1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> 2<html> 3<head> 4 <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> 5 <title>The LLVM Lexicon</title> 6 <link rel="stylesheet" href="llvm.css" type="text/css"> 7 <meta name="author" content="Various"> 8 <meta name="description" 9 content="A glossary of terms used with the LLVM project."> 10</head> 11<body> 12<h1>The LLVM Lexicon</h1> 13<p class="doc_warning">NOTE: This document is a work in progress!</p> 14<!-- *********************************************************************** --> 15<h2>Table Of Contents</h2> 16<!-- *********************************************************************** --> 17<div> 18 <table> 19 <tr><th colspan="8"><b>- <a href="#A">A</a> -</b></th></tr> 20 <tr> 21 <td><a href="#ADCE">ADCE</a></td> 22 </tr> 23 <tr><th colspan="8"><b>- <a href="#B">B</a> -</b></th></tr> 24 <tr> 25 <td><a href="#BURS">BURS</a></td> 26 </tr> 27 <tr><th colspan="8"><b>- <a href="#C">C</a> -</b></th></tr> 28 <tr> 29 <td><a href="#CSE">CSE</a></td> 30 </tr> 31 <tr><th colspan="8"><b>- <a href="#D">D</a> -</b></th></tr> 32 <tr> 33 <td><a href="#DAG">DAG</a></td> 34 <td><a href="#Derived_Pointer">Derived Pointer</a></td> 35 <td><a href="#DSA">DSA</a></td> 36 <td><a href="#DSE">DSE</a></td> 37 </tr> 38 <tr><th colspan="8"><b>- <a href="#F">F</a> -</b></th></tr> 39 <tr> 40 <td><a href="#FCA">FCA</a></td> 41 </tr> 42 <tr><th colspan="8"><b>- <a href="#G">G</a> -</b></th></tr> 43 <tr> 44 <td><a href="#GC">GC</a></td> 45 </tr> 46 <tr><th colspan="8"><b>- <a href="#I">I</a> -</b></th></tr> 47 <tr> 48 <td><a href="#IPA">IPA</a></td> 49 <td><a href="#IPO">IPO</a></td> 50 <td><a href="#ISel">ISel</a></td> 51 </tr> 52 <tr><th colspan="8"><b>- <a href="#L">L</a> -</b></th></tr> 53 <tr> 54 <td><a href="#LCSSA">LCSSA</a></td> 55 <td><a href="#LICM">LICM</a></td> 56 <td><a href="#Load-VN">Load-VN</a></td> 57 <td><a href="#LTO">LTO</a></td> 58 </tr> 59 <tr><th colspan="8"><b>- <a href="#M">M</a> -</b></th></tr> 60 <tr> 61 <td><a href="#MC">MC</a></td> 62 </tr> 63 <tr><th colspan="8"><b>- <a href="#O">O</a> -</b></th></tr> 64 <tr> 65 <td><a href="#Object_Pointer">Object Pointer</a></td> 66 </tr> 67 <tr><th colspan="8"><b>- <a href="#P">P</a> -</b></th></tr> 68 <tr> 69 <td><a href="#PRE">PRE</a></td> 70 </tr> 71 <tr><th colspan="8"><b>- <a href="#R">R</a> -</b></th></tr> 72 <tr> 73 <td><a href="#RAUW">RAUW</a></td> 74 <td><a href="#Reassociation">Reassociation</a></td> 75 <td><a href="#Root">Root</a></td> 76 </tr> 77 <tr><th colspan="8"><b>- <a href="#S">S</a> -</b></th></tr> 78 <tr> 79 <td><a href="#Safe_Point">Safe Point</a></td> 80 <td><a href="#SCC">SCC</a></td> 81 <td><a href="#SCCP">SCCP</a></td> 82 <td><a href="#SDISel">SDISel</a></td> 83 <td><a href="#SRoA">SRoA</a></td> 84 <td><a href="#Stack_Map">Stack Map</a></td> 85 </tr> 86 </table> 87</div> 88 89<!-- *********************************************************************** --> 90<h2>Definitions</h2> 91<!-- *********************************************************************** --> 92<div> 93<!-- _______________________________________________________________________ --> 94<h3><a name="A">- A -</a></h3> 95<div> 96 <dl> 97 <dt><a name="ADCE"><b>ADCE</b></a></dt> 98 <dd>Aggressive Dead Code Elimination</dd> 99 </dl> 100</div> 101<!-- _______________________________________________________________________ --> 102<h3><a name="B">- B -</a></h3> 103<div> 104 <dl> 105 <dt><a name="BURS"><b>BURS</b></a></dt> 106 <dd>Bottom Up Rewriting System—A method of instruction selection for 107 code generation. An example is the <a 108href="http://www.program-transformation.org/Transform/BURG">BURG</a> tool.</dd> 109 </dl> 110</div> 111<!