docs/Lexicon.html

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