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|
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<title>LLVM Assembly Language Reference Manual</title>
<link rel="stylesheet" href="llvm.css" type="text/css">
</head>
<body>
<div class="doc_title"> LLVM Language Reference Manual </div>
<ol>
<li><a href="#abstract">Abstract</a></li>
<li><a href="#introduction">Introduction</a></li>
<li><a href="#identifiers">Identifiers</a></li>
<li><a href="#typesystem">Type System</a>
<ol>
<li><a href="#t_primitive">Primitive Types</a>
<ol>
<li><a href="#t_classifications">Type Classifications</a></li>
</ol>
</li>
<li><a href="#t_derived">Derived Types</a>
<ol>
<li><a href="#t_array">Array Type</a></li>
<li><a href="#t_function">Function Type</a></li>
<li><a href="#t_pointer">Pointer Type</a></li>
<li><a href="#t_struct">Structure Type</a></li>
<!-- <li><a href="#t_packed" >Packed Type</a> -->
</ol>
</li>
</ol>
</li>
<li><a href="#highlevel">High Level Structure</a>
<ol>
<li><a href="#modulestructure">Module Structure</a></li>
<li><a href="#globalvars">Global Variables</a></li>
<li><a href="#functionstructure">Function Structure</a></li>
</ol>
</li>
<li><a href="#instref">Instruction Reference</a>
<ol>
<li><a href="#terminators">Terminator Instructions</a>
<ol>
<li><a href="#i_ret">'<tt>ret</tt>' Instruction</a></li>
<li><a href="#i_br">'<tt>br</tt>' Instruction</a></li>
<li><a href="#i_switch">'<tt>switch</tt>' Instruction</a></li>
<li><a href="#i_invoke">'<tt>invoke</tt>' Instruction</a></li>
<li><a href="#i_unwind">'<tt>unwind</tt>' Instruction</a></li>
</ol>
</li>
<li><a href="#binaryops">Binary Operations</a>
<ol>
<li><a href="#i_add">'<tt>add</tt>' Instruction</a></li>
<li><a href="#i_sub">'<tt>sub</tt>' Instruction</a></li>
<li><a href="#i_mul">'<tt>mul</tt>' Instruction</a></li>
<li><a href="#i_div">'<tt>div</tt>' Instruction</a></li>
<li><a href="#i_rem">'<tt>rem</tt>' Instruction</a></li>
<li><a href="#i_setcc">'<tt>set<i>cc</i></tt>' Instructions</a></li>
</ol>
</li>
<li><a href="#bitwiseops">Bitwise Binary Operations</a>
<ol>
<li><a href="#i_and">'<tt>and</tt>' Instruction</a></li>
<li><a href="#i_or">'<tt>or</tt>' Instruction</a></li>
<li><a href="#i_xor">'<tt>xor</tt>' Instruction</a></li>
<li><a href="#i_shl">'<tt>shl</tt>' Instruction</a></li>
<li><a href="#i_shr">'<tt>shr</tt>' Instruction</a></li>
</ol>
</li>
<li><a href="#memoryops">Memory Access Operations</a>
<ol>
<li><a href="#i_malloc">'<tt>malloc</tt>' Instruction</a></li>
<li><a href="#i_free">'<tt>free</tt>' Instruction</a></li>
<li><a href="#i_alloca">'<tt>alloca</tt>' Instruction</a></li>
<li><a href="#i_load">'<tt>load</tt>' Instruction</a></li>
<li><a href="#i_store">'<tt>store</tt>' Instruction</a></li>
<li><a href="#i_getelementptr">'<tt>getelementptr</tt>' Instruction</a></li>
</ol>
</li>
<li><a href="#otherops">Other Operations</a>
<ol>
<li><a href="#i_phi">'<tt>phi</tt>' Instruction</a></li>
<li><a href="#i_cast">'<tt>cast .. to</tt>' Instruction</a></li>
<li><a href="#i_select">'<tt>select</tt>' Instruction</a></li>
<li><a href="#i_call">'<tt>call</tt>' Instruction</a></li>
<li><a href="#i_vanext">'<tt>vanext</tt>' Instruction</a></li>
<li><a href="#i_vaarg">'<tt>vaarg</tt>' Instruction</a></li>
</ol>
</li>
</ol>
</li>
<li><a href="#intrinsics">Intrinsic Functions</a>
<ol>
<li><a href="#int_varargs">Variable Argument Handling Intrinsics</a>
<ol>
<li><a href="#i_va_start">'<tt>llvm.va_start</tt>' Intrinsic</a></li>
<li><a href="#i_va_end">'<tt>llvm.va_end</tt>' Intrinsic</a></li>
<li><a href="#i_va_copy">'<tt>llvm.va_copy</tt>' Intrinsic</a></li>
</ol>
</li>
<li><a href="#int_codegen">Code Generator Intrinsics</a>
<ol>
<li><a href="#i_returnaddress">'<tt>llvm.returnaddress</tt>' Intrinsic</a></li>
<li><a href="#i_frameaddress">'<tt>llvm.frameaddress</tt>' Intrinsic</a></li>
</ol>
</li>
<li><a href="#int_libc">Standard C Library Intrinsics</a>
<ol>
<li><a href="#i_memcpy">'<tt>llvm.memcpy</tt>' Intrinsic</a></li>
<li><a href="#i_memmove">'<tt>llvm.memmove</tt>' Intrinsic</a></li>
<li><a href="#i_memset">'<tt>llvm.memset</tt>' Intrinsic</a></li>
</ol>
</li>
<li><a href="#int_debugger">Debugger intrinsics</a>
</ol>
</li>
</ol>
<div class="doc_text">
<p><b>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>
and <a href="mailto:vadve@cs.uiuc.edu">Vikram Adve</a></b></p>
<p> </p>
</div>
<!-- *********************************************************************** -->
<div class="doc_section"> <a name="abstract">Abstract </a></div>
<!-- *********************************************************************** -->
<div class="doc_text">
<p>This document is a reference manual for the LLVM assembly language.
LLVM is an SSA based representation that provides type safety,
low-level operations, flexibility, and the capability of representing
'all' high-level languages cleanly. It is the common code
representation used throughout all phases of the LLVM compilation
strategy.</p>
</div>
<!-- *********************************************************************** -->
<div class="doc_section"> <a name="introduction">Introduction</a> </div>
<!-- *********************************************************************** -->
<div class="doc_text">
<p>The LLVM code representation is designed to be used in three
different forms: as an in-memory compiler IR, as an on-disk bytecode
representation (suitable for fast loading by a Just-In-Time compiler),
and as a human readable assembly language representation. This allows
LLVM to provide a powerful intermediate representation for efficient
compiler transformations and analysis, while providing a natural means
to debug and visualize the transformations. The three different forms
of LLVM are all equivalent. This document describes the human readable
representation and notation.</p>
<p>The LLVM representation aims to be a light-weight and low-level
while being expressive, typed, and extensible at the same time. It
aims to be a "universal IR" of sorts, by being at a low enough level
that high-level ideas may be cleanly mapped to it (similar to how
microprocessors are "universal IR's", allowing many source languages to
be mapped to them). By providing type information, LLVM can be used as
the target of optimizations: for example, through pointer analysis, it
can be proven that a C automatic variable is never accessed outside of
the current function... allowing it to be promoted to a simple SSA
value instead of a memory location.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="wellformed">Well-Formedness</a> </div>
<div class="doc_text">
<p>It is important to note that this document describes 'well formed'
LLVM assembly language. There is a difference between what the parser
accepts and what is considered 'well formed'. For example, the
following instruction is syntactically okay, but not well formed:</p>
<pre> %x = <a href="#i_add">add</a> int 1, %x<br></pre>
<p>...because the definition of <tt>%x</tt> does not dominate all of
its uses. The LLVM infrastructure provides a verification pass that may
be used to verify that an LLVM module is well formed. This pass is
automatically run by the parser after parsing input assembly, and by
the optimizer before it outputs bytecode. The violations pointed out
by the verifier pass indicate bugs in transformation passes or input to
the parser.</p>
<!-- Describe the typesetting conventions here. --> </div>
<!-- *********************************************************************** -->
<div class="doc_section"> <a name="identifiers">Identifiers</a> </div>
<!-- *********************************************************************** -->
<div class="doc_text">
<p>LLVM uses three different forms of identifiers, for different
purposes:</p>
<ol>
<li>Numeric constants are represented as you would expect: 12, -3
123.421, etc. Floating point constants have an optional hexidecimal
notation.</li>
<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>'.
Identifiers which require other characters in their names can be
surrounded with quotes. In this way, anything except a <tt>"</tt>
character can be used in a name.</li>
<li>Unnamed values are represented as an unsigned numeric value with
a '%' prefix. For example, %12, %2, %44.</li>
</ol>
<p>LLVM requires that values start with a '%' sign for two reasons:
Compilers don't need to worry about name clashes with reserved words,
and the set of reserved words may be expanded in the future without
penalty. Additionally, unnamed identifiers allow a compiler to quickly
come up with a temporary variable without having to avoid symbol table
conflicts.</p>
<p>Reserved words in LLVM are very similar to reserved words in other
languages. There are keywords for different opcodes ('<tt><a
href="#i_add">add</a></tt>', '<tt><a href="#i_cast">cast</a></tt>', '<tt><a
href="#i_ret">ret</a></tt>', etc...), for primitive type names ('<tt><a
href="#t_void">void</a></tt>', '<tt><a href="#t_uint">uint</a></tt>',
etc...), and others. These reserved words cannot conflict with
variable names, because none of them start with a '%' character.</p>
<p>Here is an example of LLVM code to multiply the integer variable '<tt>%X</tt>'
by 8:</p>
<p>The easy way:</p>
<pre> %result = <a href="#i_mul">mul</a> uint %X, 8<br></pre>
<p>After strength reduction:</p>
<pre> %result = <a href="#i_shl">shl</a> uint %X, ubyte 3<br></pre>
<p>And the hard way:</p>
<pre> <a href="#i_add">add</a> uint %X, %X <i>; yields {uint}:%0</i>
<a
href="#i_add">add</a> uint %0, %0 <i>; yields {uint}:%1</i>
%result = <a
href="#i_add">add</a> uint %1, %1<br></pre>
<p>This last way of multiplying <tt>%X</tt> by 8 illustrates several
important lexical features of LLVM:</p>
<ol>
<li>Comments are delimited with a '<tt>;</tt>' and go until the end
of line.</li>
<li>Unnamed temporaries are created when the result of a computation
is not assigned to a named value.</li>
<li>Unnamed temporaries are numbered sequentially</li>
</ol>
<p>...and it also show a convention that we follow in this document.
