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4<head>
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Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]6 <title>LLVM Programmer's Manual</title>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]7 <link rel="stylesheet" href="llvm.css" type="text/css">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]8</head>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]9<body>
10
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]11<h1>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]12 LLVM Programmer's Manual
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]13</h1>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]14
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]15<ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]16 <li><a href="#introduction">Introduction</a></li>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]17 <li><a href="#general">General Information</a>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]18 <ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]19 <li><a href="#stl">The C++ Standard Template Library</a></li>
20<!--
21 <li>The <tt>-time-passes</tt> option</li>
22 <li>How to use the LLVM Makefile system</li>
23 <li>How to write a regression test</li>
Chris Lattner61db4652004-12-08 19:05:44 +0000[diff] [blame]24
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]25-->
Chris Lattner84b7f8d2003-08-01 22:20:59 +0000[diff] [blame]26 </ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]27 </li>
28 <li><a href="#apis">Important and useful LLVM APIs</a>
29 <ul>
30 <li><a href="#isa">The <tt>isa&lt;&gt;</tt>, <tt>cast&lt;&gt;</tt>
31and <tt>dyn_cast&lt;&gt;</tt> templates</a> </li>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]32 <li><a href="#string_apis">Passing strings (the <tt>StringRef</tt>
Benjamin Kramere15192b2009-08-05 15:42:44 +0000[diff] [blame]33and <tt>Twine</tt> classes)</a>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]34 <ul>
35 <li><a href="#StringRef">The <tt>StringRef</tt> class</a> </li>
36 <li><a href="#Twine">The <tt>Twine</tt> class</a> </li>
37 </ul>
Benjamin Kramere15192b2009-08-05 15:42:44 +0000[diff] [blame]38 </li>
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]39 <li><a href="#DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]40option</a>
41 <ul>
42 <li><a href="#DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt>
43and the <tt>-debug-only</tt> option</a> </li>
44 </ul>
45 </li>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]46 <li><a href="#Statistic">The <tt>Statistic</tt> class &amp; <tt>-stats</tt>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]47option</a></li>
48<!--
49 <li>The <tt>InstVisitor</tt> template
50 <li>The general graph API
51-->
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]52 <li><a href="#ViewGraph">Viewing graphs while debugging code</a></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]53 </ul>
54 </li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]55 <li><a href="#datastructure">Picking the Right Data Structure for a Task</a>
56 <ul>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]57 <li><a href="#ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
58 <ul>
Chris Lattner8ae42612011-04-05 23:18:20 +0000[diff] [blame]59 <li><a href="#dss_arrayref">llvm/ADT/ArrayRef.h</a></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]60 <li><a href="#dss_fixedarrays">Fixed Size Arrays</a></li>
61 <li><a href="#dss_heaparrays">Heap Allocated Arrays</a></li>
62 <li><a href="#dss_smallvector">"llvm/ADT/SmallVector.h"</a></li>
63 <li><a href="#dss_vector">&lt;vector&gt;</a></li>
64 <li><a href="#dss_deque">&lt;deque&gt;</a></li>
65 <li><a href="#dss_list">&lt;list&gt;</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]66 <li><a href="#dss_ilist">llvm/ADT/ilist.h</a></li>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]67 <li><a href="#dss_other">Other Sequential Container Options</a></li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]68 </ul></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]69 <li><a href="#ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
70 <ul>
71 <li><a href="#dss_sortedvectorset">A sorted 'vector'</a></li>
72 <li><a href="#dss_smallset">"llvm/ADT/SmallSet.h"</a></li>
73 <li><a href="#dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a></li>
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]74 <li><a href="#dss_denseset">"llvm/ADT/DenseSet.h"</a></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]75 <li><a href="#dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a></li>
76 <li><a href="#dss_set">&lt;set&gt;</a></li>
77 <li><a href="#dss_setvector">"llvm/ADT/SetVector.h"</a></li>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]78 <li><a href="#dss_uniquevector">"llvm/ADT/UniqueVector.h"</a></li>
79 <li><a href="#dss_otherset">Other Set-Like ContainerOptions</a></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]80 </ul></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]81 <li><a href="#ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
82 <ul>
83 <li><a href="#dss_sortedvectormap">A sorted 'vector'</a></li>
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]84 <li><a href="#dss_stringmap">"llvm/ADT/StringMap.h"</a></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]85 <li><a href="#dss_indexedmap">"llvm/ADT/IndexedMap.h"</a></li>
86 <li><a href="#dss_densemap">"llvm/ADT/DenseMap.h"</a></li>
Jeffrey Yasskin71a5c222009-10-22 22:11:22 +0000[diff] [blame]87 <li><a href="#dss_valuemap">"llvm/ADT/ValueMap.h"</a></li>
Jakob Stoklund Olesenaca0da62010-12-14 00:55:51 +0000[diff] [blame]88 <li><a href="#dss_intervalmap">"llvm/ADT/IntervalMap.h"</a></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]89 <li><a href="#dss_map">&lt;map&gt;</a></li>
Jakob Stoklund Olesen4359e5e2011-04-05 20:56:08 +0000[diff] [blame]90 <li><a href="#dss_inteqclasses">"llvm/ADT/IntEqClasses.h"</a></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]91 <li><a href="#dss_othermap">Other Map-Like Container Options</a></li>
92 </ul></li>
Chris Lattnerdced9fb2009-07-25 07:22:20 +0000[diff] [blame]93 <li><a href="#ds_string">String-like containers</a>
Benjamin Kramere15192b2009-08-05 15:42:44 +0000[diff] [blame]94 <!--<ul>
95 todo
96 </ul>--></li>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]97 <li><a href="#ds_bit">BitVector-like containers</a>
98 <ul>
99 <li><a href="#dss_bitvector">A dense bitvector</a></li>
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]100 <li><a href="#dss_smallbitvector">A "small" dense bitvector</a></li>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]101 <li><a href="#dss_sparsebitvector">A sparse bitvector</a></li>
102 </ul></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]103 </ul>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]104 </li>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]105 <li><a href="#common">Helpful Hints for Common Operations</a>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]106 <ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]107 <li><a href="#inspection">Basic Inspection and Traversal Routines</a>
108 <ul>
109 <li><a href="#iterate_function">Iterating over the <tt>BasicBlock</tt>s
110in a <tt>Function</tt></a> </li>
111 <li><a href="#iterate_basicblock">Iterating over the <tt>Instruction</tt>s
112in a <tt>BasicBlock</tt></a> </li>
113 <li><a href="#iterate_institer">Iterating over the <tt>Instruction</tt>s
114in a <tt>Function</tt></a> </li>
115 <li><a href="#iterate_convert">Turning an iterator into a
116class pointer</a> </li>
117 <li><a href="#iterate_complex">Finding call sites: a more
118complex example</a> </li>
119 <li><a href="#calls_and_invokes">Treating calls and invokes
120the same way</a> </li>
121 <li><a href="#iterate_chains">Iterating over def-use &amp;
122use-def chains</a> </li>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]123 <li><a href="#iterate_preds">Iterating over predecessors &amp;
124successors of blocks</a></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]125 </ul>
126 </li>
127 <li><a href="#simplechanges">Making simple changes</a>
128 <ul>
129 <li><a href="#schanges_creating">Creating and inserting new
130 <tt>Instruction</tt>s</a> </li>
131 <li><a href="#schanges_deleting">Deleting <tt>Instruction</tt>s</a> </li>
132 <li><a href="#schanges_replacing">Replacing an <tt>Instruction</tt>
133with another <tt>Value</tt></a> </li>
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]134 <li><a href="#schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a> </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]135 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]136 </li>
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]137 <li><a href="#create_types">How to Create Types</a></li>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]138<!--
139 <li>Working with the Control Flow Graph
140 <ul>
141 <li>Accessing predecessors and successors of a <tt>BasicBlock</tt>
142 <li>
143 <li>
144 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]145-->
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]146 </ul>
147 </li>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]148
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]149 <li><a href="#threading">Threads and LLVM</a>
150 <ul>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]151 <li><a href="#startmultithreaded">Entering and Exiting Multithreaded Mode
152 </a></li>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]153 <li><a href="#shutdown">Ending execution with <tt>llvm_shutdown()</tt></a></li>
154 <li><a href="#managedstatic">Lazy initialization with <tt>ManagedStatic</tt></a></li>
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]155 <li><a href="#llvmcontext">Achieving Isolation with <tt>LLVMContext</tt></a></li>
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]156 <li><a href="#jitthreading">Threads and the JIT</a></li>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]157 </ul>
158 </li>
159
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]160 <li><a href="#advanced">Advanced Topics</a>
161 <ul>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]162 <li><a href="#TypeResolve">LLVM Type Resolution</a>
163 <ul>
164 <li><a href="#BuildRecType">Basic Recursive Type Construction</a></li>
165 <li><a href="#refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a></li>
166 <li><a href="#PATypeHolder">The PATypeHolder Class</a></li>
167 <li><a href="#AbstractTypeUser">The AbstractTypeUser Class</a></li>
168 </ul></li>
169
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]170 <li><a href="#SymbolTable">The <tt>ValueSymbolTable</tt> and <tt>TypeSymbolTable</tt> classes</a></li>
171 <li><a href="#UserLayout">The <tt>User</tt> and owned <tt>Use</tt> classes' memory layout</a></li>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]172 </ul></li>
173
Joel Stanley9b96c442002-09-06 21:55:13 +0000[diff] [blame]174 <li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]175 <ul>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]176 <li><a href="#Type">The <tt>Type</tt> class</a> </li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]177 <li><a href="#Module">The <tt>Module</tt> class</a></li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]178 <li><a href="#Value">The <tt>Value</tt> class</a>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]179 <ul>
180 <li><a href="#User">The <tt>User</tt> class</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]181 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]182 <li><a href="#Instruction">The <tt>Instruction</tt> class</a></li>
183 <li><a href="#Constant">The <tt>Constant</tt> class</a>
184 <ul>
185 <li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]186 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]187 <li><a href="#Function">The <tt>Function</tt> class</a></li>
188 <li><a href="#GlobalVariable">The <tt>GlobalVariable</tt> class</a></li>
189 </ul>
190 </li>
191 </ul>
192 </li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]193 </ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]194 </li>
195 <li><a href="#BasicBlock">The <tt>BasicBlock</tt> class</a></li>
196 <li><a href="#Argument">The <tt>Argument</tt> class</a></li>
197 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]198 </li>
199 </ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]200 </li>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]201</ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]202
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]203<div class="doc_author">
204 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>,
Chris Lattner94c43592004-05-26 16:52:55 +0000[diff] [blame]205 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a>,
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]206 <a href="mailto:ggreif@gmail.com">Gabor Greif</a>,
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]207 <a href="mailto:jstanley@cs.uiuc.edu">Joel Stanley</a>,
208 <a href="mailto:rspencer@x10sys.com">Reid Spencer</a> and
209 <a href="mailto:owen@apple.com">Owen Anderson</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]210</div>
211
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]212<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]213<h2>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]214 <a name="introduction">Introduction </a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]215</h2>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]216<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]217
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]218<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]219
220<p>This document is meant to highlight some of the important classes and
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]221interfaces available in the LLVM source-base. This manual is not
222intended to explain what LLVM is, how it works, and what LLVM code looks
223like. It assumes that you know the basics of LLVM and are interested
224in writing transformations or otherwise analyzing or manipulating the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]225code.</p>
226
227<p>This document should get you oriented so that you can find your
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]228way in the continuously growing source code that makes up the LLVM
229infrastructure. Note that this manual is not intended to serve as a
230replacement for reading the source code, so if you think there should be
231a method in one of these classes to do something, but it's not listed,
232check the source. Links to the <a href="/doxygen/">doxygen</a> sources
233are provided to make this as easy as possible.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]234
235<p>The first section of this document describes general information that is
236useful to know when working in the LLVM infrastructure, and the second describes
237the Core LLVM classes. In the future this manual will be extended with
238information describing how to use extension libraries, such as dominator
239information, CFG traversal routines, and useful utilities like the <tt><a
240href="/doxygen/InstVisitor_8h-source.html">InstVisitor</a></tt> template.</p>
241
242</div>
243
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]244<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]245<h2>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]246 <a name="general">General Information</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]247</h2>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]248<!-- *********************************************************************** -->
249
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]250<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]251
252<p>This section contains general information that is useful if you are working
253in the LLVM source-base, but that isn't specific to any particular API.</p>
254
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]255<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]256<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]257 <a name="stl">The C++ Standard Template Library</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]258</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]259
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]260<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]261
262<p>LLVM makes heavy use of the C++ Standard Template Library (STL),
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]263perhaps much more than you are used to, or have seen before. Because of
264this, you might want to do a little background reading in the
265techniques used and capabilities of the library. There are many good
266pages that discuss the STL, and several books on the subject that you
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]267can get, so it will not be discussed in this document.</p>
268
269<p>Here are some useful links:</p>
270
271<ol>
272
Nick Lewyckyea1fe2c2010-10-09 21:12:29 +0000[diff] [blame]273<li><a href="http://www.dinkumware.com/manuals/#Standard C++ Library">Dinkumware
274C++ Library reference</a> - an excellent reference for the STL and other parts
275of the standard C++ library.</li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]276
277<li><a href="http://www.tempest-sw.com/cpp/">C++ In a Nutshell</a> - This is an
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]278O'Reilly book in the making. It has a decent Standard Library
279Reference that rivals Dinkumware's, and is unfortunately no longer free since the
280book has been published.</li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]281
282<li><a href="http://www.parashift.com/c++-faq-lite/">C++ Frequently Asked
283Questions</a></li>
284
285<li><a href="http://www.sgi.com/tech/stl/">SGI's STL Programmer's Guide</a> -
286Contains a useful <a
287href="http://www.sgi.com/tech/stl/stl_introduction.html">Introduction to the
288STL</a>.</li>
289
290<li><a href="http://www.research.att.com/%7Ebs/C++.html">Bjarne Stroustrup's C++
291Page</a></li>
292
Tanya Lattner79445ba2004-12-08 18:34:56 +0000[diff] [blame]293<li><a href="http://64.78.49.204/">
Reid Spencer096603a2004-05-26 08:41:35 +0000[diff] [blame]294Bruce Eckel's Thinking in C++, 2nd ed. Volume 2 Revision 4.0 (even better, get
295the book).</a></li>
296
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]297</ol>
298
299<p>You are also encouraged to take a look at the <a
300href="CodingStandards.html">LLVM Coding Standards</a> guide which focuses on how
301to write maintainable code more than where to put your curly braces.</p>
302
303</div>
304
305<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]306<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]307 <a name="stl">Other useful references</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]308</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]309
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]310<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]311
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]312<ol>
Misha Brukmana0f71e42004-06-18 18:39:00 +0000[diff] [blame]313<li><a href="http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html">Using
314static and shared libraries across platforms</a></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]315</ol>
316
317</div>
318
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]319</div>
320
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]321<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]322<h2>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]323 <a name="apis">Important and useful LLVM APIs</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]324</h2>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]325<!-- *********************************************************************** -->
326
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]327<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]328
329<p>Here we highlight some LLVM APIs that are generally useful and good to
330know about when writing transformations.</p>
331
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]332<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]333<h3>
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]334 <a name="isa">The <tt>isa&lt;&gt;</tt>, <tt>cast&lt;&gt;</tt> and
335 <tt>dyn_cast&lt;&gt;</tt> templates</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]336</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]337
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]338<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]339
340<p>The LLVM source-base makes extensive use of a custom form of RTTI.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]341These templates have many similarities to the C++ <tt>dynamic_cast&lt;&gt;</tt>
342operator, but they don't have some drawbacks (primarily stemming from
343the fact that <tt>dynamic_cast&lt;&gt;</tt> only works on classes that
344have a v-table). Because they are used so often, you must know what they
345do and how they work. All of these templates are defined in the <a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]346 href="/doxygen/Casting_8h-source.html"><tt>llvm/Support/Casting.h</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]347file (note that you very rarely have to include this file directly).</p>
348
349<dl>
350 <dt><tt>isa&lt;&gt;</tt>: </dt>
351
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]352 <dd><p>The <tt>isa&lt;&gt;</tt> operator works exactly like the Java
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]353 "<tt>instanceof</tt>" operator. It returns true or false depending on whether
354 a reference or pointer points to an instance of the specified class. This can
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]355 be very useful for constraint checking of various sorts (example below).</p>
356 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]357
358 <dt><tt>cast&lt;&gt;</tt>: </dt>
359
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]360 <dd><p>The <tt>cast&lt;&gt;</tt> operator is a "checked cast" operation. It
Chris Lattner28e6ff52008-06-20 05:03:17 +0000[diff] [blame]361 converts a pointer or reference from a base class to a derived class, causing
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]362 an assertion failure if it is not really an instance of the right type. This
363 should be used in cases where you have some information that makes you believe
364 that something is of the right type. An example of the <tt>isa&lt;&gt;</tt>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]365 and <tt>cast&lt;&gt;</tt> template is:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]366
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]367<div class="doc_code">
368<pre>
369static bool isLoopInvariant(const <a href="#Value">Value</a> *V, const Loop *L) {
370 if (isa&lt;<a href="#Constant">Constant</a>&gt;(V) || isa&lt;<a href="#Argument">Argument</a>&gt;(V) || isa&lt;<a href="#GlobalValue">GlobalValue</a>&gt;(V))
371 return true;
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]372
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]373 // <i>Otherwise, it must be an instruction...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]374 return !L-&gt;contains(cast&lt;<a href="#Instruction">Instruction</a>&gt;(V)-&gt;getParent());
375}
376</pre>
377</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]378
379 <p>Note that you should <b>not</b> use an <tt>isa&lt;&gt;</tt> test followed
380 by a <tt>cast&lt;&gt;</tt>, for that use the <tt>dyn_cast&lt;&gt;</tt>
381 operator.</p>
382
383 </dd>
384
385 <dt><tt>dyn_cast&lt;&gt;</tt>:</dt>
386
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]387 <dd><p>The <tt>dyn_cast&lt;&gt;</tt> operator is a "checking cast" operation.
