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5 <title>The LLVM Lexicon</title>
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Reid Spencer85baf762004-08-17 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 Spencerd3f876c2004-11-01 08:19:36 +0000[diff] [blame]19 <tr><th colspan="8"><b>- <a href="#A">A</a> -</b></th></tr>
Reid Spencer85baf762004-08-17 09:38:50 +0000[diff] [blame]20 <tr>
21 <td><a href="#ADCE">ADCE</a></td>
Reid Spencer85baf762004-08-17 09:38:50 +0000[diff] [blame]22 </tr>
Reid Spencerd3f876c2004-11-01 08:19:36 +0000[diff] [blame]23 <tr><th colspan="8"><b>- <a href="#B">B</a> -</b></th></tr>
Reid Spencerce6be332004-08-24 18:34:10 +0000[diff] [blame]24 <tr>
25 <td><a href="#BURS">BURS</a></td>
Reid Spencerce6be332004-08-24 18:34:10 +0000[diff] [blame]26 </tr>
Reid Spencerd3f876c2004-11-01 08:19:36 +0000[diff] [blame]27 <tr><th colspan="8"><b>- <a href="#C">C</a> -</b></th></tr>
Reid Spencera07e0b52004-10-30 21:40:28 +0000[diff] [blame]28 <tr>
29 <td><a href="#CSE">CSE</a></td>
Reid Spencera07e0b52004-10-30 21:40:28 +0000[diff] [blame]30 </tr>
Reid Spencerd3f876c2004-11-01 08:19:36 +0000[diff] [blame]31 <tr><th colspan="8"><b>- <a href="#D">D</a> -</b></th></tr>
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]32 <tr>
Gordon Henriksen326e24f2007-09-27 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 Brukman9a4c9042004-09-05 03:00:20 +0000[diff] [blame]35 <td><a href="#DSA">DSA</a></td>
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]36 <td><a href="#DSE">DSE</a></td>
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]37 </tr>
Gordon Henriksen326e24f2007-09-27 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 Spencerd3f876c2004-11-01 08:19:36 +0000[diff] [blame]41 <tr><th colspan="8"><b>- <a href="#I">I</a> -</b></th></tr>
Reid Spencera07e0b52004-10-30 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 Henriksen326e24f2007-09-27 19:31:36 +0000[diff] [blame]45 <td><a href="#ISel">ISel</a></td>
Reid Spencera07e0b52004-10-30 21:40:28 +0000[diff] [blame]46 </tr>
Reid Spencerd3f876c2004-11-01 08:19:36 +0000[diff] [blame]47 <tr><th colspan="8"><b>- <a href="#L">L</a> -</b></th></tr>
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]48 <tr>
Owen Andersona6fc5012006-10-18 05:50:12 +0000[diff] [blame]49 <td><a href="#LCSSA">LCSSA</a></td>
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]50 <td><a href="#LICM">LICM</a></td>
Misha Brukman183cfc22004-08-24 04:13:17 +0000[diff] [blame]51 <td><a href="#Load-VN">Load-VN</a></td>
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]52 </tr>
Gordon Henriksen326e24f2007-09-27 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 Spencerd3f876c2004-11-01 08:19:36 +0000[diff] [blame]57 <tr><th colspan="8"><b>- <a href="#P">P</a> -</b></th></tr>
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]58 <tr>
59 <td><a href="#PRE">PRE</a></td>
Chris Lattnerdbb85852005-05-13 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 Henriksen326e24f2007-09-27 19:31:36 +0000[diff] [blame]64 <td><a href="#Root">Root</a></td>
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]65 </tr>
Reid Spencerd3f876c2004-11-01 08:19:36 +0000[diff] [blame]66 <tr><th colspan="8"><b>- <a href="#S">S</a> -</b></th></tr>
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]67 <tr>
Gordon Henriksen326e24f2007-09-27 19:31:36 +0000[diff] [blame]68 <td><a href="#Safe_Point">Safe Point</a></td>
Chris Lattner59f7f212005-11-29 01:34:50 +0000[diff] [blame]69 <td><a href="#SCC">SCC</a></td>
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]70 <td><a href="#SCCP">SCCP</a></td>
Gordon Henriksen326e24f2007-09-27 19:31:36 +0000[diff] [blame]71 <td><a href="#SDISel">SDISel</a></td>
Chris Lattnered51a0f2006-02-08 16:59:49 +0000[diff] [blame]72 <td><a href="#SRoA">SRoA</a></td>
Gordon Henriksen326e24f2007-09-27 19:31:36 +0000[diff] [blame]73 <td><a href="#Stack_Map">Stack Map</a></td>
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]74 </tr>
Reid Spencer85baf762004-08-17 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 Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]85 <dt><a name="ADCE"><b>ADCE</b></a></dt>
86 <dd>Aggressive Dead Code Elimination</dd>
Reid Spencer85baf762004-08-17 09:38:50 +0000[diff] [blame]87 </dl>
88</div>
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]89<!-- _______________________________________________________________________ -->
Reid Spencerce6be332004-08-24 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>
Bill Wendling7c6d4102008-07-22 06:46:17 +0000[diff] [blame^]94 <dd>Bottom Up Rewriting System&mdash;A method of instruction selection for
Chris Lattnerc4985ba2004-08-24 18:53:39 +0000[diff] [blame]95 code generation. An example is the <a
96href="http://www.program-transformation.org/Transform/BURG">BURG</a> tool.</dd>
Reid Spencerce6be332004-08-24 18:34:10 +0000[diff] [blame]97 </dl>
98</div>
99<!-- _______________________________________________________________________ -->
Reid Spencera07e0b52004-10-30 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 Henriksen326e24f2007-09-27 19:31:36 +0000[diff] [blame]108 it's compulationally correct/safe).
