the syntax "%mytype".</p>
815 <p>Note that type names are aliases for the structural type that they indicate,
816 and that you can therefore specify multiple names for the same type. This
817 often leads to confusing behavior when dumping out a .ll file. Since LLVM IR
818 uses structural typing, the name is not part of the type. When printing out
819 LLVM IR, the printer will pick <em>one name</em> to render all types of a
820 particular shape. This means that if you have code where two different
821 source types end up having the same LLVM type, that the dumper will sometimes
822 print the "wrong" or unexpected type. This is an important design point and
823 isn't going to change.</p>
827 <!-- ======================================================================= -->
829 <a name="globalvars">Global Variables</a>
834 <p>Global variables define regions of memory allocated at compilation time
835 instead of run-time. Global variables may optionally be initialized, may
836 have an explicit section to be placed in, and may have an optional explicit
837 alignment specified. A variable may be defined as "thread_local", which
838 means that it will not be shared by threads (each thread will have a
839 separated copy of the variable). A variable may be defined as a global
840 "constant," which indicates that the contents of the variable
841 will <b>never</b> be modified (enabling better optimization, allowing the
842 global data to be placed in the read-only section of an executable, etc).
843 Note that variables that need runtime initialization cannot be marked
844 "constant" as there is a store to the variable.</p>
846 <p>LLVM explicitly allows <em>declarations</em> of global variables to be marked
847 constant, even if the final definition of the global is not. This capability
848 can be used to enable slightly better optimization of the program, but
849 requires the language definition to guarantee that optimizations based on the
850 'constantness' are valid for the translation units that do not include the
853 <p>As SSA values, global variables define pointer values that are in scope
854 (i.e. they dominate) all basic blocks in the program. Global variables
855 always define a pointer to their "content" type because they describe a
856 region of memory, and all memory objects in LLVM are accessed through
859 <p>Global variables can be marked with <tt>unnamed_addr</tt> which indicates
860 that the address is not significant, only the content. Constants marked
861 like this can be merged with other constants if they have the same
862 initializer. Note that a constant with significant address <em>can</em>
863 be merged with a <tt>unnamed_addr</tt> constant, the result being a
864 constant whose address is significant.</p>
866 <p>A global variable may be declared to reside in a target-specific numbered
867 address space. For targets that support them, address spaces may affect how
868 optimizations are performed and/or what target instructions are used to
869 access the variable. The default address space is zero. The address space
870 qualifier must precede any other attributes.</p>
872 <p>LLVM allows an explicit section to be specified for globals. If the target
873 supports it, it will emit globals to the section specified.</p>
875 <p>An explicit alignment may be specified for a global, which must be a power
876 of 2. If not present, or if the alignment is set to zero, the alignment of
877 the global is set by the target to whatever it feels convenient. If an
878 explicit alignment is specified, the global is forced to have exactly that
879 alignment. Targets and optimizers are not allowed to over-align the global
880 if the global has an assigned section. In this case, the extra alignment
881 could be observable: for example, code could assume that the globals are
882 densely packed in their section and try to iterate over them as an array,
883 alignment padding would break this iteration.</p>
885 <p>For example, the following defines a global in a numbered address space with
886 an initializer, section, and alignment:</p>
888 <pre class="doc_code">
889 @G = addrspace(5) constant float 1.0, section "foo", align 4
895 <!-- ======================================================================= -->
897 <a name="functionstructure">Functions</a>
902 <p>LLVM function definitions consist of the "<tt>define</tt>" keyword, an
903 optional <a href="#linkage">linkage type</a>, an optional
904 <a href="#visibility">visibility style</a>, an optional
905 <a href="#callingconv">calling convention</a>,
906 an optional <tt>unnamed_addr</tt> attribute, a return type, an optional
907 <a href="#paramattrs">parameter attribute</a> for the return type, a function
908 name, a (possibly empty) argument list (each with optional
909 <a href="#paramattrs">parameter attributes</a>), optional
910 <a href="#fnattrs">function attributes</a>, an optional section, an optional
911 alignment, an optional <a href="#gc">garbage collector name</a>, an opening
912 curly brace, a list of basic blocks, and a closing curly brace.</p>
914 <p>LLVM function declarations consist of the "<tt>declare</tt>" keyword, an
915 optional <a href="#linkage">linkage type</a>, an optional
916 <a href="#visibility">visibility style</a>, an optional
917 <a href="#callingconv">calling convention</a>,
918 an optional <tt>unnamed_addr</tt> attribute, a return type, an optional
919 <a href="#paramattrs">parameter attribute</a> for the return type, a function
920 name, a possibly empty list of arguments, an optional alignment, and an
921 optional <a href="#gc">garbage collector name</a>.</p>
923 <p>A function definition contains a list of basic blocks, forming the CFG
924 (Control Flow Graph) for the function. Each basic block may optionally start
925 with a label (giving the basic block a symbol table entry), contains a list
926 of instructions, and ends with a <a href="#terminators">terminator</a>
927 instruction (such as a branch or function return).</p>
929 <p>The first basic block in a function is special in two ways: it is immediately
930 executed on entrance to the function, and it is not allowed to have
931 predecessor basic blocks (i.e. there can not be any branches to the entry
932 block of a function). Because the block can have no predecessors, it also
933 cannot have any <a href="#i_phi">PHI nodes</a>.</p>
935 <p>LLVM allows an explicit section to be specified for functions. If the target
936 supports it, it will emit functions to the section specified.</p>
938 <p>An explicit alignment may be specified for a function. If not present, or if
939 the alignment is set to zero, the alignment of the function is set by the
940 target to whatever it feels convenient. If an explicit alignment is
941 specified, the function is forced to have at least that much alignment. All
942 alignments must be a power of 2.</p>
944 <p>If the <tt>unnamed_addr</tt> attribute is given, the address is know to not
945 be significant and two identical functions can be merged</p>.
948 <pre class="doc_code">
949 define [<a href="#linkage">linkage</a>] [<a href="#visibility">visibility</a>]
950 [<a href="#callingconv">cconv</a>] [<a href="#paramattrs">ret attrs</a>]
951 <ResultType> @<FunctionName> ([argument list])
952 [<a href="#fnattrs">fn Attrs</a>] [section "name"] [align N]
953 [<a href="#gc">gc</a>] { ... }
958 <!-- ======================================================================= -->
960 <a name="aliasstructure">Aliases</a>
965 <p>Aliases act as "second name" for the aliasee value (which can be either
966 function, global variable, another alias or bitcast of global value). Aliases
967 may have an optional <a href="#linkage">linkage type</a>, and an
968 optional <a href="#visibility">visibility style</a>.</p>
971 <pre class="doc_code">
972 @<Name> = alias [Linkage] [Visibility] <AliaseeTy> @<Aliasee>
977 <!-- ======================================================================= -->
979 <a name="namedmetadatastructure">Named Metadata</a>
984 <p>Named metadata is a collection of metadata. <a href="#metadata">Metadata
985 nodes</a> (but not metadata strings) are the only valid operands for
986 a named metadata.</p>
989 <pre class="doc_code">
990 ; Some unnamed metadata nodes, which are referenced by the named metadata.
991 !0 = metadata !{metadata !"zero"}
992 !1 = metadata !{metadata !"one"}
993 !2 = metadata !{metadata !"two"}
995 !name = !{!0, !1, !2}
1000 <!-- ======================================================================= -->
1002 <a name="paramattrs">Parameter Attributes</a>
1007 <p>The return type and each parameter of a function type may have a set of
1008 <i>parameter attributes</i> associated with them. Parameter attributes are
1009 used to communicate additional information about the result or parameters of
1010 a function. Parameter attributes are considered to be part of the function,
1011 not of the function type, so functions with different parameter attributes
1012 can have the same function type.</p>
1014 <p>Parameter attributes are simple keywords that follow the type specified. If
1015 multiple parameter attributes are needed, they are space separated. For
1018 <pre class="doc_code">
1019 declare i32 @printf(i8* noalias nocapture, ...)
1020 declare i32 @atoi(i8 zeroext)
1021 declare signext i8 @returns_signed_char()
1024 <p>Note that any attributes for the function result (<tt>nounwind</tt>,
1025 <tt>readonly</tt>) come immediately after the argument list.</p>
1027 <p>Currently, only the following parameter attributes are defined:</p>
1030 <dt><tt><b>zeroext</b></tt></dt>
1031 <dd>This indicates to the code generator that the parameter or return value
1032 should be zero-extended to the extent required by the target's ABI (which
1033 is usually 32-bits, but is 8-bits for a i1 on x86-64) by the caller (for a
1034 parameter) or the callee (for a return value).</dd>
1036 <dt><tt><b>signext</b></tt></dt>
1037 <dd>This indicates to the code generator that the parameter or return value
1038 should be sign-extended to the extent required by the target's ABI (which
1039 is usually 32-bits) by the caller (for a parameter) or the callee (for a
1042 <dt><tt><b>inreg</b></tt></dt>
1043 <dd>This indicates that this parameter or return value should be treated in a
1044 special target-dependent fashion during while emitting code for a function
1045 call or return (usually, by putting it in a register as opposed to memory,
1046 though some targets use it to distinguish between two different kinds of
1047 registers). Use of this attribute is target-specific.</dd>
1049 <dt><tt><b><a name="byval">byval</a></b></tt></dt>
1050 <dd><p>This indicates that the pointer parameter should really be passed by
1051 value to the function. The attribute implies that a hidden copy of the
1053 is made between the caller and the callee, so the callee is unable to
1054 modify the value in the callee. This attribute is only valid on LLVM
1055 pointer arguments. It is generally used to pass structs and arrays by
1056 value, but is also valid on pointers to scalars. The copy is considered
1057 to belong to the caller not the callee (for example,
1058 <tt><a href="#readonly">readonly</a></tt> functions should not write to
1059 <tt>byval</tt> parameters). This is not a valid attribute for return
1062 <p>The byval attribute also supports specifying an alignment with
1063 the align attribute. It indicates the alignment of the stack slot to
1064 form and the known alignment of the pointer specified to the call site. If
1065 the alignment is not specified, then the code generator makes a
1066 target-specific assumption.</p></dd>
1068 <dt><tt><b><a name="sret">sret</a></b></tt></dt>
1069 <dd>This indicates that the pointer parameter specifies the address of a
1070 structure that is the return value of the function in the source program.
1071 This pointer must be guaranteed by the caller to be valid: loads and
1072 stores to the structure may be assumed by the callee to not to trap. This
1073 may only be applied to the first parameter. This is not a valid attribute
1074 for return values. </dd>
1076 <dt><tt><b><a name="noalias">noalias</a></b></tt></dt>
1077 <dd>This indicates that pointer values
1078 <a href="#pointeraliasing"><i>based</i></a> on the argument or return
1079 value do not alias pointer values which are not <i>based</i> on it,
1080 ignoring certain "irrelevant" dependencies.
1081 For a call to the parent function, dependencies between memory
1082 references from before or after the call and from those during the call
1083 are "irrelevant" to the <tt>noalias</tt> keyword for the arguments and
1084 return value used in that call.
1085 The caller shares the responsibility with the callee for ensuring that
1086 these requirements are met.
1087 For further details, please see the discussion of the NoAlias response in
1088 <a href="AliasAnalysis.html#MustMayNo">alias analysis</a>.<br>
1090 Note that this definition of <tt>noalias</tt> is intentionally
1091 similar to the definition of <tt>restrict</tt> in C99 for function
1092 arguments, though it is slightly weaker.
1094 For function return values, C99's <tt>restrict</tt> is not meaningful,
1095 while LLVM's <tt>noalias</tt> is.
1098 <dt><tt><b><a name="nocapture">nocapture</a></b></tt></dt>
1099 <dd>This indicates that the callee does not make any copies of the pointer
1100 that outlive the callee itself. This is not a valid attribute for return
1103 <dt><tt><b><a name="nest">nest</a></b></tt></dt>
1104 <dd>This indicates that the pointer parameter can be excised using the
1105 <a href="#int_trampoline">trampoline intrinsics</a>. This is not a valid
1106 attribute for return values.</dd>
1111 <!-- ======================================================================= -->
1113 <a name="gc">Garbage Collector Names</a>
1118 <p>Each function may specify a garbage collector name, which is simply a
1121 <pre class="doc_code">
1122 define void @f() gc "name" { ... }
1125 <p>The compiler declares the supported values of <i>name</i>. Specifying a
1126 collector which will cause the compiler to alter its output in order to
1127 support the named garbage collection algorithm.</p>
1131 <!-- ======================================================================= -->
1133 <a name="fnattrs">Function Attributes</a>
1138 <p>Function attributes are set to communicate additional information about a
1139 function. Function attributes are considered to be part of the function, not
1140 of the function type, so functions with different parameter attributes can
1141 have the same function type.</p>
1143 <p>Function attributes are simple keywords that follow the type specified. If
1144 multiple attributes are needed, they are space separated. For example:</p>
1146 <pre class="doc_code">
1147 define void @f() noinline { ... }
1148 define void @f() alwaysinline { ... }
1149 define void @f() alwaysinline optsize { ... }
1150 define void @f() optsize { ... }
1154 <dt><tt><b>alignstack(<<em>n</em>>)</b></tt></dt>
1155 <dd>This attribute indicates that, when emitting the prologue and epilogue,
1156 the backend should forcibly align the stack pointer. Specify the
1157 desired alignment, which must be a power of two, in parentheses.
1159 <dt><tt><b>alwaysinline</b></tt></dt>
1160 <dd>This attribute indicates that the inliner should attempt to inline this
1161 function into callers whenever possible, ignoring any active inlining size
1162 threshold for this caller.</dd>
1164 <dt><tt><b>hotpatch</b></tt></dt>
1165 <dd>This attribute indicates that the function should be 'hotpatchable',
1166 meaning the function can be patched and/or hooked even while it is
1167 loaded into memory. On x86, the function prologue will be preceded
1168 by six bytes of padding and will begin with a two-byte instruction.
1169 Most of the functions in the Windows system DLLs in Windows XP SP2 or
1170 higher were compiled in this fashion.</dd>
1172 <dt><tt><b>nonlazybind</b></tt></dt>
1173 <dd>This attribute suppresses lazy symbol binding for the function. This
1174 may make calls to the function faster, at the cost of extra program
1175 startup time if the function is not called during program startup.</dd>
1177 <dt><tt><b>inlinehint</b></tt></dt>
1178 <dd>This attribute indicates that the source code contained a hint that inlining
1179 this function is desirable (such as the "inline" keyword in C/C++). It
1180 is just a hint; it imposes no requirements on the inliner.</dd>
1182 <dt><tt><b>naked</b></tt></dt>
1183 <dd>This attribute disables prologue / epilogue emission for the function.
1184 This can have very system-specific consequences.</dd>
1186 <dt><tt><b>noimplicitfloat</b></tt></dt>
1187 <dd>This attributes disables implicit floating point instructions.</dd>
1189 <dt><tt><b>noinline</b></tt></dt>
1190 <dd>This attribute indicates that the inliner should never inline this
1191 function in any situation. This attribute may not be used together with
1192 the <tt>alwaysinline</tt> attribute.</dd>
1194 <dt><tt><b>noredzone</b></tt></dt>
1195 <dd>This attribute indicates that the code generator should not use a red
1196 zone, even if the target-specific ABI normally permits it.</dd>
1198 <dt><tt><b>noreturn</b></tt></dt>
1199 <dd>This function attribute indicates that the function never returns
1200 normally. This produces undefined behavior at runtime if the function
1201 ever does dynamically return.</dd>
1203 <dt><tt><b>nounwind</b></tt></dt>
1204 <dd>This function attribute indicates that the function never returns with an
1205 unwind or exceptional control flow. If the function does unwind, its
1206 runtime behavior is undefined.</dd>
1208 <dt><tt><b>optsize</b></tt></dt>
1209 <dd>This attribute suggests that optimization passes and code generator passes
1210 make choices that keep the code size of this function low, and otherwise
1211 do optimizations specifically to reduce code size.</dd>
1213 <dt><tt><b>readnone</b></tt></dt>
1214 <dd>This attribute indicates that the function computes its result (or decides
1215 to unwind an exception) based strictly on its arguments, without
1216 dereferencing any pointer arguments or otherwise accessing any mutable
1217 state (e.g. memory, control registers, etc) visible to caller functions.
1218 It does not write through any pointer arguments
1219 (including <tt><a href="#byval">byval</a></tt> arguments) and never
1220 changes any state visible to callers. This means that it cannot unwind
1221 exceptions by calling the <tt>C++</tt> exception throwing methods, but
1222 could use the <tt>unwind</tt> instruction.</dd>
1224 <dt><tt><b><a name="readonly">readonly</a></b></tt></dt>
1225 <dd>This attribute indicates that the function does not write through any
1226 pointer arguments (including <tt><a href="#byval">byval</a></tt>
1227 arguments) or otherwise modify any state (e.g. memory, control registers,
1228 etc) visible to caller functions. It may dereference pointer arguments
1229 and read state that may be set in the caller. A readonly function always
1230 returns the same value (or unwinds an exception identically) when called
1231 with the same set of arguments and global state. It cannot unwind an
1232 exception by calling the <tt>C++</tt> exception throwing methods, but may
1233 use the <tt>unwind</tt> instruction.</dd>
1235 <dt><tt><b><a name="ssp">ssp</a></b></tt></dt>
1236 <dd>This attribute indicates that the function should emit a stack smashing
1237 protector. It is in the form of a "canary"—a random value placed on
1238 the stack before the local variables that's checked upon return from the
1239 function to see if it has been overwritten. A heuristic is used to
1240 determine if a function needs stack protectors or not.<br>
1242 If a function that has an <tt>ssp</tt> attribute is inlined into a
1243 function that doesn't have an <tt>ssp</tt> attribute, then the resulting
1244 function will have an <tt>ssp</tt> attribute.</dd>
1246 <dt><tt><b>sspreq</b></tt></dt>
1247 <dd>This attribute indicates that the function should <em>always</em> emit a
1248 stack smashing protector. This overrides
1249 the <tt><a href="#ssp">ssp</a></tt> function attribute.<br>
1251 If a function that has an <tt>sspreq</tt> attribute is inlined into a
1252 function that doesn't have an <tt>sspreq</tt> attribute or which has
1253 an <tt>ssp</tt> attribute, then the resulting function will have
1254 an <tt>sspreq</tt> attribute.</dd>
1256 <dt><tt><b><a name="uwtable">uwtable</a></b></tt></dt>
1257 <dd>This attribute indicates that the ABI being targeted requires that
1258 an unwind table entry be produce for this function even if we can
1259 show that no exceptions passes by it. This is normally the case for
1260 the ELF x86-64 abi, but it can be disabled for some compilation
1267 <!-- ======================================================================= -->
1269 <a name="moduleasm">Module-Level Inline Assembly</a>
1274 <p>Modules may contain "module-level inline asm" blocks, which corresponds to
1275 the GCC "file scope inline asm" blocks. These blocks are internally
1276 concatenated by LLVM and treated as a single unit, but may be separated in
1277 the <tt>.ll</tt> file if desired. The syntax is very simple:</p>
1279 <pre class="doc_code">
1280 module asm "inline asm code goes here"
1281 module asm "more can go here"
1284 <p>The strings can contain any character by escaping non-printable characters.
1285 The escape sequence used is simply "\xx" where "xx" is the two digit hex code
1288 <p>The inline asm code is simply printed to the machine code .s file when
1289 assembly code is generated.</p>
1293 <!-- ======================================================================= -->
1295 <a name="datalayout">Data Layout</a>
1300 <p>A module may specify a target specific data layout string that specifies how
1301 data is to be laid out in memory. The syntax for the data layout is
1304 <pre class="doc_code">
1305 target datalayout = "<i>layout specification</i>"
1308 <p>The <i>layout specification</i> consists of a list of specifications
1309 separated by the minus sign character ('-'). Each specification starts with
1310 a letter and may include other information after the letter to define some
1311 aspect of the data layout. The specifications accepted are as follows:</p>
1315 <dd>Specifies that the target lays out data in big-endian form. That is, the
1316 bits with the most significance have the lowest address location.</dd>
1319 <dd>Specifies that the target lays out data in little-endian form. That is,
1320 the bits with the least significance have the lowest address
1323 <dt><tt>p:<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
1324 <dd>This specifies the <i>size</i> of a pointer and its <i>abi</i> and
1325 <i>preferred</i> alignments. All sizes are in bits. Specifying
1326 the <i>pref</i> alignment is optional. If omitted, the
1327 preceding <tt>:</tt> should be omitted too.</dd>
1329 <dt><tt>i<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
1330 <dd>This specifies the alignment for an integer type of a given bit
1331 <i>size</i>. The value of <i>size</i> must be in the range [1,2^23).</dd>
1333 <dt><tt>v<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
1334 <dd>This specifies the alignment for a vector type of a given bit
1337 <dt><tt>f<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
1338 <dd>This specifies the alignment for a floating point type of a given bit
1339 <i>size</i>. Only values of <i>size</i> that are supported by the target
1340 will work. 32 (float) and 64 (double) are supported on all targets;
1341 80 or 128 (different flavors of long double) are also supported on some
1344 <dt><tt>a<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
1345 <dd>This specifies the alignment for an aggregate type of a given bit
1348 <dt><tt>s<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
1349 <dd>This specifies the alignment for a stack object of a given bit
1352 <dt><tt>n<i>size1</i>:<i>size2</i>:<i>size3</i>...</tt></dt>
1353 <dd>This specifies a set of native integer widths for the target CPU
1354 in bits. For example, it might contain "n32" for 32-bit PowerPC,
1355 "n32:64" for PowerPC 64, or "n8:16:32:64" for X86-64. Elements of
1356 this set are considered to support most general arithmetic
1357 operations efficiently.</dd>
1360 <p>When constructing the data layout for a given target, LLVM starts with a
1361 default set of specifications which are then (possibly) overridden by the
1362 specifications in the <tt>datalayout</tt> keyword. The default specifications
1363 are given in this list:</p>
1366 <li><tt>E</tt> - big endian</li>
1367 <li><tt>p:64:64:64</tt> - 64-bit pointers with 64-bit alignment</li>
1368 <li><tt>i1:8:8</tt> - i1 is 8-bit (byte) aligned</li>
1369 <li><tt>i8:8:8</tt> - i8 is 8-bit (byte) aligned</li>
1370 <li><tt>i16:16:16</tt> - i16 is 16-bit aligned</li>
1371 <li><tt>i32:32:32</tt> - i32 is 32-bit aligned</li>
1372 <li><tt>i64:32:64</tt> - i64 has ABI alignment of 32-bits but preferred
1373 alignment of 64-bits</li>
1374 <li><tt>f32:32:32</tt> - float is 32-bit aligned</li>
1375 <li><tt>f64:64:64</tt> - double is 64-bit aligned</li>
1376 <li><tt>v64:64:64</tt> - 64-bit vector is 64-bit aligned</li>
1377 <li><tt>v128:128:128</tt> - 128-bit vector is 128-bit aligned</li>
1378 <li><tt>a0:0:1</tt> - aggregates are 8-bit aligned</li>
1379 <li><tt>s0:64:64</tt> - stack objects are 64-bit aligned</li>
1382 <p>When LLVM is determining the alignment for a given type, it uses the
1383 following rules:</p>
1386 <li>If the type sought is an exact match for one of the specifications, that
1387 specification is used.</li>
1389 <li>If no match is found, and the type sought is an integer type, then the
1390 smallest integer type that is larger than the bitwidth of the sought type
1391 is used. If none of the specifications are larger than the bitwidth then
1392 the the largest integer type is used. For example, given the default
1393 specifications above, the i7 type will use the alignment of i8 (next
1394 largest) while both i65 and i256 will use the alignment of i64 (largest
1397 <li>If no match is found, and the type sought is a vector type, then the
1398 largest vector type that is smaller than the sought vector type will be
1399 used as a fall back. This happens because <128 x double> can be
1400 implemented in terms of 64 <2 x double>, for example.</li>
1405 <!-- ======================================================================= -->
1407 <a name="pointeraliasing">Pointer Aliasing Rules</a>
1412 <p>Any memory access must be done through a pointer value associated
1413 with an address range of the memory access, otherwise the behavior
1414 is undefined. Pointer values are associated with address ranges
1415 according to the following rules:</p>
1418 <li>A pointer value is associated with the addresses associated with
1419 any value it is <i>based</i> on.
1420 <li>An address of a global variable is associated with the address
1421 range of the variable's storage.</li>
1422 <li>The result value of an allocation instruction is associated with
1423 the address range of the allocated storage.</li>
1424 <li>A null pointer in the default address-space is associated with
1426 <li>An integer constant other than zero or a pointer value returned
1427 from a function not defined within LLVM may be associated with address
1428 ranges allocated through mechanisms other than those provided by
1429 LLVM. Such ranges shall not overlap with any ranges of addresses
1430 allocated by mechanisms provided by LLVM.</li>
1433 <p>A pointer value is <i>based</i> on another pointer value according
1434 to the following rules:</p>
1437 <li>A pointer value formed from a
1438 <tt><a href="#i_getelementptr">getelementptr</a></tt> operation
1439 is <i>based</i> on the first operand of the <tt>getelementptr</tt>.</li>
1440 <li>The result value of a
1441 <tt><a href="#i_bitcast">bitcast</a></tt> is <i>based</i> on the operand
1442 of the <tt>bitcast</tt>.</li>
1443 <li>A pointer value formed by an
1444 <tt><a href="#i_inttoptr">inttoptr</a></tt> is <i>based</i> on all
1445 pointer values that contribute (directly or indirectly) to the
1446 computation of the pointer's value.</li>
1447 <li>The "<i>based</i> on" relationship is transitive.</li>
1450 <p>Note that this definition of <i>"based"</i> is intentionally
1451 similar to the definition of <i>"based"</i> in C99, though it is
1452 slightly weaker.</p>
1454 <p>LLVM IR does not associate types with memory. The result type of a
1455 <tt><a href="#i_load">load</a></tt> merely indicates the size and
1456 alignment of the memory from which to load, as well as the
1457 interpretation of the value. The first operand type of a
1458 <tt><a href="#i_store">store</a></tt> similarly only indicates the size
1459 and alignment of the store.</p>
1461 <p>Consequently, type-based alias analysis, aka TBAA, aka
1462 <tt>-fstrict-aliasing</tt>, is not applicable to general unadorned
1463 LLVM IR. <a href="#metadata">Metadata</a> may be used to encode
1464 additional information which specialized optimization passes may use
1465 to implement type-based alias analysis.</p>
1469 <!-- ======================================================================= -->
1471 <a name="volatile">Volatile Memory Accesses</a>
1476 <p>Certain memory accesses, such as <a href="#i_load"><tt>load</tt></a>s, <a
1477 href="#i_store"><tt>store</tt></a>s, and <a
1478 href="#int_memcpy"><tt>llvm.memcpy</tt></a>s may be marked <tt>volatile</tt>.
1479 The optimizers must not change the number of volatile operations or change their
1480 order of execution relative to other volatile operations. The optimizers
1481 <i>may</i> change the order of volatile operations relative to non-volatile
1482 operations. This is not Java's "volatile" and has no cross-thread
1483 synchronization behavior.</p>
1487 <!-- ======================================================================= -->
1489 <a name="memmodel">Memory Model for Concurrent Operations</a>
1494 <p>The LLVM IR does not define any way to start parallel threads of execution
1495 or to register signal handlers. Nonetheless, there are platform-specific
1496 ways to create them, and we define LLVM IR's behavior in their presence. This
1497 model is inspired by the C++0x memory model.</p>
1499 <p>We define a <i>happens-before</i> partial order as the least partial order
1502 <li>Is a superset of single-thread program order, and</li>
1503 <li>When a <i>synchronizes-with</i> <tt>b</tt>, includes an edge from
1504 <tt>a</tt> to <tt>b</tt>. <i>Synchronizes-with</i> pairs are introduced
1505 by platform-specific techniques, like pthread locks, thread
1506 creation, thread joining, etc., and by atomic instructions.
1507 (See also <a href="#ordering">Atomic Memory Ordering Constraints</a>).
1511 <p>Note that program order does not introduce <i>happens-before</i> edges
1512 between a thread and signals executing inside that thread.</p>
1514 <p>Every (defined) read operation (load instructions, memcpy, atomic
1515 loads/read-modify-writes, etc.) <var>R</var> reads a series of bytes written by
1516 (defined) write operations (store instructions, atomic
1517 stores/read-modify-writes, memcpy, etc.). For the purposes of this section,
1518 initialized globals are considered to have a write of the initializer which is
1519 atomic and happens before any other read or write of the memory in question.
1520 For each byte of a read <var>R</var>, <var>R<sub>byte</sub></var> may see
1521 any write to the same byte, except:</p>
1524 <li>If <var>write<sub>1</sub></var> happens before
1525 <var>write<sub>2</sub></var>, and <var>write<sub>2</sub></var> happens
1526 before <var>R<sub>byte</sub></var>, then <var>R<sub>byte</sub></var>
1527 does not see <var>write<sub>1</sub></var>.
1528 <li>If <var>R<sub>byte</sub></var> happens before
1529 <var>write<sub>3</sub></var>, then <var>R<sub>byte</sub></var> does not
1530 see <var>write<sub>3</sub></var>.
1533 <p>Given that definition, <var>R<sub>byte</sub></var> is defined as follows:
1535 <li>If there is no write to the same byte that happens before
1536 <var>R<sub>byte</sub></var>, <var>R<sub>byte</sub></var> returns
1537 <tt>undef</tt> for that byte.
1538 <li>Otherwise, if <var>R<sub>byte</sub></var> may see exactly one write,
1539 <var>R<sub>byte</sub></var> returns the value written by that
1541 <li>Otherwise, if <var>R</var> is atomic, and all the writes
1542 <var>R<sub>byte</sub></var> may see are atomic, it chooses one of the
1543 values written. See the <a href="#ordering">Atomic Memory Ordering
1544 Constraints</a> section for additional constraints on how the choice
1546 <li>Otherwise <var>R<sub>byte</sub></var> returns <tt>undef</tt>.</li>
1549 <p><var>R</var> returns the value composed of the series of bytes it read.
1550 This implies that some bytes within the value may be <tt>undef</tt>
1551 <b>without</b> the entire value being <tt>undef</tt>. Note that this only
1552 defines the semantics of the operation; it doesn't mean that targets will
1553 emit more than one instruction to read the series of bytes.</p>
1555 <p>Note that in cases where none of the atomic intrinsics are used, this model
1556 places only one restriction on IR transformations on top of what is required
1557 for single-threaded execution: introducing a store to a byte which might not
1558 otherwise be stored to can introduce undefined behavior. (Specifically, in
1559 the case where another thread might write to and read from an address,
1560 introducing a store can change a load that may see exactly one write into
1561 a load that may see multiple writes.)</p>
1563 <!-- FIXME: This model assumes all targets where concurrency is relevant have
1564 a byte-size store which doesn't affect adjacent bytes. As far as I can tell,
1565 none of the backends currently in the tree fall into this category; however,
1566 there might be targets which care. If there are, we want a paragraph
1569 Targets may specify that stores narrower than a certain width are not
1570 available; on such a target, for the purposes of this model, treat any
1571 non-atomic write with an alignment or width less than the minimum width
1572 as if it writes to the relevant surrounding bytes.
1577 <!-- ======================================================================= -->
1578 <div class="doc_subsection">
1579 <a name="ordering">Atomic Memory Ordering Constraints</a>
1582 <div class="doc_text">
1584 <p>Atomic instructions (<a href="#i_cmpxchg"><code>cmpxchg</code></a>,
1585 <a href="#i_atomicrmw"><code>atomicrmw</code></a>, and
1586 <a href="#i_fence"><code>fence</code></a>) take an ordering parameter
1587 that determines which other atomic instructions on the same address they
1588 <i>synchronize with</i>. These semantics are borrowed from Java and C++0x,
1589 but are somewhat more colloquial. If these descriptions aren't precise enough,
1590 check those specs. <a href="#i_fence"><code>fence</code></a> instructions
1591 treat these orderings somewhat differently since they don't take an address.
1592 See that instruction's documentation for details.</p>
1594 <!-- FIXME Note atomic load+store here once those get added. -->
1597 <!-- FIXME: unordered is intended to be used for atomic load and store;
1598 it isn't allowed for any instruction yet. -->
1599 <dt><code>unordered</code></dt>
1600 <dd>The set of values that can be read is governed by the happens-before
1601 partial order. A value cannot be read unless some operation wrote it.
