1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
2 "http://www.w3.org/TR/html4/strict.dtd">
5 <title>LLVM Assembly Language Reference Manual</title>
6 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
7 <meta name="author" content="Chris Lattner">
8 <meta name="description"
9 content="LLVM Assembly Language Reference Manual.">
10 <link rel="stylesheet" href="llvm.css" type="text/css">
15 <div class="doc_title"> LLVM Language Reference Manual </div>
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_internal">'<tt>internal</tt>' Linkage</a></li>
29 <li><a href="#linkage_available_externally">'<tt>available_externally</tt>' Linkage</a></li>
30 <li><a href="#linkage_linkonce">'<tt>linkonce</tt>' Linkage</a></li>
31 <li><a href="#linkage_common">'<tt>common</tt>' Linkage</a></li>
32 <li><a href="#linkage_weak">'<tt>weak</tt>' Linkage</a></li>
33 <li><a href="#linkage_appending">'<tt>appending</tt>' Linkage</a></li>
34 <li><a href="#linkage_externweak">'<tt>extern_weak</tt>' Linkage</a></li>
35 <li><a href="#linkage_linkonce_odr">'<tt>linkonce_odr</tt>' Linkage</a></li>
36 <li><a href="#linkage_weak">'<tt>weak_odr</tt>' Linkage</a></li>
37 <li><a href="#linkage_external">'<tt>externally visible</tt>' Linkage</a></li>
38 <li><a href="#linkage_dllimport">'<tt>dllimport</tt>' Linkage</a></li>
39 <li><a href="#linkage_dllexport">'<tt>dllexport</tt>' Linkage</a></li>
42 <li><a href="#callingconv">Calling Conventions</a></li>
43 <li><a href="#namedtypes">Named Types</a></li>
44 <li><a href="#globalvars">Global Variables</a></li>
45 <li><a href="#functionstructure">Functions</a></li>
46 <li><a href="#aliasstructure">Aliases</a></li>
47 <li><a href="#namedmetadatastructure">Named Metadata</a></li>
48 <li><a href="#paramattrs">Parameter Attributes</a></li>
49 <li><a href="#fnattrs">Function Attributes</a></li>
50 <li><a href="#gc">Garbage Collector Names</a></li>
51 <li><a href="#moduleasm">Module-Level Inline Assembly</a></li>
52 <li><a href="#datalayout">Data Layout</a></li>
53 <li><a href="#pointeraliasing">Pointer Aliasing Rules</a></li>
54 <li><a href="#volatile">Volatile Memory Accesses</a></li>
57 <li><a href="#typesystem">Type System</a>
59 <li><a href="#t_classifications">Type Classifications</a></li>
60 <li><a href="#t_primitive">Primitive Types</a>
62 <li><a href="#t_integer">Integer Type</a></li>
63 <li><a href="#t_floating">Floating Point Types</a></li>
64 <li><a href="#t_void">Void Type</a></li>
65 <li><a href="#t_label">Label Type</a></li>
66 <li><a href="#t_metadata">Metadata Type</a></li>
69 <li><a href="#t_derived">Derived Types</a>
71 <li><a href="#t_aggregate">Aggregate Types</a>
73 <li><a href="#t_array">Array Type</a></li>
74 <li><a href="#t_struct">Structure Type</a></li>
75 <li><a href="#t_pstruct">Packed Structure Type</a></li>
76 <li><a href="#t_union">Union Type</a></li>
77 <li><a href="#t_vector">Vector Type</a></li>
80 <li><a href="#t_function">Function Type</a></li>
81 <li><a href="#t_pointer">Pointer Type</a></li>
82 <li><a href="#t_opaque">Opaque Type</a></li>
85 <li><a href="#t_uprefs">Type Up-references</a></li>
88 <li><a href="#constants">Constants</a>
90 <li><a href="#simpleconstants">Simple Constants</a></li>
91 <li><a href="#complexconstants">Complex Constants</a></li>
92 <li><a href="#globalconstants">Global Variable and Function Addresses</a></li>
93 <li><a href="#undefvalues">Undefined Values</a></li>
94 <li><a href="#trapvalues">Trap Values</a></li>
95 <li><a href="#blockaddress">Addresses of Basic Blocks</a></li>
96 <li><a href="#constantexprs">Constant Expressions</a></li>
99 <li><a href="#othervalues">Other Values</a>
101 <li><a href="#inlineasm">Inline Assembler Expressions</a></li>
102 <li><a href="#metadata">Metadata Nodes and Metadata Strings</a></li>
105 <li><a href="#intrinsic_globals">Intrinsic Global Variables</a>
107 <li><a href="#intg_used">The '<tt>llvm.used</tt>' Global Variable</a></li>
108 <li><a href="#intg_compiler_used">The '<tt>llvm.compiler.used</tt>'
109 Global Variable</a></li>
110 <li><a href="#intg_global_ctors">The '<tt>llvm.global_ctors</tt>'
111 Global Variable</a></li>
112 <li><a href="#intg_global_dtors">The '<tt>llvm.global_dtors</tt>'
113 Global Variable</a></li>
116 <li><a href="#instref">Instruction Reference</a>
118 <li><a href="#terminators">Terminator Instructions</a>
120 <li><a href="#i_ret">'<tt>ret</tt>' Instruction</a></li>
121 <li><a href="#i_br">'<tt>br</tt>' Instruction</a></li>
122 <li><a href="#i_switch">'<tt>switch</tt>' Instruction</a></li>
123 <li><a href="#i_indirectbr">'<tt>indirectbr</tt>' Instruction</a></li>
124 <li><a href="#i_invoke">'<tt>invoke</tt>' Instruction</a></li>
125 <li><a href="#i_unwind">'<tt>unwind</tt>' Instruction</a></li>
126 <li><a href="#i_unreachable">'<tt>unreachable</tt>' Instruction</a></li>
129 <li><a href="#binaryops">Binary Operations</a>
131 <li><a href="#i_add">'<tt>add</tt>' Instruction</a></li>
132 <li><a href="#i_fadd">'<tt>fadd</tt>' Instruction</a></li>
133 <li><a href="#i_sub">'<tt>sub</tt>' Instruction</a></li>
134 <li><a href="#i_fsub">'<tt>fsub</tt>' Instruction</a></li>
135 <li><a href="#i_mul">'<tt>mul</tt>' Instruction</a></li>
136 <li><a href="#i_fmul">'<tt>fmul</tt>' Instruction</a></li>
137 <li><a href="#i_udiv">'<tt>udiv</tt>' Instruction</a></li>
138 <li><a href="#i_sdiv">'<tt>sdiv</tt>' Instruction</a></li>
139 <li><a href="#i_fdiv">'<tt>fdiv</tt>' Instruction</a></li>
140 <li><a href="#i_urem">'<tt>urem</tt>' Instruction</a></li>
141 <li><a href="#i_srem">'<tt>srem</tt>' Instruction</a></li>
142 <li><a href="#i_frem">'<tt>frem</tt>' Instruction</a></li>
145 <li><a href="#bitwiseops">Bitwise Binary Operations</a>
147 <li><a href="#i_shl">'<tt>shl</tt>' Instruction</a></li>
148 <li><a href="#i_lshr">'<tt>lshr</tt>' Instruction</a></li>
149 <li><a href="#i_ashr">'<tt>ashr</tt>' Instruction</a></li>
150 <li><a href="#i_and">'<tt>and</tt>' Instruction</a></li>
151 <li><a href="#i_or">'<tt>or</tt>' Instruction</a></li>
152 <li><a href="#i_xor">'<tt>xor</tt>' Instruction</a></li>
155 <li><a href="#vectorops">Vector Operations</a>
157 <li><a href="#i_extractelement">'<tt>extractelement</tt>' Instruction</a></li>
158 <li><a href="#i_insertelement">'<tt>insertelement</tt>' Instruction</a></li>
159 <li><a href="#i_shufflevector">'<tt>shufflevector</tt>' Instruction</a></li>
162 <li><a href="#aggregateops">Aggregate Operations</a>
164 <li><a href="#i_extractvalue">'<tt>extractvalue</tt>' Instruction</a></li>
165 <li><a href="#i_insertvalue">'<tt>insertvalue</tt>' Instruction</a></li>
168 <li><a href="#memoryops">Memory Access and Addressing Operations</a>
170 <li><a href="#i_alloca">'<tt>alloca</tt>' Instruction</a></li>
171 <li><a href="#i_load">'<tt>load</tt>' Instruction</a></li>
172 <li><a href="#i_store">'<tt>store</tt>' Instruction</a></li>
173 <li><a href="#i_getelementptr">'<tt>getelementptr</tt>' Instruction</a></li>
176 <li><a href="#convertops">Conversion Operations</a>
178 <li><a href="#i_trunc">'<tt>trunc .. to</tt>' Instruction</a></li>
179 <li><a href="#i_zext">'<tt>zext .. to</tt>' Instruction</a></li>
180 <li><a href="#i_sext">'<tt>sext .. to</tt>' Instruction</a></li>
181 <li><a href="#i_fptrunc">'<tt>fptrunc .. to</tt>' Instruction</a></li>
182 <li><a href="#i_fpext">'<tt>fpext .. to</tt>' Instruction</a></li>
183 <li><a href="#i_fptoui">'<tt>fptoui .. to</tt>' Instruction</a></li>
184 <li><a href="#i_fptosi">'<tt>fptosi .. to</tt>' Instruction</a></li>
185 <li><a href="#i_uitofp">'<tt>uitofp .. to</tt>' Instruction</a></li>
186 <li><a href="#i_sitofp">'<tt>sitofp .. to</tt>' Instruction</a></li>
187 <li><a href="#i_ptrtoint">'<tt>ptrtoint .. to</tt>' Instruction</a></li>
188 <li><a href="#i_inttoptr">'<tt>inttoptr .. to</tt>' Instruction</a></li>
189 <li><a href="#i_bitcast">'<tt>bitcast .. to</tt>' Instruction</a></li>
192 <li><a href="#otherops">Other Operations</a>
194 <li><a href="#i_icmp">'<tt>icmp</tt>' Instruction</a></li>
195 <li><a href="#i_fcmp">'<tt>fcmp</tt>' Instruction</a></li>
196 <li><a href="#i_phi">'<tt>phi</tt>' Instruction</a></li>
197 <li><a href="#i_select">'<tt>select</tt>' Instruction</a></li>
198 <li><a href="#i_call">'<tt>call</tt>' Instruction</a></li>
199 <li><a href="#i_va_arg">'<tt>va_arg</tt>' Instruction</a></li>
204 <li><a href="#intrinsics">Intrinsic Functions</a>
206 <li><a href="#int_varargs">Variable Argument Handling Intrinsics</a>
208 <li><a href="#int_va_start">'<tt>llvm.va_start</tt>' Intrinsic</a></li>
209 <li><a href="#int_va_end">'<tt>llvm.va_end</tt>' Intrinsic</a></li>
210 <li><a href="#int_va_copy">'<tt>llvm.va_copy</tt>' Intrinsic</a></li>
213 <li><a href="#int_gc">Accurate Garbage Collection Intrinsics</a>
215 <li><a href="#int_gcroot">'<tt>llvm.gcroot</tt>' Intrinsic</a></li>
216 <li><a href="#int_gcread">'<tt>llvm.gcread</tt>' Intrinsic</a></li>
217 <li><a href="#int_gcwrite">'<tt>llvm.gcwrite</tt>' Intrinsic</a></li>
220 <li><a href="#int_codegen">Code Generator Intrinsics</a>
222 <li><a href="#int_returnaddress">'<tt>llvm.returnaddress</tt>' Intrinsic</a></li>
223 <li><a href="#int_frameaddress">'<tt>llvm.frameaddress</tt>' Intrinsic</a></li>
224 <li><a href="#int_stacksave">'<tt>llvm.stacksave</tt>' Intrinsic</a></li>
225 <li><a href="#int_stackrestore">'<tt>llvm.stackrestore</tt>' Intrinsic</a></li>
226 <li><a href="#int_prefetch">'<tt>llvm.prefetch</tt>' Intrinsic</a></li>
227 <li><a href="#int_pcmarker">'<tt>llvm.pcmarker</tt>' Intrinsic</a></li>
228 <li><a href="#int_readcyclecounter">'<tt>llvm.readcyclecounter</tt>' Intrinsic</a></li>
231 <li><a href="#int_libc">Standard C Library Intrinsics</a>
233 <li><a href="#int_memcpy">'<tt>llvm.memcpy.*</tt>' Intrinsic</a></li>
234 <li><a href="#int_memmove">'<tt>llvm.memmove.*</tt>' Intrinsic</a></li>
235 <li><a href="#int_memset">'<tt>llvm.memset.*</tt>' Intrinsic</a></li>
236 <li><a href="#int_sqrt">'<tt>llvm.sqrt.*</tt>' Intrinsic</a></li>
237 <li><a href="#int_powi">'<tt>llvm.powi.*</tt>' Intrinsic</a></li>
238 <li><a href="#int_sin">'<tt>llvm.sin.*</tt>' Intrinsic</a></li>
239 <li><a href="#int_cos">'<tt>llvm.cos.*</tt>' Intrinsic</a></li>
240 <li><a href="#int_pow">'<tt>llvm.pow.*</tt>' Intrinsic</a></li>
243 <li><a href="#int_manip">Bit Manipulation Intrinsics</a>
245 <li><a href="#int_bswap">'<tt>llvm.bswap.*</tt>' Intrinsics</a></li>
246 <li><a href="#int_ctpop">'<tt>llvm.ctpop.*</tt>' Intrinsic </a></li>
247 <li><a href="#int_ctlz">'<tt>llvm.ctlz.*</tt>' Intrinsic </a></li>
248 <li><a href="#int_cttz">'<tt>llvm.cttz.*</tt>' Intrinsic </a></li>
251 <li><a href="#int_overflow">Arithmetic with Overflow Intrinsics</a>
253 <li><a href="#int_sadd_overflow">'<tt>llvm.sadd.with.overflow.*</tt> Intrinsics</a></li>
254 <li><a href="#int_uadd_overflow">'<tt>llvm.uadd.with.overflow.*</tt> Intrinsics</a></li>
255 <li><a href="#int_ssub_overflow">'<tt>llvm.ssub.with.overflow.*</tt> Intrinsics</a></li>
256 <li><a href="#int_usub_overflow">'<tt>llvm.usub.with.overflow.*</tt> Intrinsics</a></li>
257 <li><a href="#int_smul_overflow">'<tt>llvm.smul.with.overflow.*</tt> Intrinsics</a></li>
258 <li><a href="#int_umul_overflow">'<tt>llvm.umul.with.overflow.*</tt> Intrinsics</a></li>
261 <li><a href="#int_fp16">Half Precision Floating Point Intrinsics</a>
263 <li><a href="#int_convert_to_fp16">'<tt>llvm.convert.to.fp16</tt>' Intrinsic</a></li>
264 <li><a href="#int_convert_from_fp16">'<tt>llvm.convert.from.fp16</tt>' Intrinsic</a></li>
267 <li><a href="#int_debugger">Debugger intrinsics</a></li>
268 <li><a href="#int_eh">Exception Handling intrinsics</a></li>
269 <li><a href="#int_trampoline">Trampoline Intrinsic</a>
271 <li><a href="#int_it">'<tt>llvm.init.trampoline</tt>' Intrinsic</a></li>
274 <li><a href="#int_atomics">Atomic intrinsics</a>
276 <li><a href="#int_memory_barrier"><tt>llvm.memory_barrier</tt></a></li>
277 <li><a href="#int_atomic_cmp_swap"><tt>llvm.atomic.cmp.swap</tt></a></li>
278 <li><a href="#int_atomic_swap"><tt>llvm.atomic.swap</tt></a></li>
279 <li><a href="#int_atomic_load_add"><tt>llvm.atomic.load.add</tt></a></li>
280 <li><a href="#int_atomic_load_sub"><tt>llvm.atomic.load.sub</tt></a></li>
281 <li><a href="#int_atomic_load_and"><tt>llvm.atomic.load.and</tt></a></li>
282 <li><a href="#int_atomic_load_nand"><tt>llvm.atomic.load.nand</tt></a></li>
283 <li><a href="#int_atomic_load_or"><tt>llvm.atomic.load.or</tt></a></li>
284 <li><a href="#int_atomic_load_xor"><tt>llvm.atomic.load.xor</tt></a></li>
285 <li><a href="#int_atomic_load_max"><tt>llvm.atomic.load.max</tt></a></li>
286 <li><a href="#int_atomic_load_min"><tt>llvm.atomic.load.min</tt></a></li>
287 <li><a href="#int_atomic_load_umax"><tt>llvm.atomic.load.umax</tt></a></li>
288 <li><a href="#int_atomic_load_umin"><tt>llvm.atomic.load.umin</tt></a></li>
291 <li><a href="#int_memorymarkers">Memory Use Markers</a>
293 <li><a href="#int_lifetime_start"><tt>llvm.lifetime.start</tt></a></li>
294 <li><a href="#int_lifetime_end"><tt>llvm.lifetime.end</tt></a></li>
295 <li><a href="#int_invariant_start"><tt>llvm.invariant.start</tt></a></li>
296 <li><a href="#int_invariant_end"><tt>llvm.invariant.end</tt></a></li>
299 <li><a href="#int_general">General intrinsics</a>
301 <li><a href="#int_var_annotation">
302 '<tt>llvm.var.annotation</tt>' Intrinsic</a></li>
303 <li><a href="#int_annotation">
304 '<tt>llvm.annotation.*</tt>' Intrinsic</a></li>
305 <li><a href="#int_trap">
306 '<tt>llvm.trap</tt>' Intrinsic</a></li>
307 <li><a href="#int_stackprotector">
308 '<tt>llvm.stackprotector</tt>' Intrinsic</a></li>
309 <li><a href="#int_objectsize">
310 '<tt>llvm.objectsize</tt>' Intrinsic</a></li>
317 <div class="doc_author">
318 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>
319 and <a href="mailto:vadve@cs.uiuc.edu">Vikram Adve</a></p>
322 <!-- *********************************************************************** -->
323 <div class="doc_section"> <a name="abstract">Abstract </a></div>
324 <!-- *********************************************************************** -->
326 <div class="doc_text">
328 <p>This document is a reference manual for the LLVM assembly language. LLVM is
329 a Static Single Assignment (SSA) based representation that provides type
330 safety, low-level operations, flexibility, and the capability of representing
331 'all' high-level languages cleanly. It is the common code representation
332 used throughout all phases of the LLVM compilation strategy.</p>
336 <!-- *********************************************************************** -->
337 <div class="doc_section"> <a name="introduction">Introduction</a> </div>
338 <!-- *********************************************************************** -->
340 <div class="doc_text">
342 <p>The LLVM code representation is designed to be used in three different forms:
343 as an in-memory compiler IR, as an on-disk bitcode representation (suitable
344 for fast loading by a Just-In-Time compiler), and as a human readable
345 assembly language representation. This allows LLVM to provide a powerful
346 intermediate representation for efficient compiler transformations and
347 analysis, while providing a natural means to debug and visualize the
348 transformations. The three different forms of LLVM are all equivalent. This
349 document describes the human readable representation and notation.</p>
351 <p>The LLVM representation aims to be light-weight and low-level while being
352 expressive, typed, and extensible at the same time. It aims to be a
353 "universal IR" of sorts, by being at a low enough level that high-level ideas
354 may be cleanly mapped to it (similar to how microprocessors are "universal
355 IR's", allowing many source languages to be mapped to them). By providing
356 type information, LLVM can be used as the target of optimizations: for
357 example, through pointer analysis, it can be proven that a C automatic
358 variable is never accessed outside of the current function, allowing it to
359 be promoted to a simple SSA value instead of a memory location.</p>
363 <!-- _______________________________________________________________________ -->
364 <div class="doc_subsubsection"> <a name="wellformed">Well-Formedness</a> </div>
366 <div class="doc_text">
368 <p>It is important to note that this document describes 'well formed' LLVM
369 assembly language. There is a difference between what the parser accepts and
370 what is considered 'well formed'. For example, the following instruction is
371 syntactically okay, but not well formed:</p>
373 <pre class="doc_code">
374 %x = <a href="#i_add">add</a> i32 1, %x
377 <p>because the definition of <tt>%x</tt> does not dominate all of its uses. The
378 LLVM infrastructure provides a verification pass that may be used to verify
379 that an LLVM module is well formed. This pass is automatically run by the
380 parser after parsing input assembly and by the optimizer before it outputs
381 bitcode. The violations pointed out by the verifier pass indicate bugs in
382 transformation passes or input to the parser.</p>
386 <!-- Describe the typesetting conventions here. -->
388 <!-- *********************************************************************** -->
389 <div class="doc_section"> <a name="identifiers">Identifiers</a> </div>
390 <!-- *********************************************************************** -->
392 <div class="doc_text">
394 <p>LLVM identifiers come in two basic types: global and local. Global
395 identifiers (functions, global variables) begin with the <tt>'@'</tt>
396 character. Local identifiers (register names, types) begin with
397 the <tt>'%'</tt> character. Additionally, there are three different formats
398 for identifiers, for different purposes:</p>
401 <li>Named values are represented as a string of characters with their prefix.
402 For example, <tt>%foo</tt>, <tt>@DivisionByZero</tt>,
403 <tt>%a.really.long.identifier</tt>. The actual regular expression used is
404 '<tt>[%@][a-zA-Z$._][a-zA-Z$._0-9]*</tt>'. Identifiers which require
405 other characters in their names can be surrounded with quotes. Special
406 characters may be escaped using <tt>"\xx"</tt> where <tt>xx</tt> is the
407 ASCII code for the character in hexadecimal. In this way, any character
408 can be used in a name value, even quotes themselves.</li>
410 <li>Unnamed values are represented as an unsigned numeric value with their
411 prefix. For example, <tt>%12</tt>, <tt>@2</tt>, <tt>%44</tt>.</li>
413 <li>Constants, which are described in a <a href="#constants">section about
414 constants</a>, below.</li>
417 <p>LLVM requires that values start with a prefix for two reasons: Compilers
418 don't need to worry about name clashes with reserved words, and the set of
419 reserved words may be expanded in the future without penalty. Additionally,
420 unnamed identifiers allow a compiler to quickly come up with a temporary
421 variable without having to avoid symbol table conflicts.</p>
423 <p>Reserved words in LLVM are very similar to reserved words in other
424 languages. There are keywords for different opcodes
425 ('<tt><a href="#i_add">add</a></tt>',
426 '<tt><a href="#i_bitcast">bitcast</a></tt>',
427 '<tt><a href="#i_ret">ret</a></tt>', etc...), for primitive type names
428 ('<tt><a href="#t_void">void</a></tt>',
429 '<tt><a href="#t_primitive">i32</a></tt>', etc...), and others. These
430 reserved words cannot conflict with variable names, because none of them
431 start with a prefix character (<tt>'%'</tt> or <tt>'@'</tt>).</p>
433 <p>Here is an example of LLVM code to multiply the integer variable
434 '<tt>%X</tt>' by 8:</p>
438 <pre class="doc_code">
439 %result = <a href="#i_mul">mul</a> i32 %X, 8
442 <p>After strength reduction:</p>
444 <pre class="doc_code">
445 %result = <a href="#i_shl">shl</a> i32 %X, i8 3
448 <p>And the hard way:</p>
450 <pre class="doc_code">
451 %0 = <a href="#i_add">add</a> i32 %X, %X <i>; yields {i32}:%0</i>
452 %1 = <a href="#i_add">add</a> i32 %0, %0 <i>; yields {i32}:%1</i>
453 %result = <a href="#i_add">add</a> i32 %1, %1
456 <p>This last way of multiplying <tt>%X</tt> by 8 illustrates several important
457 lexical features of LLVM:</p>
460 <li>Comments are delimited with a '<tt>;</tt>' and go until the end of
463 <li>Unnamed temporaries are created when the result of a computation is not
464 assigned to a named value.</li>
466 <li>Unnamed temporaries are numbered sequentially</li>
469 <p>It also shows a convention that we follow in this document. When
470 demonstrating instructions, we will follow an instruction with a comment that
471 defines the type and name of value produced. Comments are shown in italic
476 <!-- *********************************************************************** -->
477 <div class="doc_section"> <a name="highlevel">High Level Structure</a> </div>
478 <!-- *********************************************************************** -->
480 <!-- ======================================================================= -->
481 <div class="doc_subsection"> <a name="modulestructure">Module Structure</a>
484 <div class="doc_text">
486 <p>LLVM programs are composed of "Module"s, each of which is a translation unit
487 of the input programs. Each module consists of functions, global variables,
488 and symbol table entries. Modules may be combined together with the LLVM
489 linker, which merges function (and global variable) definitions, resolves
490 forward declarations, and merges symbol table entries. Here is an example of
491 the "hello world" module:</p>
493 <pre class="doc_code">
494 <i>; Declare the string constant as a global constant.</i>
495 <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>
497 <i>; External declaration of the puts function</i>
498 <a href="#functionstructure">declare</a> i32 @puts(i8*) <i>; i32 (i8*)* </i>
500 <i>; Definition of main function</i>
501 define i32 @main() { <i>; i32()* </i>
502 <i>; Convert [13 x i8]* to i8 *...</i>
503 %cast210 = <a href="#i_getelementptr">getelementptr</a> [13 x i8]* @.LC0, i64 0, i64 0 <i>; i8*</i>
505 <i>; Call puts function to write out the string to stdout.</i>
506 <a href="#i_call">call</a> i32 @puts(i8* %cast210) <i>; i32</i>
507 <a href="#i_ret">ret</a> i32 0<br>}
509 <i>; Named metadata</i>
510 !1 = metadata !{i32 41}
514 <p>This example is made up of a <a href="#globalvars">global variable</a> named
515 "<tt>.LC0</tt>", an external declaration of the "<tt>puts</tt>" function,
516 a <a href="#functionstructure">function definition</a> for
517 "<tt>main</tt>" and <a href="#namedmetadatastructure">named metadata</a>
520 <p>In general, a module is made up of a list of global values, where both
521 functions and global variables are global values. Global values are
522 represented by a pointer to a memory location (in this case, a pointer to an
523 array of char, and a pointer to a function), and have one of the
524 following <a href="#linkage">linkage types</a>.</p>
528 <!-- ======================================================================= -->
529 <div class="doc_subsection">
530 <a name="linkage">Linkage Types</a>
533 <div class="doc_text">
535 <p>All Global Variables and Functions have one of the following types of
539 <dt><tt><b><a name="linkage_private">private</a></b></tt></dt>
540 <dd>Global values with "<tt>private</tt>" linkage are only directly accessible
541 by objects in the current module. In particular, linking code into a
542 module with an private global value may cause the private to be renamed as
543 necessary to avoid collisions. Because the symbol is private to the
544 module, all references can be updated. This doesn't show up in any symbol
545 table in the object file.</dd>
547 <dt><tt><b><a name="linkage_linker_private">linker_private</a></b></tt></dt>
548 <dd>Similar to <tt>private</tt>, but the symbol is passed through the
549 assembler and evaluated by the linker. Unlike normal strong symbols, they
550 are removed by the linker from the final linked image (executable or
551 dynamic library).</dd>
553 <dt><tt><b><a name="linkage_linker_private_weak">linker_private_weak</a></b></tt></dt>
554 <dd>Similar to "<tt>linker_private</tt>", but the symbol is weak. Note that
555 <tt>linker_private_weak</tt> symbols are subject to coalescing by the
556 linker. The symbols are removed by the linker from the final linked image
557 (executable or dynamic library).</dd>
559 <dt><tt><b><a name="linkage_internal">internal</a></b></tt></dt>
560 <dd>Similar to private, but the value shows as a local symbol
561 (<tt>STB_LOCAL</tt> in the case of ELF) in the object file. This
562 corresponds to the notion of the '<tt>static</tt>' keyword in C.</dd>
564 <dt><tt><b><a name="linkage_available_externally">available_externally</a></b></tt></dt>
565 <dd>Globals with "<tt>available_externally</tt>" linkage are never emitted
566 into the object file corresponding to the LLVM module. They exist to
567 allow inlining and other optimizations to take place given knowledge of
568 the definition of the global, which is known to be somewhere outside the
569 module. Globals with <tt>available_externally</tt> linkage are allowed to
570 be discarded at will, and are otherwise the same as <tt>linkonce_odr</tt>.
571 This linkage type is only allowed on definitions, not declarations.</dd>
573 <dt><tt><b><a name="linkage_linkonce">linkonce</a></b></tt></dt>
574 <dd>Globals with "<tt>linkonce</tt>" linkage are merged with other globals of
575 the same name when linkage occurs. This can be used to implement
576 some forms of inline functions, templates, or other code which must be
577 generated in each translation unit that uses it, but where the body may
578 be overridden with a more definitive definition later. Unreferenced
579 <tt>linkonce</tt> globals are allowed to be discarded. Note that
580 <tt>linkonce</tt> linkage does not actually allow the optimizer to
581 inline the body of this function into callers because it doesn't know if
582 this definition of the function is the definitive definition within the
583 program or whether it will be overridden by a stronger definition.
584 To enable inlining and other optimizations, use "<tt>linkonce_odr</tt>"
587 <dt><tt><b><a name="linkage_weak">weak</a></b></tt></dt>
588 <dd>"<tt>weak</tt>" linkage has the same merging semantics as
589 <tt>linkonce</tt> linkage, except that unreferenced globals with
590 <tt>weak</tt> linkage may not be discarded. This is used for globals that
591 are declared "weak" in C source code.</dd>
593 <dt><tt><b><a name="linkage_common">common</a></b></tt></dt>
594 <dd>"<tt>common</tt>" linkage is most similar to "<tt>weak</tt>" linkage, but
595 they are used for tentative definitions in C, such as "<tt>int X;</tt>" at
597 Symbols with "<tt>common</tt>" linkage are merged in the same way as
598 <tt>weak symbols</tt>, and they may not be deleted if unreferenced.
599 <tt>common</tt> symbols may not have an explicit section,
600 must have a zero initializer, and may not be marked '<a
601 href="#globalvars"><tt>constant</tt></a>'. Functions and aliases may not
602 have common linkage.</dd>
605 <dt><tt><b><a name="linkage_appending">appending</a></b></tt></dt>
606 <dd>"<tt>appending</tt>" linkage may only be applied to global variables of
607 pointer to array type. When two global variables with appending linkage
608 are linked together, the two global arrays are appended together. This is
609 the LLVM, typesafe, equivalent of having the system linker append together
610 "sections" with identical names when .o files are linked.</dd>
612 <dt><tt><b><a name="linkage_externweak">extern_weak</a></b></tt></dt>
613 <dd>The semantics of this linkage follow the ELF object file model: the symbol
614 is weak until linked, if not linked, the symbol becomes null instead of
615 being an undefined reference.</dd>
617 <dt><tt><b><a name="linkage_linkonce_odr">linkonce_odr</a></b></tt></dt>
618 <dt><tt><b><a name="linkage_weak_odr">weak_odr</a></b></tt></dt>
619 <dd>Some languages allow differing globals to be merged, such as two functions
620 with different semantics. Other languages, such as <tt>C++</tt>, ensure
621 that only equivalent globals are ever merged (the "one definition rule"
622 — "ODR"). Such languages can use the <tt>linkonce_odr</tt>
623 and <tt>weak_odr</tt> linkage types to indicate that the global will only
624 be merged with equivalent globals. These linkage types are otherwise the
625 same as their non-<tt>odr</tt> versions.</dd>
627 <dt><tt><b><a name="linkage_external">externally visible</a></b></tt>:</dt>
628 <dd>If none of the above identifiers are used, the global is externally
629 visible, meaning that it participates in linkage and can be used to
630 resolve external symbol references.</dd>
633 <p>The next two types of linkage are targeted for Microsoft Windows platform
634 only. They are designed to support importing (exporting) symbols from (to)
635 DLLs (Dynamic Link Libraries).</p>
638 <dt><tt><b><a name="linkage_dllimport">dllimport</a></b></tt></dt>
639 <dd>"<tt>dllimport</tt>" linkage causes the compiler to reference a function
640 or variable via a global pointer to a pointer that is set up by the DLL
641 exporting the symbol. On Microsoft Windows targets, the pointer name is
642 formed by combining <code>__imp_</code> and the function or variable
645 <dt><tt><b><a name="linkage_dllexport">dllexport</a></b></tt></dt>
646 <dd>"<tt>dllexport</tt>" linkage causes the compiler to provide a global
647 pointer to a pointer in a DLL, so that it can be referenced with the
648 <tt>dllimport</tt> attribute. On Microsoft Windows targets, the pointer
649 name is formed by combining <code>__imp_</code> and the function or
653 <p>For example, since the "<tt>.LC0</tt>" variable is defined to be internal, if
654 another module defined a "<tt>.LC0</tt>" variable and was linked with this
655 one, one of the two would be renamed, preventing a collision. Since
656 "<tt>main</tt>" and "<tt>puts</tt>" are external (i.e., lacking any linkage
657 declarations), they are accessible outside of the current module.</p>
659 <p>It is illegal for a function <i>declaration</i> to have any linkage type
660 other than "externally visible", <tt>dllimport</tt>
661 or <tt>extern_weak</tt>.</p>
663 <p>Aliases can have only <tt>external</tt>, <tt>internal</tt>, <tt>weak</tt>
664 or <tt>weak_odr</tt> linkages.</p>
668 <!-- ======================================================================= -->
669 <div class="doc_subsection">
670 <a name="callingconv">Calling Conventions</a>
673 <div class="doc_text">
675 <p>LLVM <a href="#functionstructure">functions</a>, <a href="#i_call">calls</a>
676 and <a href="#i_invoke">invokes</a> can all have an optional calling
677 convention specified for the call. The calling convention of any pair of
678 dynamic caller/callee must match, or the behavior of the program is
679 undefined. The following calling conventions are supported by LLVM, and more
680 may be added in the future:</p>
683 <dt><b>"<tt>ccc</tt>" - The C calling convention</b>:</dt>
684 <dd>This calling convention (the default if no other calling convention is
685 specified) matches the target C calling conventions. This calling
686 convention supports varargs function calls and tolerates some mismatch in
687 the declared prototype and implemented declaration of the function (as
690 <dt><b>"<tt>fastcc</tt>" - The fast calling convention</b>:</dt>
691 <dd>This calling convention attempts to make calls as fast as possible
692 (e.g. by passing things in registers). This calling convention allows the
693 target to use whatever tricks it wants to produce fast code for the
694 target, without having to conform to an externally specified ABI
695 (Application Binary Interface).
696 <a href="CodeGenerator.html#tailcallopt">Tail calls can only be optimized
697 when this or the GHC convention is used.</a> This calling convention
698 does not support varargs and requires the prototype of all callees to
699 exactly match the prototype of the function definition.</dd>
701 <dt><b>"<tt>coldcc</tt>" - The cold calling convention</b>:</dt>
702 <dd>This calling convention attempts to make code in the caller as efficient
703 as possible under the assumption that the call is not commonly executed.
704 As such, these calls often preserve all registers so that the call does
705 not break any live ranges in the caller side. This calling convention
706 does not support varargs and requires the prototype of all callees to
707 exactly match the prototype of the function definition.</dd>
709 <dt><b>"<tt>cc <em>10</em></tt>" - GHC convention</b>:</dt>
710 <dd>This calling convention has been implemented specifically for use by the
711 <a href="http://www.haskell.org/ghc">Glasgow Haskell Compiler (GHC)</a>.
712 It passes everything in registers, going to extremes to achieve this by
713 disabling callee save registers. This calling convention should not be
714 used lightly but only for specific situations such as an alternative to
715 the <em>register pinning</em> performance technique often used when
716 implementing functional programming languages.At the moment only X86
717 supports this convention and it has the following limitations:
719 <li>On <em>X86-32</em> only supports up to 4 bit type parameters. No
720 floating point types are supported.</li>
721 <li>On <em>X86-64</em> only supports up to 10 bit type parameters and
722 6 floating point parameters.</li>
724 This calling convention supports
725 <a href="CodeGenerator.html#tailcallopt">tail call optimization</a> but
726 requires both the caller and callee are using it.
