[llvm-commits] [www-releases] r170871 [3/6] - in /www-releases/trunk/3.2/docs: ./ CommandGuide/ _sources/ _sources/CommandGuide/ _static/ tutorial/
Pawel Wodnicki
pawel at 32bitmicro.com
Fri Dec 21 01:14:45 PST 2012
Added: www-releases/trunk/3.2/docs/LangRef.html
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.2/docs/LangRef.html?rev=170871&view=auto
==============================================================================
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+<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+<html>
+<head>
+ <title>LLVM Assembly Language Reference Manual</title>
+ <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
+ <meta name="author" content="Chris Lattner">
+ <meta name="description"
+ content="LLVM Assembly Language Reference Manual.">
+ <link rel="stylesheet" href="_static/llvm.css" type="text/css">
+</head>
+
+<body>
+
+<h1>LLVM Language Reference Manual</h1>
+<ol>
+ <li><a href="#abstract">Abstract</a></li>
+ <li><a href="#introduction">Introduction</a></li>
+ <li><a href="#identifiers">Identifiers</a></li>
+ <li><a href="#highlevel">High Level Structure</a>
+ <ol>
+ <li><a href="#modulestructure">Module Structure</a></li>
+ <li><a href="#linkage">Linkage Types</a>
+ <ol>
+ <li><a href="#linkage_private">'<tt>private</tt>' Linkage</a></li>
+ <li><a href="#linkage_linker_private">'<tt>linker_private</tt>' Linkage</a></li>
+ <li><a href="#linkage_linker_private_weak">'<tt>linker_private_weak</tt>' Linkage</a></li>
+ <li><a href="#linkage_internal">'<tt>internal</tt>' Linkage</a></li>
+ <li><a href="#linkage_available_externally">'<tt>available_externally</tt>' Linkage</a></li>
+ <li><a href="#linkage_linkonce">'<tt>linkonce</tt>' Linkage</a></li>
+ <li><a href="#linkage_common">'<tt>common</tt>' Linkage</a></li>
+ <li><a href="#linkage_weak">'<tt>weak</tt>' Linkage</a></li>
+ <li><a href="#linkage_appending">'<tt>appending</tt>' Linkage</a></li>
+ <li><a href="#linkage_externweak">'<tt>extern_weak</tt>' Linkage</a></li>
+ <li><a href="#linkage_linkonce_odr">'<tt>linkonce_odr</tt>' Linkage</a></li>
+ <li><a href="#linkage_linkonce_odr_auto_hide">'<tt>linkonce_odr_auto_hide</tt>' Linkage</a></li>
+ <li><a href="#linkage_weak">'<tt>weak_odr</tt>' Linkage</a></li>
+ <li><a href="#linkage_external">'<tt>external</tt>' Linkage</a></li>
+ <li><a href="#linkage_dllimport">'<tt>dllimport</tt>' Linkage</a></li>
+ <li><a href="#linkage_dllexport">'<tt>dllexport</tt>' Linkage</a></li>
+ </ol>
+ </li>
+ <li><a href="#callingconv">Calling Conventions</a></li>
+ <li><a href="#namedtypes">Named Types</a></li>
+ <li><a href="#globalvars">Global Variables</a></li>
+ <li><a href="#functionstructure">Functions</a></li>
+ <li><a href="#aliasstructure">Aliases</a></li>
+ <li><a href="#namedmetadatastructure">Named Metadata</a></li>
+ <li><a href="#paramattrs">Parameter Attributes</a></li>
+ <li><a href="#fnattrs">Function Attributes</a></li>
+ <li><a href="#gc">Garbage Collector Names</a></li>
+ <li><a href="#moduleasm">Module-Level Inline Assembly</a></li>
+ <li><a href="#datalayout">Data Layout</a></li>
+ <li><a href="#pointeraliasing">Pointer Aliasing Rules</a></li>
+ <li><a href="#volatile">Volatile Memory Accesses</a></li>
+ <li><a href="#memmodel">Memory Model for Concurrent Operations</a></li>
+ <li><a href="#ordering">Atomic Memory Ordering Constraints</a></li>
+ </ol>
+ </li>
+ <li><a href="#typesystem">Type System</a>
+ <ol>
+ <li><a href="#t_classifications">Type Classifications</a></li>
+ <li><a href="#t_primitive">Primitive Types</a>
+ <ol>
+ <li><a href="#t_integer">Integer Type</a></li>
+ <li><a href="#t_floating">Floating Point Types</a></li>
+ <li><a href="#t_x86mmx">X86mmx Type</a></li>
+ <li><a href="#t_void">Void Type</a></li>
+ <li><a href="#t_label">Label Type</a></li>
+ <li><a href="#t_metadata">Metadata Type</a></li>
+ </ol>
+ </li>
+ <li><a href="#t_derived">Derived Types</a>
+ <ol>
+ <li><a href="#t_aggregate">Aggregate Types</a>
+ <ol>
+ <li><a href="#t_array">Array Type</a></li>
+ <li><a href="#t_struct">Structure Type</a></li>
+ <li><a href="#t_opaque">Opaque Structure Types</a></li>
+ <li><a href="#t_vector">Vector Type</a></li>
+ </ol>
+ </li>
+ <li><a href="#t_function">Function Type</a></li>
+ <li><a href="#t_pointer">Pointer Type</a></li>
+ </ol>
+ </li>
+ </ol>
+ </li>
+ <li><a href="#constants">Constants</a>
+ <ol>
+ <li><a href="#simpleconstants">Simple Constants</a></li>
+ <li><a href="#complexconstants">Complex Constants</a></li>
+ <li><a href="#globalconstants">Global Variable and Function Addresses</a></li>
+ <li><a href="#undefvalues">Undefined Values</a></li>
+ <li><a href="#poisonvalues">Poison Values</a></li>
+ <li><a href="#blockaddress">Addresses of Basic Blocks</a></li>
+ <li><a href="#constantexprs">Constant Expressions</a></li>
+ </ol>
+ </li>
+ <li><a href="#othervalues">Other Values</a>
+ <ol>
+ <li><a href="#inlineasm">Inline Assembler Expressions</a></li>
+ <li><a href="#metadata">Metadata Nodes and Metadata Strings</a>
+ <ol>
+ <li><a href="#tbaa">'<tt>tbaa</tt>' Metadata</a></li>
+ <li><a href="#tbaa.struct">'<tt>tbaa.struct</tt>' Metadata</a></li>
+ <li><a href="#fpmath">'<tt>fpmath</tt>' Metadata</a></li>
+ <li><a href="#range">'<tt>range</tt>' Metadata</a></li>
+ </ol>
+ </li>
+ </ol>
+ </li>
+ <li><a href="#module_flags">Module Flags Metadata</a>
+ <ol>
+ <li><a href="#objc_gc_flags">Objective-C Garbage Collection Module Flags Metadata</a></li>
+ </ol>
+ </li>
+ <li><a href="#intrinsic_globals">Intrinsic Global Variables</a>
+ <ol>
+ <li><a href="#intg_used">The '<tt>llvm.used</tt>' Global Variable</a></li>
+ <li><a href="#intg_compiler_used">The '<tt>llvm.compiler.used</tt>'
+ Global Variable</a></li>
+ <li><a href="#intg_global_ctors">The '<tt>llvm.global_ctors</tt>'
+ Global Variable</a></li>
+ <li><a href="#intg_global_dtors">The '<tt>llvm.global_dtors</tt>'
+ Global Variable</a></li>
+ </ol>
+ </li>
+ <li><a href="#instref">Instruction Reference</a>
+ <ol>
+ <li><a href="#terminators">Terminator Instructions</a>
+ <ol>
+ <li><a href="#i_ret">'<tt>ret</tt>' Instruction</a></li>
+ <li><a href="#i_br">'<tt>br</tt>' Instruction</a></li>
+ <li><a href="#i_switch">'<tt>switch</tt>' Instruction</a></li>
+ <li><a href="#i_indirectbr">'<tt>indirectbr</tt>' Instruction</a></li>
+ <li><a href="#i_invoke">'<tt>invoke</tt>' Instruction</a></li>
+ <li><a href="#i_resume">'<tt>resume</tt>' Instruction</a></li>
+ <li><a href="#i_unreachable">'<tt>unreachable</tt>' Instruction</a></li>
+ </ol>
+ </li>
+ <li><a href="#binaryops">Binary Operations</a>
+ <ol>
+ <li><a href="#i_add">'<tt>add</tt>' Instruction</a></li>
+ <li><a href="#i_fadd">'<tt>fadd</tt>' Instruction</a></li>
+ <li><a href="#i_sub">'<tt>sub</tt>' Instruction</a></li>
+ <li><a href="#i_fsub">'<tt>fsub</tt>' Instruction</a></li>
+ <li><a href="#i_mul">'<tt>mul</tt>' Instruction</a></li>
+ <li><a href="#i_fmul">'<tt>fmul</tt>' Instruction</a></li>
+ <li><a href="#i_udiv">'<tt>udiv</tt>' Instruction</a></li>
+ <li><a href="#i_sdiv">'<tt>sdiv</tt>' Instruction</a></li>
+ <li><a href="#i_fdiv">'<tt>fdiv</tt>' Instruction</a></li>
+ <li><a href="#i_urem">'<tt>urem</tt>' Instruction</a></li>
+ <li><a href="#i_srem">'<tt>srem</tt>' Instruction</a></li>
+ <li><a href="#i_frem">'<tt>frem</tt>' Instruction</a></li>
+ </ol>
+ </li>
+ <li><a href="#bitwiseops">Bitwise Binary Operations</a>
+ <ol>
+ <li><a href="#i_shl">'<tt>shl</tt>' Instruction</a></li>
+ <li><a href="#i_lshr">'<tt>lshr</tt>' Instruction</a></li>
+ <li><a href="#i_ashr">'<tt>ashr</tt>' Instruction</a></li>
+ <li><a href="#i_and">'<tt>and</tt>' Instruction</a></li>
+ <li><a href="#i_or">'<tt>or</tt>' Instruction</a></li>
+ <li><a href="#i_xor">'<tt>xor</tt>' Instruction</a></li>
+ </ol>
+ </li>
+ <li><a href="#vectorops">Vector Operations</a>
+ <ol>
+ <li><a href="#i_extractelement">'<tt>extractelement</tt>' Instruction</a></li>
+ <li><a href="#i_insertelement">'<tt>insertelement</tt>' Instruction</a></li>
+ <li><a href="#i_shufflevector">'<tt>shufflevector</tt>' Instruction</a></li>
+ </ol>
+ </li>
+ <li><a href="#aggregateops">Aggregate Operations</a>
+ <ol>
+ <li><a href="#i_extractvalue">'<tt>extractvalue</tt>' Instruction</a></li>
+ <li><a href="#i_insertvalue">'<tt>insertvalue</tt>' Instruction</a></li>
+ </ol>
+ </li>
+ <li><a href="#memoryops">Memory Access and Addressing Operations</a>
+ <ol>
+ <li><a href="#i_alloca">'<tt>alloca</tt>' Instruction</a></li>
+ <li><a href="#i_load">'<tt>load</tt>' Instruction</a></li>
+ <li><a href="#i_store">'<tt>store</tt>' Instruction</a></li>
+ <li><a href="#i_fence">'<tt>fence</tt>' Instruction</a></li>
+ <li><a href="#i_cmpxchg">'<tt>cmpxchg</tt>' Instruction</a></li>
+ <li><a href="#i_atomicrmw">'<tt>atomicrmw</tt>' Instruction</a></li>
+ <li><a href="#i_getelementptr">'<tt>getelementptr</tt>' Instruction</a></li>
+ </ol>
+ </li>
+ <li><a href="#convertops">Conversion Operations</a>
+ <ol>
+ <li><a href="#i_trunc">'<tt>trunc .. to</tt>' Instruction</a></li>
+ <li><a href="#i_zext">'<tt>zext .. to</tt>' Instruction</a></li>
+ <li><a href="#i_sext">'<tt>sext .. to</tt>' Instruction</a></li>
+ <li><a href="#i_fptrunc">'<tt>fptrunc .. to</tt>' Instruction</a></li>
+ <li><a href="#i_fpext">'<tt>fpext .. to</tt>' Instruction</a></li>
+ <li><a href="#i_fptoui">'<tt>fptoui .. to</tt>' Instruction</a></li>
+ <li><a href="#i_fptosi">'<tt>fptosi .. to</tt>' Instruction</a></li>
+ <li><a href="#i_uitofp">'<tt>uitofp .. to</tt>' Instruction</a></li>
+ <li><a href="#i_sitofp">'<tt>sitofp .. to</tt>' Instruction</a></li>
+ <li><a href="#i_ptrtoint">'<tt>ptrtoint .. to</tt>' Instruction</a></li>
+ <li><a href="#i_inttoptr">'<tt>inttoptr .. to</tt>' Instruction</a></li>
+ <li><a href="#i_bitcast">'<tt>bitcast .. to</tt>' Instruction</a></li>
+ </ol>
+ </li>
+ <li><a href="#otherops">Other Operations</a>
+ <ol>
+ <li><a href="#i_icmp">'<tt>icmp</tt>' Instruction</a></li>
+ <li><a href="#i_fcmp">'<tt>fcmp</tt>' Instruction</a></li>
+ <li><a href="#i_phi">'<tt>phi</tt>' Instruction</a></li>
+ <li><a href="#i_select">'<tt>select</tt>' Instruction</a></li>
+ <li><a href="#i_call">'<tt>call</tt>' Instruction</a></li>
+ <li><a href="#i_va_arg">'<tt>va_arg</tt>' Instruction</a></li>
+ <li><a href="#i_landingpad">'<tt>landingpad</tt>' Instruction</a></li>
+ </ol>
+ </li>
+ </ol>
+ </li>
+ <li><a href="#intrinsics">Intrinsic Functions</a>
+ <ol>
+ <li><a href="#int_varargs">Variable Argument Handling Intrinsics</a>
+ <ol>
+ <li><a href="#int_va_start">'<tt>llvm.va_start</tt>' Intrinsic</a></li>
+ <li><a href="#int_va_end">'<tt>llvm.va_end</tt>' Intrinsic</a></li>
+ <li><a href="#int_va_copy">'<tt>llvm.va_copy</tt>' Intrinsic</a></li>
+ </ol>
+ </li>
+ <li><a href="#int_gc">Accurate Garbage Collection Intrinsics</a>
+ <ol>
+ <li><a href="#int_gcroot">'<tt>llvm.gcroot</tt>' Intrinsic</a></li>
+ <li><a href="#int_gcread">'<tt>llvm.gcread</tt>' Intrinsic</a></li>
+ <li><a href="#int_gcwrite">'<tt>llvm.gcwrite</tt>' Intrinsic</a></li>
+ </ol>
+ </li>
+ <li><a href="#int_codegen">Code Generator Intrinsics</a>
+ <ol>
+ <li><a href="#int_returnaddress">'<tt>llvm.returnaddress</tt>' Intrinsic</a></li>
+ <li><a href="#int_frameaddress">'<tt>llvm.frameaddress</tt>' Intrinsic</a></li>
+ <li><a href="#int_stacksave">'<tt>llvm.stacksave</tt>' Intrinsic</a></li>
+ <li><a href="#int_stackrestore">'<tt>llvm.stackrestore</tt>' Intrinsic</a></li>
+ <li><a href="#int_prefetch">'<tt>llvm.prefetch</tt>' Intrinsic</a></li>
+ <li><a href="#int_pcmarker">'<tt>llvm.pcmarker</tt>' Intrinsic</a></li>
+ <li><a href="#int_readcyclecounter">'<tt>llvm.readcyclecounter</tt>' Intrinsic</a></li>
+ </ol>
+ </li>
+ <li><a href="#int_libc">Standard C Library Intrinsics</a>
+ <ol>
+ <li><a href="#int_memcpy">'<tt>llvm.memcpy.*</tt>' Intrinsic</a></li>
+ <li><a href="#int_memmove">'<tt>llvm.memmove.*</tt>' Intrinsic</a></li>
+ <li><a href="#int_memset">'<tt>llvm.memset.*</tt>' Intrinsic</a></li>
+ <li><a href="#int_sqrt">'<tt>llvm.sqrt.*</tt>' Intrinsic</a></li>
+ <li><a href="#int_powi">'<tt>llvm.powi.*</tt>' Intrinsic</a></li>
+ <li><a href="#int_sin">'<tt>llvm.sin.*</tt>' Intrinsic</a></li>
+ <li><a href="#int_cos">'<tt>llvm.cos.*</tt>' Intrinsic</a></li>
+ <li><a href="#int_pow">'<tt>llvm.pow.*</tt>' Intrinsic</a></li>
+ <li><a href="#int_exp">'<tt>llvm.exp.*</tt>' Intrinsic</a></li>
+ <li><a href="#int_log">'<tt>llvm.log.*</tt>' Intrinsic</a></li>
+ <li><a href="#int_fma">'<tt>llvm.fma.*</tt>' Intrinsic</a></li>
+ <li><a href="#int_fabs">'<tt>llvm.fabs.*</tt>' Intrinsic</a></li>
+ <li><a href="#int_floor">'<tt>llvm.floor.*</tt>' Intrinsic</a></li>
+ </ol>
+ </li>
+ <li><a href="#int_manip">Bit Manipulation Intrinsics</a>
+ <ol>
+ <li><a href="#int_bswap">'<tt>llvm.bswap.*</tt>' Intrinsics</a></li>
+ <li><a href="#int_ctpop">'<tt>llvm.ctpop.*</tt>' Intrinsic </a></li>
+ <li><a href="#int_ctlz">'<tt>llvm.ctlz.*</tt>' Intrinsic </a></li>
+ <li><a href="#int_cttz">'<tt>llvm.cttz.*</tt>' Intrinsic </a></li>
+ </ol>
+ </li>
+ <li><a href="#int_overflow">Arithmetic with Overflow Intrinsics</a>
+ <ol>
+ <li><a href="#int_sadd_overflow">'<tt>llvm.sadd.with.overflow.*</tt> Intrinsics</a></li>
+ <li><a href="#int_uadd_overflow">'<tt>llvm.uadd.with.overflow.*</tt> Intrinsics</a></li>
+ <li><a href="#int_ssub_overflow">'<tt>llvm.ssub.with.overflow.*</tt> Intrinsics</a></li>
+ <li><a href="#int_usub_overflow">'<tt>llvm.usub.with.overflow.*</tt> Intrinsics</a></li>
+ <li><a href="#int_smul_overflow">'<tt>llvm.smul.with.overflow.*</tt> Intrinsics</a></li>
+ <li><a href="#int_umul_overflow">'<tt>llvm.umul.with.overflow.*</tt> Intrinsics</a></li>
+ </ol>
+ </li>
+ <li><a href="#spec_arithmetic">Specialised Arithmetic Intrinsics</a>
+ <ol>
+ <li><a href="#fmuladd">'<tt>llvm.fmuladd</tt> Intrinsic</a></li>
+ </ol>
+ </li>
+ <li><a href="#int_fp16">Half Precision Floating Point Intrinsics</a>
+ <ol>
+ <li><a href="#int_convert_to_fp16">'<tt>llvm.convert.to.fp16</tt>' Intrinsic</a></li>
+ <li><a href="#int_convert_from_fp16">'<tt>llvm.convert.from.fp16</tt>' Intrinsic</a></li>
+ </ol>
+ </li>
+ <li><a href="#int_debugger">Debugger intrinsics</a></li>
+ <li><a href="#int_eh">Exception Handling intrinsics</a></li>
+ <li><a href="#int_trampoline">Trampoline Intrinsics</a>
+ <ol>
+ <li><a href="#int_it">'<tt>llvm.init.trampoline</tt>' Intrinsic</a></li>
+ <li><a href="#int_at">'<tt>llvm.adjust.trampoline</tt>' Intrinsic</a></li>
+ </ol>
+ </li>
+ <li><a href="#int_memorymarkers">Memory Use Markers</a>
+ <ol>
+ <li><a href="#int_lifetime_start">'<tt>llvm.lifetime.start</tt>' Intrinsic</a></li>
+ <li><a href="#int_lifetime_end">'<tt>llvm.lifetime.end</tt>' Intrinsic</a></li>
+ <li><a href="#int_invariant_start">'<tt>llvm.invariant.start</tt>' Intrinsic</a></li>
+ <li><a href="#int_invariant_end">'<tt>llvm.invariant.end</tt>' Intrinsic</a></li>
+ </ol>
+ </li>
+ <li><a href="#int_general">General intrinsics</a>
+ <ol>
+ <li><a href="#int_var_annotation">
+ '<tt>llvm.var.annotation</tt>' Intrinsic</a></li>
+ <li><a href="#int_annotation">
+ '<tt>llvm.annotation.*</tt>' Intrinsic</a></li>
+ <li><a href="#int_trap">
+ '<tt>llvm.trap</tt>' Intrinsic</a></li>
+ <li><a href="#int_debugtrap">
+ '<tt>llvm.debugtrap</tt>' Intrinsic</a></li>
+ <li><a href="#int_stackprotector">
+ '<tt>llvm.stackprotector</tt>' Intrinsic</a></li>
+ <li><a href="#int_objectsize">
+ '<tt>llvm.objectsize</tt>' Intrinsic</a></li>
+ <li><a href="#int_expect">
+ '<tt>llvm.expect</tt>' Intrinsic</a></li>
+ <li><a href="#int_donothing">
+ '<tt>llvm.donothing</tt>' Intrinsic</a></li>
+ </ol>
+ </li>
+ </ol>
+ </li>
+</ol>
+
+<div class="doc_author">
+ <p>Written by <a href="mailto:sabre at nondot.org">Chris Lattner</a>
+ and <a href="mailto:vadve at cs.uiuc.edu">Vikram Adve</a></p>
+</div>
+
+<!-- *********************************************************************** -->
+<h2><a name="abstract">Abstract</a></h2>
+<!-- *********************************************************************** -->
+
+<div>
+
+<p>This document is a reference manual for the LLVM assembly language. LLVM is
+ a Static Single Assignment (SSA) based representation that provides type
+ safety, low-level operations, flexibility, and the capability of representing
+ 'all' high-level languages cleanly. It is the common code representation
+ used throughout all phases of the LLVM compilation strategy.</p>
+
+</div>
+
+<!-- *********************************************************************** -->
+<h2><a name="introduction">Introduction</a></h2>
+<!-- *********************************************************************** -->
+
+<div>
+
+<p>The LLVM code representation is designed to be used in three different forms:
+ as an in-memory compiler IR, as an on-disk bitcode representation (suitable
+ for fast loading by a Just-In-Time compiler), and as a human readable
+ assembly language representation. This allows LLVM to provide a powerful
+ intermediate representation for efficient compiler transformations and
+ analysis, while providing a natural means to debug and visualize the
+ transformations. The three different forms of LLVM are all equivalent. This
+ document describes the human readable representation and notation.</p>
+
+<p>The LLVM representation aims to be light-weight and low-level while being
+ expressive, typed, and extensible at the same time. It aims to be a
+ "universal IR" of sorts, by being at a low enough level that high-level ideas
+ may be cleanly mapped to it (similar to how microprocessors are "universal
+ IR's", allowing many source languages to be mapped to them). By providing
+ type information, LLVM can be used as the target of optimizations: for
+ example, through pointer analysis, it can be proven that a C automatic
+ variable is never accessed outside of the current function, allowing it to
+ be promoted to a simple SSA value instead of a memory location.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="wellformed">Well-Formedness</a>
+</h4>
+
+<div>
+
+<p>It is important to note that this document describes 'well formed' LLVM
+ assembly language. There is a difference between what the parser accepts and
+ what is considered 'well formed'. For example, the following instruction is
+ syntactically okay, but not well formed:</p>
+
+<pre class="doc_code">
+%x = <a href="#i_add">add</a> i32 1, %x
+</pre>
+
+<p>because the definition of <tt>%x</tt> does not dominate all of its uses. The
+ LLVM infrastructure provides a verification pass that may be used to verify
+ that an LLVM module is well formed. This pass is automatically run by the
+ parser after parsing input assembly and by the optimizer before it outputs
+ bitcode. The violations pointed out by the verifier pass indicate bugs in
+ transformation passes or input to the parser.</p>
+
+</div>
+
+</div>
+
+<!-- Describe the typesetting conventions here. -->
+
+<!-- *********************************************************************** -->
+<h2><a name="identifiers">Identifiers</a></h2>
+<!-- *********************************************************************** -->
+
+<div>
+
+<p>LLVM identifiers come in two basic types: global and local. Global
+ identifiers (functions, global variables) begin with the <tt>'@'</tt>
+ character. Local identifiers (register names, types) begin with
+ the <tt>'%'</tt> character. Additionally, there are three different formats
+ for identifiers, for different purposes:</p>
+
+<ol>
+ <li>Named values are represented as a string of characters with their prefix.
+ For example, <tt>%foo</tt>, <tt>@DivisionByZero</tt>,
+ <tt>%a.really.long.identifier</tt>. The actual regular expression used is
+ '<tt>[%@][a-zA-Z$._][a-zA-Z$._0-9]*</tt>'. Identifiers which require
+ other characters in their names can be surrounded with quotes. Special
+ characters may be escaped using <tt>"\xx"</tt> where <tt>xx</tt> is the
+ ASCII code for the character in hexadecimal. In this way, any character
+ can be used in a name value, even quotes themselves.</li>
+
+ <li>Unnamed values are represented as an unsigned numeric value with their
+ prefix. For example, <tt>%12</tt>, <tt>@2</tt>, <tt>%44</tt>.</li>
+
+ <li>Constants, which are described in a <a href="#constants">section about
+ constants</a>, below.</li>
+</ol>
+
+<p>LLVM requires that values start with a prefix for two reasons: Compilers
+ don't need to worry about name clashes with reserved words, and the set of
+ reserved words may be expanded in the future without penalty. Additionally,
+ unnamed identifiers allow a compiler to quickly come up with a temporary
+ variable without having to avoid symbol table conflicts.</p>
+
+<p>Reserved words in LLVM are very similar to reserved words in other
+ languages. There are keywords for different opcodes
+ ('<tt><a href="#i_add">add</a></tt>',
+ '<tt><a href="#i_bitcast">bitcast</a></tt>',
+ '<tt><a href="#i_ret">ret</a></tt>', etc...), for primitive type names
+ ('<tt><a href="#t_void">void</a></tt>',
+ '<tt><a href="#t_primitive">i32</a></tt>', etc...), and others. These
+ reserved words cannot conflict with variable names, because none of them
+ start with a prefix character (<tt>'%'</tt> or <tt>'@'</tt>).</p>
+
+<p>Here is an example of LLVM code to multiply the integer variable
+ '<tt>%X</tt>' by 8:</p>
+
+<p>The easy way:</p>
+
+<pre class="doc_code">
+%result = <a href="#i_mul">mul</a> i32 %X, 8
+</pre>
+
+<p>After strength reduction:</p>
+
+<pre class="doc_code">
+%result = <a href="#i_shl">shl</a> i32 %X, i8 3
+</pre>
+
+<p>And the hard way:</p>
+
+<pre class="doc_code">
+%0 = <a href="#i_add">add</a> i32 %X, %X <i>; yields {i32}:%0</i>
+%1 = <a href="#i_add">add</a> i32 %0, %0 <i>; yields {i32}:%1</i>
+%result = <a href="#i_add">add</a> i32 %1, %1
+</pre>
+
+<p>This last way of multiplying <tt>%X</tt> by 8 illustrates several important
+ lexical features of LLVM:</p>
+
+<ol>
+ <li>Comments are delimited with a '<tt>;</tt>' and go until the end of
+ line.</li>
+
+ <li>Unnamed temporaries are created when the result of a computation is not
+ assigned to a named value.</li>
+
+ <li>Unnamed temporaries are numbered sequentially</li>
+</ol>
+
+<p>It also shows a convention that we follow in this document. When
+ demonstrating instructions, we will follow an instruction with a comment that
+ defines the type and name of value produced. Comments are shown in italic
+ text.</p>
+
+</div>
+
+<!-- *********************************************************************** -->
+<h2><a name="highlevel">High Level Structure</a></h2>
+<!-- *********************************************************************** -->
+<div>
+<!-- ======================================================================= -->
+<h3>
+ <a name="modulestructure">Module Structure</a>
+</h3>
+
+<div>
+
+<p>LLVM programs are composed of <tt>Module</tt>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 class="doc_code">
+<i>; Declare the string constant as a global constant.</i>
+<a href="#identifiers">@.str</a> = <a href="#linkage_private">private</a> <a href="#globalvars">unnamed_addr</a> <a href="#globalvars">constant</a> <a href="#t_array">[13 x i8]</a> c"hello world\0A\00"
+
+<i>; External declaration of the puts function</i>
+<a href="#functionstructure">declare</a> i32 @puts(i8* <a href="#nocapture">nocapture</a>) <a href="#fnattrs">nounwind</a>
+
+<i>; Definition of main function</i>
+define i32 @main() { <i>; i32()* </i>
+ <i>; Convert [13 x i8]* to i8 *...</i>
+ %cast210 = <a href="#i_getelementptr">getelementptr</a> [13 x i8]* @.str, i64 0, i64 0
+
+ <i>; Call puts function to write out the string to stdout.</i>
+ <a href="#i_call">call</a> i32 @puts(i8* %cast210)
+ <a href="#i_ret">ret</a> i32 0
+}
+
+<i>; Named metadata</i>
+!1 = metadata !{i32 42}
+!foo = !{!1, null}
+</pre>
+
+<p>This example is made up of a <a href="#globalvars">global variable</a> named
+ "<tt>.str</tt>", an external declaration of the "<tt>puts</tt>" function,
+ a <a href="#functionstructure">function definition</a> for
+ "<tt>main</tt>" and <a href="#namedmetadatastructure">named metadata</a>
+ "<tt>foo</tt>".</p>
+
+<p>In general, a module is made up of a list of global values (where both
+ functions and global variables are global values). Global values are
+ represented by a pointer to a memory location (in this case, a pointer to an
+ array of char, and a pointer to a function), and have one of the
+ following <a href="#linkage">linkage types</a>.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="linkage">Linkage Types</a>
+</h3>
+
+<div>
+
+<p>All Global Variables and Functions have one of the following types of
+ linkage:</p>
+
+<dl>
+ <dt><tt><b><a name="linkage_private">private</a></b></tt></dt>
+ <dd>Global values with "<tt>private</tt>" linkage are only directly accessible
+ by objects in the current module. In particular, linking code into a
+ module with an private global value may cause the private to be renamed as
+ necessary to avoid collisions. Because the symbol is private to the
+ module, all references can be updated. This doesn't show up in any symbol
+ table in the object file.</dd>
+
+ <dt><tt><b><a name="linkage_linker_private">linker_private</a></b></tt></dt>
+ <dd>Similar to <tt>private</tt>, but the symbol is passed through the
+ assembler and evaluated by the linker. Unlike normal strong symbols, they
+ are removed by the linker from the final linked image (executable or
+ dynamic library).</dd>
+
+ <dt><tt><b><a name="linkage_linker_private_weak">linker_private_weak</a></b></tt></dt>
+ <dd>Similar to "<tt>linker_private</tt>", but the symbol is weak. Note that
+ <tt>linker_private_weak</tt> symbols are subject to coalescing by the
+ linker. The symbols are removed by the linker from the final linked image
+ (executable or dynamic library).</dd>
+
+ <dt><tt><b><a name="linkage_internal">internal</a></b></tt></dt>
+ <dd>Similar to private, but the value shows as a local symbol
+ (<tt>STB_LOCAL</tt> in the case of ELF) in the object file. This
+ corresponds to the notion of the '<tt>static</tt>' keyword in C.</dd>
+
+ <dt><tt><b><a name="linkage_available_externally">available_externally</a></b></tt></dt>
+ <dd>Globals with "<tt>available_externally</tt>" linkage are never emitted
+ into the object file corresponding to the LLVM module. They exist to
+ allow inlining and other optimizations to take place given knowledge of
+ the definition of the global, which is known to be somewhere outside the
+ module. Globals with <tt>available_externally</tt> linkage are allowed to
+ be discarded at will, and are otherwise the same as <tt>linkonce_odr</tt>.
+ This linkage type is only allowed on definitions, not declarations.</dd>
+
+ <dt><tt><b><a name="linkage_linkonce">linkonce</a></b></tt></dt>
+ <dd>Globals with "<tt>linkonce</tt>" linkage are merged with other globals of
+ the same name when linkage occurs. This can be used to implement
+ some forms of inline functions, templates, or other code which must be
+ generated in each translation unit that uses it, but where the body may
+ be overridden with a more definitive definition later. Unreferenced
+ <tt>linkonce</tt> globals are allowed to be discarded. Note that
+ <tt>linkonce</tt> linkage does not actually allow the optimizer to
+ inline the body of this function into callers because it doesn't know if
+ this definition of the function is the definitive definition within the
+ program or whether it will be overridden by a stronger definition.
+ To enable inlining and other optimizations, use "<tt>linkonce_odr</tt>"
+ linkage.</dd>
+
+ <dt><tt><b><a name="linkage_weak">weak</a></b></tt></dt>
+ <dd>"<tt>weak</tt>" linkage has the same merging semantics as
+ <tt>linkonce</tt> linkage, except that unreferenced globals with
+ <tt>weak</tt> linkage may not be discarded. This is used for globals that
+ are declared "weak" in C source code.</dd>
+
+ <dt><tt><b><a name="linkage_common">common</a></b></tt></dt>
+ <dd>"<tt>common</tt>" linkage is most similar to "<tt>weak</tt>" linkage, but
+ they are used for tentative definitions in C, such as "<tt>int X;</tt>" at
+ global scope.
+ Symbols with "<tt>common</tt>" linkage are merged in the same way as
+ <tt>weak symbols</tt>, and they may not be deleted if unreferenced.
+ <tt>common</tt> symbols may not have an explicit section,
+ must have a zero initializer, and may not be marked '<a
+ href="#globalvars"><tt>constant</tt></a>'. Functions and aliases may not
+ have common linkage.</dd>
+
+
+ <dt><tt><b><a name="linkage_appending">appending</a></b></tt></dt>
+ <dd>"<tt>appending</tt>" linkage may only be applied to global variables of
+ pointer to array type. When two global variables with appending linkage
+ are linked together, the two global arrays are appended together. This is
+ the LLVM, typesafe, equivalent of having the system linker append together
+ "sections" with identical names when .o files are linked.</dd>
+
+ <dt><tt><b><a name="linkage_externweak">extern_weak</a></b></tt></dt>
+ <dd>The semantics of this linkage follow the ELF object file model: the symbol
+ is weak until linked, if not linked, the symbol becomes null instead of
+ being an undefined reference.</dd>
+
+ <dt><tt><b><a name="linkage_linkonce_odr">linkonce_odr</a></b></tt></dt>
+ <dt><tt><b><a name="linkage_weak_odr">weak_odr</a></b></tt></dt>
+ <dd>Some languages allow differing globals to be merged, such as two functions
+ with different semantics. Other languages, such as <tt>C++</tt>, ensure
+ that only equivalent globals are ever merged (the "one definition rule"
+ — "ODR"). Such languages can use the <tt>linkonce_odr</tt>
+ and <tt>weak_odr</tt> linkage types to indicate that the global will only
+ be merged with equivalent globals. These linkage types are otherwise the
+ same as their non-<tt>odr</tt> versions.</dd>
+
+ <dt><tt><b><a name="linkage_linkonce_odr_auto_hide">linkonce_odr_auto_hide</a></b></tt></dt>
+ <dd>Similar to "<tt>linkonce_odr</tt>", but nothing in the translation unit
+ takes the address of this definition. For instance, functions that had an
+ inline definition, but the compiler decided not to inline it.
+ <tt>linkonce_odr_auto_hide</tt> may have only <tt>default</tt> visibility.
+ The symbols are removed by the linker from the final linked image
+ (executable or dynamic library).</dd>
+
+ <dt><tt><b><a name="linkage_external">external</a></b></tt></dt>
+ <dd>If none of the above identifiers are used, the global is externally
+ visible, meaning that it participates in linkage and can be used to
+ resolve external symbol references.</dd>
+</dl>
+
+<p>The next two types of linkage are targeted for Microsoft Windows platform
+ only. They are designed to support importing (exporting) symbols from (to)
+ DLLs (Dynamic Link Libraries).</p>
+
+<dl>
+ <dt><tt><b><a name="linkage_dllimport">dllimport</a></b></tt></dt>
+ <dd>"<tt>dllimport</tt>" linkage causes the compiler to reference a function
+ or variable via a global pointer to a pointer that is set up by the DLL
+ exporting the symbol. On Microsoft Windows targets, the pointer name is
+ formed by combining <code>__imp_</code> and the function or variable
+ name.</dd>
+
+ <dt><tt><b><a name="linkage_dllexport">dllexport</a></b></tt></dt>
+ <dd>"<tt>dllexport</tt>" linkage causes the compiler to provide a global
+ pointer to a pointer in a DLL, so that it can be referenced with the
+ <tt>dllimport</tt> attribute. On Microsoft Windows targets, the pointer
+ name is formed by combining <code>__imp_</code> and the function or
+ variable name.</dd>
+</dl>
+
+<p>For example, since the "<tt>.LC0</tt>" variable is defined to be internal, if
+ another module defined a "<tt>.LC0</tt>" variable and was linked with this
+ one, one of the two would be renamed, preventing a collision. Since
+ "<tt>main</tt>" and "<tt>puts</tt>" are external (i.e., lacking any linkage
+ declarations), they are accessible outside of the current module.</p>
+
+<p>It is illegal for a function <i>declaration</i> to have any linkage type
+ other than <tt>external</tt>, <tt>dllimport</tt>
+ or <tt>extern_weak</tt>.</p>
+
+<p>Aliases can have only <tt>external</tt>, <tt>internal</tt>, <tt>weak</tt>
+ or <tt>weak_odr</tt> linkages.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="callingconv">Calling Conventions</a>
+</h3>
+
+<div>
+
+<p>LLVM <a href="#functionstructure">functions</a>, <a href="#i_call">calls</a>
+ and <a href="#i_invoke">invokes</a> can all have an optional calling
+ convention specified for the call. The calling convention of any pair of
+ dynamic caller/callee must match, or the behavior of the program is
+ undefined. The following calling conventions are supported by LLVM, and more
+ may be added in the future:</p>
+
+<dl>
+ <dt><b>"<tt>ccc</tt>" - The C calling convention</b>:</dt>
+ <dd>This calling convention (the default if no other calling convention is
+ specified) matches the target C calling conventions. This calling
+ convention supports varargs function calls and tolerates some mismatch in
+ the declared prototype and implemented declaration of the function (as
+ does normal C).</dd>
+
+ <dt><b>"<tt>fastcc</tt>" - The fast calling convention</b>:</dt>
+ <dd>This calling convention attempts to make calls as fast as possible
+ (e.g. by passing things in registers). This calling convention allows the
+ target to use whatever tricks it wants to produce fast code for the
+ target, without having to conform to an externally specified ABI
+ (Application Binary Interface).
+ <a href="CodeGenerator.html#tailcallopt">Tail calls can only be optimized
+ when this or the GHC convention is used.</a> This calling convention
+ does not support varargs and requires the prototype of all callees to
+ exactly match the prototype of the function definition.</dd>
+
+ <dt><b>"<tt>coldcc</tt>" - The cold calling convention</b>:</dt>
+ <dd>This calling convention attempts to make code in the caller as efficient
+ as possible under the assumption that the call is not commonly executed.
+ As such, these calls often preserve all registers so that the call does
+ not break any live ranges in the caller side. This calling convention
+ does not support varargs and requires the prototype of all callees to
+ exactly match the prototype of the function definition.</dd>
+
+ <dt><b>"<tt>cc <em>10</em></tt>" - GHC convention</b>:</dt>
+ <dd>This calling convention has been implemented specifically for use by the
+ <a href="http://www.haskell.org/ghc">Glasgow Haskell Compiler (GHC)</a>.
+ It passes everything in registers, going to extremes to achieve this by
+ disabling callee save registers. This calling convention should not be
+ used lightly but only for specific situations such as an alternative to
+ the <em>register pinning</em> performance technique often used when
+ implementing functional programming languages.At the moment only X86
+ supports this convention and it has the following limitations:
+ <ul>
+ <li>On <em>X86-32</em> only supports up to 4 bit type parameters. No
+ floating point types are supported.</li>
+ <li>On <em>X86-64</em> only supports up to 10 bit type parameters and
+ 6 floating point parameters.</li>
+ </ul>
+ This calling convention supports
+ <a href="CodeGenerator.html#tailcallopt">tail call optimization</a> but
+ requires both the caller and callee are using it.
+ </dd>
+
+ <dt><b>"<tt>cc <<em>n</em>></tt>" - Numbered convention</b>:</dt>
+ <dd>Any calling convention may be specified by number, allowing
+ target-specific calling conventions to be used. Target specific calling
+ conventions start at 64.</dd>
+</dl>
+
+<p>More calling conventions can be added/defined on an as-needed basis, to
+ support Pascal conventions or any other well-known target-independent
+ convention.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="visibility">Visibility Styles</a>
+</h3>
+
+<div>
+
+<p>All Global Variables and Functions have one of the following visibility
+ styles:</p>
+
+<dl>
+ <dt><b>"<tt>default</tt>" - Default style</b>:</dt>
+ <dd>On targets that use the ELF object file format, default visibility means
+ that the declaration is visible to other modules and, in shared libraries,
+ means that the declared entity may be overridden. On Darwin, default
+ visibility means that the declaration is visible to other modules. Default
+ visibility corresponds to "external linkage" in the language.</dd>
+
+ <dt><b>"<tt>hidden</tt>" - Hidden style</b>:</dt>
+ <dd>Two declarations of an object with hidden visibility refer to the same
+ object if they are in the same shared object. Usually, hidden visibility
+ indicates that the symbol will not be placed into the dynamic symbol
+ table, so no other module (executable or shared library) can reference it
+ directly.</dd>
+
+ <dt><b>"<tt>protected</tt>" - Protected style</b>:</dt>
+ <dd>On ELF, protected visibility indicates that the symbol will be placed in
+ the dynamic symbol table, but that references within the defining module
+ will bind to the local symbol. That is, the symbol cannot be overridden by
+ another module.</dd>
+</dl>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="namedtypes">Named Types</a>
+</h3>
+
+<div>
+
+<p>LLVM IR allows you to specify name aliases for certain types. This can make
+ it easier to read the IR and make the IR more condensed (particularly when
+ recursive types are involved). An example of a name specification is:</p>
+
+<pre class="doc_code">
+%mytype = type { %mytype*, i32 }
+</pre>
+
+<p>You may give a name to any <a href="#typesystem">type</a> except
+ "<a href="#t_void">void</a>". Type name aliases may be used anywhere a type
+ is expected with the syntax "%mytype".</p>
+
+<p>Note that type names are aliases for the structural type that they indicate,
+ and that you can therefore specify multiple names for the same type. This
+ often leads to confusing behavior when dumping out a .ll file. Since LLVM IR
+ uses structural typing, the name is not part of the type. When printing out
+ LLVM IR, the printer will pick <em>one name</em> to render all types of a
+ particular shape. This means that if you have code where two different
+ source types end up having the same LLVM type, that the dumper will sometimes
+ print the "wrong" or unexpected type. This is an important design point and
+ isn't going to change.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="globalvars">Global Variables</a>
+</h3>
+
+<div>
+
+<p>Global variables define regions of memory allocated at compilation time
+ instead of run-time. Global variables may optionally be initialized, may
+ have an explicit section to be placed in, and may have an optional explicit
+ alignment specified.</p>
+
+<p>A variable may be defined as <tt>thread_local</tt>, which
+ means that it will not be shared by threads (each thread will have a
+ separated copy of the variable). Not all targets support thread-local
+ variables. Optionally, a TLS model may be specified:</p>
+
+<dl>
+ <dt><b><tt>localdynamic</tt></b>:</dt>
+ <dd>For variables that are only used within the current shared library.</dd>
+
+ <dt><b><tt>initialexec</tt></b>:</dt>
+ <dd>For variables in modules that will not be loaded dynamically.</dd>
+
+ <dt><b><tt>localexec</tt></b>:</dt>
+ <dd>For variables defined in the executable and only used within it.</dd>
+</dl>
+
+<p>The models correspond to the ELF TLS models; see
+ <a href="http://people.redhat.com/drepper/tls.pdf">ELF
+ Handling For Thread-Local Storage</a> for more information on under which
+ circumstances the different models may be used. The target may choose a
+ different TLS model if the specified model is not supported, or if a better
+ choice of model can be made.</p>
+
+<p>A variable may be defined as a global
+ "constant," which indicates that the contents of the variable
+ will <b>never</b> be modified (enabling better optimization, allowing the
+ global data to be placed in the read-only section of an executable, etc).
+ Note that variables that need runtime initialization cannot be marked
+ "constant" as there is a store to the variable.</p>
+
+<p>LLVM explicitly allows <em>declarations</em> of global variables to be marked
+ constant, even if the final definition of the global is not. This capability
+ can be used to enable slightly better optimization of the program, but
+ requires the language definition to guarantee that optimizations based on the
+ 'constantness' are valid for the translation units that do not include the
+ definition.</p>
+
+<p>As SSA values, global variables define pointer values that are in scope
+ (i.e. they dominate) all basic blocks in the program. Global variables
+ always define a pointer to their "content" type because they describe a
+ region of memory, and all memory objects in LLVM are accessed through
+ pointers.</p>
+
+<p>Global variables can be marked with <tt>unnamed_addr</tt> which indicates
+ that the address is not significant, only the content. Constants marked
+ like this can be merged with other constants if they have the same
+ initializer. Note that a constant with significant address <em>can</em>
+ be merged with a <tt>unnamed_addr</tt> constant, the result being a
+ constant whose address is significant.</p>
+
+<p>A global variable may be declared to reside in a target-specific numbered
+ address space. For targets that support them, address spaces may affect how
+ optimizations are performed and/or what target instructions are used to
+ access the variable. The default address space is zero. The address space
+ qualifier must precede any other attributes.</p>
+
+<p>LLVM allows an explicit section to be specified for globals. If the target
+ supports it, it will emit globals to the section specified.</p>
+
+<p>An explicit alignment may be specified for a global, which must be a power
+ of 2. If not present, or if the alignment is set to zero, the alignment of
+ the global is set by the target to whatever it feels convenient. If an
+ explicit alignment is specified, the global is forced to have exactly that
+ alignment. Targets and optimizers are not allowed to over-align the global
+ if the global has an assigned section. In this case, the extra alignment
+ could be observable: for example, code could assume that the globals are
+ densely packed in their section and try to iterate over them as an array,
+ alignment padding would break this iteration.</p>
+
+<p>For example, the following defines a global in a numbered address space with
+ an initializer, section, and alignment:</p>
+
+<pre class="doc_code">
+ at G = addrspace(5) constant float 1.0, section "foo", align 4
+</pre>
+
+<p>The following example defines a thread-local global with
+ the <tt>initialexec</tt> TLS model:</p>
+
+<pre class="doc_code">
+ at G = thread_local(initialexec) global i32 0, align 4
+</pre>
+
+</div>
+
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="functionstructure">Functions</a>
+</h3>
+
+<div>
+
+<p>LLVM function definitions consist of the "<tt>define</tt>" keyword, an
+ optional <a href="#linkage">linkage type</a>, an optional
+ <a href="#visibility">visibility style</a>, an optional
+ <a href="#callingconv">calling convention</a>,
+ an optional <tt>unnamed_addr</tt> attribute, a return type, an optional
+ <a href="#paramattrs">parameter attribute</a> for the return type, a function
+ name, a (possibly empty) argument list (each with optional
+ <a href="#paramattrs">parameter attributes</a>), optional
+ <a href="#fnattrs">function attributes</a>, an optional section, an optional
+ alignment, an optional <a href="#gc">garbage collector name</a>, an opening
+ curly brace, a list of basic blocks, and a closing curly brace.</p>
+
+<p>LLVM function declarations consist of the "<tt>declare</tt>" keyword, an
+ optional <a href="#linkage">linkage type</a>, an optional
+ <a href="#visibility">visibility style</a>, an optional
+ <a href="#callingconv">calling convention</a>,
+ an optional <tt>unnamed_addr</tt> attribute, a return type, an optional
+ <a href="#paramattrs">parameter attribute</a> for the return type, a function
+ name, a possibly empty list of arguments, an optional alignment, and an
+ optional <a href="#gc">garbage collector name</a>.</p>
+
+<p>A function definition contains a list of basic blocks, forming the CFG
+ (Control Flow Graph) for the function. Each basic block may optionally start
+ with a label (giving the basic block a symbol table entry), contains a list
+ of instructions, and ends with a <a href="#terminators">terminator</a>
+ instruction (such as a branch or function return).</p>
+
+<p>The first basic block in a function is special in two ways: it is immediately
+ executed on entrance to the function, and it is not allowed to have
+ predecessor basic blocks (i.e. there can not be any branches to the entry
+ block of a function). Because the block can have no predecessors, it also
+ cannot have any <a href="#i_phi">PHI nodes</a>.</p>
+
+<p>LLVM allows an explicit section to be specified for functions. If the target
+ supports it, it will emit functions to the section specified.</p>
+
+<p>An explicit alignment may be specified for a function. If not present, or if
+ the alignment is set to zero, the alignment of the function is set by the
+ target to whatever it feels convenient. If an explicit alignment is
+ specified, the function is forced to have at least that much alignment. All
+ alignments must be a power of 2.</p>
+
+<p>If the <tt>unnamed_addr</tt> attribute is given, the address is know to not
+ be significant and two identical functions can be merged.</p>
+
+<h5>Syntax:</h5>
+<pre class="doc_code">
+define [<a href="#linkage">linkage</a>] [<a href="#visibility">visibility</a>]
+ [<a href="#callingconv">cconv</a>] [<a href="#paramattrs">ret attrs</a>]
+ <ResultType> @<FunctionName> ([argument list])
+ [<a href="#fnattrs">fn Attrs</a>] [section "name"] [align N]
+ [<a href="#gc">gc</a>] { ... }
+</pre>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="aliasstructure">Aliases</a>
+</h3>
+
+<div>
+
+<p>Aliases act as "second name" for the aliasee value (which can be either
+ function, global variable, another alias or bitcast of global value). Aliases
+ may have an optional <a href="#linkage">linkage type</a>, and an
+ optional <a href="#visibility">visibility style</a>.</p>
+
+<h5>Syntax:</h5>
+<pre class="doc_code">
+@<Name> = alias [Linkage] [Visibility] <AliaseeTy> @<Aliasee>
+</pre>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="namedmetadatastructure">Named Metadata</a>
+</h3>
+
+<div>
+
+<p>Named metadata is a collection of metadata. <a href="#metadata">Metadata
+ nodes</a> (but not metadata strings) are the only valid operands for
+ a named metadata.</p>
+
+<h5>Syntax:</h5>
+<pre class="doc_code">
+; Some unnamed metadata nodes, which are referenced by the named metadata.
+!0 = metadata !{metadata !"zero"}
+!1 = metadata !{metadata !"one"}
+!2 = metadata !{metadata !"two"}
+; A named metadata.
+!name = !{!0, !1, !2}
+</pre>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="paramattrs">Parameter Attributes</a>
+</h3>
+
+<div>
+
+<p>The return type and each parameter of a function type may have a set of
+ <i>parameter attributes</i> associated with them. Parameter attributes are
+ used to communicate additional information about the result or parameters of
+ a function. Parameter attributes are considered to be part of the function,
+ not of the function type, so functions with different parameter attributes
+ can have the same function type.</p>
+
+<p>Parameter attributes are simple keywords that follow the type specified. If
+ multiple parameter attributes are needed, they are space separated. For
+ example:</p>
+
+<pre class="doc_code">
+declare i32 @printf(i8* noalias nocapture, ...)
+declare i32 @atoi(i8 zeroext)
+declare signext i8 @returns_signed_char()
+</pre>
+
+<p>Note that any attributes for the function result (<tt>nounwind</tt>,
+ <tt>readonly</tt>) come immediately after the argument list.</p>
+
+<p>Currently, only the following parameter attributes are defined:</p>
+
+<dl>
+ <dt><tt><b>zeroext</b></tt></dt>
+ <dd>This indicates to the code generator that the parameter or return value
+ should be zero-extended to the extent required by the target's ABI (which
+ is usually 32-bits, but is 8-bits for a i1 on x86-64) by the caller (for a
+ parameter) or the callee (for a return value).</dd>
+
+ <dt><tt><b>signext</b></tt></dt>
+ <dd>This indicates to the code generator that the parameter or return value
+ should be sign-extended to the extent required by the target's ABI (which
+ is usually 32-bits) by the caller (for a parameter) or the callee (for a
+ return value).</dd>
+
+ <dt><tt><b>inreg</b></tt></dt>
+ <dd>This indicates that this parameter or return value should be treated in a
+ special target-dependent fashion during while emitting code for a function
+ call or return (usually, by putting it in a register as opposed to memory,
+ though some targets use it to distinguish between two different kinds of
+ registers). Use of this attribute is target-specific.</dd>
+
+ <dt><tt><b><a name="byval">byval</a></b></tt></dt>
+ <dd><p>This indicates that the pointer parameter should really be passed by
+ value to the function. The attribute implies that a hidden copy of the
+ pointee
+ is made between the caller and the callee, so the callee is unable to
+ modify the value in the caller. This attribute is only valid on LLVM
+ pointer arguments. It is generally used to pass structs and arrays by
+ value, but is also valid on pointers to scalars. The copy is considered
+ to belong to the caller not the callee (for example,
+ <tt><a href="#readonly">readonly</a></tt> functions should not write to
+ <tt>byval</tt> parameters). This is not a valid attribute for return
+ values.</p>
+
+ <p>The byval attribute also supports specifying an alignment with
+ the align attribute. It indicates the alignment of the stack slot to
+ form and the known alignment of the pointer specified to the call site. If
+ the alignment is not specified, then the code generator makes a
+ target-specific assumption.</p></dd>
+
+ <dt><tt><b><a name="sret">sret</a></b></tt></dt>
+ <dd>This indicates that the pointer parameter specifies the address of a
+ structure that is the return value of the function in the source program.
+ This pointer must be guaranteed by the caller to be valid: loads and
+ stores to the structure may be assumed by the callee to not to trap and
+ to be properly aligned. This may only be applied to the first parameter.
+ This is not a valid attribute for return values. </dd>
+
+ <dt><tt><b><a name="noalias">noalias</a></b></tt></dt>
+ <dd>This indicates that pointer values
+ <a href="#pointeraliasing"><i>based</i></a> on the argument or return
+ value do not alias pointer values which are not <i>based</i> on it,
+ ignoring certain "irrelevant" dependencies.
+ For a call to the parent function, dependencies between memory
+ references from before or after the call and from those during the call
+ are "irrelevant" to the <tt>noalias</tt> keyword for the arguments and
+ return value used in that call.
+ The caller shares the responsibility with the callee for ensuring that
+ these requirements are met.
+ For further details, please see the discussion of the NoAlias response in
+ <a href="AliasAnalysis.html#MustMayNo">alias analysis</a>.<br>
+<br>
+ Note that this definition of <tt>noalias</tt> is intentionally
+ similar to the definition of <tt>restrict</tt> in C99 for function
+ arguments, though it is slightly weaker.
+<br>
+ For function return values, C99's <tt>restrict</tt> is not meaningful,
+ while LLVM's <tt>noalias</tt> is.
+ </dd>
+
+ <dt><tt><b><a name="nocapture">nocapture</a></b></tt></dt>
+ <dd>This indicates that the callee does not make any copies of the pointer
+ that outlive the callee itself. This is not a valid attribute for return
+ values.</dd>
+
+ <dt><tt><b><a name="nest">nest</a></b></tt></dt>
+ <dd>This indicates that the pointer parameter can be excised using the
+ <a href="#int_trampoline">trampoline intrinsics</a>. This is not a valid
+ attribute for return values.</dd>
+</dl>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="gc">Garbage Collector Names</a>
+</h3>
+
+<div>
+
+<p>Each function may specify a garbage collector name, which is simply a
+ string:</p>
+
+<pre class="doc_code">
+define void @f() gc "name" { ... }
+</pre>
+
+<p>The compiler declares the supported values of <i>name</i>. Specifying a
+ collector which will cause the compiler to alter its output in order to
+ support the named garbage collection algorithm.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="fnattrs">Function Attributes</a>
+</h3>
+
+<div>
+
+<p>Function attributes are set to communicate additional information about a
+ function. Function attributes are considered to be part of the function, not
+ of the function type, so functions with different parameter attributes can
+ have the same function type.</p>
+
+<p>Function attributes are simple keywords that follow the type specified. If
+ multiple attributes are needed, they are space separated. For example:</p>
+
+<pre class="doc_code">
+define void @f() noinline { ... }
+define void @f() alwaysinline { ... }
+define void @f() alwaysinline optsize { ... }
+define void @f() optsize { ... }
+</pre>
+
+<dl>
+ <dt><tt><b>address_safety</b></tt></dt>
+ <dd>This attribute indicates that the address safety analysis
+ is enabled for this function. </dd>
+
+ <dt><tt><b>alignstack(<<em>n</em>>)</b></tt></dt>
+ <dd>This attribute indicates that, when emitting the prologue and epilogue,
+ the backend should forcibly align the stack pointer. Specify the
+ desired alignment, which must be a power of two, in parentheses.
+
+ <dt><tt><b>alwaysinline</b></tt></dt>
+ <dd>This attribute indicates that the inliner should attempt to inline this
+ function into callers whenever possible, ignoring any active inlining size
+ threshold for this caller.</dd>
+
+ <dt><tt><b>nonlazybind</b></tt></dt>
+ <dd>This attribute suppresses lazy symbol binding for the function. This
+ may make calls to the function faster, at the cost of extra program
+ startup time if the function is not called during program startup.</dd>
+
+ <dt><tt><b>inlinehint</b></tt></dt>
+ <dd>This attribute indicates that the source code contained a hint that inlining
+ this function is desirable (such as the "inline" keyword in C/C++). It
+ is just a hint; it imposes no requirements on the inliner.</dd>
+
+ <dt><tt><b>naked</b></tt></dt>
+ <dd>This attribute disables prologue / epilogue emission for the function.
+ This can have very system-specific consequences.</dd>
+
+ <dt><tt><b>noimplicitfloat</b></tt></dt>
+ <dd>This attributes disables implicit floating point instructions.</dd>
+
+ <dt><tt><b>noinline</b></tt></dt>
+ <dd>This attribute indicates that the inliner should never inline this
+ function in any situation. This attribute may not be used together with
+ the <tt>alwaysinline</tt> attribute.</dd>
+
+ <dt><tt><b>noredzone</b></tt></dt>
+ <dd>This attribute indicates that the code generator should not use a red
+ zone, even if the target-specific ABI normally permits it.</dd>
+
+ <dt><tt><b>noreturn</b></tt></dt>
+ <dd>This function attribute indicates that the function never returns
+ normally. This produces undefined behavior at runtime if the function
+ ever does dynamically return.</dd>
+
+ <dt><tt><b>nounwind</b></tt></dt>
+ <dd>This function attribute indicates that the function never returns with an
+ unwind or exceptional control flow. If the function does unwind, its
+ runtime behavior is undefined.</dd>
+
+ <dt><tt><b>optsize</b></tt></dt>
+ <dd>This attribute suggests that optimization passes and code generator passes
+ make choices that keep the code size of this function low, and otherwise
+ do optimizations specifically to reduce code size.</dd>
+
+ <dt><tt><b>readnone</b></tt></dt>
+ <dd>This attribute indicates that the function computes its result (or decides
+ to unwind an exception) based strictly on its arguments, without
+ dereferencing any pointer arguments or otherwise accessing any mutable
+ state (e.g. memory, control registers, etc) visible to caller functions.
+ It does not write through any pointer arguments
+ (including <tt><a href="#byval">byval</a></tt> arguments) and never
+ changes any state visible to callers. This means that it cannot unwind
+ exceptions by calling the <tt>C++</tt> exception throwing methods.</dd>
+
+ <dt><tt><b><a name="readonly">readonly</a></b></tt></dt>
+ <dd>This attribute indicates that the function does not write through any
+ pointer arguments (including <tt><a href="#byval">byval</a></tt>
+ arguments) or otherwise modify any state (e.g. memory, control registers,
+ etc) visible to caller functions. It may dereference pointer arguments
+ and read state that may be set in the caller. A readonly function always
+ returns the same value (or unwinds an exception identically) when called
+ with the same set of arguments and global state. It cannot unwind an
+ exception by calling the <tt>C++</tt> exception throwing methods.</dd>
+
+ <dt><tt><b><a name="returns_twice">returns_twice</a></b></tt></dt>
+ <dd>This attribute indicates that this function can return twice. The
+ C <code>setjmp</code> is an example of such a function. The compiler
+ disables some optimizations (like tail calls) in the caller of these
+ functions.</dd>
+
+ <dt><tt><b><a name="ssp">ssp</a></b></tt></dt>
+ <dd>This attribute indicates that the function should emit a stack smashing
+ protector. It is in the form of a "canary"—a random value placed on
+ the stack before the local variables that's checked upon return from the
+ function to see if it has been overwritten. A heuristic is used to
+ determine if a function needs stack protectors or not.<br>
+<br>
+ If a function that has an <tt>ssp</tt> attribute is inlined into a
+ function that doesn't have an <tt>ssp</tt> attribute, then the resulting
+ function will have an <tt>ssp</tt> attribute.</dd>
+
+ <dt><tt><b>sspreq</b></tt></dt>
+ <dd>This attribute indicates that the function should <em>always</em> emit a
+ stack smashing protector. This overrides
+ the <tt><a href="#ssp">ssp</a></tt> function attribute.<br>
+<br>
+ If a function that has an <tt>sspreq</tt> attribute is inlined into a
+ function that doesn't have an <tt>sspreq</tt> attribute or which has
+ an <tt>ssp</tt> attribute, then the resulting function will have
+ an <tt>sspreq</tt> attribute.</dd>
+
+ <dt><tt><b><a name="uwtable">uwtable</a></b></tt></dt>
+ <dd>This attribute indicates that the ABI being targeted requires that
+ an unwind table entry be produce for this function even if we can
+ show that no exceptions passes by it. This is normally the case for
+ the ELF x86-64 abi, but it can be disabled for some compilation
+ units.</dd>
+</dl>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="moduleasm">Module-Level Inline Assembly</a>
+</h3>
+
+<div>
+
+<p>Modules may contain "module-level inline asm" blocks, which corresponds to
+ the GCC "file scope inline asm" blocks. These blocks are internally
+ concatenated by LLVM and treated as a single unit, but may be separated in
+ the <tt>.ll</tt> file if desired. The syntax is very simple:</p>
+
+<pre class="doc_code">
+module asm "inline asm code goes here"
+module asm "more can go here"
+</pre>
+
+<p>The strings can contain any character by escaping non-printable characters.
+ The escape sequence used is simply "\xx" where "xx" is the two digit hex code
+ for the number.</p>
+
+<p>The inline asm code is simply printed to the machine code .s file when
+ assembly code is generated.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="datalayout">Data Layout</a>
+</h3>
+
+<div>
+
+<p>A module may specify a target specific data layout string that specifies how
+ data is to be laid out in memory. The syntax for the data layout is
+ simply:</p>
+
+<pre class="doc_code">
+target datalayout = "<i>layout specification</i>"
+</pre>
+
+<p>The <i>layout specification</i> consists of a list of specifications
+ separated by the minus sign character ('-'). Each specification starts with
+ a letter and may include other information after the letter to define some
+ aspect of the data layout. The specifications accepted are as follows:</p>
+
+<dl>
+ <dt><tt>E</tt></dt>
+ <dd>Specifies that the target lays out data in big-endian form. That is, the
+ bits with the most significance have the lowest address location.</dd>
+
+ <dt><tt>e</tt></dt>
+ <dd>Specifies that the target lays out data in little-endian form. That is,
+ the bits with the least significance have the lowest address
+ location.</dd>
+
+ <dt><tt>S<i>size</i></tt></dt>
+ <dd>Specifies the natural alignment of the stack in bits. Alignment promotion
+ of stack variables is limited to the natural stack alignment to avoid
+ dynamic stack realignment. The stack alignment must be a multiple of
+ 8-bits. If omitted, the natural stack alignment defaults to "unspecified",
+ which does not prevent any alignment promotions.</dd>
+
+ <dt><tt>p[n]:<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
+ <dd>This specifies the <i>size</i> of a pointer and its <i>abi</i> and
+ <i>preferred</i> alignments for address space <i>n</i>. All sizes are in
+ bits. Specifying the <i>pref</i> alignment is optional. If omitted, the
+ preceding <tt>:</tt> should be omitted too. The address space,
+ <i>n</i> is optional, and if not specified, denotes the default address
+ space 0. The value of <i>n</i> must be in the range [1,2^23).</dd>
+
+ <dt><tt>i<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
+ <dd>This specifies the alignment for an integer type of a given bit
+ <i>size</i>. The value of <i>size</i> must be in the range [1,2^23).</dd>
+
+ <dt><tt>v<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
+ <dd>This specifies the alignment for a vector type of a given bit
+ <i>size</i>.</dd>
+
+ <dt><tt>f<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
+ <dd>This specifies the alignment for a floating point type of a given bit
+ <i>size</i>. Only values of <i>size</i> that are supported by the target
+ will work. 32 (float) and 64 (double) are supported on all targets;
+ 80 or 128 (different flavors of long double) are also supported on some
+ targets.
+
+ <dt><tt>a<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
+ <dd>This specifies the alignment for an aggregate type of a given bit
+ <i>size</i>.</dd>
+
+ <dt><tt>s<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
+ <dd>This specifies the alignment for a stack object of a given bit
+ <i>size</i>.</dd>
+
+ <dt><tt>n<i>size1</i>:<i>size2</i>:<i>size3</i>...</tt></dt>
+ <dd>This specifies a set of native integer widths for the target CPU
+ in bits. For example, it might contain "n32" for 32-bit PowerPC,
+ "n32:64" for PowerPC 64, or "n8:16:32:64" for X86-64. Elements of
+ this set are considered to support most general arithmetic
+ operations efficiently.</dd>
+</dl>
+
+<p>When constructing the data layout for a given target, LLVM starts with a
+ default set of specifications which are then (possibly) overridden by the
+ specifications in the <tt>datalayout</tt> keyword. The default specifications
+ are given in this list:</p>
+
+<ul>
+ <li><tt>E</tt> - big endian</li>
+ <li><tt>p:64:64:64</tt> - 64-bit pointers with 64-bit alignment</li>
+ <li><tt>p1:32:32:32</tt> - 32-bit pointers with 32-bit alignment for
+ address space 1</li>
+ <li><tt>p2:16:32:32</tt> - 16-bit pointers with 32-bit alignment for
+ address space 2</li>
+ <li><tt>i1:8:8</tt> - i1 is 8-bit (byte) aligned</li>
+ <li><tt>i8:8:8</tt> - i8 is 8-bit (byte) aligned</li>
+ <li><tt>i16:16:16</tt> - i16 is 16-bit aligned</li>
+ <li><tt>i32:32:32</tt> - i32 is 32-bit aligned</li>
+ <li><tt>i64:32:64</tt> - i64 has ABI alignment of 32-bits but preferred
+ alignment of 64-bits</li>
+ <li><tt>f32:32:32</tt> - float is 32-bit aligned</li>
+ <li><tt>f64:64:64</tt> - double is 64-bit aligned</li>
+ <li><tt>v64:64:64</tt> - 64-bit vector is 64-bit aligned</li>
+ <li><tt>v128:128:128</tt> - 128-bit vector is 128-bit aligned</li>
+ <li><tt>a0:0:1</tt> - aggregates are 8-bit aligned</li>
+ <li><tt>s0:64:64</tt> - stack objects are 64-bit aligned</li>
+</ul>
+
+<p>When LLVM is determining the alignment for a given type, it uses the
+ following rules:</p>
+
+<ol>
+ <li>If the type sought is an exact match for one of the specifications, that
+ specification is used.</li>
+
+ <li>If no match is found, and the type sought is an integer type, then the
+ smallest integer type that is larger than the bitwidth of the sought type
+ is used. If none of the specifications are larger than the bitwidth then
+ the largest integer type is used. For example, given the default
+ specifications above, the i7 type will use the alignment of i8 (next
+ largest) while both i65 and i256 will use the alignment of i64 (largest
+ specified).</li>
+
+ <li>If no match is found, and the type sought is a vector type, then the
+ largest vector type that is smaller than the sought vector type will be
+ used as a fall back. This happens because <128 x double> can be
+ implemented in terms of 64 <2 x double>, for example.</li>
+</ol>
+
+<p>The function of the data layout string may not be what you expect. Notably,
+ this is not a specification from the frontend of what alignment the code
+ generator should use.</p>
+
+<p>Instead, if specified, the target data layout is required to match what the
+ ultimate <em>code generator</em> expects. This string is used by the
+ mid-level optimizers to
+ improve code, and this only works if it matches what the ultimate code
+ generator uses. If you would like to generate IR that does not embed this
+ target-specific detail into the IR, then you don't have to specify the
+ string. This will disable some optimizations that require precise layout
+ information, but this also prevents those optimizations from introducing
+ target specificity into the IR.</p>
+
+
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="pointeraliasing">Pointer Aliasing Rules</a>
+</h3>
+
+<div>
+
+<p>Any memory access must be done through a pointer value associated
+with an address range of the memory access, otherwise the behavior
+is undefined. Pointer values are associated with address ranges
+according to the following rules:</p>
+
+<ul>
+ <li>A pointer value is associated with the addresses associated with
+ any value it is <i>based</i> on.
+ <li>An address of a global variable is associated with the address
+ range of the variable's storage.</li>
+ <li>The result value of an allocation instruction is associated with
+ the address range of the allocated storage.</li>
+ <li>A null pointer in the default address-space is associated with
+ no address.</li>
+ <li>An integer constant other than zero or a pointer value returned
+ from a function not defined within LLVM may be associated with address
+ ranges allocated through mechanisms other than those provided by
+ LLVM. Such ranges shall not overlap with any ranges of addresses
+ allocated by mechanisms provided by LLVM.</li>
+</ul>
+
+<p>A pointer value is <i>based</i> on another pointer value according
+ to the following rules:</p>
+
+<ul>
+ <li>A pointer value formed from a
+ <tt><a href="#i_getelementptr">getelementptr</a></tt> operation
+ is <i>based</i> on the first operand of the <tt>getelementptr</tt>.</li>
+ <li>The result value of a
+ <tt><a href="#i_bitcast">bitcast</a></tt> is <i>based</i> on the operand
+ of the <tt>bitcast</tt>.</li>
+ <li>A pointer value formed by an
+ <tt><a href="#i_inttoptr">inttoptr</a></tt> is <i>based</i> on all
+ pointer values that contribute (directly or indirectly) to the
+ computation of the pointer's value.</li>
+ <li>The "<i>based</i> on" relationship is transitive.</li>
+</ul>
+
+<p>Note that this definition of <i>"based"</i> is intentionally
+ similar to the definition of <i>"based"</i> in C99, though it is
+ slightly weaker.</p>
+
+<p>LLVM IR does not associate types with memory. The result type of a
+<tt><a href="#i_load">load</a></tt> merely indicates the size and
+alignment of the memory from which to load, as well as the
+interpretation of the value. The first operand type of a
+<tt><a href="#i_store">store</a></tt> similarly only indicates the size
+and alignment of the store.</p>
+
+<p>Consequently, type-based alias analysis, aka TBAA, aka
+<tt>-fstrict-aliasing</tt>, is not applicable to general unadorned
+LLVM IR. <a href="#metadata">Metadata</a> may be used to encode
+additional information which specialized optimization passes may use
+to implement type-based alias analysis.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="volatile">Volatile Memory Accesses</a>
+</h3>
+
+<div>
+
+<p>Certain memory accesses, such as <a href="#i_load"><tt>load</tt></a>s, <a
+href="#i_store"><tt>store</tt></a>s, and <a
+href="#int_memcpy"><tt>llvm.memcpy</tt></a>s may be marked <tt>volatile</tt>.
+The optimizers must not change the number of volatile operations or change their
+order of execution relative to other volatile operations. The optimizers
+<i>may</i> change the order of volatile operations relative to non-volatile
+operations. This is not Java's "volatile" and has no cross-thread
+synchronization behavior.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="memmodel">Memory Model for Concurrent Operations</a>
+</h3>
+
+<div>
+
+<p>The LLVM IR does not define any way to start parallel threads of execution
+or to register signal handlers. Nonetheless, there are platform-specific
+ways to create them, and we define LLVM IR's behavior in their presence. This
+model is inspired by the C++0x memory model.</p>
+
+<p>For a more informal introduction to this model, see the
+<a href="Atomics.html">LLVM Atomic Instructions and Concurrency Guide</a>.
+
+<p>We define a <i>happens-before</i> partial order as the least partial order
+that</p>
+<ul>
+ <li>Is a superset of single-thread program order, and</li>
+ <li>When a <i>synchronizes-with</i> <tt>b</tt>, includes an edge from
+ <tt>a</tt> to <tt>b</tt>. <i>Synchronizes-with</i> pairs are introduced
+ by platform-specific techniques, like pthread locks, thread
+ creation, thread joining, etc., and by atomic instructions.
+ (See also <a href="#ordering">Atomic Memory Ordering Constraints</a>).
+ </li>
+</ul>
+
+<p>Note that program order does not introduce <i>happens-before</i> edges
+between a thread and signals executing inside that thread.</p>
+
+<p>Every (defined) read operation (load instructions, memcpy, atomic
+loads/read-modify-writes, etc.) <var>R</var> reads a series of bytes written by
+(defined) write operations (store instructions, atomic
+stores/read-modify-writes, memcpy, etc.). For the purposes of this section,
+initialized globals are considered to have a write of the initializer which is
+atomic and happens before any other read or write of the memory in question.
+For each byte of a read <var>R</var>, <var>R<sub>byte</sub></var> may see
+any write to the same byte, except:</p>
+
+<ul>
+ <li>If <var>write<sub>1</sub></var> happens before
+ <var>write<sub>2</sub></var>, and <var>write<sub>2</sub></var> happens
+ before <var>R<sub>byte</sub></var>, then <var>R<sub>byte</sub></var>
+ does not see <var>write<sub>1</sub></var>.
+ <li>If <var>R<sub>byte</sub></var> happens before
+ <var>write<sub>3</sub></var>, then <var>R<sub>byte</sub></var> does not
+ see <var>write<sub>3</sub></var>.
+</ul>
+
+<p>Given that definition, <var>R<sub>byte</sub></var> is defined as follows:
+<ul>
+ <li>If <var>R</var> is volatile, the result is target-dependent. (Volatile
+ is supposed to give guarantees which can support
+ <code>sig_atomic_t</code> in C/C++, and may be used for accesses to
+ addresses which do not behave like normal memory. It does not generally
+ provide cross-thread synchronization.)
+ <li>Otherwise, if there is no write to the same byte that happens before
+ <var>R<sub>byte</sub></var>, <var>R<sub>byte</sub></var> returns
+ <tt>undef</tt> for that byte.
+ <li>Otherwise, if <var>R<sub>byte</sub></var> may see exactly one write,
+ <var>R<sub>byte</sub></var> returns the value written by that
+ write.</li>
+ <li>Otherwise, if <var>R</var> is atomic, and all the writes
+ <var>R<sub>byte</sub></var> may see are atomic, it chooses one of the
+ values written. See the <a href="#ordering">Atomic Memory Ordering
+ Constraints</a> section for additional constraints on how the choice
+ is made.
+ <li>Otherwise <var>R<sub>byte</sub></var> returns <tt>undef</tt>.</li>
+</ul>
+
+<p><var>R</var> returns the value composed of the series of bytes it read.
+This implies that some bytes within the value may be <tt>undef</tt>
+<b>without</b> the entire value being <tt>undef</tt>. Note that this only
+defines the semantics of the operation; it doesn't mean that targets will
+emit more than one instruction to read the series of bytes.</p>
+
+<p>Note that in cases where none of the atomic intrinsics are used, this model
+places only one restriction on IR transformations on top of what is required
+for single-threaded execution: introducing a store to a byte which might not
+otherwise be stored is not allowed in general. (Specifically, in the case
+where another thread might write to and read from an address, introducing a
+store can change a load that may see exactly one write into a load that may
+see multiple writes.)</p>
+
+<!-- FIXME: This model assumes all targets where concurrency is relevant have
+a byte-size store which doesn't affect adjacent bytes. As far as I can tell,
+none of the backends currently in the tree fall into this category; however,
+there might be targets which care. If there are, we want a paragraph
+like the following:
+
+Targets may specify that stores narrower than a certain width are not
+available; on such a target, for the purposes of this model, treat any
+non-atomic write with an alignment or width less than the minimum width
+as if it writes to the relevant surrounding bytes.
+-->
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="ordering">Atomic Memory Ordering Constraints</a>
+</h3>
+
+<div>
+
+<p>Atomic instructions (<a href="#i_cmpxchg"><code>cmpxchg</code></a>,
+<a href="#i_atomicrmw"><code>atomicrmw</code></a>,
+<a href="#i_fence"><code>fence</code></a>,
+<a href="#i_load"><code>atomic load</code></a>, and
+<a href="#i_store"><code>atomic store</code></a>) take an ordering parameter
+that determines which other atomic instructions on the same address they
+<i>synchronize with</i>. These semantics are borrowed from Java and C++0x,
+but are somewhat more colloquial. If these descriptions aren't precise enough,
+check those specs (see spec references in the
+<a href="Atomics.html#introduction">atomics guide</a>).
+<a href="#i_fence"><code>fence</code></a> instructions
+treat these orderings somewhat differently since they don't take an address.
+See that instruction's documentation for details.</p>
+
+<p>For a simpler introduction to the ordering constraints, see the
+<a href="Atomics.html">LLVM Atomic Instructions and Concurrency Guide</a>.</p>
+
+<dl>
+<dt><code>unordered</code></dt>
+<dd>The set of values that can be read is governed by the happens-before
+partial order. A value cannot be read unless some operation wrote it.
+This is intended to provide a guarantee strong enough to model Java's
+non-volatile shared variables. This ordering cannot be specified for
+read-modify-write operations; it is not strong enough to make them atomic
+in any interesting way.</dd>
+<dt><code>monotonic</code></dt>
+<dd>In addition to the guarantees of <code>unordered</code>, there is a single
+total order for modifications by <code>monotonic</code> operations on each
+address. All modification orders must be compatible with the happens-before
+order. There is no guarantee that the modification orders can be combined to
+a global total order for the whole program (and this often will not be
+possible). The read in an atomic read-modify-write operation
+(<a href="#i_cmpxchg"><code>cmpxchg</code></a> and
+<a href="#i_atomicrmw"><code>atomicrmw</code></a>)
+reads the value in the modification order immediately before the value it
+writes. If one atomic read happens before another atomic read of the same
+address, the later read must see the same value or a later value in the
+address's modification order. This disallows reordering of
+<code>monotonic</code> (or stronger) operations on the same address. If an
+address is written <code>monotonic</code>ally by one thread, and other threads
+<code>monotonic</code>ally read that address repeatedly, the other threads must
+eventually see the write. This corresponds to the C++0x/C1x
+<code>memory_order_relaxed</code>.</dd>
+<dt><code>acquire</code></dt>
+<dd>In addition to the guarantees of <code>monotonic</code>,
+a <i>synchronizes-with</i> edge may be formed with a <code>release</code>
+operation. This is intended to model C++'s <code>memory_order_acquire</code>.</dd>
+<dt><code>release</code></dt>
+<dd>In addition to the guarantees of <code>monotonic</code>, if this operation
+writes a value which is subsequently read by an <code>acquire</code> operation,
+it <i>synchronizes-with</i> that operation. (This isn't a complete
+description; see the C++0x definition of a release sequence.) This corresponds
+to the C++0x/C1x <code>memory_order_release</code>.</dd>
+<dt><code>acq_rel</code> (acquire+release)</dt><dd>Acts as both an
+<code>acquire</code> and <code>release</code> operation on its address.
+This corresponds to the C++0x/C1x <code>memory_order_acq_rel</code>.</dd>
+<dt><code>seq_cst</code> (sequentially consistent)</dt><dd>
+<dd>In addition to the guarantees of <code>acq_rel</code>
+(<code>acquire</code> for an operation which only reads, <code>release</code>
+for an operation which only writes), there is a global total order on all
+sequentially-consistent operations on all addresses, which is consistent with
+the <i>happens-before</i> partial order and with the modification orders of
+all the affected addresses. Each sequentially-consistent read sees the last
+preceding write to the same address in this global order. This corresponds
+to the C++0x/C1x <code>memory_order_seq_cst</code> and Java volatile.</dd>
+</dl>
+
+<p id="singlethread">If an atomic operation is marked <code>singlethread</code>,
+it only <i>synchronizes with</i> or participates in modification and seq_cst
+total orderings with other operations running in the same thread (for example,
+in signal handlers).</p>
+
+</div>
+
+</div>
+
+<!-- *********************************************************************** -->
+<h2><a name="typesystem">Type System</a></h2>
+<!-- *********************************************************************** -->
+
+<div>
+
+<p>The LLVM type system is one of the most important features of the
+ intermediate representation. Being typed enables a number of optimizations
+ to be performed on the intermediate representation directly, without having
+ to do extra analyses on the side before the transformation. A strong type
+ system makes it easier to read the generated code and enables novel analyses
+ and transformations that are not feasible to perform on normal three address
+ code representations.</p>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="t_classifications">Type Classifications</a>
+</h3>
+
+<div>
+
+<p>The types fall into a few useful classifications:</p>
+
+<table border="1" cellspacing="0" cellpadding="4">
+ <tbody>
+ <tr><th>Classification</th><th>Types</th></tr>
+ <tr>
+ <td><a href="#t_integer">integer</a></td>
+ <td><tt>i1, i2, i3, ... i8, ... i16, ... i32, ... i64, ... </tt></td>
+ </tr>
+ <tr>
+ <td><a href="#t_floating">floating point</a></td>
+ <td><tt>half, float, double, x86_fp80, fp128, ppc_fp128</tt></td>
+ </tr>
+ <tr>
+ <td><a name="t_firstclass">first class</a></td>
+ <td><a href="#t_integer">integer</a>,
+ <a href="#t_floating">floating point</a>,
+ <a href="#t_pointer">pointer</a>,
+ <a href="#t_vector">vector</a>,
+ <a href="#t_struct">structure</a>,
+ <a href="#t_array">array</a>,
+ <a href="#t_label">label</a>,
+ <a href="#t_metadata">metadata</a>.
+ </td>
+ </tr>
+ <tr>
+ <td><a href="#t_primitive">primitive</a></td>
+ <td><a href="#t_label">label</a>,
+ <a href="#t_void">void</a>,
+ <a href="#t_integer">integer</a>,
+ <a href="#t_floating">floating point</a>,
+ <a href="#t_x86mmx">x86mmx</a>,
+ <a href="#t_metadata">metadata</a>.</td>
+ </tr>
+ <tr>
+ <td><a href="#t_derived">derived</a></td>
+ <td><a href="#t_array">array</a>,
+ <a href="#t_function">function</a>,
+ <a href="#t_pointer">pointer</a>,
+ <a href="#t_struct">structure</a>,
+ <a href="#t_vector">vector</a>,
+ <a href="#t_opaque">opaque</a>.
+ </td>
+ </tr>
+ </tbody>
+</table>
+
+<p>The <a href="#t_firstclass">first class</a> types are perhaps the most
+ important. Values of these types are the only ones which can be produced by
+ instructions.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="t_primitive">Primitive Types</a>
+</h3>
+
+<div>
+
+<p>The primitive types are the fundamental building blocks of the LLVM
+ system.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="t_integer">Integer Type</a>
+</h4>
+
+<div>
+
+<h5>Overview:</h5>
+<p>The integer type is a very simple type that simply specifies an arbitrary
+ bit width for the integer type desired. Any bit width from 1 bit to
+ 2<sup>23</sup>-1 (about 8 million) can be specified.</p>
+
+<h5>Syntax:</h5>
+<pre>
+ iN
+</pre>
+
+<p>The number of bits the integer will occupy is specified by the <tt>N</tt>
+ value.</p>
+
+<h5>Examples:</h5>
+<table class="layout">
+ <tr class="layout">
+ <td class="left"><tt>i1</tt></td>
+ <td class="left">a single-bit integer.</td>
+ </tr>
+ <tr class="layout">
+ <td class="left"><tt>i32</tt></td>
+ <td class="left">a 32-bit integer.</td>
+ </tr>
+ <tr class="layout">
+ <td class="left"><tt>i1942652</tt></td>
+ <td class="left">a really big integer of over 1 million bits.</td>
+ </tr>
+</table>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="t_floating">Floating Point Types</a>
+</h4>
+
+<div>
+
+<table>
+ <tbody>
+ <tr><th>Type</th><th>Description</th></tr>
+ <tr><td><tt>half</tt></td><td>16-bit floating point value</td></tr>
+ <tr><td><tt>float</tt></td><td>32-bit floating point value</td></tr>
+ <tr><td><tt>double</tt></td><td>64-bit floating point value</td></tr>
+ <tr><td><tt>fp128</tt></td><td>128-bit floating point value (112-bit mantissa)</td></tr>
+ <tr><td><tt>x86_fp80</tt></td><td>80-bit floating point value (X87)</td></tr>
+ <tr><td><tt>ppc_fp128</tt></td><td>128-bit floating point value (two 64-bits)</td></tr>
+ </tbody>
+</table>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="t_x86mmx">X86mmx Type</a>
+</h4>
+
+<div>
+
+<h5>Overview:</h5>
+<p>The x86mmx type represents a value held in an MMX register on an x86 machine. The operations allowed on it are quite limited: parameters and return values, load and store, and bitcast. User-specified MMX instructions are represented as intrinsic or asm calls with arguments and/or results of this type. There are no arrays, vectors or constants of this type.</p>
+
+<h5>Syntax:</h5>
+<pre>
+ x86mmx
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="t_void">Void Type</a>
+</h4>
+
+<div>
+
+<h5>Overview:</h5>
+<p>The void type does not represent any value and has no size.</p>
+
+<h5>Syntax:</h5>
+<pre>
+ void
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="t_label">Label Type</a>
+</h4>
+
+<div>
+
+<h5>Overview:</h5>
+<p>The label type represents code labels.</p>
+
+<h5>Syntax:</h5>
+<pre>
+ label
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="t_metadata">Metadata Type</a>
+</h4>
+
+<div>
+
+<h5>Overview:</h5>
+<p>The metadata type represents embedded metadata. No derived types may be
+ created from metadata except for <a href="#t_function">function</a>
+ arguments.
+
+<h5>Syntax:</h5>
+<pre>
+ metadata
+</pre>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="t_derived">Derived Types</a>
+</h3>
+
+<div>
+
+<p>The real power in LLVM comes from the derived types in the system. This is
+ what allows a programmer to represent arrays, functions, pointers, and other
+ useful types. Each of these types contain one or more element types which
+ may be a primitive type, or another derived type. For example, it is
+ possible to have a two dimensional array, using an array as the element type
+ of another array.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="t_aggregate">Aggregate Types</a>
+</h4>
+
+<div>
+
+<p>Aggregate Types are a subset of derived types that can contain multiple
+ member types. <a href="#t_array">Arrays</a> and
+ <a href="#t_struct">structs</a> are aggregate types.
+ <a href="#t_vector">Vectors</a> are not considered to be aggregate types.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="t_array">Array Type</a>
+</h4>
+
+<div>
+
+<h5>Overview:</h5>
+<p>The array type is a very simple derived type that arranges elements
+ sequentially in memory. The array type requires a size (number of elements)
+ and an underlying data type.</p>
+
+<h5>Syntax:</h5>
+<pre>
+ [<# elements> x <elementtype>]
+</pre>
+
+<p>The number of elements is a constant integer value; <tt>elementtype</tt> may
+ be any type with a size.</p>
+
+<h5>Examples:</h5>
+<table class="layout">
+ <tr class="layout">
+ <td class="left"><tt>[40 x i32]</tt></td>
+ <td class="left">Array of 40 32-bit integer values.</td>
+ </tr>
+ <tr class="layout">
+ <td class="left"><tt>[41 x i32]</tt></td>
+ <td class="left">Array of 41 32-bit integer values.</td>
+ </tr>
+ <tr class="layout">
+ <td class="left"><tt>[4 x i8]</tt></td>
+ <td class="left">Array of 4 8-bit integer values.</td>
+ </tr>
+</table>
+<p>Here are some examples of multidimensional arrays:</p>
+<table class="layout">
+ <tr class="layout">
+ <td class="left"><tt>[3 x [4 x i32]]</tt></td>
+ <td class="left">3x4 array of 32-bit integer values.</td>
+ </tr>
+ <tr class="layout">
+ <td class="left"><tt>[12 x [10 x float]]</tt></td>
+ <td class="left">12x10 array of single precision floating point values.</td>
+ </tr>
+ <tr class="layout">
+ <td class="left"><tt>[2 x [3 x [4 x i16]]]</tt></td>
+ <td class="left">2x3x4 array of 16-bit integer values.</td>
+ </tr>
+</table>
+
+<p>There is no restriction on indexing beyond the end of the array implied by
+ a static type (though there are restrictions on indexing beyond the bounds
+ of an allocated object in some cases). This means that single-dimension
+ 'variable sized array' addressing can be implemented in LLVM with a zero
+ length array type. An implementation of 'pascal style arrays' in LLVM could
+ use the type "<tt>{ i32, [0 x float]}</tt>", for example.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="t_function">Function Type</a>
+</h4>
+
+<div>
+
+<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. The return type of a
+ function type is a first class type or a void type.</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. '<tt><returntype></tt>' is any type except
+ <a href="#t_label">label</a>.</p>
+
+<h5>Examples:</h5>
+<table class="layout">
+ <tr class="layout">
+ <td class="left"><tt>i32 (i32)</tt></td>
+ <td class="left">function taking an <tt>i32</tt>, returning an <tt>i32</tt>
+ </td>
+ </tr><tr class="layout">
+ <td class="left"><tt>float (i16, i32 *) *
+ </tt></td>
+ <td class="left"><a href="#t_pointer">Pointer</a> to a function that takes
+ an <tt>i16</tt> and a <a href="#t_pointer">pointer</a> to <tt>i32</tt>,
+ returning <tt>float</tt>.
+ </td>
+ </tr><tr class="layout">
+ <td class="left"><tt>i32 (i8*, ...)</tt></td>
+ <td class="left">A vararg function that takes at least one
+ <a href="#t_pointer">pointer</a> to <tt>i8 </tt> (char in C),
+ which returns an integer. This is the signature for <tt>printf</tt> in
+ LLVM.
+ </td>
+ </tr><tr class="layout">
+ <td class="left"><tt>{i32, i32} (i32)</tt></td>
+ <td class="left">A function taking an <tt>i32</tt>, returning a
+ <a href="#t_struct">structure</a> containing two <tt>i32</tt> values
+ </td>
+ </tr>
+</table>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="t_struct">Structure Type</a>
+</h4>
+
+<div>
+
+<h5>Overview:</h5>
+<p>The structure type is used to represent a collection of data members together
+ in memory. The elements of a structure may be any type that has a size.</p>
+
+<p>Structures in memory 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.
+ Structures in registers are accessed using the
+ '<tt><a href="#i_extractvalue">extractvalue</a></tt>' and
+ '<tt><a href="#i_insertvalue">insertvalue</a></tt>' instructions.</p>
+
+<p>Structures may optionally be "packed" structures, which indicate that the
+ alignment of the struct is one byte, and that there is no padding between
+ the elements. In non-packed structs, padding between field types is inserted
+ as defined by the DataLayout string in the module, which is required to match
+ what the underlying code generator expects.</p>
+
+<p>Structures can either be "literal" or "identified". A literal structure is
+ defined inline with other types (e.g. <tt>{i32, i32}*</tt>) whereas identified
+ types are always defined at the top level with a name. Literal types are
+ uniqued by their contents and can never be recursive or opaque since there is
+ no way to write one. Identified types can be recursive, can be opaqued, and are
+ never uniqued.
+</p>
+
+<h5>Syntax:</h5>
+<pre>
+ %T1 = type { <type list> } <i>; Identified normal struct type</i>
+ %T2 = type <{ <type list> }> <i>; Identified packed struct type</i>
+</pre>
+
+<h5>Examples:</h5>
+<table class="layout">
+ <tr class="layout">
+ <td class="left"><tt>{ i32, i32, i32 }</tt></td>
+ <td class="left">A triple of three <tt>i32</tt> values</td>
+ </tr>
+ <tr class="layout">
+ <td class="left"><tt>{ float, i32 (i32) * }</tt></td>
+ <td class="left">A pair, where the first element is a <tt>float</tt> and the
+ second element is a <a href="#t_pointer">pointer</a> to a
+ <a href="#t_function">function</a> that takes an <tt>i32</tt>, returning
+ an <tt>i32</tt>.</td>
+ </tr>
+ <tr class="layout">
+ <td class="left"><tt><{ i8, i32 }></tt></td>
+ <td class="left">A packed struct known to be 5 bytes in size.</td>
+ </tr>
+</table>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="t_opaque">Opaque Structure Types</a>
+</h4>
+
+<div>
+
+<h5>Overview:</h5>
+<p>Opaque structure types are used to represent named structure types that do
+ not have a body specified. This corresponds (for example) to the C notion of
+ a forward declared structure.</p>
+
+<h5>Syntax:</h5>
+<pre>
+ %X = type opaque
+ %52 = type opaque
+</pre>
+
+<h5>Examples:</h5>
+<table class="layout">
+ <tr class="layout">
+ <td class="left"><tt>opaque</tt></td>
+ <td class="left">An opaque type.</td>
+ </tr>
+</table>
+
+</div>
+
+
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="t_pointer">Pointer Type</a>
+</h4>
+
+<div>
+
+<h5>Overview:</h5>
+<p>The pointer type is used to specify memory locations.
+ Pointers are commonly used to reference objects in memory.</p>
+
+<p>Pointer types may have an optional address space attribute defining the
+ numbered address space where the pointed-to object resides. The default
+ address space is number zero. The semantics of non-zero address
+ spaces are target-specific.</p>
+
+<p>Note that LLVM does not permit pointers to void (<tt>void*</tt>) nor does it
+ permit pointers to labels (<tt>label*</tt>). Use <tt>i8*</tt> instead.</p>
+
+<h5>Syntax:</h5>
+<pre>
+ <type> *
+</pre>
+
+<h5>Examples:</h5>
+<table class="layout">
+ <tr class="layout">
+ <td class="left"><tt>[4 x i32]*</tt></td>
+ <td class="left">A <a href="#t_pointer">pointer</a> to <a
+ href="#t_array">array</a> of four <tt>i32</tt> values.</td>
+ </tr>
+ <tr class="layout">
+ <td class="left"><tt>i32 (i32*) *</tt></td>
+ <td class="left"> A <a href="#t_pointer">pointer</a> to a <a
+ href="#t_function">function</a> that takes an <tt>i32*</tt>, returning an
+ <tt>i32</tt>.</td>
+ </tr>
+ <tr class="layout">
+ <td class="left"><tt>i32 addrspace(5)*</tt></td>
+ <td class="left">A <a href="#t_pointer">pointer</a> to an <tt>i32</tt> value
+ that resides in address space #5.</td>
+ </tr>
+</table>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="t_vector">Vector Type</a>
+</h4>
+
+<div>
+
+<h5>Overview:</h5>
+<p>A vector type is a simple derived type that represents a vector of elements.
+ Vector types are used when multiple primitive data are operated in parallel
+ using a single instruction (SIMD). A vector type requires a size (number of
+ elements) and an underlying primitive data type. Vector types are considered
+ <a href="#t_firstclass">first class</a>.</p>
+
+<h5>Syntax:</h5>
+<pre>
+ < <# elements> x <elementtype> >
+</pre>
+
+<p>The number of elements is a constant integer value larger than 0; elementtype
+ may be any integer or floating point type, or a pointer to these types.
+ Vectors of size zero are not allowed. </p>
+
+<h5>Examples:</h5>
+<table class="layout">
+ <tr class="layout">
+ <td class="left"><tt><4 x i32></tt></td>
+ <td class="left">Vector of 4 32-bit integer values.</td>
+ </tr>
+ <tr class="layout">
+ <td class="left"><tt><8 x float></tt></td>
+ <td class="left">Vector of 8 32-bit floating-point values.</td>
+ </tr>
+ <tr class="layout">
+ <td class="left"><tt><2 x i64></tt></td>
+ <td class="left">Vector of 2 64-bit integer values.</td>
+ </tr>
+ <tr class="layout">
+ <td class="left"><tt><4 x i64*></tt></td>
+ <td class="left">Vector of 4 pointers to 64-bit integer values.</td>
+ </tr>
+</table>
+
+</div>
+
+</div>
+
+</div>
+
+<!-- *********************************************************************** -->
+<h2><a name="constants">Constants</a></h2>
+<!-- *********************************************************************** -->
+
+<div>
+
+<p>LLVM has several different basic types of constants. This section describes
+ them all and their syntax.</p>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="simpleconstants">Simple Constants</a>
+</h3>
+
+<div>
+
+<dl>
+ <dt><b>Boolean constants</b></dt>
+ <dd>The two strings '<tt>true</tt>' and '<tt>false</tt>' are both valid
+ constants of the <tt><a href="#t_integer">i1</a></tt> type.</dd>
+
+ <dt><b>Integer constants</b></dt>
+ <dd>Standard integers (such as '4') are constants of
+ the <a href="#t_integer">integer</a> type. Negative numbers may be used
+ with integer types.</dd>
+
+ <dt><b>Floating point constants</b></dt>
+ <dd>Floating point constants use standard decimal notation (e.g. 123.421),
+ exponential notation (e.g. 1.23421e+2), or a more precise hexadecimal
+ notation (see below). The assembler requires the exact decimal value of a
+ floating-point constant. For example, the assembler accepts 1.25 but
+ rejects 1.3 because 1.3 is a repeating decimal in binary. Floating point
+ constants must have a <a href="#t_floating">floating point</a> type. </dd>
+
+ <dt><b>Null pointer constants</b></dt>
+ <dd>The identifier '<tt>null</tt>' is recognized as a null pointer constant
+ and must be of <a href="#t_pointer">pointer type</a>.</dd>
+</dl>
+
+<p>The one non-intuitive notation for constants is the hexadecimal form of
+ floating point constants. For example, the form '<tt>double
+ 0x432ff973cafa8000</tt>' is equivalent to (but harder to read than)
+ '<tt>double 4.5e+15</tt>'. The only time hexadecimal floating point
+ constants are required (and the only time that they are generated by the
+ disassembler) is when a floating point constant must be emitted but it cannot
+ be represented as a decimal floating point number in a reasonable number of
+ digits. For example, NaN's, infinities, and other special values are
+ represented in their IEEE hexadecimal format so that assembly and disassembly
+ do not cause any bits to change in the constants.</p>
+
+<p>When using the hexadecimal form, constants of types half, float, and double are
+ represented using the 16-digit form shown above (which matches the IEEE754
+ representation for double); half and float values must, however, be exactly
+ representable as IEE754 half and single precision, respectively.
+ Hexadecimal format is always used
+ for long double, and there are three forms of long double. The 80-bit format
+ used by x86 is represented as <tt>0xK</tt> followed by 20 hexadecimal digits.
+ The 128-bit format used by PowerPC (two adjacent doubles) is represented
+ by <tt>0xM</tt> followed by 32 hexadecimal digits. The IEEE 128-bit format
+ is represented by <tt>0xL</tt> followed by 32 hexadecimal digits; no
+ currently supported target uses this format. Long doubles will only work if
+ they match the long double format on your target. The IEEE 16-bit format
+ (half precision) is represented by <tt>0xH</tt> followed by 4 hexadecimal
+ digits. All hexadecimal formats are big-endian (sign bit at the left).</p>
+
+<p>There are no constants of type x86mmx.</p>
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+<a name="aggregateconstants"></a> <!-- old anchor -->
+<a name="complexconstants">Complex Constants</a>
+</h3>
+
+<div>
+
+<p>Complex constants are a (potentially recursive) combination of simple
+ constants and smaller complex constants.</p>
+
+<dl>
+ <dt><b>Structure constants</b></dt>
+ <dd>Structure constants are represented with notation similar to structure
+ type definitions (a comma separated list of elements, surrounded by braces
+ (<tt>{}</tt>)). For example: "<tt>{ i32 4, float 17.0, i32* @G }</tt>",
+ where "<tt>@G</tt>" is declared as "<tt>@G = external global i32</tt>".
+ Structure constants must have <a href="#t_struct">structure type</a>, and
+ the number and types of elements must match those specified by the
+ type.</dd>
+
+ <dt><b>Array constants</b></dt>
+ <dd>Array constants are represented with notation similar to array type
+ definitions (a comma separated list of elements, surrounded by square
+ brackets (<tt>[]</tt>)). For example: "<tt>[ i32 42, i32 11, i32 74
+ ]</tt>". Array constants must have <a href="#t_array">array type</a>, and
+ the number and types of elements must match those specified by the
+ type.</dd>
+
+ <dt><b>Vector constants</b></dt>
+ <dd>Vector constants are represented with notation similar to vector type
+ definitions (a comma separated list of elements, surrounded by
+ less-than/greater-than's (<tt><></tt>)). For example: "<tt>< i32
+ 42, i32 11, i32 74, i32 100 ></tt>". Vector constants must
+ have <a href="#t_vector">vector type</a>, and the number and types of
+ elements must match those specified by the type.</dd>
+
+ <dt><b>Zero initialization</b></dt>
+ <dd>The string '<tt>zeroinitializer</tt>' can be used to zero initialize a
+ value to zero of <em>any</em> type, including scalar and
+ <a href="#t_aggregate">aggregate</a> types.
+ This is often used to avoid having to print large zero initializers
+ (e.g. for large arrays) and is always exactly equivalent to using explicit
+ zero initializers.</dd>
+
+ <dt><b>Metadata node</b></dt>
+ <dd>A metadata node is a structure-like constant with
+ <a href="#t_metadata">metadata type</a>. For example: "<tt>metadata !{
+ i32 0, metadata !"test" }</tt>". Unlike other constants that are meant to
+ be interpreted as part of the instruction stream, metadata is a place to
+ attach additional information such as debug info.</dd>
+</dl>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="globalconstants">Global Variable and Function Addresses</a>
+</h3>
+
+<div>
+
+<p>The addresses of <a href="#globalvars">global variables</a>
+ and <a href="#functionstructure">functions</a> are always implicitly valid
+ (link-time) constants. These constants are explicitly referenced when
+ the <a href="#identifiers">identifier for the global</a> is used and always
+ have <a href="#t_pointer">pointer</a> type. For example, the following is a
+ legal LLVM file:</p>
+
+<pre class="doc_code">
+ at X = global i32 17
+ at Y = global i32 42
+ at Z = global [2 x i32*] [ i32* @X, i32* @Y ]
+</pre>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="undefvalues">Undefined Values</a>
+</h3>
+
+<div>
+
+<p>The string '<tt>undef</tt>' can be used anywhere a constant is expected, and
+ indicates that the user of the value may receive an unspecified bit-pattern.
+ Undefined values may be of any type (other than '<tt>label</tt>'
+ or '<tt>void</tt>') and be used anywhere a constant is permitted.</p>
+
+<p>Undefined values are useful because they indicate to the compiler that the
+ program is well defined no matter what value is used. This gives the
+ compiler more freedom to optimize. Here are some examples of (potentially
+ surprising) transformations that are valid (in pseudo IR):</p>
+
+
+<pre class="doc_code">
+ %A = add %X, undef
+ %B = sub %X, undef
+ %C = xor %X, undef
+Safe:
+ %A = undef
+ %B = undef
+ %C = undef
+</pre>
+
+<p>This is safe because all of the output bits are affected by the undef bits.
+ Any output bit can have a zero or one depending on the input bits.</p>
+
+<pre class="doc_code">
+ %A = or %X, undef
+ %B = and %X, undef
+Safe:
+ %A = -1
+ %B = 0
+Unsafe:
+ %A = undef
+ %B = undef
+</pre>
+
+<p>These logical operations have bits that are not always affected by the input.
+ For example, if <tt>%X</tt> has a zero bit, then the output of the
+ '<tt>and</tt>' operation will always be a zero for that bit, no matter what
+ the corresponding bit from the '<tt>undef</tt>' is. As such, it is unsafe to
+ optimize or assume that the result of the '<tt>and</tt>' is '<tt>undef</tt>'.