1602 This is intended to provide a guarantee strong enough to model Java's
1603 non-volatile shared variables. This ordering cannot be specified for
1604 read-modify-write operations; it is not strong enough to make them atomic
1605 in any interesting way.</dd>
1606 <dt><code>monotonic</code></dt>
1607 <dd>In addition to the guarantees of <code>unordered</code>, there is a single
1608 total order for modifications by <code>monotonic</code> operations on each
1609 address. All modification orders must be compatible with the happens-before
1610 order. There is no guarantee that the modification orders can be combined to
1611 a global total order for the whole program (and this often will not be
1612 possible). The read in an atomic read-modify-write operation
1613 (<a href="#i_cmpxchg"><code>cmpxchg</code></a> and
1614 <a href="#i_atomicrmw"><code>atomicrmw</code></a>)
1615 reads the value in the modification order immediately before the value it
1616 writes. If one atomic read happens before another atomic read of the same
1617 address, the later read must see the same value or a later value in the
1618 address's modification order. This disallows reordering of
1619 <code>monotonic</code> (or stronger) operations on the same address. If an
1620 address is written <code>monotonic</code>ally by one thread, and other threads
1621 <code>monotonic</code>ally read that address repeatedly, the other threads must
1622 eventually see the write. This is intended to model C++'s relaxed atomic
1624 <dt><code>acquire</code></dt>
1625 <dd>In addition to the guarantees of <code>monotonic</code>, if this operation
1626 reads a value written by a <code>release</code> atomic operation, it
1627 <i>synchronizes-with</i> that operation.</dd>
1628 <dt><code>release</code></dt>
1629 <dd>In addition to the guarantees of <code>monotonic</code>,
1630 a <i>synchronizes-with</i> edge may be formed by an <code>acquire</code>
1632 <dt><code>acq_rel</code> (acquire+release)</dt><dd>Acts as both an
1633 <code>acquire</code> and <code>release</code> operation on its address.</dd>
1634 <dt><code>seq_cst</code> (sequentially consistent)</dt><dd>
1635 <dd>In addition to the guarantees of <code>acq_rel</code>
1636 (<code>acquire</code> for an operation which only reads, <code>release</code>
1637 for an operation which only writes), there is a global total order on all
1638 sequentially-consistent operations on all addresses, which is consistent with
1639 the <i>happens-before</i> partial order and with the modification orders of
1640 all the affected addresses. Each sequentially-consistent read sees the last
1641 preceding write to the same address in this global order. This is intended
1642 to model C++'s sequentially-consistent atomic variables and Java's volatile
1643 shared variables.</dd>
1646 <p id="singlethread">If an atomic operation is marked <code>singlethread</code>,
1647 it only <i>synchronizes with</i> or participates in modification and seq_cst
1648 total orderings with other operations running in the same thread (for example,
1649 in signal handlers).</p>
1655 <!-- *********************************************************************** -->
1656 <h2><a name="typesystem">Type System</a></h2>
1657 <!-- *********************************************************************** -->
1661 <p>The LLVM type system is one of the most important features of the
1662 intermediate representation. Being typed enables a number of optimizations
1663 to be performed on the intermediate representation directly, without having
1664 to do extra analyses on the side before the transformation. A strong type
1665 system makes it easier to read the generated code and enables novel analyses
1666 and transformations that are not feasible to perform on normal three address
1667 code representations.</p>
1669 <!-- ======================================================================= -->
1671 <a name="t_classifications">Type Classifications</a>
1676 <p>The types fall into a few useful classifications:</p>
1678 <table border="1" cellspacing="0" cellpadding="4">
1680 <tr><th>Classification</th><th>Types</th></tr>
1682 <td><a href="#t_integer">integer</a></td>
1683 <td><tt>i1, i2, i3, ... i8, ... i16, ... i32, ... i64, ... </tt></td>
1686 <td><a href="#t_floating">floating point</a></td>
1687 <td><tt>float, double, x86_fp80, fp128, ppc_fp128</tt></td>
1690 <td><a name="t_firstclass">first class</a></td>
1691 <td><a href="#t_integer">integer</a>,
1692 <a href="#t_floating">floating point</a>,
1693 <a href="#t_pointer">pointer</a>,
1694 <a href="#t_vector">vector</a>,
1695 <a href="#t_struct">structure</a>,
1696 <a href="#t_array">array</a>,
1697 <a href="#t_label">label</a>,
1698 <a href="#t_metadata">metadata</a>.
1702 <td><a href="#t_primitive">primitive</a></td>
1703 <td><a href="#t_label">label</a>,
1704 <a href="#t_void">void</a>,
1705 <a href="#t_integer">integer</a>,
1706 <a href="#t_floating">floating point</a>,
1707 <a href="#t_x86mmx">x86mmx</a>,
1708 <a href="#t_metadata">metadata</a>.</td>
1711 <td><a href="#t_derived">derived</a></td>
1712 <td><a href="#t_array">array</a>,
1713 <a href="#t_function">function</a>,
1714 <a href="#t_pointer">pointer</a>,
1715 <a href="#t_struct">structure</a>,
1716 <a href="#t_vector">vector</a>,
1717 <a href="#t_opaque">opaque</a>.
1723 <p>The <a href="#t_firstclass">first class</a> types are perhaps the most
1724 important. Values of these types are the only ones which can be produced by
1729 <!-- ======================================================================= -->
1731 <a name="t_primitive">Primitive Types</a>
1736 <p>The primitive types are the fundamental building blocks of the LLVM
1739 <!-- _______________________________________________________________________ -->
1741 <a name="t_integer">Integer Type</a>
1747 <p>The integer type is a very simple type that simply specifies an arbitrary
1748 bit width for the integer type desired. Any bit width from 1 bit to
1749 2<sup>23</sup>-1 (about 8 million) can be specified.</p>
1756 <p>The number of bits the integer will occupy is specified by the <tt>N</tt>
1760 <table class="layout">
1762 <td class="left"><tt>i1</tt></td>
1763 <td class="left">a single-bit integer.</td>
1766 <td class="left"><tt>i32</tt></td>
1767 <td class="left">a 32-bit integer.</td>
1770 <td class="left"><tt>i1942652</tt></td>
1771 <td class="left">a really big integer of over 1 million bits.</td>
1777 <!-- _______________________________________________________________________ -->
1779 <a name="t_floating">Floating Point Types</a>
1786 <tr><th>Type</th><th>Description</th></tr>
1787 <tr><td><tt>float</tt></td><td>32-bit floating point value</td></tr>
1788 <tr><td><tt>double</tt></td><td>64-bit floating point value</td></tr>
1789 <tr><td><tt>fp128</tt></td><td>128-bit floating point value (112-bit mantissa)</td></tr>
1790 <tr><td><tt>x86_fp80</tt></td><td>80-bit floating point value (X87)</td></tr>
1791 <tr><td><tt>ppc_fp128</tt></td><td>128-bit floating point value (two 64-bits)</td></tr>
1797 <!-- _______________________________________________________________________ -->
1799 <a name="t_x86mmx">X86mmx Type</a>
1805 <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>
1814 <!-- _______________________________________________________________________ -->
1816 <a name="t_void">Void Type</a>
1822 <p>The void type does not represent any value and has no size.</p>
1831 <!-- _______________________________________________________________________ -->
1833 <a name="t_label">Label Type</a>
1839 <p>The label type represents code labels.</p>
1848 <!-- _______________________________________________________________________ -->
1850 <a name="t_metadata">Metadata Type</a>
1856 <p>The metadata type represents embedded metadata. No derived types may be
1857 created from metadata except for <a href="#t_function">function</a>
1869 <!-- ======================================================================= -->
1871 <a name="t_derived">Derived Types</a>
1876 <p>The real power in LLVM comes from the derived types in the system. This is
1877 what allows a programmer to represent arrays, functions, pointers, and other
1878 useful types. Each of these types contain one or more element types which
1879 may be a primitive type, or another derived type. For example, it is
1880 possible to have a two dimensional array, using an array as the element type
1881 of another array.</p>
1886 <!-- _______________________________________________________________________ -->
1888 <a name="t_aggregate">Aggregate Types</a>
1893 <p>Aggregate Types are a subset of derived types that can contain multiple
1894 member types. <a href="#t_array">Arrays</a>,
1895 <a href="#t_struct">structs</a>, and <a href="#t_vector">vectors</a> are
1896 aggregate types.</p>
1900 <!-- _______________________________________________________________________ -->
1902 <a name="t_array">Array Type</a>
1908 <p>The array type is a very simple derived type that arranges elements
1909 sequentially in memory. The array type requires a size (number of elements)
1910 and an underlying data type.</p>
1914 [<# elements> x <elementtype>]
1917 <p>The number of elements is a constant integer value; <tt>elementtype</tt> may
1918 be any type with a size.</p>
1921 <table class="layout">
1923 <td class="left"><tt>[40 x i32]</tt></td>
1924 <td class="left">Array of 40 32-bit integer values.</td>
1927 <td class="left"><tt>[41 x i32]</tt></td>
1928 <td class="left">Array of 41 32-bit integer values.</td>
1931 <td class="left"><tt>[4 x i8]</tt></td>
1932 <td class="left">Array of 4 8-bit integer values.</td>
1935 <p>Here are some examples of multidimensional arrays:</p>
1936 <table class="layout">
1938 <td class="left"><tt>[3 x [4 x i32]]</tt></td>
1939 <td class="left">3x4 array of 32-bit integer values.</td>
1942 <td class="left"><tt>[12 x [10 x float]]</tt></td>
1943 <td class="left">12x10 array of single precision floating point values.</td>
1946 <td class="left"><tt>[2 x [3 x [4 x i16]]]</tt></td>
1947 <td class="left">2x3x4 array of 16-bit integer values.</td>
1951 <p>There is no restriction on indexing beyond the end of the array implied by
1952 a static type (though there are restrictions on indexing beyond the bounds
1953 of an allocated object in some cases). This means that single-dimension
1954 'variable sized array' addressing can be implemented in LLVM with a zero
1955 length array type. An implementation of 'pascal style arrays' in LLVM could
1956 use the type "<tt>{ i32, [0 x float]}</tt>", for example.</p>
1960 <!-- _______________________________________________________________________ -->
1962 <a name="t_function">Function Type</a>
1968 <p>The function type can be thought of as a function signature. It consists of
1969 a return type and a list of formal parameter types. The return type of a
1970 function type is a first class type or a void type.</p>
1974 <returntype> (<parameter list>)
1977 <p>...where '<tt><parameter list></tt>' is a comma-separated list of type
1978 specifiers. Optionally, the parameter list may include a type <tt>...</tt>,
1979 which indicates that the function takes a variable number of arguments.
1980 Variable argument functions can access their arguments with
1981 the <a href="#int_varargs">variable argument handling intrinsic</a>
1982 functions. '<tt><returntype></tt>' is any type except
1983 <a href="#t_label">label</a>.</p>
1986 <table class="layout">
1988 <td class="left"><tt>i32 (i32)</tt></td>
1989 <td class="left">function taking an <tt>i32</tt>, returning an <tt>i32</tt>
1991 </tr><tr class="layout">
1992 <td class="left"><tt>float (i16, i32 *) *
1994 <td class="left"><a href="#t_pointer">Pointer</a> to a function that takes
1995 an <tt>i16</tt> and a <a href="#t_pointer">pointer</a> to <tt>i32</tt>,
1996 returning <tt>float</tt>.
1998 </tr><tr class="layout">
1999 <td class="left"><tt>i32 (i8*, ...)</tt></td>
2000 <td class="left">A vararg function that takes at least one
2001 <a href="#t_pointer">pointer</a> to <tt>i8 </tt> (char in C),
2002 which returns an integer. This is the signature for <tt>printf</tt> in
2005 </tr><tr class="layout">
2006 <td class="left"><tt>{i32, i32} (i32)</tt></td>
2007 <td class="left">A function taking an <tt>i32</tt>, returning a
2008 <a href="#t_struct">structure</a> containing two <tt>i32</tt> values
2015 <!-- _______________________________________________________________________ -->
2017 <a name="t_struct">Structure Type</a>
2023 <p>The structure type is used to represent a collection of data members together
2024 in memory. The elements of a structure may be any type that has a size.</p>
2026 <p>Structures in memory are accessed using '<tt><a href="#i_load">load</a></tt>'
2027 and '<tt><a href="#i_store">store</a></tt>' by getting a pointer to a field
2028 with the '<tt><a href="#i_getelementptr">getelementptr</a></tt>' instruction.
2029 Structures in registers are accessed using the
2030 '<tt><a href="#i_extractvalue">extractvalue</a></tt>' and
2031 '<tt><a href="#i_insertvalue">insertvalue</a></tt>' instructions.</p>
2033 <p>Structures may optionally be "packed" structures, which indicate that the
2034 alignment of the struct is one byte, and that there is no padding between
2035 the elements. In non-packed structs, padding between field types is defined
2036 by the target data string to match the underlying processor.</p>
2038 <p>Structures can either be "anonymous" or "named". An anonymous structure is
2039 defined inline with other types (e.g. <tt>{i32, i32}*</tt>) and a named types
2040 are always defined at the top level with a name. Anonmyous types are uniqued
2041 by their contents and can never be recursive since there is no way to write
2042 one. Named types can be recursive.
2047 %T1 = type { <type list> } <i>; Named normal struct type</i>
2048 %T2 = type <{ <type list> }> <i>; Named packed struct type</i>
2052 <table class="layout">
2054 <td class="left"><tt>{ i32, i32, i32 }</tt></td>
2055 <td class="left">A triple of three <tt>i32</tt> values</td>
2058 <td class="left"><tt>{ float, i32 (i32) * }</tt></td>
2059 <td class="left">A pair, where the first element is a <tt>float</tt> and the
2060 second element is a <a href="#t_pointer">pointer</a> to a
2061 <a href="#t_function">function</a> that takes an <tt>i32</tt>, returning
2062 an <tt>i32</tt>.</td>
2065 <td class="left"><tt><{ i8, i32 }></tt></td>
2066 <td class="left">A packed struct known to be 5 bytes in size.</td>
2072 <!-- _______________________________________________________________________ -->
2074 <a name="t_opaque">Opaque Structure Types</a>
2080 <p>Opaque structure types are used to represent named structure types that do
2081 not have a body specified. This corresponds (for example) to the C notion of
2082 a forward declared structure.</p>
2091 <table class="layout">
2093 <td class="left"><tt>opaque</tt></td>
2094 <td class="left">An opaque type.</td>
2102 <!-- _______________________________________________________________________ -->
2104 <a name="t_pointer">Pointer Type</a>
2110 <p>The pointer type is used to specify memory locations.
2111 Pointers are commonly used to reference objects in memory.</p>
2113 <p>Pointer types may have an optional address space attribute defining the
2114 numbered address space where the pointed-to object resides. The default
2115 address space is number zero. The semantics of non-zero address
2116 spaces are target-specific.</p>
2118 <p>Note that LLVM does not permit pointers to void (<tt>void*</tt>) nor does it
2119 permit pointers to labels (<tt>label*</tt>). Use <tt>i8*</tt> instead.</p>
2127 <table class="layout">
2129 <td class="left"><tt>[4 x i32]*</tt></td>
2130 <td class="left">A <a href="#t_pointer">pointer</a> to <a
2131 href="#t_array">array</a> of four <tt>i32</tt> values.</td>
2134 <td class="left"><tt>i32 (i32*) *</tt></td>
2135 <td class="left"> A <a href="#t_pointer">pointer</a> to a <a
2136 href="#t_function">function</a> that takes an <tt>i32*</tt>, returning an
2140 <td class="left"><tt>i32 addrspace(5)*</tt></td>
2141 <td class="left">A <a href="#t_pointer">pointer</a> to an <tt>i32</tt> value
2142 that resides in address space #5.</td>
2148 <!-- _______________________________________________________________________ -->
2150 <a name="t_vector">Vector Type</a>
2156 <p>A vector type is a simple derived type that represents a vector of elements.
2157 Vector types are used when multiple primitive data are operated in parallel
2158 using a single instruction (SIMD). A vector type requires a size (number of
2159 elements) and an underlying primitive data type. Vector types are considered
2160 <a href="#t_firstclass">first class</a>.</p>
2164 < <# elements> x <elementtype> >
2167 <p>The number of elements is a constant integer value larger than 0; elementtype
2168 may be any integer or floating point type. Vectors of size zero are not
2169 allowed, and pointers are not allowed as the element type.</p>
2172 <table class="layout">
2174 <td class="left"><tt><4 x i32></tt></td>
2175 <td class="left">Vector of 4 32-bit integer values.</td>
2178 <td class="left"><tt><8 x float></tt></td>
2179 <td class="left">Vector of 8 32-bit floating-point values.</td>
2182 <td class="left"><tt><2 x i64></tt></td>
2183 <td class="left">Vector of 2 64-bit integer values.</td>
2189 <!-- *********************************************************************** -->
2190 <h2><a name="constants">Constants</a></h2>
2191 <!-- *********************************************************************** -->
2195 <p>LLVM has several different basic types of constants. This section describes
2196 them all and their syntax.</p>
2198 <!-- ======================================================================= -->
2200 <a name="simpleconstants">Simple Constants</a>
2206 <dt><b>Boolean constants</b></dt>
2207 <dd>The two strings '<tt>true</tt>' and '<tt>false</tt>' are both valid
2208 constants of the <tt><a href="#t_integer">i1</a></tt> type.</dd>
2210 <dt><b>Integer constants</b></dt>
2211 <dd>Standard integers (such as '4') are constants of
2212 the <a href="#t_integer">integer</a> type. Negative numbers may be used
2213 with integer types.</dd>
2215 <dt><b>Floating point constants</b></dt>
2216 <dd>Floating point constants use standard decimal notation (e.g. 123.421),
2217 exponential notation (e.g. 1.23421e+2), or a more precise hexadecimal
2218 notation (see below). The assembler requires the exact decimal value of a
2219 floating-point constant. For example, the assembler accepts 1.25 but
2220 rejects 1.3 because 1.3 is a repeating decimal in binary. Floating point
2221 constants must have a <a href="#t_floating">floating point</a> type. </dd>
2223 <dt><b>Null pointer constants</b></dt>
2224 <dd>The identifier '<tt>null</tt>' is recognized as a null pointer constant
2225 and must be of <a href="#t_pointer">pointer type</a>.</dd>
2228 <p>The one non-intuitive notation for constants is the hexadecimal form of
2229 floating point constants. For example, the form '<tt>double
2230 0x432ff973cafa8000</tt>' is equivalent to (but harder to read than)
2231 '<tt>double 4.5e+15</tt>'. The only time hexadecimal floating point
2232 constants are required (and the only time that they are generated by the
2233 disassembler) is when a floating point constant must be emitted but it cannot
2234 be represented as a decimal floating point number in a reasonable number of
2235 digits. For example, NaN's, infinities, and other special values are
2236 represented in their IEEE hexadecimal format so that assembly and disassembly
2237 do not cause any bits to change in the constants.</p>
2239 <p>When using the hexadecimal form, constants of types float and double are
2240 represented using the 16-digit form shown above (which matches the IEEE754
2241 representation for double); float values must, however, be exactly
2242 representable as IEE754 single precision. Hexadecimal format is always used
2243 for long double, and there are three forms of long double. The 80-bit format
2244 used by x86 is represented as <tt>0xK</tt> followed by 20 hexadecimal digits.
2245 The 128-bit format used by PowerPC (two adjacent doubles) is represented
2246 by <tt>0xM</tt> followed by 32 hexadecimal digits. The IEEE 128-bit format
2247 is represented by <tt>0xL</tt> followed by 32 hexadecimal digits; no
2248 currently supported target uses this format. Long doubles will only work if
2249 they match the long double format on your target. All hexadecimal formats
2250 are big-endian (sign bit at the left).</p>
2252 <p>There are no constants of type x86mmx.</p>
2255 <!-- ======================================================================= -->
2257 <a name="aggregateconstants"></a> <!-- old anchor -->
2258 <a name="complexconstants">Complex Constants</a>
2263 <p>Complex constants are a (potentially recursive) combination of simple
2264 constants and smaller complex constants.</p>
2267 <dt><b>Structure constants</b></dt>
2268 <dd>Structure constants are represented with notation similar to structure
2269 type definitions (a comma separated list of elements, surrounded by braces
2270 (<tt>{}</tt>)). For example: "<tt>{ i32 4, float 17.0, i32* @G }</tt>",
2271 where "<tt>@G</tt>" is declared as "<tt>@G = external global i32</tt>".
2272 Structure constants must have <a href="#t_struct">structure type</a>, and
2273 the number and types of elements must match those specified by the
2276 <dt><b>Array constants</b></dt>
2277 <dd>Array constants are represented with notation similar to array type
2278 definitions (a comma separated list of elements, surrounded by square
2279 brackets (<tt>[]</tt>)). For example: "<tt>[ i32 42, i32 11, i32 74
2280 ]</tt>". Array constants must have <a href="#t_array">array type</a>, and
2281 the number and types of elements must match those specified by the
2284 <dt><b>Vector constants</b></dt>
2285 <dd>Vector constants are represented with notation similar to vector type
2286 definitions (a comma separated list of elements, surrounded by
2287 less-than/greater-than's (<tt><></tt>)). For example: "<tt>< i32
2288 42, i32 11, i32 74, i32 100 ></tt>". Vector constants must
2289 have <a href="#t_vector">vector type</a>, and the number and types of
2290 elements must match those specified by the type.</dd>
2292 <dt><b>Zero initialization</b></dt>
2293 <dd>The string '<tt>zeroinitializer</tt>' can be used to zero initialize a
2294 value to zero of <em>any</em> type, including scalar and
2295 <a href="#t_aggregate">aggregate</a> types.
2296 This is often used to avoid having to print large zero initializers
2297 (e.g. for large arrays) and is always exactly equivalent to using explicit
2298 zero initializers.</dd>
2300 <dt><b>Metadata node</b></dt>
2301 <dd>A metadata node is a structure-like constant with
2302 <a href="#t_metadata">metadata type</a>. For example: "<tt>metadata !{
2303 i32 0, metadata !"test" }</tt>". Unlike other constants that are meant to
2304 be interpreted as part of the instruction stream, metadata is a place to
2305 attach additional information such as debug info.</dd>
2310 <!-- ======================================================================= -->
2312 <a name="globalconstants">Global Variable and Function Addresses</a>
2317 <p>The addresses of <a href="#globalvars">global variables</a>
2318 and <a href="#functionstructure">functions</a> are always implicitly valid
2319 (link-time) constants. These constants are explicitly referenced when
2320 the <a href="#identifiers">identifier for the global</a> is used and always
2321 have <a href="#t_pointer">pointer</a> type. For example, the following is a
2322 legal LLVM file:</p>
2324 <pre class="doc_code">
2327 @Z = global [2 x i32*] [ i32* @X, i32* @Y ]
2332 <!-- ======================================================================= -->
2334 <a name="undefvalues">Undefined Values</a>
2339 <p>The string '<tt>undef</tt>' can be used anywhere a constant is expected, and
2340 indicates that the user of the value may receive an unspecified bit-pattern.
2341 Undefined values may be of any type (other than '<tt>label</tt>'
2342 or '<tt>void</tt>') and be used anywhere a constant is permitted.</p>
2344 <p>Undefined values are useful because they indicate to the compiler that the
2345 program is well defined no matter what value is used. This gives the
2346 compiler more freedom to optimize. Here are some examples of (potentially
2347 surprising) transformations that are valid (in pseudo IR):</p>
2350 <pre class="doc_code">
2360 <p>This is safe because all of the output bits are affected by the undef bits.
2361 Any output bit can have a zero or one depending on the input bits.</p>
2363 <pre class="doc_code">
2374 <p>These logical operations have bits that are not always affected by the input.
2375 For example, if <tt>%X</tt> has a zero bit, then the output of the
2376 '<tt>and</tt>' operation will always be a zero for that bit, no matter what
2377 the corresponding bit from the '<tt>undef</tt>' is. As such, it is unsafe to
2378 optimize or assume that the result of the '<tt>and</tt>' is '<tt>undef</tt>'.
2379 However, it is safe to assume that all bits of the '<tt>undef</tt>' could be
2380 0, and optimize the '<tt>and</tt>' to 0. Likewise, it is safe to assume that
2381 all the bits of the '<tt>undef</tt>' operand to the '<tt>or</tt>' could be
2382 set, allowing the '<tt>or</tt>' to be folded to -1.</p>
2384 <pre class="doc_code">
2385 %A = select undef, %X, %Y
2386 %B = select undef, 42, %Y
2387 %C = select %X, %Y, undef
2398 <p>This set of examples shows that undefined '<tt>select</tt>' (and conditional
2399 branch) conditions can go <em>either way</em>, but they have to come from one
2400 of the two operands. In the <tt>%A</tt> example, if <tt>%X</tt> and
2401 <tt>%Y</tt> were both known to have a clear low bit, then <tt>%A</tt> would
2402 have to have a cleared low bit. However, in the <tt>%C</tt> example, the
2403 optimizer is allowed to assume that the '<tt>undef</tt>' operand could be the
2404 same as <tt>%Y</tt>, allowing the whole '<tt>select</tt>' to be
2407 <pre class="doc_code">
2408 %A = xor undef, undef
2426 <p>This example points out that two '<tt>undef</tt>' operands are not
2427 necessarily the same. This can be surprising to people (and also matches C
2428 semantics) where they assume that "<tt>X^X</tt>" is always zero, even
2429 if <tt>X</tt> is undefined. This isn't true for a number of reasons, but the
2430 short answer is that an '<tt>undef</tt>' "variable" can arbitrarily change
2431 its value over its "live range". This is true because the variable doesn't
2432 actually <em>have a live range</em>. Instead, the value is logically read
2433 from arbitrary registers that happen to be around when needed, so the value
2434 is not necessarily consistent over time. In fact, <tt>%A</tt> and <tt>%C</tt>
2435 need to have the same semantics or the core LLVM "replace all uses with"
2436 concept would not hold.</p>
2438 <pre class="doc_code">
2446 <p>These examples show the crucial difference between an <em>undefined
2447 value</em> and <em>undefined behavior</em>. An undefined value (like
2448 '<tt>undef</tt>') is allowed to have an arbitrary bit-pattern. This means that
2449 the <tt>%A</tt> operation can be constant folded to '<tt>undef</tt>', because
2450 the '<tt>undef</tt>' could be an SNaN, and <tt>fdiv</tt> is not (currently)
2451 defined on SNaN's. However, in the second example, we can make a more
2452 aggressive assumption: because the <tt>undef</tt> is allowed to be an
2453 arbitrary value, we are allowed to assume that it could be zero. Since a
2454 divide by zero has <em>undefined behavior</em>, we are allowed to assume that
2455 the operation does not execute at all. This allows us to delete the divide and
2456 all code after it. Because the undefined operation "can't happen", the
2457 optimizer can assume that it occurs in dead code.</p>
2459 <pre class="doc_code">
2460 a: store undef -> %X
2461 b: store %X -> undef
2467 <p>These examples reiterate the <tt>fdiv</tt> example: a store <em>of</em> an
2468 undefined value can be assumed to not have any effect; we can assume that the
2469 value is overwritten with bits that happen to match what was already there.
2470 However, a store <em>to</em> an undefined location could clobber arbitrary
2471 memory, therefore, it has undefined behavior.</p>
2475 <!-- ======================================================================= -->
2477 <a name="trapvalues">Trap Values</a>
2482 <p>Trap values are similar to <a href="#undefvalues">undef values</a>, however
2483 instead of representing an unspecified bit pattern, they represent the
2484 fact that an instruction or constant expression which cannot evoke side
2485 effects has nevertheless detected a condition which results in undefined
2488 <p>There is currently no way of representing a trap value in the IR; they
2489 only exist when produced by operations such as
2490 <a href="#i_add"><tt>add</tt></a> with the <tt>nsw</tt> flag.</p>
2492 <p>Trap value behavior is defined in terms of value <i>dependence</i>:</p>
2495 <li>Values other than <a href="#i_phi"><tt>phi</tt></a> nodes depend on
2496 their operands.</li>
2498 <li><a href="#i_phi"><tt>Phi</tt></a> nodes depend on the operand corresponding
2499 to their dynamic predecessor basic block.</li>
2501 <li>Function arguments depend on the corresponding actual argument values in
2502 the dynamic callers of their functions.</li>
2504 <li><a href="#i_call"><tt>Call</tt></a> instructions depend on the
2505 <a href="#i_ret"><tt>ret</tt></a> instructions that dynamically transfer
2506 control back to them.</li>
2508 <li><a href="#i_invoke"><tt>Invoke</tt></a> instructions depend on the
2509 <a href="#i_ret"><tt>ret</tt></a>, <a href="#i_unwind"><tt>unwind</tt></a>,
2510 or exception-throwing call instructions that dynamically transfer control
2513 <li>Non-volatile loads and stores depend on the most recent stores to all of the
2514 referenced memory addresses, following the order in the IR
2515 (including loads and stores implied by intrinsics such as
2516 <a href="#int_memcpy"><tt>@llvm.memcpy</tt></a>.)</li>
2518 <!-- TODO: In the case of multiple threads, this only applies if the store
2519 "happens-before" the load or store. -->
2521 <!-- TODO: floating-point exception state -->
2523 <li>An instruction with externally visible side effects depends on the most
2524 recent preceding instruction with externally visible side effects, following
2525 the order in the IR. (This includes
2526 <a href="#volatile">volatile operations</a>.)</li>
2528 <li>An instruction <i>control-depends</i> on a
2529 <a href="#terminators">terminator instruction</a>
2530 if the terminator instruction has multiple successors and the instruction
2531 is always executed when control transfers to one of the successors, and
2532 may not be executed when control is transferred to another.</li>
2534 <li>Additionally, an instruction also <i>control-depends</i> on a terminator
2535 instruction if the set of instructions it otherwise depends on would be
2536 different if the terminator had transferred control to a different
2539 <li>Dependence is transitive.</li>
2543 <p>Whenever a trap value is generated, all values which depend on it evaluate
2544 to trap. If they have side effects, the evoke their side effects as if each
2545 operand with a trap value were undef. If they have externally-visible side
2546 effects, the behavior is undefined.</p>
2548 <p>Here are some examples:</p>
2550 <pre class="doc_code">
2552 %trap = sub nuw i32 0, 1 ; Results in a trap value.
2553 %still_trap = and i32 %trap, 0 ; Whereas (and i32 undef, 0) would return 0.
2554 %trap_yet_again = getelementptr i32* @h, i32 %still_trap
2555 store i32 0, i32* %trap_yet_again ; undefined behavior
2557 store i32 %trap, i32* @g ; Trap value conceptually stored to memory.
2558 %trap2 = load i32* @g ; Returns a trap value, not just undef.
2560 volatile store i32 %trap, i32* @g ; External observation; undefined behavior.
2562 %narrowaddr = bitcast i32* @g to i16*
2563 %wideaddr = bitcast i32* @g to i64*
2564 %trap3 = load i16* %narrowaddr ; Returns a trap value.
2565 %trap4 = load i64* %wideaddr ; Returns a trap value.
2567 %cmp = icmp slt i32 %trap, 0 ; Returns a trap value.
2568 br i1 %cmp, label %true, label %end ; Branch to either destination.
2571 volatile store i32 0, i32* @g ; This is control-dependent on %cmp, so
2572 ; it has undefined behavior.
2576 %p = phi i32 [ 0, %entry ], [ 1, %true ]
2577 ; Both edges into this PHI are
2578 ; control-dependent on %cmp, so this
2579 ; always results in a trap value.
2581 volatile store i32 0, i32* @g ; This would depend on the store in %true
2582 ; if %cmp is true, or the store in %entry
2583 ; otherwise, so this is undefined behavior.
2585 br i1 %cmp, label %second_true, label %second_end
2586 ; The same branch again, but this time the
2587 ; true block doesn't have side effects.
2594 volatile store i32 0, i32* @g ; This time, the instruction always depends
2595 ; on the store in %end. Also, it is
2596 ; control-equivalent to %end, so this is
2597 ; well-defined (again, ignoring earlier
2598 ; undefined behavior in this example).