729 <dt><b>"<tt>cc <<em>n</em>></tt>" - Numbered convention</b>:</dt>
730 <dd>Any calling convention may be specified by number, allowing
731 target-specific calling conventions to be used. Target specific calling
732 conventions start at 64.</dd>
735 <p>More calling conventions can be added/defined on an as-needed basis, to
736 support Pascal conventions or any other well-known target-independent
741 <!-- ======================================================================= -->
742 <div class="doc_subsection">
743 <a name="visibility">Visibility Styles</a>
746 <div class="doc_text">
748 <p>All Global Variables and Functions have one of the following visibility
752 <dt><b>"<tt>default</tt>" - Default style</b>:</dt>
753 <dd>On targets that use the ELF object file format, default visibility means
754 that the declaration is visible to other modules and, in shared libraries,
755 means that the declared entity may be overridden. On Darwin, default
756 visibility means that the declaration is visible to other modules. Default
757 visibility corresponds to "external linkage" in the language.</dd>
759 <dt><b>"<tt>hidden</tt>" - Hidden style</b>:</dt>
760 <dd>Two declarations of an object with hidden visibility refer to the same
761 object if they are in the same shared object. Usually, hidden visibility
762 indicates that the symbol will not be placed into the dynamic symbol
763 table, so no other module (executable or shared library) can reference it
766 <dt><b>"<tt>protected</tt>" - Protected style</b>:</dt>
767 <dd>On ELF, protected visibility indicates that the symbol will be placed in
768 the dynamic symbol table, but that references within the defining module
769 will bind to the local symbol. That is, the symbol cannot be overridden by
775 <!-- ======================================================================= -->
776 <div class="doc_subsection">
777 <a name="namedtypes">Named Types</a>
780 <div class="doc_text">
782 <p>LLVM IR allows you to specify name aliases for certain types. This can make
783 it easier to read the IR and make the IR more condensed (particularly when
784 recursive types are involved). An example of a name specification is:</p>
786 <pre class="doc_code">
787 %mytype = type { %mytype*, i32 }
790 <p>You may give a name to any <a href="#typesystem">type</a> except
791 "<a href="t_void">void</a>". Type name aliases may be used anywhere a type
792 is expected with the syntax "%mytype".</p>
794 <p>Note that type names are aliases for the structural type that they indicate,
795 and that you can therefore specify multiple names for the same type. This
796 often leads to confusing behavior when dumping out a .ll file. Since LLVM IR
797 uses structural typing, the name is not part of the type. When printing out
798 LLVM IR, the printer will pick <em>one name</em> to render all types of a
799 particular shape. This means that if you have code where two different
800 source types end up having the same LLVM type, that the dumper will sometimes
801 print the "wrong" or unexpected type. This is an important design point and
802 isn't going to change.</p>
806 <!-- ======================================================================= -->
807 <div class="doc_subsection">
808 <a name="globalvars">Global Variables</a>
811 <div class="doc_text">
813 <p>Global variables define regions of memory allocated at compilation time
814 instead of run-time. Global variables may optionally be initialized, may
815 have an explicit section to be placed in, and may have an optional explicit
816 alignment specified. A variable may be defined as "thread_local", which
817 means that it will not be shared by threads (each thread will have a
818 separated copy of the variable). A variable may be defined as a global
819 "constant," which indicates that the contents of the variable
820 will <b>never</b> be modified (enabling better optimization, allowing the
821 global data to be placed in the read-only section of an executable, etc).
822 Note that variables that need runtime initialization cannot be marked
823 "constant" as there is a store to the variable.</p>
825 <p>LLVM explicitly allows <em>declarations</em> of global variables to be marked
826 constant, even if the final definition of the global is not. This capability
827 can be used to enable slightly better optimization of the program, but
828 requires the language definition to guarantee that optimizations based on the
829 'constantness' are valid for the translation units that do not include the
832 <p>As SSA values, global variables define pointer values that are in scope
833 (i.e. they dominate) all basic blocks in the program. Global variables
834 always define a pointer to their "content" type because they describe a
835 region of memory, and all memory objects in LLVM are accessed through
838 <p>A global variable may be declared to reside in a target-specific numbered
839 address space. For targets that support them, address spaces may affect how
840 optimizations are performed and/or what target instructions are used to
841 access the variable. The default address space is zero. The address space
842 qualifier must precede any other attributes.</p>
844 <p>LLVM allows an explicit section to be specified for globals. If the target
845 supports it, it will emit globals to the section specified.</p>
847 <p>An explicit alignment may be specified for a global, which must be a power
848 of 2. If not present, or if the alignment is set to zero, the alignment of
849 the global is set by the target to whatever it feels convenient. If an
850 explicit alignment is specified, the global is forced to have exactly that
851 alignment. Targets and optimizers are not allowed to over-align the global
852 if the global has an assigned section. In this case, the extra alignment
853 could be observable: for example, code could assume that the globals are
854 densely packed in their section and try to iterate over them as an array,
855 alignment padding would break this iteration.</p>
857 <p>For example, the following defines a global in a numbered address space with
858 an initializer, section, and alignment:</p>
860 <pre class="doc_code">
861 @G = addrspace(5) constant float 1.0, section "foo", align 4
867 <!-- ======================================================================= -->
868 <div class="doc_subsection">
869 <a name="functionstructure">Functions</a>
872 <div class="doc_text">
874 <p>LLVM function definitions consist of the "<tt>define</tt>" keyword, an
875 optional <a href="#linkage">linkage type</a>, an optional
876 <a href="#visibility">visibility style</a>, an optional
877 <a href="#callingconv">calling convention</a>, a return type, an optional
878 <a href="#paramattrs">parameter attribute</a> for the return type, a function
879 name, a (possibly empty) argument list (each with optional
880 <a href="#paramattrs">parameter attributes</a>), optional
881 <a href="#fnattrs">function attributes</a>, an optional section, an optional
882 alignment, an optional <a href="#gc">garbage collector name</a>, an opening
883 curly brace, a list of basic blocks, and a closing curly brace.</p>
885 <p>LLVM function declarations consist of the "<tt>declare</tt>" keyword, an
886 optional <a href="#linkage">linkage type</a>, an optional
887 <a href="#visibility">visibility style</a>, an optional
888 <a href="#callingconv">calling convention</a>, a return type, an optional
889 <a href="#paramattrs">parameter attribute</a> for the return type, a function
890 name, a possibly empty list of arguments, an optional alignment, and an
891 optional <a href="#gc">garbage collector name</a>.</p>
893 <p>A function definition contains a list of basic blocks, forming the CFG
894 (Control Flow Graph) for the function. Each basic block may optionally start
895 with a label (giving the basic block a symbol table entry), contains a list
896 of instructions, and ends with a <a href="#terminators">terminator</a>
897 instruction (such as a branch or function return).</p>
899 <p>The first basic block in a function is special in two ways: it is immediately
900 executed on entrance to the function, and it is not allowed to have
901 predecessor basic blocks (i.e. there can not be any branches to the entry
902 block of a function). Because the block can have no predecessors, it also
903 cannot have any <a href="#i_phi">PHI nodes</a>.</p>
905 <p>LLVM allows an explicit section to be specified for functions. If the target
906 supports it, it will emit functions to the section specified.</p>
908 <p>An explicit alignment may be specified for a function. If not present, or if
909 the alignment is set to zero, the alignment of the function is set by the
910 target to whatever it feels convenient. If an explicit alignment is
911 specified, the function is forced to have at least that much alignment. All
912 alignments must be a power of 2.</p>
915 <pre class="doc_code">
916 define [<a href="#linkage">linkage</a>] [<a href="#visibility">visibility</a>]
917 [<a href="#callingconv">cconv</a>] [<a href="#paramattrs">ret attrs</a>]
918 <ResultType> @<FunctionName> ([argument list])
919 [<a href="#fnattrs">fn Attrs</a>] [section "name"] [align N]
920 [<a href="#gc">gc</a>] { ... }
925 <!-- ======================================================================= -->
926 <div class="doc_subsection">
927 <a name="aliasstructure">Aliases</a>
930 <div class="doc_text">
932 <p>Aliases act as "second name" for the aliasee value (which can be either
933 function, global variable, another alias or bitcast of global value). Aliases
934 may have an optional <a href="#linkage">linkage type</a>, and an
935 optional <a href="#visibility">visibility style</a>.</p>
938 <pre class="doc_code">
939 @<Name> = alias [Linkage] [Visibility] <AliaseeTy> @<Aliasee>
944 <!-- ======================================================================= -->
945 <div class="doc_subsection">
946 <a name="namedmetadatastructure">Named Metadata</a>
949 <div class="doc_text">
951 <p>Named metadata is a collection of metadata. <a href="#metadata">Metadata
952 nodes</a> (but not metadata strings) and null are the only valid operands for
953 a named metadata.</p>
956 <pre class="doc_code">
957 !1 = metadata !{metadata !"one"}
963 <!-- ======================================================================= -->
964 <div class="doc_subsection"><a name="paramattrs">Parameter Attributes</a></div>
966 <div class="doc_text">
968 <p>The return type and each parameter of a function type may have a set of
969 <i>parameter attributes</i> associated with them. Parameter attributes are
970 used to communicate additional information about the result or parameters of
971 a function. Parameter attributes are considered to be part of the function,
972 not of the function type, so functions with different parameter attributes
973 can have the same function type.</p>
975 <p>Parameter attributes are simple keywords that follow the type specified. If
976 multiple parameter attributes are needed, they are space separated. For
979 <pre class="doc_code">
980 declare i32 @printf(i8* noalias nocapture, ...)
981 declare i32 @atoi(i8 zeroext)
982 declare signext i8 @returns_signed_char()
985 <p>Note that any attributes for the function result (<tt>nounwind</tt>,
986 <tt>readonly</tt>) come immediately after the argument list.</p>
988 <p>Currently, only the following parameter attributes are defined:</p>
991 <dt><tt><b>zeroext</b></tt></dt>
992 <dd>This indicates to the code generator that the parameter or return value
993 should be zero-extended to a 32-bit value by the caller (for a parameter)
994 or the callee (for a return value).</dd>
996 <dt><tt><b>signext</b></tt></dt>
997 <dd>This indicates to the code generator that the parameter or return value
998 should be sign-extended to a 32-bit value by the caller (for a parameter)
999 or the callee (for a return value).</dd>
1001 <dt><tt><b>inreg</b></tt></dt>
1002 <dd>This indicates that this parameter or return value should be treated in a
1003 special target-dependent fashion during while emitting code for a function
1004 call or return (usually, by putting it in a register as opposed to memory,
1005 though some targets use it to distinguish between two different kinds of
1006 registers). Use of this attribute is target-specific.</dd>
1008 <dt><tt><b><a name="byval">byval</a></b></tt></dt>
1009 <dd>This indicates that the pointer parameter should really be passed by value
1010 to the function. The attribute implies that a hidden copy of the pointee
1011 is made between the caller and the callee, so the callee is unable to
1012 modify the value in the callee. This attribute is only valid on LLVM
1013 pointer arguments. It is generally used to pass structs and arrays by
1014 value, but is also valid on pointers to scalars. The copy is considered
1015 to belong to the caller not the callee (for example,
1016 <tt><a href="#readonly">readonly</a></tt> functions should not write to
1017 <tt>byval</tt> parameters). This is not a valid attribute for return
1018 values. The byval attribute also supports specifying an alignment with
1019 the align attribute. This has a target-specific effect on the code
1020 generator that usually indicates a desired alignment for the synthesized
1023 <dt><tt><b><a name="sret">sret</a></b></tt></dt>
1024 <dd>This indicates that the pointer parameter specifies the address of a
1025 structure that is the return value of the function in the source program.
1026 This pointer must be guaranteed by the caller to be valid: loads and
1027 stores to the structure may be assumed by the callee to not to trap. This
1028 may only be applied to the first parameter. This is not a valid attribute
1029 for return values. </dd>
1031 <dt><tt><b><a name="noalias">noalias</a></b></tt></dt>
1032 <dd>This indicates that pointer values
1033 <a href="#pointeraliasing"><i>based</i></a> on the argument or return
1034 value do not alias pointer values which are not <i>based</i> on it,
1035 ignoring certain "irrelevant" dependencies.
1036 For a call to the parent function, dependencies between memory
1037 references from before or after the call and from those during the call
1038 are "irrelevant" to the <tt>noalias</tt> keyword for the arguments and
1039 return value used in that call.
1040 The caller shares the responsibility with the callee for ensuring that
1041 these requirements are met.
1042 For further details, please see the discussion of the NoAlias response in
1043 <a href="AliasAnalysis.html#MustMayNo">alias analysis</a>.<br>
1045 Note that this definition of <tt>noalias</tt> is intentionally
1046 similar to the definition of <tt>restrict</tt> in C99 for function
1047 arguments, though it is slightly weaker.
1049 For function return values, C99's <tt>restrict</tt> is not meaningful,
1050 while LLVM's <tt>noalias</tt> is.
1053 <dt><tt><b><a name="nocapture">nocapture</a></b></tt></dt>
1054 <dd>This indicates that the callee does not make any copies of the pointer
1055 that outlive the callee itself. This is not a valid attribute for return
1058 <dt><tt><b><a name="nest">nest</a></b></tt></dt>
1059 <dd>This indicates that the pointer parameter can be excised using the
1060 <a href="#int_trampoline">trampoline intrinsics</a>. This is not a valid
1061 attribute for return values.</dd>
1066 <!-- ======================================================================= -->
1067 <div class="doc_subsection">
1068 <a name="gc">Garbage Collector Names</a>
1071 <div class="doc_text">
1073 <p>Each function may specify a garbage collector name, which is simply a
1076 <pre class="doc_code">
1077 define void @f() gc "name" { ... }
1080 <p>The compiler declares the supported values of <i>name</i>. Specifying a
1081 collector which will cause the compiler to alter its output in order to
1082 support the named garbage collection algorithm.</p>
1086 <!-- ======================================================================= -->
1087 <div class="doc_subsection">
1088 <a name="fnattrs">Function Attributes</a>
1091 <div class="doc_text">
1093 <p>Function attributes are set to communicate additional information about a
1094 function. Function attributes are considered to be part of the function, not
1095 of the function type, so functions with different parameter attributes can
1096 have the same function type.</p>
1098 <p>Function attributes are simple keywords that follow the type specified. If
1099 multiple attributes are needed, they are space separated. For example:</p>
1101 <pre class="doc_code">
1102 define void @f() noinline { ... }
1103 define void @f() alwaysinline { ... }
1104 define void @f() alwaysinline optsize { ... }
1105 define void @f() optsize { ... }
1109 <dt><tt><b>alignstack(<<em>n</em>>)</b></tt></dt>
1110 <dd>This attribute indicates that, when emitting the prologue and epilogue,
1111 the backend should forcibly align the stack pointer. Specify the
1112 desired alignment, which must be a power of two, in parentheses.
1114 <dt><tt><b>alwaysinline</b></tt></dt>
1115 <dd>This attribute indicates that the inliner should attempt to inline this
1116 function into callers whenever possible, ignoring any active inlining size
1117 threshold for this caller.</dd>
1119 <dt><tt><b>inlinehint</b></tt></dt>
1120 <dd>This attribute indicates that the source code contained a hint that inlining
1121 this function is desirable (such as the "inline" keyword in C/C++). It
1122 is just a hint; it imposes no requirements on the inliner.</dd>
1124 <dt><tt><b>naked</b></tt></dt>
1125 <dd>This attribute disables prologue / epilogue emission for the function.
1126 This can have very system-specific consequences.</dd>
1128 <dt><tt><b>noimplicitfloat</b></tt></dt>
1129 <dd>This attributes disables implicit floating point instructions.</dd>
1131 <dt><tt><b>noinline</b></tt></dt>
1132 <dd>This attribute indicates that the inliner should never inline this
1133 function in any situation. This attribute may not be used together with
1134 the <tt>alwaysinline</tt> attribute.</dd>
1136 <dt><tt><b>noredzone</b></tt></dt>
1137 <dd>This attribute indicates that the code generator should not use a red
1138 zone, even if the target-specific ABI normally permits it.</dd>
1140 <dt><tt><b>noreturn</b></tt></dt>
1141 <dd>This function attribute indicates that the function never returns
1142 normally. This produces undefined behavior at runtime if the function
1143 ever does dynamically return.</dd>
1145 <dt><tt><b>nounwind</b></tt></dt>
1146 <dd>This function attribute indicates that the function never returns with an
1147 unwind or exceptional control flow. If the function does unwind, its
1148 runtime behavior is undefined.</dd>
1150 <dt><tt><b>optsize</b></tt></dt>
1151 <dd>This attribute suggests that optimization passes and code generator passes
1152 make choices that keep the code size of this function low, and otherwise
1153 do optimizations specifically to reduce code size.</dd>
1155 <dt><tt><b>readnone</b></tt></dt>
1156 <dd>This attribute indicates that the function computes its result (or decides
1157 to unwind an exception) based strictly on its arguments, without
1158 dereferencing any pointer arguments or otherwise accessing any mutable
1159 state (e.g. memory, control registers, etc) visible to caller functions.
1160 It does not write through any pointer arguments
1161 (including <tt><a href="#byval">byval</a></tt> arguments) and never
1162 changes any state visible to callers. This means that it cannot unwind
1163 exceptions by calling the <tt>C++</tt> exception throwing methods, but
1164 could use the <tt>unwind</tt> instruction.</dd>
1166 <dt><tt><b><a name="readonly">readonly</a></b></tt></dt>
1167 <dd>This attribute indicates that the function does not write through any
1168 pointer arguments (including <tt><a href="#byval">byval</a></tt>
1169 arguments) or otherwise modify any state (e.g. memory, control registers,
1170 etc) visible to caller functions. It may dereference pointer arguments
1171 and read state that may be set in the caller. A readonly function always
1172 returns the same value (or unwinds an exception identically) when called
1173 with the same set of arguments and global state. It cannot unwind an
1174 exception by calling the <tt>C++</tt> exception throwing methods, but may
1175 use the <tt>unwind</tt> instruction.</dd>
1177 <dt><tt><b><a name="ssp">ssp</a></b></tt></dt>
1178 <dd>This attribute indicates that the function should emit a stack smashing
1179 protector. It is in the form of a "canary"—a random value placed on
1180 the stack before the local variables that's checked upon return from the
1181 function to see if it has been overwritten. A heuristic is used to
1182 determine if a function needs stack protectors or not.<br>
1184 If a function that has an <tt>ssp</tt> attribute is inlined into a
1185 function that doesn't have an <tt>ssp</tt> attribute, then the resulting
1186 function will have an <tt>ssp</tt> attribute.</dd>
1188 <dt><tt><b>sspreq</b></tt></dt>
1189 <dd>This attribute indicates that the function should <em>always</em> emit a
1190 stack smashing protector. This overrides
1191 the <tt><a href="#ssp">ssp</a></tt> function attribute.<br>
1193 If a function that has an <tt>sspreq</tt> attribute is inlined into a
1194 function that doesn't have an <tt>sspreq</tt> attribute or which has
1195 an <tt>ssp</tt> attribute, then the resulting function will have
1196 an <tt>sspreq</tt> attribute.</dd>
1201 <!-- ======================================================================= -->
1202 <div class="doc_subsection">
1203 <a name="moduleasm">Module-Level Inline Assembly</a>
1206 <div class="doc_text">
1208 <p>Modules may contain "module-level inline asm" blocks, which corresponds to
1209 the GCC "file scope inline asm" blocks. These blocks are internally
1210 concatenated by LLVM and treated as a single unit, but may be separated in
1211 the <tt>.ll</tt> file if desired. The syntax is very simple:</p>
1213 <pre class="doc_code">
1214 module asm "inline asm code goes here"
1215 module asm "more can go here"
1218 <p>The strings can contain any character by escaping non-printable characters.
1219 The escape sequence used is simply "\xx" where "xx" is the two digit hex code
1222 <p>The inline asm code is simply printed to the machine code .s file when
1223 assembly code is generated.</p>
1227 <!-- ======================================================================= -->
1228 <div class="doc_subsection">
1229 <a name="datalayout">Data Layout</a>
1232 <div class="doc_text">
1234 <p>A module may specify a target specific data layout string that specifies how
1235 data is to be laid out in memory. The syntax for the data layout is
1238 <pre class="doc_code">
1239 target datalayout = "<i>layout specification</i>"
1242 <p>The <i>layout specification</i> consists of a list of specifications
1243 separated by the minus sign character ('-'). Each specification starts with
1244 a letter and may include other information after the letter to define some
1245 aspect of the data layout. The specifications accepted are as follows:</p>
1249 <dd>Specifies that the target lays out data in big-endian form. That is, the
1250 bits with the most significance have the lowest address location.</dd>
1253 <dd>Specifies that the target lays out data in little-endian form. That is,
1254 the bits with the least significance have the lowest address
1257 <dt><tt>p:<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
1258 <dd>This specifies the <i>size</i> of a pointer and its <i>abi</i> and
1259 <i>preferred</i> alignments. All sizes are in bits. Specifying
1260 the <i>pref</i> alignment is optional. If omitted, the
1261 preceding <tt>:</tt> should be omitted too.</dd>
1263 <dt><tt>i<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
1264 <dd>This specifies the alignment for an integer type of a given bit
1265 <i>size</i>. The value of <i>size</i> must be in the range [1,2^23).</dd>
1267 <dt><tt>v<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
1268 <dd>This specifies the alignment for a vector type of a given bit
1271 <dt><tt>f<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
1272 <dd>This specifies the alignment for a floating point type of a given bit
1273 <i>size</i>. Only values of <i>size</i> that are supported by the target
1274 will work. 32 (float) and 64 (double) are supported on all targets;
1275 80 or 128 (different flavors of long double) are also supported on some
1278 <dt><tt>a<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
1279 <dd>This specifies the alignment for an aggregate type of a given bit
1282 <dt><tt>s<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
1283 <dd>This specifies the alignment for a stack object of a given bit
1286 <dt><tt>n<i>size1</i>:<i>size2</i>:<i>size3</i>...</tt></dt>
1287 <dd>This specifies a set of native integer widths for the target CPU
1288 in bits. For example, it might contain "n32" for 32-bit PowerPC,
1289 "n32:64" for PowerPC 64, or "n8:16:32:64" for X86-64. Elements of
1290 this set are considered to support most general arithmetic
1291 operations efficiently.</dd>
1294 <p>When constructing the data layout for a given target, LLVM starts with a
1295 default set of specifications which are then (possibly) overridden by the
1296 specifications in the <tt>datalayout</tt> keyword. The default specifications
1297 are given in this list:</p>
1300 <li><tt>E</tt> - big endian</li>
1301 <li><tt>p:64:64:64</tt> - 64-bit pointers with 64-bit alignment</li>
1302 <li><tt>i1:8:8</tt> - i1 is 8-bit (byte) aligned</li>
1303 <li><tt>i8:8:8</tt> - i8 is 8-bit (byte) aligned</li>
1304 <li><tt>i16:16:16</tt> - i16 is 16-bit aligned</li>
1305 <li><tt>i32:32:32</tt> - i32 is 32-bit aligned</li>
1306 <li><tt>i64:32:64</tt> - i64 has ABI alignment of 32-bits but preferred
1307 alignment of 64-bits</li>
1308 <li><tt>f32:32:32</tt> - float is 32-bit aligned</li>
1309 <li><tt>f64:64:64</tt> - double is 64-bit aligned</li>
1310 <li><tt>v64:64:64</tt> - 64-bit vector is 64-bit aligned</li>
1311 <li><tt>v128:128:128</tt> - 128-bit vector is 128-bit aligned</li>
1312 <li><tt>a0:0:1</tt> - aggregates are 8-bit aligned</li>
1313 <li><tt>s0:64:64</tt> - stack objects are 64-bit aligned</li>
1316 <p>When LLVM is determining the alignment for a given type, it uses the
1317 following rules:</p>
1320 <li>If the type sought is an exact match for one of the specifications, that
1321 specification is used.</li>
1323 <li>If no match is found, and the type sought is an integer type, then the
1324 smallest integer type that is larger than the bitwidth of the sought type
1325 is used. If none of the specifications are larger than the bitwidth then
1326 the the largest integer type is used. For example, given the default
1327 specifications above, the i7 type will use the alignment of i8 (next
1328 largest) while both i65 and i256 will use the alignment of i64 (largest
1331 <li>If no match is found, and the type sought is a vector type, then the
1332 largest vector type that is smaller than the sought vector type will be
1333 used as a fall back. This happens because <128 x double> can be
1334 implemented in terms of 64 <2 x double>, for example.</li>
1339 <!-- ======================================================================= -->
1340 <div class="doc_subsection">
1341 <a name="pointeraliasing">Pointer Aliasing Rules</a>
1344 <div class="doc_text">
1346 <p>Any memory access must be done through a pointer value associated
1347 with an address range of the memory access, otherwise the behavior
1348 is undefined. Pointer values are associated with address ranges
1349 according to the following rules:</p>
1352 <li>A pointer value is associated with the addresses associated with
1353 any value it is <i>based</i> on.
1354 <li>An address of a global variable is associated with the address
1355 range of the variable's storage.</li>
1356 <li>The result value of an allocation instruction is associated with
1357 the address range of the allocated storage.</li>
1358 <li>A null pointer in the default address-space is associated with
1360 <li>An integer constant other than zero or a pointer value returned
1361 from a function not defined within LLVM may be associated with address
1362 ranges allocated through mechanisms other than those provided by
1363 LLVM. Such ranges shall not overlap with any ranges of addresses
1364 allocated by mechanisms provided by LLVM.</li>
1367 <p>A pointer value is <i>based</i> on another pointer value according
1368 to the following rules:</p>
1371 <li>A pointer value formed from a
1372 <tt><a href="#i_getelementptr">getelementptr</a></tt> operation
1373 is <i>based</i> on the first operand of the <tt>getelementptr</tt>.</li>
1374 <li>The result value of a
1375 <tt><a href="#i_bitcast">bitcast</a></tt> is <i>based</i> on the operand
1376 of the <tt>bitcast</tt>.</li>
1377 <li>A pointer value formed by an
1378 <tt><a href="#i_inttoptr">inttoptr</a></tt> is <i>based</i> on all
1379 pointer values that contribute (directly or indirectly) to the
1380 computation of the pointer's value.</li>
1381 <li>The "<i>based</i> on" relationship is transitive.</li>
1384 <p>Note that this definition of <i>"based"</i> is intentionally
1385 similar to the definition of <i>"based"</i> in C99, though it is
1386 slightly weaker.</p>
1388 <p>LLVM IR does not associate types with memory. The result type of a
1389 <tt><a href="#i_load">load</a></tt> merely indicates the size and
1390 alignment of the memory from which to load, as well as the
1391 interpretation of the value. The first operand type of a
1392 <tt><a href="#i_store">store</a></tt> similarly only indicates the size
1393 and alignment of the store.</p>
1395 <p>Consequently, type-based alias analysis, aka TBAA, aka
1396 <tt>-fstrict-aliasing</tt>, is not applicable to general unadorned
1397 LLVM IR. <a href="#metadata">Metadata</a> may be used to encode
1398 additional information which specialized optimization passes may use
1399 to implement type-based alias analysis.</p>
1403 <!-- ======================================================================= -->
1404 <div class="doc_subsection">
1405 <a name="volatile">Volatile Memory Accesses</a>
1408 <div class="doc_text">
1410 <p>Certain memory accesses, such as <a href="#i_load"><tt>load</tt></a>s, <a
1411 href="#i_store"><tt>store</tt></a>s, and <a
1412 href="#int_memcpy"><tt>llvm.memcpy</tt></a>s may be marked <tt>volatile</tt>.
1413 The optimizers must not change the number of volatile operations or change their
1414 order of execution relative to other volatile operations. The optimizers
1415 <i>may</i> change the order of volatile operations relative to non-volatile
1416 operations. This is not Java's "volatile" and has no cross-thread
1417 synchronization behavior.</p>
1421 <!-- *********************************************************************** -->
1422 <div class="doc_section"> <a name="typesystem">Type System</a> </div>
1423 <!-- *********************************************************************** -->
1425 <div class="doc_text">
1427 <p>The LLVM type system is one of the most important features of the
1428 intermediate representation. Being typed enables a number of optimizations
1429 to be performed on the intermediate representation directly, without having
1430 to do extra analyses on the side before the transformation. A strong type
1431 system makes it easier to read the generated code and enables novel analyses
1432 and transformations that are not feasible to perform on normal three address
1433 code representations.</p>
1437 <!-- ======================================================================= -->
1438 <div class="doc_subsection"> <a name="t_classifications">Type
1439 Classifications</a> </div>
1441 <div class="doc_text">
1443 <p>The types fall into a few useful classifications:</p>
1445 <table border="1" cellspacing="0" cellpadding="4">
1447 <tr><th>Classification</th><th>Types</th></tr>
1449 <td><a href="#t_integer">integer</a></td>
1450 <td><tt>i1, i2, i3, ... i8, ... i16, ... i32, ... i64, ... </tt></td>
1453 <td><a href="#t_floating">floating point</a></td>
1454 <td><tt>float, double, x86_fp80, fp128, ppc_fp128</tt></td>
1457 <td><a name="t_firstclass">first class</a></td>
1458 <td><a href="#t_integer">integer</a>,
1459 <a href="#t_floating">floating point</a>,
1460 <a href="#t_pointer">pointer</a>,
1461 <a href="#t_vector">vector</a>,
1462 <a href="#t_struct">structure</a>,
1463 <a href="#t_union">union</a>,
1464 <a href="#t_array">array</a>,
1465 <a href="#t_label">label</a>,
1466 <a href="#t_metadata">metadata</a>.
1470 <td><a href="#t_primitive">primitive</a></td>
1471 <td><a href="#t_label">label</a>,
1472 <a href="#t_void">void</a>,
1473 <a href="#t_floating">floating point</a>,
1474 <a href="#t_metadata">metadata</a>.</td>
1477 <td><a href="#t_derived">derived</a></td>
1478 <td><a href="#t_array">array</a>,
1479 <a href="#t_function">function</a>,
1480 <a href="#t_pointer">pointer</a>,
1481 <a href="#t_struct">structure</a>,
1482 <a href="#t_pstruct">packed structure</a>,
1483 <a href="#t_union">union</a>,
1484 <a href="#t_vector">vector</a>,
1485 <a href="#t_opaque">opaque</a>.
1491 <p>The <a href="#t_firstclass">first class</a> types are perhaps the most
1492 important. Values of these types are the only ones which can be produced by
1497 <!-- ======================================================================= -->
1498 <div class="doc_subsection"> <a name="t_primitive">Primitive Types</a> </div>
1500 <div class="doc_text">
1502 <p>The primitive types are the fundamental building blocks of the LLVM
1507 <!-- _______________________________________________________________________ -->
1508 <div class="doc_subsubsection"> <a name="t_integer">Integer Type</a> </div>
1510 <div class="doc_text">
1513 <p>The integer type is a very simple type that simply specifies an arbitrary
1514 bit width for the integer type desired. Any bit width from 1 bit to
1515 2<sup>23</sup>-1 (about 8 million) can be specified.</p>
1522 <p>The number of bits the integer will occupy is specified by the <tt>N</tt>
1526 <table class="layout">
1528 <td class="left"><tt>i1</tt></td>
1529 <td class="left">a single-bit integer.</td>
1532 <td class="left"><tt>i32</tt></td>
1533 <td class="left">a 32-bit integer.</td>
1536 <td class="left"><tt>i1942652</tt></td>
1537 <td class="left">a really big integer of over 1 million bits.</td>
1543 <!-- _______________________________________________________________________ -->
1544 <div class="doc_subsubsection"> <a name="t_floating">Floating Point Types</a> </div>
1546 <div class="doc_text">
1550 <tr><th>Type</th><th>Description</th></tr>
1551 <tr><td><tt>float</tt></td><td>32-bit floating point value</td></tr>
1552 <tr><td><tt>double</tt></td><td>64-bit floating point value</td></tr>
1553 <tr><td><tt>fp128</tt></td><td>128-bit floating point value (112-bit mantissa)</td></tr>
1554 <tr><td><tt>x86_fp80</tt></td><td>80-bit floating point value (X87)</td></tr>
1555 <tr><td><tt>ppc_fp128</tt></td><td>128-bit floating point value (two 64-bits)</td></tr>
1561 <!-- _______________________________________________________________________ -->
1562 <div class="doc_subsubsection"> <a name="t_void">Void Type</a> </div>
1564 <div class="doc_text">
1567 <p>The void type does not represent any value and has no size.</p>
1576 <!-- _______________________________________________________________________ -->
1577 <div class="doc_subsubsection"> <a name="t_label">Label Type</a> </div>
1579 <div class="doc_text">
1582 <p>The label type represents code labels.</p>
1591 <!-- _______________________________________________________________________ -->
1592 <div class="doc_subsubsection"> <a name="t_metadata">Metadata Type</a> </div>
1594 <div class="doc_text">
1597 <p>The metadata type represents embedded metadata. No derived types may be
1598 created from metadata except for <a href="#t_function">function</a>
1609 <!-- ======================================================================= -->
1610 <div class="doc_subsection"> <a name="t_derived">Derived Types</a> </div>
1612 <div class="doc_text">
1614 <p>The real power in LLVM comes from the derived types in the system. This is
1615 what allows a programmer to represent arrays, functions, pointers, and other
1616 useful types. Each of these types contain one or more element types which
1617 may be a primitive type, or another derived type. For example, it is
1618 possible to have a two dimensional array, using an array as the element type
1619 of another array.</p>
1624 <!-- _______________________________________________________________________ -->
1625 <div class="doc_subsubsection"> <a name="t_aggregate">Aggregate Types</a> </div>
1627 <div class="doc_text">
1629 <p>Aggregate Types are a subset of derived types that can contain multiple
1630 member types. <a href="#t_array">Arrays</a>,
1631 <a href="#t_struct">structs</a>, <a href="#t_vector">vectors</a> and
1632 <a href="#t_union">unions</a> are aggregate types.</p>
1636 <!-- _______________________________________________________________________ -->
1637 <div class="doc_subsubsection"> <a name="t_array">Array Type</a> </div>
1639 <div class="doc_text">
1642 <p>The array type is a very simple derived type that arranges elements
1643 sequentially in memory. The array type requires a size (number of elements)
1644 and an underlying data type.</p>
1648 [<# elements> x <elementtype>]
1651 <p>The number of elements is a constant integer value; <tt>elementtype</tt> may
1652 be any type with a size.</p>
1655 <table class="layout">
1657 <td class="left"><tt>[40 x i32]</tt></td>
1658 <td class="left">Array of 40 32-bit integer values.</td>
1661 <td class="left"><tt>[41 x i32]</tt></td>
1662 <td class="left">Array of 41 32-bit integer values.</td>
1665 <td class="left"><tt>[4 x i8]</tt></td>
1666 <td class="left">Array of 4 8-bit integer values.</td>
1669 <p>Here are some examples of multidimensional arrays:</p>
1670 <table class="layout">
1672 <td class="left"><tt>[3 x [4 x i32]]</tt></td>
1673 <td class="left">3x4 array of 32-bit integer values.</td>
1676 <td class="left"><tt>[12 x [10 x float]]</tt></td>
1677 <td class="left">12x10 array of single precision floating point values.</td>
1680 <td class="left"><tt>[2 x [3 x [4 x i16]]]</tt></td>
1681 <td class="left">2x3x4 array of 16-bit integer values.</td>
1685 <p>There is no restriction on indexing beyond the end of the array implied by
1686 a static type (though there are restrictions on indexing beyond the bounds
1687 of an allocated object in some cases). This means that single-dimension
1688 'variable sized array' addressing can be implemented in LLVM with a zero
1689 length array type. An implementation of 'pascal style arrays' in LLVM could
1690 use the type "<tt>{ i32, [0 x float]}</tt>", for example.</p>
1694 <!-- _______________________________________________________________________ -->
1695 <div class="doc_subsubsection"> <a name="t_function">Function Type</a> </div>
1697 <div class="doc_text">
1700 <p>The function type can be thought of as a function signature. It consists of
1701 a return type and a list of formal parameter types. The return type of a
1702 function type is a scalar type, a void type, a struct type, or a union
1703 type. If the return type is a struct type then all struct elements must be
1704 of first class types, and the struct must have at least one element.</p>
1708 <returntype> (<parameter list>)
1711 <p>...where '<tt><parameter list></tt>' is a comma-separated list of type
1712 specifiers. Optionally, the parameter list may include a type <tt>...</tt>,
1713 which indicates that the function takes a variable number of arguments.
1714 Variable argument functions can access their arguments with
1715 the <a href="#int_varargs">variable argument handling intrinsic</a>
1716 functions. '<tt><returntype></tt>' is any type except
1717 <a href="#t_label">label</a>.</p>
1720 <table class="layout">
1722 <td class="left"><tt>i32 (i32)</tt></td>
1723 <td class="left">function taking an <tt>i32</tt>, returning an <tt>i32</tt>
1725 </tr><tr class="layout">
1726 <td class="left"><tt>float (i16, i32 *) *
1728 <td class="left"><a href="#t_pointer">Pointer</a> to a function that takes
1729 an <tt>i16</tt> and a <a href="#t_pointer">pointer</a> to <tt>i32</tt>,
1730 returning <tt>float</tt>.