+ However, it is safe to assume that all bits of the '<tt>undef</tt>' could be
+ 0, and optimize the '<tt>and</tt>' to 0. Likewise, it is safe to assume that
+ all the bits of the '<tt>undef</tt>' operand to the '<tt>or</tt>' could be
+ set, allowing the '<tt>or</tt>' to be folded to -1.</p>
+
+<pre class="doc_code">
+ %A = select undef, %X, %Y
+ %B = select undef, 42, %Y
+ %C = select %X, %Y, undef
+Safe:
+ %A = %X (or %Y)
+ %B = 42 (or %Y)
+ %C = %Y
+Unsafe:
+ %A = undef
+ %B = undef
+ %C = undef
+</pre>
+
+<p>This set of examples shows that undefined '<tt>select</tt>' (and conditional
+ branch) conditions can go <em>either way</em>, but they have to come from one
+ of the two operands. In the <tt>%A</tt> example, if <tt>%X</tt> and
+ <tt>%Y</tt> were both known to have a clear low bit, then <tt>%A</tt> would
+ have to have a cleared low bit. However, in the <tt>%C</tt> example, the
+ optimizer is allowed to assume that the '<tt>undef</tt>' operand could be the
+ same as <tt>%Y</tt>, allowing the whole '<tt>select</tt>' to be
+ eliminated.</p>
+
+<pre class="doc_code">
+ %A = xor undef, undef
+
+ %B = undef
+ %C = xor %B, %B
+
+ %D = undef
+ %E = icmp lt %D, 4
+ %F = icmp gte %D, 4
+
+Safe:
+ %A = undef
+ %B = undef
+ %C = undef
+ %D = undef
+ %E = undef
+ %F = undef
+</pre>
+
+<p>This example points out that two '<tt>undef</tt>' operands are not
+ necessarily the same. This can be surprising to people (and also matches C
+ semantics) where they assume that "<tt>X^X</tt>" is always zero, even
+ if <tt>X</tt> is undefined. This isn't true for a number of reasons, but the
+ short answer is that an '<tt>undef</tt>' "variable" can arbitrarily change
+ its value over its "live range". This is true because the variable doesn't
+ actually <em>have a live range</em>. Instead, the value is logically read
+ from arbitrary registers that happen to be around when needed, so the value
+ is not necessarily consistent over time. In fact, <tt>%A</tt> and <tt>%C</tt>
+ need to have the same semantics or the core LLVM "replace all uses with"
+ concept would not hold.</p>
+
+<pre class="doc_code">
+ %A = fdiv undef, %X
+ %B = fdiv %X, undef
+Safe:
+ %A = undef
+b: unreachable
+</pre>
+
+<p>These examples show the crucial difference between an <em>undefined
+ value</em> and <em>undefined behavior</em>. An undefined value (like
+ '<tt>undef</tt>') is allowed to have an arbitrary bit-pattern. This means that
+ the <tt>%A</tt> operation can be constant folded to '<tt>undef</tt>', because
+ the '<tt>undef</tt>' could be an SNaN, and <tt>fdiv</tt> is not (currently)
+ defined on SNaN's. However, in the second example, we can make a more
+ aggressive assumption: because the <tt>undef</tt> is allowed to be an
+ arbitrary value, we are allowed to assume that it could be zero. Since a
+ divide by zero has <em>undefined behavior</em>, we are allowed to assume that
+ the operation does not execute at all. This allows us to delete the divide and
+ all code after it. Because the undefined operation "can't happen", the
+ optimizer can assume that it occurs in dead code.</p>
+
+<pre class="doc_code">
+a: store undef -> %X
+b: store %X -> undef
+Safe:
+a: <deleted>
+b: unreachable
+</pre>
+
+<p>These examples reiterate the <tt>fdiv</tt> example: a store <em>of</em> an
+ undefined value can be assumed to not have any effect; we can assume that the
+ value is overwritten with bits that happen to match what was already there.
+ However, a store <em>to</em> an undefined location could clobber arbitrary
+ memory, therefore, it has undefined behavior.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="poisonvalues">Poison Values</a>
+</h3>
+
+<div>
+
+<p>Poison values are similar to <a href="#undefvalues">undef values</a>, however
+ they also represent the fact that an instruction or constant expression which
+ cannot evoke side effects has nevertheless detected a condition which results
+ in undefined behavior.</p>
+
+<p>There is currently no way of representing a poison value in the IR; they
+ only exist when produced by operations such as
+ <a href="#i_add"><tt>add</tt></a> with the <tt>nsw</tt> flag.</p>
+
+<p>Poison value behavior is defined in terms of value <i>dependence</i>:</p>
+
+<ul>
+<li>Values other than <a href="#i_phi"><tt>phi</tt></a> nodes depend on
+ their operands.</li>
+
+<li><a href="#i_phi"><tt>Phi</tt></a> nodes depend on the operand corresponding
+ to their dynamic predecessor basic block.</li>
+
+<li>Function arguments depend on the corresponding actual argument values in
+ the dynamic callers of their functions.</li>
+
+<li><a href="#i_call"><tt>Call</tt></a> instructions depend on the
+ <a href="#i_ret"><tt>ret</tt></a> instructions that dynamically transfer
+ control back to them.</li>
+
+<li><a href="#i_invoke"><tt>Invoke</tt></a> instructions depend on the
+ <a href="#i_ret"><tt>ret</tt></a>, <a href="#i_resume"><tt>resume</tt></a>,
+ or exception-throwing call instructions that dynamically transfer control
+ back to them.</li>
+
+<li>Non-volatile loads and stores depend on the most recent stores to all of the
+ referenced memory addresses, following the order in the IR
+ (including loads and stores implied by intrinsics such as
+ <a href="#int_memcpy"><tt>@llvm.memcpy</tt></a>.)</li>
+
+<!-- TODO: In the case of multiple threads, this only applies if the store
+ "happens-before" the load or store. -->
+
+<!-- TODO: floating-point exception state -->
+
+<li>An instruction with externally visible side effects depends on the most
+ recent preceding instruction with externally visible side effects, following
+ the order in the IR. (This includes
+ <a href="#volatile">volatile operations</a>.)</li>
+
+<li>An instruction <i>control-depends</i> on a
+ <a href="#terminators">terminator instruction</a>
+ if the terminator instruction has multiple successors and the instruction
+ is always executed when control transfers to one of the successors, and
+ may not be executed when control is transferred to another.</li>
+
+<li>Additionally, an instruction also <i>control-depends</i> on a terminator
+ instruction if the set of instructions it otherwise depends on would be
+ different if the terminator had transferred control to a different
+ successor.</li>
+
+<li>Dependence is transitive.</li>
+
+</ul>
+
+<p>Poison Values have the same behavior as <a href="#undefvalues">undef values</a>,
+ with the additional affect that any instruction which has a <i>dependence</i>
+ on a poison value has undefined behavior.</p>
+
+<p>Here are some examples:</p>
+
+<pre class="doc_code">
+entry:
+ %poison = sub nuw i32 0, 1 ; Results in a poison value.
+ %still_poison = and i32 %poison, 0 ; 0, but also poison.
+ %poison_yet_again = getelementptr i32* @h, i32 %still_poison
+ store i32 0, i32* %poison_yet_again ; memory at @h[0] is poisoned
+
+ store i32 %poison, i32* @g ; Poison value stored to memory.
+ %poison2 = load i32* @g ; Poison value loaded back from memory.
+
+ store volatile i32 %poison, i32* @g ; External observation; undefined behavior.
+
+ %narrowaddr = bitcast i32* @g to i16*
+ %wideaddr = bitcast i32* @g to i64*
+ %poison3 = load i16* %narrowaddr ; Returns a poison value.
+ %poison4 = load i64* %wideaddr ; Returns a poison value.
+
+ %cmp = icmp slt i32 %poison, 0 ; Returns a poison value.
+ br i1 %cmp, label %true, label %end ; Branch to either destination.
+
+true:
+ store volatile i32 0, i32* @g ; This is control-dependent on %cmp, so
+ ; it has undefined behavior.
+ br label %end
+
+end:
+ %p = phi i32 [ 0, %entry ], [ 1, %true ]
+ ; Both edges into this PHI are
+ ; control-dependent on %cmp, so this
+ ; always results in a poison value.
+
+ store volatile i32 0, i32* @g ; This would depend on the store in %true
+ ; if %cmp is true, or the store in %entry
+ ; otherwise, so this is undefined behavior.
+
+ br i1 %cmp, label %second_true, label %second_end
+ ; The same branch again, but this time the
+ ; true block doesn't have side effects.
+
+second_true:
+ ; No side effects!
+ ret void
+
+second_end:
+ store volatile i32 0, i32* @g ; This time, the instruction always depends
+ ; on the store in %end. Also, it is
+ ; control-equivalent to %end, so this is
+ ; well-defined (ignoring earlier undefined
+ ; behavior in this example).
+</pre>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="blockaddress">Addresses of Basic Blocks</a>
+</h3>
+
+<div>
+
+<p><b><tt>blockaddress(@function, %block)</tt></b></p>
+
+<p>The '<tt>blockaddress</tt>' constant computes the address of the specified
+ basic block in the specified function, and always has an i8* type. Taking
+ the address of the entry block is illegal.</p>
+
+<p>This value only has defined behavior when used as an operand to the
+ '<a href="#i_indirectbr"><tt>indirectbr</tt></a>' instruction, or for
+ comparisons against null. Pointer equality tests between labels addresses
+ results in undefined behavior — though, again, comparison against null
+ is ok, and no label is equal to the null pointer. This may be passed around
+ as an opaque pointer sized value as long as the bits are not inspected. This
+ allows <tt>ptrtoint</tt> and arithmetic to be performed on these values so
+ long as the original value is reconstituted before the <tt>indirectbr</tt>
+ instruction.</p>
+
+<p>Finally, some targets may provide defined semantics when using the value as
+ the operand to an inline assembly, but that is target specific.</p>
+
+</div>
+
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="constantexprs">Constant Expressions</a>
+</h3>
+
+<div>
+
+<p>Constant expressions are used to allow expressions involving other constants
+ to be used as constants. Constant expressions may be of
+ any <a href="#t_firstclass">first class</a> type and may involve any LLVM
+ operation that does not have side effects (e.g. load and call are not
+ supported). The following is the syntax for constant expressions:</p>
+
+<dl>
+ <dt><b><tt>trunc (CST to TYPE)</tt></b></dt>
+ <dd>Truncate a constant to another type. The bit size of CST must be larger
+ than the bit size of TYPE. Both types must be integers.</dd>
+
+ <dt><b><tt>zext (CST to TYPE)</tt></b></dt>
+ <dd>Zero extend a constant to another type. The bit size of CST must be
+ smaller than the bit size of TYPE. Both types must be integers.</dd>
+
+ <dt><b><tt>sext (CST to TYPE)</tt></b></dt>
+ <dd>Sign extend a constant to another type. The bit size of CST must be
+ smaller than the bit size of TYPE. Both types must be integers.</dd>
+
+ <dt><b><tt>fptrunc (CST to TYPE)</tt></b></dt>
+ <dd>Truncate a floating point constant to another floating point type. The
+ size of CST must be larger than the size of TYPE. Both types must be
+ floating point.</dd>
+
+ <dt><b><tt>fpext (CST to TYPE)</tt></b></dt>
+ <dd>Floating point extend a constant to another type. The size of CST must be
+ smaller or equal to the size of TYPE. Both types must be floating
+ point.</dd>
+
+ <dt><b><tt>fptoui (CST to TYPE)</tt></b></dt>
+ <dd>Convert a floating point constant to the corresponding unsigned integer
+ constant. TYPE must be a scalar or vector integer type. CST must be of
+ scalar or vector floating point type. Both CST and TYPE must be scalars,
+ or vectors of the same number of elements. If the value won't fit in the
+ integer type, the results are undefined.</dd>
+
+ <dt><b><tt>fptosi (CST to TYPE)</tt></b></dt>
+ <dd>Convert a floating point constant to the corresponding signed integer
+ constant. TYPE must be a scalar or vector integer type. CST must be of
+ scalar or vector floating point type. Both CST and TYPE must be scalars,
+ or vectors of the same number of elements. If the value won't fit in the
+ integer type, the results are undefined.</dd>
+
+ <dt><b><tt>uitofp (CST to TYPE)</tt></b></dt>
+ <dd>Convert an unsigned integer constant to the corresponding floating point
+ constant. TYPE must be a scalar or vector floating point type. CST must be
+ of scalar or vector integer type. Both CST and TYPE must be scalars, or
+ vectors of the same number of elements. If the value won't fit in the
+ floating point type, the results are undefined.</dd>
+
+ <dt><b><tt>sitofp (CST to TYPE)</tt></b></dt>
+ <dd>Convert a signed integer constant to the corresponding floating point
+ constant. TYPE must be a scalar or vector floating point type. CST must be
+ of scalar or vector integer type. Both CST and TYPE must be scalars, or
+ vectors of the same number of elements. If the value won't fit in the
+ floating point type, the results are undefined.</dd>
+
+ <dt><b><tt>ptrtoint (CST to TYPE)</tt></b></dt>
+ <dd>Convert a pointer typed constant to the corresponding integer constant
+ <tt>TYPE</tt> must be an integer type. <tt>CST</tt> must be of pointer
+ type. The <tt>CST</tt> value is zero extended, truncated, or unchanged to
+ make it fit in <tt>TYPE</tt>.</dd>
+
+ <dt><b><tt>inttoptr (CST to TYPE)</tt></b></dt>
+ <dd>Convert an integer constant to a pointer constant. TYPE must be a pointer
+ type. CST must be of integer type. The CST value is zero extended,
+ truncated, or unchanged to make it fit in a pointer size. This one is
+ <i>really</i> dangerous!</dd>
+
+ <dt><b><tt>bitcast (CST to TYPE)</tt></b></dt>
+ <dd>Convert a constant, CST, to another TYPE. The constraints of the operands
+ are the same as those for the <a href="#i_bitcast">bitcast
+ instruction</a>.</dd>
+
+ <dt><b><tt>getelementptr (CSTPTR, IDX0, IDX1, ...)</tt></b></dt>
+ <dt><b><tt>getelementptr inbounds (CSTPTR, IDX0, IDX1, ...)</tt></b></dt>
+ <dd>Perform the <a href="#i_getelementptr">getelementptr operation</a> on
+ constants. As with the <a href="#i_getelementptr">getelementptr</a>
+ instruction, the index list may have zero or more indexes, which are
+ required to make sense for the type of "CSTPTR".</dd>
+
+ <dt><b><tt>select (COND, VAL1, VAL2)</tt></b></dt>
+ <dd>Perform the <a href="#i_select">select operation</a> on constants.</dd>
+
+ <dt><b><tt>icmp COND (VAL1, VAL2)</tt></b></dt>
+ <dd>Performs the <a href="#i_icmp">icmp operation</a> on constants.</dd>
+
+ <dt><b><tt>fcmp COND (VAL1, VAL2)</tt></b></dt>
+ <dd>Performs the <a href="#i_fcmp">fcmp operation</a> on constants.</dd>
+
+ <dt><b><tt>extractelement (VAL, IDX)</tt></b></dt>
+ <dd>Perform the <a href="#i_extractelement">extractelement operation</a> on
+ constants.</dd>
+
+ <dt><b><tt>insertelement (VAL, ELT, IDX)</tt></b></dt>
+ <dd>Perform the <a href="#i_insertelement">insertelement operation</a> on
+ constants.</dd>
+
+ <dt><b><tt>shufflevector (VEC1, VEC2, IDXMASK)</tt></b></dt>
+ <dd>Perform the <a href="#i_shufflevector">shufflevector operation</a> on
+ constants.</dd>
+
+ <dt><b><tt>extractvalue (VAL, IDX0, IDX1, ...)</tt></b></dt>
+ <dd>Perform the <a href="#i_extractvalue">extractvalue operation</a> on
+ constants. The index list is interpreted in a similar manner as indices in
+ a '<a href="#i_getelementptr">getelementptr</a>' operation. At least one
+ index value must be specified.</dd>
+
+ <dt><b><tt>insertvalue (VAL, ELT, IDX0, IDX1, ...)</tt></b></dt>
+ <dd>Perform the <a href="#i_insertvalue">insertvalue operation</a> on
+ constants. The index list is interpreted in a similar manner as indices in
+ a '<a href="#i_getelementptr">getelementptr</a>' operation. At least one
+ index value must be specified.</dd>
+
+ <dt><b><tt>OPCODE (LHS, RHS)</tt></b></dt>
+ <dd>Perform the specified operation of the LHS and RHS constants. OPCODE may
+ be any of the <a href="#binaryops">binary</a>
+ or <a href="#bitwiseops">bitwise binary</a> operations. The constraints
+ on operands are the same as those for the corresponding instruction
+ (e.g. no bitwise operations on floating point values are allowed).</dd>
+</dl>
+
+</div>
+
+</div>
+
+<!-- *********************************************************************** -->
+<h2><a name="othervalues">Other Values</a></h2>
+<!-- *********************************************************************** -->
+<div>
+<!-- ======================================================================= -->
+<h3>
+<a name="inlineasm">Inline Assembler Expressions</a>
+</h3>
+
+<div>
+
+<p>LLVM supports inline assembler expressions (as opposed
+ to <a href="#moduleasm">Module-Level Inline Assembly</a>) through the use of
+ a special value. This value represents the inline assembler as a string
+ (containing the instructions to emit), a list of operand constraints (stored
+ as a string), a flag that indicates whether or not the inline asm
+ expression has side effects, and a flag indicating whether the function
+ containing the asm needs to align its stack conservatively. An example
+ inline assembler expression is:</p>
+
+<pre class="doc_code">
+i32 (i32) asm "bswap $0", "=r,r"
+</pre>
+
+<p>Inline assembler expressions may <b>only</b> be used as the callee operand of
+ a <a href="#i_call"><tt>call</tt></a> or an
+ <a href="#i_invoke"><tt>invoke</tt></a> instruction.
+ Thus, typically we have:</p>
+
+<pre class="doc_code">
+%X = call i32 asm "<a href="#int_bswap">bswap</a> $0", "=r,r"(i32 %Y)
+</pre>
+
+<p>Inline asms with side effects not visible in the constraint list must be
+ marked as having side effects. This is done through the use of the
+ '<tt>sideeffect</tt>' keyword, like so:</p>
+
+<pre class="doc_code">
+call void asm sideeffect "eieio", ""()
+</pre>
+
+<p>In some cases inline asms will contain code that will not work unless the
+ stack is aligned in some way, such as calls or SSE instructions on x86,
+ yet will not contain code that does that alignment within the asm.
+ The compiler should make conservative assumptions about what the asm might
+ contain and should generate its usual stack alignment code in the prologue
+ if the '<tt>alignstack</tt>' keyword is present:</p>
+
+<pre class="doc_code">
+call void asm alignstack "eieio", ""()
+</pre>
+
+<p>Inline asms also support using non-standard assembly dialects. The assumed
+ dialect is ATT. When the '<tt>inteldialect</tt>' keyword is present, the
+ inline asm is using the Intel dialect. Currently, ATT and Intel are the
+ only supported dialects. An example is:</p>
+
+<pre class="doc_code">
+call void asm inteldialect "eieio", ""()
+</pre>
+
+<p>If multiple keywords appear the '<tt>sideeffect</tt>' keyword must come
+ first, the '<tt>alignstack</tt>' keyword second and the
+ '<tt>inteldialect</tt>' keyword last.</p>
+
+<!--
+<p>TODO: The format of the asm and constraints string still need to be
+ documented here. Constraints on what can be done (e.g. duplication, moving,
+ etc need to be documented). This is probably best done by reference to
+ another document that covers inline asm from a holistic perspective.</p>
+ -->
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="inlineasm_md">Inline Asm Metadata</a>
+</h4>
+
+<div>
+
+<p>The call instructions that wrap inline asm nodes may have a
+ "<tt>!srcloc</tt>" MDNode attached to it that contains a list of constant
+ integers. If present, the code generator will use the integer as the
+ location cookie value when report errors through the <tt>LLVMContext</tt>
+ error reporting mechanisms. This allows a front-end to correlate backend
+ errors that occur with inline asm back to the source code that produced it.
+ For example:</p>
+
+<pre class="doc_code">
+call void asm sideeffect "something bad", ""()<b>, !srcloc !42</b>
+...
+!42 = !{ i32 1234567 }
+</pre>
+
+<p>It is up to the front-end to make sense of the magic numbers it places in the
+ IR. If the MDNode contains multiple constants, the code generator will use
+ the one that corresponds to the line of the asm that the error occurs on.</p>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="metadata">Metadata Nodes and Metadata Strings</a>
+</h3>
+
+<div>
+
+<p>LLVM IR allows metadata to be attached to instructions in the program that
+ can convey extra information about the code to the optimizers and code
+ generator. One example application of metadata is source-level debug
+ information. There are two metadata primitives: strings and nodes. All
+ metadata has the <tt>metadata</tt> type and is identified in syntax by a
+ preceding exclamation point ('<tt>!</tt>').</p>
+
+<p>A metadata string is a string surrounded by double quotes. It can contain
+ any character by escaping non-printable characters with "<tt>\xx</tt>" where
+ "<tt>xx</tt>" is the two digit hex code. For example:
+ "<tt>!"test\00"</tt>".</p>
+
+<p>Metadata nodes are represented with notation similar to structure constants
+ (a comma separated list of elements, surrounded by braces and preceded by an
+ exclamation point). Metadata nodes can have any values as their operand. For
+ example:</p>
+
+<div class="doc_code">
+<pre>
+!{ metadata !"test\00", i32 10}
+</pre>
+</div>
+
+<p>A <a href="#namedmetadatastructure">named metadata</a> is a collection of
+ metadata nodes, which can be looked up in the module symbol table. For
+ example:</p>
+
+<div class="doc_code">
+<pre>
+!foo = metadata !{!4, !3}
+</pre>
+</div>
+
+<p>Metadata can be used as function arguments. Here <tt>llvm.dbg.value</tt>
+ function is using two metadata arguments:</p>
+
+<div class="doc_code">
+<pre>
+call void @llvm.dbg.value(metadata !24, i64 0, metadata !25)
+</pre>
+</div>
+
+<p>Metadata can be attached with an instruction. Here metadata <tt>!21</tt> is
+ attached to the <tt>add</tt> instruction using the <tt>!dbg</tt>
+ identifier:</p>
+
+<div class="doc_code">
+<pre>
+%indvar.next = add i64 %indvar, 1, !dbg !21
+</pre>
+</div>
+
+<p>More information about specific metadata nodes recognized by the optimizers
+ and code generator is found below.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="tbaa">'<tt>tbaa</tt>' Metadata</a>
+</h4>
+
+<div>
+
+<p>In LLVM IR, memory does not have types, so LLVM's own type system is not
+ suitable for doing TBAA. Instead, metadata is added to the IR to describe
+ a type system of a higher level language. This can be used to implement
+ typical C/C++ TBAA, but it can also be used to implement custom alias
+ analysis behavior for other languages.</p>
+
+<p>The current metadata format is very simple. TBAA metadata nodes have up to
+ three fields, e.g.:</p>
+
+<div class="doc_code">
+<pre>
+!0 = metadata !{ metadata !"an example type tree" }
+!1 = metadata !{ metadata !"int", metadata !0 }
+!2 = metadata !{ metadata !"float", metadata !0 }
+!3 = metadata !{ metadata !"const float", metadata !2, i64 1 }
+</pre>
+</div>
+
+<p>The first field is an identity field. It can be any value, usually
+ a metadata string, which uniquely identifies the type. The most important
+ name in the tree is the name of the root node. Two trees with
+ different root node names are entirely disjoint, even if they
+ have leaves with common names.</p>
+
+<p>The second field identifies the type's parent node in the tree, or
+ is null or omitted for a root node. A type is considered to alias
+ all of its descendants and all of its ancestors in the tree. Also,
+ a type is considered to alias all types in other trees, so that
+ bitcode produced from multiple front-ends is handled conservatively.</p>
+
+<p>If the third field is present, it's an integer which if equal to 1
+ indicates that the type is "constant" (meaning
+ <tt>pointsToConstantMemory</tt> should return true; see
+ <a href="AliasAnalysis.html#OtherItfs">other useful
+ <tt>AliasAnalysis</tt> methods</a>).</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="tbaa.struct">'<tt>tbaa.struct</tt>' Metadata</a>
+</h4>
+
+<div>
+
+<p>The <a href="#int_memcpy"><tt>llvm.memcpy</tt></a> is often used to implement
+aggregate assignment operations in C and similar languages, however it is
+defined to copy a contiguous region of memory, which is more than strictly
+necessary for aggregate types which contain holes due to padding. Also, it
+doesn't contain any TBAA information about the fields of the aggregate.</p>
+
+<p><tt>!tbaa.struct</tt> metadata can describe which memory subregions in a memcpy
+are padding and what the TBAA tags of the struct are.</p>
+
+<p>The current metadata format is very simple. <tt>!tbaa.struct</tt> metadata nodes
+ are a list of operands which are in conceptual groups of three. For each
+ group of three, the first operand gives the byte offset of a field in bytes,
+ the second gives its size in bytes, and the third gives its
+ tbaa tag. e.g.:</p>
+
+<div class="doc_code">
+<pre>
+!4 = metadata !{ i64 0, i64 4, metadata !1, i64 8, i64 4, metadata !2 }
+</pre>
+</div>
+
+<p>This describes a struct with two fields. The first is at offset 0 bytes
+ with size 4 bytes, and has tbaa tag !1. The second is at offset 8 bytes
+ and has size 4 bytes and has tbaa tag !2.</p>
+
+<p>Note that the fields need not be contiguous. In this example, there is a
+ 4 byte gap between the two fields. This gap represents padding which
+ does not carry useful data and need not be preserved.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="fpmath">'<tt>fpmath</tt>' Metadata</a>
+</h4>
+
+<div>
+
+<p><tt>fpmath</tt> metadata may be attached to any instruction of floating point
+ type. It can be used to express the maximum acceptable error in the result of
+ that instruction, in ULPs, thus potentially allowing the compiler to use a
+ more efficient but less accurate method of computing it. ULP is defined as
+ follows:</p>
+
+<blockquote>
+
+<p>If <tt>x</tt> is a real number that lies between two finite consecutive
+ floating-point numbers <tt>a</tt> and <tt>b</tt>, without being equal to one
+ of them, then <tt>ulp(x) = |b - a|</tt>, otherwise <tt>ulp(x)</tt> is the
+ distance between the two non-equal finite floating-point numbers nearest
+ <tt>x</tt>. Moreover, <tt>ulp(NaN)</tt> is <tt>NaN</tt>.</p>
+
+</blockquote>
+
+<p>The metadata node shall consist of a single positive floating point number
+ representing the maximum relative error, for example:</p>
+
+<div class="doc_code">
+<pre>
+!0 = metadata !{ float 2.5 } ; maximum acceptable inaccuracy is 2.5 ULPs
+</pre>
+</div>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="range">'<tt>range</tt>' Metadata</a>
+</h4>
+
+<div>
+<p><tt>range</tt> metadata may be attached only to loads of integer types. It
+ expresses the possible ranges the loaded value is in. The ranges are
+ represented with a flattened list of integers. The loaded value is known to
+ be in the union of the ranges defined by each consecutive pair. Each pair
+ has the following properties:</p>
+<ul>
+ <li>The type must match the type loaded by the instruction.</li>
+ <li>The pair <tt>a,b</tt> represents the range <tt>[a,b)</tt>.</li>
+ <li>Both <tt>a</tt> and <tt>b</tt> are constants.</li>
+ <li>The range is allowed to wrap.</li>
+ <li>The range should not represent the full or empty set. That is,
+ <tt>a!=b</tt>. </li>
+</ul>
+<p> In addition, the pairs must be in signed order of the lower bound and
+ they must be non-contiguous.</p>
+
+<p>Examples:</p>
+<div class="doc_code">
+<pre>
+ %a = load i8* %x, align 1, !range !0 ; Can only be 0 or 1
+ %b = load i8* %y, align 1, !range !1 ; Can only be 255 (-1), 0 or 1
+ %c = load i8* %z, align 1, !range !2 ; Can only be 0, 1, 3, 4 or 5
+ %d = load i8* %z, align 1, !range !3 ; Can only be -2, -1, 3, 4 or 5
+...
+!0 = metadata !{ i8 0, i8 2 }
+!1 = metadata !{ i8 255, i8 2 }
+!2 = metadata !{ i8 0, i8 2, i8 3, i8 6 }
+!3 = metadata !{ i8 -2, i8 0, i8 3, i8 6 }
+</pre>
+</div>
+</div>
+</div>
+
+</div>
+
+<!-- *********************************************************************** -->
+<h2>
+ <a name="module_flags">Module Flags Metadata</a>
+</h2>
+<!-- *********************************************************************** -->
+
+<div>
+
+<p>Information about the module as a whole is difficult to convey to LLVM's
+ subsystems. The LLVM IR isn't sufficient to transmit this
+ information. The <tt>llvm.module.flags</tt> named metadata exists in order to
+ facilitate this. These flags are in the form of key / value pairs —
+ much like a dictionary — making it easy for any subsystem who cares
+ about a flag to look it up.</p>
+
+<p>The <tt>llvm.module.flags</tt> metadata contains a list of metadata
+ triplets. Each triplet has the following form:</p>
+
+<ul>
+ <li>The first element is a <i>behavior</i> flag, which specifies the behavior
+ when two (or more) modules are merged together, and it encounters two (or
+ more) metadata with the same ID. The supported behaviors are described
+ below.</li>
+
+ <li>The second element is a metadata string that is a unique ID for the
+ metadata. How each ID is interpreted is documented below.</li>
+
+ <li>The third element is the value of the flag.</li>
+</ul>
+
+<p>When two (or more) modules are merged together, the resulting
+ <tt>llvm.module.flags</tt> metadata is the union of the
+ modules' <tt>llvm.module.flags</tt> metadata. The only exception being a flag
+ with the <i>Override</i> behavior, which may override another flag's value
+ (see below).</p>
+
+<p>The following behaviors are supported:</p>
+
+<table border="1" cellspacing="0" cellpadding="4">
+ <tbody>
+ <tr>
+ <th>Value</th>
+ <th>Behavior</th>
+ </tr>
+ <tr>
+ <td>1</td>
+ <td align="left">
+ <dl>
+ <dt><b>Error</b></dt>
+ <dd>Emits an error if two values disagree. It is an error to have an ID
+ with both an Error and a Warning behavior.</dd>
+ </dl>
+ </td>
+ </tr>
+ <tr>
+ <td>2</td>
+ <td align="left">
+ <dl>
+ <dt><b>Warning</b></dt>
+ <dd>Emits a warning if two values disagree.</dd>
+ </dl>
+ </td>
+ </tr>
+ <tr>
+ <td>3</td>
+ <td align="left">
+ <dl>
+ <dt><b>Require</b></dt>
+ <dd>Emits an error when the specified value is not present or doesn't
+ have the specified value. It is an error for two (or more)
+ <tt>llvm.module.flags</tt> with the same ID to have the Require
+ behavior but different values. There may be multiple Require flags
+ per ID.</dd>
+ </dl>
+ </td>
+ </tr>
+ <tr>
+ <td>4</td>
+ <td align="left">
+ <dl>
+ <dt><b>Override</b></dt>
+ <dd>Uses the specified value if the two values disagree. It is an
+ error for two (or more) <tt>llvm.module.flags</tt> with the same
+ ID to have the Override behavior but different values.</dd>
+ </dl>
+ </td>
+ </tr>
+ </tbody>
+</table>
+
+<p>An example of module flags:</p>
+
+<pre class="doc_code">
+!0 = metadata !{ i32 1, metadata !"foo", i32 1 }
+!1 = metadata !{ i32 4, metadata !"bar", i32 37 }
+!2 = metadata !{ i32 2, metadata !"qux", i32 42 }
+!3 = metadata !{ i32 3, metadata !"qux",
+ metadata !{
+ metadata !"foo", i32 1
+ }
+}
+!llvm.module.flags = !{ !0, !1, !2, !3 }
+</pre>
+
+<ul>
+ <li><p>Metadata <tt>!0</tt> has the ID <tt>!"foo"</tt> and the value '1'. The
+ behavior if two or more <tt>!"foo"</tt> flags are seen is to emit an
+ error if their values are not equal.</p></li>
+
+ <li><p>Metadata <tt>!1</tt> has the ID <tt>!"bar"</tt> and the value '37'. The
+ behavior if two or more <tt>!"bar"</tt> flags are seen is to use the
+ value '37' if their values are not equal.</p></li>
+
+ <li><p>Metadata <tt>!2</tt> has the ID <tt>!"qux"</tt> and the value '42'. The
+ behavior if two or more <tt>!"qux"</tt> flags are seen is to emit a
+ warning if their values are not equal.</p></li>
+
+ <li><p>Metadata <tt>!3</tt> has the ID <tt>!"qux"</tt> and the value:</p>
+
+<pre class="doc_code">
+metadata !{ metadata !"foo", i32 1 }
+</pre>
+
+ <p>The behavior is to emit an error if the <tt>llvm.module.flags</tt> does
+ not contain a flag with the ID <tt>!"foo"</tt> that has the value
+ '1'. If two or more <tt>!"qux"</tt> flags exist, then they must have
+ the same value or an error will be issued.</p></li>
+</ul>
+
+
+<!-- ======================================================================= -->
+<h3>
+<a name="objc_gc_flags">Objective-C Garbage Collection Module Flags Metadata</a>
+</h3>
+
+<div>
+
+<p>On the Mach-O platform, Objective-C stores metadata about garbage collection
+ in a special section called "image info". The metadata consists of a version
+ number and a bitmask specifying what types of garbage collection are
+ supported (if any) by the file. If two or more modules are linked together
+ their garbage collection metadata needs to be merged rather than appended
+ together.</p>
+
+<p>The Objective-C garbage collection module flags metadata consists of the
+ following key-value pairs:</p>
+
+<table border="1" cellspacing="0" cellpadding="4">
+ <col width="30%">
+ <tbody>
+ <tr>
+ <th>Key</th>
+ <th>Value</th>
+ </tr>
+ <tr>
+ <td><tt>Objective-C Version</tt></td>
+ <td align="left"><b>[Required]</b> — The Objective-C ABI
+ version. Valid values are 1 and 2.</td>
+ </tr>
+ <tr>
+ <td><tt>Objective-C Image Info Version</tt></td>
+ <td align="left"><b>[Required]</b> — The version of the image info
+ section. Currently always 0.</td>
+ </tr>
+ <tr>
+ <td><tt>Objective-C Image Info Section</tt></td>
+ <td align="left"><b>[Required]</b> — The section to place the
+ metadata. Valid values are <tt>"__OBJC, __image_info, regular"</tt> for
+ Objective-C ABI version 1, and <tt>"__DATA,__objc_imageinfo, regular,
+ no_dead_strip"</tt> for Objective-C ABI version 2.</td>
+ </tr>
+ <tr>
+ <td><tt>Objective-C Garbage Collection</tt></td>
+ <td align="left"><b>[Required]</b> — Specifies whether garbage
+ collection is supported or not. Valid values are 0, for no garbage
+ collection, and 2, for garbage collection supported.</td>
+ </tr>
+ <tr>
+ <td><tt>Objective-C GC Only</tt></td>
+ <td align="left"><b>[Optional]</b> — Specifies that only garbage
+ collection is supported. If present, its value must be 6. This flag
+ requires that the <tt>Objective-C Garbage Collection</tt> flag have the
+ value 2.</td>
+ </tr>
+ </tbody>
+</table>
+
+<p>Some important flag interactions:</p>
+
+<ul>
+ <li>If a module with <tt>Objective-C Garbage Collection</tt> set to 0 is
+ merged with a module with <tt>Objective-C Garbage Collection</tt> set to
+ 2, then the resulting module has the <tt>Objective-C Garbage
+ Collection</tt> flag set to 0.</li>
+
+ <li>A module with <tt>Objective-C Garbage Collection</tt> set to 0 cannot be
+ merged with a module with <tt>Objective-C GC Only</tt> set to 6.</li>
+</ul>
+
+</div>
+
+</div>
+
+<!-- *********************************************************************** -->
+<h2>
+ <a name="intrinsic_globals">Intrinsic Global Variables</a>
+</h2>
+<!-- *********************************************************************** -->
+<div>
+<p>LLVM has a number of "magic" global variables that contain data that affect
+code generation or other IR semantics. These are documented here. All globals
+of this sort should have a section specified as "<tt>llvm.metadata</tt>". This
+section and all globals that start with "<tt>llvm.</tt>" are reserved for use
+by LLVM.</p>
+
+<!-- ======================================================================= -->
+<h3>
+<a name="intg_used">The '<tt>llvm.used</tt>' Global Variable</a>
+</h3>
+
+<div>
+
+<p>The <tt>@llvm.used</tt> global is an array with i8* element type which has <a
+href="#linkage_appending">appending linkage</a>. This array contains a list of
+pointers to global variables and functions which may optionally have a pointer
+cast formed of bitcast or getelementptr. For example, a legal use of it is:</p>
+
+<div class="doc_code">
+<pre>
+ at X = global i8 4
+ at Y = global i32 123
+
+ at llvm.used = appending global [2 x i8*] [
+ i8* @X,
+ i8* bitcast (i32* @Y to i8*)
+], section "llvm.metadata"
+</pre>
+</div>
+
+<p>If a global variable appears in the <tt>@llvm.used</tt> list, then the
+ compiler, assembler, and linker are required to treat the symbol as if there
+ is a reference to the global that it cannot see. For example, if a variable
+ has internal linkage and no references other than that from
+ the <tt>@llvm.used</tt> list, it cannot be deleted. This is commonly used to
+ represent references from inline asms and other things the compiler cannot
+ "see", and corresponds to "<tt>attribute((used))</tt>" in GNU C.</p>
+
+<p>On some targets, the code generator must emit a directive to the assembler or
+ object file to prevent the assembler and linker from molesting the
+ symbol.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="intg_compiler_used">
+ The '<tt>llvm.compiler.used</tt>' Global Variable
+ </a>
+</h3>
+
+<div>
+
+<p>The <tt>@llvm.compiler.used</tt> directive is the same as the
+ <tt>@llvm.used</tt> directive, except that it only prevents the compiler from
+ touching the symbol. On targets that support it, this allows an intelligent
+ linker to optimize references to the symbol without being impeded as it would
+ be by <tt>@llvm.used</tt>.</p>
+
+<p>This is a rare construct that should only be used in rare circumstances, and
+ should not be exposed to source languages.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+<a name="intg_global_ctors">The '<tt>llvm.global_ctors</tt>' Global Variable</a>
+</h3>
+
+<div>
+
+<div class="doc_code">
+<pre>
+%0 = type { i32, void ()* }
+ at llvm.global_ctors = appending global [1 x %0] [%0 { i32 65535, void ()* @ctor }]
+</pre>
+</div>
+
+<p>The <tt>@llvm.global_ctors</tt> array contains a list of constructor
+ functions and associated priorities. The functions referenced by this array
+ will be called in ascending order of priority (i.e. lowest first) when the
+ module is loaded. The order of functions with the same priority is not
+ defined.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+<a name="intg_global_dtors">The '<tt>llvm.global_dtors</tt>' Global Variable</a>
+</h3>
+
+<div>
+
+<div class="doc_code">
+<pre>
+%0 = type { i32, void ()* }
+ at llvm.global_dtors = appending global [1 x %0] [%0 { i32 65535, void ()* @dtor }]
+</pre>
+</div>
+
+<p>The <tt>@llvm.global_dtors</tt> array contains a list of destructor functions
+ and associated priorities. The functions referenced by this array will be
+ called in descending order of priority (i.e. highest first) when the module
+ is loaded. The order of functions with the same priority is not defined.</p>
+
+</div>
+
+</div>
+
+<!-- *********************************************************************** -->
+<h2><a name="instref">Instruction Reference</a></h2>
+<!-- *********************************************************************** -->
+
+<div>
+
+<p>The LLVM instruction set consists of several different classifications of
+ instructions: <a href="#terminators">terminator
+ instructions</a>, <a href="#binaryops">binary instructions</a>,
+ <a href="#bitwiseops">bitwise binary instructions</a>,
+ <a href="#memoryops">memory instructions</a>, and
+ <a href="#otherops">other instructions</a>.</p>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="terminators">Terminator Instructions</a>
+</h3>
+
+<div>
+
+<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>The terminator instructions are:
+ '<a href="#i_ret"><tt>ret</tt></a>',
+ '<a href="#i_br"><tt>br</tt></a>',
+ '<a href="#i_switch"><tt>switch</tt></a>',
+ '<a href="#i_indirectbr"><tt>indirectbr</tt></a>',
+ '<a href="#i_invoke"><tt>invoke</tt></a>',
+ '<a href="#i_resume"><tt>resume</tt></a>', and
+ '<a href="#i_unreachable"><tt>unreachable</tt></a>'.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_ret">'<tt>ret</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<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 optionally
+ a value) from a function back to the caller.</p>
+
+<p>There are two forms of the '<tt>ret</tt>' instruction: one that returns a
+ value and then causes control flow, and one that just causes control flow to
+ occur.</p>
+
+<h5>Arguments:</h5>
+<p>The '<tt>ret</tt>' instruction optionally accepts a single argument, the
+ return value. The type of the return value must be a
+ '<a href="#t_firstclass">first class</a>' type.</p>
+
+<p>A function is not <a href="#wellformed">well formed</a> if it it has a
+ non-void return type and contains a '<tt>ret</tt>' instruction with no return
+ value or a return value with a type that does not match its type, or if it
+ has a void return type and contains a '<tt>ret</tt>' instruction with a
+ return value.</p>
+
+<h5>Semantics:</h5>
+<p>When the '<tt>ret</tt>' instruction is executed, control flow returns back to
+ the calling function's context. If the caller is a
+ "<a href="#i_call"><tt>call</tt></a>" instruction, execution continues at the
+ instruction after the call. If the caller was an
+ "<a href="#i_invoke"><tt>invoke</tt></a>" instruction, execution continues at
+ the beginning of the "normal" destination block. If the instruction returns
+ a value, that value shall set the call or invoke instruction's return
+ value.</p>
+
+<h5>Example:</h5>
+<pre>
+ ret i32 5 <i>; Return an integer value of 5</i>
+ ret void <i>; Return from a void function</i>
+ ret { i32, i8 } { i32 4, i8 2 } <i>; Return a struct of values 4 and 2</i>
+</pre>
+
+</div>
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_br">'<tt>br</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ br i1 <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>i1</tt>' value and two '<tt>label</tt>' values. The unconditional form
+ of the '<tt>br</tt>' instruction takes a single '<tt>label</tt>' value as a
+ target.</p>
+
+<h5>Semantics:</h5>
+<p>Upon execution of a conditional '<tt>br</tt>' instruction, the '<tt>i1</tt>'
+ argument is evaluated. If the value is <tt>true</tt>, control flows to the
+ '<tt>iftrue</tt>' <tt>label</tt> argument. If "cond" is <tt>false</tt>,
+ control flows to the '<tt>iffalse</tt>' <tt>label</tt> argument.</p>
+
+<h5>Example:</h5>
+<pre>
+Test:
+ %cond = <a href="#i_icmp">icmp</a> eq i32 %a, %b
+ br i1 %cond, label %IfEqual, label %IfUnequal
+IfEqual:
+ <a href="#i_ret">ret</a> i32 1
+IfUnequal:
+ <a href="#i_ret">ret</a> i32 0
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_switch">'<tt>switch</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ switch <intty> <value>, label <defaultdest> [ <intty> <val>, label <dest> ... ]
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>switch</tt>' instruction is used to transfer control flow to one of
+ several different places. It is a generalization of the '<tt>br</tt>'
+ instruction, allowing a branch to occur to one of many possible
+ destinations.</p>
+
+<h5>Arguments:</h5>
+<p>The '<tt>switch</tt>' instruction uses three parameters: an integer
+ comparison value '<tt>value</tt>', a default '<tt>label</tt>' destination,
+ and an array of pairs of comparison value constants and '<tt>label</tt>'s.
+ The table is not allowed to contain duplicate constant entries.</p>
+
+<h5>Semantics:</h5>
+<p>The <tt>switch</tt> instruction specifies a table of values and
+ destinations. When the '<tt>switch</tt>' instruction is executed, this table
+ is searched for the given value. If the value is found, control flow is
+ transferred to the corresponding destination; otherwise, control flow is
+ transferred to the default destination.</p>
+
+<h5>Implementation:</h5>
+<p>Depending on properties of the target machine and the particular
+ <tt>switch</tt> instruction, this instruction may be code generated in
+ different ways. For example, it could be generated as a series of chained
+ conditional branches or with a lookup table.</p>
+
+<h5>Example:</h5>
+<pre>
+ <i>; Emulate a conditional br instruction</i>
+ %Val = <a href="#i_zext">zext</a> i1 %value to i32
+ switch i32 %Val, label %truedest [ i32 0, label %falsedest ]
+
+ <i>; Emulate an unconditional br instruction</i>
+ switch i32 0, label %dest [ ]
+
+ <i>; Implement a jump table:</i>
+ switch i32 %val, label %otherwise [ i32 0, label %onzero
+ i32 1, label %onone
+ i32 2, label %ontwo ]
+</pre>
+
+</div>
+
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_indirectbr">'<tt>indirectbr</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ indirectbr <somety>* <address>, [ label <dest1>, label <dest2>, ... ]
+</pre>
+
+<h5>Overview:</h5>
+
+<p>The '<tt>indirectbr</tt>' instruction implements an indirect branch to a label
+ within the current function, whose address is specified by
+ "<tt>address</tt>". Address must be derived from a <a
+ href="#blockaddress">blockaddress</a> constant.</p>
+
+<h5>Arguments:</h5>
+
+<p>The '<tt>address</tt>' argument is the address of the label to jump to. The
+ rest of the arguments indicate the full set of possible destinations that the
+ address may point to. Blocks are allowed to occur multiple times in the
+ destination list, though this isn't particularly useful.</p>
+
+<p>This destination list is required so that dataflow analysis has an accurate
+ understanding of the CFG.</p>
+
+<h5>Semantics:</h5>
+
+<p>Control transfers to the block specified in the address argument. All
+ possible destination blocks must be listed in the label list, otherwise this
+ instruction has undefined behavior. This implies that jumps to labels
+ defined in other functions have undefined behavior as well.</p>
+
+<h5>Implementation:</h5>
+
+<p>This is typically implemented with a jump through a register.</p>
+
+<h5>Example:</h5>
+<pre>
+ indirectbr i8* %Addr, [ label %bb1, label %bb2, label %bb3 ]
+</pre>
+
+</div>
+
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_invoke">'<tt>invoke</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = invoke [<a href="#callingconv">cconv</a>] [<a href="#paramattrs">ret attrs</a>] <ptr to function ty> <function ptr val>(<function args>) [<a href="#fnattrs">fn attrs</a>]
+ to label <normal label> unwind 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>' label or the '<tt>exception</tt>' label. If the callee
+ function returns with the "<tt><a href="#i_ret">ret</a></tt>" instruction,
+ control flow will return to the "normal" label. If the callee (or any
+ indirect callees) returns via the "<a href="#i_resume"><tt>resume</tt></a>"
+ instruction or other exception handling mechanism, control is interrupted and
+ continued at the dynamically nearest "exception" label.</p>
+
+<p>The '<tt>exception</tt>' label is a
+ <i><a href="ExceptionHandling.html#overview">landing pad</a></i> for the
+ exception. As such, '<tt>exception</tt>' label is required to have the
+ "<a href="#i_landingpad"><tt>landingpad</tt></a>" instruction, which contains
+ the information about the behavior of the program after unwinding
+ happens, as its first non-PHI instruction. The restrictions on the
+ "<tt>landingpad</tt>" instruction's tightly couples it to the
+ "<tt>invoke</tt>" instruction, so that the important information contained
+ within the "<tt>landingpad</tt>" instruction can't be lost through normal
+ code motion.</p>
+
+<h5>Arguments:</h5>
+<p>This instruction requires several arguments:</p>
+
+<ol>
+ <li>The optional "cconv" marker indicates which <a href="#callingconv">calling
+ convention</a> the call should use. If none is specified, the call
+ defaults to using C calling conventions.</li>
+
+ <li>The optional <a href="#paramattrs">Parameter Attributes</a> list for
+ return values. Only '<tt>zeroext</tt>', '<tt>signext</tt>', and
+ '<tt>inreg</tt>' attributes are valid here.</li>
+
+ <li>'<tt>ptr to function ty</tt>': shall be the signature of the pointer to
+ function value being invoked. In most cases, this is a direct function
+ invocation, but indirect <tt>invoke</tt>s are just as possible, branching
+ off an arbitrary pointer to function value.</li>
+
+ <li>'<tt>function ptr val</tt>': An LLVM value containing a pointer to a
+ function to be invoked. </li>
+
+ <li>'<tt>function args</tt>': argument list whose types match the function
+ signature argument types and parameter attributes. All arguments must be
+ of <a href="#t_firstclass">first class</a> type. If the function
+ signature indicates the function accepts a variable number of arguments,
+ the extra arguments can be specified.</li>
+
+ <li>'<tt>normal label</tt>': the label reached when the called function
+ executes a '<tt><a href="#i_ret">ret</a></tt>' instruction. </li>
+
+ <li>'<tt>exception label</tt>': the label reached when a callee returns via
+ the <a href="#i_resume"><tt>resume</tt></a> instruction or other exception
+ handling mechanism.</li>
+
+ <li>The optional <a href="#fnattrs">function attributes</a> list. Only
+ '<tt>noreturn</tt>', '<tt>nounwind</tt>', '<tt>readonly</tt>' and
+ '<tt>readnone</tt>' attributes are valid here.</li>
+</ol>
+
+<h5>Semantics:</h5>
+<p>This instruction is designed to operate as a standard
+ '<tt><a href="#i_call">call</a></tt>' instruction in most regards. The
+ primary difference is that it establishes an association with a label, which
+ is used by the runtime library to unwind the stack.</p>
+
+<p>This instruction is used in languages with destructors to ensure that proper
+ cleanup is performed in the case of either a <tt>longjmp</tt> or a thrown
+ exception. Additionally, this is important for implementation of
+ '<tt>catch</tt>' clauses in high-level languages that support them.</p>
+
+<p>For the purposes of the SSA form, the definition of the value returned by the
+ '<tt>invoke</tt>' instruction is deemed to occur on the edge from the current
+ block to the "normal" label. If the callee unwinds then no return value is
+ available.</p>
+
+<h5>Example:</h5>
+<pre>
+ %retval = invoke i32 @Test(i32 15) to label %Continue
+ unwind label %TestCleanup <i>; {i32}:retval set</i>
+ %retval = invoke <a href="#callingconv">coldcc</a> i32 %Testfnptr(i32 15) to label %Continue
+ unwind label %TestCleanup <i>; {i32}:retval set</i>
+</pre>
+
+</div>
+
+ <!-- _______________________________________________________________________ -->
+
+<h4>
+ <a name="i_resume">'<tt>resume</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ resume <type> <value>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>resume</tt>' instruction is a terminator instruction that has no
+ successors.</p>
+
+<h5>Arguments:</h5>
+<p>The '<tt>resume</tt>' instruction requires one argument, which must have the
+ same type as the result of any '<tt>landingpad</tt>' instruction in the same
+ function.</p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>resume</tt>' instruction resumes propagation of an existing
+ (in-flight) exception whose unwinding was interrupted with
+ a <a href="#i_landingpad"><tt>landingpad</tt></a> instruction.</p>
+
+<h5>Example:</h5>
+<pre>
+ resume { i8*, i32 } %exn
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+
+<h4>
+ <a name="i_unreachable">'<tt>unreachable</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ unreachable
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>unreachable</tt>' instruction has no defined semantics. This
+ instruction is used to inform the optimizer that a particular portion of the
+ code is not reachable. This can be used to indicate that the code after a
+ no-return function cannot be reached, and other facts.</p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>unreachable</tt>' instruction has no defined semantics.</p>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="binaryops">Binary Operations</a>
+</h3>
+
+<div>
+
+<p>Binary operators are used to do most of the computation in a program. They
+ require two operands of the same type, execute an operation on them, and
+ produce a single value. The operands might represent multiple data, as is
+ the case with the <a href="#t_vector">vector</a> data type. The result value
+ has the same type as its operands.</p>
+
+<p>There are several different binary operators:</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_add">'<tt>add</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = add <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+ <result> = add nuw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+ <result> = add nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+ <result> = add nuw nsw <ty> <op1>, <op2> <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 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of
+ integer values. Both arguments must have identical types.</p>
+
+<h5>Semantics:</h5>
+<p>The value produced is the integer sum of the two operands.</p>
+
+<p>If the sum has unsigned overflow, the result returned is the mathematical
+ result modulo 2<sup>n</sup>, where n is the bit width of the result.</p>
+
+<p>Because LLVM integers use a two's complement representation, this instruction
+ is appropriate for both signed and unsigned integers.</p>
+
+<p><tt>nuw</tt> and <tt>nsw</tt> stand for "No Unsigned Wrap"
+ and "No Signed Wrap", respectively. If the <tt>nuw</tt> and/or
+ <tt>nsw</tt> keywords are present, the result value of the <tt>add</tt>
+ is a <a href="#poisonvalues">poison value</a> if unsigned and/or signed overflow,
+ respectively, occurs.</p>
+
+<h5>Example:</h5>
+<pre>
+ <result> = add i32 4, %var <i>; yields {i32}:result = 4 + %var</i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_fadd">'<tt>fadd</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = fadd <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>fadd</tt>' instruction returns the sum of its two operands.</p>
+
+<h5>Arguments:</h5>
+<p>The two arguments to the '<tt>fadd</tt>' instruction must be
+ <a href="#t_floating">floating point</a> or <a href="#t_vector">vector</a> of
+ floating point values. Both arguments must have identical types.</p>
+
+<h5>Semantics:</h5>
+<p>The value produced is the floating point sum of the two operands.</p>
+
+<h5>Example:</h5>
+<pre>
+ <result> = fadd float 4.0, %var <i>; yields {float}:result = 4.0 + %var</i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_sub">'<tt>sub</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = sub <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+ <result> = sub nuw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+ <result> = sub nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+ <result> = sub nuw nsw <ty> <op1>, <op2> <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 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of
+ integer values. Both arguments must have identical types.</p>
+
+<h5>Semantics:</h5>
+<p>The value produced is the integer difference of the two operands.</p>
+
+<p>If the difference has unsigned overflow, the result returned is the
+ mathematical result modulo 2<sup>n</sup>, where n is the bit width of the
+ result.</p>
+
+<p>Because LLVM integers use a two's complement representation, this instruction
+ is appropriate for both signed and unsigned integers.</p>
+
+<p><tt>nuw</tt> and <tt>nsw</tt> stand for "No Unsigned Wrap"
+ and "No Signed Wrap", respectively. If the <tt>nuw</tt> and/or
+ <tt>nsw</tt> keywords are present, the result value of the <tt>sub</tt>
+ is a <a href="#poisonvalues">poison value</a> if unsigned and/or signed overflow,
+ respectively, occurs.</p>
+
+<h5>Example:</h5>
+<pre>
+ <result> = sub i32 4, %var <i>; yields {i32}:result = 4 - %var</i>
+ <result> = sub i32 0, %val <i>; yields {i32}:result = -%var</i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_fsub">'<tt>fsub</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = fsub <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>fsub</tt>' instruction returns the difference of its two
+ operands.</p>
+
+<p>Note that the '<tt>fsub</tt>' instruction is used to represent the
+ '<tt>fneg</tt>' instruction present in most other intermediate
+ representations.</p>
+
+<h5>Arguments:</h5>
+<p>The two arguments to the '<tt>fsub</tt>' instruction must be
+ <a href="#t_floating">floating point</a> or <a href="#t_vector">vector</a> of
+ floating point values. Both arguments must have identical types.</p>
+
+<h5>Semantics:</h5>
+<p>The value produced is the floating point difference of the two operands.</p>
+
+<h5>Example:</h5>
+<pre>
+ <result> = fsub float 4.0, %var <i>; yields {float}:result = 4.0 - %var</i>
+ <result> = fsub float -0.0, %val <i>; yields {float}:result = -%var</i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_mul">'<tt>mul</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = mul <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+ <result> = mul nuw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+ <result> = mul nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+ <result> = mul nuw nsw <ty> <op1>, <op2> <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 <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of
+ integer values. Both arguments must have identical types.</p>
+
+<h5>Semantics:</h5>
+<p>The value produced is the integer product of the two operands.</p>
+
+<p>If the result of the multiplication has unsigned overflow, the result
+ returned is the mathematical result modulo 2<sup>n</sup>, where n is the bit
+ width of the result.</p>
+
+<p>Because LLVM integers use a two's complement representation, and the result
+ is the same width as the operands, this instruction returns the correct
+ result for both signed and unsigned integers. If a full product
+ (e.g. <tt>i32</tt>x<tt>i32</tt>-><tt>i64</tt>) is needed, the operands should
+ be sign-extended or zero-extended as appropriate to the width of the full
+ product.</p>
+
+<p><tt>nuw</tt> and <tt>nsw</tt> stand for "No Unsigned Wrap"
+ and "No Signed Wrap", respectively. If the <tt>nuw</tt> and/or
+ <tt>nsw</tt> keywords are present, the result value of the <tt>mul</tt>
+ is a <a href="#poisonvalues">poison value</a> if unsigned and/or signed overflow,
+ respectively, occurs.</p>
+
+<h5>Example:</h5>
+<pre>
+ <result> = mul i32 4, %var <i>; yields {i32}:result = 4 * %var</i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_fmul">'<tt>fmul</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = fmul <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>fmul</tt>' instruction returns the product of its two operands.</p>
+
+<h5>Arguments:</h5>
+<p>The two arguments to the '<tt>fmul</tt>' instruction must be
+ <a href="#t_floating">floating point</a> or <a href="#t_vector">vector</a> of
+ floating point values. Both arguments must have identical types.</p>
+
+<h5>Semantics:</h5>
+<p>The value produced is the floating point product of the two operands.</p>
+
+<h5>Example:</h5>
+<pre>
+ <result> = fmul float 4.0, %var <i>; yields {float}:result = 4.0 * %var</i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_udiv">'<tt>udiv</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = udiv <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+ <result> = udiv exact <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>udiv</tt>' instruction returns the quotient of its two operands.</p>
+
+<h5>Arguments:</h5>
+<p>The two arguments to the '<tt>udiv</tt>' instruction must be
+ <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
+ values. Both arguments must have identical types.</p>
+
+<h5>Semantics:</h5>
+<p>The value produced is the unsigned integer quotient of the two operands.</p>
+
+<p>Note that unsigned integer division and signed integer division are distinct
+ operations; for signed integer division, use '<tt>sdiv</tt>'.</p>
+
+<p>Division by zero leads to undefined behavior.</p>
+
+<p>If the <tt>exact</tt> keyword is present, the result value of the
+ <tt>udiv</tt> is a <a href="#poisonvalues">poison value</a> if %op1 is not a
+ multiple of %op2 (as such, "((a udiv exact b) mul b) == a").</p>
+
+
+<h5>Example:</h5>
+<pre>
+ <result> = udiv i32 4, %var <i>; yields {i32}:result = 4 / %var</i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_sdiv">'<tt>sdiv</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = sdiv <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+ <result> = sdiv exact <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>sdiv</tt>' instruction returns the quotient of its two operands.</p>
+
+<h5>Arguments:</h5>
+<p>The two arguments to the '<tt>sdiv</tt>' instruction must be
+ <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
+ values. Both arguments must have identical types.</p>
+
+<h5>Semantics:</h5>
+<p>The value produced is the signed integer quotient of the two operands rounded
+ towards zero.</p>
+
+<p>Note that signed integer division and unsigned integer division are distinct
+ operations; for unsigned integer division, use '<tt>udiv</tt>'.</p>
+
+<p>Division by zero leads to undefined behavior. Overflow also leads to
+ undefined behavior; this is a rare case, but can occur, for example, by doing
+ a 32-bit division of -2147483648 by -1.</p>
+
+<p>If the <tt>exact</tt> keyword is present, the result value of the
+ <tt>sdiv</tt> is a <a href="#poisonvalues">poison value</a> if the result would
+ be rounded.</p>
+
+<h5>Example:</h5>
+<pre>
+ <result> = sdiv i32 4, %var <i>; yields {i32}:result = 4 / %var</i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_fdiv">'<tt>fdiv</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = fdiv <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>fdiv</tt>' instruction returns the quotient of its two operands.</p>
+
+<h5>Arguments:</h5>
+<p>The two arguments to the '<tt>fdiv</tt>' instruction must be
+ <a href="#t_floating">floating point</a> or <a href="#t_vector">vector</a> of
+ floating point values. Both arguments must have identical types.</p>
+
+<h5>Semantics:</h5>
+<p>The value produced is the floating point quotient of the two operands.</p>
+
+<h5>Example:</h5>
+<pre>
+ <result> = fdiv float 4.0, %var <i>; yields {float}:result = 4.0 / %var</i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_urem">'<tt>urem</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = urem <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>urem</tt>' instruction returns the remainder from the unsigned
+ division of its two arguments.</p>
+
+<h5>Arguments:</h5>
+<p>The two arguments to the '<tt>urem</tt>' instruction must be
+ <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
+ values. Both arguments must have identical types.</p>
+
+<h5>Semantics:</h5>
+<p>This instruction returns the unsigned integer <i>remainder</i> of a division.
+ This instruction always performs an unsigned division to get the
+ remainder.</p>
+
+<p>Note that unsigned integer remainder and signed integer remainder are
+ distinct operations; for signed integer remainder, use '<tt>srem</tt>'.</p>
+
+<p>Taking the remainder of a division by zero leads to undefined behavior.</p>
+
+<h5>Example:</h5>
+<pre>
+ <result> = urem i32 4, %var <i>; yields {i32}:result = 4 % %var</i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_srem">'<tt>srem</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = srem <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>srem</tt>' instruction returns the remainder from the signed
+ division of its two operands. This instruction can also take
+ <a href="#t_vector">vector</a> versions of the values in which case the
+ elements must be integers.</p>
+
+<h5>Arguments:</h5>
+<p>The two arguments to the '<tt>srem</tt>' instruction must be
+ <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
+ values. Both arguments must have identical types.</p>
+
+<h5>Semantics:</h5>
+<p>This instruction returns the <i>remainder</i> of a division (where the result
+ is either zero or has the same sign as the dividend, <tt>op1</tt>), not the
+ <i>modulo</i> operator (where the result is either zero or has the same sign
+ as the divisor, <tt>op2</tt>) of a value.
+ For more information about the difference,
+ see <a href="http://mathforum.org/dr.math/problems/anne.4.28.99.html">The
+ Math Forum</a>. For a table of how this is implemented in various languages,
+ please see <a href="http://en.wikipedia.org/wiki/Modulo_operation">
+ Wikipedia: modulo operation</a>.</p>
+
+<p>Note that signed integer remainder and unsigned integer remainder are
+ distinct operations; for unsigned integer remainder, use '<tt>urem</tt>'.</p>
+
+<p>Taking the remainder of a division by zero leads to undefined behavior.
+ Overflow also leads to undefined behavior; this is a rare case, but can
+ occur, for example, by taking the remainder of a 32-bit division of
+ -2147483648 by -1. (The remainder doesn't actually overflow, but this rule
+ lets srem be implemented using instructions that return both the result of
+ the division and the remainder.)</p>
+
+<h5>Example:</h5>
+<pre>
+ <result> = srem i32 4, %var <i>; yields {i32}:result = 4 % %var</i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_frem">'<tt>frem</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = frem <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>frem</tt>' instruction returns the remainder from the division of
+ its two operands.</p>
+
+<h5>Arguments:</h5>
+<p>The two arguments to the '<tt>frem</tt>' instruction must be
+ <a href="#t_floating">floating point</a> or <a href="#t_vector">vector</a> of
+ floating point values. Both arguments must have identical types.</p>
+
+<h5>Semantics:</h5>
+<p>This instruction returns the <i>remainder</i> of a division. The remainder
+ has the same sign as the dividend.</p>
+
+<h5>Example:</h5>
+<pre>
+ <result> = frem float 4.0, %var <i>; yields {float}:result = 4.0 % %var</i>
+</pre>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="bitwiseops">Bitwise Binary Operations</a>
+</h3>
+
+<div>
+
+<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 of the
+ same type, execute an operation on them, and produce a single value. The
+ resulting value is the same type as its operands.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_shl">'<tt>shl</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = shl <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+ <result> = shl nuw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+ <result> = shl nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+ <result> = shl nuw nsw <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>shl</tt>' instruction returns the first operand shifted to the left
+ a specified number of bits.</p>
+
+<h5>Arguments:</h5>
+<p>Both arguments to the '<tt>shl</tt>' instruction must be the
+ same <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of
+ integer type. '<tt>op2</tt>' is treated as an unsigned value.</p>
+
+<h5>Semantics:</h5>
+<p>The value produced is <tt>op1</tt> * 2<sup><tt>op2</tt></sup> mod
+ 2<sup>n</sup>, where <tt>n</tt> is the width of the result. If <tt>op2</tt>
+ is (statically or dynamically) negative or equal to or larger than the number
+ of bits in <tt>op1</tt>, the result is undefined. If the arguments are
+ vectors, each vector element of <tt>op1</tt> is shifted by the corresponding
+ shift amount in <tt>op2</tt>.</p>
+
+<p>If the <tt>nuw</tt> keyword is present, then the shift produces a
+ <a href="#poisonvalues">poison value</a> if it shifts out any non-zero bits. If
+ the <tt>nsw</tt> keyword is present, then the shift produces a
+ <a href="#poisonvalues">poison value</a> if it shifts out any bits that disagree
+ with the resultant sign bit. As such, NUW/NSW have the same semantics as
+ they would if the shift were expressed as a mul instruction with the same
+ nsw/nuw bits in (mul %op1, (shl 1, %op2)).</p>
+
+<h5>Example:</h5>
+<pre>
+ <result> = shl i32 4, %var <i>; yields {i32}: 4 << %var</i>
+ <result> = shl i32 4, 2 <i>; yields {i32}: 16</i>
+ <result> = shl i32 1, 10 <i>; yields {i32}: 1024</i>
+ <result> = shl i32 1, 32 <i>; undefined</i>
+ <result> = shl <2 x i32> < i32 1, i32 1>, < i32 1, i32 2> <i>; yields: result=<2 x i32> < i32 2, i32 4></i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_lshr">'<tt>lshr</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = lshr <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+ <result> = lshr exact <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>lshr</tt>' instruction (logical shift right) returns the first
+ operand shifted to the right a specified number of bits with zero fill.</p>
+
+<h5>Arguments:</h5>
+<p>Both arguments to the '<tt>lshr</tt>' instruction must be the same
+ <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
+ type. '<tt>op2</tt>' is treated as an unsigned value.</p>
+
+<h5>Semantics:</h5>
+<p>This instruction always performs a logical shift right operation. The most
+ significant bits of the result will be filled with zero bits after the shift.
+ If <tt>op2</tt> is (statically or dynamically) equal to or larger than the
+ number of bits in <tt>op1</tt>, the result is undefined. If the arguments are
+ vectors, each vector element of <tt>op1</tt> is shifted by the corresponding
+ shift amount in <tt>op2</tt>.</p>
+
+<p>If the <tt>exact</tt> keyword is present, the result value of the
+ <tt>lshr</tt> is a <a href="#poisonvalues">poison value</a> if any of the bits
+ shifted out are non-zero.</p>
+
+
+<h5>Example:</h5>
+<pre>
+ <result> = lshr i32 4, 1 <i>; yields {i32}:result = 2</i>
+ <result> = lshr i32 4, 2 <i>; yields {i32}:result = 1</i>
+ <result> = lshr i8 4, 3 <i>; yields {i8}:result = 0</i>
+ <result> = lshr i8 -2, 1 <i>; yields {i8}:result = 0x7FFFFFFF </i>
+ <result> = lshr i32 1, 32 <i>; undefined</i>
+ <result> = lshr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 2> <i>; yields: result=<2 x i32> < i32 0x7FFFFFFF, i32 1></i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_ashr">'<tt>ashr</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = ashr <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+ <result> = ashr exact <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>ashr</tt>' instruction (arithmetic shift right) returns the first
+ operand shifted to the right a specified number of bits with sign
+ extension.</p>
+
+<h5>Arguments:</h5>
+<p>Both arguments to the '<tt>ashr</tt>' instruction must be the same
+ <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
+ type. '<tt>op2</tt>' is treated as an unsigned value.</p>
+
+<h5>Semantics:</h5>
+<p>This instruction always performs an arithmetic shift right operation, The
+ most significant bits of the result will be filled with the sign bit
+ of <tt>op1</tt>. If <tt>op2</tt> is (statically or dynamically) equal to or
+ larger than the number of bits in <tt>op1</tt>, the result is undefined. If
+ the arguments are vectors, each vector element of <tt>op1</tt> is shifted by
+ the corresponding shift amount in <tt>op2</tt>.</p>
+
+<p>If the <tt>exact</tt> keyword is present, the result value of the
+ <tt>ashr</tt> is a <a href="#poisonvalues">poison value</a> if any of the bits
+ shifted out are non-zero.</p>
+
+<h5>Example:</h5>
+<pre>
+ <result> = ashr i32 4, 1 <i>; yields {i32}:result = 2</i>
+ <result> = ashr i32 4, 2 <i>; yields {i32}:result = 1</i>
+ <result> = ashr i8 4, 3 <i>; yields {i8}:result = 0</i>
+ <result> = ashr i8 -2, 1 <i>; yields {i8}:result = -1</i>
+ <result> = ashr i32 1, 32 <i>; undefined</i>
+ <result> = ashr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 3> <i>; yields: result=<2 x i32> < i32 -1, i32 0></i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_and">'<tt>and</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = and <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>and</tt>' instruction returns the bitwise logical and of its two
+ operands.</p>
+
+<h5>Arguments:</h5>
+<p>The two arguments to the '<tt>and</tt>' instruction must be
+ <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
+ values. Both arguments must have identical types.</p>
+
+<h5>Semantics:</h5>
+<p>The truth table used for the '<tt>and</tt>' instruction is:</p>
+
+<table border="1" cellspacing="0" cellpadding="4">
+ <tbody>
+ <tr>
+ <th>In0</th>
+ <th>In1</th>
+ <th>Out</th>
+ </tr>
+ <tr>
+ <td>0</td>
+ <td>0</td>
+ <td>0</td>
+ </tr>
+ <tr>
+ <td>0</td>
+ <td>1</td>
+ <td>0</td>
+ </tr>
+ <tr>
+ <td>1</td>
+ <td>0</td>
+ <td>0</td>
+ </tr>
+ <tr>
+ <td>1</td>
+ <td>1</td>
+ <td>1</td>
+ </tr>
+ </tbody>
+</table>
+
+<h5>Example:</h5>
+<pre>
+ <result> = and i32 4, %var <i>; yields {i32}:result = 4 & %var</i>
+ <result> = and i32 15, 40 <i>; yields {i32}:result = 8</i>
+ <result> = and i32 4, 8 <i>; yields {i32}:result = 0</i>
+</pre>
+</div>
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_or">'<tt>or</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = or <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>or</tt>' instruction returns the bitwise logical inclusive or of its
+ two operands.</p>
+
+<h5>Arguments:</h5>
+<p>The two arguments to the '<tt>or</tt>' instruction must be
+ <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
+ values. Both arguments must have identical types.</p>
+
+<h5>Semantics:</h5>
+<p>The truth table used for the '<tt>or</tt>' instruction is:</p>
+
+<table border="1" cellspacing="0" cellpadding="4">
+ <tbody>
+ <tr>
+ <th>In0</th>
+ <th>In1</th>
+ <th>Out</th>
+ </tr>
+ <tr>
+ <td>0</td>
+ <td>0</td>
+ <td>0</td>
+ </tr>
+ <tr>
+ <td>0</td>
+ <td>1</td>
+ <td>1</td>
+ </tr>
+ <tr>
+ <td>1</td>
+ <td>0</td>
+ <td>1</td>
+ </tr>
+ <tr>
+ <td>1</td>
+ <td>1</td>
+ <td>1</td>
+ </tr>
+ </tbody>
+</table>
+
+<h5>Example:</h5>
+<pre>
+ <result> = or i32 4, %var <i>; yields {i32}:result = 4 | %var</i>
+ <result> = or i32 15, 40 <i>; yields {i32}:result = 47</i>
+ <result> = or i32 4, 8 <i>; yields {i32}:result = 12</i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_xor">'<tt>xor</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = xor <ty> <op1>, <op2> <i>; yields {ty}:result</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>xor</tt>' instruction returns the bitwise logical exclusive or of
+ its two operands. The <tt>xor</tt> is used to implement the "one's
+ complement" operation, which is the "~" operator in C.</p>
+
+<h5>Arguments:</h5>
+<p>The two arguments to the '<tt>xor</tt>' instruction must be
+ <a href="#t_integer">integer</a> or <a href="#t_vector">vector</a> of integer
+ values. Both arguments must have identical types.</p>
+
+<h5>Semantics:</h5>
+<p>The truth table used for the '<tt>xor</tt>' instruction is:</p>
+
+<table border="1" cellspacing="0" cellpadding="4">
+ <tbody>
+ <tr>
+ <th>In0</th>
+ <th>In1</th>
+ <th>Out</th>
+ </tr>
+ <tr>
+ <td>0</td>
+ <td>0</td>
+ <td>0</td>
+ </tr>
+ <tr>
+ <td>0</td>
+ <td>1</td>
+ <td>1</td>
+ </tr>
+ <tr>
+ <td>1</td>
+ <td>0</td>
+ <td>1</td>
+ </tr>
+ <tr>
+ <td>1</td>
+ <td>1</td>
+ <td>0</td>
+ </tr>
+ </tbody>
+</table>
+
+<h5>Example:</h5>
+<pre>
+ <result> = xor i32 4, %var <i>; yields {i32}:result = 4 ^ %var</i>
+ <result> = xor i32 15, 40 <i>; yields {i32}:result = 39</i>
+ <result> = xor i32 4, 8 <i>; yields {i32}:result = 12</i>
+ <result> = xor i32 %V, -1 <i>; yields {i32}:result = ~%V</i>
+</pre>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="vectorops">Vector Operations</a>
+</h3>
+
+<div>
+
+<p>LLVM supports several instructions to represent vector operations in a
+ target-independent manner. These instructions cover the element-access and
+ vector-specific operations needed to process vectors effectively. While LLVM
+ does directly support these vector operations, many sophisticated algorithms
+ will want to use target-specific intrinsics to take full advantage of a
+ specific target.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_extractelement">'<tt>extractelement</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = extractelement <n x <ty>> <val>, i32 <idx> <i>; yields <ty></i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>extractelement</tt>' instruction extracts a single scalar element
+ from a vector at a specified index.</p>
+
+
+<h5>Arguments:</h5>
+<p>The first operand of an '<tt>extractelement</tt>' instruction is a value
+ of <a href="#t_vector">vector</a> type. The second operand is an index
+ indicating the position from which to extract the element. The index may be
+ a variable.</p>
+
+<h5>Semantics:</h5>
+<p>The result is a scalar of the same type as the element type of
+ <tt>val</tt>. Its value is the value at position <tt>idx</tt> of
+ <tt>val</tt>. If <tt>idx</tt> exceeds the length of <tt>val</tt>, the
+ results are undefined.</p>
+
+<h5>Example:</h5>
+<pre>
+ <result> = extractelement <4 x i32> %vec, i32 0 <i>; yields i32</i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_insertelement">'<tt>insertelement</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = insertelement <n x <ty>> <val>, <ty> <elt>, i32 <idx> <i>; yields <n x <ty>></i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>insertelement</tt>' instruction inserts a scalar element into a
+ vector at a specified index.</p>
+
+<h5>Arguments:</h5>
+<p>The first operand of an '<tt>insertelement</tt>' instruction is a value
+ of <a href="#t_vector">vector</a> type. The second operand is a scalar value
+ whose type must equal the element type of the first operand. The third
+ operand is an index indicating the position at which to insert the value.
+ The index may be a variable.</p>
+
+<h5>Semantics:</h5>
+<p>The result is a vector of the same type as <tt>val</tt>. Its element values
+ are those of <tt>val</tt> except at position <tt>idx</tt>, where it gets the
+ value <tt>elt</tt>. If <tt>idx</tt> exceeds the length of <tt>val</tt>, the
+ results are undefined.</p>
+
+<h5>Example:</h5>
+<pre>
+ <result> = insertelement <4 x i32> %vec, i32 1, i32 0 <i>; yields <4 x i32></i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_shufflevector">'<tt>shufflevector</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = shufflevector <n x <ty>> <v1>, <n x <ty>> <v2>, <m x i32> <mask> <i>; yields <m x <ty>></i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>shufflevector</tt>' instruction constructs a permutation of elements
+ from two input vectors, returning a vector with the same element type as the
+ input and length that is the same as the shuffle mask.</p>
+
+<h5>Arguments:</h5>
+<p>The first two operands of a '<tt>shufflevector</tt>' instruction are vectors
+ with the same type. The third argument is a shuffle mask whose
+ element type is always 'i32'. The result of the instruction is a vector
+ whose length is the same as the shuffle mask and whose element type is the
+ same as the element type of the first two operands.</p>
+
+<p>The shuffle mask operand is required to be a constant vector with either
+ constant integer or undef values.</p>
+
+<h5>Semantics:</h5>
+<p>The elements of the two input vectors are numbered from left to right across
+ both of the vectors. The shuffle mask operand specifies, for each element of
+ the result vector, which element of the two input vectors the result element
+ gets. The element selector may be undef (meaning "don't care") and the
+ second operand may be undef if performing a shuffle from only one vector.</p>
+
+<h5>Example:</h5>
+<pre>
+ <result> = shufflevector <4 x i32> %v1, <4 x i32> %v2,
+ <4 x i32> <i32 0, i32 4, i32 1, i32 5> <i>; yields <4 x i32></i>
+ <result> = shufflevector <4 x i32> %v1, <4 x i32> undef,
+ <4 x i32> <i32 0, i32 1, i32 2, i32 3> <i>; yields <4 x i32></i> - Identity shuffle.
+ <result> = shufflevector <8 x i32> %v1, <8 x i32> undef,
+ <4 x i32> <i32 0, i32 1, i32 2, i32 3> <i>; yields <4 x i32></i>
+ <result> = shufflevector <4 x i32> %v1, <4 x i32> %v2,
+ <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7 > <i>; yields <8 x i32></i>
+</pre>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="aggregateops">Aggregate Operations</a>
+</h3>
+
+<div>
+
+<p>LLVM supports several instructions for working with
+ <a href="#t_aggregate">aggregate</a> values.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_extractvalue">'<tt>extractvalue</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = extractvalue <aggregate type> <val>, <idx>{, <idx>}*
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>extractvalue</tt>' instruction extracts the value of a member field
+ from an <a href="#t_aggregate">aggregate</a> value.</p>
+
+<h5>Arguments:</h5>
+<p>The first operand of an '<tt>extractvalue</tt>' instruction is a value
+ of <a href="#t_struct">struct</a> or
+ <a href="#t_array">array</a> type. The operands are constant indices to
+ specify which value to extract in a similar manner as indices in a
+ '<tt><a href="#i_getelementptr">getelementptr</a></tt>' instruction.</p>
+ <p>The major differences to <tt>getelementptr</tt> indexing are:</p>
+ <ul>
+ <li>Since the value being indexed is not a pointer, the first index is
+ omitted and assumed to be zero.</li>
+ <li>At least one index must be specified.</li>
+ <li>Not only struct indices but also array indices must be in
+ bounds.</li>
+ </ul>
+
+<h5>Semantics:</h5>
+<p>The result is the value at the position in the aggregate specified by the
+ index operands.</p>
+
+<h5>Example:</h5>
+<pre>
+ <result> = extractvalue {i32, float} %agg, 0 <i>; yields i32</i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_insertvalue">'<tt>insertvalue</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = insertvalue <aggregate type> <val>, <ty> <elt>, <idx>{, <idx>}* <i>; yields <aggregate type></i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>insertvalue</tt>' instruction inserts a value into a member field
+ in an <a href="#t_aggregate">aggregate</a> value.</p>
+
+<h5>Arguments:</h5>
+<p>The first operand of an '<tt>insertvalue</tt>' instruction is a value
+ of <a href="#t_struct">struct</a> or
+ <a href="#t_array">array</a> type. The second operand is a first-class
+ value to insert. The following operands are constant indices indicating
+ the position at which to insert the value in a similar manner as indices in a
+ '<tt><a href="#i_extractvalue">extractvalue</a></tt>' instruction. The
+ value to insert must have the same type as the value identified by the
+ indices.</p>
+
+<h5>Semantics:</h5>
+<p>The result is an aggregate of the same type as <tt>val</tt>. Its value is
+ that of <tt>val</tt> except that the value at the position specified by the
+ indices is that of <tt>elt</tt>.</p>
+
+<h5>Example:</h5>
+<pre>
+ %agg1 = insertvalue {i32, float} undef, i32 1, 0 <i>; yields {i32 1, float undef}</i>
+ %agg2 = insertvalue {i32, float} %agg1, float %val, 1 <i>; yields {i32 1, float %val}</i>
+ %agg3 = insertvalue {i32, {float}} %agg1, float %val, 1, 0 <i>; yields {i32 1, float %val}</i>
+</pre>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="memoryops">Memory Access and Addressing Operations</a>
+</h3>
+
+<div>
+
+<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, and allocate
+ memory in LLVM.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_alloca">'<tt>alloca</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = alloca <type>[, <ty> <NumElements>][, align <alignment>] <i>; yields {type*}:result</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>alloca</tt>' instruction allocates memory on the stack frame of the
+ currently executing function, to be automatically released when this function
+ returns to its caller. The object is always allocated in the generic address
+ space (address space zero).</p>
+
+<h5>Arguments:</h5>
+<p>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.
+ If "NumElements" is specified, it is the number of elements allocated,
+ otherwise "NumElements" is defaulted to be one. If a constant alignment is
+ specified, the value result of the allocation is guaranteed to be aligned to
+ at least that boundary. If not specified, or if zero, the target can choose
+ to align the allocation on any convenient boundary compatible with the
+ type.</p>
+
+<p>'<tt>type</tt>' may be any sized type.</p>
+
+<h5>Semantics:</h5>
+<p>Memory is allocated; a pointer is returned. The operation is undefined if
+ there is insufficient stack space for the allocation. '<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_resume">resume</a></tt> instructions), the memory is
+ reclaimed. Allocating zero bytes is legal, but the result is undefined.
+ The order in which memory is allocated (ie., which way the stack grows) is
+ not specified.</p>
+
+<p>
+
+<h5>Example:</h5>
+<pre>
+ %ptr = alloca i32 <i>; yields {i32*}:ptr</i>
+ %ptr = alloca i32, i32 4 <i>; yields {i32*}:ptr</i>
+ %ptr = alloca i32, i32 4, align 1024 <i>; yields {i32*}:ptr</i>
+ %ptr = alloca i32, align 1024 <i>; yields {i32*}:ptr</i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_load">'<tt>load</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = load [volatile] <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>][, !invariant.load !<index>]
+ <result> = load atomic [volatile] <ty>* <pointer> [singlethread] <ordering>, align <alignment>
+ !<index> = !{ i32 1 }
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>load</tt>' instruction is used to read from memory.</p>
+
+<h5>Arguments:</h5>
+<p>The argument to the '<tt>load</tt>' instruction specifies the memory address
+ from which to load. The pointer must point to
+ a <a href="#t_firstclass">first class</a> type. If the <tt>load</tt> is
+ marked as <tt>volatile</tt>, then the optimizer is not allowed to modify the
+ number or order of execution of this <tt>load</tt> with other <a
+ href="#volatile">volatile operations</a>.</p>
+
+<p>If the <code>load</code> is marked as <code>atomic</code>, it takes an extra
+ <a href="#ordering">ordering</a> and optional <code>singlethread</code>
+ argument. The <code>release</code> and <code>acq_rel</code> orderings are
+ not valid on <code>load</code> instructions. Atomic loads produce <a
+ href="#memorymodel">defined</a> results when they may see multiple atomic
+ stores. The type of the pointee must be an integer type whose bit width
+ is a power of two greater than or equal to eight and less than or equal
+ to a target-specific size limit. <code>align</code> must be explicitly
+ specified on atomic loads, and the load has undefined behavior if the
+ alignment is not set to a value which is at least the size in bytes of
+ the pointee. <code>!nontemporal</code> does not have any defined semantics
+ for atomic loads.</p>
+
+<p>The optional constant <tt>align</tt> argument specifies the alignment of the
+ operation (that is, the alignment of the memory address). A value of 0 or an
+ omitted <tt>align</tt> argument means that the operation has the abi
+ alignment for the target. It is the responsibility of the code emitter to
+ ensure that the alignment information is correct. Overestimating the
+ alignment results in undefined behavior. Underestimating the alignment may
+ produce less efficient code. An alignment of 1 is always safe.</p>
+
+<p>The optional <tt>!nontemporal</tt> metadata must reference a single
+ metatadata name <index> corresponding to a metadata node with
+ one <tt>i32</tt> entry of value 1. The existence of
+ the <tt>!nontemporal</tt> metatadata on the instruction tells the optimizer
+ and code generator that this load is not expected to be reused in the cache.
+ The code generator may select special instructions to save cache bandwidth,
+ such as the <tt>MOVNT</tt> instruction on x86.</p>
+
+<p>The optional <tt>!invariant.load</tt> metadata must reference a single
+ metatadata name <index> corresponding to a metadata node with no
+ entries. The existence of the <tt>!invariant.load</tt> metatadata on the
+ instruction tells the optimizer and code generator that this load address
+ points to memory which does not change value during program execution.
+ The optimizer may then move this load around, for example, by hoisting it
+ out of loops using loop invariant code motion.</p>
+
+<h5>Semantics:</h5>
+<p>The location of memory pointed to is loaded. If the value being loaded is of
+ scalar type then the number of bytes read does not exceed the minimum number
+ of bytes needed to hold all bits of the type. For example, loading an
+ <tt>i24</tt> reads at most three bytes. When loading a value of a type like
+ <tt>i20</tt> with a size that is not an integral number of bytes, the result
+ is undefined if the value was not originally written using a store of the
+ same type.</p>
+
+<h5>Examples:</h5>
+<pre>
+ %ptr = <a href="#i_alloca">alloca</a> i32 <i>; yields {i32*}:ptr</i>
+ <a href="#i_store">store</a> i32 3, i32* %ptr <i>; yields {void}</i>
+ %val = load i32* %ptr <i>; yields {i32}:val = i32 3</i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_store">'<tt>store</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ store [volatile] <ty> <value>, <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>] <i>; yields {void}</i>
+ store atomic [volatile] <ty> <value>, <ty>* <pointer> [singlethread] <ordering>, align <alignment> <i>; yields {void}</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>store</tt>' instruction is used to write to memory.</p>
+
+<h5>Arguments:</h5>
+<p>There are two arguments to the '<tt>store</tt>' instruction: a value to store
+ and an address at which to store it. The type of the
+ '<tt><pointer></tt>' operand must be a pointer to
+ the <a href="#t_firstclass">first class</a> 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 <a
+ href="#volatile">volatile operations</a>.</p>
+
+<p>If the <code>store</code> is marked as <code>atomic</code>, it takes an extra
+ <a href="#ordering">ordering</a> and optional <code>singlethread</code>
+ argument. The <code>acquire</code> and <code>acq_rel</code> orderings aren't
+ valid on <code>store</code> instructions. Atomic loads produce <a
+ href="#memorymodel">defined</a> results when they may see multiple atomic
+ stores. The type of the pointee must be an integer type whose bit width
+ is a power of two greater than or equal to eight and less than or equal
+ to a target-specific size limit. <code>align</code> must be explicitly
+ specified on atomic stores, and the store has undefined behavior if the
+ alignment is not set to a value which is at least the size in bytes of
+ the pointee. <code>!nontemporal</code> does not have any defined semantics
+ for atomic stores.</p>
+
+<p>The optional constant "align" argument specifies the alignment of the
+ operation (that is, the alignment of the memory address). A value of 0 or an
+ omitted "align" argument means that the operation has the abi
+ alignment for the target. It is the responsibility of the code emitter to
+ ensure that the alignment information is correct. Overestimating the
+ alignment results in an undefined behavior. Underestimating the alignment may
+ produce less efficient code. An alignment of 1 is always safe.</p>
+
+<p>The optional !nontemporal metadata must reference a single metatadata
+ name <index> corresponding to a metadata node with one i32 entry of
+ value 1. The existence of the !nontemporal metatadata on the
+ instruction tells the optimizer and code generator that this load is
+ not expected to be reused in the cache. The code generator may
+ select special instructions to save cache bandwidth, such as the
+ MOVNT instruction on x86.</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. If
+ '<tt><value></tt>' is of scalar type then the number of bytes written
+ does not exceed the minimum number of bytes needed to hold all bits of the
+ type. For example, storing an <tt>i24</tt> writes at most three bytes. When
+ writing a value of a type like <tt>i20</tt> with a size that is not an
+ integral number of bytes, it is unspecified what happens to the extra bits
+ that do not belong to the type, but they will typically be overwritten.</p>
+
+<h5>Example:</h5>
+<pre>
+ %ptr = <a href="#i_alloca">alloca</a> i32 <i>; yields {i32*}:ptr</i>
+ store i32 3, i32* %ptr <i>; yields {void}</i>
+ %val = <a href="#i_load">load</a> i32* %ptr <i>; yields {i32}:val = i32 3</i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+<a name="i_fence">'<tt>fence</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ fence [singlethread] <ordering> <i>; yields {void}</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>fence</tt>' instruction is used to introduce happens-before edges
+between operations.</p>
+
+<h5>Arguments:</h5> <p>'<code>fence</code>' instructions take an <a
+href="#ordering">ordering</a> argument which defines what
+<i>synchronizes-with</i> edges they add. They can only be given
+<code>acquire</code>, <code>release</code>, <code>acq_rel</code>, and
+<code>seq_cst</code> orderings.</p>
+
+<h5>Semantics:</h5>
+<p>A fence <var>A</var> which has (at least) <code>release</code> ordering
+semantics <i>synchronizes with</i> a fence <var>B</var> with (at least)
+<code>acquire</code> ordering semantics if and only if there exist atomic
+operations <var>X</var> and <var>Y</var>, both operating on some atomic object
+<var>M</var>, such that <var>A</var> is sequenced before <var>X</var>,
+<var>X</var> modifies <var>M</var> (either directly or through some side effect
+of a sequence headed by <var>X</var>), <var>Y</var> is sequenced before
+<var>B</var>, and <var>Y</var> observes <var>M</var>. This provides a
+<i>happens-before</i> dependency between <var>A</var> and <var>B</var>. Rather
+than an explicit <code>fence</code>, one (but not both) of the atomic operations
+<var>X</var> or <var>Y</var> might provide a <code>release</code> or
+<code>acquire</code> (resp.) ordering constraint and still
+<i>synchronize-with</i> the explicit <code>fence</code> and establish the
+<i>happens-before</i> edge.</p>
+
+<p>A <code>fence</code> which has <code>seq_cst</code> ordering, in addition to
+having both <code>acquire</code> and <code>release</code> semantics specified
+above, participates in the global program order of other <code>seq_cst</code>
+operations and/or fences.</p>
+
+<p>The optional "<a href="#singlethread"><code>singlethread</code></a>" argument
+specifies that the fence only synchronizes with other fences in the same
+thread. (This is useful for interacting with signal handlers.)</p>
+
+<h5>Example:</h5>
+<pre>
+ fence acquire <i>; yields {void}</i>
+ fence singlethread seq_cst <i>; yields {void}</i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+<a name="i_cmpxchg">'<tt>cmpxchg</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ cmpxchg [volatile] <ty>* <pointer>, <ty> <cmp>, <ty> <new> [singlethread] <ordering> <i>; yields {ty}</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>cmpxchg</tt>' instruction is used to atomically modify memory.
+It loads a value in memory and compares it to a given value. If they are
+equal, it stores a new value into the memory.</p>
+
+<h5>Arguments:</h5>
+<p>There are three arguments to the '<code>cmpxchg</code>' instruction: an
+address to operate on, a value to compare to the value currently be at that
+address, and a new value to place at that address if the compared values are
+equal. The type of '<var><cmp></var>' must be an integer type whose
+bit width is a power of two greater than or equal to eight and less than
+or equal to a target-specific size limit. '<var><cmp></var>' and
+'<var><new></var>' must have the same type, and the type of
+'<var><pointer></var>' must be a pointer to that type. If the
+<code>cmpxchg</code> is marked as <code>volatile</code>, then the
+optimizer is not allowed to modify the number or order of execution
+of this <code>cmpxchg</code> with other <a href="#volatile">volatile
+operations</a>.</p>
+
+<!-- FIXME: Extend allowed types. -->
+
+<p>The <a href="#ordering"><var>ordering</var></a> argument specifies how this
+<code>cmpxchg</code> synchronizes with other atomic operations.</p>
+
+<p>The optional "<code>singlethread</code>" argument declares that the
+<code>cmpxchg</code> is only atomic with respect to code (usually signal
+handlers) running in the same thread as the <code>cmpxchg</code>. Otherwise the
+cmpxchg is atomic with respect to all other code in the system.</p>
+
+<p>The pointer passed into cmpxchg must have alignment greater than or equal to
+the size in memory of the operand.
+
+<h5>Semantics:</h5>
+<p>The contents of memory at the location specified by the
+'<tt><pointer></tt>' operand is read and compared to
+'<tt><cmp></tt>'; if the read value is the equal,
+'<tt><new></tt>' is written. The original value at the location
+is returned.
+
+<p>A successful <code>cmpxchg</code> is a read-modify-write instruction for the
+purpose of identifying <a href="#release_sequence">release sequences</a>. A
+failed <code>cmpxchg</code> is equivalent to an atomic load with an ordering
+parameter determined by dropping any <code>release</code> part of the
+<code>cmpxchg</code>'s ordering.</p>
+
+<!--
+FIXME: Is compare_exchange_weak() necessary? (Consider after we've done
+optimization work on ARM.)
+
+FIXME: Is a weaker ordering constraint on failure helpful in practice?
+-->
+
+<h5>Example:</h5>
+<pre>
+entry:
+ %orig = atomic <a href="#i_load">load</a> i32* %ptr unordered <i>; yields {i32}</i>
+ <a href="#i_br">br</a> label %loop
+
+loop:
+ %cmp = <a href="#i_phi">phi</a> i32 [ %orig, %entry ], [%old, %loop]
+ %squared = <a href="#i_mul">mul</a> i32 %cmp, %cmp
+ %old = cmpxchg i32* %ptr, i32 %cmp, i32 %squared <i>; yields {i32}</i>
+ %success = <a href="#i_icmp">icmp</a> eq i32 %cmp, %old
+ <a href="#i_br">br</a> i1 %success, label %done, label %loop
+
+done:
+ ...
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+<a name="i_atomicrmw">'<tt>atomicrmw</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ atomicrmw [volatile] <operation> <ty>* <pointer>, <ty> <value> [singlethread] <ordering> <i>; yields {ty}</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>atomicrmw</tt>' instruction is used to atomically modify memory.</p>
+
+<h5>Arguments:</h5>
+<p>There are three arguments to the '<code>atomicrmw</code>' instruction: an
+operation to apply, an address whose value to modify, an argument to the
+operation. The operation must be one of the following keywords:</p>
+<ul>
+ <li>xchg</li>
+ <li>add</li>
+ <li>sub</li>
+ <li>and</li>
+ <li>nand</li>
+ <li>or</li>
+ <li>xor</li>
+ <li>max</li>
+ <li>min</li>
+ <li>umax</li>
+ <li>umin</li>
+</ul>
+
+<p>The type of '<var><value></var>' must be an integer type whose
+bit width is a power of two greater than or equal to eight and less than
+or equal to a target-specific size limit. The type of the
+'<code><pointer></code>' operand must be a pointer to that type.
+If the <code>atomicrmw</code> is marked as <code>volatile</code>, then the
+optimizer is not allowed to modify the number or order of execution of this
+<code>atomicrmw</code> with other <a href="#volatile">volatile
+ operations</a>.</p>
+
+<!-- FIXME: Extend allowed types. -->
+
+<h5>Semantics:</h5>
+<p>The contents of memory at the location specified by the
+'<tt><pointer></tt>' operand are atomically read, modified, and written
+back. The original value at the location is returned. The modification is
+specified by the <var>operation</var> argument:</p>
+
+<ul>
+ <li>xchg: <code>*ptr = val</code></li>
+ <li>add: <code>*ptr = *ptr + val</code></li>
+ <li>sub: <code>*ptr = *ptr - val</code></li>
+ <li>and: <code>*ptr = *ptr & val</code></li>
+ <li>nand: <code>*ptr = ~(*ptr & val)</code></li>
+ <li>or: <code>*ptr = *ptr | val</code></li>
+ <li>xor: <code>*ptr = *ptr ^ val</code></li>
+ <li>max: <code>*ptr = *ptr > val ? *ptr : val</code> (using a signed comparison)</li>
+ <li>min: <code>*ptr = *ptr < val ? *ptr : val</code> (using a signed comparison)</li>
+ <li>umax: <code>*ptr = *ptr > val ? *ptr : val</code> (using an unsigned comparison)</li>
+ <li>umin: <code>*ptr = *ptr < val ? *ptr : val</code> (using an unsigned comparison)</li>
+</ul>
+
+<h5>Example:</h5>
+<pre>
+ %old = atomicrmw add i32* %ptr, i32 1 acquire <i>; yields {i32}</i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_getelementptr">'<tt>getelementptr</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = getelementptr <pty>* <ptrval>{, <ty> <idx>}*
+ <result> = getelementptr inbounds <pty>* <ptrval>{, <ty> <idx>}*
+ <result> = getelementptr <ptr vector> ptrval, <vector index type> idx
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>getelementptr</tt>' instruction is used to get the address of a
+ subelement of an <a href="#t_aggregate">aggregate</a> data structure.
+ It performs address calculation only and does not access memory.</p>
+
+<h5>Arguments:</h5>
+<p>The first argument is always a pointer or a vector of pointers,
+ and forms the basis of the
+ calculation. The remaining arguments are indices that indicate which of the
+ elements of the aggregate object are indexed. The interpretation of each
+ index is dependent on the type being indexed into. The first index always
+ indexes the pointer value given as the first argument, the second index
+ indexes a value of the type pointed to (not necessarily the value directly
+ pointed to, since the first index can be non-zero), etc. The first type
+ indexed into must be a pointer value, subsequent types can be arrays,
+ vectors, and structs. Note that subsequent types being indexed into
+ can never be pointers, since that would require loading the pointer before
+ continuing calculation.</p>
+
+<p>The type of each index argument depends on the type it is indexing into.
+ When indexing into a (optionally packed) structure, only <tt>i32</tt>
+ integer <b>constants</b> are allowed. When indexing into an array, pointer
+ or vector, integers of any width are allowed, and they are not required to be
+ constant. These integers are treated as signed values where relevant.</p>
+
+<p>For example, let's consider a C code fragment and how it gets compiled to
+ LLVM:</p>
+
+<pre class="doc_code">
+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 Clang is:</p>
+
+<pre class="doc_code">
+%struct.RT = <a href="#namedtypes">type</a> { i8, [10 x [20 x i32]], i8 }
+%struct.ST = <a href="#namedtypes">type</a> { i32, double, %struct.RT }
+
+define i32* @foo(%struct.ST* %s) nounwind uwtable readnone optsize ssp {
+entry:
+ %arrayidx = getelementptr inbounds %struct.ST* %s, i64 1, i32 2, i32 1, i64 5, i64 13
+ ret i32* %arrayidx
+}
+</pre>
+
+<h5>Semantics:</h5>
+<p>In the example above, the first index is indexing into the
+ '<tt>%struct.ST*</tt>' type, which is a pointer, yielding a
+ '<tt>%struct.ST</tt>' = '<tt>{ i32, double, %struct.RT }</tt>' type, a
+ structure. The second index indexes into the third element of the structure,
+ yielding a '<tt>%struct.RT</tt>' = '<tt>{ i8 , [10 x [20 x i32]], i8 }</tt>'
+ type, another structure. The third index indexes into the second element of
+ the structure, yielding a '<tt>[10 x [20 x i32]]</tt>' type, an array. The
+ two dimensions of the array are subscripted into, yielding an '<tt>i32</tt>'
+ type. The '<tt>getelementptr</tt>' instruction returns a pointer to this
+ element, thus computing a value of '<tt>i32*</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 class="doc_code">
+define i32* @foo(%struct.ST* %s) {
+ %t1 = getelementptr %struct.ST* %s, i32 1 <i>; yields %struct.ST*:%t1</i>
+ %t2 = getelementptr %struct.ST* %t1, i32 0, i32 2 <i>; yields %struct.RT*:%t2</i>
+ %t3 = getelementptr %struct.RT* %t2, i32 0, i32 1 <i>; yields [10 x [20 x i32]]*:%t3</i>
+ %t4 = getelementptr [10 x [20 x i32]]* %t3, i32 0, i32 5 <i>; yields [20 x i32]*:%t4</i>
+ %t5 = getelementptr [20 x i32]* %t4, i32 0, i32 13 <i>; yields i32*:%t5</i>
+ ret i32* %t5
+}
+</pre>
+
+<p>If the <tt>inbounds</tt> keyword is present, the result value of the
+ <tt>getelementptr</tt> is a <a href="#poisonvalues">poison value</a> if the
+ base pointer is not an <i>in bounds</i> address of an allocated object,
+ or if any of the addresses that would be formed by successive addition of
+ the offsets implied by the indices to the base address with infinitely
+ precise signed arithmetic are not an <i>in bounds</i> address of that
+ allocated object. The <i>in bounds</i> addresses for an allocated object
+ are all the addresses that point into the object, plus the address one
+ byte past the end.
+ In cases where the base is a vector of pointers the <tt>inbounds</tt> keyword
+ applies to each of the computations element-wise. </p>
+
+<p>If the <tt>inbounds</tt> keyword is not present, the offsets are added to
+ the base address with silently-wrapping two's complement arithmetic. If the
+ offsets have a different width from the pointer, they are sign-extended or
+ truncated to the width of the pointer. The result value of the
+ <tt>getelementptr</tt> may be outside the object pointed to by the base
+ pointer. The result value may not necessarily be used to access memory
+ though, even if it happens to point into allocated storage. See the
+ <a href="#pointeraliasing">Pointer Aliasing Rules</a> section for more
+ information.</p>
+
+<p>The getelementptr instruction is often confusing. For some more insight into
+ how it works, see <a href="GetElementPtr.html">the getelementptr FAQ</a>.</p>
+
+<h5>Example:</h5>
+<pre>
+ <i>; yields [12 x i8]*:aptr</i>
+ %aptr = getelementptr {i32, [12 x i8]}* %saptr, i64 0, i32 1
+ <i>; yields i8*:vptr</i>
+ %vptr = getelementptr {i32, <2 x i8>}* %svptr, i64 0, i32 1, i32 1
+ <i>; yields i8*:eptr</i>
+ %eptr = getelementptr [12 x i8]* %aptr, i64 0, i32 1
+ <i>; yields i32*:iptr</i>
+ %iptr = getelementptr [10 x i32]* @arr, i16 0, i16 0
+</pre>
+
+<p>In cases where the pointer argument is a vector of pointers, only a
+ single index may be used, and the number of vector elements has to be
+ the same. For example: </p>
+<pre class="doc_code">
+ %A = getelementptr <4 x i8*> %ptrs, <4 x i64> %offsets,
+</pre>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="convertops">Conversion Operations</a>
+</h3>
+
+<div>
+
+<p>The instructions in this category are the conversion instructions (casting)
+ which all take a single operand and a type. They perform various bit
+ conversions on the operand.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_trunc">'<tt>trunc .. to</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = trunc <ty> <value> to <ty2> <i>; yields ty2</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>trunc</tt>' instruction truncates its operand to the
+ type <tt>ty2</tt>.</p>
+
+<h5>Arguments:</h5>
+<p>The '<tt>trunc</tt>' instruction takes a value to trunc, and a type to trunc it to.
+ Both types must be of <a href="#t_integer">integer</a> types, or vectors
+ of the same number of integers.
+ The bit size of the <tt>value</tt> must be larger than
+ the bit size of the destination type, <tt>ty2</tt>.