2603 <!-- ======================================================================= -->
2605 <a name="blockaddress">Addresses of Basic Blocks</a>
2610 <p><b><tt>blockaddress(@function, %block)</tt></b></p>
2612 <p>The '<tt>blockaddress</tt>' constant computes the address of the specified
2613 basic block in the specified function, and always has an i8* type. Taking
2614 the address of the entry block is illegal.</p>
2616 <p>This value only has defined behavior when used as an operand to the
2617 '<a href="#i_indirectbr"><tt>indirectbr</tt></a>' instruction, or for
2618 comparisons against null. Pointer equality tests between labels addresses
2619 results in undefined behavior — though, again, comparison against null
2620 is ok, and no label is equal to the null pointer. This may be passed around
2621 as an opaque pointer sized value as long as the bits are not inspected. This
2622 allows <tt>ptrtoint</tt> and arithmetic to be performed on these values so
2623 long as the original value is reconstituted before the <tt>indirectbr</tt>
2626 <p>Finally, some targets may provide defined semantics when using the value as
2627 the operand to an inline assembly, but that is target specific.</p>
2632 <!-- ======================================================================= -->
2634 <a name="constantexprs">Constant Expressions</a>
2639 <p>Constant expressions are used to allow expressions involving other constants
2640 to be used as constants. Constant expressions may be of
2641 any <a href="#t_firstclass">first class</a> type and may involve any LLVM
2642 operation that does not have side effects (e.g. load and call are not
2643 supported). The following is the syntax for constant expressions:</p>
2646 <dt><b><tt>trunc (CST to TYPE)</tt></b></dt>
2647 <dd>Truncate a constant to another type. The bit size of CST must be larger
2648 than the bit size of TYPE. Both types must be integers.</dd>
2650 <dt><b><tt>zext (CST to TYPE)</tt></b></dt>
2651 <dd>Zero extend a constant to another type. The bit size of CST must be
2652 smaller than the bit size of TYPE. Both types must be integers.</dd>
2654 <dt><b><tt>sext (CST to TYPE)</tt></b></dt>
2655 <dd>Sign extend a constant to another type. The bit size of CST must be
2656 smaller than the bit size of TYPE. Both types must be integers.</dd>
2658 <dt><b><tt>fptrunc (CST to TYPE)</tt></b></dt>
2659 <dd>Truncate a floating point constant to another floating point type. The
2660 size of CST must be larger than the size of TYPE. Both types must be
2661 floating point.</dd>
2663 <dt><b><tt>fpext (CST to TYPE)</tt></b></dt>
2664 <dd>Floating point extend a constant to another type. The size of CST must be
2665 smaller or equal to the size of TYPE. Both types must be floating
2668 <dt><b><tt>fptoui (CST to TYPE)</tt></b></dt>
2669 <dd>Convert a floating point constant to the corresponding unsigned integer
2670 constant. TYPE must be a scalar or vector integer type. CST must be of
2671 scalar or vector floating point type. Both CST and TYPE must be scalars,
2672 or vectors of the same number of elements. If the value won't fit in the
2673 integer type, the results are undefined.</dd>
2675 <dt><b><tt>fptosi (CST to TYPE)</tt></b></dt>
2676 <dd>Convert a floating point constant to the corresponding signed integer
2677 constant. TYPE must be a scalar or vector integer type. CST must be of
2678 scalar or vector floating point type. Both CST and TYPE must be scalars,
2679 or vectors of the same number of elements. If the value won't fit in the
2680 integer type, the results are undefined.</dd>
2682 <dt><b><tt>uitofp (CST to TYPE)</tt></b></dt>
2683 <dd>Convert an unsigned integer constant to the corresponding floating point
2684 constant. TYPE must be a scalar or vector floating point type. CST must be
2685 of scalar or vector integer type. Both CST and TYPE must be scalars, or
2686 vectors of the same number of elements. If the value won't fit in the
2687 floating point type, the results are undefined.</dd>
2689 <dt><b><tt>sitofp (CST to TYPE)</tt></b></dt>
2690 <dd>Convert a signed integer constant to the corresponding floating point
2691 constant. TYPE must be a scalar or vector floating point type. CST must be
2692 of scalar or vector integer type. Both CST and TYPE must be scalars, or
2693 vectors of the same number of elements. If the value won't fit in the
2694 floating point type, the results are undefined.</dd>
2696 <dt><b><tt>ptrtoint (CST to TYPE)</tt></b></dt>
2697 <dd>Convert a pointer typed constant to the corresponding integer constant
2698 <tt>TYPE</tt> must be an integer type. <tt>CST</tt> must be of pointer
2699 type. The <tt>CST</tt> value is zero extended, truncated, or unchanged to
2700 make it fit in <tt>TYPE</tt>.</dd>
2702 <dt><b><tt>inttoptr (CST to TYPE)</tt></b></dt>
2703 <dd>Convert a integer constant to a pointer constant. TYPE must be a pointer
2704 type. CST must be of integer type. The CST value is zero extended,
2705 truncated, or unchanged to make it fit in a pointer size. This one is
2706 <i>really</i> dangerous!</dd>
2708 <dt><b><tt>bitcast (CST to TYPE)</tt></b></dt>
2709 <dd>Convert a constant, CST, to another TYPE. The constraints of the operands
2710 are the same as those for the <a href="#i_bitcast">bitcast
2711 instruction</a>.</dd>
2713 <dt><b><tt>getelementptr (CSTPTR, IDX0, IDX1, ...)</tt></b></dt>
2714 <dt><b><tt>getelementptr inbounds (CSTPTR, IDX0, IDX1, ...)</tt></b></dt>
2715 <dd>Perform the <a href="#i_getelementptr">getelementptr operation</a> on
2716 constants. As with the <a href="#i_getelementptr">getelementptr</a>
2717 instruction, the index list may have zero or more indexes, which are
2718 required to make sense for the type of "CSTPTR".</dd>
2720 <dt><b><tt>select (COND, VAL1, VAL2)</tt></b></dt>
2721 <dd>Perform the <a href="#i_select">select operation</a> on constants.</dd>
2723 <dt><b><tt>icmp COND (VAL1, VAL2)</tt></b></dt>
2724 <dd>Performs the <a href="#i_icmp">icmp operation</a> on constants.</dd>
2726 <dt><b><tt>fcmp COND (VAL1, VAL2)</tt></b></dt>
2727 <dd>Performs the <a href="#i_fcmp">fcmp operation</a> on constants.</dd>
2729 <dt><b><tt>extractelement (VAL, IDX)</tt></b></dt>
2730 <dd>Perform the <a href="#i_extractelement">extractelement operation</a> on
2733 <dt><b><tt>insertelement (VAL, ELT, IDX)</tt></b></dt>
2734 <dd>Perform the <a href="#i_insertelement">insertelement operation</a> on
2737 <dt><b><tt>shufflevector (VEC1, VEC2, IDXMASK)</tt></b></dt>
2738 <dd>Perform the <a href="#i_shufflevector">shufflevector operation</a> on
2741 <dt><b><tt>extractvalue (VAL, IDX0, IDX1, ...)</tt></b></dt>
2742 <dd>Perform the <a href="#i_extractvalue">extractvalue operation</a> on
2743 constants. The index list is interpreted in a similar manner as indices in
2744 a '<a href="#i_getelementptr">getelementptr</a>' operation. At least one
2745 index value must be specified.</dd>
2747 <dt><b><tt>insertvalue (VAL, ELT, IDX0, IDX1, ...)</tt></b></dt>
2748 <dd>Perform the <a href="#i_insertvalue">insertvalue operation</a> on
2749 constants. The index list is interpreted in a similar manner as indices in
2750 a '<a href="#i_getelementptr">getelementptr</a>' operation. At least one
2751 index value must be specified.</dd>
2753 <dt><b><tt>OPCODE (LHS, RHS)</tt></b></dt>
2754 <dd>Perform the specified operation of the LHS and RHS constants. OPCODE may
2755 be any of the <a href="#binaryops">binary</a>
2756 or <a href="#bitwiseops">bitwise binary</a> operations. The constraints
2757 on operands are the same as those for the corresponding instruction
2758 (e.g. no bitwise operations on floating point values are allowed).</dd>
2765 <!-- *********************************************************************** -->
2766 <h2><a name="othervalues">Other Values</a></h2>
2767 <!-- *********************************************************************** -->
2769 <!-- ======================================================================= -->
2771 <a name="inlineasm">Inline Assembler Expressions</a>
2776 <p>LLVM supports inline assembler expressions (as opposed
2777 to <a href="#moduleasm"> Module-Level Inline Assembly</a>) through the use of
2778 a special value. This value represents the inline assembler as a string
2779 (containing the instructions to emit), a list of operand constraints (stored
2780 as a string), a flag that indicates whether or not the inline asm
2781 expression has side effects, and a flag indicating whether the function
2782 containing the asm needs to align its stack conservatively. An example
2783 inline assembler expression is:</p>
2785 <pre class="doc_code">
2786 i32 (i32) asm "bswap $0", "=r,r"
2789 <p>Inline assembler expressions may <b>only</b> be used as the callee operand of
2790 a <a href="#i_call"><tt>call</tt> instruction</a>. Thus, typically we
2793 <pre class="doc_code">
2794 %X = call i32 asm "<a href="#int_bswap">bswap</a> $0", "=r,r"(i32 %Y)
2797 <p>Inline asms with side effects not visible in the constraint list must be
2798 marked as having side effects. This is done through the use of the
2799 '<tt>sideeffect</tt>' keyword, like so:</p>
2801 <pre class="doc_code">
2802 call void asm sideeffect "eieio", ""()
2805 <p>In some cases inline asms will contain code that will not work unless the
2806 stack is aligned in some way, such as calls or SSE instructions on x86,
2807 yet will not contain code that does that alignment within the asm.
2808 The compiler should make conservative assumptions about what the asm might
2809 contain and should generate its usual stack alignment code in the prologue
2810 if the '<tt>alignstack</tt>' keyword is present:</p>
2812 <pre class="doc_code">
2813 call void asm alignstack "eieio", ""()
2816 <p>If both keywords appear the '<tt>sideeffect</tt>' keyword must come
2819 <p>TODO: The format of the asm and constraints string still need to be
2820 documented here. Constraints on what can be done (e.g. duplication, moving,
2821 etc need to be documented). This is probably best done by reference to
2822 another document that covers inline asm from a holistic perspective.</p>
2825 <a name="inlineasm_md">Inline Asm Metadata</a>
2830 <p>The call instructions that wrap inline asm nodes may have a "!srcloc" MDNode
2831 attached to it that contains a list of constant integers. If present, the
2832 code generator will use the integer as the location cookie value when report
2833 errors through the LLVMContext error reporting mechanisms. This allows a
2834 front-end to correlate backend errors that occur with inline asm back to the
2835 source code that produced it. For example:</p>
2837 <pre class="doc_code">
2838 call void asm sideeffect "something bad", ""()<b>, !srcloc !42</b>
2840 !42 = !{ i32 1234567 }
2843 <p>It is up to the front-end to make sense of the magic numbers it places in the
2844 IR. If the MDNode contains multiple constants, the code generator will use
2845 the one that corresponds to the line of the asm that the error occurs on.</p>
2851 <!-- ======================================================================= -->
2853 <a name="metadata">Metadata Nodes and Metadata Strings</a>
2858 <p>LLVM IR allows metadata to be attached to instructions in the program that
2859 can convey extra information about the code to the optimizers and code
2860 generator. One example application of metadata is source-level debug
2861 information. There are two metadata primitives: strings and nodes. All
2862 metadata has the <tt>metadata</tt> type and is identified in syntax by a
2863 preceding exclamation point ('<tt>!</tt>').</p>
2865 <p>A metadata string is a string surrounded by double quotes. It can contain
2866 any character by escaping non-printable characters with "\xx" where "xx" is
2867 the two digit hex code. For example: "<tt>!"test\00"</tt>".</p>
2869 <p>Metadata nodes are represented with notation similar to structure constants
2870 (a comma separated list of elements, surrounded by braces and preceded by an
2871 exclamation point). For example: "<tt>!{ metadata !"test\00", i32
2872 10}</tt>". Metadata nodes can have any values as their operand.</p>
2874 <p>A <a href="#namedmetadatastructure">named metadata</a> is a collection of
2875 metadata nodes, which can be looked up in the module symbol table. For
2876 example: "<tt>!foo = metadata !{!4, !3}</tt>".
2878 <p>Metadata can be used as function arguments. Here <tt>llvm.dbg.value</tt>
2879 function is using two metadata arguments.</p>
2881 <div class="doc_code">
2883 call void @llvm.dbg.value(metadata !24, i64 0, metadata !25)
2887 <p>Metadata can be attached with an instruction. Here metadata <tt>!21</tt> is
2888 attached with <tt>add</tt> instruction using <tt>!dbg</tt> identifier.</p>
2890 <div class="doc_code">
2892 %indvar.next = add i64 %indvar, 1, !dbg !21
2900 <!-- *********************************************************************** -->
2902 <a name="intrinsic_globals">Intrinsic Global Variables</a>
2904 <!-- *********************************************************************** -->
2906 <p>LLVM has a number of "magic" global variables that contain data that affect
2907 code generation or other IR semantics. These are documented here. All globals
2908 of this sort should have a section specified as "<tt>llvm.metadata</tt>". This
2909 section and all globals that start with "<tt>llvm.</tt>" are reserved for use
2912 <!-- ======================================================================= -->
2914 <a name="intg_used">The '<tt>llvm.used</tt>' Global Variable</a>
2919 <p>The <tt>@llvm.used</tt> global is an array with i8* element type which has <a
2920 href="#linkage_appending">appending linkage</a>. This array contains a list of
2921 pointers to global variables and functions which may optionally have a pointer
2922 cast formed of bitcast or getelementptr. For example, a legal use of it is:</p>
2928 @llvm.used = appending global [2 x i8*] [
2930 i8* bitcast (i32* @Y to i8*)
2931 ], section "llvm.metadata"
2934 <p>If a global variable appears in the <tt>@llvm.used</tt> list, then the
2935 compiler, assembler, and linker are required to treat the symbol as if there is
2936 a reference to the global that it cannot see. For example, if a variable has
2937 internal linkage and no references other than that from the <tt>@llvm.used</tt>
2938 list, it cannot be deleted. This is commonly used to represent references from
2939 inline asms and other things the compiler cannot "see", and corresponds to
2940 "attribute((used))" in GNU C.</p>
2942 <p>On some targets, the code generator must emit a directive to the assembler or
2943 object file to prevent the assembler and linker from molesting the symbol.</p>
2947 <!-- ======================================================================= -->
2949 <a name="intg_compiler_used">
2950 The '<tt>llvm.compiler.used</tt>' Global Variable
2956 <p>The <tt>@llvm.compiler.used</tt> directive is the same as the
2957 <tt>@llvm.used</tt> directive, except that it only prevents the compiler from
2958 touching the symbol. On targets that support it, this allows an intelligent
2959 linker to optimize references to the symbol without being impeded as it would be
2960 by <tt>@llvm.used</tt>.</p>
2962 <p>This is a rare construct that should only be used in rare circumstances, and
2963 should not be exposed to source languages.</p>
2967 <!-- ======================================================================= -->
2969 <a name="intg_global_ctors">The '<tt>llvm.global_ctors</tt>' Global Variable</a>
2974 %0 = type { i32, void ()* }
2975 @llvm.global_ctors = appending global [1 x %0] [%0 { i32 65535, void ()* @ctor }]
2977 <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.
2982 <!-- ======================================================================= -->
2984 <a name="intg_global_dtors">The '<tt>llvm.global_dtors</tt>' Global Variable</a>
2989 %0 = type { i32, void ()* }
2990 @llvm.global_dtors = appending global [1 x %0] [%0 { i32 65535, void ()* @dtor }]
2993 <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.
3000 <!-- *********************************************************************** -->
3001 <h2><a name="instref">Instruction Reference</a></h2>
3002 <!-- *********************************************************************** -->
3006 <p>The LLVM instruction set consists of several different classifications of
3007 instructions: <a href="#terminators">terminator
3008 instructions</a>, <a href="#binaryops">binary instructions</a>,
3009 <a href="#bitwiseops">bitwise binary instructions</a>,
3010 <a href="#memoryops">memory instructions</a>, and
3011 <a href="#otherops">other instructions</a>.</p>
3013 <!-- ======================================================================= -->
3015 <a name="terminators">Terminator Instructions</a>
3020 <p>As mentioned <a href="#functionstructure">previously</a>, every basic block
3021 in a program ends with a "Terminator" instruction, which indicates which
3022 block should be executed after the current block is finished. These
3023 terminator instructions typically yield a '<tt>void</tt>' value: they produce
3024 control flow, not values (the one exception being the
3025 '<a href="#i_invoke"><tt>invoke</tt></a>' instruction).</p>
3027 <p>There are eight different terminator instructions: the
3028 '<a href="#i_ret"><tt>ret</tt></a>' instruction, the
3029 '<a href="#i_br"><tt>br</tt></a>' instruction, the
3030 '<a href="#i_switch"><tt>switch</tt></a>' instruction, the
3031 '<a href="#i_indirectbr">'<tt>indirectbr</tt></a>' Instruction, the
3032 '<a href="#i_invoke"><tt>invoke</tt></a>' instruction, the
3033 '<a href="#i_unwind"><tt>unwind</tt></a>' instruction, the
3034 '<a href="#i_resume"><tt>resume</tt></a>' instruction, and the
3035 '<a href="#i_unreachable"><tt>unreachable</tt></a>' instruction.</p>
3037 <!-- _______________________________________________________________________ -->
3039 <a name="i_ret">'<tt>ret</tt>' Instruction</a>
3046 ret <type> <value> <i>; Return a value from a non-void function</i>
3047 ret void <i>; Return from void function</i>
3051 <p>The '<tt>ret</tt>' instruction is used to return control flow (and optionally
3052 a value) from a function back to the caller.</p>
3054 <p>There are two forms of the '<tt>ret</tt>' instruction: one that returns a
3055 value and then causes control flow, and one that just causes control flow to
3059 <p>The '<tt>ret</tt>' instruction optionally accepts a single argument, the
3060 return value. The type of the return value must be a
3061 '<a href="#t_firstclass">first class</a>' type.</p>
3063 <p>A function is not <a href="#wellformed">well formed</a> if it it has a
3064 non-void return type and contains a '<tt>ret</tt>' instruction with no return
3065 value or a return value with a type that does not match its type, or if it
3066 has a void return type and contains a '<tt>ret</tt>' instruction with a
3070 <p>When the '<tt>ret</tt>' instruction is executed, control flow returns back to
3071 the calling function's context. If the caller is a
3072 "<a href="#i_call"><tt>call</tt></a>" instruction, execution continues at the
3073 instruction after the call. If the caller was an
3074 "<a href="#i_invoke"><tt>invoke</tt></a>" instruction, execution continues at
3075 the beginning of the "normal" destination block. If the instruction returns
3076 a value, that value shall set the call or invoke instruction's return
3081 ret i32 5 <i>; Return an integer value of 5</i>
3082 ret void <i>; Return from a void function</i>
3083 ret { i32, i8 } { i32 4, i8 2 } <i>; Return a struct of values 4 and 2</i>
3087 <!-- _______________________________________________________________________ -->
3089 <a name="i_br">'<tt>br</tt>' Instruction</a>
3096 br i1 <cond>, label <iftrue>, label <iffalse>
3097 br label <dest> <i>; Unconditional branch</i>
3101 <p>The '<tt>br</tt>' instruction is used to cause control flow to transfer to a
3102 different basic block in the current function. There are two forms of this
3103 instruction, corresponding to a conditional branch and an unconditional
3107 <p>The conditional branch form of the '<tt>br</tt>' instruction takes a single
3108 '<tt>i1</tt>' value and two '<tt>label</tt>' values. The unconditional form
3109 of the '<tt>br</tt>' instruction takes a single '<tt>label</tt>' value as a
3113 <p>Upon execution of a conditional '<tt>br</tt>' instruction, the '<tt>i1</tt>'
3114 argument is evaluated. If the value is <tt>true</tt>, control flows to the
3115 '<tt>iftrue</tt>' <tt>label</tt> argument. If "cond" is <tt>false</tt>,
3116 control flows to the '<tt>iffalse</tt>' <tt>label</tt> argument.</p>
3121 %cond = <a href="#i_icmp">icmp</a> eq i32 %a, %b
3122 br i1 %cond, label %IfEqual, label %IfUnequal
3124 <a href="#i_ret">ret</a> i32 1
3126 <a href="#i_ret">ret</a> i32 0
3131 <!-- _______________________________________________________________________ -->
3133 <a name="i_switch">'<tt>switch</tt>' Instruction</a>
3140 switch <intty> <value>, label <defaultdest> [ <intty> <val>, label <dest> ... ]
3144 <p>The '<tt>switch</tt>' instruction is used to transfer control flow to one of
3145 several different places. It is a generalization of the '<tt>br</tt>'
3146 instruction, allowing a branch to occur to one of many possible
3150 <p>The '<tt>switch</tt>' instruction uses three parameters: an integer
3151 comparison value '<tt>value</tt>', a default '<tt>label</tt>' destination,
3152 and an array of pairs of comparison value constants and '<tt>label</tt>'s.
3153 The table is not allowed to contain duplicate constant entries.</p>
3156 <p>The <tt>switch</tt> instruction specifies a table of values and
3157 destinations. When the '<tt>switch</tt>' instruction is executed, this table
3158 is searched for the given value. If the value is found, control flow is
3159 transferred to the corresponding destination; otherwise, control flow is
3160 transferred to the default destination.</p>
3162 <h5>Implementation:</h5>
3163 <p>Depending on properties of the target machine and the particular
3164 <tt>switch</tt> instruction, this instruction may be code generated in
3165 different ways. For example, it could be generated as a series of chained
3166 conditional branches or with a lookup table.</p>
3170 <i>; Emulate a conditional br instruction</i>
3171 %Val = <a href="#i_zext">zext</a> i1 %value to i32
3172 switch i32 %Val, label %truedest [ i32 0, label %falsedest ]
3174 <i>; Emulate an unconditional br instruction</i>
3175 switch i32 0, label %dest [ ]
3177 <i>; Implement a jump table:</i>
3178 switch i32 %val, label %otherwise [ i32 0, label %onzero
3180 i32 2, label %ontwo ]
3186 <!-- _______________________________________________________________________ -->
3188 <a name="i_indirectbr">'<tt>indirectbr</tt>' Instruction</a>
3195 indirectbr <somety>* <address>, [ label <dest1>, label <dest2>, ... ]
3200 <p>The '<tt>indirectbr</tt>' instruction implements an indirect branch to a label
3201 within the current function, whose address is specified by
3202 "<tt>address</tt>". Address must be derived from a <a
3203 href="#blockaddress">blockaddress</a> constant.</p>
3207 <p>The '<tt>address</tt>' argument is the address of the label to jump to. The
3208 rest of the arguments indicate the full set of possible destinations that the
3209 address may point to. Blocks are allowed to occur multiple times in the
3210 destination list, though this isn't particularly useful.</p>
3212 <p>This destination list is required so that dataflow analysis has an accurate
3213 understanding of the CFG.</p>
3217 <p>Control transfers to the block specified in the address argument. All
3218 possible destination blocks must be listed in the label list, otherwise this
3219 instruction has undefined behavior. This implies that jumps to labels
3220 defined in other functions have undefined behavior as well.</p>
3222 <h5>Implementation:</h5>
3224 <p>This is typically implemented with a jump through a register.</p>
3228 indirectbr i8* %Addr, [ label %bb1, label %bb2, label %bb3 ]
3234 <!-- _______________________________________________________________________ -->
3236 <a name="i_invoke">'<tt>invoke</tt>' Instruction</a>
3243 <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>]
3244 to label <normal label> unwind label <exception label>
3248 <p>The '<tt>invoke</tt>' instruction causes control to transfer to a specified
3249 function, with the possibility of control flow transfer to either the
3250 '<tt>normal</tt>' label or the '<tt>exception</tt>' label. If the callee
3251 function returns with the "<tt><a href="#i_ret">ret</a></tt>" instruction,
3252 control flow will return to the "normal" label. If the callee (or any
3253 indirect callees) returns with the "<a href="#i_unwind"><tt>unwind</tt></a>"
3254 instruction, control is interrupted and continued at the dynamically nearest
3255 "exception" label.</p>
3258 <p>This instruction requires several arguments:</p>
3261 <li>The optional "cconv" marker indicates which <a href="#callingconv">calling
3262 convention</a> the call should use. If none is specified, the call
3263 defaults to using C calling conventions.</li>
3265 <li>The optional <a href="#paramattrs">Parameter Attributes</a> list for
3266 return values. Only '<tt>zeroext</tt>', '<tt>signext</tt>', and
3267 '<tt>inreg</tt>' attributes are valid here.</li>
3269 <li>'<tt>ptr to function ty</tt>': shall be the signature of the pointer to
3270 function value being invoked. In most cases, this is a direct function
3271 invocation, but indirect <tt>invoke</tt>s are just as possible, branching
3272 off an arbitrary pointer to function value.</li>
3274 <li>'<tt>function ptr val</tt>': An LLVM value containing a pointer to a
3275 function to be invoked. </li>
3277 <li>'<tt>function args</tt>': argument list whose types match the function
3278 signature argument types and parameter attributes. All arguments must be
3279 of <a href="#t_firstclass">first class</a> type. If the function
3280 signature indicates the function accepts a variable number of arguments,
3281 the extra arguments can be specified.</li>
3283 <li>'<tt>normal label</tt>': the label reached when the called function
3284 executes a '<tt><a href="#i_ret">ret</a></tt>' instruction. </li>
3286 <li>'<tt>exception label</tt>': the label reached when a callee returns with
3287 the <a href="#i_unwind"><tt>unwind</tt></a> instruction. </li>
3289 <li>The optional <a href="#fnattrs">function attributes</a> list. Only
3290 '<tt>noreturn</tt>', '<tt>nounwind</tt>', '<tt>readonly</tt>' and
3291 '<tt>readnone</tt>' attributes are valid here.</li>
3295 <p>This instruction is designed to operate as a standard
3296 '<tt><a href="#i_call">call</a></tt>' instruction in most regards. The
3297 primary difference is that it establishes an association with a label, which
3298 is used by the runtime library to unwind the stack.</p>
3300 <p>This instruction is used in languages with destructors to ensure that proper
3301 cleanup is performed in the case of either a <tt>longjmp</tt> or a thrown
3302 exception. Additionally, this is important for implementation of
3303 '<tt>catch</tt>' clauses in high-level languages that support them.</p>
3305 <p>For the purposes of the SSA form, the definition of the value returned by the
3306 '<tt>invoke</tt>' instruction is deemed to occur on the edge from the current
3307 block to the "normal" label. If the callee unwinds then no return value is
3310 <p>Note that the code generator does not yet completely support unwind, and
3311 that the invoke/unwind semantics are likely to change in future versions.</p>
3315 %retval = invoke i32 @Test(i32 15) to label %Continue
3316 unwind label %TestCleanup <i>; {i32}:retval set</i>
3317 %retval = invoke <a href="#callingconv">coldcc</a> i32 %Testfnptr(i32 15) to label %Continue
3318 unwind label %TestCleanup <i>; {i32}:retval set</i>
3323 <!-- _______________________________________________________________________ -->
3326 <a name="i_unwind">'<tt>unwind</tt>' Instruction</a>
3337 <p>The '<tt>unwind</tt>' instruction unwinds the stack, continuing control flow
3338 at the first callee in the dynamic call stack which used
3339 an <a href="#i_invoke"><tt>invoke</tt></a> instruction to perform the call.
3340 This is primarily used to implement exception handling.</p>
3343 <p>The '<tt>unwind</tt>' instruction causes execution of the current function to
3344 immediately halt. The dynamic call stack is then searched for the
3345 first <a href="#i_invoke"><tt>invoke</tt></a> instruction on the call stack.
3346 Once found, execution continues at the "exceptional" destination block
3347 specified by the <tt>invoke</tt> instruction. If there is no <tt>invoke</tt>
3348 instruction in the dynamic call chain, undefined behavior results.</p>
3350 <p>Note that the code generator does not yet completely support unwind, and
3351 that the invoke/unwind semantics are likely to change in future versions.</p>
3355 <!-- _______________________________________________________________________ -->
3358 <a name="i_resume">'<tt>resume</tt>' Instruction</a>
3365 resume <type> <value>
3369 <p>The '<tt>resume</tt>' instruction is a terminator instruction that has no
3373 <p>The '<tt>resume</tt>' instruction's argument must have the same type as the
3374 result of any '<tt>landingpad</tt>' instruction in the same function.</p>
3377 <p>The '<tt>resume</tt>' instruction resumes propagation of an existing
3378 (in-flight) exception whose unwinding was interrupted with
3379 a landingpad instruction.</p>
3383 resume { i8*, i32 } %exn
3388 <!-- _______________________________________________________________________ -->
3391 <a name="i_unreachable">'<tt>unreachable</tt>' Instruction</a>
3402 <p>The '<tt>unreachable</tt>' instruction has no defined semantics. This
3403 instruction is used to inform the optimizer that a particular portion of the
3404 code is not reachable. This can be used to indicate that the code after a
3405 no-return function cannot be reached, and other facts.</p>
3408 <p>The '<tt>unreachable</tt>' instruction has no defined semantics.</p>
3414 <!-- ======================================================================= -->
3416 <a name="binaryops">Binary Operations</a>
3421 <p>Binary operators are used to do most of the computation in a program. They
3422 require two operands of the same type, execute an operation on them, and
3423 produce a single value. The operands might represent multiple data, as is
3424 the case with the <a href="#t_vector">vector</a> data type. The result value
3425 has the same type as its operands.</p>
3427 <p>There are several different binary operators:</p>
3429 <!-- _______________________________________________________________________ -->
3431 <a name="i_add">'<tt>add</tt>' Instruction</a>
3438 <result> = add <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3439 <result> = add nuw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3440 <result> = add nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3441 <result> = add nuw nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3445 <p>The '<tt>add</tt>' instruction returns the sum of its two operands.</p>
3448 <p>The two arguments to the '<tt>add</tt>' instruction must
3449 be <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of
3450 integer values. Both arguments must have identical types.</p>
3453 <p>The value produced is the integer sum of the two operands.</p>
3455 <p>If the sum has unsigned overflow, the result returned is the mathematical
3456 result modulo 2<sup>n</sup>, where n is the bit width of the result.</p>
3458 <p>Because LLVM integers use a two's complement representation, this instruction
3459 is appropriate for both signed and unsigned integers.</p>
3461 <p><tt>nuw</tt> and <tt>nsw</tt> stand for "No Unsigned Wrap"
3462 and "No Signed Wrap", respectively. If the <tt>nuw</tt> and/or
3463 <tt>nsw</tt> keywords are present, the result value of the <tt>add</tt>
3464 is a <a href="#trapvalues">trap value</a> if unsigned and/or signed overflow,
3465 respectively, occurs.</p>
3469 <result> = add i32 4, %var <i>; yields {i32}:result = 4 + %var</i>
3474 <!-- _______________________________________________________________________ -->
3476 <a name="i_fadd">'<tt>fadd</tt>' Instruction</a>
3483 <result> = fadd <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3487 <p>The '<tt>fadd</tt>' instruction returns the sum of its two operands.</p>
3490 <p>The two arguments to the '<tt>fadd</tt>' instruction must be
3491 <a href="#t_floating">floating point</a> or <a href="#t_vector">vector</a> of
3492 floating point values. Both arguments must have identical types.</p>
3495 <p>The value produced is the floating point sum of the two operands.</p>
3499 <result> = fadd float 4.0, %var <i>; yields {float}:result = 4.0 + %var</i>
3504 <!-- _______________________________________________________________________ -->
3506 <a name="i_sub">'<tt>sub</tt>' Instruction</a>
3513 <result> = sub <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3514 <result> = sub nuw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3515 <result> = sub nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3516 <result> = sub nuw nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3520 <p>The '<tt>sub</tt>' instruction returns the difference of its two
3523 <p>Note that the '<tt>sub</tt>' instruction is used to represent the
3524 '<tt>neg</tt>' instruction present in most other intermediate
3525 representations.</p>
3528 <p>The two arguments to the '<tt>sub</tt>' instruction must
3529 be <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of
3530 integer values. Both arguments must have identical types.</p>
3533 <p>The value produced is the integer difference of the two operands.</p>
3535 <p>If the difference has unsigned overflow, the result returned is the
3536 mathematical result modulo 2<sup>n</sup>, where n is the bit width of the
3539 <p>Because LLVM integers use a two's complement representation, this instruction
3540 is appropriate for both signed and unsigned integers.</p>
3542 <p><tt>nuw</tt> and <tt>nsw</tt> stand for "No Unsigned Wrap"
3543 and "No Signed Wrap", respectively. If the <tt>nuw</tt> and/or
3544 <tt>nsw</tt> keywords are present, the result value of the <tt>sub</tt>
3545 is a <a href="#trapvalues">trap value</a> if unsigned and/or signed overflow,
3546 respectively, occurs.</p>
3550 <result> = sub i32 4, %var <i>; yields {i32}:result = 4 - %var</i>
3551 <result> = sub i32 0, %val <i>; yields {i32}:result = -%var</i>
3556 <!-- _______________________________________________________________________ -->
3558 <a name="i_fsub">'<tt>fsub</tt>' Instruction</a>
3565 <result> = fsub <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3569 <p>The '<tt>fsub</tt>' instruction returns the difference of its two
3572 <p>Note that the '<tt>fsub</tt>' instruction is used to represent the
3573 '<tt>fneg</tt>' instruction present in most other intermediate
3574 representations.</p>
3577 <p>The two arguments to the '<tt>fsub</tt>' instruction must be
3578 <a href="#t_floating">floating point</a> or <a href="#t_vector">vector</a> of
3579 floating point values. Both arguments must have identical types.</p>
3582 <p>The value produced is the floating point difference of the two operands.</p>
3586 <result> = fsub float 4.0, %var <i>; yields {float}:result = 4.0 - %var</i>
3587 <result> = fsub float -0.0, %val <i>; yields {float}:result = -%var</i>
3592 <!-- _______________________________________________________________________ -->
3594 <a name="i_mul">'<tt>mul</tt>' Instruction</a>
3601 <result> = mul <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3602 <result> = mul nuw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3603 <result> = mul nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3604 <result> = mul nuw nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3608 <p>The '<tt>mul</tt>' instruction returns the product of its two operands.</p>
3611 <p>The two arguments to the '<tt>mul</tt>' instruction must
3612 be <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of
3613 integer values. Both arguments must have identical types.</p>
3616 <p>The value produced is the integer product of the two operands.</p>
3618 <p>If the result of the multiplication has unsigned overflow, the result
3619 returned is the mathematical result modulo 2<sup>n</sup>, where n is the bit
3620 width of the result.</p>
3622 <p>Because LLVM integers use a two's complement representation, and the result
3623 is the same width as the operands, this instruction returns the correct
3624 result for both signed and unsigned integers. If a full product
3625 (e.g. <tt>i32</tt>x<tt>i32</tt>-><tt>i64</tt>) is needed, the operands should
3626 be sign-extended or zero-extended as appropriate to the width of the full
3629 <p><tt>nuw</tt> and <tt>nsw</tt> stand for "No Unsigned Wrap"
3630 and "No Signed Wrap", respectively. If the <tt>nuw</tt> and/or
3631 <tt>nsw</tt> keywords are present, the result value of the <tt>mul</tt>
3632 is a <a href="#trapvalues">trap value</a> if unsigned and/or signed overflow,
3633 respectively, occurs.</p>
3637 <result> = mul i32 4, %var <i>; yields {i32}:result = 4 * %var</i>
3642 <!-- _______________________________________________________________________ -->
3644 <a name="i_fmul">'<tt>fmul</tt>' Instruction</a>
3651 <result> = fmul <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3655 <p>The '<tt>fmul</tt>' instruction returns the product of its two operands.</p>
3658 <p>The two arguments to the '<tt>fmul</tt>' instruction must be
3659 <a href="#t_floating">floating point</a> or <a href="#t_vector">vector</a> of
3660 floating point values. Both arguments must have identical types.</p>
3663 <p>The value produced is the floating point product of the two operands.</p>
3667 <result> = fmul float 4.0, %var <i>; yields {float}:result = 4.0 * %var</i>
3672 <!-- _______________________________________________________________________ -->
3674 <a name="i_udiv">'<tt>udiv</tt>' Instruction</a>
3681 <result> = udiv <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3682 <result> = udiv exact <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3686 <p>The '<tt>udiv</tt>' instruction returns the quotient of its two operands.</p>
3689 <p>The two arguments to the '<tt>udiv</tt>' instruction must be
3690 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
3691 values. Both arguments must have identical types.</p>
3694 <p>The value produced is the unsigned integer quotient of the two operands.</p>
3696 <p>Note that unsigned integer division and signed integer division are distinct
3697 operations; for signed integer division, use '<tt>sdiv</tt>'.</p>
3699 <p>Division by zero leads to undefined behavior.</p>
3701 <p>If the <tt>exact</tt> keyword is present, the result value of the
3702 <tt>udiv</tt> is a <a href="#trapvalues">trap value</a> if %op1 is not a
3703 multiple of %op2 (as such, "((a udiv exact b) mul b) == a").</p>
3708 <result> = udiv i32 4, %var <i>; yields {i32}:result = 4 / %var</i>
3713 <!-- _______________________________________________________________________ -->
3715 <a name="i_sdiv">'<tt>sdiv</tt>' Instruction</a>
3722 <result> = sdiv <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3723 <result> = sdiv exact <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3727 <p>The '<tt>sdiv</tt>' instruction returns the quotient of its two operands.</p>
3730 <p>The two arguments to the '<tt>sdiv</tt>' instruction must be
3731 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
3732 values. Both arguments must have identical types.</p>
3735 <p>The value produced is the signed integer quotient of the two operands rounded
3738 <p>Note that signed integer division and unsigned integer division are distinct
3739 operations; for unsigned integer division, use '<tt>udiv</tt>'.</p>
3741 <p>Division by zero leads to undefined behavior. Overflow also leads to
3742 undefined behavior; this is a rare case, but can occur, for example, by doing
3743 a 32-bit division of -2147483648 by -1.</p>
3745 <p>If the <tt>exact</tt> keyword is present, the result value of the
3746 <tt>sdiv</tt> is a <a href="#trapvalues">trap value</a> if the result would
3751 <result> = sdiv i32 4, %var <i>; yields {i32}:result = 4 / %var</i>
3756 <!-- _______________________________________________________________________ -->
3758 <a name="i_fdiv">'<tt>fdiv</tt>' Instruction</a>
3765 <result> = fdiv <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3769 <p>The '<tt>fdiv</tt>' instruction returns the quotient of its two operands.</p>
3772 <p>The two arguments to the '<tt>fdiv</tt>' instruction must be
3773 <a href="#t_floating">floating point</a> or <a href="#t_vector">vector</a> of
3774 floating point values. Both arguments must have identical types.</p>
3777 <p>The value produced is the floating point quotient of the two operands.</p>
3781 <result> = fdiv float 4.0, %var <i>; yields {float}:result = 4.0 / %var</i>
3786 <!-- _______________________________________________________________________ -->
3788 <a name="i_urem">'<tt>urem</tt>' Instruction</a>
3795 <result> = urem <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3799 <p>The '<tt>urem</tt>' instruction returns the remainder from the unsigned
3800 division of its two arguments.</p>
3803 <p>The two arguments to the '<tt>urem</tt>' instruction must be
3804 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
3805 values. Both arguments must have identical types.</p>
3808 <p>This instruction returns the unsigned integer <i>remainder</i> of a division.