1732 </tr><tr class="layout">
1733 <td class="left"><tt>i32 (i8*, ...)</tt></td>
1734 <td class="left">A vararg function that takes at least one
1735 <a href="#t_pointer">pointer</a> to <tt>i8 </tt> (char in C),
1736 which returns an integer. This is the signature for <tt>printf</tt> in
1739 </tr><tr class="layout">
1740 <td class="left"><tt>{i32, i32} (i32)</tt></td>
1741 <td class="left">A function taking an <tt>i32</tt>, returning a
1742 <a href="#t_struct">structure</a> containing two <tt>i32</tt> values
1749 <!-- _______________________________________________________________________ -->
1750 <div class="doc_subsubsection"> <a name="t_struct">Structure Type</a> </div>
1752 <div class="doc_text">
1755 <p>The structure type is used to represent a collection of data members together
1756 in memory. The packing of the field types is defined to match the ABI of the
1757 underlying processor. The elements of a structure may be any type that has a
1760 <p>Structures in memory are accessed using '<tt><a href="#i_load">load</a></tt>'
1761 and '<tt><a href="#i_store">store</a></tt>' by getting a pointer to a field
1762 with the '<tt><a href="#i_getelementptr">getelementptr</a></tt>' instruction.
1763 Structures in registers are accessed using the
1764 '<tt><a href="#i_extractvalue">extractvalue</a></tt>' and
1765 '<tt><a href="#i_insertvalue">insertvalue</a></tt>' instructions.</p>
1768 { <type list> }
1772 <table class="layout">
1774 <td class="left"><tt>{ i32, i32, i32 }</tt></td>
1775 <td class="left">A triple of three <tt>i32</tt> values</td>
1776 </tr><tr class="layout">
1777 <td class="left"><tt>{ float, i32 (i32) * }</tt></td>
1778 <td class="left">A pair, where the first element is a <tt>float</tt> and the
1779 second element is a <a href="#t_pointer">pointer</a> to a
1780 <a href="#t_function">function</a> that takes an <tt>i32</tt>, returning
1781 an <tt>i32</tt>.</td>
1787 <!-- _______________________________________________________________________ -->
1788 <div class="doc_subsubsection"> <a name="t_pstruct">Packed Structure Type</a>
1791 <div class="doc_text">
1794 <p>The packed structure type is used to represent a collection of data members
1795 together in memory. There is no padding between fields. Further, the
1796 alignment of a packed structure is 1 byte. The elements of a packed
1797 structure may be any type that has a size.</p>
1799 <p>Structures are accessed using '<tt><a href="#i_load">load</a></tt> and
1800 '<tt><a href="#i_store">store</a></tt>' by getting a pointer to a field with
1801 the '<tt><a href="#i_getelementptr">getelementptr</a></tt>' instruction.</p>
1805 < { <type list> } >
1809 <table class="layout">
1811 <td class="left"><tt>< { i32, i32, i32 } ></tt></td>
1812 <td class="left">A triple of three <tt>i32</tt> values</td>
1813 </tr><tr class="layout">
1815 <tt>< { float, i32 (i32)* } ></tt></td>
1816 <td class="left">A pair, where the first element is a <tt>float</tt> and the
1817 second element is a <a href="#t_pointer">pointer</a> to a
1818 <a href="#t_function">function</a> that takes an <tt>i32</tt>, returning
1819 an <tt>i32</tt>.</td>
1825 <!-- _______________________________________________________________________ -->
1826 <div class="doc_subsubsection"> <a name="t_union">Union Type</a> </div>
1828 <div class="doc_text">
1831 <p>A union type describes an object with size and alignment suitable for
1832 an object of any one of a given set of types (also known as an "untagged"
1833 union). It is similar in concept and usage to a
1834 <a href="#t_struct">struct</a>, except that all members of the union
1835 have an offset of zero. The elements of a union may be any type that has a
1836 size. Unions must have at least one member - empty unions are not allowed.
1839 <p>The size of the union as a whole will be the size of its largest member,
1840 and the alignment requirements of the union as a whole will be the largest
1841 alignment requirement of any member.</p>
1843 <p>Union members are accessed using '<tt><a href="#i_load">load</a></tt> and
1844 '<tt><a href="#i_store">store</a></tt>' by getting a pointer to a field with
1845 the '<tt><a href="#i_getelementptr">getelementptr</a></tt>' instruction.
1846 Since all members are at offset zero, the getelementptr instruction does
1847 not affect the address, only the type of the resulting pointer.</p>
1851 union { <type list> }
1855 <table class="layout">
1857 <td class="left"><tt>union { i32, i32*, float }</tt></td>
1858 <td class="left">A union of three types: an <tt>i32</tt>, a pointer to
1859 an <tt>i32</tt>, and a <tt>float</tt>.</td>
1860 </tr><tr class="layout">
1862 <tt>union { float, i32 (i32) * }</tt></td>
1863 <td class="left">A union, where the first element is a <tt>float</tt> and the
1864 second element is a <a href="#t_pointer">pointer</a> to a
1865 <a href="#t_function">function</a> that takes an <tt>i32</tt>, returning
1866 an <tt>i32</tt>.</td>
1872 <!-- _______________________________________________________________________ -->
1873 <div class="doc_subsubsection"> <a name="t_pointer">Pointer Type</a> </div>
1875 <div class="doc_text">
1878 <p>The pointer type is used to specify memory locations.
1879 Pointers are commonly used to reference objects in memory.</p>
1881 <p>Pointer types may have an optional address space attribute defining the
1882 numbered address space where the pointed-to object resides. The default
1883 address space is number zero. The semantics of non-zero address
1884 spaces are target-specific.</p>
1886 <p>Note that LLVM does not permit pointers to void (<tt>void*</tt>) nor does it
1887 permit pointers to labels (<tt>label*</tt>). Use <tt>i8*</tt> instead.</p>
1895 <table class="layout">
1897 <td class="left"><tt>[4 x i32]*</tt></td>
1898 <td class="left">A <a href="#t_pointer">pointer</a> to <a
1899 href="#t_array">array</a> of four <tt>i32</tt> values.</td>
1902 <td class="left"><tt>i32 (i32*) *</tt></td>
1903 <td class="left"> A <a href="#t_pointer">pointer</a> to a <a
1904 href="#t_function">function</a> that takes an <tt>i32*</tt>, returning an
1908 <td class="left"><tt>i32 addrspace(5)*</tt></td>
1909 <td class="left">A <a href="#t_pointer">pointer</a> to an <tt>i32</tt> value
1910 that resides in address space #5.</td>
1916 <!-- _______________________________________________________________________ -->
1917 <div class="doc_subsubsection"> <a name="t_vector">Vector Type</a> </div>
1919 <div class="doc_text">
1922 <p>A vector type is a simple derived type that represents a vector of elements.
1923 Vector types are used when multiple primitive data are operated in parallel
1924 using a single instruction (SIMD). A vector type requires a size (number of
1925 elements) and an underlying primitive data type. Vector types are considered
1926 <a href="#t_firstclass">first class</a>.</p>
1930 < <# elements> x <elementtype> >
1933 <p>The number of elements is a constant integer value; elementtype may be any
1934 integer or floating point type.</p>
1937 <table class="layout">
1939 <td class="left"><tt><4 x i32></tt></td>
1940 <td class="left">Vector of 4 32-bit integer values.</td>
1943 <td class="left"><tt><8 x float></tt></td>
1944 <td class="left">Vector of 8 32-bit floating-point values.</td>
1947 <td class="left"><tt><2 x i64></tt></td>
1948 <td class="left">Vector of 2 64-bit integer values.</td>
1954 <!-- _______________________________________________________________________ -->
1955 <div class="doc_subsubsection"> <a name="t_opaque">Opaque Type</a> </div>
1956 <div class="doc_text">
1959 <p>Opaque types are used to represent unknown types in the system. This
1960 corresponds (for example) to the C notion of a forward declared structure
1961 type. In LLVM, opaque types can eventually be resolved to any type (not just
1962 a structure type).</p>
1970 <table class="layout">
1972 <td class="left"><tt>opaque</tt></td>
1973 <td class="left">An opaque type.</td>
1979 <!-- ======================================================================= -->
1980 <div class="doc_subsection">
1981 <a name="t_uprefs">Type Up-references</a>
1984 <div class="doc_text">
1987 <p>An "up reference" allows you to refer to a lexically enclosing type without
1988 requiring it to have a name. For instance, a structure declaration may
1989 contain a pointer to any of the types it is lexically a member of. Example
1990 of up references (with their equivalent as named type declarations)
1994 { \2 * } %x = type { %x* }
1995 { \2 }* %y = type { %y }*
1999 <p>An up reference is needed by the asmprinter for printing out cyclic types
2000 when there is no declared name for a type in the cycle. Because the
2001 asmprinter does not want to print out an infinite type string, it needs a
2002 syntax to handle recursive types that have no names (all names are optional
2010 <p>The level is the count of the lexical type that is being referred to.</p>
2013 <table class="layout">
2015 <td class="left"><tt>\1*</tt></td>
2016 <td class="left">Self-referential pointer.</td>
2019 <td class="left"><tt>{ { \3*, i8 }, i32 }</tt></td>
2020 <td class="left">Recursive structure where the upref refers to the out-most
2027 <!-- *********************************************************************** -->
2028 <div class="doc_section"> <a name="constants">Constants</a> </div>
2029 <!-- *********************************************************************** -->
2031 <div class="doc_text">
2033 <p>LLVM has several different basic types of constants. This section describes
2034 them all and their syntax.</p>
2038 <!-- ======================================================================= -->
2039 <div class="doc_subsection"><a name="simpleconstants">Simple Constants</a></div>
2041 <div class="doc_text">
2044 <dt><b>Boolean constants</b></dt>
2045 <dd>The two strings '<tt>true</tt>' and '<tt>false</tt>' are both valid
2046 constants of the <tt><a href="#t_integer">i1</a></tt> type.</dd>
2048 <dt><b>Integer constants</b></dt>
2049 <dd>Standard integers (such as '4') are constants of
2050 the <a href="#t_integer">integer</a> type. Negative numbers may be used
2051 with integer types.</dd>
2053 <dt><b>Floating point constants</b></dt>
2054 <dd>Floating point constants use standard decimal notation (e.g. 123.421),
2055 exponential notation (e.g. 1.23421e+2), or a more precise hexadecimal
2056 notation (see below). The assembler requires the exact decimal value of a
2057 floating-point constant. For example, the assembler accepts 1.25 but
2058 rejects 1.3 because 1.3 is a repeating decimal in binary. Floating point
2059 constants must have a <a href="#t_floating">floating point</a> type. </dd>
2061 <dt><b>Null pointer constants</b></dt>
2062 <dd>The identifier '<tt>null</tt>' is recognized as a null pointer constant
2063 and must be of <a href="#t_pointer">pointer type</a>.</dd>
2066 <p>The one non-intuitive notation for constants is the hexadecimal form of
2067 floating point constants. For example, the form '<tt>double
2068 0x432ff973cafa8000</tt>' is equivalent to (but harder to read than)
2069 '<tt>double 4.5e+15</tt>'. The only time hexadecimal floating point
2070 constants are required (and the only time that they are generated by the
2071 disassembler) is when a floating point constant must be emitted but it cannot
2072 be represented as a decimal floating point number in a reasonable number of
2073 digits. For example, NaN's, infinities, and other special values are
2074 represented in their IEEE hexadecimal format so that assembly and disassembly
2075 do not cause any bits to change in the constants.</p>
2077 <p>When using the hexadecimal form, constants of types float and double are
2078 represented using the 16-digit form shown above (which matches the IEEE754
2079 representation for double); float values must, however, be exactly
2080 representable as IEE754 single precision. Hexadecimal format is always used
2081 for long double, and there are three forms of long double. The 80-bit format
2082 used by x86 is represented as <tt>0xK</tt> followed by 20 hexadecimal digits.
2083 The 128-bit format used by PowerPC (two adjacent doubles) is represented
2084 by <tt>0xM</tt> followed by 32 hexadecimal digits. The IEEE 128-bit format
2085 is represented by <tt>0xL</tt> followed by 32 hexadecimal digits; no
2086 currently supported target uses this format. Long doubles will only work if
2087 they match the long double format on your target. All hexadecimal formats
2088 are big-endian (sign bit at the left).</p>
2092 <!-- ======================================================================= -->
2093 <div class="doc_subsection">
2094 <a name="aggregateconstants"></a> <!-- old anchor -->
2095 <a name="complexconstants">Complex Constants</a>
2098 <div class="doc_text">
2100 <p>Complex constants are a (potentially recursive) combination of simple
2101 constants and smaller complex constants.</p>
2104 <dt><b>Structure constants</b></dt>
2105 <dd>Structure constants are represented with notation similar to structure
2106 type definitions (a comma separated list of elements, surrounded by braces
2107 (<tt>{}</tt>)). For example: "<tt>{ i32 4, float 17.0, i32* @G }</tt>",
2108 where "<tt>@G</tt>" is declared as "<tt>@G = external global i32</tt>".
2109 Structure constants must have <a href="#t_struct">structure type</a>, and
2110 the number and types of elements must match those specified by the
2113 <dt><b>Union constants</b></dt>
2114 <dd>Union constants are represented with notation similar to a structure with
2115 a single element - that is, a single typed element surrounded
2116 by braces (<tt>{}</tt>)). For example: "<tt>{ i32 4 }</tt>". The
2117 <a href="#t_union">union type</a> can be initialized with a single-element
2118 struct as long as the type of the struct element matches the type of
2119 one of the union members.</dd>
2121 <dt><b>Array constants</b></dt>
2122 <dd>Array constants are represented with notation similar to array type
2123 definitions (a comma separated list of elements, surrounded by square
2124 brackets (<tt>[]</tt>)). For example: "<tt>[ i32 42, i32 11, i32 74
2125 ]</tt>". Array constants must have <a href="#t_array">array type</a>, and
2126 the number and types of elements must match those specified by the
2129 <dt><b>Vector constants</b></dt>
2130 <dd>Vector constants are represented with notation similar to vector type
2131 definitions (a comma separated list of elements, surrounded by
2132 less-than/greater-than's (<tt><></tt>)). For example: "<tt>< i32
2133 42, i32 11, i32 74, i32 100 ></tt>". Vector constants must
2134 have <a href="#t_vector">vector type</a>, and the number and types of
2135 elements must match those specified by the type.</dd>
2137 <dt><b>Zero initialization</b></dt>
2138 <dd>The string '<tt>zeroinitializer</tt>' can be used to zero initialize a
2139 value to zero of <em>any</em> type, including scalar and
2140 <a href="#t_aggregate">aggregate</a> types.
2141 This is often used to avoid having to print large zero initializers
2142 (e.g. for large arrays) and is always exactly equivalent to using explicit
2143 zero initializers.</dd>
2145 <dt><b>Metadata node</b></dt>
2146 <dd>A metadata node is a structure-like constant with
2147 <a href="#t_metadata">metadata type</a>. For example: "<tt>metadata !{
2148 i32 0, metadata !"test" }</tt>". Unlike other constants that are meant to
2149 be interpreted as part of the instruction stream, metadata is a place to
2150 attach additional information such as debug info.</dd>
2155 <!-- ======================================================================= -->
2156 <div class="doc_subsection">
2157 <a name="globalconstants">Global Variable and Function Addresses</a>
2160 <div class="doc_text">
2162 <p>The addresses of <a href="#globalvars">global variables</a>
2163 and <a href="#functionstructure">functions</a> are always implicitly valid
2164 (link-time) constants. These constants are explicitly referenced when
2165 the <a href="#identifiers">identifier for the global</a> is used and always
2166 have <a href="#t_pointer">pointer</a> type. For example, the following is a
2167 legal LLVM file:</p>
2169 <pre class="doc_code">
2172 @Z = global [2 x i32*] [ i32* @X, i32* @Y ]
2177 <!-- ======================================================================= -->
2178 <div class="doc_subsection"><a name="undefvalues">Undefined Values</a></div>
2179 <div class="doc_text">
2181 <p>The string '<tt>undef</tt>' can be used anywhere a constant is expected, and
2182 indicates that the user of the value may receive an unspecified bit-pattern.
2183 Undefined values may be of any type (other than label or void) and be used
2184 anywhere a constant is permitted.</p>
2186 <p>Undefined values are useful because they indicate to the compiler that the
2187 program is well defined no matter what value is used. This gives the
2188 compiler more freedom to optimize. Here are some examples of (potentially
2189 surprising) transformations that are valid (in pseudo IR):</p>
2192 <pre class="doc_code">
2202 <p>This is safe because all of the output bits are affected by the undef bits.
2203 Any output bit can have a zero or one depending on the input bits.</p>
2205 <pre class="doc_code">
2216 <p>These logical operations have bits that are not always affected by the input.
2217 For example, if "%X" has a zero bit, then the output of the 'and' operation will
2218 always be a zero, no matter what the corresponding bit from the undef is. As
2219 such, it is unsafe to optimize or assume that the result of the and is undef.
2220 However, it is safe to assume that all bits of the undef could be 0, and
2221 optimize the and to 0. Likewise, it is safe to assume that all the bits of
2222 the undef operand to the or could be set, allowing the or to be folded to
2225 <pre class="doc_code">
2226 %A = select undef, %X, %Y
2227 %B = select undef, 42, %Y
2228 %C = select %X, %Y, undef
2239 <p>This set of examples show that undefined select (and conditional branch)
2240 conditions can go "either way" but they have to come from one of the two
2241 operands. In the %A example, if %X and %Y were both known to have a clear low
2242 bit, then %A would have to have a cleared low bit. However, in the %C example,
2243 the optimizer is allowed to assume that the undef operand could be the same as
2244 %Y, allowing the whole select to be eliminated.</p>
2247 <pre class="doc_code">
2248 %A = xor undef, undef
2266 <p>This example points out that two undef operands are not necessarily the same.
2267 This can be surprising to people (and also matches C semantics) where they
2268 assume that "X^X" is always zero, even if X is undef. This isn't true for a
2269 number of reasons, but the short answer is that an undef "variable" can
2270 arbitrarily change its value over its "live range". This is true because the
2271 "variable" doesn't actually <em>have a live range</em>. Instead, the value is
2272 logically read from arbitrary registers that happen to be around when needed,
2273 so the value is not necessarily consistent over time. In fact, %A and %C need
2274 to have the same semantics or the core LLVM "replace all uses with" concept
2277 <pre class="doc_code">
2285 <p>These examples show the crucial difference between an <em>undefined
2286 value</em> and <em>undefined behavior</em>. An undefined value (like undef) is
2287 allowed to have an arbitrary bit-pattern. This means that the %A operation
2288 can be constant folded to undef because the undef could be an SNaN, and fdiv is
2289 not (currently) defined on SNaN's. However, in the second example, we can make
2290 a more aggressive assumption: because the undef is allowed to be an arbitrary
2291 value, we are allowed to assume that it could be zero. Since a divide by zero
2292 has <em>undefined behavior</em>, we are allowed to assume that the operation
2293 does not execute at all. This allows us to delete the divide and all code after
2294 it: since the undefined operation "can't happen", the optimizer can assume that
2295 it occurs in dead code.
2298 <pre class="doc_code">
2299 a: store undef -> %X
2300 b: store %X -> undef
2306 <p>These examples reiterate the fdiv example: a store "of" an undefined value
2307 can be assumed to not have any effect: we can assume that the value is
2308 overwritten with bits that happen to match what was already there. However, a
2309 store "to" an undefined location could clobber arbitrary memory, therefore, it
2310 has undefined behavior.</p>
2314 <!-- ======================================================================= -->
2315 <div class="doc_subsection"><a name="trapvalues">Trap Values</a></div>
2316 <div class="doc_text">
2318 <p>Trap values are similar to <a href="#undefvalues">undef values</a>, however
2319 instead of representing an unspecified bit pattern, they represent the
2320 fact that an instruction or constant expression which cannot evoke side
2321 effects has nevertheless detected a condition which results in undefined
2324 <p>There is currently no way of representing a trap value in the IR; they
2325 only exist when produced by operations such as
2326 <a href="#i_add"><tt>add</tt></a> with the <tt>nsw</tt> flag.</p>
2328 <p>Trap value behavior is defined in terms of value <i>dependence</i>:</p>
2331 <li>Values other than <a href="#i_phi"><tt>phi</tt></a> nodes depend on
2332 their operands.</li>
2334 <li><a href="#i_phi"><tt>Phi</tt></a> nodes depend on the operand corresponding
2335 to their dynamic predecessor basic block.</li>
2337 <li>Function arguments depend on the corresponding actual argument values in
2338 the dynamic callers of their functions.</li>
2340 <li><a href="#i_call"><tt>Call</tt></a> instructions depend on the
2341 <a href="#i_ret"><tt>ret</tt></a> instructions that dynamically transfer
2342 control back to them.</li>
2344 <li><a href="#i_invoke"><tt>Invoke</tt></a> instructions depend on the
2345 <a href="#i_ret"><tt>ret</tt></a>, <a href="#i_unwind"><tt>unwind</tt></a>,
2346 or exception-throwing call instructions that dynamically transfer control
2349 <li>Non-volatile loads and stores depend on the most recent stores to all of the
2350 referenced memory addresses, following the order in the IR
2351 (including loads and stores implied by intrinsics such as
2352 <a href="#int_memcpy"><tt>@llvm.memcpy</tt></a>.)</li>
2354 <!-- TODO: In the case of multiple threads, this only applies if the store
2355 "happens-before" the load or store. -->
2357 <!-- TODO: floating-point exception state -->
2359 <li>An instruction with externally visible side effects depends on the most
2360 recent preceding instruction with externally visible side effects, following
2361 the order in the IR. (This includes
2362 <a href="#volatile">volatile operations</a>.)</li>
2364 <li>An instruction <i>control-depends</i> on a
2365 <a href="#terminators">terminator instruction</a>
2366 if the terminator instruction has multiple successors and the instruction
2367 is always executed when control transfers to one of the successors, and
2368 may not be executed when control is transfered to another.</li>
2370 <li>Dependence is transitive.</li>
2374 <p>Whenever a trap value is generated, all values which depend on it evaluate
2375 to trap. If they have side effects, the evoke their side effects as if each
2376 operand with a trap value were undef. If they have externally-visible side
2377 effects, the behavior is undefined.</p>
2379 <p>Here are some examples:</p>
2381 <pre class="doc_code">
2383 %trap = sub nuw i32 0, 1 ; Results in a trap value.
2384 %still_trap = and i32 %trap, 0 ; Whereas (and i32 undef, 0) would return 0.
2385 %trap_yet_again = getelementptr i32* @h, i32 %still_trap
2386 store i32 0, i32* %trap_yet_again ; undefined behavior
2388 store i32 %trap, i32* @g ; Trap value conceptually stored to memory.
2389 %trap2 = load i32* @g ; Returns a trap value, not just undef.
2391 volatile store i32 %trap, i32* @g ; External observation; undefined behavior.
2393 %narrowaddr = bitcast i32* @g to i16*
2394 %wideaddr = bitcast i32* @g to i64*
2395 %trap3 = load 16* %narrowaddr ; Returns a trap value.
2396 %trap4 = load i64* %widaddr ; Returns a trap value.
2398 %cmp = icmp i32 slt %trap, 0 ; Returns a trap value.
2399 %br i1 %cmp, %true, %end ; Branch to either destination.
2402 volatile store i32 0, i32* @g ; This is control-dependent on %cmp, so
2403 ; it has undefined behavior.
2407 %p = phi i32 [ 0, %entry ], [ 1, %true ]
2408 ; Both edges into this PHI are
2409 ; control-dependent on %cmp, so this
2410 ; always results in a trap value.
2412 volatile store i32 0, i32* @g ; %end is control-equivalent to %entry
2413 ; so this is defined (ignoring earlier
2414 ; undefined behavior in this example).
2419 <!-- ======================================================================= -->
2420 <div class="doc_subsection"><a name="blockaddress">Addresses of Basic
2422 <div class="doc_text">
2424 <p><b><tt>blockaddress(@function, %block)</tt></b></p>
2426 <p>The '<tt>blockaddress</tt>' constant computes the address of the specified
2427 basic block in the specified function, and always has an i8* type. Taking
2428 the address of the entry block is illegal.</p>
2430 <p>This value only has defined behavior when used as an operand to the
2431 '<a href="#i_indirectbr"><tt>indirectbr</tt></a>' instruction or for comparisons
2432 against null. Pointer equality tests between labels addresses is undefined
2433 behavior - though, again, comparison against null is ok, and no label is
2434 equal to the null pointer. This may also be passed around as an opaque
2435 pointer sized value as long as the bits are not inspected. This allows
2436 <tt>ptrtoint</tt> and arithmetic to be performed on these values so long as
2437 the original value is reconstituted before the <tt>indirectbr</tt>.</p>
2439 <p>Finally, some targets may provide defined semantics when
2440 using the value as the operand to an inline assembly, but that is target
2447 <!-- ======================================================================= -->
2448 <div class="doc_subsection"><a name="constantexprs">Constant Expressions</a>
2451 <div class="doc_text">
2453 <p>Constant expressions are used to allow expressions involving other constants
2454 to be used as constants. Constant expressions may be of
2455 any <a href="#t_firstclass">first class</a> type and may involve any LLVM
2456 operation that does not have side effects (e.g. load and call are not
2457 supported). The following is the syntax for constant expressions:</p>
2460 <dt><b><tt>trunc (CST to TYPE)</tt></b></dt>
2461 <dd>Truncate a constant to another type. The bit size of CST must be larger
2462 than the bit size of TYPE. Both types must be integers.</dd>
2464 <dt><b><tt>zext (CST to TYPE)</tt></b></dt>
2465 <dd>Zero extend a constant to another type. The bit size of CST must be
2466 smaller than the bit size of TYPE. Both types must be integers.</dd>
2468 <dt><b><tt>sext (CST to TYPE)</tt></b></dt>
2469 <dd>Sign extend a constant to another type. The bit size of CST must be
2470 smaller than the bit size of TYPE. Both types must be integers.</dd>
2472 <dt><b><tt>fptrunc (CST to TYPE)</tt></b></dt>
2473 <dd>Truncate a floating point constant to another floating point type. The
2474 size of CST must be larger than the size of TYPE. Both types must be
2475 floating point.</dd>
2477 <dt><b><tt>fpext (CST to TYPE)</tt></b></dt>
2478 <dd>Floating point extend a constant to another type. The size of CST must be
2479 smaller or equal to the size of TYPE. Both types must be floating
2482 <dt><b><tt>fptoui (CST to TYPE)</tt></b></dt>
2483 <dd>Convert a floating point constant to the corresponding unsigned integer
2484 constant. TYPE must be a scalar or vector integer type. CST must be of
2485 scalar or vector floating point type. Both CST and TYPE must be scalars,
2486 or vectors of the same number of elements. If the value won't fit in the
2487 integer type, the results are undefined.</dd>
2489 <dt><b><tt>fptosi (CST to TYPE)</tt></b></dt>
2490 <dd>Convert a floating point constant to the corresponding signed integer
2491 constant. TYPE must be a scalar or vector integer type. CST must be of
2492 scalar or vector floating point type. Both CST and TYPE must be scalars,
2493 or vectors of the same number of elements. If the value won't fit in the
2494 integer type, the results are undefined.</dd>
2496 <dt><b><tt>uitofp (CST to TYPE)</tt></b></dt>
2497 <dd>Convert an unsigned integer constant to the corresponding floating point
2498 constant. TYPE must be a scalar or vector floating point type. CST must be
2499 of scalar or vector integer type. Both CST and TYPE must be scalars, or
2500 vectors of the same number of elements. If the value won't fit in the
2501 floating point type, the results are undefined.</dd>
2503 <dt><b><tt>sitofp (CST to TYPE)</tt></b></dt>
2504 <dd>Convert a signed integer constant to the corresponding floating point
2505 constant. TYPE must be a scalar or vector floating point type. CST must be
2506 of scalar or vector integer type. Both CST and TYPE must be scalars, or
2507 vectors of the same number of elements. If the value won't fit in the
2508 floating point type, the results are undefined.</dd>
2510 <dt><b><tt>ptrtoint (CST to TYPE)</tt></b></dt>
2511 <dd>Convert a pointer typed constant to the corresponding integer constant
2512 <tt>TYPE</tt> must be an integer type. <tt>CST</tt> must be of pointer
2513 type. The <tt>CST</tt> value is zero extended, truncated, or unchanged to
2514 make it fit in <tt>TYPE</tt>.</dd>
2516 <dt><b><tt>inttoptr (CST to TYPE)</tt></b></dt>
2517 <dd>Convert a integer constant to a pointer constant. TYPE must be a pointer
2518 type. CST must be of integer type. The CST value is zero extended,
2519 truncated, or unchanged to make it fit in a pointer size. This one is
2520 <i>really</i> dangerous!</dd>
2522 <dt><b><tt>bitcast (CST to TYPE)</tt></b></dt>
2523 <dd>Convert a constant, CST, to another TYPE. The constraints of the operands
2524 are the same as those for the <a href="#i_bitcast">bitcast
2525 instruction</a>.</dd>
2527 <dt><b><tt>getelementptr (CSTPTR, IDX0, IDX1, ...)</tt></b></dt>
2528 <dt><b><tt>getelementptr inbounds (CSTPTR, IDX0, IDX1, ...)</tt></b></dt>
2529 <dd>Perform the <a href="#i_getelementptr">getelementptr operation</a> on
2530 constants. As with the <a href="#i_getelementptr">getelementptr</a>
2531 instruction, the index list may have zero or more indexes, which are
2532 required to make sense for the type of "CSTPTR".</dd>
2534 <dt><b><tt>select (COND, VAL1, VAL2)</tt></b></dt>
2535 <dd>Perform the <a href="#i_select">select operation</a> on constants.</dd>
2537 <dt><b><tt>icmp COND (VAL1, VAL2)</tt></b></dt>
2538 <dd>Performs the <a href="#i_icmp">icmp operation</a> on constants.</dd>
2540 <dt><b><tt>fcmp COND (VAL1, VAL2)</tt></b></dt>
2541 <dd>Performs the <a href="#i_fcmp">fcmp operation</a> on constants.</dd>
2543 <dt><b><tt>extractelement (VAL, IDX)</tt></b></dt>
2544 <dd>Perform the <a href="#i_extractelement">extractelement operation</a> on
2547 <dt><b><tt>insertelement (VAL, ELT, IDX)</tt></b></dt>
2548 <dd>Perform the <a href="#i_insertelement">insertelement operation</a> on
2551 <dt><b><tt>shufflevector (VEC1, VEC2, IDXMASK)</tt></b></dt>
2552 <dd>Perform the <a href="#i_shufflevector">shufflevector operation</a> on
2555 <dt><b><tt>extractvalue (VAL, IDX0, IDX1, ...)</tt></b></dt>
2556 <dd>Perform the <a href="#i_extractvalue">extractvalue operation</a> on
2557 constants. The index list is interpreted in a similar manner as indices in
2558 a '<a href="#i_getelementptr">getelementptr</a>' operation. At least one
2559 index value must be specified.</dd>
2561 <dt><b><tt>insertvalue (VAL, ELT, IDX0, IDX1, ...)</tt></b></dt>
2562 <dd>Perform the <a href="#i_insertvalue">insertvalue operation</a> on
2563 constants. The index list is interpreted in a similar manner as indices in
2564 a '<a href="#i_getelementptr">getelementptr</a>' operation. At least one
2565 index value must be specified.</dd>
2567 <dt><b><tt>OPCODE (LHS, RHS)</tt></b></dt>
2568 <dd>Perform the specified operation of the LHS and RHS constants. OPCODE may
2569 be any of the <a href="#binaryops">binary</a>
2570 or <a href="#bitwiseops">bitwise binary</a> operations. The constraints
2571 on operands are the same as those for the corresponding instruction
2572 (e.g. no bitwise operations on floating point values are allowed).</dd>
2577 <!-- *********************************************************************** -->
2578 <div class="doc_section"> <a name="othervalues">Other Values</a> </div>
2579 <!-- *********************************************************************** -->
2581 <!-- ======================================================================= -->
2582 <div class="doc_subsection">
2583 <a name="inlineasm">Inline Assembler Expressions</a>
2586 <div class="doc_text">
2588 <p>LLVM supports inline assembler expressions (as opposed
2589 to <a href="#moduleasm"> Module-Level Inline Assembly</a>) through the use of
2590 a special value. This value represents the inline assembler as a string
2591 (containing the instructions to emit), a list of operand constraints (stored
2592 as a string), a flag that indicates whether or not the inline asm
2593 expression has side effects, and a flag indicating whether the function
2594 containing the asm needs to align its stack conservatively. An example
2595 inline assembler expression is:</p>
2597 <pre class="doc_code">
2598 i32 (i32) asm "bswap $0", "=r,r"
2601 <p>Inline assembler expressions may <b>only</b> be used as the callee operand of
2602 a <a href="#i_call"><tt>call</tt> instruction</a>. Thus, typically we
2605 <pre class="doc_code">
2606 %X = call i32 asm "<a href="#int_bswap">bswap</a> $0", "=r,r"(i32 %Y)
2609 <p>Inline asms with side effects not visible in the constraint list must be
2610 marked as having side effects. This is done through the use of the
2611 '<tt>sideeffect</tt>' keyword, like so:</p>
2613 <pre class="doc_code">
2614 call void asm sideeffect "eieio", ""()
2617 <p>In some cases inline asms will contain code that will not work unless the
2618 stack is aligned in some way, such as calls or SSE instructions on x86,
2619 yet will not contain code that does that alignment within the asm.
2620 The compiler should make conservative assumptions about what the asm might
2621 contain and should generate its usual stack alignment code in the prologue
2622 if the '<tt>alignstack</tt>' keyword is present:</p>
2624 <pre class="doc_code">
2625 call void asm alignstack "eieio", ""()
2628 <p>If both keywords appear the '<tt>sideeffect</tt>' keyword must come
2631 <p>TODO: The format of the asm and constraints string still need to be
2632 documented here. Constraints on what can be done (e.g. duplication, moving,
2633 etc need to be documented). This is probably best done by reference to
2634 another document that covers inline asm from a holistic perspective.</p>
2637 <div class="doc_subsubsection">
2638 <a name="inlineasm_md">Inline Asm Metadata</a>
2641 <div class="doc_text">
2643 <p>The call instructions that wrap inline asm nodes may have a "!srcloc" MDNode
2644 attached to it that contains a constant integer. If present, the code
2645 generator will use the integer as the location cookie value when report
2646 errors through the LLVMContext error reporting mechanisms. This allows a
2647 front-end to correlate backend errors that occur with inline asm back to the
2648 source code that produced it. For example:</p>
2650 <pre class="doc_code">
2651 call void asm sideeffect "something bad", ""()<b>, !srcloc !42</b>
2653 !42 = !{ i32 1234567 }
2656 <p>It is up to the front-end to make sense of the magic numbers it places in the
2661 <!-- ======================================================================= -->
2662 <div class="doc_subsection"><a name="metadata">Metadata Nodes and Metadata
2666 <div class="doc_text">
2668 <p>LLVM IR allows metadata to be attached to instructions in the program that
2669 can convey extra information about the code to the optimizers and code
2670 generator. One example application of metadata is source-level debug
2671 information. There are two metadata primitives: strings and nodes. All
2672 metadata has the <tt>metadata</tt> type and is identified in syntax by a
2673 preceding exclamation point ('<tt>!</tt>').</p>
2675 <p>A metadata string is a string surrounded by double quotes. It can contain
2676 any character by escaping non-printable characters with "\xx" where "xx" is
2677 the two digit hex code. For example: "<tt>!"test\00"</tt>".</p>
2679 <p>Metadata nodes are represented with notation similar to structure constants
2680 (a comma separated list of elements, surrounded by braces and preceded by an
2681 exclamation point). For example: "<tt>!{ metadata !"test\00", i32
2682 10}</tt>". Metadata nodes can have any values as their operand.</p>
2684 <p>A <a href="#namedmetadatastructure">named metadata</a> is a collection of
2685 metadata nodes, which can be looked up in the module symbol table. For
2686 example: "<tt>!foo = metadata !{!4, !3}</tt>".
