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9 content="A glossary of terms used with the LLVM project.">
12 <h1>The LLVM Lexicon</h1>
13 <p class="doc_warning">NOTE: This document is a work in progress!</p>
14 <!-- *********************************************************************** -->
15 <h2>Table Of Contents</h2>
16 <!-- *********************************************************************** -->
19 <tr><th colspan="8"><b>- <a href="#A">A</a> -</b></th></tr>
21 <td><a href="#ADCE">ADCE</a></td>
23 <tr><th colspan="8"><b>- <a href="#B">B</a> -</b></th></tr>
25 <td><a href="#BURS">BURS</a></td>
27 <tr><th colspan="8"><b>- <a href="#C">C</a> -</b></th></tr>
29 <td><a href="#CSE">CSE</a></td>
31 <tr><th colspan="8"><b>- <a href="#D">D</a> -</b></th></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>
38 <tr><th colspan="8"><b>- <a href="#F">F</a> -</b></th></tr>
40 <td><a href="#FCA">FCA</a></td>
42 <tr><th colspan="8"><b>- <a href="#G">G</a> -</b></th></tr>
44 <td><a href="#GC">GC</a></td>
46 <tr><th colspan="8"><b>- <a href="#I">I</a> -</b></th></tr>
48 <td><a href="#IPA">IPA</a></td>
49 <td><a href="#IPO">IPO</a></td>
50 <td><a href="#ISel">ISel</a></td>
52 <tr><th colspan="8"><b>- <a href="#L">L</a> -</b></th></tr>
54 <td><a href="#LCSSA">LCSSA</a></td>
55 <td><a href="#LICM">LICM</a></td>
56 <td><a href="#Load-VN">Load-VN</a></td>
57 <td><a href="#LTO">LTO</a></td>
59 <tr><th colspan="8"><b>- <a href="#M">M</a> -</b></th></tr>
61 <td><a href="#MC">MC</a></td>
63 <tr><th colspan="8"><b>- <a href="#O">O</a> -</b></th></tr>
65 <td><a href="#Object_Pointer">Object Pointer</a></td>
67 <tr><th colspan="8"><b>- <a href="#P">P</a> -</b></th></tr>
69 <td><a href="#PRE">PRE</a></td>
71 <tr><th colspan="8"><b>- <a href="#R">R</a> -</b></th></tr>
73 <td><a href="#RAUW">RAUW</a></td>
74 <td><a href="#Reassociation">Reassociation</a></td>
75 <td><a href="#Root">Root</a></td>
76 <td><a href="#RPO">RPO</a></td>
78 <tr><th colspan="8"><b>- <a href="#S">S</a> -</b></th></tr>
80 <td><a href="#Safe_Point">Safe Point</a></td>
81 <td><a href="#SCC">SCC</a></td>
82 <td><a href="#SCCP">SCCP</a></td>
83 <td><a href="#SDISel">SDISel</a></td>
84 <td><a href="#SRoA">SRoA</a></td>
85 <td><a href="#Stack_Map">Stack Map</a></td>
90 <!-- *********************************************************************** -->
92 <!-- *********************************************************************** -->
94 <!-- _______________________________________________________________________ -->
95 <h3><a name="A">- A -</a></h3>
98 <dt><a name="ADCE"><b>ADCE</b></a></dt>
99 <dd>Aggressive Dead Code Elimination</dd>
102 <!-- _______________________________________________________________________ -->
103 <h3><a name="B">- B -</a></h3>
106 <dt><a name="BURS"><b>BURS</b></a></dt>
107 <dd>Bottom Up Rewriting System—A method of instruction selection for
108 code generation. An example is the <a
109 href="http://www.program-transformation.org/Transform/BURG">BURG</a> tool.</dd>
112 <!-- _______________________________________________________________________ -->
113 <h3><a name="C">- C -</a></h3>
116 <dt><a name="CSE"><b>CSE</b></a></dt>
117 <dd>Common Subexpression Elimination. An optimization that removes common
118 subexpression compuation. For example <tt>(a+b)*(a+b)</tt> has two
119 subexpressions that are the same: <tt>(a+b)</tt>. This optimization would
120 perform the addition only once and then perform the multiply (but only if
121 it's compulationally correct/safe).