+ Equal sized types are not allowed.</p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>trunc</tt>' instruction truncates the high order bits
+ in <tt>value</tt> and converts the remaining bits to <tt>ty2</tt>. Since the
+ source size must be larger than the destination size, <tt>trunc</tt> cannot
+ be a <i>no-op cast</i>. It will always truncate bits.</p>
+
+<h5>Example:</h5>
+<pre>
+ %X = trunc i32 257 to i8 <i>; yields i8:1</i>
+ %Y = trunc i32 123 to i1 <i>; yields i1:true</i>
+ %Z = trunc i32 122 to i1 <i>; yields i1:false</i>
+ %W = trunc <2 x i16> <i16 8, i16 7> to <2 x i8> <i>; yields <i8 8, i8 7></i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_zext">'<tt>zext .. to</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = zext <ty> <value> to <ty2> <i>; yields ty2</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>zext</tt>' instruction zero extends its operand to type
+ <tt>ty2</tt>.</p>
+
+
+<h5>Arguments:</h5>
+<p>The '<tt>zext</tt>' instruction takes a value to cast, and a type to cast it to.
+ Both types must be of <a href="#t_integer">integer</a> types, or vectors
+ of the same number of integers.
+ The bit size of the <tt>value</tt> must be smaller than
+ the bit size of the destination type,
+ <tt>ty2</tt>.</p>
+
+<h5>Semantics:</h5>
+<p>The <tt>zext</tt> fills the high order bits of the <tt>value</tt> with zero
+ bits until it reaches the size of the destination type, <tt>ty2</tt>.</p>
+
+<p>When zero extending from i1, the result will always be either 0 or 1.</p>
+
+<h5>Example:</h5>
+<pre>
+ %X = zext i32 257 to i64 <i>; yields i64:257</i>
+ %Y = zext i1 true to i32 <i>; yields i32:1</i>
+ %Z = zext <2 x i16> <i16 8, i16 7> to <2 x i32> <i>; yields <i32 8, i32 7></i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_sext">'<tt>sext .. to</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = sext <ty> <value> to <ty2> <i>; yields ty2</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>sext</tt>' sign extends <tt>value</tt> to the type <tt>ty2</tt>.</p>
+
+<h5>Arguments:</h5>
+<p>The '<tt>sext</tt>' instruction takes a value to cast, and a type to cast it to.
+ Both types must be of <a href="#t_integer">integer</a> types, or vectors
+ of the same number of integers.
+ The bit size of the <tt>value</tt> must be smaller than
+ the bit size of the destination type,
+ <tt>ty2</tt>.</p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>sext</tt>' instruction performs a sign extension by copying the sign
+ bit (highest order bit) of the <tt>value</tt> until it reaches the bit size
+ of the type <tt>ty2</tt>.</p>
+
+<p>When sign extending from i1, the extension always results in -1 or 0.</p>
+
+<h5>Example:</h5>
+<pre>
+ %X = sext i8 -1 to i16 <i>; yields i16 :65535</i>
+ %Y = sext i1 true to i32 <i>; yields i32:-1</i>
+ %Z = sext <2 x i16> <i16 8, i16 7> to <2 x i32> <i>; yields <i32 8, i32 7></i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_fptrunc">'<tt>fptrunc .. to</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = fptrunc <ty> <value> to <ty2> <i>; yields ty2</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>fptrunc</tt>' instruction truncates <tt>value</tt> to type
+ <tt>ty2</tt>.</p>
+
+<h5>Arguments:</h5>
+<p>The '<tt>fptrunc</tt>' instruction takes a <a href="#t_floating">floating
+ point</a> value to cast and a <a href="#t_floating">floating point</a> type
+ to cast it to. The size of <tt>value</tt> must be larger than the size of
+ <tt>ty2</tt>. This implies that <tt>fptrunc</tt> cannot be used to make a
+ <i>no-op cast</i>.</p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>fptrunc</tt>' instruction truncates a <tt>value</tt> from a larger
+ <a href="#t_floating">floating point</a> type to a smaller
+ <a href="#t_floating">floating point</a> type. If the value cannot fit
+ within the destination type, <tt>ty2</tt>, then the results are
+ undefined.</p>
+
+<h5>Example:</h5>
+<pre>
+ %X = fptrunc double 123.0 to float <i>; yields float:123.0</i>
+ %Y = fptrunc double 1.0E+300 to float <i>; yields undefined</i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_fpext">'<tt>fpext .. to</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = fpext <ty> <value> to <ty2> <i>; yields ty2</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>fpext</tt>' extends a floating point <tt>value</tt> to a larger
+ floating point value.</p>
+
+<h5>Arguments:</h5>
+<p>The '<tt>fpext</tt>' instruction takes a
+ <a href="#t_floating">floating point</a> <tt>value</tt> to cast, and
+ a <a href="#t_floating">floating point</a> type to cast it to. The source
+ type must be smaller than the destination type.</p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>fpext</tt>' instruction extends the <tt>value</tt> from a smaller
+ <a href="#t_floating">floating point</a> type to a larger
+ <a href="#t_floating">floating point</a> type. The <tt>fpext</tt> cannot be
+ used to make a <i>no-op cast</i> because it always changes bits. Use
+ <tt>bitcast</tt> to make a <i>no-op cast</i> for a floating point cast.</p>
+
+<h5>Example:</h5>
+<pre>
+ %X = fpext float 3.125 to double <i>; yields double:3.125000e+00</i>
+ %Y = fpext double %X to fp128 <i>; yields fp128:0xL00000000000000004000900000000000</i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_fptoui">'<tt>fptoui .. to</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = fptoui <ty> <value> to <ty2> <i>; yields ty2</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>fptoui</tt>' converts a floating point <tt>value</tt> to its
+ unsigned integer equivalent of type <tt>ty2</tt>.</p>
+
+<h5>Arguments:</h5>
+<p>The '<tt>fptoui</tt>' instruction takes a value to cast, which must be a
+ scalar or vector <a href="#t_floating">floating point</a> value, and a type
+ to cast it to <tt>ty2</tt>, which must be an <a href="#t_integer">integer</a>
+ type. If <tt>ty</tt> is a vector floating point type, <tt>ty2</tt> must be a
+ vector integer type with the same number of elements as <tt>ty</tt></p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>fptoui</tt>' instruction converts its
+ <a href="#t_floating">floating point</a> operand into the nearest (rounding
+ towards zero) unsigned integer value. If the value cannot fit
+ in <tt>ty2</tt>, the results are undefined.</p>
+
+<h5>Example:</h5>
+<pre>
+ %X = fptoui double 123.0 to i32 <i>; yields i32:123</i>
+ %Y = fptoui float 1.0E+300 to i1 <i>; yields undefined:1</i>
+ %Z = fptoui float 1.04E+17 to i8 <i>; yields undefined:1</i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_fptosi">'<tt>fptosi .. to</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = fptosi <ty> <value> to <ty2> <i>; yields ty2</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>fptosi</tt>' instruction converts
+ <a href="#t_floating">floating point</a> <tt>value</tt> to
+ type <tt>ty2</tt>.</p>
+
+<h5>Arguments:</h5>
+<p>The '<tt>fptosi</tt>' instruction takes a value to cast, which must be a
+ scalar or vector <a href="#t_floating">floating point</a> value, and a type
+ to cast it to <tt>ty2</tt>, which must be an <a href="#t_integer">integer</a>
+ type. If <tt>ty</tt> is a vector floating point type, <tt>ty2</tt> must be a
+ vector integer type with the same number of elements as <tt>ty</tt></p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>fptosi</tt>' instruction converts its
+ <a href="#t_floating">floating point</a> operand into the nearest (rounding
+ towards zero) signed integer value. If the value cannot fit in <tt>ty2</tt>,
+ the results are undefined.</p>
+
+<h5>Example:</h5>
+<pre>
+ %X = fptosi double -123.0 to i32 <i>; yields i32:-123</i>
+ %Y = fptosi float 1.0E-247 to i1 <i>; yields undefined:1</i>
+ %Z = fptosi float 1.04E+17 to i8 <i>; yields undefined:1</i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_uitofp">'<tt>uitofp .. to</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = uitofp <ty> <value> to <ty2> <i>; yields ty2</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>uitofp</tt>' instruction regards <tt>value</tt> as an unsigned
+ integer and converts that value to the <tt>ty2</tt> type.</p>
+
+<h5>Arguments:</h5>
+<p>The '<tt>uitofp</tt>' instruction takes a value to cast, which must be a
+ scalar or vector <a href="#t_integer">integer</a> value, and a type to cast
+ it to <tt>ty2</tt>, which must be an <a href="#t_floating">floating point</a>
+ type. If <tt>ty</tt> is a vector integer type, <tt>ty2</tt> must be a vector
+ floating point type with the same number of elements as <tt>ty</tt></p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>uitofp</tt>' instruction interprets its operand as an unsigned
+ integer quantity and converts it to the corresponding floating point
+ value. If the value cannot fit in the floating point value, the results are
+ undefined.</p>
+
+<h5>Example:</h5>
+<pre>
+ %X = uitofp i32 257 to float <i>; yields float:257.0</i>
+ %Y = uitofp i8 -1 to double <i>; yields double:255.0</i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_sitofp">'<tt>sitofp .. to</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = sitofp <ty> <value> to <ty2> <i>; yields ty2</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>sitofp</tt>' instruction regards <tt>value</tt> as a signed integer
+ and converts that value to the <tt>ty2</tt> type.</p>
+
+<h5>Arguments:</h5>
+<p>The '<tt>sitofp</tt>' instruction takes a value to cast, which must be a
+ scalar or vector <a href="#t_integer">integer</a> value, and a type to cast
+ it to <tt>ty2</tt>, which must be an <a href="#t_floating">floating point</a>
+ type. If <tt>ty</tt> is a vector integer type, <tt>ty2</tt> must be a vector
+ floating point type with the same number of elements as <tt>ty</tt></p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>sitofp</tt>' instruction interprets its operand as a signed integer
+ quantity and converts it to the corresponding floating point value. If the
+ value cannot fit in the floating point value, the results are undefined.</p>
+
+<h5>Example:</h5>
+<pre>
+ %X = sitofp i32 257 to float <i>; yields float:257.0</i>
+ %Y = sitofp i8 -1 to double <i>; yields double:-1.0</i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_ptrtoint">'<tt>ptrtoint .. to</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = ptrtoint <ty> <value> to <ty2> <i>; yields ty2</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>ptrtoint</tt>' instruction converts the pointer or a vector of
+ pointers <tt>value</tt> to
+ the integer (or vector of integers) type <tt>ty2</tt>.</p>
+
+<h5>Arguments:</h5>
+<p>The '<tt>ptrtoint</tt>' instruction takes a <tt>value</tt> to cast, which
+ must be a a value of type <a href="#t_pointer">pointer</a> or a vector of
+ pointers, and a type to cast it to
+ <tt>ty2</tt>, which must be an <a href="#t_integer">integer</a> or a vector
+ of integers type.</p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>ptrtoint</tt>' instruction converts <tt>value</tt> to integer type
+ <tt>ty2</tt> by interpreting the pointer value as an integer and either
+ truncating or zero extending that value to the size of the integer type. If
+ <tt>value</tt> is smaller than <tt>ty2</tt> then a zero extension is done. If
+ <tt>value</tt> is larger than <tt>ty2</tt> then a truncation is done. If they
+ are the same size, then nothing is done (<i>no-op cast</i>) other than a type
+ change.</p>
+
+<h5>Example:</h5>
+<pre>
+ %X = ptrtoint i32* %P to i8 <i>; yields truncation on 32-bit architecture</i>
+ %Y = ptrtoint i32* %P to i64 <i>; yields zero extension on 32-bit architecture</i>
+ %Z = ptrtoint <4 x i32*> %P to <4 x i64><i>; yields vector zero extension for a vector of addresses on 32-bit architecture</i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_inttoptr">'<tt>inttoptr .. to</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = inttoptr <ty> <value> to <ty2> <i>; yields ty2</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>inttoptr</tt>' instruction converts an integer <tt>value</tt> to a
+ pointer type, <tt>ty2</tt>.</p>
+
+<h5>Arguments:</h5>
+<p>The '<tt>inttoptr</tt>' instruction takes an <a href="#t_integer">integer</a>
+ value to cast, and a type to cast it to, which must be a
+ <a href="#t_pointer">pointer</a> type.</p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>inttoptr</tt>' instruction converts <tt>value</tt> to type
+ <tt>ty2</tt> by applying either a zero extension or a truncation depending on
+ the size of the integer <tt>value</tt>. If <tt>value</tt> is larger than the
+ size of a pointer then a truncation is done. If <tt>value</tt> is smaller
+ than the size of a pointer then a zero extension is done. If they are the
+ same size, nothing is done (<i>no-op cast</i>).</p>
+
+<h5>Example:</h5>
+<pre>
+ %X = inttoptr i32 255 to i32* <i>; yields zero extension on 64-bit architecture</i>
+ %Y = inttoptr i32 255 to i32* <i>; yields no-op on 32-bit architecture</i>
+ %Z = inttoptr i64 0 to i32* <i>; yields truncation on 32-bit architecture</i>
+ %Z = inttoptr <4 x i32> %G to <4 x i8*><i>; yields truncation of vector G to four pointers</i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_bitcast">'<tt>bitcast .. to</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = bitcast <ty> <value> to <ty2> <i>; yields ty2</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>bitcast</tt>' instruction converts <tt>value</tt> to type
+ <tt>ty2</tt> without changing any bits.</p>
+
+<h5>Arguments:</h5>
+<p>The '<tt>bitcast</tt>' instruction takes a value to cast, which must be a
+ non-aggregate first class value, and a type to cast it to, which must also be
+ a non-aggregate <a href="#t_firstclass">first class</a> type. The bit sizes
+ of <tt>value</tt> and the destination type, <tt>ty2</tt>, must be
+ identical. If the source type is a pointer, the destination type must also be
+ a pointer. This instruction supports bitwise conversion of vectors to
+ integers and to vectors of other types (as long as they have the same
+ size).</p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>bitcast</tt>' instruction converts <tt>value</tt> to type
+ <tt>ty2</tt>. It is always a <i>no-op cast</i> because no bits change with
+ this conversion. The conversion is done as if the <tt>value</tt> had been
+ stored to memory and read back as type <tt>ty2</tt>.
+ Pointer (or vector of pointers) types may only be converted to other pointer
+ (or vector of pointers) types with this instruction. To convert
+ pointers to other types, use the <a href="#i_inttoptr">inttoptr</a> or
+ <a href="#i_ptrtoint">ptrtoint</a> instructions first.</p>
+
+<h5>Example:</h5>
+<pre>
+ %X = bitcast i8 255 to i8 <i>; yields i8 :-1</i>
+ %Y = bitcast i32* %x to sint* <i>; yields sint*:%x</i>
+ %Z = bitcast <2 x int> %V to i64; <i>; yields i64: %V</i>
+ %Z = bitcast <2 x i32*> %V to <2 x i64*> <i>; yields <2 x i64*></i>
+</pre>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="otherops">Other Operations</a>
+</h3>
+
+<div>
+
+<p>The instructions in this category are the "miscellaneous" instructions, which
+ defy better classification.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_icmp">'<tt>icmp</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = icmp <cond> <ty> <op1>, <op2> <i>; yields {i1} or {<N x i1>}:result</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>icmp</tt>' instruction returns a boolean value or a vector of
+ boolean values based on comparison of its two integer, integer vector,
+ pointer, or pointer vector operands.</p>
+
+<h5>Arguments:</h5>
+<p>The '<tt>icmp</tt>' instruction takes three operands. The first operand is
+ the condition code indicating the kind of comparison to perform. It is not a
+ value, just a keyword. The possible condition code are:</p>
+
+<ol>
+ <li><tt>eq</tt>: equal</li>
+ <li><tt>ne</tt>: not equal </li>
+ <li><tt>ugt</tt>: unsigned greater than</li>
+ <li><tt>uge</tt>: unsigned greater or equal</li>
+ <li><tt>ult</tt>: unsigned less than</li>
+ <li><tt>ule</tt>: unsigned less or equal</li>
+ <li><tt>sgt</tt>: signed greater than</li>
+ <li><tt>sge</tt>: signed greater or equal</li>
+ <li><tt>slt</tt>: signed less than</li>
+ <li><tt>sle</tt>: signed less or equal</li>
+</ol>
+
+<p>The remaining two arguments must be <a href="#t_integer">integer</a> or
+ <a href="#t_pointer">pointer</a> or integer <a href="#t_vector">vector</a>
+ typed. They must also be identical types.</p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>icmp</tt>' compares <tt>op1</tt> and <tt>op2</tt> according to the
+ condition code given as <tt>cond</tt>. The comparison performed always yields
+ either an <a href="#t_integer"><tt>i1</tt></a> or vector of <tt>i1</tt>
+ result, as follows:</p>
+
+<ol>
+ <li><tt>eq</tt>: yields <tt>true</tt> if the operands are equal,
+ <tt>false</tt> otherwise. No sign interpretation is necessary or
+ performed.</li>
+
+ <li><tt>ne</tt>: yields <tt>true</tt> if the operands are unequal,
+ <tt>false</tt> otherwise. No sign interpretation is necessary or
+ performed.</li>
+
+ <li><tt>ugt</tt>: interprets the operands as unsigned values and yields
+ <tt>true</tt> if <tt>op1</tt> is greater than <tt>op2</tt>.</li>
+
+ <li><tt>uge</tt>: interprets the operands as unsigned values and yields
+ <tt>true</tt> if <tt>op1</tt> is greater than or equal
+ to <tt>op2</tt>.</li>
+
+ <li><tt>ult</tt>: interprets the operands as unsigned values and yields
+ <tt>true</tt> if <tt>op1</tt> is less than <tt>op2</tt>.</li>
+
+ <li><tt>ule</tt>: interprets the operands as unsigned values and yields
+ <tt>true</tt> if <tt>op1</tt> is less than or equal to <tt>op2</tt>.</li>
+
+ <li><tt>sgt</tt>: interprets the operands as signed values and yields
+ <tt>true</tt> if <tt>op1</tt> is greater than <tt>op2</tt>.</li>
+
+ <li><tt>sge</tt>: interprets the operands as signed values and yields
+ <tt>true</tt> if <tt>op1</tt> is greater than or equal
+ to <tt>op2</tt>.</li>
+
+ <li><tt>slt</tt>: interprets the operands as signed values and yields
+ <tt>true</tt> if <tt>op1</tt> is less than <tt>op2</tt>.</li>
+
+ <li><tt>sle</tt>: interprets the operands as signed values and yields
+ <tt>true</tt> if <tt>op1</tt> is less than or equal to <tt>op2</tt>.</li>
+</ol>
+
+<p>If the operands are <a href="#t_pointer">pointer</a> typed, the pointer
+ values are compared as if they were integers.</p>
+
+<p>If the operands are integer vectors, then they are compared element by
+ element. The result is an <tt>i1</tt> vector with the same number of elements
+ as the values being compared. Otherwise, the result is an <tt>i1</tt>.</p>
+
+<h5>Example:</h5>
+<pre>
+ <result> = icmp eq i32 4, 5 <i>; yields: result=false</i>
+ <result> = icmp ne float* %X, %X <i>; yields: result=false</i>
+ <result> = icmp ult i16 4, 5 <i>; yields: result=true</i>
+ <result> = icmp sgt i16 4, 5 <i>; yields: result=false</i>
+ <result> = icmp ule i16 -4, 5 <i>; yields: result=false</i>
+ <result> = icmp sge i16 4, 5 <i>; yields: result=false</i>
+</pre>
+
+<p>Note that the code generator does not yet support vector types with
+ the <tt>icmp</tt> instruction.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_fcmp">'<tt>fcmp</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = fcmp <cond> <ty> <op1>, <op2> <i>; yields {i1} or {<N x i1>}:result</i>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>fcmp</tt>' instruction returns a boolean value or vector of boolean
+ values based on comparison of its operands.</p>
+
+<p>If the operands are floating point scalars, then the result type is a boolean
+(<a href="#t_integer"><tt>i1</tt></a>).</p>
+
+<p>If the operands are floating point vectors, then the result type is a vector
+ of boolean with the same number of elements as the operands being
+ compared.</p>
+
+<h5>Arguments:</h5>
+<p>The '<tt>fcmp</tt>' instruction takes three operands. The first operand is
+ the condition code indicating the kind of comparison to perform. It is not a
+ value, just a keyword. The possible condition code are:</p>
+
+<ol>
+ <li><tt>false</tt>: no comparison, always returns false</li>
+ <li><tt>oeq</tt>: ordered and equal</li>
+ <li><tt>ogt</tt>: ordered and greater than </li>
+ <li><tt>oge</tt>: ordered and greater than or equal</li>
+ <li><tt>olt</tt>: ordered and less than </li>
+ <li><tt>ole</tt>: ordered and less than or equal</li>
+ <li><tt>one</tt>: ordered and not equal</li>
+ <li><tt>ord</tt>: ordered (no nans)</li>
+ <li><tt>ueq</tt>: unordered or equal</li>
+ <li><tt>ugt</tt>: unordered or greater than </li>
+ <li><tt>uge</tt>: unordered or greater than or equal</li>
+ <li><tt>ult</tt>: unordered or less than </li>
+ <li><tt>ule</tt>: unordered or less than or equal</li>
+ <li><tt>une</tt>: unordered or not equal</li>
+ <li><tt>uno</tt>: unordered (either nans)</li>
+ <li><tt>true</tt>: no comparison, always returns true</li>
+</ol>
+
+<p><i>Ordered</i> means that neither operand is a QNAN while
+ <i>unordered</i> means that either operand may be a QNAN.</p>
+
+<p>Each of <tt>val1</tt> and <tt>val2</tt> arguments must be either
+ a <a href="#t_floating">floating point</a> type or
+ a <a href="#t_vector">vector</a> of floating point type. They must have
+ identical types.</p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>fcmp</tt>' instruction compares <tt>op1</tt> and <tt>op2</tt>
+ according to the condition code given as <tt>cond</tt>. If the operands are
+ vectors, then the vectors are compared element by element. Each comparison
+ performed always yields an <a href="#t_integer">i1</a> result, as
+ follows:</p>
+
+<ol>
+ <li><tt>false</tt>: always yields <tt>false</tt>, regardless of operands.</li>
+
+ <li><tt>oeq</tt>: yields <tt>true</tt> if both operands are not a QNAN and
+ <tt>op1</tt> is equal to <tt>op2</tt>.</li>
+
+ <li><tt>ogt</tt>: yields <tt>true</tt> if both operands are not a QNAN and
+ <tt>op1</tt> is greater than <tt>op2</tt>.</li>
+
+ <li><tt>oge</tt>: yields <tt>true</tt> if both operands are not a QNAN and
+ <tt>op1</tt> is greater than or equal to <tt>op2</tt>.</li>
+
+ <li><tt>olt</tt>: yields <tt>true</tt> if both operands are not a QNAN and
+ <tt>op1</tt> is less than <tt>op2</tt>.</li>
+
+ <li><tt>ole</tt>: yields <tt>true</tt> if both operands are not a QNAN and
+ <tt>op1</tt> is less than or equal to <tt>op2</tt>.</li>
+
+ <li><tt>one</tt>: yields <tt>true</tt> if both operands are not a QNAN and
+ <tt>op1</tt> is not equal to <tt>op2</tt>.</li>
+
+ <li><tt>ord</tt>: yields <tt>true</tt> if both operands are not a QNAN.</li>
+
+ <li><tt>ueq</tt>: yields <tt>true</tt> if either operand is a QNAN or
+ <tt>op1</tt> is equal to <tt>op2</tt>.</li>
+
+ <li><tt>ugt</tt>: yields <tt>true</tt> if either operand is a QNAN or
+ <tt>op1</tt> is greater than <tt>op2</tt>.</li>
+
+ <li><tt>uge</tt>: yields <tt>true</tt> if either operand is a QNAN or
+ <tt>op1</tt> is greater than or equal to <tt>op2</tt>.</li>
+
+ <li><tt>ult</tt>: yields <tt>true</tt> if either operand is a QNAN or
+ <tt>op1</tt> is less than <tt>op2</tt>.</li>
+
+ <li><tt>ule</tt>: yields <tt>true</tt> if either operand is a QNAN or
+ <tt>op1</tt> is less than or equal to <tt>op2</tt>.</li>
+
+ <li><tt>une</tt>: yields <tt>true</tt> if either operand is a QNAN or
+ <tt>op1</tt> is not equal to <tt>op2</tt>.</li>
+
+ <li><tt>uno</tt>: yields <tt>true</tt> if either operand is a QNAN.</li>
+
+ <li><tt>true</tt>: always yields <tt>true</tt>, regardless of operands.</li>
+</ol>
+
+<h5>Example:</h5>
+<pre>
+ <result> = fcmp oeq float 4.0, 5.0 <i>; yields: result=false</i>
+ <result> = fcmp one float 4.0, 5.0 <i>; yields: result=true</i>
+ <result> = fcmp olt float 4.0, 5.0 <i>; yields: result=true</i>
+ <result> = fcmp ueq double 1.0, 2.0 <i>; yields: result=false</i>
+</pre>
+
+<p>Note that the code generator does not yet support vector types with
+ the <tt>fcmp</tt> instruction.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_phi">'<tt>phi</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<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 is 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>
+
+<p>For the purposes of the SSA form, the use of each incoming value is deemed to
+ occur on the edge from the corresponding predecessor block to the current
+ block (but after any definition of an '<tt>invoke</tt>' instruction's return
+ value on the same edge).</p>
+
+<h5>Semantics:</h5>
+<p>At runtime, the '<tt>phi</tt>' instruction logically takes on the value
+ specified by the pair corresponding to the predecessor basic block that
+ executed just prior to the current block.</p>
+
+<h5>Example:</h5>
+<pre>
+Loop: ; Infinite loop that counts from 0 on up...
+ %indvar = phi i32 [ 0, %LoopHeader ], [ %nextindvar, %Loop ]
+ %nextindvar = add i32 %indvar, 1
+ br label %Loop
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_select">'<tt>select</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = select <i>selty</i> <cond>, <ty> <val1>, <ty> <val2> <i>; yields ty</i>
+
+ <i>selty</i> is either i1 or {<N x i1>}
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>select</tt>' instruction is used to choose one value based on a
+ condition, without branching.</p>
+
+
+<h5>Arguments:</h5>
+<p>The '<tt>select</tt>' instruction requires an 'i1' value or a vector of 'i1'
+ values indicating the condition, and two values of the
+ same <a href="#t_firstclass">first class</a> type. If the val1/val2 are
+ vectors and the condition is a scalar, then entire vectors are selected, not
+ individual elements.</p>
+
+<h5>Semantics:</h5>
+<p>If the condition is an i1 and it evaluates to 1, the instruction returns the
+ first value argument; otherwise, it returns the second value argument.</p>
+
+<p>If the condition is a vector of i1, then the value arguments must be vectors
+ of the same size, and the selection is done element by element.</p>
+
+<h5>Example:</h5>
+<pre>
+ %X = select i1 true, i8 17, i8 42 <i>; yields i8:17</i>
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_call">'<tt>call</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <result> = [tail] call [<a href="#callingconv">cconv</a>] [<a href="#paramattrs">ret attrs</a>] <ty> [<fnty>*] <fnptrval>(<function args>) [<a href="#fnattrs">fn attrs</a>]
+</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>The optional "tail" marker indicates that the callee function does not
+ access any allocas or varargs in the caller. Note that calls may be
+ marked "tail" even if they do not occur before
+ a <a href="#i_ret"><tt>ret</tt></a> instruction. If the "tail" marker is
+ present, the function call is eligible for tail call optimization,
+ but <a href="CodeGenerator.html#tailcallopt">might not in fact be
+ optimized into a jump</a>. The code generator may optimize calls marked
+ "tail" with either 1) automatic <a href="CodeGenerator.html#sibcallopt">
+ sibling call optimization</a> when the caller and callee have
+ matching signatures, or 2) forced tail call optimization when the
+ following extra requirements are met:
+ <ul>
+ <li>Caller and callee both have the calling
+ convention <tt>fastcc</tt>.</li>
+ <li>The call is in tail position (ret immediately follows call and ret
+ uses value of call or is void).</li>
+ <li>Option <tt>-tailcallopt</tt> is enabled,
+ or <code>llvm::GuaranteedTailCallOpt</code> is <code>true</code>.</li>
+ <li><a href="CodeGenerator.html#tailcallopt">Platform specific
+ constraints are met.</a></li>
+ </ul>
+ </li>
+
+ <li>The optional "cconv" marker indicates which <a href="#callingconv">calling
+ convention</a> the call should use. If none is specified, the call
+ defaults to using C calling conventions. The calling convention of the
+ call must match the calling convention of the target function, or else the
+ behavior is undefined.</li>
+
+ <li>The optional <a href="#paramattrs">Parameter Attributes</a> list for
+ return values. Only '<tt>zeroext</tt>', '<tt>signext</tt>', and
+ '<tt>inreg</tt>' attributes are valid here.</li>
+
+ <li>'<tt>ty</tt>': the type of the call instruction itself which is also the
+ type of the return value. Functions that return no value are marked
+ <tt><a href="#t_void">void</a></tt>.</li>
+
+ <li>'<tt>fnty</tt>': shall be the signature of the pointer to function value
+ being invoked. The argument types must match the types implied by this
+ signature. This type can be omitted if the function is not varargs and if
+ the function type does not return a pointer to a function.</li>
+
+ <li>'<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 value.</li>
+
+ <li>'<tt>function args</tt>': argument list whose types match the function
+ signature argument types and parameter attributes. All arguments must be
+ of <a href="#t_firstclass">first class</a> type. If the function
+ signature indicates the function accepts a variable number of arguments,
+ the extra arguments can be specified.</li>
+
+ <li>The optional <a href="#fnattrs">function attributes</a> list. Only
+ '<tt>noreturn</tt>', '<tt>nounwind</tt>', '<tt>readonly</tt>' and
+ '<tt>readnone</tt>' attributes are valid here.</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.</p>
+
+<h5>Example:</h5>
+<pre>
+ %retval = call i32 @test(i32 %argc)
+ call i32 (i8*, ...)* @printf(i8* %msg, i32 12, i8 42) <i>; yields i32</i>
+ %X = tail call i32 @foo() <i>; yields i32</i>
+ %Y = tail call <a href="#callingconv">fastcc</a> i32 @foo() <i>; yields i32</i>
+ call void %foo(i8 97 signext)
+
+ %struct.A = type { i32, i8 }
+ %r = call %struct.A @foo() <i>; yields { 32, i8 }</i>
+ %gr = extractvalue %struct.A %r, 0 <i>; yields i32</i>
+ %gr1 = extractvalue %struct.A %r, 1 <i>; yields i8</i>
+ %Z = call void @foo() noreturn <i>; indicates that %foo never returns normally</i>
+ %ZZ = call zeroext i32 @bar() <i>; Return value is %zero extended</i>
+</pre>
+
+<p>llvm treats calls to some functions with names and arguments that match the
+standard C99 library as being the C99 library functions, and may perform
+optimizations or generate code for them under that assumption. This is
+something we'd like to change in the future to provide better support for
+freestanding environments and non-C-based languages.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_va_arg">'<tt>va_arg</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <resultval> = va_arg <va_list*> <arglist>, <argty>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>va_arg</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>va_list*</tt> value and the type of the
+ argument. It returns a value of the specified argument type and increments
+ the <tt>va_list</tt> to point to the next argument. The actual type
+ of <tt>va_list</tt> is target specific.</p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>va_arg</tt>' instruction loads an argument of the specified type
+ from the specified <tt>va_list</tt> and causes the <tt>va_list</tt> to point
+ to the next argument. 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>va_arg</tt> is an LLVM instruction instead of
+ an <a href="#intrinsics">intrinsic function</a> because it takes a type as an
+ argument.</p>
+
+<h5>Example:</h5>
+<p>See the <a href="#int_varargs">variable argument processing</a> section.</p>
+
+<p>Note that the code generator does not yet fully support va_arg on many
+ targets. Also, it does not currently support va_arg with aggregate types on
+ any target.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="i_landingpad">'<tt>landingpad</tt>' Instruction</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ <resultval> = landingpad <resultty> personality <type> <pers_fn> <clause>+
+ <resultval> = landingpad <resultty> personality <type> <pers_fn> cleanup <clause>*
+
+ <clause> := catch <type> <value>
+ <clause> := filter <array constant type> <array constant>
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>landingpad</tt>' instruction is used by
+ <a href="ExceptionHandling.html#overview">LLVM's exception handling
+ system</a> to specify that a basic block is a landing pad — one where
+ the exception lands, and corresponds to the code found in the
+ <i><tt>catch</tt></i> portion of a <i><tt>try/catch</tt></i> sequence. It
+ defines values supplied by the personality function (<tt>pers_fn</tt>) upon
+ re-entry to the function. The <tt>resultval</tt> has the
+ type <tt>resultty</tt>.</p>
+
+<h5>Arguments:</h5>
+<p>This instruction takes a <tt>pers_fn</tt> value. This is the personality
+ function associated with the unwinding mechanism. The optional
+ <tt>cleanup</tt> flag indicates that the landing pad block is a cleanup.</p>
+
+<p>A <tt>clause</tt> begins with the clause type — <tt>catch</tt>
+ or <tt>filter</tt> — and contains the global variable representing the
+ "type" that may be caught or filtered respectively. Unlike the
+ <tt>catch</tt> clause, the <tt>filter</tt> clause takes an array constant as
+ its argument. Use "<tt>[0 x i8**] undef</tt>" for a filter which cannot
+ throw. The '<tt>landingpad</tt>' instruction must contain <em>at least</em>
+ one <tt>clause</tt> or the <tt>cleanup</tt> flag.</p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>landingpad</tt>' instruction defines the values which are set by the
+ personality function (<tt>pers_fn</tt>) upon re-entry to the function, and
+ therefore the "result type" of the <tt>landingpad</tt> instruction. As with
+ calling conventions, how the personality function results are represented in
+ LLVM IR is target specific.</p>
+
+<p>The clauses are applied in order from top to bottom. If two
+ <tt>landingpad</tt> instructions are merged together through inlining, the
+ clauses from the calling function are appended to the list of clauses.
+ When the call stack is being unwound due to an exception being thrown, the
+ exception is compared against each <tt>clause</tt> in turn. If it doesn't
+ match any of the clauses, and the <tt>cleanup</tt> flag is not set, then
+ unwinding continues further up the call stack.</p>
+
+<p>The <tt>landingpad</tt> instruction has several restrictions:</p>
+
+<ul>
+ <li>A landing pad block is a basic block which is the unwind destination of an
+ '<tt>invoke</tt>' instruction.</li>
+ <li>A landing pad block must have a '<tt>landingpad</tt>' instruction as its
+ first non-PHI instruction.</li>
+ <li>There can be only one '<tt>landingpad</tt>' instruction within the landing
+ pad block.</li>
+ <li>A basic block that is not a landing pad block may not include a
+ '<tt>landingpad</tt>' instruction.</li>
+ <li>All '<tt>landingpad</tt>' instructions in a function must have the same
+ personality function.</li>
+</ul>
+
+<h5>Example:</h5>
+<pre>
+ ;; A landing pad which can catch an integer.
+ %res = landingpad { i8*, i32 } personality i32 (...)* @__gxx_personality_v0
+ catch i8** @_ZTIi
+ ;; A landing pad that is a cleanup.
+ %res = landingpad { i8*, i32 } personality i32 (...)* @__gxx_personality_v0
+ cleanup
+ ;; A landing pad which can catch an integer and can only throw a double.
+ %res = landingpad { i8*, i32 } personality i32 (...)* @__gxx_personality_v0
+ catch i8** @_ZTIi
+ filter [1 x i8**] [@_ZTId]
+</pre>
+
+</div>
+
+</div>
+
+</div>
+
+<!-- *********************************************************************** -->
+<h2><a name="intrinsics">Intrinsic Functions</a></h2>
+<!-- *********************************************************************** -->
+
+<div>
+
+<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 intrinsics represent an extension mechanism for
+ the LLVM language that does not require changing all of the transformations
+ in LLVM when adding to the language (or the bitcode 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, function names may not
+ begin with this prefix. 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 if any are added that
+ they be documented here.</p>
+
+<p>Some intrinsic functions can be overloaded, i.e., the intrinsic represents a
+ family of functions that perform the same operation but on different data
+ types. Because LLVM can represent over 8 million different integer types,
+ overloading is used commonly to allow an intrinsic function to operate on any
+ integer type. One or more of the argument types or the result type can be
+ overloaded to accept any integer type. Argument types may also be defined as
+ exactly matching a previous argument's type or the result type. This allows
+ an intrinsic function which accepts multiple arguments, but needs all of them
+ to be of the same type, to only be overloaded with respect to a single
+ argument or the result.</p>
+
+<p>Overloaded intrinsics will have the names of its overloaded argument types
+ encoded into its function name, each preceded by a period. Only those types
+ which are overloaded result in a name suffix. Arguments whose type is matched
+ against another type do not. For example, the <tt>llvm.ctpop</tt> function
+ can take an integer of any width and returns an integer of exactly the same
+ integer width. This leads to a family of functions such as
+ <tt>i8 @llvm.ctpop.i8(i8 %val)</tt> and <tt>i29 @llvm.ctpop.i29(i29
+ %val)</tt>. Only one type, the return type, is overloaded, and only one type
+ suffix is required. Because the argument's type is matched against the return
+ type, it does not require its own name suffix.</p>
+
+<p>To learn how to add an intrinsic function, please see the
+ <a href="ExtendingLLVM.html">Extending LLVM Guide</a>.</p>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="int_varargs">Variable Argument Handling Intrinsics</a>
+</h3>
+
+<div>
+
+<p>Variable argument support is defined in LLVM with
+ the <a href="#i_va_arg"><tt>va_arg</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 these functions regardless of the type used.</p>
+
+<p>This example shows how the <a href="#i_va_arg"><tt>va_arg</tt></a>
+ instruction and the variable argument handling intrinsic functions are
+ used.</p>
+
+<pre class="doc_code">
+define i32 @test(i32 %X, ...) {
+ ; Initialize variable argument processing
+ %ap = alloca i8*
+ %ap2 = bitcast i8** %ap to i8*
+ call void @llvm.va_start(i8* %ap2)
+
+ ; Read a single integer argument
+ %tmp = va_arg i8** %ap, i32
+
+ ; Demonstrate usage of llvm.va_copy and llvm.va_end
+ %aq = alloca i8*
+ %aq2 = bitcast i8** %aq to i8*
+ call void @llvm.va_copy(i8* %aq2, i8* %ap2)
+ call void @llvm.va_end(i8* %aq2)
+
+ ; Stop processing of arguments.
+ call void @llvm.va_end(i8* %ap2)
+ ret i32 %tmp
+}
+
+declare void @llvm.va_start(i8*)
+declare void @llvm.va_copy(i8*, i8*)
+declare void @llvm.va_end(i8*)
+</pre>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_va_start">'<tt>llvm.va_start</tt>' Intrinsic</a>
+</h4>
+
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ declare void %llvm.va_start(i8* <arglist>)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.va_start</tt>' intrinsic initializes <tt>*<arglist></tt>
+ for subsequent use by <tt><a href="#i_va_arg">va_arg</a></tt>.</p>
+
+<h5>Arguments:</h5>
+<p>The argument is a pointer to a <tt>va_list</tt> element to initialize.</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
+ the <tt>va_list</tt> element to which the argument points, so that the next
+ call to <tt>va_arg</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 as the compiler can figure
+ that out.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_va_end">'<tt>llvm.va_end</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ declare void @llvm.va_end(i8* <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="#int_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 pointer to 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> element to which the argument points. Calls
+ to <a href="#int_va_start"><tt>llvm.va_start</tt></a>
+ and <a href="#int_va_copy"> <tt>llvm.va_copy</tt></a> must be matched exactly
+ with calls to <tt>llvm.va_end</tt>.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_va_copy">'<tt>llvm.va_copy</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ declare void @llvm.va_copy(i8* <destarglist>, i8* <srcarglist>)
+</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 first argument is a pointer to a <tt>va_list</tt> element to initialize.
+ The second argument is a pointer to a <tt>va_list</tt> element to copy
+ from.</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 destination <tt>va_list</tt>
+ element. This intrinsic is necessary because
+ the <tt><a href="#int_va_start"> llvm.va_start</a></tt> intrinsic may be
+ arbitrarily complex and require, for example, memory allocation.</p>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="int_gc">Accurate Garbage Collection Intrinsics</a>
+</h3>
+
+<div>
+
+<p>LLVM support for <a href="GarbageCollection.html">Accurate Garbage
+Collection</a> (GC) requires the implementation and generation of these
+intrinsics. These intrinsics allow identification of <a href="#int_gcroot">GC
+roots on the stack</a>, as well as garbage collector implementations that
+require <a href="#int_gcread">read</a> and <a href="#int_gcwrite">write</a>
+barriers. Front-ends for type-safe garbage collected languages should generate
+these intrinsics to make use of the LLVM garbage collectors. For more details,
+see <a href="GarbageCollection.html">Accurate Garbage Collection with
+LLVM</a>.</p>
+
+<p>The garbage collection intrinsics only operate on objects in the generic
+ address space (address space zero).</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_gcroot">'<tt>llvm.gcroot</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ declare void @llvm.gcroot(i8** %ptrloc, i8* %metadata)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.gcroot</tt>' intrinsic declares the existence of a GC root to
+ the code generator, and allows some metadata to be associated with it.</p>
+
+<h5>Arguments:</h5>
+<p>The first argument specifies the address of a stack object that contains the
+ root pointer. The second pointer (which must be either a constant or a
+ global value address) contains the meta-data to be associated with the
+ root.</p>
+
+<h5>Semantics:</h5>
+<p>At runtime, a call to this intrinsic stores a null pointer into the "ptrloc"
+ location. At compile-time, the code generator generates information to allow
+ the runtime to find the pointer at GC safe points. The '<tt>llvm.gcroot</tt>'
+ intrinsic may only be used in a function which <a href="#gc">specifies a GC
+ algorithm</a>.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_gcread">'<tt>llvm.gcread</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ declare i8* @llvm.gcread(i8* %ObjPtr, i8** %Ptr)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.gcread</tt>' intrinsic identifies reads of references from heap
+ locations, allowing garbage collector implementations that require read
+ barriers.</p>
+
+<h5>Arguments:</h5>
+<p>The second argument is the address to read from, which should be an address
+ allocated from the garbage collector. The first object is a pointer to the
+ start of the referenced object, if needed by the language runtime (otherwise
+ null).</p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>llvm.gcread</tt>' intrinsic has the same semantics as a load
+ instruction, but may be replaced with substantially more complex code by the
+ garbage collector runtime, as needed. The '<tt>llvm.gcread</tt>' intrinsic
+ may only be used in a function which <a href="#gc">specifies a GC
+ algorithm</a>.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_gcwrite">'<tt>llvm.gcwrite</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ declare void @llvm.gcwrite(i8* %P1, i8* %Obj, i8** %P2)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.gcwrite</tt>' intrinsic identifies writes of references to heap
+ locations, allowing garbage collector implementations that require write
+ barriers (such as generational or reference counting collectors).</p>
+
+<h5>Arguments:</h5>
+<p>The first argument is the reference to store, the second is the start of the
+ object to store it to, and the third is the address of the field of Obj to
+ store to. If the runtime does not require a pointer to the object, Obj may
+ be null.</p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>llvm.gcwrite</tt>' intrinsic has the same semantics as a store
+ instruction, but may be replaced with substantially more complex code by the
+ garbage collector runtime, as needed. The '<tt>llvm.gcwrite</tt>' intrinsic
+ may only be used in a function which <a href="#gc">specifies a GC
+ algorithm</a>.</p>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="int_codegen">Code Generator Intrinsics</a>
+</h3>
+
+<div>
+
+<p>These intrinsics are provided by LLVM to expose special features that may
+ only be implemented with code generator support.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_returnaddress">'<tt>llvm.returnaddress</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ declare i8 *@llvm.returnaddress(i32 <level>)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.returnaddress</tt>' intrinsic attempts to compute a
+ target-specific value indicating the return address of the current function
+ or one of its callers.</p>
+
+<h5>Arguments:</h5>
+<p>The argument to this intrinsic indicates which function to return the address
+ for. Zero indicates the calling function, one indicates its caller, etc.
+ The argument is <b>required</b> to be a constant integer value.</p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>llvm.returnaddress</tt>' intrinsic either returns a pointer
+ indicating the return address of the specified call frame, or zero if it
+ cannot be identified. The value returned by this intrinsic is likely to be
+ incorrect or 0 for arguments other than zero, so it should only be used for
+ debugging purposes.</p>
+
+<p>Note that calling this intrinsic does not prevent function inlining or other
+ aggressive transformations, so the value returned may not be that of the
+ obvious source-language caller.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_frameaddress">'<tt>llvm.frameaddress</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ declare i8* @llvm.frameaddress(i32 <level>)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.frameaddress</tt>' intrinsic attempts to return the
+ target-specific frame pointer value for the specified stack frame.</p>
+
+<h5>Arguments:</h5>
+<p>The argument to this intrinsic indicates which function to return the frame
+ pointer for. Zero indicates the calling function, one indicates its caller,
+ etc. The argument is <b>required</b> to be a constant integer value.</p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>llvm.frameaddress</tt>' intrinsic either returns a pointer
+ indicating the frame address of the specified call frame, or zero if it
+ cannot be identified. The value returned by this intrinsic is likely to be
+ incorrect or 0 for arguments other than zero, so it should only be used for
+ debugging purposes.</p>
+
+<p>Note that calling this intrinsic does not prevent function inlining or other
+ aggressive transformations, so the value returned may not be that of the
+ obvious source-language caller.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_stacksave">'<tt>llvm.stacksave</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ declare i8* @llvm.stacksave()
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.stacksave</tt>' intrinsic is used to remember the current state
+ of the function stack, for use
+ with <a href="#int_stackrestore"> <tt>llvm.stackrestore</tt></a>. This is
+ useful for implementing language features like scoped automatic variable
+ sized arrays in C99.</p>
+
+<h5>Semantics:</h5>
+<p>This intrinsic returns a opaque pointer value that can be passed
+ to <a href="#int_stackrestore"><tt>llvm.stackrestore</tt></a>. When
+ an <tt>llvm.stackrestore</tt> intrinsic is executed with a value saved
+ from <tt>llvm.stacksave</tt>, it effectively restores the state of the stack
+ to the state it was in when the <tt>llvm.stacksave</tt> intrinsic executed.
+ In practice, this pops any <a href="#i_alloca">alloca</a> blocks from the
+ stack that were allocated after the <tt>llvm.stacksave</tt> was executed.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_stackrestore">'<tt>llvm.stackrestore</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ declare void @llvm.stackrestore(i8* %ptr)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.stackrestore</tt>' intrinsic is used to restore the state of
+ the function stack to the state it was in when the
+ corresponding <a href="#int_stacksave"><tt>llvm.stacksave</tt></a> intrinsic
+ executed. This is useful for implementing language features like scoped
+ automatic variable sized arrays in C99.</p>
+
+<h5>Semantics:</h5>
+<p>See the description
+ for <a href="#int_stacksave"><tt>llvm.stacksave</tt></a>.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_prefetch">'<tt>llvm.prefetch</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ declare void @llvm.prefetch(i8* <address>, i32 <rw>, i32 <locality>, i32 <cache type>)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.prefetch</tt>' intrinsic is a hint to the code generator to
+ insert a prefetch instruction if supported; otherwise, it is a noop.
+ Prefetches have no effect on the behavior of the program but can change its
+ performance characteristics.</p>
+
+<h5>Arguments:</h5>
+<p><tt>address</tt> is the address to be prefetched, <tt>rw</tt> is the
+ specifier determining if the fetch should be for a read (0) or write (1),
+ and <tt>locality</tt> is a temporal locality specifier ranging from (0) - no
+ locality, to (3) - extremely local keep in cache. The <tt>cache type</tt>
+ specifies whether the prefetch is performed on the data (1) or instruction (0)
+ cache. The <tt>rw</tt>, <tt>locality</tt> and <tt>cache type</tt> arguments
+ must be constant integers.</p>
+
+<h5>Semantics:</h5>
+<p>This intrinsic does not modify the behavior of the program. In particular,
+ prefetches cannot trap and do not produce a value. On targets that support
+ this intrinsic, the prefetch can provide hints to the processor cache for
+ better performance.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_pcmarker">'<tt>llvm.pcmarker</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ declare void @llvm.pcmarker(i32 <id>)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.pcmarker</tt>' intrinsic is a method to export a Program
+ Counter (PC) in a region of code to simulators and other tools. The method
+ is target specific, but it is expected that the marker will use exported
+ symbols to transmit the PC of the marker. The marker makes no guarantees
+ that it will remain with any specific instruction after optimizations. It is
+ possible that the presence of a marker will inhibit optimizations. The
+ intended use is to be inserted after optimizations to allow correlations of
+ simulation runs.</p>
+
+<h5>Arguments:</h5>
+<p><tt>id</tt> is a numerical id identifying the marker.</p>
+
+<h5>Semantics:</h5>
+<p>This intrinsic does not modify the behavior of the program. Backends that do
+ not support this intrinsic may ignore it.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_readcyclecounter">'<tt>llvm.readcyclecounter</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ declare i64 @llvm.readcyclecounter()
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.readcyclecounter</tt>' intrinsic provides access to the cycle
+ counter register (or similar low latency, high accuracy clocks) on those
+ targets that support it. On X86, it should map to RDTSC. On Alpha, it
+ should map to RPCC. As the backing counters overflow quickly (on the order
+ of 9 seconds on alpha), this should only be used for small timings.</p>
+
+<h5>Semantics:</h5>
+<p>When directly supported, reading the cycle counter should not modify any
+ memory. Implementations are allowed to either return a application specific
+ value or a system wide value. On backends without support, this is lowered
+ to a constant 0.</p>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="int_libc">Standard C Library Intrinsics</a>
+</h3>
+
+<div>
+
+<p>LLVM provides intrinsics for a few important standard C library functions.
+ These intrinsics allow source-language front-ends to pass information about
+ the alignment of the pointer arguments to the code generator, providing
+ opportunity for more efficient code generation.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_memcpy">'<tt>llvm.memcpy</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<p>This is an overloaded intrinsic. You can use <tt>llvm.memcpy</tt> on any
+ integer bit width and for different address spaces. Not all targets support
+ all bit widths however.</p>
+
+<pre>
+ declare void @llvm.memcpy.p0i8.p0i8.i32(i8* <dest>, i8* <src>,
+ i32 <len>, i32 <align>, i1 <isvolatile>)
+ declare void @llvm.memcpy.p0i8.p0i8.i64(i8* <dest>, i8* <src>,
+ i64 <len>, i32 <align>, i1 <isvolatile>)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.memcpy.*</tt>' intrinsics copy a block of memory from the
+ source location to the destination location.</p>
+
+<p>Note that, unlike the standard libc function, the <tt>llvm.memcpy.*</tt>
+ intrinsics do not return a value, takes extra alignment/isvolatile arguments
+ and the pointers can be in specified address spaces.</p>
+
+<h5>Arguments:</h5>
+
+<p>The first argument is a pointer to the destination, the second is a pointer
+ to the source. The third argument is an integer argument specifying the
+ number of bytes to copy, the fourth argument is the alignment of the
+ source and destination locations, and the fifth is a boolean indicating a
+ volatile access.</p>
+
+<p>If the call to this intrinsic has an alignment value that is not 0 or 1,
+ then the caller guarantees that both the source and destination pointers are
+ aligned to that boundary.</p>
+
+<p>If the <tt>isvolatile</tt> parameter is <tt>true</tt>, the
+ <tt>llvm.memcpy</tt> call is a <a href="#volatile">volatile operation</a>.
+ The detailed access behavior is not very cleanly specified and it is unwise
+ to depend on it.</p>
+
+<h5>Semantics:</h5>
+
+<p>The '<tt>llvm.memcpy.*</tt>' intrinsics copy a block of memory from the
+ source location to the destination location, which are not allowed to
+ overlap. It copies "len" bytes of memory over. If the argument is known to
+ be aligned to some boundary, this can be specified as the fourth argument,
+ otherwise it should be set to 0 or 1.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_memmove">'<tt>llvm.memmove</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<p>This is an overloaded intrinsic. You can use llvm.memmove on any integer bit
+ width and for different address space. Not all targets support all bit
+ widths however.</p>
+
+<pre>
+ declare void @llvm.memmove.p0i8.p0i8.i32(i8* <dest>, i8* <src>,
+ i32 <len>, i32 <align>, i1 <isvolatile>)
+ declare void @llvm.memmove.p0i8.p0i8.i64(i8* <dest>, i8* <src>,
+ i64 <len>, i32 <align>, i1 <isvolatile>)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.memmove.*</tt>' intrinsics move a block of memory from the
+ source location to the destination location. It is similar to the
+ '<tt>llvm.memcpy</tt>' intrinsic but allows the two memory locations to
+ overlap.</p>
+
+<p>Note that, unlike the standard libc function, the <tt>llvm.memmove.*</tt>
+ intrinsics do not return a value, takes extra alignment/isvolatile arguments
+ and the pointers can be in specified address spaces.</p>
+
+<h5>Arguments:</h5>
+
+<p>The first argument is a pointer to the destination, the second is a pointer
+ to the source. The third argument is an integer argument specifying the
+ number of bytes to copy, the fourth argument is the alignment of the
+ source and destination locations, and the fifth is a boolean indicating a
+ volatile access.</p>
+
+<p>If the call to this intrinsic has an alignment value that is not 0 or 1,
+ then the caller guarantees that the source and destination pointers are
+ aligned to that boundary.</p>
+
+<p>If the <tt>isvolatile</tt> parameter is <tt>true</tt>, the
+ <tt>llvm.memmove</tt> call is a <a href="#volatile">volatile operation</a>.
+ The detailed access behavior is not very cleanly specified and it is unwise
+ to depend on it.</p>
+
+<h5>Semantics:</h5>
+
+<p>The '<tt>llvm.memmove.*</tt>' intrinsics copy a block of memory from the
+ source location to the destination location, which may overlap. It copies
+ "len" bytes of memory over. If the argument is known to be aligned to some
+ boundary, this can be specified as the fourth argument, otherwise it should
+ be set to 0 or 1.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_memset">'<tt>llvm.memset.*</tt>' Intrinsics</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<p>This is an overloaded intrinsic. You can use llvm.memset on any integer bit
+ width and for different address spaces. However, not all targets support all
+ bit widths.</p>
+
+<pre>
+ declare void @llvm.memset.p0i8.i32(i8* <dest>, i8 <val>,
+ i32 <len>, i32 <align>, i1 <isvolatile>)
+ declare void @llvm.memset.p0i8.i64(i8* <dest>, i8 <val>,
+ i64 <len>, i32 <align>, i1 <isvolatile>)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.memset.*</tt>' intrinsics fill a block of memory with a
+ particular byte value.</p>
+
+<p>Note that, unlike the standard libc function, the <tt>llvm.memset</tt>
+ intrinsic does not return a value and takes extra alignment/volatile
+ arguments. Also, the destination can be in an arbitrary address space.</p>
+
+<h5>Arguments:</h5>
+<p>The first argument is a pointer to the destination to fill, the second is the
+ byte value with which to fill it, the third argument is an integer argument
+ specifying the number of bytes to fill, and the fourth argument is the known
+ alignment of the destination location.</p>
+
+<p>If the call to this intrinsic has an alignment value that is not 0 or 1,
+ then the caller guarantees that the destination pointer is aligned to that
+ boundary.</p>
+
+<p>If the <tt>isvolatile</tt> parameter is <tt>true</tt>, the
+ <tt>llvm.memset</tt> call is a <a href="#volatile">volatile operation</a>.
+ The detailed access behavior is not very cleanly specified and it is unwise
+ to depend on it.</p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>llvm.memset.*</tt>' intrinsics fill "len" bytes of memory starting
+ at the destination location. If the argument is known to be aligned to some
+ boundary, this can be specified as the fourth argument, otherwise it should
+ be set to 0 or 1.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_sqrt">'<tt>llvm.sqrt.*</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<p>This is an overloaded intrinsic. You can use <tt>llvm.sqrt</tt> on any
+ floating point or vector of floating point type. Not all targets support all
+ types however.</p>
+
+<pre>
+ declare float @llvm.sqrt.f32(float %Val)
+ declare double @llvm.sqrt.f64(double %Val)
+ declare x86_fp80 @llvm.sqrt.f80(x86_fp80 %Val)
+ declare fp128 @llvm.sqrt.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.sqrt.ppcf128(ppc_fp128 %Val)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.sqrt</tt>' intrinsics return the sqrt of the specified operand,
+ returning the same value as the libm '<tt>sqrt</tt>' functions would.
+ Unlike <tt>sqrt</tt> in libm, however, <tt>llvm.sqrt</tt> has undefined
+ behavior for negative numbers other than -0.0 (which allows for better
+ optimization, because there is no need to worry about errno being
+ set). <tt>llvm.sqrt(-0.0)</tt> is defined to return -0.0 like IEEE sqrt.</p>
+
+<h5>Arguments:</h5>
+<p>The argument and return value are floating point numbers of the same
+ type.</p>
+
+<h5>Semantics:</h5>
+<p>This function returns the sqrt of the specified operand if it is a
+ nonnegative floating point number.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_powi">'<tt>llvm.powi.*</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<p>This is an overloaded intrinsic. You can use <tt>llvm.powi</tt> on any
+ floating point or vector of floating point type. Not all targets support all
+ types however.</p>
+
+<pre>
+ declare float @llvm.powi.f32(float %Val, i32 %power)
+ declare double @llvm.powi.f64(double %Val, i32 %power)
+ declare x86_fp80 @llvm.powi.f80(x86_fp80 %Val, i32 %power)
+ declare fp128 @llvm.powi.f128(fp128 %Val, i32 %power)
+ declare ppc_fp128 @llvm.powi.ppcf128(ppc_fp128 %Val, i32 %power)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.powi.*</tt>' intrinsics return the first operand raised to the
+ specified (positive or negative) power. The order of evaluation of
+ multiplications is not defined. When a vector of floating point type is
+ used, the second argument remains a scalar integer value.</p>
+
+<h5>Arguments:</h5>
+<p>The second argument is an integer power, and the first is a value to raise to
+ that power.</p>
+
+<h5>Semantics:</h5>
+<p>This function returns the first value raised to the second power with an
+ unspecified sequence of rounding operations.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_sin">'<tt>llvm.sin.*</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<p>This is an overloaded intrinsic. You can use <tt>llvm.sin</tt> on any
+ floating point or vector of floating point type. Not all targets support all
+ types however.</p>
+
+<pre>
+ declare float @llvm.sin.f32(float %Val)
+ declare double @llvm.sin.f64(double %Val)
+ declare x86_fp80 @llvm.sin.f80(x86_fp80 %Val)
+ declare fp128 @llvm.sin.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.sin.ppcf128(ppc_fp128 %Val)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.sin.*</tt>' intrinsics return the sine of the operand.</p>
+
+<h5>Arguments:</h5>
+<p>The argument and return value are floating point numbers of the same
+ type.</p>
+
+<h5>Semantics:</h5>
+<p>This function returns the sine of the specified operand, returning the same
+ values as the libm <tt>sin</tt> functions would, and handles error conditions
+ in the same way.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_cos">'<tt>llvm.cos.*</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<p>This is an overloaded intrinsic. You can use <tt>llvm.cos</tt> on any
+ floating point or vector of floating point type. Not all targets support all
+ types however.</p>
+
+<pre>
+ declare float @llvm.cos.f32(float %Val)
+ declare double @llvm.cos.f64(double %Val)
+ declare x86_fp80 @llvm.cos.f80(x86_fp80 %Val)
+ declare fp128 @llvm.cos.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.cos.ppcf128(ppc_fp128 %Val)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.cos.*</tt>' intrinsics return the cosine of the operand.</p>
+
+<h5>Arguments:</h5>
+<p>The argument and return value are floating point numbers of the same
+ type.</p>
+
+<h5>Semantics:</h5>
+<p>This function returns the cosine of the specified operand, returning the same
+ values as the libm <tt>cos</tt> functions would, and handles error conditions
+ in the same way.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_pow">'<tt>llvm.pow.*</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<p>This is an overloaded intrinsic. You can use <tt>llvm.pow</tt> on any
+ floating point or vector of floating point type. Not all targets support all
+ types however.</p>
+
+<pre>
+ declare float @llvm.pow.f32(float %Val, float %Power)
+ declare double @llvm.pow.f64(double %Val, double %Power)
+ declare x86_fp80 @llvm.pow.f80(x86_fp80 %Val, x86_fp80 %Power)
+ declare fp128 @llvm.pow.f128(fp128 %Val, fp128 %Power)
+ declare ppc_fp128 @llvm.pow.ppcf128(ppc_fp128 %Val, ppc_fp128 Power)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.pow.*</tt>' intrinsics return the first operand raised to the
+ specified (positive or negative) power.</p>
+
+<h5>Arguments:</h5>
+<p>The second argument is a floating point power, and the first is a value to
+ raise to that power.</p>
+
+<h5>Semantics:</h5>
+<p>This function returns the first value raised to the second power, returning
+ the same values as the libm <tt>pow</tt> functions would, and handles error
+ conditions in the same way.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_exp">'<tt>llvm.exp.*</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<p>This is an overloaded intrinsic. You can use <tt>llvm.exp</tt> on any
+ floating point or vector of floating point type. Not all targets support all
+ types however.</p>
+
+<pre>
+ declare float @llvm.exp.f32(float %Val)
+ declare double @llvm.exp.f64(double %Val)
+ declare x86_fp80 @llvm.exp.f80(x86_fp80 %Val)
+ declare fp128 @llvm.exp.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.exp.ppcf128(ppc_fp128 %Val)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.exp.*</tt>' intrinsics perform the exp function.</p>
+
+<h5>Arguments:</h5>
+<p>The argument and return value are floating point numbers of the same
+ type.</p>
+
+<h5>Semantics:</h5>
+<p>This function returns the same values as the libm <tt>exp</tt> functions
+ would, and handles error conditions in the same way.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_log">'<tt>llvm.log.*</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<p>This is an overloaded intrinsic. You can use <tt>llvm.log</tt> on any
+ floating point or vector of floating point type. Not all targets support all
+ types however.</p>
+
+<pre>
+ declare float @llvm.log.f32(float %Val)
+ declare double @llvm.log.f64(double %Val)
+ declare x86_fp80 @llvm.log.f80(x86_fp80 %Val)
+ declare fp128 @llvm.log.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.log.ppcf128(ppc_fp128 %Val)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.log.*</tt>' intrinsics perform the log function.</p>
+
+<h5>Arguments:</h5>
+<p>The argument and return value are floating point numbers of the same
+ type.</p>
+
+<h5>Semantics:</h5>
+<p>This function returns the same values as the libm <tt>log</tt> functions
+ would, and handles error conditions in the same way.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_fma">'<tt>llvm.fma.*</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<p>This is an overloaded intrinsic. You can use <tt>llvm.fma</tt> on any
+ floating point or vector of floating point type. Not all targets support all
+ types however.</p>
+
+<pre>
+ declare float @llvm.fma.f32(float %a, float %b, float %c)
+ declare double @llvm.fma.f64(double %a, double %b, double %c)
+ declare x86_fp80 @llvm.fma.f80(x86_fp80 %a, x86_fp80 %b, x86_fp80 %c)
+ declare fp128 @llvm.fma.f128(fp128 %a, fp128 %b, fp128 %c)
+ declare ppc_fp128 @llvm.fma.ppcf128(ppc_fp128 %a, ppc_fp128 %b, ppc_fp128 %c)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.fma.*</tt>' intrinsics perform the fused multiply-add
+ operation.</p>
+
+<h5>Arguments:</h5>
+<p>The argument and return value are floating point numbers of the same
+ type.</p>
+
+<h5>Semantics:</h5>
+<p>This function returns the same values as the libm <tt>fma</tt> functions
+ would.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_fabs">'<tt>llvm.fabs.*</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<p>This is an overloaded intrinsic. You can use <tt>llvm.fabs</tt> on any
+ floating point or vector of floating point type. Not all targets support all
+ types however.</p>
+
+<pre>
+ declare float @llvm.fabs.f32(float %Val)
+ declare double @llvm.fabs.f64(double %Val)
+ declare x86_fp80 @llvm.fabs.f80(x86_fp80 %Val)
+ declare fp128 @llvm.fabs.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.fabs.ppcf128(ppc_fp128 %Val)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.fabs.*</tt>' intrinsics return the absolute value of
+ the operand.</p>
+
+<h5>Arguments:</h5>
+<p>The argument and return value are floating point numbers of the same
+ type.</p>
+
+<h5>Semantics:</h5>
+<p>This function returns the same values as the libm <tt>fabs</tt> functions
+ would, and handles error conditions in the same way.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_floor">'<tt>llvm.floor.*</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<p>This is an overloaded intrinsic. You can use <tt>llvm.floor</tt> on any
+ floating point or vector of floating point type. Not all targets support all
+ types however.</p>
+
+<pre>
+ declare float @llvm.floor.f32(float %Val)
+ declare double @llvm.floor.f64(double %Val)
+ declare x86_fp80 @llvm.floor.f80(x86_fp80 %Val)
+ declare fp128 @llvm.floor.f128(fp128 %Val)
+ declare ppc_fp128 @llvm.floor.ppcf128(ppc_fp128 %Val)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.floor.*</tt>' intrinsics return the floor of
+ the operand.</p>
+
+<h5>Arguments:</h5>
+<p>The argument and return value are floating point numbers of the same
+ type.</p>
+
+<h5>Semantics:</h5>
+<p>This function returns the same values as the libm <tt>floor</tt> functions
+ would, and handles error conditions in the same way.</p>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="int_manip">Bit Manipulation Intrinsics</a>
+</h3>
+
+<div>
+
+<p>LLVM provides intrinsics for a few important bit manipulation operations.
+ These allow efficient code generation for some algorithms.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_bswap">'<tt>llvm.bswap.*</tt>' Intrinsics</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<p>This is an overloaded intrinsic function. You can use bswap on any integer
+ type that is an even number of bytes (i.e. BitWidth % 16 == 0).</p>
+
+<pre>
+ declare i16 @llvm.bswap.i16(i16 <id>)
+ declare i32 @llvm.bswap.i32(i32 <id>)
+ declare i64 @llvm.bswap.i64(i64 <id>)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.bswap</tt>' family of intrinsics is used to byte swap integer
+ values with an even number of bytes (positive multiple of 16 bits). These
+ are useful for performing operations on data that is not in the target's
+ native byte order.</p>
+
+<h5>Semantics:</h5>
+<p>The <tt>llvm.bswap.i16</tt> intrinsic returns an i16 value that has the high
+ and low byte of the input i16 swapped. Similarly,
+ the <tt>llvm.bswap.i32</tt> intrinsic returns an i32 value that has the four
+ bytes of the input i32 swapped, so that if the input bytes are numbered 0, 1,
+ 2, 3 then the returned i32 will have its bytes in 3, 2, 1, 0 order.
+ The <tt>llvm.bswap.i48</tt>, <tt>llvm.bswap.i64</tt> and other intrinsics
+ extend this concept to additional even-byte lengths (6 bytes, 8 bytes and
+ more, respectively).</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_ctpop">'<tt>llvm.ctpop.*</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<p>This is an overloaded intrinsic. You can use llvm.ctpop on any integer bit
+ width, or on any vector with integer elements. Not all targets support all
+ bit widths or vector types, however.</p>
+
+<pre>
+ declare i8 @llvm.ctpop.i8(i8 <src>)
+ declare i16 @llvm.ctpop.i16(i16 <src>)
+ declare i32 @llvm.ctpop.i32(i32 <src>)
+ declare i64 @llvm.ctpop.i64(i64 <src>)
+ declare i256 @llvm.ctpop.i256(i256 <src>)
+ declare <2 x i32> @llvm.ctpop.v2i32(<2 x i32> <src>)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.ctpop</tt>' family of intrinsics counts the number of bits set
+ in a value.</p>
+
+<h5>Arguments:</h5>
+<p>The only argument is the value to be counted. The argument may be of any
+ integer type, or a vector with integer elements.
+ The return type must match the argument type.</p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>llvm.ctpop</tt>' intrinsic counts the 1's in a variable, or within each
+ element of a vector.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_ctlz">'<tt>llvm.ctlz.*</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<p>This is an overloaded intrinsic. You can use <tt>llvm.ctlz</tt> on any
+ integer bit width, or any vector whose elements are integers. Not all
+ targets support all bit widths or vector types, however.</p>
+
+<pre>
+ declare i8 @llvm.ctlz.i8 (i8 <src>, i1 <is_zero_undef>)
+ declare i16 @llvm.ctlz.i16 (i16 <src>, i1 <is_zero_undef>)
+ declare i32 @llvm.ctlz.i32 (i32 <src>, i1 <is_zero_undef>)
+ declare i64 @llvm.ctlz.i64 (i64 <src>, i1 <is_zero_undef>)
+ declare i256 @llvm.ctlz.i256(i256 <src>, i1 <is_zero_undef>)
+ declase <2 x i32> @llvm.ctlz.v2i32(<2 x i32> <src>, i1 <is_zero_undef>)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.ctlz</tt>' family of intrinsic functions counts the number of
+ leading zeros in a variable.</p>
+
+<h5>Arguments:</h5>
+<p>The first argument is the value to be counted. This argument may be of any
+ integer type, or a vectory with integer element type. The return type
+ must match the first argument type.</p>
+
+<p>The second argument must be a constant and is a flag to indicate whether the
+ intrinsic should ensure that a zero as the first argument produces a defined
+ result. Historically some architectures did not provide a defined result for
+ zero values as efficiently, and many algorithms are now predicated on
+ avoiding zero-value inputs.</p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>llvm.ctlz</tt>' intrinsic counts the leading (most significant)
+ zeros in a variable, or within each element of the vector.
+ If <tt>src == 0</tt> then the result is the size in bits of the type of
+ <tt>src</tt> if <tt>is_zero_undef == 0</tt> and <tt>undef</tt> otherwise.
+ For example, <tt>llvm.ctlz(i32 2) = 30</tt>.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_cttz">'<tt>llvm.cttz.*</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<p>This is an overloaded intrinsic. You can use <tt>llvm.cttz</tt> on any
+ integer bit width, or any vector of integer elements. Not all targets
+ support all bit widths or vector types, however.</p>
+
+<pre>
+ declare i8 @llvm.cttz.i8 (i8 <src>, i1 <is_zero_undef>)
+ declare i16 @llvm.cttz.i16 (i16 <src>, i1 <is_zero_undef>)
+ declare i32 @llvm.cttz.i32 (i32 <src>, i1 <is_zero_undef>)
+ declare i64 @llvm.cttz.i64 (i64 <src>, i1 <is_zero_undef>)
+ declare i256 @llvm.cttz.i256(i256 <src>, i1 <is_zero_undef>)
+ declase <2 x i32> @llvm.cttz.v2i32(<2 x i32> <src>, i1 <is_zero_undef>)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.cttz</tt>' family of intrinsic functions counts the number of
+ trailing zeros.</p>
+
+<h5>Arguments:</h5>
+<p>The first argument is the value to be counted. This argument may be of any
+ integer type, or a vectory with integer element type. The return type
+ must match the first argument type.</p>
+
+<p>The second argument must be a constant and is a flag to indicate whether the
+ intrinsic should ensure that a zero as the first argument produces a defined
+ result. Historically some architectures did not provide a defined result for
+ zero values as efficiently, and many algorithms are now predicated on
+ avoiding zero-value inputs.</p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>llvm.cttz</tt>' intrinsic counts the trailing (least significant)
+ zeros in a variable, or within each element of a vector.
+ If <tt>src == 0</tt> then the result is the size in bits of the type of
+ <tt>src</tt> if <tt>is_zero_undef == 0</tt> and <tt>undef</tt> otherwise.
+ For example, <tt>llvm.cttz(2) = 1</tt>.</p>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="int_overflow">Arithmetic with Overflow Intrinsics</a>
+</h3>
+
+<div>
+
+<p>LLVM provides intrinsics for some arithmetic with overflow operations.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_sadd_overflow">
+ '<tt>llvm.sadd.with.overflow.*</tt>' Intrinsics
+ </a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<p>This is an overloaded intrinsic. You can use <tt>llvm.sadd.with.overflow</tt>
+ on any integer bit width.</p>
+
+<pre>
+ declare {i16, i1} @llvm.sadd.with.overflow.i16(i16 %a, i16 %b)
+ declare {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b)
+ declare {i64, i1} @llvm.sadd.with.overflow.i64(i64 %a, i64 %b)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.sadd.with.overflow</tt>' family of intrinsic functions perform
+ a signed addition of the two arguments, and indicate whether an overflow
+ occurred during the signed summation.</p>
+
+<h5>Arguments:</h5>
+<p>The arguments (%a and %b) and the first element of the result structure may
+ be of integer types of any bit width, but they must have the same bit
+ width. The second element of the result structure must be of
+ type <tt>i1</tt>. <tt>%a</tt> and <tt>%b</tt> are the two values that will
+ undergo signed addition.</p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>llvm.sadd.with.overflow</tt>' family of intrinsic functions perform
+ a signed addition of the two variables. They return a structure — the
+ first element of which is the signed summation, and the second element of
+ which is a bit specifying if the signed summation resulted in an
+ overflow.</p>
+
+<h5>Examples:</h5>
+<pre>
+ %res = call {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b)
+ %sum = extractvalue {i32, i1} %res, 0
+ %obit = extractvalue {i32, i1} %res, 1
+ br i1 %obit, label %overflow, label %normal
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_uadd_overflow">
+ '<tt>llvm.uadd.with.overflow.*</tt>' Intrinsics
+ </a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<p>This is an overloaded intrinsic. You can use <tt>llvm.uadd.with.overflow</tt>
+ on any integer bit width.</p>
+
+<pre>
+ declare {i16, i1} @llvm.uadd.with.overflow.i16(i16 %a, i16 %b)
+ declare {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)
+ declare {i64, i1} @llvm.uadd.with.overflow.i64(i64 %a, i64 %b)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.uadd.with.overflow</tt>' family of intrinsic functions perform
+ an unsigned addition of the two arguments, and indicate whether a carry
+ occurred during the unsigned summation.</p>
+
+<h5>Arguments:</h5>
+<p>The arguments (%a and %b) and the first element of the result structure may
+ be of integer types of any bit width, but they must have the same bit
+ width. The second element of the result structure must be of
+ type <tt>i1</tt>. <tt>%a</tt> and <tt>%b</tt> are the two values that will
+ undergo unsigned addition.</p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>llvm.uadd.with.overflow</tt>' family of intrinsic functions perform
+ an unsigned addition of the two arguments. They return a structure —
+ the first element of which is the sum, and the second element of which is a
+ bit specifying if the unsigned summation resulted in a carry.</p>
+
+<h5>Examples:</h5>
+<pre>
+ %res = call {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)
+ %sum = extractvalue {i32, i1} %res, 0
+ %obit = extractvalue {i32, i1} %res, 1
+ br i1 %obit, label %carry, label %normal
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_ssub_overflow">
+ '<tt>llvm.ssub.with.overflow.*</tt>' Intrinsics
+ </a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<p>This is an overloaded intrinsic. You can use <tt>llvm.ssub.with.overflow</tt>
+ on any integer bit width.</p>
+
+<pre>
+ declare {i16, i1} @llvm.ssub.with.overflow.i16(i16 %a, i16 %b)
+ declare {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b)
+ declare {i64, i1} @llvm.ssub.with.overflow.i64(i64 %a, i64 %b)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.ssub.with.overflow</tt>' family of intrinsic functions perform
+ a signed subtraction of the two arguments, and indicate whether an overflow
+ occurred during the signed subtraction.</p>
+
+<h5>Arguments:</h5>
+<p>The arguments (%a and %b) and the first element of the result structure may
+ be of integer types of any bit width, but they must have the same bit
+ width. The second element of the result structure must be of
+ type <tt>i1</tt>. <tt>%a</tt> and <tt>%b</tt> are the two values that will
+ undergo signed subtraction.</p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>llvm.ssub.with.overflow</tt>' family of intrinsic functions perform
+ a signed subtraction of the two arguments. They return a structure —
+ the first element of which is the subtraction, and the second element of
+ which is a bit specifying if the signed subtraction resulted in an
+ overflow.</p>
+
+<h5>Examples:</h5>
+<pre>
+ %res = call {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b)
+ %sum = extractvalue {i32, i1} %res, 0
+ %obit = extractvalue {i32, i1} %res, 1
+ br i1 %obit, label %overflow, label %normal
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_usub_overflow">
+ '<tt>llvm.usub.with.overflow.*</tt>' Intrinsics
+ </a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<p>This is an overloaded intrinsic. You can use <tt>llvm.usub.with.overflow</tt>
+ on any integer bit width.</p>
+
+<pre>
+ declare {i16, i1} @llvm.usub.with.overflow.i16(i16 %a, i16 %b)
+ declare {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b)
+ declare {i64, i1} @llvm.usub.with.overflow.i64(i64 %a, i64 %b)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.usub.with.overflow</tt>' family of intrinsic functions perform
+ an unsigned subtraction of the two arguments, and indicate whether an
+ overflow occurred during the unsigned subtraction.</p>
+
+<h5>Arguments:</h5>
+<p>The arguments (%a and %b) and the first element of the result structure may
+ be of integer types of any bit width, but they must have the same bit
+ width. The second element of the result structure must be of
+ type <tt>i1</tt>. <tt>%a</tt> and <tt>%b</tt> are the two values that will
+ undergo unsigned subtraction.</p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>llvm.usub.with.overflow</tt>' family of intrinsic functions perform
+ an unsigned subtraction of the two arguments. They return a structure —
+ the first element of which is the subtraction, and the second element of
+ which is a bit specifying if the unsigned subtraction resulted in an
+ overflow.</p>
+
+<h5>Examples:</h5>
+<pre>
+ %res = call {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b)
+ %sum = extractvalue {i32, i1} %res, 0
+ %obit = extractvalue {i32, i1} %res, 1
+ br i1 %obit, label %overflow, label %normal
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_smul_overflow">
+ '<tt>llvm.smul.with.overflow.*</tt>' Intrinsics
+ </a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<p>This is an overloaded intrinsic. You can use <tt>llvm.smul.with.overflow</tt>
+ on any integer bit width.</p>
+
+<pre>
+ declare {i16, i1} @llvm.smul.with.overflow.i16(i16 %a, i16 %b)
+ declare {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b)
+ declare {i64, i1} @llvm.smul.with.overflow.i64(i64 %a, i64 %b)
+</pre>
+
+<h5>Overview:</h5>
+
+<p>The '<tt>llvm.smul.with.overflow</tt>' family of intrinsic functions perform
+ a signed multiplication of the two arguments, and indicate whether an
+ overflow occurred during the signed multiplication.</p>
+
+<h5>Arguments:</h5>
+<p>The arguments (%a and %b) and the first element of the result structure may
+ be of integer types of any bit width, but they must have the same bit
+ width. The second element of the result structure must be of
+ type <tt>i1</tt>. <tt>%a</tt> and <tt>%b</tt> are the two values that will
+ undergo signed multiplication.</p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>llvm.smul.with.overflow</tt>' family of intrinsic functions perform
+ a signed multiplication of the two arguments. They return a structure —
+ the first element of which is the multiplication, and the second element of
+ which is a bit specifying if the signed multiplication resulted in an
+ overflow.</p>
+
+<h5>Examples:</h5>
+<pre>
+ %res = call {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b)
+ %sum = extractvalue {i32, i1} %res, 0
+ %obit = extractvalue {i32, i1} %res, 1
+ br i1 %obit, label %overflow, label %normal
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_umul_overflow">
+ '<tt>llvm.umul.with.overflow.*</tt>' Intrinsics
+ </a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<p>This is an overloaded intrinsic. You can use <tt>llvm.umul.with.overflow</tt>
+ on any integer bit width.</p>
+
+<pre>
+ declare {i16, i1} @llvm.umul.with.overflow.i16(i16 %a, i16 %b)
+ declare {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b)
+ declare {i64, i1} @llvm.umul.with.overflow.i64(i64 %a, i64 %b)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.umul.with.overflow</tt>' family of intrinsic functions perform
+ a unsigned multiplication of the two arguments, and indicate whether an
+ overflow occurred during the unsigned multiplication.</p>
+
+<h5>Arguments:</h5>
+<p>The arguments (%a and %b) and the first element of the result structure may
+ be of integer types of any bit width, but they must have the same bit
+ width. The second element of the result structure must be of
+ type <tt>i1</tt>. <tt>%a</tt> and <tt>%b</tt> are the two values that will
+ undergo unsigned multiplication.</p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>llvm.umul.with.overflow</tt>' family of intrinsic functions perform
+ an unsigned multiplication of the two arguments. They return a structure
+ — the first element of which is the multiplication, and the second
+ element of which is a bit specifying if the unsigned multiplication resulted
+ in an overflow.</p>
+
+<h5>Examples:</h5>
+<pre>
+ %res = call {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b)
+ %sum = extractvalue {i32, i1} %res, 0
+ %obit = extractvalue {i32, i1} %res, 1
+ br i1 %obit, label %overflow, label %normal
+</pre>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="spec_arithmetic">Specialised Arithmetic Intrinsics</a>
+</h3>
+
+<!-- _______________________________________________________________________ -->
+
+<h4>
+ <a name="fmuladd">'<tt>llvm.fmuladd.*</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ declare float @llvm.fmuladd.f32(float %a, float %b, float %c)
+ declare double @llvm.fmuladd.f64(double %a, double %b, double %c)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.fmuladd.*</tt>' intrinsic functions represent multiply-add
+expressions that can be fused if the code generator determines that the fused
+expression would be legal and efficient.</p>
+
+<h5>Arguments:</h5>
+<p>The '<tt>llvm.fmuladd.*</tt>' intrinsics each take three arguments: two
+multiplicands, a and b, and an addend c.</p>
+
+<h5>Semantics:</h5>
+<p>The expression:</p>
+<pre>
+ %0 = call float @llvm.fmuladd.f32(%a, %b, %c)
+</pre>
+<p>is equivalent to the expression a * b + c, except that rounding will not be
+performed between the multiplication and addition steps if the code generator
+fuses the operations. Fusion is not guaranteed, even if the target platform
+supports it. If a fused multiply-add is required the corresponding llvm.fma.*
+intrinsic function should be used instead.</p>
+
+<h5>Examples:</h5>
+<pre>
+ %r2 = call float @llvm.fmuladd.f32(float %a, float %b, float %c) ; yields {float}:r2 = (a * b) + c
+</pre>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="int_fp16">Half Precision Floating Point Intrinsics</a>
+</h3>
+
+<div>
+
+<p>For most target platforms, half precision floating point is a storage-only
+ format. This means that it is
+ a dense encoding (in memory) but does not support computation in the
+ format.</p>
+
+<p>This means that code must first load the half-precision floating point
+ value as an i16, then convert it to float with <a
+ href="#int_convert_from_fp16"><tt>llvm.convert.from.fp16</tt></a>.
+ Computation can then be performed on the float value (including extending to
+ double etc). To store the value back to memory, it is first converted to
+ float if needed, then converted to i16 with
+ <a href="#int_convert_to_fp16"><tt>llvm.convert.to.fp16</tt></a>, then
+ storing as an i16 value.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_convert_to_fp16">
+ '<tt>llvm.convert.to.fp16</tt>' Intrinsic
+ </a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ declare i16 @llvm.convert.to.fp16(f32 %a)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.convert.to.fp16</tt>' intrinsic function performs
+ a conversion from single precision floating point format to half precision
+ floating point format.</p>
+
+<h5>Arguments:</h5>
+<p>The intrinsic function contains single argument - the value to be
+ converted.</p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>llvm.convert.to.fp16</tt>' intrinsic function performs
+ a conversion from single precision floating point format to half precision
+ floating point format. The return value is an <tt>i16</tt> which
+ contains the converted number.</p>
+
+<h5>Examples:</h5>
+<pre>
+ %res = call i16 @llvm.convert.to.fp16(f32 %a)
+ store i16 %res, i16* @x, align 2
+</pre>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_convert_from_fp16">
+ '<tt>llvm.convert.from.fp16</tt>' Intrinsic
+ </a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ declare f32 @llvm.convert.from.fp16(i16 %a)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.convert.from.fp16</tt>' intrinsic function performs
+ a conversion from half precision floating point format to single precision
+ floating point format.</p>
+
+<h5>Arguments:</h5>
+<p>The intrinsic function contains single argument - the value to be
+ converted.</p>
+
+<h5>Semantics:</h5>
+<p>The '<tt>llvm.convert.from.fp16</tt>' intrinsic function performs a
+ conversion from half single precision floating point format to single
+ precision floating point format. The input half-float value is represented by
+ an <tt>i16</tt> value.</p>
+
+<h5>Examples:</h5>
+<pre>
+ %a = load i16* @x, align 2
+ %res = call f32 @llvm.convert.from.fp16(i16 %a)
+</pre>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="int_debugger">Debugger Intrinsics</a>
+</h3>
+
+<div>
+
+<p>The LLVM debugger intrinsics (which all start with <tt>llvm.dbg.</tt>
+ prefix), are described in
+ the <a href="SourceLevelDebugging.html#format_common_intrinsics">LLVM Source
+ Level Debugging</a> document.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="int_eh">Exception Handling Intrinsics</a>
+</h3>
+
+<div>
+
+<p>The LLVM exception handling intrinsics (which all start with
+ <tt>llvm.eh.</tt> prefix), are described in
+ the <a href="ExceptionHandling.html#format_common_intrinsics">LLVM Exception
+ Handling</a> document.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="int_trampoline">Trampoline Intrinsics</a>
+</h3>
+
+<div>
+
+<p>These intrinsics make it possible to excise one parameter, marked with
+ the <a href="#nest"><tt>nest</tt></a> attribute, from a function.
+ The result is a callable
+ function pointer lacking the nest parameter - the caller does not need to
+ provide a value for it. Instead, the value to use is stored in advance in a
+ "trampoline", a block of memory usually allocated on the stack, which also
+ contains code to splice the nest value into the argument list. This is used
+ to implement the GCC nested function address extension.</p>
+
+<p>For example, if the function is
+ <tt>i32 f(i8* nest %c, i32 %x, i32 %y)</tt> then the resulting function
+ pointer has signature <tt>i32 (i32, i32)*</tt>. It can be created as
+ follows:</p>
+
+<pre class="doc_code">
+ %tramp = alloca [10 x i8], align 4 ; size and alignment only correct for X86
+ %tramp1 = getelementptr [10 x i8]* %tramp, i32 0, i32 0
+ call i8* @llvm.init.trampoline(i8* %tramp1, i8* bitcast (i32 (i8*, i32, i32)* @f to i8*), i8* %nval)
+ %p = call i8* @llvm.adjust.trampoline(i8* %tramp1)
+ %fp = bitcast i8* %p to i32 (i32, i32)*
+</pre>
+
+<p>The call <tt>%val = call i32 %fp(i32 %x, i32 %y)</tt> is then equivalent
+ to <tt>%val = call i32 %f(i8* %nval, i32 %x, i32 %y)</tt>.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_it">
+ '<tt>llvm.init.trampoline</tt>' Intrinsic
+ </a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ declare void @llvm.init.trampoline(i8* <tramp>, i8* <func>, i8* <nval>)
+</pre>
+
+<h5>Overview:</h5>
+<p>This fills the memory pointed to by <tt>tramp</tt> with executable code,
+ turning it into a trampoline.</p>
+
+<h5>Arguments:</h5>
+<p>The <tt>llvm.init.trampoline</tt> intrinsic takes three arguments, all
+ pointers. The <tt>tramp</tt> argument must point to a sufficiently large and
+ sufficiently aligned block of memory; this memory is written to by the
+ intrinsic. Note that the size and the alignment are target-specific - LLVM
+ currently provides no portable way of determining them, so a front-end that
+ generates this intrinsic needs to have some target-specific knowledge.
+ The <tt>func</tt> argument must hold a function bitcast to
+ an <tt>i8*</tt>.</p>
+
+<h5>Semantics:</h5>
+<p>The block of memory pointed to by <tt>tramp</tt> is filled with target
+ dependent code, turning it into a function. Then <tt>tramp</tt> needs to be
+ passed to <a href="#int_at">llvm.adjust.trampoline</a> to get a pointer
+ which can be <a href="#int_trampoline">bitcast (to a new function) and
+ called</a>. The new function's signature is the same as that of
+ <tt>func</tt> with any arguments marked with the <tt>nest</tt> attribute
+ removed. At most one such <tt>nest</tt> argument is allowed, and it must be of
+ pointer type. Calling the new function is equivalent to calling <tt>func</tt>
+ with the same argument list, but with <tt>nval</tt> used for the missing
+ <tt>nest</tt> argument. If, after calling <tt>llvm.init.trampoline</tt>, the
+ memory pointed to by <tt>tramp</tt> is modified, then the effect of any later call
+ to the returned function pointer is undefined.</p>
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_at">
+ '<tt>llvm.adjust.trampoline</tt>' Intrinsic
+ </a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ declare i8* @llvm.adjust.trampoline(i8* <tramp>)
+</pre>
+
+<h5>Overview:</h5>
+<p>This performs any required machine-specific adjustment to the address of a
+ trampoline (passed as <tt>tramp</tt>).</p>
+
+<h5>Arguments:</h5>
+<p><tt>tramp</tt> must point to a block of memory which already has trampoline code
+ filled in by a previous call to <a href="#int_it"><tt>llvm.init.trampoline</tt>
+ </a>.</p>
+
+<h5>Semantics:</h5>
+<p>On some architectures the address of the code to be executed needs to be
+ different to the address where the trampoline is actually stored. This
+ intrinsic returns the executable address corresponding to <tt>tramp</tt>
+ after performing the required machine specific adjustments.
+ The pointer returned can then be <a href="#int_trampoline"> bitcast and
+ executed</a>.
+</p>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="int_memorymarkers">Memory Use Markers</a>
+</h3>
+
+<div>
+
+<p>This class of intrinsics exists to information about the lifetime of memory
+ objects and ranges where variables are immutable.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_lifetime_start">'<tt>llvm.lifetime.start</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ declare void @llvm.lifetime.start(i64 <size>, i8* nocapture <ptr>)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.lifetime.start</tt>' intrinsic specifies the start of a memory
+ object's lifetime.</p>
+
+<h5>Arguments:</h5>
+<p>The first argument is a constant integer representing the size of the
+ object, or -1 if it is variable sized. The second argument is a pointer to
+ the object.</p>
+
+<h5>Semantics:</h5>
+<p>This intrinsic indicates that before this point in the code, the value of the
+ memory pointed to by <tt>ptr</tt> is dead. This means that it is known to
+ never be used and has an undefined value. A load from the pointer that
+ precedes this intrinsic can be replaced with
+ <tt>'<a href="#undefvalues">undef</a>'</tt>.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_lifetime_end">'<tt>llvm.lifetime.end</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ declare void @llvm.lifetime.end(i64 <size>, i8* nocapture <ptr>)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.lifetime.end</tt>' intrinsic specifies the end of a memory
+ object's lifetime.</p>
+
+<h5>Arguments:</h5>
+<p>The first argument is a constant integer representing the size of the
+ object, or -1 if it is variable sized. The second argument is a pointer to
+ the object.</p>
+
+<h5>Semantics:</h5>
+<p>This intrinsic indicates that after this point in the code, the value of the
+ memory pointed to by <tt>ptr</tt> is dead. This means that it is known to
+ never be used and has an undefined value. Any stores into the memory object
+ following this intrinsic may be removed as dead.
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_invariant_start">'<tt>llvm.invariant.start</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ declare {}* @llvm.invariant.start(i64 <size>, i8* nocapture <ptr>)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.invariant.start</tt>' intrinsic specifies that the contents of
+ a memory object will not change.</p>
+
+<h5>Arguments:</h5>
+<p>The first argument is a constant integer representing the size of the
+ object, or -1 if it is variable sized. The second argument is a pointer to
+ the object.</p>
+
+<h5>Semantics:</h5>
+<p>This intrinsic indicates that until an <tt>llvm.invariant.end</tt> that uses
+ the return value, the referenced memory location is constant and
+ unchanging.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_invariant_end">'<tt>llvm.invariant.end</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ declare void @llvm.invariant.end({}* <start>, i64 <size>, i8* nocapture <ptr>)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.invariant.end</tt>' intrinsic specifies that the contents of
+ a memory object are mutable.</p>
+
+<h5>Arguments:</h5>
+<p>The first argument is the matching <tt>llvm.invariant.start</tt> intrinsic.
+ The second argument is a constant integer representing the size of the
+ object, or -1 if it is variable sized and the third argument is a pointer
+ to the object.</p>
+
+<h5>Semantics:</h5>
+<p>This intrinsic indicates that the memory is mutable again.</p>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="int_general">General Intrinsics</a>
+</h3>
+
+<div>
+
+<p>This class of intrinsics is designed to be generic and has no specific
+ purpose.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_var_annotation">'<tt>llvm.var.annotation</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ declare void @llvm.var.annotation(i8* <val>, i8* <str>, i8* <str>, i32 <int>)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.var.annotation</tt>' intrinsic.</p>
+
+<h5>Arguments:</h5>
+<p>The first argument is a pointer to a value, the second is a pointer to a
+ global string, the third is a pointer to a global string which is the source
+ file name, and the last argument is the line number.</p>
+
+<h5>Semantics:</h5>
+<p>This intrinsic allows annotation of local variables with arbitrary strings.
+ This can be useful for special purpose optimizations that want to look for
+ these annotations. These have no other defined use; they are ignored by code
+ generation and optimization.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_annotation">'<tt>llvm.annotation.*</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<p>This is an overloaded intrinsic. You can use '<tt>llvm.annotation</tt>' on
+ any integer bit width.</p>
+
+<pre>
+ declare i8 @llvm.annotation.i8(i8 <val>, i8* <str>, i8* <str>, i32 <int>)
+ declare i16 @llvm.annotation.i16(i16 <val>, i8* <str>, i8* <str>, i32 <int>)
+ declare i32 @llvm.annotation.i32(i32 <val>, i8* <str>, i8* <str>, i32 <int>)
+ declare i64 @llvm.annotation.i64(i64 <val>, i8* <str>, i8* <str>, i32 <int>)
+ declare i256 @llvm.annotation.i256(i256 <val>, i8* <str>, i8* <str>, i32 <int>)
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.annotation</tt>' intrinsic.</p>
+
+<h5>Arguments:</h5>
+<p>The first argument is an integer value (result of some expression), the
+ second is a pointer to a global string, the third is a pointer to a global
+ string which is the source file name, and the last argument is the line
+ number. It returns the value of the first argument.</p>
+
+<h5>Semantics:</h5>
+<p>This intrinsic allows annotations to be put on arbitrary expressions with
+ arbitrary strings. This can be useful for special purpose optimizations that
+ want to look for these annotations. These have no other defined use; they
+ are ignored by code generation and optimization.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_trap">'<tt>llvm.trap</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ declare void @llvm.trap() noreturn nounwind
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.trap</tt>' intrinsic.</p>
+
+<h5>Arguments:</h5>
+<p>None.</p>
+
+<h5>Semantics:</h5>
+<p>This intrinsic is lowered to the target dependent trap instruction. If the
+ target does not have a trap instruction, this intrinsic will be lowered to
+ a call of the <tt>abort()</tt> function.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_debugtrap">'<tt>llvm.debugtrap</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ declare void @llvm.debugtrap() nounwind
+</pre>
+
+<h5>Overview:</h5>
+<p>The '<tt>llvm.debugtrap</tt>' intrinsic.</p>
+
+<h5>Arguments:</h5>
+<p>None.</p>
+
+<h5>Semantics:</h5>
+<p>This intrinsic is lowered to code which is intended to cause an execution
+ trap with the intention of requesting the attention of a debugger.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_stackprotector">'<tt>llvm.stackprotector</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ declare void @llvm.stackprotector(i8* <guard>, i8** <slot>)
+</pre>
+
+<h5>Overview:</h5>
+<p>The <tt>llvm.stackprotector</tt> intrinsic takes the <tt>guard</tt> and
+ stores it onto the stack at <tt>slot</tt>. The stack slot is adjusted to
+ ensure that it is placed on the stack before local variables.</p>
+
+<h5>Arguments:</h5>
+<p>The <tt>llvm.stackprotector</tt> intrinsic requires two pointer
+ arguments. The first argument is the value loaded from the stack
+ guard <tt>@__stack_chk_guard</tt>. The second variable is an <tt>alloca</tt>
+ that has enough space to hold the value of the guard.</p>
+
+<h5>Semantics:</h5>
+<p>This intrinsic causes the prologue/epilogue inserter to force the position of
+ the <tt>AllocaInst</tt> stack slot to be before local variables on the
+ stack. This is to ensure that if a local variable on the stack is
+ overwritten, it will destroy the value of the guard. When the function exits,
+ the guard on the stack is checked against the original guard. If they are
+ different, then the program aborts by calling the <tt>__stack_chk_fail()</tt>
+ function.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_objectsize">'<tt>llvm.objectsize</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ declare i32 @llvm.objectsize.i32(i8* <object>, i1 <min>)
+ declare i64 @llvm.objectsize.i64(i8* <object>, i1 <min>)
+</pre>
+
+<h5>Overview:</h5>
+<p>The <tt>llvm.objectsize</tt> intrinsic is designed to provide information to
+ the optimizers to determine at compile time whether a) an operation (like
+ memcpy) will overflow a buffer that corresponds to an object, or b) that a
+ runtime check for overflow isn't necessary. An object in this context means
+ an allocation of a specific class, structure, array, or other object.</p>
+
+<h5>Arguments:</h5>
+<p>The <tt>llvm.objectsize</tt> intrinsic takes two arguments. The first
+ argument is a pointer to or into the <tt>object</tt>. The second argument
+ is a boolean and determines whether <tt>llvm.objectsize</tt> returns 0 (if
+ true) or -1 (if false) when the object size is unknown.
