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6 <tr><td> <font size=+5 color="#EEEEFF" face="Georgia,Palatino,Times,Roman"><b>llvm Assembly Language Reference Manual</b></font></td>
10 <li><a href="#abstract">Abstract</a>
11 <li><a href="#introduction">Introduction</a>
12 <li><a href="#identifiers">Identifiers</a>
13 <li><a href="#typesystem">Type System</a>
15 <li><a href="#t_primitive">Primitive Types</a>
17 <li><a href="#t_classifications">Type Classifications</a>
19 <li><a href="#t_derived">Derived Types</a>
21 <li><a href="#t_array" >Array Type</a>
22 <li><a href="#t_function">Function Type</a>
23 <li><a href="#t_pointer">Pointer Type</a>
24 <li><a href="#t_struct" >Structure Type</a>
25 <li><a href="#t_packed" >Packed Type</a>
28 <li><a href="#highlevel">High Level Structure</a>
30 <li><a href="#modulestructure">Module Structure</a>
31 <li><a href="#globalvars">Global Variables</a>
32 <li><a href="#functionstructure">Function Structure</a>
34 <li><a href="#instref">Instruction Reference</a>
36 <li><a href="#terminators">Terminator Instructions</a>
38 <li><a href="#i_ret" >'<tt>ret</tt>' Instruction</a>
39 <li><a href="#i_br" >'<tt>br</tt>' Instruction</a>
40 <li><a href="#i_switch">'<tt>switch</tt>' Instruction</a>
41 <li><a href="#i_invoke">'<tt>invoke</tt>' Instruction</a>
43 <li><a href="#unaryops">Unary Operations</a>
45 <li><a href="#i_not" >'<tt>not</tt>' Instruction</a>
47 <li><a href="#binaryops">Binary Operations</a>
49 <li><a href="#i_add" >'<tt>add</tt>' Instruction</a>
50 <li><a href="#i_sub" >'<tt>sub</tt>' Instruction</a>
51 <li><a href="#i_mul" >'<tt>mul</tt>' Instruction</a>
52 <li><a href="#i_div" >'<tt>div</tt>' Instruction</a>
53 <li><a href="#i_rem" >'<tt>rem</tt>' Instruction</a>
54 <li><a href="#i_setcc">'<tt>set<i>cc</i></tt>' Instructions</a>
56 <li><a href="#bitwiseops">Bitwise Binary Operations</a>
58 <li><a href="#i_and">'<tt>and</tt>' Instruction</a>
59 <li><a href="#i_or" >'<tt>or</tt>' Instruction</a>
60 <li><a href="#i_xor">'<tt>xor</tt>' Instruction</a>
61 <li><a href="#i_shl">'<tt>shl</tt>' Instruction</a>
62 <li><a href="#i_shr">'<tt>shr</tt>' Instruction</a>
64 <li><a href="#memoryops">Memory Access Operations</a>
66 <li><a href="#i_malloc" >'<tt>malloc</tt>' Instruction</a>
67 <li><a href="#i_free" >'<tt>free</tt>' Instruction</a>
68 <li><a href="#i_alloca" >'<tt>alloca</tt>' Instruction</a>
69 <li><a href="#i_load" >'<tt>load</tt>' Instruction</a>
70 <li><a href="#i_store" >'<tt>store</tt>' Instruction</a>
71 <li><a href="#i_getelementptr">'<tt>getelementptr</tt>' Instruction</a>
73 <li><a href="#otherops">Other Operations</a>
75 <li><a href="#i_phi" >'<tt>phi</tt>' Instruction</a>
76 <li><a href="#i_cast">'<tt>cast .. to</tt>' Instruction</a>
77 <li><a href="#i_call" >'<tt>call</tt>' Instruction</a>
81 <li><a href="#related">Related Work</a>
86 <!-- *********************************************************************** -->
87 <p><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
88 <tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
89 <a name="abstract">Abstract
90 </b></font></td></tr></table><ul>
91 <!-- *********************************************************************** -->
94 This document is a reference manual for the LLVM assembly language. LLVM is
95 an SSA based representation that provides type safety, low level operations,
96 flexibility, and the capability of representing 'all' high level languages
97 cleanly. It is the common code representation used throughout all phases of
98 the LLVM compilation strategy.
104 <!-- *********************************************************************** -->
105 </ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
106 <tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
107 <a name="introduction">Introduction
108 </b></font></td></tr></table><ul>
109 <!-- *********************************************************************** -->
111 The LLVM code representation is designed to be used in three different forms: as
112 an in-memory compiler IR, as an on-disk bytecode representation, suitable for
113 fast loading by a dynamic compiler, and as a human readable assembly language
114 representation. This allows LLVM to provide a powerful intermediate
115 representation for efficient compiler transformations and analysis, while
116 providing a natural means to debug and visualize the transformations. The three
117 different forms of LLVM are all equivalent. This document describes the human
118 readable representation and notation.<p>
120 The LLVM representation aims to be a light weight and low level while being
121 expressive, typed, and extensible at the same time. It aims to be a "universal
122 IR" of sorts, by being at a low enough level that high level ideas may be
123 cleanly mapped to it (similar to how microprocessors are "universal IR's",
124 allowing many source languages to be mapped to them). By providing type
125 information, LLVM can be used as the target of optimizations: for example,
126 through pointer analysis, it can be proven that a C automatic variable is never
127 accessed outside of the current function... allowing it to be promoted to a
128 simple SSA value instead of a memory location.<p>
130 <!-- _______________________________________________________________________ -->
131 </ul><a name="wellformed"><h4><hr size=0>Well Formedness</h4><ul>
133 It is important to note that this document describes 'well formed' llvm assembly
134 language. There is a difference between what the parser accepts and what is
135 considered 'well formed'. For example, the following instruction is
136 syntactically okay, but not well formed:<p>
139 %x = <a href="#i_add">add</a> int 1, %x
142 ...because the definition of %x does not dominate all of its uses. The LLVM
143 infrastructure provides a verification pass that may be used to verify that an
144 LLVM module is well formed. This pass is automatically run by the parser after
145 parsing input assembly, and by the optimizer before it outputs bytecode. The
146 violations pointed out by the verifier pass indicate bugs in transformation
147 passes or input to the parser.<p>
149 <!-- Describe the typesetting conventions here. -->
152 <!-- *********************************************************************** -->
153 </ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
154 <tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
155 <a name="identifiers">Identifiers
156 </b></font></td></tr></table><ul>
157 <!-- *********************************************************************** -->
159 LLVM uses three different forms of identifiers, for different purposes:<p>
162 <li>Numeric constants are represented as you would expect: 12, -3 123.421, etc. Floating point constants have an optional hexidecimal notation.
163 <li>Named values are represented as a string of characters with a '%' prefix. For example, %foo, %DivisionByZero, %a.really.long.identifier. The actual regular expression used is '<tt>%[a-zA-Z$._][a-zA-Z$._0-9]*</tt>'.
164 <li>Unnamed values are represented as an unsigned numeric value with a '%' prefix. For example, %12, %2, %44.