3809 This instruction always performs an unsigned division to get the
3812 <p>Note that unsigned integer remainder and signed integer remainder are
3813 distinct operations; for signed integer remainder, use '<tt>srem</tt>'.</p>
3815 <p>Taking the remainder of a division by zero leads to undefined behavior.</p>
3819 <result> = urem i32 4, %var <i>; yields {i32}:result = 4 % %var</i>
3824 <!-- _______________________________________________________________________ -->
3826 <a name="i_srem">'<tt>srem</tt>' Instruction</a>
3833 <result> = srem <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3837 <p>The '<tt>srem</tt>' instruction returns the remainder from the signed
3838 division of its two operands. This instruction can also take
3839 <a href="#t_vector">vector</a> versions of the values in which case the
3840 elements must be integers.</p>
3843 <p>The two arguments to the '<tt>srem</tt>' instruction must be
3844 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
3845 values. Both arguments must have identical types.</p>
3848 <p>This instruction returns the <i>remainder</i> of a division (where the result
3849 is either zero or has the same sign as the dividend, <tt>op1</tt>), not the
3850 <i>modulo</i> operator (where the result is either zero or has the same sign
3851 as the divisor, <tt>op2</tt>) of a value.
3852 For more information about the difference,
3853 see <a href="http://mathforum.org/dr.math/problems/anne.4.28.99.html">The
3854 Math Forum</a>. For a table of how this is implemented in various languages,
3855 please see <a href="http://en.wikipedia.org/wiki/Modulo_operation">
3856 Wikipedia: modulo operation</a>.</p>
3858 <p>Note that signed integer remainder and unsigned integer remainder are
3859 distinct operations; for unsigned integer remainder, use '<tt>urem</tt>'.</p>
3861 <p>Taking the remainder of a division by zero leads to undefined behavior.
3862 Overflow also leads to undefined behavior; this is a rare case, but can
3863 occur, for example, by taking the remainder of a 32-bit division of
3864 -2147483648 by -1. (The remainder doesn't actually overflow, but this rule
3865 lets srem be implemented using instructions that return both the result of
3866 the division and the remainder.)</p>
3870 <result> = srem i32 4, %var <i>; yields {i32}:result = 4 % %var</i>
3875 <!-- _______________________________________________________________________ -->
3877 <a name="i_frem">'<tt>frem</tt>' Instruction</a>
3884 <result> = frem <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3888 <p>The '<tt>frem</tt>' instruction returns the remainder from the division of
3889 its two operands.</p>
3892 <p>The two arguments to the '<tt>frem</tt>' instruction must be
3893 <a href="#t_floating">floating point</a> or <a href="#t_vector">vector</a> of
3894 floating point values. Both arguments must have identical types.</p>
3897 <p>This instruction returns the <i>remainder</i> of a division. The remainder
3898 has the same sign as the dividend.</p>
3902 <result> = frem float 4.0, %var <i>; yields {float}:result = 4.0 % %var</i>
3909 <!-- ======================================================================= -->
3911 <a name="bitwiseops">Bitwise Binary Operations</a>
3916 <p>Bitwise binary operators are used to do various forms of bit-twiddling in a
3917 program. They are generally very efficient instructions and can commonly be
3918 strength reduced from other instructions. They require two operands of the
3919 same type, execute an operation on them, and produce a single value. The
3920 resulting value is the same type as its operands.</p>
3922 <!-- _______________________________________________________________________ -->
3924 <a name="i_shl">'<tt>shl</tt>' Instruction</a>
3931 <result> = shl <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3932 <result> = shl nuw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3933 <result> = shl nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3934 <result> = shl nuw nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3938 <p>The '<tt>shl</tt>' instruction returns the first operand shifted to the left
3939 a specified number of bits.</p>
3942 <p>Both arguments to the '<tt>shl</tt>' instruction must be the
3943 same <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of
3944 integer type. '<tt>op2</tt>' is treated as an unsigned value.</p>
3947 <p>The value produced is <tt>op1</tt> * 2<sup><tt>op2</tt></sup> mod
3948 2<sup>n</sup>, where <tt>n</tt> is the width of the result. If <tt>op2</tt>
3949 is (statically or dynamically) negative or equal to or larger than the number
3950 of bits in <tt>op1</tt>, the result is undefined. If the arguments are
3951 vectors, each vector element of <tt>op1</tt> is shifted by the corresponding
3952 shift amount in <tt>op2</tt>.</p>
3954 <p>If the <tt>nuw</tt> keyword is present, then the shift produces a
3955 <a href="#trapvalues">trap value</a> if it shifts out any non-zero bits. If
3956 the <tt>nsw</tt> keyword is present, then the shift produces a
3957 <a href="#trapvalues">trap value</a> if it shifts out any bits that disagree
3958 with the resultant sign bit. As such, NUW/NSW have the same semantics as
3959 they would if the shift were expressed as a mul instruction with the same
3960 nsw/nuw bits in (mul %op1, (shl 1, %op2)).</p>
3964 <result> = shl i32 4, %var <i>; yields {i32}: 4 << %var</i>
3965 <result> = shl i32 4, 2 <i>; yields {i32}: 16</i>
3966 <result> = shl i32 1, 10 <i>; yields {i32}: 1024</i>
3967 <result> = shl i32 1, 32 <i>; undefined</i>
3968 <result> = shl <2 x i32> < i32 1, i32 1>, < i32 1, i32 2> <i>; yields: result=<2 x i32> < i32 2, i32 4></i>
3973 <!-- _______________________________________________________________________ -->
3975 <a name="i_lshr">'<tt>lshr</tt>' Instruction</a>
3982 <result> = lshr <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3983 <result> = lshr exact <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3987 <p>The '<tt>lshr</tt>' instruction (logical shift right) returns the first
3988 operand shifted to the right a specified number of bits with zero fill.</p>
3991 <p>Both arguments to the '<tt>lshr</tt>' instruction must be the same
3992 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
3993 type. '<tt>op2</tt>' is treated as an unsigned value.</p>
3996 <p>This instruction always performs a logical shift right operation. The most
3997 significant bits of the result will be filled with zero bits after the shift.
3998 If <tt>op2</tt> is (statically or dynamically) equal to or larger than the
3999 number of bits in <tt>op1</tt>, the result is undefined. If the arguments are
4000 vectors, each vector element of <tt>op1</tt> is shifted by the corresponding
4001 shift amount in <tt>op2</tt>.</p>
4003 <p>If the <tt>exact</tt> keyword is present, the result value of the
4004 <tt>lshr</tt> is a <a href="#trapvalues">trap value</a> if any of the bits
4005 shifted out are non-zero.</p>
4010 <result> = lshr i32 4, 1 <i>; yields {i32}:result = 2</i>
4011 <result> = lshr i32 4, 2 <i>; yields {i32}:result = 1</i>
4012 <result> = lshr i8 4, 3 <i>; yields {i8}:result = 0</i>
4013 <result> = lshr i8 -2, 1 <i>; yields {i8}:result = 0x7FFFFFFF </i>
4014 <result> = lshr i32 1, 32 <i>; undefined</i>
4015 <result> = lshr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 2> <i>; yields: result=<2 x i32> < i32 0x7FFFFFFF, i32 1></i>
4020 <!-- _______________________________________________________________________ -->
4022 <a name="i_ashr">'<tt>ashr</tt>' Instruction</a>
4029 <result> = ashr <ty> <op1>, <op2> <i>; yields {ty}:result</i>
4030 <result> = ashr exact <ty> <op1>, <op2> <i>; yields {ty}:result</i>
4034 <p>The '<tt>ashr</tt>' instruction (arithmetic shift right) returns the first
4035 operand shifted to the right a specified number of bits with sign
4039 <p>Both arguments to the '<tt>ashr</tt>' instruction must be the same
4040 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
4041 type. '<tt>op2</tt>' is treated as an unsigned value.</p>
4044 <p>This instruction always performs an arithmetic shift right operation, The
4045 most significant bits of the result will be filled with the sign bit
4046 of <tt>op1</tt>. If <tt>op2</tt> is (statically or dynamically) equal to or
4047 larger than the number of bits in <tt>op1</tt>, the result is undefined. If
4048 the arguments are vectors, each vector element of <tt>op1</tt> is shifted by
4049 the corresponding shift amount in <tt>op2</tt>.</p>
4051 <p>If the <tt>exact</tt> keyword is present, the result value of the
4052 <tt>ashr</tt> is a <a href="#trapvalues">trap value</a> if any of the bits
4053 shifted out are non-zero.</p>
4057 <result> = ashr i32 4, 1 <i>; yields {i32}:result = 2</i>
4058 <result> = ashr i32 4, 2 <i>; yields {i32}:result = 1</i>
4059 <result> = ashr i8 4, 3 <i>; yields {i8}:result = 0</i>
4060 <result> = ashr i8 -2, 1 <i>; yields {i8}:result = -1</i>
4061 <result> = ashr i32 1, 32 <i>; undefined</i>
4062 <result> = ashr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 3> <i>; yields: result=<2 x i32> < i32 -1, i32 0></i>
4067 <!-- _______________________________________________________________________ -->
4069 <a name="i_and">'<tt>and</tt>' Instruction</a>
4076 <result> = and <ty> <op1>, <op2> <i>; yields {ty}:result</i>
4080 <p>The '<tt>and</tt>' instruction returns the bitwise logical and of its two
4084 <p>The two arguments to the '<tt>and</tt>' instruction must be
4085 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
4086 values. Both arguments must have identical types.</p>
4089 <p>The truth table used for the '<tt>and</tt>' instruction is:</p>
4091 <table border="1" cellspacing="0" cellpadding="4">
4123 <result> = and i32 4, %var <i>; yields {i32}:result = 4 & %var</i>
4124 <result> = and i32 15, 40 <i>; yields {i32}:result = 8</i>
4125 <result> = and i32 4, 8 <i>; yields {i32}:result = 0</i>
4128 <!-- _______________________________________________________________________ -->
4130 <a name="i_or">'<tt>or</tt>' Instruction</a>
4137 <result> = or <ty> <op1>, <op2> <i>; yields {ty}:result</i>
4141 <p>The '<tt>or</tt>' instruction returns the bitwise logical inclusive or of its
4145 <p>The two arguments to the '<tt>or</tt>' instruction must be
4146 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
4147 values. Both arguments must have identical types.</p>
4150 <p>The truth table used for the '<tt>or</tt>' instruction is:</p>
4152 <table border="1" cellspacing="0" cellpadding="4">
4184 <result> = or i32 4, %var <i>; yields {i32}:result = 4 | %var</i>
4185 <result> = or i32 15, 40 <i>; yields {i32}:result = 47</i>
4186 <result> = or i32 4, 8 <i>; yields {i32}:result = 12</i>
4191 <!-- _______________________________________________________________________ -->
4193 <a name="i_xor">'<tt>xor</tt>' Instruction</a>
4200 <result> = xor <ty> <op1>, <op2> <i>; yields {ty}:result</i>
4204 <p>The '<tt>xor</tt>' instruction returns the bitwise logical exclusive or of
4205 its two operands. The <tt>xor</tt> is used to implement the "one's
4206 complement" operation, which is the "~" operator in C.</p>
4209 <p>The two arguments to the '<tt>xor</tt>' instruction must be
4210 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
4211 values. Both arguments must have identical types.</p>
4214 <p>The truth table used for the '<tt>xor</tt>' instruction is:</p>
4216 <table border="1" cellspacing="0" cellpadding="4">
4248 <result> = xor i32 4, %var <i>; yields {i32}:result = 4 ^ %var</i>
4249 <result> = xor i32 15, 40 <i>; yields {i32}:result = 39</i>
4250 <result> = xor i32 4, 8 <i>; yields {i32}:result = 12</i>
4251 <result> = xor i32 %V, -1 <i>; yields {i32}:result = ~%V</i>
4258 <!-- ======================================================================= -->
4260 <a name="vectorops">Vector Operations</a>
4265 <p>LLVM supports several instructions to represent vector operations in a
4266 target-independent manner. These instructions cover the element-access and
4267 vector-specific operations needed to process vectors effectively. While LLVM
4268 does directly support these vector operations, many sophisticated algorithms
4269 will want to use target-specific intrinsics to take full advantage of a
4270 specific target.</p>
4272 <!-- _______________________________________________________________________ -->
4274 <a name="i_extractelement">'<tt>extractelement</tt>' Instruction</a>
4281 <result> = extractelement <n x <ty>> <val>, i32 <idx> <i>; yields <ty></i>
4285 <p>The '<tt>extractelement</tt>' instruction extracts a single scalar element
4286 from a vector at a specified index.</p>
4290 <p>The first operand of an '<tt>extractelement</tt>' instruction is a value
4291 of <a href="#t_vector">vector</a> type. The second operand is an index
4292 indicating the position from which to extract the element. The index may be
4296 <p>The result is a scalar of the same type as the element type of
4297 <tt>val</tt>. Its value is the value at position <tt>idx</tt> of
4298 <tt>val</tt>. If <tt>idx</tt> exceeds the length of <tt>val</tt>, the
4299 results are undefined.</p>
4303 <result> = extractelement <4 x i32> %vec, i32 0 <i>; yields i32</i>
4308 <!-- _______________________________________________________________________ -->
4310 <a name="i_insertelement">'<tt>insertelement</tt>' Instruction</a>
4317 <result> = insertelement <n x <ty>> <val>, <ty> <elt>, i32 <idx> <i>; yields <n x <ty>></i>
4321 <p>The '<tt>insertelement</tt>' instruction inserts a scalar element into a
4322 vector at a specified index.</p>
4325 <p>The first operand of an '<tt>insertelement</tt>' instruction is a value
4326 of <a href="#t_vector">vector</a> type. The second operand is a scalar value
4327 whose type must equal the element type of the first operand. The third
4328 operand is an index indicating the position at which to insert the value.
4329 The index may be a variable.</p>
4332 <p>The result is a vector of the same type as <tt>val</tt>. Its element values
4333 are those of <tt>val</tt> except at position <tt>idx</tt>, where it gets the
4334 value <tt>elt</tt>. If <tt>idx</tt> exceeds the length of <tt>val</tt>, the
4335 results are undefined.</p>
4339 <result> = insertelement <4 x i32> %vec, i32 1, i32 0 <i>; yields <4 x i32></i>
4344 <!-- _______________________________________________________________________ -->
4346 <a name="i_shufflevector">'<tt>shufflevector</tt>' Instruction</a>
4353 <result> = shufflevector <n x <ty>> <v1>, <n x <ty>> <v2>, <m x i32> <mask> <i>; yields <m x <ty>></i>
4357 <p>The '<tt>shufflevector</tt>' instruction constructs a permutation of elements
4358 from two input vectors, returning a vector with the same element type as the
4359 input and length that is the same as the shuffle mask.</p>
4362 <p>The first two operands of a '<tt>shufflevector</tt>' instruction are vectors
4363 with types that match each other. The third argument is a shuffle mask whose
4364 element type is always 'i32'. The result of the instruction is a vector
4365 whose length is the same as the shuffle mask and whose element type is the
4366 same as the element type of the first two operands.</p>
4368 <p>The shuffle mask operand is required to be a constant vector with either
4369 constant integer or undef values.</p>
4372 <p>The elements of the two input vectors are numbered from left to right across
4373 both of the vectors. The shuffle mask operand specifies, for each element of
4374 the result vector, which element of the two input vectors the result element
4375 gets. The element selector may be undef (meaning "don't care") and the
4376 second operand may be undef if performing a shuffle from only one vector.</p>
4380 <result> = shufflevector <4 x i32> %v1, <4 x i32> %v2,
4381 <4 x i32> <i32 0, i32 4, i32 1, i32 5> <i>; yields <4 x i32></i>
4382 <result> = shufflevector <4 x i32> %v1, <4 x i32> undef,
4383 <4 x i32> <i32 0, i32 1, i32 2, i32 3> <i>; yields <4 x i32></i> - Identity shuffle.
4384 <result> = shufflevector <8 x i32> %v1, <8 x i32> undef,
4385 <4 x i32> <i32 0, i32 1, i32 2, i32 3> <i>; yields <4 x i32></i>
4386 <result> = shufflevector <4 x i32> %v1, <4 x i32> %v2,
4387 <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>
4394 <!-- ======================================================================= -->
4396 <a name="aggregateops">Aggregate Operations</a>
4401 <p>LLVM supports several instructions for working with
4402 <a href="#t_aggregate">aggregate</a> values.</p>
4404 <!-- _______________________________________________________________________ -->
4406 <a name="i_extractvalue">'<tt>extractvalue</tt>' Instruction</a>
4413 <result> = extractvalue <aggregate type> <val>, <idx>{, <idx>}*
4417 <p>The '<tt>extractvalue</tt>' instruction extracts the value of a member field
4418 from an <a href="#t_aggregate">aggregate</a> value.</p>
4421 <p>The first operand of an '<tt>extractvalue</tt>' instruction is a value
4422 of <a href="#t_struct">struct</a> or
4423 <a href="#t_array">array</a> type. The operands are constant indices to
4424 specify which value to extract in a similar manner as indices in a
4425 '<tt><a href="#i_getelementptr">getelementptr</a></tt>' instruction.</p>
4426 <p>The major differences to <tt>getelementptr</tt> indexing are:</p>
4428 <li>Since the value being indexed is not a pointer, the first index is
4429 omitted and assumed to be zero.</li>
4430 <li>At least one index must be specified.</li>
4431 <li>Not only struct indices but also array indices must be in
4436 <p>The result is the value at the position in the aggregate specified by the
4441 <result> = extractvalue {i32, float} %agg, 0 <i>; yields i32</i>
4446 <!-- _______________________________________________________________________ -->
4448 <a name="i_insertvalue">'<tt>insertvalue</tt>' Instruction</a>
4455 <result> = insertvalue <aggregate type> <val>, <ty> <elt>, <idx>{, <idx>}* <i>; yields <aggregate type></i>
4459 <p>The '<tt>insertvalue</tt>' instruction inserts a value into a member field
4460 in an <a href="#t_aggregate">aggregate</a> value.</p>
4463 <p>The first operand of an '<tt>insertvalue</tt>' instruction is a value
4464 of <a href="#t_struct">struct</a> or
4465 <a href="#t_array">array</a> type. The second operand is a first-class
4466 value to insert. The following operands are constant indices indicating
4467 the position at which to insert the value in a similar manner as indices in a
4468 '<tt><a href="#i_extractvalue">extractvalue</a></tt>' instruction. The
4469 value to insert must have the same type as the value identified by the
4473 <p>The result is an aggregate of the same type as <tt>val</tt>. Its value is
4474 that of <tt>val</tt> except that the value at the position specified by the
4475 indices is that of <tt>elt</tt>.</p>
4479 %agg1 = insertvalue {i32, float} undef, i32 1, 0 <i>; yields {i32 1, float undef}</i>
4480 %agg2 = insertvalue {i32, float} %agg1, float %val, 1 <i>; yields {i32 1, float %val}</i>
4481 %agg3 = insertvalue {i32, {float}} %agg1, float %val, 1, 0 <i>; yields {i32 1, float %val}</i>
4488 <!-- ======================================================================= -->
4490 <a name="memoryops">Memory Access and Addressing Operations</a>
4495 <p>A key design point of an SSA-based representation is how it represents
4496 memory. In LLVM, no memory locations are in SSA form, which makes things
4497 very simple. This section describes how to read, write, and allocate
4500 <!-- _______________________________________________________________________ -->
4502 <a name="i_alloca">'<tt>alloca</tt>' Instruction</a>
4509 <result> = alloca <type>[, <ty> <NumElements>][, align <alignment>] <i>; yields {type*}:result</i>
4513 <p>The '<tt>alloca</tt>' instruction allocates memory on the stack frame of the
4514 currently executing function, to be automatically released when this function
4515 returns to its caller. The object is always allocated in the generic address
4516 space (address space zero).</p>
4519 <p>The '<tt>alloca</tt>' instruction
4520 allocates <tt>sizeof(<type>)*NumElements</tt> bytes of memory on the
4521 runtime stack, returning a pointer of the appropriate type to the program.
4522 If "NumElements" is specified, it is the number of elements allocated,
4523 otherwise "NumElements" is defaulted to be one. If a constant alignment is
4524 specified, the value result of the allocation is guaranteed to be aligned to
4525 at least that boundary. If not specified, or if zero, the target can choose
4526 to align the allocation on any convenient boundary compatible with the
4529 <p>'<tt>type</tt>' may be any sized type.</p>
4532 <p>Memory is allocated; a pointer is returned. The operation is undefined if
4533 there is insufficient stack space for the allocation. '<tt>alloca</tt>'d
4534 memory is automatically released when the function returns. The
4535 '<tt>alloca</tt>' instruction is commonly used to represent automatic
4536 variables that must have an address available. When the function returns
4537 (either with the <tt><a href="#i_ret">ret</a></tt>
4538 or <tt><a href="#i_unwind">unwind</a></tt> instructions), the memory is
4539 reclaimed. Allocating zero bytes is legal, but the result is undefined.</p>
4543 %ptr = alloca i32 <i>; yields {i32*}:ptr</i>
4544 %ptr = alloca i32, i32 4 <i>; yields {i32*}:ptr</i>
4545 %ptr = alloca i32, i32 4, align 1024 <i>; yields {i32*}:ptr</i>
4546 %ptr = alloca i32, align 1024 <i>; yields {i32*}:ptr</i>
4551 <!-- _______________________________________________________________________ -->
4553 <a name="i_load">'<tt>load</tt>' Instruction</a>
4560 <result> = load <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>]
4561 <result> = volatile load <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>]
4562 !<index> = !{ i32 1 }
4566 <p>The '<tt>load</tt>' instruction is used to read from memory.</p>
4569 <p>The argument to the '<tt>load</tt>' instruction specifies the memory address
4570 from which to load. The pointer must point to
4571 a <a href="#t_firstclass">first class</a> type. If the <tt>load</tt> is
4572 marked as <tt>volatile</tt>, then the optimizer is not allowed to modify the
4573 number or order of execution of this <tt>load</tt> with other <a
4574 href="#volatile">volatile operations</a>.</p>
4576 <p>The optional constant <tt>align</tt> argument specifies the alignment of the
4577 operation (that is, the alignment of the memory address). A value of 0 or an
4578 omitted <tt>align</tt> argument means that the operation has the preferential
4579 alignment for the target. It is the responsibility of the code emitter to
4580 ensure that the alignment information is correct. Overestimating the
4581 alignment results in undefined behavior. Underestimating the alignment may
4582 produce less efficient code. An alignment of 1 is always safe.</p>
4584 <p>The optional <tt>!nontemporal</tt> metadata must reference a single
4585 metatadata name <index> corresponding to a metadata node with
4586 one <tt>i32</tt> entry of value 1. The existence of
4587 the <tt>!nontemporal</tt> metatadata on the instruction tells the optimizer
4588 and code generator that this load is not expected to be reused in the cache.
4589 The code generator may select special instructions to save cache bandwidth,
4590 such as the <tt>MOVNT</tt> instruction on x86.</p>
4593 <p>The location of memory pointed to is loaded. If the value being loaded is of
4594 scalar type then the number of bytes read does not exceed the minimum number
4595 of bytes needed to hold all bits of the type. For example, loading an
4596 <tt>i24</tt> reads at most three bytes. When loading a value of a type like
4597 <tt>i20</tt> with a size that is not an integral number of bytes, the result
4598 is undefined if the value was not originally written using a store of the
4603 %ptr = <a href="#i_alloca">alloca</a> i32 <i>; yields {i32*}:ptr</i>
4604 <a href="#i_store">store</a> i32 3, i32* %ptr <i>; yields {void}</i>
4605 %val = load i32* %ptr <i>; yields {i32}:val = i32 3</i>
4610 <!-- _______________________________________________________________________ -->
4612 <a name="i_store">'<tt>store</tt>' Instruction</a>
4619 store <ty> <value>, <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>] <i>; yields {void}</i>
4620 volatile store <ty> <value>, <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>] <i>; yields {void}</i>
4624 <p>The '<tt>store</tt>' instruction is used to write to memory.</p>
4627 <p>There are two arguments to the '<tt>store</tt>' instruction: a value to store
4628 and an address at which to store it. The type of the
4629 '<tt><pointer></tt>' operand must be a pointer to
4630 the <a href="#t_firstclass">first class</a> type of the
4631 '<tt><value></tt>' operand. If the <tt>store</tt> is marked as
4632 <tt>volatile</tt>, then the optimizer is not allowed to modify the number or
4633 order of execution of this <tt>store</tt> with other <a
4634 href="#volatile">volatile operations</a>.</p>
4636 <p>The optional constant "align" argument specifies the alignment of the
4637 operation (that is, the alignment of the memory address). A value of 0 or an
4638 omitted "align" argument means that the operation has the preferential
4639 alignment for the target. It is the responsibility of the code emitter to
4640 ensure that the alignment information is correct. Overestimating the
4641 alignment results in an undefined behavior. Underestimating the alignment may
4642 produce less efficient code. An alignment of 1 is always safe.</p>
4644 <p>The optional !nontemporal metadata must reference a single metatadata
4645 name <index> corresponding to a metadata node with one i32 entry of
4646 value 1. The existence of the !nontemporal metatadata on the
4647 instruction tells the optimizer and code generator that this load is
4648 not expected to be reused in the cache. The code generator may
4649 select special instructions to save cache bandwidth, such as the
4650 MOVNT instruction on x86.</p>
4654 <p>The contents of memory are updated to contain '<tt><value></tt>' at the
4655 location specified by the '<tt><pointer></tt>' operand. If
4656 '<tt><value></tt>' is of scalar type then the number of bytes written
4657 does not exceed the minimum number of bytes needed to hold all bits of the
4658 type. For example, storing an <tt>i24</tt> writes at most three bytes. When
4659 writing a value of a type like <tt>i20</tt> with a size that is not an
4660 integral number of bytes, it is unspecified what happens to the extra bits
4661 that do not belong to the type, but they will typically be overwritten.</p>
4665 %ptr = <a href="#i_alloca">alloca</a> i32 <i>; yields {i32*}:ptr</i>
4666 store i32 3, i32* %ptr <i>; yields {void}</i>
4667 %val = <a href="#i_load">load</a> i32* %ptr <i>; yields {i32}:val = i32 3</i>
4672 <!-- _______________________________________________________________________ -->
4673 <div class="doc_subsubsection"> <a name="i_fence">'<tt>fence</tt>'
4674 Instruction</a> </div>
4676 <div class="doc_text">
4680 fence [singlethread] <ordering> <i>; yields {void}</i>
4684 <p>The '<tt>fence</tt>' instruction is used to introduce happens-before edges
4685 between operations.</p>
4687 <h5>Arguments:</h5> <p>'<code>fence</code>' instructions take an <a
4688 href="#ordering">ordering</a> argument which defines what
4689 <i>synchronizes-with</i> edges they add. They can only be given
4690 <code>acquire</code>, <code>release</code>, <code>acq_rel</code>, and
4691 <code>seq_cst</code> orderings.</p>
4694 <p>A fence <var>A</var> which has (at least) <code>release</code> ordering
4695 semantics <i>synchronizes with</i> a fence <var>B</var> with (at least)
4696 <code>acquire</code> ordering semantics if and only if there exist atomic
4697 operations <var>X</var> and <var>Y</var>, both operating on some atomic object
4698 <var>M</var>, such that <var>A</var> is sequenced before <var>X</var>,
4699 <var>X</var> modifies <var>M</var> (either directly or through some side effect
4700 of a sequence headed by <var>X</var>), <var>Y</var> is sequenced before
4701 <var>B</var>, and <var>Y</var> observes <var>M</var>. This provides a
4702 <i>happens-before</i> dependency between <var>A</var> and <var>B</var>. Rather
4703 than an explicit <code>fence</code>, one (but not both) of the atomic operations
4704 <var>X</var> or <var>Y</var> might provide a <code>release</code> or
4705 <code>acquire</code> (resp.) ordering constraint and still
4706 <i>synchronize-with</i> the explicit <code>fence</code> and establish the
4707 <i>happens-before</i> edge.</p>
4709 <p>A <code>fence</code> which has <code>seq_cst</code> ordering, in addition to
4710 having both <code>acquire</code> and <code>release</code> semantics specified
4711 above, participates in the global program order of other <code>seq_cst</code>
4712 operations and/or fences.</p>
4714 <p>The optional "<a href="#singlethread"><code>singlethread</code></a>" argument
4715 specifies that the fence only synchronizes with other fences in the same
4716 thread. (This is useful for interacting with signal handlers.)</p>
4718 <p>FIXME: This instruction is a work in progress; until it is finished, use
4719 llvm.memory.barrier.
