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5 <title>The LLVM Lexicon</title>
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Reid Spencer9f093ed2004-08-17 09:38:50 +0000[diff] [blame]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>
Reid Spencerc3c4c4f2004-11-01 08:19:36 +0000[diff] [blame]19 <tr><th colspan="8"><b>- <a href="#A">A</a> -</b></th></tr>
Reid Spencer9f093ed2004-08-17 09:38:50 +0000[diff] [blame]20 <tr>
21 <td><a href="#ADCE">ADCE</a></td>
Reid Spencer9f093ed2004-08-17 09:38:50 +0000[diff] [blame]22 </tr>
Reid Spencerc3c4c4f2004-11-01 08:19:36 +0000[diff] [blame]23 <tr><th colspan="8"><b>- <a href="#B">B</a> -</b></th></tr>
Reid Spencer7c8d6582004-08-24 18:34:10 +0000[diff] [blame]24 <tr>
25 <td><a href="#BURS">BURS</a></td>
Reid Spencer7c8d6582004-08-24 18:34:10 +0000[diff] [blame]26 </tr>
Reid Spencerc3c4c4f2004-11-01 08:19:36 +0000[diff] [blame]27 <tr><th colspan="8"><b>- <a href="#C">C</a> -</b></th></tr>
Reid Spencer965ff462004-10-30 21:40:28 +0000[diff] [blame]28 <tr>
29 <td><a href="#CSE">CSE</a></td>
Reid Spencer965ff462004-10-30 21:40:28 +0000[diff] [blame]30 </tr>
Reid Spencerc3c4c4f2004-11-01 08:19:36 +0000[diff] [blame]31 <tr><th colspan="8"><b>- <a href="#D">D</a> -</b></th></tr>
Misha Brukman00b21ae2004-08-24 01:57:02 +0000[diff] [blame]32 <tr>
Gordon Henriksen0076a672007-09-27 19:31:36 +0000[diff] [blame^]33 <td><a href="#DAG">DAG</a></td>
34 <td><a href="#Derived_Pointer">Derived Pointer</a></td>
Misha Brukmanadfa8b82004-09-05 03:00:20 +0000[diff] [blame]35 <td><a href="#DSA">DSA</a></td>
Misha Brukman00b21ae2004-08-24 01:57:02 +0000[diff] [blame]36 <td><a href="#DSE">DSE</a></td>
Misha Brukman00b21ae2004-08-24 01:57:02 +0000[diff] [blame]37 </tr>
Gordon Henriksen0076a672007-09-27 19:31:36 +0000[diff] [blame^]38 <tr><th colspan="8"><b>- <a href="#G">G</a> -</b></th></tr>
39 <td><a href="#GC">GC</a></td>
40 </tr>
Reid Spencerc3c4c4f2004-11-01 08:19:36 +0000[diff] [blame]41 <tr><th colspan="8"><b>- <a href="#I">I</a> -</b></th></tr>
Reid Spencer965ff462004-10-30 21:40:28 +0000[diff] [blame]42 <tr>
43 <td><a href="#IPA">IPA</a></td>
44 <td><a href="#IPO">IPO</a></td>
Gordon Henriksen0076a672007-09-27 19:31:36 +0000[diff] [blame^]45 <td><a href="#ISel">ISel</a></td>
Reid Spencer965ff462004-10-30 21:40:28 +0000[diff] [blame]46 </tr>
Reid Spencerc3c4c4f2004-11-01 08:19:36 +0000[diff] [blame]47 <tr><th colspan="8"><b>- <a href="#L">L</a> -</b></th></tr>
Misha Brukman00b21ae2004-08-24 01:57:02 +0000[diff] [blame]48 <tr>
Owen Anderson7a312482006-10-18 05:50:12 +0000[diff] [blame]49 <td><a href="#LCSSA">LCSSA</a></td>
Misha Brukman00b21ae2004-08-24 01:57:02 +0000[diff] [blame]50 <td><a href="#LICM">LICM</a></td>
Misha Brukman2ace8cb2004-08-24 04:13:17 +0000[diff] [blame]51 <td><a href="#Load-VN">Load-VN</a></td>