167 LLVM requires the values start with a '%' sign for two reasons: Compilers don't
168 need to worry about name clashes with reserved words, and the set of reserved
169 words may be expanded in the future without penalty. Additionally, unnamed
170 identifiers allow a compiler to quickly come up with a temporary variable
171 without having to avoid symbol table conflicts.<p>
173 Reserved words in LLVM are very similar to reserved words in other languages.
174 There are keywords for different opcodes ('<tt><a href="#i_add">add</a></tt>',
175 '<tt><a href="#i_cast">cast</a></tt>', '<tt><a href="#i_ret">ret</a></tt>',
176 etc...), for primitive type names ('<tt><a href="#t_void">void</a></tt>',
177 '<tt><a href="#t_uint">uint</a></tt>', etc...), and others. These reserved
178 words cannot conflict with variable names, because none of them start with a '%'
181 Here is an example of LLVM code to multiply the integer variable '<tt>%X</tt>'
186 %result = <a href="#i_mul">mul</a> uint %X, 8
189 After strength reduction:
191 %result = <a href="#i_shl">shl</a> uint %X, ubyte 3
196 <a href="#i_add">add</a> uint %X, %X <i>; yields {uint}:%0</i>
197 <a href="#i_add">add</a> uint %0, %0 <i>; yields {uint}:%1</i>
198 %result = <a href="#i_add">add</a> uint %1, %1
201 This last way of multiplying <tt>%X</tt> by 8 illustrates several important lexical features of LLVM:<p>
204 <li>Comments are delimited with a '<tt>;</tt>' and go until the end of line.
205 <li>Unnamed temporaries are created when the result of a computation is not
206 assigned to a named value.
207 <li>Unnamed temporaries are numbered sequentially
210 ...and it also show a convention that we follow in this document. When
211 demonstrating instructions, we will follow an instruction with a comment that
212 defines the type and name of value produced. Comments are shown in italic
215 The one unintuitive notation for constants is the optional hexidecimal form of
216 floating point constants. For example, the form '<tt>double
217 0x432ff973cafa8000</tt>' is equivalent to (but harder to read than) '<tt>double
218 4.5e+15</tt>' which is also supported by the parser. The only time hexadecimal
219 floating point constants are useful (and the only time that they are generated
220 by the disassembler) is when an FP constant has to be emitted that is not
221 representable as a decimal floating point number exactly. For example, NaN's,
222 infinities, and other special cases are represented in their IEEE hexadecimal
223 format so that assembly and disassembly do not cause any bits to change in the
227 <!-- *********************************************************************** -->
228 </ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
229 <tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
230 <a name="typesystem">Type System
231 </b></font></td></tr></table><ul>
232 <!-- *********************************************************************** -->
234 The LLVM type system is one of the most important features of the intermediate
235 representation. Being typed enables a number of optimizations to be performed
236 on the IR directly, without having to do extra analyses on the side before the
237 transformation. A strong type system makes it easier to read the generated code
238 and enables novel analyses and transformations that are not feasible to perform
239 on normal three address code representations.<p>
241 <!-- The written form for the type system was heavily influenced by the
242 syntactic problems with types in the C language<sup><a
243 href="#rw_stroustrup">1</a></sup>.<p> -->
247 <!-- ======================================================================= -->
248 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
249 <tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b>
250 <a name="t_primitive">Primitive Types
251 </b></font></td></tr></table><ul>
253 The primitive types are the fundemental building blocks of the LLVM system. The
254 current set of primitive types are as follows:<p>
256 <table border=0 align=center><tr><td>
258 <table border=1 cellspacing=0 cellpadding=4 align=center>
259 <tr><td><tt>void</tt></td> <td>No value</td></tr>
260 <tr><td><tt>ubyte</tt></td> <td>Unsigned 8 bit value</td></tr>
261 <tr><td><tt>ushort</tt></td><td>Unsigned 16 bit value</td></tr>
262 <tr><td><tt>uint</tt></td> <td>Unsigned 32 bit value</td></tr>
263 <tr><td><tt>ulong</tt></td> <td>Unsigned 64 bit value</td></tr>
264 <tr><td><tt>float</tt></td> <td>32 bit floating point value</td></tr>
265 <tr><td><tt>label</tt></td> <td>Branch destination</td></tr>
270 <table border=1 cellspacing=0 cellpadding=4 align=center>
271 <tr><td><tt>bool</tt></td> <td>True or False value</td></tr>
272 <tr><td><tt>sbyte</tt></td> <td>Signed 8 bit value</td></tr>
273 <tr><td><tt>short</tt></td> <td>Signed 16 bit value</td></tr>
274 <tr><td><tt>int</tt></td> <td>Signed 32 bit value</td></tr>
275 <tr><td><tt>long</tt></td> <td>Signed 64 bit value</td></tr>
276 <tr><td><tt>double</tt></td><td>64 bit floating point value</td></tr>
279 </td></tr></table><p>
283 <!-- _______________________________________________________________________ -->
284 </ul><a name="t_classifications"><h4><hr size=0>Type Classifications</h4><ul>
286 These different primitive types fall into a few useful classifications:<p>
288 <table border=1 cellspacing=0 cellpadding=4 align=center>
289 <tr><td><a name="t_signed">signed</td> <td><tt>sbyte, short, int, long, float, double</tt></td></tr>
290 <tr><td><a name="t_unsigned">unsigned</td><td><tt>ubyte, ushort, uint, ulong</tt></td></tr>
291 <tr><td><a name="t_integral">integral</td><td><tt>ubyte, sbyte, ushort, short, uint, int, ulong, long</tt></td></tr>
292 <tr><td><a name="t_floating">floating point</td><td><tt>float, double</tt></td></tr>
293 <tr><td><a name="t_firstclass">first class</td><td><tt>bool, ubyte, sbyte, ushort, short,<br> uint, int, ulong, long, float, double, <a href="#t_pointer">pointer</a></tt></td></tr>
300 <!-- ======================================================================= -->
301 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0><tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b>
302 <a name="t_derived">Derived Types
303 </b></font></td></tr></table><ul>
305 The real power in LLVM comes from the derived types in the system. This is what
306 allows a programmer to represent arrays, functions, pointers, and other useful
307 types. Note that these derived types may be recursive: For example, it is
308 possible to have a two dimensional array.<p>
312 <!-- _______________________________________________________________________ -->
313 </ul><a name="t_array"><h4><hr size=0>Array Type</h4><ul>
317 The array type is a very simple derived type that arranges elements sequentially
318 in memory. The array type requires a size (number of elements) and an
319 underlying data type.<p>
323 [<# elements> x <elementtype>]
326 The number of elements is a constant integer value, elementtype may be any type
331 <tt>[40 x int ]</tt>: Array of 40 integer values.<br>
332 <tt>[41 x int ]</tt>: Array of 41 integer values.<br>
333 <tt>[40 x uint]</tt>: Array of 40 unsigned integer values.<p>
336 Here are some examples of multidimensional arrays:<p>
338 <table border=0 cellpadding=0 cellspacing=0>
339 <tr><td><tt>[3 x [4 x int]]</tt></td><td>: 3x4 array integer values.</td></tr>
340 <tr><td><tt>[12 x [10 x float]]</tt></td><td>: 2x10 array of single precision floating point values.</td></tr>
341 <tr><td><tt>[2 x [3 x [4 x uint]]]</tt></td><td>: 2x3x4 array of unsigned integer values.</td></tr>
346 <!-- _______________________________________________________________________ -->
347 </ul><a name="t_function"><h4><hr size=0>Function Type</h4><ul>
351 The function type can be thought of as a function signature. It consists of a
352 return type and a list of formal parameter types. Function types are usually
353 used when to build virtual function tables (which are structures of pointers to
354 functions), for indirect function calls, and when defining a function.<p>
358 <returntype> (<parameter list>)
361 Where '<tt><parameter list></tt>' is a comma seperated list of type
362 specifiers. Optionally, the parameter list may include a type <tt>...</tt>,
363 which indicates that the function takes a variable number of arguments. Note
364 that there currently is no way to define a function in LLVM that takes a
365 variable number of arguments, but it is possible to <b>call</b> a function that
