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<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="#highlevel">High Level Structure</a>
<ol>
<li><a href="#modulestructure">Module Structure</a></li>
<li><a href="#linkage">Linkage Types</a></li>
<li><a href="#callingconv">Calling Conventions</a></li>
<li><a href="#globalvars">Global Variables</a></li>
<li><a href="#functionstructure">Functions</a></li>
<li><a href="#aliasstructure">Aliases</a>
<li><a href="#paramattrs">Parameter Attributes</a></li>
<li><a href="#moduleasm">Module-Level Inline Assembly</a></li>
<li><a href="#datalayout">Data Layout</a></li>
</ol>
</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_pstruct">Packed Structure Type</a></li>
<li><a href="#t_vector">Vector Type</a></li>
<li><a href="#t_opaque">Opaque Type</a></li>
</ol>
</li>
</ol>
</li>
<li><a href="#constants">Constants</a>
<ol>
<li><a href="#simpleconstants">Simple Constants</a>
<li><a href="#aggregateconstants">Aggregate Constants</a>
<li><a href="#globalconstants">Global Variable and Function Addresses</a>
<li><a href="#undefvalues">Undefined Values</a>
<li><a href="#constantexprs">Constant Expressions</a>
</ol>
</li>
<li><a href="#othervalues">Other Values</a>
<ol>
<li><a href="#inlineasm">Inline Assembler Expressions</a>
</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>
<li><a href="#i_unreachable">'<tt>unreachable</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_udiv">'<tt>udiv</tt>' Instruction</a></li>
<li><a href="#i_sdiv">'<tt>sdiv</tt>' Instruction</a></li>
<li><a href="#i_fdiv">'<tt>fdiv</tt>' Instruction</a></li>
<li><a href="#i_urem">'<tt>urem</tt>' Instruction</a></li>
<li><a href="#i_srem">'<tt>srem</tt>' Instruction</a></li>
<li><a href="#i_frem">'<tt>frem</tt>' Instruction</a></li>
</ol>
</li>
<li><a href="#bitwiseops">Bitwise Binary Operations</a>
<ol>
<li><a href="#i_shl">'<tt>shl</tt>' Instruction</a></li>
<li><a href="#i_lshr">'<tt>lshr</tt>' Instruction</a></li>
<li><a href="#i_ashr">'<tt>ashr</tt>' Instruction</a></li>
<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>
</ol>
</li>
<li><a href="#vectorops">Vector Operations</a>
<ol>
<li><a href="#i_extractelement">'<tt>extractelement</tt>' Instruction</a></li>
<li><a href="#i_insertelement">'<tt>insertelement</tt>' Instruction</a></li>
<li><a href="#i_shufflevector">'<tt>shufflevector</tt>' Instruction</a></li>
</ol>
</li>
<li><a href="#memoryops">Memory Access and Addressing 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="#convertops">Conversion Operations</a>
<ol>
<li><a href="#i_trunc">'<tt>trunc .. to</tt>' Instruction</a></li>
<li><a href="#i_zext">'<tt>zext .. to</tt>' Instruction</a></li>
<li><a href="#i_sext">'<tt>sext .. to</tt>' Instruction</a></li>
<li><a href="#i_fptrunc">'<tt>fptrunc .. to</tt>' Instruction</a></li>
<li><a href="#i_fpext">'<tt>fpext .. to</tt>' Instruction</a></li>
<li><a href="#i_fptoui">'<tt>fptoui .. to</tt>' Instruction</a></li>
<li><a href="#i_fptosi">'<tt>fptosi .. to</tt>' Instruction</a></li>
<li><a href="#i_uitofp">'<tt>uitofp .. to</tt>' Instruction</a></li>
<li><a href="#i_sitofp">'<tt>sitofp .. to</tt>' Instruction</a></li>
<li><a href="#i_ptrtoint">'<tt>ptrtoint .. to</tt>' Instruction</a></li>
<li><a href="#i_inttoptr">'<tt>inttoptr .. to</tt>' Instruction</a></li>
<li><a href="#i_bitcast">'<tt>bitcast .. to</tt>' Instruction</a></li>
</ol>
<li><a href="#otherops">Other Operations</a>
<ol>
<li><a href="#i_icmp">'<tt>icmp</tt>' Instruction</a></li>
<li><a href="#i_fcmp">'<tt>fcmp</tt>' Instruction</a></li>
<li><a href="#i_phi">'<tt>phi</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_va_arg">'<tt>va_arg</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="#int_va_start">'<tt>llvm.va_start</tt>' Intrinsic</a></li>
<li><a href="#int_va_end">'<tt>llvm.va_end</tt>' Intrinsic</a></li>
<li><a href="#int_va_copy">'<tt>llvm.va_copy</tt>' Intrinsic</a></li>
</ol>
</li>
<li><a href="#int_gc">Accurate Garbage Collection Intrinsics</a>
<ol>
<li><a href="#int_gcroot">'<tt>llvm.gcroot</tt>' Intrinsic</a></li>
<li><a href="#int_gcread">'<tt>llvm.gcread</tt>' Intrinsic</a></li>
<li><a href="#int_gcwrite">'<tt>llvm.gcwrite</tt>' Intrinsic</a></li>
</ol>
</li>
<li><a href="#int_codegen">Code Generator Intrinsics</a>
<ol>
<li><a href="#int_returnaddress">'<tt>llvm.returnaddress</tt>' Intrinsic</a></li>
<li><a href="#int_frameaddress">'<tt>llvm.frameaddress</tt>' Intrinsic</a></li>
<li><a href="#int_stacksave">'<tt>llvm.stacksave</tt>' Intrinsic</a></li>
<li><a href="#int_stackrestore">'<tt>llvm.stackrestore</tt>' Intrinsic</a></li>
<li><a href="#int_prefetch">'<tt>llvm.prefetch</tt>' Intrinsic</a></li>
<li><a href="#int_pcmarker">'<tt>llvm.pcmarker</tt>' Intrinsic</a></li>
<li><a href="#int_readcyclecounter"><tt>llvm.readcyclecounter</tt>' Intrinsic</a></li>
</ol>
</li>
<li><a href="#int_libc">Standard C Library Intrinsics</a>
<ol>
<li><a href="#int_memcpy">'<tt>llvm.memcpy.*</tt>' Intrinsic</a></li>
<li><a href="#int_memmove">'<tt>llvm.memmove.*</tt>' Intrinsic</a></li>
<li><a href="#int_memset">'<tt>llvm.memset.*</tt>' Intrinsic</a></li>
<li><a href="#int_sqrt">'<tt>llvm.sqrt.*</tt>' Intrinsic</a></li>
<li><a href="#int_powi">'<tt>llvm.powi.*</tt>' Intrinsic</a></li>
</ol>
</li>
<li><a href="#int_manip">Bit Manipulation Intrinsics</a>
<ol>
<li><a href="#int_bswap">'<tt>llvm.bswap.*</tt>' Intrinsics</a></li>
<li><a href="#int_ctpop">'<tt>llvm.ctpop.*</tt>' Intrinsic </a></li>
<li><a href="#int_ctlz">'<tt>llvm.ctlz.*</tt>' Intrinsic </a></li>
<li><a href="#int_cttz">'<tt>llvm.cttz.*</tt>' Intrinsic </a></li>
<li><a href="#int_part_select">'<tt>llvm.part.select.*</tt>' Intrinsic </a></li>
<li><a href="#int_part_set">'<tt>llvm.part.set.*</tt>' Intrinsic </a></li>
</ol>
</li>
<li><a href="#int_debugger">Debugger intrinsics</a></li>
<li><a href="#int_eh">Exception Handling intrinsics</a></li>
<li><a href="#int_atomics">Atomic Operations and Synchronization Intrinsics</a>
<ol>
<li><a href="#int_lcs">'<tt>llvm.atomic.lcs.*</tt>' Intrinsic</a></li>
<li><a href="#int_ls">'<tt>llvm.atomic.ls.*</tt>' Intrinsic</a></li>
<li><a href="#int_las">'<tt>llvm.atomic.las.*</tt>' Intrinsic</a></li>
<li><a href="#int_lss">'<tt>llvm.atomic.lss.*</tt>' Intrinsic</a></li>
<li><a href="#int_memory_barrier">'<tt>llvm.memory.barrier</tt>' Intrinsic</a></li>
</ol>
</li>
<li><a href="#int_trampoline">Trampoline Intrinsic</a>
<ol>
<li><a href="#int_it">'<tt>llvm.init.trampoline</tt>' Intrinsic</a></li>
</ol>
</li>
<li><a href="#int_general">General intrinsics</a>
<ol>
<li><a href="#int_var_annotation">
<tt>llvm.var.annotation</tt>' Intrinsic</a></li>
</ol>
</li>
</ol>
</li>
</ol>
<div class="doc_author">
<p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>
and <a href="mailto:vadve@cs.uiuc.edu">Vikram Adve</a></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 bitcode
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 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>
<div class="doc_code">
<pre>
%x = <a href="#i_add">add</a> i32 1, %x
</pre>
</div>
<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 bitcode. The violations pointed out
by the verifier pass indicate bugs in transformation passes or input to
the parser.</p>
</div>
<!-- Describe the typesetting conventions here. -->
<!-- *********************************************************************** -->
<div class="doc_section"> <a name="identifiers">Identifiers</a> </div>
<!-- *********************************************************************** -->
<div class="doc_text">
<p>LLVM identifiers come in two basic types: global and local. Global
identifiers (functions, global variables) begin with the @ character. Local
identifiers (register names, types) begin with the % character. Additionally,
there are three different formats for identifiers, for different purposes:
<ol>
<li>Named values are represented as a string of characters with their 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>&quot;</tt> character can
be used in a named value.</li>
<li>Unnamed values are represented as an unsigned numeric value with their
prefix. For example, %12, @2, %44.</li>
<li>Constants, which are described in a <a href="#constants">section about
constants</a>, below.</li>
</ol>
<p>LLVM requires that values start with a prefix 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_bitcast">bitcast</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_primitive">i32</a></tt>', etc...),
and others. These reserved words cannot conflict with variable names, because
none of them start with a prefix character ('%' or '@').</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>
<div class="doc_code">
<pre>
