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2315 lines
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2315 lines
76 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
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"http://www.w3.org/TR/html4/strict.dtd">
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<html>
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<head>
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<title>LLVM Assembly Language Reference Manual</title>
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<link rel="stylesheet" href="llvm.css" type="text/css">
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</head>
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<body>
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<div class="doc_title">
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LLVM Language Reference Manual
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</div>
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<ol>
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<li><a href="#abstract">Abstract</a></li>
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<li><a href="#introduction">Introduction</a></li>
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<li><a href="#identifiers">Identifiers</a></li>
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<li><a href="#typesystem">Type System</a>
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<ol>
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<li><a href="#t_primitive">Primitive Types</a>
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<ol>
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<li><a href="#t_classifications">Type Classifications</a></li>
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</ol></li>
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<li><a href="#t_derived">Derived Types</a>
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<ol>
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<li><a href="#t_array" >Array Type</a></li>
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<li><a href="#t_function">Function Type</a></li>
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<li><a href="#t_pointer">Pointer Type</a></li>
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<li><a href="#t_struct" >Structure Type</a></li>
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<!-- <li><a href="#t_packed" >Packed Type</a> -->
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</ol></li>
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</ol></li>
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<li><a href="#highlevel">High Level Structure</a>
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<ol>
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<li><a href="#modulestructure">Module Structure</a></li>
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<li><a href="#globalvars">Global Variables</a></li>
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<li><a href="#functionstructure">Function Structure</a></li>
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</ol></li>
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<li><a href="#instref">Instruction Reference</a>
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<ol>
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<li><a href="#terminators">Terminator Instructions</a>
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<ol>
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<li><a href="#i_ret" >'<tt>ret</tt>' Instruction</a></li>
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<li><a href="#i_br" >'<tt>br</tt>' Instruction</a></li>
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<li><a href="#i_switch">'<tt>switch</tt>' Instruction</a></li>
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<li><a href="#i_invoke">'<tt>invoke</tt>' Instruction</a></li>
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<li><a href="#i_unwind" >'<tt>unwind</tt>' Instruction</a></li>
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</ol></li>
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<li><a href="#binaryops">Binary Operations</a>
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<ol>
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<li><a href="#i_add" >'<tt>add</tt>' Instruction</a></li>
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<li><a href="#i_sub" >'<tt>sub</tt>' Instruction</a></li>
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<li><a href="#i_mul" >'<tt>mul</tt>' Instruction</a></li>
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<li><a href="#i_div" >'<tt>div</tt>' Instruction</a></li>
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<li><a href="#i_rem" >'<tt>rem</tt>' Instruction</a></li>
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<li><a href="#i_setcc">'<tt>set<i>cc</i></tt>' Instructions</a></li>
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</ol></li>
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<li><a href="#bitwiseops">Bitwise Binary Operations</a>
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<ol>
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<li><a href="#i_and">'<tt>and</tt>' Instruction</a></li>
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<li><a href="#i_or" >'<tt>or</tt>' Instruction</a></li>
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<li><a href="#i_xor">'<tt>xor</tt>' Instruction</a></li>
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<li><a href="#i_shl">'<tt>shl</tt>' Instruction</a></li>
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<li><a href="#i_shr">'<tt>shr</tt>' Instruction</a></li>
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</ol></li>
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<li><a href="#memoryops">Memory Access Operations</a>
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<ol>
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<li><a href="#i_malloc" >'<tt>malloc</tt>' Instruction</a></li>
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<li><a href="#i_free" >'<tt>free</tt>' Instruction</a></li>
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<li><a href="#i_alloca" >'<tt>alloca</tt>' Instruction</a></li>
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<li><a href="#i_load" >'<tt>load</tt>' Instruction</a></li>
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<li><a href="#i_store" >'<tt>store</tt>' Instruction</a></li>
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<li><a href="#i_getelementptr">'<tt>getelementptr</tt>' Instruction</a></li>
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</ol></li>
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<li><a href="#otherops">Other Operations</a>
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<ol>
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<li><a href="#i_phi" >'<tt>phi</tt>' Instruction</a></li>
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<li><a href="#i_cast">'<tt>cast .. to</tt>' Instruction</a></li>
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<li><a href="#i_call" >'<tt>call</tt>' Instruction</a></li>
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<li><a href="#i_vanext">'<tt>vanext</tt>' Instruction</a></li>
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<li><a href="#i_vaarg" >'<tt>vaarg</tt>' Instruction</a></li>
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</ol>
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</ol>
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<li><a href="#intrinsics">Intrinsic Functions</a>
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<ol>
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<li><a href="#int_varargs">Variable Argument Handling Intrinsics</a>
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<ol>
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<li><a href="#i_va_start">'<tt>llvm.va_start</tt>' Intrinsic</a></li>
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<li><a href="#i_va_end" >'<tt>llvm.va_end</tt>' Intrinsic</a></li>
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<li><a href="#i_va_copy" >'<tt>llvm.va_copy</tt>' Intrinsic</a></li>
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</ol></li>
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</ol></li>
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</ol>
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<div class="doc_text">
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<p><b>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> and <A href="mailto:vadve@cs.uiuc.edu">Vikram Adve</a></b><p>
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</div>
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<!-- *********************************************************************** -->
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<div class="doc_section">
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<a name="abstract">Abstract
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</div>
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<!-- *********************************************************************** -->
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<div class="doc_text">
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<p>This document is a reference manual for the LLVM assembly language. LLVM is
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an SSA based representation that provides type safety, low-level operations,
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flexibility, and the capability of representing 'all' high-level languages
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cleanly. It is the common code representation used throughout all phases of the
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LLVM compilation strategy.</p>
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</div>
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<!-- *********************************************************************** -->
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<div class="doc_section">
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<a name="introduction">Introduction</a>
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</div>
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<!-- *********************************************************************** -->
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<div class="doc_text">
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<p>The LLVM code representation is designed to be used in three different forms:
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as an in-memory compiler IR, as an on-disk bytecode representation (suitable for
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fast loading by a Just-In-Time compiler), and as a human readable assembly
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language representation. This allows LLVM to provide a powerful intermediate
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representation for efficient compiler transformations and analysis, while
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providing a natural means to debug and visualize the transformations. The three
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different forms of LLVM are all equivalent. This document describes the human
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readable representation and notation.</p>
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<p>The LLVM representation aims to be a light-weight and low-level while being
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expressive, typed, and extensible at the same time. It aims to be a "universal
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IR" of sorts, by being at a low enough level that high-level ideas may be
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cleanly mapped to it (similar to how microprocessors are "universal IR's",
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allowing many source languages to be mapped to them). By providing type
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information, LLVM can be used as the target of optimizations: for example,
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through pointer analysis, it can be proven that a C automatic variable is never
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accessed outside of the current function... allowing it to be promoted to a
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simple SSA value instead of a memory location.</p>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsubsection">
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<a name="wellformed">Well-Formedness</a>
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</div>
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<div class="doc_text">
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<p>It is important to note that this document describes 'well formed' LLVM
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assembly language. There is a difference between what the parser accepts and
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what is considered 'well formed'. For example, the following instruction is
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syntactically okay, but not well formed:</p>
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<pre>
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%x = <a href="#i_add">add</a> int 1, %x
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</pre>
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<p>...because the definition of <tt>%x</tt> does not dominate all of its uses.
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The LLVM infrastructure provides a verification pass that may be used to verify
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that an LLVM module is well formed. This pass is automatically run by the
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parser after parsing input assembly, and by the optimizer before it outputs
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bytecode. The violations pointed out by the verifier pass indicate bugs in
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transformation passes or input to the parser.</p>
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<!-- Describe the typesetting conventions here. -->
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</div>
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<!-- *********************************************************************** -->
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<div class="doc_section">
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<a name="identifiers">Identifiers</a>
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</div>
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<!-- *********************************************************************** -->
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<div class="doc_text">
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<p>LLVM uses three different forms of identifiers, for different purposes:</p>
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<ol>
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<li>Numeric constants are represented as you would expect: 12, -3 123.421,
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etc. Floating point constants have an optional hexidecimal notation.</li>
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<li>Named values are represented as a string of characters with a '%' prefix.
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For example, %foo, %DivisionByZero, %a.really.long.identifier. The actual
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regular expression used is '<tt>%[a-zA-Z$._][a-zA-Z$._0-9]*</tt>'.
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Identifiers which require other characters in their names can be surrounded
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with quotes. In this way, anything except a <tt>"</tt> character can be used
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in a name.</li>
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<li>Unnamed values are represented as an unsigned numeric value with a '%'
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prefix. For example, %12, %2, %44.</li>
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</ol>
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<p>LLVM requires the values start with a '%' sign for two reasons: Compilers
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don't need to worry about name clashes with reserved words, and the set of
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reserved words may be expanded in the future without penalty. Additionally,
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unnamed identifiers allow a compiler to quickly come up with a temporary
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variable without having to avoid symbol table conflicts.</p>
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<p>Reserved words in LLVM are very similar to reserved words in other languages.