370 <table border=0 cellpadding=0 cellspacing=0>
372 <tr><td><tt>int (int)</tt></td><td>: function taking an <tt>int</tt>, returning
373 an <tt>int</tt></td></tr>
375 <tr><td><tt>float (int, int *) *</tt></td><td>: <a href="#t_pointer">Pointer</a>
376 to a function that takes an <tt>int</tt> and a <a href="#t_pointer">pointer</a>
377 to <tt>int</tt>, returning <tt>float</tt>.</td></tr>
379 <tr><td><tt>int (sbyte *, ...)</tt></td><td>: A vararg function that takes at
380 least one <a href="#t_pointer">pointer</a> to <tt>sbyte</tt> (signed char in C),
381 which returns an integer. This is the signature for <tt>printf</tt> in
389 <!-- _______________________________________________________________________ -->
390 </ul><a name="t_struct"><h4><hr size=0>Structure Type</h4><ul>
394 The structure type is used to represent a collection of data members together in
395 memory. The packing of the field types is defined to match the ABI of the
396 underlying processor. The elements of a structure may be any type that has a
399 Structures are accessed using '<tt><a href="#i_load">load</a></tt> and '<tt><a
400 href="#i_store">store</a></tt>' by getting a pointer to a field with the '<tt><a
401 href="#i_getelementptr">getelementptr</a></tt>' instruction.<p>
405 { <type list> }
410 <table border=0 cellpadding=0 cellspacing=0>
412 <tr><td><tt>{ int, int, int }</tt></td><td>: a triple of three <tt>int</tt>
415 <tr><td><tt>{ float, int (int) * }</tt></td><td>: A pair, where the first
416 element is a <tt>float</tt> and the second element is a <a
417 href="#t_pointer">pointer</a> to a <a href="t_function">function</a> that takes
418 an <tt>int</tt>, returning an <tt>int</tt>.</td></tr>
423 <!-- _______________________________________________________________________ -->
424 </ul><a name="t_pointer"><h4><hr size=0>Pointer Type</h4><ul>
428 As in many languages, the pointer type represents a pointer or reference to
429 another object, which must live in memory.<p>
438 <table border=0 cellpadding=0 cellspacing=0>
440 <tr><td><tt>[4x int]*</tt></td><td>: <a href="#t_pointer">pointer</a> to <a
441 href="#t_array">array</a> of four <tt>int</tt> values</td></tr>
443 <tr><td><tt>int (int *) *</tt></td><td>: A <a href="#t_pointer">pointer</a> to a
444 <a href="t_function">function</a> that takes an <tt>int</tt>, returning an
445 <tt>int</tt>.</td></tr>
451 <!-- _______________________________________________________________________ -->
453 </ul><a name="t_packed"><h4><hr size=0>Packed Type</h4><ul>
455 Mention/decide that packed types work with saturation or not. Maybe have a packed+saturated type in addition to just a packed type.<p>
457 Packed types should be 'nonsaturated' because standard data types are not saturated. Maybe have a saturated packed type?<p>
462 <!-- *********************************************************************** -->
463 </ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
464 <tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
465 <a name="highlevel">High Level Structure
466 </b></font></td></tr></table><ul>
467 <!-- *********************************************************************** -->
470 <!-- ======================================================================= -->
471 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
472 <tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b>
473 <a name="modulestructure">Module Structure
474 </b></font></td></tr></table><ul>
476 LLVM programs are composed of "Module"s, each of which is a translation unit of
477 the input programs. Each module consists of functions, global variables, and
478 symbol table entries. Modules may be combined together with the LLVM linker,
479 which merges function (and global variable) definitions, resolves forward
480 declarations, and merges symbol table entries. Here is an example of the "hello world" module:<p>
483 <i>; Declare the string constant as a global constant...</i>
484 <a href="#identifiers">%.LC0</a> = <a href="#linkage_decl">internal</a> <a href="#globalvars">constant</a> <a href="#t_array">[13 x sbyte]</a> c"hello world\0A\00" <i>; [13 x sbyte]*</i>
486 <i>; Forward declaration of puts</i>
487 <a href="#functionstructure">declare</a> int "puts"(sbyte*) <i>; int(sbyte*)* </i>
489 <i>; Definition of main function</i>
490 int "main"() { <i>; int()* </i>
491 <i>; Convert [13x sbyte]* to sbyte *...</i>
492 %cast210 = <a href="#i_getelementptr">getelementptr</a> [13 x sbyte]* %.LC0, uint 0, uint 0 <i>; sbyte*</i>
494 <i>; Call puts function to write out the string to stdout...</i>
495 <a href="#i_call">call</a> int %puts(sbyte* %cast210) <i>; int</i>
496 <a href="#i_ret">ret</a> int 0
500 This example is made up of a <a href="#globalvars">global variable</a> named
501 "<tt>.LC0</tt>", an external declaration of the "<tt>puts</tt>" function, and a
502 <a href="#functionstructure">function definition</a> for "<tt>main</tt>".<p>
504 <a name="linkage_decl">
505 In general, a module is made up of a list of global values, where both functions
506 and global variables are global values. Global values are represented by a
507 pointer to a memory location (in this case, a pointer to an array of char, and a
508 pointer to a function), and can be either "internal" or externally accessible
509 (which corresponds to the static keyword in C, when used at global scope).<p>
511 For example, since the "<tt>.LC0</tt>" variable is defined to be internal, if
512 another module defined a "<tt>.LC0</tt>" variable and was linked with this one,
513 one of the two would be renamed, preventing a collision. Since "<tt>main</tt>"
514 and "<tt>puts</tt>" are external (i.e., lacking "<tt>internal</tt>"
515 declarations), they are accessible outside of the current module. It is illegal
516 for a function declaration to be "<tt>internal</tt>".<p>
519 <!-- ======================================================================= -->
520 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
521 <tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b>
522 <a name="globalvars">Global Variables
523 </b></font></td></tr></table><ul>
525 Global variables define regions of memory allocated at compilation time instead
526 of run-time. Global variables may optionally be initialized. A variable may
527 be defined as a global "constant", which indicates that the contents of the
528 variable will never be modified (opening options for optimization). Constants
529 must always have an initial value.<p>
531 As SSA values, global variables define pointer values that are in scope
532 (i.e. they dominate) for all basic blocks in the program. Global variables
533 always define a pointer to their "content" type because they describe a region
534 of memory, and all memory objects in LLVM are accessed through pointers.<p>
538 <!-- ======================================================================= -->
539 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
540 <tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b>
541 <a name="functionstructure">Function Structure
542 </b></font></td></tr></table><ul>
544 LLVM functions definitions are composed of a (possibly empty) argument list, an
545 opening curly brace, a list of basic blocks, and a closing curly brace. LLVM
546 function declarations are defined with the "<tt>declare</tt>" keyword, a
547 function name and a function signature.<p>
549 A function definition contains a list of basic blocks, forming the CFG for the
550 function. Each basic block may optionally start with a label (giving the basic
551 block a symbol table entry), contains a list of instructions, and ends with a <a
552 href="#terminators">terminator</a> instruction (such as a branch or function
555 The first basic block in program is special in two ways: it is immediately
556 executed on entrance to the function, and it is not allowed to have predecessor
557 basic blocks (i.e. there can not be any branches to the entry block of a
561 <!-- *********************************************************************** -->
562 </ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
563 <tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
564 <a name="instref">Instruction Reference
565 </b></font></td></tr></table><ul>
566 <!-- *********************************************************************** -->
568 The LLVM instruction set consists of several different classifications of
569 instructions: <a href="#terminators">terminator instructions</a>, a <a
570 href="#unaryops">unary instruction</a>, <a href="#binaryops">binary