388 It checks to see if the operand is of the specified type, and if so, returns a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]389 pointer to it (this operator does not work with references). If the operand is
390 not of the correct type, a null pointer is returned. Thus, this works very
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]391 much like the <tt>dynamic_cast&lt;&gt;</tt> operator in C++, and should be
392 used in the same circumstances. Typically, the <tt>dyn_cast&lt;&gt;</tt>
393 operator is used in an <tt>if</tt> statement or some other flow control
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]394 statement like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]395
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]396<div class="doc_code">
397<pre>
398if (<a href="#AllocationInst">AllocationInst</a> *AI = dyn_cast&lt;<a href="#AllocationInst">AllocationInst</a>&gt;(Val)) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]399 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]400}
401</pre>
402</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]403
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]404 <p>This form of the <tt>if</tt> statement effectively combines together a call
405 to <tt>isa&lt;&gt;</tt> and a call to <tt>cast&lt;&gt;</tt> into one
406 statement, which is very convenient.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]407
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]408 <p>Note that the <tt>dyn_cast&lt;&gt;</tt> operator, like C++'s
409 <tt>dynamic_cast&lt;&gt;</tt> or Java's <tt>instanceof</tt> operator, can be
410 abused. In particular, you should not use big chained <tt>if/then/else</tt>
411 blocks to check for lots of different variants of classes. If you find
412 yourself wanting to do this, it is much cleaner and more efficient to use the
413 <tt>InstVisitor</tt> class to dispatch over the instruction type directly.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]414
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]415 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]416
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]417 <dt><tt>cast_or_null&lt;&gt;</tt>: </dt>
418
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]419 <dd><p>The <tt>cast_or_null&lt;&gt;</tt> operator works just like the
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]420 <tt>cast&lt;&gt;</tt> operator, except that it allows for a null pointer as an
421 argument (which it then propagates). This can sometimes be useful, allowing
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]422 you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]423
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]424 <dt><tt>dyn_cast_or_null&lt;&gt;</tt>: </dt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]425
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]426 <dd><p>The <tt>dyn_cast_or_null&lt;&gt;</tt> operator works just like the
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]427 <tt>dyn_cast&lt;&gt;</tt> operator, except that it allows for a null pointer
428 as an argument (which it then propagates). This can sometimes be useful,
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]429 allowing you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]430
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]431</dl>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]432
433<p>These five templates can be used with any classes, whether they have a
434v-table or not. To add support for these templates, you simply need to add
435<tt>classof</tt> static methods to the class you are interested casting
436to. Describing this is currently outside the scope of this document, but there
437are lots of examples in the LLVM source base.</p>
438
439</div>
440
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]441
442<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]443<h3>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]444 <a name="string_apis">Passing strings (the <tt>StringRef</tt>
445and <tt>Twine</tt> classes)</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]446</h3>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]447
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]448<div>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]449
450<p>Although LLVM generally does not do much string manipulation, we do have
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]451several important APIs which take strings. Two important examples are the
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]452Value class -- which has names for instructions, functions, etc. -- and the
453StringMap class which is used extensively in LLVM and Clang.</p>
454
455<p>These are generic classes, and they need to be able to accept strings which
456may have embedded null characters. Therefore, they cannot simply take
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]457a <tt>const char *</tt>, and taking a <tt>const std::string&amp;</tt> requires
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]458clients to perform a heap allocation which is usually unnecessary. Instead,
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]459many LLVM APIs use a <tt>StringRef</tt> or a <tt>const Twine&amp;</tt> for
460passing strings efficiently.</p>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]461
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]462<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]463<h4>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]464 <a name="StringRef">The <tt>StringRef</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]465</h4>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]466
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]467<div>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]468
469<p>The <tt>StringRef</tt> data type represents a reference to a constant string
470(a character array and a length) and supports the common operations available
471on <tt>std:string</tt>, but does not require heap allocation.</p>
472
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]473<p>It can be implicitly constructed using a C style null-terminated string,
474an <tt>std::string</tt>, or explicitly with a character pointer and length.
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]475For example, the <tt>StringRef</tt> find function is declared as:</p>
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]476
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]477<pre class="doc_code">
478 iterator find(StringRef Key);
479</pre>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]480
481<p>and clients can call it using any one of:</p>
482
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]483<pre class="doc_code">
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]484 Map.find("foo"); <i>// Lookup "foo"</i>
485 Map.find(std::string("bar")); <i>// Lookup "bar"</i>
486 Map.find(StringRef("\0baz", 4)); <i>// Lookup "\0baz"</i>
487</pre>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]488
489<p>Similarly, APIs which need to return a string may return a <tt>StringRef</tt>
490instance, which can be used directly or converted to an <tt>std::string</tt>
491using the <tt>str</tt> member function. See
492"<tt><a href="/doxygen/classllvm_1_1StringRef_8h-source.html">llvm/ADT/StringRef.h</a></tt>"
493for more information.</p>
494
495<p>You should rarely use the <tt>StringRef</tt> class directly, because it contains
496pointers to external memory it is not generally safe to store an instance of the
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]497class (unless you know that the external storage will not be freed). StringRef is
498small and pervasive enough in LLVM that it should always be passed by value.</p>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]499
500</div>
501
502<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]503<h4>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]504 <a name="Twine">The <tt>Twine</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]505</h4>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]506
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]507<div>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]508
509<p>The <tt>Twine</tt> class is an efficient way for APIs to accept concatenated
510strings. For example, a common LLVM paradigm is to name one instruction based on
511the name of another instruction with a suffix, for example:</p>
512
513<div class="doc_code">
514<pre>
515 New = CmpInst::Create(<i>...</i>, SO->getName() + ".cmp");
516</pre>
517</div>
518
519<p>The <tt>Twine</tt> class is effectively a
520lightweight <a href="http://en.wikipedia.org/wiki/Rope_(computer_science)">rope</a>
521which points to temporary (stack allocated) objects. Twines can be implicitly
522constructed as the result of the plus operator applied to strings (i.e., a C
523strings, an <tt>std::string</tt>, or a <tt>StringRef</tt>). The twine delays the
Dan Gohmancf0c9bc2010-02-25 23:51:27 +0000[diff] [blame]524actual concatenation of strings until it is actually required, at which point
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]525it can be efficiently rendered directly into a character array. This avoids
526unnecessary heap allocation involved in constructing the temporary results of
527string concatenation. See
528"<tt><a href="/doxygen/classllvm_1_1Twine_8h-source.html">llvm/ADT/Twine.h</a></tt>"
Benjamin Kramere15192b2009-08-05 15:42:44 +0000[diff] [blame]529for more information.</p>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]530
531<p>As with a <tt>StringRef</tt>, <tt>Twine</tt> objects point to external memory
532and should almost never be stored or mentioned directly. They are intended
533solely for use when defining a function which should be able to efficiently
534accept concatenated strings.</p>
535
536</div>
537
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]538</div>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]539
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]540<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]541<h3>
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]542 <a name="DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt> option</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]543</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]544
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]545<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]546
547<p>Often when working on your pass you will put a bunch of debugging printouts
548and other code into your pass. After you get it working, you want to remove
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]549it, but you may need it again in the future (to work out new bugs that you run
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]550across).</p>
551
552<p> Naturally, because of this, you don't want to delete the debug printouts,
553but you don't want them to always be noisy. A standard compromise is to comment
554them out, allowing you to enable them if you need them in the future.</p>
555
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]556<p>The "<tt><a href="/doxygen/Debug_8h-source.html">llvm/Support/Debug.h</a></tt>"
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]557file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
558this problem. Basically, you can put arbitrary code into the argument of the
559<tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
560tool) is run with the '<tt>-debug</tt>' command line argument:</p>
561
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]562<div class="doc_code">
563<pre>
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]564DEBUG(errs() &lt;&lt; "I am here!\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]565</pre>
566</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]567
568<p>Then you can run your pass like this:</p>
569
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]570<div class="doc_code">
571<pre>
572$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]573<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]574$ opt &lt; a.bc &gt; /dev/null -mypass -debug
575I am here!
576</pre>
577</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]578
579<p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
580to not have to create "yet another" command line option for the debug output for
581your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
582so they do not cause a performance impact at all (for the same reason, they
583should also not contain side-effects!).</p>
584
585<p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
586enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
587"<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
588program hasn't been started yet, you can always just run it with
589<tt>-debug</tt>.</p>
590
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]591<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]592<h4>
Chris Lattnerc9151082005-04-26 22:57:07 +0000[diff] [blame]593 <a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt> and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]594 the <tt>-debug-only</tt> option</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]595</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]596
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]597<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]598
599<p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
600just turns on <b>too much</b> information (such as when working on the code
601generator). If you want to enable debug information with more fine-grained
602control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
603option as follows:</p>
604
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]605<div class="doc_code">
606<pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]607#undef DEBUG_TYPE
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]608DEBUG(errs() &lt;&lt; "No debug type\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]609#define DEBUG_TYPE "foo"
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]610DEBUG(errs() &lt;&lt; "'foo' debug type\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]611#undef DEBUG_TYPE
612#define DEBUG_TYPE "bar"
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]613DEBUG(errs() &lt;&lt; "'bar' debug type\n"));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]614#undef DEBUG_TYPE
615#define DEBUG_TYPE ""
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]616DEBUG(errs() &lt;&lt; "No debug type (2)\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]617</pre>
618</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]619
620<p>Then you can run your pass like this:</p>
621
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]622<div class="doc_code">
623<pre>
624$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]625<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]626$ opt &lt; a.bc &gt; /dev/null -mypass -debug
627No debug type
628'foo' debug type
629'bar' debug type
630No debug type (2)
631$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=foo
632'foo' debug type
633$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=bar
634'bar' debug type
635</pre>
636</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]637
638<p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
639a file, to specify the debug type for the entire module (if you do this before
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]640you <tt>#include "llvm/Support/Debug.h"</tt>, you don't have to insert the ugly
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]641<tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
642"bar", because there is no system in place to ensure that names do not
643conflict. If two different modules use the same string, they will all be turned
644on when the name is specified. This allows, for example, all debug information
645for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]646even if the source lives in multiple files.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]647
Daniel Dunbarc3c92392009-08-07 23:48:59 +0000[diff] [blame]648<p>The <tt>DEBUG_WITH_TYPE</tt> macro is also available for situations where you
649would like to set <tt>DEBUG_TYPE</tt>, but only for one specific <tt>DEBUG</tt>
650statement. It takes an additional first parameter, which is the type to use. For
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]651example, the preceding example could be written as:</p>
Daniel Dunbarc3c92392009-08-07 23:48:59 +0000[diff] [blame]652
653
654<div class="doc_code">
655<pre>
656DEBUG_WITH_TYPE("", errs() &lt;&lt; "No debug type\n");
657DEBUG_WITH_TYPE("foo", errs() &lt;&lt; "'foo' debug type\n");
658DEBUG_WITH_TYPE("bar", errs() &lt;&lt; "'bar' debug type\n"));
659DEBUG_WITH_TYPE("", errs() &lt;&lt; "No debug type (2)\n");
660</pre>
661</div>
662
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]663</div>
664
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]665</div>
666
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]667<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]668<h3>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]669 <a name="Statistic">The <tt>Statistic</tt> class &amp; <tt>-stats</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]670 option</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]671</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]672
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]673<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]674
675<p>The "<tt><a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]676href="/doxygen/Statistic_8h-source.html">llvm/ADT/Statistic.h</a></tt>" file
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]677provides a class named <tt>Statistic</tt> that is used as a unified way to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]678keep track of what the LLVM compiler is doing and how effective various
679optimizations are. It is useful to see what optimizations are contributing to
680making a particular program run faster.</p>
681
682<p>Often you may run your pass on some big program, and you're interested to see
683how many times it makes a certain transformation. Although you can do this with
684hand inspection, or some ad-hoc method, this is a real pain and not very useful
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]685for big programs. Using the <tt>Statistic</tt> class makes it very easy to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]686keep track of this information, and the calculated information is presented in a
687uniform manner with the rest of the passes being executed.</p>
688
689<p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
690it are as follows:</p>
691
692<ol>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]693 <li><p>Define your statistic like this:</p>
694
695<div class="doc_code">
696<pre>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]697#define <a href="#DEBUG_TYPE">DEBUG_TYPE</a> "mypassname" <i>// This goes before any #includes.</i>
698STATISTIC(NumXForms, "The # of times I did stuff");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]699</pre>
700</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]701
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]702 <p>The <tt>STATISTIC</tt> macro defines a static variable, whose name is
703 specified by the first argument. The pass name is taken from the DEBUG_TYPE
704 macro, and the description is taken from the second argument. The variable
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]705 defined ("NumXForms" in this case) acts like an unsigned integer.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]706
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]707 <li><p>Whenever you make a transformation, bump the counter:</p>
708
709<div class="doc_code">
710<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]711++NumXForms; // <i>I did stuff!</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]712</pre>
713</div>
714
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]715 </li>
716 </ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]717
718 <p>That's all you have to do. To get '<tt>opt</tt>' to print out the
719 statistics gathered, use the '<tt>-stats</tt>' option:</p>
720
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]721<div class="doc_code">
722<pre>
723$ opt -stats -mypassname &lt; program.bc &gt; /dev/null
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]724<i>... statistics output ...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]725</pre>
726</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]727
Reid Spencer6b6c73e2007-02-09 16:00:28 +0000[diff] [blame]728 <p> When running <tt>opt</tt> on a C file from the SPEC benchmark
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]729suite, it gives a report that looks like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]730
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]731<div class="doc_code">
732<pre>
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]733 7646 bitcodewriter - Number of normal instructions
734 725 bitcodewriter - Number of oversized instructions
735 129996 bitcodewriter - Number of bitcode bytes written
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]736 2817 raise - Number of insts DCEd or constprop'd
737 3213 raise - Number of cast-of-self removed
738 5046 raise - Number of expression trees converted
739 75 raise - Number of other getelementptr's formed
740 138 raise - Number of load/store peepholes
741 42 deadtypeelim - Number of unused typenames removed from symtab
742 392 funcresolve - Number of varargs functions resolved
743 27 globaldce - Number of global variables removed
744 2 adce - Number of basic blocks removed
745 134 cee - Number of branches revectored
746 49 cee - Number of setcc instruction eliminated
747 532 gcse - Number of loads removed
748 2919 gcse - Number of instructions removed
749 86 indvars - Number of canonical indvars added
750 87 indvars - Number of aux indvars removed
751 25 instcombine - Number of dead inst eliminate
752 434 instcombine - Number of insts combined
753 248 licm - Number of load insts hoisted
754 1298 licm - Number of insts hoisted to a loop pre-header
755 3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
756 75 mem2reg - Number of alloca's promoted
757 1444 cfgsimplify - Number of blocks simplified
758</pre>
759</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]760
761<p>Obviously, with so many optimizations, having a unified framework for this
762stuff is very nice. Making your pass fit well into the framework makes it more
763maintainable and useful.</p>
764
765</div>
766
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]767<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]768<h3>
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]769 <a name="ViewGraph">Viewing graphs while debugging code</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]770</h3>
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]771
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]772<div>
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]773
774<p>Several of the important data structures in LLVM are graphs: for example
775CFGs made out of LLVM <a href="#BasicBlock">BasicBlock</a>s, CFGs made out of
776LLVM <a href="CodeGenerator.html#machinebasicblock">MachineBasicBlock</a>s, and
777<a href="CodeGenerator.html#selectiondag_intro">Instruction Selection
778DAGs</a>. In many cases, while debugging various parts of the compiler, it is
779nice to instantly visualize these graphs.</p>
780
781<p>LLVM provides several callbacks that are available in a debug build to do
782exactly that. If you call the <tt>Function::viewCFG()</tt> method, for example,
783the current LLVM tool will pop up a window containing the CFG for the function
784where each basic block is a node in the graph, and each node contains the
785instructions in the block. Similarly, there also exists
786<tt>Function::viewCFGOnly()</tt> (does not include the instructions), the
787<tt>MachineFunction::viewCFG()</tt> and <tt>MachineFunction::viewCFGOnly()</tt>,
788and the <tt>SelectionDAG::viewGraph()</tt> methods. Within GDB, for example,
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]789you can usually use something like <tt>call DAG.viewGraph()</tt> to pop
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]790up a window. Alternatively, you can sprinkle calls to these functions in your
791code in places you want to debug.</p>
792
793<p>Getting this to work requires a small amount of configuration. On Unix
794systems with X11, install the <a href="http://www.graphviz.org">graphviz</a>
795toolkit, and make sure 'dot' and 'gv' are in your path. If you are running on
796Mac OS/X, download and install the Mac OS/X <a
797href="http://www.pixelglow.com/graphviz/">Graphviz program</a>, and add
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]798<tt>/Applications/Graphviz.app/Contents/MacOS/</tt> (or wherever you install
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]799it) to your path. Once in your system and path are set up, rerun the LLVM
800configure script and rebuild LLVM to enable this functionality.</p>
801
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]802<p><tt>SelectionDAG</tt> has been extended to make it easier to locate
803<i>interesting</i> nodes in large complex graphs. From gdb, if you
804<tt>call DAG.setGraphColor(<i>node</i>, "<i>color</i>")</tt>, then the
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]805next <tt>call DAG.viewGraph()</tt> would highlight the node in the
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]806specified color (choices of colors can be found at <a
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]807href="http://www.graphviz.org/doc/info/colors.html">colors</a>.) More
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]808complex node attributes can be provided with <tt>call
809DAG.setGraphAttrs(<i>node</i>, "<i>attributes</i>")</tt> (choices can be
810found at <a href="http://www.graphviz.org/doc/info/attrs.html">Graph
811Attributes</a>.) If you want to restart and clear all the current graph
812attributes, then you can <tt>call DAG.clearGraphAttrs()</tt>. </p>
813
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]814</div>
815
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]816</div>
817
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]818<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]819<h2>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]820 <a name="datastructure">Picking the Right Data Structure for a Task</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]821</h2>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]822<!-- *********************************************************************** -->
823
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]824<div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]825
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]826<p>LLVM has a plethora of data structures in the <tt>llvm/ADT/</tt> directory,
827 and we commonly use STL data structures. This section describes the trade-offs
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]828 you should consider when you pick one.</p>
829
830<p>
831The first step is a choose your own adventure: do you want a sequential
832container, a set-like container, or a map-like container? The most important
833thing when choosing a container is the algorithmic properties of how you plan to
834access the container. Based on that, you should use:</p>
835
836<ul>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]837<li>a <a href="#ds_map">map-like</a> container if you need efficient look-up
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]838 of an value based on another value. Map-like containers also support
839 efficient queries for containment (whether a key is in the map). Map-like
840 containers generally do not support efficient reverse mapping (values to
841 keys). If you need that, use two maps. Some map-like containers also
842 support efficient iteration through the keys in sorted order. Map-like
843 containers are the most expensive sort, only use them if you need one of
844 these capabilities.</li>
845
846<li>a <a href="#ds_set">set-like</a> container if you need to put a bunch of
847 stuff into a container that automatically eliminates duplicates. Some
848 set-like containers support efficient iteration through the elements in
849 sorted order. Set-like containers are more expensive than sequential
850 containers.
851</li>
852
853<li>a <a href="#ds_sequential">sequential</a> container provides
854 the most efficient way to add elements and keeps track of the order they are
855 added to the collection. They permit duplicates and support efficient
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]856 iteration, but do not support efficient look-up based on a key.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]857</li>
858
Chris Lattnerdced9fb2009-07-25 07:22:20 +0000[diff] [blame]859<li>a <a href="#ds_string">string</a> container is a specialized sequential
860 container or reference structure that is used for character or byte
861 arrays.</li>
862
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]863<li>a <a href="#ds_bit">bit</a> container provides an efficient way to store and
864 perform set operations on sets of numeric id's, while automatically
865 eliminating duplicates. Bit containers require a maximum of 1 bit for each
866 identifier you want to store.
867</li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]868</ul>
869
870<p>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]871Once the proper category of container is determined, you can fine tune the
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]872memory use, constant factors, and cache behaviors of access by intelligently
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]873picking a member of the category. Note that constant factors and cache behavior
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]874can be a big deal. If you have a vector that usually only contains a few
875elements (but could contain many), for example, it's much better to use
876<a href="#dss_smallvector">SmallVector</a> than <a href="#dss_vector">vector</a>
877. Doing so avoids (relatively) expensive malloc/free calls, which dwarf the
878cost of adding the elements to the container. </p>
879
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]880<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]881<h3>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]882 <a name="ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]883</h3>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]884
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]885<div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]886There are a variety of sequential containers available for you, based on your
887needs. Pick the first in this section that will do what you want.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]888
889<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]890<h4>
Chris Lattner8ae42612011-04-05 23:18:20 +0000[diff] [blame]891 <a name="dss_arrayref">llvm/ADT/ArrayRef.h</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]892</h4>
Chris Lattner8ae42612011-04-05 23:18:20 +0000[diff] [blame]893
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]894<div>
Chris Lattner8ae42612011-04-05 23:18:20 +0000[diff] [blame]895<p>The llvm::ArrayRef class is the preferred class to use in an interface that
896 accepts a sequential list of elements in memory and just reads from them. By
897 taking an ArrayRef, the API can be passed a fixed size array, an std::vector,
898 an llvm::SmallVector and anything else that is contiguous in memory.