2688 <p>Metadata can be used as function arguments. Here <tt>llvm.dbg.value</tt>
2689 function is using two metadata arguments.</p>
2691 <pre class="doc_code">
2692 call void @llvm.dbg.value(metadata !24, i64 0, metadata !25)
2695 <p>Metadata can be attached with an instruction. Here metadata <tt>!21</tt> is
2696 attached with <tt>add</tt> instruction using <tt>!dbg</tt> identifier.</p>
2698 <pre class="doc_code">
2699 %indvar.next = add i64 %indvar, 1, !dbg !21
2704 <!-- *********************************************************************** -->
2705 <div class="doc_section">
2706 <a name="intrinsic_globals">Intrinsic Global Variables</a>
2708 <!-- *********************************************************************** -->
2710 <p>LLVM has a number of "magic" global variables that contain data that affect
2711 code generation or other IR semantics. These are documented here. All globals
2712 of this sort should have a section specified as "<tt>llvm.metadata</tt>". This
2713 section and all globals that start with "<tt>llvm.</tt>" are reserved for use
2716 <!-- ======================================================================= -->
2717 <div class="doc_subsection">
2718 <a name="intg_used">The '<tt>llvm.used</tt>' Global Variable</a>
2721 <div class="doc_text">
2723 <p>The <tt>@llvm.used</tt> global is an array with i8* element type which has <a
2724 href="#linkage_appending">appending linkage</a>. This array contains a list of
2725 pointers to global variables and functions which may optionally have a pointer
2726 cast formed of bitcast or getelementptr. For example, a legal use of it is:</p>
2732 @llvm.used = appending global [2 x i8*] [
2734 i8* bitcast (i32* @Y to i8*)
2735 ], section "llvm.metadata"
2738 <p>If a global variable appears in the <tt>@llvm.used</tt> list, then the
2739 compiler, assembler, and linker are required to treat the symbol as if there is
2740 a reference to the global that it cannot see. For example, if a variable has
2741 internal linkage and no references other than that from the <tt>@llvm.used</tt>
2742 list, it cannot be deleted. This is commonly used to represent references from
2743 inline asms and other things the compiler cannot "see", and corresponds to
2744 "attribute((used))" in GNU C.</p>
2746 <p>On some targets, the code generator must emit a directive to the assembler or
2747 object file to prevent the assembler and linker from molesting the symbol.</p>
2751 <!-- ======================================================================= -->
2752 <div class="doc_subsection">
2753 <a name="intg_compiler_used">The '<tt>llvm.compiler.used</tt>' Global Variable</a>
2756 <div class="doc_text">
2758 <p>The <tt>@llvm.compiler.used</tt> directive is the same as the
2759 <tt>@llvm.used</tt> directive, except that it only prevents the compiler from
2760 touching the symbol. On targets that support it, this allows an intelligent
2761 linker to optimize references to the symbol without being impeded as it would be
2762 by <tt>@llvm.used</tt>.</p>
2764 <p>This is a rare construct that should only be used in rare circumstances, and
2765 should not be exposed to source languages.</p>
2769 <!-- ======================================================================= -->
2770 <div class="doc_subsection">
2771 <a name="intg_global_ctors">The '<tt>llvm.global_ctors</tt>' Global Variable</a>
2774 <div class="doc_text">
2776 %0 = type { i32, void ()* }
2777 @llvm.global_ctors = appending global [1 x %0] [%0 { i32 65535, void ()* @ctor }]
2779 <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.
2784 <!-- ======================================================================= -->
2785 <div class="doc_subsection">
2786 <a name="intg_global_dtors">The '<tt>llvm.global_dtors</tt>' Global Variable</a>
2789 <div class="doc_text">
2791 %0 = type { i32, void ()* }
2792 @llvm.global_dtors = appending global [1 x %0] [%0 { i32 65535, void ()* @dtor }]
2795 <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.
2801 <!-- *********************************************************************** -->
2802 <div class="doc_section"> <a name="instref">Instruction Reference</a> </div>
2803 <!-- *********************************************************************** -->
2805 <div class="doc_text">
2807 <p>The LLVM instruction set consists of several different classifications of
2808 instructions: <a href="#terminators">terminator
2809 instructions</a>, <a href="#binaryops">binary instructions</a>,
2810 <a href="#bitwiseops">bitwise binary instructions</a>,
2811 <a href="#memoryops">memory instructions</a>, and
2812 <a href="#otherops">other instructions</a>.</p>
2816 <!-- ======================================================================= -->
2817 <div class="doc_subsection"> <a name="terminators">Terminator
2818 Instructions</a> </div>
2820 <div class="doc_text">
2822 <p>As mentioned <a href="#functionstructure">previously</a>, every basic block
2823 in a program ends with a "Terminator" instruction, which indicates which
2824 block should be executed after the current block is finished. These
2825 terminator instructions typically yield a '<tt>void</tt>' value: they produce
2826 control flow, not values (the one exception being the
2827 '<a href="#i_invoke"><tt>invoke</tt></a>' instruction).</p>
2829 <p>There are seven different terminator instructions: the
2830 '<a href="#i_ret"><tt>ret</tt></a>' instruction, the
2831 '<a href="#i_br"><tt>br</tt></a>' instruction, the
2832 '<a href="#i_switch"><tt>switch</tt></a>' instruction, the
2833 '<a href="#i_indirectbr">'<tt>indirectbr</tt></a>' Instruction, the
2834 '<a href="#i_invoke"><tt>invoke</tt></a>' instruction, the
2835 '<a href="#i_unwind"><tt>unwind</tt></a>' instruction, and the
2836 '<a href="#i_unreachable"><tt>unreachable</tt></a>' instruction.</p>
2840 <!-- _______________________________________________________________________ -->
2841 <div class="doc_subsubsection"> <a name="i_ret">'<tt>ret</tt>'
2842 Instruction</a> </div>
2844 <div class="doc_text">
2848 ret <type> <value> <i>; Return a value from a non-void function</i>
2849 ret void <i>; Return from void function</i>
2853 <p>The '<tt>ret</tt>' instruction is used to return control flow (and optionally
2854 a value) from a function back to the caller.</p>
2856 <p>There are two forms of the '<tt>ret</tt>' instruction: one that returns a
2857 value and then causes control flow, and one that just causes control flow to
2861 <p>The '<tt>ret</tt>' instruction optionally accepts a single argument, the
2862 return value. The type of the return value must be a
2863 '<a href="#t_firstclass">first class</a>' type.</p>
2865 <p>A function is not <a href="#wellformed">well formed</a> if it it has a
2866 non-void return type and contains a '<tt>ret</tt>' instruction with no return
2867 value or a return value with a type that does not match its type, or if it
2868 has a void return type and contains a '<tt>ret</tt>' instruction with a
2872 <p>When the '<tt>ret</tt>' instruction is executed, control flow returns back to
2873 the calling function's context. If the caller is a
2874 "<a href="#i_call"><tt>call</tt></a>" instruction, execution continues at the
2875 instruction after the call. If the caller was an
2876 "<a href="#i_invoke"><tt>invoke</tt></a>" instruction, execution continues at
2877 the beginning of the "normal" destination block. If the instruction returns
2878 a value, that value shall set the call or invoke instruction's return
2883 ret i32 5 <i>; Return an integer value of 5</i>
2884 ret void <i>; Return from a void function</i>
2885 ret { i32, i8 } { i32 4, i8 2 } <i>; Return a struct of values 4 and 2</i>
2889 <!-- _______________________________________________________________________ -->
2890 <div class="doc_subsubsection"> <a name="i_br">'<tt>br</tt>' Instruction</a> </div>
2892 <div class="doc_text">
2896 br i1 <cond>, label <iftrue>, label <iffalse><br> br label <dest> <i>; Unconditional branch</i>
2900 <p>The '<tt>br</tt>' instruction is used to cause control flow to transfer to a
2901 different basic block in the current function. There are two forms of this
2902 instruction, corresponding to a conditional branch and an unconditional
2906 <p>The conditional branch form of the '<tt>br</tt>' instruction takes a single
2907 '<tt>i1</tt>' value and two '<tt>label</tt>' values. The unconditional form
2908 of the '<tt>br</tt>' instruction takes a single '<tt>label</tt>' value as a
2912 <p>Upon execution of a conditional '<tt>br</tt>' instruction, the '<tt>i1</tt>'
2913 argument is evaluated. If the value is <tt>true</tt>, control flows to the
2914 '<tt>iftrue</tt>' <tt>label</tt> argument. If "cond" is <tt>false</tt>,
2915 control flows to the '<tt>iffalse</tt>' <tt>label</tt> argument.</p>
2920 %cond = <a href="#i_icmp">icmp</a> eq i32 %a, %b
2921 br i1 %cond, label %IfEqual, label %IfUnequal
2923 <a href="#i_ret">ret</a> i32 1
2925 <a href="#i_ret">ret</a> i32 0
2930 <!-- _______________________________________________________________________ -->
2931 <div class="doc_subsubsection">
2932 <a name="i_switch">'<tt>switch</tt>' Instruction</a>
2935 <div class="doc_text">
2939 switch <intty> <value>, label <defaultdest> [ <intty> <val>, label <dest> ... ]
2943 <p>The '<tt>switch</tt>' instruction is used to transfer control flow to one of
2944 several different places. It is a generalization of the '<tt>br</tt>'
2945 instruction, allowing a branch to occur to one of many possible
2949 <p>The '<tt>switch</tt>' instruction uses three parameters: an integer
2950 comparison value '<tt>value</tt>', a default '<tt>label</tt>' destination,
2951 and an array of pairs of comparison value constants and '<tt>label</tt>'s.
2952 The table is not allowed to contain duplicate constant entries.</p>
2955 <p>The <tt>switch</tt> instruction specifies a table of values and
2956 destinations. When the '<tt>switch</tt>' instruction is executed, this table
2957 is searched for the given value. If the value is found, control flow is
2958 transferred to the corresponding destination; otherwise, control flow is
2959 transferred to the default destination.</p>
2961 <h5>Implementation:</h5>
2962 <p>Depending on properties of the target machine and the particular
2963 <tt>switch</tt> instruction, this instruction may be code generated in
2964 different ways. For example, it could be generated as a series of chained
2965 conditional branches or with a lookup table.</p>
2969 <i>; Emulate a conditional br instruction</i>
2970 %Val = <a href="#i_zext">zext</a> i1 %value to i32
2971 switch i32 %Val, label %truedest [ i32 0, label %falsedest ]
2973 <i>; Emulate an unconditional br instruction</i>
2974 switch i32 0, label %dest [ ]
2976 <i>; Implement a jump table:</i>
2977 switch i32 %val, label %otherwise [ i32 0, label %onzero
2979 i32 2, label %ontwo ]
2985 <!-- _______________________________________________________________________ -->
2986 <div class="doc_subsubsection">
2987 <a name="i_indirectbr">'<tt>indirectbr</tt>' Instruction</a>
2990 <div class="doc_text">
2994 indirectbr <somety>* <address>, [ label <dest1>, label <dest2>, ... ]
2999 <p>The '<tt>indirectbr</tt>' instruction implements an indirect branch to a label
3000 within the current function, whose address is specified by
3001 "<tt>address</tt>". Address must be derived from a <a
3002 href="#blockaddress">blockaddress</a> constant.</p>
3006 <p>The '<tt>address</tt>' argument is the address of the label to jump to. The
3007 rest of the arguments indicate the full set of possible destinations that the
3008 address may point to. Blocks are allowed to occur multiple times in the
3009 destination list, though this isn't particularly useful.</p>
3011 <p>This destination list is required so that dataflow analysis has an accurate
3012 understanding of the CFG.</p>
3016 <p>Control transfers to the block specified in the address argument. All
3017 possible destination blocks must be listed in the label list, otherwise this
3018 instruction has undefined behavior. This implies that jumps to labels
3019 defined in other functions have undefined behavior as well.</p>
3021 <h5>Implementation:</h5>
3023 <p>This is typically implemented with a jump through a register.</p>
3027 indirectbr i8* %Addr, [ label %bb1, label %bb2, label %bb3 ]
3033 <!-- _______________________________________________________________________ -->
3034 <div class="doc_subsubsection">
3035 <a name="i_invoke">'<tt>invoke</tt>' Instruction</a>
3038 <div class="doc_text">
3042 <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>]
3043 to label <normal label> unwind label <exception label>
3047 <p>The '<tt>invoke</tt>' instruction causes control to transfer to a specified
3048 function, with the possibility of control flow transfer to either the
3049 '<tt>normal</tt>' label or the '<tt>exception</tt>' label. If the callee
3050 function returns with the "<tt><a href="#i_ret">ret</a></tt>" instruction,
3051 control flow will return to the "normal" label. If the callee (or any
3052 indirect callees) returns with the "<a href="#i_unwind"><tt>unwind</tt></a>"
3053 instruction, control is interrupted and continued at the dynamically nearest
3054 "exception" label.</p>
3057 <p>This instruction requires several arguments:</p>
3060 <li>The optional "cconv" marker indicates which <a href="#callingconv">calling
3061 convention</a> the call should use. If none is specified, the call
3062 defaults to using C calling conventions.</li>
3064 <li>The optional <a href="#paramattrs">Parameter Attributes</a> list for
3065 return values. Only '<tt>zeroext</tt>', '<tt>signext</tt>', and
3066 '<tt>inreg</tt>' attributes are valid here.</li>
3068 <li>'<tt>ptr to function ty</tt>': shall be the signature of the pointer to
3069 function value being invoked. In most cases, this is a direct function
3070 invocation, but indirect <tt>invoke</tt>s are just as possible, branching
3071 off an arbitrary pointer to function value.</li>
3073 <li>'<tt>function ptr val</tt>': An LLVM value containing a pointer to a
3074 function to be invoked. </li>
3076 <li>'<tt>function args</tt>': argument list whose types match the function
3077 signature argument types and parameter attributes. All arguments must be
3078 of <a href="#t_firstclass">first class</a> type. If the function
3079 signature indicates the function accepts a variable number of arguments,
3080 the extra arguments can be specified.</li>
3082 <li>'<tt>normal label</tt>': the label reached when the called function
3083 executes a '<tt><a href="#i_ret">ret</a></tt>' instruction. </li>
3085 <li>'<tt>exception label</tt>': the label reached when a callee returns with
3086 the <a href="#i_unwind"><tt>unwind</tt></a> instruction. </li>
3088 <li>The optional <a href="#fnattrs">function attributes</a> list. Only
3089 '<tt>noreturn</tt>', '<tt>nounwind</tt>', '<tt>readonly</tt>' and
3090 '<tt>readnone</tt>' attributes are valid here.</li>
3094 <p>This instruction is designed to operate as a standard
3095 '<tt><a href="#i_call">call</a></tt>' instruction in most regards. The
3096 primary difference is that it establishes an association with a label, which
3097 is used by the runtime library to unwind the stack.</p>
3099 <p>This instruction is used in languages with destructors to ensure that proper
3100 cleanup is performed in the case of either a <tt>longjmp</tt> or a thrown
3101 exception. Additionally, this is important for implementation of
3102 '<tt>catch</tt>' clauses in high-level languages that support them.</p>
3104 <p>For the purposes of the SSA form, the definition of the value returned by the
3105 '<tt>invoke</tt>' instruction is deemed to occur on the edge from the current
3106 block to the "normal" label. If the callee unwinds then no return value is
3109 <p>Note that the code generator does not yet completely support unwind, and
3110 that the invoke/unwind semantics are likely to change in future versions.</p>
3114 %retval = invoke i32 @Test(i32 15) to label %Continue
3115 unwind label %TestCleanup <i>; {i32}:retval set</i>
3116 %retval = invoke <a href="#callingconv">coldcc</a> i32 %Testfnptr(i32 15) to label %Continue
3117 unwind label %TestCleanup <i>; {i32}:retval set</i>
3122 <!-- _______________________________________________________________________ -->
3124 <div class="doc_subsubsection"> <a name="i_unwind">'<tt>unwind</tt>'
3125 Instruction</a> </div>
3127 <div class="doc_text">
3135 <p>The '<tt>unwind</tt>' instruction unwinds the stack, continuing control flow
3136 at the first callee in the dynamic call stack which used
3137 an <a href="#i_invoke"><tt>invoke</tt></a> instruction to perform the call.
3138 This is primarily used to implement exception handling.</p>
3141 <p>The '<tt>unwind</tt>' instruction causes execution of the current function to
3142 immediately halt. The dynamic call stack is then searched for the
3143 first <a href="#i_invoke"><tt>invoke</tt></a> instruction on the call stack.
3144 Once found, execution continues at the "exceptional" destination block
3145 specified by the <tt>invoke</tt> instruction. If there is no <tt>invoke</tt>
3146 instruction in the dynamic call chain, undefined behavior results.</p>
3148 <p>Note that the code generator does not yet completely support unwind, and
3149 that the invoke/unwind semantics are likely to change in future versions.</p>
3153 <!-- _______________________________________________________________________ -->
3155 <div class="doc_subsubsection"> <a name="i_unreachable">'<tt>unreachable</tt>'
3156 Instruction</a> </div>
3158 <div class="doc_text">
3166 <p>The '<tt>unreachable</tt>' instruction has no defined semantics. This
3167 instruction is used to inform the optimizer that a particular portion of the
3168 code is not reachable. This can be used to indicate that the code after a
3169 no-return function cannot be reached, and other facts.</p>
3172 <p>The '<tt>unreachable</tt>' instruction has no defined semantics.</p>
3176 <!-- ======================================================================= -->
3177 <div class="doc_subsection"> <a name="binaryops">Binary Operations</a> </div>
3179 <div class="doc_text">
3181 <p>Binary operators are used to do most of the computation in a program. They
3182 require two operands of the same type, execute an operation on them, and
3183 produce a single value. The operands might represent multiple data, as is
3184 the case with the <a href="#t_vector">vector</a> data type. The result value
3185 has the same type as its operands.</p>
3187 <p>There are several different binary operators:</p>
3191 <!-- _______________________________________________________________________ -->
3192 <div class="doc_subsubsection">
3193 <a name="i_add">'<tt>add</tt>' Instruction</a>
3196 <div class="doc_text">
3200 <result> = add <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3201 <result> = add nuw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3202 <result> = add nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3203 <result> = add nuw nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3207 <p>The '<tt>add</tt>' instruction returns the sum of its two operands.</p>
3210 <p>The two arguments to the '<tt>add</tt>' instruction must
3211 be <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of
3212 integer values. Both arguments must have identical types.</p>
3215 <p>The value produced is the integer sum of the two operands.</p>
3217 <p>If the sum has unsigned overflow, the result returned is the mathematical
3218 result modulo 2<sup>n</sup>, where n is the bit width of the result.</p>
3220 <p>Because LLVM integers use a two's complement representation, this instruction
3221 is appropriate for both signed and unsigned integers.</p>
3223 <p><tt>nuw</tt> and <tt>nsw</tt> stand for "No Unsigned Wrap"
3224 and "No Signed Wrap", respectively. If the <tt>nuw</tt> and/or
3225 <tt>nsw</tt> keywords are present, the result value of the <tt>add</tt>
3226 is a <a href="#trapvalues">trap value</a> if unsigned and/or signed overflow,
3227 respectively, occurs.</p>
3231 <result> = add i32 4, %var <i>; yields {i32}:result = 4 + %var</i>
3236 <!-- _______________________________________________________________________ -->
3237 <div class="doc_subsubsection">
3238 <a name="i_fadd">'<tt>fadd</tt>' Instruction</a>
3241 <div class="doc_text">
3245 <result> = fadd <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3249 <p>The '<tt>fadd</tt>' instruction returns the sum of its two operands.</p>
3252 <p>The two arguments to the '<tt>fadd</tt>' instruction must be
3253 <a href="#t_floating">floating point</a> or <a href="#t_vector">vector</a> of
3254 floating point values. Both arguments must have identical types.</p>
3257 <p>The value produced is the floating point sum of the two operands.</p>
3261 <result> = fadd float 4.0, %var <i>; yields {float}:result = 4.0 + %var</i>
3266 <!-- _______________________________________________________________________ -->
3267 <div class="doc_subsubsection">
3268 <a name="i_sub">'<tt>sub</tt>' Instruction</a>
3271 <div class="doc_text">
3275 <result> = sub <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3276 <result> = sub nuw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3277 <result> = sub nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3278 <result> = sub nuw nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3282 <p>The '<tt>sub</tt>' instruction returns the difference of its two
3285 <p>Note that the '<tt>sub</tt>' instruction is used to represent the
3286 '<tt>neg</tt>' instruction present in most other intermediate
3287 representations.</p>
3290 <p>The two arguments to the '<tt>sub</tt>' instruction must
3291 be <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of
3292 integer values. Both arguments must have identical types.</p>
3295 <p>The value produced is the integer difference of the two operands.</p>
3297 <p>If the difference has unsigned overflow, the result returned is the
3298 mathematical result modulo 2<sup>n</sup>, where n is the bit width of the
3301 <p>Because LLVM integers use a two's complement representation, this instruction
3302 is appropriate for both signed and unsigned integers.</p>
3304 <p><tt>nuw</tt> and <tt>nsw</tt> stand for "No Unsigned Wrap"
3305 and "No Signed Wrap", respectively. If the <tt>nuw</tt> and/or
3306 <tt>nsw</tt> keywords are present, the result value of the <tt>sub</tt>
3307 is a <a href="#trapvalues">trap value</a> if unsigned and/or signed overflow,
3308 respectively, occurs.</p>
3312 <result> = sub i32 4, %var <i>; yields {i32}:result = 4 - %var</i>
3313 <result> = sub i32 0, %val <i>; yields {i32}:result = -%var</i>
3318 <!-- _______________________________________________________________________ -->
3319 <div class="doc_subsubsection">
3320 <a name="i_fsub">'<tt>fsub</tt>' Instruction</a>
3323 <div class="doc_text">
3327 <result> = fsub <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3331 <p>The '<tt>fsub</tt>' instruction returns the difference of its two
3334 <p>Note that the '<tt>fsub</tt>' instruction is used to represent the
3335 '<tt>fneg</tt>' instruction present in most other intermediate
3336 representations.</p>
3339 <p>The two arguments to the '<tt>fsub</tt>' instruction must be
3340 <a href="#t_floating">floating point</a> or <a href="#t_vector">vector</a> of
3341 floating point values. Both arguments must have identical types.</p>
3344 <p>The value produced is the floating point difference of the two operands.</p>
3348 <result> = fsub float 4.0, %var <i>; yields {float}:result = 4.0 - %var</i>
3349 <result> = fsub float -0.0, %val <i>; yields {float}:result = -%var</i>
3354 <!-- _______________________________________________________________________ -->
3355 <div class="doc_subsubsection">
3356 <a name="i_mul">'<tt>mul</tt>' Instruction</a>
3359 <div class="doc_text">
3363 <result> = mul <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3364 <result> = mul nuw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3365 <result> = mul nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3366 <result> = mul nuw nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3370 <p>The '<tt>mul</tt>' instruction returns the product of its two operands.</p>
3373 <p>The two arguments to the '<tt>mul</tt>' instruction must
3374 be <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of
3375 integer values. Both arguments must have identical types.</p>
3378 <p>The value produced is the integer product of the two operands.</p>
3380 <p>If the result of the multiplication has unsigned overflow, the result
3381 returned is the mathematical result modulo 2<sup>n</sup>, where n is the bit
3382 width of the result.</p>
3384 <p>Because LLVM integers use a two's complement representation, and the result
3385 is the same width as the operands, this instruction returns the correct
3386 result for both signed and unsigned integers. If a full product
3387 (e.g. <tt>i32</tt>x<tt>i32</tt>-><tt>i64</tt>) is needed, the operands should
3388 be sign-extended or zero-extended as appropriate to the width of the full
3391 <p><tt>nuw</tt> and <tt>nsw</tt> stand for "No Unsigned Wrap"
3392 and "No Signed Wrap", respectively. If the <tt>nuw</tt> and/or
3393 <tt>nsw</tt> keywords are present, the result value of the <tt>mul</tt>
3394 is a <a href="#trapvalues">trap value</a> if unsigned and/or signed overflow,
3395 respectively, occurs.</p>
3399 <result> = mul i32 4, %var <i>; yields {i32}:result = 4 * %var</i>
3404 <!-- _______________________________________________________________________ -->
3405 <div class="doc_subsubsection">
3406 <a name="i_fmul">'<tt>fmul</tt>' Instruction</a>
3409 <div class="doc_text">
3413 <result> = fmul <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3417 <p>The '<tt>fmul</tt>' instruction returns the product of its two operands.</p>
3420 <p>The two arguments to the '<tt>fmul</tt>' instruction must be
3421 <a href="#t_floating">floating point</a> or <a href="#t_vector">vector</a> of
3422 floating point values. Both arguments must have identical types.</p>
3425 <p>The value produced is the floating point product of the two operands.</p>
3429 <result> = fmul float 4.0, %var <i>; yields {float}:result = 4.0 * %var</i>
3434 <!-- _______________________________________________________________________ -->
3435 <div class="doc_subsubsection"> <a name="i_udiv">'<tt>udiv</tt>' Instruction
3438 <div class="doc_text">
3442 <result> = udiv <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3446 <p>The '<tt>udiv</tt>' instruction returns the quotient of its two operands.</p>
3449 <p>The two arguments to the '<tt>udiv</tt>' instruction must be
3450 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
3451 values. Both arguments must have identical types.</p>
3454 <p>The value produced is the unsigned integer quotient of the two operands.</p>
3456 <p>Note that unsigned integer division and signed integer division are distinct
3457 operations; for signed integer division, use '<tt>sdiv</tt>'.</p>
3459 <p>Division by zero leads to undefined behavior.</p>
3463 <result> = udiv i32 4, %var <i>; yields {i32}:result = 4 / %var</i>
3468 <!-- _______________________________________________________________________ -->
3469 <div class="doc_subsubsection"> <a name="i_sdiv">'<tt>sdiv</tt>' Instruction
3472 <div class="doc_text">
3476 <result> = sdiv <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3477 <result> = sdiv exact <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3481 <p>The '<tt>sdiv</tt>' instruction returns the quotient of its two operands.</p>
3484 <p>The two arguments to the '<tt>sdiv</tt>' instruction must be
3485 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
3486 values. Both arguments must have identical types.</p>
3489 <p>The value produced is the signed integer quotient of the two operands rounded
3492 <p>Note that signed integer division and unsigned integer division are distinct
3493 operations; for unsigned integer division, use '<tt>udiv</tt>'.</p>
3495 <p>Division by zero leads to undefined behavior. Overflow also leads to
3496 undefined behavior; this is a rare case, but can occur, for example, by doing
3497 a 32-bit division of -2147483648 by -1.</p>
3499 <p>If the <tt>exact</tt> keyword is present, the result value of the
3500 <tt>sdiv</tt> is a <a href="#trapvalues">trap value</a> if the result would
3505 <result> = sdiv i32 4, %var <i>; yields {i32}:result = 4 / %var</i>
3510 <!-- _______________________________________________________________________ -->
3511 <div class="doc_subsubsection"> <a name="i_fdiv">'<tt>fdiv</tt>'
3512 Instruction</a> </div>
3514 <div class="doc_text">
3518 <result> = fdiv <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3522 <p>The '<tt>fdiv</tt>' instruction returns the quotient of its two operands.</p>
3525 <p>The two arguments to the '<tt>fdiv</tt>' instruction must be
3526 <a href="#t_floating">floating point</a> or <a href="#t_vector">vector</a> of
3527 floating point values. Both arguments must have identical types.</p>
3530 <p>The value produced is the floating point quotient of the two operands.</p>
3534 <result> = fdiv float 4.0, %var <i>; yields {float}:result = 4.0 / %var</i>
3539 <!-- _______________________________________________________________________ -->
3540 <div class="doc_subsubsection"> <a name="i_urem">'<tt>urem</tt>' Instruction</a>
3543 <div class="doc_text">
3547 <result> = urem <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3551 <p>The '<tt>urem</tt>' instruction returns the remainder from the unsigned
3552 division of its two arguments.</p>
3555 <p>The two arguments to the '<tt>urem</tt>' instruction must be
3556 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
3557 values. Both arguments must have identical types.</p>
3560 <p>This instruction returns the unsigned integer <i>remainder</i> of a division.
3561 This instruction always performs an unsigned division to get the
3564 <p>Note that unsigned integer remainder and signed integer remainder are
3565 distinct operations; for signed integer remainder, use '<tt>srem</tt>'.</p>
3567 <p>Taking the remainder of a division by zero leads to undefined behavior.</p>
3571 <result> = urem i32 4, %var <i>; yields {i32}:result = 4 % %var</i>
3576 <!-- _______________________________________________________________________ -->
3577 <div class="doc_subsubsection">
3578 <a name="i_srem">'<tt>srem</tt>' Instruction</a>
3581 <div class="doc_text">
3585 <result> = srem <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3589 <p>The '<tt>srem</tt>' instruction returns the remainder from the signed
3590 division of its two operands. This instruction can also take
3591 <a href="#t_vector">vector</a> versions of the values in which case the
3592 elements must be integers.</p>
3595 <p>The two arguments to the '<tt>srem</tt>' instruction must be
3596 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
3597 values. Both arguments must have identical types.</p>
3600 <p>This instruction returns the <i>remainder</i> of a division (where the result
3601 has the same sign as the dividend, <tt>op1</tt>), not the <i>modulo</i>
3602 operator (where the result has the same sign as the divisor, <tt>op2</tt>) of
3603 a value. For more information about the difference,
3604 see <a href="http://mathforum.org/dr.math/problems/anne.4.28.99.html">The
3605 Math Forum</a>. For a table of how this is implemented in various languages,
3606 please see <a href="http://en.wikipedia.org/wiki/Modulo_operation">
3607 Wikipedia: modulo operation</a>.</p>
3609 <p>Note that signed integer remainder and unsigned integer remainder are
3610 distinct operations; for unsigned integer remainder, use '<tt>urem</tt>'.</p>
3612 <p>Taking the remainder of a division by zero leads to undefined behavior.
3613 Overflow also leads to undefined behavior; this is a rare case, but can
3614 occur, for example, by taking the remainder of a 32-bit division of
3615 -2147483648 by -1. (The remainder doesn't actually overflow, but this rule
3616 lets srem be implemented using instructions that return both the result of
3617 the division and the remainder.)</p>
3621 <result> = srem i32 4, %var <i>; yields {i32}:result = 4 % %var</i>
3626 <!-- _______________________________________________________________________ -->
3627 <div class="doc_subsubsection">
3628 <a name="i_frem">'<tt>frem</tt>' Instruction</a> </div>
3630 <div class="doc_text">
3634 <result> = frem <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3638 <p>The '<tt>frem</tt>' instruction returns the remainder from the division of
3639 its two operands.</p>
3642 <p>The two arguments to the '<tt>frem</tt>' instruction must be
3643 <a href="#t_floating">floating point</a> or <a href="#t_vector">vector</a> of
3644 floating point values. Both arguments must have identical types.</p>
3647 <p>This instruction returns the <i>remainder</i> of a division. The remainder
3648 has the same sign as the dividend.</p>
3652 <result> = frem float 4.0, %var <i>; yields {float}:result = 4.0 % %var</i>
3657 <!-- ======================================================================= -->
3658 <div class="doc_subsection"> <a name="bitwiseops">Bitwise Binary
3659 Operations</a> </div>
3661 <div class="doc_text">
3663 <p>Bitwise binary operators are used to do various forms of bit-twiddling in a
3664 program. They are generally very efficient instructions and can commonly be
3665 strength reduced from other instructions. They require two operands of the
3666 same type, execute an operation on them, and produce a single value. The
3667 resulting value is the same type as its operands.</p>
3671 <!-- _______________________________________________________________________ -->
3672 <div class="doc_subsubsection"> <a name="i_shl">'<tt>shl</tt>'
3673 Instruction</a> </div>
3675 <div class="doc_text">
3679 <result> = shl <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3683 <p>The '<tt>shl</tt>' instruction returns the first operand shifted to the left
3684 a specified number of bits.</p>
3687 <p>Both arguments to the '<tt>shl</tt>' instruction must be the
3688 same <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of
3689 integer type. '<tt>op2</tt>' is treated as an unsigned value.</p>
3692 <p>The value produced is <tt>op1</tt> * 2<sup><tt>op2</tt></sup> mod
3693 2<sup>n</sup>, where <tt>n</tt> is the width of the result. If <tt>op2</tt>
3694 is (statically or dynamically) negative or equal to or larger than the number
3695 of bits in <tt>op1</tt>, the result is undefined. If the arguments are
3696 vectors, each vector element of <tt>op1</tt> is shifted by the corresponding
3697 shift amount in <tt>op2</tt>.</p>
3701 <result> = shl i32 4, %var <i>; yields {i32}: 4 << %var</i>
3702 <result> = shl i32 4, 2 <i>; yields {i32}: 16</i>
3703 <result> = shl i32 1, 10 <i>; yields {i32}: 1024</i>
3704 <result> = shl i32 1, 32 <i>; undefined</i>
3705 <result> = shl <2 x i32> < i32 1, i32 1>, < i32 1, i32 2> <i>; yields: result=<2 x i32> < i32 2, i32 4></i>
3710 <!-- _______________________________________________________________________ -->
3711 <div class="doc_subsubsection"> <a name="i_lshr">'<tt>lshr</tt>'
3712 Instruction</a> </div>
3714 <div class="doc_text">
3718 <result> = lshr <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3722 <p>The '<tt>lshr</tt>' instruction (logical shift right) returns the first
3723 operand shifted to the right a specified number of bits with zero fill.</p>
3726 <p>Both arguments to the '<tt>lshr</tt>' instruction must be the same
3727 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
3728 type. '<tt>op2</tt>' is treated as an unsigned value.</p>
3731 <p>This instruction always performs a logical shift right operation. The most
3732 significant bits of the result will be filled with zero bits after the shift.