571 instructions</a>, <a href="#memoryops">memory instructions</a>, and <a
572 href="#otherops">other instructions</a>.<p>
575 <!-- ======================================================================= -->
576 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
577 <tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b>
578 <a name="terminators">Terminator Instructions
579 </b></font></td></tr></table><ul>
581 As mentioned <a href="#functionstructure">previously</a>, every basic block in a
582 program ends with a "Terminator" instruction, which indicates which block should
583 be executed after the current block is finished. These terminator instructions
584 typically yield a '<tt>void</tt>' value: they produce control flow, not values
585 (the one exception being the '<a href="#i_invoke"><tt>invoke</tt></a>'
588 There are four different terminator instructions: the '<a
589 href="#i_ret"><tt>ret</tt></a>' instruction, the '<a
590 href="#i_br"><tt>br</tt></a>' instruction, the '<a
591 href="#i_switch"><tt>switch</tt></a>' instruction, and the '<a
592 href="#i_invoke"><tt>invoke</tt></a>' instruction.<p>
595 <!-- _______________________________________________________________________ -->
596 </ul><a name="i_ret"><h4><hr size=0>'<tt>ret</tt>' Instruction</h4><ul>
600 ret <type> <value> <i>; Return a value from a non-void function</i>
601 ret void <i>; Return from void function</i>
606 The '<tt>ret</tt>' instruction is used to return control flow (and a value) from
607 a function, back to the caller.<p>
609 There are two forms of the '<tt>ret</tt>' instructruction: one that returns a
610 value and then causes control flow, and one that just causes control flow to
615 The '<tt>ret</tt>' instruction may return any '<a href="#t_firstclass">first
616 class</a>' type. Notice that a function is not <a href="#wellformed">well
617 formed</a> if there exists a '<tt>ret</tt>' instruction inside of the function
618 that returns a value that does not match the return type of the function.<p>
622 When the '<tt>ret</tt>' instruction is executed, control flow returns back to
623 the calling function's context. If the instruction returns a value, that value
624 shall be propogated into the calling function's data space.<p>
628 ret int 5 <i>; Return an integer value of 5</i>
629 ret void <i>; Return from a void function</i>
633 <!-- _______________________________________________________________________ -->
634 </ul><a name="i_br"><h4><hr size=0>'<tt>br</tt>' Instruction</h4><ul>
638 br bool <cond>, label <iftrue>, label <iffalse>
639 br label <dest> <i>; Unconditional branch</i>
644 The '<tt>br</tt>' instruction is used to cause control flow to transfer to a
645 different basic block in the current function. There are two forms of this
646 instruction, corresponding to a conditional branch and an unconditional
651 The conditional branch form of the '<tt>br</tt>' instruction takes a single
652 '<tt>bool</tt>' value and two '<tt>label</tt>' values. The unconditional form
653 of the '<tt>br</tt>' instruction takes a single '<tt>label</tt>' value as a
658 Upon execution of a conditional '<tt>br</tt>' instruction, the '<tt>bool</tt>'
659 argument is evaluated. If the value is <tt>true</tt>, control flows to the
660 '<tt>iftrue</tt>' '<tt>label</tt>' argument. If "cond" is <tt>false</tt>,
661 control flows to the '<tt>iffalse</tt>' '<tt>label</tt>' argument.<p>
666 %cond = <a href="#i_setcc">seteq</a> int %a, %b
667 br bool %cond, label %IfEqual, label %IfUnequal
669 <a href="#i_ret">ret</a> int 1
671 <a href="#i_ret">ret</a> int 0
675 <!-- _______________________________________________________________________ -->
676 </ul><a name="i_switch"><h4><hr size=0>'<tt>switch</tt>' Instruction</h4><ul>
680 <i>; Definitions for lookup indirect branch</i>
681 %switchtype = type [<anysize> x { uint, label }]
683 <i>; Lookup indirect branch</i>
684 switch uint <value>, label <defaultdest>, %switchtype <switchtable>
686 <i>; Indexed indirect branch</i>
687 switch uint <idxvalue>, label <defaultdest>, [<anysize> x label] <desttable>
692 The '<tt>switch</tt>' instruction is used to transfer control flow to one of
693 several different places. It is a generalization of the '<tt>br</tt>'
694 instruction, allowing a branch to occur to one of many possible destinations.<p>
696 The '<tt>switch</tt>' statement supports two different styles of indirect
697 branching: lookup branching and indexed branching. Lookup branching is
698 generally useful if the values to switch on are spread far appart, where index
699 branching is useful if the values to switch on are generally dense.<p>
701 The two different forms of the '<tt>switch</tt>' statement are simple hints to
702 the underlying implementation. For example, the compiler may choose to
703 implement a small indirect branch table as a series of predicated comparisons:
704 if it is faster for the target architecture.<p>
708 The lookup form of the '<tt>switch</tt>' instruction uses three parameters: a
709 '<tt>uint</tt>' comparison value '<tt>value</tt>', a default '<tt>label</tt>'
710 destination, and an array of pairs of comparison value constants and
711 '<tt>label</tt>'s. The sized array must be a constant value.<p>
713 The indexed form of the '<tt>switch</tt>' instruction uses three parameters: an
714 '<tt>uint</tt>' index value, a default '<tt>label</tt>' and a sized array of
715 '<tt>label</tt>'s. The '<tt>dests</tt>' array must be a constant array.
719 The lookup style switch statement specifies a table of values and destinations.
720 When the '<tt>switch</tt>' instruction is executed, this table is searched for
721 the given value. If the value is found, the corresponding destination is
724 The index branch form simply looks up a label element directly in a table and
727 In either case, the compiler knows the static size of the array, because it is
728 provided as part of the constant values type.<p>
732 <i>; Emulate a conditional br instruction</i>
733 %Val = <a href="#i_cast">cast</a> bool %value to uint
734 switch uint %Val, label %truedest, [1 x label] [label %falsedest ]
736 <i>; Emulate an unconditional br instruction</i>
737 switch uint 0, label %dest, [ 0 x label] [ ]
739 <i>; Implement a jump table:</i>
740 switch uint %val, label %otherwise, [3 x label] [ label %onzero,
748 <!-- _______________________________________________________________________ -->
749 </ul><a name="i_invoke"><h4><hr size=0>'<tt>invoke</tt>' Instruction</h4><ul>
753 <result> = invoke <ptr to function ty> %<function ptr val>(<function args>)
754 to label <normal label> except label <exception label>
759 The '<tt>invoke</tt>' instruction is used to cause control flow to transfer to a
760 specified function, with the possibility of control flow transfer to either the
761 '<tt>normal label</tt>' label or the '<tt>exception label</tt>'. The '<tt><a
762 href="#i_call">call</a></tt>' instruction is closely related, but guarantees
763 that control flow either never returns from the called function, or that it
764 returns to the instruction following the '<tt><a href="#i_call">call</a></tt>'
769 This instruction requires several arguments:<p>
772 <li>'<tt>ptr to function ty</tt>': shall be the signature of the pointer to
773 function value being invoked. In most cases, this is a direct function
774 invocation, but indirect <tt>invoke</tt>'s are just as possible, branching off
775 an arbitrary pointer to function value.<p>
777 <li>'<tt>function ptr val</tt>': An LLVM value containing a pointer to a
778 function to be invoked.
780 <li>'<tt>function args</tt>': argument list whose types match the function
781 signature argument types. If the function signature indicates the function
782 accepts a variable number of arguments, the extra arguments can be specified.
784 <li>'<tt>normal label</tt>': the label reached when the called function executes
785 a '<tt><a href="#i_ret">ret</a></tt>' instruction.
787 <li>'<tt>exception label</tt>': the label reached when an exception is thrown.
792 This instruction is designed to operate as a standard '<tt><a
793 href="#i_call">call</a></tt>' instruction in most regards. The primary
794 difference is that it associates a label with the function invocation that may
795 be accessed via the runtime library provided by the execution environment. This
796 instruction is used in languages with destructors to ensure that proper cleanup
797 is performed in the case of either a <tt>longjmp</tt> or a thrown exception.