When demonstrating instructions, we will follow an instruction with a
comment that defines the type and name of value produced. Comments are
shown in italic text.</p>
<p>The one non-intuitive notation for constants is the optional
hexidecimal form of floating point constants. For example, the form '<tt>double
0x432ff973cafa8000</tt>' is equivalent to (but harder to read than) '<tt>double
4.5e+15</tt>' which is also supported by the parser. The only time
hexadecimal floating point constants are useful (and the only time that
they are generated by the disassembler) is when an FP constant has to
be emitted that is not representable as a decimal floating point number
exactly. For example, NaN's, infinities, and other special cases are
represented in their IEEE hexadecimal format so that assembly and
disassembly do not cause any bits to change in the constants.</p>
</div>
<!-- *********************************************************************** -->
<div class="doc_section"> <a name="typesystem">Type System</a> </div>
<!-- *********************************************************************** -->
<div class="doc_text">
<p>The LLVM type system is one of the most important features of the
intermediate representation. Being typed enables a number of
optimizations to be performed on the IR directly, without having to do
extra analyses on the side before the transformation. A strong type
system makes it easier to read the generated code and enables novel
analyses and transformations that are not feasible to perform on normal
three address code representations.</p>
<!-- The written form for the type system was heavily influenced by the
syntactic problems with types in the C language<sup><a
href="#rw_stroustrup">1</a></sup>.<p> --> </div>
<!-- ======================================================================= -->
<div class="doc_subsection"> <a name="t_primitive">Primitive Types</a> </div>
<div class="doc_text">
<p>The primitive types are the fundemental building blocks of the LLVM
system. The current set of primitive types are as follows:</p>
<table border="0" style="align: center">
<tbody>
<tr>
<td>
<table border="1" cellspacing="0" cellpadding="4" style="align: center">
<tbody>
<tr>
<td><tt>void</tt></td>
<td>No value</td>
</tr>
<tr>
<td><tt>ubyte</tt></td>
<td>Unsigned 8 bit value</td>
</tr>
<tr>
<td><tt>ushort</tt></td>
<td>Unsigned 16 bit value</td>
</tr>
<tr>
<td><tt>uint</tt></td>
<td>Unsigned 32 bit value</td>
</tr>
<tr>
<td><tt>ulong</tt></td>
<td>Unsigned 64 bit value</td>
</tr>
<tr>
<td><tt>float</tt></td>
<td>32 bit floating point value</td>
</tr>
<tr>
<td><tt>label</tt></td>
<td>Branch destination</td>
</tr>
</tbody>
</table>
</td>
<td valign="top">
<table border="1" cellspacing="0" cellpadding="4">
<tbody>
<tr>
<td><tt>bool</tt></td>
<td>True or False value</td>
</tr>
<tr>
<td><tt>sbyte</tt></td>
<td>Signed 8 bit value</td>
</tr>
<tr>
<td><tt>short</tt></td>
<td>Signed 16 bit value</td>
</tr>
<tr>
<td><tt>int</tt></td>
<td>Signed 32 bit value</td>
</tr>
<tr>
<td><tt>long</tt></td>
<td>Signed 64 bit value</td>
</tr>
<tr>
<td><tt>double</tt></td>
<td>64 bit floating point value</td>
</tr>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="t_classifications">Type
Classifications</a> </div>
<div class="doc_text">
<p>These different primitive types fall into a few useful
classifications:</p>
<table border="1" cellspacing="0" cellpadding="4">
<tbody>
<tr>
<td><a name="t_signed">signed</a></td>
<td><tt>sbyte, short, int, long, float, double</tt></td>
</tr>
<tr>
<td><a name="t_unsigned">unsigned</a></td>
<td><tt>ubyte, ushort, uint, ulong</tt></td>
</tr>
<tr>
<td><a name="t_integer">integer</a></td>
<td><tt>ubyte, sbyte, ushort, short, uint, int, ulong, long</tt></td>
</tr>
<tr>
<td><a name="t_integral">integral</a></td>
<td><tt>bool, ubyte, sbyte, ushort, short, uint, int, ulong, long</tt></td>
</tr>
<tr>
<td><a name="t_floating">floating point</a></td>
<td><tt>float, double</tt></td>
</tr>
<tr>
<td><a name="t_firstclass">first class</a></td>
<td><tt>bool, ubyte, sbyte, ushort, short,<br>
uint, int, ulong, long, float, double, <a href="#t_pointer">pointer</a></tt></td>
</tr>
</tbody>
</table>
<p>The <a href="#t_firstclass">first class</a> types are perhaps the
most important. Values of these types are the only ones which can be
produced by instructions, passed as arguments, or used as operands to
instructions. This means that all structures and arrays must be
manipulated either by pointer or by component.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"> <a name="t_derived">Derived Types</a> </div>
<div class="doc_text">
<p>The real power in LLVM comes from the derived types in the system.
This is what allows a programmer to represent arrays, functions,
pointers, and other useful types. Note that these derived types may be
recursive: For example, it is possible to have a two dimensional array.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="t_array">Array Type</a> </div>
<div class="doc_text">
<h5>Overview:</h5>
<p>The array type is a very simple derived type that arranges elements
sequentially in memory. The array type requires a size (number of
elements) and an underlying data type.</p>
<h5>Syntax:</h5>
<pre> [<# elements> x <elementtype>]<br></pre>
<p>The number of elements is a constant integer value, elementtype may
be any type with a size.</p>
<h5>Examples:</h5>
<p> <tt>[40 x int ]</tt>: Array of 40 integer values.<br>
<tt>[41 x int ]</tt>: Array of 41 integer values.<br>
<tt>[40 x uint]</tt>: Array of 40 unsigned integer values.</p>
<p> </p>
<p>Here are some examples of multidimensional arrays:</p>
<table border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td><tt>[3 x [4 x int]]</tt></td>
<td>: 3x4 array integer values.</td>
</tr>
<tr>
<td><tt>[12 x [10 x float]]</tt></td>
<td>: 12x10 array of single precision floating point values.</td>
</tr>
<tr>
<td><tt>[2 x [3 x [4 x uint]]]</tt></td>
<td>: 2x3x4 array of unsigned integer values.</td>
</tr>
</tbody>
</table>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="t_function">Function Type</a> </div>
<div class="doc_text">
<h5>Overview:</h5>
<p>The function type can be thought of as a function signature. It
consists of a return type and a list of formal parameter types.
Function types are usually used to build virtual function tables
(which are structures of pointers to functions), for indirect function
calls, and when defining a function.</p>
<p>
The return type of a function type cannot be an aggregate type.
</p>
<h5>Syntax:</h5>
<pre> <returntype> (<parameter list>)<br></pre>
<p>Where '<tt><parameter list></tt>' is a comma-separated list of
type specifiers. Optionally, the parameter list may include a type <tt>...</tt>,
which indicates that the function takes a variable number of arguments.