%result = <a href="#i_mul">mul</a> i32 %X, 8
</pre>
</div>
<p>After strength reduction:</p>
<div class="doc_code">
<pre>
%result = <a href="#i_shl">shl</a> i32 %X, i8 3
</pre>
</div>
<p>And the hard way:</p>
<div class="doc_code">
<pre>
<a href="#i_add">add</a> i32 %X, %X <i>; yields {i32}:%0</i>
<a href="#i_add">add</a> i32 %0, %0 <i>; yields {i32}:%1</i>
%result = <a href="#i_add">add</a> i32 %1, %1
</pre>
</div>
<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 shows 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>
</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>
<div class="doc_code">
<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 i8]</a> c"hello world\0A\00" <i>; [13 x i8]*</i>
<i>; External declaration of the puts function</i>
<a href="#functionstructure">declare</a> i32 @puts(i8 *) <i>; i32(i8 *)* </i>
<i>; Definition of main function</i>
define i32 @main() { <i>; i32()* </i>
<i>; Convert [13x i8 ]* to i8 *...</i>
%cast210 = <a
href="#i_getelementptr">getelementptr</a> [13 x i8 ]* @.LC0, i64 0, i64 0 <i>; i8 *</i>
<i>; Call puts function to write out the string to stdout...</i>
<a
href="#i_call">call</a> i32 @puts(i8 * %cast210) <i>; i32</i>
<a
href="#i_ret">ret</a> i32 0<br>}<br>
</pre>
</div>
<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>
<p>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 <a
href="#linkage">linkage types</a>.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="linkage">Linkage Types</a>
</div>
<div class="doc_text">
<p>
All Global Variables and Functions have one of the following types of linkage:
</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.
</dd>
<dt><tt><b><a name="linkage_linkonce">linkonce</a></b></tt>: </dt>
<dd>Globals with "<tt>linkonce</tt>" linkage are merged with other globals of
the same name when linkage occurs. This is typically used to implement
inline functions, templates, or other code which must be generated in each
translation unit that uses it. Unreferenced <tt>linkonce</tt> globals are
allowed to be discarded.
</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 for globals that may be emitted in multiple translation units, but that
are not guaranteed to be emitted into every translation unit that uses them.
One example of this are common globals in C, such as "<tt>int X;</tt>" at
global scope.
</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.
</dd>
<dt><tt><b><a name="linkage_externweak">extern_weak</a></b></tt>: </dt>
<dd>The semantics of this linkage follow the ELF model: the symbol is weak
until linked, if not linked, the symbol becomes null instead of being an
undefined reference.
</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.
</dd>
</dl>
<p>
The next two types of linkage are targeted for Microsoft Windows platform
only. They are designed to support importing (exporting) symbols from (to)
DLLs.
</p>
<dl>
<dt><tt><b><a name="linkage_dllimport">dllimport</a></b></tt>: </dt>
<dd>"<tt>dllimport</tt>" linkage causes the compiler to reference a function
or variable via a global pointer to a pointer that is set up by the DLL
exporting the symbol. On Microsoft Windows targets, the pointer name is
formed by combining <code>_imp__</code> and the function or variable name.
</dd>
<dt><tt><b><a name="linkage_dllexport">dllexport</a></b></tt>: </dt>
<dd>"<tt>dllexport</tt>" linkage causes the compiler to provide a global
pointer to a pointer in a DLL, so that it can be referenced with the
<tt>dllimport</tt> attribute. On Microsoft Windows targets, the pointer
name is formed by combining <code>_imp__</code> and the function or variable
name.
</dd>
</dl>
<p><a name="linkage_external"></a>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.</p>
<p>It is illegal for a function <i>declaration</i>
to have any linkage type other than "externally visible", <tt>dllimport</tt>,
or <tt>extern_weak</tt>.</p>
<p>Aliases can have only <tt>external</tt>, <tt>internal</tt> and <tt>weak</tt>
linkages.
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="callingconv">Calling Conventions</a>
</div>
<div class="doc_text">
<p>LLVM <a href="#functionstructure">functions</a>, <a href="#i_call">calls</a>
and <a href="#i_invoke">invokes</a> can all have an optional calling convention
specified for the call. The calling convention of any pair of dynamic
caller/callee must match, or the behavior of the program is undefined. The
following calling conventions are supported by LLVM, and more may be added in
the future:</p>
<dl>
<dt><b>"<tt>ccc</tt>" - The C calling convention</b>:</dt>
<dd>This calling convention (the default if no other calling convention is
specified) matches the target C calling conventions. This calling convention
supports varargs function calls and tolerates some mismatch in the declared
prototype and implemented declaration of the function (as does normal C).
</dd>
<dt><b>"<tt>fastcc</tt>" - The fast calling convention</b>:</dt>
<dd>This calling convention attempts to make calls as fast as possible
(e.g. by passing things in registers). This calling convention allows the
target to use whatever tricks it wants to produce fast code for the target,
without having to conform to an externally specified ABI. Implementations of
this convention should allow arbitrary tail call optimization to be supported.
This calling convention does not support varargs and requires the prototype of
all callees to exactly match the prototype of the function definition.
</dd>
<dt><b>"<tt>coldcc</tt>" - The cold calling convention</b>:</dt>
<dd>This calling convention attempts to make code in the caller as efficient
as possible under the assumption that the call is not commonly executed. As
such, these calls often preserve all registers so that the call does not break
any live ranges in the caller side. This calling convention does not support
varargs and requires the prototype of all callees to exactly match the
prototype of the function definition.
</dd>
<dt><b>"<tt>cc &lt;<em>n</em>&gt;</tt>" - Numbered convention</b>:</dt>
<dd>Any calling convention may be specified by number, allowing
target-specific calling conventions to be used. Target specific calling
conventions start at 64.
</dd>
</dl>
<p>More calling conventions can be added/defined on an as-needed basis, to
support pascal conventions or any other well-known target-independent
convention.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="visibility">Visibility Styles</a>
</div>
<div class="doc_text">
<p>
All Global Variables and Functions have one of the following visibility styles:
</p>
<dl>
<dt><b>"<tt>default</tt>" - Default style</b>:</dt>
<dd>On ELF, default visibility means that the declaration is visible to other
modules and, in shared libraries, means that the declared entity may be
overridden. On Darwin, default visibility means that the declaration is
visible to other modules. Default visibility corresponds to "external
linkage" in the language.
</dd>
<dt><b>"<tt>hidden</tt>" - Hidden style</b>:</dt>
<dd>Two declarations of an object with hidden visibility refer to the same
object if they are in the same shared object. Usually, hidden visibility
indicates that the symbol will not be placed into the dynamic symbol table,
so no other module (executable or shared library) can reference it
directly.
</dd>
<dt><b>"<tt>protected</tt>" - Protected style</b>:</dt>
<dd>On ELF, protected visibility indicates that the symbol will be placed in
the dynamic symbol table, but that references within the defining module will
bind to the local symbol. That is, the symbol cannot be overridden by another
module.
</dd>
</dl>
</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, may have
an explicit section to be placed in, and may have an optional explicit alignment
specified. A variable may be defined as "thread_local", which means that it
will not be shared by threads (each thread will have a separated copy of the
variable). A variable may be defined as a global "constant," which indicates
that the contents of the variable will <b>never</b> be modified (enabling better
optimization, allowing the global data to be placed in the read-only section of
an executable, etc). Note that variables that need runtime initialization
cannot be marked "constant" as there is a store to the variable.</p>
<p>
LLVM explicitly allows <em>declarations</em> of global variables to be marked
constant, even if the final definition of the global is not. This capability
can be used to enable slightly better optimization of the program, but requires
the language definition to guarantee that optimizations based on the
'constantness' are valid for the translation units that do not include the
definition.