4723 fence acquire <i>; yields {void}</i>
4724 fence singlethread seq_cst <i>; yields {void}</i>
4729 <!-- _______________________________________________________________________ -->
4730 <div class="doc_subsubsection"> <a name="i_cmpxchg">'<tt>cmpxchg</tt>'
4731 Instruction</a> </div>
4733 <div class="doc_text">
4737 [volatile] cmpxchg <ty>* <pointer>, <ty> <cmp>, <ty> <new> [singlethread] <ordering> <i>; yields {ty}</i>
4741 <p>The '<tt>cmpxchg</tt>' instruction is used to atomically modify memory.
4742 It loads a value in memory and compares it to a given value. If they are
4743 equal, it stores a new value into the memory.</p>
4746 <p>There are three arguments to the '<code>cmpxchg</code>' instruction: an
4747 address to operate on, a value to compare to the value currently be at that
4748 address, and a new value to place at that address if the compared values are
4749 equal. The type of '<var><cmp></var>' must be an integer type whose
4750 bit width is a power of two greater than or equal to eight and less than
4751 or equal to a target-specific size limit. '<var><cmp></var>' and
4752 '<var><new></var>' must have the same type, and the type of
4753 '<var><pointer></var>' must be a pointer to that type. If the
4754 <code>cmpxchg</code> is marked as <code>volatile</code>, then the
4755 optimizer is not allowed to modify the number or order of execution
4756 of this <code>cmpxchg</code> with other <a href="#volatile">volatile
4759 <!-- FIXME: Extend allowed types. -->
4761 <p>The <a href="#ordering"><var>ordering</var></a> argument specifies how this
4762 <code>cmpxchg</code> synchronizes with other atomic operations.</p>
4764 <p>The optional "<code>singlethread</code>" argument declares that the
4765 <code>cmpxchg</code> is only atomic with respect to code (usually signal
4766 handlers) running in the same thread as the <code>cmpxchg</code>. Otherwise the
4767 cmpxchg is atomic with respect to all other code in the system.</p>
4769 <p>The pointer passed into cmpxchg must have alignment greater than or equal to
4770 the size in memory of the operand.
4773 <p>The contents of memory at the location specified by the
4774 '<tt><pointer></tt>' operand is read and compared to
4775 '<tt><cmp></tt>'; if the read value is the equal,
4776 '<tt><new></tt>' is written. The original value at the location
4779 <p>A successful <code>cmpxchg</code> is a read-modify-write instruction for the
4780 purpose of identifying <a href="#release_sequence">release sequences</a>. A
4781 failed <code>cmpxchg</code> is equivalent to an atomic load with an ordering
4782 parameter determined by dropping any <code>release</code> part of the
4783 <code>cmpxchg</code>'s ordering.</p>
4786 FIXME: Is compare_exchange_weak() necessary? (Consider after we've done
4787 optimization work on ARM.)
4789 FIXME: Is a weaker ordering constraint on failure helpful in practice?
4795 %orig = atomic <a href="#i_load">load</a> i32* %ptr unordered <i>; yields {i32}</i>
4796 <a href="#i_br">br</a> label %loop
4799 %cmp = <a href="#i_phi">phi</a> i32 [ %orig, %entry ], [%old, %loop]
4800 %squared = <a href="#i_mul">mul</a> i32 %cmp, %cmp
4801 %old = cmpxchg i32* %ptr, i32 %cmp, i32 %squared <i>; yields {i32}</i>
4802 %success = <a href="#i_icmp">icmp</a> eq i32 %cmp, %old
4803 <a href="#i_br">br</a> i1 %success, label %done, label %loop
4811 <!-- _______________________________________________________________________ -->
4812 <div class="doc_subsubsection"> <a name="i_atomicrmw">'<tt>atomicrmw</tt>'
4813 Instruction</a> </div>
4815 <div class="doc_text">
4819 [volatile] atomicrmw <operation> <ty>* <pointer>, <ty> <value> [singlethread] <ordering> <i>; yields {ty}</i>
4823 <p>The '<tt>atomicrmw</tt>' instruction is used to atomically modify memory.</p>
4826 <p>There are three arguments to the '<code>atomicrmw</code>' instruction: an
4827 operation to apply, an address whose value to modify, an argument to the
4828 operation. The operation must be one of the following keywords:</p>
4843 <p>The type of '<var><value></var>' must be an integer type whose
4844 bit width is a power of two greater than or equal to eight and less than
4845 or equal to a target-specific size limit. The type of the
4846 '<code><pointer></code>' operand must be a pointer to that type.
4847 If the <code>atomicrmw</code> is marked as <code>volatile</code>, then the
4848 optimizer is not allowed to modify the number or order of execution of this
4849 <code>atomicrmw</code> with other <a href="#volatile">volatile
4852 <!-- FIXME: Extend allowed types. -->
4855 <p>The contents of memory at the location specified by the
4856 '<tt><pointer></tt>' operand are atomically read, modified, and written
4857 back. The original value at the location is returned. The modification is
4858 specified by the <var>operation</var> argument:</p>
4861 <li>xchg: <code>*ptr = val</code></li>
4862 <li>add: <code>*ptr = *ptr + val</code></li>
4863 <li>sub: <code>*ptr = *ptr - val</code></li>
4864 <li>and: <code>*ptr = *ptr & val</code></li>
4865 <li>nand: <code>*ptr = ~(*ptr & val)</code></li>
4866 <li>or: <code>*ptr = *ptr | val</code></li>
4867 <li>xor: <code>*ptr = *ptr ^ val</code></li>
4868 <li>max: <code>*ptr = *ptr > val ? *ptr : val</code> (using a signed comparison)</li>
4869 <li>min: <code>*ptr = *ptr < val ? *ptr : val</code> (using a signed comparison)</li>
4870 <li>umax: <code>*ptr = *ptr > val ? *ptr : val</code> (using an unsigned comparison)</li>
4871 <li>umin: <code>*ptr = *ptr < val ? *ptr : val</code> (using an unsigned comparison)</li>
4876 %old = atomicrmw add i32* %ptr, i32 1 acquire <i>; yields {i32}</i>
4881 <!-- _______________________________________________________________________ -->
4883 <a name="i_getelementptr">'<tt>getelementptr</tt>' Instruction</a>
4890 <result> = getelementptr <pty>* <ptrval>{, <ty> <idx>}*
4891 <result> = getelementptr inbounds <pty>* <ptrval>{, <ty> <idx>}*
4895 <p>The '<tt>getelementptr</tt>' instruction is used to get the address of a
4896 subelement of an <a href="#t_aggregate">aggregate</a> data structure.
4897 It performs address calculation only and does not access memory.</p>
4900 <p>The first argument is always a pointer, and forms the basis of the
4901 calculation. The remaining arguments are indices that indicate which of the
4902 elements of the aggregate object are indexed. The interpretation of each
4903 index is dependent on the type being indexed into. The first index always
4904 indexes the pointer value given as the first argument, the second index
4905 indexes a value of the type pointed to (not necessarily the value directly
4906 pointed to, since the first index can be non-zero), etc. The first type
4907 indexed into must be a pointer value, subsequent types can be arrays,
4908 vectors, and structs. Note that subsequent types being indexed into
4909 can never be pointers, since that would require loading the pointer before
4910 continuing calculation.</p>
4912 <p>The type of each index argument depends on the type it is indexing into.
4913 When indexing into a (optionally packed) structure, only <tt>i32</tt>
4914 integer <b>constants</b> are allowed. When indexing into an array, pointer
4915 or vector, integers of any width are allowed, and they are not required to be
4918 <p>For example, let's consider a C code fragment and how it gets compiled to
4921 <pre class="doc_code">
4933 int *foo(struct ST *s) {
4934 return &s[1].Z.B[5][13];
4938 <p>The LLVM code generated by the GCC frontend is:</p>
4940 <pre class="doc_code">
4941 %RT = <a href="#namedtypes">type</a> { i8 , [10 x [20 x i32]], i8 }
4942 %ST = <a href="#namedtypes">type</a> { i32, double, %RT }
4944 define i32* @foo(%ST* %s) {
4946 %reg = getelementptr %ST* %s, i32 1, i32 2, i32 1, i32 5, i32 13
4952 <p>In the example above, the first index is indexing into the '<tt>%ST*</tt>'
4953 type, which is a pointer, yielding a '<tt>%ST</tt>' = '<tt>{ i32, double, %RT
4954 }</tt>' type, a structure. The second index indexes into the third element
4955 of the structure, yielding a '<tt>%RT</tt>' = '<tt>{ i8 , [10 x [20 x i32]],
4956 i8 }</tt>' type, another structure. The third index indexes into the second
4957 element of the structure, yielding a '<tt>[10 x [20 x i32]]</tt>' type, an
4958 array. The two dimensions of the array are subscripted into, yielding an
4959 '<tt>i32</tt>' type. The '<tt>getelementptr</tt>' instruction returns a
4960 pointer to this element, thus computing a value of '<tt>i32*</tt>' type.</p>
4962 <p>Note that it is perfectly legal to index partially through a structure,
4963 returning a pointer to an inner element. Because of this, the LLVM code for
4964 the given testcase is equivalent to:</p>
4967 define i32* @foo(%ST* %s) {
4968 %t1 = getelementptr %ST* %s, i32 1 <i>; yields %ST*:%t1</i>
4969 %t2 = getelementptr %ST* %t1, i32 0, i32 2 <i>; yields %RT*:%t2</i>
4970 %t3 = getelementptr %RT* %t2, i32 0, i32 1 <i>; yields [10 x [20 x i32]]*:%t3</i>
4971 %t4 = getelementptr [10 x [20 x i32]]* %t3, i32 0, i32 5 <i>; yields [20 x i32]*:%t4</i>
4972 %t5 = getelementptr [20 x i32]* %t4, i32 0, i32 13 <i>; yields i32*:%t5</i>
4977 <p>If the <tt>inbounds</tt> keyword is present, the result value of the
4978 <tt>getelementptr</tt> is a <a href="#trapvalues">trap value</a> if the
4979 base pointer is not an <i>in bounds</i> address of an allocated object,
4980 or if any of the addresses that would be formed by successive addition of
4981 the offsets implied by the indices to the base address with infinitely
4982 precise arithmetic are not an <i>in bounds</i> address of that allocated
4983 object. The <i>in bounds</i> addresses for an allocated object are all
4984 the addresses that point into the object, plus the address one byte past
4987 <p>If the <tt>inbounds</tt> keyword is not present, the offsets are added to
4988 the base address with silently-wrapping two's complement arithmetic, and
4989 the result value of the <tt>getelementptr</tt> may be outside the object
4990 pointed to by the base pointer. The result value may not necessarily be
4991 used to access memory though, even if it happens to point into allocated
4992 storage. See the <a href="#pointeraliasing">Pointer Aliasing Rules</a>
4993 section for more information.</p>
4995 <p>The getelementptr instruction is often confusing. For some more insight into
4996 how it works, see <a href="GetElementPtr.html">the getelementptr FAQ</a>.</p>
5000 <i>; yields [12 x i8]*:aptr</i>
5001 %aptr = getelementptr {i32, [12 x i8]}* %saptr, i64 0, i32 1
5002 <i>; yields i8*:vptr</i>
5003 %vptr = getelementptr {i32, <2 x i8>}* %svptr, i64 0, i32 1, i32 1
5004 <i>; yields i8*:eptr</i>
5005 %eptr = getelementptr [12 x i8]* %aptr, i64 0, i32 1
5006 <i>; yields i32*:iptr</i>
5007 %iptr = getelementptr [10 x i32]* @arr, i16 0, i16 0
5014 <!-- ======================================================================= -->
5016 <a name="convertops">Conversion Operations</a>
5021 <p>The instructions in this category are the conversion instructions (casting)
5022 which all take a single operand and a type. They perform various bit
5023 conversions on the operand.</p>
5025 <!-- _______________________________________________________________________ -->
5027 <a name="i_trunc">'<tt>trunc .. to</tt>' Instruction</a>
5034 <result> = trunc <ty> <value> to <ty2> <i>; yields ty2</i>
5038 <p>The '<tt>trunc</tt>' instruction truncates its operand to the
5039 type <tt>ty2</tt>.</p>
5042 <p>The '<tt>trunc</tt>' instruction takes a value to trunc, and a type to trunc it to.
5043 Both types must be of <a href="#t_integer">integer</a> types, or vectors
5044 of the same number of integers.
5045 The bit size of the <tt>value</tt> must be larger than
5046 the bit size of the destination type, <tt>ty2</tt>.
5047 Equal sized types are not allowed.</p>
5050 <p>The '<tt>trunc</tt>' instruction truncates the high order bits
5051 in <tt>value</tt> and converts the remaining bits to <tt>ty2</tt>. Since the
5052 source size must be larger than the destination size, <tt>trunc</tt> cannot
5053 be a <i>no-op cast</i>. It will always truncate bits.</p>
5057 %X = trunc i32 257 to i8 <i>; yields i8:1</i>
5058 %Y = trunc i32 123 to i1 <i>; yields i1:true</i>
5059 %Z = trunc i32 122 to i1 <i>; yields i1:false</i>
5060 %W = trunc <2 x i16> <i16 8, i16 7> to <2 x i8> <i>; yields <i8 8, i8 7></i>
5065 <!-- _______________________________________________________________________ -->
5067 <a name="i_zext">'<tt>zext .. to</tt>' Instruction</a>
5074 <result> = zext <ty> <value> to <ty2> <i>; yields ty2</i>
5078 <p>The '<tt>zext</tt>' instruction zero extends its operand to type
5083 <p>The '<tt>zext</tt>' instruction takes a value to cast, and a type to cast it to.
5084 Both types must be of <a href="#t_integer">integer</a> types, or vectors
5085 of the same number of integers.
5086 The bit size of the <tt>value</tt> must be smaller than
5087 the bit size of the destination type,
5091 <p>The <tt>zext</tt> fills the high order bits of the <tt>value</tt> with zero
5092 bits until it reaches the size of the destination type, <tt>ty2</tt>.</p>
5094 <p>When zero extending from i1, the result will always be either 0 or 1.</p>
5098 %X = zext i32 257 to i64 <i>; yields i64:257</i>
5099 %Y = zext i1 true to i32 <i>; yields i32:1</i>
5100 %Z = zext <2 x i16> <i16 8, i16 7> to <2 x i32> <i>; yields <i32 8, i32 7></i>
5105 <!-- _______________________________________________________________________ -->
5107 <a name="i_sext">'<tt>sext .. to</tt>' Instruction</a>
5114 <result> = sext <ty> <value> to <ty2> <i>; yields ty2</i>
5118 <p>The '<tt>sext</tt>' sign extends <tt>value</tt> to the type <tt>ty2</tt>.</p>
5121 <p>The '<tt>sext</tt>' instruction takes a value to cast, and a type to cast it to.
5122 Both types must be of <a href="#t_integer">integer</a> types, or vectors
5123 of the same number of integers.
5124 The bit size of the <tt>value</tt> must be smaller than
5125 the bit size of the destination type,
5129 <p>The '<tt>sext</tt>' instruction performs a sign extension by copying the sign
5130 bit (highest order bit) of the <tt>value</tt> until it reaches the bit size
5131 of the type <tt>ty2</tt>.</p>
5133 <p>When sign extending from i1, the extension always results in -1 or 0.</p>
5137 %X = sext i8 -1 to i16 <i>; yields i16 :65535</i>
5138 %Y = sext i1 true to i32 <i>; yields i32:-1</i>
5139 %Z = sext <2 x i16> <i16 8, i16 7> to <2 x i32> <i>; yields <i32 8, i32 7></i>
5144 <!-- _______________________________________________________________________ -->
5146 <a name="i_fptrunc">'<tt>fptrunc .. to</tt>' Instruction</a>
5153 <result> = fptrunc <ty> <value> to <ty2> <i>; yields ty2</i>
5157 <p>The '<tt>fptrunc</tt>' instruction truncates <tt>value</tt> to type
5161 <p>The '<tt>fptrunc</tt>' instruction takes a <a href="#t_floating">floating
5162 point</a> value to cast and a <a href="#t_floating">floating point</a> type
5163 to cast it to. The size of <tt>value</tt> must be larger than the size of
5164 <tt>ty2</tt>. This implies that <tt>fptrunc</tt> cannot be used to make a
5165 <i>no-op cast</i>.</p>
5168 <p>The '<tt>fptrunc</tt>' instruction truncates a <tt>value</tt> from a larger
5169 <a href="#t_floating">floating point</a> type to a smaller
5170 <a href="#t_floating">floating point</a> type. If the value cannot fit
5171 within the destination type, <tt>ty2</tt>, then the results are
5176 %X = fptrunc double 123.0 to float <i>; yields float:123.0</i>
5177 %Y = fptrunc double 1.0E+300 to float <i>; yields undefined</i>
5182 <!-- _______________________________________________________________________ -->
5184 <a name="i_fpext">'<tt>fpext .. to</tt>' Instruction</a>
5191 <result> = fpext <ty> <value> to <ty2> <i>; yields ty2</i>
5195 <p>The '<tt>fpext</tt>' extends a floating point <tt>value</tt> to a larger
5196 floating point value.</p>
5199 <p>The '<tt>fpext</tt>' instruction takes a
5200 <a href="#t_floating">floating point</a> <tt>value</tt> to cast, and
5201 a <a href="#t_floating">floating point</a> type to cast it to. The source
5202 type must be smaller than the destination type.</p>
5205 <p>The '<tt>fpext</tt>' instruction extends the <tt>value</tt> from a smaller
5206 <a href="#t_floating">floating point</a> type to a larger
5207 <a href="#t_floating">floating point</a> type. The <tt>fpext</tt> cannot be
5208 used to make a <i>no-op cast</i> because it always changes bits. Use
5209 <tt>bitcast</tt> to make a <i>no-op cast</i> for a floating point cast.</p>
5213 %X = fpext float 3.125 to double <i>; yields double:3.125000e+00</i>
5214 %Y = fpext double %X to fp128 <i>; yields fp128:0xL00000000000000004000900000000000</i>
5219 <!-- _______________________________________________________________________ -->
5221 <a name="i_fptoui">'<tt>fptoui .. to</tt>' Instruction</a>
5228 <result> = fptoui <ty> <value> to <ty2> <i>; yields ty2</i>
5232 <p>The '<tt>fptoui</tt>' converts a floating point <tt>value</tt> to its
5233 unsigned integer equivalent of type <tt>ty2</tt>.</p>
5236 <p>The '<tt>fptoui</tt>' instruction takes a value to cast, which must be a
5237 scalar or vector <a href="#t_floating">floating point</a> value, and a type
5238 to cast it to <tt>ty2</tt>, which must be an <a href="#t_integer">integer</a>
5239 type. If <tt>ty</tt> is a vector floating point type, <tt>ty2</tt> must be a
5240 vector integer type with the same number of elements as <tt>ty</tt></p>
5243 <p>The '<tt>fptoui</tt>' instruction converts its
5244 <a href="#t_floating">floating point</a> operand into the nearest (rounding
5245 towards zero) unsigned integer value. If the value cannot fit
5246 in <tt>ty2</tt>, the results are undefined.</p>
5250 %X = fptoui double 123.0 to i32 <i>; yields i32:123</i>
5251 %Y = fptoui float 1.0E+300 to i1 <i>; yields undefined:1</i>
5252 %Z = fptoui float 1.04E+17 to i8 <i>; yields undefined:1</i>
5257 <!-- _______________________________________________________________________ -->
5259 <a name="i_fptosi">'<tt>fptosi .. to</tt>' Instruction</a>
5266 <result> = fptosi <ty> <value> to <ty2> <i>; yields ty2</i>
5270 <p>The '<tt>fptosi</tt>' instruction converts
5271 <a href="#t_floating">floating point</a> <tt>value</tt> to
5272 type <tt>ty2</tt>.</p>
5275 <p>The '<tt>fptosi</tt>' instruction takes a value to cast, which must be a
5276 scalar or vector <a href="#t_floating">floating point</a> value, and a type
5277 to cast it to <tt>ty2</tt>, which must be an <a href="#t_integer">integer</a>
5278 type. If <tt>ty</tt> is a vector floating point type, <tt>ty2</tt> must be a
5279 vector integer type with the same number of elements as <tt>ty</tt></p>
5282 <p>The '<tt>fptosi</tt>' instruction converts its
5283 <a href="#t_floating">floating point</a> operand into the nearest (rounding
5284 towards zero) signed integer value. If the value cannot fit in <tt>ty2</tt>,
5285 the results are undefined.</p>
5289 %X = fptosi double -123.0 to i32 <i>; yields i32:-123</i>
5290 %Y = fptosi float 1.0E-247 to i1 <i>; yields undefined:1</i>
5291 %Z = fptosi float 1.04E+17 to i8 <i>; yields undefined:1</i>
5296 <!-- _______________________________________________________________________ -->
5298 <a name="i_uitofp">'<tt>uitofp .. to</tt>' Instruction</a>
5305 <result> = uitofp <ty> <value> to <ty2> <i>; yields ty2</i>
5309 <p>The '<tt>uitofp</tt>' instruction regards <tt>value</tt> as an unsigned
5310 integer and converts that value to the <tt>ty2</tt> type.</p>
5313 <p>The '<tt>uitofp</tt>' instruction takes a value to cast, which must be a
5314 scalar or vector <a href="#t_integer">integer</a> value, and a type to cast
5315 it to <tt>ty2</tt>, which must be an <a href="#t_floating">floating point</a>
5316 type. If <tt>ty</tt> is a vector integer type, <tt>ty2</tt> must be a vector
5317 floating point type with the same number of elements as <tt>ty</tt></p>
5320 <p>The '<tt>uitofp</tt>' instruction interprets its operand as an unsigned
5321 integer quantity and converts it to the corresponding floating point
5322 value. If the value cannot fit in the floating point value, the results are
5327 %X = uitofp i32 257 to float <i>; yields float:257.0</i>
5328 %Y = uitofp i8 -1 to double <i>; yields double:255.0</i>
5333 <!-- _______________________________________________________________________ -->
5335 <a name="i_sitofp">'<tt>sitofp .. to</tt>' Instruction</a>
5342 <result> = sitofp <ty> <value> to <ty2> <i>; yields ty2</i>
5346 <p>The '<tt>sitofp</tt>' instruction regards <tt>value</tt> as a signed integer
5347 and converts that value to the <tt>ty2</tt> type.</p>
5350 <p>The '<tt>sitofp</tt>' instruction takes a value to cast, which must be a
5351 scalar or vector <a href="#t_integer">integer</a> value, and a type to cast
5352 it to <tt>ty2</tt>, which must be an <a href="#t_floating">floating point</a>
5353 type. If <tt>ty</tt> is a vector integer type, <tt>ty2</tt> must be a vector
5354 floating point type with the same number of elements as <tt>ty</tt></p>
5357 <p>The '<tt>sitofp</tt>' instruction interprets its operand as a signed integer
5358 quantity and converts it to the corresponding floating point value. If the
5359 value cannot fit in the floating point value, the results are undefined.</p>
5363 %X = sitofp i32 257 to float <i>; yields float:257.0</i>
5364 %Y = sitofp i8 -1 to double <i>; yields double:-1.0</i>
5369 <!-- _______________________________________________________________________ -->
5371 <a name="i_ptrtoint">'<tt>ptrtoint .. to</tt>' Instruction</a>
5378 <result> = ptrtoint <ty> <value> to <ty2> <i>; yields ty2</i>
5382 <p>The '<tt>ptrtoint</tt>' instruction converts the pointer <tt>value</tt> to
5383 the integer type <tt>ty2</tt>.</p>
5386 <p>The '<tt>ptrtoint</tt>' instruction takes a <tt>value</tt> to cast, which
5387 must be a <a href="#t_pointer">pointer</a> value, and a type to cast it to
5388 <tt>ty2</tt>, which must be an <a href="#t_integer">integer</a> type.</p>
5391 <p>The '<tt>ptrtoint</tt>' instruction converts <tt>value</tt> to integer type
5392 <tt>ty2</tt> by interpreting the pointer value as an integer and either
5393 truncating or zero extending that value to the size of the integer type. If
5394 <tt>value</tt> is smaller than <tt>ty2</tt> then a zero extension is done. If
5395 <tt>value</tt> is larger than <tt>ty2</tt> then a truncation is done. If they
5396 are the same size, then nothing is done (<i>no-op cast</i>) other than a type
5401 %X = ptrtoint i32* %X to i8 <i>; yields truncation on 32-bit architecture</i>
5402 %Y = ptrtoint i32* %x to i64 <i>; yields zero extension on 32-bit architecture</i>
5407 <!-- _______________________________________________________________________ -->
5409 <a name="i_inttoptr">'<tt>inttoptr .. to</tt>' Instruction</a>
5416 <result> = inttoptr <ty> <value> to <ty2> <i>; yields ty2</i>
5420 <p>The '<tt>inttoptr</tt>' instruction converts an integer <tt>value</tt> to a
5421 pointer type, <tt>ty2</tt>.</p>
5424 <p>The '<tt>inttoptr</tt>' instruction takes an <a href="#t_integer">integer</a>
5425 value to cast, and a type to cast it to, which must be a
5426 <a href="#t_pointer">pointer</a> type.</p>
5429 <p>The '<tt>inttoptr</tt>' instruction converts <tt>value</tt> to type
5430 <tt>ty2</tt> by applying either a zero extension or a truncation depending on
5431 the size of the integer <tt>value</tt>. If <tt>value</tt> is larger than the
5432 size of a pointer then a truncation is done. If <tt>value</tt> is smaller
5433 than the size of a pointer then a zero extension is done. If they are the
5434 same size, nothing is done (<i>no-op cast</i>).</p>
5438 %X = inttoptr i32 255 to i32* <i>; yields zero extension on 64-bit architecture</i>
5439 %Y = inttoptr i32 255 to i32* <i>; yields no-op on 32-bit architecture</i>
5440 %Z = inttoptr i64 0 to i32* <i>; yields truncation on 32-bit architecture</i>
5445 <!-- _______________________________________________________________________ -->
5447 <a name="i_bitcast">'<tt>bitcast .. to</tt>' Instruction</a>
5454 <result> = bitcast <ty> <value> to <ty2> <i>; yields ty2</i>
5458 <p>The '<tt>bitcast</tt>' instruction converts <tt>value</tt> to type
5459 <tt>ty2</tt> without changing any bits.</p>
5462 <p>The '<tt>bitcast</tt>' instruction takes a value to cast, which must be a
5463 non-aggregate first class value, and a type to cast it to, which must also be
5464 a non-aggregate <a href="#t_firstclass">first class</a> type. The bit sizes
5465 of <tt>value</tt> and the destination type, <tt>ty2</tt>, must be
5466 identical. If the source type is a pointer, the destination type must also be
5467 a pointer. This instruction supports bitwise conversion of vectors to
5468 integers and to vectors of other types (as long as they have the same
5472 <p>The '<tt>bitcast</tt>' instruction converts <tt>value</tt> to type
5473 <tt>ty2</tt>. It is always a <i>no-op cast</i> because no bits change with
5474 this conversion. The conversion is done as if the <tt>value</tt> had been
5475 stored to memory and read back as type <tt>ty2</tt>. Pointer types may only
5476 be converted to other pointer types with this instruction. To convert
5477 pointers to other types, use the <a href="#i_inttoptr">inttoptr</a> or
5478 <a href="#i_ptrtoint">ptrtoint</a> instructions first.</p>
5482 %X = bitcast i8 255 to i8 <i>; yields i8 :-1</i>
5483 %Y = bitcast i32* %x to sint* <i>; yields sint*:%x</i>
5484 %Z = bitcast <2 x int> %V to i64; <i>; yields i64: %V</i>
5491 <!-- ======================================================================= -->
5493 <a name="otherops">Other Operations</a>
5498 <p>The instructions in this category are the "miscellaneous" instructions, which
5499 defy better classification.</p>
5501 <!-- _______________________________________________________________________ -->
5503 <a name="i_icmp">'<tt>icmp</tt>' Instruction</a>
5510 <result> = icmp <cond> <ty> <op1>, <op2> <i>; yields {i1} or {<N x i1>}:result</i>
5514 <p>The '<tt>icmp</tt>' instruction returns a boolean value or a vector of
5515 boolean values based on comparison of its two integer, integer vector, or
5516 pointer operands.</p>
5519 <p>The '<tt>icmp</tt>' instruction takes three operands. The first operand is
5520 the condition code indicating the kind of comparison to perform. It is not a
5521 value, just a keyword. The possible condition code are:</p>
5524 <li><tt>eq</tt>: equal</li>
5525 <li><tt>ne</tt>: not equal </li>
5526 <li><tt>ugt</tt>: unsigned greater than</li>
5527 <li><tt>uge</tt>: unsigned greater or equal</li>
5528 <li><tt>ult</tt>: unsigned less than</li>
5529 <li><tt>ule</tt>: unsigned less or equal</li>
5530 <li><tt>sgt</tt>: signed greater than</li>
5531 <li><tt>sge</tt>: signed greater or equal</li>
5532 <li><tt>slt</tt>: signed less than</li>
5533 <li><tt>sle</tt>: signed less or equal</li>
5536 <p>The remaining two arguments must be <a href="#t_integer">integer</a> or
5537 <a href="#t_pointer">pointer</a> or integer <a href="#t_vector">vector</a>
5538 typed. They must also be identical types.</p>
5541 <p>The '<tt>icmp</tt>' compares <tt>op1</tt> and <tt>op2</tt> according to the
5542 condition code given as <tt>cond</tt>. The comparison performed always yields
5543 either an <a href="#t_integer"><tt>i1</tt></a> or vector of <tt>i1</tt>
5544 result, as follows:</p>
5547 <li><tt>eq</tt>: yields <tt>true</tt> if the operands are equal,
5548 <tt>false</tt> otherwise. No sign interpretation is necessary or
5551 <li><tt>ne</tt>: yields <tt>true</tt> if the operands are unequal,
5552 <tt>false</tt> otherwise. No sign interpretation is necessary or
5555 <li><tt>ugt</tt>: interprets the operands as unsigned values and yields
5556 <tt>true</tt> if <tt>op1</tt> is greater than <tt>op2</tt>.</li>
5558 <li><tt>uge</tt>: interprets the operands as unsigned values and yields
5559 <tt>true</tt> if <tt>op1</tt> is greater than or equal
5560 to <tt>op2</tt>.</li>
5562 <li><tt>ult</tt>: interprets the operands as unsigned values and yields
5563 <tt>true</tt> if <tt>op1</tt> is less than <tt>op2</tt>.</li>
5565 <li><tt>ule</tt>: interprets the operands as unsigned values and yields
5566 <tt>true</tt> if <tt>op1</tt> is less than or equal to <tt>op2</tt>.</li>
5568 <li><tt>sgt</tt>: interprets the operands as signed values and yields
5569 <tt>true</tt> if <tt>op1</tt> is greater than <tt>op2</tt>.</li>
5571 <li><tt>sge</tt>: interprets the operands as signed values and yields
5572 <tt>true</tt> if <tt>op1</tt> is greater than or equal
5573 to <tt>op2</tt>.</li>
5575 <li><tt>slt</tt>: interprets the operands as signed values and yields
5576 <tt>true</tt> if <tt>op1</tt> is less than <tt>op2</tt>.</li>
5578 <li><tt>sle</tt>: interprets the operands as signed values and yields
5579 <tt>true</tt> if <tt>op1</tt> is less than or equal to <tt>op2</tt>.</li>
5582 <p>If the operands are <a href="#t_pointer">pointer</a> typed, the pointer
5583 values are compared as if they were integers.</p>
5585 <p>If the operands are integer vectors, then they are compared element by
5586 element. The result is an <tt>i1</tt> vector with the same number of elements
5587 as the values being compared. Otherwise, the result is an <tt>i1</tt>.</p>
5591 <result> = icmp eq i32 4, 5 <i>; yields: result=false</i>
5592 <result> = icmp ne float* %X, %X <i>; yields: result=false</i>
5593 <result> = icmp ult i16 4, 5 <i>; yields: result=true</i>
5594 <result> = icmp sgt i16 4, 5 <i>; yields: result=false</i>
5595 <result> = icmp ule i16 -4, 5 <i>; yields: result=false</i>
5596 <result> = icmp sge i16 4, 5 <i>; yields: result=false</i>
5599 <p>Note that the code generator does not yet support vector types with
5600 the <tt>icmp</tt> instruction.</p>
5604 <!-- _______________________________________________________________________ -->
5606 <a name="i_fcmp">'<tt>fcmp</tt>' Instruction</a>
5613 <result> = fcmp <cond> <ty> <op1>, <op2> <i>; yields {i1} or {<N x i1>}:result</i>
5617 <p>The '<tt>fcmp</tt>' instruction returns a boolean value or vector of boolean
5618 values based on comparison of its operands.</p>
5620 <p>If the operands are floating point scalars, then the result type is a boolean
5621 (<a href="#t_integer"><tt>i1</tt></a>).</p>
5623 <p>If the operands are floating point vectors, then the result type is a vector
5624 of boolean with the same number of elements as the operands being
5628 <p>The '<tt>fcmp</tt>' instruction takes three operands. The first operand is
5629 the condition code indicating the kind of comparison to perform. It is not a
5630 value, just a keyword. The possible condition code are:</p>
5633 <li><tt>false</tt>: no comparison, always returns false</li>
5634 <li><tt>oeq</tt>: ordered and equal</li>
5635 <li><tt>ogt</tt>: ordered and greater than </li>
5636 <li><tt>oge</tt>: ordered and greater than or equal</li>
5637 <li><tt>olt</tt>: ordered and less than </li>
5638 <li><tt>ole</tt>: ordered and less than or equal</li>
5639 <li><tt>one</tt>: ordered and not equal</li>
5640 <li><tt>ord</tt>: ordered (no nans)</li>
5641 <li><tt>ueq</tt>: unordered or equal</li>
5642 <li><tt>ugt</tt>: unordered or greater than </li>
5643 <li><tt>uge</tt>: unordered or greater than or equal</li>
5644 <li><tt>ult</tt>: unordered or less than </li>
5645 <li><tt>ule</tt>: unordered or less than or equal</li>
5646 <li><tt>une</tt>: unordered or not equal</li>
5647 <li><tt>uno</tt>: unordered (either nans)</li>
5648 <li><tt>true</tt>: no comparison, always returns true</li>
5651 <p><i>Ordered</i> means that neither operand is a QNAN while
5652 <i>unordered</i> means that either operand may be a QNAN.</p>
5654 <p>Each of <tt>val1</tt> and <tt>val2</tt> arguments must be either
5655 a <a href="#t_floating">floating point</a> type or
5656 a <a href="#t_vector">vector</a> of floating point type. They must have
5657 identical types.</p>
5660 <p>The '<tt>fcmp</tt>' instruction compares <tt>op1</tt> and <tt>op2</tt>
5661 according to the condition code given as <tt>cond</tt>. If the operands are
5662 vectors, then the vectors are compared element by element. Each comparison
5663 performed always yields an <a href="#t_integer">i1</a> result, as
5667 <li><tt>false</tt>: always yields <tt>false</tt>, regardless of operands.</li>
5669 <li><tt>oeq</tt>: yields <tt>true</tt> if both operands are not a QNAN and
5670 <tt>op1</tt> is equal to <tt>op2</tt>.</li>
5672 <li><tt>ogt</tt>: yields <tt>true</tt> if both operands are not a QNAN and
5673 <tt>op1</tt> is greater than <tt>op2</tt>.</li>
5675 <li><tt>oge</tt>: yields <tt>true</tt> if both operands are not a QNAN and
5676 <tt>op1</tt> is greater than or equal to <tt>op2</tt>.</li>
5678 <li><tt>olt</tt>: yields <tt>true</tt> if both operands are not a QNAN and
5679 <tt>op1</tt> is less than <tt>op2</tt>.</li>
5681 <li><tt>ole</tt>: yields <tt>true</tt> if both operands are not a QNAN and
5682 <tt>op1</tt> is less than or equal to <tt>op2</tt>.</li>
5684 <li><tt>one</tt>: yields <tt>true</tt> if both operands are not a QNAN and
5685 <tt>op1</tt> is not equal to <tt>op2</tt>.</li>
5687 <li><tt>ord</tt>: yields <tt>true</tt> if both operands are not a QNAN.</li>
5689 <li><tt>ueq</tt>: yields <tt>true</tt> if either operand is a QNAN or
5690 <tt>op1</tt> is equal to <tt>op2</tt>.</li>
5692 <li><tt>ugt</tt>: yields <tt>true</tt> if either operand is a QNAN or
5693 <tt>op1</tt> is greater than <tt>op2</tt>.</li>
5695 <li><tt>uge</tt>: yields <tt>true</tt> if either operand is a QNAN or
5696 <tt>op1</tt> is greater than or equal to <tt>op2</tt>.</li>
5698 <li><tt>ult</tt>: yields <tt>true</tt> if either operand is a QNAN or
5699 <tt>op1</tt> is less than <tt>op2</tt>.</li>
5701 <li><tt>ule</tt>: yields <tt>true</tt> if either operand is a QNAN or
5702 <tt>op1</tt> is less than or equal to <tt>op2</tt>.</li>
5704 <li><tt>une</tt>: yields <tt>true</tt> if either operand is a QNAN or
5705 <tt>op1</tt> is not equal to <tt>op2</tt>.</li>
5707 <li><tt>uno</tt>: yields <tt>true</tt> if either operand is a QNAN.</li>
5709 <li><tt>true</tt>: always yields <tt>true</tt>, regardless of operands.</li>
5714 <result> = fcmp oeq float 4.0, 5.0 <i>; yields: result=false</i>
5715 <result> = fcmp one float 4.0, 5.0 <i>; yields: result=true</i>
5716 <result> = fcmp olt float 4.0, 5.0 <i>; yields: result=true</i>
5717 <result> = fcmp ueq double 1.0, 2.0 <i>; yields: result=false</i>
5720 <p>Note that the code generator does not yet support vector types with
5721 the <tt>fcmp</tt> instruction.</p>
5725 <!-- _______________________________________________________________________ -->
5727 <a name="i_phi">'<tt>phi</tt>' Instruction</a>
5734 <result> = phi <ty> [ <val0>, <label0>], ...