124 <!-- _______________________________________________________________________ -->
125 <h3><a name="D">- D -</a></h3>
128 <dt><a name="DAG"><b>DAG</b></a></dt>
129 <dd>Directed Acyclic Graph</dd>
130 <dt><a name="Derived_Pointer"><b>Derived Pointer</b></a></dt>
131 <dd>A pointer to the interior of an object, such that a garbage collector
132 is unable to use the pointer for reachability analysis. While a derived
133 pointer is live, the corresponding object pointer must be kept in a root,
134 otherwise the collector might free the referenced object. With copying
135 collectors, derived pointers pose an additional hazard that they may be
136 invalidated at any <a href="Safe_Point">safe point</a>. This term is used in
137 opposition to <a href="#Object_Pointer">object pointer</a>.</dd>
138 <dt><a name="DSA"><b>DSA</b></a></dt>
139 <dd>Data Structure Analysis</dd>
140 <dt><a name="DSE"><b>DSE</b></a></dt>
141 <dd>Dead Store Elimination</dd>
144 <!-- _______________________________________________________________________ -->
145 <h3><a name="F">- F -</a></h3>
148 <dt><a name="FCA"><b>FCA</b></a></dt>
149 <dd>First Class Aggregate</dd>
152 <!-- _______________________________________________________________________ -->
153 <h3><a name="G">- G -</a></h3>
156 <dt><a name="GC"><b>GC</b></a></dt>
157 <dd>Garbage Collection. The practice of using reachability analysis instead
158 of explicit memory management to reclaim unused memory.</dd>
161 <!-- _______________________________________________________________________ -->
162 <h3><a name="H">- H -</a></h3>
165 <dt><a name="Heap"><b>Heap</b></a></dt>
166 <dd>In garbage collection, the region of memory which is managed using
167 reachability analysis.</dd>
170 <!-- _______________________________________________________________________ -->
171 <h3><a name="I">- I -</a></h3>
174 <dt><a name="IPA"><b>IPA</b></a></dt>
175 <dd>Inter-Procedural Analysis. Refers to any variety of code analysis that
176 occurs between procedures, functions or compilation units (modules).</dd>
177 <dt><a name="IPO"><b>IPO</b></a></dt>
178 <dd>Inter-Procedural Optimization. Refers to any variety of code
179 optimization that occurs between procedures, functions or compilation units
181 <dt><a name="ISel"><b>ISel</b></a></dt>
182 <dd>Instruction Selection.</dd>
185 <!-- _______________________________________________________________________ -->
186 <h3><a name="L">- L -</a></h3>
189 <dt><a name="LCSSA"><b>LCSSA</b></a></dt>
190 <dd>Loop-Closed Static Single Assignment Form</dd>
191 <dt><a name="LICM"><b>LICM</b></a></dt>
192 <dd>Loop Invariant Code Motion</dd>
193 <dt><a name="Load-VN"><b>Load-VN</b></a></dt>
194 <dd>Load Value Numbering</dd>
195 <dt><a name="LTO"><b>LTO</b></a></dt>
196 <dd>Link-Time Optimization</dd>
199 <!-- _______________________________________________________________________ -->
200 <h3><a name="M">- M -</a></h3>
203 <dt><a name="MC"><b>MC</b></a></dt>
204 <dd>Machine Code</dd>
207 <!-- _______________________________________________________________________ -->
208 <h3><a name="O">- O -</a></h3>
211 <dt><a name="Object_Pointer"><b>Object Pointer</b></a></dt>
212 <dd>A pointer to an object such that the garbage collector is able to trace
213 references contained within the object. This term is used in opposition to
214 <a href="#Derived_Pointer">derived pointer</a>.</dd>
218 <!-- _______________________________________________________________________ -->
219 <h3><a name="P">- P -</a></h3>
222 <dt><a name="PRE"><b>PRE</b></a></dt>
223 <dd>Partial Redundancy Elimination</dd>
227 <!-- _______________________________________________________________________ -->
228 <h3><a name="R">- R -</a></h3>
231 <dt><a name="RAUW"><b>RAUW</b></a></dt> <dd>An abbreviation for Replace
232 All Uses With. The functions User::replaceUsesOfWith(),
233 Value::replaceAllUsesWith(), and Constant::replaceUsesOfWithOnConstant()
234 implement the replacement of one Value with another by iterating over its
235 def/use chain and fixing up all of the pointers to point to the new value.
236 See also <a href="ProgrammersManual.html#iterate_chains">def/use chains</a>.
238 <dt><a name="Reassociation"><b>Reassociation</b></a></dt> <dd>Rearranging
239 associative expressions to promote better redundancy elimination and other
240 optimization. For example, changing (A+B-A) into (B+A-A), permitting it to
241 be optimized into (B+0) then (B).</dd>
242 <dt><a name="Root"><b>Root</b></a></dt> <dd>In garbage collection, a
243 pointer variable lying outside of the <a href="#Heap">heap</a> from which
244 the collector begins its reachability analysis. In the context of code
245 generation, "root" almost always refers to a "stack root" -- a local or
246 temporary variable within an executing function.</dd>
247 <dt><a name="RPO"><b>RPO</b></a></dt> <dd>Reverse postorder</dd>
251 <!-- _______________________________________________________________________ -->
252 <h3><a name="S">- S -</a></h3>
255 <dt><a name="Safe_Point"><b>Safe Point</b></a></dt>
256 <dd>In garbage collection, it is necessary to identify <a href="#Root">stack
257 roots</a> so that reachability analysis may proceed. It may be infeasible to
258 provide this information for every instruction, so instead the information
259 may is calculated only at designated safe points. With a copying collector,
260 <a href="#Derived_Pointers">derived pointers</a> must not be retained across
261 safe points and <a href="#Object_Pointers">object pointers</a> must be
262 reloaded from stack roots.</dd>
263 <dt><a name="SDISel"><b>SDISel</b></a></dt>
264 <dd>Selection DAG Instruction Selection.</dd>
265 <dt><a name="SCC"><b>SCC</b></a></dt>
266 <dd>Strongly Connected Component</dd>
267 <dt><a name="SCCP"><b>SCCP</b></a></dt>
268 <dd>Sparse Conditional Constant Propagation</dd>
269 <dt><a name="SRoA"><b>SRoA</b></a></dt>
270 <dd>Scalar Replacement of Aggregates</dd>
271 <dt><a name="SSA"><b>SSA</b></a></dt>
272 <dd>Static Single Assignment</dd>
273 <dt><a name="Stack_Map"><b>Stack Map</b></a></dt>
274 <dd>In garbage collection, metadata emitted by the code generator which
275 identifies <a href="#Root">roots</a> within the stack frame of an executing
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