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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_extractelement">'<tt>extractelement</tt>' Instruction</a></li>
104 <li><a href="#i_call">'<tt>call</tt>' Instruction</a></li>
105 <li><a href="#i_vaarg">'<tt>vaarg</tt>' Instruction</a></li>
110 <li><a href="#intrinsics">Intrinsic Functions</a>
112 <li><a href="#int_varargs">Variable Argument Handling Intrinsics</a>
114 <li><a href="#i_va_start">'<tt>llvm.va_start</tt>' Intrinsic</a></li>
115 <li><a href="#i_va_end">'<tt>llvm.va_end</tt>' Intrinsic</a></li>
116 <li><a href="#i_va_copy">'<tt>llvm.va_copy</tt>' Intrinsic</a></li>
119 <li><a href="#int_gc">Accurate Garbage Collection Intrinsics</a>
121 <li><a href="#i_gcroot">'<tt>llvm.gcroot</tt>' Intrinsic</a></li>
122 <li><a href="#i_gcread">'<tt>llvm.gcread</tt>' Intrinsic</a></li>
123 <li><a href="#i_gcwrite">'<tt>llvm.gcwrite</tt>' Intrinsic</a></li>
126 <li><a href="#int_codegen">Code Generator Intrinsics</a>
128 <li><a href="#i_returnaddress">'<tt>llvm.returnaddress</tt>' Intrinsic</a></li>
129 <li><a href="#i_frameaddress">'<tt>llvm.frameaddress</tt>' Intrinsic</a></li>
130 <li><a href="#i_prefetch">'<tt>llvm.prefetch</tt>' Intrinsic</a></li>
131 <li><a href="#i_pcmarker">'<tt>llvm.pcmarker</tt>' Intrinsic</a></li>
132 <li><a href="#i_readcyclecounter"><tt>llvm.readcyclecounter</tt>' Intrinsic</a></li>
135 <li><a href="#int_os">Operating System Intrinsics</a>
137 <li><a href="#i_readport">'<tt>llvm.readport</tt>' Intrinsic</a></li>
138 <li><a href="#i_writeport">'<tt>llvm.writeport</tt>' Intrinsic</a></li>
139 <li><a href="#i_readio">'<tt>llvm.readio</tt>' Intrinsic</a></li>
140 <li><a href="#i_writeio">'<tt>llvm.writeio</tt>' Intrinsic</a></li>
142 <li><a href="#int_libc">Standard C Library Intrinsics</a>
144 <li><a href="#i_memcpy">'<tt>llvm.memcpy</tt>' Intrinsic</a></li>
145 <li><a href="#i_memmove">'<tt>llvm.memmove</tt>' Intrinsic</a></li>
146 <li><a href="#i_memset">'<tt>llvm.memset</tt>' Intrinsic</a></li>
147 <li><a href="#i_isunordered">'<tt>llvm.isunordered</tt>' Intrinsic</a></li>
148 <li><a href="#i_sqrt">'<tt>llvm.sqrt</tt>' Intrinsic</a></li>
152 <li><a href="#int_count">Bit counting Intrinsics</a>
154 <li><a href="#int_ctpop">'<tt>llvm.ctpop</tt>' Intrinsic </a></li>
155 <li><a href="#int_ctlz">'<tt>llvm.ctlz</tt>' Intrinsic </a></li>
156 <li><a href="#int_cttz">'<tt>llvm.cttz</tt>' Intrinsic </a></li>
159 <li><a href="#int_debugger">Debugger intrinsics</a></li>
164 <div class="doc_author">
165 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>
166 and <a href="mailto:vadve@cs.uiuc.edu">Vikram Adve</a></p>
169 <!-- *********************************************************************** -->
170 <div class="doc_section"> <a name="abstract">Abstract </a></div>
171 <!-- *********************************************************************** -->
173 <div class="doc_text">
174 <p>This document is a reference manual for the LLVM assembly language.
175 LLVM is an SSA based representation that provides type safety,
176 low-level operations, flexibility, and the capability of representing
177 'all' high-level languages cleanly. It is the common code
178 representation used throughout all phases of the LLVM compilation
182 <!-- *********************************************************************** -->
183 <div class="doc_section"> <a name="introduction">Introduction</a> </div>
184 <!-- *********************************************************************** -->
186 <div class="doc_text">
188 <p>The LLVM code representation is designed to be used in three
189 different forms: as an in-memory compiler IR, as an on-disk bytecode
190 representation (suitable for fast loading by a Just-In-Time compiler),
191 and as a human readable assembly language representation. This allows
192 LLVM to provide a powerful intermediate representation for efficient
193 compiler transformations and analysis, while providing a natural means
194 to debug and visualize the transformations. The three different forms
195 of LLVM are all equivalent. This document describes the human readable
196 representation and notation.</p>
198 <p>The LLVM representation aims to be light-weight and low-level
199 while being expressive, typed, and extensible at the same time. It
200 aims to be a "universal IR" of sorts, by being at a low enough level
201 that high-level ideas may be cleanly mapped to it (similar to how
202 microprocessors are "universal IR's", allowing many source languages to
203 be mapped to them). By providing type information, LLVM can be used as
204 the target of optimizations: for example, through pointer analysis, it
205 can be proven that a C automatic variable is never accessed outside of
206 the current function... allowing it to be promoted to a simple SSA
207 value instead of a memory location.</p>
211 <!-- _______________________________________________________________________ -->
212 <div class="doc_subsubsection"> <a name="wellformed">Well-Formedness</a> </div>
214 <div class="doc_text">
216 <p>It is important to note that this document describes 'well formed'
217 LLVM assembly language. There is a difference between what the parser
218 accepts and what is considered 'well formed'. For example, the
219 following instruction is syntactically okay, but not well formed:</p>
222 %x = <a href="#i_add">add</a> int 1, %x
225 <p>...because the definition of <tt>%x</tt> does not dominate all of
226 its uses. The LLVM infrastructure provides a verification pass that may
227 be used to verify that an LLVM module is well formed. This pass is
228 automatically run by the parser after parsing input assembly and by
229 the optimizer before it outputs bytecode. The violations pointed out
230 by the verifier pass indicate bugs in transformation passes or input to
233 <!-- Describe the typesetting conventions here. --> </div>
235 <!-- *********************************************************************** -->
236 <div class="doc_section"> <a name="identifiers">Identifiers</a> </div>
237 <!-- *********************************************************************** -->
239 <div class="doc_text">
241 <p>LLVM uses three different forms of identifiers, for different
245 <li>Named values are represented as a string of characters with a '%' prefix.
246 For example, %foo, %DivisionByZero, %a.really.long.identifier. The actual
247 regular expression used is '<tt>%[a-zA-Z$._][a-zA-Z$._0-9]*</tt>'.
248 Identifiers which require other characters in their names can be surrounded
249 with quotes. In this way, anything except a <tt>"</tt> character can be used
252 <li>Unnamed values are represented as an unsigned numeric value with a '%'
253 prefix. For example, %12, %2, %44.</li>
255 <li>Constants, which are described in a <a href="#constants">section about
256 constants</a>, below.</li>
259 <p>LLVM requires that values start with a '%' sign for two reasons: Compilers
260 don't need to worry about name clashes with reserved words, and the set of
261 reserved words may be expanded in the future without penalty. Additionally,
262 unnamed identifiers allow a compiler to quickly come up with a temporary
263 variable without having to avoid symbol table conflicts.</p>
265 <p>Reserved words in LLVM are very similar to reserved words in other
266 languages. There are keywords for different opcodes ('<tt><a
267 href="#i_add">add</a></tt>', '<tt><a href="#i_cast">cast</a></tt>', '<tt><a
268 href="#i_ret">ret</a></tt>', etc...), for primitive type names ('<tt><a
269 href="#t_void">void</a></tt>', '<tt><a href="#t_uint">uint</a></tt>', etc...),
270 and others. These reserved words cannot conflict with variable names, because
271 none of them start with a '%' character.</p>
273 <p>Here is an example of LLVM code to multiply the integer variable
274 '<tt>%X</tt>' by 8:</p>
279 %result = <a href="#i_mul">mul</a> uint %X, 8
282 <p>After strength reduction:</p>
285 %result = <a href="#i_shl">shl</a> uint %X, ubyte 3
288 <p>And the hard way:</p>
291 <a href="#i_add">add</a> uint %X, %X <i>; yields {uint}:%0</i>
292 <a href="#i_add">add</a> uint %0, %0 <i>; yields {uint}:%1</i>
293 %result = <a href="#i_add">add</a> uint %1, %1
296 <p>This last way of multiplying <tt>%X</tt> by 8 illustrates several
297 important lexical features of LLVM:</p>
301 <li>Comments are delimited with a '<tt>;</tt>' and go until the end of
304 <li>Unnamed temporaries are created when the result of a computation is not
305 assigned to a named value.</li>
307 <li>Unnamed temporaries are numbered sequentially</li>
311 <p>...and it also shows a convention that we follow in this document. When
312 demonstrating instructions, we will follow an instruction with a comment that
313 defines the type and name of value produced. Comments are shown in italic
318 <!-- *********************************************************************** -->
319 <div class="doc_section"> <a name="highlevel">High Level Structure</a> </div>
320 <!-- *********************************************************************** -->
322 <!-- ======================================================================= -->
323 <div class="doc_subsection"> <a name="modulestructure">Module Structure</a>
326 <div class="doc_text">
328 <p>LLVM programs are composed of "Module"s, each of which is a
329 translation unit of the input programs. Each module consists of
330 functions, global variables, and symbol table entries. Modules may be
331 combined together with the LLVM linker, which merges function (and
332 global variable) definitions, resolves forward declarations, and merges
333 symbol table entries. Here is an example of the "hello world" module:</p>
335 <pre><i>; Declare the string constant as a global constant...</i>
336 <a href="#identifiers">%.LC0</a> = <a href="#linkage_internal">internal</a> <a
337 href="#globalvars">constant</a> <a href="#t_array">[13 x sbyte]</a> c"hello world\0A\00" <i>; [13 x sbyte]*</i>
339 <i>; External declaration of the puts function</i>
340 <a href="#functionstructure">declare</a> int %puts(sbyte*) <i>; int(sbyte*)* </i>
342 <i>; Definition of main function</i>
343 int %main() { <i>; int()* </i>
344 <i>; Convert [13x sbyte]* to sbyte *...</i>
346 href="#i_getelementptr">getelementptr</a> [13 x sbyte]* %.LC0, long 0, long 0 <i>; sbyte*</i>
348 <i>; Call puts function to write out the string to stdout...</i>
350 href="#i_call">call</a> int %puts(sbyte* %cast210) <i>; int</i>
352 href="#i_ret">ret</a> int 0<br>}<br></pre>
354 <p>This example is made up of a <a href="#globalvars">global variable</a>
355 named "<tt>.LC0</tt>", an external declaration of the "<tt>puts</tt>"
356 function, and a <a href="#functionstructure">function definition</a>
357 for "<tt>main</tt>".</p>
359 <p>In general, a module is made up of a list of global values,
360 where both functions and global variables are global values. Global values are
361 represented by a pointer to a memory location (in this case, a pointer to an
362 array of char, and a pointer to a function), and have one of the following <a
363 href="#linkage">linkage types</a>.</p>
367 <!-- ======================================================================= -->
368 <div class="doc_subsection">
369 <a name="linkage">Linkage Types</a>
372 <div class="doc_text">
375 All Global Variables and Functions have one of the following types of linkage:
380 <dt><tt><b><a name="linkage_internal">internal</a></b></tt> </dt>
382 <dd>Global values with internal linkage are only directly accessible by
383 objects in the current module. In particular, linking code into a module with
384 an internal global value may cause the internal to be renamed as necessary to
385 avoid collisions. Because the symbol is internal to the module, all
386 references can be updated. This corresponds to the notion of the
387 '<tt>static</tt>' keyword in C, or the idea of "anonymous namespaces" in C++.
390 <dt><tt><b><a name="linkage_linkonce">linkonce</a></b></tt>: </dt>
392 <dd>"<tt>linkonce</tt>" linkage is similar to <tt>internal</tt> linkage, with
393 the twist that linking together two modules defining the same
394 <tt>linkonce</tt> globals will cause one of the globals to be discarded. This
395 is typically used to implement inline functions. Unreferenced
396 <tt>linkonce</tt> globals are allowed to be discarded.
399 <dt><tt><b><a name="linkage_weak">weak</a></b></tt>: </dt>
401 <dd>"<tt>weak</tt>" linkage is exactly the same as <tt>linkonce</tt> linkage,
402 except that unreferenced <tt>weak</tt> globals may not be discarded. This is
403 used to implement constructs in C such as "<tt>int X;</tt>" at global scope.
406 <dt><tt><b><a name="linkage_appending">appending</a></b></tt>: </dt>
408 <dd>"<tt>appending</tt>" linkage may only be applied to global variables of
409 pointer to array type. When two global variables with appending linkage are
410 linked together, the two global arrays are appended together. This is the
411 LLVM, typesafe, equivalent of having the system linker append together
412 "sections" with identical names when .o files are linked.
415 <dt><tt><b><a name="linkage_external">externally visible</a></b></tt>:</dt>
417 <dd>If none of the above identifiers are used, the global is externally
418 visible, meaning that it participates in linkage and can be used to resolve
419 external symbol references.
