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9 content="LLVM Assembly Language Reference Manual.">
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15 <h1>LLVM Language Reference Manual</h1>
17 <li><a href="#abstract">Abstract</a></li>
18 <li><a href="#introduction">Introduction</a></li>
19 <li><a href="#identifiers">Identifiers</a></li>
20 <li><a href="#highlevel">High Level Structure</a>
22 <li><a href="#modulestructure">Module Structure</a></li>
23 <li><a href="#linkage">Linkage Types</a>
25 <li><a href="#linkage_private">'<tt>private</tt>' Linkage</a></li>
26 <li><a href="#linkage_linker_private">'<tt>linker_private</tt>' Linkage</a></li>
27 <li><a href="#linkage_linker_private_weak">'<tt>linker_private_weak</tt>' Linkage</a></li>
28 <li><a href="#linkage_linker_private_weak_def_auto">'<tt>linker_private_weak_def_auto</tt>' Linkage</a></li>
29 <li><a href="#linkage_internal">'<tt>internal</tt>' Linkage</a></li>
30 <li><a href="#linkage_available_externally">'<tt>available_externally</tt>' Linkage</a></li>
31 <li><a href="#linkage_linkonce">'<tt>linkonce</tt>' Linkage</a></li>
32 <li><a href="#linkage_common">'<tt>common</tt>' Linkage</a></li>
33 <li><a href="#linkage_weak">'<tt>weak</tt>' Linkage</a></li>
34 <li><a href="#linkage_appending">'<tt>appending</tt>' Linkage</a></li>
35 <li><a href="#linkage_externweak">'<tt>extern_weak</tt>' Linkage</a></li>
36 <li><a href="#linkage_linkonce_odr">'<tt>linkonce_odr</tt>' Linkage</a></li>
37 <li><a href="#linkage_weak">'<tt>weak_odr</tt>' Linkage</a></li>
38 <li><a href="#linkage_external">'<tt>external</tt>' Linkage</a></li>
39 <li><a href="#linkage_dllimport">'<tt>dllimport</tt>' Linkage</a></li>
40 <li><a href="#linkage_dllexport">'<tt>dllexport</tt>' Linkage</a></li>
43 <li><a href="#callingconv">Calling Conventions</a></li>
44 <li><a href="#namedtypes">Named Types</a></li>
45 <li><a href="#globalvars">Global Variables</a></li>
46 <li><a href="#functionstructure">Functions</a></li>
47 <li><a href="#aliasstructure">Aliases</a></li>
48 <li><a href="#namedmetadatastructure">Named Metadata</a></li>
49 <li><a href="#paramattrs">Parameter Attributes</a></li>
50 <li><a href="#fnattrs">Function Attributes</a></li>
51 <li><a href="#gc">Garbage Collector Names</a></li>
52 <li><a href="#moduleasm">Module-Level Inline Assembly</a></li>
53 <li><a href="#datalayout">Data Layout</a></li>
54 <li><a href="#pointeraliasing">Pointer Aliasing Rules</a></li>
55 <li><a href="#volatile">Volatile Memory Accesses</a></li>
56 <li><a href="#memmodel">Memory Model for Concurrent Operations</a></li>
57 <li><a href="#ordering">Atomic Memory Ordering Constraints</a></li>
60 <li><a href="#typesystem">Type System</a>
62 <li><a href="#t_classifications">Type Classifications</a></li>
63 <li><a href="#t_primitive">Primitive Types</a>
65 <li><a href="#t_integer">Integer Type</a></li>
66 <li><a href="#t_floating">Floating Point Types</a></li>
67 <li><a href="#t_x86mmx">X86mmx Type</a></li>
68 <li><a href="#t_void">Void Type</a></li>
69 <li><a href="#t_label">Label Type</a></li>
70 <li><a href="#t_metadata">Metadata Type</a></li>
73 <li><a href="#t_derived">Derived Types</a>
75 <li><a href="#t_aggregate">Aggregate Types</a>
77 <li><a href="#t_array">Array Type</a></li>
78 <li><a href="#t_struct">Structure Type</a></li>
79 <li><a href="#t_opaque">Opaque Structure Types</a></li>
80 <li><a href="#t_vector">Vector Type</a></li>
83 <li><a href="#t_function">Function Type</a></li>
84 <li><a href="#t_pointer">Pointer Type</a></li>
89 <li><a href="#constants">Constants</a>
91 <li><a href="#simpleconstants">Simple Constants</a></li>
92 <li><a href="#complexconstants">Complex Constants</a></li>
93 <li><a href="#globalconstants">Global Variable and Function Addresses</a></li>
94 <li><a href="#undefvalues">Undefined Values</a></li>
95 <li><a href="#poisonvalues">Poison Values</a></li>
96 <li><a href="#blockaddress">Addresses of Basic Blocks</a></li>
97 <li><a href="#constantexprs">Constant Expressions</a></li>
100 <li><a href="#othervalues">Other Values</a>
102 <li><a href="#inlineasm">Inline Assembler Expressions</a></li>
103 <li><a href="#metadata">Metadata Nodes and Metadata Strings</a>
105 <li><a href="#tbaa">'<tt>tbaa</tt>' Metadata</a></li>
106 <li><a href="#fpaccuracy">'<tt>fpaccuracy</tt>' Metadata</a></li>
111 <li><a href="#intrinsic_globals">Intrinsic Global Variables</a>
113 <li><a href="#intg_used">The '<tt>llvm.used</tt>' Global Variable</a></li>
114 <li><a href="#intg_compiler_used">The '<tt>llvm.compiler.used</tt>'
115 Global Variable</a></li>
116 <li><a href="#intg_global_ctors">The '<tt>llvm.global_ctors</tt>'
117 Global Variable</a></li>
118 <li><a href="#intg_global_dtors">The '<tt>llvm.global_dtors</tt>'
119 Global Variable</a></li>
122 <li><a href="#instref">Instruction Reference</a>
124 <li><a href="#terminators">Terminator Instructions</a>
126 <li><a href="#i_ret">'<tt>ret</tt>' Instruction</a></li>
127 <li><a href="#i_br">'<tt>br</tt>' Instruction</a></li>
128 <li><a href="#i_switch">'<tt>switch</tt>' Instruction</a></li>
129 <li><a href="#i_indirectbr">'<tt>indirectbr</tt>' Instruction</a></li>
130 <li><a href="#i_invoke">'<tt>invoke</tt>' Instruction</a></li>
131 <li><a href="#i_unwind">'<tt>unwind</tt>' Instruction</a></li>
132 <li><a href="#i_resume">'<tt>resume</tt>' Instruction</a></li>
133 <li><a href="#i_unreachable">'<tt>unreachable</tt>' Instruction</a></li>
136 <li><a href="#binaryops">Binary Operations</a>
138 <li><a href="#i_add">'<tt>add</tt>' Instruction</a></li>
139 <li><a href="#i_fadd">'<tt>fadd</tt>' Instruction</a></li>
140 <li><a href="#i_sub">'<tt>sub</tt>' Instruction</a></li>
141 <li><a href="#i_fsub">'<tt>fsub</tt>' Instruction</a></li>
142 <li><a href="#i_mul">'<tt>mul</tt>' Instruction</a></li>
143 <li><a href="#i_fmul">'<tt>fmul</tt>' Instruction</a></li>
144 <li><a href="#i_udiv">'<tt>udiv</tt>' Instruction</a></li>
145 <li><a href="#i_sdiv">'<tt>sdiv</tt>' Instruction</a></li>
146 <li><a href="#i_fdiv">'<tt>fdiv</tt>' Instruction</a></li>
147 <li><a href="#i_urem">'<tt>urem</tt>' Instruction</a></li>
148 <li><a href="#i_srem">'<tt>srem</tt>' Instruction</a></li>
149 <li><a href="#i_frem">'<tt>frem</tt>' Instruction</a></li>
152 <li><a href="#bitwiseops">Bitwise Binary Operations</a>
154 <li><a href="#i_shl">'<tt>shl</tt>' Instruction</a></li>
155 <li><a href="#i_lshr">'<tt>lshr</tt>' Instruction</a></li>
156 <li><a href="#i_ashr">'<tt>ashr</tt>' Instruction</a></li>
157 <li><a href="#i_and">'<tt>and</tt>' Instruction</a></li>
158 <li><a href="#i_or">'<tt>or</tt>' Instruction</a></li>
159 <li><a href="#i_xor">'<tt>xor</tt>' Instruction</a></li>
162 <li><a href="#vectorops">Vector Operations</a>
164 <li><a href="#i_extractelement">'<tt>extractelement</tt>' Instruction</a></li>
165 <li><a href="#i_insertelement">'<tt>insertelement</tt>' Instruction</a></li>
166 <li><a href="#i_shufflevector">'<tt>shufflevector</tt>' Instruction</a></li>
169 <li><a href="#aggregateops">Aggregate Operations</a>
171 <li><a href="#i_extractvalue">'<tt>extractvalue</tt>' Instruction</a></li>
172 <li><a href="#i_insertvalue">'<tt>insertvalue</tt>' Instruction</a></li>
175 <li><a href="#memoryops">Memory Access and Addressing Operations</a>
177 <li><a href="#i_alloca">'<tt>alloca</tt>' Instruction</a></li>
178 <li><a href="#i_load">'<tt>load</tt>' Instruction</a></li>
179 <li><a href="#i_store">'<tt>store</tt>' Instruction</a></li>
180 <li><a href="#i_fence">'<tt>fence</tt>' Instruction</a></li>
181 <li><a href="#i_cmpxchg">'<tt>cmpxchg</tt>' Instruction</a></li>
182 <li><a href="#i_atomicrmw">'<tt>atomicrmw</tt>' Instruction</a></li>
183 <li><a href="#i_getelementptr">'<tt>getelementptr</tt>' Instruction</a></li>
186 <li><a href="#convertops">Conversion Operations</a>
188 <li><a href="#i_trunc">'<tt>trunc .. to</tt>' Instruction</a></li>
189 <li><a href="#i_zext">'<tt>zext .. to</tt>' Instruction</a></li>
190 <li><a href="#i_sext">'<tt>sext .. to</tt>' Instruction</a></li>
191 <li><a href="#i_fptrunc">'<tt>fptrunc .. to</tt>' Instruction</a></li>
192 <li><a href="#i_fpext">'<tt>fpext .. to</tt>' Instruction</a></li>
193 <li><a href="#i_fptoui">'<tt>fptoui .. to</tt>' Instruction</a></li>
194 <li><a href="#i_fptosi">'<tt>fptosi .. to</tt>' Instruction</a></li>
195 <li><a href="#i_uitofp">'<tt>uitofp .. to</tt>' Instruction</a></li>
196 <li><a href="#i_sitofp">'<tt>sitofp .. to</tt>' Instruction</a></li>
197 <li><a href="#i_ptrtoint">'<tt>ptrtoint .. to</tt>' Instruction</a></li>
198 <li><a href="#i_inttoptr">'<tt>inttoptr .. to</tt>' Instruction</a></li>
199 <li><a href="#i_bitcast">'<tt>bitcast .. to</tt>' Instruction</a></li>
202 <li><a href="#otherops">Other Operations</a>
204 <li><a href="#i_icmp">'<tt>icmp</tt>' Instruction</a></li>
205 <li><a href="#i_fcmp">'<tt>fcmp</tt>' Instruction</a></li>
206 <li><a href="#i_phi">'<tt>phi</tt>' Instruction</a></li>
207 <li><a href="#i_select">'<tt>select</tt>' Instruction</a></li>
208 <li><a href="#i_call">'<tt>call</tt>' Instruction</a></li>
209 <li><a href="#i_va_arg">'<tt>va_arg</tt>' Instruction</a></li>
210 <li><a href="#i_landingpad">'<tt>landingpad</tt>' Instruction</a></li>
215 <li><a href="#intrinsics">Intrinsic Functions</a>
217 <li><a href="#int_varargs">Variable Argument Handling Intrinsics</a>
219 <li><a href="#int_va_start">'<tt>llvm.va_start</tt>' Intrinsic</a></li>
220 <li><a href="#int_va_end">'<tt>llvm.va_end</tt>' Intrinsic</a></li>
221 <li><a href="#int_va_copy">'<tt>llvm.va_copy</tt>' Intrinsic</a></li>
224 <li><a href="#int_gc">Accurate Garbage Collection Intrinsics</a>
226 <li><a href="#int_gcroot">'<tt>llvm.gcroot</tt>' Intrinsic</a></li>
227 <li><a href="#int_gcread">'<tt>llvm.gcread</tt>' Intrinsic</a></li>
228 <li><a href="#int_gcwrite">'<tt>llvm.gcwrite</tt>' Intrinsic</a></li>
231 <li><a href="#int_codegen">Code Generator Intrinsics</a>
233 <li><a href="#int_returnaddress">'<tt>llvm.returnaddress</tt>' Intrinsic</a></li>
234 <li><a href="#int_frameaddress">'<tt>llvm.frameaddress</tt>' Intrinsic</a></li>
235 <li><a href="#int_stacksave">'<tt>llvm.stacksave</tt>' Intrinsic</a></li>
236 <li><a href="#int_stackrestore">'<tt>llvm.stackrestore</tt>' Intrinsic</a></li>
237 <li><a href="#int_prefetch">'<tt>llvm.prefetch</tt>' Intrinsic</a></li>
238 <li><a href="#int_pcmarker">'<tt>llvm.pcmarker</tt>' Intrinsic</a></li>
239 <li><a href="#int_readcyclecounter">'<tt>llvm.readcyclecounter</tt>' Intrinsic</a></li>
242 <li><a href="#int_libc">Standard C Library Intrinsics</a>
244 <li><a href="#int_memcpy">'<tt>llvm.memcpy.*</tt>' Intrinsic</a></li>
245 <li><a href="#int_memmove">'<tt>llvm.memmove.*</tt>' Intrinsic</a></li>
246 <li><a href="#int_memset">'<tt>llvm.memset.*</tt>' Intrinsic</a></li>
247 <li><a href="#int_sqrt">'<tt>llvm.sqrt.*</tt>' Intrinsic</a></li>
248 <li><a href="#int_powi">'<tt>llvm.powi.*</tt>' Intrinsic</a></li>
249 <li><a href="#int_sin">'<tt>llvm.sin.*</tt>' Intrinsic</a></li>
250 <li><a href="#int_cos">'<tt>llvm.cos.*</tt>' Intrinsic</a></li>
251 <li><a href="#int_pow">'<tt>llvm.pow.*</tt>' Intrinsic</a></li>
252 <li><a href="#int_exp">'<tt>llvm.exp.*</tt>' Intrinsic</a></li>
253 <li><a href="#int_log">'<tt>llvm.log.*</tt>' Intrinsic</a></li>
254 <li><a href="#int_fma">'<tt>llvm.fma.*</tt>' Intrinsic</a></li>
257 <li><a href="#int_manip">Bit Manipulation Intrinsics</a>
259 <li><a href="#int_bswap">'<tt>llvm.bswap.*</tt>' Intrinsics</a></li>
260 <li><a href="#int_ctpop">'<tt>llvm.ctpop.*</tt>' Intrinsic </a></li>
261 <li><a href="#int_ctlz">'<tt>llvm.ctlz.*</tt>' Intrinsic </a></li>
262 <li><a href="#int_cttz">'<tt>llvm.cttz.*</tt>' Intrinsic </a></li>
265 <li><a href="#int_overflow">Arithmetic with Overflow Intrinsics</a>
267 <li><a href="#int_sadd_overflow">'<tt>llvm.sadd.with.overflow.*</tt> Intrinsics</a></li>
268 <li><a href="#int_uadd_overflow">'<tt>llvm.uadd.with.overflow.*</tt> Intrinsics</a></li>
269 <li><a href="#int_ssub_overflow">'<tt>llvm.ssub.with.overflow.*</tt> Intrinsics</a></li>
270 <li><a href="#int_usub_overflow">'<tt>llvm.usub.with.overflow.*</tt> Intrinsics</a></li>
271 <li><a href="#int_smul_overflow">'<tt>llvm.smul.with.overflow.*</tt> Intrinsics</a></li>
272 <li><a href="#int_umul_overflow">'<tt>llvm.umul.with.overflow.*</tt> Intrinsics</a></li>
275 <li><a href="#int_fp16">Half Precision Floating Point Intrinsics</a>
277 <li><a href="#int_convert_to_fp16">'<tt>llvm.convert.to.fp16</tt>' Intrinsic</a></li>
278 <li><a href="#int_convert_from_fp16">'<tt>llvm.convert.from.fp16</tt>' Intrinsic</a></li>
281 <li><a href="#int_debugger">Debugger intrinsics</a></li>
282 <li><a href="#int_eh">Exception Handling intrinsics</a></li>
283 <li><a href="#int_trampoline">Trampoline Intrinsics</a>
285 <li><a href="#int_it">'<tt>llvm.init.trampoline</tt>' Intrinsic</a></li>
286 <li><a href="#int_at">'<tt>llvm.adjust.trampoline</tt>' Intrinsic</a></li>
289 <li><a href="#int_memorymarkers">Memory Use Markers</a>
291 <li><a href="#int_lifetime_start">'<tt>llvm.lifetime.start</tt>' Intrinsic</a></li>
292 <li><a href="#int_lifetime_end">'<tt>llvm.lifetime.end</tt>' Intrinsic</a></li>
293 <li><a href="#int_invariant_start">'<tt>llvm.invariant.start</tt>' Intrinsic</a></li>
294 <li><a href="#int_invariant_end">'<tt>llvm.invariant.end</tt>' Intrinsic</a></li>
297 <li><a href="#int_general">General intrinsics</a>
299 <li><a href="#int_var_annotation">
300 '<tt>llvm.var.annotation</tt>' Intrinsic</a></li>
301 <li><a href="#int_annotation">
302 '<tt>llvm.annotation.*</tt>' Intrinsic</a></li>
303 <li><a href="#int_trap">
304 '<tt>llvm.trap</tt>' Intrinsic</a></li>
305 <li><a href="#int_stackprotector">
306 '<tt>llvm.stackprotector</tt>' Intrinsic</a></li>
307 <li><a href="#int_objectsize">
308 '<tt>llvm.objectsize</tt>' Intrinsic</a></li>
309 <li><a href="#int_expect">
310 '<tt>llvm.expect</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 <h2><a name="abstract">Abstract</a></h2>
324 <!-- *********************************************************************** -->
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 <h2><a name="introduction">Introduction</a></h2>
338 <!-- *********************************************************************** -->
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>
361 <!-- _______________________________________________________________________ -->
363 <a name="wellformed">Well-Formedness</a>
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>
388 <!-- Describe the typesetting conventions here. -->
390 <!-- *********************************************************************** -->
391 <h2><a name="identifiers">Identifiers</a></h2>
392 <!-- *********************************************************************** -->
396 <p>LLVM identifiers come in two basic types: global and local. Global
397 identifiers (functions, global variables) begin with the <tt>'@'</tt>
398 character. Local identifiers (register names, types) begin with
399 the <tt>'%'</tt> character. Additionally, there are three different formats
400 for identifiers, for different purposes:</p>
403 <li>Named values are represented as a string of characters with their prefix.
404 For example, <tt>%foo</tt>, <tt>@DivisionByZero</tt>,
405 <tt>%a.really.long.identifier</tt>. The actual regular expression used is
406 '<tt>[%@][a-zA-Z$._][a-zA-Z$._0-9]*</tt>'. Identifiers which require
407 other characters in their names can be surrounded with quotes. Special
408 characters may be escaped using <tt>"\xx"</tt> where <tt>xx</tt> is the
409 ASCII code for the character in hexadecimal. In this way, any character
410 can be used in a name value, even quotes themselves.</li>
412 <li>Unnamed values are represented as an unsigned numeric value with their
413 prefix. For example, <tt>%12</tt>, <tt>@2</tt>, <tt>%44</tt>.</li>
415 <li>Constants, which are described in a <a href="#constants">section about
416 constants</a>, below.</li>
419 <p>LLVM requires that values start with a prefix for two reasons: Compilers
420 don't need to worry about name clashes with reserved words, and the set of
421 reserved words may be expanded in the future without penalty. Additionally,
422 unnamed identifiers allow a compiler to quickly come up with a temporary
423 variable without having to avoid symbol table conflicts.</p>
425 <p>Reserved words in LLVM are very similar to reserved words in other
426 languages. There are keywords for different opcodes
427 ('<tt><a href="#i_add">add</a></tt>',
428 '<tt><a href="#i_bitcast">bitcast</a></tt>',
429 '<tt><a href="#i_ret">ret</a></tt>', etc...), for primitive type names
430 ('<tt><a href="#t_void">void</a></tt>',
431 '<tt><a href="#t_primitive">i32</a></tt>', etc...), and others. These
432 reserved words cannot conflict with variable names, because none of them
433 start with a prefix character (<tt>'%'</tt> or <tt>'@'</tt>).</p>
435 <p>Here is an example of LLVM code to multiply the integer variable
436 '<tt>%X</tt>' by 8:</p>
440 <pre class="doc_code">
441 %result = <a href="#i_mul">mul</a> i32 %X, 8
444 <p>After strength reduction:</p>
446 <pre class="doc_code">
447 %result = <a href="#i_shl">shl</a> i32 %X, i8 3
450 <p>And the hard way:</p>
452 <pre class="doc_code">
453 %0 = <a href="#i_add">add</a> i32 %X, %X <i>; yields {i32}:%0</i>
454 %1 = <a href="#i_add">add</a> i32 %0, %0 <i>; yields {i32}:%1</i>
455 %result = <a href="#i_add">add</a> i32 %1, %1
458 <p>This last way of multiplying <tt>%X</tt> by 8 illustrates several important
459 lexical features of LLVM:</p>
462 <li>Comments are delimited with a '<tt>;</tt>' and go until the end of
465 <li>Unnamed temporaries are created when the result of a computation is not
466 assigned to a named value.</li>
468 <li>Unnamed temporaries are numbered sequentially</li>
471 <p>It also shows a convention that we follow in this document. When
472 demonstrating instructions, we will follow an instruction with a comment that
473 defines the type and name of value produced. Comments are shown in italic
478 <!-- *********************************************************************** -->
479 <h2><a name="highlevel">High Level Structure</a></h2>
480 <!-- *********************************************************************** -->
482 <!-- ======================================================================= -->
484 <a name="modulestructure">Module Structure</a>
489 <p>LLVM programs are composed of "Module"s, each of which is a translation unit
490 of the input programs. Each module consists of functions, global variables,
491 and symbol table entries. Modules may be combined together with the LLVM
492 linker, which merges function (and global variable) definitions, resolves
493 forward declarations, and merges symbol table entries. Here is an example of
494 the "hello world" module:</p>
496 <pre class="doc_code">
497 <i>; Declare the string constant as a global constant.</i>
498 <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>
500 <i>; External declaration of the puts function</i>
501 <a href="#functionstructure">declare</a> i32 @puts(i8*) <i>; i32 (i8*)* </i>
503 <i>; Definition of main function</i>
504 define i32 @main() { <i>; i32()* </i>
505 <i>; Convert [13 x i8]* to i8 *...</i>
506 %cast210 = <a href="#i_getelementptr">getelementptr</a> [13 x i8]* @.LC0, i64 0, i64 0 <i>; i8*</i>
508 <i>; Call puts function to write out the string to stdout.</i>
509 <a href="#i_call">call</a> i32 @puts(i8* %cast210) <i>; i32</i>
510 <a href="#i_ret">ret</a> i32 0
513 <i>; Named metadata</i>
514 !1 = metadata !{i32 41}
518 <p>This example is made up of a <a href="#globalvars">global variable</a> named
519 "<tt>.LC0</tt>", an external declaration of the "<tt>puts</tt>" function,
520 a <a href="#functionstructure">function definition</a> for
521 "<tt>main</tt>" and <a href="#namedmetadatastructure">named metadata</a>
524 <p>In general, a module is made up of a list of global values, where both
525 functions and global variables are global values. Global values are
526 represented by a pointer to a memory location (in this case, a pointer to an
527 array of char, and a pointer to a function), and have one of the
528 following <a href="#linkage">linkage types</a>.</p>
532 <!-- ======================================================================= -->
534 <a name="linkage">Linkage Types</a>
539 <p>All Global Variables and Functions have one of the following types of
543 <dt><tt><b><a name="linkage_private">private</a></b></tt></dt>
544 <dd>Global values with "<tt>private</tt>" linkage are only directly accessible
545 by objects in the current module. In particular, linking code into a
546 module with an private global value may cause the private to be renamed as
547 necessary to avoid collisions. Because the symbol is private to the
548 module, all references can be updated. This doesn't show up in any symbol
549 table in the object file.</dd>
551 <dt><tt><b><a name="linkage_linker_private">linker_private</a></b></tt></dt>
552 <dd>Similar to <tt>private</tt>, but the symbol is passed through the
553 assembler and evaluated by the linker. Unlike normal strong symbols, they
554 are removed by the linker from the final linked image (executable or
555 dynamic library).</dd>
557 <dt><tt><b><a name="linkage_linker_private_weak">linker_private_weak</a></b></tt></dt>
558 <dd>Similar to "<tt>linker_private</tt>", but the symbol is weak. Note that
559 <tt>linker_private_weak</tt> symbols are subject to coalescing by the
560 linker. The symbols are removed by the linker from the final linked image
561 (executable or dynamic library).</dd>
563 <dt><tt><b><a name="linkage_linker_private_weak_def_auto">linker_private_weak_def_auto</a></b></tt></dt>
564 <dd>Similar to "<tt>linker_private_weak</tt>", but it's known that the address
565 of the object is not taken. For instance, functions that had an inline
566 definition, but the compiler decided not to inline it. Note,
567 unlike <tt>linker_private</tt> and <tt>linker_private_weak</tt>,
568 <tt>linker_private_weak_def_auto</tt> may have only <tt>default</tt>
569 visibility. The symbols are removed by the linker from the final linked
570 image (executable or dynamic library).</dd>
572 <dt><tt><b><a name="linkage_internal">internal</a></b></tt></dt>
573 <dd>Similar to private, but the value shows as a local symbol
574 (<tt>STB_LOCAL</tt> in the case of ELF) in the object file. This
575 corresponds to the notion of the '<tt>static</tt>' keyword in C.</dd>
577 <dt><tt><b><a name="linkage_available_externally">available_externally</a></b></tt></dt>
578 <dd>Globals with "<tt>available_externally</tt>" linkage are never emitted
579 into the object file corresponding to the LLVM module. They exist to
580 allow inlining and other optimizations to take place given knowledge of
581 the definition of the global, which is known to be somewhere outside the
582 module. Globals with <tt>available_externally</tt> linkage are allowed to
583 be discarded at will, and are otherwise the same as <tt>linkonce_odr</tt>.
584 This linkage type is only allowed on definitions, not declarations.</dd>
586 <dt><tt><b><a name="linkage_linkonce">linkonce</a></b></tt></dt>
587 <dd>Globals with "<tt>linkonce</tt>" linkage are merged with other globals of
588 the same name when linkage occurs. This can be used to implement
589 some forms of inline functions, templates, or other code which must be
590 generated in each translation unit that uses it, but where the body may
591 be overridden with a more definitive definition later. Unreferenced
592 <tt>linkonce</tt> globals are allowed to be discarded. Note that
593 <tt>linkonce</tt> linkage does not actually allow the optimizer to
594 inline the body of this function into callers because it doesn't know if
595 this definition of the function is the definitive definition within the
596 program or whether it will be overridden by a stronger definition.
597 To enable inlining and other optimizations, use "<tt>linkonce_odr</tt>"
600 <dt><tt><b><a name="linkage_weak">weak</a></b></tt></dt>
601 <dd>"<tt>weak</tt>" linkage has the same merging semantics as
602 <tt>linkonce</tt> linkage, except that unreferenced globals with
603 <tt>weak</tt> linkage may not be discarded. This is used for globals that
604 are declared "weak" in C source code.</dd>
606 <dt><tt><b><a name="linkage_common">common</a></b></tt></dt>
607 <dd>"<tt>common</tt>" linkage is most similar to "<tt>weak</tt>" linkage, but
608 they are used for tentative definitions in C, such as "<tt>int X;</tt>" at
610 Symbols with "<tt>common</tt>" linkage are merged in the same way as
611 <tt>weak symbols</tt>, and they may not be deleted if unreferenced.
612 <tt>common</tt> symbols may not have an explicit section,
613 must have a zero initializer, and may not be marked '<a
614 href="#globalvars"><tt>constant</tt></a>'. Functions and aliases may not
615 have common linkage.</dd>
618 <dt><tt><b><a name="linkage_appending">appending</a></b></tt></dt>
619 <dd>"<tt>appending</tt>" linkage may only be applied to global variables of
620 pointer to array type. When two global variables with appending linkage
621 are linked together, the two global arrays are appended together. This is
622 the LLVM, typesafe, equivalent of having the system linker append together
623 "sections" with identical names when .o files are linked.</dd>
625 <dt><tt><b><a name="linkage_externweak">extern_weak</a></b></tt></dt>
626 <dd>The semantics of this linkage follow the ELF object file model: the symbol
627 is weak until linked, if not linked, the symbol becomes null instead of
628 being an undefined reference.</dd>
630 <dt><tt><b><a name="linkage_linkonce_odr">linkonce_odr</a></b></tt></dt>
631 <dt><tt><b><a name="linkage_weak_odr">weak_odr</a></b></tt></dt>
632 <dd>Some languages allow differing globals to be merged, such as two functions
633 with different semantics. Other languages, such as <tt>C++</tt>, ensure
634 that only equivalent globals are ever merged (the "one definition rule"
635 — "ODR"). Such languages can use the <tt>linkonce_odr</tt>
636 and <tt>weak_odr</tt> linkage types to indicate that the global will only
637 be merged with equivalent globals. These linkage types are otherwise the
638 same as their non-<tt>odr</tt> versions.</dd>
640 <dt><tt><b><a name="linkage_external">external</a></b></tt></dt>
641 <dd>If none of the above identifiers are used, the global is externally
642 visible, meaning that it participates in linkage and can be used to
643 resolve external symbol references.</dd>
646 <p>The next two types of linkage are targeted for Microsoft Windows platform
647 only. They are designed to support importing (exporting) symbols from (to)
648 DLLs (Dynamic Link Libraries).</p>
651 <dt><tt><b><a name="linkage_dllimport">dllimport</a></b></tt></dt>
652 <dd>"<tt>dllimport</tt>" linkage causes the compiler to reference a function
653 or variable via a global pointer to a pointer that is set up by the DLL
654 exporting the symbol. On Microsoft Windows targets, the pointer name is
655 formed by combining <code>__imp_</code> and the function or variable
658 <dt><tt><b><a name="linkage_dllexport">dllexport</a></b></tt></dt>
659 <dd>"<tt>dllexport</tt>" linkage causes the compiler to provide a global
660 pointer to a pointer in a DLL, so that it can be referenced with the
661 <tt>dllimport</tt> attribute. On Microsoft Windows targets, the pointer
662 name is formed by combining <code>__imp_</code> and the function or
666 <p>For example, since the "<tt>.LC0</tt>" variable is defined to be internal, if
667 another module defined a "<tt>.LC0</tt>" variable and was linked with this
668 one, one of the two would be renamed, preventing a collision. Since
669 "<tt>main</tt>" and "<tt>puts</tt>" are external (i.e., lacking any linkage
670 declarations), they are accessible outside of the current module.</p>
672 <p>It is illegal for a function <i>declaration</i> to have any linkage type
673 other than <tt>external</tt>, <tt>dllimport</tt>
674 or <tt>extern_weak</tt>.</p>
676 <p>Aliases can have only <tt>external</tt>, <tt>internal</tt>, <tt>weak</tt>
677 or <tt>weak_odr</tt> linkages.</p>
681 <!-- ======================================================================= -->
683 <a name="callingconv">Calling Conventions</a>
688 <p>LLVM <a href="#functionstructure">functions</a>, <a href="#i_call">calls</a>
689 and <a href="#i_invoke">invokes</a> can all have an optional calling
690 convention specified for the call. The calling convention of any pair of
691 dynamic caller/callee must match, or the behavior of the program is
692 undefined. The following calling conventions are supported by LLVM, and more
693 may be added in the future:</p>
696 <dt><b>"<tt>ccc</tt>" - The C calling convention</b>:</dt>
697 <dd>This calling convention (the default if no other calling convention is
698 specified) matches the target C calling conventions. This calling
699 convention supports varargs function calls and tolerates some mismatch in
700 the declared prototype and implemented declaration of the function (as
703 <dt><b>"<tt>fastcc</tt>" - The fast calling convention</b>:</dt>
704 <dd>This calling convention attempts to make calls as fast as possible
705 (e.g. by passing things in registers). This calling convention allows the
706 target to use whatever tricks it wants to produce fast code for the
707 target, without having to conform to an externally specified ABI
708 (Application Binary Interface).
709 <a href="CodeGenerator.html#tailcallopt">Tail calls can only be optimized
710 when this or the GHC convention is used.</a> This calling convention
711 does not support varargs and requires the prototype of all callees to
712 exactly match the prototype of the function definition.</dd>
714 <dt><b>"<tt>coldcc</tt>" - The cold calling convention</b>:</dt>
715 <dd>This calling convention attempts to make code in the caller as efficient
716 as possible under the assumption that the call is not commonly executed.
717 As such, these calls often preserve all registers so that the call does
718 not break any live ranges in the caller side. This calling convention
719 does not support varargs and requires the prototype of all callees to
720 exactly match the prototype of the function definition.</dd>
722 <dt><b>"<tt>cc <em>10</em></tt>" - GHC convention</b>:</dt>
723 <dd>This calling convention has been implemented specifically for use by the
724 <a href="http://www.haskell.org/ghc">Glasgow Haskell Compiler (GHC)</a>.
725 It passes everything in registers, going to extremes to achieve this by
726 disabling callee save registers. This calling convention should not be
727 used lightly but only for specific situations such as an alternative to
728 the <em>register pinning</em> performance technique often used when
729 implementing functional programming languages.At the moment only X86
730 supports this convention and it has the following limitations:
732 <li>On <em>X86-32</em> only supports up to 4 bit type parameters. No
733 floating point types are supported.</li>
734 <li>On <em>X86-64</em> only supports up to 10 bit type parameters and
735 6 floating point parameters.</li>
737 This calling convention supports
738 <a href="CodeGenerator.html#tailcallopt">tail call optimization</a> but
739 requires both the caller and callee are using it.
742 <dt><b>"<tt>cc <<em>n</em>></tt>" - Numbered convention</b>:</dt>
743 <dd>Any calling convention may be specified by number, allowing
744 target-specific calling conventions to be used. Target specific calling
745 conventions start at 64.</dd>
748 <p>More calling conventions can be added/defined on an as-needed basis, to
749 support Pascal conventions or any other well-known target-independent
754 <!-- ======================================================================= -->
756 <a name="visibility">Visibility Styles</a>
761 <p>All Global Variables and Functions have one of the following visibility
765 <dt><b>"<tt>default</tt>" - Default style</b>:</dt>
766 <dd>On targets that use the ELF object file format, default visibility means
767 that the declaration is visible to other modules and, in shared libraries,
768 means that the declared entity may be overridden. On Darwin, default
769 visibility means that the declaration is visible to other modules. Default
770 visibility corresponds to "external linkage" in the language.</dd>
772 <dt><b>"<tt>hidden</tt>" - Hidden style</b>:</dt>
773 <dd>Two declarations of an object with hidden visibility refer to the same
774 object if they are in the same shared object. Usually, hidden visibility
775 indicates that the symbol will not be placed into the dynamic symbol
776 table, so no other module (executable or shared library) can reference it
779 <dt><b>"<tt>protected</tt>" - Protected style</b>:</dt>
780 <dd>On ELF, protected visibility indicates that the symbol will be placed in
781 the dynamic symbol table, but that references within the defining module
782 will bind to the local symbol. That is, the symbol cannot be overridden by
788 <!-- ======================================================================= -->
790 <a name="namedtypes">Named Types</a>
795 <p>LLVM IR allows you to specify name aliases for certain types. This can make
796 it easier to read the IR and make the IR more condensed (particularly when
797 recursive types are involved). An example of a name specification is:</p>
799 <pre class="doc_code">
800 %mytype = type { %mytype*, i32 }
803 <p>You may give a name to any <a href="#typesystem">type</a> except
804 "<a href="#t_void">void</a>". Type name aliases may be used anywhere a type
805 is expected with the syntax "%mytype".</p>
807 <p>Note that type names are aliases for the structural type that they indicate,
808 and that you can therefore specify multiple names for the same type. This
809 often leads to confusing behavior when dumping out a .ll file. Since LLVM IR
810 uses structural typing, the name is not part of the type. When printing out
811 LLVM IR, the printer will pick <em>one name</em> to render all types of a
812 particular shape. This means that if you have code where two different
813 source types end up having the same LLVM type, that the dumper will sometimes
814 print the "wrong" or unexpected type. This is an important design point and
815 isn't going to change.</p>
819 <!-- ======================================================================= -->
821 <a name="globalvars">Global Variables</a>
826 <p>Global variables define regions of memory allocated at compilation time
827 instead of run-time. Global variables may optionally be initialized, may
828 have an explicit section to be placed in, and may have an optional explicit
829 alignment specified. A variable may be defined as "thread_local", which
830 means that it will not be shared by threads (each thread will have a
831 separated copy of the variable). A variable may be defined as a global
832 "constant," which indicates that the contents of the variable
833 will <b>never</b> be modified (enabling better optimization, allowing the
834 global data to be placed in the read-only section of an executable, etc).