3733 If <tt>op2</tt> is (statically or dynamically) equal to or larger than the
3734 number of bits in <tt>op1</tt>, the result is undefined. If the arguments are
3735 vectors, each vector element of <tt>op1</tt> is shifted by the corresponding
3736 shift amount in <tt>op2</tt>.</p>
3740 <result> = lshr i32 4, 1 <i>; yields {i32}:result = 2</i>
3741 <result> = lshr i32 4, 2 <i>; yields {i32}:result = 1</i>
3742 <result> = lshr i8 4, 3 <i>; yields {i8}:result = 0</i>
3743 <result> = lshr i8 -2, 1 <i>; yields {i8}:result = 0x7FFFFFFF </i>
3744 <result> = lshr i32 1, 32 <i>; undefined</i>
3745 <result> = lshr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 2> <i>; yields: result=<2 x i32> < i32 0x7FFFFFFF, i32 1></i>
3750 <!-- _______________________________________________________________________ -->
3751 <div class="doc_subsubsection"> <a name="i_ashr">'<tt>ashr</tt>'
3752 Instruction</a> </div>
3753 <div class="doc_text">
3757 <result> = ashr <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3761 <p>The '<tt>ashr</tt>' instruction (arithmetic shift right) returns the first
3762 operand shifted to the right a specified number of bits with sign
3766 <p>Both arguments to the '<tt>ashr</tt>' instruction must be the same
3767 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
3768 type. '<tt>op2</tt>' is treated as an unsigned value.</p>
3771 <p>This instruction always performs an arithmetic shift right operation, The
3772 most significant bits of the result will be filled with the sign bit
3773 of <tt>op1</tt>. If <tt>op2</tt> is (statically or dynamically) equal to or
3774 larger than the number of bits in <tt>op1</tt>, the result is undefined. If
3775 the arguments are vectors, each vector element of <tt>op1</tt> is shifted by
3776 the corresponding shift amount in <tt>op2</tt>.</p>
3780 <result> = ashr i32 4, 1 <i>; yields {i32}:result = 2</i>
3781 <result> = ashr i32 4, 2 <i>; yields {i32}:result = 1</i>
3782 <result> = ashr i8 4, 3 <i>; yields {i8}:result = 0</i>
3783 <result> = ashr i8 -2, 1 <i>; yields {i8}:result = -1</i>
3784 <result> = ashr i32 1, 32 <i>; undefined</i>
3785 <result> = ashr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 3> <i>; yields: result=<2 x i32> < i32 -1, i32 0></i>
3790 <!-- _______________________________________________________________________ -->
3791 <div class="doc_subsubsection"> <a name="i_and">'<tt>and</tt>'
3792 Instruction</a> </div>
3794 <div class="doc_text">
3798 <result> = and <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3802 <p>The '<tt>and</tt>' instruction returns the bitwise logical and of its two
3806 <p>The two arguments to the '<tt>and</tt>' instruction must be
3807 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
3808 values. Both arguments must have identical types.</p>
3811 <p>The truth table used for the '<tt>and</tt>' instruction is:</p>
3813 <table border="1" cellspacing="0" cellpadding="4">
3845 <result> = and i32 4, %var <i>; yields {i32}:result = 4 & %var</i>
3846 <result> = and i32 15, 40 <i>; yields {i32}:result = 8</i>
3847 <result> = and i32 4, 8 <i>; yields {i32}:result = 0</i>
3850 <!-- _______________________________________________________________________ -->
3851 <div class="doc_subsubsection"> <a name="i_or">'<tt>or</tt>' Instruction</a> </div>
3853 <div class="doc_text">
3857 <result> = or <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3861 <p>The '<tt>or</tt>' instruction returns the bitwise logical inclusive or of its
3865 <p>The two arguments to the '<tt>or</tt>' instruction must be
3866 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
3867 values. Both arguments must have identical types.</p>
3870 <p>The truth table used for the '<tt>or</tt>' instruction is:</p>
3872 <table border="1" cellspacing="0" cellpadding="4">
3904 <result> = or i32 4, %var <i>; yields {i32}:result = 4 | %var</i>
3905 <result> = or i32 15, 40 <i>; yields {i32}:result = 47</i>
3906 <result> = or i32 4, 8 <i>; yields {i32}:result = 12</i>
3911 <!-- _______________________________________________________________________ -->
3912 <div class="doc_subsubsection"> <a name="i_xor">'<tt>xor</tt>'
3913 Instruction</a> </div>
3915 <div class="doc_text">
3919 <result> = xor <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3923 <p>The '<tt>xor</tt>' instruction returns the bitwise logical exclusive or of
3924 its two operands. The <tt>xor</tt> is used to implement the "one's
3925 complement" operation, which is the "~" operator in C.</p>
3928 <p>The two arguments to the '<tt>xor</tt>' instruction must be
3929 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
3930 values. Both arguments must have identical types.</p>
3933 <p>The truth table used for the '<tt>xor</tt>' instruction is:</p>
3935 <table border="1" cellspacing="0" cellpadding="4">
3967 <result> = xor i32 4, %var <i>; yields {i32}:result = 4 ^ %var</i>
3968 <result> = xor i32 15, 40 <i>; yields {i32}:result = 39</i>
3969 <result> = xor i32 4, 8 <i>; yields {i32}:result = 12</i>
3970 <result> = xor i32 %V, -1 <i>; yields {i32}:result = ~%V</i>
3975 <!-- ======================================================================= -->
3976 <div class="doc_subsection">
3977 <a name="vectorops">Vector Operations</a>
3980 <div class="doc_text">
3982 <p>LLVM supports several instructions to represent vector operations in a
3983 target-independent manner. These instructions cover the element-access and
3984 vector-specific operations needed to process vectors effectively. While LLVM
3985 does directly support these vector operations, many sophisticated algorithms
3986 will want to use target-specific intrinsics to take full advantage of a
3987 specific target.</p>
3991 <!-- _______________________________________________________________________ -->
3992 <div class="doc_subsubsection">
3993 <a name="i_extractelement">'<tt>extractelement</tt>' Instruction</a>
3996 <div class="doc_text">
4000 <result> = extractelement <n x <ty>> <val>, i32 <idx> <i>; yields <ty></i>
4004 <p>The '<tt>extractelement</tt>' instruction extracts a single scalar element
4005 from a vector at a specified index.</p>
4009 <p>The first operand of an '<tt>extractelement</tt>' instruction is a value
4010 of <a href="#t_vector">vector</a> type. The second operand is an index
4011 indicating the position from which to extract the element. The index may be
4015 <p>The result is a scalar of the same type as the element type of
4016 <tt>val</tt>. Its value is the value at position <tt>idx</tt> of
4017 <tt>val</tt>. If <tt>idx</tt> exceeds the length of <tt>val</tt>, the
4018 results are undefined.</p>
4022 <result> = extractelement <4 x i32> %vec, i32 0 <i>; yields i32</i>
4027 <!-- _______________________________________________________________________ -->
4028 <div class="doc_subsubsection">
4029 <a name="i_insertelement">'<tt>insertelement</tt>' Instruction</a>
4032 <div class="doc_text">
4036 <result> = insertelement <n x <ty>> <val>, <ty> <elt>, i32 <idx> <i>; yields <n x <ty>></i>
4040 <p>The '<tt>insertelement</tt>' instruction inserts a scalar element into a
4041 vector at a specified index.</p>
4044 <p>The first operand of an '<tt>insertelement</tt>' instruction is a value
4045 of <a href="#t_vector">vector</a> type. The second operand is a scalar value
4046 whose type must equal the element type of the first operand. The third
4047 operand is an index indicating the position at which to insert the value.
4048 The index may be a variable.</p>
4051 <p>The result is a vector of the same type as <tt>val</tt>. Its element values
4052 are those of <tt>val</tt> except at position <tt>idx</tt>, where it gets the
4053 value <tt>elt</tt>. If <tt>idx</tt> exceeds the length of <tt>val</tt>, the
4054 results are undefined.</p>
4058 <result> = insertelement <4 x i32> %vec, i32 1, i32 0 <i>; yields <4 x i32></i>
4063 <!-- _______________________________________________________________________ -->
4064 <div class="doc_subsubsection">
4065 <a name="i_shufflevector">'<tt>shufflevector</tt>' Instruction</a>
4068 <div class="doc_text">
4072 <result> = shufflevector <n x <ty>> <v1>, <n x <ty>> <v2>, <m x i32> <mask> <i>; yields <m x <ty>></i>
4076 <p>The '<tt>shufflevector</tt>' instruction constructs a permutation of elements
4077 from two input vectors, returning a vector with the same element type as the
4078 input and length that is the same as the shuffle mask.</p>
4081 <p>The first two operands of a '<tt>shufflevector</tt>' instruction are vectors
4082 with types that match each other. The third argument is a shuffle mask whose
4083 element type is always 'i32'. The result of the instruction is a vector
4084 whose length is the same as the shuffle mask and whose element type is the
4085 same as the element type of the first two operands.</p>
4087 <p>The shuffle mask operand is required to be a constant vector with either
4088 constant integer or undef values.</p>
4091 <p>The elements of the two input vectors are numbered from left to right across
4092 both of the vectors. The shuffle mask operand specifies, for each element of
4093 the result vector, which element of the two input vectors the result element
4094 gets. The element selector may be undef (meaning "don't care") and the
4095 second operand may be undef if performing a shuffle from only one vector.</p>
4099 <result> = shufflevector <4 x i32> %v1, <4 x i32> %v2,
4100 <4 x i32> <i32 0, i32 4, i32 1, i32 5> <i>; yields <4 x i32></i>
4101 <result> = shufflevector <4 x i32> %v1, <4 x i32> undef,
4102 <4 x i32> <i32 0, i32 1, i32 2, i32 3> <i>; yields <4 x i32></i> - Identity shuffle.
4103 <result> = shufflevector <8 x i32> %v1, <8 x i32> undef,
4104 <4 x i32> <i32 0, i32 1, i32 2, i32 3> <i>; yields <4 x i32></i>
4105 <result> = shufflevector <4 x i32> %v1, <4 x i32> %v2,
4106 <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>
4111 <!-- ======================================================================= -->
4112 <div class="doc_subsection">
4113 <a name="aggregateops">Aggregate Operations</a>
4116 <div class="doc_text">
4118 <p>LLVM supports several instructions for working with
4119 <a href="#t_aggregate">aggregate</a> values.</p>
4123 <!-- _______________________________________________________________________ -->
4124 <div class="doc_subsubsection">
4125 <a name="i_extractvalue">'<tt>extractvalue</tt>' Instruction</a>
4128 <div class="doc_text">
4132 <result> = extractvalue <aggregate type> <val>, <idx>{, <idx>}*
4136 <p>The '<tt>extractvalue</tt>' instruction extracts the value of a member field
4137 from an <a href="#t_aggregate">aggregate</a> value.</p>
4140 <p>The first operand of an '<tt>extractvalue</tt>' instruction is a value
4141 of <a href="#t_struct">struct</a>, <a href="#t_union">union</a> or
4142 <a href="#t_array">array</a> type. The operands are constant indices to
4143 specify which value to extract in a similar manner as indices in a
4144 '<tt><a href="#i_getelementptr">getelementptr</a></tt>' instruction.</p>
4147 <p>The result is the value at the position in the aggregate specified by the
4152 <result> = extractvalue {i32, float} %agg, 0 <i>; yields i32</i>
4157 <!-- _______________________________________________________________________ -->
4158 <div class="doc_subsubsection">
4159 <a name="i_insertvalue">'<tt>insertvalue</tt>' Instruction</a>
4162 <div class="doc_text">
4166 <result> = insertvalue <aggregate type> <val>, <ty> <elt>, <idx> <i>; yields <aggregate type></i>
4170 <p>The '<tt>insertvalue</tt>' instruction inserts a value into a member field
4171 in an <a href="#t_aggregate">aggregate</a> value.</p>
4174 <p>The first operand of an '<tt>insertvalue</tt>' instruction is a value
4175 of <a href="#t_struct">struct</a>, <a href="#t_union">union</a> or
4176 <a href="#t_array">array</a> type. The second operand is a first-class
4177 value to insert. The following operands are constant indices indicating
4178 the position at which to insert the value in a similar manner as indices in a
4179 '<tt><a href="#i_getelementptr">getelementptr</a></tt>' instruction. The
4180 value to insert must have the same type as the value identified by the
4184 <p>The result is an aggregate of the same type as <tt>val</tt>. Its value is
4185 that of <tt>val</tt> except that the value at the position specified by the
4186 indices is that of <tt>elt</tt>.</p>
4190 %agg1 = insertvalue {i32, float} undef, i32 1, 0 <i>; yields {i32 1, float undef}</i>
4191 %agg2 = insertvalue {i32, float} %agg1, float %val, 1 <i>; yields {i32 1, float %val}</i>
4197 <!-- ======================================================================= -->
4198 <div class="doc_subsection">
4199 <a name="memoryops">Memory Access and Addressing Operations</a>
4202 <div class="doc_text">
4204 <p>A key design point of an SSA-based representation is how it represents
4205 memory. In LLVM, no memory locations are in SSA form, which makes things
4206 very simple. This section describes how to read, write, and allocate
4211 <!-- _______________________________________________________________________ -->
4212 <div class="doc_subsubsection">
4213 <a name="i_alloca">'<tt>alloca</tt>' Instruction</a>
4216 <div class="doc_text">
4220 <result> = alloca <type>[, <ty> <NumElements>][, align <alignment>] <i>; yields {type*}:result</i>
4224 <p>The '<tt>alloca</tt>' instruction allocates memory on the stack frame of the
4225 currently executing function, to be automatically released when this function
4226 returns to its caller. The object is always allocated in the generic address
4227 space (address space zero).</p>
4230 <p>The '<tt>alloca</tt>' instruction
4231 allocates <tt>sizeof(<type>)*NumElements</tt> bytes of memory on the
4232 runtime stack, returning a pointer of the appropriate type to the program.
4233 If "NumElements" is specified, it is the number of elements allocated,
4234 otherwise "NumElements" is defaulted to be one. If a constant alignment is
4235 specified, the value result of the allocation is guaranteed to be aligned to
4236 at least that boundary. If not specified, or if zero, the target can choose
4237 to align the allocation on any convenient boundary compatible with the
4240 <p>'<tt>type</tt>' may be any sized type.</p>
4243 <p>Memory is allocated; a pointer is returned. The operation is undefined if
4244 there is insufficient stack space for the allocation. '<tt>alloca</tt>'d
4245 memory is automatically released when the function returns. The
4246 '<tt>alloca</tt>' instruction is commonly used to represent automatic
4247 variables that must have an address available. When the function returns
4248 (either with the <tt><a href="#i_ret">ret</a></tt>
4249 or <tt><a href="#i_unwind">unwind</a></tt> instructions), the memory is
4250 reclaimed. Allocating zero bytes is legal, but the result is undefined.</p>
4254 %ptr = alloca i32 <i>; yields {i32*}:ptr</i>
4255 %ptr = alloca i32, i32 4 <i>; yields {i32*}:ptr</i>
4256 %ptr = alloca i32, i32 4, align 1024 <i>; yields {i32*}:ptr</i>
4257 %ptr = alloca i32, align 1024 <i>; yields {i32*}:ptr</i>
4262 <!-- _______________________________________________________________________ -->
4263 <div class="doc_subsubsection"> <a name="i_load">'<tt>load</tt>'
4264 Instruction</a> </div>
4266 <div class="doc_text">
4270 <result> = load <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>]
4271 <result> = volatile load <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>]
4272 !<index> = !{ i32 1 }
4276 <p>The '<tt>load</tt>' instruction is used to read from memory.</p>
4279 <p>The argument to the '<tt>load</tt>' instruction specifies the memory address
4280 from which to load. The pointer must point to
4281 a <a href="#t_firstclass">first class</a> type. If the <tt>load</tt> is
4282 marked as <tt>volatile</tt>, then the optimizer is not allowed to modify the
4283 number or order of execution of this <tt>load</tt> with other <a
4284 href="#volatile">volatile operations</a>.</p>
4286 <p>The optional constant <tt>align</tt> argument specifies the alignment of the
4287 operation (that is, the alignment of the memory address). A value of 0 or an
4288 omitted <tt>align</tt> argument means that the operation has the preferential
4289 alignment for the target. It is the responsibility of the code emitter to
4290 ensure that the alignment information is correct. Overestimating the
4291 alignment results in undefined behavior. Underestimating the alignment may
4292 produce less efficient code. An alignment of 1 is always safe.</p>
4294 <p>The optional <tt>!nontemporal</tt> metadata must reference a single
4295 metatadata name <index> corresponding to a metadata node with
4296 one <tt>i32</tt> entry of value 1. The existence of
4297 the <tt>!nontemporal</tt> metatadata on the instruction tells the optimizer
4298 and code generator that this load is not expected to be reused in the cache.
4299 The code generator may select special instructions to save cache bandwidth,
4300 such as the <tt>MOVNT</tt> instruction on x86.</p>
4303 <p>The location of memory pointed to is loaded. If the value being loaded is of
4304 scalar type then the number of bytes read does not exceed the minimum number
4305 of bytes needed to hold all bits of the type. For example, loading an
4306 <tt>i24</tt> reads at most three bytes. When loading a value of a type like
4307 <tt>i20</tt> with a size that is not an integral number of bytes, the result
4308 is undefined if the value was not originally written using a store of the
4313 %ptr = <a href="#i_alloca">alloca</a> i32 <i>; yields {i32*}:ptr</i>
4314 <a href="#i_store">store</a> i32 3, i32* %ptr <i>; yields {void}</i>
4315 %val = load i32* %ptr <i>; yields {i32}:val = i32 3</i>
4320 <!-- _______________________________________________________________________ -->
4321 <div class="doc_subsubsection"> <a name="i_store">'<tt>store</tt>'
4322 Instruction</a> </div>
4324 <div class="doc_text">
4328 store <ty> <value>, <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>] <i>; yields {void}</i>
4329 volatile store <ty> <value>, <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>] <i>; yields {void}</i>
4333 <p>The '<tt>store</tt>' instruction is used to write to memory.</p>
4336 <p>There are two arguments to the '<tt>store</tt>' instruction: a value to store
4337 and an address at which to store it. The type of the
4338 '<tt><pointer></tt>' operand must be a pointer to
4339 the <a href="#t_firstclass">first class</a> type of the
4340 '<tt><value></tt>' operand. If the <tt>store</tt> is marked as
4341 <tt>volatile</tt>, then the optimizer is not allowed to modify the number or
4342 order of execution of this <tt>store</tt> with other <a
4343 href="#volatile">volatile operations</a>.</p>
4345 <p>The optional constant "align" argument specifies the alignment of the
4346 operation (that is, the alignment of the memory address). A value of 0 or an
4347 omitted "align" argument means that the operation has the preferential
4348 alignment for the target. It is the responsibility of the code emitter to
4349 ensure that the alignment information is correct. Overestimating the
4350 alignment results in an undefined behavior. Underestimating the alignment may
4351 produce less efficient code. An alignment of 1 is always safe.</p>
4353 <p>The optional !nontemporal metadata must reference a single metatadata
4354 name <index> corresponding to a metadata node with one i32 entry of
4355 value 1. The existence of the !nontemporal metatadata on the
4356 instruction tells the optimizer and code generator that this load is
4357 not expected to be reused in the cache. The code generator may
4358 select special instructions to save cache bandwidth, such as the
4359 MOVNT instruction on x86.</p>
4363 <p>The contents of memory are updated to contain '<tt><value></tt>' at the
4364 location specified by the '<tt><pointer></tt>' operand. If
4365 '<tt><value></tt>' is of scalar type then the number of bytes written
4366 does not exceed the minimum number of bytes needed to hold all bits of the
4367 type. For example, storing an <tt>i24</tt> writes at most three bytes. When
4368 writing a value of a type like <tt>i20</tt> with a size that is not an
4369 integral number of bytes, it is unspecified what happens to the extra bits
4370 that do not belong to the type, but they will typically be overwritten.</p>
4374 %ptr = <a href="#i_alloca">alloca</a> i32 <i>; yields {i32*}:ptr</i>
4375 store i32 3, i32* %ptr <i>; yields {void}</i>
4376 %val = <a href="#i_load">load</a> i32* %ptr <i>; yields {i32}:val = i32 3</i>
4381 <!-- _______________________________________________________________________ -->
4382 <div class="doc_subsubsection">
4383 <a name="i_getelementptr">'<tt>getelementptr</tt>' Instruction</a>
4386 <div class="doc_text">
4390 <result> = getelementptr <pty>* <ptrval>{, <ty> <idx>}*
4391 <result> = getelementptr inbounds <pty>* <ptrval>{, <ty> <idx>}*
4395 <p>The '<tt>getelementptr</tt>' instruction is used to get the address of a
4396 subelement of an <a href="#t_aggregate">aggregate</a> data structure.
4397 It performs address calculation only and does not access memory.</p>
4400 <p>The first argument is always a pointer, and forms the basis of the
4401 calculation. The remaining arguments are indices that indicate which of the
4402 elements of the aggregate object are indexed. The interpretation of each
4403 index is dependent on the type being indexed into. The first index always
4404 indexes the pointer value given as the first argument, the second index
4405 indexes a value of the type pointed to (not necessarily the value directly
4406 pointed to, since the first index can be non-zero), etc. The first type
4407 indexed into must be a pointer value, subsequent types can be arrays,
4408 vectors, structs and unions. Note that subsequent types being indexed into
4409 can never be pointers, since that would require loading the pointer before
4410 continuing calculation.</p>
4412 <p>The type of each index argument depends on the type it is indexing into.
4413 When indexing into a (optionally packed) structure or union, only <tt>i32</tt>
4414 integer <b>constants</b> are allowed. When indexing into an array, pointer
4415 or vector, integers of any width are allowed, and they are not required to be
4418 <p>For example, let's consider a C code fragment and how it gets compiled to
4421 <pre class="doc_code">
4433 int *foo(struct ST *s) {
4434 return &s[1].Z.B[5][13];
4438 <p>The LLVM code generated by the GCC frontend is:</p>
4440 <pre class="doc_code">
4441 %RT = <a href="#namedtypes">type</a> { i8 , [10 x [20 x i32]], i8 }
4442 %ST = <a href="#namedtypes">type</a> { i32, double, %RT }
4444 define i32* @foo(%ST* %s) {
4446 %reg = getelementptr %ST* %s, i32 1, i32 2, i32 1, i32 5, i32 13
4452 <p>In the example above, the first index is indexing into the '<tt>%ST*</tt>'
4453 type, which is a pointer, yielding a '<tt>%ST</tt>' = '<tt>{ i32, double, %RT
4454 }</tt>' type, a structure. The second index indexes into the third element
4455 of the structure, yielding a '<tt>%RT</tt>' = '<tt>{ i8 , [10 x [20 x i32]],
4456 i8 }</tt>' type, another structure. The third index indexes into the second
4457 element of the structure, yielding a '<tt>[10 x [20 x i32]]</tt>' type, an
4458 array. The two dimensions of the array are subscripted into, yielding an
4459 '<tt>i32</tt>' type. The '<tt>getelementptr</tt>' instruction returns a
4460 pointer to this element, thus computing a value of '<tt>i32*</tt>' type.</p>
4462 <p>Note that it is perfectly legal to index partially through a structure,
4463 returning a pointer to an inner element. Because of this, the LLVM code for
4464 the given testcase is equivalent to:</p>
4467 define i32* @foo(%ST* %s) {
4468 %t1 = getelementptr %ST* %s, i32 1 <i>; yields %ST*:%t1</i>
4469 %t2 = getelementptr %ST* %t1, i32 0, i32 2 <i>; yields %RT*:%t2</i>
4470 %t3 = getelementptr %RT* %t2, i32 0, i32 1 <i>; yields [10 x [20 x i32]]*:%t3</i>
4471 %t4 = getelementptr [10 x [20 x i32]]* %t3, i32 0, i32 5 <i>; yields [20 x i32]*:%t4</i>
4472 %t5 = getelementptr [20 x i32]* %t4, i32 0, i32 13 <i>; yields i32*:%t5</i>
4477 <p>If the <tt>inbounds</tt> keyword is present, the result value of the
4478 <tt>getelementptr</tt> is a <a href="#trapvalues">trap value</a> if the
4479 base pointer is not an <i>in bounds</i> address of an allocated object,
4480 or if any of the addresses that would be formed by successive addition of
4481 the offsets implied by the indices to the base address with infinitely
4482 precise arithmetic are not an <i>in bounds</i> address of that allocated
4483 object. The <i>in bounds</i> addresses for an allocated object are all
4484 the addresses that point into the object, plus the address one byte past
4487 <p>If the <tt>inbounds</tt> keyword is not present, the offsets are added to
4488 the base address with silently-wrapping two's complement arithmetic, and
4489 the result value of the <tt>getelementptr</tt> may be outside the object
4490 pointed to by the base pointer. The result value may not necessarily be
4491 used to access memory though, even if it happens to point into allocated
4492 storage. See the <a href="#pointeraliasing">Pointer Aliasing Rules</a>
4493 section for more information.</p>
4495 <p>The getelementptr instruction is often confusing. For some more insight into
4496 how it works, see <a href="GetElementPtr.html">the getelementptr FAQ</a>.</p>
4500 <i>; yields [12 x i8]*:aptr</i>
4501 %aptr = getelementptr {i32, [12 x i8]}* %saptr, i64 0, i32 1
4502 <i>; yields i8*:vptr</i>
4503 %vptr = getelementptr {i32, <2 x i8>}* %svptr, i64 0, i32 1, i32 1
4504 <i>; yields i8*:eptr</i>
4505 %eptr = getelementptr [12 x i8]* %aptr, i64 0, i32 1
4506 <i>; yields i32*:iptr</i>
4507 %iptr = getelementptr [10 x i32]* @arr, i16 0, i16 0
4512 <!-- ======================================================================= -->
4513 <div class="doc_subsection"> <a name="convertops">Conversion Operations</a>
4516 <div class="doc_text">
4518 <p>The instructions in this category are the conversion instructions (casting)
4519 which all take a single operand and a type. They perform various bit
4520 conversions on the operand.</p>
4524 <!-- _______________________________________________________________________ -->
4525 <div class="doc_subsubsection">
4526 <a name="i_trunc">'<tt>trunc .. to</tt>' Instruction</a>
4528 <div class="doc_text">
4532 <result> = trunc <ty> <value> to <ty2> <i>; yields ty2</i>
4536 <p>The '<tt>trunc</tt>' instruction truncates its operand to the
4537 type <tt>ty2</tt>.</p>
4540 <p>The '<tt>trunc</tt>' instruction takes a <tt>value</tt> to trunc, which must
4541 be an <a href="#t_integer">integer</a> type, and a type that specifies the
4542 size and type of the result, which must be
4543 an <a href="#t_integer">integer</a> type. The bit size of <tt>value</tt> must
4544 be larger than the bit size of <tt>ty2</tt>. Equal sized types are not
4548 <p>The '<tt>trunc</tt>' instruction truncates the high order bits
4549 in <tt>value</tt> and converts the remaining bits to <tt>ty2</tt>. Since the
4550 source size must be larger than the destination size, <tt>trunc</tt> cannot
4551 be a <i>no-op cast</i>. It will always truncate bits.</p>
4555 %X = trunc i32 257 to i8 <i>; yields i8:1</i>
4556 %Y = trunc i32 123 to i1 <i>; yields i1:true</i>
4557 %Z = trunc i32 122 to i1 <i>; yields i1:false</i>
4562 <!-- _______________________________________________________________________ -->
4563 <div class="doc_subsubsection">
4564 <a name="i_zext">'<tt>zext .. to</tt>' Instruction</a>
4566 <div class="doc_text">
4570 <result> = zext <ty> <value> to <ty2> <i>; yields ty2</i>
4574 <p>The '<tt>zext</tt>' instruction zero extends its operand to type
4579 <p>The '<tt>zext</tt>' instruction takes a value to cast, which must be of
4580 <a href="#t_integer">integer</a> type, and a type to cast it to, which must
4581 also be of <a href="#t_integer">integer</a> type. The bit size of the
4582 <tt>value</tt> must be smaller than the bit size of the destination type,
4586 <p>The <tt>zext</tt> fills the high order bits of the <tt>value</tt> with zero
4587 bits until it reaches the size of the destination type, <tt>ty2</tt>.</p>
4589 <p>When zero extending from i1, the result will always be either 0 or 1.</p>
4593 %X = zext i32 257 to i64 <i>; yields i64:257</i>
4594 %Y = zext i1 true to i32 <i>; yields i32:1</i>
4599 <!-- _______________________________________________________________________ -->
4600 <div class="doc_subsubsection">
4601 <a name="i_sext">'<tt>sext .. to</tt>' Instruction</a>
4603 <div class="doc_text">
4607 <result> = sext <ty> <value> to <ty2> <i>; yields ty2</i>
4611 <p>The '<tt>sext</tt>' sign extends <tt>value</tt> to the type <tt>ty2</tt>.</p>
4614 <p>The '<tt>sext</tt>' instruction takes a value to cast, which must be of
4615 <a href="#t_integer">integer</a> type, and a type to cast it to, which must
4616 also be of <a href="#t_integer">integer</a> type. The bit size of the
4617 <tt>value</tt> must be smaller than the bit size of the destination type,
4621 <p>The '<tt>sext</tt>' instruction performs a sign extension by copying the sign
4622 bit (highest order bit) of the <tt>value</tt> until it reaches the bit size
4623 of the type <tt>ty2</tt>.</p>
4625 <p>When sign extending from i1, the extension always results in -1 or 0.</p>
4629 %X = sext i8 -1 to i16 <i>; yields i16 :65535</i>
4630 %Y = sext i1 true to i32 <i>; yields i32:-1</i>
4635 <!-- _______________________________________________________________________ -->
4636 <div class="doc_subsubsection">
4637 <a name="i_fptrunc">'<tt>fptrunc .. to</tt>' Instruction</a>
4640 <div class="doc_text">
4644 <result> = fptrunc <ty> <value> to <ty2> <i>; yields ty2</i>
4648 <p>The '<tt>fptrunc</tt>' instruction truncates <tt>value</tt> to type
4652 <p>The '<tt>fptrunc</tt>' instruction takes a <a href="#t_floating">floating
4653 point</a> value to cast and a <a href="#t_floating">floating point</a> type
4654 to cast it to. The size of <tt>value</tt> must be larger than the size of
4655 <tt>ty2</tt>. This implies that <tt>fptrunc</tt> cannot be used to make a
4656 <i>no-op cast</i>.</p>
4659 <p>The '<tt>fptrunc</tt>' instruction truncates a <tt>value</tt> from a larger
4660 <a href="#t_floating">floating point</a> type to a smaller
4661 <a href="#t_floating">floating point</a> type. If the value cannot fit
4662 within the destination type, <tt>ty2</tt>, then the results are
4667 %X = fptrunc double 123.0 to float <i>; yields float:123.0</i>
4668 %Y = fptrunc double 1.0E+300 to float <i>; yields undefined</i>
4673 <!-- _______________________________________________________________________ -->
4674 <div class="doc_subsubsection">
4675 <a name="i_fpext">'<tt>fpext .. to</tt>' Instruction</a>
4677 <div class="doc_text">
4681 <result> = fpext <ty> <value> to <ty2> <i>; yields ty2</i>
4685 <p>The '<tt>fpext</tt>' extends a floating point <tt>value</tt> to a larger
4686 floating point value.</p>
4689 <p>The '<tt>fpext</tt>' instruction takes a
4690 <a href="#t_floating">floating point</a> <tt>value</tt> to cast, and
4691 a <a href="#t_floating">floating point</a> type to cast it to. The source
4692 type must be smaller than the destination type.</p>
4695 <p>The '<tt>fpext</tt>' instruction extends the <tt>value</tt> from a smaller
4696 <a href="#t_floating">floating point</a> type to a larger
4697 <a href="#t_floating">floating point</a> type. The <tt>fpext</tt> cannot be
4698 used to make a <i>no-op cast</i> because it always changes bits. Use
4699 <tt>bitcast</tt> to make a <i>no-op cast</i> for a floating point cast.</p>
4703 %X = fpext float 3.1415 to double <i>; yields double:3.1415</i>
4704 %Y = fpext float 1.0 to float <i>; yields float:1.0 (no-op)</i>
4709 <!-- _______________________________________________________________________ -->
4710 <div class="doc_subsubsection">
4711 <a name="i_fptoui">'<tt>fptoui .. to</tt>' Instruction</a>
4713 <div class="doc_text">
4717 <result> = fptoui <ty> <value> to <ty2> <i>; yields ty2</i>
4721 <p>The '<tt>fptoui</tt>' converts a floating point <tt>value</tt> to its
4722 unsigned integer equivalent of type <tt>ty2</tt>.</p>
4725 <p>The '<tt>fptoui</tt>' instruction takes a value to cast, which must be a
4726 scalar or vector <a href="#t_floating">floating point</a> value, and a type
4727 to cast it to <tt>ty2</tt>, which must be an <a href="#t_integer">integer</a>
4728 type. If <tt>ty</tt> is a vector floating point type, <tt>ty2</tt> must be a
4729 vector integer type with the same number of elements as <tt>ty</tt></p>
4732 <p>The '<tt>fptoui</tt>' instruction converts its
4733 <a href="#t_floating">floating point</a> operand into the nearest (rounding
4734 towards zero) unsigned integer value. If the value cannot fit
4735 in <tt>ty2</tt>, the results are undefined.</p>
4739 %X = fptoui double 123.0 to i32 <i>; yields i32:123</i>
4740 %Y = fptoui float 1.0E+300 to i1 <i>; yields undefined:1</i>
4741 %Z = fptoui float 1.04E+17 to i8 <i>; yields undefined:1</i>
4746 <!-- _______________________________________________________________________ -->
4747 <div class="doc_subsubsection">
4748 <a name="i_fptosi">'<tt>fptosi .. to</tt>' Instruction</a>
4750 <div class="doc_text">
4754 <result> = fptosi <ty> <value> to <ty2> <i>; yields ty2</i>
4758 <p>The '<tt>fptosi</tt>' instruction converts
4759 <a href="#t_floating">floating point</a> <tt>value</tt> to
4760 type <tt>ty2</tt>.</p>
4763 <p>The '<tt>fptosi</tt>' instruction takes a value to cast, which must be a
4764 scalar or vector <a href="#t_floating">floating point</a> value, and a type
4765 to cast it to <tt>ty2</tt>, which must be an <a href="#t_integer">integer</a>
4766 type. If <tt>ty</tt> is a vector floating point type, <tt>ty2</tt> must be a
4767 vector integer type with the same number of elements as <tt>ty</tt></p>
4770 <p>The '<tt>fptosi</tt>' instruction converts its
4771 <a href="#t_floating">floating point</a> operand into the nearest (rounding
4772 towards zero) signed integer value. If the value cannot fit in <tt>ty2</tt>,
4773 the results are undefined.</p>
4777 %X = fptosi double -123.0 to i32 <i>; yields i32:-123</i>
4778 %Y = fptosi float 1.0E-247 to i1 <i>; yields undefined:1</i>
4779 %Z = fptosi float 1.04E+17 to i8 <i>; yields undefined:1</i>
4784 <!-- _______________________________________________________________________ -->
4785 <div class="doc_subsubsection">
4786 <a name="i_uitofp">'<tt>uitofp .. to</tt>' Instruction</a>
4788 <div class="doc_text">
4792 <result> = uitofp <ty> <value> to <ty2> <i>; yields ty2</i>
4796 <p>The '<tt>uitofp</tt>' instruction regards <tt>value</tt> as an unsigned
4797 integer and converts that value to the <tt>ty2</tt> type.</p>
4800 <p>The '<tt>uitofp</tt>' instruction takes a value to cast, which must be a
4801 scalar or vector <a href="#t_integer">integer</a> value, and a type to cast
4802 it to <tt>ty2</tt>, which must be an <a href="#t_floating">floating point</a>
4803 type. If <tt>ty</tt> is a vector integer type, <tt>ty2</tt> must be a vector
4804 floating point type with the same number of elements as <tt>ty</tt></p>
4807 <p>The '<tt>uitofp</tt>' instruction interprets its operand as an unsigned
4808 integer quantity and converts it to the corresponding floating point
4809 value. If the value cannot fit in the floating point value, the results are
4814 %X = uitofp i32 257 to float <i>; yields float:257.0</i>
4815 %Y = uitofp i8 -1 to double <i>; yields double:255.0</i>
4820 <!-- _______________________________________________________________________ -->
4821 <div class="doc_subsubsection">
4822 <a name="i_sitofp">'<tt>sitofp .. to</tt>' Instruction</a>
4824 <div class="doc_text">
4828 <result> = sitofp <ty> <value> to <ty2> <i>; yields ty2</i>
4832 <p>The '<tt>sitofp</tt>' instruction regards <tt>value</tt> as a signed integer
4833 and converts that value to the <tt>ty2</tt> type.</p>
4836 <p>The '<tt>sitofp</tt>' instruction takes a value to cast, which must be a
4837 scalar or vector <a href="#t_integer">integer</a> value, and a type to cast
4838 it to <tt>ty2</tt>, which must be an <a href="#t_floating">floating point</a>
4839 type. If <tt>ty</tt> is a vector integer type, <tt>ty2</tt> must be a vector
4840 floating point type with the same number of elements as <tt>ty</tt></p>
4843 <p>The '<tt>sitofp</tt>' instruction interprets its operand as a signed integer
4844 quantity and converts it to the corresponding floating point value. If the
4845 value cannot fit in the floating point value, the results are undefined.</p>
4849 %X = sitofp i32 257 to float <i>; yields float:257.0</i>
4850 %Y = sitofp i8 -1 to double <i>; yields double:-1.0</i>
4855 <!-- _______________________________________________________________________ -->
4856 <div class="doc_subsubsection">
4857 <a name="i_ptrtoint">'<tt>ptrtoint .. to</tt>' Instruction</a>
4859 <div class="doc_text">
4863 <result> = ptrtoint <ty> <value> to <ty2> <i>; yields ty2</i>
4867 <p>The '<tt>ptrtoint</tt>' instruction converts the pointer <tt>value</tt> to
4868 the integer type <tt>ty2</tt>.</p>
4871 <p>The '<tt>ptrtoint</tt>' instruction takes a <tt>value</tt> to cast, which
4872 must be a <a href="#t_pointer">pointer</a> value, and a type to cast it to
4873 <tt>ty2</tt>, which must be an <a href="#t_integer">integer</a> type.</p>
4876 <p>The '<tt>ptrtoint</tt>' instruction converts <tt>value</tt> to integer type