Variable argument functions can access their arguments with the <a
href="#int_varargs">variable argument handling intrinsic</a> functions.</p>
<h5>Examples:</h5>
<table border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td><tt>int (int)</tt></td>
<td>: function taking an <tt>int</tt>, returning an <tt>int</tt></td>
</tr>
<tr>
<td><tt>float (int, int *) *</tt></td>
<td>: <a href="#t_pointer">Pointer</a> to a function that takes
an <tt>int</tt> and a <a href="#t_pointer">pointer</a> to <tt>int</tt>,
returning <tt>float</tt>.</td>
</tr>
<tr>
<td><tt>int (sbyte *, ...)</tt></td>
<td>: A vararg function that takes at least one <a
href="#t_pointer">pointer</a> to <tt>sbyte</tt> (signed char in C),
which returns an integer. This is the signature for <tt>printf</tt>
in LLVM.</td>
</tr>
</tbody>
</table>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="t_struct">Structure Type</a> </div>
<div class="doc_text">
<h5>Overview:</h5>
<p>The structure type is used to represent a collection of data members
together in memory. The packing of the field types is defined to match
the ABI of the underlying processor. The elements of a structure may
be any type that has a size.</p>
<p>Structures are accessed using '<tt><a href="#i_load">load</a></tt>
and '<tt><a href="#i_store">store</a></tt>' by getting a pointer to a
field with the '<tt><a href="#i_getelementptr">getelementptr</a></tt>'
instruction.</p>
<h5>Syntax:</h5>
<pre> { <type list> }<br></pre>
<h5>Examples:</h5>
<table border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td><tt>{ int, int, int }</tt></td>
<td>: a triple of three <tt>int</tt> values</td>
</tr>
<tr>
<td><tt>{ float, int (int) * }</tt></td>
<td>: A pair, where the first element is a <tt>float</tt> and the
second element is a <a href="#t_pointer">pointer</a> to a <a
href="t_function">function</a> that takes an <tt>int</tt>, returning
an <tt>int</tt>.</td>
</tr>
</tbody>
</table>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="t_pointer">Pointer Type</a> </div>
<div class="doc_text">
<h5>Overview:</h5>
<p>As in many languages, the pointer type represents a pointer or
reference to another object, which must live in memory.</p>
<h5>Syntax:</h5>
<pre> <type> *<br></pre>
<h5>Examples:</h5>
<table border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td><tt>[4x int]*</tt></td>
<td>: <a href="#t_pointer">pointer</a> to <a href="#t_array">array</a>
of four <tt>int</tt> values</td>
</tr>
<tr>
<td><tt>int (int *) *</tt></td>
<td>: A <a href="#t_pointer">pointer</a> to a <a
href="t_function">function</a> that takes an <tt>int</tt>, returning
an <tt>int</tt>.</td>
</tr>
</tbody>
</table>
</div>
<!-- _______________________________________________________________________ --><!--
<div class="doc_subsubsection">
<a name="t_packed">Packed Type</a>
</div>
<div class="doc_text">
Mention/decide that packed types work with saturation or not. Maybe have a packed+saturated type in addition to just a packed type.<p>
Packed types should be 'nonsaturated' because standard data types are not saturated. Maybe have a saturated packed type?<p>
</div>
--><!-- *********************************************************************** -->
<div class="doc_section"> <a name="highlevel">High Level Structure</a> </div>
<!-- *********************************************************************** --><!-- ======================================================================= -->
<div class="doc_subsection"> <a name="modulestructure">Module Structure</a> </div>
<div class="doc_text">
<p>LLVM programs are composed of "Module"s, each of which is a
translation unit of the input programs. Each module consists of
functions, global variables, and symbol table entries. Modules may be
combined together with the LLVM linker, which merges function (and
global variable) definitions, resolves forward declarations, and merges
symbol table entries. Here is an example of the "hello world" module:</p>
<pre><i>; Declare the string constant as a global constant...</i>
<a href="#identifiers">%.LC0</a> = <a href="#linkage_internal">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>
<i>; External declaration of the puts function</i>
<a href="#functionstructure">declare</a> int %puts(sbyte*) <i>; int(sbyte*)* </i>
<i>; Definition of main function</i>
int %main() { <i>; int()* </i>
<i>; Convert [13x sbyte]* to sbyte *...</i>
%cast210 = <a
href="#i_getelementptr">getelementptr</a> [13 x sbyte]* %.LC0, long 0, long 0 <i>; sbyte*</i>
<i>; Call puts function to write out the string to stdout...</i>
<a
href="#i_call">call</a> int %puts(sbyte* %cast210) <i>; int</i>
<a
href="#i_ret">ret</a> int 0<br>}<br></pre>
<p>This example is made up of a <a href="#globalvars">global variable</a>
named "<tt>.LC0</tt>", an external declaration of the "<tt>puts</tt>"
function, and a <a href="#functionstructure">function definition</a>
for "<tt>main</tt>".</p>
<a name="linkage"> In general, a module is made up of a list of global
values, where both functions and global variables are global values.
Global values are represented by a pointer to a memory location (in
this case, a pointer to an array of char, and a pointer to a function),
and have one of the following linkage types:</a>
<p> </p>
<dl>
<dt><tt><b><a name="linkage_internal">internal</a></b></tt> </dt>
<dd>Global values with internal linkage are only directly accessible
by objects in the current module. In particular, linking code into a
module with an internal global value may cause the internal to be
renamed as necessary to avoid collisions. Because the symbol is
internal to the module, all references can be updated. This
corresponds to the notion of the '<tt>static</tt>' keyword in C, or the
idea of "anonymous namespaces" in C++.
<p> </p>
</dd>
<dt><tt><b><a name="linkage_linkonce">linkonce</a></b></tt>: </dt>
<dd>"<tt>linkonce</tt>" linkage is similar to <tt>internal</tt>
linkage, with the twist that linking together two modules defining the
same <tt>linkonce</tt> globals will cause one of the globals to be
discarded. This is typically used to implement inline functions.
Unreferenced <tt>linkonce</tt> globals are allowed to be discarded.
<p> </p>
</dd>
<dt><tt><b><a name="linkage_weak">weak</a></b></tt>: </dt>
<dd>"<tt>weak</tt>" linkage is exactly the same as <tt>linkonce</tt>
linkage, except that unreferenced <tt>weak</tt> globals may not be
discarded. This is used to implement constructs in C such as "<tt>int
X;</tt>" at global scope.
<p> </p>
</dd>
<dt><tt><b><a name="linkage_appending">appending</a></b></tt>: </dt>
<dd>"<tt>appending</tt>" linkage may only be applied to global
variables of pointer to array type. When two global variables with
appending linkage are linked together, the two global arrays are
appended together. This is the LLVM, typesafe, equivalent of having
the system linker append together "sections" with identical names when
.o files are linked.
<p> </p>
</dd>
<dt><tt><b><a name="linkage_external">externally visible</a></b></tt>:</dt>
<dd>If none of the above identifiers are used, the global is
externally visible, meaning that it participates in linkage and can be
used to resolve external symbol references.
<p> </p>
</dd>
</dl>
<p> </p>
<p><a name="linkage_external">For example, since the "<tt>.LC0</tt>"
variable is defined to be internal, if another module defined a "<tt>.LC0</tt>"
variable and was linked with this one, one of the two would be renamed,
preventing a collision. Since "<tt>main</tt>" and "<tt>puts</tt>" are
external (i.e., lacking any linkage declarations), they are accessible
outside of the current module. It is illegal for a function <i>declaration</i>
to have any linkage type other than "externally visible".</a></p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="globalvars">Global Variables</a>
</div>
<div class="doc_text">
<p>Global variables define regions of memory allocated at compilation
time instead of run-time. Global variables may optionally be
initialized. A variable may be defined as a global "constant", which
indicates that the contents of the variable will never be modified
(opening options for optimization).</p>
<p>As SSA values, global variables define pointer values that are in
scope (i.e. they dominate) for all basic blocks in the program. Global
variables always define a pointer to their "content" type because they
describe a region of memory, and all memory objects in LLVM are
accessed through pointers.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="functionstructure">Functions</a>
</div>
<div class="doc_text">
<p>LLVM function definitions are composed of a (possibly empty) argument list,
an opening curly brace, a list of basic blocks, and a closing curly brace. LLVM
function declarations are defined with the "<tt>declare</tt>" keyword, a
function name, and a function signature.</p>
<p>A function definition contains a list of basic blocks, forming the CFG for
the function. Each basic block may optionally start with a label (giving the
basic block a symbol table entry), contains a list of instructions, and ends
with a <a href="#terminators">terminator</a> instruction (such as a branch or
function return).</p>
<p>The first basic block in program is special in two ways: it is immediately
executed on entrance to the function, and it is not allowed to have predecessor
basic blocks (i.e. there can not be any branches to the entry block of a
function). Because the block can have no predecessors, it also cannot have any
<a href="#i_phi">PHI nodes</a>.</p>
<p>LLVM functions are identified by their name and type signature. Hence, two
functions with the same name but different parameter lists or return values are
considered different functions, and LLVM will resolves references to each
appropriately.</p>
</div>
<!-- *********************************************************************** -->
<div class="doc_section"> <a name="instref">Instruction Reference</a> </div>
<!-- *********************************************************************** -->
<div class="doc_text">
<p>The LLVM instruction set consists of several different
classifications of instructions: <a href="#terminators">terminator
instructions</a>, <a href="#binaryops">binary instructions</a>, <a
href="#memoryops">memory instructions</a>, and <a href="#otherops">other
instructions</a>.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"> <a name="terminators">Terminator
Instructions</a> </div>
<div class="doc_text">
<p>As mentioned <a href="#functionstructure">previously</a>, every