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There are keywords for different opcodes ('<tt><a href="#i_add">add</a></tt>',
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'<tt><a href="#i_cast">cast</a></tt>', '<tt><a href="#i_ret">ret</a></tt>',
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etc...), for primitive type names ('<tt><a href="#t_void">void</a></tt>',
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'<tt><a href="#t_uint">uint</a></tt>', etc...), and others. These reserved
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words cannot conflict with variable names, because none of them start with a '%'
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character.</p>
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<p>Here is an example of LLVM code to multiply the integer variable
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'<tt>%X</tt>' by 8:</p>
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<p>The easy way:</p>
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<pre>
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%result = <a href="#i_mul">mul</a> uint %X, 8
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</pre>
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<p>After strength reduction:</p>
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<pre>
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%result = <a href="#i_shl">shl</a> uint %X, ubyte 3
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</pre>
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<p>And the hard way:</p>
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<pre>
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<a href="#i_add">add</a> uint %X, %X <i>; yields {uint}:%0</i>
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<a href="#i_add">add</a> uint %0, %0 <i>; yields {uint}:%1</i>
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%result = <a href="#i_add">add</a> uint %1, %1
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</pre>
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<p>This last way of multiplying <tt>%X</tt> by 8 illustrates several important
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lexical features of LLVM:</p>
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<ol>
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<li>Comments are delimited with a '<tt>;</tt>' and go until the end of
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line.</li>
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<li>Unnamed temporaries are created when the result of a computation is not
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assigned to a named value.</li>
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<li>Unnamed temporaries are numbered sequentially</li>
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</ol>
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<p>...and it also show a convention that we follow in this document. When
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demonstrating instructions, we will follow an instruction with a comment that
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defines the type and name of value produced. Comments are shown in italic
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text.</p>
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<p>The one non-intuitive notation for constants is the optional hexidecimal form
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of floating point constants. For example, the form '<tt>double
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0x432ff973cafa8000</tt>' is equivalent to (but harder to read than) '<tt>double
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4.5e+15</tt>' which is also supported by the parser. The only time hexadecimal
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floating point constants are useful (and the only time that they are generated
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by the disassembler) is when an FP constant has to be emitted that is not
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representable as a decimal floating point number exactly. For example, NaN's,
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infinities, and other special cases are represented in their IEEE hexadecimal
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format so that assembly and disassembly do not cause any bits to change in the
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constants.</p>
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</div>
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<!-- *********************************************************************** -->
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<div class="doc_section">
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<a name="typesystem">Type System</a>
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</div>
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<!-- *********************************************************************** -->
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<div class="doc_text">
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<p>The LLVM type system is one of the most important features of the
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intermediate representation. Being typed enables a number of optimizations to
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be performed on the IR directly, without having to do extra analyses on the side
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before the transformation. A strong type system makes it easier to read the
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generated code and enables novel analyses and transformations that are not
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feasible to perform on normal three address code representations.</p>
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<!-- The written form for the type system was heavily influenced by the
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syntactic problems with types in the C language<sup><a
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href="#rw_stroustrup">1</a></sup>.<p> -->
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</div>
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<!-- ======================================================================= -->
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<div class="doc_subsection">
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<a name="t_primitive">Primitive Types</a>
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</div>
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<div class="doc_text">
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<p>The primitive types are the fundemental building blocks of the LLVM system.
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The current set of primitive types are as follows:</p>
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<p>
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<table border="0" align="center">
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<tr>
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<td>
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<table border="1" cellspacing="0" cellpadding="4" align="center">
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<tr><td><tt>void</tt></td> <td>No value</td></tr>
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<tr><td><tt>ubyte</tt></td> <td>Unsigned 8 bit value</td></tr>
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<tr><td><tt>ushort</tt></td><td>Unsigned 16 bit value</td></tr>
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<tr><td><tt>uint</tt></td> <td>Unsigned 32 bit value</td></tr>
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<tr><td><tt>ulong</tt></td> <td>Unsigned 64 bit value</td></tr>
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<tr><td><tt>float</tt></td> <td>32 bit floating point value</td></tr>
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<tr><td><tt>label</tt></td> <td>Branch destination</td></tr>
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</table>
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</td><td valign=top>
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<table border="1" cellspacing="0" cellpadding="4" align=center">
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<tr><td><tt>bool</tt></td> <td>True or False value</td></tr>
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<tr><td><tt>sbyte</tt></td> <td>Signed 8 bit value</td></tr>
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<tr><td><tt>short</tt></td> <td>Signed 16 bit value</td></tr>
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<tr><td><tt>int</tt></td> <td>Signed 32 bit value</td></tr>
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<tr><td><tt>long</tt></td> <td>Signed 64 bit value</td></tr>
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<tr><td><tt>double</tt></td><td>64 bit floating point value</td></tr>
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</table>
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</td>
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</tr>
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</table>
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</p>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsubsection">
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<a name="t_classifications">Type Classifications</a>
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</div>
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<div class="doc_text">
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<p>These different primitive types fall into a few useful classifications:</p>
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<p>
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<table border="1" cellspacing="0" cellpadding="4" align="center">
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<tr>
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<td><a name="t_signed">signed</td>
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<td><tt>sbyte, short, int, long, float, double</tt></td>
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</tr>
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<tr>
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<td><a name="t_unsigned">unsigned</td>
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<td><tt>ubyte, ushort, uint, ulong</tt></td>
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</tr>
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<tr>
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<td><a name="t_integer">integer</td>
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<td><tt>ubyte, sbyte, ushort, short, uint, int, ulong, long</tt></td>
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</tr>
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<tr>
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<td><a name="t_integral">integral</td>
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<td><tt>bool, ubyte, sbyte, ushort, short, uint, int, ulong, long</tt></td>
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</tr>
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<tr>
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<td><a name="t_floating">floating point</td>
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<td><tt>float, double</tt></td>
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</tr>
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<tr>
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<td><a name="t_firstclass">first class</td>
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<td><tt>bool, ubyte, sbyte, ushort, short,<br>
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uint, int, ulong, long, float, double,
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<a href="#t_pointer">pointer</a></tt></td>
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</tr>
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</table>
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</p>
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<p>The <a href="#t_firstclass">first class</a> types are perhaps the most
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important. Values of these types are the only ones which can be produced by
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instructions, passed as arguments, or used as operands to instructions. This
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means that all structures and arrays must be manipulated either by pointer or by
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component.</p>
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</div>
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<!-- ======================================================================= -->
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<div class="doc_subsection">
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<a name="t_derived">Derived Types</a>
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</div>
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<div class="doc_text">
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<p>The real power in LLVM comes from the derived types in the system. This is
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what allows a programmer to represent arrays, functions, pointers, and other
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useful types. Note that these derived types may be recursive: For example, it
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is possible to have a two dimensional array.</p>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsubsection">
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<a name="t_array">Array Type</a>
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</div>
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<div class="doc_text">
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<h5>Overview:</h5>
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<p>The array type is a very simple derived type that arranges elements
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sequentially in memory. The array type requires a size (number of elements) and
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an underlying data type.</p>
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<h5>Syntax:</h5>
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|
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<pre>
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|
[<# elements> x <elementtype>]
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</pre>
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<p>The number of elements is a constant integer value, elementtype may be any
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type with a size.</p>
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<h5>Examples:</h5>
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<p>
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<tt>[40 x int ]</tt>: Array of 40 integer values.<br>
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<tt>[41 x int ]</tt>: Array of 41 integer values.<br>
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<tt>[40 x uint]</tt>: Array of 40 unsigned integer values.<p>
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</p>
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<p>Here are some examples of multidimensional arrays:</p>
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<p>
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<table border="0" cellpadding="0" cellspacing="0">
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<tr>
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<td><tt>[3 x [4 x int]]</tt></td>
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<td>: 3x4 array integer values.</td>
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</tr>
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<tr>
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<td><tt>[12 x [10 x float]]</tt></td>
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<td>: 12x10 array of single precision floating point values.</td>
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</tr>
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<tr>
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<td><tt>[2 x [3 x [4 x uint]]]</tt></td>
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<td>: 2x3x4 array of unsigned integer values.</td>
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</tr>
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</table>
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</p>
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</div>
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<!-- _______________________________________________________________________ -->
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<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 when to build virtual function tables (which are structures of pointers to
|
|
functions), for indirect function calls, and when defining a function.</p>
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
<returntype> (<parameter list>)
|
|
</pre>
|
|
|
|
<p>Where '<tt><parameter list></tt>' is a comma-separated list of type
|
|
specifiers. Optionally, the parameter list may include a type <tt>...</tt>,
|
|
which indicates that the function takes a variable number of arguments.