835 Note that variables that need runtime initialization cannot be marked
836 "constant" as there is a store to the variable.</p>
838 <p>LLVM explicitly allows <em>declarations</em> of global variables to be marked
839 constant, even if the final definition of the global is not. This capability
840 can be used to enable slightly better optimization of the program, but
841 requires the language definition to guarantee that optimizations based on the
842 'constantness' are valid for the translation units that do not include the
845 <p>As SSA values, global variables define pointer values that are in scope
846 (i.e. they dominate) all basic blocks in the program. Global variables
847 always define a pointer to their "content" type because they describe a
848 region of memory, and all memory objects in LLVM are accessed through
851 <p>Global variables can be marked with <tt>unnamed_addr</tt> which indicates
852 that the address is not significant, only the content. Constants marked
853 like this can be merged with other constants if they have the same
854 initializer. Note that a constant with significant address <em>can</em>
855 be merged with a <tt>unnamed_addr</tt> constant, the result being a
856 constant whose address is significant.</p>
858 <p>A global variable may be declared to reside in a target-specific numbered
859 address space. For targets that support them, address spaces may affect how
860 optimizations are performed and/or what target instructions are used to
861 access the variable. The default address space is zero. The address space
862 qualifier must precede any other attributes.</p>
864 <p>LLVM allows an explicit section to be specified for globals. If the target
865 supports it, it will emit globals to the section specified.</p>
867 <p>An explicit alignment may be specified for a global, which must be a power
868 of 2. If not present, or if the alignment is set to zero, the alignment of
869 the global is set by the target to whatever it feels convenient. If an
870 explicit alignment is specified, the global is forced to have exactly that
871 alignment. Targets and optimizers are not allowed to over-align the global
872 if the global has an assigned section. In this case, the extra alignment
873 could be observable: for example, code could assume that the globals are
874 densely packed in their section and try to iterate over them as an array,
875 alignment padding would break this iteration.</p>
877 <p>For example, the following defines a global in a numbered address space with
878 an initializer, section, and alignment:</p>
880 <pre class="doc_code">
881 @G = addrspace(5) constant float 1.0, section "foo", align 4
887 <!-- ======================================================================= -->
889 <a name="functionstructure">Functions</a>
894 <p>LLVM function definitions consist of the "<tt>define</tt>" keyword, an
895 optional <a href="#linkage">linkage type</a>, an optional
896 <a href="#visibility">visibility style</a>, an optional
897 <a href="#callingconv">calling convention</a>,
898 an optional <tt>unnamed_addr</tt> attribute, a return type, an optional
899 <a href="#paramattrs">parameter attribute</a> for the return type, a function
900 name, a (possibly empty) argument list (each with optional
901 <a href="#paramattrs">parameter attributes</a>), optional
902 <a href="#fnattrs">function attributes</a>, an optional section, an optional
903 alignment, an optional <a href="#gc">garbage collector name</a>, an opening
904 curly brace, a list of basic blocks, and a closing curly brace.</p>
906 <p>LLVM function declarations consist of the "<tt>declare</tt>" keyword, an
907 optional <a href="#linkage">linkage type</a>, an optional
908 <a href="#visibility">visibility style</a>, an optional
909 <a href="#callingconv">calling convention</a>,
910 an optional <tt>unnamed_addr</tt> attribute, a return type, an optional
911 <a href="#paramattrs">parameter attribute</a> for the return type, a function
912 name, a possibly empty list of arguments, an optional alignment, and an
913 optional <a href="#gc">garbage collector name</a>.</p>
915 <p>A function definition contains a list of basic blocks, forming the CFG
916 (Control Flow Graph) for the function. Each basic block may optionally start
917 with a label (giving the basic block a symbol table entry), contains a list
918 of instructions, and ends with a <a href="#terminators">terminator</a>
919 instruction (such as a branch or function return).</p>
921 <p>The first basic block in a function is special in two ways: it is immediately
922 executed on entrance to the function, and it is not allowed to have
923 predecessor basic blocks (i.e. there can not be any branches to the entry
924 block of a function). Because the block can have no predecessors, it also
925 cannot have any <a href="#i_phi">PHI nodes</a>.</p>
927 <p>LLVM allows an explicit section to be specified for functions. If the target
928 supports it, it will emit functions to the section specified.</p>
930 <p>An explicit alignment may be specified for a function. If not present, or if
931 the alignment is set to zero, the alignment of the function is set by the
932 target to whatever it feels convenient. If an explicit alignment is
933 specified, the function is forced to have at least that much alignment. All
934 alignments must be a power of 2.</p>
936 <p>If the <tt>unnamed_addr</tt> attribute is given, the address is know to not
937 be significant and two identical functions can be merged.</p>
940 <pre class="doc_code">
941 define [<a href="#linkage">linkage</a>] [<a href="#visibility">visibility</a>]
942 [<a href="#callingconv">cconv</a>] [<a href="#paramattrs">ret attrs</a>]
943 <ResultType> @<FunctionName> ([argument list])
944 [<a href="#fnattrs">fn Attrs</a>] [section "name"] [align N]
945 [<a href="#gc">gc</a>] { ... }
950 <!-- ======================================================================= -->
952 <a name="aliasstructure">Aliases</a>
957 <p>Aliases act as "second name" for the aliasee value (which can be either
958 function, global variable, another alias or bitcast of global value). Aliases
959 may have an optional <a href="#linkage">linkage type</a>, and an
960 optional <a href="#visibility">visibility style</a>.</p>
963 <pre class="doc_code">
964 @<Name> = alias [Linkage] [Visibility] <AliaseeTy> @<Aliasee>
969 <!-- ======================================================================= -->
971 <a name="namedmetadatastructure">Named Metadata</a>
976 <p>Named metadata is a collection of metadata. <a href="#metadata">Metadata
977 nodes</a> (but not metadata strings) are the only valid operands for
978 a named metadata.</p>
981 <pre class="doc_code">
982 ; Some unnamed metadata nodes, which are referenced by the named metadata.
983 !0 = metadata !{metadata !"zero"}
984 !1 = metadata !{metadata !"one"}
985 !2 = metadata !{metadata !"two"}
987 !name = !{!0, !1, !2}
992 <!-- ======================================================================= -->
994 <a name="paramattrs">Parameter Attributes</a>
999 <p>The return type and each parameter of a function type may have a set of
1000 <i>parameter attributes</i> associated with them. Parameter attributes are
1001 used to communicate additional information about the result or parameters of
1002 a function. Parameter attributes are considered to be part of the function,
1003 not of the function type, so functions with different parameter attributes
1004 can have the same function type.</p>
1006 <p>Parameter attributes are simple keywords that follow the type specified. If
1007 multiple parameter attributes are needed, they are space separated. For
1010 <pre class="doc_code">
1011 declare i32 @printf(i8* noalias nocapture, ...)
1012 declare i32 @atoi(i8 zeroext)
1013 declare signext i8 @returns_signed_char()
1016 <p>Note that any attributes for the function result (<tt>nounwind</tt>,
1017 <tt>readonly</tt>) come immediately after the argument list.</p>
1019 <p>Currently, only the following parameter attributes are defined:</p>
1022 <dt><tt><b>zeroext</b></tt></dt>
1023 <dd>This indicates to the code generator that the parameter or return value
1024 should be zero-extended to the extent required by the target's ABI (which
1025 is usually 32-bits, but is 8-bits for a i1 on x86-64) by the caller (for a
1026 parameter) or the callee (for a return value).</dd>
1028 <dt><tt><b>signext</b></tt></dt>
1029 <dd>This indicates to the code generator that the parameter or return value
1030 should be sign-extended to the extent required by the target's ABI (which
1031 is usually 32-bits) by the caller (for a parameter) or the callee (for a
1034 <dt><tt><b>inreg</b></tt></dt>
1035 <dd>This indicates that this parameter or return value should be treated in a
1036 special target-dependent fashion during while emitting code for a function
1037 call or return (usually, by putting it in a register as opposed to memory,
1038 though some targets use it to distinguish between two different kinds of
1039 registers). Use of this attribute is target-specific.</dd>
1041 <dt><tt><b><a name="byval">byval</a></b></tt></dt>
1042 <dd><p>This indicates that the pointer parameter should really be passed by
1043 value to the function. The attribute implies that a hidden copy of the
1045 is made between the caller and the callee, so the callee is unable to
1046 modify the value in the callee. This attribute is only valid on LLVM
1047 pointer arguments. It is generally used to pass structs and arrays by
1048 value, but is also valid on pointers to scalars. The copy is considered
1049 to belong to the caller not the callee (for example,
1050 <tt><a href="#readonly">readonly</a></tt> functions should not write to
1051 <tt>byval</tt> parameters). This is not a valid attribute for return
1054 <p>The byval attribute also supports specifying an alignment with
1055 the align attribute. It indicates the alignment of the stack slot to
1056 form and the known alignment of the pointer specified to the call site. If
1057 the alignment is not specified, then the code generator makes a
1058 target-specific assumption.</p></dd>
1060 <dt><tt><b><a name="sret">sret</a></b></tt></dt>
1061 <dd>This indicates that the pointer parameter specifies the address of a
1062 structure that is the return value of the function in the source program.
1063 This pointer must be guaranteed by the caller to be valid: loads and
1064 stores to the structure may be assumed by the callee to not to trap. This
1065 may only be applied to the first parameter. This is not a valid attribute
1066 for return values. </dd>
1068 <dt><tt><b><a name="noalias">noalias</a></b></tt></dt>
1069 <dd>This indicates that pointer values
1070 <a href="#pointeraliasing"><i>based</i></a> on the argument or return
1071 value do not alias pointer values which are not <i>based</i> on it,
1072 ignoring certain "irrelevant" dependencies.
1073 For a call to the parent function, dependencies between memory
1074 references from before or after the call and from those during the call
1075 are "irrelevant" to the <tt>noalias</tt> keyword for the arguments and
1076 return value used in that call.
1077 The caller shares the responsibility with the callee for ensuring that
1078 these requirements are met.
1079 For further details, please see the discussion of the NoAlias response in
1080 <a href="AliasAnalysis.html#MustMayNo">alias analysis</a>.<br>
1082 Note that this definition of <tt>noalias</tt> is intentionally
1083 similar to the definition of <tt>restrict</tt> in C99 for function
1084 arguments, though it is slightly weaker.
1086 For function return values, C99's <tt>restrict</tt> is not meaningful,
1087 while LLVM's <tt>noalias</tt> is.
1090 <dt><tt><b><a name="nocapture">nocapture</a></b></tt></dt>
1091 <dd>This indicates that the callee does not make any copies of the pointer
1092 that outlive the callee itself. This is not a valid attribute for return
1095 <dt><tt><b><a name="nest">nest</a></b></tt></dt>
1096 <dd>This indicates that the pointer parameter can be excised using the
1097 <a href="#int_trampoline">trampoline intrinsics</a>. This is not a valid
1098 attribute for return values.</dd>
1103 <!-- ======================================================================= -->
1105 <a name="gc">Garbage Collector Names</a>
1110 <p>Each function may specify a garbage collector name, which is simply a
1113 <pre class="doc_code">
1114 define void @f() gc "name" { ... }
1117 <p>The compiler declares the supported values of <i>name</i>. Specifying a
1118 collector which will cause the compiler to alter its output in order to
1119 support the named garbage collection algorithm.</p>
1123 <!-- ======================================================================= -->
1125 <a name="fnattrs">Function Attributes</a>
1130 <p>Function attributes are set to communicate additional information about a
1131 function. Function attributes are considered to be part of the function, not
1132 of the function type, so functions with different parameter attributes can
1133 have the same function type.</p>
1135 <p>Function attributes are simple keywords that follow the type specified. If
1136 multiple attributes are needed, they are space separated. For example:</p>
1138 <pre class="doc_code">
1139 define void @f() noinline { ... }
1140 define void @f() alwaysinline { ... }
1141 define void @f() alwaysinline optsize { ... }
1142 define void @f() optsize { ... }
1146 <dt><tt><b>alignstack(<<em>n</em>>)</b></tt></dt>
1147 <dd>This attribute indicates that, when emitting the prologue and epilogue,
1148 the backend should forcibly align the stack pointer. Specify the
1149 desired alignment, which must be a power of two, in parentheses.
1151 <dt><tt><b>alwaysinline</b></tt></dt>
1152 <dd>This attribute indicates that the inliner should attempt to inline this
1153 function into callers whenever possible, ignoring any active inlining size
1154 threshold for this caller.</dd>
1156 <dt><tt><b>nonlazybind</b></tt></dt>
1157 <dd>This attribute suppresses lazy symbol binding for the function. This
1158 may make calls to the function faster, at the cost of extra program
1159 startup time if the function is not called during program startup.</dd>
1161 <dt><tt><b>inlinehint</b></tt></dt>
1162 <dd>This attribute indicates that the source code contained a hint that inlining
1163 this function is desirable (such as the "inline" keyword in C/C++). It
1164 is just a hint; it imposes no requirements on the inliner.</dd>
1166 <dt><tt><b>naked</b></tt></dt>
1167 <dd>This attribute disables prologue / epilogue emission for the function.
1168 This can have very system-specific consequences.</dd>
1170 <dt><tt><b>noimplicitfloat</b></tt></dt>
1171 <dd>This attributes disables implicit floating point instructions.</dd>
1173 <dt><tt><b>noinline</b></tt></dt>
1174 <dd>This attribute indicates that the inliner should never inline this
1175 function in any situation. This attribute may not be used together with
1176 the <tt>alwaysinline</tt> attribute.</dd>
1178 <dt><tt><b>noredzone</b></tt></dt>
1179 <dd>This attribute indicates that the code generator should not use a red
1180 zone, even if the target-specific ABI normally permits it.</dd>
1182 <dt><tt><b>noreturn</b></tt></dt>
1183 <dd>This function attribute indicates that the function never returns
1184 normally. This produces undefined behavior at runtime if the function
1185 ever does dynamically return.</dd>
1187 <dt><tt><b>nounwind</b></tt></dt>
1188 <dd>This function attribute indicates that the function never returns with an
1189 unwind or exceptional control flow. If the function does unwind, its
1190 runtime behavior is undefined.</dd>
1192 <dt><tt><b>optsize</b></tt></dt>
1193 <dd>This attribute suggests that optimization passes and code generator passes
1194 make choices that keep the code size of this function low, and otherwise
1195 do optimizations specifically to reduce code size.</dd>
1197 <dt><tt><b>readnone</b></tt></dt>
1198 <dd>This attribute indicates that the function computes its result (or decides
1199 to unwind an exception) based strictly on its arguments, without
1200 dereferencing any pointer arguments or otherwise accessing any mutable
1201 state (e.g. memory, control registers, etc) visible to caller functions.
1202 It does not write through any pointer arguments
1203 (including <tt><a href="#byval">byval</a></tt> arguments) and never
1204 changes any state visible to callers. This means that it cannot unwind
1205 exceptions by calling the <tt>C++</tt> exception throwing methods, but
1206 could use the <tt>unwind</tt> instruction.</dd>
1208 <dt><tt><b><a name="readonly">readonly</a></b></tt></dt>
1209 <dd>This attribute indicates that the function does not write through any
1210 pointer arguments (including <tt><a href="#byval">byval</a></tt>
1211 arguments) or otherwise modify any state (e.g. memory, control registers,
1212 etc) visible to caller functions. It may dereference pointer arguments
1213 and read state that may be set in the caller. A readonly function always
1214 returns the same value (or unwinds an exception identically) when called
1215 with the same set of arguments and global state. It cannot unwind an
1216 exception by calling the <tt>C++</tt> exception throwing methods, but may
1217 use the <tt>unwind</tt> instruction.</dd>
1219 <dt><tt><b><a name="returns_twice">returns_twice</a></b></tt></dt>
1220 <dd>This attribute indicates that this function can return twice. The
1221 C <code>setjmp</code> is an example of such a function. The compiler
1222 disables some optimizations (like tail calls) in the caller of these
1225 <dt><tt><b><a name="ssp">ssp</a></b></tt></dt>
1226 <dd>This attribute indicates that the function should emit a stack smashing
1227 protector. It is in the form of a "canary"—a random value placed on
1228 the stack before the local variables that's checked upon return from the
1229 function to see if it has been overwritten. A heuristic is used to
1230 determine if a function needs stack protectors or not.<br>
1232 If a function that has an <tt>ssp</tt> attribute is inlined into a
1233 function that doesn't have an <tt>ssp</tt> attribute, then the resulting
1234 function will have an <tt>ssp</tt> attribute.</dd>
1236 <dt><tt><b>sspreq</b></tt></dt>
1237 <dd>This attribute indicates that the function should <em>always</em> emit a
1238 stack smashing protector. This overrides
1239 the <tt><a href="#ssp">ssp</a></tt> function attribute.<br>
1241 If a function that has an <tt>sspreq</tt> attribute is inlined into a
1242 function that doesn't have an <tt>sspreq</tt> attribute or which has
1243 an <tt>ssp</tt> attribute, then the resulting function will have
1244 an <tt>sspreq</tt> attribute.</dd>
1246 <dt><tt><b><a name="uwtable">uwtable</a></b></tt></dt>
1247 <dd>This attribute indicates that the ABI being targeted requires that
1248 an unwind table entry be produce for this function even if we can
1249 show that no exceptions passes by it. This is normally the case for
1250 the ELF x86-64 abi, but it can be disabled for some compilation
1256 <!-- ======================================================================= -->
1258 <a name="moduleasm">Module-Level Inline Assembly</a>
1263 <p>Modules may contain "module-level inline asm" blocks, which corresponds to
1264 the GCC "file scope inline asm" blocks. These blocks are internally
1265 concatenated by LLVM and treated as a single unit, but may be separated in
1266 the <tt>.ll</tt> file if desired. The syntax is very simple:</p>
1268 <pre class="doc_code">
1269 module asm "inline asm code goes here"
1270 module asm "more can go here"
1273 <p>The strings can contain any character by escaping non-printable characters.
1274 The escape sequence used is simply "\xx" where "xx" is the two digit hex code
1277 <p>The inline asm code is simply printed to the machine code .s file when
1278 assembly code is generated.</p>
1282 <!-- ======================================================================= -->
1284 <a name="datalayout">Data Layout</a>
1289 <p>A module may specify a target specific data layout string that specifies how
1290 data is to be laid out in memory. The syntax for the data layout is
1293 <pre class="doc_code">
1294 target datalayout = "<i>layout specification</i>"
1297 <p>The <i>layout specification</i> consists of a list of specifications
1298 separated by the minus sign character ('-'). Each specification starts with
1299 a letter and may include other information after the letter to define some
1300 aspect of the data layout. The specifications accepted are as follows:</p>
1304 <dd>Specifies that the target lays out data in big-endian form. That is, the
1305 bits with the most significance have the lowest address location.</dd>
1308 <dd>Specifies that the target lays out data in little-endian form. That is,
1309 the bits with the least significance have the lowest address
1312 <dt><tt>S<i>size</i></tt></dt>
1313 <dd>Specifies the natural alignment of the stack in bits. Alignment promotion
1314 of stack variables is limited to the natural stack alignment to avoid
1315 dynamic stack realignment. The stack alignment must be a multiple of
1316 8-bits. If omitted, the natural stack alignment defaults to "unspecified",
1317 which does not prevent any alignment promotions.</dd>
1319 <dt><tt>p:<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
1320 <dd>This specifies the <i>size</i> of a pointer and its <i>abi</i> and
1321 <i>preferred</i> alignments. All sizes are in bits. Specifying
1322 the <i>pref</i> alignment is optional. If omitted, the
1323 preceding <tt>:</tt> should be omitted too.</dd>
1325 <dt><tt>i<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
1326 <dd>This specifies the alignment for an integer type of a given bit
1327 <i>size</i>. The value of <i>size</i> must be in the range [1,2^23).</dd>
1329 <dt><tt>v<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
1330 <dd>This specifies the alignment for a vector type of a given bit
1333 <dt><tt>f<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
1334 <dd>This specifies the alignment for a floating point type of a given bit
1335 <i>size</i>. Only values of <i>size</i> that are supported by the target
1336 will work. 32 (float) and 64 (double) are supported on all targets;
1337 80 or 128 (different flavors of long double) are also supported on some
1340 <dt><tt>a<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
1341 <dd>This specifies the alignment for an aggregate type of a given bit
1344 <dt><tt>s<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
1345 <dd>This specifies the alignment for a stack object of a given bit
1348 <dt><tt>n<i>size1</i>:<i>size2</i>:<i>size3</i>...</tt></dt>
1349 <dd>This specifies a set of native integer widths for the target CPU
1350 in bits. For example, it might contain "n32" for 32-bit PowerPC,
1351 "n32:64" for PowerPC 64, or "n8:16:32:64" for X86-64. Elements of
1352 this set are considered to support most general arithmetic
1353 operations efficiently.</dd>
1356 <p>When constructing the data layout for a given target, LLVM starts with a
1357 default set of specifications which are then (possibly) overridden by the
1358 specifications in the <tt>datalayout</tt> keyword. The default specifications
1359 are given in this list:</p>
1362 <li><tt>E</tt> - big endian</li>
1363 <li><tt>p:64:64:64</tt> - 64-bit pointers with 64-bit alignment</li>
1364 <li><tt>i1:8:8</tt> - i1 is 8-bit (byte) aligned</li>
1365 <li><tt>i8:8:8</tt> - i8 is 8-bit (byte) aligned</li>
1366 <li><tt>i16:16:16</tt> - i16 is 16-bit aligned</li>
1367 <li><tt>i32:32:32</tt> - i32 is 32-bit aligned</li>
1368 <li><tt>i64:32:64</tt> - i64 has ABI alignment of 32-bits but preferred
1369 alignment of 64-bits</li>
1370 <li><tt>f32:32:32</tt> - float is 32-bit aligned</li>
1371 <li><tt>f64:64:64</tt> - double is 64-bit aligned</li>
1372 <li><tt>v64:64:64</tt> - 64-bit vector is 64-bit aligned</li>
1373 <li><tt>v128:128:128</tt> - 128-bit vector is 128-bit aligned</li>
1374 <li><tt>a0:0:1</tt> - aggregates are 8-bit aligned</li>
1375 <li><tt>s0:64:64</tt> - stack objects are 64-bit aligned</li>
1378 <p>When LLVM is determining the alignment for a given type, it uses the
1379 following rules:</p>
1382 <li>If the type sought is an exact match for one of the specifications, that
1383 specification is used.</li>
1385 <li>If no match is found, and the type sought is an integer type, then the
1386 smallest integer type that is larger than the bitwidth of the sought type
1387 is used. If none of the specifications are larger than the bitwidth then
1388 the the largest integer type is used. For example, given the default
1389 specifications above, the i7 type will use the alignment of i8 (next
1390 largest) while both i65 and i256 will use the alignment of i64 (largest
1393 <li>If no match is found, and the type sought is a vector type, then the
1394 largest vector type that is smaller than the sought vector type will be
1395 used as a fall back. This happens because <128 x double> can be
1396 implemented in terms of 64 <2 x double>, for example.</li>
1399 <p>The function of the data layout string may not be what you expect. Notably,
1400 this is not a specification from the frontend of what alignment the code
1401 generator should use.</p>
1403 <p>Instead, if specified, the target data layout is required to match what the
1404 ultimate <em>code generator</em> expects. This string is used by the
1405 mid-level optimizers to
1406 improve code, and this only works if it matches what the ultimate code
1407 generator uses. If you would like to generate IR that does not embed this
1408 target-specific detail into the IR, then you don't have to specify the
1409 string. This will disable some optimizations that require precise layout
1410 information, but this also prevents those optimizations from introducing
1411 target specificity into the IR.</p>
1417 <!-- ======================================================================= -->
1419 <a name="pointeraliasing">Pointer Aliasing Rules</a>
1424 <p>Any memory access must be done through a pointer value associated
1425 with an address range of the memory access, otherwise the behavior
1426 is undefined. Pointer values are associated with address ranges
1427 according to the following rules:</p>
1430 <li>A pointer value is associated with the addresses associated with
1431 any value it is <i>based</i> on.
1432 <li>An address of a global variable is associated with the address
1433 range of the variable's storage.</li>
1434 <li>The result value of an allocation instruction is associated with
1435 the address range of the allocated storage.</li>
1436 <li>A null pointer in the default address-space is associated with
1438 <li>An integer constant other than zero or a pointer value returned
1439 from a function not defined within LLVM may be associated with address
1440 ranges allocated through mechanisms other than those provided by
1441 LLVM. Such ranges shall not overlap with any ranges of addresses
1442 allocated by mechanisms provided by LLVM.</li>
1445 <p>A pointer value is <i>based</i> on another pointer value according
1446 to the following rules:</p>
1449 <li>A pointer value formed from a
1450 <tt><a href="#i_getelementptr">getelementptr</a></tt> operation
1451 is <i>based</i> on the first operand of the <tt>getelementptr</tt>.</li>
1452 <li>The result value of a
1453 <tt><a href="#i_bitcast">bitcast</a></tt> is <i>based</i> on the operand
1454 of the <tt>bitcast</tt>.</li>
1455 <li>A pointer value formed by an
1456 <tt><a href="#i_inttoptr">inttoptr</a></tt> is <i>based</i> on all
1457 pointer values that contribute (directly or indirectly) to the
1458 computation of the pointer's value.</li>
1459 <li>The "<i>based</i> on" relationship is transitive.</li>
1462 <p>Note that this definition of <i>"based"</i> is intentionally
1463 similar to the definition of <i>"based"</i> in C99, though it is
1464 slightly weaker.</p>
1466 <p>LLVM IR does not associate types with memory. The result type of a
1467 <tt><a href="#i_load">load</a></tt> merely indicates the size and
1468 alignment of the memory from which to load, as well as the
1469 interpretation of the value. The first operand type of a
1470 <tt><a href="#i_store">store</a></tt> similarly only indicates the size
1471 and alignment of the store.</p>
1473 <p>Consequently, type-based alias analysis, aka TBAA, aka
1474 <tt>-fstrict-aliasing</tt>, is not applicable to general unadorned
1475 LLVM IR. <a href="#metadata">Metadata</a> may be used to encode
1476 additional information which specialized optimization passes may use
1477 to implement type-based alias analysis.</p>
1481 <!-- ======================================================================= -->
1483 <a name="volatile">Volatile Memory Accesses</a>
1488 <p>Certain memory accesses, such as <a href="#i_load"><tt>load</tt></a>s, <a
1489 href="#i_store"><tt>store</tt></a>s, and <a
1490 href="#int_memcpy"><tt>llvm.memcpy</tt></a>s may be marked <tt>volatile</tt>.
1491 The optimizers must not change the number of volatile operations or change their
1492 order of execution relative to other volatile operations. The optimizers
1493 <i>may</i> change the order of volatile operations relative to non-volatile
1494 operations. This is not Java's "volatile" and has no cross-thread
1495 synchronization behavior.</p>
1499 <!-- ======================================================================= -->
1501 <a name="memmodel">Memory Model for Concurrent Operations</a>
1506 <p>The LLVM IR does not define any way to start parallel threads of execution
1507 or to register signal handlers. Nonetheless, there are platform-specific
1508 ways to create them, and we define LLVM IR's behavior in their presence. This
1509 model is inspired by the C++0x memory model.</p>
1511 <p>For a more informal introduction to this model, see the
1512 <a href="Atomics.html">LLVM Atomic Instructions and Concurrency Guide</a>.
1514 <p>We define a <i>happens-before</i> partial order as the least partial order
1517 <li>Is a superset of single-thread program order, and</li>
1518 <li>When a <i>synchronizes-with</i> <tt>b</tt>, includes an edge from
1519 <tt>a</tt> to <tt>b</tt>. <i>Synchronizes-with</i> pairs are introduced
1520 by platform-specific techniques, like pthread locks, thread
1521 creation, thread joining, etc., and by atomic instructions.
1522 (See also <a href="#ordering">Atomic Memory Ordering Constraints</a>).
1526 <p>Note that program order does not introduce <i>happens-before</i> edges
1527 between a thread and signals executing inside that thread.</p>
1529 <p>Every (defined) read operation (load instructions, memcpy, atomic
1530 loads/read-modify-writes, etc.) <var>R</var> reads a series of bytes written by
1531 (defined) write operations (store instructions, atomic
1532 stores/read-modify-writes, memcpy, etc.). For the purposes of this section,
1533 initialized globals are considered to have a write of the initializer which is
1534 atomic and happens before any other read or write of the memory in question.
1535 For each byte of a read <var>R</var>, <var>R<sub>byte</sub></var> may see
1536 any write to the same byte, except:</p>
1539 <li>If <var>write<sub>1</sub></var> happens before
1540 <var>write<sub>2</sub></var>, and <var>write<sub>2</sub></var> happens
1541 before <var>R<sub>byte</sub></var>, then <var>R<sub>byte</sub></var>
1542 does not see <var>write<sub>1</sub></var>.
1543 <li>If <var>R<sub>byte</sub></var> happens before
1544 <var>write<sub>3</sub></var>, then <var>R<sub>byte</sub></var> does not
1545 see <var>write<sub>3</sub></var>.
1548 <p>Given that definition, <var>R<sub>byte</sub></var> is defined as follows:
1550 <li>If <var>R</var> is volatile, the result is target-dependent. (Volatile
1551 is supposed to give guarantees which can support
1552 <code>sig_atomic_t</code> in C/C++, and may be used for accesses to
1553 addresses which do not behave like normal memory. It does not generally
1554 provide cross-thread synchronization.)
1555 <li>Otherwise, if there is no write to the same byte that happens before
1556 <var>R<sub>byte</sub></var>, <var>R<sub>byte</sub></var> returns
1557 <tt>undef</tt> for that byte.
1558 <li>Otherwise, if <var>R<sub>byte</sub></var> may see exactly one write,
1559 <var>R<sub>byte</sub></var> returns the value written by that
1561 <li>Otherwise, if <var>R</var> is atomic, and all the writes
1562 <var>R<sub>byte</sub></var> may see are atomic, it chooses one of the
1563 values written. See the <a href="#ordering">Atomic Memory Ordering
1564 Constraints</a> section for additional constraints on how the choice
1566 <li>Otherwise <var>R<sub>byte</sub></var> returns <tt>undef</tt>.</li>
1569 <p><var>R</var> returns the value composed of the series of bytes it read.
1570 This implies that some bytes within the value may be <tt>undef</tt>
1571 <b>without</b> the entire value being <tt>undef</tt>. Note that this only
1572 defines the semantics of the operation; it doesn't mean that targets will
1573 emit more than one instruction to read the series of bytes.</p>
1575 <p>Note that in cases where none of the atomic intrinsics are used, this model
1576 places only one restriction on IR transformations on top of what is required
1577 for single-threaded execution: introducing a store to a byte which might not
1578 otherwise be stored is not allowed in general. (Specifically, in the case
1579 where another thread might write to and read from an address, introducing a
1580 store can change a load that may see exactly one write into a load that may
1581 see multiple writes.)</p>
1583 <!-- FIXME: This model assumes all targets where concurrency is relevant have
1584 a byte-size store which doesn't affect adjacent bytes. As far as I can tell,
1585 none of the backends currently in the tree fall into this category; however,
1586 there might be targets which care. If there are, we want a paragraph
1589 Targets may specify that stores narrower than a certain width are not
1590 available; on such a target, for the purposes of this model, treat any
1591 non-atomic write with an alignment or width less than the minimum width
1592 as if it writes to the relevant surrounding bytes.
1597 <!-- ======================================================================= -->
1599 <a name="ordering">Atomic Memory Ordering Constraints</a>
1604 <p>Atomic instructions (<a href="#i_cmpxchg"><code>cmpxchg</code></a>,
1605 <a href="#i_atomicrmw"><code>atomicrmw</code></a>,
1606 <a href="#i_fence"><code>fence</code></a>,
1607 <a href="#i_load"><code>atomic load</code></a>, and
1608 <a href="#i_store"><code>atomic store</code></a>) take an ordering parameter
1609 that determines which other atomic instructions on the same address they
1610 <i>synchronize with</i>. These semantics are borrowed from Java and C++0x,
1611 but are somewhat more colloquial. If these descriptions aren't precise enough,
1612 check those specs (see spec references in the
1613 <a href="Atomic.html#introduction">atomics guide</a>).
1614 <a href="#i_fence"><code>fence</code></a> instructions
1615 treat these orderings somewhat differently since they don't take an address.
1616 See that instruction's documentation for details.</p>
1618 <p>For a simpler introduction to the ordering constraints, see the
1619 <a href="Atomics.html">LLVM Atomic Instructions and Concurrency Guide</a>.</p>
1622 <dt><code>unordered</code></dt>
1623 <dd>The set of values that can be read is governed by the happens-before
1624 partial order. A value cannot be read unless some operation wrote it.
1625 This is intended to provide a guarantee strong enough to model Java's
1626 non-volatile shared variables. This ordering cannot be specified for
1627 read-modify-write operations; it is not strong enough to make them atomic
1628 in any interesting way.</dd>
1629 <dt><code>monotonic</code></dt>
1630 <dd>In addition to the guarantees of <code>unordered</code>, there is a single
1631 total order for modifications by <code>monotonic</code> operations on each
1632 address. All modification orders must be compatible with the happens-before
1633 order. There is no guarantee that the modification orders can be combined to
1634 a global total order for the whole program (and this often will not be
1635 possible). The read in an atomic read-modify-write operation
1636 (<a href="#i_cmpxchg"><code>cmpxchg</code></a> and
1637 <a href="#i_atomicrmw"><code>atomicrmw</code></a>)
1638 reads the value in the modification order immediately before the value it
1639 writes. If one atomic read happens before another atomic read of the same
1640 address, the later read must see the same value or a later value in the
1641 address's modification order. This disallows reordering of
1642 <code>monotonic</code> (or stronger) operations on the same address. If an
1643 address is written <code>monotonic</code>ally by one thread, and other threads
1644 <code>monotonic</code>ally read that address repeatedly, the other threads must
1645 eventually see the write. This corresponds to the C++0x/C1x
1646 <code>memory_order_relaxed</code>.</dd>
1647 <dt><code>acquire</code></dt>
1648 <dd>In addition to the guarantees of <code>monotonic</code>,
1649 a <i>synchronizes-with</i> edge may be formed with a <code>release</code>
1650 operation. This is intended to model C++'s <code>memory_order_acquire</code>.</dd>
1651 <dt><code>release</code></dt>
1652 <dd>In addition to the guarantees of <code>monotonic</code>, if this operation
1653 writes a value which is subsequently read by an <code>acquire</code> operation,
1654 it <i>synchronizes-with</i> that operation. (This isn't a complete
1655 description; see the C++0x definition of a release sequence.) This corresponds
1656 to the C++0x/C1x <code>memory_order_release</code>.</dd>
1657 <dt><code>acq_rel</code> (acquire+release)</dt><dd>Acts as both an
1658 <code>acquire</code> and <code>release</code> operation on its address.