-- _______________________________________________________________________ --> 112<h3><a name="C">- C -</a></h3> 113<div> 114 <dl> 115 <dt><a name="CSE"><b>CSE</b></a></dt> 116 <dd>Common Subexpression Elimination. An optimization that removes common 117 subexpression compuation. For example <tt>(a+b)*(a+b)</tt> has two 118 subexpressions that are the same: <tt>(a+b)</tt>. This optimization would 119 perform the addition only once and then perform the multiply (but only if 120 it's compulationally correct/safe). 121 </dl> 122</div> 123<!-- _______________________________________________________________________ --> 124<h3><a name="D">- D -</a></h3> 125<div> 126 <dl> 127 <dt><a name="DAG"><b>DAG</b></a></dt> 128 <dd>Directed Acyclic Graph</dd> 129 <dt><a name="Derived_Pointer"><b>Derived Pointer</b></a></dt> 130 <dd>A pointer to the interior of an object, such that a garbage collector 131 is unable to use the pointer for reachability analysis. While a derived 132 pointer is live, the corresponding object pointer must be kept in a root, 133 otherwise the collector might free the referenced object. With copying 134 collectors, derived pointers pose an additional hazard that they may be 135 invalidated at any <a href="Safe_Point">safe point</a>. This term is used in 136 opposition to <a href="#Object_Pointer">object pointer</a>.</dd> 137 <dt><a name="DSA"><b>DSA</b></a></dt> 138 <dd>Data Structure Analysis</dd> 139 <dt><a name="DSE"><b>DSE</b></a></dt> 140 <dd>Dead Store Elimination</dd> 141 </dl> 142</div> 143<!-- _______________________________________________________________________ --> 144<h3><a name="F">- F -</a></h3> 145<div> 146 <dl> 147 <dt><a name="FCA"><b>FCA</b></a></dt> 148 <dd>First Class Aggregate</dd> 149 </dl> 150</div> 151<!-- _______________________________________________________________________ --> 152<h3><a name="G">- G -</a></h3> 153<div> 154 <dl> 155 <dt><a name="GC"><b>GC</b></a></dt> 156 <dd>Garbage Collection. The practice of using reachability analysis instead 157 of explicit memory management to reclaim unused memory.</dd> 158 </dl> 159</div> 160<!-- _______________________________________________________________________ --> 161<h3><a name="H">- H -</a></h3> 162<div> 163 <dl> 164 <dt><a name="Heap"><b>Heap</b></a></dt> 165 <dd>In garbage collection, the region of memory which is managed using 166 reachability analysis.</dd> 167 </dl> 168</div> 169<!-- _______________________________________________________________________ --> 170<h3><a name="I">- I -</a></h3> 171<div> 172 <dl> 173 <dt><a name="IPA"><b>IPA</b></a></dt> 174 <dd>Inter-Procedural Analysis. Refers to any variety of code analysis that 175 occurs between procedures, functions or compilation units (modules).</dd> 176 <dt><a name="IPO"><b>IPO</b></a></dt> 177 <dd>Inter-Procedural Optimization. Refers to any variety of code 178 optimization that occurs between procedures, functions or compilation units 179 (modules).</dd> 180 <dt><a name="ISel"><b>ISel</b></a></dt> 181 <dd>Instruction Selection.</dd> 182 </dl> 183</div> 184<!-- _______________________________________________________________________ --> 185<h3><a name="L">- L -</a></h3> 186<div> 187 <dl> 188 <dt><a name="LCSSA"><b>LCSSA</b></a></dt> 189 <dd>Loop-Closed Static Single Assignment Form</dd> 190 <dt><a name="LICM"><b>LICM</b></a></dt> 191 <dd>Loop Invariant Code Motion</dd> 192 <dt><a name="Load-VN"><b>Load-VN</b></a></dt> 193 <dd>Load Value Numbering</dd> 194 <dt><a name="LTO"><b>LTO</b></a></dt> 195 <dd>Link-Time Optimization</dd> 196 </dl> 197</div> 198<!-- _______________________________________________________________________ --> 199<h3><a name="M">- M -</a></h3> 200<div> 201 <dl> 202 <dt><a name="MC"><b>MC</b></a></dt> 203 <dd>Machine Code</dd> 204 </dl> 205</div> 206<!