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5 <title>LLVM Assembly Language Reference Manual</title>
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9 content="LLVM Assembly Language Reference Manual.">
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15 <div class="doc_title"> LLVM Language Reference Manual </div>
17 <li><a href="#abstract">Abstract</a></li>
18 <li><a href="#introduction">Introduction</a></li>
19 <li><a href="#identifiers">Identifiers</a></li>
20 <li><a href="#highlevel">High Level Structure</a>
22 <li><a href="#modulestructure">Module Structure</a></li>
23 <li><a href="#linkage">Linkage Types</a></li>
24 <li><a href="#callingconv">Calling Conventions</a></li>
25 <li><a href="#globalvars">Global Variables</a></li>
26 <li><a href="#functionstructure">Function Structure</a></li>
29 <li><a href="#typesystem">Type System</a>
31 <li><a href="#t_primitive">Primitive Types</a>
33 <li><a href="#t_classifications">Type Classifications</a></li>
36 <li><a href="#t_derived">Derived Types</a>
38 <li><a href="#t_array">Array Type</a></li>
39 <li><a href="#t_function">Function Type</a></li>
40 <li><a href="#t_pointer">Pointer Type</a></li>
41 <li><a href="#t_struct">Structure Type</a></li>
42 <li><a href="#t_packed">Packed Type</a></li>
43 <li><a href="#t_opaque">Opaque Type</a></li>
48 <li><a href="#constants">Constants</a>
50 <li><a href="#simpleconstants">Simple Constants</a>
51 <li><a href="#aggregateconstants">Aggregate Constants</a>
52 <li><a href="#globalconstants">Global Variable and Function Addresses</a>
53 <li><a href="#undefvalues">Undefined Values</a>
54 <li><a href="#constantexprs">Constant Expressions</a>
57 <li><a href="#instref">Instruction Reference</a>
59 <li><a href="#terminators">Terminator Instructions</a>
61 <li><a href="#i_ret">'<tt>ret</tt>' Instruction</a></li>
62 <li><a href="#i_br">'<tt>br</tt>' Instruction</a></li>
63 <li><a href="#i_switch">'<tt>switch</tt>' Instruction</a></li>
64 <li><a href="#i_invoke">'<tt>invoke</tt>' Instruction</a></li>
65 <li><a href="#i_unwind">'<tt>unwind</tt>' Instruction</a></li>
66 <li><a href="#i_unreachable">'<tt>unreachable</tt>' Instruction</a></li>
69 <li><a href="#binaryops">Binary Operations</a>
71 <li><a href="#i_add">'<tt>add</tt>' Instruction</a></li>
72 <li><a href="#i_sub">'<tt>sub</tt>' Instruction</a></li>
73 <li><a href="#i_mul">'<tt>mul</tt>' Instruction</a></li>
74 <li><a href="#i_div">'<tt>div</tt>' Instruction</a></li>
75 <li><a href="#i_rem">'<tt>rem</tt>' Instruction</a></li>
76 <li><a href="#i_setcc">'<tt>set<i>cc</i></tt>' Instructions</a></li>
79 <li><a href="#bitwiseops">Bitwise Binary Operations</a>
81 <li><a href="#i_and">'<tt>and</tt>' Instruction</a></li>
82 <li><a href="#i_or">'<tt>or</tt>' Instruction</a></li>
83 <li><a href="#i_xor">'<tt>xor</tt>' Instruction</a></li>
84 <li><a href="#i_shl">'<tt>shl</tt>' Instruction</a></li>
85 <li><a href="#i_shr">'<tt>shr</tt>' Instruction</a></li>
88 <li><a href="#memoryops">Memory Access Operations</a>
90 <li><a href="#i_malloc">'<tt>malloc</tt>' Instruction</a></li>
91 <li><a href="#i_free">'<tt>free</tt>' Instruction</a></li>
92 <li><a href="#i_alloca">'<tt>alloca</tt>' Instruction</a></li>
93 <li><a href="#i_load">'<tt>load</tt>' Instruction</a></li>
94 <li><a href="#i_store">'<tt>store</tt>' Instruction</a></li>
95 <li><a href="#i_getelementptr">'<tt>getelementptr</tt>' Instruction</a></li>
98 <li><a href="#otherops">Other Operations</a>
100 <li><a href="#i_phi">'<tt>phi</tt>' Instruction</a></li>
101 <li><a href="#i_cast">'<tt>cast .. to</tt>' Instruction</a></li>
102 <li><a href="#i_select">'<tt>select</tt>' Instruction</a></li>
103 <li><a href="#i_call">'<tt>call</tt>' Instruction</a></li>
104 <li><a href="#i_vaarg">'<tt>vaarg</tt>' Instruction</a></li>
109 <li><a href="#intrinsics">Intrinsic Functions</a>
111 <li><a href="#int_varargs">Variable Argument Handling Intrinsics</a>
113 <li><a href="#i_va_start">'<tt>llvm.va_start</tt>' Intrinsic</a></li>
114 <li><a href="#i_va_end">'<tt>llvm.va_end</tt>' Intrinsic</a></li>
115 <li><a href="#i_va_copy">'<tt>llvm.va_copy</tt>' Intrinsic</a></li>
118 <li><a href="#int_gc">Accurate Garbage Collection Intrinsics</a>
120 <li><a href="#i_gcroot">'<tt>llvm.gcroot</tt>' Intrinsic</a></li>
121 <li><a href="#i_gcread">'<tt>llvm.gcread</tt>' Intrinsic</a></li>
122 <li><a href="#i_gcwrite">'<tt>llvm.gcwrite</tt>' Intrinsic</a></li>
125 <li><a href="#int_codegen">Code Generator Intrinsics</a>
127 <li><a href="#i_returnaddress">'<tt>llvm.returnaddress</tt>' Intrinsic</a></li>
128 <li><a href="#i_frameaddress">'<tt>llvm.frameaddress</tt>' Intrinsic</a></li>
129 <li><a href="#i_prefetch">'<tt>llvm.prefetch</tt>' Intrinsic</a></li>
130 <li><a href="#i_pcmarker">'<tt>llvm.pcmarker</tt>' Intrinsic</a></li>
133 <li><a href="#int_os">Operating System Intrinsics</a>
135 <li><a href="#i_readport">'<tt>llvm.readport</tt>' Intrinsic</a></li>
136 <li><a href="#i_writeport">'<tt>llvm.writeport</tt>' Intrinsic</a></li>
137 <li><a href="#i_readio">'<tt>llvm.readio</tt>' Intrinsic</a></li>
138 <li><a href="#i_writeio">'<tt>llvm.writeio</tt>' Intrinsic</a></li>
140 <li><a href="#int_libc">Standard C Library Intrinsics</a>
142 <li><a href="#i_memcpy">'<tt>llvm.memcpy</tt>' Intrinsic</a></li>
143 <li><a href="#i_memmove">'<tt>llvm.memmove</tt>' Intrinsic</a></li>
144 <li><a href="#i_memset">'<tt>llvm.memset</tt>' Intrinsic</a></li>
145 <li><a href="#i_isunordered">'<tt>llvm.isunordered</tt>' Intrinsic</a></li>
146 <li><a href="#i_sqrt">'<tt>llvm.sqrt</tt>' Intrinsic</a></li>
150 <li><a href="#int_count">Bit counting Intrinsics</a>
152 <li><a href="#int_ctpop">'<tt>llvm.ctpop</tt>' Intrinsic </a></li>
153 <li><a href="#int_ctlz">'<tt>llvm.ctlz</tt>' Intrinsic </a></li>
154 <li><a href="#int_cttz">'<tt>llvm.cttz</tt>' Intrinsic </a></li>
157 <li><a href="#int_debugger">Debugger intrinsics</a></li>
162 <div class="doc_author">
163 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>
164 and <a href="mailto:vadve@cs.uiuc.edu">Vikram Adve</a></p>
167 <!-- *********************************************************************** -->
168 <div class="doc_section"> <a name="abstract">Abstract </a></div>
169 <!-- *********************************************************************** -->
171 <div class="doc_text">
172 <p>This document is a reference manual for the LLVM assembly language.
173 LLVM is an SSA based representation that provides type safety,
174 low-level operations, flexibility, and the capability of representing
175 'all' high-level languages cleanly. It is the common code
176 representation used throughout all phases of the LLVM compilation
180 <!-- *********************************************************************** -->
181 <div class="doc_section"> <a name="introduction">Introduction</a> </div>
182 <!-- *********************************************************************** -->
184 <div class="doc_text">
186 <p>The LLVM code representation is designed to be used in three
187 different forms: as an in-memory compiler IR, as an on-disk bytecode
188 representation (suitable for fast loading by a Just-In-Time compiler),
189 and as a human readable assembly language representation. This allows
190 LLVM to provide a powerful intermediate representation for efficient
191 compiler transformations and analysis, while providing a natural means
192 to debug and visualize the transformations. The three different forms
193 of LLVM are all equivalent. This document describes the human readable
194 representation and notation.</p>
196 <p>The LLVM representation aims to be light-weight and low-level
197 while being expressive, typed, and extensible at the same time. It
198 aims to be a "universal IR" of sorts, by being at a low enough level
199 that high-level ideas may be cleanly mapped to it (similar to how
200 microprocessors are "universal IR's", allowing many source languages to
201 be mapped to them). By providing type information, LLVM can be used as
202 the target of optimizations: for example, through pointer analysis, it
203 can be proven that a C automatic variable is never accessed outside of
204 the current function... allowing it to be promoted to a simple SSA
205 value instead of a memory location.</p>
209 <!-- _______________________________________________________________________ -->
210 <div class="doc_subsubsection"> <a name="wellformed">Well-Formedness</a> </div>
212 <div class="doc_text">
214 <p>It is important to note that this document describes 'well formed'
215 LLVM assembly language. There is a difference between what the parser
216 accepts and what is considered 'well formed'. For example, the
217 following instruction is syntactically okay, but not well formed:</p>
220 %x = <a href="#i_add">add</a> int 1, %x
223 <p>...because the definition of <tt>%x</tt> does not dominate all of
224 its uses. The LLVM infrastructure provides a verification pass that may
225 be used to verify that an LLVM module is well formed. This pass is
226 automatically run by the parser after parsing input assembly and by
227 the optimizer before it outputs bytecode. The violations pointed out
228 by the verifier pass indicate bugs in transformation passes or input to
231 <!-- Describe the typesetting conventions here. --> </div>
233 <!-- *********************************************************************** -->
234 <div class="doc_section"> <a name="identifiers">Identifiers</a> </div>
235 <!-- *********************************************************************** -->
237 <div class="doc_text">
239 <p>LLVM uses three different forms of identifiers, for different
243 <li>Named values are represented as a string of characters with a '%' prefix.
244 For example, %foo, %DivisionByZero, %a.really.long.identifier. The actual
245 regular expression used is '<tt>%[a-zA-Z$._][a-zA-Z$._0-9]*</tt>'.
246 Identifiers which require other characters in their names can be surrounded
247 with quotes. In this way, anything except a <tt>"</tt> character can be used
250 <li>Unnamed values are represented as an unsigned numeric value with a '%'
251 prefix. For example, %12, %2, %44.</li>
253 <li>Constants, which are described in a <a href="#constants">section about
254 constants</a>, below.</li>
257 <p>LLVM requires that values start with a '%' sign for two reasons: Compilers
258 don't need to worry about name clashes with reserved words, and the set of
259 reserved words may be expanded in the future without penalty. Additionally,
260 unnamed identifiers allow a compiler to quickly come up with a temporary
261 variable without having to avoid symbol table conflicts.</p>
263 <p>Reserved words in LLVM are very similar to reserved words in other
264 languages. There are keywords for different opcodes ('<tt><a
265 href="#i_add">add</a></tt>', '<tt><a href="#i_cast">cast</a></tt>', '<tt><a
266 href="#i_ret">ret</a></tt>', etc...), for primitive type names ('<tt><a
267 href="#t_void">void</a></tt>', '<tt><a href="#t_uint">uint</a></tt>', etc...),
268 and others. These reserved words cannot conflict with variable names, because
269 none of them start with a '%' character.</p>
271 <p>Here is an example of LLVM code to multiply the integer variable
272 '<tt>%X</tt>' by 8:</p>
277 %result = <a href="#i_mul">mul</a> uint %X, 8
280 <p>After strength reduction:</p>
283 %result = <a href="#i_shl">shl</a> uint %X, ubyte 3
286 <p>And the hard way:</p>
289 <a href="#i_add">add</a> uint %X, %X <i>; yields {uint}:%0</i>
290 <a href="#i_add">add</a> uint %0, %0 <i>; yields {uint}:%1</i>
291 %result = <a href="#i_add">add</a> uint %1, %1
294 <p>This last way of multiplying <tt>%X</tt> by 8 illustrates several
295 important lexical features of LLVM:</p>
299 <li>Comments are delimited with a '<tt>;</tt>' and go until the end of
302 <li>Unnamed temporaries are created when the result of a computation is not
303 assigned to a named value.</li>
305 <li>Unnamed temporaries are numbered sequentially</li>
309 <p>...and it also shows a convention that we follow in this document. When
310 demonstrating instructions, we will follow an instruction with a comment that
311 defines the type and name of value produced. Comments are shown in italic
316 <!-- *********************************************************************** -->
317 <div class="doc_section"> <a name="highlevel">High Level Structure</a> </div>
318 <!-- *********************************************************************** -->
320 <!-- ======================================================================= -->
321 <div class="doc_subsection"> <a name="modulestructure">Module Structure</a>
324 <div class="doc_text">
326 <p>LLVM programs are composed of "Module"s, each of which is a
327 translation unit of the input programs. Each module consists of
328 functions, global variables, and symbol table entries. Modules may be
329 combined together with the LLVM linker, which merges function (and
330 global variable) definitions, resolves forward declarations, and merges
331 symbol table entries. Here is an example of the "hello world" module:</p>
333 <pre><i>; Declare the string constant as a global constant...</i>
334 <a href="#identifiers">%.LC0</a> = <a href="#linkage_internal">internal</a> <a
335 href="#globalvars">constant</a> <a href="#t_array">[13 x sbyte]</a> c"hello world\0A\00" <i>; [13 x sbyte]*</i>
337 <i>; External declaration of the puts function</i>
338 <a href="#functionstructure">declare</a> int %puts(sbyte*) <i>; int(sbyte*)* </i>
340 <i>; Definition of main function</i>
341 int %main() { <i>; int()* </i>
342 <i>; Convert [13x sbyte]* to sbyte *...</i>
344 href="#i_getelementptr">getelementptr</a> [13 x sbyte]* %.LC0, long 0, long 0 <i>; sbyte*</i>
346 <i>; Call puts function to write out the string to stdout...</i>
348 href="#i_call">call</a> int %puts(sbyte* %cast210) <i>; int</i>
350 href="#i_ret">ret</a> int 0<br>}<br></pre>
352 <p>This example is made up of a <a href="#globalvars">global variable</a>
353 named "<tt>.LC0</tt>", an external declaration of the "<tt>puts</tt>"
354 function, and a <a href="#functionstructure">function definition</a>
355 for "<tt>main</tt>".</p>
357 <p>In general, a module is made up of a list of global values,
358 where both functions and global variables are global values. Global values are
359 represented by a pointer to a memory location (in this case, a pointer to an
360 array of char, and a pointer to a function), and have one of the following <a
361 href="#linkage">linkage types</a>.</p>
365 <!-- ======================================================================= -->
366 <div class="doc_subsection">
367 <a name="linkage">Linkage Types</a>
370 <div class="doc_text">
373 All Global Variables and Functions have one of the following types of linkage:
378 <dt><tt><b><a name="linkage_internal">internal</a></b></tt> </dt>
380 <dd>Global values with internal linkage are only directly accessible by
381 objects in the current module. In particular, linking code into a module with
382 an internal global value may cause the internal to be renamed as necessary to
383 avoid collisions. Because the symbol is internal to the module, all
384 references can be updated. This corresponds to the notion of the
385 '<tt>static</tt>' keyword in C, or the idea of "anonymous namespaces" in C++.