basic block in a program ends with a "Terminator" instruction, which
indicates which block should be executed after the current block is
finished. These terminator instructions typically yield a '<tt>void</tt>'
value: they produce control flow, not values (the one exception being
the '<a href="#i_invoke"><tt>invoke</tt></a>' instruction).</p>
<p>There are five different terminator instructions: the '<a
href="#i_ret"><tt>ret</tt></a>' instruction, the '<a href="#i_br"><tt>br</tt></a>'
instruction, the '<a href="#i_switch"><tt>switch</tt></a>' instruction,
the '<a href="#i_invoke"><tt>invoke</tt></a>' instruction, and the '<a
href="#i_unwind"><tt>unwind</tt></a>' instruction.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_ret">'<tt>ret</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> ret <type> <value> <i>; Return a value from a non-void function</i>
ret void <i>; Return from void function</i>
</pre>
<h5>Overview:</h5>
<p>The '<tt>ret</tt>' instruction is used to return control flow (and a
value) from a function, back to the caller.</p>
<p>There are two forms of the '<tt>ret</tt>' instructruction: one that
returns a value and then causes control flow, and one that just causes
control flow to occur.</p>
<h5>Arguments:</h5>
<p>The '<tt>ret</tt>' instruction may return any '<a
href="#t_firstclass">first class</a>' type. Notice that a function is
not <a href="#wellformed">well formed</a> if there exists a '<tt>ret</tt>'
instruction inside of the function that returns a value that does not
match the return type of the function.</p>
<h5>Semantics:</h5>
<p>When the '<tt>ret</tt>' instruction is executed, control flow
returns back to the calling function's context. If the caller is a "<a
href="#i_call"><tt>call</tt></a> instruction, execution continues at
the instruction after the call. If the caller was an "<a
href="#i_invoke"><tt>invoke</tt></a>" instruction, execution continues
at the beginning "normal" of the destination block. If the instruction
returns a value, that value shall set the call or invoke instruction's
return value.</p>
<h5>Example:</h5>
<pre> ret int 5 <i>; Return an integer value of 5</i>
ret void <i>; Return from a void function</i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_br">'<tt>br</tt>' Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> br bool <cond>, label <iftrue>, label <iffalse><br> br label <dest> <i>; Unconditional branch</i>
</pre>
<h5>Overview:</h5>
<p>The '<tt>br</tt>' instruction is used to cause control flow to
transfer to a different basic block in the current function. There are
two forms of this instruction, corresponding to a conditional branch
and an unconditional branch.</p>
<h5>Arguments:</h5>
<p>The conditional branch form of the '<tt>br</tt>' instruction takes a
single '<tt>bool</tt>' value and two '<tt>label</tt>' values. The
unconditional form of the '<tt>br</tt>' instruction takes a single '<tt>label</tt>'
value as a target.</p>
<h5>Semantics:</h5>
<p>Upon execution of a conditional '<tt>br</tt>' instruction, the '<tt>bool</tt>'
argument is evaluated. If the value is <tt>true</tt>, control flows
to the '<tt>iftrue</tt>' <tt>label</tt> argument. If "cond" is <tt>false</tt>,
control flows to the '<tt>iffalse</tt>' <tt>label</tt> argument.</p>
<h5>Example:</h5>
<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
href="#i_ret">ret</a> int 1<br>IfUnequal:<br> <a href="#i_ret">ret</a> int 0<br></pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="i_switch">'<tt>switch</tt>' Instruction</a>
</div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre>
switch <intty> <value>, label <defaultdest> [ <intty> <val>, label <dest> ... ]
</pre>
<h5>Overview:</h5>
<p>The '<tt>switch</tt>' instruction is used to transfer control flow to one of
several different places. It is a generalization of the '<tt>br</tt>'
instruction, allowing a branch to occur to one of many possible
destinations.</p>
<h5>Arguments:</h5>
<p>The '<tt>switch</tt>' instruction uses three parameters: an integer
comparison value '<tt>value</tt>', a default '<tt>label</tt>' destination, and
an array of pairs of comparison value constants and '<tt>label</tt>'s. The
table is not allowed to contain duplicate constant entries.</p>
<h5>Semantics:</h5>
<p>The <tt>switch</tt> instruction specifies a table of values and
destinations. When the '<tt>switch</tt>' instruction is executed, this
table is searched for the given value. If the value is found, the
corresponding destination is branched to, otherwise the default value
it transfered to.</p>
<h5>Implementation:</h5>
<p>Depending on properties of the target machine and the particular
<tt>switch</tt> instruction, this instruction may be code generated in different
ways, for example as a series of chained conditional branches, or with a lookup
table.</p>
<h5>Example:</h5>
<pre>
<i>; Emulate a conditional br instruction</i>
%Val = <a href="#i_cast">cast</a> bool %value to int
switch int %Val, label %truedest [int 0, label %falsedest ]
<i>; Emulate an unconditional br instruction</i>
switch uint 0, label %dest [ ]
<i>; Implement a jump table:</i>
switch uint %val, label %otherwise [ uint 0, label %onzero
uint 1, label %onone
uint 2, label %ontwo ]
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_invoke">'<tt>invoke</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> <result> = invoke <ptr to function ty> %<function ptr val>(<function args>)<br> to label <normal label> except label <exception label><br></pre>
<h5>Overview:</h5>
<p>The '<tt>invoke</tt>' instruction causes control to transfer to a
specified function, with the possibility of control flow transfer to
either the '<tt>normal</tt>' <tt>label</tt> label or the '<tt>exception</tt>'<tt>label</tt>.
If the callee function returns with the "<tt><a href="#i_ret">ret</a></tt>"
instruction, control flow will return to the "normal" label. If the
callee (or any indirect callees) returns with the "<a href="#i_unwind"><tt>unwind</tt></a>"
instruction, control is interrupted, and continued at the dynamically
nearest "except" label.</p>
<h5>Arguments:</h5>
<p>This instruction requires several arguments:</p>
<ol>
<li>'<tt>ptr to function ty</tt>': shall be the signature of the
pointer to function value being invoked. In most cases, this is a
direct function invocation, but indirect <tt>invoke</tt>s are just as
possible, branching off an arbitrary pointer to function value. </li>
<li>'<tt>function ptr val</tt>': An LLVM value containing a pointer
to a function to be invoked. </li>
<li>'<tt>function args</tt>': argument list whose types match the
function signature argument types. If the function signature indicates
the function accepts a variable number of arguments, the extra
arguments can be specified. </li>
<li>'<tt>normal label</tt>': the label reached when the called
function executes a '<tt><a href="#i_ret">ret</a></tt>' instruction. </li>
<li>'<tt>exception label</tt>': the label reached when a callee
returns with the <a href="#i_unwind"><tt>unwind</tt></a> instruction. </li>
</ol>
<h5>Semantics:</h5>
<p>This instruction is designed to operate as a standard '<tt><a
href="#i_call">call</a></tt>' instruction in most regards. The
primary difference is that it establishes an association with a label,
which is used by the runtime library to unwind the stack.</p>
<p>This instruction is used in languages with destructors to ensure
that proper cleanup is performed in the case of either a <tt>longjmp</tt>
or a thrown exception. Additionally, this is important for
implementation of '<tt>catch</tt>' clauses in high-level languages that
support them.</p>
<h5>Example:</h5>
<pre> %retval = invoke int %Test(int 15)<br> to label %Continue<br> except label %TestCleanup <i>; {int}:retval set</i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_unwind">'<tt>unwind</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> unwind<br></pre>
<h5>Overview:</h5>
<p>The '<tt>unwind</tt>' instruction unwinds the stack, continuing
control flow at the first callee in the dynamic call stack which used
an <a href="#i_invoke"><tt>invoke</tt></a> instruction to perform the
call. This is primarily used to implement exception handling.</p>
<h5>Semantics:</h5>
<p>The '<tt>unwind</tt>' intrinsic causes execution of the current
function to immediately halt. The dynamic call stack is then searched
for the first <a href="#i_invoke"><tt>invoke</tt></a> instruction on
the call stack. Once found, execution continues at the "exceptional"
destination block specified by the <tt>invoke</tt> instruction. If
there is no <tt>invoke</tt> instruction in the dynamic call chain,
undefined behavior results.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"> <a name="binaryops">Binary Operations</a> </div>
<div class="doc_text">
<p>Binary operators are used to do most of the computation in a
program. They require two operands, execute an operation on them, and
produce a single value. The result value of a binary operator is not
necessarily the same type as its operands.</p>
<p>There are several different binary operators:</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_add">'<tt>add</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> <result> = add <ty> <var1>, <var2> <i>; yields {ty}:result</i>
</pre>
<h5>Overview:</h5>
<p>The '<tt>add</tt>' instruction returns the sum of its two operands.</p>
<h5>Arguments:</h5>
<p>The two arguments to the '<tt>add</tt>' instruction must be either <a
href="#t_integer">integer</a> or <a href="#t_floating">floating point</a>
values. Both arguments must have identical types.</p>
<h5>Semantics:</h5>
<p>The value produced is the integer or floating point sum of the two
operands.</p>
<h5>Example:</h5>
<pre> <result> = add int 4, %var <i>; yields {int}:result = 4 + %var</i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_sub">'<tt>sub</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> <result> = sub <ty> <var1>, <var2> <i>; yields {ty}:result</i>
</pre>
<h5>Overview:</h5>
<p>The '<tt>sub</tt>' instruction returns the difference of its two
operands.</p>
<p>Note that the '<tt>sub</tt>' instruction is used to represent the '<tt>neg</tt>'
instruction present in most other intermediate representations.</p>
<h5>Arguments:</h5>
<p>The two arguments to the '<tt>sub</tt>' instruction must be either <a
href="#t_integer">integer</a> or <a href="#t_floating">floating point</a>
values. Both arguments must have identical types.</p>
<h5>Semantics:</h5>
<p>The value produced is the integer or floating point difference of