4877 <tt>ty2</tt> by interpreting the pointer value as an integer and either
4878 truncating or zero extending that value to the size of the integer type. If
4879 <tt>value</tt> is smaller than <tt>ty2</tt> then a zero extension is done. If
4880 <tt>value</tt> is larger than <tt>ty2</tt> then a truncation is done. If they
4881 are the same size, then nothing is done (<i>no-op cast</i>) other than a type
4886 %X = ptrtoint i32* %X to i8 <i>; yields truncation on 32-bit architecture</i>
4887 %Y = ptrtoint i32* %x to i64 <i>; yields zero extension on 32-bit architecture</i>
4892 <!-- _______________________________________________________________________ -->
4893 <div class="doc_subsubsection">
4894 <a name="i_inttoptr">'<tt>inttoptr .. to</tt>' Instruction</a>
4896 <div class="doc_text">
4900 <result> = inttoptr <ty> <value> to <ty2> <i>; yields ty2</i>
4904 <p>The '<tt>inttoptr</tt>' instruction converts an integer <tt>value</tt> to a
4905 pointer type, <tt>ty2</tt>.</p>
4908 <p>The '<tt>inttoptr</tt>' instruction takes an <a href="#t_integer">integer</a>
4909 value to cast, and a type to cast it to, which must be a
4910 <a href="#t_pointer">pointer</a> type.</p>
4913 <p>The '<tt>inttoptr</tt>' instruction converts <tt>value</tt> to type
4914 <tt>ty2</tt> by applying either a zero extension or a truncation depending on
4915 the size of the integer <tt>value</tt>. If <tt>value</tt> is larger than the
4916 size of a pointer then a truncation is done. If <tt>value</tt> is smaller
4917 than the size of a pointer then a zero extension is done. If they are the
4918 same size, nothing is done (<i>no-op cast</i>).</p>
4922 %X = inttoptr i32 255 to i32* <i>; yields zero extension on 64-bit architecture</i>
4923 %Y = inttoptr i32 255 to i32* <i>; yields no-op on 32-bit architecture</i>
4924 %Z = inttoptr i64 0 to i32* <i>; yields truncation on 32-bit architecture</i>
4929 <!-- _______________________________________________________________________ -->
4930 <div class="doc_subsubsection">
4931 <a name="i_bitcast">'<tt>bitcast .. to</tt>' Instruction</a>
4933 <div class="doc_text">
4937 <result> = bitcast <ty> <value> to <ty2> <i>; yields ty2</i>
4941 <p>The '<tt>bitcast</tt>' instruction converts <tt>value</tt> to type
4942 <tt>ty2</tt> without changing any bits.</p>
4945 <p>The '<tt>bitcast</tt>' instruction takes a value to cast, which must be a
4946 non-aggregate first class value, and a type to cast it to, which must also be
4947 a non-aggregate <a href="#t_firstclass">first class</a> type. The bit sizes
4948 of <tt>value</tt> and the destination type, <tt>ty2</tt>, must be
4949 identical. If the source type is a pointer, the destination type must also be
4950 a pointer. This instruction supports bitwise conversion of vectors to
4951 integers and to vectors of other types (as long as they have the same
4955 <p>The '<tt>bitcast</tt>' instruction converts <tt>value</tt> to type
4956 <tt>ty2</tt>. It is always a <i>no-op cast</i> because no bits change with
4957 this conversion. The conversion is done as if the <tt>value</tt> had been
4958 stored to memory and read back as type <tt>ty2</tt>. Pointer types may only
4959 be converted to other pointer types with this instruction. To convert
4960 pointers to other types, use the <a href="#i_inttoptr">inttoptr</a> or
4961 <a href="#i_ptrtoint">ptrtoint</a> instructions first.</p>
4965 %X = bitcast i8 255 to i8 <i>; yields i8 :-1</i>
4966 %Y = bitcast i32* %x to sint* <i>; yields sint*:%x</i>
4967 %Z = bitcast <2 x int> %V to i64; <i>; yields i64: %V</i>
4972 <!-- ======================================================================= -->
4973 <div class="doc_subsection"> <a name="otherops">Other Operations</a> </div>
4975 <div class="doc_text">
4977 <p>The instructions in this category are the "miscellaneous" instructions, which
4978 defy better classification.</p>
4982 <!-- _______________________________________________________________________ -->
4983 <div class="doc_subsubsection"><a name="i_icmp">'<tt>icmp</tt>' Instruction</a>
4986 <div class="doc_text">
4990 <result> = icmp <cond> <ty> <op1>, <op2> <i>; yields {i1} or {<N x i1>}:result</i>
4994 <p>The '<tt>icmp</tt>' instruction returns a boolean value or a vector of
4995 boolean values based on comparison of its two integer, integer vector, or
4996 pointer operands.</p>
4999 <p>The '<tt>icmp</tt>' instruction takes three operands. The first operand is
5000 the condition code indicating the kind of comparison to perform. It is not a
5001 value, just a keyword. The possible condition code are:</p>
5004 <li><tt>eq</tt>: equal</li>
5005 <li><tt>ne</tt>: not equal </li>
5006 <li><tt>ugt</tt>: unsigned greater than</li>
5007 <li><tt>uge</tt>: unsigned greater or equal</li>
5008 <li><tt>ult</tt>: unsigned less than</li>
5009 <li><tt>ule</tt>: unsigned less or equal</li>
5010 <li><tt>sgt</tt>: signed greater than</li>
5011 <li><tt>sge</tt>: signed greater or equal</li>
5012 <li><tt>slt</tt>: signed less than</li>
5013 <li><tt>sle</tt>: signed less or equal</li>
5016 <p>The remaining two arguments must be <a href="#t_integer">integer</a> or
5017 <a href="#t_pointer">pointer</a> or integer <a href="#t_vector">vector</a>
5018 typed. They must also be identical types.</p>
5021 <p>The '<tt>icmp</tt>' compares <tt>op1</tt> and <tt>op2</tt> according to the
5022 condition code given as <tt>cond</tt>. The comparison performed always yields
5023 either an <a href="#t_integer"><tt>i1</tt></a> or vector of <tt>i1</tt>
5024 result, as follows:</p>
5027 <li><tt>eq</tt>: yields <tt>true</tt> if the operands are equal,
5028 <tt>false</tt> otherwise. No sign interpretation is necessary or
5031 <li><tt>ne</tt>: yields <tt>true</tt> if the operands are unequal,
5032 <tt>false</tt> otherwise. No sign interpretation is necessary or
5035 <li><tt>ugt</tt>: interprets the operands as unsigned values and yields
5036 <tt>true</tt> if <tt>op1</tt> is greater than <tt>op2</tt>.</li>
5038 <li><tt>uge</tt>: interprets the operands as unsigned values and yields
5039 <tt>true</tt> if <tt>op1</tt> is greater than or equal
5040 to <tt>op2</tt>.</li>
5042 <li><tt>ult</tt>: interprets the operands as unsigned values and yields
5043 <tt>true</tt> if <tt>op1</tt> is less than <tt>op2</tt>.</li>
5045 <li><tt>ule</tt>: interprets the operands as unsigned values and yields
5046 <tt>true</tt> if <tt>op1</tt> is less than or equal to <tt>op2</tt>.</li>
5048 <li><tt>sgt</tt>: interprets the operands as signed values and yields
5049 <tt>true</tt> if <tt>op1</tt> is greater than <tt>op2</tt>.</li>
5051 <li><tt>sge</tt>: interprets the operands as signed values and yields
5052 <tt>true</tt> if <tt>op1</tt> is greater than or equal
5053 to <tt>op2</tt>.</li>
5055 <li><tt>slt</tt>: interprets the operands as signed values and yields
5056 <tt>true</tt> if <tt>op1</tt> is less than <tt>op2</tt>.</li>
5058 <li><tt>sle</tt>: interprets the operands as signed values and yields
5059 <tt>true</tt> if <tt>op1</tt> is less than or equal to <tt>op2</tt>.</li>
5062 <p>If the operands are <a href="#t_pointer">pointer</a> typed, the pointer
5063 values are compared as if they were integers.</p>
5065 <p>If the operands are integer vectors, then they are compared element by
5066 element. The result is an <tt>i1</tt> vector with the same number of elements
5067 as the values being compared. Otherwise, the result is an <tt>i1</tt>.</p>
5071 <result> = icmp eq i32 4, 5 <i>; yields: result=false</i>
5072 <result> = icmp ne float* %X, %X <i>; yields: result=false</i>
5073 <result> = icmp ult i16 4, 5 <i>; yields: result=true</i>
5074 <result> = icmp sgt i16 4, 5 <i>; yields: result=false</i>
5075 <result> = icmp ule i16 -4, 5 <i>; yields: result=false</i>
5076 <result> = icmp sge i16 4, 5 <i>; yields: result=false</i>
5079 <p>Note that the code generator does not yet support vector types with
5080 the <tt>icmp</tt> instruction.</p>
5084 <!-- _______________________________________________________________________ -->
5085 <div class="doc_subsubsection"><a name="i_fcmp">'<tt>fcmp</tt>' Instruction</a>
5088 <div class="doc_text">
5092 <result> = fcmp <cond> <ty> <op1>, <op2> <i>; yields {i1} or {<N x i1>}:result</i>
5096 <p>The '<tt>fcmp</tt>' instruction returns a boolean value or vector of boolean
5097 values based on comparison of its operands.</p>
5099 <p>If the operands are floating point scalars, then the result type is a boolean
5100 (<a href="#t_integer"><tt>i1</tt></a>).</p>
5102 <p>If the operands are floating point vectors, then the result type is a vector
5103 of boolean with the same number of elements as the operands being
5107 <p>The '<tt>fcmp</tt>' instruction takes three operands. The first operand is
5108 the condition code indicating the kind of comparison to perform. It is not a
5109 value, just a keyword. The possible condition code are:</p>
5112 <li><tt>false</tt>: no comparison, always returns false</li>
5113 <li><tt>oeq</tt>: ordered and equal</li>
5114 <li><tt>ogt</tt>: ordered and greater than </li>
5115 <li><tt>oge</tt>: ordered and greater than or equal</li>
5116 <li><tt>olt</tt>: ordered and less than </li>
5117 <li><tt>ole</tt>: ordered and less than or equal</li>
5118 <li><tt>one</tt>: ordered and not equal</li>
5119 <li><tt>ord</tt>: ordered (no nans)</li>
5120 <li><tt>ueq</tt>: unordered or equal</li>
5121 <li><tt>ugt</tt>: unordered or greater than </li>
5122 <li><tt>uge</tt>: unordered or greater than or equal</li>
5123 <li><tt>ult</tt>: unordered or less than </li>
5124 <li><tt>ule</tt>: unordered or less than or equal</li>
5125 <li><tt>une</tt>: unordered or not equal</li>
5126 <li><tt>uno</tt>: unordered (either nans)</li>
5127 <li><tt>true</tt>: no comparison, always returns true</li>
5130 <p><i>Ordered</i> means that neither operand is a QNAN while
5131 <i>unordered</i> means that either operand may be a QNAN.</p>
5133 <p>Each of <tt>val1</tt> and <tt>val2</tt> arguments must be either
5134 a <a href="#t_floating">floating point</a> type or
5135 a <a href="#t_vector">vector</a> of floating point type. They must have
5136 identical types.</p>
5139 <p>The '<tt>fcmp</tt>' instruction compares <tt>op1</tt> and <tt>op2</tt>
5140 according to the condition code given as <tt>cond</tt>. If the operands are
5141 vectors, then the vectors are compared element by element. Each comparison
5142 performed always yields an <a href="#t_integer">i1</a> result, as
5146 <li><tt>false</tt>: always yields <tt>false</tt>, regardless of operands.</li>
5148 <li><tt>oeq</tt>: yields <tt>true</tt> if both operands are not a QNAN and
5149 <tt>op1</tt> is equal to <tt>op2</tt>.</li>
5151 <li><tt>ogt</tt>: yields <tt>true</tt> if both operands are not a QNAN and
5152 <tt>op1</tt> is greater than <tt>op2</tt>.</li>
5154 <li><tt>oge</tt>: yields <tt>true</tt> if both operands are not a QNAN and
5155 <tt>op1</tt> is greater than or equal to <tt>op2</tt>.</li>
5157 <li><tt>olt</tt>: yields <tt>true</tt> if both operands are not a QNAN and
5158 <tt>op1</tt> is less than <tt>op2</tt>.</li>
5160 <li><tt>ole</tt>: yields <tt>true</tt> if both operands are not a QNAN and
5161 <tt>op1</tt> is less than or equal to <tt>op2</tt>.</li>
5163 <li><tt>one</tt>: yields <tt>true</tt> if both operands are not a QNAN and
5164 <tt>op1</tt> is not equal to <tt>op2</tt>.</li>
5166 <li><tt>ord</tt>: yields <tt>true</tt> if both operands are not a QNAN.</li>
5168 <li><tt>ueq</tt>: yields <tt>true</tt> if either operand is a QNAN or
5169 <tt>op1</tt> is equal to <tt>op2</tt>.</li>
5171 <li><tt>ugt</tt>: yields <tt>true</tt> if either operand is a QNAN or
5172 <tt>op1</tt> is greater than <tt>op2</tt>.</li>
5174 <li><tt>uge</tt>: yields <tt>true</tt> if either operand is a QNAN or
5175 <tt>op1</tt> is greater than or equal to <tt>op2</tt>.</li>
5177 <li><tt>ult</tt>: yields <tt>true</tt> if either operand is a QNAN or
5178 <tt>op1</tt> is less than <tt>op2</tt>.</li>
5180 <li><tt>ule</tt>: yields <tt>true</tt> if either operand is a QNAN or
5181 <tt>op1</tt> is less than or equal to <tt>op2</tt>.</li>
5183 <li><tt>une</tt>: yields <tt>true</tt> if either operand is a QNAN or
5184 <tt>op1</tt> is not equal to <tt>op2</tt>.</li>
5186 <li><tt>uno</tt>: yields <tt>true</tt> if either operand is a QNAN.</li>
5188 <li><tt>true</tt>: always yields <tt>true</tt>, regardless of operands.</li>
5193 <result> = fcmp oeq float 4.0, 5.0 <i>; yields: result=false</i>
5194 <result> = fcmp one float 4.0, 5.0 <i>; yields: result=true</i>
5195 <result> = fcmp olt float 4.0, 5.0 <i>; yields: result=true</i>
5196 <result> = fcmp ueq double 1.0, 2.0 <i>; yields: result=false</i>
5199 <p>Note that the code generator does not yet support vector types with
5200 the <tt>fcmp</tt> instruction.</p>
5204 <!-- _______________________________________________________________________ -->
5205 <div class="doc_subsubsection">
5206 <a name="i_phi">'<tt>phi</tt>' Instruction</a>
5209 <div class="doc_text">
5213 <result> = phi <ty> [ <val0>, <label0>], ...
5217 <p>The '<tt>phi</tt>' instruction is used to implement the φ node in the
5218 SSA graph representing the function.</p>
5221 <p>The type of the incoming values is specified with the first type field. After
5222 this, the '<tt>phi</tt>' instruction takes a list of pairs as arguments, with
5223 one pair for each predecessor basic block of the current block. Only values
5224 of <a href="#t_firstclass">first class</a> type may be used as the value
5225 arguments to the PHI node. Only labels may be used as the label
5228 <p>There must be no non-phi instructions between the start of a basic block and
5229 the PHI instructions: i.e. PHI instructions must be first in a basic
5232 <p>For the purposes of the SSA form, the use of each incoming value is deemed to
5233 occur on the edge from the corresponding predecessor block to the current
5234 block (but after any definition of an '<tt>invoke</tt>' instruction's return
5235 value on the same edge).</p>
5238 <p>At runtime, the '<tt>phi</tt>' instruction logically takes on the value
5239 specified by the pair corresponding to the predecessor basic block that
5240 executed just prior to the current block.</p>
5244 Loop: ; Infinite loop that counts from 0 on up...
5245 %indvar = phi i32 [ 0, %LoopHeader ], [ %nextindvar, %Loop ]
5246 %nextindvar = add i32 %indvar, 1
5252 <!-- _______________________________________________________________________ -->
5253 <div class="doc_subsubsection">
5254 <a name="i_select">'<tt>select</tt>' Instruction</a>
5257 <div class="doc_text">
5261 <result> = select <i>selty</i> <cond>, <ty> <val1>, <ty> <val2> <i>; yields ty</i>
5263 <i>selty</i> is either i1 or {<N x i1>}
5267 <p>The '<tt>select</tt>' instruction is used to choose one value based on a
5268 condition, without branching.</p>
5272 <p>The '<tt>select</tt>' instruction requires an 'i1' value or a vector of 'i1'
5273 values indicating the condition, and two values of the
5274 same <a href="#t_firstclass">first class</a> type. If the val1/val2 are
5275 vectors and the condition is a scalar, then entire vectors are selected, not
5276 individual elements.</p>
5279 <p>If the condition is an i1 and it evaluates to 1, the instruction returns the
5280 first value argument; otherwise, it returns the second value argument.</p>
5282 <p>If the condition is a vector of i1, then the value arguments must be vectors
5283 of the same size, and the selection is done element by element.</p>
5287 %X = select i1 true, i8 17, i8 42 <i>; yields i8:17</i>
5290 <p>Note that the code generator does not yet support conditions
5291 with vector type.</p>
5295 <!-- _______________________________________________________________________ -->
5296 <div class="doc_subsubsection">
5297 <a name="i_call">'<tt>call</tt>' Instruction</a>
5300 <div class="doc_text">
5304 <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>]
5308 <p>The '<tt>call</tt>' instruction represents a simple function call.</p>
5311 <p>This instruction requires several arguments:</p>
5314 <li>The optional "tail" marker indicates that the callee function does not
5315 access any allocas or varargs in the caller. Note that calls may be
5316 marked "tail" even if they do not occur before
5317 a <a href="#i_ret"><tt>ret</tt></a> instruction. If the "tail" marker is
5318 present, the function call is eligible for tail call optimization,
5319 but <a href="CodeGenerator.html#tailcallopt">might not in fact be
5320 optimized into a jump</a>. The code generator may optimize calls marked
5321 "tail" with either 1) automatic <a href="CodeGenerator.html#sibcallopt">
5322 sibling call optimization</a> when the caller and callee have
5323 matching signatures, or 2) forced tail call optimization when the
5324 following extra requirements are met:
5326 <li>Caller and callee both have the calling
5327 convention <tt>fastcc</tt>.</li>
5328 <li>The call is in tail position (ret immediately follows call and ret
5329 uses value of call or is void).</li>
5330 <li>Option <tt>-tailcallopt</tt> is enabled,
5331 or <code>llvm::GuaranteedTailCallOpt</code> is <code>true</code>.</li>
5332 <li><a href="CodeGenerator.html#tailcallopt">Platform specific
5333 constraints are met.</a></li>
5337 <li>The optional "cconv" marker indicates which <a href="#callingconv">calling
5338 convention</a> the call should use. If none is specified, the call
5339 defaults to using C calling conventions. The calling convention of the
5340 call must match the calling convention of the target function, or else the
5341 behavior is undefined.</li>
5343 <li>The optional <a href="#paramattrs">Parameter Attributes</a> list for
5344 return values. Only '<tt>zeroext</tt>', '<tt>signext</tt>', and
5345 '<tt>inreg</tt>' attributes are valid here.</li>
5347 <li>'<tt>ty</tt>': the type of the call instruction itself which is also the
5348 type of the return value. Functions that return no value are marked
5349 <tt><a href="#t_void">void</a></tt>.</li>
5351 <li>'<tt>fnty</tt>': shall be the signature of the pointer to function value
5352 being invoked. The argument types must match the types implied by this
5353 signature. This type can be omitted if the function is not varargs and if
5354 the function type does not return a pointer to a function.</li>
5356 <li>'<tt>fnptrval</tt>': An LLVM value containing a pointer to a function to
5357 be invoked. In most cases, this is a direct function invocation, but
5358 indirect <tt>call</tt>s are just as possible, calling an arbitrary pointer
5359 to function value.</li>
5361 <li>'<tt>function args</tt>': argument list whose types match the function
5362 signature argument types and parameter attributes. All arguments must be
5363 of <a href="#t_firstclass">first class</a> type. If the function
5364 signature indicates the function accepts a variable number of arguments,
5365 the extra arguments can be specified.</li>
5367 <li>The optional <a href="#fnattrs">function attributes</a> list. Only
5368 '<tt>noreturn</tt>', '<tt>nounwind</tt>', '<tt>readonly</tt>' and
5369 '<tt>readnone</tt>' attributes are valid here.</li>
5373 <p>The '<tt>call</tt>' instruction is used to cause control flow to transfer to
5374 a specified function, with its incoming arguments bound to the specified
5375 values. Upon a '<tt><a href="#i_ret">ret</a></tt>' instruction in the called
5376 function, control flow continues with the instruction after the function
5377 call, and the return value of the function is bound to the result
5382 %retval = call i32 @test(i32 %argc)
5383 call i32 (i8*, ...)* @printf(i8* %msg, i32 12, i8 42) <i>; yields i32</i>
5384 %X = tail call i32 @foo() <i>; yields i32</i>
5385 %Y = tail call <a href="#callingconv">fastcc</a> i32 @foo() <i>; yields i32</i>
5386 call void %foo(i8 97 signext)
5388 %struct.A = type { i32, i8 }
5389 %r = call %struct.A @foo() <i>; yields { 32, i8 }</i>
5390 %gr = extractvalue %struct.A %r, 0 <i>; yields i32</i>
5391 %gr1 = extractvalue %struct.A %r, 1 <i>; yields i8</i>
5392 %Z = call void @foo() noreturn <i>; indicates that %foo never returns normally</i>
5393 %ZZ = call zeroext i32 @bar() <i>; Return value is %zero extended</i>
5396 <p>llvm treats calls to some functions with names and arguments that match the
5397 standard C99 library as being the C99 library functions, and may perform
5398 optimizations or generate code for them under that assumption. This is
5399 something we'd like to change in the future to provide better support for
5400 freestanding environments and non-C-based languages.</p>
5404 <!-- _______________________________________________________________________ -->
5405 <div class="doc_subsubsection">
5406 <a name="i_va_arg">'<tt>va_arg</tt>' Instruction</a>
5409 <div class="doc_text">
5413 <resultval> = va_arg <va_list*> <arglist>, <argty>
5417 <p>The '<tt>va_arg</tt>' instruction is used to access arguments passed through
5418 the "variable argument" area of a function call. It is used to implement the
5419 <tt>va_arg</tt> macro in C.</p>
5422 <p>This instruction takes a <tt>va_list*</tt> value and the type of the
5423 argument. It returns a value of the specified argument type and increments
5424 the <tt>va_list</tt> to point to the next argument. The actual type
5425 of <tt>va_list</tt> is target specific.</p>
5428 <p>The '<tt>va_arg</tt>' instruction loads an argument of the specified type
5429 from the specified <tt>va_list</tt> and causes the <tt>va_list</tt> to point
5430 to the next argument. For more information, see the variable argument
5431 handling <a href="#int_varargs">Intrinsic Functions</a>.</p>
5433 <p>It is legal for this instruction to be called in a function which does not
5434 take a variable number of arguments, for example, the <tt>vfprintf</tt>
5437 <p><tt>va_arg</tt> is an LLVM instruction instead of
5438 an <a href="#intrinsics">intrinsic function</a> because it takes a type as an
5442 <p>See the <a href="#int_varargs">variable argument processing</a> section.</p>
5444 <p>Note that the code generator does not yet fully support va_arg on many
5445 targets. Also, it does not currently support va_arg with aggregate types on
5450 <!-- *********************************************************************** -->
5451 <div class="doc_section"> <a name="intrinsics">Intrinsic Functions</a> </div>
5452 <!-- *********************************************************************** -->
5454 <div class="doc_text">
5456 <p>LLVM supports the notion of an "intrinsic function". These functions have
5457 well known names and semantics and are required to follow certain
5458 restrictions. Overall, these intrinsics represent an extension mechanism for
5459 the LLVM language that does not require changing all of the transformations
5460 in LLVM when adding to the language (or the bitcode reader/writer, the
5461 parser, etc...).</p>
5463 <p>Intrinsic function names must all start with an "<tt>llvm.</tt>" prefix. This
5464 prefix is reserved in LLVM for intrinsic names; thus, function names may not
5465 begin with this prefix. Intrinsic functions must always be external
5466 functions: you cannot define the body of intrinsic functions. Intrinsic
5467 functions may only be used in call or invoke instructions: it is illegal to
5468 take the address of an intrinsic function. Additionally, because intrinsic
5469 functions are part of the LLVM language, it is required if any are added that
5470 they be documented here.</p>
5472 <p>Some intrinsic functions can be overloaded, i.e., the intrinsic represents a
5473 family of functions that perform the same operation but on different data
5474 types. Because LLVM can represent over 8 million different integer types,
5475 overloading is used commonly to allow an intrinsic function to operate on any
5476 integer type. One or more of the argument types or the result type can be
5477 overloaded to accept any integer type. Argument types may also be defined as
5478 exactly matching a previous argument's type or the result type. This allows
5479 an intrinsic function which accepts multiple arguments, but needs all of them
5480 to be of the same type, to only be overloaded with respect to a single
5481 argument or the result.</p>
5483 <p>Overloaded intrinsics will have the names of its overloaded argument types
5484 encoded into its function name, each preceded by a period. Only those types
5485 which are overloaded result in a name suffix. Arguments whose type is matched
5486 against another type do not. For example, the <tt>llvm.ctpop</tt> function
5487 can take an integer of any width and returns an integer of exactly the same
5488 integer width. This leads to a family of functions such as
5489 <tt>i8 @llvm.ctpop.i8(i8 %val)</tt> and <tt>i29 @llvm.ctpop.i29(i29
5490 %val)</tt>. Only one type, the return type, is overloaded, and only one type
5491 suffix is required. Because the argument's type is matched against the return
5492 type, it does not require its own name suffix.</p>
5494 <p>To learn how to add an intrinsic function, please see the
5495 <a href="ExtendingLLVM.html">Extending LLVM Guide</a>.</p>
5499 <!-- ======================================================================= -->
5500 <div class="doc_subsection">
5501 <a name="int_varargs">Variable Argument Handling Intrinsics</a>
5504 <div class="doc_text">
5506 <p>Variable argument support is defined in LLVM with
5507 the <a href="#i_va_arg"><tt>va_arg</tt></a> instruction and these three
5508 intrinsic functions. These functions are related to the similarly named
5509 macros defined in the <tt><stdarg.h></tt> header file.</p>
5511 <p>All of these functions operate on arguments that use a target-specific value
5512 type "<tt>va_list</tt>". The LLVM assembly language reference manual does
5513 not define what this type is, so all transformations should be prepared to
5514 handle these functions regardless of the type used.</p>
5516 <p>This example shows how the <a href="#i_va_arg"><tt>va_arg</tt></a>
5517 instruction and the variable argument handling intrinsic functions are
5520 <pre class="doc_code">
5521 define i32 @test(i32 %X, ...) {
5522 ; Initialize variable argument processing
5524 %ap2 = bitcast i8** %ap to i8*
5525 call void @llvm.va_start(i8* %ap2)
5527 ; Read a single integer argument
5528 %tmp = va_arg i8** %ap, i32
5530 ; Demonstrate usage of llvm.va_copy and llvm.va_end
5532 %aq2 = bitcast i8** %aq to i8*
5533 call void @llvm.va_copy(i8* %aq2, i8* %ap2)
5534 call void @llvm.va_end(i8* %aq2)
5536 ; Stop processing of arguments.
5537 call void @llvm.va_end(i8* %ap2)
5541 declare void @llvm.va_start(i8*)
5542 declare void @llvm.va_copy(i8*, i8*)
5543 declare void @llvm.va_end(i8*)
5548 <!-- _______________________________________________________________________ -->
5549 <div class="doc_subsubsection">
5550 <a name="int_va_start">'<tt>llvm.va_start</tt>' Intrinsic</a>
5554 <div class="doc_text">
5558 declare void %llvm.va_start(i8* <arglist>)
5562 <p>The '<tt>llvm.va_start</tt>' intrinsic initializes <tt>*<arglist></tt>
5563 for subsequent use by <tt><a href="#i_va_arg">va_arg</a></tt>.</p>
5566 <p>The argument is a pointer to a <tt>va_list</tt> element to initialize.</p>
5569 <p>The '<tt>llvm.va_start</tt>' intrinsic works just like the <tt>va_start</tt>
5570 macro available in C. In a target-dependent way, it initializes
5571 the <tt>va_list</tt> element to which the argument points, so that the next
5572 call to <tt>va_arg</tt> will produce the first variable argument passed to
5573 the function. Unlike the C <tt>va_start</tt> macro, this intrinsic does not
5574 need to know the last argument of the function as the compiler can figure
5579 <!-- _______________________________________________________________________ -->
5580 <div class="doc_subsubsection">
5581 <a name="int_va_end">'<tt>llvm.va_end</tt>' Intrinsic</a>
5584 <div class="doc_text">
5588 declare void @llvm.va_end(i8* <arglist>)
5592 <p>The '<tt>llvm.va_end</tt>' intrinsic destroys <tt>*<arglist></tt>,
5593 which has been initialized previously
5594 with <tt><a href="#int_va_start">llvm.va_start</a></tt>
5595 or <tt><a href="#i_va_copy">llvm.va_copy</a></tt>.</p>
5598 <p>The argument is a pointer to a <tt>va_list</tt> to destroy.</p>
5601 <p>The '<tt>llvm.va_end</tt>' intrinsic works just like the <tt>va_end</tt>
5602 macro available in C. In a target-dependent way, it destroys
5603 the <tt>va_list</tt> element to which the argument points. Calls
5604 to <a href="#int_va_start"><tt>llvm.va_start</tt></a>
5605 and <a href="#int_va_copy"> <tt>llvm.va_copy</tt></a> must be matched exactly
5606 with calls to <tt>llvm.va_end</tt>.</p>
5610 <!-- _______________________________________________________________________ -->
5611 <div class="doc_subsubsection">
5612 <a name="int_va_copy">'<tt>llvm.va_copy</tt>' Intrinsic</a>
5615 <div class="doc_text">
5619 declare void @llvm.va_copy(i8* <destarglist>, i8* <srcarglist>)
5623 <p>The '<tt>llvm.va_copy</tt>' intrinsic copies the current argument position
5624 from the source argument list to the destination argument list.</p>
5627 <p>The first argument is a pointer to a <tt>va_list</tt> element to initialize.
5628 The second argument is a pointer to a <tt>va_list</tt> element to copy
5632 <p>The '<tt>llvm.va_copy</tt>' intrinsic works just like the <tt>va_copy</tt>
5633 macro available in C. In a target-dependent way, it copies the
5634 source <tt>va_list</tt> element into the destination <tt>va_list</tt>
5635 element. This intrinsic is necessary because
5636 the <tt><a href="#int_va_start"> llvm.va_start</a></tt> intrinsic may be
5637 arbitrarily complex and require, for example, memory allocation.</p>
5641 <!-- ======================================================================= -->
5642 <div class="doc_subsection">
5643 <a name="int_gc">Accurate Garbage Collection Intrinsics</a>
5646 <div class="doc_text">
5648 <p>LLVM support for <a href="GarbageCollection.html">Accurate Garbage
5649 Collection</a> (GC) requires the implementation and generation of these
5650 intrinsics. These intrinsics allow identification of <a href="#int_gcroot">GC
5651 roots on the stack</a>, as well as garbage collector implementations that
5652 require <a href="#int_gcread">read</a> and <a href="#int_gcwrite">write</a>
5653 barriers. Front-ends for type-safe garbage collected languages should generate
5654 these intrinsics to make use of the LLVM garbage collectors. For more details,
5655 see <a href="GarbageCollection.html">Accurate Garbage Collection with
5658 <p>The garbage collection intrinsics only operate on objects in the generic
5659 address space (address space zero).</p>
5663 <!-- _______________________________________________________________________ -->
5664 <div class="doc_subsubsection">
5665 <a name="int_gcroot">'<tt>llvm.gcroot</tt>' Intrinsic</a>
5668 <div class="doc_text">
5672 declare void @llvm.gcroot(i8** %ptrloc, i8* %metadata)
5676 <p>The '<tt>llvm.gcroot</tt>' intrinsic declares the existence of a GC root to
5677 the code generator, and allows some metadata to be associated with it.</p>
5680 <p>The first argument specifies the address of a stack object that contains the
5681 root pointer. The second pointer (which must be either a constant or a
5682 global value address) contains the meta-data to be associated with the
5686 <p>At runtime, a call to this intrinsic stores a null pointer into the "ptrloc"
5687 location. At compile-time, the code generator generates information to allow
5688 the runtime to find the pointer at GC safe points. The '<tt>llvm.gcroot</tt>'
5689 intrinsic may only be used in a function which <a href="#gc">specifies a GC
5694 <!-- _______________________________________________________________________ -->
5695 <div class="doc_subsubsection">
5696 <a name="int_gcread">'<tt>llvm.gcread</tt>' Intrinsic</a>
5699 <div class="doc_text">
5703 declare i8* @llvm.gcread(i8* %ObjPtr, i8** %Ptr)
5707 <p>The '<tt>llvm.gcread</tt>' intrinsic identifies reads of references from heap
5708 locations, allowing garbage collector implementations that require read
5712 <p>The second argument is the address to read from, which should be an address
5713 allocated from the garbage collector. The first object is a pointer to the
5714 start of the referenced object, if needed by the language runtime (otherwise
5718 <p>The '<tt>llvm.gcread</tt>' intrinsic has the same semantics as a load
5719 instruction, but may be replaced with substantially more complex code by the
5720 garbage collector runtime, as needed. The '<tt>llvm.gcread</tt>' intrinsic
5721 may only be used in a function which <a href="#gc">specifies a GC
5726 <!-- _______________________________________________________________________ -->
5727 <div class="doc_subsubsection">
5728 <a name="int_gcwrite">'<tt>llvm.gcwrite</tt>' Intrinsic</a>
5731 <div class="doc_text">
5735 declare void @llvm.gcwrite(i8* %P1, i8* %Obj, i8** %P2)
5739 <p>The '<tt>llvm.gcwrite</tt>' intrinsic identifies writes of references to heap
5740 locations, allowing garbage collector implementations that require write
5741 barriers (such as generational or reference counting collectors).</p>
5744 <p>The first argument is the reference to store, the second is the start of the
5745 object to store it to, and the third is the address of the field of Obj to
5746 store to. If the runtime does not require a pointer to the object, Obj may
5750 <p>The '<tt>llvm.gcwrite</tt>' intrinsic has the same semantics as a store
5751 instruction, but may be replaced with substantially more complex code by the
5752 garbage collector runtime, as needed. The '<tt>llvm.gcwrite</tt>' intrinsic
5753 may only be used in a function which <a href="#gc">specifies a GC
5758 <!-- ======================================================================= -->
5759 <div class="doc_subsection">
5760 <a name="int_codegen">Code Generator Intrinsics</a>
5763 <div class="doc_text">
5765 <p>These intrinsics are provided by LLVM to expose special features that may
5766 only be implemented with code generator support.</p>
5770 <!-- _______________________________________________________________________ -->
5771 <div class="doc_subsubsection">
5772 <a name="int_returnaddress">'<tt>llvm.returnaddress</tt>' Intrinsic</a>
5775 <div class="doc_text">
5779 declare i8 *@llvm.returnaddress(i32 <level>)
5783 <p>The '<tt>llvm.returnaddress</tt>' intrinsic attempts to compute a
5784 target-specific value indicating the return address of the current function
5785 or one of its callers.</p>
5788 <p>The argument to this intrinsic indicates which function to return the address
5789 for. Zero indicates the calling function, one indicates its caller, etc.
5790 The argument is <b>required</b> to be a constant integer value.</p>
5793 <p>The '<tt>llvm.returnaddress</tt>' intrinsic either returns a pointer
5794 indicating the return address of the specified call frame, or zero if it
5795 cannot be identified. The value returned by this intrinsic is likely to be
5796 incorrect or 0 for arguments other than zero, so it should only be used for
5797 debugging purposes.</p>
5799 <p>Note that calling this intrinsic does not prevent function inlining or other
5800 aggressive transformations, so the value returned may not be that of the
5801 obvious source-language caller.</p>
5805 <!-- _______________________________________________________________________ -->
5806 <div class="doc_subsubsection">
5807 <a name="int_frameaddress">'<tt>llvm.frameaddress</tt>' Intrinsic</a>
5810 <div class="doc_text">
5814 declare i8* @llvm.frameaddress(i32 <level>)
5818 <p>The '<tt>llvm.frameaddress</tt>' intrinsic attempts to return the
5819 target-specific frame pointer value for the specified stack frame.</p>
5822 <p>The argument to this intrinsic indicates which function to return the frame
5823 pointer for. Zero indicates the calling function, one indicates its caller,
5824 etc. The argument is <b>required</b> to be a constant integer value.</p>
5827 <p>The '<tt>llvm.frameaddress</tt>' intrinsic either returns a pointer
5828 indicating the frame address of the specified call frame, or zero if it
5829 cannot be identified. The value returned by this intrinsic is likely to be
5830 incorrect or 0 for arguments other than zero, so it should only be used for
5831 debugging purposes.</p>
5833 <p>Note that calling this intrinsic does not prevent function inlining or other
5834 aggressive transformations, so the value returned may not be that of the
5835 obvious source-language caller.</p>
5839 <!-- _______________________________________________________________________ -->
5840 <div class="doc_subsubsection">
5841 <a name="int_stacksave">'<tt>llvm.stacksave</tt>' Intrinsic</a>
5844 <div class="doc_text">
5848 declare i8* @llvm.stacksave()
5852 <p>The '<tt>llvm.stacksave</tt>' intrinsic is used to remember the current state
5853 of the function stack, for use
5854 with <a href="#int_stackrestore"> <tt>llvm.stackrestore</tt></a>. This is
5855 useful for implementing language features like scoped automatic variable
5856 sized arrays in C99.</p>
5859 <p>This intrinsic returns a opaque pointer value that can be passed
5860 to <a href="#int_stackrestore"><tt>llvm.stackrestore</tt></a>. When
5861 an <tt>llvm.stackrestore</tt> intrinsic is executed with a value saved
5862 from <tt>llvm.stacksave</tt>, it effectively restores the state of the stack
5863 to the state it was in when the <tt>llvm.stacksave</tt> intrinsic executed.