1659 This corresponds to the C++0x/C1x <code>memory_order_acq_rel</code>.</dd>
1660 <dt><code>seq_cst</code> (sequentially consistent)</dt><dd>
1661 <dd>In addition to the guarantees of <code>acq_rel</code>
1662 (<code>acquire</code> for an operation which only reads, <code>release</code>
1663 for an operation which only writes), there is a global total order on all
1664 sequentially-consistent operations on all addresses, which is consistent with
1665 the <i>happens-before</i> partial order and with the modification orders of
1666 all the affected addresses. Each sequentially-consistent read sees the last
1667 preceding write to the same address in this global order. This corresponds
1668 to the C++0x/C1x <code>memory_order_seq_cst</code> and Java volatile.</dd>
1671 <p id="singlethread">If an atomic operation is marked <code>singlethread</code>,
1672 it only <i>synchronizes with</i> or participates in modification and seq_cst
1673 total orderings with other operations running in the same thread (for example,
1674 in signal handlers).</p>
1680 <!-- *********************************************************************** -->
1681 <h2><a name="typesystem">Type System</a></h2>
1682 <!-- *********************************************************************** -->
1686 <p>The LLVM type system is one of the most important features of the
1687 intermediate representation. Being typed enables a number of optimizations
1688 to be performed on the intermediate representation directly, without having
1689 to do extra analyses on the side before the transformation. A strong type
1690 system makes it easier to read the generated code and enables novel analyses
1691 and transformations that are not feasible to perform on normal three address
1692 code representations.</p>
1694 <!-- ======================================================================= -->
1696 <a name="t_classifications">Type Classifications</a>
1701 <p>The types fall into a few useful classifications:</p>
1703 <table border="1" cellspacing="0" cellpadding="4">
1705 <tr><th>Classification</th><th>Types</th></tr>
1707 <td><a href="#t_integer">integer</a></td>
1708 <td><tt>i1, i2, i3, ... i8, ... i16, ... i32, ... i64, ... </tt></td>
1711 <td><a href="#t_floating">floating point</a></td>
1712 <td><tt>float, double, x86_fp80, fp128, ppc_fp128</tt></td>
1715 <td><a name="t_firstclass">first class</a></td>
1716 <td><a href="#t_integer">integer</a>,
1717 <a href="#t_floating">floating point</a>,
1718 <a href="#t_pointer">pointer</a>,
1719 <a href="#t_vector">vector</a>,
1720 <a href="#t_struct">structure</a>,
1721 <a href="#t_array">array</a>,
1722 <a href="#t_label">label</a>,
1723 <a href="#t_metadata">metadata</a>.
1727 <td><a href="#t_primitive">primitive</a></td>
1728 <td><a href="#t_label">label</a>,
1729 <a href="#t_void">void</a>,
1730 <a href="#t_integer">integer</a>,
1731 <a href="#t_floating">floating point</a>,
1732 <a href="#t_x86mmx">x86mmx</a>,
1733 <a href="#t_metadata">metadata</a>.</td>
1736 <td><a href="#t_derived">derived</a></td>
1737 <td><a href="#t_array">array</a>,
1738 <a href="#t_function">function</a>,
1739 <a href="#t_pointer">pointer</a>,
1740 <a href="#t_struct">structure</a>,
1741 <a href="#t_vector">vector</a>,
1742 <a href="#t_opaque">opaque</a>.
1748 <p>The <a href="#t_firstclass">first class</a> types are perhaps the most
1749 important. Values of these types are the only ones which can be produced by
1754 <!-- ======================================================================= -->
1756 <a name="t_primitive">Primitive Types</a>
1761 <p>The primitive types are the fundamental building blocks of the LLVM
1764 <!-- _______________________________________________________________________ -->
1766 <a name="t_integer">Integer Type</a>
1772 <p>The integer type is a very simple type that simply specifies an arbitrary
1773 bit width for the integer type desired. Any bit width from 1 bit to
1774 2<sup>23</sup>-1 (about 8 million) can be specified.</p>
1781 <p>The number of bits the integer will occupy is specified by the <tt>N</tt>
1785 <table class="layout">
1787 <td class="left"><tt>i1</tt></td>
1788 <td class="left">a single-bit integer.</td>
1791 <td class="left"><tt>i32</tt></td>
1792 <td class="left">a 32-bit integer.</td>
1795 <td class="left"><tt>i1942652</tt></td>
1796 <td class="left">a really big integer of over 1 million bits.</td>
1802 <!-- _______________________________________________________________________ -->
1804 <a name="t_floating">Floating Point Types</a>
1811 <tr><th>Type</th><th>Description</th></tr>
1812 <tr><td><tt>float</tt></td><td>32-bit floating point value</td></tr>
1813 <tr><td><tt>double</tt></td><td>64-bit floating point value</td></tr>
1814 <tr><td><tt>fp128</tt></td><td>128-bit floating point value (112-bit mantissa)</td></tr>
1815 <tr><td><tt>x86_fp80</tt></td><td>80-bit floating point value (X87)</td></tr>
1816 <tr><td><tt>ppc_fp128</tt></td><td>128-bit floating point value (two 64-bits)</td></tr>
1822 <!-- _______________________________________________________________________ -->
1824 <a name="t_x86mmx">X86mmx Type</a>
1830 <p>The x86mmx type represents a value held in an MMX register on an x86 machine. The operations allowed on it are quite limited: parameters and return values, load and store, and bitcast. User-specified MMX instructions are represented as intrinsic or asm calls with arguments and/or results of this type. There are no arrays, vectors or constants of this type.</p>
1839 <!-- _______________________________________________________________________ -->
1841 <a name="t_void">Void Type</a>
1847 <p>The void type does not represent any value and has no size.</p>
1856 <!-- _______________________________________________________________________ -->
1858 <a name="t_label">Label Type</a>
1864 <p>The label type represents code labels.</p>
1873 <!-- _______________________________________________________________________ -->
1875 <a name="t_metadata">Metadata Type</a>
1881 <p>The metadata type represents embedded metadata. No derived types may be
1882 created from metadata except for <a href="#t_function">function</a>
1894 <!-- ======================================================================= -->
1896 <a name="t_derived">Derived Types</a>
1901 <p>The real power in LLVM comes from the derived types in the system. This is
1902 what allows a programmer to represent arrays, functions, pointers, and other
1903 useful types. Each of these types contain one or more element types which
1904 may be a primitive type, or another derived type. For example, it is
1905 possible to have a two dimensional array, using an array as the element type
1906 of another array.</p>
1908 <!-- _______________________________________________________________________ -->
1910 <a name="t_aggregate">Aggregate Types</a>
1915 <p>Aggregate Types are a subset of derived types that can contain multiple
1916 member types. <a href="#t_array">Arrays</a>,
1917 <a href="#t_struct">structs</a>, and <a href="#t_vector">vectors</a> are
1918 aggregate types.</p>
1922 <!-- _______________________________________________________________________ -->
1924 <a name="t_array">Array Type</a>
1930 <p>The array type is a very simple derived type that arranges elements
1931 sequentially in memory. The array type requires a size (number of elements)
1932 and an underlying data type.</p>
1936 [<# elements> x <elementtype>]
1939 <p>The number of elements is a constant integer value; <tt>elementtype</tt> may
1940 be any type with a size.</p>
1943 <table class="layout">
1945 <td class="left"><tt>[40 x i32]</tt></td>
1946 <td class="left">Array of 40 32-bit integer values.</td>
1949 <td class="left"><tt>[41 x i32]</tt></td>
1950 <td class="left">Array of 41 32-bit integer values.</td>
1953 <td class="left"><tt>[4 x i8]</tt></td>
1954 <td class="left">Array of 4 8-bit integer values.</td>
1957 <p>Here are some examples of multidimensional arrays:</p>
1958 <table class="layout">
1960 <td class="left"><tt>[3 x [4 x i32]]</tt></td>
1961 <td class="left">3x4 array of 32-bit integer values.</td>
1964 <td class="left"><tt>[12 x [10 x float]]</tt></td>
1965 <td class="left">12x10 array of single precision floating point values.</td>
1968 <td class="left"><tt>[2 x [3 x [4 x i16]]]</tt></td>
1969 <td class="left">2x3x4 array of 16-bit integer values.</td>
1973 <p>There is no restriction on indexing beyond the end of the array implied by
1974 a static type (though there are restrictions on indexing beyond the bounds
1975 of an allocated object in some cases). This means that single-dimension
1976 'variable sized array' addressing can be implemented in LLVM with a zero
1977 length array type. An implementation of 'pascal style arrays' in LLVM could
1978 use the type "<tt>{ i32, [0 x float]}</tt>", for example.</p>
1982 <!-- _______________________________________________________________________ -->
1984 <a name="t_function">Function Type</a>
1990 <p>The function type can be thought of as a function signature. It consists of
1991 a return type and a list of formal parameter types. The return type of a
1992 function type is a first class type or a void type.</p>
1996 <returntype> (<parameter list>)
1999 <p>...where '<tt><parameter list></tt>' is a comma-separated list of type
2000 specifiers. Optionally, the parameter list may include a type <tt>...</tt>,
2001 which indicates that the function takes a variable number of arguments.
2002 Variable argument functions can access their arguments with
2003 the <a href="#int_varargs">variable argument handling intrinsic</a>
2004 functions. '<tt><returntype></tt>' is any type except
2005 <a href="#t_label">label</a>.</p>
2008 <table class="layout">
2010 <td class="left"><tt>i32 (i32)</tt></td>
2011 <td class="left">function taking an <tt>i32</tt>, returning an <tt>i32</tt>
2013 </tr><tr class="layout">
2014 <td class="left"><tt>float (i16, i32 *) *
2016 <td class="left"><a href="#t_pointer">Pointer</a> to a function that takes
2017 an <tt>i16</tt> and a <a href="#t_pointer">pointer</a> to <tt>i32</tt>,
2018 returning <tt>float</tt>.
2020 </tr><tr class="layout">
2021 <td class="left"><tt>i32 (i8*, ...)</tt></td>
2022 <td class="left">A vararg function that takes at least one
2023 <a href="#t_pointer">pointer</a> to <tt>i8 </tt> (char in C),
2024 which returns an integer. This is the signature for <tt>printf</tt> in
2027 </tr><tr class="layout">
2028 <td class="left"><tt>{i32, i32} (i32)</tt></td>
2029 <td class="left">A function taking an <tt>i32</tt>, returning a
2030 <a href="#t_struct">structure</a> containing two <tt>i32</tt> values
2037 <!-- _______________________________________________________________________ -->
2039 <a name="t_struct">Structure Type</a>
2045 <p>The structure type is used to represent a collection of data members together
2046 in memory. The elements of a structure may be any type that has a size.</p>
2048 <p>Structures in memory are accessed using '<tt><a href="#i_load">load</a></tt>'
2049 and '<tt><a href="#i_store">store</a></tt>' by getting a pointer to a field
2050 with the '<tt><a href="#i_getelementptr">getelementptr</a></tt>' instruction.
2051 Structures in registers are accessed using the
2052 '<tt><a href="#i_extractvalue">extractvalue</a></tt>' and
2053 '<tt><a href="#i_insertvalue">insertvalue</a></tt>' instructions.</p>
2055 <p>Structures may optionally be "packed" structures, which indicate that the
2056 alignment of the struct is one byte, and that there is no padding between
2057 the elements. In non-packed structs, padding between field types is inserted
2058 as defined by the TargetData string in the module, which is required to match
2059 what the underlying code generator expects.</p>
2061 <p>Structures can either be "literal" or "identified". A literal structure is
2062 defined inline with other types (e.g. <tt>{i32, i32}*</tt>) whereas identified
2063 types are always defined at the top level with a name. Literal types are
2064 uniqued by their contents and can never be recursive or opaque since there is
2065 no way to write one. Identified types can be recursive, can be opaqued, and are
2071 %T1 = type { <type list> } <i>; Identified normal struct type</i>
2072 %T2 = type <{ <type list> }> <i>; Identified packed struct type</i>
2076 <table class="layout">
2078 <td class="left"><tt>{ i32, i32, i32 }</tt></td>
2079 <td class="left">A triple of three <tt>i32</tt> values</td>
2082 <td class="left"><tt>{ float, i32 (i32) * }</tt></td>
2083 <td class="left">A pair, where the first element is a <tt>float</tt> and the
2084 second element is a <a href="#t_pointer">pointer</a> to a
2085 <a href="#t_function">function</a> that takes an <tt>i32</tt>, returning
2086 an <tt>i32</tt>.</td>
2089 <td class="left"><tt><{ i8, i32 }></tt></td>
2090 <td class="left">A packed struct known to be 5 bytes in size.</td>
2096 <!-- _______________________________________________________________________ -->
2098 <a name="t_opaque">Opaque Structure Types</a>
2104 <p>Opaque structure types are used to represent named structure types that do
2105 not have a body specified. This corresponds (for example) to the C notion of
2106 a forward declared structure.</p>
2115 <table class="layout">
2117 <td class="left"><tt>opaque</tt></td>
2118 <td class="left">An opaque type.</td>
2126 <!-- _______________________________________________________________________ -->
2128 <a name="t_pointer">Pointer Type</a>
2134 <p>The pointer type is used to specify memory locations.
2135 Pointers are commonly used to reference objects in memory.</p>
2137 <p>Pointer types may have an optional address space attribute defining the
2138 numbered address space where the pointed-to object resides. The default
2139 address space is number zero. The semantics of non-zero address
2140 spaces are target-specific.</p>
2142 <p>Note that LLVM does not permit pointers to void (<tt>void*</tt>) nor does it
2143 permit pointers to labels (<tt>label*</tt>). Use <tt>i8*</tt> instead.</p>
2151 <table class="layout">
2153 <td class="left"><tt>[4 x i32]*</tt></td>
2154 <td class="left">A <a href="#t_pointer">pointer</a> to <a
2155 href="#t_array">array</a> of four <tt>i32</tt> values.</td>
2158 <td class="left"><tt>i32 (i32*) *</tt></td>
2159 <td class="left"> A <a href="#t_pointer">pointer</a> to a <a
2160 href="#t_function">function</a> that takes an <tt>i32*</tt>, returning an
2164 <td class="left"><tt>i32 addrspace(5)*</tt></td>
2165 <td class="left">A <a href="#t_pointer">pointer</a> to an <tt>i32</tt> value
2166 that resides in address space #5.</td>
2172 <!-- _______________________________________________________________________ -->
2174 <a name="t_vector">Vector Type</a>
2180 <p>A vector type is a simple derived type that represents a vector of elements.
2181 Vector types are used when multiple primitive data are operated in parallel
2182 using a single instruction (SIMD). A vector type requires a size (number of
2183 elements) and an underlying primitive data type. Vector types are considered
2184 <a href="#t_firstclass">first class</a>.</p>
2188 < <# elements> x <elementtype> >
2191 <p>The number of elements is a constant integer value larger than 0; elementtype
2192 may be any integer or floating point type, or a pointer to these types.
2193 Vectors of size zero are not allowed. </p>
2196 <table class="layout">
2198 <td class="left"><tt><4 x i32></tt></td>
2199 <td class="left">Vector of 4 32-bit integer values.</td>
2202 <td class="left"><tt><8 x float></tt></td>
2203 <td class="left">Vector of 8 32-bit floating-point values.</td>
2206 <td class="left"><tt><2 x i64></tt></td>
2207 <td class="left">Vector of 2 64-bit integer values.</td>
2210 <td class="left"><tt><4 x i64*></tt></td>
2211 <td class="left">Vector of 4 pointers to 64-bit integer values.</td>
2221 <!-- *********************************************************************** -->
2222 <h2><a name="constants">Constants</a></h2>
2223 <!-- *********************************************************************** -->
2227 <p>LLVM has several different basic types of constants. This section describes
2228 them all and their syntax.</p>
2230 <!-- ======================================================================= -->
2232 <a name="simpleconstants">Simple Constants</a>
2238 <dt><b>Boolean constants</b></dt>
2239 <dd>The two strings '<tt>true</tt>' and '<tt>false</tt>' are both valid
2240 constants of the <tt><a href="#t_integer">i1</a></tt> type.</dd>
2242 <dt><b>Integer constants</b></dt>
2243 <dd>Standard integers (such as '4') are constants of
2244 the <a href="#t_integer">integer</a> type. Negative numbers may be used
2245 with integer types.</dd>
2247 <dt><b>Floating point constants</b></dt>
2248 <dd>Floating point constants use standard decimal notation (e.g. 123.421),
2249 exponential notation (e.g. 1.23421e+2), or a more precise hexadecimal
2250 notation (see below). The assembler requires the exact decimal value of a
2251 floating-point constant. For example, the assembler accepts 1.25 but
2252 rejects 1.3 because 1.3 is a repeating decimal in binary. Floating point
2253 constants must have a <a href="#t_floating">floating point</a> type. </dd>
2255 <dt><b>Null pointer constants</b></dt>
2256 <dd>The identifier '<tt>null</tt>' is recognized as a null pointer constant
2257 and must be of <a href="#t_pointer">pointer type</a>.</dd>
2260 <p>The one non-intuitive notation for constants is the hexadecimal form of
2261 floating point constants. For example, the form '<tt>double
2262 0x432ff973cafa8000</tt>' is equivalent to (but harder to read than)
2263 '<tt>double 4.5e+15</tt>'. The only time hexadecimal floating point
2264 constants are required (and the only time that they are generated by the
2265 disassembler) is when a floating point constant must be emitted but it cannot
2266 be represented as a decimal floating point number in a reasonable number of
2267 digits. For example, NaN's, infinities, and other special values are
2268 represented in their IEEE hexadecimal format so that assembly and disassembly
2269 do not cause any bits to change in the constants.</p>
2271 <p>When using the hexadecimal form, constants of types float and double are
2272 represented using the 16-digit form shown above (which matches the IEEE754
2273 representation for double); float values must, however, be exactly
2274 representable as IEE754 single precision. Hexadecimal format is always used
2275 for long double, and there are three forms of long double. The 80-bit format
2276 used by x86 is represented as <tt>0xK</tt> followed by 20 hexadecimal digits.
2277 The 128-bit format used by PowerPC (two adjacent doubles) is represented
2278 by <tt>0xM</tt> followed by 32 hexadecimal digits. The IEEE 128-bit format
2279 is represented by <tt>0xL</tt> followed by 32 hexadecimal digits; no
2280 currently supported target uses this format. Long doubles will only work if
2281 they match the long double format on your target. All hexadecimal formats
2282 are big-endian (sign bit at the left).</p>
2284 <p>There are no constants of type x86mmx.</p>
2287 <!-- ======================================================================= -->
2289 <a name="aggregateconstants"></a> <!-- old anchor -->
2290 <a name="complexconstants">Complex Constants</a>
2295 <p>Complex constants are a (potentially recursive) combination of simple
2296 constants and smaller complex constants.</p>
2299 <dt><b>Structure constants</b></dt>
2300 <dd>Structure constants are represented with notation similar to structure
2301 type definitions (a comma separated list of elements, surrounded by braces
2302 (<tt>{}</tt>)). For example: "<tt>{ i32 4, float 17.0, i32* @G }</tt>",
2303 where "<tt>@G</tt>" is declared as "<tt>@G = external global i32</tt>".
2304 Structure constants must have <a href="#t_struct">structure type</a>, and
2305 the number and types of elements must match those specified by the
2308 <dt><b>Array constants</b></dt>
2309 <dd>Array constants are represented with notation similar to array type
2310 definitions (a comma separated list of elements, surrounded by square
2311 brackets (<tt>[]</tt>)). For example: "<tt>[ i32 42, i32 11, i32 74
2312 ]</tt>". Array constants must have <a href="#t_array">array type</a>, and
2313 the number and types of elements must match those specified by the
2316 <dt><b>Vector constants</b></dt>
2317 <dd>Vector constants are represented with notation similar to vector type
2318 definitions (a comma separated list of elements, surrounded by
2319 less-than/greater-than's (<tt><></tt>)). For example: "<tt>< i32
2320 42, i32 11, i32 74, i32 100 ></tt>". Vector constants must
2321 have <a href="#t_vector">vector type</a>, and the number and types of
2322 elements must match those specified by the type.</dd>
2324 <dt><b>Zero initialization</b></dt>
2325 <dd>The string '<tt>zeroinitializer</tt>' can be used to zero initialize a
2326 value to zero of <em>any</em> type, including scalar and
2327 <a href="#t_aggregate">aggregate</a> types.
2328 This is often used to avoid having to print large zero initializers
2329 (e.g. for large arrays) and is always exactly equivalent to using explicit
2330 zero initializers.</dd>
2332 <dt><b>Metadata node</b></dt>
2333 <dd>A metadata node is a structure-like constant with
2334 <a href="#t_metadata">metadata type</a>. For example: "<tt>metadata !{
2335 i32 0, metadata !"test" }</tt>". Unlike other constants that are meant to
2336 be interpreted as part of the instruction stream, metadata is a place to
2337 attach additional information such as debug info.</dd>
2342 <!-- ======================================================================= -->
2344 <a name="globalconstants">Global Variable and Function Addresses</a>
2349 <p>The addresses of <a href="#globalvars">global variables</a>
2350 and <a href="#functionstructure">functions</a> are always implicitly valid
2351 (link-time) constants. These constants are explicitly referenced when
2352 the <a href="#identifiers">identifier for the global</a> is used and always
2353 have <a href="#t_pointer">pointer</a> type. For example, the following is a
2354 legal LLVM file:</p>
2356 <pre class="doc_code">
2359 @Z = global [2 x i32*] [ i32* @X, i32* @Y ]
2364 <!-- ======================================================================= -->
2366 <a name="undefvalues">Undefined Values</a>
2371 <p>The string '<tt>undef</tt>' can be used anywhere a constant is expected, and
2372 indicates that the user of the value may receive an unspecified bit-pattern.
2373 Undefined values may be of any type (other than '<tt>label</tt>'
2374 or '<tt>void</tt>') and be used anywhere a constant is permitted.</p>
2376 <p>Undefined values are useful because they indicate to the compiler that the
2377 program is well defined no matter what value is used. This gives the
2378 compiler more freedom to optimize. Here are some examples of (potentially
2379 surprising) transformations that are valid (in pseudo IR):</p>
2382 <pre class="doc_code">
2392 <p>This is safe because all of the output bits are affected by the undef bits.
2393 Any output bit can have a zero or one depending on the input bits.</p>
2395 <pre class="doc_code">
2406 <p>These logical operations have bits that are not always affected by the input.
2407 For example, if <tt>%X</tt> has a zero bit, then the output of the
2408 '<tt>and</tt>' operation will always be a zero for that bit, no matter what
2409 the corresponding bit from the '<tt>undef</tt>' is. As such, it is unsafe to
2410 optimize or assume that the result of the '<tt>and</tt>' is '<tt>undef</tt>'.
2411 However, it is safe to assume that all bits of the '<tt>undef</tt>' could be
2412 0, and optimize the '<tt>and</tt>' to 0. Likewise, it is safe to assume that
2413 all the bits of the '<tt>undef</tt>' operand to the '<tt>or</tt>' could be
2414 set, allowing the '<tt>or</tt>' to be folded to -1.</p>
2416 <pre class="doc_code">
2417 %A = select undef, %X, %Y
2418 %B = select undef, 42, %Y
2419 %C = select %X, %Y, undef
2430 <p>This set of examples shows that undefined '<tt>select</tt>' (and conditional
2431 branch) conditions can go <em>either way</em>, but they have to come from one
2432 of the two operands. In the <tt>%A</tt> example, if <tt>%X</tt> and
2433 <tt>%Y</tt> were both known to have a clear low bit, then <tt>%A</tt> would
2434 have to have a cleared low bit. However, in the <tt>%C</tt> example, the
2435 optimizer is allowed to assume that the '<tt>undef</tt>' operand could be the
2436 same as <tt>%Y</tt>, allowing the whole '<tt>select</tt>' to be
2439 <pre class="doc_code">
2440 %A = xor undef, undef
2458 <p>This example points out that two '<tt>undef</tt>' operands are not
2459 necessarily the same. This can be surprising to people (and also matches C
2460 semantics) where they assume that "<tt>X^X</tt>" is always zero, even
2461 if <tt>X</tt> is undefined. This isn't true for a number of reasons, but the
2462 short answer is that an '<tt>undef</tt>' "variable" can arbitrarily change
2463 its value over its "live range". This is true because the variable doesn't
2464 actually <em>have a live range</em>. Instead, the value is logically read
2465 from arbitrary registers that happen to be around when needed, so the value
2466 is not necessarily consistent over time. In fact, <tt>%A</tt> and <tt>%C</tt>
2467 need to have the same semantics or the core LLVM "replace all uses with"
2468 concept would not hold.</p>
2470 <pre class="doc_code">
2478 <p>These examples show the crucial difference between an <em>undefined
2479 value</em> and <em>undefined behavior</em>. An undefined value (like
2480 '<tt>undef</tt>') is allowed to have an arbitrary bit-pattern. This means that
2481 the <tt>%A</tt> operation can be constant folded to '<tt>undef</tt>', because
2482 the '<tt>undef</tt>' could be an SNaN, and <tt>fdiv</tt> is not (currently)
2483 defined on SNaN's. However, in the second example, we can make a more
2484 aggressive assumption: because the <tt>undef</tt> is allowed to be an
2485 arbitrary value, we are allowed to assume that it could be zero. Since a
2486 divide by zero has <em>undefined behavior</em>, we are allowed to assume that
2487 the operation does not execute at all. This allows us to delete the divide and
2488 all code after it. Because the undefined operation "can't happen", the
2489 optimizer can assume that it occurs in dead code.</p>
2491 <pre class="doc_code">
2492 a: store undef -> %X
2493 b: store %X -> undef
2499 <p>These examples reiterate the <tt>fdiv</tt> example: a store <em>of</em> an
2500 undefined value can be assumed to not have any effect; we can assume that the
2501 value is overwritten with bits that happen to match what was already there.
2502 However, a store <em>to</em> an undefined location could clobber arbitrary
2503 memory, therefore, it has undefined behavior.</p>
2507 <!-- ======================================================================= -->
2509 <a name="poisonvalues">Poison Values</a>
2514 <p>Poison values are similar to <a href="#undefvalues">undef values</a>, however
2515 they also represent the fact that an instruction or constant expression which
2516 cannot evoke side effects has nevertheless detected a condition which results
2517 in undefined behavior.</p>
2519 <p>There is currently no way of representing a poison value in the IR; they
2520 only exist when produced by operations such as
2521 <a href="#i_add"><tt>add</tt></a> with the <tt>nsw</tt> flag.</p>
2523 <p>Poison value behavior is defined in terms of value <i>dependence</i>:</p>
2526 <li>Values other than <a href="#i_phi"><tt>phi</tt></a> nodes depend on
2527 their operands.</li>
2529 <li><a href="#i_phi"><tt>Phi</tt></a> nodes depend on the operand corresponding
2530 to their dynamic predecessor basic block.</li>
2532 <li>Function arguments depend on the corresponding actual argument values in
2533 the dynamic callers of their functions.</li>
2535 <li><a href="#i_call"><tt>Call</tt></a> instructions depend on the
2536 <a href="#i_ret"><tt>ret</tt></a> instructions that dynamically transfer
2537 control back to them.</li>
2539 <li><a href="#i_invoke"><tt>Invoke</tt></a> instructions depend on the
2540 <a href="#i_ret"><tt>ret</tt></a>, <a href="#i_unwind"><tt>unwind</tt></a>,
2541 or exception-throwing call instructions that dynamically transfer control
2544 <li>Non-volatile loads and stores depend on the most recent stores to all of the
2545 referenced memory addresses, following the order in the IR
2546 (including loads and stores implied by intrinsics such as
2547 <a href="#int_memcpy"><tt>@llvm.memcpy</tt></a>.)</li>
2549 <!-- TODO: In the case of multiple threads, this only applies if the store
2550 "happens-before" the load or store. -->
2552 <!-- TODO: floating-point exception state -->
2554 <li>An instruction with externally visible side effects depends on the most
2555 recent preceding instruction with externally visible side effects, following
2556 the order in the IR. (This includes
2557 <a href="#volatile">volatile operations</a>.)</li>
2559 <li>An instruction <i>control-depends</i> on a
2560 <a href="#terminators">terminator instruction</a>
2561 if the terminator instruction has multiple successors and the instruction
2562 is always executed when control transfers to one of the successors, and
2563 may not be executed when control is transferred to another.</li>
2565 <li>Additionally, an instruction also <i>control-depends</i> on a terminator
2566 instruction if the set of instructions it otherwise depends on would be
2567 different if the terminator had transferred control to a different
2570 <li>Dependence is transitive.</li>
2574 <p>Poison Values have the same behavior as <a href="#undefvalues">undef values</a>,
2575 with the additional affect that any instruction which has a <i>dependence</i>
2576 on a poison value has undefined behavior.</p>
2578 <p>Here are some examples:</p>
2580 <pre class="doc_code">
2582 %poison = sub nuw i32 0, 1 ; Results in a poison value.
2583 %still_poison = and i32 %poison, 0 ; 0, but also poison.
2584 %poison_yet_again = getelementptr i32* @h, i32 %still_poison
2585 store i32 0, i32* %poison_yet_again ; memory at @h[0] is poisoned
2587 store i32 %poison, i32* @g ; Poison value stored to memory.
2588 %poison2 = load i32* @g ; Poison value loaded back from memory.
2590 store volatile i32 %poison, i32* @g ; External observation; undefined behavior.
2592 %narrowaddr = bitcast i32* @g to i16*
2593 %wideaddr = bitcast i32* @g to i64*
2594 %poison3 = load i16* %narrowaddr ; Returns a poison value.
2595 %poison4 = load i64* %wideaddr ; Returns a poison value.
2597 %cmp = icmp slt i32 %poison, 0 ; Returns a poison value.
2598 br i1 %cmp, label %true, label %end ; Branch to either destination.
2601 store volatile i32 0, i32* @g ; This is control-dependent on %cmp, so
2602 ; it has undefined behavior.
2606 %p = phi i32 [ 0, %entry ], [ 1, %true ]
2607 ; Both edges into this PHI are
2608 ; control-dependent on %cmp, so this
2609 ; always results in a poison value.
2611 store volatile i32 0, i32* @g ; This would depend on the store in %true
2612 ; if %cmp is true, or the store in %entry
2613 ; otherwise, so this is undefined behavior.
2615 br i1 %cmp, label %second_true, label %second_end
2616 ; The same branch again, but this time the
2617 ; true block doesn't have side effects.
2624 store volatile i32 0, i32* @g ; This time, the instruction always depends
2625 ; on the store in %end. Also, it is
2626 ; control-equivalent to %end, so this is
2627 ; well-defined (ignoring earlier undefined
2628 ; behavior in this example).
2633 <!-- ======================================================================= -->
2635 <a name="blockaddress">Addresses of Basic Blocks</a>
2640 <p><b><tt>blockaddress(@function, %block)</tt></b></p>
2642 <p>The '<tt>blockaddress</tt>' constant computes the address of the specified
2643 basic block in the specified function, and always has an i8* type. Taking
2644 the address of the entry block is illegal.</p>
2646 <p>This value only has defined behavior when used as an operand to the
2647 '<a href="#i_indirectbr"><tt>indirectbr</tt></a>' instruction, or for
2648 comparisons against null. Pointer equality tests between labels addresses
2649 results in undefined behavior — though, again, comparison against null
2650 is ok, and no label is equal to the null pointer. This may be passed around
2651 as an opaque pointer sized value as long as the bits are not inspected. This
2652 allows <tt>ptrtoint</tt> and arithmetic to be performed on these values so
2653 long as the original value is reconstituted before the <tt>indirectbr</tt>
2656 <p>Finally, some targets may provide defined semantics when using the value as
2657 the operand to an inline assembly, but that is target specific.</p>
2662 <!-- ======================================================================= -->
2664 <a name="constantexprs">Constant Expressions</a>
2669 <p>Constant expressions are used to allow expressions involving other constants
2670 to be used as constants. Constant expressions may be of
2671 any <a href="#t_firstclass">first class</a> type and may involve any LLVM
2672 operation that does not have side effects (e.g. load and call are not
2673 supported). The following is the syntax for constant expressions:</p>
2676 <dt><b><tt>trunc (CST to TYPE)</tt></b></dt>
2677 <dd>Truncate a constant to another type. The bit size of CST must be larger
2678 than the bit size of TYPE. Both types must be integers.</dd>
2680 <dt><b><tt>zext (CST to TYPE)</tt></b></dt>
2681 <dd>Zero extend a constant to another type. The bit size of CST must be
2682 smaller than the bit size of TYPE. Both types must be integers.</dd>
2684 <dt><b><tt>sext (CST to TYPE)</tt></b></dt>
2685 <dd>Sign extend a constant to another type. The bit size of CST must be
2686 smaller than the bit size of TYPE. Both types must be integers.</dd>
2688 <dt><b><tt>fptrunc (CST to TYPE)</tt></b></dt>
2689 <dd>Truncate a floating point constant to another floating point type. The
2690 size of CST must be larger than the size of TYPE. Both types must be
2691 floating point.</dd>
2693 <dt><b><tt>fpext (CST to TYPE)</tt></b></dt>
2694 <dd>Floating point extend a constant to another type. The size of CST must be
2695 smaller or equal to the size of TYPE. Both types must be floating
2698 <dt><b><tt>fptoui (CST to TYPE)</tt></b></dt>
2699 <dd>Convert a floating point constant to the corresponding unsigned integer
2700 constant. TYPE must be a scalar or vector integer type. CST must be of
2701 scalar or vector floating point type. Both CST and TYPE must be scalars,
2702 or vectors of the same number of elements. If the value won't fit in the
2703 integer type, the results are undefined.</dd>
2705 <dt><b><tt>fptosi (CST to TYPE)</tt></b></dt>
2706 <dd>Convert a floating point constant to the corresponding signed integer
2707 constant. TYPE must be a scalar or vector integer type. CST must be of
2708 scalar or vector floating point type. Both CST and TYPE must be scalars,
2709 or vectors of the same number of elements. If the value won't fit in the
2710 integer type, the results are undefined.</dd>
2712 <dt><b><tt>uitofp (CST to TYPE)</tt></b></dt>
2713 <dd>Convert an unsigned integer constant to the corresponding floating point
2714 constant. TYPE must be a scalar or vector floating point type. CST must be
2715 of scalar or vector integer type. Both CST and TYPE must be scalars, or
2716 vectors of the same number of elements. If the value won't fit in the
2717 floating point type, the results are undefined.</dd>
2719 <dt><b><tt>sitofp (CST to TYPE)</tt></b></dt>
2720 <dd>Convert a signed integer constant to the corresponding floating point
2721 constant. TYPE must be a scalar or vector floating point type. CST must be
2722 of scalar or vector integer type. Both CST and TYPE must be scalars, or
2723 vectors of the same number of elements. If the value won't fit in the
2724 floating point type, the results are undefined.</dd>
2726 <dt><b><tt>ptrtoint (CST to TYPE)</tt></b></dt>
2727 <dd>Convert a pointer typed constant to the corresponding integer constant
2728 <tt>TYPE</tt> must be an integer type. <tt>CST</tt> must be of pointer
2729 type. The <tt>CST</tt> value is zero extended, truncated, or unchanged to
2730 make it fit in <tt>TYPE</tt>.</dd>
2732 <dt><b><tt>inttoptr (CST to TYPE)</tt></b></dt>
2733 <dd>Convert a integer constant to a pointer constant. TYPE must be a pointer
2734 type. CST must be of integer type. The CST value is zero extended,
2735 truncated, or unchanged to make it fit in a pointer size. This one is
2736 <i>really</i> dangerous!</dd>
2738 <dt><b><tt>bitcast (CST to TYPE)</tt></b></dt>
2739 <dd>Convert a constant, CST, to another TYPE. The constraints of the operands
2740 are the same as those for the <a href="#i_bitcast">bitcast
2741 instruction</a>.</dd>
2743 <dt><b><tt>getelementptr (CSTPTR, IDX0, IDX1, ...)</tt></b></dt>
2744 <dt><b><tt>getelementptr inbounds (CSTPTR, IDX0, IDX1, ...)</tt></b></dt>
2745 <dd>Perform the <a href="#i_getelementptr">getelementptr operation</a> on
2746 constants. As with the <a href="#i_getelementptr">getelementptr</a>
2747 instruction, the index list may have zero or more indexes, which are
2748 required to make sense for the type of "CSTPTR".</dd>
2750 <dt><b><tt>select (COND, VAL1, VAL2)</tt></b></dt>
2751 <dd>Perform the <a href="#i_select">select operation</a> on constants.</dd>
2753 <dt><b><tt>icmp COND (VAL1, VAL2)</tt></b></dt>
2754 <dd>Performs the <a href="#i_icmp">icmp operation</a> on constants.</dd>
2756 <dt><b><tt>fcmp COND (VAL1, VAL2)</tt></b></dt>
2757 <dd>Performs the <a href="#i_fcmp">fcmp operation</a> on constants.</dd>
2759 <dt><b><tt>extractelement (VAL, IDX)</tt></b></dt>
2760 <dd>Perform the <a href="#i_extractelement">extractelement operation</a> on
2763 <dt><b><tt>insertelement (VAL, ELT, IDX)</tt></b></dt>
2764 <dd>Perform the <a href="#i_insertelement">insertelement operation</a> on
2767 <dt><b><tt>shufflevector (VEC1, VEC2, IDXMASK)</tt></b></dt>
2768 <dd>Perform the <a href="#i_shufflevector">shufflevector operation</a> on
2771 <dt><b><tt>extractvalue (VAL, IDX0, IDX1, ...)</tt></b></dt>
2772 <dd>Perform the <a href="#i_extractvalue">extractvalue operation</a> on
2773 constants. The index list is interpreted in a similar manner as indices in
2774 a '<a href="#i_getelementptr">getelementptr</a>' operation. At least one
2775 index value must be specified.</dd>
2777 <dt><b><tt>insertvalue (VAL, ELT, IDX0, IDX1, ...)</tt></b></dt>
2778 <dd>Perform the <a href="#i_insertvalue">insertvalue operation</a> on
2779 constants. The index list is interpreted in a similar manner as indices in
2780 a '<a href="#i_getelementptr">getelementptr</a>' operation. At least one
2781 index value must be specified.</dd>
2783 <dt><b><tt>OPCODE (LHS, RHS)</tt></b></dt>
2784 <dd>Perform the specified operation of the LHS and RHS constants. OPCODE may
2785 be any of the <a href="#binaryops">binary</a>
2786 or <a href="#bitwiseops">bitwise binary</a> operations. The constraints
2787 on operands are the same as those for the corresponding instruction
2788 (e.g. no bitwise operations on floating point values are allowed).</dd>
2795 <!-- *********************************************************************** -->
2796 <h2><a name="othervalues">Other Values</a></h2>
2797 <!-- *********************************************************************** -->
2799 <!-- ======================================================================= -->
2801 <a name="inlineasm">Inline Assembler Expressions</a>
2806 <p>LLVM supports inline assembler expressions (as opposed
2807 to <a href="#moduleasm">Module-Level Inline Assembly</a>) through the use of
2808 a special value. This value represents the inline assembler as a string
2809 (containing the instructions to emit), a list of operand constraints (stored
2810 as a string), a flag that indicates whether or not the inline asm
2811 expression has side effects, and a flag indicating whether the function
2812 containing the asm needs to align its stack conservatively. An example
2813 inline assembler expression is:</p>
2815 <pre class="doc_code">
2816 i32 (i32) asm "bswap $0", "=r,r"
2819 <p>Inline assembler expressions may <b>only</b> be used as the callee operand of
2820 a <a href="#i_call"><tt>call</tt> instruction</a>. Thus, typically we
2823 <pre class="doc_code">
2824 %X = call i32 asm "<a href="#int_bswap">bswap</a> $0", "=r,r"(i32 %Y)
2827 <p>Inline asms with side effects not visible in the constraint list must be
2828 marked as having side effects. This is done through the use of the
2829 '<tt>sideeffect</tt>' keyword, like so:</p>
2831 <pre class="doc_code">
2832 call void asm sideeffect "eieio", ""()
2835 <p>In some cases inline asms will contain code that will not work unless the
2836 stack is aligned in some way, such as calls or SSE instructions on x86,
2837 yet will not contain code that does that alignment within the asm.