798 Additionally, this is important for implementation of '<tt>catch</tt>' clauses
799 in high-level languages that support them.<p>
801 <!-- For a more comprehensive explanation of how this instruction is used, look in the llvm/docs/2001-05-18-ExceptionHandling.txt document.<p> -->
805 %retval = invoke int %Test(int 15)
806 to label %Continue except label %TestCleanup <i>; {int}:retval set</i>
811 <!-- ======================================================================= -->
812 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
813 <tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b>
814 <a name="unaryops">Unary Operations
815 </b></font></td></tr></table><ul>
817 Unary operators are used to do a simple operation to a single value.<p>
819 There is only one unary operator: the '<a href="#i_not"><tt>not</tt></a>' instruction.<p>
822 <!-- _______________________________________________________________________ -->
823 </ul><a name="i_not"><h4><hr size=0>'<tt>not</tt>' Instruction</h4><ul>
827 <result> = not <ty> <var> <i>; yields {ty}:result</i>
831 The '<tt>not</tt>' instruction returns the bitwise complement of its operand.<p>
834 The single argument to '<tt>not</tt>' must be of of <a href="#t_integral">integral</a> or bool type.<p>
837 <h5>Semantics:</h5> The '<tt>not</tt>' instruction returns the bitwise
838 complement (AKA ones complement) of an <a href="#t_integral">integral</a>
842 <result> = xor bool true, <var> <i>; yields {bool}:result</i>
847 %x = not int 1 <i>; {int}:x is now equal to -2</i>
848 %x = not bool true <i>; {bool}:x is now equal to false</i>
853 <!-- ======================================================================= -->
854 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0><tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b>
855 <a name="binaryops">Binary Operations
856 </b></font></td></tr></table><ul>
858 Binary operators are used to do most of the computation in a program. They
859 require two operands, execute an operation on them, and produce a single value.
860 The result value of a binary operator is not neccesarily the same type as its
863 There are several different binary operators:<p>
866 <!-- _______________________________________________________________________ -->
867 </ul><a name="i_add"><h4><hr size=0>'<tt>add</tt>' Instruction</h4><ul>
871 <result> = add <ty> <var1>, <var2> <i>; yields {ty}:result</i>
875 The '<tt>add</tt>' instruction returns the sum of its two operands.<p>
878 The two arguments to the '<tt>add</tt>' instruction must be either <a href="#t_integral">integral</a> or <a href="#t_floating">floating point</a> values. Both arguments must have identical types.<p>
882 The value produced is the integral or floating point sum of the two operands.<p>
886 <result> = add int 4, %var <i>; yields {int}:result = 4 + %var</i>
890 <!-- _______________________________________________________________________ -->
891 </ul><a name="i_sub"><h4><hr size=0>'<tt>sub</tt>' Instruction</h4><ul>
895 <result> = sub <ty> <var1>, <var2> <i>; yields {ty}:result</i>
900 The '<tt>sub</tt>' instruction returns the difference of its two operands.<p>
902 Note that the '<tt>sub</tt>' instruction is used to represent the '<tt>neg</tt>'
903 instruction present in most other intermediate representations.<p>
907 The two arguments to the '<tt>sub</tt>' instruction must be either <a
908 href="#t_integral">integral</a> or <a href="#t_floating">floating point</a>
909 values. Both arguments must have identical types.<p>
913 The value produced is the integral or floating point difference of the two
918 <result> = sub int 4, %var <i>; yields {int}:result = 4 - %var</i>
919 <result> = sub int 0, %val <i>; yields {int}:result = -%var</i>
922 <!-- _______________________________________________________________________ -->
923 </ul><a name="i_mul"><h4><hr size=0>'<tt>mul</tt>' Instruction</h4><ul>
927 <result> = mul <ty> <var1>, <var2> <i>; yields {ty}:result</i>
931 The '<tt>mul</tt>' instruction returns the product of its two operands.<p>
934 The two arguments to the '<tt>mul</tt>' instruction must be either <a href="#t_integral">integral</a> or <a href="#t_floating">floating point</a> values. Both arguments must have identical types.<p>
938 The value produced is the integral or floating point product of the two
941 There is no signed vs unsigned multiplication. The appropriate action is taken
942 based on the type of the operand. <p>
947 <result> = mul int 4, %var <i>; yields {int}:result = 4 * %var</i>
951 <!-- _______________________________________________________________________ -->
952 </ul><a name="i_div"><h4><hr size=0>'<tt>div</tt>' Instruction</h4><ul>
956 <result> = div <ty> <var1>, <var2> <i>; yields {ty}:result</i>
961 The '<tt>div</tt>' instruction returns the quotient of its two operands.<p>
965 The two arguments to the '<tt>div</tt>' instruction must be either <a
966 href="#t_integral">integral</a> or <a href="#t_floating">floating point</a>
967 values. Both arguments must have identical types.<p>
971 The value produced is the integral or floating point quotient of the two
976 <result> = div int 4, %var <i>; yields {int}:result = 4 / %var</i>
980 <!-- _______________________________________________________________________ -->
981 </ul><a name="i_rem"><h4><hr size=0>'<tt>rem</tt>' Instruction</h4><ul>
985 <result> = rem <ty> <var1>, <var2> <i>; yields {ty}:result</i>
989 The '<tt>rem</tt>' instruction returns the remainder from the division of its two operands.<p>
992 The two arguments to the '<tt>rem</tt>' instruction must be either <a href="#t_integral">integral</a> or <a href="#t_floating">floating point</a> values. Both arguments must have identical types.<p>
996 This returns the <i>remainder</i> of a division (where the result has the same
997 sign as the divisor), not the <i>modulus</i> (where the result has the same sign
998 as the dividend) of a value. For more information about the difference, see: <a
999 href="http://mathforum.org/dr.math/problems/anne.4.28.99.html">The Math
1004 <result> = rem int 4, %var <i>; yields {int}:result = 4 % %var</i>
1008 <!-- _______________________________________________________________________ -->
1009 </ul><a name="i_setcc"><h4><hr size=0>'<tt>set<i>cc</i></tt>' Instructions</h4><ul>
1013 <result> = seteq <ty> <var1>, <var2> <i>; yields {bool}:result</i>
1014 <result> = setne <ty> <var1>, <var2> <i>; yields {bool}:result</i>
1015 <result> = setlt <ty> <var1>, <var2> <i>; yields {bool}:result</i>
1016 <result> = setgt <ty> <var1>, <var2> <i>; yields {bool}:result</i>
1017 <result> = setle <ty> <var1>, <var2> <i>; yields {bool}:result</i>
1018 <result> = setge <ty> <var1>, <var2> <i>; yields {bool}:result</i>
1021 <h5>Overview:</h5> The '<tt>set<i>cc</i></tt>' family of instructions returns a
