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