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2<html>
3<head>
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>
33 <td><a href="#DAG">DAG</a></td>
34 <td><a href="#Derived_Pointer">Derived Pointer</a></td>
35 <td><a href="#DSA">DSA</a></td>
36 <td><a href="#DSE">DSE</a></td>
37 </tr>
38 <tr><th colspan="8"><b>- <a href="#G">G</a> -</b></th></tr>
39 <tr>
40 <td><a href="#GC">GC</a></td>
41 </tr>
42 <tr><th colspan="8"><b>- <a href="#I">I</a> -</b></th></tr>
43 <tr>
44 <td><a href="#IPA">IPA</a></td>
45 <td><a href="#IPO">IPO</a></td>
46 <td><a href="#ISel">ISel</a></td>
47 </tr>
48 <tr><th colspan="8"><b>- <a href="#L">L</a> -</b></th></tr>
49 <tr>
50 <td><a href="#LCSSA">LCSSA</a></td>
51 <td><a href="#LICM">LICM</a></td>
52 <td><a href="#Load-VN">Load-VN</a></td>
53 </tr>
54 <tr><th colspan="8"><b>- <a href="#O">O</a> -</b></th></tr>
55 <tr>
56 <td><a href="#Object_Pointer">Object Pointer</a></td>
57 </tr>
58 <tr><th colspan="8"><b>- <a href="#P">P</a> -</b></th></tr>
59 <tr>
60 <td><a href="#PRE">PRE</a></td>
61 </tr>
62 <tr><th colspan="8"><b>- <a href="#R">R</a> -</b></th></tr>
63 <tr>
64 <td><a href="#RAUW">RAUW</a></td>
65 <td><a href="#Reassociation">Reassociation</a></td>
66 <td><a href="#Root">Root</a></td>
67 </tr>
68 <tr><th colspan="8"><b>- <a href="#S">S</a> -</b></th></tr>
69 <tr>
70 <td><a href="#Safe_Point">Safe Point</a></td>
71 <td><a href="#SCC">SCC</a></td>
72 <td><a href="#SCCP">SCCP</a></td>
73 <td><a href="#SDISel">SDISel</a></td>
74 <td><a href="#SRoA">SRoA</a></td>
75 <td><a href="#Stack_Map">Stack Map</a></td>
76 </tr>
77 </table>
78</div>
79
80<!-- *********************************************************************** -->
81<div class="doc_section">Definitions</div>
82<!-- *********************************************************************** -->
83<!-- _______________________________________________________________________ -->
84<div class="doc_subsection"><a name="A">- A -</a></div>
85<div class="doc_text">
86 <dl>
87 <dt><a name="ADCE"><b>ADCE</b></a></dt>
88 <dd>Aggressive Dead Code Elimination</dd>
89 </dl>
90</div>
91<!-- _______________________________________________________________________ -->
92<div class="doc_subsection"><a name="B">- B -</a></div>
93<div class="doc_text">
94 <dl>
95 <dt><a name="BURS"><b>BURS</b></a></dt>
96 <dd>Bottom Up Rewriting System&mdash;A method of instruction selection for
97 code generation. An example is the <a
98href="http://www.program-transformation.org/Transform/BURG">BURG</a> tool.</dd>
99 </dl>
100</div>
101<!-- _______________________________________________________________________ -->
102<div class="doc_subsection"><a name="C">- C -</a></div>
103<div class="doc_text">
104 <dl>
105 <dt><a name="CSE"><b>CSE</b></a></dt>
106 <dd>Common Subexpression Elimination. An optimization that removes common
107 subexpression compuation. For example <tt>(a+b)*(a+b)</tt> has two
108 subexpressions that are the same: <tt>(a+b)</tt>. This optimization would
109 perform the addition only once and then perform the multiply (but only if
110 it's compulationally correct/safe).