5864 In practice, this pops any <a href="#i_alloca">alloca</a> blocks from the
5865 stack that were allocated after the <tt>llvm.stacksave</tt> was executed.</p>
5869 <!-- _______________________________________________________________________ -->
5870 <div class="doc_subsubsection">
5871 <a name="int_stackrestore">'<tt>llvm.stackrestore</tt>' Intrinsic</a>
5874 <div class="doc_text">
5878 declare void @llvm.stackrestore(i8* %ptr)
5882 <p>The '<tt>llvm.stackrestore</tt>' intrinsic is used to restore the state of
5883 the function stack to the state it was in when the
5884 corresponding <a href="#int_stacksave"><tt>llvm.stacksave</tt></a> intrinsic
5885 executed. This is useful for implementing language features like scoped
5886 automatic variable sized arrays in C99.</p>
5889 <p>See the description
5890 for <a href="#int_stacksave"><tt>llvm.stacksave</tt></a>.</p>
5894 <!-- _______________________________________________________________________ -->
5895 <div class="doc_subsubsection">
5896 <a name="int_prefetch">'<tt>llvm.prefetch</tt>' Intrinsic</a>
5899 <div class="doc_text">
5903 declare void @llvm.prefetch(i8* <address>, i32 <rw>, i32 <locality>)
5907 <p>The '<tt>llvm.prefetch</tt>' intrinsic is a hint to the code generator to
5908 insert a prefetch instruction if supported; otherwise, it is a noop.
5909 Prefetches have no effect on the behavior of the program but can change its
5910 performance characteristics.</p>
5913 <p><tt>address</tt> is the address to be prefetched, <tt>rw</tt> is the
5914 specifier determining if the fetch should be for a read (0) or write (1),
5915 and <tt>locality</tt> is a temporal locality specifier ranging from (0) - no
5916 locality, to (3) - extremely local keep in cache. The <tt>rw</tt>
5917 and <tt>locality</tt> arguments must be constant integers.</p>
5920 <p>This intrinsic does not modify the behavior of the program. In particular,
5921 prefetches cannot trap and do not produce a value. On targets that support
5922 this intrinsic, the prefetch can provide hints to the processor cache for
5923 better performance.</p>
5927 <!-- _______________________________________________________________________ -->
5928 <div class="doc_subsubsection">
5929 <a name="int_pcmarker">'<tt>llvm.pcmarker</tt>' Intrinsic</a>
5932 <div class="doc_text">
5936 declare void @llvm.pcmarker(i32 <id>)
5940 <p>The '<tt>llvm.pcmarker</tt>' intrinsic is a method to export a Program
5941 Counter (PC) in a region of code to simulators and other tools. The method
5942 is target specific, but it is expected that the marker will use exported
5943 symbols to transmit the PC of the marker. The marker makes no guarantees
5944 that it will remain with any specific instruction after optimizations. It is
5945 possible that the presence of a marker will inhibit optimizations. The
5946 intended use is to be inserted after optimizations to allow correlations of
5947 simulation runs.</p>
5950 <p><tt>id</tt> is a numerical id identifying the marker.</p>
5953 <p>This intrinsic does not modify the behavior of the program. Backends that do
5954 not support this intrinsic may ignore it.</p>
5958 <!-- _______________________________________________________________________ -->
5959 <div class="doc_subsubsection">
5960 <a name="int_readcyclecounter">'<tt>llvm.readcyclecounter</tt>' Intrinsic</a>
5963 <div class="doc_text">
5967 declare i64 @llvm.readcyclecounter()
5971 <p>The '<tt>llvm.readcyclecounter</tt>' intrinsic provides access to the cycle
5972 counter register (or similar low latency, high accuracy clocks) on those
5973 targets that support it. On X86, it should map to RDTSC. On Alpha, it
5974 should map to RPCC. As the backing counters overflow quickly (on the order
5975 of 9 seconds on alpha), this should only be used for small timings.</p>
5978 <p>When directly supported, reading the cycle counter should not modify any
5979 memory. Implementations are allowed to either return a application specific
5980 value or a system wide value. On backends without support, this is lowered
5981 to a constant 0.</p>
5985 <!-- ======================================================================= -->
5986 <div class="doc_subsection">
5987 <a name="int_libc">Standard C Library Intrinsics</a>
5990 <div class="doc_text">
5992 <p>LLVM provides intrinsics for a few important standard C library functions.
5993 These intrinsics allow source-language front-ends to pass information about
5994 the alignment of the pointer arguments to the code generator, providing
5995 opportunity for more efficient code generation.</p>
5999 <!-- _______________________________________________________________________ -->
6000 <div class="doc_subsubsection">
6001 <a name="int_memcpy">'<tt>llvm.memcpy</tt>' Intrinsic</a>
6004 <div class="doc_text">
6007 <p>This is an overloaded intrinsic. You can use <tt>llvm.memcpy</tt> on any
6008 integer bit width and for different address spaces. Not all targets support
6009 all bit widths however.</p>
6012 declare void @llvm.memcpy.p0i8.p0i8.i32(i8* <dest>, i8* <src>,
6013 i32 <len>, i32 <align>, i1 <isvolatile>)
6014 declare void @llvm.memcpy.p0i8.p0i8.i64(i8* <dest>, i8* <src>,
6015 i64 <len>, i32 <align>, i1 <isvolatile>)
6019 <p>The '<tt>llvm.memcpy.*</tt>' intrinsics copy a block of memory from the
6020 source location to the destination location.</p>
6022 <p>Note that, unlike the standard libc function, the <tt>llvm.memcpy.*</tt>
6023 intrinsics do not return a value, takes extra alignment/isvolatile arguments
6024 and the pointers can be in specified address spaces.</p>
6028 <p>The first argument is a pointer to the destination, the second is a pointer
6029 to the source. The third argument is an integer argument specifying the
6030 number of bytes to copy, the fourth argument is the alignment of the
6031 source and destination locations, and the fifth is a boolean indicating a
6032 volatile access.</p>
6034 <p>If the call to this intrinsic has an alignment value that is not 0 or 1,
6035 then the caller guarantees that both the source and destination pointers are
6036 aligned to that boundary.</p>
6038 <p>If the <tt>isvolatile</tt> parameter is <tt>true</tt>, the
6039 <tt>llvm.memcpy</tt> call is a <a href="#volatile">volatile operation</a>.
6040 The detailed access behavior is not very cleanly specified and it is unwise
6041 to depend on it.</p>
6045 <p>The '<tt>llvm.memcpy.*</tt>' intrinsics copy a block of memory from the
6046 source location to the destination location, which are not allowed to
6047 overlap. It copies "len" bytes of memory over. If the argument is known to
6048 be aligned to some boundary, this can be specified as the fourth argument,
6049 otherwise it should be set to 0 or 1.</p>
6053 <!-- _______________________________________________________________________ -->
6054 <div class="doc_subsubsection">
6055 <a name="int_memmove">'<tt>llvm.memmove</tt>' Intrinsic</a>
6058 <div class="doc_text">
6061 <p>This is an overloaded intrinsic. You can use llvm.memmove on any integer bit
6062 width and for different address space. Not all targets support all bit
6066 declare void @llvm.memmove.p0i8.p0i8.i32(i8* <dest>, i8* <src>,
6067 i32 <len>, i32 <align>, i1 <isvolatile>)
6068 declare void @llvm.memmove.p0i8.p0i8.i64(i8* <dest>, i8* <src>,
6069 i64 <len>, i32 <align>, i1 <isvolatile>)
6073 <p>The '<tt>llvm.memmove.*</tt>' intrinsics move a block of memory from the
6074 source location to the destination location. It is similar to the
6075 '<tt>llvm.memcpy</tt>' intrinsic but allows the two memory locations to
6078 <p>Note that, unlike the standard libc function, the <tt>llvm.memmove.*</tt>
6079 intrinsics do not return a value, takes extra alignment/isvolatile arguments
6080 and the pointers can be in specified address spaces.</p>
6084 <p>The first argument is a pointer to the destination, the second is a pointer
6085 to the source. The third argument is an integer argument specifying the
6086 number of bytes to copy, the fourth argument is the alignment of the
6087 source and destination locations, and the fifth is a boolean indicating a
6088 volatile access.</p>
6090 <p>If the call to this intrinsic has an alignment value that is not 0 or 1,
6091 then the caller guarantees that the source and destination pointers are
6092 aligned to that boundary.</p>
6094 <p>If the <tt>isvolatile</tt> parameter is <tt>true</tt>, the
6095 <tt>llvm.memmove</tt> call is a <a href="#volatile">volatile operation</a>.
6096 The detailed access behavior is not very cleanly specified and it is unwise
6097 to depend on it.</p>
6101 <p>The '<tt>llvm.memmove.*</tt>' intrinsics copy a block of memory from the
6102 source location to the destination location, which may overlap. It copies
6103 "len" bytes of memory over. If the argument is known to be aligned to some
6104 boundary, this can be specified as the fourth argument, otherwise it should
6105 be set to 0 or 1.</p>
6109 <!-- _______________________________________________________________________ -->
6110 <div class="doc_subsubsection">
6111 <a name="int_memset">'<tt>llvm.memset.*</tt>' Intrinsics</a>
6114 <div class="doc_text">
6117 <p>This is an overloaded intrinsic. You can use llvm.memset on any integer bit
6118 width and for different address spaces. Not all targets support all bit
6122 declare void @llvm.memset.p0i8.i32(i8* <dest>, i8 <val>,
6123 i32 <len>, i32 <align>, i1 <isvolatile>)
6124 declare void @llvm.memset.p0i8.i64(i8* <dest>, i8 <val>,
6125 i64 <len>, i32 <align>, i1 <isvolatile>)
6129 <p>The '<tt>llvm.memset.*</tt>' intrinsics fill a block of memory with a
6130 particular byte value.</p>
6132 <p>Note that, unlike the standard libc function, the <tt>llvm.memset</tt>
6133 intrinsic does not return a value, takes extra alignment/volatile arguments,
6134 and the destination can be in an arbitrary address space.</p>
6137 <p>The first argument is a pointer to the destination to fill, the second is the
6138 byte value to fill it with, the third argument is an integer argument
6139 specifying the number of bytes to fill, and the fourth argument is the known
6140 alignment of destination location.</p>
6142 <p>If the call to this intrinsic has an alignment value that is not 0 or 1,
6143 then the caller guarantees that the destination pointer is aligned to that
6146 <p>If the <tt>isvolatile</tt> parameter is <tt>true</tt>, the
6147 <tt>llvm.memset</tt> call is a <a href="#volatile">volatile operation</a>.
6148 The detailed access behavior is not very cleanly specified and it is unwise
6149 to depend on it.</p>
6152 <p>The '<tt>llvm.memset.*</tt>' intrinsics fill "len" bytes of memory starting
6153 at the destination location. If the argument is known to be aligned to some
6154 boundary, this can be specified as the fourth argument, otherwise it should
6155 be set to 0 or 1.</p>
6159 <!-- _______________________________________________________________________ -->
6160 <div class="doc_subsubsection">
6161 <a name="int_sqrt">'<tt>llvm.sqrt.*</tt>' Intrinsic</a>
6164 <div class="doc_text">
6167 <p>This is an overloaded intrinsic. You can use <tt>llvm.sqrt</tt> on any
6168 floating point or vector of floating point type. Not all targets support all
6172 declare float @llvm.sqrt.f32(float %Val)
6173 declare double @llvm.sqrt.f64(double %Val)
6174 declare x86_fp80 @llvm.sqrt.f80(x86_fp80 %Val)
6175 declare fp128 @llvm.sqrt.f128(fp128 %Val)
6176 declare ppc_fp128 @llvm.sqrt.ppcf128(ppc_fp128 %Val)
6180 <p>The '<tt>llvm.sqrt</tt>' intrinsics return the sqrt of the specified operand,
6181 returning the same value as the libm '<tt>sqrt</tt>' functions would.
6182 Unlike <tt>sqrt</tt> in libm, however, <tt>llvm.sqrt</tt> has undefined
6183 behavior for negative numbers other than -0.0 (which allows for better
6184 optimization, because there is no need to worry about errno being
6185 set). <tt>llvm.sqrt(-0.0)</tt> is defined to return -0.0 like IEEE sqrt.</p>
6188 <p>The argument and return value are floating point numbers of the same
6192 <p>This function returns the sqrt of the specified operand if it is a
6193 nonnegative floating point number.</p>
6197 <!-- _______________________________________________________________________ -->
6198 <div class="doc_subsubsection">
6199 <a name="int_powi">'<tt>llvm.powi.*</tt>' Intrinsic</a>
6202 <div class="doc_text">
6205 <p>This is an overloaded intrinsic. You can use <tt>llvm.powi</tt> on any
6206 floating point or vector of floating point type. Not all targets support all
6210 declare float @llvm.powi.f32(float %Val, i32 %power)
6211 declare double @llvm.powi.f64(double %Val, i32 %power)
6212 declare x86_fp80 @llvm.powi.f80(x86_fp80 %Val, i32 %power)
6213 declare fp128 @llvm.powi.f128(fp128 %Val, i32 %power)
6214 declare ppc_fp128 @llvm.powi.ppcf128(ppc_fp128 %Val, i32 %power)
6218 <p>The '<tt>llvm.powi.*</tt>' intrinsics return the first operand raised to the
6219 specified (positive or negative) power. The order of evaluation of
6220 multiplications is not defined. When a vector of floating point type is
6221 used, the second argument remains a scalar integer value.</p>
6224 <p>The second argument is an integer power, and the first is a value to raise to
6228 <p>This function returns the first value raised to the second power with an
6229 unspecified sequence of rounding operations.</p>
6233 <!-- _______________________________________________________________________ -->
6234 <div class="doc_subsubsection">
6235 <a name="int_sin">'<tt>llvm.sin.*</tt>' Intrinsic</a>
6238 <div class="doc_text">
6241 <p>This is an overloaded intrinsic. You can use <tt>llvm.sin</tt> on any
6242 floating point or vector of floating point type. Not all targets support all
6246 declare float @llvm.sin.f32(float %Val)
6247 declare double @llvm.sin.f64(double %Val)
6248 declare x86_fp80 @llvm.sin.f80(x86_fp80 %Val)
6249 declare fp128 @llvm.sin.f128(fp128 %Val)
6250 declare ppc_fp128 @llvm.sin.ppcf128(ppc_fp128 %Val)
6254 <p>The '<tt>llvm.sin.*</tt>' intrinsics return the sine of the operand.</p>
6257 <p>The argument and return value are floating point numbers of the same
6261 <p>This function returns the sine of the specified operand, returning the same
6262 values as the libm <tt>sin</tt> functions would, and handles error conditions
6263 in the same way.</p>
6267 <!-- _______________________________________________________________________ -->
6268 <div class="doc_subsubsection">
6269 <a name="int_cos">'<tt>llvm.cos.*</tt>' Intrinsic</a>
6272 <div class="doc_text">
6275 <p>This is an overloaded intrinsic. You can use <tt>llvm.cos</tt> on any
6276 floating point or vector of floating point type. Not all targets support all
6280 declare float @llvm.cos.f32(float %Val)
6281 declare double @llvm.cos.f64(double %Val)
6282 declare x86_fp80 @llvm.cos.f80(x86_fp80 %Val)
6283 declare fp128 @llvm.cos.f128(fp128 %Val)
6284 declare ppc_fp128 @llvm.cos.ppcf128(ppc_fp128 %Val)
6288 <p>The '<tt>llvm.cos.*</tt>' intrinsics return the cosine of the operand.</p>
6291 <p>The argument and return value are floating point numbers of the same
6295 <p>This function returns the cosine of the specified operand, returning the same
6296 values as the libm <tt>cos</tt> functions would, and handles error conditions
6297 in the same way.</p>
6301 <!-- _______________________________________________________________________ -->
6302 <div class="doc_subsubsection">
6303 <a name="int_pow">'<tt>llvm.pow.*</tt>' Intrinsic</a>
6306 <div class="doc_text">
6309 <p>This is an overloaded intrinsic. You can use <tt>llvm.pow</tt> on any
6310 floating point or vector of floating point type. Not all targets support all
6314 declare float @llvm.pow.f32(float %Val, float %Power)
6315 declare double @llvm.pow.f64(double %Val, double %Power)
6316 declare x86_fp80 @llvm.pow.f80(x86_fp80 %Val, x86_fp80 %Power)
6317 declare fp128 @llvm.pow.f128(fp128 %Val, fp128 %Power)
6318 declare ppc_fp128 @llvm.pow.ppcf128(ppc_fp128 %Val, ppc_fp128 Power)
6322 <p>The '<tt>llvm.pow.*</tt>' intrinsics return the first operand raised to the
6323 specified (positive or negative) power.</p>
6326 <p>The second argument is a floating point power, and the first is a value to
6327 raise to that power.</p>
6330 <p>This function returns the first value raised to the second power, returning
6331 the same values as the libm <tt>pow</tt> functions would, and handles error
6332 conditions in the same way.</p>
6336 <!-- ======================================================================= -->
6337 <div class="doc_subsection">
6338 <a name="int_manip">Bit Manipulation Intrinsics</a>
6341 <div class="doc_text">
6343 <p>LLVM provides intrinsics for a few important bit manipulation operations.
6344 These allow efficient code generation for some algorithms.</p>
6348 <!-- _______________________________________________________________________ -->
6349 <div class="doc_subsubsection">
6350 <a name="int_bswap">'<tt>llvm.bswap.*</tt>' Intrinsics</a>
6353 <div class="doc_text">
6356 <p>This is an overloaded intrinsic function. You can use bswap on any integer
6357 type that is an even number of bytes (i.e. BitWidth % 16 == 0).</p>
6360 declare i16 @llvm.bswap.i16(i16 <id>)
6361 declare i32 @llvm.bswap.i32(i32 <id>)
6362 declare i64 @llvm.bswap.i64(i64 <id>)
6366 <p>The '<tt>llvm.bswap</tt>' family of intrinsics is used to byte swap integer
6367 values with an even number of bytes (positive multiple of 16 bits). These
6368 are useful for performing operations on data that is not in the target's
6369 native byte order.</p>
6372 <p>The <tt>llvm.bswap.i16</tt> intrinsic returns an i16 value that has the high
6373 and low byte of the input i16 swapped. Similarly,
6374 the <tt>llvm.bswap.i32</tt> intrinsic returns an i32 value that has the four
6375 bytes of the input i32 swapped, so that if the input bytes are numbered 0, 1,
6376 2, 3 then the returned i32 will have its bytes in 3, 2, 1, 0 order.
6377 The <tt>llvm.bswap.i48</tt>, <tt>llvm.bswap.i64</tt> and other intrinsics
6378 extend this concept to additional even-byte lengths (6 bytes, 8 bytes and
6379 more, respectively).</p>
6383 <!-- _______________________________________________________________________ -->
6384 <div class="doc_subsubsection">
6385 <a name="int_ctpop">'<tt>llvm.ctpop.*</tt>' Intrinsic</a>
6388 <div class="doc_text">
6391 <p>This is an overloaded intrinsic. You can use llvm.ctpop on any integer bit
6392 width. Not all targets support all bit widths however.</p>
6395 declare i8 @llvm.ctpop.i8(i8 <src>)
6396 declare i16 @llvm.ctpop.i16(i16 <src>)
6397 declare i32 @llvm.ctpop.i32(i32 <src>)
6398 declare i64 @llvm.ctpop.i64(i64 <src>)
6399 declare i256 @llvm.ctpop.i256(i256 <src>)
6403 <p>The '<tt>llvm.ctpop</tt>' family of intrinsics counts the number of bits set
6407 <p>The only argument is the value to be counted. The argument may be of any
6408 integer type. The return type must match the argument type.</p>
6411 <p>The '<tt>llvm.ctpop</tt>' intrinsic counts the 1's in a variable.</p>
6415 <!-- _______________________________________________________________________ -->
6416 <div class="doc_subsubsection">
6417 <a name="int_ctlz">'<tt>llvm.ctlz.*</tt>' Intrinsic</a>
6420 <div class="doc_text">
6423 <p>This is an overloaded intrinsic. You can use <tt>llvm.ctlz</tt> on any
6424 integer bit width. Not all targets support all bit widths however.</p>
6427 declare i8 @llvm.ctlz.i8 (i8 <src>)
6428 declare i16 @llvm.ctlz.i16(i16 <src>)
6429 declare i32 @llvm.ctlz.i32(i32 <src>)
6430 declare i64 @llvm.ctlz.i64(i64 <src>)
6431 declare i256 @llvm.ctlz.i256(i256 <src>)
6435 <p>The '<tt>llvm.ctlz</tt>' family of intrinsic functions counts the number of
6436 leading zeros in a variable.</p>
6439 <p>The only argument is the value to be counted. The argument may be of any
6440 integer type. The return type must match the argument type.</p>
6443 <p>The '<tt>llvm.ctlz</tt>' intrinsic counts the leading (most significant)
6444 zeros in a variable. If the src == 0 then the result is the size in bits of
6445 the type of src. For example, <tt>llvm.ctlz(i32 2) = 30</tt>.</p>
6449 <!-- _______________________________________________________________________ -->
6450 <div class="doc_subsubsection">
6451 <a name="int_cttz">'<tt>llvm.cttz.*</tt>' Intrinsic</a>
6454 <div class="doc_text">
6457 <p>This is an overloaded intrinsic. You can use <tt>llvm.cttz</tt> on any
6458 integer bit width. Not all targets support all bit widths however.</p>
6461 declare i8 @llvm.cttz.i8 (i8 <src>)
6462 declare i16 @llvm.cttz.i16(i16 <src>)
6463 declare i32 @llvm.cttz.i32(i32 <src>)
6464 declare i64 @llvm.cttz.i64(i64 <src>)
6465 declare i256 @llvm.cttz.i256(i256 <src>)
6469 <p>The '<tt>llvm.cttz</tt>' family of intrinsic functions counts the number of
6473 <p>The only argument is the value to be counted. The argument may be of any
6474 integer type. The return type must match the argument type.</p>
6477 <p>The '<tt>llvm.cttz</tt>' intrinsic counts the trailing (least significant)
6478 zeros in a variable. If the src == 0 then the result is the size in bits of
6479 the type of src. For example, <tt>llvm.cttz(2) = 1</tt>.</p>
6483 <!-- ======================================================================= -->
6484 <div class="doc_subsection">
6485 <a name="int_overflow">Arithmetic with Overflow Intrinsics</a>
6488 <div class="doc_text">
6490 <p>LLVM provides intrinsics for some arithmetic with overflow operations.</p>
6494 <!-- _______________________________________________________________________ -->
6495 <div class="doc_subsubsection">
6496 <a name="int_sadd_overflow">'<tt>llvm.sadd.with.overflow.*</tt>' Intrinsics</a>
6499 <div class="doc_text">
6502 <p>This is an overloaded intrinsic. You can use <tt>llvm.sadd.with.overflow</tt>
6503 on any integer bit width.</p>
6506 declare {i16, i1} @llvm.sadd.with.overflow.i16(i16 %a, i16 %b)
6507 declare {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b)
6508 declare {i64, i1} @llvm.sadd.with.overflow.i64(i64 %a, i64 %b)
6512 <p>The '<tt>llvm.sadd.with.overflow</tt>' family of intrinsic functions perform
6513 a signed addition of the two arguments, and indicate whether an overflow
6514 occurred during the signed summation.</p>
6517 <p>The arguments (%a and %b) and the first element of the result structure may
6518 be of integer types of any bit width, but they must have the same bit
6519 width. The second element of the result structure must be of
6520 type <tt>i1</tt>. <tt>%a</tt> and <tt>%b</tt> are the two values that will
6521 undergo signed addition.</p>
6524 <p>The '<tt>llvm.sadd.with.overflow</tt>' family of intrinsic functions perform
6525 a signed addition of the two variables. They return a structure — the
6526 first element of which is the signed summation, and the second element of
6527 which is a bit specifying if the signed summation resulted in an
6532 %res = call {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b)
6533 %sum = extractvalue {i32, i1} %res, 0
6534 %obit = extractvalue {i32, i1} %res, 1
6535 br i1 %obit, label %overflow, label %normal
6540 <!-- _______________________________________________________________________ -->
6541 <div class="doc_subsubsection">
6542 <a name="int_uadd_overflow">'<tt>llvm.uadd.with.overflow.*</tt>' Intrinsics</a>
6545 <div class="doc_text">
6548 <p>This is an overloaded intrinsic. You can use <tt>llvm.uadd.with.overflow</tt>
6549 on any integer bit width.</p>
6552 declare {i16, i1} @llvm.uadd.with.overflow.i16(i16 %a, i16 %b)
6553 declare {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)
6554 declare {i64, i1} @llvm.uadd.with.overflow.i64(i64 %a, i64 %b)
6558 <p>The '<tt>llvm.uadd.with.overflow</tt>' family of intrinsic functions perform
6559 an unsigned addition of the two arguments, and indicate whether a carry
6560 occurred during the unsigned summation.</p>
6563 <p>The arguments (%a and %b) and the first element of the result structure may
6564 be of integer types of any bit width, but they must have the same bit
6565 width. The second element of the result structure must be of
6566 type <tt>i1</tt>. <tt>%a</tt> and <tt>%b</tt> are the two values that will
6567 undergo unsigned addition.</p>
6570 <p>The '<tt>llvm.uadd.with.overflow</tt>' family of intrinsic functions perform
6571 an unsigned addition of the two arguments. They return a structure —
6572 the first element of which is the sum, and the second element of which is a
6573 bit specifying if the unsigned summation resulted in a carry.</p>
6577 %res = call {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)
6578 %sum = extractvalue {i32, i1} %res, 0
6579 %obit = extractvalue {i32, i1} %res, 1
6580 br i1 %obit, label %carry, label %normal
6585 <!-- _______________________________________________________________________ -->
6586 <div class="doc_subsubsection">
6587 <a name="int_ssub_overflow">'<tt>llvm.ssub.with.overflow.*</tt>' Intrinsics</a>
6590 <div class="doc_text">
6593 <p>This is an overloaded intrinsic. You can use <tt>llvm.ssub.with.overflow</tt>
6594 on any integer bit width.</p>
6597 declare {i16, i1} @llvm.ssub.with.overflow.i16(i16 %a, i16 %b)
6598 declare {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b)
6599 declare {i64, i1} @llvm.ssub.with.overflow.i64(i64 %a, i64 %b)
6603 <p>The '<tt>llvm.ssub.with.overflow</tt>' family of intrinsic functions perform
6604 a signed subtraction of the two arguments, and indicate whether an overflow
6605 occurred during the signed subtraction.</p>
6608 <p>The arguments (%a and %b) and the first element of the result structure may
6609 be of integer types of any bit width, but they must have the same bit
6610 width. The second element of the result structure must be of
6611 type <tt>i1</tt>. <tt>%a</tt> and <tt>%b</tt> are the two values that will
6612 undergo signed subtraction.</p>
6615 <p>The '<tt>llvm.ssub.with.overflow</tt>' family of intrinsic functions perform
6616 a signed subtraction of the two arguments. They return a structure —
6617 the first element of which is the subtraction, and the second element of
6618 which is a bit specifying if the signed subtraction resulted in an
6623 %res = call {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b)
6624 %sum = extractvalue {i32, i1} %res, 0
6625 %obit = extractvalue {i32, i1} %res, 1
6626 br i1 %obit, label %overflow, label %normal
6631 <!-- _______________________________________________________________________ -->
6632 <div class="doc_subsubsection">
6633 <a name="int_usub_overflow">'<tt>llvm.usub.with.overflow.*</tt>' Intrinsics</a>
6636 <div class="doc_text">
6639 <p>This is an overloaded intrinsic. You can use <tt>llvm.usub.with.overflow</tt>
6640 on any integer bit width.</p>
6643 declare {i16, i1} @llvm.usub.with.overflow.i16(i16 %a, i16 %b)
6644 declare {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b)
6645 declare {i64, i1} @llvm.usub.with.overflow.i64(i64 %a, i64 %b)
6649 <p>The '<tt>llvm.usub.with.overflow</tt>' family of intrinsic functions perform
6650 an unsigned subtraction of the two arguments, and indicate whether an
6651 overflow occurred during the unsigned subtraction.</p>
6654 <p>The arguments (%a and %b) and the first element of the result structure may
6655 be of integer types of any bit width, but they must have the same bit
6656 width. The second element of the result structure must be of
6657 type <tt>i1</tt>. <tt>%a</tt> and <tt>%b</tt> are the two values that will
6658 undergo unsigned subtraction.</p>
6661 <p>The '<tt>llvm.usub.with.overflow</tt>' family of intrinsic functions perform
6662 an unsigned subtraction of the two arguments. They return a structure —
6663 the first element of which is the subtraction, and the second element of
6664 which is a bit specifying if the unsigned subtraction resulted in an
6669 %res = call {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b)
6670 %sum = extractvalue {i32, i1} %res, 0
6671 %obit = extractvalue {i32, i1} %res, 1
6672 br i1 %obit, label %overflow, label %normal
6677 <!-- _______________________________________________________________________ -->
6678 <div class="doc_subsubsection">
6679 <a name="int_smul_overflow">'<tt>llvm.smul.with.overflow.*</tt>' Intrinsics</a>
6682 <div class="doc_text">
6685 <p>This is an overloaded intrinsic. You can use <tt>llvm.smul.with.overflow</tt>
6686 on any integer bit width.</p>
6689 declare {i16, i1} @llvm.smul.with.overflow.i16(i16 %a, i16 %b)
6690 declare {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b)
6691 declare {i64, i1} @llvm.smul.with.overflow.i64(i64 %a, i64 %b)
6696 <p>The '<tt>llvm.smul.with.overflow</tt>' family of intrinsic functions perform
6697 a signed multiplication of the two arguments, and indicate whether an
6698 overflow occurred during the signed multiplication.</p>
6701 <p>The arguments (%a and %b) and the first element of the result structure may
6702 be of integer types of any bit width, but they must have the same bit
6703 width. The second element of the result structure must be of
6704 type <tt>i1</tt>. <tt>%a</tt> and <tt>%b</tt> are the two values that will
6705 undergo signed multiplication.</p>
6708 <p>The '<tt>llvm.smul.with.overflow</tt>' family of intrinsic functions perform
6709 a signed multiplication of the two arguments. They return a structure —
6710 the first element of which is the multiplication, and the second element of
6711 which is a bit specifying if the signed multiplication resulted in an
6716 %res = call {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b)
6717 %sum = extractvalue {i32, i1} %res, 0
6718 %obit = extractvalue {i32, i1} %res, 1
6719 br i1 %obit, label %overflow, label %normal
6724 <!-- _______________________________________________________________________ -->
6725 <div class="doc_subsubsection">
6726 <a name="int_umul_overflow">'<tt>llvm.umul.with.overflow.*</tt>' Intrinsics</a>
6729 <div class="doc_text">
6732 <p>This is an overloaded intrinsic. You can use <tt>llvm.umul.with.overflow</tt>
6733 on any integer bit width.</p>
6736 declare {i16, i1} @llvm.umul.with.overflow.i16(i16 %a, i16 %b)
6737 declare {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b)
6738 declare {i64, i1} @llvm.umul.with.overflow.i64(i64 %a, i64 %b)
6742 <p>The '<tt>llvm.umul.with.overflow</tt>' family of intrinsic functions perform
6743 a unsigned multiplication of the two arguments, and indicate whether an
6744 overflow occurred during the unsigned multiplication.</p>
6747 <p>The arguments (%a and %b) and the first element of the result structure may
6748 be of integer types of any bit width, but they must have the same bit
6749 width. The second element of the result structure must be of
6750 type <tt>i1</tt>. <tt>%a</tt> and <tt>%b</tt> are the two values that will
6751 undergo unsigned multiplication.</p>
6754 <p>The '<tt>llvm.umul.with.overflow</tt>' family of intrinsic functions perform
6755 an unsigned multiplication of the two arguments. They return a structure
6756 — the first element of which is the multiplication, and the second
6757 element of which is a bit specifying if the unsigned multiplication resulted
6762 %res = call {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b)
6763 %sum = extractvalue {i32, i1} %res, 0
6764 %obit = extractvalue {i32, i1} %res, 1
6765 br i1 %obit, label %overflow, label %normal
6770 <!-- ======================================================================= -->
6771 <div class="doc_subsection">
6772 <a name="int_fp16">Half Precision Floating Point Intrinsics</a>
6775 <div class="doc_text">
6777 <p>Half precision floating point is a storage-only format. This means that it is
6778 a dense encoding (in memory) but does not support computation in the
6781 <p>This means that code must first load the half-precision floating point
6782 value as an i16, then convert it to float with <a
6783 href="#int_convert_from_fp16"><tt>llvm.convert.from.fp16</tt></a>.
6784 Computation can then be performed on the float value (including extending to
6785 double etc). To store the value back to memory, it is first converted to
6786 float if needed, then converted to i16 with
6787 <a href="#int_convert_to_fp16"><tt>llvm.convert.to.fp16</tt></a>, then
6788 storing as an i16 value.</p>
6791 <!-- _______________________________________________________________________ -->
6792 <div class="doc_subsubsection">
6793 <a name="int_convert_to_fp16">'<tt>llvm.convert.to.fp16</tt>' Intrinsic</a>
6796 <div class="doc_text">
6800 declare i16 @llvm.convert.to.fp16(f32 %a)
6804 <p>The '<tt>llvm.convert.to.fp16</tt>' intrinsic function performs
6805 a conversion from single precision floating point format to half precision
6806 floating point format.</p>
6809 <p>The intrinsic function contains single argument - the value to be
6813 <p>The '<tt>llvm.convert.to.fp16</tt>' intrinsic function performs
6814 a conversion from single precision floating point format to half precision
6815 floating point format. The return value is an <tt>i16</tt> which
6816 contains the converted number.</p>
6820 %res = call i16 @llvm.convert.to.fp16(f32 %a)
6821 store i16 %res, i16* @x, align 2
6826 <!-- _______________________________________________________________________ -->
6827 <div class="doc_subsubsection">
6828 <a name="int_convert_from_fp16">'<tt>llvm.convert.from.fp16</tt>' Intrinsic</a>
6831 <div class="doc_text">
6835 declare f32 @llvm.convert.from.fp16(i16 %a)
6839 <p>The '<tt>llvm.convert.from.fp16</tt>' intrinsic function performs
6840 a conversion from half precision floating point format to single precision
6841 floating point format.</p>
6844 <p>The intrinsic function contains single argument - the value to be
6848 <p>The '<tt>llvm.convert.from.fp16</tt>' intrinsic function performs a
6849 conversion from half single precision floating point format to single
6850 precision floating point format. The input half-float value is represented by
6851 an <tt>i16</tt> value.</p>
6855 %a = load i16* @x, align 2
6856 %res = call f32 @llvm.convert.from.fp16(i16 %a)
6861 <!-- ======================================================================= -->
6862 <div class="doc_subsection">
6863 <a name="int_debugger">Debugger Intrinsics</a>
6866 <div class="doc_text">
6868 <p>The LLVM debugger intrinsics (which all start with <tt>llvm.dbg.</tt>
6869 prefix), are described in
6870 the <a href="SourceLevelDebugging.html#format_common_intrinsics">LLVM Source
6871 Level Debugging</a> document.</p>
6875 <!-- ======================================================================= -->
6876 <div class="doc_subsection">
6877 <a name="int_eh">Exception Handling Intrinsics</a>
6880 <div class="doc_text">
6882 <p>The LLVM exception handling intrinsics (which all start with
6883 <tt>llvm.eh.</tt> prefix), are described in
6884 the <a href="ExceptionHandling.html#format_common_intrinsics">LLVM Exception
6885 Handling</a> document.</p>
6889 <!-- ======================================================================= -->
6890 <div class="doc_subsection">
6891 <a name="int_trampoline">Trampoline Intrinsic</a>
6894 <div class="doc_text">
6896 <p>This intrinsic makes it possible to excise one parameter, marked with
6897 the <a href="#nest"><tt>nest</tt></a> attribute, from a function.