</p>
<p>As SSA values, global variables define pointer values that are in
scope (i.e. they dominate) 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>
<p>LLVM allows an explicit section to be specified for globals. If the target
supports it, it will emit globals to the section specified.</p>
<p>An explicit alignment may be specified for a global. If not present, or if
the alignment is set to zero, the alignment of the global is set by the target
to whatever it feels convenient. If an explicit alignment is specified, the
global is forced to have at least that much alignment. All alignments must be
a power of 2.</p>
<p>For example, the following defines a global with an initializer, section,
and alignment:</p>
<div class="doc_code">
<pre>
@G = constant float 1.0, section "foo", align 4
</pre>
</div>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="functionstructure">Functions</a>
</div>
<div class="doc_text">
<p>LLVM function definitions consist of the "<tt>define</tt>" keyord,
an optional <a href="#linkage">linkage type</a>, an optional
<a href="#visibility">visibility style</a>, an optional
<a href="#callingconv">calling convention</a>, a return type, an optional
<a href="#paramattrs">parameter attribute</a> for the return type, a function
name, a (possibly empty) argument list (each with optional
<a href="#paramattrs">parameter attributes</a>), an optional section, an
optional alignment, an opening curly brace, a list of basic blocks, and a
closing curly brace.
LLVM function declarations consist of the "<tt>declare</tt>" keyword, an
optional <a href="#linkage">linkage type</a>, an optional
<a href="#visibility">visibility style</a>, an optional
<a href="#callingconv">calling convention</a>, a return type, an optional
<a href="#paramattrs">parameter attribute</a> for the return type, a function
name, a possibly empty list of arguments, and an optional alignment.</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 a function 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 allows an explicit section to be specified for functions. If the target
supports it, it will emit functions to the section specified.</p>
<p>An explicit alignment may be specified for a function. If not present, or if
the alignment is set to zero, the alignment of the function is set by the target
to whatever it feels convenient. If an explicit alignment is specified, the
function is forced to have at least that much alignment. All alignments must be
a power of 2.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="aliasstructure">Aliases</a>
</div>
<div class="doc_text">
<p>Aliases act as "second name" for the aliasee value (which can be either
function or global variable or bitcast of global value). Aliases may have an
optional <a href="#linkage">linkage type</a>, and an
optional <a href="#visibility">visibility style</a>.</p>
<h5>Syntax:</h5>
<div class="doc_code">
<pre>
@&lt;Name&gt; = [Linkage] [Visibility] alias &lt;AliaseeTy&gt; @&lt;Aliasee&gt;
</pre>
</div>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"><a name="paramattrs">Parameter Attributes</a></div>
<div class="doc_text">
<p>The return type and each parameter of a function type may have a set of
<i>parameter attributes</i> associated with them. Parameter attributes are
used to communicate additional information about the result or parameters of
a function. Parameter attributes are considered to be part of the function
type so two functions types that differ only by the parameter attributes
are different function types.</p>
<p>Parameter attributes are simple keywords that follow the type specified. If
multiple parameter attributes are needed, they are space separated. For
example:</p>
<div class="doc_code">
<pre>
%someFunc = i16 (i8 signext %someParam) zeroext
%someFunc = i16 (i8 zeroext %someParam) zeroext
</pre>
</div>
<p>Note that the two function types above are unique because the parameter has
a different attribute (<tt>signext</tt> in the first one, <tt>zeroext</tt> in
the second). Also note that the attribute for the function result
(<tt>zeroext</tt>) comes immediately after the argument list.</p>
<p>Currently, only the following parameter attributes are defined:</p>
<dl>
<dt><tt>zeroext</tt></dt>
<dd>This indicates that the parameter should be zero extended just before
a call to this function.</dd>
<dt><tt>signext</tt></dt>
<dd>This indicates that the parameter should be sign extended just before
a call to this function.</dd>
<dt><tt>inreg</tt></dt>
<dd>This indicates that the parameter should be placed in register (if
possible) during assembling function call. Support for this attribute is
target-specific</dd>
<dt><tt>sret</tt></dt>
<dd>This indicates that the parameter specifies the address of a structure
that is the return value of the function in the source program.</dd>
<dt><tt>noalias</tt></dt>
<dd>This indicates that the parameter not alias any other object or any
other "noalias" objects during the function call.
<dt><tt>noreturn</tt></dt>
<dd>This function attribute indicates that the function never returns. This
indicates to LLVM that every call to this function should be treated as if
an <tt>unreachable</tt> instruction immediately followed the call.</dd>
<dt><tt>nounwind</tt></dt>
<dd>This function attribute indicates that the function type does not use
the unwind instruction and does not allow stack unwinding to propagate
through it.</dd>
<dt><tt>nest</tt></dt>
<dd>This indicates that the parameter can be excised using the
<a href="#int_trampoline">trampoline intrinsics</a>.</dd>
</dl>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="moduleasm">Module-Level Inline Assembly</a>
</div>
<div class="doc_text">
<p>
Modules may contain "module-level inline asm" blocks, which corresponds to the
GCC "file scope inline asm" blocks. These blocks are internally concatenated by
LLVM and treated as a single unit, but may be separated in the .ll file if
desired. The syntax is very simple:
</p>
<div class="doc_code">
<pre>
module asm "inline asm code goes here"
module asm "more can go here"
</pre>
</div>
<p>The strings can contain any character by escaping non-printable characters.
The escape sequence used is simply "\xx" where "xx" is the two digit hex code
for the number.
</p>
<p>
The inline asm code is simply printed to the machine code .s file when
assembly code is generated.
</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="datalayout">Data Layout</a>
</div>
<div class="doc_text">
<p>A module may specify a target specific data layout string that specifies how
data is to be laid out in memory. The syntax for the data layout is simply:</p>
<pre> target datalayout = "<i>layout specification</i>"</pre>
<p>The <i>layout specification</i> consists of a list of specifications
separated by the minus sign character ('-'). Each specification starts with a
letter and may include other information after the letter to define some
aspect of the data layout. The specifications accepted are as follows: </p>
<dl>
<dt><tt>E</tt></dt>
<dd>Specifies that the target lays out data in big-endian form. That is, the
bits with the most significance have the lowest address location.</dd>
<dt><tt>e</tt></dt>
<dd>Specifies that hte target lays out data in little-endian form. That is,
the bits with the least significance have the lowest address location.</dd>
<dt><tt>p:<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
<dd>This specifies the <i>size</i> of a pointer and its <i>abi</i> and
<i>preferred</i> alignments. All sizes are in bits. Specifying the <i>pref</i>
alignment is optional. If omitted, the preceding <tt>:</tt> should be omitted
too.</dd>
<dt><tt>i<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
<dd>This specifies the alignment for an integer type of a given bit
<i>size</i>. The value of <i>size</i> must be in the range [1,2^23).</dd>
<dt><tt>v<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
<dd>This specifies the alignment for a vector type of a given bit
<i>size</i>.</dd>
<dt><tt>f<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
<dd>This specifies the alignment for a floating point type of a given bit
<i>size</i>. The value of <i>size</i> must be either 32 (float) or 64
(double).</dd>
<dt><tt>a<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
<dd>This specifies the alignment for an aggregate type of a given bit
<i>size</i>.</dd>
</dl>
<p>When constructing the data layout for a given target, LLVM starts with a
default set of specifications which are then (possibly) overriden by the
specifications in the <tt>datalayout</tt> keyword. The default specifications
are given in this list:</p>
<ul>
<li><tt>E</tt> - big endian</li>
<li><tt>p:32:64:64</tt> - 32-bit pointers with 64-bit alignment</li>
<li><tt>i1:8:8</tt> - i1 is 8-bit (byte) aligned</li>
<li><tt>i8:8:8</tt> - i8 is 8-bit (byte) aligned</li>
<li><tt>i16:16:16</tt> - i16 is 16-bit aligned</li>
<li><tt>i32:32:32</tt> - i32 is 32-bit aligned</li>
<li><tt>i64:32:64</tt> - i64 has abi alignment of 32-bits but preferred