2838 The compiler should make conservative assumptions about what the asm might
2839 contain and should generate its usual stack alignment code in the prologue
2840 if the '<tt>alignstack</tt>' keyword is present:</p>
2842 <pre class="doc_code">
2843 call void asm alignstack "eieio", ""()
2846 <p>If both keywords appear the '<tt>sideeffect</tt>' keyword must come
2850 <p>TODO: The format of the asm and constraints string still need to be
2851 documented here. Constraints on what can be done (e.g. duplication, moving,
2852 etc need to be documented). This is probably best done by reference to
2853 another document that covers inline asm from a holistic perspective.</p>
2856 <!-- _______________________________________________________________________ -->
2858 <a name="inlineasm_md">Inline Asm Metadata</a>
2863 <p>The call instructions that wrap inline asm nodes may have a
2864 "<tt>!srcloc</tt>" MDNode attached to it that contains a list of constant
2865 integers. If present, the code generator will use the integer as the
2866 location cookie value when report errors through the <tt>LLVMContext</tt>
2867 error reporting mechanisms. This allows a front-end to correlate backend
2868 errors that occur with inline asm back to the source code that produced it.
2871 <pre class="doc_code">
2872 call void asm sideeffect "something bad", ""()<b>, !srcloc !42</b>
2874 !42 = !{ i32 1234567 }
2877 <p>It is up to the front-end to make sense of the magic numbers it places in the
2878 IR. If the MDNode contains multiple constants, the code generator will use
2879 the one that corresponds to the line of the asm that the error occurs on.</p>
2885 <!-- ======================================================================= -->
2887 <a name="metadata">Metadata Nodes and Metadata Strings</a>
2892 <p>LLVM IR allows metadata to be attached to instructions in the program that
2893 can convey extra information about the code to the optimizers and code
2894 generator. One example application of metadata is source-level debug
2895 information. There are two metadata primitives: strings and nodes. All
2896 metadata has the <tt>metadata</tt> type and is identified in syntax by a
2897 preceding exclamation point ('<tt>!</tt>').</p>
2899 <p>A metadata string is a string surrounded by double quotes. It can contain
2900 any character by escaping non-printable characters with "<tt>\xx</tt>" where
2901 "<tt>xx</tt>" is the two digit hex code. For example:
2902 "<tt>!"test\00"</tt>".</p>
2904 <p>Metadata nodes are represented with notation similar to structure constants
2905 (a comma separated list of elements, surrounded by braces and preceded by an
2906 exclamation point). Metadata nodes can have any values as their operand. For
2909 <div class="doc_code">
2911 !{ metadata !"test\00", i32 10}
2915 <p>A <a href="#namedmetadatastructure">named metadata</a> is a collection of
2916 metadata nodes, which can be looked up in the module symbol table. For
2919 <div class="doc_code">
2921 !foo = metadata !{!4, !3}
2925 <p>Metadata can be used as function arguments. Here <tt>llvm.dbg.value</tt>
2926 function is using two metadata arguments:</p>
2928 <div class="doc_code">
2930 call void @llvm.dbg.value(metadata !24, i64 0, metadata !25)
2934 <p>Metadata can be attached with an instruction. Here metadata <tt>!21</tt> is
2935 attached to the <tt>add</tt> instruction using the <tt>!dbg</tt>
2938 <div class="doc_code">
2940 %indvar.next = add i64 %indvar, 1, !dbg !21
2944 <p>More information about specific metadata nodes recognized by the optimizers
2945 and code generator is found below.</p>
2947 <!-- _______________________________________________________________________ -->
2949 <a name="tbaa">'<tt>tbaa</tt>' Metadata</a>
2954 <p>In LLVM IR, memory does not have types, so LLVM's own type system is not
2955 suitable for doing TBAA. Instead, metadata is added to the IR to describe
2956 a type system of a higher level language. This can be used to implement
2957 typical C/C++ TBAA, but it can also be used to implement custom alias
2958 analysis behavior for other languages.</p>
2960 <p>The current metadata format is very simple. TBAA metadata nodes have up to
2961 three fields, e.g.:</p>
2963 <div class="doc_code">
2965 !0 = metadata !{ metadata !"an example type tree" }
2966 !1 = metadata !{ metadata !"int", metadata !0 }
2967 !2 = metadata !{ metadata !"float", metadata !0 }
2968 !3 = metadata !{ metadata !"const float", metadata !2, i64 1 }
2972 <p>The first field is an identity field. It can be any value, usually
2973 a metadata string, which uniquely identifies the type. The most important
2974 name in the tree is the name of the root node. Two trees with
2975 different root node names are entirely disjoint, even if they
2976 have leaves with common names.</p>
2978 <p>The second field identifies the type's parent node in the tree, or
2979 is null or omitted for a root node. A type is considered to alias
2980 all of its descendants and all of its ancestors in the tree. Also,
2981 a type is considered to alias all types in other trees, so that
2982 bitcode produced from multiple front-ends is handled conservatively.</p>
2984 <p>If the third field is present, it's an integer which if equal to 1
2985 indicates that the type is "constant" (meaning
2986 <tt>pointsToConstantMemory</tt> should return true; see
2987 <a href="AliasAnalysis.html#OtherItfs">other useful
2988 <tt>AliasAnalysis</tt> methods</a>).</p>
2992 <!-- _______________________________________________________________________ -->
2994 <a name="fpaccuracy">'<tt>fpaccuracy</tt>' Metadata</a>
2999 <p><tt>fpaccuracy</tt> metadata may be attached to any instruction of floating
3000 point type. It expresses the maximum relative error of the result of
3001 that instruction, in ULPs. ULP is defined as follows:</p>
3005 <p>If <tt>x</tt> is a real number that lies between two finite consecutive
3006 floating-point numbers <tt>a</tt> and <tt>b</tt>, without being equal to one
3007 of them, then <tt>ulp(x) = |b - a|</tt>, otherwise <tt>ulp(x)</tt> is the
3008 distance between the two non-equal finite floating-point numbers nearest
3009 <tt>x</tt>. Moreover, <tt>ulp(NaN)</tt> is <tt>NaN</tt>.</p>
3013 <p>The maximum relative error may be any rational number. The metadata node
3014 shall consist of a pair of unsigned integers respectively representing
3015 the numerator and denominator. For example, 2.5 ULP:</p>
3017 <div class="doc_code">
3019 !0 = metadata !{ i32 5, i32 2 }
3029 <!-- *********************************************************************** -->
3031 <a name="intrinsic_globals">Intrinsic Global Variables</a>
3033 <!-- *********************************************************************** -->
3035 <p>LLVM has a number of "magic" global variables that contain data that affect
3036 code generation or other IR semantics. These are documented here. All globals
3037 of this sort should have a section specified as "<tt>llvm.metadata</tt>". This
3038 section and all globals that start with "<tt>llvm.</tt>" are reserved for use
3041 <!-- ======================================================================= -->
3043 <a name="intg_used">The '<tt>llvm.used</tt>' Global Variable</a>
3048 <p>The <tt>@llvm.used</tt> global is an array with i8* element type which has <a
3049 href="#linkage_appending">appending linkage</a>. This array contains a list of
3050 pointers to global variables and functions which may optionally have a pointer
3051 cast formed of bitcast or getelementptr. For example, a legal use of it is:</p>
3053 <div class="doc_code">
3058 @llvm.used = appending global [2 x i8*] [
3060 i8* bitcast (i32* @Y to i8*)
3061 ], section "llvm.metadata"
3065 <p>If a global variable appears in the <tt>@llvm.used</tt> list, then the
3066 compiler, assembler, and linker are required to treat the symbol as if there
3067 is a reference to the global that it cannot see. For example, if a variable
3068 has internal linkage and no references other than that from
3069 the <tt>@llvm.used</tt> list, it cannot be deleted. This is commonly used to
3070 represent references from inline asms and other things the compiler cannot
3071 "see", and corresponds to "<tt>attribute((used))</tt>" in GNU C.</p>
3073 <p>On some targets, the code generator must emit a directive to the assembler or
3074 object file to prevent the assembler and linker from molesting the
3079 <!-- ======================================================================= -->
3081 <a name="intg_compiler_used">
3082 The '<tt>llvm.compiler.used</tt>' Global Variable
3088 <p>The <tt>@llvm.compiler.used</tt> directive is the same as the
3089 <tt>@llvm.used</tt> directive, except that it only prevents the compiler from
3090 touching the symbol. On targets that support it, this allows an intelligent
3091 linker to optimize references to the symbol without being impeded as it would
3092 be by <tt>@llvm.used</tt>.</p>
3094 <p>This is a rare construct that should only be used in rare circumstances, and
3095 should not be exposed to source languages.</p>
3099 <!-- ======================================================================= -->
3101 <a name="intg_global_ctors">The '<tt>llvm.global_ctors</tt>' Global Variable</a>
3106 <div class="doc_code">
3108 %0 = type { i32, void ()* }
3109 @llvm.global_ctors = appending global [1 x %0] [%0 { i32 65535, void ()* @ctor }]
3113 <p>The <tt>@llvm.global_ctors</tt> array contains a list of constructor
3114 functions and associated priorities. The functions referenced by this array
3115 will be called in ascending order of priority (i.e. lowest first) when the
3116 module is loaded. The order of functions with the same priority is not
3121 <!-- ======================================================================= -->
3123 <a name="intg_global_dtors">The '<tt>llvm.global_dtors</tt>' Global Variable</a>
3128 <div class="doc_code">
3130 %0 = type { i32, void ()* }
3131 @llvm.global_dtors = appending global [1 x %0] [%0 { i32 65535, void ()* @dtor }]
3135 <p>The <tt>@llvm.global_dtors</tt> array contains a list of destructor functions
3136 and associated priorities. The functions referenced by this array will be
3137 called in descending order of priority (i.e. highest first) when the module
3138 is loaded. The order of functions with the same priority is not defined.</p>
3144 <!-- *********************************************************************** -->
3145 <h2><a name="instref">Instruction Reference</a></h2>
3146 <!-- *********************************************************************** -->
3150 <p>The LLVM instruction set consists of several different classifications of
3151 instructions: <a href="#terminators">terminator
3152 instructions</a>, <a href="#binaryops">binary instructions</a>,
3153 <a href="#bitwiseops">bitwise binary instructions</a>,
3154 <a href="#memoryops">memory instructions</a>, and
3155 <a href="#otherops">other instructions</a>.</p>
3157 <!-- ======================================================================= -->
3159 <a name="terminators">Terminator Instructions</a>
3164 <p>As mentioned <a href="#functionstructure">previously</a>, every basic block
3165 in a program ends with a "Terminator" instruction, which indicates which
3166 block should be executed after the current block is finished. These
3167 terminator instructions typically yield a '<tt>void</tt>' value: they produce
3168 control flow, not values (the one exception being the
3169 '<a href="#i_invoke"><tt>invoke</tt></a>' instruction).</p>
3171 <p>The terminator instructions are:
3172 '<a href="#i_ret"><tt>ret</tt></a>',
3173 '<a href="#i_br"><tt>br</tt></a>',
3174 '<a href="#i_switch"><tt>switch</tt></a>',
3175 '<a href="#i_indirectbr"><tt>indirectbr</tt></a>',
3176 '<a href="#i_invoke"><tt>invoke</tt></a>',
3177 '<a href="#i_unwind"><tt>unwind</tt></a>',
3178 '<a href="#i_resume"><tt>resume</tt></a>', and
3179 '<a href="#i_unreachable"><tt>unreachable</tt></a>'.</p>
3181 <!-- _______________________________________________________________________ -->
3183 <a name="i_ret">'<tt>ret</tt>' Instruction</a>
3190 ret <type> <value> <i>; Return a value from a non-void function</i>
3191 ret void <i>; Return from void function</i>
3195 <p>The '<tt>ret</tt>' instruction is used to return control flow (and optionally
3196 a value) from a function back to the caller.</p>
3198 <p>There are two forms of the '<tt>ret</tt>' instruction: one that returns a
3199 value and then causes control flow, and one that just causes control flow to
3203 <p>The '<tt>ret</tt>' instruction optionally accepts a single argument, the
3204 return value. The type of the return value must be a
3205 '<a href="#t_firstclass">first class</a>' type.</p>
3207 <p>A function is not <a href="#wellformed">well formed</a> if it it has a
3208 non-void return type and contains a '<tt>ret</tt>' instruction with no return
3209 value or a return value with a type that does not match its type, or if it
3210 has a void return type and contains a '<tt>ret</tt>' instruction with a
3214 <p>When the '<tt>ret</tt>' instruction is executed, control flow returns back to
3215 the calling function's context. If the caller is a
3216 "<a href="#i_call"><tt>call</tt></a>" instruction, execution continues at the
3217 instruction after the call. If the caller was an
3218 "<a href="#i_invoke"><tt>invoke</tt></a>" instruction, execution continues at
3219 the beginning of the "normal" destination block. If the instruction returns
3220 a value, that value shall set the call or invoke instruction's return
3225 ret i32 5 <i>; Return an integer value of 5</i>
3226 ret void <i>; Return from a void function</i>
3227 ret { i32, i8 } { i32 4, i8 2 } <i>; Return a struct of values 4 and 2</i>
3231 <!-- _______________________________________________________________________ -->
3233 <a name="i_br">'<tt>br</tt>' Instruction</a>
3240 br i1 <cond>, label <iftrue>, label <iffalse>
3241 br label <dest> <i>; Unconditional branch</i>
3245 <p>The '<tt>br</tt>' instruction is used to cause control flow to transfer to a
3246 different basic block in the current function. There are two forms of this
3247 instruction, corresponding to a conditional branch and an unconditional
3251 <p>The conditional branch form of the '<tt>br</tt>' instruction takes a single
3252 '<tt>i1</tt>' value and two '<tt>label</tt>' values. The unconditional form
3253 of the '<tt>br</tt>' instruction takes a single '<tt>label</tt>' value as a
3257 <p>Upon execution of a conditional '<tt>br</tt>' instruction, the '<tt>i1</tt>'
3258 argument is evaluated. If the value is <tt>true</tt>, control flows to the
3259 '<tt>iftrue</tt>' <tt>label</tt> argument. If "cond" is <tt>false</tt>,
3260 control flows to the '<tt>iffalse</tt>' <tt>label</tt> argument.</p>
3265 %cond = <a href="#i_icmp">icmp</a> eq i32 %a, %b
3266 br i1 %cond, label %IfEqual, label %IfUnequal
3268 <a href="#i_ret">ret</a> i32 1
3270 <a href="#i_ret">ret</a> i32 0
3275 <!-- _______________________________________________________________________ -->
3277 <a name="i_switch">'<tt>switch</tt>' Instruction</a>
3284 switch <intty> <value>, label <defaultdest> [ <intty> <val>, label <dest> ... ]
3288 <p>The '<tt>switch</tt>' instruction is used to transfer control flow to one of
3289 several different places. It is a generalization of the '<tt>br</tt>'
3290 instruction, allowing a branch to occur to one of many possible
3294 <p>The '<tt>switch</tt>' instruction uses three parameters: an integer
3295 comparison value '<tt>value</tt>', a default '<tt>label</tt>' destination,
3296 and an array of pairs of comparison value constants and '<tt>label</tt>'s.
3297 The table is not allowed to contain duplicate constant entries.</p>
3300 <p>The <tt>switch</tt> instruction specifies a table of values and
3301 destinations. When the '<tt>switch</tt>' instruction is executed, this table
3302 is searched for the given value. If the value is found, control flow is
3303 transferred to the corresponding destination; otherwise, control flow is
3304 transferred to the default destination.</p>
3306 <h5>Implementation:</h5>
3307 <p>Depending on properties of the target machine and the particular
3308 <tt>switch</tt> instruction, this instruction may be code generated in
3309 different ways. For example, it could be generated as a series of chained
3310 conditional branches or with a lookup table.</p>
3314 <i>; Emulate a conditional br instruction</i>
3315 %Val = <a href="#i_zext">zext</a> i1 %value to i32
3316 switch i32 %Val, label %truedest [ i32 0, label %falsedest ]
3318 <i>; Emulate an unconditional br instruction</i>
3319 switch i32 0, label %dest [ ]
3321 <i>; Implement a jump table:</i>
3322 switch i32 %val, label %otherwise [ i32 0, label %onzero
3324 i32 2, label %ontwo ]
3330 <!-- _______________________________________________________________________ -->
3332 <a name="i_indirectbr">'<tt>indirectbr</tt>' Instruction</a>
3339 indirectbr <somety>* <address>, [ label <dest1>, label <dest2>, ... ]
3344 <p>The '<tt>indirectbr</tt>' instruction implements an indirect branch to a label
3345 within the current function, whose address is specified by
3346 "<tt>address</tt>". Address must be derived from a <a
3347 href="#blockaddress">blockaddress</a> constant.</p>
3351 <p>The '<tt>address</tt>' argument is the address of the label to jump to. The
3352 rest of the arguments indicate the full set of possible destinations that the
3353 address may point to. Blocks are allowed to occur multiple times in the
3354 destination list, though this isn't particularly useful.</p>
3356 <p>This destination list is required so that dataflow analysis has an accurate
3357 understanding of the CFG.</p>
3361 <p>Control transfers to the block specified in the address argument. All
3362 possible destination blocks must be listed in the label list, otherwise this
3363 instruction has undefined behavior. This implies that jumps to labels
3364 defined in other functions have undefined behavior as well.</p>
3366 <h5>Implementation:</h5>
3368 <p>This is typically implemented with a jump through a register.</p>
3372 indirectbr i8* %Addr, [ label %bb1, label %bb2, label %bb3 ]
3378 <!-- _______________________________________________________________________ -->
3380 <a name="i_invoke">'<tt>invoke</tt>' Instruction</a>
3387 <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>]
3388 to label <normal label> unwind label <exception label>
3392 <p>The '<tt>invoke</tt>' instruction causes control to transfer to a specified
3393 function, with the possibility of control flow transfer to either the
3394 '<tt>normal</tt>' label or the '<tt>exception</tt>' label. If the callee
3395 function returns with the "<tt><a href="#i_ret">ret</a></tt>" instruction,
3396 control flow will return to the "normal" label. If the callee (or any
3397 indirect callees) returns with the "<a href="#i_unwind"><tt>unwind</tt></a>"
3398 instruction, control is interrupted and continued at the dynamically nearest
3399 "exception" label.</p>
3401 <p>The '<tt>exception</tt>' label is a
3402 <i><a href="ExceptionHandling.html#overview">landing pad</a></i> for the
3403 exception. As such, '<tt>exception</tt>' label is required to have the
3404 "<a href="#i_landingpad"><tt>landingpad</tt></a>" instruction, which contains
3405 the information about about the behavior of the program after unwinding
3406 happens, as its first non-PHI instruction. The restrictions on the
3407 "<tt>landingpad</tt>" instruction's tightly couples it to the
3408 "<tt>invoke</tt>" instruction, so that the important information contained
3409 within the "<tt>landingpad</tt>" instruction can't be lost through normal
3413 <p>This instruction requires several arguments:</p>
3416 <li>The optional "cconv" marker indicates which <a href="#callingconv">calling
3417 convention</a> the call should use. If none is specified, the call
3418 defaults to using C calling conventions.</li>
3420 <li>The optional <a href="#paramattrs">Parameter Attributes</a> list for
3421 return values. Only '<tt>zeroext</tt>', '<tt>signext</tt>', and
3422 '<tt>inreg</tt>' attributes are valid here.</li>
3424 <li>'<tt>ptr to function ty</tt>': shall be the signature of the pointer to
3425 function value being invoked. In most cases, this is a direct function
3426 invocation, but indirect <tt>invoke</tt>s are just as possible, branching
3427 off an arbitrary pointer to function value.</li>
3429 <li>'<tt>function ptr val</tt>': An LLVM value containing a pointer to a
3430 function to be invoked. </li>
3432 <li>'<tt>function args</tt>': argument list whose types match the function
3433 signature argument types and parameter attributes. All arguments must be
3434 of <a href="#t_firstclass">first class</a> type. If the function
3435 signature indicates the function accepts a variable number of arguments,
3436 the extra arguments can be specified.</li>
3438 <li>'<tt>normal label</tt>': the label reached when the called function
3439 executes a '<tt><a href="#i_ret">ret</a></tt>' instruction. </li>
3441 <li>'<tt>exception label</tt>': the label reached when a callee returns with
3442 the <a href="#i_unwind"><tt>unwind</tt></a> instruction. </li>
3444 <li>The optional <a href="#fnattrs">function attributes</a> list. Only
3445 '<tt>noreturn</tt>', '<tt>nounwind</tt>', '<tt>readonly</tt>' and
3446 '<tt>readnone</tt>' attributes are valid here.</li>
3450 <p>This instruction is designed to operate as a standard
3451 '<tt><a href="#i_call">call</a></tt>' instruction in most regards. The
3452 primary difference is that it establishes an association with a label, which
3453 is used by the runtime library to unwind the stack.</p>
3455 <p>This instruction is used in languages with destructors to ensure that proper
3456 cleanup is performed in the case of either a <tt>longjmp</tt> or a thrown
3457 exception. Additionally, this is important for implementation of
3458 '<tt>catch</tt>' clauses in high-level languages that support them.</p>
3460 <p>For the purposes of the SSA form, the definition of the value returned by the
3461 '<tt>invoke</tt>' instruction is deemed to occur on the edge from the current
3462 block to the "normal" label. If the callee unwinds then no return value is
3465 <p>Note that the code generator does not yet completely support unwind, and
3466 that the invoke/unwind semantics are likely to change in future versions.</p>
3470 %retval = invoke i32 @Test(i32 15) to label %Continue
3471 unwind label %TestCleanup <i>; {i32}:retval set</i>
3472 %retval = invoke <a href="#callingconv">coldcc</a> i32 %Testfnptr(i32 15) to label %Continue
3473 unwind label %TestCleanup <i>; {i32}:retval set</i>
3478 <!-- _______________________________________________________________________ -->
3481 <a name="i_unwind">'<tt>unwind</tt>' Instruction</a>
3492 <p>The '<tt>unwind</tt>' instruction unwinds the stack, continuing control flow
3493 at the first callee in the dynamic call stack which used
3494 an <a href="#i_invoke"><tt>invoke</tt></a> instruction to perform the call.
3495 This is primarily used to implement exception handling.</p>
3498 <p>The '<tt>unwind</tt>' instruction causes execution of the current function to
3499 immediately halt. The dynamic call stack is then searched for the
3500 first <a href="#i_invoke"><tt>invoke</tt></a> instruction on the call stack.
3501 Once found, execution continues at the "exceptional" destination block
3502 specified by the <tt>invoke</tt> instruction. If there is no <tt>invoke</tt>
3503 instruction in the dynamic call chain, undefined behavior results.</p>
3505 <p>Note that the code generator does not yet completely support unwind, and
3506 that the invoke/unwind semantics are likely to change in future versions.</p>
3510 <!-- _______________________________________________________________________ -->
3513 <a name="i_resume">'<tt>resume</tt>' Instruction</a>
3520 resume <type> <value>
3524 <p>The '<tt>resume</tt>' instruction is a terminator instruction that has no
3528 <p>The '<tt>resume</tt>' instruction requires one argument, which must have the
3529 same type as the result of any '<tt>landingpad</tt>' instruction in the same
3533 <p>The '<tt>resume</tt>' instruction resumes propagation of an existing
3534 (in-flight) exception whose unwinding was interrupted with
3535 a <a href="#i_landingpad"><tt>landingpad</tt></a> instruction.</p>
3539 resume { i8*, i32 } %exn
3544 <!-- _______________________________________________________________________ -->
3547 <a name="i_unreachable">'<tt>unreachable</tt>' Instruction</a>
3558 <p>The '<tt>unreachable</tt>' instruction has no defined semantics. This
3559 instruction is used to inform the optimizer that a particular portion of the
3560 code is not reachable. This can be used to indicate that the code after a
3561 no-return function cannot be reached, and other facts.</p>
3564 <p>The '<tt>unreachable</tt>' instruction has no defined semantics.</p>
3570 <!-- ======================================================================= -->
3572 <a name="binaryops">Binary Operations</a>
3577 <p>Binary operators are used to do most of the computation in a program. They
3578 require two operands of the same type, execute an operation on them, and
3579 produce a single value. The operands might represent multiple data, as is
3580 the case with the <a href="#t_vector">vector</a> data type. The result value
3581 has the same type as its operands.</p>
3583 <p>There are several different binary operators:</p>
3585 <!-- _______________________________________________________________________ -->
3587 <a name="i_add">'<tt>add</tt>' Instruction</a>
3594 <result> = add <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3595 <result> = add nuw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3596 <result> = add nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3597 <result> = add nuw nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3601 <p>The '<tt>add</tt>' instruction returns the sum of its two operands.</p>
3604 <p>The two arguments to the '<tt>add</tt>' instruction must
3605 be <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of
3606 integer values. Both arguments must have identical types.</p>
3609 <p>The value produced is the integer sum of the two operands.</p>
3611 <p>If the sum has unsigned overflow, the result returned is the mathematical
3612 result modulo 2<sup>n</sup>, where n is the bit width of the result.</p>
3614 <p>Because LLVM integers use a two's complement representation, this instruction
3615 is appropriate for both signed and unsigned integers.</p>
3617 <p><tt>nuw</tt> and <tt>nsw</tt> stand for "No Unsigned Wrap"
3618 and "No Signed Wrap", respectively. If the <tt>nuw</tt> and/or
3619 <tt>nsw</tt> keywords are present, the result value of the <tt>add</tt>
3620 is a <a href="#poisonvalues">poison value</a> if unsigned and/or signed overflow,
3621 respectively, occurs.</p>
3625 <result> = add i32 4, %var <i>; yields {i32}:result = 4 + %var</i>
3630 <!-- _______________________________________________________________________ -->
3632 <a name="i_fadd">'<tt>fadd</tt>' Instruction</a>
3639 <result> = fadd <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3643 <p>The '<tt>fadd</tt>' instruction returns the sum of its two operands.</p>
3646 <p>The two arguments to the '<tt>fadd</tt>' instruction must be
3647 <a href="#t_floating">floating point</a> or <a href="#t_vector">vector</a> of
3648 floating point values. Both arguments must have identical types.</p>
3651 <p>The value produced is the floating point sum of the two operands.</p>
3655 <result> = fadd float 4.0, %var <i>; yields {float}:result = 4.0 + %var</i>
3660 <!-- _______________________________________________________________________ -->
3662 <a name="i_sub">'<tt>sub</tt>' Instruction</a>
3669 <result> = sub <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3670 <result> = sub nuw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3671 <result> = sub nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3672 <result> = sub nuw nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3676 <p>The '<tt>sub</tt>' instruction returns the difference of its two
3679 <p>Note that the '<tt>sub</tt>' instruction is used to represent the
3680 '<tt>neg</tt>' instruction present in most other intermediate
3681 representations.</p>
3684 <p>The two arguments to the '<tt>sub</tt>' instruction must
3685 be <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of
3686 integer values. Both arguments must have identical types.</p>
3689 <p>The value produced is the integer difference of the two operands.</p>
3691 <p>If the difference has unsigned overflow, the result returned is the
3692 mathematical result modulo 2<sup>n</sup>, where n is the bit width of the
3695 <p>Because LLVM integers use a two's complement representation, this instruction
3696 is appropriate for both signed and unsigned integers.</p>
3698 <p><tt>nuw</tt> and <tt>nsw</tt> stand for "No Unsigned Wrap"
3699 and "No Signed Wrap", respectively. If the <tt>nuw</tt> and/or
3700 <tt>nsw</tt> keywords are present, the result value of the <tt>sub</tt>
3701 is a <a href="#poisonvalues">poison value</a> if unsigned and/or signed overflow,
3702 respectively, occurs.</p>
3706 <result> = sub i32 4, %var <i>; yields {i32}:result = 4 - %var</i>
3707 <result> = sub i32 0, %val <i>; yields {i32}:result = -%var</i>
3712 <!-- _______________________________________________________________________ -->
3714 <a name="i_fsub">'<tt>fsub</tt>' Instruction</a>
3721 <result> = fsub <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3725 <p>The '<tt>fsub</tt>' instruction returns the difference of its two
3728 <p>Note that the '<tt>fsub</tt>' instruction is used to represent the
3729 '<tt>fneg</tt>' instruction present in most other intermediate
3730 representations.</p>
3733 <p>The two arguments to the '<tt>fsub</tt>' instruction must be
3734 <a href="#t_floating">floating point</a> or <a href="#t_vector">vector</a> of
3735 floating point values. Both arguments must have identical types.</p>
3738 <p>The value produced is the floating point difference of the two operands.</p>
3742 <result> = fsub float 4.0, %var <i>; yields {float}:result = 4.0 - %var</i>
3743 <result> = fsub float -0.0, %val <i>; yields {float}:result = -%var</i>
3748 <!-- _______________________________________________________________________ -->
3750 <a name="i_mul">'<tt>mul</tt>' Instruction</a>
3757 <result> = mul <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3758 <result> = mul nuw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3759 <result> = mul nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3760 <result> = mul nuw nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3764 <p>The '<tt>mul</tt>' instruction returns the product of its two operands.</p>
3767 <p>The two arguments to the '<tt>mul</tt>' instruction must
3768 be <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of
3769 integer values. Both arguments must have identical types.</p>
3772 <p>The value produced is the integer product of the two operands.</p>
3774 <p>If the result of the multiplication has unsigned overflow, the result
3775 returned is the mathematical result modulo 2<sup>n</sup>, where n is the bit
3776 width of the result.</p>
3778 <p>Because LLVM integers use a two's complement representation, and the result
3779 is the same width as the operands, this instruction returns the correct
3780 result for both signed and unsigned integers. If a full product
3781 (e.g. <tt>i32</tt>x<tt>i32</tt>-><tt>i64</tt>) is needed, the operands should
3782 be sign-extended or zero-extended as appropriate to the width of the full
3785 <p><tt>nuw</tt> and <tt>nsw</tt> stand for "No Unsigned Wrap"
3786 and "No Signed Wrap", respectively. If the <tt>nuw</tt> and/or
3787 <tt>nsw</tt> keywords are present, the result value of the <tt>mul</tt>
3788 is a <a href="#poisonvalues">poison value</a> if unsigned and/or signed overflow,
3789 respectively, occurs.</p>
3793 <result> = mul i32 4, %var <i>; yields {i32}:result = 4 * %var</i>
3798 <!-- _______________________________________________________________________ -->
3800 <a name="i_fmul">'<tt>fmul</tt>' Instruction</a>
3807 <result> = fmul <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3811 <p>The '<tt>fmul</tt>' instruction returns the product of its two operands.</p>
3814 <p>The two arguments to the '<tt>fmul</tt>' instruction must be
3815 <a href="#t_floating">floating point</a> or <a href="#t_vector">vector</a> of
3816 floating point values. Both arguments must have identical types.</p>
3819 <p>The value produced is the floating point product of the two operands.</p>
3823 <result> = fmul float 4.0, %var <i>; yields {float}:result = 4.0 * %var</i>
3828 <!-- _______________________________________________________________________ -->
3830 <a name="i_udiv">'<tt>udiv</tt>' Instruction</a>
3837 <result> = udiv <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3838 <result> = udiv exact <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3842 <p>The '<tt>udiv</tt>' instruction returns the quotient of its two operands.</p>
3845 <p>The two arguments to the '<tt>udiv</tt>' instruction must be
3846 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
3847 values. Both arguments must have identical types.</p>
3850 <p>The value produced is the unsigned integer quotient of the two operands.</p>
3852 <p>Note that unsigned integer division and signed integer division are distinct
3853 operations; for signed integer division, use '<tt>sdiv</tt>'.</p>
3855 <p>Division by zero leads to undefined behavior.</p>
3857 <p>If the <tt>exact</tt> keyword is present, the result value of the
3858 <tt>udiv</tt> is a <a href="#poisonvalues">poison value</a> if %op1 is not a
3859 multiple of %op2 (as such, "((a udiv exact b) mul b) == a").</p>
3864 <result> = udiv i32 4, %var <i>; yields {i32}:result = 4 / %var</i>
3869 <!-- _______________________________________________________________________ -->
3871 <a name="i_sdiv">'<tt>sdiv</tt>' Instruction</a>
3878 <result> = sdiv <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3879 <result> = sdiv exact <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3883 <p>The '<tt>sdiv</tt>' instruction returns the quotient of its two operands.</p>
3886 <p>The two arguments to the '<tt>sdiv</tt>' instruction must be
3887 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
3888 values. Both arguments must have identical types.</p>
3891 <p>The value produced is the signed integer quotient of the two operands rounded
3894 <p>Note that signed integer division and unsigned integer division are distinct
3895 operations; for unsigned integer division, use '<tt>udiv</tt>'.</p>
3897 <p>Division by zero leads to undefined behavior. Overflow also leads to
3898 undefined behavior; this is a rare case, but can occur, for example, by doing
3899 a 32-bit division of -2147483648 by -1.</p>
3901 <p>If the <tt>exact</tt> keyword is present, the result value of the
3902 <tt>sdiv</tt> is a <a href="#poisonvalues">poison value</a> if the result would
3907 <result> = sdiv i32 4, %var <i>; yields {i32}:result = 4 / %var</i>
3912 <!-- _______________________________________________________________________ -->
3914 <a name="i_fdiv">'<tt>fdiv</tt>' Instruction</a>
3921 <result> = fdiv <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3925 <p>The '<tt>fdiv</tt>' instruction returns the quotient of its two operands.</p>
3928 <p>The two arguments to the '<tt>fdiv</tt>' instruction must be
3929 <a href="#t_floating">floating point</a> or <a href="#t_vector">vector</a> of
3930 floating point values. Both arguments must have identical types.</p>
3933 <p>The value produced is the floating point quotient of the two operands.</p>
3937 <result> = fdiv float 4.0, %var <i>; yields {float}:result = 4.0 / %var</i>
3942 <!-- _______________________________________________________________________ -->
3944 <a name="i_urem">'<tt>urem</tt>' Instruction</a>
3951 <result> = urem <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3955 <p>The '<tt>urem</tt>' instruction returns the remainder from the unsigned
3956 division of its two arguments.</p>
3959 <p>The two arguments to the '<tt>urem</tt>' instruction must be
3960 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
3961 values. Both arguments must have identical types.</p>
3964 <p>This instruction returns the unsigned integer <i>remainder</i> of a division.