|
|
Variable argument functions can access their arguments with the <a
|
|
href="#int_varargs">variable argument handling intrinsic</a> functions.</p>
|
|
|
|
<h5>Examples:</h5>
|
|
|
|
<p>
|
|
<table border="0" cellpadding="0" cellspacing="0">
|
|
|
|
<tr>
|
|
<td><tt>int (int)</tt></td>
|
|
<td>: function taking an <tt>int</tt>, returning an <tt>int</tt></td>
|
|
</tr>
|
|
<tr>
|
|
<td><tt>float (int, int *) *</tt></td>
|
|
<td>: <a href="#t_pointer">Pointer</a> to a function that takes an
|
|
<tt>int</tt> and a <a href="#t_pointer">pointer</a> to <tt>int</tt>,
|
|
returning <tt>float</tt>.</td>
|
|
</tr>
|
|
<tr>
|
|
<td><tt>int (sbyte *, ...)</tt></td>
|
|
<td>: A vararg function that takes at least one <a
|
|
href="#t_pointer">pointer</a> to <tt>sbyte</tt> (signed char in C), which
|
|
returns an integer. This is the signature for <tt>printf</tt> in
|
|
LLVM.</td>
|
|
</tr>
|
|
</table>
|
|
</p>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="t_struct">Structure Type</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The structure type is used to represent a collection of data members together
|
|
in memory. The packing of the field types is defined to match the ABI of the
|
|
underlying processor. The elements of a structure may be any type that has a
|
|
size.</p>
|
|
|
|
<p>Structures are accessed using '<tt><a href="#i_load">load</a></tt> and
|
|
'<tt><a href="#i_store">store</a></tt>' by getting a pointer to a field with the
|
|
'<tt><a href="#i_getelementptr">getelementptr</a></tt>' instruction.</p>
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
{ <type list> }
|
|
</pre>
|
|
|
|
<h5>Examples:</h5>
|
|
|
|
<p>
|
|
<table border="0" cellpadding="0" cellspacing="0">
|
|
<tr>
|
|
<td><tt>{ int, int, int }</tt></td>
|
|
<td>: a triple of three <tt>int</tt> values</td>
|
|
</tr>
|
|
<tr>
|
|
<td><tt>{ float, int (int) * }</tt></td>
|
|
<td>: A pair, where the first element is a <tt>float</tt> and the second
|
|
element is a <a href="#t_pointer">pointer</a> to a <a
|
|
href="t_function">function</a> that takes an <tt>int</tt>, returning an
|
|
<tt>int</tt>.</td>
|
|
</tr>
|
|
</table>
|
|
</p>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="t_pointer">Pointer Type</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>As in many languages, the pointer type represents a pointer or reference to
|
|
another object, which must live in memory.</p>
|
|
|
|
<h5>Syntax:</h5>
|
|
<pre>
|
|
<type> *
|
|
</pre>
|
|
|
|
<h5>Examples:</h5>
|
|
|
|
<p>
|
|
<table border="0" cellpadding="0" cellspacing="0">
|
|
<tr>
|
|
<td><tt>[4x int]*</tt></td>
|
|
<td>: <a href="#t_pointer">pointer</a> to <a href="#t_array">array</a> of four
|
|
<tt>int</tt> values</td>
|
|
</tr>
|
|
<tr>
|
|
<td><tt>int (int *) *</tt></td>
|
|
<td>: A <a href="#t_pointer">pointer</a> to a <a
|
|
href="t_function">function</a> that takes an <tt>int</tt>, returning an
|
|
<tt>int</tt>.</td>
|
|
</tr>
|
|
</table>
|
|
</p>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<!--
|
|
<div class="doc_subsubsection">
|
|
<a name="t_packed">Packed Type</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
Mention/decide that packed types work with saturation or not. Maybe have a packed+saturated type in addition to just a packed type.<p>
|
|
|
|
Packed types should be 'nonsaturated' because standard data types are not saturated. Maybe have a saturated packed type?<p>
|
|
|
|
</div>
|
|
|
|
-->
|
|
|
|
|
|
<!-- *********************************************************************** -->
|
|
<div class="doc_section">
|
|
<a name="highlevel">High Level Structure</a>
|
|
</div>
|
|
<!-- *********************************************************************** -->
|
|
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsection">
|
|
<a name="modulestructure">Module Structure</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>LLVM programs are composed of "Module"s, each of which is a translation unit
|
|
of the input programs. Each module consists of functions, global variables, and
|
|
symbol table entries. Modules may be combined together with the LLVM linker,
|
|
which merges function (and global variable) definitions, resolves forward
|
|
declarations, and merges symbol table entries. Here is an example of the "hello
|
|
world" module:</p>
|
|
|
|
<pre>
|
|
<i>; Declare the string constant as a global constant...</i>
|
|
<a href="#identifiers">%.LC0</a> = <a href="#linkage_internal">internal</a> <a href="#globalvars">constant</a> <a href="#t_array">[13 x sbyte]</a> c"hello world\0A\00" <i>; [13 x sbyte]*</i>
|
|
|
|
<i>; External declaration of the puts function</i>
|
|
<a href="#functionstructure">declare</a> int %puts(sbyte*) <i>; int(sbyte*)* </i>
|
|
|
|
<i>; Definition of main function</i>
|
|
int %main() { <i>; int()* </i>
|
|
<i>; Convert [13x sbyte]* to sbyte *...</i>
|
|
%cast210 = <a href="#i_getelementptr">getelementptr</a> [13 x sbyte]* %.LC0, long 0, long 0 <i>; sbyte*</i>
|
|
|
|
<i>; Call puts function to write out the string to stdout...</i>
|
|
<a href="#i_call">call</a> int %puts(sbyte* %cast210) <i>; int</i>
|
|
<a href="#i_ret">ret</a> int 0
|
|
}
|
|
</pre>
|
|
|
|
<p>This example is made up of a <a href="#globalvars">global variable</a> named
|
|
"<tt>.LC0</tt>", an external declaration of the "<tt>puts</tt>" function, and a
|
|
<a href="#functionstructure">function definition</a> for "<tt>main</tt>".</p>
|
|
|
|
<a name="linkage">
|
|
In general, a module is made up of a list of global values, where both functions
|
|
and global variables are global values. Global values are represented by a
|
|
pointer to a memory location (in this case, a pointer to an array of char, and a
|
|
pointer to a function), and have one of the following linkage types:<p>
|
|
|
|
<dl>
|
|
<a name="linkage_internal">
|
|
<dt><tt><b>internal</b></tt>
|
|
|
|
<dd>Global values with internal linkage are only directly accessible by objects
|
|
in the current module. In particular, linking code into a module with an
|
|
internal global value may cause the internal to be renamed as necessary to avoid
|
|
collisions. Because the symbol is internal to the module, all references can be
|
|
updated. This corresponds to the notion of the '<tt>static</tt>' keyword in C,
|
|
or the idea of "anonymous namespaces" in C++.<p>
|
|
|
|
<a name="linkage_linkonce">
|
|
<dt><tt><b>linkonce</b></tt>:
|
|
|
|
<dd>"<tt>linkonce</tt>" linkage is similar to <tt>internal</tt> linkage, with
|
|
the twist that linking together two modules defining the same <tt>linkonce</tt>
|
|
globals will cause one of the globals to be discarded. This is typically used
|
|
to implement inline functions. Unreferenced <tt>linkonce</tt> globals are
|
|
allowed to be discarded.<p>
|
|
|
|
<a name="linkage_weak">
|
|
<dt><tt><b>weak</b></tt>:
|
|
|
|
<dd>"<tt>weak</tt>" linkage is exactly the same as <tt>linkonce</tt> linkage,
|
|
except that unreferenced <tt>weak</tt> globals may not be discarded. This is
|
|
used to implement constructs in C such as "<tt>int X;</tt>" at global scope.<p>
|
|
|
|
<a name="linkage_appending">
|
|
<dt><tt><b>appending</b></tt>:
|
|
|
|
<dd>"<tt>appending</tt>" linkage may only applied to global variables of pointer
|
|
to array type. When two global variables with appending linkage are linked
|
|
together, the two global arrays are appended together. This is the LLVM,
|
|
typesafe, equivalent of having the system linker append together "sections" with
|
|
identical names when .o files are linked.<p>
|
|
|
|
<a name="linkage_external">
|
|
<dt><tt><b>externally visible</b></tt>:
|
|
|
|
<dd>If none of the above identifiers are used, the global is externally visible,
|
|
meaning that it participates in linkage and can be used to resolve external
|
|
symbol references.<p>
|
|
|
|
</dl><p>
|
|
|
|
<p>For example, since the "<tt>.LC0</tt>" variable is defined to be internal, if
|
|
another module defined a "<tt>.LC0</tt>" variable and was linked with this one,
|
|
one of the two would be renamed, preventing a collision. Since "<tt>main</tt>"
|
|
and "<tt>puts</tt>" are external (i.e., lacking any linkage declarations), they
|
|
are accessible outside of the current module. It is illegal for a function
|
|
<i>declaration</i> to have any linkage type other than "externally visible".</p>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsection">
|
|
<a name="globalvars">Global Variables</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>Global variables define regions of memory allocated at compilation time
|
|
instead of run-time. Global variables may optionally be initialized. A
|
|
variable may be defined as a global "constant", which indicates that the
|
|
contents of the variable will never be modified (opening options for
|
|
optimization). Constants must always have an initial value.</p>
|
|
|
|
<p>As SSA values, global variables define pointer values that are in scope
|
|
(i.e. they dominate) for all basic blocks in the program. Global variables
|
|
always define a pointer to their "content" type because they describe a region
|
|
of memory, and all memory objects in LLVM are accessed through pointers.</p>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsection">
|
|
<a name="functionstructure">Functions</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>LLVM functions definitions are composed of a (possibly empty) argument list,
|
|
an opening curly brace, a list of basic blocks, and a closing curly brace. LLVM
|
|
function declarations are defined with the "<tt>declare</tt>" keyword, a
|
|
function name and a function signature.</p>
|
|
|
|
<p>A function definition contains a list of basic blocks, forming the CFG for
|
|
the function. Each basic block may optionally start with a label (giving the
|
|
basic block a symbol table entry), contains a list of instructions, and ends
|
|
with a <a href="#terminators">terminator</a> instruction (such as a branch or
|
|
function return).</p>
|
|
|
|
<p>The first basic block in program is special in two ways: it is immediately
|
|
executed on entrance to the function, and it is not allowed to have predecessor
|
|
basic blocks (i.e. there can not be any branches to the entry block of a
|
|
function). Because the block can have no predecessors, it also cannot have any
