<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> <title>The LLVM Lexicon</title> <link rel="stylesheet" href="llvm.css" type="text/css"> <meta name="author" content="Various"> <meta name="description" content="A glossary of terms used with the LLVM project."> </head> <body> <div class="doc_title">The LLVM Lexicon</div> <p class="doc_warning">NOTE: This document is a work in progress!</p> <!-- *********************************************************************** --> <div class="doc_section">Table Of Contents</div> <!-- *********************************************************************** --> <div class="doc_text"> <table> <tr><th colspan="8"><b>- <a href="#A">A</a> -</b></th></tr> <tr> <td><a href="#ADCE">ADCE</a></td> </tr> <tr><th colspan="8"><b>- <a href="#B">B</a> -</b></th></tr> <tr> <td><a href="#BURS">BURS</a></td> </tr> <tr><th colspan="8"><b>- <a href="#C">C</a> -</b></th></tr> <tr> <td><a href="#CSE">CSE</a></td> </tr> <tr><th colspan="8"><b>- <a href="#D">D</a> -</b></th></tr> <tr> <td><a href="#DAG">DAG</a></td> <td><a href="#Derived_Pointer">Derived Pointer</a></td> <td><a href="#DSA">DSA</a></td> <td><a href="#DSE">DSE</a></td> </tr> <tr><th colspan="8"><b>- <a href="#G">G</a> -</b></th></tr> <td><a href="#GC">GC</a></td> </tr> <tr><th colspan="8"><b>- <a href="#I">I</a> -</b></th></tr> <tr> <td><a href="#IPA">IPA</a></td> <td><a href="#IPO">IPO</a></td> <td><a href="#ISel">ISel</a></td> </tr> <tr><th colspan="8"><b>- <a href="#L">L</a> -</b></th></tr> <tr> <td><a href="#LCSSA">LCSSA</a></td> <td><a href="#LICM">LICM</a></td> <td><a href="#Load-VN">Load-VN</a></td> </tr> <tr><th colspan="8"><b>- <a href="#O">O</a> -</b></th></tr> <tr> <td><a href="#Object_Pointer">Object Pointer</a></td> </tr> <tr><th colspan="8"><b>- <a href="#P">P</a> -</b></th></tr> <tr> <td><a href="#PRE">PRE</a></td> </tr> <tr><th colspan="8"><b>- <a href="#R">R</a> -</b></th></tr> <tr> <td><a href="#Reassociation">Reassociation</a></td> <td><a href="#Root">Root</a></td> </tr> <tr><th colspan="8"><b>- <a href="#S">S</a> -</b></th></tr> <tr> <td><a href="#Safe_Point">Safe Point</a></td> <td><a href="#SCC">SCC</a></td> <td><a href="#SCCP">SCCP</a></td> <td><a href="#SDISel">SDISel</a></td> <td><a href="#SRoA">SRoA</a></td> <td><a href="#Stack_Map">Stack Map</a></td> </tr> </table> </div> <!-- *********************************************************************** --> <div class="doc_section">Definitions</div> <!-- *********************************************************************** --> <!-- _______________________________________________________________________ --> <div class="doc_subsection"><a name="A">- A -</a></div> <div class="doc_text"> <dl> <dt><a name="ADCE"><b>ADCE</b></a></dt> <dd>Aggressive Dead Code Elimination</dd> </dl> </div> <!-- _______________________________________________________________________ --> <div class="doc_subsection"><a name="B">- B -</a></div> <div class="doc_text"> <dl> <dt><a name="BURS"><b>BURS</b></a></dt> <dd>Bottom Up Rewriting System—A method of instruction selection for code generation. An example is the <a href="http://www.program-transformation.org/Transform/BURG">BURG</a> tool.</dd> </dl> </div> <!-- _______________________________________________________________________ --> <div class="doc_subsection"><a name="C">- C -</a></div> <div class="doc_text"> <dl> <dt><a name="CSE"><b>CSE</b></a></dt> <dd>Common Subexpression Elimination. An optimization that removes common subexpression compuation. For example <tt>(a+b)*(a+b)</tt> has two subexpressions that are the same: <tt>(a+b)</tt>. This optimization would perform the addition only once and then perform the multiply (but only if it's compulationally correct/safe). </dl> </div> <!-- _______________________________________________________________________ --> <div class="doc_subsection"><a name="D">- D -</a></div> <div class="doc_text"> <dl> <dt><a name="DAG"><b>DAG</b></a></dt> <dd>Directed Acyclic Graph</dd> <dt><a name="Derived_Pointer"><b>Derived Pointer</b></a></dt> <dd>A pointer to the interior of an object, such that a garbage collector is unable to use the pointer for reachability analysis. While a derived pointer is live, the corresponding object pointer must be kept in a root, otherwise the collector might free the referenced object. With copying collectors, derived pointers pose an additional hazard that they may be invalidated at any <a href="Safe_Point">safe point</a>. This term is used in opposition to <a href="#Object_Pointer">object pointer</a>.</dd> <dt><a name="DSA"><b>DSA</b></a></dt> <dd>Data Structure Analysis</dd> <dt><a name="DSE"><b>DSE</b></a></dt> <dd>Dead Store Elimination</dd> </dl> </div> <!-- _______________________________________________________________________ --> <div class="doc_subsection"><a name="G">- G -</a></div> <div class="doc_text"> <dl> <dt><a name="GC"><b>GC</b></a></dt> <dd>Garbage Collection. The practice of using reachability analysis instead of explicit memory management to reclaim unused memory.