6898 The result is a callable
6899 function pointer lacking the nest parameter - the caller does not need to
6900 provide a value for it. Instead, the value to use is stored in advance in a
6901 "trampoline", a block of memory usually allocated on the stack, which also
6902 contains code to splice the nest value into the argument list. This is used
6903 to implement the GCC nested function address extension.</p>
6905 <p>For example, if the function is
6906 <tt>i32 f(i8* nest %c, i32 %x, i32 %y)</tt> then the resulting function
6907 pointer has signature <tt>i32 (i32, i32)*</tt>. It can be created as
6910 <pre class="doc_code">
6911 %tramp = alloca [10 x i8], align 4 ; size and alignment only correct for X86
6912 %tramp1 = getelementptr [10 x i8]* %tramp, i32 0, i32 0
6913 %p = call i8* @llvm.init.trampoline(i8* %tramp1, i8* bitcast (i32 (i8* nest , i32, i32)* @f to i8*), i8* %nval)
6914 %fp = bitcast i8* %p to i32 (i32, i32)*
6917 <p>The call <tt>%val = call i32 %fp(i32 %x, i32 %y)</tt> is then equivalent
6918 to <tt>%val = call i32 %f(i8* %nval, i32 %x, i32 %y)</tt>.</p>
6922 <!-- _______________________________________________________________________ -->
6923 <div class="doc_subsubsection">
6924 <a name="int_it">'<tt>llvm.init.trampoline</tt>' Intrinsic</a>
6927 <div class="doc_text">
6931 declare i8* @llvm.init.trampoline(i8* <tramp>, i8* <func>, i8* <nval>)
6935 <p>This fills the memory pointed to by <tt>tramp</tt> with code and returns a
6936 function pointer suitable for executing it.</p>
6939 <p>The <tt>llvm.init.trampoline</tt> intrinsic takes three arguments, all
6940 pointers. The <tt>tramp</tt> argument must point to a sufficiently large and
6941 sufficiently aligned block of memory; this memory is written to by the
6942 intrinsic. Note that the size and the alignment are target-specific - LLVM
6943 currently provides no portable way of determining them, so a front-end that
6944 generates this intrinsic needs to have some target-specific knowledge.
6945 The <tt>func</tt> argument must hold a function bitcast to
6946 an <tt>i8*</tt>.</p>
6949 <p>The block of memory pointed to by <tt>tramp</tt> is filled with target
6950 dependent code, turning it into a function. A pointer to this function is
6951 returned, but needs to be bitcast to an <a href="#int_trampoline">appropriate
6952 function pointer type</a> before being called. The new function's signature
6953 is the same as that of <tt>func</tt> with any arguments marked with
6954 the <tt>nest</tt> attribute removed. At most one such <tt>nest</tt> argument
6955 is allowed, and it must be of pointer type. Calling the new function is
6956 equivalent to calling <tt>func</tt> with the same argument list, but
6957 with <tt>nval</tt> used for the missing <tt>nest</tt> argument. If, after
6958 calling <tt>llvm.init.trampoline</tt>, the memory pointed to
6959 by <tt>tramp</tt> is modified, then the effect of any later call to the
6960 returned function pointer is undefined.</p>
6964 <!-- ======================================================================= -->
6965 <div class="doc_subsection">
6966 <a name="int_atomics">Atomic Operations and Synchronization Intrinsics</a>
6969 <div class="doc_text">
6971 <p>These intrinsic functions expand the "universal IR" of LLVM to represent
6972 hardware constructs for atomic operations and memory synchronization. This
6973 provides an interface to the hardware, not an interface to the programmer. It
6974 is aimed at a low enough level to allow any programming models or APIs
6975 (Application Programming Interfaces) which need atomic behaviors to map
6976 cleanly onto it. It is also modeled primarily on hardware behavior. Just as
6977 hardware provides a "universal IR" for source languages, it also provides a
6978 starting point for developing a "universal" atomic operation and
6979 synchronization IR.</p>
6981 <p>These do <em>not</em> form an API such as high-level threading libraries,
6982 software transaction memory systems, atomic primitives, and intrinsic
6983 functions as found in BSD, GNU libc, atomic_ops, APR, and other system and
6984 application libraries. The hardware interface provided by LLVM should allow
6985 a clean implementation of all of these APIs and parallel programming models.
6986 No one model or paradigm should be selected above others unless the hardware
6987 itself ubiquitously does so.</p>
6991 <!-- _______________________________________________________________________ -->
6992 <div class="doc_subsubsection">
6993 <a name="int_memory_barrier">'<tt>llvm.memory.barrier</tt>' Intrinsic</a>
6995 <div class="doc_text">
6998 declare void @llvm.memory.barrier(i1 <ll>, i1 <ls>, i1 <sl>, i1 <ss>, i1 <device>)
7002 <p>The <tt>llvm.memory.barrier</tt> intrinsic guarantees ordering between
7003 specific pairs of memory access types.</p>
7006 <p>The <tt>llvm.memory.barrier</tt> intrinsic requires five boolean arguments.
7007 The first four arguments enables a specific barrier as listed below. The
7008 fifth argument specifies that the barrier applies to io or device or uncached
7012 <li><tt>ll</tt>: load-load barrier</li>
7013 <li><tt>ls</tt>: load-store barrier</li>
7014 <li><tt>sl</tt>: store-load barrier</li>
7015 <li><tt>ss</tt>: store-store barrier</li>
7016 <li><tt>device</tt>: barrier applies to device and uncached memory also.</li>
7020 <p>This intrinsic causes the system to enforce some ordering constraints upon
7021 the loads and stores of the program. This barrier does not
7022 indicate <em>when</em> any events will occur, it only enforces
7023 an <em>order</em> in which they occur. For any of the specified pairs of load
7024 and store operations (f.ex. load-load, or store-load), all of the first
7025 operations preceding the barrier will complete before any of the second
7026 operations succeeding the barrier begin. Specifically the semantics for each
7027 pairing is as follows:</p>
7030 <li><tt>ll</tt>: All loads before the barrier must complete before any load
7031 after the barrier begins.</li>
7032 <li><tt>ls</tt>: All loads before the barrier must complete before any
7033 store after the barrier begins.</li>
7034 <li><tt>ss</tt>: All stores before the barrier must complete before any
7035 store after the barrier begins.</li>
7036 <li><tt>sl</tt>: All stores before the barrier must complete before any
7037 load after the barrier begins.</li>
7040 <p>These semantics are applied with a logical "and" behavior when more than one
7041 is enabled in a single memory barrier intrinsic.</p>
7043 <p>Backends may implement stronger barriers than those requested when they do
7044 not support as fine grained a barrier as requested. Some architectures do
7045 not need all types of barriers and on such architectures, these become
7050 %mallocP = tail call i8* @malloc(i32 ptrtoint (i32* getelementptr (i32* null, i32 1) to i32))
7051 %ptr = bitcast i8* %mallocP to i32*
7054 %result1 = load i32* %ptr <i>; yields {i32}:result1 = 4</i>
7055 call void @llvm.memory.barrier(i1 false, i1 true, i1 false, i1 false)
7056 <i>; guarantee the above finishes</i>
7057 store i32 8, %ptr <i>; before this begins</i>
7062 <!-- _______________________________________________________________________ -->
7063 <div class="doc_subsubsection">
7064 <a name="int_atomic_cmp_swap">'<tt>llvm.atomic.cmp.swap.*</tt>' Intrinsic</a>
7067 <div class="doc_text">
7070 <p>This is an overloaded intrinsic. You can use <tt>llvm.atomic.cmp.swap</tt> on
7071 any integer bit width and for different address spaces. Not all targets
7072 support all bit widths however.</p>
7075 declare i8 @llvm.atomic.cmp.swap.i8.p0i8(i8* <ptr>, i8 <cmp>, i8 <val>)
7076 declare i16 @llvm.atomic.cmp.swap.i16.p0i16(i16* <ptr>, i16 <cmp>, i16 <val>)
7077 declare i32 @llvm.atomic.cmp.swap.i32.p0i32(i32* <ptr>, i32 <cmp>, i32 <val>)
7078 declare i64 @llvm.atomic.cmp.swap.i64.p0i64(i64* <ptr>, i64 <cmp>, i64 <val>)
7082 <p>This loads a value in memory and compares it to a given value. If they are
7083 equal, it stores a new value into the memory.</p>
7086 <p>The <tt>llvm.atomic.cmp.swap</tt> intrinsic takes three arguments. The result
7087 as well as both <tt>cmp</tt> and <tt>val</tt> must be integer values with the
7088 same bit width. The <tt>ptr</tt> argument must be a pointer to a value of
7089 this integer type. While any bit width integer may be used, targets may only
7090 lower representations they support in hardware.</p>
7093 <p>This entire intrinsic must be executed atomically. It first loads the value
7094 in memory pointed to by <tt>ptr</tt> and compares it with the
7095 value <tt>cmp</tt>. If they are equal, <tt>val</tt> is stored into the
7096 memory. The loaded value is yielded in all cases. This provides the
7097 equivalent of an atomic compare-and-swap operation within the SSA
7102 %mallocP = tail call i8* @malloc(i32 ptrtoint (i32* getelementptr (i32* null, i32 1) to i32))
7103 %ptr = bitcast i8* %mallocP to i32*
7106 %val1 = add i32 4, 4
7107 %result1 = call i32 @llvm.atomic.cmp.swap.i32.p0i32(i32* %ptr, i32 4, %val1)
7108 <i>; yields {i32}:result1 = 4</i>
7109 %stored1 = icmp eq i32 %result1, 4 <i>; yields {i1}:stored1 = true</i>
7110 %memval1 = load i32* %ptr <i>; yields {i32}:memval1 = 8</i>
7112 %val2 = add i32 1, 1
7113 %result2 = call i32 @llvm.atomic.cmp.swap.i32.p0i32(i32* %ptr, i32 5, %val2)
7114 <i>; yields {i32}:result2 = 8</i>
7115 %stored2 = icmp eq i32 %result2, 5 <i>; yields {i1}:stored2 = false</i>
7117 %memval2 = load i32* %ptr <i>; yields {i32}:memval2 = 8</i>
7122 <!-- _______________________________________________________________________ -->
7123 <div class="doc_subsubsection">
7124 <a name="int_atomic_swap">'<tt>llvm.atomic.swap.*</tt>' Intrinsic</a>
7126 <div class="doc_text">
7129 <p>This is an overloaded intrinsic. You can use <tt>llvm.atomic.swap</tt> on any
7130 integer bit width. Not all targets support all bit widths however.</p>
7133 declare i8 @llvm.atomic.swap.i8.p0i8(i8* <ptr>, i8 <val>)
7134 declare i16 @llvm.atomic.swap.i16.p0i16(i16* <ptr>, i16 <val>)
7135 declare i32 @llvm.atomic.swap.i32.p0i32(i32* <ptr>, i32 <val>)
7136 declare i64 @llvm.atomic.swap.i64.p0i64(i64* <ptr>, i64 <val>)
7140 <p>This intrinsic loads the value stored in memory at <tt>ptr</tt> and yields
7141 the value from memory. It then stores the value in <tt>val</tt> in the memory
7142 at <tt>ptr</tt>.</p>
7145 <p>The <tt>llvm.atomic.swap</tt> intrinsic takes two arguments. Both
7146 the <tt>val</tt> argument and the result must be integers of the same bit
7147 width. The first argument, <tt>ptr</tt>, must be a pointer to a value of this
7148 integer type. The targets may only lower integer representations they
7152 <p>This intrinsic loads the value pointed to by <tt>ptr</tt>, yields it, and
7153 stores <tt>val</tt> back into <tt>ptr</tt> atomically. This provides the
7154 equivalent of an atomic swap operation within the SSA framework.</p>
7158 %mallocP = tail call i8* @malloc(i32 ptrtoint (i32* getelementptr (i32* null, i32 1) to i32))
7159 %ptr = bitcast i8* %mallocP to i32*
7162 %val1 = add i32 4, 4
7163 %result1 = call i32 @llvm.atomic.swap.i32.p0i32(i32* %ptr, i32 %val1)
7164 <i>; yields {i32}:result1 = 4</i>
7165 %stored1 = icmp eq i32 %result1, 4 <i>; yields {i1}:stored1 = true</i>
7166 %memval1 = load i32* %ptr <i>; yields {i32}:memval1 = 8</i>
7168 %val2 = add i32 1, 1
7169 %result2 = call i32 @llvm.atomic.swap.i32.p0i32(i32* %ptr, i32 %val2)
7170 <i>; yields {i32}:result2 = 8</i>
7172 %stored2 = icmp eq i32 %result2, 8 <i>; yields {i1}:stored2 = true</i>
7173 %memval2 = load i32* %ptr <i>; yields {i32}:memval2 = 2</i>
7178 <!-- _______________________________________________________________________ -->
7179 <div class="doc_subsubsection">
7180 <a name="int_atomic_load_add">'<tt>llvm.atomic.load.add.*</tt>' Intrinsic</a>
7184 <div class="doc_text">
7187 <p>This is an overloaded intrinsic. You can use <tt>llvm.atomic.load.add</tt> on
7188 any integer bit width. Not all targets support all bit widths however.</p>
7191 declare i8 @llvm.atomic.load.add.i8.p0i8(i8* <ptr>, i8 <delta>)
7192 declare i16 @llvm.atomic.load.add.i16.p0i16(i16* <ptr>, i16 <delta>)
7193 declare i32 @llvm.atomic.load.add.i32.p0i32(i32* <ptr>, i32 <delta>)
7194 declare i64 @llvm.atomic.load.add.i64.p0i64(i64* <ptr>, i64 <delta>)
7198 <p>This intrinsic adds <tt>delta</tt> to the value stored in memory
7199 at <tt>ptr</tt>. It yields the original value at <tt>ptr</tt>.</p>
7202 <p>The intrinsic takes two arguments, the first a pointer to an integer value
7203 and the second an integer value. The result is also an integer value. These
7204 integer types can have any bit width, but they must all have the same bit
7205 width. The targets may only lower integer representations they support.</p>
7208 <p>This intrinsic does a series of operations atomically. It first loads the
7209 value stored at <tt>ptr</tt>. It then adds <tt>delta</tt>, stores the result
7210 to <tt>ptr</tt>. It yields the original value stored at <tt>ptr</tt>.</p>
7214 %mallocP = tail call i8* @malloc(i32 ptrtoint (i32* getelementptr (i32* null, i32 1) to i32))
7215 %ptr = bitcast i8* %mallocP to i32*
7217 %result1 = call i32 @llvm.atomic.load.add.i32.p0i32(i32* %ptr, i32 4)
7218 <i>; yields {i32}:result1 = 4</i>
7219 %result2 = call i32 @llvm.atomic.load.add.i32.p0i32(i32* %ptr, i32 2)
7220 <i>; yields {i32}:result2 = 8</i>
7221 %result3 = call i32 @llvm.atomic.load.add.i32.p0i32(i32* %ptr, i32 5)
7222 <i>; yields {i32}:result3 = 10</i>
7223 %memval1 = load i32* %ptr <i>; yields {i32}:memval1 = 15</i>
7228 <!-- _______________________________________________________________________ -->
7229 <div class="doc_subsubsection">
7230 <a name="int_atomic_load_sub">'<tt>llvm.atomic.load.sub.*</tt>' Intrinsic</a>
7234 <div class="doc_text">
7237 <p>This is an overloaded intrinsic. You can use <tt>llvm.atomic.load.sub</tt> on
7238 any integer bit width and for different address spaces. Not all targets
7239 support all bit widths however.</p>
7242 declare i8 @llvm.atomic.load.sub.i8.p0i32(i8* <ptr>, i8 <delta>)
7243 declare i16 @llvm.atomic.load.sub.i16.p0i32(i16* <ptr>, i16 <delta>)
7244 declare i32 @llvm.atomic.load.sub.i32.p0i32(i32* <ptr>, i32 <delta>)
7245 declare i64 @llvm.atomic.load.sub.i64.p0i32(i64* <ptr>, i64 <delta>)
7249 <p>This intrinsic subtracts <tt>delta</tt> to the value stored in memory at
7250 <tt>ptr</tt>. It yields the original value at <tt>ptr</tt>.</p>
7253 <p>The intrinsic takes two arguments, the first a pointer to an integer value
7254 and the second an integer value. The result is also an integer value. These
7255 integer types can have any bit width, but they must all have the same bit
7256 width. The targets may only lower integer representations they support.</p>
7259 <p>This intrinsic does a series of operations atomically. It first loads the
7260 value stored at <tt>ptr</tt>. It then subtracts <tt>delta</tt>, stores the
7261 result to <tt>ptr</tt>. It yields the original value stored
7262 at <tt>ptr</tt>.</p>
7266 %mallocP = tail call i8* @malloc(i32 ptrtoint (i32* getelementptr (i32* null, i32 1) to i32))
7267 %ptr = bitcast i8* %mallocP to i32*
7269 %result1 = call i32 @llvm.atomic.load.sub.i32.p0i32(i32* %ptr, i32 4)
7270 <i>; yields {i32}:result1 = 8</i>
7271 %result2 = call i32 @llvm.atomic.load.sub.i32.p0i32(i32* %ptr, i32 2)
7272 <i>; yields {i32}:result2 = 4</i>
7273 %result3 = call i32 @llvm.atomic.load.sub.i32.p0i32(i32* %ptr, i32 5)
7274 <i>; yields {i32}:result3 = 2</i>
7275 %memval1 = load i32* %ptr <i>; yields {i32}:memval1 = -3</i>
7280 <!-- _______________________________________________________________________ -->
7281 <div class="doc_subsubsection">
7282 <a name="int_atomic_load_and">'<tt>llvm.atomic.load.and.*</tt>' Intrinsic</a><br>
7283 <a name="int_atomic_load_nand">'<tt>llvm.atomic.load.nand.*</tt>' Intrinsic</a><br>
7284 <a name="int_atomic_load_or">'<tt>llvm.atomic.load.or.*</tt>' Intrinsic</a><br>
7285 <a name="int_atomic_load_xor">'<tt>llvm.atomic.load.xor.*</tt>' Intrinsic</a><br>
7288 <div class="doc_text">
7291 <p>These are overloaded intrinsics. You can
7292 use <tt>llvm.atomic.load_and</tt>, <tt>llvm.atomic.load_nand</tt>,
7293 <tt>llvm.atomic.load_or</tt>, and <tt>llvm.atomic.load_xor</tt> on any integer
7294 bit width and for different address spaces. Not all targets support all bit
7298 declare i8 @llvm.atomic.load.and.i8.p0i8(i8* <ptr>, i8 <delta>)
7299 declare i16 @llvm.atomic.load.and.i16.p0i16(i16* <ptr>, i16 <delta>)
7300 declare i32 @llvm.atomic.load.and.i32.p0i32(i32* <ptr>, i32 <delta>)
7301 declare i64 @llvm.atomic.load.and.i64.p0i64(i64* <ptr>, i64 <delta>)
7305 declare i8 @llvm.atomic.load.or.i8.p0i8(i8* <ptr>, i8 <delta>)
7306 declare i16 @llvm.atomic.load.or.i16.p0i16(i16* <ptr>, i16 <delta>)
7307 declare i32 @llvm.atomic.load.or.i32.p0i32(i32* <ptr>, i32 <delta>)
7308 declare i64 @llvm.atomic.load.or.i64.p0i64(i64* <ptr>, i64 <delta>)
7312 declare i8 @llvm.atomic.load.nand.i8.p0i32(i8* <ptr>, i8 <delta>)
7313 declare i16 @llvm.atomic.load.nand.i16.p0i32(i16* <ptr>, i16 <delta>)
7314 declare i32 @llvm.atomic.load.nand.i32.p0i32(i32* <ptr>, i32 <delta>)
7315 declare i64 @llvm.atomic.load.nand.i64.p0i32(i64* <ptr>, i64 <delta>)
7319 declare i8 @llvm.atomic.load.xor.i8.p0i32(i8* <ptr>, i8 <delta>)
7320 declare i16 @llvm.atomic.load.xor.i16.p0i32(i16* <ptr>, i16 <delta>)
7321 declare i32 @llvm.atomic.load.xor.i32.p0i32(i32* <ptr>, i32 <delta>)
7322 declare i64 @llvm.atomic.load.xor.i64.p0i32(i64* <ptr>, i64 <delta>)
7326 <p>These intrinsics bitwise the operation (and, nand, or, xor) <tt>delta</tt> to
7327 the value stored in memory at <tt>ptr</tt>. It yields the original value
7328 at <tt>ptr</tt>.</p>
7331 <p>These intrinsics take two arguments, the first a pointer to an integer value
7332 and the second an integer value. The result is also an integer value. These
7333 integer types can have any bit width, but they must all have the same bit
7334 width. The targets may only lower integer representations they support.</p>
7337 <p>These intrinsics does a series of operations atomically. They first load the
7338 value stored at <tt>ptr</tt>. They then do the bitwise
7339 operation <tt>delta</tt>, store the result to <tt>ptr</tt>. They yield the
7340 original value stored at <tt>ptr</tt>.</p>
7344 %mallocP = tail call i8* @malloc(i32 ptrtoint (i32* getelementptr (i32* null, i32 1) to i32))
7345 %ptr = bitcast i8* %mallocP to i32*
7346 store i32 0x0F0F, %ptr
7347 %result0 = call i32 @llvm.atomic.load.nand.i32.p0i32(i32* %ptr, i32 0xFF)
7348 <i>; yields {i32}:result0 = 0x0F0F</i>
7349 %result1 = call i32 @llvm.atomic.load.and.i32.p0i32(i32* %ptr, i32 0xFF)
7350 <i>; yields {i32}:result1 = 0xFFFFFFF0</i>
7351 %result2 = call i32 @llvm.atomic.load.or.i32.p0i32(i32* %ptr, i32 0F)
7352 <i>; yields {i32}:result2 = 0xF0</i>
7353 %result3 = call i32 @llvm.atomic.load.xor.i32.p0i32(i32* %ptr, i32 0F)
7354 <i>; yields {i32}:result3 = FF</i>
7355 %memval1 = load i32* %ptr <i>; yields {i32}:memval1 = F0</i>
7360 <!-- _______________________________________________________________________ -->
7361 <div class="doc_subsubsection">
7362 <a name="int_atomic_load_max">'<tt>llvm.atomic.load.max.*</tt>' Intrinsic</a><br>
7363 <a name="int_atomic_load_min">'<tt>llvm.atomic.load.min.*</tt>' Intrinsic</a><br>
7364 <a name="int_atomic_load_umax">'<tt>llvm.atomic.load.umax.*</tt>' Intrinsic</a><br>
7365 <a name="int_atomic_load_umin">'<tt>llvm.atomic.load.umin.*</tt>' Intrinsic</a><br>
7368 <div class="doc_text">
7371 <p>These are overloaded intrinsics. You can use <tt>llvm.atomic.load_max</tt>,
7372 <tt>llvm.atomic.load_min</tt>, <tt>llvm.atomic.load_umax</tt>, and
7373 <tt>llvm.atomic.load_umin</tt> on any integer bit width and for different
7374 address spaces. Not all targets support all bit widths however.</p>
7377 declare i8 @llvm.atomic.load.max.i8.p0i8(i8* <ptr>, i8 <delta>)
7378 declare i16 @llvm.atomic.load.max.i16.p0i16(i16* <ptr>, i16 <delta>)
7379 declare i32 @llvm.atomic.load.max.i32.p0i32(i32* <ptr>, i32 <delta>)
7380 declare i64 @llvm.atomic.load.max.i64.p0i64(i64* <ptr>, i64 <delta>)
7384 declare i8 @llvm.atomic.load.min.i8.p0i8(i8* <ptr>, i8 <delta>)
7385 declare i16 @llvm.atomic.load.min.i16.p0i16(i16* <ptr>, i16 <delta>)
7386 declare i32 @llvm.atomic.load.min.i32.p0i32(i32* <ptr>, i32 <delta>)
7387 declare i64 @llvm.atomic.load.min.i64.p0i64(i64* <ptr>, i64 <delta>)
7391 declare i8 @llvm.atomic.load.umax.i8.p0i8(i8* <ptr>, i8 <delta>)
7392 declare i16 @llvm.atomic.load.umax.i16.p0i16(i16* <ptr>, i16 <delta>)
7393 declare i32 @llvm.atomic.load.umax.i32.p0i32(i32* <ptr>, i32 <delta>)
7394 declare i64 @llvm.atomic.load.umax.i64.p0i64(i64* <ptr>, i64 <delta>)
7398 declare i8 @llvm.atomic.load.umin.i8.p0i8(i8* <ptr>, i8 <delta>)
7399 declare i16 @llvm.atomic.load.umin.i16.p0i16(i16* <ptr>, i16 <delta>)
7400 declare i32 @llvm.atomic.load.umin.i32.p0i32(i32* <ptr>, i32 <delta>)
7401 declare i64 @llvm.atomic.load.umin.i64.p0i64(i64* <ptr>, i64 <delta>)
7405 <p>These intrinsics takes the signed or unsigned minimum or maximum of
7406 <tt>delta</tt> and the value stored in memory at <tt>ptr</tt>. It yields the
7407 original value at <tt>ptr</tt>.</p>
7410 <p>These intrinsics take two arguments, the first a pointer to an integer value
7411 and the second an integer value. The result is also an integer value. These
7412 integer types can have any bit width, but they must all have the same bit
7413 width. The targets may only lower integer representations they support.</p>
7416 <p>These intrinsics does a series of operations atomically. They first load the
7417 value stored at <tt>ptr</tt>. They then do the signed or unsigned min or
7418 max <tt>delta</tt> and the value, store the result to <tt>ptr</tt>. They
7419 yield the original value stored at <tt>ptr</tt>.</p>
7423 %mallocP = tail call i8* @malloc(i32 ptrtoint (i32* getelementptr (i32* null, i32 1) to i32))
7424 %ptr = bitcast i8* %mallocP to i32*
7426 %result0 = call i32 @llvm.atomic.load.min.i32.p0i32(i32* %ptr, i32 -2)
7427 <i>; yields {i32}:result0 = 7</i>
7428 %result1 = call i32 @llvm.atomic.load.max.i32.p0i32(i32* %ptr, i32 8)
7429 <i>; yields {i32}:result1 = -2</i>
7430 %result2 = call i32 @llvm.atomic.load.umin.i32.p0i32(i32* %ptr, i32 10)
7431 <i>; yields {i32}:result2 = 8</i>
7432 %result3 = call i32 @llvm.atomic.load.umax.i32.p0i32(i32* %ptr, i32 30)
7433 <i>; yields {i32}:result3 = 8</i>
7434 %memval1 = load i32* %ptr <i>; yields {i32}:memval1 = 30</i>
7440 <!-- ======================================================================= -->
7441 <div class="doc_subsection">
7442 <a name="int_memorymarkers">Memory Use Markers</a>
7445 <div class="doc_text">
7447 <p>This class of intrinsics exists to information about the lifetime of memory
7448 objects and ranges where variables are immutable.</p>
7452 <!-- _______________________________________________________________________ -->
7453 <div class="doc_subsubsection">
7454 <a name="int_lifetime_start">'<tt>llvm.lifetime.start</tt>' Intrinsic</a>
7457 <div class="doc_text">
7461 declare void @llvm.lifetime.start(i64 <size>, i8* nocapture <ptr>)
7465 <p>The '<tt>llvm.lifetime.start</tt>' intrinsic specifies the start of a memory
7466 object's lifetime.</p>
7469 <p>The first argument is a constant integer representing the size of the
7470 object, or -1 if it is variable sized. The second argument is a pointer to
7474 <p>This intrinsic indicates that before this point in the code, the value of the
7475 memory pointed to by <tt>ptr</tt> is dead. This means that it is known to
7476 never be used and has an undefined value. A load from the pointer that
7477 precedes this intrinsic can be replaced with
7478 <tt>'<a href="#undefvalues">undef</a>'</tt>.</p>
7482 <!-- _______________________________________________________________________ -->
7483 <div class="doc_subsubsection">
7484 <a name="int_lifetime_end">'<tt>llvm.lifetime.end</tt>' Intrinsic</a>
7487 <div class="doc_text">
7491 declare void @llvm.lifetime.end(i64 <size>, i8* nocapture <ptr>)
7495 <p>The '<tt>llvm.lifetime.end</tt>' intrinsic specifies the end of a memory
7496 object's lifetime.</p>
7499 <p>The first argument is a constant integer representing the size of the
7500 object, or -1 if it is variable sized. The second argument is a pointer to
7504 <p>This intrinsic indicates that after this point in the code, the value of the
7505 memory pointed to by <tt>ptr</tt> is dead. This means that it is known to
7506 never be used and has an undefined value. Any stores into the memory object
7507 following this intrinsic may be removed as dead.
7511 <!-- _______________________________________________________________________ -->
7512 <div class="doc_subsubsection">
7513 <a name="int_invariant_start">'<tt>llvm.invariant.start</tt>' Intrinsic</a>
7516 <div class="doc_text">
7520 declare {}* @llvm.invariant.start(i64 <size>, i8* nocapture <ptr>) readonly
7524 <p>The '<tt>llvm.invariant.start</tt>' intrinsic specifies that the contents of
7525 a memory object will not change.</p>
7528 <p>The first argument is a constant integer representing the size of the
7529 object, or -1 if it is variable sized. The second argument is a pointer to
7533 <p>This intrinsic indicates that until an <tt>llvm.invariant.end</tt> that uses
7534 the return value, the referenced memory location is constant and
7539 <!-- _______________________________________________________________________ -->
7540 <div class="doc_subsubsection">
7541 <a name="int_invariant_end">'<tt>llvm.invariant.end</tt>' Intrinsic</a>
7544 <div class="doc_text">
7548 declare void @llvm.invariant.end({}* <start>, i64 <size>, i8* nocapture <ptr>)
7552 <p>The '<tt>llvm.invariant.end</tt>' intrinsic specifies that the contents of
7553 a memory object are mutable.</p>
7556 <p>The first argument is the matching <tt>llvm.invariant.start</tt> intrinsic.
7557 The second argument is a constant integer representing the size of the
7558 object, or -1 if it is variable sized and the third argument is a pointer
7562 <p>This intrinsic indicates that the memory is mutable again.</p>
7566 <!-- ======================================================================= -->
7567 <div class="doc_subsection">
7568 <a name="int_general">General Intrinsics</a>
7571 <div class="doc_text">
7573 <p>This class of intrinsics is designed to be generic and has no specific
7578 <!-- _______________________________________________________________________ -->
7579 <div class="doc_subsubsection">
7580 <a name="int_var_annotation">'<tt>llvm.var.annotation</tt>' Intrinsic</a>
7583 <div class="doc_text">
7587 declare void @llvm.var.annotation(i8* <val>, i8* <str>, i8* <str>, i32 <int>)
7591 <p>The '<tt>llvm.var.annotation</tt>' intrinsic.</p>
7594 <p>The first argument is a pointer to a value, the second is a pointer to a
7595 global string, the third is a pointer to a global string which is the source
7596 file name, and the last argument is the line number.</p>
7599 <p>This intrinsic allows annotation of local variables with arbitrary strings.
7600 This can be useful for special purpose optimizations that want to look for
7601 these annotations. These have no other defined use, they are ignored by code
7602 generation and optimization.</p>
7606 <!-- _______________________________________________________________________ -->
7607 <div class="doc_subsubsection">
7608 <a name="int_annotation">'<tt>llvm.annotation.*</tt>' Intrinsic</a>
7611 <div class="doc_text">
7614 <p>This is an overloaded intrinsic. You can use '<tt>llvm.annotation</tt>' on
7615 any integer bit width.</p>
7618 declare i8 @llvm.annotation.i8(i8 <val>, i8* <str>, i8* <str>, i32 <int>)
7619 declare i16 @llvm.annotation.i16(i16 <val>, i8* <str>, i8* <str>, i32 <int>)
7620 declare i32 @llvm.annotation.i32(i32 <val>, i8* <str>, i8* <str>, i32 <int>)
7621 declare i64 @llvm.annotation.i64(i64 <val>, i8* <str>, i8* <str>, i32 <int>)
7622 declare i256 @llvm.annotation.i256(i256 <val>, i8* <str>, i8* <str>, i32 <int>)
7626 <p>The '<tt>llvm.annotation</tt>' intrinsic.</p>
7629 <p>The first argument is an integer value (result of some expression), the
7630 second is a pointer to a global string, the third is a pointer to a global
7631 string which is the source file name, and the last argument is the line
7632 number. It returns the value of the first argument.</p>
7635 <p>This intrinsic allows annotations to be put on arbitrary expressions with
7636 arbitrary strings. This can be useful for special purpose optimizations that
7637 want to look for these annotations. These have no other defined use, they
7638 are ignored by code generation and optimization.</p>
7642 <!-- _______________________________________________________________________ -->
7643 <div class="doc_subsubsection">
7644 <a name="int_trap">'<tt>llvm.trap</tt>' Intrinsic</a>
7647 <div class="doc_text">
7651 declare void @llvm.trap()
7655 <p>The '<tt>llvm.trap</tt>' intrinsic.</p>
7661 <p>This intrinsics is lowered to the target dependent trap instruction. If the
7662 target does not have a trap instruction, this intrinsic will be lowered to
7663 the call of the <tt>abort()</tt> function.</p>
7667 <!-- _______________________________________________________________________ -->
7668 <div class="doc_subsubsection">
7669 <a name="int_stackprotector">'<tt>llvm.stackprotector</tt>' Intrinsic</a>
7672 <div class="doc_text">
7676 declare void @llvm.stackprotector(i8* <guard>, i8** <slot>)
7680 <p>The <tt>llvm.stackprotector</tt> intrinsic takes the <tt>guard</tt> and
7681 stores it onto the stack at <tt>slot</tt>. The stack slot is adjusted to
7682 ensure that it is placed on the stack before local variables.</p>
7685 <p>The <tt>llvm.stackprotector</tt> intrinsic requires two pointer
7686 arguments. The first argument is the value loaded from the stack
7687 guard <tt>@__stack_chk_guard</tt>. The second variable is an <tt>alloca</tt>
7688 that has enough space to hold the value of the guard.</p>
7691 <p>This intrinsic causes the prologue/epilogue inserter to force the position of
7692 the <tt>AllocaInst</tt> stack slot to be before local variables on the
7693 stack. This is to ensure that if a local variable on the stack is
7694 overwritten, it will destroy the value of the guard. When the function exits,
7695 the guard on the stack is checked against the original guard. If they're
7696 different, then the program aborts by calling the <tt>__stack_chk_fail()</tt>
7701 <!-- _______________________________________________________________________ -->
7702 <div class="doc_subsubsection">
7703 <a name="int_objectsize">'<tt>llvm.objectsize</tt>' Intrinsic</a>
7706 <div class="doc_text">
7710 declare i32 @llvm.objectsize.i32(i8* <object>, i1 <type>)
7711 declare i64 @llvm.objectsize.i64(i8* <object>, i1 <type>)
7715 <p>The <tt>llvm.objectsize</tt> intrinsic is designed to provide information
7716 to the optimizers to discover at compile time either a) when an
7717 operation like memcpy will either overflow a buffer that corresponds to
7718 an object, or b) to determine that a runtime check for overflow isn't
7719 necessary. An object in this context means an allocation of a
7720 specific class, structure, array, or other object.</p>
7723 <p>The <tt>llvm.objectsize</tt> intrinsic takes two arguments. The first
7724 argument is a pointer to or into the <tt>object</tt>. The second argument
7725 is a boolean 0 or 1. This argument determines whether you want the
7726 maximum (0) or minimum (1) bytes remaining. This needs to be a literal 0 or
7727 1, variables are not allowed.</p>
7730 <p>The <tt>llvm.objectsize</tt> intrinsic is lowered to either a constant
7731 representing the size of the object concerned or <tt>i32/i64 -1 or 0</tt>
7732 (depending on the <tt>type</tt> argument if the size cannot be determined
7733 at compile time.</p>
7737 <!-- *********************************************************************** -->
7740 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
7741 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
7742 <a href="http://validator.w3.org/check/referer"><img
7743 src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a>
7745 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
7746 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
7747 Last modified: $Date$