|
|
<a href="#i_phi">PHI nodes</a>.</p>
|
|
|
|
</div>
|
|
|
|
<!-- *********************************************************************** -->
|
|
<div class="doc_section">
|
|
<a name="instref">Instruction Reference</a>
|
|
</div>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>The LLVM instruction set consists of several different classifications of
|
|
instructions: <a href="#terminators">terminator instructions</a>, <a
|
|
href="#binaryops">binary instructions</a>, <a href="#memoryops">memory
|
|
instructions</a>, and <a href="#otherops">other instructions</a>.</p>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsection">
|
|
<a name="terminators">Terminator Instructions</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>As mentioned <a href="#functionstructure">previously</a>, every basic block
|
|
in a program ends with a "Terminator" instruction, which indicates which block
|
|
should be executed after the current block is finished. These terminator
|
|
instructions typically yield a '<tt>void</tt>' value: they produce control flow,
|
|
not values (the one exception being the '<a
|
|
href="#i_invoke"><tt>invoke</tt></a>' instruction).</p>
|
|
|
|
<p>There are five different terminator instructions: the '<a
|
|
href="#i_ret"><tt>ret</tt></a>' instruction, the '<a
|
|
href="#i_br"><tt>br</tt></a>' instruction, the '<a
|
|
href="#i_switch"><tt>switch</tt></a>' instruction, the '<a
|
|
href="#i_invoke"><tt>invoke</tt></a>' instruction, and the '<a
|
|
href="#i_unwind"><tt>unwind</tt></a>' instruction.</p>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="i_ret">'<tt>ret</tt>' Instruction</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Syntax:</h5>
|
|
<pre>
|
|
ret <type> <value> <i>; Return a value from a non-void function</i>
|
|
ret void <i>; Return from void function</i>
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>ret</tt>' instruction is used to return control flow (and a value)
|
|
from a function, back to the caller.</p>
|
|
|
|
<p>There are two forms of the '<tt>ret</tt>' instructruction: one that returns a
|
|
value and then causes control flow, and one that just causes control flow to
|
|
occur.</p>
|
|
|
|
<h5>Arguments:</h5>
|
|
|
|
<p>The '<tt>ret</tt>' instruction may return any '<a href="#t_firstclass">first
|
|
class</a>' type. Notice that a function is not <a href="#wellformed">well
|
|
formed</a> if there exists a '<tt>ret</tt>' instruction inside of the function
|
|
that returns a value that does not match the return type of the function.</p>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>When the '<tt>ret</tt>' instruction is executed, control flow returns back to
|
|
the calling function's context. If the caller is a "<a
|
|
href="#i_call"><tt>call</tt></a> instruction, execution continues at the
|
|
instruction after the call. If the caller was an "<a
|
|
href="#i_invoke"><tt>invoke</tt></a>" instruction, execution continues at the
|
|
beginning "normal" of the destination block. If the instruction returns a
|
|
value, that value shall set the call or invoke instruction's return value.</p>
|
|
|
|
<h5>Example:</h5>
|
|
<pre>
|
|
ret int 5 <i>; Return an integer value of 5</i>
|
|
ret void <i>; Return from a void function</i>
|
|
</pre>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="i_br">'<tt>br</tt>' Instruction</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
br bool <cond>, label <iftrue>, label <iffalse>
|
|
br label <dest> <i>; Unconditional branch</i>
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>br</tt>' instruction is used to cause control flow to transfer to a
|
|
different basic block in the current function. There are two forms of this
|
|
instruction, corresponding to a conditional branch and an unconditional
|
|
branch.</p>
|
|
|
|
<h5>Arguments:</h5>
|
|
|
|
<p>The conditional branch form of the '<tt>br</tt>' instruction takes a single
|
|
'<tt>bool</tt>' value and two '<tt>label</tt>' values. The unconditional form
|
|
of the '<tt>br</tt>' instruction takes a single '<tt>label</tt>' value as a
|
|
target.</p>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>Upon execution of a conditional '<tt>br</tt>' instruction, the
|
|
'<tt>bool</tt>' argument is evaluated. If the value is <tt>true</tt>, control
|
|
flows to the '<tt>iftrue</tt>' <tt>label</tt> argument. If "cond" is
|
|
<tt>false</tt>, control flows to the '<tt>iffalse</tt>' <tt>label</tt>
|
|
argument.</p>
|
|
|
|
<h5>Example:</h5>
|
|
|
|
<pre>
|
|
Test:
|
|
%cond = <a href="#i_setcc">seteq</a> int %a, %b
|
|
br bool %cond, label %IfEqual, label %IfUnequal
|
|
IfEqual:
|
|
<a href="#i_ret">ret</a> int 1
|
|
IfUnequal:
|
|
<a href="#i_ret">ret</a> int 0
|
|
</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 uint <value>, label <defaultdest> [ int <val>, label &dest>, ... ]
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>switch</tt>' instruction is used to transfer control flow to one of
|
|
several different places. It is a generalization of the '<tt>br</tt>'
|
|
instruction, allowing a branch to occur to one of many possible
|
|
destinations.</p>
|
|
|
|
<h5>Arguments:</h5>
|
|
|
|
<p>The '<tt>switch</tt>' instruction uses three parameters: a '<tt>uint</tt>'
|
|
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.</p>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>The <tt>switch</tt> instruction specifies a table of values and destinations.
|
|
When the '<tt>switch</tt>' instruction is executed, this table is searched for
|
|
the given value. If the value is found, the corresponding destination is
|
|
branched to, otherwise the default value it transfered to.</p>
|
|
|
|
<h5>Implementation:</h5>
|
|
|
|
<p>Depending on properties of the target machine and the particular
|
|
<tt>switch</tt> instruction, this instruction may be code generated as a series
|
|
of chained conditional branches, or with a lookup table.</p>
|
|
|
|
<h5>Example:</h5>
|
|
|
|
<pre>
|
|
<i>; Emulate a conditional br instruction</i>
|
|
%Val = <a href="#i_cast">cast</a> bool %value to uint
|
|
switch uint %Val, label %truedest [int 0, label %falsedest ]
|
|
|
|
<i>; Emulate an unconditional br instruction</i>
|
|
switch uint 0, label %dest [ ]
|
|
|
|
<i>; Implement a jump table:</i>
|
|
switch uint %val, label %otherwise [ int 0, label %onzero,
|
|
int 1, label %onone,
|
|
int 2, label %ontwo ]
|
|
</pre>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="i_invoke">'<tt>invoke</tt>' Instruction</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
<result> = invoke <ptr to function ty> %<function ptr val>(<function args>)
|
|
to label <normal label> except label <exception label>
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>invoke</tt>' instruction causes control to transfer to a specified
|
|
function, with the possibility of control flow transfer to either the
|
|
'<tt>normal</tt>' <tt>label</tt> label or the '<tt>exception</tt>'
|
|
<tt>label</tt>. If the callee function returns with the "<tt><a
|
|
href="#i_ret">ret</a></tt>" instruction, control flow will return to the
|
|
"normal" label. If the callee (or any indirect callees) returns with the "<a
|
|
href="#i_unwind"><tt>unwind</tt></a>" instruction, control is interrupted, and
|
|
continued at the dynamically nearest "except" label.</p>
|
|
|
|
<h5>Arguments:</h5>
|
|
|
|
<p>This instruction requires several arguments:</p>
|
|
|
|
<ol>
|
|
|
|
<li>'<tt>ptr to function ty</tt>': shall be the signature of the pointer to
|
|
function value being invoked. In most cases, this is a direct function
|
|
invocation, but indirect <tt>invoke</tt>s are just as possible, branching off
|
|
an arbitrary pointer to function value.
|
|
|
|
<li>'<tt>function ptr val</tt>': An LLVM value containing a pointer to a
|
|
function to be invoked.
|
|
|
|
<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>'<tt>normal label</tt>': the label reached when the called function executes
|
|
a '<tt><a href="#i_ret">ret</a></tt>' instruction.
|
|
|
|
<li>'<tt>exception label</tt>': the label reached when a callee returns with the
|
|
<a href="#i_unwind"><tt>unwind</tt></a> instruction.
|
|
</ol>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>This instruction is designed to operate as a standard '<tt><a
|
|
href="#i_call">call</a></tt>' instruction in most regards. The primary
|
|
difference is that it establishes an association with a label, which is used by the runtime library to unwind the stack.</p>
|
|
|
|
<p>This instruction is used in languages with destructors to ensure that proper
|
|
cleanup is performed in the case of either a <tt>longjmp</tt> or a thrown
|
|
exception. Additionally, this is important for implementation of
|
|
'<tt>catch</tt>' clauses in high-level languages that support them.</p>
|
|
|
|
<h5>Example:</h5>
|
|
|
|
<pre>
|
|
%retval = invoke int %Test(int 15)
|
|
to label %Continue
|
|
except label %TestCleanup <i>; {int}:retval set</i>
|
|
</pre>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="i_unwind">'<tt>unwind</tt>' Instruction</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
unwind
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>unwind</tt>' instruction unwinds the stack, continuing control flow
|
|
at the first callee in the dynamic call stack which used an <a
|
|
href="#i_invoke"><tt>invoke</tt></a> instruction to perform the call. This is
|
|
primarily used to implement exception handling.</p>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>The '<tt>unwind</tt>' intrinsic causes execution of the current function to
|
|
immediately halt. The dynamic call stack is then searched for the first <a
|
|
href="#i_invoke"><tt>invoke</tt></a> instruction on the call stack. Once found,
|
|
execution continues at the "exceptional" destination block specified by the
|
|
<tt>invoke</tt> instruction. If there is no <tt>invoke</tt> instruction in the
|
|
dynamic call chain, undefined behavior results.</p>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsection">
|
|
<a name="binaryops">Binary Operations</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>Binary operators are used to do most of the computation in a program. They
|
|
require two operands, execute an operation on them, and produce a single value.