899</p>
900</div>
901
902
903
904<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]905<h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]906 <a name="dss_fixedarrays">Fixed Size Arrays</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]907</h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]908
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]909<div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]910<p>Fixed size arrays are very simple and very fast. They are good if you know
911exactly how many elements you have, or you have a (low) upper bound on how many
912you have.</p>
913</div>
914
915<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]916<h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]917 <a name="dss_heaparrays">Heap Allocated Arrays</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]918</h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]919
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]920<div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]921<p>Heap allocated arrays (new[] + delete[]) are also simple. They are good if
922the number of elements is variable, if you know how many elements you will need
923before the array is allocated, and if the array is usually large (if not,
924consider a <a href="#dss_smallvector">SmallVector</a>). The cost of a heap
925allocated array is the cost of the new/delete (aka malloc/free). Also note that
926if you are allocating an array of a type with a constructor, the constructor and
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]927destructors will be run for every element in the array (re-sizable vectors only
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]928construct those elements actually used).</p>
929</div>
930
931<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]932<h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]933 <a name="dss_smallvector">"llvm/ADT/SmallVector.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]934</h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]935
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]936<div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]937<p><tt>SmallVector&lt;Type, N&gt;</tt> is a simple class that looks and smells
938just like <tt>vector&lt;Type&gt;</tt>:
939it supports efficient iteration, lays out elements in memory order (so you can
940do pointer arithmetic between elements), supports efficient push_back/pop_back
941operations, supports efficient random access to its elements, etc.</p>
942
943<p>The advantage of SmallVector is that it allocates space for
944some number of elements (N) <b>in the object itself</b>. Because of this, if
945the SmallVector is dynamically smaller than N, no malloc is performed. This can
946be a big win in cases where the malloc/free call is far more expensive than the
947code that fiddles around with the elements.</p>
948
949<p>This is good for vectors that are "usually small" (e.g. the number of
950predecessors/successors of a block is usually less than 8). On the other hand,
951this makes the size of the SmallVector itself large, so you don't want to
952allocate lots of them (doing so will waste a lot of space). As such,
953SmallVectors are most useful when on the stack.</p>
954
955<p>SmallVector also provides a nice portable and efficient replacement for
956<tt>alloca</tt>.</p>
957
958</div>
959
960<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]961<h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]962 <a name="dss_vector">&lt;vector&gt;</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]963</h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]964
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]965<div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]966<p>
967std::vector is well loved and respected. It is useful when SmallVector isn't:
968when the size of the vector is often large (thus the small optimization will
969rarely be a benefit) or if you will be allocating many instances of the vector
970itself (which would waste space for elements that aren't in the container).
971vector is also useful when interfacing with code that expects vectors :).
972</p>
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]973
974<p>One worthwhile note about std::vector: avoid code like this:</p>
975
976<div class="doc_code">
977<pre>
978for ( ... ) {
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]979 std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]980 use V;
981}
982</pre>
983</div>
984
985<p>Instead, write this as:</p>
986
987<div class="doc_code">
988<pre>
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]989std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]990for ( ... ) {
991 use V;
992 V.clear();
993}
994</pre>
995</div>
996
997<p>Doing so will save (at least) one heap allocation and free per iteration of
998the loop.</p>
999
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1000</div>
1001
1002<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1003<h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1004 <a name="dss_deque">&lt;deque&gt;</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1005</h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1006
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1007<div>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1008<p>std::deque is, in some senses, a generalized version of std::vector. Like
1009std::vector, it provides constant time random access and other similar
1010properties, but it also provides efficient access to the front of the list. It
1011does not guarantee continuity of elements within memory.</p>
1012
1013<p>In exchange for this extra flexibility, std::deque has significantly higher
1014constant factor costs than std::vector. If possible, use std::vector or
1015something cheaper.</p>
1016</div>
1017
1018<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1019<h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1020 <a name="dss_list">&lt;list&gt;</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1021</h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1022
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1023<div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1024<p>std::list is an extremely inefficient class that is rarely useful.
1025It performs a heap allocation for every element inserted into it, thus having an
1026extremely high constant factor, particularly for small data types. std::list
1027also only supports bidirectional iteration, not random access iteration.</p>
1028
1029<p>In exchange for this high cost, std::list supports efficient access to both
1030ends of the list (like std::deque, but unlike std::vector or SmallVector). In
1031addition, the iterator invalidation characteristics of std::list are stronger
1032than that of a vector class: inserting or removing an element into the list does
1033not invalidate iterator or pointers to other elements in the list.</p>
1034</div>
1035
1036<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1037<h4>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1038 <a name="dss_ilist">llvm/ADT/ilist.h</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1039</h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1040
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1041<div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1042<p><tt>ilist&lt;T&gt;</tt> implements an 'intrusive' doubly-linked list. It is
1043intrusive, because it requires the element to store and provide access to the
1044prev/next pointers for the list.</p>
1045
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1046<p><tt>ilist</tt> has the same drawbacks as <tt>std::list</tt>, and additionally
1047requires an <tt>ilist_traits</tt> implementation for the element type, but it
1048provides some novel characteristics. In particular, it can efficiently store
1049polymorphic objects, the traits class is informed when an element is inserted or
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]1050removed from the list, and <tt>ilist</tt>s are guaranteed to support a
1051constant-time splice operation.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1052
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]1053<p>These properties are exactly what we want for things like
1054<tt>Instruction</tt>s and basic blocks, which is why these are implemented with
1055<tt>ilist</tt>s.</p>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1056
1057Related classes of interest are explained in the following subsections:
1058 <ul>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1059 <li><a href="#dss_ilist_traits">ilist_traits</a></li>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1060 <li><a href="#dss_iplist">iplist</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1061 <li><a href="#dss_ilist_node">llvm/ADT/ilist_node.h</a></li>
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]1062 <li><a href="#dss_ilist_sentinel">Sentinels</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1063 </ul>
1064</div>
1065
1066<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1067<h4>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1068 <a name="dss_ilist_traits">ilist_traits</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1069</h4>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1070
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1071<div>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1072<p><tt>ilist_traits&lt;T&gt;</tt> is <tt>ilist&lt;T&gt;</tt>'s customization
1073mechanism. <tt>iplist&lt;T&gt;</tt> (and consequently <tt>ilist&lt;T&gt;</tt>)
1074publicly derive from this traits class.</p>
1075</div>
1076
1077<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1078<h4>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1079 <a name="dss_iplist">iplist</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1080</h4>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1081
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1082<div>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1083<p><tt>iplist&lt;T&gt;</tt> is <tt>ilist&lt;T&gt;</tt>'s base and as such
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]1084supports a slightly narrower interface. Notably, inserters from
1085<tt>T&amp;</tt> are absent.</p>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1086
1087<p><tt>ilist_traits&lt;T&gt;</tt> is a public base of this class and can be
1088used for a wide variety of customizations.</p>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1089</div>
1090
1091<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1092<h4>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1093 <a name="dss_ilist_node">llvm/ADT/ilist_node.h</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1094</h4>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1095
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1096<div>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1097<p><tt>ilist_node&lt;T&gt;</tt> implements a the forward and backward links
1098that are expected by the <tt>ilist&lt;T&gt;</tt> (and analogous containers)
1099in the default manner.</p>
1100
1101<p><tt>ilist_node&lt;T&gt;</tt>s are meant to be embedded in the node type
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]1102<tt>T</tt>, usually <tt>T</tt> publicly derives from
1103<tt>ilist_node&lt;T&gt;</tt>.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1104</div>
1105
1106<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1107<h4>
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]1108 <a name="dss_ilist_sentinel">Sentinels</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1109</h4>
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]1110
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1111<div>
Dan Gohmancf0c9bc2010-02-25 23:51:27 +0000[diff] [blame]1112<p><tt>ilist</tt>s have another specialty that must be considered. To be a good
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]1113citizen in the C++ ecosystem, it needs to support the standard container
1114operations, such as <tt>begin</tt> and <tt>end</tt> iterators, etc. Also, the
1115<tt>operator--</tt> must work correctly on the <tt>end</tt> iterator in the
1116case of non-empty <tt>ilist</tt>s.</p>
1117
1118<p>The only sensible solution to this problem is to allocate a so-called
1119<i>sentinel</i> along with the intrusive list, which serves as the <tt>end</tt>
1120iterator, providing the back-link to the last element. However conforming to the
1121C++ convention it is illegal to <tt>operator++</tt> beyond the sentinel and it
1122also must not be dereferenced.</p>
1123
1124<p>These constraints allow for some implementation freedom to the <tt>ilist</tt>
1125how to allocate and store the sentinel. The corresponding policy is dictated
1126by <tt>ilist_traits&lt;T&gt;</tt>. By default a <tt>T</tt> gets heap-allocated
1127whenever the need for a sentinel arises.</p>
1128
1129<p>While the default policy is sufficient in most cases, it may break down when
1130<tt>T</tt> does not provide a default constructor. Also, in the case of many
1131instances of <tt>ilist</tt>s, the memory overhead of the associated sentinels
1132is wasted. To alleviate the situation with numerous and voluminous
1133<tt>T</tt>-sentinels, sometimes a trick is employed, leading to <i>ghostly
1134sentinels</i>.</p>
1135
1136<p>Ghostly sentinels are obtained by specially-crafted <tt>ilist_traits&lt;T&gt;</tt>
1137which superpose the sentinel with the <tt>ilist</tt> instance in memory. Pointer
1138arithmetic is used to obtain the sentinel, which is relative to the
1139<tt>ilist</tt>'s <tt>this</tt> pointer. The <tt>ilist</tt> is augmented by an
1140extra pointer, which serves as the back-link of the sentinel. This is the only
1141field in the ghostly sentinel which can be legally accessed.</p>
1142</div>
1143
1144<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1145<h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1146 <a name="dss_other">Other Sequential Container options</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1147</h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1148
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1149<div>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1150<p>Other STL containers are available, such as std::string.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1151
1152<p>There are also various STL adapter classes such as std::queue,
1153std::priority_queue, std::stack, etc. These provide simplified access to an
1154underlying container but don't affect the cost of the container itself.</p>
1155
1156</div>
1157
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1158</div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1159
1160<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1161<h3>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1162 <a name="ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1163</h3>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1164
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1165<div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1166
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1167<p>Set-like containers are useful when you need to canonicalize multiple values
1168into a single representation. There are several different choices for how to do
1169this, providing various trade-offs.</p>
1170
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1171<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1172<h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1173 <a name="dss_sortedvectorset">A sorted 'vector'</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1174</h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1175
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1176<div>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1177
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]1178<p>If you intend to insert a lot of elements, then do a lot of queries, a
1179great approach is to use a vector (or other sequential container) with
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1180std::sort+std::unique to remove duplicates. This approach works really well if
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]1181your usage pattern has these two distinct phases (insert then query), and can be
1182coupled with a good choice of <a href="#ds_sequential">sequential container</a>.
1183</p>
1184
1185<p>
1186This combination provides the several nice properties: the result data is
1187contiguous in memory (good for cache locality), has few allocations, is easy to
1188address (iterators in the final vector are just indices or pointers), and can be
1189efficiently queried with a standard binary or radix search.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1190
1191</div>
1192
1193<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1194<h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1195 <a name="dss_smallset">"llvm/ADT/SmallSet.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1196</h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1197
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1198<div>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1199
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1200<p>If you have a set-like data structure that is usually small and whose elements
Chris Lattner4ddfac12007-02-03 07:59:51 +0000[diff] [blame]1201are reasonably small, a <tt>SmallSet&lt;Type, N&gt;</tt> is a good choice. This set
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1202has space for N elements in place (thus, if the set is dynamically smaller than
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1203N, no malloc traffic is required) and accesses them with a simple linear search.
1204When the set grows beyond 'N' elements, it allocates a more expensive representation that
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1205guarantees efficient access (for most types, it falls back to std::set, but for
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1206pointers it uses something far better, <a
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1207href="#dss_smallptrset">SmallPtrSet</a>).</p>
1208
1209<p>The magic of this class is that it handles small sets extremely efficiently,
1210but gracefully handles extremely large sets without loss of efficiency. The
1211drawback is that the interface is quite small: it supports insertion, queries
1212and erasing, but does not support iteration.</p>
1213
1214</div>
1215
1216<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1217<h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1218 <a name="dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1219</h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1220
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1221<div>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1222
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]1223<p>SmallPtrSet has all the advantages of <tt>SmallSet</tt> (and a <tt>SmallSet</tt> of pointers is
1224transparently implemented with a <tt>SmallPtrSet</tt>), but also supports iterators. If
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1225more than 'N' insertions are performed, a single quadratically
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1226probed hash table is allocated and grows as needed, providing extremely
1227efficient access (constant time insertion/deleting/queries with low constant
1228factors) and is very stingy with malloc traffic.</p>
1229
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]1230<p>Note that, unlike <tt>std::set</tt>, the iterators of <tt>SmallPtrSet</tt> are invalidated
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1231whenever an insertion occurs. Also, the values visited by the iterators are not
1232visited in sorted order.</p>
1233
1234</div>
1235
1236<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1237<h4>
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]1238 <a name="dss_denseset">"llvm/ADT/DenseSet.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1239</h4>
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]1240
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1241<div>
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]1242
1243<p>
1244DenseSet is a simple quadratically probed hash table. It excels at supporting
1245small values: it uses a single allocation to hold all of the pairs that
1246are currently inserted in the set. DenseSet is a great way to unique small
1247values that are not simple pointers (use <a
1248href="#dss_smallptrset">SmallPtrSet</a> for pointers). Note that DenseSet has
1249the same requirements for the value type that <a
1250href="#dss_densemap">DenseMap</a> has.
1251</p>
1252
1253</div>
1254
1255<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1256<h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1257 <a name="dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1258</h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1259
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1260<div>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1261
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1262<p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1263FoldingSet is an aggregate class that is really good at uniquing
1264expensive-to-create or polymorphic objects. It is a combination of a chained
1265hash table with intrusive links (uniqued objects are required to inherit from
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1266FoldingSetNode) that uses <a href="#dss_smallvector">SmallVector</a> as part of
1267its ID process.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1268
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1269<p>Consider a case where you want to implement a "getOrCreateFoo" method for
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1270a complex object (for example, a node in the code generator). The client has a
1271description of *what* it wants to generate (it knows the opcode and all the
1272operands), but we don't want to 'new' a node, then try inserting it into a set
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1273only to find out it already exists, at which point we would have to delete it
1274and return the node that already exists.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1275</p>
1276
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1277<p>To support this style of client, FoldingSet perform a query with a
1278FoldingSetNodeID (which wraps SmallVector) that can be used to describe the
1279element that we want to query for. The query either returns the element
1280matching the ID or it returns an opaque ID that indicates where insertion should
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1281take place. Construction of the ID usually does not require heap traffic.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1282
1283<p>Because FoldingSet uses intrusive links, it can support polymorphic objects
1284in the set (for example, you can have SDNode instances mixed with LoadSDNodes).
1285Because the elements are individually allocated, pointers to the elements are
1286stable: inserting or removing elements does not invalidate any pointers to other
1287elements.
1288</p>
1289
1290</div>
1291
1292<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1293<h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1294 <a name="dss_set">&lt;set&gt;</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1295</h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1296
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1297<div>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1298
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1299<p><tt>std::set</tt> is a reasonable all-around set class, which is decent at
1300many things but great at nothing. std::set allocates memory for each element
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1301inserted (thus it is very malloc intensive) and typically stores three pointers
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1302per element in the set (thus adding a large amount of per-element space
1303overhead). It offers guaranteed log(n) performance, which is not particularly
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1304fast from a complexity standpoint (particularly if the elements of the set are
1305expensive to compare, like strings), and has extremely high constant factors for
1306lookup, insertion and removal.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1307
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1308<p>The advantages of std::set are that its iterators are stable (deleting or
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1309inserting an element from the set does not affect iterators or pointers to other
1310elements) and that iteration over the set is guaranteed to be in sorted order.
1311If the elements in the set are large, then the relative overhead of the pointers
1312and malloc traffic is not a big deal, but if the elements of the set are small,
1313std::set is almost never a good choice.</p>
1314
1315</div>
1316
1317<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1318<h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1319 <a name="dss_setvector">"llvm/ADT/SetVector.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1320</h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1321
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1322<div>
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1323<p>LLVM's SetVector&lt;Type&gt; is an adapter class that combines your choice of
1324a set-like container along with a <a href="#ds_sequential">Sequential
1325Container</a>. The important property
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1326that this provides is efficient insertion with uniquing (duplicate elements are
1327ignored) with iteration support. It implements this by inserting elements into
1328both a set-like container and the sequential container, using the set-like
1329container for uniquing and the sequential container for iteration.
1330</p>
1331
1332<p>The difference between SetVector and other sets is that the order of
1333iteration is guaranteed to match the order of insertion into the SetVector.
1334This property is really important for things like sets of pointers. Because
1335pointer values are non-deterministic (e.g. vary across runs of the program on
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1336different machines), iterating over the pointers in the set will
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1337not be in a well-defined order.</p>
1338
1339<p>
1340The drawback of SetVector is that it requires twice as much space as a normal
1341set and has the sum of constant factors from the set-like container and the
1342sequential container that it uses. Use it *only* if you need to iterate over
1343the elements in a deterministic order. SetVector is also expensive to delete
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1344elements out of (linear time), unless you use it's "pop_back" method, which is
1345faster.
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1346</p>
1347
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1348<p>SetVector is an adapter class that defaults to using std::vector and std::set
1349for the underlying containers, so it is quite expensive. However,
1350<tt>"llvm/ADT/SetVector.h"</tt> also provides a SmallSetVector class, which
1351defaults to using a SmallVector and SmallSet of a specified size. If you use
1352this, and if your sets are dynamically smaller than N, you will save a lot of
1353heap traffic.</p>
1354
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1355</div>
1356
1357<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1358<h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1359 <a name="dss_uniquevector">"llvm/ADT/UniqueVector.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1360</h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1361
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1362<div>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1363
1364<p>
1365UniqueVector is similar to <a href="#dss_setvector">SetVector</a>, but it
1366retains a unique ID for each element inserted into the set. It internally
1367contains a map and a vector, and it assigns a unique ID for each value inserted
1368into the set.</p>
1369
1370<p>UniqueVector is very expensive: its cost is the sum of the cost of
1371maintaining both the map and vector, it has high complexity, high constant
1372factors, and produces a lot of malloc traffic. It should be avoided.</p>
1373
1374</div>
1375
1376
1377<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1378<h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1379 <a name="dss_otherset">Other Set-Like Container Options</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1380</h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1381
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1382<div>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1383
1384<p>
1385The STL provides several other options, such as std::multiset and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame]1386"hash_set" like containers (whether from C++ TR1 or from the SGI library). We
1387never use hash_set and unordered_set because they are generally very expensive
1388(each insertion requires a malloc) and very non-portable.