1022 boolean value based on a comparison of their two operands.<p>
1024 <h5>Arguments:</h5> The two arguments to the '<tt>set<i>cc</i></tt>'
1025 instructions must be of <a href="#t_firstclass">first class</a> or <a
1026 href="#t_pointer">pointer</a> type (it is not possible to compare
1027 '<tt>label</tt>'s, '<tt>array</tt>'s, '<tt>structure</tt>' or '<tt>void</tt>'
1028 values, etc...). Both arguments must have identical types.<p>
1030 The '<tt>setlt</tt>', '<tt>setgt</tt>', '<tt>setle</tt>', and '<tt>setge</tt>'
1031 instructions do not operate on '<tt>bool</tt>' typed arguments.<p>
1035 The '<tt>seteq</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>' value if
1036 both operands are equal.<br>
1038 The '<tt>setne</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>' value if
1039 both operands are unequal.<br>
1041 The '<tt>setlt</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>' value if
1042 the first operand is less than the second operand.<br>
1044 The '<tt>setgt</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>' value if
1045 the first operand is greater than the second operand.<br>
1047 The '<tt>setle</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>' value if
1048 the first operand is less than or equal to the second operand.<br>
1050 The '<tt>setge</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>' value if
1051 the first operand is greater than or equal to the second operand.<p>
1055 <result> = seteq int 4, 5 <i>; yields {bool}:result = false</i>
1056 <result> = setne float 4, 5 <i>; yields {bool}:result = true</i>
1057 <result> = setlt uint 4, 5 <i>; yields {bool}:result = true</i>
1058 <result> = setgt sbyte 4, 5 <i>; yields {bool}:result = false</i>
1059 <result> = setle sbyte 4, 5 <i>; yields {bool}:result = true</i>
1060 <result> = setge sbyte 4, 5 <i>; yields {bool}:result = false</i>
1065 <!-- ======================================================================= -->
1066 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
1067 <tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b>
1068 <a name="bitwiseops">Bitwise Binary Operations
1069 </b></font></td></tr></table><ul>
1071 Bitwise binary operators are used to do various forms of bit-twiddling in a
1072 program. They are generally very efficient instructions, and can commonly be
1073 strength reduced from other instructions. They require two operands, execute an
1074 operation on them, and produce a single value. The resulting value of the
1075 bitwise binary operators is always the same type as its first operand.<p>
1077 <!-- _______________________________________________________________________ -->
1078 </ul><a name="i_and"><h4><hr size=0>'<tt>and</tt>' Instruction</h4><ul>
1082 <result> = and <ty> <var1>, <var2> <i>; yields {ty}:result</i>
1086 The '<tt>and</tt>' instruction returns the bitwise logical and of its two operands.<p>
1090 The two arguments to the '<tt>and</tt>' instruction must be either <a
1091 href="#t_integral">integral</a> or <tt>bool</tt> values. Both arguments must
1092 have identical types.<p>
1097 The truth table used for the '<tt>and</tt>' instruction is:<p>
1099 <center><table border=1 cellspacing=0 cellpadding=4>
1100 <tr><td>In0</td> <td>In1</td> <td>Out</td></tr>
1101 <tr><td>0</td> <td>0</td> <td>0</td></tr>
1102 <tr><td>0</td> <td>1</td> <td>0</td></tr>
1103 <tr><td>1</td> <td>0</td> <td>0</td></tr>
1104 <tr><td>1</td> <td>1</td> <td>1</td></tr>
1105 </table></center><p>
1110 <result> = and int 4, %var <i>; yields {int}:result = 4 & %var</i>
1111 <result> = and int 15, 40 <i>; yields {int}:result = 8</i>
1112 <result> = and int 4, 8 <i>; yields {int}:result = 0</i>
1117 <!-- _______________________________________________________________________ -->
1118 </ul><a name="i_or"><h4><hr size=0>'<tt>or</tt>' Instruction</h4><ul>
1122 <result> = or <ty> <var1>, <var2> <i>; yields {ty}:result</i>
1125 <h5>Overview:</h5> The '<tt>or</tt>' instruction returns the bitwise logical
1126 inclusive or of its two operands.<p>
1130 The two arguments to the '<tt>or</tt>' instruction must be either <a
1131 href="#t_integral">integral</a> or <tt>bool</tt> values. Both arguments must
1132 have identical types.<p>
1137 The truth table used for the '<tt>or</tt>' instruction is:<p>
1139 <center><table border=1 cellspacing=0 cellpadding=4>
1140 <tr><td>In0</td> <td>In1</td> <td>Out</td></tr>
1141 <tr><td>0</td> <td>0</td> <td>0</td></tr>
1142 <tr><td>0</td> <td>1</td> <td>1</td></tr>
1143 <tr><td>1</td> <td>0</td> <td>1</td></tr>
1144 <tr><td>1</td> <td>1</td> <td>1</td></tr>
1145 </table></center><p>
1150 <result> = or int 4, %var <i>; yields {int}:result = 4 | %var</i>
1151 <result> = or int 15, 40 <i>; yields {int}:result = 47</i>
1152 <result> = or int 4, 8 <i>; yields {int}:result = 12</i>
1156 <!-- _______________________________________________________________________ -->
1157 </ul><a name="i_xor"><h4><hr size=0>'<tt>xor</tt>' Instruction</h4><ul>
1161 <result> = xor <ty> <var1>, <var2> <i>; yields {ty}:result</i>
1166 The '<tt>xor</tt>' instruction returns the bitwise logical exclusive or of its
1171 The two arguments to the '<tt>xor</tt>' instruction must be either <a
1172 href="#t_integral">integral</a> or <tt>bool</tt> values. Both arguments must
1173 have identical types.<p>
1178 The truth table used for the '<tt>xor</tt>' instruction is:<p>
1180 <center><table border=1 cellspacing=0 cellpadding=4>
1181 <tr><td>In0</td> <td>In1</td> <td>Out</td></tr>
1182 <tr><td>0</td> <td>0</td> <td>0</td></tr>
1183 <tr><td>0</td> <td>1</td> <td>1</td></tr>
1184 <tr><td>1</td> <td>0</td> <td>1</td></tr>
1185 <tr><td>1</td> <td>1</td> <td>0</td></tr>
1186 </table></center><p>
1191 <result> = xor int 4, %var <i>; yields {int}:result = 4 ^ %var</i>
1192 <result> = xor int 15, 40 <i>; yields {int}:result = 39</i>
1193 <result> = xor int 4, 8 <i>; yields {int}:result = 12</i>
1197 <!-- _______________________________________________________________________ -->
1198 </ul><a name="i_shl"><h4><hr size=0>'<tt>shl</tt>' Instruction</h4><ul>
1202 <result> = shl <ty> <var1>, ubyte <var2> <i>; yields {ty}:result</i>
1207 The '<tt>shl</tt>' instruction returns the first operand shifted to the left a
1208 specified number of bits.
1212 The first argument to the '<tt>shl</tt>' instruction must be an <a
1213 href="#t_integral">integral</a> type. The second argument must be an
1214 '<tt>ubyte</tt>' type.<p>
1218 The value produced is <tt>var1</tt> * 2<sup><tt>var2</tt></sup>.<p>
1223 <result> = shl int 4, ubyte %var <i>; yields {int}:result = 4 << %var</i>
1224 <result> = shl int 4, ubyte 2 <i>; yields {int}:result = 16</i>
1225 <result> = shl int 1, ubyte 10 <i>; yields {int}:result = 1024</i>
1229 <!-- _______________________________________________________________________ -->