3965 This instruction always performs an unsigned division to get the
3968 <p>Note that unsigned integer remainder and signed integer remainder are
3969 distinct operations; for signed integer remainder, use '<tt>srem</tt>'.</p>
3971 <p>Taking the remainder of a division by zero leads to undefined behavior.</p>
3975 <result> = urem i32 4, %var <i>; yields {i32}:result = 4 % %var</i>
3980 <!-- _______________________________________________________________________ -->
3982 <a name="i_srem">'<tt>srem</tt>' Instruction</a>
3989 <result> = srem <ty> <op1>, <op2> <i>; yields {ty}:result</i>
3993 <p>The '<tt>srem</tt>' instruction returns the remainder from the signed
3994 division of its two operands. This instruction can also take
3995 <a href="#t_vector">vector</a> versions of the values in which case the
3996 elements must be integers.</p>
3999 <p>The two arguments to the '<tt>srem</tt>' instruction must be
4000 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
4001 values. Both arguments must have identical types.</p>
4004 <p>This instruction returns the <i>remainder</i> of a division (where the result
4005 is either zero or has the same sign as the dividend, <tt>op1</tt>), not the
4006 <i>modulo</i> operator (where the result is either zero or has the same sign
4007 as the divisor, <tt>op2</tt>) of a value.
4008 For more information about the difference,
4009 see <a href="http://mathforum.org/dr.math/problems/anne.4.28.99.html">The
4010 Math Forum</a>. For a table of how this is implemented in various languages,
4011 please see <a href="http://en.wikipedia.org/wiki/Modulo_operation">
4012 Wikipedia: modulo operation</a>.</p>
4014 <p>Note that signed integer remainder and unsigned integer remainder are
4015 distinct operations; for unsigned integer remainder, use '<tt>urem</tt>'.</p>
4017 <p>Taking the remainder of a division by zero leads to undefined behavior.
4018 Overflow also leads to undefined behavior; this is a rare case, but can
4019 occur, for example, by taking the remainder of a 32-bit division of
4020 -2147483648 by -1. (The remainder doesn't actually overflow, but this rule
4021 lets srem be implemented using instructions that return both the result of
4022 the division and the remainder.)</p>
4026 <result> = srem i32 4, %var <i>; yields {i32}:result = 4 % %var</i>
4031 <!-- _______________________________________________________________________ -->
4033 <a name="i_frem">'<tt>frem</tt>' Instruction</a>
4040 <result> = frem <ty> <op1>, <op2> <i>; yields {ty}:result</i>
4044 <p>The '<tt>frem</tt>' instruction returns the remainder from the division of
4045 its two operands.</p>
4048 <p>The two arguments to the '<tt>frem</tt>' instruction must be
4049 <a href="#t_floating">floating point</a> or <a href="#t_vector">vector</a> of
4050 floating point values. Both arguments must have identical types.</p>
4053 <p>This instruction returns the <i>remainder</i> of a division. The remainder
4054 has the same sign as the dividend.</p>
4058 <result> = frem float 4.0, %var <i>; yields {float}:result = 4.0 % %var</i>
4065 <!-- ======================================================================= -->
4067 <a name="bitwiseops">Bitwise Binary Operations</a>
4072 <p>Bitwise binary operators are used to do various forms of bit-twiddling in a
4073 program. They are generally very efficient instructions and can commonly be
4074 strength reduced from other instructions. They require two operands of the
4075 same type, execute an operation on them, and produce a single value. The
4076 resulting value is the same type as its operands.</p>
4078 <!-- _______________________________________________________________________ -->
4080 <a name="i_shl">'<tt>shl</tt>' Instruction</a>
4087 <result> = shl <ty> <op1>, <op2> <i>; yields {ty}:result</i>
4088 <result> = shl nuw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
4089 <result> = shl nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
4090 <result> = shl nuw nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
4094 <p>The '<tt>shl</tt>' instruction returns the first operand shifted to the left
4095 a specified number of bits.</p>
4098 <p>Both arguments to the '<tt>shl</tt>' instruction must be the
4099 same <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of
4100 integer type. '<tt>op2</tt>' is treated as an unsigned value.</p>
4103 <p>The value produced is <tt>op1</tt> * 2<sup><tt>op2</tt></sup> mod
4104 2<sup>n</sup>, where <tt>n</tt> is the width of the result. If <tt>op2</tt>
4105 is (statically or dynamically) negative or equal to or larger than the number
4106 of bits in <tt>op1</tt>, the result is undefined. If the arguments are
4107 vectors, each vector element of <tt>op1</tt> is shifted by the corresponding
4108 shift amount in <tt>op2</tt>.</p>
4110 <p>If the <tt>nuw</tt> keyword is present, then the shift produces a
4111 <a href="#poisonvalues">poison value</a> if it shifts out any non-zero bits. If
4112 the <tt>nsw</tt> keyword is present, then the shift produces a
4113 <a href="#poisonvalues">poison value</a> if it shifts out any bits that disagree
4114 with the resultant sign bit. As such, NUW/NSW have the same semantics as
4115 they would if the shift were expressed as a mul instruction with the same
4116 nsw/nuw bits in (mul %op1, (shl 1, %op2)).</p>
4120 <result> = shl i32 4, %var <i>; yields {i32}: 4 << %var</i>
4121 <result> = shl i32 4, 2 <i>; yields {i32}: 16</i>
4122 <result> = shl i32 1, 10 <i>; yields {i32}: 1024</i>
4123 <result> = shl i32 1, 32 <i>; undefined</i>
4124 <result> = shl <2 x i32> < i32 1, i32 1>, < i32 1, i32 2> <i>; yields: result=<2 x i32> < i32 2, i32 4></i>
4129 <!-- _______________________________________________________________________ -->
4131 <a name="i_lshr">'<tt>lshr</tt>' Instruction</a>
4138 <result> = lshr <ty> <op1>, <op2> <i>; yields {ty}:result</i>
4139 <result> = lshr exact <ty> <op1>, <op2> <i>; yields {ty}:result</i>
4143 <p>The '<tt>lshr</tt>' instruction (logical shift right) returns the first
4144 operand shifted to the right a specified number of bits with zero fill.</p>
4147 <p>Both arguments to the '<tt>lshr</tt>' instruction must be the same
4148 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
4149 type. '<tt>op2</tt>' is treated as an unsigned value.</p>
4152 <p>This instruction always performs a logical shift right operation. The most
4153 significant bits of the result will be filled with zero bits after the shift.
4154 If <tt>op2</tt> is (statically or dynamically) equal to or larger than the
4155 number of bits in <tt>op1</tt>, the result is undefined. If the arguments are
4156 vectors, each vector element of <tt>op1</tt> is shifted by the corresponding
4157 shift amount in <tt>op2</tt>.</p>
4159 <p>If the <tt>exact</tt> keyword is present, the result value of the
4160 <tt>lshr</tt> is a <a href="#poisonvalues">poison value</a> if any of the bits
4161 shifted out are non-zero.</p>
4166 <result> = lshr i32 4, 1 <i>; yields {i32}:result = 2</i>
4167 <result> = lshr i32 4, 2 <i>; yields {i32}:result = 1</i>
4168 <result> = lshr i8 4, 3 <i>; yields {i8}:result = 0</i>
4169 <result> = lshr i8 -2, 1 <i>; yields {i8}:result = 0x7FFFFFFF </i>
4170 <result> = lshr i32 1, 32 <i>; undefined</i>
4171 <result> = lshr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 2> <i>; yields: result=<2 x i32> < i32 0x7FFFFFFF, i32 1></i>
4176 <!-- _______________________________________________________________________ -->
4178 <a name="i_ashr">'<tt>ashr</tt>' Instruction</a>
4185 <result> = ashr <ty> <op1>, <op2> <i>; yields {ty}:result</i>
4186 <result> = ashr exact <ty> <op1>, <op2> <i>; yields {ty}:result</i>
4190 <p>The '<tt>ashr</tt>' instruction (arithmetic shift right) returns the first
4191 operand shifted to the right a specified number of bits with sign
4195 <p>Both arguments to the '<tt>ashr</tt>' instruction must be the same
4196 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
4197 type. '<tt>op2</tt>' is treated as an unsigned value.</p>
4200 <p>This instruction always performs an arithmetic shift right operation, The
4201 most significant bits of the result will be filled with the sign bit
4202 of <tt>op1</tt>. If <tt>op2</tt> is (statically or dynamically) equal to or
4203 larger than the number of bits in <tt>op1</tt>, the result is undefined. If
4204 the arguments are vectors, each vector element of <tt>op1</tt> is shifted by
4205 the corresponding shift amount in <tt>op2</tt>.</p>
4207 <p>If the <tt>exact</tt> keyword is present, the result value of the
4208 <tt>ashr</tt> is a <a href="#poisonvalues">poison value</a> if any of the bits
4209 shifted out are non-zero.</p>
4213 <result> = ashr i32 4, 1 <i>; yields {i32}:result = 2</i>
4214 <result> = ashr i32 4, 2 <i>; yields {i32}:result = 1</i>
4215 <result> = ashr i8 4, 3 <i>; yields {i8}:result = 0</i>
4216 <result> = ashr i8 -2, 1 <i>; yields {i8}:result = -1</i>
4217 <result> = ashr i32 1, 32 <i>; undefined</i>
4218 <result> = ashr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 3> <i>; yields: result=<2 x i32> < i32 -1, i32 0></i>
4223 <!-- _______________________________________________________________________ -->
4225 <a name="i_and">'<tt>and</tt>' Instruction</a>
4232 <result> = and <ty> <op1>, <op2> <i>; yields {ty}:result</i>
4236 <p>The '<tt>and</tt>' instruction returns the bitwise logical and of its two
4240 <p>The two arguments to the '<tt>and</tt>' instruction must be
4241 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
4242 values. Both arguments must have identical types.</p>
4245 <p>The truth table used for the '<tt>and</tt>' instruction is:</p>
4247 <table border="1" cellspacing="0" cellpadding="4">
4279 <result> = and i32 4, %var <i>; yields {i32}:result = 4 & %var</i>
4280 <result> = and i32 15, 40 <i>; yields {i32}:result = 8</i>
4281 <result> = and i32 4, 8 <i>; yields {i32}:result = 0</i>
4284 <!-- _______________________________________________________________________ -->
4286 <a name="i_or">'<tt>or</tt>' Instruction</a>
4293 <result> = or <ty> <op1>, <op2> <i>; yields {ty}:result</i>
4297 <p>The '<tt>or</tt>' instruction returns the bitwise logical inclusive or of its
4301 <p>The two arguments to the '<tt>or</tt>' instruction must be
4302 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
4303 values. Both arguments must have identical types.</p>
4306 <p>The truth table used for the '<tt>or</tt>' instruction is:</p>
4308 <table border="1" cellspacing="0" cellpadding="4">
4340 <result> = or i32 4, %var <i>; yields {i32}:result = 4 | %var</i>
4341 <result> = or i32 15, 40 <i>; yields {i32}:result = 47</i>
4342 <result> = or i32 4, 8 <i>; yields {i32}:result = 12</i>
4347 <!-- _______________________________________________________________________ -->
4349 <a name="i_xor">'<tt>xor</tt>' Instruction</a>
4356 <result> = xor <ty> <op1>, <op2> <i>; yields {ty}:result</i>
4360 <p>The '<tt>xor</tt>' instruction returns the bitwise logical exclusive or of
4361 its two operands. The <tt>xor</tt> is used to implement the "one's
4362 complement" operation, which is the "~" operator in C.</p>
4365 <p>The two arguments to the '<tt>xor</tt>' instruction must be
4366 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
4367 values. Both arguments must have identical types.</p>
4370 <p>The truth table used for the '<tt>xor</tt>' instruction is:</p>
4372 <table border="1" cellspacing="0" cellpadding="4">
4404 <result> = xor i32 4, %var <i>; yields {i32}:result = 4 ^ %var</i>
4405 <result> = xor i32 15, 40 <i>; yields {i32}:result = 39</i>
4406 <result> = xor i32 4, 8 <i>; yields {i32}:result = 12</i>
4407 <result> = xor i32 %V, -1 <i>; yields {i32}:result = ~%V</i>
4414 <!-- ======================================================================= -->
4416 <a name="vectorops">Vector Operations</a>
4421 <p>LLVM supports several instructions to represent vector operations in a
4422 target-independent manner. These instructions cover the element-access and
4423 vector-specific operations needed to process vectors effectively. While LLVM
4424 does directly support these vector operations, many sophisticated algorithms
4425 will want to use target-specific intrinsics to take full advantage of a
4426 specific target.</p>
4428 <!-- _______________________________________________________________________ -->
4430 <a name="i_extractelement">'<tt>extractelement</tt>' Instruction</a>
4437 <result> = extractelement <n x <ty>> <val>, i32 <idx> <i>; yields <ty></i>
4441 <p>The '<tt>extractelement</tt>' instruction extracts a single scalar element
4442 from a vector at a specified index.</p>
4446 <p>The first operand of an '<tt>extractelement</tt>' instruction is a value
4447 of <a href="#t_vector">vector</a> type. The second operand is an index
4448 indicating the position from which to extract the element. The index may be
4452 <p>The result is a scalar of the same type as the element type of
4453 <tt>val</tt>. Its value is the value at position <tt>idx</tt> of
4454 <tt>val</tt>. If <tt>idx</tt> exceeds the length of <tt>val</tt>, the
4455 results are undefined.</p>
4459 <result> = extractelement <4 x i32> %vec, i32 0 <i>; yields i32</i>
4464 <!-- _______________________________________________________________________ -->
4466 <a name="i_insertelement">'<tt>insertelement</tt>' Instruction</a>
4473 <result> = insertelement <n x <ty>> <val>, <ty> <elt>, i32 <idx> <i>; yields <n x <ty>></i>
4477 <p>The '<tt>insertelement</tt>' instruction inserts a scalar element into a
4478 vector at a specified index.</p>
4481 <p>The first operand of an '<tt>insertelement</tt>' instruction is a value
4482 of <a href="#t_vector">vector</a> type. The second operand is a scalar value
4483 whose type must equal the element type of the first operand. The third
4484 operand is an index indicating the position at which to insert the value.
4485 The index may be a variable.</p>
4488 <p>The result is a vector of the same type as <tt>val</tt>. Its element values
4489 are those of <tt>val</tt> except at position <tt>idx</tt>, where it gets the
4490 value <tt>elt</tt>. If <tt>idx</tt> exceeds the length of <tt>val</tt>, the
4491 results are undefined.</p>
4495 <result> = insertelement <4 x i32> %vec, i32 1, i32 0 <i>; yields <4 x i32></i>
4500 <!-- _______________________________________________________________________ -->
4502 <a name="i_shufflevector">'<tt>shufflevector</tt>' Instruction</a>
4509 <result> = shufflevector <n x <ty>> <v1>, <n x <ty>> <v2>, <m x i32> <mask> <i>; yields <m x <ty>></i>
4513 <p>The '<tt>shufflevector</tt>' instruction constructs a permutation of elements
4514 from two input vectors, returning a vector with the same element type as the
4515 input and length that is the same as the shuffle mask.</p>
4518 <p>The first two operands of a '<tt>shufflevector</tt>' instruction are vectors
4519 with types that match each other. The third argument is a shuffle mask whose
4520 element type is always 'i32'. The result of the instruction is a vector
4521 whose length is the same as the shuffle mask and whose element type is the
4522 same as the element type of the first two operands.</p>
4524 <p>The shuffle mask operand is required to be a constant vector with either
4525 constant integer or undef values.</p>
4528 <p>The elements of the two input vectors are numbered from left to right across
4529 both of the vectors. The shuffle mask operand specifies, for each element of
4530 the result vector, which element of the two input vectors the result element
4531 gets. The element selector may be undef (meaning "don't care") and the
4532 second operand may be undef if performing a shuffle from only one vector.</p>
4536 <result> = shufflevector <4 x i32> %v1, <4 x i32> %v2,
4537 <4 x i32> <i32 0, i32 4, i32 1, i32 5> <i>; yields <4 x i32></i>
4538 <result> = shufflevector <4 x i32> %v1, <4 x i32> undef,
4539 <4 x i32> <i32 0, i32 1, i32 2, i32 3> <i>; yields <4 x i32></i> - Identity shuffle.
4540 <result> = shufflevector <8 x i32> %v1, <8 x i32> undef,
4541 <4 x i32> <i32 0, i32 1, i32 2, i32 3> <i>; yields <4 x i32></i>
4542 <result> = shufflevector <4 x i32> %v1, <4 x i32> %v2,
4543 <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>
4550 <!-- ======================================================================= -->
4552 <a name="aggregateops">Aggregate Operations</a>
4557 <p>LLVM supports several instructions for working with
4558 <a href="#t_aggregate">aggregate</a> values.</p>
4560 <!-- _______________________________________________________________________ -->
4562 <a name="i_extractvalue">'<tt>extractvalue</tt>' Instruction</a>
4569 <result> = extractvalue <aggregate type> <val>, <idx>{, <idx>}*
4573 <p>The '<tt>extractvalue</tt>' instruction extracts the value of a member field
4574 from an <a href="#t_aggregate">aggregate</a> value.</p>
4577 <p>The first operand of an '<tt>extractvalue</tt>' instruction is a value
4578 of <a href="#t_struct">struct</a> or
4579 <a href="#t_array">array</a> type. The operands are constant indices to
4580 specify which value to extract in a similar manner as indices in a
4581 '<tt><a href="#i_getelementptr">getelementptr</a></tt>' instruction.</p>
4582 <p>The major differences to <tt>getelementptr</tt> indexing are:</p>
4584 <li>Since the value being indexed is not a pointer, the first index is
4585 omitted and assumed to be zero.</li>
4586 <li>At least one index must be specified.</li>
4587 <li>Not only struct indices but also array indices must be in
4592 <p>The result is the value at the position in the aggregate specified by the
4597 <result> = extractvalue {i32, float} %agg, 0 <i>; yields i32</i>
4602 <!-- _______________________________________________________________________ -->
4604 <a name="i_insertvalue">'<tt>insertvalue</tt>' Instruction</a>
4611 <result> = insertvalue <aggregate type> <val>, <ty> <elt>, <idx>{, <idx>}* <i>; yields <aggregate type></i>
4615 <p>The '<tt>insertvalue</tt>' instruction inserts a value into a member field
4616 in an <a href="#t_aggregate">aggregate</a> value.</p>
4619 <p>The first operand of an '<tt>insertvalue</tt>' instruction is a value
4620 of <a href="#t_struct">struct</a> or
4621 <a href="#t_array">array</a> type. The second operand is a first-class
4622 value to insert. The following operands are constant indices indicating
4623 the position at which to insert the value in a similar manner as indices in a
4624 '<tt><a href="#i_extractvalue">extractvalue</a></tt>' instruction. The
4625 value to insert must have the same type as the value identified by the
4629 <p>The result is an aggregate of the same type as <tt>val</tt>. Its value is
4630 that of <tt>val</tt> except that the value at the position specified by the
4631 indices is that of <tt>elt</tt>.</p>
4635 %agg1 = insertvalue {i32, float} undef, i32 1, 0 <i>; yields {i32 1, float undef}</i>
4636 %agg2 = insertvalue {i32, float} %agg1, float %val, 1 <i>; yields {i32 1, float %val}</i>
4637 %agg3 = insertvalue {i32, {float}} %agg1, float %val, 1, 0 <i>; yields {i32 1, float %val}</i>
4644 <!-- ======================================================================= -->
4646 <a name="memoryops">Memory Access and Addressing Operations</a>
4651 <p>A key design point of an SSA-based representation is how it represents
4652 memory. In LLVM, no memory locations are in SSA form, which makes things
4653 very simple. This section describes how to read, write, and allocate
4656 <!-- _______________________________________________________________________ -->
4658 <a name="i_alloca">'<tt>alloca</tt>' Instruction</a>
4665 <result> = alloca <type>[, <ty> <NumElements>][, align <alignment>] <i>; yields {type*}:result</i>
4669 <p>The '<tt>alloca</tt>' instruction allocates memory on the stack frame of the
4670 currently executing function, to be automatically released when this function
4671 returns to its caller. The object is always allocated in the generic address
4672 space (address space zero).</p>
4675 <p>The '<tt>alloca</tt>' instruction
4676 allocates <tt>sizeof(<type>)*NumElements</tt> bytes of memory on the
4677 runtime stack, returning a pointer of the appropriate type to the program.
4678 If "NumElements" is specified, it is the number of elements allocated,
4679 otherwise "NumElements" is defaulted to be one. If a constant alignment is
4680 specified, the value result of the allocation is guaranteed to be aligned to
4681 at least that boundary. If not specified, or if zero, the target can choose
4682 to align the allocation on any convenient boundary compatible with the
4685 <p>'<tt>type</tt>' may be any sized type.</p>
4688 <p>Memory is allocated; a pointer is returned. The operation is undefined if
4689 there is insufficient stack space for the allocation. '<tt>alloca</tt>'d
4690 memory is automatically released when the function returns. The
4691 '<tt>alloca</tt>' instruction is commonly used to represent automatic
4692 variables that must have an address available. When the function returns
4693 (either with the <tt><a href="#i_ret">ret</a></tt>
4694 or <tt><a href="#i_unwind">unwind</a></tt> instructions), the memory is
4695 reclaimed. Allocating zero bytes is legal, but the result is undefined.</p>
4699 %ptr = alloca i32 <i>; yields {i32*}:ptr</i>
4700 %ptr = alloca i32, i32 4 <i>; yields {i32*}:ptr</i>
4701 %ptr = alloca i32, i32 4, align 1024 <i>; yields {i32*}:ptr</i>
4702 %ptr = alloca i32, align 1024 <i>; yields {i32*}:ptr</i>
4707 <!-- _______________________________________________________________________ -->
4709 <a name="i_load">'<tt>load</tt>' Instruction</a>
4716 <result> = load [volatile] <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>]
4717 <result> = load atomic [volatile] <ty>* <pointer> [singlethread] <ordering>, align <alignment>
4718 !<index> = !{ i32 1 }
4722 <p>The '<tt>load</tt>' instruction is used to read from memory.</p>
4725 <p>The argument to the '<tt>load</tt>' instruction specifies the memory address
4726 from which to load. The pointer must point to
4727 a <a href="#t_firstclass">first class</a> type. If the <tt>load</tt> is
4728 marked as <tt>volatile</tt>, then the optimizer is not allowed to modify the
4729 number or order of execution of this <tt>load</tt> with other <a
4730 href="#volatile">volatile operations</a>.</p>
4732 <p>If the <code>load</code> is marked as <code>atomic</code>, it takes an extra
4733 <a href="#ordering">ordering</a> and optional <code>singlethread</code>
4734 argument. The <code>release</code> and <code>acq_rel</code> orderings are
4735 not valid on <code>load</code> instructions. Atomic loads produce <a
4736 href="#memorymodel">defined</a> results when they may see multiple atomic
4737 stores. The type of the pointee must be an integer type whose bit width
4738 is a power of two greater than or equal to eight and less than or equal
4739 to a target-specific size limit. <code>align</code> must be explicitly
4740 specified on atomic loads, and the load has undefined behavior if the
4741 alignment is not set to a value which is at least the size in bytes of
4742 the pointee. <code>!nontemporal</code> does not have any defined semantics
4743 for atomic loads.</p>
4745 <p>The optional constant <tt>align</tt> argument specifies the alignment of the
4746 operation (that is, the alignment of the memory address). A value of 0 or an
4747 omitted <tt>align</tt> argument means that the operation has the preferential
4748 alignment for the target. It is the responsibility of the code emitter to
4749 ensure that the alignment information is correct. Overestimating the
4750 alignment results in undefined behavior. Underestimating the alignment may
4751 produce less efficient code. An alignment of 1 is always safe.</p>
4753 <p>The optional <tt>!nontemporal</tt> metadata must reference a single
4754 metatadata name <index> corresponding to a metadata node with
4755 one <tt>i32</tt> entry of value 1. The existence of
4756 the <tt>!nontemporal</tt> metatadata on the instruction tells the optimizer
4757 and code generator that this load is not expected to be reused in the cache.
4758 The code generator may select special instructions to save cache bandwidth,
4759 such as the <tt>MOVNT</tt> instruction on x86.</p>
4762 <p>The location of memory pointed to is loaded. If the value being loaded is of
4763 scalar type then the number of bytes read does not exceed the minimum number
4764 of bytes needed to hold all bits of the type. For example, loading an
4765 <tt>i24</tt> reads at most three bytes. When loading a value of a type like
4766 <tt>i20</tt> with a size that is not an integral number of bytes, the result
4767 is undefined if the value was not originally written using a store of the
4772 %ptr = <a href="#i_alloca">alloca</a> i32 <i>; yields {i32*}:ptr</i>
4773 <a href="#i_store">store</a> i32 3, i32* %ptr <i>; yields {void}</i>
4774 %val = load i32* %ptr <i>; yields {i32}:val = i32 3</i>
4779 <!-- _______________________________________________________________________ -->
4781 <a name="i_store">'<tt>store</tt>' Instruction</a>
4788 store [volatile] <ty> <value>, <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>] <i>; yields {void}</i>
4789 store atomic [volatile] <ty> <value>, <ty>* <pointer> [singlethread] <ordering>, align <alignment> <i>; yields {void}</i>
4793 <p>The '<tt>store</tt>' instruction is used to write to memory.</p>
4796 <p>There are two arguments to the '<tt>store</tt>' instruction: a value to store
4797 and an address at which to store it. The type of the
4798 '<tt><pointer></tt>' operand must be a pointer to
4799 the <a href="#t_firstclass">first class</a> type of the
4800 '<tt><value></tt>' operand. If the <tt>store</tt> is marked as
4801 <tt>volatile</tt>, then the optimizer is not allowed to modify the number or
4802 order of execution of this <tt>store</tt> with other <a
4803 href="#volatile">volatile operations</a>.</p>
4805 <p>If the <code>store</code> is marked as <code>atomic</code>, it takes an extra
4806 <a href="#ordering">ordering</a> and optional <code>singlethread</code>
4807 argument. The <code>acquire</code> and <code>acq_rel</code> orderings aren't
4808 valid on <code>store</code> instructions. Atomic loads produce <a
4809 href="#memorymodel">defined</a> results when they may see multiple atomic
4810 stores. The type of the pointee must be an integer type whose bit width
4811 is a power of two greater than or equal to eight and less than or equal
4812 to a target-specific size limit. <code>align</code> must be explicitly
4813 specified on atomic stores, and the store has undefined behavior if the
4814 alignment is not set to a value which is at least the size in bytes of
4815 the pointee. <code>!nontemporal</code> does not have any defined semantics
4816 for atomic stores.</p>
4818 <p>The optional constant "align" argument specifies the alignment of the
4819 operation (that is, the alignment of the memory address). A value of 0 or an
4820 omitted "align" argument means that the operation has the preferential
4821 alignment for the target. It is the responsibility of the code emitter to
4822 ensure that the alignment information is correct. Overestimating the
4823 alignment results in an undefined behavior. Underestimating the alignment may
4824 produce less efficient code. An alignment of 1 is always safe.</p>
4826 <p>The optional !nontemporal metadata must reference a single metatadata
4827 name <index> corresponding to a metadata node with one i32 entry of
4828 value 1. The existence of the !nontemporal metatadata on the
4829 instruction tells the optimizer and code generator that this load is
4830 not expected to be reused in the cache. The code generator may
4831 select special instructions to save cache bandwidth, such as the
4832 MOVNT instruction on x86.</p>
4836 <p>The contents of memory are updated to contain '<tt><value></tt>' at the
4837 location specified by the '<tt><pointer></tt>' operand. If
4838 '<tt><value></tt>' is of scalar type then the number of bytes written
4839 does not exceed the minimum number of bytes needed to hold all bits of the
4840 type. For example, storing an <tt>i24</tt> writes at most three bytes. When
4841 writing a value of a type like <tt>i20</tt> with a size that is not an
4842 integral number of bytes, it is unspecified what happens to the extra bits
4843 that do not belong to the type, but they will typically be overwritten.</p>
4847 %ptr = <a href="#i_alloca">alloca</a> i32 <i>; yields {i32*}:ptr</i>
4848 store i32 3, i32* %ptr <i>; yields {void}</i>
4849 %val = <a href="#i_load">load</a> i32* %ptr <i>; yields {i32}:val = i32 3</i>
4854 <!-- _______________________________________________________________________ -->
4856 <a name="i_fence">'<tt>fence</tt>' Instruction</a>
4863 fence [singlethread] <ordering> <i>; yields {void}</i>
4867 <p>The '<tt>fence</tt>' instruction is used to introduce happens-before edges
4868 between operations.</p>
4870 <h5>Arguments:</h5> <p>'<code>fence</code>' instructions take an <a
4871 href="#ordering">ordering</a> argument which defines what
4872 <i>synchronizes-with</i> edges they add. They can only be given
4873 <code>acquire</code>, <code>release</code>, <code>acq_rel</code>, and
4874 <code>seq_cst</code> orderings.</p>
4877 <p>A fence <var>A</var> which has (at least) <code>release</code> ordering
4878 semantics <i>synchronizes with</i> a fence <var>B</var> with (at least)
4879 <code>acquire</code> ordering semantics if and only if there exist atomic
4880 operations <var>X</var> and <var>Y</var>, both operating on some atomic object
4881 <var>M</var>, such that <var>A</var> is sequenced before <var>X</var>,
4882 <var>X</var> modifies <var>M</var> (either directly or through some side effect
4883 of a sequence headed by <var>X</var>), <var>Y</var> is sequenced before
4884 <var>B</var>, and <var>Y</var> observes <var>M</var>. This provides a
4885 <i>happens-before</i> dependency between <var>A</var> and <var>B</var>. Rather
4886 than an explicit <code>fence</code>, one (but not both) of the atomic operations
4887 <var>X</var> or <var>Y</var> might provide a <code>release</code> or
4888 <code>acquire</code> (resp.) ordering constraint and still
4889 <i>synchronize-with</i> the explicit <code>fence</code> and establish the
4890 <i>happens-before</i> edge.</p>
4892 <p>A <code>fence</code> which has <code>seq_cst</code> ordering, in addition to
4893 having both <code>acquire</code> and <code>release</code> semantics specified
4894 above, participates in the global program order of other <code>seq_cst</code>
4895 operations and/or fences.</p>
4897 <p>The optional "<a href="#singlethread"><code>singlethread</code></a>" argument
4898 specifies that the fence only synchronizes with other fences in the same
4899 thread. (This is useful for interacting with signal handlers.)</p>
4903 fence acquire <i>; yields {void}</i>
4904 fence singlethread seq_cst <i>; yields {void}</i>
4909 <!-- _______________________________________________________________________ -->
4911 <a name="i_cmpxchg">'<tt>cmpxchg</tt>' Instruction</a>
4918 cmpxchg [volatile] <ty>* <pointer>, <ty> <cmp>, <ty> <new> [singlethread] <ordering> <i>; yields {ty}</i>
4922 <p>The '<tt>cmpxchg</tt>' instruction is used to atomically modify memory.
4923 It loads a value in memory and compares it to a given value. If they are
4924 equal, it stores a new value into the memory.</p>
4927 <p>There are three arguments to the '<code>cmpxchg</code>' instruction: an
4928 address to operate on, a value to compare to the value currently be at that
4929 address, and a new value to place at that address if the compared values are
4930 equal. The type of '<var><cmp></var>' must be an integer type whose
4931 bit width is a power of two greater than or equal to eight and less than
4932 or equal to a target-specific size limit. '<var><cmp></var>' and
4933 '<var><new></var>' must have the same type, and the type of
4934 '<var><pointer></var>' must be a pointer to that type. If the
4935 <code>cmpxchg</code> is marked as <code>volatile</code>, then the
4936 optimizer is not allowed to modify the number or order of execution
4937 of this <code>cmpxchg</code> with other <a href="#volatile">volatile
4940 <!-- FIXME: Extend allowed types. -->
4942 <p>The <a href="#ordering"><var>ordering</var></a> argument specifies how this
4943 <code>cmpxchg</code> synchronizes with other atomic operations.</p>
4945 <p>The optional "<code>singlethread</code>" argument declares that the
4946 <code>cmpxchg</code> is only atomic with respect to code (usually signal
4947 handlers) running in the same thread as the <code>cmpxchg</code>. Otherwise the
4948 cmpxchg is atomic with respect to all other code in the system.</p>
4950 <p>The pointer passed into cmpxchg must have alignment greater than or equal to
4951 the size in memory of the operand.
4954 <p>The contents of memory at the location specified by the
4955 '<tt><pointer></tt>' operand is read and compared to
4956 '<tt><cmp></tt>'; if the read value is the equal,
4957 '<tt><new></tt>' is written. The original value at the location
4960 <p>A successful <code>cmpxchg</code> is a read-modify-write instruction for the
4961 purpose of identifying <a href="#release_sequence">release sequences</a>. A
4962 failed <code>cmpxchg</code> is equivalent to an atomic load with an ordering
4963 parameter determined by dropping any <code>release</code> part of the
4964 <code>cmpxchg</code>'s ordering.</p>
4967 FIXME: Is compare_exchange_weak() necessary? (Consider after we've done
4968 optimization work on ARM.)
4970 FIXME: Is a weaker ordering constraint on failure helpful in practice?
4976 %orig = atomic <a href="#i_load">load</a> i32* %ptr unordered <i>; yields {i32}</i>
4977 <a href="#i_br">br</a> label %loop
4980 %cmp = <a href="#i_phi">phi</a> i32 [ %orig, %entry ], [%old, %loop]
4981 %squared = <a href="#i_mul">mul</a> i32 %cmp, %cmp
4982 %old = cmpxchg i32* %ptr, i32 %cmp, i32 %squared <i>; yields {i32}</i>
4983 %success = <a href="#i_icmp">icmp</a> eq i32 %cmp, %old
4984 <a href="#i_br">br</a> i1 %success, label %done, label %loop
4992 <!-- _______________________________________________________________________ -->
4994 <a name="i_atomicrmw">'<tt>atomicrmw</tt>' Instruction</a>
5001 atomicrmw [volatile] <operation> <ty>* <pointer>, <ty> <value> [singlethread] <ordering> <i>; yields {ty}</i>
5005 <p>The '<tt>atomicrmw</tt>' instruction is used to atomically modify memory.</p>
5008 <p>There are three arguments to the '<code>atomicrmw</code>' instruction: an
5009 operation to apply, an address whose value to modify, an argument to the
5010 operation. The operation must be one of the following keywords:</p>
5025 <p>The type of '<var><value></var>' must be an integer type whose
5026 bit width is a power of two greater than or equal to eight and less than
5027 or equal to a target-specific size limit. The type of the
5028 '<code><pointer></code>' operand must be a pointer to that type.
5029 If the <code>atomicrmw</code> is marked as <code>volatile</code>, then the
5030 optimizer is not allowed to modify the number or order of execution of this
5031 <code>atomicrmw</code> with other <a href="#volatile">volatile
5034 <!-- FIXME: Extend allowed types. -->
5037 <p>The contents of memory at the location specified by the
5038 '<tt><pointer></tt>' operand are atomically read, modified, and written
5039 back. The original value at the location is returned. The modification is
5040 specified by the <var>operation</var> argument:</p>
5043 <li>xchg: <code>*ptr = val</code></li>
5044 <li>add: <code>*ptr = *ptr + val</code></li>
5045 <li>sub: <code>*ptr = *ptr - val</code></li>
5046 <li>and: <code>*ptr = *ptr & val</code></li>
5047 <li>nand: <code>*ptr = ~(*ptr & val)</code></li>
5048 <li>or: <code>*ptr = *ptr | val</code></li>
5049 <li>xor: <code>*ptr = *ptr ^ val</code></li>
5050 <li>max: <code>*ptr = *ptr > val ? *ptr : val</code> (using a signed comparison)</li>
5051 <li>min: <code>*ptr = *ptr < val ? *ptr : val</code> (using a signed comparison)</li>
5052 <li>umax: <code>*ptr = *ptr > val ? *ptr : val</code> (using an unsigned comparison)</li>
5053 <li>umin: <code>*ptr = *ptr < val ? *ptr : val</code> (using an unsigned comparison)</li>
5058 %old = atomicrmw add i32* %ptr, i32 1 acquire <i>; yields {i32}</i>
5063 <!-- _______________________________________________________________________ -->
5065 <a name="i_getelementptr">'<tt>getelementptr</tt>' Instruction</a>
5072 <result> = getelementptr <pty>* <ptrval>{, <ty> <idx>}*
5073 <result> = getelementptr inbounds <pty>* <ptrval>{, <ty> <idx>}*
5074 <result> = getelementptr <ptr vector> ptrval, <vector index type> idx
5078 <p>The '<tt>getelementptr</tt>' instruction is used to get the address of a
5079 subelement of an <a href="#t_aggregate">aggregate</a> data structure.
