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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>
Dan Gohman7bb6b402008-11-07 20:29:17 +0000[diff] [blame]63 <td><a href="#RAUW">RAUW</a></td>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]64 <td><a href="#Reassociation">Reassociation</a></td>
Gordon Henriksenfba997d2007-09-27 19:31:36 +0000[diff] [blame]65 <td><a href="#Root">Root</a></td>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]66 </tr>
67 <tr><th colspan="8"><b>- <a href="#S">S</a> -</b></th></tr>
68 <tr>
Gordon Henriksenfba997d2007-09-27 19:31:36 +0000[diff] [blame]69 <td><a href="#Safe_Point">Safe Point</a></td>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]70 <td><a href="#SCC">SCC</a></td>
71 <td><a href="#SCCP">SCCP</a></td>
Gordon Henriksenfba997d2007-09-27 19:31:36 +0000[diff] [blame]72 <td><a href="#SDISel">SDISel</a></td>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]73 <td><a href="#SRoA">SRoA</a></td>
Gordon Henriksenfba997d2007-09-27 19:31:36 +0000[diff] [blame]74 <td><a href="#Stack_Map">Stack Map</a></td>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]75 </tr>
76 </table>
77</div>
78
79<!-- *********************************************************************** -->
80<div class="doc_section">Definitions</div>
81<!-- *********************************************************************** -->
82<!-- _______________________________________________________________________ -->
83<div class="doc_subsection"><a name="A">- A -</a></div>
84<div class="doc_text">
85 <dl>
86 <dt><a name="ADCE"><b>ADCE</b></a></dt>
87 <dd>Aggressive Dead Code Elimination</dd>
88 </dl>
89</div>
90<!-- _______________________________________________________________________ -->
91<div class="doc_subsection"><a name="B">- B -</a></div>
92<div class="doc_text">
93 <dl>
94 <dt><a name="BURS"><b>BURS</b></a></dt>
Bill Wendling0a70c0b2008-07-22 06:46:17 +0000[diff] [blame]95 <dd>Bottom Up Rewriting System&mdash;A method of instruction selection for
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]96 code generation. An example is the <a
97href="http://www.program-transformation.org/Transform/BURG">BURG</a> tool.</dd>
98 </dl>
99</div>
100<!-- _______________________________________________________________________ -->
101<div class="doc_subsection"><a name="C">- C -</a></div>
102<div class="doc_text">
103 <dl>
104 <dt><a name="CSE"><b>CSE</b></a></dt>
105 <dd>Common Subexpression Elimination. An optimization that removes common
106 subexpression compuation. For example <tt>(a+b)*(a+b)</tt> has two
107 subexpressions that are the same: <tt>(a+b)</tt>. This optimization would
108 perform the addition only once and then perform the multiply (but only if
Gordon Henriksenfba997d2007-09-27 19:31:36 +0000[diff] [blame]109 it's compulationally correct/safe).
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]110 </dl>
111</div>
112<!-- _______________________________________________________________________ -->
113<div class="doc_subsection"><a name="D">- D -</a></div>
114<div class="doc_text">
115 <dl>
Gordon Henriksenfba997d2007-09-27 19:31:36 +0000[diff] [blame]116 <dt><a name="DAG"><b>DAG</b></a></dt>
117 <dd>Directed Acyclic Graph</dd>
118 <dt><a name="Derived_Pointer"><b>Derived Pointer</b></a></dt>
119 <dd>A pointer to the interior of an object, such that a garbage collector
120 is unable to use the pointer for reachability analysis. While a derived
121 pointer is live, the corresponding object pointer must be kept in a root,
122 otherwise the collector might free the referenced object. With copying
123 collectors, derived pointers pose an additional hazard that they may be
124 invalidated at any <a href="Safe_Point">safe point</a>. This term is used in
125 opposition to <a href="#Object_Pointer">object pointer</a>.</dd>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]126 <dt><a name="DSA"><b>DSA</b></a></dt>
127 <dd>Data Structure Analysis</dd>
128 <dt><a name="DSE"><b>DSE</b></a></dt>
129 <dd>Dead Store Elimination</dd>
130 </dl>
131</div>
132<!-- _______________________________________________________________________ -->
Gordon Henriksenfba997d2007-09-27 19:31:36 +0000[diff] [blame]133<div class="doc_subsection"><a name="G">- G -</a></div>
134<div class="doc_text">
135 <dl>
136 <dt><a name="GC"><b>GC</b></a></dt>
137 <dd>Garbage Collection. The practice of using reachability analysis instead
138 of explicit memory management to reclaim unused memory.</dd>
139 </dl>
140</div>
141<!-- _______________________________________________________________________ -->
142<div class="doc_subsection"><a name="H">- H -</a></div>
143<div class="doc_text">
144 <dl>
145 <dt><a name="Heap"><b>Heap</b></a></dt>
146 <dd>In garbage collection, the region of memory which is managed using
147 reachability analysis.</dd>
148 </dl>
149</div>
150<!-- _______________________________________________________________________ -->
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]151<div class="doc_subsection"><a name="I">- I -</a></div>
152<div class="doc_text">
153 <dl>
154 <dt><a name="IPA"><b>IPA</b></a></dt>
155 <dd>Inter-Procedural Analysis. Refers to any variety of code analysis that
156 occurs between procedures, functions or compilation units (modules).</dd>