the two operands.</p>
<h5>Example:</h5>
<pre> <result> = sub int 4, %var <i>; yields {int}:result = 4 - %var</i>
<result> = sub int 0, %val <i>; yields {int}:result = -%var</i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_mul">'<tt>mul</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> <result> = mul <ty> <var1>, <var2> <i>; yields {ty}:result</i>
</pre>
<h5>Overview:</h5>
<p>The '<tt>mul</tt>' instruction returns the product of its two
operands.</p>
<h5>Arguments:</h5>
<p>The two arguments to the '<tt>mul</tt>' instruction must be either <a
href="#t_integer">integer</a> or <a href="#t_floating">floating point</a>
values. Both arguments must have identical types.</p>
<h5>Semantics:</h5>
<p>The value produced is the integer or floating point product of the
two operands.</p>
<p>There is no signed vs unsigned multiplication. The appropriate
action is taken based on the type of the operand.</p>
<h5>Example:</h5>
<pre> <result> = mul int 4, %var <i>; yields {int}:result = 4 * %var</i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_div">'<tt>div</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> <result> = div <ty> <var1>, <var2> <i>; yields {ty}:result</i>
</pre>
<h5>Overview:</h5>
<p>The '<tt>div</tt>' instruction returns the quotient of its two
operands.</p>
<h5>Arguments:</h5>
<p>The two arguments to the '<tt>div</tt>' instruction must be either <a
href="#t_integer">integer</a> or <a href="#t_floating">floating point</a>
values. Both arguments must have identical types.</p>
<h5>Semantics:</h5>
<p>The value produced is the integer or floating point quotient of the
two operands.</p>
<h5>Example:</h5>
<pre> <result> = div int 4, %var <i>; yields {int}:result = 4 / %var</i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_rem">'<tt>rem</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> <result> = rem <ty> <var1>, <var2> <i>; yields {ty}:result</i>
</pre>
<h5>Overview:</h5>
<p>The '<tt>rem</tt>' instruction returns the remainder from the
division of its two operands.</p>
<h5>Arguments:</h5>
<p>The two arguments to the '<tt>rem</tt>' instruction must be either <a
href="#t_integer">integer</a> or <a href="#t_floating">floating point</a>
values. Both arguments must have identical types.</p>
<h5>Semantics:</h5>
<p>This returns the <i>remainder</i> of a division (where the result
has the same sign as the divisor), not the <i>modulus</i> (where the
result has the same sign as the dividend) of a value. For more
information about the difference, see: <a
href="http://mathforum.org/dr.math/problems/anne.4.28.99.html">The
Math Forum</a>.</p>
<h5>Example:</h5>
<pre> <result> = rem int 4, %var <i>; yields {int}:result = 4 % %var</i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_setcc">'<tt>set<i>cc</i></tt>'
Instructions</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> <result> = seteq <ty> <var1>, <var2> <i>; yields {bool}:result</i>
<result> = setne <ty> <var1>, <var2> <i>; yields {bool}:result</i>
<result> = setlt <ty> <var1>, <var2> <i>; yields {bool}:result</i>
<result> = setgt <ty> <var1>, <var2> <i>; yields {bool}:result</i>
<result> = setle <ty> <var1>, <var2> <i>; yields {bool}:result</i>
<result> = setge <ty> <var1>, <var2> <i>; yields {bool}:result</i>
</pre>
<h5>Overview:</h5>
<p>The '<tt>set<i>cc</i></tt>' family of instructions returns a boolean
value based on a comparison of their two operands.</p>
<h5>Arguments:</h5>
<p>The two arguments to the '<tt>set<i>cc</i></tt>' instructions must
be of <a href="#t_firstclass">first class</a> type (it is not possible
to compare '<tt>label</tt>'s, '<tt>array</tt>'s, '<tt>structure</tt>'
or '<tt>void</tt>' values, etc...). Both arguments must have identical
types.</p>
<h5>Semantics:</h5>
<p>The '<tt>seteq</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>'
value if both operands are equal.<br>
The '<tt>setne</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>'
value if both operands are unequal.<br>
The '<tt>setlt</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>'
value if the first operand is less than the second operand.<br>
The '<tt>setgt</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>'
value if the first operand is greater than the second operand.<br>
The '<tt>setle</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>'
value if the first operand is less than or equal to the second operand.<br>
The '<tt>setge</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>'
value if the first operand is greater than or equal to the second
operand.</p>
<h5>Example:</h5>
<pre> <result> = seteq int 4, 5 <i>; yields {bool}:result = false</i>
<result> = setne float 4, 5 <i>; yields {bool}:result = true</i>
<result> = setlt uint 4, 5 <i>; yields {bool}:result = true</i>
<result> = setgt sbyte 4, 5 <i>; yields {bool}:result = false</i>
<result> = setle sbyte 4, 5 <i>; yields {bool}:result = true</i>
<result> = setge sbyte 4, 5 <i>; yields {bool}:result = false</i>
</pre>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"> <a name="bitwiseops">Bitwise Binary
Operations</a> </div>
<div class="doc_text">
<p>Bitwise binary operators are used to do various forms of
bit-twiddling in a program. They are generally very efficient
instructions, and can commonly be strength reduced from other
instructions. They require two operands, execute an operation on them,
and produce a single value. The resulting value of the bitwise binary
operators is always the same type as its first operand.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_and">'<tt>and</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> <result> = and <ty> <var1>, <var2> <i>; yields {ty}:result</i>
</pre>
<h5>Overview:</h5>
<p>The '<tt>and</tt>' instruction returns the bitwise logical and of
its two operands.</p>
<h5>Arguments:</h5>
<p>The two arguments to the '<tt>and</tt>' instruction must be <a
href="#t_integral">integral</a> values. Both arguments must have
identical types.</p>
<h5>Semantics:</h5>
<p>The truth table used for the '<tt>and</tt>' instruction is:</p>
<p> </p>
<div style="align: center">
<table border="1" cellspacing="0" cellpadding="4">
<tbody>
<tr>
<td>In0</td>
<td>In1</td>
<td>Out</td>
</tr>
<tr>
<td>0</td>
<td>0</td>
<td>0</td>
</tr>
<tr>
<td>0</td>
<td>1</td>
<td>0</td>
</tr>
<tr>
<td>1</td>
<td>0</td>
<td>0</td>
</tr>
<tr>
<td>1</td>
<td>1</td>
<td>1</td>
</tr>
</tbody>
</table>
</div>
<h5>Example:</h5>
<pre> <result> = and int 4, %var <i>; yields {int}:result = 4 & %var</i>
<result> = and int 15, 40 <i>; yields {int}:result = 8</i>
<result> = and int 4, 8 <i>; yields {int}:result = 0</i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_or">'<tt>or</tt>' Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> <result> = or <ty> <var1>, <var2> <i>; yields {ty}:result</i>
</pre>
<h5>Overview:</h5>
<p>The '<tt>or</tt>' instruction returns the bitwise logical inclusive
or of its two operands.</p>
<h5>Arguments:</h5>
<p>The two arguments to the '<tt>or</tt>' instruction must be <a
href="#t_integral">integral</a> values. Both arguments must have
identical types.</p>
<h5>Semantics:</h5>
<p>The truth table used for the '<tt>or</tt>' instruction is:</p>
<p> </p>
<div style="align: center">
<table border="1" cellspacing="0" cellpadding="4">
<tbody>
<tr>
<td>In0</td>
<td>In1</td>
<td>Out</td>
</tr>
<tr>
<td>0</td>
<td>0</td>
<td>0</td>
</tr>
<tr>
<td>0</td>
<td>1</td>
<td>1</td>
</tr>
<tr>
<td>1</td>
<td>0</td>
<td>1</td>
</tr>
<tr>
<td>1</td>
<td>1</td>
<td>1</td>
</tr>
</tbody>
</table>
</div>
<h5>Example:</h5>
<pre> <result> = or int 4, %var <i>; yields {int}:result = 4 | %var</i>
<result> = or int 15, 40 <i>; yields {int}:result = 47</i>
<result> = or int 4, 8 <i>; yields {int}:result = 12</i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_xor">'<tt>xor</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> <result> = xor <ty> <var1>, <var2> <i>; yields {ty}:result</i>
</pre>
<h5>Overview:</h5>
<p>The '<tt>xor</tt>' instruction returns the bitwise logical exclusive
or of its two operands. The <tt>xor</tt> is used to implement the
"one's complement" operation, which is the "~" operator in C.</p>
<h5>Arguments:</h5>
<p>The two arguments to the '<tt>xor</tt>' instruction must be <a
href="#t_integral">integral</a> values. Both arguments must have
identical types.</p>
<h5>Semantics:</h5>
<p>The truth table used for the '<tt>xor</tt>' instruction is:</p>
<p> </p>
<div style="align: center">
<table border="1" cellspacing="0" cellpadding="4">
<tbody>
<tr>
<td>In0</td>
<td>In1</td>
<td>Out</td>
</tr>
<tr>
<td>0</td>
<td>0</td>
<td>0</td>
</tr>
<tr>
<td>0</td>
<td>1</td>
<td>1</td>
</tr>
<tr>
<td>1</td>
<td>0</td>
<td>1</td>
</tr>
<tr>
<td>1</td>
<td>1</td>
<td>0</td>
</tr>
</tbody>
</table>
</div>
<p> </p>
<h5>Example:</h5>
<pre> <result> = xor int 4, %var <i>; yields {int}:result = 4 ^ %var</i>
<result> = xor int 15, 40 <i>; yields {int}:result = 39</i>
<result> = xor int 4, 8 <i>; yields {int}:result = 12</i>
<result> = xor int %V, -1 <i>; yields {int}:result = ~%V</i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_shl">'<tt>shl</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> <result> = shl <ty> <var1>, ubyte <var2> <i>; yields {ty}:result</i>
</pre>
<h5>Overview:</h5>
<p>The '<tt>shl</tt>' instruction returns the first operand shifted to
the left a specified number of bits.</p>
<h5>Arguments:</h5>
<p>The first argument to the '<tt>shl</tt>' instruction must be an <a
href="#t_integer">integer</a> type. The second argument must be an '<tt>ubyte</tt>'
type.</p>
<h5>Semantics:</h5>
<p>The value produced is <tt>var1</tt> * 2<sup><tt>var2</tt></sup>.</p>
<h5>Example:</h5>
<pre> <result> = shl int 4, ubyte %var <i>; yields {int}:result = 4 << %var</i>
<result> = shl int 4, ubyte 2 <i>; yields {int}:result = 16</i>
<result> = shl int 1, ubyte 10 <i>; yields {int}:result = 1024</i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_shr">'<tt>shr</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> <result> = shr <ty> <var1>, ubyte <var2> <i>; yields {ty}:result</i>
</pre>
<h5>Overview:</h5>
<p>The '<tt>shr</tt>' instruction returns the first operand shifted to
the right a specified number of bits.</p>
<h5>Arguments:</h5>
<p>The first argument to the '<tt>shr</tt>' instruction must be an <a
href="#t_integer">integer</a> type. The second argument must be an '<tt>ubyte</tt>'
type.</p>
<h5>Semantics:</h5>
<p>If the first argument is a <a href="#t_signed">signed</a> type, the
most significant bit is duplicated in the newly free'd bit positions.