5738 <p>The '<tt>phi</tt>' instruction is used to implement the φ node in the
5739 SSA graph representing the function.</p>
5742 <p>The type of the incoming values is specified with the first type field. After
5743 this, the '<tt>phi</tt>' instruction takes a list of pairs as arguments, with
5744 one pair for each predecessor basic block of the current block. Only values
5745 of <a href="#t_firstclass">first class</a> type may be used as the value
5746 arguments to the PHI node. Only labels may be used as the label
5749 <p>There must be no non-phi instructions between the start of a basic block and
5750 the PHI instructions: i.e. PHI instructions must be first in a basic
5753 <p>For the purposes of the SSA form, the use of each incoming value is deemed to
5754 occur on the edge from the corresponding predecessor block to the current
5755 block (but after any definition of an '<tt>invoke</tt>' instruction's return
5756 value on the same edge).</p>
5759 <p>At runtime, the '<tt>phi</tt>' instruction logically takes on the value
5760 specified by the pair corresponding to the predecessor basic block that
5761 executed just prior to the current block.</p>
5765 Loop: ; Infinite loop that counts from 0 on up...
5766 %indvar = phi i32 [ 0, %LoopHeader ], [ %nextindvar, %Loop ]
5767 %nextindvar = add i32 %indvar, 1
5773 <!-- _______________________________________________________________________ -->
5775 <a name="i_select">'<tt>select</tt>' Instruction</a>
5782 <result> = select <i>selty</i> <cond>, <ty> <val1>, <ty> <val2> <i>; yields ty</i>
5784 <i>selty</i> is either i1 or {<N x i1>}
5788 <p>The '<tt>select</tt>' instruction is used to choose one value based on a
5789 condition, without branching.</p>
5793 <p>The '<tt>select</tt>' instruction requires an 'i1' value or a vector of 'i1'
5794 values indicating the condition, and two values of the
5795 same <a href="#t_firstclass">first class</a> type. If the val1/val2 are
5796 vectors and the condition is a scalar, then entire vectors are selected, not
5797 individual elements.</p>
5800 <p>If the condition is an i1 and it evaluates to 1, the instruction returns the
5801 first value argument; otherwise, it returns the second value argument.</p>
5803 <p>If the condition is a vector of i1, then the value arguments must be vectors
5804 of the same size, and the selection is done element by element.</p>
5808 %X = select i1 true, i8 17, i8 42 <i>; yields i8:17</i>
5811 <p>Note that the code generator does not yet support conditions
5812 with vector type.</p>
5816 <!-- _______________________________________________________________________ -->
5818 <a name="i_call">'<tt>call</tt>' Instruction</a>
5825 <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>]
5829 <p>The '<tt>call</tt>' instruction represents a simple function call.</p>
5832 <p>This instruction requires several arguments:</p>
5835 <li>The optional "tail" marker indicates that the callee function does not
5836 access any allocas or varargs in the caller. Note that calls may be
5837 marked "tail" even if they do not occur before
5838 a <a href="#i_ret"><tt>ret</tt></a> instruction. If the "tail" marker is
5839 present, the function call is eligible for tail call optimization,
5840 but <a href="CodeGenerator.html#tailcallopt">might not in fact be
5841 optimized into a jump</a>. The code generator may optimize calls marked
5842 "tail" with either 1) automatic <a href="CodeGenerator.html#sibcallopt">
5843 sibling call optimization</a> when the caller and callee have
5844 matching signatures, or 2) forced tail call optimization when the
5845 following extra requirements are met:
5847 <li>Caller and callee both have the calling
5848 convention <tt>fastcc</tt>.</li>
5849 <li>The call is in tail position (ret immediately follows call and ret
5850 uses value of call or is void).</li>
5851 <li>Option <tt>-tailcallopt</tt> is enabled,
5852 or <code>llvm::GuaranteedTailCallOpt</code> is <code>true</code>.</li>
5853 <li><a href="CodeGenerator.html#tailcallopt">Platform specific
5854 constraints are met.</a></li>
5858 <li>The optional "cconv" marker indicates which <a href="#callingconv">calling
5859 convention</a> the call should use. If none is specified, the call
5860 defaults to using C calling conventions. The calling convention of the
5861 call must match the calling convention of the target function, or else the
5862 behavior is undefined.</li>
5864 <li>The optional <a href="#paramattrs">Parameter Attributes</a> list for
5865 return values. Only '<tt>zeroext</tt>', '<tt>signext</tt>', and
5866 '<tt>inreg</tt>' attributes are valid here.</li>
5868 <li>'<tt>ty</tt>': the type of the call instruction itself which is also the
5869 type of the return value. Functions that return no value are marked
5870 <tt><a href="#t_void">void</a></tt>.</li>
5872 <li>'<tt>fnty</tt>': shall be the signature of the pointer to function value
5873 being invoked. The argument types must match the types implied by this
5874 signature. This type can be omitted if the function is not varargs and if
5875 the function type does not return a pointer to a function.</li>
5877 <li>'<tt>fnptrval</tt>': An LLVM value containing a pointer to a function to
5878 be invoked. In most cases, this is a direct function invocation, but
5879 indirect <tt>call</tt>s are just as possible, calling an arbitrary pointer
5880 to function value.</li>
5882 <li>'<tt>function args</tt>': argument list whose types match the function
5883 signature argument types and parameter attributes. All arguments must be
5884 of <a href="#t_firstclass">first class</a> type. If the function
5885 signature indicates the function accepts a variable number of arguments,
5886 the extra arguments can be specified.</li>
5888 <li>The optional <a href="#fnattrs">function attributes</a> list. Only
5889 '<tt>noreturn</tt>', '<tt>nounwind</tt>', '<tt>readonly</tt>' and
5890 '<tt>readnone</tt>' attributes are valid here.</li>
5894 <p>The '<tt>call</tt>' instruction is used to cause control flow to transfer to
5895 a specified function, with its incoming arguments bound to the specified
5896 values. Upon a '<tt><a href="#i_ret">ret</a></tt>' instruction in the called
5897 function, control flow continues with the instruction after the function
5898 call, and the return value of the function is bound to the result
5903 %retval = call i32 @test(i32 %argc)
5904 call i32 (i8*, ...)* @printf(i8* %msg, i32 12, i8 42) <i>; yields i32</i>
5905 %X = tail call i32 @foo() <i>; yields i32</i>
5906 %Y = tail call <a href="#callingconv">fastcc</a> i32 @foo() <i>; yields i32</i>
5907 call void %foo(i8 97 signext)
5909 %struct.A = type { i32, i8 }
5910 %r = call %struct.A @foo() <i>; yields { 32, i8 }</i>
5911 %gr = extractvalue %struct.A %r, 0 <i>; yields i32</i>
5912 %gr1 = extractvalue %struct.A %r, 1 <i>; yields i8</i>
5913 %Z = call void @foo() noreturn <i>; indicates that %foo never returns normally</i>
5914 %ZZ = call zeroext i32 @bar() <i>; Return value is %zero extended</i>
5917 <p>llvm treats calls to some functions with names and arguments that match the
5918 standard C99 library as being the C99 library functions, and may perform
5919 optimizations or generate code for them under that assumption. This is
5920 something we'd like to change in the future to provide better support for
5921 freestanding environments and non-C-based languages.</p>
5925 <!-- _______________________________________________________________________ -->
5927 <a name="i_va_arg">'<tt>va_arg</tt>' Instruction</a>
5934 <resultval> = va_arg <va_list*> <arglist>, <argty>
5938 <p>The '<tt>va_arg</tt>' instruction is used to access arguments passed through
5939 the "variable argument" area of a function call. It is used to implement the
5940 <tt>va_arg</tt> macro in C.</p>
5943 <p>This instruction takes a <tt>va_list*</tt> value and the type of the
5944 argument. It returns a value of the specified argument type and increments
5945 the <tt>va_list</tt> to point to the next argument. The actual type
5946 of <tt>va_list</tt> is target specific.</p>
5949 <p>The '<tt>va_arg</tt>' instruction loads an argument of the specified type
5950 from the specified <tt>va_list</tt> and causes the <tt>va_list</tt> to point
5951 to the next argument. For more information, see the variable argument
5952 handling <a href="#int_varargs">Intrinsic Functions</a>.</p>
5954 <p>It is legal for this instruction to be called in a function which does not
5955 take a variable number of arguments, for example, the <tt>vfprintf</tt>
5958 <p><tt>va_arg</tt> is an LLVM instruction instead of
5959 an <a href="#intrinsics">intrinsic function</a> because it takes a type as an
5963 <p>See the <a href="#int_varargs">variable argument processing</a> section.</p>
5965 <p>Note that the code generator does not yet fully support va_arg on many
5966 targets. Also, it does not currently support va_arg with aggregate types on
5975 <!-- *********************************************************************** -->
5976 <h2><a name="intrinsics">Intrinsic Functions</a></h2>
5977 <!-- *********************************************************************** -->
5981 <p>LLVM supports the notion of an "intrinsic function". These functions have
5982 well known names and semantics and are required to follow certain
5983 restrictions. Overall, these intrinsics represent an extension mechanism for
5984 the LLVM language that does not require changing all of the transformations
5985 in LLVM when adding to the language (or the bitcode reader/writer, the
5986 parser, etc...).</p>
5988 <p>Intrinsic function names must all start with an "<tt>llvm.</tt>" prefix. This
5989 prefix is reserved in LLVM for intrinsic names; thus, function names may not
5990 begin with this prefix. Intrinsic functions must always be external
5991 functions: you cannot define the body of intrinsic functions. Intrinsic
5992 functions may only be used in call or invoke instructions: it is illegal to
5993 take the address of an intrinsic function. Additionally, because intrinsic
5994 functions are part of the LLVM language, it is required if any are added that
5995 they be documented here.</p>
5997 <p>Some intrinsic functions can be overloaded, i.e., the intrinsic represents a
5998 family of functions that perform the same operation but on different data
5999 types. Because LLVM can represent over 8 million different integer types,
6000 overloading is used commonly to allow an intrinsic function to operate on any
6001 integer type. One or more of the argument types or the result type can be
6002 overloaded to accept any integer type. Argument types may also be defined as
6003 exactly matching a previous argument's type or the result type. This allows
6004 an intrinsic function which accepts multiple arguments, but needs all of them
6005 to be of the same type, to only be overloaded with respect to a single
6006 argument or the result.</p>
6008 <p>Overloaded intrinsics will have the names of its overloaded argument types
6009 encoded into its function name, each preceded by a period. Only those types
6010 which are overloaded result in a name suffix. Arguments whose type is matched
6011 against another type do not. For example, the <tt>llvm.ctpop</tt> function
6012 can take an integer of any width and returns an integer of exactly the same
6013 integer width. This leads to a family of functions such as
6014 <tt>i8 @llvm.ctpop.i8(i8 %val)</tt> and <tt>i29 @llvm.ctpop.i29(i29
6015 %val)</tt>. Only one type, the return type, is overloaded, and only one type
6016 suffix is required. Because the argument's type is matched against the return
6017 type, it does not require its own name suffix.</p>
6019 <p>To learn how to add an intrinsic function, please see the
6020 <a href="ExtendingLLVM.html">Extending LLVM Guide</a>.</p>
6022 <!-- ======================================================================= -->
6024 <a name="int_varargs">Variable Argument Handling Intrinsics</a>
6029 <p>Variable argument support is defined in LLVM with
6030 the <a href="#i_va_arg"><tt>va_arg</tt></a> instruction and these three
6031 intrinsic functions. These functions are related to the similarly named
6032 macros defined in the <tt><stdarg.h></tt> header file.</p>
6034 <p>All of these functions operate on arguments that use a target-specific value
6035 type "<tt>va_list</tt>". The LLVM assembly language reference manual does
6036 not define what this type is, so all transformations should be prepared to
6037 handle these functions regardless of the type used.</p>
6039 <p>This example shows how the <a href="#i_va_arg"><tt>va_arg</tt></a>
6040 instruction and the variable argument handling intrinsic functions are
6043 <pre class="doc_code">
6044 define i32 @test(i32 %X, ...) {
6045 ; Initialize variable argument processing
6047 %ap2 = bitcast i8** %ap to i8*
6048 call void @llvm.va_start(i8* %ap2)
6050 ; Read a single integer argument
6051 %tmp = va_arg i8** %ap, i32
6053 ; Demonstrate usage of llvm.va_copy and llvm.va_end
6055 %aq2 = bitcast i8** %aq to i8*
6056 call void @llvm.va_copy(i8* %aq2, i8* %ap2)
6057 call void @llvm.va_end(i8* %aq2)
6059 ; Stop processing of arguments.
6060 call void @llvm.va_end(i8* %ap2)
6064 declare void @llvm.va_start(i8*)
6065 declare void @llvm.va_copy(i8*, i8*)
6066 declare void @llvm.va_end(i8*)
6069 <!-- _______________________________________________________________________ -->
6071 <a name="int_va_start">'<tt>llvm.va_start</tt>' Intrinsic</a>
6079 declare void %llvm.va_start(i8* <arglist>)
6083 <p>The '<tt>llvm.va_start</tt>' intrinsic initializes <tt>*<arglist></tt>
6084 for subsequent use by <tt><a href="#i_va_arg">va_arg</a></tt>.</p>
6087 <p>The argument is a pointer to a <tt>va_list</tt> element to initialize.</p>
6090 <p>The '<tt>llvm.va_start</tt>' intrinsic works just like the <tt>va_start</tt>
6091 macro available in C. In a target-dependent way, it initializes
6092 the <tt>va_list</tt> element to which the argument points, so that the next
6093 call to <tt>va_arg</tt> will produce the first variable argument passed to
6094 the function. Unlike the C <tt>va_start</tt> macro, this intrinsic does not
6095 need to know the last argument of the function as the compiler can figure
6100 <!-- _______________________________________________________________________ -->
6102 <a name="int_va_end">'<tt>llvm.va_end</tt>' Intrinsic</a>
6109 declare void @llvm.va_end(i8* <arglist>)
6113 <p>The '<tt>llvm.va_end</tt>' intrinsic destroys <tt>*<arglist></tt>,
6114 which has been initialized previously
6115 with <tt><a href="#int_va_start">llvm.va_start</a></tt>
6116 or <tt><a href="#i_va_copy">llvm.va_copy</a></tt>.</p>
6119 <p>The argument is a pointer to a <tt>va_list</tt> to destroy.</p>
6122 <p>The '<tt>llvm.va_end</tt>' intrinsic works just like the <tt>va_end</tt>
6123 macro available in C. In a target-dependent way, it destroys
6124 the <tt>va_list</tt> element to which the argument points. Calls
6125 to <a href="#int_va_start"><tt>llvm.va_start</tt></a>
6126 and <a href="#int_va_copy"> <tt>llvm.va_copy</tt></a> must be matched exactly
6127 with calls to <tt>llvm.va_end</tt>.</p>
6131 <!-- _______________________________________________________________________ -->
6133 <a name="int_va_copy">'<tt>llvm.va_copy</tt>' Intrinsic</a>
6140 declare void @llvm.va_copy(i8* <destarglist>, i8* <srcarglist>)
6144 <p>The '<tt>llvm.va_copy</tt>' intrinsic copies the current argument position
6145 from the source argument list to the destination argument list.</p>
6148 <p>The first argument is a pointer to a <tt>va_list</tt> element to initialize.
6149 The second argument is a pointer to a <tt>va_list</tt> element to copy
6153 <p>The '<tt>llvm.va_copy</tt>' intrinsic works just like the <tt>va_copy</tt>
6154 macro available in C. In a target-dependent way, it copies the
6155 source <tt>va_list</tt> element into the destination <tt>va_list</tt>
6156 element. This intrinsic is necessary because
6157 the <tt><a href="#int_va_start"> llvm.va_start</a></tt> intrinsic may be
6158 arbitrarily complex and require, for example, memory allocation.</p>
6166 <!-- ======================================================================= -->
6168 <a name="int_gc">Accurate Garbage Collection Intrinsics</a>
6173 <p>LLVM support for <a href="GarbageCollection.html">Accurate Garbage
6174 Collection</a> (GC) requires the implementation and generation of these
6175 intrinsics. These intrinsics allow identification of <a href="#int_gcroot">GC
6176 roots on the stack</a>, as well as garbage collector implementations that
6177 require <a href="#int_gcread">read</a> and <a href="#int_gcwrite">write</a>
6178 barriers. Front-ends for type-safe garbage collected languages should generate
6179 these intrinsics to make use of the LLVM garbage collectors. For more details,
6180 see <a href="GarbageCollection.html">Accurate Garbage Collection with
6183 <p>The garbage collection intrinsics only operate on objects in the generic
6184 address space (address space zero).</p>
6186 <!-- _______________________________________________________________________ -->
6188 <a name="int_gcroot">'<tt>llvm.gcroot</tt>' Intrinsic</a>
6195 declare void @llvm.gcroot(i8** %ptrloc, i8* %metadata)
6199 <p>The '<tt>llvm.gcroot</tt>' intrinsic declares the existence of a GC root to
6200 the code generator, and allows some metadata to be associated with it.</p>
6203 <p>The first argument specifies the address of a stack object that contains the
6204 root pointer. The second pointer (which must be either a constant or a
6205 global value address) contains the meta-data to be associated with the
6209 <p>At runtime, a call to this intrinsic stores a null pointer into the "ptrloc"
6210 location. At compile-time, the code generator generates information to allow
6211 the runtime to find the pointer at GC safe points. The '<tt>llvm.gcroot</tt>'
6212 intrinsic may only be used in a function which <a href="#gc">specifies a GC
6217 <!-- _______________________________________________________________________ -->
6219 <a name="int_gcread">'<tt>llvm.gcread</tt>' Intrinsic</a>
6226 declare i8* @llvm.gcread(i8* %ObjPtr, i8** %Ptr)
6230 <p>The '<tt>llvm.gcread</tt>' intrinsic identifies reads of references from heap
6231 locations, allowing garbage collector implementations that require read
6235 <p>The second argument is the address to read from, which should be an address
6236 allocated from the garbage collector. The first object is a pointer to the
6237 start of the referenced object, if needed by the language runtime (otherwise
6241 <p>The '<tt>llvm.gcread</tt>' intrinsic has the same semantics as a load
6242 instruction, but may be replaced with substantially more complex code by the
6243 garbage collector runtime, as needed. The '<tt>llvm.gcread</tt>' intrinsic
6244 may only be used in a function which <a href="#gc">specifies a GC
6249 <!-- _______________________________________________________________________ -->
6251 <a name="int_gcwrite">'<tt>llvm.gcwrite</tt>' Intrinsic</a>
6258 declare void @llvm.gcwrite(i8* %P1, i8* %Obj, i8** %P2)
6262 <p>The '<tt>llvm.gcwrite</tt>' intrinsic identifies writes of references to heap
6263 locations, allowing garbage collector implementations that require write
6264 barriers (such as generational or reference counting collectors).</p>
6267 <p>The first argument is the reference to store, the second is the start of the
6268 object to store it to, and the third is the address of the field of Obj to
6269 store to. If the runtime does not require a pointer to the object, Obj may
6273 <p>The '<tt>llvm.gcwrite</tt>' intrinsic has the same semantics as a store
6274 instruction, but may be replaced with substantially more complex code by the
6275 garbage collector runtime, as needed. The '<tt>llvm.gcwrite</tt>' intrinsic
6276 may only be used in a function which <a href="#gc">specifies a GC
6283 <!-- ======================================================================= -->
6285 <a name="int_codegen">Code Generator Intrinsics</a>
6290 <p>These intrinsics are provided by LLVM to expose special features that may
6291 only be implemented with code generator support.</p>
6293 <!-- _______________________________________________________________________ -->
6295 <a name="int_returnaddress">'<tt>llvm.returnaddress</tt>' Intrinsic</a>
6302 declare i8 *@llvm.returnaddress(i32 <level>)
6306 <p>The '<tt>llvm.returnaddress</tt>' intrinsic attempts to compute a
6307 target-specific value indicating the return address of the current function
6308 or one of its callers.</p>
6311 <p>The argument to this intrinsic indicates which function to return the address
6312 for. Zero indicates the calling function, one indicates its caller, etc.
6313 The argument is <b>required</b> to be a constant integer value.</p>
6316 <p>The '<tt>llvm.returnaddress</tt>' intrinsic either returns a pointer
6317 indicating the return address of the specified call frame, or zero if it
6318 cannot be identified. The value returned by this intrinsic is likely to be
6319 incorrect or 0 for arguments other than zero, so it should only be used for
6320 debugging purposes.</p>
6322 <p>Note that calling this intrinsic does not prevent function inlining or other
6323 aggressive transformations, so the value returned may not be that of the
6324 obvious source-language caller.</p>
6328 <!-- _______________________________________________________________________ -->
6330 <a name="int_frameaddress">'<tt>llvm.frameaddress</tt>' Intrinsic</a>
6337 declare i8* @llvm.frameaddress(i32 <level>)
6341 <p>The '<tt>llvm.frameaddress</tt>' intrinsic attempts to return the
6342 target-specific frame pointer value for the specified stack frame.</p>
6345 <p>The argument to this intrinsic indicates which function to return the frame
6346 pointer for. Zero indicates the calling function, one indicates its caller,
6347 etc. The argument is <b>required</b> to be a constant integer value.</p>
6350 <p>The '<tt>llvm.frameaddress</tt>' intrinsic either returns a pointer
6351 indicating the frame address of the specified call frame, or zero if it
6352 cannot be identified. The value returned by this intrinsic is likely to be
6353 incorrect or 0 for arguments other than zero, so it should only be used for
6354 debugging purposes.</p>
6356 <p>Note that calling this intrinsic does not prevent function inlining or other
6357 aggressive transformations, so the value returned may not be that of the
6358 obvious source-language caller.</p>
6362 <!-- _______________________________________________________________________ -->
6364 <a name="int_stacksave">'<tt>llvm.stacksave</tt>' Intrinsic</a>
6371 declare i8* @llvm.stacksave()
6375 <p>The '<tt>llvm.stacksave</tt>' intrinsic is used to remember the current state
6376 of the function stack, for use
6377 with <a href="#int_stackrestore"> <tt>llvm.stackrestore</tt></a>. This is
6378 useful for implementing language features like scoped automatic variable
6379 sized arrays in C99.</p>
6382 <p>This intrinsic returns a opaque pointer value that can be passed
6383 to <a href="#int_stackrestore"><tt>llvm.stackrestore</tt></a>. When
6384 an <tt>llvm.stackrestore</tt> intrinsic is executed with a value saved
6385 from <tt>llvm.stacksave</tt>, it effectively restores the state of the stack
6386 to the state it was in when the <tt>llvm.stacksave</tt> intrinsic executed.
6387 In practice, this pops any <a href="#i_alloca">alloca</a> blocks from the
6388 stack that were allocated after the <tt>llvm.stacksave</tt> was executed.</p>
6392 <!-- _______________________________________________________________________ -->
6394 <a name="int_stackrestore">'<tt>llvm.stackrestore</tt>' Intrinsic</a>
6401 declare void @llvm.stackrestore(i8* %ptr)
6405 <p>The '<tt>llvm.stackrestore</tt>' intrinsic is used to restore the state of
6406 the function stack to the state it was in when the
6407 corresponding <a href="#int_stacksave"><tt>llvm.stacksave</tt></a> intrinsic
6408 executed. This is useful for implementing language features like scoped
6409 automatic variable sized arrays in C99.</p>
6412 <p>See the description
6413 for <a href="#int_stacksave"><tt>llvm.stacksave</tt></a>.</p>
6417 <!-- _______________________________________________________________________ -->
6419 <a name="int_prefetch">'<tt>llvm.prefetch</tt>' Intrinsic</a>
6426 declare void @llvm.prefetch(i8* <address>, i32 <rw>, i32 <locality>, i32 <cache type>)
6430 <p>The '<tt>llvm.prefetch</tt>' intrinsic is a hint to the code generator to
6431 insert a prefetch instruction if supported; otherwise, it is a noop.
6432 Prefetches have no effect on the behavior of the program but can change its
6433 performance characteristics.</p>
6436 <p><tt>address</tt> is the address to be prefetched, <tt>rw</tt> is the
6437 specifier determining if the fetch should be for a read (0) or write (1),
6438 and <tt>locality</tt> is a temporal locality specifier ranging from (0) - no
6439 locality, to (3) - extremely local keep in cache. The <tt>cache type</tt>
6440 specifies whether the prefetch is performed on the data (1) or instruction (0)
6441 cache. The <tt>rw</tt>, <tt>locality</tt> and <tt>cache type</tt> arguments
6442 must be constant integers.</p>
6445 <p>This intrinsic does not modify the behavior of the program. In particular,
6446 prefetches cannot trap and do not produce a value. On targets that support
6447 this intrinsic, the prefetch can provide hints to the processor cache for
6448 better performance.</p>
6452 <!-- _______________________________________________________________________ -->
6454 <a name="int_pcmarker">'<tt>llvm.pcmarker</tt>' Intrinsic</a>
6461 declare void @llvm.pcmarker(i32 <id>)
6465 <p>The '<tt>llvm.pcmarker</tt>' intrinsic is a method to export a Program
6466 Counter (PC) in a region of code to simulators and other tools. The method
6467 is target specific, but it is expected that the marker will use exported
6468 symbols to transmit the PC of the marker. The marker makes no guarantees
6469 that it will remain with any specific instruction after optimizations. It is
6470 possible that the presence of a marker will inhibit optimizations. The
6471 intended use is to be inserted after optimizations to allow correlations of
6472 simulation runs.</p>
6475 <p><tt>id</tt> is a numerical id identifying the marker.</p>
6478 <p>This intrinsic does not modify the behavior of the program. Backends that do
6479 not support this intrinsic may ignore it.</p>
6483 <!-- _______________________________________________________________________ -->
6485 <a name="int_readcyclecounter">'<tt>llvm.readcyclecounter</tt>' Intrinsic</a>
6492 declare i64 @llvm.readcyclecounter()
6496 <p>The '<tt>llvm.readcyclecounter</tt>' intrinsic provides access to the cycle
6497 counter register (or similar low latency, high accuracy clocks) on those
6498 targets that support it. On X86, it should map to RDTSC. On Alpha, it
6499 should map to RPCC. As the backing counters overflow quickly (on the order
6500 of 9 seconds on alpha), this should only be used for small timings.</p>
6503 <p>When directly supported, reading the cycle counter should not modify any
6504 memory. Implementations are allowed to either return a application specific
6505 value or a system wide value. On backends without support, this is lowered
6506 to a constant 0.</p>
6512 <!-- ======================================================================= -->
6514 <a name="int_libc">Standard C Library Intrinsics</a>
6519 <p>LLVM provides intrinsics for a few important standard C library functions.
6520 These intrinsics allow source-language front-ends to pass information about
6521 the alignment of the pointer arguments to the code generator, providing
6522 opportunity for more efficient code generation.</p>
6524 <!-- _______________________________________________________________________ -->
6526 <a name="int_memcpy">'<tt>llvm.memcpy</tt>' Intrinsic</a>
6532 <p>This is an overloaded intrinsic. You can use <tt>llvm.memcpy</tt> on any
6533 integer bit width and for different address spaces. Not all targets support
6534 all bit widths however.</p>
6537 declare void @llvm.memcpy.p0i8.p0i8.i32(i8* <dest>, i8* <src>,
6538 i32 <len>, i32 <align>, i1 <isvolatile>)
6539 declare void @llvm.memcpy.p0i8.p0i8.i64(i8* <dest>, i8* <src>,
6540 i64 <len>, i32 <align>, i1 <isvolatile>)
6544 <p>The '<tt>llvm.memcpy.*</tt>' intrinsics copy a block of memory from the
6545 source location to the destination location.</p>
6547 <p>Note that, unlike the standard libc function, the <tt>llvm.memcpy.*</tt>
6548 intrinsics do not return a value, takes extra alignment/isvolatile arguments
6549 and the pointers can be in specified address spaces.</p>
6553 <p>The first argument is a pointer to the destination, the second is a pointer
6554 to the source. The third argument is an integer argument specifying the
6555 number of bytes to copy, the fourth argument is the alignment of the
6556 source and destination locations, and the fifth is a boolean indicating a
6557 volatile access.</p>
6559 <p>If the call to this intrinsic has an alignment value that is not 0 or 1,
6560 then the caller guarantees that both the source and destination pointers are
6561 aligned to that boundary.</p>
6563 <p>If the <tt>isvolatile</tt> parameter is <tt>true</tt>, the
6564 <tt>llvm.memcpy</tt> call is a <a href="#volatile">volatile operation</a>.