423 <p><a name="linkage_external">For example, since the "<tt>.LC0</tt>"
424 variable is defined to be internal, if another module defined a "<tt>.LC0</tt>"
425 variable and was linked with this one, one of the two would be renamed,
426 preventing a collision. Since "<tt>main</tt>" and "<tt>puts</tt>" are
427 external (i.e., lacking any linkage declarations), they are accessible
428 outside of the current module. It is illegal for a function <i>declaration</i>
429 to have any linkage type other than "externally visible".</a></p>
433 <!-- ======================================================================= -->
434 <div class="doc_subsection">
435 <a name="callingconv">Calling Conventions</a>
438 <div class="doc_text">
440 <p>LLVM <a href="#functionstructure">functions</a>, <a href="#i_call">calls</a>
441 and <a href="#i_invoke">invokes</a> can all have an optional calling convention
442 specified for the call. The calling convention of any pair of dynamic
443 caller/callee must match, or the behavior of the program is undefined. The
444 following calling conventions are supported by LLVM, and more may be added in
448 <dt><b>"<tt>ccc</tt>" - The C calling convention</b>:</dt>
450 <dd>This calling convention (the default if no other calling convention is
451 specified) matches the target C calling conventions. This calling convention
452 supports varargs function calls and tolerates some mismatch in the declared
453 prototype and implemented declaration of the function (as does normal C).
456 <dt><b>"<tt>fastcc</tt>" - The fast calling convention</b>:</dt>
458 <dd>This calling convention attempts to make calls as fast as possible
459 (e.g. by passing things in registers). This calling convention allows the
460 target to use whatever tricks it wants to produce fast code for the target,
461 without having to conform to an externally specified ABI. Implementations of
462 this convention should allow arbitrary tail call optimization to be supported.
463 This calling convention does not support varargs and requires the prototype of
464 all callees to exactly match the prototype of the function definition.
467 <dt><b>"<tt>coldcc</tt>" - The cold calling convention</b>:</dt>
469 <dd>This calling convention attempts to make code in the caller as efficient
470 as possible under the assumption that the call is not commonly executed. As
471 such, these calls often preserve all registers so that the call does not break
472 any live ranges in the caller side. This calling convention does not support
473 varargs and requires the prototype of all callees to exactly match the
474 prototype of the function definition.
477 <dt><b>"<tt>cc <<em>n</em>></tt>" - Numbered convention</b>:</dt>
479 <dd>Any calling convention may be specified by number, allowing
480 target-specific calling conventions to be used. Target specific calling
481 conventions start at 64.
485 <p>More calling conventions can be added/defined on an as-needed basis, to
486 support pascal conventions or any other well-known target-independent
491 <!-- ======================================================================= -->
492 <div class="doc_subsection">
493 <a name="globalvars">Global Variables</a>
496 <div class="doc_text">
498 <p>Global variables define regions of memory allocated at compilation time
499 instead of run-time. Global variables may optionally be initialized, may have
500 an explicit section to be placed in, and may
501 have an optional explicit alignment specified. A
502 variable may be defined as a global "constant," which indicates that the
503 contents of the variable will <b>never</b> be modified (enabling better
504 optimization, allowing the global data to be placed in the read-only section of
505 an executable, etc). Note that variables that need runtime initialization
506 cannot be marked "constant" as there is a store to the variable.</p>
509 LLVM explicitly allows <em>declarations</em> of global variables to be marked
510 constant, even if the final definition of the global is not. This capability
511 can be used to enable slightly better optimization of the program, but requires
512 the language definition to guarantee that optimizations based on the
513 'constantness' are valid for the translation units that do not include the
517 <p>As SSA values, global variables define pointer values that are in
518 scope (i.e. they dominate) all basic blocks in the program. Global
519 variables always define a pointer to their "content" type because they
520 describe a region of memory, and all memory objects in LLVM are
521 accessed through pointers.</p>
523 <p>LLVM allows an explicit section to be specified for globals. If the target
524 supports it, it will emit globals to the section specified.</p>
526 <p>An explicit alignment may be specified for a global. If not present, or if
527 the alignment is set to zero, the alignment of the global is set by the target
528 to whatever it feels convenient. If an explicit alignment is specified, the
529 global is forced to have at least that much alignment. All alignments must be
535 <!-- ======================================================================= -->
536 <div class="doc_subsection">
537 <a name="functionstructure">Functions</a>
540 <div class="doc_text">
542 <p>LLVM function definitions consist of an optional <a href="#linkage">linkage
543 type</a>, an optional <a href="#callingconv">calling convention</a>, a return
544 type, a function name, a (possibly empty) argument list, an optional section,
545 an optional alignment, an opening curly brace,
546 a list of basic blocks, and a closing curly brace. LLVM function declarations
547 are defined with the "<tt>declare</tt>" keyword, an optional <a
548 href="#callingconv">calling convention</a>, a return type, a function name,
549 a possibly empty list of arguments, and an optional alignment.</p>
551 <p>A function definition contains a list of basic blocks, forming the CFG for
552 the function. Each basic block may optionally start with a label (giving the
553 basic block a symbol table entry), contains a list of instructions, and ends
554 with a <a href="#terminators">terminator</a> instruction (such as a branch or
555 function return).</p>
557 <p>The first basic block in a program is special in two ways: it is immediately
558 executed on entrance to the function, and it is not allowed to have predecessor
559 basic blocks (i.e. there can not be any branches to the entry block of a
560 function). Because the block can have no predecessors, it also cannot have any
561 <a href="#i_phi">PHI nodes</a>.</p>
563 <p>LLVM functions are identified by their name and type signature. Hence, two
564 functions with the same name but different parameter lists or return values are
565 considered different functions, and LLVM will resolve references to each
568 <p>LLVM allows an explicit section to be specified for functions. If the target
569 supports it, it will emit functions to the section specified.</p>
571 <p>An explicit alignment may be specified for a function. If not present, or if
572 the alignment is set to zero, the alignment of the function is set by the target
573 to whatever it feels convenient. If an explicit alignment is specified, the
574 function is forced to have at least that much alignment. All alignments must be
581 <!-- *********************************************************************** -->
582 <div class="doc_section"> <a name="typesystem">Type System</a> </div>
583 <!-- *********************************************************************** -->
585 <div class="doc_text">
587 <p>The LLVM type system is one of the most important features of the
588 intermediate representation. Being typed enables a number of
589 optimizations to be performed on the IR directly, without having to do
590 extra analyses on the side before the transformation. A strong type
591 system makes it easier to read the generated code and enables novel
592 analyses and transformations that are not feasible to perform on normal
593 three address code representations.</p>
597 <!-- ======================================================================= -->
598 <div class="doc_subsection"> <a name="t_primitive">Primitive Types</a> </div>
599 <div class="doc_text">
600 <p>The primitive types are the fundamental building blocks of the LLVM
601 system. The current set of primitive types is as follows:</p>
603 <table class="layout">
608 <tr><th>Type</th><th>Description</th></tr>
609 <tr><td><tt>void</tt></td><td>No value</td></tr>
610 <tr><td><tt>ubyte</tt></td><td>Unsigned 8-bit value</td></tr>
611 <tr><td><tt>ushort</tt></td><td>Unsigned 16-bit value</td></tr>
612 <tr><td><tt>uint</tt></td><td>Unsigned 32-bit value</td></tr>
613 <tr><td><tt>ulong</tt></td><td>Unsigned 64-bit value</td></tr>
614 <tr><td><tt>float</tt></td><td>32-bit floating point value</td></tr>
615 <tr><td><tt>label</tt></td><td>Branch destination</td></tr>
622 <tr><th>Type</th><th>Description</th></tr>
623 <tr><td><tt>bool</tt></td><td>True or False value</td></tr>
624 <tr><td><tt>sbyte</tt></td><td>Signed 8-bit value</td></tr>
625 <tr><td><tt>short</tt></td><td>Signed 16-bit value</td></tr>
626 <tr><td><tt>int</tt></td><td>Signed 32-bit value</td></tr>
627 <tr><td><tt>long</tt></td><td>Signed 64-bit value</td></tr>
628 <tr><td><tt>double</tt></td><td>64-bit floating point value</td></tr>
636 <!-- _______________________________________________________________________ -->
637 <div class="doc_subsubsection"> <a name="t_classifications">Type
638 Classifications</a> </div>
639 <div class="doc_text">
640 <p>These different primitive types fall into a few useful
643 <table border="1" cellspacing="0" cellpadding="4">
645 <tr><th>Classification</th><th>Types</th></tr>
647 <td><a name="t_signed">signed</a></td>
648 <td><tt>sbyte, short, int, long, float, double</tt></td>
651 <td><a name="t_unsigned">unsigned</a></td>
652 <td><tt>ubyte, ushort, uint, ulong</tt></td>
655 <td><a name="t_integer">integer</a></td>
656 <td><tt>ubyte, sbyte, ushort, short, uint, int, ulong, long</tt></td>
659 <td><a name="t_integral">integral</a></td>
660 <td><tt>bool, ubyte, sbyte, ushort, short, uint, int, ulong, long</tt>
664 <td><a name="t_floating">floating point</a></td>
665 <td><tt>float, double</tt></td>
668 <td><a name="t_firstclass">first class</a></td>
669 <td><tt>bool, ubyte, sbyte, ushort, short, uint, int, ulong, long,<br>
670 float, double, <a href="#t_pointer">pointer</a>,
671 <a href="#t_packed">packed</a></tt></td>
676 <p>The <a href="#t_firstclass">first class</a> types are perhaps the
677 most important. Values of these types are the only ones which can be
678 produced by instructions, passed as arguments, or used as operands to
679 instructions. This means that all structures and arrays must be
680 manipulated either by pointer or by component.</p>
683 <!-- ======================================================================= -->
684 <div class="doc_subsection"> <a name="t_derived">Derived Types</a> </div>
686 <div class="doc_text">
688 <p>The real power in LLVM comes from the derived types in the system.
689 This is what allows a programmer to represent arrays, functions,
690 pointers, and other useful types. Note that these derived types may be
691 recursive: For example, it is possible to have a two dimensional array.</p>
695 <!-- _______________________________________________________________________ -->
696 <div class="doc_subsubsection"> <a name="t_array">Array Type</a> </div>
698 <div class="doc_text">
702 <p>The array type is a very simple derived type that arranges elements
703 sequentially in memory. The array type requires a size (number of
704 elements) and an underlying data type.</p>
709 [<# elements> x <elementtype>]
712 <p>The number of elements is a constant integer value; elementtype may
713 be any type with a size.</p>
716 <table class="layout">
719 <tt>[40 x int ]</tt><br/>
720 <tt>[41 x int ]</tt><br/>
721 <tt>[40 x uint]</tt><br/>
724 Array of 40 integer values.<br/>
725 Array of 41 integer values.<br/>
726 Array of 40 unsigned integer values.<br/>
730 <p>Here are some examples of multidimensional arrays:</p>
731 <table class="layout">
734 <tt>[3 x [4 x int]]</tt><br/>
735 <tt>[12 x [10 x float]]</tt><br/>
736 <tt>[2 x [3 x [4 x uint]]]</tt><br/>
739 3x4 array of integer values.<br/>
740 12x10 array of single precision floating point values.<br/>
741 2x3x4 array of unsigned integer values.<br/>
746 <p>Note that 'variable sized arrays' can be implemented in LLVM with a zero
747 length array. Normally, accesses past the end of an array are undefined in
748 LLVM (e.g. it is illegal to access the 5th element of a 3 element array).
749 As a special case, however, zero length arrays are recognized to be variable
750 length. This allows implementation of 'pascal style arrays' with the LLVM
751 type "{ int, [0 x float]}", for example.</p>
755 <!-- _______________________________________________________________________ -->
756 <div class="doc_subsubsection"> <a name="t_function">Function Type</a> </div>
757 <div class="doc_text">
759 <p>The function type can be thought of as a function signature. It
760 consists of a return type and a list of formal parameter types.
761 Function types are usually used to build virtual function tables
762 (which are structures of pointers to functions), for indirect function
763 calls, and when defining a function.</p>
765 The return type of a function type cannot be an aggregate type.
768 <pre> <returntype> (<parameter list>)<br></pre>
769 <p>...where '<tt><parameter list></tt>' is a comma-separated list of type
770 specifiers. Optionally, the parameter list may include a type <tt>...</tt>,
771 which indicates that the function takes a variable number of arguments.
772 Variable argument functions can access their arguments with the <a
773 href="#int_varargs">variable argument handling intrinsic</a> functions.</p>
775 <table class="layout">
778 <tt>int (int)</tt> <br/>
779 <tt>float (int, int *) *</tt><br/>
780 <tt>int (sbyte *, ...)</tt><br/>
783 function taking an <tt>int</tt>, returning an <tt>int</tt><br/>
784 <a href="#t_pointer">Pointer</a> to a function that takes an
785 <tt>int</tt> and a <a href="#t_pointer">pointer</a> to <tt>int</tt>,
786 returning <tt>float</tt>.<br/>
787 A vararg function that takes at least one <a href="#t_pointer">pointer</a>
788 to <tt>sbyte</tt> (signed char in C), which returns an integer. This is
789 the signature for <tt>printf</tt> in LLVM.<br/>
795 <!-- _______________________________________________________________________ -->
796 <div class="doc_subsubsection"> <a name="t_struct">Structure Type</a> </div>
797 <div class="doc_text">
799 <p>The structure type is used to represent a collection of data members
800 together in memory. The packing of the field types is defined to match
801 the ABI of the underlying processor. The elements of a structure may
802 be any type that has a size.</p>
803 <p>Structures are accessed using '<tt><a href="#i_load">load</a></tt>
804 and '<tt><a href="#i_store">store</a></tt>' by getting a pointer to a
805 field with the '<tt><a href="#i_getelementptr">getelementptr</a></tt>'
808 <pre> { <type list> }<br></pre>
810 <table class="layout">
813 <tt>{ int, int, int }</tt><br/>
814 <tt>{ float, int (int) * }</tt><br/>
817 a triple of three <tt>int</tt> values<br/>
818 A pair, where the first element is a <tt>float</tt> and the second element
819 is a <a href="#t_pointer">pointer</a> to a <a href="#t_function">function</a>
820 that takes an <tt>int</tt>, returning an <tt>int</tt>.<br/>
826 <!-- _______________________________________________________________________ -->
827 <div class="doc_subsubsection"> <a name="t_pointer">Pointer Type</a> </div>
828 <div class="doc_text">
830 <p>As in many languages, the pointer type represents a pointer or
831 reference to another object, which must live in memory.</p>
833 <pre> <type> *<br></pre>
835 <table class="layout">
838 <tt>[4x int]*</tt><br/>
839 <tt>int (int *) *</tt><br/>
842 A <a href="#t_pointer">pointer</a> to <a href="#t_array">array</a> of
843 four <tt>int</tt> values<br/>
844 A <a href="#t_pointer">pointer</a> to a <a
845 href="#t_function">function</a> that takes an <tt>int*</tt>, returning an
852 <!-- _______________________________________________________________________ -->
853 <div class="doc_subsubsection"> <a name="t_packed">Packed Type</a> </div>
854 <div class="doc_text">
858 <p>A packed type is a simple derived type that represents a vector
859 of elements. Packed types are used when multiple primitive data
860 are operated in parallel using a single instruction (SIMD).
