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