1230 </ul><a name="i_shr"><h4><hr size=0>'<tt>shr</tt>' Instruction</h4><ul>
1235 <result> = shr <ty> <var1>, ubyte <var2> <i>; yields {ty}:result</i>
1239 The '<tt>shr</tt>' instruction returns the first operand shifted to the right a specified number of bits.
1242 The first argument to the '<tt>shr</tt>' instruction must be an <a href="#t_integral">integral</a> type. The second argument must be an '<tt>ubyte</tt>' type.<p>
1246 If the first argument is a <a href="#t_signed">signed</a> type, the most
1247 significant bit is duplicated in the newly free'd bit positions. If the first
1248 argument is unsigned, zero bits shall fill the empty positions.<p>
1252 <result> = shr int 4, ubyte %var <i>; yields {int}:result = 4 >> %var</i>
1253 <result> = shr int 4, ubyte 1 <i>; yields {int}:result = 2</i>
1254 <result> = shr int 4, ubyte 2 <i>; yields {int}:result = 1</i>
1255 <result> = shr int 4, ubyte 3 <i>; yields {int}:result = 0</i>
1262 <!-- ======================================================================= -->
1263 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
1264 <tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b>
1265 <a name="memoryops">Memory Access Operations
1266 </b></font></td></tr></table><ul>
1268 Accessing memory in SSA form is, well, sticky at best. This section describes how to read, write, allocate and free memory in LLVM.<p>
1271 <!-- _______________________________________________________________________ -->
1272 </ul><a name="i_malloc"><h4><hr size=0>'<tt>malloc</tt>' Instruction</h4><ul>
1276 <result> = malloc <type>, uint <NumElements> <i>; yields {type*}:result</i>
1277 <result> = malloc <type> <i>; yields {type*}:result</i>
1281 The '<tt>malloc</tt>' instruction allocates memory from the system heap and returns a pointer to it.<p>
1285 The the '<tt>malloc</tt>' instruction allocates
1286 <tt>sizeof(<type>)*NumElements</tt> bytes of memory from the operating
1287 system, and returns a pointer of the appropriate type to the program. The
1288 second form of the instruction is a shorter version of the first instruction
1289 that defaults to allocating one element.<p>
1291 '<tt>type</tt>' must be a sized type<p>
1294 Memory is allocated, a pointer is returned.<p>
1298 %array = malloc [4 x ubyte ] <i>; yields {[%4 x ubyte]*}:array</i>
1300 %size = <a href="#i_add">add</a> uint 2, 2 <i>; yields {uint}:size = uint 4</i>
1301 %array1 = malloc ubyte, uint 4 <i>; yields {ubyte*}:array1</i>
1302 %array2 = malloc [12 x ubyte], uint %size <i>; yields {[12 x ubyte]*}:array2</i>
1306 <!-- _______________________________________________________________________ -->
1307 </ul><a name="i_free"><h4><hr size=0>'<tt>free</tt>' Instruction</h4><ul>
1311 free <type> <value> <i>; yields {void}</i>
1316 The '<tt>free</tt>' instruction returns memory back to the unused memory heap, to be reallocated in the future.<p>
1321 '<tt>value</tt>' shall be a pointer value that points to a value that was
1322 allocated with the '<tt><a href="#i_malloc">malloc</a></tt>' instruction.<p>
1327 Access to the memory pointed to by the pointer is not longer defined after this instruction executes.<p>
1331 %array = <a href="#i_malloc">malloc</a> [4 x ubyte] <i>; yields {[4 x ubyte]*}:array</i>
1332 free [4 x ubyte]* %array
1336 <!-- _______________________________________________________________________ -->
1337 </ul><a name="i_alloca"><h4><hr size=0>'<tt>alloca</tt>' Instruction</h4><ul>
1341 <result> = alloca <type>, uint <NumElements> <i>; yields {type*}:result</i>
1342 <result> = alloca <type> <i>; yields {type*}:result</i>
1347 The '<tt>alloca</tt>' instruction allocates memory on the current stack frame of
1348 the procedure that is live until the current function returns to its caller.<p>
1352 The the '<tt>alloca</tt>' instruction allocates
1353 <tt>sizeof(<type>)*NumElements</tt> bytes of memory on the runtime stack,
1354 returning a pointer of the appropriate type to the program. The second form of
1355 the instruction is a shorter version of the first that defaults to allocating
1358 '<tt>type</tt>' may be any sized type.<p>
1362 Memory is allocated, a pointer is returned. '<tt>alloca</tt>'d memory is
1363 automatically released when the function returns. The '<tt>alloca</tt>'
1364 instruction is commonly used to represent automatic variables that must have an
1365 address available, as well as spilled variables.<p>
1369 %ptr = alloca int <i>; yields {int*}:ptr</i>
1370 %ptr = alloca int, uint 4 <i>; yields {int*}:ptr</i>
1374 <!-- _______________________________________________________________________ -->
1375 </ul><a name="i_load"><h4><hr size=0>'<tt>load</tt>' Instruction</h4><ul>
1379 <result> = load <ty>* <pointer>
1383 The '<tt>load</tt>' instruction is used to read from memory.<p>
1387 The argument to the '<tt>load</tt>' instruction specifies the memory address to load from. The pointer must point to a <a href="t_firstclass">first class</a> type.<p>
1391 The location of memory pointed to is loaded.
1395 %ptr = <a href="#i_alloca">alloca</a> int <i>; yields {int*}:ptr</i>
1396 <a href="#i_store">store</a> int 3, int* %ptr <i>; yields {void}</i>
1397 %val = load int* %ptr <i>; yields {int}:val = int 3</i>
1403 <!-- _______________________________________________________________________ -->
1404 </ul><a name="i_store"><h4><hr size=0>'<tt>store</tt>' Instruction</h4><ul>
1408 store <ty> <value>, <ty>* <pointer> <i>; yields {void}</i>
1412 The '<tt>store</tt>' instruction is used to write to memory.<p>
1416 There are two arguments to the '<tt>store</tt>' instruction: a value to store
1417 and an address to store it into. The type of the '<tt><pointer></tt>'
1418 operand must be a pointer to the type of the '<tt><value></tt>'
1421 <h5>Semantics:</h5> The contents of memory are updated to contain
1422 '<tt><value></tt>' at the location specified by the
1423 '<tt><pointer></tt>' operand.<p>
1427 %ptr = <a href="#i_alloca">alloca</a> int <i>; yields {int*}:ptr</i>
1428 <a href="#i_store">store</a> int 3, int* %ptr <i>; yields {void}</i>
1429 %val = load int* %ptr <i>; yields {int}:val = int 3</i>
1435 <!-- _______________________________________________________________________ -->
1436 </ul><a name="i_getelementptr"><h4><hr size=0>'<tt>getelementptr</tt>' Instruction</h4><ul>
1440 <result> = getelementptr <ty>* <ptrval>{, uint <aidx>|, ubyte <sidx>}*
1445 The '<tt>getelementptr</tt>' instruction is used to get the address of a
1446 subelement of an aggregate data structure.<p>
1450 This instruction takes a list of <tt>uint</tt> values and <tt>ubyte</tt>
1451 constants that indicate what form of addressing to perform. The actual types of
1452 the arguments provided depend on the type of the first pointer argument. The
1453 '<tt>getelementptr</tt>' instruction is used to index down through the type
1454 levels of a structure.<p>
1456 For example, lets consider a C code fragment and how it gets compiled to
1471 int *foo(struct ST *s) {
1472 return &s[1].Z.B[5][13];
1476 The LLVM code generated by the GCC frontend is:
1479 %RT = type { sbyte, [10 x [20 x int]], sbyte }
1480 %ST = type { int, double, %RT }
1482 int* "foo"(%ST* %s) {
1483 %reg = getelementptr %ST* %s, uint 1, ubyte 2, ubyte 1, uint 5, uint 13
1490 The index types specified for the '<tt>getelementptr</tt>' instruction depend on
1491 the pointer type that is being index into. <a href="t_pointer">Pointer</a> and
1492 <a href="t_array">array</a> types require '<tt>uint</tt>' values, and <a
1493 href="t_struct">structure</a> types require '<tt>ubyte</tt>'
1494 <b>constants</b>.<p>
1496 In the example above, the first index is indexing into the '<tt>%ST*</tt>' type,
1497 which is a pointer, yielding a '<tt>%ST</tt>' = '<tt>{ int, double, %RT }</tt>'
1498 type, a structure. The second index indexes into the third element of the
1499 structure, yielding a '<tt>%RT</tt>' = '<tt>{ sbyte, [10 x [20 x int]], sbyte
1500 }</tt>' type, another structure. The third index indexes into the second
1501 element of the structure, yielding a '<tt>[10 x [20 x int]]</tt>' type, an
1502 array. The two dimensions of the array are subscripted into, yielding an
1503 '<tt>int</tt>' type. The '<tt>getelementptr</tt>' instruction return a pointer
1504 to this element, thus yielding a '<tt>int*</tt>' type.<p>
1506 Note that it is perfectly legal to index partially through a structure,
1507 returning a pointer to an inner element. Because of this, the LLVM code for the
1508 given testcase is equivalent to:<p>
1511 int* "foo"(%ST* %s) {
1512 %t1 = getelementptr %ST* %s , uint 1 <i>; yields %ST*:%t1</i>
1513 %t2 = getelementptr %ST* %t1, uint 0, ubyte 2 <i>; yields %RT*:%t2</i>
1514 %t3 = getelementptr %RT* %t2, uint 0, ubyte 1 <i>; yields [10 x [20 x int]]*:%t3</i>
1515 %t4 = getelementptr [10 x [20 x int]]* %t3, uint 0, uint 5 <i>; yields [20 x int]*:%t4</i>
1516 %t5 = getelementptr [20 x int]* %t4, uint 0, uint 13 <i>; yields int*:%t5</i>
1525 <i>; yields {[12 x ubyte]*}:aptr</i>
1526 %aptr = getelementptr {int, [12 x ubyte]}* %sptr, uint 0, ubyte 1
1531 <!-- ======================================================================= -->
1532 </ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
1533 <tr><td> </td><td width="100%"> <font color="#EEEEFF" face="Georgia,Palatino"><b>
1534 <a name="otherops">Other Operations
1535 </b></font></td></tr></table><ul>
1537 The instructions in this catagory are the "miscellaneous" functions, that defy better classification.<p>
1540 <!-- _______________________________________________________________________ -->
1541 </ul><a name="i_phi"><h4><hr size=0>'<tt>phi</tt>' Instruction</h4><ul>
1545 <result> = phi <ty> [ <val0>, <label0>], ...