861 A packed type requires a size (number of
862 elements) and an underlying primitive data type. Vectors must have a power
863 of two length (1, 2, 4, 8, 16 ...). Packed types are
864 considered <a href="#t_firstclass">first class</a>.</p>
869 < <# elements> x <elementtype> >
872 <p>The number of elements is a constant integer value; elementtype may
873 be any integral or floating point type.</p>
877 <table class="layout">
880 <tt><4 x int></tt><br/>
881 <tt><8 x float></tt><br/>
882 <tt><2 x uint></tt><br/>
885 Packed vector of 4 integer values.<br/>
886 Packed vector of 8 floating-point values.<br/>
887 Packed vector of 2 unsigned integer values.<br/>
893 <!-- _______________________________________________________________________ -->
894 <div class="doc_subsubsection"> <a name="t_opaque">Opaque Type</a> </div>
895 <div class="doc_text">
899 <p>Opaque types are used to represent unknown types in the system. This
900 corresponds (for example) to the C notion of a foward declared structure type.
901 In LLVM, opaque types can eventually be resolved to any type (not just a
912 <table class="layout">
925 <!-- *********************************************************************** -->
926 <div class="doc_section"> <a name="constants">Constants</a> </div>
927 <!-- *********************************************************************** -->
929 <div class="doc_text">
931 <p>LLVM has several different basic types of constants. This section describes
932 them all and their syntax.</p>
936 <!-- ======================================================================= -->
937 <div class="doc_subsection"><a name="simpleconstants">Simple Constants</a></div>
939 <div class="doc_text">
942 <dt><b>Boolean constants</b></dt>
944 <dd>The two strings '<tt>true</tt>' and '<tt>false</tt>' are both valid
945 constants of the <tt><a href="#t_primitive">bool</a></tt> type.
948 <dt><b>Integer constants</b></dt>
950 <dd>Standard integers (such as '4') are constants of the <a
951 href="#t_integer">integer</a> type. Negative numbers may be used with signed
955 <dt><b>Floating point constants</b></dt>
957 <dd>Floating point constants use standard decimal notation (e.g. 123.421),
958 exponential notation (e.g. 1.23421e+2), or a more precise hexadecimal
959 notation (see below). Floating point constants must have a <a
960 href="#t_floating">floating point</a> type. </dd>
962 <dt><b>Null pointer constants</b></dt>
964 <dd>The identifier '<tt>null</tt>' is recognized as a null pointer constant
965 and must be of <a href="#t_pointer">pointer type</a>.</dd>
969 <p>The one non-intuitive notation for constants is the optional hexadecimal form
970 of floating point constants. For example, the form '<tt>double
971 0x432ff973cafa8000</tt>' is equivalent to (but harder to read than) '<tt>double
972 4.5e+15</tt>'. The only time hexadecimal floating point constants are required
973 (and the only time that they are generated by the disassembler) is when a
974 floating point constant must be emitted but it cannot be represented as a
975 decimal floating point number. For example, NaN's, infinities, and other
976 special values are represented in their IEEE hexadecimal format so that
977 assembly and disassembly do not cause any bits to change in the constants.</p>
981 <!-- ======================================================================= -->
982 <div class="doc_subsection"><a name="aggregateconstants">Aggregate Constants</a>
985 <div class="doc_text">
986 <p>Aggregate constants arise from aggregation of simple constants
987 and smaller aggregate constants.</p>
990 <dt><b>Structure constants</b></dt>
992 <dd>Structure constants are represented with notation similar to structure
993 type definitions (a comma separated list of elements, surrounded by braces
994 (<tt>{}</tt>)). For example: "<tt>{ int 4, float 17.0, int* %G }</tt>",
995 where "<tt>%G</tt>" is declared as "<tt>%G = external global int</tt>". Structure constants
996 must have <a href="#t_struct">structure type</a>, and the number and
997 types of elements must match those specified by the type.
1000 <dt><b>Array constants</b></dt>
1002 <dd>Array constants are represented with notation similar to array type
1003 definitions (a comma separated list of elements, surrounded by square brackets
1004 (<tt>[]</tt>)). For example: "<tt>[ int 42, int 11, int 74 ]</tt>". Array
1005 constants must have <a href="#t_array">array type</a>, and the number and
1006 types of elements must match those specified by the type.
1009 <dt><b>Packed constants</b></dt>
1011 <dd>Packed constants are represented with notation similar to packed type
1012 definitions (a comma separated list of elements, surrounded by
1013 less-than/greater-than's (<tt><></tt>)). For example: "<tt>< int 42,
1014 int 11, int 74, int 100 ></tt>". Packed constants must have <a
1015 href="#t_packed">packed type</a>, and the number and types of elements must
1016 match those specified by the type.
1019 <dt><b>Zero initialization</b></dt>
1021 <dd>The string '<tt>zeroinitializer</tt>' can be used to zero initialize a
1022 value to zero of <em>any</em> type, including scalar and aggregate types.
1023 This is often used to avoid having to print large zero initializers (e.g. for
1024 large arrays) and is always exactly equivalent to using explicit zero
1031 <!-- ======================================================================= -->
1032 <div class="doc_subsection">
1033 <a name="globalconstants">Global Variable and Function Addresses</a>
1036 <div class="doc_text">
1038 <p>The addresses of <a href="#globalvars">global variables</a> and <a
1039 href="#functionstructure">functions</a> are always implicitly valid (link-time)
1040 constants. These constants are explicitly referenced when the <a
1041 href="#identifiers">identifier for the global</a> is used and always have <a
1042 href="#t_pointer">pointer</a> type. For example, the following is a legal LLVM
1048 %Z = global [2 x int*] [ int* %X, int* %Y ]
1053 <!-- ======================================================================= -->
1054 <div class="doc_subsection"><a name="undefvalues">Undefined Values</a></div>
1055 <div class="doc_text">
1056 <p>The string '<tt>undef</tt>' is recognized as a type-less constant that has
1057 no specific value. Undefined values may be of any type and be used anywhere
1058 a constant is permitted.</p>
1060 <p>Undefined values indicate to the compiler that the program is well defined
1061 no matter what value is used, giving the compiler more freedom to optimize.
1065 <!-- ======================================================================= -->
1066 <div class="doc_subsection"><a name="constantexprs">Constant Expressions</a>
1069 <div class="doc_text">
1071 <p>Constant expressions are used to allow expressions involving other constants
1072 to be used as constants. Constant expressions may be of any <a
1073 href="#t_firstclass">first class</a> type and may involve any LLVM operation
1074 that does not have side effects (e.g. load and call are not supported). The
1075 following is the syntax for constant expressions:</p>
1078 <dt><b><tt>cast ( CST to TYPE )</tt></b></dt>
1080 <dd>Cast a constant to another type.</dd>
1082 <dt><b><tt>getelementptr ( CSTPTR, IDX0, IDX1, ... )</tt></b></dt>
1084 <dd>Perform the <a href="#i_getelementptr">getelementptr operation</a> on
1085 constants. As with the <a href="#i_getelementptr">getelementptr</a>
1086 instruction, the index list may have zero or more indexes, which are required
1087 to make sense for the type of "CSTPTR".</dd>
1089 <dt><b><tt>OPCODE ( LHS, RHS )</tt></b></dt>
1091 <dd>Perform the specified operation of the LHS and RHS constants. OPCODE may
1092 be any of the <a href="#binaryops">binary</a> or <a href="#bitwiseops">bitwise
1093 binary</a> operations. The constraints on operands are the same as those for
1094 the corresponding instruction (e.g. no bitwise operations on floating point
1095 values are allowed).</dd>
1099 <!-- *********************************************************************** -->
1100 <div class="doc_section"> <a name="instref">Instruction Reference</a> </div>
1101 <!-- *********************************************************************** -->
1103 <div class="doc_text">
1105 <p>The LLVM instruction set consists of several different
1106 classifications of instructions: <a href="#terminators">terminator
1107 instructions</a>, <a href="#binaryops">binary instructions</a>,
1108 <a href="#bitwiseops">bitwise binary instructions</a>, <a
1109 href="#memoryops">memory instructions</a>, and <a href="#otherops">other
1110 instructions</a>.</p>
1114 <!-- ======================================================================= -->
1115 <div class="doc_subsection"> <a name="terminators">Terminator
1116 Instructions</a> </div>
1118 <div class="doc_text">
1120 <p>As mentioned <a href="#functionstructure">previously</a>, every
1121 basic block in a program ends with a "Terminator" instruction, which
1122 indicates which block should be executed after the current block is
1123 finished. These terminator instructions typically yield a '<tt>void</tt>'
1124 value: they produce control flow, not values (the one exception being
1125 the '<a href="#i_invoke"><tt>invoke</tt></a>' instruction).</p>
1126 <p>There are six different terminator instructions: the '<a
1127 href="#i_ret"><tt>ret</tt></a>' instruction, the '<a href="#i_br"><tt>br</tt></a>'
1128 instruction, the '<a href="#i_switch"><tt>switch</tt></a>' instruction,
1129 the '<a href="#i_invoke"><tt>invoke</tt></a>' instruction, the '<a
1130 href="#i_unwind"><tt>unwind</tt></a>' instruction, and the '<a
1131 href="#i_unreachable"><tt>unreachable</tt></a>' instruction.</p>
1135 <!-- _______________________________________________________________________ -->
1136 <div class="doc_subsubsection"> <a name="i_ret">'<tt>ret</tt>'
1137 Instruction</a> </div>
1138 <div class="doc_text">
1140 <pre> ret <type> <value> <i>; Return a value from a non-void function</i>
1141 ret void <i>; Return from void function</i>
1144 <p>The '<tt>ret</tt>' instruction is used to return control flow (and a
1145 value) from a function back to the caller.</p>
1146 <p>There are two forms of the '<tt>ret</tt>' instruction: one that
1147 returns a value and then causes control flow, and one that just causes
1148 control flow to occur.</p>
1150 <p>The '<tt>ret</tt>' instruction may return any '<a
1151 href="#t_firstclass">first class</a>' type. Notice that a function is
1152 not <a href="#wellformed">well formed</a> if there exists a '<tt>ret</tt>'
1153 instruction inside of the function that returns a value that does not
1154 match the return type of the function.</p>
1156 <p>When the '<tt>ret</tt>' instruction is executed, control flow
1157 returns back to the calling function's context. If the caller is a "<a
1158 href="#i_call"><tt>call</tt></a>" instruction, execution continues at
1159 the instruction after the call. If the caller was an "<a
1160 href="#i_invoke"><tt>invoke</tt></a>" instruction, execution continues
1161 at the beginning of the "normal" destination block. If the instruction
1162 returns a value, that value shall set the call or invoke instruction's
1165 <pre> ret int 5 <i>; Return an integer value of 5</i>
1166 ret void <i>; Return from a void function</i>
1169 <!-- _______________________________________________________________________ -->
1170 <div class="doc_subsubsection"> <a name="i_br">'<tt>br</tt>' Instruction</a> </div>
1171 <div class="doc_text">
1173 <pre> br bool <cond>, label <iftrue>, label <iffalse><br> br label <dest> <i>; Unconditional branch</i>
1176 <p>The '<tt>br</tt>' instruction is used to cause control flow to
1177 transfer to a different basic block in the current function. There are
1178 two forms of this instruction, corresponding to a conditional branch
1179 and an unconditional branch.</p>
1181 <p>The conditional branch form of the '<tt>br</tt>' instruction takes a
1182 single '<tt>bool</tt>' value and two '<tt>label</tt>' values. The
1183 unconditional form of the '<tt>br</tt>' instruction takes a single '<tt>label</tt>'
1184 value as a target.</p>
1186 <p>Upon execution of a conditional '<tt>br</tt>' instruction, the '<tt>bool</tt>'
1187 argument is evaluated. If the value is <tt>true</tt>, control flows
1188 to the '<tt>iftrue</tt>' <tt>label</tt> argument. If "cond" is <tt>false</tt>,
1189 control flows to the '<tt>iffalse</tt>' <tt>label</tt> argument.</p>
1191 <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
1192 href="#i_ret">ret</a> int 1<br>IfUnequal:<br> <a href="#i_ret">ret</a> int 0<br></pre>
1194 <!-- _______________________________________________________________________ -->
1195 <div class="doc_subsubsection">
1196 <a name="i_switch">'<tt>switch</tt>' Instruction</a>
1199 <div class="doc_text">
1203 switch <intty> <value>, label <defaultdest> [ <intty> <val>, label <dest> ... ]
1208 <p>The '<tt>switch</tt>' instruction is used to transfer control flow to one of
1209 several different places. It is a generalization of the '<tt>br</tt>'
1210 instruction, allowing a branch to occur to one of many possible
1216 <p>The '<tt>switch</tt>' instruction uses three parameters: an integer
1217 comparison value '<tt>value</tt>', a default '<tt>label</tt>' destination, and
1218 an array of pairs of comparison value constants and '<tt>label</tt>'s. The
1219 table is not allowed to contain duplicate constant entries.</p>
1223 <p>The <tt>switch</tt> instruction specifies a table of values and
1224 destinations. When the '<tt>switch</tt>' instruction is executed, this
1225 table is searched for the given value. If the value is found, control flow is
1226 transfered to the corresponding destination; otherwise, control flow is
1227 transfered to the default destination.</p>
1229 <h5>Implementation:</h5>
1231 <p>Depending on properties of the target machine and the particular
1232 <tt>switch</tt> instruction, this instruction may be code generated in different
1233 ways. For example, it could be generated as a series of chained conditional
1234 branches or with a lookup table.</p>
1239 <i>; Emulate a conditional br instruction</i>
1240 %Val = <a href="#i_cast">cast</a> bool %value to int
1241 switch int %Val, label %truedest [int 0, label %falsedest ]
1243 <i>; Emulate an unconditional br instruction</i>
1244 switch uint 0, label %dest [ ]
1246 <i>; Implement a jump table:</i>
1247 switch uint %val, label %otherwise [ uint 0, label %onzero
1248 uint 1, label %onone
1249 uint 2, label %ontwo ]
1253 <!-- _______________________________________________________________________ -->
1254 <div class="doc_subsubsection">
1255 <a name="i_invoke">'<tt>invoke</tt>' Instruction</a>
1258 <div class="doc_text">
1263 <result> = invoke [<a href="#callingconv">cconv</a>] <ptr to function ty> %<function ptr val>(<function args>)
1264 to label <normal label> except label <exception label>
1269 <p>The '<tt>invoke</tt>' instruction causes control to transfer to a specified
1270 function, with the possibility of control flow transfer to either the
1271 '<tt>normal</tt>' label or the
1272 '<tt>exception</tt>' label. If the callee function returns with the
1273 "<tt><a href="#i_ret">ret</a></tt>" instruction, control flow will return to the
1274 "normal" label. If the callee (or any indirect callees) returns with the "<a
1275 href="#i_unwind"><tt>unwind</tt></a>" instruction, control is interrupted and
1276 continued at the dynamically nearest "exception" label.</p>
1280 <p>This instruction requires several arguments:</p>
1284 The optional "cconv" marker indicates which <a href="callingconv">calling
1285 convention</a> the call should use. If none is specified, the call defaults
1286 to using C calling conventions.