If the first argument is unsigned, zero bits shall fill the empty
positions.</p>
<h5>Example:</h5>
<pre> <result> = shr int 4, ubyte %var <i>; yields {int}:result = 4 >> %var</i>
<result> = shr uint 4, ubyte 1 <i>; yields {uint}:result = 2</i>
<result> = shr int 4, ubyte 2 <i>; yields {int}:result = 1</i>
<result> = shr sbyte 4, ubyte 3 <i>; yields {sbyte}:result = 0</i>
<result> = shr sbyte -2, ubyte 1 <i>; yields {sbyte}:result = -1</i>
</pre>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"> <a name="memoryops">Memory Access
Operations</a></div>
<div class="doc_text">
<p>A key design point of an SSA-based representation is how it
represents memory. In LLVM, no memory locations are in SSA form, which
makes things very simple. This section describes how to read, write,
allocate and free memory in LLVM.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_malloc">'<tt>malloc</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> <result> = malloc <type>, uint <NumElements> <i>; yields {type*}:result</i>
<result> = malloc <type> <i>; yields {type*}:result</i>
</pre>
<h5>Overview:</h5>
<p>The '<tt>malloc</tt>' instruction allocates memory from the system
heap and returns a pointer to it.</p>
<h5>Arguments:</h5>
<p>The '<tt>malloc</tt>' instruction allocates <tt>sizeof(<type>)*NumElements</tt>
bytes of memory from the operating system and returns a pointer of the
appropriate type to the program. The second form of the instruction is
a shorter version of the first instruction that defaults to allocating
one element.</p>
<p>'<tt>type</tt>' must be a sized type.</p>
<h5>Semantics:</h5>
<p>Memory is allocated using the system "<tt>malloc</tt>" function, and
a pointer is returned.</p>
<h5>Example:</h5>
<pre> %array = malloc [4 x ubyte ] <i>; yields {[%4 x ubyte]*}:array</i>
%size = <a
href="#i_add">add</a> uint 2, 2 <i>; yields {uint}:size = uint 4</i>
%array1 = malloc ubyte, uint 4 <i>; yields {ubyte*}:array1</i>
%array2 = malloc [12 x ubyte], uint %size <i>; yields {[12 x ubyte]*}:array2</i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_free">'<tt>free</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> free <type> <value> <i>; yields {void}</i>
</pre>
<h5>Overview:</h5>
<p>The '<tt>free</tt>' instruction returns memory back to the unused
memory heap, to be reallocated in the future.</p>
<p> </p>
<h5>Arguments:</h5>
<p>'<tt>value</tt>' shall be a pointer value that points to a value
that was allocated with the '<tt><a href="#i_malloc">malloc</a></tt>'
instruction.</p>
<h5>Semantics:</h5>
<p>Access to the memory pointed to by the pointer is not longer defined
after this instruction executes.</p>
<h5>Example:</h5>
<pre> %array = <a href="#i_malloc">malloc</a> [4 x ubyte] <i>; yields {[4 x ubyte]*}:array</i>
free [4 x ubyte]* %array
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_alloca">'<tt>alloca</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> <result> = alloca <type>, uint <NumElements> <i>; yields {type*}:result</i>
<result> = alloca <type> <i>; yields {type*}:result</i>
</pre>
<h5>Overview:</h5>
<p>The '<tt>alloca</tt>' instruction allocates memory on the current
stack frame of the procedure that is live until the current function
returns to its caller.</p>
<h5>Arguments:</h5>
<p>The the '<tt>alloca</tt>' instruction allocates <tt>sizeof(<type>)*NumElements</tt>
bytes of memory on the runtime stack, returning a pointer of the
appropriate type to the program. The second form of the instruction is
a shorter version of the first that defaults to allocating one element.</p>
<p>'<tt>type</tt>' may be any sized type.</p>
<h5>Semantics:</h5>
<p>Memory is allocated, a pointer is returned. '<tt>alloca</tt>'d
memory is automatically released when the function returns. The '<tt>alloca</tt>'
instruction is commonly used to represent automatic variables that must
have an address available. When the function returns (either with the <tt><a
href="#i_ret">ret</a></tt> or <tt><a href="#i_invoke">invoke</a></tt>
instructions), the memory is reclaimed.</p>
<h5>Example:</h5>
<pre> %ptr = alloca int <i>; yields {int*}:ptr</i>
%ptr = alloca int, uint 4 <i>; yields {int*}:ptr</i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_load">'<tt>load</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> <result> = load <ty>* <pointer><br> <result> = volatile load <ty>* <pointer><br></pre>
<h5>Overview:</h5>
<p>The '<tt>load</tt>' instruction is used to read from memory.</p>
<h5>Arguments:</h5>
<p>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. If the <tt>load</tt> is
marked as <tt>volatile</tt> then the optimizer is not allowed to modify
the number or order of execution of this <tt>load</tt> with other
volatile <tt>load</tt> and <tt><a href="#i_store">store</a></tt>
instructions. </p>
<h5>Semantics:</h5>
<p>The location of memory pointed to is loaded.</p>
<h5>Examples:</h5>
<pre> %ptr = <a href="#i_alloca">alloca</a> int <i>; yields {int*}:ptr</i>
<a
href="#i_store">store</a> int 3, int* %ptr <i>; yields {void}</i>
%val = load int* %ptr <i>; yields {int}:val = int 3</i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_store">'<tt>store</tt>'
Instruction</a> </div>
<h5>Syntax:</h5>
<pre> store <ty> <value>, <ty>* <pointer> <i>; yields {void}</i>
volatile store <ty> <value>, <ty>* <pointer> <i>; yields {void}</i>
</pre>
<h5>Overview:</h5>
<p>The '<tt>store</tt>' instruction is used to write to memory.</p>
<h5>Arguments:</h5>
<p>There are two arguments to the '<tt>store</tt>' instruction: a value
to store and an address to store it into. The type of the '<tt><pointer></tt>'
operand must be a pointer to the type of the '<tt><value></tt>'
operand. If the <tt>store</tt> is marked as <tt>volatile</tt> then the
optimizer is not allowed to modify the number or order of execution of
this <tt>store</tt> with other volatile <tt>load</tt> and <tt><a
href="#i_store">store</a></tt> instructions.</p>
<h5>Semantics:</h5>
<p>The contents of memory are updated to contain '<tt><value></tt>'
at the location specified by the '<tt><pointer></tt>' operand.</p>
<h5>Example:</h5>
<pre> %ptr = <a href="#i_alloca">alloca</a> int <i>; yields {int*}:ptr</i>
<a
href="#i_store">store</a> int 3, int* %ptr <i>; yields {void}</i>
%val = load int* %ptr <i>; yields {int}:val = int 3</i>
</pre>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_getelementptr">'<tt>getelementptr</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> <result> = getelementptr <ty>* <ptrval>{, long <aidx>|, ubyte <sidx>}*<br></pre>
<h5>Overview:</h5>
<p>The '<tt>getelementptr</tt>' instruction is used to get the address
of a subelement of an aggregate data structure.</p>
<h5>Arguments:</h5>
<p>This instruction takes a list of <tt>long</tt> values and <tt>ubyte</tt>
constants that indicate what form of addressing to perform. The actual
types of the arguments provided depend on the type of the first pointer
argument. The '<tt>getelementptr</tt>' instruction is used to index
down through the type levels of a structure.</p>
<p>For example, let's consider a C code fragment and how it gets
compiled to LLVM:</p>
<pre>struct RT {<br> char A;<br> int B[10][20];<br> char C;<br>};<br>struct ST {<br> int X;<br> double Y;<br> struct RT Z;<br>};<br><br>int *foo(struct ST *s) {<br> return &s[1].Z.B[5][13];<br>}<br></pre>
<p>The LLVM code generated by the GCC frontend is:</p>
<pre>%RT = type { sbyte, [10 x [20 x int]], sbyte }<br>%ST = type { int, double, %RT }<br><br>int* "foo"(%ST* %s) {<br> %reg = getelementptr %ST* %s, long 1, ubyte 2, ubyte 1, long 5, long 13<br> ret int* %reg<br>}<br></pre>
<h5>Semantics:</h5>
<p>The index types specified for the '<tt>getelementptr</tt>'
instruction depend on the pointer type that is being index into. <a
href="t_pointer">Pointer</a> and <a href="t_array">array</a> types
require '<tt>long</tt>' values, and <a href="t_struct">structure</a>
types require '<tt>ubyte</tt>' <b>constants</b>.</p>
<p>In the example above, the first index is indexing into the '<tt>%ST*</tt>'
type, which is a pointer, yielding a '<tt>%ST</tt>' = '<tt>{ int,
double, %RT }</tt>' type, a structure. The second index indexes into
the third element of the structure, yielding a '<tt>%RT</tt>' = '<tt>{
sbyte, [10 x [20 x int]], sbyte }</tt>' type, another structure. The
third index indexes into the second element of the structure, yielding
a '<tt>[10 x [20 x int]]</tt>' type, an array. The two dimensions of
the array are subscripted into, yielding an '<tt>int</tt>' type. The '<tt>getelementptr</tt>'
instruction return a pointer to this element, thus yielding a '<tt>int*</tt>'
type.</p>
<p>Note that it is perfectly legal to index partially through a
structure, returning a pointer to an inner element. Because of this,
the LLVM code for the given testcase is equivalent to:</p>
<pre>int* "foo"(%ST* %s) {<br> %t1 = getelementptr %ST* %s , long 1 <i>; yields %ST*:%t1</i>
%t2 = getelementptr %ST* %t1, long 0, ubyte 2 <i>; yields %RT*:%t2</i>
%t3 = getelementptr %RT* %t2, long 0, ubyte 1 <i>; yields [10 x [20 x int]]*:%t3</i>
%t4 = getelementptr [10 x [20 x int]]* %t3, long 0, long 5 <i>; yields [20 x int]*:%t4</i>
%t5 = getelementptr [20 x int]* %t4, long 0, long 13 <i>; yields int*:%t5</i>
ret int* %t5
}
</pre>
<h5>Example:</h5>
<pre> <i>; yields [12 x ubyte]*:aptr</i>
%aptr = getelementptr {int, [12 x ubyte]}* %sptr, long 0, ubyte 1<br></pre>
<h5> Note To The Novice:</h5>
When using indexing into global arrays with the '<tt>getelementptr</tt>'
instruction, you must remember that the </div>
<!-- ======================================================================= -->
<div class="doc_subsection"> <a name="otherops">Other Operations</a> </div>
<div class="doc_text">
<p>The instructions in this catagory are the "miscellaneous"
instructions, which defy better classification.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_phi">'<tt>phi</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> <result> = phi <ty> [ <val0>, <label0>], ...<br></pre>
<h5>Overview:</h5>
<p>The '<tt>phi</tt>' instruction is used to implement the φ node in
the SSA graph representing the function.</p>
<h5>Arguments:</h5>
<p>The type of the incoming values are specified with the first type
field. After this, the '<tt>phi</tt>' instruction takes a list of pairs
as arguments, with one pair for each predecessor basic block of the
current block. Only values of <a href="#t_firstclass">first class</a>
type may be used as the value arguments to the PHI node. Only labels
may be used as the label arguments.</p>
<p>There must be no non-phi instructions between the start of a basic
block and the PHI instructions: i.e. PHI instructions must be first in
a basic block.</p>
<h5>Semantics:</h5>
<p>At runtime, the '<tt>phi</tt>' instruction logically takes on the
value specified by the parameter, depending on which basic block we
came from in the last <a href="#terminators">terminator</a> instruction.</p>
<h5>Example:</h5>
<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>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="i_cast">'<tt>cast .. to</tt>' Instruction</a>
</div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre>
<result> = cast <ty> <value> to <ty2> <i>; yields ty2</i>
</pre>
<h5>Overview:</h5>
<p>
The '<tt>cast</tt>' instruction is used as the primitive means to convert
integers to floating point, change data type sizes, and break type safety (by
casting pointers).
