docs/Lexicon.html

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