388 <dt><tt><b><a name="linkage_linkonce">linkonce</a></b></tt>: </dt>
390 <dd>"<tt>linkonce</tt>" linkage is similar to <tt>internal</tt> linkage, with
391 the twist that linking together two modules defining the same
392 <tt>linkonce</tt> globals will cause one of the globals to be discarded. This
393 is typically used to implement inline functions. Unreferenced
394 <tt>linkonce</tt> globals are allowed to be discarded.
397 <dt><tt><b><a name="linkage_weak">weak</a></b></tt>: </dt>
399 <dd>"<tt>weak</tt>" linkage is exactly the same as <tt>linkonce</tt> linkage,
400 except that unreferenced <tt>weak</tt> globals may not be discarded. This is
401 used to implement constructs in C such as "<tt>int X;</tt>" at global scope.
404 <dt><tt><b><a name="linkage_appending">appending</a></b></tt>: </dt>
406 <dd>"<tt>appending</tt>" linkage may only be applied to global variables of
407 pointer to array type. When two global variables with appending linkage are
408 linked together, the two global arrays are appended together. This is the
409 LLVM, typesafe, equivalent of having the system linker append together
410 "sections" with identical names when .o files are linked.
413 <dt><tt><b><a name="linkage_external">externally visible</a></b></tt>:</dt>
415 <dd>If none of the above identifiers are used, the global is externally
416 visible, meaning that it participates in linkage and can be used to resolve
417 external symbol references.
421 <p><a name="linkage_external">For example, since the "<tt>.LC0</tt>"
422 variable is defined to be internal, if another module defined a "<tt>.LC0</tt>"
423 variable and was linked with this one, one of the two would be renamed,
424 preventing a collision. Since "<tt>main</tt>" and "<tt>puts</tt>" are
425 external (i.e., lacking any linkage declarations), they are accessible
426 outside of the current module. It is illegal for a function <i>declaration</i>
427 to have any linkage type other than "externally visible".</a></p>
431 <!-- ======================================================================= -->
432 <div class="doc_subsection">
433 <a name="callingconv">Calling Conventions</a>
436 <div class="doc_text">
438 <p>LLVM <a href="#functionstructure">functions</a>, <a href="#i_call">calls</a>
439 and <a href="#i_invoke">invokes</a> can all have an optional calling convention
440 specified for the call. The calling convention of any pair of dynamic
441 caller/callee must match, or the behavior of the program is undefined. The
442 following calling conventions are supported by LLVM, and more may be added in
446 <dt><b>"<tt>ccc</tt>" - The C calling convention</b>:</dt>
448 <dd>This calling convention (the default if no other calling convention is
449 specified) matches the target C calling conventions. This calling convention
450 supports varargs function calls and tolerates some mismatch in the declared
451 prototype and implemented declaration of the function (as does normal C).
454 <dt><b>"<tt>fastcc</tt>" - The fast calling convention</b>:</dt>
456 <dd>This calling convention attempts to make calls as fast as possible
457 (e.g. by passing things in registers). This calling convention allows the
458 target to use whatever tricks it wants to produce fast code for the target,
459 without having to conform to an externally specified ABI. Implementations of
460 this convention should allow arbitrary tail call optimization to be supported.
461 This calling convention does not support varargs and requires the prototype of
462 all callees to exactly match the prototype of the function definition.
465 <dt><b>"<tt>coldcc</tt>" - The cold calling convention</b>:</dt>
467 <dd>This calling convention attempts to make code in the caller as efficient
468 as possible under the assumption that the call is not commonly executed. As
469 such, these calls often preserve all registers so that the call does not break
470 any live ranges in the caller side. This calling convention does not support
471 varargs and requires the prototype of all callees to exactly match the
472 prototype of the function definition.
475 <dt><b>"<tt>cc <<em>n</em>></tt>" - Numbered convention</b>:</dt>
477 <dd>Any calling convention may be specified by number, allowing
478 target-specific calling conventions to be used. Target specific calling
479 conventions start at 64.
483 <p>More calling conventions can be added/defined on an as-needed basis, to
484 support pascal conventions or any other well-known target-independent
489 <!-- ======================================================================= -->
490 <div class="doc_subsection">
491 <a name="globalvars">Global Variables</a>
494 <div class="doc_text">
496 <p>Global variables define regions of memory allocated at compilation time
497 instead of run-time. Global variables may optionally be initialized, and may
498 have an optional explicit alignment specified. A
499 variable may be defined as a global "constant," which indicates that the
500 contents of the variable will <b>never</b> be modified (enabling better
501 optimization, allowing the global data to be placed in the read-only section of
502 an executable, etc). Note that variables that need runtime initialization
503 cannot be marked "constant" as there is a store to the variable.</p>
506 LLVM explicitly allows <em>declarations</em> of global variables to be marked
507 constant, even if the final definition of the global is not. This capability
508 can be used to enable slightly better optimization of the program, but requires
509 the language definition to guarantee that optimizations based on the
510 'constantness' are valid for the translation units that do not include the
514 <p>As SSA values, global variables define pointer values that are in
515 scope (i.e. they dominate) all basic blocks in the program. Global
516 variables always define a pointer to their "content" type because they
517 describe a region of memory, and all memory objects in LLVM are
518 accessed through pointers.</p>
520 <p>An explicit alignment may be specified for a global. If not present, or if
521 the alignment is set to zero, the alignment of the global is set by the target
522 to whatever it feels convenient. If an explicit alignment is specified, the
523 global is forced to have at least that much alignment. All alignments must be
529 <!-- ======================================================================= -->
530 <div class="doc_subsection">
531 <a name="functionstructure">Functions</a>
534 <div class="doc_text">
536 <p>LLVM function definitions consist of an optional <a href="#linkage">linkage
537 type</a>, an optional <a href="#callingconv">calling convention</a>, a return
538 type, a function name, a (possibly empty) argument list, an optional alignment,
539 an opening curly brace,
540 a list of basic blocks, and a closing curly brace. LLVM function declarations
541 are defined with the "<tt>declare</tt>" keyword, an optional <a
542 href="#callingconv">calling convention</a>, a return type, a function name,
543 a possibly empty list of arguments, and an optional alignment.</p>
545 <p>A function definition contains a list of basic blocks, forming the CFG for
546 the function. Each basic block may optionally start with a label (giving the
547 basic block a symbol table entry), contains a list of instructions, and ends
548 with a <a href="#terminators">terminator</a> instruction (such as a branch or
549 function return).</p>
551 <p>The first basic block in a program is special in two ways: it is immediately
552 executed on entrance to the function, and it is not allowed to have predecessor
553 basic blocks (i.e. there can not be any branches to the entry block of a
554 function). Because the block can have no predecessors, it also cannot have any
555 <a href="#i_phi">PHI nodes</a>.</p>
557 <p>LLVM functions are identified by their name and type signature. Hence, two
558 functions with the same name but different parameter lists or return values are
559 considered different functions, and LLVM will resolve references to each
562 <p>An explicit alignment may be specified for a function. If not present, or if
563 the alignment is set to zero, the alignment of the function is set by the target
564 to whatever it feels convenient. If an explicit alignment is specified, the
565 function is forced to have at least that much alignment. All alignments must be
572 <!-- *********************************************************************** -->
573 <div class="doc_section"> <a name="typesystem">Type System</a> </div>
574 <!-- *********************************************************************** -->
576 <div class="doc_text">
578 <p>The LLVM type system is one of the most important features of the
579 intermediate representation. Being typed enables a number of
580 optimizations to be performed on the IR directly, without having to do
581 extra analyses on the side before the transformation. A strong type
582 system makes it easier to read the generated code and enables novel
583 analyses and transformations that are not feasible to perform on normal
584 three address code representations.</p>
588 <!-- ======================================================================= -->
589 <div class="doc_subsection"> <a name="t_primitive">Primitive Types</a> </div>
590 <div class="doc_text">
591 <p>The primitive types are the fundamental building blocks of the LLVM
592 system. The current set of primitive types is as follows:</p>
594 <table class="layout">
599 <tr><th>Type</th><th>Description</th></tr>
600 <tr><td><tt>void</tt></td><td>No value</td></tr>
601 <tr><td><tt>ubyte</tt></td><td>Unsigned 8-bit value</td></tr>
602 <tr><td><tt>ushort</tt></td><td>Unsigned 16-bit value</td></tr>
603 <tr><td><tt>uint</tt></td><td>Unsigned 32-bit value</td></tr>
604 <tr><td><tt>ulong</tt></td><td>Unsigned 64-bit value</td></tr>
605 <tr><td><tt>float</tt></td><td>32-bit floating point value</td></tr>
606 <tr><td><tt>label</tt></td><td>Branch destination</td></tr>
613 <tr><th>Type</th><th>Description</th></tr>
614 <tr><td><tt>bool</tt></td><td>True or False value</td></tr>
615 <tr><td><tt>sbyte</tt></td><td>Signed 8-bit value</td></tr>
616 <tr><td><tt>short</tt></td><td>Signed 16-bit value</td></tr>
617 <tr><td><tt>int</tt></td><td>Signed 32-bit value</td></tr>
618 <tr><td><tt>long</tt></td><td>Signed 64-bit value</td></tr>
619 <tr><td><tt>double</tt></td><td>64-bit floating point value</td></tr>
627 <!-- _______________________________________________________________________ -->
628 <div class="doc_subsubsection"> <a name="t_classifications">Type
629 Classifications</a> </div>
630 <div class="doc_text">
631 <p>These different primitive types fall into a few useful
634 <table border="1" cellspacing="0" cellpadding="4">
636 <tr><th>Classification</th><th>Types</th></tr>
638 <td><a name="t_signed">signed</a></td>
639 <td><tt>sbyte, short, int, long, float, double</tt></td>
642 <td><a name="t_unsigned">unsigned</a></td>
643 <td><tt>ubyte, ushort, uint, ulong</tt></td>
646 <td><a name="t_integer">integer</a></td>
647 <td><tt>ubyte, sbyte, ushort, short, uint, int, ulong, long</tt></td>
650 <td><a name="t_integral">integral</a></td>
651 <td><tt>bool, ubyte, sbyte, ushort, short, uint, int, ulong, long</tt>
655 <td><a name="t_floating">floating point</a></td>
656 <td><tt>float, double</tt></td>
659 <td><a name="t_firstclass">first class</a></td>
660 <td><tt>bool, ubyte, sbyte, ushort, short, uint, int, ulong, long,<br>
661 float, double, <a href="#t_pointer">pointer</a>,
662 <a href="#t_packed">packed</a></tt></td>
667 <p>The <a href="#t_firstclass">first class</a> types are perhaps the
668 most important. Values of these types are the only ones which can be
669 produced by instructions, passed as arguments, or used as operands to
670 instructions. This means that all structures and arrays must be
671 manipulated either by pointer or by component.</p>
674 <!-- ======================================================================= -->
675 <div class="doc_subsection"> <a name="t_derived">Derived Types</a> </div>
677 <div class="doc_text">
679 <p>The real power in LLVM comes from the derived types in the system.