|
|
The result value of a binary operator is not necessarily the same type as its
|
|
operands.</p>
|
|
|
|
<p>There are several different binary operators:</p>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="i_add">'<tt>add</tt>' Instruction</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
<result> = add <ty> <var1>, <var2> <i>; yields {ty}:result</i>
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>add</tt>' instruction returns the sum of its two operands.</p>
|
|
|
|
<h5>Arguments:</h5>
|
|
|
|
<p>The two arguments to the '<tt>add</tt>' instruction must be either <a
|
|
href="#t_integer">integer</a> or <a href="#t_floating">floating point</a>
|
|
values. Both arguments must have identical types.</p>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>The value produced is the integer or floating point sum of the two
|
|
operands.</p>
|
|
|
|
<h5>Example:</h5>
|
|
|
|
<pre>
|
|
<result> = add int 4, %var <i>; yields {int}:result = 4 + %var</i>
|
|
</pre>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="i_sub">'<tt>sub</tt>' Instruction</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
<result> = sub <ty> <var1>, <var2> <i>; yields {ty}:result</i>
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>sub</tt>' instruction returns the difference of its two
|
|
operands.</p>
|
|
|
|
<p>Note that the '<tt>sub</tt>' instruction is used to represent the
|
|
'<tt>neg</tt>' instruction present in most other intermediate
|
|
representations.</p>
|
|
|
|
<h5>Arguments:</h5>
|
|
|
|
<p>The two arguments to the '<tt>sub</tt>' instruction must be either <a
|
|
href="#t_integer">integer</a> or <a href="#t_floating">floating point</a>
|
|
values. Both arguments must have identical types.</p>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>The value produced is the integer or floating point difference of the two
|
|
operands.</p>
|
|
|
|
<h5>Example:</h5>
|
|
|
|
<pre>
|
|
<result> = sub int 4, %var <i>; yields {int}:result = 4 - %var</i>
|
|
<result> = sub int 0, %val <i>; yields {int}:result = -%var</i>
|
|
</pre>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="i_mul">'<tt>mul</tt>' Instruction</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
<result> = mul <ty> <var1>, <var2> <i>; yields {ty}:result</i>
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>mul</tt>' instruction returns the product of its two operands.</p>
|
|
|
|
<h5>Arguments:</h5>
|
|
|
|
<p>The two arguments to the '<tt>mul</tt>' instruction must be either <a
|
|
href="#t_integer">integer</a> or <a href="#t_floating">floating point</a>
|
|
values. Both arguments must have identical types.</p>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>The value produced is the integer or floating point product of the two
|
|
operands.</p>
|
|
|
|
<p>There is no signed vs unsigned multiplication. The appropriate action is
|
|
taken based on the type of the operand.</p>
|
|
|
|
<h5>Example:</h5>
|
|
|
|
<pre>
|
|
<result> = mul int 4, %var <i>; yields {int}:result = 4 * %var</i>
|
|
</pre>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="i_div">'<tt>div</tt>' Instruction</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
<result> = div <ty> <var1>, <var2> <i>; yields {ty}:result</i>
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>div</tt>' instruction returns the quotient of its two operands.</p>
|
|
|
|
<h5>Arguments:</h5>
|
|
|
|
<p>The two arguments to the '<tt>div</tt>' instruction must be either <a
|
|
href="#t_integer">integer</a> or <a href="#t_floating">floating point</a>
|
|
values. Both arguments must have identical types.</p>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>The value produced is the integer or floating point quotient of the two
|
|
operands.</p>
|
|
|
|
<h5>Example:</h5>
|
|
|
|
<pre>
|
|
<result> = div int 4, %var <i>; yields {int}:result = 4 / %var</i>
|
|
</pre>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="i_rem">'<tt>rem</tt>' Instruction</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
<result> = rem <ty> <var1>, <var2> <i>; yields {ty}:result</i>
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>rem</tt>' instruction returns the remainder from the division of its
|
|
two operands.</p>
|
|
|
|
<h5>Arguments:</h5>
|
|
|
|
<p>The two arguments to the '<tt>rem</tt>' instruction must be either <a
|
|
href="#t_integer">integer</a> or <a href="#t_floating">floating point</a>
|
|
values. Both arguments must have identical types.</p>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>This returns the <i>remainder</i> of a division (where the result has the
|
|
same sign as the divisor), not the <i>modulus</i> (where the result has the same
|
|
sign as the dividend) of a value. For more information about the difference,
|
|
see: <a href="http://mathforum.org/dr.math/problems/anne.4.28.99.html">The Math
|
|
Forum</a>.</p>
|
|
|
|
<h5>Example:</h5>
|
|
|
|
<pre>
|
|
<result> = rem int 4, %var <i>; yields {int}:result = 4 % %var</i>
|
|
</pre>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="i_setcc">'<tt>set<i>cc</i></tt>' Instructions</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
<result> = seteq <ty> <var1>, <var2> <i>; yields {bool}:result</i>
|
|
<result> = setne <ty> <var1>, <var2> <i>; yields {bool}:result</i>
|
|
<result> = setlt <ty> <var1>, <var2> <i>; yields {bool}:result</i>
|
|
<result> = setgt <ty> <var1>, <var2> <i>; yields {bool}:result</i>
|
|
<result> = setle <ty> <var1>, <var2> <i>; yields {bool}:result</i>
|
|
<result> = setge <ty> <var1>, <var2> <i>; yields {bool}:result</i>
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>set<i>cc</i></tt>' family of instructions returns a boolean value
|
|
based on a comparison of their two operands.</p>
|
|
|
|
<h5>Arguments:</h5>
|
|
|
|
<p>The two arguments to the '<tt>set<i>cc</i></tt>' instructions must be of <a
|
|
href="#t_firstclass">first class</a> type (it is not possible to compare
|
|
'<tt>label</tt>'s, '<tt>array</tt>'s, '<tt>structure</tt>' or '<tt>void</tt>'
|
|
values, etc...). Both arguments must have identical types.</p>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>The '<tt>seteq</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>' value
|
|
if both operands are equal.<br>
|
|
|
|
The '<tt>setne</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>' value if
|
|
both operands are unequal.<br>
|
|
|
|
The '<tt>setlt</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>' value if
|
|
the first operand is less than the second operand.<br>
|
|
|
|
The '<tt>setgt</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>' value if
|
|
the first operand is greater than the second operand.<br>
|
|
|
|
The '<tt>setle</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>' value if
|
|
the first operand is less than or equal to the second operand.<br>
|
|
|
|
The '<tt>setge</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>' value if
|
|
the first operand is greater than or equal to the second operand.</p>
|
|
|
|
<h5>Example:</h5>
|
|
|
|
<pre>
|
|
<result> = seteq int 4, 5 <i>; yields {bool}:result = false</i>
|
|
<result> = setne float 4, 5 <i>; yields {bool}:result = true</i>
|
|
<result> = setlt uint 4, 5 <i>; yields {bool}:result = true</i>
|
|
<result> = setgt sbyte 4, 5 <i>; yields {bool}:result = false</i>
|
|
<result> = setle sbyte 4, 5 <i>; yields {bool}:result = true</i>
|
|
<result> = setge sbyte 4, 5 <i>; yields {bool}:result = false</i>
|
|
</pre>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsection">
|
|
<a name="bitwiseops">Bitwise Binary Operations</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>Bitwise binary operators are used to do various forms of bit-twiddling in a
|
|
program. They are generally very efficient instructions, and can commonly be
|
|
strength reduced from other instructions. They require two operands, execute an
|
|
operation on them, and produce a single value. The resulting value of the
|
|
bitwise binary operators is always the same type as its first operand.</p>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="i_and">'<tt>and</tt>' Instruction</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
<result> = and <ty> <var1>, <var2> <i>; yields {ty}:result</i>
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>and</tt>' instruction returns the bitwise logical and of its two
|
|
operands.</p>
|
|
|
|
<h5>Arguments:</h5>
|
|
|
|
<p>The two arguments to the '<tt>and</tt>' instruction must be <a
|
|
href="#t_integral">integral</a> values. Both arguments must have identical
|
|
types.</p>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>The truth table used for the '<tt>and</tt>' instruction is:</p>
|
|
|
|
<p>
|
|
<center>
|
|
<table border="1" cellspacing="0" cellpadding="4">
|
|
<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>
|
|
</table></center>
|
|
</p>
|
|
|
|
<h5>Example:</h5>
|
|
|
|
<pre>
|
|
<result> = and int 4, %var <i>; yields {int}:result = 4 & %var</i>
|
|
<result> = and int 15, 40 <i>; yields {int}:result = 8</i>
|
|
<result> = and int 4, 8 <i>; yields {int}:result = 0</i>
|
|
</pre>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="i_or">'<tt>or</tt>' Instruction</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
<result> = or <ty> <var1>, <var2> <i>; yields {ty}:result</i>
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>or</tt>' instruction returns the bitwise logical inclusive or of its
|
|
two operands.</p>
|
|
|
|
<h5>Arguments:</h5>
|
|
|
|
<p>The two arguments to the '<tt>or</tt>' instruction must be <a
|
|
href="#t_integral">integral</a> values. Both arguments must have identical
|
|
types.</p>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>The truth table used for the '<tt>or</tt>' instruction is:</p>
|
|
|
|
<p>
|
|
<center><table border="1" cellspacing="0" cellpadding="4">
|
|
