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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<title>The LLVM Lexicon</title>
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<link rel="stylesheet" href="llvm.css" type="text/css">
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<meta name="author" content="Various">
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<meta name="description"
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content="A glossary of terms used with the LLVM project.">
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</head>
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<body>
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<div class="doc_title">The LLVM Lexicon</div>
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<p class="doc_warning">NOTE: This document is a work in progress!</p>
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<!-- *********************************************************************** -->
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<div class="doc_section">Table Of Contents</div>
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<!-- *********************************************************************** -->
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<div class="doc_text">
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<table>
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<tr><th colspan="8"><b>- <a href="#A">A</a> -</b></th></tr>
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<tr>
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<td><a href="#ADCE">ADCE</a></td>
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</tr>
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<tr><th colspan="8"><b>- <a href="#B">B</a> -</b></th></tr>
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<tr>
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<td><a href="#BURS">BURS</a></td>
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</tr>
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<tr><th colspan="8"><b>- <a href="#C">C</a> -</b></th></tr>
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<tr>
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<td><a href="#CSE">CSE</a></td>
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</tr>
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<tr><th colspan="8"><b>- <a href="#D">D</a> -</b></th></tr>
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<tr>
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<td><a href="#DAG">DAG</a></td>
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<td><a href="#Derived_Pointer">Derived Pointer</a></td>
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<td><a href="#DSA">DSA</a></td>
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<td><a href="#DSE">DSE</a></td>
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</tr>
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<tr><th colspan="8"><b>- <a href="#G">G</a> -</b></th></tr>
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<td><a href="#GC">GC</a></td>
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</tr>
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<tr><th colspan="8"><b>- <a href="#I">I</a> -</b></th></tr>
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<tr>
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<td><a href="#IPA">IPA</a></td>
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<td><a href="#IPO">IPO</a></td>
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<td><a href="#ISel">ISel</a></td>
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</tr>
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<tr><th colspan="8"><b>- <a href="#L">L</a> -</b></th></tr>
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<tr>
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<td><a href="#LCSSA">LCSSA</a></td>
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<td><a href="#LICM">LICM</a></td>
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<td><a href="#Load-VN">Load-VN</a></td>
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</tr>
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<tr><th colspan="8"><b>- <a href="#O">O</a> -</b></th></tr>
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<tr>
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<td><a href="#Object_Pointer">Object Pointer</a></td>
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</tr>
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<tr><th colspan="8"><b>- <a href="#P">P</a> -</b></th></tr>
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<tr>
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<td><a href="#PRE">PRE</a></td>
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</tr>
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<tr><th colspan="8"><b>- <a href="#R">R</a> -</b></th></tr>
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<tr>
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<td><a href="#Reassociation">Reassociation</a></td>
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<td><a href="#Root">Root</a></td>
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</tr>
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<tr><th colspan="8"><b>- <a href="#S">S</a> -</b></th></tr>
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<tr>
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<td><a href="#Safe_Point">Safe Point</a></td>
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<td><a href="#SCC">SCC</a></td>
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<td><a href="#SCCP">SCCP</a></td>
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<td><a href="#SDISel">SDISel</a></td>
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<td><a href="#SRoA">SRoA</a></td>
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<td><a href="#Stack_Map">Stack Map</a></td>
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</tr>
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</table>
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</div>
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<!-- *********************************************************************** -->
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<div class="doc_section">Definitions</div>
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<!-- *********************************************************************** -->
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"><a name="A">- A -</a></div>
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<div class="doc_text">
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<dl>
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<dt><a name="ADCE"><b>ADCE</b></a></dt>
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<dd>Aggressive Dead Code Elimination</dd>
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</dl>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"><a name="B">- B -</a></div>
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<div class="doc_text">
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<dl>
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<dt><a name="BURS"><b>BURS</b></a></dt>
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<dd>Bottom Up Rewriting System—A method of instruction selection for
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code generation. An example is the <a
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href="http://www.program-transformation.org/Transform/BURG">BURG</a> tool.</dd>
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</dl>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"><a name="C">- C -</a></div>
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<div class="doc_text">
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<dl>
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<dt><a name="CSE"><b>CSE</b></a></dt>
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<dd>Common Subexpression Elimination. An optimization that removes common
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subexpression compuation. For example <tt>(a+b)*(a+b)</tt> has two
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subexpressions that are the same: <tt>(a+b)</tt>. This optimization would
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perform the addition only once and then perform the multiply (but only if
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it's compulationally correct/safe).