alignment of 64-bits</li>
<li><tt>f32:32:32</tt> - float is 32-bit aligned</li>
<li><tt>f64:64:64</tt> - double is 64-bit aligned</li>
<li><tt>v64:64:64</tt> - 64-bit vector is 64-bit aligned</li>
<li><tt>v128:128:128</tt> - 128-bit vector is 128-bit aligned</li>
<li><tt>a0:0:1</tt> - aggregates are 8-bit aligned</li>
</ul>
<p>When llvm is determining the alignment for a given type, it uses the
following rules:
<ol>
<li>If the type sought is an exact match for one of the specifications, that
specification is used.</li>
<li>If no match is found, and the type sought is an integer type, then the
smallest integer type that is larger than the bitwidth of the sought type is
used. If none of the specifications are larger than the bitwidth then the the
largest integer type is used. For example, given the default specifications
above, the i7 type will use the alignment of i8 (next largest) while both
i65 and i256 will use the alignment of i64 (largest specified).</li>
<li>If no match is found, and the type sought is a vector type, then the
largest vector type that is smaller than the sought vector type will be used
as a fall back. This happens because <128 x double> can be implemented in
terms of 64 <2 x double>, for example.</li>
</ol>
</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>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"> <a name="t_primitive">Primitive Types</a> </div>
<div class="doc_text">
<p>The primitive types are the fundamental building blocks of the LLVM
system. The current set of primitive types is as follows:</p>
<table class="layout">
<tr class="layout">
<td class="left">
<table>
<tbody>
<tr><th>Type</th><th>Description</th></tr>
<tr><td><tt><a name="t_void">void</a></tt></td><td>No value</td></tr>
<tr><td><tt>label</tt></td><td>Branch destination</td></tr>
</tbody>
</table>
</td>
<td class="right">
<table>
<tbody>
<tr><th>Type</th><th>Description</th></tr>
<tr><td><tt>float</tt></td><td>32-bit floating point value</td></tr>
<tr><td><tt>double</tt></td><td>64-bit floating point value</td></tr>
</tbody>
</table>
</td>
</tr>
</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><th>Classification</th><th>Types</th></tr>
<tr>
<td><a name="t_integer">integer</a></td>
<td><tt>i1, i2, i3, ... i8, ... i16, ... i32, ... i64, ... </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>i1, ..., float, double, <br/>
<a href="#t_pointer">pointer</a>,<a href="#t_vector">vector</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_integer">Integer Type</a> </div>
<div class="doc_text">
<h5>Overview:</h5>
<p>The integer type is a very simple derived type that simply specifies an
arbitrary bit width for the integer type desired. Any bit width from 1 bit to
2^23-1 (about 8 million) can be specified.</p>
<h5>Syntax:</h5>
<pre>
iN
</pre>
<p>The number of bits the integer will occupy is specified by the <tt>N</tt>
value.</p>
<h5>Examples:</h5>
<table class="layout">
<tr class="layout">
<td class="left">
<tt>i1</tt><br/>
<tt>i4</tt><br/>
<tt>i8</tt><br/>
<tt>i16</tt><br/>
<tt>i32</tt><br/>
<tt>i42</tt><br/>
<tt>i64</tt><br/>
<tt>i1942652</tt><br/>
</td>
<td class="left">
A boolean integer of 1 bit<br/>
A nibble sized integer of 4 bits.<br/>
A byte sized integer of 8 bits.<br/>
A half word sized integer of 16 bits.<br/>
A word sized integer of 32 bits.<br/>
An integer whose bit width is the answer. <br/>
A double word sized integer of 64 bits.<br/>
A really big integer of over 1 million bits.<br/>
</td>
</tr>
</table>
</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>
[&lt;# elements&gt; x &lt;elementtype&gt;]
</pre>
<p>The number of elements is a constant integer value; elementtype may
be any type with a size.</p>
<h5>Examples:</h5>
<table class="layout">
<tr class="layout">
<td class="left">
<tt>[40 x i32 ]</tt><br/>
<tt>[41 x i32 ]</tt><br/>
<tt>[40 x i8]</tt><br/>
</td>
<td class="left">
Array of 40 32-bit integer values.<br/>
Array of 41 32-bit integer values.<br/>
Array of 40 8-bit integer values.<br/>
</td>
</tr>
</table>
<p>Here are some examples of multidimensional arrays:</p>
<table class="layout">
<tr class="layout">
<td class="left">
<tt>[3 x [4 x i32]]</tt><br/>
<tt>[12 x [10 x float]]</tt><br/>
<tt>[2 x [3 x [4 x i16]]]</tt><br/>
</td>
<td class="left">
3x4 array of 32-bit integer values.<br/>
12x10 array of single precision floating point values.<br/>
2x3x4 array of 16-bit integer values.<br/>
</td>
</tr>
</table>
<p>Note that 'variable sized arrays' can be implemented in LLVM with a zero
length array. Normally, accesses past the end of an array are undefined in
LLVM (e.g. it is illegal to access the 5th element of a 3 element array).
As a special case, however, zero length arrays are recognized to be variable
length. This allows implementation of 'pascal style arrays' with the LLVM
type "{ i32, [0 x float]}", for example.</p>
</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> &lt;returntype&gt; (&lt;parameter list&gt;)<br></pre>
<p>...where '<tt>&lt;parameter list&gt;</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 class="layout">
<tr class="layout">
<td class="left"><tt>i32 (i32)</tt></td>
<td class="left">function taking an <tt>i32</tt>, returning an <tt>i32</tt>
</td>
</tr><tr class="layout">
<td class="left"><tt>float&nbsp;(i16&nbsp;signext,&nbsp;i32&nbsp;*)&nbsp;*
</tt></td>
<td class="left"><a href="#t_pointer">Pointer</a> to a function that takes
an <tt>i16</tt> that should be sign extended and a
<a href="#t_pointer">pointer</a> to <tt>i32</tt>, returning
<tt>float</tt>.
</td>
</tr><tr class="layout">
<td class="left"><tt>i32 (i8*, ...)</tt></td>
<td class="left">A vararg function that takes at least one
<a href="#t_pointer">pointer</a> to <tt>i8 </tt> (char in C),
which returns an integer. This is the signature for <tt>printf</tt> in
LLVM.
</td>
</tr>
</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> { &lt;type list&gt; }<br></pre>
<h5>Examples:</h5>
<table class="layout">
<tr class="layout">
<td class="left"><tt>{ i32, i32, i32 }</tt></td>
<td class="left">A triple of three <tt>i32</tt> values</td>
</tr><tr class="layout">
<td class="left"><tt>{&nbsp;float,&nbsp;i32&nbsp;(i32)&nbsp;*&nbsp;}</tt></td>
<td class="left">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>i32</tt>, returning
an <tt>i32</tt>.</td>
</tr>
</table>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="t_pstruct">Packed Structure Type</a>
</div>
<div class="doc_text">
<h5>Overview:</h5>
<p>The packed structure type is used to represent a collection of data members
together in memory. There is no padding between fields. Further, the alignment
of a packed structure is 1 byte. The elements of a packed 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> &lt; { &lt;type list&gt; } &gt; <br></pre>
<h5>Examples:</h5>
<table class="layout">
<tr class="layout">
<td class="left"><tt>&lt; { i32, i32, i32 } &gt;</tt></td>
<td class="left">A triple of three <tt>i32</tt> values</td>
</tr><tr class="layout">
<td class="left"><tt>&lt;&nbsp;{&nbsp;float,&nbsp;i32&nbsp;(i32)&nbsp;*&nbsp;}&nbsp;&gt;</tt></td>
<td class="left">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>i32</tt>, returning
an <tt>i32</tt>.</td>
</tr>
</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> &lt;type&gt; *<br></pre>
<h5>Examples:</h5>
<table class="layout">
<tr class="layout">
<td class="left">
<tt>[4x i32]*</tt><br/>
<tt>i32 (i32 *) *</tt><br/>
</td>
<td class="left">
A <a href="#t_pointer">pointer</a> to <a href="#t_array">array</a> of
four <tt>i32</tt> values<br/>
A <a href="#t_pointer">pointer</a> to a <a
href="#t_function">function</a> that takes an <tt>i32*</tt>, returning an
<tt>i32</tt>.<br/>
</td>
</tr>
</table>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="t_vector">Vector Type</a> </div>
<div class="doc_text">
<h5>Overview:</h5>
<p>A vector type is a simple derived type that represents a vector
of elements. Vector types are used when multiple primitive data
are operated in parallel using a single instruction (SIMD).
A vector type requires a size (number of
elements) and an underlying primitive data type. Vectors must have a power
of two length (1, 2, 4, 8, 16 ...). Vector types are
considered <a href="#t_firstclass">first class</a>.</p>
<h5>Syntax:</h5>
<pre>
&lt; &lt;# elements&gt; x &lt;elementtype&gt; &gt;
</pre>
<p>The number of elements is a constant integer value; elementtype may
be any integer or floating point type.</p>
<h5>Examples:</h5>
<table class="layout">
<tr class="layout">
<td class="left">
<tt>&lt;4 x i32&gt;</tt><br/>
<tt>&lt;8 x float&gt;</tt><br/>
<tt>&lt;2 x i64&gt;</tt><br/>
</td>
<td class="left">
Vector of 4 32-bit integer values.<br/>
Vector of 8 floating-point values.<br/>
Vector of 2 64-bit integer values.<br/>
</td>
</tr>
</table>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="t_opaque">Opaque Type</a> </div>
<div class="doc_text">
<h5>Overview:</h5>
<p>Opaque types are used to represent unknown types in the system. This
corresponds (for example) to the C notion of a foward declared structure type.