</p>
<h5>Arguments:</h5>
<p>
The '<tt>cast</tt>' instruction takes a value to cast, which must be a first
class value, and a type to cast it to, which must also be a <a
href="#t_firstclass">first class</a> type.
</p>
<h5>Semantics:</h5>
<p>
This instruction follows the C rules for explicit casts when determining how the
data being cast must change to fit in its new container.
</p>
<p>
When casting to bool, any value that would be considered true in the context of
a C '<tt>if</tt>' condition is converted to the boolean '<tt>true</tt>' values,
all else are '<tt>false</tt>'.
</p>
<p>
When extending an integral value from a type of one signness to another (for
example '<tt>sbyte</tt>' to '<tt>ulong</tt>'), the value is sign-extended if the
<b>source</b> value is signed, and zero-extended if the source value is
unsigned. <tt>bool</tt> values are always zero extended into either zero or
one.
</p>
<h5>Example:</h5>
<pre>
%X = cast int 257 to ubyte <i>; yields ubyte:1</i>
%Y = cast int 123 to bool <i>; yields bool:true</i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="i_select">'<tt>select</tt>' Instruction</a>
</div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre>
<result> = select bool <cond>, <ty> <val1>, <ty> <val2> <i>; yields ty</i>
</pre>
<h5>Overview:</h5>
<p>
The '<tt>select</tt>' instruction is used to choose one value based on a
condition, without branching.
</p>
<h5>Arguments:</h5>
<p>
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.
</p>
<h5>Semantics:</h5>
<p>
If the boolean condition evaluates to true, the instruction returns the first
value argument, otherwise it returns the second value argument.
</p>
<h5>Example:</h5>
<pre>
%X = select bool true, ubyte 17, ubyte 42 <i>; yields ubyte:17</i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_call">'<tt>call</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> <result> = call <ty>* <fnptrval>(<param list>)<br></pre>
<h5>Overview:</h5>
<p>The '<tt>call</tt>' instruction represents a simple function call.</p>
<h5>Arguments:</h5>
<p>This instruction requires several arguments:</p>
<ol>
<li>
<p>'<tt>ty</tt>': shall be the signature of the pointer to function
value being invoked. The argument types must match the types implied
by this signature.</p>
</li>
<li>
<p>'<tt>fnptrval</tt>': An LLVM value containing a pointer to a
function to be invoked. In most cases, this is a direct function
invocation, but indirect <tt>call</tt>s are just as possible,
calling an arbitrary pointer to function values.</p>
</li>
<li>
<p>'<tt>function args</tt>': argument list whose types match the
function signature argument types. If the function signature
indicates the function accepts a variable number of arguments, the
extra arguments can be specified.</p>
</li>
</ol>
<h5>Semantics:</h5>
<p>The '<tt>call</tt>' instruction is used to cause control flow to
transfer to a specified function, with its incoming arguments bound to
the specified values. Upon a '<tt><a href="#i_ret">ret</a></tt>'
instruction in the called function, control flow continues with the
instruction after the function call, and the return value of the
function is bound to the result argument. This is a simpler case of
the <a href="#i_invoke">invoke</a> instruction.</p>
<h5>Example:</h5>
<pre> %retval = call int %test(int %argc)<br> call int(sbyte*, ...) *%printf(sbyte* %msg, int 12, sbyte 42);<br></pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_vanext">'<tt>vanext</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> <resultarglist> = vanext <va_list> <arglist>, <argty><br></pre>
<h5>Overview:</h5>
<p>The '<tt>vanext</tt>' instruction is used to access arguments passed
through the "variable argument" area of a function call. It is used to
implement the <tt>va_arg</tt> macro in C.</p>
<h5>Arguments:</h5>
<p>This instruction takes a <tt>valist</tt> value and the type of the
argument. It returns another <tt>valist</tt>.</p>
<h5>Semantics:</h5>
<p>The '<tt>vanext</tt>' instruction advances the specified <tt>valist</tt>
past an argument of the specified type. In conjunction with the <a
href="#i_vaarg"><tt>vaarg</tt></a> instruction, it is used to implement
the <tt>va_arg</tt> macro available in C. For more information, see
the variable argument handling <a href="#int_varargs">Intrinsic
Functions</a>.</p>
<p>It is legal for this instruction to be called in a function which
does not take a variable number of arguments, for example, the <tt>vfprintf</tt>
function.</p>
<p><tt>vanext</tt> is an LLVM instruction instead of an <a
href="#intrinsics">intrinsic function</a> because it takes an type as
an argument.</p>
<h5>Example:</h5>
<p>See the <a href="#int_varargs">variable argument processing</a>
section.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_vaarg">'<tt>vaarg</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> <resultval> = vaarg <va_list> <arglist>, <argty><br></pre>
<h5>Overview:</h5>
<p>The '<tt>vaarg</tt>' instruction is used to access arguments passed
through the "variable argument" area of a function call. It is used to
implement the <tt>va_arg</tt> macro in C.</p>
<h5>Arguments:</h5>
<p>This instruction takes a <tt>valist</tt> value and the type of the
argument. It returns a value of the specified argument type.</p>
<h5>Semantics:</h5>
<p>The '<tt>vaarg</tt>' instruction loads an argument of the specified
type from the specified <tt>va_list</tt>. In conjunction with the <a
href="#i_vanext"><tt>vanext</tt></a> instruction, it is used to
implement the <tt>va_arg</tt> macro available in C. For more
information, see the variable argument handling <a href="#int_varargs">Intrinsic
Functions</a>.</p>
<p>It is legal for this instruction to be called in a function which
does not take a variable number of arguments, for example, the <tt>vfprintf</tt>
function.</p>
<p><tt>vaarg</tt> is an LLVM instruction instead of an <a
href="#intrinsics">intrinsic function</a> because it takes an type as
an argument.</p>
<h5>Example:</h5>
<p>See the <a href="#int_varargs">variable argument processing</a>
section.</p>
</div>
<!-- *********************************************************************** -->
<div class="doc_section"> <a name="intrinsics">Intrinsic Functions</a> </div>
<!-- *********************************************************************** -->
<div class="doc_text">
<p>LLVM supports the notion of an "intrinsic function". These functions have
well known names and semantics, and are required to follow certain
restrictions. Overall, these instructions represent an extension mechanism for
the LLVM language that does not require changing all of the transformations in
LLVM to add to the language (or the bytecode reader/writer, the parser,
etc...).</p>
<p>Intrinsic function names must all start with an "<tt>llvm.</tt>" prefix, this
prefix is reserved in LLVM for intrinsic names, thus functions may not be named
this. Intrinsic functions must always be external functions: you cannot define
the body of intrinsic functions. Intrinsic functions may only be used in call
or invoke instructions: it is illegal to take the address of an intrinsic
function. Additionally, because intrinsic functions are part of the LLVM
language, it is required that they all be documented here if any are added.</p>
<p>
Adding an intrinsic to LLVM is straight-forward if it is possible to express the
concept in LLVM directly (ie, code generator support is not _required_). To do
this, extend the default implementation of the IntrinsicLowering class to handle
the intrinsic. Code generators use this class to lower intrinsics they do not
understand to raw LLVM instructions that they do.