+ The second argument only accepts constants.</p>
+
+<h5>Semantics:</h5>
+<p>The <tt>llvm.objectsize</tt> intrinsic is lowered to a constant representing
+ the size of the object concerned. If the size cannot be determined at compile
+ time, <tt>llvm.objectsize</tt> returns <tt>i32/i64 -1 or 0</tt>
+ (depending on the <tt>min</tt> argument).</p>
+
+</div>
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_expect">'<tt>llvm.expect</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ declare i32 @llvm.expect.i32(i32 <val>, i32 <expected_val>)
+ declare i64 @llvm.expect.i64(i64 <val>, i64 <expected_val>)
+</pre>
+
+<h5>Overview:</h5>
+<p>The <tt>llvm.expect</tt> intrinsic provides information about expected (the
+ most probable) value of <tt>val</tt>, which can be used by optimizers.</p>
+
+<h5>Arguments:</h5>
+<p>The <tt>llvm.expect</tt> intrinsic takes two arguments. The first
+ argument is a value. The second argument is an expected value, this needs to
+ be a constant value, variables are not allowed.</p>
+
+<h5>Semantics:</h5>
+<p>This intrinsic is lowered to the <tt>val</tt>.</p>
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="int_donothing">'<tt>llvm.donothing</tt>' Intrinsic</a>
+</h4>
+
+<div>
+
+<h5>Syntax:</h5>
+<pre>
+ declare void @llvm.donothing() nounwind readnone
+</pre>
+
+<h5>Overview:</h5>
+<p>The <tt>llvm.donothing</tt> intrinsic doesn't perform any operation. It's the
+only intrinsic that can be called with an invoke instruction.</p>
+
+<h5>Arguments:</h5>
+<p>None.</p>
+
+<h5>Semantics:</h5>
+<p>This intrinsic does nothing, and it's removed by optimizers and ignored by
+codegen.</p>
+</div>
+
+</div>
+
+</div>
+<!-- *********************************************************************** -->
+<hr>
+<address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
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+ <a href="mailto:sabre at nondot.org">Chris Lattner</a><br>
+ <a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date: 2012-10-29 09:12:44 -0500 (Mon, 29 Oct 2012) $
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+<li><a class="reference internal" href="#">The LLVM Lexicon</a><ul>
+<li><a class="reference internal" href="#definitions">Definitions</a><ul>
+<li><a class="reference internal" href="#a">A</a></li>
+<li><a class="reference internal" href="#b">B</a></li>
+<li><a class="reference internal" href="#c">C</a></li>
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+<li><a class="reference internal" href="#i">I</a></li>
+<li><a class="reference internal" href="#l">L</a></li>
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+<li><a class="reference internal" href="#o">O</a></li>
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+<li><a class="reference internal" href="#r">R</a></li>
+<li><a class="reference internal" href="#s">S</a></li>
+<li><a class="reference internal" href="#t">T</a></li>
+</ul>
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+ <div class="section" id="the-llvm-lexicon">
+<span id="lexicon"></span><h1>The LLVM Lexicon<a class="headerlink" href="#the-llvm-lexicon" title="Permalink to this headline">¶</a></h1>
+<div class="admonition note">
+<p class="first admonition-title">Note</p>
+<p class="last">This document is a work in progress!</p>
+</div>
+<div class="section" id="definitions">
+<h2>Definitions<a class="headerlink" href="#definitions" title="Permalink to this headline">¶</a></h2>
+<div class="section" id="a">
+<h3>A<a class="headerlink" href="#a" title="Permalink to this headline">¶</a></h3>
+<dl class="docutils">
+<dt><strong>ADCE</strong></dt>
+<dd>Aggressive Dead Code Elimination</dd>
+</dl>
+</div>
+<div class="section" id="b">
+<h3>B<a class="headerlink" href="#b" title="Permalink to this headline">¶</a></h3>
+<dl class="docutils">
+<dt><strong>BB Vectorization</strong></dt>
+<dd>Basic Block Vectorization</dd>
+<dt><strong>BURS</strong></dt>
+<dd>Bottom Up Rewriting System — A method of instruction selection for code
+generation. An example is the <a class="reference external" href="http://www.program-transformation.org/Transform/BURG">BURG</a> tool.</dd>
+</dl>
+</div>
+<div class="section" id="c">
+<h3>C<a class="headerlink" href="#c" title="Permalink to this headline">¶</a></h3>
+<dl class="docutils">
+<dt><strong>CSE</strong></dt>
+<dd>Common Subexpression Elimination. An optimization that removes common
+subexpression compuation. For example <tt class="docutils literal"><span class="pre">(a+b)*(a+b)</span></tt> has two subexpressions
+that are the same: <tt class="docutils literal"><span class="pre">(a+b)</span></tt>. This optimization would perform the addition
+only once and then perform the multiply (but only if it’s compulationally
+correct/safe).</dd>
+</dl>
+</div>
+<div class="section" id="d">
+<h3>D<a class="headerlink" href="#d" title="Permalink to this headline">¶</a></h3>
+<dl class="docutils">
+<dt><strong>DAG</strong></dt>
+<dd>Directed Acyclic Graph</dd>
+</dl>
+<dl class="docutils" id="derived-pointers">
+<span id="derived-pointer"></span><dt><strong>Derived Pointer</strong></dt>
+<dd>A pointer to the interior of an object, such that a garbage collector is
+unable to use the pointer for reachability analysis. While a derived pointer
+is live, the corresponding object pointer must be kept in a root, otherwise
+the collector might free the referenced object. With copying collectors,
+derived pointers pose an additional hazard that they may be invalidated at
+any <a class="reference internal" href="#safe-point">safe point</a>. This term is used in opposition to <a class="reference internal" href="#object-pointer">object pointer</a>.</dd>
+<dt><strong>DSA</strong></dt>
+<dd>Data Structure Analysis</dd>
+<dt><strong>DSE</strong></dt>
+<dd>Dead Store Elimination</dd>
+</dl>
+</div>
+<div class="section" id="f">
+<h3>F<a class="headerlink" href="#f" title="Permalink to this headline">¶</a></h3>
+<dl class="docutils">
+<dt><strong>FCA</strong></dt>
+<dd>First Class Aggregate</dd>
+</dl>
+</div>
+<div class="section" id="g">
+<h3>G<a class="headerlink" href="#g" title="Permalink to this headline">¶</a></h3>
+<dl class="docutils">
+<dt><strong>GC</strong></dt>
+<dd>Garbage Collection. The practice of using reachability analysis instead of
+explicit memory management to reclaim unused memory.</dd>
+</dl>
+</div>
+<div class="section" id="h">
+<h3>H<a class="headerlink" href="#h" title="Permalink to this headline">¶</a></h3>
+<dl class="docutils" id="heap">
+<dt><strong>Heap</strong></dt>
+<dd>In garbage collection, the region of memory which is managed using
+reachability analysis.</dd>
+</dl>
+</div>
+<div class="section" id="i">
+<h3>I<a class="headerlink" href="#i" title="Permalink to this headline">¶</a></h3>
+<dl class="docutils">
+<dt><strong>IPA</strong></dt>
+<dd>Inter-Procedural Analysis. Refers to any variety of code analysis that
+occurs between procedures, functions or compilation units (modules).</dd>
+<dt><strong>IPO</strong></dt>
+<dd>Inter-Procedural Optimization. Refers to any variety of code optimization
+that occurs between procedures, functions or compilation units (modules).</dd>
+<dt><strong>ISel</strong></dt>
+<dd>Instruction Selection</dd>
+</dl>
+</div>
+<div class="section" id="l">
+<h3>L<a class="headerlink" href="#l" title="Permalink to this headline">¶</a></h3>
+<dl class="docutils">
+<dt><strong>LCSSA</strong></dt>
+<dd>Loop-Closed Static Single Assignment Form</dd>
+<dt><strong>LICM</strong></dt>
+<dd>Loop Invariant Code Motion</dd>
+<dt><strong>Load-VN</strong></dt>
+<dd>Load Value Numbering</dd>
+<dt><strong>LTO</strong></dt>
+<dd>Link-Time Optimization</dd>
+</dl>
+</div>
+<div class="section" id="m">
+<h3>M<a class="headerlink" href="#m" title="Permalink to this headline">¶</a></h3>
+<dl class="docutils">
+<dt><strong>MC</strong></dt>
+<dd>Machine Code</dd>
+</dl>
+</div>
+<div class="section" id="o">
+<h3>O<a class="headerlink" href="#o" title="Permalink to this headline">¶</a></h3>
+<dl class="docutils" id="object-pointers">
+<span id="object-pointer"></span><dt><strong>Object Pointer</strong></dt>
+<dd>A pointer to an object such that the garbage collector is able to trace
+references contained within the object. This term is used in opposition to
+<a class="reference internal" href="#derived-pointer">derived pointer</a>.</dd>
+</dl>
+</div>
+<div class="section" id="p">
+<h3>P<a class="headerlink" href="#p" title="Permalink to this headline">¶</a></h3>
+<dl class="docutils">
+<dt><strong>PRE</strong></dt>
+<dd>Partial Redundancy Elimination</dd>
+</dl>
+</div>
+<div class="section" id="r">
+<h3>R<a class="headerlink" href="#r" title="Permalink to this headline">¶</a></h3>
+<p><strong>RAUW</strong></p>
+<blockquote>
+<div>Replace All Uses With. The functions <tt class="docutils literal"><span class="pre">User::replaceUsesOfWith()</span></tt>,
+<tt class="docutils literal"><span class="pre">Value::replaceAllUsesWith()</span></tt>, and
+<tt class="docutils literal"><span class="pre">Constant::replaceUsesOfWithOnConstant()</span></tt> implement the replacement of one
+Value with another by iterating over its def/use chain and fixing up all of
+the pointers to point to the new value. See
+also <a class="reference external" href="ProgrammersManual.html#iterate_chains">def/use chains</a>.</div></blockquote>
+<dl class="docutils">
+<dt><strong>Reassociation</strong></dt>
+<dd>Rearranging associative expressions to promote better redundancy elimination
+and other optimization. For example, changing <tt class="docutils literal"><span class="pre">(A+B-A)</span></tt> into <tt class="docutils literal"><span class="pre">(B+A-A)</span></tt>,
+permitting it to be optimized into <tt class="docutils literal"><span class="pre">(B+0)</span></tt> then <tt class="docutils literal"><span class="pre">(B)</span></tt>.</dd>
+</dl>
+<dl class="docutils" id="stack-roots">
+<span id="roots"></span><dt><strong>Root</strong></dt>
+<dd>In garbage collection, a pointer variable lying outside of the <a class="reference internal" href="#heap">heap</a> from
+which the collector begins its reachability analysis. In the context of code
+generation, “root” almost always refers to a “stack root” — a local or
+temporary variable within an executing function.</dd>
+<dt><strong>RPO</strong></dt>
+<dd>Reverse postorder</dd>
+</dl>
+</div>
+<div class="section" id="s">
+<h3>S<a class="headerlink" href="#s" title="Permalink to this headline">¶</a></h3>
+<dl class="docutils" id="safe-point">
+<dt><strong>Safe Point</strong></dt>
+<dd>In garbage collection, it is necessary to identify <a class="reference internal" href="#stack-roots">stack roots</a> so that
+reachability analysis may proceed. It may be infeasible to provide this
+information for every instruction, so instead the information may is
+calculated only at designated safe points. With a copying collector,
+<a class="reference internal" href="#derived-pointers">derived pointers</a> must not be retained across safe points and <a class="reference internal" href="#object-pointers">object
+pointers</a> must be reloaded from stack roots.</dd>
+<dt><strong>SDISel</strong></dt>
+<dd>Selection DAG Instruction Selection.</dd>
+<dt><strong>SCC</strong></dt>
+<dd>Strongly Connected Component</dd>
+<dt><strong>SCCP</strong></dt>
+<dd>Sparse Conditional Constant Propagation</dd>
+<dt><strong>SRoA</strong></dt>
+<dd>Scalar Replacement of Aggregates</dd>
+<dt><strong>SSA</strong></dt>
+<dd>Static Single Assignment</dd>
+<dt><strong>Stack Map</strong></dt>
+<dd>In garbage collection, metadata emitted by the code generator which
+identifies <a class="reference internal" href="#roots">roots</a> within the stack frame of an executing function.</dd>
+</dl>
+</div>
+<div class="section" id="t">
+<h3>T<a class="headerlink" href="#t" title="Permalink to this headline">¶</a></h3>
+<dl class="docutils">
+<dt><strong>TBAA</strong></dt>
+<dd>Type-Based Alias Analysis</dd>
+</dl>
+</div>
+</div>
+</div>
+
+
+ </div>
+ </div>
+ </div>
+ <div class="clearer"></div>
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+ <h3><a href="index.html">Table Of Contents</a></h3>
+ <ul>
+<li><a class="reference internal" href="#">LLVM Link Time Optimization: Design and Implementation</a><ul>
+<li><a class="reference internal" href="#description">Description</a></li>
+<li><a class="reference internal" href="#design-philosophy">Design Philosophy</a><ul>
+<li><a class="reference internal" href="#example-of-link-time-optimization">Example of link time optimization</a></li>
+<li><a class="reference internal" href="#alternative-approaches">Alternative Approaches</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#multi-phase-communication-between-liblto-and-linker">Multi-phase communication between <tt class="docutils literal"><span class="pre">libLTO</span></tt> and linker</a><ul>
+<li><a class="reference internal" href="#phase-1-read-llvm-bitcode-files">Phase 1 : Read LLVM Bitcode Files</a></li>
+<li><a class="reference internal" href="#phase-2-symbol-resolution">Phase 2 : Symbol Resolution</a></li>
+<li><a class="reference internal" href="#phase-3-optimize-bitcode-files">Phase 3 : Optimize Bitcode Files</a></li>
+<li><a class="reference internal" href="#phase-4-symbol-resolution-after-optimization">Phase 4 : Symbol Resolution after optimization</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#liblto"><tt class="docutils literal"><span class="pre">libLTO</span></tt></a><ul>
+<li><a class="reference internal" href="#lto-module-t"><tt class="docutils literal"><span class="pre">lto_module_t</span></tt></a></li>
+<li><a class="reference internal" href="#lto-code-gen-t"><tt class="docutils literal"><span class="pre">lto_code_gen_t</span></tt></a></li>
+</ul>
+</li>
+</ul>
+</li>
+</ul>
+
+ <h4>Previous topic</h4>
+ <p class="topless"><a href="ExceptionHandling.html"
+ title="previous chapter">Exception Handling in LLVM</a></p>
+ <h4>Next topic</h4>
+ <p class="topless"><a href="SegmentedStacks.html"
+ title="next chapter">Segmented Stacks in LLVM</a></p>
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+
+ <div class="section" id="llvm-link-time-optimization-design-and-implementation">
+<span id="lto"></span><h1>LLVM Link Time Optimization: Design and Implementation<a class="headerlink" href="#llvm-link-time-optimization-design-and-implementation" title="Permalink to this headline">¶</a></h1>
+<div class="contents local topic" id="contents">
+<ul class="simple">
+<li><a class="reference internal" href="#description" id="id2">Description</a></li>
+<li><a class="reference internal" href="#design-philosophy" id="id3">Design Philosophy</a><ul>
+<li><a class="reference internal" href="#example-of-link-time-optimization" id="id4">Example of link time optimization</a></li>
+<li><a class="reference internal" href="#alternative-approaches" id="id5">Alternative Approaches</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#multi-phase-communication-between-liblto-and-linker" id="id6">Multi-phase communication between <tt class="docutils literal"><span class="pre">libLTO</span></tt> and linker</a><ul>
+<li><a class="reference internal" href="#phase-1-read-llvm-bitcode-files" id="id7">Phase 1 : Read LLVM Bitcode Files</a></li>
+<li><a class="reference internal" href="#phase-2-symbol-resolution" id="id8">Phase 2 : Symbol Resolution</a></li>
+<li><a class="reference internal" href="#phase-3-optimize-bitcode-files" id="id9">Phase 3 : Optimize Bitcode Files</a></li>
+<li><a class="reference internal" href="#phase-4-symbol-resolution-after-optimization" id="id10">Phase 4 : Symbol Resolution after optimization</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#liblto" id="id11"><tt class="docutils literal"><span class="pre">libLTO</span></tt></a><ul>
+<li><a class="reference internal" href="#lto-module-t" id="id12"><tt class="docutils literal"><span class="pre">lto_module_t</span></tt></a></li>
+<li><a class="reference internal" href="#lto-code-gen-t" id="id13"><tt class="docutils literal"><span class="pre">lto_code_gen_t</span></tt></a></li>
+</ul>
+</li>
+</ul>
+</div>
+<div class="section" id="description">
+<h2><a class="toc-backref" href="#id2">Description</a><a class="headerlink" href="#description" title="Permalink to this headline">¶</a></h2>
+<p>LLVM features powerful intermodular optimizations which can be used at link
+time. Link Time Optimization (LTO) is another name for intermodular
+optimization when performed during the link stage. This document describes the
+interface and design between the LTO optimizer and the linker.</p>
+</div>
+<div class="section" id="design-philosophy">
+<h2><a class="toc-backref" href="#id3">Design Philosophy</a><a class="headerlink" href="#design-philosophy" title="Permalink to this headline">¶</a></h2>
+<p>The LLVM Link Time Optimizer provides complete transparency, while doing
+intermodular optimization, in the compiler tool chain. Its main goal is to let
+the developer take advantage of intermodular optimizations without making any
+significant changes to the developer’s makefiles or build system. This is
+achieved through tight integration with the linker. In this model, the linker
+treates LLVM bitcode files like native object files and allows mixing and
+matching among them. The linker uses <a class="reference internal" href="#liblto">libLTO</a>, a shared object, to handle LLVM
+bitcode files. This tight integration between the linker and LLVM optimizer
+helps to do optimizations that are not possible in other models. The linker
+input allows the optimizer to avoid relying on conservative escape analysis.</p>
+<div class="section" id="example-of-link-time-optimization">
+<span id="liblto-example"></span><h3><a class="toc-backref" href="#id4">Example of link time optimization</a><a class="headerlink" href="#example-of-link-time-optimization" title="Permalink to this headline">¶</a></h3>
+<p>The following example illustrates the advantages of LTO’s integrated approach
+and clean interface. This example requires a system linker which supports LTO
+through the interface described in this document. Here, clang transparently
+invokes system linker.</p>
+<ul class="simple">
+<li>Input source file <tt class="docutils literal"><span class="pre">a.c</span></tt> is compiled into LLVM bitcode form.</li>
+<li>Input source file <tt class="docutils literal"><span class="pre">main.c</span></tt> is compiled into native object code.</li>
+</ul>
+<div class="highlight-c++"><div class="highlight"><pre><span class="o">---</span> <span class="n">a</span><span class="p">.</span><span class="n">h</span> <span class="o">---</span>
+<span class="k">extern</span> <span class="kt">int</span> <span class="n">foo1</span><span class="p">(</span><span class="kt">void</span><span class="p">);</span>
+<span class="k">extern</span> <span class="kt">void</span> <span class="n">foo2</span><span class="p">(</span><span class="kt">void</span><span class="p">);</span>
+<span class="k">extern</span> <span class="kt">void</span> <span class="n">foo4</span><span class="p">(</span><span class="kt">void</span><span class="p">);</span>
+
+<span class="o">---</span> <span class="n">a</span><span class="p">.</span><span class="n">c</span> <span class="o">---</span>
+<span class="cp">#include "a.h"</span>
+
+<span class="k">static</span> <span class="kt">signed</span> <span class="kt">int</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+
+<span class="kt">void</span> <span class="n">foo2</span><span class="p">(</span><span class="kt">void</span><span class="p">)</span> <span class="p">{</span>
+ <span class="n">i</span> <span class="o">=</span> <span class="o">-</span><span class="mi">1</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="k">static</span> <span class="kt">int</span> <span class="n">foo3</span><span class="p">()</span> <span class="p">{</span>
+ <span class="n">foo4</span><span class="p">();</span>
+ <span class="k">return</span> <span class="mi">10</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="kt">int</span> <span class="n">foo1</span><span class="p">(</span><span class="kt">void</span><span class="p">)</span> <span class="p">{</span>
+ <span class="kt">int</span> <span class="n">data</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+
+ <span class="k">if</span> <span class="p">(</span><span class="n">i</span> <span class="o"><</span> <span class="mi">0</span><span class="p">)</span>
+ <span class="n">data</span> <span class="o">=</span> <span class="n">foo3</span><span class="p">();</span>
+
+ <span class="n">data</span> <span class="o">=</span> <span class="n">data</span> <span class="o">+</span> <span class="mi">42</span><span class="p">;</span>
+ <span class="k">return</span> <span class="n">data</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="o">---</span> <span class="n">main</span><span class="p">.</span><span class="n">c</span> <span class="o">---</span>
+<span class="cp">#include <stdio.h></span>
+<span class="cp">#include "a.h"</span>
+
+<span class="kt">void</span> <span class="n">foo4</span><span class="p">(</span><span class="kt">void</span><span class="p">)</span> <span class="p">{</span>
+ <span class="n">printf</span><span class="p">(</span><span class="s">"Hi</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="kt">int</span> <span class="n">main</span><span class="p">()</span> <span class="p">{</span>
+ <span class="k">return</span> <span class="n">foo1</span><span class="p">();</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<div class="highlight-bash"><div class="highlight"><pre>--- <span class="nb">command </span>lines ---
+% clang -emit-llvm -c a.c -o a.o <span class="c"># <-- a.o is LLVM bitcode file</span>
+% clang -c main.c -o main.o <span class="c"># <-- main.o is native object file</span>
+% clang a.o main.o -o main <span class="c"># <-- standard link command without modifications</span>
+</pre></div>
+</div>
+<ul class="simple">
+<li>In this example, the linker recognizes that <tt class="docutils literal"><span class="pre">foo2()</span></tt> is an externally
+visible symbol defined in LLVM bitcode file. The linker completes its usual
+symbol resolution pass and finds that <tt class="docutils literal"><span class="pre">foo2()</span></tt> is not used
+anywhere. This information is used by the LLVM optimizer and it
+removes <tt class="docutils literal"><span class="pre">foo2()</span></tt>.</li></li>
+<li>As soon as <tt class="docutils literal"><span class="pre">foo2()</span></tt> is removed, the optimizer recognizes that condition <tt class="docutils literal"><span class="pre">i</span>
+<span class="pre"><</span> <span class="pre">0</span></tt> is always false, which means <tt class="docutils literal"><span class="pre">foo3()</span></tt> is never used. Hence, the
+optimizer also removes <tt class="docutils literal"><span class="pre">foo3()</span></tt>.</li>
+<li>And this in turn, enables linker to remove <tt class="docutils literal"><span class="pre">foo4()</span></tt>.</li>
+</ul>
+<p>This example illustrates the advantage of tight integration with the
+linker. Here, the optimizer can not remove <tt class="docutils literal"><span class="pre">foo3()</span></tt> without the linker’s
+input.</p>
+</div>
+<div class="section" id="alternative-approaches">
+<h3><a class="toc-backref" href="#id5">Alternative Approaches</a><a class="headerlink" href="#alternative-approaches" title="Permalink to this headline">¶</a></h3>
+<dl class="docutils">
+<dt><strong>Compiler driver invokes link time optimizer separately.</strong></dt>
+<dd>In this model the link time optimizer is not able to take advantage of
+information collected during the linker’s normal symbol resolution phase.
+In the above example, the optimizer can not remove <tt class="docutils literal"><span class="pre">foo2()</span></tt> without the
+linker’s input because it is externally visible. This in turn prohibits the
+optimizer from removing <tt class="docutils literal"><span class="pre">foo3()</span></tt>.</dd>
+<dt><strong>Use separate tool to collect symbol information from all object files.</strong></dt>
+<dd>In this model, a new, separate, tool or library replicates the linker’s
+capability to collect information for link time optimization. Not only is
+this code duplication difficult to justify, but it also has several other
+disadvantages. For example, the linking semantics and the features provided
+by the linker on various platform are not unique. This means, this new tool
+needs to support all such features and platforms in one super tool or a
+separate tool per platform is required. This increases maintenance cost for
+link time optimizer significantly, which is not necessary. This approach
+also requires staying synchronized with linker developements on various
+platforms, which is not the main focus of the link time optimizer. Finally,
+this approach increases end user’s build time due to the duplication of work
+done by this separate tool and the linker itself.</dd>
+</dl>
+</div>
+</div>
+<div class="section" id="multi-phase-communication-between-liblto-and-linker">
+<h2><a class="toc-backref" href="#id6">Multi-phase communication between <tt class="docutils literal"><span class="pre">libLTO</span></tt> and linker</a><a class="headerlink" href="#multi-phase-communication-between-liblto-and-linker" title="Permalink to this headline">¶</a></h2>
+<p>The linker collects information about symbol defininitions and uses in various
+link objects which is more accurate than any information collected by other
+tools during typical build cycles. The linker collects this information by
+looking at the definitions and uses of symbols in native .o files and using
+symbol visibility information. The linker also uses user-supplied information,
+such as a list of exported symbols. LLVM optimizer collects control flow
+information, data flow information and knows much more about program structure
+from the optimizer’s point of view. Our goal is to take advantage of tight
+integration between the linker and the optimizer by sharing this information
+during various linking phases.</p>
+<div class="section" id="phase-1-read-llvm-bitcode-files">
+<h3><a class="toc-backref" href="#id7">Phase 1 : Read LLVM Bitcode Files</a><a class="headerlink" href="#phase-1-read-llvm-bitcode-files" title="Permalink to this headline">¶</a></h3>
+<p>The linker first reads all object files in natural order and collects symbol
+information. This includes native object files as well as LLVM bitcode files.
+To minimize the cost to the linker in the case that all .o files are native
+object files, the linker only calls <tt class="docutils literal"><span class="pre">lto_module_create()</span></tt> when a supplied
+object file is found to not be a native object file. If <tt class="docutils literal"><span class="pre">lto_module_create()</span></tt>
+returns that the file is an LLVM bitcode file, the linker then iterates over the
+module using <tt class="docutils literal"><span class="pre">lto_module_get_symbol_name()</span></tt> and
+<tt class="docutils literal"><span class="pre">lto_module_get_symbol_attribute()</span></tt> to get all symbols defined and referenced.
+This information is added to the linker’s global symbol table.</p>
+<p>The lto* functions are all implemented in a shared object libLTO. This allows
+the LLVM LTO code to be updated independently of the linker tool. On platforms
+that support it, the shared object is lazily loaded.</p>
+</div>
+<div class="section" id="phase-2-symbol-resolution">
+<h3><a class="toc-backref" href="#id8">Phase 2 : Symbol Resolution</a><a class="headerlink" href="#phase-2-symbol-resolution" title="Permalink to this headline">¶</a></h3>
+<p>In this stage, the linker resolves symbols using global symbol table. It may
+report undefined symbol errors, read archive members, replace weak symbols, etc.
+The linker is able to do this seamlessly even though it does not know the exact
+content of input LLVM bitcode files. If dead code stripping is enabled then the
+linker collects the list of live symbols.</p>
+</div>
+<div class="section" id="phase-3-optimize-bitcode-files">
+<h3><a class="toc-backref" href="#id9">Phase 3 : Optimize Bitcode Files</a><a class="headerlink" href="#phase-3-optimize-bitcode-files" title="Permalink to this headline">¶</a></h3>
+<p>After symbol resolution, the linker tells the LTO shared object which symbols
+are needed by native object files. In the example above, the linker reports
+that only <tt class="docutils literal"><span class="pre">foo1()</span></tt> is used by native object files using
+<tt class="docutils literal"><span class="pre">lto_codegen_add_must_preserve_symbol()</span></tt>. Next the linker invokes the LLVM
+optimizer and code generators using <tt class="docutils literal"><span class="pre">lto_codegen_compile()</span></tt> which returns a
+native object file creating by merging the LLVM bitcode files and applying
+various optimization passes.</p>
+</div>
+<div class="section" id="phase-4-symbol-resolution-after-optimization">
+<h3><a class="toc-backref" href="#id10">Phase 4 : Symbol Resolution after optimization</a><a class="headerlink" href="#phase-4-symbol-resolution-after-optimization" title="Permalink to this headline">¶</a></h3>
+<p>In this phase, the linker reads optimized a native object file and updates the
+internal global symbol table to reflect any changes. The linker also collects
+information about any changes in use of external symbols by LLVM bitcode
+files. In the example above, the linker notes that <tt class="docutils literal"><span class="pre">foo4()</span></tt> is not used any
+more. If dead code stripping is enabled then the linker refreshes the live
+symbol information appropriately and performs dead code stripping.</p>
+<p>After this phase, the linker continues linking as if it never saw LLVM bitcode
+files.</p>
+</div>
+</div>
+<div class="section" id="liblto">
+<span id="id1"></span><h2><a class="toc-backref" href="#id11"><tt class="docutils literal"><span class="pre">libLTO</span></tt></a><a class="headerlink" href="#liblto" title="Permalink to this headline">¶</a></h2>
+<p><tt class="docutils literal"><span class="pre">libLTO</span></tt> is a shared object that is part of the LLVM tools, and is intended
+for use by a linker. <tt class="docutils literal"><span class="pre">libLTO</span></tt> provides an abstract C interface to use the LLVM
+interprocedural optimizer without exposing details of LLVM’s internals. The
+intention is to keep the interface as stable as possible even when the LLVM
+optimizer continues to evolve. It should even be possible for a completely
+different compilation technology to provide a different libLTO that works with
+their object files and the standard linker tool.</p>
+<div class="section" id="lto-module-t">
+<h3><a class="toc-backref" href="#id12"><tt class="docutils literal"><span class="pre">lto_module_t</span></tt></a><a class="headerlink" href="#lto-module-t" title="Permalink to this headline">¶</a></h3>
+<p>A non-native object file is handled via an <tt class="docutils literal"><span class="pre">lto_module_t</span></tt>. The following
+functions allow the linker to check if a file (on disk or in a memory buffer) is
+a file which libLTO can process:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="n">lto_module_is_object_file</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span><span class="o">*</span><span class="p">)</span>
+<span class="n">lto_module_is_object_file_for_target</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span><span class="o">*</span><span class="p">,</span> <span class="k">const</span> <span class="kt">char</span><span class="o">*</span><span class="p">)</span>
+<span class="n">lto_module_is_object_file_in_memory</span><span class="p">(</span><span class="k">const</span> <span class="kt">void</span><span class="o">*</span><span class="p">,</span> <span class="kt">size_t</span><span class="p">)</span>
+<span class="n">lto_module_is_object_file_in_memory_for_target</span><span class="p">(</span><span class="k">const</span> <span class="kt">void</span><span class="o">*</span><span class="p">,</span> <span class="kt">size_t</span><span class="p">,</span> <span class="k">const</span> <span class="kt">char</span><span class="o">*</span><span class="p">)</span>
+</pre></div>
+</div>
+<p>If the object file can be processed by <tt class="docutils literal"><span class="pre">libLTO</span></tt>, the linker creates a
+<tt class="docutils literal"><span class="pre">lto_module_t</span></tt> by using one of:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="n">lto_module_create</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span><span class="o">*</span><span class="p">)</span>
+<span class="n">lto_module_create_from_memory</span><span class="p">(</span><span class="k">const</span> <span class="kt">void</span><span class="o">*</span><span class="p">,</span> <span class="kt">size_t</span><span class="p">)</span>
+</pre></div>
+</div>
+<p>and when done, the handle is released via</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="n">lto_module_dispose</span><span class="p">(</span><span class="n">lto_module_t</span><span class="p">)</span>
+</pre></div>
+</div>
+<p>The linker can introspect the non-native object file by getting the number of
+symbols and getting the name and attributes of each symbol via:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="n">lto_module_get_num_symbols</span><span class="p">(</span><span class="n">lto_module_t</span><span class="p">)</span>
+<span class="n">lto_module_get_symbol_name</span><span class="p">(</span><span class="n">lto_module_t</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="kt">int</span><span class="p">)</span>
+<span class="n">lto_module_get_symbol_attribute</span><span class="p">(</span><span class="n">lto_module_t</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="kt">int</span><span class="p">)</span>
+</pre></div>
+</div>
+<p>The attributes of a symbol include the alignment, visibility, and kind.</p>
+</div>
+<div class="section" id="lto-code-gen-t">
+<h3><a class="toc-backref" href="#id13"><tt class="docutils literal"><span class="pre">lto_code_gen_t</span></tt></a><a class="headerlink" href="#lto-code-gen-t" title="Permalink to this headline">¶</a></h3>
+<p>Once the linker has loaded each non-native object files into an
+<tt class="docutils literal"><span class="pre">lto_module_t</span></tt>, it can request <tt class="docutils literal"><span class="pre">libLTO</span></tt> to process them all and generate a
+native object file. This is done in a couple of steps. First, a code generator
+is created with:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="n">lto_codegen_create</span><span class="p">()</span>
+</pre></div>
+</div>
+<p>Then, each non-native object file is added to the code generator with:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="n">lto_codegen_add_module</span><span class="p">(</span><span class="n">lto_code_gen_t</span><span class="p">,</span> <span class="n">lto_module_t</span><span class="p">)</span>
+</pre></div>
+</div>
+<p>The linker then has the option of setting some codegen options. Whether or not
+to generate DWARF debug info is set with:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="n">lto_codegen_set_debug_model</span><span class="p">(</span><span class="n">lto_code_gen_t</span><span class="p">)</span>
+</pre></div>
+</div>
+<p>Which kind of position independence is set with:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="n">lto_codegen_set_pic_model</span><span class="p">(</span><span class="n">lto_code_gen_t</span><span class="p">)</span>
+</pre></div>
+</div>
+<p>And each symbol that is referenced by a native object file or otherwise must not
+be optimized away is set with:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="n">lto_codegen_add_must_preserve_symbol</span><span class="p">(</span><span class="n">lto_code_gen_t</span><span class="p">,</span> <span class="k">const</span> <span class="kt">char</span><span class="o">*</span><span class="p">)</span>
+</pre></div>
+</div>
+<p>After all these settings are done, the linker requests that a native object file
+be created from the modules with the settings using:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="n">lto_codegen_compile</span><span class="p">(</span><span class="n">lto_code_gen_t</span><span class="p">,</span> <span class="n">size</span><span class="o">*</span><span class="p">)</span>
+</pre></div>
+</div>
+<p>which returns a pointer to a buffer containing the generated native object file.
+The linker then parses that and links it with the rest of the native object
+files.</p>
+</div>
+</div>
+</div>
+
+
+ </div>
+ </div>
+ </div>
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+<li><a class="reference internal" href="#introduction">Introduction</a></li>
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+<li><a class="reference internal" href="#projects" id="id5">Projects</a></li>
+<li><a class="reference internal" href="#variable-values" id="id6">Variable Values</a></li>
+<li><a class="reference internal" href="#including-makefiles" id="id7">Including Makefiles</a><ul>
+<li><a class="reference internal" href="#makefile" id="id8"><tt class="docutils literal"><span class="pre">Makefile</span></tt></a></li>
+<li><a class="reference internal" href="#makefile-common" id="id9"><tt class="docutils literal"><span class="pre">Makefile.common</span></tt></a></li>
+<li><a class="reference internal" href="#makefile-config" id="id10"><tt class="docutils literal"><span class="pre">Makefile.config</span></tt></a></li>
+<li><a class="reference internal" href="#makefile-rules" id="id11"><tt class="docutils literal"><span class="pre">Makefile.rules</span></tt></a></li>
+<li><a class="reference internal" href="#comments" id="id12">Comments</a></li>
+</ul>
+</li>
+</ul>
+</li>
+<li><a class="reference internal" href="#tutorial" id="id13">Tutorial</a><ul>
+<li><a class="reference internal" href="#libraries" id="id14">Libraries</a><ul>
+<li><a class="reference internal" href="#bitcode-modules" id="id15">Bitcode Modules</a></li>
+<li><a class="reference internal" href="#loadable-modules" id="id16">Loadable Modules</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#tools" id="id17">Tools</a><ul>
+<li><a class="reference internal" href="#jit-tools" id="id18">JIT Tools</a></li>
+</ul>
+</li>
+</ul>
+</li>
+<li><a class="reference internal" href="#targets-supported" id="id19">Targets Supported</a><ul>
+<li><a class="reference internal" href="#all-default" id="id20"><tt class="docutils literal"><span class="pre">all</span></tt> (default)</a></li>
+<li><a class="reference internal" href="#all-local" id="id21"><tt class="docutils literal"><span class="pre">all-local</span></tt></a></li>
+<li><a class="reference internal" href="#check" id="id22"><tt class="docutils literal"><span class="pre">check</span></tt></a></li>
+<li><a class="reference internal" href="#check-local" id="id23"><tt class="docutils literal"><span class="pre">check-local</span></tt></a></li>
+<li><a class="reference internal" href="#clean" id="id24"><tt class="docutils literal"><span class="pre">clean</span></tt></a></li>
+<li><a class="reference internal" href="#clean-local" id="id25"><tt class="docutils literal"><span class="pre">clean-local</span></tt></a></li>
+<li><a class="reference internal" href="#dist" id="id26"><tt class="docutils literal"><span class="pre">dist</span></tt></a></li>
+<li><a class="reference internal" href="#dist-check" id="id27"><tt class="docutils literal"><span class="pre">dist-check</span></tt></a></li>
+<li><a class="reference internal" href="#dist-clean" id="id28"><tt class="docutils literal"><span class="pre">dist-clean</span></tt></a></li>
+<li><a class="reference internal" href="#install" id="id29"><tt class="docutils literal"><span class="pre">install</span></tt></a></li>
+<li><a class="reference internal" href="#preconditions" id="id30"><tt class="docutils literal"><span class="pre">preconditions</span></tt></a></li>
+<li><a class="reference internal" href="#printvars" id="id31"><tt class="docutils literal"><span class="pre">printvars</span></tt></a></li>
+<li><a class="reference internal" href="#reconfigure" id="id32"><tt class="docutils literal"><span class="pre">reconfigure</span></tt></a></li>
+<li><a class="reference internal" href="#spotless" id="id33"><tt class="docutils literal"><span class="pre">spotless</span></tt></a></li>
+<li><a class="reference internal" href="#tags" id="id34"><tt class="docutils literal"><span class="pre">tags</span></tt></a></li>
+<li><a class="reference internal" href="#uninstall" id="id35"><tt class="docutils literal"><span class="pre">uninstall</span></tt></a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#variables" id="id36">Variables</a><ul>
+<li><a class="reference internal" href="#control-variables" id="id37">Control Variables</a></li>
+<li><a class="reference internal" href="#override-variables" id="id38">Override Variables</a></li>
+<li><a class="reference internal" href="#readable-variables" id="id39">Readable Variables</a></li>
+<li><a class="reference internal" href="#internal-variables" id="id40">Internal Variables</a></li>
+</ul>
+</li>
+</ul>
+</div>
+<div class="section" id="introduction">
+<h2><a class="toc-backref" href="#id3">Introduction</a><a class="headerlink" href="#introduction" title="Permalink to this headline">¶</a></h2>
+<p>This document provides <em>usage</em> information about the LLVM makefile system. While
+loosely patterned after the BSD makefile system, LLVM has taken a departure from
+BSD in order to implement additional features needed by LLVM. Although makefile
+systems, such as <tt class="docutils literal"><span class="pre">automake</span></tt>, were attempted at one point, it has become clear
+that the features needed by LLVM and the <tt class="docutils literal"><span class="pre">Makefile</span></tt> norm are too great to use
+a more limited tool. Consequently, LLVM requires simply GNU Make 3.79, a widely
+portable makefile processor. LLVM unabashedly makes heavy use of the features of
+GNU Make so the dependency on GNU Make is firm. If you’re not familiar with
+<tt class="docutils literal"><span class="pre">make</span></tt>, it is recommended that you read the <a class="reference external" href="http://www.gnu.org/software/make/manual/make.html">GNU Makefile Manual</a>.</p>
+<p>While this document is rightly part of the <a class="reference external" href="ProgrammersManual.html">LLVM Programmer’s
+Manual</a>, it is treated separately here because of the
+volume of content and because it is often an early source of bewilderment for
+new developers.</p>
+</div>
+<div class="section" id="general-concepts">
+<h2><a class="toc-backref" href="#id4">General Concepts</a><a class="headerlink" href="#general-concepts" title="Permalink to this headline">¶</a></h2>
+<p>The LLVM Makefile System is the component of LLVM that is responsible for
+building the software, testing it, generating distributions, checking those
+distributions, installing and uninstalling, etc. It consists of a several files
+throughout the source tree. These files and other general concepts are described
+in this section.</p>
+<div class="section" id="projects">
+<h3><a class="toc-backref" href="#id5">Projects</a><a class="headerlink" href="#projects" title="Permalink to this headline">¶</a></h3>
+<p>The LLVM Makefile System is quite generous. It not only builds its own software,
+but it can build yours too. Built into the system is knowledge of the
+<tt class="docutils literal"><span class="pre">llvm/projects</span></tt> directory. Any directory under <tt class="docutils literal"><span class="pre">projects</span></tt> that has both a
+<tt class="docutils literal"><span class="pre">configure</span></tt> script and a <tt class="docutils literal"><span class="pre">Makefile</span></tt> is assumed to be a project that uses the
+LLVM Makefile system. Building software that uses LLVM does not require the
+LLVM Makefile System nor even placement in the <tt class="docutils literal"><span class="pre">llvm/projects</span></tt>
+directory. However, doing so will allow your project to get up and running
+quickly by utilizing the built-in features that are used to compile LLVM. LLVM
+compiles itself using the same features of the makefile system as used for
+projects.</p>
+<p>For complete details on setting up your projects configuration, simply mimic the
+<tt class="docutils literal"><span class="pre">llvm/projects/sample</span></tt> project. Or for further details, consult the
+<a class="reference external" href="Projects.html">Projects</a> page.</p>
+</div>
+<div class="section" id="variable-values">
+<h3><a class="toc-backref" href="#id6">Variable Values</a><a class="headerlink" href="#variable-values" title="Permalink to this headline">¶</a></h3>
+<p>To use the makefile system, you simply create a file named <tt class="docutils literal"><span class="pre">Makefile</span></tt> in your
+directory and declare values for certain variables. The variables and values
+that you select determine what the makefile system will do. These variables
+enable rules and processing in the makefile system that automatically Do The
+Right Thing™.</p>
+</div>
+<div class="section" id="including-makefiles">
+<h3><a class="toc-backref" href="#id7">Including Makefiles</a><a class="headerlink" href="#including-makefiles" title="Permalink to this headline">¶</a></h3>
+<p>Setting variables alone is not enough. You must include into your Makefile
+additional files that provide the rules of the LLVM Makefile system. The various
+files involved are described in the sections that follow.</p>
+<div class="section" id="makefile">
+<h4><a class="toc-backref" href="#id8"><tt class="docutils literal"><span class="pre">Makefile</span></tt></a><a class="headerlink" href="#makefile" title="Permalink to this headline">¶</a></h4>
+<p>Each directory to participate in the build needs to have a file named
+<tt class="docutils literal"><span class="pre">Makefile</span></tt>. This is the file first read by <tt class="docutils literal"><span class="pre">make</span></tt>. It has three
+sections:</p>
+<ol class="arabic simple">
+<li>Settable Variables — Required that must be set first.</li>
+<li><tt class="docutils literal"><span class="pre">include</span> <span class="pre">$(LEVEL)/Makefile.common</span></tt> — include the LLVM Makefile system.</li>
+<li>Override Variables — Override variables set by the LLVM Makefile system.</li>
+</ol>
+</div>
+<div class="section" id="makefile-common">
+<span id="level-makefile-common"></span><h4><a class="toc-backref" href="#id9"><tt class="docutils literal"><span class="pre">Makefile.common</span></tt></a><a class="headerlink" href="#makefile-common" title="Permalink to this headline">¶</a></h4>
+<p>Every project must have a <tt class="docutils literal"><span class="pre">Makefile.common</span></tt> file at its top source
+directory. This file serves three purposes:</p>
+<ol class="arabic simple">
+<li>It includes the project’s configuration makefile to obtain values determined
+by the <tt class="docutils literal"><span class="pre">configure</span></tt> script. This is done by including the
+<a class="reference internal" href="#level-makefile-config">$(LEVEL)/Makefile.config</a> file.</li>
+<li>It specifies any other (static) values that are needed throughout the
+project. Only values that are used in all or a large proportion of the
+project’s directories should be placed here.</li>
+<li>It includes the standard rules for the LLVM Makefile system,
+<a class="reference internal" href="#llvm-src-root-makefile-rules">$(LLVM_SRC_ROOT)/Makefile.rules</a>. This file is the <em>guts</em> of the LLVM
+<tt class="docutils literal"><span class="pre">Makefile</span></tt> system.</li>
+</ol>
+</div>
+<div class="section" id="makefile-config">
+<span id="level-makefile-config"></span><h4><a class="toc-backref" href="#id10"><tt class="docutils literal"><span class="pre">Makefile.config</span></tt></a><a class="headerlink" href="#makefile-config" title="Permalink to this headline">¶</a></h4>
+<p>Every project must have a <tt class="docutils literal"><span class="pre">Makefile.config</span></tt> at the top of its <em>build</em>
+directory. This file is <strong>generated</strong> by the <tt class="docutils literal"><span class="pre">configure</span></tt> script from the
+pattern provided by the <tt class="docutils literal"><span class="pre">Makefile.config.in</span></tt> file located at the top of the
+project’s <em>source</em> directory. The contents of this file depend largely on what
+configuration items the project uses, however most projects can get what they
+need by just relying on LLVM’s configuration found in
+<tt class="docutils literal"><span class="pre">$(LLVM_OBJ_ROOT)/Makefile.config</span></tt>.</p>
+</div>
+<div class="section" id="makefile-rules">
+<span id="llvm-src-root-makefile-rules"></span><h4><a class="toc-backref" href="#id11"><tt class="docutils literal"><span class="pre">Makefile.rules</span></tt></a><a class="headerlink" href="#makefile-rules" title="Permalink to this headline">¶</a></h4>
+<p>This file, located at <tt class="docutils literal"><span class="pre">$(LLVM_SRC_ROOT)/Makefile.rules</span></tt> is the heart of the
+LLVM Makefile System. It provides all the logic, dependencies, and rules for
+building the targets supported by the system. What it does largely depends on
+the values of <tt class="docutils literal"><span class="pre">make</span></tt> <a class="reference internal" href="#variables">variables</a> that have been set <em>before</em>
+<tt class="docutils literal"><span class="pre">Makefile.rules</span></tt> is included.</p>
+</div>
+<div class="section" id="comments">
+<h4><a class="toc-backref" href="#id12">Comments</a><a class="headerlink" href="#comments" title="Permalink to this headline">¶</a></h4>
+<p>User <tt class="docutils literal"><span class="pre">Makefile</span></tt>s need not have comments in them unless the construction is
+unusual or it does not strictly follow the rules and patterns of the LLVM
+makefile system. Makefile comments are invoked with the pound (<tt class="docutils literal"><span class="pre">#</span></tt>) character.
+The <tt class="docutils literal"><span class="pre">#</span></tt> character and any text following it, to the end of the line, are
+ignored by <tt class="docutils literal"><span class="pre">make</span></tt>.</p>
+</div>
+</div>
+</div>
+<div class="section" id="tutorial">
+<h2><a class="toc-backref" href="#id13">Tutorial</a><a class="headerlink" href="#tutorial" title="Permalink to this headline">¶</a></h2>
+<p>This section provides some examples of the different kinds of modules you can
+build with the LLVM makefile system. In general, each directory you provide will
+build a single object although that object may be composed of additionally
+compiled components.</p>
+<div class="section" id="libraries">
+<h3><a class="toc-backref" href="#id14">Libraries</a><a class="headerlink" href="#libraries" title="Permalink to this headline">¶</a></h3>
+<p>Only a few variable definitions are needed to build a regular library.
+Normally, the makefile system will build all the software into a single
+<tt class="docutils literal"><span class="pre">libname.o</span></tt> (pre-linked) object. This means the library is not searchable and
+that the distinction between compilation units has been dissolved. Optionally,
+you can ask for a shared library (.so) or archive library (.a) built. Archive
+libraries are the default. For example:</p>
+<div class="highlight-makefile"><div class="highlight"><pre><span class="nv">LIBRARYNAME</span> <span class="o">=</span> mylib
+<span class="nv">SHARED_LIBRARY</span> <span class="o">=</span> 1
+<span class="nv">ARCHIVE_LIBRARY</span> <span class="o">=</span> 1
+</pre></div>
+</div>
+<p>says to build a library named <tt class="docutils literal"><span class="pre">mylib</span></tt> with both a shared library
+(<tt class="docutils literal"><span class="pre">mylib.so</span></tt>) and an archive library (<tt class="docutils literal"><span class="pre">mylib.a</span></tt>) version. The contents of all
+the libraries produced will be the same, they are just constructed differently.
+Note that you normally do not need to specify the sources involved. The LLVM
+Makefile system will infer the source files from the contents of the source
+directory.</p>
+<p>The <tt class="docutils literal"><span class="pre">LOADABLE_MODULE=1</span></tt> directive can be used in conjunction with
+<tt class="docutils literal"><span class="pre">SHARED_LIBRARY=1</span></tt> to indicate that the resulting shared library should be
+openable with the <tt class="docutils literal"><span class="pre">dlopen</span></tt> function and searchable with the <tt class="docutils literal"><span class="pre">dlsym</span></tt> function
+(or your operating system’s equivalents). While this isn’t strictly necessary on
+Linux and a few other platforms, it is required on systems like HP-UX and
+Darwin. You should use <tt class="docutils literal"><span class="pre">LOADABLE_MODULE</span></tt> for any shared library that you
+intend to be loaded into an tool via the <tt class="docutils literal"><span class="pre">-load</span></tt> option. See the
+<a class="reference external" href="WritingAnLLVMPass.html#makefile">WritingAnLLVMPass.html</a> document for an
+example of why you might want to do this.</p>
+<div class="section" id="bitcode-modules">
+<h4><a class="toc-backref" href="#id15">Bitcode Modules</a><a class="headerlink" href="#bitcode-modules" title="Permalink to this headline">¶</a></h4>
+<p>In some situations, it is desirable to build a single bitcode module from a
+variety of sources, instead of an archive, shared library, or bitcode
+library. Bitcode modules can be specified in addition to any of the other types
+of libraries by defining the <a class="reference internal" href="#module-name">MODULE_NAME</a> variable. For example:</p>
+<div class="highlight-makefile"><div class="highlight"><pre><span class="nv">LIBRARYNAME</span> <span class="o">=</span> mylib
+<span class="nv">BYTECODE_LIBRARY</span> <span class="o">=</span> 1
+<span class="nv">MODULE_NAME</span> <span class="o">=</span> mymod
+</pre></div>
+</div>
+<p>will build a module named <tt class="docutils literal"><span class="pre">mymod.bc</span></tt> from the sources in the directory. This
+module will be an aggregation of all the bitcode modules derived from the
+sources. The example will also build a bitcode archive containing a bitcode
+module for each compiled source file. The difference is subtle, but important
+depending on how the module or library is to be linked.</p>
+</div>
+<div class="section" id="loadable-modules">
+<h4><a class="toc-backref" href="#id16">Loadable Modules</a><a class="headerlink" href="#loadable-modules" title="Permalink to this headline">¶</a></h4>
+<p>In some situations, you need to create a loadable module. Loadable modules can
+be loaded into programs like <tt class="docutils literal"><span class="pre">opt</span></tt> or <tt class="docutils literal"><span class="pre">llc</span></tt> to specify additional passes to
+run or targets to support. Loadable modules are also useful for debugging a
+pass or providing a pass with another package if that pass can’t be included in
+LLVM.</p>
+<p>LLVM provides complete support for building such a module. All you need to do is
+use the <tt class="docutils literal"><span class="pre">LOADABLE_MODULE</span></tt> variable in your <tt class="docutils literal"><span class="pre">Makefile</span></tt>. For example, to build
+a loadable module named <tt class="docutils literal"><span class="pre">MyMod</span></tt> that uses the LLVM libraries <tt class="docutils literal"><span class="pre">LLVMSupport.a</span></tt>
+and <tt class="docutils literal"><span class="pre">LLVMSystem.a</span></tt>, you would specify:</p>
+<div class="highlight-makefile"><div class="highlight"><pre><span class="nv">LIBRARYNAME</span> <span class="o">:=</span> MyMod
+LOADABLE_MODULE :<span class="o">=</span> 1
+LINK_COMPONENTS :<span class="o">=</span> support system
+</pre></div>
+</div>
+<p>Use of the <tt class="docutils literal"><span class="pre">LOADABLE_MODULE</span></tt> facility implies several things:</p>
+<ol class="arabic">
+<li><dl class="first docutils">
+<dt>There will be no “<tt class="docutils literal"><span class="pre">lib</span></tt>” prefix on the module. This differentiates it from</dt>
+<dd><p class="first last">a standard shared library of the same name.</p>
+</dd>
+</dl>
+</li>
+<li><p class="first">The <a class="reference internal" href="#shared-library">SHARED_LIBRARY</a> variable is turned on.</p>
+</li>
+<li><p class="first">The <a class="reference internal" href="#link-libs-in-shared">LINK_LIBS_IN_SHARED</a> variable is turned on.</p>
+</li>
+</ol>
+<p>A loadable module is loaded by LLVM via the facilities of libtool’s libltdl
+library which is part of <tt class="docutils literal"><span class="pre">lib/System</span></tt> implementation.</p>
+</div>
+</div>
+<div class="section" id="tools">
+<h3><a class="toc-backref" href="#id17">Tools</a><a class="headerlink" href="#tools" title="Permalink to this headline">¶</a></h3>
+<p>For building executable programs (tools), you must provide the name of the tool
+and the names of the libraries you wish to link with the tool. For example:</p>
+<div class="highlight-makefile"><div class="highlight"><pre><span class="nv">TOOLNAME</span> <span class="o">=</span> mytool
+<span class="nv">USEDLIBS</span> <span class="o">=</span> mylib
+<span class="nv">LINK_COMPONENTS</span> <span class="o">=</span> support system
+</pre></div>
+</div>
+<p>says that we are to build a tool name <tt class="docutils literal"><span class="pre">mytool</span></tt> and that it requires three
+libraries: <tt class="docutils literal"><span class="pre">mylib</span></tt>, <tt class="docutils literal"><span class="pre">LLVMSupport.a</span></tt> and <tt class="docutils literal"><span class="pre">LLVMSystem.a</span></tt>.</p>
+<p>Note that two different variables are use to indicate which libraries are
+linked: <tt class="docutils literal"><span class="pre">USEDLIBS</span></tt> and <tt class="docutils literal"><span class="pre">LLVMLIBS</span></tt>. This distinction is necessary to support
+projects. <tt class="docutils literal"><span class="pre">LLVMLIBS</span></tt> refers to the LLVM libraries found in the LLVM object
+directory. <tt class="docutils literal"><span class="pre">USEDLIBS</span></tt> refers to the libraries built by your project. In the
+case of building LLVM tools, <tt class="docutils literal"><span class="pre">USEDLIBS</span></tt> and <tt class="docutils literal"><span class="pre">LLVMLIBS</span></tt> can be used
+interchangeably since the “project” is LLVM itself and <tt class="docutils literal"><span class="pre">USEDLIBS</span></tt> refers to
+the same place as <tt class="docutils literal"><span class="pre">LLVMLIBS</span></tt>.</p>
+<p>Also note that there are two different ways of specifying a library: with a
+<tt class="docutils literal"><span class="pre">.a</span></tt> suffix and without. Without the suffix, the entry refers to the re-linked
+(.o) file which will include <em>all</em> symbols of the library. This is
+useful, for example, to include all passes from a library of passes. If the
+<tt class="docutils literal"><span class="pre">.a</span></tt> suffix is used then the library is linked as a searchable library (with
+the <tt class="docutils literal"><span class="pre">-l</span></tt> option). In this case, only the symbols that are unresolved <em>at
+that point</em> will be resolved from the library, if they exist. Other
+(unreferenced) symbols will not be included when the <tt class="docutils literal"><span class="pre">.a</span></tt> syntax is used. Note
+that in order to use the <tt class="docutils literal"><span class="pre">.a</span></tt> suffix, the library in question must have been
+built with the <tt class="docutils literal"><span class="pre">ARCHIVE_LIBRARY</span></tt> option set.</p>
+<div class="section" id="jit-tools">
+<h4><a class="toc-backref" href="#id18">JIT Tools</a><a class="headerlink" href="#jit-tools" title="Permalink to this headline">¶</a></h4>
+<p>Many tools will want to use the JIT features of LLVM. To do this, you simply
+specify that you want an execution ‘engine’, and the makefiles will
+automatically link in the appropriate JIT for the host or an interpreter if none
+is available:</p>
+<div class="highlight-makefile"><div class="highlight"><pre><span class="nv">TOOLNAME</span> <span class="o">=</span> my_jit_tool
+<span class="nv">USEDLIBS</span> <span class="o">=</span> mylib
+<span class="nv">LINK_COMPONENTS</span> <span class="o">=</span> engine
+</pre></div>
+</div>
+<p>Of course, any additional libraries may be listed as other components. To get a
+full understanding of how this changes the linker command, it is recommended
+that you:</p>
+<div class="highlight-bash"><div class="highlight"><pre>% <span class="nb">cd </span>examples/Fibonacci
+% make <span class="nv">VERBOSE</span><span class="o">=</span>1
+</pre></div>
+</div>
+</div>
+</div>
+</div>
+<div class="section" id="targets-supported">
+<h2><a class="toc-backref" href="#id19">Targets Supported</a><a class="headerlink" href="#targets-supported" title="Permalink to this headline">¶</a></h2>
+<p>This section describes each of the targets that can be built using the LLVM
+Makefile system. Any target can be invoked from any directory but not all are
+applicable to a given directory (e.g. “check”, “dist” and “install” will always
+operate as if invoked from the top level directory).</p>
+<table border="1" class="docutils">
+<colgroup>
+<col width="12%" />
+<col width="10%" />
+<col width="78%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">Target Name</th>
+<th class="head">Implied Targets</th>
+<th class="head">Target Description</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td><tt class="docutils literal"><span class="pre">all</span></tt></td>
+<td></td>
+<td>Compile the software recursively. Default target.</td>
+</tr>
+<tr class="row-odd"><td><tt class="docutils literal"><span class="pre">all-local</span></tt></td>
+<td></td>
+<td>Compile the software in the local directory only.</td>
+</tr>
+<tr class="row-even"><td><tt class="docutils literal"><span class="pre">check</span></tt></td>
+<td></td>
+<td>Change to the <tt class="docutils literal"><span class="pre">test</span></tt> directory in a project and run the test suite there.</td>
+</tr>
+<tr class="row-odd"><td><tt class="docutils literal"><span class="pre">check-local</span></tt></td>
+<td></td>
+<td>Run a local test suite. Generally this is only defined in the <tt class="docutils literal"><span class="pre">Makefile</span></tt> of the project’s <tt class="docutils literal"><span class="pre">test</span></tt> directory.</td>
+</tr>
+<tr class="row-even"><td><tt class="docutils literal"><span class="pre">clean</span></tt></td>
+<td></td>
+<td>Remove built objects recursively.</td>
+</tr>
+<tr class="row-odd"><td><tt class="docutils literal"><span class="pre">clean-local</span></tt></td>
+<td></td>
+<td>Remove built objects from the local directory only.</td>
+</tr>
+<tr class="row-even"><td><tt class="docutils literal"><span class="pre">dist</span></tt></td>
+<td><tt class="docutils literal"><span class="pre">all</span></tt></td>
+<td>Prepare a source distribution tarball.</td>
+</tr>
+<tr class="row-odd"><td><tt class="docutils literal"><span class="pre">dist-check</span></tt></td>
+<td><tt class="docutils literal"><span class="pre">all</span></tt></td>
+<td>Prepare a source distribution tarball and check that it builds.</td>
+</tr>
+<tr class="row-even"><td><tt class="docutils literal"><span class="pre">dist-clean</span></tt></td>
+<td><tt class="docutils literal"><span class="pre">clean</span></tt></td>
+<td>Clean source distribution tarball temporary files.</td>
+</tr>
+<tr class="row-odd"><td><tt class="docutils literal"><span class="pre">install</span></tt></td>
+<td><tt class="docutils literal"><span class="pre">all</span></tt></td>
+<td>Copy built objects to installation directory.</td>
+</tr>
+<tr class="row-even"><td><tt class="docutils literal"><span class="pre">preconditions</span></tt></td>
+<td><tt class="docutils literal"><span class="pre">all</span></tt></td>
+<td>Check to make sure configuration and makefiles are up to date.</td>
+</tr>
+<tr class="row-odd"><td><tt class="docutils literal"><span class="pre">printvars</span></tt></td>
+<td><tt class="docutils literal"><span class="pre">all</span></tt></td>
+<td>Prints variables defined by the makefile system (for debugging).</td>
+</tr>
+<tr class="row-even"><td><tt class="docutils literal"><span class="pre">tags</span></tt></td>
+<td></td>
+<td>Make C and C++ tags files for emacs and vi.</td>
+</tr>
+<tr class="row-odd"><td><tt class="docutils literal"><span class="pre">uninstall</span></tt></td>
+<td></td>
+<td>Remove built objects from installation directory.</td>
+</tr>
+</tbody>
+</table>
+<div class="section" id="all-default">
+<span id="all"></span><h3><a class="toc-backref" href="#id20"><tt class="docutils literal"><span class="pre">all</span></tt> (default)</a><a class="headerlink" href="#all-default" title="Permalink to this headline">¶</a></h3>
+<p>When you invoke <tt class="docutils literal"><span class="pre">make</span></tt> with no arguments, you are implicitly instructing it to
+seek the <tt class="docutils literal"><span class="pre">all</span></tt> target (goal). This target is used for building the software
+recursively and will do different things in different directories. For example,
+in a <tt class="docutils literal"><span class="pre">lib</span></tt> directory, the <tt class="docutils literal"><span class="pre">all</span></tt> target will compile source files and
+generate libraries. But, in a <tt class="docutils literal"><span class="pre">tools</span></tt> directory, it will link libraries and
+generate executables.</p>
+</div>
+<div class="section" id="all-local">
+<h3><a class="toc-backref" href="#id21"><tt class="docutils literal"><span class="pre">all-local</span></tt></a><a class="headerlink" href="#all-local" title="Permalink to this headline">¶</a></h3>
+<p>This target is the same as <a class="reference internal" href="#all">all</a> but it operates only on the current directory
+instead of recursively.</p>
+</div>
+<div class="section" id="check">
+<h3><a class="toc-backref" href="#id22"><tt class="docutils literal"><span class="pre">check</span></tt></a><a class="headerlink" href="#check" title="Permalink to this headline">¶</a></h3>
+<p>This target can be invoked from anywhere within a project’s directories but
+always invokes the <a class="reference internal" href="#check-local">check-local</a> target in the project’s <tt class="docutils literal"><span class="pre">test</span></tt> directory, if
+it exists and has a <tt class="docutils literal"><span class="pre">Makefile</span></tt>. A warning is produced otherwise. If
+<a class="reference internal" href="#testsuite">TESTSUITE</a> is defined on the <tt class="docutils literal"><span class="pre">make</span></tt> command line, it will be passed down to
+the invocation of <tt class="docutils literal"><span class="pre">make</span> <span class="pre">check-local</span></tt> in the <tt class="docutils literal"><span class="pre">test</span></tt> directory. The intended
+usage for this is to assist in running specific suites of tests. If
+<tt class="docutils literal"><span class="pre">TESTSUITE</span></tt> is not set, the implementation of <tt class="docutils literal"><span class="pre">check-local</span></tt> should run all
+normal tests. It is up to the project to define what different values for
+<tt class="docutils literal"><span class="pre">TESTSUTE</span></tt> will do. See the <a class="reference external" href="TestingGuide.html">Testing Guide</a> for further
+details.</p>
+</div>
+<div class="section" id="check-local">
+<h3><a class="toc-backref" href="#id23"><tt class="docutils literal"><span class="pre">check-local</span></tt></a><a class="headerlink" href="#check-local" title="Permalink to this headline">¶</a></h3>
+<p>This target should be implemented by the <tt class="docutils literal"><span class="pre">Makefile</span></tt> in the project’s <tt class="docutils literal"><span class="pre">test</span></tt>
+directory. It is invoked by the <tt class="docutils literal"><span class="pre">check</span></tt> target elsewhere. Each project is
+free to define the actions of <tt class="docutils literal"><span class="pre">check-local</span></tt> as appropriate for that
+project. The LLVM project itself uses dejagnu to run a suite of feature and
+regresson tests. Other projects may choose to use dejagnu or any other testing
+mechanism.</p>
+</div>
+<div class="section" id="clean">
+<h3><a class="toc-backref" href="#id24"><tt class="docutils literal"><span class="pre">clean</span></tt></a><a class="headerlink" href="#clean" title="Permalink to this headline">¶</a></h3>
+<p>This target cleans the build directory, recursively removing all things that the
+Makefile builds. The cleaning rules have been made guarded so they shouldn’t go
+awry (via <tt class="docutils literal"><span class="pre">rm</span> <span class="pre">-f</span> <span class="pre">$(UNSET_VARIABLE)/*</span></tt> which will attempt to erase the entire
+directory structure.</p>
+</div>
+<div class="section" id="clean-local">
+<h3><a class="toc-backref" href="#id25"><tt class="docutils literal"><span class="pre">clean-local</span></tt></a><a class="headerlink" href="#clean-local" title="Permalink to this headline">¶</a></h3>
+<p>This target does the same thing as <tt class="docutils literal"><span class="pre">clean</span></tt> but only for the current (local)
+directory.</p>
+</div>
+<div class="section" id="dist">
+<h3><a class="toc-backref" href="#id26"><tt class="docutils literal"><span class="pre">dist</span></tt></a><a class="headerlink" href="#dist" title="Permalink to this headline">¶</a></h3>
+<p>This target builds a distribution tarball. It first builds the entire project
+using the <tt class="docutils literal"><span class="pre">all</span></tt> target and then tars up the necessary files and compresses
+it. The generated tarball is sufficient for a casual source distribution, but
+probably not for a release (see <tt class="docutils literal"><span class="pre">dist-check</span></tt>).</p>
+</div>
+<div class="section" id="dist-check">
+<h3><a class="toc-backref" href="#id27"><tt class="docutils literal"><span class="pre">dist-check</span></tt></a><a class="headerlink" href="#dist-check" title="Permalink to this headline">¶</a></h3>
+<p>This target does the same thing as the <tt class="docutils literal"><span class="pre">dist</span></tt> target but also checks the
+distribution tarball. The check is made by unpacking the tarball to a new
+directory, configuring it, building it, installing it, and then verifying that
+the installation results are correct (by comparing to the original build). This
+target can take a long time to run but should be done before a release goes out
+to make sure that the distributed tarball can actually be built into a working
+release.</p>
+</div>
+<div class="section" id="dist-clean">
+<h3><a class="toc-backref" href="#id28"><tt class="docutils literal"><span class="pre">dist-clean</span></tt></a><a class="headerlink" href="#dist-clean" title="Permalink to this headline">¶</a></h3>
+<p>This is a special form of the <tt class="docutils literal"><span class="pre">clean</span></tt> clean target. It performs a normal
+<tt class="docutils literal"><span class="pre">clean</span></tt> but also removes things pertaining to building the distribution.</p>
+</div>
+<div class="section" id="install">
+<h3><a class="toc-backref" href="#id29"><tt class="docutils literal"><span class="pre">install</span></tt></a><a class="headerlink" href="#install" title="Permalink to this headline">¶</a></h3>
+<p>This target finalizes shared objects and executables and copies all libraries,
+headers, executables and documentation to the directory given with the
+<tt class="docutils literal"><span class="pre">--prefix</span></tt> option to <tt class="docutils literal"><span class="pre">configure</span></tt>. When completed, the prefix directory will
+have everything needed to <strong>use</strong> LLVM.</p>
+<p>The LLVM makefiles can generate complete <strong>internal</strong> documentation for all the
+classes by using <tt class="docutils literal"><span class="pre">doxygen</span></tt>. By default, this feature is <strong>not</strong> enabled
+because it takes a long time and generates a massive amount of data (>100MB). If
+you want this feature, you must configure LLVM with the –enable-doxygen switch
+and ensure that a modern version of doxygen (1.3.7 or later) is available in
+your <tt class="docutils literal"><span class="pre">PATH</span></tt>. You can download doxygen from <a class="reference external" href="http://www.stack.nl/~dimitri/doxygen/download.html#latestsrc">here</a>.</p>
+</div>
+<div class="section" id="preconditions">
+<h3><a class="toc-backref" href="#id30"><tt class="docutils literal"><span class="pre">preconditions</span></tt></a><a class="headerlink" href="#preconditions" title="Permalink to this headline">¶</a></h3>
+<p>This utility target checks to see if the <tt class="docutils literal"><span class="pre">Makefile</span></tt> in the object directory is
+older than the <tt class="docutils literal"><span class="pre">Makefile</span></tt> in the source directory and copies it if so. It also
+reruns the <tt class="docutils literal"><span class="pre">configure</span></tt> script if that needs to be done and rebuilds the
+<tt class="docutils literal"><span class="pre">Makefile.config</span></tt> file similarly. Users may overload this target to ensure
+that sanity checks are run <em>before</em> any building of targets as all the targets
+depend on <tt class="docutils literal"><span class="pre">preconditions</span></tt>.</p>
+</div>
+<div class="section" id="printvars">
+<h3><a class="toc-backref" href="#id31"><tt class="docutils literal"><span class="pre">printvars</span></tt></a><a class="headerlink" href="#printvars" title="Permalink to this headline">¶</a></h3>
+<p>This utility target just causes the LLVM makefiles to print out some of the
+makefile variables so that you can double check how things are set.</p>
+</div>
+<div class="section" id="reconfigure">
+<h3><a class="toc-backref" href="#id32"><tt class="docutils literal"><span class="pre">reconfigure</span></tt></a><a class="headerlink" href="#reconfigure" title="Permalink to this headline">¶</a></h3>
+<p>This utility target will force a reconfigure of LLVM or your project. It simply
+runs <tt class="docutils literal"><span class="pre">$(PROJ_OBJ_ROOT)/config.status</span> <span class="pre">--recheck</span></tt> to rerun the configuration
+tests and rebuild the configured files. This isn’t generally useful as the
+makefiles will reconfigure themselves whenever its necessary.</p>
+</div>
+<div class="section" id="spotless">
+<h3><a class="toc-backref" href="#id33"><tt class="docutils literal"><span class="pre">spotless</span></tt></a><a class="headerlink" href="#spotless" title="Permalink to this headline">¶</a></h3>
+<div class="admonition warning">
+<p class="first admonition-title">Warning</p>
+<p class="last">Use with caution!</p>
+</div>
+<p>This utility target, only available when <tt class="docutils literal"><span class="pre">$(PROJ_OBJ_ROOT)</span></tt> is not the same as
+<tt class="docutils literal"><span class="pre">$(PROJ_SRC_ROOT)</span></tt>, will completely clean the <tt class="docutils literal"><span class="pre">$(PROJ_OBJ_ROOT)</span></tt> directory
+by removing its content entirely and reconfiguring the directory. This returns
+the <tt class="docutils literal"><span class="pre">$(PROJ_OBJ_ROOT)</span></tt> directory to a completely fresh state. All content in
+the directory except configured files and top-level makefiles will be lost.</p>
+</div>
+<div class="section" id="tags">
+<h3><a class="toc-backref" href="#id34"><tt class="docutils literal"><span class="pre">tags</span></tt></a><a class="headerlink" href="#tags" title="Permalink to this headline">¶</a></h3>
+<p>This target will generate a <tt class="docutils literal"><span class="pre">TAGS</span></tt> file in the top-level source directory. It
+is meant for use with emacs, XEmacs, or ViM. The TAGS file provides an index of
+symbol definitions so that the editor can jump you to the definition
+quickly.</p>
+</div>
+<div class="section" id="uninstall">
+<h3><a class="toc-backref" href="#id35"><tt class="docutils literal"><span class="pre">uninstall</span></tt></a><a class="headerlink" href="#uninstall" title="Permalink to this headline">¶</a></h3>
+<p>This target is the opposite of the <tt class="docutils literal"><span class="pre">install</span></tt> target. It removes the header,
+library and executable files from the installation directories. Note that the
+directories themselves are not removed because it is not guaranteed that LLVM is
+the only thing installing there (e.g. <tt class="docutils literal"><span class="pre">--prefix=/usr</span></tt>).</p>
+</div>
+</div>
+<div class="section" id="variables">
+<span id="id2"></span><h2><a class="toc-backref" href="#id36">Variables</a><a class="headerlink" href="#variables" title="Permalink to this headline">¶</a></h2>
+<p>Variables are used to tell the LLVM Makefile System what to do and to obtain
+information from it. Variables are also used internally by the LLVM Makefile
+System. Variable names that contain only the upper case alphabetic letters and
+underscore are intended for use by the end user. All other variables are
+internal to the LLVM Makefile System and should not be relied upon nor
+modified. The sections below describe how to use the LLVM Makefile
+variables.</p>
+<div class="section" id="control-variables">
+<h3><a class="toc-backref" href="#id37">Control Variables</a><a class="headerlink" href="#control-variables" title="Permalink to this headline">¶</a></h3>
+<p>Variables listed in the table below should be set <em>before</em> the inclusion of
+<a class="reference internal" href="#level-makefile-common">$(LEVEL)/Makefile.common</a>. These variables provide input to the LLVM make
+system that tell it what to do for the current directory.</p>
+<dl class="docutils">
+<dt><tt class="docutils literal"><span class="pre">BUILD_ARCHIVE</span></tt></dt>
+<dd>If set to any value, causes an archive (.a) library to be built.</dd>
+<dt><tt class="docutils literal"><span class="pre">BUILT_SOURCES</span></tt></dt>
+<dd>Specifies a set of source files that are generated from other source
+files. These sources will be built before any other target processing to
+ensure they are present.</dd>
+<dt><tt class="docutils literal"><span class="pre">BYTECODE_LIBRARY</span></tt></dt>
+<dd>If set to any value, causes a bitcode library (.bc) to be built.</dd>
+<dt><tt class="docutils literal"><span class="pre">CONFIG_FILES</span></tt></dt>
+<dd>Specifies a set of configuration files to be installed.</dd>
+<dt><tt class="docutils literal"><span class="pre">DEBUG_SYMBOLS</span></tt></dt>
+<dd>If set to any value, causes the build to include debugging symbols even in
+optimized objects, libraries and executables. This alters the flags
+specified to the compilers and linkers. Debugging isn’t fun in an optimized
+build, but it is possible.</dd>
+<dt><tt class="docutils literal"><span class="pre">DIRS</span></tt></dt>
+<dd>Specifies a set of directories, usually children of the current directory,
+that should also be made using the same goal. These directories will be
+built serially.</dd>
+<dt><tt class="docutils literal"><span class="pre">DISABLE_AUTO_DEPENDENCIES</span></tt></dt>
+<dd>If set to any value, causes the makefiles to <strong>not</strong> automatically generate
+dependencies when running the compiler. Use of this feature is discouraged
+and it may be removed at a later date.</dd>
+<dt><tt class="docutils literal"><span class="pre">ENABLE_OPTIMIZED</span></tt></dt>
+<dd>If set to 1, causes the build to generate optimized objects, libraries and
+executables. This alters the flags specified to the compilers and
+linkers. Generally debugging won’t be a fun experience with an optimized
+build.</dd>
+<dt><tt class="docutils literal"><span class="pre">ENABLE_PROFILING</span></tt></dt>
+<dd>If set to 1, causes the build to generate both optimized and profiled
+objects, libraries and executables. This alters the flags specified to the
+compilers and linkers to ensure that profile data can be collected from the
+tools built. Use the <tt class="docutils literal"><span class="pre">gprof</span></tt> tool to analyze the output from the profiled
+tools (<tt class="docutils literal"><span class="pre">gmon.out</span></tt>).</dd>
+<dt><tt class="docutils literal"><span class="pre">DISABLE_ASSERTIONS</span></tt></dt>
+<dd>If set to 1, causes the build to disable assertions, even if building a
+debug or profile build. This will exclude all assertion check code from the
+build. LLVM will execute faster, but with little help when things go
+wrong.</dd>
+<dt><tt class="docutils literal"><span class="pre">EXPERIMENTAL_DIRS</span></tt></dt>
+<dd>Specify a set of directories that should be built, but if they fail, it
+should not cause the build to fail. Note that this should only be used
+temporarily while code is being written.</dd>
+<dt><tt class="docutils literal"><span class="pre">EXPORTED_SYMBOL_FILE</span></tt></dt>
+<dd>Specifies the name of a single file that contains a list of the symbols to
+be exported by the linker. One symbol per line.</dd>
+<dt><tt class="docutils literal"><span class="pre">EXPORTED_SYMBOL_LIST</span></tt></dt>
+<dd>Specifies a set of symbols to be exported by the linker.</dd>
+<dt><tt class="docutils literal"><span class="pre">EXTRA_DIST</span></tt></dt>
+<dd>Specifies additional files that should be distributed with LLVM. All source
+files, all built sources, all Makefiles, and most documentation files will
+be automatically distributed. Use this variable to distribute any files that
+are not automatically distributed.</dd>
+<dt><tt class="docutils literal"><span class="pre">KEEP_SYMBOLS</span></tt></dt>
+<dd>If set to any value, specifies that when linking executables the makefiles
+should retain debug symbols in the executable. Normally, symbols are
+stripped from the executable.</dd>
+<dt><tt class="docutils literal"><span class="pre">LEVEL</span></tt> (required)</dt>
+<dd>Specify the level of nesting from the top level. This variable must be set
+in each makefile as it is used to find the top level and thus the other
+makefiles.</dd>
+<dt><tt class="docutils literal"><span class="pre">LIBRARYNAME</span></tt></dt>
+<dd>Specify the name of the library to be built. (Required For Libraries)</dd>
+<dt><tt class="docutils literal"><span class="pre">LINK_COMPONENTS</span></tt></dt>
+<dd>When specified for building a tool, the value of this variable will be
+passed to the <tt class="docutils literal"><span class="pre">llvm-config</span></tt> tool to generate a link line for the
+tool. Unlike <tt class="docutils literal"><span class="pre">USEDLIBS</span></tt> and <tt class="docutils literal"><span class="pre">LLVMLIBS</span></tt>, not all libraries need to be
+specified. The <tt class="docutils literal"><span class="pre">llvm-config</span></tt> tool will figure out the library dependencies
+and add any libraries that are needed. The <tt class="docutils literal"><span class="pre">USEDLIBS</span></tt> variable can still
+be used in conjunction with <tt class="docutils literal"><span class="pre">LINK_COMPONENTS</span></tt> so that additional
+project-specific libraries can be linked with the LLVM libraries specified
+by <tt class="docutils literal"><span class="pre">LINK_COMPONENTS</span></tt>.</dd>
+</dl>
+<dl class="docutils" id="link-libs-in-shared">
+<dt><tt class="docutils literal"><span class="pre">LINK_LIBS_IN_SHARED</span></tt></dt>
+<dd>By default, shared library linking will ignore any libraries specified with
+the <a class="reference internal" href="#llvmlibs">LLVMLIBS</a> or <a class="reference internal" href="#usedlibs">USEDLIBS</a>. This prevents shared libs from including
+things that will be in the LLVM tool the shared library will be loaded
+into. However, sometimes it is useful to link certain libraries into your
+shared library and this option enables that feature.</dd>
+</dl>
+<dl class="docutils" id="llvmlibs">
+<dt><tt class="docutils literal"><span class="pre">LLVMLIBS</span></tt></dt>
+<dd>Specifies the set of libraries from the LLVM <tt class="docutils literal"><span class="pre">$(ObjDir)</span></tt> that will be
+linked into the tool or library.</dd>
+<dt><tt class="docutils literal"><span class="pre">LOADABLE_MODULE</span></tt></dt>
+<dd>If set to any value, causes the shared library being built to also be a
+loadable module. Loadable modules can be opened with the dlopen() function
+and searched with dlsym (or the operating system’s equivalent). Note that
+setting this variable without also setting <tt class="docutils literal"><span class="pre">SHARED_LIBRARY</span></tt> will have no
+effect.</dd>
+</dl>
+<dl class="docutils" id="module-name">
+<dt><tt class="docutils literal"><span class="pre">MODULE_NAME</span></tt></dt>
+<dd>Specifies the name of a bitcode module to be created. A bitcode module can
+be specified in conjunction with other kinds of library builds or by
+itself. It constructs from the sources a single linked bitcode file.</dd>
+<dt><tt class="docutils literal"><span class="pre">NO_INSTALL</span></tt></dt>
+<dd>Specifies that the build products of the directory should not be installed
+but should be built even if the <tt class="docutils literal"><span class="pre">install</span></tt> target is given. This is handy
+for directories that build libraries or tools that are only used as part of
+the build process, such as code generators (e.g. <tt class="docutils literal"><span class="pre">tblgen</span></tt>).</dd>
+<dt><tt class="docutils literal"><span class="pre">OPTIONAL_DIRS</span></tt></dt>
+<dd>Specify a set of directories that may be built, if they exist, but its not
+an error for them not to exist.</dd>
+<dt><tt class="docutils literal"><span class="pre">PARALLEL_DIRS</span></tt></dt>
+<dd>Specify a set of directories to build recursively and in parallel if the
+<tt class="docutils literal"><span class="pre">-j</span></tt> option was used with <tt class="docutils literal"><span class="pre">make</span></tt>.</dd>
+</dl>
+<dl class="docutils" id="shared-library">
+<dt><tt class="docutils literal"><span class="pre">SHARED_LIBRARY</span></tt></dt>
+<dd>If set to any value, causes a shared library (<tt class="docutils literal"><span class="pre">.so</span></tt>) to be built in
+addition to any other kinds of libraries. Note that this option will cause
+all source files to be built twice: once with options for position
+independent code and once without. Use it only where you really need a
+shared library.</dd>
+<dt><tt class="docutils literal"><span class="pre">SOURCES</span></tt> (optional)</dt>
+<dd>Specifies the list of source files in the current directory to be
+built. Source files of any type may be specified (programs, documentation,
+config files, etc.). If not specified, the makefile system will infer the
+set of source files from the files present in the current directory.</dd>
+<dt><tt class="docutils literal"><span class="pre">SUFFIXES</span></tt></dt>
+<dd>Specifies a set of filename suffixes that occur in suffix match rules. Only
+set this if your local <tt class="docutils literal"><span class="pre">Makefile</span></tt> specifies additional suffix match
+rules.</dd>
+<dt><tt class="docutils literal"><span class="pre">TARGET</span></tt></dt>
+<dd>Specifies the name of the LLVM code generation target that the current
+directory builds. Setting this variable enables additional rules to build
+<tt class="docutils literal"><span class="pre">.inc</span></tt> files from <tt class="docutils literal"><span class="pre">.td</span></tt> files.</dd>
+</dl>
+<dl class="docutils" id="testsuite">
+<dt><tt class="docutils literal"><span class="pre">TESTSUITE</span></tt></dt>
+<dd>Specifies the directory of tests to run in <tt class="docutils literal"><span class="pre">llvm/test</span></tt>.</dd>
+<dt><tt class="docutils literal"><span class="pre">TOOLNAME</span></tt></dt>
+<dd>Specifies the name of the tool that the current directory should build.</dd>
+<dt><tt class="docutils literal"><span class="pre">TOOL_VERBOSE</span></tt></dt>
+<dd>Implies <tt class="docutils literal"><span class="pre">VERBOSE</span></tt> and also tells each tool invoked to be verbose. This is
+handy when you’re trying to see the sub-tools invoked by each tool invoked
+by the makefile. For example, this will pass <tt class="docutils literal"><span class="pre">-v</span></tt> to the GCC compilers
+which causes it to print out the command lines it uses to invoke sub-tools
+(compiler, assembler, linker).</dd>
+</dl>
+<dl class="docutils" id="usedlibs">
+<dt><tt class="docutils literal"><span class="pre">USEDLIBS</span></tt></dt>
+<dd>Specifies the list of project libraries that will be linked into the tool or
+library.</dd>
+<dt><tt class="docutils literal"><span class="pre">VERBOSE</span></tt></dt>
+<dd>Tells the Makefile system to produce detailed output of what it is doing
+instead of just summary comments. This will generate a LOT of output.</dd>
+</dl>
+</div>
+<div class="section" id="override-variables">
+<h3><a class="toc-backref" href="#id38">Override Variables</a><a class="headerlink" href="#override-variables" title="Permalink to this headline">¶</a></h3>
+<p>Override variables can be used to override the default values provided by the
+LLVM makefile system. These variables can be set in several ways:</p>
+<ul class="simple">
+<li>In the environment (e.g. setenv, export) — not recommended.</li>
+<li>On the <tt class="docutils literal"><span class="pre">make</span></tt> command line — recommended.</li>
+<li>On the <tt class="docutils literal"><span class="pre">configure</span></tt> command line.</li>
+<li>In the Makefile (only <em>after</em> the inclusion of <a class="reference internal" href="#level-makefile-common">$(LEVEL)/Makefile.common</a>).</li>
+</ul>
+<p>The override variables are given below:</p>
+<dl class="docutils">
+<dt><tt class="docutils literal"><span class="pre">AR</span></tt> (defaulted)</dt>
+<dd>Specifies the path to the <tt class="docutils literal"><span class="pre">ar</span></tt> tool.</dd>
+<dt><tt class="docutils literal"><span class="pre">PROJ_OBJ_DIR</span></tt></dt>
+<dd>The directory into which the products of build rules will be placed. This
+might be the same as <a class="reference internal" href="#proj-src-dir">PROJ_SRC_DIR</a> but typically is not.</dd>
+</dl>
+<dl class="docutils" id="proj-src-dir">
+<dt><tt class="docutils literal"><span class="pre">PROJ_SRC_DIR</span></tt></dt>
+<dd>The directory which contains the source files to be built.</dd>
+<dt><tt class="docutils literal"><span class="pre">BUILD_EXAMPLES</span></tt></dt>
+<dd>If set to 1, build examples in <tt class="docutils literal"><span class="pre">examples</span></tt> and (if building Clang)
+<tt class="docutils literal"><span class="pre">tools/clang/examples</span></tt> directories.</dd>
+<dt><tt class="docutils literal"><span class="pre">BZIP2</span></tt> (configured)</dt>
+<dd>The path to the <tt class="docutils literal"><span class="pre">bzip2</span></tt> tool.</dd>
+<dt><tt class="docutils literal"><span class="pre">CC</span></tt> (configured)</dt>
+<dd>The path to the ‘C’ compiler.</dd>
+<dt><tt class="docutils literal"><span class="pre">CFLAGS</span></tt></dt>
+<dd>Additional flags to be passed to the ‘C’ compiler.</dd>
+<dt><tt class="docutils literal"><span class="pre">CXX</span></tt></dt>
+<dd>Specifies the path to the C++ compiler.</dd>
+<dt><tt class="docutils literal"><span class="pre">CXXFLAGS</span></tt></dt>
+<dd>Additional flags to be passed to the C++ compiler.</dd>
+<dt><tt class="docutils literal"><span class="pre">DATE</span></tt> (configured)</dt>
+<dd>Specifies the path to the <tt class="docutils literal"><span class="pre">date</span></tt> program or any program that can generate
+the current date and time on its standard output.</dd>
+<dt><tt class="docutils literal"><span class="pre">DOT</span></tt> (configured)</dt>
+<dd>Specifies the path to the <tt class="docutils literal"><span class="pre">dot</span></tt> tool or <tt class="docutils literal"><span class="pre">false</span></tt> if there isn’t one.</dd>
+<dt><tt class="docutils literal"><span class="pre">ECHO</span></tt> (configured)</dt>
+<dd>Specifies the path to the <tt class="docutils literal"><span class="pre">echo</span></tt> tool for printing output.</dd>
+<dt><tt class="docutils literal"><span class="pre">EXEEXT</span></tt> (configured)</dt>
+<dd>Provides the extension to be used on executables built by the makefiles.
+The value may be empty on platforms that do not use file extensions for
+executables (e.g. Unix).</dd>
+<dt><tt class="docutils literal"><span class="pre">INSTALL</span></tt> (configured)</dt>
+<dd>Specifies the path to the <tt class="docutils literal"><span class="pre">install</span></tt> tool.</dd>
+<dt><tt class="docutils literal"><span class="pre">LDFLAGS</span></tt> (configured)</dt>
+<dd>Allows users to specify additional flags to pass to the linker.</dd>
+<dt><tt class="docutils literal"><span class="pre">LIBS</span></tt> (configured)</dt>
+<dd>The list of libraries that should be linked with each tool.</dd>
+<dt><tt class="docutils literal"><span class="pre">LIBTOOL</span></tt> (configured)</dt>
+<dd>Specifies the path to the <tt class="docutils literal"><span class="pre">libtool</span></tt> tool. This tool is renamed <tt class="docutils literal"><span class="pre">mklib</span></tt>
+by the <tt class="docutils literal"><span class="pre">configure</span></tt> script.</dd>
+<dt><tt class="docutils literal"><span class="pre">LLVMAS</span></tt> (defaulted)</dt>
+<dd>Specifies the path to the <tt class="docutils literal"><span class="pre">llvm-as</span></tt> tool.</dd>
+<dt><tt class="docutils literal"><span class="pre">LLVMCC</span></tt></dt>
+<dd>Specifies the path to the LLVM capable compiler.</dd>
+<dt><tt class="docutils literal"><span class="pre">LLVMCXX</span></tt></dt>
+<dd>Specifies the path to the LLVM C++ capable compiler.</dd>
+<dt><tt class="docutils literal"><span class="pre">LLVMGCC</span></tt> (defaulted)</dt>
+<dd>Specifies the path to the LLVM version of the GCC ‘C’ Compiler.</dd>
+<dt><tt class="docutils literal"><span class="pre">LLVMGXX</span></tt> (defaulted)</dt>
+<dd>Specifies the path to the LLVM version of the GCC C++ Compiler.</dd>
+<dt><tt class="docutils literal"><span class="pre">LLVMLD</span></tt> (defaulted)</dt>
+<dd>Specifies the path to the LLVM bitcode linker tool</dd>
+<dt><tt class="docutils literal"><span class="pre">LLVM_OBJ_ROOT</span></tt> (configured)</dt>
+<dd>Specifies the top directory into which the output of the build is placed.</dd>
+<dt><tt class="docutils literal"><span class="pre">LLVM_SRC_ROOT</span></tt> (configured)</dt>
+<dd>Specifies the top directory in which the sources are found.</dd>
+<dt><tt class="docutils literal"><span class="pre">LLVM_TARBALL_NAME</span></tt> (configured)</dt>
+<dd>Specifies the name of the distribution tarball to create. This is configured
+from the name of the project and its version number.</dd>
+<dt><tt class="docutils literal"><span class="pre">MKDIR</span></tt> (defaulted)</dt>
+<dd>Specifies the path to the <tt class="docutils literal"><span class="pre">mkdir</span></tt> tool that creates directories.</dd>
+<dt><tt class="docutils literal"><span class="pre">ONLY_TOOLS</span></tt></dt>
+<dd>If set, specifies the list of tools to build.</dd>
+<dt><tt class="docutils literal"><span class="pre">PLATFORMSTRIPOPTS</span></tt></dt>
+<dd>The options to provide to the linker to specify that a stripped (no symbols)
+executable should be built.</dd>
+<dt><tt class="docutils literal"><span class="pre">RANLIB</span></tt> (defaulted)</dt>
+<dd>Specifies the path to the <tt class="docutils literal"><span class="pre">ranlib</span></tt> tool.</dd>
+<dt><tt class="docutils literal"><span class="pre">RM</span></tt> (defaulted)</dt>
+<dd>Specifies the path to the <tt class="docutils literal"><span class="pre">rm</span></tt> tool.</dd>
+<dt><tt class="docutils literal"><span class="pre">SED</span></tt> (defaulted)</dt>
+<dd>Specifies the path to the <tt class="docutils literal"><span class="pre">sed</span></tt> tool.</dd>
+<dt><tt class="docutils literal"><span class="pre">SHLIBEXT</span></tt> (configured)</dt>
+<dd>Provides the filename extension to use for shared libraries.</dd>
+<dt><tt class="docutils literal"><span class="pre">TBLGEN</span></tt> (defaulted)</dt>
+<dd>Specifies the path to the <tt class="docutils literal"><span class="pre">tblgen</span></tt> tool.</dd>
+<dt><tt class="docutils literal"><span class="pre">TAR</span></tt> (defaulted)</dt>
+<dd>Specifies the path to the <tt class="docutils literal"><span class="pre">tar</span></tt> tool.</dd>
+<dt><tt class="docutils literal"><span class="pre">ZIP</span></tt> (defaulted)</dt>
+<dd>Specifies the path to the <tt class="docutils literal"><span class="pre">zip</span></tt> tool.</dd>
+</dl>
+</div>
+<div class="section" id="readable-variables">
+<h3><a class="toc-backref" href="#id39">Readable Variables</a><a class="headerlink" href="#readable-variables" title="Permalink to this headline">¶</a></h3>
+<p>Variables listed in the table below can be used by the user’s Makefile but
+should not be changed. Changing the value will generally cause the build to go
+wrong, so don’t do it.</p>
+<dl class="docutils">
+<dt><tt class="docutils literal"><span class="pre">bindir</span></tt></dt>
+<dd>The directory into which executables will ultimately be installed. This
+value is derived from the <tt class="docutils literal"><span class="pre">--prefix</span></tt> option given to <tt class="docutils literal"><span class="pre">configure</span></tt>.</dd>
+<dt><tt class="docutils literal"><span class="pre">BuildMode</span></tt></dt>
+<dd>The name of the type of build being performed: Debug, Release, or
+Profile.</dd>
+<dt><tt class="docutils literal"><span class="pre">bytecode_libdir</span></tt></dt>
+<dd>The directory into which bitcode libraries will ultimately be installed.
+This value is derived from the <tt class="docutils literal"><span class="pre">--prefix</span></tt> option given to <tt class="docutils literal"><span class="pre">configure</span></tt>.</dd>
+<dt><tt class="docutils literal"><span class="pre">ConfigureScriptFLAGS</span></tt></dt>
+<dd>Additional flags given to the <tt class="docutils literal"><span class="pre">configure</span></tt> script when reconfiguring.</dd>
+<dt><tt class="docutils literal"><span class="pre">DistDir</span></tt></dt>
+<dd>The <em>current</em> directory for which a distribution copy is being made.</dd>
+</dl>
+<dl class="docutils" id="echo">
+<dt><tt class="docutils literal"><span class="pre">Echo</span></tt></dt>
+<dd>The LLVM Makefile System output command. This provides the <tt class="docutils literal"><span class="pre">llvm[n]</span></tt>
+prefix and starts with <tt class="docutils literal"><span class="pre">@</span></tt> so the command itself is not printed by
+<tt class="docutils literal"><span class="pre">make</span></tt>.</dd>
+<dt><tt class="docutils literal"><span class="pre">EchoCmd</span></tt></dt>
+<dd>Same as <a class="reference internal" href="#echo">Echo</a> but without the leading <tt class="docutils literal"><span class="pre">@</span></tt>.</dd>
+<dt><tt class="docutils literal"><span class="pre">includedir</span></tt></dt>
+<dd>The directory into which include files will ultimately be installed. This
+value is derived from the <tt class="docutils literal"><span class="pre">--prefix</span></tt> option given to <tt class="docutils literal"><span class="pre">configure</span></tt>.</dd>
+<dt><tt class="docutils literal"><span class="pre">libdir</span></tt></dt>
+<dd>The directory into which native libraries will ultimately be installed.
+This value is derived from the <tt class="docutils literal"><span class="pre">--prefix</span></tt> option given to
+<tt class="docutils literal"><span class="pre">configure</span></tt>.</dd>
+<dt><tt class="docutils literal"><span class="pre">LibDir</span></tt></dt>
+<dd>The configuration specific directory into which libraries are placed before
+installation.</dd>
+<dt><tt class="docutils literal"><span class="pre">MakefileConfig</span></tt></dt>
+<dd>Full path of the <tt class="docutils literal"><span class="pre">Makefile.config</span></tt> file.</dd>
+<dt><tt class="docutils literal"><span class="pre">MakefileConfigIn</span></tt></dt>
+<dd>Full path of the <tt class="docutils literal"><span class="pre">Makefile.config.in</span></tt> file.</dd>
+<dt><tt class="docutils literal"><span class="pre">ObjDir</span></tt></dt>
+<dd>The configuration and directory specific directory where build objects
+(compilation results) are placed.</dd>
+<dt><tt class="docutils literal"><span class="pre">SubDirs</span></tt></dt>
+<dd>The complete list of sub-directories of the current directory as
+specified by other variables.</dd>
+<dt><tt class="docutils literal"><span class="pre">Sources</span></tt></dt>
+<dd>The complete list of source files.</dd>
+<dt><tt class="docutils literal"><span class="pre">sysconfdir</span></tt></dt>
+<dd>The directory into which configuration files will ultimately be
+installed. This value is derived from the <tt class="docutils literal"><span class="pre">--prefix</span></tt> option given to
+<tt class="docutils literal"><span class="pre">configure</span></tt>.</dd>
+<dt><tt class="docutils literal"><span class="pre">ToolDir</span></tt></dt>
+<dd>The configuration specific directory into which executables are placed
+before they are installed.</dd>
+<dt><tt class="docutils literal"><span class="pre">TopDistDir</span></tt></dt>
+<dd>The top most directory into which the distribution files are copied.</dd>
+<dt><tt class="docutils literal"><span class="pre">Verb</span></tt></dt>
+<dd>Use this as the first thing on your build script lines to enable or disable
+verbose mode. It expands to either an <tt class="docutils literal"><span class="pre">@</span></tt> (quiet mode) or nothing (verbose
+mode).</dd>
+</dl>
+</div>
+<div class="section" id="internal-variables">
+<h3><a class="toc-backref" href="#id40">Internal Variables</a><a class="headerlink" href="#internal-variables" title="Permalink to this headline">¶</a></h3>
+<p>Variables listed below are used by the LLVM Makefile System and considered
+internal. You should not use these variables under any circumstances.</p>
+<div class="highlight-makefile"><pre>Archive
+AR.Flags
+BaseNameSources
+BCCompile.C
+BCCompile.CXX
+BCLinkLib
+C.Flags
+Compile.C
+CompileCommonOpts
+Compile.CXX
+ConfigStatusScript
+ConfigureScript
+CPP.Flags
+CPP.Flags
+CXX.Flags
+DependFiles
+DestArchiveLib
+DestBitcodeLib
+DestModule
+DestSharedLib
+DestTool
+DistAlways
+DistCheckDir
+DistCheckTop
+DistFiles
+DistName
+DistOther
+DistSources
+DistSubDirs
+DistTarBZ2
+DistTarGZip
+DistZip
+ExtraLibs
+FakeSources
+INCFiles
+InternalTargets
+LD.Flags
+LibName.A
+LibName.BC
+LibName.LA
+LibName.O
+LibTool.Flags
+Link
+LinkModule
+LLVMLibDir
+LLVMLibsOptions
+LLVMLibsPaths
+LLVMToolDir
+LLVMUsedLibs
+LocalTargets
+Module
+ObjectsBC
+ObjectsLO
+ObjectsO
+ObjMakefiles
+ParallelTargets
+PreConditions
+ProjLibsOptions
+ProjLibsPaths
+ProjUsedLibs
+Ranlib
+RecursiveTargets
+SrcMakefiles
+Strip
+StripWarnMsg
+TableGen
+TDFiles
+ToolBuildPath
+TopLevelTargets
+UserTargets</pre>
+</div>
+</div>
+</div>
+</div>
+
+
+ </div>
+ </div>
+ </div>
+ <div class="clearer"></div>
+ </div>
+ <div class="related">
+ <h3>Navigation</h3>
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+ <ul>
+<li><a class="reference internal" href="#">LLVM’s Optional Rich Disassembly Output</a><ul>
+<li><a class="reference internal" href="#introduction">Introduction</a></li>
+<li><a class="reference internal" href="#instruction-annotations">Instruction Annotations</a><ul>
+<li><a class="reference internal" href="#contextual-markups">Contextual markups</a></li>
+<li><a class="reference internal" href="#c-api-details">C API Details</a></li>
+</ul>
+</li>
+</ul>
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+
+ <div class="section" id="llvm-s-optional-rich-disassembly-output">
+<span id="marked-up-disassembly"></span><h1>LLVM’s Optional Rich Disassembly Output<a class="headerlink" href="#llvm-s-optional-rich-disassembly-output" title="Permalink to this headline">¶</a></h1>
+<div class="contents local topic" id="contents">
+<ul class="simple">
+<li><a class="reference internal" href="#introduction" id="id2">Introduction</a></li>
+<li><a class="reference internal" href="#instruction-annotations" id="id3">Instruction Annotations</a><ul>
+<li><a class="reference internal" href="#contextual-markups" id="id4">Contextual markups</a></li>
+<li><a class="reference internal" href="#c-api-details" id="id5">C API Details</a></li>
+</ul>
+</li>
+</ul>
+</div>
+<div class="section" id="introduction">
+<h2><a class="toc-backref" href="#id2">Introduction</a><a class="headerlink" href="#introduction" title="Permalink to this headline">¶</a></h2>
+<p>LLVM’s default disassembly output is raw text. To allow consumers more ability
+to introspect the instructions’ textual representation or to reformat for a more
+user friendly display there is an optional rich disassembly output.</p>
+<p>This optional output is sufficient to reference into individual portions of the
+instruction text. This is intended for clients like disassemblers, list file
+generators, and pretty-printers, which need more than the raw instructions and
+the ability to print them.</p>
+<p>To provide this functionality the assembly text is marked up with annotations.
+The markup is simple enough in syntax to be robust even in the case of version
+mismatches between consumers and producers. That is, the syntax generally does
+not carry semantics beyond “this text has an annotation,” so consumers can
+simply ignore annotations they do not understand or do not care about.</p>
+<p>After calling <tt class="docutils literal"><span class="pre">LLVMCreateDisasm()</span></tt> to create a disassembler context the
+optional output is enable with this call:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="n">LLVMSetDisasmOptions</span><span class="p">(</span><span class="n">DC</span><span class="p">,</span> <span class="n">LLVMDisassembler_Option_UseMarkup</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>Then subsequent calls to <tt class="docutils literal"><span class="pre">LLVMDisasmInstruction()</span></tt> will return output strings
+with the marked up annotations.</p>
+</div>
+<div class="section" id="instruction-annotations">
+<h2><a class="toc-backref" href="#id3">Instruction Annotations</a><a class="headerlink" href="#instruction-annotations" title="Permalink to this headline">¶</a></h2>
+<div class="section" id="contextual-markups">
+<span id="id1"></span><h3><a class="toc-backref" href="#id4">Contextual markups</a><a class="headerlink" href="#contextual-markups" title="Permalink to this headline">¶</a></h3>
+<p>Annoated assembly display will supply contextual markup to help clients more
+efficiently implement things like pretty printers. Most markup will be target
+independent, so clients can effectively provide good display without any target
+specific knowledge.</p>
+<p>Annotated assembly goes through the normal instruction printer, but optionally
+includes contextual tags on portions of the instruction string. An annotation
+is any ‘<’ ‘>’ delimited section of text(1).</p>
+<div class="highlight-bat"><div class="highlight"><pre>annotation: <span class="s1">'<'</span> tag-name tag-modifier-list <span class="s1">':'</span> annotated-text <span class="s1">'>'</span>
+tag-name: identifier
+tag-modifier-list: comma delimited identifier list
+</pre></div>
+</div>
+<p>The tag-name is an identifier which gives the type of the annotation. For the
+first pass, this will be very simple, with memory references, registers, and
+immediates having the tag names “mem”, “reg”, and “imm”, respectively.</p>
+<p>The tag-modifier-list is typically additional target-specific context, such as
+register class.</p>
+<p>Clients should accept and ignore any tag-names or tag-modifiers they do not
+understand, allowing the annotations to grow in richness without breaking older
+clients.</p>
+<p>For example, a possible annotation of an ARM load of a stack-relative location
+might be annotated as:</p>
+<div class="highlight-nasm"><pre>ldr <reg gpr:r0>, <mem regoffset:[<reg gpr:sp>, <imm:#4>]></pre>
+</div>
+<p>1: For assembly dialects in which ‘<’ and/or ‘>’ are legal tokens, a literal token is escaped by following immediately with a repeat of the character. For example, a literal ‘<’ character is output as ‘<<’ in an annotated assembly string.</p>
+</div>
+<div class="section" id="c-api-details">
+<h3><a class="toc-backref" href="#id5">C API Details</a><a class="headerlink" href="#c-api-details" title="Permalink to this headline">¶</a></h3>
+<p>The intended consumers of this information use the C API, therefore the new C
+API function for the disassembler will be added to provide an option to produce
+disassembled instructions with annotations, <tt class="docutils literal"><span class="pre">LLVMSetDisasmOptions()</span></tt> and the
+<tt class="docutils literal"><span class="pre">LLVMDisassembler_Option_UseMarkup</span></tt> option (see above).</p>
+</div>
+</div>
+</div>
+
+
+ </div>
+ </div>
+ </div>
+ <div class="clearer"></div>
+ </div>
+ <div class="related">
+ <h3>Navigation</h3>
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==============================================================================
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+++ www-releases/trunk/3.2/docs/Packaging.html Fri Dec 21 03:14:44 2012
@@ -0,0 +1,215 @@
+
+
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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+ <script type="text/javascript" src="_static/underscore.js"></script>
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+ <a href="index.html">
+ <img src="_static/logo.png"
+ alt="LLVM Logo" width="250" height="88"/></a>
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+ <li class="right" style="margin-right: 10px">
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+ accesskey="I">index</a></li>
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+ <a href="HowToAddABuilder.html" title="How To Add Your Build Configuration To LLVM Buildbot Infrastructure"
+ accesskey="N">next</a> |</li>
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+
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+ <h3><a href="index.html">Table Of Contents</a></h3>
+ <ul>
+<li><a class="reference internal" href="#">Advice on Packaging LLVM</a><ul>
+<li><a class="reference internal" href="#overview">Overview</a></li>
+<li><a class="reference internal" href="#compile-flags">Compile Flags</a></li>
+<li><a class="reference internal" href="#c-features">C++ Features</a></li>
+<li><a class="reference internal" href="#shared-library">Shared Library</a></li>
+<li><a class="reference internal" href="#dependencies">Dependencies</a></li>
+</ul>
+</li>
+</ul>
+
+ <h4>Previous topic</h4>
+ <p class="topless"><a href="Lexicon.html"
+ title="previous chapter">The LLVM Lexicon</a></p>
+ <h4>Next topic</h4>
+ <p class="topless"><a href="HowToAddABuilder.html"
+ title="next chapter">How To Add Your Build Configuration To LLVM Buildbot Infrastructure</a></p>
+ <h3>This Page</h3>
+ <ul class="this-page-menu">
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+
+ <div class="section" id="advice-on-packaging-llvm">
+<span id="packaging"></span><h1>Advice on Packaging LLVM<a class="headerlink" href="#advice-on-packaging-llvm" title="Permalink to this headline">¶</a></h1>
+<div class="contents local topic" id="contents">
+<ul class="simple">
+<li><a class="reference internal" href="#overview" id="id1">Overview</a></li>
+<li><a class="reference internal" href="#compile-flags" id="id2">Compile Flags</a></li>
+<li><a class="reference internal" href="#c-features" id="id3">C++ Features</a></li>
+<li><a class="reference internal" href="#shared-library" id="id4">Shared Library</a></li>
+<li><a class="reference internal" href="#dependencies" id="id5">Dependencies</a></li>
+</ul>
+</div>
+<div class="section" id="overview">
+<h2><a class="toc-backref" href="#id1">Overview</a><a class="headerlink" href="#overview" title="Permalink to this headline">¶</a></h2>
+<p>LLVM sets certain default configure options to make sure our developers don’t
+break things for constrained platforms. These settings are not optimal for most
+desktop systems, and we hope that packagers (e.g., Redhat, Debian, MacPorts,
+etc.) will tweak them. This document lists settings we suggest you tweak.</p>
+<p>LLVM’s API changes with each release, so users are likely to want, for example,
+both LLVM-2.6 and LLVM-2.7 installed at the same time to support apps developed
+against each.</p>
+</div>
+<div class="section" id="compile-flags">
+<h2><a class="toc-backref" href="#id2">Compile Flags</a><a class="headerlink" href="#compile-flags" title="Permalink to this headline">¶</a></h2>
+<p>LLVM runs much more quickly when it’s optimized and assertions are removed.
+However, such a build is currently incompatible with users who build without
+defining <tt class="docutils literal"><span class="pre">NDEBUG</span></tt>, and the lack of assertions makes it hard to debug problems
+in user code. We recommend allowing users to install both optimized and debug
+versions of LLVM in parallel. The following configure flags are relevant:</p>
+<dl class="docutils">
+<dt><tt class="docutils literal"><span class="pre">--disable-assertions</span></tt></dt>
+<dd>Builds LLVM with <tt class="docutils literal"><span class="pre">NDEBUG</span></tt> defined. Changes the LLVM ABI. Also available
+by setting <tt class="docutils literal"><span class="pre">DISABLE_ASSERTIONS=0|1</span></tt> in <tt class="docutils literal"><span class="pre">make</span></tt>‘s environment. This
+defaults to enabled regardless of the optimization setting, but it slows
+things down.</dd>
+<dt><tt class="docutils literal"><span class="pre">--enable-debug-symbols</span></tt></dt>
+<dd>Builds LLVM with <tt class="docutils literal"><span class="pre">-g</span></tt>. Also available by setting <tt class="docutils literal"><span class="pre">DEBUG_SYMBOLS=0|1</span></tt> in
+<tt class="docutils literal"><span class="pre">make</span></tt>‘s environment. This defaults to disabled when optimizing, so you
+should turn it back on to let users debug their programs.</dd>
+<dt><tt class="docutils literal"><span class="pre">--enable-optimized</span></tt></dt>
+<dd>(For svn checkouts) Builds LLVM with <tt class="docutils literal"><span class="pre">-O2</span></tt> and, by default, turns off
+debug symbols. Also available by setting <tt class="docutils literal"><span class="pre">ENABLE_OPTIMIZED=0|1</span></tt> in
+<tt class="docutils literal"><span class="pre">make</span></tt>‘s environment. This defaults to enabled when not in a
+checkout.</dd>
+</dl>
+</div>
+<div class="section" id="c-features">
+<h2><a class="toc-backref" href="#id3">C++ Features</a><a class="headerlink" href="#c-features" title="Permalink to this headline">¶</a></h2>
+<dl class="docutils">
+<dt>RTTI</dt>
+<dd>LLVM disables RTTI by default. Add <tt class="docutils literal"><span class="pre">REQUIRES_RTTI=1</span></tt> to your environment
+while running <tt class="docutils literal"><span class="pre">make</span></tt> to re-enable it. This will allow users to build with
+RTTI enabled and still inherit from LLVM classes.</dd>
+</dl>
+</div>
+<div class="section" id="shared-library">
+<h2><a class="toc-backref" href="#id4">Shared Library</a><a class="headerlink" href="#shared-library" title="Permalink to this headline">¶</a></h2>
+<p>Configure with <tt class="docutils literal"><span class="pre">--enable-shared</span></tt> to build
+<tt class="docutils literal"><span class="pre">libLLVM-<major>.<minor>.(so|dylib)</span></tt> and link the tools against it. This
+saves lots of binary size at the cost of some startup time.</p>
+</div>
+<div class="section" id="dependencies">
+<h2><a class="toc-backref" href="#id5">Dependencies</a><a class="headerlink" href="#dependencies" title="Permalink to this headline">¶</a></h2>
+<dl class="docutils">
+<dt><tt class="docutils literal"><span class="pre">--enable-libffi</span></tt></dt>
+<dd>Depend on <a class="reference external" href="http://sources.redhat.com/libffi/">libffi</a> to allow the LLVM
+interpreter to call external functions.</dd>
+</dl>
+<p><tt class="docutils literal"><span class="pre">--with-oprofile</span></tt></p>
+<blockquote>
+<div>Depend on <a class="reference external" href="http://oprofile.sourceforge.net/doc/devel/index.html">libopagent</a> (>=version 0.9.4)
+to let the LLVM JIT tell oprofile about function addresses and line
+numbers.</div></blockquote>
+</div>
+</div>
+
+
+ </div>
+ </div>
+ </div>
+ <div class="clearer"></div>
+ </div>
+ <div class="related">
+ <h3>Navigation</h3>
+ <ul>
+ <li class="right" style="margin-right: 10px">
+ <a href="genindex.html" title="General Index"
+ >index</a></li>
+ <li class="right" >
+ <a href="HowToAddABuilder.html" title="How To Add Your Build Configuration To LLVM Buildbot Infrastructure"
+ >next</a> |</li>
+ <li class="right" >
+ <a href="Lexicon.html" title="The LLVM Lexicon"
+ >previous</a> |</li>
+ <li><a href="http://llvm.org/">LLVM Home</a> | </li>
+ <li><a href="index.html">Documentation</a>»</li>
+
+ <li><a href="userguides.html" >User Guides</a> »</li>
+ </ul>
+ </div>
+ <div class="footer">
+ © Copyright 2012, LLVM Project.