Reid Spencera07e0b52004-10-30 21:40:28 +0000[diff] [blame]109 </dl>
110</div>
111<!-- _______________________________________________________________________ -->
Misha Brukmanec8fe3c2004-08-24 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 Henriksen326e24f2007-09-27 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 Brukman9a4c9042004-09-05 03:00:20 +0000[diff] [blame]125 <dt><a name="DSA"><b>DSA</b></a></dt>
Misha Brukman100bd712004-09-05 03:57:23 +0000[diff] [blame]126 <dd>Data Structure Analysis</dd>
Misha Brukmanec8fe3c2004-08-24 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 Henriksen326e24f2007-09-27 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 Spencera07e0b52004-10-30 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 Henriksen326e24f2007-09-27 19:31:36 +0000[diff] [blame]160 <dt><a name="IPO"><b>ISel</b></a></dt>
161 <dd>Instruction Selection.</dd>
Reid Spencera07e0b52004-10-30 21:40:28 +0000[diff] [blame]162 </dl>
163</div>
164<!-- _______________________________________________________________________ -->
Misha Brukmanec8fe3c2004-08-24 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 Andersona6fc5012006-10-18 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 Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]170 <dt><a name="LICM"><b>LICM</b></a></dt>
171 <dd>Loop Invariant Code Motion</dd>
Misha Brukman183cfc22004-08-24 04:13:17 +0000[diff] [blame]172 <dt><a name="Load-VN"><b>Load-VN</b></a></dt>
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]173 <dd>Load Value Numbering</dd>
174 </dl>
175</div>
Chris Lattnerdbb85852005-05-13 20:18:49 +0000[diff] [blame]176
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]177<!-- _______________________________________________________________________ -->
Gordon Henriksen326e24f2007-09-27 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 Brukmanec8fe3c2004-08-24 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 Lattnerdbb85852005-05-13 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 Henriksen326e24f2007-09-27 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 Lattnerdbb85852005-05-13 20:18:49 +0000[diff] [blame]210 </dl>
211</div>
212
Misha Brukmanec8fe3c2004-08-24 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 Henriksen326e24f2007-09-27 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 Lattner59f7f212005-11-29 01:34:50 +0000[diff] [blame]227 <dt><a name="SCC"><b>SCC</b></a></dt>
228 <dd>Strongly Connected Component</dd>
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]229 <dt><a name="SCCP"><b>SCCP</b></a></dt>
Chris Lattner59f7f212005-11-29 01:34:50 +0000[diff] [blame]230 <dd>Sparse Conditional Constant Propagation</dd>
Chris Lattnered51a0f2006-02-08 16:59:49 +0000[diff] [blame]231 <dt><a name="SRoA"><b>SRoA</b></a></dt>
232 <dd>Scalar Replacement of Aggregates</dd>
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]233 <dt><a name="SSA"><b>SSA</b></a></dt>
234 <dd>Static Single Assignment</dd>
Gordon Henriksen326e24f2007-09-27 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 Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]239 </dl>
240</div>
Reid Spencer85baf762004-08-17 09:38:50 +0000[diff] [blame]241<!-- *********************************************************************** -->
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