680 This is what allows a programmer to represent arrays, functions,
681 pointers, and other useful types. Note that these derived types may be
682 recursive: For example, it is possible to have a two dimensional array.</p>
686 <!-- _______________________________________________________________________ -->
687 <div class="doc_subsubsection"> <a name="t_array">Array Type</a> </div>
689 <div class="doc_text">
693 <p>The array type is a very simple derived type that arranges elements
694 sequentially in memory. The array type requires a size (number of
695 elements) and an underlying data type.</p>
700 [<# elements> x <elementtype>]
703 <p>The number of elements is a constant integer value; elementtype may
704 be any type with a size.</p>
707 <table class="layout">
710 <tt>[40 x int ]</tt><br/>
711 <tt>[41 x int ]</tt><br/>
712 <tt>[40 x uint]</tt><br/>
715 Array of 40 integer values.<br/>
716 Array of 41 integer values.<br/>
717 Array of 40 unsigned integer values.<br/>
721 <p>Here are some examples of multidimensional arrays:</p>
722 <table class="layout">
725 <tt>[3 x [4 x int]]</tt><br/>
726 <tt>[12 x [10 x float]]</tt><br/>
727 <tt>[2 x [3 x [4 x uint]]]</tt><br/>
730 3x4 array of integer values.<br/>
731 12x10 array of single precision floating point values.<br/>
732 2x3x4 array of unsigned integer values.<br/>
737 <p>Note that 'variable sized arrays' can be implemented in LLVM with a zero
738 length array. Normally, accesses past the end of an array are undefined in
739 LLVM (e.g. it is illegal to access the 5th element of a 3 element array).
740 As a special case, however, zero length arrays are recognized to be variable
741 length. This allows implementation of 'pascal style arrays' with the LLVM
742 type "{ int, [0 x float]}", for example.</p>
746 <!-- _______________________________________________________________________ -->
747 <div class="doc_subsubsection"> <a name="t_function">Function Type</a> </div>
748 <div class="doc_text">
750 <p>The function type can be thought of as a function signature. It
751 consists of a return type and a list of formal parameter types.
752 Function types are usually used to build virtual function tables
753 (which are structures of pointers to functions), for indirect function
754 calls, and when defining a function.</p>
756 The return type of a function type cannot be an aggregate type.
759 <pre> <returntype> (<parameter list>)<br></pre>
760 <p>...where '<tt><parameter list></tt>' is a comma-separated list of type
761 specifiers. Optionally, the parameter list may include a type <tt>...</tt>,
762 which indicates that the function takes a variable number of arguments.
763 Variable argument functions can access their arguments with the <a
764 href="#int_varargs">variable argument handling intrinsic</a> functions.</p>
766 <table class="layout">
769 <tt>int (int)</tt> <br/>
770 <tt>float (int, int *) *</tt><br/>
771 <tt>int (sbyte *, ...)</tt><br/>
774 function taking an <tt>int</tt>, returning an <tt>int</tt><br/>
775 <a href="#t_pointer">Pointer</a> to a function that takes an
776 <tt>int</tt> and a <a href="#t_pointer">pointer</a> to <tt>int</tt>,
777 returning <tt>float</tt>.<br/>
778 A vararg function that takes at least one <a href="#t_pointer">pointer</a>
779 to <tt>sbyte</tt> (signed char in C), which returns an integer. This is
780 the signature for <tt>printf</tt> in LLVM.<br/>
786 <!-- _______________________________________________________________________ -->
787 <div class="doc_subsubsection"> <a name="t_struct">Structure Type</a> </div>
788 <div class="doc_text">
790 <p>The structure type is used to represent a collection of data members
791 together in memory. The packing of the field types is defined to match
792 the ABI of the underlying processor. The elements of a structure may
793 be any type that has a size.</p>
794 <p>Structures are accessed using '<tt><a href="#i_load">load</a></tt>
795 and '<tt><a href="#i_store">store</a></tt>' by getting a pointer to a
796 field with the '<tt><a href="#i_getelementptr">getelementptr</a></tt>'
799 <pre> { <type list> }<br></pre>
801 <table class="layout">
804 <tt>{ int, int, int }</tt><br/>
805 <tt>{ float, int (int) * }</tt><br/>
808 a triple of three <tt>int</tt> values<br/>
809 A pair, where the first element is a <tt>float</tt> and the second element
810 is a <a href="#t_pointer">pointer</a> to a <a href="#t_function">function</a>
811 that takes an <tt>int</tt>, returning an <tt>int</tt>.<br/>
817 <!-- _______________________________________________________________________ -->
818 <div class="doc_subsubsection"> <a name="t_pointer">Pointer Type</a> </div>
819 <div class="doc_text">
821 <p>As in many languages, the pointer type represents a pointer or
822 reference to another object, which must live in memory.</p>
824 <pre> <type> *<br></pre>
826 <table class="layout">
829 <tt>[4x int]*</tt><br/>
830 <tt>int (int *) *</tt><br/>
833 A <a href="#t_pointer">pointer</a> to <a href="#t_array">array</a> of
834 four <tt>int</tt> values<br/>
835 A <a href="#t_pointer">pointer</a> to a <a
836 href="#t_function">function</a> that takes an <tt>int*</tt>, returning an
843 <!-- _______________________________________________________________________ -->
844 <div class="doc_subsubsection"> <a name="t_packed">Packed Type</a> </div>
845 <div class="doc_text">
849 <p>A packed type is a simple derived type that represents a vector
850 of elements. Packed types are used when multiple primitive data
851 are operated in parallel using a single instruction (SIMD).
852 A packed type requires a size (number of
853 elements) and an underlying primitive data type. Vectors must have a power
854 of two length (1, 2, 4, 8, 16 ...). Packed types are
855 considered <a href="#t_firstclass">first class</a>.</p>
860 < <# elements> x <elementtype> >
863 <p>The number of elements is a constant integer value; elementtype may
864 be any integral or floating point type.</p>
868 <table class="layout">
871 <tt><4 x int></tt><br/>
872 <tt><8 x float></tt><br/>
873 <tt><2 x uint></tt><br/>
876 Packed vector of 4 integer values.<br/>
877 Packed vector of 8 floating-point values.<br/>
878 Packed vector of 2 unsigned integer values.<br/>
884 <!-- _______________________________________________________________________ -->
885 <div class="doc_subsubsection"> <a name="t_opaque">Opaque Type</a> </div>
886 <div class="doc_text">
890 <p>Opaque types are used to represent unknown types in the system. This
891 corresponds (for example) to the C notion of a foward declared structure type.
892 In LLVM, opaque types can eventually be resolved to any type (not just a
903 <table class="layout">
916 <!-- *********************************************************************** -->
917 <div class="doc_section"> <a name="constants">Constants</a> </div>
918 <!-- *********************************************************************** -->
920 <div class="doc_text">
922 <p>LLVM has several different basic types of constants. This section describes
923 them all and their syntax.</p>
927 <!-- ======================================================================= -->
928 <div class="doc_subsection"><a name="simpleconstants">Simple Constants</a></div>
930 <div class="doc_text">
933 <dt><b>Boolean constants</b></dt>
935 <dd>The two strings '<tt>true</tt>' and '<tt>false</tt>' are both valid
936 constants of the <tt><a href="#t_primitive">bool</a></tt> type.
939 <dt><b>Integer constants</b></dt>
941 <dd>Standard integers (such as '4') are constants of the <a
942 href="#t_integer">integer</a> type. Negative numbers may be used with signed
946 <dt><b>Floating point constants</b></dt>
948 <dd>Floating point constants use standard decimal notation (e.g. 123.421),
949 exponential notation (e.g. 1.23421e+2), or a more precise hexadecimal
950 notation (see below). Floating point constants must have a <a
951 href="#t_floating">floating point</a> type. </dd>
953 <dt><b>Null pointer constants</b></dt>
955 <dd>The identifier '<tt>null</tt>' is recognized as a null pointer constant
956 and must be of <a href="#t_pointer">pointer type</a>.</dd>
960 <p>The one non-intuitive notation for constants is the optional hexadecimal form
961 of floating point constants. For example, the form '<tt>double
962 0x432ff973cafa8000</tt>' is equivalent to (but harder to read than) '<tt>double
963 4.5e+15</tt>'. The only time hexadecimal floating point constants are required
964 (and the only time that they are generated by the disassembler) is when a
965 floating point constant must be emitted but it cannot be represented as a
966 decimal floating point number. For example, NaN's, infinities, and other
967 special values are represented in their IEEE hexadecimal format so that
968 assembly and disassembly do not cause any bits to change in the constants.</p>
972 <!-- ======================================================================= -->
973 <div class="doc_subsection"><a name="aggregateconstants">Aggregate Constants</a>
976 <div class="doc_text">
977 <p>Aggregate constants arise from aggregation of simple constants
978 and smaller aggregate constants.</p>
981 <dt><b>Structure constants</b></dt>
983 <dd>Structure constants are represented with notation similar to structure
984 type definitions (a comma separated list of elements, surrounded by braces
985 (<tt>{}</tt>)). For example: "<tt>{ int 4, float 17.0, int* %G }</tt>",
986 where "<tt>%G</tt>" is declared as "<tt>%G = external global int</tt>". Structure constants
987 must have <a href="#t_struct">structure type</a>, and the number and
988 types of elements must match those specified by the type.
991 <dt><b>Array constants</b></dt>
993 <dd>Array constants are represented with notation similar to array type
994 definitions (a comma separated list of elements, surrounded by square brackets
995 (<tt>[]</tt>)). For example: "<tt>[ int 42, int 11, int 74 ]</tt>". Array
996 constants must have <a href="#t_array">array type</a>, and the number and
997 types of elements must match those specified by the type.
1000 <dt><b>Packed constants</b></dt>
1002 <dd>Packed constants are represented with notation similar to packed type
1003 definitions (a comma separated list of elements, surrounded by
1004 less-than/greater-than's (<tt><></tt>)). For example: "<tt>< int 42,
1005 int 11, int 74, int 100 ></tt>". Packed constants must have <a
1006 href="#t_packed">packed type</a>, and the number and types of elements must
1007 match those specified by the type.
1010 <dt><b>Zero initialization</b></dt>
1012 <dd>The string '<tt>zeroinitializer</tt>' can be used to zero initialize a
1013 value to zero of <em>any</em> type, including scalar and aggregate types.
1014 This is often used to avoid having to print large zero initializers (e.g. for
1015 large arrays) and is always exactly equivalent to using explicit zero
1022 <!-- ======================================================================= -->
1023 <div class="doc_subsection">
1024 <a name="globalconstants">Global Variable and Function Addresses</a>
1027 <div class="doc_text">
1029 <p>The addresses of <a href="#globalvars">global variables</a> and <a
1030 href="#functionstructure">functions</a> are always implicitly valid (link-time)
1031 constants. These constants are explicitly referenced when the <a
1032 href="#identifiers">identifier for the global</a> is used and always have <a
1033 href="#t_pointer">pointer</a> type. For example, the following is a legal LLVM
1039 %Z = global [2 x int*] [ int* %X, int* %Y ]
1044 <!-- ======================================================================= -->
1045 <div class="doc_subsection"><a name="undefvalues">Undefined Values</a></div>
1046 <div class="doc_text">
1047 <p>The string '<tt>undef</tt>' is recognized as a type-less constant that has
1048 no specific value. Undefined values may be of any type and be used anywhere
1049 a constant is permitted.</p>
1051 <p>Undefined values indicate to the compiler that the program is well defined
1052 no matter what value is used, giving the compiler more freedom to optimize.