1389</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1390
1391<p>std::multiset is useful if you're not interested in elimination of
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1392duplicates, but has all the drawbacks of std::set. A sorted vector (where you
1393don't delete duplicate entries) or some other approach is almost always
1394better.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1395
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1396</div>
1397
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1398</div>
1399
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1400<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1401<h3>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1402 <a name="ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1403</h3>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1404
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1405<div>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1406Map-like containers are useful when you want to associate data to a key. As
1407usual, there are a lot of different ways to do this. :)
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1408
1409<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1410<h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1411 <a name="dss_sortedvectormap">A sorted 'vector'</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1412</h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1413
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1414<div>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1415
1416<p>
1417If your usage pattern follows a strict insert-then-query approach, you can
1418trivially use the same approach as <a href="#dss_sortedvectorset">sorted vectors
1419for set-like containers</a>. The only difference is that your query function
1420(which uses std::lower_bound to get efficient log(n) lookup) should only compare
1421the key, not both the key and value. This yields the same advantages as sorted
1422vectors for sets.
1423</p>
1424</div>
1425
1426<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1427<h4>
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1428 <a name="dss_stringmap">"llvm/ADT/StringMap.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1429</h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1430
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1431<div>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1432
1433<p>
1434Strings are commonly used as keys in maps, and they are difficult to support
1435efficiently: they are variable length, inefficient to hash and compare when
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1436long, expensive to copy, etc. StringMap is a specialized container designed to
1437cope with these issues. It supports mapping an arbitrary range of bytes to an
1438arbitrary other object.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1439
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1440<p>The StringMap implementation uses a quadratically-probed hash table, where
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1441the buckets store a pointer to the heap allocated entries (and some other
1442stuff). The entries in the map must be heap allocated because the strings are
1443variable length. The string data (key) and the element object (value) are
1444stored in the same allocation with the string data immediately after the element
1445object. This container guarantees the "<tt>(char*)(&amp;Value+1)</tt>" points
1446to the key string for a value.</p>
1447
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1448<p>The StringMap is very fast for several reasons: quadratic probing is very
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1449cache efficient for lookups, the hash value of strings in buckets is not
Nick Lewycky2a80aca2010-08-01 23:18:45 +0000[diff] [blame]1450recomputed when looking up an element, StringMap rarely has to touch the
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1451memory for unrelated objects when looking up a value (even when hash collisions
1452happen), hash table growth does not recompute the hash values for strings
1453already in the table, and each pair in the map is store in a single allocation
1454(the string data is stored in the same allocation as the Value of a pair).</p>
1455
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1456<p>StringMap also provides query methods that take byte ranges, so it only ever
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1457copies a string if a value is inserted into the table.</p>
1458</div>
1459
1460<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1461<h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1462 <a name="dss_indexedmap">"llvm/ADT/IndexedMap.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1463</h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1464
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1465<div>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1466<p>
1467IndexedMap is a specialized container for mapping small dense integers (or
1468values that can be mapped to small dense integers) to some other type. It is
1469internally implemented as a vector with a mapping function that maps the keys to
1470the dense integer range.
1471</p>
1472
1473<p>
1474This is useful for cases like virtual registers in the LLVM code generator: they
1475have a dense mapping that is offset by a compile-time constant (the first
1476virtual register ID).</p>
1477
1478</div>
1479
1480<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1481<h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1482 <a name="dss_densemap">"llvm/ADT/DenseMap.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1483</h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1484
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1485<div>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1486
1487<p>
1488DenseMap is a simple quadratically probed hash table. It excels at supporting
1489small keys and values: it uses a single allocation to hold all of the pairs that
1490are currently inserted in the map. DenseMap is a great way to map pointers to
1491pointers, or map other small types to each other.
1492</p>
1493
1494<p>
1495There are several aspects of DenseMap that you should be aware of, however. The
1496iterators in a densemap are invalidated whenever an insertion occurs, unlike
1497map. Also, because DenseMap allocates space for a large number of key/value
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1498pairs (it starts with 64 by default), it will waste a lot of space if your keys
1499or values are large. Finally, you must implement a partial specialization of
Chris Lattner76c1b972007-09-17 18:34:04 +0000[diff] [blame]1500DenseMapInfo for the key that you want, if it isn't already supported. This
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1501is required to tell DenseMap about two special marker values (which can never be
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1502inserted into the map) that it needs internally.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1503
1504</div>
1505
1506<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1507<h4>
Jeffrey Yasskin71a5c222009-10-22 22:11:22 +0000[diff] [blame]1508 <a name="dss_valuemap">"llvm/ADT/ValueMap.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1509</h4>
Jeffrey Yasskin71a5c222009-10-22 22:11:22 +0000[diff] [blame]1510
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1511<div>
Jeffrey Yasskin71a5c222009-10-22 22:11:22 +0000[diff] [blame]1512
1513<p>
1514ValueMap is a wrapper around a <a href="#dss_densemap">DenseMap</a> mapping
1515Value*s (or subclasses) to another type. When a Value is deleted or RAUW'ed,
1516ValueMap will update itself so the new version of the key is mapped to the same
1517value, just as if the key were a WeakVH. You can configure exactly how this
1518happens, and what else happens on these two events, by passing
1519a <code>Config</code> parameter to the ValueMap template.</p>
1520
1521</div>
1522
1523<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1524<h4>
Jakob Stoklund Olesenaca0da62010-12-14 00:55:51 +0000[diff] [blame]1525 <a name="dss_intervalmap">"llvm/ADT/IntervalMap.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1526</h4>
Jakob Stoklund Olesenaca0da62010-12-14 00:55:51 +0000[diff] [blame]1527
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1528<div>
Jakob Stoklund Olesenaca0da62010-12-14 00:55:51 +0000[diff] [blame]1529
1530<p> IntervalMap is a compact map for small keys and values. It maps key
1531intervals instead of single keys, and it will automatically coalesce adjacent
1532intervals. When then map only contains a few intervals, they are stored in the
1533map object itself to avoid allocations.</p>
1534
1535<p> The IntervalMap iterators are quite big, so they should not be passed around
1536as STL iterators. The heavyweight iterators allow a smaller data structure.</p>
1537
1538</div>
1539
1540<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1541<h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1542 <a name="dss_map">&lt;map&gt;</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1543</h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1544
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1545<div>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1546
1547<p>
1548std::map has similar characteristics to <a href="#dss_set">std::set</a>: it uses
1549a single allocation per pair inserted into the map, it offers log(n) lookup with
1550an extremely large constant factor, imposes a space penalty of 3 pointers per
1551pair in the map, etc.</p>
1552
1553<p>std::map is most useful when your keys or values are very large, if you need
1554to iterate over the collection in sorted order, or if you need stable iterators
1555into the map (i.e. they don't get invalidated if an insertion or deletion of
1556another element takes place).</p>
1557
1558</div>
1559
1560<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1561<h4>
Jakob Stoklund Olesen4359e5e2011-04-05 20:56:08 +0000[diff] [blame]1562 <a name="dss_inteqclasses">"llvm/ADT/IntEqClasses.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1563</h4>
Jakob Stoklund Olesen4359e5e2011-04-05 20:56:08 +0000[diff] [blame]1564
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1565<div>
Jakob Stoklund Olesen4359e5e2011-04-05 20:56:08 +0000[diff] [blame]1566
1567<p>IntEqClasses provides a compact representation of equivalence classes of
1568small integers. Initially, each integer in the range 0..n-1 has its own
1569equivalence class. Classes can be joined by passing two class representatives to
1570the join(a, b) method. Two integers are in the same class when findLeader()
1571returns the same representative.</p>
1572
1573<p>Once all equivalence classes are formed, the map can be compressed so each
1574integer 0..n-1 maps to an equivalence class number in the range 0..m-1, where m
1575is the total number of equivalence classes. The map must be uncompressed before
1576it can be edited again.</p>
1577
1578</div>
1579
1580<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1581<h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1582 <a name="dss_othermap">Other Map-Like Container Options</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1583</h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1584
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1585<div>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1586
1587<p>
1588The STL provides several other options, such as std::multimap and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame]1589"hash_map" like containers (whether from C++ TR1 or from the SGI library). We
1590never use hash_set and unordered_set because they are generally very expensive
1591(each insertion requires a malloc) and very non-portable.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1592
1593<p>std::multimap is useful if you want to map a key to multiple values, but has
1594all the drawbacks of std::map. A sorted vector or some other approach is almost
1595always better.</p>
1596
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1597</div>
1598
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1599</div>
1600
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1601<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1602<h3>
Chris Lattnerdced9fb2009-07-25 07:22:20 +0000[diff] [blame]1603 <a name="ds_string">String-like containers</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1604</h3>
Chris Lattnerdced9fb2009-07-25 07:22:20 +0000[diff] [blame]1605
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1606<div>
Chris Lattnerdced9fb2009-07-25 07:22:20 +0000[diff] [blame]1607
1608<p>
1609TODO: const char* vs stringref vs smallstring vs std::string. Describe twine,
1610xref to #string_apis.
1611</p>
1612
1613</div>
1614
1615<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1616<h3>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1617 <a name="ds_bit">Bit storage containers (BitVector, SparseBitVector)</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1618</h3>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1619
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1620<div>
Chris Lattner7086ce72007-09-25 22:37:50 +0000[diff] [blame]1621<p>Unlike the other containers, there are only two bit storage containers, and
1622choosing when to use each is relatively straightforward.</p>
1623
1624<p>One additional option is
1625<tt>std::vector&lt;bool&gt;</tt>: we discourage its use for two reasons 1) the
1626implementation in many common compilers (e.g. commonly available versions of
1627GCC) is extremely inefficient and 2) the C++ standards committee is likely to
1628deprecate this container and/or change it significantly somehow. In any case,
1629please don't use it.</p>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1630
1631<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1632<h4>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1633 <a name="dss_bitvector">BitVector</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1634</h4>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1635
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1636<div>
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]1637<p> The BitVector container provides a dynamic size set of bits for manipulation.
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1638It supports individual bit setting/testing, as well as set operations. The set
1639operations take time O(size of bitvector), but operations are performed one word
1640at a time, instead of one bit at a time. This makes the BitVector very fast for
1641set operations compared to other containers. Use the BitVector when you expect
1642the number of set bits to be high (IE a dense set).
1643</p>
1644</div>
1645
1646<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1647<h4>
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]1648 <a name="dss_smallbitvector">SmallBitVector</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1649</h4>
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]1650
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1651<div>
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]1652<p> The SmallBitVector container provides the same interface as BitVector, but
1653it is optimized for the case where only a small number of bits, less than
165425 or so, are needed. It also transparently supports larger bit counts, but
1655slightly less efficiently than a plain BitVector, so SmallBitVector should
1656only be used when larger counts are rare.
1657</p>
1658
1659<p>
1660At this time, SmallBitVector does not support set operations (and, or, xor),
1661and its operator[] does not provide an assignable lvalue.
1662</p>
1663</div>
1664
1665<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1666<h4>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1667 <a name="dss_sparsebitvector">SparseBitVector</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1668</h4>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1669
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1670<div>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1671<p> The SparseBitVector container is much like BitVector, with one major
1672difference: Only the bits that are set, are stored. This makes the
1673SparseBitVector much more space efficient than BitVector when the set is sparse,
1674as well as making set operations O(number of set bits) instead of O(size of
1675universe). The downside to the SparseBitVector is that setting and testing of random bits is O(N), and on large SparseBitVectors, this can be slower than BitVector. In our implementation, setting or testing bits in sorted order
1676(either forwards or reverse) is O(1) worst case. Testing and setting bits within 128 bits (depends on size) of the current bit is also O(1). As a general statement, testing/setting bits in a SparseBitVector is O(distance away from last set bit).
1677</p>
1678</div>
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]1679
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1680</div>
1681
1682</div>
1683
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1684<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1685<h2>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1686 <a name="common">Helpful Hints for Common Operations</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1687</h2>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1688<!-- *********************************************************************** -->
1689
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1690<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1691
1692<p>This section describes how to perform some very simple transformations of
1693LLVM code. This is meant to give examples of common idioms used, showing the
1694practical side of LLVM transformations. <p> Because this is a "how-to" section,
1695you should also read about the main classes that you will be working with. The
1696<a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
1697and descriptions of the main classes that you should know about.</p>
1698
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1699<!-- NOTE: this section should be heavy on example code -->
1700<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1701<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1702 <a name="inspection">Basic Inspection and Traversal Routines</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1703</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1704
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1705<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1706
1707<p>The LLVM compiler infrastructure have many different data structures that may
1708be traversed. Following the example of the C++ standard template library, the
1709techniques used to traverse these various data structures are all basically the
1710same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
1711method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
1712function returns an iterator pointing to one past the last valid element of the
1713sequence, and there is some <tt>XXXiterator</tt> data type that is common
1714between the two operations.</p>
1715
1716<p>Because the pattern for iteration is common across many different aspects of
1717the program representation, the standard template library algorithms may be used
1718on them, and it is easier to remember how to iterate. First we show a few common
1719examples of the data structures that need to be traversed. Other data
1720structures are traversed in very similar ways.</p>
1721
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1722<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1723<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1724 <a name="iterate_function">Iterating over the </a><a
1725 href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
1726 href="#Function"><tt>Function</tt></a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1727</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1728
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1729<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1730
1731<p>It's quite common to have a <tt>Function</tt> instance that you'd like to
1732transform in some way; in particular, you'd like to manipulate its
1733<tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
1734the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
1735an example that prints the name of a <tt>BasicBlock</tt> and the number of
1736<tt>Instruction</tt>s it contains:</p>
1737
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1738<div class="doc_code">
1739<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1740// <i>func is a pointer to a Function instance</i>
1741for (Function::iterator i = func-&gt;begin(), e = func-&gt;end(); i != e; ++i)
1742 // <i>Print out the name of the basic block if it has one, and then the</i>
1743 // <i>number of instructions that it contains</i>
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1744 errs() &lt;&lt; "Basic block (name=" &lt;&lt; i-&gt;getName() &lt;&lt; ") has "
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1745 &lt;&lt; i-&gt;size() &lt;&lt; " instructions.\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1746</pre>
1747</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1748
1749<p>Note that i can be used as if it were a pointer for the purposes of
Joel Stanley9b96c442002-09-06 21:55:13 +0000[diff] [blame]1750invoking member functions of the <tt>Instruction</tt> class. This is
1751because the indirection operator is overloaded for the iterator
Chris Lattner7496ec52003-08-05 22:54:23 +0000[diff] [blame]1752classes. In the above code, the expression <tt>i-&gt;size()</tt> is
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1753exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
1754
1755</div>
1756
1757<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1758<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1759 <a name="iterate_basicblock">Iterating over the </a><a
1760 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1761 href="#BasicBlock"><tt>BasicBlock</tt></a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1762</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1763
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1764<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1765
1766<p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
1767easy to iterate over the individual instructions that make up
1768<tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
1769a <tt>BasicBlock</tt>:</p>
1770
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1771<div class="doc_code">
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1772<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1773// <i>blk is a pointer to a BasicBlock instance</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1774for (BasicBlock::iterator i = blk-&gt;begin(), e = blk-&gt;end(); i != e; ++i)
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1775 // <i>The next statement works since operator&lt;&lt;(ostream&amp;,...)</i>
1776 // <i>is overloaded for Instruction&amp;</i>
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1777 errs() &lt;&lt; *i &lt;&lt; "\n";
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1778</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1779</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1780
1781<p>However, this isn't really the best way to print out the contents of a
1782<tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
1783anything you'll care about, you could have just invoked the print routine on the
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1784basic block itself: <tt>errs() &lt;&lt; *blk &lt;&lt; "\n";</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1785
1786</div>
1787
1788<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1789<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1790 <a name="iterate_institer">Iterating over the </a><a
1791 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1792 href="#Function"><tt>Function</tt></a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1793</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1794
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1795<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1796
1797<p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
1798<tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
1799<tt>InstIterator</tt> should be used instead. You'll need to include <a
1800href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
1801and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1802small example that shows how to dump all instructions in a function to the standard error stream:<p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1803
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1804<div class="doc_code">
1805<pre>
1806#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"
1807
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1808// <i>F is a pointer to a Function instance</i>
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1809for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1810 errs() &lt;&lt; *I &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1811</pre>
1812</div>
1813
1814<p>Easy, isn't it? You can also use <tt>InstIterator</tt>s to fill a
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1815work list with its initial contents. For example, if you wanted to
1816initialize a work list to contain all instructions in a <tt>Function</tt>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1817F, all you would need to do is something like:</p>
1818
1819<div class="doc_code">
1820<pre>
1821std::set&lt;Instruction*&gt; worklist;
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1822// or better yet, SmallPtrSet&lt;Instruction*, 64&gt; worklist;
1823
1824for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
1825 worklist.insert(&amp;*I);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1826</pre>
1827</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1828
1829<p>The STL set <tt>worklist</tt> would now contain all instructions in the
1830<tt>Function</tt> pointed to by F.</p>
1831
1832</div>
1833
1834<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1835<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1836 <a name="iterate_convert">Turning an iterator into a class pointer (and
1837 vice-versa)</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1838</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1839
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1840<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1841
1842<p>Sometimes, it'll be useful to grab a reference (or pointer) to a class
Joel Stanley9b96c442002-09-06 21:55:13 +0000[diff] [blame]1843instance when all you've got at hand is an iterator. Well, extracting
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1844a reference or a pointer from an iterator is very straight-forward.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1845Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1846is a <tt>BasicBlock::const_iterator</tt>:</p>
1847
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1848<div class="doc_code">
1849<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1850Instruction&amp; inst = *i; // <i>Grab reference to instruction reference</i>
1851Instruction* pinst = &amp;*i; // <i>Grab pointer to instruction reference</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1852const Instruction&amp; inst = *j;
1853</pre>
1854</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1855
1856<p>However, the iterators you'll be working with in the LLVM framework are
1857special: they will automatically convert to a ptr-to-instance type whenever they
1858need to. Instead of dereferencing the iterator and then taking the address of
1859the result, you can simply assign the iterator to the proper pointer type and
1860you get the dereference and address-of operation as a result of the assignment
1861(behind the scenes, this is a result of overloading casting mechanisms). Thus
1862the last line of the last example,</p>
1863
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1864<div class="doc_code">
1865<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1866Instruction *pinst = &amp;*i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1867</pre>
1868</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1869
1870<p>is semantically equivalent to</p>
1871
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1872<div class="doc_code">
1873<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1874Instruction *pinst = i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1875</pre>
1876</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1877
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1878<p>It's also possible to turn a class pointer into the corresponding iterator,
1879and this is a constant time operation (very efficient). The following code
1880snippet illustrates use of the conversion constructors provided by LLVM
1881iterators. By using these, you can explicitly grab the iterator of something
1882without actually obtaining it via iteration over some structure:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1883
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1884<div class="doc_code">
1885<pre>
1886void printNextInstruction(Instruction* inst) {
1887 BasicBlock::iterator it(inst);
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1888 ++it; // <i>After this line, it refers to the instruction after *inst</i>
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1889 if (it != inst-&gt;getParent()-&gt;end()) errs() &lt;&lt; *it &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1890}
1891</pre>
1892</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1893
Dan Gohman525bf8e2010-03-26 19:39:05 +0000[diff] [blame]1894<p>Unfortunately, these implicit conversions come at a cost; they prevent
1895these iterators from conforming to standard iterator conventions, and thus
Dan Gohman0d91c112010-03-26 19:51:14 +0000[diff] [blame]1896from being usable with standard algorithms and containers. For example, they
1897prevent the following code, where <tt>B</tt> is a <tt>BasicBlock</tt>,
Dan Gohman525bf8e2010-03-26 19:39:05 +0000[diff] [blame]1898from compiling:</p>
1899
1900<div class="doc_code">
1901<pre>
1902 llvm::SmallVector&lt;llvm::Instruction *, 16&gt;(B-&gt;begin(), B-&gt;end());
1903</pre>
1904</div>
1905
1906<p>Because of this, these implicit conversions may be removed some day,
Dan Gohman0d91c112010-03-26 19:51:14 +0000[diff] [blame]1907and <tt>operator*</tt> changed to return a pointer instead of a reference.</p>
Dan Gohman525bf8e2010-03-26 19:39:05 +0000[diff] [blame]1908
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1909</div>
1910
1911<!--_______________________________________________________________________-->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1912<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1913 <a name="iterate_complex">Finding call sites: a slightly more complex
1914 example</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1915</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1916
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1917<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1918
1919<p>Say that you're writing a FunctionPass and would like to count all the
1920locations in the entire module (that is, across every <tt>Function</tt>) where a
1921certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
1922learn later, you may want to use an <tt>InstVisitor</tt> to accomplish this in a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1923much more straight-forward manner, but this example will allow us to explore how
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1924you'd do it if you didn't have <tt>InstVisitor</tt> around. In pseudo-code, this
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1925is what we want to do:</p>
1926
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1927<div class="doc_code">
1928<pre>
1929initialize callCounter to zero
1930for each Function f in the Module
1931 for each BasicBlock b in f
1932 for each Instruction i in b
1933 if (i is a CallInst and calls the given function)
1934 increment callCounter
1935</pre>
1936</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1937
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1938<p>And the actual code is (remember, because we're writing a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1939<tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1940override the <tt>runOnFunction</tt> method):</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1941
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1942<div class="doc_code">
1943<pre>
1944Function* targetFunc = ...;
1945
1946class OurFunctionPass : public FunctionPass {
1947 public:
1948 OurFunctionPass(): callCounter(0) { }
1949
1950 virtual runOnFunction(Function&amp; F) {
1951 for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
Eric Christopher203e71d2008-11-08 08:20:49 +0000[diff] [blame]1952 for (BasicBlock::iterator i = b-&gt;begin(), ie = b-&gt;end(); i != ie; ++i) {
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1953 if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a>&lt;<a
1954 href="#CallInst">CallInst</a>&gt;(&amp;*i)) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1955 // <i>We know we've encountered a call instruction, so we</i>
1956 // <i>need to determine if it's a call to the</i>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1957 // <i>function pointed to by m_func or not.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1958 if (callInst-&gt;getCalledFunction() == targetFunc)
1959 ++callCounter;
1960 }
1961 }
1962 }
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1963 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1964
1965 private:
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1966 unsigned callCounter;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1967};
1968</pre>
1969</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1970
1971</div>
1972
Brian Gaekef1972c62003-11-07 19:25:45 +0000[diff] [blame]1973<!--_______________________________________________________________________-->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1974<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1975 <a name="calls_and_invokes">Treating calls and invokes the same way</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1976</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1977
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1978<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1979
1980<p>You may have noticed that the previous example was a bit oversimplified in
1981that it did not deal with call sites generated by 'invoke' instructions. In
1982this, and in other situations, you may find that you want to treat
1983<tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
1984most-specific common base class is <tt>Instruction</tt>, which includes lots of
1985less closely-related things. For these cases, LLVM provides a handy wrapper
1986class called <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1987href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1988It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
1989methods that provide functionality common to <tt>CallInst</tt>s and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1990<tt>InvokeInst</tt>s.</p>
1991
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1992<p>This class has "value semantics": it should be passed by value, not by
1993reference and it should not be dynamically allocated or deallocated using
1994<tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
1995assignable and constructable, with costs equivalents to that of a bare pointer.