1288 <li>'<tt>ptr to function ty</tt>': shall be the signature of the pointer to
1289 function value being invoked. In most cases, this is a direct function
1290 invocation, but indirect <tt>invoke</tt>s are just as possible, branching off
1291 an arbitrary pointer to function value.
1294 <li>'<tt>function ptr val</tt>': An LLVM value containing a pointer to a
1295 function to be invoked. </li>
1297 <li>'<tt>function args</tt>': argument list whose types match the function
1298 signature argument types. If the function signature indicates the function
1299 accepts a variable number of arguments, the extra arguments can be
1302 <li>'<tt>normal label</tt>': the label reached when the called function
1303 executes a '<tt><a href="#i_ret">ret</a></tt>' instruction. </li>
1305 <li>'<tt>exception label</tt>': the label reached when a callee returns with
1306 the <a href="#i_unwind"><tt>unwind</tt></a> instruction. </li>
1312 <p>This instruction is designed to operate as a standard '<tt><a
1313 href="#i_call">call</a></tt>' instruction in most regards. The primary
1314 difference is that it establishes an association with a label, which is used by
1315 the runtime library to unwind the stack.</p>
1317 <p>This instruction is used in languages with destructors to ensure that proper
1318 cleanup is performed in the case of either a <tt>longjmp</tt> or a thrown
1319 exception. Additionally, this is important for implementation of
1320 '<tt>catch</tt>' clauses in high-level languages that support them.</p>
1324 %retval = invoke int %Test(int 15) to label %Continue
1325 except label %TestCleanup <i>; {int}:retval set</i>
1326 %retval = invoke <a href="#callingconv">coldcc</a> int %Test(int 15) to label %Continue
1327 except label %TestCleanup <i>; {int}:retval set</i>
1332 <!-- _______________________________________________________________________ -->
1334 <div class="doc_subsubsection"> <a name="i_unwind">'<tt>unwind</tt>'
1335 Instruction</a> </div>
1337 <div class="doc_text">
1346 <p>The '<tt>unwind</tt>' instruction unwinds the stack, continuing control flow
1347 at the first callee in the dynamic call stack which used an <a
1348 href="#i_invoke"><tt>invoke</tt></a> instruction to perform the call. This is
1349 primarily used to implement exception handling.</p>
1353 <p>The '<tt>unwind</tt>' intrinsic causes execution of the current function to
1354 immediately halt. The dynamic call stack is then searched for the first <a
1355 href="#i_invoke"><tt>invoke</tt></a> instruction on the call stack. Once found,
1356 execution continues at the "exceptional" destination block specified by the
1357 <tt>invoke</tt> instruction. If there is no <tt>invoke</tt> instruction in the
1358 dynamic call chain, undefined behavior results.</p>
1361 <!-- _______________________________________________________________________ -->
1363 <div class="doc_subsubsection"> <a name="i_unreachable">'<tt>unreachable</tt>'
1364 Instruction</a> </div>
1366 <div class="doc_text">
1375 <p>The '<tt>unreachable</tt>' instruction has no defined semantics. This
1376 instruction is used to inform the optimizer that a particular portion of the
1377 code is not reachable. This can be used to indicate that the code after a
1378 no-return function cannot be reached, and other facts.</p>
1382 <p>The '<tt>unreachable</tt>' instruction has no defined semantics.</p>
1387 <!-- ======================================================================= -->
1388 <div class="doc_subsection"> <a name="binaryops">Binary Operations</a> </div>
1389 <div class="doc_text">
1390 <p>Binary operators are used to do most of the computation in a
1391 program. They require two operands, execute an operation on them, and
1392 produce a single value. The operands might represent
1393 multiple data, as is the case with the <a href="#t_packed">packed</a> data type.
1394 The result value of a binary operator is not
1395 necessarily the same type as its operands.</p>
1396 <p>There are several different binary operators:</p>
1398 <!-- _______________________________________________________________________ -->
1399 <div class="doc_subsubsection"> <a name="i_add">'<tt>add</tt>'
1400 Instruction</a> </div>
1401 <div class="doc_text">
1403 <pre> <result> = add <ty> <var1>, <var2> <i>; yields {ty}:result</i>
1406 <p>The '<tt>add</tt>' instruction returns the sum of its two operands.</p>
1408 <p>The two arguments to the '<tt>add</tt>' instruction must be either <a
1409 href="#t_integer">integer</a> or <a href="#t_floating">floating point</a> values.
1410 This instruction can also take <a href="#t_packed">packed</a> versions of the values.
1411 Both arguments must have identical types.</p>
1413 <p>The value produced is the integer or floating point sum of the two
1416 <pre> <result> = add int 4, %var <i>; yields {int}:result = 4 + %var</i>
1419 <!-- _______________________________________________________________________ -->
1420 <div class="doc_subsubsection"> <a name="i_sub">'<tt>sub</tt>'
1421 Instruction</a> </div>
1422 <div class="doc_text">
1424 <pre> <result> = sub <ty> <var1>, <var2> <i>; yields {ty}:result</i>
1427 <p>The '<tt>sub</tt>' instruction returns the difference of its two
1429 <p>Note that the '<tt>sub</tt>' instruction is used to represent the '<tt>neg</tt>'
1430 instruction present in most other intermediate representations.</p>
1432 <p>The two arguments to the '<tt>sub</tt>' instruction must be either <a
1433 href="#t_integer">integer</a> or <a href="#t_floating">floating point</a>
1435 This instruction can also take <a href="#t_packed">packed</a> versions of the values.
1436 Both arguments must have identical types.</p>
1438 <p>The value produced is the integer or floating point difference of
1439 the two operands.</p>
1441 <pre> <result> = sub int 4, %var <i>; yields {int}:result = 4 - %var</i>
1442 <result> = sub int 0, %val <i>; yields {int}:result = -%var</i>
1445 <!-- _______________________________________________________________________ -->
1446 <div class="doc_subsubsection"> <a name="i_mul">'<tt>mul</tt>'
1447 Instruction</a> </div>
1448 <div class="doc_text">
1450 <pre> <result> = mul <ty> <var1>, <var2> <i>; yields {ty}:result</i>
1453 <p>The '<tt>mul</tt>' instruction returns the product of its two
1456 <p>The two arguments to the '<tt>mul</tt>' instruction must be either <a
1457 href="#t_integer">integer</a> or <a href="#t_floating">floating point</a>
1459 This instruction can also take <a href="#t_packed">packed</a> versions of the values.
1460 Both arguments must have identical types.</p>
1462 <p>The value produced is the integer or floating point product of the
1464 <p>There is no signed vs unsigned multiplication. The appropriate
1465 action is taken based on the type of the operand.</p>
1467 <pre> <result> = mul int 4, %var <i>; yields {int}:result = 4 * %var</i>
1470 <!-- _______________________________________________________________________ -->
1471 <div class="doc_subsubsection"> <a name="i_div">'<tt>div</tt>'
1472 Instruction</a> </div>
1473 <div class="doc_text">
1475 <pre> <result> = div <ty> <var1>, <var2> <i>; yields {ty}:result</i>
1478 <p>The '<tt>div</tt>' instruction returns the quotient of its two
1481 <p>The two arguments to the '<tt>div</tt>' instruction must be either <a
1482 href="#t_integer">integer</a> or <a href="#t_floating">floating point</a>
1484 This instruction can also take <a href="#t_packed">packed</a> versions of the values.
1485 Both arguments must have identical types.</p>
1487 <p>The value produced is the integer or floating point quotient of the
1490 <pre> <result> = div int 4, %var <i>; yields {int}:result = 4 / %var</i>
1493 <!-- _______________________________________________________________________ -->
1494 <div class="doc_subsubsection"> <a name="i_rem">'<tt>rem</tt>'