6565 The detailed access behavior is not very cleanly specified and it is unwise
6566 to depend on it.</p>
6570 <p>The '<tt>llvm.memcpy.*</tt>' intrinsics copy a block of memory from the
6571 source location to the destination location, which are not allowed to
6572 overlap. It copies "len" bytes of memory over. If the argument is known to
6573 be aligned to some boundary, this can be specified as the fourth argument,
6574 otherwise it should be set to 0 or 1.</p>
6578 <!-- _______________________________________________________________________ -->
6580 <a name="int_memmove">'<tt>llvm.memmove</tt>' Intrinsic</a>
6586 <p>This is an overloaded intrinsic. You can use llvm.memmove on any integer bit
6587 width and for different address space. Not all targets support all bit
6591 declare void @llvm.memmove.p0i8.p0i8.i32(i8* <dest>, i8* <src>,
6592 i32 <len>, i32 <align>, i1 <isvolatile>)
6593 declare void @llvm.memmove.p0i8.p0i8.i64(i8* <dest>, i8* <src>,
6594 i64 <len>, i32 <align>, i1 <isvolatile>)
6598 <p>The '<tt>llvm.memmove.*</tt>' intrinsics move a block of memory from the
6599 source location to the destination location. It is similar to the
6600 '<tt>llvm.memcpy</tt>' intrinsic but allows the two memory locations to
6603 <p>Note that, unlike the standard libc function, the <tt>llvm.memmove.*</tt>
6604 intrinsics do not return a value, takes extra alignment/isvolatile arguments
6605 and the pointers can be in specified address spaces.</p>
6609 <p>The first argument is a pointer to the destination, the second is a pointer
6610 to the source. The third argument is an integer argument specifying the
6611 number of bytes to copy, the fourth argument is the alignment of the
6612 source and destination locations, and the fifth is a boolean indicating a
6613 volatile access.</p>
6615 <p>If the call to this intrinsic has an alignment value that is not 0 or 1,
6616 then the caller guarantees that the source and destination pointers are
6617 aligned to that boundary.</p>
6619 <p>If the <tt>isvolatile</tt> parameter is <tt>true</tt>, the
6620 <tt>llvm.memmove</tt> call is a <a href="#volatile">volatile operation</a>.
6621 The detailed access behavior is not very cleanly specified and it is unwise
6622 to depend on it.</p>
6626 <p>The '<tt>llvm.memmove.*</tt>' intrinsics copy a block of memory from the
6627 source location to the destination location, which may overlap. It copies
6628 "len" bytes of memory over. If the argument is known to be aligned to some
6629 boundary, this can be specified as the fourth argument, otherwise it should
6630 be set to 0 or 1.</p>
6634 <!-- _______________________________________________________________________ -->
6636 <a name="int_memset">'<tt>llvm.memset.*</tt>' Intrinsics</a>
6642 <p>This is an overloaded intrinsic. You can use llvm.memset on any integer bit
6643 width and for different address spaces. However, not all targets support all
6647 declare void @llvm.memset.p0i8.i32(i8* <dest>, i8 <val>,
6648 i32 <len>, i32 <align>, i1 <isvolatile>)
6649 declare void @llvm.memset.p0i8.i64(i8* <dest>, i8 <val>,
6650 i64 <len>, i32 <align>, i1 <isvolatile>)
6654 <p>The '<tt>llvm.memset.*</tt>' intrinsics fill a block of memory with a
6655 particular byte value.</p>
6657 <p>Note that, unlike the standard libc function, the <tt>llvm.memset</tt>
6658 intrinsic does not return a value and takes extra alignment/volatile
6659 arguments. Also, the destination can be in an arbitrary address space.</p>
6662 <p>The first argument is a pointer to the destination to fill, the second is the
6663 byte value with which to fill it, the third argument is an integer argument
6664 specifying the number of bytes to fill, and the fourth argument is the known
6665 alignment of the destination location.</p>
6667 <p>If the call to this intrinsic has an alignment value that is not 0 or 1,
6668 then the caller guarantees that the destination pointer is aligned to that
6671 <p>If the <tt>isvolatile</tt> parameter is <tt>true</tt>, the
6672 <tt>llvm.memset</tt> call is a <a href="#volatile">volatile operation</a>.
6673 The detailed access behavior is not very cleanly specified and it is unwise
6674 to depend on it.</p>
6677 <p>The '<tt>llvm.memset.*</tt>' intrinsics fill "len" bytes of memory starting
6678 at the destination location. If the argument is known to be aligned to some
6679 boundary, this can be specified as the fourth argument, otherwise it should
6680 be set to 0 or 1.</p>
6684 <!-- _______________________________________________________________________ -->
6686 <a name="int_sqrt">'<tt>llvm.sqrt.*</tt>' Intrinsic</a>
6692 <p>This is an overloaded intrinsic. You can use <tt>llvm.sqrt</tt> on any
6693 floating point or vector of floating point type. Not all targets support all
6697 declare float @llvm.sqrt.f32(float %Val)
6698 declare double @llvm.sqrt.f64(double %Val)
6699 declare x86_fp80 @llvm.sqrt.f80(x86_fp80 %Val)
6700 declare fp128 @llvm.sqrt.f128(fp128 %Val)
6701 declare ppc_fp128 @llvm.sqrt.ppcf128(ppc_fp128 %Val)
6705 <p>The '<tt>llvm.sqrt</tt>' intrinsics return the sqrt of the specified operand,
6706 returning the same value as the libm '<tt>sqrt</tt>' functions would.
6707 Unlike <tt>sqrt</tt> in libm, however, <tt>llvm.sqrt</tt> has undefined
6708 behavior for negative numbers other than -0.0 (which allows for better
6709 optimization, because there is no need to worry about errno being
6710 set). <tt>llvm.sqrt(-0.0)</tt> is defined to return -0.0 like IEEE sqrt.</p>
6713 <p>The argument and return value are floating point numbers of the same
6717 <p>This function returns the sqrt of the specified operand if it is a
6718 nonnegative floating point number.</p>
6722 <!-- _______________________________________________________________________ -->
6724 <a name="int_powi">'<tt>llvm.powi.*</tt>' Intrinsic</a>
6730 <p>This is an overloaded intrinsic. You can use <tt>llvm.powi</tt> on any
6731 floating point or vector of floating point type. Not all targets support all
6735 declare float @llvm.powi.f32(float %Val, i32 %power)
6736 declare double @llvm.powi.f64(double %Val, i32 %power)
6737 declare x86_fp80 @llvm.powi.f80(x86_fp80 %Val, i32 %power)
6738 declare fp128 @llvm.powi.f128(fp128 %Val, i32 %power)
6739 declare ppc_fp128 @llvm.powi.ppcf128(ppc_fp128 %Val, i32 %power)
6743 <p>The '<tt>llvm.powi.*</tt>' intrinsics return the first operand raised to the
6744 specified (positive or negative) power. The order of evaluation of
6745 multiplications is not defined. When a vector of floating point type is
6746 used, the second argument remains a scalar integer value.</p>
6749 <p>The second argument is an integer power, and the first is a value to raise to
6753 <p>This function returns the first value raised to the second power with an
6754 unspecified sequence of rounding operations.</p>
6758 <!-- _______________________________________________________________________ -->
6760 <a name="int_sin">'<tt>llvm.sin.*</tt>' Intrinsic</a>
6766 <p>This is an overloaded intrinsic. You can use <tt>llvm.sin</tt> on any
6767 floating point or vector of floating point type. Not all targets support all
6771 declare float @llvm.sin.f32(float %Val)
6772 declare double @llvm.sin.f64(double %Val)
6773 declare x86_fp80 @llvm.sin.f80(x86_fp80 %Val)
6774 declare fp128 @llvm.sin.f128(fp128 %Val)
6775 declare ppc_fp128 @llvm.sin.ppcf128(ppc_fp128 %Val)
6779 <p>The '<tt>llvm.sin.*</tt>' intrinsics return the sine of the operand.</p>
6782 <p>The argument and return value are floating point numbers of the same
6786 <p>This function returns the sine of the specified operand, returning the same
6787 values as the libm <tt>sin</tt> functions would, and handles error conditions
6788 in the same way.</p>
6792 <!-- _______________________________________________________________________ -->
6794 <a name="int_cos">'<tt>llvm.cos.*</tt>' Intrinsic</a>
6800 <p>This is an overloaded intrinsic. You can use <tt>llvm.cos</tt> on any
6801 floating point or vector of floating point type. Not all targets support all
6805 declare float @llvm.cos.f32(float %Val)
6806 declare double @llvm.cos.f64(double %Val)
6807 declare x86_fp80 @llvm.cos.f80(x86_fp80 %Val)
6808 declare fp128 @llvm.cos.f128(fp128 %Val)
6809 declare ppc_fp128 @llvm.cos.ppcf128(ppc_fp128 %Val)
6813 <p>The '<tt>llvm.cos.*</tt>' intrinsics return the cosine of the operand.</p>
6816 <p>The argument and return value are floating point numbers of the same
6820 <p>This function returns the cosine of the specified operand, returning the same
6821 values as the libm <tt>cos</tt> functions would, and handles error conditions
6822 in the same way.</p>
6826 <!-- _______________________________________________________________________ -->
6828 <a name="int_pow">'<tt>llvm.pow.*</tt>' Intrinsic</a>
6834 <p>This is an overloaded intrinsic. You can use <tt>llvm.pow</tt> on any
6835 floating point or vector of floating point type. Not all targets support all
6839 declare float @llvm.pow.f32(float %Val, float %Power)
6840 declare double @llvm.pow.f64(double %Val, double %Power)
6841 declare x86_fp80 @llvm.pow.f80(x86_fp80 %Val, x86_fp80 %Power)
6842 declare fp128 @llvm.pow.f128(fp128 %Val, fp128 %Power)
6843 declare ppc_fp128 @llvm.pow.ppcf128(ppc_fp128 %Val, ppc_fp128 Power)
6847 <p>The '<tt>llvm.pow.*</tt>' intrinsics return the first operand raised to the
6848 specified (positive or negative) power.</p>
6851 <p>The second argument is a floating point power, and the first is a value to
6852 raise to that power.</p>
6855 <p>This function returns the first value raised to the second power, returning
6856 the same values as the libm <tt>pow</tt> functions would, and handles error
6857 conditions in the same way.</p>
6863 <!-- _______________________________________________________________________ -->
6865 <a name="int_exp">'<tt>llvm.exp.*</tt>' Intrinsic</a>
6871 <p>This is an overloaded intrinsic. You can use <tt>llvm.exp</tt> on any
6872 floating point or vector of floating point type. Not all targets support all
6876 declare float @llvm.exp.f32(float %Val)
6877 declare double @llvm.exp.f64(double %Val)
6878 declare x86_fp80 @llvm.exp.f80(x86_fp80 %Val)
6879 declare fp128 @llvm.exp.f128(fp128 %Val)
6880 declare ppc_fp128 @llvm.exp.ppcf128(ppc_fp128 %Val)
6884 <p>The '<tt>llvm.exp.*</tt>' intrinsics perform the exp function.</p>
6887 <p>The argument and return value are floating point numbers of the same
6891 <p>This function returns the same values as the libm <tt>exp</tt> functions
6892 would, and handles error conditions in the same way.</p>
6896 <!-- _______________________________________________________________________ -->
6898 <a name="int_log">'<tt>llvm.log.*</tt>' Intrinsic</a>
6904 <p>This is an overloaded intrinsic. You can use <tt>llvm.log</tt> on any
6905 floating point or vector of floating point type. Not all targets support all
6909 declare float @llvm.log.f32(float %Val)
6910 declare double @llvm.log.f64(double %Val)
6911 declare x86_fp80 @llvm.log.f80(x86_fp80 %Val)
6912 declare fp128 @llvm.log.f128(fp128 %Val)
6913 declare ppc_fp128 @llvm.log.ppcf128(ppc_fp128 %Val)
6917 <p>The '<tt>llvm.log.*</tt>' intrinsics perform the log function.</p>
6920 <p>The argument and return value are floating point numbers of the same
6924 <p>This function returns the same values as the libm <tt>log</tt> functions
6925 would, and handles error conditions in the same way.</p>
6928 <a name="int_fma">'<tt>llvm.fma.*</tt>' Intrinsic</a>
6934 <p>This is an overloaded intrinsic. You can use <tt>llvm.fma</tt> on any
6935 floating point or vector of floating point type. Not all targets support all
6939 declare float @llvm.fma.f32(float %a, float %b, float %c)
6940 declare double @llvm.fma.f64(double %a, double %b, double %c)
6941 declare x86_fp80 @llvm.fma.f80(x86_fp80 %a, x86_fp80 %b, x86_fp80 %c)
6942 declare fp128 @llvm.fma.f128(fp128 %a, fp128 %b, fp128 %c)
6943 declare ppc_fp128 @llvm.fma.ppcf128(ppc_fp128 %a, ppc_fp128 %b, ppc_fp128 %c)
6947 <p>The '<tt>llvm.fma.*</tt>' intrinsics perform the fused multiply-add
6951 <p>The argument and return value are floating point numbers of the same
6955 <p>This function returns the same values as the libm <tt>fma</tt> functions
6960 <!-- ======================================================================= -->
6962 <a name="int_manip">Bit Manipulation Intrinsics</a>
6967 <p>LLVM provides intrinsics for a few important bit manipulation operations.
6968 These allow efficient code generation for some algorithms.</p>
6970 <!-- _______________________________________________________________________ -->
6972 <a name="int_bswap">'<tt>llvm.bswap.*</tt>' Intrinsics</a>
6978 <p>This is an overloaded intrinsic function. You can use bswap on any integer
6979 type that is an even number of bytes (i.e. BitWidth % 16 == 0).</p>
6982 declare i16 @llvm.bswap.i16(i16 <id>)
6983 declare i32 @llvm.bswap.i32(i32 <id>)
6984 declare i64 @llvm.bswap.i64(i64 <id>)
6988 <p>The '<tt>llvm.bswap</tt>' family of intrinsics is used to byte swap integer
6989 values with an even number of bytes (positive multiple of 16 bits). These
6990 are useful for performing operations on data that is not in the target's
6991 native byte order.</p>
6994 <p>The <tt>llvm.bswap.i16</tt> intrinsic returns an i16 value that has the high
6995 and low byte of the input i16 swapped. Similarly,
6996 the <tt>llvm.bswap.i32</tt> intrinsic returns an i32 value that has the four
6997 bytes of the input i32 swapped, so that if the input bytes are numbered 0, 1,
6998 2, 3 then the returned i32 will have its bytes in 3, 2, 1, 0 order.
6999 The <tt>llvm.bswap.i48</tt>, <tt>llvm.bswap.i64</tt> and other intrinsics
7000 extend this concept to additional even-byte lengths (6 bytes, 8 bytes and
7001 more, respectively).</p>
7005 <!-- _______________________________________________________________________ -->
7007 <a name="int_ctpop">'<tt>llvm.ctpop.*</tt>' Intrinsic</a>
7013 <p>This is an overloaded intrinsic. You can use llvm.ctpop on any integer bit
7014 width, or on any vector with integer elements. Not all targets support all
7015 bit widths or vector types, however.</p>
7018 declare i8 @llvm.ctpop.i8(i8 <src>)
7019 declare i16 @llvm.ctpop.i16(i16 <src>)
7020 declare i32 @llvm.ctpop.i32(i32 <src>)
7021 declare i64 @llvm.ctpop.i64(i64 <src>)
7022 declare i256 @llvm.ctpop.i256(i256 <src>)
7023 declare <2 x i32> @llvm.ctpop.v2i32(<2 x i32> <src>)
7027 <p>The '<tt>llvm.ctpop</tt>' family of intrinsics counts the number of bits set
7031 <p>The only argument is the value to be counted. The argument may be of any
7032 integer type, or a vector with integer elements.
7033 The return type must match the argument type.</p>
7036 <p>The '<tt>llvm.ctpop</tt>' intrinsic counts the 1's in a variable, or within each
7037 element of a vector.</p>
7041 <!-- _______________________________________________________________________ -->
7043 <a name="int_ctlz">'<tt>llvm.ctlz.*</tt>' Intrinsic</a>
7049 <p>This is an overloaded intrinsic. You can use <tt>llvm.ctlz</tt> on any
7050 integer bit width, or any vector whose elements are integers. Not all
7051 targets support all bit widths or vector types, however.</p>
7054 declare i8 @llvm.ctlz.i8 (i8 <src>)
7055 declare i16 @llvm.ctlz.i16(i16 <src>)
7056 declare i32 @llvm.ctlz.i32(i32 <src>)
7057 declare i64 @llvm.ctlz.i64(i64 <src>)
7058 declare i256 @llvm.ctlz.i256(i256 <src>)
7059 declare <2 x i32> @llvm.ctlz.v2i32(<2 x i32> <src;gt)
7063 <p>The '<tt>llvm.ctlz</tt>' family of intrinsic functions counts the number of
7064 leading zeros in a variable.</p>
7067 <p>The only argument is the value to be counted. The argument may be of any
7068 integer type, or any vector type with integer element type.
7069 The return type must match the argument type.</p>
7072 <p>The '<tt>llvm.ctlz</tt>' intrinsic counts the leading (most significant)
7073 zeros in a variable, or within each element of the vector if the operation
7074 is of vector type. If the src == 0 then the result is the size in bits of
7075 the type of src. For example, <tt>llvm.ctlz(i32 2) = 30</tt>.</p>
7079 <!-- _______________________________________________________________________ -->
7081 <a name="int_cttz">'<tt>llvm.cttz.*</tt>' Intrinsic</a>
7087 <p>This is an overloaded intrinsic. You can use <tt>llvm.cttz</tt> on any
7088 integer bit width, or any vector of integer elements. Not all targets
7089 support all bit widths or vector types, however.</p>
7092 declare i8 @llvm.cttz.i8 (i8 <src>)
7093 declare i16 @llvm.cttz.i16(i16 <src>)
7094 declare i32 @llvm.cttz.i32(i32 <src>)
7095 declare i64 @llvm.cttz.i64(i64 <src>)
7096 declare i256 @llvm.cttz.i256(i256 <src>)
7097 declase <2 x i32> @llvm.cttz.v2i32(<2 x i32> <src>)
7101 <p>The '<tt>llvm.cttz</tt>' family of intrinsic functions counts the number of
7105 <p>The only argument is the value to be counted. The argument may be of any
7106 integer type, or a vectory with integer element type.. The return type
7107 must match the argument type.</p>
7110 <p>The '<tt>llvm.cttz</tt>' intrinsic counts the trailing (least significant)
7111 zeros in a variable, or within each element of a vector.
7112 If the src == 0 then the result is the size in bits of
7113 the type of src. For example, <tt>llvm.cttz(2) = 1</tt>.</p>
7119 <!-- ======================================================================= -->
7121 <a name="int_overflow">Arithmetic with Overflow Intrinsics</a>
7126 <p>LLVM provides intrinsics for some arithmetic with overflow operations.</p>
7128 <!-- _______________________________________________________________________ -->
7130 <a name="int_sadd_overflow">
7131 '<tt>llvm.sadd.with.overflow.*</tt>' Intrinsics
7138 <p>This is an overloaded intrinsic. You can use <tt>llvm.sadd.with.overflow</tt>
7139 on any integer bit width.</p>
7142 declare {i16, i1} @llvm.sadd.with.overflow.i16(i16 %a, i16 %b)
7143 declare {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b)
7144 declare {i64, i1} @llvm.sadd.with.overflow.i64(i64 %a, i64 %b)
7148 <p>The '<tt>llvm.sadd.with.overflow</tt>' family of intrinsic functions perform
7149 a signed addition of the two arguments, and indicate whether an overflow
7150 occurred during the signed summation.</p>
7153 <p>The arguments (%a and %b) and the first element of the result structure may
7154 be of integer types of any bit width, but they must have the same bit
7155 width. The second element of the result structure must be of
7156 type <tt>i1</tt>. <tt>%a</tt> and <tt>%b</tt> are the two values that will
7157 undergo signed addition.</p>
7160 <p>The '<tt>llvm.sadd.with.overflow</tt>' family of intrinsic functions perform
7161 a signed addition of the two variables. They return a structure — the
7162 first element of which is the signed summation, and the second element of
7163 which is a bit specifying if the signed summation resulted in an
7168 %res = call {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b)
7169 %sum = extractvalue {i32, i1} %res, 0
7170 %obit = extractvalue {i32, i1} %res, 1
7171 br i1 %obit, label %overflow, label %normal
7176 <!-- _______________________________________________________________________ -->
7178 <a name="int_uadd_overflow">
7179 '<tt>llvm.uadd.with.overflow.*</tt>' Intrinsics
7186 <p>This is an overloaded intrinsic. You can use <tt>llvm.uadd.with.overflow</tt>
7187 on any integer bit width.</p>
7190 declare {i16, i1} @llvm.uadd.with.overflow.i16(i16 %a, i16 %b)
7191 declare {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)
7192 declare {i64, i1} @llvm.uadd.with.overflow.i64(i64 %a, i64 %b)
7196 <p>The '<tt>llvm.uadd.with.overflow</tt>' family of intrinsic functions perform
7197 an unsigned addition of the two arguments, and indicate whether a carry
7198 occurred during the unsigned summation.</p>
7201 <p>The arguments (%a and %b) and the first element of the result structure may
7202 be of integer types of any bit width, but they must have the same bit
7203 width. The second element of the result structure must be of
7204 type <tt>i1</tt>. <tt>%a</tt> and <tt>%b</tt> are the two values that will
7205 undergo unsigned addition.</p>
7208 <p>The '<tt>llvm.uadd.with.overflow</tt>' family of intrinsic functions perform
7209 an unsigned addition of the two arguments. They return a structure —
7210 the first element of which is the sum, and the second element of which is a
7211 bit specifying if the unsigned summation resulted in a carry.</p>
7215 %res = call {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)
7216 %sum = extractvalue {i32, i1} %res, 0
7217 %obit = extractvalue {i32, i1} %res, 1
7218 br i1 %obit, label %carry, label %normal
7223 <!-- _______________________________________________________________________ -->
7225 <a name="int_ssub_overflow">
7226 '<tt>llvm.ssub.with.overflow.*</tt>' Intrinsics
7233 <p>This is an overloaded intrinsic. You can use <tt>llvm.ssub.with.overflow</tt>
7234 on any integer bit width.</p>
7237 declare {i16, i1} @llvm.ssub.with.overflow.i16(i16 %a, i16 %b)
7238 declare {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b)
7239 declare {i64, i1} @llvm.ssub.with.overflow.i64(i64 %a, i64 %b)
7243 <p>The '<tt>llvm.ssub.with.overflow</tt>' family of intrinsic functions perform
7244 a signed subtraction of the two arguments, and indicate whether an overflow
7245 occurred during the signed subtraction.</p>
7248 <p>The arguments (%a and %b) and the first element of the result structure may
7249 be of integer types of any bit width, but they must have the same bit
7250 width. The second element of the result structure must be of
7251 type <tt>i1</tt>. <tt>%a</tt> and <tt>%b</tt> are the two values that will
7252 undergo signed subtraction.</p>
7255 <p>The '<tt>llvm.ssub.with.overflow</tt>' family of intrinsic functions perform
7256 a signed subtraction of the two arguments. They return a structure —
7257 the first element of which is the subtraction, and the second element of
7258 which is a bit specifying if the signed subtraction resulted in an
7263 %res = call {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b)
7264 %sum = extractvalue {i32, i1} %res, 0
7265 %obit = extractvalue {i32, i1} %res, 1
7266 br i1 %obit, label %overflow, label %normal
7271 <!-- _______________________________________________________________________ -->
7273 <a name="int_usub_overflow">
7274 '<tt>llvm.usub.with.overflow.*</tt>' Intrinsics
7281 <p>This is an overloaded intrinsic. You can use <tt>llvm.usub.with.overflow</tt>
7282 on any integer bit width.</p>
7285 declare {i16, i1} @llvm.usub.with.overflow.i16(i16 %a, i16 %b)
7286 declare {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b)
7287 declare {i64, i1} @llvm.usub.with.overflow.i64(i64 %a, i64 %b)
7291 <p>The '<tt>llvm.usub.with.overflow</tt>' family of intrinsic functions perform
7292 an unsigned subtraction of the two arguments, and indicate whether an
7293 overflow occurred during the unsigned subtraction.</p>
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 unsigned subtraction.</p>
7303 <p>The '<tt>llvm.usub.with.overflow</tt>' family of intrinsic functions perform
7304 an unsigned subtraction of the two arguments. They return a structure —
7305 the first element of which is the subtraction, and the second element of
7306 which is a bit specifying if the unsigned subtraction resulted in an
7311 %res = call {i32, i1} @llvm.usub.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
7319 <!-- _______________________________________________________________________ -->
7321 <a name="int_smul_overflow">
7322 '<tt>llvm.smul.with.overflow.*</tt>' Intrinsics
7329 <p>This is an overloaded intrinsic. You can use <tt>llvm.smul.with.overflow</tt>
7330 on any integer bit width.</p>
7333 declare {i16, i1} @llvm.smul.with.overflow.i16(i16 %a, i16 %b)
7334 declare {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b)
7335 declare {i64, i1} @llvm.smul.with.overflow.i64(i64 %a, i64 %b)
7340 <p>The '<tt>llvm.smul.with.overflow</tt>' family of intrinsic functions perform
7341 a signed multiplication of the two arguments, and indicate whether an
7342 overflow occurred during the signed multiplication.</p>
7345 <p>The arguments (%a and %b) and the first element of the result structure may
7346 be of integer types of any bit width, but they must have the same bit
7347 width. The second element of the result structure must be of
7348 type <tt>i1</tt>. <tt>%a</tt> and <tt>%b</tt> are the two values that will
7349 undergo signed multiplication.</p>
7352 <p>The '<tt>llvm.smul.with.overflow</tt>' family of intrinsic functions perform
7353 a signed multiplication of the two arguments. They return a structure —
7354 the first element of which is the multiplication, and the second element of
7355 which is a bit specifying if the signed multiplication resulted in an
7360 %res = call {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b)
7361 %sum = extractvalue {i32, i1} %res, 0
7362 %obit = extractvalue {i32, i1} %res, 1
7363 br i1 %obit, label %overflow, label %normal
7368 <!-- _______________________________________________________________________ -->
7370 <a name="int_umul_overflow">
7371 '<tt>llvm.umul.with.overflow.*</tt>' Intrinsics
7378 <p>This is an overloaded intrinsic. You can use <tt>llvm.umul.with.overflow</tt>
7379 on any integer bit width.</p>
7382 declare {i16, i1} @llvm.umul.with.overflow.i16(i16 %a, i16 %b)
7383 declare {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b)
7384 declare {i64, i1} @llvm.umul.with.overflow.i64(i64 %a, i64 %b)
7388 <p>The '<tt>llvm.umul.with.overflow</tt>' family of intrinsic functions perform
7389 a unsigned multiplication of the two arguments, and indicate whether an
7390 overflow occurred during the unsigned multiplication.</p>
7393 <p>The arguments (%a and %b) and the first element of the result structure may
7394 be of integer types of any bit width, but they must have the same bit
7395 width. The second element of the result structure must be of
7396 type <tt>i1</tt>. <tt>%a</tt> and <tt>%b</tt> are the two values that will
7397 undergo unsigned multiplication.</p>
7400 <p>The '<tt>llvm.umul.with.overflow</tt>' family of intrinsic functions perform
7401 an unsigned multiplication of the two arguments. They return a structure
7402 — the first element of which is the multiplication, and the second
7403 element of which is a bit specifying if the unsigned multiplication resulted
7408 %res = call {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b)
7409 %sum = extractvalue {i32, i1} %res, 0
7410 %obit = extractvalue {i32, i1} %res, 1
7411 br i1 %obit, label %overflow, label %normal
7418 <!-- ======================================================================= -->
7420 <a name="int_fp16">Half Precision Floating Point Intrinsics</a>
7425 <p>Half precision floating point is a storage-only format. This means that it is
7426 a dense encoding (in memory) but does not support computation in the
7429 <p>This means that code must first load the half-precision floating point
7430 value as an i16, then convert it to float with <a
7431 href="#int_convert_from_fp16"><tt>llvm.convert.from.fp16</tt></a>.
7432 Computation can then be performed on the float value (including extending to
7433 double etc). To store the value back to memory, it is first converted to
7434 float if needed, then converted to i16 with
7435 <a href="#int_convert_to_fp16"><tt>llvm.convert.to.fp16</tt></a>, then
7436 storing as an i16 value.</p>
7438 <!-- _______________________________________________________________________ -->
7440 <a name="int_convert_to_fp16">
7441 '<tt>llvm.convert.to.fp16</tt>' Intrinsic
7449 declare i16 @llvm.convert.to.fp16(f32 %a)
7453 <p>The '<tt>llvm.convert.to.fp16</tt>' intrinsic function performs
7454 a conversion from single precision floating point format to half precision
7455 floating point format.</p>
7458 <p>The intrinsic function contains single argument - the value to be
7462 <p>The '<tt>llvm.convert.to.fp16</tt>' intrinsic function performs
7463 a conversion from single precision floating point format to half precision
7464 floating point format. The return value is an <tt>i16</tt> which
7465 contains the converted number.</p>
7469 %res = call i16 @llvm.convert.to.fp16(f32 %a)
7470 store i16 %res, i16* @x, align 2
7475 <!-- _______________________________________________________________________ -->
7477 <a name="int_convert_from_fp16">
7478 '<tt>llvm.convert.from.fp16</tt>' Intrinsic
7486 declare f32 @llvm.convert.from.fp16(i16 %a)
7490 <p>The '<tt>llvm.convert.from.fp16</tt>' intrinsic function performs
7491 a conversion from half precision floating point format to single precision
7492 floating point format.</p>
7495 <p>The intrinsic function contains single argument - the value to be
7499 <p>The '<tt>llvm.convert.from.fp16</tt>' intrinsic function performs a
7500 conversion from half single precision floating point format to single
7501 precision floating point format. The input half-float value is represented by
7502 an <tt>i16</tt> value.</p>
7506 %a = load i16* @x, align 2
7507 %res = call f32 @llvm.convert.from.fp16(i16 %a)
7514 <!-- ======================================================================= -->
7516 <a name="int_debugger">Debugger Intrinsics</a>
7521 <p>The LLVM debugger intrinsics (which all start with <tt>llvm.dbg.</tt>
7522 prefix), are described in
7523 the <a href="SourceLevelDebugging.html#format_common_intrinsics">LLVM Source
7524 Level Debugging</a> document.</p>
7528 <!-- ======================================================================= -->
7530 <a name="int_eh">Exception Handling Intrinsics</a>
7535 <p>The LLVM exception handling intrinsics (which all start with
7536 <tt>llvm.eh.</tt> prefix), are described in
7537 the <a href="ExceptionHandling.html#format_common_intrinsics">LLVM Exception
7538 Handling</a> document.</p>
7542 <!-- ======================================================================= -->
7544 <a name="int_trampoline">Trampoline Intrinsic</a>
7549 <p>This intrinsic makes it possible to excise one parameter, marked with
7550 the <a href="#nest"><tt>nest</tt></a> attribute, from a function.
7551 The result is a callable
7552 function pointer lacking the nest parameter - the caller does not need to
7553 provide a value for it. Instead, the value to use is stored in advance in a
7554 "trampoline", a block of memory usually allocated on the stack, which also
7555 contains code to splice the nest value into the argument list. This is used
7556 to implement the GCC nested function address extension.</p>
7558 <p>For example, if the function is
7559 <tt>i32 f(i8* nest %c, i32 %x, i32 %y)</tt> then the resulting function
7560 pointer has signature <tt>i32 (i32, i32)*</tt>. It can be created as
7563 <pre class="doc_code">
7564 %tramp = alloca [10 x i8], align 4 ; size and alignment only correct for X86
7565 %tramp1 = getelementptr [10 x i8]* %tramp, i32 0, i32 0
7566 %p = call i8* @llvm.init.trampoline(i8* %tramp1, i8* bitcast (i32 (i8* nest , i32, i32)* @f to i8*), i8* %nval)
7567 %fp = bitcast i8* %p to i32 (i32, i32)*
7570 <p>The call <tt>%val = call i32 %fp(i32 %x, i32 %y)</tt> is then equivalent
7571 to <tt>%val = call i32 %f(i8* %nval, i32 %x, i32 %y)</tt>.</p>
7573 <!-- _______________________________________________________________________ -->
7576 '<tt>llvm.init.trampoline</tt>' Intrinsic
7584 declare i8* @llvm.init.trampoline(i8* <tramp>, i8* <func>, i8* <nval>)
7588 <p>This fills the memory pointed to by <tt>tramp</tt> with code and returns a
7589 function pointer suitable for executing it.</p>
7592 <p>The <tt>llvm.init.trampoline</tt> intrinsic takes three arguments, all
7593 pointers. The <tt>tramp</tt> argument must point to a sufficiently large and
7594 sufficiently aligned block of memory; this memory is written to by the
7595 intrinsic. Note that the size and the alignment are target-specific - LLVM
7596 currently provides no portable way of determining them, so a front-end that
7597 generates this intrinsic needs to have some target-specific knowledge.
