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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>
Dan Gohmanc4479a72008-11-07 20:29:17 +0000[diff] [blame^]63 <td><a href="#RAUW">RAUW</a></td>
Chris Lattnerdbb85852005-05-13 20:18:49 +0000[diff] [blame]64 <td><a href="#Reassociation">Reassociation</a></td>
Gordon Henriksen326e24f2007-09-27 19:31:36 +0000[diff] [blame]65 <td><a href="#Root">Root</a></td>
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]66 </tr>
Reid Spencerd3f876c2004-11-01 08:19:36 +0000[diff] [blame]67 <tr><th colspan="8"><b>- <a href="#S">S</a> -</b></th></tr>
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]68 <tr>
Gordon Henriksen326e24f2007-09-27 19:31:36 +0000[diff] [blame]69 <td><a href="#Safe_Point">Safe Point</a></td>
Chris Lattner59f7f212005-11-29 01:34:50 +0000[diff] [blame]70 <td><a href="#SCC">SCC</a></td>
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]71 <td><a href="#SCCP">SCCP</a></td>
Gordon Henriksen326e24f2007-09-27 19:31:36 +0000[diff] [blame]72 <td><a href="#SDISel">SDISel</a></td>
Chris Lattnered51a0f2006-02-08 16:59:49 +0000[diff] [blame]73 <td><a href="#SRoA">SRoA</a></td>
Gordon Henriksen326e24f2007-09-27 19:31:36 +0000[diff] [blame]74 <td><a href="#Stack_Map">Stack Map</a></td>
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]75 </tr>
Reid Spencer85baf762004-08-17 09:38:50 +0000[diff] [blame]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>
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]86 <dt><a name="ADCE"><b>ADCE</b></a></dt>
87 <dd>Aggressive Dead Code Elimination</dd>
Reid Spencer85baf762004-08-17 09:38:50 +0000[diff] [blame]88 </dl>
89</div>
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]90<!-- _______________________________________________________________________ -->
Reid Spencerce6be332004-08-24 18:34:10 +0000[diff] [blame]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 Wendling7c6d4102008-07-22 06:46:17 +0000[diff] [blame]95 <dd>Bottom Up Rewriting System&mdash;A method of instruction selection for
Chris Lattnerc4985ba2004-08-24 18:53:39 +0000[diff] [blame]96 code generation. An example is the <a
97href="http://www.program-transformation.org/Transform/BURG">BURG</a> tool.</dd>
Reid Spencerce6be332004-08-24 18:34:10 +0000[diff] [blame]98 </dl>
99</div>
100<!-- _______________________________________________________________________ -->
Reid Spencera07e0b52004-10-30 21:40:28 +0000[diff] [blame]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 Henriksen326e24f2007-09-27 19:31:36 +0000[diff] [blame]109 it's compulationally correct/safe).
Reid Spencera07e0b52004-10-30 21:40:28 +0000[diff] [blame]110 </dl>
111</div>
112<!-- _______________________________________________________________________ -->
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]113<div class="doc_subsection"><a name="D">- D -</a></div>
114<div class="doc_text">
115 <dl>
Gordon Henriksen326e24f2007-09-27 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>
Misha Brukman9a4c9042004-09-05 03:00:20 +0000[diff] [blame]126 <dt><a name="DSA"><b>DSA</b></a></dt>
Misha Brukman100bd712004-09-05 03:57:23 +0000[diff] [blame]127 <dd>Data Structure Analysis</dd>
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]128 <dt><a name="DSE"><b>DSE</b></a></dt>
129 <dd>Dead Store Elimination</dd>
130 </dl>
131</div>
132<!-- _______________________________________________________________________ -->
Gordon Henriksen326e24f2007-09-27 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<!-- _______________________________________________________________________ -->
Reid Spencera07e0b52004-10-30 21:40:28 +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>
Torok Edwin2b9cbf12008-10-28 16:54:34 +0000[diff] [blame]161 <dt><a name="ISel"><b>ISel</b></a></dt>
Gordon Henriksen326e24f2007-09-27 19:31:36 +0000[diff] [blame]162 <dd>Instruction Selection.</dd>
Reid Spencera07e0b52004-10-30 21:40:28 +0000[diff] [blame]163 </dl>
164</div>
165<!-- _______________________________________________________________________ -->
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]166<div class="doc_subsection"><a name="L">- L -</a></div>
167<div class="doc_text">
168 <dl>
Owen Andersona6fc5012006-10-18 05:50:12 +0000[diff] [blame]169 <dt><a name="LCSSA"><b>LCSSA</b></a></dt>
170 <dd>Loop-Closed Static Single Assignment Form</dd>
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]171 <dt><a name="LICM"><b>LICM</b></a></dt>
172 <dd>Loop Invariant Code Motion</dd>
Misha Brukman183cfc22004-08-24 04:13:17 +0000[diff] [blame]173 <dt><a name="Load-VN"><b>Load-VN</b></a></dt>
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]174 <dd>Load Value Numbering</dd>
175 </dl>
176</div>
Chris Lattnerdbb85852005-05-13 20:18:49 +0000[diff] [blame]177
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]178<!-- _______________________________________________________________________ -->
Torok Edwin2b9cbf12008-10-28 16:54:34 +0000[diff] [blame]179<div class="doc_subsection"><a name="O">- O -</a></div>
Gordon Henriksen326e24f2007-09-27 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<!-- _______________________________________________________________________ -->
Misha Brukmanec8fe3c2004-08-24 01:57:02 +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>
Chris Lattnerdbb85852005-05-13 20:18:49 +0000[diff] [blame]197
198<!-- _______________________________________________________________________ -->
199<div class="doc_subsection"><a name="R">- R -</a></div>
200<div class="doc_text">
201 <dl>
Dan Gohmanc4479a72008-11-07 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>
Chris Lattnerdbb85852005-05-13 20:18:49 +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 Henriksen326e24f2007-09-27 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>
Chris Lattnerdbb85852005-05-13 20:18:49 +0000[diff] [blame]218 </dl>
219</div>
220
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]221<!-- _______________________________________________________________________ -->
222<div class="doc_subsection"><a name="S">- S -</a></div>
223<div class="doc_text">
224 <dl>
Torok Edwin2b9cbf12008-10-28 16:54:34 +0000[diff] [blame]225 <dt><a name="Safe_Point"><b>Safe Point</b></a></dt>
Gordon Henriksen326e24f2007-09-27 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>
Chris Lattner59f7f212005-11-29 01:34:50 +0000[diff] [blame]235 <dt><a name="SCC"><b>SCC</b></a></dt>
236 <dd>Strongly Connected Component</dd>
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]237 <dt><a name="SCCP"><b>SCCP</b></a></dt>
Chris Lattner59f7f212005-11-29 01:34:50 +0000[diff] [blame]238 <dd>Sparse Conditional Constant Propagation</dd>
Chris Lattnered51a0f2006-02-08 16:59:49 +0000[diff] [blame]239 <dt><a name="SRoA"><b>SRoA</b></a></dt>
240 <dd>Scalar Replacement of Aggregates</dd>
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]241 <dt><a name="SSA"><b>SSA</b></a></dt>
242 <dd>Static Single Assignment</dd>
Gordon Henriksen326e24f2007-09-27 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>
Misha Brukmanec8fe3c2004-08-24 01:57:02 +0000[diff] [blame]247 </dl>
248</div>
Reid Spencer85baf762004-08-17 09:38:50 +0000[diff] [blame]249<!-- *********************************************************************** -->
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