1495 Instruction</a> </div>
1496 <div class="doc_text">
1498 <pre> <result> = rem <ty> <var1>, <var2> <i>; yields {ty}:result</i>
1501 <p>The '<tt>rem</tt>' instruction returns the remainder from the
1502 division of its two operands.</p>
1504 <p>The two arguments to the '<tt>rem</tt>' instruction must be either <a
1505 href="#t_integer">integer</a> or <a href="#t_floating">floating point</a>
1507 This instruction can also take <a href="#t_packed">packed</a> versions of the values.
1508 Both arguments must have identical types.</p>
1510 <p>This returns the <i>remainder</i> of a division (where the result
1511 has the same sign as the divisor), not the <i>modulus</i> (where the
1512 result has the same sign as the dividend) of a value. For more
1513 information about the difference, see <a
1514 href="http://mathforum.org/dr.math/problems/anne.4.28.99.html">The
1517 <pre> <result> = rem int 4, %var <i>; yields {int}:result = 4 % %var</i>
1520 <!-- _______________________________________________________________________ -->
1521 <div class="doc_subsubsection"> <a name="i_setcc">'<tt>set<i>cc</i></tt>'
1522 Instructions</a> </div>
1523 <div class="doc_text">
1525 <pre> <result> = seteq <ty> <var1>, <var2> <i>; yields {bool}:result</i>
1526 <result> = setne <ty> <var1>, <var2> <i>; yields {bool}:result</i>
1527 <result> = setlt <ty> <var1>, <var2> <i>; yields {bool}:result</i>
1528 <result> = setgt <ty> <var1>, <var2> <i>; yields {bool}:result</i>
1529 <result> = setle <ty> <var1>, <var2> <i>; yields {bool}:result</i>
1530 <result> = setge <ty> <var1>, <var2> <i>; yields {bool}:result</i>
1533 <p>The '<tt>set<i>cc</i></tt>' family of instructions returns a boolean
1534 value based on a comparison of their two operands.</p>
1536 <p>The two arguments to the '<tt>set<i>cc</i></tt>' instructions must
1537 be of <a href="#t_firstclass">first class</a> type (it is not possible
1538 to compare '<tt>label</tt>'s, '<tt>array</tt>'s, '<tt>structure</tt>'
1539 or '<tt>void</tt>' values, etc...). Both arguments must have identical
1542 <p>The '<tt>seteq</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>'
1543 value if both operands are equal.<br>
1544 The '<tt>setne</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>'
1545 value if both operands are unequal.<br>
1546 The '<tt>setlt</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>'
1547 value if the first operand is less than the second operand.<br>
1548 The '<tt>setgt</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>'
1549 value if the first operand is greater than the second operand.<br>
1550 The '<tt>setle</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>'
1551 value if the first operand is less than or equal to the second operand.<br>
1552 The '<tt>setge</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>'
1553 value if the first operand is greater than or equal to the second
1556 <pre> <result> = seteq int 4, 5 <i>; yields {bool}:result = false</i>
1557 <result> = setne float 4, 5 <i>; yields {bool}:result = true</i>
1558 <result> = setlt uint 4, 5 <i>; yields {bool}:result = true</i>
1559 <result> = setgt sbyte 4, 5 <i>; yields {bool}:result = false</i>
1560 <result> = setle sbyte 4, 5 <i>; yields {bool}:result = true</i>
1561 <result> = setge sbyte 4, 5 <i>; yields {bool}:result = false</i>
1564 <!-- ======================================================================= -->
1565 <div class="doc_subsection"> <a name="bitwiseops">Bitwise Binary
1566 Operations</a> </div>
1567 <div class="doc_text">
1568 <p>Bitwise binary operators are used to do various forms of
1569 bit-twiddling in a program. They are generally very efficient
1570 instructions and can commonly be strength reduced from other
1571 instructions. They require two operands, execute an operation on them,
1572 and produce a single value. The resulting value of the bitwise binary
1573 operators is always the same type as its first operand.</p>
1575 <!-- _______________________________________________________________________ -->
1576 <div class="doc_subsubsection"> <a name="i_and">'<tt>and</tt>'
1577 Instruction</a> </div>
1578 <div class="doc_text">
1580 <pre> <result> = and <ty> <var1>, <var2> <i>; yields {ty}:result</i>
1583 <p>The '<tt>and</tt>' instruction returns the bitwise logical and of
1584 its two operands.</p>
1586 <p>The two arguments to the '<tt>and</tt>' instruction must be <a
1587 href="#t_integral">integral</a> values. Both arguments must have
1588 identical types.</p>
1590 <p>The truth table used for the '<tt>and</tt>' instruction is:</p>
1592 <div style="align: center">
1593 <table border="1" cellspacing="0" cellpadding="4">
1624 <pre> <result> = and int 4, %var <i>; yields {int}:result = 4 & %var</i>
1625 <result> = and int 15, 40 <i>; yields {int}:result = 8</i>
1626 <result> = and int 4, 8 <i>; yields {int}:result = 0</i>
1629 <!-- _______________________________________________________________________ -->
1630 <div class="doc_subsubsection"> <a name="i_or">'<tt>or</tt>' Instruction</a> </div>
1631 <div class="doc_text">
1633 <pre> <result> = or <ty> <var1>, <var2> <i>; yields {ty}:result</i>
1636 <p>The '<tt>or</tt>' instruction returns the bitwise logical inclusive
1637 or of its two operands.</p>
1639 <p>The two arguments to the '<tt>or</tt>' instruction must be <a
1640 href="#t_integral">integral</a> values. Both arguments must have
1641 identical types.</p>
1643 <p>The truth table used for the '<tt>or</tt>' instruction is:</p>
1645 <div style="align: center">
1646 <table border="1" cellspacing="0" cellpadding="4">
1677 <pre> <result> = or int 4, %var <i>; yields {int}:result = 4 | %var</i>
1678 <result> = or int 15, 40 <i>; yields {int}:result = 47</i>
1679 <result> = or int 4, 8 <i>; yields {int}:result = 12</i>
1682 <!-- _______________________________________________________________________ -->
1683 <div class="doc_subsubsection"> <a name="i_xor">'<tt>xor</tt>'
1684 Instruction</a> </div>
1685 <div class="doc_text">
1687 <pre> <result> = xor <ty> <var1>, <var2> <i>; yields {ty}:result</i>
1690 <p>The '<tt>xor</tt>' instruction returns the bitwise logical exclusive
1691 or of its two operands. The <tt>xor</tt> is used to implement the
1692 "one's complement" operation, which is the "~" operator in C.</p>
1694 <p>The two arguments to the '<tt>xor</tt>' instruction must be <a
1695 href="#t_integral">integral</a> values. Both arguments must have
1696 identical types.</p>
1698 <p>The truth table used for the '<tt>xor</tt>' instruction is:</p>
1700 <div style="align: center">
1701 <table border="1" cellspacing="0" cellpadding="4">
1733 <pre> <result> = xor int 4, %var <i>; yields {int}:result = 4 ^ %var</i>
1734 <result> = xor int 15, 40 <i>; yields {int}:result = 39</i>
1735 <result> = xor int 4, 8 <i>; yields {int}:result = 12</i>
1736 <result> = xor int %V, -1 <i>; yields {int}:result = ~%V</i>
1739 <!-- _______________________________________________________________________ -->
1740 <div class="doc_subsubsection"> <a name="i_shl">'<tt>shl</tt>'
1741 Instruction</a> </div>
1742 <div class="doc_text">
1744 <pre> <result> = shl <ty> <var1>, ubyte <var2> <i>; yields {ty}:result</i>
1747 <p>The '<tt>shl</tt>' instruction returns the first operand shifted to
1748 the left a specified number of bits.</p>
1750 <p>The first argument to the '<tt>shl</tt>' instruction must be an <a
1751 href="#t_integer">integer</a> type. The second argument must be an '<tt>ubyte</tt>'
1754 <p>The value produced is <tt>var1</tt> * 2<sup><tt>var2</tt></sup>.</p>
1756 <pre> <result> = shl int 4, ubyte %var <i>; yields {int}:result = 4 << %var</i>
1757 <result> = shl int 4, ubyte 2 <i>; yields {int}:result = 16</i>
1758 <result> = shl int 1, ubyte 10 <i>; yields {int}:result = 1024</i>
1761 <!-- _______________________________________________________________________ -->
1762 <div class="doc_subsubsection"> <a name="i_shr">'<tt>shr</tt>'
1763 Instruction</a> </div>
1764 <div class="doc_text">
1766 <pre> <result> = shr <ty> <var1>, ubyte <var2> <i>; yields {ty}:result</i>
1769 <p>The '<tt>shr</tt>' instruction returns the first operand shifted to
1770 the right a specified number of bits.</p>
1772 <p>The first argument to the '<tt>shr</tt>' instruction must be an <a
1773 href="#t_integer">integer</a> type. The second argument must be an '<tt>ubyte</tt>'
1776 <p>If the first argument is a <a href="#t_signed">signed</a> type, the
1777 most significant bit is duplicated in the newly free'd bit positions.
1778 If the first argument is unsigned, zero bits shall fill the empty
1781 <pre> <result> = shr int 4, ubyte %var <i>; yields {int}:result = 4 >> %var</i>
1782 <result> = shr uint 4, ubyte 1 <i>; yields {uint}:result = 2</i>
1783 <result> = shr int 4, ubyte 2 <i>; yields {int}:result = 1</i>
1784 <result> = shr sbyte 4, ubyte 3 <i>; yields {sbyte}:result = 0</i>
1785 <result> = shr sbyte -2, ubyte 1 <i>; yields {sbyte}:result = -1</i>
1789 <!-- ======================================================================= -->
1790 <div class="doc_subsection">
1791 <a name="memoryops">Memory Access Operations</a>
1794 <div class="doc_text">
1796 <p>A key design point of an SSA-based representation is how it
1797 represents memory. In LLVM, no memory locations are in SSA form, which
1798 makes things very simple. This section describes how to read, write,
1799 allocate, and free memory in LLVM.</p>
1803 <!-- _______________________________________________________________________ -->
1804 <div class="doc_subsubsection">
1805 <a name="i_malloc">'<tt>malloc</tt>' Instruction</a>
1808 <div class="doc_text">
1813 <result> = malloc <type>[, uint <NumElements>][, align <alignment>] <i>; yields {type*}:result</i>
1818 <p>The '<tt>malloc</tt>' instruction allocates memory from the system
1819 heap and returns a pointer to it.</p>
1823 <p>The '<tt>malloc</tt>' instruction allocates
1824 <tt>sizeof(<type>)*NumElements</tt>
1825 bytes of memory from the operating system and returns a pointer of the
1826 appropriate type to the program. If "NumElements" is specified, it is the
1827 number of elements allocated. If an alignment is specified, the value result
1828 of the allocation is guaranteed to be aligned to at least that boundary. If
1829 not specified, or if zero, the target can choose to align the allocation on any
1830 convenient boundary.</p>
1832 <p>'<tt>type</tt>' must be a sized type.</p>
1836 <p>Memory is allocated using the system "<tt>malloc</tt>" function, and
1837 a pointer is returned.</p>
1842 %array = malloc [4 x ubyte ] <i>; yields {[%4 x ubyte]*}:array</i>
1844 %size = <a href="#i_add">add</a> uint 2, 2 <i>; yields {uint}:size = uint 4</i>
1845 %array1 = malloc ubyte, uint 4 <i>; yields {ubyte*}:array1</i>
1846 %array2 = malloc [12 x ubyte], uint %size <i>; yields {[12 x ubyte]*}:array2</i>
1847 %array3 = malloc int, uint 4, align 1024 <i>; yields {int*}:array3</i>
1848 %array4 = malloc int, align 1024 <i>; yields {int*}:array4</i>
1852 <!-- _______________________________________________________________________ -->
1853 <div class="doc_subsubsection">
1854 <a name="i_free">'<tt>free</tt>' Instruction</a>
1857 <div class="doc_text">
1862 free <type> <value> <i>; yields {void}</i>
1867 <p>The '<tt>free</tt>' instruction returns memory back to the unused
1868 memory heap to be reallocated in the future.</p>
1872 <p>'<tt>value</tt>' shall be a pointer value that points to a value
1873 that was allocated with the '<tt><a href="#i_malloc">malloc</a></tt>'
1878 <p>Access to the memory pointed to by the pointer is no longer defined
1879 after this instruction executes.</p>
1884 %array = <a href="#i_malloc">malloc</a> [4 x ubyte] <i>; yields {[4 x ubyte]*}:array</i>
1885 free [4 x ubyte]* %array
1889 <!-- _______________________________________________________________________ -->
1890 <div class="doc_subsubsection">
1891 <a name="i_alloca">'<tt>alloca</tt>' Instruction</a>
1894 <div class="doc_text">
1899 <result> = alloca <type>[, uint <NumElements>][, align <alignment>] <i>; yields {type*}:result</i>
1904 <p>The '<tt>alloca</tt>' instruction allocates memory on the current
1905 stack frame of the procedure that is live until the current function
1906 returns to its caller.</p>
1910 <p>The '<tt>alloca</tt>' instruction allocates <tt>sizeof(<type>)*NumElements</tt>
1911 bytes of memory on the runtime stack, returning a pointer of the
1912 appropriate type to the program. If "NumElements" is specified, it is the
1913 number of elements allocated. If an alignment is specified, the value result
1914 of the allocation is guaranteed to be aligned to at least that boundary. If
1915 not specified, or if zero, the target can choose to align the allocation on any
1916 convenient boundary.</p>
1918 <p>'<tt>type</tt>' may be any sized type.</p>
1922 <p>Memory is allocated; a pointer is returned. '<tt>alloca</tt>'d
1923 memory is automatically released when the function returns. The '<tt>alloca</tt>'
1924 instruction is commonly used to represent automatic variables that must
1925 have an address available. When the function returns (either with the <tt><a
1926 href="#i_ret">ret</a></tt> or <tt><a href="#i_unwind">unwind</a></tt>
1927 instructions), the memory is reclaimed.</p>
1932 %ptr = alloca int <i>; yields {int*}:ptr</i>
1933 %ptr = alloca int, uint 4 <i>; yields {int*}:ptr</i>
1934 %ptr = alloca int, uint 4, align 1024 <i>; yields {int*}:ptr</i>
1935 %ptr = alloca int, align 1024 <i>; yields {int*}:ptr</i>
1939 <!-- _______________________________________________________________________ -->
1940 <div class="doc_subsubsection"> <a name="i_load">'<tt>load</tt>'
1941 Instruction</a> </div>
1942 <div class="doc_text">
1944 <pre> <result> = load <ty>* <pointer><br> <result> = volatile load <ty>* <pointer><br></pre>
1946 <p>The '<tt>load</tt>' instruction is used to read from memory.</p>
1948 <p>The argument to the '<tt>load</tt>' instruction specifies the memory
1949 address from which to load. The pointer must point to a <a
1950 href="#t_firstclass">first class</a> type. If the <tt>load</tt> is
1951 marked as <tt>volatile</tt>, then the optimizer is not allowed to modify
1952 the number or order of execution of this <tt>load</tt> with other
1953 volatile <tt>load</tt> and <tt><a href="#i_store">store</a></tt>
1956 <p>The location of memory pointed to is loaded.</p>
1958 <pre> %ptr = <a href="#i_alloca">alloca</a> int <i>; yields {int*}:ptr</i>
1960 href="#i_store">store</a> int 3, int* %ptr <i>; yields {void}</i>
1961 %val = load int* %ptr <i>; yields {int}:val = int 3</i>
1964 <!-- _______________________________________________________________________ -->
1965 <div class="doc_subsubsection"> <a name="i_store">'<tt>store</tt>'
1966 Instruction</a> </div>