Misha Brukman00b21ae2004-08-24 01:57:02 +0000[diff] [blame]52 </tr>
Gordon Henriksen0076a672007-09-27 19:31:36 +0000[diff] [blame^]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>
Reid Spencerc3c4c4f2004-11-01 08:19:36 +0000[diff] [blame]57 <tr><th colspan="8"><b>- <a href="#P">P</a> -</b></th></tr>
Misha Brukman00b21ae2004-08-24 01:57:02 +0000[diff] [blame]58 <tr>
59 <td><a href="#PRE">PRE</a></td>
Chris Lattner153827b2005-05-13 20:18:49 +0000[diff] [blame]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>
Gordon Henriksen0076a672007-09-27 19:31:36 +0000[diff] [blame^]64 <td><a href="#Root">Root</a></td>
Misha Brukman00b21ae2004-08-24 01:57:02 +0000[diff] [blame]65 </tr>
Reid Spencerc3c4c4f2004-11-01 08:19:36 +0000[diff] [blame]66 <tr><th colspan="8"><b>- <a href="#S">S</a> -</b></th></tr>
Misha Brukman00b21ae2004-08-24 01:57:02 +0000[diff] [blame]67 <tr>
Gordon Henriksen0076a672007-09-27 19:31:36 +0000[diff] [blame^]68 <td><a href="#Safe_Point">Safe Point</a></td>
Chris Lattnera3198312005-11-29 01:34:50 +0000[diff] [blame]69 <td><a href="#SCC">SCC</a></td>
Misha Brukman00b21ae2004-08-24 01:57:02 +0000[diff] [blame]70 <td><a href="#SCCP">SCCP</a></td>
Gordon Henriksen0076a672007-09-27 19:31:36 +0000[diff] [blame^]71 <td><a href="#SDISel">SDISel</a></td>
Chris Lattner4999a5c2006-02-08 16:59:49 +0000[diff] [blame]72 <td><a href="#SRoA">SRoA</a></td>
Gordon Henriksen0076a672007-09-27 19:31:36 +0000[diff] [blame^]73 <td><a href="#Stack_Map">Stack Map</a></td>
Misha Brukman00b21ae2004-08-24 01:57:02 +0000[diff] [blame]74 </tr>
Reid Spencer9f093ed2004-08-17 09:38:50 +0000[diff] [blame]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>
Misha Brukman00b21ae2004-08-24 01:57:02 +0000[diff] [blame]85 <dt><a name="ADCE"><b>ADCE</b></a></dt>
86 <dd>Aggressive Dead Code Elimination</dd>
Reid Spencer9f093ed2004-08-17 09:38:50 +0000[diff] [blame]87 </dl>
88</div>
Misha Brukman00b21ae2004-08-24 01:57:02 +0000[diff] [blame]89<!-- _______________________________________________________________________ -->
Reid Spencer7c8d6582004-08-24 18:34:10 +0000[diff] [blame]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>
Chris Lattner7bf499c2004-08-24 18:53:39 +0000[diff] [blame]94 <dd>Bottom Up Rewriting System - A method of instruction selection for
95 code generation. An example is the <a
96href="http://www.program-transformation.org/Transform/BURG">BURG</a> tool.</dd>
Reid Spencer7c8d6582004-08-24 18:34:10 +0000[diff] [blame]97 </dl>
98</div>
99<!-- _______________________________________________________________________ -->
Reid Spencer965ff462004-10-30 21:40:28 +0000[diff] [blame]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
Gordon Henriksen0076a672007-09-27 19:31:36 +0000[diff] [blame^]108 it's compulationally correct/safe).