In LLVM, opaque types can eventually be resolved to any type (not just a
structure type).</p>
<h5>Syntax:</h5>
<pre>
opaque
</pre>
<h5>Examples:</h5>
<table class="layout">
<tr class="layout">
<td class="left">
<tt>opaque</tt>
</td>
<td class="left">
An opaque type.<br/>
</td>
</tr>
</table>
</div>
<!-- *********************************************************************** -->
<div class="doc_section"> <a name="constants">Constants</a> </div>
<!-- *********************************************************************** -->
<div class="doc_text">
<p>LLVM has several different basic types of constants. This section describes
them all and their syntax.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"><a name="simpleconstants">Simple Constants</a></div>
<div class="doc_text">
<dl>
<dt><b>Boolean constants</b></dt>
<dd>The two strings '<tt>true</tt>' and '<tt>false</tt>' are both valid
constants of the <tt><a href="#t_primitive">i1</a></tt> type.
</dd>
<dt><b>Integer constants</b></dt>
<dd>Standard integers (such as '4') are constants of the <a
href="#t_integer">integer</a> type. Negative numbers may be used with
integer types.
</dd>
<dt><b>Floating point constants</b></dt>
<dd>Floating point constants use standard decimal notation (e.g. 123.421),
exponential notation (e.g. 1.23421e+2), or a more precise hexadecimal
notation (see below). Floating point constants must have a <a
href="#t_floating">floating point</a> type. </dd>
<dt><b>Null pointer constants</b></dt>
<dd>The identifier '<tt>null</tt>' is recognized as a null pointer constant
and must be of <a href="#t_pointer">pointer type</a>.</dd>
</dl>
<p>The one non-intuitive notation for constants is the optional hexadecimal 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>'. The only time hexadecimal floating point constants are required
(and the only time that they are generated by the disassembler) is when a
floating point constant must be emitted but it cannot be represented as a
decimal floating point number. For example, NaN's, infinities, and other
special values 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_subsection"><a name="aggregateconstants">Aggregate Constants</a>
</div>
<div class="doc_text">
<p>Aggregate constants arise from aggregation of simple constants
and smaller aggregate constants.</p>
<dl>
<dt><b>Structure constants</b></dt>
<dd>Structure constants are represented with notation similar to structure
type definitions (a comma separated list of elements, surrounded by braces
(<tt>{}</tt>)). For example: "<tt>{ i32 4, float 17.0, i32* %G }</tt>",
where "<tt>%G</tt>" is declared as "<tt>@G = external global i32</tt>". Structure constants
must have <a href="#t_struct">structure type</a>, and the number and
types of elements must match those specified by the type.
</dd>
<dt><b>Array constants</b></dt>
<dd>Array constants are represented with notation similar to array type
definitions (a comma separated list of elements, surrounded by square brackets
(<tt>[]</tt>)). For example: "<tt>[ i32 42, i32 11, i32 74 ]</tt>". Array
constants must have <a href="#t_array">array type</a>, and the number and
types of elements must match those specified by the type.
</dd>
<dt><b>Vector constants</b></dt>
<dd>Vector constants are represented with notation similar to vector type
definitions (a comma separated list of elements, surrounded by
less-than/greater-than's (<tt>&lt;&gt;</tt>)). For example: "<tt>&lt; i32 42,
i32 11, i32 74, i32 100 &gt;</tt>". Vector constants must have <a
href="#t_vector">vector type</a>, and the number and types of elements must
match those specified by the type.
</dd>
<dt><b>Zero initialization</b></dt>
<dd>The string '<tt>zeroinitializer</tt>' can be used to zero initialize a
value to zero of <em>any</em> type, including scalar and aggregate types.
This is often used to avoid having to print large zero initializers (e.g. for
large arrays) and is always exactly equivalent to using explicit zero
initializers.
</dd>
</dl>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="globalconstants">Global Variable and Function Addresses</a>
</div>
<div class="doc_text">
<p>The addresses of <a href="#globalvars">global variables</a> and <a
href="#functionstructure">functions</a> are always implicitly valid (link-time)
constants. These constants are explicitly referenced when the <a
href="#identifiers">identifier for the global</a> is used and always have <a
href="#t_pointer">pointer</a> type. For example, the following is a legal LLVM
file:</p>
<div class="doc_code">
<pre>
@X = global i32 17
@Y = global i32 42
@Z = global [2 x i32*] [ i32* @X, i32* @Y ]
</pre>
</div>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"><a name="undefvalues">Undefined Values</a></div>
<div class="doc_text">
<p>The string '<tt>undef</tt>' is recognized as a type-less constant that has
no specific value. Undefined values may be of any type and be used anywhere
a constant is permitted.</p>
<p>Undefined values indicate to the compiler that the program is well defined
no matter what value is used, giving the compiler more freedom to optimize.
</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"><a name="constantexprs">Constant Expressions</a>
</div>
<div class="doc_text">
<p>Constant expressions are used to allow expressions involving other constants
to be used as constants. Constant expressions may be of any <a
href="#t_firstclass">first class</a> type and may involve any LLVM operation
that does not have side effects (e.g. load and call are not supported). The
following is the syntax for constant expressions:</p>
<dl>
<dt><b><tt>trunc ( CST to TYPE )</tt></b></dt>
<dd>Truncate a constant to another type. The bit size of CST must be larger
than the bit size of TYPE. Both types must be integers.</dd>
<dt><b><tt>zext ( CST to TYPE )</tt></b></dt>
<dd>Zero extend a constant to another type. The bit size of CST must be
smaller or equal to the bit size of TYPE. Both types must be integers.</dd>
<dt><b><tt>sext ( CST to TYPE )</tt></b></dt>
<dd>Sign extend a constant to another type. The bit size of CST must be
smaller or equal to the bit size of TYPE. Both types must be integers.</dd>
<dt><b><tt>fptrunc ( CST to TYPE )</tt></b></dt>
<dd>Truncate a floating point constant to another floating point type. The
size of CST must be larger than the size of TYPE. Both types must be
floating point.</dd>
<dt><b><tt>fpext ( CST to TYPE )</tt></b></dt>
<dd>Floating point extend a constant to another type. The size of CST must be
smaller or equal to the size of TYPE. Both types must be floating point.</dd>
<dt><b><tt>fptoui ( CST to TYPE )</tt></b></dt>
<dd>Convert a floating point constant to the corresponding unsigned integer
constant. TYPE must be an integer type. CST must be floating point. If the
value won't fit in the integer type, the results are undefined.</dd>
<dt><b><tt>fptosi ( CST to TYPE )</tt></b></dt>
<dd>Convert a floating point constant to the corresponding signed integer
constant. TYPE must be an integer type. CST must be floating point. If the
value won't fit in the integer type, the results are undefined.</dd>
<dt><b><tt>uitofp ( CST to TYPE )</tt></b></dt>
<dd>Convert an unsigned integer constant to the corresponding floating point
constant. TYPE must be floating point. CST must be of integer type. If the
value won't fit in the floating point type, the results are undefined.</dd>
<dt><b><tt>sitofp ( CST to TYPE )</tt></b></dt>
<dd>Convert a signed integer constant to the corresponding floating point
constant. TYPE must be floating point. CST must be of integer type. If the
value won't fit in the floating point type, the results are undefined.</dd>
<dt><b><tt>ptrtoint ( CST to TYPE )</tt></b></dt>
<dd>Convert a pointer typed constant to the corresponding integer constant
TYPE must be an integer type. CST must be of pointer type. The CST value is
zero extended, truncated, or unchanged to make it fit in TYPE.</dd>
<dt><b><tt>inttoptr ( CST to TYPE )</tt></b></dt>
<dd>Convert a integer constant to a pointer constant. TYPE must be a
pointer type. CST must be of integer type. The CST value is zero extended,
truncated, or unchanged to make it fit in a pointer size. This one is
<i>really</i> dangerous!</dd>
<dt><b><tt>bitcast ( CST to TYPE )</tt></b></dt>
<dd>Convert a constant, CST, to another TYPE. The size of CST and TYPE must be
identical (same number of bits). The conversion is done as if the CST value
was stored to memory and read back as TYPE. In other words, no bits change
with this operator, just the type. This can be used for conversion of
vector types to any other type, as long as they have the same bit width. For
pointers it is only valid to cast to another pointer type.
</dd>
<dt><b><tt>getelementptr ( CSTPTR, IDX0, IDX1, ... )</tt></b></dt>
<dd>Perform the <a href="#i_getelementptr">getelementptr operation</a> on
constants. As with the <a href="#i_getelementptr">getelementptr</a>
instruction, the index list may have zero or more indexes, which are required
to make sense for the type of "CSTPTR".</dd>
<dt><b><tt>select ( COND, VAL1, VAL2 )</tt></b></dt>
<dd>Perform the <a href="#i_select">select operation</a> on
constants.</dd>
<dt><b><tt>icmp COND ( VAL1, VAL2 )</tt></b></dt>
<dd>Performs the <a href="#i_icmp">icmp operation</a> on constants.</dd>
<dt><b><tt>fcmp COND ( VAL1, VAL2 )</tt></b></dt>
<dd>Performs the <a href="#i_fcmp">fcmp operation</a> on constants.</dd>
<dt><b><tt>extractelement ( VAL, IDX )</tt></b></dt>
<dd>Perform the <a href="#i_extractelement">extractelement
operation</a> on constants.