7598 The <tt>func</tt> argument must hold a function bitcast to
7599 an <tt>i8*</tt>.</p>
7602 <p>The block of memory pointed to by <tt>tramp</tt> is filled with target
7603 dependent code, turning it into a function. A pointer to this function is
7604 returned, but needs to be bitcast to an <a href="#int_trampoline">appropriate
7605 function pointer type</a> before being called. The new function's signature
7606 is the same as that of <tt>func</tt> with any arguments marked with
7607 the <tt>nest</tt> attribute removed. At most one such <tt>nest</tt> argument
7608 is allowed, and it must be of pointer type. Calling the new function is
7609 equivalent to calling <tt>func</tt> with the same argument list, but
7610 with <tt>nval</tt> used for the missing <tt>nest</tt> argument. If, after
7611 calling <tt>llvm.init.trampoline</tt>, the memory pointed to
7612 by <tt>tramp</tt> is modified, then the effect of any later call to the
7613 returned function pointer is undefined.</p>
7619 <!-- ======================================================================= -->
7621 <a name="int_atomics">Atomic Operations and Synchronization Intrinsics</a>
7626 <p>These intrinsic functions expand the "universal IR" of LLVM to represent
7627 hardware constructs for atomic operations and memory synchronization. This
7628 provides an interface to the hardware, not an interface to the programmer. It
7629 is aimed at a low enough level to allow any programming models or APIs
7630 (Application Programming Interfaces) which need atomic behaviors to map
7631 cleanly onto it. It is also modeled primarily on hardware behavior. Just as
7632 hardware provides a "universal IR" for source languages, it also provides a
7633 starting point for developing a "universal" atomic operation and
7634 synchronization IR.</p>
7636 <p>These do <em>not</em> form an API such as high-level threading libraries,
7637 software transaction memory systems, atomic primitives, and intrinsic
7638 functions as found in BSD, GNU libc, atomic_ops, APR, and other system and
7639 application libraries. The hardware interface provided by LLVM should allow
7640 a clean implementation of all of these APIs and parallel programming models.
7641 No one model or paradigm should be selected above others unless the hardware
7642 itself ubiquitously does so.</p>
7644 <!-- _______________________________________________________________________ -->
7646 <a name="int_memory_barrier">'<tt>llvm.memory.barrier</tt>' Intrinsic</a>
7652 declare void @llvm.memory.barrier(i1 <ll>, i1 <ls>, i1 <sl>, i1 <ss>, i1 <device>)
7656 <p>The <tt>llvm.memory.barrier</tt> intrinsic guarantees ordering between
7657 specific pairs of memory access types.</p>
7660 <p>The <tt>llvm.memory.barrier</tt> intrinsic requires five boolean arguments.
7661 The first four arguments enables a specific barrier as listed below. The
7662 fifth argument specifies that the barrier applies to io or device or uncached
7666 <li><tt>ll</tt>: load-load barrier</li>
7667 <li><tt>ls</tt>: load-store barrier</li>
7668 <li><tt>sl</tt>: store-load barrier</li>
7669 <li><tt>ss</tt>: store-store barrier</li>
7670 <li><tt>device</tt>: barrier applies to device and uncached memory also.</li>
7674 <p>This intrinsic causes the system to enforce some ordering constraints upon
7675 the loads and stores of the program. This barrier does not
7676 indicate <em>when</em> any events will occur, it only enforces
7677 an <em>order</em> in which they occur. For any of the specified pairs of load
7678 and store operations (f.ex. load-load, or store-load), all of the first
7679 operations preceding the barrier will complete before any of the second
7680 operations succeeding the barrier begin. Specifically the semantics for each
7681 pairing is as follows:</p>
7684 <li><tt>ll</tt>: All loads before the barrier must complete before any load
7685 after the barrier begins.</li>
7686 <li><tt>ls</tt>: All loads before the barrier must complete before any
7687 store after the barrier begins.</li>
7688 <li><tt>ss</tt>: All stores before the barrier must complete before any
7689 store after the barrier begins.</li>
7690 <li><tt>sl</tt>: All stores before the barrier must complete before any
7691 load after the barrier begins.</li>
7694 <p>These semantics are applied with a logical "and" behavior when more than one
7695 is enabled in a single memory barrier intrinsic.</p>
7697 <p>Backends may implement stronger barriers than those requested when they do
7698 not support as fine grained a barrier as requested. Some architectures do
7699 not need all types of barriers and on such architectures, these become
7704 %mallocP = tail call i8* @malloc(i32 ptrtoint (i32* getelementptr (i32* null, i32 1) to i32))
7705 %ptr = bitcast i8* %mallocP to i32*
7708 %result1 = load i32* %ptr <i>; yields {i32}:result1 = 4</i>
7709 call void @llvm.memory.barrier(i1 false, i1 true, i1 false, i1 false, i1 true)
7710 <i>; guarantee the above finishes</i>
7711 store i32 8, %ptr <i>; before this begins</i>
7716 <!-- _______________________________________________________________________ -->
7718 <a name="int_atomic_cmp_swap">'<tt>llvm.atomic.cmp.swap.*</tt>' Intrinsic</a>
7724 <p>This is an overloaded intrinsic. You can use <tt>llvm.atomic.cmp.swap</tt> on
7725 any integer bit width and for different address spaces. Not all targets
7726 support all bit widths however.</p>
7729 declare i8 @llvm.atomic.cmp.swap.i8.p0i8(i8* <ptr>, i8 <cmp>, i8 <val>)
7730 declare i16 @llvm.atomic.cmp.swap.i16.p0i16(i16* <ptr>, i16 <cmp>, i16 <val>)
7731 declare i32 @llvm.atomic.cmp.swap.i32.p0i32(i32* <ptr>, i32 <cmp>, i32 <val>)
7732 declare i64 @llvm.atomic.cmp.swap.i64.p0i64(i64* <ptr>, i64 <cmp>, i64 <val>)
7736 <p>This loads a value in memory and compares it to a given value. If they are
7737 equal, it stores a new value into the memory.</p>
7740 <p>The <tt>llvm.atomic.cmp.swap</tt> intrinsic takes three arguments. The result
7741 as well as both <tt>cmp</tt> and <tt>val</tt> must be integer values with the
7742 same bit width. The <tt>ptr</tt> argument must be a pointer to a value of
7743 this integer type. While any bit width integer may be used, targets may only
7744 lower representations they support in hardware.</p>
7747 <p>This entire intrinsic must be executed atomically. It first loads the value
7748 in memory pointed to by <tt>ptr</tt> and compares it with the
7749 value <tt>cmp</tt>. If they are equal, <tt>val</tt> is stored into the
7750 memory. The loaded value is yielded in all cases. This provides the
7751 equivalent of an atomic compare-and-swap operation within the SSA
7756 %mallocP = tail call i8* @malloc(i32 ptrtoint (i32* getelementptr (i32* null, i32 1) to i32))
7757 %ptr = bitcast i8* %mallocP to i32*
7760 %val1 = add i32 4, 4
7761 %result1 = call i32 @llvm.atomic.cmp.swap.i32.p0i32(i32* %ptr, i32 4, %val1)
7762 <i>; yields {i32}:result1 = 4</i>
7763 %stored1 = icmp eq i32 %result1, 4 <i>; yields {i1}:stored1 = true</i>
7764 %memval1 = load i32* %ptr <i>; yields {i32}:memval1 = 8</i>
7766 %val2 = add i32 1, 1
7767 %result2 = call i32 @llvm.atomic.cmp.swap.i32.p0i32(i32* %ptr, i32 5, %val2)
7768 <i>; yields {i32}:result2 = 8</i>
7769 %stored2 = icmp eq i32 %result2, 5 <i>; yields {i1}:stored2 = false</i>
7771 %memval2 = load i32* %ptr <i>; yields {i32}:memval2 = 8</i>
7776 <!-- _______________________________________________________________________ -->
7778 <a name="int_atomic_swap">'<tt>llvm.atomic.swap.*</tt>' Intrinsic</a>
7784 <p>This is an overloaded intrinsic. You can use <tt>llvm.atomic.swap</tt> on any
7785 integer bit width. Not all targets support all bit widths however.</p>
7788 declare i8 @llvm.atomic.swap.i8.p0i8(i8* <ptr>, i8 <val>)
7789 declare i16 @llvm.atomic.swap.i16.p0i16(i16* <ptr>, i16 <val>)
7790 declare i32 @llvm.atomic.swap.i32.p0i32(i32* <ptr>, i32 <val>)
7791 declare i64 @llvm.atomic.swap.i64.p0i64(i64* <ptr>, i64 <val>)
7795 <p>This intrinsic loads the value stored in memory at <tt>ptr</tt> and yields
7796 the value from memory. It then stores the value in <tt>val</tt> in the memory
7797 at <tt>ptr</tt>.</p>
7800 <p>The <tt>llvm.atomic.swap</tt> intrinsic takes two arguments. Both
7801 the <tt>val</tt> argument and the result must be integers of the same bit
7802 width. The first argument, <tt>ptr</tt>, must be a pointer to a value of this
7803 integer type. The targets may only lower integer representations they
7807 <p>This intrinsic loads the value pointed to by <tt>ptr</tt>, yields it, and
7808 stores <tt>val</tt> back into <tt>ptr</tt> atomically. This provides the
7809 equivalent of an atomic swap operation within the SSA framework.</p>
7813 %mallocP = tail call i8* @malloc(i32 ptrtoint (i32* getelementptr (i32* null, i32 1) to i32))
7814 %ptr = bitcast i8* %mallocP to i32*
7817 %val1 = add i32 4, 4
7818 %result1 = call i32 @llvm.atomic.swap.i32.p0i32(i32* %ptr, i32 %val1)
7819 <i>; yields {i32}:result1 = 4</i>
7820 %stored1 = icmp eq i32 %result1, 4 <i>; yields {i1}:stored1 = true</i>
7821 %memval1 = load i32* %ptr <i>; yields {i32}:memval1 = 8</i>
7823 %val2 = add i32 1, 1
7824 %result2 = call i32 @llvm.atomic.swap.i32.p0i32(i32* %ptr, i32 %val2)
7825 <i>; yields {i32}:result2 = 8</i>
7827 %stored2 = icmp eq i32 %result2, 8 <i>; yields {i1}:stored2 = true</i>
7828 %memval2 = load i32* %ptr <i>; yields {i32}:memval2 = 2</i>
7833 <!-- _______________________________________________________________________ -->
7835 <a name="int_atomic_load_add">'<tt>llvm.atomic.load.add.*</tt>' Intrinsic</a>
7841 <p>This is an overloaded intrinsic. You can use <tt>llvm.atomic.load.add</tt> on
7842 any integer bit width. Not all targets support all bit widths however.</p>
7845 declare i8 @llvm.atomic.load.add.i8.p0i8(i8* <ptr>, i8 <delta>)
7846 declare i16 @llvm.atomic.load.add.i16.p0i16(i16* <ptr>, i16 <delta>)
7847 declare i32 @llvm.atomic.load.add.i32.p0i32(i32* <ptr>, i32 <delta>)
7848 declare i64 @llvm.atomic.load.add.i64.p0i64(i64* <ptr>, i64 <delta>)
7852 <p>This intrinsic adds <tt>delta</tt> to the value stored in memory
7853 at <tt>ptr</tt>. It yields the original value at <tt>ptr</tt>.</p>
7856 <p>The intrinsic takes two arguments, the first a pointer to an integer value
7857 and the second an integer value. The result is also an integer value. These
7858 integer types can have any bit width, but they must all have the same bit
7859 width. The targets may only lower integer representations they support.</p>
7862 <p>This intrinsic does a series of operations atomically. It first loads the
7863 value stored at <tt>ptr</tt>. It then adds <tt>delta</tt>, stores the result
7864 to <tt>ptr</tt>. It yields the original value stored at <tt>ptr</tt>.</p>
7868 %mallocP = tail call i8* @malloc(i32 ptrtoint (i32* getelementptr (i32* null, i32 1) to i32))
7869 %ptr = bitcast i8* %mallocP to i32*
7871 %result1 = call i32 @llvm.atomic.load.add.i32.p0i32(i32* %ptr, i32 4)
7872 <i>; yields {i32}:result1 = 4</i>
7873 %result2 = call i32 @llvm.atomic.load.add.i32.p0i32(i32* %ptr, i32 2)
7874 <i>; yields {i32}:result2 = 8</i>
7875 %result3 = call i32 @llvm.atomic.load.add.i32.p0i32(i32* %ptr, i32 5)
7876 <i>; yields {i32}:result3 = 10</i>
7877 %memval1 = load i32* %ptr <i>; yields {i32}:memval1 = 15</i>
7882 <!-- _______________________________________________________________________ -->
7884 <a name="int_atomic_load_sub">'<tt>llvm.atomic.load.sub.*</tt>' Intrinsic</a>
7890 <p>This is an overloaded intrinsic. You can use <tt>llvm.atomic.load.sub</tt> on
7891 any integer bit width and for different address spaces. Not all targets
7892 support all bit widths however.</p>
7895 declare i8 @llvm.atomic.load.sub.i8.p0i32(i8* <ptr>, i8 <delta>)
7896 declare i16 @llvm.atomic.load.sub.i16.p0i32(i16* <ptr>, i16 <delta>)
7897 declare i32 @llvm.atomic.load.sub.i32.p0i32(i32* <ptr>, i32 <delta>)
7898 declare i64 @llvm.atomic.load.sub.i64.p0i32(i64* <ptr>, i64 <delta>)
7902 <p>This intrinsic subtracts <tt>delta</tt> to the value stored in memory at
7903 <tt>ptr</tt>. It yields the original value at <tt>ptr</tt>.</p>
7906 <p>The intrinsic takes two arguments, the first a pointer to an integer value
7907 and the second an integer value. The result is also an integer value. These
7908 integer types can have any bit width, but they must all have the same bit
7909 width. The targets may only lower integer representations they support.</p>
7912 <p>This intrinsic does a series of operations atomically. It first loads the
7913 value stored at <tt>ptr</tt>. It then subtracts <tt>delta</tt>, stores the
7914 result to <tt>ptr</tt>. It yields the original value stored
7915 at <tt>ptr</tt>.</p>
7919 %mallocP = tail call i8* @malloc(i32 ptrtoint (i32* getelementptr (i32* null, i32 1) to i32))
7920 %ptr = bitcast i8* %mallocP to i32*
7922 %result1 = call i32 @llvm.atomic.load.sub.i32.p0i32(i32* %ptr, i32 4)
7923 <i>; yields {i32}:result1 = 8</i>
7924 %result2 = call i32 @llvm.atomic.load.sub.i32.p0i32(i32* %ptr, i32 2)
7925 <i>; yields {i32}:result2 = 4</i>
7926 %result3 = call i32 @llvm.atomic.load.sub.i32.p0i32(i32* %ptr, i32 5)
7927 <i>; yields {i32}:result3 = 2</i>
7928 %memval1 = load i32* %ptr <i>; yields {i32}:memval1 = -3</i>
7933 <!-- _______________________________________________________________________ -->
7935 <a name="int_atomic_load_and">
7936 '<tt>llvm.atomic.load.and.*</tt>' Intrinsic
7939 <a name="int_atomic_load_nand">
7940 '<tt>llvm.atomic.load.nand.*</tt>' Intrinsic
7943 <a name="int_atomic_load_or">
7944 '<tt>llvm.atomic.load.or.*</tt>' Intrinsic
7947 <a name="int_atomic_load_xor">
7948 '<tt>llvm.atomic.load.xor.*</tt>' Intrinsic
7955 <p>These are overloaded intrinsics. You can
7956 use <tt>llvm.atomic.load_and</tt>, <tt>llvm.atomic.load_nand</tt>,
7957 <tt>llvm.atomic.load_or</tt>, and <tt>llvm.atomic.load_xor</tt> on any integer
7958 bit width and for different address spaces. Not all targets support all bit
7962 declare i8 @llvm.atomic.load.and.i8.p0i8(i8* <ptr>, i8 <delta>)
7963 declare i16 @llvm.atomic.load.and.i16.p0i16(i16* <ptr>, i16 <delta>)
7964 declare i32 @llvm.atomic.load.and.i32.p0i32(i32* <ptr>, i32 <delta>)
7965 declare i64 @llvm.atomic.load.and.i64.p0i64(i64* <ptr>, i64 <delta>)
7969 declare i8 @llvm.atomic.load.or.i8.p0i8(i8* <ptr>, i8 <delta>)
7970 declare i16 @llvm.atomic.load.or.i16.p0i16(i16* <ptr>, i16 <delta>)
7971 declare i32 @llvm.atomic.load.or.i32.p0i32(i32* <ptr>, i32 <delta>)
7972 declare i64 @llvm.atomic.load.or.i64.p0i64(i64* <ptr>, i64 <delta>)
7976 declare i8 @llvm.atomic.load.nand.i8.p0i32(i8* <ptr>, i8 <delta>)
7977 declare i16 @llvm.atomic.load.nand.i16.p0i32(i16* <ptr>, i16 <delta>)
7978 declare i32 @llvm.atomic.load.nand.i32.p0i32(i32* <ptr>, i32 <delta>)
7979 declare i64 @llvm.atomic.load.nand.i64.p0i32(i64* <ptr>, i64 <delta>)
7983 declare i8 @llvm.atomic.load.xor.i8.p0i32(i8* <ptr>, i8 <delta>)
7984 declare i16 @llvm.atomic.load.xor.i16.p0i32(i16* <ptr>, i16 <delta>)
7985 declare i32 @llvm.atomic.load.xor.i32.p0i32(i32* <ptr>, i32 <delta>)
7986 declare i64 @llvm.atomic.load.xor.i64.p0i32(i64* <ptr>, i64 <delta>)
7990 <p>These intrinsics bitwise the operation (and, nand, or, xor) <tt>delta</tt> to
7991 the value stored in memory at <tt>ptr</tt>. It yields the original value
7992 at <tt>ptr</tt>.</p>
7995 <p>These intrinsics take two arguments, the first a pointer to an integer value
7996 and the second an integer value. The result is also an integer value. These
7997 integer types can have any bit width, but they must all have the same bit
7998 width. The targets may only lower integer representations they support.</p>
8001 <p>These intrinsics does a series of operations atomically. They first load the
8002 value stored at <tt>ptr</tt>. They then do the bitwise
8003 operation <tt>delta</tt>, store the result to <tt>ptr</tt>. They yield the
8004 original value stored at <tt>ptr</tt>.</p>
8008 %mallocP = tail call i8* @malloc(i32 ptrtoint (i32* getelementptr (i32* null, i32 1) to i32))
8009 %ptr = bitcast i8* %mallocP to i32*
8010 store i32 0x0F0F, %ptr
8011 %result0 = call i32 @llvm.atomic.load.nand.i32.p0i32(i32* %ptr, i32 0xFF)
8012 <i>; yields {i32}:result0 = 0x0F0F</i>
8013 %result1 = call i32 @llvm.atomic.load.and.i32.p0i32(i32* %ptr, i32 0xFF)
8014 <i>; yields {i32}:result1 = 0xFFFFFFF0</i>
8015 %result2 = call i32 @llvm.atomic.load.or.i32.p0i32(i32* %ptr, i32 0F)
8016 <i>; yields {i32}:result2 = 0xF0</i>
8017 %result3 = call i32 @llvm.atomic.load.xor.i32.p0i32(i32* %ptr, i32 0F)
8018 <i>; yields {i32}:result3 = FF</i>
8019 %memval1 = load i32* %ptr <i>; yields {i32}:memval1 = F0</i>
8024 <!-- _______________________________________________________________________ -->
8026 <a name="int_atomic_load_max">
8027 '<tt>llvm.atomic.load.max.*</tt>' Intrinsic
8030 <a name="int_atomic_load_min">
8031 '<tt>llvm.atomic.load.min.*</tt>' Intrinsic
8034 <a name="int_atomic_load_umax">
8035 '<tt>llvm.atomic.load.umax.*</tt>' Intrinsic
8038 <a name="int_atomic_load_umin">
8039 '<tt>llvm.atomic.load.umin.*</tt>' Intrinsic
8046 <p>These are overloaded intrinsics. You can use <tt>llvm.atomic.load_max</tt>,
8047 <tt>llvm.atomic.load_min</tt>, <tt>llvm.atomic.load_umax</tt>, and
8048 <tt>llvm.atomic.load_umin</tt> on any integer bit width and for different
8049 address spaces. Not all targets support all bit widths however.</p>
8052 declare i8 @llvm.atomic.load.max.i8.p0i8(i8* <ptr>, i8 <delta>)
8053 declare i16 @llvm.atomic.load.max.i16.p0i16(i16* <ptr>, i16 <delta>)
8054 declare i32 @llvm.atomic.load.max.i32.p0i32(i32* <ptr>, i32 <delta>)
8055 declare i64 @llvm.atomic.load.max.i64.p0i64(i64* <ptr>, i64 <delta>)
8059 declare i8 @llvm.atomic.load.min.i8.p0i8(i8* <ptr>, i8 <delta>)
8060 declare i16 @llvm.atomic.load.min.i16.p0i16(i16* <ptr>, i16 <delta>)
8061 declare i32 @llvm.atomic.load.min.i32.p0i32(i32* <ptr>, i32 <delta>)
8062 declare i64 @llvm.atomic.load.min.i64.p0i64(i64* <ptr>, i64 <delta>)
8066 declare i8 @llvm.atomic.load.umax.i8.p0i8(i8* <ptr>, i8 <delta>)
8067 declare i16 @llvm.atomic.load.umax.i16.p0i16(i16* <ptr>, i16 <delta>)
8068 declare i32 @llvm.atomic.load.umax.i32.p0i32(i32* <ptr>, i32 <delta>)
8069 declare i64 @llvm.atomic.load.umax.i64.p0i64(i64* <ptr>, i64 <delta>)
8073 declare i8 @llvm.atomic.load.umin.i8.p0i8(i8* <ptr>, i8 <delta>)
8074 declare i16 @llvm.atomic.load.umin.i16.p0i16(i16* <ptr>, i16 <delta>)
8075 declare i32 @llvm.atomic.load.umin.i32.p0i32(i32* <ptr>, i32 <delta>)
8076 declare i64 @llvm.atomic.load.umin.i64.p0i64(i64* <ptr>, i64 <delta>)
8080 <p>These intrinsics takes the signed or unsigned minimum or maximum of
8081 <tt>delta</tt> and the value stored in memory at <tt>ptr</tt>. It yields the
8082 original value at <tt>ptr</tt>.</p>
8085 <p>These intrinsics take two arguments, the first a pointer to an integer value
8086 and the second an integer value. The result is also an integer value. These
8087 integer types can have any bit width, but they must all have the same bit
8088 width. The targets may only lower integer representations they support.</p>
8091 <p>These intrinsics does a series of operations atomically. They first load the
8092 value stored at <tt>ptr</tt>. They then do the signed or unsigned min or
8093 max <tt>delta</tt> and the value, store the result to <tt>ptr</tt>. They
8094 yield the original value stored at <tt>ptr</tt>.</p>
8098 %mallocP = tail call i8* @malloc(i32 ptrtoint (i32* getelementptr (i32* null, i32 1) to i32))
8099 %ptr = bitcast i8* %mallocP to i32*
8101 %result0 = call i32 @llvm.atomic.load.min.i32.p0i32(i32* %ptr, i32 -2)
8102 <i>; yields {i32}:result0 = 7</i>
8103 %result1 = call i32 @llvm.atomic.load.max.i32.p0i32(i32* %ptr, i32 8)
8104 <i>; yields {i32}:result1 = -2</i>
8105 %result2 = call i32 @llvm.atomic.load.umin.i32.p0i32(i32* %ptr, i32 10)
8106 <i>; yields {i32}:result2 = 8</i>
8107 %result3 = call i32 @llvm.atomic.load.umax.i32.p0i32(i32* %ptr, i32 30)
8108 <i>; yields {i32}:result3 = 8</i>
8109 %memval1 = load i32* %ptr <i>; yields {i32}:memval1 = 30</i>
8116 <!-- ======================================================================= -->
8118 <a name="int_memorymarkers">Memory Use Markers</a>
8123 <p>This class of intrinsics exists to information about the lifetime of memory
8124 objects and ranges where variables are immutable.</p>
8126 <!-- _______________________________________________________________________ -->
8128 <a name="int_lifetime_start">'<tt>llvm.lifetime.start</tt>' Intrinsic</a>
8135 declare void @llvm.lifetime.start(i64 <size>, i8* nocapture <ptr>)
8139 <p>The '<tt>llvm.lifetime.start</tt>' intrinsic specifies the start of a memory
8140 object's lifetime.</p>
8143 <p>The first argument is a constant integer representing the size of the
8144 object, or -1 if it is variable sized. The second argument is a pointer to
8148 <p>This intrinsic indicates that before this point in the code, the value of the
8149 memory pointed to by <tt>ptr</tt> is dead. This means that it is known to
8150 never be used and has an undefined value. A load from the pointer that
8151 precedes this intrinsic can be replaced with
8152 <tt>'<a href="#undefvalues">undef</a>'</tt>.</p>
8156 <!-- _______________________________________________________________________ -->
8158 <a name="int_lifetime_end">'<tt>llvm.lifetime.end</tt>' Intrinsic</a>
8165 declare void @llvm.lifetime.end(i64 <size>, i8* nocapture <ptr>)
8169 <p>The '<tt>llvm.lifetime.end</tt>' intrinsic specifies the end of a memory
8170 object's lifetime.</p>
8173 <p>The first argument is a constant integer representing the size of the
8174 object, or -1 if it is variable sized. The second argument is a pointer to
8178 <p>This intrinsic indicates that after this point in the code, the value of the
8179 memory pointed to by <tt>ptr</tt> is dead. This means that it is known to
8180 never be used and has an undefined value. Any stores into the memory object
8181 following this intrinsic may be removed as dead.
8185 <!-- _______________________________________________________________________ -->
8187 <a name="int_invariant_start">'<tt>llvm.invariant.start</tt>' Intrinsic</a>
8194 declare {}* @llvm.invariant.start(i64 <size>, i8* nocapture <ptr>)
8198 <p>The '<tt>llvm.invariant.start</tt>' intrinsic specifies that the contents of
8199 a memory object will not change.</p>
8202 <p>The first argument is a constant integer representing the size of the
8203 object, or -1 if it is variable sized. The second argument is a pointer to
8207 <p>This intrinsic indicates that until an <tt>llvm.invariant.end</tt> that uses
8208 the return value, the referenced memory location is constant and
8213 <!-- _______________________________________________________________________ -->
8215 <a name="int_invariant_end">'<tt>llvm.invariant.end</tt>' Intrinsic</a>
8222 declare void @llvm.invariant.end({}* <start>, i64 <size>, i8* nocapture <ptr>)
8226 <p>The '<tt>llvm.invariant.end</tt>' intrinsic specifies that the contents of
8227 a memory object are mutable.</p>
8230 <p>The first argument is the matching <tt>llvm.invariant.start</tt> intrinsic.
8231 The second argument is a constant integer representing the size of the
8232 object, or -1 if it is variable sized and the third argument is a pointer
8236 <p>This intrinsic indicates that the memory is mutable again.</p>
8242 <!-- ======================================================================= -->
8244 <a name="int_general">General Intrinsics</a>
8249 <p>This class of intrinsics is designed to be generic and has no specific
8252 <!-- _______________________________________________________________________ -->
8254 <a name="int_var_annotation">'<tt>llvm.var.annotation</tt>' Intrinsic</a>
8261 declare void @llvm.var.annotation(i8* <val>, i8* <str>, i8* <str>, i32 <int>)
8265 <p>The '<tt>llvm.var.annotation</tt>' intrinsic.</p>
8268 <p>The first argument is a pointer to a value, the second is a pointer to a
8269 global string, the third is a pointer to a global string which is the source
8270 file name, and the last argument is the line number.</p>
8273 <p>This intrinsic allows annotation of local variables with arbitrary strings.
8274 This can be useful for special purpose optimizations that want to look for
8275 these annotations. These have no other defined use, they are ignored by code
8276 generation and optimization.</p>
8280 <!-- _______________________________________________________________________ -->
8282 <a name="int_annotation">'<tt>llvm.annotation.*</tt>' Intrinsic</a>
8288 <p>This is an overloaded intrinsic. You can use '<tt>llvm.annotation</tt>' on
8289 any integer bit width.</p>
8292 declare i8 @llvm.annotation.i8(i8 <val>, i8* <str>, i8* <str>, i32 <int>)
8293 declare i16 @llvm.annotation.i16(i16 <val>, i8* <str>, i8* <str>, i32 <int>)
8294 declare i32 @llvm.annotation.i32(i32 <val>, i8* <str>, i8* <str>, i32 <int>)
8295 declare i64 @llvm.annotation.i64(i64 <val>, i8* <str>, i8* <str>, i32 <int>)
8296 declare i256 @llvm.annotation.i256(i256 <val>, i8* <str>, i8* <str>, i32 <int>)
8300 <p>The '<tt>llvm.annotation</tt>' intrinsic.</p>
8303 <p>The first argument is an integer value (result of some expression), the
8304 second is a pointer to a global string, the third is a pointer to a global
8305 string which is the source file name, and the last argument is the line
8306 number. It returns the value of the first argument.</p>
8309 <p>This intrinsic allows annotations to be put on arbitrary expressions with
8310 arbitrary strings. This can be useful for special purpose optimizations that
8311 want to look for these annotations. These have no other defined use, they
8312 are ignored by code generation and optimization.</p>
8316 <!-- _______________________________________________________________________ -->
8318 <a name="int_trap">'<tt>llvm.trap</tt>' Intrinsic</a>
8325 declare void @llvm.trap()
8329 <p>The '<tt>llvm.trap</tt>' intrinsic.</p>
8335 <p>This intrinsics is lowered to the target dependent trap instruction. If the
8336 target does not have a trap instruction, this intrinsic will be lowered to
8337 the call of the <tt>abort()</tt> function.</p>
8341 <!-- _______________________________________________________________________ -->
8343 <a name="int_stackprotector">'<tt>llvm.stackprotector</tt>' Intrinsic</a>
8350 declare void @llvm.stackprotector(i8* <guard>, i8** <slot>)
8354 <p>The <tt>llvm.stackprotector</tt> intrinsic takes the <tt>guard</tt> and
8355 stores it onto the stack at <tt>slot</tt>. The stack slot is adjusted to
8356 ensure that it is placed on the stack before local variables.</p>
8359 <p>The <tt>llvm.stackprotector</tt> intrinsic requires two pointer
8360 arguments. The first argument is the value loaded from the stack
8361 guard <tt>@__stack_chk_guard</tt>. The second variable is an <tt>alloca</tt>
8362 that has enough space to hold the value of the guard.</p>
8365 <p>This intrinsic causes the prologue/epilogue inserter to force the position of
8366 the <tt>AllocaInst</tt> stack slot to be before local variables on the
8367 stack. This is to ensure that if a local variable on the stack is
8368 overwritten, it will destroy the value of the guard. When the function exits,
8369 the guard on the stack is checked against the original guard. If they are
8370 different, then the program aborts by calling the <tt>__stack_chk_fail()</tt>
8375 <!-- _______________________________________________________________________ -->
8377 <a name="int_objectsize">'<tt>llvm.objectsize</tt>' Intrinsic</a>
8384 declare i32 @llvm.objectsize.i32(i8* <object>, i1 <type>)
8385 declare i64 @llvm.objectsize.i64(i8* <object>, i1 <type>)
8389 <p>The <tt>llvm.objectsize</tt> intrinsic is designed to provide information to
8390 the optimizers to determine at compile time whether a) an operation (like
8391 memcpy) will overflow a buffer that corresponds to an object, or b) that a
8392 runtime check for overflow isn't necessary. An object in this context means
8393 an allocation of a specific class, structure, array, or other object.</p>
8396 <p>The <tt>llvm.objectsize</tt> intrinsic takes two arguments. The first
8397 argument is a pointer to or into the <tt>object</tt>. The second argument
8398 is a boolean 0 or 1. This argument determines whether you want the
8399 maximum (0) or minimum (1) bytes remaining. This needs to be a literal 0 or
8400 1, variables are not allowed.</p>
8403 <p>The <tt>llvm.objectsize</tt> intrinsic is lowered to either a constant
8404 representing the size of the object concerned, or <tt>i32/i64 -1 or 0</tt>,
8405 depending on the <tt>type</tt> argument, if the size cannot be determined at
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