+ Last updated on 2012-12-21.
+ Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
+ </div>
+ </body>
+</html>
\ No newline at end of file
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==============================================================================
--- www-releases/trunk/3.2/docs/Passes.html (added)
+++ www-releases/trunk/3.2/docs/Passes.html Fri Dec 21 03:14:44 2012
@@ -0,0 +1,2049 @@
+<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+<html>
+<head>
+ <title>LLVM's Analysis and Transform Passes</title>
+ <link rel="stylesheet" href="_static/llvm.css" type="text/css">
+ <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
+</head>
+<body>
+
+<!--
+
+If Passes.html is up to date, the following "one-liner" should print
+an empty diff.
+
+egrep -e '^<tr><td><a href="#.*">-.*</a></td><td>.*</td></tr>$' \
+ -e '^ <a name=".*">.*</a>$' < Passes.html >html; \
+perl >help <<'EOT' && diff -u help html; rm -f help html
+open HTML, "<Passes.html" or die "open: Passes.html: $!\n";
+while (<HTML>) {
+ m:^<tr><td><a href="#(.*)">-.*</a></td><td>.*</td></tr>$: or next;
+ $order{$1} = sprintf("%03d", 1 + int %order);
+}
+open HELP, "../Release/bin/opt -help|" or die "open: opt -help: $!\n";
+while (<HELP>) {
+ m:^ -([^ ]+) +- (.*)$: or next;
+ my $o = $order{$1};
+ $o = "000" unless defined $o;
+ push @x, "$o<tr><td><a href=\"#$1\">-$1</a></td><td>$2</td></tr>\n";
+ push @y, "$o <a name=\"$1\">-$1: $2</a>\n";
+}
+ at x = map { s/^\d\d\d//; $_ } sort @x;
+ at y = map { s/^\d\d\d//; $_ } sort @y;
+print @x, @y;
+EOT
+
+This (real) one-liner can also be helpful when converting comments to HTML:
+
+perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print " <p>\n" if !$on && $_ =~ /\S/; print " </p>\n" if $on && $_ =~ /^\s*$/; print " $_\n"; $on = ($_ =~ /\S/); } print " </p>\n" if $on'
+
+ -->
+
+<h1>LLVM's Analysis and Transform Passes</h1>
+
+<ol>
+ <li><a href="#intro">Introduction</a></li>
+ <li><a href="#analyses">Analysis Passes</a>
+ <li><a href="#transforms">Transform Passes</a></li>
+ <li><a href="#utilities">Utility Passes</a></li>
+</ol>
+
+<div class="doc_author">
+ <p>Written by <a href="mailto:rspencer at x10sys.com">Reid Spencer</a>
+ and Gordon Henriksen</p>
+</div>
+
+<!-- ======================================================================= -->
+<h2><a name="intro">Introduction</a></h2>
+<div>
+ <p>This document serves as a high level summary of the optimization features
+ that LLVM provides. Optimizations are implemented as Passes that traverse some
+ portion of a program to either collect information or transform the program.
+ The table below divides the passes that LLVM provides into three categories.
+ Analysis passes compute information that other passes can use or for debugging
+ or program visualization purposes. Transform passes can use (or invalidate)
+ the analysis passes. Transform passes all mutate the program in some way.
+ Utility passes provides some utility but don't otherwise fit categorization.
+ For example passes to extract functions to bitcode or write a module to
+ bitcode are neither analysis nor transform passes.
+ <p>The table below provides a quick summary of each pass and links to the more
+ complete pass description later in the document.</p>
+
+<table>
+<tr><th colspan="2"><b>ANALYSIS PASSES</b></th></tr>
+<tr><th>Option</th><th>Name</th></tr>
+<tr><td><a href="#aa-eval">-aa-eval</a></td><td>Exhaustive Alias Analysis Precision Evaluator</td></tr>
+<tr><td><a href="#basicaa">-basicaa</a></td><td>Basic Alias Analysis (stateless AA impl)</td></tr>
+<tr><td><a href="#basiccg">-basiccg</a></td><td>Basic CallGraph Construction</td></tr>
+<tr><td><a href="#count-aa">-count-aa</a></td><td>Count Alias Analysis Query Responses</td></tr>
+<tr><td><a href="#da">-da</a></td><td>Dependence Analysis</td></tr>
+<tr><td><a href="#debug-aa">-debug-aa</a></td><td>AA use debugger</td></tr>
+<tr><td><a href="#domfrontier">-domfrontier</a></td><td>Dominance Frontier Construction</td></tr>
+<tr><td><a href="#domtree">-domtree</a></td><td>Dominator Tree Construction</td></tr>
+<tr><td><a href="#dot-callgraph">-dot-callgraph</a></td><td>Print Call Graph to 'dot' file</td></tr>
+<tr><td><a href="#dot-cfg">-dot-cfg</a></td><td>Print CFG of function to 'dot' file</td></tr>
+<tr><td><a href="#dot-cfg-only">-dot-cfg-only</a></td><td>Print CFG of function to 'dot' file (with no function bodies)</td></tr>
+<tr><td><a href="#dot-dom">-dot-dom</a></td><td>Print dominance tree of function to 'dot' file</td></tr>
+<tr><td><a href="#dot-dom-only">-dot-dom-only</a></td><td>Print dominance tree of function to 'dot' file (with no function bodies)</td></tr>
+<tr><td><a href="#dot-postdom">-dot-postdom</a></td><td>Print postdominance tree of function to 'dot' file</td></tr>
+<tr><td><a href="#dot-postdom-only">-dot-postdom-only</a></td><td>Print postdominance tree of function to 'dot' file (with no function bodies)</td></tr>
+<tr><td><a href="#globalsmodref-aa">-globalsmodref-aa</a></td><td>Simple mod/ref analysis for globals</td></tr>
+<tr><td><a href="#instcount">-instcount</a></td><td>Counts the various types of Instructions</td></tr>
+<tr><td><a href="#intervals">-intervals</a></td><td>Interval Partition Construction</td></tr>
+<tr><td><a href="#iv-users">-iv-users</a></td><td>Induction Variable Users</td></tr>
+<tr><td><a href="#lazy-value-info">-lazy-value-info</a></td><td>Lazy Value Information Analysis</td></tr>
+<tr><td><a href="#libcall-aa">-libcall-aa</a></td><td>LibCall Alias Analysis</td></tr>
+<tr><td><a href="#lint">-lint</a></td><td>Statically lint-checks LLVM IR</td></tr>
+<tr><td><a href="#loops">-loops</a></td><td>Natural Loop Information</td></tr>
+<tr><td><a href="#memdep">-memdep</a></td><td>Memory Dependence Analysis</td></tr>
+<tr><td><a href="#module-debuginfo">-module-debuginfo</a></td><td>Decodes module-level debug info</td></tr>
+<tr><td><a href="#no-aa">-no-aa</a></td><td>No Alias Analysis (always returns 'may' alias)</td></tr>
+<tr><td><a href="#no-profile">-no-profile</a></td><td>No Profile Information</td></tr>
+<tr><td><a href="#postdomtree">-postdomtree</a></td><td>Post-Dominator Tree Construction</td></tr>
+<tr><td><a href="#print-alias-sets">-print-alias-sets</a></td><td>Alias Set Printer</td></tr>
+<tr><td><a href="#print-callgraph">-print-callgraph</a></td><td>Print a call graph</td></tr>
+<tr><td><a href="#print-callgraph-sccs">-print-callgraph-sccs</a></td><td>Print SCCs of the Call Graph</td></tr>
+<tr><td><a href="#print-cfg-sccs">-print-cfg-sccs</a></td><td>Print SCCs of each function CFG</td></tr>
+<tr><td><a href="#print-dbginfo">-print-dbginfo</a></td><td>Print debug info in human readable form</td></tr>
+<tr><td><a href="#print-dom-info">-print-dom-info</a></td><td>Dominator Info Printer</td></tr>
+<tr><td><a href="#print-externalfnconstants">-print-externalfnconstants</a></td><td>Print external fn callsites passed constants</td></tr>
+<tr><td><a href="#print-function">-print-function</a></td><td>Print function to stderr</td></tr>
+<tr><td><a href="#print-module">-print-module</a></td><td>Print module to stderr</td></tr>
+<tr><td><a href="#print-used-types">-print-used-types</a></td><td>Find Used Types</td></tr>
+<tr><td><a href="#profile-estimator">-profile-estimator</a></td><td>Estimate profiling information</td></tr>
+<tr><td><a href="#profile-loader">-profile-loader</a></td><td>Load profile information from llvmprof.out</td></tr>
+<tr><td><a href="#profile-verifier">-profile-verifier</a></td><td>Verify profiling information</td></tr>
+<tr><td><a href="#regions">-regions</a></td><td>Detect single entry single exit regions</td></tr>
+<tr><td><a href="#scalar-evolution">-scalar-evolution</a></td><td>Scalar Evolution Analysis</td></tr>
+<tr><td><a href="#scev-aa">-scev-aa</a></td><td>ScalarEvolution-based Alias Analysis</td></tr>
+<tr><td><a href="#targetdata">-targetdata</a></td><td>Target Data Layout</td></tr>
+
+
+<tr><th colspan="2"><b>TRANSFORM PASSES</b></th></tr>
+<tr><th>Option</th><th>Name</th></tr>
+<tr><td><a href="#adce">-adce</a></td><td>Aggressive Dead Code Elimination</td></tr>
+<tr><td><a href="#always-inline">-always-inline</a></td><td>Inliner for always_inline functions</td></tr>
+<tr><td><a href="#argpromotion">-argpromotion</a></td><td>Promote 'by reference' arguments to scalars</td></tr>
+<tr><td><a href="#bb-vectorize">-bb-vectorize</a></td><td>Combine instructions to form vector instructions within basic blocks</td></tr>
+<tr><td><a href="#block-placement">-block-placement</a></td><td>Profile Guided Basic Block Placement</td></tr>
+<tr><td><a href="#break-crit-edges">-break-crit-edges</a></td><td>Break critical edges in CFG</td></tr>
+<tr><td><a href="#codegenprepare">-codegenprepare</a></td><td>Optimize for code generation</td></tr>
+<tr><td><a href="#constmerge">-constmerge</a></td><td>Merge Duplicate Global Constants</td></tr>
+<tr><td><a href="#constprop">-constprop</a></td><td>Simple constant propagation</td></tr>
+<tr><td><a href="#dce">-dce</a></td><td>Dead Code Elimination</td></tr>
+<tr><td><a href="#deadargelim">-deadargelim</a></td><td>Dead Argument Elimination</td></tr>
+<tr><td><a href="#deadtypeelim">-deadtypeelim</a></td><td>Dead Type Elimination</td></tr>
+<tr><td><a href="#die">-die</a></td><td>Dead Instruction Elimination</td></tr>
+<tr><td><a href="#dse">-dse</a></td><td>Dead Store Elimination</td></tr>
+<tr><td><a href="#functionattrs">-functionattrs</a></td><td>Deduce function attributes</td></tr>
+<tr><td><a href="#globaldce">-globaldce</a></td><td>Dead Global Elimination</td></tr>
+<tr><td><a href="#globalopt">-globalopt</a></td><td>Global Variable Optimizer</td></tr>
+<tr><td><a href="#gvn">-gvn</a></td><td>Global Value Numbering</td></tr>
+<tr><td><a href="#indvars">-indvars</a></td><td>Canonicalize Induction Variables</td></tr>
+<tr><td><a href="#inline">-inline</a></td><td>Function Integration/Inlining</td></tr>
+<tr><td><a href="#insert-edge-profiling">-insert-edge-profiling</a></td><td>Insert instrumentation for edge profiling</td></tr>
+<tr><td><a href="#insert-optimal-edge-profiling">-insert-optimal-edge-profiling</a></td><td>Insert optimal instrumentation for edge profiling</td></tr>
+<tr><td><a href="#instcombine">-instcombine</a></td><td>Combine redundant instructions</td></tr>
+<tr><td><a href="#internalize">-internalize</a></td><td>Internalize Global Symbols</td></tr>
+<tr><td><a href="#ipconstprop">-ipconstprop</a></td><td>Interprocedural constant propagation</td></tr>
+<tr><td><a href="#ipsccp">-ipsccp</a></td><td>Interprocedural Sparse Conditional Constant Propagation</td></tr>
+<tr><td><a href="#jump-threading">-jump-threading</a></td><td>Jump Threading</td></tr>
+<tr><td><a href="#lcssa">-lcssa</a></td><td>Loop-Closed SSA Form Pass</td></tr>
+<tr><td><a href="#licm">-licm</a></td><td>Loop Invariant Code Motion</td></tr>
+<tr><td><a href="#loop-deletion">-loop-deletion</a></td><td>Delete dead loops</td></tr>
+<tr><td><a href="#loop-extract">-loop-extract</a></td><td>Extract loops into new functions</td></tr>
+<tr><td><a href="#loop-extract-single">-loop-extract-single</a></td><td>Extract at most one loop into a new function</td></tr>
+<tr><td><a href="#loop-reduce">-loop-reduce</a></td><td>Loop Strength Reduction</td></tr>
+<tr><td><a href="#loop-rotate">-loop-rotate</a></td><td>Rotate Loops</td></tr>
+<tr><td><a href="#loop-simplify">-loop-simplify</a></td><td>Canonicalize natural loops</td></tr>
+<tr><td><a href="#loop-unroll">-loop-unroll</a></td><td>Unroll loops</td></tr>
+<tr><td><a href="#loop-unswitch">-loop-unswitch</a></td><td>Unswitch loops</td></tr>
+<tr><td><a href="#loweratomic">-loweratomic</a></td><td>Lower atomic intrinsics to non-atomic form</td></tr>
+<tr><td><a href="#lowerinvoke">-lowerinvoke</a></td><td>Lower invoke and unwind, for unwindless code generators</td></tr>
+<tr><td><a href="#lowerswitch">-lowerswitch</a></td><td>Lower SwitchInst's to branches</td></tr>
+<tr><td><a href="#mem2reg">-mem2reg</a></td><td>Promote Memory to Register</td></tr>
+<tr><td><a href="#memcpyopt">-memcpyopt</a></td><td>MemCpy Optimization</td></tr>
+<tr><td><a href="#mergefunc">-mergefunc</a></td><td>Merge Functions</td></tr>
+<tr><td><a href="#mergereturn">-mergereturn</a></td><td>Unify function exit nodes</td></tr>
+<tr><td><a href="#partial-inliner">-partial-inliner</a></td><td>Partial Inliner</td></tr>
+<tr><td><a href="#prune-eh">-prune-eh</a></td><td>Remove unused exception handling info</td></tr>
+<tr><td><a href="#reassociate">-reassociate</a></td><td>Reassociate expressions</td></tr>
+<tr><td><a href="#reg2mem">-reg2mem</a></td><td>Demote all values to stack slots</td></tr>
+<tr><td><a href="#scalarrepl">-scalarrepl</a></td><td>Scalar Replacement of Aggregates (DT)</td></tr>
+<tr><td><a href="#sccp">-sccp</a></td><td>Sparse Conditional Constant Propagation</td></tr>
+<tr><td><a href="#simplify-libcalls">-simplify-libcalls</a></td><td>Simplify well-known library calls</td></tr>
+<tr><td><a href="#simplifycfg">-simplifycfg</a></td><td>Simplify the CFG</td></tr>
+<tr><td><a href="#sink">-sink</a></td><td>Code sinking</td></tr>
+<tr><td><a href="#sretpromotion">-sretpromotion</a></td><td>Promote sret arguments to multiple ret values</td></tr>
+<tr><td><a href="#strip">-strip</a></td><td>Strip all symbols from a module</td></tr>
+<tr><td><a href="#strip-dead-debug-info">-strip-dead-debug-info</a></td><td>Strip debug info for unused symbols</td></tr>
+<tr><td><a href="#strip-dead-prototypes">-strip-dead-prototypes</a></td><td>Strip Unused Function Prototypes</td></tr>
+<tr><td><a href="#strip-debug-declare">-strip-debug-declare</a></td><td>Strip all llvm.dbg.declare intrinsics</td></tr>
+<tr><td><a href="#strip-nondebug">-strip-nondebug</a></td><td>Strip all symbols, except dbg symbols, from a module</td></tr>
+<tr><td><a href="#tailcallelim">-tailcallelim</a></td><td>Tail Call Elimination</td></tr>
+
+
+<tr><th colspan="2"><b>UTILITY PASSES</b></th></tr>
+<tr><th>Option</th><th>Name</th></tr>
+<tr><td><a href="#deadarghaX0r">-deadarghaX0r</a></td><td>Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)</td></tr>
+<tr><td><a href="#extract-blocks">-extract-blocks</a></td><td>Extract Basic Blocks From Module (for bugpoint use)</td></tr>
+<tr><td><a href="#instnamer">-instnamer</a></td><td>Assign names to anonymous instructions</td></tr>
+<tr><td><a href="#preverify">-preverify</a></td><td>Preliminary module verification</td></tr>
+<tr><td><a href="#verify">-verify</a></td><td>Module Verifier</td></tr>
+<tr><td><a href="#view-cfg">-view-cfg</a></td><td>View CFG of function</td></tr>
+<tr><td><a href="#view-cfg-only">-view-cfg-only</a></td><td>View CFG of function (with no function bodies)</td></tr>
+<tr><td><a href="#view-dom">-view-dom</a></td><td>View dominance tree of function</td></tr>
+<tr><td><a href="#view-dom-only">-view-dom-only</a></td><td>View dominance tree of function (with no function bodies)</td></tr>
+<tr><td><a href="#view-postdom">-view-postdom</a></td><td>View postdominance tree of function</td></tr>
+<tr><td><a href="#view-postdom-only">-view-postdom-only</a></td><td>View postdominance tree of function (with no function bodies)</td></tr>
+</table>
+
+</div>
+
+<!-- ======================================================================= -->
+<h2><a name="analyses">Analysis Passes</a></h2>
+<div>
+ <p>This section describes the LLVM Analysis Passes.</p>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="aa-eval">-aa-eval: Exhaustive Alias Analysis Precision Evaluator</a>
+</h3>
+<div>
+ <p>This is a simple N^2 alias analysis accuracy evaluator.
+ Basically, for each function in the program, it simply queries to see how the
+ alias analysis implementation answers alias queries between each pair of
+ pointers in the function.</p>
+
+ <p>This is inspired and adapted from code by: Naveen Neelakantam, Francesco
+ Spadini, and Wojciech Stryjewski.</p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="basicaa">-basicaa: Basic Alias Analysis (stateless AA impl)</a>
+</h3>
+<div>
+ <p>A basic alias analysis pass that implements identities (two different
+ globals cannot alias, etc), but does no stateful analysis.</p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="basiccg">-basiccg: Basic CallGraph Construction</a>
+</h3>
+<div>
+ <p>Yet to be written.</p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="count-aa">-count-aa: Count Alias Analysis Query Responses</a>
+</h3>
+<div>
+ <p>
+ A pass which can be used to count how many alias queries
+ are being made and how the alias analysis implementation being used responds.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="da">-da: Dependence Analysis</a>
+</h3>
+<div>
+ <p>Dependence analysis framework, which is used to detect dependences in
+ memory accesses.</p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="debug-aa">-debug-aa: AA use debugger</a>
+</h3>
+<div>
+ <p>
+ This simple pass checks alias analysis users to ensure that if they
+ create a new value, they do not query AA without informing it of the value.
+ It acts as a shim over any other AA pass you want.
+ </p>
+
+ <p>
+ Yes keeping track of every value in the program is expensive, but this is
+ a debugging pass.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="domfrontier">-domfrontier: Dominance Frontier Construction</a>
+</h3>
+<div>
+ <p>
+ This pass is a simple dominator construction algorithm for finding forward
+ dominator frontiers.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="domtree">-domtree: Dominator Tree Construction</a>
+</h3>
+<div>
+ <p>
+ This pass is a simple dominator construction algorithm for finding forward
+ dominators.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="dot-callgraph">-dot-callgraph: Print Call Graph to 'dot' file</a>
+</h3>
+<div>
+ <p>
+ This pass, only available in <code>opt</code>, prints the call graph into a
+ <code>.dot</code> graph. This graph can then be processed with the "dot" tool
+ to convert it to postscript or some other suitable format.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="dot-cfg">-dot-cfg: Print CFG of function to 'dot' file</a>
+</h3>
+<div>
+ <p>
+ This pass, only available in <code>opt</code>, prints the control flow graph
+ into a <code>.dot</code> graph. This graph can then be processed with the
+ "dot" tool to convert it to postscript or some other suitable format.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="dot-cfg-only">-dot-cfg-only: Print CFG of function to 'dot' file (with no function bodies)</a>
+</h3>
+<div>
+ <p>
+ This pass, only available in <code>opt</code>, prints the control flow graph
+ into a <code>.dot</code> graph, omitting the function bodies. This graph can
+ then be processed with the "dot" tool to convert it to postscript or some
+ other suitable format.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="dot-dom">-dot-dom: Print dominance tree of function to 'dot' file</a>
+</h3>
+<div>
+ <p>
+ This pass, only available in <code>opt</code>, prints the dominator tree
+ into a <code>.dot</code> graph. This graph can then be processed with the
+ "dot" tool to convert it to postscript or some other suitable format.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="dot-dom-only">-dot-dom-only: Print dominance tree of function to 'dot' file (with no function bodies)</a>
+</h3>
+<div>
+ <p>
+ This pass, only available in <code>opt</code>, prints the dominator tree
+ into a <code>.dot</code> graph, omitting the function bodies. This graph can
+ then be processed with the "dot" tool to convert it to postscript or some
+ other suitable format.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="dot-postdom">-dot-postdom: Print postdominance tree of function to 'dot' file</a>
+</h3>
+<div>
+ <p>
+ This pass, only available in <code>opt</code>, prints the post dominator tree
+ into a <code>.dot</code> graph. This graph can then be processed with the
+ "dot" tool to convert it to postscript or some other suitable format.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="dot-postdom-only">-dot-postdom-only: Print postdominance tree of function to 'dot' file (with no function bodies)</a>
+</h3>
+<div>
+ <p>
+ This pass, only available in <code>opt</code>, prints the post dominator tree
+ into a <code>.dot</code> graph, omitting the function bodies. This graph can
+ then be processed with the "dot" tool to convert it to postscript or some
+ other suitable format.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="globalsmodref-aa">-globalsmodref-aa: Simple mod/ref analysis for globals</a>
+</h3>
+<div>
+ <p>
+ This simple pass provides alias and mod/ref information for global values
+ that do not have their address taken, and keeps track of whether functions
+ read or write memory (are "pure"). For this simple (but very common) case,
+ we can provide pretty accurate and useful information.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="instcount">-instcount: Counts the various types of Instructions</a>
+</h3>
+<div>
+ <p>
+ This pass collects the count of all instructions and reports them
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="intervals">-intervals: Interval Partition Construction</a>
+</h3>
+<div>
+ <p>
+ This analysis calculates and represents the interval partition of a function,
+ or a preexisting interval partition.
+ </p>
+
+ <p>
+ In this way, the interval partition may be used to reduce a flow graph down
+ to its degenerate single node interval partition (unless it is irreducible).
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="iv-users">-iv-users: Induction Variable Users</a>
+</h3>
+<div>
+ <p>Bookkeeping for "interesting" users of expressions computed from
+ induction variables.</p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="lazy-value-info">-lazy-value-info: Lazy Value Information Analysis</a>
+</h3>
+<div>
+ <p>Interface for lazy computation of value constraint information.</p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="libcall-aa">-libcall-aa: LibCall Alias Analysis</a>
+</h3>
+<div>
+ <p>LibCall Alias Analysis.</p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="lint">-lint: Statically lint-checks LLVM IR</a>
+</h3>
+<div>
+ <p>This pass statically checks for common and easily-identified constructs
+ which produce undefined or likely unintended behavior in LLVM IR.</p>
+
+ <p>It is not a guarantee of correctness, in two ways. First, it isn't
+ comprehensive. There are checks which could be done statically which are
+ not yet implemented. Some of these are indicated by TODO comments, but
+ those aren't comprehensive either. Second, many conditions cannot be
+ checked statically. This pass does no dynamic instrumentation, so it
+ can't check for all possible problems.</p>
+
+ <p>Another limitation is that it assumes all code will be executed. A store
+ through a null pointer in a basic block which is never reached is harmless,
+ but this pass will warn about it anyway.</p>
+
+ <p>Optimization passes may make conditions that this pass checks for more or
+ less obvious. If an optimization pass appears to be introducing a warning,
+ it may be that the optimization pass is merely exposing an existing
+ condition in the code.</p>
+
+ <p>This code may be run before instcombine. In many cases, instcombine checks
+ for the same kinds of things and turns instructions with undefined behavior
+ into unreachable (or equivalent). Because of this, this pass makes some
+ effort to look through bitcasts and so on.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="loops">-loops: Natural Loop Information</a>
+</h3>
+<div>
+ <p>
+ This analysis is used to identify natural loops and determine the loop depth
+ of various nodes of the CFG. Note that the loops identified may actually be
+ several natural loops that share the same header node... not just a single
+ natural loop.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="memdep">-memdep: Memory Dependence Analysis</a>
+</h3>
+<div>
+ <p>
+ An analysis that determines, for a given memory operation, what preceding
+ memory operations it depends on. It builds on alias analysis information, and
+ tries to provide a lazy, caching interface to a common kind of alias
+ information query.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="module-debuginfo">-module-debuginfo: Decodes module-level debug info</a>
+</h3>
+<div>
+ <p>This pass decodes the debug info metadata in a module and prints in a
+ (sufficiently-prepared-) human-readable form.
+
+ For example, run this pass from opt along with the -analyze option, and
+ it'll print to standard output.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="no-aa">-no-aa: No Alias Analysis (always returns 'may' alias)</a>
+</h3>
+<div>
+ <p>
+ This is the default implementation of the Alias Analysis interface. It always
+ returns "I don't know" for alias queries. NoAA is unlike other alias analysis
+ implementations, in that it does not chain to a previous analysis. As such it
+ doesn't follow many of the rules that other alias analyses must.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="no-profile">-no-profile: No Profile Information</a>
+</h3>
+<div>
+ <p>
+ The default "no profile" implementation of the abstract
+ <code>ProfileInfo</code> interface.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="postdomfrontier">-postdomfrontier: Post-Dominance Frontier Construction</a>
+</h3>
+<div>
+ <p>
+ This pass is a simple post-dominator construction algorithm for finding
+ post-dominator frontiers.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="postdomtree">-postdomtree: Post-Dominator Tree Construction</a>
+</h3>
+<div>
+ <p>
+ This pass is a simple post-dominator construction algorithm for finding
+ post-dominators.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="print-alias-sets">-print-alias-sets: Alias Set Printer</a>
+</h3>
+<div>
+ <p>Yet to be written.</p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="print-callgraph">-print-callgraph: Print a call graph</a>
+</h3>
+<div>
+ <p>
+ This pass, only available in <code>opt</code>, prints the call graph to
+ standard error in a human-readable form.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="print-callgraph-sccs">-print-callgraph-sccs: Print SCCs of the Call Graph</a>
+</h3>
+<div>
+ <p>
+ This pass, only available in <code>opt</code>, prints the SCCs of the call
+ graph to standard error in a human-readable form.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="print-cfg-sccs">-print-cfg-sccs: Print SCCs of each function CFG</a>
+</h3>
+<div>
+ <p>
+ This pass, only available in <code>opt</code>, prints the SCCs of each
+ function CFG to standard error in a human-readable form.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="print-dbginfo">-print-dbginfo: Print debug info in human readable form</a>
+</h3>
+<div>
+ <p>Pass that prints instructions, and associated debug info:</p>
+ <ul>
+
+ <li>source/line/col information</li>
+ <li>original variable name</li>
+ <li>original type name</li>
+ </ul>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="print-dom-info">-print-dom-info: Dominator Info Printer</a>
+</h3>
+<div>
+ <p>Dominator Info Printer.</p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="print-externalfnconstants">-print-externalfnconstants: Print external fn callsites passed constants</a>
+</h3>
+<div>
+ <p>
+ This pass, only available in <code>opt</code>, prints out call sites to
+ external functions that are called with constant arguments. This can be
+ useful when looking for standard library functions we should constant fold
+ or handle in alias analyses.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="print-function">-print-function: Print function to stderr</a>
+</h3>
+<div>
+ <p>
+ The <code>PrintFunctionPass</code> class is designed to be pipelined with
+ other <code>FunctionPass</code>es, and prints out the functions of the module
+ as they are processed.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="print-module">-print-module: Print module to stderr</a>
+</h3>
+<div>
+ <p>
+ This pass simply prints out the entire module when it is executed.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="print-used-types">-print-used-types: Find Used Types</a>
+</h3>
+<div>
+ <p>
+ This pass is used to seek out all of the types in use by the program. Note
+ that this analysis explicitly does not include types only used by the symbol
+ table.
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="profile-estimator">-profile-estimator: Estimate profiling information</a>
+</h3>
+<div>
+ <p>Profiling information that estimates the profiling information
+ in a very crude and unimaginative way.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="profile-loader">-profile-loader: Load profile information from llvmprof.out</a>
+</h3>
+<div>
+ <p>
+ A concrete implementation of profiling information that loads the information
+ from a profile dump file.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="profile-verifier">-profile-verifier: Verify profiling information</a>
+</h3>
+<div>
+ <p>Pass that checks profiling information for plausibility.</p>
+</div>
+<h3>
+ <a name="regions">-regions: Detect single entry single exit regions</a>
+</h3>
+<div>
+ <p>
+ The <code>RegionInfo</code> pass detects single entry single exit regions in a
+ function, where a region is defined as any subgraph that is connected to the
+ remaining graph at only two spots. Furthermore, an hierarchical region tree is
+ built.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="scalar-evolution">-scalar-evolution: Scalar Evolution Analysis</a>
+</h3>
+<div>
+ <p>
+ The <code>ScalarEvolution</code> analysis can be used to analyze and
+ catagorize scalar expressions in loops. It specializes in recognizing general
+ induction variables, representing them with the abstract and opaque
+ <code>SCEV</code> class. Given this analysis, trip counts of loops and other
+ important properties can be obtained.
+ </p>
+
+ <p>
+ This analysis is primarily useful for induction variable substitution and
+ strength reduction.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="scev-aa">-scev-aa: ScalarEvolution-based Alias Analysis</a>
+</h3>
+<div>
+ <p>Simple alias analysis implemented in terms of ScalarEvolution queries.
+
+ This differs from traditional loop dependence analysis in that it tests
+ for dependencies within a single iteration of a loop, rather than
+ dependencies between different iterations.
+
+ ScalarEvolution has a more complete understanding of pointer arithmetic
+ than BasicAliasAnalysis' collection of ad-hoc analyses.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="targetdata">-targetdata: Target Data Layout</a>
+</h3>
+<div>
+ <p>Provides other passes access to information on how the size and alignment
+ required by the target ABI for various data types.</p>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h2><a name="transforms">Transform Passes</a></h2>
+<div>
+ <p>This section describes the LLVM Transform Passes.</p>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="adce">-adce: Aggressive Dead Code Elimination</a>
+</h3>
+<div>
+ <p>ADCE aggressively tries to eliminate code. This pass is similar to
+ <a href="#dce">DCE</a> but it assumes that values are dead until proven
+ otherwise. This is similar to <a href="#sccp">SCCP</a>, except applied to
+ the liveness of values.</p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="always-inline">-always-inline: Inliner for always_inline functions</a>
+</h3>
+<div>
+ <p>A custom inliner that handles only functions that are marked as
+ "always inline".</p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="argpromotion">-argpromotion: Promote 'by reference' arguments to scalars</a>
+</h3>
+<div>
+ <p>
+ This pass promotes "by reference" arguments to be "by value" arguments. In
+ practice, this means looking for internal functions that have pointer
+ arguments. If it can prove, through the use of alias analysis, that an
+ argument is *only* loaded, then it can pass the value into the function
+ instead of the address of the value. This can cause recursive simplification
+ of code and lead to the elimination of allocas (especially in C++ template
+ code like the STL).
+ </p>
+
+ <p>
+ This pass also handles aggregate arguments that are passed into a function,
+ scalarizing them if the elements of the aggregate are only loaded. Note that
+ it refuses to scalarize aggregates which would require passing in more than
+ three operands to the function, because passing thousands of operands for a
+ large array or structure is unprofitable!
+ </p>
+
+ <p>
+ Note that this transformation could also be done for arguments that are only
+ stored to (returning the value instead), but does not currently. This case
+ would be best handled when and if LLVM starts supporting multiple return
+ values from functions.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="bb-vectorize">-bb-vectorize: Basic-Block Vectorization</a>
+</h3>
+<div>
+ <p>This pass combines instructions inside basic blocks to form vector
+ instructions. It iterates over each basic block, attempting to pair
+ compatible instructions, repeating this process until no additional
+ pairs are selected for vectorization. When the outputs of some pair
+ of compatible instructions are used as inputs by some other pair of
+ compatible instructions, those pairs are part of a potential
+ vectorization chain. Instruction pairs are only fused into vector
+ instructions when they are part of a chain longer than some
+ threshold length. Moreover, the pass attempts to find the best
+ possible chain for each pair of compatible instructions. These
+ heuristics are intended to prevent vectorization in cases where
+ it would not yield a performance increase of the resulting code.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="block-placement">-block-placement: Profile Guided Basic Block Placement</a>
+</h3>
+<div>
+ <p>This pass is a very simple profile guided basic block placement algorithm.
+ The idea is to put frequently executed blocks together at the start of the
+ function and hopefully increase the number of fall-through conditional
+ branches. If there is no profile information for a particular function, this
+ pass basically orders blocks in depth-first order.</p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="break-crit-edges">-break-crit-edges: Break critical edges in CFG</a>
+</h3>
+<div>
+ <p>
+ Break all of the critical edges in the CFG by inserting a dummy basic block.
+ It may be "required" by passes that cannot deal with critical edges. This
+ transformation obviously invalidates the CFG, but can update forward dominator
+ (set, immediate dominators, tree, and frontier) information.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="codegenprepare">-codegenprepare: Optimize for code generation</a>
+</h3>
+<div>
+ This pass munges the code in the input function to better prepare it for
+ SelectionDAG-based code generation. This works around limitations in it's
+ basic-block-at-a-time approach. It should eventually be removed.
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="constmerge">-constmerge: Merge Duplicate Global Constants</a>
+</h3>
+<div>
+ <p>
+ Merges duplicate global constants together into a single constant that is
+ shared. This is useful because some passes (ie TraceValues) insert a lot of
+ string constants into the program, regardless of whether or not an existing
+ string is available.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="constprop">-constprop: Simple constant propagation</a>
+</h3>
+<div>
+ <p>This file implements constant propagation and merging. It looks for
+ instructions involving only constant operands and replaces them with a
+ constant value instead of an instruction. For example:</p>
+ <blockquote><pre>add i32 1, 2</pre></blockquote>
+ <p>becomes</p>
+ <blockquote><pre>i32 3</pre></blockquote>
+ <p>NOTE: this pass has a habit of making definitions be dead. It is a good
+ idea to to run a <a href="#die">DIE</a> (Dead Instruction Elimination) pass
+ sometime after running this pass.</p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="dce">-dce: Dead Code Elimination</a>
+</h3>
+<div>
+ <p>
+ Dead code elimination is similar to <a href="#die">dead instruction
+ elimination</a>, but it rechecks instructions that were used by removed
+ instructions to see if they are newly dead.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="deadargelim">-deadargelim: Dead Argument Elimination</a>
+</h3>
+<div>
+ <p>
+ This pass deletes dead arguments from internal functions. Dead argument
+ elimination removes arguments which are directly dead, as well as arguments
+ only passed into function calls as dead arguments of other functions. This
+ pass also deletes dead arguments in a similar way.
+ </p>
+
+ <p>
+ This pass is often useful as a cleanup pass to run after aggressive
+ interprocedural passes, which add possibly-dead arguments.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="deadtypeelim">-deadtypeelim: Dead Type Elimination</a>
+</h3>
+<div>
+ <p>
+ This pass is used to cleanup the output of GCC. It eliminate names for types
+ that are unused in the entire translation unit, using the <a
+ href="#findusedtypes">find used types</a> pass.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="die">-die: Dead Instruction Elimination</a>
+</h3>
+<div>
+ <p>
+ Dead instruction elimination performs a single pass over the function,
+ removing instructions that are obviously dead.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="dse">-dse: Dead Store Elimination</a>
+</h3>
+<div>
+ <p>
+ A trivial dead store elimination that only considers basic-block local
+ redundant stores.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="functionattrs">-functionattrs: Deduce function attributes</a>
+</h3>
+<div>
+ <p>A simple interprocedural pass which walks the call-graph, looking for
+ functions which do not access or only read non-local memory, and marking them
+ readnone/readonly. In addition, it marks function arguments (of pointer type)
+ 'nocapture' if a call to the function does not create any copies of the pointer
+ value that outlive the call. This more or less means that the pointer is only
+ dereferenced, and not returned from the function or stored in a global.
+ This pass is implemented as a bottom-up traversal of the call-graph.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="globaldce">-globaldce: Dead Global Elimination</a>
+</h3>
+<div>
+ <p>
+ This transform is designed to eliminate unreachable internal globals from the
+ program. It uses an aggressive algorithm, searching out globals that are
+ known to be alive. After it finds all of the globals which are needed, it
+ deletes whatever is left over. This allows it to delete recursive chunks of
+ the program which are unreachable.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="globalopt">-globalopt: Global Variable Optimizer</a>
+</h3>
+<div>
+ <p>
+ This pass transforms simple global variables that never have their address
+ taken. If obviously true, it marks read/write globals as constant, deletes
+ variables only stored to, etc.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="gvn">-gvn: Global Value Numbering</a>
+</h3>
+<div>
+ <p>
+ This pass performs global value numbering to eliminate fully and partially
+ redundant instructions. It also performs redundant load elimination.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="indvars">-indvars: Canonicalize Induction Variables</a>
+</h3>
+<div>
+ <p>
+ This transformation analyzes and transforms the induction variables (and
+ computations derived from them) into simpler forms suitable for subsequent
+ analysis and transformation.
+ </p>
+
+ <p>
+ This transformation makes the following changes to each loop with an
+ identifiable induction variable:
+ </p>
+
+ <ol>
+ <li>All loops are transformed to have a <em>single</em> canonical
+ induction variable which starts at zero and steps by one.</li>
+ <li>The canonical induction variable is guaranteed to be the first PHI node
+ in the loop header block.</li>
+ <li>Any pointer arithmetic recurrences are raised to use array
+ subscripts.</li>
+ </ol>
+
+ <p>
+ If the trip count of a loop is computable, this pass also makes the following
+ changes:
+ </p>
+
+ <ol>
+ <li>The exit condition for the loop is canonicalized to compare the
+ induction value against the exit value. This turns loops like:
+ <blockquote><pre>for (i = 7; i*i < 1000; ++i)</pre></blockquote>
+ into
+ <blockquote><pre>for (i = 0; i != 25; ++i)</pre></blockquote></li>
+ <li>Any use outside of the loop of an expression derived from the indvar
+ is changed to compute the derived value outside of the loop, eliminating
+ the dependence on the exit value of the induction variable. If the only
+ purpose of the loop is to compute the exit value of some derived
+ expression, this transformation will make the loop dead.</li>
+ </ol>
+
+ <p>
+ This transformation should be followed by strength reduction after all of the
+ desired loop transformations have been performed. Additionally, on targets
+ where it is profitable, the loop could be transformed to count down to zero
+ (the "do loop" optimization).
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="inline">-inline: Function Integration/Inlining</a>
+</h3>
+<div>
+ <p>
+ Bottom-up inlining of functions into callees.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="insert-edge-profiling">-insert-edge-profiling: Insert instrumentation for edge profiling</a>
+</h3>
+<div>
+ <p>
+ This pass instruments the specified program with counters for edge profiling.
+ Edge profiling can give a reasonable approximation of the hot paths through a
+ program, and is used for a wide variety of program transformations.
+ </p>
+
+ <p>
+ Note that this implementation is very naïve. It inserts a counter for
+ <em>every</em> edge in the program, instead of using control flow information
+ to prune the number of counters inserted.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="insert-optimal-edge-profiling">-insert-optimal-edge-profiling: Insert optimal instrumentation for edge profiling</a>
+</h3>
+<div>
+ <p>This pass instruments the specified program with counters for edge profiling.
+ Edge profiling can give a reasonable approximation of the hot paths through a
+ program, and is used for a wide variety of program transformations.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="instcombine">-instcombine: Combine redundant instructions</a>
+</h3>
+<div>
+ <p>
+ Combine instructions to form fewer, simple
+ instructions. This pass does not modify the CFG This pass is where algebraic
+ simplification happens.
+ </p>
+
+ <p>
+ This pass combines things like:
+ </p>
+
+<blockquote><pre
+>%Y = add i32 %X, 1
+%Z = add i32 %Y, 1</pre></blockquote>
+
+ <p>
+ into:
+ </p>
+
+<blockquote><pre
+>%Z = add i32 %X, 2</pre></blockquote>
+
+ <p>
+ This is a simple worklist driven algorithm.
+ </p>
+
+ <p>
+ This pass guarantees that the following canonicalizations are performed on
+ the program:
+ </p>
+
+ <ul>
+ <li>If a binary operator has a constant operand, it is moved to the right-
+ hand side.</li>
+ <li>Bitwise operators with constant operands are always grouped so that
+ shifts are performed first, then <code>or</code>s, then
+ <code>and</code>s, then <code>xor</code>s.</li>
+ <li>Compare instructions are converted from <code><</code>,
+ <code>></code>, <code>â¤</code>, or <code>â¥</code> to
+ <code>=</code> or <code>â </code> if possible.</li>
+ <li>All <code>cmp</code> instructions on boolean values are replaced with
+ logical operations.</li>
+ <li><code>add <var>X</var>, <var>X</var></code> is represented as
+ <code>mul <var>X</var>, 2</code> â <code>shl <var>X</var>, 1</code></li>
+ <li>Multiplies with a constant power-of-two argument are transformed into
+ shifts.</li>
+ <li>⦠etc.</li>
+ </ul>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="internalize">-internalize: Internalize Global Symbols</a>
+</h3>
+<div>
+ <p>
+ This pass loops over all of the functions in the input module, looking for a
+ main function. If a main function is found, all other functions and all
+ global variables with initializers are marked as internal.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="ipconstprop">-ipconstprop: Interprocedural constant propagation</a>
+</h3>
+<div>
+ <p>
+ This pass implements an <em>extremely</em> simple interprocedural constant
+ propagation pass. It could certainly be improved in many different ways,
+ like using a worklist. This pass makes arguments dead, but does not remove
+ them. The existing dead argument elimination pass should be run after this
+ to clean up the mess.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="ipsccp">-ipsccp: Interprocedural Sparse Conditional Constant Propagation</a>
+</h3>
+<div>
+ <p>
+ An interprocedural variant of <a href="#sccp">Sparse Conditional Constant
+ Propagation</a>.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="jump-threading">-jump-threading: Jump Threading</a>
+</h3>
+<div>
+ <p>
+ Jump threading tries to find distinct threads of control flow running through
+ a basic block. This pass looks at blocks that have multiple predecessors and
+ multiple successors. If one or more of the predecessors of the block can be
+ proven to always cause a jump to one of the successors, we forward the edge
+ from the predecessor to the successor by duplicating the contents of this
+ block.
+ </p>
+ <p>
+ An example of when this can occur is code like this:
+ </p>
+
+ <pre
+>if () { ...
+ X = 4;
+}
+if (X < 3) {</pre>
+
+ <p>
+ In this case, the unconditional branch at the end of the first if can be
+ revectored to the false side of the second if.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="lcssa">-lcssa: Loop-Closed SSA Form Pass</a>
+</h3>
+<div>
+ <p>
+ This pass transforms loops by placing phi nodes at the end of the loops for
+ all values that are live across the loop boundary. For example, it turns
+ the left into the right code:
+ </p>
+
+ <pre
+>for (...) for (...)
+ if (c) if (c)
+ X1 = ... X1 = ...
+ else else
+ X2 = ... X2 = ...
+ X3 = phi(X1, X2) X3 = phi(X1, X2)
+... = X3 + 4 X4 = phi(X3)
+ ... = X4 + 4</pre>
+
+ <p>
+ This is still valid LLVM; the extra phi nodes are purely redundant, and will
+ be trivially eliminated by <code>InstCombine</code>. The major benefit of
+ this transformation is that it makes many other loop optimizations, such as
+ LoopUnswitching, simpler.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="licm">-licm: Loop Invariant Code Motion</a>
+</h3>
+<div>
+ <p>
+ This pass performs loop invariant code motion, attempting to remove as much
+ code from the body of a loop as possible. It does this by either hoisting
+ code into the preheader block, or by sinking code to the exit blocks if it is
+ safe. This pass also promotes must-aliased memory locations in the loop to
+ live in registers, thus hoisting and sinking "invariant" loads and stores.
+ </p>
+
+ <p>
+ This pass uses alias analysis for two purposes:
+ </p>
+
+ <ul>
+ <li>Moving loop invariant loads and calls out of loops. If we can determine
+ that a load or call inside of a loop never aliases anything stored to,
+ we can hoist it or sink it like any other instruction.</li>
+ <li>Scalar Promotion of Memory - If there is a store instruction inside of
+ the loop, we try to move the store to happen AFTER the loop instead of
+ inside of the loop. This can only happen if a few conditions are true:
+ <ul>
+ <li>The pointer stored through is loop invariant.</li>
+ <li>There are no stores or loads in the loop which <em>may</em> alias
+ the pointer. There are no calls in the loop which mod/ref the
+ pointer.</li>
+ </ul>
+ If these conditions are true, we can promote the loads and stores in the
+ loop of the pointer to use a temporary alloca'd variable. We then use
+ the mem2reg functionality to construct the appropriate SSA form for the
+ variable.</li>
+ </ul>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="loop-deletion">-loop-deletion: Delete dead loops</a>
+</h3>
+<div>
+ <p>
+ This file implements the Dead Loop Deletion Pass. This pass is responsible
+ for eliminating loops with non-infinite computable trip counts that have no
+ side effects or volatile instructions, and do not contribute to the
+ computation of the function's return value.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="loop-extract">-loop-extract: Extract loops into new functions</a>
+</h3>
+<div>
+ <p>
+ A pass wrapper around the <code>ExtractLoop()</code> scalar transformation to
+ extract each top-level loop into its own new function. If the loop is the
+ <em>only</em> loop in a given function, it is not touched. This is a pass most
+ useful for debugging via bugpoint.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="loop-extract-single">-loop-extract-single: Extract at most one loop into a new function</a>
+</h3>
+<div>
+ <p>
+ Similar to <a href="#loop-extract">Extract loops into new functions</a>,
+ this pass extracts one natural loop from the program into a function if it
+ can. This is used by bugpoint.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="loop-reduce">-loop-reduce: Loop Strength Reduction</a>
+</h3>
+<div>
+ <p>
+ This pass performs a strength reduction on array references inside loops that
+ have as one or more of their components the loop induction variable. This is
+ accomplished by creating a new value to hold the initial value of the array
+ access for the first iteration, and then creating a new GEP instruction in
+ the loop to increment the value by the appropriate amount.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="loop-rotate">-loop-rotate: Rotate Loops</a>
+</h3>
+<div>
+ <p>A simple loop rotation transformation.</p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="loop-simplify">-loop-simplify: Canonicalize natural loops</a>
+</h3>
+<div>
+ <p>
+ This pass performs several transformations to transform natural loops into a
+ simpler form, which makes subsequent analyses and transformations simpler and
+ more effective.
+ </p>
+
+ <p>
+ Loop pre-header insertion guarantees that there is a single, non-critical
+ entry edge from outside of the loop to the loop header. This simplifies a
+ number of analyses and transformations, such as LICM.
+ </p>
+
+ <p>
+ Loop exit-block insertion guarantees that all exit blocks from the loop
+ (blocks which are outside of the loop that have predecessors inside of the
+ loop) only have predecessors from inside of the loop (and are thus dominated
+ by the loop header). This simplifies transformations such as store-sinking
+ that are built into LICM.
+ </p>
+
+ <p>
+ This pass also guarantees that loops will have exactly one backedge.
+ </p>
+
+ <p>
+ Note that the simplifycfg pass will clean up blocks which are split out but
+ end up being unnecessary, so usage of this pass should not pessimize
+ generated code.
+ </p>
+
+ <p>
+ This pass obviously modifies the CFG, but updates loop information and
+ dominator information.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="loop-unroll">-loop-unroll: Unroll loops</a>
+</h3>
+<div>
+ <p>
+ This pass implements a simple loop unroller. It works best when loops have
+ been canonicalized by the <a href="#indvars"><tt>-indvars</tt></a> pass,
+ allowing it to determine the trip counts of loops easily.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="loop-unswitch">-loop-unswitch: Unswitch loops</a>
+</h3>
+<div>
+ <p>
+ This pass transforms loops that contain branches on loop-invariant conditions
+ to have multiple loops. For example, it turns the left into the right code:
+ </p>
+
+ <pre
+>for (...) if (lic)
+ A for (...)
+ if (lic) A; B; C
+ B else
+ C for (...)
+ A; C</pre>
+
+ <p>
+ This can increase the size of the code exponentially (doubling it every time
+ a loop is unswitched) so we only unswitch if the resultant code will be
+ smaller than a threshold.
+ </p>
+
+ <p>
+ This pass expects LICM to be run before it to hoist invariant conditions out
+ of the loop, to make the unswitching opportunity obvious.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="loweratomic">-loweratomic: Lower atomic intrinsics to non-atomic form</a>
+</h3>
+<div>
+ <p>
+ This pass lowers atomic intrinsics to non-atomic form for use in a known
+ non-preemptible environment.
+ </p>
+
+ <p>
+ The pass does not verify that the environment is non-preemptible (in
+ general this would require knowledge of the entire call graph of the
+ program including any libraries which may not be available in bitcode form);
+ it simply lowers every atomic intrinsic.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="lowerinvoke">-lowerinvoke: Lower invoke and unwind, for unwindless code generators</a>
+</h3>
+<div>
+ <p>
+ This transformation is designed for use by code generators which do not yet
+ support stack unwinding. This pass supports two models of exception handling
+ lowering, the 'cheap' support and the 'expensive' support.
+ </p>
+
+ <p>
+ 'Cheap' exception handling support gives the program the ability to execute
+ any program which does not "throw an exception", by turning 'invoke'
+ instructions into calls and by turning 'unwind' instructions into calls to
+ abort(). If the program does dynamically use the unwind instruction, the
+ program will print a message then abort.
+ </p>
+
+ <p>
+ 'Expensive' exception handling support gives the full exception handling
+ support to the program at the cost of making the 'invoke' instruction
+ really expensive. It basically inserts setjmp/longjmp calls to emulate the
+ exception handling as necessary.
+ </p>
+
+ <p>
+ Because the 'expensive' support slows down programs a lot, and EH is only
+ used for a subset of the programs, it must be specifically enabled by the
+ <tt>-enable-correct-eh-support</tt> option.
+ </p>
+
+ <p>
+ Note that after this pass runs the CFG is not entirely accurate (exceptional
+ control flow edges are not correct anymore) so only very simple things should
+ be done after the lowerinvoke pass has run (like generation of native code).
+ This should not be used as a general purpose "my LLVM-to-LLVM pass doesn't
+ support the invoke instruction yet" lowering pass.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="lowerswitch">-lowerswitch: Lower SwitchInst's to branches</a>
+</h3>
+<div>
+ <p>
+ Rewrites <tt>switch</tt> instructions with a sequence of branches, which
+ allows targets to get away with not implementing the switch instruction until
+ it is convenient.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="mem2reg">-mem2reg: Promote Memory to Register</a>
+</h3>
+<div>
+ <p>
+ This file promotes memory references to be register references. It promotes
+ <tt>alloca</tt> instructions which only have <tt>load</tt>s and
+ <tt>store</tt>s as uses. An <tt>alloca</tt> is transformed by using dominator
+ frontiers to place <tt>phi</tt> nodes, then traversing the function in
+ depth-first order to rewrite <tt>load</tt>s and <tt>store</tt>s as
+ appropriate. This is just the standard SSA construction algorithm to construct
+ "pruned" SSA form.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="memcpyopt">-memcpyopt: MemCpy Optimization</a>
+</h3>
+<div>
+ <p>
+ This pass performs various transformations related to eliminating memcpy
+ calls, or transforming sets of stores into memset's.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="mergefunc">-mergefunc: Merge Functions</a>
+</h3>
+<div>
+ <p>This pass looks for equivalent functions that are mergable and folds them.
+
+ A hash is computed from the function, based on its type and number of
+ basic blocks.
+
+ Once all hashes are computed, we perform an expensive equality comparison
+ on each function pair. This takes n^2/2 comparisons per bucket, so it's
+ important that the hash function be high quality. The equality comparison
+ iterates through each instruction in each basic block.
+
+ When a match is found the functions are folded. If both functions are
+ overridable, we move the functionality into a new internal function and
+ leave two overridable thunks to it.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="mergereturn">-mergereturn: Unify function exit nodes</a>
+</h3>
+<div>
+ <p>
+ Ensure that functions have at most one <tt>ret</tt> instruction in them.
+ Additionally, it keeps track of which node is the new exit node of the CFG.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="partial-inliner">-partial-inliner: Partial Inliner</a>
+</h3>
+<div>
+ <p>This pass performs partial inlining, typically by inlining an if
+ statement that surrounds the body of the function.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="prune-eh">-prune-eh: Remove unused exception handling info</a>
+</h3>
+<div>
+ <p>
+ This file implements a simple interprocedural pass which walks the call-graph,
+ turning <tt>invoke</tt> instructions into <tt>call</tt> instructions if and
+ only if the callee cannot throw an exception. It implements this as a
+ bottom-up traversal of the call-graph.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="reassociate">-reassociate: Reassociate expressions</a>
+</h3>
+<div>
+ <p>
+ This pass reassociates commutative expressions in an order that is designed
+ to promote better constant propagation, GCSE, LICM, PRE, etc.
+ </p>
+
+ <p>
+ For example: 4 + (<var>x</var> + 5) â <var>x</var> + (4 + 5)
+ </p>
+
+ <p>
+ In the implementation of this algorithm, constants are assigned rank = 0,
+ function arguments are rank = 1, and other values are assigned ranks
+ corresponding to the reverse post order traversal of current function
+ (starting at 2), which effectively gives values in deep loops higher rank
+ than values not in loops.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="reg2mem">-reg2mem: Demote all values to stack slots</a>
+</h3>
+<div>
+ <p>
+ This file demotes all registers to memory references. It is intended to be
+ the inverse of <a href="#mem2reg"><tt>-mem2reg</tt></a>. By converting to
+ <tt>load</tt> instructions, the only values live across basic blocks are
+ <tt>alloca</tt> instructions and <tt>load</tt> instructions before
+ <tt>phi</tt> nodes. It is intended that this should make CFG hacking much
+ easier. To make later hacking easier, the entry block is split into two, such
+ that all introduced <tt>alloca</tt> instructions (and nothing else) are in the
+ entry block.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="scalarrepl">-scalarrepl: Scalar Replacement of Aggregates (DT)</a>
+</h3>
+<div>
+ <p>
+ The well-known scalar replacement of aggregates transformation. This
+ transform breaks up <tt>alloca</tt> instructions of aggregate type (structure
+ or array) into individual <tt>alloca</tt> instructions for each member if
+ possible. Then, if possible, it transforms the individual <tt>alloca</tt>
+ instructions into nice clean scalar SSA form.
+ </p>
+
+ <p>
+ This combines a simple scalar replacement of aggregates algorithm with the <a
+ href="#mem2reg"><tt>mem2reg</tt></a> algorithm because often interact,
+ especially for C++ programs. As such, iterating between <tt>scalarrepl</tt>,
+ then <a href="#mem2reg"><tt>mem2reg</tt></a> until we run out of things to
+ promote works well.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="sccp">-sccp: Sparse Conditional Constant Propagation</a>
+</h3>
+<div>
+ <p>
+ Sparse conditional constant propagation and merging, which can be summarized
+ as:
+ </p>
+
+ <ol>
+ <li>Assumes values are constant unless proven otherwise</li>
+ <li>Assumes BasicBlocks are dead unless proven otherwise</li>
+ <li>Proves values to be constant, and replaces them with constants</li>
+ <li>Proves conditional branches to be unconditional</li>
+ </ol>
+
+ <p>
+ Note that this pass has a habit of making definitions be dead. It is a good
+ idea to to run a DCE pass sometime after running this pass.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="simplify-libcalls">-simplify-libcalls: Simplify well-known library calls</a>
+</h3>
+<div>
+ <p>
+ Applies a variety of small optimizations for calls to specific well-known
+ function calls (e.g. runtime library functions). For example, a call
+ <tt>exit(3)</tt> that occurs within the <tt>main()</tt> function can be
+ transformed into simply <tt>return 3</tt>.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="simplifycfg">-simplifycfg: Simplify the CFG</a>
+</h3>
+<div>
+ <p>
+ Performs dead code elimination and basic block merging. Specifically:
+ </p>
+
+ <ol>
+ <li>Removes basic blocks with no predecessors.</li>
+ <li>Merges a basic block into its predecessor if there is only one and the
+ predecessor only has one successor.</li>
+ <li>Eliminates PHI nodes for basic blocks with a single predecessor.</li>
+ <li>Eliminates a basic block that only contains an unconditional
+ branch.</li>
+ </ol>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="sink">-sink: Code sinking</a>
+</h3>
+<div>
+ <p>This pass moves instructions into successor blocks, when possible, so that
+ they aren't executed on paths where their results aren't needed.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="sretpromotion">-sretpromotion: Promote sret arguments to multiple ret values</a>
+</h3>
+<div>
+ <p>
+ This pass finds functions that return a struct (using a pointer to the struct
+ as the first argument of the function, marked with the '<tt>sret</tt>' attribute) and
+ replaces them with a new function that simply returns each of the elements of
+ that struct (using multiple return values).
+ </p>
+
+ <p>
+ This pass works under a number of conditions:
+ </p>
+
+ <ul>
+ <li>The returned struct must not contain other structs</li>
+ <li>The returned struct must only be used to load values from</li>
+ <li>The placeholder struct passed in is the result of an <tt>alloca</tt></li>
+ </ul>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="strip">-strip: Strip all symbols from a module</a>
+</h3>
+<div>
+ <p>
+ performs code stripping. this transformation can delete:
+ </p>
+
+ <ol>
+ <li>names for virtual registers</li>
+ <li>symbols for internal globals and functions</li>
+ <li>debug information</li>
+ </ol>
+
+ <p>
+ note that this transformation makes code much less readable, so it should
+ only be used in situations where the <tt>strip</tt> utility would be used,
+ such as reducing code size or making it harder to reverse engineer code.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="strip-dead-debug-info">-strip-dead-debug-info: Strip debug info for unused symbols</a>
+</h3>
+<div>
+ <p>
+ performs code stripping. this transformation can delete:
+ </p>
+
+ <ol>
+ <li>names for virtual registers</li>
+ <li>symbols for internal globals and functions</li>
+ <li>debug information</li>
+ </ol>
+
+ <p>
+ note that this transformation makes code much less readable, so it should
+ only be used in situations where the <tt>strip</tt> utility would be used,
+ such as reducing code size or making it harder to reverse engineer code.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="strip-dead-prototypes">-strip-dead-prototypes: Strip Unused Function Prototypes</a>
+</h3>
+<div>
+ <p>
+ This pass loops over all of the functions in the input module, looking for
+ dead declarations and removes them. Dead declarations are declarations of
+ functions for which no implementation is available (i.e., declarations for
+ unused library functions).
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="strip-debug-declare">-strip-debug-declare: Strip all llvm.dbg.declare intrinsics</a>
+</h3>
+<div>
+ <p>This pass implements code stripping. Specifically, it can delete:</p>
+ <ul>
+ <li>names for virtual registers</li>
+ <li>symbols for internal globals and functions</li>
+ <li>debug information</li>
+ </ul>
+ <p>
+ Note that this transformation makes code much less readable, so it should
+ only be used in situations where the 'strip' utility would be used, such as
+ reducing code size or making it harder to reverse engineer code.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="strip-nondebug">-strip-nondebug: Strip all symbols, except dbg symbols, from a module</a>
+</h3>
+<div>
+ <p>This pass implements code stripping. Specifically, it can delete:</p>
+ <ul>
+ <li>names for virtual registers</li>
+ <li>symbols for internal globals and functions</li>
+ <li>debug information</li>
+ </ul>
+ <p>
+ Note that this transformation makes code much less readable, so it should
+ only be used in situations where the 'strip' utility would be used, such as
+ reducing code size or making it harder to reverse engineer code.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="tailcallelim">-tailcallelim: Tail Call Elimination</a>
+</h3>
+<div>
+ <p>
+ This file transforms calls of the current function (self recursion) followed
+ by a return instruction with a branch to the entry of the function, creating
+ a loop. This pass also implements the following extensions to the basic
+ algorithm:
+ </p>
+
+ <ul>
+ <li>Trivial instructions between the call and return do not prevent the
+ transformation from taking place, though currently the analysis cannot
+ support moving any really useful instructions (only dead ones).
+ <li>This pass transforms functions that are prevented from being tail
+ recursive by an associative expression to use an accumulator variable,
+ thus compiling the typical naive factorial or <tt>fib</tt> implementation
+ into efficient code.
+ <li>TRE is performed if the function returns void, if the return
+ returns the result returned by the call, or if the function returns a
+ run-time constant on all exits from the function. It is possible, though
+ unlikely, that the return returns something else (like constant 0), and
+ can still be TRE'd. It can be TRE'd if <em>all other</em> return
+ instructions in the function return the exact same value.
+ <li>If it can prove that callees do not access theier caller stack frame,
+ they are marked as eligible for tail call elimination (by the code
+ generator).
+ </ul>
+</div>
+
+<!-- ======================================================================= -->
+<h2><a name="utilities">Utility Passes</a></h2>
+<div>
+ <p>This section describes the LLVM Utility Passes.</p>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="deadarghaX0r">-deadarghaX0r: Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)</a>
+</h3>
+<div>
+ <p>
+ Same as dead argument elimination, but deletes arguments to functions which
+ are external. This is only for use by <a
+ href="Bugpoint.html">bugpoint</a>.</p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="extract-blocks">-extract-blocks: Extract Basic Blocks From Module (for bugpoint use)</a>
+</h3>
+<div>
+ <p>
+ This pass is used by bugpoint to extract all blocks from the module into their
+ own functions.</p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="instnamer">-instnamer: Assign names to anonymous instructions</a>
+</h3>
+<div>
+ <p>This is a little utility pass that gives instructions names, this is mostly
+ useful when diffing the effect of an optimization because deleting an
+ unnamed instruction can change all other instruction numbering, making the
+ diff very noisy.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="preverify">-preverify: Preliminary module verification</a>
+</h3>
+<div>
+ <p>
+ Ensures that the module is in the form required by the <a
+ href="#verifier">Module Verifier</a> pass.
+ </p>
+
+ <p>
+ Running the verifier runs this pass automatically, so there should be no need
+ to use it directly.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="verify">-verify: Module Verifier</a>
+</h3>
+<div>
+ <p>
+ Verifies an LLVM IR code. This is useful to run after an optimization which is
+ undergoing testing. Note that <tt>llvm-as</tt> verifies its input before
+ emitting bitcode, and also that malformed bitcode is likely to make LLVM
+ crash. All language front-ends are therefore encouraged to verify their output
+ before performing optimizing transformations.
+ </p>
+
+ <ul>
+ <li>Both of a binary operator's parameters are of the same type.</li>
+ <li>Verify that the indices of mem access instructions match other
+ operands.</li>
+ <li>Verify that arithmetic and other things are only performed on
+ first-class types. Verify that shifts and logicals only happen on
+ integrals f.e.</li>
+ <li>All of the constants in a switch statement are of the correct type.</li>
+ <li>The code is in valid SSA form.</li>
+ <li>It is illegal to put a label into any other type (like a structure) or
+ to return one.</li>
+ <li>Only phi nodes can be self referential: <tt>%x = add i32 %x, %x</tt> is
+ invalid.</li>
+ <li>PHI nodes must have an entry for each predecessor, with no extras.</li>
+ <li>PHI nodes must be the first thing in a basic block, all grouped
+ together.</li>
+ <li>PHI nodes must have at least one entry.</li>
+ <li>All basic blocks should only end with terminator insts, not contain
+ them.</li>
+ <li>The entry node to a function must not have predecessors.</li>
+ <li>All Instructions must be embedded into a basic block.</li>
+ <li>Functions cannot take a void-typed parameter.</li>
+ <li>Verify that a function's argument list agrees with its declared
+ type.</li>
+ <li>It is illegal to specify a name for a void value.</li>
+ <li>It is illegal to have an internal global value with no initializer.</li>
+ <li>It is illegal to have a ret instruction that returns a value that does
+ not agree with the function return value type.</li>
+ <li>Function call argument types match the function prototype.</li>
+ <li>All other things that are tested by asserts spread about the code.</li>
+ </ul>
+
+ <p>
+ Note that this does not provide full security verification (like Java), but
+ instead just tries to ensure that code is well-formed.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="view-cfg">-view-cfg: View CFG of function</a>
+</h3>
+<div>
+ <p>
+ Displays the control flow graph using the GraphViz tool.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="view-cfg-only">-view-cfg-only: View CFG of function (with no function bodies)</a>
+</h3>
+<div>
+ <p>
+ Displays the control flow graph using the GraphViz tool, but omitting function
+ bodies.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="view-dom">-view-dom: View dominance tree of function</a>
+</h3>
+<div>
+ <p>
+ Displays the dominator tree using the GraphViz tool.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="view-dom-only">-view-dom-only: View dominance tree of function (with no function bodies)</a>
+</h3>
+<div>
+ <p>
+ Displays the dominator tree using the GraphViz tool, but omitting function
+ bodies.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="view-postdom">-view-postdom: View postdominance tree of function</a>
+</h3>
+<div>
+ <p>
+ Displays the post dominator tree using the GraphViz tool.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="view-postdom-only">-view-postdom-only: View postdominance tree of function (with no function bodies)</a>
+</h3>
+<div>
+ <p>
+ Displays the post dominator tree using the GraphViz tool, but omitting
+ function bodies.
+ </p>
+</div>
+
+</div>
+
+<!-- *********************************************************************** -->
+
+<hr>
+<address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
+ src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
+ <a href="http://validator.w3.org/check/referer"><img
+ src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a>
+
+ <a href="mailto:rspencer at x10sys.com">Reid Spencer</a><br>
+ <a href="http://llvm.org/">LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date: 2012-10-31 12:25:31 -0500 (Wed, 31 Oct 2012) $
+</address>
+
+</body>
+</html>
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+</ul>
+</div>
+<p>If you prefer to use a web user interface for code reviews,
+you can now submit your patches for Clang and LLVM at
+<a class="reference external" href="http://llvm-reviews.chandlerc.com">LLVM’s Phabricator</a>.</p>
+<div class="section" id="sign-up">
+<h2><a class="toc-backref" href="#id1">Sign up</a><a class="headerlink" href="#sign-up" title="Permalink to this headline">¶</a></h2>
+<p>There are two options to get an account on Phabricator. You can sign up
+immediately with one of the supported OAuth account types if you’re comfortable
+with OAuth, but you can also email <a class="reference external" href="mailto:chandlerc%40gmail.com">chandlerc<span>@</span>gmail<span>.</span>com</a> to request an account to
+be created manually without using OAuth. We’re working to get support in
+Phabricator to directly create new accounts, but currently this is a manual
+process.</p>
+<p>Note that if you use your Subversion user name as Phabricator user name,
+Phabricator will automatically connect your submits to your Phabricator user in
+the <a class="reference external" href="http://llvm-reviews.chandlerc.com/diffusion/">Code Repository Browser</a>.</p>
+</div>
+<div class="section" id="requesting-a-review-via-the-command-line">
+<h2><a class="toc-backref" href="#id2">Requesting a review via the command line</a><a class="headerlink" href="#requesting-a-review-via-the-command-line" title="Permalink to this headline">¶</a></h2>
+<p>Phabricator has a tool called <em>Arcanist</em> to upload patches from
+the command line. To get you set up, follow the
+<a class="reference external" href="http://www.phabricator.com/docs/phabricator/article/Arcanist_Quick_Start.html">Arcanist Quick Start</a> instructions.</p>
+<p>You can learn more about how to use arc to interact with
+Phabricator in the <a class="reference external" href="http://www.phabricator.com/docs/phabricator/article/Arcanist_User_Guide.html">Arcanist User Guide</a>.</p>
+</div>
+<div class="section" id="requesting-a-review-via-the-web-interface">
+<h2><a class="toc-backref" href="#id3">Requesting a review via the web interface</a><a class="headerlink" href="#requesting-a-review-via-the-web-interface" title="Permalink to this headline">¶</a></h2>
+<p>The tool to create and review patches in Phabricator is called
+<em>Differential</em>.</p>
+<p>Note that you can upload patches created through various diff tools,
+including git and svn. To make reviews easier, please always include
+<strong>as much context as possible</strong> with your diff! Don’t worry, Phabricator
+will automatically send a diff with a smaller context in the review
+email, but having the full file in the web interface will help the
+reviewer understand your code.</p>
+<p>To get a full diff, use one of the following commands (or just use Arcanist
+to upload your patch):</p>
+<ul class="simple">
+<li><tt class="docutils literal"><span class="pre">git</span> <span class="pre">diff</span> <span class="pre">-U999999</span> <span class="pre">other-branch</span></tt></li>
+<li><tt class="docutils literal"><span class="pre">svn</span> <span class="pre">diff</span> <span class="pre">--diff-cmd=diff</span> <span class="pre">-x</span> <span class="pre">-U999999</span></tt></li>
+</ul>
+<p>To upload a new patch:</p>
+<ul class="simple">
+<li>Click <em>Differential</em>.</li>
+<li>Click <em>Create Revision</em>.</li>
+<li>Paste the text diff or upload the patch file.
+Note that TODO</li>
+<li>Leave the drop down on <em>Create a new Revision...</em> and click <em>Continue</em>.</li>
+<li>Enter a descriptive title and summary; add reviewers and mailing
+lists that you want to be included in the review. If your patch is
+for LLVM, cc llvm-commits; if your patch is for Clang, cc cfe-commits.</li>
+<li>Click <em>Save</em>.</li>
+</ul>
+<p>To submit an updated patch:</p>
+<ul class="simple">
+<li>Click <em>Differential</em>.</li>
+<li>Click <em>Create Revision</em>.</li>
+<li>Paste the updated diff.</li>
+<li>Select the review you want to from the <em>Attach To</em> dropdown and click
+<em>Continue</em>.</li>
+<li>Click <em>Save</em>.</li>
+</ul>
+</div>
+<div class="section" id="reviewing-code-with-phabricator">
+<h2><a class="toc-backref" href="#id4">Reviewing code with Phabricator</a><a class="headerlink" href="#reviewing-code-with-phabricator" title="Permalink to this headline">¶</a></h2>
+<p>Phabricator allows you to add inline comments as well as overall comments
+to a revision. To add an inline comment, select the lines of code you want
+to comment on by clicking and dragging the line numbers in the diff pane.</p>
+<p>You can add overall comments or submit your comments at the bottom of the page.</p>
+<p>Phabricator has many useful features, for example allowing you to select
+diffs between different versions of the patch as it was reviewed in the
+<em>Revision Update History</em>. Most features are self descriptive - explore, and
+if you have a question, drop by on #llvm in IRC to get help.</p>
+</div>
+<div class="section" id="status">
+<h2><a class="toc-backref" href="#id5">Status</a><a class="headerlink" href="#status" title="Permalink to this headline">¶</a></h2>
+<p>Currently, we’re testing Phabricator for use with Clang/LLVM. Please let us
+know whether you like it and what could be improved!</p>
+</div>
+</div>
+
+
+ </div>
+ </div>
+ </div>
+ <div class="clearer"></div>
+ </div>
+ <div class="related">
+ <h3>Navigation</h3>
+ <ul>
+ <li class="right" style="margin-right: 10px">
+ <a href="genindex.html" title="General Index"
+ >index</a></li>
+ <li class="right" >
+ <a href="programming.html" title="Programming Documentation"
+ >next</a> |</li>
+ <li class="right" >
+ <a href="SphinxQuickstartTemplate.html" title="Sphinx Quickstart Template"
+ >previous</a> |</li>
+ <li><a href="http://llvm.org/">LLVM Home</a> | </li>
+ <li><a href="index.html">Documentation</a>»</li>
+
+ <li><a href="userguides.html" >User Guides</a> »</li>
+ </ul>
+ </div>
+ <div class="footer">
+ © Copyright 2012, LLVM Project.
+ Last updated on 2012-12-21.
+ Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
+ </div>
+ </body>
+</html>
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@@ -0,0 +1,4156 @@
+<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+<html>
+<head>
+ <meta http-equiv="Content-type" content="text/html;charset=UTF-8">
+ <title>LLVM Programmer's Manual</title>
+ <link rel="stylesheet" href="_static/llvm.css" type="text/css">
+</head>
+<body>
+
+<h1>
+ LLVM Programmer's Manual
+</h1>
+
+<ol>
+ <li><a href="#introduction">Introduction</a></li>
+ <li><a href="#general">General Information</a>
+ <ul>
+ <li><a href="#stl">The C++ Standard Template Library</a></li>
+<!--
+ <li>The <tt>-time-passes</tt> option</li>
+ <li>How to use the LLVM Makefile system</li>
+ <li>How to write a regression test</li>
+
+-->
+ </ul>
+ </li>
+ <li><a href="#apis">Important and useful LLVM APIs</a>
+ <ul>
+ <li><a href="#isa">The <tt>isa<></tt>, <tt>cast<></tt>
+and <tt>dyn_cast<></tt> templates</a> </li>
+ <li><a href="#string_apis">Passing strings (the <tt>StringRef</tt>
+and <tt>Twine</tt> classes)</a>
+ <ul>
+ <li><a href="#StringRef">The <tt>StringRef</tt> class</a> </li>
+ <li><a href="#Twine">The <tt>Twine</tt> class</a> </li>
+ </ul>
+ </li>
+ <li><a href="#DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt>
+option</a>
+ <ul>
+ <li><a href="#DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt>
+and the <tt>-debug-only</tt> option</a> </li>
+ </ul>
+ </li>
+ <li><a href="#Statistic">The <tt>Statistic</tt> class & <tt>-stats</tt>
+option</a></li>
+<!--
+ <li>The <tt>InstVisitor</tt> template
+ <li>The general graph API
+-->
+ <li><a href="#ViewGraph">Viewing graphs while debugging code</a></li>
+ </ul>
+ </li>
+ <li><a href="#datastructure">Picking the Right Data Structure for a Task</a>
+ <ul>
+ <li><a href="#ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
+ <ul>
+ <li><a href="#dss_arrayref">llvm/ADT/ArrayRef.h</a></li>
+ <li><a href="#dss_fixedarrays">Fixed Size Arrays</a></li>
+ <li><a href="#dss_heaparrays">Heap Allocated Arrays</a></li>
+ <li><a href="#dss_tinyptrvector">"llvm/ADT/TinyPtrVector.h"</a></li>
+ <li><a href="#dss_smallvector">"llvm/ADT/SmallVector.h"</a></li>
+ <li><a href="#dss_vector"><vector></a></li>
+ <li><a href="#dss_deque"><deque></a></li>
+ <li><a href="#dss_list"><list></a></li>
+ <li><a href="#dss_ilist">llvm/ADT/ilist.h</a></li>
+ <li><a href="#dss_packedvector">llvm/ADT/PackedVector.h</a></li>
+ <li><a href="#dss_other">Other Sequential Container Options</a></li>
+ </ul></li>
+ <li><a href="#ds_string">String-like containers</a>
+ <ul>
+ <li><a href="#dss_stringref">llvm/ADT/StringRef.h</a></li>
+ <li><a href="#dss_twine">llvm/ADT/Twine.h</a></li>
+ <li><a href="#dss_smallstring">llvm/ADT/SmallString.h</a></li>
+ <li><a href="#dss_stdstring">std::string</a></li>
+ </ul></li>
+ <li><a href="#ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
+ <ul>
+ <li><a href="#dss_sortedvectorset">A sorted 'vector'</a></li>
+ <li><a href="#dss_smallset">"llvm/ADT/SmallSet.h"</a></li>
+ <li><a href="#dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a></li>
+ <li><a href="#dss_denseset">"llvm/ADT/DenseSet.h"</a></li>
+ <li><a href="#dss_sparseset">"llvm/ADT/SparseSet.h"</a></li>
+ <li><a href="#dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a></li>
+ <li><a href="#dss_set"><set></a></li>
+ <li><a href="#dss_setvector">"llvm/ADT/SetVector.h"</a></li>
+ <li><a href="#dss_uniquevector">"llvm/ADT/UniqueVector.h"</a></li>
+ <li><a href="#dss_immutableset">"llvm/ADT/ImmutableSet.h"</a></li>
+ <li><a href="#dss_otherset">Other Set-Like Container Options</a></li>
+ </ul></li>
+ <li><a href="#ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
+ <ul>
+ <li><a href="#dss_sortedvectormap">A sorted 'vector'</a></li>
+ <li><a href="#dss_stringmap">"llvm/ADT/StringMap.h"</a></li>
+ <li><a href="#dss_indexedmap">"llvm/ADT/IndexedMap.h"</a></li>
+ <li><a href="#dss_densemap">"llvm/ADT/DenseMap.h"</a></li>
+ <li><a href="#dss_valuemap">"llvm/ADT/ValueMap.h"</a></li>
+ <li><a href="#dss_intervalmap">"llvm/ADT/IntervalMap.h"</a></li>
+ <li><a href="#dss_map"><map></a></li>
+ <li><a href="#dss_mapvector">"llvm/ADT/MapVector.h"</a></li>
+ <li><a href="#dss_inteqclasses">"llvm/ADT/IntEqClasses.h"</a></li>
+ <li><a href="#dss_immutablemap">"llvm/ADT/ImmutableMap.h"</a></li>
+ <li><a href="#dss_othermap">Other Map-Like Container Options</a></li>
+ </ul></li>
+ <li><a href="#ds_bit">BitVector-like containers</a>
+ <ul>
+ <li><a href="#dss_bitvector">A dense bitvector</a></li>
+ <li><a href="#dss_smallbitvector">A "small" dense bitvector</a></li>
+ <li><a href="#dss_sparsebitvector">A sparse bitvector</a></li>
+ </ul></li>
+ </ul>
+ </li>
+ <li><a href="#common">Helpful Hints for Common Operations</a>
+ <ul>
+ <li><a href="#inspection">Basic Inspection and Traversal Routines</a>
+ <ul>
+ <li><a href="#iterate_function">Iterating over the <tt>BasicBlock</tt>s
+in a <tt>Function</tt></a> </li>
+ <li><a href="#iterate_basicblock">Iterating over the <tt>Instruction</tt>s
+in a <tt>BasicBlock</tt></a> </li>
+ <li><a href="#iterate_institer">Iterating over the <tt>Instruction</tt>s
+in a <tt>Function</tt></a> </li>
+ <li><a href="#iterate_convert">Turning an iterator into a
+class pointer</a> </li>
+ <li><a href="#iterate_complex">Finding call sites: a more
+complex example</a> </li>
+ <li><a href="#calls_and_invokes">Treating calls and invokes
+the same way</a> </li>
+ <li><a href="#iterate_chains">Iterating over def-use &
+use-def chains</a> </li>
+ <li><a href="#iterate_preds">Iterating over predecessors &
+successors of blocks</a></li>
+ </ul>
+ </li>
+ <li><a href="#simplechanges">Making simple changes</a>
+ <ul>
+ <li><a href="#schanges_creating">Creating and inserting new
+ <tt>Instruction</tt>s</a> </li>
+ <li><a href="#schanges_deleting">Deleting <tt>Instruction</tt>s</a> </li>
+ <li><a href="#schanges_replacing">Replacing an <tt>Instruction</tt>
+with another <tt>Value</tt></a> </li>
+ <li><a href="#schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a> </li>
+ </ul>
+ </li>
+ <li><a href="#create_types">How to Create Types</a></li>
+<!--
+ <li>Working with the Control Flow Graph
+ <ul>
+ <li>Accessing predecessors and successors of a <tt>BasicBlock</tt>
+ <li>
+ <li>
+ </ul>
+-->
+ </ul>
+ </li>
+
+ <li><a href="#threading">Threads and LLVM</a>
+ <ul>
+ <li><a href="#startmultithreaded">Entering and Exiting Multithreaded Mode
+ </a></li>
+ <li><a href="#shutdown">Ending execution with <tt>llvm_shutdown()</tt></a></li>
+ <li><a href="#managedstatic">Lazy initialization with <tt>ManagedStatic</tt></a></li>
+ <li><a href="#llvmcontext">Achieving Isolation with <tt>LLVMContext</tt></a></li>
+ <li><a href="#jitthreading">Threads and the JIT</a></li>
+ </ul>
+ </li>
+
+ <li><a href="#advanced">Advanced Topics</a>
+ <ul>
+
+ <li><a href="#SymbolTable">The <tt>ValueSymbolTable</tt> class</a></li>
+ <li><a href="#UserLayout">The <tt>User</tt> and owned <tt>Use</tt> classes' memory layout</a></li>
+ </ul></li>
+
+ <li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>
+ <ul>
+ <li><a href="#Type">The <tt>Type</tt> class</a> </li>
+ <li><a href="#Module">The <tt>Module</tt> class</a></li>
+ <li><a href="#Value">The <tt>Value</tt> class</a>
+ <ul>
+ <li><a href="#User">The <tt>User</tt> class</a>
+ <ul>
+ <li><a href="#Instruction">The <tt>Instruction</tt> class</a></li>
+ <li><a href="#Constant">The <tt>Constant</tt> class</a>
+ <ul>
+ <li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
+ <ul>
+ <li><a href="#Function">The <tt>Function</tt> class</a></li>
+ <li><a href="#GlobalVariable">The <tt>GlobalVariable</tt> class</a></li>
+ </ul>
+ </li>
+ </ul>
+ </li>
+ </ul>
+ </li>
+ <li><a href="#BasicBlock">The <tt>BasicBlock</tt> class</a></li>
+ <li><a href="#Argument">The <tt>Argument</tt> class</a></li>
+ </ul>
+ </li>
+ </ul>
+ </li>
+</ol>
+
+<div class="doc_author">
+ <p>Written by <a href="mailto:sabre at nondot.org">Chris Lattner</a>,
+ <a href="mailto:dhurjati at cs.uiuc.edu">Dinakar Dhurjati</a>,
+ <a href="mailto:ggreif at gmail.com">Gabor Greif</a>,
+ <a href="mailto:jstanley at cs.uiuc.edu">Joel Stanley</a>,
+ <a href="mailto:rspencer at x10sys.com">Reid Spencer</a> and
+ <a href="mailto:owen at apple.com">Owen Anderson</a></p>
+</div>
+
+<!-- *********************************************************************** -->
+<h2>
+ <a name="introduction">Introduction </a>
+</h2>
+<!-- *********************************************************************** -->
+
+<div>
+
+<p>This document is meant to highlight some of the important classes and
+interfaces available in the LLVM source-base. This manual is not
+intended to explain what LLVM is, how it works, and what LLVM code looks
+like. It assumes that you know the basics of LLVM and are interested
+in writing transformations or otherwise analyzing or manipulating the
+code.</p>
+
+<p>This document should get you oriented so that you can find your
+way in the continuously growing source code that makes up the LLVM
+infrastructure. Note that this manual is not intended to serve as a
+replacement for reading the source code, so if you think there should be
+a method in one of these classes to do something, but it's not listed,
+check the source. Links to the <a href="/doxygen/">doxygen</a> sources
+are provided to make this as easy as possible.</p>
+
+<p>The first section of this document describes general information that is
+useful to know when working in the LLVM infrastructure, and the second describes
+the Core LLVM classes. In the future this manual will be extended with
+information describing how to use extension libraries, such as dominator
+information, CFG traversal routines, and useful utilities like the <tt><a
+href="/doxygen/InstVisitor_8h-source.html">InstVisitor</a></tt> template.</p>
+
+</div>
+
+<!-- *********************************************************************** -->
+<h2>
+ <a name="general">General Information</a>
+</h2>
+<!-- *********************************************************************** -->
+
+<div>
+
+<p>This section contains general information that is useful if you are working
+in the LLVM source-base, but that isn't specific to any particular API.</p>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="stl">The C++ Standard Template Library</a>
+</h3>
+
+<div>
+
+<p>LLVM makes heavy use of the C++ Standard Template Library (STL),
+perhaps much more than you are used to, or have seen before. Because of
+this, you might want to do a little background reading in the
+techniques used and capabilities of the library. There are many good
+pages that discuss the STL, and several books on the subject that you
+can get, so it will not be discussed in this document.</p>
+
+<p>Here are some useful links:</p>
+
+<ol>
+
+<li><a href="http://www.dinkumware.com/manuals/#Standard C++ Library">Dinkumware
+C++ Library reference</a> - an excellent reference for the STL and other parts
+of the standard C++ library.</li>
+
+<li><a href="http://www.tempest-sw.com/cpp/">C++ In a Nutshell</a> - This is an
+O'Reilly book in the making. It has a decent Standard Library
+Reference that rivals Dinkumware's, and is unfortunately no longer free since the
+book has been published.</li>
+
+<li><a href="http://www.parashift.com/c++-faq-lite/">C++ Frequently Asked
+Questions</a></li>
+
+<li><a href="http://www.sgi.com/tech/stl/">SGI's STL Programmer's Guide</a> -
+Contains a useful <a
+href="http://www.sgi.com/tech/stl/stl_introduction.html">Introduction to the
+STL</a>.</li>
+
+<li><a href="http://www.research.att.com/%7Ebs/C++.html">Bjarne Stroustrup's C++
+Page</a></li>
+
+<li><a href="http://64.78.49.204/">
+Bruce Eckel's Thinking in C++, 2nd ed. Volume 2 Revision 4.0 (even better, get
+the book).</a></li>
+
+</ol>
+
+<p>You are also encouraged to take a look at the <a
+href="CodingStandards.html">LLVM Coding Standards</a> guide which focuses on how
+to write maintainable code more than where to put your curly braces.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="stl">Other useful references</a>
+</h3>
+
+<div>
+
+<ol>
+<li><a href="http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html">Using
+static and shared libraries across platforms</a></li>
+</ol>
+
+</div>
+
+</div>
+
+<!-- *********************************************************************** -->
+<h2>
+ <a name="apis">Important and useful LLVM APIs</a>
+</h2>
+<!-- *********************************************************************** -->
+
+<div>
+
+<p>Here we highlight some LLVM APIs that are generally useful and good to
+know about when writing transformations.</p>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="isa">The <tt>isa<></tt>, <tt>cast<></tt> and
+ <tt>dyn_cast<></tt> templates</a>
+</h3>
+
+<div>
+
+<p>The LLVM source-base makes extensive use of a custom form of RTTI.
+These templates have many similarities to the C++ <tt>dynamic_cast<></tt>
+operator, but they don't have some drawbacks (primarily stemming from
+the fact that <tt>dynamic_cast<></tt> only works on classes that
+have a v-table). Because they are used so often, you must know what they
+do and how they work. All of these templates are defined in the <a
+ href="/doxygen/Casting_8h-source.html"><tt>llvm/Support/Casting.h</tt></a>
+file (note that you very rarely have to include this file directly).</p>
+
+<dl>
+ <dt><tt>isa<></tt>: </dt>
+
+ <dd><p>The <tt>isa<></tt> operator works exactly like the Java
+ "<tt>instanceof</tt>" operator. It returns true or false depending on whether
+ a reference or pointer points to an instance of the specified class. This can
+ be very useful for constraint checking of various sorts (example below).</p>
+ </dd>
+
+ <dt><tt>cast<></tt>: </dt>
+
+ <dd><p>The <tt>cast<></tt> operator is a "checked cast" operation. It
+ converts a pointer or reference from a base class to a derived class, causing
+ an assertion failure if it is not really an instance of the right type. This
+ should be used in cases where you have some information that makes you believe
+ that something is of the right type. An example of the <tt>isa<></tt>
+ and <tt>cast<></tt> template is:</p>
+
+<div class="doc_code">
+<pre>
+static bool isLoopInvariant(const <a href="#Value">Value</a> *V, const Loop *L) {
+ if (isa<<a href="#Constant">Constant</a>>(V) || isa<<a href="#Argument">Argument</a>>(V) || isa<<a href="#GlobalValue">GlobalValue</a>>(V))
+ return true;
+
+ // <i>Otherwise, it must be an instruction...</i>
+ return !L->contains(cast<<a href="#Instruction">Instruction</a>>(V)->getParent());
+}
+</pre>
+</div>
+
+ <p>Note that you should <b>not</b> use an <tt>isa<></tt> test followed
+ by a <tt>cast<></tt>, for that use the <tt>dyn_cast<></tt>
+ operator.</p>
+
+ </dd>
+
+ <dt><tt>dyn_cast<></tt>:</dt>
+
+ <dd><p>The <tt>dyn_cast<></tt> operator is a "checking cast" operation.
+ It checks to see if the operand is of the specified type, and if so, returns a
+ pointer to it (this operator does not work with references). If the operand is
+ not of the correct type, a null pointer is returned. Thus, this works very
+ much like the <tt>dynamic_cast<></tt> operator in C++, and should be
+ used in the same circumstances. Typically, the <tt>dyn_cast<></tt>
+ operator is used in an <tt>if</tt> statement or some other flow control
+ statement like this:</p>
+
+<div class="doc_code">
+<pre>
+if (<a href="#AllocationInst">AllocationInst</a> *AI = dyn_cast<<a href="#AllocationInst">AllocationInst</a>>(Val)) {
+ // <i>...</i>
+}
+</pre>
+</div>
+
+ <p>This form of the <tt>if</tt> statement effectively combines together a call
+ to <tt>isa<></tt> and a call to <tt>cast<></tt> into one
+ statement, which is very convenient.</p>
+
+ <p>Note that the <tt>dyn_cast<></tt> operator, like C++'s
+ <tt>dynamic_cast<></tt> or Java's <tt>instanceof</tt> operator, can be
+ abused. In particular, you should not use big chained <tt>if/then/else</tt>
+ blocks to check for lots of different variants of classes. If you find
+ yourself wanting to do this, it is much cleaner and more efficient to use the
+ <tt>InstVisitor</tt> class to dispatch over the instruction type directly.</p>
+
+ </dd>
+
+ <dt><tt>cast_or_null<></tt>: </dt>
+
+ <dd><p>The <tt>cast_or_null<></tt> operator works just like the
+ <tt>cast<></tt> operator, except that it allows for a null pointer as an
+ argument (which it then propagates). This can sometimes be useful, allowing
+ you to combine several null checks into one.</p></dd>
+
+ <dt><tt>dyn_cast_or_null<></tt>: </dt>
+
+ <dd><p>The <tt>dyn_cast_or_null<></tt> operator works just like the
+ <tt>dyn_cast<></tt> operator, except that it allows for a null pointer
+ as an argument (which it then propagates). This can sometimes be useful,
+ allowing you to combine several null checks into one.</p></dd>
+
+</dl>
+
+<p>These five templates can be used with any classes, whether they have a
+v-table or not. If you want to add support for these templates, see the
+document <a href="HowToSetUpLLVMStyleRTTI.html">How to set up LLVM-style
+RTTI for your class hierarchy </a>.
+</p>
+
+</div>
+
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="string_apis">Passing strings (the <tt>StringRef</tt>
+and <tt>Twine</tt> classes)</a>
+</h3>
+
+<div>
+
+<p>Although LLVM generally does not do much string manipulation, we do have
+several important APIs which take strings. Two important examples are the
+Value class -- which has names for instructions, functions, etc. -- and the
+StringMap class which is used extensively in LLVM and Clang.</p>
+
+<p>These are generic classes, and they need to be able to accept strings which
+may have embedded null characters. Therefore, they cannot simply take
+a <tt>const char *</tt>, and taking a <tt>const std::string&</tt> requires
+clients to perform a heap allocation which is usually unnecessary. Instead,
+many LLVM APIs use a <tt>StringRef</tt> or a <tt>const Twine&</tt> for
+passing strings efficiently.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="StringRef">The <tt>StringRef</tt> class</a>
+</h4>
+
+<div>
+
+<p>The <tt>StringRef</tt> data type represents a reference to a constant string
+(a character array and a length) and supports the common operations available
+on <tt>std:string</tt>, but does not require heap allocation.</p>
+
+<p>It can be implicitly constructed using a C style null-terminated string,
+an <tt>std::string</tt>, or explicitly with a character pointer and length.
+For example, the <tt>StringRef</tt> find function is declared as:</p>
+
+<pre class="doc_code">
+ iterator find(StringRef Key);
+</pre>
+
+<p>and clients can call it using any one of:</p>
+
+<pre class="doc_code">
+ Map.find("foo"); <i>// Lookup "foo"</i>
+ Map.find(std::string("bar")); <i>// Lookup "bar"</i>
+ Map.find(StringRef("\0baz", 4)); <i>// Lookup "\0baz"</i>
+</pre>
+
+<p>Similarly, APIs which need to return a string may return a <tt>StringRef</tt>
+instance, which can be used directly or converted to an <tt>std::string</tt>
+using the <tt>str</tt> member function. See
+"<tt><a href="/doxygen/classllvm_1_1StringRef_8h-source.html">llvm/ADT/StringRef.h</a></tt>"
+for more information.</p>
+
+<p>You should rarely use the <tt>StringRef</tt> class directly, because it contains
+pointers to external memory it is not generally safe to store an instance of the
+class (unless you know that the external storage will not be freed). StringRef is
+small and pervasive enough in LLVM that it should always be passed by value.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="Twine">The <tt>Twine</tt> class</a>
+</h4>
+
+<div>
+
+<p>The <tt><a href="/doxygen/classllvm_1_1Twine.html">Twine</a></tt> class is an
+efficient way for APIs to accept concatenated strings. For example, a common
+LLVM paradigm is to name one instruction based on
+the name of another instruction with a suffix, for example:</p>
+
+<div class="doc_code">
+<pre>
+ New = CmpInst::Create(<i>...</i>, SO->getName() + ".cmp");
+</pre>
+</div>
+
+<p>The <tt>Twine</tt> class is effectively a lightweight
+<a href="http://en.wikipedia.org/wiki/Rope_(computer_science)">rope</a>
+which points to temporary (stack allocated) objects. Twines can be implicitly
+constructed as the result of the plus operator applied to strings (i.e., a C
+strings, an <tt>std::string</tt>, or a <tt>StringRef</tt>). The twine delays
+the actual concatenation of strings until it is actually required, at which
+point it can be efficiently rendered directly into a character array. This
+avoids unnecessary heap allocation involved in constructing the temporary
+results of string concatenation. See
+"<tt><a href="/doxygen/Twine_8h_source.html">llvm/ADT/Twine.h</a></tt>"
+and <a href="#dss_twine">here</a> for more information.</p>
+
+<p>As with a <tt>StringRef</tt>, <tt>Twine</tt> objects point to external memory
+and should almost never be stored or mentioned directly. They are intended
+solely for use when defining a function which should be able to efficiently
+accept concatenated strings.</p>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt> option</a>
+</h3>
+
+<div>
+
+<p>Often when working on your pass you will put a bunch of debugging printouts
+and other code into your pass. After you get it working, you want to remove
+it, but you may need it again in the future (to work out new bugs that you run
+across).</p>
+
+<p> Naturally, because of this, you don't want to delete the debug printouts,
+but you don't want them to always be noisy. A standard compromise is to comment
+them out, allowing you to enable them if you need them in the future.</p>
+
+<p>The "<tt><a href="/doxygen/Debug_8h-source.html">llvm/Support/Debug.h</a></tt>"
+file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
+this problem. Basically, you can put arbitrary code into the argument of the
+<tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
+tool) is run with the '<tt>-debug</tt>' command line argument:</p>
+
+<div class="doc_code">
+<pre>
+DEBUG(errs() << "I am here!\n");
+</pre>
+</div>
+
+<p>Then you can run your pass like this:</p>
+
+<div class="doc_code">
+<pre>
+$ opt < a.bc > /dev/null -mypass
+<i><no output></i>
+$ opt < a.bc > /dev/null -mypass -debug
+I am here!
+</pre>
+</div>
+
+<p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
+to not have to create "yet another" command line option for the debug output for
+your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
+so they do not cause a performance impact at all (for the same reason, they
+should also not contain side-effects!).</p>
+
+<p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
+enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
+"<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
+program hasn't been started yet, you can always just run it with
+<tt>-debug</tt>.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt> and
+ the <tt>-debug-only</tt> option</a>
+</h4>
+
+<div>
+
+<p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
+just turns on <b>too much</b> information (such as when working on the code
+generator). If you want to enable debug information with more fine-grained
+control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
+option as follows:</p>
+
+<div class="doc_code">
+<pre>
+#undef DEBUG_TYPE
+DEBUG(errs() << "No debug type\n");
+#define DEBUG_TYPE "foo"
+DEBUG(errs() << "'foo' debug type\n");
+#undef DEBUG_TYPE
+#define DEBUG_TYPE "bar"
+DEBUG(errs() << "'bar' debug type\n"));
+#undef DEBUG_TYPE
+#define DEBUG_TYPE ""
+DEBUG(errs() << "No debug type (2)\n");
+</pre>
+</div>
+
+<p>Then you can run your pass like this:</p>
+
+<div class="doc_code">
+<pre>
+$ opt < a.bc > /dev/null -mypass
+<i><no output></i>
+$ opt < a.bc > /dev/null -mypass -debug
+No debug type
+'foo' debug type
+'bar' debug type
+No debug type (2)
+$ opt < a.bc > /dev/null -mypass -debug-only=foo
+'foo' debug type
+$ opt < a.bc > /dev/null -mypass -debug-only=bar
+'bar' debug type
+</pre>
+</div>
+
+<p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
+a file, to specify the debug type for the entire module (if you do this before
+you <tt>#include "llvm/Support/Debug.h"</tt>, you don't have to insert the ugly
+<tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
+"bar", because there is no system in place to ensure that names do not
+conflict. If two different modules use the same string, they will all be turned
+on when the name is specified. This allows, for example, all debug information
+for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
+even if the source lives in multiple files.</p>
+
+<p>The <tt>DEBUG_WITH_TYPE</tt> macro is also available for situations where you
+would like to set <tt>DEBUG_TYPE</tt>, but only for one specific <tt>DEBUG</tt>
+statement. It takes an additional first parameter, which is the type to use. For
+example, the preceding example could be written as:</p>
+
+
+<div class="doc_code">
+<pre>
+DEBUG_WITH_TYPE("", errs() << "No debug type\n");
+DEBUG_WITH_TYPE("foo", errs() << "'foo' debug type\n");
+DEBUG_WITH_TYPE("bar", errs() << "'bar' debug type\n"));
+DEBUG_WITH_TYPE("", errs() << "No debug type (2)\n");
+</pre>
+</div>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="Statistic">The <tt>Statistic</tt> class & <tt>-stats</tt>
+ option</a>
+</h3>
+
+<div>
+
+<p>The "<tt><a
+href="/doxygen/Statistic_8h-source.html">llvm/ADT/Statistic.h</a></tt>" file
+provides a class named <tt>Statistic</tt> that is used as a unified way to
+keep track of what the LLVM compiler is doing and how effective various
+optimizations are. It is useful to see what optimizations are contributing to
+making a particular program run faster.</p>
+
+<p>Often you may run your pass on some big program, and you're interested to see
+how many times it makes a certain transformation. Although you can do this with
+hand inspection, or some ad-hoc method, this is a real pain and not very useful
+for big programs. Using the <tt>Statistic</tt> class makes it very easy to
+keep track of this information, and the calculated information is presented in a
+uniform manner with the rest of the passes being executed.</p>
+
+<p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
+it are as follows:</p>
+
+<ol>
+ <li><p>Define your statistic like this:</p>
+
+<div class="doc_code">
+<pre>
+#define <a href="#DEBUG_TYPE">DEBUG_TYPE</a> "mypassname" <i>// This goes before any #includes.</i>
+STATISTIC(NumXForms, "The # of times I did stuff");
+</pre>
+</div>
+
+ <p>The <tt>STATISTIC</tt> macro defines a static variable, whose name is
+ specified by the first argument. The pass name is taken from the DEBUG_TYPE
+ macro, and the description is taken from the second argument. The variable
+ defined ("NumXForms" in this case) acts like an unsigned integer.</p></li>
+
+ <li><p>Whenever you make a transformation, bump the counter:</p>
+
+<div class="doc_code">
+<pre>
+++NumXForms; // <i>I did stuff!</i>
+</pre>
+</div>
+
+ </li>
+ </ol>
+
+ <p>That's all you have to do. To get '<tt>opt</tt>' to print out the
+ statistics gathered, use the '<tt>-stats</tt>' option:</p>
+
+<div class="doc_code">
+<pre>
+$ opt -stats -mypassname < program.bc > /dev/null
+<i>... statistics output ...</i>
+</pre>
+</div>
+
+ <p> When running <tt>opt</tt> on a C file from the SPEC benchmark
+suite, it gives a report that looks like this:</p>
+
+<div class="doc_code">
+<pre>
+ 7646 bitcodewriter - Number of normal instructions
+ 725 bitcodewriter - Number of oversized instructions
+ 129996 bitcodewriter - Number of bitcode bytes written
+ 2817 raise - Number of insts DCEd or constprop'd
+ 3213 raise - Number of cast-of-self removed
+ 5046 raise - Number of expression trees converted
+ 75 raise - Number of other getelementptr's formed
+ 138 raise - Number of load/store peepholes
+ 42 deadtypeelim - Number of unused typenames removed from symtab
+ 392 funcresolve - Number of varargs functions resolved
+ 27 globaldce - Number of global variables removed
+ 2 adce - Number of basic blocks removed
+ 134 cee - Number of branches revectored
+ 49 cee - Number of setcc instruction eliminated
+ 532 gcse - Number of loads removed
+ 2919 gcse - Number of instructions removed
+ 86 indvars - Number of canonical indvars added
+ 87 indvars - Number of aux indvars removed
+ 25 instcombine - Number of dead inst eliminate
+ 434 instcombine - Number of insts combined
+ 248 licm - Number of load insts hoisted
+ 1298 licm - Number of insts hoisted to a loop pre-header
+ 3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
+ 75 mem2reg - Number of alloca's promoted
+ 1444 cfgsimplify - Number of blocks simplified
+</pre>
+</div>
+
+<p>Obviously, with so many optimizations, having a unified framework for this
+stuff is very nice. Making your pass fit well into the framework makes it more
+maintainable and useful.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="ViewGraph">Viewing graphs while debugging code</a>
+</h3>
+
+<div>
+
+<p>Several of the important data structures in LLVM are graphs: for example
+CFGs made out of LLVM <a href="#BasicBlock">BasicBlock</a>s, CFGs made out of
+LLVM <a href="CodeGenerator.html#machinebasicblock">MachineBasicBlock</a>s, and
+<a href="CodeGenerator.html#selectiondag_intro">Instruction Selection
+DAGs</a>. In many cases, while debugging various parts of the compiler, it is
+nice to instantly visualize these graphs.</p>
+
+<p>LLVM provides several callbacks that are available in a debug build to do
+exactly that. If you call the <tt>Function::viewCFG()</tt> method, for example,
+the current LLVM tool will pop up a window containing the CFG for the function
+where each basic block is a node in the graph, and each node contains the
+instructions in the block. Similarly, there also exists
+<tt>Function::viewCFGOnly()</tt> (does not include the instructions), the
+<tt>MachineFunction::viewCFG()</tt> and <tt>MachineFunction::viewCFGOnly()</tt>,
+and the <tt>SelectionDAG::viewGraph()</tt> methods. Within GDB, for example,
+you can usually use something like <tt>call DAG.viewGraph()</tt> to pop
+up a window. Alternatively, you can sprinkle calls to these functions in your
+code in places you want to debug.</p>
+
+<p>Getting this to work requires a small amount of configuration. On Unix
+systems with X11, install the <a href="http://www.graphviz.org">graphviz</a>
+toolkit, and make sure 'dot' and 'gv' are in your path. If you are running on
+Mac OS/X, download and install the Mac OS/X <a
+href="http://www.pixelglow.com/graphviz/">Graphviz program</a>, and add
+<tt>/Applications/Graphviz.app/Contents/MacOS/</tt> (or wherever you install
+it) to your path. Once in your system and path are set up, rerun the LLVM
+configure script and rebuild LLVM to enable this functionality.</p>
+
+<p><tt>SelectionDAG</tt> has been extended to make it easier to locate
+<i>interesting</i> nodes in large complex graphs. From gdb, if you
+<tt>call DAG.setGraphColor(<i>node</i>, "<i>color</i>")</tt>, then the
+next <tt>call DAG.viewGraph()</tt> would highlight the node in the
+specified color (choices of colors can be found at <a
+href="http://www.graphviz.org/doc/info/colors.html">colors</a>.) More
+complex node attributes can be provided with <tt>call
+DAG.setGraphAttrs(<i>node</i>, "<i>attributes</i>")</tt> (choices can be
+found at <a href="http://www.graphviz.org/doc/info/attrs.html">Graph
+Attributes</a>.) If you want to restart and clear all the current graph
+attributes, then you can <tt>call DAG.clearGraphAttrs()</tt>. </p>
+
+<p>Note that graph visualization features are compiled out of Release builds
+to reduce file size. This means that you need a Debug+Asserts or
+Release+Asserts build to use these features.</p>
+
+</div>
+
+</div>
+
+<!-- *********************************************************************** -->
+<h2>
+ <a name="datastructure">Picking the Right Data Structure for a Task</a>
+</h2>
+<!-- *********************************************************************** -->
+
+<div>
+
+<p>LLVM has a plethora of data structures in the <tt>llvm/ADT/</tt> directory,
+ and we commonly use STL data structures. This section describes the trade-offs
+ you should consider when you pick one.</p>
+
+<p>
+The first step is a choose your own adventure: do you want a sequential
+container, a set-like container, or a map-like container? The most important
+thing when choosing a container is the algorithmic properties of how you plan to
+access the container. Based on that, you should use:</p>
+
+<ul>
+<li>a <a href="#ds_map">map-like</a> container if you need efficient look-up
+ of an value based on another value. Map-like containers also support
+ efficient queries for containment (whether a key is in the map). Map-like
+ containers generally do not support efficient reverse mapping (values to
+ keys). If you need that, use two maps. Some map-like containers also
+ support efficient iteration through the keys in sorted order. Map-like
+ containers are the most expensive sort, only use them if you need one of
+ these capabilities.</li>
+
+<li>a <a href="#ds_set">set-like</a> container if you need to put a bunch of
+ stuff into a container that automatically eliminates duplicates. Some
+ set-like containers support efficient iteration through the elements in
+ sorted order. Set-like containers are more expensive than sequential
+ containers.