<dt><b><tt>insertelement ( VAL, ELT, IDX )</tt></b></dt>
<dd>Perform the <a href="#i_insertelement">insertelement
operation</a> on constants.</dd>
<dt><b><tt>shufflevector ( VEC1, VEC2, IDXMASK )</tt></b></dt>
<dd>Perform the <a href="#i_shufflevector">shufflevector
operation</a> on constants.</dd>
<dt><b><tt>OPCODE ( LHS, RHS )</tt></b></dt>
<dd>Perform the specified operation of the LHS and RHS constants. OPCODE may
be any of the <a href="#binaryops">binary</a> or <a href="#bitwiseops">bitwise
binary</a> operations. The constraints on operands are the same as those for
the corresponding instruction (e.g. no bitwise operations on floating point
values are allowed).</dd>
</dl>
</div>
<!-- *********************************************************************** -->
<div class="doc_section"> <a name="othervalues">Other Values</a> </div>
<!-- *********************************************************************** -->
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="inlineasm">Inline Assembler Expressions</a>
</div>
<div class="doc_text">
<p>
LLVM supports inline assembler expressions (as opposed to <a href="#moduleasm">
Module-Level Inline Assembly</a>) through the use of a special value. This
value represents the inline assembler as a string (containing the instructions
to emit), a list of operand constraints (stored as a string), and a flag that
indicates whether or not the inline asm expression has side effects. An example
inline assembler expression is:
</p>
<div class="doc_code">
<pre>
i32 (i32) asm "bswap $0", "=r,r"
</pre>
</div>
<p>
Inline assembler expressions may <b>only</b> be used as the callee operand of
a <a href="#i_call"><tt>call</tt> instruction</a>. Thus, typically we have:
</p>
<div class="doc_code">
<pre>
%X = call i32 asm "<a href="#int_bswap">bswap</a> $0", "=r,r"(i32 %Y)
</pre>
</div>
<p>
Inline asms with side effects not visible in the constraint list must be marked
as having side effects. This is done through the use of the
'<tt>sideeffect</tt>' keyword, like so:
</p>
<div class="doc_code">
<pre>
call void asm sideeffect "eieio", ""()
</pre>
</div>
<p>TODO: The format of the asm and constraints string still need to be
documented here. Constraints on what can be done (e.g. duplication, moving, etc
need to be documented).
</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="#bitwiseops">bitwise 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 six 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, the '<a
href="#i_unwind"><tt>unwind</tt></a>' instruction, and the '<a
href="#i_unreachable"><tt>unreachable</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 &lt;type&gt; &lt;value&gt; <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>' instruction: 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 of the "normal" 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 i32 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 i1 &lt;cond&gt;, label &lt;iftrue&gt;, label &lt;iffalse&gt;<br> br label &lt;dest&gt; <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>i1</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>i1</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_icmp">icmp</a> eq, i32 %a, %b<br> br i1 %cond, label %IfEqual, label %IfUnequal<br>IfEqual:<br> <a
href="#i_ret">ret</a> i32 1<br>IfUnequal:<br> <a href="#i_ret">ret</a> i32 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 &lt;intty&gt; &lt;value&gt;, label &lt;defaultdest&gt; [ &lt;intty&gt; &lt;val&gt;, label &lt;dest&gt; ... ]
</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, control flow is
transfered to the corresponding destination; otherwise, control flow is
transfered to the default destination.</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, it could be generated 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_zext">zext</a> i1 %value to i32
switch i32 %Val, label %truedest [i32 0, label %falsedest ]
<i>; Emulate an unconditional br instruction</i>
switch i32 0, label %dest [ ]
<i>; Implement a jump table:</i>
switch i32 %val, label %otherwise [ i32 0, label %onzero
i32 1, label %onone
i32 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>
&lt;result&gt; = invoke [<a href="#callingconv">cconv</a>] &lt;ptr to function ty&gt; %&lt;function ptr val&gt;(&lt;function args&gt;)
to label &lt;normal label&gt; unwind label &lt;exception label&gt;
</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>' label or the
'<tt>exception</tt>' label. 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 "exception" label.</p>
<h5>Arguments:</h5>
<p>This instruction requires several arguments:</p>
<ol>
<li>
The optional "cconv" marker indicates which <a href="#callingconv">calling
convention</a> the call should use. If none is specified, the call defaults
to using C calling conventions.
</li>
<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 i32 %Test(i32 15) to label %Continue
unwind label %TestCleanup <i>; {i32}:retval set</i>
%retval = invoke <a href="#callingconv">coldcc</a> i32 %Test(i32 15) to label %Continue
unwind label %TestCleanup <i>; {i32}: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
</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_subsubsection"> <a name="i_unreachable">'<tt>unreachable</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre>
unreachable
</pre>
<h5>Overview:</h5>
<p>The '<tt>unreachable</tt>' instruction has no defined semantics. This
instruction is used to inform the optimizer that a particular portion of the
code is not reachable. This can be used to indicate that the code after a
no-return function cannot be reached, and other facts.</p>
<h5>Semantics:</h5>
<p>The '<tt>unreachable</tt>' instruction has no defined semantics.</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 operands might represent
multiple data, as is the case with the <a href="#t_vector">vector</a> data type.
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> &lt;result&gt; = add &lt;ty&gt; &lt;var1&gt;, &lt;var2&gt; <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.
This instruction can also take <a href="#t_vector">vector</a> versions of the 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> &lt;result&gt; = add i32 4, %var <i>; yields {i32}: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> &lt;result&gt; = sub &lt;ty&gt; &lt;var1&gt;, &lt;var2&gt; <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.
This instruction can also take <a href="#t_vector">vector</a> versions of the 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>
&lt;result&gt; = sub i32 4, %var <i>; yields {i32}:result = 4 - %var</i>
&lt;result&gt; = sub i32 0, %val <i>; yields {i32}: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> &lt;result&gt; = mul &lt;ty&gt; &lt;var1&gt;, &lt;var2&gt; <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.
This instruction can also take <a href="#t_vector">vector</a> versions of the 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>Because the operands are the same width, the result of an integer
multiplication is the same whether the operands should be deemed unsigned or
signed.</p>
<h5>Example:</h5>
<pre> &lt;result&gt; = mul i32 4, %var <i>; yields {i32}:result = 4 * %var</i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_udiv">'<tt>udiv</tt>' Instruction
</a></div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> &lt;result&gt; = udiv &lt;ty&gt; &lt;var1&gt;, &lt;var2&gt; <i>; yields {ty}:result</i>
</pre>
<h5>Overview:</h5>
<p>The '<tt>udiv</tt>' instruction returns the quotient of its two
operands.</p>
<h5>Arguments:</h5>
<p>The two arguments to the '<tt>udiv</tt>' instruction must be
<a href="#t_integer">integer</a> values. Both arguments must have identical
types. This instruction can also take <a href="#t_vector">vector</a> versions
of the values in which case the elements must be integers.</p>
<h5>Semantics:</h5>
<p>The value produced is the unsigned integer quotient of the two operands. This
instruction always performs an unsigned division operation, regardless of
whether the arguments are unsigned or not.</p>
<h5>Example:</h5>
<pre> &lt;result&gt; = udiv i32 4, %var <i>; yields {i32}:result = 4 / %var</i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_sdiv">'<tt>sdiv</tt>' Instruction
</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> &lt;result&gt; = sdiv &lt;ty&gt; &lt;var1&gt;, &lt;var2&gt; <i>; yields {ty}:result</i>
</pre>
<h5>Overview:</h5>
<p>The '<tt>sdiv</tt>' instruction returns the quotient of its two
operands.</p>
<h5>Arguments:</h5>
<p>The two arguments to the '<tt>sdiv</tt>' instruction must be
<a href="#t_integer">integer</a> values. Both arguments must have identical
types. This instruction can also take <a href="#t_vector">vector</a> versions
of the values in which case the elements must be integers.</p>
<h5>Semantics:</h5>
<p>The value produced is the signed integer quotient of the two operands. This
instruction always performs a signed division operation, regardless of whether
the arguments are signed or not.</p>
<h5>Example:</h5>
<pre> &lt;result&gt; = sdiv i32 4, %var <i>; yields {i32}:result = 4 / %var</i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_fdiv">'<tt>fdiv</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> &lt;result&gt; = fdiv &lt;ty&gt; &lt;var1&gt;, &lt;var2&gt; <i>; yields {ty}:result</i>
</pre>
<h5>Overview:</h5>
<p>The '<tt>fdiv</tt>' instruction returns the quotient of its two
operands.</p>
<h5>Arguments:</h5>
<p>The two arguments to the '<tt>fdiv</tt>' instruction must be
<a href="#t_floating">floating point</a> values. Both arguments must have
identical types. This instruction can also take <a href="#t_vector">vector</a>
versions of floating point values.</p>
<h5>Semantics:</h5>
<p>The value produced is the floating point quotient of the two operands.</p>
<h5>Example:</h5>
<pre> &lt;result&gt; = fdiv float 4.0, %var <i>; yields {float}:result = 4.0 / %var</i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_urem">'<tt>urem</tt>' Instruction</a>
</div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> &lt;result&gt; = urem &lt;ty&gt; &lt;var1&gt;, &lt;var2&gt; <i>; yields {ty}:result</i>
</pre>
<h5>Overview:</h5>
<p>The '<tt>urem</tt>' instruction returns the remainder from the
unsigned division of its two arguments.</p>
<h5>Arguments:</h5>
<p>The two arguments to the '<tt>urem</tt>' instruction must be
<a href="#t_integer">integer</a> values. Both arguments must have identical
types.</p>
<h5>Semantics:</h5>
<p>This instruction returns the unsigned integer <i>remainder</i> of a division.