</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="int_varargs">Variable Argument Handling Intrinsics</a>
</div>
<div class="doc_text">
<p>Variable argument support is defined in LLVM with the <a
href="#i_vanext"><tt>vanext</tt></a> instruction and these three
intrinsic functions. These functions are related to the similarly
named macros defined in the <tt><stdarg.h></tt> header file.</p>
<p>All of these functions operate on arguments that use a
target-specific value type "<tt>va_list</tt>". The LLVM assembly
language reference manual does not define what this type is, so all
transformations should be prepared to handle intrinsics with any type
used.</p>
<p>This example shows how the <a href="#i_vanext"><tt>vanext</tt></a>
instruction and the variable argument handling intrinsic functions are
used.</p>
<pre>
int %test(int %X, ...) {
; Initialize variable argument processing
%ap = call sbyte* %<a href="#i_va_start">llvm.va_start</a>()
; Read a single integer argument
%tmp = vaarg sbyte* %ap, int
; Advance to the next argument
%ap2 = vanext sbyte* %ap, int
; Demonstrate usage of llvm.va_copy and llvm.va_end
%aq = call sbyte* %<a href="#i_va_copy">llvm.va_copy</a>(sbyte* %ap2)
call void %<a href="#i_va_end">llvm.va_end</a>(sbyte* %aq)
; Stop processing of arguments.
call void %<a href="#i_va_end">llvm.va_end</a>(sbyte* %ap2)
ret int %tmp
}
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="i_va_start">'<tt>llvm.va_start</tt>' Intrinsic</a>
</div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> call va_list ()* %llvm.va_start()<br></pre>
<h5>Overview:</h5>
<p>The '<tt>llvm.va_start</tt>' intrinsic returns a new <tt><arglist></tt>
for subsequent use by the variable argument intrinsics.</p>
<h5>Semantics:</h5>
<p>The '<tt>llvm.va_start</tt>' intrinsic works just like the <tt>va_start</tt>
macro available in C. In a target-dependent way, it initializes and
returns a <tt>va_list</tt> element, so that the next <tt>vaarg</tt>
will produce the first variable argument passed to the function. Unlike
the C <tt>va_start</tt> macro, this intrinsic does not need to know the
last argument of the function, the compiler can figure that out.</p>
<p>Note that this intrinsic function is only legal to be called from
within the body of a variable argument function.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="i_va_end">'<tt>llvm.va_end</tt>' Intrinsic</a>
</div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> call void (va_list)* %llvm.va_end(va_list <arglist>)<br></pre>
<h5>Overview:</h5>
<p>The '<tt>llvm.va_end</tt>' intrinsic destroys <tt><arglist></tt>
which has been initialized previously with <tt><a href="#i_va_start">llvm.va_start</a></tt>
or <tt><a href="#i_va_copy">llvm.va_copy</a></tt>.</p>
<h5>Arguments:</h5>
<p>The argument is a <tt>va_list</tt> to destroy.</p>
<h5>Semantics:</h5>
<p>The '<tt>llvm.va_end</tt>' intrinsic works just like the <tt>va_end</tt>
macro available in C. In a target-dependent way, it destroys the <tt>va_list</tt>.
Calls to <a href="#i_va_start"><tt>llvm.va_start</tt></a> and <a
href="#i_va_copy"><tt>llvm.va_copy</tt></a> must be matched exactly
with calls to <tt>llvm.va_end</tt>.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="i_va_copy">'<tt>llvm.va_copy</tt>' Intrinsic</a>
</div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> call va_list (va_list)* %llvm.va_copy(va_list <destarglist>)<br></pre>
<h5>Overview:</h5>
<p>The '<tt>llvm.va_copy</tt>' intrinsic copies the current argument
position from the source argument list to the destination argument list.</p>
<h5>Arguments:</h5>
<p>The argument is the <tt>va_list</tt> to copy.</p>
<h5>Semantics:</h5>
<p>The '<tt>llvm.va_copy</tt>' intrinsic works just like the <tt>va_copy</tt>
macro available in C. In a target-dependent way, it copies the source <tt>va_list</tt>
element into the returned list. This intrinsic is necessary because the <tt><a
href="i_va_start">llvm.va_start</a></tt> intrinsic may be arbitrarily
complex and require memory allocation, for example.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="int_codegen">Code Generator Intrinsics</a>
</div>
<div class="doc_text">
<p>
These intrinsics are provided by LLVM to expose special features that may only
be implemented with code generator support.
</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="i_returnaddress">'<tt>llvm.returnaddress</tt>' Intrinsic</a>
</div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre>
call void* ()* %llvm.returnaddress(uint <level>)
</pre>
<h5>Overview:</h5>
<p>
The '<tt>llvm.returnaddress</tt>' intrinsic returns a target-specific value
indicating the return address of the current function or one of its callers.
</p>
<h5>Arguments:</h5>
<p>
The argument to this intrinsic indicates which function to return the address
for. Zero indicates the calling function, one indicates its caller, etc. The
argument is <b>required</b> to be a constant integer value.
</p>
<h5>Semantics:</h5>
<p>
The '<tt>llvm.returnaddress</tt>' intrinsic either returns a pointer indicating
the return address of the specified call frame, or zero if it cannot be
identified. The value returned by this intrinsic is likely to be incorrect or 0
for arguments other than zero, so it should only be used for debugging purposes.
</p>
<p>
Note that calling this intrinsic does not prevent function inlining or other
aggressive transformations, so the value returned may not that of the obvious
source-language caller.
</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="i_frameaddress">'<tt>llvm.frameaddress</tt>' Intrinsic</a>
</div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre>
call void* ()* %llvm.frameaddress(uint <level>)
</pre>
<h5>Overview:</h5>
<p>
The '<tt>llvm.frameaddress</tt>' intrinsic returns the target-specific frame
pointer value for the specified stack frame.
</p>
<h5>Arguments:</h5>
<p>
The argument to this intrinsic indicates which function to return the frame
pointer for. Zero indicates the calling function, one indicates its caller,
etc. The argument is <b>required</b> to be a constant integer value.
</p>
<h5>Semantics:</h5>
<p>
The '<tt>llvm.frameaddress</tt>' intrinsic either returns a pointer indicating
the frame address of the specified call frame, or zero if it cannot be
identified. The value returned by this intrinsic is likely to be incorrect or 0
for arguments other than zero, so it should only be used for debugging purposes.
</p>
<p>
Note that calling this intrinsic does not prevent function inlining or other
aggressive transformations, so the value returned may not that of the obvious
source-language caller.
</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="int_libc">Standard C Library Intrinsics</a>
</div>
<div class="doc_text">
<p>
LLVM provides intrinsics for a few important standard C library functions.
These intrinsics allow source-language front-ends to pass information about the
alignment of the pointer arguments to the code generator, providing opportunity
for more efficient code generation.
</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="i_memcpy">'<tt>llvm.memcpy</tt>' Intrinsic</a>
</div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre>
call void (sbyte*, sbyte*, uint, uint)* %llvm.memcpy(sbyte* <dest>, sbyte* <src>,
uint <len>, uint <align>)
</pre>
<h5>Overview:</h5>
<p>
The '<tt>llvm.memcpy</tt>' intrinsic copies a block of memory from the source
location to the destination location.
</p>
<p>
Note that, unlike the standard libc function, the <tt>llvm.memcpy</tt> intrinsic
does not return a value, and takes an extra alignment argument.
</p>
<h5>Arguments:</h5>
<p>
The first argument is a pointer to the destination, the second is a pointer to
the source. The third argument is an (arbitrarily sized) integer argument
specifying the number of bytes to copy, and the fourth argument is the alignment
of the source and destination locations.
</p>
<p>
If the call to this intrinisic has an alignment value that is not 0 or 1, then
the caller guarantees that the size of the copy is a multiple of the alignment
and that both the source and destination pointers are aligned to that boundary.
</p>
<h5>Semantics:</h5>
<p>
The '<tt>llvm.memcpy</tt>' intrinsic copies a block of memory from the source
location to the destination location, which are not allowed to overlap. It
copies "len" bytes of memory over. If the argument is known to be aligned to
some boundary, this can be specified as the fourth argument, otherwise it should
be set to 0 or 1.
</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="i_memmove">'<tt>llvm.memmove</tt>' Intrinsic</a>
</div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre>
call void (sbyte*, sbyte*, uint, uint)* %llvm.memmove(sbyte* <dest>, sbyte* <src>,
uint <len>, uint <align>)
</pre>
<h5>Overview:</h5>
<p>
The '<tt>llvm.memmove</tt>' intrinsic moves a block of memory from the source
location to the destination location. It is similar to the '<tt>llvm.memcpy</tt>'
intrinsic but allows the two memory locations to overlap.
</p>
<p>
Note that, unlike the standard libc function, the <tt>llvm.memmove</tt> intrinsic
does not return a value, and takes an extra alignment argument.
</p>
<h5>Arguments:</h5>
<p>
The first argument is a pointer to the destination, the second is a pointer to
the source. The third argument is an (arbitrarily sized) integer argument
specifying the number of bytes to copy, and the fourth argument is the alignment
of the source and destination locations.
</p>
<p>
If the call to this intrinisic has an alignment value that is not 0 or 1, then
the caller guarantees that the size of the copy is a multiple of the alignment
and that both the source and destination pointers are aligned to that boundary.
</p>
<h5>Semantics:</h5>
<p>
The '<tt>llvm.memmove</tt>' intrinsic copies a block of memory from the source
location to the destination location, which may overlap. It
copies "len" bytes of memory over. If the argument is known to be aligned to
some boundary, this can be specified as the fourth argument, otherwise it should
be set to 0 or 1.
</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="i_memset">'<tt>llvm.memset</tt>' Intrinsic</a>
</div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre>
call void (sbyte*, ubyte, uint, uint)* %llvm.memset(sbyte* <dest>, ubyte <val>,
uint <len>, uint <align>)
</pre>
<h5>Overview:</h5>
<p>
The '<tt>llvm.memset</tt>' intrinsic fills a block of memory with a particular
byte value.
</p>
<p>
Note that, unlike the standard libc function, the <tt>llvm.memset</tt> intrinsic
does not return a value, and takes an extra alignment argument.
</p>
<h5>Arguments:</h5>
<p>
The first argument is a pointer to the destination to fill, the second is the
byte value to fill it with, the third argument is an (arbitrarily sized) integer
argument specifying the number of bytes to fill, and the fourth argument is the
known alignment of destination location.
</p>
<p>
If the call to this intrinisic has an alignment value that is not 0 or 1, then
the caller guarantees that the size of the copy is a multiple of the alignment
and that the destination pointer is aligned to that boundary.
</p>
<h5>Semantics:</h5>
<p>
The '<tt>llvm.memset</tt>' intrinsic fills "len" bytes of memory starting at the
destination location. If the argument is known to be aligned to some boundary,
this can be specified as the fourth argument, otherwise it should be set to 0 or
1.
</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="int_debugger">Debugger Intrinsics</a>
</div>
<div class="doc_text">
<p>
The LLVM debugger intrinsics (which all start with <tt>llvm.dbg.</tt> prefix),
are described in the <a
href="SourceLevelDebugging.html#format_common_intrinsics">LLVM Source Level
Debugging</a> document.
</p>
</div>
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