5080 It performs address calculation only and does not access memory.</p>
5083 <p>The first argument is always a pointer or a vector of pointers,
5084 and forms the basis of the
5085 calculation. The remaining arguments are indices that indicate which of the
5086 elements of the aggregate object are indexed. The interpretation of each
5087 index is dependent on the type being indexed into. The first index always
5088 indexes the pointer value given as the first argument, the second index
5089 indexes a value of the type pointed to (not necessarily the value directly
5090 pointed to, since the first index can be non-zero), etc. The first type
5091 indexed into must be a pointer value, subsequent types can be arrays,
5092 vectors, and structs. Note that subsequent types being indexed into
5093 can never be pointers, since that would require loading the pointer before
5094 continuing calculation.</p>
5096 <p>The type of each index argument depends on the type it is indexing into.
5097 When indexing into a (optionally packed) structure, only <tt>i32</tt>
5098 integer <b>constants</b> are allowed. When indexing into an array, pointer
5099 or vector, integers of any width are allowed, and they are not required to be
5100 constant. These integers are treated as signed values where relevant.</p>
5102 <p>For example, let's consider a C code fragment and how it gets compiled to
5105 <pre class="doc_code">
5117 int *foo(struct ST *s) {
5118 return &s[1].Z.B[5][13];
5122 <p>The LLVM code generated by the GCC frontend is:</p>
5124 <pre class="doc_code">
5125 %RT = <a href="#namedtypes">type</a> { i8 , [10 x [20 x i32]], i8 }
5126 %ST = <a href="#namedtypes">type</a> { i32, double, %RT }
5128 define i32* @foo(%ST* %s) {
5130 %reg = getelementptr %ST* %s, i32 1, i32 2, i32 1, i32 5, i32 13
5136 <p>In the example above, the first index is indexing into the '<tt>%ST*</tt>'
5137 type, which is a pointer, yielding a '<tt>%ST</tt>' = '<tt>{ i32, double, %RT
5138 }</tt>' type, a structure. The second index indexes into the third element
5139 of the structure, yielding a '<tt>%RT</tt>' = '<tt>{ i8 , [10 x [20 x i32]],
5140 i8 }</tt>' type, another structure. The third index indexes into the second
5141 element of the structure, yielding a '<tt>[10 x [20 x i32]]</tt>' type, an
5142 array. The two dimensions of the array are subscripted into, yielding an
5143 '<tt>i32</tt>' type. The '<tt>getelementptr</tt>' instruction returns a
5144 pointer to this element, thus computing a value of '<tt>i32*</tt>' type.</p>
5146 <p>Note that it is perfectly legal to index partially through a structure,
5147 returning a pointer to an inner element. Because of this, the LLVM code for
5148 the given testcase is equivalent to:</p>
5151 define i32* @foo(%ST* %s) {
5152 %t1 = getelementptr %ST* %s, i32 1 <i>; yields %ST*:%t1</i>
5153 %t2 = getelementptr %ST* %t1, i32 0, i32 2 <i>; yields %RT*:%t2</i>
5154 %t3 = getelementptr %RT* %t2, i32 0, i32 1 <i>; yields [10 x [20 x i32]]*:%t3</i>
5155 %t4 = getelementptr [10 x [20 x i32]]* %t3, i32 0, i32 5 <i>; yields [20 x i32]*:%t4</i>
5156 %t5 = getelementptr [20 x i32]* %t4, i32 0, i32 13 <i>; yields i32*:%t5</i>
5161 <p>If the <tt>inbounds</tt> keyword is present, the result value of the
5162 <tt>getelementptr</tt> is a <a href="#poisonvalues">poison value</a> if the
5163 base pointer is not an <i>in bounds</i> address of an allocated object,
5164 or if any of the addresses that would be formed by successive addition of
5165 the offsets implied by the indices to the base address with infinitely
5166 precise signed arithmetic are not an <i>in bounds</i> address of that
5167 allocated object. The <i>in bounds</i> addresses for an allocated object
5168 are all the addresses that point into the object, plus the address one
5170 In cases where the base is a vector of pointers the <tt>inbounds</tt> keyword
5171 applies to each of the computations element-wise. </p>
5173 <p>If the <tt>inbounds</tt> keyword is not present, the offsets are added to
5174 the base address with silently-wrapping two's complement arithmetic. If the
5175 offsets have a different width from the pointer, they are sign-extended or
5176 truncated to the width of the pointer. The result value of the
5177 <tt>getelementptr</tt> may be outside the object pointed to by the base
5178 pointer. The result value may not necessarily be used to access memory
5179 though, even if it happens to point into allocated storage. See the
5180 <a href="#pointeraliasing">Pointer Aliasing Rules</a> section for more
5183 <p>The getelementptr instruction is often confusing. For some more insight into
5184 how it works, see <a href="GetElementPtr.html">the getelementptr FAQ</a>.</p>
5188 <i>; yields [12 x i8]*:aptr</i>
5189 %aptr = getelementptr {i32, [12 x i8]}* %saptr, i64 0, i32 1
5190 <i>; yields i8*:vptr</i>
5191 %vptr = getelementptr {i32, <2 x i8>}* %svptr, i64 0, i32 1, i32 1
5192 <i>; yields i8*:eptr</i>
5193 %eptr = getelementptr [12 x i8]* %aptr, i64 0, i32 1
5194 <i>; yields i32*:iptr</i>
5195 %iptr = getelementptr [10 x i32]* @arr, i16 0, i16 0
5198 <p>In cases where the pointer argument is a vector of pointers, only a
5199 single index may be used, and the number of vector elements has to be
5200 the same. For example: </p>
5201 <pre class="doc_code">
5202 %A = getelementptr <4 x i8*> %ptrs, <4 x i64> %offsets,
5209 <!-- ======================================================================= -->
5211 <a name="convertops">Conversion Operations</a>
5216 <p>The instructions in this category are the conversion instructions (casting)
5217 which all take a single operand and a type. They perform various bit
5218 conversions on the operand.</p>
5220 <!-- _______________________________________________________________________ -->
5222 <a name="i_trunc">'<tt>trunc .. to</tt>' Instruction</a>
5229 <result> = trunc <ty> <value> to <ty2> <i>; yields ty2</i>
5233 <p>The '<tt>trunc</tt>' instruction truncates its operand to the
5234 type <tt>ty2</tt>.</p>
5237 <p>The '<tt>trunc</tt>' instruction takes a value to trunc, and a type to trunc it to.
5238 Both types must be of <a href="#t_integer">integer</a> types, or vectors
5239 of the same number of integers.
5240 The bit size of the <tt>value</tt> must be larger than
5241 the bit size of the destination type, <tt>ty2</tt>.
5242 Equal sized types are not allowed.</p>
5245 <p>The '<tt>trunc</tt>' instruction truncates the high order bits
5246 in <tt>value</tt> and converts the remaining bits to <tt>ty2</tt>. Since the
5247 source size must be larger than the destination size, <tt>trunc</tt> cannot
5248 be a <i>no-op cast</i>. It will always truncate bits.</p>
5252 %X = trunc i32 257 to i8 <i>; yields i8:1</i>
5253 %Y = trunc i32 123 to i1 <i>; yields i1:true</i>
5254 %Z = trunc i32 122 to i1 <i>; yields i1:false</i>
5255 %W = trunc <2 x i16> <i16 8, i16 7> to <2 x i8> <i>; yields <i8 8, i8 7></i>
5260 <!-- _______________________________________________________________________ -->
5262 <a name="i_zext">'<tt>zext .. to</tt>' Instruction</a>
5269 <result> = zext <ty> <value> to <ty2> <i>; yields ty2</i>
5273 <p>The '<tt>zext</tt>' instruction zero extends its operand to type
5278 <p>The '<tt>zext</tt>' instruction takes a value to cast, and a type to cast it to.
5279 Both types must be of <a href="#t_integer">integer</a> types, or vectors
5280 of the same number of integers.
5281 The bit size of the <tt>value</tt> must be smaller than
5282 the bit size of the destination type,
5286 <p>The <tt>zext</tt> fills the high order bits of the <tt>value</tt> with zero
5287 bits until it reaches the size of the destination type, <tt>ty2</tt>.</p>
5289 <p>When zero extending from i1, the result will always be either 0 or 1.</p>
5293 %X = zext i32 257 to i64 <i>; yields i64:257</i>
5294 %Y = zext i1 true to i32 <i>; yields i32:1</i>
5295 %Z = zext <2 x i16> <i16 8, i16 7> to <2 x i32> <i>; yields <i32 8, i32 7></i>
5300 <!-- _______________________________________________________________________ -->
5302 <a name="i_sext">'<tt>sext .. to</tt>' Instruction</a>
5309 <result> = sext <ty> <value> to <ty2> <i>; yields ty2</i>
5313 <p>The '<tt>sext</tt>' sign extends <tt>value</tt> to the type <tt>ty2</tt>.</p>
5316 <p>The '<tt>sext</tt>' instruction takes a value to cast, and a type to cast it to.
5317 Both types must be of <a href="#t_integer">integer</a> types, or vectors
5318 of the same number of integers.
5319 The bit size of the <tt>value</tt> must be smaller than
5320 the bit size of the destination type,
5324 <p>The '<tt>sext</tt>' instruction performs a sign extension by copying the sign
5325 bit (highest order bit) of the <tt>value</tt> until it reaches the bit size
5326 of the type <tt>ty2</tt>.</p>
5328 <p>When sign extending from i1, the extension always results in -1 or 0.</p>
5332 %X = sext i8 -1 to i16 <i>; yields i16 :65535</i>
5333 %Y = sext i1 true to i32 <i>; yields i32:-1</i>
5334 %Z = sext <2 x i16> <i16 8, i16 7> to <2 x i32> <i>; yields <i32 8, i32 7></i>
5339 <!-- _______________________________________________________________________ -->
5341 <a name="i_fptrunc">'<tt>fptrunc .. to</tt>' Instruction</a>
5348 <result> = fptrunc <ty> <value> to <ty2> <i>; yields ty2</i>
5352 <p>The '<tt>fptrunc</tt>' instruction truncates <tt>value</tt> to type
5356 <p>The '<tt>fptrunc</tt>' instruction takes a <a href="#t_floating">floating
5357 point</a> value to cast and a <a href="#t_floating">floating point</a> type
5358 to cast it to. The size of <tt>value</tt> must be larger than the size of
5359 <tt>ty2</tt>. This implies that <tt>fptrunc</tt> cannot be used to make a
5360 <i>no-op cast</i>.</p>
5363 <p>The '<tt>fptrunc</tt>' instruction truncates a <tt>value</tt> from a larger
5364 <a href="#t_floating">floating point</a> type to a smaller
5365 <a href="#t_floating">floating point</a> type. If the value cannot fit
5366 within the destination type, <tt>ty2</tt>, then the results are
5371 %X = fptrunc double 123.0 to float <i>; yields float:123.0</i>
5372 %Y = fptrunc double 1.0E+300 to float <i>; yields undefined</i>
5377 <!-- _______________________________________________________________________ -->
5379 <a name="i_fpext">'<tt>fpext .. to</tt>' Instruction</a>
5386 <result> = fpext <ty> <value> to <ty2> <i>; yields ty2</i>
5390 <p>The '<tt>fpext</tt>' extends a floating point <tt>value</tt> to a larger
5391 floating point value.</p>
5394 <p>The '<tt>fpext</tt>' instruction takes a
5395 <a href="#t_floating">floating point</a> <tt>value</tt> to cast, and
5396 a <a href="#t_floating">floating point</a> type to cast it to. The source
5397 type must be smaller than the destination type.</p>
5400 <p>The '<tt>fpext</tt>' instruction extends the <tt>value</tt> from a smaller
5401 <a href="#t_floating">floating point</a> type to a larger
5402 <a href="#t_floating">floating point</a> type. The <tt>fpext</tt> cannot be
5403 used to make a <i>no-op cast</i> because it always changes bits. Use
5404 <tt>bitcast</tt> to make a <i>no-op cast</i> for a floating point cast.</p>
5408 %X = fpext float 3.125 to double <i>; yields double:3.125000e+00</i>
5409 %Y = fpext double %X to fp128 <i>; yields fp128:0xL00000000000000004000900000000000</i>
5414 <!-- _______________________________________________________________________ -->
5416 <a name="i_fptoui">'<tt>fptoui .. to</tt>' Instruction</a>
5423 <result> = fptoui <ty> <value> to <ty2> <i>; yields ty2</i>
5427 <p>The '<tt>fptoui</tt>' converts a floating point <tt>value</tt> to its
5428 unsigned integer equivalent of type <tt>ty2</tt>.</p>
5431 <p>The '<tt>fptoui</tt>' instruction takes a value to cast, which must be a
5432 scalar or vector <a href="#t_floating">floating point</a> value, and a type
5433 to cast it to <tt>ty2</tt>, which must be an <a href="#t_integer">integer</a>
5434 type. If <tt>ty</tt> is a vector floating point type, <tt>ty2</tt> must be a
5435 vector integer type with the same number of elements as <tt>ty</tt></p>
5438 <p>The '<tt>fptoui</tt>' instruction converts its
5439 <a href="#t_floating">floating point</a> operand into the nearest (rounding
5440 towards zero) unsigned integer value. If the value cannot fit
5441 in <tt>ty2</tt>, the results are undefined.</p>
5445 %X = fptoui double 123.0 to i32 <i>; yields i32:123</i>
5446 %Y = fptoui float 1.0E+300 to i1 <i>; yields undefined:1</i>
5447 %Z = fptoui float 1.04E+17 to i8 <i>; yields undefined:1</i>
5452 <!-- _______________________________________________________________________ -->
5454 <a name="i_fptosi">'<tt>fptosi .. to</tt>' Instruction</a>
5461 <result> = fptosi <ty> <value> to <ty2> <i>; yields ty2</i>
5465 <p>The '<tt>fptosi</tt>' instruction converts
5466 <a href="#t_floating">floating point</a> <tt>value</tt> to
5467 type <tt>ty2</tt>.</p>
5470 <p>The '<tt>fptosi</tt>' instruction takes a value to cast, which must be a
5471 scalar or vector <a href="#t_floating">floating point</a> value, and a type
5472 to cast it to <tt>ty2</tt>, which must be an <a href="#t_integer">integer</a>
5473 type. If <tt>ty</tt> is a vector floating point type, <tt>ty2</tt> must be a
5474 vector integer type with the same number of elements as <tt>ty</tt></p>
5477 <p>The '<tt>fptosi</tt>' instruction converts its
5478 <a href="#t_floating">floating point</a> operand into the nearest (rounding
5479 towards zero) signed integer value. If the value cannot fit in <tt>ty2</tt>,
5480 the results are undefined.</p>
5484 %X = fptosi double -123.0 to i32 <i>; yields i32:-123</i>
5485 %Y = fptosi float 1.0E-247 to i1 <i>; yields undefined:1</i>
5486 %Z = fptosi float 1.04E+17 to i8 <i>; yields undefined:1</i>
5491 <!-- _______________________________________________________________________ -->
5493 <a name="i_uitofp">'<tt>uitofp .. to</tt>' Instruction</a>
5500 <result> = uitofp <ty> <value> to <ty2> <i>; yields ty2</i>
5504 <p>The '<tt>uitofp</tt>' instruction regards <tt>value</tt> as an unsigned
5505 integer and converts that value to the <tt>ty2</tt> type.</p>
5508 <p>The '<tt>uitofp</tt>' instruction takes a value to cast, which must be a
5509 scalar or vector <a href="#t_integer">integer</a> value, and a type to cast
5510 it to <tt>ty2</tt>, which must be an <a href="#t_floating">floating point</a>
5511 type. If <tt>ty</tt> is a vector integer type, <tt>ty2</tt> must be a vector
5512 floating point type with the same number of elements as <tt>ty</tt></p>
5515 <p>The '<tt>uitofp</tt>' instruction interprets its operand as an unsigned
5516 integer quantity and converts it to the corresponding floating point
5517 value. If the value cannot fit in the floating point value, the results are
5522 %X = uitofp i32 257 to float <i>; yields float:257.0</i>
5523 %Y = uitofp i8 -1 to double <i>; yields double:255.0</i>
5528 <!-- _______________________________________________________________________ -->
5530 <a name="i_sitofp">'<tt>sitofp .. to</tt>' Instruction</a>
5537 <result> = sitofp <ty> <value> to <ty2> <i>; yields ty2</i>
5541 <p>The '<tt>sitofp</tt>' instruction regards <tt>value</tt> as a signed integer
5542 and converts that value to the <tt>ty2</tt> type.</p>
5545 <p>The '<tt>sitofp</tt>' instruction takes a value to cast, which must be a
5546 scalar or vector <a href="#t_integer">integer</a> value, and a type to cast
5547 it to <tt>ty2</tt>, which must be an <a href="#t_floating">floating point</a>
5548 type. If <tt>ty</tt> is a vector integer type, <tt>ty2</tt> must be a vector
5549 floating point type with the same number of elements as <tt>ty</tt></p>
5552 <p>The '<tt>sitofp</tt>' instruction interprets its operand as a signed integer
5553 quantity and converts it to the corresponding floating point value. If the
5554 value cannot fit in the floating point value, the results are undefined.</p>
5558 %X = sitofp i32 257 to float <i>; yields float:257.0</i>
5559 %Y = sitofp i8 -1 to double <i>; yields double:-1.0</i>
5564 <!-- _______________________________________________________________________ -->
5566 <a name="i_ptrtoint">'<tt>ptrtoint .. to</tt>' Instruction</a>
5573 <result> = ptrtoint <ty> <value> to <ty2> <i>; yields ty2</i>
5577 <p>The '<tt>ptrtoint</tt>' instruction converts the pointer or a vector of
5578 pointers <tt>value</tt> to
5579 the integer (or vector of integers) type <tt>ty2</tt>.</p>
5582 <p>The '<tt>ptrtoint</tt>' instruction takes a <tt>value</tt> to cast, which
5583 must be a a value of type <a href="#t_pointer">pointer</a> or a vector of
5584 pointers, and a type to cast it to
5585 <tt>ty2</tt>, which must be an <a href="#t_integer">integer</a> or a vector
5586 of integers type.</p>
5589 <p>The '<tt>ptrtoint</tt>' instruction converts <tt>value</tt> to integer type
5590 <tt>ty2</tt> by interpreting the pointer value as an integer and either
5591 truncating or zero extending that value to the size of the integer type. If
5592 <tt>value</tt> is smaller than <tt>ty2</tt> then a zero extension is done. If
5593 <tt>value</tt> is larger than <tt>ty2</tt> then a truncation is done. If they
5594 are the same size, then nothing is done (<i>no-op cast</i>) other than a type
5599 %X = ptrtoint i32* %P to i8 <i>; yields truncation on 32-bit architecture</i>
5600 %Y = ptrtoint i32* %P to i64 <i>; yields zero extension on 32-bit architecture</i>
5601 %Z = ptrtoint <4 x i32*> %P to <4 x i64><i>; yields vector zero extension for a vector of addresses on 32-bit architecture</i>
5606 <!-- _______________________________________________________________________ -->
5608 <a name="i_inttoptr">'<tt>inttoptr .. to</tt>' Instruction</a>
5615 <result> = inttoptr <ty> <value> to <ty2> <i>; yields ty2</i>
5619 <p>The '<tt>inttoptr</tt>' instruction converts an integer <tt>value</tt> to a
5620 pointer type, <tt>ty2</tt>.</p>
5623 <p>The '<tt>inttoptr</tt>' instruction takes an <a href="#t_integer">integer</a>
5624 value to cast, and a type to cast it to, which must be a
5625 <a href="#t_pointer">pointer</a> type.</p>
5628 <p>The '<tt>inttoptr</tt>' instruction converts <tt>value</tt> to type
5629 <tt>ty2</tt> by applying either a zero extension or a truncation depending on
5630 the size of the integer <tt>value</tt>. If <tt>value</tt> is larger than the
5631 size of a pointer then a truncation is done. If <tt>value</tt> is smaller
5632 than the size of a pointer then a zero extension is done. If they are the
5633 same size, nothing is done (<i>no-op cast</i>).</p>
5637 %X = inttoptr i32 255 to i32* <i>; yields zero extension on 64-bit architecture</i>
5638 %Y = inttoptr i32 255 to i32* <i>; yields no-op on 32-bit architecture</i>
5639 %Z = inttoptr i64 0 to i32* <i>; yields truncation on 32-bit architecture</i>
5640 %Z = inttoptr <4 x i32> %G to <4 x i8*><i>; yields truncation of vector G to four pointers</i>
5645 <!-- _______________________________________________________________________ -->
5647 <a name="i_bitcast">'<tt>bitcast .. to</tt>' Instruction</a>
5654 <result> = bitcast <ty> <value> to <ty2> <i>; yields ty2</i>
5658 <p>The '<tt>bitcast</tt>' instruction converts <tt>value</tt> to type
5659 <tt>ty2</tt> without changing any bits.</p>
5662 <p>The '<tt>bitcast</tt>' instruction takes a value to cast, which must be a
5663 non-aggregate first class value, and a type to cast it to, which must also be
5664 a non-aggregate <a href="#t_firstclass">first class</a> type. The bit sizes
5665 of <tt>value</tt> and the destination type, <tt>ty2</tt>, must be
5666 identical. If the source type is a pointer, the destination type must also be
5667 a pointer. This instruction supports bitwise conversion of vectors to
5668 integers and to vectors of other types (as long as they have the same
5672 <p>The '<tt>bitcast</tt>' instruction converts <tt>value</tt> to type
5673 <tt>ty2</tt>. It is always a <i>no-op cast</i> because no bits change with
5674 this conversion. The conversion is done as if the <tt>value</tt> had been
5675 stored to memory and read back as type <tt>ty2</tt>.
5676 Pointer (or vector of pointers) types may only be converted to other pointer
5677 (or vector of pointers) types with this instruction. To convert
5678 pointers to other types, use the <a href="#i_inttoptr">inttoptr</a> or
5679 <a href="#i_ptrtoint">ptrtoint</a> instructions first.</p>
5683 %X = bitcast i8 255 to i8 <i>; yields i8 :-1</i>
5684 %Y = bitcast i32* %x to sint* <i>; yields sint*:%x</i>
5685 %Z = bitcast <2 x int> %V to i64; <i>; yields i64: %V</i>
5686 %Z = bitcast <2 x i32*> %V to <2 x i64*> <i>; yields <2 x i64*></i>
5693 <!-- ======================================================================= -->
5695 <a name="otherops">Other Operations</a>
5700 <p>The instructions in this category are the "miscellaneous" instructions, which
5701 defy better classification.</p>
5703 <!-- _______________________________________________________________________ -->
5705 <a name="i_icmp">'<tt>icmp</tt>' Instruction</a>
5712 <result> = icmp <cond> <ty> <op1>, <op2> <i>; yields {i1} or {<N x i1>}:result</i>
5716 <p>The '<tt>icmp</tt>' instruction returns a boolean value or a vector of
5717 boolean values based on comparison of its two integer, integer vector,
5718 pointer, or pointer vector operands.</p>
5721 <p>The '<tt>icmp</tt>' instruction takes three operands. The first operand is
5722 the condition code indicating the kind of comparison to perform. It is not a
5723 value, just a keyword. The possible condition code are:</p>
5726 <li><tt>eq</tt>: equal</li>
5727 <li><tt>ne</tt>: not equal </li>
5728 <li><tt>ugt</tt>: unsigned greater than</li>
5729 <li><tt>uge</tt>: unsigned greater or equal</li>
5730 <li><tt>ult</tt>: unsigned less than</li>
5731 <li><tt>ule</tt>: unsigned less or equal</li>
5732 <li><tt>sgt</tt>: signed greater than</li>
5733 <li><tt>sge</tt>: signed greater or equal</li>
5734 <li><tt>slt</tt>: signed less than</li>
5735 <li><tt>sle</tt>: signed less or equal</li>
5738 <p>The remaining two arguments must be <a href="#t_integer">integer</a> or
5739 <a href="#t_pointer">pointer</a> or integer <a href="#t_vector">vector</a>
5740 typed. They must also be identical types.</p>
5743 <p>The '<tt>icmp</tt>' compares <tt>op1</tt> and <tt>op2</tt> according to the
5744 condition code given as <tt>cond</tt>. The comparison performed always yields
5745 either an <a href="#t_integer"><tt>i1</tt></a> or vector of <tt>i1</tt>
5746 result, as follows:</p>
5749 <li><tt>eq</tt>: yields <tt>true</tt> if the operands are equal,
5750 <tt>false</tt> otherwise. No sign interpretation is necessary or
5753 <li><tt>ne</tt>: yields <tt>true</tt> if the operands are unequal,
5754 <tt>false</tt> otherwise. No sign interpretation is necessary or
5757 <li><tt>ugt</tt>: interprets the operands as unsigned values and yields
5758 <tt>true</tt> if <tt>op1</tt> is greater than <tt>op2</tt>.</li>
5760 <li><tt>uge</tt>: interprets the operands as unsigned values and yields
5761 <tt>true</tt> if <tt>op1</tt> is greater than or equal
5762 to <tt>op2</tt>.</li>
5764 <li><tt>ult</tt>: interprets the operands as unsigned values and yields
5765 <tt>true</tt> if <tt>op1</tt> is less than <tt>op2</tt>.</li>
5767 <li><tt>ule</tt>: interprets the operands as unsigned values and yields
5768 <tt>true</tt> if <tt>op1</tt> is less than or equal to <tt>op2</tt>.</li>
5770 <li><tt>sgt</tt>: interprets the operands as signed values and yields
5771 <tt>true</tt> if <tt>op1</tt> is greater than <tt>op2</tt>.</li>
5773 <li><tt>sge</tt>: interprets the operands as signed values and yields
5774 <tt>true</tt> if <tt>op1</tt> is greater than or equal
5775 to <tt>op2</tt>.</li>
5777 <li><tt>slt</tt>: interprets the operands as signed values and yields
5778 <tt>true</tt> if <tt>op1</tt> is less than <tt>op2</tt>.</li>
5780 <li><tt>sle</tt>: interprets the operands as signed values and yields
5781 <tt>true</tt> if <tt>op1</tt> is less than or equal to <tt>op2</tt>.</li>
5784 <p>If the operands are <a href="#t_pointer">pointer</a> typed, the pointer
5785 values are compared as if they were integers.</p>
5787 <p>If the operands are integer vectors, then they are compared element by
5788 element. The result is an <tt>i1</tt> vector with the same number of elements
5789 as the values being compared. Otherwise, the result is an <tt>i1</tt>.</p>
5793 <result> = icmp eq i32 4, 5 <i>; yields: result=false</i>
5794 <result> = icmp ne float* %X, %X <i>; yields: result=false</i>
5795 <result> = icmp ult i16 4, 5 <i>; yields: result=true</i>
5796 <result> = icmp sgt i16 4, 5 <i>; yields: result=false</i>
5797 <result> = icmp ule i16 -4, 5 <i>; yields: result=false</i>
5798 <result> = icmp sge i16 4, 5 <i>; yields: result=false</i>
5801 <p>Note that the code generator does not yet support vector types with
5802 the <tt>icmp</tt> instruction.</p>
5806 <!-- _______________________________________________________________________ -->
5808 <a name="i_fcmp">'<tt>fcmp</tt>' Instruction</a>
5815 <result> = fcmp <cond> <ty> <op1>, <op2> <i>; yields {i1} or {<N x i1>}:result</i>
5819 <p>The '<tt>fcmp</tt>' instruction returns a boolean value or vector of boolean
5820 values based on comparison of its operands.</p>
5822 <p>If the operands are floating point scalars, then the result type is a boolean
5823 (<a href="#t_integer"><tt>i1</tt></a>).</p>
5825 <p>If the operands are floating point vectors, then the result type is a vector
5826 of boolean with the same number of elements as the operands being
5830 <p>The '<tt>fcmp</tt>' instruction takes three operands. The first operand is
5831 the condition code indicating the kind of comparison to perform. It is not a
5832 value, just a keyword. The possible condition code are:</p>
5835 <li><tt>false</tt>: no comparison, always returns false</li>
5836 <li><tt>oeq</tt>: ordered and equal</li>
5837 <li><tt>ogt</tt>: ordered and greater than </li>
5838 <li><tt>oge</tt>: ordered and greater than or equal</li>
5839 <li><tt>olt</tt>: ordered and less than </li>
5840 <li><tt>ole</tt>: ordered and less than or equal</li>
5841 <li><tt>one</tt>: ordered and not equal</li>
5842 <li><tt>ord</tt>: ordered (no nans)</li>
5843 <li><tt>ueq</tt>: unordered or equal</li>
5844 <li><tt>ugt</tt>: unordered or greater than </li>
5845 <li><tt>uge</tt>: unordered or greater than or equal</li>
5846 <li><tt>ult</tt>: unordered or less than </li>
5847 <li><tt>ule</tt>: unordered or less than or equal</li>
5848 <li><tt>une</tt>: unordered or not equal</li>
5849 <li><tt>uno</tt>: unordered (either nans)</li>
5850 <li><tt>true</tt>: no comparison, always returns true</li>
5853 <p><i>Ordered</i> means that neither operand is a QNAN while
5854 <i>unordered</i> means that either operand may be a QNAN.</p>
5856 <p>Each of <tt>val1</tt> and <tt>val2</tt> arguments must be either
5857 a <a href="#t_floating">floating point</a> type or
5858 a <a href="#t_vector">vector</a> of floating point type. They must have
5859 identical types.</p>
5862 <p>The '<tt>fcmp</tt>' instruction compares <tt>op1</tt> and <tt>op2</tt>
5863 according to the condition code given as <tt>cond</tt>. If the operands are
5864 vectors, then the vectors are compared element by element. Each comparison
5865 performed always yields an <a href="#t_integer">i1</a> result, as
5869 <li><tt>false</tt>: always yields <tt>false</tt>, regardless of operands.</li>
5871 <li><tt>oeq</tt>: yields <tt>true</tt> if both operands are not a QNAN and
5872 <tt>op1</tt> is equal to <tt>op2</tt>.</li>
5874 <li><tt>ogt</tt>: yields <tt>true</tt> if both operands are not a QNAN and
5875 <tt>op1</tt> is greater than <tt>op2</tt>.</li>
5877 <li><tt>oge</tt>: yields <tt>true</tt> if both operands are not a QNAN and
5878 <tt>op1</tt> is greater than or equal to <tt>op2</tt>.</li>
5880 <li><tt>olt</tt>: yields <tt>true</tt> if both operands are not a QNAN and
5881 <tt>op1</tt> is less than <tt>op2</tt>.</li>
5883 <li><tt>ole</tt>: yields <tt>true</tt> if both operands are not a QNAN and
5884 <tt>op1</tt> is less than or equal to <tt>op2</tt>.</li>
5886 <li><tt>one</tt>: yields <tt>true</tt> if both operands are not a QNAN and
5887 <tt>op1</tt> is not equal to <tt>op2</tt>.</li>
5889 <li><tt>ord</tt>: yields <tt>true</tt> if both operands are not a QNAN.</li>
5891 <li><tt>ueq</tt>: yields <tt>true</tt> if either operand is a QNAN or
5892 <tt>op1</tt> is equal to <tt>op2</tt>.</li>
5894 <li><tt>ugt</tt>: yields <tt>true</tt> if either operand is a QNAN or
5895 <tt>op1</tt> is greater than <tt>op2</tt>.</li>
5897 <li><tt>uge</tt>: yields <tt>true</tt> if either operand is a QNAN or
5898 <tt>op1</tt> is greater than or equal to <tt>op2</tt>.</li>
5900 <li><tt>ult</tt>: yields <tt>true</tt> if either operand is a QNAN or
5901 <tt>op1</tt> is less than <tt>op2</tt>.</li>
5903 <li><tt>ule</tt>: yields <tt>true</tt> if either operand is a QNAN or
5904 <tt>op1</tt> is less than or equal to <tt>op2</tt>.</li>
5906 <li><tt>une</tt>: yields <tt>true</tt> if either operand is a QNAN or
5907 <tt>op1</tt> is not equal to <tt>op2</tt>.</li>
5909 <li><tt>uno</tt>: yields <tt>true</tt> if either operand is a QNAN.</li>
5911 <li><tt>true</tt>: always yields <tt>true</tt>, regardless of operands.</li>
5916 <result> = fcmp oeq float 4.0, 5.0 <i>; yields: result=false</i>
5917 <result> = fcmp one float 4.0, 5.0 <i>; yields: result=true</i>
5918 <result> = fcmp olt float 4.0, 5.0 <i>; yields: result=true</i>
5919 <result> = fcmp ueq double 1.0, 2.0 <i>; yields: result=false</i>
5922 <p>Note that the code generator does not yet support vector types with
5923 the <tt>fcmp</tt> instruction.</p>
5927 <!-- _______________________________________________________________________ -->
5929 <a name="i_phi">'<tt>phi</tt>' Instruction</a>
5936 <result> = phi <ty> [ <val0>, <label0>], ...