1056 <!-- ======================================================================= -->
1057 <div class="doc_subsection"><a name="constantexprs">Constant Expressions</a>
1060 <div class="doc_text">
1062 <p>Constant expressions are used to allow expressions involving other constants
1063 to be used as constants. Constant expressions may be of any <a
1064 href="#t_firstclass">first class</a> type and may involve any LLVM operation
1065 that does not have side effects (e.g. load and call are not supported). The
1066 following is the syntax for constant expressions:</p>
1069 <dt><b><tt>cast ( CST to TYPE )</tt></b></dt>
1071 <dd>Cast a constant to another type.</dd>
1073 <dt><b><tt>getelementptr ( CSTPTR, IDX0, IDX1, ... )</tt></b></dt>
1075 <dd>Perform the <a href="#i_getelementptr">getelementptr operation</a> on
1076 constants. As with the <a href="#i_getelementptr">getelementptr</a>
1077 instruction, the index list may have zero or more indexes, which are required
1078 to make sense for the type of "CSTPTR".</dd>
1080 <dt><b><tt>OPCODE ( LHS, RHS )</tt></b></dt>
1082 <dd>Perform the specified operation of the LHS and RHS constants. OPCODE may
1083 be any of the <a href="#binaryops">binary</a> or <a href="#bitwiseops">bitwise
1084 binary</a> operations. The constraints on operands are the same as those for
1085 the corresponding instruction (e.g. no bitwise operations on floating point
1086 values are allowed).</dd>
1090 <!-- *********************************************************************** -->
1091 <div class="doc_section"> <a name="instref">Instruction Reference</a> </div>
1092 <!-- *********************************************************************** -->
1094 <div class="doc_text">
1096 <p>The LLVM instruction set consists of several different
1097 classifications of instructions: <a href="#terminators">terminator
1098 instructions</a>, <a href="#binaryops">binary instructions</a>,
1099 <a href="#bitwiseops">bitwise binary instructions</a>, <a
1100 href="#memoryops">memory instructions</a>, and <a href="#otherops">other
1101 instructions</a>.</p>
1105 <!-- ======================================================================= -->
1106 <div class="doc_subsection"> <a name="terminators">Terminator
1107 Instructions</a> </div>
1109 <div class="doc_text">
1111 <p>As mentioned <a href="#functionstructure">previously</a>, every
1112 basic block in a program ends with a "Terminator" instruction, which
1113 indicates which block should be executed after the current block is
1114 finished. These terminator instructions typically yield a '<tt>void</tt>'
1115 value: they produce control flow, not values (the one exception being
1116 the '<a href="#i_invoke"><tt>invoke</tt></a>' instruction).</p>
1117 <p>There are six different terminator instructions: the '<a
1118 href="#i_ret"><tt>ret</tt></a>' instruction, the '<a href="#i_br"><tt>br</tt></a>'
1119 instruction, the '<a href="#i_switch"><tt>switch</tt></a>' instruction,
1120 the '<a href="#i_invoke"><tt>invoke</tt></a>' instruction, the '<a
1121 href="#i_unwind"><tt>unwind</tt></a>' instruction, and the '<a
1122 href="#i_unreachable"><tt>unreachable</tt></a>' instruction.</p>
1126 <!-- _______________________________________________________________________ -->
1127 <div class="doc_subsubsection"> <a name="i_ret">'<tt>ret</tt>'
1128 Instruction</a> </div>
1129 <div class="doc_text">
1131 <pre> ret <type> <value> <i>; Return a value from a non-void function</i>
1132 ret void <i>; Return from void function</i>
1135 <p>The '<tt>ret</tt>' instruction is used to return control flow (and a
1136 value) from a function back to the caller.</p>
1137 <p>There are two forms of the '<tt>ret</tt>' instruction: one that
1138 returns a value and then causes control flow, and one that just causes
1139 control flow to occur.</p>
1141 <p>The '<tt>ret</tt>' instruction may return any '<a
1142 href="#t_firstclass">first class</a>' type. Notice that a function is
1143 not <a href="#wellformed">well formed</a> if there exists a '<tt>ret</tt>'
1144 instruction inside of the function that returns a value that does not
1145 match the return type of the function.</p>
1147 <p>When the '<tt>ret</tt>' instruction is executed, control flow
1148 returns back to the calling function's context. If the caller is a "<a
1149 href="#i_call"><tt>call</tt></a>" instruction, execution continues at
1150 the instruction after the call. If the caller was an "<a
1151 href="#i_invoke"><tt>invoke</tt></a>" instruction, execution continues
1152 at the beginning of the "normal" destination block. If the instruction
1153 returns a value, that value shall set the call or invoke instruction's
1156 <pre> ret int 5 <i>; Return an integer value of 5</i>
1157 ret void <i>; Return from a void function</i>
1160 <!-- _______________________________________________________________________ -->
1161 <div class="doc_subsubsection"> <a name="i_br">'<tt>br</tt>' Instruction</a> </div>
1162 <div class="doc_text">
1164 <pre> br bool <cond>, label <iftrue>, label <iffalse><br> br label <dest> <i>; Unconditional branch</i>
1167 <p>The '<tt>br</tt>' instruction is used to cause control flow to
1168 transfer to a different basic block in the current function. There are
1169 two forms of this instruction, corresponding to a conditional branch
1170 and an unconditional branch.</p>
1172 <p>The conditional branch form of the '<tt>br</tt>' instruction takes a
1173 single '<tt>bool</tt>' value and two '<tt>label</tt>' values. The
1174 unconditional form of the '<tt>br</tt>' instruction takes a single '<tt>label</tt>'
1175 value as a target.</p>
1177 <p>Upon execution of a conditional '<tt>br</tt>' instruction, the '<tt>bool</tt>'
1178 argument is evaluated. If the value is <tt>true</tt>, control flows
1179 to the '<tt>iftrue</tt>' <tt>label</tt> argument. If "cond" is <tt>false</tt>,
1180 control flows to the '<tt>iffalse</tt>' <tt>label</tt> argument.</p>
1182 <pre>Test:<br> %cond = <a href="#i_setcc">seteq</a> int %a, %b<br> br bool %cond, label %IfEqual, label %IfUnequal<br>IfEqual:<br> <a
1183 href="#i_ret">ret</a> int 1<br>IfUnequal:<br> <a href="#i_ret">ret</a> int 0<br></pre>
1185 <!-- _______________________________________________________________________ -->
1186 <div class="doc_subsubsection">
1187 <a name="i_switch">'<tt>switch</tt>' Instruction</a>
1190 <div class="doc_text">
1194 switch <intty> <value>, label <defaultdest> [ <intty> <val>, label <dest> ... ]
1199 <p>The '<tt>switch</tt>' instruction is used to transfer control flow to one of
1200 several different places. It is a generalization of the '<tt>br</tt>'
1201 instruction, allowing a branch to occur to one of many possible
1207 <p>The '<tt>switch</tt>' instruction uses three parameters: an integer
1208 comparison value '<tt>value</tt>', a default '<tt>label</tt>' destination, and
1209 an array of pairs of comparison value constants and '<tt>label</tt>'s. The
1210 table is not allowed to contain duplicate constant entries.</p>
1214 <p>The <tt>switch</tt> instruction specifies a table of values and
1215 destinations. When the '<tt>switch</tt>' instruction is executed, this
1216 table is searched for the given value. If the value is found, control flow is
1217 transfered to the corresponding destination; otherwise, control flow is
1218 transfered to the default destination.</p>
1220 <h5>Implementation:</h5>
1222 <p>Depending on properties of the target machine and the particular
1223 <tt>switch</tt> instruction, this instruction may be code generated in different
1224 ways. For example, it could be generated as a series of chained conditional
1225 branches or with a lookup table.</p>
1230 <i>; Emulate a conditional br instruction</i>
1231 %Val = <a href="#i_cast">cast</a> bool %value to int
1232 switch int %Val, label %truedest [int 0, label %falsedest ]
1234 <i>; Emulate an unconditional br instruction</i>
1235 switch uint 0, label %dest [ ]
1237 <i>; Implement a jump table:</i>
1238 switch uint %val, label %otherwise [ uint 0, label %onzero
1239 uint 1, label %onone
1240 uint 2, label %ontwo ]
1244 <!-- _______________________________________________________________________ -->
1245 <div class="doc_subsubsection">
1246 <a name="i_invoke">'<tt>invoke</tt>' Instruction</a>
1249 <div class="doc_text">
1254 <result> = invoke [<a href="#callingconv">cconv</a>] <ptr to function ty> %<function ptr val>(<function args>)
1255 to label <normal label> except label <exception label>
1260 <p>The '<tt>invoke</tt>' instruction causes control to transfer to a specified
1261 function, with the possibility of control flow transfer to either the
1262 '<tt>normal</tt>' label or the
1263 '<tt>exception</tt>' label. If the callee function returns with the
1264 "<tt><a href="#i_ret">ret</a></tt>" instruction, control flow will return to the
1265 "normal" label. If the callee (or any indirect callees) returns with the "<a
1266 href="#i_unwind"><tt>unwind</tt></a>" instruction, control is interrupted and
1267 continued at the dynamically nearest "exception" label.</p>
1271 <p>This instruction requires several arguments:</p>
1275 The optional "cconv" marker indicates which <a href="callingconv">calling
1276 convention</a> the call should use. If none is specified, the call defaults
1277 to using C calling conventions.
1279 <li>'<tt>ptr to function ty</tt>': shall be the signature of the pointer to
1280 function value being invoked. In most cases, this is a direct function
1281 invocation, but indirect <tt>invoke</tt>s are just as possible, branching off
1282 an arbitrary pointer to function value.
1285 <li>'<tt>function ptr val</tt>': An LLVM value containing a pointer to a
1286 function to be invoked. </li>
1288 <li>'<tt>function args</tt>': argument list whose types match the function
1289 signature argument types. If the function signature indicates the function
1290 accepts a variable number of arguments, the extra arguments can be
1293 <li>'<tt>normal label</tt>': the label reached when the called function
1294 executes a '<tt><a href="#i_ret">ret</a></tt>' instruction. </li>
1296 <li>'<tt>exception label</tt>': the label reached when a callee returns with
1297 the <a href="#i_unwind"><tt>unwind</tt></a> instruction. </li>
1303 <p>This instruction is designed to operate as a standard '<tt><a
1304 href="#i_call">call</a></tt>' instruction in most regards. The primary
1305 difference is that it establishes an association with a label, which is used by
1306 the runtime library to unwind the stack.</p>
1308 <p>This instruction is used in languages with destructors to ensure that proper
1309 cleanup is performed in the case of either a <tt>longjmp</tt> or a thrown
1310 exception. Additionally, this is important for implementation of
1311 '<tt>catch</tt>' clauses in high-level languages that support them.</p>
1315 %retval = invoke int %Test(int 15) to label %Continue
1316 except label %TestCleanup <i>; {int}:retval set</i>
1317 %retval = invoke <a href="#callingconv">coldcc</a> int %Test(int 15) to label %Continue
1318 except label %TestCleanup <i>; {int}:retval set</i>
1323 <!-- _______________________________________________________________________ -->
1325 <div class="doc_subsubsection"> <a name="i_unwind">'<tt>unwind</tt>'
1326 Instruction</a> </div>
1328 <div class="doc_text">
1337 <p>The '<tt>unwind</tt>' instruction unwinds the stack, continuing control flow
1338 at the first callee in the dynamic call stack which used an <a
1339 href="#i_invoke"><tt>invoke</tt></a> instruction to perform the call. This is
1340 primarily used to implement exception handling.</p>
1344 <p>The '<tt>unwind</tt>' intrinsic causes execution of the current function to
1345 immediately halt. The dynamic call stack is then searched for the first <a
1346 href="#i_invoke"><tt>invoke</tt></a> instruction on the call stack. Once found,
1347 execution continues at the "exceptional" destination block specified by the
1348 <tt>invoke</tt> instruction. If there is no <tt>invoke</tt> instruction in the
1349 dynamic call chain, undefined behavior results.</p>
1352 <!-- _______________________________________________________________________ -->
1354 <div class="doc_subsubsection"> <a name="i_unreachable">'<tt>unreachable</tt>'
1355 Instruction</a> </div>
1357 <div class="doc_text">
1366 <p>The '<tt>unreachable</tt>' instruction has no defined semantics. This
1367 instruction is used to inform the optimizer that a particular portion of the
1368 code is not reachable. This can be used to indicate that the code after a
1369 no-return function cannot be reached, and other facts.</p>
1373 <p>The '<tt>unreachable</tt>' instruction has no defined semantics.</p>
1378 <!-- ======================================================================= -->
1379 <div class="doc_subsection"> <a name="binaryops">Binary Operations</a> </div>
1380 <div class="doc_text">
1381 <p>Binary operators are used to do most of the computation in a
1382 program. They require two operands, execute an operation on them, and
1383 produce a single value. The operands might represent
1384 multiple data, as is the case with the <a href="#t_packed">packed</a> data type.
1385 The result value of a binary operator is not
1386 necessarily the same type as its operands.</p>
1387 <p>There are several different binary operators:</p>
1389 <!-- _______________________________________________________________________ -->
1390 <div class="doc_subsubsection"> <a name="i_add">'<tt>add</tt>'
1391 Instruction</a> </div>
1392 <div class="doc_text">
1394 <pre> <result> = add <ty> <var1>, <var2> <i>; yields {ty}:result</i>
1397 <p>The '<tt>add</tt>' instruction returns the sum of its two operands.</p>
1399 <p>The two arguments to the '<tt>add</tt>' instruction must be either <a
1400 href="#t_integer">integer</a> or <a href="#t_floating">floating point</a> values.
1401 This instruction can also take <a href="#t_packed">packed</a> versions of the values.
1402 Both arguments must have identical types.</p>
1404 <p>The value produced is the integer or floating point sum of the two
1407 <pre> <result> = add int 4, %var <i>; yields {int}:result = 4 + %var</i>
1410 <!-- _______________________________________________________________________ -->
1411 <div class="doc_subsubsection"> <a name="i_sub">'<tt>sub</tt>'
1412 Instruction</a> </div>
1413 <div class="doc_text">
1415 <pre> <result> = sub <ty> <var1>, <var2> <i>; yields {ty}:result</i>
1418 <p>The '<tt>sub</tt>' instruction returns the difference of its two
1420 <p>Note that the '<tt>sub</tt>' instruction is used to represent the '<tt>neg</tt>'
1421 instruction present in most other intermediate representations.</p>
1423 <p>The two arguments to the '<tt>sub</tt>' instruction must be either <a
1424 href="#t_integer">integer</a> or <a href="#t_floating">floating point</a>
1426 This instruction can also take <a href="#t_packed">packed</a> versions of the values.
1427 Both arguments must have identical types.</p>
1429 <p>The value produced is the integer or floating point difference of
1430 the two operands.</p>
1432 <pre> <result> = sub int 4, %var <i>; yields {int}:result = 4 - %var</i>
1433 <result> = sub int 0, %val <i>; yields {int}:result = -%var</i>
1436 <!-- _______________________________________________________________________ -->
1437 <div class="doc_subsubsection"> <a name="i_mul">'<tt>mul</tt>'
1438 Instruction</a> </div>
1439 <div class="doc_text">
1441 <pre> <result> = mul <ty> <var1>, <var2> <i>; yields {ty}:result</i>
1444 <p>The '<tt>mul</tt>' instruction returns the product of its two
1447 <p>The two arguments to the '<tt>mul</tt>' instruction must be either <a
1448 href="#t_integer">integer</a> or <a href="#t_floating">floating point</a>
1450 This instruction can also take <a href="#t_packed">packed</a> versions of the values.
1451 Both arguments must have identical types.</p>
1453 <p>The value produced is the integer or floating point product of the
1455 <p>There is no signed vs unsigned multiplication. The appropriate
1456 action is taken based on the type of the operand.</p>
1458 <pre> <result> = mul int 4, %var <i>; yields {int}:result = 4 * %var</i>
1461 <!-- _______________________________________________________________________ -->
1462 <div class="doc_subsubsection"> <a name="i_div">'<tt>div</tt>'
1463 Instruction</a> </div>
1464 <div class="doc_text">
1466 <pre> <result> = div <ty> <var1>, <var2> <i>; yields {ty}:result</i>
1469 <p>The '<tt>div</tt>' instruction returns the quotient of its two
1472 <p>The two arguments to the '<tt>div</tt>' instruction must be either <a
1473 href="#t_integer">integer</a> or <a href="#t_floating">floating point</a>
1475 This instruction can also take <a href="#t_packed">packed</a> versions of the values.
1476 Both arguments must have identical types.</p>
1478 <p>The value produced is the integer or floating point quotient of the
1481 <pre> <result> = div int 4, %var <i>; yields {int}:result = 4 / %var</i>
1484 <!-- _______________________________________________________________________ -->
1485 <div class="doc_subsubsection"> <a name="i_rem">'<tt>rem</tt>'