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</dl>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"><a name="D">- D -</a></div>
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<div class="doc_text">
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<dl>
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<dt><a name="DAG"><b>DAG</b></a></dt>
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<dd>Directed Acyclic Graph</dd>
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<dt><a name="Derived_Pointer"><b>Derived Pointer</b></a></dt>
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<dd>A pointer to the interior of an object, such that a garbage collector
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is unable to use the pointer for reachability analysis. While a derived
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pointer is live, the corresponding object pointer must be kept in a root,
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otherwise the collector might free the referenced object. With copying
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collectors, derived pointers pose an additional hazard that they may be
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invalidated at any <a href="Safe_Point">safe point</a>. This term is used in
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opposition to <a href="#Object_Pointer">object pointer</a>.</dd>
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<dt><a name="DSA"><b>DSA</b></a></dt>
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<dd>Data Structure Analysis</dd>
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<dt><a name="DSE"><b>DSE</b></a></dt>
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<dd>Dead Store Elimination</dd>
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</dl>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"><a name="G">- G -</a></div>
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<div class="doc_text">
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<dl>
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<dt><a name="GC"><b>GC</b></a></dt>
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<dd>Garbage Collection. The practice of using reachability analysis instead
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of explicit memory management to reclaim unused memory.</dd>
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</dl>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"><a name="H">- H -</a></div>
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<div class="doc_text">
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<dl>
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<dt><a name="Heap"><b>Heap</b></a></dt>
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<dd>In garbage collection, the region of memory which is managed using
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reachability analysis.</dd>
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</dl>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"><a name="I">- I -</a></div>
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<div class="doc_text">
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<dl>
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<dt><a name="IPA"><b>IPA</b></a></dt>
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<dd>Inter-Procedural Analysis. Refers to any variety of code analysis that
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occurs between procedures, functions or compilation units (modules).</dd>
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<dt><a name="IPO"><b>IPO</b></a></dt>
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<dd>Inter-Procedural Optimization. Refers to any variety of code
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optimization that occurs between procedures, functions or compilation units
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(modules).</dd>
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<dt><a name="IPO"><b>ISel</b></a></dt>
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<dd>Instruction Selection.</dd>
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</dl>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"><a name="L">- L -</a></div>
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<div class="doc_text">
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<dl>
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<dt><a name="LCSSA"><b>LCSSA</b></a></dt>
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<dd>Loop-Closed Static Single Assignment Form</dd>
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<dt><a name="LICM"><b>LICM</b></a></dt>
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<dd>Loop Invariant Code Motion</dd>
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<dt><a name="Load-VN"><b>Load-VN</b></a></dt>
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<dd>Load Value Numbering</dd>
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</dl>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"><a name="P">- O -</a></div>
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<div class="doc_text">
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<dl>
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<dt><a name="Object_Pointer"><b>Object Pointer</b></a></dt>
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<dd>A pointer to an object such that the garbage collector is able to trace
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references contained within the object. This term is used in opposition to
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<a href="#Derived_Pointer">derived pointer</a>.</dd>
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</dl>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"><a name="P">- P -</a></div>
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<div class="doc_text">
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<dl>
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<dt><a name="PRE"><b>PRE</b></a></dt>
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<dd>Partial Redundancy Elimination</dd>
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</dl>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"><a name="R">- R -</a></div>
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<div class="doc_text">
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<dl>
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<dt><a name="Reassociation"><b>Reassociation</b></a></dt> <dd>Rearranging
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associative expressions to promote better redundancy elimination and other
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optimization. For example, changing (A+B-A) into (B+A-A), permitting it to
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be optimized into (B+0) then (B).</dd>
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<dt><a name="Root"><b>Root</b></a></dt> <dd>In garbage collection, a
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pointer variable lying outside of the <a href="#Heap">heap</a> from which
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the collector begins its reachability analysis. In the context of code
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generation, "root" almost always refers to a "stack root"—a local or
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temporary variable within an executing function.</dd>
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</dl>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"><a name="S">- S -</a></div>
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<div class="doc_text">
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<dl>
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<dt><a name="SCC"><b>Safe Point</b></a></dt>
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<dd>In garbage collection, it is necessary to identify <a href="#Root">stack
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roots</a> so that reachability analysis may proceed. It may be infeasible to
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provide this information for every instruction, so instead the information
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may is calculated only at designated safe points. With a copying collector,
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<a href="#Derived_Pointers">derived pointers</a> must not be retained across
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safe points and <a href="#Object_Pointers">object pointers</a> must be
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reloaded from stack roots.</dd>
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<dt><a name="SDISel"><b>SDISel</b></a></dt>
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<dd>Selection DAG Instruction Selection.</dd>
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<dt><a name="SCC"><b>SCC</b></a></dt>
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<dd>Strongly Connected Component</dd>
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<dt><a name="SCCP"><b>SCCP</b></a></dt>
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<dd>Sparse Conditional Constant Propagation</dd>
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<dt><a name="SRoA"><b>SRoA</b></a></dt>
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<dd>Scalar Replacement of Aggregates</dd>
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<dt><a name="SSA"><b>SSA</b></a></dt>
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<dd>Static Single Assignment</dd>
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<dt><a name="Stack_Map"><b>Stack Map</b></a></dt>
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<dd>In garbage collection, metadata emitted by the code generator which
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identifies <a href="#Root">roots</a> within the stack frame of an executing
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function.</dd>
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</dl>
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</div>
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<!-- *********************************************************************** -->
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<hr>
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<address> <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
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href="http://llvm.org/">The LLVM Team</a><br>
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<a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
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Last modified: $Date$
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</address>
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