</dd> </dl> </div> <!-- _______________________________________________________________________ --> <div class="doc_subsection"><a name="H">- H -</a></div> <div class="doc_text"> <dl> <dt><a name="Heap"><b>Heap</b></a></dt> <dd>In garbage collection, the region of memory which is managed using reachability analysis.</dd> </dl> </div> <!-- _______________________________________________________________________ --> <div class="doc_subsection"><a name="I">- I -</a></div> <div class="doc_text"> <dl> <dt><a name="IPA"><b>IPA</b></a></dt> <dd>Inter-Procedural Analysis. Refers to any variety of code analysis that occurs between procedures, functions or compilation units (modules).</dd> <dt><a name="IPO"><b>IPO</b></a></dt> <dd>Inter-Procedural Optimization. Refers to any variety of code optimization that occurs between procedures, functions or compilation units (modules).</dd> <dt><a name="IPO"><b>ISel</b></a></dt> <dd>Instruction Selection.</dd> </dl> </div> <!-- _______________________________________________________________________ --> <div class="doc_subsection"><a name="L">- L -</a></div> <div class="doc_text"> <dl> <dt><a name="LCSSA"><b>LCSSA</b></a></dt> <dd>Loop-Closed Static Single Assignment Form</dd> <dt><a name="LICM"><b>LICM</b></a></dt> <dd>Loop Invariant Code Motion</dd> <dt><a name="Load-VN"><b>Load-VN</b></a></dt> <dd>Load Value Numbering</dd> </dl> </div> <!-- _______________________________________________________________________ --> <div class="doc_subsection"><a name="P">- O -</a></div> <div class="doc_text"> <dl> <dt><a name="Object_Pointer"><b>Object Pointer</b></a></dt> <dd>A pointer to an object such that the garbage collector is able to trace references contained within the object. This term is used in opposition to <a href="#Derived_Pointer">derived pointer</a>.</dd> </dl> </div> <!-- _______________________________________________________________________ --> <div class="doc_subsection"><a name="P">- P -</a></div> <div class="doc_text"> <dl> <dt><a name="PRE"><b>PRE</b></a></dt> <dd>Partial Redundancy Elimination</dd> </dl> </div> <!-- _______________________________________________________________________ --> <div class="doc_subsection"><a name="R">- R -</a></div> <div class="doc_text"> <dl> <dt><a name="Reassociation"><b>Reassociation</b></a></dt> <dd>Rearranging associative expressions to promote better redundancy elimination and other optimization. For example, changing (A+B-A) into (B+A-A), permitting it to be optimized into (B+0) then (B).</dd> <dt><a name="Root"><b>Root</b></a></dt> <dd>In garbage collection, a pointer variable lying outside of the <a href="#Heap">heap</a> from which the collector begins its reachability analysis. In the context of code generation, "root" almost always refers to a "stack root"—a local or temporary variable within an executing function.</dd> </dl> </div> <!-- _______________________________________________________________________ --> <div class="doc_subsection"><a name="S">- S -</a></div> <div class="doc_text"> <dl> <dt><a name="SCC"><b>Safe Point</b></a></dt> <dd>In garbage collection, it is necessary to identify <a href="#Root">stack roots</a> so that reachability analysis may proceed. It may be infeasible to provide this information for every instruction, so instead the information may is calculated only at designated safe points. With a copying collector, <a href="#Derived_Pointers">derived pointers</a> must not be retained across safe points and <a href="#Object_Pointers">object pointers</a> must be reloaded from stack roots.</dd> <dt><a name="SDISel"><b>SDISel</b></a></dt> <dd>Selection DAG Instruction Selection.</dd> <dt><a name="SCC"><b>SCC</b></a></dt> <dd>Strongly Connected Component</dd> <dt><a name="SCCP"><b>SCCP</b></a></dt> <dd>Sparse Conditional Constant Propagation</dd> <dt><a name="SRoA"><b>SRoA</b></a></dt> <dd>Scalar Replacement of Aggregates</dd> <dt><a name="SSA"><b>SSA</b></a></dt> <dd>Static Single Assignment</dd> <dt><a name="Stack_Map"><b>Stack Map</b></a></dt> <dd>In garbage collection, metadata emitted by the code generator which identifies <a href="#Root">roots</a> within the stack frame of an executing function.</dd> </dl> </div> <!-- *********************************************************************** --> <hr> <address> <a href="http://jigsaw.w3.org/css-validator/check/referer"><img src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a><a href="http://validator.w3.org/check/referer"><img src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a><a href="http://llvm.org/">The LLVM Team</a><br> <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br> Last modified: $Date$ </address> <!-- vim: sw=2 --> </body> </html>