1486 Instruction</a> </div>
1487 <div class="doc_text">
1489 <pre> <result> = rem <ty> <var1>, <var2> <i>; yields {ty}:result</i>
1492 <p>The '<tt>rem</tt>' instruction returns the remainder from the
1493 division of its two operands.</p>
1495 <p>The two arguments to the '<tt>rem</tt>' instruction must be either <a
1496 href="#t_integer">integer</a> or <a href="#t_floating">floating point</a>
1498 This instruction can also take <a href="#t_packed">packed</a> versions of the values.
1499 Both arguments must have identical types.</p>
1501 <p>This returns the <i>remainder</i> of a division (where the result
1502 has the same sign as the divisor), not the <i>modulus</i> (where the
1503 result has the same sign as the dividend) of a value. For more
1504 information about the difference, see <a
1505 href="http://mathforum.org/dr.math/problems/anne.4.28.99.html">The
1508 <pre> <result> = rem int 4, %var <i>; yields {int}:result = 4 % %var</i>
1511 <!-- _______________________________________________________________________ -->
1512 <div class="doc_subsubsection"> <a name="i_setcc">'<tt>set<i>cc</i></tt>'
1513 Instructions</a> </div>
1514 <div class="doc_text">
1516 <pre> <result> = seteq <ty> <var1>, <var2> <i>; yields {bool}:result</i>
1517 <result> = setne <ty> <var1>, <var2> <i>; yields {bool}:result</i>
1518 <result> = setlt <ty> <var1>, <var2> <i>; yields {bool}:result</i>
1519 <result> = setgt <ty> <var1>, <var2> <i>; yields {bool}:result</i>
1520 <result> = setle <ty> <var1>, <var2> <i>; yields {bool}:result</i>
1521 <result> = setge <ty> <var1>, <var2> <i>; yields {bool}:result</i>
1524 <p>The '<tt>set<i>cc</i></tt>' family of instructions returns a boolean
1525 value based on a comparison of their two operands.</p>
1527 <p>The two arguments to the '<tt>set<i>cc</i></tt>' instructions must
1528 be of <a href="#t_firstclass">first class</a> type (it is not possible
1529 to compare '<tt>label</tt>'s, '<tt>array</tt>'s, '<tt>structure</tt>'
1530 or '<tt>void</tt>' values, etc...). Both arguments must have identical
1533 <p>The '<tt>seteq</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>'
1534 value if both operands are equal.<br>
1535 The '<tt>setne</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>'
1536 value if both operands are unequal.<br>
1537 The '<tt>setlt</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>'
1538 value if the first operand is less than the second operand.<br>
1539 The '<tt>setgt</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>'
1540 value if the first operand is greater than the second operand.<br>
1541 The '<tt>setle</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>'
1542 value if the first operand is less than or equal to the second operand.<br>
1543 The '<tt>setge</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>'
1544 value if the first operand is greater than or equal to the second
1547 <pre> <result> = seteq int 4, 5 <i>; yields {bool}:result = false</i>
1548 <result> = setne float 4, 5 <i>; yields {bool}:result = true</i>
1549 <result> = setlt uint 4, 5 <i>; yields {bool}:result = true</i>
1550 <result> = setgt sbyte 4, 5 <i>; yields {bool}:result = false</i>
1551 <result> = setle sbyte 4, 5 <i>; yields {bool}:result = true</i>
1552 <result> = setge sbyte 4, 5 <i>; yields {bool}:result = false</i>
1555 <!-- ======================================================================= -->
1556 <div class="doc_subsection"> <a name="bitwiseops">Bitwise Binary
1557 Operations</a> </div>
1558 <div class="doc_text">
1559 <p>Bitwise binary operators are used to do various forms of
1560 bit-twiddling in a program. They are generally very efficient
1561 instructions and can commonly be strength reduced from other
1562 instructions. They require two operands, execute an operation on them,
1563 and produce a single value. The resulting value of the bitwise binary
1564 operators is always the same type as its first operand.</p>
1566 <!-- _______________________________________________________________________ -->
1567 <div class="doc_subsubsection"> <a name="i_and">'<tt>and</tt>'
1568 Instruction</a> </div>
1569 <div class="doc_text">
1571 <pre> <result> = and <ty> <var1>, <var2> <i>; yields {ty}:result</i>
1574 <p>The '<tt>and</tt>' instruction returns the bitwise logical and of
1575 its two operands.</p>
1577 <p>The two arguments to the '<tt>and</tt>' instruction must be <a
1578 href="#t_integral">integral</a> values. Both arguments must have
1579 identical types.</p>
1581 <p>The truth table used for the '<tt>and</tt>' instruction is:</p>
1583 <div style="align: center">
1584 <table border="1" cellspacing="0" cellpadding="4">
1615 <pre> <result> = and int 4, %var <i>; yields {int}:result = 4 & %var</i>
1616 <result> = and int 15, 40 <i>; yields {int}:result = 8</i>
1617 <result> = and int 4, 8 <i>; yields {int}:result = 0</i>
1620 <!-- _______________________________________________________________________ -->
1621 <div class="doc_subsubsection"> <a name="i_or">'<tt>or</tt>' Instruction</a> </div>
1622 <div class="doc_text">
1624 <pre> <result> = or <ty> <var1>, <var2> <i>; yields {ty}:result</i>
1627 <p>The '<tt>or</tt>' instruction returns the bitwise logical inclusive
1628 or of its two operands.</p>
1630 <p>The two arguments to the '<tt>or</tt>' instruction must be <a
1631 href="#t_integral">integral</a> values. Both arguments must have
1632 identical types.</p>
1634 <p>The truth table used for the '<tt>or</tt>' instruction is:</p>
1636 <div style="align: center">
1637 <table border="1" cellspacing="0" cellpadding="4">
1668 <pre> <result> = or int 4, %var <i>; yields {int}:result = 4 | %var</i>
1669 <result> = or int 15, 40 <i>; yields {int}:result = 47</i>
1670 <result> = or int 4, 8 <i>; yields {int}:result = 12</i>
1673 <!-- _______________________________________________________________________ -->
1674 <div class="doc_subsubsection"> <a name="i_xor">'<tt>xor</tt>'
1675 Instruction</a> </div>
1676 <div class="doc_text">
1678 <pre> <result> = xor <ty> <var1>, <var2> <i>; yields {ty}:result</i>
1681 <p>The '<tt>xor</tt>' instruction returns the bitwise logical exclusive
1682 or of its two operands. The <tt>xor</tt> is used to implement the
1683 "one's complement" operation, which is the "~" operator in C.</p>
1685 <p>The two arguments to the '<tt>xor</tt>' instruction must be <a
1686 href="#t_integral">integral</a> values. Both arguments must have
1687 identical types.</p>
1689 <p>The truth table used for the '<tt>xor</tt>' instruction is:</p>
1691 <div style="align: center">
1692 <table border="1" cellspacing="0" cellpadding="4">
1724 <pre> <result> = xor int 4, %var <i>; yields {int}:result = 4 ^ %var</i>
1725 <result> = xor int 15, 40 <i>; yields {int}:result = 39</i>
1726 <result> = xor int 4, 8 <i>; yields {int}:result = 12</i>
1727 <result> = xor int %V, -1 <i>; yields {int}:result = ~%V</i>
1730 <!-- _______________________________________________________________________ -->
1731 <div class="doc_subsubsection"> <a name="i_shl">'<tt>shl</tt>'
1732 Instruction</a> </div>
1733 <div class="doc_text">
1735 <pre> <result> = shl <ty> <var1>, ubyte <var2> <i>; yields {ty}:result</i>
1738 <p>The '<tt>shl</tt>' instruction returns the first operand shifted to
1739 the left a specified number of bits.</p>
1741 <p>The first argument to the '<tt>shl</tt>' instruction must be an <a
1742 href="#t_integer">integer</a> type. The second argument must be an '<tt>ubyte</tt>'
1745 <p>The value produced is <tt>var1</tt> * 2<sup><tt>var2</tt></sup>.</p>
1747 <pre> <result> = shl int 4, ubyte %var <i>; yields {int}:result = 4 << %var</i>
1748 <result> = shl int 4, ubyte 2 <i>; yields {int}:result = 16</i>
1749 <result> = shl int 1, ubyte 10 <i>; yields {int}:result = 1024</i>
1752 <!-- _______________________________________________________________________ -->
1753 <div class="doc_subsubsection"> <a name="i_shr">'<tt>shr</tt>'
1754 Instruction</a> </div>
1755 <div class="doc_text">
1757 <pre> <result> = shr <ty> <var1>, ubyte <var2> <i>; yields {ty}:result</i>
1760 <p>The '<tt>shr</tt>' instruction returns the first operand shifted to
1761 the right a specified number of bits.</p>
1763 <p>The first argument to the '<tt>shr</tt>' instruction must be an <a
1764 href="#t_integer">integer</a> type. The second argument must be an '<tt>ubyte</tt>'
1767 <p>If the first argument is a <a href="#t_signed">signed</a> type, the
1768 most significant bit is duplicated in the newly free'd bit positions.
1769 If the first argument is unsigned, zero bits shall fill the empty
1772 <pre> <result> = shr int 4, ubyte %var <i>; yields {int}:result = 4 >> %var</i>
1773 <result> = shr uint 4, ubyte 1 <i>; yields {uint}:result = 2</i>
1774 <result> = shr int 4, ubyte 2 <i>; yields {int}:result = 1</i>
1775 <result> = shr sbyte 4, ubyte 3 <i>; yields {sbyte}:result = 0</i>
1776 <result> = shr sbyte -2, ubyte 1 <i>; yields {sbyte}:result = -1</i>
1780 <!-- ======================================================================= -->
1781 <div class="doc_subsection">
1782 <a name="memoryops">Memory Access Operations</a>
1785 <div class="doc_text">
1787 <p>A key design point of an SSA-based representation is how it
1788 represents memory. In LLVM, no memory locations are in SSA form, which
1789 makes things very simple. This section describes how to read, write,
1790 allocate, and free memory in LLVM.</p>
1794 <!-- _______________________________________________________________________ -->
1795 <div class="doc_subsubsection">
1796 <a name="i_malloc">'<tt>malloc</tt>' Instruction</a>
1799 <div class="doc_text">
1804 <result> = malloc <type>[, uint <NumElements>][, align <alignment>] <i>; yields {type*}:result</i>
1809 <p>The '<tt>malloc</tt>' instruction allocates memory from the system
1810 heap and returns a pointer to it.</p>
1814 <p>The '<tt>malloc</tt>' instruction allocates
1815 <tt>sizeof(<type>)*NumElements</tt>
1816 bytes of memory from the operating system and returns a pointer of the
1817 appropriate type to the program. If "NumElements" is specified, it is the
1818 number of elements allocated. If an alignment is specified, the value result
1819 of the allocation is guaranteed to be aligned to at least that boundary. If
1820 not specified, or if zero, the target can choose to align the allocation on any
1821 convenient boundary.</p>
1823 <p>'<tt>type</tt>' must be a sized type.</p>
1827 <p>Memory is allocated using the system "<tt>malloc</tt>" function, and
1828 a pointer is returned.</p>
1833 %array = malloc [4 x ubyte ] <i>; yields {[%4 x ubyte]*}:array</i>
1835 %size = <a href="#i_add">add</a> uint 2, 2 <i>; yields {uint}:size = uint 4</i>
1836 %array1 = malloc ubyte, uint 4 <i>; yields {ubyte*}:array1</i>
1837 %array2 = malloc [12 x ubyte], uint %size <i>; yields {[12 x ubyte]*}:array2</i>
1838 %array3 = malloc int, uint 4, align 1024 <i>; yields {int*}:array3</i>
1839 %array4 = malloc int, align 1024 <i>; yields {int*}:array4</i>
1843 <!-- _______________________________________________________________________ -->
1844 <div class="doc_subsubsection">
1845 <a name="i_free">'<tt>free</tt>' Instruction</a>
1848 <div class="doc_text">
1853 free <type> <value> <i>; yields {void}</i>
1858 <p>The '<tt>free</tt>' instruction returns memory back to the unused
1859 memory heap to be reallocated in the future.</p>
1863 <p>'<tt>value</tt>' shall be a pointer value that points to a value
1864 that was allocated with the '<tt><a href="#i_malloc">malloc</a></tt>'
1869 <p>Access to the memory pointed to by the pointer is no longer defined
1870 after this instruction executes.</p>
1875 %array = <a href="#i_malloc">malloc</a> [4 x ubyte] <i>; yields {[4 x ubyte]*}:array</i>
1876 free [4 x ubyte]* %array
1880 <!-- _______________________________________________________________________ -->
1881 <div class="doc_subsubsection">
1882 <a name="i_alloca">'<tt>alloca</tt>' Instruction</a>
1885 <div class="doc_text">
1890 <result> = alloca <type>[, uint <NumElements>][, align <alignment>] <i>; yields {type*}:result</i>
1895 <p>The '<tt>alloca</tt>' instruction allocates memory on the current
1896 stack frame of the procedure that is live until the current function
1897 returns to its caller.</p>
1901 <p>The '<tt>alloca</tt>' instruction allocates <tt>sizeof(<type>)*NumElements</tt>
1902 bytes of memory on the runtime stack, returning a pointer of the
1903 appropriate type to the program. If "NumElements" is specified, it is the
1904 number of elements allocated. If an alignment is specified, the value result
1905 of the allocation is guaranteed to be aligned to at least that boundary. If
1906 not specified, or if zero, the target can choose to align the allocation on any
1907 convenient boundary.</p>
1909 <p>'<tt>type</tt>' may be any sized type.</p>
1913 <p>Memory is allocated; a pointer is returned. '<tt>alloca</tt>'d
1914 memory is automatically released when the function returns. The '<tt>alloca</tt>'
1915 instruction is commonly used to represent automatic variables that must
1916 have an address available. When the function returns (either with the <tt><a
1917 href="#i_ret">ret</a></tt> or <tt><a href="#i_unwind">unwind</a></tt>
1918 instructions), the memory is reclaimed.</p>
1923 %ptr = alloca int <i>; yields {int*}:ptr</i>
1924 %ptr = alloca int, uint 4 <i>; yields {int*}:ptr</i>
1925 %ptr = alloca int, uint 4, align 1024 <i>; yields {int*}:ptr</i>
1926 %ptr = alloca int, align 1024 <i>; yields {int*}:ptr</i>
1930 <!-- _______________________________________________________________________ -->
1931 <div class="doc_subsubsection"> <a name="i_load">'<tt>load</tt>'
1932 Instruction</a> </div>
1933 <div class="doc_text">
1935 <pre> <result> = load <ty>* <pointer><br> <result> = volatile load <ty>* <pointer><br></pre>
1937 <p>The '<tt>load</tt>' instruction is used to read from memory.</p>
1939 <p>The argument to the '<tt>load</tt>' instruction specifies the memory
1940 address from which to load. The pointer must point to a <a
1941 href="#t_firstclass">first class</a> type. If the <tt>load</tt> is
1942 marked as <tt>volatile</tt>, then the optimizer is not allowed to modify
1943 the number or order of execution of this <tt>load</tt> with other
1944 volatile <tt>load</tt> and <tt><a href="#i_store">store</a></tt>
1947 <p>The location of memory pointed to is loaded.</p>