157 <dt><a name="IPO"><b>IPO</b></a></dt>
158 <dd>Inter-Procedural Optimization. Refers to any variety of code
159 optimization that occurs between procedures, functions or compilation units
160 (modules).</dd>
Edwin Törökff6c21f2008-10-28 16:54:34 +0000[diff] [blame]161 <dt><a name="ISel"><b>ISel</b></a></dt>
Gordon Henriksenfba997d2007-09-27 19:31:36 +0000[diff] [blame]162 <dd>Instruction Selection.</dd>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]163 </dl>
164</div>
165<!-- _______________________________________________________________________ -->
166<div class="doc_subsection"><a name="L">- L -</a></div>
167<div class="doc_text">
168 <dl>
169 <dt><a name="LCSSA"><b>LCSSA</b></a></dt>
170 <dd>Loop-Closed Static Single Assignment Form</dd>
171 <dt><a name="LICM"><b>LICM</b></a></dt>
172 <dd>Loop Invariant Code Motion</dd>
173 <dt><a name="Load-VN"><b>Load-VN</b></a></dt>
174 <dd>Load Value Numbering</dd>
175 </dl>
176</div>
177
178<!-- _______________________________________________________________________ -->
Edwin Törökff6c21f2008-10-28 16:54:34 +0000[diff] [blame]179<div class="doc_subsection"><a name="O">- O -</a></div>
Gordon Henriksenfba997d2007-09-27 19:31:36 +0000[diff] [blame]180<div class="doc_text">
181 <dl>
182 <dt><a name="Object_Pointer"><b>Object Pointer</b></a></dt>
183 <dd>A pointer to an object such that the garbage collector is able to trace
184 references contained within the object. This term is used in opposition to
185 <a href="#Derived_Pointer">derived pointer</a>.</dd>
186 </dl>
187</div>
188
189<!-- _______________________________________________________________________ -->
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]190<div class="doc_subsection"><a name="P">- P -</a></div>
191<div class="doc_text">
192 <dl>
193 <dt><a name="PRE"><b>PRE</b></a></dt>
194 <dd>Partial Redundancy Elimination</dd>
195 </dl>
196</div>
197
198<!-- _______________________________________________________________________ -->
199<div class="doc_subsection"><a name="R">- R -</a></div>
200<div class="doc_text">
201 <dl>
Dan Gohman7bb6b402008-11-07 20:29:17 +0000[diff] [blame]202 <dt><a name="RAUW"><b>RAUW</b></a></dt> <dd>An abbreviation for Replace
203 All Uses With. The functions User::replaceUsesOfWith(),
204 Value::replaceAllUsesWith(), and Constant::replaceUsesOfWithOnConstant()
205 implement the replacement of one Value with another by iterating over its
206 def/use chain and fixing up all of the pointers to point to the new value.
207 See also <a href="ProgrammersManual.html#iterate_chains">def/use chains</a>.
208 </dd>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]209 <dt><a name="Reassociation"><b>Reassociation</b></a></dt> <dd>Rearranging
210 associative expressions to promote better redundancy elimination and other
211 optimization. For example, changing (A+B-A) into (B+A-A), permitting it to
Gordon Henriksenfba997d2007-09-27 19:31:36 +0000[diff] [blame]212 be optimized into (B+0) then (B).</dd>
213 <dt><a name="Root"><b>Root</b></a></dt> <dd>In garbage collection, a
214 pointer variable lying outside of the <a href="#Heap">heap</a> from which
215 the collector begins its reachability analysis. In the context of code
216 generation, "root" almost always refers to a "stack root"&#151;a local or
217 temporary variable within an executing function.</dd>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]218 </dl>
219</div>
220
221<!-- _______________________________________________________________________ -->
222<div class="doc_subsection"><a name="S">- S -</a></div>
223<div class="doc_text">
224 <dl>
Edwin Törökff6c21f2008-10-28 16:54:34 +0000[diff] [blame]225 <dt><a name="Safe_Point"><b>Safe Point</b></a></dt>
Gordon Henriksenfba997d2007-09-27 19:31:36 +0000[diff] [blame]226 <dd>In garbage collection, it is necessary to identify <a href="#Root">stack
227 roots</a> so that reachability analysis may proceed. It may be infeasible to
228 provide this information for every instruction, so instead the information
229 may is calculated only at designated safe points. With a copying collector,
230 <a href="#Derived_Pointers">derived pointers</a> must not be retained across
231 safe points and <a href="#Object_Pointers">object pointers</a> must be
232 reloaded from stack roots.</dd>
233 <dt><a name="SDISel"><b>SDISel</b></a></dt>
234 <dd>Selection DAG Instruction Selection.</dd>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]235 <dt><a name="SCC"><b>SCC</b></a></dt>
236 <dd>Strongly Connected Component</dd>
237 <dt><a name="SCCP"><b>SCCP</b></a></dt>
238 <dd>Sparse Conditional Constant Propagation</dd>
239 <dt><a name="SRoA"><b>SRoA</b></a></dt>
240 <dd>Scalar Replacement of Aggregates</dd>
241 <dt><a name="SSA"><b>SSA</b></a></dt>
242 <dd>Static Single Assignment</dd>
Gordon Henriksenfba997d2007-09-27 19:31:36 +0000[diff] [blame]243 <dt><a name="Stack_Map"><b>Stack Map</b></a></dt>
244 <dd>In garbage collection, metadata emitted by the code generator which
245 identifies <a href="#Root">roots</a> within the stack frame of an executing
246 function.</dd>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]247 </dl>
248</div>
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