5940 <p>The '<tt>phi</tt>' instruction is used to implement the φ node in the
5941 SSA graph representing the function.</p>
5944 <p>The type of the incoming values is specified with the first type field. After
5945 this, the '<tt>phi</tt>' instruction takes a list of pairs as arguments, with
5946 one pair for each predecessor basic block of the current block. Only values
5947 of <a href="#t_firstclass">first class</a> type may be used as the value
5948 arguments to the PHI node. Only labels may be used as the label
5951 <p>There must be no non-phi instructions between the start of a basic block and
5952 the PHI instructions: i.e. PHI instructions must be first in a basic
5955 <p>For the purposes of the SSA form, the use of each incoming value is deemed to
5956 occur on the edge from the corresponding predecessor block to the current
5957 block (but after any definition of an '<tt>invoke</tt>' instruction's return
5958 value on the same edge).</p>
5961 <p>At runtime, the '<tt>phi</tt>' instruction logically takes on the value
5962 specified by the pair corresponding to the predecessor basic block that
5963 executed just prior to the current block.</p>
5967 Loop: ; Infinite loop that counts from 0 on up...
5968 %indvar = phi i32 [ 0, %LoopHeader ], [ %nextindvar, %Loop ]
5969 %nextindvar = add i32 %indvar, 1
5975 <!-- _______________________________________________________________________ -->
5977 <a name="i_select">'<tt>select</tt>' Instruction</a>
5984 <result> = select <i>selty</i> <cond>, <ty> <val1>, <ty> <val2> <i>; yields ty</i>
5986 <i>selty</i> is either i1 or {<N x i1>}
5990 <p>The '<tt>select</tt>' instruction is used to choose one value based on a
5991 condition, without branching.</p>
5995 <p>The '<tt>select</tt>' instruction requires an 'i1' value or a vector of 'i1'
5996 values indicating the condition, and two values of the
5997 same <a href="#t_firstclass">first class</a> type. If the val1/val2 are
5998 vectors and the condition is a scalar, then entire vectors are selected, not
5999 individual elements.</p>
6002 <p>If the condition is an i1 and it evaluates to 1, the instruction returns the
6003 first value argument; otherwise, it returns the second value argument.</p>
6005 <p>If the condition is a vector of i1, then the value arguments must be vectors
6006 of the same size, and the selection is done element by element.</p>
6010 %X = select i1 true, i8 17, i8 42 <i>; yields i8:17</i>
6013 <p>Note that the code generator does not yet support conditions
6014 with vector type.</p>
6018 <!-- _______________________________________________________________________ -->
6020 <a name="i_call">'<tt>call</tt>' Instruction</a>
6027 <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>]
6031 <p>The '<tt>call</tt>' instruction represents a simple function call.</p>
6034 <p>This instruction requires several arguments:</p>
6037 <li>The optional "tail" marker indicates that the callee function does not
6038 access any allocas or varargs in the caller. Note that calls may be
6039 marked "tail" even if they do not occur before
6040 a <a href="#i_ret"><tt>ret</tt></a> instruction. If the "tail" marker is
6041 present, the function call is eligible for tail call optimization,
6042 but <a href="CodeGenerator.html#tailcallopt">might not in fact be
6043 optimized into a jump</a>. The code generator may optimize calls marked
6044 "tail" with either 1) automatic <a href="CodeGenerator.html#sibcallopt">
6045 sibling call optimization</a> when the caller and callee have
6046 matching signatures, or 2) forced tail call optimization when the
6047 following extra requirements are met:
6049 <li>Caller and callee both have the calling
6050 convention <tt>fastcc</tt>.</li>
6051 <li>The call is in tail position (ret immediately follows call and ret
6052 uses value of call or is void).</li>
6053 <li>Option <tt>-tailcallopt</tt> is enabled,
6054 or <code>llvm::GuaranteedTailCallOpt</code> is <code>true</code>.</li>
6055 <li><a href="CodeGenerator.html#tailcallopt">Platform specific
6056 constraints are met.</a></li>
6060 <li>The optional "cconv" marker indicates which <a href="#callingconv">calling
6061 convention</a> the call should use. If none is specified, the call
6062 defaults to using C calling conventions. The calling convention of the
6063 call must match the calling convention of the target function, or else the
6064 behavior is undefined.</li>
6066 <li>The optional <a href="#paramattrs">Parameter Attributes</a> list for
6067 return values. Only '<tt>zeroext</tt>', '<tt>signext</tt>', and
6068 '<tt>inreg</tt>' attributes are valid here.</li>
6070 <li>'<tt>ty</tt>': the type of the call instruction itself which is also the
6071 type of the return value. Functions that return no value are marked
6072 <tt><a href="#t_void">void</a></tt>.</li>
6074 <li>'<tt>fnty</tt>': shall be the signature of the pointer to function value
6075 being invoked. The argument types must match the types implied by this
6076 signature. This type can be omitted if the function is not varargs and if
6077 the function type does not return a pointer to a function.</li>
6079 <li>'<tt>fnptrval</tt>': An LLVM value containing a pointer to a function to
6080 be invoked. In most cases, this is a direct function invocation, but
6081 indirect <tt>call</tt>s are just as possible, calling an arbitrary pointer
6082 to function value.</li>
6084 <li>'<tt>function args</tt>': argument list whose types match the function
6085 signature argument types and parameter attributes. All arguments must be
6086 of <a href="#t_firstclass">first class</a> type. If the function
6087 signature indicates the function accepts a variable number of arguments,
6088 the extra arguments can be specified.</li>
6090 <li>The optional <a href="#fnattrs">function attributes</a> list. Only
6091 '<tt>noreturn</tt>', '<tt>nounwind</tt>', '<tt>readonly</tt>' and
6092 '<tt>readnone</tt>' attributes are valid here.</li>
6096 <p>The '<tt>call</tt>' instruction is used to cause control flow to transfer to
6097 a specified function, with its incoming arguments bound to the specified
6098 values. Upon a '<tt><a href="#i_ret">ret</a></tt>' instruction in the called
6099 function, control flow continues with the instruction after the function
6100 call, and the return value of the function is bound to the result
6105 %retval = call i32 @test(i32 %argc)
6106 call i32 (i8*, ...)* @printf(i8* %msg, i32 12, i8 42) <i>; yields i32</i>
6107 %X = tail call i32 @foo() <i>; yields i32</i>
6108 %Y = tail call <a href="#callingconv">fastcc</a> i32 @foo() <i>; yields i32</i>
6109 call void %foo(i8 97 signext)
6111 %struct.A = type { i32, i8 }
6112 %r = call %struct.A @foo() <i>; yields { 32, i8 }</i>
6113 %gr = extractvalue %struct.A %r, 0 <i>; yields i32</i>
6114 %gr1 = extractvalue %struct.A %r, 1 <i>; yields i8</i>
6115 %Z = call void @foo() noreturn <i>; indicates that %foo never returns normally</i>
6116 %ZZ = call zeroext i32 @bar() <i>; Return value is %zero extended</i>
6119 <p>llvm treats calls to some functions with names and arguments that match the
6120 standard C99 library as being the C99 library functions, and may perform
6121 optimizations or generate code for them under that assumption. This is
6122 something we'd like to change in the future to provide better support for
6123 freestanding environments and non-C-based languages.</p>
6127 <!-- _______________________________________________________________________ -->
6129 <a name="i_va_arg">'<tt>va_arg</tt>' Instruction</a>
6136 <resultval> = va_arg <va_list*> <arglist>, <argty>
6140 <p>The '<tt>va_arg</tt>' instruction is used to access arguments passed through
6141 the "variable argument" area of a function call. It is used to implement the
6142 <tt>va_arg</tt> macro in C.</p>
6145 <p>This instruction takes a <tt>va_list*</tt> value and the type of the
6146 argument. It returns a value of the specified argument type and increments
6147 the <tt>va_list</tt> to point to the next argument. The actual type
6148 of <tt>va_list</tt> is target specific.</p>
6151 <p>The '<tt>va_arg</tt>' instruction loads an argument of the specified type
6152 from the specified <tt>va_list</tt> and causes the <tt>va_list</tt> to point
6153 to the next argument. For more information, see the variable argument
6154 handling <a href="#int_varargs">Intrinsic Functions</a>.</p>
6156 <p>It is legal for this instruction to be called in a function which does not
6157 take a variable number of arguments, for example, the <tt>vfprintf</tt>
6160 <p><tt>va_arg</tt> is an LLVM instruction instead of
6161 an <a href="#intrinsics">intrinsic function</a> because it takes a type as an
6165 <p>See the <a href="#int_varargs">variable argument processing</a> section.</p>
6167 <p>Note that the code generator does not yet fully support va_arg on many
6168 targets. Also, it does not currently support va_arg with aggregate types on
6173 <!-- _______________________________________________________________________ -->
6175 <a name="i_landingpad">'<tt>landingpad</tt>' Instruction</a>
6182 <resultval> = landingpad <somety> personality <type> <pers_fn> <clause>+
6183 <resultval> = landingpad <somety> personality <type> <pers_fn> cleanup <clause>*
6185 <clause> := catch <type> <value>
6186 <clause> := filter <array constant type> <array constant>
6190 <p>The '<tt>landingpad</tt>' instruction is used by
6191 <a href="ExceptionHandling.html#overview">LLVM's exception handling
6192 system</a> to specify that a basic block is a landing pad — one where
6193 the exception lands, and corresponds to the code found in the
6194 <i><tt>catch</tt></i> portion of a <i><tt>try/catch</tt></i> sequence. It
6195 defines values supplied by the personality function (<tt>pers_fn</tt>) upon
6196 re-entry to the function. The <tt>resultval</tt> has the
6197 type <tt>somety</tt>.</p>
6200 <p>This instruction takes a <tt>pers_fn</tt> value. This is the personality
6201 function associated with the unwinding mechanism. The optional
6202 <tt>cleanup</tt> flag indicates that the landing pad block is a cleanup.</p>
6204 <p>A <tt>clause</tt> begins with the clause type — <tt>catch</tt>
6205 or <tt>filter</tt> — and contains the global variable representing the
6206 "type" that may be caught or filtered respectively. Unlike the
6207 <tt>catch</tt> clause, the <tt>filter</tt> clause takes an array constant as
6208 its argument. Use "<tt>[0 x i8**] undef</tt>" for a filter which cannot
6209 throw. The '<tt>landingpad</tt>' instruction must contain <em>at least</em>
6210 one <tt>clause</tt> or the <tt>cleanup</tt> flag.</p>
6213 <p>The '<tt>landingpad</tt>' instruction defines the values which are set by the
6214 personality function (<tt>pers_fn</tt>) upon re-entry to the function, and
6215 therefore the "result type" of the <tt>landingpad</tt> instruction. As with
6216 calling conventions, how the personality function results are represented in
6217 LLVM IR is target specific.</p>
6219 <p>The clauses are applied in order from top to bottom. If two
6220 <tt>landingpad</tt> instructions are merged together through inlining, the
6221 clauses from the calling function are appended to the list of clauses.</p>
6223 <p>The <tt>landingpad</tt> instruction has several restrictions:</p>
6226 <li>A landing pad block is a basic block which is the unwind destination of an
6227 '<tt>invoke</tt>' instruction.</li>
6228 <li>A landing pad block must have a '<tt>landingpad</tt>' instruction as its
6229 first non-PHI instruction.</li>
6230 <li>There can be only one '<tt>landingpad</tt>' instruction within the landing
6232 <li>A basic block that is not a landing pad block may not include a
6233 '<tt>landingpad</tt>' instruction.</li>
6234 <li>All '<tt>landingpad</tt>' instructions in a function must have the same
6235 personality function.</li>
6240 ;; A landing pad which can catch an integer.
6241 %res = landingpad { i8*, i32 } personality i32 (...)* @__gxx_personality_v0
6243 ;; A landing pad that is a cleanup.
6244 %res = landingpad { i8*, i32 } personality i32 (...)* @__gxx_personality_v0
6246 ;; A landing pad which can catch an integer and can only throw a double.
6247 %res = landingpad { i8*, i32 } personality i32 (...)* @__gxx_personality_v0
6249 filter [1 x i8**] [@_ZTId]
6258 <!-- *********************************************************************** -->
6259 <h2><a name="intrinsics">Intrinsic Functions</a></h2>
6260 <!-- *********************************************************************** -->
6264 <p>LLVM supports the notion of an "intrinsic function". These functions have
6265 well known names and semantics and are required to follow certain
6266 restrictions. Overall, these intrinsics represent an extension mechanism for
6267 the LLVM language that does not require changing all of the transformations
6268 in LLVM when adding to the language (or the bitcode reader/writer, the
6269 parser, etc...).</p>
6271 <p>Intrinsic function names must all start with an "<tt>llvm.</tt>" prefix. This
6272 prefix is reserved in LLVM for intrinsic names; thus, function names may not
6273 begin with this prefix. Intrinsic functions must always be external
6274 functions: you cannot define the body of intrinsic functions. Intrinsic
6275 functions may only be used in call or invoke instructions: it is illegal to
6276 take the address of an intrinsic function. Additionally, because intrinsic
6277 functions are part of the LLVM language, it is required if any are added that
6278 they be documented here.</p>
6280 <p>Some intrinsic functions can be overloaded, i.e., the intrinsic represents a
6281 family of functions that perform the same operation but on different data
6282 types. Because LLVM can represent over 8 million different integer types,
6283 overloading is used commonly to allow an intrinsic function to operate on any
6284 integer type. One or more of the argument types or the result type can be
6285 overloaded to accept any integer type. Argument types may also be defined as
6286 exactly matching a previous argument's type or the result type. This allows
6287 an intrinsic function which accepts multiple arguments, but needs all of them
6288 to be of the same type, to only be overloaded with respect to a single
6289 argument or the result.</p>
6291 <p>Overloaded intrinsics will have the names of its overloaded argument types
6292 encoded into its function name, each preceded by a period. Only those types
6293 which are overloaded result in a name suffix. Arguments whose type is matched
6294 against another type do not. For example, the <tt>llvm.ctpop</tt> function
6295 can take an integer of any width and returns an integer of exactly the same
6296 integer width. This leads to a family of functions such as
6297 <tt>i8 @llvm.ctpop.i8(i8 %val)</tt> and <tt>i29 @llvm.ctpop.i29(i29
6298 %val)</tt>. Only one type, the return type, is overloaded, and only one type
6299 suffix is required. Because the argument's type is matched against the return
6300 type, it does not require its own name suffix.</p>
6302 <p>To learn how to add an intrinsic function, please see the
6303 <a href="ExtendingLLVM.html">Extending LLVM Guide</a>.</p>
6305 <!-- ======================================================================= -->
6307 <a name="int_varargs">Variable Argument Handling Intrinsics</a>
6312 <p>Variable argument support is defined in LLVM with
6313 the <a href="#i_va_arg"><tt>va_arg</tt></a> instruction and these three
6314 intrinsic functions. These functions are related to the similarly named
6315 macros defined in the <tt><stdarg.h></tt> header file.</p>
6317 <p>All of these functions operate on arguments that use a target-specific value
6318 type "<tt>va_list</tt>". The LLVM assembly language reference manual does
6319 not define what this type is, so all transformations should be prepared to
6320 handle these functions regardless of the type used.</p>
6322 <p>This example shows how the <a href="#i_va_arg"><tt>va_arg</tt></a>
6323 instruction and the variable argument handling intrinsic functions are
6326 <pre class="doc_code">
6327 define i32 @test(i32 %X, ...) {
6328 ; Initialize variable argument processing
6330 %ap2 = bitcast i8** %ap to i8*
6331 call void @llvm.va_start(i8* %ap2)
6333 ; Read a single integer argument
6334 %tmp = va_arg i8** %ap, i32
6336 ; Demonstrate usage of llvm.va_copy and llvm.va_end
6338 %aq2 = bitcast i8** %aq to i8*
6339 call void @llvm.va_copy(i8* %aq2, i8* %ap2)
6340 call void @llvm.va_end(i8* %aq2)
6342 ; Stop processing of arguments.
6343 call void @llvm.va_end(i8* %ap2)
6347 declare void @llvm.va_start(i8*)
6348 declare void @llvm.va_copy(i8*, i8*)
6349 declare void @llvm.va_end(i8*)
6352 <!-- _______________________________________________________________________ -->
6354 <a name="int_va_start">'<tt>llvm.va_start</tt>' Intrinsic</a>
6362 declare void %llvm.va_start(i8* <arglist>)
6366 <p>The '<tt>llvm.va_start</tt>' intrinsic initializes <tt>*<arglist></tt>
6367 for subsequent use by <tt><a href="#i_va_arg">va_arg</a></tt>.</p>
6370 <p>The argument is a pointer to a <tt>va_list</tt> element to initialize.</p>
6373 <p>The '<tt>llvm.va_start</tt>' intrinsic works just like the <tt>va_start</tt>
6374 macro available in C. In a target-dependent way, it initializes
6375 the <tt>va_list</tt> element to which the argument points, so that the next
6376 call to <tt>va_arg</tt> will produce the first variable argument passed to
6377 the function. Unlike the C <tt>va_start</tt> macro, this intrinsic does not
6378 need to know the last argument of the function as the compiler can figure
6383 <!-- _______________________________________________________________________ -->
6385 <a name="int_va_end">'<tt>llvm.va_end</tt>' Intrinsic</a>
6392 declare void @llvm.va_end(i8* <arglist>)
6396 <p>The '<tt>llvm.va_end</tt>' intrinsic destroys <tt>*<arglist></tt>,
6397 which has been initialized previously
6398 with <tt><a href="#int_va_start">llvm.va_start</a></tt>
6399 or <tt><a href="#i_va_copy">llvm.va_copy</a></tt>.</p>
6402 <p>The argument is a pointer to a <tt>va_list</tt> to destroy.</p>
6405 <p>The '<tt>llvm.va_end</tt>' intrinsic works just like the <tt>va_end</tt>
6406 macro available in C. In a target-dependent way, it destroys
6407 the <tt>va_list</tt> element to which the argument points. Calls
6408 to <a href="#int_va_start"><tt>llvm.va_start</tt></a>
6409 and <a href="#int_va_copy"> <tt>llvm.va_copy</tt></a> must be matched exactly
6410 with calls to <tt>llvm.va_end</tt>.</p>
6414 <!-- _______________________________________________________________________ -->
6416 <a name="int_va_copy">'<tt>llvm.va_copy</tt>' Intrinsic</a>
6423 declare void @llvm.va_copy(i8* <destarglist>, i8* <srcarglist>)
6427 <p>The '<tt>llvm.va_copy</tt>' intrinsic copies the current argument position
6428 from the source argument list to the destination argument list.</p>
6431 <p>The first argument is a pointer to a <tt>va_list</tt> element to initialize.
6432 The second argument is a pointer to a <tt>va_list</tt> element to copy
6436 <p>The '<tt>llvm.va_copy</tt>' intrinsic works just like the <tt>va_copy</tt>
6437 macro available in C. In a target-dependent way, it copies the
6438 source <tt>va_list</tt> element into the destination <tt>va_list</tt>
6439 element. This intrinsic is necessary because
6440 the <tt><a href="#int_va_start"> llvm.va_start</a></tt> intrinsic may be
6441 arbitrarily complex and require, for example, memory allocation.</p>
6447 <!-- ======================================================================= -->
6449 <a name="int_gc">Accurate Garbage Collection Intrinsics</a>
6454 <p>LLVM support for <a href="GarbageCollection.html">Accurate Garbage
6455 Collection</a> (GC) requires the implementation and generation of these
6456 intrinsics. These intrinsics allow identification of <a href="#int_gcroot">GC
6457 roots on the stack</a>, as well as garbage collector implementations that
6458 require <a href="#int_gcread">read</a> and <a href="#int_gcwrite">write</a>
6459 barriers. Front-ends for type-safe garbage collected languages should generate
6460 these intrinsics to make use of the LLVM garbage collectors. For more details,
6461 see <a href="GarbageCollection.html">Accurate Garbage Collection with
6464 <p>The garbage collection intrinsics only operate on objects in the generic
6465 address space (address space zero).</p>
6467 <!-- _______________________________________________________________________ -->
6469 <a name="int_gcroot">'<tt>llvm.gcroot</tt>' Intrinsic</a>
6476 declare void @llvm.gcroot(i8** %ptrloc, i8* %metadata)
6480 <p>The '<tt>llvm.gcroot</tt>' intrinsic declares the existence of a GC root to
6481 the code generator, and allows some metadata to be associated with it.</p>
6484 <p>The first argument specifies the address of a stack object that contains the
6485 root pointer. The second pointer (which must be either a constant or a
6486 global value address) contains the meta-data to be associated with the
6490 <p>At runtime, a call to this intrinsic stores a null pointer into the "ptrloc"
6491 location. At compile-time, the code generator generates information to allow
6492 the runtime to find the pointer at GC safe points. The '<tt>llvm.gcroot</tt>'
6493 intrinsic may only be used in a function which <a href="#gc">specifies a GC
6498 <!-- _______________________________________________________________________ -->
6500 <a name="int_gcread">'<tt>llvm.gcread</tt>' Intrinsic</a>
6507 declare i8* @llvm.gcread(i8* %ObjPtr, i8** %Ptr)
6511 <p>The '<tt>llvm.gcread</tt>' intrinsic identifies reads of references from heap
6512 locations, allowing garbage collector implementations that require read
6516 <p>The second argument is the address to read from, which should be an address
6517 allocated from the garbage collector. The first object is a pointer to the
6518 start of the referenced object, if needed by the language runtime (otherwise
6522 <p>The '<tt>llvm.gcread</tt>' intrinsic has the same semantics as a load
6523 instruction, but may be replaced with substantially more complex code by the
6524 garbage collector runtime, as needed. The '<tt>llvm.gcread</tt>' intrinsic
6525 may only be used in a function which <a href="#gc">specifies a GC
6530 <!-- _______________________________________________________________________ -->
6532 <a name="int_gcwrite">'<tt>llvm.gcwrite</tt>' Intrinsic</a>
6539 declare void @llvm.gcwrite(i8* %P1, i8* %Obj, i8** %P2)
6543 <p>The '<tt>llvm.gcwrite</tt>' intrinsic identifies writes of references to heap
6544 locations, allowing garbage collector implementations that require write
6545 barriers (such as generational or reference counting collectors).</p>
6548 <p>The first argument is the reference to store, the second is the start of the
6549 object to store it to, and the third is the address of the field of Obj to
6550 store to. If the runtime does not require a pointer to the object, Obj may
6554 <p>The '<tt>llvm.gcwrite</tt>' intrinsic has the same semantics as a store
6555 instruction, but may be replaced with substantially more complex code by the
6556 garbage collector runtime, as needed. The '<tt>llvm.gcwrite</tt>' intrinsic
6557 may only be used in a function which <a href="#gc">specifies a GC
6564 <!-- ======================================================================= -->
6566 <a name="int_codegen">Code Generator Intrinsics</a>
6571 <p>These intrinsics are provided by LLVM to expose special features that may
6572 only be implemented with code generator support.</p>
6574 <!-- _______________________________________________________________________ -->
6576 <a name="int_returnaddress">'<tt>llvm.returnaddress</tt>' Intrinsic</a>
6583 declare i8 *@llvm.returnaddress(i32 <level>)
6587 <p>The '<tt>llvm.returnaddress</tt>' intrinsic attempts to compute a
6588 target-specific value indicating the return address of the current function
6589 or one of its callers.</p>
6592 <p>The argument to this intrinsic indicates which function to return the address
6593 for. Zero indicates the calling function, one indicates its caller, etc.
6594 The argument is <b>required</b> to be a constant integer value.</p>
6597 <p>The '<tt>llvm.returnaddress</tt>' intrinsic either returns a pointer
6598 indicating the return address of the specified call frame, or zero if it
6599 cannot be identified. The value returned by this intrinsic is likely to be
6600 incorrect or 0 for arguments other than zero, so it should only be used for
6601 debugging purposes.</p>
6603 <p>Note that calling this intrinsic does not prevent function inlining or other
6604 aggressive transformations, so the value returned may not be that of the
6605 obvious source-language caller.</p>
6609 <!-- _______________________________________________________________________ -->
6611 <a name="int_frameaddress">'<tt>llvm.frameaddress</tt>' Intrinsic</a>
6618 declare i8* @llvm.frameaddress(i32 <level>)
6622 <p>The '<tt>llvm.frameaddress</tt>' intrinsic attempts to return the
6623 target-specific frame pointer value for the specified stack frame.</p>
6626 <p>The argument to this intrinsic indicates which function to return the frame
6627 pointer for. Zero indicates the calling function, one indicates its caller,
6628 etc. The argument is <b>required</b> to be a constant integer value.</p>
6631 <p>The '<tt>llvm.frameaddress</tt>' intrinsic either returns a pointer
6632 indicating the frame address of the specified call frame, or zero if it
6633 cannot be identified. The value returned by this intrinsic is likely to be
6634 incorrect or 0 for arguments other than zero, so it should only be used for
6635 debugging purposes.</p>
6637 <p>Note that calling this intrinsic does not prevent function inlining or other
6638 aggressive transformations, so the value returned may not be that of the
6639 obvious source-language caller.</p>
6643 <!-- _______________________________________________________________________ -->
6645 <a name="int_stacksave">'<tt>llvm.stacksave</tt>' Intrinsic</a>
6652 declare i8* @llvm.stacksave()
6656 <p>The '<tt>llvm.stacksave</tt>' intrinsic is used to remember the current state
6657 of the function stack, for use
6658 with <a href="#int_stackrestore"> <tt>llvm.stackrestore</tt></a>. This is
6659 useful for implementing language features like scoped automatic variable
6660 sized arrays in C99.</p>
6663 <p>This intrinsic returns a opaque pointer value that can be passed
6664 to <a href="#int_stackrestore"><tt>llvm.stackrestore</tt></a>. When
6665 an <tt>llvm.stackrestore</tt> intrinsic is executed with a value saved
6666 from <tt>llvm.stacksave</tt>, it effectively restores the state of the stack
6667 to the state it was in when the <tt>llvm.stacksave</tt> intrinsic executed.
6668 In practice, this pops any <a href="#i_alloca">alloca</a> blocks from the
6669 stack that were allocated after the <tt>llvm.stacksave</tt> was executed.</p>
6673 <!-- _______________________________________________________________________ -->
6675 <a name="int_stackrestore">'<tt>llvm.stackrestore</tt>' Intrinsic</a>
6682 declare void @llvm.stackrestore(i8* %ptr)
6686 <p>The '<tt>llvm.stackrestore</tt>' intrinsic is used to restore the state of
6687 the function stack to the state it was in when the
6688 corresponding <a href="#int_stacksave"><tt>llvm.stacksave</tt></a> intrinsic
6689 executed. This is useful for implementing language features like scoped
6690 automatic variable sized arrays in C99.</p>
6693 <p>See the description
6694 for <a href="#int_stacksave"><tt>llvm.stacksave</tt></a>.</p>
6698 <!-- _______________________________________________________________________ -->
6700 <a name="int_prefetch">'<tt>llvm.prefetch</tt>' Intrinsic</a>
6707 declare void @llvm.prefetch(i8* <address>, i32 <rw>, i32 <locality>, i32 <cache type>)
6711 <p>The '<tt>llvm.prefetch</tt>' intrinsic is a hint to the code generator to
6712 insert a prefetch instruction if supported; otherwise, it is a noop.
6713 Prefetches have no effect on the behavior of the program but can change its
6714 performance characteristics.</p>
6717 <p><tt>address</tt> is the address to be prefetched, <tt>rw</tt> is the
6718 specifier determining if the fetch should be for a read (0) or write (1),
6719 and <tt>locality</tt> is a temporal locality specifier ranging from (0) - no
6720 locality, to (3) - extremely local keep in cache. The <tt>cache type</tt>
6721 specifies whether the prefetch is performed on the data (1) or instruction (0)
6722 cache. The <tt>rw</tt>, <tt>locality</tt> and <tt>cache type</tt> arguments
6723 must be constant integers.</p>
6726 <p>This intrinsic does not modify the behavior of the program. In particular,
6727 prefetches cannot trap and do not produce a value. On targets that support
6728 this intrinsic, the prefetch can provide hints to the processor cache for
6729 better performance.</p>
6733 <!-- _______________________________________________________________________ -->
6735 <a name="int_pcmarker">'<tt>llvm.pcmarker</tt>' Intrinsic</a>
6742 declare void @llvm.pcmarker(i32 <id>)
6746 <p>The '<tt>llvm.pcmarker</tt>' intrinsic is a method to export a Program
6747 Counter (PC) in a region of code to simulators and other tools. The method
6748 is target specific, but it is expected that the marker will use exported
6749 symbols to transmit the PC of the marker. The marker makes no guarantees
6750 that it will remain with any specific instruction after optimizations. It is
6751 possible that the presence of a marker will inhibit optimizations. The
6752 intended use is to be inserted after optimizations to allow correlations of
6753 simulation runs.</p>
6756 <p><tt>id</tt> is a numerical id identifying the marker.</p>
6759 <p>This intrinsic does not modify the behavior of the program. Backends that do
6760 not support this intrinsic may ignore it.</p>
6764 <!-- _______________________________________________________________________ -->
6766 <a name="int_readcyclecounter">'<tt>llvm.readcyclecounter</tt>' Intrinsic</a>
6773 declare i64 @llvm.readcyclecounter()
6777 <p>The '<tt>llvm.readcyclecounter</tt>' intrinsic provides access to the cycle
6778 counter register (or similar low latency, high accuracy clocks) on those
6779 targets that support it. On X86, it should map to RDTSC. On Alpha, it
6780 should map to RPCC. As the backing counters overflow quickly (on the order
6781 of 9 seconds on alpha), this should only be used for small timings.</p>
6784 <p>When directly supported, reading the cycle counter should not modify any
6785 memory. Implementations are allowed to either return a application specific
6786 value or a system wide value. On backends without support, this is lowered
6787 to a constant 0.</p>
6793 <!-- ======================================================================= -->
6795 <a name="int_libc">Standard C Library Intrinsics</a>
6800 <p>LLVM provides intrinsics for a few important standard C library functions.
6801 These intrinsics allow source-language front-ends to pass information about
6802 the alignment of the pointer arguments to the code generator, providing
6803 opportunity for more efficient code generation.</p>
6805 <!-- _______________________________________________________________________ -->
6807 <a name="int_memcpy">'<tt>llvm.memcpy</tt>' Intrinsic</a>
6813 <p>This is an overloaded intrinsic. You can use <tt>llvm.memcpy</tt> on any
6814 integer bit width and for different address spaces. Not all targets support
6815 all bit widths however.</p>
6818 declare void @llvm.memcpy.p0i8.p0i8.i32(i8* <dest>, i8* <src>,
6819 i32 <len>, i32 <align>, i1 <isvolatile>)
6820 declare void @llvm.memcpy.p0i8.p0i8.i64(i8* <dest>, i8* <src>,
6821 i64 <len>, i32 <align>, i1 <isvolatile>)
6825 <p>The '<tt>llvm.memcpy.*</tt>' intrinsics copy a block of memory from the
6826 source location to the destination location.</p>
6828 <p>Note that, unlike the standard libc function, the <tt>llvm.memcpy.*</tt>
6829 intrinsics do not return a value, takes extra alignment/isvolatile arguments
6830 and the pointers can be in specified address spaces.</p>
6834 <p>The first argument is a pointer to the destination, the second is a pointer
6835 to the source. The third argument is an integer argument specifying the
6836 number of bytes to copy, the fourth argument is the alignment of the
6837 source and destination locations, and the fifth is a boolean indicating a
6838 volatile access.</p>
6840 <p>If the call to this intrinsic has an alignment value that is not 0 or 1,
6841 then the caller guarantees that both the source and destination pointers are
6842 aligned to that boundary.</p>
6844 <p>If the <tt>isvolatile</tt> parameter is <tt>true</tt>, the
6845 <tt>llvm.memcpy</tt> call is a <a href="#volatile">volatile operation</a>.
6846 The detailed access behavior is not very cleanly specified and it is unwise
6847 to depend on it.</p>
6851 <p>The '<tt>llvm.memcpy.*</tt>' intrinsics copy a block of memory from the
6852 source location to the destination location, which are not allowed to
6853 overlap. It copies "len" bytes of memory over. If the argument is known to
6854 be aligned to some boundary, this can be specified as the fourth argument,
6855 otherwise it should be set to 0 or 1.</p>
6859 <!-- _______________________________________________________________________ -->
6861 <a name="int_memmove">'<tt>llvm.memmove</tt>' Intrinsic</a>
6867 <p>This is an overloaded intrinsic. You can use llvm.memmove on any integer bit
6868 width and for different address space. Not all targets support all bit
6872 declare void @llvm.memmove.p0i8.p0i8.i32(i8* <dest>, i8* <src>,
6873 i32 <len>, i32 <align>, i1 <isvolatile>)
6874 declare void @llvm.memmove.p0i8.p0i8.i64(i8* <dest>, i8* <src>,
6875 i64 <len>, i32 <align>, i1 <isvolatile>)
6879 <p>The '<tt>llvm.memmove.*</tt>' intrinsics move a block of memory from the
6880 source location to the destination location. It is similar to the
6881 '<tt>llvm.memcpy</tt>' intrinsic but allows the two memory locations to
6884 <p>Note that, unlike the standard libc function, the <tt>llvm.memmove.*</tt>
6885 intrinsics do not return a value, takes extra alignment/isvolatile arguments
6886 and the pointers can be in specified address spaces.</p>
6890 <p>The first argument is a pointer to the destination, the second is a pointer
6891 to the source. The third argument is an integer argument specifying the
6892 number of bytes to copy, the fourth argument is the alignment of the
6893 source and destination locations, and the fifth is a boolean indicating a
6894 volatile access.</p>
6896 <p>If the call to this intrinsic has an alignment value that is not 0 or 1,
6897 then the caller guarantees that the source and destination pointers are
6898 aligned to that boundary.</p>
6900 <p>If the <tt>isvolatile</tt> parameter is <tt>true</tt>, the
6901 <tt>llvm.memmove</tt> call is a <a href="#volatile">volatile operation</a>.
6902 The detailed access behavior is not very cleanly specified and it is unwise
6903 to depend on it.</p>
6907 <p>The '<tt>llvm.memmove.*</tt>' intrinsics copy a block of memory from the
6908 source location to the destination location, which may overlap. It copies
6909 "len" bytes of memory over. If the argument is known to be aligned to some
6910 boundary, this can be specified as the fourth argument, otherwise it should
6911 be set to 0 or 1.</p>
6915 <!-- _______________________________________________________________________ -->
6917 <a name="int_memset">'<tt>llvm.memset.*</tt>' Intrinsics</a>
6923 <p>This is an overloaded intrinsic. You can use llvm.memset on any integer bit
6924 width and for different address spaces. However, not all targets support all
6928 declare void @llvm.memset.p0i8.i32(i8* <dest>, i8 <val>,
6929 i32 <len>, i32 <align>, i1 <isvolatile>)
6930 declare void @llvm.memset.p0i8.i64(i8* <dest>, i8 <val>,
6931 i64 <len>, i32 <align>, i1 <isvolatile>)
6935 <p>The '<tt>llvm.memset.*</tt>' intrinsics fill a block of memory with a
6936 particular byte value.</p>
6938 <p>Note that, unlike the standard libc function, the <tt>llvm.memset</tt>
6939 intrinsic does not return a value and takes extra alignment/volatile
6940 arguments. Also, the destination can be in an arbitrary address space.</p>
6943 <p>The first argument is a pointer to the destination to fill, the second is the
6944 byte value with which to fill it, the third argument is an integer argument
6945 specifying the number of bytes to fill, and the fourth argument is the known
6946 alignment of the destination location.</p>
6948 <p>If the call to this intrinsic has an alignment value that is not 0 or 1,
6949 then the caller guarantees that the destination pointer is aligned to that
6952 <p>If the <tt>isvolatile</tt> parameter is <tt>true</tt>, the
6953 <tt>llvm.memset</tt> call is a <a href="#volatile">volatile operation</a>.
6954 The detailed access behavior is not very cleanly specified and it is unwise
6955 to depend on it.</p>
6958 <p>The '<tt>llvm.memset.*</tt>' intrinsics fill "len" bytes of memory starting
6959 at the destination location. If the argument is known to be aligned to some
6960 boundary, this can be specified as the fourth argument, otherwise it should
6961 be set to 0 or 1.</p>
6965 <!-- _______________________________________________________________________ -->
6967 <a name="int_sqrt">'<tt>llvm.sqrt.*</tt>' Intrinsic</a>
6973 <p>This is an overloaded intrinsic. You can use <tt>llvm.sqrt</tt> on any
6974 floating point or vector of floating point type. Not all targets support all
6978 declare float @llvm.sqrt.f32(float %Val)
6979 declare double @llvm.sqrt.f64(double %Val)
6980 declare x86_fp80 @llvm.sqrt.f80(x86_fp80 %Val)
6981 declare fp128 @llvm.sqrt.f128(fp128 %Val)
6982 declare ppc_fp128 @llvm.sqrt.ppcf128(ppc_fp128 %Val)
6986 <p>The '<tt>llvm.sqrt</tt>' intrinsics return the sqrt of the specified operand,
6987 returning the same value as the libm '<tt>sqrt</tt>' functions would.