1996If you look at its definition, it has only a single pointer member.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1997
1998</div>
1999
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]2000<!--_______________________________________________________________________-->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2001<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2002 <a name="iterate_chains">Iterating over def-use &amp; use-def chains</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2003</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2004
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2005<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2006
2007<p>Frequently, we might have an instance of the <a
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]2008href="/doxygen/classllvm_1_1Value.html">Value Class</a> and we want to
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2009determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
2010<tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
2011For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
2012particular function <tt>foo</tt>. Finding all of the instructions that
2013<i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
2014of <tt>F</tt>:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2015
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2016<div class="doc_code">
2017<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2018Function *F = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2019
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2020for (Value::use_iterator i = F-&gt;use_begin(), e = F-&gt;use_end(); i != e; ++i)
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2021 if (Instruction *Inst = dyn_cast&lt;Instruction&gt;(*i)) {
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]2022 errs() &lt;&lt; "F is used in instruction:\n";
2023 errs() &lt;&lt; *Inst &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2024 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2025</pre>
Gabor Greif394fdfb2010-03-26 19:35:48 +0000[diff] [blame]2026</div>
2027
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]2028<p>Note that dereferencing a <tt>Value::use_iterator</tt> is not a very cheap
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]2029operation. Instead of performing <tt>*i</tt> above several times, consider
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]2030doing it only once in the loop body and reusing its result.</p>
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]2031
Gabor Greif6091ff32010-03-26 19:04:42 +0000[diff] [blame]2032<p>Alternatively, it's common to have an instance of the <a
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2033href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2034<tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
2035<tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
2036<tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
2037all of the values that a particular instruction uses (that is, the operands of
2038the particular <tt>Instruction</tt>):</p>
2039
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2040<div class="doc_code">
2041<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2042Instruction *pi = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2043
2044for (User::op_iterator i = pi-&gt;op_begin(), e = pi-&gt;op_end(); i != e; ++i) {
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2045 Value *v = *i;
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2046 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2047}
2048</pre>
2049</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2050
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]2051<p>Declaring objects as <tt>const</tt> is an important tool of enforcing
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]2052mutation free algorithms (such as analyses, etc.). For this purpose above
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]2053iterators come in constant flavors as <tt>Value::const_use_iterator</tt>
2054and <tt>Value::const_op_iterator</tt>. They automatically arise when
2055calling <tt>use/op_begin()</tt> on <tt>const Value*</tt>s or
2056<tt>const User*</tt>s respectively. Upon dereferencing, they return
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]2057<tt>const Use*</tt>s. Otherwise the above patterns remain unchanged.</p>
2058
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2059</div>
2060
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2061<!--_______________________________________________________________________-->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2062<h4>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2063 <a name="iterate_preds">Iterating over predecessors &amp;
2064successors of blocks</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2065</h4>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2066
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2067<div>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2068
2069<p>Iterating over the predecessors and successors of a block is quite easy
2070with the routines defined in <tt>"llvm/Support/CFG.h"</tt>. Just use code like
2071this to iterate over all predecessors of BB:</p>
2072
2073<div class="doc_code">
2074<pre>
2075#include "llvm/Support/CFG.h"
2076BasicBlock *BB = ...;
2077
2078for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2079 BasicBlock *Pred = *PI;
2080 // <i>...</i>
2081}
2082</pre>
2083</div>
2084
2085<p>Similarly, to iterate over successors use
2086succ_iterator/succ_begin/succ_end.</p>
2087
2088</div>
2089
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2090</div>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2091
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2092<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2093<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2094 <a name="simplechanges">Making simple changes</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2095</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2096
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2097<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2098
2099<p>There are some primitive transformation operations present in the LLVM
Joel Stanley753eb712002-09-11 22:32:24 +0000[diff] [blame]2100infrastructure that are worth knowing about. When performing
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2101transformations, it's fairly common to manipulate the contents of basic
2102blocks. This section describes some of the common methods for doing so
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2103and gives example code.</p>
2104
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2105<!--_______________________________________________________________________-->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2106<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2107 <a name="schanges_creating">Creating and inserting new
2108 <tt>Instruction</tt>s</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2109</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2110
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2111<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2112
2113<p><i>Instantiating Instructions</i></p>
2114
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]2115<p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2116constructor for the kind of instruction to instantiate and provide the necessary
2117parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
2118(const-ptr-to) <tt>Type</tt>. Thus:</p>
2119
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2120<div class="doc_code">
2121<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2122AllocaInst* ai = new AllocaInst(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2123</pre>
2124</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2125
2126<p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2127one integer in the current stack frame, at run time. Each <tt>Instruction</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2128subclass is likely to have varying default parameters which change the semantics
2129of the instruction, so refer to the <a
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]2130href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2131Instruction</a> that you're interested in instantiating.</p>
2132
2133<p><i>Naming values</i></p>
2134
2135<p>It is very useful to name the values of instructions when you're able to, as
2136this facilitates the debugging of your transformations. If you end up looking
2137at generated LLVM machine code, you definitely want to have logical names
2138associated with the results of instructions! By supplying a value for the
2139<tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
2140associate a logical name with the result of the instruction's execution at
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2141run time. For example, say that I'm writing a transformation that dynamically
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2142allocates space for an integer on the stack, and that integer is going to be
2143used as some kind of index by some other code. To accomplish this, I place an
2144<tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
2145<tt>Function</tt>, and I'm intending to use it within the same
2146<tt>Function</tt>. I might do:</p>
2147
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2148<div class="doc_code">
2149<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2150AllocaInst* pa = new AllocaInst(Type::Int32Ty, 0, "indexLoc");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2151</pre>
2152</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2153
2154<p>where <tt>indexLoc</tt> is now the logical name of the instruction's
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2155execution value, which is a pointer to an integer on the run time stack.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2156
2157<p><i>Inserting instructions</i></p>
2158
2159<p>There are essentially two ways to insert an <tt>Instruction</tt>
2160into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
2161
Joel Stanley9dd1ad62002-09-18 03:17:23 +0000[diff] [blame]2162<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2163 <li>Insertion into an explicit instruction list
2164
2165 <p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
2166 <tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
2167 before <tt>*pi</tt>, we do the following: </p>
2168
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2169<div class="doc_code">
2170<pre>
2171BasicBlock *pb = ...;
2172Instruction *pi = ...;
2173Instruction *newInst = new Instruction(...);
2174
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2175pb-&gt;getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2176</pre>
2177</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2178
2179 <p>Appending to the end of a <tt>BasicBlock</tt> is so common that
2180 the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
2181 classes provide constructors which take a pointer to a
2182 <tt>BasicBlock</tt> to be appended to. For example code that
2183 looked like: </p>
2184
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2185<div class="doc_code">
2186<pre>
2187BasicBlock *pb = ...;
2188Instruction *newInst = new Instruction(...);
2189
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2190pb-&gt;getInstList().push_back(newInst); // <i>Appends newInst to pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2191</pre>
2192</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2193
2194 <p>becomes: </p>
2195
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2196<div class="doc_code">
2197<pre>
2198BasicBlock *pb = ...;
2199Instruction *newInst = new Instruction(..., pb);
2200</pre>
2201</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2202
2203 <p>which is much cleaner, especially if you are creating
2204 long instruction streams.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2205
2206 <li>Insertion into an implicit instruction list
2207
2208 <p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
2209 are implicitly associated with an existing instruction list: the instruction
2210 list of the enclosing basic block. Thus, we could have accomplished the same
2211 thing as the above code without being given a <tt>BasicBlock</tt> by doing:
2212 </p>
2213
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2214<div class="doc_code">
2215<pre>
2216Instruction *pi = ...;
2217Instruction *newInst = new Instruction(...);
2218
2219pi-&gt;getParent()-&gt;getInstList().insert(pi, newInst);
2220</pre>
2221</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2222
2223 <p>In fact, this sequence of steps occurs so frequently that the
2224 <tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
2225 constructors which take (as a default parameter) a pointer to an
2226 <tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
2227 precede. That is, <tt>Instruction</tt> constructors are capable of
2228 inserting the newly-created instance into the <tt>BasicBlock</tt> of a
2229 provided instruction, immediately before that instruction. Using an
2230 <tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
2231 parameter, the above code becomes:</p>
2232
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2233<div class="doc_code">
2234<pre>
2235Instruction* pi = ...;
2236Instruction* newInst = new Instruction(..., pi);
2237</pre>
2238</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2239
2240 <p>which is much cleaner, especially if you're creating a lot of
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2241 instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2242</ul>
2243
2244</div>
2245
2246<!--_______________________________________________________________________-->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2247<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2248 <a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2249</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2250
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2251<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2252
2253<p>Deleting an instruction from an existing sequence of instructions that form a
Chris Lattner49e0ccf2011-03-24 16:13:31 +0000[diff] [blame]2254<a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward: just
2255call the instruction's eraseFromParent() method. For example:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2256
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2257<div class="doc_code">
2258<pre>
2259<a href="#Instruction">Instruction</a> *I = .. ;
Chris Lattner9f8ec252008-02-15 22:57:17 +0000[diff] [blame]2260I-&gt;eraseFromParent();
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2261</pre>
2262</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2263
Chris Lattner49e0ccf2011-03-24 16:13:31 +0000[diff] [blame]2264<p>This unlinks the instruction from its containing basic block and deletes
2265it. If you'd just like to unlink the instruction from its containing basic
2266block but not delete it, you can use the <tt>removeFromParent()</tt> method.</p>
2267
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2268</div>
2269
2270<!--_______________________________________________________________________-->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2271<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2272 <a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
2273 <tt>Value</tt></a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2274</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2275
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2276<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2277
2278<p><i>Replacing individual instructions</i></p>
2279
2280<p>Including "<a href="/doxygen/BasicBlockUtils_8h-source.html">llvm/Transforms/Utils/BasicBlockUtils.h</a>"
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2281permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2282and <tt>ReplaceInstWithInst</tt>.</p>
2283
NAKAMURA Takumi06c6d9a2011-04-18 01:17:51 +0000[diff] [blame]2284<h5><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h5>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2285
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2286<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2287 <li><tt>ReplaceInstWithValue</tt>
2288
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]2289 <p>This function replaces all uses of a given instruction with a value,
2290 and then removes the original instruction. The following example
2291 illustrates the replacement of the result of a particular
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]2292 <tt>AllocaInst</tt> that allocates memory for a single integer with a null
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2293 pointer to an integer.</p>
2294
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2295<div class="doc_code">
2296<pre>
2297AllocaInst* instToReplace = ...;
2298BasicBlock::iterator ii(instToReplace);
2299
2300ReplaceInstWithValue(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]2301 Constant::getNullValue(PointerType::getUnqual(Type::Int32Ty)));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2302</pre></div></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2303
2304 <li><tt>ReplaceInstWithInst</tt>
2305
2306 <p>This function replaces a particular instruction with another
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]2307 instruction, inserting the new instruction into the basic block at the
2308 location where the old instruction was, and replacing any uses of the old
2309 instruction with the new instruction. The following example illustrates
2310 the replacement of one <tt>AllocaInst</tt> with another.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2311
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2312<div class="doc_code">
2313<pre>
2314AllocaInst* instToReplace = ...;
2315BasicBlock::iterator ii(instToReplace);
2316
2317ReplaceInstWithInst(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2318 new AllocaInst(Type::Int32Ty, 0, "ptrToReplacedInt"));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2319</pre></div></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2320</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2321
2322<p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
2323
2324<p>You can use <tt>Value::replaceAllUsesWith</tt> and
2325<tt>User::replaceUsesOfWith</tt> to change more than one use at a time. See the
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]2326doxygen documentation for the <a href="/doxygen/classllvm_1_1Value.html">Value Class</a>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2327and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2328information.</p>
2329
2330<!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
2331include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
2332ReplaceInstWithValue, ReplaceInstWithInst -->
2333
2334</div>
2335
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2336<!--_______________________________________________________________________-->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2337<h4>
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2338 <a name="schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2339</h4>
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2340
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2341<div>
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2342
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2343<p>Deleting a global variable from a module is just as easy as deleting an
2344Instruction. First, you must have a pointer to the global variable that you wish
2345 to delete. You use this pointer to erase it from its parent, the module.
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2346 For example:</p>
2347
2348<div class="doc_code">
2349<pre>
2350<a href="#GlobalVariable">GlobalVariable</a> *GV = .. ;
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2351
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2352GV-&gt;eraseFromParent();
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2353</pre>
2354</div>
2355
2356</div>
2357
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2358</div>
2359
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2360<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2361<h3>
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2362 <a name="create_types">How to Create Types</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2363</h3>
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2364
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2365<div>
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2366
2367<p>In generating IR, you may need some complex types. If you know these types
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2368statically, you can use <tt>TypeBuilder&lt;...&gt;::get()</tt>, defined
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2369in <tt>llvm/Support/TypeBuilder.h</tt>, to retrieve them. <tt>TypeBuilder</tt>
2370has two forms depending on whether you're building types for cross-compilation
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2371or native library use. <tt>TypeBuilder&lt;T, true&gt;</tt> requires
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2372that <tt>T</tt> be independent of the host environment, meaning that it's built
2373out of types from
2374the <a href="/doxygen/namespacellvm_1_1types.html"><tt>llvm::types</tt></a>
2375namespace and pointers, functions, arrays, etc. built of
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2376those. <tt>TypeBuilder&lt;T, false&gt;</tt> additionally allows native C types
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2377whose size may depend on the host compiler. For example,</p>
2378
2379<div class="doc_code">
2380<pre>
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2381FunctionType *ft = TypeBuilder&lt;types::i&lt;8&gt;(types::i&lt;32&gt;*), true&gt;::get();
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2382</pre>
2383</div>
2384
2385<p>is easier to read and write than the equivalent</p>
2386
2387<div class="doc_code">
2388<pre>
Owen Anderson5e8c50e2009-06-16 17:40:28 +0000[diff] [blame]2389std::vector&lt;const Type*&gt; params;
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2390params.push_back(PointerType::getUnqual(Type::Int32Ty));
2391FunctionType *ft = FunctionType::get(Type::Int8Ty, params, false);
2392</pre>
2393</div>
2394
2395<p>See the <a href="/doxygen/TypeBuilder_8h-source.html#l00001">class
2396comment</a> for more details.</p>
2397
2398</div>
2399
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2400</div>
2401
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2402<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2403<h2>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2404 <a name="threading">Threads and LLVM</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2405</h2>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2406<!-- *********************************************************************** -->
2407
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2408<div>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2409<p>
2410This section describes the interaction of the LLVM APIs with multithreading,
2411both on the part of client applications, and in the JIT, in the hosted
2412application.
2413</p>
2414
2415<p>
2416Note that LLVM's support for multithreading is still relatively young. Up
2417through version 2.5, the execution of threaded hosted applications was
2418supported, but not threaded client access to the APIs. While this use case is
2419now supported, clients <em>must</em> adhere to the guidelines specified below to
2420ensure proper operation in multithreaded mode.
2421</p>
2422
2423<p>
2424Note that, on Unix-like platforms, LLVM requires the presence of GCC's atomic
2425intrinsics in order to support threaded operation. If you need a
2426multhreading-capable LLVM on a platform without a suitably modern system
2427compiler, consider compiling LLVM and LLVM-GCC in single-threaded mode, and
2428using the resultant compiler to build a copy of LLVM with multithreading
2429support.