1949 <pre> %ptr = <a href="#i_alloca">alloca</a> int <i>; yields {int*}:ptr</i>
1951 href="#i_store">store</a> int 3, int* %ptr <i>; yields {void}</i>
1952 %val = load int* %ptr <i>; yields {int}:val = int 3</i>
1955 <!-- _______________________________________________________________________ -->
1956 <div class="doc_subsubsection"> <a name="i_store">'<tt>store</tt>'
1957 Instruction</a> </div>
1959 <pre> store <ty> <value>, <ty>* <pointer> <i>; yields {void}</i>
1960 volatile store <ty> <value>, <ty>* <pointer> <i>; yields {void}</i>
1963 <p>The '<tt>store</tt>' instruction is used to write to memory.</p>
1965 <p>There are two arguments to the '<tt>store</tt>' instruction: a value
1966 to store and an address in which to store it. The type of the '<tt><pointer></tt>'
1967 operand must be a pointer to the type of the '<tt><value></tt>'
1968 operand. If the <tt>store</tt> is marked as <tt>volatile</tt>, then the
1969 optimizer is not allowed to modify the number or order of execution of
1970 this <tt>store</tt> with other volatile <tt>load</tt> and <tt><a
1971 href="#i_store">store</a></tt> instructions.</p>
1973 <p>The contents of memory are updated to contain '<tt><value></tt>'
1974 at the location specified by the '<tt><pointer></tt>' operand.</p>
1976 <pre> %ptr = <a href="#i_alloca">alloca</a> int <i>; yields {int*}:ptr</i>
1978 href="#i_store">store</a> int 3, int* %ptr <i>; yields {void}</i>
1979 %val = load int* %ptr <i>; yields {int}:val = int 3</i>
1981 <!-- _______________________________________________________________________ -->
1982 <div class="doc_subsubsection">
1983 <a name="i_getelementptr">'<tt>getelementptr</tt>' Instruction</a>
1986 <div class="doc_text">
1989 <result> = getelementptr <ty>* <ptrval>{, <ty> <idx>}*
1995 The '<tt>getelementptr</tt>' instruction is used to get the address of a
1996 subelement of an aggregate data structure.</p>
2000 <p>This instruction takes a list of integer constants that indicate what
2001 elements of the aggregate object to index to. The actual types of the arguments
2002 provided depend on the type of the first pointer argument. The
2003 '<tt>getelementptr</tt>' instruction is used to index down through the type
2004 levels of a structure or to a specific index in an array. When indexing into a
2005 structure, only <tt>uint</tt>
2006 integer constants are allowed. When indexing into an array or pointer,
2007 <tt>int</tt> and <tt>long</tt> indexes are allowed of any sign.</p>
2009 <p>For example, let's consider a C code fragment and how it gets
2010 compiled to LLVM:</p>
2024 int *foo(struct ST *s) {
2025 return &s[1].Z.B[5][13];
2029 <p>The LLVM code generated by the GCC frontend is:</p>
2032 %RT = type { sbyte, [10 x [20 x int]], sbyte }
2033 %ST = type { int, double, %RT }
2037 int* %foo(%ST* %s) {
2039 %reg = getelementptr %ST* %s, int 1, uint 2, uint 1, int 5, int 13
2046 <p>The index types specified for the '<tt>getelementptr</tt>' instruction depend
2047 on the pointer type that is being indexed into. <a href="#t_pointer">Pointer</a>
2048 and <a href="#t_array">array</a> types require <tt>uint</tt>, <tt>int</tt>,
2049 <tt>ulong</tt>, or <tt>long</tt> values, and <a href="#t_struct">structure</a>
2050 types require <tt>uint</tt> <b>constants</b>.</p>
2052 <p>In the example above, the first index is indexing into the '<tt>%ST*</tt>'
2053 type, which is a pointer, yielding a '<tt>%ST</tt>' = '<tt>{ int, double, %RT
2054 }</tt>' type, a structure. The second index indexes into the third element of
2055 the structure, yielding a '<tt>%RT</tt>' = '<tt>{ sbyte, [10 x [20 x int]],
2056 sbyte }</tt>' type, another structure. The third index indexes into the second
2057 element of the structure, yielding a '<tt>[10 x [20 x int]]</tt>' type, an
2058 array. The two dimensions of the array are subscripted into, yielding an
2059 '<tt>int</tt>' type. The '<tt>getelementptr</tt>' instruction returns a pointer
2060 to this element, thus computing a value of '<tt>int*</tt>' type.</p>
2062 <p>Note that it is perfectly legal to index partially through a
2063 structure, returning a pointer to an inner element. Because of this,
2064 the LLVM code for the given testcase is equivalent to:</p>
2067 int* %foo(%ST* %s) {
2068 %t1 = getelementptr %ST* %s, int 1 <i>; yields %ST*:%t1</i>
2069 %t2 = getelementptr %ST* %t1, int 0, uint 2 <i>; yields %RT*:%t2</i>
2070 %t3 = getelementptr %RT* %t2, int 0, uint 1 <i>; yields [10 x [20 x int]]*:%t3</i>
2071 %t4 = getelementptr [10 x [20 x int]]* %t3, int 0, int 5 <i>; yields [20 x int]*:%t4</i>
2072 %t5 = getelementptr [20 x int]* %t4, int 0, int 13 <i>; yields int*:%t5</i>
2077 <p>Note that it is undefined to access an array out of bounds: array and
2078 pointer indexes must always be within the defined bounds of the array type.
2079 The one exception for this rules is zero length arrays. These arrays are
2080 defined to be accessible as variable length arrays, which requires access
2081 beyond the zero'th element.</p>
2086 <i>; yields [12 x ubyte]*:aptr</i>
2087 %aptr = getelementptr {int, [12 x ubyte]}* %sptr, long 0, uint 1
2091 <!-- ======================================================================= -->
2092 <div class="doc_subsection"> <a name="otherops">Other Operations</a> </div>
2093 <div class="doc_text">
2094 <p>The instructions in this category are the "miscellaneous"
2095 instructions, which defy better classification.</p>
2097 <!-- _______________________________________________________________________ -->
2098 <div class="doc_subsubsection"> <a name="i_phi">'<tt>phi</tt>'
2099 Instruction</a> </div>
2100 <div class="doc_text">
2102 <pre> <result> = phi <ty> [ <val0>, <label0>], ...<br></pre>
2104 <p>The '<tt>phi</tt>' instruction is used to implement the φ node in
2105 the SSA graph representing the function.</p>
2107 <p>The type of the incoming values are specified with the first type
2108 field. After this, the '<tt>phi</tt>' instruction takes a list of pairs
2109 as arguments, with one pair for each predecessor basic block of the
2110 current block. Only values of <a href="#t_firstclass">first class</a>
2111 type may be used as the value arguments to the PHI node. Only labels
2112 may be used as the label arguments.</p>
2113 <p>There must be no non-phi instructions between the start of a basic
2114 block and the PHI instructions: i.e. PHI instructions must be first in
2117 <p>At runtime, the '<tt>phi</tt>' instruction logically takes on the
2118 value specified by the parameter, depending on which basic block we
2119 came from in the last <a href="#terminators">terminator</a> instruction.</p>
2121 <pre>Loop: ; Infinite loop that counts from 0 on up...<br> %indvar = phi uint [ 0, %LoopHeader ], [ %nextindvar, %Loop ]<br> %nextindvar = add uint %indvar, 1<br> br label %Loop<br></pre>
2124 <!-- _______________________________________________________________________ -->
2125 <div class="doc_subsubsection">
2126 <a name="i_cast">'<tt>cast .. to</tt>' Instruction</a>
2129 <div class="doc_text">
2134 <result> = cast <ty> <value> to <ty2> <i>; yields ty2</i>
2140 The '<tt>cast</tt>' instruction is used as the primitive means to convert
2141 integers to floating point, change data type sizes, and break type safety (by
2149 The '<tt>cast</tt>' instruction takes a value to cast, which must be a first
2150 class value, and a type to cast it to, which must also be a <a
2151 href="#t_firstclass">first class</a> type.
2157 This instruction follows the C rules for explicit casts when determining how the
2158 data being cast must change to fit in its new container.
2162 When casting to bool, any value that would be considered true in the context of
2163 a C '<tt>if</tt>' condition is converted to the boolean '<tt>true</tt>' values,
2164 all else are '<tt>false</tt>'.
2168 When extending an integral value from a type of one signness to another (for
2169 example '<tt>sbyte</tt>' to '<tt>ulong</tt>'), the value is sign-extended if the
2170 <b>source</b> value is signed, and zero-extended if the source value is
2171 unsigned. <tt>bool</tt> values are always zero extended into either zero or
2178 %X = cast int 257 to ubyte <i>; yields ubyte:1</i>
2179 %Y = cast int 123 to bool <i>; yields bool:true</i>
2183 <!-- _______________________________________________________________________ -->
2184 <div class="doc_subsubsection">
2185 <a name="i_select">'<tt>select</tt>' Instruction</a>
2188 <div class="doc_text">
2193 <result> = select bool <cond>, <ty> <val1>, <ty> <val2> <i>; yields ty</i>
2199 The '<tt>select</tt>' instruction is used to choose one value based on a
2200 condition, without branching.
2207 The '<tt>select</tt>' instruction requires a boolean value indicating the condition, and two values of the same <a href="#t_firstclass">first class</a> type.
2213 If the boolean condition evaluates to true, the instruction returns the first
2214 value argument; otherwise, it returns the second value argument.
2220 %X = select bool true, ubyte 17, ubyte 42 <i>; yields ubyte:17</i>
2228 <!-- _______________________________________________________________________ -->
2229 <div class="doc_subsubsection">
2230 <a name="i_call">'<tt>call</tt>' Instruction</a>
2233 <div class="doc_text">
2237 <result> = [tail] call [<a href="#callingconv">cconv</a>] <ty>* <fnptrval>(<param list>)
2242 <p>The '<tt>call</tt>' instruction represents a simple function call.</p>
2246 <p>This instruction requires several arguments:</p>
2250 <p>The optional "tail" marker indicates whether the callee function accesses
2251 any allocas or varargs in the caller. If the "tail" marker is present, the
2252 function call is eligible for tail call optimization. Note that calls may
2253 be marked "tail" even if they do not occur before a <a
2254 href="#i_ret"><tt>ret</tt></a> instruction.
2257 <p>The optional "cconv" marker indicates which <a href="callingconv">calling
2258 convention</a> the call should use. If none is specified, the call defaults
2259 to using C calling conventions.
2262 <p>'<tt>ty</tt>': shall be the signature of the pointer to function value
2263 being invoked. The argument types must match the types implied by this
2264 signature. This type can be omitted if the function is not varargs and
2265 if the function type does not return a pointer to a function.</p>
2268 <p>'<tt>fnptrval</tt>': An LLVM value containing a pointer to a function to
2269 be invoked. In most cases, this is a direct function invocation, but
2270 indirect <tt>call</tt>s are just as possible, calling an arbitrary pointer
2271 to function value.</p>
2274 <p>'<tt>function args</tt>': argument list whose types match the
2275 function signature argument types. All arguments must be of
2276 <a href="#t_firstclass">first class</a> type. If the function signature
2277 indicates the function accepts a variable number of arguments, the extra
2278 arguments can be specified.</p>
2284 <p>The '<tt>call</tt>' instruction is used to cause control flow to
2285 transfer to a specified function, with its incoming arguments bound to
2286 the specified values. Upon a '<tt><a href="#i_ret">ret</a></tt>'
2287 instruction in the called function, control flow continues with the
2288 instruction after the function call, and the return value of the
2289 function is bound to the result argument. This is a simpler case of
2290 the <a href="#i_invoke">invoke</a> instruction.</p>
2295 %retval = call int %test(int %argc)
2296 call int(sbyte*, ...) *%printf(sbyte* %msg, int 12, sbyte 42);
2297 %X = tail call int %foo()
2298 %Y = tail call <a href="#callingconv">fastcc</a> int %foo()
2303 <!-- _______________________________________________________________________ -->
2304 <div class="doc_subsubsection">
2305 <a name="i_vaarg">'<tt>vaarg</tt>' Instruction</a>
2308 <div class="doc_text">
2313 <resultval> = va_arg <va_list*> <arglist>, <argty>
2318 <p>The '<tt>va_arg</tt>' instruction is used to access arguments passed through
2319 the "variable argument" area of a function call. It is used to implement the
2320 <tt>va_arg</tt> macro in C.</p>
2324 <p>This instruction takes a <tt>va_list*</tt> value and the type of
2325 the argument. It returns a value of the specified argument type and
2326 increments the <tt>va_list</tt> to point to the next argument. Again, the
2327 actual type of <tt>va_list</tt> is target specific.</p>
2331 <p>The '<tt>va_arg</tt>' instruction loads an argument of the specified
2332 type from the specified <tt>va_list</tt> and causes the
2333 <tt>va_list</tt> to point to the next argument. For more information,
2334 see the variable argument handling <a href="#int_varargs">Intrinsic
2337 <p>It is legal for this instruction to be called in a function which does not
2338 take a variable number of arguments, for example, the <tt>vfprintf</tt>
2341 <p><tt>va_arg</tt> is an LLVM instruction instead of an <a
2342 href="#intrinsics">intrinsic function</a> because it takes a type as an
2347 <p>See the <a href="#int_varargs">variable argument processing</a> section.</p>
2351 <!-- *********************************************************************** -->
2352 <div class="doc_section"> <a name="intrinsics">Intrinsic Functions</a> </div>
2353 <!-- *********************************************************************** -->
2355 <div class="doc_text">
2357 <p>LLVM supports the notion of an "intrinsic function". These functions have
2358 well known names and semantics and are required to follow certain
2359 restrictions. Overall, these instructions represent an extension mechanism for
2360 the LLVM language that does not require changing all of the transformations in
2361 LLVM to add to the language (or the bytecode reader/writer, the parser,
2364 <p>Intrinsic function names must all start with an "<tt>llvm.</tt>" prefix. This
2365 prefix is reserved in LLVM for intrinsic names; thus, functions may not be named
2366 this. Intrinsic functions must always be external functions: you cannot define
2367 the body of intrinsic functions. Intrinsic functions may only be used in call
2368 or invoke instructions: it is illegal to take the address of an intrinsic
2369 function. Additionally, because intrinsic functions are part of the LLVM
2370 language, it is required that they all be documented here if any are added.</p>
2373 <p>To learn how to add an intrinsic function, please see the <a
2374 href="ExtendingLLVM.html">Extending LLVM Guide</a>.