<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>
|
|
</table></center>
|
|
</p>
|
|
|
|
<h5>Example:</h5>
|
|
|
|
<pre>
|
|
<result> = or int 4, %var <i>; yields {int}:result = 4 | %var</i>
|
|
<result> = or int 15, 40 <i>; yields {int}:result = 47</i>
|
|
<result> = or int 4, 8 <i>; yields {int}:result = 12</i>
|
|
</pre>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="i_xor">'<tt>xor</tt>' Instruction</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
<result> = xor <ty> <var1>, <var2> <i>; yields {ty}:result</i>
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>xor</tt>' instruction returns the bitwise logical exclusive or of
|
|
its two operands. The <tt>xor</tt> is used to implement the "one's complement"
|
|
operation, which is the "~" operator in C.</p>
|
|
|
|
<h5>Arguments:</h5>
|
|
|
|
<p>The two arguments to the '<tt>xor</tt>' instruction must be <a
|
|
href="#t_integral">integral</a> values. Both arguments must have identical
|
|
types.</p>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>The truth table used for the '<tt>xor</tt>' instruction is:</p>
|
|
|
|
<p>
|
|
<center><table border="1" cellspacing="0" cellpadding="4">
|
|
<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>
|
|
</table></center>
|
|
<p>
|
|
|
|
<h5>Example:</h5>
|
|
|
|
<pre>
|
|
<result> = xor int 4, %var <i>; yields {int}:result = 4 ^ %var</i>
|
|
<result> = xor int 15, 40 <i>; yields {int}:result = 39</i>
|
|
<result> = xor int 4, 8 <i>; yields {int}:result = 12</i>
|
|
<result> = xor int %V, -1 <i>; yields {int}:result = ~%V</i>
|
|
</pre>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="i_shl">'<tt>shl</tt>' Instruction</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
<result> = shl <ty> <var1>, ubyte <var2> <i>; yields {ty}:result</i>
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>shl</tt>' instruction returns the first operand shifted to the left
|
|
a specified number of bits.</p>
|
|
|
|
<h5>Arguments:</h5>
|
|
|
|
<p>The first argument to the '<tt>shl</tt>' instruction must be an <a
|
|
href="#t_integer">integer</a> type. The second argument must be an
|
|
'<tt>ubyte</tt>' type.</p>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>The value produced is <tt>var1</tt> * 2<sup><tt>var2</tt></sup>.</p>
|
|
|
|
<h5>Example:</h5>
|
|
|
|
<pre>
|
|
<result> = shl int 4, ubyte %var <i>; yields {int}:result = 4 << %var</i>
|
|
<result> = shl int 4, ubyte 2 <i>; yields {int}:result = 16</i>
|
|
<result> = shl int 1, ubyte 10 <i>; yields {int}:result = 1024</i>
|
|
</pre>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="i_shr">'<tt>shr</tt>' Instruction</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
<result> = shr <ty> <var1>, ubyte <var2> <i>; yields {ty}:result</i>
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>shr</tt>' instruction returns the first operand shifted to the right
|
|
a specified number of bits.</p>
|
|
|
|
<h5>Arguments:</h5>
|
|
|
|
<p>The first argument to the '<tt>shr</tt>' instruction must be an <a
|
|
href="#t_integer">integer</a> type. The second argument must be an
|
|
'<tt>ubyte</tt>' type.</p>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>If the first argument is a <a href="#t_signed">signed</a> type, the most
|
|
significant bit is duplicated in the newly free'd bit positions. If the first
|
|
argument is unsigned, zero bits shall fill the empty positions.</p>
|
|
|
|
<h5>Example:</h5>
|
|
|
|
<pre>
|
|
<result> = shr int 4, ubyte %var <i>; yields {int}:result = 4 >> %var</i>
|
|
<result> = shr uint 4, ubyte 1 <i>; yields {uint}:result = 2</i>
|
|
<result> = shr int 4, ubyte 2 <i>; yields {int}:result = 1</i>
|
|
<result> = shr sbyte 4, ubyte 3 <i>; yields {sbyte}:result = 0</i>
|
|
<result> = shr sbyte -2, ubyte 1 <i>; yields {sbyte}:result = -1</i>
|
|
</pre>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsection">
|
|
<a name="memoryops">Memory Access Operations</div>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>A key design point of an SSA-based representation is how it represents
|
|
memory. In LLVM, no memory locations are in SSA form, which makes things very
|
|
simple. This section describes how to read, write, allocate and free memory in
|
|
LLVM.</p>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="i_malloc">'<tt>malloc</tt>' Instruction</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
<result> = malloc <type>, uint <NumElements> <i>; yields {type*}:result</i>
|
|
<result> = malloc <type> <i>; yields {type*}:result</i>
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>malloc</tt>' instruction allocates memory from the system heap and
|
|
returns a pointer to it.</p>
|
|
|
|
<h5>Arguments:</h5>
|
|
|
|
<p>The the '<tt>malloc</tt>' instruction allocates
|
|
<tt>sizeof(<type>)*NumElements</tt> bytes of memory from the operating
|
|
system, and returns a pointer of the appropriate type to the program. The
|
|
second form of the instruction is a shorter version of the first instruction
|
|
that defaults to allocating one element.</p>
|
|
|
|
<p>'<tt>type</tt>' must be a sized type.</p>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>Memory is allocated using the system "<tt>malloc</tt>" function, and a
|
|
pointer is returned.</p>
|
|
|
|
<h5>Example:</h5>
|
|
|
|
<pre>
|
|
%array = malloc [4 x ubyte ] <i>; yields {[%4 x ubyte]*}:array</i>
|
|
|
|
%size = <a href="#i_add">add</a> uint 2, 2 <i>; yields {uint}:size = uint 4</i>
|
|
%array1 = malloc ubyte, uint 4 <i>; yields {ubyte*}:array1</i>
|
|
%array2 = malloc [12 x ubyte], uint %size <i>; yields {[12 x ubyte]*}:array2</i>
|
|
</pre>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="i_free">'<tt>free</tt>' Instruction</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
free <type> <value> <i>; yields {void}</i>
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>free</tt>' instruction returns memory back to the unused memory
|
|
heap, to be reallocated in the future.<p>
|
|
|
|
<h5>Arguments:</h5>
|
|
|
|
<p>'<tt>value</tt>' shall be a pointer value that points to a value that was
|
|
allocated with the '<tt><a href="#i_malloc">malloc</a></tt>' instruction.</p>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>Access to the memory pointed to by the pointer is not longer defined after
|
|
this instruction executes.</p>
|
|
|
|
<h5>Example:</h5>
|
|
<pre>
|
|
%array = <a href="#i_malloc">malloc</a> [4 x ubyte] <i>; yields {[4 x ubyte]*}:array</i>
|
|
free [4 x ubyte]* %array
|
|
</pre>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="i_alloca">'<tt>alloca</tt>' Instruction</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
<result> = alloca <type>, uint <NumElements> <i>; yields {type*}:result</i>
|
|
<result> = alloca <type> <i>; yields {type*}:result</i>
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>alloca</tt>' instruction allocates memory on the current stack frame
|
|
of the procedure that is live until the current function returns to its
|
|
caller.</p>
|
|
|
|
<h5>Arguments:</h5>
|
|
|
|
<p>The the '<tt>alloca</tt>' instruction allocates
|
|
<tt>sizeof(<type>)*NumElements</tt> bytes of memory on the runtime stack,
|
|
returning a pointer of the appropriate type to the program. The second form of
|
|
the instruction is a shorter version of the first that defaults to allocating
|
|
one element.</p>
|
|
|
|
<p>'<tt>type</tt>' may be any sized type.</p>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>Memory is allocated, a pointer is returned. '<tt>alloca</tt>'d memory is
|
|
automatically released when the function returns. The '<tt>alloca</tt>'
|
|
instruction is commonly used to represent automatic variables that must have an
|
|
address available. When the function returns (either with the <tt><a
|
|
href="#i_ret">ret</a></tt> or <tt><a href="#i_invoke">invoke</a></tt>
|
|
instructions), the memory is reclaimed.</p>
|
|
|
|
<h5>Example:</h5>
|
|
|
|
<pre>
|
|
%ptr = alloca int <i>; yields {int*}:ptr</i>
|
|
%ptr = alloca int, uint 4 <i>; yields {int*}:ptr</i>
|
|
</pre>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="i_load">'<tt>load</tt>' Instruction</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
<result> = load <ty>* <pointer>
|
|
<result> = volatile load <ty>* <pointer>
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>load</tt>' instruction is used to read from memory.</p>
|
|
|
|
<h5>Arguments:</h5>
|
|
|
|
<p>The argument to the '<tt>load</tt>' instruction specifies the memory address
|
|
to load from. The pointer must point to a <a href="t_firstclass">first
|
|
class</a> type. If the <tt>load</tt> is marked as <tt>volatile</tt> then the
|
|
optimizer is not allowed to modify the number or order of execution of this
|
|
<tt>load</tt> with other volatile <tt>load</tt> and <tt><a
|
|
href="#i_store">store</a></tt> instructions. </p>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>The location of memory pointed to is loaded.</p>
|
|
|
|
<h5>Examples:</h5>
|
|
|
|
<pre>
|
|
%ptr = <a href="#i_alloca">alloca</a> int <i>; yields {int*}:ptr</i>
|
|
<a href="#i_store">store</a> int 3, int* %ptr <i>; yields {void}</i>
|
|
%val = load int* %ptr <i>; yields {int}:val = int 3</i>
|
|
</pre>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="i_store">'<tt>store</tt>' Instruction</a>
|
|
</div>
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
store <ty> <value>, <ty>* <pointer> <i>; yields {void}</i>
|
|
volatile store <ty> <value>, <ty>* <pointer> <i>; yields {void}</i>
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>store</tt>' instruction is used to write to memory.</p>
|
|
|
|
<h5>Arguments:</h5>
|
|
|
|
<p>There are two arguments to the '<tt>store</tt>' instruction: a value to store
|
|
and an address to store it into. The type of the '<tt><pointer></tt>'
|
|
operand must be a pointer to the type of the '<tt><value></tt>' operand.