6988 Unlike <tt>sqrt</tt> in libm, however, <tt>llvm.sqrt</tt> has undefined
6989 behavior for negative numbers other than -0.0 (which allows for better
6990 optimization, because there is no need to worry about errno being
6991 set). <tt>llvm.sqrt(-0.0)</tt> is defined to return -0.0 like IEEE sqrt.</p>
6994 <p>The argument and return value are floating point numbers of the same
6998 <p>This function returns the sqrt of the specified operand if it is a
6999 nonnegative floating point number.</p>
7003 <!-- _______________________________________________________________________ -->
7005 <a name="int_powi">'<tt>llvm.powi.*</tt>' Intrinsic</a>
7011 <p>This is an overloaded intrinsic. You can use <tt>llvm.powi</tt> on any
7012 floating point or vector of floating point type. Not all targets support all
7016 declare float @llvm.powi.f32(float %Val, i32 %power)
7017 declare double @llvm.powi.f64(double %Val, i32 %power)
7018 declare x86_fp80 @llvm.powi.f80(x86_fp80 %Val, i32 %power)
7019 declare fp128 @llvm.powi.f128(fp128 %Val, i32 %power)
7020 declare ppc_fp128 @llvm.powi.ppcf128(ppc_fp128 %Val, i32 %power)
7024 <p>The '<tt>llvm.powi.*</tt>' intrinsics return the first operand raised to the
7025 specified (positive or negative) power. The order of evaluation of
7026 multiplications is not defined. When a vector of floating point type is
7027 used, the second argument remains a scalar integer value.</p>
7030 <p>The second argument is an integer power, and the first is a value to raise to
7034 <p>This function returns the first value raised to the second power with an
7035 unspecified sequence of rounding operations.</p>
7039 <!-- _______________________________________________________________________ -->
7041 <a name="int_sin">'<tt>llvm.sin.*</tt>' Intrinsic</a>
7047 <p>This is an overloaded intrinsic. You can use <tt>llvm.sin</tt> on any
7048 floating point or vector of floating point type. Not all targets support all
7052 declare float @llvm.sin.f32(float %Val)
7053 declare double @llvm.sin.f64(double %Val)
7054 declare x86_fp80 @llvm.sin.f80(x86_fp80 %Val)
7055 declare fp128 @llvm.sin.f128(fp128 %Val)
7056 declare ppc_fp128 @llvm.sin.ppcf128(ppc_fp128 %Val)
7060 <p>The '<tt>llvm.sin.*</tt>' intrinsics return the sine of the operand.</p>
7063 <p>The argument and return value are floating point numbers of the same
7067 <p>This function returns the sine of the specified operand, returning the same
7068 values as the libm <tt>sin</tt> functions would, and handles error conditions
7069 in the same way.</p>
7073 <!-- _______________________________________________________________________ -->
7075 <a name="int_cos">'<tt>llvm.cos.*</tt>' Intrinsic</a>
7081 <p>This is an overloaded intrinsic. You can use <tt>llvm.cos</tt> on any
7082 floating point or vector of floating point type. Not all targets support all
7086 declare float @llvm.cos.f32(float %Val)
7087 declare double @llvm.cos.f64(double %Val)
7088 declare x86_fp80 @llvm.cos.f80(x86_fp80 %Val)
7089 declare fp128 @llvm.cos.f128(fp128 %Val)
7090 declare ppc_fp128 @llvm.cos.ppcf128(ppc_fp128 %Val)
7094 <p>The '<tt>llvm.cos.*</tt>' intrinsics return the cosine of the operand.</p>
7097 <p>The argument and return value are floating point numbers of the same
7101 <p>This function returns the cosine of the specified operand, returning the same
7102 values as the libm <tt>cos</tt> functions would, and handles error conditions
7103 in the same way.</p>
7107 <!-- _______________________________________________________________________ -->
7109 <a name="int_pow">'<tt>llvm.pow.*</tt>' Intrinsic</a>
7115 <p>This is an overloaded intrinsic. You can use <tt>llvm.pow</tt> on any
7116 floating point or vector of floating point type. Not all targets support all
7120 declare float @llvm.pow.f32(float %Val, float %Power)
7121 declare double @llvm.pow.f64(double %Val, double %Power)
7122 declare x86_fp80 @llvm.pow.f80(x86_fp80 %Val, x86_fp80 %Power)
7123 declare fp128 @llvm.pow.f128(fp128 %Val, fp128 %Power)
7124 declare ppc_fp128 @llvm.pow.ppcf128(ppc_fp128 %Val, ppc_fp128 Power)
7128 <p>The '<tt>llvm.pow.*</tt>' intrinsics return the first operand raised to the
7129 specified (positive or negative) power.</p>
7132 <p>The second argument is a floating point power, and the first is a value to
7133 raise to that power.</p>
7136 <p>This function returns the first value raised to the second power, returning
7137 the same values as the libm <tt>pow</tt> functions would, and handles error
7138 conditions in the same way.</p>
7142 <!-- _______________________________________________________________________ -->
7144 <a name="int_exp">'<tt>llvm.exp.*</tt>' Intrinsic</a>
7150 <p>This is an overloaded intrinsic. You can use <tt>llvm.exp</tt> on any
7151 floating point or vector of floating point type. Not all targets support all
7155 declare float @llvm.exp.f32(float %Val)
7156 declare double @llvm.exp.f64(double %Val)
7157 declare x86_fp80 @llvm.exp.f80(x86_fp80 %Val)
7158 declare fp128 @llvm.exp.f128(fp128 %Val)
7159 declare ppc_fp128 @llvm.exp.ppcf128(ppc_fp128 %Val)
7163 <p>The '<tt>llvm.exp.*</tt>' intrinsics perform the exp function.</p>
7166 <p>The argument and return value are floating point numbers of the same
7170 <p>This function returns the same values as the libm <tt>exp</tt> functions
7171 would, and handles error conditions in the same way.</p>
7175 <!-- _______________________________________________________________________ -->
7177 <a name="int_log">'<tt>llvm.log.*</tt>' Intrinsic</a>
7183 <p>This is an overloaded intrinsic. You can use <tt>llvm.log</tt> on any
7184 floating point or vector of floating point type. Not all targets support all
7188 declare float @llvm.log.f32(float %Val)
7189 declare double @llvm.log.f64(double %Val)
7190 declare x86_fp80 @llvm.log.f80(x86_fp80 %Val)
7191 declare fp128 @llvm.log.f128(fp128 %Val)
7192 declare ppc_fp128 @llvm.log.ppcf128(ppc_fp128 %Val)
7196 <p>The '<tt>llvm.log.*</tt>' intrinsics perform the log function.</p>
7199 <p>The argument and return value are floating point numbers of the same
7203 <p>This function returns the same values as the libm <tt>log</tt> functions
7204 would, and handles error conditions in the same way.</p>
7208 <!-- _______________________________________________________________________ -->
7210 <a name="int_fma">'<tt>llvm.fma.*</tt>' Intrinsic</a>
7216 <p>This is an overloaded intrinsic. You can use <tt>llvm.fma</tt> on any
7217 floating point or vector of floating point type. Not all targets support all
7221 declare float @llvm.fma.f32(float %a, float %b, float %c)
7222 declare double @llvm.fma.f64(double %a, double %b, double %c)
7223 declare x86_fp80 @llvm.fma.f80(x86_fp80 %a, x86_fp80 %b, x86_fp80 %c)
7224 declare fp128 @llvm.fma.f128(fp128 %a, fp128 %b, fp128 %c)
7225 declare ppc_fp128 @llvm.fma.ppcf128(ppc_fp128 %a, ppc_fp128 %b, ppc_fp128 %c)
7229 <p>The '<tt>llvm.fma.*</tt>' intrinsics perform the fused multiply-add
7233 <p>The argument and return value are floating point numbers of the same
7237 <p>This function returns the same values as the libm <tt>fma</tt> functions
7244 <!-- ======================================================================= -->
7246 <a name="int_manip">Bit Manipulation Intrinsics</a>
7251 <p>LLVM provides intrinsics for a few important bit manipulation operations.
7252 These allow efficient code generation for some algorithms.</p>
7254 <!-- _______________________________________________________________________ -->
7256 <a name="int_bswap">'<tt>llvm.bswap.*</tt>' Intrinsics</a>
7262 <p>This is an overloaded intrinsic function. You can use bswap on any integer
7263 type that is an even number of bytes (i.e. BitWidth % 16 == 0).</p>
7266 declare i16 @llvm.bswap.i16(i16 <id>)
7267 declare i32 @llvm.bswap.i32(i32 <id>)
7268 declare i64 @llvm.bswap.i64(i64 <id>)
7272 <p>The '<tt>llvm.bswap</tt>' family of intrinsics is used to byte swap integer
7273 values with an even number of bytes (positive multiple of 16 bits). These
7274 are useful for performing operations on data that is not in the target's
7275 native byte order.</p>
7278 <p>The <tt>llvm.bswap.i16</tt> intrinsic returns an i16 value that has the high
7279 and low byte of the input i16 swapped. Similarly,
7280 the <tt>llvm.bswap.i32</tt> intrinsic returns an i32 value that has the four
7281 bytes of the input i32 swapped, so that if the input bytes are numbered 0, 1,
7282 2, 3 then the returned i32 will have its bytes in 3, 2, 1, 0 order.
7283 The <tt>llvm.bswap.i48</tt>, <tt>llvm.bswap.i64</tt> and other intrinsics
7284 extend this concept to additional even-byte lengths (6 bytes, 8 bytes and
7285 more, respectively).</p>
7289 <!-- _______________________________________________________________________ -->
7291 <a name="int_ctpop">'<tt>llvm.ctpop.*</tt>' Intrinsic</a>
7297 <p>This is an overloaded intrinsic. You can use llvm.ctpop on any integer bit
7298 width, or on any vector with integer elements. Not all targets support all
7299 bit widths or vector types, however.</p>
7302 declare i8 @llvm.ctpop.i8(i8 <src>)
7303 declare i16 @llvm.ctpop.i16(i16 <src>)
7304 declare i32 @llvm.ctpop.i32(i32 <src>)
7305 declare i64 @llvm.ctpop.i64(i64 <src>)
7306 declare i256 @llvm.ctpop.i256(i256 <src>)
7307 declare <2 x i32> @llvm.ctpop.v2i32(<2 x i32> <src>)
7311 <p>The '<tt>llvm.ctpop</tt>' family of intrinsics counts the number of bits set
7315 <p>The only argument is the value to be counted. The argument may be of any
7316 integer type, or a vector with integer elements.
7317 The return type must match the argument type.</p>
7320 <p>The '<tt>llvm.ctpop</tt>' intrinsic counts the 1's in a variable, or within each
7321 element of a vector.</p>
7325 <!-- _______________________________________________________________________ -->
7327 <a name="int_ctlz">'<tt>llvm.ctlz.*</tt>' Intrinsic</a>
7333 <p>This is an overloaded intrinsic. You can use <tt>llvm.ctlz</tt> on any
7334 integer bit width, or any vector whose elements are integers. Not all
7335 targets support all bit widths or vector types, however.</p>
7338 declare i8 @llvm.ctlz.i8 (i8 <src>)
7339 declare i16 @llvm.ctlz.i16(i16 <src>)
7340 declare i32 @llvm.ctlz.i32(i32 <src>)
7341 declare i64 @llvm.ctlz.i64(i64 <src>)
7342 declare i256 @llvm.ctlz.i256(i256 <src>)
7343 declare <2 x i32> @llvm.ctlz.v2i32(<2 x i32> <src;gt)
7347 <p>The '<tt>llvm.ctlz</tt>' family of intrinsic functions counts the number of
7348 leading zeros in a variable.</p>
7351 <p>The only argument is the value to be counted. The argument may be of any
7352 integer type, or any vector type with integer element type.
7353 The return type must match the argument type.</p>
7356 <p>The '<tt>llvm.ctlz</tt>' intrinsic counts the leading (most significant)
7357 zeros in a variable, or within each element of the vector if the operation
7358 is of vector type. If the src == 0 then the result is the size in bits of
7359 the type of src. For example, <tt>llvm.ctlz(i32 2) = 30</tt>.</p>
7363 <!-- _______________________________________________________________________ -->
7365 <a name="int_cttz">'<tt>llvm.cttz.*</tt>' Intrinsic</a>
7371 <p>This is an overloaded intrinsic. You can use <tt>llvm.cttz</tt> on any
7372 integer bit width, or any vector of integer elements. Not all targets
7373 support all bit widths or vector types, however.</p>
7376 declare i8 @llvm.cttz.i8 (i8 <src>)
7377 declare i16 @llvm.cttz.i16(i16 <src>)
7378 declare i32 @llvm.cttz.i32(i32 <src>)
7379 declare i64 @llvm.cttz.i64(i64 <src>)
7380 declare i256 @llvm.cttz.i256(i256 <src>)
7381 declase <2 x i32> @llvm.cttz.v2i32(<2 x i32> <src>)
7385 <p>The '<tt>llvm.cttz</tt>' family of intrinsic functions counts the number of
7389 <p>The only argument is the value to be counted. The argument may be of any
7390 integer type, or a vectory with integer element type.. The return type
7391 must match the argument type.</p>
7394 <p>The '<tt>llvm.cttz</tt>' intrinsic counts the trailing (least significant)
7395 zeros in a variable, or within each element of a vector.
7396 If the src == 0 then the result is the size in bits of
7397 the type of src. For example, <tt>llvm.cttz(2) = 1</tt>.</p>
7403 <!-- ======================================================================= -->
7405 <a name="int_overflow">Arithmetic with Overflow Intrinsics</a>
7410 <p>LLVM provides intrinsics for some arithmetic with overflow operations.</p>
7412 <!-- _______________________________________________________________________ -->
7414 <a name="int_sadd_overflow">
7415 '<tt>llvm.sadd.with.overflow.*</tt>' Intrinsics
7422 <p>This is an overloaded intrinsic. You can use <tt>llvm.sadd.with.overflow</tt>
7423 on any integer bit width.</p>
7426 declare {i16, i1} @llvm.sadd.with.overflow.i16(i16 %a, i16 %b)
7427 declare {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b)
7428 declare {i64, i1} @llvm.sadd.with.overflow.i64(i64 %a, i64 %b)
7432 <p>The '<tt>llvm.sadd.with.overflow</tt>' family of intrinsic functions perform
7433 a signed addition of the two arguments, and indicate whether an overflow
7434 occurred during the signed summation.</p>
7437 <p>The arguments (%a and %b) and the first element of the result structure may
7438 be of integer types of any bit width, but they must have the same bit
7439 width. The second element of the result structure must be of
7440 type <tt>i1</tt>. <tt>%a</tt> and <tt>%b</tt> are the two values that will
7441 undergo signed addition.</p>
7444 <p>The '<tt>llvm.sadd.with.overflow</tt>' family of intrinsic functions perform
7445 a signed addition of the two variables. They return a structure — the
7446 first element of which is the signed summation, and the second element of
7447 which is a bit specifying if the signed summation resulted in an
7452 %res = call {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b)
7453 %sum = extractvalue {i32, i1} %res, 0
7454 %obit = extractvalue {i32, i1} %res, 1
7455 br i1 %obit, label %overflow, label %normal
7460 <!-- _______________________________________________________________________ -->
7462 <a name="int_uadd_overflow">
7463 '<tt>llvm.uadd.with.overflow.*</tt>' Intrinsics
7470 <p>This is an overloaded intrinsic. You can use <tt>llvm.uadd.with.overflow</tt>
7471 on any integer bit width.</p>
7474 declare {i16, i1} @llvm.uadd.with.overflow.i16(i16 %a, i16 %b)
7475 declare {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)
7476 declare {i64, i1} @llvm.uadd.with.overflow.i64(i64 %a, i64 %b)
7480 <p>The '<tt>llvm.uadd.with.overflow</tt>' family of intrinsic functions perform
7481 an unsigned addition of the two arguments, and indicate whether a carry
7482 occurred during the unsigned summation.</p>
7485 <p>The arguments (%a and %b) and the first element of the result structure may
7486 be of integer types of any bit width, but they must have the same bit
7487 width. The second element of the result structure must be of
7488 type <tt>i1</tt>. <tt>%a</tt> and <tt>%b</tt> are the two values that will
7489 undergo unsigned addition.</p>
7492 <p>The '<tt>llvm.uadd.with.overflow</tt>' family of intrinsic functions perform
7493 an unsigned addition of the two arguments. They return a structure —
7494 the first element of which is the sum, and the second element of which is a
7495 bit specifying if the unsigned summation resulted in a carry.</p>
7499 %res = call {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)
7500 %sum = extractvalue {i32, i1} %res, 0
7501 %obit = extractvalue {i32, i1} %res, 1
7502 br i1 %obit, label %carry, label %normal
7507 <!-- _______________________________________________________________________ -->
7509 <a name="int_ssub_overflow">
7510 '<tt>llvm.ssub.with.overflow.*</tt>' Intrinsics
7517 <p>This is an overloaded intrinsic. You can use <tt>llvm.ssub.with.overflow</tt>
7518 on any integer bit width.</p>
7521 declare {i16, i1} @llvm.ssub.with.overflow.i16(i16 %a, i16 %b)
7522 declare {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b)
7523 declare {i64, i1} @llvm.ssub.with.overflow.i64(i64 %a, i64 %b)
7527 <p>The '<tt>llvm.ssub.with.overflow</tt>' family of intrinsic functions perform
7528 a signed subtraction of the two arguments, and indicate whether an overflow
7529 occurred during the signed subtraction.</p>
7532 <p>The arguments (%a and %b) and the first element of the result structure may
7533 be of integer types of any bit width, but they must have the same bit
7534 width. The second element of the result structure must be of
7535 type <tt>i1</tt>. <tt>%a</tt> and <tt>%b</tt> are the two values that will
7536 undergo signed subtraction.</p>
7539 <p>The '<tt>llvm.ssub.with.overflow</tt>' family of intrinsic functions perform
7540 a signed subtraction of the two arguments. They return a structure —
7541 the first element of which is the subtraction, and the second element of
7542 which is a bit specifying if the signed subtraction resulted in an
7547 %res = call {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b)
7548 %sum = extractvalue {i32, i1} %res, 0
7549 %obit = extractvalue {i32, i1} %res, 1
7550 br i1 %obit, label %overflow, label %normal
7555 <!-- _______________________________________________________________________ -->
7557 <a name="int_usub_overflow">
7558 '<tt>llvm.usub.with.overflow.*</tt>' Intrinsics
7565 <p>This is an overloaded intrinsic. You can use <tt>llvm.usub.with.overflow</tt>
7566 on any integer bit width.</p>
7569 declare {i16, i1} @llvm.usub.with.overflow.i16(i16 %a, i16 %b)
7570 declare {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b)
7571 declare {i64, i1} @llvm.usub.with.overflow.i64(i64 %a, i64 %b)
7575 <p>The '<tt>llvm.usub.with.overflow</tt>' family of intrinsic functions perform
7576 an unsigned subtraction of the two arguments, and indicate whether an
7577 overflow occurred during the unsigned subtraction.</p>
7580 <p>The arguments (%a and %b) and the first element of the result structure may
7581 be of integer types of any bit width, but they must have the same bit
7582 width. The second element of the result structure must be of
7583 type <tt>i1</tt>. <tt>%a</tt> and <tt>%b</tt> are the two values that will
7584 undergo unsigned subtraction.</p>
7587 <p>The '<tt>llvm.usub.with.overflow</tt>' family of intrinsic functions perform
7588 an unsigned subtraction of the two arguments. They return a structure —
7589 the first element of which is the subtraction, and the second element of
7590 which is a bit specifying if the unsigned subtraction resulted in an
7595 %res = call {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b)
7596 %sum = extractvalue {i32, i1} %res, 0
7597 %obit = extractvalue {i32, i1} %res, 1
7598 br i1 %obit, label %overflow, label %normal
7603 <!-- _______________________________________________________________________ -->
7605 <a name="int_smul_overflow">
7606 '<tt>llvm.smul.with.overflow.*</tt>' Intrinsics
7613 <p>This is an overloaded intrinsic. You can use <tt>llvm.smul.with.overflow</tt>
7614 on any integer bit width.</p>
7617 declare {i16, i1} @llvm.smul.with.overflow.i16(i16 %a, i16 %b)
7618 declare {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b)
7619 declare {i64, i1} @llvm.smul.with.overflow.i64(i64 %a, i64 %b)
7624 <p>The '<tt>llvm.smul.with.overflow</tt>' family of intrinsic functions perform
7625 a signed multiplication of the two arguments, and indicate whether an
7626 overflow occurred during the signed multiplication.</p>
7629 <p>The arguments (%a and %b) and the first element of the result structure may
7630 be of integer types of any bit width, but they must have the same bit
7631 width. The second element of the result structure must be of
7632 type <tt>i1</tt>. <tt>%a</tt> and <tt>%b</tt> are the two values that will
7633 undergo signed multiplication.</p>
7636 <p>The '<tt>llvm.smul.with.overflow</tt>' family of intrinsic functions perform
7637 a signed multiplication of the two arguments. They return a structure —
7638 the first element of which is the multiplication, and the second element of
7639 which is a bit specifying if the signed multiplication resulted in an
7644 %res = call {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b)
7645 %sum = extractvalue {i32, i1} %res, 0
7646 %obit = extractvalue {i32, i1} %res, 1
7647 br i1 %obit, label %overflow, label %normal
7652 <!-- _______________________________________________________________________ -->
7654 <a name="int_umul_overflow">
7655 '<tt>llvm.umul.with.overflow.*</tt>' Intrinsics
7662 <p>This is an overloaded intrinsic. You can use <tt>llvm.umul.with.overflow</tt>
7663 on any integer bit width.</p>
7666 declare {i16, i1} @llvm.umul.with.overflow.i16(i16 %a, i16 %b)
7667 declare {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b)
7668 declare {i64, i1} @llvm.umul.with.overflow.i64(i64 %a, i64 %b)
7672 <p>The '<tt>llvm.umul.with.overflow</tt>' family of intrinsic functions perform
7673 a unsigned multiplication of the two arguments, and indicate whether an
7674 overflow occurred during the unsigned multiplication.</p>
7677 <p>The arguments (%a and %b) and the first element of the result structure may
7678 be of integer types of any bit width, but they must have the same bit
7679 width. The second element of the result structure must be of
7680 type <tt>i1</tt>. <tt>%a</tt> and <tt>%b</tt> are the two values that will
7681 undergo unsigned multiplication.</p>
7684 <p>The '<tt>llvm.umul.with.overflow</tt>' family of intrinsic functions perform
7685 an unsigned multiplication of the two arguments. They return a structure
7686 — the first element of which is the multiplication, and the second
7687 element of which is a bit specifying if the unsigned multiplication resulted
7692 %res = call {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b)
7693 %sum = extractvalue {i32, i1} %res, 0
7694 %obit = extractvalue {i32, i1} %res, 1
7695 br i1 %obit, label %overflow, label %normal
7702 <!-- ======================================================================= -->
7704 <a name="int_fp16">Half Precision Floating Point Intrinsics</a>
7709 <p>Half precision floating point is a storage-only format. This means that it is
7710 a dense encoding (in memory) but does not support computation in the
7713 <p>This means that code must first load the half-precision floating point
7714 value as an i16, then convert it to float with <a
7715 href="#int_convert_from_fp16"><tt>llvm.convert.from.fp16</tt></a>.
7716 Computation can then be performed on the float value (including extending to
7717 double etc). To store the value back to memory, it is first converted to
7718 float if needed, then converted to i16 with
7719 <a href="#int_convert_to_fp16"><tt>llvm.convert.to.fp16</tt></a>, then
7720 storing as an i16 value.</p>
7722 <!-- _______________________________________________________________________ -->
7724 <a name="int_convert_to_fp16">
7725 '<tt>llvm.convert.to.fp16</tt>' Intrinsic
7733 declare i16 @llvm.convert.to.fp16(f32 %a)
7737 <p>The '<tt>llvm.convert.to.fp16</tt>' intrinsic function performs
7738 a conversion from single precision floating point format to half precision
7739 floating point format.</p>
7742 <p>The intrinsic function contains single argument - the value to be
7746 <p>The '<tt>llvm.convert.to.fp16</tt>' intrinsic function performs
7747 a conversion from single precision floating point format to half precision
7748 floating point format. The return value is an <tt>i16</tt> which
7749 contains the converted number.</p>
7753 %res = call i16 @llvm.convert.to.fp16(f32 %a)
7754 store i16 %res, i16* @x, align 2
7759 <!-- _______________________________________________________________________ -->
7761 <a name="int_convert_from_fp16">
7762 '<tt>llvm.convert.from.fp16</tt>' Intrinsic
7770 declare f32 @llvm.convert.from.fp16(i16 %a)
7774 <p>The '<tt>llvm.convert.from.fp16</tt>' intrinsic function performs
7775 a conversion from half precision floating point format to single precision
7776 floating point format.</p>
7779 <p>The intrinsic function contains single argument - the value to be
7783 <p>The '<tt>llvm.convert.from.fp16</tt>' intrinsic function performs a
7784 conversion from half single precision floating point format to single
7785 precision floating point format. The input half-float value is represented by
7786 an <tt>i16</tt> value.</p>
7790 %a = load i16* @x, align 2
7791 %res = call f32 @llvm.convert.from.fp16(i16 %a)
7798 <!-- ======================================================================= -->
7800 <a name="int_debugger">Debugger Intrinsics</a>
7805 <p>The LLVM debugger intrinsics (which all start with <tt>llvm.dbg.</tt>
7806 prefix), are described in
7807 the <a href="SourceLevelDebugging.html#format_common_intrinsics">LLVM Source
7808 Level Debugging</a> document.</p>
7812 <!-- ======================================================================= -->
7814 <a name="int_eh">Exception Handling Intrinsics</a>
7819 <p>The LLVM exception handling intrinsics (which all start with
7820 <tt>llvm.eh.</tt> prefix), are described in
7821 the <a href="ExceptionHandling.html#format_common_intrinsics">LLVM Exception
7822 Handling</a> document.</p>
7826 <!-- ======================================================================= -->
7828 <a name="int_trampoline">Trampoline Intrinsics</a>
7833 <p>These intrinsics make it possible to excise one parameter, marked with
7834 the <a href="#nest"><tt>nest</tt></a> attribute, from a function.
7835 The result is a callable
7836 function pointer lacking the nest parameter - the caller does not need to
7837 provide a value for it. Instead, the value to use is stored in advance in a
7838 "trampoline", a block of memory usually allocated on the stack, which also
7839 contains code to splice the nest value into the argument list. This is used
7840 to implement the GCC nested function address extension.</p>
7842 <p>For example, if the function is
7843 <tt>i32 f(i8* nest %c, i32 %x, i32 %y)</tt> then the resulting function
7844 pointer has signature <tt>i32 (i32, i32)*</tt>. It can be created as
7847 <pre class="doc_code">
7848 %tramp = alloca [10 x i8], align 4 ; size and alignment only correct for X86
7849 %tramp1 = getelementptr [10 x i8]* %tramp, i32 0, i32 0
7850 call i8* @llvm.init.trampoline(i8* %tramp1, i8* bitcast (i32 (i8*, i32, i32)* @f to i8*), i8* %nval)
7851 %p = call i8* @llvm.adjust.trampoline(i8* %tramp1)
7852 %fp = bitcast i8* %p to i32 (i32, i32)*
7855 <p>The call <tt>%val = call i32 %fp(i32 %x, i32 %y)</tt> is then equivalent
7856 to <tt>%val = call i32 %f(i8* %nval, i32 %x, i32 %y)</tt>.</p>
7858 <!-- _______________________________________________________________________ -->
7861 '<tt>llvm.init.trampoline</tt>' Intrinsic
7869 declare void @llvm.init.trampoline(i8* <tramp>, i8* <func>, i8* <nval>)
7873 <p>This fills the memory pointed to by <tt>tramp</tt> with executable code,
7874 turning it into a trampoline.</p>
7877 <p>The <tt>llvm.init.trampoline</tt> intrinsic takes three arguments, all
7878 pointers. The <tt>tramp</tt> argument must point to a sufficiently large and
7879 sufficiently aligned block of memory; this memory is written to by the
7880 intrinsic. Note that the size and the alignment are target-specific - LLVM
7881 currently provides no portable way of determining them, so a front-end that
7882 generates this intrinsic needs to have some target-specific knowledge.
7883 The <tt>func</tt> argument must hold a function bitcast to
7884 an <tt>i8*</tt>.</p>
7887 <p>The block of memory pointed to by <tt>tramp</tt> is filled with target
7888 dependent code, turning it into a function. Then <tt>tramp</tt> needs to be
7889 passed to <a href="#int_at">llvm.adjust.trampoline</a> to get a pointer
7890 which can be <a href="#int_trampoline">bitcast (to a new function) and
7891 called</a>. The new function's signature is the same as that of
7892 <tt>func</tt> with any arguments marked with the <tt>nest</tt> attribute
7893 removed. At most one such <tt>nest</tt> argument is allowed, and it must be of
7894 pointer type. Calling the new function is equivalent to calling <tt>func</tt>
7895 with the same argument list, but with <tt>nval</tt> used for the missing
7896 <tt>nest</tt> argument. If, after calling <tt>llvm.init.trampoline</tt>, the
7897 memory pointed to by <tt>tramp</tt> is modified, then the effect of any later call
7898 to the returned function pointer is undefined.</p>
7901 <!-- _______________________________________________________________________ -->
7904 '<tt>llvm.adjust.trampoline</tt>' Intrinsic
7912 declare i8* @llvm.adjust.trampoline(i8* <tramp>)
7916 <p>This performs any required machine-specific adjustment to the address of a
7917 trampoline (passed as <tt>tramp</tt>).</p>
7920 <p><tt>tramp</tt> must point to a block of memory which already has trampoline code
7921 filled in by a previous call to <a href="#int_it"><tt>llvm.init.trampoline</tt>
7925 <p>On some architectures the address of the code to be executed needs to be
7926 different to the address where the trampoline is actually stored. This
7927 intrinsic returns the executable address corresponding to <tt>tramp</tt>
7928 after performing the required machine specific adjustments.
7929 The pointer returned can then be <a href="#int_trampoline"> bitcast and
7937 <!-- ======================================================================= -->
7939 <a name="int_memorymarkers">Memory Use Markers</a>
7944 <p>This class of intrinsics exists to information about the lifetime of memory
7945 objects and ranges where variables are immutable.</p>
7947 <!-- _______________________________________________________________________ -->
7949 <a name="int_lifetime_start">'<tt>llvm.lifetime.start</tt>' Intrinsic</a>
7956 declare void @llvm.lifetime.start(i64 <size>, i8* nocapture <ptr>)
7960 <p>The '<tt>llvm.lifetime.start</tt>' intrinsic specifies the start of a memory
7961 object's lifetime.</p>
7964 <p>The first argument is a constant integer representing the size of the
7965 object, or -1 if it is variable sized. The second argument is a pointer to
7969 <p>This intrinsic indicates that before this point in the code, the value of the
7970 memory pointed to by <tt>ptr</tt> is dead. This means that it is known to
7971 never be used and has an undefined value. A load from the pointer that
7972 precedes this intrinsic can be replaced with
7973 <tt>'<a href="#undefvalues">undef</a>'</tt>.</p>
7977 <!-- _______________________________________________________________________ -->
7979 <a name="int_lifetime_end">'<tt>llvm.lifetime.end</tt>' Intrinsic</a>
7986 declare void @llvm.lifetime.end(i64 <size>, i8* nocapture <ptr>)
7990 <p>The '<tt>llvm.lifetime.end</tt>' intrinsic specifies the end of a memory
7991 object's lifetime.</p>
7994 <p>The first argument is a constant integer representing the size of the
7995 object, or -1 if it is variable sized. The second argument is a pointer to
7999 <p>This intrinsic indicates that after this point in the code, the value of the
8000 memory pointed to by <tt>ptr</tt> is dead. This means that it is known to
8001 never be used and has an undefined value. Any stores into the memory object
8002 following this intrinsic may be removed as dead.
8006 <!-- _______________________________________________________________________ -->
8008 <a name="int_invariant_start">'<tt>llvm.invariant.start</tt>' Intrinsic</a>
8015 declare {}* @llvm.invariant.start(i64 <size>, i8* nocapture <ptr>)
8019 <p>The '<tt>llvm.invariant.start</tt>' intrinsic specifies that the contents of
8020 a memory object will not change.</p>
8023 <p>The first argument is a constant integer representing the size of the
8024 object, or -1 if it is variable sized. The second argument is a pointer to
8028 <p>This intrinsic indicates that until an <tt>llvm.invariant.end</tt> that uses
8029 the return value, the referenced memory location is constant and
8034 <!-- _______________________________________________________________________ -->
8036 <a name="int_invariant_end">'<tt>llvm.invariant.end</tt>' Intrinsic</a>
8043 declare void @llvm.invariant.end({}* <start>, i64 <size>, i8* nocapture <ptr>)
8047 <p>The '<tt>llvm.invariant.end</tt>' intrinsic specifies that the contents of
8048 a memory object are mutable.</p>
8051 <p>The first argument is the matching <tt>llvm.invariant.start</tt> intrinsic.
8052 The second argument is a constant integer representing the size of the
8053 object, or -1 if it is variable sized and the third argument is a pointer
8057 <p>This intrinsic indicates that the memory is mutable again.</p>
8063 <!-- ======================================================================= -->
8065 <a name="int_general">General Intrinsics</a>
8070 <p>This class of intrinsics is designed to be generic and has no specific
8073 <!-- _______________________________________________________________________ -->
8075 <a name="int_var_annotation">'<tt>llvm.var.annotation</tt>' Intrinsic</a>
8082 declare void @llvm.var.annotation(i8* <val>, i8* <str>, i8* <str>, i32 <int>)
8086 <p>The '<tt>llvm.var.annotation</tt>' intrinsic.</p>
8089 <p>The first argument is a pointer to a value, the second is a pointer to a
8090 global string, the third is a pointer to a global string which is the source
8091 file name, and the last argument is the line number.</p>
8094 <p>This intrinsic allows annotation of local variables with arbitrary strings.
8095 This can be useful for special purpose optimizations that want to look for
8096 these annotations. These have no other defined use; they are ignored by code
8097 generation and optimization.</p>
8101 <!-- _______________________________________________________________________ -->
8103 <a name="int_annotation">'<tt>llvm.annotation.*</tt>' Intrinsic</a>
8109 <p>This is an overloaded intrinsic. You can use '<tt>llvm.annotation</tt>' on
8110 any integer bit width.</p>
8113 declare i8 @llvm.annotation.i8(i8 <val>, i8* <str>, i8* <str>, i32 <int>)
8114 declare i16 @llvm.annotation.i16(i16 <val>, i8* <str>, i8* <str>, i32 <int>)
8115 declare i32 @llvm.annotation.i32(i32 <val>, i8* <str>, i8* <str>, i32 <int>)
8116 declare i64 @llvm.annotation.i64(i64 <val>, i8* <str>, i8* <str>, i32 <int>)
8117 declare i256 @llvm.annotation.i256(i256 <val>, i8* <str>, i8* <str>, i32 <int>)
8121 <p>The '<tt>llvm.annotation</tt>' intrinsic.</p>
8124 <p>The first argument is an integer value (result of some expression), the
8125 second is a pointer to a global string, the third is a pointer to a global
8126 string which is the source file name, and the last argument is the line
8127 number. It returns the value of the first argument.</p>
8130 <p>This intrinsic allows annotations to be put on arbitrary expressions with
8131 arbitrary strings. This can be useful for special purpose optimizations that
8132 want to look for these annotations. These have no other defined use; they
8133 are ignored by code generation and optimization.</p>
8137 <!-- _______________________________________________________________________ -->
8139 <a name="int_trap">'<tt>llvm.trap</tt>' Intrinsic</a>
8146 declare void @llvm.trap()
8150 <p>The '<tt>llvm.trap</tt>' intrinsic.</p>
8156 <p>This intrinsics is lowered to the target dependent trap instruction. If the
8157 target does not have a trap instruction, this intrinsic will be lowered to
8158 the call of the <tt>abort()</tt> function.</p>
8162 <!-- _______________________________________________________________________ -->
8164 <a name="int_stackprotector">'<tt>llvm.stackprotector</tt>' Intrinsic</a>
8171 declare void @llvm.stackprotector(i8* <guard>, i8** <slot>)
8175 <p>The <tt>llvm.stackprotector</tt> intrinsic takes the <tt>guard</tt> and
8176 stores it onto the stack at <tt>slot</tt>. The stack slot is adjusted to
8177 ensure that it is placed on the stack before local variables.</p>
8180 <p>The <tt>llvm.stackprotector</tt> intrinsic requires two pointer
8181 arguments. The first argument is the value loaded from the stack
8182 guard <tt>@__stack_chk_guard</tt>. The second variable is an <tt>alloca</tt>
8183 that has enough space to hold the value of the guard.</p>
8186 <p>This intrinsic causes the prologue/epilogue inserter to force the position of
8187 the <tt>AllocaInst</tt> stack slot to be before local variables on the
8188 stack. This is to ensure that if a local variable on the stack is
8189 overwritten, it will destroy the value of the guard. When the function exits,
8190 the guard on the stack is checked against the original guard. If they are
8191 different, then the program aborts by calling the <tt>__stack_chk_fail()</tt>
8196 <!-- _______________________________________________________________________ -->
8198 <a name="int_objectsize">'<tt>llvm.objectsize</tt>' Intrinsic</a>
8205 declare i32 @llvm.objectsize.i32(i8* <object>, i1 <type>)
8206 declare i64 @llvm.objectsize.i64(i8* <object>, i1 <type>)
8210 <p>The <tt>llvm.objectsize</tt> intrinsic is designed to provide information to
8211 the optimizers to determine at compile time whether a) an operation (like
8212 memcpy) will overflow a buffer that corresponds to an object, or b) that a
8213 runtime check for overflow isn't necessary. An object in this context means
8214 an allocation of a specific class, structure, array, or other object.</p>
8217 <p>The <tt>llvm.objectsize</tt> intrinsic takes two arguments. The first
8218 argument is a pointer to or into the <tt>object</tt>. The second argument
8219 is a boolean 0 or 1. This argument determines whether you want the
8220 maximum (0) or minimum (1) bytes remaining. This needs to be a literal 0 or
8221 1, variables are not allowed.</p>
8224 <p>The <tt>llvm.objectsize</tt> intrinsic is lowered to either a constant
8225 representing the size of the object concerned, or <tt>i32/i64 -1 or 0</tt>,
8226 depending on the <tt>type</tt> argument, if the size cannot be determined at
8230 <!-- _______________________________________________________________________ -->
8232 <a name="int_expect">'<tt>llvm.expect</tt>' Intrinsic</a>
8239 declare i32 @llvm.expect.i32(i32 <val>, i32 <expected_val>)
8240 declare i64 @llvm.expect.i64(i64 <val>, i64 <expected_val>)
8244 <p>The <tt>llvm.expect</tt> intrinsic provides information about expected (the
8245 most probable) value of <tt>val</tt>, which can be used by optimizers.</p>
8248 <p>The <tt>llvm.expect</tt> intrinsic takes two arguments. The first
8249 argument is a value. The second argument is an expected value, this needs to
8250 be a constant value, variables are not allowed.</p>
8253 <p>This intrinsic is lowered to the <tt>val</tt>.</p>
8259 <!-- *********************************************************************** -->
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