+</li>
+
+<li>a <a href="#ds_sequential">sequential</a> container provides
+ the most efficient way to add elements and keeps track of the order they are
+ added to the collection. They permit duplicates and support efficient
+ iteration, but do not support efficient look-up based on a key.
+</li>
+
+<li>a <a href="#ds_string">string</a> container is a specialized sequential
+ container or reference structure that is used for character or byte
+ arrays.</li>
+
+<li>a <a href="#ds_bit">bit</a> container provides an efficient way to store and
+ perform set operations on sets of numeric id's, while automatically
+ eliminating duplicates. Bit containers require a maximum of 1 bit for each
+ identifier you want to store.
+</li>
+</ul>
+
+<p>
+Once the proper category of container is determined, you can fine tune the
+memory use, constant factors, and cache behaviors of access by intelligently
+picking a member of the category. Note that constant factors and cache behavior
+can be a big deal. If you have a vector that usually only contains a few
+elements (but could contain many), for example, it's much better to use
+<a href="#dss_smallvector">SmallVector</a> than <a href="#dss_vector">vector</a>
+. Doing so avoids (relatively) expensive malloc/free calls, which dwarf the
+cost of adding the elements to the container. </p>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
+</h3>
+
+<div>
+There are a variety of sequential containers available for you, based on your
+needs. Pick the first in this section that will do what you want.
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_arrayref">llvm/ADT/ArrayRef.h</a>
+</h4>
+
+<div>
+<p>The llvm::ArrayRef class is the preferred class to use in an interface that
+ accepts a sequential list of elements in memory and just reads from them. By
+ taking an ArrayRef, the API can be passed a fixed size array, an std::vector,
+ an llvm::SmallVector and anything else that is contiguous in memory.
+</p>
+</div>
+
+
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_fixedarrays">Fixed Size Arrays</a>
+</h4>
+
+<div>
+<p>Fixed size arrays are very simple and very fast. They are good if you know
+exactly how many elements you have, or you have a (low) upper bound on how many
+you have.</p>
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_heaparrays">Heap Allocated Arrays</a>
+</h4>
+
+<div>
+<p>Heap allocated arrays (new[] + delete[]) are also simple. They are good if
+the number of elements is variable, if you know how many elements you will need
+before the array is allocated, and if the array is usually large (if not,
+consider a <a href="#dss_smallvector">SmallVector</a>). The cost of a heap
+allocated array is the cost of the new/delete (aka malloc/free). Also note that
+if you are allocating an array of a type with a constructor, the constructor and
+destructors will be run for every element in the array (re-sizable vectors only
+construct those elements actually used).</p>
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_tinyptrvector">"llvm/ADT/TinyPtrVector.h"</a>
+</h4>
+
+
+<div>
+<p><tt>TinyPtrVector<Type></tt> is a highly specialized collection class
+that is optimized to avoid allocation in the case when a vector has zero or one
+elements. It has two major restrictions: 1) it can only hold values of pointer
+type, and 2) it cannot hold a null pointer.</p>
+
+<p>Since this container is highly specialized, it is rarely used.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_smallvector">"llvm/ADT/SmallVector.h"</a>
+</h4>
+
+<div>
+<p><tt>SmallVector<Type, N></tt> is a simple class that looks and smells
+just like <tt>vector<Type></tt>:
+it supports efficient iteration, lays out elements in memory order (so you can
+do pointer arithmetic between elements), supports efficient push_back/pop_back
+operations, supports efficient random access to its elements, etc.</p>
+
+<p>The advantage of SmallVector is that it allocates space for
+some number of elements (N) <b>in the object itself</b>. Because of this, if
+the SmallVector is dynamically smaller than N, no malloc is performed. This can
+be a big win in cases where the malloc/free call is far more expensive than the
+code that fiddles around with the elements.</p>
+
+<p>This is good for vectors that are "usually small" (e.g. the number of
+predecessors/successors of a block is usually less than 8). On the other hand,
+this makes the size of the SmallVector itself large, so you don't want to
+allocate lots of them (doing so will waste a lot of space). As such,
+SmallVectors are most useful when on the stack.</p>
+
+<p>SmallVector also provides a nice portable and efficient replacement for
+<tt>alloca</tt>.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_vector"><vector></a>
+</h4>
+
+<div>
+<p>
+std::vector is well loved and respected. It is useful when SmallVector isn't:
+when the size of the vector is often large (thus the small optimization will
+rarely be a benefit) or if you will be allocating many instances of the vector
+itself (which would waste space for elements that aren't in the container).
+vector is also useful when interfacing with code that expects vectors :).
+</p>
+
+<p>One worthwhile note about std::vector: avoid code like this:</p>
+
+<div class="doc_code">
+<pre>
+for ( ... ) {
+ std::vector<foo> V;
+ // make use of V.
+}
+</pre>
+</div>
+
+<p>Instead, write this as:</p>
+
+<div class="doc_code">
+<pre>
+std::vector<foo> V;
+for ( ... ) {
+ // make use of V.
+ V.clear();
+}
+</pre>
+</div>
+
+<p>Doing so will save (at least) one heap allocation and free per iteration of
+the loop.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_deque"><deque></a>
+</h4>
+
+<div>
+<p>std::deque is, in some senses, a generalized version of std::vector. Like
+std::vector, it provides constant time random access and other similar
+properties, but it also provides efficient access to the front of the list. It
+does not guarantee continuity of elements within memory.</p>
+
+<p>In exchange for this extra flexibility, std::deque has significantly higher
+constant factor costs than std::vector. If possible, use std::vector or
+something cheaper.</p>
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_list"><list></a>
+</h4>
+
+<div>
+<p>std::list is an extremely inefficient class that is rarely useful.
+It performs a heap allocation for every element inserted into it, thus having an
+extremely high constant factor, particularly for small data types. std::list
+also only supports bidirectional iteration, not random access iteration.</p>
+
+<p>In exchange for this high cost, std::list supports efficient access to both
+ends of the list (like std::deque, but unlike std::vector or SmallVector). In
+addition, the iterator invalidation characteristics of std::list are stronger
+than that of a vector class: inserting or removing an element into the list does
+not invalidate iterator or pointers to other elements in the list.</p>
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_ilist">llvm/ADT/ilist.h</a>
+</h4>
+
+<div>
+<p><tt>ilist<T></tt> implements an 'intrusive' doubly-linked list. It is
+intrusive, because it requires the element to store and provide access to the
+prev/next pointers for the list.</p>
+
+<p><tt>ilist</tt> has the same drawbacks as <tt>std::list</tt>, and additionally
+requires an <tt>ilist_traits</tt> implementation for the element type, but it
+provides some novel characteristics. In particular, it can efficiently store
+polymorphic objects, the traits class is informed when an element is inserted or
+removed from the list, and <tt>ilist</tt>s are guaranteed to support a
+constant-time splice operation.</p>
+
+<p>These properties are exactly what we want for things like
+<tt>Instruction</tt>s and basic blocks, which is why these are implemented with
+<tt>ilist</tt>s.</p>
+
+Related classes of interest are explained in the following subsections:
+ <ul>
+ <li><a href="#dss_ilist_traits">ilist_traits</a></li>
+ <li><a href="#dss_iplist">iplist</a></li>
+ <li><a href="#dss_ilist_node">llvm/ADT/ilist_node.h</a></li>
+ <li><a href="#dss_ilist_sentinel">Sentinels</a></li>
+ </ul>
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_packedvector">llvm/ADT/PackedVector.h</a>
+</h4>
+
+<div>
+<p>
+Useful for storing a vector of values using only a few number of bits for each
+value. Apart from the standard operations of a vector-like container, it can
+also perform an 'or' set operation.
+</p>
+
+<p>For example:</p>
+
+<div class="doc_code">
+<pre>
+enum State {
+ None = 0x0,
+ FirstCondition = 0x1,
+ SecondCondition = 0x2,
+ Both = 0x3
+};
+
+State get() {
+ PackedVector<State, 2> Vec1;
+ Vec1.push_back(FirstCondition);
+
+ PackedVector<State, 2> Vec2;
+ Vec2.push_back(SecondCondition);
+
+ Vec1 |= Vec2;
+ return Vec1[0]; // returns 'Both'.
+}
+</pre>
+</div>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_ilist_traits">ilist_traits</a>
+</h4>
+
+<div>
+<p><tt>ilist_traits<T></tt> is <tt>ilist<T></tt>'s customization
+mechanism. <tt>iplist<T></tt> (and consequently <tt>ilist<T></tt>)
+publicly derive from this traits class.</p>
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_iplist">iplist</a>
+</h4>
+
+<div>
+<p><tt>iplist<T></tt> is <tt>ilist<T></tt>'s base and as such
+supports a slightly narrower interface. Notably, inserters from
+<tt>T&</tt> are absent.</p>
+
+<p><tt>ilist_traits<T></tt> is a public base of this class and can be
+used for a wide variety of customizations.</p>
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_ilist_node">llvm/ADT/ilist_node.h</a>
+</h4>
+
+<div>
+<p><tt>ilist_node<T></tt> implements a the forward and backward links
+that are expected by the <tt>ilist<T></tt> (and analogous containers)
+in the default manner.</p>
+
+<p><tt>ilist_node<T></tt>s are meant to be embedded in the node type
+<tt>T</tt>, usually <tt>T</tt> publicly derives from
+<tt>ilist_node<T></tt>.</p>
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_ilist_sentinel">Sentinels</a>
+</h4>
+
+<div>
+<p><tt>ilist</tt>s have another specialty that must be considered. To be a good
+citizen in the C++ ecosystem, it needs to support the standard container
+operations, such as <tt>begin</tt> and <tt>end</tt> iterators, etc. Also, the
+<tt>operator--</tt> must work correctly on the <tt>end</tt> iterator in the
+case of non-empty <tt>ilist</tt>s.</p>
+
+<p>The only sensible solution to this problem is to allocate a so-called
+<i>sentinel</i> along with the intrusive list, which serves as the <tt>end</tt>
+iterator, providing the back-link to the last element. However conforming to the
+C++ convention it is illegal to <tt>operator++</tt> beyond the sentinel and it
+also must not be dereferenced.</p>
+
+<p>These constraints allow for some implementation freedom to the <tt>ilist</tt>
+how to allocate and store the sentinel. The corresponding policy is dictated
+by <tt>ilist_traits<T></tt>. By default a <tt>T</tt> gets heap-allocated
+whenever the need for a sentinel arises.</p>
+
+<p>While the default policy is sufficient in most cases, it may break down when
+<tt>T</tt> does not provide a default constructor. Also, in the case of many
+instances of <tt>ilist</tt>s, the memory overhead of the associated sentinels
+is wasted. To alleviate the situation with numerous and voluminous
+<tt>T</tt>-sentinels, sometimes a trick is employed, leading to <i>ghostly
+sentinels</i>.</p>
+
+<p>Ghostly sentinels are obtained by specially-crafted <tt>ilist_traits<T></tt>
+which superpose the sentinel with the <tt>ilist</tt> instance in memory. Pointer
+arithmetic is used to obtain the sentinel, which is relative to the
+<tt>ilist</tt>'s <tt>this</tt> pointer. The <tt>ilist</tt> is augmented by an
+extra pointer, which serves as the back-link of the sentinel. This is the only
+field in the ghostly sentinel which can be legally accessed.</p>
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_other">Other Sequential Container options</a>
+</h4>
+
+<div>
+<p>Other STL containers are available, such as std::string.</p>
+
+<p>There are also various STL adapter classes such as std::queue,
+std::priority_queue, std::stack, etc. These provide simplified access to an
+underlying container but don't affect the cost of the container itself.</p>
+
+</div>
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="ds_string">String-like containers</a>
+</h3>
+
+<div>
+
+<p>
+There are a variety of ways to pass around and use strings in C and C++, and
+LLVM adds a few new options to choose from. Pick the first option on this list
+that will do what you need, they are ordered according to their relative cost.
+</p>
+<p>
+Note that is is generally preferred to <em>not</em> pass strings around as
+"<tt>const char*</tt>"'s. These have a number of problems, including the fact
+that they cannot represent embedded nul ("\0") characters, and do not have a
+length available efficiently. The general replacement for '<tt>const
+char*</tt>' is StringRef.
+</p>
+
+<p>For more information on choosing string containers for APIs, please see
+<a href="#string_apis">Passing strings</a>.</p>
+
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_stringref">llvm/ADT/StringRef.h</a>
+</h4>
+
+<div>
+<p>
+The StringRef class is a simple value class that contains a pointer to a
+character and a length, and is quite related to the <a
+href="#dss_arrayref">ArrayRef</a> class (but specialized for arrays of
+characters). Because StringRef carries a length with it, it safely handles
+strings with embedded nul characters in it, getting the length does not require
+a strlen call, and it even has very convenient APIs for slicing and dicing the
+character range that it represents.
+</p>
+
+<p>
+StringRef is ideal for passing simple strings around that are known to be live,
+either because they are C string literals, std::string, a C array, or a
+SmallVector. Each of these cases has an efficient implicit conversion to
+StringRef, which doesn't result in a dynamic strlen being executed.
+</p>
+
+<p>StringRef has a few major limitations which make more powerful string
+containers useful:</p>
+
+<ol>
+<li>You cannot directly convert a StringRef to a 'const char*' because there is
+no way to add a trailing nul (unlike the .c_str() method on various stronger
+classes).</li>
+
+
+<li>StringRef doesn't own or keep alive the underlying string bytes.
+As such it can easily lead to dangling pointers, and is not suitable for
+embedding in datastructures in most cases (instead, use an std::string or
+something like that).</li>
+
+<li>For the same reason, StringRef cannot be used as the return value of a
+method if the method "computes" the result string. Instead, use
+std::string.</li>
+
+<li>StringRef's do not allow you to mutate the pointed-to string bytes and it
+doesn't allow you to insert or remove bytes from the range. For editing
+operations like this, it interoperates with the <a
+href="#dss_twine">Twine</a> class.</li>
+</ol>
+
+<p>Because of its strengths and limitations, it is very common for a function to
+take a StringRef and for a method on an object to return a StringRef that
+points into some string that it owns.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_twine">llvm/ADT/Twine.h</a>
+</h4>
+
+<div>
+ <p>
+ The Twine class is used as an intermediary datatype for APIs that want to take
+ a string that can be constructed inline with a series of concatenations.
+ Twine works by forming recursive instances of the Twine datatype (a simple
+ value object) on the stack as temporary objects, linking them together into a
+ tree which is then linearized when the Twine is consumed. Twine is only safe
+ to use as the argument to a function, and should always be a const reference,
+ e.g.:
+ </p>
+
+ <pre>
+ void foo(const Twine &T);
+ ...
+ StringRef X = ...
+ unsigned i = ...
+ foo(X + "." + Twine(i));
+ </pre>
+
+ <p>This example forms a string like "blarg.42" by concatenating the values
+ together, and does not form intermediate strings containing "blarg" or
+ "blarg.".
+ </p>
+
+ <p>Because Twine is constructed with temporary objects on the stack, and
+ because these instances are destroyed at the end of the current statement,
+ it is an inherently dangerous API. For example, this simple variant contains
+ undefined behavior and will probably crash:</p>
+
+ <pre>
+ void foo(const Twine &T);
+ ...
+ StringRef X = ...
+ unsigned i = ...
+ const Twine &Tmp = X + "." + Twine(i);
+ foo(Tmp);
+ </pre>
+
+ <p>... because the temporaries are destroyed before the call. That said,
+ Twine's are much more efficient than intermediate std::string temporaries, and
+ they work really well with StringRef. Just be aware of their limitations.</p>
+
+</div>
+
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_smallstring">llvm/ADT/SmallString.h</a>
+</h4>
+
+<div>
+
+<p>SmallString is a subclass of <a href="#dss_smallvector">SmallVector</a> that
+adds some convenience APIs like += that takes StringRef's. SmallString avoids
+allocating memory in the case when the preallocated space is enough to hold its
+data, and it calls back to general heap allocation when required. Since it owns
+its data, it is very safe to use and supports full mutation of the string.</p>
+
+<p>Like SmallVector's, the big downside to SmallString is their sizeof. While
+they are optimized for small strings, they themselves are not particularly
+small. This means that they work great for temporary scratch buffers on the
+stack, but should not generally be put into the heap: it is very rare to
+see a SmallString as the member of a frequently-allocated heap data structure
+or returned by-value.
+</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_stdstring">std::string</a>
+</h4>
+
+<div>
+
+ <p>The standard C++ std::string class is a very general class that (like
+ SmallString) owns its underlying data. sizeof(std::string) is very reasonable
+ so it can be embedded into heap data structures and returned by-value.
+ On the other hand, std::string is highly inefficient for inline editing (e.g.
+ concatenating a bunch of stuff together) and because it is provided by the
+ standard library, its performance characteristics depend a lot of the host
+ standard library (e.g. libc++ and MSVC provide a highly optimized string
+ class, GCC contains a really slow implementation).
+ </p>
+
+ <p>The major disadvantage of std::string is that almost every operation that
+ makes them larger can allocate memory, which is slow. As such, it is better
+ to use SmallVector or Twine as a scratch buffer, but then use std::string to
+ persist the result.</p>
+
+
+</div>
+
+<!-- end of strings -->
+</div>
+
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
+</h3>
+
+<div>
+
+<p>Set-like containers are useful when you need to canonicalize multiple values
+into a single representation. There are several different choices for how to do
+this, providing various trade-offs.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_sortedvectorset">A sorted 'vector'</a>
+</h4>
+
+<div>
+
+<p>If you intend to insert a lot of elements, then do a lot of queries, a
+great approach is to use a vector (or other sequential container) with
+std::sort+std::unique to remove duplicates. This approach works really well if
+your usage pattern has these two distinct phases (insert then query), and can be
+coupled with a good choice of <a href="#ds_sequential">sequential container</a>.
+</p>
+
+<p>
+This combination provides the several nice properties: the result data is
+contiguous in memory (good for cache locality), has few allocations, is easy to
+address (iterators in the final vector are just indices or pointers), and can be
+efficiently queried with a standard binary or radix search.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_smallset">"llvm/ADT/SmallSet.h"</a>
+</h4>
+
+<div>
+
+<p>If you have a set-like data structure that is usually small and whose elements
+are reasonably small, a <tt>SmallSet<Type, N></tt> is a good choice. This set
+has space for N elements in place (thus, if the set is dynamically smaller than
+N, no malloc traffic is required) and accesses them with a simple linear search.
+When the set grows beyond 'N' elements, it allocates a more expensive representation that
+guarantees efficient access (for most types, it falls back to std::set, but for
+pointers it uses something far better, <a
+href="#dss_smallptrset">SmallPtrSet</a>).</p>
+
+<p>The magic of this class is that it handles small sets extremely efficiently,
+but gracefully handles extremely large sets without loss of efficiency. The
+drawback is that the interface is quite small: it supports insertion, queries
+and erasing, but does not support iteration.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a>
+</h4>
+
+<div>
+
+<p>SmallPtrSet has all the advantages of <tt>SmallSet</tt> (and a <tt>SmallSet</tt> of pointers is
+transparently implemented with a <tt>SmallPtrSet</tt>), but also supports iterators. If
+more than 'N' insertions are performed, a single quadratically
+probed hash table is allocated and grows as needed, providing extremely
+efficient access (constant time insertion/deleting/queries with low constant
+factors) and is very stingy with malloc traffic.</p>
+
+<p>Note that, unlike <tt>std::set</tt>, the iterators of <tt>SmallPtrSet</tt> are invalidated
+whenever an insertion occurs. Also, the values visited by the iterators are not
+visited in sorted order.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_denseset">"llvm/ADT/DenseSet.h"</a>
+</h4>
+
+<div>
+
+<p>
+DenseSet is a simple quadratically probed hash table. It excels at supporting
+small values: it uses a single allocation to hold all of the pairs that
+are currently inserted in the set. DenseSet is a great way to unique small
+values that are not simple pointers (use <a
+href="#dss_smallptrset">SmallPtrSet</a> for pointers). Note that DenseSet has
+the same requirements for the value type that <a
+href="#dss_densemap">DenseMap</a> has.
+</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_sparseset">"llvm/ADT/SparseSet.h"</a>
+</h4>
+
+<div>
+
+<p>SparseSet holds a small number of objects identified by unsigned keys of
+moderate size. It uses a lot of memory, but provides operations that are
+almost as fast as a vector. Typical keys are physical registers, virtual
+registers, or numbered basic blocks.</p>
+
+<p>SparseSet is useful for algorithms that need very fast clear/find/insert/erase
+and fast iteration over small sets. It is not intended for building composite
+data structures.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a>
+</h4>
+
+<div>
+
+<p>
+FoldingSet is an aggregate class that is really good at uniquing
+expensive-to-create or polymorphic objects. It is a combination of a chained
+hash table with intrusive links (uniqued objects are required to inherit from
+FoldingSetNode) that uses <a href="#dss_smallvector">SmallVector</a> as part of
+its ID process.</p>
+
+<p>Consider a case where you want to implement a "getOrCreateFoo" method for
+a complex object (for example, a node in the code generator). The client has a
+description of *what* it wants to generate (it knows the opcode and all the
+operands), but we don't want to 'new' a node, then try inserting it into a set
+only to find out it already exists, at which point we would have to delete it
+and return the node that already exists.
+</p>
+
+<p>To support this style of client, FoldingSet perform a query with a
+FoldingSetNodeID (which wraps SmallVector) that can be used to describe the
+element that we want to query for. The query either returns the element
+matching the ID or it returns an opaque ID that indicates where insertion should
+take place. Construction of the ID usually does not require heap traffic.</p>
+
+<p>Because FoldingSet uses intrusive links, it can support polymorphic objects
+in the set (for example, you can have SDNode instances mixed with LoadSDNodes).
+Because the elements are individually allocated, pointers to the elements are
+stable: inserting or removing elements does not invalidate any pointers to other
+elements.
+</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_set"><set></a>
+</h4>
+
+<div>
+
+<p><tt>std::set</tt> is a reasonable all-around set class, which is decent at
+many things but great at nothing. std::set allocates memory for each element
+inserted (thus it is very malloc intensive) and typically stores three pointers
+per element in the set (thus adding a large amount of per-element space
+overhead). It offers guaranteed log(n) performance, which is not particularly
+fast from a complexity standpoint (particularly if the elements of the set are
+expensive to compare, like strings), and has extremely high constant factors for
+lookup, insertion and removal.</p>
+
+<p>The advantages of std::set are that its iterators are stable (deleting or
+inserting an element from the set does not affect iterators or pointers to other
+elements) and that iteration over the set is guaranteed to be in sorted order.
+If the elements in the set are large, then the relative overhead of the pointers
+and malloc traffic is not a big deal, but if the elements of the set are small,
+std::set is almost never a good choice.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_setvector">"llvm/ADT/SetVector.h"</a>
+</h4>
+
+<div>
+<p>LLVM's SetVector<Type> is an adapter class that combines your choice of
+a set-like container along with a <a href="#ds_sequential">Sequential
+Container</a>. The important property
+that this provides is efficient insertion with uniquing (duplicate elements are
+ignored) with iteration support. It implements this by inserting elements into
+both a set-like container and the sequential container, using the set-like
+container for uniquing and the sequential container for iteration.
+</p>
+
+<p>The difference between SetVector and other sets is that the order of
+iteration is guaranteed to match the order of insertion into the SetVector.
+This property is really important for things like sets of pointers. Because
+pointer values are non-deterministic (e.g. vary across runs of the program on
+different machines), iterating over the pointers in the set will
+not be in a well-defined order.</p>
+
+<p>
+The drawback of SetVector is that it requires twice as much space as a normal
+set and has the sum of constant factors from the set-like container and the
+sequential container that it uses. Use it *only* if you need to iterate over
+the elements in a deterministic order. SetVector is also expensive to delete
+elements out of (linear time), unless you use it's "pop_back" method, which is
+faster.
+</p>
+
+<p><tt>SetVector</tt> is an adapter class that defaults to
+ using <tt>std::vector</tt> and a size 16 <tt>SmallSet</tt> for the underlying
+ containers, so it is quite expensive. However,
+ <tt>"llvm/ADT/SetVector.h"</tt> also provides a <tt>SmallSetVector</tt>
+ class, which defaults to using a <tt>SmallVector</tt> and <tt>SmallSet</tt>
+ of a specified size. If you use this, and if your sets are dynamically
+ smaller than <tt>N</tt>, you will save a lot of heap traffic.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_uniquevector">"llvm/ADT/UniqueVector.h"</a>
+</h4>
+
+<div>
+
+<p>
+UniqueVector is similar to <a href="#dss_setvector">SetVector</a>, but it
+retains a unique ID for each element inserted into the set. It internally
+contains a map and a vector, and it assigns a unique ID for each value inserted
+into the set.</p>
+
+<p>UniqueVector is very expensive: its cost is the sum of the cost of
+maintaining both the map and vector, it has high complexity, high constant
+factors, and produces a lot of malloc traffic. It should be avoided.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_immutableset">"llvm/ADT/ImmutableSet.h"</a>
+</h4>
+
+<div>
+
+<p>
+ImmutableSet is an immutable (functional) set implementation based on an AVL
+tree.
+Adding or removing elements is done through a Factory object and results in the
+creation of a new ImmutableSet object.
+If an ImmutableSet already exists with the given contents, then the existing one
+is returned; equality is compared with a FoldingSetNodeID.
+The time and space complexity of add or remove operations is logarithmic in the
+size of the original set.
+
+<p>
+There is no method for returning an element of the set, you can only check for
+membership.
+
+</div>
+
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_otherset">Other Set-Like Container Options</a>
+</h4>
+
+<div>
+
+<p>
+The STL provides several other options, such as std::multiset and the various
+"hash_set" like containers (whether from C++ TR1 or from the SGI library). We
+never use hash_set and unordered_set because they are generally very expensive
+(each insertion requires a malloc) and very non-portable.
+</p>
+
+<p>std::multiset is useful if you're not interested in elimination of
+duplicates, but has all the drawbacks of std::set. A sorted vector (where you
+don't delete duplicate entries) or some other approach is almost always
+better.</p>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
+</h3>
+
+<div>
+Map-like containers are useful when you want to associate data to a key. As
+usual, there are a lot of different ways to do this. :)
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_sortedvectormap">A sorted 'vector'</a>
+</h4>
+
+<div>
+
+<p>
+If your usage pattern follows a strict insert-then-query approach, you can
+trivially use the same approach as <a href="#dss_sortedvectorset">sorted vectors
+for set-like containers</a>. The only difference is that your query function
+(which uses std::lower_bound to get efficient log(n) lookup) should only compare
+the key, not both the key and value. This yields the same advantages as sorted
+vectors for sets.
+</p>
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_stringmap">"llvm/ADT/StringMap.h"</a>
+</h4>
+
+<div>
+
+<p>
+Strings are commonly used as keys in maps, and they are difficult to support
+efficiently: they are variable length, inefficient to hash and compare when
+long, expensive to copy, etc. StringMap is a specialized container designed to
+cope with these issues. It supports mapping an arbitrary range of bytes to an
+arbitrary other object.</p>
+
+<p>The StringMap implementation uses a quadratically-probed hash table, where
+the buckets store a pointer to the heap allocated entries (and some other
+stuff). The entries in the map must be heap allocated because the strings are
+variable length. The string data (key) and the element object (value) are
+stored in the same allocation with the string data immediately after the element
+object. This container guarantees the "<tt>(char*)(&Value+1)</tt>" points
+to the key string for a value.</p>
+
+<p>The StringMap is very fast for several reasons: quadratic probing is very
+cache efficient for lookups, the hash value of strings in buckets is not
+recomputed when looking up an element, StringMap rarely has to touch the
+memory for unrelated objects when looking up a value (even when hash collisions
+happen), hash table growth does not recompute the hash values for strings
+already in the table, and each pair in the map is store in a single allocation
+(the string data is stored in the same allocation as the Value of a pair).</p>
+
+<p>StringMap also provides query methods that take byte ranges, so it only ever
+copies a string if a value is inserted into the table.</p>
+
+<p>StringMap iteratation order, however, is not guaranteed to be deterministic,
+so any uses which require that should instead use a std::map.</p>
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_indexedmap">"llvm/ADT/IndexedMap.h"</a>
+</h4>
+
+<div>
+<p>
+IndexedMap is a specialized container for mapping small dense integers (or
+values that can be mapped to small dense integers) to some other type. It is
+internally implemented as a vector with a mapping function that maps the keys to
+the dense integer range.
+</p>
+
+<p>
+This is useful for cases like virtual registers in the LLVM code generator: they
+have a dense mapping that is offset by a compile-time constant (the first
+virtual register ID).</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_densemap">"llvm/ADT/DenseMap.h"</a>
+</h4>
+
+<div>
+
+<p>
+DenseMap is a simple quadratically probed hash table. It excels at supporting
+small keys and values: it uses a single allocation to hold all of the pairs that
+are currently inserted in the map. DenseMap is a great way to map pointers to
+pointers, or map other small types to each other.
+</p>
+
+<p>
+There are several aspects of DenseMap that you should be aware of, however. The
+iterators in a DenseMap are invalidated whenever an insertion occurs, unlike
+map. Also, because DenseMap allocates space for a large number of key/value
+pairs (it starts with 64 by default), it will waste a lot of space if your keys
+or values are large. Finally, you must implement a partial specialization of
+DenseMapInfo for the key that you want, if it isn't already supported. This
+is required to tell DenseMap about two special marker values (which can never be
+inserted into the map) that it needs internally.</p>
+
+<p>
+DenseMap's find_as() method supports lookup operations using an alternate key
+type. This is useful in cases where the normal key type is expensive to
+construct, but cheap to compare against. The DenseMapInfo is responsible for
+defining the appropriate comparison and hashing methods for each alternate
+key type used.
+</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_valuemap">"llvm/ADT/ValueMap.h"</a>
+</h4>
+
+<div>
+
+<p>
+ValueMap is a wrapper around a <a href="#dss_densemap">DenseMap</a> mapping
+Value*s (or subclasses) to another type. When a Value is deleted or RAUW'ed,
+ValueMap will update itself so the new version of the key is mapped to the same
+value, just as if the key were a WeakVH. You can configure exactly how this
+happens, and what else happens on these two events, by passing
+a <code>Config</code> parameter to the ValueMap template.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_intervalmap">"llvm/ADT/IntervalMap.h"</a>
+</h4>
+
+<div>
+
+<p> IntervalMap is a compact map for small keys and values. It maps key
+intervals instead of single keys, and it will automatically coalesce adjacent
+intervals. When then map only contains a few intervals, they are stored in the
+map object itself to avoid allocations.</p>
+
+<p> The IntervalMap iterators are quite big, so they should not be passed around
+as STL iterators. The heavyweight iterators allow a smaller data structure.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_map"><map></a>
+</h4>
+
+<div>
+
+<p>
+std::map has similar characteristics to <a href="#dss_set">std::set</a>: it uses
+a single allocation per pair inserted into the map, it offers log(n) lookup with
+an extremely large constant factor, imposes a space penalty of 3 pointers per
+pair in the map, etc.</p>
+
+<p>std::map is most useful when your keys or values are very large, if you need
+to iterate over the collection in sorted order, or if you need stable iterators
+into the map (i.e. they don't get invalidated if an insertion or deletion of
+another element takes place).</p>
+
+</div>
+
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_mapvector">"llvm/ADT/MapVector.h"</a>
+</h4>
+<div>
+
+<p> MapVector<KeyT,ValueT> provides a subset of the DenseMap interface.
+ The main difference is that the iteration order is guaranteed to be
+ the insertion order, making it an easy (but somewhat expensive) solution
+ for non-deterministic iteration over maps of pointers. </p>
+
+<p> It is implemented by mapping from key to an index in a vector of key,value
+ pairs. This provides fast lookup and iteration, but has two main drawbacks:
+ The key is stored twice and it doesn't support removing elements. </p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_inteqclasses">"llvm/ADT/IntEqClasses.h"</a>
+</h4>
+
+<div>
+
+<p>IntEqClasses provides a compact representation of equivalence classes of
+small integers. Initially, each integer in the range 0..n-1 has its own
+equivalence class. Classes can be joined by passing two class representatives to
+the join(a, b) method. Two integers are in the same class when findLeader()
+returns the same representative.</p>
+
+<p>Once all equivalence classes are formed, the map can be compressed so each
+integer 0..n-1 maps to an equivalence class number in the range 0..m-1, where m
+is the total number of equivalence classes. The map must be uncompressed before
+it can be edited again.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_immutablemap">"llvm/ADT/ImmutableMap.h"</a>
+</h4>
+
+<div>
+
+<p>
+ImmutableMap is an immutable (functional) map implementation based on an AVL
+tree.
+Adding or removing elements is done through a Factory object and results in the
+creation of a new ImmutableMap object.
+If an ImmutableMap already exists with the given key set, then the existing one
+is returned; equality is compared with a FoldingSetNodeID.
+The time and space complexity of add or remove operations is logarithmic in the
+size of the original map.
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_othermap">Other Map-Like Container Options</a>
+</h4>
+
+<div>
+
+<p>
+The STL provides several other options, such as std::multimap and the various
+"hash_map" like containers (whether from C++ TR1 or from the SGI library). We
+never use hash_set and unordered_set because they are generally very expensive
+(each insertion requires a malloc) and very non-portable.</p>
+
+<p>std::multimap is useful if you want to map a key to multiple values, but has
+all the drawbacks of std::map. A sorted vector or some other approach is almost
+always better.</p>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="ds_bit">Bit storage containers (BitVector, SparseBitVector)</a>
+</h3>
+
+<div>
+<p>Unlike the other containers, there are only two bit storage containers, and
+choosing when to use each is relatively straightforward.</p>
+
+<p>One additional option is
+<tt>std::vector<bool></tt>: we discourage its use for two reasons 1) the
+implementation in many common compilers (e.g. commonly available versions of
+GCC) is extremely inefficient and 2) the C++ standards committee is likely to
+deprecate this container and/or change it significantly somehow. In any case,
+please don't use it.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_bitvector">BitVector</a>
+</h4>
+
+<div>
+<p> The BitVector container provides a dynamic size set of bits for manipulation.
+It supports individual bit setting/testing, as well as set operations. The set
+operations take time O(size of bitvector), but operations are performed one word
+at a time, instead of one bit at a time. This makes the BitVector very fast for
+set operations compared to other containers. Use the BitVector when you expect
+the number of set bits to be high (IE a dense set).
+</p>
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_smallbitvector">SmallBitVector</a>
+</h4>
+
+<div>
+<p> The SmallBitVector container provides the same interface as BitVector, but
+it is optimized for the case where only a small number of bits, less than
+25 or so, are needed. It also transparently supports larger bit counts, but
+slightly less efficiently than a plain BitVector, so SmallBitVector should
+only be used when larger counts are rare.
+</p>
+
+<p>
+At this time, SmallBitVector does not support set operations (and, or, xor),
+and its operator[] does not provide an assignable lvalue.
+</p>
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="dss_sparsebitvector">SparseBitVector</a>
+</h4>
+
+<div>
+<p> The SparseBitVector container is much like BitVector, with one major
+difference: Only the bits that are set, are stored. This makes the
+SparseBitVector much more space efficient than BitVector when the set is sparse,
+as well as making set operations O(number of set bits) instead of O(size of
+universe). The downside to the SparseBitVector is that setting and testing of random bits is O(N), and on large SparseBitVectors, this can be slower than BitVector. In our implementation, setting or testing bits in sorted order
+(either forwards or reverse) is O(1) worst case. Testing and setting bits within 128 bits (depends on size) of the current bit is also O(1). As a general statement, testing/setting bits in a SparseBitVector is O(distance away from last set bit).
+</p>
+</div>
+
+</div>
+
+</div>
+
+<!-- *********************************************************************** -->
+<h2>
+ <a name="common">Helpful Hints for Common Operations</a>
+</h2>
+<!-- *********************************************************************** -->
+
+<div>
+
+<p>This section describes how to perform some very simple transformations of
+LLVM code. This is meant to give examples of common idioms used, showing the
+practical side of LLVM transformations. <p> Because this is a "how-to" section,
+you should also read about the main classes that you will be working with. The
+<a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
+and descriptions of the main classes that you should know about.</p>
+
+<!-- NOTE: this section should be heavy on example code -->
+<!-- ======================================================================= -->
+<h3>
+ <a name="inspection">Basic Inspection and Traversal Routines</a>
+</h3>
+
+<div>
+
+<p>The LLVM compiler infrastructure have many different data structures that may
+be traversed. Following the example of the C++ standard template library, the
+techniques used to traverse these various data structures are all basically the
+same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
+method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
+function returns an iterator pointing to one past the last valid element of the
+sequence, and there is some <tt>XXXiterator</tt> data type that is common
+between the two operations.</p>
+
+<p>Because the pattern for iteration is common across many different aspects of
+the program representation, the standard template library algorithms may be used
+on them, and it is easier to remember how to iterate. First we show a few common
+examples of the data structures that need to be traversed. Other data
+structures are traversed in very similar ways.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="iterate_function">Iterating over the </a><a
+ href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
+ href="#Function"><tt>Function</tt></a>
+</h4>
+
+<div>
+
+<p>It's quite common to have a <tt>Function</tt> instance that you'd like to
+transform in some way; in particular, you'd like to manipulate its
+<tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
+the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
+an example that prints the name of a <tt>BasicBlock</tt> and the number of
+<tt>Instruction</tt>s it contains:</p>
+
+<div class="doc_code">
+<pre>
+// <i>func is a pointer to a Function instance</i>
+for (Function::iterator i = func->begin(), e = func->end(); i != e; ++i)
+ // <i>Print out the name of the basic block if it has one, and then the</i>
+ // <i>number of instructions that it contains</i>
+ errs() << "Basic block (name=" << i->getName() << ") has "
+ << i->size() << " instructions.\n";
+</pre>
+</div>
+
+<p>Note that i can be used as if it were a pointer for the purposes of
+invoking member functions of the <tt>Instruction</tt> class. This is
+because the indirection operator is overloaded for the iterator
+classes. In the above code, the expression <tt>i->size()</tt> is
+exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="iterate_basicblock">Iterating over the </a><a
+ href="#Instruction"><tt>Instruction</tt></a>s in a <a
+ href="#BasicBlock"><tt>BasicBlock</tt></a>
+</h4>
+
+<div>
+
+<p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
+easy to iterate over the individual instructions that make up
+<tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
+a <tt>BasicBlock</tt>:</p>
+
+<div class="doc_code">
+<pre>
+// <i>blk is a pointer to a BasicBlock instance</i>
+for (BasicBlock::iterator i = blk->begin(), e = blk->end(); i != e; ++i)
+ // <i>The next statement works since operator<<(ostream&,...)</i>
+ // <i>is overloaded for Instruction&</i>
+ errs() << *i << "\n";
+</pre>
+</div>
+
+<p>However, this isn't really the best way to print out the contents of a
+<tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
+anything you'll care about, you could have just invoked the print routine on the
+basic block itself: <tt>errs() << *blk << "\n";</tt>.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="iterate_institer">Iterating over the </a><a
+ href="#Instruction"><tt>Instruction</tt></a>s in a <a
+ href="#Function"><tt>Function</tt></a>
+</h4>
+
+<div>
+
+<p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
+<tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
+<tt>InstIterator</tt> should be used instead. You'll need to include <a
+href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
+and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
+small example that shows how to dump all instructions in a function to the standard error stream:<p>
+
+<div class="doc_code">
+<pre>
+#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"
+
+// <i>F is a pointer to a Function instance</i>
+for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
+ errs() << *I << "\n";
+</pre>
+</div>
+
+<p>Easy, isn't it? You can also use <tt>InstIterator</tt>s to fill a
+work list with its initial contents. For example, if you wanted to
+initialize a work list to contain all instructions in a <tt>Function</tt>
+F, all you would need to do is something like:</p>
+
+<div class="doc_code">
+<pre>
+std::set<Instruction*> worklist;
+// or better yet, SmallPtrSet<Instruction*, 64> worklist;
+
+for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
+ worklist.insert(&*I);
+</pre>
+</div>
+
+<p>The STL set <tt>worklist</tt> would now contain all instructions in the
+<tt>Function</tt> pointed to by F.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="iterate_convert">Turning an iterator into a class pointer (and
+ vice-versa)</a>
+</h4>
+
+<div>
+
+<p>Sometimes, it'll be useful to grab a reference (or pointer) to a class
+instance when all you've got at hand is an iterator. Well, extracting
+a reference or a pointer from an iterator is very straight-forward.
+Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
+is a <tt>BasicBlock::const_iterator</tt>:</p>
+
+<div class="doc_code">
+<pre>
+Instruction& inst = *i; // <i>Grab reference to instruction reference</i>
+Instruction* pinst = &*i; // <i>Grab pointer to instruction reference</i>
+const Instruction& inst = *j;
+</pre>
+</div>
+
+<p>However, the iterators you'll be working with in the LLVM framework are
+special: they will automatically convert to a ptr-to-instance type whenever they
+need to. Instead of dereferencing the iterator and then taking the address of
+the result, you can simply assign the iterator to the proper pointer type and
+you get the dereference and address-of operation as a result of the assignment
+(behind the scenes, this is a result of overloading casting mechanisms). Thus
+the last line of the last example,</p>
+
+<div class="doc_code">
+<pre>
+Instruction *pinst = &*i;
+</pre>
+</div>
+
+<p>is semantically equivalent to</p>
+
+<div class="doc_code">
+<pre>
+Instruction *pinst = i;
+</pre>
+</div>
+
+<p>It's also possible to turn a class pointer into the corresponding iterator,
+and this is a constant time operation (very efficient). The following code
+snippet illustrates use of the conversion constructors provided by LLVM
+iterators. By using these, you can explicitly grab the iterator of something
+without actually obtaining it via iteration over some structure:</p>
+
+<div class="doc_code">
+<pre>
+void printNextInstruction(Instruction* inst) {
+ BasicBlock::iterator it(inst);
+ ++it; // <i>After this line, it refers to the instruction after *inst</i>
+ if (it != inst->getParent()->end()) errs() << *it << "\n";
+}
+</pre>
+</div>
+
+<p>Unfortunately, these implicit conversions come at a cost; they prevent
+these iterators from conforming to standard iterator conventions, and thus
+from being usable with standard algorithms and containers. For example, they
+prevent the following code, where <tt>B</tt> is a <tt>BasicBlock</tt>,
+from compiling:</p>
+
+<div class="doc_code">
+<pre>
+ llvm::SmallVector<llvm::Instruction *, 16>(B->begin(), B->end());
+</pre>
+</div>
+
+<p>Because of this, these implicit conversions may be removed some day,
+and <tt>operator*</tt> changed to return a pointer instead of a reference.</p>
+
+</div>
+
+<!--_______________________________________________________________________-->
+<h4>
+ <a name="iterate_complex">Finding call sites: a slightly more complex
+ example</a>
+</h4>
+
+<div>
+
+<p>Say that you're writing a FunctionPass and would like to count all the
+locations in the entire module (that is, across every <tt>Function</tt>) where a
+certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
+learn later, you may want to use an <tt>InstVisitor</tt> to accomplish this in a
+much more straight-forward manner, but this example will allow us to explore how
+you'd do it if you didn't have <tt>InstVisitor</tt> around. In pseudo-code, this
+is what we want to do:</p>
+
+<div class="doc_code">
+<pre>
+initialize callCounter to zero
+for each Function f in the Module
+ for each BasicBlock b in f
+ for each Instruction i in b
+ if (i is a CallInst and calls the given function)
+ increment callCounter
+</pre>
+</div>
+
+<p>And the actual code is (remember, because we're writing a
+<tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
+override the <tt>runOnFunction</tt> method):</p>
+
+<div class="doc_code">
+<pre>
+Function* targetFunc = ...;
+
+class OurFunctionPass : public FunctionPass {
+ public:
+ OurFunctionPass(): callCounter(0) { }
+
+ virtual runOnFunction(Function& F) {
+ for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
+ for (BasicBlock::iterator i = b->begin(), ie = b->end(); i != ie; ++i) {
+ if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a><<a
+ href="#CallInst">CallInst</a>>(&*i)) {
+ // <i>We know we've encountered a call instruction, so we</i>
+ // <i>need to determine if it's a call to the</i>
+ // <i>function pointed to by m_func or not.</i>
+ if (callInst->getCalledFunction() == targetFunc)
+ ++callCounter;
+ }
+ }
+ }
+ }
+
+ private:
+ unsigned callCounter;
+};
+</pre>
+</div>
+
+</div>
+
+<!--_______________________________________________________________________-->
+<h4>
+ <a name="calls_and_invokes">Treating calls and invokes the same way</a>
+</h4>
+
+<div>
+
+<p>You may have noticed that the previous example was a bit oversimplified in
+that it did not deal with call sites generated by 'invoke' instructions. In
+this, and in other situations, you may find that you want to treat
+<tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
+most-specific common base class is <tt>Instruction</tt>, which includes lots of
+less closely-related things. For these cases, LLVM provides a handy wrapper
+class called <a
+href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
+It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
+methods that provide functionality common to <tt>CallInst</tt>s and
+<tt>InvokeInst</tt>s.</p>
+
+<p>This class has "value semantics": it should be passed by value, not by
+reference and it should not be dynamically allocated or deallocated using
+<tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
+assignable and constructable, with costs equivalents to that of a bare pointer.
+If you look at its definition, it has only a single pointer member.</p>
+
+</div>
+
+<!--_______________________________________________________________________-->
+<h4>
+ <a name="iterate_chains">Iterating over def-use & use-def chains</a>
+</h4>
+
+<div>
+
+<p>Frequently, we might have an instance of the <a
+href="/doxygen/classllvm_1_1Value.html">Value Class</a> and we want to
+determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
+<tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
+For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
+particular function <tt>foo</tt>. Finding all of the instructions that
+<i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
+of <tt>F</tt>:</p>
+
+<div class="doc_code">
+<pre>
+Function *F = ...;
+
+for (Value::use_iterator i = F->use_begin(), e = F->use_end(); i != e; ++i)
+ if (Instruction *Inst = dyn_cast<Instruction>(*i)) {
+ errs() << "F is used in instruction:\n";
+ errs() << *Inst << "\n";
+ }
+</pre>
+</div>
+
+<p>Note that dereferencing a <tt>Value::use_iterator</tt> is not a very cheap
+operation. Instead of performing <tt>*i</tt> above several times, consider
+doing it only once in the loop body and reusing its result.</p>
+
+<p>Alternatively, it's common to have an instance of the <a
+href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
+<tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
+<tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
+<tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
+all of the values that a particular instruction uses (that is, the operands of
+the particular <tt>Instruction</tt>):</p>
+
+<div class="doc_code">
+<pre>
+Instruction *pi = ...;
+
+for (User::op_iterator i = pi->op_begin(), e = pi->op_end(); i != e; ++i) {
+ Value *v = *i;
+ // <i>...</i>
+}
+</pre>
+</div>
+
+<p>Declaring objects as <tt>const</tt> is an important tool of enforcing
+mutation free algorithms (such as analyses, etc.). For this purpose above
+iterators come in constant flavors as <tt>Value::const_use_iterator</tt>
+and <tt>Value::const_op_iterator</tt>. They automatically arise when
+calling <tt>use/op_begin()</tt> on <tt>const Value*</tt>s or
+<tt>const User*</tt>s respectively. Upon dereferencing, they return
+<tt>const Use*</tt>s. Otherwise the above patterns remain unchanged.</p>
+
+</div>
+
+<!--_______________________________________________________________________-->
+<h4>
+ <a name="iterate_preds">Iterating over predecessors &
+successors of blocks</a>
+</h4>
+
+<div>
+
+<p>Iterating over the predecessors and successors of a block is quite easy
+with the routines defined in <tt>"llvm/Support/CFG.h"</tt>. Just use code like
+this to iterate over all predecessors of BB:</p>
+
+<div class="doc_code">
+<pre>
+#include "llvm/Support/CFG.h"
+BasicBlock *BB = ...;
+
+for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
+ BasicBlock *Pred = *PI;
+ // <i>...</i>
+}
+</pre>
+</div>
+
+<p>Similarly, to iterate over successors use
+succ_iterator/succ_begin/succ_end.</p>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="simplechanges">Making simple changes</a>
+</h3>
+
+<div>
+
+<p>There are some primitive transformation operations present in the LLVM
+infrastructure that are worth knowing about. When performing
+transformations, it's fairly common to manipulate the contents of basic
+blocks. This section describes some of the common methods for doing so
+and gives example code.</p>
+
+<!--_______________________________________________________________________-->
+<h4>
+ <a name="schanges_creating">Creating and inserting new
+ <tt>Instruction</tt>s</a>
+</h4>
+
+<div>
+
+<p><i>Instantiating Instructions</i></p>
+
+<p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
+constructor for the kind of instruction to instantiate and provide the necessary
+parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
+(const-ptr-to) <tt>Type</tt>. Thus:</p>
+
+<div class="doc_code">
+<pre>
+AllocaInst* ai = new AllocaInst(Type::Int32Ty);
+</pre>
+</div>
+
+<p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
+one integer in the current stack frame, at run time. Each <tt>Instruction</tt>
+subclass is likely to have varying default parameters which change the semantics
+of the instruction, so refer to the <a
+href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
+Instruction</a> that you're interested in instantiating.</p>
+
+<p><i>Naming values</i></p>
+
+<p>It is very useful to name the values of instructions when you're able to, as
+this facilitates the debugging of your transformations. If you end up looking
+at generated LLVM machine code, you definitely want to have logical names
+associated with the results of instructions! By supplying a value for the
+<tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
+associate a logical name with the result of the instruction's execution at
+run time. For example, say that I'm writing a transformation that dynamically
+allocates space for an integer on the stack, and that integer is going to be
+used as some kind of index by some other code. To accomplish this, I place an
+<tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
+<tt>Function</tt>, and I'm intending to use it within the same
+<tt>Function</tt>. I might do:</p>
+
+<div class="doc_code">
+<pre>
+AllocaInst* pa = new AllocaInst(Type::Int32Ty, 0, "indexLoc");
+</pre>
+</div>
+
+<p>where <tt>indexLoc</tt> is now the logical name of the instruction's
+execution value, which is a pointer to an integer on the run time stack.</p>
+
+<p><i>Inserting instructions</i></p>
+
+<p>There are essentially two ways to insert an <tt>Instruction</tt>
+into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
+
+<ul>
+ <li>Insertion into an explicit instruction list
+
+ <p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
+ <tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
+ before <tt>*pi</tt>, we do the following: </p>
+
+<div class="doc_code">
+<pre>
+BasicBlock *pb = ...;
+Instruction *pi = ...;
+Instruction *newInst = new Instruction(...);
+
+pb->getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>
+</pre>
+</div>
+
+ <p>Appending to the end of a <tt>BasicBlock</tt> is so common that
+ the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
+ classes provide constructors which take a pointer to a
+ <tt>BasicBlock</tt> to be appended to. For example code that
+ looked like: </p>
+
+<div class="doc_code">
+<pre>
+BasicBlock *pb = ...;
+Instruction *newInst = new Instruction(...);
+
+pb->getInstList().push_back(newInst); // <i>Appends newInst to pb</i>
+</pre>
+</div>
+
+ <p>becomes: </p>
+
+<div class="doc_code">
+<pre>
+BasicBlock *pb = ...;
+Instruction *newInst = new Instruction(..., pb);
+</pre>
+</div>
+
+ <p>which is much cleaner, especially if you are creating
+ long instruction streams.</p></li>
+
+ <li>Insertion into an implicit instruction list
+
+ <p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
+ are implicitly associated with an existing instruction list: the instruction
+ list of the enclosing basic block. Thus, we could have accomplished the same
+ thing as the above code without being given a <tt>BasicBlock</tt> by doing:
+ </p>
+
+<div class="doc_code">
+<pre>
+Instruction *pi = ...;
+Instruction *newInst = new Instruction(...);
+
+pi->getParent()->getInstList().insert(pi, newInst);
+</pre>
+</div>
+
+ <p>In fact, this sequence of steps occurs so frequently that the
+ <tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
+ constructors which take (as a default parameter) a pointer to an
+ <tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
+ precede. That is, <tt>Instruction</tt> constructors are capable of
+ inserting the newly-created instance into the <tt>BasicBlock</tt> of a
+ provided instruction, immediately before that instruction. Using an
+ <tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
+ parameter, the above code becomes:</p>
+
+<div class="doc_code">
+<pre>
+Instruction* pi = ...;
+Instruction* newInst = new Instruction(..., pi);
+</pre>
+</div>
+
+ <p>which is much cleaner, especially if you're creating a lot of
+ instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
+</ul>
+
+</div>
+
+<!--_______________________________________________________________________-->
+<h4>
+ <a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
+</h4>
+
+<div>
+
+<p>Deleting an instruction from an existing sequence of instructions that form a
+<a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward: just
+call the instruction's eraseFromParent() method. For example:</p>
+
+<div class="doc_code">
+<pre>
+<a href="#Instruction">Instruction</a> *I = .. ;
+I->eraseFromParent();
+</pre>
+</div>
+
+<p>This unlinks the instruction from its containing basic block and deletes
+it. If you'd just like to unlink the instruction from its containing basic
+block but not delete it, you can use the <tt>removeFromParent()</tt> method.</p>
+
+</div>
+
+<!--_______________________________________________________________________-->
+<h4>
+ <a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
+ <tt>Value</tt></a>
+</h4>
+
+<div>
+
+<h5><i>Replacing individual instructions</i></h5>
+
+<p>Including "<a href="/doxygen/BasicBlockUtils_8h-source.html">llvm/Transforms/Utils/BasicBlockUtils.h</a>"
+permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
+and <tt>ReplaceInstWithInst</tt>.</p>
+
+<h5><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h5>
+
+<div>
+<ul>
+ <li><tt>ReplaceInstWithValue</tt>
+
+ <p>This function replaces all uses of a given instruction with a value,
+ and then removes the original instruction. The following example
+ illustrates the replacement of the result of a particular
+ <tt>AllocaInst</tt> that allocates memory for a single integer with a null
+ pointer to an integer.</p>
+
+<div class="doc_code">
+<pre>
+AllocaInst* instToReplace = ...;
+BasicBlock::iterator ii(instToReplace);
+
+ReplaceInstWithValue(instToReplace->getParent()->getInstList(), ii,
+ Constant::getNullValue(PointerType::getUnqual(Type::Int32Ty)));
+</pre></div></li>
+
+ <li><tt>ReplaceInstWithInst</tt>
+
+ <p>This function replaces a particular instruction with another
+ instruction, inserting the new instruction into the basic block at the
+ location where the old instruction was, and replacing any uses of the old
+ instruction with the new instruction. The following example illustrates
+ the replacement of one <tt>AllocaInst</tt> with another.</p>
+
+<div class="doc_code">
+<pre>
+AllocaInst* instToReplace = ...;
+BasicBlock::iterator ii(instToReplace);
+
+ReplaceInstWithInst(instToReplace->getParent()->getInstList(), ii,
+ new AllocaInst(Type::Int32Ty, 0, "ptrToReplacedInt"));
+</pre></div></li>
+</ul>
+
+</div>
+
+<h5><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></h5>
+
+<p>You can use <tt>Value::replaceAllUsesWith</tt> and
+<tt>User::replaceUsesOfWith</tt> to change more than one use at a time. See the
+doxygen documentation for the <a href="/doxygen/classllvm_1_1Value.html">Value Class</a>
+and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
+information.</p>
+
+<!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
+include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
+ReplaceInstWithValue, ReplaceInstWithInst -->
+
+</div>
+
+<!--_______________________________________________________________________-->
+<h4>
+ <a name="schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a>
+</h4>
+
+<div>
+
+<p>Deleting a global variable from a module is just as easy as deleting an
+Instruction. First, you must have a pointer to the global variable that you wish
+ to delete. You use this pointer to erase it from its parent, the module.
+ For example:</p>
+
+<div class="doc_code">
+<pre>
+<a href="#GlobalVariable">GlobalVariable</a> *GV = .. ;
+
+GV->eraseFromParent();
+</pre>
+</div>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="create_types">How to Create Types</a>
+</h3>
+
+<div>
+
+<p>In generating IR, you may need some complex types. If you know these types
+statically, you can use <tt>TypeBuilder<...>::get()</tt>, defined
+in <tt>llvm/Support/TypeBuilder.h</tt>, to retrieve them. <tt>TypeBuilder</tt>
+has two forms depending on whether you're building types for cross-compilation
+or native library use. <tt>TypeBuilder<T, true></tt> requires
+that <tt>T</tt> be independent of the host environment, meaning that it's built
+out of types from
+the <a href="/doxygen/namespacellvm_1_1types.html"><tt>llvm::types</tt></a>
+namespace and pointers, functions, arrays, etc. built of
+those. <tt>TypeBuilder<T, false></tt> additionally allows native C types
+whose size may depend on the host compiler. For example,</p>
+
+<div class="doc_code">
+<pre>
+FunctionType *ft = TypeBuilder<types::i<8>(types::i<32>*), true>::get();
+</pre>
+</div>
+
+<p>is easier to read and write than the equivalent</p>
+
+<div class="doc_code">
+<pre>
+std::vector<const Type*> params;
+params.push_back(PointerType::getUnqual(Type::Int32Ty));
+FunctionType *ft = FunctionType::get(Type::Int8Ty, params, false);
+</pre>
+</div>
+
+<p>See the <a href="/doxygen/TypeBuilder_8h-source.html#l00001">class
+comment</a> for more details.</p>
+
+</div>
+
+</div>
+
+<!-- *********************************************************************** -->
+<h2>
+ <a name="threading">Threads and LLVM</a>
+</h2>
+<!-- *********************************************************************** -->
+
+<div>
+<p>
+This section describes the interaction of the LLVM APIs with multithreading,
+both on the part of client applications, and in the JIT, in the hosted
+application.
+</p>
+
+<p>
+Note that LLVM's support for multithreading is still relatively young. Up
+through version 2.5, the execution of threaded hosted applications was
+supported, but not threaded client access to the APIs. While this use case is
+now supported, clients <em>must</em> adhere to the guidelines specified below to
+ensure proper operation in multithreaded mode.
+</p>
+
+<p>
+Note that, on Unix-like platforms, LLVM requires the presence of GCC's atomic
+intrinsics in order to support threaded operation. If you need a
+multhreading-capable LLVM on a platform without a suitably modern system
+compiler, consider compiling LLVM and LLVM-GCC in single-threaded mode, and
+using the resultant compiler to build a copy of LLVM with multithreading
+support.
+</p>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="startmultithreaded">Entering and Exiting Multithreaded Mode</a>
+</h3>
+
+<div>
+
+<p>
+In order to properly protect its internal data structures while avoiding
+excessive locking overhead in the single-threaded case, the LLVM must intialize
+certain data structures necessary to provide guards around its internals. To do
+so, the client program must invoke <tt>llvm_start_multithreaded()</tt> before
+making any concurrent LLVM API calls. To subsequently tear down these
+structures, use the <tt>llvm_stop_multithreaded()</tt> call. You can also use
+the <tt>llvm_is_multithreaded()</tt> call to check the status of multithreaded
+mode.
+</p>
+
+<p>
+Note that both of these calls must be made <em>in isolation</em>. That is to
+say that no other LLVM API calls may be executing at any time during the
+execution of <tt>llvm_start_multithreaded()</tt> or <tt>llvm_stop_multithreaded
+</tt>. It's is the client's responsibility to enforce this isolation.
+</p>
+
+<p>
+The return value of <tt>llvm_start_multithreaded()</tt> indicates the success or
+failure of the initialization. Failure typically indicates that your copy of
+LLVM was built without multithreading support, typically because GCC atomic
+intrinsics were not found in your system compiler. In this case, the LLVM API
+will not be safe for concurrent calls. However, it <em>will</em> be safe for
+hosting threaded applications in the JIT, though <a href="#jitthreading">care
+must be taken</a> to ensure that side exits and the like do not accidentally
+result in concurrent LLVM API calls.
+</p>
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="shutdown">Ending Execution with <tt>llvm_shutdown()</tt></a>
+</h3>
+
+<div>
+<p>
+When you are done using the LLVM APIs, you should call <tt>llvm_shutdown()</tt>
+to deallocate memory used for internal structures. This will also invoke
+<tt>llvm_stop_multithreaded()</tt> if LLVM is operating in multithreaded mode.
+As such, <tt>llvm_shutdown()</tt> requires the same isolation guarantees as
+<tt>llvm_stop_multithreaded()</tt>.
+</p>
+
+<p>
+Note that, if you use scope-based shutdown, you can use the
+<tt>llvm_shutdown_obj</tt> class, which calls <tt>llvm_shutdown()</tt> in its
+destructor.
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="managedstatic">Lazy Initialization with <tt>ManagedStatic</tt></a>
+</h3>
+
+<div>
+<p>
+<tt>ManagedStatic</tt> is a utility class in LLVM used to implement static
+initialization of static resources, such as the global type tables. Before the
+invocation of <tt>llvm_shutdown()</tt>, it implements a simple lazy
+initialization scheme. Once <tt>llvm_start_multithreaded()</tt> returns,
+however, it uses double-checked locking to implement thread-safe lazy
+initialization.
+</p>
+
+<p>
+Note that, because no other threads are allowed to issue LLVM API calls before
+<tt>llvm_start_multithreaded()</tt> returns, it is possible to have
+<tt>ManagedStatic</tt>s of <tt>llvm::sys::Mutex</tt>s.
+</p>
+
+<p>
+The <tt>llvm_acquire_global_lock()</tt> and <tt>llvm_release_global_lock</tt>
+APIs provide access to the global lock used to implement the double-checked
+locking for lazy initialization. These should only be used internally to LLVM,
+and only if you know what you're doing!
+</p>
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="llvmcontext">Achieving Isolation with <tt>LLVMContext</tt></a>
+</h3>
+
+<div>
+<p>
+<tt>LLVMContext</tt> is an opaque class in the LLVM API which clients can use
+to operate multiple, isolated instances of LLVM concurrently within the same
+address space. For instance, in a hypothetical compile-server, the compilation
+of an individual translation unit is conceptually independent from all the
+others, and it would be desirable to be able to compile incoming translation
+units concurrently on independent server threads. Fortunately,
+<tt>LLVMContext</tt> exists to enable just this kind of scenario!
+</p>
+
+<p>
+Conceptually, <tt>LLVMContext</tt> provides isolation. Every LLVM entity
+(<tt>Module</tt>s, <tt>Value</tt>s, <tt>Type</tt>s, <tt>Constant</tt>s, etc.)
+in LLVM's in-memory IR belongs to an <tt>LLVMContext</tt>. Entities in
+different contexts <em>cannot</em> interact with each other: <tt>Module</tt>s in
+different contexts cannot be linked together, <tt>Function</tt>s cannot be added
+to <tt>Module</tt>s in different contexts, etc. What this means is that is is
+safe to compile on multiple threads simultaneously, as long as no two threads
+operate on entities within the same context.
+</p>
+
+<p>
+In practice, very few places in the API require the explicit specification of a
+<tt>LLVMContext</tt>, other than the <tt>Type</tt> creation/lookup APIs.
+Because every <tt>Type</tt> carries a reference to its owning context, most
+other entities can determine what context they belong to by looking at their
+own <tt>Type</tt>. If you are adding new entities to LLVM IR, please try to
+maintain this interface design.
+</p>
+
+<p>
+For clients that do <em>not</em> require the benefits of isolation, LLVM
+provides a convenience API <tt>getGlobalContext()</tt>. This returns a global,
+lazily initialized <tt>LLVMContext</tt> that may be used in situations where
+isolation is not a concern.
+</p>
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="jitthreading">Threads and the JIT</a>
+</h3>
+
+<div>
+<p>
+LLVM's "eager" JIT compiler is safe to use in threaded programs. Multiple
+threads can call <tt>ExecutionEngine::getPointerToFunction()</tt> or
+<tt>ExecutionEngine::runFunction()</tt> concurrently, and multiple threads can
+run code output by the JIT concurrently. The user must still ensure that only
+one thread accesses IR in a given <tt>LLVMContext</tt> while another thread
+might be modifying it. One way to do that is to always hold the JIT lock while
+accessing IR outside the JIT (the JIT <em>modifies</em> the IR by adding
+<tt>CallbackVH</tt>s). Another way is to only
+call <tt>getPointerToFunction()</tt> from the <tt>LLVMContext</tt>'s thread.
+</p>
+
+<p>When the JIT is configured to compile lazily (using
+<tt>ExecutionEngine::DisableLazyCompilation(false)</tt>), there is currently a
+<a href="http://llvm.org/bugs/show_bug.cgi?id=5184">race condition</a> in
+updating call sites after a function is lazily-jitted. It's still possible to
+use the lazy JIT in a threaded program if you ensure that only one thread at a
+time can call any particular lazy stub and that the JIT lock guards any IR
+access, but we suggest using only the eager JIT in threaded programs.
+</p>
+</div>
+
+</div>
+
+<!-- *********************************************************************** -->
+<h2>
+ <a name="advanced">Advanced Topics</a>
+</h2>
+<!-- *********************************************************************** -->
+
+<div>
+<p>
+This section describes some of the advanced or obscure API's that most clients
+do not need to be aware of. These API's tend manage the inner workings of the
+LLVM system, and only need to be accessed in unusual circumstances.
+</p>
+
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="SymbolTable">The <tt>ValueSymbolTable</tt> class</a>
+</h3>
+
+<div>
+<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1ValueSymbolTable.html">
+ValueSymbolTable</a></tt> class provides a symbol table that the <a
+href="#Function"><tt>Function</tt></a> and <a href="#Module">
+<tt>Module</tt></a> classes use for naming value definitions. The symbol table
+can provide a name for any <a href="#Value"><tt>Value</tt></a>.
+</p>
+
+<p>Note that the <tt>SymbolTable</tt> class should not be directly accessed
+by most clients. It should only be used when iteration over the symbol table
+names themselves are required, which is very special purpose. Note that not
+all LLVM
+<tt><a href="#Value">Value</a></tt>s have names, and those without names (i.e. they have
+an empty name) do not exist in the symbol table.
+</p>
+
+<p>Symbol tables support iteration over the values in the symbol
+table with <tt>begin/end/iterator</tt> and supports querying to see if a
+specific name is in the symbol table (with <tt>lookup</tt>). The
+<tt>ValueSymbolTable</tt> class exposes no public mutator methods, instead,
+simply call <tt>setName</tt> on a value, which will autoinsert it into the
+appropriate symbol table.</p>
+
+</div>
+
+
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="UserLayout">The <tt>User</tt> and owned <tt>Use</tt> classes' memory layout</a>
+</h3>
+
+<div>
+<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1User.html">
+User</a></tt> class provides a basis for expressing the ownership of <tt>User</tt>
+towards other <tt><a href="http://llvm.org/doxygen/classllvm_1_1Value.html">
+Value</a></tt>s. The <tt><a href="http://llvm.org/doxygen/classllvm_1_1Use.html">
+Use</a></tt> helper class is employed to do the bookkeeping and to facilitate <i>O(1)</i>
+addition and removal.</p>
+
+<!-- ______________________________________________________________________ -->
+<h4>
+ <a name="Use2User">
+ Interaction and relationship between <tt>User</tt> and <tt>Use</tt> objects
+ </a>
+</h4>
+
+<div>
+<p>
+A subclass of <tt>User</tt> can choose between incorporating its <tt>Use</tt> objects
+or refer to them out-of-line by means of a pointer. A mixed variant
+(some <tt>Use</tt>s inline others hung off) is impractical and breaks the invariant
+that the <tt>Use</tt> objects belonging to the same <tt>User</tt> form a contiguous array.
+</p>
+
+<p>
+We have 2 different layouts in the <tt>User</tt> (sub)classes:
+<ul>
+<li><p>Layout a)
+The <tt>Use</tt> object(s) are inside (resp. at fixed offset) of the <tt>User</tt>
+object and there are a fixed number of them.</p>
+
+<li><p>Layout b)
+The <tt>Use</tt> object(s) are referenced by a pointer to an
+array from the <tt>User</tt> object and there may be a variable
+number of them.</p>
+</ul>
+<p>
+As of v2.4 each layout still possesses a direct pointer to the
+start of the array of <tt>Use</tt>s. Though not mandatory for layout a),
+we stick to this redundancy for the sake of simplicity.
+The <tt>User</tt> object also stores the number of <tt>Use</tt> objects it
+has. (Theoretically this information can also be calculated
+given the scheme presented below.)</p>
+<p>
+Special forms of allocation operators (<tt>operator new</tt>)
+enforce the following memory layouts:</p>
+
+<ul>
+<li><p>Layout a) is modelled by prepending the <tt>User</tt> object by the <tt>Use[]</tt> array.</p>
+
+<pre>
+...---.---.---.---.-------...
+ | P | P | P | P | User
+'''---'---'---'---'-------'''
+</pre>
+
+<li><p>Layout b) is modelled by pointing at the <tt>Use[]</tt> array.</p>
+<pre>
+.-------...
+| User
+'-------'''
+ |
+ v
+ .---.---.---.---...
+ | P | P | P | P |
+ '---'---'---'---'''
+</pre>
+</ul>
+<i>(In the above figures '<tt>P</tt>' stands for the <tt>Use**</tt> that
+ is stored in each <tt>Use</tt> object in the member <tt>Use::Prev</tt>)</i>
+
+</div>
+
+<!-- ______________________________________________________________________ -->
+<h4>
+ <a name="Waymarking">The waymarking algorithm</a>
+</h4>
+
+<div>
+<p>
+Since the <tt>Use</tt> objects are deprived of the direct (back)pointer to
+their <tt>User</tt> objects, there must be a fast and exact method to
+recover it. This is accomplished by the following scheme:</p>
+
+A bit-encoding in the 2 LSBits (least significant bits) of the <tt>Use::Prev</tt> allows to find the
+start of the <tt>User</tt> object:
+<ul>
+<li><tt>00</tt> —> binary digit 0</li>
+<li><tt>01</tt> —> binary digit 1</li>
+<li><tt>10</tt> —> stop and calculate (<tt>s</tt>)</li>
+<li><tt>11</tt> —> full stop (<tt>S</tt>)</li>
+</ul>
+<p>
+Given a <tt>Use*</tt>, all we have to do is to walk till we get
+a stop and we either have a <tt>User</tt> immediately behind or
+we have to walk to the next stop picking up digits
+and calculating the offset:</p>
+<pre>
+.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.----------------
+| 1 | s | 1 | 0 | 1 | 0 | s | 1 | 1 | 0 | s | 1 | 1 | s | 1 | S | User (or User*)
+'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'----------------
+ |+15 |+10 |+6 |+3 |+1
+ | | | | |__>
+ | | | |__________>
+ | | |______________________>
+ | |______________________________________>
+ |__________________________________________________________>
+</pre>
+<p>
+Only the significant number of bits need to be stored between the
+stops, so that the <i>worst case is 20 memory accesses</i> when there are
+1000 <tt>Use</tt> objects associated with a <tt>User</tt>.</p>
+
+</div>
+
+<!-- ______________________________________________________________________ -->
+<h4>
+ <a name="ReferenceImpl">Reference implementation</a>
+</h4>
+
+<div>
+<p>
+The following literate Haskell fragment demonstrates the concept:</p>
+
+<div class="doc_code">
+<pre>
+> import Test.QuickCheck
+>
+> digits :: Int -> [Char] -> [Char]
+> digits 0 acc = '0' : acc
+> digits 1 acc = '1' : acc
+> digits n acc = digits (n `div` 2) $ digits (n `mod` 2) acc
+>
+> dist :: Int -> [Char] -> [Char]
+> dist 0 [] = ['S']
+> dist 0 acc = acc
+> dist 1 acc = let r = dist 0 acc in 's' : digits (length r) r
+> dist n acc = dist (n - 1) $ dist 1 acc
+>
+> takeLast n ss = reverse $ take n $ reverse ss
+>
+> test = takeLast 40 $ dist 20 []
+>
+</pre>
+</div>
+<p>
+Printing <test> gives: <tt>"1s100000s11010s10100s1111s1010s110s11s1S"</tt></p>
+<p>
+The reverse algorithm computes the length of the string just by examining
+a certain prefix:</p>
+
+<div class="doc_code">
+<pre>
+> pref :: [Char] -> Int
+> pref "S" = 1
+> pref ('s':'1':rest) = decode 2 1 rest
+> pref (_:rest) = 1 + pref rest
+>
+> decode walk acc ('0':rest) = decode (walk + 1) (acc * 2) rest
+> decode walk acc ('1':rest) = decode (walk + 1) (acc * 2 + 1) rest
+> decode walk acc _ = walk + acc
+>
+</pre>
+</div>
+<p>
+Now, as expected, printing <pref test> gives <tt>40</tt>.</p>
+<p>
+We can <i>quickCheck</i> this with following property:</p>
+
+<div class="doc_code">
+<pre>
+> testcase = dist 2000 []
+> testcaseLength = length testcase
+>
+> identityProp n = n > 0 && n <= testcaseLength ==> length arr == pref arr
+> where arr = takeLast n testcase
+>
+</pre>
+</div>
+<p>
+As expected <quickCheck identityProp> gives:</p>
+
+<pre>
+*Main> quickCheck identityProp
+OK, passed 100 tests.
+</pre>
+<p>
+Let's be a bit more exhaustive:</p>
+
+<div class="doc_code">
+<pre>
+>
+> deepCheck p = check (defaultConfig { configMaxTest = 500 }) p
+>
+</pre>
+</div>
+<p>
+And here is the result of <deepCheck identityProp>:</p>
+
+<pre>
+*Main> deepCheck identityProp
+OK, passed 500 tests.
+</pre>
+
+</div>
+
+<!-- ______________________________________________________________________ -->
+<h4>
+ <a name="Tagging">Tagging considerations</a>
+</h4>
+
+<div>
+
+<p>
+To maintain the invariant that the 2 LSBits of each <tt>Use**</tt> in <tt>Use</tt>
+never change after being set up, setters of <tt>Use::Prev</tt> must re-tag the
+new <tt>Use**</tt> on every modification. Accordingly getters must strip the
+tag bits.</p>
+<p>
+For layout b) instead of the <tt>User</tt> we find a pointer (<tt>User*</tt> with LSBit set).
+Following this pointer brings us to the <tt>User</tt>. A portable trick ensures
+that the first bytes of <tt>User</tt> (if interpreted as a pointer) never has
+the LSBit set. (Portability is relying on the fact that all known compilers place the
+<tt>vptr</tt> in the first word of the instances.)</p>
+
+</div>
+
+</div>
+
+</div>
+
+<!-- *********************************************************************** -->
+<h2>
+ <a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
+</h2>
+<!-- *********************************************************************** -->
+
+<div>
+<p><tt>#include "<a href="/doxygen/Type_8h-source.html">llvm/Type.h</a>"</tt>
+<br>doxygen info: <a href="/doxygen/classllvm_1_1Type.html">Type Class</a></p>
+
+<p>The Core LLVM classes are the primary means of representing the program
+being inspected or transformed. The core LLVM classes are defined in
+header files in the <tt>include/llvm/</tt> directory, and implemented in
+the <tt>lib/VMCore</tt> directory.</p>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="Type">The <tt>Type</tt> class and Derived Types</a>
+</h3>
+
+<div>
+
+ <p><tt>Type</tt> is a superclass of all type classes. Every <tt>Value</tt> has
+ a <tt>Type</tt>. <tt>Type</tt> cannot be instantiated directly but only
+ through its subclasses. Certain primitive types (<tt>VoidType</tt>,
+ <tt>LabelType</tt>, <tt>FloatType</tt> and <tt>DoubleType</tt>) have hidden
+ subclasses. They are hidden because they offer no useful functionality beyond
+ what the <tt>Type</tt> class offers except to distinguish themselves from
+ other subclasses of <tt>Type</tt>.</p>
+ <p>All other types are subclasses of <tt>DerivedType</tt>. Types can be
+ named, but this is not a requirement. There exists exactly
+ one instance of a given shape at any one time. This allows type equality to
+ be performed with address equality of the Type Instance. That is, given two
+ <tt>Type*</tt> values, the types are identical if the pointers are identical.
+ </p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="m_Type">Important Public Methods</a>
+</h4>
+
+<div>
+
+<ul>
+ <li><tt>bool isIntegerTy() const</tt>: Returns true for any integer type.</li>
+
+ <li><tt>bool isFloatingPointTy()</tt>: Return true if this is one of the five
+ floating point types.</li>
+
+ <li><tt>bool isSized()</tt>: Return true if the type has known size. Things
+ that don't have a size are abstract types, labels and void.</li>
+
+</ul>
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="derivedtypes">Important Derived Types</a>
+</h4>
+<div>
+<dl>
+ <dt><tt>IntegerType</tt></dt>
+ <dd>Subclass of DerivedType that represents integer types of any bit width.
+ Any bit width between <tt>IntegerType::MIN_INT_BITS</tt> (1) and
+ <tt>IntegerType::MAX_INT_BITS</tt> (~8 million) can be represented.
+ <ul>
+ <li><tt>static const IntegerType* get(unsigned NumBits)</tt>: get an integer
+ type of a specific bit width.</li>
+ <li><tt>unsigned getBitWidth() const</tt>: Get the bit width of an integer
+ type.</li>
+ </ul>
+ </dd>
+ <dt><tt>SequentialType</tt></dt>
+ <dd>This is subclassed by ArrayType, PointerType and VectorType.
+ <ul>
+ <li><tt>const Type * getElementType() const</tt>: Returns the type of each
+ of the elements in the sequential type. </li>
+ </ul>
+ </dd>
+ <dt><tt>ArrayType</tt></dt>
+ <dd>This is a subclass of SequentialType and defines the interface for array
+ types.
+ <ul>
+ <li><tt>unsigned getNumElements() const</tt>: Returns the number of
+ elements in the array. </li>
+ </ul>
+ </dd>
+ <dt><tt>PointerType</tt></dt>
+ <dd>Subclass of SequentialType for pointer types.</dd>
+ <dt><tt>VectorType</tt></dt>
+ <dd>Subclass of SequentialType for vector types. A
+ vector type is similar to an ArrayType but is distinguished because it is
+ a first class type whereas ArrayType is not. Vector types are used for
+ vector operations and are usually small vectors of of an integer or floating
+ point type.</dd>
+ <dt><tt>StructType</tt></dt>
+ <dd>Subclass of DerivedTypes for struct types.</dd>
+ <dt><tt><a name="FunctionType">FunctionType</a></tt></dt>
+ <dd>Subclass of DerivedTypes for function types.
+ <ul>
+ <li><tt>bool isVarArg() const</tt>: Returns true if it's a vararg
+ function</li>
+ <li><tt> const Type * getReturnType() const</tt>: Returns the
+ return type of the function.</li>
+ <li><tt>const Type * getParamType (unsigned i)</tt>: Returns
+ the type of the ith parameter.</li>
+ <li><tt> const unsigned getNumParams() const</tt>: Returns the
+ number of formal parameters.</li>
+ </ul>
+ </dd>
+</dl>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="Module">The <tt>Module</tt> class</a>
+</h3>
+
+<div>
+
+<p><tt>#include "<a
+href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
+<a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
+
+<p>The <tt>Module</tt> class represents the top level structure present in LLVM
+programs. An LLVM module is effectively either a translation unit of the
+original program or a combination of several translation units merged by the
+linker. The <tt>Module</tt> class keeps track of a list of <a
+href="#Function"><tt>Function</tt></a>s, a list of <a
+href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
+href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
+helpful member functions that try to make common operations easy.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
+</h4>
+
+<div>
+
+<ul>
+ <li><tt>Module::Module(std::string name = "")</tt>
+
+ <p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
+provide a name for it (probably based on the name of the translation unit).</p>
+ </li>
+
+ <li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
+ <tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
+
+ <tt>begin()</tt>, <tt>end()</tt>
+ <tt>size()</tt>, <tt>empty()</tt>
+
+ <p>These are forwarding methods that make it easy to access the contents of
+ a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
+ list.</p></li>
+
+ <li><tt>Module::FunctionListType &getFunctionList()</tt>
+
+ <p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
+ necessary to use when you need to update the list or perform a complex
+ action that doesn't have a forwarding method.</p>
+
+ <p><!-- Global Variable --></p></li>
+</ul>
+
+<hr>
+
+<ul>
+ <li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>
+
+ <tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>
+
+ <tt>global_begin()</tt>, <tt>global_end()</tt>
+ <tt>global_size()</tt>, <tt>global_empty()</tt>
+
+ <p> These are forwarding methods that make it easy to access the contents of
+ a <tt>Module</tt> object's <a
+ href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
+
+ <li><tt>Module::GlobalListType &getGlobalList()</tt>
+
+ <p>Returns the list of <a
+ href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
+ use when you need to update the list or perform a complex action that
+ doesn't have a forwarding method.</p>
+
+ <p><!-- Symbol table stuff --> </p></li>
+</ul>
+
+<hr>
+
+<ul>
+ <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
+
+ <p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
+ for this <tt>Module</tt>.</p>
+
+ <p><!-- Convenience methods --></p></li>
+</ul>
+
+<hr>
+
+<ul>
+
+ <li><tt><a href="#Function">Function</a> *getFunction(StringRef Name) const
+ </tt>
+
+ <p>Look up the specified function in the <tt>Module</tt> <a
+ href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
+ <tt>null</tt>.</p></li>
+
+ <li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
+ std::string &Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
+
+ <p>Look up the specified function in the <tt>Module</tt> <a
+ href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
+ external declaration for the function and return it.</p></li>
+
+ <li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
+
+ <p>If there is at least one entry in the <a
+ href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
+ href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
+ string.</p></li>
+
+ <li><tt>bool addTypeName(const std::string &Name, const <a
+ href="#Type">Type</a> *Ty)</tt>
+
+ <p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
+ mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
+ name, true is returned and the <a
+ href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
+</ul>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="Value">The <tt>Value</tt> class</a>
+</h3>
+
+<div>
+
+<p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
+<br>
+doxygen info: <a href="/doxygen/classllvm_1_1Value.html">Value Class</a></p>
+
+<p>The <tt>Value</tt> class is the most important class in the LLVM Source
+base. It represents a typed value that may be used (among other things) as an
+operand to an instruction. There are many different types of <tt>Value</tt>s,
+such as <a href="#Constant"><tt>Constant</tt></a>s,<a
+href="#Argument"><tt>Argument</tt></a>s. Even <a
+href="#Instruction"><tt>Instruction</tt></a>s and <a
+href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
+
+<p>A particular <tt>Value</tt> may be used many times in the LLVM representation
+for a program. For example, an incoming argument to a function (represented
+with an instance of the <a href="#Argument">Argument</a> class) is "used" by
+every instruction in the function that references the argument. To keep track
+of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
+href="#User"><tt>User</tt></a>s that is using it (the <a
+href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
+graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
+def-use information in the program, and is accessible through the <tt>use_</tt>*
+methods, shown below.</p>
+
+<p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
+and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
+method. In addition, all LLVM values can be named. The "name" of the
+<tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
+
+<div class="doc_code">
+<pre>
+%<b>foo</b> = add i32 1, 2
+</pre>
+</div>
+
+<p><a name="nameWarning">The name of this instruction is "foo".</a> <b>NOTE</b>
+that the name of any value may be missing (an empty string), so names should
+<b>ONLY</b> be used for debugging (making the source code easier to read,
+debugging printouts), they should not be used to keep track of values or map
+between them. For this purpose, use a <tt>std::map</tt> of pointers to the
+<tt>Value</tt> itself instead.</p>
+
+<p>One important aspect of LLVM is that there is no distinction between an SSA
+variable and the operation that produces it. Because of this, any reference to
+the value produced by an instruction (or the value available as an incoming
+argument, for example) is represented as a direct pointer to the instance of
+the class that
+represents this value. Although this may take some getting used to, it
+simplifies the representation and makes it easier to manipulate.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
+</h4>
+
+<div>
+
+<ul>
+ <li><tt>Value::use_iterator</tt> - Typedef for iterator over the
+use-list<br>
+ <tt>Value::const_use_iterator</tt> - Typedef for const_iterator over
+the use-list<br>
+ <tt>unsigned use_size()</tt> - Returns the number of users of the
+value.<br>
+ <tt>bool use_empty()</tt> - Returns true if there are no users.<br>
+ <tt>use_iterator use_begin()</tt> - Get an iterator to the start of
+the use-list.<br>
+ <tt>use_iterator use_end()</tt> - Get an iterator to the end of the
+use-list.<br>
+ <tt><a href="#User">User</a> *use_back()</tt> - Returns the last
+element in the list.
+ <p> These methods are the interface to access the def-use
+information in LLVM. As with all other iterators in LLVM, the naming
+conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
+ </li>
+ <li><tt><a href="#Type">Type</a> *getType() const</tt>
+ <p>This method returns the Type of the Value.</p>
+ </li>
+ <li><tt>bool hasName() const</tt><br>
+ <tt>std::string getName() const</tt><br>
+ <tt>void setName(const std::string &Name)</tt>
+ <p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
+be aware of the <a href="#nameWarning">precaution above</a>.</p>
+ </li>
+ <li><tt>void replaceAllUsesWith(Value *V)</tt>
+
+ <p>This method traverses the use list of a <tt>Value</tt> changing all <a
+ href="#User"><tt>User</tt>s</a> of the current value to refer to
+ "<tt>V</tt>" instead. For example, if you detect that an instruction always
+ produces a constant value (for example through constant folding), you can
+ replace all uses of the instruction with the constant like this:</p>
+
+<div class="doc_code">
+<pre>
+Inst->replaceAllUsesWith(ConstVal);
+</pre>
+</div>
+
+</ul>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="User">The <tt>User</tt> class</a>
+</h3>
+
+<div>
+
+<p>
+<tt>#include "<a href="/doxygen/User_8h-source.html">llvm/User.h</a>"</tt><br>
+doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
+Superclass: <a href="#Value"><tt>Value</tt></a></p>
+
+<p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
+refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
+that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
+referring to. The <tt>User</tt> class itself is a subclass of
+<tt>Value</tt>.</p>
+
+<p>The operands of a <tt>User</tt> point directly to the LLVM <a
+href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
+Single Assignment (SSA) form, there can only be one definition referred to,
+allowing this direct connection. This connection provides the use-def
+information in LLVM.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="m_User">Important Public Members of the <tt>User</tt> class</a>
+</h4>
+
+<div>
+
+<p>The <tt>User</tt> class exposes the operand list in two ways: through
+an index access interface and through an iterator based interface.</p>
+
+<ul>
+ <li><tt>Value *getOperand(unsigned i)</tt><br>
+ <tt>unsigned getNumOperands()</tt>
+ <p> These two methods expose the operands of the <tt>User</tt> in a
+convenient form for direct access.</p></li>
+
+ <li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
+list<br>
+ <tt>op_iterator op_begin()</tt> - Get an iterator to the start of
+the operand list.<br>
+ <tt>op_iterator op_end()</tt> - Get an iterator to the end of the
+operand list.
+ <p> Together, these methods make up the iterator based interface to
+the operands of a <tt>User</tt>.</p></li>
+</ul>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="Instruction">The <tt>Instruction</tt> class</a>
+</h3>
+
+<div>
+
+<p><tt>#include "</tt><tt><a
+href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
+doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
+Superclasses: <a href="#User"><tt>User</tt></a>, <a
+href="#Value"><tt>Value</tt></a></p>
+
+<p>The <tt>Instruction</tt> class is the common base class for all LLVM
+instructions. It provides only a few methods, but is a very commonly used
+class. The primary data tracked by the <tt>Instruction</tt> class itself is the
+opcode (instruction type) and the parent <a
+href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
+into. To represent a specific type of instruction, one of many subclasses of
+<tt>Instruction</tt> are used.</p>
+
+<p> Because the <tt>Instruction</tt> class subclasses the <a
+href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
+way as for other <a href="#User"><tt>User</tt></a>s (with the
+<tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
+<tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
+the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
+file contains some meta-data about the various different types of instructions
+in LLVM. It describes the enum values that are used as opcodes (for example
+<tt>Instruction::Add</tt> and <tt>Instruction::ICmp</tt>), as well as the
+concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
+example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
+href="#CmpInst">CmpInst</a></tt>). Unfortunately, the use of macros in
+this file confuses doxygen, so these enum values don't show up correctly in the
+<a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="s_Instruction">
+ Important Subclasses of the <tt>Instruction</tt> class
+ </a>
+</h4>
+<div>
+ <ul>
+ <li><tt><a name="BinaryOperator">BinaryOperator</a></tt>
+ <p>This subclasses represents all two operand instructions whose operands
+ must be the same type, except for the comparison instructions.</p></li>
+ <li><tt><a name="CastInst">CastInst</a></tt>
+ <p>This subclass is the parent of the 12 casting instructions. It provides
+ common operations on cast instructions.</p>
+ <li><tt><a name="CmpInst">CmpInst</a></tt>
+ <p>This subclass respresents the two comparison instructions,
+ <a href="LangRef.html#i_icmp">ICmpInst</a> (integer opreands), and
+ <a href="LangRef.html#i_fcmp">FCmpInst</a> (floating point operands).</p>
+ <li><tt><a name="TerminatorInst">TerminatorInst</a></tt>
+ <p>This subclass is the parent of all terminator instructions (those which
+ can terminate a block).</p>
+ </ul>
+ </div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="m_Instruction">
+ Important Public Members of the <tt>Instruction</tt> class
+ </a>
+</h4>
+
+<div>
+
+<ul>
+ <li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
+ <p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
+this <tt>Instruction</tt> is embedded into.</p></li>
+ <li><tt>bool mayWriteToMemory()</tt>
+ <p>Returns true if the instruction writes to memory, i.e. it is a
+ <tt>call</tt>,<tt>free</tt>,<tt>invoke</tt>, or <tt>store</tt>.</p></li>
+ <li><tt>unsigned getOpcode()</tt>
+ <p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
+ <li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
+ <p>Returns another instance of the specified instruction, identical
+in all ways to the original except that the instruction has no parent
+(ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
+and it has no name</p></li>
+</ul>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="Constant">The <tt>Constant</tt> class and subclasses</a>
+</h3>
+
+<div>
+
+<p>Constant represents a base class for different types of constants. It
+is subclassed by ConstantInt, ConstantArray, etc. for representing
+the various types of Constants. <a href="#GlobalValue">GlobalValue</a> is also
+a subclass, which represents the address of a global variable or function.
+</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>Important Subclasses of Constant</h4>
+<div>
+<ul>
+ <li>ConstantInt : This subclass of Constant represents an integer constant of
+ any width.
+ <ul>
+ <li><tt>const APInt& getValue() const</tt>: Returns the underlying
+ value of this constant, an APInt value.</li>
+ <li><tt>int64_t getSExtValue() const</tt>: Converts the underlying APInt
+ value to an int64_t via sign extension. If the value (not the bit width)
+ of the APInt is too large to fit in an int64_t, an assertion will result.
+ For this reason, use of this method is discouraged.</li>
+ <li><tt>uint64_t getZExtValue() const</tt>: Converts the underlying APInt
+ value to a uint64_t via zero extension. IF the value (not the bit width)
+ of the APInt is too large to fit in a uint64_t, an assertion will result.
+ For this reason, use of this method is discouraged.</li>
+ <li><tt>static ConstantInt* get(const APInt& Val)</tt>: Returns the
+ ConstantInt object that represents the value provided by <tt>Val</tt>.
+ The type is implied as the IntegerType that corresponds to the bit width
+ of <tt>Val</tt>.</li>
+ <li><tt>static ConstantInt* get(const Type *Ty, uint64_t Val)</tt>:
+ Returns the ConstantInt object that represents the value provided by
+ <tt>Val</tt> for integer type <tt>Ty</tt>.</li>
+ </ul>
+ </li>
+ <li>ConstantFP : This class represents a floating point constant.
+ <ul>
+ <li><tt>double getValue() const</tt>: Returns the underlying value of
+ this constant. </li>
+ </ul>
+ </li>
+ <li>ConstantArray : This represents a constant array.
+ <ul>
+ <li><tt>const std::vector<Use> &getValues() const</tt>: Returns
+ a vector of component constants that makeup this array. </li>
+ </ul>
+ </li>
+ <li>ConstantStruct : This represents a constant struct.
+ <ul>
+ <li><tt>const std::vector<Use> &getValues() const</tt>: Returns
+ a vector of component constants that makeup this array. </li>
+ </ul>
+ </li>
+ <li>GlobalValue : This represents either a global variable or a function. In
+ either case, the value is a constant fixed address (after linking).
+ </li>
+</ul>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
+</h3>
+
+<div>
+
+<p><tt>#include "<a
+href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
+doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
+Class</a><br>
+Superclasses: <a href="#Constant"><tt>Constant</tt></a>,
+<a href="#User"><tt>User</tt></a>, <a href="#Value"><tt>Value</tt></a></p>
+
+<p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
+href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
+visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
+Because they are visible at global scope, they are also subject to linking with
+other globals defined in different translation units. To control the linking
+process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
+<tt>GlobalValue</tt>s know whether they have internal or external linkage, as
+defined by the <tt>LinkageTypes</tt> enumeration.</p>
+
+<p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
+<tt>static</tt> in C), it is not visible to code outside the current translation
+unit, and does not participate in linking. If it has external linkage, it is
+visible to external code, and does participate in linking. In addition to
+linkage information, <tt>GlobalValue</tt>s keep track of which <a
+href="#Module"><tt>Module</tt></a> they are currently part of.</p>
+
+<p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
+by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
+global is always a pointer to its contents. It is important to remember this
+when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
+be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
+subclass of <tt>GlobalValue)</tt> that is an array of 24 ints, type <tt>[24 x
+i32]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
+the address of the first element of this array and the value of the
+<tt>GlobalVariable</tt> are the same, they have different types. The
+<tt>GlobalVariable</tt>'s type is <tt>[24 x i32]</tt>. The first element's type
+is <tt>i32.</tt> Because of this, accessing a global value requires you to
+dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
+can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
+Language Reference Manual</a>.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="m_GlobalValue">
+ Important Public Members of the <tt>GlobalValue</tt> class
+ </a>
+</h4>
+
+<div>
+
+<ul>
+ <li><tt>bool hasInternalLinkage() const</tt><br>
+ <tt>bool hasExternalLinkage() const</tt><br>
+ <tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
+ <p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
+ <p> </p>
+ </li>
+ <li><tt><a href="#Module">Module</a> *getParent()</tt>
+ <p> This returns the <a href="#Module"><tt>Module</tt></a> that the
+GlobalValue is currently embedded into.</p></li>
+</ul>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="Function">The <tt>Function</tt> class</a>
+</h3>
+
+<div>
+
+<p><tt>#include "<a
+href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
+info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
+Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
+<a href="#Constant"><tt>Constant</tt></a>,
+<a href="#User"><tt>User</tt></a>,
+<a href="#Value"><tt>Value</tt></a></p>
+
+<p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
+actually one of the more complex classes in the LLVM hierarchy because it must
+keep track of a large amount of data. The <tt>Function</tt> class keeps track
+of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal
+<a href="#Argument"><tt>Argument</tt></a>s, and a
+<a href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
+
+<p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
+commonly used part of <tt>Function</tt> objects. The list imposes an implicit
+ordering of the blocks in the function, which indicate how the code will be
+laid out by the backend. Additionally, the first <a
+href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
+<tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
+block. There are no implicit exit nodes, and in fact there may be multiple exit
+nodes from a single <tt>Function</tt>. If the <a
+href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
+the <tt>Function</tt> is actually a function declaration: the actual body of the
+function hasn't been linked in yet.</p>
+
+<p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
+<tt>Function</tt> class also keeps track of the list of formal <a
+href="#Argument"><tt>Argument</tt></a>s that the function receives. This
+container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
+nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
+the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
+
+<p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
+LLVM feature that is only used when you have to look up a value by name. Aside
+from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
+internally to make sure that there are not conflicts between the names of <a
+href="#Instruction"><tt>Instruction</tt></a>s, <a
+href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
+href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
+
+<p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
+and therefore also a <a href="#Constant">Constant</a>. The value of the function
+is its address (after linking) which is guaranteed to be constant.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="m_Function">
+ Important Public Members of the <tt>Function</tt> class
+ </a>
+</h4>
+
+<div>
+
+<ul>
+ <li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
+ *Ty, LinkageTypes Linkage, const std::string &N = "", Module* Parent = 0)</tt>
+
+ <p>Constructor used when you need to create new <tt>Function</tt>s to add
+ the program. The constructor must specify the type of the function to
+ create and what type of linkage the function should have. The <a
+ href="#FunctionType"><tt>FunctionType</tt></a> argument
+ specifies the formal arguments and return value for the function. The same
+ <a href="#FunctionType"><tt>FunctionType</tt></a> value can be used to
+ create multiple functions. The <tt>Parent</tt> argument specifies the Module
+ in which the function is defined. If this argument is provided, the function
+ will automatically be inserted into that module's list of
+ functions.</p></li>
+
+ <li><tt>bool isDeclaration()</tt>
+
+ <p>Return whether or not the <tt>Function</tt> has a body defined. If the
+ function is "external", it does not have a body, and thus must be resolved
+ by linking with a function defined in a different translation unit.</p></li>
+
+ <li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
+ <tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
+
+ <tt>begin()</tt>, <tt>end()</tt>
+ <tt>size()</tt>, <tt>empty()</tt>
+
+ <p>These are forwarding methods that make it easy to access the contents of
+ a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
+ list.</p></li>
+
+ <li><tt>Function::BasicBlockListType &getBasicBlockList()</tt>
+
+ <p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
+ is necessary to use when you need to update the list or perform a complex
+ action that doesn't have a forwarding method.</p></li>
+
+ <li><tt>Function::arg_iterator</tt> - Typedef for the argument list
+iterator<br>
+ <tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>
+
+ <tt>arg_begin()</tt>, <tt>arg_end()</tt>
+ <tt>arg_size()</tt>, <tt>arg_empty()</tt>
+
+ <p>These are forwarding methods that make it easy to access the contents of
+ a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
+ list.</p></li>
+
+ <li><tt>Function::ArgumentListType &getArgumentList()</tt>
+
+ <p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
+ necessary to use when you need to update the list or perform a complex
+ action that doesn't have a forwarding method.</p></li>
+
+ <li><tt><a href="#BasicBlock">BasicBlock</a> &getEntryBlock()</tt>
+
+ <p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
+ function. Because the entry block for the function is always the first
+ block, this returns the first block of the <tt>Function</tt>.</p></li>
+
+ <li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
+ <tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
+
+ <p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
+ <tt>Function</tt> and returns the return type of the function, or the <a
+ href="#FunctionType"><tt>FunctionType</tt></a> of the actual
+ function.</p></li>
+
+ <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
+
+ <p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
+ for this <tt>Function</tt>.</p></li>
+</ul>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
+</h3>
+
+<div>
+
+<p><tt>#include "<a
+href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
+<br>
+doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
+ Class</a><br>
+Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
+<a href="#Constant"><tt>Constant</tt></a>,
+<a href="#User"><tt>User</tt></a>,
+<a href="#Value"><tt>Value</tt></a></p>
+
+<p>Global variables are represented with the (surprise surprise)
+<tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
+subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
+always referenced by their address (global values must live in memory, so their
+"name" refers to their constant address). See
+<a href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global
+variables may have an initial value (which must be a
+<a href="#Constant"><tt>Constant</tt></a>), and if they have an initializer,
+they may be marked as "constant" themselves (indicating that their contents
+never change at runtime).</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="m_GlobalVariable">
+ Important Public Members of the <tt>GlobalVariable</tt> class
+ </a>
+</h4>
+
+<div>
+
+<ul>
+ <li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
+ isConstant, LinkageTypes& Linkage, <a href="#Constant">Constant</a>
+ *Initializer = 0, const std::string &Name = "", Module* Parent = 0)</tt>
+
+ <p>Create a new global variable of the specified type. If
+ <tt>isConstant</tt> is true then the global variable will be marked as
+ unchanging for the program. The Linkage parameter specifies the type of
+ linkage (internal, external, weak, linkonce, appending) for the variable.