|
|
If the <tt>store</tt> is marked as <tt>volatile</tt> then the optimizer is not
|
|
allowed to modify the number or order of execution of this <tt>store</tt> with
|
|
other volatile <tt>load</tt> and <tt><a href="#i_store">store</a></tt>
|
|
instructions.</p>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>The contents of memory are updated to contain '<tt><value></tt>' at the
|
|
location specified by the '<tt><pointer></tt>' operand.</p>
|
|
|
|
<h5>Example:</h5>
|
|
|
|
<pre>
|
|
%ptr = <a href="#i_alloca">alloca</a> int <i>; yields {int*}:ptr</i>
|
|
<a href="#i_store">store</a> int 3, int* %ptr <i>; yields {void}</i>
|
|
%val = load int* %ptr <i>; yields {int}:val = int 3</i>
|
|
</pre>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="i_getelementptr">'<tt>getelementptr</tt>' Instruction</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
<result> = getelementptr <ty>* <ptrval>{, long <aidx>|, ubyte <sidx>}*
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>getelementptr</tt>' instruction is used to get the address of a
|
|
subelement of an aggregate data structure.</p>
|
|
|
|
<h5>Arguments:</h5>
|
|
|
|
<p>This instruction takes a list of <tt>long</tt> values and <tt>ubyte</tt>
|
|
constants that indicate what form of addressing to perform. The actual types of
|
|
the arguments provided depend on the type of the first pointer argument. The
|
|
'<tt>getelementptr</tt>' instruction is used to index down through the type
|
|
levels of a structure.</p>
|
|
|
|
<p>For example, let's consider a C code fragment and how it gets compiled to
|
|
LLVM:</p>
|
|
|
|
<pre>
|
|
struct RT {
|
|
char A;
|
|
int B[10][20];
|
|
char C;
|
|
};
|
|
struct ST {
|
|
int X;
|
|
double Y;
|
|
struct RT Z;
|
|
};
|
|
|
|
int *foo(struct ST *s) {
|
|
return &s[1].Z.B[5][13];
|
|
}
|
|
</pre>
|
|
|
|
<p>The LLVM code generated by the GCC frontend is:</p>
|
|
|
|
<pre>
|
|
%RT = type { sbyte, [10 x [20 x int]], sbyte }
|
|
%ST = type { int, double, %RT }
|
|
|
|
int* "foo"(%ST* %s) {
|
|
%reg = getelementptr %ST* %s, long 1, ubyte 2, ubyte 1, long 5, long 13
|
|
ret int* %reg
|
|
}
|
|
</pre>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>The index types specified for the '<tt>getelementptr</tt>' instruction depend
|
|
on the pointer type that is being index into. <a href="t_pointer">Pointer</a>
|
|
and <a href="t_array">array</a> types require '<tt>long</tt>' values, and <a
|
|
href="t_struct">structure</a> types require '<tt>ubyte</tt>'
|
|
<b>constants</b>.</p>
|
|
|
|
<p>In the example above, the first index is indexing into the '<tt>%ST*</tt>'
|
|
type, which is a pointer, yielding a '<tt>%ST</tt>' = '<tt>{ int, double, %RT
|
|
}</tt>' type, a structure. The second index indexes into the third element of
|
|
the structure, yielding a '<tt>%RT</tt>' = '<tt>{ sbyte, [10 x [20 x int]],
|
|
sbyte }</tt>' type, another structure. The third index indexes into the second
|
|
element of the structure, yielding a '<tt>[10 x [20 x int]]</tt>' type, an
|
|
array. The two dimensions of the array are subscripted into, yielding an
|
|
'<tt>int</tt>' type. The '<tt>getelementptr</tt>' instruction return a pointer
|
|
to this element, thus yielding a '<tt>int*</tt>' type.</p>
|
|
|
|
<p>Note that it is perfectly legal to index partially through a structure,
|
|
returning a pointer to an inner element. Because of this, the LLVM code for the
|
|
given testcase is equivalent to:</p>
|
|
|
|
<pre>
|
|
int* "foo"(%ST* %s) {
|
|
%t1 = getelementptr %ST* %s , long 1 <i>; yields %ST*:%t1</i>
|
|
%t2 = getelementptr %ST* %t1, long 0, ubyte 2 <i>; yields %RT*:%t2</i>
|
|
%t3 = getelementptr %RT* %t2, long 0, ubyte 1 <i>; yields [10 x [20 x int]]*:%t3</i>
|
|
%t4 = getelementptr [10 x [20 x int]]* %t3, long 0, long 5 <i>; yields [20 x int]*:%t4</i>
|
|
%t5 = getelementptr [20 x int]* %t4, long 0, long 13 <i>; yields int*:%t5</i>
|
|
ret int* %t5
|
|
}
|
|
</pre>
|
|
|
|
<h5>Example:</h5>
|
|
|
|
<pre>
|
|
<i>; yields [12 x ubyte]*:aptr</i>
|
|
%aptr = getelementptr {int, [12 x ubyte]}* %sptr, long 0, ubyte 1
|
|
</pre>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsection">
|
|
<a name="otherops">Other Operations</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>The instructions in this catagory are the "miscellaneous" instructions, which
|
|
defy better classification.</p>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="i_phi">'<tt>phi</tt>' Instruction</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
<result> = phi <ty> [ <val0>, <label0>], ...
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>phi</tt>' instruction is used to implement the φ node in the SSA
|
|
graph representing the function.</p>
|
|
|
|
<h5>Arguments:</h5>
|
|
|
|
<p>The type of the incoming values are specified with the first type field.
|
|
After this, the '<tt>phi</tt>' instruction takes a list of pairs as arguments,
|
|
with one pair for each predecessor basic block of the current block. Only
|
|
values of <a href="#t_firstclass">first class</a> type may be used as the value
|
|
arguments to the PHI node. Only labels may be used as the label arguments.</p>
|
|
|
|
<p>There must be no non-phi instructions between the start of a basic block and
|
|
the PHI instructions: i.e. PHI instructions must be first in a basic block.</p>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>At runtime, the '<tt>phi</tt>' instruction logically takes on the value
|
|
specified by the parameter, depending on which basic block we came from in the
|
|
last <a href="#terminators">terminator</a> instruction.</p>
|
|
|
|
<h5>Example:</h5>
|
|
|
|
<pre>
|
|
Loop: ; Infinite loop that counts from 0 on up...
|
|
%indvar = phi uint [ 0, %LoopHeader ], [ %nextindvar, %Loop ]
|
|
%nextindvar = add uint %indvar, 1
|
|
br label %Loop
|
|
</pre>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="i_cast">'<tt>cast .. to</tt>' Instruction</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
<result> = cast <ty> <value> to <ty2> <i>; yields ty2</i>
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>cast</tt>' instruction is used as the primitive means to convert
|
|
integers to floating point, change data type sizes, and break type safety (by
|
|
casting pointers).</p>
|
|
|
|
<h5>Arguments:</h5>
|
|
|
|
<p>The '<tt>cast</tt>' instruction takes a value to cast, which must be a first
|
|
class value, and a type to cast it to, which must also be a <a
|
|
href="#t_firstclass">first class</a> type.</p>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>This instruction follows the C rules for explicit casts when determining how
|
|
the data being cast must change to fit in its new container.</p>
|
|
|
|
<p>When casting to bool, any value that would be considered true in the context
|
|
of a C '<tt>if</tt>' condition is converted to the boolean '<tt>true</tt>'
|
|
values, all else are '<tt>false</tt>'.</p>
|
|
|
|
<p>When extending an integral value from a type of one signness to another (for
|
|
example '<tt>sbyte</tt>' to '<tt>ulong</tt>'), the value is sign-extended if the
|
|
<b>source</b> value is signed, and zero-extended if the source value is
|
|
unsigned. <tt>bool</tt> values are always zero extended into either zero or
|
|
one.</p>
|
|
|
|
<h5>Example:</h5>
|
|
|
|
<pre>
|
|
%X = cast int 257 to ubyte <i>; yields ubyte:1</i>
|
|
%Y = cast int 123 to bool <i>; yields bool:true</i>
|
|
</pre>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="i_call">'<tt>call</tt>' Instruction</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
<result> = call <ty>* <fnptrval>(<param list>)
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>call</tt>' instruction represents a simple function call.</p>
|
|
|
|
<h5>Arguments:</h5>
|
|
|
|
<p>This instruction requires several arguments:</p>
|
|
|
|
<ol>
|
|
|
|
<li><p>'<tt>ty</tt>': shall be the signature of the pointer to function value
|
|
being invoked. The argument types must match the types implied by this
|
|
signature.</p></li>
|
|
|
|
<li><p>'<tt>fnptrval</tt>': An LLVM value containing a pointer to a function
|
|
to be invoked. In most cases, this is a direct function invocation, but
|
|
indirect <tt>call</tt>s are just as possible, calling an arbitrary pointer to
|
|
function values.</p></li>
|
|
|
|
<li><p>'<tt>function args</tt>': argument list whose types match the function
|
|
signature argument types. If the function signature indicates the function
|
|
accepts a variable number of arguments, the extra arguments can be
|
|
specified.</p></li>
|
|
|
|
</ol>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>The '<tt>call</tt>' instruction is used to cause control flow to transfer to
|
|
a specified function, with its incoming arguments bound to the specified values.