1550 The '<tt>phi</tt>' instruction is used to implement the φ node in the SSA
1551 graph representing the function.<p>
1555 The type of the incoming values are specified with the first type field. After
1556 this, the '<tt>phi</tt>' instruction takes a list of pairs as arguments, with
1557 one pair for each predecessor basic block of the current block.<p>
1559 There must be no non-phi instructions between the start of a basic block and the
1560 PHI instructions: i.e. PHI instructions must be first in a basic block.<p>
1564 At runtime, the '<tt>phi</tt>' instruction logically takes on the value
1565 specified by the parameter, depending on which basic block we came from in the
1566 last <a href="#terminators">terminator</a> instruction.<p>
1571 Loop: ; Infinite loop that counts from 0 on up...
1572 %indvar = phi uint [ 0, %LoopHeader ], [ %nextindvar, %Loop ]
1573 %nextindvar = add uint %indvar, 1
1578 <!-- _______________________________________________________________________ -->
1579 </ul><a name="i_cast"><h4><hr size=0>'<tt>cast .. to</tt>' Instruction</h4><ul>
1583 <result> = cast <ty> <value> to <ty2> <i>; yields ty2</i>
1588 The '<tt>cast</tt>' instruction is used as the primitive means to convert
1589 integers to floating point, change data type sizes, and break type safety (by
1590 casting pointers).<p>
1594 The '<tt>cast</tt>' instruction takes a value to cast, which must be a first
1595 class value, and a type to cast it to, which must also be a first class type.<p>
1599 This instruction follows the C rules for explicit casts when determining how the
1600 data being cast must change to fit in its new container.<p>
1602 When casting to bool, any value that would be considered true in the context of
1603 a C '<tt>if</tt>' condition is converted to the boolean '<tt>true</tt>' values,
1604 all else are '<tt>false</tt>'.<p>
1608 %X = cast int 257 to ubyte <i>; yields ubyte:1</i>
1609 %Y = cast int 123 to bool <i>; yields bool:true</i>
1614 <!-- _______________________________________________________________________ -->
1615 </ul><a name="i_call"><h4><hr size=0>'<tt>call</tt>' Instruction</h4><ul>
1619 <result> = call <ty>* <fnptrval>(<param list>)
1624 The '<tt>call</tt>' instruction represents a simple function call.<p>
1628 This instruction requires several arguments:<p>
1631 <li>'<tt>ty</tt>': shall be the signature of the pointer to function value being
1632 invoked. The argument types must match the types implied by this signature.<p>
1634 <li>'<tt>fnptrval</tt>': An LLVM value containing a pointer to a function to be
1635 invoked. In most cases, this is a direct function invocation, but indirect
1636 <tt>call</tt>'s are just as possible, calling an arbitrary pointer to function
1639 <li>'<tt>function args</tt>': argument list whose types match the function
1640 signature argument types. If the function signature indicates the function
1641 accepts a variable number of arguments, the extra arguments can be specified.
1646 The '<tt>call</tt>' instruction is used to cause control flow to transfer to a
1647 specified function, with its incoming arguments bound to the specified values.
1648 Upon a '<tt><a href="#i_ret">ret</a></tt>' instruction in the called function,
1649 control flow continues with the instruction after the function call, and the
1650 return value of the function is bound to the result argument. This is a simpler
1651 case of the <a href="#i_invoke">invoke</a> instruction.<p>
1655 %retval = call int %test(int %argc)
1656 call int(sbyte*, ...) *%printf(sbyte* %msg, int 12, sbyte 42);
1662 <!x- *********************************************************************** -x>
1663 </ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
1664 <tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
1665 <a name="related">Related Work
1666 </b></font></td></tr></table><ul>
1667 <!x- *********************************************************************** -x>
1670 Codesigned virtual machines.<p>
1673 <a name="rw_safetsa">
1675 <DD>Description here<p>
1678 <dt><a href="http://www.javasoft.com">Java</a>
1679 <DD>Desciption here<p>
1682 <dt><a href="http://www.microsoft.com/net">Microsoft .net</a>
1683 <DD>Desciption here<p>
1685 <a name="rw_gccrtl">
1686 <dt><a href="http://www.math.umn.edu/systems_guide/gcc-2.95.1/gcc_15.html">GNU RTL Intermediate Representation</a>
1687 <DD>Desciption here<p>
1690 <dt><a href="http://developer.intel.com/design/ia-64/index.htm">IA64 Architecture & Instruction Set</a>
1691 <DD>Desciption here<p>
1694 <dt><a href="http://www-cs-faculty.stanford.edu/~knuth/mmix-news.html">MMIX Instruction Set</a>
1695 <DD>Desciption here<p>
1697 <a name="rw_stroustrup">
1698 <dt><a href="http://www.research.att.com/~bs/devXinterview.html">"Interview With Bjarne Stroustrup"</a>
1699 <DD>This interview influenced the design and thought process behind LLVM in several ways, most notably the way that derived types are written in text format. See the question that starts with "you defined the C declarator syntax as an experiment that failed".<p>
1702 <!x- _______________________________________________________________________ -x>
1703 </ul><a name="rw_vectorization"><h3><hr size=0>Vectorized Architectures</h3><ul>
1706 <a name="rw_intel_simd">
1707 <dt>Intel MMX, MMX2, SSE, SSE2
1708 <DD>Description here<p>
1710 <a name="rw_amd_simd">
1711 <dt><a href="http://www.nondot.org/~sabre/os/H1ChipFeatures/3DNow!TechnologyManual.pdf">AMD 3Dnow!, 3Dnow! 2</a>
1712 <DD>Desciption here<p>
1714 <a name="rw_sun_simd">
1715 <dt><a href="http://www.nondot.org/~sabre/os/H1ChipFeatures/VISInstructionSetUsersManual.pdf">Sun VIS ISA</a>
1716 <DD>Desciption here<p>
1718 <a name="rw_powerpc_simd">
1720 <DD>Desciption here<p>
1729 <!-- *********************************************************************** -->
1731 <!-- *********************************************************************** -->
1736 <address><a href="mailto:sabre@nondot.org">Chris Lattner</a></address>
1737 <!-- Created: Tue Jan 23 15:19:28 CST 2001 -->
1738 <!-- hhmts start -->
1739 Last modified: Tue Jun 25 15:19:34 CDT 2002