+ If the linkage is InternalLinkage, WeakAnyLinkage, WeakODRLinkage,
+ LinkOnceAnyLinkage or LinkOnceODRLinkage, then the resultant
+ global variable will have internal linkage. AppendingLinkage concatenates
+ together all instances (in different translation units) of the variable
+ into a single variable but is only applicable to arrays. See
+ the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
+ further details on linkage types. Optionally an initializer, a name, and the
+ module to put the variable into may be specified for the global variable as
+ well.</p></li>
+
+ <li><tt>bool isConstant() const</tt>
+
+ <p>Returns true if this is a global variable that is known not to
+ be modified at runtime.</p></li>
+
+ <li><tt>bool hasInitializer()</tt>
+
+ <p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
+
+ <li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
+
+ <p>Returns the initial value for a <tt>GlobalVariable</tt>. It is not legal
+ to call this method if there is no initializer.</p></li>
+</ul>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
+</h3>
+
+<div>
+
+<p><tt>#include "<a
+href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
+doxygen info: <a href="/doxygen/classllvm_1_1BasicBlock.html">BasicBlock
+Class</a><br>
+Superclass: <a href="#Value"><tt>Value</tt></a></p>
+
+<p>This class represents a single entry single exit section of the code,
+commonly known as a basic block by the compiler community. The
+<tt>BasicBlock</tt> class maintains a list of <a
+href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
+Matching the language definition, the last element of this list of instructions
+is always a terminator instruction (a subclass of the <a
+href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
+
+<p>In addition to tracking the list of instructions that make up the block, the
+<tt>BasicBlock</tt> class also keeps track of the <a
+href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
+
+<p>Note that <tt>BasicBlock</tt>s themselves are <a
+href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
+like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
+<tt>label</tt>.</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="m_BasicBlock">
+ Important Public Members of the <tt>BasicBlock</tt> class
+ </a>
+</h4>
+
+<div>
+<ul>
+
+<li><tt>BasicBlock(const std::string &Name = "", </tt><tt><a
+ href="#Function">Function</a> *Parent = 0)</tt>
+
+<p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
+insertion into a function. The constructor optionally takes a name for the new
+block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
+the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
+automatically inserted at the end of the specified <a
+href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
+manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
+
+<li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
+<tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
+<tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
+<tt>size()</tt>, <tt>empty()</tt>
+STL-style functions for accessing the instruction list.
+
+<p>These methods and typedefs are forwarding functions that have the same
+semantics as the standard library methods of the same names. These methods
+expose the underlying instruction list of a basic block in a way that is easy to
+manipulate. To get the full complement of container operations (including
+operations to update the list), you must use the <tt>getInstList()</tt>
+method.</p></li>
+
+<li><tt>BasicBlock::InstListType &getInstList()</tt>
+
+<p>This method is used to get access to the underlying container that actually
+holds the Instructions. This method must be used when there isn't a forwarding
+function in the <tt>BasicBlock</tt> class for the operation that you would like
+to perform. Because there are no forwarding functions for "updating"
+operations, you need to use this if you want to update the contents of a
+<tt>BasicBlock</tt>.</p></li>
+
+<li><tt><a href="#Function">Function</a> *getParent()</tt>
+
+<p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
+embedded into, or a null pointer if it is homeless.</p></li>
+
+<li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
+
+<p> Returns a pointer to the terminator instruction that appears at the end of
+the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
+instruction in the block is not a terminator, then a null pointer is
+returned.</p></li>
+
+</ul>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="Argument">The <tt>Argument</tt> class</a>
+</h3>
+
+<div>
+
+<p>This subclass of Value defines the interface for incoming formal
+arguments to a function. A Function maintains a list of its formal
+arguments. An argument has a pointer to the parent Function.</p>
+
+</div>
+
+</div>
+
+<!-- *********************************************************************** -->
+<hr>
+<address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
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+ <a href="mailto:dhurjati at cs.uiuc.edu">Dinakar Dhurjati</a> and
+ <a href="mailto:sabre at nondot.org">Chris Lattner</a><br>
+ <a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date: 2012-10-06 19:56:09 -0500 (Sat, 06 Oct 2012) $
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+ <h3><a href="index.html">Table Of Contents</a></h3>
+ <ul>
+<li><a class="reference internal" href="#">Creating an LLVM Project</a><ul>
+<li><a class="reference internal" href="#overview">Overview</a></li>
+<li><a class="reference internal" href="#create-a-project-from-the-sample-project">Create a Project from the Sample Project</a></li>
+<li><a class="reference internal" href="#source-tree-layout">Source Tree Layout</a></li>
+<li><a class="reference internal" href="#writing-llvm-style-makefiles">Writing LLVM Style Makefiles</a><ul>
+<li><a class="reference internal" href="#required-variables">Required Variables</a></li>
+<li><a class="reference internal" href="#variables-for-building-subdirectories">Variables for Building Subdirectories</a></li>
+<li><a class="reference internal" href="#variables-for-building-libraries">Variables for Building Libraries</a></li>
+<li><a class="reference internal" href="#variables-for-building-programs">Variables for Building Programs</a></li>
+<li><a class="reference internal" href="#miscellaneous-variables">Miscellaneous Variables</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#placement-of-object-code">Placement of Object Code</a></li>
+<li><a class="reference internal" href="#further-help">Further Help</a></li>
+</ul>
+</li>
+</ul>
+
+ <h4>Previous topic</h4>
+ <p class="topless"><a href="MakefileGuide.html"
+ title="previous chapter">LLVM Makefile Guide</a></p>
+ <h4>Next topic</h4>
+ <p class="topless"><a href="mailing_lists.html"
+ title="next chapter">Mailing Lists</a></p>
+ <h3>This Page</h3>
+ <ul class="this-page-menu">
+ <li><a href="_sources/Projects.txt"
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+ <div class="documentwrapper">
+ <div class="bodywrapper">
+ <div class="body">
+
+ <div class="section" id="creating-an-llvm-project">
+<span id="projects"></span><h1>Creating an LLVM Project<a class="headerlink" href="#creating-an-llvm-project" title="Permalink to this headline">¶</a></h1>
+<div class="contents local topic" id="contents">
+<ul class="simple">
+<li><a class="reference internal" href="#overview" id="id1">Overview</a></li>
+<li><a class="reference internal" href="#create-a-project-from-the-sample-project" id="id2">Create a Project from the Sample Project</a></li>
+<li><a class="reference internal" href="#source-tree-layout" id="id3">Source Tree Layout</a></li>
+<li><a class="reference internal" href="#writing-llvm-style-makefiles" id="id4">Writing LLVM Style Makefiles</a><ul>
+<li><a class="reference internal" href="#required-variables" id="id5">Required Variables</a></li>
+<li><a class="reference internal" href="#variables-for-building-subdirectories" id="id6">Variables for Building Subdirectories</a></li>
+<li><a class="reference internal" href="#variables-for-building-libraries" id="id7">Variables for Building Libraries</a></li>
+<li><a class="reference internal" href="#variables-for-building-programs" id="id8">Variables for Building Programs</a></li>
+<li><a class="reference internal" href="#miscellaneous-variables" id="id9">Miscellaneous Variables</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#placement-of-object-code" id="id10">Placement of Object Code</a></li>
+<li><a class="reference internal" href="#further-help" id="id11">Further Help</a></li>
+</ul>
+</div>
+<div class="section" id="overview">
+<h2><a class="toc-backref" href="#id1">Overview</a><a class="headerlink" href="#overview" title="Permalink to this headline">¶</a></h2>
+<p>The LLVM build system is designed to facilitate the building of third party
+projects that use LLVM header files, libraries, and tools. In order to use
+these facilities, a <tt class="docutils literal"><span class="pre">Makefile</span></tt> from a project must do the following things:</p>
+<ul class="simple">
+<li>Set <tt class="docutils literal"><span class="pre">make</span></tt> variables. There are several variables that a <tt class="docutils literal"><span class="pre">Makefile</span></tt> needs
+to set to use the LLVM build system:<ul>
+<li><tt class="docutils literal"><span class="pre">PROJECT_NAME</span></tt> - The name by which your project is known.</li>
+<li><tt class="docutils literal"><span class="pre">LLVM_SRC_ROOT</span></tt> - The root of the LLVM source tree.</li>
+<li><tt class="docutils literal"><span class="pre">LLVM_OBJ_ROOT</span></tt> - The root of the LLVM object tree.</li>
+<li><tt class="docutils literal"><span class="pre">PROJ_SRC_ROOT</span></tt> - The root of the project’s source tree.</li>
+<li><tt class="docutils literal"><span class="pre">PROJ_OBJ_ROOT</span></tt> - The root of the project’s object tree.</li>
+<li><tt class="docutils literal"><span class="pre">PROJ_INSTALL_ROOT</span></tt> - The root installation directory.</li>
+<li><tt class="docutils literal"><span class="pre">LEVEL</span></tt> - The relative path from the current directory to the
+project’s root <tt class="docutils literal"><span class="pre">($PROJ_OBJ_ROOT)</span></tt>.</li>
+</ul>
+</li>
+<li>Include <tt class="docutils literal"><span class="pre">Makefile.config</span></tt> from <tt class="docutils literal"><span class="pre">$(LLVM_OBJ_ROOT)</span></tt>.</li>
+<li>Include <tt class="docutils literal"><span class="pre">Makefile.rules</span></tt> from <tt class="docutils literal"><span class="pre">$(LLVM_SRC_ROOT)</span></tt>.</li>
+</ul>
+<p>There are two ways that you can set all of these variables:</p>
+<ul class="simple">
+<li>You can write your own <tt class="docutils literal"><span class="pre">Makefiles</span></tt> which hard-code these values.</li>
+<li>You can use the pre-made LLVM sample project. This sample project includes
+<tt class="docutils literal"><span class="pre">Makefiles</span></tt>, a configure script that can be used to configure the location
+of LLVM, and the ability to support multiple object directories from a single
+source directory.</li>
+</ul>
+<p>This document assumes that you will base your project on the LLVM sample project
+found in <tt class="docutils literal"><span class="pre">llvm/projects/sample</span></tt>. If you want to devise your own build system,
+studying the sample project and LLVM <tt class="docutils literal"><span class="pre">Makefiles</span></tt> will probably provide enough
+information on how to write your own <tt class="docutils literal"><span class="pre">Makefiles</span></tt>.</p>
+</div>
+<div class="section" id="create-a-project-from-the-sample-project">
+<h2><a class="toc-backref" href="#id2">Create a Project from the Sample Project</a><a class="headerlink" href="#create-a-project-from-the-sample-project" title="Permalink to this headline">¶</a></h2>
+<p>Follow these simple steps to start your project:</p>
+<ol class="arabic">
+<li><p class="first">Copy the <tt class="docutils literal"><span class="pre">llvm/projects/sample</span></tt> directory to any place of your choosing.
+You can place it anywhere you like. Rename the directory to match the name
+of your project.</p>
+</li>
+<li><p class="first">If you downloaded LLVM using Subversion, remove all the directories named
+<tt class="docutils literal"><span class="pre">.svn</span></tt> (and all the files therein) from your project’s new source tree.
+This will keep Subversion from thinking that your project is inside
+<tt class="docutils literal"><span class="pre">llvm/trunk/projects/sample</span></tt>.</p>
+</li>
+<li><p class="first">Add your source code and Makefiles to your source tree.</p>
+</li>
+<li><p class="first">If you want your project to be configured with the <tt class="docutils literal"><span class="pre">configure</span></tt> script then
+you need to edit <tt class="docutils literal"><span class="pre">autoconf/configure.ac</span></tt> as follows:</p>
+<ul class="simple">
+<li><strong>AC_INIT</strong> - Place the name of your project, its version number and a
+contact email address for your project as the arguments to this macro</li>
+<li><strong>AC_CONFIG_AUX_DIR</strong> - If your project isn’t in the <tt class="docutils literal"><span class="pre">llvm/projects</span></tt>
+directory then you might need to adjust this so that it specifies a
+relative path to the <tt class="docutils literal"><span class="pre">llvm/autoconf</span></tt> directory.</li>
+<li><strong>LLVM_CONFIG_PROJECT</strong> - Just leave this alone.</li>
+<li><strong>AC_CONFIG_SRCDIR</strong> - Specify a path to a file name that identifies your
+project; or just leave it at <tt class="docutils literal"><span class="pre">Makefile.common.in</span></tt>.</li>
+<li><strong>AC_CONFIG_FILES</strong> - Do not change.</li>
+<li><strong>AC_CONFIG_MAKEFILE</strong> - Use one of these macros for each Makefile that
+your project uses. This macro arranges for your makefiles to be copied from
+the source directory, unmodified, to the build directory.</li>
+</ul>
+</li>
+<li><p class="first">After updating <tt class="docutils literal"><span class="pre">autoconf/configure.ac</span></tt>, regenerate the configure script
+with these commands. (You must be using <tt class="docutils literal"><span class="pre">Autoconf</span></tt> version 2.59 or later
+and your <tt class="docutils literal"><span class="pre">aclocal</span></tt> version should be 1.9 or later.)</p>
+<blockquote>
+<div><div class="highlight-bash"><div class="highlight"><pre>% <span class="nb">cd </span>autoconf
+% ./AutoRegen.sh
+</pre></div>
+</div>
+</div></blockquote>
+</li>
+<li><p class="first">Run <tt class="docutils literal"><span class="pre">configure</span></tt> in the directory in which you want to place object code.
+Use the following options to tell your project where it can find LLVM:</p>
+<dl class="docutils">
+<dt><tt class="docutils literal"><span class="pre">--with-llvmsrc=<directory></span></tt></dt>
+<dd><p class="first last">Tell your project where the LLVM source tree is located.</p>
+</dd>
+<dt><tt class="docutils literal"><span class="pre">--with-llvmobj=<directory></span></tt></dt>
+<dd><p class="first last">Tell your project where the LLVM object tree is located.</p>
+</dd>
+<dt><tt class="docutils literal"><span class="pre">--prefix=<directory></span></tt></dt>
+<dd><p class="first last">Tell your project where it should get installed.</p>
+</dd>
+</dl>
+</li>
+</ol>
+<p>That’s it! Now all you have to do is type <tt class="docutils literal"><span class="pre">gmake</span></tt> (or <tt class="docutils literal"><span class="pre">make</span></tt> if you’re on a
+GNU/Linux system) in the root of your object directory, and your project should
+build.</p>
+</div>
+<div class="section" id="source-tree-layout">
+<h2><a class="toc-backref" href="#id3">Source Tree Layout</a><a class="headerlink" href="#source-tree-layout" title="Permalink to this headline">¶</a></h2>
+<p>In order to use the LLVM build system, you will want to organize your source
+code so that it can benefit from the build system’s features. Mainly, you want
+your source tree layout to look similar to the LLVM source tree layout. The
+best way to do this is to just copy the project tree from
+<tt class="docutils literal"><span class="pre">llvm/projects/sample</span></tt> and modify it to meet your needs, but you can certainly
+add to it if you want.</p>
+<p>Underneath your top level directory, you should have the following directories:</p>
+<p><strong>lib</strong></p>
+<blockquote>
+<div><p>This subdirectory should contain all of your library source code. For each
+library that you build, you will have one directory in <strong>lib</strong> that will
+contain that library’s source code.</p>
+<p>Libraries can be object files, archives, or dynamic libraries. The <strong>lib</strong>
+directory is just a convenient place for libraries as it places them all in
+a directory from which they can be linked later.</p>
+</div></blockquote>
+<p><strong>include</strong></p>
+<blockquote>
+<div><p>This subdirectory should contain any header files that are global to your
+project. By global, we mean that they are used by more than one library or
+executable of your project.</p>
+<p>By placing your header files in <strong>include</strong>, they will be found
+automatically by the LLVM build system. For example, if you have a file
+<strong>include/jazz/note.h</strong>, then your source files can include it simply with
+<strong>#include “jazz/note.h”</strong>.</p>
+</div></blockquote>
+<p><strong>tools</strong></p>
+<blockquote>
+<div>This subdirectory should contain all of your source code for executables.
+For each program that you build, you will have one directory in <strong>tools</strong>
+that will contain that program’s source code.</div></blockquote>
+<p><strong>test</strong></p>
+<blockquote>
+<div><p>This subdirectory should contain tests that verify that your code works
+correctly. Automated tests are especially useful.</p>
+<p>Currently, the LLVM build system provides basic support for tests. The LLVM
+system provides the following:</p>
+</div></blockquote>
+<ul>
+<li><p class="first">LLVM provides a <tt class="docutils literal"><span class="pre">tcl</span></tt> procedure that is used by <tt class="docutils literal"><span class="pre">Dejagnu</span></tt> to run tests.
+It can be found in <tt class="docutils literal"><span class="pre">llvm/lib/llvm-dg.exp</span></tt>. This test procedure uses <tt class="docutils literal"><span class="pre">RUN</span></tt>
+lines in the actual test case to determine how to run the test. See the
+<a class="reference external" href="TestingGuide.html">TestingGuide</a> for more details. You can easily write
+Makefile support similar to the Makefiles in <tt class="docutils literal"><span class="pre">llvm/test</span></tt> to use <tt class="docutils literal"><span class="pre">Dejagnu</span></tt>
+to run your project’s tests.</p>
+</li>
+<li><p class="first">LLVM contains an optional package called <tt class="docutils literal"><span class="pre">llvm-test</span></tt>, which provides
+benchmarks and programs that are known to compile with the Clang front
+end. You can use these programs to test your code, gather statistical
+information, and compare it to the current LLVM performance statistics.</p>
+<p>Currently, there is no way to hook your tests directly into the <tt class="docutils literal"><span class="pre">llvm/test</span></tt>
+testing harness. You will simply need to find a way to use the source
+provided within that directory on your own.</p>
+</li>
+</ul>
+<p>Typically, you will want to build your <strong>lib</strong> directory first followed by your
+<strong>tools</strong> directory.</p>
+</div>
+<div class="section" id="writing-llvm-style-makefiles">
+<h2><a class="toc-backref" href="#id4">Writing LLVM Style Makefiles</a><a class="headerlink" href="#writing-llvm-style-makefiles" title="Permalink to this headline">¶</a></h2>
+<p>The LLVM build system provides a convenient way to build libraries and
+executables. Most of your project Makefiles will only need to define a few
+variables. Below is a list of the variables one can set and what they can
+do:</p>
+<div class="section" id="required-variables">
+<h3><a class="toc-backref" href="#id5">Required Variables</a><a class="headerlink" href="#required-variables" title="Permalink to this headline">¶</a></h3>
+<p><tt class="docutils literal"><span class="pre">LEVEL</span></tt></p>
+<blockquote>
+<div>This variable is the relative path from this <tt class="docutils literal"><span class="pre">Makefile</span></tt> to the top
+directory of your project’s source code. For example, if your source code
+is in <tt class="docutils literal"><span class="pre">/tmp/src</span></tt>, then the <tt class="docutils literal"><span class="pre">Makefile</span></tt> in <tt class="docutils literal"><span class="pre">/tmp/src/jump/high</span></tt>
+would set <tt class="docutils literal"><span class="pre">LEVEL</span></tt> to <tt class="docutils literal"><span class="pre">"../.."</span></tt>.</div></blockquote>
+</div>
+<div class="section" id="variables-for-building-subdirectories">
+<h3><a class="toc-backref" href="#id6">Variables for Building Subdirectories</a><a class="headerlink" href="#variables-for-building-subdirectories" title="Permalink to this headline">¶</a></h3>
+<p><tt class="docutils literal"><span class="pre">DIRS</span></tt></p>
+<blockquote>
+<div>This is a space separated list of subdirectories that should be built. They
+will be built, one at a time, in the order specified.</div></blockquote>
+<p><tt class="docutils literal"><span class="pre">PARALLEL_DIRS</span></tt></p>
+<blockquote>
+<div>This is a list of directories that can be built in parallel. These will be
+built after the directories in DIRS have been built.</div></blockquote>
+<p><tt class="docutils literal"><span class="pre">OPTIONAL_DIRS</span></tt></p>
+<blockquote>
+<div>This is a list of directories that can be built if they exist, but will not
+cause an error if they do not exist. They are built serially in the order
+in which they are listed.</div></blockquote>
+</div>
+<div class="section" id="variables-for-building-libraries">
+<h3><a class="toc-backref" href="#id7">Variables for Building Libraries</a><a class="headerlink" href="#variables-for-building-libraries" title="Permalink to this headline">¶</a></h3>
+<p><tt class="docutils literal"><span class="pre">LIBRARYNAME</span></tt></p>
+<blockquote>
+<div>This variable contains the base name of the library that will be built. For
+example, to build a library named <tt class="docutils literal"><span class="pre">libsample.a</span></tt>, <tt class="docutils literal"><span class="pre">LIBRARYNAME</span></tt> should
+be set to <tt class="docutils literal"><span class="pre">sample</span></tt>.</div></blockquote>
+<p><tt class="docutils literal"><span class="pre">BUILD_ARCHIVE</span></tt></p>
+<blockquote>
+<div>By default, a library is a <tt class="docutils literal"><span class="pre">.o</span></tt> file that is linked directly into a
+program. To build an archive (also known as a static library), set the
+<tt class="docutils literal"><span class="pre">BUILD_ARCHIVE</span></tt> variable.</div></blockquote>
+<p><tt class="docutils literal"><span class="pre">SHARED_LIBRARY</span></tt></p>
+<blockquote>
+<div>If <tt class="docutils literal"><span class="pre">SHARED_LIBRARY</span></tt> is defined in your Makefile, a shared (or dynamic)
+library will be built.</div></blockquote>
+</div>
+<div class="section" id="variables-for-building-programs">
+<h3><a class="toc-backref" href="#id8">Variables for Building Programs</a><a class="headerlink" href="#variables-for-building-programs" title="Permalink to this headline">¶</a></h3>
+<p><tt class="docutils literal"><span class="pre">TOOLNAME</span></tt></p>
+<blockquote>
+<div>This variable contains the name of the program that will be built. For
+example, to build an executable named <tt class="docutils literal"><span class="pre">sample</span></tt>, <tt class="docutils literal"><span class="pre">TOOLNAME</span></tt> should be set
+to <tt class="docutils literal"><span class="pre">sample</span></tt>.</div></blockquote>
+<p><tt class="docutils literal"><span class="pre">USEDLIBS</span></tt></p>
+<blockquote>
+<div><p>This variable holds a space separated list of libraries that should be
+linked into the program. These libraries must be libraries that come from
+your <strong>lib</strong> directory. The libraries must be specified without their
+<tt class="docutils literal"><span class="pre">lib</span></tt> prefix. For example, to link <tt class="docutils literal"><span class="pre">libsample.a</span></tt>, you would set
+<tt class="docutils literal"><span class="pre">USEDLIBS</span></tt> to <tt class="docutils literal"><span class="pre">sample.a</span></tt>.</p>
+<p>Note that this works only for statically linked libraries.</p>
+</div></blockquote>
+<p><tt class="docutils literal"><span class="pre">LLVMLIBS</span></tt></p>
+<blockquote>
+<div><p>This variable holds a space separated list of libraries that should be
+linked into the program. These libraries must be LLVM libraries. The
+libraries must be specified without their <tt class="docutils literal"><span class="pre">lib</span></tt> prefix. For example, to
+link with a driver that performs an IR transformation you might set
+<tt class="docutils literal"><span class="pre">LLVMLIBS</span></tt> to this minimal set of libraries <tt class="docutils literal"><span class="pre">LLVMSupport.a</span> <span class="pre">LLVMCore.a</span>
+<span class="pre">LLVMBitReader.a</span> <span class="pre">LLVMAsmParser.a</span> <span class="pre">LLVMAnalysis.a</span> <span class="pre">LLVMTransformUtils.a</span>
+<span class="pre">LLVMScalarOpts.a</span> <span class="pre">LLVMTarget.a</span></tt>.</p>
+<p>Note that this works only for statically linked libraries. LLVM is split
+into a large number of static libraries, and the list of libraries you
+require may be much longer than the list above. To see a full list of
+libraries use: <tt class="docutils literal"><span class="pre">llvm-config</span> <span class="pre">--libs</span> <span class="pre">all</span></tt>. Using <tt class="docutils literal"><span class="pre">LINK_COMPONENTS</span></tt> as
+described below, obviates the need to set <tt class="docutils literal"><span class="pre">LLVMLIBS</span></tt>.</p>
+</div></blockquote>
+<p><tt class="docutils literal"><span class="pre">LINK_COMPONENTS</span></tt></p>
+<blockquote>
+<div>This variable holds a space separated list of components that the LLVM
+<tt class="docutils literal"><span class="pre">Makefiles</span></tt> pass to the <tt class="docutils literal"><span class="pre">llvm-config</span></tt> tool to generate a link line for
+the program. For example, to link with all LLVM libraries use
+<tt class="docutils literal"><span class="pre">LINK_COMPONENTS</span> <span class="pre">=</span> <span class="pre">all</span></tt>.</div></blockquote>
+<p><tt class="docutils literal"><span class="pre">LIBS</span></tt></p>
+<blockquote>
+<div><p>To link dynamic libraries, add <tt class="docutils literal"><span class="pre">-l<library</span> <span class="pre">base</span> <span class="pre">name></span></tt> to the <tt class="docutils literal"><span class="pre">LIBS</span></tt>
+variable. The LLVM build system will look in the same places for dynamic
+libraries as it does for static libraries.</p>
+<p>For example, to link <tt class="docutils literal"><span class="pre">libsample.so</span></tt>, you would have the following line in
+your <tt class="docutils literal"><span class="pre">Makefile</span></tt>:</p>
+<blockquote>
+<div><div class="highlight-makefile"><div class="highlight"><pre><span class="nv">LIBS</span> <span class="o">+=</span> -lsample
+</pre></div>
+</div>
+</div></blockquote>
+</div></blockquote>
+<p>Note that <tt class="docutils literal"><span class="pre">LIBS</span></tt> must occur in the Makefile after the inclusion of
+<tt class="docutils literal"><span class="pre">Makefile.common</span></tt>.</p>
+</div>
+<div class="section" id="miscellaneous-variables">
+<h3><a class="toc-backref" href="#id9">Miscellaneous Variables</a><a class="headerlink" href="#miscellaneous-variables" title="Permalink to this headline">¶</a></h3>
+<p><tt class="docutils literal"><span class="pre">CFLAGS</span></tt> & <tt class="docutils literal"><span class="pre">CPPFLAGS</span></tt></p>
+<blockquote>
+<div><p>This variable can be used to add options to the C and C++ compiler,
+respectively. It is typically used to add options that tell the compiler
+the location of additional directories to search for header files.</p>
+<p>It is highly suggested that you append to <tt class="docutils literal"><span class="pre">CFLAGS</span></tt> and <tt class="docutils literal"><span class="pre">CPPFLAGS</span></tt> as
+opposed to overwriting them. The master <tt class="docutils literal"><span class="pre">Makefiles</span></tt> may already have
+useful options in them that you may not want to overwrite.</p>
+</div></blockquote>
+</div>
+</div>
+<div class="section" id="placement-of-object-code">
+<h2><a class="toc-backref" href="#id10">Placement of Object Code</a><a class="headerlink" href="#placement-of-object-code" title="Permalink to this headline">¶</a></h2>
+<p>The final location of built libraries and executables will depend upon whether
+you do a <tt class="docutils literal"><span class="pre">Debug</span></tt>, <tt class="docutils literal"><span class="pre">Release</span></tt>, or <tt class="docutils literal"><span class="pre">Profile</span></tt> build.</p>
+<p>Libraries</p>
+<blockquote>
+<div>All libraries (static and dynamic) will be stored in
+<tt class="docutils literal"><span class="pre">PROJ_OBJ_ROOT/<type>/lib</span></tt>, where <em>type</em> is <tt class="docutils literal"><span class="pre">Debug</span></tt>, <tt class="docutils literal"><span class="pre">Release</span></tt>, or
+<tt class="docutils literal"><span class="pre">Profile</span></tt> for a debug, optimized, or profiled build, respectively.</div></blockquote>
+<p>Executables</p>
+<blockquote>
+<div>All executables will be stored in <tt class="docutils literal"><span class="pre">PROJ_OBJ_ROOT/<type>/bin</span></tt>, where <em>type</em>
+is <tt class="docutils literal"><span class="pre">Debug</span></tt>, <tt class="docutils literal"><span class="pre">Release</span></tt>, or <tt class="docutils literal"><span class="pre">Profile</span></tt> for a debug, optimized, or
+profiled build, respectively.</div></blockquote>
+</div>
+<div class="section" id="further-help">
+<h2><a class="toc-backref" href="#id11">Further Help</a><a class="headerlink" href="#further-help" title="Permalink to this headline">¶</a></h2>
+<p>If you have any questions or need any help creating an LLVM project, the LLVM
+team would be more than happy to help. You can always post your questions to
+the <a class="reference external" href="http://lists.cs.uiuc.edu/pipermail/llvmdev/">LLVM Developers Mailing List</a>.</p>
+</div>
+</div>
+
+
+ </div>
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+ </div>
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+ © Copyright 2012, LLVM Project.
+ Last updated on 2012-12-21.
+ Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
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+</html>
\ No newline at end of file
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+ <li class="right" style="margin-right: 10px">
+ <a href="genindex.html" title="General Index"
+ accesskey="I">index</a></li>
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+ <a href="TableGenFundamentals.html" title="TableGen Fundamentals"
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+ <h3><a href="index.html">Table Of Contents</a></h3>
+ <ul>
+<li><a class="reference internal" href="#">Segmented Stacks in LLVM</a><ul>
+<li><a class="reference internal" href="#introduction">Introduction</a></li>
+<li><a class="reference internal" href="#implementation-details">Implementation Details</a><ul>
+<li><a class="reference internal" href="#allocating-stacklets">Allocating Stacklets</a></li>
+<li><a class="reference internal" href="#variable-sized-allocas">Variable Sized Allocas</a></li>
+</ul>
+</li>
+</ul>
+</li>
+</ul>
+
+ <h4>Previous topic</h4>
+ <p class="topless"><a href="LinkTimeOptimization.html"
+ title="previous chapter">LLVM Link Time Optimization: Design and Implementation</a></p>
+ <h4>Next topic</h4>
+ <p class="topless"><a href="TableGenFundamentals.html"
+ title="next chapter">TableGen Fundamentals</a></p>
+ <h3>This Page</h3>
+ <ul class="this-page-menu">
+ <li><a href="_sources/SegmentedStacks.txt"
+ rel="nofollow">Show Source</a></li>
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+ <div class="documentwrapper">
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+ <div class="body">
+
+ <div class="section" id="segmented-stacks-in-llvm">
+<span id="segmented-stacks"></span><h1>Segmented Stacks in LLVM<a class="headerlink" href="#segmented-stacks-in-llvm" title="Permalink to this headline">¶</a></h1>
+<div class="contents local topic" id="contents">
+<ul class="simple">
+<li><a class="reference internal" href="#introduction" id="id2">Introduction</a></li>
+<li><a class="reference internal" href="#implementation-details" id="id3">Implementation Details</a><ul>
+<li><a class="reference internal" href="#allocating-stacklets" id="id4">Allocating Stacklets</a></li>
+<li><a class="reference internal" href="#variable-sized-allocas" id="id5">Variable Sized Allocas</a></li>
+</ul>
+</li>
+</ul>
+</div>
+<div class="section" id="introduction">
+<h2><a class="toc-backref" href="#id2">Introduction</a><a class="headerlink" href="#introduction" title="Permalink to this headline">¶</a></h2>
+<p>Segmented stack allows stack space to be allocated incrementally than as a
+monolithic chunk (of some worst case size) at thread initialization. This is
+done by allocating stack blocks (henceforth called <em>stacklets</em>) and linking them
+into a doubly linked list. The function prologue is responsible for checking if
+the current stacklet has enough space for the function to execute; and if not,
+call into the libgcc runtime to allocate more stack space. When using <tt class="docutils literal"><span class="pre">llc</span></tt>,
+segmented stacks can be enabled by adding <tt class="docutils literal"><span class="pre">-segmented-stacks</span></tt> to the command
+line.</p>
+<p>The runtime functionality is <a class="reference external" href="http://gcc.gnu.org/wiki/SplitStacks">already there in libgcc</a>.</p>
+</div>
+<div class="section" id="implementation-details">
+<h2><a class="toc-backref" href="#id3">Implementation Details</a><a class="headerlink" href="#implementation-details" title="Permalink to this headline">¶</a></h2>
+<div class="section" id="allocating-stacklets">
+<span id="id1"></span><h3><a class="toc-backref" href="#id4">Allocating Stacklets</a><a class="headerlink" href="#allocating-stacklets" title="Permalink to this headline">¶</a></h3>
+<p>As mentioned above, the function prologue checks if the current stacklet has
+enough space. The current approach is to use a slot in the TCB to store the
+current stack limit (minus the amount of space needed to allocate a new block) -
+this slot’s offset is again dictated by <tt class="docutils literal"><span class="pre">libgcc</span></tt>. The generated
+assembly looks like this on x86-64:</p>
+<div class="highlight-nasm"><pre> leaq -8(%rsp), %r10
+ cmpq %fs:112, %r10
+ jg .LBB0_2
+
+ # More stack space needs to be allocated
+ movabsq $8, %r10 # The amount of space needed
+ movabsq $0, %r11 # The total size of arguments passed on stack
+ callq __morestack
+ ret # The reason for this extra return is explained below
+.LBB0_2:
+ # Usual prologue continues here</pre>
+</div>
+<p>The size of function arguments on the stack needs to be passed to
+<tt class="docutils literal"><span class="pre">__morestack</span></tt> (this function is implemented in <tt class="docutils literal"><span class="pre">libgcc</span></tt>) since that number
+of bytes has to be copied from the previous stacklet to the current one. This is
+so that SP (and FP) relative addressing of function arguments work as expected.</p>
+<p>The unusual <tt class="docutils literal"><span class="pre">ret</span></tt> is needed to have the function which made a call to
+<tt class="docutils literal"><span class="pre">__morestack</span></tt> return correctly. <tt class="docutils literal"><span class="pre">__morestack</span></tt>, instead of returning, calls
+into <tt class="docutils literal"><span class="pre">.LBB0_2</span></tt>. This is possible since both, the size of the <tt class="docutils literal"><span class="pre">ret</span></tt>
+instruction and the PC of call to <tt class="docutils literal"><span class="pre">__morestack</span></tt> are known. When the function
+body returns, control is transferred back to <tt class="docutils literal"><span class="pre">__morestack</span></tt>. <tt class="docutils literal"><span class="pre">__morestack</span></tt>
+then de-allocates the new stacklet, restores the correct SP value, and does a
+second return, which returns control to the correct caller.</p>
+</div>
+<div class="section" id="variable-sized-allocas">
+<h3><a class="toc-backref" href="#id5">Variable Sized Allocas</a><a class="headerlink" href="#variable-sized-allocas" title="Permalink to this headline">¶</a></h3>
+<p>The section on <a class="reference internal" href="#allocating-stacklets">allocating stacklets</a> automatically assumes that every stack
+frame will be of fixed size. However, LLVM allows the use of the <tt class="docutils literal"><span class="pre">llvm.alloca</span></tt>
+intrinsic to allocate dynamically sized blocks of memory on the stack. When
+faced with such a variable-sized alloca, code is generated to:</p>
+<ul class="simple">
+<li>Check if the current stacklet has enough space. If yes, just bump the SP, like
+in the normal case.</li>
+<li>If not, generate a call to <tt class="docutils literal"><span class="pre">libgcc</span></tt>, which allocates the memory from the
+heap.</li>
+</ul>
+<p>The memory allocated from the heap is linked into a list in the current
+stacklet, and freed along with the same. This prevents a memory leak.</p>
+</div>
+</div>
+</div>
+
+
+ </div>
+ </div>
+ </div>
+ <div class="clearer"></div>
+ </div>
+ <div class="related">
+ <h3>Navigation</h3>
+ <ul>
+ <li class="right" style="margin-right: 10px">
+ <a href="genindex.html" title="General Index"
+ >index</a></li>
+ <li class="right" >
+ <a href="TableGenFundamentals.html" title="TableGen Fundamentals"
+ >next</a> |</li>
+ <li class="right" >
+ <a href="LinkTimeOptimization.html" title="LLVM Link Time Optimization: Design and Implementation"
+ >previous</a> |</li>
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+ <li><a href="index.html">Documentation</a>»</li>
+
+ <li><a href="subsystems.html" >Subsystem Documentation</a> »</li>
+ </ul>
+ </div>
+ <div class="footer">
+ © Copyright 2012, LLVM Project.
+ Last updated on 2012-12-21.
+ Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
+ </div>
+ </body>
+</html>
\ No newline at end of file
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+++ www-releases/trunk/3.2/docs/SourceLevelDebugging.html Fri Dec 21 03:14:44 2012
@@ -0,0 +1,2858 @@
+<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+<html>
+<head>
+ <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
+ <title>Source Level Debugging with LLVM</title>
+ <link rel="stylesheet" href="_static/llvm.css" type="text/css">
+</head>
+<body>
+
+<h1>Source Level Debugging with LLVM</h1>
+
+<table class="layout" style="width:100%">
+ <tr class="layout">
+ <td class="left">
+<ul>
+ <li><a href="#introduction">Introduction</a>
+ <ol>
+ <li><a href="#phil">Philosophy behind LLVM debugging information</a></li>
+ <li><a href="#consumers">Debug information consumers</a></li>
+ <li><a href="#debugopt">Debugging optimized code</a></li>
+ </ol></li>
+ <li><a href="#format">Debugging information format</a>
+ <ol>
+ <li><a href="#debug_info_descriptors">Debug information descriptors</a>
+ <ul>
+ <li><a href="#format_compile_units">Compile unit descriptors</a></li>
+ <li><a href="#format_files">File descriptors</a></li>
+ <li><a href="#format_global_variables">Global variable descriptors</a></li>
+ <li><a href="#format_subprograms">Subprogram descriptors</a></li>
+ <li><a href="#format_blocks">Block descriptors</a></li>
+ <li><a href="#format_basic_type">Basic type descriptors</a></li>
+ <li><a href="#format_derived_type">Derived type descriptors</a></li>
+ <li><a href="#format_composite_type">Composite type descriptors</a></li>
+ <li><a href="#format_subrange">Subrange descriptors</a></li>
+ <li><a href="#format_enumeration">Enumerator descriptors</a></li>
+ <li><a href="#format_variables">Local variables</a></li>
+ </ul></li>
+ <li><a href="#format_common_intrinsics">Debugger intrinsic functions</a>
+ <ul>
+ <li><a href="#format_common_declare">llvm.dbg.declare</a></li>
+ <li><a href="#format_common_value">llvm.dbg.value</a></li>
+ </ul></li>
+ </ol></li>
+ <li><a href="#format_common_lifetime">Object lifetimes and scoping</a></li>
+ <li><a href="#ccxx_frontend">C/C++ front-end specific debug information</a>
+ <ol>
+ <li><a href="#ccxx_compile_units">C/C++ source file information</a></li>
+ <li><a href="#ccxx_global_variable">C/C++ global variable information</a></li>
+ <li><a href="#ccxx_subprogram">C/C++ function information</a></li>
+ <li><a href="#ccxx_basic_types">C/C++ basic types</a></li>
+ <li><a href="#ccxx_derived_types">C/C++ derived types</a></li>
+ <li><a href="#ccxx_composite_types">C/C++ struct/union types</a></li>
+ <li><a href="#ccxx_enumeration_types">C/C++ enumeration types</a></li>
+ </ol></li>
+ <li><a href="#llvmdwarfextension">LLVM Dwarf Extensions</a>
+ <ol>
+ <li><a href="#objcproperty">Debugging Information Extension
+ for Objective C Properties</a>
+ <ul>
+ <li><a href="#objcpropertyintroduction">Introduction</a></li>
+ <li><a href="#objcpropertyproposal">Proposal</a></li>
+ <li><a href="#objcpropertynewattributes">New DWARF Attributes</a></li>
+ <li><a href="#objcpropertynewconstants">New DWARF Constants</a></li>
+ </ul>
+ </li>
+ <li><a href="#acceltable">Name Accelerator Tables</a>
+ <ul>
+ <li><a href="#acceltableintroduction">Introduction</a></li>
+ <li><a href="#acceltablehashes">Hash Tables</a></li>
+ <li><a href="#acceltabledetails">Details</a></li>
+ <li><a href="#acceltablecontents">Contents</a></li>
+ <li><a href="#acceltableextensions">Language Extensions and File Format Changes</a></li>
+ </ul>
+ </li>
+ </ol>
+ </li>
+</ul>
+</td>
+</tr></table>
+
+<div class="doc_author">
+ <p>Written by <a href="mailto:sabre at nondot.org">Chris Lattner</a>
+ and <a href="mailto:jlaskey at mac.com">Jim Laskey</a></p>
+</div>
+
+
+<!-- *********************************************************************** -->
+<h2><a name="introduction">Introduction</a></h2>
+<!-- *********************************************************************** -->
+
+<div>
+
+<p>This document is the central repository for all information pertaining to
+ debug information in LLVM. It describes the <a href="#format">actual format
+ that the LLVM debug information</a> takes, which is useful for those
+ interested in creating front-ends or dealing directly with the information.
+ Further, this document provides specific examples of what debug information
+ for C/C++ looks like.</p>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="phil">Philosophy behind LLVM debugging information</a>
+</h3>
+
+<div>
+
+<p>The idea of the LLVM debugging information is to capture how the important
+ pieces of the source-language's Abstract Syntax Tree map onto LLVM code.
+ Several design aspects have shaped the solution that appears here. The
+ important ones are:</p>
+
+<ul>
+ <li>Debugging information should have very little impact on the rest of the
+ compiler. No transformations, analyses, or code generators should need to
+ be modified because of debugging information.</li>
+
+ <li>LLVM optimizations should interact in <a href="#debugopt">well-defined and
+ easily described ways</a> with the debugging information.</li>
+
+ <li>Because LLVM is designed to support arbitrary programming languages,
+ LLVM-to-LLVM tools should not need to know anything about the semantics of
+ the source-level-language.</li>
+
+ <li>Source-level languages are often <b>widely</b> different from one another.
+ LLVM should not put any restrictions of the flavor of the source-language,
+ and the debugging information should work with any language.</li>
+
+ <li>With code generator support, it should be possible to use an LLVM compiler
+ to compile a program to native machine code and standard debugging
+ formats. This allows compatibility with traditional machine-code level
+ debuggers, like GDB or DBX.</li>
+</ul>
+
+<p>The approach used by the LLVM implementation is to use a small set
+ of <a href="#format_common_intrinsics">intrinsic functions</a> to define a
+ mapping between LLVM program objects and the source-level objects. The
+ description of the source-level program is maintained in LLVM metadata
+ in an <a href="#ccxx_frontend">implementation-defined format</a>
+ (the C/C++ front-end currently uses working draft 7 of
+ the <a href="http://www.eagercon.com/dwarf/dwarf3std.htm">DWARF 3
+ standard</a>).</p>
+
+<p>When a program is being debugged, a debugger interacts with the user and
+ turns the stored debug information into source-language specific information.
+ As such, a debugger must be aware of the source-language, and is thus tied to
+ a specific language or family of languages.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="consumers">Debug information consumers</a>
+</h3>
+
+<div>
+
+<p>The role of debug information is to provide meta information normally
+ stripped away during the compilation process. This meta information provides
+ an LLVM user a relationship between generated code and the original program
+ source code.</p>
+
+<p>Currently, debug information is consumed by DwarfDebug to produce dwarf
+ information used by the gdb debugger. Other targets could use the same
+ information to produce stabs or other debug forms.</p>
+
+<p>It would also be reasonable to use debug information to feed profiling tools
+ for analysis of generated code, or, tools for reconstructing the original
+ source from generated code.</p>
+
+<p>TODO - expound a bit more.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="debugopt">Debugging optimized code</a>
+</h3>
+
+<div>
+
+<p>An extremely high priority of LLVM debugging information is to make it
+ interact well with optimizations and analysis. In particular, the LLVM debug
+ information provides the following guarantees:</p>
+
+<ul>
+ <li>LLVM debug information <b>always provides information to accurately read
+ the source-level state of the program</b>, regardless of which LLVM
+ optimizations have been run, and without any modification to the
+ optimizations themselves. However, some optimizations may impact the
+ ability to modify the current state of the program with a debugger, such
+ as setting program variables, or calling functions that have been
+ deleted.</li>
+
+ <li>As desired, LLVM optimizations can be upgraded to be aware of the LLVM
+ debugging information, allowing them to update the debugging information
+ as they perform aggressive optimizations. This means that, with effort,
+ the LLVM optimizers could optimize debug code just as well as non-debug
+ code.</li>
+
+ <li>LLVM debug information does not prevent optimizations from
+ happening (for example inlining, basic block reordering/merging/cleanup,
+ tail duplication, etc).</li>
+
+ <li>LLVM debug information is automatically optimized along with the rest of
+ the program, using existing facilities. For example, duplicate
+ information is automatically merged by the linker, and unused information
+ is automatically removed.</li>
+</ul>
+
+<p>Basically, the debug information allows you to compile a program with
+ "<tt>-O0 -g</tt>" and get full debug information, allowing you to arbitrarily
+ modify the program as it executes from a debugger. Compiling a program with
+ "<tt>-O3 -g</tt>" gives you full debug information that is always available
+ and accurate for reading (e.g., you get accurate stack traces despite tail
+ call elimination and inlining), but you might lose the ability to modify the
+ program and call functions where were optimized out of the program, or
+ inlined away completely.</p>
+
+<p><a href="TestingGuide.html#quicktestsuite">LLVM test suite</a> provides a
+ framework to test optimizer's handling of debugging information. It can be
+ run like this:</p>
+
+<div class="doc_code">
+<pre>
+% cd llvm/projects/test-suite/MultiSource/Benchmarks # or some other level
+% make TEST=dbgopt
+</pre>
+</div>
+
+<p>This will test impact of debugging information on optimization passes. If
+ debugging information influences optimization passes then it will be reported
+ as a failure. See <a href="TestingGuide.html">TestingGuide</a> for more
+ information on LLVM test infrastructure and how to run various tests.</p>
+
+</div>
+
+</div>
+
+<!-- *********************************************************************** -->
+<h2>
+ <a name="format">Debugging information format</a>
+</h2>
+<!-- *********************************************************************** -->
+
+<div>
+
+<p>LLVM debugging information has been carefully designed to make it possible
+ for the optimizer to optimize the program and debugging information without
+ necessarily having to know anything about debugging information. In
+ particular, the use of metadata avoids duplicated debugging information from
+ the beginning, and the global dead code elimination pass automatically
+ deletes debugging information for a function if it decides to delete the
+ function. </p>
+
+<p>To do this, most of the debugging information (descriptors for types,
+ variables, functions, source files, etc) is inserted by the language
+ front-end in the form of LLVM metadata. </p>
+
+<p>Debug information is designed to be agnostic about the target debugger and
+ debugging information representation (e.g. DWARF/Stabs/etc). It uses a
+ generic pass to decode the information that represents variables, types,
+ functions, namespaces, etc: this allows for arbitrary source-language
+ semantics and type-systems to be used, as long as there is a module
+ written for the target debugger to interpret the information. </p>
+
+<p>To provide basic functionality, the LLVM debugger does have to make some
+ assumptions about the source-level language being debugged, though it keeps
+ these to a minimum. The only common features that the LLVM debugger assumes
+ exist are <a href="#format_files">source files</a>,
+ and <a href="#format_global_variables">program objects</a>. These abstract
+ objects are used by a debugger to form stack traces, show information about
+ local variables, etc.</p>
+
+<p>This section of the documentation first describes the representation aspects
+ common to any source-language. The <a href="#ccxx_frontend">next section</a>
+ describes the data layout conventions used by the C and C++ front-ends.</p>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="debug_info_descriptors">Debug information descriptors</a>
+</h3>
+
+<div>
+
+<p>In consideration of the complexity and volume of debug information, LLVM
+ provides a specification for well formed debug descriptors. </p>
+
+<p>Consumers of LLVM debug information expect the descriptors for program
+ objects to start in a canonical format, but the descriptors can include
+ additional information appended at the end that is source-language
+ specific. All LLVM debugging information is versioned, allowing backwards
+ compatibility in the case that the core structures need to change in some
+ way. Also, all debugging information objects start with a tag to indicate
+ what type of object it is. The source-language is allowed to define its own
+ objects, by using unreserved tag numbers. We recommend using with tags in
+ the range 0x1000 through 0x2000 (there is a defined enum DW_TAG_user_base =
+ 0x1000.)</p>
+
+<p>The fields of debug descriptors used internally by LLVM
+ are restricted to only the simple data types <tt>i32</tt>, <tt>i1</tt>,
+ <tt>float</tt>, <tt>double</tt>, <tt>mdstring</tt> and <tt>mdnode</tt>. </p>
+
+<div class="doc_code">
+<pre>
+!1 = metadata !{
+ i32, ;; A tag
+ ...
+}
+</pre>
+</div>
+
+<p><a name="LLVMDebugVersion">The first field of a descriptor is always an
+ <tt>i32</tt> containing a tag value identifying the content of the
+ descriptor. The remaining fields are specific to the descriptor. The values
+ of tags are loosely bound to the tag values of DWARF information entries.
+ However, that does not restrict the use of the information supplied to DWARF
+ targets. To facilitate versioning of debug information, the tag is augmented
+ with the current debug version (LLVMDebugVersion = 8 << 16 or
+ 0x80000 or 524288.)</a></p>
+
+<p>The details of the various descriptors follow.</p>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="format_compile_units">Compile unit descriptors</a>
+</h4>
+
+<div>
+
+<div class="doc_code">
+<pre>
+!0 = metadata !{
+ i32, ;; Tag = 17 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
+ ;; (DW_TAG_compile_unit)
+ i32, ;; Unused field.
+ i32, ;; DWARF language identifier (ex. DW_LANG_C89)
+ metadata, ;; Source file name
+ metadata, ;; Source file directory (includes trailing slash)
+ metadata ;; Producer (ex. "4.0.1 LLVM (LLVM research group)")
+ i1, ;; True if this is a main compile unit.
+ i1, ;; True if this is optimized.
+ metadata, ;; Flags
+ i32 ;; Runtime version
+ metadata ;; List of enums types
+ metadata ;; List of retained types
+ metadata ;; List of subprograms
+ metadata ;; List of global variables
+}
+</pre>
+</div>
+
+<p>These descriptors contain a source language ID for the file (we use the DWARF
+ 3.0 ID numbers, such as <tt>DW_LANG_C89</tt>, <tt>DW_LANG_C_plus_plus</tt>,
+ <tt>DW_LANG_Cobol74</tt>, etc), three strings describing the filename,
+ working directory of the compiler, and an identifier string for the compiler
+ that produced it.</p>
+
+<p>Compile unit descriptors provide the root context for objects declared in a
+ specific compilation unit. File descriptors are defined using this context.
+ These descriptors are collected by a named metadata
+ <tt>!llvm.dbg.cu</tt>. Compile unit descriptor keeps track of subprograms,
+ global variables and type information.
+
+</div>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="format_files">File descriptors</a>
+</h4>
+
+<div>
+
+<div class="doc_code">
+<pre>
+!0 = metadata !{
+ i32, ;; Tag = 41 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
+ ;; (DW_TAG_file_type)
+ metadata, ;; Source file name
+ metadata, ;; Source file directory (includes trailing slash)
+ metadata ;; Unused
+}
+</pre>
+</div>
+
+<p>These descriptors contain information for a file. Global variables and top
+ level functions would be defined using this context.k File descriptors also
+ provide context for source line correspondence. </p>
+
+<p>Each input file is encoded as a separate file descriptor in LLVM debugging
+ information output. </p>
+
+</div>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="format_global_variables">Global variable descriptors</a>
+</h4>
+
+<div>
+
+<div class="doc_code">
+<pre>
+!1 = metadata !{
+ i32, ;; Tag = 52 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
+ ;; (DW_TAG_variable)
+ i32, ;; Unused field.
+ metadata, ;; Reference to context descriptor
+ metadata, ;; Name
+ metadata, ;; Display name (fully qualified C++ name)
+ metadata, ;; MIPS linkage name (for C++)
+ metadata, ;; Reference to file where defined
+ i32, ;; Line number where defined
+ metadata, ;; Reference to type descriptor
+ i1, ;; True if the global is local to compile unit (static)
+ i1, ;; True if the global is defined in the compile unit (not extern)
+ {}* ;; Reference to the global variable
+}
+</pre>
+</div>
+
+<p>These descriptors provide debug information about globals variables. The
+provide details such as name, type and where the variable is defined. All
+global variables are collected inside the named metadata
+<tt>!llvm.dbg.cu</tt>.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="format_subprograms">Subprogram descriptors</a>
+</h4>
+
+<div>
+
+<div class="doc_code">
+<pre>
+!2 = metadata !{
+ i32, ;; Tag = 46 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
+ ;; (DW_TAG_subprogram)
+ i32, ;; Unused field.
+ metadata, ;; Reference to context descriptor
+ metadata, ;; Name
+ metadata, ;; Display name (fully qualified C++ name)
+ metadata, ;; MIPS linkage name (for C++)
+ metadata, ;; Reference to file where defined
+ i32, ;; Line number where defined
+ metadata, ;; Reference to type descriptor
+ i1, ;; True if the global is local to compile unit (static)
+ i1, ;; True if the global is defined in the compile unit (not extern)
+ i32, ;; Line number where the scope of the subprogram begins
+ i32, ;; Virtuality, e.g. dwarf::DW_VIRTUALITY__virtual
+ i32, ;; Index into a virtual function
+ metadata, ;; indicates which base type contains the vtable pointer for the
+ ;; derived class
+ i32, ;; Flags - Artifical, Private, Protected, Explicit, Prototyped.
+ i1, ;; isOptimized
+ Function *,;; Pointer to LLVM function
+ metadata, ;; Lists function template parameters
+ metadata ;; Function declaration descriptor
+ metadata ;; List of function variables
+}
+</pre>
+</div>
+
+<p>These descriptors provide debug information about functions, methods and
+ subprograms. They provide details such as name, return types and the source
+ location where the subprogram is defined.
+</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="format_blocks">Block descriptors</a>
+</h4>
+
+<div>
+
+<div class="doc_code">
+<pre>
+!3 = metadata !{
+ i32, ;; Tag = 11 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_lexical_block)
+ metadata,;; Reference to context descriptor
+ i32, ;; Line number
+ i32, ;; Column number
+ metadata,;; Reference to source file
+ i32 ;; Unique ID to identify blocks from a template function
+}
+</pre>
+</div>
+
+<p>This descriptor provides debug information about nested blocks within a
+ subprogram. The line number and column numbers are used to dinstinguish
+ two lexical blocks at same depth. </p>
+
+<div class="doc_code">
+<pre>
+!3 = metadata !{
+ i32, ;; Tag = 11 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_lexical_block)
+ metadata ;; Reference to the scope we're annotating with a file change
+ metadata,;; Reference to the file the scope is enclosed in.
+}
+</pre>
+</div>
+
+<p>This descriptor provides a wrapper around a lexical scope to handle file
+ changes in the middle of a lexical block.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="format_basic_type">Basic type descriptors</a>
+</h4>
+
+<div>
+
+<div class="doc_code">
+<pre>
+!4 = metadata !{
+ i32, ;; Tag = 36 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
+ ;; (DW_TAG_base_type)
+ metadata, ;; Reference to context
+ metadata, ;; Name (may be "" for anonymous types)
+ metadata, ;; Reference to file where defined (may be NULL)
+ i32, ;; Line number where defined (may be 0)
+ i64, ;; Size in bits
+ i64, ;; Alignment in bits
+ i64, ;; Offset in bits
+ i32, ;; Flags
+ i32 ;; DWARF type encoding
+}
+</pre>
+</div>
+
+<p>These descriptors define primitive types used in the code. Example int, bool
+ and float. The context provides the scope of the type, which is usually the
+ top level. Since basic types are not usually user defined the context
+ and line number can be left as NULL and 0. The size, alignment and offset
+ are expressed in bits and can be 64 bit values. The alignment is used to
+ round the offset when embedded in a
+ <a href="#format_composite_type">composite type</a> (example to keep float
+ doubles on 64 bit boundaries.) The offset is the bit offset if embedded in
+ a <a href="#format_composite_type">composite type</a>.</p>
+
+<p>The type encoding provides the details of the type. The values are typically
+ one of the following:</p>
+
+<div class="doc_code">
+<pre>
+DW_ATE_address = 1
+DW_ATE_boolean = 2
+DW_ATE_float = 4
+DW_ATE_signed = 5
+DW_ATE_signed_char = 6
+DW_ATE_unsigned = 7
+DW_ATE_unsigned_char = 8
+</pre>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="format_derived_type">Derived type descriptors</a>
+</h4>
+
+<div>
+
+<div class="doc_code">
+<pre>
+!5 = metadata !{
+ i32, ;; Tag (see below)
+ metadata, ;; Reference to context
+ metadata, ;; Name (may be "" for anonymous types)
+ metadata, ;; Reference to file where defined (may be NULL)
+ i32, ;; Line number where defined (may be 0)
+ i64, ;; Size in bits
+ i64, ;; Alignment in bits
+ i64, ;; Offset in bits
+ i32, ;; Flags to encode attributes, e.g. private
+ metadata, ;; Reference to type derived from
+ metadata, ;; (optional) Name of the Objective C property associated with
+ ;; Objective-C an ivar
+ metadata, ;; (optional) Name of the Objective C property getter selector.
+ metadata, ;; (optional) Name of the Objective C property setter selector.
+ i32 ;; (optional) Objective C property attributes.
+}
+</pre>
+</div>
+
+<p>These descriptors are used to define types derived from other types. The
+value of the tag varies depending on the meaning. The following are possible
+tag values:</p>
+
+<div class="doc_code">
+<pre>
+DW_TAG_formal_parameter = 5
+DW_TAG_member = 13
+DW_TAG_pointer_type = 15
+DW_TAG_reference_type = 16
+DW_TAG_typedef = 22
+DW_TAG_const_type = 38
+DW_TAG_volatile_type = 53
+DW_TAG_restrict_type = 55
+</pre>
+</div>
+
+<p><tt>DW_TAG_member</tt> is used to define a member of
+ a <a href="#format_composite_type">composite type</a>
+ or <a href="#format_subprograms">subprogram</a>. The type of the member is
+ the <a href="#format_derived_type">derived
+ type</a>. <tt>DW_TAG_formal_parameter</tt> is used to define a member which
+ is a formal argument of a subprogram.</p>
+
+<p><tt>DW_TAG_typedef</tt> is used to provide a name for the derived type.</p>
+
+<p><tt>DW_TAG_pointer_type</tt>, <tt>DW_TAG_reference_type</tt>,
+ <tt>DW_TAG_const_type</tt>, <tt>DW_TAG_volatile_type</tt> and
+ <tt>DW_TAG_restrict_type</tt> are used to qualify
+ the <a href="#format_derived_type">derived type</a>. </p>
+
+<p><a href="#format_derived_type">Derived type</a> location can be determined
+ from the context and line number. The size, alignment and offset are
+ expressed in bits and can be 64 bit values. The alignment is used to round
+ the offset when embedded in a <a href="#format_composite_type">composite
+ type</a> (example to keep float doubles on 64 bit boundaries.) The offset is
+ the bit offset if embedded in a <a href="#format_composite_type">composite
+ type</a>.</p>
+
+<p>Note that the <tt>void *</tt> type is expressed as a type derived from NULL.
+</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="format_composite_type">Composite type descriptors</a>
+</h4>
+
+<div>
+
+<div class="doc_code">
+<pre>
+!6 = metadata !{
+ i32, ;; Tag (see below)
+ metadata, ;; Reference to context
+ metadata, ;; Name (may be "" for anonymous types)
+ metadata, ;; Reference to file where defined (may be NULL)
+ i32, ;; Line number where defined (may be 0)
+ i64, ;; Size in bits
+ i64, ;; Alignment in bits
+ i64, ;; Offset in bits
+ i32, ;; Flags
+ metadata, ;; Reference to type derived from
+ metadata, ;; Reference to array of member descriptors
+ i32 ;; Runtime languages
+}
+</pre>
+</div>
+
+<p>These descriptors are used to define types that are composed of 0 or more
+elements. The value of the tag varies depending on the meaning. The following
+are possible tag values:</p>
+
+<div class="doc_code">
+<pre>
+DW_TAG_array_type = 1
+DW_TAG_enumeration_type = 4
+DW_TAG_structure_type = 19
+DW_TAG_union_type = 23
+DW_TAG_vector_type = 259
+DW_TAG_subroutine_type = 21
+DW_TAG_inheritance = 28
+</pre>
+</div>
+
+<p>The vector flag indicates that an array type is a native packed vector.</p>
+
+<p>The members of array types (tag = <tt>DW_TAG_array_type</tt>) or vector types
+ (tag = <tt>DW_TAG_vector_type</tt>) are <a href="#format_subrange">subrange
+ descriptors</a>, each representing the range of subscripts at that level of
+ indexing.</p>
+
+<p>The members of enumeration types (tag = <tt>DW_TAG_enumeration_type</tt>) are
+ <a href="#format_enumeration">enumerator descriptors</a>, each representing
+ the definition of enumeration value for the set. All enumeration type
+ descriptors are collected inside the named metadata
+ <tt>!llvm.dbg.cu</tt>.</p>
+
+<p>The members of structure (tag = <tt>DW_TAG_structure_type</tt>) or union (tag
+ = <tt>DW_TAG_union_type</tt>) types are any one of
+ the <a href="#format_basic_type">basic</a>,
+ <a href="#format_derived_type">derived</a>
+ or <a href="#format_composite_type">composite</a> type descriptors, each
+ representing a field member of the structure or union.</p>
+
+<p>For C++ classes (tag = <tt>DW_TAG_structure_type</tt>), member descriptors
+ provide information about base classes, static members and member
+ functions. If a member is a <a href="#format_derived_type">derived type
+ descriptor</a> and has a tag of <tt>DW_TAG_inheritance</tt>, then the type
+ represents a base class. If the member of is
+ a <a href="#format_global_variables">global variable descriptor</a> then it
+ represents a static member. And, if the member is
+ a <a href="#format_subprograms">subprogram descriptor</a> then it represents
+ a member function. For static members and member
+ functions, <tt>getName()</tt> returns the members link or the C++ mangled
+ name. <tt>getDisplayName()</tt> the simplied version of the name.</p>
+
+<p>The first member of subroutine (tag = <tt>DW_TAG_subroutine_type</tt>) type
+ elements is the return type for the subroutine. The remaining elements are
+ the formal arguments to the subroutine.</p>
+
+<p><a href="#format_composite_type">Composite type</a> location can be
+ determined from the context and line number. The size, alignment and
+ offset are expressed in bits and can be 64 bit values. The alignment is used
+ to round the offset when embedded in
+ a <a href="#format_composite_type">composite type</a> (as an example, to keep
+ float doubles on 64 bit boundaries.) The offset is the bit offset if embedded
+ in a <a href="#format_composite_type">composite type</a>.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="format_subrange">Subrange descriptors</a>
+</h4>
+
+<div>
+
+<div class="doc_code">
+<pre>
+!42 = metadata !{
+ i32, ;; Tag = 33 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_subrange_type)
+ i64, ;; Low value
+ i64 ;; High value
+}
+</pre>
+</div>
+
+<p>These descriptors are used to define ranges of array subscripts for an array
+ <a href="#format_composite_type">composite type</a>. The low value defines
+ the lower bounds typically zero for C/C++. The high value is the upper
+ bounds. Values are 64 bit. High - low + 1 is the size of the array. If low
+ > high the array bounds are not included in generated debugging information.
+</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="format_enumeration">Enumerator descriptors</a>
+</h4>
+
+<div>
+
+<div class="doc_code">
+<pre>
+!6 = metadata !{
+ i32, ;; Tag = 40 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
+ ;; (DW_TAG_enumerator)
+ metadata, ;; Name
+ i64 ;; Value
+}
+</pre>
+</div>
+
+<p>These descriptors are used to define members of an
+ enumeration <a href="#format_composite_type">composite type</a>, it
+ associates the name to the value.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="format_variables">Local variables</a>
+</h4>
+
+<div>
+
+<div class="doc_code">
+<pre>
+!7 = metadata !{
+ i32, ;; Tag (see below)
+ metadata, ;; Context
+ metadata, ;; Name
+ metadata, ;; Reference to file where defined
+ i32, ;; 24 bit - Line number where defined
+ ;; 8 bit - Argument number. 1 indicates 1st argument.
+ metadata, ;; Type descriptor
+ i32, ;; flags
+ metadata ;; (optional) Reference to inline location
+}
+</pre>
+</div>
+
+<p>These descriptors are used to define variables local to a sub program. The
+ value of the tag depends on the usage of the variable:</p>
+
+<div class="doc_code">
+<pre>
+DW_TAG_auto_variable = 256
+DW_TAG_arg_variable = 257
+DW_TAG_return_variable = 258
+</pre>
+</div>
+
+<p>An auto variable is any variable declared in the body of the function. An
+ argument variable is any variable that appears as a formal argument to the
+ function. A return variable is used to track the result of a function and
+ has no source correspondent.</p>
+
+<p>The context is either the subprogram or block where the variable is defined.
+ Name the source variable name. Context and line indicate where the
+ variable was defined. Type descriptor defines the declared type of the
+ variable.</p>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="format_common_intrinsics">Debugger intrinsic functions</a>
+</h3>
+
+<div>
+
+<p>LLVM uses several intrinsic functions (name prefixed with "llvm.dbg") to
+ provide debug information at various points in generated code.</p>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="format_common_declare">llvm.dbg.declare</a>
+</h4>
+
+<div>
+<pre>
+ void %<a href="#format_common_declare">llvm.dbg.declare</a>(metadata, metadata)
+</pre>
+
+<p>This intrinsic provides information about a local element (e.g., variable). The
+ first argument is metadata holding the alloca for the variable. The
+ second argument is metadata containing a description of the variable.</p>
+</div>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="format_common_value">llvm.dbg.value</a>
+</h4>
+
+<div>
+<pre>
+ void %<a href="#format_common_value">llvm.dbg.value</a>(metadata, i64, metadata)
+</pre>
+
+<p>This intrinsic provides information when a user source variable is set to a
+ new value. The first argument is the new value (wrapped as metadata). The
+ second argument is the offset in the user source variable where the new value
+ is written. The third argument is metadata containing a description of the
+ user source variable.</p>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="format_common_lifetime">Object lifetimes and scoping</a>
+</h3>
+
+<div>
+<p>In many languages, the local variables in functions can have their lifetimes
+ or scopes limited to a subset of a function. In the C family of languages,
+ for example, variables are only live (readable and writable) within the
+ source block that they are defined in. In functional languages, values are
+ only readable after they have been defined. Though this is a very obvious
+ concept, it is non-trivial to model in LLVM, because it has no notion of
+ scoping in this sense, and does not want to be tied to a language's scoping
+ rules.</p>
+
+<p>In order to handle this, the LLVM debug format uses the metadata attached to
+ llvm instructions to encode line number and scoping information. Consider
+ the following C fragment, for example:</p>
+
+<div class="doc_code">
+<pre>
+1. void foo() {
+2. int X = 21;
+3. int Y = 22;
+4. {
+5. int Z = 23;
+6. Z = X;
+7. }
+8. X = Y;
+9. }
+</pre>
+</div>
+
+<p>Compiled to LLVM, this function would be represented like this:</p>
+
+<div class="doc_code">
+<pre>
+define void @foo() nounwind ssp {
+entry:
+ %X = alloca i32, align 4 ; <i32*> [#uses=4]
+ %Y = alloca i32, align 4 ; <i32*> [#uses=4]
+ %Z = alloca i32, align 4 ; <i32*> [#uses=3]
+ %0 = bitcast i32* %X to {}* ; <{}*> [#uses=1]
+ call void @llvm.dbg.declare(metadata !{i32 * %X}, metadata !0), !dbg !7
+ store i32 21, i32* %X, !dbg !8
+ %1 = bitcast i32* %Y to {}* ; <{}*> [#uses=1]
+ call void @llvm.dbg.declare(metadata !{i32 * %Y}, metadata !9), !dbg !10
+ store i32 22, i32* %Y, !dbg !11
+ %2 = bitcast i32* %Z to {}* ; <{}*> [#uses=1]
+ call void @llvm.dbg.declare(metadata !{i32 * %Z}, metadata !12), !dbg !14
+ store i32 23, i32* %Z, !dbg !15
+ %tmp = load i32* %X, !dbg !16 ; <i32> [#uses=1]
+ %tmp1 = load i32* %Y, !dbg !16 ; <i32> [#uses=1]
+ %add = add nsw i32 %tmp, %tmp1, !dbg !16 ; <i32> [#uses=1]
+ store i32 %add, i32* %Z, !dbg !16
+ %tmp2 = load i32* %Y, !dbg !17 ; <i32> [#uses=1]
+ store i32 %tmp2, i32* %X, !dbg !17
+ ret void, !dbg !18
+}
+
+declare void @llvm.dbg.declare(metadata, metadata) nounwind readnone
+
+!0 = metadata !{i32 459008, metadata !1, metadata !"X",
+ metadata !3, i32 2, metadata !6}; [ DW_TAG_auto_variable ]
+!1 = metadata !{i32 458763, metadata !2}; [DW_TAG_lexical_block ]
+!2 = metadata !{i32 458798, i32 0, metadata !3, metadata !"foo", metadata !"foo",
+ metadata !"foo", metadata !3, i32 1, metadata !4,
+ i1 false, i1 true}; [DW_TAG_subprogram ]
+!3 = metadata !{i32 458769, i32 0, i32 12, metadata !"foo.c",
+ metadata !"/private/tmp", metadata !"clang 1.1", i1 true,
+ i1 false, metadata !"", i32 0}; [DW_TAG_compile_unit ]
+!4 = metadata !{i32 458773, metadata !3, metadata !"", null, i32 0, i64 0, i64 0,
+ i64 0, i32 0, null, metadata !5, i32 0}; [DW_TAG_subroutine_type ]
+!5 = metadata !{null}
+!6 = metadata !{i32 458788, metadata !3, metadata !"int", metadata !3, i32 0,
+ i64 32, i64 32, i64 0, i32 0, i32 5}; [DW_TAG_base_type ]
+!7 = metadata !{i32 2, i32 7, metadata !1, null}
+!8 = metadata !{i32 2, i32 3, metadata !1, null}
+!9 = metadata !{i32 459008, metadata !1, metadata !"Y", metadata !3, i32 3,
+ metadata !6}; [ DW_TAG_auto_variable ]
+!10 = metadata !{i32 3, i32 7, metadata !1, null}
+!11 = metadata !{i32 3, i32 3, metadata !1, null}
+!12 = metadata !{i32 459008, metadata !13, metadata !"Z", metadata !3, i32 5,
+ metadata !6}; [ DW_TAG_auto_variable ]
+!13 = metadata !{i32 458763, metadata !1}; [DW_TAG_lexical_block ]
+!14 = metadata !{i32 5, i32 9, metadata !13, null}
+!15 = metadata !{i32 5, i32 5, metadata !13, null}
+!16 = metadata !{i32 6, i32 5, metadata !13, null}
+!17 = metadata !{i32 8, i32 3, metadata !1, null}
+!18 = metadata !{i32 9, i32 1, metadata !2, null}
+</pre>
+</div>
+
+<p>This example illustrates a few important details about LLVM debugging
+ information. In particular, it shows how the <tt>llvm.dbg.declare</tt>
+ intrinsic and location information, which are attached to an instruction,
+ are applied together to allow a debugger to analyze the relationship between
+ statements, variable definitions, and the code used to implement the
+ function.</p>
+
+<div class="doc_code">
+<pre>
+call void @llvm.dbg.declare(metadata, metadata !0), !dbg !7
+</pre>
+</div>
+
+<p>The first intrinsic
+ <tt>%<a href="#format_common_declare">llvm.dbg.declare</a></tt>
+ encodes debugging information for the variable <tt>X</tt>. The metadata
+ <tt>!dbg !7</tt> attached to the intrinsic provides scope information for the
+ variable <tt>X</tt>.</p>
+
+<div class="doc_code">
+<pre>
+!7 = metadata !{i32 2, i32 7, metadata !1, null}
+!1 = metadata !{i32 458763, metadata !2}; [DW_TAG_lexical_block ]
+!2 = metadata !{i32 458798, i32 0, metadata !3, metadata !"foo",
+ metadata !"foo", metadata !"foo", metadata !3, i32 1,
+ metadata !4, i1 false, i1 true}; [DW_TAG_subprogram ]
+</pre>
+</div>
+
+<p>Here <tt>!7</tt> is metadata providing location information. It has four
+ fields: line number, column number, scope, and original scope. The original
+ scope represents inline location if this instruction is inlined inside a
+ caller, and is null otherwise. In this example, scope is encoded by
+ <tt>!1</tt>. <tt>!1</tt> represents a lexical block inside the scope
+ <tt>!2</tt>, where <tt>!2</tt> is a
+ <a href="#format_subprograms">subprogram descriptor</a>. This way the
+ location information attached to the intrinsics indicates that the
+ variable <tt>X</tt> is declared at line number 2 at a function level scope in
+ function <tt>foo</tt>.</p>
+
+<p>Now lets take another example.</p>
+
+<div class="doc_code">
+<pre>
+call void @llvm.dbg.declare(metadata, metadata !12), !dbg !14
+</pre>
+</div>
+
+<p>The second intrinsic
+ <tt>%<a href="#format_common_declare">llvm.dbg.declare</a></tt>
+ encodes debugging information for variable <tt>Z</tt>. The metadata
+ <tt>!dbg !14</tt> attached to the intrinsic provides scope information for
+ the variable <tt>Z</tt>.</p>
+
+<div class="doc_code">
+<pre>
+!13 = metadata !{i32 458763, metadata !1}; [DW_TAG_lexical_block ]
+!14 = metadata !{i32 5, i32 9, metadata !13, null}
+</pre>
+</div>
+
+<p>Here <tt>!14</tt> indicates that <tt>Z</tt> is declared at line number 5 and
+ column number 9 inside of lexical scope <tt>!13</tt>. The lexical scope
+ itself resides inside of lexical scope <tt>!1</tt> described above.</p>
+
+<p>The scope information attached with each instruction provides a
+ straightforward way to find instructions covered by a scope.</p>
+
+</div>
+
+</div>
+
+<!-- *********************************************************************** -->
+<h2>
+ <a name="ccxx_frontend">C/C++ front-end specific debug information</a>
+</h2>
+<!-- *********************************************************************** -->
+
+<div>
+
+<p>The C and C++ front-ends represent information about the program in a format
+ that is effectively identical
+ to <a href="http://www.eagercon.com/dwarf/dwarf3std.htm">DWARF 3.0</a> in
+ terms of information content. This allows code generators to trivially
+ support native debuggers by generating standard dwarf information, and
+ contains enough information for non-dwarf targets to translate it as
+ needed.</p>
+
+<p>This section describes the forms used to represent C and C++ programs. Other
+ languages could pattern themselves after this (which itself is tuned to
+ representing programs in the same way that DWARF 3 does), or they could
+ choose to provide completely different forms if they don't fit into the DWARF
+ model. As support for debugging information gets added to the various LLVM
+ source-language front-ends, the information used should be documented
+ here.</p>
+
+<p>The following sections provide examples of various C/C++ constructs and the
+ debug information that would best describe those constructs.</p>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="ccxx_compile_units">C/C++ source file information</a>
+</h3>
+
+<div>
+
+<p>Given the source files <tt>MySource.cpp</tt> and <tt>MyHeader.h</tt> located
+ in the directory <tt>/Users/mine/sources</tt>, the following code:</p>
+
+<div class="doc_code">
+<pre>
+#include "MyHeader.h"
+
+int main(int argc, char *argv[]) {
+ return 0;
+}
+</pre>
+</div>
+
+<p>a C/C++ front-end would generate the following descriptors:</p>
+
+<div class="doc_code">
+<pre>
+...
+;;
+;; Define the compile unit for the main source file "/Users/mine/sources/MySource.cpp".
+;;
+!2 = metadata !{
+ i32 524305, ;; Tag
+ i32 0, ;; Unused
+ i32 4, ;; Language Id
+ metadata !"MySource.cpp",
+ metadata !"/Users/mine/sources",
+ metadata !"4.2.1 (Based on Apple Inc. build 5649) (LLVM build 00)",
+ i1 true, ;; Main Compile Unit
+ i1 false, ;; Optimized compile unit
+ metadata !"", ;; Compiler flags
+ i32 0} ;; Runtime version
+
+;;
+;; Define the file for the file "/Users/mine/sources/MySource.cpp".
+;;
+!1 = metadata !{
+ i32 524329, ;; Tag
+ metadata !"MySource.cpp",
+ metadata !"/Users/mine/sources",
+ metadata !2 ;; Compile unit
+}
+
+;;
+;; Define the file for the file "/Users/mine/sources/Myheader.h"
+;;
+!3 = metadata !{
+ i32 524329, ;; Tag
+ metadata !"Myheader.h"
+ metadata !"/Users/mine/sources",
+ metadata !2 ;; Compile unit
+}
+
+...
+</pre>
+</div>
+
+<p>llvm::Instruction provides easy access to metadata attached with an
+instruction. One can extract line number information encoded in LLVM IR
+using <tt>Instruction::getMetadata()</tt> and
+<tt>DILocation::getLineNumber()</tt>.
+<pre>
+ if (MDNode *N = I->getMetadata("dbg")) { // Here I is an LLVM instruction
+ DILocation Loc(N); // DILocation is in DebugInfo.h
+ unsigned Line = Loc.getLineNumber();
+ StringRef File = Loc.getFilename();
+ StringRef Dir = Loc.getDirectory();
+ }
+</pre>
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="ccxx_global_variable">C/C++ global variable information</a>
+</h3>
+
+<div>
+
+<p>Given an integer global variable declared as follows:</p>
+
+<div class="doc_code">
+<pre>
+int MyGlobal = 100;
+</pre>
+</div>
+
+<p>a C/C++ front-end would generate the following descriptors:</p>
+
+<div class="doc_code">
+<pre>
+;;
+;; Define the global itself.
+;;
+%MyGlobal = global int 100
+...
+;;
+;; List of debug info of globals
+;;
+!llvm.dbg.cu = !{!0}
+
+;; Define the compile unit.
+!0 = metadata !{
+ i32 786449, ;; Tag
+ i32 0, ;; Context
+ i32 4, ;; Language
+ metadata !"foo.cpp", ;; File
+ metadata !"/Volumes/Data/tmp", ;; Directory
+ metadata !"clang version 3.1 ", ;; Producer
+ i1 true, ;; Deprecated field
+ i1 false, ;; "isOptimized"?
+ metadata !"", ;; Flags
+ i32 0, ;; Runtime Version
+ metadata !1, ;; Enum Types
+ metadata !1, ;; Retained Types
+ metadata !1, ;; Subprograms
+ metadata !3 ;; Global Variables
+} ; [ DW_TAG_compile_unit ]
+
+;; The Array of Global Variables
+!3 = metadata !{
+ metadata !4
+}
+
+!4 = metadata !{
+ metadata !5
+}
+
+;;
+;; Define the global variable itself.
+;;
+!5 = metadata !{
+ i32 786484, ;; Tag
+ i32 0, ;; Unused
+ null, ;; Unused
+ metadata !"MyGlobal", ;; Name
+ metadata !"MyGlobal", ;; Display Name
+ metadata !"", ;; Linkage Name
+ metadata !6, ;; File
+ i32 1, ;; Line
+ metadata !7, ;; Type
+ i32 0, ;; IsLocalToUnit
+ i32 1, ;; IsDefinition
+ i32* @MyGlobal ;; LLVM-IR Value
+} ; [ DW_TAG_variable ]
+
+;;
+;; Define the file
+;;
+!6 = metadata !{
+ i32 786473, ;; Tag
+ metadata !"foo.cpp", ;; File
+ metadata !"/Volumes/Data/tmp", ;; Directory
+ null ;; Unused
+} ; [ DW_TAG_file_type ]
+
+;;
+;; Define the type
+;;
+!7 = metadata !{
+ i32 786468, ;; Tag
+ null, ;; Unused
+ metadata !"int", ;; Name
+ null, ;; Unused
+ i32 0, ;; Line
+ i64 32, ;; Size in Bits
+ i64 32, ;; Align in Bits
+ i64 0, ;; Offset
+ i32 0, ;; Flags
+ i32 5 ;; Encoding
+} ; [ DW_TAG_base_type ]
+
+</pre>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="ccxx_subprogram">C/C++ function information</a>
+</h3>
+
+<div>
+
+<p>Given a function declared as follows:</p>
+
+<div class="doc_code">
+<pre>
+int main(int argc, char *argv[]) {
+ return 0;
+}
+</pre>
+</div>
+
+<p>a C/C++ front-end would generate the following descriptors:</p>
+
+<div class="doc_code">
+<pre>
+;;
+;; Define the anchor for subprograms. Note that the second field of the
+;; anchor is 46, which is the same as the tag for subprograms
+;; (46 = DW_TAG_subprogram.)
+;;
+!6 = metadata !{
+ i32 524334, ;; Tag
+ i32 0, ;; Unused
+ metadata !1, ;; Context
+ metadata !"main", ;; Name
+ metadata !"main", ;; Display name
+ metadata !"main", ;; Linkage name
+ metadata !1, ;; File
+ i32 1, ;; Line number
+ metadata !4, ;; Type
+ i1 false, ;; Is local
+ i1 true, ;; Is definition
+ i32 0, ;; Virtuality attribute, e.g. pure virtual function
+ i32 0, ;; Index into virtual table for C++ methods
+ i32 0, ;; Type that holds virtual table.
+ i32 0, ;; Flags
+ i1 false, ;; True if this function is optimized
+ Function *, ;; Pointer to llvm::Function
+ null ;; Function template parameters
+}
+;;
+;; Define the subprogram itself.
+;;
+define i32 @main(i32 %argc, i8** %argv) {
+...
+}
+</pre>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="ccxx_basic_types">C/C++ basic types</a>
+</h3>
+
+<div>
+
+<p>The following are the basic type descriptors for C/C++ core types:</p>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="ccxx_basic_type_bool">bool</a>
+</h4>
+
+<div>
+
+<div class="doc_code">
+<pre>
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"bool", ;; Name
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 8, ;; Size in Bits
+ i64 8, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 2 ;; Encoding
+}
+</pre>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="ccxx_basic_char">char</a>
+</h4>
+
+<div>
+
+<div class="doc_code">
+<pre>
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"char", ;; Name
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 8, ;; Size in Bits
+ i64 8, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 6 ;; Encoding
+}
+</pre>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="ccxx_basic_unsigned_char">unsigned char</a>
+</h4>
+
+<div>
+
+<div class="doc_code">
+<pre>
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"unsigned char",
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 8, ;; Size in Bits
+ i64 8, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 8 ;; Encoding
+}
+</pre>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="ccxx_basic_short">short</a>
+</h4>
+
+<div>
+
+<div class="doc_code">
+<pre>
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"short int",
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 16, ;; Size in Bits
+ i64 16, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 5 ;; Encoding
+}
+</pre>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="ccxx_basic_unsigned_short">unsigned short</a>
+</h4>
+
+<div>
+
+<div class="doc_code">
+<pre>
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"short unsigned int",
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 16, ;; Size in Bits
+ i64 16, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 7 ;; Encoding
+}
+</pre>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="ccxx_basic_int">int</a>
+</h4>
+
+<div>
+
+<div class="doc_code">
+<pre>
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"int", ;; Name
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 32, ;; Size in Bits
+ i64 32, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 5 ;; Encoding
+}
+</pre></div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="ccxx_basic_unsigned_int">unsigned int</a>
+</h4>
+
+<div>
+
+<div class="doc_code">
+<pre>
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"unsigned int",
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 32, ;; Size in Bits
+ i64 32, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 7 ;; Encoding
+}
+</pre>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="ccxx_basic_long_long">long long</a>
+</h4>
+
+<div>
+
+<div class="doc_code">
+<pre>
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"long long int",
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 64, ;; Size in Bits
+ i64 64, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 5 ;; Encoding
+}
+</pre>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="ccxx_basic_unsigned_long_long">unsigned long long</a>
+</h4>
+
+<div>
+
+<div class="doc_code">
+<pre>
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"long long unsigned int",
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 64, ;; Size in Bits
+ i64 64, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 7 ;; Encoding
+}
+</pre>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="ccxx_basic_float">float</a>
+</h4>
+
+<div>
+
+<div class="doc_code">
+<pre>
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"float",
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 32, ;; Size in Bits
+ i64 32, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 4 ;; Encoding
+}
+</pre>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="ccxx_basic_double">double</a>
+</h4>
+
+<div>
+
+<div class="doc_code">
+<pre>
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"double",;; Name
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 64, ;; Size in Bits
+ i64 64, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 4 ;; Encoding
+}
+</pre>
+</div>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="ccxx_derived_types">C/C++ derived types</a>
+</h3>
+
+<div>
+
+<p>Given the following as an example of C/C++ derived type:</p>
+
+<div class="doc_code">
+<pre>
+typedef const int *IntPtr;
+</pre>
+</div>
+
+<p>a C/C++ front-end would generate the following descriptors:</p>
+
+<div class="doc_code">
+<pre>
+;;
+;; Define the typedef "IntPtr".
+;;
+!2 = metadata !{
+ i32 524310, ;; Tag
+ metadata !1, ;; Context
+ metadata !"IntPtr", ;; Name
+ metadata !3, ;; File
+ i32 0, ;; Line number
+ i64 0, ;; Size in bits
+ i64 0, ;; Align in bits
+ i64 0, ;; Offset in bits
+ i32 0, ;; Flags
+ metadata !4 ;; Derived From type
+}
+
+;;
+;; Define the pointer type.
+;;
+!4 = metadata !{
+ i32 524303, ;; Tag
+ metadata !1, ;; Context
+ metadata !"", ;; Name
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 64, ;; Size in bits
+ i64 64, ;; Align in bits
+ i64 0, ;; Offset in bits
+ i32 0, ;; Flags
+ metadata !5 ;; Derived From type
+}
+;;
+;; Define the const type.
+;;
+!5 = metadata !{
+ i32 524326, ;; Tag
+ metadata !1, ;; Context
+ metadata !"", ;; Name
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 32, ;; Size in bits
+ i64 32, ;; Align in bits
+ i64 0, ;; Offset in bits
+ i32 0, ;; Flags
+ metadata !6 ;; Derived From type
+}
+;;
+;; Define the int type.
+;;
+!6 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"int", ;; Name
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 32, ;; Size in bits
+ i64 32, ;; Align in bits
+ i64 0, ;; Offset in bits
+ i32 0, ;; Flags
+ 5 ;; Encoding
+}
+</pre>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="ccxx_composite_types">C/C++ struct/union types</a>
+</h3>
+
+<div>
+
+<p>Given the following as an example of C/C++ struct type:</p>
+
+<div class="doc_code">
+<pre>
+struct Color {
+ unsigned Red;
+ unsigned Green;
+ unsigned Blue;
+};
+</pre>
+</div>
+
+<p>a C/C++ front-end would generate the following descriptors:</p>
+
+<div class="doc_code">
+<pre>
+;;
+;; Define basic type for unsigned int.
+;;
+!5 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"unsigned int",
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 32, ;; Size in Bits
+ i64 32, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 7 ;; Encoding
+}
+;;
+;; Define composite type for struct Color.
+;;
+!2 = metadata !{
+ i32 524307, ;; Tag
+ metadata !1, ;; Context
+ metadata !"Color", ;; Name
+ metadata !1, ;; Compile unit
+ i32 1, ;; Line number
+ i64 96, ;; Size in bits
+ i64 32, ;; Align in bits
+ i64 0, ;; Offset in bits
+ i32 0, ;; Flags
+ null, ;; Derived From
+ metadata !3, ;; Elements
+ i32 0 ;; Runtime Language
+}
+
+;;
+;; Define the Red field.
+;;
+!4 = metadata !{
+ i32 524301, ;; Tag
+ metadata !1, ;; Context
+ metadata !"Red", ;; Name
+ metadata !1, ;; File
+ i32 2, ;; Line number
+ i64 32, ;; Size in bits
+ i64 32, ;; Align in bits
+ i64 0, ;; Offset in bits
+ i32 0, ;; Flags
+ metadata !5 ;; Derived From type
+}
+
+;;
+;; Define the Green field.
+;;
+!6 = metadata !{
+ i32 524301, ;; Tag
+ metadata !1, ;; Context
+ metadata !"Green", ;; Name
+ metadata !1, ;; File
+ i32 3, ;; Line number
+ i64 32, ;; Size in bits
+ i64 32, ;; Align in bits
+ i64 32, ;; Offset in bits
+ i32 0, ;; Flags
+ metadata !5 ;; Derived From type
+}
+
+;;
+;; Define the Blue field.
+;;
+!7 = metadata !{
+ i32 524301, ;; Tag
+ metadata !1, ;; Context
+ metadata !"Blue", ;; Name
+ metadata !1, ;; File
+ i32 4, ;; Line number
+ i64 32, ;; Size in bits
+ i64 32, ;; Align in bits
+ i64 64, ;; Offset in bits
+ i32 0, ;; Flags
+ metadata !5 ;; Derived From type
+}
+
+;;
+;; Define the array of fields used by the composite type Color.
+;;
+!3 = metadata !{metadata !4, metadata !6, metadata !7}
+</pre>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="ccxx_enumeration_types">C/C++ enumeration types</a>
+</h3>
+
+<div>
+
+<p>Given the following as an example of C/C++ enumeration type:</p>
+
+<div class="doc_code">
+<pre>
+enum Trees {
+ Spruce = 100,
+ Oak = 200,
+ Maple = 300
+};
+</pre>
+</div>
+
+<p>a C/C++ front-end would generate the following descriptors:</p>
+
+<div class="doc_code">
+<pre>
+;;
+;; Define composite type for enum Trees
+;;
+!2 = metadata !{
+ i32 524292, ;; Tag
+ metadata !1, ;; Context
+ metadata !"Trees", ;; Name
+ metadata !1, ;; File
+ i32 1, ;; Line number
+ i64 32, ;; Size in bits
+ i64 32, ;; Align in bits
+ i64 0, ;; Offset in bits
+ i32 0, ;; Flags
+ null, ;; Derived From type
+ metadata !3, ;; Elements
+ i32 0 ;; Runtime language
+}
+
+;;
+;; Define the array of enumerators used by composite type Trees.
+;;
+!3 = metadata !{metadata !4, metadata !5, metadata !6}
+
+;;
+;; Define Spruce enumerator.
+;;
+!4 = metadata !{i32 524328, metadata !"Spruce", i64 100}
+
+;;
+;; Define Oak enumerator.
+;;
+!5 = metadata !{i32 524328, metadata !"Oak", i64 200}
+
+;;
+;; Define Maple enumerator.
+;;
+!6 = metadata !{i32 524328, metadata !"Maple", i64 300}
+
+</pre>
+</div>
+
+</div>
+
+</div>
+
+
+<!-- *********************************************************************** -->
+<h2>
+ <a name="llvmdwarfextension">Debugging information format</a>
+</h2>
+<!-- *********************************************************************** -->
+<div>
+<!-- ======================================================================= -->
+<h3>
+ <a name="objcproperty">Debugging Information Extension for Objective C Properties</a>
+</h3>
+<div>
+<!-- *********************************************************************** -->
+<h4>
+ <a name="objcpropertyintroduction">Introduction</a>
+</h4>
+<!-- *********************************************************************** -->
+
+<div>
+<p>Objective C provides a simpler way to declare and define accessor methods
+using declared properties. The language provides features to declare a
+property and to let compiler synthesize accessor methods.
+</p>
+
+<p>The debugger lets developer inspect Objective C interfaces and their
+instance variables and class variables. However, the debugger does not know
+anything about the properties defined in Objective C interfaces. The debugger
+consumes information generated by compiler in DWARF format. The format does
+not support encoding of Objective C properties. This proposal describes DWARF
+extensions to encode Objective C properties, which the debugger can use to let
+developers inspect Objective C properties.
+</p>
+
+</div>
+
+
+<!-- *********************************************************************** -->
+<h4>
+ <a name="objcpropertyproposal">Proposal</a>
+</h4>
+<!-- *********************************************************************** -->
+
+<div>
+<p>Objective C properties exist separately from class members. A property
+can be defined only by "setter" and "getter" selectors, and
+be calculated anew on each access. Or a property can just be a direct access
+to some declared ivar. Finally it can have an ivar "automatically
+synthesized" for it by the compiler, in which case the property can be
+referred to in user code directly using the standard C dereference syntax as
+well as through the property "dot" syntax, but there is no entry in
+the @interface declaration corresponding to this ivar.
+</p>
+<p>
+To facilitate debugging, these properties we will add a new DWARF TAG into the
+DW_TAG_structure_type definition for the class to hold the description of a
+given property, and a set of DWARF attributes that provide said description.
+The property tag will also contain the name and declared type of the property.
+</p>
+<p>
+If there is a related ivar, there will also be a DWARF property attribute placed
+in the DW_TAG_member DIE for that ivar referring back to the property TAG for
+that property. And in the case where the compiler synthesizes the ivar directly,
+the compiler is expected to generate a DW_TAG_member for that ivar (with the
+DW_AT_artificial set to 1), whose name will be the name used to access this
+ivar directly in code, and with the property attribute pointing back to the
+property it is backing.
+</p>
+<p>
+The following examples will serve as illustration for our discussion:
+</p>
+
+<div class="doc_code">
+<pre>
+ at interface I1 {
+ int n2;
+}
+
+ at property int p1;
+ at property int p2;
+ at end
+
+ at implementation I1
+ at synthesize p1;
+ at synthesize p2 = n2;
+ at end
+</pre>
+</div>
+
+<p>
+This produces the following DWARF (this is a "pseudo dwarfdump" output):
+</p>
+<div class="doc_code">
+<pre>
+0x00000100: TAG_structure_type [7] *
+ AT_APPLE_runtime_class( 0x10 )
+ AT_name( "I1" )
+ AT_decl_file( "Objc_Property.m" )
+ AT_decl_line( 3 )
+
+0x00000110 TAG_APPLE_property
+ AT_name ( "p1" )
+ AT_type ( {0x00000150} ( int ) )
+
+0x00000120: TAG_APPLE_property
+ AT_name ( "p2" )
+ AT_type ( {0x00000150} ( int ) )
+
+0x00000130: TAG_member [8]
+ AT_name( "_p1" )
+ AT_APPLE_property ( {0x00000110} "p1" )
+ AT_type( {0x00000150} ( int ) )
+ AT_artificial ( 0x1 )
+
+0x00000140: TAG_member [8]
+ AT_name( "n2" )
+ AT_APPLE_property ( {0x00000120} "p2" )
+ AT_type( {0x00000150} ( int ) )
+
+0x00000150: AT_type( ( int ) )
+</pre>
+</div>
+
+<p> Note, the current convention is that the name of the ivar for an
+auto-synthesized property is the name of the property from which it derives with
+an underscore prepended, as is shown in the example.
+But we actually don't need to know this convention, since we are given the name
+of the ivar directly.
+</p>
+
+<p>
+Also, it is common practice in ObjC to have different property declarations in
+the @interface and @implementation - e.g. to provide a read-only property in
+the interface,and a read-write interface in the implementation. In that case,
+the compiler should emit whichever property declaration will be in force in the
+current translation unit.
+</p>
+
+<p> Developers can decorate a property with attributes which are encoded using
+DW_AT_APPLE_property_attribute.
+</p>
+
+<div class="doc_code">
+<pre>
+ at property (readonly, nonatomic) int pr;
+</pre>
+</div>
+<p>
+Which produces a property tag:
+<p>
+<div class="doc_code">
+<pre>
+TAG_APPLE_property [8]
+ AT_name( "pr" )
+ AT_type ( {0x00000147} (int) )
+ AT_APPLE_property_attribute (DW_APPLE_PROPERTY_readonly, DW_APPLE_PROPERTY_nonatomic)
+</pre>
+</div>
+
+<p> The setter and getter method names are attached to the property using
+DW_AT_APPLE_property_setter and DW_AT_APPLE_property_getter attributes.
+</p>
+<div class="doc_code">
+<pre>
+ at interface I1
+ at property (setter=myOwnP3Setter:) int p3;
+-(void)myOwnP3Setter:(int)a;
+ at end
+
+ at implementation I1
+ at synthesize p3;
+-(void)myOwnP3Setter:(int)a{ }
+ at end
+</pre>
+</div>
+
+<p>
+The DWARF for this would be:
+</p>
+<div class="doc_code">
+<pre>
+0x000003bd: TAG_structure_type [7] *
+ AT_APPLE_runtime_class( 0x10 )
+ AT_name( "I1" )
+ AT_decl_file( "Objc_Property.m" )
+ AT_decl_line( 3 )
+
+0x000003cd TAG_APPLE_property
+ AT_name ( "p3" )
+ AT_APPLE_property_setter ( "myOwnP3Setter:" )
+ AT_type( {0x00000147} ( int ) )
+
+0x000003f3: TAG_member [8]
+ AT_name( "_p3" )
+ AT_type ( {0x00000147} ( int ) )
+ AT_APPLE_property ( {0x000003cd} )
+ AT_artificial ( 0x1 )
+</pre>
+</div>
+
+</div>
+
+<!-- *********************************************************************** -->
+<h4>
+ <a name="objcpropertynewtags">New DWARF Tags</a>
+</h4>
+<!-- *********************************************************************** -->
+
+<div>
+<table border="1" cellspacing="0">
+ <col width="200">
+ <col width="200">
+ <tr>
+ <th>TAG</th>
+ <th>Value</th>
+ </tr>
+ <tr>
+ <td>DW_TAG_APPLE_property</td>
+ <td>0x4200</td>
+ </tr>
+</table>
+
+</div>
+
+<!-- *********************************************************************** -->
+<h4>
+ <a name="objcpropertynewattributes">New DWARF Attributes</a>
+</h4>
+<!-- *********************************************************************** -->
+
+<div>
+<table border="1" cellspacing="0">
+ <col width="200">
+ <col width="200">
+ <col width="200">
+ <tr>
+ <th>Attribute</th>
+ <th>Value</th>
+ <th>Classes</th>
+ </tr>
+ <tr>
+ <td>DW_AT_APPLE_property</td>
+ <td>0x3fed</td>
+ <td>Reference</td>
+ </tr>
+ <tr>
+ <td>DW_AT_APPLE_property_getter</td>
+ <td>0x3fe9</td>
+ <td>String</td>
+ </tr>
+ <tr>
+ <td>DW_AT_APPLE_property_setter</td>
+ <td>0x3fea</td>
+ <td>String</td>
+ </tr>
+ <tr>
+ <td>DW_AT_APPLE_property_attribute</td>
+ <td>0x3feb</td>
+ <td>Constant</td>
+ </tr>
+</table>
+
+</div>
+
+<!-- *********************************************************************** -->
+<h4>
+ <a name="objcpropertynewconstants">New DWARF Constants</a>
+</h4>
+<!-- *********************************************************************** -->
+
+<div>
+<table border="1" cellspacing="0">
+ <col width="200">
+ <col width="200">
+ <tr>
+ <th>Name</th>
+ <th>Value</th>
+ </tr>
+ <tr>
+ <td>DW_AT_APPLE_PROPERTY_readonly</td>
+ <td>0x1</td>
+ </tr>
+ <tr>
+ <td>DW_AT_APPLE_PROPERTY_readwrite</td>
+ <td>0x2</td>
+ </tr>
+ <tr>
+ <td>DW_AT_APPLE_PROPERTY_assign</td>
+ <td>0x4</td>
+ </tr>
+ <tr>
+ <td>DW_AT_APPLE_PROPERTY_retain</td>
+ <td>0x8</td>
+ </tr>
+ <tr>
+ <td>DW_AT_APPLE_PROPERTY_copy</td>
+ <td>0x10</td>
+ </tr>
+ <tr>
+ <td>DW_AT_APPLE_PROPERTY_nonatomic</td>
+ <td>0x20</td>
+ </tr>
+</table>
+
+</div>
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="acceltable">Name Accelerator Tables</a>
+</h3>
+<!-- ======================================================================= -->
+<div>
+<!-- ======================================================================= -->
+<h4>
+ <a name="acceltableintroduction">Introduction</a>
+</h4>
+<!-- ======================================================================= -->
+<div>
+<p>The .debug_pubnames and .debug_pubtypes formats are not what a debugger
+ needs. The "pub" in the section name indicates that the entries in the
+ table are publicly visible names only. This means no static or hidden
+ functions show up in the .debug_pubnames. No static variables or private class
+ variables are in the .debug_pubtypes. Many compilers add different things to
+ these tables, so we can't rely upon the contents between gcc, icc, or clang.</p>
+
+<p>The typical query given by users tends not to match up with the contents of
+ these tables. For example, the DWARF spec states that "In the case of the
+ name of a function member or static data member of a C++ structure, class or
+ union, the name presented in the .debug_pubnames section is not the simple
+ name given by the DW_AT_name attribute of the referenced debugging information
+ entry, but rather the fully qualified name of the data or function member."
+ So the only names in these tables for complex C++ entries is a fully
+ qualified name. Debugger users tend not to enter their search strings as
+ "a::b::c(int,const Foo&) const", but rather as "c", "b::c" , or "a::b::c". So
+ the name entered in the name table must be demangled in order to chop it up
+ appropriately and additional names must be manually entered into the table
+ to make it effective as a name lookup table for debuggers to use.</p>
+
+<p>All debuggers currently ignore the .debug_pubnames table as a result of
+ its inconsistent and useless public-only name content making it a waste of
+ space in the object file. These tables, when they are written to disk, are
+ not sorted in any way, leaving every debugger to do its own parsing
+ and sorting. These tables also include an inlined copy of the string values
+ in the table itself making the tables much larger than they need to be on
+ disk, especially for large C++ programs.</p>
+
+<p>Can't we just fix the sections by adding all of the names we need to this
+ table? No, because that is not what the tables are defined to contain and we
+ won't know the difference between the old bad tables and the new good tables.
+ At best we could make our own renamed sections that contain all of the data
+ we need.</p>
+
+<p>These tables are also insufficient for what a debugger like LLDB needs.
+ LLDB uses clang for its expression parsing where LLDB acts as a PCH. LLDB is
+ then often asked to look for type "foo" or namespace "bar", or list items in
+ namespace "baz". Namespaces are not included in the pubnames or pubtypes
+ tables. Since clang asks a lot of questions when it is parsing an expression,
+ we need to be very fast when looking up names, as it happens a lot. Having new
+ accelerator tables that are optimized for very quick lookups will benefit
+ this type of debugging experience greatly.</p>
+
+<p>We would like to generate name lookup tables that can be mapped into
+ memory from disk, and used as is, with little or no up-front parsing. We would
+ also be able to control the exact content of these different tables so they
+ contain exactly what we need. The Name Accelerator Tables were designed
+ to fix these issues. In order to solve these issues we need to:</p>
+
+<ul>
+ <li>Have a format that can be mapped into memory from disk and used as is</li>
+ <li>Lookups should be very fast</li>
+ <li>Extensible table format so these tables can be made by many producers</li>
+ <li>Contain all of the names needed for typical lookups out of the box</li>
+ <li>Strict rules for the contents of tables</li>
+</ul>
+
+<p>Table size is important and the accelerator table format should allow the
+ reuse of strings from common string tables so the strings for the names are
+ not duplicated. We also want to make sure the table is ready to be used as-is
+ by simply mapping the table into memory with minimal header parsing.</p>
+
+<p>The name lookups need to be fast and optimized for the kinds of lookups
+ that debuggers tend to do. Optimally we would like to touch as few parts of
+ the mapped table as possible when doing a name lookup and be able to quickly
+ find the name entry we are looking for, or discover there are no matches. In
+ the case of debuggers we optimized for lookups that fail most of the time.</p>
+
+<p>Each table that is defined should have strict rules on exactly what is in
+ the accelerator tables and documented so clients can rely on the content.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="acceltablehashes">Hash Tables</a>
+</h4>
+<!-- ======================================================================= -->
+
+<div>
+<h5>Standard Hash Tables</h5>
+
+<p>Typical hash tables have a header, buckets, and each bucket points to the
+bucket contents:
+</p>
+
+<div class="doc_code">
+<pre>
+.------------.
+| HEADER |
+|------------|
+| BUCKETS |
+|------------|
+| DATA |
+`------------'
+</pre>
+</div>
+
+<p>The BUCKETS are an array of offsets to DATA for each hash:</p>
+
+<div class="doc_code">
+<pre>
+.------------.
+| 0x00001000 | BUCKETS[0]
+| 0x00002000 | BUCKETS[1]
+| 0x00002200 | BUCKETS[2]
+| 0x000034f0 | BUCKETS[3]
+| | ...
+| 0xXXXXXXXX | BUCKETS[n_buckets]
+'------------'
+</pre>
+</div>
+
+<p>So for bucket[3] in the example above, we have an offset into the table
+ 0x000034f0 which points to a chain of entries for the bucket. Each bucket
+ must contain a next pointer, full 32 bit hash value, the string itself,
+ and the data for the current string value.</p>
+
+<div class="doc_code">
+<pre>
+ .------------.