2379 <!-- ======================================================================= -->
2380 <div class="doc_subsection">
2381 <a name="int_varargs">Variable Argument Handling Intrinsics</a>
2384 <div class="doc_text">
2386 <p>Variable argument support is defined in LLVM with the <a
2387 href="#i_vanext"><tt>vanext</tt></a> instruction and these three
2388 intrinsic functions. These functions are related to the similarly
2389 named macros defined in the <tt><stdarg.h></tt> header file.</p>
2391 <p>All of these functions operate on arguments that use a
2392 target-specific value type "<tt>va_list</tt>". The LLVM assembly
2393 language reference manual does not define what this type is, so all
2394 transformations should be prepared to handle intrinsics with any type
2397 <p>This example shows how the <a href="#i_vanext"><tt>vanext</tt></a>
2398 instruction and the variable argument handling intrinsic functions are
2402 int %test(int %X, ...) {
2403 ; Initialize variable argument processing
2405 call void %<a href="#i_va_start">llvm.va_start</a>(sbyte** %ap)
2407 ; Read a single integer argument
2408 %tmp = va_arg sbyte** %ap, int
2410 ; Demonstrate usage of llvm.va_copy and llvm.va_end
2412 call void %<a href="#i_va_copy">llvm.va_copy</a>(sbyte** %aq, sbyte** %ap)
2413 call void %<a href="#i_va_end">llvm.va_end</a>(sbyte** %aq)
2415 ; Stop processing of arguments.
2416 call void %<a href="#i_va_end">llvm.va_end</a>(sbyte** %ap)
2422 <!-- _______________________________________________________________________ -->
2423 <div class="doc_subsubsection">
2424 <a name="i_va_start">'<tt>llvm.va_start</tt>' Intrinsic</a>
2428 <div class="doc_text">
2430 <pre> declare void %llvm.va_start(<va_list>* <arglist>)<br></pre>
2432 <P>The '<tt>llvm.va_start</tt>' intrinsic initializes
2433 <tt>*<arglist></tt> for subsequent use by <tt><a
2434 href="#i_va_arg">va_arg</a></tt>.</p>
2438 <P>The argument is a pointer to a <tt>va_list</tt> element to initialize.</p>
2442 <P>The '<tt>llvm.va_start</tt>' intrinsic works just like the <tt>va_start</tt>
2443 macro available in C. In a target-dependent way, it initializes the
2444 <tt>va_list</tt> element the argument points to, so that the next call to
2445 <tt>va_arg</tt> will produce the first variable argument passed to the function.
2446 Unlike the C <tt>va_start</tt> macro, this intrinsic does not need to know the
2447 last argument of the function, the compiler can figure that out.</p>
2451 <!-- _______________________________________________________________________ -->
2452 <div class="doc_subsubsection">
2453 <a name="i_va_end">'<tt>llvm.va_end</tt>' Intrinsic</a>
2456 <div class="doc_text">
2458 <pre> declare void %llvm.va_end(<va_list*> <arglist>)<br></pre>
2460 <p>The '<tt>llvm.va_end</tt>' intrinsic destroys <tt><arglist></tt>
2461 which has been initialized previously with <tt><a href="#i_va_start">llvm.va_start</a></tt>
2462 or <tt><a href="#i_va_copy">llvm.va_copy</a></tt>.</p>
2464 <p>The argument is a <tt>va_list</tt> to destroy.</p>
2466 <p>The '<tt>llvm.va_end</tt>' intrinsic works just like the <tt>va_end</tt>
2467 macro available in C. In a target-dependent way, it destroys the <tt>va_list</tt>.
2468 Calls to <a href="#i_va_start"><tt>llvm.va_start</tt></a> and <a
2469 href="#i_va_copy"><tt>llvm.va_copy</tt></a> must be matched exactly
2470 with calls to <tt>llvm.va_end</tt>.</p>
2473 <!-- _______________________________________________________________________ -->
2474 <div class="doc_subsubsection">
2475 <a name="i_va_copy">'<tt>llvm.va_copy</tt>' Intrinsic</a>
2478 <div class="doc_text">
2483 declare void %llvm.va_copy(<va_list>* <destarglist>,
2484 <va_list>* <srcarglist>)
2489 <p>The '<tt>llvm.va_copy</tt>' intrinsic copies the current argument position from
2490 the source argument list to the destination argument list.</p>
2494 <p>The first argument is a pointer to a <tt>va_list</tt> element to initialize.
2495 The second argument is a pointer to a <tt>va_list</tt> element to copy from.</p>
2500 <p>The '<tt>llvm.va_copy</tt>' intrinsic works just like the <tt>va_copy</tt> macro
2501 available in C. In a target-dependent way, it copies the source
2502 <tt>va_list</tt> element into the destination list. This intrinsic is necessary
2503 because the <tt><a href="i_va_begin">llvm.va_begin</a></tt> intrinsic may be
2504 arbitrarily complex and require memory allocation, for example.</p>
2508 <!-- ======================================================================= -->
2509 <div class="doc_subsection">
2510 <a name="int_gc">Accurate Garbage Collection Intrinsics</a>
2513 <div class="doc_text">
2516 LLVM support for <a href="GarbageCollection.html">Accurate Garbage
2517 Collection</a> requires the implementation and generation of these intrinsics.
2518 These intrinsics allow identification of <a href="#i_gcroot">GC roots on the
2519 stack</a>, as well as garbage collector implementations that require <a
2520 href="#i_gcread">read</a> and <a href="#i_gcwrite">write</a> barriers.
2521 Front-ends for type-safe garbage collected languages should generate these
2522 intrinsics to make use of the LLVM garbage collectors. For more details, see <a
2523 href="GarbageCollection.html">Accurate Garbage Collection with LLVM</a>.
2527 <!-- _______________________________________________________________________ -->
2528 <div class="doc_subsubsection">
2529 <a name="i_gcroot">'<tt>llvm.gcroot</tt>' Intrinsic</a>
2532 <div class="doc_text">
2537 declare void %llvm.gcroot(<ty>** %ptrloc, <ty2>* %metadata)
2542 <p>The '<tt>llvm.gcroot</tt>' intrinsic declares the existence of a GC root to
2543 the code generator, and allows some metadata to be associated with it.</p>
2547 <p>The first argument specifies the address of a stack object that contains the
2548 root pointer. The second pointer (which must be either a constant or a global
2549 value address) contains the meta-data to be associated with the root.</p>
2553 <p>At runtime, a call to this intrinsics stores a null pointer into the "ptrloc"
2554 location. At compile-time, the code generator generates information to allow
2555 the runtime to find the pointer at GC safe points.
2561 <!-- _______________________________________________________________________ -->
2562 <div class="doc_subsubsection">
2563 <a name="i_gcread">'<tt>llvm.gcread</tt>' Intrinsic</a>
2566 <div class="doc_text">
2571 declare sbyte* %llvm.gcread(sbyte** %Ptr)
2576 <p>The '<tt>llvm.gcread</tt>' intrinsic identifies reads of references from heap
2577 locations, allowing garbage collector implementations that require read
2582 <p>The argument is the address to read from, which should be an address
2583 allocated from the garbage collector.</p>
2587 <p>The '<tt>llvm.gcread</tt>' intrinsic has the same semantics as a load
2588 instruction, but may be replaced with substantially more complex code by the
2589 garbage collector runtime, as needed.</p>
2594 <!-- _______________________________________________________________________ -->
2595 <div class="doc_subsubsection">
2596 <a name="i_gcwrite">'<tt>llvm.gcwrite</tt>' Intrinsic</a>
2599 <div class="doc_text">
2604 declare void %llvm.gcwrite(sbyte* %P1, sbyte** %P2)
2609 <p>The '<tt>llvm.gcwrite</tt>' intrinsic identifies writes of references to heap
2610 locations, allowing garbage collector implementations that require write
2611 barriers (such as generational or reference counting collectors).</p>
2615 <p>The first argument is the reference to store, and the second is the heap
2616 location to store to.</p>
2620 <p>The '<tt>llvm.gcwrite</tt>' intrinsic has the same semantics as a store
2621 instruction, but may be replaced with substantially more complex code by the
2622 garbage collector runtime, as needed.</p>
2628 <!-- ======================================================================= -->
2629 <div class="doc_subsection">
2630 <a name="int_codegen">Code Generator Intrinsics</a>
2633 <div class="doc_text">
2635 These intrinsics are provided by LLVM to expose special features that may only
2636 be implemented with code generator support.
2641 <!-- _______________________________________________________________________ -->
2642 <div class="doc_subsubsection">
2643 <a name="i_returnaddress">'<tt>llvm.returnaddress</tt>' Intrinsic</a>
2646 <div class="doc_text">
2650 declare void* %llvm.returnaddress(uint <level>)
2656 The '<tt>llvm.returnaddress</tt>' intrinsic returns a target-specific value
2657 indicating the return address of the current function or one of its callers.
2663 The argument to this intrinsic indicates which function to return the address
2664 for. Zero indicates the calling function, one indicates its caller, etc. The
2665 argument is <b>required</b> to be a constant integer value.
2671 The '<tt>llvm.returnaddress</tt>' intrinsic either returns a pointer indicating
2672 the return address of the specified call frame, or zero if it cannot be
2673 identified. The value returned by this intrinsic is likely to be incorrect or 0
2674 for arguments other than zero, so it should only be used for debugging purposes.
2678 Note that calling this intrinsic does not prevent function inlining or other
2679 aggressive transformations, so the value returned may not be that of the obvious
2680 source-language caller.
2685 <!-- _______________________________________________________________________ -->
2686 <div class="doc_subsubsection">
2687 <a name="i_frameaddress">'<tt>llvm.frameaddress</tt>' Intrinsic</a>
2690 <div class="doc_text">
2694 declare void* %llvm.frameaddress(uint <level>)
2700 The '<tt>llvm.frameaddress</tt>' intrinsic returns the target-specific frame
2701 pointer value for the specified stack frame.
2707 The argument to this intrinsic indicates which function to return the frame
2708 pointer for. Zero indicates the calling function, one indicates its caller,
2709 etc. The argument is <b>required</b> to be a constant integer value.
2715 The '<tt>llvm.frameaddress</tt>' intrinsic either returns a pointer indicating
2716 the frame address of the specified call frame, or zero if it cannot be
2717 identified. The value returned by this intrinsic is likely to be incorrect or 0
2718 for arguments other than zero, so it should only be used for debugging purposes.
2722 Note that calling this intrinsic does not prevent function inlining or other
2723 aggressive transformations, so the value returned may not be that of the obvious
2724 source-language caller.
2728 <!-- _______________________________________________________________________ -->
2729 <div class="doc_subsubsection">
2730 <a name="i_prefetch">'<tt>llvm.prefetch</tt>' Intrinsic</a>
2733 <div class="doc_text">
2737 declare void %llvm.prefetch(sbyte * <address>,
2738 uint <rw>, uint <locality>)
2745 The '<tt>llvm.prefetch</tt>' intrinsic is a hint to the code generator to insert
2746 a prefetch instruction if supported; otherwise, it is a noop. Prefetches have
2748 effect on the behavior of the program but can change its performance
2755 <tt>address</tt> is the address to be prefetched, <tt>rw</tt> is the specifier
2756 determining if the fetch should be for a read (0) or write (1), and
2757 <tt>locality</tt> is a temporal locality specifier ranging from (0) - no
2758 locality, to (3) - extremely local keep in cache. The <tt>rw</tt> and
2759 <tt>locality</tt> arguments must be constant integers.
2765 This intrinsic does not modify the behavior of the program. In particular,
2766 prefetches cannot trap and do not produce a value. On targets that support this
2767 intrinsic, the prefetch can provide hints to the processor cache for better
2773 <!-- _______________________________________________________________________ -->
2774 <div class="doc_subsubsection">
2775 <a name="i_pcmarker">'<tt>llvm.pcmarker</tt>' Intrinsic</a>
2778 <div class="doc_text">
2782 declare void %llvm.pcmarker( uint <id> )
2789 The '<tt>llvm.pcmarker</tt>' intrinsic is a method to export a Program Counter
2791 code to simulators and other tools. The method is target specific, but it is
2792 expected that the marker will use exported symbols to transmit the PC of the marker.