2430</p>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2431
2432<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2433<h3>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2434 <a name="startmultithreaded">Entering and Exiting Multithreaded Mode</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2435</h3>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2436
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2437<div>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2438
2439<p>
2440In order to properly protect its internal data structures while avoiding
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2441excessive locking overhead in the single-threaded case, the LLVM must intialize
2442certain data structures necessary to provide guards around its internals. To do
2443so, the client program must invoke <tt>llvm_start_multithreaded()</tt> before
2444making any concurrent LLVM API calls. To subsequently tear down these
2445structures, use the <tt>llvm_stop_multithreaded()</tt> call. You can also use
2446the <tt>llvm_is_multithreaded()</tt> call to check the status of multithreaded
2447mode.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2448</p>
2449
2450<p>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2451Note that both of these calls must be made <em>in isolation</em>. That is to
2452say that no other LLVM API calls may be executing at any time during the
2453execution of <tt>llvm_start_multithreaded()</tt> or <tt>llvm_stop_multithreaded
2454</tt>. It's is the client's responsibility to enforce this isolation.
2455</p>
2456
2457<p>
2458The return value of <tt>llvm_start_multithreaded()</tt> indicates the success or
2459failure of the initialization. Failure typically indicates that your copy of
2460LLVM was built without multithreading support, typically because GCC atomic
2461intrinsics were not found in your system compiler. In this case, the LLVM API
2462will not be safe for concurrent calls. However, it <em>will</em> be safe for
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]2463hosting threaded applications in the JIT, though <a href="#jitthreading">care
2464must be taken</a> to ensure that side exits and the like do not accidentally
2465result in concurrent LLVM API calls.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2466</p>
2467</div>
2468
2469<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2470<h3>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2471 <a name="shutdown">Ending Execution with <tt>llvm_shutdown()</tt></a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2472</h3>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2473
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2474<div>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2475<p>
2476When you are done using the LLVM APIs, you should call <tt>llvm_shutdown()</tt>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2477to deallocate memory used for internal structures. This will also invoke
2478<tt>llvm_stop_multithreaded()</tt> if LLVM is operating in multithreaded mode.
2479As such, <tt>llvm_shutdown()</tt> requires the same isolation guarantees as
2480<tt>llvm_stop_multithreaded()</tt>.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2481</p>
2482
2483<p>
2484Note that, if you use scope-based shutdown, you can use the
2485<tt>llvm_shutdown_obj</tt> class, which calls <tt>llvm_shutdown()</tt> in its
2486destructor.
2487</div>
2488
2489<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2490<h3>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2491 <a name="managedstatic">Lazy Initialization with <tt>ManagedStatic</tt></a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2492</h3>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2493
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2494<div>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2495<p>
2496<tt>ManagedStatic</tt> is a utility class in LLVM used to implement static
2497initialization of static resources, such as the global type tables. Before the
2498invocation of <tt>llvm_shutdown()</tt>, it implements a simple lazy
2499initialization scheme. Once <tt>llvm_start_multithreaded()</tt> returns,
2500however, it uses double-checked locking to implement thread-safe lazy
2501initialization.
2502</p>
2503
2504<p>
2505Note that, because no other threads are allowed to issue LLVM API calls before
2506<tt>llvm_start_multithreaded()</tt> returns, it is possible to have
2507<tt>ManagedStatic</tt>s of <tt>llvm::sys::Mutex</tt>s.
2508</p>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2509
2510<p>
2511The <tt>llvm_acquire_global_lock()</tt> and <tt>llvm_release_global_lock</tt>
2512APIs provide access to the global lock used to implement the double-checked
2513locking for lazy initialization. These should only be used internally to LLVM,
2514and only if you know what you're doing!
2515</p>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2516</div>
2517
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]2518<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2519<h3>
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]2520 <a name="llvmcontext">Achieving Isolation with <tt>LLVMContext</tt></a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2521</h3>
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]2522
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2523<div>
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]2524<p>
2525<tt>LLVMContext</tt> is an opaque class in the LLVM API which clients can use
2526to operate multiple, isolated instances of LLVM concurrently within the same
2527address space. For instance, in a hypothetical compile-server, the compilation
2528of an individual translation unit is conceptually independent from all the
2529others, and it would be desirable to be able to compile incoming translation
2530units concurrently on independent server threads. Fortunately,
2531<tt>LLVMContext</tt> exists to enable just this kind of scenario!
2532</p>
2533
2534<p>
2535Conceptually, <tt>LLVMContext</tt> provides isolation. Every LLVM entity
2536(<tt>Module</tt>s, <tt>Value</tt>s, <tt>Type</tt>s, <tt>Constant</tt>s, etc.)
Chris Lattner38eee3c2009-08-20 03:10:14 +0000[diff] [blame]2537in LLVM's in-memory IR belongs to an <tt>LLVMContext</tt>. Entities in
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]2538different contexts <em>cannot</em> interact with each other: <tt>Module</tt>s in
2539different contexts cannot be linked together, <tt>Function</tt>s cannot be added
2540to <tt>Module</tt>s in different contexts, etc. What this means is that is is
2541safe to compile on multiple threads simultaneously, as long as no two threads
2542operate on entities within the same context.
2543</p>
2544
2545<p>
2546In practice, very few places in the API require the explicit specification of a
2547<tt>LLVMContext</tt>, other than the <tt>Type</tt> creation/lookup APIs.
2548Because every <tt>Type</tt> carries a reference to its owning context, most
2549other entities can determine what context they belong to by looking at their
2550own <tt>Type</tt>. If you are adding new entities to LLVM IR, please try to
2551maintain this interface design.
2552</p>
2553
2554<p>
2555For clients that do <em>not</em> require the benefits of isolation, LLVM
2556provides a convenience API <tt>getGlobalContext()</tt>. This returns a global,
2557lazily initialized <tt>LLVMContext</tt> that may be used in situations where
2558isolation is not a concern.
2559</p>
2560</div>
2561
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]2562<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2563<h3>
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]2564 <a name="jitthreading">Threads and the JIT</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2565</h3>
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]2566
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2567<div>
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]2568<p>
2569LLVM's "eager" JIT compiler is safe to use in threaded programs. Multiple
2570threads can call <tt>ExecutionEngine::getPointerToFunction()</tt> or
2571<tt>ExecutionEngine::runFunction()</tt> concurrently, and multiple threads can
2572run code output by the JIT concurrently. The user must still ensure that only
2573one thread accesses IR in a given <tt>LLVMContext</tt> while another thread
2574might be modifying it. One way to do that is to always hold the JIT lock while
2575accessing IR outside the JIT (the JIT <em>modifies</em> the IR by adding
2576<tt>CallbackVH</tt>s). Another way is to only
2577call <tt>getPointerToFunction()</tt> from the <tt>LLVMContext</tt>'s thread.
2578</p>
2579
2580<p>When the JIT is configured to compile lazily (using
2581<tt>ExecutionEngine::DisableLazyCompilation(false)</tt>), there is currently a
2582<a href="http://llvm.org/bugs/show_bug.cgi?id=5184">race condition</a> in
2583updating call sites after a function is lazily-jitted. It's still possible to
2584use the lazy JIT in a threaded program if you ensure that only one thread at a
2585time can call any particular lazy stub and that the JIT lock guards any IR
2586access, but we suggest using only the eager JIT in threaded programs.
2587</p>
2588</div>
2589
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2590</div>
2591
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2592<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2593<h2>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2594 <a name="advanced">Advanced Topics</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2595</h2>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2596<!-- *********************************************************************** -->
2597
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2598<div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2599<p>
2600This section describes some of the advanced or obscure API's that most clients
2601do not need to be aware of. These API's tend manage the inner workings of the
2602LLVM system, and only need to be accessed in unusual circumstances.
2603</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2604
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2605<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2606<h3>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2607 <a name="TypeResolve">LLVM Type Resolution</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2608</h3>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2609
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2610<div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2611
2612<p>
2613The LLVM type system has a very simple goal: allow clients to compare types for
2614structural equality with a simple pointer comparison (aka a shallow compare).
2615This goal makes clients much simpler and faster, and is used throughout the LLVM
2616system.
2617</p>
2618
2619<p>
2620Unfortunately achieving this goal is not a simple matter. In particular,
2621recursive types and late resolution of opaque types makes the situation very
2622difficult to handle. Fortunately, for the most part, our implementation makes
2623most clients able to be completely unaware of the nasty internal details. The
2624primary case where clients are exposed to the inner workings of it are when
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]2625building a recursive type. In addition to this case, the LLVM bitcode reader,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2626assembly parser, and linker also have to be aware of the inner workings of this
2627system.
2628</p>
2629
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2630<p>
2631For our purposes below, we need three concepts. First, an "Opaque Type" is
2632exactly as defined in the <a href="LangRef.html#t_opaque">language
2633reference</a>. Second an "Abstract Type" is any type which includes an
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2634opaque type as part of its type graph (for example "<tt>{ opaque, i32 }</tt>").
2635Third, a concrete type is a type that is not an abstract type (e.g. "<tt>{ i32,
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2636float }</tt>").
2637</p>
2638
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2639<!-- ______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2640<h4>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2641 <a name="BuildRecType">Basic Recursive Type Construction</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2642</h4>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2643
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2644<div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2645
2646<p>
2647Because the most common question is "how do I build a recursive type with LLVM",
2648we answer it now and explain it as we go. Here we include enough to cause this
2649to be emitted to an output .ll file:
2650</p>
2651
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2652<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2653<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2654%mylist = type { %mylist*, i32 }
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2655</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2656</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2657
2658<p>
2659To build this, use the following LLVM APIs:
2660</p>
2661
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2662<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2663<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2664// <i>Create the initial outer struct</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2665<a href="#PATypeHolder">PATypeHolder</a> StructTy = OpaqueType::get();
2666std::vector&lt;const Type*&gt; Elts;
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]2667Elts.push_back(PointerType::getUnqual(StructTy));
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2668Elts.push_back(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2669StructType *NewSTy = StructType::get(Elts);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2670
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2671// <i>At this point, NewSTy = "{ opaque*, i32 }". Tell VMCore that</i>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2672// <i>the struct and the opaque type are actually the same.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2673cast&lt;OpaqueType&gt;(StructTy.get())-&gt;<a href="#refineAbstractTypeTo">refineAbstractTypeTo</a>(NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2674
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2675// <i>NewSTy is potentially invalidated, but StructTy (a <a href="#PATypeHolder">PATypeHolder</a>) is</i>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2676// <i>kept up-to-date</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2677NewSTy = cast&lt;StructType&gt;(StructTy.get());
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2678
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2679// <i>Add a name for the type to the module symbol table (optional)</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2680MyModule-&gt;addTypeName("mylist", NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2681</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2682</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2683
2684<p>
2685This code shows the basic approach used to build recursive types: build a
2686non-recursive type using 'opaque', then use type unification to close the cycle.
2687The type unification step is performed by the <tt><a
Chris Lattneraff26d12007-02-03 03:06:52 +0000[diff] [blame]2688href="#refineAbstractTypeTo">refineAbstractTypeTo</a></tt> method, which is
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2689described next. After that, we describe the <a
2690href="#PATypeHolder">PATypeHolder class</a>.
2691</p>
2692
2693</div>
2694
2695<!-- ______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2696<h4>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2697 <a name="refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2698</h4>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2699
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2700<div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2701<p>
2702The <tt>refineAbstractTypeTo</tt> method starts the type unification process.
2703While this method is actually a member of the DerivedType class, it is most
2704often used on OpaqueType instances. Type unification is actually a recursive
2705process. After unification, types can become structurally isomorphic to
2706existing types, and all duplicates are deleted (to preserve pointer equality).
2707</p>
2708
2709<p>
2710In the example above, the OpaqueType object is definitely deleted.
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2711Additionally, if there is an "{ \2*, i32}" type already created in the system,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2712the pointer and struct type created are <b>also</b> deleted. Obviously whenever
2713a type is deleted, any "Type*" pointers in the program are invalidated. As
2714such, it is safest to avoid having <i>any</i> "Type*" pointers to abstract types
2715live across a call to <tt>refineAbstractTypeTo</tt> (note that non-abstract
2716types can never move or be deleted). To deal with this, the <a
2717href="#PATypeHolder">PATypeHolder</a> class is used to maintain a stable
2718reference to a possibly refined type, and the <a
2719href="#AbstractTypeUser">AbstractTypeUser</a> class is used to update more
2720complex datastructures.
2721</p>
2722
2723</div>
2724
2725<!-- ______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2726<h4>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2727 <a name="PATypeHolder">The PATypeHolder Class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2728</h4>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2729
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2730<div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2731<p>
2732PATypeHolder is a form of a "smart pointer" for Type objects. When VMCore
2733happily goes about nuking types that become isomorphic to existing types, it
2734automatically updates all PATypeHolder objects to point to the new type. In the
2735example above, this allows the code to maintain a pointer to the resultant
2736resolved recursive type, even though the Type*'s are potentially invalidated.
2737</p>
2738
2739<p>
2740PATypeHolder is an extremely light-weight object that uses a lazy union-find
2741implementation to update pointers. For example the pointer from a Value to its
2742Type is maintained by PATypeHolder objects.
2743</p>
2744
2745</div>
2746
2747<!-- ______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2748<h4>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2749 <a name="AbstractTypeUser">The AbstractTypeUser Class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2750</h4>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2751
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2752<div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2753
2754<p>
2755Some data structures need more to perform more complex updates when types get
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2756resolved. To support this, a class can derive from the AbstractTypeUser class.
2757This class
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2758allows it to get callbacks when certain types are resolved. To register to get
2759callbacks for a particular type, the DerivedType::{add/remove}AbstractTypeUser
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2760methods can be called on a type. Note that these methods only work for <i>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2761 abstract</i> types. Concrete types (those that do not include any opaque
2762objects) can never be refined.
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2763</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2764</div>
2765
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2766</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2767
2768<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2769<h3>
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2770 <a name="SymbolTable">The <tt>ValueSymbolTable</tt> and
2771 <tt>TypeSymbolTable</tt> classes</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2772</h3>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2773
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2774<div>
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2775<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1ValueSymbolTable.html">
2776ValueSymbolTable</a></tt> class provides a symbol table that the <a
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2777href="#Function"><tt>Function</tt></a> and <a href="#Module">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2778<tt>Module</tt></a> classes use for naming value definitions. The symbol table
2779can provide a name for any <a href="#Value"><tt>Value</tt></a>.
2780The <tt><a href="http://llvm.org/doxygen/classllvm_1_1TypeSymbolTable.html">
2781TypeSymbolTable</a></tt> class is used by the <tt>Module</tt> class to store
2782names for types.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2783
Reid Spencera6362242007-01-07 00:41:39 +0000[diff] [blame]2784<p>Note that the <tt>SymbolTable</tt> class should not be directly accessed
2785by most clients. It should only be used when iteration over the symbol table
2786names themselves are required, which is very special purpose. Note that not
2787all LLVM
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2788<tt><a href="#Value">Value</a></tt>s have names, and those without names (i.e. they have
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2789an empty name) do not exist in the symbol table.
2790</p>
2791
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2792<p>These symbol tables support iteration over the values/types in the symbol
2793table with <tt>begin/end/iterator</tt> and supports querying to see if a
2794specific name is in the symbol table (with <tt>lookup</tt>). The
2795<tt>ValueSymbolTable</tt> class exposes no public mutator methods, instead,
2796simply call <tt>setName</tt> on a value, which will autoinsert it into the
2797appropriate symbol table. For types, use the Module::addTypeName method to
2798insert entries into the symbol table.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2799
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2800</div>
2801
2802
2803
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2804<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2805<h3>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2806 <a name="UserLayout">The <tt>User</tt> and owned <tt>Use</tt> classes' memory layout</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2807</h3>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2808
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2809<div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2810<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1User.html">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2811User</a></tt> class provides a basis for expressing the ownership of <tt>User</tt>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2812towards other <tt><a href="http://llvm.org/doxygen/classllvm_1_1Value.html">
2813Value</a></tt>s. The <tt><a href="http://llvm.org/doxygen/classllvm_1_1Use.html">
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2814Use</a></tt> helper class is employed to do the bookkeeping and to facilitate <i>O(1)</i>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2815addition and removal.</p>
2816
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2817<!-- ______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2818<h4>
2819 <a name="Use2User">
2820 Interaction and relationship between <tt>User</tt> and <tt>Use</tt> objects
2821 </a>
2822</h4>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2823
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2824<div>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2825<p>
2826A subclass of <tt>User</tt> can choose between incorporating its <tt>Use</tt> objects
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2827or refer to them out-of-line by means of a pointer. A mixed variant
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2828(some <tt>Use</tt>s inline others hung off) is impractical and breaks the invariant
2829that the <tt>Use</tt> objects belonging to the same <tt>User</tt> form a contiguous array.
2830</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2831
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2832<p>
2833We have 2 different layouts in the <tt>User</tt> (sub)classes:
2834<ul>
2835<li><p>Layout a)
2836The <tt>Use</tt> object(s) are inside (resp. at fixed offset) of the <tt>User</tt>
2837object and there are a fixed number of them.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2838
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2839<li><p>Layout b)
2840The <tt>Use</tt> object(s) are referenced by a pointer to an
2841array from the <tt>User</tt> object and there may be a variable
2842number of them.</p>
2843</ul>
2844<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2845As of v2.4 each layout still possesses a direct pointer to the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2846start of the array of <tt>Use</tt>s. Though not mandatory for layout a),
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2847we stick to this redundancy for the sake of simplicity.
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2848The <tt>User</tt> object also stores the number of <tt>Use</tt> objects it
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2849has. (Theoretically this information can also be calculated
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2850given the scheme presented below.)</p>
2851<p>
2852Special forms of allocation operators (<tt>operator new</tt>)
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2853enforce the following memory layouts:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2854
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2855<ul>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2856<li><p>Layout a) is modelled by prepending the <tt>User</tt> object by the <tt>Use[]</tt> array.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2857
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2858<pre>
2859...---.---.---.---.-------...
2860 | P | P | P | P | User
2861'''---'---'---'---'-------'''
2862</pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2863
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2864<li><p>Layout b) is modelled by pointing at the <tt>Use[]</tt> array.</p>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2865<pre>
2866.-------...
2867| User
2868'-------'''
2869 |
2870 v
2871 .---.---.---.---...