+0x000034f0: | 0x00003500 | next pointer
+ | 0x12345678 | 32 bit hash
+ | "erase" | string value
+ | data[n] | HashData for this bucket
+ |------------|
+0x00003500: | 0x00003550 | next pointer
+ | 0x29273623 | 32 bit hash
+ | "dump" | string value
+ | data[n] | HashData for this bucket
+ |------------|
+0x00003550: | 0x00000000 | next pointer
+ | 0x82638293 | 32 bit hash
+ | "main" | string value
+ | data[n] | HashData for this bucket
+ `------------'
+</pre>
+</div>
+
+<p>The problem with this layout for debuggers is that we need to optimize for
+ the negative lookup case where the symbol we're searching for is not present.
+ So if we were to lookup "printf" in the table above, we would make a 32 hash
+ for "printf", it might match bucket[3]. We would need to go to the offset
+ 0x000034f0 and start looking to see if our 32 bit hash matches. To do so, we
+ need to read the next pointer, then read the hash, compare it, and skip to
+ the next bucket. Each time we are skipping many bytes in memory and touching
+ new cache pages just to do the compare on the full 32 bit hash. All of these
+ accesses then tell us that we didn't have a match.</p>
+
+<h5>Name Hash Tables</h5>
+
+<p>To solve the issues mentioned above we have structured the hash tables
+ a bit differently: a header, buckets, an array of all unique 32 bit hash
+ values, followed by an array of hash value data offsets, one for each hash
+ value, then the data for all hash values:</p>
+
+<div class="doc_code">
+<pre>
+.-------------.
+| HEADER |
+|-------------|
+| BUCKETS |
+|-------------|
+| HASHES |
+|-------------|
+| OFFSETS |
+|-------------|
+| DATA |
+`-------------'
+</pre>
+</div>
+
+<p>The BUCKETS in the name tables are an index into the HASHES array. By
+ making all of the full 32 bit hash values contiguous in memory, we allow
+ ourselves to efficiently check for a match while touching as little
+ memory as possible. Most often checking the 32 bit hash values is as far as
+ the lookup goes. If it does match, it usually is a match with no collisions.
+ So for a table with "n_buckets" buckets, and "n_hashes" unique 32 bit hash
+ values, we can clarify the contents of the BUCKETS, HASHES and OFFSETS as:</p>
+
+<div class="doc_code">
+<pre>
+.-------------------------.
+| HEADER.magic | uint32_t
+| HEADER.version | uint16_t
+| HEADER.hash_function | uint16_t
+| HEADER.bucket_count | uint32_t
+| HEADER.hashes_count | uint32_t
+| HEADER.header_data_len | uint32_t
+| HEADER_DATA | HeaderData
+|-------------------------|
+| BUCKETS | uint32_t[bucket_count] // 32 bit hash indexes
+|-------------------------|
+| HASHES | uint32_t[hashes_count] // 32 bit hash values
+|-------------------------|
+| OFFSETS | uint32_t[hashes_count] // 32 bit offsets to hash value data
+|-------------------------|
+| ALL HASH DATA |
+`-------------------------'
+</pre>
+</div>
+
+<p>So taking the exact same data from the standard hash example above we end up
+ with:</p>
+
+<div class="doc_code">
+<pre>
+ .------------.
+ | HEADER |
+ |------------|
+ | 0 | BUCKETS[0]
+ | 2 | BUCKETS[1]
+ | 5 | BUCKETS[2]
+ | 6 | BUCKETS[3]
+ | | ...
+ | ... | BUCKETS[n_buckets]
+ |------------|
+ | 0x........ | HASHES[0]
+ | 0x........ | HASHES[1]
+ | 0x........ | HASHES[2]
+ | 0x........ | HASHES[3]
+ | 0x........ | HASHES[4]
+ | 0x........ | HASHES[5]
+ | 0x12345678 | HASHES[6] hash for BUCKETS[3]
+ | 0x29273623 | HASHES[7] hash for BUCKETS[3]
+ | 0x82638293 | HASHES[8] hash for BUCKETS[3]
+ | 0x........ | HASHES[9]
+ | 0x........ | HASHES[10]
+ | 0x........ | HASHES[11]
+ | 0x........ | HASHES[12]
+ | 0x........ | HASHES[13]
+ | 0x........ | HASHES[n_hashes]
+ |------------|
+ | 0x........ | OFFSETS[0]
+ | 0x........ | OFFSETS[1]
+ | 0x........ | OFFSETS[2]
+ | 0x........ | OFFSETS[3]
+ | 0x........ | OFFSETS[4]
+ | 0x........ | OFFSETS[5]
+ | 0x000034f0 | OFFSETS[6] offset for BUCKETS[3]
+ | 0x00003500 | OFFSETS[7] offset for BUCKETS[3]
+ | 0x00003550 | OFFSETS[8] offset for BUCKETS[3]
+ | 0x........ | OFFSETS[9]
+ | 0x........ | OFFSETS[10]
+ | 0x........ | OFFSETS[11]
+ | 0x........ | OFFSETS[12]
+ | 0x........ | OFFSETS[13]
+ | 0x........ | OFFSETS[n_hashes]
+ |------------|
+ | |
+ | |
+ | |
+ | |
+ | |
+ |------------|
+0x000034f0: | 0x00001203 | .debug_str ("erase")
+ | 0x00000004 | A 32 bit array count - number of HashData with name "erase"
+ | 0x........ | HashData[0]
+ | 0x........ | HashData[1]
+ | 0x........ | HashData[2]
+ | 0x........ | HashData[3]
+ | 0x00000000 | String offset into .debug_str (terminate data for hash)
+ |------------|
+0x00003500: | 0x00001203 | String offset into .debug_str ("collision")
+ | 0x00000002 | A 32 bit array count - number of HashData with name "collision"
+ | 0x........ | HashData[0]
+ | 0x........ | HashData[1]
+ | 0x00001203 | String offset into .debug_str ("dump")
+ | 0x00000003 | A 32 bit array count - number of HashData with name "dump"
+ | 0x........ | HashData[0]
+ | 0x........ | HashData[1]
+ | 0x........ | HashData[2]
+ | 0x00000000 | String offset into .debug_str (terminate data for hash)
+ |------------|
+0x00003550: | 0x00001203 | String offset into .debug_str ("main")
+ | 0x00000009 | A 32 bit array count - number of HashData with name "main"
+ | 0x........ | HashData[0]
+ | 0x........ | HashData[1]
+ | 0x........ | HashData[2]
+ | 0x........ | HashData[3]
+ | 0x........ | HashData[4]
+ | 0x........ | HashData[5]
+ | 0x........ | HashData[6]
+ | 0x........ | HashData[7]
+ | 0x........ | HashData[8]
+ | 0x00000000 | String offset into .debug_str (terminate data for hash)
+ `------------'
+</pre>
+</div>
+
+<p>So we still have all of the same data, we just organize it more efficiently
+ for debugger lookup. If we repeat the same "printf" lookup from above, we
+ would hash "printf" and find it matches BUCKETS[3] by taking the 32 bit hash
+ value and modulo it by n_buckets. BUCKETS[3] contains "6" which is the index
+ into the HASHES table. We would then compare any consecutive 32 bit hashes
+ values in the HASHES array as long as the hashes would be in BUCKETS[3]. We
+ do this by verifying that each subsequent hash value modulo n_buckets is still
+ 3. In the case of a failed lookup we would access the memory for BUCKETS[3], and
+ then compare a few consecutive 32 bit hashes before we know that we have no match.
+ We don't end up marching through multiple words of memory and we really keep the
+ number of processor data cache lines being accessed as small as possible.</p>
+
+<p>The string hash that is used for these lookup tables is the Daniel J.
+ Bernstein hash which is also used in the ELF GNU_HASH sections. It is a very
+ good hash for all kinds of names in programs with very few hash collisions.</p>
+
+<p>Empty buckets are designated by using an invalid hash index of UINT32_MAX.</p>
+</div>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="acceltabledetails">Details</a>
+</h4>
+<!-- ======================================================================= -->
+<div>
+<p>These name hash tables are designed to be generic where specializations of
+ the table get to define additional data that goes into the header
+ ("HeaderData"), how the string value is stored ("KeyType") and the content
+ of the data for each hash value.</p>
+
+<h5>Header Layout</h5>
+<p>The header has a fixed part, and the specialized part. The exact format of
+ the header is:</p>
+<div class="doc_code">
+<pre>
+struct Header
+{
+ uint32_t magic; // 'HASH' magic value to allow endian detection
+ uint16_t version; // Version number
+ uint16_t hash_function; // The hash function enumeration that was used
+ uint32_t bucket_count; // The number of buckets in this hash table
+ uint32_t hashes_count; // The total number of unique hash values and hash data offsets in this table
+ uint32_t header_data_len; // The bytes to skip to get to the hash indexes (buckets) for correct alignment
+ // Specifically the length of the following HeaderData field - this does not
+ // include the size of the preceding fields
+ HeaderData header_data; // Implementation specific header data
+};
+</pre>
+</div>
+<p>The header starts with a 32 bit "magic" value which must be 'HASH' encoded as
+ an ASCII integer. This allows the detection of the start of the hash table and
+ also allows the table's byte order to be determined so the table can be
+ correctly extracted. The "magic" value is followed by a 16 bit version number
+ which allows the table to be revised and modified in the future. The current
+ version number is 1. "hash_function" is a uint16_t enumeration that specifies
+ which hash function was used to produce this table. The current values for the
+ hash function enumerations include:</p>
+<div class="doc_code">
+<pre>
+enum HashFunctionType
+{
+ eHashFunctionDJB = 0u, // Daniel J Bernstein hash function
+};
+</pre>
+</div>
+<p>"bucket_count" is a 32 bit unsigned integer that represents how many buckets
+ are in the BUCKETS array. "hashes_count" is the number of unique 32 bit hash
+ values that are in the HASHES array, and is the same number of offsets are
+ contained in the OFFSETS array. "header_data_len" specifies the size in
+ bytes of the HeaderData that is filled in by specialized versions of this
+ table.</p>
+
+<h5>Fixed Lookup</h5>
+<p>The header is followed by the buckets, hashes, offsets, and hash value
+ data.
+<div class="doc_code">
+<pre>
+struct FixedTable
+{
+ uint32_t buckets[Header.bucket_count]; // An array of hash indexes into the "hashes[]" array below
+ uint32_t hashes [Header.hashes_count]; // Every unique 32 bit hash for the entire table is in this table
+ uint32_t offsets[Header.hashes_count]; // An offset that corresponds to each item in the "hashes[]" array above
+};
+</pre>
+</div>
+<p>"buckets" is an array of 32 bit indexes into the "hashes" array. The
+ "hashes" array contains all of the 32 bit hash values for all names in the
+ hash table. Each hash in the "hashes" table has an offset in the "offsets"
+ array that points to the data for the hash value.</p>
+
+<p>This table setup makes it very easy to repurpose these tables to contain
+ different data, while keeping the lookup mechanism the same for all tables.
+ This layout also makes it possible to save the table to disk and map it in
+ later and do very efficient name lookups with little or no parsing.</p>
+
+<p>DWARF lookup tables can be implemented in a variety of ways and can store
+ a lot of information for each name. We want to make the DWARF tables
+ extensible and able to store the data efficiently so we have used some of the
+ DWARF features that enable efficient data storage to define exactly what kind
+ of data we store for each name.</p>
+
+<p>The "HeaderData" contains a definition of the contents of each HashData
+ chunk. We might want to store an offset to all of the debug information
+ entries (DIEs) for each name. To keep things extensible, we create a list of
+ items, or Atoms, that are contained in the data for each name. First comes the
+ type of the data in each atom:</p>
+<div class="doc_code">
+<pre>
+enum AtomType
+{
+ eAtomTypeNULL = 0u,
+ eAtomTypeDIEOffset = 1u, // DIE offset, check form for encoding
+ eAtomTypeCUOffset = 2u, // DIE offset of the compiler unit header that contains the item in question
+ eAtomTypeTag = 3u, // DW_TAG_xxx value, should be encoded as DW_FORM_data1 (if no tags exceed 255) or DW_FORM_data2
+ eAtomTypeNameFlags = 4u, // Flags from enum NameFlags
+ eAtomTypeTypeFlags = 5u, // Flags from enum TypeFlags
+};
+</pre>
+</div>
+<p>The enumeration values and their meanings are:</p>
+<div class="doc_code">
+<pre>
+ eAtomTypeNULL - a termination atom that specifies the end of the atom list
+ eAtomTypeDIEOffset - an offset into the .debug_info section for the DWARF DIE for this name
+ eAtomTypeCUOffset - an offset into the .debug_info section for the CU that contains the DIE
+ eAtomTypeDIETag - The DW_TAG_XXX enumeration value so you don't have to parse the DWARF to see what it is
+ eAtomTypeNameFlags - Flags for functions and global variables (isFunction, isInlined, isExternal...)
+ eAtomTypeTypeFlags - Flags for types (isCXXClass, isObjCClass, ...)
+</pre>
+</div>
+<p>Then we allow each atom type to define the atom type and how the data for
+ each atom type data is encoded:</p>
+<div class="doc_code">
+<pre>
+struct Atom
+{
+ uint16_t type; // AtomType enum value
+ uint16_t form; // DWARF DW_FORM_XXX defines
+};
+</pre>
+</div>
+<p>The "form" type above is from the DWARF specification and defines the
+ exact encoding of the data for the Atom type. See the DWARF specification for
+ the DW_FORM_ definitions.</p>
+<div class="doc_code">
+<pre>
+struct HeaderData
+{
+ uint32_t die_offset_base;
+ uint32_t atom_count;
+ Atoms atoms[atom_count0];
+};
+</pre>
+</div>
+<p>"HeaderData" defines the base DIE offset that should be added to any atoms
+ that are encoded using the DW_FORM_ref1, DW_FORM_ref2, DW_FORM_ref4,
+ DW_FORM_ref8 or DW_FORM_ref_udata. It also defines what is contained in
+ each "HashData" object -- Atom.form tells us how large each field will be in
+ the HashData and the Atom.type tells us how this data should be interpreted.</p>
+
+<p>For the current implementations of the ".apple_names" (all functions + globals),
+ the ".apple_types" (names of all types that are defined), and the
+ ".apple_namespaces" (all namespaces), we currently set the Atom array to be:</p>
+<div class="doc_code">
+<pre>
+HeaderData.atom_count = 1;
+HeaderData.atoms[0].type = eAtomTypeDIEOffset;
+HeaderData.atoms[0].form = DW_FORM_data4;
+</pre>
+</div>
+<p>This defines the contents to be the DIE offset (eAtomTypeDIEOffset) that is
+ encoded as a 32 bit value (DW_FORM_data4). This allows a single name to have
+ multiple matching DIEs in a single file, which could come up with an inlined
+ function for instance. Future tables could include more information about the
+ DIE such as flags indicating if the DIE is a function, method, block,
+ or inlined.</p>
+
+<p>The KeyType for the DWARF table is a 32 bit string table offset into the
+ ".debug_str" table. The ".debug_str" is the string table for the DWARF which
+ may already contain copies of all of the strings. This helps make sure, with
+ help from the compiler, that we reuse the strings between all of the DWARF
+ sections and keeps the hash table size down. Another benefit to having the
+ compiler generate all strings as DW_FORM_strp in the debug info, is that
+ DWARF parsing can be made much faster.</p>
+
+<p>After a lookup is made, we get an offset into the hash data. The hash data
+ needs to be able to deal with 32 bit hash collisions, so the chunk of data
+ at the offset in the hash data consists of a triple:</p>
+<div class="doc_code">
+<pre>
+uint32_t str_offset
+uint32_t hash_data_count
+HashData[hash_data_count]
+</pre>
+</div>
+<p>If "str_offset" is zero, then the bucket contents are done. 99.9% of the
+ hash data chunks contain a single item (no 32 bit hash collision):</p>
+<div class="doc_code">
+<pre>
+.------------.
+| 0x00001023 | uint32_t KeyType (.debug_str[0x0001023] => "main")
+| 0x00000004 | uint32_t HashData count
+| 0x........ | uint32_t HashData[0] DIE offset
+| 0x........ | uint32_t HashData[1] DIE offset
+| 0x........ | uint32_t HashData[2] DIE offset
+| 0x........ | uint32_t HashData[3] DIE offset
+| 0x00000000 | uint32_t KeyType (end of hash chain)
+`------------'
+</pre>
+</div>
+<p>If there are collisions, you will have multiple valid string offsets:</p>
+<div class="doc_code">
+<pre>
+.------------.
+| 0x00001023 | uint32_t KeyType (.debug_str[0x0001023] => "main")
+| 0x00000004 | uint32_t HashData count
+| 0x........ | uint32_t HashData[0] DIE offset
+| 0x........ | uint32_t HashData[1] DIE offset
+| 0x........ | uint32_t HashData[2] DIE offset
+| 0x........ | uint32_t HashData[3] DIE offset
+| 0x00002023 | uint32_t KeyType (.debug_str[0x0002023] => "print")
+| 0x00000002 | uint32_t HashData count
+| 0x........ | uint32_t HashData[0] DIE offset
+| 0x........ | uint32_t HashData[1] DIE offset
+| 0x00000000 | uint32_t KeyType (end of hash chain)
+`------------'
+</pre>
+</div>
+<p>Current testing with real world C++ binaries has shown that there is around 1
+ 32 bit hash collision per 100,000 name entries.</p>
+</div>
+<!-- ======================================================================= -->
+<h4>
+ <a name="acceltablecontents">Contents</a>
+</h4>
+<!-- ======================================================================= -->
+<div>
+<p>As we said, we want to strictly define exactly what is included in the
+ different tables. For DWARF, we have 3 tables: ".apple_names", ".apple_types",
+ and ".apple_namespaces".</p>
+
+<p>".apple_names" sections should contain an entry for each DWARF DIE whose
+ DW_TAG is a DW_TAG_label, DW_TAG_inlined_subroutine, or DW_TAG_subprogram that
+ has address attributes: DW_AT_low_pc, DW_AT_high_pc, DW_AT_ranges or
+ DW_AT_entry_pc. It also contains DW_TAG_variable DIEs that have a DW_OP_addr
+ in the location (global and static variables). All global and static variables
+ should be included, including those scoped within functions and classes. For
+ example using the following code:</p>
+<div class="doc_code">
+<pre>
+static int var = 0;
+
+void f ()
+{
+ static int var = 0;
+}
+</pre>
+</div>
+<p>Both of the static "var" variables would be included in the table. All
+ functions should emit both their full names and their basenames. For C or C++,
+ the full name is the mangled name (if available) which is usually in the
+ DW_AT_MIPS_linkage_name attribute, and the DW_AT_name contains the function
+ basename. If global or static variables have a mangled name in a
+ DW_AT_MIPS_linkage_name attribute, this should be emitted along with the
+ simple name found in the DW_AT_name attribute.</p>
+
+<p>".apple_types" sections should contain an entry for each DWARF DIE whose
+ tag is one of:</p>
+<ul>
+ <li>DW_TAG_array_type</li>
+ <li>DW_TAG_class_type</li>
+ <li>DW_TAG_enumeration_type</li>
+ <li>DW_TAG_pointer_type</li>
+ <li>DW_TAG_reference_type</li>
+ <li>DW_TAG_string_type</li>
+ <li>DW_TAG_structure_type</li>
+ <li>DW_TAG_subroutine_type</li>
+ <li>DW_TAG_typedef</li>
+ <li>DW_TAG_union_type</li>
+ <li>DW_TAG_ptr_to_member_type</li>
+ <li>DW_TAG_set_type</li>
+ <li>DW_TAG_subrange_type</li>
+ <li>DW_TAG_base_type</li>
+ <li>DW_TAG_const_type</li>
+ <li>DW_TAG_constant</li>
+ <li>DW_TAG_file_type</li>
+ <li>DW_TAG_namelist</li>
+ <li>DW_TAG_packed_type</li>
+ <li>DW_TAG_volatile_type</li>
+ <li>DW_TAG_restrict_type</li>
+ <li>DW_TAG_interface_type</li>
+ <li>DW_TAG_unspecified_type</li>
+ <li>DW_TAG_shared_type</li>
+</ul>
+<p>Only entries with a DW_AT_name attribute are included, and the entry must
+ not be a forward declaration (DW_AT_declaration attribute with a non-zero value).
+ For example, using the following code:</p>
+<div class="doc_code">
+<pre>
+int main ()
+{
+ int *b = 0;
+ return *b;
+}
+</pre>
+</div>
+<p>We get a few type DIEs:</p>
+<div class="doc_code">
+<pre>
+0x00000067: TAG_base_type [5]
+ AT_encoding( DW_ATE_signed )
+ AT_name( "int" )
+ AT_byte_size( 0x04 )
+
+0x0000006e: TAG_pointer_type [6]
+ AT_type( {0x00000067} ( int ) )
+ AT_byte_size( 0x08 )
+</pre>
+</div>
+<p>The DW_TAG_pointer_type is not included because it does not have a DW_AT_name.</p>
+
+<p>".apple_namespaces" section should contain all DW_TAG_namespace DIEs. If
+ we run into a namespace that has no name this is an anonymous namespace,
+ and the name should be output as "(anonymous namespace)" (without the quotes).
+ Why? This matches the output of the abi::cxa_demangle() that is in the standard
+ C++ library that demangles mangled names.</p>
+</div>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="acceltableextensions">Language Extensions and File Format Changes</a>
+</h4>
+<!-- ======================================================================= -->
+<div>
+<h5>Objective-C Extensions</h5>
+<p>".apple_objc" section should contain all DW_TAG_subprogram DIEs for an
+ Objective-C class. The name used in the hash table is the name of the
+ Objective-C class itself. If the Objective-C class has a category, then an
+ entry is made for both the class name without the category, and for the class
+ name with the category. So if we have a DIE at offset 0x1234 with a name
+ of method "-[NSString(my_additions) stringWithSpecialString:]", we would add
+ an entry for "NSString" that points to DIE 0x1234, and an entry for
+ "NSString(my_additions)" that points to 0x1234. This allows us to quickly
+ track down all Objective-C methods for an Objective-C class when doing
+ expressions. It is needed because of the dynamic nature of Objective-C where
+ anyone can add methods to a class. The DWARF for Objective-C methods is also
+ emitted differently from C++ classes where the methods are not usually
+ contained in the class definition, they are scattered about across one or more
+ compile units. Categories can also be defined in different shared libraries.
+ So we need to be able to quickly find all of the methods and class functions
+ given the Objective-C class name, or quickly find all methods and class
+ functions for a class + category name. This table does not contain any selector
+ names, it just maps Objective-C class names (or class names + category) to all
+ of the methods and class functions. The selectors are added as function
+ basenames in the .debug_names section.</p>
+
+<p>In the ".apple_names" section for Objective-C functions, the full name is the
+ entire function name with the brackets ("-[NSString stringWithCString:]") and the
+ basename is the selector only ("stringWithCString:").</p>
+
+<h5>Mach-O Changes</h5>
+<p>The sections names for the apple hash tables are for non mach-o files. For
+ mach-o files, the sections should be contained in the "__DWARF" segment with
+ names as follows:</p>
+<ul>
+ <li>".apple_names" -> "__apple_names"</li>
+ <li>".apple_types" -> "__apple_types"</li>
+ <li>".apple_namespaces" -> "__apple_namespac" (16 character limit)</li>
+ <li> ".apple_objc" -> "__apple_objc"</li>
+</ul>
+</div>
+</div>
+</div>
+
+<!-- *********************************************************************** -->
+
+<hr>
+<address>
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+ <a href="mailto:sabre at nondot.org">Chris Lattner</a><br>
+ <a href="http://llvm.org/">LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date: 2012-10-08 18:54:10 -0500 (Mon, 08 Oct 2012) $
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+<div class="section" id="introduction-and-quickstart">
+<h2>Introduction and Quickstart<a class="headerlink" href="#introduction-and-quickstart" title="Permalink to this headline">¶</a></h2>
+<p>This document is meant to get you writing documentation as fast as possible
+even if you have no previous experience with Sphinx. The goal is to take
+someone in the state of “I want to write documentation and get it added to
+LLVM’s docs” and turn that into useful documentation mailed to llvm-commits
+with as little nonsense as possible.</p>
+<p>You can find this document in <tt class="docutils literal"><span class="pre">docs/SphinxQuickstartTemplate.rst</span></tt>. You
+should copy it, open the new file in your text editor, write your docs, and
+then send the new document to llvm-commits for review.</p>
+<p>Focus on <em>content</em>. It is easy to fix the Sphinx (reStructuredText) syntax
+later if necessary, although reStructuredText tries to imitate common
+plain-text conventions so it should be quite natural. A basic knowledge of
+reStructuredText syntax is useful when writing the document, so the last
+~half of this document (starting with <a class="reference internal" href="#example-section">Example Section</a>) gives examples
+which should cover 99% of use cases.</p>
+<p>Let me say that again: focus on <em>content</em>.</p>
+<p>Once you have finished with the content, please send the <tt class="docutils literal"><span class="pre">.rst</span></tt> file to
+llvm-commits for review.</p>
+</div>
+<div class="section" id="guidelines">
+<h2>Guidelines<a class="headerlink" href="#guidelines" title="Permalink to this headline">¶</a></h2>
+<p>Try to answer the following questions in your first section:</p>
+<ol class="arabic simple">
+<li>Why would I want to read this document?</li>
+<li>What should I know to be able to follow along with this document?</li>
+<li>What will I have learned by the end of this document?</li>
+</ol>
+<p>Common names for the first section are <tt class="docutils literal"><span class="pre">Introduction</span></tt>, <tt class="docutils literal"><span class="pre">Overview</span></tt>, or
+<tt class="docutils literal"><span class="pre">Background</span></tt>.</p>
+<p>If possible, make your document a “how to”. Give it a name <tt class="docutils literal"><span class="pre">HowTo*.rst</span></tt>
+like the other “how to” documents. This format is usually the easiest
+for another person to understand and also the most useful.</p>
+<p>You generally should not be writing documentation other than a “how to”
+unless there is already a “how to” about your topic. The reason for this
+is that without a “how to” document to read first, it is difficult for a
+person to understand a more advanced document.</p>
+<p>Focus on content (yes, I had to say it again).</p>
+<p>The rest of this document shows example reStructuredText markup constructs
+that are meant to be read by you in your text editor after you have copied
+this file into a new file for the documentation you are about to write.</p>
+</div>
+<div class="section" id="example-section">
+<h2>Example Section<a class="headerlink" href="#example-section" title="Permalink to this headline">¶</a></h2>
+<p>Your text can be <em>emphasized</em>, <strong>bold</strong>, or <tt class="docutils literal"><span class="pre">monospace</span></tt>.</p>
+<p>Use blank lines to separate paragraphs.</p>
+<p>Headings (like <tt class="docutils literal"><span class="pre">Example</span> <span class="pre">Section</span></tt> just above) give your document
+structure. Use the same kind of adornments (e.g. <tt class="docutils literal"><span class="pre">======</span></tt> vs. <tt class="docutils literal"><span class="pre">------</span></tt>)
+as are used in this document. The adornment must be the same length as the
+text above it. For Vim users, variations of <tt class="docutils literal"><span class="pre">yypVr=</span></tt> might be handy.</p>
+<div class="section" id="example-subsection">
+<h3>Example Subsection<a class="headerlink" href="#example-subsection" title="Permalink to this headline">¶</a></h3>
+<p>Make a link <a class="reference external" href="http://llvm.org/">like this</a>. There is also a more
+sophisticated syntax which <a class="reference external" href="http://en.wikipedia.org/wiki/LLVM">can be more readable</a> for longer links since
+it disrupts the flow less. You can put the <tt class="docutils literal"><span class="pre">..</span> <span class="pre">_`link</span> <span class="pre">text`:</span> <span class="pre"><URL></span></tt> block
+pretty much anywhere later in the document.</p>
+<p>Lists can be made like this:</p>
+<ol class="arabic simple">
+<li>A list starting with <tt class="docutils literal"><span class="pre">#.</span></tt> will be automatically numbered.</li>
+<li>This is a second list element.<ol class="arabic">
+<li>They nest too.</li>
+</ol>
+</li>
+</ol>
+<p>You can also use unordered lists.</p>
+<ul class="simple">
+<li>Stuff.<ul>
+<li>Deeper stuff.</li>
+</ul>
+</li>
+<li>More stuff.</li>
+</ul>
+<div class="section" id="example-subsubsection">
+<h4>Example Subsubsection<a class="headerlink" href="#example-subsubsection" title="Permalink to this headline">¶</a></h4>
+<p>You can make blocks of code like this:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="kt">int</span> <span class="n">main</span><span class="p">()</span> <span class="p">{</span>
+ <span class="k">return</span> <span class="mi">0</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>For a shell session, use a <tt class="docutils literal"><span class="pre">bash</span></tt> code block:</p>
+<div class="highlight-bash"><div class="highlight"><pre><span class="nv">$ </span><span class="nb">echo</span> <span class="s2">"Goodbye cruel world!"</span>
+<span class="nv">$ </span>rm -rf /
+</pre></div>
+</div>
+<p>If you need to show LLVM IR use the <tt class="docutils literal"><span class="pre">llvm</span></tt> code block.</p>
+<div class="section" id="hopefully-you-won-t-need-to-be-this-deep">
+<h5>Hopefully you won’t need to be this deep<a class="headerlink" href="#hopefully-you-won-t-need-to-be-this-deep" title="Permalink to this headline">¶</a></h5>
+<p>If you need to do fancier things than what has been shown in this document,
+you can mail the list or check Sphinx’s <a class="reference external" href="http://sphinx.pocoo.org/rest.html">reStructuredText Primer</a>.</p>
+</div>
+</div>
+</div>
+</div>
+</div>
+
+
+ </div>
+ </div>
+ </div>
+ <div class="clearer"></div>
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+ <div class="related">
+ <h3>Navigation</h3>
+ <ul>
+ <li class="right" style="margin-right: 10px">
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+<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+<html>
+<head>
+ <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
+ <title>System Library</title>
+ <link rel="stylesheet" href="_static/llvm.css" type="text/css">
+</head>
+<body>
+
+<h1>System Library</h1>
+<ul>
+ <li><a href="#abstract">Abstract</a></li>
+ <li><a href="#requirements">Keeping LLVM Portable</a>
+ <ol>
+ <li><a href="#headers">Don't Include System Headers</a></li>
+ <li><a href="#expose">Don't Expose System Headers</a></li>
+ <li><a href="#c_headers">Allow Standard C Header Files</a></li>
+ <li><a href="#cpp_headers">Allow Standard C++ Header Files</a></li>
+ <li><a href="#highlev">High-Level Interface</a></li>
+ <li><a href="#nofunc">No Exposed Functions</a></li>
+ <li><a href="#nodata">No Exposed Data</a></li>
+ <li><a href="#nodupl">No Duplicate Implementations</a></li>
+ <li><a href="#nounused">No Unused Functionality</a></li>
+ <li><a href="#virtuals">No Virtual Methods</a></li>
+ <li><a href="#softerrors">Minimize Soft Errors</a></li>
+ <li><a href="#throw_spec">No throw() Specifications</a></li>
+ <li><a href="#organization">Code Organization</a></li>
+ <li><a href="#semantics">Consistent Semantics</a></li>
+ <li><a href="#bug">Tracking Bugzilla Bug: 351</a></li>
+ </ol></li>
+</ul>
+
+<div class="doc_author">
+ <p>Written by <a href="mailto:rspencer at x10sys.com">Reid Spencer</a></p>
+</div>
+
+
+<!-- *********************************************************************** -->
+<h2><a name="abstract">Abstract</a></h2>
+<div>
+ <p>This document provides some details on LLVM's System Library, located in
+ the source at <tt>lib/System</tt> and <tt>include/llvm/System</tt>. The
+ library's purpose is to shield LLVM from the differences between operating
+ systems for the few services LLVM needs from the operating system. Much of
+ LLVM is written using portability features of standard C++. However, in a few
+ areas, system dependent facilities are needed and the System Library is the
+ wrapper around those system calls.</p>
+ <p>By centralizing LLVM's use of operating system interfaces, we make it
+ possible for the LLVM tool chain and runtime libraries to be more easily
+ ported to new platforms since (theoretically) only <tt>lib/System</tt> needs
+ to be ported. This library also unclutters the rest of LLVM from #ifdef use
+ and special cases for specific operating systems. Such uses are replaced
+ with simple calls to the interfaces provided in <tt>include/llvm/System</tt>.
+ </p>
+ <p>Note that the System Library is not intended to be a complete operating
+ system wrapper (such as the Adaptive Communications Environment (ACE) or
+ Apache Portable Runtime (APR)), but only provides the functionality necessary
+ to support LLVM.
+ <p>The System Library was written by Reid Spencer who formulated the
+ design based on similar work originating from the eXtensible Programming
+ System (XPS). Several people helped with the effort; especially,
+ Jeff Cohen and Henrik Bach on the Win32 port.</p>
+</div>
+
+<!-- *********************************************************************** -->
+<h2>
+ <a name="requirements">Keeping LLVM Portable</a>
+</h2>
+<div>
+ <p>In order to keep LLVM portable, LLVM developers should adhere to a set of
+ portability rules associated with the System Library. Adherence to these rules
+ should help the System Library achieve its goal of shielding LLVM from the
+ variations in operating system interfaces and doing so efficiently. The
+ following sections define the rules needed to fulfill this objective.</p>
+
+<!-- ======================================================================= -->
+<h3><a name="headers">Don't Include System Headers</a></h3>
+<div>
+ <p>Except in <tt>lib/System</tt>, no LLVM source code should directly
+ <tt>#include</tt> a system header. Care has been taken to remove all such
+ <tt>#includes</tt> from LLVM while <tt>lib/System</tt> was being
+ developed. Specifically this means that header files like "unistd.h",
+ "windows.h", "stdio.h", and "string.h" are forbidden to be included by LLVM
+ source code outside the implementation of <tt>lib/System</tt>.</p>
+ <p>To obtain system-dependent functionality, existing interfaces to the system
+ found in <tt>include/llvm/System</tt> should be used. If an appropriate
+ interface is not available, it should be added to <tt>include/llvm/System</tt>
+ and implemented in <tt>lib/System</tt> for all supported platforms.</p>
+</div>
+
+<!-- ======================================================================= -->
+<h3><a name="expose">Don't Expose System Headers</a></h3>
+<div>
+ <p>The System Library must shield LLVM from <em>all</em> system headers. To
+ obtain system level functionality, LLVM source must
+ <tt>#include "llvm/System/Thing.h"</tt> and nothing else. This means that
+ <tt>Thing.h</tt> cannot expose any system header files. This protects LLVM
+ from accidentally using system specific functionality and only allows it
+ via the <tt>lib/System</tt> interface.</p>
+</div>
+
+<!-- ======================================================================= -->
+<h3><a name="c_headers">Use Standard C Headers</a></h3>
+<div>
+ <p>The <em>standard</em> C headers (the ones beginning with "c") are allowed
+ to be exposed through the <tt>lib/System</tt> interface. These headers and
+ the things they declare are considered to be platform agnostic. LLVM source
+ files may include them directly or obtain their inclusion through
+ <tt>lib/System</tt> interfaces.</p>
+</div>
+
+<!-- ======================================================================= -->
+<h3><a name="cpp_headers">Use Standard C++ Headers</a></h3>
+<div>
+ <p>The <em>standard</em> C++ headers from the standard C++ library and
+ standard template library may be exposed through the <tt>lib/System</tt>
+ interface. These headers and the things they declare are considered to be
+ platform agnostic. LLVM source files may include them or obtain their
+ inclusion through lib/System interfaces.</p>
+</div>
+
+<!-- ======================================================================= -->
+<h3><a name="highlev">High Level Interface</a></h3>
+<div>
+ <p>The entry points specified in the interface of lib/System must be aimed at
+ completing some reasonably high level task needed by LLVM. We do not want to
+ simply wrap each operating system call. It would be preferable to wrap several
+ operating system calls that are always used in conjunction with one another by
+ LLVM.</p>
+ <p>For example, consider what is needed to execute a program, wait for it to
+ complete, and return its result code. On Unix, this involves the following
+ operating system calls: <tt>getenv, fork, execve,</tt> and <tt>wait</tt>. The
+ correct thing for lib/System to provide is a function, say
+ <tt>ExecuteProgramAndWait</tt>, that implements the functionality completely.
+ what we don't want is wrappers for the operating system calls involved.</p>
+ <p>There must <em>not</em> be a one-to-one relationship between operating
+ system calls and the System library's interface. Any such interface function
+ will be suspicious.</p>
+</div>
+
+<!-- ======================================================================= -->
+<h3><a name="nounused">No Unused Functionality</a></h3>
+<div>
+ <p>There must be no functionality specified in the interface of lib/System
+ that isn't actually used by LLVM. We're not writing a general purpose
+ operating system wrapper here, just enough to satisfy LLVM's needs. And, LLVM
+ doesn't need much. This design goal aims to keep the lib/System interface
+ small and understandable which should foster its actual use and adoption.</p>
+</div>
+
+<!-- ======================================================================= -->
+<h3><a name="nodupl">No Duplicate Implementations</a></h3>
+<div>
+ <p>The implementation of a function for a given platform must be written
+ exactly once. This implies that it must be possible to apply a function's
+ implementation to multiple operating systems if those operating systems can
+ share the same implementation. This rule applies to the set of operating
+ systems supported for a given class of operating system (e.g. Unix, Win32).
+ </p>
+</div>
+
+<!-- ======================================================================= -->
+<h3><a name="virtuals">No Virtual Methods</a></h3>
+<div>
+ <p>The System Library interfaces can be called quite frequently by LLVM. In
+ order to make those calls as efficient as possible, we discourage the use of
+ virtual methods. There is no need to use inheritance for implementation
+ differences, it just adds complexity. The <tt>#include</tt> mechanism works
+ just fine.</p>
+</div>
+
+<!-- ======================================================================= -->
+<h3><a name="nofunc">No Exposed Functions</a></h3>
+<div>
+ <p>Any functions defined by system libraries (i.e. not defined by lib/System)
+ must not be exposed through the lib/System interface, even if the header file
+ for that function is not exposed. This prevents inadvertent use of system
+ specific functionality.</p>
+ <p>For example, the <tt>stat</tt> system call is notorious for having
+ variations in the data it provides. <tt>lib/System</tt> must not declare
+ <tt>stat</tt> nor allow it to be declared. Instead it should provide its own
+ interface to discovering information about files and directories. Those
+ interfaces may be implemented in terms of <tt>stat</tt> but that is strictly
+ an implementation detail. The interface provided by the System Library must
+ be implemented on all platforms (even those without <tt>stat</tt>).</p>
+</div>
+
+<!-- ======================================================================= -->
+<h3><a name="nodata">No Exposed Data</a></h3>
+<div>
+ <p>Any data defined by system libraries (i.e. not defined by lib/System) must
+ not be exposed through the lib/System interface, even if the header file for
+ that function is not exposed. As with functions, this prevents inadvertent use
+ of data that might not exist on all platforms.</p>
+</div>
+
+<!-- ======================================================================= -->
+<h3><a name="softerrors">Minimize Soft Errors</a></h3>
+<div>
+ <p>Operating system interfaces will generally provide error results for every
+ little thing that could go wrong. In almost all cases, you can divide these
+ error results into two groups: normal/good/soft and abnormal/bad/hard. That
+ is, some of the errors are simply information like "file not found",
+ "insufficient privileges", etc. while other errors are much harder like
+ "out of space", "bad disk sector", or "system call interrupted". We'll call
+ the first group "<i>soft</i>" errors and the second group "<i>hard</i>"
+ errors.<p>
+ <p>lib/System must always attempt to minimize soft errors.
+ This is a design requirement because the
+ minimization of soft errors can affect the granularity and the nature of the
+ interface. In general, if you find that you're wanting to throw soft errors,
+ you must review the granularity of the interface because it is likely you're
+ trying to implement something that is too low level. The rule of thumb is to
+ provide interface functions that <em>can't</em> fail, except when faced with
+ hard errors.</p>
+ <p>For a trivial example, suppose we wanted to add an "OpenFileForWriting"
+ function. For many operating systems, if the file doesn't exist, attempting
+ to open the file will produce an error. However, lib/System should not
+ simply throw that error if it occurs because its a soft error. The problem
+ is that the interface function, OpenFileForWriting is too low level. It should
+ be OpenOrCreateFileForWriting. In the case of the soft "doesn't exist" error,
+ this function would just create it and then open it for writing.</p>
+ <p>This design principle needs to be maintained in lib/System because it
+ avoids the propagation of soft error handling throughout the rest of LLVM.
+ Hard errors will generally just cause a termination for an LLVM tool so don't
+ be bashful about throwing them.</p>
+ <p>Rules of thumb:</p>
+ <ol>
+ <li>Don't throw soft errors, only hard errors.</li>
+ <li>If you're tempted to throw a soft error, re-think the interface.</li>
+ <li>Handle internally the most common normal/good/soft error conditions
+ so the rest of LLVM doesn't have to.</li>
+ </ol>
+</div>
+
+<!-- ======================================================================= -->
+<h3><a name="throw_spec">No throw Specifications</a></h3>
+<div>
+ <p>None of the lib/System interface functions may be declared with C++
+ <tt>throw()</tt> specifications on them. This requirement makes sure that the
+ compiler does not insert additional exception handling code into the interface
+ functions. This is a performance consideration: lib/System functions are at
+ the bottom of many call chains and as such can be frequently called. We
+ need them to be as efficient as possible. However, no routines in the
+ system library should actually throw exceptions.</p>
+</div>
+
+<!-- ======================================================================= -->
+<h3><a name="organization">Code Organization</a></h3>
+<div>
+ <p>Implementations of the System Library interface are separated by their
+ general class of operating system. Currently only Unix and Win32 classes are
+ defined but more could be added for other operating system classifications.
+ To distinguish which implementation to compile, the code in lib/System uses
+ the LLVM_ON_UNIX and LLVM_ON_WIN32 #defines provided via configure through the
+ llvm/Config/config.h file. Each source file in lib/System, after implementing
+ the generic (operating system independent) functionality needs to include the
+ correct implementation using a set of <tt>#if defined(LLVM_ON_XYZ)</tt>
+ directives. For example, if we had lib/System/File.cpp, we'd expect to see in
+ that file:</p>
+ <pre><tt>
+ #if defined(LLVM_ON_UNIX)
+ #include "Unix/File.cpp"
+ #endif
+ #if defined(LLVM_ON_WIN32)
+ #include "Win32/File.cpp"
+ #endif
+ </tt></pre>
+ <p>The implementation in lib/System/Unix/File.cpp should handle all Unix
+ variants. The implementation in lib/System/Win32/File.cpp should handle all
+ Win32 variants. What this does is quickly differentiate the basic class of
+ operating system that will provide the implementation. The specific details
+ for a given platform must still be determined through the use of
+ <tt>#ifdef</tt>.</p>
+</div>
+
+<!-- ======================================================================= -->
+<h3><a name="semantics">Consistent Semantics</a></h3>
+<div>
+ <p>The implementation of a lib/System interface can vary drastically between
+ platforms. That's okay as long as the end result of the interface function
+ is the same. For example, a function to create a directory is pretty straight
+ forward on all operating system. System V IPC on the other hand isn't even
+ supported on all platforms. Instead of "supporting" System V IPC, lib/System
+ should provide an interface to the basic concept of inter-process
+ communications. The implementations might use System V IPC if that was
+ available or named pipes, or whatever gets the job done effectively for a
+ given operating system. In all cases, the interface and the implementation
+ must be semantically consistent. </p>
+</div>
+
+<!-- ======================================================================= -->
+<h3><a name="bug">Bug 351</a></h3>
+<div>
+ <p>See <a href="http://llvm.org/PR351">bug 351</a>
+ for further details on the progress of this work</p>
+</div>
+
+</div>
+
+<!-- *********************************************************************** -->
+
+<hr>
+<address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
+ src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
+ <a href="http://validator.w3.org/check/referer"><img
+ src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a>
+
+ <a href="mailto:rspencer at x10sys.com">Reid Spencer</a><br>
+ <a href="http://llvm.org/">LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date: 2012-04-19 15:20:34 -0500 (Thu, 19 Apr 2012) $
+</address>
+</body>
+</html>
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+ <h3><a href="index.html">Table Of Contents</a></h3>
+ <ul>
+<li><a class="reference internal" href="#">TableGen Fundamentals</a><ul>
+<li><a class="reference internal" href="#introduction">Introduction</a><ul>
+<li><a class="reference internal" href="#basic-concepts">Basic concepts</a></li>
+<li><a class="reference internal" href="#an-example-record">An example record</a></li>
+<li><a class="reference internal" href="#running-tablegen">Running TableGen</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#tablegen-syntax">TableGen syntax</a><ul>
+<li><a class="reference internal" href="#tablegen-primitives">TableGen primitives</a><ul>
+<li><a class="reference internal" href="#tablegen-comments">TableGen comments</a></li>
+<li><a class="reference internal" href="#the-tablegen-type-system">The TableGen type system</a></li>
+<li><a class="reference internal" href="#tablegen-values-and-expressions">TableGen values and expressions</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#classes-and-definitions">Classes and definitions</a><ul>
+<li><a class="reference internal" href="#value-definitions">Value definitions</a></li>
+<li><a class="reference internal" href="#let-expressions-within-a-record">‘let’ expressions</a></li>
+<li><a class="reference internal" href="#class-template-arguments">Class template arguments</a></li>
+<li><a class="reference internal" href="#multiclass-definitions-and-instances">Multiclass definitions and instances</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#file-scope-entities">File scope entities</a><ul>
+<li><a class="reference internal" href="#file-inclusion">File inclusion</a></li>
+<li><a class="reference internal" href="#id3">‘let’ expressions</a></li>
+<li><a class="reference internal" href="#looping">Looping</a></li>
+</ul>
+</li>
+</ul>
+</li>
+<li><a class="reference internal" href="#code-generator-backend-info">Code Generator backend info</a></li>
+<li><a class="reference internal" href="#write-a-backend">TableGen backends</a></li>
+</ul>
+</li>
+</ul>
+
+ <h4>Previous topic</h4>
+ <p class="topless"><a href="SegmentedStacks.html"
+ title="previous chapter">Segmented Stacks in LLVM</a></p>
+ <h4>Next topic</h4>
+ <p class="topless"><a href="DebuggingJITedCode.html"
+ title="next chapter">Debugging JIT-ed Code With GDB</a></p>
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+
+ <div class="section" id="tablegen-fundamentals">
+<span id="tablegen"></span><h1>TableGen Fundamentals<a class="headerlink" href="#tablegen-fundamentals" title="Permalink to this headline">¶</a></h1>
+<div class="contents local topic" id="contents">
+<ul class="simple">
+<li><a class="reference internal" href="#introduction" id="id5">Introduction</a><ul>
+<li><a class="reference internal" href="#basic-concepts" id="id6">Basic concepts</a></li>
+<li><a class="reference internal" href="#an-example-record" id="id7">An example record</a></li>
+<li><a class="reference internal" href="#running-tablegen" id="id8">Running TableGen</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#tablegen-syntax" id="id9">TableGen syntax</a><ul>
+<li><a class="reference internal" href="#tablegen-primitives" id="id10">TableGen primitives</a><ul>
+<li><a class="reference internal" href="#tablegen-comments" id="id11">TableGen comments</a></li>
+<li><a class="reference internal" href="#the-tablegen-type-system" id="id12">The TableGen type system</a></li>
+<li><a class="reference internal" href="#tablegen-values-and-expressions" id="id13">TableGen values and expressions</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#classes-and-definitions" id="id14">Classes and definitions</a><ul>
+<li><a class="reference internal" href="#value-definitions" id="id15">Value definitions</a></li>
+<li><a class="reference internal" href="#let-expressions-within-a-record" id="id16">‘let’ expressions</a></li>
+<li><a class="reference internal" href="#class-template-arguments" id="id17">Class template arguments</a></li>
+<li><a class="reference internal" href="#multiclass-definitions-and-instances" id="id18">Multiclass definitions and instances</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#file-scope-entities" id="id19">File scope entities</a><ul>
+<li><a class="reference internal" href="#file-inclusion" id="id20">File inclusion</a></li>
+<li><a class="reference internal" href="#id3" id="id21">‘let’ expressions</a></li>
+<li><a class="reference internal" href="#looping" id="id22">Looping</a></li>
+</ul>
+</li>
+</ul>
+</li>
+<li><a class="reference internal" href="#code-generator-backend-info" id="id23">Code Generator backend info</a></li>
+<li><a class="reference internal" href="#write-a-backend" id="id24">TableGen backends</a></li>
+</ul>
+</div>
+<div class="section" id="introduction">
+<h2><a class="toc-backref" href="#id5">Introduction</a><a class="headerlink" href="#introduction" title="Permalink to this headline">¶</a></h2>
+<p>TableGen’s purpose is to help a human develop and maintain records of
+domain-specific information. Because there may be a large number of these
+records, it is specifically designed to allow writing flexible descriptions and
+for common features of these records to be factored out. This reduces the
+amount of duplication in the description, reduces the chance of error, and makes
+it easier to structure domain specific information.</p>
+<p>The core part of TableGen <a class="reference internal" href="#parses-a-file">parses a file</a>, instantiates the declarations, and
+hands the result off to a domain-specific <a class="reference internal" href="#tablegen-backend">TableGen backend</a> for processing.
+The current major user of TableGen is the <a class="reference external" href="CodeGenerator.html">LLVM code
+generator</a>.</p>
+<p>Note that if you work on TableGen much, and use emacs or vim, that you can find
+an emacs “TableGen mode” and a vim language file in the <tt class="docutils literal"><span class="pre">llvm/utils/emacs</span></tt> and
+<tt class="docutils literal"><span class="pre">llvm/utils/vim</span></tt> directories of your LLVM distribution, respectively.</p>
+<div class="section" id="basic-concepts">
+<span id="intro"></span><h3><a class="toc-backref" href="#id6">Basic concepts</a><a class="headerlink" href="#basic-concepts" title="Permalink to this headline">¶</a></h3>
+<p>TableGen files consist of two key parts: ‘classes’ and ‘definitions’, both of
+which are considered ‘records’.</p>
+<p><strong>TableGen records</strong> have a unique name, a list of values, and a list of
+superclasses. The list of values is the main data that TableGen builds for each
+record; it is this that holds the domain specific information for the
+application. The interpretation of this data is left to a specific <a class="reference internal" href="#tablegen-backend">TableGen
+backend</a>, but the structure and format rules are taken care of and are fixed by
+TableGen.</p>
+<p><strong>TableGen definitions</strong> are the concrete form of ‘records’. These generally do
+not have any undefined values, and are marked with the ‘<tt class="docutils literal"><span class="pre">def</span></tt>‘ keyword.</p>
+<p><strong>TableGen classes</strong> are abstract records that are used to build and describe
+other records. These ‘classes’ allow the end-user to build abstractions for
+either the domain they are targeting (such as “Register”, “RegisterClass”, and
+“Instruction” in the LLVM code generator) or for the implementor to help factor
+out common properties of records (such as “FPInst”, which is used to represent
+floating point instructions in the X86 backend). TableGen keeps track of all of
+the classes that are used to build up a definition, so the backend can find all
+definitions of a particular class, such as “Instruction”.</p>
+<p><strong>TableGen multiclasses</strong> are groups of abstract records that are instantiated
+all at once. Each instantiation can result in multiple TableGen definitions.
+If a multiclass inherits from another multiclass, the definitions in the
+sub-multiclass become part of the current multiclass, as if they were declared
+in the current multiclass.</p>
+</div>
+<div class="section" id="an-example-record">
+<span id="described-above"></span><h3><a class="toc-backref" href="#id7">An example record</a><a class="headerlink" href="#an-example-record" title="Permalink to this headline">¶</a></h3>
+<p>With no other arguments, TableGen parses the specified file and prints out all
+of the classes, then all of the definitions. This is a good way to see what the
+various definitions expand to fully. Running this on the <tt class="docutils literal"><span class="pre">X86.td</span></tt> file prints
+this (at the time of this writing):</p>
+<div class="highlight-llvm"><pre>...
+def ADD32rr { // Instruction X86Inst I
+ string Namespace = "X86";
+ dag OutOperandList = (outs GR32:$dst);
+ dag InOperandList = (ins GR32:$src1, GR32:$src2);
+ string AsmString = "add{l}\t{$src2, $dst|$dst, $src2}";
+ list<dag> Pattern = [(set GR32:$dst, (add GR32:$src1, GR32:$src2))];
+ list<Register> Uses = [];
+ list<Register> Defs = [EFLAGS];
+ list<Predicate> Predicates = [];
+ int CodeSize = 3;
+ int AddedComplexity = 0;
+ bit isReturn = 0;
+ bit isBranch = 0;
+ bit isIndirectBranch = 0;
+ bit isBarrier = 0;
+ bit isCall = 0;
+ bit canFoldAsLoad = 0;
+ bit mayLoad = 0;
+ bit mayStore = 0;
+ bit isImplicitDef = 0;
+ bit isConvertibleToThreeAddress = 1;
+ bit isCommutable = 1;
+ bit isTerminator = 0;
+ bit isReMaterializable = 0;
+ bit isPredicable = 0;
+ bit hasDelaySlot = 0;
+ bit usesCustomInserter = 0;
+ bit hasCtrlDep = 0;
+ bit isNotDuplicable = 0;
+ bit hasSideEffects = 0;
+ bit neverHasSideEffects = 0;
+ InstrItinClass Itinerary = NoItinerary;
+ string Constraints = "";
+ string DisableEncoding = "";
+ bits<8> Opcode = { 0, 0, 0, 0, 0, 0, 0, 1 };
+ Format Form = MRMDestReg;
+ bits<6> FormBits = { 0, 0, 0, 0, 1, 1 };
+ ImmType ImmT = NoImm;
+ bits<3> ImmTypeBits = { 0, 0, 0 };
+ bit hasOpSizePrefix = 0;
+ bit hasAdSizePrefix = 0;
+ bits<4> Prefix = { 0, 0, 0, 0 };
+ bit hasREX_WPrefix = 0;
+ FPFormat FPForm = ?;
+ bits<3> FPFormBits = { 0, 0, 0 };
+}
+...</pre>
+</div>
+<p>This definition corresponds to a 32-bit register-register add instruction in the
+X86. The string after the ‘<tt class="docutils literal"><span class="pre">def</span></tt>‘ string indicates the name of the
+record—”<tt class="docutils literal"><span class="pre">ADD32rr</span></tt>” in this case—and the comment at the end of the line
+indicates the superclasses of the definition. The body of the record contains
+all of the data that TableGen assembled for the record, indicating that the
+instruction is part of the “X86” namespace, the pattern indicating how the the
+instruction should be emitted into the assembly file, that it is a two-address
+instruction, has a particular encoding, etc. The contents and semantics of the
+information in the record is specific to the needs of the X86 backend, and is
+only shown as an example.</p>
+<p>As you can see, a lot of information is needed for every instruction supported
+by the code generator, and specifying it all manually would be unmaintainable,
+prone to bugs, and tiring to do in the first place. Because we are using
+TableGen, all of the information was derived from the following definition:</p>
+<div class="highlight-llvm"><pre>let Defs = [EFLAGS],
+ isCommutable = 1, // X = ADD Y,Z --> X = ADD Z,Y
+ isConvertibleToThreeAddress = 1 in // Can transform into LEA.
+def ADD32rr : I<0x01, MRMDestReg, (outs GR32:$dst),
+ (ins GR32:$src1, GR32:$src2),
+ "add{l}\t{$src2, $dst|$dst, $src2}",
+ [(set GR32:$dst, (add GR32:$src1, GR32:$src2))]>;</pre>
+</div>
+<p>This definition makes use of the custom class <tt class="docutils literal"><span class="pre">I</span></tt> (extended from the custom
+class <tt class="docutils literal"><span class="pre">X86Inst</span></tt>), which is defined in the X86-specific TableGen file, to
+factor out the common features that instructions of its class share. A key
+feature of TableGen is that it allows the end-user to define the abstractions
+they prefer to use when describing their information.</p>
+<p>Each def record has a special entry called “<tt class="docutils literal"><span class="pre">NAME</span></tt>.” This is the name of the
+def (“<tt class="docutils literal"><span class="pre">ADD32rr</span></tt>” above). In the general case def names can be formed from
+various kinds of string processing expressions and <tt class="docutils literal"><span class="pre">NAME</span></tt> resolves to the
+final value obtained after resolving all of those expressions. The user may
+refer to <tt class="docutils literal"><span class="pre">NAME</span></tt> anywhere she desires to use the ultimate name of the def.
+<tt class="docutils literal"><span class="pre">NAME</span></tt> should not be defined anywhere else in user code to avoid conflict
+problems.</p>
+</div>
+<div class="section" id="running-tablegen">
+<h3><a class="toc-backref" href="#id8">Running TableGen</a><a class="headerlink" href="#running-tablegen" title="Permalink to this headline">¶</a></h3>
+<p>TableGen runs just like any other LLVM tool. The first (optional) argument
+specifies the file to read. If a filename is not specified, <tt class="docutils literal"><span class="pre">llvm-tblgen</span></tt>
+reads from standard input.</p>
+<p>To be useful, one of the <a class="reference internal" href="#tablegen-backends">TableGen backends</a> must be used. These backends are
+selectable on the command line (type ‘<tt class="docutils literal"><span class="pre">llvm-tblgen</span> <span class="pre">-help</span></tt>‘ for a list). For
+example, to get a list of all of the definitions that subclass a particular type
+(which can be useful for building up an enum list of these records), use the
+<tt class="docutils literal"><span class="pre">-print-enums</span></tt> option:</p>
+<div class="highlight-bash"><div class="highlight"><pre><span class="nv">$ </span>llvm-tblgen X86.td -print-enums -class<span class="o">=</span>Register
+AH, AL, AX, BH, BL, BP, BPL, BX, CH, CL, CX, DH, DI, DIL, DL, DX, EAX, EBP, EBX,
+ECX, EDI, EDX, EFLAGS, EIP, ESI, ESP, FP0, FP1, FP2, FP3, FP4, FP5, FP6, IP,
+MM0, MM1, MM2, MM3, MM4, MM5, MM6, MM7, R10, R10B, R10D, R10W, R11, R11B, R11D,
+R11W, R12, R12B, R12D, R12W, R13, R13B, R13D, R13W, R14, R14B, R14D, R14W, R15,
+R15B, R15D, R15W, R8, R8B, R8D, R8W, R9, R9B, R9D, R9W, RAX, RBP, RBX, RCX, RDI,
+RDX, RIP, RSI, RSP, SI, SIL, SP, SPL, ST0, ST1, ST2, ST3, ST4, ST5, ST6, ST7,
+XMM0, XMM1, XMM10, XMM11, XMM12, XMM13, XMM14, XMM15, XMM2, XMM3, XMM4, XMM5,
+XMM6, XMM7, XMM8, XMM9,
+
+<span class="nv">$ </span>llvm-tblgen X86.td -print-enums -class<span class="o">=</span>Instruction
+ABS_F, ABS_Fp32, ABS_Fp64, ABS_Fp80, ADC32mi, ADC32mi8, ADC32mr, ADC32ri,
+ADC32ri8, ADC32rm, ADC32rr, ADC64mi32, ADC64mi8, ADC64mr, ADC64ri32, ADC64ri8,
+ADC64rm, ADC64rr, ADD16mi, ADD16mi8, ADD16mr, ADD16ri, ADD16ri8, ADD16rm,
+ADD16rr, ADD32mi, ADD32mi8, ADD32mr, ADD32ri, ADD32ri8, ADD32rm, ADD32rr,
+ADD64mi32, ADD64mi8, ADD64mr, ADD64ri32, ...
+</pre></div>
+</div>
+<p>The default backend prints out all of the records, as <a class="reference internal" href="#described-above">described above</a>.</p>
+<p>If you plan to use TableGen, you will most likely have to <a class="reference internal" href="#write-a-backend">write a backend</a>
+that extracts the information specific to what you need and formats it in the
+appropriate way.</p>
+</div>
+</div>
+<div class="section" id="tablegen-syntax">
+<span id="parses-a-file"></span><h2><a class="toc-backref" href="#id9">TableGen syntax</a><a class="headerlink" href="#tablegen-syntax" title="Permalink to this headline">¶</a></h2>
+<p>TableGen doesn’t care about the meaning of data (that is up to the backend to
+define), but it does care about syntax, and it enforces a simple type system.
+This section describes the syntax and the constructs allowed in a TableGen file.</p>
+<div class="section" id="tablegen-primitives">
+<h3><a class="toc-backref" href="#id10">TableGen primitives</a><a class="headerlink" href="#tablegen-primitives" title="Permalink to this headline">¶</a></h3>
+<div class="section" id="tablegen-comments">
+<h4><a class="toc-backref" href="#id11">TableGen comments</a><a class="headerlink" href="#tablegen-comments" title="Permalink to this headline">¶</a></h4>
+<p>TableGen supports BCPL style “<tt class="docutils literal"><span class="pre">//</span></tt>” comments, which run to the end of the
+line, and it also supports <strong>nestable</strong> “<tt class="docutils literal"><span class="pre">/*</span> <span class="pre">*/</span></tt>” comments.</p>
+</div>
+<div class="section" id="the-tablegen-type-system">
+<span id="tablegen-type"></span><h4><a class="toc-backref" href="#id12">The TableGen type system</a><a class="headerlink" href="#the-tablegen-type-system" title="Permalink to this headline">¶</a></h4>
+<p>TableGen files are strongly typed, in a simple (but complete) type-system.
+These types are used to perform automatic conversions, check for errors, and to
+help interface designers constrain the input that they allow. Every <a class="reference internal" href="#value-definition">value
+definition</a> is required to have an associated type.</p>
+<p>TableGen supports a mixture of very low-level types (such as <tt class="docutils literal"><span class="pre">bit</span></tt>) and very
+high-level types (such as <tt class="docutils literal"><span class="pre">dag</span></tt>). This flexibility is what allows it to
+describe a wide range of information conveniently and compactly. The TableGen
+types are:</p>
+<dl class="docutils">
+<dt><tt class="docutils literal"><span class="pre">bit</span></tt></dt>
+<dd>A ‘bit’ is a boolean value that can hold either 0 or 1.</dd>
+<dt><tt class="docutils literal"><span class="pre">int</span></tt></dt>
+<dd>The ‘int’ type represents a simple 32-bit integer value, such as 5.</dd>
+<dt><tt class="docutils literal"><span class="pre">string</span></tt></dt>
+<dd>The ‘string’ type represents an ordered sequence of characters of arbitrary
+length.</dd>
+<dt><tt class="docutils literal"><span class="pre">bits<n></span></tt></dt>
+<dd>A ‘bits’ type is an arbitrary, but fixed, size integer that is broken up
+into individual bits. This type is useful because it can handle some bits
+being defined while others are undefined.</dd>
+<dt><tt class="docutils literal"><span class="pre">list<ty></span></tt></dt>
+<dd>This type represents a list whose elements are some other type. The
+contained type is arbitrary: it can even be another list type.</dd>
+<dt>Class type</dt>
+<dd>Specifying a class name in a type context means that the defined value must
+be a subclass of the specified class. This is useful in conjunction with
+the <tt class="docutils literal"><span class="pre">list</span></tt> type, for example, to constrain the elements of the list to a
+common base class (e.g., a <tt class="docutils literal"><span class="pre">list<Register></span></tt> can only contain definitions
+derived from the “<tt class="docutils literal"><span class="pre">Register</span></tt>” class).</dd>
+<dt><tt class="docutils literal"><span class="pre">dag</span></tt></dt>
+<dd>This type represents a nestable directed graph of elements.</dd>
+<dt><tt class="docutils literal"><span class="pre">code</span></tt></dt>
+<dd>This represents a big hunk of text. This is lexically distinct from string
+values because it doesn’t require escaping double quotes and other common
+characters that occur in code.</dd>
+</dl>
+<p>To date, these types have been sufficient for describing things that TableGen
+has been used for, but it is straight-forward to extend this list if needed.</p>
+</div>
+<div class="section" id="tablegen-values-and-expressions">
+<span id="tablegen-expressions"></span><h4><a class="toc-backref" href="#id13">TableGen values and expressions</a><a class="headerlink" href="#tablegen-values-and-expressions" title="Permalink to this headline">¶</a></h4>
+<p>TableGen allows for a pretty reasonable number of different expression forms
+when building up values. These forms allow the TableGen file to be written in a
+natural syntax and flavor for the application. The current expression forms
+supported include:</p>
+<dl class="docutils">
+<dt><tt class="docutils literal"><span class="pre">?</span></tt></dt>
+<dd>uninitialized field</dd>
+<dt><tt class="docutils literal"><span class="pre">0b1001011</span></tt></dt>
+<dd>binary integer value</dd>
+<dt><tt class="docutils literal"><span class="pre">07654321</span></tt></dt>
+<dd>octal integer value (indicated by a leading 0)</dd>
+<dt><tt class="docutils literal"><span class="pre">7</span></tt></dt>
+<dd>decimal integer value</dd>
+<dt><tt class="docutils literal"><span class="pre">0x7F</span></tt></dt>
+<dd>hexadecimal integer value</dd>
+<dt><tt class="docutils literal"><span class="pre">"foo"</span></tt></dt>
+<dd>string value</dd>
+<dt><tt class="docutils literal"><span class="pre">[{</span> <span class="pre">...</span> <span class="pre">}]</span></tt></dt>
+<dd>code fragment</dd>
+<dt><tt class="docutils literal"><span class="pre">[</span> <span class="pre">X,</span> <span class="pre">Y,</span> <span class="pre">Z</span> <span class="pre">]<type></span></tt></dt>
+<dd>list value. <type> is the type of the list element and is usually optional.
+In rare cases, TableGen is unable to deduce the element type in which case
+the user must specify it explicitly.</dd>
+<dt><tt class="docutils literal"><span class="pre">{</span> <span class="pre">a,</span> <span class="pre">b,</span> <span class="pre">c</span> <span class="pre">}</span></tt></dt>
+<dd>initializer for a “bits<3>” value</dd>
+<dt><tt class="docutils literal"><span class="pre">value</span></tt></dt>
+<dd>value reference</dd>
+<dt><tt class="docutils literal"><span class="pre">value{17}</span></tt></dt>
+<dd>access to one bit of a value</dd>
+<dt><tt class="docutils literal"><span class="pre">value{15-17}</span></tt></dt>
+<dd>access to multiple bits of a value</dd>
+<dt><tt class="docutils literal"><span class="pre">DEF</span></tt></dt>
+<dd>reference to a record definition</dd>
+<dt><tt class="docutils literal"><span class="pre">CLASS<val</span> <span class="pre">list></span></tt></dt>
+<dd>reference to a new anonymous definition of CLASS with the specified template
+arguments.</dd>
+<dt><tt class="docutils literal"><span class="pre">X.Y</span></tt></dt>
+<dd>reference to the subfield of a value</dd>
+<dt><tt class="docutils literal"><span class="pre">list[4-7,17,2-3]</span></tt></dt>
+<dd>A slice of the ‘list’ list, including elements 4,5,6,7,17,2, and 3 from it.
+Elements may be included multiple times.</dd>
+</dl>
+<p><tt class="docutils literal"><span class="pre">foreach</span> <span class="pre"><var></span> <span class="pre">=</span> <span class="pre">[</span> <span class="pre"><list></span> <span class="pre">]</span> <span class="pre">in</span> <span class="pre">{</span> <span class="pre"><body></span> <span class="pre">}</span></tt></p>
+<dl class="docutils">
+<dt><tt class="docutils literal"><span class="pre">foreach</span> <span class="pre"><var></span> <span class="pre">=</span> <span class="pre">[</span> <span class="pre"><list></span> <span class="pre">]</span> <span class="pre">in</span> <span class="pre"><def></span></tt></dt>
+<dd>Replicate <body> or <def>, replacing instances of <var> with each value
+in <list>. <var> is scoped at the level of the <tt class="docutils literal"><span class="pre">foreach</span></tt> loop and must
+not conflict with any other object introduced in <body> or <def>. Currently
+only <tt class="docutils literal"><span class="pre">def</span></tt>s are expanded within <body>.</dd>
+</dl>
+<p><tt class="docutils literal"><span class="pre">foreach</span> <span class="pre"><var></span> <span class="pre">=</span> <span class="pre">0-15</span> <span class="pre">in</span> <span class="pre">...</span></tt></p>
+<dl class="docutils">
+<dt><tt class="docutils literal"><span class="pre">foreach</span> <span class="pre"><var></span> <span class="pre">=</span> <span class="pre">{0-15,32-47}</span> <span class="pre">in</span> <span class="pre">...</span></tt></dt>
+<dd>Loop over ranges of integers. The braces are required for multiple ranges.</dd>
+<dt><tt class="docutils literal"><span class="pre">(DEF</span> <span class="pre">a,</span> <span class="pre">b)</span></tt></dt>
+<dd>a dag value. The first element is required to be a record definition, the
+remaining elements in the list may be arbitrary other values, including
+nested <tt class="docutils literal"><span class="pre">`dag</span></tt>‘ values.</dd>
+<dt><tt class="docutils literal"><span class="pre">!strconcat(a,</span> <span class="pre">b)</span></tt></dt>
+<dd>A string value that is the result of concatenating the ‘a’ and ‘b’ strings.</dd>
+<dt><tt class="docutils literal"><span class="pre">str1#str2</span></tt></dt>
+<dd>“#” (paste) is a shorthand for !strconcat. It may concatenate things that
+are not quoted strings, in which case an implicit !cast<string> is done on
+the operand of the paste.</dd>
+<dt><tt class="docutils literal"><span class="pre">!cast<type>(a)</span></tt></dt>
+<dd>A symbol of type <em>type</em> obtained by looking up the string ‘a’ in the symbol
+table. If the type of ‘a’ does not match <em>type</em>, TableGen aborts with an
+error. !cast<string> is a special case in that the argument must be an
+object defined by a ‘def’ construct.</dd>
+<dt><tt class="docutils literal"><span class="pre">!subst(a,</span> <span class="pre">b,</span> <span class="pre">c)</span></tt></dt>
+<dd>If ‘a’ and ‘b’ are of string type or are symbol references, substitute ‘b’
+for ‘a’ in ‘c.’ This operation is analogous to $(subst) in GNU make.</dd>
+<dt><tt class="docutils literal"><span class="pre">!foreach(a,</span> <span class="pre">b,</span> <span class="pre">c)</span></tt></dt>
+<dd>For each member ‘b’ of dag or list ‘a’ apply operator ‘c.’ ‘b’ is a dummy
+variable that should be declared as a member variable of an instantiated
+class. This operation is analogous to $(foreach) in GNU make.</dd>
+<dt><tt class="docutils literal"><span class="pre">!head(a)</span></tt></dt>
+<dd>The first element of list ‘a.’</dd>
+<dt><tt class="docutils literal"><span class="pre">!tail(a)</span></tt></dt>
+<dd>The 2nd-N elements of list ‘a.’</dd>
+<dt><tt class="docutils literal"><span class="pre">!empty(a)</span></tt></dt>
+<dd>An integer {0,1} indicating whether list ‘a’ is empty.</dd>
+<dt><tt class="docutils literal"><span class="pre">!if(a,b,c)</span></tt></dt>
+<dd>‘b’ if the result of ‘int’ or ‘bit’ operator ‘a’ is nonzero, ‘c’ otherwise.</dd>
+<dt><tt class="docutils literal"><span class="pre">!eq(a,b)</span></tt></dt>
+<dd>‘bit 1’ if string a is equal to string b, 0 otherwise. This only operates
+on string, int and bit objects. Use !cast<string> to compare other types of
+objects.</dd>
+</dl>
+<p>Note that all of the values have rules specifying how they convert to values
+for different types. These rules allow you to assign a value like “<tt class="docutils literal"><span class="pre">7</span></tt>”
+to a “<tt class="docutils literal"><span class="pre">bits<4></span></tt>” value, for example.</p>
+</div>
+</div>
+<div class="section" id="classes-and-definitions">
+<h3><a class="toc-backref" href="#id14">Classes and definitions</a><a class="headerlink" href="#classes-and-definitions" title="Permalink to this headline">¶</a></h3>
+<p>As mentioned in the <a class="reference internal" href="#intro">intro</a>, classes and definitions (collectively known as
+‘records’) in TableGen are the main high-level unit of information that TableGen
+collects. Records are defined with a <tt class="docutils literal"><span class="pre">def</span></tt> or <tt class="docutils literal"><span class="pre">class</span></tt> keyword, the record
+name, and an optional list of “<a class="reference internal" href="#template-arguments">template arguments</a>”. If the record has
+superclasses, they are specified as a comma separated list that starts with a
+colon character (“<tt class="docutils literal"><span class="pre">:</span></tt>”). If <a class="reference internal" href="#value-definitions">value definitions</a> or <a class="reference internal" href="#let-expressions">let expressions</a> are
+needed for the class, they are enclosed in curly braces (“<tt class="docutils literal"><span class="pre">{}</span></tt>”); otherwise,
+the record ends with a semicolon.</p>
+<p>Here is a simple TableGen file:</p>
+<div class="highlight-llvm"><pre>class C { bit V = 1; }
+def X : C;
+def Y : C {
+ string Greeting = "hello";
+}</pre>
+</div>
+<p>This example defines two definitions, <tt class="docutils literal"><span class="pre">X</span></tt> and <tt class="docutils literal"><span class="pre">Y</span></tt>, both of which derive from
+the <tt class="docutils literal"><span class="pre">C</span></tt> class. Because of this, they both get the <tt class="docutils literal"><span class="pre">V</span></tt> bit value. The <tt class="docutils literal"><span class="pre">Y</span></tt>
+definition also gets the Greeting member as well.</p>
+<p>In general, classes are useful for collecting together the commonality between a
+group of records and isolating it in a single place. Also, classes permit the
+specification of default values for their subclasses, allowing the subclasses to
+override them as they wish.</p>
+<div class="section" id="value-definitions">
+<span id="value-definition"></span><span id="id1"></span><h4><a class="toc-backref" href="#id15">Value definitions</a><a class="headerlink" href="#value-definitions" title="Permalink to this headline">¶</a></h4>
+<p>Value definitions define named entries in records. A value must be defined
+before it can be referred to as the operand for another value definition or
+before the value is reset with a <a class="reference internal" href="#let-expression">let expression</a>. A value is defined by
+specifying a <a class="reference internal" href="#tablegen-type">TableGen type</a> and a name. If an initial value is available, it
+may be specified after the type with an equal sign. Value definitions require
+terminating semicolons.</p>
+</div>
+<div class="section" id="let-expressions-within-a-record">
+<span id="let-expressions"></span><span id="let-expression"></span><span id="id2"></span><h4><a class="toc-backref" href="#id16">‘let’ expressions</a><a class="headerlink" href="#let-expressions-within-a-record" title="Permalink to this headline">¶</a></h4>
+<p>A record-level let expression is used to change the value of a value definition
+in a record. This is primarily useful when a superclass defines a value that a
+derived class or definition wants to override. Let expressions consist of the
+‘<tt class="docutils literal"><span class="pre">let</span></tt>‘ keyword followed by a value name, an equal sign (“<tt class="docutils literal"><span class="pre">=</span></tt>”), and a new
+value. For example, a new class could be added to the example above, redefining
+the <tt class="docutils literal"><span class="pre">V</span></tt> field for all of its subclasses:</p>
+<div class="highlight-llvm"><pre>class D : C { let V = 0; }
+def Z : D;</pre>
+</div>
+<p>In this case, the <tt class="docutils literal"><span class="pre">Z</span></tt> definition will have a zero value for its <tt class="docutils literal"><span class="pre">V</span></tt> value,
+despite the fact that it derives (indirectly) from the <tt class="docutils literal"><span class="pre">C</span></tt> class, because the
+<tt class="docutils literal"><span class="pre">D</span></tt> class overrode its value.</p>
+</div>
+<div class="section" id="class-template-arguments">
+<span id="template-arguments"></span><h4><a class="toc-backref" href="#id17">Class template arguments</a><a class="headerlink" href="#class-template-arguments" title="Permalink to this headline">¶</a></h4>
+<p>TableGen permits the definition of parameterized classes as well as normal
+concrete classes. Parameterized TableGen classes specify a list of variable
+bindings (which may optionally have defaults) that are bound when used. Here is
+a simple example:</p>
+<div class="highlight-llvm"><pre>class FPFormat<bits<3> val> {
+ bits<3> Value = val;
+}
+def NotFP : FPFormat<0>;
+def ZeroArgFP : FPFormat<1>;
+def OneArgFP : FPFormat<2>;
+def OneArgFPRW : FPFormat<3>;
+def TwoArgFP : FPFormat<4>;
+def CompareFP : FPFormat<5>;
+def CondMovFP : FPFormat<6>;
+def SpecialFP : FPFormat<7>;</pre>
+</div>
+<p>In this case, template arguments are used as a space efficient way to specify a
+list of “enumeration values”, each with a “<tt class="docutils literal"><span class="pre">Value</span></tt>” field set to the specified
+integer.</p>
+<p>The more esoteric forms of <a class="reference internal" href="#tablegen-expressions">TableGen expressions</a> are useful in conjunction
+with template arguments. As an example:</p>
+<div class="highlight-llvm"><pre>class ModRefVal<bits<2> val> {
+ bits<2> Value = val;
+}
+
+def None : ModRefVal<0>;
+def Mod : ModRefVal<1>;
+def Ref : ModRefVal<2>;
+def ModRef : ModRefVal<3>;
+
+class Value<ModRefVal MR> {
+ // Decode some information into a more convenient format, while providing
+ // a nice interface to the user of the "Value" class.
+ bit isMod = MR.Value{0};
+ bit isRef = MR.Value{1};
+
+ // other stuff...
+}
+
+// Example uses
+def bork : Value<Mod>;
+def zork : Value<Ref>;
+def hork : Value<ModRef>;</pre>
+</div>
+<p>This is obviously a contrived example, but it shows how template arguments can
+be used to decouple the interface provided to the user of the class from the
+actual internal data representation expected by the class. In this case,
+running <tt class="docutils literal"><span class="pre">llvm-tblgen</span></tt> on the example prints the following definitions:</p>
+<div class="highlight-llvm"><pre>def bork { // Value
+ bit isMod = 1;
+ bit isRef = 0;
+}
+def hork { // Value
+ bit isMod = 1;
+ bit isRef = 1;
+}
+def zork { // Value
+ bit isMod = 0;
+ bit isRef = 1;
+}</pre>
+</div>
+<p>This shows that TableGen was able to dig into the argument and extract a piece
+of information that was requested by the designer of the “Value” class. For
+more realistic examples, please see existing users of TableGen, such as the X86
+backend.</p>
+</div>
+<div class="section" id="multiclass-definitions-and-instances">
+<h4><a class="toc-backref" href="#id18">Multiclass definitions and instances</a><a class="headerlink" href="#multiclass-definitions-and-instances" title="Permalink to this headline">¶</a></h4>
+<p>While classes with template arguments are a good way to factor commonality
+between two instances of a definition, multiclasses allow a convenient notation
+for defining multiple definitions at once (instances of implicitly constructed
+classes). For example, consider an 3-address instruction set whose instructions
+come in two forms: “<tt class="docutils literal"><span class="pre">reg</span> <span class="pre">=</span> <span class="pre">reg</span> <span class="pre">op</span> <span class="pre">reg</span></tt>” and “<tt class="docutils literal"><span class="pre">reg</span> <span class="pre">=</span> <span class="pre">reg</span> <span class="pre">op</span> <span class="pre">imm</span></tt>”
+(e.g. SPARC). In this case, you’d like to specify in one place that this
+commonality exists, then in a separate place indicate what all the ops are.</p>
+<p>Here is an example TableGen fragment that shows this idea:</p>
+<div class="highlight-llvm"><pre>def ops;
+def GPR;
+def Imm;
+class inst<int opc, string asmstr, dag operandlist>;
+
+multiclass ri_inst<int opc, string asmstr> {
+ def _rr : inst<opc, !strconcat(asmstr, " $dst, $src1, $src2"),
+ (ops GPR:$dst, GPR:$src1, GPR:$src2)>;
+ def _ri : inst<opc, !strconcat(asmstr, " $dst, $src1, $src2"),
+ (ops GPR:$dst, GPR:$src1, Imm:$src2)>;
+}
+
+// Instantiations of the ri_inst multiclass.
+defm ADD : ri_inst<0b111, "add">;
+defm SUB : ri_inst<0b101, "sub">;
+defm MUL : ri_inst<0b100, "mul">;
+...</pre>
+</div>
+<p>The name of the resultant definitions has the multidef fragment names appended
+to them, so this defines <tt class="docutils literal"><span class="pre">ADD_rr</span></tt>, <tt class="docutils literal"><span class="pre">ADD_ri</span></tt>, <tt class="docutils literal"><span class="pre">SUB_rr</span></tt>, etc. A defm may
+inherit from multiple multiclasses, instantiating definitions from each
+multiclass. Using a multiclass this way is exactly equivalent to instantiating
+the classes multiple times yourself, e.g. by writing:</p>
+<div class="highlight-llvm"><pre>def ops;
+def GPR;
+def Imm;
+class inst<int opc, string asmstr, dag operandlist>;
+
+class rrinst<int opc, string asmstr>
+ : inst<opc, !strconcat(asmstr, " $dst, $src1, $src2"),
+ (ops GPR:$dst, GPR:$src1, GPR:$src2)>;
+
+class riinst<int opc, string asmstr>
+ : inst<opc, !strconcat(asmstr, " $dst, $src1, $src2"),
+ (ops GPR:$dst, GPR:$src1, Imm:$src2)>;
+
+// Instantiations of the ri_inst multiclass.
+def ADD_rr : rrinst<0b111, "add">;
+def ADD_ri : riinst<0b111, "add">;
+def SUB_rr : rrinst<0b101, "sub">;
+def SUB_ri : riinst<0b101, "sub">;
+def MUL_rr : rrinst<0b100, "mul">;
+def MUL_ri : riinst<0b100, "mul">;
+...</pre>
+</div>
+<p>A <tt class="docutils literal"><span class="pre">defm</span></tt> can also be used inside a multiclass providing several levels of
+multiclass instanciations.</p>
+<div class="highlight-llvm"><pre>class Instruction<bits<4> opc, string Name> {
+ bits<4> opcode = opc;
+ string name = Name;
+}
+
+multiclass basic_r<bits<4> opc> {
+ def rr : Instruction<opc, "rr">;
+ def rm : Instruction<opc, "rm">;
+}
+
+multiclass basic_s<bits<4> opc> {
+ defm SS : basic_r<opc>;
+ defm SD : basic_r<opc>;
+ def X : Instruction<opc, "x">;
+}
+
+multiclass basic_p<bits<4> opc> {
+ defm PS : basic_r<opc>;
+ defm PD : basic_r<opc>;
+ def Y : Instruction<opc, "y">;
+}
+
+defm ADD : basic_s<0xf>, basic_p<0xf>;
+...
+
+// Results
+def ADDPDrm { ...
+def ADDPDrr { ...
+def ADDPSrm { ...
+def ADDPSrr { ...
+def ADDSDrm { ...
+def ADDSDrr { ...
+def ADDY { ...
+def ADDX { ...</pre>
+</div>
+<p><tt class="docutils literal"><span class="pre">defm</span></tt> declarations can inherit from classes too, the rule to follow is that
+the class list must start after the last multiclass, and there must be at least
+one multiclass before them.</p>
+<div class="highlight-llvm"><pre>class XD { bits<4> Prefix = 11; }
+class XS { bits<4> Prefix = 12; }
+
+class I<bits<4> op> {
+ bits<4> opcode = op;
+}
+
+multiclass R {
+ def rr : I<4>;
+ def rm : I<2>;
+}
+
+multiclass Y {
+ defm SS : R, XD;
+ defm SD : R, XS;
+}
+
+defm Instr : Y;
+
+// Results
+def InstrSDrm {
+ bits<4> opcode = { 0, 0, 1, 0 };
+ bits<4> Prefix = { 1, 1, 0, 0 };
+}
+...
+def InstrSSrr {
+ bits<4> opcode = { 0, 1, 0, 0 };
+ bits<4> Prefix = { 1, 0, 1, 1 };
+}</pre>
+</div>
+</div>
+</div>
+<div class="section" id="file-scope-entities">
+<h3><a class="toc-backref" href="#id19">File scope entities</a><a class="headerlink" href="#file-scope-entities" title="Permalink to this headline">¶</a></h3>
+<div class="section" id="file-inclusion">
+<h4><a class="toc-backref" href="#id20">File inclusion</a><a class="headerlink" href="#file-inclusion" title="Permalink to this headline">¶</a></h4>
+<p>TableGen supports the ‘<tt class="docutils literal"><span class="pre">include</span></tt>‘ token, which textually substitutes the
+specified file in place of the include directive. The filename should be
+specified as a double quoted string immediately after the ‘<tt class="docutils literal"><span class="pre">include</span></tt>‘ keyword.
+Example:</p>
+<div class="highlight-llvm"><pre>include "foo.td"</pre>
+</div>
+</div>
+<div class="section" id="id3">
+<h4><a class="toc-backref" href="#id21">‘let’ expressions</a><a class="headerlink" href="#id3" title="Permalink to this headline">¶</a></h4>
+<p>“Let” expressions at file scope are similar to <a class="reference internal" href="#let-expressions-within-a-record">“let” expressions within a
+record</a>, except they can specify a value binding for multiple records at a
+time, and may be useful in certain other cases. File-scope let expressions are
+really just another way that TableGen allows the end-user to factor out
+commonality from the records.</p>
+<p>File-scope “let” expressions take a comma-separated list of bindings to apply,
+and one or more records to bind the values in. Here are some examples:</p>
+<div class="highlight-llvm"><pre>let isTerminator = 1, isReturn = 1, isBarrier = 1, hasCtrlDep = 1 in
+ def RET : I<0xC3, RawFrm, (outs), (ins), "ret", [(X86retflag 0)]>;
+
+let isCall = 1 in
+ // All calls clobber the non-callee saved registers...
+ let Defs = [EAX, ECX, EDX, FP0, FP1, FP2, FP3, FP4, FP5, FP6, ST0,
+ MM0, MM1, MM2, MM3, MM4, MM5, MM6, MM7,
+ XMM0, XMM1, XMM2, XMM3, XMM4, XMM5, XMM6, XMM7, EFLAGS] in {
+ def CALLpcrel32 : Ii32<0xE8, RawFrm, (outs), (ins i32imm:$dst,variable_ops),
+ "call\t${dst:call}", []>;
+ def CALL32r : I<0xFF, MRM2r, (outs), (ins GR32:$dst, variable_ops),
+ "call\t{*}$dst", [(X86call GR32:$dst)]>;
+ def CALL32m : I<0xFF, MRM2m, (outs), (ins i32mem:$dst, variable_ops),
+ "call\t{*}$dst", []>;
+ }</pre>
+</div>
+<p>File-scope “let” expressions are often useful when a couple of definitions need
+to be added to several records, and the records do not otherwise need to be
+opened, as in the case with the <tt class="docutils literal"><span class="pre">CALL*</span></tt> instructions above.</p>
+<p>It’s also possible to use “let” expressions inside multiclasses, providing more
+ways to factor out commonality from the records, specially if using several
+levels of multiclass instanciations. This also avoids the need of using “let”
+expressions within subsequent records inside a multiclass.</p>
+<div class="highlight-llvm"><pre>multiclass basic_r<bits<4> opc> {
+ let Predicates = [HasSSE2] in {
+ def rr : Instruction<opc, "rr">;
+ def rm : Instruction<opc, "rm">;
+ }
+ let Predicates = [HasSSE3] in
+ def rx : Instruction<opc, "rx">;
+}
+
+multiclass basic_ss<bits<4> opc> {
+ let IsDouble = 0 in
+ defm SS : basic_r<opc>;
+
+ let IsDouble = 1 in
+ defm SD : basic_r<opc>;
+}
+
+defm ADD : basic_ss<0xf>;</pre>
+</div>
+</div>
+<div class="section" id="looping">
+<h4><a class="toc-backref" href="#id22">Looping</a><a class="headerlink" href="#looping" title="Permalink to this headline">¶</a></h4>
+<p>TableGen supports the ‘<tt class="docutils literal"><span class="pre">foreach</span></tt>‘ block, which textually replicates the loop
+body, substituting iterator values for iterator references in the body.
+Example:</p>
+<div class="highlight-llvm"><pre>foreach i = [0, 1, 2, 3] in {
+ def R#i : Register<...>;
+ def F#i : Register<...>;
+}</pre>
+</div>
+<p>This will create objects <tt class="docutils literal"><span class="pre">R0</span></tt>, <tt class="docutils literal"><span class="pre">R1</span></tt>, <tt class="docutils literal"><span class="pre">R2</span></tt> and <tt class="docutils literal"><span class="pre">R3</span></tt>. <tt class="docutils literal"><span class="pre">foreach</span></tt> blocks
+may be nested. If there is only one item in the body the braces may be
+elided:</p>
+<div class="highlight-llvm"><pre>foreach i = [0, 1, 2, 3] in
+ def R#i : Register<...>;</pre>
+</div>
+</div>
+</div>
+</div>
+<div class="section" id="code-generator-backend-info">
+<h2><a class="toc-backref" href="#id23">Code Generator backend info</a><a class="headerlink" href="#code-generator-backend-info" title="Permalink to this headline">¶</a></h2>
+<p>Expressions used by code generator to describe instructions and isel patterns:</p>
+<dl class="docutils">
+<dt><tt class="docutils literal"><span class="pre">(implicit</span> <span class="pre">a)</span></tt></dt>
+<dd>an implicitly defined physical register. This tells the dag instruction
+selection emitter the input pattern’s extra definitions matches implicit
+physical register definitions.</dd>
+</dl>
+</div>
+<div class="section" id="write-a-backend">
+<span id="tablegen-backends"></span><span id="tablegen-backend"></span><span id="id4"></span><h2><a class="toc-backref" href="#id24">TableGen backends</a><a class="headerlink" href="#write-a-backend" title="Permalink to this headline">¶</a></h2>
+<p>TODO: How they work, how to write one. This section should not contain details
+about any particular backend, except maybe <tt class="docutils literal"><span class="pre">-print-enums</span></tt> as an example. This
+should highlight the APIs in <tt class="docutils literal"><span class="pre">TableGen/Record.h</span></tt>.</p>
+</div>
+</div>
+
+
+ </div>
+ </div>
+ </div>
+ <div class="clearer"></div>
+ </div>
+ <div class="related">
+ <h3>Navigation</h3>
+ <ul>
+ <li class="right" style="margin-right: 10px">
+ <a href="genindex.html" title="General Index"
+ >index</a></li>
+ <li class="right" >
+ <a href="DebuggingJITedCode.html" title="Debugging JIT-ed Code With GDB"
+ >next</a> |</li>
+ <li class="right" >
+ <a href="SegmentedStacks.html" title="Segmented Stacks in LLVM"
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+<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
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+ <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
+ <title>LLVM test-suite Makefile Guide</title>
+ <link rel="stylesheet" href="_static/llvm.css" type="text/css">
+</head>
+<body>
+
+<h1>
+ LLVM test-suite Makefile Guide
+</h1>
+
+<ol>
+ <li><a href="#overview">Overview</a></li>
+ <li><a href="#testsuitestructure">Test suite structure</a></li>
+ <li><a href="#testsuiterun">Running the test suite</a>
+ <ul>
+ <li><a href="#testsuiteexternal">Configuring External Tests</a></li>
+ <li><a href="#testsuitetests">Running different tests</a></li>
+ <li><a href="#testsuiteoutput">Generating test output</a></li>
+ <li><a href="#testsuitecustom">Writing custom tests for test-suite</a></li>
+ </ul>
+ </li>
+</ol>
+
+<div class="doc_author">
+ <p>Written by John T. Criswell, Daniel Dunbar, Reid Spencer, and Tanya Lattner</p>
+</div>
+
+<!--=========================================================================-->
+<h2><a name="overview">Overview</a></h2>
+<!--=========================================================================-->
+
+<div>
+
+<p>This document describes the features of the Makefile-based LLVM
+test-suite. This way of interacting with the test-suite is deprecated in favor
+of running the test-suite using LNT, but may continue to prove useful for some
+users. See the Testing
+Guide's <a href="TestingGuide.html#testsuitequickstart">test-suite
+Quickstart</a> section for more information.</p>
+
+</div>
+
+<!--=========================================================================-->
+<h2><a name="testsuitestructure">Test suite Structure</a></h2>
+<!--=========================================================================-->
+
+<div>
+
+<p>The <tt>test-suite</tt> module contains a number of programs that can be compiled
+with LLVM and executed. These programs are compiled using the native compiler
+and various LLVM backends. The output from the program compiled with the
+native compiler is assumed correct; the results from the other programs are
+compared to the native program output and pass if they match.</p>
+
+<p>When executing tests, it is usually a good idea to start out with a subset of
+the available tests or programs. This makes test run times smaller at first and
+later on this is useful to investigate individual test failures. To run some
+test only on a subset of programs, simply change directory to the programs you
+want tested and run <tt>gmake</tt> there. Alternatively, you can run a different
+test using the <tt>TEST</tt> variable to change what tests or run on the
+selected programs (see below for more info).</p>
+
+<p>In addition for testing correctness, the <tt>test-suite</tt> directory also
+performs timing tests of various LLVM optimizations. It also records
+compilation times for the compilers and the JIT. This information can be
+used to compare the effectiveness of LLVM's optimizations and code
+generation.</p>
+
+<p><tt>test-suite</tt> tests are divided into three types of tests: MultiSource,
+SingleSource, and External.</p>
+
+<ul>
+<li><tt>test-suite/SingleSource</tt>
+<p>The SingleSource directory contains test programs that are only a single
+source file in size. These are usually small benchmark programs or small
+programs that calculate a particular value. Several such programs are grouped
+together in each directory.</p></li>
+
+<li><tt>test-suite/MultiSource</tt>
+<p>The MultiSource directory contains subdirectories which contain entire
+programs with multiple source files. Large benchmarks and whole applications
+go here.</p></li>
+
+<li><tt>test-suite/External</tt>
+<p>The External directory contains Makefiles for building code that is external
+to (i.e., not distributed with) LLVM. The most prominent members of this
+directory are the SPEC 95 and SPEC 2000 benchmark suites. The <tt>External</tt>
+directory does not contain these actual tests, but only the Makefiles that know
+how to properly compile these programs from somewhere else. The presence and
+location of these external programs is configured by the test-suite
+<tt>configure</tt> script.</p></li>
+</ul>
+
+<p>Each tree is then subdivided into several categories, including applications,
+benchmarks, regression tests, code that is strange grammatically, etc. These
+organizations should be relatively self explanatory.</p>
+
+<p>Some tests are known to fail. Some are bugs that we have not fixed yet;
+others are features that we haven't added yet (or may never add). In the
+regression tests, the result for such tests will be XFAIL (eXpected FAILure).
+In this way, you can tell the difference between an expected and unexpected
+failure.</p>
+
+<p>The tests in the test suite have no such feature at this time. If the
+test passes, only warnings and other miscellaneous output will be generated. If
+a test fails, a large <program> FAILED message will be displayed. This
+will help you separate benign warnings from actual test failures.</p>
+
+</div>
+
+<!--=========================================================================-->
+<h2><a name="testsuiterun">Running the test suite</a></h2>
+<!--=========================================================================-->
+
+<div>
+
+<p>First, all tests are executed within the LLVM object directory tree. They
+<i>are not</i> executed inside of the LLVM source tree. This is because the
+test suite creates temporary files during execution.</p>
+
+<p>To run the test suite, you need to use the following steps:</p>
+
+<ol>
+ <li><tt>cd</tt> into the <tt>llvm/projects</tt> directory in your source tree.
+ </li>
+
+ <li><p>Check out the <tt>test-suite</tt> module with:</p>
+
+<div class="doc_code">
+<pre>
+% svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite
+</pre>
+</div>
+ <p>This will get the test suite into <tt>llvm/projects/test-suite</tt>.</p>
+ </li>
+ <li><p>Configure and build <tt>llvm</tt>.</p></li>
+ <li><p>Configure and build <tt>llvm-gcc</tt>.</p></li>
+ <li><p>Install <tt>llvm-gcc</tt> somewhere.</p></li>
+ <li><p><em>Re-configure</em> <tt>llvm</tt> from the top level of
+ each build tree (LLVM object directory tree) in which you want
+ to run the test suite, just as you do before building LLVM.</p>
+ <p>During the <em>re-configuration</em>, you must either: (1)
+ have <tt>llvm-gcc</tt> you just built in your path, or (2)
+ specify the directory where your just-built <tt>llvm-gcc</tt> is
+ installed using <tt>--with-llvmgccdir=$LLVM_GCC_DIR</tt>.</p>
+ <p>You must also tell the configure machinery that the test suite
+ is available so it can be configured for your build tree:</p>
+<div class="doc_code">
+<pre>
+% cd $LLVM_OBJ_ROOT ; $LLVM_SRC_ROOT/configure [--with-llvmgccdir=$LLVM_GCC_DIR]
+</pre>
+</div>
+ <p>[Remember that <tt>$LLVM_GCC_DIR</tt> is the directory where you
+ <em>installed</em> llvm-gcc, not its src or obj directory.]</p>
+ </li>
+
+ <li><p>You can now run the test suite from your build tree as follows:</p>
+<div class="doc_code">
+<pre>
+% cd $LLVM_OBJ_ROOT/projects/test-suite
+% make
+</pre>
+</div>
+ </li>
+</ol>
+<p>Note that the second and third steps only need to be done once. After you
+have the suite checked out and configured, you don't need to do it again (unless
+the test code or configure script changes).</p>
+
+<!-- _______________________________________________________________________ -->
+<h3>
+ <a name="testsuiteexternal">Configuring External Tests</a>
+</h3>
+<!-- _______________________________________________________________________ -->
+
+<div>
+<p>In order to run the External tests in the <tt>test-suite</tt>
+ module, you must specify <i>--with-externals</i>. This
+ must be done during the <em>re-configuration</em> step (see above),
+ and the <tt>llvm</tt> re-configuration must recognize the
+ previously-built <tt>llvm-gcc</tt>. If any of these is missing or
+ neglected, the External tests won't work.</p>
+<dl>
+<dt><i>--with-externals</i></dt>
+<dt><i>--with-externals=<<tt>directory</tt>></i></dt>
+</dl>
+ This tells LLVM where to find any external tests. They are expected to be
+ in specifically named subdirectories of <<tt>directory</tt>>.
+ If <tt>directory</tt> is left unspecified,
+ <tt>configure</tt> uses the default value
+ <tt>/home/vadve/shared/benchmarks/speccpu2000/benchspec</tt>.
+ Subdirectory names known to LLVM include:
+ <dl>
+ <dt>spec95</dt>
+ <dt>speccpu2000</dt>
+ <dt>speccpu2006</dt>
+ <dt>povray31</dt>
+ </dl>
+ Others are added from time to time, and can be determined from
+ <tt>configure</tt>.
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h3>
+ <a name="testsuitetests">Running different tests</a>
+</h3>
+<!-- _______________________________________________________________________ -->
+<div>
+<p>In addition to the regular "whole program" tests, the <tt>test-suite</tt>
+module also provides a mechanism for compiling the programs in different ways.
+If the variable TEST is defined on the <tt>gmake</tt> command line, the test system will
+include a Makefile named <tt>TEST.<value of TEST variable>.Makefile</tt>.
+This Makefile can modify build rules to yield different results.</p>
+
+<p>For example, the LLVM nightly tester uses <tt>TEST.nightly.Makefile</tt> to
+create the nightly test reports. To run the nightly tests, run <tt>gmake
+TEST=nightly</tt>.</p>
+
+<p>There are several TEST Makefiles available in the tree. Some of them are
+designed for internal LLVM research and will not work outside of the LLVM
+research group. They may still be valuable, however, as a guide to writing your
+own TEST Makefile for any optimization or analysis passes that you develop with
+LLVM.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h3>
+ <a name="testsuiteoutput">Generating test output</a>
+</h3>
+<!-- _______________________________________________________________________ -->
+<div>
+ <p>There are a number of ways to run the tests and generate output. The most
+ simple one is simply running <tt>gmake</tt> with no arguments. This will
+ compile and run all programs in the tree using a number of different methods
+ and compare results. Any failures are reported in the output, but are likely
+ drowned in the other output. Passes are not reported explicitly.</p>
+
+ <p>Somewhat better is running <tt>gmake TEST=sometest test</tt>, which runs
+ the specified test and usually adds per-program summaries to the output
+ (depending on which sometest you use). For example, the <tt>nightly</tt> test
+ explicitly outputs TEST-PASS or TEST-FAIL for every test after each program.
+ Though these lines are still drowned in the output, it's easy to grep the
+ output logs in the Output directories.</p>
+
+ <p>Even better are the <tt>report</tt> and <tt>report.format</tt> targets
+ (where <tt>format</tt> is one of <tt>html</tt>, <tt>csv</tt>, <tt>text</tt> or
+ <tt>graphs</tt>). The exact contents of the report are dependent on which
+ <tt>TEST</tt> you are running, but the text results are always shown at the
+ end of the run and the results are always stored in the
+ <tt>report.<type>.format</tt> file (when running with
+ <tt>TEST=<type></tt>).
+
+ The <tt>report</tt> also generate a file called
+ <tt>report.<type>.raw.out</tt> containing the output of the entire test
+ run.
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h3>
+ <a name="testsuitecustom">Writing custom tests for the test suite</a>
+</h3>
+<!-- _______________________________________________________________________ -->
+
+<div>
+
+<p>Assuming you can run the test suite, (e.g. "<tt>gmake TEST=nightly report</tt>"
+should work), it is really easy to run optimizations or code generator
+components against every program in the tree, collecting statistics or running
+custom checks for correctness. At base, this is how the nightly tester works,
+it's just one example of a general framework.</p>
+
+<p>Lets say that you have an LLVM optimization pass, and you want to see how
+many times it triggers. First thing you should do is add an LLVM
+<a href="ProgrammersManual.html#Statistic">statistic</a> to your pass, which
+will tally counts of things you care about.</p>
+
+<p>Following this, you can set up a test and a report that collects these and
+formats them for easy viewing. This consists of two files, a
+"<tt>test-suite/TEST.XXX.Makefile</tt>" fragment (where XXX is the name of your
+test) and a "<tt>test-suite/TEST.XXX.report</tt>" file that indicates how to
+format the output into a table. There are many example reports of various
+levels of sophistication included with the test suite, and the framework is very
+general.</p>
+
+<p>If you are interested in testing an optimization pass, check out the
+"libcalls" test as an example. It can be run like this:<p>
+
+<div class="doc_code">
+<pre>
+% cd llvm/projects/test-suite/MultiSource/Benchmarks # or some other level
+% make TEST=libcalls report
+</pre>
+</div>
+
+<p>This will do a bunch of stuff, then eventually print a table like this:</p>
+
+<div class="doc_code">
+<pre>
+Name | total | #exit |
+...
+FreeBench/analyzer/analyzer | 51 | 6 |
+FreeBench/fourinarow/fourinarow | 1 | 1 |
+FreeBench/neural/neural | 19 | 9 |
+FreeBench/pifft/pifft | 5 | 3 |
+MallocBench/cfrac/cfrac | 1 | * |
+MallocBench/espresso/espresso | 52 | 12 |
+MallocBench/gs/gs | 4 | * |
+Prolangs-C/TimberWolfMC/timberwolfmc | 302 | * |
+Prolangs-C/agrep/agrep | 33 | 12 |
+Prolangs-C/allroots/allroots | * | * |
+Prolangs-C/assembler/assembler | 47 | * |
+Prolangs-C/bison/mybison | 74 | * |
+...
+</pre>
+</div>
+
+<p>This basically is grepping the -stats output and displaying it in a table.
+You can also use the "TEST=libcalls report.html" target to get the table in HTML
+form, similarly for report.csv and report.tex.</p>
+
+<p>The source for this is in test-suite/TEST.libcalls.*. The format is pretty
+simple: the Makefile indicates how to run the test (in this case,
+"<tt>opt -simplify-libcalls -stats</tt>"), and the report contains one line for
+each column of the output. The first value is the header for the column and the
+second is the regex to grep the output of the command for. There are lots of
+example reports that can do fancy stuff.</p>
+
+</div>
+
+</div>
+
+<!-- *********************************************************************** -->
+
+<hr>
+<address>
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+ John T. Criswell, Daniel Dunbar, Reid Spencer, and Tanya Lattner<br>
+ <a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date$
+</address>
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