-- _______________________________________________________________________ --> 207<h3><a name="O">- O -</a></h3> 208<div> 209 <dl> 210 <dt><a name="Object_Pointer"><b>Object Pointer</b></a></dt> 211 <dd>A pointer to an object such that the garbage collector is able to trace 212 references contained within the object. This term is used in opposition to 213 <a href="#Derived_Pointer">derived pointer</a>.</dd> 214 </dl> 215</div> 216 217<!-- _______________________________________________________________________ --> 218<h3><a name="P">- P -</a></h3> 219<div> 220 <dl> 221 <dt><a name="PRE"><b>PRE</b></a></dt> 222 <dd>Partial Redundancy Elimination</dd> 223 </dl> 224</div> 225 226<!-- _______________________________________________________________________ --> 227<h3><a name="R">- R -</a></h3> 228<div> 229 <dl> 230 <dt><a name="RAUW"><b>RAUW</b></a></dt> <dd>An abbreviation for Replace 231 All Uses With. The functions User::replaceUsesOfWith(), 232 Value::replaceAllUsesWith(), and Constant::replaceUsesOfWithOnConstant() 233 implement the replacement of one Value with another by iterating over its 234 def/use chain and fixing up all of the pointers to point to the new value. 235 See also <a href="ProgrammersManual.html#iterate_chains">def/use chains</a>. 236 </dd> 237 <dt><a name="Reassociation"><b>Reassociation</b></a></dt> <dd>Rearranging 238 associative expressions to promote better redundancy elimination and other 239 optimization. For example, changing (A+B-A) into (B+A-A), permitting it to 240 be optimized into (B+0) then (B).</dd> 241 <dt><a name="Root"><b>Root</b></a></dt> <dd>In garbage collection, a 242 pointer variable lying outside of the <a href="#Heap">heap</a> from which 243 the collector begins its reachability analysis. In the context of code 244 generation, "root" almost always refers to a "stack root" -- a local or 245 temporary variable within an executing function.</dd> 246 </dl> 247</div> 248 249<!-- _______________________________________________________________________ --> 250<h3><a name="S">- S -</a></h3> 251<div> 252 <dl> 253 <dt><a name="Safe_Point"><b>Safe Point</b></a></dt> 254 <dd>In garbage collection, it is necessary to identify <a href="#Root">stack 255 roots</a> so that reachability analysis may proceed. It may be infeasible to 256 provide this information for every instruction, so instead the information 257 may is calculated only at designated safe points. With a copying collector, 258 <a href="#Derived_Pointers">derived pointers</a> must not be retained across 259 safe points and <a href="#Object_Pointers">object pointers</a> must be 260 reloaded from stack roots.</dd> 261 <dt><a name="SDISel"><b>SDISel</b></a></dt> 262 <dd>Selection DAG Instruction Selection.</dd> 263 <dt><a name="SCC"><b>SCC</b></a></dt> 264 <dd>Strongly Connected Component</dd> 265 <dt><a name="SCCP"><b>SCCP</b></a></dt> 266 <dd>Sparse Conditional Constant Propagation</dd> 267 <dt><a name="SRoA"><b>SRoA</b></a></dt> 268 <dd>Scalar Replacement of Aggregates</dd> 269 <dt><a name="SSA"><b>SSA</b></a></dt> 270 <dd>Static Single Assignment</dd> 271 <dt><a name="Stack_Map"><b>Stack Map</b></a></dt> 272 <dd>In garbage collection, metadata emitted by the code generator which 273 identifies <a href="#Root">roots</a> within the stack frame of an executing 274 function.</dd> 275 </dl> 276</div> 277 278</div> 279<!-- *********************************************************************** --> 280<hr> 281<address> <a href="http://jigsaw.w3.org/css-validator/check/referer"><img 282 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a><a 283 href="http://validator.w3.org/check/referer"><img 284 src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a><a 285 href="http://llvm.org/">The LLVM Team</a><br> 286<a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br> 287Last modified: $Date: 2011-09-27 14:44:01 -0400 (Tue, 27 Sep 2011) $ 288</address> 289<!-- vim: sw=2 290--> 291</body> 292</html> 293