2872 | P | P | P | P |
2873 '---'---'---'---'''
2874</pre>
2875</ul>
2876<i>(In the above figures '<tt>P</tt>' stands for the <tt>Use**</tt> that
2877 is stored in each <tt>Use</tt> object in the member <tt>Use::Prev</tt>)</i>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2878
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2879</div>
2880
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2881<!-- ______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2882<h4>
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2883 <a name="Waymarking">The waymarking algorithm</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2884</h4>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2885
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2886<div>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2887<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2888Since the <tt>Use</tt> objects are deprived of the direct (back)pointer to
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2889their <tt>User</tt> objects, there must be a fast and exact method to
2890recover it. This is accomplished by the following scheme:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2891
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2892A bit-encoding in the 2 LSBits (least significant bits) of the <tt>Use::Prev</tt> allows to find the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2893start of the <tt>User</tt> object:
2894<ul>
2895<li><tt>00</tt> &mdash;&gt; binary digit 0</li>
2896<li><tt>01</tt> &mdash;&gt; binary digit 1</li>
2897<li><tt>10</tt> &mdash;&gt; stop and calculate (<tt>s</tt>)</li>
2898<li><tt>11</tt> &mdash;&gt; full stop (<tt>S</tt>)</li>
2899</ul>
2900<p>
2901Given a <tt>Use*</tt>, all we have to do is to walk till we get
2902a stop and we either have a <tt>User</tt> immediately behind or
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2903we have to walk to the next stop picking up digits
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2904and calculating the offset:</p>
2905<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2906.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.----------------
2907| 1 | s | 1 | 0 | 1 | 0 | s | 1 | 1 | 0 | s | 1 | 1 | s | 1 | S | User (or User*)
2908'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'----------------
2909 |+15 |+10 |+6 |+3 |+1
2910 | | | | |__>
2911 | | | |__________>
2912 | | |______________________>
2913 | |______________________________________>
2914 |__________________________________________________________>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2915</pre>
2916<p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2917Only the significant number of bits need to be stored between the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2918stops, so that the <i>worst case is 20 memory accesses</i> when there are
29191000 <tt>Use</tt> objects associated with a <tt>User</tt>.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2920
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2921</div>
2922
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2923<!-- ______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2924<h4>
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2925 <a name="ReferenceImpl">Reference implementation</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2926</h4>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2927
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2928<div>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2929<p>
2930The following literate Haskell fragment demonstrates the concept:</p>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2931
2932<div class="doc_code">
2933<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2934> import Test.QuickCheck
2935>
2936> digits :: Int -> [Char] -> [Char]
2937> digits 0 acc = '0' : acc
2938> digits 1 acc = '1' : acc
2939> digits n acc = digits (n `div` 2) $ digits (n `mod` 2) acc
2940>
2941> dist :: Int -> [Char] -> [Char]
2942> dist 0 [] = ['S']
2943> dist 0 acc = acc
2944> dist 1 acc = let r = dist 0 acc in 's' : digits (length r) r
2945> dist n acc = dist (n - 1) $ dist 1 acc
2946>
2947> takeLast n ss = reverse $ take n $ reverse ss
2948>
2949> test = takeLast 40 $ dist 20 []
2950>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2951</pre>
2952</div>
2953<p>
2954Printing &lt;test&gt; gives: <tt>"1s100000s11010s10100s1111s1010s110s11s1S"</tt></p>
2955<p>
2956The reverse algorithm computes the length of the string just by examining
2957a certain prefix:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2958
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2959<div class="doc_code">
2960<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2961> pref :: [Char] -> Int
2962> pref "S" = 1
2963> pref ('s':'1':rest) = decode 2 1 rest
2964> pref (_:rest) = 1 + pref rest
2965>
2966> decode walk acc ('0':rest) = decode (walk + 1) (acc * 2) rest
2967> decode walk acc ('1':rest) = decode (walk + 1) (acc * 2 + 1) rest
2968> decode walk acc _ = walk + acc
2969>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2970</pre>
2971</div>
2972<p>
2973Now, as expected, printing &lt;pref test&gt; gives <tt>40</tt>.</p>
2974<p>
2975We can <i>quickCheck</i> this with following property:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2976
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2977<div class="doc_code">
2978<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2979> testcase = dist 2000 []
2980> testcaseLength = length testcase
2981>
2982> identityProp n = n > 0 && n <= testcaseLength ==> length arr == pref arr
2983> where arr = takeLast n testcase
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2984>
2985</pre>
2986</div>
2987<p>
2988As expected &lt;quickCheck identityProp&gt; gives:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2989
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2990<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2991*Main> quickCheck identityProp
2992OK, passed 100 tests.
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2993</pre>
2994<p>
2995Let's be a bit more exhaustive:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2996
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2997<div class="doc_code">
2998<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2999>
3000> deepCheck p = check (defaultConfig { configMaxTest = 500 }) p
3001>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3002</pre>
3003</div>
3004<p>
3005And here is the result of &lt;deepCheck identityProp&gt;:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3006
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3007<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3008*Main> deepCheck identityProp
3009OK, passed 500 tests.
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3010</pre>
3011
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3012</div>
3013
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3014<!-- ______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3015<h4>
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]3016 <a name="Tagging">Tagging considerations</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3017</h4>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3018
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3019<div>
3020
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3021<p>
3022To maintain the invariant that the 2 LSBits of each <tt>Use**</tt> in <tt>Use</tt>
3023never change after being set up, setters of <tt>Use::Prev</tt> must re-tag the
3024new <tt>Use**</tt> on every modification. Accordingly getters must strip the
3025tag bits.</p>
3026<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]3027For layout b) instead of the <tt>User</tt> we find a pointer (<tt>User*</tt> with LSBit set).
3028Following this pointer brings us to the <tt>User</tt>. A portable trick ensures
3029that the first bytes of <tt>User</tt> (if interpreted as a pointer) never has
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]3030the LSBit set. (Portability is relying on the fact that all known compilers place the
3031<tt>vptr</tt> in the first word of the instances.)</p>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3032
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3033</div>
3034
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3035</div>
3036
3037</div>
3038
3039<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3040<h2>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3041 <a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3042</h2>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3043<!-- *********************************************************************** -->
3044
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3045<div>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3046<p><tt>#include "<a href="/doxygen/Type_8h-source.html">llvm/Type.h</a>"</tt>
3047<br>doxygen info: <a href="/doxygen/classllvm_1_1Type.html">Type Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3048
3049<p>The Core LLVM classes are the primary means of representing the program
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3050being inspected or transformed. The core LLVM classes are defined in
3051header files in the <tt>include/llvm/</tt> directory, and implemented in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3052the <tt>lib/VMCore</tt> directory.</p>
3053
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3054<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3055<h3>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3056 <a name="Type">The <tt>Type</tt> class and Derived Types</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3057</h3>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3058
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3059<div>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3060
3061 <p><tt>Type</tt> is a superclass of all type classes. Every <tt>Value</tt> has
3062 a <tt>Type</tt>. <tt>Type</tt> cannot be instantiated directly but only
3063 through its subclasses. Certain primitive types (<tt>VoidType</tt>,
3064 <tt>LabelType</tt>, <tt>FloatType</tt> and <tt>DoubleType</tt>) have hidden
3065 subclasses. They are hidden because they offer no useful functionality beyond
3066 what the <tt>Type</tt> class offers except to distinguish themselves from
3067 other subclasses of <tt>Type</tt>.</p>
3068 <p>All other types are subclasses of <tt>DerivedType</tt>. Types can be
3069 named, but this is not a requirement. There exists exactly
3070 one instance of a given shape at any one time. This allows type equality to
3071 be performed with address equality of the Type Instance. That is, given two
3072 <tt>Type*</tt> values, the types are identical if the pointers are identical.
3073 </p>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3074
3075<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3076<h4>
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]3077 <a name="m_Type">Important Public Methods</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3078</h4>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3079
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3080<div>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3081
3082<ul>
Duncan Sandsb0bc6c32010-02-15 16:12:20 +0000[diff] [blame]3083 <li><tt>bool isIntegerTy() const</tt>: Returns true for any integer type.</li>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3084
Duncan Sandsb0bc6c32010-02-15 16:12:20 +0000[diff] [blame]3085 <li><tt>bool isFloatingPointTy()</tt>: Return true if this is one of the five
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3086 floating point types.</li>
3087
3088 <li><tt>bool isAbstract()</tt>: Return true if the type is abstract (contains
3089 an OpaqueType anywhere in its definition).</li>
3090
3091 <li><tt>bool isSized()</tt>: Return true if the type has known size. Things
3092 that don't have a size are abstract types, labels and void.</li>
3093
3094</ul>
3095</div>
3096
3097<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3098<h4>
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]3099 <a name="derivedtypes">Important Derived Types</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3100</h4>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3101<div>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3102<dl>
3103 <dt><tt>IntegerType</tt></dt>
3104 <dd>Subclass of DerivedType that represents integer types of any bit width.
3105 Any bit width between <tt>IntegerType::MIN_INT_BITS</tt> (1) and
3106 <tt>IntegerType::MAX_INT_BITS</tt> (~8 million) can be represented.
3107 <ul>
3108 <li><tt>static const IntegerType* get(unsigned NumBits)</tt>: get an integer
3109 type of a specific bit width.</li>
3110 <li><tt>unsigned getBitWidth() const</tt>: Get the bit width of an integer
3111 type.</li>
3112 </ul>
3113 </dd>
3114 <dt><tt>SequentialType</tt></dt>
3115 <dd>This is subclassed by ArrayType and PointerType
3116 <ul>
3117 <li><tt>const Type * getElementType() const</tt>: Returns the type of each
3118 of the elements in the sequential type. </li>
3119 </ul>
3120 </dd>
3121 <dt><tt>ArrayType</tt></dt>
3122 <dd>This is a subclass of SequentialType and defines the interface for array
3123 types.
3124 <ul>
3125 <li><tt>unsigned getNumElements() const</tt>: Returns the number of
3126 elements in the array. </li>
3127 </ul>
3128 </dd>
3129 <dt><tt>PointerType</tt></dt>
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]3130 <dd>Subclass of SequentialType for pointer types.</dd>
Reid Spencer9d6565a2007-02-15 02:26:10 +0000[diff] [blame]3131 <dt><tt>VectorType</tt></dt>
Reid Spencer485bad12007-02-15 03:07:05 +0000[diff] [blame]3132 <dd>Subclass of SequentialType for vector types. A
3133 vector type is similar to an ArrayType but is distinguished because it is
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3134 a first class type whereas ArrayType is not. Vector types are used for
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3135 vector operations and are usually small vectors of of an integer or floating
3136 point type.</dd>
3137 <dt><tt>StructType</tt></dt>
3138 <dd>Subclass of DerivedTypes for struct types.</dd>
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3139 <dt><tt><a name="FunctionType">FunctionType</a></tt></dt>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3140 <dd>Subclass of DerivedTypes for function types.
3141 <ul>
Dan Gohman4bb31bf2010-03-30 20:04:57 +0000[diff] [blame]3142 <li><tt>bool isVarArg() const</tt>: Returns true if it's a vararg
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3143 function</li>
3144 <li><tt> const Type * getReturnType() const</tt>: Returns the
3145 return type of the function.</li>
3146 <li><tt>const Type * getParamType (unsigned i)</tt>: Returns
3147 the type of the ith parameter.</li>
3148 <li><tt> const unsigned getNumParams() const</tt>: Returns the
3149 number of formal parameters.</li>
3150 </ul>
3151 </dd>
3152 <dt><tt>OpaqueType</tt></dt>
3153 <dd>Sublcass of DerivedType for abstract types. This class
3154 defines no content and is used as a placeholder for some other type. Note
3155 that OpaqueType is used (temporarily) during type resolution for forward
3156 references of types. Once the referenced type is resolved, the OpaqueType
3157 is replaced with the actual type. OpaqueType can also be used for data
3158 abstraction. At link time opaque types can be resolved to actual types
3159 of the same name.</dd>
3160</dl>
3161</div>
3162
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3163</div>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3164
3165<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3166<h3>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3167 <a name="Module">The <tt>Module</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3168</h3>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3169
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3170<div>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3171
3172<p><tt>#include "<a
3173href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
3174<a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
3175
3176<p>The <tt>Module</tt> class represents the top level structure present in LLVM
3177programs. An LLVM module is effectively either a translation unit of the
3178original program or a combination of several translation units merged by the
3179linker. The <tt>Module</tt> class keeps track of a list of <a
3180href="#Function"><tt>Function</tt></a>s, a list of <a
3181href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
3182href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
3183helpful member functions that try to make common operations easy.</p>
3184
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3185<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3186<h4>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3187 <a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3188</h4>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3189
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3190<div>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3191
3192<ul>
3193 <li><tt>Module::Module(std::string name = "")</tt></li>
3194</ul>
3195
3196<p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
3197provide a name for it (probably based on the name of the translation unit).</p>
3198
3199<ul>
3200 <li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
3201 <tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
3202
3203 <tt>begin()</tt>, <tt>end()</tt>
3204 <tt>size()</tt>, <tt>empty()</tt>
3205
3206 <p>These are forwarding methods that make it easy to access the contents of
3207 a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
3208 list.</p></li>
3209
3210 <li><tt>Module::FunctionListType &amp;getFunctionList()</tt>
3211
3212 <p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
3213 necessary to use when you need to update the list or perform a complex
3214 action that doesn't have a forwarding method.</p>
3215
3216 <p><!-- Global Variable --></p></li>
3217</ul>
3218
3219<hr>
3220
3221<ul>
3222 <li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>
3223
3224 <tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>
3225
3226 <tt>global_begin()</tt>, <tt>global_end()</tt>
3227 <tt>global_size()</tt>, <tt>global_empty()</tt>
3228
3229 <p> These are forwarding methods that make it easy to access the contents of
3230 a <tt>Module</tt> object's <a
3231 href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
3232
3233 <li><tt>Module::GlobalListType &amp;getGlobalList()</tt>
3234
3235 <p>Returns the list of <a
3236 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
3237 use when you need to update the list or perform a complex action that
3238 doesn't have a forwarding method.</p>
3239
3240 <p><!-- Symbol table stuff --> </p></li>
3241</ul>
3242
3243<hr>
3244
3245<ul>
3246 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
3247
3248 <p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
3249 for this <tt>Module</tt>.</p>
3250
3251 <p><!-- Convenience methods --></p></li>
3252</ul>
3253
3254<hr>
3255
3256<ul>
3257 <li><tt><a href="#Function">Function</a> *getFunction(const std::string
3258 &amp;Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
3259
3260 <p>Look up the specified function in the <tt>Module</tt> <a
3261 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
3262 <tt>null</tt>.</p></li>
3263
3264 <li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
3265 std::string &amp;Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
3266
3267 <p>Look up the specified function in the <tt>Module</tt> <a
3268 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
3269 external declaration for the function and return it.</p></li>
3270
3271 <li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
3272
3273 <p>If there is at least one entry in the <a
3274 href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
3275 href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
3276 string.</p></li>
3277
3278 <li><tt>bool addTypeName(const std::string &amp;Name, const <a
3279 href="#Type">Type</a> *Ty)</tt>
3280
3281 <p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
3282 mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
3283 name, true is returned and the <a
3284 href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
3285</ul>
3286
3287</div>
3288
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3289</div>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3290
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3291<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3292<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3293 <a name="Value">The <tt>Value</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3294</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3295
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3296<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3297
3298<p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
3299<br>
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]3300doxygen info: <a href="/doxygen/classllvm_1_1Value.html">Value Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3301
3302<p>The <tt>Value</tt> class is the most important class in the LLVM Source
3303base. It represents a typed value that may be used (among other things) as an
3304operand to an instruction. There are many different types of <tt>Value</tt>s,
3305such as <a href="#Constant"><tt>Constant</tt></a>s,<a
3306href="#Argument"><tt>Argument</tt></a>s. Even <a
3307href="#Instruction"><tt>Instruction</tt></a>s and <a
3308href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
3309
3310<p>A particular <tt>Value</tt> may be used many times in the LLVM representation
3311for a program. For example, an incoming argument to a function (represented
3312with an instance of the <a href="#Argument">Argument</a> class) is "used" by
3313every instruction in the function that references the argument. To keep track
3314of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
3315href="#User"><tt>User</tt></a>s that is using it (the <a
3316href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
3317graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
3318def-use information in the program, and is accessible through the <tt>use_</tt>*
3319methods, shown below.</p>
3320
3321<p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
3322and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
3323method. In addition, all LLVM values can be named. The "name" of the
3324<tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
3325
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3326<div class="doc_code">
3327<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]3328%<b>foo</b> = add i32 1, 2
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3329</pre>
3330</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3331
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3332<p><a name="nameWarning">The name of this instruction is "foo".</a> <b>NOTE</b>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3333that the name of any value may be missing (an empty string), so names should
3334<b>ONLY</b> be used for debugging (making the source code easier to read,
3335debugging printouts), they should not be used to keep track of values or map
3336between them. For this purpose, use a <tt>std::map</tt> of pointers to the
3337<tt>Value</tt> itself instead.</p>
3338
3339<p>One important aspect of LLVM is that there is no distinction between an SSA
3340variable and the operation that produces it. Because of this, any reference to
3341the value produced by an instruction (or the value available as an incoming
Chris Lattnerd5fc4fc2004-03-18 14:58:55 +0000[diff] [blame]3342argument, for example) is represented as a direct pointer to the instance of
3343the class that
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3344represents this value. Although this may take some getting used to, it
3345simplifies the representation and makes it easier to manipulate.</p>
3346
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3347<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3348<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3349 <a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3350</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3351
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3352<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3353
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3354<ul>
3355 <li><tt>Value::use_iterator</tt> - Typedef for iterator over the
3356use-list<br>
Gabor Greifbbbf9a22010-03-26 19:59:25 +0000[diff] [blame]3357 <tt>Value::const_use_iterator</tt> - Typedef for const_iterator over
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3358the use-list<br>
3359 <tt>unsigned use_size()</tt> - Returns the number of users of the
3360value.<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3361 <tt>bool use_empty()</tt> - Returns true if there are no users.<br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3362 <tt>use_iterator use_begin()</tt> - Get an iterator to the start of
3363the use-list.<br>
3364 <tt>use_iterator use_end()</tt> - Get an iterator to the end of the
3365use-list.<br>
3366 <tt><a href="#User">User</a> *use_back()</tt> - Returns the last
3367element in the list.
3368 <p> These methods are the interface to access the def-use
3369information in LLVM. As with all other iterators in LLVM, the naming
3370conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3371 </li>
3372 <li><tt><a href="#Type">Type</a> *getType() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3373 <p>This method returns the Type of the Value.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3374 </li>
3375 <li><tt>bool hasName() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3376 <tt>std::string getName() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3377 <tt>void setName(const std::string &amp;Name)</tt>
3378 <p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
3379be aware of the <a href="#nameWarning">precaution above</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3380 </li>
3381 <li><tt>void replaceAllUsesWith(Value *V)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3382
3383 <p>This method traverses the use list of a <tt>Value</tt> changing all <a
3384 href="#User"><tt>User</tt>s</a> of the current value to refer to
3385 "<tt>V</tt>" instead. For example, if you detect that an instruction always
3386 produces a constant value (for example through constant folding), you can
3387 replace all uses of the instruction with the constant like this:</p>
3388
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3389<div class="doc_code">
3390<pre>
3391Inst-&gt;replaceAllUsesWith(ConstVal);
3392</pre>
3393</div>
3394
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3395</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3396
3397</div>
3398
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3399</div>
3400
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3401<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3402<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3403 <a name="User">The <tt>User</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3404</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3405
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3406<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3407
3408<p>
3409<tt>#include "<a href="/doxygen/User_8h-source.html">llvm/User.h</a>"</tt><br>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]3410doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3411Superclass: <a href="#Value"><tt>Value</tt></a></p>
3412
3413<p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
3414refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
3415that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
3416referring to. The <tt>User</tt> class itself is a subclass of
3417<tt>Value</tt>.</p>
3418
3419<p>The operands of a <tt>User</tt> point directly to the LLVM <a
3420href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
3421Single Assignment (SSA) form, there can only be one definition referred to,
3422allowing this direct connection. This connection provides the use-def
3423information in LLVM.</p>
3424
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3425<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3426<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3427 <a name="m_User">Important Public Members of the <tt>User</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3428</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3429
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3430<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3431
3432<p>The <tt>User</tt> class exposes the operand list in two ways: through
3433an index access interface and through an iterator based interface.</p>
3434
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3435<ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3436 <li><tt>Value *getOperand(unsigned i)</tt><br>
3437 <tt>unsigned getNumOperands()</tt>
3438 <p> These two methods expose the operands of the <tt>User</tt> in a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3439convenient form for direct access.</p></li>
3440
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3441 <li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
3442list<br>
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3443 <tt>op_iterator op_begin()</tt> - Get an iterator to the start of
3444the operand list.<br>
3445 <tt>op_iterator op_end()</tt> - Get an iterator to the end of the
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3446operand list.