This instruction always performs an unsigned division to get the remainder,
regardless of whether the arguments are unsigned or not.</p>
<h5>Example:</h5>
<pre> &lt;result&gt; = urem i32 4, %var <i>; yields {i32}:result = 4 % %var</i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_srem">'<tt>srem</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> &lt;result&gt; = srem &lt;ty&gt; &lt;var1&gt;, &lt;var2&gt; <i>; yields {ty}:result</i>
</pre>
<h5>Overview:</h5>
<p>The '<tt>srem</tt>' instruction returns the remainder from the
signed division of its two operands.</p>
<h5>Arguments:</h5>
<p>The two arguments to the '<tt>srem</tt>' instruction must be
<a href="#t_integer">integer</a> values. Both arguments must have identical
types.</p>
<h5>Semantics:</h5>
<p>This instruction returns the <i>remainder</i> of a division (where the result
has the same sign as the dividend, <tt>var1</tt>), not the <i>modulo</i>
operator (where the result has the same sign as the divisor, <tt>var2</tt>) 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>. For a table of how this is implemented in various languages,
please see <a href="http://en.wikipedia.org/wiki/Modulo_operation">
Wikipedia: modulo operation</a>.</p>
<h5>Example:</h5>
<pre> &lt;result&gt; = srem i32 4, %var <i>; yields {i32}:result = 4 % %var</i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_frem">'<tt>frem</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> &lt;result&gt; = frem &lt;ty&gt; &lt;var1&gt;, &lt;var2&gt; <i>; yields {ty}:result</i>
</pre>
<h5>Overview:</h5>
<p>The '<tt>frem</tt>' instruction returns the remainder from the
division of its two operands.</p>
<h5>Arguments:</h5>
<p>The two arguments to the '<tt>frem</tt>' instruction must be
<a href="#t_floating">floating point</a> values. Both arguments must have
identical types.</p>
<h5>Semantics:</h5>
<p>This instruction returns the <i>remainder</i> of a division.</p>
<h5>Example:</h5>
<pre> &lt;result&gt; = frem float 4.0, %var <i>; yields {float}:result = 4.0 % %var</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_shl">'<tt>shl</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> &lt;result&gt; = shl &lt;ty&gt; &lt;var1&gt;, &lt;var2&gt; <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>Both arguments to the '<tt>shl</tt>' instruction must be the same <a
href="#t_integer">integer</a> type.</p>
<h5>Semantics:</h5>
<p>The value produced is <tt>var1</tt> * 2<sup><tt>var2</tt></sup>.</p>
<h5>Example:</h5><pre>
&lt;result&gt; = shl i32 4, %var <i>; yields {i32}: 4 &lt;&lt; %var</i>
&lt;result&gt; = shl i32 4, 2 <i>; yields {i32}: 16</i>
&lt;result&gt; = shl i32 1, 10 <i>; yields {i32}: 1024</i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_lshr">'<tt>lshr</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> &lt;result&gt; = lshr &lt;ty&gt; &lt;var1&gt;, &lt;var2&gt; <i>; yields {ty}:result</i>
</pre>
<h5>Overview:</h5>
<p>The '<tt>lshr</tt>' instruction (logical shift right) returns the first
operand shifted to the right a specified number of bits with zero fill.</p>
<h5>Arguments:</h5>
<p>Both arguments to the '<tt>lshr</tt>' instruction must be the same
<a href="#t_integer">integer</a> type.</p>
<h5>Semantics:</h5>
<p>This instruction always performs a logical shift right operation. The most
significant bits of the result will be filled with zero bits after the
shift.</p>
<h5>Example:</h5>
<pre>
&lt;result&gt; = lshr i32 4, 1 <i>; yields {i32}:result = 2</i>
&lt;result&gt; = lshr i32 4, 2 <i>; yields {i32}:result = 1</i>
&lt;result&gt; = lshr i8 4, 3 <i>; yields {i8}:result = 0</i>
&lt;result&gt; = lshr i8 -2, 1 <i>; yields {i8}:result = 0x7FFFFFFF </i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_ashr">'<tt>ashr</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> &lt;result&gt; = ashr &lt;ty&gt; &lt;var1&gt;, &lt;var2&gt; <i>; yields {ty}:result</i>
</pre>
<h5>Overview:</h5>
<p>The '<tt>ashr</tt>' instruction (arithmetic shift right) returns the first
operand shifted to the right a specified number of bits with sign extension.</p>
<h5>Arguments:</h5>
<p>Both arguments to the '<tt>ashr</tt>' instruction must be the same
<a href="#t_integer">integer</a> type.</p>
<h5>Semantics:</h5>
<p>This instruction always performs an arithmetic shift right operation,
The most significant bits of the result will be filled with the sign bit
of <tt>var1</tt>.</p>
<h5>Example:</h5>
<pre>
&lt;result&gt; = ashr i32 4, 1 <i>; yields {i32}:result = 2</i>
&lt;result&gt; = ashr i32 4, 2 <i>; yields {i32}:result = 1</i>
&lt;result&gt; = ashr i8 4, 3 <i>; yields {i8}:result = 0</i>
&lt;result&gt; = ashr i8 -2, 1 <i>; yields {i8}:result = -1</i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_and">'<tt>and</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> &lt;result&gt; = and &lt;ty&gt; &lt;var1&gt;, &lt;var2&gt; <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_integer">integer</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> &lt;result&gt; = and i32 4, %var <i>; yields {i32}:result = 4 &amp; %var</i>
&lt;result&gt; = and i32 15, 40 <i>; yields {i32}:result = 8</i>
&lt;result&gt; = and i32 4, 8 <i>; yields {i32}: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> &lt;result&gt; = or &lt;ty&gt; &lt;var1&gt;, &lt;var2&gt; <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_integer">integer</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> &lt;result&gt; = or i32 4, %var <i>; yields {i32}:result = 4 | %var</i>
&lt;result&gt; = or i32 15, 40 <i>; yields {i32}:result = 47</i>
&lt;result&gt; = or i32 4, 8 <i>; yields {i32}: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> &lt;result&gt; = xor &lt;ty&gt; &lt;var1&gt;, &lt;var2&gt; <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_integer">integer</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> &lt;result&gt; = xor i32 4, %var <i>; yields {i32}:result = 4 ^ %var</i>
&lt;result&gt; = xor i32 15, 40 <i>; yields {i32}:result = 39</i>
&lt;result&gt; = xor i32 4, 8 <i>; yields {i32}:result = 12</i>
&lt;result&gt; = xor i32 %V, -1 <i>; yields {i32}:result = ~%V</i>
</pre>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="vectorops">Vector Operations</a>
</div>
<div class="doc_text">
<p>LLVM supports several instructions to represent vector operations in a
target-independent manner. These instructions cover the element-access and
vector-specific operations needed to process vectors effectively. While LLVM
does directly support these vector operations, many sophisticated algorithms
will want to use target-specific intrinsics to take full advantage of a specific
target.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="i_extractelement">'<tt>extractelement</tt>' Instruction</a>
</div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre>
&lt;result&gt; = extractelement &lt;n x &lt;ty&gt;&gt; &lt;val&gt;, i32 &lt;idx&gt; <i>; yields &lt;ty&gt;</i>
</pre>
<h5>Overview:</h5>
<p>
The '<tt>extractelement</tt>' instruction extracts a single scalar
element from a vector at a specified index.
</p>
<h5>Arguments:</h5>
<p>
The first operand of an '<tt>extractelement</tt>' instruction is a
value of <a href="#t_vector">vector</a> type. The second operand is
an index indicating the position from which to extract the element.
The index may be a variable.</p>
<h5>Semantics:</h5>
<p>
The result is a scalar of the same type as the element type of
<tt>val</tt>. Its value is the value at position <tt>idx</tt> of
<tt>val</tt>. If <tt>idx</tt> exceeds the length of <tt>val</tt>, the
results are undefined.