1968 <pre> store <ty> <value>, <ty>* <pointer> <i>; yields {void}</i>
1969 volatile store <ty> <value>, <ty>* <pointer> <i>; yields {void}</i>
1972 <p>The '<tt>store</tt>' instruction is used to write to memory.</p>
1974 <p>There are two arguments to the '<tt>store</tt>' instruction: a value
1975 to store and an address in which to store it. The type of the '<tt><pointer></tt>'
1976 operand must be a pointer to the type of the '<tt><value></tt>'
1977 operand. If the <tt>store</tt> is marked as <tt>volatile</tt>, then the
1978 optimizer is not allowed to modify the number or order of execution of
1979 this <tt>store</tt> with other volatile <tt>load</tt> and <tt><a
1980 href="#i_store">store</a></tt> instructions.</p>
1982 <p>The contents of memory are updated to contain '<tt><value></tt>'
1983 at the location specified by the '<tt><pointer></tt>' operand.</p>
1985 <pre> %ptr = <a href="#i_alloca">alloca</a> int <i>; yields {int*}:ptr</i>
1987 href="#i_store">store</a> int 3, int* %ptr <i>; yields {void}</i>
1988 %val = load int* %ptr <i>; yields {int}:val = int 3</i>
1990 <!-- _______________________________________________________________________ -->
1991 <div class="doc_subsubsection">
1992 <a name="i_getelementptr">'<tt>getelementptr</tt>' Instruction</a>
1995 <div class="doc_text">
1998 <result> = getelementptr <ty>* <ptrval>{, <ty> <idx>}*
2004 The '<tt>getelementptr</tt>' instruction is used to get the address of a
2005 subelement of an aggregate data structure.</p>
2009 <p>This instruction takes a list of integer constants that indicate what
2010 elements of the aggregate object to index to. The actual types of the arguments
2011 provided depend on the type of the first pointer argument. The
2012 '<tt>getelementptr</tt>' instruction is used to index down through the type
2013 levels of a structure or to a specific index in an array. When indexing into a
2014 structure, only <tt>uint</tt>
2015 integer constants are allowed. When indexing into an array or pointer,
2016 <tt>int</tt> and <tt>long</tt> indexes are allowed of any sign.</p>
2018 <p>For example, let's consider a C code fragment and how it gets
2019 compiled to LLVM:</p>
2033 int *foo(struct ST *s) {
2034 return &s[1].Z.B[5][13];
2038 <p>The LLVM code generated by the GCC frontend is:</p>
2041 %RT = type { sbyte, [10 x [20 x int]], sbyte }
2042 %ST = type { int, double, %RT }
2046 int* %foo(%ST* %s) {
2048 %reg = getelementptr %ST* %s, int 1, uint 2, uint 1, int 5, int 13
2055 <p>The index types specified for the '<tt>getelementptr</tt>' instruction depend
2056 on the pointer type that is being indexed into. <a href="#t_pointer">Pointer</a>
2057 and <a href="#t_array">array</a> types require <tt>uint</tt>, <tt>int</tt>,
2058 <tt>ulong</tt>, or <tt>long</tt> values, and <a href="#t_struct">structure</a>
2059 types require <tt>uint</tt> <b>constants</b>.</p>
2061 <p>In the example above, the first index is indexing into the '<tt>%ST*</tt>'
2062 type, which is a pointer, yielding a '<tt>%ST</tt>' = '<tt>{ int, double, %RT
2063 }</tt>' type, a structure. The second index indexes into the third element of
2064 the structure, yielding a '<tt>%RT</tt>' = '<tt>{ sbyte, [10 x [20 x int]],
2065 sbyte }</tt>' type, another structure. The third index indexes into the second
2066 element of the structure, yielding a '<tt>[10 x [20 x int]]</tt>' type, an
2067 array. The two dimensions of the array are subscripted into, yielding an
2068 '<tt>int</tt>' type. The '<tt>getelementptr</tt>' instruction returns a pointer
2069 to this element, thus computing a value of '<tt>int*</tt>' type.</p>
2071 <p>Note that it is perfectly legal to index partially through a
2072 structure, returning a pointer to an inner element. Because of this,
2073 the LLVM code for the given testcase is equivalent to:</p>
2076 int* %foo(%ST* %s) {
2077 %t1 = getelementptr %ST* %s, int 1 <i>; yields %ST*:%t1</i>
2078 %t2 = getelementptr %ST* %t1, int 0, uint 2 <i>; yields %RT*:%t2</i>
2079 %t3 = getelementptr %RT* %t2, int 0, uint 1 <i>; yields [10 x [20 x int]]*:%t3</i>
2080 %t4 = getelementptr [10 x [20 x int]]* %t3, int 0, int 5 <i>; yields [20 x int]*:%t4</i>
2081 %t5 = getelementptr [20 x int]* %t4, int 0, int 13 <i>; yields int*:%t5</i>
2086 <p>Note that it is undefined to access an array out of bounds: array and
2087 pointer indexes must always be within the defined bounds of the array type.
2088 The one exception for this rules is zero length arrays. These arrays are
2089 defined to be accessible as variable length arrays, which requires access
2090 beyond the zero'th element.</p>
2095 <i>; yields [12 x ubyte]*:aptr</i>
2096 %aptr = getelementptr {int, [12 x ubyte]}* %sptr, long 0, uint 1
2100 <!-- ======================================================================= -->
2101 <div class="doc_subsection"> <a name="otherops">Other Operations</a> </div>
2102 <div class="doc_text">
2103 <p>The instructions in this category are the "miscellaneous"
2104 instructions, which defy better classification.</p>
2106 <!-- _______________________________________________________________________ -->
2107 <div class="doc_subsubsection"> <a name="i_phi">'<tt>phi</tt>'
2108 Instruction</a> </div>
2109 <div class="doc_text">
2111 <pre> <result> = phi <ty> [ <val0>, <label0>], ...<br></pre>
2113 <p>The '<tt>phi</tt>' instruction is used to implement the φ node in
2114 the SSA graph representing the function.</p>
2116 <p>The type of the incoming values are specified with the first type
2117 field. After this, the '<tt>phi</tt>' instruction takes a list of pairs
2118 as arguments, with one pair for each predecessor basic block of the
2119 current block. Only values of <a href="#t_firstclass">first class</a>
2120 type may be used as the value arguments to the PHI node. Only labels
2121 may be used as the label arguments.</p>
2122 <p>There must be no non-phi instructions between the start of a basic
2123 block and the PHI instructions: i.e. PHI instructions must be first in
2126 <p>At runtime, the '<tt>phi</tt>' instruction logically takes on the
2127 value specified by the parameter, depending on which basic block we
2128 came from in the last <a href="#terminators">terminator</a> instruction.</p>
2130 <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>
2133 <!-- _______________________________________________________________________ -->
2134 <div class="doc_subsubsection">
2135 <a name="i_cast">'<tt>cast .. to</tt>' Instruction</a>
2138 <div class="doc_text">
2143 <result> = cast <ty> <value> to <ty2> <i>; yields ty2</i>
2149 The '<tt>cast</tt>' instruction is used as the primitive means to convert
2150 integers to floating point, change data type sizes, and break type safety (by
2158 The '<tt>cast</tt>' instruction takes a value to cast, which must be a first
2159 class value, and a type to cast it to, which must also be a <a
2160 href="#t_firstclass">first class</a> type.
2166 This instruction follows the C rules for explicit casts when determining how the
2167 data being cast must change to fit in its new container.
2171 When casting to bool, any value that would be considered true in the context of
2172 a C '<tt>if</tt>' condition is converted to the boolean '<tt>true</tt>' values,
2173 all else are '<tt>false</tt>'.
2177 When extending an integral value from a type of one signness to another (for
2178 example '<tt>sbyte</tt>' to '<tt>ulong</tt>'), the value is sign-extended if the
2179 <b>source</b> value is signed, and zero-extended if the source value is
2180 unsigned. <tt>bool</tt> values are always zero extended into either zero or
2187 %X = cast int 257 to ubyte <i>; yields ubyte:1</i>
2188 %Y = cast int 123 to bool <i>; yields bool:true</i>
2192 <!-- _______________________________________________________________________ -->
2193 <div class="doc_subsubsection">
2194 <a name="i_select">'<tt>select</tt>' Instruction</a>
2197 <div class="doc_text">
2202 <result> = select bool <cond>, <ty> <val1>, <ty> <val2> <i>; yields ty</i>
2208 The '<tt>select</tt>' instruction is used to choose one value based on a
2209 condition, without branching.
2216 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.
2222 If the boolean condition evaluates to true, the instruction returns the first
2223 value argument; otherwise, it returns the second value argument.
2229 %X = select bool true, ubyte 17, ubyte 42 <i>; yields ubyte:17</i>
2234 <!-- _______________________________________________________________________ -->
2235 <div class="doc_subsubsection">
2236 <a name="i_extractelement">'<tt>extractelement</tt>' Instruction</a>
2239 <div class="doc_text">
2244 <result> = extractelement <n x <ty>> <val>, uint <idx> <i>; yields <ty></i>
2250 The '<tt>extractelement</tt>' instruction extracts a single scalar
2251 element from a vector at a specified index.
2258 The first operand of an '<tt>extractelement</tt>' instruction is a
2259 value of <a href="#t_packed">packed</a> type. The second operand is
2260 an index indicating the position from which to extract the element.
2261 The index may be a variable.</p>
2266 The result is a scalar of the same type as the element type of
2267 <tt>val</tt>. Its value is the value at position <tt>idx</tt> of
2268 <tt>val</tt>. If <tt>idx</tt> exceeds the length of <tt>val</tt>, the
2269 results are undefined.
2275 %result = extractelement <4 x int> %vec, uint 0 <i>; yields int</i>
2280 <!-- _______________________________________________________________________ -->
2281 <div class="doc_subsubsection">
2282 <a name="i_call">'<tt>call</tt>' Instruction</a>
2285 <div class="doc_text">
2289 <result> = [tail] call [<a href="#callingconv">cconv</a>] <ty>* <fnptrval>(<param list>)
2294 <p>The '<tt>call</tt>' instruction represents a simple function call.</p>
2298 <p>This instruction requires several arguments:</p>
2302 <p>The optional "tail" marker indicates whether the callee function accesses
2303 any allocas or varargs in the caller. If the "tail" marker is present, the
2304 function call is eligible for tail call optimization. Note that calls may
2305 be marked "tail" even if they do not occur before a <a
2306 href="#i_ret"><tt>ret</tt></a> instruction.
2309 <p>The optional "cconv" marker indicates which <a href="callingconv">calling
2310 convention</a> the call should use. If none is specified, the call defaults
2311 to using C calling conventions.
2314 <p>'<tt>ty</tt>': shall be the signature of the pointer to function value
2315 being invoked. The argument types must match the types implied by this
2316 signature. This type can be omitted if the function is not varargs and
2317 if the function type does not return a pointer to a function.</p>
2320 <p>'<tt>fnptrval</tt>': An LLVM value containing a pointer to a function to
2321 be invoked. In most cases, this is a direct function invocation, but
2322 indirect <tt>call</tt>s are just as possible, calling an arbitrary pointer
2323 to function value.</p>
2326 <p>'<tt>function args</tt>': argument list whose types match the
2327 function signature argument types. All arguments must be of
2328 <a href="#t_firstclass">first class</a> type. If the function signature
2329 indicates the function accepts a variable number of arguments, the extra
2330 arguments can be specified.</p>
2336 <p>The '<tt>call</tt>' instruction is used to cause control flow to
2337 transfer to a specified function, with its incoming arguments bound to
2338 the specified values. Upon a '<tt><a href="#i_ret">ret</a></tt>'
2339 instruction in the called function, control flow continues with the
2340 instruction after the function call, and the return value of the
2341 function is bound to the result argument. This is a simpler case of
2342 the <a href="#i_invoke">invoke</a> instruction.</p>
2347 %retval = call int %test(int %argc)
2348 call int(sbyte*, ...) *%printf(sbyte* %msg, int 12, sbyte 42);
2349 %X = tail call int %foo()
2350 %Y = tail call <a href="#callingconv">fastcc</a> int %foo()
2355 <!-- _______________________________________________________________________ -->
2356 <div class="doc_subsubsection">
2357 <a name="i_vaarg">'<tt>vaarg</tt>' Instruction</a>
2360 <div class="doc_text">
2365 <resultval> = va_arg <va_list*> <arglist>, <argty>
2370 <p>The '<tt>va_arg</tt>' instruction is used to access arguments passed through
2371 the "variable argument" area of a function call. It is used to implement the
2372 <tt>va_arg</tt> macro in C.</p>
2376 <p>This instruction takes a <tt>va_list*</tt> value and the type of
2377 the argument. It returns a value of the specified argument type and
2378 increments the <tt>va_list</tt> to point to the next argument. Again, the
2379 actual type of <tt>va_list</tt> is target specific.</p>
2383 <p>The '<tt>va_arg</tt>' instruction loads an argument of the specified
2384 type from the specified <tt>va_list</tt> and causes the
2385 <tt>va_list</tt> to point to the next argument. For more information,
2386 see the variable argument handling <a href="#int_varargs">Intrinsic
2389 <p>It is legal for this instruction to be called in a function which does not
2390 take a variable number of arguments, for example, the <tt>vfprintf</tt>
2393 <p><tt>va_arg</tt> is an LLVM instruction instead of an <a
2394 href="#intrinsics">intrinsic function</a> because it takes a type as an
2399 <p>See the <a href="#int_varargs">variable argument processing</a> section.</p>
2403 <!-- *********************************************************************** -->
2404 <div class="doc_section"> <a name="intrinsics">Intrinsic Functions</a> </div>
2405 <!-- *********************************************************************** -->
2407 <div class="doc_text">
2409 <p>LLVM supports the notion of an "intrinsic function". These functions have
2410 well known names and semantics and are required to follow certain
2411 restrictions. Overall, these instructions represent an extension mechanism for
2412 the LLVM language that does not require changing all of the transformations in
2413 LLVM to add to the language (or the bytecode reader/writer, the parser,
2416 <p>Intrinsic function names must all start with an "<tt>llvm.</tt>" prefix. This
2417 prefix is reserved in LLVM for intrinsic names; thus, functions may not be named
2418 this. Intrinsic functions must always be external functions: you cannot define
2419 the body of intrinsic functions. Intrinsic functions may only be used in call
2420 or invoke instructions: it is illegal to take the address of an intrinsic
2421 function. Additionally, because intrinsic functions are part of the LLVM
2422 language, it is required that they all be documented here if any are added.</p>
2425 <p>To learn how to add an intrinsic function, please see the <a
2426 href="ExtendingLLVM.html">Extending LLVM Guide</a>.