2793 The marker makes no guarantees that it will remain with any specific instruction
2794 after optimizations. It is possible that the presense of a marker will inhibit
2795 optimizations. The intended use is to be inserted after optmizations to allow
2796 correlations of simulation runs.
2802 <tt>id</tt> is a numerical id identifying the marker.
2808 This intrinsic does not modify the behavior of the program. Backends that do not
2809 support this intrinisic may ignore it.
2815 <!-- ======================================================================= -->
2816 <div class="doc_subsection">
2817 <a name="int_os">Operating System Intrinsics</a>
2820 <div class="doc_text">
2822 These intrinsics are provided by LLVM to support the implementation of
2823 operating system level code.
2828 <!-- _______________________________________________________________________ -->
2829 <div class="doc_subsubsection">
2830 <a name="i_readport">'<tt>llvm.readport</tt>' Intrinsic</a>
2833 <div class="doc_text">
2837 declare <integer type> %llvm.readport (<integer type> <address>)
2843 The '<tt>llvm.readport</tt>' intrinsic reads data from the specified hardware
2850 The argument to this intrinsic indicates the hardware I/O address from which
2851 to read the data. The address is in the hardware I/O address namespace (as
2852 opposed to being a memory location for memory mapped I/O).
2858 The '<tt>llvm.readport</tt>' intrinsic reads data from the hardware I/O port
2859 specified by <i>address</i> and returns the value. The address and return
2860 value must be integers, but the size is dependent upon the platform upon which
2861 the program is code generated. For example, on x86, the address must be an
2862 unsigned 16-bit value, and the return value must be 8, 16, or 32 bits.
2867 <!-- _______________________________________________________________________ -->
2868 <div class="doc_subsubsection">
2869 <a name="i_writeport">'<tt>llvm.writeport</tt>' Intrinsic</a>
2872 <div class="doc_text">
2876 call void (<integer type>, <integer type>)*
2877 %llvm.writeport (<integer type> <value>,
2878 <integer type> <address>)
2884 The '<tt>llvm.writeport</tt>' intrinsic writes data to the specified hardware
2891 The first argument is the value to write to the I/O port.
2895 The second argument indicates the hardware I/O address to which data should be
2896 written. The address is in the hardware I/O address namespace (as opposed to
2897 being a memory location for memory mapped I/O).
2903 The '<tt>llvm.writeport</tt>' intrinsic writes <i>value</i> to the I/O port
2904 specified by <i>address</i>. The address and value must be integers, but the
2905 size is dependent upon the platform upon which the program is code generated.
2906 For example, on x86, the address must be an unsigned 16-bit value, and the
2907 value written must be 8, 16, or 32 bits in length.
2912 <!-- _______________________________________________________________________ -->
2913 <div class="doc_subsubsection">
2914 <a name="i_readio">'<tt>llvm.readio</tt>' Intrinsic</a>
2917 <div class="doc_text">
2921 declare <result> %llvm.readio (<ty> * <pointer>)
2927 The '<tt>llvm.readio</tt>' intrinsic reads data from a memory mapped I/O
2934 The argument to this intrinsic is a pointer indicating the memory address from
2935 which to read the data. The data must be a
2936 <a href="#t_firstclass">first class</a> type.
2942 The '<tt>llvm.readio</tt>' intrinsic reads data from a memory mapped I/O
2943 location specified by <i>pointer</i> and returns the value. The argument must
2944 be a pointer, and the return value must be a
2945 <a href="#t_firstclass">first class</a> type. However, certain architectures
2946 may not support I/O on all first class types. For example, 32-bit processors
2947 may only support I/O on data types that are 32 bits or less.
2951 This intrinsic enforces an in-order memory model for llvm.readio and
2952 llvm.writeio calls on machines that use dynamic scheduling. Dynamically
2953 scheduled processors may execute loads and stores out of order, re-ordering at
2954 run time accesses to memory mapped I/O registers. Using these intrinsics
2955 ensures that accesses to memory mapped I/O registers occur in program order.
2960 <!-- _______________________________________________________________________ -->
2961 <div class="doc_subsubsection">
2962 <a name="i_writeio">'<tt>llvm.writeio</tt>' Intrinsic</a>
2965 <div class="doc_text">
2969 declare void %llvm.writeio (<ty1> <value>, <ty2> * <pointer>)
2975 The '<tt>llvm.writeio</tt>' intrinsic writes data to the specified memory
2982 The first argument is the value to write to the memory mapped I/O location.
2983 The second argument is a pointer indicating the memory address to which the
2984 data should be written.
2990 The '<tt>llvm.writeio</tt>' intrinsic writes <i>value</i> to the memory mapped
2991 I/O address specified by <i>pointer</i>. The value must be a
2992 <a href="#t_firstclass">first class</a> type. However, certain architectures
2993 may not support I/O on all first class types. For example, 32-bit processors
2994 may only support I/O on data types that are 32 bits or less.
2998 This intrinsic enforces an in-order memory model for llvm.readio and
2999 llvm.writeio calls on machines that use dynamic scheduling. Dynamically
3000 scheduled processors may execute loads and stores out of order, re-ordering at
3001 run time accesses to memory mapped I/O registers. Using these intrinsics
3002 ensures that accesses to memory mapped I/O registers occur in program order.
3007 <!-- ======================================================================= -->
3008 <div class="doc_subsection">
3009 <a name="int_libc">Standard C Library Intrinsics</a>
3012 <div class="doc_text">
3014 LLVM provides intrinsics for a few important standard C library functions.
3015 These intrinsics allow source-language front-ends to pass information about the
3016 alignment of the pointer arguments to the code generator, providing opportunity
3017 for more efficient code generation.
3022 <!-- _______________________________________________________________________ -->
3023 <div class="doc_subsubsection">
3024 <a name="i_memcpy">'<tt>llvm.memcpy</tt>' Intrinsic</a>
3027 <div class="doc_text">
3031 declare void %llvm.memcpy(sbyte* <dest>, sbyte* <src>,
3032 uint <len>, uint <align>)
3038 The '<tt>llvm.memcpy</tt>' intrinsic copies a block of memory from the source
3039 location to the destination location.
3043 Note that, unlike the standard libc function, the <tt>llvm.memcpy</tt> intrinsic
3044 does not return a value, and takes an extra alignment argument.
3050 The first argument is a pointer to the destination, the second is a pointer to
3051 the source. The third argument is an (arbitrarily sized) integer argument
3052 specifying the number of bytes to copy, and the fourth argument is the alignment
3053 of the source and destination locations.
3057 If the call to this intrinisic has an alignment value that is not 0 or 1, then
3058 the caller guarantees that the size of the copy is a multiple of the alignment
3059 and that both the source and destination pointers are aligned to that boundary.
3065 The '<tt>llvm.memcpy</tt>' intrinsic copies a block of memory from the source
3066 location to the destination location, which are not allowed to overlap. It
3067 copies "len" bytes of memory over. If the argument is known to be aligned to
3068 some boundary, this can be specified as the fourth argument, otherwise it should
3074 <!-- _______________________________________________________________________ -->
3075 <div class="doc_subsubsection">
3076 <a name="i_memmove">'<tt>llvm.memmove</tt>' Intrinsic</a>
3079 <div class="doc_text">
3083 declare void %llvm.memmove(sbyte* <dest>, sbyte* <src>,
3084 uint <len>, uint <align>)
3090 The '<tt>llvm.memmove</tt>' intrinsic moves a block of memory from the source
3091 location to the destination location. It is similar to the '<tt>llvm.memcpy</tt>'
3092 intrinsic but allows the two memory locations to overlap.
3096 Note that, unlike the standard libc function, the <tt>llvm.memmove</tt> intrinsic
3097 does not return a value, and takes an extra alignment argument.
3103 The first argument is a pointer to the destination, the second is a pointer to
3104 the source. The third argument is an (arbitrarily sized) integer argument
3105 specifying the number of bytes to copy, and the fourth argument is the alignment
3106 of the source and destination locations.
3110 If the call to this intrinisic has an alignment value that is not 0 or 1, then
3111 the caller guarantees that the size of the copy is a multiple of the alignment
3112 and that both the source and destination pointers are aligned to that boundary.
3118 The '<tt>llvm.memmove</tt>' intrinsic copies a block of memory from the source
3119 location to the destination location, which may overlap. It
3120 copies "len" bytes of memory over. If the argument is known to be aligned to
3121 some boundary, this can be specified as the fourth argument, otherwise it should
3127 <!-- _______________________________________________________________________ -->
3128 <div class="doc_subsubsection">
3129 <a name="i_memset">'<tt>llvm.memset</tt>' Intrinsic</a>
3132 <div class="doc_text">
3136 declare void %llvm.memset(sbyte* <dest>, ubyte <val>,
3137 uint <len>, uint <align>)
3143 The '<tt>llvm.memset</tt>' intrinsic fills a block of memory with a particular
3148 Note that, unlike the standard libc function, the <tt>llvm.memset</tt> intrinsic
3149 does not return a value, and takes an extra alignment argument.
3155 The first argument is a pointer to the destination to fill, the second is the
3156 byte value to fill it with, the third argument is an (arbitrarily sized) integer
3157 argument specifying the number of bytes to fill, and the fourth argument is the
3158 known alignment of destination location.
3162 If the call to this intrinisic has an alignment value that is not 0 or 1, then
3163 the caller guarantees that the size of the copy is a multiple of the alignment
3164 and that the destination pointer is aligned to that boundary.
3170 The '<tt>llvm.memset</tt>' intrinsic fills "len" bytes of memory starting at the
3171 destination location. If the argument is known to be aligned to some boundary,
3172 this can be specified as the fourth argument, otherwise it should be set to 0 or
3178 <!-- _______________________________________________________________________ -->
3179 <div class="doc_subsubsection">
3180 <a name="i_isunordered">'<tt>llvm.isunordered</tt>' Intrinsic</a>
3183 <div class="doc_text">
3187 declare bool %llvm.isunordered(<float or double> Val1, <float or double> Val2)
3193 The '<tt>llvm.isunordered</tt>' intrinsic returns true if either or both of the
3194 specified floating point values is a NAN.
3200 The arguments are floating point numbers of the same type.
3206 If either or both of the arguments is a SNAN or QNAN, it returns true, otherwise
3212 <!-- _______________________________________________________________________ -->
3213 <div class="doc_subsubsection">
3214 <a name="i_sqrt">'<tt>llvm.sqrt</tt>' Intrinsic</a>
3217 <div class="doc_text">
3221 declare <float or double> %llvm.sqrt(<float or double> Val)
3227 The '<tt>llvm.sqrt</tt>' intrinsic returns the sqrt of the specified operand,
3228 returning the same value as the libm '<tt>sqrt</tt>' function would. Unlike
3229 <tt>sqrt</tt> in libm, however, <tt>llvm.sqrt</tt> has undefined behavior for
3230 negative numbers (which allows for better optimization).
3236 The argument and return value are floating point numbers of the same type.
3242 This function returns the sqrt of the specified operand if it is a positive
3243 floating point number.
3247 <!-- ======================================================================= -->
3248 <div class="doc_subsection">
3249 <a name="int_count">Bit Counting Intrinsics</a>
3252 <div class="doc_text">
3254 LLVM provides intrinsics for a few important bit counting operations.
3255 These allow efficient code generation for some algorithms.
3260 <!-- _______________________________________________________________________ -->
3261 <div class="doc_subsubsection">
3262 <a name="int_ctpop">'<tt>llvm.ctpop</tt>' Intrinsic</a>
3265 <div class="doc_text">
3269 declare int %llvm.ctpop(int <src>)
3276 The '<tt>llvm.ctpop</tt>' intrinsic counts the number of ones in a variable.
3282 The only argument is the value to be counted. The argument may be of any
3283 integer type. The return type must match the argument type.
3289 The '<tt>llvm.ctpop</tt>' intrinsic counts the 1's in a variable.
3293 <!-- _______________________________________________________________________ -->
3294 <div class="doc_subsubsection">
3295 <a name="int_ctlz">'<tt>llvm.ctlz</tt>' Intrinsic</a>
3298 <div class="doc_text">
3302 declare int %llvm.ctlz(int <src>)
3309 The '<tt>llvm.ctlz</tt>' intrinsic counts the number of leading zeros in a
3316 The only argument is the value to be counted. The argument may be of any
3317 integer type. The return type must match the argument type.
3323 The '<tt>llvm.ctlz</tt>' intrinsic counts the leading (most significant) zeros
3324 in a variable. If the src == 0 then the result is the size in bits of the type
3325 of src. For example, <tt>llvm.cttz(int 2) = 30</tt>.
3331 <!-- _______________________________________________________________________ -->
3332 <div class="doc_subsubsection">
3333 <a name="int_cttz">'<tt>llvm.cttz</tt>' Intrinsic</a>
3336 <div class="doc_text">
3340 declare int %llvm.cttz(int <src>)
3347 The '<tt>llvm.cttz</tt>' intrinsic counts the number of trailing zeros.
3353 The only argument is the value to be counted. The argument may be of any
3354 integer type. The return type must match the argument type.
3360 The '<tt>llvm.cttz</tt>' intrinsic counts the trailing (least significant) zeros
3361 in a variable. If the src == 0 then the result is the size in bits of the type
3362 of src. For example, <tt>llvm.cttz(2) = 1</tt>.
3366 <!-- ======================================================================= -->
3367 <div class="doc_subsection">
3368 <a name="int_debugger">Debugger Intrinsics</a>
3371 <div class="doc_text">
3373 The LLVM debugger intrinsics (which all start with <tt>llvm.dbg.</tt> prefix),
3374 are described in the <a
3375 href="SourceLevelDebugging.html#format_common_intrinsics">LLVM Source Level
3376 Debugging</a> document.
3381 <!-- *********************************************************************** -->
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3389 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
3390 <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a><br>
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