111 </dl>
112</div>
113<!-- _______________________________________________________________________ -->
114<div class="doc_subsection"><a name="D">- D -</a></div>
115<div class="doc_text">
116 <dl>
117 <dt><a name="DAG"><b>DAG</b></a></dt>
118 <dd>Directed Acyclic Graph</dd>
119 <dt><a name="Derived_Pointer"><b>Derived Pointer</b></a></dt>
120 <dd>A pointer to the interior of an object, such that a garbage collector
121 is unable to use the pointer for reachability analysis. While a derived
122 pointer is live, the corresponding object pointer must be kept in a root,
123 otherwise the collector might free the referenced object. With copying
124 collectors, derived pointers pose an additional hazard that they may be
125 invalidated at any <a href="Safe_Point">safe point</a>. This term is used in
126 opposition to <a href="#Object_Pointer">object pointer</a>.</dd>
127 <dt><a name="DSA"><b>DSA</b></a></dt>
128 <dd>Data Structure Analysis</dd>
129 <dt><a name="DSE"><b>DSE</b></a></dt>
130 <dd>Dead Store Elimination</dd>
131 </dl>
132</div>
133<!-- _______________________________________________________________________ -->
134<div class="doc_subsection"><a name="G">- G -</a></div>
135<div class="doc_text">
136 <dl>
137 <dt><a name="GC"><b>GC</b></a></dt>
138 <dd>Garbage Collection. The practice of using reachability analysis instead
139 of explicit memory management to reclaim unused memory.</dd>
140 </dl>
141</div>
142<!-- _______________________________________________________________________ -->
143<div class="doc_subsection"><a name="H">- H -</a></div>
144<div class="doc_text">
145 <dl>
146 <dt><a name="Heap"><b>Heap</b></a></dt>
147 <dd>In garbage collection, the region of memory which is managed using
148 reachability analysis.</dd>
149 </dl>
150</div>
151<!-- _______________________________________________________________________ -->
152<div class="doc_subsection"><a name="I">- I -</a></div>
153<div class="doc_text">
154 <dl>
155 <dt><a name="IPA"><b>IPA</b></a></dt>
156 <dd>Inter-Procedural Analysis. Refers to any variety of code analysis that
157 occurs between procedures, functions or compilation units (modules).</dd>
158 <dt><a name="IPO"><b>IPO</b></a></dt>
159 <dd>Inter-Procedural Optimization. Refers to any variety of code
160 optimization that occurs between procedures, functions or compilation units
161 (modules).</dd>
162 <dt><a name="ISel"><b>ISel</b></a></dt>
163 <dd>Instruction Selection.</dd>
164 </dl>
165</div>
166<!-- _______________________________________________________________________ -->
167<div class="doc_subsection"><a name="L">- L -</a></div>
168<div class="doc_text">
169 <dl>
170 <dt><a name="LCSSA"><b>LCSSA</b></a></dt>
171 <dd>Loop-Closed Static Single Assignment Form</dd>
172 <dt><a name="LICM"><b>LICM</b></a></dt>
173 <dd>Loop Invariant Code Motion</dd>
174 <dt><a name="Load-VN"><b>Load-VN</b></a></dt>
175 <dd>Load Value Numbering</dd>
176 </dl>
177</div>
178
179<!-- _______________________________________________________________________ -->
180<div class="doc_subsection"><a name="O">- O -</a></div>
181<div class="doc_text">
182 <dl>
183 <dt><a name="Object_Pointer"><b>Object Pointer</b></a></dt>
184 <dd>A pointer to an object such that the garbage collector is able to trace
185 references contained within the object. This term is used in opposition to
186 <a href="#Derived_Pointer">derived pointer</a>.</dd>
187 </dl>
188</div>
189
190<!-- _______________________________________________________________________ -->
191<div class="doc_subsection"><a name="P">- P -</a></div>
192<div class="doc_text">
193 <dl>
194 <dt><a name="PRE"><b>PRE</b></a></dt>
195 <dd>Partial Redundancy Elimination</dd>
196 </dl>
197</div>
198
199<!-- _______________________________________________________________________ -->
200<div class="doc_subsection"><a name="R">- R -</a></div>
201<div class="doc_text">
202 <dl>
203 <dt><a name="RAUW"><b>RAUW</b></a></dt> <dd>An abbreviation for Replace
204 All Uses With. The functions User::replaceUsesOfWith(),
205 Value::replaceAllUsesWith(), and Constant::replaceUsesOfWithOnConstant()
206 implement the replacement of one Value with another by iterating over its
207 def/use chain and fixing up all of the pointers to point to the new value.
208 See also <a href="ProgrammersManual.html#iterate_chains">def/use chains</a>.
209 </dd>
210 <dt><a name="Reassociation"><b>Reassociation</b></a></dt> <dd>Rearranging
211 associative expressions to promote better redundancy elimination and other
212 optimization. For example, changing (A+B-A) into (B+A-A), permitting it to
213 be optimized into (B+0) then (B).</dd>
214 <dt><a name="Root"><b>Root</b></a></dt> <dd>In garbage collection, a
215 pointer variable lying outside of the <a href="#Heap">heap</a> from which
216 the collector begins its reachability analysis. In the context of code
217 generation, "root" almost always refers to a "stack root" -- a local or
218 temporary variable within an executing function.</dd>
219 </dl>
220</div>
221
222<!-- _______________________________________________________________________ -->
223<div class="doc_subsection"><a name="S">- S -</a></div>
224<div class="doc_text">
225 <dl>
226 <dt><a name="Safe_Point"><b>Safe Point</b></a></dt>
227 <dd>In garbage collection, it is necessary to identify <a href="#Root">stack
228 roots</a> so that reachability analysis may proceed. It may be infeasible to
229 provide this information for every instruction, so instead the information
230 may is calculated only at designated safe points. With a copying collector,
231 <a href="#Derived_Pointers">derived pointers</a> must not be retained across
232 safe points and <a href="#Object_Pointers">object pointers</a> must be
233 reloaded from stack roots.</dd>
234 <dt><a name="SDISel"><b>SDISel</b></a></dt>
235 <dd>Selection DAG Instruction Selection.</dd>
236 <dt><a name="SCC"><b>SCC</b></a></dt>
237 <dd>Strongly Connected Component</dd>
238 <dt><a name="SCCP"><b>SCCP</b></a></dt>
239 <dd>Sparse Conditional Constant Propagation</dd>
240 <dt><a name="SRoA"><b>SRoA</b></a></dt>
241 <dd>Scalar Replacement of Aggregates</dd>
242 <dt><a name="SSA"><b>SSA</b></a></dt>
243 <dd>Static Single Assignment</dd>
244 <dt><a name="Stack_Map"><b>Stack Map</b></a></dt>
245 <dd>In garbage collection, metadata emitted by the code generator which
246 identifies <a href="#Root">roots</a> within the stack frame of an executing
247 function.</dd>
248 </dl>
249</div>
250<!-- *********************************************************************** -->
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