2431 <!-- ======================================================================= -->
2432 <div class="doc_subsection">
2433 <a name="int_varargs">Variable Argument Handling Intrinsics</a>
2436 <div class="doc_text">
2438 <p>Variable argument support is defined in LLVM with the <a
2439 href="#i_vanext"><tt>vanext</tt></a> instruction and these three
2440 intrinsic functions. These functions are related to the similarly
2441 named macros defined in the <tt><stdarg.h></tt> header file.</p>
2443 <p>All of these functions operate on arguments that use a
2444 target-specific value type "<tt>va_list</tt>". The LLVM assembly
2445 language reference manual does not define what this type is, so all
2446 transformations should be prepared to handle intrinsics with any type
2449 <p>This example shows how the <a href="#i_vanext"><tt>vanext</tt></a>
2450 instruction and the variable argument handling intrinsic functions are
2454 int %test(int %X, ...) {
2455 ; Initialize variable argument processing
2457 call void %<a href="#i_va_start">llvm.va_start</a>(sbyte** %ap)
2459 ; Read a single integer argument
2460 %tmp = va_arg sbyte** %ap, int
2462 ; Demonstrate usage of llvm.va_copy and llvm.va_end
2464 call void %<a href="#i_va_copy">llvm.va_copy</a>(sbyte** %aq, sbyte** %ap)
2465 call void %<a href="#i_va_end">llvm.va_end</a>(sbyte** %aq)
2467 ; Stop processing of arguments.
2468 call void %<a href="#i_va_end">llvm.va_end</a>(sbyte** %ap)
2474 <!-- _______________________________________________________________________ -->
2475 <div class="doc_subsubsection">
2476 <a name="i_va_start">'<tt>llvm.va_start</tt>' Intrinsic</a>
2480 <div class="doc_text">
2482 <pre> declare void %llvm.va_start(<va_list>* <arglist>)<br></pre>
2484 <P>The '<tt>llvm.va_start</tt>' intrinsic initializes
2485 <tt>*<arglist></tt> for subsequent use by <tt><a
2486 href="#i_va_arg">va_arg</a></tt>.</p>
2490 <P>The argument is a pointer to a <tt>va_list</tt> element to initialize.</p>
2494 <P>The '<tt>llvm.va_start</tt>' intrinsic works just like the <tt>va_start</tt>
2495 macro available in C. In a target-dependent way, it initializes the
2496 <tt>va_list</tt> element the argument points to, so that the next call to
2497 <tt>va_arg</tt> will produce the first variable argument passed to the function.
2498 Unlike the C <tt>va_start</tt> macro, this intrinsic does not need to know the
2499 last argument of the function, the compiler can figure that out.</p>
2503 <!-- _______________________________________________________________________ -->
2504 <div class="doc_subsubsection">
2505 <a name="i_va_end">'<tt>llvm.va_end</tt>' Intrinsic</a>
2508 <div class="doc_text">
2510 <pre> declare void %llvm.va_end(<va_list*> <arglist>)<br></pre>
2512 <p>The '<tt>llvm.va_end</tt>' intrinsic destroys <tt><arglist></tt>
2513 which has been initialized previously with <tt><a href="#i_va_start">llvm.va_start</a></tt>
2514 or <tt><a href="#i_va_copy">llvm.va_copy</a></tt>.</p>
2516 <p>The argument is a <tt>va_list</tt> to destroy.</p>
2518 <p>The '<tt>llvm.va_end</tt>' intrinsic works just like the <tt>va_end</tt>
2519 macro available in C. In a target-dependent way, it destroys the <tt>va_list</tt>.
2520 Calls to <a href="#i_va_start"><tt>llvm.va_start</tt></a> and <a
2521 href="#i_va_copy"><tt>llvm.va_copy</tt></a> must be matched exactly
2522 with calls to <tt>llvm.va_end</tt>.</p>
2525 <!-- _______________________________________________________________________ -->
2526 <div class="doc_subsubsection">
2527 <a name="i_va_copy">'<tt>llvm.va_copy</tt>' Intrinsic</a>
2530 <div class="doc_text">
2535 declare void %llvm.va_copy(<va_list>* <destarglist>,
2536 <va_list>* <srcarglist>)
2541 <p>The '<tt>llvm.va_copy</tt>' intrinsic copies the current argument position from
2542 the source argument list to the destination argument list.</p>
2546 <p>The first argument is a pointer to a <tt>va_list</tt> element to initialize.
2547 The second argument is a pointer to a <tt>va_list</tt> element to copy from.</p>
2552 <p>The '<tt>llvm.va_copy</tt>' intrinsic works just like the <tt>va_copy</tt> macro
2553 available in C. In a target-dependent way, it copies the source
2554 <tt>va_list</tt> element into the destination list. This intrinsic is necessary
2555 because the <tt><a href="i_va_begin">llvm.va_begin</a></tt> intrinsic may be
2556 arbitrarily complex and require memory allocation, for example.</p>
2560 <!-- ======================================================================= -->
2561 <div class="doc_subsection">
2562 <a name="int_gc">Accurate Garbage Collection Intrinsics</a>
2565 <div class="doc_text">
2568 LLVM support for <a href="GarbageCollection.html">Accurate Garbage
2569 Collection</a> requires the implementation and generation of these intrinsics.
2570 These intrinsics allow identification of <a href="#i_gcroot">GC roots on the
2571 stack</a>, as well as garbage collector implementations that require <a
2572 href="#i_gcread">read</a> and <a href="#i_gcwrite">write</a> barriers.
2573 Front-ends for type-safe garbage collected languages should generate these
2574 intrinsics to make use of the LLVM garbage collectors. For more details, see <a
2575 href="GarbageCollection.html">Accurate Garbage Collection with LLVM</a>.
2579 <!-- _______________________________________________________________________ -->
2580 <div class="doc_subsubsection">
2581 <a name="i_gcroot">'<tt>llvm.gcroot</tt>' Intrinsic</a>
2584 <div class="doc_text">
2589 declare void %llvm.gcroot(<ty>** %ptrloc, <ty2>* %metadata)
2594 <p>The '<tt>llvm.gcroot</tt>' intrinsic declares the existence of a GC root to
2595 the code generator, and allows some metadata to be associated with it.</p>
2599 <p>The first argument specifies the address of a stack object that contains the
2600 root pointer. The second pointer (which must be either a constant or a global
2601 value address) contains the meta-data to be associated with the root.</p>
2605 <p>At runtime, a call to this intrinsics stores a null pointer into the "ptrloc"
2606 location. At compile-time, the code generator generates information to allow
2607 the runtime to find the pointer at GC safe points.
2613 <!-- _______________________________________________________________________ -->
2614 <div class="doc_subsubsection">
2615 <a name="i_gcread">'<tt>llvm.gcread</tt>' Intrinsic</a>
2618 <div class="doc_text">
2623 declare sbyte* %llvm.gcread(sbyte** %Ptr)
2628 <p>The '<tt>llvm.gcread</tt>' intrinsic identifies reads of references from heap
2629 locations, allowing garbage collector implementations that require read
2634 <p>The argument is the address to read from, which should be an address
2635 allocated from the garbage collector.</p>
2639 <p>The '<tt>llvm.gcread</tt>' intrinsic has the same semantics as a load
2640 instruction, but may be replaced with substantially more complex code by the
2641 garbage collector runtime, as needed.</p>
2646 <!-- _______________________________________________________________________ -->
2647 <div class="doc_subsubsection">
2648 <a name="i_gcwrite">'<tt>llvm.gcwrite</tt>' Intrinsic</a>
2651 <div class="doc_text">
2656 declare void %llvm.gcwrite(sbyte* %P1, sbyte** %P2)
2661 <p>The '<tt>llvm.gcwrite</tt>' intrinsic identifies writes of references to heap
2662 locations, allowing garbage collector implementations that require write
2663 barriers (such as generational or reference counting collectors).</p>
2667 <p>The first argument is the reference to store, and the second is the heap
2668 location to store to.</p>
2672 <p>The '<tt>llvm.gcwrite</tt>' intrinsic has the same semantics as a store
2673 instruction, but may be replaced with substantially more complex code by the
2674 garbage collector runtime, as needed.</p>
2680 <!-- ======================================================================= -->
2681 <div class="doc_subsection">
2682 <a name="int_codegen">Code Generator Intrinsics</a>
2685 <div class="doc_text">
2687 These intrinsics are provided by LLVM to expose special features that may only
2688 be implemented with code generator support.
2693 <!-- _______________________________________________________________________ -->
2694 <div class="doc_subsubsection">
2695 <a name="i_returnaddress">'<tt>llvm.returnaddress</tt>' Intrinsic</a>
2698 <div class="doc_text">
2702 declare void* %llvm.returnaddress(uint <level>)
2708 The '<tt>llvm.returnaddress</tt>' intrinsic returns a target-specific value
2709 indicating the return address of the current function or one of its callers.
2715 The argument to this intrinsic indicates which function to return the address
2716 for. Zero indicates the calling function, one indicates its caller, etc. The
2717 argument is <b>required</b> to be a constant integer value.
2723 The '<tt>llvm.returnaddress</tt>' intrinsic either returns a pointer indicating
2724 the return address of the specified call frame, or zero if it cannot be
2725 identified. The value returned by this intrinsic is likely to be incorrect or 0
2726 for arguments other than zero, so it should only be used for debugging purposes.
2730 Note that calling this intrinsic does not prevent function inlining or other
2731 aggressive transformations, so the value returned may not be that of the obvious
2732 source-language caller.
2737 <!-- _______________________________________________________________________ -->
2738 <div class="doc_subsubsection">
2739 <a name="i_frameaddress">'<tt>llvm.frameaddress</tt>' Intrinsic</a>
2742 <div class="doc_text">
2746 declare void* %llvm.frameaddress(uint <level>)
2752 The '<tt>llvm.frameaddress</tt>' intrinsic returns the target-specific frame
2753 pointer value for the specified stack frame.
2759 The argument to this intrinsic indicates which function to return the frame
2760 pointer for. Zero indicates the calling function, one indicates its caller,
2761 etc. The argument is <b>required</b> to be a constant integer value.
2767 The '<tt>llvm.frameaddress</tt>' intrinsic either returns a pointer indicating
2768 the frame address of the specified call frame, or zero if it cannot be
2769 identified. The value returned by this intrinsic is likely to be incorrect or 0
2770 for arguments other than zero, so it should only be used for debugging purposes.
2774 Note that calling this intrinsic does not prevent function inlining or other
2775 aggressive transformations, so the value returned may not be that of the obvious
2776 source-language caller.
2780 <!-- _______________________________________________________________________ -->
2781 <div class="doc_subsubsection">
2782 <a name="i_prefetch">'<tt>llvm.prefetch</tt>' Intrinsic</a>
2785 <div class="doc_text">
2789 declare void %llvm.prefetch(sbyte * <address>,
2790 uint <rw>, uint <locality>)
2797 The '<tt>llvm.prefetch</tt>' intrinsic is a hint to the code generator to insert
2798 a prefetch instruction if supported; otherwise, it is a noop. Prefetches have
2800 effect on the behavior of the program but can change its performance
2807 <tt>address</tt> is the address to be prefetched, <tt>rw</tt> is the specifier
2808 determining if the fetch should be for a read (0) or write (1), and
2809 <tt>locality</tt> is a temporal locality specifier ranging from (0) - no
2810 locality, to (3) - extremely local keep in cache. The <tt>rw</tt> and
2811 <tt>locality</tt> arguments must be constant integers.
2817 This intrinsic does not modify the behavior of the program. In particular,
2818 prefetches cannot trap and do not produce a value. On targets that support this
2819 intrinsic, the prefetch can provide hints to the processor cache for better
2825 <!-- _______________________________________________________________________ -->
2826 <div class="doc_subsubsection">
2827 <a name="i_pcmarker">'<tt>llvm.pcmarker</tt>' Intrinsic</a>
2830 <div class="doc_text">
2834 declare void %llvm.pcmarker( uint <id> )
2841 The '<tt>llvm.pcmarker</tt>' intrinsic is a method to export a Program Counter
2843 code to simulators and other tools. The method is target specific, but it is
2844 expected that the marker will use exported symbols to transmit the PC of the marker.
2845 The marker makes no guarantees that it will remain with any specific instruction
2846 after optimizations. It is possible that the presence of a marker will inhibit
2847 optimizations. The intended use is to be inserted after optmizations to allow
2848 correlations of simulation runs.
2854 <tt>id</tt> is a numerical id identifying the marker.
2860 This intrinsic does not modify the behavior of the program. Backends that do not
2861 support this intrinisic may ignore it.
2866 <!-- _______________________________________________________________________ -->
2867 <div class="doc_subsubsection">
2868 <a name="i_readcyclecounter">'<tt>llvm.readcyclecounter</tt>' Intrinsic</a>
2871 <div class="doc_text">
2875 declare ulong %llvm.readcyclecounter( )
2882 The '<tt>llvm.readcyclecounter</tt>' intrinsic provides access to the cycle
2883 counter register (or similar low latency, high accuracy clocks) on those targets
2884 that support it. On X86, it should map to RDTSC. On Alpha, it should map to RPCC.
2885 As the backing counters overflow quickly (on the order of 9 seconds on alpha), this
2886 should only be used for small timings.