3447 <p> Together, these methods make up the iterator based interface to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3448the operands of a <tt>User</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3449</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3450
3451</div>
3452
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3453</div>
3454
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3455<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3456<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3457 <a name="Instruction">The <tt>Instruction</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3458</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3459
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3460<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3461
3462<p><tt>#include "</tt><tt><a
3463href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3464doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3465Superclasses: <a href="#User"><tt>User</tt></a>, <a
3466href="#Value"><tt>Value</tt></a></p>
3467
3468<p>The <tt>Instruction</tt> class is the common base class for all LLVM
3469instructions. It provides only a few methods, but is a very commonly used
3470class. The primary data tracked by the <tt>Instruction</tt> class itself is the
3471opcode (instruction type) and the parent <a
3472href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
3473into. To represent a specific type of instruction, one of many subclasses of
3474<tt>Instruction</tt> are used.</p>
3475
3476<p> Because the <tt>Instruction</tt> class subclasses the <a
3477href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
3478way as for other <a href="#User"><tt>User</tt></a>s (with the
3479<tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
3480<tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
3481the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
3482file contains some meta-data about the various different types of instructions
3483in LLVM. It describes the enum values that are used as opcodes (for example
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3484<tt>Instruction::Add</tt> and <tt>Instruction::ICmp</tt>), as well as the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3485concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
3486example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3487href="#CmpInst">CmpInst</a></tt>). Unfortunately, the use of macros in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3488this file confuses doxygen, so these enum values don't show up correctly in the
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3489<a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3490
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3491<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3492<h4>
3493 <a name="s_Instruction">
3494 Important Subclasses of the <tt>Instruction</tt> class
3495 </a>
3496</h4>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3497<div>
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3498 <ul>
3499 <li><tt><a name="BinaryOperator">BinaryOperator</a></tt>
3500 <p>This subclasses represents all two operand instructions whose operands
3501 must be the same type, except for the comparison instructions.</p></li>
3502 <li><tt><a name="CastInst">CastInst</a></tt>
3503 <p>This subclass is the parent of the 12 casting instructions. It provides
3504 common operations on cast instructions.</p>
3505 <li><tt><a name="CmpInst">CmpInst</a></tt>
3506 <p>This subclass respresents the two comparison instructions,
3507 <a href="LangRef.html#i_icmp">ICmpInst</a> (integer opreands), and
3508 <a href="LangRef.html#i_fcmp">FCmpInst</a> (floating point operands).</p>
3509 <li><tt><a name="TerminatorInst">TerminatorInst</a></tt>
3510 <p>This subclass is the parent of all terminator instructions (those which
3511 can terminate a block).</p>
3512 </ul>
3513 </div>
3514
3515<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3516<h4>
3517 <a name="m_Instruction">
3518 Important Public Members of the <tt>Instruction</tt> class
3519 </a>
3520</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3521
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3522<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3523
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3524<ul>
3525 <li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3526 <p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
3527this <tt>Instruction</tt> is embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3528 <li><tt>bool mayWriteToMemory()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3529 <p>Returns true if the instruction writes to memory, i.e. it is a
3530 <tt>call</tt>,<tt>free</tt>,<tt>invoke</tt>, or <tt>store</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3531 <li><tt>unsigned getOpcode()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3532 <p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3533 <li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3534 <p>Returns another instance of the specified instruction, identical
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3535in all ways to the original except that the instruction has no parent
3536(ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3537and it has no name</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3538</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3539
3540</div>
3541
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3542</div>
3543
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3544<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3545<h3>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3546 <a name="Constant">The <tt>Constant</tt> class and subclasses</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3547</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3548
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3549<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3550
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3551<p>Constant represents a base class for different types of constants. It
3552is subclassed by ConstantInt, ConstantArray, etc. for representing
3553the various types of Constants. <a href="#GlobalValue">GlobalValue</a> is also
3554a subclass, which represents the address of a global variable or function.
3555</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3556
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3557<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3558<h4>Important Subclasses of Constant</h4>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3559<div>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3560<ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3561 <li>ConstantInt : This subclass of Constant represents an integer constant of
3562 any width.
3563 <ul>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3564 <li><tt>const APInt&amp; getValue() const</tt>: Returns the underlying
3565 value of this constant, an APInt value.</li>
3566 <li><tt>int64_t getSExtValue() const</tt>: Converts the underlying APInt
3567 value to an int64_t via sign extension. If the value (not the bit width)
3568 of the APInt is too large to fit in an int64_t, an assertion will result.
3569 For this reason, use of this method is discouraged.</li>
3570 <li><tt>uint64_t getZExtValue() const</tt>: Converts the underlying APInt
3571 value to a uint64_t via zero extension. IF the value (not the bit width)
3572 of the APInt is too large to fit in a uint64_t, an assertion will result.
Reid Spencer4474d872007-03-02 01:31:31 +0000[diff] [blame]3573 For this reason, use of this method is discouraged.</li>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3574 <li><tt>static ConstantInt* get(const APInt&amp; Val)</tt>: Returns the
3575 ConstantInt object that represents the value provided by <tt>Val</tt>.
3576 The type is implied as the IntegerType that corresponds to the bit width
3577 of <tt>Val</tt>.</li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3578 <li><tt>static ConstantInt* get(const Type *Ty, uint64_t Val)</tt>:
3579 Returns the ConstantInt object that represents the value provided by
3580 <tt>Val</tt> for integer type <tt>Ty</tt>.</li>
3581 </ul>
3582 </li>
3583 <li>ConstantFP : This class represents a floating point constant.
3584 <ul>
3585 <li><tt>double getValue() const</tt>: Returns the underlying value of
3586 this constant. </li>
3587 </ul>
3588 </li>
3589 <li>ConstantArray : This represents a constant array.
3590 <ul>
3591 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3592 a vector of component constants that makeup this array. </li>
3593 </ul>
3594 </li>
3595 <li>ConstantStruct : This represents a constant struct.
3596 <ul>
3597 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3598 a vector of component constants that makeup this array. </li>
3599 </ul>
3600 </li>
3601 <li>GlobalValue : This represents either a global variable or a function. In
3602 either case, the value is a constant fixed address (after linking).
3603 </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3604</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3605</div>
3606
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3607</div>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3608
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3609<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3610<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3611 <a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3612</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3613
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3614<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3615
3616<p><tt>#include "<a
3617href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]3618doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
3619Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3620Superclasses: <a href="#Constant"><tt>Constant</tt></a>,
3621<a href="#User"><tt>User</tt></a>, <a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3622
3623<p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
3624href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
3625visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
3626Because they are visible at global scope, they are also subject to linking with
3627other globals defined in different translation units. To control the linking
3628process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
3629<tt>GlobalValue</tt>s know whether they have internal or external linkage, as
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3630defined by the <tt>LinkageTypes</tt> enumeration.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3631
3632<p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
3633<tt>static</tt> in C), it is not visible to code outside the current translation
3634unit, and does not participate in linking. If it has external linkage, it is
3635visible to external code, and does participate in linking. In addition to
3636linkage information, <tt>GlobalValue</tt>s keep track of which <a
3637href="#Module"><tt>Module</tt></a> they are currently part of.</p>
3638
3639<p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
3640by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
3641global is always a pointer to its contents. It is important to remember this
3642when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
3643be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
3644subclass of <tt>GlobalValue)</tt> that is an array of 24 ints, type <tt>[24 x
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]3645i32]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3646the address of the first element of this array and the value of the
3647<tt>GlobalVariable</tt> are the same, they have different types. The
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]3648<tt>GlobalVariable</tt>'s type is <tt>[24 x i32]</tt>. The first element's type
3649is <tt>i32.</tt> Because of this, accessing a global value requires you to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3650dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
3651can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
3652Language Reference Manual</a>.</p>
3653
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3654<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3655<h4>
3656 <a name="m_GlobalValue">
3657 Important Public Members of the <tt>GlobalValue</tt> class
3658 </a>
3659</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3660
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3661<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3662
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3663<ul>
3664 <li><tt>bool hasInternalLinkage() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3665 <tt>bool hasExternalLinkage() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3666 <tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
3667 <p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
3668 <p> </p>
3669 </li>
3670 <li><tt><a href="#Module">Module</a> *getParent()</tt>
3671 <p> This returns the <a href="#Module"><tt>Module</tt></a> that the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3672GlobalValue is currently embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3673</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3674
3675</div>
3676
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3677</div>
3678
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3679<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3680<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3681 <a name="Function">The <tt>Function</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3682</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3683
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3684<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3685
3686<p><tt>#include "<a
3687href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3688info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3689Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3690<a href="#Constant"><tt>Constant</tt></a>,
3691<a href="#User"><tt>User</tt></a>,
3692<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3693
3694<p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
Torok Edwin87469292009-10-12 13:37:29 +0000[diff] [blame]3695actually one of the more complex classes in the LLVM hierarchy because it must
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3696keep track of a large amount of data. The <tt>Function</tt> class keeps track
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3697of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal
3698<a href="#Argument"><tt>Argument</tt></a>s, and a
3699<a href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3700
3701<p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
3702commonly used part of <tt>Function</tt> objects. The list imposes an implicit
3703ordering of the blocks in the function, which indicate how the code will be
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3704laid out by the backend. Additionally, the first <a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3705href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
3706<tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
3707block. There are no implicit exit nodes, and in fact there may be multiple exit
3708nodes from a single <tt>Function</tt>. If the <a
3709href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
3710the <tt>Function</tt> is actually a function declaration: the actual body of the
3711function hasn't been linked in yet.</p>
3712
3713<p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
3714<tt>Function</tt> class also keeps track of the list of formal <a
3715href="#Argument"><tt>Argument</tt></a>s that the function receives. This
3716container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
3717nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
3718the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
3719
3720<p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
3721LLVM feature that is only used when you have to look up a value by name. Aside
3722from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
3723internally to make sure that there are not conflicts between the names of <a
3724href="#Instruction"><tt>Instruction</tt></a>s, <a
3725href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
3726href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
3727
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3728<p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
3729and therefore also a <a href="#Constant">Constant</a>. The value of the function
3730is its address (after linking) which is guaranteed to be constant.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3731
3732<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3733<h4>
3734 <a name="m_Function">
3735 Important Public Members of the <tt>Function</tt> class
3736 </a>
3737</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3738
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3739<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3740
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3741<ul>
3742 <li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3743 *Ty, LinkageTypes Linkage, const std::string &amp;N = "", Module* Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3744
3745 <p>Constructor used when you need to create new <tt>Function</tt>s to add
3746 the the program. The constructor must specify the type of the function to
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3747 create and what type of linkage the function should have. The <a
3748 href="#FunctionType"><tt>FunctionType</tt></a> argument
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3749 specifies the formal arguments and return value for the function. The same
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3750 <a href="#FunctionType"><tt>FunctionType</tt></a> value can be used to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3751 create multiple functions. The <tt>Parent</tt> argument specifies the Module
3752 in which the function is defined. If this argument is provided, the function
3753 will automatically be inserted into that module's list of
3754 functions.</p></li>
3755
Chris Lattner62810e32008-11-25 18:34:50 +0000[diff] [blame]3756 <li><tt>bool isDeclaration()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3757
3758 <p>Return whether or not the <tt>Function</tt> has a body defined. If the
3759 function is "external", it does not have a body, and thus must be resolved
3760 by linking with a function defined in a different translation unit.</p></li>
3761
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3762 <li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3763 <tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3764
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3765 <tt>begin()</tt>, <tt>end()</tt>
3766 <tt>size()</tt>, <tt>empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3767
3768 <p>These are forwarding methods that make it easy to access the contents of
3769 a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
3770 list.</p></li>
3771
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3772 <li><tt>Function::BasicBlockListType &amp;getBasicBlockList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3773
3774 <p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
3775 is necessary to use when you need to update the list or perform a complex
3776 action that doesn't have a forwarding method.</p></li>
3777
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3778 <li><tt>Function::arg_iterator</tt> - Typedef for the argument list
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3779iterator<br>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3780 <tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3781
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3782 <tt>arg_begin()</tt>, <tt>arg_end()</tt>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3783 <tt>arg_size()</tt>, <tt>arg_empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3784
3785 <p>These are forwarding methods that make it easy to access the contents of
3786 a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
3787 list.</p></li>
3788
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3789 <li><tt>Function::ArgumentListType &amp;getArgumentList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3790
3791 <p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
3792 necessary to use when you need to update the list or perform a complex
3793 action that doesn't have a forwarding method.</p></li>
3794
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3795 <li><tt><a href="#BasicBlock">BasicBlock</a> &amp;getEntryBlock()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3796
3797 <p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
3798 function. Because the entry block for the function is always the first
3799 block, this returns the first block of the <tt>Function</tt>.</p></li>
3800
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3801 <li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
3802 <tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3803
3804 <p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
3805 <tt>Function</tt> and returns the return type of the function, or the <a
3806 href="#FunctionType"><tt>FunctionType</tt></a> of the actual
3807 function.</p></li>
3808
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3809 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3810
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3811 <p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3812 for this <tt>Function</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3813</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3814
3815</div>
3816
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3817</div>
3818
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3819<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3820<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3821 <a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3822</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3823
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3824<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3825
3826<p><tt>#include "<a
3827href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
3828<br>
Tanya Lattnera3da7772004-06-22 08:02:25 +0000[diff] [blame]3829doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3830 Class</a><br>
3831Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3832<a href="#Constant"><tt>Constant</tt></a>,
3833<a href="#User"><tt>User</tt></a>,
3834<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3835
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3836<p>Global variables are represented with the (surprise surprise)
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3837<tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
3838subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
3839always referenced by their address (global values must live in memory, so their
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3840"name" refers to their constant address). See
3841<a href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global
3842variables may have an initial value (which must be a
3843<a href="#Constant"><tt>Constant</tt></a>), and if they have an initializer,
3844they may be marked as "constant" themselves (indicating that their contents
3845never change at runtime).</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3846
3847<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3848<h4>
3849 <a name="m_GlobalVariable">
3850 Important Public Members of the <tt>GlobalVariable</tt> class
3851 </a>
3852</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3853
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3854<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3855
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3856<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3857 <li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
3858 isConstant, LinkageTypes&amp; Linkage, <a href="#Constant">Constant</a>
3859 *Initializer = 0, const std::string &amp;Name = "", Module* Parent = 0)</tt>
3860
3861 <p>Create a new global variable of the specified type. If
3862 <tt>isConstant</tt> is true then the global variable will be marked as
3863 unchanging for the program. The Linkage parameter specifies the type of
Duncan Sands667d4b82009-03-07 15:45:40 +0000[diff] [blame]3864 linkage (internal, external, weak, linkonce, appending) for the variable.
3865 If the linkage is InternalLinkage, WeakAnyLinkage, WeakODRLinkage,
3866 LinkOnceAnyLinkage or LinkOnceODRLinkage,&nbsp; then the resultant
3867 global variable will have internal linkage. AppendingLinkage concatenates
3868 together all instances (in different translation units) of the variable
3869 into a single variable but is only applicable to arrays. &nbsp;See
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3870 the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
3871 further details on linkage types. Optionally an initializer, a name, and the
3872 module to put the variable into may be specified for the global variable as
3873 well.</p></li>
3874
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3875 <li><tt>bool isConstant() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3876
3877 <p>Returns true if this is a global variable that is known not to
3878 be modified at runtime.</p></li>
3879
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3880 <li><tt>bool hasInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3881
3882 <p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
3883
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3884 <li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3885
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3886 <p>Returns the initial value for a <tt>GlobalVariable</tt>. It is not legal
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3887 to call this method if there is no initializer.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3888</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3889
3890</div>
3891
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3892</div>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3893
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3894<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3895<h3>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3896 <a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3897</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3898
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3899<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3900
3901<p><tt>#include "<a
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3902href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
Stefanus Du Toit24e04112009-06-17 21:12:26 +0000[diff] [blame]3903doxygen info: <a href="/doxygen/classllvm_1_1BasicBlock.html">BasicBlock
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3904Class</a><br>
3905Superclass: <a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3906
Nick Lewyckyccd279d2011-02-17 02:19:22 +0000[diff] [blame]3907<p>This class represents a single entry single exit section of the code,
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3908commonly known as a basic block by the compiler community. The
3909<tt>BasicBlock</tt> class maintains a list of <a
3910href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
3911Matching the language definition, the last element of this list of instructions
3912is always a terminator instruction (a subclass of the <a
3913href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
3914
3915<p>In addition to tracking the list of instructions that make up the block, the
3916<tt>BasicBlock</tt> class also keeps track of the <a
3917href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
3918
3919<p>Note that <tt>BasicBlock</tt>s themselves are <a
3920href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
3921like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
3922<tt>label</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3923
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3924<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3925<h4>
3926 <a name="m_BasicBlock">
3927 Important Public Members of the <tt>BasicBlock</tt> class
3928 </a>
3929</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3930
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3931<div>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3932<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3933
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3934<li><tt>BasicBlock(const std::string &amp;Name = "", </tt><tt><a
3935 href="#Function">Function</a> *Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3936
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3937<p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
3938insertion into a function. The constructor optionally takes a name for the new
3939block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
3940the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
3941automatically inserted at the end of the specified <a
3942href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
3943manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3944
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3945<li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
3946<tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
3947<tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
3948<tt>size()</tt>, <tt>empty()</tt>
3949STL-style functions for accessing the instruction list.
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3950
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3951<p>These methods and typedefs are forwarding functions that have the same
3952semantics as the standard library methods of the same names. These methods
3953expose the underlying instruction list of a basic block in a way that is easy to
3954manipulate. To get the full complement of container operations (including
3955operations to update the list), you must use the <tt>getInstList()</tt>
3956method.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3957
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3958<li><tt>BasicBlock::InstListType &amp;getInstList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3959
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3960<p>This method is used to get access to the underlying container that actually
3961holds the Instructions. This method must be used when there isn't a forwarding
3962function in the <tt>BasicBlock</tt> class for the operation that you would like
3963to perform. Because there are no forwarding functions for "updating"
3964operations, you need to use this if you want to update the contents of a
3965<tt>BasicBlock</tt>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3966
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3967<li><tt><a href="#Function">Function</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3968
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3969<p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
3970embedded into, or a null pointer if it is homeless.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3971
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3972<li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3973
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3974<p> Returns a pointer to the terminator instruction that appears at the end of
3975the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
3976instruction in the block is not a terminator, then a null pointer is
3977returned.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3978
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3979</ul>
3980
3981</div>
3982
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3983</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3984
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3985<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3986<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3987 <a name="Argument">The <tt>Argument</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3988</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3989
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3990<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3991
3992<p>This subclass of Value defines the interface for incoming formal
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3993arguments to a function. A Function maintains a list of its formal
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3994arguments. An argument has a pointer to the parent Function.</p>
3995
3996</div>
3997
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3998</div>
3999
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]4000<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4001<hr>
4002<address>
4003 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
Misha Brukman44408702008-12-11 17:34:48 +0000[diff] [blame]4004 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4005 <a href="http://validator.w3.org/check/referer"><img
Gabor Greifa9c0f2b2008-06-18 14:05:31 +0000[diff] [blame]4006 src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01 Strict"></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4007
4008 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
4009 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
NAKAMURA Takumib9a33632011-04-09 02:13:37 +0000[diff] [blame]4010 <a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4011 Last modified: $Date$
4012</address>
4013
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]4014</body>
4015</html>