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4 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
5 <title>The LLVM Lexicon</title>
6 <link rel="stylesheet" href="llvm.css" type="text/css">
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>
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>
Gordon Henriksenfba997d2007-09-27 19:31:36 +0000[diff] [blame]33 <td><a href="#DAG">DAG</a></td>
34 <td><a href="#Derived_Pointer">Derived Pointer</a></td>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]35 <td><a href="#DSA">DSA</a></td>
36 <td><a href="#DSE">DSE</a></td>
37 </tr>
Gordon Henriksenfba997d2007-09-27 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>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]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>
Gordon Henriksenfba997d2007-09-27 19:31:36 +0000[diff] [blame]45 <td><a href="#ISel">ISel</a></td>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]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>
Gordon Henriksenfba997d2007-09-27 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>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]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>
Gordon Henriksenfba997d2007-09-27 19:31:36 +0000[diff] [blame]64 <td><a href="#Root">Root</a></td>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]65 </tr>
66 <tr><th colspan="8"><b>- <a href="#S">S</a> -</b></th></tr>
67 <tr>
Gordon Henriksenfba997d2007-09-27 19:31:36 +0000[diff] [blame]68 <td><a href="#Safe_Point">Safe Point</a></td>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]69 <td><a href="#SCC">SCC</a></td>
70 <td><a href="#SCCP">SCCP</a></td>
Gordon Henriksenfba997d2007-09-27 19:31:36 +0000[diff] [blame]71 <td><a href="#SDISel">SDISel</a></td>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]72 <td><a href="#SRoA">SRoA</a></td>
Gordon Henriksenfba997d2007-09-27 19:31:36 +0000[diff] [blame]73 <td><a href="#Stack_Map">Stack Map</a></td>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]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>
Bill Wendling0a70c0b2008-07-22 06:46:17 +0000[diff] [blame^]94 <dd>Bottom Up Rewriting System&mdash;A method of instruction selection for
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]95 code generation. An example is the <a
96href="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
Gordon Henriksenfba997d2007-09-27 19:31:36 +0000[diff] [blame]108 it's compulationally correct/safe).
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]109 </dl>
110</div>
111<!-- _______________________________________________________________________ -->
112<div class="doc_subsection"><a name="D">- D -</a></div>
113<div class="doc_text">
114 <dl>
Gordon Henriksenfba997d2007-09-27 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>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]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<!-- _______________________________________________________________________ -->
Gordon Henriksenfba997d2007-09-27 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<!-- _______________________________________________________________________ -->
Dan Gohmanf17a25c2007-07-18 16:29:46 +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 Henriksenfba997d2007-09-27 19:31:36 +0000[diff] [blame]160 <dt><a name="IPO"><b>ISel</b></a></dt>
161 <dd>Instruction Selection.</dd>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]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<!-- _______________________________________________________________________ -->
Gordon Henriksenfba997d2007-09-27 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<!-- _______________________________________________________________________ -->
Dan Gohmanf17a25c2007-07-18 16:29:46 +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>
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 Henriksenfba997d2007-09-27 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>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]210 </dl>
211</div>
212
213<!-- _______________________________________________________________________ -->
214<div class="doc_subsection"><a name="S">- S -</a></div>
215<div class="doc_text">
216 <dl>
Gordon Henriksenfba997d2007-09-27 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>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]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>
Gordon Henriksenfba997d2007-09-27 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>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]239 </dl>
240</div>
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