|
|
Upon a '<tt><a href="#i_ret">ret</a></tt>' instruction in the called function,
|
|
control flow continues with the instruction after the function call, and the
|
|
return value of the function is bound to the result argument. This is a simpler
|
|
case of the <a href="#i_invoke">invoke</a> instruction.</p>
|
|
|
|
<h5>Example:</h5>
|
|
|
|
<pre>
|
|
%retval = call int %test(int %argc)
|
|
call int(sbyte*, ...) *%printf(sbyte* %msg, int 12, sbyte 42);
|
|
</pre>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="i_vanext">'<tt>vanext</tt>' Instruction</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
<resultarglist> = vanext <va_list> <arglist>, <argty>
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>vanext</tt>' instruction is used to access arguments passed through
|
|
the "variable argument" area of a function call. It is used to implement the
|
|
<tt>va_arg</tt> macro in C.</p>
|
|
|
|
<h5>Arguments:</h5>
|
|
|
|
<p>This instruction takes a <tt>valist</tt> value and the type of the argument.
|
|
It returns another <tt>valist</tt>.</p>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>The '<tt>vanext</tt>' instruction advances the specified <tt>valist</tt> past
|
|
an argument of the specified type. In conjunction with the <a
|
|
href="#i_vaarg"><tt>vaarg</tt></a> instruction, it is used to implement the
|
|
<tt>va_arg</tt> macro available in C. For more information, see the variable
|
|
argument handling <a href="#int_varargs">Intrinsic Functions</a>.</p>
|
|
|
|
<p>It is legal for this instruction to be called in a function which does not
|
|
take a variable number of arguments, for example, the <tt>vfprintf</tt>
|
|
function.</p>
|
|
|
|
<p><tt>vanext</tt> is an LLVM instruction instead of an <a
|
|
href="#intrinsics">intrinsic function</a> because it takes an type as an
|
|
argument.</p>
|
|
|
|
<h5>Example:</h5>
|
|
|
|
<p>See the <a href="#int_varargs">variable argument processing</a> section.</p>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="i_vaarg">'<tt>vaarg</tt>' Instruction</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
<resultval> = vaarg <va_list> <arglist>, <argty>
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>vaarg</tt>' instruction is used to access arguments passed through
|
|
the "variable argument" area of a function call. It is used to implement the
|
|
<tt>va_arg</tt> macro in C.</p>
|
|
|
|
<h5>Arguments:</h5>
|
|
|
|
<p>This instruction takes a <tt>valist</tt> value and the type of the argument.
|
|
It returns a value of the specified argument type.</p>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>The '<tt>vaarg</tt>' instruction loads an argument of the specified type from
|
|
the specified <tt>va_list</tt>. In conjunction with the <a
|
|
href="#i_vanext"><tt>vanext</tt></a> instruction, it is used to implement the
|
|
<tt>va_arg</tt> macro available in C. For more information, see the variable
|
|
argument handling <a href="#int_varargs">Intrinsic Functions</a>.</p>
|
|
|
|
<p>It is legal for this instruction to be called in a function which does not
|
|
take a variable number of arguments, for example, the <tt>vfprintf</tt>
|
|
function.</p>
|
|
|
|
<p><tt>vaarg</tt> is an LLVM instruction instead of an <a
|
|
href="#intrinsics">intrinsic function</a> because it takes an type as an
|
|
argument.</p>
|
|
|
|
<h5>Example:</h5>
|
|
|
|
<p>See the <a href="#int_varargs">variable argument processing</a> section.</p>
|
|
|
|
</div>
|
|
|
|
<!-- *********************************************************************** -->
|
|
<div class="doc_section">
|
|
<a name="intrinsics">Intrinsic Functions</a>
|
|
</div>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>LLVM supports the notion of an "intrinsic function". These functions have
|
|
well known names and semantics, and are required to follow certain restrictions.
|
|
Overall, these instructions represent an extension mechanism for the LLVM
|
|
language that does not require changing all of the transformations in LLVM to
|
|
add to the language (or the bytecode reader/writer, the parser, etc...).</p>
|
|
|
|
<p>Intrinsic function names must all start with an "<tt>llvm.</tt>" prefix, this
|
|
prefix is reserved in LLVM for intrinsic names, thus functions may not be named
|
|
this. Intrinsic functions must always be external functions: you cannot define
|
|
the body of intrinsic functions. Intrinsic functions may only be used in call
|
|
or invoke instructions: it is illegal to take the address of an intrinsic
|
|
function. Additionally, because intrinsic functions are part of the LLVM
|
|
language, it is required that they all be documented here if any are added.</p>
|
|
|
|
<p>Unless an intrinsic function is target-specific, there must be a lowering
|
|
pass to eliminate the intrinsic or all backends must support the intrinsic
|
|
function.</p>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsection">
|
|
<a name="int_varargs">Variable Argument Handling Intrinsics</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>Variable argument support is defined in LLVM with the <a
|
|
href="#i_vanext"><tt>vanext</tt></a> instruction and these three intrinsic
|
|
functions. These functions are related to the similarly named macros defined in
|
|
the <tt><stdarg.h></tt> header file.</p>
|
|
|
|
<p>All of these functions operate on arguments that use a target-specific value
|
|
type "<tt>va_list</tt>". The LLVM assembly language reference manual does not
|
|
define what this type is, so all transformations should be prepared to handle
|
|
intrinsics with any type used.</p>
|
|
|
|
<p>This example shows how the <a href="#i_vanext"><tt>vanext</tt></a>
|
|
instruction and the variable argument handling intrinsic functions are used.</p>
|
|
|
|
<pre>
|
|
int %test(int %X, ...) {
|
|
; Initialize variable argument processing
|
|
%ap = call sbyte*()* %<a href="#i_va_start">llvm.va_start</a>()
|
|
|
|
; Read a single integer argument
|
|
%tmp = vaarg sbyte* %ap, int
|
|
|
|
; Advance to the next argument
|
|
%ap2 = vanext sbyte* %ap, int
|
|
|
|
; Demonstrate usage of llvm.va_copy and llvm.va_end
|
|
%aq = call sbyte* (sbyte*)* %<a href="#i_va_copy">llvm.va_copy</a>(sbyte* %ap2)
|
|
call void %<a href="#i_va_end">llvm.va_end</a>(sbyte* %aq)
|
|
|
|
; Stop processing of arguments.
|
|
call void %<a href="#i_va_end">llvm.va_end</a>(sbyte* %ap2)
|
|
ret int %tmp
|
|
}
|
|
</pre>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="i_va_start">'<tt>llvm.va_start</tt>' Intrinsic</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
call va_list ()* %llvm.va_start()
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>llvm.va_start</tt>' intrinsic returns a new <tt><arglist></tt>
|
|
for subsequent use by the variable argument intrinsics.</p>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>The '<tt>llvm.va_start</tt>' intrinsic works just like the <tt>va_start</tt>
|
|
macro available in C. In a target-dependent way, it initializes and returns a
|
|
<tt>va_list</tt> element, so that the next <tt>vaarg</tt> will produce the first
|
|
variable argument passed to the function. Unlike the C <tt>va_start</tt> macro,
|
|
this intrinsic does not need to know the last argument of the function, the
|
|
compiler can figure that out.</p>
|
|
|
|
<p>Note that this intrinsic function is only legal to be called from within the
|
|
body of a variable argument function.</p>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="i_va_end">'<tt>llvm.va_end</tt>' Intrinsic</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
call void (va_list)* %llvm.va_end(va_list <arglist>)
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>llvm.va_end</tt>' intrinsic destroys <tt><arglist></tt> which
|
|
has been initialized previously with <tt><a
|
|
href="#i_va_start">llvm.va_start</a></tt> or <tt><a
|
|
href="#i_va_copy">llvm.va_copy</a></tt>.</p>
|
|
|
|
<h5>Arguments:</h5>
|
|
|
|
<p>The argument is a <tt>va_list</tt> to destroy.</p>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>The '<tt>llvm.va_end</tt>' intrinsic works just like the <tt>va_end</tt>
|
|
macro available in C. In a target-dependent way, it destroys the
|
|
<tt>va_list</tt>. Calls to <a href="#i_va_start"><tt>llvm.va_start</tt></a> and
|
|
<a href="#i_va_copy"><tt>llvm.va_copy</tt></a> must be matched exactly with
|
|
calls to <tt>llvm.va_end</tt>.</p>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
<a name="i_va_copy">'<tt>llvm.va_copy</tt>' Intrinsic</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<h5>Syntax:</h5>
|
|
|
|
<pre>
|
|
call va_list (va_list)* %llvm.va_copy(va_list <destarglist>)
|
|
</pre>
|
|
|
|
<h5>Overview:</h5>
|
|
|
|
<p>The '<tt>llvm.va_copy</tt>' intrinsic copies the current argument position
|
|
from the source argument list to the destination argument list.</p>
|
|
|
|
<h5>Arguments:</h5>
|
|
|
|
<p>The argument is the <tt>va_list</tt> to copy.</p>
|
|
|
|
<h5>Semantics:</h5>
|
|
|
|
<p>The '<tt>llvm.va_copy</tt>' intrinsic works just like the <tt>va_copy</tt>
|
|
macro available in C. In a target-dependent way, it copies the source
|
|
<tt>va_list</tt> element into the returned list. This intrinsic is necessary
|
|
because the <tt><a href="i_va_start">llvm.va_start</a></tt> intrinsic may be
|
|
arbitrarily complex and require memory allocation, for example.</p>
|
|
|
|
</div>
|
|
|
|
<!-- *********************************************************************** -->
|
|
|
|
<hr>
|
|
<div class="doc_footer">
|
|
<address><a href="mailto:sabre@nondot.org">Chris Lattner</a></address>
|
|
<a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a>
|
|
<br>
|
|
Last modified: $Date$
|
|
</div>
|
|
|
|
</body>
|
|
</html>
|