</p>
<h5>Example:</h5>
<pre>
%result = extractelement &lt;4 x i32&gt; %vec, i32 0 <i>; yields i32</i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="i_insertelement">'<tt>insertelement</tt>' Instruction</a>
</div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre>
&lt;result&gt; = insertelement &lt;n x &lt;ty&gt;&gt; &lt;val&gt;, &lt;ty&gt; &lt;elt&gt, i32 &lt;idx&gt; <i>; yields &lt;n x &lt;ty&gt;&gt;</i>
</pre>
<h5>Overview:</h5>
<p>
The '<tt>insertelement</tt>' instruction inserts a scalar
element into a vector at a specified index.
</p>
<h5>Arguments:</h5>
<p>
The first operand of an '<tt>insertelement</tt>' instruction is a
value of <a href="#t_vector">vector</a> type. The second operand is a
scalar value whose type must equal the element type of the first
operand. The third operand is an index indicating the position at
which to insert the value. The index may be a variable.</p>
<h5>Semantics:</h5>
<p>
The result is a vector of the same type as <tt>val</tt>. Its
element values are those of <tt>val</tt> except at position
<tt>idx</tt>, where it gets the value <tt>elt</tt>. If <tt>idx</tt>
exceeds the length of <tt>val</tt>, the results are undefined.
</p>
<h5>Example:</h5>
<pre>
%result = insertelement &lt;4 x i32&gt; %vec, i32 1, i32 0 <i>; yields &lt;4 x i32&gt;</i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="i_shufflevector">'<tt>shufflevector</tt>' Instruction</a>
</div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre>
&lt;result&gt; = shufflevector &lt;n x &lt;ty&gt;&gt; &lt;v1&gt;, &lt;n x &lt;ty&gt;&gt; &lt;v2&gt;, &lt;n x i32&gt; &lt;mask&gt; <i>; yields &lt;n x &lt;ty&gt;&gt;</i>
</pre>
<h5>Overview:</h5>
<p>
The '<tt>shufflevector</tt>' instruction constructs a permutation of elements
from two input vectors, returning a vector of the same type.
</p>
<h5>Arguments:</h5>
<p>
The first two operands of a '<tt>shufflevector</tt>' instruction are vectors
with types that match each other and types that match the result of the
instruction. The third argument is a shuffle mask, which has the same number
of elements as the other vector type, but whose element type is always 'i32'.
</p>
<p>
The shuffle mask operand is required to be a constant vector with either
constant integer or undef values.
</p>
<h5>Semantics:</h5>
<p>
The elements of the two input vectors are numbered from left to right across
both of the vectors. The shuffle mask operand specifies, for each element of
the result vector, which element of the two input registers the result element
gets. The element selector may be undef (meaning "don't care") and the second
operand may be undef if performing a shuffle from only one vector.
</p>
<h5>Example:</h5>
<pre>
%result = shufflevector &lt;4 x i32&gt; %v1, &lt;4 x i32&gt; %v2,
&lt;4 x i32&gt; &lt;i32 0, i32 4, i32 1, i32 5&gt; <i>; yields &lt;4 x i32&gt;</i>
%result = shufflevector &lt;4 x i32&gt; %v1, &lt;4 x i32&gt; undef,
&lt;4 x i32&gt; &lt;i32 0, i32 1, i32 2, i32 3&gt; <i>; yields &lt;4 x i32&gt;</i> - Identity shuffle.
</pre>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="memoryops">Memory Access and Addressing 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>
&lt;result&gt; = malloc &lt;type&gt;[, i32 &lt;NumElements&gt;][, align &lt;alignment&gt;] <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(&lt;type&gt;)*NumElements</tt>
bytes of memory from the operating system and returns a pointer of the
appropriate type to the program. If "NumElements" is specified, it is the
number of elements allocated. If an alignment is specified, the value result
of the allocation is guaranteed to be aligned to at least that boundary. If
not specified, or if zero, the target can choose to align the allocation on any
convenient boundary.</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 i8 ] <i>; yields {[%4 x i8]*}:array</i>
%size = <a href="#i_add">add</a> i32 2, 2 <i>; yields {i32}:size = i32 4</i>
%array1 = malloc i8, i32 4 <i>; yields {i8*}:array1</i>
%array2 = malloc [12 x i8], i32 %size <i>; yields {[12 x i8]*}:array2</i>
%array3 = malloc i32, i32 4, align 1024 <i>; yields {i32*}:array3</i>
%array4 = malloc i32, align 1024 <i>; yields {i32*}:array4</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 &lt;type&gt; &lt;value&gt; <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>
<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 no longer defined
after this instruction executes.</p>
<h5>Example:</h5>
<pre>
%array = <a href="#i_malloc">malloc</a> [4 x i8] <i>; yields {[4 x i8]*}:array</i>
free [4 x i8]* %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>
&lt;result&gt; = alloca &lt;type&gt;[, i32 &lt;NumElements&gt;][, align &lt;alignment&gt;] <i>; yields {type*}:result</i>
</pre>
<h5>Overview:</h5>
<p>The '<tt>alloca</tt>' instruction allocates memory on the stack frame of the
currently executing function, to be automatically released when this function
returns to its caller.</p>
<h5>Arguments:</h5>
<p>The '<tt>alloca</tt>' instruction allocates <tt>sizeof(&lt;type&gt;)*NumElements</tt>
bytes of memory on the runtime stack, returning a pointer of the
appropriate type to the program. If "NumElements" is specified, it is the
number of elements allocated. If an alignment is specified, the value result
of the allocation is guaranteed to be aligned to at least that boundary. If
not specified, or if zero, the target can choose to align the allocation on any
convenient boundary.</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_unwind">unwind</a></tt>
instructions), the memory is reclaimed.</p>
<h5>Example:</h5>
<pre>
%ptr = alloca i32 <i>; yields {i32*}:ptr</i>
%ptr = alloca i32, i32 4 <i>; yields {i32*}:ptr</i>
%ptr = alloca i32, i32 4, align 1024 <i>; yields {i32*}:ptr</i>
%ptr = alloca i32, align 1024 <i>; yields {i32*}: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> &lt;result&gt; = load &lt;ty&gt;* &lt;pointer&gt;[, align &lt;alignment&gt;]<br> &lt;result&gt; = volatile load &lt;ty&gt;* &lt;pointer&gt;[, align &lt;alignment&gt;]<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 from which to load. 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> i32 <i>; yields {i32*}:ptr</i>
<a
href="#i_store">store</a> i32 3, i32* %ptr <i>; yields {void}</i>
%val = load i32* %ptr <i>; yields {i32}:val = i32 3</i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_store">'<tt>store</tt>'
Instruction</a> </div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> store &lt;ty&gt; &lt;value&gt;, &lt;ty&gt;* &lt;pointer&gt;[, align &lt;alignment&gt;] <i>; yields {void}</i>
volatile store &lt;ty&gt; &lt;value&gt;, &lt;ty&gt;* &lt;pointer&gt;[, align &lt;alignment&gt;] <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 at which to store it. The type of the '<tt>&lt;pointer&gt;</tt>'
operand must be a pointer to the type of the '<tt>&lt;value&gt;</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>&lt;value&gt;</tt>'
at the location specified by the '<tt>&lt;pointer&gt;</tt>' operand.</p>
<h5>Example:</h5>
<pre> %ptr = <a href="#i_alloca">alloca</a> i32 <i>; yields {i32*}:ptr</i>
<a
href="#i_store">store</a> i32 3, i32* %ptr <i>; yields {void}</i>
%val = load i32* %ptr <i>; yields {i32}:val = i32 3</i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="i_getelementptr">'<tt>getelementptr</tt>' Instruction</a>
</div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre>
&lt;result&gt; = getelementptr &lt;ty&gt;* &lt;ptrval&gt;{, &lt;ty&gt; &lt;idx&gt;}*
</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 integer operands that indicate what
elements of the aggregate object to index to. 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 or to a specific index in an array. When indexing into a
structure, only <tt>i32</tt> integer constants are allowed. When indexing
into an array or pointer, only integers of 32 or 64 bits are allowed, and will
be sign extended to 64-bit values.</p>
<p>For example, let's consider a C code fragment and how it gets
compiled to LLVM:</p>
<div class="doc_code">
<pre>
struct RT {
char A;
int B[10][20];
char C;
};
struct ST {
int X;
double Y;
struct RT Z;
};
int *foo(struct ST *s) {
return &amp;s[1].Z.B[5][13];
}
</pre>
</div>
<p>The LLVM code generated by the GCC frontend is:</p>
<div class="doc_code">
<pre>
%RT = type { i8 , [10 x [20 x i32]], i8 }
%ST = type { i32, double, %RT }
define i32* %foo(%ST* %s) {
entry:
%reg = getelementptr %ST* %s, i32 1, i32 2, i32 1, i32 5, i32 13
ret i32* %reg
}
</pre>
</div>
<h5>Semantics:</h5>
<p>The index types specified for the '<tt>getelementptr</tt>' instruct