Reid Spencer965ff462004-10-30 21:40:28 +0000[diff] [blame]109 </dl>
110</div>
111<!-- _______________________________________________________________________ -->
Misha Brukman00b21ae2004-08-24 01:57:02 +0000[diff] [blame]112<div class="doc_subsection"><a name="D">- D -</a></div>
113<div class="doc_text">
114 <dl>
Gordon Henriksen0076a672007-09-27 19:31:36 +0000[diff] [blame^]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>
Misha Brukmanadfa8b82004-09-05 03:00:20 +0000[diff] [blame]125 <dt><a name="DSA"><b>DSA</b></a></dt>
Misha Brukman0d68e4c2004-09-05 03:57:23 +0000[diff] [blame]126 <dd>Data Structure Analysis</dd>
Misha Brukman00b21ae2004-08-24 01:57:02 +0000[diff] [blame]127 <dt><a name="DSE"><b>DSE</b></a></dt>
128 <dd>Dead Store Elimination</dd>
129 </dl>
130</div>
131<!-- _______________________________________________________________________ -->
Gordon Henriksen0076a672007-09-27 19:31:36 +0000[diff] [blame^]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<!-- _______________________________________________________________________ -->
Reid Spencer965ff462004-10-30 21:40:28 +0000[diff] [blame]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>
Gordon Henriksen0076a672007-09-27 19:31:36 +0000[diff] [blame^]160 <dt><a name="IPO"><b>ISel</b></a></dt>
161 <dd>Instruction Selection.</dd>
Reid Spencer965ff462004-10-30 21:40:28 +0000[diff] [blame]162 </dl>
163</div>
164<!-- _______________________________________________________________________ -->
Misha Brukman00b21ae2004-08-24 01:57:02 +0000[diff] [blame]165<div class="doc_subsection"><a name="L">- L -</a></div>
166<div class="doc_text">
167 <dl>
Owen Anderson7a312482006-10-18 05:50:12 +0000[diff] [blame]168 <dt><a name="LCSSA"><b>LCSSA</b></a></dt>
169 <dd>Loop-Closed Static Single Assignment Form</dd>
Misha Brukman00b21ae2004-08-24 01:57:02 +0000[diff] [blame]170 <dt><a name="LICM"><b>LICM</b></a></dt>
171 <dd>Loop Invariant Code Motion</dd>
Misha Brukman2ace8cb2004-08-24 04:13:17 +0000[diff] [blame]172 <dt><a name="Load-VN"><b>Load-VN</b></a></dt>
Misha Brukman00b21ae2004-08-24 01:57:02 +0000[diff] [blame]173 <dd>Load Value Numbering</dd>
174 </dl>
175</div>
Chris Lattner153827b2005-05-13 20:18:49 +0000[diff] [blame]176
Misha Brukman00b21ae2004-08-24 01:57:02 +0000[diff] [blame]177<!-- _______________________________________________________________________ -->
Gordon Henriksen0076a672007-09-27 19:31:36 +0000[diff] [blame^]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<!-- _______________________________________________________________________ -->
Misha Brukman00b21ae2004-08-24 01:57:02 +0000[diff] [blame]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>
Chris Lattner153827b2005-05-13 20:18:49 +0000[diff] [blame]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
Gordon Henriksen0076a672007-09-27 19:31:36 +0000[diff] [blame^]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>
Chris Lattner153827b2005-05-13 20:18:49 +0000[diff] [blame]210 </dl>
211</div>
212
Misha Brukman00b21ae2004-08-24 01:57:02 +0000[diff] [blame]213<!-- _______________________________________________________________________ -->
214<div class="doc_subsection"><a name="S">- S -</a></div>
215<div class="doc_text">
216 <dl>
Gordon Henriksen0076a672007-09-27 19:31:36 +0000[diff] [blame^]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>
Chris Lattnera3198312005-11-29 01:34:50 +0000[diff] [blame]227 <dt><a name="SCC"><b>SCC</b></a></dt>
228 <dd>Strongly Connected Component</dd>
Misha Brukman00b21ae2004-08-24 01:57:02 +0000[diff] [blame]229 <dt><a name="SCCP"><b>SCCP</b></a></dt>
Chris Lattnera3198312005-11-29 01:34:50 +0000[diff] [blame]230 <dd>Sparse Conditional Constant Propagation</dd>
Chris Lattner4999a5c2006-02-08 16:59:49 +0000[diff] [blame]231 <dt><a name="SRoA"><b>SRoA</b></a></dt>
232 <dd>Scalar Replacement of Aggregates</dd>
Misha Brukman00b21ae2004-08-24 01:57:02 +0000[diff] [blame]233 <dt><a name="SSA"><b>SSA</b></a></dt>
234 <dd>Static Single Assignment</dd>
Gordon Henriksen0076a672007-09-27 19:31:36 +0000[diff] [blame^]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>
Misha Brukman00b21ae2004-08-24 01:57:02 +0000[diff] [blame]239 </dl>
240</div>
Reid Spencer9f093ed2004-08-17 09:38:50 +0000[diff] [blame]241<!-- *********************************************************************** -->
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