2892 When directly supported, reading the cycle counter should not modify any memory.
2893 Implementations are allowed to either return a application specific value or a
2894 system wide value. On backends without support, this is lowered to a constant 0.
2900 <!-- ======================================================================= -->
2901 <div class="doc_subsection">
2902 <a name="int_os">Operating System Intrinsics</a>
2905 <div class="doc_text">
2907 These intrinsics are provided by LLVM to support the implementation of
2908 operating system level code.
2913 <!-- _______________________________________________________________________ -->
2914 <div class="doc_subsubsection">
2915 <a name="i_readport">'<tt>llvm.readport</tt>' Intrinsic</a>
2918 <div class="doc_text">
2922 declare <integer type> %llvm.readport (<integer type> <address>)
2928 The '<tt>llvm.readport</tt>' intrinsic reads data from the specified hardware
2935 The argument to this intrinsic indicates the hardware I/O address from which
2936 to read the data. The address is in the hardware I/O address namespace (as
2937 opposed to being a memory location for memory mapped I/O).
2943 The '<tt>llvm.readport</tt>' intrinsic reads data from the hardware I/O port
2944 specified by <i>address</i> and returns the value. The address and return
2945 value must be integers, but the size is dependent upon the platform upon which
2946 the program is code generated. For example, on x86, the address must be an
2947 unsigned 16-bit value, and the return value must be 8, 16, or 32 bits.
2952 <!-- _______________________________________________________________________ -->
2953 <div class="doc_subsubsection">
2954 <a name="i_writeport">'<tt>llvm.writeport</tt>' Intrinsic</a>
2957 <div class="doc_text">
2961 call void (<integer type>, <integer type>)*
2962 %llvm.writeport (<integer type> <value>,
2963 <integer type> <address>)
2969 The '<tt>llvm.writeport</tt>' intrinsic writes data to the specified hardware
2976 The first argument is the value to write to the I/O port.
2980 The second argument indicates the hardware I/O address to which data should be
2981 written. The address is in the hardware I/O address namespace (as opposed to
2982 being a memory location for memory mapped I/O).
2988 The '<tt>llvm.writeport</tt>' intrinsic writes <i>value</i> to the I/O port
2989 specified by <i>address</i>. The address and value must be integers, but the
2990 size is dependent upon the platform upon which the program is code generated.
2991 For example, on x86, the address must be an unsigned 16-bit value, and the
2992 value written must be 8, 16, or 32 bits in length.
2997 <!-- _______________________________________________________________________ -->
2998 <div class="doc_subsubsection">
2999 <a name="i_readio">'<tt>llvm.readio</tt>' Intrinsic</a>
3002 <div class="doc_text">
3006 declare <result> %llvm.readio (<ty> * <pointer>)
3012 The '<tt>llvm.readio</tt>' intrinsic reads data from a memory mapped I/O
3019 The argument to this intrinsic is a pointer indicating the memory address from
3020 which to read the data. The data must be a
3021 <a href="#t_firstclass">first class</a> type.
3027 The '<tt>llvm.readio</tt>' intrinsic reads data from a memory mapped I/O
3028 location specified by <i>pointer</i> and returns the value. The argument must
3029 be a pointer, and the return value must be a
3030 <a href="#t_firstclass">first class</a> type. However, certain architectures
3031 may not support I/O on all first class types. For example, 32-bit processors
3032 may only support I/O on data types that are 32 bits or less.
3036 This intrinsic enforces an in-order memory model for llvm.readio and
3037 llvm.writeio calls on machines that use dynamic scheduling. Dynamically
3038 scheduled processors may execute loads and stores out of order, re-ordering at
3039 run time accesses to memory mapped I/O registers. Using these intrinsics
3040 ensures that accesses to memory mapped I/O registers occur in program order.
3045 <!-- _______________________________________________________________________ -->
3046 <div class="doc_subsubsection">
3047 <a name="i_writeio">'<tt>llvm.writeio</tt>' Intrinsic</a>
3050 <div class="doc_text">
3054 declare void %llvm.writeio (<ty1> <value>, <ty2> * <pointer>)
3060 The '<tt>llvm.writeio</tt>' intrinsic writes data to the specified memory
3067 The first argument is the value to write to the memory mapped I/O location.
3068 The second argument is a pointer indicating the memory address to which the
3069 data should be written.
3075 The '<tt>llvm.writeio</tt>' intrinsic writes <i>value</i> to the memory mapped
3076 I/O address specified by <i>pointer</i>. The value must be a
3077 <a href="#t_firstclass">first class</a> type. However, certain architectures
3078 may not support I/O on all first class types. For example, 32-bit processors
3079 may only support I/O on data types that are 32 bits or less.
3083 This intrinsic enforces an in-order memory model for llvm.readio and
3084 llvm.writeio calls on machines that use dynamic scheduling. Dynamically
3085 scheduled processors may execute loads and stores out of order, re-ordering at
3086 run time accesses to memory mapped I/O registers. Using these intrinsics
3087 ensures that accesses to memory mapped I/O registers occur in program order.
3092 <!-- ======================================================================= -->
3093 <div class="doc_subsection">
3094 <a name="int_libc">Standard C Library Intrinsics</a>
3097 <div class="doc_text">
3099 LLVM provides intrinsics for a few important standard C library functions.
3100 These intrinsics allow source-language front-ends to pass information about the
3101 alignment of the pointer arguments to the code generator, providing opportunity
3102 for more efficient code generation.
3107 <!-- _______________________________________________________________________ -->
3108 <div class="doc_subsubsection">
3109 <a name="i_memcpy">'<tt>llvm.memcpy</tt>' Intrinsic</a>
3112 <div class="doc_text">
3116 declare void %llvm.memcpy(sbyte* <dest>, sbyte* <src>,
3117 uint <len>, uint <align>)
3123 The '<tt>llvm.memcpy</tt>' intrinsic copies a block of memory from the source
3124 location to the destination location.
3128 Note that, unlike the standard libc function, the <tt>llvm.memcpy</tt> intrinsic
3129 does not return a value, and takes an extra alignment argument.
3135 The first argument is a pointer to the destination, the second is a pointer to
3136 the source. The third argument is an (arbitrarily sized) integer argument
3137 specifying the number of bytes to copy, and the fourth argument is the alignment
3138 of the source and destination locations.
3142 If the call to this intrinisic has an alignment value that is not 0 or 1, then
3143 the caller guarantees that the size of the copy is a multiple of the alignment
3144 and that both the source and destination pointers are aligned to that boundary.
3150 The '<tt>llvm.memcpy</tt>' intrinsic copies a block of memory from the source
3151 location to the destination location, which are not allowed to overlap. It
3152 copies "len" bytes of memory over. If the argument is known to be aligned to
3153 some boundary, this can be specified as the fourth argument, otherwise it should
3159 <!-- _______________________________________________________________________ -->
3160 <div class="doc_subsubsection">
3161 <a name="i_memmove">'<tt>llvm.memmove</tt>' Intrinsic</a>
3164 <div class="doc_text">
3168 declare void %llvm.memmove(sbyte* <dest>, sbyte* <src>,
3169 uint <len>, uint <align>)
3175 The '<tt>llvm.memmove</tt>' intrinsic moves a block of memory from the source
3176 location to the destination location. It is similar to the '<tt>llvm.memcpy</tt>'
3177 intrinsic but allows the two memory locations to overlap.
3181 Note that, unlike the standard libc function, the <tt>llvm.memmove</tt> intrinsic
3182 does not return a value, and takes an extra alignment argument.
3188 The first argument is a pointer to the destination, the second is a pointer to
3189 the source. The third argument is an (arbitrarily sized) integer argument
3190 specifying the number of bytes to copy, and the fourth argument is the alignment
3191 of the source and destination locations.
3195 If the call to this intrinisic has an alignment value that is not 0 or 1, then
3196 the caller guarantees that the size of the copy is a multiple of the alignment
3197 and that both the source and destination pointers are aligned to that boundary.
3203 The '<tt>llvm.memmove</tt>' intrinsic copies a block of memory from the source
3204 location to the destination location, which may overlap. It
3205 copies "len" bytes of memory over. If the argument is known to be aligned to
3206 some boundary, this can be specified as the fourth argument, otherwise it should
3212 <!-- _______________________________________________________________________ -->
3213 <div class="doc_subsubsection">
3214 <a name="i_memset">'<tt>llvm.memset</tt>' Intrinsic</a>
3217 <div class="doc_text">
3221 declare void %llvm.memset(sbyte* <dest>, ubyte <val>,
3222 uint <len>, uint <align>)
3228 The '<tt>llvm.memset</tt>' intrinsic fills a block of memory with a particular
3233 Note that, unlike the standard libc function, the <tt>llvm.memset</tt> intrinsic
3234 does not return a value, and takes an extra alignment argument.
3240 The first argument is a pointer to the destination to fill, the second is the
3241 byte value to fill it with, the third argument is an (arbitrarily sized) integer
3242 argument specifying the number of bytes to fill, and the fourth argument is the
3243 known alignment of destination location.
3247 If the call to this intrinisic has an alignment value that is not 0 or 1, then
3248 the caller guarantees that the size of the copy is a multiple of the alignment
3249 and that the destination pointer is aligned to that boundary.
3255 The '<tt>llvm.memset</tt>' intrinsic fills "len" bytes of memory starting at the
3256 destination location. If the argument is known to be aligned to some boundary,
3257 this can be specified as the fourth argument, otherwise it should be set to 0 or
3263 <!-- _______________________________________________________________________ -->
3264 <div class="doc_subsubsection">
3265 <a name="i_isunordered">'<tt>llvm.isunordered</tt>' Intrinsic</a>
3268 <div class="doc_text">
3272 declare bool %llvm.isunordered(<float or double> Val1, <float or double> Val2)
3278 The '<tt>llvm.isunordered</tt>' intrinsic returns true if either or both of the
3279 specified floating point values is a NAN.
3285 The arguments are floating point numbers of the same type.
3291 If either or both of the arguments is a SNAN or QNAN, it returns true, otherwise
3297 <!-- _______________________________________________________________________ -->
3298 <div class="doc_subsubsection">
3299 <a name="i_sqrt">'<tt>llvm.sqrt</tt>' Intrinsic</a>
3302 <div class="doc_text">
3306 declare <float or double> %llvm.sqrt(<float or double> Val)
3312 The '<tt>llvm.sqrt</tt>' intrinsic returns the sqrt of the specified operand,
3313 returning the same value as the libm '<tt>sqrt</tt>' function would. Unlike
3314 <tt>sqrt</tt> in libm, however, <tt>llvm.sqrt</tt> has undefined behavior for
3315 negative numbers (which allows for better optimization).
3321 The argument and return value are floating point numbers of the same type.
3327 This function returns the sqrt of the specified operand if it is a positive
3328 floating point number.
3332 <!-- ======================================================================= -->
3333 <div class="doc_subsection">
3334 <a name="int_count">Bit Counting Intrinsics</a>
3337 <div class="doc_text">
3339 LLVM provides intrinsics for a few important bit counting operations.
3340 These allow efficient code generation for some algorithms.
3345 <!-- _______________________________________________________________________ -->
3346 <div class="doc_subsubsection">
3347 <a name="int_ctpop">'<tt>llvm.ctpop</tt>' Intrinsic</a>
3350 <div class="doc_text">
3354 declare int %llvm.ctpop(int <src>)
3361 The '<tt>llvm.ctpop</tt>' intrinsic counts the number of ones in a variable.
3367 The only argument is the value to be counted. The argument may be of any
3368 integer type. The return type must match the argument type.
3374 The '<tt>llvm.ctpop</tt>' intrinsic counts the 1's in a variable.
3378 <!-- _______________________________________________________________________ -->
3379 <div class="doc_subsubsection">
3380 <a name="int_ctlz">'<tt>llvm.ctlz</tt>' Intrinsic</a>
3383 <div class="doc_text">
3387 declare int %llvm.ctlz(int <src>)
3394 The '<tt>llvm.ctlz</tt>' intrinsic counts the number of leading zeros in a
3401 The only argument is the value to be counted. The argument may be of any
3402 integer type. The return type must match the argument type.
3408 The '<tt>llvm.ctlz</tt>' intrinsic counts the leading (most significant) zeros
3409 in a variable. If the src == 0 then the result is the size in bits of the type
3410 of src. For example, <tt>llvm.cttz(int 2) = 30</tt>.
3416 <!-- _______________________________________________________________________ -->
3417 <div class="doc_subsubsection">
3418 <a name="int_cttz">'<tt>llvm.cttz</tt>' Intrinsic</a>
3421 <div class="doc_text">
3425 declare int %llvm.cttz(int <src>)
3432 The '<tt>llvm.cttz</tt>' intrinsic counts the number of trailing zeros.
3438 The only argument is the value to be counted. The argument may be of any
3439 integer type. The return type must match the argument type.
3445 The '<tt>llvm.cttz</tt>' intrinsic counts the trailing (least significant) zeros
3446 in a variable. If the src == 0 then the result is the size in bits of the type
3447 of src. For example, <tt>llvm.cttz(2) = 1</tt>.
3451 <!-- ======================================================================= -->
3452 <div class="doc_subsection">
3453 <a name="int_debugger">Debugger Intrinsics</a>
3456 <div class="doc_text">
3458 The LLVM debugger intrinsics (which all start with <tt>llvm.dbg.</tt> prefix),
3459 are described in the <a
3460 href="SourceLevelDebugging.html#format_common_intrinsics">LLVM Source Level
3461 Debugging</a> document.
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3474 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
3475 <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a><br>
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